3,197,429 United States Patent Office Paiented July 27, 1965 2 low temperature filming ability for the emulsion produc 3,197,429 ing that film. PLYWNY ACETATE ADHES WE MIXTURE asses C. Baatz, West Springfield, Mass., assignor to Saawinigan Resins Corporation, Springfield, Mass., a Example------IW w corporation of Massachusetts 5 No Drawing. Fied Sept. 21, 1962, Ser. No. 225,375 Parts by weight 4 Caias. (C. 260-29.6) Composition: Polyvinyl acetate This invention relates to the production of improved ad easioa hesive compositions based on polyvinyl acetate; more O Gelva, S-5 Gelwa, S-55E particularly, it relates to aqueous emulsions of polyvinyl Thiourea------acetate compounded with complex mixtures of other in NCNS gredients which impart to these emulsions properties Animal glue heretofore considered antitheticai. Boric acid------Acetic acid, glacial To use polyvinyl acetate in emulsion form is of course 5 Phosphoric acid well known in the adhesive art. Yet, on applying these (85%)------Water------emulsions to substrates at low temperatures, say at 45° Gelvatoi 70.10------F., there is left on the substrates, upon drying, a chalky, Gervato 20730------Gevato 20.80 discontinuous film. This defect in filming property has Gelvatol 20,90 been remedied to some extent by the addition of coalesc 20 Water.------ing agents to the emulsions. These agents are volatile or TanolClay------731 (25% Dye, Eungicide----- ganic solvents; they increase the cold flow of the drying Emulsion Properties: polymer and then they evaporate along with the water Total soiids (per forming the emulsion. To improve the filming property cent weight) ------3.9 35.9 39.0 4. 38.8 Wiscosity, e.p.s. 3,810 4,820 3,556 4, i00 3,200 of polyvinyl acetate in this manner however, is done at Tack (wet)-- - excel- exce- v. good v. good W. good ent ent the expense of the redispersibility of the dry polymer film, Film Properties: a property that is rather important for certain applica 45 F. filming------el. good w. good good good tions. l Redispersibility----- es. w.good E v. good w, good good Polyvinyl acetate in film form its not, in the first place, 8. Wood bonding remarkably redispersible in itself. Increased redispersi Average bility is usually achieved by incorporating in the emulsion strength (p.s. i.).------. 3,207 3,700 3,333 3,288 3,700 a hydrophilic, protective colloid which may be either Wood failure natural or synthetic. Starch and certain types of poly (ave. percent) 58 8 44 50 S. vinyl alcohol illustrate the class of materials suitable for this function. Excellence in redispersibility is that degree of redis In spite of these developments, however, there remains persibility which causes a dry film of the present com a need for aqueous polyvinyl acetate emulsions which can positions to redisperse much like a wet film of ordinary deposit completely water redispersible films and yet form emulsions would, except that it occurs more slowly. Re Such films at low temperatures. dispersibility is complete, although usually accompanied It is therefore an object of this invention to provide 40 by very slight to slight evidence of shredding of the film. aqueous polyvinyl acetate emulsions which combine the The wood bond strength is the average shearing force, mutually adverse properties of low filming temperature in pounds per square inch, necessary to break maple and redispersibility of film. It is also intended that these blocks bonded by the compositions. The differences in adhesive emulsions shall have high cohesive strength when 45 average strengths given for the above examples is not too wet, i.e., they shall have excellent “wet tack.' Further, significant because of the various factors influencing the emulsions shall be stable to consecutive freezing and these values, which factors cannot be controlled practi thawing, shall Suffer little change in viscosity upon dilu cally with as much precision as would be desired, e.g., tion and shall tolerate such liquids as carbon tetrachloride wood grain structure, internal defects of blocks, rate of and the lower alkyl ethers of ethylene glycol. 50 shear and so on. Nevertheless, wood bonding character These and other objects have been accomplished by istics are considered acceptable when strength exceeds mixing an emulsion of polyvinyl acetate with an aqueous 3000 p.s. i., and when more than 40% of the test speci solution of certain types of polyvinyl alcohol and another mens break because of wood failure rather than because Solution containing thiourea or a thiocyanate as well as of adhesive bond failure. Each composition is tested on other ingredients such as starch or animal glue, boric acid 55 10 specimens by means of a hydraulic press. and so on. Emulsion viscosities are measured at room temperature The following examples will illustrate typical embodi on a Brookfield LV viscosimeter, employing a No. 3 ments of the mixtures. They are not intended to limit the spindle at 12 r.p.m. invention in any manner. The compositions and their sig "Gelva S-51" polyvinyl acetate emulsion is a com nificant properties are summarized in tabular form. 60 mercially available product. The particular batch used The compositions below, as shown by the emulsion and here had a minimum solids content of 55% by weight, film properties measured, all meet the requirements set a room temperature viscosity of 4000 centipoises and a for the adhesive compositions of the invention. pH of 4.5. The number average molecular weight of Good wet tack is that property of an adhesive which is the polymer was approximately 600,000 and the particle evidenced by the formation of stringy legs when two sur size ranged between 1 and 2 microns in diameter. Simi faces coated with a thin wet film of the adhesive are slow larly, "Gelva S-55H' was a commercially available aque ly separated. ous emulsion of polyvinyl acetate of the following charac Filming ability at 45 F. is scored excellent when the teristics: minimum total solids, 55% by weight; room compounded adhesive emulsion, after application to a temperature viscosity, 1650 centipoises; pH, 4.5; number Substrate and upon drying in air, leaves a uniform, non 70 average molecular weight, approximately 50,000; and chaiky and continuous film. A few isolated areas of particle size range, from 0.1 to 5.0 microns in diameter. whiteness on a continuous film still earns a rating of good Both emulsions contained polyvinyl alcohol as stabilizer. 8,197,429 3 4. Two types of polyvinyl alcohols were employed in the Any compound capable of providing a -i3(OH)2 examples: “Gelvatol 70/10,' a low molecular weight group is usable. Boric acid is preferred. The quantity resin having a 20° C. viscosity of 5 centipoises as a employed is dependent on the amount of polyvinyl alcohol 4% by weight solution in equivolume water-isopropyl present in the adhesive composition. Boric acid-poly alcohol, and containing approximately 70% by weight of 5 vinyl alcohol weight ratios of 0.03 to 0.20 are acceptable unhydrolyzed polyvinyl acetate; the other type, namely, while ratios of 0.06 to 0.16 function best. “Gelvatol 20/30, “Gelvatol. 20/60 and “Gelvatol 20/90' Thiourea and thiocyanate have been found to be de polyvinyl alcohols, had residual polyvinyl acetate con cisive factors for imparting low temperature filming abil tents of approximately 21% but differed in that their ity to the present adhesive emulsions. Quantities of 0.5 viscosities as 4% aqueous solutions at 20 C. were 5, 23 IO to 5.0% of the total composition weight will achieve and 40 centipoises respectively. such results. The preferred range is from 1.5 to 4.0%. The particular animal glue used was a product desig In the case of thiocyanate, the metailic cation may be nated commercially as PCS1XM. It is a standard dry any of the monovalent alkali metals. - hide glue, i.e., an impure gelatin obtained by boiling Clay may be added to the compositions in quantities water extraction of animal tissue. Tamol 731 is a 25% 5 ranging from 0 to 8% by weight. The grades selected aqueous solution of a sodium salt of a polymeric carbox should have an average particle diameter not exceeding ylic acid, a polyacrylate type. 10 microns. Other inert materials with a plate-like crystal No critical procedure need be employed to prepare habit may be substituted for this material, mica for in the adhesive emulsion of this invention. Handling the stance. Finally, specialized ingredients such as dyes and ingredients is favored however by forming a separate 20 fungicides may be used in small quantities for particu solution of the polyvinyl alcohols, a time consuming step lar applications. - - which is best done at 50 to 60° C., and another solution The compounded adhesive emulsions of this invention or slurry of the remaining materials: boric acid, starch should have a minimum solids content of 30% by weight or glue, clay, etc. When starch is used, the temperature and preferably within the range of 35 to 50%. The of the latter operation should be kept at 40 - C. or less room temperature viscosity of the emulsions can vary in order to avoid gelatinization; neither should such a between 2000 to 6000 centipoises. solution be kept at that maximum temperature for more Although these compositions have proved to be excel than 4 hours. Thiocyanate salts, when used, should be lent wood bonding adhesives, their use of course is not dissolved in a polyethylene, glass or aluminum container. limited to such applications. They may obviously be Once prepared, the solutions are added stepwise to the 30 employed to advantage wherever quick tack, redispersi polyvinyl acetate emulsion and the blending is continued bility of film and low temperature filming capacity are for about 20 minutes. -- required. The field of packaging affords excellent op The polyvinyl acetate emulsions usable in this inven portunities for the compositions. Many applications may tion are characterized by a minimum solids content of benefit from only one of the peculiar characteristics of 55% by weight, room temperature viscosities ranging 35 these emulsions. For instance, the excellent redispersi from 350 to 5000 centipoises and a pH between 3.5 and bility of the films recommends the use of the emulsions 5.5. The number average molecular weight of the poly in processes where ease of cleaning of the machinery mer in these aqueous dispersions may vary between involved is a necessity. The man skilled in the art will 20,000 and 1,000,000 and the average particle diameter, readily visualize further possibilities. from 0.2 to 2 microns. The preferred emulsions within 40 . What is claimed is: . . this class are those which are not free-filming at room 1. An adhesive composition capable of forming at 45° temperature and are stabilized with polyvinyl alcohol. F. a continuous, non-chalky, water redispersible film, The net polyvinyl acetate content of the present adhesive which comprises: (A) an aqueous dispersion of polyvinyl compositions should be between about 18 and 40% by acetate in amount sufficient to provide from 18 to 40% weight, the preferred range being from about 25 to about 45 30%. of polyvinyl acetate in the final composition; (B) from 0.5 Any partially hydrolyzed polyvinyl acetate may be used to 5% of a compound selected from the group consisting in the adhesive compositions that has a residual acetate of thiourea, ammonium thiocyanate and the monovalent group content of less than 50% by weight, calculated as alkali metal thiocyanates; (C) from 2.5 to 8% of poly polyvinyl acetate. The viscosity of these polyvinyl alco 50 vinyl alcohol, in aqueous solution, said polyvinyl alcohol hols, as 4% aqueous solutions at 20° C. may range from having a 20° C. viscosity of 1 to 70 centipoises as a 4% 1 to 70 centipoises. The preferred types will have a vis by weight aqueous solution, and a residual unhydrolyzed cosity of 4 to 45 centipoises and a residual polyvinyl ace polyvinyl acetate content of less than 50% by weight; and tate content of 15 to 25%. The compositions may con boric acid in a weight ratio of boric acid to the poly tain from about 2.5 to 8% polyvinyl alcohol by weight, 55 vinyl alcohol of 0.03 to 0.20. -- - the range of 3.5 to 6.5% being the preferred one. The 2. The adhesive composition of claim a wherein 1.5 selection of the type or types of polyvinyl alcohol actually to 4% thiourea is used. employed in a given preparation is dependent on the vis 3. The adhesive composition of claim 2 wherein 3.5 cosity of the original polyvinyl acetate emulsion used and to 6.5% of the polyvinyl alcohol is added, said polyvinyl the viscosity desired in the final adhesive product. 60 A special type of polyvinyl alcohol, "Gelvatol 70/10,”. alcohol having a 20° C. visocity of 4 to 45 centipoises as may be employed, if desired, as anti-foaming agent; 0.03 a 4% aqueous solution, and a residual polyvinyl acetate to 0.1% of the total composition weight is satisfactory. content of 15 to 25% by weight. - Other ingredients added to the present compositions 4. The adhesive composition of claim 5 containing for their particular adhesive properties are such materials 65 about 1.8% by weight of ammonium thiocyanate. as liquid animal glue, bone glue, dry hide glue, gelatin, corn starch, dextrin, starch ethers and so on. When pro References Cited by the Examiner tein adhesives are selected, their concentration in the UNITED STATES PATENTS adhesive mixture should be kept below 0.75% lest Cream 2,143,482 1/39 Hermann et al. ------260-30.8 ing and separation occur. The preferred concentrations 70 of protein glues are from 0.05 to 0.5% of the total adhe 2,399,456, 4/46 Yates et al. ------260-30.8 sive composition. Carbohydrate materials, on the other 2,850,468 9/58 Giggey et al. ------260-29.6 hand, may be used in quantities ranging from 10 to 40% of the total composition weight, the preferred percentages MURRAY TILLMAN, Primary Examiner. being from 10 to 20%. 75 LEON J. BERCOVITZ, Examiner.