Patented May 4, 1954 2,677,672 UNITED STATES PATENT OFFICE 2,677,672 ADHESIVE FOR WOOD COMPRISING AN AQUEOUS POLYVINYL ACETATE EMUL SION AND A VINYL METHYL ETHER MALEIC ANHYDRIDE COPOLYMER Stewart B. Luce, La Grange, Ill., assignor to Swift & Company, Chicago, 111., a. corporation of Illinois No Drawing. Application December 7, 1951, Serial No. 260,581 jr 6 Claims. (Cl. 260—29.6) 1 2 The present invention relates in general to an possesses a. high resistance to cold ?ow and. also improved adhesive, and more particularly to a a sufficiently high shear strength to function as polyvinyl acetate wood adhesive having a high a highly e?icient wood adhesive. resistance to cold ?ow and a high shear strength. The polyvinyl acetate emulsions which may be Adhesives and ?lms formed from polyvinyl used in the present invention are any of the com acetate emulsions are well known and have found mercially available aqueous emulsions known to widespread acceptance in many ?elds. It has the art, as, for example, P. V. A. emulsion 81-900 been recognized in the past that increased ?exi described in Du Pont’s pamphlet V3348 or the bility and toughness may be imparted to such ad Shawinigan Gelva emulsions described in their hesives or ?lms by the addition to the polyvinyl pamphlet on Gelva issued in 1948. Du Pont acetete emulsion of various plasticizers. How 81-900 has a 55% solids content, an emulsion ever, being a thermoplastic material, polyvinyl viscosity of 8-10 poises, contains 1% monomer, acetate will “?ow” if subjected to stress, particu has a pH of 4-6, and a particle size of 3 microns, larly at elevated temperatures. This inherent as speci?ed in ‘the aforesaid pamphlet. The property of the heretofore available polyvinyl Shawinigan “Gelva” emulsions as described in acetate ?lms and adhesives has presented a de? their pamphlet referred to above, have a 55% ite disadvantage in the use of such ?lms under solids content, an emulsion viscosity of 6-10 conditions where stress was to be, or might be poises, contain l-1.5% monomer, have a pH of applied to the material. Additives for improv 4-6, and a particle size of 0.5-1.0 microns. These ing the cold flow properties of polyvinyl acetate 20 emulsions, in general, are white, milky liquids ?lms have been disclosed in copending applica of creamy or watery consistency, having a pH in tions of S. B. Luce, but such additives have been the neighborhood of about 3.5 to 4.0 or above. found to reduce the shear strength of ?lms In all of these commercially available emulsions, formed from the emulsions so treated. the polymer is fully acetylated and is water in It is therefore an object of the present inven 25 soluble. Any of these commercially available tion to provide an improved polyvinyl acetate ad aqueous emulsions either with or without con hesive which has both a high shear strength and ventional plasticizers such as dicarbitol phtha a high resistance to cold flow. late, ethyl acetyl glycolate, tricresyl phosphate, It is an additional object of the invention to dibutyl phthalate or the like, may be used in the provide a method for preparing an improved present invention. The “Aroclors” (chlorinated polyvinyl acetate adhesive. biphenyls), preferably those liquid at room tem Additional objects if not speci?cally set forth peratures such as Aroclor 1260 or 1262, may also herein will be readily apparent to one skilled in be used as plasticizers. The “Aroclors” are fully the art from the following detailed description described in Application Data Bulletin No. P-l15 of the invention: of The Monsanto Chemical Company. Generally, the present invention contemplates Vinyl methyl ether-maleic anhydride copoly the addition to commercially available aqueous mers having speci?c viscosities of from about 0.6 polyvinyl acetate emulsions of a compound which to about 2.7, determined on 1 gram of copolymer has been found to possess the properties of great in 100 ml. of methyl ethyl ketone, have been found -ly increasing the resistance to cold flow of ?lms to give the best results. These copolymers are formed from polyvinyl acetate emulsions con linear in nature and consist of alternating methyl taining such compound, and also of retaining vinyl ether and maleic anhydride units, e. g. about the same high shear strength as ?lms made from the untreated polyvinyl acetate emulsions. More speci?caly, it has been found that by pre Qparing a physical mixture of a conventional poly L on an vinyl acetate emulsion and a copolymer of vinyl - \ / 0 methyl ether-maleic anhydride, an adhesive is WA4‘ ‘produced which when applied to wood and dried 50 These compounds are fully described in the 2,677,672 3 pamphlet “PVM/MA-A New Water Soluble Poly Table I mer,” New Product Bulletin No. P-103, issued [50° C. ; stress-60 p. s. 1.] January 3, 1951, by the Product Development De partment of General Aniline & Film Corporation. Higher viscosity copolymers may be used, but Percent Extension tend to cause a stringy consistency in the copoly Film — mer-polyvinyl acetate emulsion mixture. The co 10 min. 5 hrs. polymers are preferably added to the emulsion A. Plasticized Polyvinyl Acetate _____________ .. 50-— 55 in the form of an aqueous solution. However, B. Composition A plus 15% VME/MA co the adhesive may be prepared by ?rst adding a 10 polymer ____________________________________ __ 0 0 plasticizer to the polyvinyl acetate emulsion and then stirring in the aqueous solution of the co polymer, or ?rst mixing the emulsion and the Table II aqueous solution of copolymer together and then [Room temperature] adding the plasticizer, or adding the emulsion to the copolymer solution and plasticizer, without (24 hrs.) affecting the nature of the ?nal mixture. Film (Sages?) Percent The following examples demonstrate the prep p‘ ‘ ' Extension aration of typical adhesives of the present inven A. Plasticized Polyvinyl Acetate ________ _. 80 187. 5 tion, and are furnished for the purpose of illustra- 0 , )3. Composition A plus 0.05% VME/MA tion only: copolymer ............................. __ 85 150 EXAMPLE I L__ 4.5 parts of a 50% dibutyl phthalate-50% In the above tables, the VME/MA copolymer Aroclor plasticizer were added to 145.5 parts of 25 had a speci?c viscosity of 2.7. The abbreviation polyvinyl acetate emulsion 81-900 Du Font and VME/MA used in these tables and elsewhere in mixed thoroughly. To this mixture, at room the speci?cation is intended to indicate vinyl temperature, were added 125 parts of a 10% aque methyl ether-maleic anhydride copolymer. The ous solution of vinyl methyl ether-maleic anhy polyvinyl acetate emulsion used in obtaining the dride copolymer of speci?c viscosity 2.7. The above results was Du Pont P. V. A. emulsion 81 mixture was then stirred to give a uniform ad 900 containing about 5.6% of 50% dibutyl phthal hesive of viscosity 43.5 poises at 79° F. ate—50% Aroclor as a plasticizer. As can be seen from the foregoing data, the EXAMPLE II addition of varying percentages of the copolymer ' greatly improved the resistance of the dried ?lms 2.2 parts of a 50% dibutyl phthalate-50% to deformation or cold flow under stress. Aroclor plasticizer were added to 72.8 parts of Additional tests were conducted to determine the same polyvinyl acetate emulsion as in Ex the shear strength of adhesive mixtures of the ample I. After thorough mixing, 31.5 parts of present invention. Table III, below, shows the a 20% aqueous solution of vinyl methyl ether 40 maleic anhydride copolymer of speci?c viscosity general tendency of the cold flow improving ad 0.6 were added. After stirring, the viscosity of ditives disclosed and claimed in the copending the resulting adhesive was 26 poises at 78° F. applications of S. B. Luce, to drastically reduce The copolymer may be used in amounts ranging the shear strength of adhesives containing the from about 0.1% to 15% or more solid copolymer same, and indicates the superiority of the vinyl based on the polyvinyl acetate solids in the emul methyl ether-maleic anhydride copolymer in this sion. The plasticizers used may be present in respect. The determination of shear strength amounts up to about 6% by weight based on the recorded in the following tables was made by polyvinyl acetate solids in the emulsion, although gluing test blocks of maple wood and then fol the use of a plasticizer is not necessary. 50 lowing a procedure such as ASTM D-905-49. Tests were conducted, as illustrated in the fol The shear test values given are the average of lowing tables, to determine the improvement in 16 tests in each case. the resistance to cold ?ow of ?lms made in ac cordance with the present invention as compared Table iI II with ?lms made from conventional, untreated 55 polyvinyl acetate emulsions. In each case, ?lms [Room temperature] were cast on glass by means of a Bird applicator. After partly drying, the ?lms were removed and Sheer Film Strength, further dried in air. The dry ?lms were then p. s. i. cut into strips 4 inches long, and of a width 60 such as to give any desired cross-sectional area, A. l’lasticized Polyvinyl Acetate ____________________ __ 2,300 i. e. a thick ?lm would be cut narrower than B. Composition A plus 15% protein hy<li'olyzatc___ l, 590 C. Composition A plus 15% hide glue 250 g. test 1,230 a thin ?lm for a given cross-sectional area.