CA1255856B

CA1255856B - Production of paper and board

Info

Publication number: CA1255856B
Application number: CA000568679A
Authority: CA
Inventors: John G. Langley; Edward Litchfield
Original assignee: Allied Colloids Ltd
Current assignee: Ciba Specialty Chemicals Water Treatments Ltd
Priority date: 1979-03-28
Filing date: 1988-06-03
Publication date: 1989-06-20
Also published as: EP0017353B2; FI800907A; CA1168404A; JPS55152899A; AU5798780A; AU539515B2; EP0017353B1; EP0017353A1; FI68437B; NO800900L; NO157907B; DE3065576D1; NO157907C; US4305781A; JPH0159398B2

Abstract

ABSTRACT

Newsprint or fluting medium is made from an aqueous suspension of cellulosic fibres, the suspension having improved drainage and retention properties. In the suspension is included 0.005 to 0.1% dry weight based on the dry weight of the suspension of a water-soluble, high molecular weight substantially non-ionic polymer selected from a group consisting of polyethylene oxides and polyacrylamides containing not more than 10 mole % anionic groups and not more than 10 mole %
cationic groups and having a molecular weight above 100 000.
Also included in the suspension is 0.02 to 2% dry weight based on the dry weight of the suspension of bentonite-type clay to give an aqueous suspension consisting essentially of pulp, water, the polymer and fillers. The suspension is, however, substantially free of filler. The bentonite-type clay is added to the aqueous suspension and the polymer is subsequently added. The aqueous suspension is formed from pulp having a cationic demand of at least 0.1%; this demand being the amount of polyethyleneimine cationic polymer that has to be added to give a significant increase in fibre retention and improvement in drainage.

Description

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Many grades of paper include substantial levels of inorganic fillers such as kaolinite, calcium carbonate and titanium dioxide. For instance yood quality paper, often referred to as fine paper, may be made from high grade bleached chemical pulp and may contain 5 to 35~, by weight of dry paper, of inorganic filler. In the production of such papers it is common to use retention aids and drainage aids. The cost of these is more than oæfset by the increased re-tention of filler in the sheet and by the reduction of filler in the white water and the subsequent loss in effluent discharge, especially in view of increasing costs of raw materials and pressure from environmental legislation to restrict efluent discharge.
A variety of retention and drainage aids are known such as polyacrylamides (P.~M), polyethyleneimines (PEI), polyamides and polyamines.
In US Patent Specification No. 3052595 the use of polyacrylamides with filler is particularly described and it is stated that advantageous results ara obtained when bentonite provides 1 to 20% by weight of the minaral filler. In British Patent Speciflcation No. 1265496 it is described how polyacrylamides are used to retain inorganic filler and cellulosic fines but that critical conditions have to be observed ~ ' .

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for successful operation, and particular modified acrylamides are described.
Retention and drainage aids are generally used a-t levels of 100 to 500 grams/tonne o~ dry polymer on a dry paper weight. At these amounts cost ef~ective advantages can easily be demonstrated in the production of filled or fine papers.
There is, however, very large scale production o~ paper that is substantially unfilled, for instance as newsprint, kra~t and fluting medium, for instance in the production of board. The unfilled paper is substantially free of filler, generally containing less than 5~, by weight of dry paper, o~ filler and often there is no deliberate addition of filler to the pulp from which the paper or board is made. However, some grades of newsprint may contain above 5~ ~iller, for instance if they are made from filled broke and/or are particularly white. Generally, the pulp ~or the newsprint and fluting medium originates from Canada or Scandinavia and is of low grade fibres. With such pulps it would still be desirable to minimise the wastage of the components of the pulp, i.e. to improve retention of pulp components in the paper, but it is not so easy to demonstrate cost effective advantages by using ths known retention and drainage aids for this purpose since the pulps have a high cationic demand. The cationic demand is the amount of polyethyleneimine oationic polymer (for instance as sold under the trade name Polymin SK~ that has to be added to give any significant increase in fibre retention and improvement in .
::

9~55~3S6 drainage on the ~orming wire. The cationic demand of the pulp used for making newsprint or ~luting medium is often above 0.1 so that improvements are only significant wi-th polymer weights o~
above 1,000 grams dry polymer per tonne dry weight of paper and such amounts render the treatment uneconomic.
The papermaking fibres used in Canada and Scandinavia for newsprint and fluting medium are low grade ~ibres and are predominantly of the mechanical type and include groundwood, thermomechanical pulp, deinked secondary fibres, semi-chemical pulps and semi-bleached chemical kraft pulps, normally produced in situ in an integrated pulp and paper mill s~stem. The cellulosic fibres are thus rarely completely separated from the residual process liquors which contain substantial levels of both organic and inorganic impurities derived from the pulping process itself and the resins naturally present in the wood.
These impurities are present in solution and in colloidal suspension and may lnclude such substances as lignosulphonates, rosin aclds, hemicelluloses and humic acids, and impart a large negative charge on the cellulose fibres when dispersed in water as typical in the papermaking process. The level of the aforementioned impurities is further enhanced in the papermaking process by the increasing tendency for paper mills to "close-up" the paper machine white water systems and re-cycle as much white water as possible.
Thus there is a need for fibre retention drainage aids which traditional aids cannot meet and so there has been ~S5~356 extensive research into the development of new aids, but so far with limited success.
In German Specification 2262906 it is proposed to improve -the dewatering of cellulosic slurries by adding bentonite and a low molecular weight cationic polymer that serves as a polyelectrolyte. The results are not satisactory and this specification does not give a solu-tion to the problem of cost effective improvement in fibre retention and drainage of substantially filler free, low grade pulp.
It has now surprisingly been found that if the polymer is a high molecular weight substantially non-ionic polymer then dramatic improvement in dewatering properties and fibre retention is obtained in substantially filler free cellulose suspensions if a deliberate addition of a particular filler, namely bentonite type clay, is made to the suspension.
Thus the invention relates to processes in which newsprint or fluting medium is made from an aqueous suspension of cellulose fibres and is characterised in that the suspension and the newsprint or fluting medium are substantially free of filler and the drainage and retention properties of the suspension are improved by including in the suspension a water soluble, high molecular weight, substantially non-ionic polymer and a bentonite type clay.
According to the present invention there is provided a method of making newsprint or fluting medium from an aqueous suspension of cellulosic fibr~s, the improvement consisting in '- ' ~

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3~Z~ 6 improving the drainage and retention properties of the suspension are improved by including in the suspension 0.005 to 0.1% dry weight based on the dry weight o~ the suspension a water soluble, high molecular weight substantially non-ionic polymer selected from the group consisting of polyethylene oxides and polyacrylamides containing not more than lO mole ~ anionic groups and not more than 10 mole ~ cationic groups and having molecular weight above 10~,000, and 0.02 to 2~ dry weight based on the dry weight of the suspension of bentonite-type clay to give an aqueous suspension consisting essentially of pulp, water, said polymer, and fillers; wherein the suspension is substantially free of filler, the bentonite-type clay is added to the aqueous suspension and the polymer is subsequently added and wherein the aqueous suspension has been formed from pulp having a cationic demand of at least 0.1~, said cationic demand being the amount of polyethylene imine cationic polymer that has to be added to give a significant increase in ~ibre retention and improvement in drainage.
The suspension may be made from pulp by normal techniques and the newsprint or fluting medium may bs made from the aqueous suspension also by normal techniques.
Throughout this specification, unless otherwise stated all percsntages are given as dry weight of added material calculated on the dry weight of the suspension or final paper.
The suspension and the resultant newsprint or ~luting medium are substantlally free of filler and the total amount of ~Z5~356 filler, including added bentonite type clay, is generally less than 5~ by weight. However, in some instances it may be higher with amounts in -the paper of up to 8~ or even 10% being encountered in some newsprint. When the newsprint is to be particularly white, amounts of pigment may be slightly above this.
It is generally preferred that no inorganic filler other than bentonite type clay should be included in the suspension but if any such filler is included its amount is generally less than 3% and most preferclbly below 2%, in particular below 1.5~. If there is any filler other than bentonite the amount of additional ~iller is oten less than twice the amount of bentonlte and is prefe~ably less than the amount of bentonite. If additional filler is included ln the suspension it is usually a conventional predried filler, such as any of the materials listed in U.S. Patent Specifica-tion No.
3052595.
The amount of bentoni-te included in the pulp is generally between 0.02 and 2~ by weight dry bentonite-type clay, based on dry weight of paper or pulp, and most preferably is from 0.1 to 1~. -The bentonite-type clay used in the invention may be one of the common commercially available bentonites (known as montmorillonite clays), such as "Wyoming bentonite" and "Fullers Earth", and may or may not be chemically modified, e.g. by alkali treatment to convert calcium bentonite substantially to alkali , - :

(e.g. sodium, potassium or ammonium)bentoni-te. Bentonites having the property of swelling in water are preferred.
The polymers used in the invention must be high molecular weight, that is to say they must ha~e a molecular weight that is above 100,000 and is such as to give a bridging effect. The molecular weight will normally be above 500,000, generally being about or above 1 million.
The polymers must be substantially non-ionic and thus may be wholly non-ionic or they may have small amounts of anionic or cationic units. Generally the polymer will contain not more than 10 mole percent anionie units and not more than 10 mole percent eationie units although i~ both types o~ groups are present the molar amounts of each type may be higher than quoted above provided the molar amount o one ionie type in the polymer is not more than 10~, and preferably not more than 5%, above the molar amount of the other ionic type. If cationic units are present the amount is generally less than 5 mole percent bu-t preferably the polymer is free of cationie units.
Preferred polymers are polyaerylamides eontaining up to 10 mole pereent anionic units, generally acrylic acid units. For example preferred polymers-contain 1 to ~ mole percent acrylic acid with the balance acrylamide, most preferably 97 mole percent acrylamide, 3% acrylic acid, often as sodium acrylate.
Other eomonomers that may be included, especially in polyaerylamides, inelude dialkyl amino alkyl aerylates and methaerylates quanternised with for instance dimethyl sulphate or ~s~

alkyl halides, ~or lns-tance quaternised dimethyl amino ethyl acrylate or methacrylate, methacrylic acid, sodium methacrylate, diallyl dimethyl ammonium chloride. Methaarylamide ma~ be used as the main monomer instead o~ some or all of the acrylamide.
The preferred copolymars of acrylamide and acrylic acid ~or sodium acr~late) can be made by hydrolysis of the homopolymer either during or after its initial synthesis.
Other suitable non-ionic polymers for use in the invention include polyethylene oxide.
It is easily possib:Le, by routine experimentation, -to select preEerred combina-tions o~ polymers and bentonite grades.
It has surprisingly been ~ound that it is easily possible to obtain excellent retention and drainage results using polymer-bentonite combinations whereas the bentonite alone on the same pulp or the polymer alone on the same pulp give worse results than with the pulp alone. Thus there is a surprising synergistic effect between the bentonite and the polymer.
The amount o~ polymer added is generally at least 50 but generally less than 1,000 grams dry polymer ~er tonne dry paper (i.e. O.OOS to O.l~). Generally it is from O.Ol to 0.05~.
The polymer may be supplied as a trua solution ln water, as a solid grade product or as a dispersion in a aarrier oil, but in all cases should be dissolved in water and added as a dilute a~ueous solution to the pulp suspension during the papermaking process.

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_ 9 _ The polymer solution is ideally added after the last point of high shear prior to sheet formation and is typically after centri-screens and just before the flow-box, to ensure good mixing, and to avoid excessive shear which can damage the retention/drainage effect.
The bentonite may be added to the suspension either as a pre-hydrated aqueous slurry directly to thick stock or as a solid to the hydropulper or to the re-circulating white-watsr providing i-t is well dispersed during addition to enable adequate hydration and accomplish its character:Lstic swelling properties.
Preferably traditional additives such as aluminium sulphate are omitted, and preferably the main, and often the only, additives to the pulp in the process of the invention axe the described polymer and bentonite, and so the suspension preferably is formed from substantially only cellulosic pulp, water, the polymer, the bentonite-type clay and, optionally, additional filler in the amounts specified above.
The invention is of value in the production of fluting medium, for instance in the production of board, and especially in the production of newsprint from impure pulps, especially those having a cationic demand (as defined above) of at least 0.1~ and often above 1~.
We have also found that the invention gives a surprising and significant improvement in the machine runnability and this enables larger quantities of lower grade fibres to be used without increasing the risk of machine s-toppages.

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As well as providing improved retention and drainage the method of the invention also results in a significant reduction in the solvent extractable troublesome resinous pitch content of the papermachine white water system. During paper mill trial work a reduction of the extractable pitch content o~
the white water of 75% was observed.
The invention includes the described method, newsprint and fluting medium obtained by it, pulp including bentonite and the polymer, and compositions comprising the bentonite and the polymer.
The following examples illustrate the invention. In these PAM stands for polyacrylamide and all polyacr~lamides and polye-thylene oxides used have a molecular weight between 106 and 107. PAM 3~ SA stands for a copolymer of 97 mole percent acrylamide with 3% mole percent sodium acrylate. In the examples where bentonite was added it was added as a prehydrated aqueous slurry prior to the polymer addition. In none of the e~amples is aluminium sulphate added and instead in each example the aqueous suspension consisted essentially only of water, cellulosic fibres (and associated impurities from the pulp) and, when appropriate, the added polymer and/or bentonite.

Example _ A sample of thin stock taken from a Swedish newsprint mill consisted of:

~SS,~6 30% thermomechanical pulp 25% chemical sulphate pulp 35-~ groundwood lO~ broke It contained a high level of impurities such as lignosulphates.
The drainage efficiency of various conventional polymers was compared with bentonite-polymer systems acording to -this invention. The required quantity of dilute polymer solution was added to 1 litre of the stock in measuring cylinder, to give an ef~ective polymer dose level of 0.05% polymer ti.e. 500 g/tonne o~ dry polymer based on the dry weight o~ paper). The cylinder was inverted three times to effect mixing and the contents were poured onto a typical machine wire. The time taken for 250 mls o white water to drain was noted. The shorter the time the more effective the treatment. The results are given in Table 1.

Table 1 ADDITIVE Drainage ~ate S/250 ml.
. ~ . ~
No polymer addition 145 secs.
Polyamide 139 "
Polyethyleneimine 134 Polyethylene oxide 68 "
Polydimethyldiallyl ammonium chloride 139 "
Cationic PAM 125 "
PAM homopolymer 109 "
PAM 3~ SA 31 "

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PAM 10~ SA ¦ 148 "
O.Z~ sentOnite ~ PAM 3% SA ¦ 36 Examp3e_2 Using the same sample of thin stock as described in Example 1 above, the re-tention efficiency of various conventional polymers was compared with the bentonite/polymer system according to this invention. The required quantity of dilute polymer solution was added to 1 litre of thin stock in a 1 litre measuring cylinder, -to give an effactive polymer dose le~el of 0.05~ of dry polymer based on the dry weight of paper. The cylinder was inverted three times to effect mixing and then the contents were poured onto a typical machine wire. The white water draining through the wire was collected and the solids content determined. The lower the solids content the more effective the retention aid treatment. The results are given in Table 2.

Table 2 ADDITIVE Whitewater Solids Ppm.
. . . ~
No polymer addition 1080 PolyetAyleneimine 1130 Polyethyleneoxide 410 PAM low degree of cationic substitution 910 PAM homopolymer 650 PAM 3% SA 590 0.2~ Bentonite ~ PAM 3~ SA 266 .

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~2S5~6 Example 3 On an identical sample of thin stock to that used irl Examples 1 and 2, the ef~ect on drainage of varying the level of bentonite addition whilst maintaining a constant dose level of PAM 3~ SA was e~amined. The drainage rate measurements made in the same manner as in Example 1. The shorter the drainage time the more effective the treatment. The results are given in Table 3.

Table 3 Polymer ~ onBentonite % on dry Drainage Rate dry paper paper S/250 ml.

0 0 93 s 0.04 0 75 s 0.04 0.10 60 s 0.04 0.20 47 s 0.04 0.50 34 s 0.04 1.00 21 s 0.0g 2.00 19 s Example 4 On the same stock sample used in Example 3, the effect on drainage of varying the polymer (PAM 3~ SA) addition level whilst maintaining a constant level of bentonite addition, was examined. The drainage rate measurements were made in the same manner as in Example 3. The shorter the drainage rate the more effective the treatment. The resul-ts are given in Table 4.

~5~6 Table 4 Polymer ~ on~entonite ~ on dryDrainage Rate dry paper papar S/250 ml.
. _ .. ...
0 0 93 s 0 0.5 77 s 0.01 0.5 ~5 s 0.02 0.5 54 s 0.0~ 0.5 34 s 0.06 0.5 17 s 0.08 0.5 11 s Example 5 A range of various types of bentonite was evaluated at a constant addition level of 0.5~ on dry paper together with a constant dose level o 0.04~- on dry paper high molecular weight PAM 3~ SA. A sample o tha same stock was used as in Examples 3 and 4 and the bentonite/polymer system performance was again assessed by drainage rate measurements. The shorter the drainage time the more effective the treatment. ~he results are given in Table 5.

Table 5 _ ~entonite type Drainage Rate S/250 ml.

Natural American sodium montmorilloni-te 44 s sodium exchanged English calcium montmorillonits 25 s sodium montmorillonite Gresk origin 37 s .
: ~ . ' , :` - , ' - ' : `
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:ILZ5~3r,,~i Example 6 Samples of stock were taken from Just after the cen-tri-screens in a newsprin-t mill when addit:ions had been made of bentonite with various polymers, namely acrylamide homopolymer, copolymer with sodium acrylate (anionic PAM) and copolymer with dimethylaminoethyl acrylate quaternised by dimethyl sulphate (cationic PAM). Drainage tests were carried out on a modified Schopper-Reigler freeness tester. With the rear outlet blocking, the time taken for a constan-t volume of wa-ter to drain from 1 litre of stock was recorded. The following results were obtained:

Additives Polymer ionic Drainage ~ ~_ ~____ ___ content (~ time Bentonlte Polymer molar) (seaonds~

0.7~ 0.04~ PAM O 32 0.7% 0.04~ cationic 3 53 PAM
0.7~ 0.04~ cationic 9 69 PAM
0.7% O.U4% anionic 3 23 PAM
O O _ 95

Claims

1. In a method of making newsprint or fluting medium from an aqueous suspension of cellulosic fibres, the improvement consisting in improving the drainage and retention properties of the suspension by including in the suspension 0.005 to 0.1% dry weight based on the dry weight of the suspension of a water soluble, high molecular weight substantially non-ionic polymer selected from a group consisting of polyethylene oxides and polyacrylamides containing not more than 10 mole % anionic groups and not more than 10 mole % cationic groups and having molecular weight above 100,000, and 0.02 to 2% dry weight based on the dry weight of the suspension of bentonite-type clay to give an aqueous suspension consisting essentially of pulp, water, said polymer, and fillers; wherein the suspension is substantially free of filler, the bentonite-type clay is added to the aqueous suspension and the polymer is subsequently added, and wherein the aqueous suspension has been formed from pulp having a cationic demand of at least 0.1-%; said cationic demand being the amount of polyethyleneimine cationic polymer that has to be added to give a significant increase in fibre retention and improvement in drainage.

2. A method according to Claim 1, in which the amount of bentonite-type clay is 0.1 to 1% and the amount of polymer is 0.01 to 0.05% based on the dry weight of the suspension.

3. A method according to Claim 1, in which the polymer is selected from polyacrylamide homopolymer and copolymers of acrylamide with up to 10 mole percent anionic groups.

4. A method according to Claim 1, in which the polymer is a copolymer of about 97 mole percent acrylamide and 3 mole percent sodium acrylate.

5. A method according to Claim :1 in which the total amount of filler in the newsprint or fluting medium is less than 5%.

6. Newsprint or fluting medium made by a method according to Claim 1.