ADHERING CURED POLYMERS OR PREPOLYMERS TO CURED ELASTOMER UTILIZING HYPOCHLOROUS ACID TREATING AGENT

Abstract: Use of hypochlorous acid as the treating agent in the bonding of cured elastomer and polyurethane/polyurea increases adhesion. The process is useful for repairing damaged articles of cured elastomer and also for bonding together layers of cured elastomer.

Description: Description ADHERING CURED POLYMERS OR PREPOLYMERS TO CURED ELASTOMER UTILIZING HYPOCHLOROUS ACID TREATING AGENT Technical Field This invention relates to a method of bonding cured elastomer and amine cured polymer or prepolymer and the articles produced thereby. It is especially useful for repairing tires, conveyor belts, hoses, rubber boots or the like or for bonding elastomer layers e.g. in the application of tire treads. Background of the Invention For many years, repairs on cured elastomer have been carried out utilizing gum rubber and curing in a mold under the application of heat. This is messy since gum rubber is not pourable and requires relatively high heat curing conditions (e.g. 3280F. for 30-45 minutes). More recently, consideration has been given to use of pourable compositions in the form of amine curable polymer or prepolymer for such repairs. These have the additional advantage of being curable at lower temperatures, e.g. at ambient temperatures thereby allowing repairs in the field. Hausch U.S. Patent 4,327,138 discloses an ambient temperature cure method which involves chemical treatment of the elastomer surface to be repaired with halogen containing oxidant (N-halosulfonamides, N-halohydantoins, N-haloamides and N-haloimides are mentioned and trichloroisocyanuric acid is used in the specific examples). A search has been going on to increase the adhesion performance attributes in the process generally described in the Hausch specific examples. The application of Fieldhouse, Koch and Oziomek entitled "Adhering Cured Polymers or Prepolymers To High Natural Rubber Content Elastomer" filed concurrently herewith is addressed to applying the chemical treating agent dissolved in a particular solvent to obtain increased adhesion results for natural rubber and high natural rubber content elastomers; but this method does not provide significant adhesion improvement for other elastomers. Summary Of The Invention It has now been discovered that utilizing hypochlorous acid as the chemical treating agent in the process involving the application of pourable amine curable composition and reduced curing conditions provides the benefit of increased adhesion even with synthetic elastomer substrates or bases. The process of the invention for bonding cured elastomer and amine cured polymer or prepolymer comprises the steps of (a) cleaning the portion of the surface of the cured elastomer which is to undergo bonding; (b) applying hypochlorous acid to that portion (i.e. chemically treating that portion with hypochlorous acid); (c) applying to the hypochlorous acid treated portion an amine curable polymer or prepolymer in polar solvent; (d) curing the amine curable polymer or prepolymer; whereby the cured polymer or prepolymer is bonded to the elastomer. Detailed Description The cured elastomer referred to above comprises those elastomers made from rubber compounds known to those skilled in the art cured by methods known to those skilled in the art and the like. Such elastomers are selected from the group consisting of polymers or copolymers of conjugated dienes, copolymers prepared from conjugated dienes and vinyl substituted aromatic compounds, butyl rubbers, nitrile rubbers and neoprene. The conjugated dienes referred to are those having from 4 to 12 carbon atoms. Specific examples of these include butadiene, isoprene, pentadiene, hexaciene, heptadiene, octadiene, 2, 3-dimethyl-1,3-butadiene, 2-methyl-1,3-pentadiene, and the like. The vinyl substituted aromatic compounds referred to are those containing from 8 to 15 carbon atoms. Specific examples of these include styrene, alpha-methylstyrene, 4-t-butylstyrene, vinyl toluene, divinyl benzene, isopropenyl benzene, diisopropenyl benzene, and the like. Examples of polymers and/or copolymers of conjugated dienes include natural rubber (the elastomeric substance obtained from various trees and plants which generally grow in the tropics or desert portions of the world, which contains in excess of 90% and often in excess of 95% cis-1,4-polyisoprene) and polymers prepared from butadiene and/or isoprene. Examples of copolymers of conjugated dienes and vinyl substituted aromatic compounds include poly-styrenebutadiene (SBR), poly-alpha-methylstyrene-butadiene, and poly-4-t-butylstyrene-butadiene. Preferred elastomers for use in the present invention include copolymers of styrene and butadiene (SBR), i.e. styrene-butadiene rubber, and blends of this with up to about 20% of the blend of natural rubber. Turning now to the processing steps, the step of cleaning the portion of the surface of the cured elastomer which is to undergo bonding constitutes cleaning such portion as by buffing and/or treatment with a conventional organic solvent. Another method of cleaning involves skiving, that is, cutting and removing a portion as for example in the situation where the surface contains an opening. In the succeeding chemical treatment step the hypochlorous acid is conveniently applied with a suitable solvent, e.g. at a concentration ranging from about 0.05 to about 1M to activate the elastomer surface to be bonded. Examples of solvents include lower alkyl acetates (e.g. ethyl acetate, propyl acetate, and butyl acetate) and ethylene glycol diacetate. Apparently the chemical treating agent reacts quantitatively and efficiently with double bonds in the elastomer to produce a reactive substrate (chlorohydrins) which then reacts with the free isocyanate of the applied polymer or prepolymer thus producing a chemical bond between the elastomer and applied polymer to increase the adhesion between such and produce greater durability (i.e. a longer lasting bond). The combination of the amine-curable polymer or prepolymer, amine curing agent and polar solvent applied in step (c) form a liquid (pourable) system which is readily applied to the cleaned activated elastomer surface. The admixture of these ingredients is readily accomplished in conventional mixers such as dough mixers, high speed impellers, paddle-type mixers and the like. Small batches can be mixed by stirring with a spatula. Cure of the curable polymer or prepolymer commences upon admixture of the cure system ingredients so the mixing step should not be of a length of time such that any significant cure occurs during mixing. The admixture is readily applied to the portion of the article to be repaired by coating, pouring, casting, molding or the like. A plasticizer can optionally be included in the admixture to facilitate processing. An optional ingredient can also be included to reduce cure time. The equivalent weight of the amine curing agent with regard to the curable polymer or prepolymer normally ranges from about 85% to about 115%, with from about 95% to about 105% being preferred. Ordinarily the amount of polar solvent per 100 parts by weight of the curable polymer or prepolymer ranges from about 2 to about 20, more preferably from about 5 to about 15. Preferred amine curable polymers or prepolymers are urethanes, especially polyurethanes. These can be formed by reacting a polyether polyol or a polyester polyol with a molar excess of an organo-diisocyanate to form a prepolymr having terminal isocyanato groups; curing can be carried out to increase the molecular weight from less than about 3,000 upwards to over 10,000 to form polymer. Examples of such polymers are set forth in U.S. Patent Nos. 2,620,516; 2,777,831; 2,843,568; 2,866,774; 2,900,368; 2,929,800; 2,948,691; 2,948,707; and 3,114,735, all of which are hereby fully incorporated by reference. Typical specific examples of such polyurethanes include Adiprene L-367, polytetramethylene ether glycol containing approximately 6.4 percent isocyanate end groups by weight, manufactured by Dupont; Adiprene L-42, polytetramethylene ether glycol containing approximately 2.8 percent isocyanate end groups by weight, manufactured by DuPont; and Cyanaprene A-7, a polyester based coating polymer with approximately 2.4 percent isocyanate end groups, manufactured by American Cyanamid. Blends of these polyurethanes are readily utilized. Other amine curable polymers or prepolymers include the compounds set forth in U.S. Patent No. 3,755,261 which is hereby fully incorporated by reference. Briefly, such compounds are the various epoxy resins such as those disclosed in the "Encyclopedia of Polymer Science and Technology" Interscience Publishers, New York (1967), Volume 6, pages 212-221; halogen-containing hydrocarbon polymers such as chloroprene polymers, chlorinated butyl rubber, and chlorinated polyethylene and polypropylene; chlorosulfonated polymers such as those described in U.S. Patent No. 2,723,257; polymers containing acid halide groups such as EMI6.1 and haloformate groups such as EMI6.2 polymers containing anhydride groups which on reaction with diamines yield amide-acide linkages, and organopolysiloxanes as described in U.S. Patent No. 2,938,010. The amine curing agents can be, for example, any of such agents known or useful for such purpose. A multiplicity of such are well known. Preferred ones include a complex of 4,4'-methylene dianiline (MDA) and a salt, or a complex of racemic 2,3-di-(4-aminophenyl) butane and a halide salt, as set forth in U.S. Patent No. 3,755,261 to VanGulick which is hereby fully incorporated by reference. The methods for preparing the complexes are set forth in U.S. Patent No. 3,755,261. A preferred salt utilized with the 4,4'-methylene dianiline compound is sodium chloride or lithium chloride. Due generally to availability and costs, the complexes or salts derived from 4,4'-methylene dianiline are highly preferred. Another class of amine curing agents which are especially useful are the various Versamids, that is the condensation products of polyamides and dibasic acids obtained when certain unsaturated fatty acids are polymerized, and are manufactured by General Mills Chemical Company. Suitable polar solvents for the admixture are set forth in U.S. Patent No. 3,888,831 to Kogon which is hereby fully incorporated by reference. Preferred solvents include dimethylformamide, tetrahydrofuran, cyclohexanone, ethyl acetate, nitromethane, nitroethane, nitropropane, and more preferably methyl ethyl ketone and acetone. Preferred plasticizers include dioctyl-plithalate and tetraethylene glycol bis(2-ethyl hexanoate). MDA-salt (sodium chloride) complex in combination with dioctylphthalate (50% weight basis) is sold under the name Caytur 21. The tetraethylene glycol bis(2-ethyl hexanoate) is marketed by Union Carbide under the name Flexol 4-GO. A cure time reducing agent is tributylphosphate used at a level of 0.1% to 10%, more preferably from 0.5% to 5%, based on the total weight of curing agent and tributylphosphate. Curing is readily carried out at ambient or room temperature, that is, the ordinary prevailing temperatures as from about 100C. to about 500C. Often ambient temperatures will range from about 150C. to about 350C. or 400C. Curing times at ambient temperature ordinarily range from about 12 hours to about 72 hours with 16 to 24 hours being preferred. Curing at ambient temperature is ordinarily carried out simply by maintaining the cure composition coated article at such temperature during a period as aforestated. If desired, curing times can be speeded up by utilizing cure temperatures higher than ambient, e.g. up to 2500F. At 2500F. curing is readily carried out in a time period ranging from about one-half to one hour. The disadvantage of this is that this usually requires transporting to a shop while ambient temperature cures are readily carried out in the field. The process is readily used to repair damaged articles of the cured elastomer, and the amine cured polymer or prepolymer is the repair agent. In such case, the damaged area is cleaned and chemically treated as set forth above. The liquid system os amine-curable polymer or prepolymer and curing agent, etc., is readily poured into or over the damaged area, and curing causes the repair agent to bond to the elastomer. The article repaired in this way resists debonding (delamination) and the use of the hypochlorous acid treating agent increases adhesion and durability of bonding compared to the specific examples in the aforementioned Hausch patent. The bond has good adhesion characteristics even at elevated temperatures. The process is also readily used to bond layers of cured elastomer. In this case, the portions of the layers that are to be joined are cleaned and chemically treated as set forth above, the liquid system of polymer and curing agent etc. is applied (e.g. poured or brushed on) to at least one cleaned activated layer and the layers are brought together and curing is carried out whereby the layers are bonded together. The bond has good durability and good adhesion characteristics even at elevated temperature. The invention is illustrated in the following specific examples: EXAMPLE I Each test specimen was a peel adhesion pad of styrene/butadiene rubber (100 gauge) reinforced with nylon cord. Each pad was treated as follows: the surface was bluffed with a wire brush to a RMA-1 buff rating, then washed with acetone or ethyl acetate on Rymplecloth and then allowed to dry thoroughly. The pad was then primed with the appropriate primer solution as specified. The clean, primed surface was coated with a formulation of 300 parts Adiprene L-42 ttoluene diisocyanate capped poly(oxytetramethylene) diol, 2.7% free NCO, duPont Chemical Co.] 30 parts acetone, 20 parts Flexol 4GO (triethyleneglycol di-2-ethyhexanoate, Union Carbide) and 43 parts Caytur 21 (complex of 3 moles of 4,4'-methylene bis(dianiline) and 1 mole sodium chloride in dioctylphthalate plasticizer, duPont Chemical Co.). A nylon reinforcing mesh is placed in the coating for stabilization and the coating is kept slightly apart from the pad at one end. The coated pad is cured for 1 hour at 2500F. The coating was bonded well to the rubber pad except for the end that was kept apart. Each pad was cut into one inch strips and each strip was subjected to pulling at the split end utilizing an Instron Tester to measure in pounds per linear inch (p.l.i.) the force required to pull the coating away from the rubber pad. For each pad, two strips were tested at room temperature and two strips were tested at 2120F. A difference of 10-15 p.l.i. on the Instron Tester results indicates a difference in an actual repair situation. Testing was carried out utilizing as primer solutions (i.e. solutions of chemical treating agent) hypochlorous acid in ethyl acetate at a concentration of 0.9meq/ml (Run 1) and hypochlorous acid in butyl acetate at a concentration of 0.7 meq/ml (Run 2) and 3% by weight trichlorocyanuric acid (trichloro-s-triazinetrione) in ethyl acetate (Run 3 - representing the prior art). Test results were as follows: Peel Adhesion Data (p.l.i.) Room Temperature 2120F. Run 1 36 32 50 35 Run 2 126 50 60 48 Run 3 36 10 34 12 As indicated above by comparison of Runs 1, 2 and 3, the invention (Runs 1 and 2) provides significant elevated temperature adhesion advantages over the use of the Hausch patent primer (i.e. trichloroisocyanuric acid (Run 3) and the invention run where butyl acetate is used as solvent for the primer (Run 2) provides significant adhesion advantages both at room temperature and elevated temperature compared to the Hausch patent primer of trichloroisocyanuric acid. EXAMPLE II This example was carried out the same as Example I except that the primer solvent was ethylene glycol acetate and curing was carried out for 24 hours at room temperature. Two runs were carried out. Run 1 (within the scope of the invention) involved using approximately 0.13 meq/ml hypochlorous acid in ethylene glycol diacetate for the chemical treatment step and Run 2 (representing use of the primer of the Hausch patent) involved using 3 weight % trichloroisocyanuric acid in ethylene glycol diacetate for the chemical treatment step. Test results were as follows: Peel Adhesion Data (p.l.i.) Room Temperature 2120F. Run 1 100+ 30 100+ 30 Run 2 16 16 30 28 As indicated above the run within the scope of the invention (Run 1) showed much superior adhesion results at room temperature. Similar results of improved bonding are obtained when the elastomer was 95% SBR and 5% natural rubber. Results of improved bonding are also obtained when peel adhesion pads of other elastomers (e.g. 100% natural rubber or butyl rubber or neoprene or nitrile rubbers) are utilized. Good results are also obtained when other primer solvents, e.g. 1,2-dichloroethane, are utilized. While the foregoing describes certain preferred embodiments of the invention, modifications will be readily apparent to those skilled in the art. Thus, the scope of the invention is intended to be defined by the following claims.

Claims: WHAT IS CLAIMED IS: 1. A process for bonding cured elastomer and amine cured polymer or prepolymer, said process comprising the steps of (a) cleaning the portions of the surface of the cured elastomer which is to undergo bonding; (b) applying hypochlorous acid to that portion; (c) applying to the hypochlorous acid treated portion an amine curable polymer or prepolymer and an amine curing agent in polar solvent; (d) curing the amine curable polymer or prepolymer; whereby the cured polymer or prepolymer is bonded to the elastomer. 2. A process as recited in claim 1, wherein the amine curable polymer or prepolymer is polyurethane. 3. A process as recited in claim 2, wherein the hypochlorous acid is applied as a solution in which the solvent is selected from the group consisting of lower alkyl acetates and ethyleneglycol diacetate. 4. A process as recited in claim 3, wherein the hypochlorous acid is dissolved in butyl acetate. 5. A process as recited in claim 4, wherein the amine curing agent comprises 4,4'-methylene dianiline and the polar solvent is acetone. 6. A process as recited in claim 5, wherein cured elastomer is styrene butadiene rubber or blends thereof with up to about 20% by weight of the blend of natural rubber. 7. A process as recited in claim 6, wherein the process is for repairing damaged articles of cured elastomer and the amine cured polymer or prepolymer is the repair agent. 8. A process as recited in claim 1 for bonding layers of cured elastomer, comprising the steps of (a) cleaning the portion of each layer which is to undergo bonding; (b) applying hypochlorous acid to said portions; (c) applying to the hypochlorous acid treated portion of at least layer amine curable polymer or prepolymer and an amine curing agent in polar solvent; (d) bringing together the portions to be joined; (e) curing the amine curable polymer or prepolymer; whereby said layers are bonded to each other by the amine cured polymer or prepolymer. 9. A process as recited in claim 8, wherein the amine curable polymer or prepolymer is polyurethane. 10. A process as recited in claim 8, wherein the hypochlorous acid is applied as a solution in which the solvent is selected from the group consisting of lower alkyl acetates and ethyleneglycol diacetate. 11. A process as recited in claim 10, wherein the hypochlorous acid is dissolved in butyl acetate. 12. A process as recited in claim 11, wherein the amine curing agent comprises 4,4'-methylene dianiline and the polar solvent is acetone. 13. A process as recited in claim 12, wherein the cured elastomer is styrene butadiene rubber or blends thereof with up to about 20% by weight of the blend of natural rubber. 14. An article repaired or prepared by the process of claim 1.

Inventors: FIELDHOUSE, JOHN W., KOCH, RUSSELL W.
Applicants: THE FIRESTONE TIRE & RUBBER COMPANY
Application year: 1984
Main classification: C08J5
IPC codes: B29C65, C08J7, C08J5, B29K21