US2943971A - Pigmented paper and preparation - Google Patents

Description

July 5, 1960 L. B. TAYLOR PIGMENTED PAPERAND PREPARATIONTHEREOF Original Filed Oct. 31, 1955 in ilml mi lDVdO .LNSD '33:! HEN 3 INVENTOR.

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.LNBD lid AJJDVdO United States Patent PIGMENTED PAPER AND PREPARATION THEREOF Continuation of application Ser. No. 543,835, Oct-31, 1955. This application July 31, 1959, Ser. No.

13 Claims. (Cl. 162-181) The present invention deals with pigmented paper and the manufacture thereof, and more particularly involves enhancing the opacity, brightness and other desirable properties of paper by pigmentation with titanium dioxide and finely divided, amorphous siliceous materials.

Heretofore, various proposals have been otfered for improving paper quality, especially with printing papers, by pigmentation with materials, one T of the most noteworthy ofv which is titanium dioxide. Due to its high cost, titanium dioxide is not economically suitable for all grades of paper but finds favor in only the more expensive papers. Also, the retention of titanium dioxide in paper during the paper sheeting step leaves room for betterment. Among other things, the recovery and recirculation of unretained titanium dioxide in the white waters is cumbersome and inelficient.

According to the present invention, the disadvantage and high costs which accompany titanium dioxide pigmentation are minimized and/or obviated. It is possible to reduce the required quantity of titanium dioxide, and consequently the cost of pigmentation, while not sacrificing paper quality. Instead, paper of improved opacity and brightness is obtained. Further realized is increased pigment retention in the paper sheeting step.

Now it has been discovered that such benefits ensue from sheeting a pulp slurry which includes both titanium dioxide and a finely divided, amorphous siliceous pigmentary material, notably calcium silicate. Viewed otherwise, it has been found that up to 90 weight percent of titanium dioxide normally required for a given pigmentation may be replaced with finely divided, amorphous siliceous pigments of much less cost. As a consequence, costs are reduced and a pigmented paper is prepared which has high opacity, brightness and increased quantities of pigment. Often these paper qualities are superior to those which can be obtained using either titanium dioxide or the siliceous material individually.

Figures I and II in the drawing pictorially demonstate the synergistic effects observed in connection with the practice of this invention. Thus, in Figure I, the variations in opacity and ash (pigment retained in the paper) for difiering ratios of titanium dioxide and calcium silicate are graphically shown. With only titanium dioxide the papers opacity is about 86.5, yet opacities in excess of this value are achieved with pigmenting materials containing from about 40 percent to about 95 percent titanium dioxide by weight of titanium dioxideand calcium silicate. Furthermore, even with larger percentages of calcium silicate opacities are of values which are in excess of those which might be expected from the contribution thereto of the respective pigments.

In a similar fashion, greatly increased ash contents are observed by'practice of this invention. For the given conditions, hereinafter detailed, ashes are of'about 6.5 percent with either pigment, yet when using combinations thereof, ashes range substantially above 6.5 percent and as high as about 8.3 percent (when the pigment comprises 80 7 2,943,911 Patented July 5, 1960.

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percent titanium dioxide by weight thereof and calcium silicate).

Thus, according to one embodiment, the utilization of calcium silicate or comparable pigmentary siliceous material oifers an expedient for increasing the concentration of pigment composition including titanium dioxide in paper. In another embodiment, paper opacities in excess of those possible with titanium dioxide are realized. And in a still further embodiment, the value of calcium silicate or other siliceous material, particularly those of low cost, may be increased as an opacifying agent. In practice, the advantages of the present invention are realized by recourse to any of a number of procedures. Briefly, both titanium dioxide and the siliceous ingredient, notably finely divided calcium silicate, are added to a pulp slurry most advantageously after the pulp has been beaten suitably following usual paper beating practices. Thereafter, the slurry pH is adjusted to within the range of about 4 to 6.5, notably pH 5, by adding an acidic material such as aluminum sulphate or other sulphuric acid salt including sodium sulphate and sodium bisulphate or sulphuric acid itself. Also, other acidic materials, generally inorganic acids such as hydrochloric acid, carbonic acid, etc. or their anhydrides or acid salts are etfective. Aluminum sulphate (alum) finds widest use, not only because it is particularly effective but also because it is a common material used in paper manufacture for other reasons. Because of its low cost, sulphuric acid is an excellent replacement for part or all of the alum. This acidified slurry is sheeted into paper on recognized apparatus, e.g. a Fourdrinier or cylinder machine.

Sometimes, after including the pigments in the pulp slurry, even following substantial beating, the dispersion of the pigments is enhanced by further agitation of the pulp slurry as by mechanical stirring or even beating. This facilitates uniform distribution of the pigment throughout the slurry. i

Depending to some extent upon the exact paper employed, the particular quality of paper desired, and other peculiarities of any given paper forming operation, the ratio of the two pigments may be varied. Beneficial results are obtained when employing from about 10 to about percent titanium dioxide by weight of titanium dioxide and calcium silicate. With lower titanium dioxide concentrations, the pigmenting qualities of calcium silicate are upgraded strikingly and according to one em-' bodiment hereof, this constitutes an important consideration in utilizing the concepts of this invention. Thus, when papers of opacities slightly higher than are otherwise attained with calcium silicate or comparable siliceous material are the object, a minor quantity of titanium dioxide sufiices.

However, in a preferred embodiment, the titanium dioxide is employed in quantities ranging from about 35 or 40 percent to about 95 percent by weight thereof and calcium silicate. Opacities exceeding those of titanium dioxide pigmented papers are realized within this range, see Figure I of the drawing and Example I hereinafter.

With certain pulps, the contribution to'opacity and other paper characteristics by both the combination of titanium dioxide and calcium silicate appears even more noticeable, note Example II hereinafter and Figure II of the drawings. There, paperprepared from a pulp fumish consisting solely of kraft pulp to which had been added both pigmentary materials was of superior opacity and brightness by comparison with the values obtained with the individual pigments regardless of the ratio of the titanium dioxide and calcium silicate.

Mixtures of titanium dioxide and calcium silicate, for this invention, may be provided directly in the pulp slurry by addition of requisite quantities ofindepeudently prerior-to being added to the slurry.

In the case of siliceous materials, such as the preferred calcium silcate, the pH adjustment of the slurry may include a chemical change. Aluminum sulphate reacts with calcium silicate, probably to provide a'calcium aluminum silicate and calcium sulphate, the latter having some water solubility whichmay, at least in part, account for removal of calcium sulphate-in the white waters. Chemical reactions may be encountered with other silicates, notably between alkaline earth metal silicates, and othenuseful acidic materials which form water insoluble alkaline. earthmetal salts. For the most part, the acidic material requirements for pH adjustment are less-than the stoichiometric quantity needed to react completely with "the siliceous pigment. Hence, usually at least a portion or silceous pigment such ascalcium silicate reacts withthe acidic material, e.g. aluminum sulphate. Under specialized circumstances the calcium silicate may be completely reacted or decomposed. In many instances, the reaction between the acidic material and siliceous pigment proceeds so slowly that the acidic material is not completely consumed prior to sheeting.

A large variety of finely divided, amorphous pigmentary siliceous materials containing at leastabout 50 percent SiO byweight (anhydrous or water free basis)-are useful either alone or in combination. Foremost among these are the finely divided, amorphous, pigmentary calcium silicates ranging in surface areasfrorn to 60 square meters per gram, as measured by theBrunauer-Emmett- Teller method described in the Journal of American Chemical Society, volume 60, page 309 (1938) which corresponds to the formula CaO(Si0 x ranging from about 2 to 5, and particularly from 2.9 to 3.8. Those calciumsilcates having packed bulk densities prefer-ably from 0.1 to 0.4 gram per cubic centimeter as measured at three pounds per square inch give pronounced benc- Bound water is the difierence between the free water and that water which is removed by heating at ignition temperatures, e.g. 1000 to 1200" C. It appears the bound water is chemically united, whereas the free water is more loosely contained by, the siliceous material.

I The titanium dioxide component is comprised of the usual paper-pigment quality titanium dioxide, e .-g. a'finely divided, particulate material having particles on the average of 0.3 micron diameter. Other grades of pigmenting titanium 'dioxid'e inay find utility, especially in view. of the beneficiating effect of the siliceous material.

The following examples illustrate the manner in which this invention may be practiced:

' EXAMPLE 1 p A pulp'beatei was "charged with 2 50 grams of kraft pulp and 25-0 grams of sulfite pulp, dispersed in 23 liters of water and beaten in a Niagara beater to a freeness of 550'millilit'ers (Canadian standard). To this beaten pulp was added 400 cubic centimeters of aqeuous slurry containing 35 grams of pigment comprised of titanium di oxide and/or calcium silicate, as indicated in Table I, followed by mixing for five minutes. A smallquantity of aluminuin sulphate octadecahydrate, as indicated in Table I, was added adjusting the slurry PH at 5.0. The resulting acidic slurry was then sheeted on a laboratory Noble-Wood sheeting machine and the opacity, brightness and ash, content of the paper determined.

ficating effects. Such calcium silicates appear to be in the form of fiocs of finely divided ultimate calcium silicateparticles when viewed under high magnification.

Under the electron microscope, the flocs resemble clusters of grapes and appear to be a loosely connected agglomeration of ultimate particles. Their ultimate particle size is below' 1.0 micron, usually in the range of 0.015 to 0.2 with the average particle size being from 0.04 to 0.08 micron. The flocs range in size from about 0.6 or 1 mimom to as high as 10 microns, the majority thereof, e.g. at least about 55 per cent by weight, being from 1 to 5 microns. I

The beneficial effects are not limited to use of the preferred calcium silicates, but may be obtained by recourse to other finely divided, amorphous siliceous materials. Somewhat finer calcium silicates which have BET surface areas ranging upwards of 50 or 60 to from 120 to 200 square meters per gram comprise a useful component. Still other amorphous, finely'divided calcium silicates and mixed calcium silicates containing at least about 50 weight percent SiO and of below 1.0 micron particle size, more preferably below 0.3 micron, are included. Among .these'are calcium aluminum silicate, calcium sodium silicate, potassium "silicate, aluminum silicate,'calcum zinc silicate, andthe like. strontium silicates. and barium silicates possessing the above enumerated physical and chemical characteristics are likewise of utility.

Finely divided, amorphous, precipitated pigmentary silica can be employed. Usually these, silicas are of from 20 to 120 square meters per gram BET surface area and have ultimate particle sizes on the order of those of the described calcium silicates, e.g. below 1.0 micronand notably less than 0.3 micron. They too are composed of fiocs of ultimate particles. I

The preferred siliceous materials contain both bound water and free water. Free water is that water which isxremoved .byheating for 24 hours at 105 C.

Magnesium silicates,

The titanium dioxide charged comprised paper grade materialand had an average particle size of 0.3 micron. The calcium silicate used had a BE-T surface area of '31 square meters per grain, and an average ultimate particle size or 0.04 to 0.08, with particles ranging from 0.015 to 0.20'micron. By chemical analysis it was comprised of 66.4 percent SiO 18.6 percent CaO, 0.39 percent Na and 0.60 percent chlorine. In aqueous slurry it had a pH of 10.6. Upon heating at ignition temperature 1000 (1., it lost 15.1 percent by weight, and upon heating at 105 C. iii a laboratory drier for 24 hours it lost 5.2 percent by weight, indicating a free water content of 5.2 percent and a bound water content of 9.9 percent by weight.

Table I lists the various reaction variables along with the properties of the prepared paper.

Table I Loading-Weight, Percent Paper Properties Calcium Ash Opacity, Bright- Silieate T10, Alum Weight Percent ness,

Percent Percent 0 10 0. 3' 6. s7 86. 4 s5. 9 2 8 1. 7 8.31 88. 5 86. 7 4 5 3. 1 7:95 83. 1 86. 7 6 .4 4. 6 7. 5D 86. 9 85. 7 8 2 6. O 6. 85 34. 6 84. .7 10 0 7. 5 6. 60 81. 4 82:2

Total pigment'loadin'g is 10 percent by weight. I Weight percent, based. on dry pulp, of AMS O0z.18H,O.

Figure l of the drawings graphically correlates milliliters freeness paper wasprepared. Table 11, here after, lists the experimental variables and properties of the resulting papers.-

v 1 Total pigment loading is 10 percent by weight.

. Welght percent; based on dry pulp, of A1:(S0:)4.18H|O.

Figure 2 of the drawings graphically shows the variationsfin-paper opacity. observed as the pigment components were varied. It.will benoted that whenever the pigment comprised both titanium dioxide and calcium silicate,the paper opacity exceededthe opacity of paper pigmented individually withcach component. A substantial improvement inopacity isYobserved over a wide rangeof mixtures. A

EXAMPLE III A pulp beater was charged as follows:

I Y j Grams Unbleached sulfite pulp 90 Bleached kraft pulp 180 Hard white envelope cuttings 90 This charge was dispersed in 23 liters of water and the resulting slurry was beaten in a Niagara heater for about 80 minutes to approximately 400 .milliliters freeness, Canadian standard (TAPPI Standard T227 111 50). One

hundred milliliters of prepared rosin of about 5 percent by weight size'was then added. Thereafter, 9 grams of pregelatinized starch was added and, the pulp was circulated in the beater long enough to insure complete mixing. Aluminum sulphate in the amount of 3 percent by weight, based on the dry weight of pulp, was added as a solution containing 12.92 grams of aluminum sulphate octadecahydrate per liter. At this stage, the pulp consistency was approximately 1.1 percent. Stirring was continued for 2 minutes. Immediately thereafter, the amounts of calcium silicate having the composition CaO(SiO and titanium dioxide indicated in the table were added. The amounts are expressed as percentages ofthe dry Weight of the pulp. Stirring of the mixture was continued for 10 minutes more, and the resulting stock was diluted to 8,000 milliliters, divided into ten 800-milliliter portions, and sheeted into paper. The paper was tested for brightness, opacity, bursting strength, weight and thickness, and ash and moisture content, with the following results:

Table III Percent titanium dioxide by weight Percent calcium silicate by weight Brightness:

Green li ht Blue light Contrast ratio (green light):

Reflectance, black backing lRtegectance, white backing Contrast ratio (blue light):

Reflectance, black backing Reflectance, white backing Ratio- Bursting strength, lb./ln

Percent ash in oven dry paper oremq new around: rah-c: we on:-

prior paper making operations can be included. From 3 to 6 percent by weight of the slurry is pulp (dry basis) in accordance with normal operations.

Suificient pigments are added to constitute from 0.5 to 30 percent by weight of the pulp on a dry basis. Ash values of the paper, by virtue of the high pigment retention obtained hereby, range from about 50 to 80 or 90 percent of the pigment concentration in the slurry on a dry pulp basis. I

In practicing paper pigmentation according 'to this invention, other paper making operations may be included. Sized or unsized paper can be prepared. For sized paper, a rosin size such as asoluble alkali metal rosin soap, e.g. sodium rcsinate or other typical size is included in the pulp slurry and precipitated by use of a trivalent or tetravalent metal such as titanic sulphate or aluminum sulphate.

Coloring matter, if desired, man be included in th pulp slurry during the beating cycle. Also, the pulp may be bleached by treatment with chlorine in an oxidizing form or with other bleaching agents.

Subsequent to sheet formation, the sheet is suitably dried and, when necessary, calendered. Coatings may be applied to the sheet in the preparation of high grade printing papers of the type used in more expensive magazines. A typical coating agent is finely divided clay.

This application is a continuation of application Serial No. 543,835, filed October 31, 1955, now abandoned, which is a continuation-in-part of prior applications Serial Nos. 352,295 now abandoned, and 393,522, filed respectively on April 30, 1953. andNovember 20, 1953. 1

Although the present invention is described with ref-.-

erence to particular details of special'embodiments, it is not intended that it .be limited thereto except insofar as the invention is defined in the claims. Y I Iclaim:

1. The method of preparing paper of enhanced opacity which comprises -adding titanium dioxide and a floccu lent finely divided, pigmentary, amorphous, precipitated siliceous material having an average ultimate particle size below 1.0 micron in an aqueous paper pulp slurry, adjusting the pH of such slurry to between 4 and 6.5 by inclusion in the aqueous pulp slurry of an acidic material prior to sheeting and sheeting the slurry.

2. The method of preparing paper of enhanced opacity which comprises adding titanium dioxide and a flocculent finedly divided, pigmentary, amorphous, precipitated alkaline earth metal silicate having an average ultimate particle size below 1.0 micron in an aqueous pulp slurry, adjusting the pH of said slurry to between 4 and 6.5 by inclusion in the aqueous pulp slurry prior to sheeting an acidic material which forms a water insoluble alkaline earth metal salt and sheeting the slurry.

3. The method of preparing paper of enhanced opacity which comprises adding titanium dioxide and a flocculent finely divided, pigmentary, amorphous, precipitated calcium silicate having an average ultimate particle size below 1.0 micron in an aqueous pulp slurry, adjusting the pH of said slurry to between 4 and 6.5 by inclusion in the aqueous pulp slurry prior to sheeting an acidic material which forms a water insoluble calcium salt and sheeting the slurry. I

4. The method of preparing paper of enhanced opacity which comprises adding titanium dioxide and fiocculent' finely divided, pigmentary, amorphous, precipitated calcium silicate having an average ultimate particle size below 1.0 micron in an aqueous pulp slurry, adjusting the pH of such slurry to between 4 and 6.5 by inclusion in the aqueous pulp slurry of aluminum sulphate prior to sheeting, and sheeting the slurry.

'5. The method of claim 4 wherein the calcium silicate corresponds to the formula, CaO(SiO,) x ranging from 2 to 5.

6. The method of claim 4 wherein the calcium silicate corresponds to the formula, CaO(SiO x ranging from particle'sizebelo'vv 1".0 micron and containing at: least 7 50 percent SiO by weight. a

*8. Pigmente'd-fcellulosic paperof enhanced opacity -c'ontainiri'g independently prep'ared titanium dioxide and fa floccnle rit-finely divided, ipigmentary, amorphous, precipitated siliceous -'material' 'having an'avera'g'e ultimate particle 'size below 1.0 micron and ofgat least 50 percent 7 Sit): eentem by -vveigh't, the; tit'aniiim dioxide constituting 'froi'ni 10 m 95 erCnfbYWEight thereofand the siliceous material. e s

p 9. 'Pigine "ted cellulosic paper of enhanced opacity conspasm 7t taming'mdepenqenuyg reparea titanium dioxide and a H succulent finely divided', pigrnenta1 y, amorphous, precipitated siliceous material haying 'an'average ultimate particle size belovvyltdmicron and "of at least 50 'p'ereent SiO content by weight, the titaniumdioxide constituting firom 35th 95 percent by Weight thereof and the siliceous mate- I I a 10,; Pigmented cellulosic paper of enhanced opacity 'as opacity enhancing components flocculent amorphous, precipitated siliceous pigavmgan average ultimate particle size of dioxidejconstiti iting rromss't 'Qs percent by weight of the titanium dioxide and said siliceous material, the

remaining-at least 50 percent SiO b'y we 3O crop and titanium dioxide, said titanium V opacity of' said paper being :"gr'eater than that of paper 0 containing as its opacity "enhancing component titanium dioxide an amonnt equal to that of the siliceous material'andjtitanium dioxide in the paper.

11. A paper pigment composition effective in enhancing the opacity of oellulosic paper-containing as opacity enhancing components flocculent finely divided, amorphous, precipitated siliceous pigmentary material'containing at least percent SiQ by weight and having an average ultimate par'ticiefsize of less than '1 micron and umtd ox desaid an um diox desqnstitu ins 10 to a percent by weight of the titanium dioxide and siliceous material.

12. :A paper pigment composition effective in'enhancing the opacity of cellulosicpaper containing as opacity enhancing components independently prepared, flocculent finely divided amorphous, precipitated "siliceous pigmentary material containig at least '50 percentfSiO, by weight and having average ultimate particle of thfan m 'mn an t di xid tt e' o ns u n 35.3 4 95.1

pa of ephap i th greater degree than the fs amount of. titanium dioxide Without h l ic ousr' atena r 13. A paper pigment composition enhancing the opacity of cellulosic paper containing as opacityenhancing components fldcculent :finely divided precipitatedsiliceous pigmentary, material containing at least 50 percent SiO: by weight and'havin'g an average ultimate particle size of less than 0.3 micron ancl titanium dioxide, said titanium dioxide constituting 351:; 9,5 percent'by weight: the titanium dioxide andsiliceou's material.

References Cited in the file of this patent STATES P TENTS 2,000,031 Lat-song--- a 1, 1935 237 :2 9 June 12, 1945 2,739,068 I Eichmeier Mar. 20, 19.56 2,786,757 Taylor L-.. Mar. 26 1957 Allen Mar. 26, 1957 j t mum I ercent hy weight of the. titanium dioxide and 's'iliceousmaterial; pigmentgbeing v UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTION Patent Nor-2,943,971 July 5, 1960 Louis B. Taylor R It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below'.

Column 8 lines 37 and 38, for "-beneficating" read beneficiating column 5, Table III first column line 14 thereof for "Bursting strength, lb./in read Bursting 2 strength lb./ in. column 6, line 4L? for "finedly" read finely column 8, line 14, for "containig" read containing I Signed and sealed this 25th day of July 1961.

(SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents

Claims (1)

1. 7. PIGMENTED CELLULOISE PAPER OF ENCHANCED OPACITY PIGMENTED WITH INDEPENDENTLY PREPARED TITANUIM DIOXIDE AND A FLOCCULENT FINELY DIVIDED, PIGMENTARY, AMORPHOUS, PRECIPATED SILICEOUS MATERIAL HAVING AN AVERAGE ULTIMATE PARTICLE SIZE BELOW 1.0 MICRON AND CONTAINING AT LEAST 50 PERCENT SIO2 BY WEIGHT.

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