US3794558A - Loading of paper furnishes with gelatinizable material - Google Patents

Abstract

A METHOD OF PREPARING A PAPER PULP IS DISCLOSED WHERE AN UNCOOKED STARCH OR STARCH DERIVATIVE IS ADDED TO A CELLULOSIC FIBER PULP AND THE PULP IS FURTHER REFINED AT A TEMPERATURE ABOVE THE GELATINIZING TEMPERATURE OF THE STARCH ADDITIVE SO THAT THE STARCH ADDITIVE IS GELATINIZED IN SITU IN THE REFINER. A METHOD OF MAKING PAPER PRODUCTS FROM THE TREATED PULP IS ALSO DISCLOSED.

Description

Feb. 26, 1974 s. E. BACK LOADING OF PAPER FURNISHES WITH GELATINIZABLE MATERIAL Filed June 19, 1969 Sangho E.Bc1ck BY INVENTOR fii r nited' states Patent'Ofi 3,794,558 Patented Feb. 26, 1974 3,794,558 LOADING OF PAPER FURNISHES WITH GELATINIZABLE MATERIAL Sangho E. Back, Vancouver, Wasln, assignor to Crown Zellerbach Corporation, San Francisco, Calif. Filed June 19, 1969, Ser. No. 834,790 Int. Cl. D21d 3/28 US. Cl. 162-175 14 Claims ABSTRACT OF THE DISCLOSURE This invention relates to the loading of cellulosic pulps, and to new and improved paper products produced from such pulps.

Certain properties of paper products such as strength, internal bond, holdout, etc. are enhanced by the loading of the pulps from which they are prepared with a gelatinizable material such as starch. One method in which such material is introduced into a pulp is by adding the material to the pulp as a cooked dispersion, i.e., a dispersion of the material where such has been heated above the gelatinization temperature of the material whereby the material has been converted into a gel. The cooked material and the cellulosic fibers in the pulp are then intimately mixed, and the furnish produced is directed to a paper machine for conversion into paper.

While the loading of cellulosic pulps is well known, there are problems involved in doing such with conventional procedures which have imposed certain limitations with respect to the amount of loading that may be performed and the types of paper products that are producible from the pulp mixtures produced. Considering briefly some of these difficulties, if the percentage of gelatinizable material which is incorporated with the pulp is ap preciably above about 2% (based on the dry weight of the fiber in the pulp), what might be described as a sticky quality is imparted to the pulp which causes what is known as picking in the paper-making machine that converts the pulp to paper. The pulp, when laid out as a web tends to adhere to the paper-making machine and this is particularly evident in the heated regions of the machine, causing the web to be pulled apart with the production of an unsatisfactory product. This picking and related difiiculties has served definitely to limit the amount of loading with a gelatinizable material such as starch which is practically possible. Difiiculties have also been encountered in obtaining proper retention using conventional approaches, both with respect to the gelatinizable material, and any fillers such as pigments which may be incorporated with the pulp, together with the gelatinizable material. Other problems associated with the loading of pulp comprise problems of drainage, and the tendency for spots to appear on a paper produced when more than certain minimum amounts of gelatinizable material are incorporated with the pulp.

Generally, an object of this invention is to provide an improved process for incorporating a gelatinizable material with a cellulosic pulp, which has been found to produce dramatic improvements in both the way that the pulp may be handled during its conversion into paper, and the physical characteristics obtainable in paper by reason of the inclusion of the material.

Another more specific object of the invention is to provide a process for preparing a paper-making pulp or furnish, which permits a far higher loading of the pulp with gelatinizable material to be attained without the difliculties normally associated with such loading.

Another object of the invention is to provide an improved pulp and process for preparing it, where such is loaded with a gelatinizable material, and such material contributes more etiectively to desirable properties in the final paper product.

Yet another object is to provide novel and improved paper products exhibiting exceptional properties such as strength, improved internal bond, holding endurance, toughness, etc., and to provide novel special type papers such as grease-proof papers, offset printing papers, etc., of a superior type. The improved strength characteristics obtainable following the invention are particularly important with papers loaded with fillers, where properties such as internal bond customarily are deleteriously affected by such fillers.

Yet another object of the invention is to provide a novel process for preparing pulp and paper therefrom, which makes possible greater efiiciency in the retention of fillers and fines incorporated with the pulp.

These and other objects and advantages will become more fully apparent as the following description is read in conjunction with the accompanying figures, which are reproductions of photomicrographs, at approximately 450 times magnification, showing cellulosic fibers with sorbed starch, such as are producible in accordance with the instant invention.

A cellulosic fiber, as is known in the art, is formed of many layers of fibrils bound together and surrounded by an outer lignin lamella. In the production of paper, it is common to separate the cellulosic fibers in wood chips or other fiber agglomerates, either mechanically or chemically, and this physical separation of the fibers is known as defibering. Defibered pulp, i.e., a pulp made up of separated fibers may be further refined to produce freeing of the fibrils in the fiber, in a refining process which is known as fibrillation. In a fibrillated pulp, the fibrils in a fiber are loosened or partially freed, whereby they project as hairlike strands from the fiber body in which they originally were tightly bound. Various types of fibrillation processes have been proposed, including fibrillation carried out at relatively low consistencies, where the pulp which includes the fibers contains sufiicient water to constitute a pumpable and flowable material, as well as fibrillation at relatively high consistencies, where the pulp generally is of a nonfluid or semisolid nature and of a nonpumpable character.

As is recognized by those skilled in the art, a gelatinizable material such as starch, when mixed with water and subsequently cooked, (i.e., raised in temperature above the gelatinization temperature of the starch), swells and becomes converted into a gel, with molecular chains in a starch particle becoming loosened, thence to extend in disassociated expanses in the water in which the starch is dispersed. In prior art practices where the starch is cooked before its introduction into the pulp, the material is introduced to the pulp as a gel, and any association which takes place between the starch with the fibers in the pulp is one which is attained through mixing of the already gelatinized material with the pulp fibers.

This invention is based on the discovery that unexpected results are obtained if the gelatinizable material is incorporated with the defibered pulp in a substantially uncooked condition, i.e., in a substantially nongelatinized state, and if this addition of the gelatinizable material is made prior to or simultaneously with the introduction of the pulp to a refiner producing fibrillation of the fibers in the pulp. Further, it is important according to this invention that the conditions be such that during the refining to produce fibrillation there is simultaneous cooking of the gelatinizable material whereby it converts into its gelatinized state. Under these conditions, the gelatinizable material swells into a gel simultaneously with loosening of the fiber fibrils, and apparently far greater sorption between the material and the fibers results. This has been confirmed by photographic studies indicating that when refining is carried out as indicated, the starch particles become transformed into gellular masses that become entwined with the fibers in the pulp, and more particularly With the fibrils of said fibers, to become 1ntimately joined in a manner unobtainable with prior approaches.

In this connection, the use of high consistency refining techniques is particularly appropriate. In high consistency refining, fibrillation is performed on pulp which is of a semisolid or nonflowable nature (the usual high consistency pulp has a consistency, i.e., a percent by weight of fiber on a dry basis, of or more), and fibril loosening is the result of interfiber friction produced by fibers rubbing against each other. Temperatures are produced as a result of such fiber friction which are above the gelatinization or cooking temperature of the starch (about 150 F.), such temperatures normally ranging from about 170 F. to well above boiling temperature (temperatures as high as 260 F. have been observed). Thus, with high consistency refining, the temperature condition needed to produce cooking is produced automatically and without the need of external heating. Furthermore, with a high consistency pulp, a greater fi ber surface area is present for a given volume of pulp than is present with a low consistency pulp, which apparently contributes to greater sorption of the gelatinizable material by reason of forced close contact of the gelatinizable material and the fibers being refined. Additionally, there is a higher concentration of gelatinizable material in a high consistency system than in a low consistency system, which is felt to contribute to the desirable results obtained by the invention.

Following the invention, it has been noted that for a given loading of gelatinizable material, substantially better internal bond and other paper strength characteristics are obtainable than producible with known loading procedures. More efiicient retention of the gelatinizable material, as well as other fillers or fines incorporated with the pulp, are also realizable. Furthermore, the degree of sorption of the gelatinizable material with the cellulosic fibers is such that appreciably greater amounts of material may be loaded into the pulp without experiencing sticking problems, problems of drainage, and other difficulties normally associated with the adding of starches when such is added at concentrations exceeding about 2% based on the dry weight of fiber. With it practicable to produce paper having an appreciably greater loading of gelatinizable material, a paper product may be produced that provides an excellent substrate for grease proofing. As a result, new and improved grease-proof papers are possible. Papers of exceptional strength can be produced, with a starch loading substantially exceeding that normally practiced in the past. Additionally, properties may be introduced into paper, such as stiffness, that make the paper available for special uses, such as for tab cards, etc.

The gelatinizable materials that may be utilized according to this invention include both the natural starches and starches that constitute derivatives of such natural starches, such as the so-called cationic starches of the type discussed in US. Pat. 2,813,093. In this connection, with cellulosic pulps being anionic in character, the use of a cationic starch produces some particularly advantageous results, although this is not to say that the invention is limited to such, as important advantages are realized regardless of the type of starch employed. Starch comprises essentially amylopectin and amylose, the various types of starches being a major part amylose or amylopectin, depending upon their origin. Starches high in either amylose or amylopectin are usable with the invention, with those high in amylopectin having certain advantages in that the more highly branched amylopectin starch molecule apparently produces a cross-linking action among the fibrils of the fibers not producible with the more linear amylose molecules. Particle size does not seem to be too critical with respect to the retention obtained in the pulp, particularly when high consistency refining techniques are employed for incorporating the starch, possibly because of the shearing action generated during the fibrillation at high consistency which causes the starch to be broken down. However, as a practical matter, best retention seems most probably to be obtained with a particular size (wet mill-ed) of 30 microns or less.

In the loading of a pulp as contemplated, it has been found that other materials can be introduced into the pulp together with the gelatinizable material such as the usla pigments (TiO, ZnO, CaCO, Clay), fibrous fillers such as CaSiO precipitated on cellulosic fibers, etc., with greater retention of the pigments or fillers in the final paper than normally realizable. These materials may be introduced into the pulp to be refined along with the gelatinizable material. In this connection, control of the particle size of a pigment has some importance, since these materials apparently do not break apart as readily as starch under the action of the refiner. Thus, it is preferable that in the case of pigments, an average particle diameter of 4 microns or less be employed for optimum results.

Cellulosic material which is suitable for use as a starting material in accordance with this invention may be derived from any species of coniferous pulpwood, such as spruce, hemlock, fir, pine, and others; deciduous pulpwood, such as poplar, birch, cottonwood, alder, and others; as Well as from fibrous, nonwoody plants suitable for paper-making, such as cereal straws, bagasse, cornstalks, grasses, and the like, and also the usual waste cellulosic sources.

When high consistency refining is employed in the fibrillation of the pulp fibers, such is performed with the pulp having a consistency of between 10% and 60%, and preferably between 20% to 45%. The pulp may be metered as by a screw conveyer into the refining apparatus, such as a conventional single-disk refiner, a double-disk refiner, or a conical-type refiner adapted for handling high consistency pulp. All of the above machines have two op posed surfaces which are spaced apart and more relative to one another, defining between them a Working space. In the case of a single-disk refiner or a conical-type refiner, one of the surfaces is stationary while the other is rotating, and in the case of the double-disk refiner, both surfaces are rotating, either in the same or in opposite directions. Any of the above-mentioned surfaces, however, should be moving with sufficiently high relative tangential velocity as to ensure that pulp fibers will move rapidly and continuously from the point of introduction or inlet toward the point of discharge or outlet.

In general, the surfaces should operate at a relative tangential velocity of no less than about 1,000 feet per minute and the rotation should be about a fixed axis to obviate relative gyratory movement which results in balling of the fiber. When one of the surfaces is stationary, the relative tangential velocity of the surfaces should preferably be at least 5,000 feet per minute, and in the case where both surfaces are moving in opposite directions, relative tangential velocity of at least 15,000 feet per minute is preferred. The velocityshould be sufiiciently great for any given spacing between the refining surfaces as to impart suflicient energy to the fibers to effect attrition therebetween and the fibrillation essential by the interfiber friction, and at the same time provide sufiicient energy to move the fibers through the refiner. The two surfaces between which the pulp is treated may be roughened by having a set of ducts, grooves, indentations or other projections of such character as to engage the high consistency pulp. The refining of high consistency pulp in order to effect fibrillation thereof is more fully discussed in US. Pat. 3,382,140.

Residence time within the refiner of the pulp being processed will vary somewhat, depending upon operating conditions. Usually, such will be less than about sec onds, with a residence time of from 0.3 to 3 seconds being typical.

The following examples are inserted to further illustrate the instant invention. A double-disk Bauer 411 refiner was used in the refining to effect fibrillation. The plate clearance in the refiner was adjusted to between 0.02 and 0.04 inch. Feed rate of pulp into the refiner was maintained between about three to four tons per hour.

In the examples, various tests were performed using standard TAPPI methods, unless otherwise indicated.

EXAMPLE 1 A softwood (Western Hemlock) sulfite pulp, bleached to a brightness of 80% G.E.R.S. (General Electric Recording Spectrophotometer) was dewatered in a Sweco screen and pressed to a consistency of 35% through a Zenith press. Such pulp was then metered into the center or eye of the Bauer 411 refiner, to produce fibrillation of the fibers in the pump. Simultaneously with the feeding of the pulp, a mixed slurry of titanium dioxide pigment and an uncooked cationic cornstarch derivative of high amylose content was injected into the eye of the refiner.

The slurry of starch and pigment was made in cold water, with a pigment to starch ratio of 10 to 4, and the concentration of slurry solids in the slurry was 25%. The pigment, Du Ponts Ti-Pure LW, having an average micron size of 0.4, was first dispersed in water at room temperature, and the uncooked starch then added to the pigment slurry with mixing. The starch utilized was a tertiary amino alkyl starch ether derivative, with a degree of substitution of about 4 amino alkyl groups per 100 anhydroglucose units. The starch contained 70% amylose, and was obtained from National Starch and Chemical Company as National Starch 77-1405. The starch had a particle size of microns. The slurry was fed into the refiner at a rate to obtain a starch addition of about 3.3% based on the oven dry weight of fiber.

The power input to the refiner was approximately 5 horsepower day/ dry ton of fiber. During the refining, the freeness of the pulp was reduced from about 680 to 470 cc. 'CSF (Canadian Standard Freeness). The pulp and slurry was fed into the refiner at approximate room temperature. The residence time of the pulp and slurry, on making a single pass through the refiner, was approximately one second. The temperature of the pulp and slurry was raised within the refiner, by interfiber friction, to approximately 235 F.

The pulp mixture or stock immediately on leaving the Bauer refiner was diluted with cold water to a consistency of 3.5%, such dilution lowering the temperature of the stock to 70 F. The stock was then further refined using a conventional Jordan, low consistency refiner, to reduce its freeness to 220 cc. CSF.

The stock or furnish was then directed to a paper-making machine for conversion into paper. The paper produced, without any size press treatment, exhibited the following properties:

TABLE I Basis wt., lbs/3,000 ft. 32.0 Caliper, mils (.001") 2.1 Bursting strength (Mullen), lbs/in? 23.9 Tensile, lbs./ in. WMD* (Instron tester) 22.1 Rupture energy, ft.-lbs./ft. WMD 2.6 Fold (MIT), WMD 993 Opacity, percent (Bausch & Lomb) 77.0

Scott internal bond, ft.-1bs./in. 1000 500+ *With machine direction.

The Scott internal bond property is indicated above as 500+, as the internal bond measured exceeded the measuring calibrations of the testing machine.

The retention of starch in the paper was noted to be about and pigment retention was noted to be about 88%. No difficulties were noted in running the stock on the paper-making machine.

EXAMPLE 2 Softwood sulfite pulp of the type used in Example 1 Was refined to produce fiber fibrillation as in Example 1, with the exception that in this instance, the mixed slurry of titanium dioxide pigment and uncooked starch was not introduced into the Bauer refiner with the pulp. Instead, the pulp was diluted on being discharged from the refiner to a consistency of about 3.5%, and the pigment and starch slurry was then added at this stage. The pulp mixture resulting was then further refined, as in Example 1, to reduce the -freeness of the stock to 200 cc. CSF. The stock or furnish was then fed to a paper machine to be converted into paper.

Trouble was experienced in running this furnish on the paper-making machine. Considerable picking was noted at the dryer portion of the machine, indicating relatively loose bonding of the starch in the body of the sheet and poor distribution of the starch. The paper prior to any size press treatment exhibited the following properties:

TABLE II Basis wt., lbs/3,000 ft. 31.0 Caliper, mils 2.0 Bursting strength, lbs/in. 16.8 Tensile, 1bs./in., WMD 16.7 Rupture energy, ft.-lbs./ft. WMD 1.7 Fold (MIT), WMD 317 Opacity, percent 73 Scott internal bond, ft.-lbs./in. 1000 290 The retention of starch in the paper was less than 65%, and the retention of pigment was noted to be about 69%.

Furnish prepared in the same manner, but with the starch added cooked, introduced such problems that the furnish was to all intents and purposes impossible to handle on the paper-making machine.

Paper produced from the furnish where the starch was added uncooked was given a starch size press treatment, to upgrade the finished paper, as is usual in the making of a business bond grade paper. In a size press treatment, a coating composition is applied to both sides of the paper which is then metered off by reason of the paper passing between the nip of opposed rolls. The coating composition used contained about 15% solids, and comprised in addition to water a mixture of parts ethylated starch (Penford Gum 260 by Pennick & Ford), 3 parts carboxylated styrene maleic anhydride resin copolymer (Scripset 500 produced by Monsanto), and 12.5 parts titanium dioxide (Ra42 by National Lead). The composition was applied at a rate to obtain a distribution of solids on the paper of about one pound per 3,000 square feet. Physical propfrties noted in this size press treated paper were as folows:

TABLE III Tensile, lbs/in. 20.7 Rupture energy, ft.-lbs./ft. 1.9 Opacity, percent 74.0 Scott internal bond, ft.-lbs./in. l000 362 It will be noted that the internal bond of this paper was still considerably lower than the internal bond of the paper prepared according to Example 1, where the un cooked starch was introduced into the Bauer refiner together with the pulp.

Further illustrating the present invention is the following example.

EXAMPLE 3 A blend was prepared comprising 60% softwood sulfite pulp of the type set forth in Example 1 and 40% of a bleached birch kraft, bleached to a brightness of 85% G.E.R.S. This blend was dewatered and pressed to produce a pulp of 37% consistency. To produce fibrillation of the pulp, the pulp was fed into a Bauer refiner at this consistency simultaneously with the feeding into the refiner of a slurry comprising uncooked natural cornstarch (20 microns average particle size) dispersed in cold water, and with a slurry solids of 35%.

The pulp was refined with a power input of about 7 horsepower day/ dry ton of fiber. The uncooked cornstarch slurry was fed at a rate to obtain a loading of starch, based on the dry weight of fiber. The temperature of the pulp and starch slurry additive reached approximately 230 F. on making a single pass through the refiner, and the freeness of the stock on leaving the refiner was 385 cc. CSF. Residence time in the refiner was determined to be about 1.5 seconds.

On leaving the refiner the pulp was diluted with cold water to approximately 4% consistency, and cooled to a temperature of 70 F. by the addition of the water. The stock was then further refined at this low consistency, in a Jordan refiner, to obtain a final freeness of 235 cc. CSF.

Paper was prepared from stock or furnish so produced, and such paper (without any size press treatment) possessed the following physical properties:

TABLE IV Basis Wt., lbs/3,000 ft. 30.0 Caliper, mils 2.4 Fold (MIT):

WMD 1946 CMD 1351 Scott internal bond, ft.-lbs./in. 1000 483 *Cross machine direction.

TABLE V Basis wt., lbs./ 3,000 ft. 31.0 Caliper, mils 2.2 Fold (MIT): I

WMD 1253 CMD 560 Scott internal bond, ft.-lbs./in. 1000 300 It will be noted that the fold and internal bond strength were substantially below what was obtained when the furnish included cornstarch added in uncooked form at the high consistency refining stage.

The following example illustrates the use of a starch which is relatively high in amylopectin, in the preparation of a stock or furnish which is free of any pigment addition.

EXAMPLE 4 A blend of softwood sulfite pulp and bleached birch kraft, as used in Example 3, was processed as in Example 3 save that the slurry used to load the pulp was an aqueous slurry (30% solids) of a cationic cornstarch derivative containing about 75% amylopectin. The starch was a tertiary amino alkyl starch ether derivative, having an average particle size of less than 20 micron, obtained from the National Starch and Chemical Company as Cato-Kote 1378. The starch slurry was fed into the refiner together with the pulp at a rate to obtain a loading of 4%, based on the dry weight of fiber. Residence time in the refiner was noted to be about 1.5 seconds and the temperature of the stock within the refiner was raised to about 240 F. The Stock On leaving the refiners was diluted with cold water as in Example 3, and further refined at low consistency to obtain a headbox freeness of 200 cc. CSF.

Stock or furnish so produced was converted into paper which possessed the following properties:

TABLE VI Basis wt., lbs/3,000 ft. 29.7 Caliper, mils 2.02 Tensile, lbs./in., WMD 29.1 Fold (MIT):

WMD 1702 CMD 1616 Scott internal bond, ft.-lbs./in. l000 850 The testing machine used in measuring the Scott internal bond in this instance was modified to enable the obtaining of a reading exceeding 500.

N0 difficulties were experienced in running the papermaking machine with the furnish so produced. There was greater than retention of the starch in the paper product produced.

EXAMPLE 5 A series of runs were performed to demonstrate the superior pigment retention obtainable when a pulp is loaded with starch and pigment in the manner contemplated by the invention. In these runs, paper products were prepared from various types of furnishes.

Furnishes were prepared from various pulp mixtures by injecting them into a Bauer refiner concurrently with continuously feeding into the refiner a mixed slurry of uncooked starch (of the type set forth in Example 1) and pigment, with the pigment to starch ratio in said slurry being 10 to 4. The consistency of the pulp entering the refiner was approximately 35% and the pulp feed rate was approximately 3.4 tons per hour. The refining power employed was 7-8 horsepower day/dry ton of fiber. The freeness of the pulp coming from the Bauer refiner was in the range of 400 to 500 cc. CSF, and after additional refining in a Jordan refiner and at the headbox the freeness of the furnish was in the range of 200 to 250 cc. CSF. The starch slurry was added at a rate sufiicient to produce a loading of 4% starch, based on the dry weight of fiber. Residence time in the Bauer refiner ranged from one to three seconds, and temperatures in the refining ranging from 200 to 250 F. were noted.

In the following table, the type of pulp furnish used in the different runs is set forth. Also indicated are the additives that were injected into the Bauer refiner together with the pulp, and the retention of titanium oxide and starch noted in the final paper products.

TABLE VII Retention, percent Furnish Additive T102 Starch A T102. 99. 0 74.8 A TiOz and asbestos 1 93. 7 82. 8 A T102 and amorphous silica 96. 0 B TiOz and asbestos 1 89. 4 94. 1 T102 and amorphous silica 1 100 100 TiOz and asbestos 1 91. 0 100 TiOz and amorphous silica 88. 6 82. 4

1 Ratio of TiOz to extender in additive was 3:1.

NoTE.--A60% bleached softwood sulfite and 40% bleached birch krait; B15% bleached softwood krait, 45% bleached softwood sulfite apii 4(1):? flileached birch kratt; C-60% bleached softwood kraft and 40% a or a The following example illustrates the preparation of a furnish, and paper from such furnish, where a very high loading of starch was employed in such furnish.

EXAMPLE 6 A pulp blend of the type utilized in Example 3 was passed through a Bauer refiner to obtain fiber fibrillation, the power input to the refiner during such fibrillation being approximately 10 horsepower day/dry ton of fiber. An aqueous slurry of uncooked starch (of the type employed in Example 1) comprising 30% starch, was injected into the Bauer refiner simultaneously with the pulp, and at a rate to produce a starch loading of 17.5%, based on dry fiber weight. The pulp on leaving the refiner was diluted to 3.5% consistency and further refined to a final headbox freeness of about 200 cc. CSF. Residence time in the refiner was approximately two seconds and the temperature of the pulp in the refiner was raised to approximately 240 F.

Furnish so prepared was converted into paper on a paper-making machine. No problems were encountered in running the furnish on the machine. The paper produced had a very fine erasable surface, with a surface strength comparable to the surface strength of the best erasable rag furnish tracing paper available commercially. The surface strength when measured (Wax pick test) showed the maximum rating of 32. The paper when measured for internal bond strength demonstrated an internal bond exceeding 500.

The following example illustrates the production of a paper having a high stiffness factor, such as may be employed in tab cards and other business form papers.

EXAMPLE 7 A blend of pulp of the type utilized in Example 3 was dewatered as in Example 3 to about 35% consistency and refined in a Bauer refiner to produce fiber fibrillation. A power input of about 8 horsepower day/dry ton of fiber was used. Simultaneously with the feeding of the pulp, a 30% slurry of uncooked starch (Cota-Kote 1448) was injected into the refiner. The residence time within the refiner was about three seconds and the temperature of the pulp mixture in the refiner was raised to approximately 240 F. The addition of the starch slurry was such as to produce a loading of 11% starch based on the dry weight of fiber. After leaving the Bauer refiner the pulp was diluted to 3.5% consistency and further refined in conventional Jordan refiner to about 230 cc. CSF.

Such furnish was converted into paper. The furnish released cleanly from the wire in the paper-making machine, and did not pick at the presses, or at any of the dry cylinders. The starch retention in the final paper was estimated to be in excess of 85% Physical properties noted in the paper produced were as follows:

EXAMPLE 8 Furnishes were prepared resembling the one prepared in Example 7, but differing in the amount of starch loading they contained. Papers prepared from such furnishes were given a size press treatment, to obtain grease resistance. A size press composition was used consisting of an aqueous mixture of 100 parts Penford Gum 280 (Penick & Fords ethylated starch), 25 parts urea, and 1.25 parts Fe 806 (fluorocarbon, by Minnesota Mining and Manufacturing). The size press coating composition contained 15% solids. In the size press treatment, the composition was applied at a rate to obtain a distribution of solids of about 1.75 to 2.0 pounds per 3000 square feet of paper.

The following table illustrates the grease holdout rating of the various papers produced. The rating was determined by a procedure devised by Minnesota Mining and Manufacturing, wherein a drop of testing solution is placed on the surface of the sheet, and the rating given is related to the type of solution that will stand on the surface for 15 seconds in the form of a drop without failing. The testing solutions used comprise a mixture of castor oil, heptane and toluene, with lower numbered solutions being high in castor oil, and the highest numbered solution (12) having no castor oil.

In another size press treatment, a coating composition was utilized comprising parts latex (carboxylated styrene-butadiene copolymer) and 33 parts alpha protein, in sufiicient water to make a 17% solids mixture. Paper so prepared exhibited good grease holdout properties com parable to the holdout properties.

To illustrate the sorption of starch to fibers which occurs when fibers are refined to produce fibrillation simultaneously with the introduction to the refiner of an uncooked starch addition, photomicrographs were taken of samples of pulp prepared as in Example 4 and on leaving the Bauer refiner. The pulp was dispersed in water, and iodine applied over a sample to prepare the sample for the taking of a photomicrograph. The application of the iodine functioned to stain the starch, better to identify the starch by rendering it blue. The photomicrographs taken were at about 450 times magnification.

FIGS. 1 and 2 are reproductions of two of such photomicrographs. It will be noted that the refining of the pulp at high consistency and with a temperature condition produced in the pulp above the gelation temperature of the starch were effective to produce cooking of the starch particles with such swelling to form gels. It Will further be noted that fibrillation occurred in the fibers by reason of such refining, as demonstrated by the hairlike strands which project out from the fiber bodies. The photomicrographs reveal a high degree of sorption of the cooked starch, as evidenced by the gelatinized starch ap pearing as globular masses sorbed against the cellulosic fiber bodies, with the fibrils of such bodies projecting through and encompassed by such globular masses.

Furnish prepared according to the invention ordinarily is subjected to a finish refining at low consistency, after the fibrillation by refining at high consistency, which has the effect of further reducing the freeness of the pulp. High consistency refining has been noted to introduce some balling and entangling of the fibers. The finish refining serves to untangle these fibers, which results in a more uniform paper product being obtained. Ordinarily, it is desired that the freeness of the pulp be reduced to below about 275 cc. CSF, to obtain the best paper products.

It will be noted from the above description that some significant advantages are obtained through the introduction of the gelatinizable material or starch in the manner contemplated. These advantages relate not only to the type of product producible, but also togthe method of preparing the paper product.

It is claimed and desired to secure by Letters Patent:

1. A method of loading a pulp of cellulosic fibers with starch which in aqueous solution and at a temperature above gelatinization temperature cooks to form a gel, comprising providing an aqueous pulp mixture of defibered cellulosic fibers, incorporating the starch with such in a nongelatinized state with the defibered pulp mixture, refining the pulp mixture together with such starch to effect fibrillation of the fibers with loosening of fiber fibrils, and concurrently with the refining and fibrillation of the fibers and with the pulp mixture raised to a. temperature which is above said gelatinization temperature cooking said starch to form a gel with such gel during such fibrillation becoming sorbed by the fibers in the pulp mixture and the fibrils which become loosened from the fibers.

2. The method of claim 1, wherein the refining of the pulp to effect fibrillation is performed with the pulp mixture having a consistency of at least about and in the form of a nonfiowable mass and the temperature of the pulp mixture is raised to a temperature above said gelatinization temperature by interfiber friction produced during the refining of the pulp mixture.

3. The method of claim 1, wherein the refining is done in a working space defined by opposed working surfaces in facing relation and in relative rotational motion with respect to each other, there being an inlet and an outlet communicating with said working space, the pulp mixture and starch is fed continuously and at a temperature below said gelatinization temperature into said working space through said inlet and being withdrawn from said outlet and the temperature of said pulp mixture is raised to above said gelatinization temperature within such working space while the pulp mixture travels from said inlet to said outlet.

4. The method of claim 1, wherein said starch is a cationic starch derivative.

5. The method of claim 4, wherein said refining and cooking is performed with the temperature of the pulp mixture exceeding 170 F.

6. The method of claim 3, wherein said refining is done with a pulp mixture having a consistency of at least about 20%, and the temperature of the pulp mixture is raised within such working space by interfiber friction in the pulp mixture.

7. A refined paper-making pulp loaded with starch and prepared by the method of claim 1.

8. A paper product prepared from the paper-making pulp of claim 7.

9. A method of preparing a paper-making pulp with a starch loading of from 3 to 30% comprising an aqueous pulp mixture of defibered cellulosic fibers, refining the pulp mixture in a high consistency refiner to effect fibrillation of the fibers in pulp with loosening of the fibrils, introducing the starch in an uncooked state to the refiner together with the pulp mixture, the pulp mixture in the refiner and during the refining having a consistency exceeding about 10%, concurrently with the refining and by interfiber friction raising the temperature of the pulp mixture including starch within the refiner to above the cooking temperature of the starch to effect cooking of the starch with such forming a gel which becomes sorbed by the fibers in the pulp mixture and the fibrils which become loosened on the fiber, after refining lowering the consistency of the refined pulp mixture to one which is fiowable, and further refining this pulp mixture at such fiowable consistency to further reduce the freeness thereof.

10. A paper product prepared from a paper-making pulp produced from the method of claim 9.

11. A method of making a paper product having improved holdout and other properties comprising providing an aqueous pulp mixture of defibered cellulosic fibers, refining the pulp mixture in a high consistency refiner to effect fibrillation of the fibers in the mixture with loosening of the fiber fibrils, introducing starch in an uncooked state into the refiner together with the pulp mixture with the starch addition being within the range of 3 to 30% based on dry fiber weight, the pulp mixture during refining having a consistency exceeding about 10%, concurrently With the refining and by interfiber friction raising the temperature of the pulp mixture including the starch in the refiner to above the cooking temperature of the starch to effect cooking of the starch with such forming a gel which becomes sorbed by the fibers in the pulp mixture, after refining lowering the consistency of the pulp mixture to one which is fiowable and further refining the mixture to reduce the freeness thereof, converting the pulp mixture into paper, and size press treating such paper with a grease-resistant formulation.

12. A paper product produced by the method of claim 11.

13. The method of claim 1, wherein a pigment is incorporated with the defibered pulp mixture together with the gelatinizable material prior to refining to effect fibrillation.

14. The method of claim 13, wherein the average particle diameter of the pigment is 4 microns or less.

References Cited UNITED STATES PATENTS 3,210,240 10/1965 Read 162-175 2,105,052 1/1938 Oltmans 162175 2,147,213 2/1939 Pattilloch 162175 2,553,412 5/1951 Heritage 162-10 2,729,561 1/ 1956 Marrone 162-l75 OTHER REFERENCES Casey: Puly and Paper, vol. II, 2nd ed., p. 960.

S. LEON BASHORE, Primary Examiner W. F. SMITH, Assistant Examiner US. Cl. X.R. 162l0, 158, 183

UNITED STATES PATENT OFFICE- CERTIFICATE' OF CORRECTION Patent No. 3,794,558 Dated Fab 25, 74

Inventor(s) S. B. Back It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below;

(1301mm: 10, line 18, in Table IX, delete 1" and insert Signed and sealed this 10th day of June 1975,

(SEAT) Attest:

C. MARSHALL DANN RUTH C. ELASON Commissioner of Patents Attesting Officer and Trademarks

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