May 29, 1962 R. c. MARTIN . 3,036,950 I, PROCESS FOR INCORPORATING RESINS INTO PAPER 1 Filed June 22, 1959






PAPER FORMED AND DRIED if. 3,036,950 United tates Patent Patented May 29, 1962 1 2 the form of an aqueous dispersion such as a suspension, 3,036,950 PROCESS FOR INCQRPORATING RESINS colloidal solution, or true solution. When they are added INTO PAPER to the polyvinylpyrrolidone-treated pulp slurry they are Ray C. Martin, Freeport, Ill., assiguor to Burgess Cel drawn to and are caused to be deposited uniformly on the lulose Company, Freeport, 111., a corporation of Dela treated pulp. The modi?ed pulp furnish may then be ware processed in a normal manner to produce the ?nished Filed June 22, 1959, Ser. No. 821,724 paper or board end product. 12 Claims. (Cl. 162-165) The drawing contains a flow diagram of the process of the invention. This invention relates to the art of paper making, and A further improvement may be realized by adding an more particularly refers to a novel method for incorpo acidic insolubilizing agent to the slurry containing the rating resins and other additive materials into papermaking polyvinylpyrrolidone-treated pulp, and thoroughly mixing pulps at that point of the paper making process generally the slurry. The insolubilizing agent aids in setting or in termed as the “wet end,” and to the novel products pro~ solubilizing of the polyvinylpyrrolidone, and enhances the duced thereby. 15 coupling action of the polyvinylpyrrolidone between the Unmodi?ed paper and paper board made by conven pulp and the subsequently added resin. The preferred tional methods have many limitations. The products are material is the linear copolymer of methylvinylether and weak, permeable to , oil and grease, and lack many maleic anhydride, or the half amide thereof. of the properties generally desired in a ?nished paper prod The incorporation of a resin during the paper making uct. To improve its properties, modifying or reinforc process has several attractive potentialities. Because the ing materials such as resins, pigments, ?llers and other addition is accomplished during the making of the paper, related materials are customarily added to the paper. the additional steps of or impregnating of the The majority of processes currently used for incorpo ?nished paper and its attendant cost is avoided. More rating these materials into paper may be characterized as over, because the resin is incorporated while the ?bers secondary operations, that is, they are methods for treat 25 are separated, an extremely uniform dispersion of the resin ing the paper after the paper itself has been fabricated. about the ?bers can result. It has been attempted in the Such secondary operations, or applications of the modify past to provide a process wherein a resin introduced in an ing materials made to the basic paper, usually from aqueous media in a paper beater would be absorbed by or hot~melt systems, succeed at best only in applying .a the pulp, leaving clear Water substantially free from resin. ?lm of the modifying material on the paper surface, and However, these efforts have not been successful in view of ?lling the interstices, but do not succeed in causing the the fact that only a small portion of the resin has been ?ilers to penetrate the ?bers themselves, since the ?bers and retained in the ?nal paper, while the major proportion additives are electrically repellent to each other. As a thereof has been lost when the water is removed during result, the full bene?t of the modifying agent is not real the paper making process. ized. Moreover, the addition of a separate treating step 35 The present process is dependent upon the discovery adds to the cost of processing. Even where wet-end that when an aqueous solution of Polyvinylpyrrolidone is processes have been used, complete retention of the addi introduced into a pulp slurry which has been adequately tive by the pulp has not been achieved, with the result that beaten it becomes deposited on the cellulose ?bers and the excess additive is generally removed in the form of strongly attached thereto. The exact nature of the reac unattached particles, which, together with the “?nes” from 40 tion or mechanism responsible for this phenomenon is the process, frequently cloud the water and render it non not fully known. It is believed that the functional group reusable. of the polyvinylpyrrolidone reacts with the functional It is an object of the present invention to provide a group of the cellulose molecules to form a bond in the process for the incorporation of resins and other modify nature of that of an addition compound. In actual prac ing materials in an aqueous mediinn into papermaking 45 tice, the Polyvinylpyrrolidone migrates to the cellulose pulp in the wet-end stage of the paper making process. ?bers and becomes ?rmly attached thereon. When an It is a further object to provide such a process wherein additive material such as a phenolic resin in aqueous dis the resins and other additives are removed from the aque persion is subsequently introduced into the slurry, it is ous medium in which they are applied, and are tenacious believed that a similar reaction takes place between a ly deposit-ed upon the individual pulp ?bers. 50 functional group of the resin molecule and a functional It is still further an object to provide such a process group of the polyvinylpyrrolidone. The polyvinylpyrro wherein modi?ed papers are produced in which the mod lidone in effect becomes a cross-linking or coupling agent ifying substance is uniformly dispersed throughout the for the cellulose-resin system. This phenomenon can be paper. easily observed, since, immediately after the addition of It is a further object to provide modi?ed paper mate— 55 the aqueous resin dispersion or other modifying agent in rials which, while having the same modifying agent or to the polyvinylpyrrolidone-treated pulp slurry, substan additive content, exhibit greatly enhanced properties over tially all of it is removed from the aqueous solution and products made by other methods. deposited on the pulp ?bers, leaving the water clear. In It is a further object to provide various useful modi?ed fact, so pure is the water that it may be reused in the paper products produced by the methods of the present paper making process without further puri?cation. invention. Polyvinylpyrrolidone is an acetylene derivative manu Other objects and advantages of the present invention factured by the so-called “Reppe” high pressure and tem will become apparent from the description which follows, perature technique. It is a water-soluble homopolymer and from the appended claims. of N~vinylpyrrolidone, having the following structure: According to the present invention, polvinylpyrrolidone 65 in aqueous solution is added and thoroughly mixed into an aqueous slurry of papermaking pulp which has been ?rst beaten in the usual manner. The Polyvinylpyrro lidone is adsorbed on the surface of the pulp ?ber and functions as a coupling agent for the attachment of mod ifying resins and other additaments. The modifying ma terials are of such nature that they may be provided in Polyvinylpyrrolidone is a white, free-?owing powder 3,036,950 3 A. having in?nite solubility in water. It is presently com ing the lower viscosity is preferred. The chemical struc mercially available in molecular weights of 40,000, 160, ture of the half-amide form is as follows: 000 and 360,000. The having the lowest molec ular weight are preferred since they require less water for dilution. In the interests of convenience, polyvinyl pyrrolidone will hereafter in the speci?cation be referred to as PVP, its customary abbreviation. In ‘the present process, the ?ber treating or coupling PVP acts somewhat like a complexing agent and will ' agents and the modifying materials, comprising resins, are combine with various materials which are used as modi added to the pulp slurry from aqueous systems. Conse fying agents for the pulp, resulting in the formation of 10 quently, they must be water-dispersible. Since the cou homogeneous mixtures. The most important of these are pling agents themselves are in?nitely soluble in water, resins. In addition to resins, other additive materials may be incorporated such as pigments or ?llers, synthetic ?bers they are introduced in the form of an aqueous solution. such as acrylic, polyester, and polyamide ?bers, and in .Where the modifying materials are themselves dispersible 15 in water, as in the case of water-dispersible phenolic resins organic ?bers and flakes such as glass, mica, silica, as the dispersion may be added to the pulp slurry. Where bestos, metallic powder, and other related materials. .they are not directly water-dispersible, they must be ?rst The copolymer of vinylmethylether and maleic an hydride, which will hereafter in the speci?cation in the conditioned, such as by forming into an aqueous , . suspension or colloidal solution, or other suitable form. interests of convenience be designated by its customary In carrying out the present process, the pulp is ?rst abbreviation as PVM/ MA, is a linear copolymer consist 20 ing of alternating vinylmethylether and maleic anhydride beaten to the desired freeness according to prior art meth ods and standards. During the beating operation, the units, and has the following general structure: rolling, shearing and cutting action to which the pulp is ‘subjected, exposes large surface areas of the ?bers, and 25 produces many ?brillae to which the coupling agents sub . sequently become attached. After the pulp has been sufficiently beaten, and the desired pulp freeness has been attained, the beater roll PVM/ MA is a white amorphous powder having in?nite .is raised and the beater itself allowed to circulate. PVP solubility in water. Its water solutions are highly polar. 30 in the desired amount is then added to the circulating ,According to the invention, water solutions of the co pulp. To insure good circulation, the point of addition acid anhydride are added to slurries of pulp should preferably be before the raised beater roll. The ‘?bers which have been ?rst treated with PVP. Cross PVP reacts immediately with the beaten cellulose, open linking of the PVP is initiated by the PVM/MA and is ing up the ?bers, and, by its wetting action, exposing a *5... subsequently completed by the heating of the ?nished larger surface area of the ?bers by separating them from product. each other. It is believed that the PVP becomes ad The sequence of steps used in the process of 'the pres sorbed on the surfaces of the ?brillae in the form of ent invention, especially with regard to the addition of a molecular layer. As a result of the reaction with the PVM/MA, is very important. The PVP is preferably PVP, the beaten pulp takes on a slimaceous appearance. added ?rst to the beaten pulp, either in its pure form or 40 The time required for reacting the beaten pulp with in the form of an aqueous solution. The PVP may also the PVP depends upon the ?ber consistency and the de be added together with the modifying resin, although the ' gree of circulation of the slurry maintained during treat 'results obtained thereby will be inferior to those ob ment. Where a pulp consistency of not greater than tained when the PVP is added ?rst by itself. The acidic .three percent is used, a reaction time of from 15 to 30 insolubilizing agent such as PVM/ MA must be added minutes is generally suf?cient. After the reaction is subsequent to the treatment of the pulp by the PVP, since complete, an aqueous dispersion, suspension or emulsion if added prior to or together with the PVP, it could pre .of the modifying material, such as a phenolic resin, or ‘ cipitate the PVP before the PVP has the opportunity to thermoplastic resin, or latex, is added and circulation become attached to the pulp ?bers. The acidic insolu continued until the modifying material has been substan bilizing agent is added as an aqueous solution. Where tially removed from the Water by the activated pulp. ‘aqueous dispersions of a modifying agent such as “A” 50 Since the PVP is in?nitely soluble in water, some means stage phenolic resins, having alcohol and water as volatile ,must be provided for cross-linking or curing it, so that constituents, are used, the PVM/MA may be incorporated when the ?nished paper product is subjected to water, directly into the resin dispersion, and subsequently added the PVP will not be removed thereby. Where the modi ' to the PVP conditioned ?brous slurry. It may also follow fying resin used is a thermosetting resin such a phenolic the resin treatment, although this is not the preferred resin, it may be added directly after the reaction of the sequence. When ?llers such as ?bers or particles are to PVP with the pulp. When the resin-modi?ed paper is be added to the pulp, it has been found effective to treat _ subsequently heated, the thermosetting resin and the PVP ‘the ?llers with PVP followed by treatment with PVM/ treated pulp become cross~linked whereby the phenolic ‘MA, all in aqueous solution. The entire mixture is then resin becomes infusible and insoluble with the applica added to the heater and incorporated with the pulp by 60 tion of heat. However, where a thermoplastic resin con mixing. stitutes the modifying agent, the PVP-containing pulp is It has been observed that PVM/ MA contributes great advantageously treated with an acidic insolubilizing agent. ly to insolubilizing, as by cross-linking, the PVP-treated Polymeric anhydride such as PVM/MA or its half homogeneous pulp~resin complex, particularly where a arnide, as described above, is the preferred material. ‘ thermosetting phenolic resin is used, as in the production 65 Either of these materials may be added directly as aque of post-forming or electrical board stock. As a result, less ous solutions to the PVP-treated pulp, where the reaction resin solids will be required while still obtaining compara .is instantaneous. Amounts of PVM/MA which have ble physical properties in the ?nished products. proven elfective are: 1 part PVM/ MA to 3 or 4 parts PVP As an alternative to PVM/MA itself, a modi?ed form solids. Other acidic materials such as polyacrylic acid thereof may be used for the same purpose, comprising 70, may be used as cross-linking agents. Even acids such the half-amide of PVM/MA. This form is available as acetic acid, sulfuric acid and formic acid have some commercially in two different grades, “Type 10,” a one ,insolubilizing effect, although they are considerably in percent solution having a viscosity of 100-200 centipoises , ferior to PVM/ MA. ,at 25° C., and “Type 30,” a solution having a viscosity Since the acidic insolubilizing agent such as PVM/MA of 2000-20,000 centipoises. The “Type 10” material hav 75 or polyacrylic acid is utilized primarily for its function 3,036,950 5 6 of insolubilizing the PVP, the amount. used will be de— area for adsorbing a large quantity of the resin. Where pendent upon the amountof PVP used. In general, an pigments or inert ?llers are to be used in the system they amount equal to about 20% or 25% of the weight of may be added and reacted thoroughly with the treated PVP is satisfactory. An amount equal to or even greater pulp before the addition of resin takes place. The addi than the weight of PVP may be used, but generally such tion of the resin may then be made. The resin, in the increase will not be attended by proportionally increased form of a water-dispersion such as a solution, suspension bene?ts. Amounts less than 20% may be used, par ticularly when used in conjunction with a thermosetting or an emulsion, is added at a low solids content, about 2% to 5% of total solids. High solid resin-varnishes, resin. in fact, as pointed out above, satisfactory results such as are used in the production of electrical board or may be obtained when using PVP with a thermosetting 10 post-forming board stock, may not tolerate dilution to resin such as a phenolic, even in the absence of the acidic insolubilizing agent. this extent. Where this is true, the resin viscosity may be reduced with water to the point just short of the pro The amount of 'PVP which need be used will vary ac cording to the amount of modifying materials to be added duction of a “cloudy condition.” The diluted resin is subsequently added in small increments, rather than in the and the type of product to be fabricated. For example, 15 form of a steady stream. it has been found that about 0.05% of PVP solids based on bone-dry ?ber solids, will sufficiently condition pulp A large variety of resinous materials may be employed, to allow small quantities of resin to be thoroughly and the choice being dictated by the characteristic properties completely incorporated. It has additionally been found desired in the end product. For example, thermoplastic, that an amount of about 0.25% of PVP solids, based elastorneric latex resins may be used for ?exibility, while on bone-dry ?ber solids, is su?icient to incorporate 100 acrylic resins may be used for barrier properties and parts of a resin with 100 parts of cellulose ?bers. When grease-proofness. Thermosetting resins such as phenolics larger quantities of PVP are utilized, the thickness of may be used for rigidity and for electrical properties. the layer thereof on the cellulose ?brillae increases, and Upon the ?rst addition of the resin, a reaction takes place resulting in an immediate combining or complexing the pulp exhibits a greater freeness. At 5% PVP solids 25 addition, based on bone-dry ?ber solids, it has been of the PVP-treated pulp with the resin. As further addi found that the thickness of the layer on the cellulose is tions are made, a noticeable “slowing down” of the for of such magnitude that the water drains rapidly upon ward movement of the mass in the beater is eifected. the deposition of this treated furnish in the couching When large amounts are added, the movement of the pulp box. Although amounts greater than 5% may be used, stock tends to be reduced considerably. In some in bene?ts from such increased addition fall off sharply. stances, when large resin additions are made, the material Additions of such materials as pigments or insert ?ller level of the beater or chest may drop, and frequently re materials should be made to the beaten and reacted pulp quires the addition of Water to restore adequate circula at suitable points along the wet-end of the paper making tion. Mixing should be continued for about 15 to 30 process. Such suitable addition points are at the beater, minutes. The stock may, if desired, be water-diluted after beater chest, machine chest, or other similar points in about ?fteen minutes. The concentrated, beaten, chemi advance of the machine headbox. This results in thor cally-treated pulp may subsequently be subjected to any ough and uniform incorporation. These additive mate suitable paper making operation. rials may be added in their normal state, or in the form Among the synthetic ?bers which may be used as modi of a water slurry. Prior to their incorporation into fying materials are: polyacrylic ?bers (Orlon), polyester the slurry, they may be treated with PVP alone, or with ?bers (Dacron), or polyamide ?bers (nylon). The ?bers PVP followed by treatment with PVM/MA. Addition add strength to the ?nal product and may be used to pro_ ally, resins or related materials such as plasticizers and duce dimensionally stable papers, paper boards, pulp barrier-inducing materials may be incorporated together moldings, and steretotype mats. Where polyester ?bers with the pigment. Regardless of the treatment to which such as Dacron are used, they contribute both excellent the ?ller materials are subjected, they should preferably dimensional stability and dielectric properties to the ?nal be added to the pulp in the form of a slurry, since this product. Because of the hydrophobic nature of most accomplishes the wetting of the solid particles prior to synthetic ?bers, it has been found desirable to soak them the addition, and aids in the subsequent reation by which for a period of about sixty minutes prior to their incor the particles are attached to the cellulose ?bers. Among poration into the treated pulp. Soaking may be accom the ?ller materials which may be used are barium sul 50 plished by placing the ?ber in a water solution of PVP and fate, calcium carbonate, clay, diatomaceous silica, , subsequently PVM / MA or its half-amide. One of several titanium pigments, and zinc sul?de. Various dye stuifs practical techniques may be employed. For example, and opacifying pigments, both natural and synthetic, half of the PVP required may be added to the pulp, and serving as colorants may also be added by the same the remaining portion used in the form of a Water solu techniques. They are preferably treated with PVP and tion to soak the synthetic ?bers. This may be followed combined with any other solids constituting the chemical by treatment with a solution of PVM/MA or PVM/MA addition. Upon reaction of the fillers and the other ad half-amide to insolubilize the PVP. It has also been ditives with the treated pulp, a complex is formed, and found that the synthetic ?bers may be added by them the water becomes clear. selves to the beaten, but undiluted and unreacted, pulp in The resinous materials which are suitable for use in the cycle beater. Subsequently the combined pulp and the present invention are those which can be readily dis synthetic ?bers are reacted by the addition of a suitable persed in water by one of several means. Where they amount of PVP. A longer time-reaction should be al are not dispersible, many resins may be conditioned by lowed for the treatment of the combined ?ber slurries. techniques well known to the art, such as by the addi In addition to synthetic ?bers, inorganic ?bers such as tion of wetting agents, dispersing agents, or emulsifying glass ?bers, add strength and dimensional stability as mod agents. Most of the resins commonly used for modi?ca i?ers of the paper making pulp systems. The handling tion and reinforcement in paper making can be made procedure is precisely the same as that previously de compatible by means of one of the methods discussed. scribed; The glass ?bers should preferably have a length The addition of the resin should be made after the pulp of about 1/4 in. and a ?ber diameter of 6 to 9 microns. has been su?iciently beaten, and after it has been treated 70 Other inorganic ?bers, such as asbestos and with PVP, or with PVP followed by treatment with ?bers, or metallic ?akes and powders may also be incor PVM/ MA. The reason for this is that ?brillation of the porated as modi?ers for the purpose of strengthening the pulp ?bers is promoted by the beating processes. The paper product, or for obtaining other properties such as subsequent treatment of the ?bers with PVP, or with PVP heat or electrical conduction or insulation. Asbestos or and PVM/MA makes available a large charged surface ceramic ?bers may be prepared by immersing in a PVP 3,036,950 7 8 solution for a period of about 60 minutes prior to incor phenolic resins in the novalac stage, and many others may poration with cellulose ?bers. They are then added to be advantageously utilized. Where ?nished products are desired which may be cured to the insoluble, infusible state, the hydrated pulp and blended prior to the addition of thermosetting resins such as phenolics, , melamines, the resin. As a means of incorporation of inorganic ?ake material alkyds, polyesters, epoxies, silicones, and many others may be used. Water soluble materials such as proteins, starches such as aluminum, dry PVP may be ?rst mixed with the dry aluminum powder or flakes and then slurried with carboxymethyl cellulose, glues, resins, caseins, etc., may also be employed. water. Subsequently, the slurry is incorporated into the For particular functional properties, specialized chemi— cellulose stock which has been ?rst treated with PVP. A cals may be incorporated among which are mold-resistant preferred method, however, is to wet the metallic ?akes 10 ?rst with water and PV P solution and subsequently treat chemicals, bacteria~resistant chemicals, insect-resistant the ?akes with PVM/ MA in order to insolubilize the PVP chemicals, rodent-resistant chemicals, or ?ame-resistant chemicals. before it is incorporated into the beater. If desired, the The pH of the solution is not critical in regard to the resin component may be combined with the treated alu minum powder and incorporated together therewith into effectiveness of the process for conditioning the paper the moving treated pulp stock in the beater. By the pres pulp with PVP and with PVM/ MA. Satisfactoly products ent method, very large amounts of aluminum powder may be prepared within a pH range of from about 4.0 to may be incorporated into paper stock. No difficulty has about 8.5. been experienced in incorporating equal parts of pulp, The amount of modifying agent that may be incorporat~ aluminum powder and resin. The product so produced 20 ed is not critical, and will generally depend upon the has excellent hiding power, and has insulating properties properties desired in the ?nished product. By using less approaching those which may be obtained by the use of than ?ve percent PVP to condition the pulp, it is possible aluminum foil. The pulp-aluminum-resin sheet may be to incorporate a resin such as a phenolic in an amount calendered to increase its brilliance. equal to the weight of the dry pulp. By the substitution of copper powder for the aluminum 25 Amounts of PVP in the range of 0.05% to 5.0%, based in the above process, paper board may also be fabricated on dry weight of pulp, have been found effective. possessing good heat properties. Amounts greater than 5% do not provide a substantial The formulation according to the present invention will improvement in relation to the amount. depend to a large extent upon the properties desired in A large number of various types of products may be the end product. For example, long-?bered pulps are 30 formed by the processes included within the scope of the effectively used in producing post-forming board and elec present invention. These products may be classi?ed in trical board, whereas shorter-?bered pulps are used for three main groups: products comprised of cellulose ?bers ?ne papers. Synthetic ?bers or inorganic ?bers may be modi?ed by resin, products comprised of cellulose ?bers used to modify long-?bered stock in order to produce modi?ed by the addition of a resin together with other dimensionally stable papers and stereotype mats. For 35 ?bers, and products comprised of cellulose ?bers modi?ed the production of packaging and barrier papers, it has by the addition of a resin together with various ?ller been found desirable to incorporate thermoplastic resins materials other than ?bers. into the pulp. These may be used alone or may be modi Among the important products of the ?rst group are: ?ed with thermosetting resins, or plasticizers to effect such post-forming ?brous board stock, electrical board, wet properties as heat sealing, waterproofness, grease'proof 40 strength papers, barrier papers, battery separators, and ness, low moisture-vapor-transmission, and others. Ther laminated structures. Post-forming board may be de?ned mosetting resins are generally used to produce post-form as resin-treated ?brous board stock which has been partial ing boards which may be subsequently cured to the in ly cured, and which may be subsequently heated and mold fusible-insoluble stage, and for the production of electrical ed under heat and pressure to produce a cured product of boards. Particular chemicals may also be employed as any desired form. It has been current practice to fabricate additives where particular properties are desired in the such post-forming boards by impregnating or saturating end product. ?nished paper stock with suitable resins such as liquid Among the paper making pulps which may be used in phenolic varnishes. After impregnation the excess is the present invention are the following but not limited generally squeezed free, and the product partially dried thereto: alpha cellulose, cotton linters, rag, recovered 50 and subsequently cured. Other methods have been used, broke, semi-chemical, sulfate, sul?te, soda, or mechanical. such as sprinkling the paper stock with a dried phenolic Any other papermaking pulp may also be employed. resin, forming a laminated structure comprised of several The resins used as additive materials may be modi?ed layers of stock and subsequently laminating the structure by the addition of plasticizers of the conventional type by heat and pressure. The products of the prior art have which are compatible with the particular resin used, and been de?cient in many respects. Impregnation of the which are capable of modifying the resins in the desired ?nished stock has resulted in uneven distribution of the manner, as for example phthalates, adipates, sebacates, di resin within the ?brous structure of the board. Moreover, benzoates, stearates, and polymeric materials. Other the resin has tended to deposit on the surface and within materials such as water soluble glycerides and glycols may the super?cial interstices, resulting in the production of also be used. 60 both “spotty” and “resin-rich” areas. Among the pigments and inerts which may be added for Post-forming boards may be produced according to the particular properties are titanium dioxide, various sulfates, present invention by treating ‘beaten pulp ?rst ‘with PVP, clays, zinc sul?de, carbonates, silicates, dyestuffs, talc, and or with PVP followed by treatment with PVM/ MA, and opacifying pigments, both natural and synthetic. ?nally by the incoporation of ‘a suitable resin while the For barrier type products various waxes may be in 65 pulp is still in the slurry stage. Among the resins which corporated, such as paraffin, microcrystalline wax, poly may be used are water-dispersible -formaldehyde ethylene, and other natural or synthetic waxes. resins, polyester resins, or epoxy resins. Thermosetting A large variety of various resins may be used as modify or heat-reactive resins are preferred as they may be in g agents according to the present invention. As previous molded and cured subsequently to the formation of the ly stated, in order to incorporate the resins it is necessary 70 board by heating to temperatures in excess of 300° F., that they be dispersible in water, since the paper making under molding pressure. process is primarily a water process. Thermoplastics such Current methods used in the art for producing electrical as various vinyl derivatives, ethylenic resins, rosin and re board generally comprise dipping ?nished paper stock into lated compounds, natural resins, chlorinated diphenols, a saturating tank containing electrical grade phenolic cellulose esters and ethers, natural and synthetic rubbers, 75 resin varnish, and removing the excess resin by feeding the 3,036,950 10 saturated paper stock between a pair of squeeze rolls. The addition of wetting agents or emulsi?ers to the base poly impregnated paper then is dried in a suitable drier, cut ester or epoxy resin, together with the necessary catalyst, to a speci?c size, and laminated under heat and pressure and by the subsequent addition of increments of water to the desired thickness. Since the cellulose, carrying under moderate to high speed agitation. In their altered a negative electrical charge, is repellant to the phenolic form, these resins may be incorporated into the slurry in varnish, and since the varnish as normally used has a high the beater in accordance with the methods of the present solids content, adequate penetration of the cellulose is invention. Prior to lamination, the retained moisture of not ‘accomplished, but rather the varnish remains sub the formed sheets, generally in amounts of from about 5% stantially on the surface of the paper stock. Consequent to 10%, is removed by heating at ‘about 250° F. A ly, in order to obtain the desired properties, it is necessary 10 plurality of boards is then placed in a press and bonded to use a large, amount of varnish. Opposed to this, elec~ and cured by the application of suitable heat and pres~ trical board made by the method of the present invention sure. accomplishes thorough complexing of the individual ?bers A second group of products which may be prepared by of the board stock with the resin, and, as a result, the the present invention are those in which various synthetic same or better properties can be obtained even though 15 ?bers are incorporated with the cellulose ?bers, in addi much smaller amounts of varnish are used. Various tion to the modifying resin. One of the most important resins such as phenolformaldehyde, »form-aldehyde, products in this group is dimensionally stable paper, such melamine~formaldehyde, silicones, polyesters, and epoxy as map and chart paper, and stereotype mat stock. In resins may be used. Moreover, the less expensive un preparing these products, the cellulose pulp ?bers are bleached kraft pulp may be used in the present method 20 treated in the normal manner with successive additions of ‘while still attaining good electrical properties in the ?nished product. PV P and PVM/MA and given about a 30—minute mixing period to assure adequate blending. The desired resin is A preferred resin for the production of electrical board then added to the slurry of treated pulp. Any desirable is a phenol-formaldehyde resole, or “A” stage resin, that ?ller such as inert pigments may be added by previously is, ‘one which is not yet advanced to the intermediate con 25 treating the ?ller with PVP and PVM/ MA, and then add densation stage. The formed material is subjected to ing it to the pulp slurry. The ?ller may also be mixed to temperatures of below 250° F. to drive olf the Water and gether with the required amount of the resin described is then ready for further processing. In order to increase above and the resulting slurry incorporated as a steady the product strength, various modifying ?bers such as stream into the beater. The heater is then given a 30-min acrylic, polyester, acrylonitrile or polyamide may be 30 ute mixing period to insure that the materials will be ade added to the slurry in the beater treating stage. The quately incorporated with the pulp. Subsequently, glass formed board stock is subsequently predried to extract any ?bers, such as those having a diameter of from 6 to 9 remaining moisture, punched, copper surfaced, pressed microns ‘and a length of about 14 inch, and which have cold to level the interstices, printed, etched, and heated been previously soaked for ‘about 60 minutes in PVP under pressure to cure ‘the resin to the infusible and in soluble state. and PVM/MA, are added. The pulp which has ‘been, treated as described is then formed on wet machines to High wet strength papers may be prepared by beating produce commercial stereotype mat stock, or on small the pulp stock to the desired freeness, treating it with screens to form hand sheets, in the usual manner, and PVP or PVP followed by PVM/MA, adding the desired dried. The mats or sheets may then be coated and prop resin, and then forming the paper in the normal manner. erly conditioned for use in the stereotype process, where The paper is subsequently heated to remove moisture the ‘additive resin and ?bers will insure the dimensional and to insolubilize the PVP more completely. Various stability of the mats during use. resins such as ‘acrylics, various elastomers, vinyl polymers Papers which are suitable for use in making dimension and copolymers, urea or melamine thermosett-ing resins, ally stable maps and charts may be produced in a manner or various combinations of resins may be used. similar to that described above by incorporating therein Barrier papers may be formed by adding nitrocellulose various resins, either thermoplastic, or mixtures containing or ethylcellulose lacquers in the form of dispersions, small amounts of thermosetting resins together with suspensions, or to a slurry of pulp which has thermoplastic resins, and with polyester ?bers such as been pretreated with PVP, or PVP followed by PVM/ MA. Dacron, or with glass ?bers. The processed pulp is then Prior to treatment with the coupling agent, the pulp is 50 formed on standard paper-making machines and subse beaten to the desired standard freeness. Among the com quently heat-treated. ' mercial products which may be formed in this manner A third group of modi?ed paper products which may are bottle cap liners, ?ne papers, ?re retardant papers, be made ‘according to the present invention are those in‘ ?exible papers, fungicide-proof papers, grease-proof which various ?llers other than ?bers are incorporated papers, milk containers, hot drink cups, multiwall bags, 55 into the pulp, and the pulp subsequently formed into and many others. paper or board products. One such product is formed by In current practice, cellulose battery separators are the incorporation of aluminum powder, preferably in the prepared by incorporating various resins such as phenolic form of ?akes, into the pre-treated pulp slurry in’ the resins into bibulous cellulosic ?ber sheets by the satura beater stage. Additives in amounts from about 0.5% tion or impregnation techniques. As a result, the product 60 to 100%, based on dry pulp weight, may thus be incor generlly suifers from the same limitations discussed porated. In carrying out the process, the pulp is ?rst above with respect to other similar products. The present beaten and then treated with PVP and PVM/MA as‘ process avoids these limitations by incorporating the resin described above. The alumintun ?akes are then separate or other additive material with the cellulose in its discrete ly treated with PVP or with PVP followed by PVM/ MA, ?brous state in the beater, and, as a result, ‘accomplishes 65 the amounts ofPVP being from about 0.05% to 0.50% an extremely uniform coating about each ?ber. More based on aluminum powder solids. When the treated over, a ?nal product exhibiting greater desired porosity aluminum powder is then ‘added to the beater containing may be obtained by the present method than by the prior art methods. pre-treated pulp, the aluminum powder becomes attached to the pulp ?bers, leaving the ‘water clear and free of all Polyester and epoxy laminates may ‘also be prepared 70 particles. The paper or board is then formed from the by the present invention with minor modi?cations. In stock, dried and eventually heat-treated to cure the re their available industrial form, polyester and epoxy resins sinous materials. The ?nal product is non-lea?ng, has cannot be added to the aqueous slurry in the beater since good hiding power, and has heat-insulation values ap they are not water-dispersible and will not directly com proaching those obtained from, aluminum foil. The bine with the pulp. This condition is overcome by the 75 ?nished sheets may be further treated by calendering, and 1 1 12 forming into rigid or semi-rigid boards, which may serve ment, and prior to the addition of the resin or additive as insulating building board, gasket material, or as dimen material. Such procedures are illustrated in the follow sionallv stable stereotype mat stock. ing examples. Other additive ?llers which may be used together with Example 3 a resin in the present invention are cork, saw dust, lignin Into a beater containing 12 gallons of water were added and other related products. These materials are gen 1000 grams of unbleached kraft. Beating was continued erally light in weight and not easily wetted by water, and until the desired freeness had been obtained, at the end therefore diflicult to incorporate with the hydrated pulp of which time the beater roll was raised and the moving in prior art paper making processes. It has been found, stock was treated with an aqueous solution containing 2.5 however, that when they are ?rst treated with PVP and 10 grams of PVP solids. The beater was allowed to circulate PVM/MA according to the present invention the addi for ‘an additional ?fteen minutes. At the end of this tive materials are more easily wetted and may be readily period 0.5 gram PVM/MA in the form of a water solu incorporated with the treated pulp. tion was added to the PVP~treated pulp. Circulation was Gasket material may be prepared by incorporating the continued for an additional 15 to 30 minutes. An aque inorganic ?bers, resin binders, or other additives such as ous dispersion containing ?ve hundred grams of a water cork or asbestos ?bers into treated pulp prepared as de dispersible phenolic resin was then added to the beater scribed above. The additive materials should be treated mixture, and the beater was allowed to circulate for still with PVP or with PVP followed by PVM/ MA prior to an additional 15 to 30 minute period. At the end of this their incorporation. time, hand sheets were formed on a screen and subse Simulated leather paper or board may be prepared quently dried. The dried hand sheets were formed into by incorporating leather shavings with the cellulose pulp. electrical board by curing the resin-containing pulp prod The shavings or strings should preferably be soaked in uct to the infusible insoluble state by heat and pressure. PVP and then in PVM/ MA prior to incorporation with The end-product possessed excellent hardness, rigidity, the pulp. Subsequent to the incorporation of the leather, dimensional stability, and high compression strength and resins such as acrylonitrile latex, butyl rubber latex, vinyl 25 modulus of elasticity at elevated temperatures. polymer or copolymer emulsion, thermosetting resins, or modi?cations of any of these, may be added. Example 4 Example 1 Three thousand pounds of mixed pulp were introduced into a commercial size beater. Beating was continued One thousand grams of unbleached kraft pulp were 30 charged into a beater containing 12 gallons of water. until a Williams freeness of 305 had been attained. The ?nished material from the beater was then dropped into Beating was continued until a Canadian speci?c freeness a beater chest and su?icient water added to effect a 3% of 400 was obtained. The beater roll was raised and the consistency. Thereafter, PVP as an aqueous solution was beater continued in circulation. A solution containing added to the circulating chest in an amount sufficient to 2.5 grams PVP in Water was added to the beater slurry. 35 The PVP is preferably added as a 2% to 5% aqueous give 0.250% PVP solids by Weight based on the pulp solution for ease in handling, although it may be di solids. The chest was circulated for one hour. PVM/ MA rectly added. Circulation in the beater was continued solids dissolved in aqueous solution, and in the amount for about 15 minutes until the PVP had been well incorpo equal to 20% based on PVP solids, were then incorpo rated into the PVP-treated pulp. Circulation was con rated. At this point an aqueous dispersion containing 40 500 grams of a water-dispersible phenolic resin was added tinued for one hour. A mixture of clay and hydrous to the circulating mixture in the beater. Additional cir oxides in equal amounts was separately slurried with wa culation of from 15 to 30 minutes was allowed for the ter containing 0.125% PVP solids, based on total inert reaction to be completed. From the resulting product, solids of 700 pounds. This was added to the chest and circulation was continued for one hour. Twenty percent hand sheets were formed on a screen in the usual manner. 45 The resulting product after drying exhibited excellent of PVM/MA solids in aqueous solution and based on PVP properties for use as either electrical board or post-form solids were then incorporated and reacted with the PVP ing board. treated inert solids. Example 2 A reactive water dispersible phenol-formaldehyde resin and an emulsi?able type of polyester resin were then Electrical board stock was prepared as follows. One separately water-diluted to non-volatile solids of 3% and thousand grams of cotton linters were placed in a beater incorporated with the moving mass in the circulating containing 12 gallons of water. Beating was initiated and chest. Circulation was continued for 11/2 hours to insure continued until a Canadian speci?c freeness of 307 had thorough incorporation of all added solids. Thereafter been obtained. The beater roll was then raised and the 55 the treated pulp was reduced to 11/z% consistency and beater continued in circulation. To the circulating mix— pumped to the wet machine-head box where the con ture, an aqueous solution containing 2.5 grams of PVP sistency was reduced to 0.1%. The material was then was then added. Circulation was continued for about 15 formed on a standard roll used in the art for forming minutes, at the end of which time 600 grams of a water stereotype mat stock, and, when dried resulted in mat dispersible phenolic resin in aqueous dispersion were stock having excellent dimensional stability. added. This was followed by an addition of 118 grams 00 of nylon ?bers. Circulation of the beater was continued Example 5 .for about an additional 30 minutes to complete the reac A novel aluminum ?ake-containing board stock was tion. Hand sheets were then ‘formed on a screen and prepared by ?rst beating 1000 grams paper pulp for 90 dried. The resulting product was then cured and ex 05 ,minutes to a Canadian standard freeness of 187. The hibited properties rendering it suitable for use as electri roll was then raised and 0.94% PVP solids in aqueous cal board. As a substitute for the pulps used in the examples above, .solution were added to the slurry. After circulation had continued for 15 minutes, 0.185% PVM/MA solids was high alpha cellulose, unbleached rag and bleached kraft added to the mixture and circulation continued for an may be advantageously used. additional 15 minutes. At the end of this period, 250 Although the use of PVP alone as a coupling agent to grams aluminum ?ake powder which had been previously react the pulp with resins and other additives, ‘as described in Examples 1 and 2, has been found entirely satisfac treated with 0.63% PVP solids and 0.13% PVM/MA solids, each as aqueous solutions, were added in aqueous tory, superior results may be obtained in many instances slurry form to the beater and an additional 10 minutes by treating the pulp with an acid insolubilizing agent such of circulation allowed. An aqueous dispersion of 250 as PVM/MA immediately subsequent to the PVP treat 75 3,036,950 13 14 grams phenol-formaldehyde resin solids was then added Example 13 and circulated for still another 15 minutes. At the end of this period the slurry was couched off on a paper Pulp ______.._ 100 making screen leaving clear white water, and dried. The PVP ______0.5 resulting product was then heated to set the resin and PVM/MA ______-g ______0.45 resulted in aluminum-containing board which was non (Buna N) Rubber latex ______10 lea?ng, had good hiding power, and good heat insulation The following examples present ‘formulations for the values. preparation of dimensionally stable stereotype mat stock. The following examples contain formulations for the Example 14 ‘ preparation of various commercial products. Although 10 detailed methods are not given with each formulation, Parts the methods described above generally, and described in Pulp ______100 Examples 1 to 5 more speci?cally, may be used. The PVP ______0.50 pulp may be conditioned as described above, particularly PVM/MA ______.. 0.10 in Examples 1, 2 and ‘3. All resinous materials should 15 Clay ______11.5 be dispersed in an aqueous medium, either as a suspen Hydrous oxide of silicon ______11.5 sion, emulsion, or any other suitable dispersed form. Water-dispersible phenol-formaldehyde resin ______5 Other additives in addition to resins should preferably Example 15 be soaked in an aqueous solution of PVP, or PVP‘ fol Pulp ______._ 100 lowed by PVM/ MA prior to their incorporation into the 20 pulp slurry. Each material addition should be followed PVP ______0.375 PVM/ MA ______0.10 by su?icient circulation to insure proper distribution. Water-dispersible phenol-formaldehyde resin_____ 5 The following example contains a formulation for the Clay ______11.5 production of post-forming board stock. Hydrous oxide of silicon ______11.5 Example 6 25 Glass ?bers ______7.5 Parts The following example lists the formulation for the Pulp ______100 preparation of gasket material stock. PVP ______0.25 PVM/tMA ______0.05 Example 16 Water dispersible phenol-formaldehyde resin ______11 Parts The examples immediately following present formula Pulp ______. 100 tions for the production of electrical board stock. PVP ______0.375 PVM/YMA ______0.075 Example 7 Water-dispersible phenol-formaldehyde resin_____ 27.5 Parts 35 Butyl rubber latex ______10 Pulp ______100 Asbestos ?bers ______50 PVP ______.. 1.00 The following examples illustrate the formulation for PVM/MA ______0.20 the preparation of metal powder-containing paper or Water-dispersible phenol-formaldehyde resin“--- 100‘ board stock. ‘ Example 8 40 Example 17 Pulp (cotton linters) ______100 Parts Pulp ______100 PVP ______0.25 PVP ______0.375 PVM/MA ______0.05 PVM/MA ______0.10 Water-dispersible phenol-formaldehyde resin ______60 45 Water-dispersible phenol-formaldehyde resin_____ 100 Glass ?bers ______5 Aluminum ?ake powder ______100 Example9 Example 18 Pulp ______-1 ______100 Pulp- ______100 PVP ______0.375 50 PVP ______01.25 PVM/MA ______0.019 PVM/MA ______0.055 Water-dispersible phenol-formaldehyde resin_____ 50 Buna N latex ______15 Example 10 Aluminum ?ake powder ______10

Pulp ______100 55 Example 19 PVP ______0.25 A pilot plant run was made utilizing unbleached kraft PVM/MA ______0.05 pulp and heat reactive phenol~forn1aldehyde resin in the Water-dispersible phenol~formaldehyde resin_____ 60 production of postforming board. 200 pounds air dried Orlon ?bers ______10 pulp were charged to the semi~production beater and Example 1] 60 beaten to a Canadian freeness of 520*. The beaten pulp was ?nish-treated in the beater. One-half pound of PVP Pulp ______.. 100 solids in aqueous solution was reacted with the pulp, fol PVP ______5.00 lowed by 1A0 pound PVM/MA solids in aqueous solu PVM/MA ______1.00 tion. Thereafter 20 pounds phenol-formaldehyde resin Water-dispersible phenol-formaldehyde resin ______100 65 as water-dispersible solids were introduced and reacted The following examples present formulations ‘for the with the PVP-PVM/MA ‘treated pulp. Complexing of preparation of barrier paper stock. the solids occurred rapidly. The beaten mass was then diluted to 11/2% consistency and pumped to the wet ma Example 12 chine where consistency was reduced to 0.1%. Parts 70 The prepared board stock was taken oil the machine Pulp ______100 cylinder and placed on the drying drum for smoothing PVP ______0 25 and expulsion of moisture. The ‘board stock was dried PVM/MA ______0.80 down to about 5% contained moisture. Sheets were cut Butyl rubber latex ______11 to ?t the size of the die mold. Sheets were ?rst dried at Acrylate polymer ______4 75 270° F. to eliminate all moisture and to preclude any 3,036,950 10 15 8. A process for depositing an emulsi?able synthetic blistering. Thereafter sheets were formed at 325° F. resin on beaten cellulose pulp ?bers comprising the steps under 1000 psi. for 30 minutes. This resulted in the in sequence of dispersing an aqueous solution of poly production of post-formed products of excellent prop vinylpyrrolidone into an aqueous slurry of said ?bers, erties. dispersing an aqueous solution of a copolymer of vinyl Although the present invention has been illustrated in methylether and maleic anhydride into said slurry, and only relatively few embodiments, it is to be understood dispersing said resin in emulsion form into said slurry, that many variations may be practiced by those skilled in the polyvinylpyrrolidone being added in an amount of the art without departing from the spirit and scope of the from about 0.5% to about 5.0% by weight based on the invention as de?ned by the appended claims. 10 dry weight of said pulp ?bers and said copolymer being Invention is claimed as follows: added in an amount su?icient to insolubilize said poly 1. A process for depositing a water~dispersible resin on vinylpyrrolidone. beaten cellulose pulp ?bers comprising ?rst dispersing 9. A process for depositing an elastorner in latex form polyvinylpyrrolidone into an aqueous slurry of said ?bers, and subsequently dispersing said resin into said slurry, on beaten cellulose pulp ?bers comprising the steps in 15 sequence of dispersing an aqueous solution of polyvinyl the polyvinylpyrrolidone being added in an amount of at pyrrolidone into an aqueous slurry of said ?bers, dis least about 0.05% by weight based on the dry weight of persing an aqueous solution of a copolymer of vinyl said pulp ?bers. methylether and maleic anhydride into said slurry, and 2. A process for depositing a resin coating on beaten cellulose pulp ?bers comprising ?rst adding polyvinyl dispersing said latex into said slurry, the polyvinylpyr 20 rolidone being added in an amount of from about 0.5% pyrrolidone to an aqueous slurry of said ?bers and mixing to about 5.0% by weight based on the dry weight of said said slurry to deposit said polyvinylpyrrolidone on said pulp ?bers and said copolymer being added in an amount ?bers, and then adding an aqueous dispersion of said resin to said slurry and mixing said slurry until said resin is su?icient to insolubilize said polyvinylpyrrolidone. deposited on said ?bers, the polyvinylpyrrolidone being 10. A process for depositing a water-dispersible resin 25 on beaten cellulose pulp ?bers comprising the steps in added in an amount of at least about 0.05% by weight sequence of uniformly dispersing polyvinylpyrrolidone based on the dry weight of said pulp ?bers. into an aqueous slurry of said ?bers, uniformly dispersing 3. A process for depositing a water-dispersible resin on a copolymer of the half-amide of vinylmethylether and beaten cellulose ?bers comprising the steps of dispersing maleic anhydride into said solution, and dispersing an polyvinylpyrrolidone into an aqueous slurry of said ?bers, aqueous dispersion of said resin into said slurry, the poly then dispersing a minor proportion of a water-soluble 30 acidic insolubilizing agent into said slurry in an amount vinylpyrrolidone being added in an amount of from su?icient to insolubilize said polyvinylpyrrolidone, and about 0.5% to about 5.0% by weight based on the dry subsequently dispersing said resin into said slurry, the weight of said pulp ?bers and said copolymer being added polyvinylpyrrolidone being added in an amount of at least in an amount su?icient to insolubilize said polyvinyl - pyrrolidone. about 0.05% by weight based on the dry weight of said 11. A modi?ed paper which may be molded at elevated pulp ?bers. . 4. A process for depositing a water-dispersible resin temperature and pressure, said paper having been pre on beaten cellulose pulp ?bers comprising the steps of pared by the steps in sequence of dispersing polyvinyl uniformly dispersing an aqueous solution of polyvinyl pyrrolidone into an aqueous slurry of beaten cellulose 40 pulp ?ber, dispersing a copolymer of vinylmethylether pyrrolidone into an aqueous slurry of said ?bers, then and maleic anhydride into said slurry, dispersing a water uniformly dispersing an aqueous solution of a polymeric dispersible resin into said slurry, and forming said paper acid anhydride into said slurry in an amount suf?cient to from said pulp ?bers on a paper making machine, the insolubilize said polyvinylpyrrolidone, and subsequently polyvinylpyrrolidone being added in an amount of from uniformly dispersing an aqueous dispersion of said resin about 0.5% to about 5.0% by weight based on the dry into said slurry, the polyvinylpyrrolidone being added in Weight of said pulp ?bers and said copolymer being added an amount of at least about 0.05% by Weight based on in an amount suf?cient to insolubilize said polyvinyl the dry weight of said pulp ?bers. pyrrolidone. 5. A process for depositing a water-dispersible resin on 12. A dimensionally stable stereotype mat prepared by beaten cellulose ?bers comprising the steps of dispersing the steps in sequence of dispersing polyvinylpyrrolidone polyvinylpyrrolidone into an aqueous slurry of said ?bers, r into an aqueous slurry of beaten cellulose pulp ?bers, next dispersing a water-soluble copolymer of vinylmethyl dispersing a copolymer of vinylmethylether and maleic ether and maleic anhydride into said slurry in an amount anhydride into said slurry, dispersing a water-dispersible su?icient to insolubilize said polyvinylpyrrolidone, and synthetic resin, a water dispersion of inert ?llers and a subsequently dispersing said resin into said slurry, the minor proportion of discrete dimensionally stable ?bers polyvinylpyrrolidone being added in an amount of at least about 0.05% by weight based on the dry weight of said into said slurry, and forming said mat ‘from said treated pulp on a paper making machine, the polyvinylpyrrolidone pulp ?bers. being added in an amount of from about 0.5 % to about 6. A process according to claim 5 wherein said poly 5.0% by weight based on the dry weight of said pulp vinylpyrrolidone is added in an amount from about 0.05% to about 5% by weight based on the dry weight of said ?bers and said copolymer being added in an amount pulp, and said copolymer is added in an amount from su?icient to insolubilize said polyvinylpyrrolidone. about 20% to about 25% based on the dry weight of said polyvinylpyrrolidone. References Cited in the ?le of this patent UNITED STATES PATENTS 7. A process for depositing a water-dispersible phenol 05 formaldehyde resin on beaten cellulose ?bers comprising 2,335,454 Schuster ______Nov. 30, 1943 the steps of ?rst dispersing polyvinylpyrrolidone into a 2,650,163 Horsey et al. ______Aug. 25, 1953 slurry of said ?bers, next dispersing a copolymer of vinyl 2,658,828 Pattilloch ______Nov. 10, 1953 methylether and maleic anhydride into said slurry, and 2,771,362 Moser et al ______Nov. 30, 1956 ?nally dispersing said resin into said slurry, the polyvinyl 70 2,901,390 Conklin et al ______Aug. 25, 1959 pyrrolidone being added in an amount of from about 2,901,457 Stoner et al ______- Aug. 25, 1959 0.05% to about 5% by weight based on ‘the dry weight 2,930,106 Wrotnowski ______Mar. 29, 1960 of said pulp and said copolymer being added in an amount su?icient to insolubilize said polyvinylpyrrolidone.