Flexible paper web and process of
US 2899353 A
Description (OCR text may contain errors)
FLEXIBLE PAPER WEB AND PROCESSOF PRODUCING SAL E EdwardWilliam Engel, New Brunswick, and Isaac'Richard Dunlap, Cranbury, N..l., assignors, byv mesne as signments, to Johnson & Johnson, New Brunswick, NJ., a corporation of New Jersey- No Drawing. Application July 16, 1953 Serial No. 368,515
16 Claims. (Cl. 162-165) This invention is concerned with new and, improved methods of incorporating polymeric materials from colloidal dispersion onto fibers prior to sheet formation.
Incorporation of ploymers into fibrous webs of eel: losic or other fibers in itself is old. Incorporation of rubbers, bitumens, or resins into paper or felt by saturation of the previously prepared web in order to improveplicated process requiring removal of the media from.
which the polymer is applied, usually by heat. It aqueous media are used, as is usual, a wet, water weakened sheet must be handled involving the hazard of loss of material due to tears or breaks, or, if organic solvent media are involved, handling of flammable and, in many cases, toxic or explosive solvents is required.
In recent years many attempts have been made to incorporate the required polymer onto the fibers prior to actual sheet formation. These processes were con cerned primarily with incorporation of rubber or rubberlike polymers from latices or dispersions, in amounts up to about forty percent by weight of the fiber, and in subsequent felting of the treated or coated fibers into a sheet on a paper machine.
Although by previously known methods incorporation of more than forty percent of the fiber weight of rubbery polymer is possible, treatment to obtain higher polymer contents is commercially impractical by these methods. This is due particularly to difiiculties with sheet formation and to the impossibility of running for more than short periods without stopping to clean the paper machine.
Paper is made by preparing a slurry of cellulose fibers in water, felting the fibers together by draining away part of the water on a porous screen, and removing water not lost through drainage by pressing and 'drying the wet sheet. The slurry of fibers in water is known as. stock, and the addition of polymers, in suitable water dispersion or solution, to the stock and causing the polymer to adhere to the fibers constitute what is known as beater impregnation, although such additions may be made to the stock at any point in the system prior to sheet. formation.
By far the greatest interest in beater impregnation re-. lates to incorporation of rubber or rubber-like synthetic polymers into paper. These polymers are readily available in the form of aqueous anionic colloidal dispersions. While saturation of a finished paper sheet with such dispersions is possible, for practical saturation speeds and efliciencies an open, porous sheet of paper is required in order to obtain penetration, and a sheet containing some wet strength is usually needed to minimize losses due to tears, breaks, and uneven stretching. Incorporaatent O 2,899,353 Patented Aug. 11, 1959 2. tionof up to forty percent of the fiber weight. of some synthetic rubber-like polymers by beater impregnation yields products of interest in fields requiring saturated papers of nottoo critical-physical requirements, for instancein the fields of shoe cover stocks and light. duty gasket stocks. However, high rubber content is necessary for applications of impregnated paper requiring v tromaqueous solution or dispersion onto fibers; from an,
maximum unification of the paper, as for instance'in the making of backings for-'pressurersensitive adhesive tape. Substantially greater resistance to: delamination is obtainable by this processwith the maximum amount of rubber-like polymer than can be obtained by. previously known methods of beater impregnation. T o the extent of applicants knowledge with the exception of the process disclosed. in U.S. patent application Serial Number 210,282, filed February 9, 1951, by Dr. C. L. Weidner and I. R. Dunlap, prior art processes of beater impregnation involved coagulation of water dispersions of rubberypolymers-by addition of aluminum. sulfate,
or acid, or the use of an acidic colloidal polymer. In
all these cases coagulation required theuse of acidic media at-some step. The-amount of polymer that could be incorporated by these methods was limited, and the type of polymer was limitedto minimum Mooney plasticities of aboutfifty. In U.S. patent application Serial Number 210,282, the use of water soluble N-basic polymers isdisclosed for precipitation of latices onto papers.
or other fibers. The use of acid is also unnecessary in connection withthe process of this application.
The objects of the present invention are as follows: (A To incorporate, greater amounts of polymers,
especially rubber-like polymers, onto fibers than has been (D) Toobtain, at lower ratios of polymer to fiber weight, sheets equivalent in physical tests to latex. saturated paper.
It has now. been found that co-precipitation of'watersoluble or water-dispersible resins-of the type representedby alkali-catalyzed phenol-formaldehyde polymers and synthetic rubbery polymers under neutral or basic conditions ontofibers by means of the poly-N-basic compounds presents marked advantages. This is true particularly as are concerned sheet formation, polymer retention, and ease of operation, particularly when soft polymers are employed. poly-N-basic compounds takes placeunder all types of conditions and operations on any hydrophobic colloid at. almostjany hydrogen ion concentration. It has been foundjthat these poly-N-basic compounds also precipitate,lvery efiiciently, water soluble or water dispersible resins of the phenol-formaldehyde type from aqueous solution or dispersion. These resins are soluble or dispersible only in alkaline media. Co-precipitation of resins ofthis type under non-acidic, conditions with any of the widely availableanionic dispersions of synthetic rubbers or rubber-like polymers onto fibers yields sheets surpassing any product or process previously known in physical properties, ease of paper machine operation, and retention of polymer.
This inventioninvolves co-preeipitation of a hydrophobic rubbery polymer from aqueous alkaline colloidal dispersion and water-soluble or water-dispersible phenolformaldehyde resin, condensed under alkaline conditions The precipitating action of rubbery polymer selected, and the amount of combined polymer may be from a fraction of one percent to more than one hundred percent of the weight of the polymer. 7
The water-dispersed fibers comprise from about 0.05 to about three percent of the total weight of the dispersion. Water-dispersible phenol-formaldehyde resin for purposes of this invention includes only those resins that are dispersible without the aid of dispersing agents other than those formed during the condensation of the resin.
In carrying out the invention it has been found convenient to prepare a mixed dispersion containing the hydrophobic polymer and the resinous, hydrophilic polymer. This is accomplished by adding a water solution or dispersion of the phenolic resin to diluted and stabilized commercial latex. The desirable degree of latex dilution will vary with the amount to be added to the fibers, the nature of the dispersion and the ratio of resinous to rubbery polymer to be used. The addition of the watersoluble polymer should take place at a pH above that at which the anionic colloid would be unstable, usually at a pH of from about 6.5 to about 8.5.
In the execution of the invention we find most advantageous for precipitation certain poly-N-basic compounds disclosed in US. patent application Serial Number 210,282, filed February 9, 1951, by Charles Leslie Weidner and Isaac Richard Dunlap. Particularly preferred are the reaction products of a guanidine in accordance with that patent application. By a guanidine, guanidine or any of its salts is meant. The guanidine reaction product may be added to the extent of from about five to about fifteen percent of the combined weight of the hydrophobic and hydrophilic polymer present in the aqueous medium.
In a typical case, a commercial acrylonitrile-butadiene copolymer latex received from the factory at 38.8 percent by weight of solids was diluted to twenty percent solids by addition of water containing one percent by weight, based on the polymer solids, of potassium rosinate. After thorough stirring of the diluted latex, a twenty percent by weight solution of the phenolic resin in water at a pH of 8.2, representing one-tenth the weight of acrylonitrilebutadiene solids in the diluted latex, Was added under stirring.
In many instances it is advantageous to agethe dispersion containing the resinous and rubber-like polymers for twentyfour hours or more before use.
In addition to wide applicability to various types of polymers, the poly-N-basic precipitation process as disclosed herein permits use of polymers of softer and more sticky nature than 'was practical under the prior art. In prior art processes involving acidic media, the resulting polymer coated fibers were quite sticky and exhibited a marked tendency to adhere to each other and to any surface with which they came in contactmachine, wire, press rolls, or paper machine felt. The process uses precipitation under neutral or basic conditions and preserves the dispersing agent, which would be destroyed by the action of acid and thus plasticize and make more sticky the precipitated rubber.
This process makes usable butadiene polymers of as low as 19 Mooney plasticity with one hundred percent retention of polymer on the fiber and with good formation of the sheet and no sticking or fouling of paper machine parts such as take place when acidic precipitation processes are used.
An advantage of operation under non-acidic conditions, with consequent preservation of the latex dispersing agent, is that sheets containing rubbery polymer incorporated by our process of beater impregnation may be repulped easily and economically in conventional equipment. This re-use of broke, which is impossible with previously known processes, makes possible the economical salvaging of the ofi-weight, wrinkled, and torn product of start- Al. ingup of the paper machine, with consequent saving of valuable fiber and polymer.
Still another advantage is the greater ease of treatment of the paper stock after precipitation with our invention than is possible under the prior art.
The phenolic type resin is limited to those which are water soluble or water dispersible. We have found that suitable resins of this type for our process may be prepared With a molar ratio of formaldehyde to phenol of from about one to about two and one-fourth. The ratio of water-soluble or water-dispersible resin to hydrophobic anionic dispersed polymer may be varied widely. Practical limits of stability of the mixed dispersion require that the ratio of resinous to rubbery polymer be not greater than about one to four on a weight of solids basis. How ever, any ratio of one component to the other may be used if mixing is immediately before addition to the paper stock, or mixing of components may be carried out in the presence of the fiber in the paper machine system. The most desirable ratio of resinous to rubbery polymer for beater impregnation in applications competitive with latex saturated papers is about one to ten. At this ratio the influence of the resin on sheet formation and operation of the paper machine is approximately at a maximum and there is a minimum of stiffening of the sheet. However, any ratio of resinous to rubbery polymer is contemplated.
The type of polymer applied from colloidal dispersion is limited only to those from which an anionic dispersion can be prepared. Any of the usually available synthetic rubbers such as copolymers of styrene and butadiene, or of acrylonitrile and butadiene, or copolymers and polymers of chlorobutadiene, acrylates, styrene, vinyl chloride, Factice or polyvinyl acetal-type polymers may be used in practicing this invention when used as anionic aqueous dispersions.
As stated above, basic catalyzed phenolic resins of formaldehyde to phenol ratio of from about one to about two and one-fourth moles of formaldehyde per mole of phenol may be used. Substituted phenols such as resorci- 1101 or cresol may also be used when suitably reacted with formaldehyde to yield water-soluble or water-dispersible polymeric material.
The fibers onto which the dispersed polymers are precipitated may be of any type. The precipitation process operates with equal efficiency with any cellulosic fiber whether subject to hydration (kraft, sulphite, etc.) or not (rayon). It also operates with such organic non-cellulosic fibers as nylon and acrylic polymer fibers and with inorganic fibers such as glass and asbestos.
In the co-pending application, impregnation was defined as the incorporation of more than ten percent of the fiber weight of polymer prior to sheet formation. This application is concerned primarily with the incorporation of amounts of polymer greater than about twenty percent by weight of fiber weight, but the incorporation of from a fraction of one percent to more than one hundred percent by the methods disclosed is possible and is contemplated. The optimum amount and type of polymer mixture on any given fiber is determined by the use anticipated for the finished sheet. In general, soft polymers yield sheets of greater tear and lesser tensile strength than an equivalent amount of a harder polymer mixture.
As a heater impregnated backing for pressure-sensitive tape, a sheet comprising about 62.5 percent by weight of kraft fiber and 37.5 percent by weight of a polymer mixture comprising ninety percent by weight of a copolymer of acrylonitrile and butadiene (forty percent acrylonitrile, sixty percent butadiene by weight), and ten percent by weight of a water-dispersible phenolic resin made by reacting one mole of phenol with one and seventy-five hundredths of a mole of formaldehyde, using five hundredths of a mole of SOdiurn hydroxide as a catalyst, is prefe red.
In general, the amount of polyN-basic-compound,re
quired to presipitate the mixtureof rubber-like and resinous-polymers onto fibers with one hundred percent efiiciency. (all of polymer fixed to fiber) is ten percent or less of the dry weight of polymer to be precipitated. However, the necessary quantity may be as low as one percent or as high astwenty: percent by weight of the polymer to be precipitated, dependingupon consistency of the pulp-polymer slurry at the time of precipitation. An excess of precipitating agent is not harmful; an inadequate amount will result in loss of polymer in white water. Other than the above factor of amount of precipitating agent required, the precipitationstep may be carried out at any convenient pulp consistency at any point in the paper machine stock system.
Temperature of stock at the time of precipitation is not critical-the operation has .been carried out at as low as thirty-four degrees Fahrenheit and ashigh as one hundred and forty degrees Fahrenheit with equal eilectiveness. No aging of the stock is required after the addition of the precipitating agent, and iffurther refinement of the stock after precipitation. of the polymer is desired, a
reasonable degree of refining may be carried out without detrimental efiect onthe, retention of polymer by the stock.
The distinguishing characteristics of our invention are:
(A) Co-precipitation of a water-soluble or water-dispersible resinous anda hydrophobic polymer'from anionic colloidal dispersion.
(B) Carrying out precipitation operation under neutral or alkaline conditions in the presence offibers.
The invention is further illustrated by the following examples:
Example I The following table illustrates the advantage to be gained by co-precipitation of rubbery polymer and phenolic resin under non-acid conditionsas described in the preparation of beater impregnated papers over similar precipitation of the rubbery polymer alone. All sheets contained thirty-sevenand one-half percent by weight of polymer based on the weight of sheet. Fibers of 750 cc. Schopper Riegler freeness of weight equivalent to a thirty pound sheet (24 x 36 x 480) was contained in allthe samples. Retention was quantitauve with all samples as shown by clear wlnte water.
Polymer Tensile, Formation lbs/in.
50 Mooney plasticity 60-40 butadiene acry- 22. Good to excellonitrile. en Above plus percent phenolic resin 23. 2 Excellent. 50 Mooney plasticity 75-25 butadiene acry- 16. 3 Good.
lonitrile. Above plus 10% phenolic resin 24. 9 Excellent. Type IV, G.R.S 19. 6 Fair to good. Above plus 10% phenolic resin- 21. 2 Good. Polychloroprene plus 10% phenolic resin.... 19 Do. High vis. polyvinyl butyral 20. 6' D0. Above plus 10% phenolic resin 24. 0 Excellent.
Note.-The phenolic resin used was a water-dispersible commercial product, obtained as a 65% solution in water at apH of8.59.
Example 11 This example illustrates. the efiect of variation in resin to rubber ratio in the carrying out of our invention. The samples differed only in ratio of phenolic resin to rubbery polymer. Sheetweight, processing and retention were as outlined in Example I above. The rubbery polymer was a butadiene-acrylonitrile copolymer of 60-40 monomer ratio with a Mooney plasticity of about fifty, and the phenolic resin was the commercial product described in Example I.
The following table gives the results obtained by varying the ratio of phenolic resin in the polymer content of the sheet from zero to twenty percent by weight of the nitrile rubber.
Tensile, 1 ply400 cc; Percent resin lbs/in. Gurley dens1t The variation in air permeability as measured by- Gurley densometer is regarded as more indicative of sheet, quality than the slight variation in tensile-strength noted, since it is a measure of the important property of delami, nation resistance or internal bonding strength.
Example III This example illustrates the efifect of variation in phenol to formaldehyde ratio in the resin used in carrying out the invention. All the resins listed below were prepared by heating the reactants in the mole ratio indicated with a minor amount of sodium hydroxide as catalyst. The rubbery polymer component was the acrylonitrile rubber used in Example II. Sheet weight and level of treatment were also as described in Example II.
Iensile, 1 ply 400 cc. Mole ratio HOHO to phenol lbs/in Gurley Width density,
Example IV The following table shows tensile strength and drain time in a standard T.A.P.P.I. sheet mold of hand sheets based on thirty pounds (24 x 36 x 480) fiber treated with from twenty to one hundred and. twenty percent of the fiber weight of the nitrilerubber used in Example II combinedwith zero, five and ten percent of the phenolic resin on the weight of the rubber described in the above example. All hand sheets were prepared in the same manner and contained thesame weight of fiber whichhad been beaten to 700' cc. Schopper-Riegler freeness.
Treatment Tensile, Drain lbs/in. line, see.
None 17. 6 6. 7 20%-10% resin in polymer. 19. 0 8. 5 40%10% resin in polymer 23. 0 12. 1 60%-10?7 resin inpolyme 22.0 10. 5 75%10% resin in polymer. 22. 5 10. 7 %10% resin in polymer 21. 4 6. 0: %l0% resin in polymer... 20. O 6. 5 20%5% resin in polymer. 19. 2 9 40%-5% resin in polymer. 18 9. 1 60%-5% resin in polymer.. 20.0 10.0 75%5% resin in polymer 20. 6 8. 5 100%5% resin in polyme 22. 7 7.1 120%5% resin in polyme 20. 4 7. 1 20%No resin in polymer. 24. 0 7. 7 40%No resin in polymer. 24. 6 7. 4 60%N0 resin in polymer-- 1S 6. l 75'7No resin in polymer" 18.6 6. 2 100 -No resin polymer 12. 9 5. 8' 120%No resin in polymer 10.8 5. 7
It might be pointed out here that drain time isimportant in two respects, as an indication of how the stock will lose water on a paper machine wire, andin so doing eilect sheet formation. A free stock losing water too readily wouldhe expected to yield a sheet, of uneven, wild formation, while a slow stock might limit production speed to a prohibitive extent.
Example V The. previous example shows in tensile strength: and,
drain time one of the processing advantages of the PRECIPITATION ACCORDING TO THIS INVENTION Preferred resinous-rubbery Rubbery polymer-No resin Composition N o refining, 850 cc. S.R.
1.5 min. refining, 820 cc. S.R. 3.0 min. refining, 820 cc. S.R. 15.0 min. refining, 820 cc. S.R.
No refining, 850 cc. S.R 1.5 min. refining, 820 cc. 5.1%.. l. 3.0 min. refining, 800 cc. S.R 15.0 min. refining, 790 cc. S.R-
ALUIVI PRECIPITATED No refining, 860 cc. S.R No refining, 880 cc. S.R.
1.5 min. refining, 850 cc. S.R 1.5 min. refining, 900 cc. S.R. 3.0 min. refining, 880 cc. S.R.
15 min. refining, 850 cc. S.R.
15 min. refining, 770 cc. Sit
Thus equivalent treatment (3 min.) brought about a reduction in freeness of 50 cc. for the resin-rubber treated pulp when prepared by our invention, compared with a reduction of only 10 cc. when the same composition was precipitated with alum. When the rubbery polymer alone was used, the same treatment yielded a reduction of 30 cc. with our invention and none when the rubbery polymer was precipitated with alum.
Example VI This example illustrates the use of broke from the disclosed process.
Five hundred grams of air dry paper from a machine run based on sixty percent treatment of kraft fiber with a mixture of ninety percent acrylonitrile-butadiene copolymer of 60-40 monomer ratio, 50 Mooney plasticity, and ten percent phenolic resin, as previously disclosed in Example I, was torn into small pieces and placed with twenty liters of cold water in a one-pound Valley beater. After five minutes of circulation without pressure, 3,500 grams was placed on the bed plate and the operation continued for ten minutes.
The following table shows physical test values obtained when varying percentages of the above defibered broke was mixed with fresh treated fiber and formed into 47 lbs/in. weight sheets.
Tensile Gurley Percent broke strength, density,
Example Vll viscous (when hot) transparent mass and the hydrogen ion concentration had fallen to a pH of about 7.5 Water was added and stirred to dissolve the reaction product. All during the heating, there was evolution of carbon dioxide from the reaction, and it was to facilitate escape of this material that water was added. After additional heating at the boiling point of the solution for one and one-half hours, the pH was about 7.2 as measured with pH paper, and heating was discontinued.
The product obtained was an almost colorless solution containing thirty-seven percent solids. The viscosity of this thirty-seven percent solution was not substantially greater than that of water. The dry reaction product was a transparent, very slightly colored, solid,
having a softening point below eight degrees centigrade.
Heating of the reaction mixture more strongly than was done in the above example by allowing substantially all the water to evaporate from the reaction components yields a light yellow, somewhat brittle solid with a softening point above one hundred degrees centigrade. Heating the reactants in the above proportions on a steam plate yielded, upon heating for about ten hours, a product having a softening point below room temperature which was colorless and transparent.
The reaction products obtained in the examples given above were substantially equivalent in precipitating power when used as described in this disclosure; yet, neither guanidine carbonate nor formaldehyde alone or in combination in an unreacted condition have significant precipitating action unless used or added in concentrations much greater than is required for their reaction product as described above.
The product we desire to use is a water-soluble condensation polymer of guanidine and/or its carbonate and formaldehyde. The above examples are based on the use of commercial materials, and some variation may be expected due to slight differences in materials or reaction conditions. The above is given by way of example only since an equivalent product might be obtained with somewhat dilferent ratios of reactants by control of reaction conditions.
In formation of one of our preferred precipitating agents, guanidine carbonate may be mixed with urea, in molar ratios of from about one mol of guanidine salt to about one and one-third mols of urea, and the resulting mixture reacted with formaldehyde at steam bath temperature until clear to form a product useful in the practice of this invention. Even high ratios of urea to guanidine salt may be used if suificient control of reaction conditions is used to yield a product soluble in water on dilution to low solids.
Similarly to the above, but at lower ratios thiourea may be employed as a co-reactant with the guanidine salt. However, if more than one mol of thiourea per two and one-half mols of guanidine salt is used, dif ficulty in obtaining a water-soluble product after resinification is encountered.
The claims are:
1. A process of producing felted, fibrous webs, comprising the steps of mixing with a water dispersion comprising from about 0.05 to about 3 percent by weight of fiber, an anionic colloidal dispersion of a hydrophobic rubbery polymer and an alkaline hydrophilic condensation product of a phenol with formaldehyde in an aqueous medium, said phenol condensation product being dispersible in water without the aid of dispersing agents other than those formed in said condensation; precipitating said hydrophobic and hydrophilic polymers onto said fibers under non-acid conditions by addition of the organic water-soluble polymer formed by reacting a guanidine compound selected from the group consisting of guanidine and the water soluble salts of guanidine with formaldehyde under basic conditions; and subsequently forming a web at a pH within the range in which the anonic colloidal dispersion is normally stable.
2. A process for producing felted fibrous webs comprising the following steps carried out at a pH of from about 6.5 to about 8.5: adding to a dispersion of fiber in water comprising from about 0.05 to about 3 percent fiber by weight of the dispersion, an aqueous anionic dispersion of a copolymer of acrylonitrile and butadiene comprising a major proportion of butadiene, mixed with a water-dispersible alkaline condensation product in an aqueous medium of phenol with formaldehyde, said mixture comprising at least 5 percent by weight of said copolymer; precipitating said copolymer and said condensation product onto said fibers under non-acid conditions by addition of from about 5 percent to about 15 percent by weight of the combined weight of said polymer and condensation product of a water-soluble cationic reaction product under basic conditions of a. guanidine compound selected from the group consisting of guanidine and the water soluble salts of guanidine with formaldehyde; and forming a felted fibrous web from the combined fiber and polymer.
3. The process of claim 2, including the step of aging the copolymer-phenol formaldehyde condensation product dispersion prior to precipitation.
4. The process as defined in claim 2, wherein said fiber is paper fiber.
5. The process as defined in claim 2, wherein said fiber is kraft paper fiber.
6. A process as defined in claim 2, wherein the guanidine of the reaction product is guanidine carbonate.
7. The process of claim 2, wherein from about ten to about one hundred percent by weight of polymeric components are incorporated into the web based on the weight of the fiber.
8. The process of claim 2, wherein from about one to about twenty percent by weight of the cationic re action product are used based on the weight of the material to be precipitated.
9. The process of claim 2, wherein the ratio of phenol formaldehyde condensation product to copolymer is less than about one to four.
10. A process in accordance with claim 9, wherein the ratio is about one to ten.
11. A process for producing felted fibrous webs comprising the steps of adding to a dispersion of a fiber in water composed of from about 0.05 to about 3% fiber by weight of the dispersion, an aqueous anionic dispersion of a copolymer of acrylonitrile and butadiene comprising a major proportion of butadiene, mixed with a waterdispersible alkaline formaldehyde condensation product, said mixture comprising at least 5% by weight of said copolymer; precipitating said copolymer and said condensation product onto said fibers under non-acid conditions by addition of from about 5% to about 15% by weight of the combined weight of said polymer and formaldehyde condensation product of a water-soluble cationic reaction product under basic conditions of a guanidine compound selected from the group consisting of guanidine and the water-soluble salts of guanidine with formaldehyde; and forming a felted fibrous web from the combined fiber and polymer.
12. The process as defined in claim 11 wherein from about 10 to about by weight of polymeric components are incorporated into the web based on the weight of the fiber.
13. A process as defined in claim 12 wherein the ratio of said formaldehyde condensation product to said copolymer of acrylonitrile and butadiene is less than about 1:4.
14. A flexible felted fibrous paper web comprising a paper fiibrous sheet, a mixture of a hydrophobic rubbery polymer and hydrophilic formaldehyde condensation product incorporated in said sheet so as to unify and internally bond said sheet, said polymer comprising about 10 to about 100% by weight based on the weight of the fiber, and the ratio of said formaldehyde condensation product to said polymer being less than about 1:4; said web characterized by high receptivity to saturation by water and aqueous impregnants and exhibiting enhanced delamination resistance, internal bonding strength and tensile strength.
15. A flexible felted fibrous paper web comprising a paper fibrous sheet, a mixture of a hydrophobic rubbery copolymer of butadiene and acrylonitrile composed of a major proportion of butadiene and a hydrophilic formaldehyde condensation product incorporated in said sheet so as to unify and internally bond said sheet, said copolymer comprising about 10 to about 100% by weight based on the weight of the fiber and the ratio of said formaldehyde condensation product to said copolymer being less than about 1:4; said web characterized by high receptivity to saturation by water and aqueous impregnants and exhibiting enhanced delamination resistance, internal bonding strength and tensile strength.
16. A flexible felted fibrous paper web comprising a paper fibrous sheet, a mixture of a hydrophobic rubbery copolymer of butadiene and acrylonitrile composed of a major proportion of butadiene and a hydrophilic phenolformaldehyde condensation product incorporated in said sheet so as to unify and internally bond said sheet, said copolymer comprising about 10 to about 100% by weight based on the weight of the fiber and the ratio of said phenol-formaldehyde condensation product to said copolymer being less than about 1:4; said web characterized by high receptivity to saturation by water and aqueous impregnants and exhibiting enhanced delamination resistance, internal bonding strength and tensile strength.
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