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Title:
AQUEOUS ADHESIVE
Document Type and Number:
WIPO Patent Application WO/1999/002583
Kind Code:
A1
Abstract:
An aqueous adhesive composition for bonding a metal substrate to an elastomeric substrate that includes an aqueous dispersible or soluble phenolic resole, at least one aromatic nitroso compound or aromatic nitroso compound precursor and at least one halogenated polyolefin.

Inventors:
Mowrey, Douglas H. (229 Parallel Street, Pleasantville, PA, 16341, US)
Application Number:
PCT/US1998/013762
Publication Date:
January 21, 1999
Filing Date:
June 30, 1998
Export Citation:
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Assignee:
LORD CORPORATION (111 Lord Drive, P.O. Box 8012 Cary, NC, 27512-8012, US)
International Classes:
C08J5/12; C09J111/02; C09J115/02; C09J123/28; C09J123/34; C09J161/06; C08L7/00; C08L9/00; C08L11/00; C08L23/28; C08L25/10; C08L27/06; C08L29/04; C08L61/00; (IPC1-7): C08J5/12; C09J111/02; C09J115/02; C09J123/28; C09J161/06
Attorney, Agent or Firm:
Rupert, Wayne W. (Lord Corporation, 111 Lord Drive P.O. Box 801, Cary NC, 27512-8012, US)
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Claims:
Claims What is claimed is:
1. An aqueous adhesive composition comprising: (a) an aqueous dispersible or soluble phenolic resole; (b) at least one aromatic nitroso compound or aromatic nitroso compound precursor; and (c) at least one halogenated polyolefin.
2. An adhesive composition according to claim 1 wherein the phenolic resole comprises a polyvinyl alcoholstabilized aqueous dispersion of a phenolic resole.
3. An adhesive composition according to claim 1 wherein the aromatic nitroso compound is a dinitrosobenzene.
4. An adhesive composition according to claim 1 wherein the aromatic nitroso compound precursor is a quinone compound derivative.
5. An adhesive composition according to claim 1 wherein the halogenated polyolefin is selected from the group consisting of chlorinated natural rubber, polychloroprene, chlorinated polychloroprene, chlorinated polybutadiene, hexachloropentadiene, butadiene/halogenated cyclic conjugated diene adduct, chlorinated butadiene styrene copolymer, chlorinated ethylene propylene copolymer, ethylene/propylene/non conjugated diene terpolymer, chlorinated polyethylene, chlorosulfonated polyethylene, poly(2,3dichloro 1 ,3butadiene), brominated poly(2,3dichloro 1 ,3butadiene), copolymer of othaloacrylonitrile and 2,3dichloro1,3butadiene, and chlorinated poly (vinyl chloride).
6. An adhesive composition according to claim 1 wherein the phenolic resole comprises a polyvinyl alcoholstabilized aqueous dispersion of a phenolic resole and is present in an amount of 10 to 60 % dry weight, the aromatic nitroso compound is a dinitrosobenzene and is present in an amount of 5 to 40 % dry weight, and the halogenated polyolefin is selected from the group consisting of chlorosulfonated polyethylene and copolymer of Ct haloacrylonitrile and 2,3dichloro1,3butadiene and is present in an amount of 20 to 80 % dry weight, wherein the % dry weight is based on the primary components of the adhesive composition.
7. A method for bonding an elastomeric substrate to a coil metal substrate comprising: (a) applying an aqueous adhesive composition to the coil metal substrate wherein the adhesive composition includes (i) an aqueous dispersible or soluble phenolic resole; (ii) at least one aromatic nitroso compound or aromatic nitroso compound precursor; and (iii) at least one halogenated polyolefin; and (b) contacting the resulting adhesive coatedmetal substrate with the elastomeric substrate under conditions sufficient to bond the metal substrate to the elastomeric substrate.
8. A method according to claim 7 wherein the phenolic resole comprises a polyvinyl alcoholstabilized aqueous dispersion of a phenolic resole, the aromatic nitroso compound is a dinitrosobenzene and the halogenated polyolefin is selected from the group consisting of chlorinated natural rubber, polychloroprene, chlorinated polychloroprene, chlorinated polybutadiene, hexachloropentadiene, butadiene/halogenated cyclic conjugated diene adduct, chlorinated butadiene styrene copolymer, chlorinated ethylene propylene copolymer, ethylene/propylene/non conjugated diene terpolymer, chlorinated polyethylene, chlorosulfonated polyethylene, poly(2,3dichloro 1 ,3butadiene), brominated poly(2,3dichloro 1 ,3butadiene), copolymer of ahaloacrylonitrile and 2,3dichloro 1 ,3butadiene, and chlorinated poly (vinyl chloride).
9. A method according to claim 7 wherein the phenolic resole is present in an amount of 10 to 60 % dry weight, the aromatic nitroso compound is present in an amount of 5 to 40 % dry weight, and the halogenated polyolefin is present in an amount of 20 to 80 % dry weight.
Description:
AQUEOUS ADHESIVE Background of the Invention The present invention relates to an aqueous adhesive for bonding a rubber or elastomeric substrate to a metal substrate, particularly a metal substrate that requires an unusually flexible, but robust adhesive.

Certain applications for elastomer-to-metal adhesives require an unusual degree of flexibility. For example, it is often desirable to apply the adhesive to an article in its preformed condition. In such a situation, the adhesive must be sufficiently flexible and robust to withstand the stresses of subsequent article-forming operations. Applying an adhesive to preformed stock is particularly important to those industries engaged in fabricating parts from metal sheet stock or coil metal such as appliance cabinets, automobile parts and metal siding, to name just a few. Typically, the adhesive is applied to a coil metal and the adhesive-treated coil metal then is dried in a continuous operation known as coil coating. The adhesive-treated coil metal then is shaped and bonded with an elastomeric substrate to produce a final article. During the shaping of the adhesive- coated coil metal, the adhesive is subjected to considerable flexing before it is used to adhere to the elastomeric substrate. The shaping and bonding usually occurs a certain time period after the adhesive is applied, sometimes ranging up to a week or more.

Organic solvent-based adhesive systems for coil metal bonding are known such <BR> <BR> <BR> <BR> as Chemlok (D 208A adhesive primer/ChemlokX 237 adhesive overcoat system commercially available from Lord Corporation. However, in light of the increasing awareness for environmental protection and workplace safety, it is very desirable to develop an aqueous-based adhesive that avoids the use of highly volatile organic solvents. It has thus far been difficult to develop a highly flexible aqueous adhesive that performs at a level equal to conventional organic solvent-based adhesives.

Various aqueous adhesives for bonding elastomeric materials have been developed in a continuing effort to obtain the same or better level of performance compared with organic solvent-based adhesives. For example, U.S. Patent No. 4,167,500 discloses an aqueous adhesive composition that includes a water dispersible phenolic novolak resin, a methylene donor such as a high molecular weight aldehyde

homopolymer or copolymer and water. U.S. Patent No. 5,030,515 discloses a bonding method that includes employing as a primer a mixture of epoxidized diene polymer and a resole type phenolic resin. A separate overcoat that includes dinitrosobenzene is used with this primer. U.S. Patent No. 5,093,203 discloses a two part adhesive system that includes a primer and an overcoat. The primer includes polychloroprene, phenolic resin and a metal oxide. The separate overcoat includes dinitrosobenzene, a halogenated polyolefin and a metal oxide. U.S. Patent No. 5,162,156 discloses a two part adhesive system that includes a primer and an overcoat. The primer includes a phenolic novolak and a halogenated polyolefin. The separate overcoat includes dinitrosobenzene and a halogenated polyolefin. U.S. Patent No. 5,200,455 discloses a two part adhesive system that includes a primer and an overcoat. The aqueous primer includes a polyvinyl alcohol- stabilized phenolic resin dispersion, halogenated polyolefin latex, metal oxide and, optionally, a formaldehyde donor. The separate overcoat includes dinitrosobenzene, a halogenated polyolefin latex and polymaleimide.

However, there continues to exist a need for aqueous adhesives for applying to flexible metal substrates that have extended shelf-life stability (in other words, they can be stored for substantial periods of time without undue gelation or loss of adhesive capability); have good layover stability (in other words, metal substrates can be coated with wet adhesive, dried and stored for a substantial period of time prior to bonding without substantial loss of adhesion properties); the adhesive is heat-reactive or activated; and the adhesive is easily applied via a coil coating operation.

Summary of the Invention According to the present invention, there is provided an aqueous adhesive composition that includes an aqueous dispersible or soluble phenolic resole, at least one aromatic nitroso compound or aromatic nitroso compound precursor and at least one halogenated polyolefin. This adhesive exhibits superior flexibility combined with sufficient stability and adhesive performance. In addition, it avoids the environmental and workplace problems associated with conventional volatile organic solvent-based adhesives since it is aqueous-based.

Detailed Description of the Preferred Embodiments As described above, the adhesive composition includes an aqueous dispersible or soluble phenolic resole, at least one aromatic nitroso compound or aromatic nitroso compound precursor and at least one halogenated polyolefin. As used herein, these components constitute the "primary components" of the invention.

An important feature of the invention is that it is surprising that the aqueous adhesive composition exhibits shelf-life stability despite the fact that it includes a combination of the aromatic nitroso compound or aromatic nitroso compound precursor and the phenolic resole. Previous attempts to commercialize adhesive compositions that include both an aromatic nitroso compound and a phenolic compound or resin have been unsuccessful. The previous compositions were unstable in that they formed a gel or paste either immediately or a brief time after formulation. According to the present invention, the use of an aqueous-based system, the addition of an aqueous dispersible or soluble phenolic resole and a lower amount of the aromatic nitroso compound have unexpectedly resulted in a stable adhesive.

The phenolic resole is an aqueous dispersible or soluble heat-reactive condensation product of an aldehyde having from 1 to 8 carbon atoms, such as formaldehyde, acetaldehyde, isobutyraldehyde, ethylhexaldehyde, and the like, with phenolic compounds such as unsubstituted phenol, or substituted phenol such as o-cresol, m-cresol, p-cresol, mixed cresols (for example, cresylic acid and m-cresol and/or p- cresol), xylenol, diphenylolpropane, p-butylphenol, p-tert-amylphenol, p-octylphenol, p,p'-dihydroxydiphenylether and the like. Mixtures of different phenolic resoles can be used. The resoles are well-known and are typically base catalyzed resins having a formaldehyde factor (in other words, parts by weight of 40 weight percent aqueous formaldehyde per 100 parts by weight of unsubstituted phenol) of the order of 90 to 180.

The phenolic resole is formulated or mixed into the adhesive as an aqueous dispersion or solution.

One particularly desirable phenolic resole is a resole produced by reacting formaldehyde with bisphenol-A in a mol ratio of 2 to 3.75 moles of formaldehyde per mole of bisphenol-A in the presence of a catalytic amount of an alkali metal or barium

oxide or hydroxide condensation catalyst wherein the reaction is carried out at elevated temperatures. The condensation product is then neutralized to a pH of 3 to 8.

A polyvinyl alcohol-stabilized aqueous dispersion of the above-described phenolic resoles is particularly preferred as the phenolic resole component of the invention. This dispersion can be prepared by a process that includes mixing the pre- formed, solid, substantially water-insoluble, phenolic resole resin; water; an organic coupling solvent; and polyvinyl alcohol, at a temperature and for a period of time sufficient to form a dispersion of the phenolic resole resin in water. Such polyvinyl alcohol-stabilized aqueous dispersions of a phenolic resole are described in more detail in U.S. Patent No. 4,124,554, incorporated herein by reference, and are available commercially from Georgia Pacific Corporation under the tradename UCARX BKUA- 2370 and UCARX BKUA-2392.

According to U.S. Patent No. 4,124,554, alcohols, glycol ethers, ethers, esters and ketones are the most useful coupling solvents. Specific examples of useful coupling solvents include ethanol, n-propanol, isopropyl alcohol, ethylene glycol monobutyl ether, ethylene glycol monoisobutyl ether, ethylene glycol monomethyl ether acetate, diethylene glycol monobutyl ether, diethylene glycol monoethyl ether acetate, propylene glycol monopropyl ether, methoxy acetone, and the like.

According to U.S. Patent No. 4,124,554, the polyvinyl alcohol is typically prepared by hydrolysis of polyvinyl acetate. The most useful polyvinyl alcohol polymers are hydrolyzed to an extent of 85 to 91 percent and have molecular weights such that a 4 percent solids solution of the polyvinyl alcohol in water has a viscosity of 4 to 25 centipoises at 250C.

The aqueous dispersible or soluble phenolic resole is present in the adhesive composition in an amount of 10 to 60, preferably 20 to 30, % dry weight (excluding water) based on the primary components of the adhesive composition.

The aromatic nitroso compound can be any aromatic hydrocarbon, such as benzenes, naphthalenes, anthracenes, biphenyls, and the like, containing at least two nitroso groups attached directly to non-adjacent ring carbon atoms. Such aromatic nitroso compounds are described, for example, in U.S. Patent No. 3,258,388; U.S. Patent No. 4,119,587 and U.S. Patent No. 5,496,884.

More particularly, such nitroso compounds are described as aromatic compounds having from 1 to 3 aromatic nuclei, including fused aromatic nuclei, having from 2 to 6 nitroso groups attached directly to non-adjacent nuclear carbon atoms. The preferred nitroso compounds are the dinitroso aromatic compounds, especially the dinitrosobenzenes and dinitrosonaphthalenes, such as the metal or para-dinitrosobenzenes and the metal or para-dinitrosonaphthalenes. The nuclear hydrogen atoms of the aromatic nucleus can be replaced by alkyl, alkoxy, cycloalkyl, aryl, aralkyl, alkaryl, arylamine, arylnitroso, amino, halogen and similar groups. Thus, where reference is made herein to "aromatic nitroso compound" it will be understood to include both substituted and unsubstituted nitroso compounds.

Particularly preferred nitroso compounds are characterized by the formula: (R) m-Ar-(NO) 2 wherein Ar is selected from the group consisting of phenylene and naphthalene; R is a monovalent organic radical selected from the group consisting of alkyl, cycloalkyl, aryl, aralkyl, alkaryl, arylamine and alkoxy radicals having from 1 to 20 carbon atoms, amino, or halogen, and is preferably an alkyl group having from 1 to 8 carbon atoms; and m is 0, 1, 2, 3, or 4, and preferably is 0.

Exemplary suitable aromatic nitroso compounds include m-dinitrosobenzene, p- dinitrosobenzene, m-dinitrosonaphthalene, p-dinitrosonaphthalene, 2,5-dinitroso-p- cymene, 2-methyl- 1 ,4-dinitrosobenzene, 2-methyl-5-chloro-l ,4- dinitrosobenzene, 2- fluoro- 1,4- dinitrosobenzene, 2-methoxy- 1 -3-dinitrosobenzene, 5-chloro- 1,3- dinitrosobenzene, 2-benzyl- 1 ,4-dinitrosobenzene, 2-cyclohexyl- 1 ,4-dinitrosobenzene and combinations thereof. Particularly preferred are m-dinitrosobenzene and p- dinitrosobenzene.

The aromatic nitroso compound precursor may be essentially any compound that is capable of being converted, typically by oxidation, to a nitroso compound at elevated temperatures, typically from about 140-200"C. The most common aromatic nitroso compound precursors are derivatives of quinone compounds. Examples of such quinone compound derivatives include quinone dioxime, dibenzoquinone dioxime,

1,2,4,5-tetrachlorobenzoquinone, 2-methyl- 1 ,4-benzoquinone dioxime, 1,4- naphthoquinone dioxime, 1,2-naphthoquinone dioxime and 2,6-naphthoquinone dioxime.

The adhesion promoting additive can be used in an amount of from 5 to 40, preferably 10 to 20, % dry weight (excluding water), based on the primary components of the inventive adhesive composition.

The halogenated polyolefin acts as a film-former and is formulated or mixed into the adhesive as an aqueous dispersion such as an emulsion or a latex. The halogenated polyolefin can essentially be any natural or synthetic halogenated polyolefin elastomer. The halogens employed in the halogenated polyolefinic elastomer are typically chlorine or bromine, although fluorine can also be used. Mixtures of halogens can also be employed in which case the halogen-containing polyolefinic elastomer will have more than one type of halogen substituted thereon. The amount of halogen does not appear critical and can range from as low as 3 weight percent to more than 70 weight percent, depending on the nature of the base elastomer or polymer. Halogenated polyolefins and their preparation are well known to those skilled in the art.

Representative halogenated polyolefins include chlorinated natural rubber, chlorine- and bromine-containing synthetic rubbers including polychloroprene, chlorinated polychloroprene, chlorinated polybutadiene, hexachloropentadiene, butadiene/halogenated cyclic conjugated diene adducts, chlorinated butadiene styrene copolymers, chlorinated ethylene propylene copolymers and ethylene/propylene/non- conjugated diene terpolymers, chlorinated polyethylene, chlorosulfonated polyethylene, poly(2,3-dichloro- 1 ,3-butadiene), brominated poly(2,3-dichloro- 1 ,3-butadiene), copolymers of (x-haloacrylonitriles and 2,3-dichloro- 1 ,3-butadiene, chlorinated polyvinyl chloride) and the like including mixtures of such halogen-containing elastomers.

The latex of the halogenated polyolefin can be prepared according to methods known in the art such as by dissolving the halogenated polyolefin in a solvent and adding a surfactant to the resulting solution. Water can then be added to the solution under high shear to emulsify the polymer. The solvent is then stripped to obtain a latex having a total solids content of from 10 to 60, preferably 25 to 50, percent by weight. The latex can also be prepared by emulsion polymerization of chlorinated ethylenically unsaturated monomers.

Chlorosulfonated polyethylene is especially effective when utilized as the halogenated polyolefin. Chlorosulfonated polyethylene latex is commercially available and can be prepared by methods well known in the art such as, for example, dissolving polyethylene in carbon tetrachloride and subjecting the resulting solution to a mixture of chlorine gas and sulfur dioxide gas under high temperature and pressure. The carbon tetrachloride is then removed to produce a powder of chlorosulfonated polyethylene. The latex of chlorosulfonated polyethylene can be prepared according to the general method for preparing lattices described above.

The preferred chlorosulfonated polyethylene typically has a molecular weight in the range of 50,000-150,000, preferably 60,000-120,000. The chlorine content of the chlorosulfonated polyethylene is typically in the range of 20-50, preferably 25 to 45, percent while the sulfur content is typically in the range of 0.5 to 2, preferably 1.0 to 1.5, percent.

Also particularly effective is a latex of a copolymer of ot-bromoacrylonitrile and 2,3-dichloro-l ,3-butadiene. An example of such latex is described in U.S. Patent No.

5,496,884, incorporated herein by reference.

The halogenated polyolefin is present in the adhesive composition in an amount of 20 to 80, preferably 40 to 60, % dry weight (excluding water) based on the primary components of the inventive adhesive composition.

The adhesive can optionally include a maleimide-based compound such as an aliphatic or aromatic bismaleimide or polymaleimide. Aromatic polymaleimides having from 2 to 100 aromatic nuclei wherein no more than one maleimide group is directly attached to each adjacent aromatic ring are preferred. Particularly preferred aromatic polymaleimide compounds have the formula:

wherein x is from 0 to 100, preferably 1 to 100. Such polymaleimides are common materials of commerce and are sold under different trade names by different companies, such as BMI-M-20 and BMI-S polymaleimides supplied by Mitsui Toatsu Fine Chemicals, Inc.

The aqueous adhesive composition can also optionally include other well known additives such as a metal oxide (for example, zinc oxide, lead oxide and zirconium oxide), lead-containing compounds (for example, polybasic lead salts of phosphorous acid and saturated and unsaturated organic dicarboxylic acids and anhydrides), plasticizers, fillers, pigments, surfactants, dispersing agents, wetting agents, reinforcing agents and the like, in amounts employed by those skilled in the adhesive arts. Examples of optional ingredients include carbon black, silica such as fumed silica, sodium aluminosilicate and titanium dioxide.

Water, preferably deionized water, is utilized in combination with the primary components and any optional components of the invention in order to provide an adhesive composition having a final solids content of between 5 and 60 weight percent, preferably between 30 and 50 weight percent.

The adhesive compositions may be prepared by any method known in the art, but are preferably prepared by combining and milling or shaking the ingredients and water in a ball-mill, sand-mill, ceramic bead-mill, steel bead-mill, high speed media-mill or the like.

The adhesive composition may be applied to a substrate for bonding by spraying, dipping, brushing, wiping, roll-coating (including reverse roll-coating) or the like, after which the adhesive composition is permitted to dry. The composition typically is applied in an amount sufficient to form a dry film thickness ranging from 2.5 to 25 ptm,

preferably from 5 to 7.5 um. The present adhesive typically is used as a one coat adhesive, although it can be used with a primer. As used herein, "one coat" adhesive means that the adhesive composition can provide sufficient bonding without the need for an additional and separate or distinct primer composition. In the instance of coil metal bonding, the coil metal is coated with the wet adhesive and then dried. Rubber is extruded over the coated coil metal profile and the assembly subsequently is cured in a hot air oven.

The adhesive composition can be used to bond any types of substrates or surfaces together, but it is particularly useful to bond a metal substrate or surface to a polymeric material substrate or surface. The polymeric material can be any elastomeric material selected from any of the natural rubbers and olefinic synthetic rubbers including polychloroprene, polybutadiene, neoprene, styrene-butadiene copolymer rubber, acrylonitrile-butadiene copolymer rubber, ethylene-propylene copolymer rubber (EPM), ethylene-propylene-diene terpolymer rubber (EPDM), butyl rubber, brominated butyl rubber, alkylated chlorosulfonated polyethylene and the like. The material may also be a thermoplastic elastomer such as those sold under the tradenames SANTOPRENE and ALCRYN by Monsanto and DuPont, respectively. This adhesive is particularly effective for bonding EPM and EPDM. The metal substrate may be selected from any of the common structural metals such as iron, steel (including stainless steel and electrogalvanized steel), lead, aluminum, copper, brass, bronze, MONEL metal alloy, nickel, zinc and the like. Prior to bonding, the metal surface is typically cleaned according to one or more methods known in the art such as degreasing, grit-blasting and zinc-phosphatizing.

The adhesive composition typically is applied to the metal surface and the coated metal surface and elastomeric substrate are then brought together under heat and pressure to complete the bonding procedure. The exact conditions selected will depend upon the particular elastomer being bonded and whether or not it is cured. In some cases, it may be desirable to preheat the metal surface prior to application of the adhesive composition to assist in drying of the adhesive composition. The coated surface of the metal and the elastomeric substrate are typically brought together under a pressure of from 20 to 175 MPa, preferably from 20 to 50 MPa. If the elastomer is uncured, the resulting elastomer-metal assembly is simultaneously heated to a temperature of from

140"C to 2000C, preferably from 1500C to 1700C. The assembly should remain under the applied pressure and temperature for a period of 3 minutes to 60 minutes, depending on the cure rate and thickness of the elastomeric substrate. If the elastomer is already cured, the bonding temperature may range from 90"C to above 180"C for 15 to 120 minutes.

The bonding process may be carried out by applying the elastomeric substrate as a semi-molten material to the metal surface as in, for example, an injection-molding process. The process may also be carried out by utilizing compression molding, transfer molding or autoclave curing techniques. After the process is complete, the bond is fully vulcanized and ready for use in a final application.

The invention will be described in more detail by way of the following non- limiting examples.

EXAMPLE 1 The ingredients listed below were mixed according to conventional practices to produce an adhesive composition according to the invention.

Ingredient Percent Dry Weight poly(2,3-dichloro- 1 ,3-butadiene) latex 42.5 p-dinitrosobenzene 29.5 phenolic resole dispersion 12.0 zinc oxide 8.5 polymaleimide2 4.1 carbon black 2.5 dispersing agent3 0.9 BKUA 2370 available from Georgia Pacific 2 BMI-M-20 available from Mitsui Toatsu MARASPERSE CBOS available from American Can Company Water was added to the above ingredients resulting in an aqueous adhesive composition having an approximately 45 percent solids content.

The adhesive composition is applied to bright stainless steel coil coupons and the coated coupons are heated (also known as pre-curing or pre-baking) to temperatures ranging from 93 "C to 232 "C to obtain a dry film thickness ranging from 2.5 to 15 ptm.

EPDM rubber is milled to form a layer having a thickness of approximately 0.3 cm. The rubber is preheated for 2 minutes at 93 "C and then contacted with the adhesive-coated substrate under minimal pressure. The rubber-to-metal assembly then is cured for 3 minutes at 2320C. This bonding method is intended to simulate commercially used rubber extrusion methods for producing a variety of parts such as automotive window channel.

Primary adhesion is tested by hand peeling the rubber from the metal coil coupons using needle nose pliers. Failure is expressed in terms of percent of rubber retained on the metal substrate. A high percent of retained rubber is desirable since this indicates that the adhesive bond is stronger than the rubber itself. In other words, a strong bond will result in the rubber tearing rather than the adhesive.

Salt spray testing is performed by hanging the bonded test assemblies in a salt spray chamber that produces a 5% salt fog and maintains a temperature of 35"C. The assemblies are tested for primary adhesion after 7 and 14 day exposures by hand peeling with needle nose pliers.

The primary adhesion and salt spray testing results are shown below in Table 1.

TABLE 1 Pre-bake temperature Primary adhesion (% Adhesion - 7 day salt Adhesion-14 day salt rubber retained on spray (% rubber spray (% rubber metal) retained on metal) retained on metal) 149"C 100% 5% 5% 177 "C 95% 0% 0% 2040C 100% 0% 0% 2320C 100% 95% 100%

EXAMPLES 2 AND 3 AND COMPARATIVE EXAMPLES 1-3 The ingredients listed below by dry weight percent were mixed according to conventional practices to produce adhesive compositions according to the invention (examples 2 and 3) and comparative examples 1-3. Ingredient Example 2 Example 3 Comparative Comparative Comparative Example 1 Example 2 Example 3 Dispersing agent1 0.52 0.58 1.60 1.60 0 Wetting agent2 0 0 1.60 1.60 0 Carbon black3 0 0 12.00 12.00 0 Polymaleimide4 0 0 4.00 4.00 0 Zinc oxide 0 0 40.00 40.00 0 P- 5.24 0 12.80 12.80 0 Dinitrosobenzene Carbon black5 10.47 12.43 0 0 0 Quinone dioxime 0 4.14 0 0 0 Chlorosulfonated 0 0 28.00 0 0 polyethylene latex6 Chlorosulfonated 52.36 49.71 0 28.00 60.00 polyethylene latex7 Phenolic resole 31.41 33.14 0 0 40.00 dispersion8 MARASPERSE CBOS available from American Can Company.

POLYWET available from Uniroyal.

STERLING NS available from Cabot Corp.

4 BMI-M-20 available from Mitsui Toatsu.

RAVEN 14 available from Columbian Chemicals Co.

6 CHEMLOK HYP-605 available from Lord Corp.

7 CSM-450 available from Sumitomo Seika 8 BKUA 2370 available from Georgia Pacific

Water was added to the above ingredients resulting in an aqueous adhesive composition having an approximately 40 percent solids content.

The adhesive compositions were applied to stainless steel and electrogalvanized steel coil coupons as described above in connection with Example 1. The pre-bake temperature was 232"C. Rubber-to-metal assemblies were cured for 3 minutes at 2320C and for four minutes at 2180C.

Primary adhesion was tested by hand with pliers as described in Example 1.

Primary adhesion also was tested by a slit bend method. According to this method, the rubber-to-metal bonded assembly is scored with a razor blade so as to cut a slit through the rubber and adhesive layer down to the metal. The assembly then is bent at the slit and the amount of rubber retained is observed. The test results (provided in percent rubber retained) for stainless steel are shown in Table 2 and for electrogalvanized steel are shown in Table 3. Comparative Example 2 was not tested for adhesion because it failed to wet the metal substrate. It is clear from these results that an adequate bond does not form if the composition lacks (1) an aromatic nitroso compound or aromatic nitroso compound precursor (comparative example 3) or (2) a phenolic resole (comparative examples 1 and 2).

TABLE 2 Composition 218"C cure - 2180C cure - 2320C cure - 2320C cure - slit bend hand strip slit bend hand strip Example 2 90% 90% 100% 85% Example 3 90% 90% 90% 90% Comparative 0% 0% 0% 0% Example 1 Comparative 40% 10% 10% 20% Example 3 TABLE 3 Composition 218°C cure - 218°C cure - 232°C cure - 232°C cure - slit bend hand strip slit bend hand strip Example 2 90% 95% 70% 80% Example 3 100% 90% Not tested 80% Comparative 0% 0% 0% 0% Example 1 Comparative 10% 10% 5% 5% Example 3