CA1229955A - Method for producing pulp stock for paper making from printed unselected waste paper - Google Patents
Method for producing pulp stock for paper making from printed unselected waste paperInfo
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- CA1229955A CA1229955A CA000451414A CA451414A CA1229955A CA 1229955 A CA1229955 A CA 1229955A CA 000451414 A CA000451414 A CA 000451414A CA 451414 A CA451414 A CA 451414A CA 1229955 A CA1229955 A CA 1229955A
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- pulp
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
- Y02W30/00—Technologies for solid waste management
- Y02W30/50—Reuse, recycling or recovery technologies
- Y02W30/64—Paper recycling
Abstract
Abstract:
A waste paper recycling process relates to the treat-ment of a mixture of waste paper containing non-cellulosic contraries and printing inks, in order to release the contraries from the fibers and further to separate them from the stock in order to produce re-usable pulp for the production of paper and board. The invention has to do with new and useful improvements in methods for first removing the non-ink contraries from the fibrous mass and second releasing and then removing the ink particles from the said fibrous mass. The invention is directed to the treatment of the fiber slurry produced during the ink separation stage, after the ink releasing stage has been applied. One aim of the process is to allow both the use of the fibers and the mineral fillers contained in that slurry, for pulp and board making, and the use of the solids-free water contained in the same slurry as the washing liquid in the previous ink-separation treatment, thus closing the fibers and the water circuits. This process includes chemical and thermo-mechanical treatments, starting under alkaline conditions, which may become neutral at the end of the process.
A waste paper recycling process relates to the treat-ment of a mixture of waste paper containing non-cellulosic contraries and printing inks, in order to release the contraries from the fibers and further to separate them from the stock in order to produce re-usable pulp for the production of paper and board. The invention has to do with new and useful improvements in methods for first removing the non-ink contraries from the fibrous mass and second releasing and then removing the ink particles from the said fibrous mass. The invention is directed to the treatment of the fiber slurry produced during the ink separation stage, after the ink releasing stage has been applied. One aim of the process is to allow both the use of the fibers and the mineral fillers contained in that slurry, for pulp and board making, and the use of the solids-free water contained in the same slurry as the washing liquid in the previous ink-separation treatment, thus closing the fibers and the water circuits. This process includes chemical and thermo-mechanical treatments, starting under alkaline conditions, which may become neutral at the end of the process.
Description
~%~ s FIELD OF THE INVENTION AND REVIEW OF THE PRIOR ART
Recycling of waste paper is possible only after most of the non-cellulosic contaminants have been removed from the fiber mass. These contaminants may have been introduced during the printing steps (carbon black, pigments, ink vehicles, ink fixating polymers, etc....), during converting, (varnishes, coats, binders, wrapping, etc...) and later during the collecting phase (metallic pieces, plastics, soils and dirt of any kind).
Removing of the contraries generally occurs based on chronological dimensional sequences, through screening, magnetic separation, first in dry conditions and later in aqueous suspension.
The fiber mass is then screened through perforated plates and finer contraries are removed by centrifugal and centripetal cleaners.
The ink particles are not substantially removed during the proceeding steps, an this operation is achieved in two steps: (a) detaching the ink particles from the fiber surface, through the combined action of chemicals, temperature and mechanical shear forces and (b) removing these particles from the pulp slurry.
Generally, all the contraries including the ink particles, are released from the fibers during the defibering phase. The waste paper is treated in a pulper, under alkaline conditions at 50-60C. temperature, in order to be well defibered and transformed into a pump able slurry. An alternative to this process is to operate the pulper in cold conditions, then thicken the pulp above 15% consistency, then heat the pulp with steam at 60C.
introducing at that point the de-inking and bleaching chemicals. The pulp then remains in a reaction tower during 2-3 hours without any mechanical action.
The first drawback of these techniques is that all contaminants are submitted to the thermal treatment, including the ones which have low melting points, such as YO-YO' , I
binders, hot melts, plastics and other "stickles". By this way, they become dispersed and cannot be removed any more by the conventional means, and will precipitate again on paper machine elements such as doctor blades, wires, felts, pipe walls, etc..., creating operating problems and loss of efficiency.
A second drawback is that these ink-releasing techniques have a weak action on the modern inks such as the rotor offset inks, where ink vehicles are made of synthetic resins which form an insoluble polymer onto the surface of the fibers. The same consideration applies for xerocopy printed paper and varnished papers, where temperatures in the range of 60C. will provide neither any softening of the ink vehicles nor any weakening of the bonding between the fibers and these vehicles.
Another limitation of these techniques is that it is not possible to increase the temperature of the ink releasing step, because the combination of the alkalinity and the temperature during a long time will result in an unacceptable yellowing of the pulp, specially if some grounded is present in the mixture to be treated.
Ink removing techniques in use to-day are essentially two: flotation and washing.
In flotation , the diluted fiber slurry is intensively mixed with air after a hydrophore ink collector has been added. Then stock is naturally decorated and air bubbles collect the ink particles during the upwards travel to the surface. The resulting black foam is then collected and treated separately through centrifuges, then skewered-In washing, a very old and well known process, the finest dispersed particles are removed through several dilutions and squeezing cycles, generally arranged as a counter-current cascade configuration. The effluent of the first squeezing sequence contains all the free fine ink particles, but also a great quantity of fine cellulosic fibers and most of the mineral fillers, and are skewered and treated according to the local pollution regulations.
Some other ink removing techniques exist such as solvent extraction but have not been followed by wide industrial application, due to high production cost and low quality of the produced pulp.
In the US. Patent N4,076,578 Pudding ton et Alp recall the fundamental concept of de-inking: (a) releasing ink from the paper fiber by means of chemico-thermo-mechanical treatment and (b) separating of dispersed ink particles from the pulp, then proposes a different method to achieve this goal, through adsorption of the ink particles onto the surface of solid particles, followed by the removal of said particles from the pulp, and then removal of the ink from those solids.
Nowadays, none of the above mentioned processes has asserted itself because each of them presents some drawbacks.
The flotation is a low consistency process (between 1% and 2%) and thus involves high volumes of pulp, with consequent high investment cost. Also, the nature of this process is essentially physico-chemical and thus its stability is greatly related to the stability of the compost-lion of the waste paper, the type of fibers (chemical or mechanical), the type and content of mineral filler, the calcium ion concentration. Consequently, the brightness of the de-inked pulp shows undesired high fluctuations, These brightness variations are also accompanied by all composition variations coming together with the raw material (waste paper), without any possibility of control or continuous measurement and monitoring.
To-day, it is generally admitted that the first condition for the good operation of a modern fast paper-machine is the constancy of operating parameters, the most important one being the composition of the stock feeding machine. Unfortunately, it is not possible to control the composition of a waste paper lot as easily as a virgin I
pulp bale. For this reason, the efficiency decrease of high-speed paper machines using high percentages of flotation de-inked pulp is mainly caused by the uncontrolled variations of the stock composition rather than by the brightness (or de-inking efficiency) variations. This problem can be solved using selected classified waste paper, at a price which makes the de-inked pulp uncompetitive respect to the virgin pulp, assuming that such type of waste is available.
lo Finally, the flotation process needs to be continuously controlled, on a three shift basis, by highly specialized chemical experts using sophisticated instrumentation and laboratory, thus appreciably increasing the production cost.
The washing process involves simpler, cleaner, and easier to control equipment, in particular when washing occurs at consistencies between 3% and 15%.
This process does not require any specialized control and it is admitted that not only the quality (cleanliness and strength) of the washed pulp is definitely higher than for the floated pulp, but this quality is much more constant and less sensitive to raw material variations of composition, thus offering a higher "tunability" of the pulp in the paper machine room.
In fact, the principle of washing on a perforated plate statistically says that elements having a smaller size than the plate openings should pass through the plate. It appears that the variations of composition of the stock to be de-inked (fines, grounded, mineral fillers) will reverberate on the fraction lost through the plate, giving a final product almost constant in quality, if not in quantity. This principle allows for the use of unselected waste paper, a lower quality product having a much lower cost and higher availability.
On the other hand, this process needs a much higher quantity of water, and produces the equivalent higher quantity of effluents which still contain a great quantity , I
35~ -of valuable products cellulosic short fibers mineral fillers, mixed together with the undesired ink. Besides that direct loss, it is necessary to consider the us-direct cost due to the abatement of the pollution created by the solids contained in the effluents.
In conclusion, it can be said that if flotation de-inking presents high investment and operating cost together with low constancy of the quality of the final product, washing de-inking also shows a high similar cost of the product due to both the intrinsically low yield of the process and the pollution abatement cost.
In order to minimize the negative aspects of each one of these basic processes, their supporters have proposed several combinations of them, keeping in mind to produce only one de-inked pulp starting from one waste paper mixture.
In the French Patent Application N79 19392, M. Fritz Zebu of Voith Cry. suggests to remove the fine fibers fraction together with the mineral fillers from a flotation de-inked pulp, using screens and strains arranged as washing elements. This process, which is only summarily described without any example, seems to add up both costs and drawbacks of flotation and washing.
In the TAIPEI magazine, vowel, N9, September 1980 M. Luther Pfalzer of the same Voith Cry., while recalls the same concept (page 116, fugue), specifies that the fine fiber fraction and mineral fillers are centrifugated and then skewered and lost. It also appears from this publication that the effluent is totally sediment Ed after having been flocculated by addition of aluminum sulfate, but it is also specified that a good dispersion of the ink particles can be obtained at high and well controlled phi These two statements are rather contradictory and make this concept hardly applicable in practice, M. Pfalzer also suggests the opposite philosophy (page 114, foggily), which consists of a total flotation so 5~ii followed by a total sedimentation of the effluents of a conventional washing process. For the same reasons as above, which are: the low yield of the washing process, the non-compatibility between ink dispersing high pi and aluminum sulfate sedimentation low phi the addition of the costs and drawbacks of each individual process, this proposal has not been applied on an industrial scale.
In the French Patent Application N78 29637, M, Calumniate of Montedison Cry. suggests in a more simple way to separate the ink particles from the fine fibers and the mineral fillers contained in the effluents of a washing process, by means of a simplified flotation process where no chemicals are added. It is also stated that the chemicals added at the beginning of the process (pulping stage) will also provide for the ink collecting function. In this process, the suckled "clarified"
effluents which actually contain most of the fibers and mineral fillers lost during the washing step, are totally recycled ahead of the process.
A tentative application of this process had to be quickly abandoned for two reasons. At first, it has not been possible to obtain a satisfactory selective removal of the ink during the flotation, because of the antagonistic functions of the two chemicals mixed together at the pulper:
(a) dispersing of the ink needed during washing, (b) keg-lotion of the ink needed during flotation, So, too much fibers and fillers were floated together with the ink resulting in a quick overloading of the sewer system, and immediate shut down of the plant.
At second, it has not been possible to recirculate continuously-ahead of the washers, an effluent which contains most of the fines and fillers lost by the same washers. This total recirculation has quickly resulted in (a) a drop of the brightness due to the poor ink removal efficiency and (b) an unacceptable drop of the hydraulic capacity of the thickening elements. Both can be attributed 1, .
so I
to the saturation of the circuit with fines and fillers, dimensions of which are of the same order of magnitude than the ink particles.
In the Italian Patent Application N26344 A/80, M. Calumniate recalls the same principle, where the effluents at a concentration of 0.14% would be selectively floated with the only addition of air, and then totally recycled ahead of the process together with their suspended solids.
M. Calumniate nevertheless suggests to install a "quick"
flotation, a third flotation, installed ahead of the washing process. This configuration does not seem to bring any answer about the two basic previous problems; (a) how is it possible to have the best dispersion together with the best coagulation, (b) how is it possible to avoid the saturation, the clogging of the thickening elements, and the loss of the ink removal efficiency, due to the recirculation of the fines and the fillers together with the effluent.
GOALS OF THE INVENTION.
The present invention aims to provide a practical and integral industrial process which allows to produce, in a continuous way and starting from a mixture of unselected waste papers, three separate products, namely:
a) a totally cleaned and de-inked pulp having constant and controlled brightness and fiber classification, having a very low and constant fillers content;
b) a totally cleaned and de-inked pulp having a fine fiber classification and a very high fillers content, these two parameters being variables both quality and quantity;
c) an effluent which does not practically contain suspended solids, which has not been submitted to any pi reversion, which does not contain any flocculation or sedimentation chemical agent, and thus is immediately and totally reusable as the dilution YO-YO
I
and washing liquid during the ink removal step of the de-inking phase.
A further aim of this invention is to provide a practical and advantageous improved method for de-inking these grades of printed papers and boards which cannot be correctly de-inked by conventional methods.
Another aim of this invention is to provide a practical and advantageous method which allows to produce high quality paper and board at high speeds using the low quality waste grades which could not be used for such noble purpose when treated by conventional methods.
The invention is also directed to the application of modified and purposely adapted ink removal processes !
such as washing, selective separation, flotation, coagulation, filtration, onto the high ink-content slurry produced by the primary itik removal process.
The invention also aims to allow for the use in paper making of the by-products of a washing de-inking process, either on the paper machine which will use the primary pulp, or on a different paper machine.
An object of this invention is to provide a means to create a constant and controlled composition of the pulp used for paper making, which can be different from the composition of the incoming waste paper mixture, This object is achieved by pumping controlled flows of each one of the two components and mixing them ahead of the paper machine(s) in the desired percentage; the capacities of the chests act as buffers between waste paper and paper machine stock compositions.
Another object of this invention is to increase the value of the by-product (the secondary pulp) by the fact that good long fibers can be extracted from the main line in order to optimize the operation both of the selective separation of the ink and of the filtration on fiber mat.
A further object of this invention is to accomplish ~L~22~ 5 g the selective separation of the ink at a stage where this ink is highly concentrated (approximately three times more than in the main pulp), thus increasing the efficiency of the chemicals.
An ulterior object of this invention is to achieve the selective separation of the ink (which is the more delicate operation of the whole recycling process), in a satellite circuit of reduced capacity (approximately one third of the flow through the main line), thus being easier to operate and requiring lower investment cost, This invention then aims to ensure the highest possible constancy of quality of the primary pulp, by the fact that the variations of fines and fillers contents will instantaneously reverberate on the fraction produced by the satellite circuit, which in turn can also be stabilized by means of a thorough mixing and high retention time in the final buffer chest, With these and other aims and objects, the nature of which will become more apparent, a fuller understanding of this invention will be gained by reference to the following detailed description and the appended claims.
SUMMARY OF TIE INVENTION
According to one aspect of the invention there is provided a method of treating a mixture of printed and contaminated waste paper in order to produce pulp for use in the manufacture of pulp and paper boards, which method comprises: (a) forming an aqueous pulp of the waste paper at low temperature and low specific mechanical energy, thereby forming a palpable slurry, and releasing non-ink contaminants from the surface of the waste paper but without dispersing the released non-ink contaminants throughout the resulting fibrous suspension; (b) separate in the non-ink contaminants from the pulp by mechanical separation, without the use of froth flotation, solvent extraction or other chemical]. process, using conventional / , of I
screens and centrifugal cleaners and without any further application of strong shear forces to the pulp; (c) softening ink particles and weakening their bonds with the surface of the fires by submitting the pulp at a consistency of more than 15% to the simultaneous actions of (i) a temperature between 85 and 130C, (ii) high shear forces and (iii) at least one de-inking agent, under alkaline conditions; (d) detaching the ink particles from the surface of the fibres'and dispersing them into the fibrous 'suspension by submitting the pulp to the simultaneous actions of (i) and (ii), as defined in step I and (iv) at least one chemical dispersing agent, under alkaline conditions; (e) removing the free ink particles to obtain the degree of brightness required by the final use of the pulp.
According to a further aspect of the invention there is provided a method of treating a mixture of printed waste paper in order to produce pulp for use in manufacture of paper and board, which method comprises: (a) forming an aqueous pulp of the waste paper; (b) removing non-ink contaminants from the pulp and releasing ink particles from the surface of the pulp fibers to obtain the degree of brightness required by the final use of the pulp; (c) removing ink particles from the remaining dispersed fine material of the pulp using at least one washing stage under alkaline conditions and in the presence of at least one ink dispersing agent, thereby producing: (i) a primary pulp having controlled and constant brightness and fiber classification with very low and constant filler content and (ii) a secondary pulp containing a variable high filler content and a variable quantity of fine fibers, together with the ink particles and some clean fibers; (d) mixing the secondary pulp (ii) with an ink-collecting hydrophobic agent, after the ink-dispersing agent has been neutralized or precipitated, under alkaline conditions, and then removing the ink particles from the effluent by I
selective separation of the hydrophobic agent from the fibrous suspension; (e) reducing the alkalinity of the slurry by addition of non-caustic insolubilizing cations and a strong mineral acid, thereby producing a filterable slurry; (f) filtering the fibrous suspension at a low filtering rate on a fibrous mat composed of fibers coming from the same process, thereby producing: (iii) a secondary de-inked pulp having a fine fiber classification and a very high filler content, both instantaneously variable, and (iv) an effluent which is practically free of suspended solids;
(g) diluting the pulp thickened by the last but one washing stage with the clarified effluent of step (f) thereby conserving the water used in the method; and (h) storing the filtered secondary pulp in a vat for several hours with intense mixing by agitation and recirculation, thereby leveling off the fluctuations of the filler content, the fiber classification and the freeness.
so I, Lo DESCRIPTION OF THE INVENTION
The following detailed description, together with the attached schematic flow-sheet, refers to one preferred practical application of the invention, although other procedures can also be applied.
Following the flow-sheet, the bales of waste paper are loaded into a pulper (2) by means of a loading mocha-noisome, together with the recycled water and eventual caustics in order to bring the pi at values above 7. It is possible but not mandatory to introduce part or all the quantity of dispersing chemicals required by the ink-releasing action, during -the pulping operation.
The pulp is then diluted using recycled water and pumped through one or several stages of screens and cleaners (3) in order to release contraries and contaminants from the paper surface, and further remove them from the pulp slurry, When the de-inked pulp is used for high quality paper production or on high-speed machines such as light weight coating base or newsprint, this operation must be done in the same way it is done with chemical or mechanical virgin pulps, using the same equipment and operating parameters.
In particular, the best results have been obtained through a combination of pressurized slotted screens equipped with 0.3mm, slot width working at I consistency followed by 4 inches size cleaners working at 2.8 bars pressure drop and 0.6% consistency in the first stage.
It is anyhow of paramount importance that the temperature of the stock is kept as low as possible so that the low melting point contaminants will remain rigid and will not extrude through the slotted screens and thus be eliminated by the screens, This pulp is then thickened (4) to the consistency required by the ink releasing process. The effluents produced by this thickening stage can easily be recycled, as they are cold and do not contain much fibers and very little ink. At the beginning of the following ink-releasing step (5) chemicals are mixed together with ~22~gS5 the fiber suspension. Caustics are added in order to raise the pi up to 9-10, together with oxidizing agent (such as hydrogen peroxide), and stabilizers (such as sodium silicate, and dispersing agents (surfactants, eta,.,). The basic parameters of this process, - temperature, pressure, specific energy, chemicals dosing - will be determined in order to ensure the optimum detachment of the ink particles from the surface of the fibers together with their finest dispersion inside the pulp.
In the hollowing examples, this operation has been made in a kneader, also called triturator, which permits to bring the temperature at the desired value (ire. above the melting point of the ink vehicles) within a few seconds and simultaneously apply very strong shear forces at high consistency and in presence of de-inking agents, The principle of the operation is that at first, the combined actions of ink-releasing chemicals and temperature (90-130C) will soften the ink vehicles and weaken the bonding between the same and the fibers, and then the combined actions of ink-dispersing chemicals and intense shear forces will detach and finely disperse these particles inside the fiber suspension. The high consistency (20-30%) allows to treat very low volumes of pulp in small machines during a very short time (2-3 minutes), thus avoiding the yellowing of the pulp and increasing the efficiency of the chemicals.
This pulp then remains 5 to 20 minutes in a latency chest (6), at a consistency between 2% and 5%. It may then be deflated in order to well separate the fiber bundles one from the other, and thus facilitate the ink removal from the slurry.
The fibrous suspension finally goes through the ink removal process (3) which can be advantageously composed of multistage counter-current, high consistency washing, The number of stages is chosen according to the quantity of ink to be removed and to the desired final brightness.
The extraction of the water is conducted through strains , . c I
or perforated plates, the dimensions of the openings of which will be selected in order to allow for a given quantity of fibers to be carried away together with the effluent, thus ensuring the optimum operation of both the following ink selective separation process, and the final filtration of the recovered satellite secondary pulp.
In case a filler-free secondary pulp is desired! the effluents from the washing step (8) can advantageously be strained again on one or several fine mesh filters (9), By this mean, it is possible to remove at each filter stage up to 80% of the mineral fillers contained in that slurry, In such a case the finest fraction must be sent to a conventional alkaline clarifier (10) and then skewered, The clarified fraction is then returned ahead or after the following ink selective separation step (11), according to the operating parameters of this last process (consistency, temperature), and according to the required brightness, The necessary chemicals are also introduced ahead of this step. In case this process is a selective flotation, ink collectors such as fatty acids or their sodium or calcium soaps can be added, taking care to ensure a mixing time of about 5 minutes at a temperature of about 35 to 45C.
It may be worthy to recall that the dispersing agent used during the washing step has a negative effect both on the coagulation produced by the collecting agents during the flotation step, and on the trainability (freeness) of the fibrous suspension during the filtration step. It will be good to inactivate or neutralize these agents for example by precipitation with calcium chloride or calcium hydroxide, The precipitation of the sodium silicate will also contribute to increase the brightness of the secondary pulp through the formation of a precipitated mineral filler It has also been observed that the quantity of mineral fillers removed together with the foam during the flotation step may vary from 30~ up to 70% according to the operating parameters of the process: flotation time, temperature, pulp consistency.
dosing and type of chemicals. The rejected foam containing " :
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the ink is then pumped to centrifuges or filter-presses and skewered. The loss of solid particles has been observed to be between 10% and 20% of the flow of secondary pulp, which means about 3% to 6% respect to the total quantity of pulp feeding the washing step (8).
It has also been observed that the maximum efficiency of the ink removal has been reached at much higher consistencies than the ones recommended by the suppliers of the cells.
For example, a cell designed to work at 1% has shown best results between 1.5% and 2%. This peculiarity allows for the treatment of lowest quantities of effluents, using higher consistencies during washing, and larger holes in the extractors perforated plates.
When the requested concentration for the ink selective separation process is higher (say 0,5% or more) than the maximum concentration which can be given to the effluent of the washing step, some heavy stock can be advantageously extracted from the latency chest (6). In this easel the small quantity of long fibers added to the secondary pulp will help in forming the filtering mat the final filtration step (12).
The selective separation of the ink (if) can also be a process based on adsorption of the ink upon the surface of non-soap solids, as recommended by Ire Pudding ton et Al, in the US. Patent N4,076,578.
The de-inked slurry leaving the process (if) is then filtered on fibrous mat up to at least 4% consistency, possibly above 10% in order to remove from the final secondary pulp the maximum possible quantity of dissolved salts.
In case this pulp contains a very high quantity of grounded fines and fillers (such as mixtures of newsprint and magazine paper), the pi ahead of the filtration step has to be dropped down to values below 8, by addition of sulfuric acid (preferably to aluminum sulfate), under intense mechanical agitation (as could be the suction side of a centrifugal pump), and after some long fibers extracted from the washed final primary pulp has been added to the I
I
satellite slurry to be filtered.
It has been observed that the application of equipment such as Polydisk or Waco Filters to the thickening process (12) has permitted to produce clear filtrate having less than 100 Pam suspended solids and consequently totally reusable in the pulping (2), cleaning (3) and washing (8) processes without any further clarification.
The final thickened secondary pulp leaving (12) must then be brought to a pi compatible with the following use - by addition of sulfuric acid or aluminum sulfate always under intense mechanical agitation, and can be stored in a buffer chest according to the final use.
EXAMPLES
The following examples will illustrate three different applications of the general procedure previously described, using different mixtures of waste paper and producing different grades of paper and board, Measurements of brightness were made with an Elrepho* meter with 457nm light filter, according to ISSUE. standards, Chemical dousings are expressed in percent by weight of the chemical at 100% concentration respect to the weight of total solids in the line where said chemical is added. Sodium silicate is considered at 38 Be and the Removing* F and L as supplied.
The raw material is a mixture of over-issued news-papers and telephone books (white and yellow pages) in a ratio approximately 50/50. The de-inked pulps are used for t-he production of newsprint and telephone directory papers (white and yellow), on only one high speed paper machine, In this installation, the pulper has a capacity of 46m3 containing 2.700 kg of waste paper, Each batch longs 30 mint Dilution water is coming from the effluent of the thickening process (4) and make-up is made using clear filtrate from the Polydisk filter (12), One percent of sodium hydroxide is added in the pulper together with 1% of a de-inking agent ' ~,~; 'Allah * trade mark Lowe such as Removing L 8001 supplied by Chemicarta Swag Milan, When this cold pulping operation is finished, the stock is pumped through turbo separator, screens and cleaners, at consistencies starting around 4% and ending at about 0.6%, The turbo separator is equipped with a perforated plate having 3mm. diameter holes and the rejected stock is then sent to a vibrating flat screen also having 3mm.
holes, rejects of which are skewered.
The accepted stock from the turbo separator is then diluted from 3% down to 1% before it passes through pressurized slotted screens fitted with 0.30mmt slot width. The rejected stock is processed through a second stage screen having the same slot size, and rejects of the same go to a vibrating flat screen, rejects of which are Seward The accepted stock from the first stage of screens is then diluted down to 0.6% consistency and processed through a conventional battery of 4 stages of Triclean cleaners. The light and the heavy rejects of the Thea stage are skewered.
The total loss of both high and low consistency turbo separating, screening and cleaning is varying between 6% and 9% by weight, depending upon the degree of contamination of the waste paper. No more stickles or hot melts can be seen in the pulp, and the eye inspection is confirmed by the Somerville test, which shows less than 0.2% of shrives.
At that point, the pulp is totally cleaned and the only remaining contaminant is the printing ink. The pulp is then thickened up to 30% consistency in two steps, using a disk filter up to 10-12% and then a screw press up to 30%. Characteristics of the pulp are: Britons ISSUE
frowns SR, filler continuity%, temperature=20-25C.
The ink releasing step (5) is achieved in a kneader under the following operating conditions: temperature C,, sodium hydroxide= 1.5%, sodium silicate= 4%, hydrogen peroxide = 1.8%, specific enrage KW.H/Ton during 3 minutes The brightness of the pulp at the end ox the treatment is * trade mark :~L22~3~355;
ISSUE, and freeness is 60-65SR. The pulp is then diluted using all the flow of effluents coming from the second stage of washers, then squeezed up to 12% in the first washing stage.
These washers are composed of inclined screws (better known as Rice-Barton or Baker's screws), where the pulp is drained under continuous and vigorous agitation through perforated plates having 1.4 mm. diameter holes, in order to produce an effluent having approximately 0.8-1% consistency, The thickened stock is then processed through two other similar counter current washing steps and the final usable pulp presents the following characteristics: brightness=59-60IS0, freeness=46-50SR, filler content 2-3%, consistency%.
This pulp represents 78% by weight of the quantity of pulp feeding the washers (8). The balance 22% is going to the satellite circuit with the first stage effluent which shows:
brightness=3S-40IS0, filler continuity%, freeness=80SR.
The capability for the ink of being removed from the fibers contained in the effluent has been verified in the laboratory as follows: an effluent sample has been hyperwashed under fresh water shower on a 200 mesh wire, and a hand sheet has been made, showing a brightness of ISSUE, which is very similar to the brightness of the final primary pulp.
This effluent has then been mixed together with 4% of a special ink-collecting agent purposely designed for this application by Chemicarta SPA, Milan, and kept for 5 min.
under agitation at 30C.
The mixture is then processed through one single stage conventional flotation cell, Voith open type, during 15 min. The loss of weight through the cell is 15-20%, which means only 3-4, 5% respect to the total quantity of pulp entering the washers. We have found that addition of 0.5% to 1% of calcium chloride or calcium hydroxide together with the collector, ahead of the flotation, helps controlling the foam and the ink coagulation when low ash content pulps are processed.
~2~95i~
The total alkalinity is then dropped down to pH=7-8 with addition of 1% of sulfuric acid on the suction side of the centrifugal pump feeding the disk filter (12) At this point, the pulp shows a brightness=53-56IS0, a filler content =15-20~ and a freeness=78-80SR.
The disk filter (12) is a Polydisk filter sized according to a specific filtering factor liters/min.lm2.
Besides this unusual value, it is also necessary to feed the mat-peeling showers with air instead of water, in order to reach the maximum possible consistency of the discharged pulp .
Using the above mentioned parameters, a final consistency of 8% to 10~ could be obtained and the clear filtrate shown less than lOOppm average suspended solids, measured on paper filter, black label.
The pulp is then brought to phi and sent to a buffer chest having 8 hours total retention time. From this point it is then pumped to the mixing chest of the paper machine at controlled flow rates according to the paper grade actually produced and in function of the mean composition of the secondary pulp.
The clear filtrate from the Polydisk filter is then totally recycled in order to dilute the stock ahead of the third washing stage and make-up is provided by fresh industrial water which does not contain aluminum ions.
The application of such a process in a paper mill having one single paper machine is offering the following advantages:
appeasability to maintain constant freeness and ash content during a grade run, independently from the incoming waste paper characteristics, thus allowing the paper machine to run at maximum speed and efficiency;
possibility to achieve very quick grade change, exactly as when using virgin pulp and fillers, without the need to intervene a long time before in the waste , paper plan, thus permitting an easier and more constant operation of that plant;
possibility to always use the highest possible quantity of recycled fibers in the paper, by the free disposal of each one of the two fractions and their use in the optimum way, possibility to produce totally cleaned pulps having the same standards of cleanliness than virgin pulps and thus offering the highest possible tunability in the paper machine room, particularly being free of any "sticky" or ought melt" or ink vehicle free particle.
The raw material is a mixture of printed continuous stationary, old books and office file, in a ratio 50/50.
The dunked pulp is used to produce, on three distinct paper machines: (a) light weight machine glazed wrapping papers, (b) fine papers for writing and printing, including wood containing printing grades, (c) stationary and continuous print-out papers, The operation is similar to example (1) up to the thickening step (4), although it is not necessary to add any chemical agent - caustics or de-inking agent - during the pulping step (2). Inn entering the ink-releasing step I
the pulp has a brightness=60IS0, a freeness=40-45SR, and a filler continuity%.
The ink-releasing equipment is the same as for example (1) but operating parameters are as follows: Removing L8001=
0.3~.; hydrogen peroxide%, sodium hydroxide%, sodium silicate= 3%. All other parameters remain unchanged. At the end of the process, the pulp has shown a brightness increase of 2 ISSUE and freeness did not show any appreciable variation.
The pulp is then washed by means of three washing stages as for example (1), but the design of the perforated plates are different: the first stage is fitted with 2mm. diameter holes, the second and the third stages are equipped with 1.4mm.
diameter holes. Also the feed consistency of the washing stages is different, being 2.5%. With these parameters, the final washed primary pulp has shown the following characteristics:
brightness=75IS0, filler content below 3%, freeness 27-30 SR.
The effluent leaving the first washers has a consistency between 1% and 1.2%, a filler continuity%, brightness=50IS0, and freeness=70SR.
The flotation cell used in this application is a high consistency Sumac type, and heavy stock has been pumped from chest (6) and mixed together with the effluent before the flotation in order to raise the consistency up to 1,5%, In this way, the two lines (primary by washing and secondary by flotation) have exactly the same solids flow rate, or the same capacity in tensed but produce two pulps having opposite characteristics. This extraction also procures long fibers which will help the final filtration (12), This extraction could have been done using washed pulp and this would have increased the brightness of the secondary pulp. But in such a case, the washing equipment would have to be sized for 30% more capacity, which is not a worthy choice in our case.
The flotation is then conducted with only 2% of the same collector (Removing F) and the retention time through the cell is only 10 min., thus producing a loss of weight of 10% (which means 5% of the total pulp).
After acidification at phi ahead of the disk filter, the pulp shows a brightness=70IS0, a filler continuity%, a frenzies.
The Polydisk filter can be sized using a filtering factor = 25 liters/min./m2, and produces an effluent containing 70-100 Pam suspended solids. The other steps of this application are similar to the ones described in example (1), The application of such a process in a paper mill having several paper machines as in this example is offering * trade mark I,. of /
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the following advantages:
appeasability to produce a pulp having physical and cleanliness characteristics similar to the ones of a virgin chemical pulp, thus usable for the production of fine light weight papers, with good Yankee dryer glazing capabilities;
possibility to produce a pulp having physical and optical characteristics of a mixture of fine chemical and/or grounded pulp, and mineral fillers, thus usable for the production of printing papers where high opacity and smoothness are requested, possibility to mix these two pulps together in a ratio which can be very much different from the original one coming together with the raw material.
The raw material is a mixture of low quality printed waste, containing old books, office waste and stationery, and some newspapers and magazines, in variable proportions.
The mill has one multiple board machine, and procures high quality folding box board, which can be on-machine coated and must show an excellent multicolor offset printing aptitude. The white top liner is composed of 100%
de-inked primary pulp and the underliner uses the secondary pulp, mixed with other pulp.
Pulping is conducted in a continuous way with the tame parameters as for example (1). The cleaning and screening treatment (3) is simplified and composed of centrifugal high-density cleaners, followed by a turbo-separator, working at 3% consistency. The following thickening stage is also simplified and composed of inclined screws producing pulp at 15% consistency, followed by a screw press. The finest contaminants will be detached and better dispersed during the ink-releasing step (5) and then carried away with the effluent during the washing stage. They will remain in the secondary pulp thus contributing to add weight and volume to the board, as the underliner does not need to be particularly cleaned.
The pulp entering the ink-releasing and dispersing step shows a brightness ISSUE, a filler content =25-30%.
The operating parameters are the same as for example (1), but the brightness drops down to ISSUE.
The following washing step has only two stages, which are fed at 2.5% consistency, The perforated plates of the inclined screws have 1.6mm. diameter holes, and it has been found that the characteristics of the effluent are very similar to the one of example (1), The washed primary pulp shows a brightness ISSUE, a filler content =4% and a freeness =45-50SR. The fine cleaning of the primary pulp is achieved with the cleaners and the screens installed ahead of the board machine, which is sufficient to reach the desired quality, It must be said that the contaminants have been thoroughly dispersed in the kneader (5) and most of them have left this primary pulp during the washing step.
The satellite circuit is also simplified because the brightness of the underliner has only a third-order influence on the final brightness of the coated board, We have observed that a brightness of the underliner secondary pulp in the ISSUE range was sufficient to ensure the required brightness ISSUE of the coated board providing that the top liner primary pulp has ISSUE, Thus, the flotation time has been reduced below 10 mint and the dosing of the collector has been kept below 2%. We have also observed that it was possible to run without any chemical when lower quality grades are produced, but no compromise can be applied on the dispersion effect, because black spots in the under_ liner are always visible even through the coated top liner.
The application of such a process to the production of stratified board is offering the following advantages:
appeasability to totally replace chemical pulp or high quality selected unprinted waste paper by a low value and large availability raw material;
~LZZ9~
simplification of the main line by eliminating the fine screening and cleaning equipment;
conquers of the total yield, by transferring in the secondary pulp (and then in the underliner or in the middle ply) all finely dispersed contaminants which are not acceptable in the top liner,
Recycling of waste paper is possible only after most of the non-cellulosic contaminants have been removed from the fiber mass. These contaminants may have been introduced during the printing steps (carbon black, pigments, ink vehicles, ink fixating polymers, etc....), during converting, (varnishes, coats, binders, wrapping, etc...) and later during the collecting phase (metallic pieces, plastics, soils and dirt of any kind).
Removing of the contraries generally occurs based on chronological dimensional sequences, through screening, magnetic separation, first in dry conditions and later in aqueous suspension.
The fiber mass is then screened through perforated plates and finer contraries are removed by centrifugal and centripetal cleaners.
The ink particles are not substantially removed during the proceeding steps, an this operation is achieved in two steps: (a) detaching the ink particles from the fiber surface, through the combined action of chemicals, temperature and mechanical shear forces and (b) removing these particles from the pulp slurry.
Generally, all the contraries including the ink particles, are released from the fibers during the defibering phase. The waste paper is treated in a pulper, under alkaline conditions at 50-60C. temperature, in order to be well defibered and transformed into a pump able slurry. An alternative to this process is to operate the pulper in cold conditions, then thicken the pulp above 15% consistency, then heat the pulp with steam at 60C.
introducing at that point the de-inking and bleaching chemicals. The pulp then remains in a reaction tower during 2-3 hours without any mechanical action.
The first drawback of these techniques is that all contaminants are submitted to the thermal treatment, including the ones which have low melting points, such as YO-YO' , I
binders, hot melts, plastics and other "stickles". By this way, they become dispersed and cannot be removed any more by the conventional means, and will precipitate again on paper machine elements such as doctor blades, wires, felts, pipe walls, etc..., creating operating problems and loss of efficiency.
A second drawback is that these ink-releasing techniques have a weak action on the modern inks such as the rotor offset inks, where ink vehicles are made of synthetic resins which form an insoluble polymer onto the surface of the fibers. The same consideration applies for xerocopy printed paper and varnished papers, where temperatures in the range of 60C. will provide neither any softening of the ink vehicles nor any weakening of the bonding between the fibers and these vehicles.
Another limitation of these techniques is that it is not possible to increase the temperature of the ink releasing step, because the combination of the alkalinity and the temperature during a long time will result in an unacceptable yellowing of the pulp, specially if some grounded is present in the mixture to be treated.
Ink removing techniques in use to-day are essentially two: flotation and washing.
In flotation , the diluted fiber slurry is intensively mixed with air after a hydrophore ink collector has been added. Then stock is naturally decorated and air bubbles collect the ink particles during the upwards travel to the surface. The resulting black foam is then collected and treated separately through centrifuges, then skewered-In washing, a very old and well known process, the finest dispersed particles are removed through several dilutions and squeezing cycles, generally arranged as a counter-current cascade configuration. The effluent of the first squeezing sequence contains all the free fine ink particles, but also a great quantity of fine cellulosic fibers and most of the mineral fillers, and are skewered and treated according to the local pollution regulations.
Some other ink removing techniques exist such as solvent extraction but have not been followed by wide industrial application, due to high production cost and low quality of the produced pulp.
In the US. Patent N4,076,578 Pudding ton et Alp recall the fundamental concept of de-inking: (a) releasing ink from the paper fiber by means of chemico-thermo-mechanical treatment and (b) separating of dispersed ink particles from the pulp, then proposes a different method to achieve this goal, through adsorption of the ink particles onto the surface of solid particles, followed by the removal of said particles from the pulp, and then removal of the ink from those solids.
Nowadays, none of the above mentioned processes has asserted itself because each of them presents some drawbacks.
The flotation is a low consistency process (between 1% and 2%) and thus involves high volumes of pulp, with consequent high investment cost. Also, the nature of this process is essentially physico-chemical and thus its stability is greatly related to the stability of the compost-lion of the waste paper, the type of fibers (chemical or mechanical), the type and content of mineral filler, the calcium ion concentration. Consequently, the brightness of the de-inked pulp shows undesired high fluctuations, These brightness variations are also accompanied by all composition variations coming together with the raw material (waste paper), without any possibility of control or continuous measurement and monitoring.
To-day, it is generally admitted that the first condition for the good operation of a modern fast paper-machine is the constancy of operating parameters, the most important one being the composition of the stock feeding machine. Unfortunately, it is not possible to control the composition of a waste paper lot as easily as a virgin I
pulp bale. For this reason, the efficiency decrease of high-speed paper machines using high percentages of flotation de-inked pulp is mainly caused by the uncontrolled variations of the stock composition rather than by the brightness (or de-inking efficiency) variations. This problem can be solved using selected classified waste paper, at a price which makes the de-inked pulp uncompetitive respect to the virgin pulp, assuming that such type of waste is available.
lo Finally, the flotation process needs to be continuously controlled, on a three shift basis, by highly specialized chemical experts using sophisticated instrumentation and laboratory, thus appreciably increasing the production cost.
The washing process involves simpler, cleaner, and easier to control equipment, in particular when washing occurs at consistencies between 3% and 15%.
This process does not require any specialized control and it is admitted that not only the quality (cleanliness and strength) of the washed pulp is definitely higher than for the floated pulp, but this quality is much more constant and less sensitive to raw material variations of composition, thus offering a higher "tunability" of the pulp in the paper machine room.
In fact, the principle of washing on a perforated plate statistically says that elements having a smaller size than the plate openings should pass through the plate. It appears that the variations of composition of the stock to be de-inked (fines, grounded, mineral fillers) will reverberate on the fraction lost through the plate, giving a final product almost constant in quality, if not in quantity. This principle allows for the use of unselected waste paper, a lower quality product having a much lower cost and higher availability.
On the other hand, this process needs a much higher quantity of water, and produces the equivalent higher quantity of effluents which still contain a great quantity , I
35~ -of valuable products cellulosic short fibers mineral fillers, mixed together with the undesired ink. Besides that direct loss, it is necessary to consider the us-direct cost due to the abatement of the pollution created by the solids contained in the effluents.
In conclusion, it can be said that if flotation de-inking presents high investment and operating cost together with low constancy of the quality of the final product, washing de-inking also shows a high similar cost of the product due to both the intrinsically low yield of the process and the pollution abatement cost.
In order to minimize the negative aspects of each one of these basic processes, their supporters have proposed several combinations of them, keeping in mind to produce only one de-inked pulp starting from one waste paper mixture.
In the French Patent Application N79 19392, M. Fritz Zebu of Voith Cry. suggests to remove the fine fibers fraction together with the mineral fillers from a flotation de-inked pulp, using screens and strains arranged as washing elements. This process, which is only summarily described without any example, seems to add up both costs and drawbacks of flotation and washing.
In the TAIPEI magazine, vowel, N9, September 1980 M. Luther Pfalzer of the same Voith Cry., while recalls the same concept (page 116, fugue), specifies that the fine fiber fraction and mineral fillers are centrifugated and then skewered and lost. It also appears from this publication that the effluent is totally sediment Ed after having been flocculated by addition of aluminum sulfate, but it is also specified that a good dispersion of the ink particles can be obtained at high and well controlled phi These two statements are rather contradictory and make this concept hardly applicable in practice, M. Pfalzer also suggests the opposite philosophy (page 114, foggily), which consists of a total flotation so 5~ii followed by a total sedimentation of the effluents of a conventional washing process. For the same reasons as above, which are: the low yield of the washing process, the non-compatibility between ink dispersing high pi and aluminum sulfate sedimentation low phi the addition of the costs and drawbacks of each individual process, this proposal has not been applied on an industrial scale.
In the French Patent Application N78 29637, M, Calumniate of Montedison Cry. suggests in a more simple way to separate the ink particles from the fine fibers and the mineral fillers contained in the effluents of a washing process, by means of a simplified flotation process where no chemicals are added. It is also stated that the chemicals added at the beginning of the process (pulping stage) will also provide for the ink collecting function. In this process, the suckled "clarified"
effluents which actually contain most of the fibers and mineral fillers lost during the washing step, are totally recycled ahead of the process.
A tentative application of this process had to be quickly abandoned for two reasons. At first, it has not been possible to obtain a satisfactory selective removal of the ink during the flotation, because of the antagonistic functions of the two chemicals mixed together at the pulper:
(a) dispersing of the ink needed during washing, (b) keg-lotion of the ink needed during flotation, So, too much fibers and fillers were floated together with the ink resulting in a quick overloading of the sewer system, and immediate shut down of the plant.
At second, it has not been possible to recirculate continuously-ahead of the washers, an effluent which contains most of the fines and fillers lost by the same washers. This total recirculation has quickly resulted in (a) a drop of the brightness due to the poor ink removal efficiency and (b) an unacceptable drop of the hydraulic capacity of the thickening elements. Both can be attributed 1, .
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to the saturation of the circuit with fines and fillers, dimensions of which are of the same order of magnitude than the ink particles.
In the Italian Patent Application N26344 A/80, M. Calumniate recalls the same principle, where the effluents at a concentration of 0.14% would be selectively floated with the only addition of air, and then totally recycled ahead of the process together with their suspended solids.
M. Calumniate nevertheless suggests to install a "quick"
flotation, a third flotation, installed ahead of the washing process. This configuration does not seem to bring any answer about the two basic previous problems; (a) how is it possible to have the best dispersion together with the best coagulation, (b) how is it possible to avoid the saturation, the clogging of the thickening elements, and the loss of the ink removal efficiency, due to the recirculation of the fines and the fillers together with the effluent.
GOALS OF THE INVENTION.
The present invention aims to provide a practical and integral industrial process which allows to produce, in a continuous way and starting from a mixture of unselected waste papers, three separate products, namely:
a) a totally cleaned and de-inked pulp having constant and controlled brightness and fiber classification, having a very low and constant fillers content;
b) a totally cleaned and de-inked pulp having a fine fiber classification and a very high fillers content, these two parameters being variables both quality and quantity;
c) an effluent which does not practically contain suspended solids, which has not been submitted to any pi reversion, which does not contain any flocculation or sedimentation chemical agent, and thus is immediately and totally reusable as the dilution YO-YO
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and washing liquid during the ink removal step of the de-inking phase.
A further aim of this invention is to provide a practical and advantageous improved method for de-inking these grades of printed papers and boards which cannot be correctly de-inked by conventional methods.
Another aim of this invention is to provide a practical and advantageous method which allows to produce high quality paper and board at high speeds using the low quality waste grades which could not be used for such noble purpose when treated by conventional methods.
The invention is also directed to the application of modified and purposely adapted ink removal processes !
such as washing, selective separation, flotation, coagulation, filtration, onto the high ink-content slurry produced by the primary itik removal process.
The invention also aims to allow for the use in paper making of the by-products of a washing de-inking process, either on the paper machine which will use the primary pulp, or on a different paper machine.
An object of this invention is to provide a means to create a constant and controlled composition of the pulp used for paper making, which can be different from the composition of the incoming waste paper mixture, This object is achieved by pumping controlled flows of each one of the two components and mixing them ahead of the paper machine(s) in the desired percentage; the capacities of the chests act as buffers between waste paper and paper machine stock compositions.
Another object of this invention is to increase the value of the by-product (the secondary pulp) by the fact that good long fibers can be extracted from the main line in order to optimize the operation both of the selective separation of the ink and of the filtration on fiber mat.
A further object of this invention is to accomplish ~L~22~ 5 g the selective separation of the ink at a stage where this ink is highly concentrated (approximately three times more than in the main pulp), thus increasing the efficiency of the chemicals.
An ulterior object of this invention is to achieve the selective separation of the ink (which is the more delicate operation of the whole recycling process), in a satellite circuit of reduced capacity (approximately one third of the flow through the main line), thus being easier to operate and requiring lower investment cost, This invention then aims to ensure the highest possible constancy of quality of the primary pulp, by the fact that the variations of fines and fillers contents will instantaneously reverberate on the fraction produced by the satellite circuit, which in turn can also be stabilized by means of a thorough mixing and high retention time in the final buffer chest, With these and other aims and objects, the nature of which will become more apparent, a fuller understanding of this invention will be gained by reference to the following detailed description and the appended claims.
SUMMARY OF TIE INVENTION
According to one aspect of the invention there is provided a method of treating a mixture of printed and contaminated waste paper in order to produce pulp for use in the manufacture of pulp and paper boards, which method comprises: (a) forming an aqueous pulp of the waste paper at low temperature and low specific mechanical energy, thereby forming a palpable slurry, and releasing non-ink contaminants from the surface of the waste paper but without dispersing the released non-ink contaminants throughout the resulting fibrous suspension; (b) separate in the non-ink contaminants from the pulp by mechanical separation, without the use of froth flotation, solvent extraction or other chemical]. process, using conventional / , of I
screens and centrifugal cleaners and without any further application of strong shear forces to the pulp; (c) softening ink particles and weakening their bonds with the surface of the fires by submitting the pulp at a consistency of more than 15% to the simultaneous actions of (i) a temperature between 85 and 130C, (ii) high shear forces and (iii) at least one de-inking agent, under alkaline conditions; (d) detaching the ink particles from the surface of the fibres'and dispersing them into the fibrous 'suspension by submitting the pulp to the simultaneous actions of (i) and (ii), as defined in step I and (iv) at least one chemical dispersing agent, under alkaline conditions; (e) removing the free ink particles to obtain the degree of brightness required by the final use of the pulp.
According to a further aspect of the invention there is provided a method of treating a mixture of printed waste paper in order to produce pulp for use in manufacture of paper and board, which method comprises: (a) forming an aqueous pulp of the waste paper; (b) removing non-ink contaminants from the pulp and releasing ink particles from the surface of the pulp fibers to obtain the degree of brightness required by the final use of the pulp; (c) removing ink particles from the remaining dispersed fine material of the pulp using at least one washing stage under alkaline conditions and in the presence of at least one ink dispersing agent, thereby producing: (i) a primary pulp having controlled and constant brightness and fiber classification with very low and constant filler content and (ii) a secondary pulp containing a variable high filler content and a variable quantity of fine fibers, together with the ink particles and some clean fibers; (d) mixing the secondary pulp (ii) with an ink-collecting hydrophobic agent, after the ink-dispersing agent has been neutralized or precipitated, under alkaline conditions, and then removing the ink particles from the effluent by I
selective separation of the hydrophobic agent from the fibrous suspension; (e) reducing the alkalinity of the slurry by addition of non-caustic insolubilizing cations and a strong mineral acid, thereby producing a filterable slurry; (f) filtering the fibrous suspension at a low filtering rate on a fibrous mat composed of fibers coming from the same process, thereby producing: (iii) a secondary de-inked pulp having a fine fiber classification and a very high filler content, both instantaneously variable, and (iv) an effluent which is practically free of suspended solids;
(g) diluting the pulp thickened by the last but one washing stage with the clarified effluent of step (f) thereby conserving the water used in the method; and (h) storing the filtered secondary pulp in a vat for several hours with intense mixing by agitation and recirculation, thereby leveling off the fluctuations of the filler content, the fiber classification and the freeness.
so I, Lo DESCRIPTION OF THE INVENTION
The following detailed description, together with the attached schematic flow-sheet, refers to one preferred practical application of the invention, although other procedures can also be applied.
Following the flow-sheet, the bales of waste paper are loaded into a pulper (2) by means of a loading mocha-noisome, together with the recycled water and eventual caustics in order to bring the pi at values above 7. It is possible but not mandatory to introduce part or all the quantity of dispersing chemicals required by the ink-releasing action, during -the pulping operation.
The pulp is then diluted using recycled water and pumped through one or several stages of screens and cleaners (3) in order to release contraries and contaminants from the paper surface, and further remove them from the pulp slurry, When the de-inked pulp is used for high quality paper production or on high-speed machines such as light weight coating base or newsprint, this operation must be done in the same way it is done with chemical or mechanical virgin pulps, using the same equipment and operating parameters.
In particular, the best results have been obtained through a combination of pressurized slotted screens equipped with 0.3mm, slot width working at I consistency followed by 4 inches size cleaners working at 2.8 bars pressure drop and 0.6% consistency in the first stage.
It is anyhow of paramount importance that the temperature of the stock is kept as low as possible so that the low melting point contaminants will remain rigid and will not extrude through the slotted screens and thus be eliminated by the screens, This pulp is then thickened (4) to the consistency required by the ink releasing process. The effluents produced by this thickening stage can easily be recycled, as they are cold and do not contain much fibers and very little ink. At the beginning of the following ink-releasing step (5) chemicals are mixed together with ~22~gS5 the fiber suspension. Caustics are added in order to raise the pi up to 9-10, together with oxidizing agent (such as hydrogen peroxide), and stabilizers (such as sodium silicate, and dispersing agents (surfactants, eta,.,). The basic parameters of this process, - temperature, pressure, specific energy, chemicals dosing - will be determined in order to ensure the optimum detachment of the ink particles from the surface of the fibers together with their finest dispersion inside the pulp.
In the hollowing examples, this operation has been made in a kneader, also called triturator, which permits to bring the temperature at the desired value (ire. above the melting point of the ink vehicles) within a few seconds and simultaneously apply very strong shear forces at high consistency and in presence of de-inking agents, The principle of the operation is that at first, the combined actions of ink-releasing chemicals and temperature (90-130C) will soften the ink vehicles and weaken the bonding between the same and the fibers, and then the combined actions of ink-dispersing chemicals and intense shear forces will detach and finely disperse these particles inside the fiber suspension. The high consistency (20-30%) allows to treat very low volumes of pulp in small machines during a very short time (2-3 minutes), thus avoiding the yellowing of the pulp and increasing the efficiency of the chemicals.
This pulp then remains 5 to 20 minutes in a latency chest (6), at a consistency between 2% and 5%. It may then be deflated in order to well separate the fiber bundles one from the other, and thus facilitate the ink removal from the slurry.
The fibrous suspension finally goes through the ink removal process (3) which can be advantageously composed of multistage counter-current, high consistency washing, The number of stages is chosen according to the quantity of ink to be removed and to the desired final brightness.
The extraction of the water is conducted through strains , . c I
or perforated plates, the dimensions of the openings of which will be selected in order to allow for a given quantity of fibers to be carried away together with the effluent, thus ensuring the optimum operation of both the following ink selective separation process, and the final filtration of the recovered satellite secondary pulp.
In case a filler-free secondary pulp is desired! the effluents from the washing step (8) can advantageously be strained again on one or several fine mesh filters (9), By this mean, it is possible to remove at each filter stage up to 80% of the mineral fillers contained in that slurry, In such a case the finest fraction must be sent to a conventional alkaline clarifier (10) and then skewered, The clarified fraction is then returned ahead or after the following ink selective separation step (11), according to the operating parameters of this last process (consistency, temperature), and according to the required brightness, The necessary chemicals are also introduced ahead of this step. In case this process is a selective flotation, ink collectors such as fatty acids or their sodium or calcium soaps can be added, taking care to ensure a mixing time of about 5 minutes at a temperature of about 35 to 45C.
It may be worthy to recall that the dispersing agent used during the washing step has a negative effect both on the coagulation produced by the collecting agents during the flotation step, and on the trainability (freeness) of the fibrous suspension during the filtration step. It will be good to inactivate or neutralize these agents for example by precipitation with calcium chloride or calcium hydroxide, The precipitation of the sodium silicate will also contribute to increase the brightness of the secondary pulp through the formation of a precipitated mineral filler It has also been observed that the quantity of mineral fillers removed together with the foam during the flotation step may vary from 30~ up to 70% according to the operating parameters of the process: flotation time, temperature, pulp consistency.
dosing and type of chemicals. The rejected foam containing " :
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the ink is then pumped to centrifuges or filter-presses and skewered. The loss of solid particles has been observed to be between 10% and 20% of the flow of secondary pulp, which means about 3% to 6% respect to the total quantity of pulp feeding the washing step (8).
It has also been observed that the maximum efficiency of the ink removal has been reached at much higher consistencies than the ones recommended by the suppliers of the cells.
For example, a cell designed to work at 1% has shown best results between 1.5% and 2%. This peculiarity allows for the treatment of lowest quantities of effluents, using higher consistencies during washing, and larger holes in the extractors perforated plates.
When the requested concentration for the ink selective separation process is higher (say 0,5% or more) than the maximum concentration which can be given to the effluent of the washing step, some heavy stock can be advantageously extracted from the latency chest (6). In this easel the small quantity of long fibers added to the secondary pulp will help in forming the filtering mat the final filtration step (12).
The selective separation of the ink (if) can also be a process based on adsorption of the ink upon the surface of non-soap solids, as recommended by Ire Pudding ton et Al, in the US. Patent N4,076,578.
The de-inked slurry leaving the process (if) is then filtered on fibrous mat up to at least 4% consistency, possibly above 10% in order to remove from the final secondary pulp the maximum possible quantity of dissolved salts.
In case this pulp contains a very high quantity of grounded fines and fillers (such as mixtures of newsprint and magazine paper), the pi ahead of the filtration step has to be dropped down to values below 8, by addition of sulfuric acid (preferably to aluminum sulfate), under intense mechanical agitation (as could be the suction side of a centrifugal pump), and after some long fibers extracted from the washed final primary pulp has been added to the I
I
satellite slurry to be filtered.
It has been observed that the application of equipment such as Polydisk or Waco Filters to the thickening process (12) has permitted to produce clear filtrate having less than 100 Pam suspended solids and consequently totally reusable in the pulping (2), cleaning (3) and washing (8) processes without any further clarification.
The final thickened secondary pulp leaving (12) must then be brought to a pi compatible with the following use - by addition of sulfuric acid or aluminum sulfate always under intense mechanical agitation, and can be stored in a buffer chest according to the final use.
EXAMPLES
The following examples will illustrate three different applications of the general procedure previously described, using different mixtures of waste paper and producing different grades of paper and board, Measurements of brightness were made with an Elrepho* meter with 457nm light filter, according to ISSUE. standards, Chemical dousings are expressed in percent by weight of the chemical at 100% concentration respect to the weight of total solids in the line where said chemical is added. Sodium silicate is considered at 38 Be and the Removing* F and L as supplied.
The raw material is a mixture of over-issued news-papers and telephone books (white and yellow pages) in a ratio approximately 50/50. The de-inked pulps are used for t-he production of newsprint and telephone directory papers (white and yellow), on only one high speed paper machine, In this installation, the pulper has a capacity of 46m3 containing 2.700 kg of waste paper, Each batch longs 30 mint Dilution water is coming from the effluent of the thickening process (4) and make-up is made using clear filtrate from the Polydisk filter (12), One percent of sodium hydroxide is added in the pulper together with 1% of a de-inking agent ' ~,~; 'Allah * trade mark Lowe such as Removing L 8001 supplied by Chemicarta Swag Milan, When this cold pulping operation is finished, the stock is pumped through turbo separator, screens and cleaners, at consistencies starting around 4% and ending at about 0.6%, The turbo separator is equipped with a perforated plate having 3mm. diameter holes and the rejected stock is then sent to a vibrating flat screen also having 3mm.
holes, rejects of which are skewered.
The accepted stock from the turbo separator is then diluted from 3% down to 1% before it passes through pressurized slotted screens fitted with 0.30mmt slot width. The rejected stock is processed through a second stage screen having the same slot size, and rejects of the same go to a vibrating flat screen, rejects of which are Seward The accepted stock from the first stage of screens is then diluted down to 0.6% consistency and processed through a conventional battery of 4 stages of Triclean cleaners. The light and the heavy rejects of the Thea stage are skewered.
The total loss of both high and low consistency turbo separating, screening and cleaning is varying between 6% and 9% by weight, depending upon the degree of contamination of the waste paper. No more stickles or hot melts can be seen in the pulp, and the eye inspection is confirmed by the Somerville test, which shows less than 0.2% of shrives.
At that point, the pulp is totally cleaned and the only remaining contaminant is the printing ink. The pulp is then thickened up to 30% consistency in two steps, using a disk filter up to 10-12% and then a screw press up to 30%. Characteristics of the pulp are: Britons ISSUE
frowns SR, filler continuity%, temperature=20-25C.
The ink releasing step (5) is achieved in a kneader under the following operating conditions: temperature C,, sodium hydroxide= 1.5%, sodium silicate= 4%, hydrogen peroxide = 1.8%, specific enrage KW.H/Ton during 3 minutes The brightness of the pulp at the end ox the treatment is * trade mark :~L22~3~355;
ISSUE, and freeness is 60-65SR. The pulp is then diluted using all the flow of effluents coming from the second stage of washers, then squeezed up to 12% in the first washing stage.
These washers are composed of inclined screws (better known as Rice-Barton or Baker's screws), where the pulp is drained under continuous and vigorous agitation through perforated plates having 1.4 mm. diameter holes, in order to produce an effluent having approximately 0.8-1% consistency, The thickened stock is then processed through two other similar counter current washing steps and the final usable pulp presents the following characteristics: brightness=59-60IS0, freeness=46-50SR, filler content 2-3%, consistency%.
This pulp represents 78% by weight of the quantity of pulp feeding the washers (8). The balance 22% is going to the satellite circuit with the first stage effluent which shows:
brightness=3S-40IS0, filler continuity%, freeness=80SR.
The capability for the ink of being removed from the fibers contained in the effluent has been verified in the laboratory as follows: an effluent sample has been hyperwashed under fresh water shower on a 200 mesh wire, and a hand sheet has been made, showing a brightness of ISSUE, which is very similar to the brightness of the final primary pulp.
This effluent has then been mixed together with 4% of a special ink-collecting agent purposely designed for this application by Chemicarta SPA, Milan, and kept for 5 min.
under agitation at 30C.
The mixture is then processed through one single stage conventional flotation cell, Voith open type, during 15 min. The loss of weight through the cell is 15-20%, which means only 3-4, 5% respect to the total quantity of pulp entering the washers. We have found that addition of 0.5% to 1% of calcium chloride or calcium hydroxide together with the collector, ahead of the flotation, helps controlling the foam and the ink coagulation when low ash content pulps are processed.
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The total alkalinity is then dropped down to pH=7-8 with addition of 1% of sulfuric acid on the suction side of the centrifugal pump feeding the disk filter (12) At this point, the pulp shows a brightness=53-56IS0, a filler content =15-20~ and a freeness=78-80SR.
The disk filter (12) is a Polydisk filter sized according to a specific filtering factor liters/min.lm2.
Besides this unusual value, it is also necessary to feed the mat-peeling showers with air instead of water, in order to reach the maximum possible consistency of the discharged pulp .
Using the above mentioned parameters, a final consistency of 8% to 10~ could be obtained and the clear filtrate shown less than lOOppm average suspended solids, measured on paper filter, black label.
The pulp is then brought to phi and sent to a buffer chest having 8 hours total retention time. From this point it is then pumped to the mixing chest of the paper machine at controlled flow rates according to the paper grade actually produced and in function of the mean composition of the secondary pulp.
The clear filtrate from the Polydisk filter is then totally recycled in order to dilute the stock ahead of the third washing stage and make-up is provided by fresh industrial water which does not contain aluminum ions.
The application of such a process in a paper mill having one single paper machine is offering the following advantages:
appeasability to maintain constant freeness and ash content during a grade run, independently from the incoming waste paper characteristics, thus allowing the paper machine to run at maximum speed and efficiency;
possibility to achieve very quick grade change, exactly as when using virgin pulp and fillers, without the need to intervene a long time before in the waste , paper plan, thus permitting an easier and more constant operation of that plant;
possibility to always use the highest possible quantity of recycled fibers in the paper, by the free disposal of each one of the two fractions and their use in the optimum way, possibility to produce totally cleaned pulps having the same standards of cleanliness than virgin pulps and thus offering the highest possible tunability in the paper machine room, particularly being free of any "sticky" or ought melt" or ink vehicle free particle.
The raw material is a mixture of printed continuous stationary, old books and office file, in a ratio 50/50.
The dunked pulp is used to produce, on three distinct paper machines: (a) light weight machine glazed wrapping papers, (b) fine papers for writing and printing, including wood containing printing grades, (c) stationary and continuous print-out papers, The operation is similar to example (1) up to the thickening step (4), although it is not necessary to add any chemical agent - caustics or de-inking agent - during the pulping step (2). Inn entering the ink-releasing step I
the pulp has a brightness=60IS0, a freeness=40-45SR, and a filler continuity%.
The ink-releasing equipment is the same as for example (1) but operating parameters are as follows: Removing L8001=
0.3~.; hydrogen peroxide%, sodium hydroxide%, sodium silicate= 3%. All other parameters remain unchanged. At the end of the process, the pulp has shown a brightness increase of 2 ISSUE and freeness did not show any appreciable variation.
The pulp is then washed by means of three washing stages as for example (1), but the design of the perforated plates are different: the first stage is fitted with 2mm. diameter holes, the second and the third stages are equipped with 1.4mm.
diameter holes. Also the feed consistency of the washing stages is different, being 2.5%. With these parameters, the final washed primary pulp has shown the following characteristics:
brightness=75IS0, filler content below 3%, freeness 27-30 SR.
The effluent leaving the first washers has a consistency between 1% and 1.2%, a filler continuity%, brightness=50IS0, and freeness=70SR.
The flotation cell used in this application is a high consistency Sumac type, and heavy stock has been pumped from chest (6) and mixed together with the effluent before the flotation in order to raise the consistency up to 1,5%, In this way, the two lines (primary by washing and secondary by flotation) have exactly the same solids flow rate, or the same capacity in tensed but produce two pulps having opposite characteristics. This extraction also procures long fibers which will help the final filtration (12), This extraction could have been done using washed pulp and this would have increased the brightness of the secondary pulp. But in such a case, the washing equipment would have to be sized for 30% more capacity, which is not a worthy choice in our case.
The flotation is then conducted with only 2% of the same collector (Removing F) and the retention time through the cell is only 10 min., thus producing a loss of weight of 10% (which means 5% of the total pulp).
After acidification at phi ahead of the disk filter, the pulp shows a brightness=70IS0, a filler continuity%, a frenzies.
The Polydisk filter can be sized using a filtering factor = 25 liters/min./m2, and produces an effluent containing 70-100 Pam suspended solids. The other steps of this application are similar to the ones described in example (1), The application of such a process in a paper mill having several paper machines as in this example is offering * trade mark I,. of /
. I..
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the following advantages:
appeasability to produce a pulp having physical and cleanliness characteristics similar to the ones of a virgin chemical pulp, thus usable for the production of fine light weight papers, with good Yankee dryer glazing capabilities;
possibility to produce a pulp having physical and optical characteristics of a mixture of fine chemical and/or grounded pulp, and mineral fillers, thus usable for the production of printing papers where high opacity and smoothness are requested, possibility to mix these two pulps together in a ratio which can be very much different from the original one coming together with the raw material.
The raw material is a mixture of low quality printed waste, containing old books, office waste and stationery, and some newspapers and magazines, in variable proportions.
The mill has one multiple board machine, and procures high quality folding box board, which can be on-machine coated and must show an excellent multicolor offset printing aptitude. The white top liner is composed of 100%
de-inked primary pulp and the underliner uses the secondary pulp, mixed with other pulp.
Pulping is conducted in a continuous way with the tame parameters as for example (1). The cleaning and screening treatment (3) is simplified and composed of centrifugal high-density cleaners, followed by a turbo-separator, working at 3% consistency. The following thickening stage is also simplified and composed of inclined screws producing pulp at 15% consistency, followed by a screw press. The finest contaminants will be detached and better dispersed during the ink-releasing step (5) and then carried away with the effluent during the washing stage. They will remain in the secondary pulp thus contributing to add weight and volume to the board, as the underliner does not need to be particularly cleaned.
The pulp entering the ink-releasing and dispersing step shows a brightness ISSUE, a filler content =25-30%.
The operating parameters are the same as for example (1), but the brightness drops down to ISSUE.
The following washing step has only two stages, which are fed at 2.5% consistency, The perforated plates of the inclined screws have 1.6mm. diameter holes, and it has been found that the characteristics of the effluent are very similar to the one of example (1), The washed primary pulp shows a brightness ISSUE, a filler content =4% and a freeness =45-50SR. The fine cleaning of the primary pulp is achieved with the cleaners and the screens installed ahead of the board machine, which is sufficient to reach the desired quality, It must be said that the contaminants have been thoroughly dispersed in the kneader (5) and most of them have left this primary pulp during the washing step.
The satellite circuit is also simplified because the brightness of the underliner has only a third-order influence on the final brightness of the coated board, We have observed that a brightness of the underliner secondary pulp in the ISSUE range was sufficient to ensure the required brightness ISSUE of the coated board providing that the top liner primary pulp has ISSUE, Thus, the flotation time has been reduced below 10 mint and the dosing of the collector has been kept below 2%. We have also observed that it was possible to run without any chemical when lower quality grades are produced, but no compromise can be applied on the dispersion effect, because black spots in the under_ liner are always visible even through the coated top liner.
The application of such a process to the production of stratified board is offering the following advantages:
appeasability to totally replace chemical pulp or high quality selected unprinted waste paper by a low value and large availability raw material;
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simplification of the main line by eliminating the fine screening and cleaning equipment;
conquers of the total yield, by transferring in the secondary pulp (and then in the underliner or in the middle ply) all finely dispersed contaminants which are not acceptable in the top liner,
Claims (45)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of treating a mixture of printed and contaminated waste paper in order to produce pulp for use in the manufacture of pulp and paper boards, which method comprises:
(a) forming an aqueous pulp of the waste paper at low temperature and low specific mechanical energy, thereby forming a pulpable slurry, and releasing non-ink contaminants from the surface of the waste paper but without dispersing the released non-ink contaminants throughout the resulting fibrous suspension;
(b) separating the non-ink contaminants from the pulp by mechanical separation, without the use of froth flotation, solvent extraction or other chemical process, using conventional screens and centrifugal cleaners and without any further application of strong shear forces to the pulp;
(c) softening ink particles and weakening their bonds with the surface of the fibres by submitting the pulp at a consistency of more than 15% to the simultaneous actions of (i) a temperature between 85 and 130°C, (ii) high shear forces and (iii) at least one de-inking agent, under alkaline conditions;
(d) detaching the ink particles from the surface of the fibres and dispersing them into the fibrous suspension by submitting the pulp to the simultaneous actions of (i) and (ii), as defined in step (c), and (iv) at least one chemical dispersing agent, under alkaline conditions;
(e) removing the free ink particles to obtain the degree of brightness required by the final use of the pulp.
(a) forming an aqueous pulp of the waste paper at low temperature and low specific mechanical energy, thereby forming a pulpable slurry, and releasing non-ink contaminants from the surface of the waste paper but without dispersing the released non-ink contaminants throughout the resulting fibrous suspension;
(b) separating the non-ink contaminants from the pulp by mechanical separation, without the use of froth flotation, solvent extraction or other chemical process, using conventional screens and centrifugal cleaners and without any further application of strong shear forces to the pulp;
(c) softening ink particles and weakening their bonds with the surface of the fibres by submitting the pulp at a consistency of more than 15% to the simultaneous actions of (i) a temperature between 85 and 130°C, (ii) high shear forces and (iii) at least one de-inking agent, under alkaline conditions;
(d) detaching the ink particles from the surface of the fibres and dispersing them into the fibrous suspension by submitting the pulp to the simultaneous actions of (i) and (ii), as defined in step (c), and (iv) at least one chemical dispersing agent, under alkaline conditions;
(e) removing the free ink particles to obtain the degree of brightness required by the final use of the pulp.
2. A method of treating a mixture of printed and contaminated waste paper in order to produce pulp for use in the manufacture of paper and paperboards, which method comprises:
(a) forming an aqueous fibrous suspension of the waste paper at room temperature without de-inking agents by applying specific mechanical energy lower than 50 KW.H/Ton to form a pulpable slurry and to release the non-ink contaminants from the surface of the paper fibers in the absence of de-inking agents and without dispersing such non-ink contaminants as finely divided particles throughout the fibrous suspension;
(b) removing the released non-ink contaminants from the fibrous suspension by screening and cleaning;
(c) softening the ink vehicles and weakening their binding with the surface of the fibers by submitting the fibrous suspension at a consistency of more than 15% to the simultaneous actions of (i) a temperature between 85 to 130°C, (ii) high shear forces substantially corresponding to a specific mechanical energy of more than 50 KW.H/Ton applied at the said consistency of more than 15% and (iii) at least one de-inking agent, under strong alkaline conditions;
(d) detaching the ink particles from the surface of the fibers and dispersing them into the fibrous suspension by submitting the fibrous suspension to the simultaneous actions of (i) and (ii), as defined in step (c), and (iv) at least one chemical dispersing agent, under strong alkaline conditions;
(e) limiting the total duration of the ink softening and detaching steps (c) and (d) to a range between 2 and 10 minutes; and (f) removing the detached ink particles to provide the degree of brightness required in the final product of the pulp from the fibrous suspension.
(a) forming an aqueous fibrous suspension of the waste paper at room temperature without de-inking agents by applying specific mechanical energy lower than 50 KW.H/Ton to form a pulpable slurry and to release the non-ink contaminants from the surface of the paper fibers in the absence of de-inking agents and without dispersing such non-ink contaminants as finely divided particles throughout the fibrous suspension;
(b) removing the released non-ink contaminants from the fibrous suspension by screening and cleaning;
(c) softening the ink vehicles and weakening their binding with the surface of the fibers by submitting the fibrous suspension at a consistency of more than 15% to the simultaneous actions of (i) a temperature between 85 to 130°C, (ii) high shear forces substantially corresponding to a specific mechanical energy of more than 50 KW.H/Ton applied at the said consistency of more than 15% and (iii) at least one de-inking agent, under strong alkaline conditions;
(d) detaching the ink particles from the surface of the fibers and dispersing them into the fibrous suspension by submitting the fibrous suspension to the simultaneous actions of (i) and (ii), as defined in step (c), and (iv) at least one chemical dispersing agent, under strong alkaline conditions;
(e) limiting the total duration of the ink softening and detaching steps (c) and (d) to a range between 2 and 10 minutes; and (f) removing the detached ink particles to provide the degree of brightness required in the final product of the pulp from the fibrous suspension.
3. The method of claim 1, wherein steps (a) and (b) are effected at ambient temperature.
4. The method of claim 1 or 3, wherein the specific energy applied during step (a) is below 50 KW.H/Ton for approximately 20 minutes.
5. The method of claim 1, 2 or 3, wherein steps (c) and (d) are effected at higher than atmospheric pressure.
6. The method of claim 1, wherein the total duration of steps (c) and (d) is between 2 and 10 minutes.
7. The method of claim 2, 3 or 6, wherein the total duration of steps (c) and (d) is between 3 and 5 minutes.
8. The method of claim 1, 2 or 3, wherein the total specific energy applied during steps (c) and (d) is 50 to 100 KW.H/Ton.
9. The method of claim 1, 2 or 3, wherein the total specific energy applied during steps (c) and (d) is 80 KW.H/Ton.
10. The method of claim 1, 2 or 3, wherein steps (c) and (d) are performed simultaneously in a single apparatus.
11. The method of claim 1, 2 or 3, wherein steps (c) and (d) are performed simultaneously in a single apparatus selected from the group consisting of a triturator, a disintegrator and a kneader.
12. The method of claim 1, 2 or 3, wherein steps (c) and (d) are performed separately in two different apparatuses.
13. The method of claim 1, 2 or 3, wherein steps (c) and (d) are performed separately in a steaming chamber and a disperser.
14. The method of claim 1, 2 or 3, wherein steps (e) or (f) are performed by washing, froth flotation or any combination thereof.
15. The method of claim 1, 2 or 3, wherein the alkalinity of steps (c) and (d) is obtained by employing a chemical selected from the group consisting of sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, sodium carbonate, sodium phosphate, sodium tripolyphosphate, sodium pyrophosphate, sodium silicate and a mixture thereof.
16. The method of claim 1, 2 or 3, wherein the alkalinity of steps (c) and (d) is at a pH greater than 9.
17. The method of claim 1, 2 or 3, wherein an oxidizing agent is added during steps (c) and (d).
18. The method of claim 1, 2 or 3, wherein bleaching is performed during steps (c) and (d).
19. The method of claim 1, 2 or 3, wherein steps (c) and (d) are performed at a consistency between 25% and 30%.
20. A method of treating a mixture of printed waste paper in order to produce pulp for use in the manu-facture of paper and board, which method comprises:
(a) forming an aqueous pulp of the waste paper;
(b) removing non-ink contaminants from the pulp and releasing ink particles from the surface of the pulp fibers to obtain the degree of brightness required by the final use of the pulp;
(c) removing ink particles from the remaining dispersed fine material of the pulp using at least one washing stage under alkaline conditions and in the presence of at least one ink-dispersing agent, thereby producing: (i) a primary pulp having controlled and constant brightness and fiber classification with very low and constant filler content and (ii) a secondary pulp containing a variable high filler content and a variable quantity of fine fibers, together with the ink particles and some clean fibers;
(d) mixing the secondary pulp (ii) with an ink-collecting hydrophobic agent, after the ink-dispersing agent has been neutralized or precipitated, under alkaline conditions, and then removing the ink particles from the effluent by selective separation of the hydrophobic agent from the fibrous suspension;
(e) reducing the alkalinity of the slurry by addition of non-caustic insolubilizing cations and a strong mineral acid, thereby producing a filtrable slurry;
(f) filtering the fibrous suspension at a low filtering rate on a fibrous mat composed of fibers coming from the same process, thereby producing: (iii) a secondary de-inked pulp having a fine fiber classification and a very high filler content, both instantaneously variable, and (iv) an effluent which is practically free of suspended solids;
(g) diluting the pulp thickened by the last but one washing stage with the clarified effluent of step (f) thereby conserving the water used in the method; and (h) storing the filtrated secondary pulp in a vat for several hours with intense mixing by agitation and recirculation, thereby levelling off the fluctuations of the filler content, the fiber classification and the freeness.
(a) forming an aqueous pulp of the waste paper;
(b) removing non-ink contaminants from the pulp and releasing ink particles from the surface of the pulp fibers to obtain the degree of brightness required by the final use of the pulp;
(c) removing ink particles from the remaining dispersed fine material of the pulp using at least one washing stage under alkaline conditions and in the presence of at least one ink-dispersing agent, thereby producing: (i) a primary pulp having controlled and constant brightness and fiber classification with very low and constant filler content and (ii) a secondary pulp containing a variable high filler content and a variable quantity of fine fibers, together with the ink particles and some clean fibers;
(d) mixing the secondary pulp (ii) with an ink-collecting hydrophobic agent, after the ink-dispersing agent has been neutralized or precipitated, under alkaline conditions, and then removing the ink particles from the effluent by selective separation of the hydrophobic agent from the fibrous suspension;
(e) reducing the alkalinity of the slurry by addition of non-caustic insolubilizing cations and a strong mineral acid, thereby producing a filtrable slurry;
(f) filtering the fibrous suspension at a low filtering rate on a fibrous mat composed of fibers coming from the same process, thereby producing: (iii) a secondary de-inked pulp having a fine fiber classification and a very high filler content, both instantaneously variable, and (iv) an effluent which is practically free of suspended solids;
(g) diluting the pulp thickened by the last but one washing stage with the clarified effluent of step (f) thereby conserving the water used in the method; and (h) storing the filtrated secondary pulp in a vat for several hours with intense mixing by agitation and recirculation, thereby levelling off the fluctuations of the filler content, the fiber classification and the freeness.
21. The method of claim 20, wherein the primary and the secondary pulps are cleaned by the method of claim 1 or 2.
22. The method of claim 20, wherein the ink particles are released from the surface of the fibers using the method of claim 1 or 2.
23. The method of claim 20, wherein the ink particles are removed from the secondary pulp by means of froth flotation under alkaline conditions.
24. The method of claim 23, wherein the hydrophobic ink-collecting agent is a high molecular weight fatty acid, or the sodium or calcium soaps thereof.
25. The method of claim 23 or 24, wherein the alkalinity is obtained by employing a chemical selected from the group consisting of sodium hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide, sodium carbonate, sodium phosphate, sodium tripolyphosphate, sodium pyrophosphate, sodium silicate and a mixture thereof.
26. The method of claim 20, wherein the consistency of the secondary pulp entering the ink-removing step (d) is maintained between 0.6% and 1.5%.
27. The method of claim 20, wherein the consistency of the secondary pulp entering the ink-removing step (d) is maintained between 1.0% and 1.2%.
28. The method of claim 26 or 27, wherein the consis-tency of the secondary pulp entering the ink-removing step (d) is increased by adding thereto thick pulp extracted from the fibrous suspension ahead of the washing step (c).
29. The method of claim 20, wherein the consistency of the secondary pulp entering the filtration step (f) is maintained between 0.8% and 2.0%.
30. The method of claim 20, wherein the consistency of the secondary pulp entering the filtration step (f) is maintained between 1.2% and 1.5%.
31. The method of claim 29 or 30, wherein the consistency of the secondary pulp entering the filtration step (f) is increased by adding thereto thick pulp extracted from the de-inked primary pulp flow.
32. The method of claim 26, wherein the desired consis-tency is reached by increasing and optimizing the size of the openings of the draining elements of the washing apparatus.
33. The method of claim 32, wherein the washing apparatus comprises inclined screws fitted with perforated plates having hole diameters varying between 1.2 and 2.2 mm.
34. The method of claim 33, wherein the diameters vary between 1.4 and 2.0 mm.
35. The method of claim 20, wherein the filtering of the de-inked secondary pulp occurs after sodium silicate has been precipitated into a mineral filler by adding insolu-bilizing cations.
36. The method of claim 35, wherein the insolubilizing cations are selected from the group consisting of calcium hydroxide, calcium chloride, magnesium hydroxide, the alkaline compounds of the Group III metals, with the exception of aluminum complexes, and a mixture thereof.
37. The method of claim 20, wherein the filtration step (f) of the de-inked secondary pulp is conducted upon a moving fabric at low flow rates, thereby creating a filtering fibrous mat which is peeled away from the fabric.
38. The method of claim 37, wherein the filtering flow rate is chosen in order to insure that the clear filtrate does not contain more than 150 ppm suspended solids.
39. The method of claim 37, wherein the filtering flow rate is chosen in order to insure that the clear filtrate does not contain more than 100 ppm suspended solids.
40. The method of claim 37, wherein the filtering flow rate is chosen in order to insure that the consistency of the filtrated and thickened secondary pulp is main-tained above 5%.
41. The method of claim 37, wherein the filtering flow rate is chosen in order to insure that the consistency of the filtrated and thickened secondary pulp is main-tained above 10%.
42. The method of claim 38, 39 or 40, wherein the filtering apparatus is a disk filter working at a flow rate between 15 and 30 liters/minute/square meter.
43. The method of claim 38, 39 or 40, wherein the filtering apparatus is a disk filter working at a flow rate between 20 and 25 liters/minute/square meter.
44. The method of claim 40, wherein the fibrous mat is peeled away from the fabric using compressed air, instead of using conventional water peeling showers.
45. The method of claim 44, wherein the compressed air is mixed with water.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000451414A CA1229955A (en) | 1984-04-06 | 1984-04-06 | Method for producing pulp stock for paper making from printed unselected waste paper |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000451414A CA1229955A (en) | 1984-04-06 | 1984-04-06 | Method for producing pulp stock for paper making from printed unselected waste paper |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1229955A true CA1229955A (en) | 1987-12-08 |
Family
ID=4127596
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000451414A Expired CA1229955A (en) | 1984-04-06 | 1984-04-06 | Method for producing pulp stock for paper making from printed unselected waste paper |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1229955A (en) |
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6001218A (en) | 1994-06-29 | 1999-12-14 | Kimberly-Clark Worldwide, Inc. | Production of soft paper products from old newspaper |
| US6027610A (en) | 1994-06-29 | 2000-02-22 | Kimberly-Clark Corporation | Production of soft paper products from old newspaper |
| US6074527A (en) | 1994-06-29 | 2000-06-13 | Kimberly-Clark Worldwide, Inc. | Production of soft paper products from coarse cellulosic fibers |
| US6296736B1 (en) | 1997-10-30 | 2001-10-02 | Kimberly-Clark Worldwide, Inc. | Process for modifying pulp from recycled newspapers |
| US6387210B1 (en) | 1998-09-30 | 2002-05-14 | Kimberly-Clark Worldwide, Inc. | Method of making sanitary paper product from coarse fibers |
| CN114059377A (en) * | 2021-11-23 | 2022-02-18 | 山鹰国际控股股份公司 | Method for producing cardboard paper by using waste paper pulp |
-
1984
- 1984-04-06 CA CA000451414A patent/CA1229955A/en not_active Expired
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6001218A (en) | 1994-06-29 | 1999-12-14 | Kimberly-Clark Worldwide, Inc. | Production of soft paper products from old newspaper |
| US6027610A (en) | 1994-06-29 | 2000-02-22 | Kimberly-Clark Corporation | Production of soft paper products from old newspaper |
| US6074527A (en) | 1994-06-29 | 2000-06-13 | Kimberly-Clark Worldwide, Inc. | Production of soft paper products from coarse cellulosic fibers |
| US6296736B1 (en) | 1997-10-30 | 2001-10-02 | Kimberly-Clark Worldwide, Inc. | Process for modifying pulp from recycled newspapers |
| US6387210B1 (en) | 1998-09-30 | 2002-05-14 | Kimberly-Clark Worldwide, Inc. | Method of making sanitary paper product from coarse fibers |
| CN114059377A (en) * | 2021-11-23 | 2022-02-18 | 山鹰国际控股股份公司 | Method for producing cardboard paper by using waste paper pulp |
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