Adhesive Composition and Method of Bonding using Alpha-Cyanoacrylate Esters and Vinyl Aromatics

United States Patent Office 3,282,773- Patented Nov. 1,» 1966 1 3,282,773 ADHESIVE COMPOSITION AND METHOD OF BONDING USING m-CYANOACRYLATE ES- TERS AND VINYL AROMATICS Thomas H. Wicker, Jr., and Newton H. Shearer, Jr., Kingsport, Tenn., assignors to Eastman Kodak Com- pany, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed July 20, 1961, Ser. No. 125,380 14 Claims. (Cl. 161-188) This invention relates -to new on-cyanoacrylate adhesive compositions and bonds formed therefrom. More par- ticularly, our invention is concerned with adhesive formu- lations comprising monomeric esters of oz-cyanoacrylic ac-id and vinyl aromatic compounds for bonding metallic or non-metallic surfaces to themselves or to each other and otherwise providing a superior bonded article. Adhesive compositions comprising one or more mono- meric esters of cc-cyanoacrylic acid have been disclosed in patents of our co-workers and are well recognized to have utility in the bond-ing of a great variety of materials. For example, there is disclosed in U.S. Patent No. 2,974,788, in which one of us is a co-inventor, esters of cc-cyano- -acrylic acid having outstanding high—strength adhesive properties and which are extremely useful in bonding all kinds of articles such as glass, metals, plastics, rubber, wood, cement, ‘paper, cloth, etc. to themselves or to each other. These on-cyanoacrylate esters may be represented by the general formula ON CH2=C—C 0 OR in which R is an alkyl group of 1-16 carbon atoms, a cyclohexyl group, a phenyl group, or an alkenyl group such as allyl -or methallyl, etc. When applied in mono- meric form on the surface to be bonded, they set up rapidly to give a high-strength adhesive bond between a variety of materials. Also one of our co-workers has disclosed in U.S. Patent No. 2,816,093 an adhesive com- position comprising styrene in conjunction with methyl acrylate, ethyl on-cyanoacrylate and a polymerization cata- lyst. After extended investigation we have now found that vinyl aromatic compounds such as monomeric styrene polymerize concomitantly with esters of a.-cyanoacrylic acid without the need for catalyst, and yield bonds which have high tensile strength and excellent water resistance. Equimolar mixtures of an ester of oz-cyanoacrylic acid and a vinyl aromatic compound such as styrene, substi- tuted styrene, etc. will polymerize upon mixing without" ithe presence of added catalyst, to give rapid high-strength bonding even of diflicult surfaces. When these oz-cyano- acrylate adhesive mixtures are applied to the same surface or to the other surface to be bonded, and the two.surfaces brought together, a rapid high-strength bond having in- creased tensile strength and improved resistance to de- terioration by water is obtained. Either of the con-. stituents of our adhesive composition may be present in excess‘ in the mixture, but a slight molar excess of the vinyl aromatic compound is preferred; although we do not wish to be bound by theoretical explanations of the mechanism, it appears that this molar excess leads to the unexpected and improved water resistance of the final adhesive bond. It is an object of this invention to provide a novel com- position and method of utilizing the adhesive action of such new wcyanoacrylate adhesive compositions so that a firm bond occurs in a minimum of time. Another ob- ject is to provide an adhesive system which forms high- strength bonds in a short period of time between a variety of materials without the use of promoters, catalysts, or the use of clamping devices -to hold the adherends in" 10 15 20 25 30 35 40 45 50 55 60 65 70 2 place. Another object of the invention is to provide high- strength bonds having improved water resistance, and to provide an adhesive system less expensive than that com- posed of 100% on-cyanoacrylic ester. A further object of the invention is to provide an adhesive system which is stable and which can be marketed and stored on dealer shelves for long periods of time without deterioration due to polymerization. Other objects will become ap- parent from the description and claims which follow. Suitable -adhesive compositions for practicing our in- vention comprise monomeric or-cyanoacrylic esters of the formula: (1) ON I CH2=C—-C 0 OR wherein R is an alkyl group of 1 to 16 carbon atoms, a cyclohexyl group, a phenyl group, or an alkenyl group such as allyl or methallyl, etc. and vinyl aromatic hydro- carbons of the type: (2) in which R1 is hydrogen or methyl, X and Y may be halo- gen, lower alkyl, hydrogen, vinyl, or alkenyl substituents. The lower alkyl ac-cyanoacrylates are preferred because their bonding is more rapid than is that of the higher esters such as ca-pryl oz-cyanoacrylate. Vinyl aromatic compounds included within the scope of this invention in- clude those which polymerize concomitantly and spon- taneously with the or-cyanocrylates. compounds do not normally polymerize without added catalyst, but in admixture with oz-cyanoacrylate monomers the entire mixture polymerizes spontaneously without added initiation. _ In commercial use, it has been the practice to stabilize such cc-cyanoacrylate monomer compositions in order to prevent premature polymerization of the monomer. Such stabilization may be accomplished by incorporating there- inphenolic inhibitors such as hydroquinone, t-butyl cate- chol, etc. Usually the monomer contains varying amounts (from about 0.001 to 0.10% by weight) of- residual gaseous inhibitors such as sulfur dioxide, nitric oxide, and hydrogen fluoride which were ‘originally intro- .duced to prevent polymerization of the monomer during its manufacture and which produce an adequate shelf life for the final adhesive formulation. For more extensive stabilization, substantial amounts of residual acidic in- hibitors such as sulfur dioxide, nitric oxide, hydrogen fluoride, ‘organic acids or anhydrides, stannic chloride, ferric chloride, and other members of the class of so- called Lewis -acids (I. M. Kolthoif, J. Phys. Chem., 48, pages 51-7, 1944) may’ have been added with or without phenolic inhibitors. However such stabilized composi- tions tend to be less active and a variety of promoters or catalysts for improving the set times -of such composi- tions has been reported in the prior art. We have now observed that, contrary to expectations, certain mixtures of the above ac-cyanoacrylic esters and vinyl aromatic compounds polymerize spontaneously upon mixing and without added catalyst. Further, this polym- erization occurs equally well even where up to several percent of acidic_inhibitor has been incorporated into the monomeric cc-cyanoacrylic ester for protection against premature polymerization. .- Consequently these or-cyanoacrylates can be manufac- tured using relatively large amounts of sulfur dioxide or other acidic inhibitors and can be stored and used with- out the removal of said inhibitors. Since the polymeriza- The vinyl aromatic . 3,282,773 3 tion of the or-cyanoacrylic ester in the system of our in- vention is not dependent upon a low concentration of an acidic inhibitor as described’ in the prior art, a very stable adhesive may be marketed. _ Advantageously, the monomer components of our ad- hesive composition may be used alone or they may be thickened by incorporating therein a viscosity regulator such as a polymeric or-cyanoacrylate, a polyacrylate, a polymethacrylate, a cellulose ester, dissolved in the oc- cyanoacrylate, or a poly(vinyl aromatic compound) dis- solved in the vinyl aromatic component, in an amount up to 25% by weight based upon the total composition weight. A plasticizer may also be advantageously added to our composition in an amount of from 1 to 20% based on the total weight of the composition; particularly suited as plasticizers are monofunctional aliphatic esters, di- functional aliphatic or aromatic esters, phosphate esters, phosphonate esters, or the like. — Thus, one illustration of an adhesive composition for use in our invention has the following weight composi- tion: MIXTURE A 92% methyl a-cyanoacrylate containing 0.01% hydro- quinone plus a variable am-ount of sulfur dioxide (0.001 to 0.10%) 5% poly(methy1 methacrylate) 3% dimethyl sebacate MIXTURE B 100% wmethylstyrene In the broader practice of our invention, the oc-cyano- acrylic ester (Mixture A) can be applied to one surface to be bonded and the vinyl aromatic compound (Mix- ture B) can be applied to the other surface, or the two Cl 10 20 25 30 35 components can be mixed‘ prior to application. The pot . life of the combined mixtures varies, but it is usually in the order of 10 to 30 minutes and may be varied by change of concentration,- size -of mix, and temperature. In the preferred embodiment of our invention, the reac- tion components are present in approximately equimolar proportions, but the invention is operable over the 25/75 to 75/25 range in molar ratios of on-cyanoacrylate to vinyl aromatic compound. In any case a rapid and strong bond results as soon as the two surfaces to be bonded are brought into contact. Alternatively, as mentioned above, the two components of the adhesive may be mixed im- mediately prior to use. The following examples will further illustrate the man- ner of practicing our invention. It will be understood, however, that these examples are included to illustrate certain preferred embodiments of our invention and are not intended to limit the scope of the invention as defined herein unless specifically indicated. Example 1 - This example illustrates the rapid polymerization of _a mixture of ‘methyl ac-cyanoacrylate and styrene. (a) To 1.11 g. (0.01 m.) of methyl on-cyanoacrylate containing 100 p.p.m. sulfur dioxide in a small vial was added 1.04 g. (0.01 m.) of styrene monomer. The mix- ture began to polymerize immediately as shown by the gradual heating up and an increase in viscosity. The mix- ture had become very viscous within 15 minutes and with- in 30 minutes had set to a solid polymer. (b) Experiment (a) was repeated with the exception that a drop of the above mixture was removed two min- utes after mixing and placed between two steel tensile specimens. A bond unbreakable by manual pressure had formed within two minutes and a bond strength of 1900 p.s.i. was obtained after a 24-hr. cure at room tempera- ture. The above results appear to clearly illustrate the elfec- tiveness of the adhesive mixtures of this invention in the bonding of metallic surfaces. 40 45 50 60 65 70 .75 A. 1: Example 2 A mixture of 1.11 -g. (0.01 m.) of methyl oc-cyano- acrylate and 1.18 g. (0.01 m.) of at-methylstyrene was prepared and a steel-steel bond was formed by placing one drop of this mixture between two steel surfaces (1 sq. in.). The bond could not be pulled apart after a 2.5 minute set time. The above experiment was repeated using a mixture _ of 0.0075 m. of methyl oz-cyanoacrylate and 0.0025 m. of ex-methylstyrene. A bond formed between two aluminum surfaces which could not be pulled apart after a three minute set time. Example 3 A mixture of 1.11 g. (0.01 m.) of methyl oc-cyano- acrylate and 1.18 g. (0.01 m.) of p—vinyl toluene was pre- pared. One drop of this mixture was placed between two plane aluminum surfaces (1 sq. in.). After curin.g 3 min- utes the two pieces of aluminum could not be pul-led apart with manual pressure. Example 4 A mixture of 2.09 g. (0.01 m.) of 2-ethylhexyl a-cyano- acrylate and 1.14 g. (0.011 m.) of styrene monomer was prepared in a small vial. One drop of this mixture was placed between two surfaces of plate glass (1 sq. in.). A bond which was unbreakable by manual pressure had formed within 10 seconds. Example 5 A mixture of 1.11 -g. (0.01 m.) of methyl a-cyano- acrylate and 1.38 g. (0.01 m.) of o-chlorostyrene mono- mer was prepared and -one drop of the mixture was placed between two steel surfaces (1 sq. in.). A. bond which was manually unbreakable had formed within 3 minutes. Example 6 A mixture of 1.11 g. (0.01 m.) of methyl a-cyano- acrylate and 1.73 g. (0.01 m.) of 2,4-dichlorostyrene was prepared and one drop of the mixture was placed between two precleaned aluminum surfaces (1- sq. in.-). A bond which could not be broken by manual pressure formed within five minutes. _ . Repetition of the above experiment using a pre-mixed adhesive consisting of 0.0025 m. of methyl a-cyano- acrylate and 0.0075 m. of 2,4-dichlorostyrene on pre- cleaned steel surfaces -gave a manually unbreakable bond after four minutes set time. Example 7 A mixture of 1.11 g. (0.01 m.). of methyl c:-cyano- acrylate and 1.32 g. (0.01 m.) of 2,4-dimethylstyrene was prepared in a clean glass vial. One drop of this mix- ture was placed between two steel surfaces (1 sq. in.). A bond which was unbreakable by manual pressure had formed within three minutes. Example 8 A mixture of 1.11 g. (0.01 In.) of methyl oc-cyano- acrylate, 0.988 g. (0.0095 m.) of styrene monomer, and 0.065 .g. (0.0005 m.) of divinylbenzene was prepared in a small vial. The mixture was checked as an adhesive by placing one drop between two steel adherends (1 sq. in.). The resulting bond was unbreakable by manual pressure after two minutes’ cure time. Example 9 On one steel tensile specimen was placed one drop of methyl ac-cyanvoacrylate monomer. On another steel tensile specimen was placed one drop of monomeric styrene. The tensile test bond Was formed by bringing the two tensile specimens together with a swinlning motion. After the -bond had cured £01" 24 hr. at room temperature, it was broken in tension on a Baldwin Southwark testing machine indicating a bond strength of 1800 p.s.i. 5 Example I 0 3,282,773 On a steel specimen l/1” x 1" x 3" was placed one drop ' of neopentyl on-cyanoacrylate. On a similar piece of steel was placed one drop of on-methylstyrene. The two specimens were «brought together so that there was a one inch overlap and the bond was formed, the two drops being mixed with a -gentle swirling motion. Within three minutes a strong bond had formed which was not break- able by manual pressure. Example 11 An equimolar mixture of methyl on-cyanoacryllate and styrene was prepared in a small vial as described in Ex- ample 1. After two minutes, five steel-steel -tensile bonds were prepared from the mixture, cured 24 hr. at room tem- perature and then 24 hr. at 75° C. The bonded speci- mens were then placed in water at 75° C. for aging. The bonds remained intact during an observation period of 750 hrs. _ A similar set of bonds was prepared using methyl cc- cyanoac-rylate alone as the ‘adhesive. These bonds came apart within 600 hrs. when cured as described above and subjected to a water stability test at 75 ° C. Using the foregoing procedures, bonds were formed between rubber and -glass, glass and aluminum, maple « wood and aluminum, two pieces of polyester plastic, felt and leather, and a variety of other aclherend combina- tions. The following example illustrates the superior water resistance of the 1:1 styrene/methyl oz-cyanoacrylate co- polymer compared with the methyl oz-cyanoacrylate homo- polymer. Example 12 (:a) An equimolar mixture of methyl on-cyanoacrylate and styrene was prepared in a small vial as described in Example 1. The polymerization was allowed to go to completion and was finished off by heating at 60° C. -for 15 hrs. The resulting polymer was dissolved in chloro- form and then precipitated into diethyl ether after filtra- tion through a fine frit-ted glass funnel. The inherent viscosiy of the polymer was 2.30. This polymer was heated in water at reflux for 24 hrs. with no decrease in inherent viscosity. No carbon dioxide was evolved from the polymer during this period, indicating that no break- down of the copolymer occurred. ' (b) A polyn1'er of methyl cc-cyanoacryilate was prepared by the 2,2’-azobi-s-(2-methylpropionitrile) catalyzed ini- tiation of the monomer in bulk at 60° C. The inherent viscosity of the polymer was 1.80. During a period of eight hours while this polymer was heated in water at reflux, the inherent viscosity decreased from 1.80 to 0.28. Carbon dioxide evolved during this period indicated that the polymer was 2.8% decarboxylated. The following example illustrates the use of solutions of vinyl aromatic hydrocarbons .-as promoters for oc-cy- anoacrylate adhesive compositions in bonding «aluminum- «glass surfaces. Example 13 On a plane glass surface was placed one drop of methyl oz-cyanoacryalate. A 30% chloroform solution of mono- meric styrene was placed on 13. similar 4-aluminum surface, and after the solvent had evaporated, the two specimens were brought together. The resulting bond was formed within 10 seconds. In «a similar manner, bonds were prepared between two pieces of maple wood using methyl on-cyanoazcrylate and a . 1% solution of monomeric styrene. From the preceding description and examples, it can readily be seen that the procedure of this invention em- ploying vinyl aromatic compounds gives unexpected bonding of surfaces when employed in combination with on-cyanoacrylic esters. Strong bonds are obtained in short time with reproducible results. The method of our inven- tion can be employed with advantage in the bonding of 10 15 20 25 30 35 40 45 50 55 60 65 70 6 materials such as metals, rubber, plastics, textiles, paper and the like. Dissimilar materials such -as different metal surfaces, etc. can also be bonded by the method of this invention. ' Similar -advantageous results are obtained with other combinations of monomers over the range of proportions as described. Usually the single cc-cy»ano~ac1ylic ester is used in conjunction with «a vinyl aromatic compound, al- -though mixtures of two or more said esters may be em- ployed as well as mixtures «of two or more such vinyl ‘aromatic compounds. Although our invention has been described in consider- ab_»le detail with particular reference to certain preferred embodiments thereof, variations and modifications can be effected within the spirit and scope of the invention as de- scribed «hereinalbove and as defined in the appended claims. We claim: « 1. An adhesive composition comprising a mixture of la monomeric u-cyanoacrylate ester consisting of up to 50% by weight of a monomeric ester of on-cyanoacry-lic acid from the class having the tformula: ([)N CHa=C——C 0 OR wherein R is a member of the group consisting of alkyl groups of 1-8 -carbon atoms, cyclohexyl groups, phenyl groups, and alkenyl groups, and at least over 50% by weight of la monomeric vinyl aromatic hydrocarbon from the class having the formula: X B1 I C=CHz ' Y in which R1 is a member of the group consisting of hy- drogen and methyl, and X and Y are alike or different and are members of the group consisting of chlorine, lower alkyl, hydrogen, vinyl and alkenyl. 2. An adhesive composition according to claim 1 wherein the on-cyanoacrylic acid ester is methyl oc-cyano- acrylate and the vinyl aromatic hydrocarbon is a-methyl- styrene. ’ 3. An adhesive composition according to claim 1 wherein the on-cyanoacrylic acid ester is 2-ethylhexyl an-cyanoacrylate and the vinyl aromatic hydrocarbon is a-methylstyrene. 4. An adhesive composition according to claim 1 wherein the cc-cyanoacrylic acid ester is neopentyl oc-cya- noacrylate and the vinyl aromatic hydrocarbon is cc-me-‘ thylstyrene. 5. An adhesive composition according to claim 1 wherein the ac-cyanoacrylic acid ester is methyl a-cyano- acrylate and the Vinyl aromatic hydrocarbon is 2,4-dichlo- rostyrene. _6. An adhesive composition according to claim 1 wherein the oc-cyanoacrylic acid ester is methyl cc-cyano- acrylate and the vinyl -aromatic ‘hydrocarbon is styrene monomer. 7. The composition of claim 1 wherein at least one of the groups X and Y is a member which will produce crosslinking. 8. The method of bonding two surfaces together in a quick and lasting bond which comprises coating one of the surfaces to be bonded with an adhesive composition of a monomeric ester of cc-cyanoacrylic acid of the for- mula: (IJN CHz=C--COOR wherein R is selected from the group consisting of alkyl groups of 1-8 carbon atoms, cyclohexyl groups, phenyl groups, and alkenyl groups; coating the other surface to 3,282,773 7 be bonded with a monomeric vinyl aromatic hydrocar- bon having the‘ formula: X R1 ‘ (l3=CHa / Y wherein R1 is a member selected from the group consist- ing of hydrogen and methyl and X and Y are selected from the group consisting of chlorine, lower _alkyl, hydro- gen, vinyl, and alkenyl; and thereafter placing together the two surfaces to be bonded, and bonding them together within a few minutes. 9. The product formed by the process of claim _8. 10. The method of claim 8 wherein X and Y are se- lected from the group consisting of chlorine, lower alkyl, hydrogen, vinyl, and alkenyl and wherein at least one of the groups X and Y is a member which will produce crosslinking. 11. The method of claim 8 wherein the monomeric vinyl arromatic hydrocarbon is ‘alpha-methylstyrene and wherein the monomeric oz-cyanoacrylic ester contains a polymerization inhibitor. 12. A bonded article ‘according to claim 8 wherein the surfaces which are to be bonded are selected from the group consisting of steel, aluminum, glass, wood, felt, and leather. 13. The method of strongly bonding a material with a quick and lasting bond comprising coating the surface to be bonded with a monomeric vinyl aromatic hydro- carbon of the formula: X I111 JC=CHg Y . wherein R1 is from the group consisting of hydrogen and methyl and X and Y are selected from the group con- 10 8 sisting of chlorine, lower alkyl, hydrogen, vinyl and alkenyl; applying an adhesive composition comprising a monomeric lower alkyl-alpha cyanoacrylate to the mon- omeric vinyl aromatic hydrocarbon coated surface, said adhesive composition containing a polymerization in- hibitor, and bringing the resulting coated surface into contact with the material being bonded thereto, and bonding said materials by polymerization, said polymer- ization being promoted by said monomeric vinyl aromatic hydrocarbon. 14. The method of strongly bonding a material with a E strong and lasting bond comprising coating the surface 15? 20‘? 30 35 40 of the material to be bonded with a monomeric lower alkyl alpha—cyanoacry1ate, said adhesive composition containing a polymerization inhibitor; applying a monom- .eric vinyl aromatic hydrocarbon of the formula: X J/ Y R1 I C=CH2 wherein R1 is from the group consisting of hydrogen and methyl, -and X and Y are selected from the group con- sisting of chlorine, lower alkyl, hydrogen, vinyl and alkenyl, to said adhesive coated surface; and bringing the resulting coated surface into contact with the ma- terial being bonded thereto, and bonding said materials by polymerization, said polymerization being promoted by said monomeric vinyl aromatic hydrocarbon. References Cited by the Examiner UNITED STATES PATENTS 176,428 4/1876 Daniels ___________ __ 154—-46 2,651,589 9/1953 Shokal et al. ____ __ l54—43 X 2,816,093 12/1957 Coover _________ __. 260—-78.5 2,817,620 12/1957 Golick et al. ______ _. 154--—118 EARL M. BERGERT, Primary Examiner. ALEXANDER WYMAN, J. M. DULIN, J. P. MELOCHE, Assistant Examiners.