Polyvinylpyrrolidone Resin Dispersion'
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May 29, 1962 R. c. MARTIN . 3,036,950 I, PROCESS FOR INCORPORATING RESINS INTO PAPER 1 Filed June 22, 1959 AQuEous SLURRY OF BEATEN CELLULOSE Fl BER POLYVINYLPYRROLIDONE ADDED AND DISPERSED INTO SLURRY \NSOLUBILIZER ADDED AND DISPERSED INTO SLURRY RESIN DISPERSION‘ ADDED AND DISPERSED INTO SLURRY OTHER ?Luzrzs AND MoDmERs ADDED AND DISPERSED lm-o SLDRRY 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 water, 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 coating 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 solvent 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 polymers 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 emulsion, . 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 .