CA1075581A - Copper coat strengthens ferrous metal bond to rubber - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

The bond strength of composite articles of rubber adhered to ferrous metal substrates through an adhesive is sub-stantially improved at ambient and elevated temperatures by depositing a loosely adhered layer of copper on the ferrous metal substrate, applying an adhesive thereover comprising an interpolymer containing about 50 to about 99% by weight of a conjugated diene, about 1-45% by weight of a vinyl substituted heterocyclic base and 0 to about 40% by weight of at least one additional copolymerizable monomer, and thereafter contacting the adhesive with the rubber to be bonded and bonding by heat and pressure,

Description

1~75581 This invention relates to a process for bonding rubber to a ferrous metal substrate and to a novel composite structure.
More particularly the present invention relates to the bonding of rubber to ferrous metal substrates by depositing a copper layer on the substrate followed by bonding through an adhesive comprising an interpolymer of a conjugated diene and a vinyl substituted heterocyclic base.
The vulcanization or the adhesion of rubber to metals has heretofore been accomplished by various processes. These include brass, bronze and zinc plating, the use of halogenated natural or synthetic rubbers with and without special adhesion promoting additives such as di-C-nitroso compounds or cobalt naphthenate, etc., isocyanates or isocyanate rubber blends, and synthetic resins of the phenol formaldehyde type. Each suffers from certain weaknesses.
Chlorinated and brominated natural and synethtic rubbers, particularly when formulated to include crosslinking and adhesion promoting additives such as di-C-nitrosated aro-matics give good adhesive bonds between various metals and natural and synthetic rubbers, Because of their somewhat polar nature, they are able to adhere to metals without covalent bond-ing with the metal surface. This lack of a chemical bond to the metal surface is clearly 2 disadvantage for the adhesive strength of such systems falls rapidly with increasing temperature.
Polyfunctional isocyanates such as P, P', P" triiso-cyanato triphenyl methane by themselves and as additives to rubber solutions have been known for many years to provide good bond strength between rubber and metals, While the mechanism of adhesion is not clearly understood, it is postulated that the isocyanates can chemically react with both the rubber and the metal surface. In the former case, active hydrogens, e.g., hydroxy or carboxyl groups generated by oxidation during rubber - 1 - ~
q~

1~755~1 , .

processing provide a reaction site for the formation of urethane and other linkages. In the bonding to the metal surface it has been suggested that oxide surfaces which frequently contain some hydroxy groups could react with the isocyanate group In any event, the solvent resistance and rate of reduction of bond strength with increasing temperature of isocyanate bonded rubber to metal parts is better than would be expected if the adhesion to metal were due only to physical forces, The disadvantages of isocyanate based systems include high moisture sensitivity and very short pot life due to the highly reactive isocyanate groups and the poor thermal aging characteristics of this bond.
Synthetic resins of the phenol-formaldehyde type, usually blended with a rubbery polymer latex also can be used to bond rubber to metal. This sort of adhesive can chemically com-bine with an unsaturated rubber either by a migration of sulfur and accelerators from the rubber into the adhesive layer followed by a covulcanization or possibly by reaction of the methylol groups of the resole with the rubber itself. However, the adhesion to the metal surface is physical in nature, i.e. Van der Waal type forces and the bond strengths to metal are generally poor, especially at elevated temperatures.
The use of a thin coating of copper by electroless deposition on a metal surface to improve the bond between the metal and vulcanlzable rubber was first patented in 1879 (U. S. Patent 215,034) Presumably, during the sulfur vulcan-ization of the unsaturated rubber in contact with the copper plated metal surface, both the copper and the unsaturated rubber compete simultaneously for the sulfur. Since the sulfur has a valance of two, it is postulated that for a portion of the sulfur at the interface one valance is satisfied by reacting with the copper while the other bonds to the rubber. In this way a covalent linkage is formed between the metal surface and the 10~5~81 ~.~

rubber thus bonding one to the other, although the bond formed is rather weak.
Numerous patented improvements followed this disclosure such as depositing the copper electrolytically instead of by the original electroless deposition (British Patent No. 929,211), depositing the copper from organic solvents, (U.S. Patent Nos.
; 1,883,973 and 1,906,~36), depositing the copper in the presence of surfactants etc. These modifications were aimed at improving the uniformity and adhesion of the copper to the metal surface 10 and obtaining a reasonable rate of deposition. Since these bonds were still weak, the copper plated metal was often coated with a tie-coat to improve the wetting of the metal surface prior to bonding to a vulcanizable rubber. These tie coats typically consisted of natural rubber plus curatives dissolved in a suitable solvent. Unfortunately none of these approaches corrects the weaknesses that prevent pure copper coatings from being commer-cially practical for bonding rubber to metal, There are two main reasons for the failure of pure copper as an adhesive.
First, it appears that the shear strength of the copper sulfide formed is comparatively weak, or perhaps the shear weakness is at the interface of the copper sulfide-unreacted copper. In any event, the bonds were too weak for commercial applications, And secondly, copper reacts very rapidly with the sulfur available at the metal-rubber interface, This can be so fast that there is no sulfur left in the immediate vicinity of the surface for bonding to and vulcanization of the unsaturated rubber. This results in no bond being formed between the metal and the rubber.
- The use of brass plating and in some applications bronze or zinc plating overcomes the bond strength deficiency of pure copper "adhesive", however these processes, while commer-cially practical, still suffer from certain serious limitations Any variations in the composition, crystal structure or thickness iO7S581 of the alloy coating can result in very poor adhesion to rubber.
The plating processes are slow, often requiring as much as a minute to develop a satisfactory coating. The plating baths, espècially for brass, use cyanides which are hazardous and result in a serious waste disposal problem, While satisfactory adhesion can be achieved between rubber and brass, bronze or zinc plated metals, the requirement of good adhesionseverely limits the rubber formulator for only certain formulations result in satisfactory adhesion. It is common practice, for example to use metal naphthenates or resorcinol-hexamethyleneimine combinations in the rubber to be bonded in order to improve the bond strength to brass, These approaches both add to the cost and adversely affect the physical properties of the rubber to be bonded.
In U, S. Patent 2,978,377 it is mentioned that copoly-mers of butadiene and a vinyl pyridine such as 2-methyl-5-vinyl pyridine have been used for bonding rubber to metal and that when used with natural rubber or a GRS (1,3 butadiene-styrene) composition an excellent bond is obtained, No mention is made of the strength of such bonds at elevated temperatures and no data are given, In any event, it has been found that there are many natural rubber and GRS compositions, which if bonded to metals with copolymers of vinyl pyridines and butadiene result in very poor bond strengths even at normal ambient temperature, The purpose of the present invention is to bond com-pounded rubber to metals, especially iron and steel, utilizing rapid, easily controlled processes, The invention further provides for the bonding of rubber to metal, especially steel bead wire and cord for use in steel reinforced tires, belts and hoses using a copper salt treat-ment of the metal surface followed by a coating of an adhesive composed of a rubbery interpolymer comprising a conjugated diene .

,,, ~07~581 and a vinyl substituted heterocyclic base.
Still further the invention permits formation of a bond between a steel wire or cord and the surrounding rubber that will retain a large measure of its bond strength at elevated temperatures often encountered during the use of the aforemen-tioned tires, belts, etc.
Still further the invention produces good bond strengths between a wide selection of compounded rubbers and an iron or steel surface, the bond retaining a large measure of its bond strength over a wide temperature range.
It has now been found that by first depositing a loosely adherent coating of copper on a ferrous surface, rinsing the surface with water, and then applying over this coating a second coating comprising a rubbery interpolymer of conjugated dienes and a vinyl substituted heterocyclic bases such a com-bination of coatings in contact with a compounded unsaturated rubber forms a bond of unexpectedly high bond strength especially at elevated temperatures during the vulcanization of the un-saturated rubber. -According to the invention there is provided a process for bonding rubber to a ferrous metal substrate which comprises depositing a copper coating onto said ferrous metal substrate by deposition from a solution of a cupric ~alt, applying an adhesive thereover, said adhesive comprising an interpolymer containing about 50 to about 99% by weight of a conjugated diene, about 1-45% by weight of a vinyl substituted heterocyclic base and 0 to about 40% by weight of at least one additional copoly-merizable monomer ~hich contains at least one polymerizable ethylenic group to a total of 100%, thereafter contacting said adhesive with a rubber to be bonded and bonding said rubber to said adhesive, after which the whole assembly is vulcanized with heat and pressure.
- ~ 5_ According to another aspect of the invention there is provided a laminated article comprising a ferrous metal substrate having a loosely adherent deposit of copper thereon, a layer of : .

-5a-: .

-- ~075581 adhesive over said copper and rubber bonded through said copper and adhesive to said ferrous metal substrate, said adhesive comprising an interpolymer containing about 50 to about 99% by weight of a conjugated diene, about 1-45% by weight of a vinyl substituted heterocyclic base and 0 to about 40% by weight of at least one additional copolymerizable monomer to a total of 100%.
The above mentioned loosely adherent coating of copper may contain halide salts and/or oxides or hydroxides of copper and iron. The combination of the copper coating and the inter-polymer adhesive shows a definite and unexpected synergistic effect on the bond strength with a variety of compounded rubbers.
It has further been determined that advantageous methods of forming the aforementioned coatings of copper are by electro-less plating and electroplating from aqueous solutions of cupric salts in the presence of the strongly accelerating halide ions.
Cuprous salts are not effectlve.
The advantages of this discovery over the prior art are readily apparent. The present process does not require the care-ful control of alloy composition characteristic of the brass and bronze processes and is much faster than either of those processes.
Careful control of the plating process is unnecessary in the present process. Another highly significant advantage of this process over the presently used brass, bronze and zinc bonding processes is the wide range of natural and synthetic rubber types and rubber formulations that can be bonded, as can be seen in the working examples. No adhesion promoting additives are needed in the rubbers to insure adequate bond strength when using the process of this invention.
The copper coatings of the invention are preferably applied by electroless plating using an aqueous solution of cupric ion containing a highly accelerating halide ion, for example, chloride or bromide. The presence of the halide ions apparently accelerates the rate of deposition of the copper coat-ing. Those skilled in the art will of course realize that many methods are known for plating copper onto a metal surface. For example, electroless plating can be accomplished from aqueous or organic solutions of copper salts; electroplating can also be used to form the copper coating from a copper salt solution. Any of these methods can be used in the practice of this invention so long as it gives loosely adherent coatings of copper similar to that obtained, for example, by electroless plating from an aqueous solution of cupric chloride. The treating time that generates the aforementioned copper coating is preferably 0.5-60 seconds, but can be as low as 0.1 seconds or less depending on the type of anion that exists in an aqueous solution of cupric salt as well as concentration, temperature and degree of agitation of the solution.
As indicated above, the preferred method for producing the loosely adherent copper coating is by electroless deposition from a cupric chloride or bromide solution. Other salts of organic and inorganic acids have been found to deposit a smooth, tightly adhered coating which does not appear to produce the improved bond strengths obtained in this invention. However such other salts, for example formates, acetates, nitrates, phosphates, sulfates, tartrates, borates, etc., can be employed in solution with added halide ions which accelerate deposition. ;
As indicated above, the electroless deposition may be accomplished by dipping the ferrous article in the cupric solution for a period of time from a fraction of a second to about sixty seconds. Other conditions of this dipping step, i.e. concentra-tion of cupric salt, temperature of the solution and degree of agitation of the solution may be widely varied by the operator, with the best results for any particular system being easily deter-mined. Generally a concentration of about 1 to 10 percent may be utilized at temperatures from 15C to 40C with or without .

1~75581 agitation. Times of more than sixty seconds may be used, but are unnecessary.
The rubbery interpolymer used as the adhesive in the present invention comprises a copolymer of a conjugated diene with a vinyl substituted heterocyclic base or an interpolymer of the above with at least one additional copolymerizable monomer.
Those polymers applicable in the present invention are comprised of about 50-99% by weight of the conjugated diene, about 1-45%
by weight of a vinyl substituted heterocyclic base with 5-15%
being preferred and 0 to about 40% by weight of at least one ; additional copolymerizable monomer, to a total of 100%. With copoIymers the amount of vinyl substituted heterocyclic base is desirably maintained at 1-25% by weight.
Within these limits the compositions of the copolymers can be varied widely without sacrificing the excellent hot bond strengths achieved with this invention. Commercially, due to the expense of some vinyl substituted heterocyclic bases, e.g.
vinyl pyridines, copolymers with relatively low levels of co~
polymerizable vinyl substituted heterocyclic base are preferred and amounts as low as 1% have been found to be effective.
These copolymers can be prepared by any method known in the art, for example, thermal, solution, suspension, mass, and emulsion polymerization. The copolymerization can be free radical or anionic, random, block or stereospecific. The pre-ferred method is by emulsion polymerization.
The conjugated dienes useful in this invention are preferably those which contain four to six, inclusive, carbon atoms per molecule but those containing more carbon atoms per molecule, e.g., eight can also be used. These compounds include hydrocarbons, for example, 1,3 butadiene, isoprene, piperylene, methyl pentadiene, 2,3 dimethyl-1,3-butadiene, 2,3-diethyl-1,3-butadiene, halohydrocarbons, for example, haloprenes, e.g.

chloroprene, methyl chloroprene and others, and alkoxy hydro-carbons, for example, methoxy and ethoxy derivatives of the above conjugated dienes e.g. 2 methoxybutadiene and 3-ethoxy-1,3-butadiene.
The preferred polymerizable vinyl substituted hetero-cyclic bases employed in this invention are those in which the hetero atom is nitrogen, particularly preferred are those of the pyridine, quinoline, and isoquinoline series which are copoly-merizable with a conjugated diene and contain one and only one CH2= C substituent and preferably the group is CH2=C R
where R is either a hydrogen or a méthyl group. That is, the substituent is either a vinyl or an alphamethylvinyl (isopropenyl) group. Of these compounds, the pyridine derivatives are pre-ferred. Various substituted derivatives are also applicable but the total number of carbon atoms in the nuclear substituted groups, for example, alkyl groups, should suitably not be greater than 15 because the polymerization ra-te decreases somewhat with increasing size of the alkyl group Compounds where the alkyl substituents are methyl and/or ethyl are available commercially and are preferred in this invention.
The preferred class of heterocyclic nitrogen bases have the formulae R R R and R R

R~ R ~ ~ ~ R R ~R

R N --R R ~:

R R R

where R is selected from the group consisting of hydrogen, alkyl vinyl, alpha-methylvinyl, alkoxy, halo, hydroxy, cyano, aryloxy, aryl and combinations of these groups, for example halo~alkyl, - :107558~
alkylaryl hydroxyaryl, and the like, one and only one of the groups being of the type CH2=C = and preferably being a vinyl or alpha-methyl vinyl group; and the total number of carbon atoms in the nuclear substituted groups being not greater than 15, As has been indicated, the preferred compounds are those wherein the R groups, other than the vinyl or alphamethylvinyl group, are hydrogen or alkyl of 1 to 4 carbon atoms. Examples of such compounds are 2-vinyl pyridine; 2-vinyl-5-ethylpyridine; 2-methyl-5-vinylpyridine; 4-vinyl pyridine; 2,3,4-trimethyl-5-vinylpyridine; 3,4,5,6 tetramethyl-2-vinylpyridine, 3-ethyl-5-vinylpyridine; 2,6-diethyl-4-vinylpyridine; 2-isopropyl-4-nonyl-5-vinylpyridine; 2-methyl-5-undecyl-3-vinylpyridine, 2-decyl-5-(alpha-methylvinyl)pyridine; 2-vinyl-3-methyl-5-ethyl-pyridine;

2-methoxy-4-chloro-6-vinylpyridine; 3-vinyl-5-ethoxypyridine 2-vinyl-4,5-dibromopyridine; 2-vinyl-4-chloro-5-bromopyridine 2(alpha-methylvinyl)-4-hydroxy-6-cyanopyridine; 2-vinyl-4-phenoxy-5-methylpyridine; 2-cyano-5-(alpha-methylvinyl)pyridine;

3-vinyl-5-phenyl pyridine; 2-(paramethylphenyl)-3-vinyl-4-methylpyridine, 3-vinyl-5-(hydroxyphenyl)pyridine; 2-vinylquino-line; 2-vinyl-4-ethylquinoline; 3-vinyl-6,7-di-n-propyl quinoline;
2-methyl-4-nonyl-6-vinylquinoline; 4(alpha-methylvinyl)-8-dodecyl quinoline; 3-vinylisoquinoline; 1,6-dimethyl-3-vinylisoquinoline;
2-vinyl-4-benzyl-quinoline; 3-vinyl-5-chloroethylquinoline;
3-vinyl-5,6-dichloroisoquinoline; 2-vinyl-6-ethoxy-7-methyl-quinoline; 3-vinyl-6-hydroxymethylisoquinoline; and the like.
Interpolymers can be prepared from a mixture of two of the previously mentioned conjugated dienes and a vinyl substitu-ted hetrocyclic base or from a conjugated diene and two different vinyl substituted heterocyclic bases. It is, however, more common to prepare interpolymers from a single conjugated diene, a single vinyl substituted heterocyclic baseand at least one other poly-merizable monomer. The latter monomer comprises an organic 10755B~

compound containing at least one polymerizable ethylenic group of the type ~ C=C = , These compounds are well known in the art and include, for example, the alkenes, alkadienes, and the styrenes, for example, ethylene, propylene, l-butylene-2-butylene, isobutylene, l-octene, 1,4-pentadiene, 1,6-hexadiene, 1,7-octadiene, vinyltoluene, vinylxylene, ethylvinylbenzene, vinyl-cumene, l,5-cyclooctadiene, cyclohexene, cyclooctene, benzyl-styrene, chlorostyrene, bromostyrene, fluorostyrene, trifluoro-: methylstyrene, iodostyrene, cyanostyrene, nitrostyrene, N,N-dimethylaminostyrene, 3-phenyl-3-butene-1-ol, p-methoxystyrene, vinyl naphthalene, acetoxystyrene, methyl 4-vinylbenzoate, phenoxystyrene, p-vinylphenyl ethyl ether, and the like, the acrylic and substituted acrylic monomers such as methyl acrylate, ethyl acrylate, methyl methacrylate, methacrylic anhydride, acrylic anhydride, cyclohexyl methacrylate, benzyl methacrylate, isopropyl methacrylate, octyl methacrylate, acrylonitrile, methacrylonitrile, methyl alpha-chloroacrylate, ethyl alpha-ethoxy-acrylate, methyl alpha-acetamidoacrylate, butyl acrylate, ethyl alpha-cyanoacrylate, 2-ethylhaxyl acrylate, phenyl acrylate, phenyl methacrylate, alpha-chloroacrylonitrile, ethyl :
methacrylate, butyl methacrylate, methyl ethacrylate, methacryl-amide, N,N-dimethyl-acrylamide, N,N-dibenzylacrylamide, N-butylacrylamide, methacrylyl formamide, and the like; the vinyl esters, vinyl halides, vinyl ethers, vinyl ketones, etc. such as vinyl acetate, vinyl chloroacetate, vinyl butyrate, isopropenyl acetate, vinyl formate, vinyl acrylate, vinyl methacrylate, vinyl methoxy acetate, vinyl benzoate, vinyl iodide, vinyl chloride, vinyl bromide, vinyl fluoride, vinylidene chloride, vinylidene cyanide, vinylidene bromide, l-chloro-l-fluoroethylene, vinyli-dene fluoride, vinyl methyl ether, vinyl ethyl ether, vinyl propyl ethers, vinyl butyl ethers, vinyl 2-ethyl-hexyl ether, ` vlnyl phenyl ether, vinyl 2-methoxyethyl ether, vinyl 2-butoxy-la7ss~l ethyl ether, 3,4-dihydro-1,2-pyran, 2-butoxy-2'-vinyloxy diethyl ether, vinyl 2-ethylmercaptoethyl ether, vinyl methyl ketone, vinyl ethyl ketone, vinyl phenyl ketone, vinyl ethyl sulfide, vinyl ethyl sulfone, N-vinyloxazolidinone, N-methyl-N-vinyl acetamide, N-vinylpyrrolidone, vinyl imidazole, divinyl sulfide, divinyl sulfoxide, divinyl sulfone, sodium vinyl sulfonate, methyl vinyl sulfonate, N-vinyl pyrrole, and the like, dimethyl fumarate, vinyl isocyanate, tetrafluoroethylene, chloro-tri-fluoroethylene, nitroethylene, vinyl furane, vinyl carbazole, vinyl acetylene, and the like.
The function of the additional monomer can be merely that of cost reduction with little or no influence on the bond strength and other properties of the adhesive or it may be in-corporated to modify a specific property of the adhesive. An example of this would be the incorporation of monomers, for example, nitriles, esters, amides, etc., that would increase the polarity of the adhesive to make it more compatible with rubbers o~ higher polarity. Such modifications can easily be made by those skilled in the art and are considered to lie within the scope of this invention.
The compounded rubbers that may be bonded by the afore-mentioned interpolymers include natural and synthetic rubbers and their blends having a fairly high degree of unsaturation, i.e.
having a minim-~m of about 70 mole per cent polymerized conjugated diene, Examples of suitable synthetic rubbers are polybutadiene, polyisoprene, copolymers of butadiene with styrene or acrylo-nitrile, polychloroprene etc.
These rubbers are conventionally compounded with one or more fillers, plasticizers, curatives and antioxidants. The total amount of filler used is generally in the range of 25 to 150 parts by weight per 100 parts by weight o~ rubber. Fillers include the various silicas, clays, calcium carbonate, calcium .:

:~0755~3I

silicate, titanium dioxide and carbon black, In preparing com-pounded stocks to be employed in the fabrication of tires, it is generally preferred that at least a portion of the filler be carbon black. The plasticizers are generally used in amounts ranging from 1.0 to 100 parts by weight of plasticizer per 100 parts by weight of rubber. The amount of plasticizer actually used will depend upon the softening effect desired. Examples of suitable plasticizers include aromatic extract oils, petroleum softeners including asphaltenes, saturated and unsaturated hydrocarbons, and nitrogen bases, coal tar products, cumarone- -indene resins, and esters, for example, dibutyl phthala-te, and tricresyl phosphate. It is to be understood that mixtures of these plasticizers can be employed. The curatives used in the curing system include a vulcanizing agent, and generally one or more vulcanization accelerators together with one or more accelerator activators, The amount of these materials used in the system generally falls in the following ranges: 0.5 to 5.0 parts by weight of the vulcanizing agent, 0.5 to 3.0 parts by weight of the accelerator, 0.5 to 20,0 parts by weight of the accelerator activator, all ranges being based on 100 parts by ~ weight of rubber. Examples of suitable vulcanizing agents are - sulfur, sulfur-liberating agents, for example, thiuram disulfide, a thiuram polysulfide, or an alkylphenolsulfide, or a peroxide, for example, dicumyl peroxide, or dibenzoyl peroxide. When peroxide compounds are used as vulcanizing agents, the accelera-; tor and the accelerator activator are frequently unnecessary.
Vulcanization accelerators which can be used include dithio-carbamates, thiuram sulfides, and mercaptobenzothiazoles.
Examples of specific compounds which are suitable vulcanization accelerators include zinc diethyl-dithiocarbamate. N,N-di-- , methyl-S-tert-butylsulfenyldithiocarbamate, tetramethylthiuram disulfide, 2,2'-dibenzothiazyl disulfide, butyraldehyde-aniline, , ~075581 mercaptobenzothiazole, N-oxydiethylene-2-benzothiazole sulfen-amide, and N-cyclohexy-2-benzothiazole sulfenamide. Materials used in the compounding which function as an accelera~or acti-vator include metal oxides, for example, zinc oxide, magnesium oxide and litharge, which are used in conjunction with an acidic material, for example, a fatty acid, for example, stearic acid, oleic acid, myristic acid, and the like. Rosin acids can also be employed as the acidic material, An antioxidant is usually included in the compounding recipe in an amount ranging, for example, from 0.5 to 3.0 parts by weight per 100 parts by weight of rubber. Examples of suitable antioxidants include phenyl-~-naphthylamine, di-tert-butylhydroquinone, 2,2,4-trimethyl-6-phenyl-1,2-dihydroquinoline, a physical mixture of a complex diaryl-amine-ketone reaction product and M,N'-diphenyl-p-phenylene diamine, and the like, It is t~ be understood that it is not intended to limit the invention to any particular compounding recipe for the invention is broadly applicable to the use of conjugated diene, vinyl substituted heterocyclic base copolymer adhesives to bond a wide range of compounded rubber formulations to iron or steel surfaces.
The Cu treatment plus the adhesives of this invention exhibit useful adhesion on ferrous (steel and iron) surfaces that have been degreased and freed of any weakly adherent oxide coatings, preferably by etching.
The adhesive is coated on the Cu++ treated surface by any of the usual methods, for example, dipping, brushing, spray-ing etc., and is then dried briefly at room temperature or by the application of heat to remove solvents and/or water, The compounded rubber stock is then contacted with the adhesive ~;~
surface and the whole assembly vulcanized with heat and pressure to complete the bonding process.

, --` 1075581 It is to be understood that is is not intended to limit the invention to any particular rubber compounding recipe, for the invention is broadly applicable to a wide range of compounded rubber formulations yielding high bond strengths through the Cu++
treatment of the metal surface followed by the conjugated diene vinyl substituted heterocyclic base copolymer or interpolymer.
The most surprising fact is that, during the vulcaniz-ation, the combination of the weakly adherent Cu-layer and afore-mentioned interpolymer layer can be converted into a vexy tight bond. The mechanism is not understood.
The properties of the interpolymer of the adhesive can be modified, e.g., tackiness, hardness, and oxidation stability, by adding one or more or a combination of plasticizers, fillers, curatives and antioxidants prior to the application to the metal surface.
The invention will be better understood by reference to the following illustrative exam~les, wherein all parts are by weight, and which are not intended to be construed as limiting the scope of the invention.
~ Further the invention is illustrated by reference to the drawings which illustrates graphically the relation between adhesion strength and heat aging time for the present invention and the prior art.
Example 1 (a) Steel bead wires (d=0.96mm) were solvent degreased, etched for 20 seconds in concentrated hydrochloric acid at 55C, rinsed in water, dipped first into a 5% aqueous cupric chloride solution for 5 seconds, rinsed in water and then dipped into a butadiene, styrene, 2-vinyl pyridine polymer latex [Composi~ion 70:15:15 weight percent, 12% resin solids (Adhesive Latex No. 1)]
and then dried at 170C for 60 seconds. The coated bead wires .

`` 1~7558~

were then vulcanized in an H-test mold under 60 kg/cm2 pressure at the indicated times and temperatures with the given rubber formulations, The vulcanized samples were allowed to relax for 24 hours at room temperature, then placed into an oven at 120C
for twenty minutes, then tested at 120C.
The H-test employed in this and other examples is con-ducted by vulcanizing the coated wire under a pressure of 60 kg/cm2 into the center of two blocks of rubber each having a width and length of 2 cm and a thickness of 1 cm. The two blocks are separated by a distance of 2.5 cm; the wire is embedded 2 cm into each block, the total wire length being 6.5 cm. The blocks are pulled apart at 200 mm per minute lineally with the wire axis until the wire is extracted from one of the blocks.
A sample prepared as above described was compared with samples prepared under identical conditions but where in one case the wire was only etched, in another case the wire was etched and copper coated but no adhesive was used, and in a third case where the wire was etched and coated with the Adhesive Latex No. 1 but without having been first copper coated.

Rubber Formulation No. 1 Natural Rubber 100 Carbon Black HAF* 50 Sulfur 5 Pine Tar 3 Stearic Acid ~-Phénylnaphthylamine Zinc Oxide 8 2-Mercaptobenzothiazole 1.5 _ _ .
Total: 169.5 ==================== ':

*ASTM N330 High Abrasion Furnace Carbon Vulcanization Time: 30 minutes Vulcanization Temperature:135C

Adhesion Condition kg/2 cm ~ 120C
Etched Wire 5 Etched wire & Copper coating 12 Etched wire & Adhesive latex No. 1 10 Etched wire & Copper coating & Adhesive latex No. 1 56 Steel bead wires were solvent degreased, electrolytic-ally etched for 5 seconds in 25% sulfuric acid at room tempera-ture at a current density of 0.5 Amp/cm2, washed with water, dipped into an aqueous solution of cupric chloride, washed with water, coated with Adhesive latex No. 2 (Composition butadiene, 2-vinyl pyridine 85:15 weight percent, 12% resin solids), dried at 120C for 45 seconds and bonded with Rubber Formulation No. 2, The tests of Example l(a) were repeated.

- 1~75581 Rubber Formulation No. 2 Natural Rubber 100 Carbon Black HAF 50 Sulfur 5 Pine Tar 3 Stearic Acid ~-Phenylnaphthylamine Cobalt napthenate 2.5 Zinc Oxide 8 2-Mercaptobenzothiazole 1.5 ~' ~
Total 172 0 Vulcanization Time: 30 minutes Vulcanization Temperature: 135C

Adhesion Condition kq/2 cm ~120C
Etched wire only 16 Etched wire & Copper coating 15 Etched wire & Adhesive latex No. 2 21 Etched wire & Copper coating & Adhesive latex No. 2 72 (c) Steel bead wires were treated as in Example l(b), and bonded to Rubber Formulation No. 1 and tested as described above.
Adhesion Condition kq/2 cm @ 120C
Etched wire 5 Etched wire & Copper coating 11 Etched wire & Adhesive latex No. 2 16 Etched wire & Copper coating & Adhesive latex No. 2 69 . . .

Example 2 This example clearly illustrates that the present invention may utilize a wide variety of elastomers of various formulations~ Steel bead wires were treated as in Example l(a), two adhesive polymers were utilized, Adhesive latex No. 1 (Composition butadiene, styrene, vinyl pyridine, 70:15:15 at 12% resin solids) and Adhesive latex No. 3 (Composition butadiene, 2-vinyl pyridine, 90:10 weight percent at 12% resin - solids), both of which coatings were dried at 170C for 60 seconds.
Again, the synergistic effect of copper plus the vinyl pyridine modified interpolymer adhesive is evident even though the rubber compositions are varied in either elastomer or filler content. See the following Tables 1 and 2.
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m m ~ ~ ~ ,, zrl ~ ~ -~ ~ ~ - X
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1C~75581 Natural ~ubber (Table lJ continued .
Adhesion kg/2 cm @ 120C :~.
.
._ __ . _ _ . .

etched wire 5 9 8 10 9 7 5 *
Etehed wire & Copper eoating12 15 151311 10 14 *
Etched wire & Adhesive latex #110 9 1211 10 16 14 *
Etched wire & Adhesive latex #3 8 131214 18 9 11 * ~::
Etehed wire & Copper coating &
: Adhesive latex 1/1 56 47 46 444145 49 Etched wire & Copper eoating &
Adhesive latex ~3 50 53 48 454740 47 . .
* Controls 1) ASTM S-301 Medium Proeess Channel 2) ASTM N-330 High Abrasion Furnace 3) 2-Mercaptobenzothiazole ` 4) 2-Benzothiazyl-S-2, 4-dinitrophenyl-thioether : - 22 -,, :-, ' ':

~075581 Synthetic Rubbers (Table 2) Formulation 8 9 10 11 Polybutadiene 100 100 Polyisoprene 100 Styrene-butadiene 100 Carbon Black MPC 70 70 Carbon Black HAF 70 70 Sulfur 3.5 1.5 3.5 1.5 Pine Tar 4 4 Stearic Acid 2 2 ~-Phenylnaphthylamine 1 1 Cobalt naphthenate 5 Zinc Oxide 10 5 10 5 AcceleratOr Dm 5)/Cz 6) 0.5/0.5 0.5/0.5 Accelerator NOBG ) 1 1.3 . _ . Total: 194,5179.5 189.5 179.8 :' _ .
Vulcanization Time, Minutes 30 30 30 30 ; Temperature, C 155 155 155 155 - ~075581 : Synthetic Rubbers (Table 2) continued Adhesion ~ - __ kg/2 cm @ 120C

Etched wire 7 5 10 5 * :~
Etched wire & Copper coating 10 8 12 11 : :
Etched wire & Adhesive latex #1 14 12 14 7 *
Etched wire & Adhesive .
. latex ~3 13 10 18 9 *
Etched wire & Copper coating :
& Adhesive latex ~1 48 41 47 38 . Etched wire & Copper coating .
. Adhesive latex #3 46 39 58 33 * Controls 5) Dibenzothiazyl disulfide 6) Cyclohexyl-benzothiazyl Sulfenamide (manufacturer's designation) 7) N-oxydiethylene benzothiazyl-2-Sulfenamide (manufacturer's designation) ., . : , .

Example 3 Steel bead wires were treated as in Example l(a) except that adhesive latices with varying amounts of vinyl pyridine were utilized, the adhesive coated wires which were vulcanized with Rubber Formulation No. 1 were dried at 170C for 60 seconds (Table 3) and the adhesive coated wires which were vulcanized with Rubber Formulation No. 2 were dried at 120C
for 45 seconds, (Table 4).

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- 1~75581 Adhesive latex No. 4, which contains no vinyl pyridine, was used as the control in the above tests. The optimum range of vinyl pyridine content is approximately 1 to 25 weight % for this series of latices.

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o , Adhesive latex No. 10, which contains no vinyl pyridine, was used as the control. The optimum range of vinyl pyridine con-tent is approximately 1 to 35 weight % for this series of latices.
Example 4 This example illustrates the invention utilizing a variety of interpolymer compositions as the adhesive.
Steel bead wires were treated as in Example l(a) except that adhesive latices with varying amounts of butadiene and styrene were utilized, the adhesive coated wires were dried at 120C for 45 seconds and bonded to Rubber Formulation No. 2.
Table 5 Adhesive latex~11# 2~13 ~1#18~ 19~20 . . .
Monomer Weight % _ _ 1,3-Butadiene 98 85 84 7060 50 40 Styrene 1 0 1 1525 35 45 2-Vinyl pyridine 1 15 1515 15 15 15 :

Adhesion _ kg/2 cmC~120C39 74 72 5945 45 20 . .
Example 5 Steel bead wires were treated as in Example l(a) except that various monomers were utilized in the adhesive coating resin, the coated wires were dried at 120C for 45 seconds and bonded with Rubber Formulation No. 2, .'-- - ' , ' .

1~7S581 Table 6 Adhesive Latex#21 ~22 #23 # 24 #25 Monomer Weight %

1, 3-Butadiene 80 80 80 74 Isoprene 80 2-Vinyl pyridine15 15 15

4-Vinyl pyridine 15 2-Methyl-5-Vinyl pyridine 10 Styrene 5 5 16 Methyl methacrylate 5 Acrylonitrile 5 . .
Adhesion kg/2 cm @ 120C 50 52 55 73 48 .

Example 6 This example demonstrates the superiority of the heat aging of the present invention in vulcanized rubber over the heat aging of brass in vulcanized rubber.
Steel bead wire was etched as in Example l(a), dipped into an aqueous 5% cupric chloride solution, rinsed with water, coated with Adhesive latex #l (Composition: butadiene, styrene, vinyl pyridine 70:15:15 weight percent, 12% resin solids), dried at 120C for 45 seconds and vulcanized with Rubber Formulation ~ 2, Conventionally produced brass samples were vulcanized in the same mold alternating with samples of the present invention.
The molded samples were allowed to relax for 24 hours at room temperature, then put into a forced air draft oven at 120C for .
the indicated time, at which point the samples were removed from the oven, allowed to relax for 24 hours at room temperature and then tested at 120C. -Adhesion strength was plotted versus heat aging time and is illustrated in the drawing figure.
The brass samples lost about 55% of their bond strength in a period of 48 hours at 120C, all samples showing varying percentages of bare metal along with rubber failure. The samples of the present invention did not show any adhesive fàilure but only a cohesive failure in the rubber. me latter loss is approximately 27% for this rubber over the 48 hour period plotted.
Example 7 Heat aging samples were prepared as in Example 6 except that Adhesive latex #2 was used in the place of Adhesive latex #1, Rubber Formulation #2 was used for sample preparation.
Similar results were obtained, with adhesion strength at 170C
declining over 48 hours from about 70 kg/2 cm to about 52 kg/2 cm for the samples of the present invention while the brass samples showed-a decline from about 56 kg/2 cm to about 26 kg/2 cm.
The brass samples lost about 55% of their bond strength in a period of 48 hours at 120C, all samples showing varying percentages of bare metal along with rubber failure. The samples of the present invention did not show any adhesive failure, but only a cohesive failure in the rubber. The latter loss is approximately 27% for this rubber over the 48 hour period.
Example 8 Heat aging samples were prepared as in Example 6 except that Adhesive latex #2 was used in the place of Adhesive latex #1 and Rubber Formulation ~12 was utilized for sample pre-paration, 10755~3~

Rubber Formulation 12 Natural Rubber 60 Styrene-Butadiene Rubber40 Carbon Black HAF 120 Sulfur 5 Stearic Acid Zinc Oxide 3 Process Oil 20 Dibenzothiazyl disulfide Total: 250 _________________ _________________ Vulcanization ~ime: 30 minutes Vulcanization Temperature: 145C

Again, similar results were obtained with adhesion strength at 120C declining over 96 hours from about 57 kg/2 cm to about 43 kg/2 cm for the samples of the present invention, while the brass samples showed a decline from about 54 kg/2 cm to about 20 ~g/2 cm.
The brass samples lost about 64% of their bond strength in a period of 96 hours at 120C, all samples showing varying percentages of bare metal along with rubber failure. The samples of the present invention did not show any adhesive failure but only a cohesive failure in the rubber, The latter loss is approximately 26% for this rubber over the 96 hour period.
Example 9 The process of Example 1 was followed using Rubber Formulation ~1 and Adhesive latex ~2 with the dip time of the wire in the cupric chloride being varied. The results were as follows:

,, `- 1075581 Table 7 dip time (seconds) in 5% ¦ ~ _ CuC12 soln ~ 1 3 ~ 7 0 H-Test results (Kg/2 cm l at 120C) 56 ~ 44 10 .

Example 10 Example 9 was repeated except instead of dipping in

5% CuC12 2H20 solution, the following solutions and times were used.

Table 8 _ . ., # of test . _ _ conc. of aq. sol'n 5% CuBr2 dip time (sec.) 2 H-Test result Kg/2 cm at 120C 44 .
Example 11 Example 10 was repeated, using the following copper salt solutions and dipping times for Rubber Formulation No. 2 and Adhesive latex No. 3. The same procedures of coating and drying as in Example 10 were used.

Table 10 . . :
.._ Experiment Adhesion Kg/2cm at 120C
_ 1 etched wire 7 .. _ . . .. ..

2 etched wire and electxoplated copper 15 _ ............ ._ .

3 etched wire and adhesive latex #.1 17 . .
4 etched wire and electroplated copper and adhesive latex ~'1 60 ...__ This Example illustrates that the means of copper deposition is not restricted to any one method for the working of this invention.
As many possible embodiments may be made of this in-vention without departing from the scope thereof, it is to be understood that all matter herein set forth is to be interpreted as illustrative and not as unduly limiting the invention.

.. .

~ 1075581 The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for bonding rubber to a ferrous metal substrate which comprises depositing a copper coating onto said ferrous metal substrate by deposition from a solution of a cupric salt, applying an adhesive thereover, said adhesive comprising an interpolymer containiny about 50 to about 99% by weight of a conjugated diene, about 1-45% by weight of a vinyl substituted heterocyclic base and O to about 40% by weight of~ -at least one additional copolymerizable monomer which contains at least one polymerizable ethylenic group to a total of 10~/o~
thereafter contacting said adhesive with a rubber to be bonded and bonding said rubber to said adhesive, after which the whole assembly is vulcanized with heat and pressure.

2. A process according to claim 1 wherein said layer of copper is deposited by electroless deposition from a solution of a cupric salt, said solution containing halide ions therein.

3. A process according to claim 2 wherein said bonding is carried out by heat and pressure and said heterocyclic base includes nitrogen as hetero atom.

4. A process according to claim 2 or 3 wherein said deposition of copper is effected by dipping the said ~errous metal substrate in said solution for less than sixty seconds.

5. A process according to claim 2 or 3 wherein said solution is a solution of cupric bromide or cupric chloride.

6. A process according to claim 1, 2 or 3 wherein said conjugated diene is a hydrocarbon containing 4 to 8 carbon atoms, a halogen-substituted hydrocarbon containing 4 to 8 carbon atoms or a lower alkoxy-substituted hydrocarbon containing 4 to 8 carbon atoms . .

Claims

7, A process according to claim 1, 2 or 3 wherein said vinyl substituted heterocyclic base has the formula or wherein R is selected from the group consisting of hydrogen, alkyl, vinyl, alpha-methylvinyl, alkoxy, halo, hydroxy, cyano aryloxy, aryl, halo-alkyl, hydroxy alkyl, alkoxy-alkyl, cyano-alkyl, halo aryl, alkoxy aryl, hydroxy aryl, cyano aryl, and alkyl aryl, one of said R's having the formula and the total number of carbon atoms in each R substituent being not greater than 15.

8. A process according to claim 1, 2 or 3 wherein said heterocyclic base is selected from the group consisting of 2-vinyl pyridine; 2-vinyl-5-ethylpyridine; 2-methyl-5-vinyl-pyridine; 4-vinyl pyridine; 2,3,4-trimeth,1-5-vinylpyridine;
3,4,5,6 tetramethyl-2-vinylpyridine; 3-ethyl-5-vinylpyridine;
2,6-diethyl-4-vinylpyridine, 2-isopropyl-4-nonyl-5-vinylpyridine;
2-methyl-5-undecyl-3-vinylpyridine; 2-decyl-5-(alpha-methylvinyl) pyridine; 2-vinyl-3-methyl-5-ethyl-pyridine; 2-methoxy-4-chloro-6-vinylpyridine; 3-vinyl-5-ethoxypyridine; 2-vinyl-4,5-dibromopyridine; 2-vinyl-4-chloro-5-bromopyridine; 2(alpha-methylvinyl)-4-hydroxy-6-cyanopyridine; 2-vinyl-4-phenoxy-5-methylpyridine; 2-cyano-5-(alpha-methylvinyl)pyridine, 3-vinyl-5-phenyl pyridine; 2-(paramethylphenyl)-3-vinyl-4-methylpyridine;

3-vinyl-5-(hydroxyphenyl)pyridine; 2-vinylquinoline; 2-vinyl-4-ethylquinoline; 3-vinyl-6,7-di-n-propyl quinoline; 2-methyl-4-nonyl-6-vinylquinoline; 4(alpha-methylvinyl)-8-dodecyl quinoline;

3-vinylisoquinoline; 1,6-dimethyl-3-vinylisoquinoline; 2-vinyl-4-benzyl-quinoline, 3-vinyl-5-chloroethylquinoline, 3-vinyl-5,6-dichloroisoquinoline, 2-vinyl-6-ethoxy-7-methylquinoline and 3-vinyl-6-hydroxymethylisoquinoline.

9, A process according to claim 1, 2 or 3 wherein said rubber is selected from the group consisting of natural rubber, polybutadiene, polyisoprene, copolymers of butadiene with styrene, copolymers of butadiene with acrylonitrile, and poly-chloroprene.

10. A process according to claim 1, 2 or 3 wherein said interpolymer is a copolymer of butadiene and 2-vinyl pyridine.

11. A process according to claim 1, 2 or 3 wherein said interpolymer contains said additional monomer, said monomer being an organic compound containing at least one polymerizable ethylenic group.

12. A process according to claim 1, 2 or 3 wherein said interpolymer contains said additional monomer, said monomer being selected from the group consisting of styrene, 3-phenyl-3-butene-l-ol, p-chlorostyrene, p-methoxy-styrene, alpha-methyl styrene, vinyl naphthalene, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, methyl ethacrylate, acrylonitrile, methacrylonitrile, methacryl-amide, methyl isopropyl ketone, methyl vinyl ketone, methyl vinyl ether, vinyl acetate, vinyl chloride, vinylidene chloride, vinyl furane, vinyl carbazole, and vinyl acetylene.

13. A process according to claim 1, 2 or 3 wherein said interpolymer is a terpolymer of styrene, butadiene and 2-vinyl pyridine.

14. A process according to claim 1, 2 or 3 wherein said interpolymer is a terpolymer of 2-vinyl pyridine, isoprene and styrene.

15. A process according to claim 1, 2 or 3 wherein said interpolymer is a terpolymer of 4-vinyl pyridine, butadiene and styrene.

16. A process according to claim 1, 2 or 3 wherein said interpolymer is a terpolymer of 2-methyl-5-vinyl pyridine, butadiene and styrene.

17. A laminated article comprising a ferrous metal sub-strate having a loosely adherent deposit of copper thereon, a layer of adhesive over said copper and rubber bonded through said copper and adhesive to said ferrous metal substrate, said adhesive comprising an interpolymer containing about 50 to about 99% by weight of a conjugated diene, about 1-45% by weight of a vinyl substituted heterocyclic base and 0 to about 40% by weight of at least one additional copolymerizable monomer, to a total of 100%.

18. A laminated article according to claim 17 wherein said base contains nitrogen as hetero atom.

19. A laminated article according to claim 17 or 18 wherein, said conjugated diene is a hydrocarbon containing 4 to 8 carbon atoms, a halogen-substituted hydrocarbon containing 4 to 8 carbon atoms or a lower alkoxy-substituted hydrocarbon containing 4 to 8 carbon atoms.

20. A laminated article according to claim 17 or 18 wherein, said vinyl substituted heterocyclic base has the formula or wherein R is selected from the group consisting of hydrogen, alkyl, vinyl, alpha-methylvinyl, alkoxy, halo, hydroxy, cyano, aryloxy, aryl, halo-alkyl, hydroxy alkyl, alkoxy-alkyl, cyano-alkyl, halo aryl, alkoxy aryl, hydroxy aryl, cyano aryl, and alkyl aryl, one of said R's having the formula and the total number of carbon atoms in each R substituent being not greater than 15.

21, A laminated article according to claim 17 or 18 wherein, said heterocyclic base is selected from the group consisting of 2-vinyl pyridine, 2-vinyl-5-ethylpyridine, 2-methyl-5-vinyl-pyridine, 4-vinyl pyridine; 2,3,4-trimethyl-5-vinylpyridine, 3,4,5,6 tetramethyl-2-vinylpyridine; 3-ethyl-5-vinylpyridine 2,6-diethyl-4-vinylpyridine; 2-isopropyl-4-nonyl-5-vinylpyridine, 2-methyl-5-undecyl-3-vinylpyridine; 2-decyl-5-(alpha-methylvinyl) pyridine, 2-vinyl-3-methyl-5-ethyl-pyridine, 2-methoxy-4-chloro-6-vinyl-pyridine, 3-vinyl-5-ethoxypyridine, 2-vinyl-4,5-dibromopyridine, 2-vinyl-4-chloro-5-bromopyridine, 2(alpha-methylvinyl)-4-hydroxy-6-cyanopyridine, 2-vinyl-4-phenoxy-5-methylpyridine, 2-cyano-5-(alpha-methylvinyl)pyridine, 3-vinyl-5-phenyl pyridine, 2-(para-methylphenyl)-3-vinyl-4-methylpyridine 3-vinyl-5-(hydroxyphenyl)-pyridine, 2-vinylquinoline, 2-vinyl-4-ethylquinoline, 3-vinyl-6,7-di-n-propyl quinoline, 2-methyl-4-nonyl-6-vinylquinoline, 4(alpha-methylvinyl)-8-dodecyl quinoline 3-vinylisoquinoline, 1,6-dimethyl-3-vinylisoquinoline, 2-vinyl-4-benzyl-quinoline, 3-vinyl-5-chloroethylquinoline, 3-vinyl-5,6-dichloroisoquinoline, 2-vinyl-6-ethoxy-7-methylquinoline and 3-vinyl-6-hydroxymethylisoquinoline.