AMINE CURABLE EPOXY COATING COMPOSITIONS HAVING AN IMPROVED ADHESION TO SUBSTRATES

Abstract: A curable coating composition comprising: (a) the constituents of an amine cure epoxy coating composition, which comprise: (a1) at least one polyepoxide; (a2) possibly at least one polyacrylate or polymethacrylate ester of a polyol; and (a3) at least one curing agent of the amine type; (b) an adhesion improving effective amount of at least a metal salt of an alpha , beta -ethylenically unsaturated carboxylic acid.

Description: AMINE CURABLE EPOXY COATING COMPOSITIONS HAVING AN IMPROVED ADHESION TO SUBSTRATES The present invention relates to an amine curable epoxy coating composition. It is well known in the industry that acrylic esters can be used as reactive diluents to partially or completely replace solvents in amine cure epoxy coating systems to reduce viscosity and improve cure speed. However, the introduction of multifunctional (meth)acrylic esters into these systems can result in a decreased adhesion to certain substrates. Thus, a need exists for coating compositions with low viscosity, high cure speed,, and improved adhesion to certain substrates. However, as a rule, this need exists even if the epoxy coating does .riot contain any (meth)acrylate groups. It is accordingly an object of this invention to overcome the disadvantages and drawbacks of the known art and to provide coating compositions with low viscosity, high cure speed, and improved adhesion to a wide variety of substrates. It is a further object of the present invention to provide coatings with low viscosity, high cure speed, and improved adhesion to a variety of substrates for use in two-component, ambient cure systems. It is yet a further object of the present invention to provide coating compositions with low viscosity, high cure speed, and improved adhesion to a variety of substrates for use in one-component, high temperature bake systems. The present invention is based on the discovery that a metal salt of an α,3-ethylenically unsaturated carboxylic acid can be advantageously employed in epoxy coating compositions and (meth)acrylate modified epoxy coating compositions. Specifically, it has been discovered that the use of metal salts of acrylic and methacrylic acids in the compositions and methods of the present invention to promote crosslinking resulted in improved adhesion of the composition to substrates. Thus, the compositions and methods of the present invention are, among others, those in which organic solvents have been partially or completely replaced by acrylates, but which compositions exhibit improved adhesion to substrates compared to conventional acrylate modified epoxy coating compositions. The present invention is directed to a curable coating composition comprising : (a) the constituents of an amine cure epoxy coating composition, which comprise : (al) at least one polyepoxide ; (a2) possibly at least one polyacrylate or polymethacrylate ester of a polyol ; and■ (a3) at least one curing agent of the amine type ; (b) an adhesion improving effective amount of at least a metal salt of an α, / 3-ethylenically unsaturated carboxylic acid. The epoxides (al) useful in the present invention are epoxide resins which contain more than one 1,2-epoxy group per molecule. They can be saturated or unsaturated, aliphatic, cycloaliphatic or heterocyclic and can be monomeric or polymeric in nature. The weights per epoxide of such resins will be within the range of about 100 to about 2,000. Preferably, the epoxide resins will contain glycidyl ether or ester groups, will be liquid rather than solid and will have weight per epoxide in the range of about 110 to about 500, most preferably about 175 to about 250. Useful epoxide resins are glycidyl polyetherε of polyhydric phenols which are derived from an epihalohydrin, e.g., epichlorohydrin, and a polyhydric phenol. Examples of such polyhydric phenols include resorcinol, hydroquinone, bis(4-hydroxyphenyl)-2,2-propane, or bisphenol A as it is commonly called, 4,4'-dihydroxybenzophenone, bis(4- hydroxyphenyl)-1,1-ethane, bis(4-hydroxyphenyl)-1,1- isobutane, bis(4-hydroxyphenyl)-2 ,2-butane, bis(2- dihydroxynaphthyl)methane, phloroglucinol, and bis(4- hydroxyphenyl)sulfone. Additional polyhydric phenols are novolac resins containing more than two phenol, or substituted phenol, moieties linked through methylene bridges as well as halogenated, e.g., brominated and chlorinated, phenolic compounds. Additional epoxide resins are glycidyl polyethers of polyhydric alcohols prepared by reacting a polyhydric alcohol with an epihalohydrin using an acidic catalyst, e.g., boron trifluoride, and subsequently treating the resulting product with an alkaline dehydrohalogenating agent. Included among the polyhydric alcohols that can be used in the preparation of these polyepoxides are glycerine, ethylene glycol, propylene glycol, diethylene glycol, hexanediol, hexanetriol, trimethylol propane, trimethylol ethane, pentaerythritol and the like. Epoxide resins and their preparations are described in United States Patents N * 2,467,171, 2,615,007, 2,615,008, 2,801,227, 2,538,072 and 2,033,803 which are herein incorporated by reference. Other epoxide resins are glycidyl esters of polycarboxylic acids which are derived from an epihalohydrin and a polycarboxylic acid using procedures described in United States Patents N' 3,859,314 and 3,576,827 which are herein incorporated by reference. Examples of polycarboxylic acids include phthalic acid or its anhydride, isophthalic acid, terephthalic acid, tetrahydrophthalic acid, hexahydrophthalic anhydride, adipic acid, dimerized fatty acids, dibasic acids made from an unsaturated fatty acid and acrylic acid and the like. The most preferred epoxide resins are glycidyl polyethers of polyhydric phenols, particularly the glycidyl polyether of bisphenol A. The polyacrylate or polymethacrylate esters of polyols (a2) useful in the present invention are those esters which contain more than one terminal acrylate or methacrylate group. These esters are the acrylic and methacrylic acid esters of aliphatic polyhydric alcohols such as, for example, the di- and polyacrylates and the di- and poly ethacrylates of alkylene glycols, alkoxylene glycols, alicyclic glycols and higher polyols, such as ethylene glycol, triethylene glycol, tetraethylene glycol, tetra ethylene glycol, the propylene glycols, hexanediol, trimethylolethane, trimethylolpropane, pentaerythritol, dipentaerythritol, tripentaerythritol and the like, or mixtures of these with each other or with their partially esterified analogs. Typical compounds include but are not limited to trimethylolpropane triacrylate, trimethylolethane triacrylate, trimethylolpropane trimethacrylate, trimethylolethane trimethacrylate, tetramethylene glycol dimethacrylate, ethylene glycol dimethacrylate, triethyleneglycol dimethacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, 1,6-hexanediol diacrylate, 1,6-hexanediol dimethacrylate, dipentaerythritol tetraacrylate, dipentaerythritol pentaacrylate, and the like. Particularly preferred esters are 1,6-hexanediol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, and pentaerythritol tetraacrylate. Additional acrylate or methacrylate esters of polyols are the acrylate or methacrylate esters of epoxide resins, wherein epoxide resins as used herein are considered to be polyols. The epoxide resins useful in reacting with acrylic or methacrylic acid are those epoxide resins described hereinbefore. The procedures for preparing these acrylate and methacrylate esters of epoxide resins are described in United States Patent N' 3,377,406 which is hereby incorporated by reference. Additional acrylate or methacrylate esters of polyols are the acrylate or methacrylate esters of polyisocyanates, wherein the polyisocyanates are considered to be polyols. The acrylate or methacrylate esters of the polyols may be blended with the polyepoxides in the weight ratio of about 5 to about 100 parts of ester for each 100 parts of polyepoxide. The preferred curing agents (a3) for the compositions of the present invention are aliphatic polyamines having at least 3 active amine hydrogen atoms per molecule. Examples of such amines are the polyalkylene polyamines, e.g., diethylene triamine, triethylene tetraamine, tetraethylene pentamine and pentaethylene hexamine. Additional useful amines are ethylene diamine, tetramethylene diamine, hexamethylene diamine, xylylene diamine, and the like. Adducts of such amines with acrylonitrile, acrylic acid, ethyl acrylate and the like are also useful if the adduct contains at least three active amine hydrogen atoms. Also included as useful amines are amidoamines obtained by reacting polyamines with fatty acids, both monomers and di ers, provided of course that the resulting amidoa ine contains at least 3 active amine hydrogen atoms per molecule. Additional curing agents which can be used with the compositions of this invention include aromatic amines, mercaptanε and anhydrides although generally soft, low strength thermoset resins are obtained. The curing agent can be used with the polyepoxide or with the polyepoxide/polyacrylate or polymethacrylate blend in approximate equivalent ratios, i.e. about 0.75 to about 1.25 amine hydrogen equivalents for each epoxy group in the epoxide or for each epoxy group in the epoxide and each acrylic unsaturated group in the ester. The amine groups react with the epoxide groups opening the epoxide ring to form a substituted amine group and a hydroxyl group. When acrylate groups are present, the amine groups add across the double bond of the acrylate group through Michael addition to form substituted amine groups and a saturated carbon to carbon linkages. Suitable acrylate modified epoxy coating compositions comprising a polyepoxide, a polyacrylate or polymethacrylate and a polyamine are disclosed in United States Patent N' 4,051,195, which is incorporated herein by reference. The metal component of the metal salt (b) is aluminum, antimony, barium, cadmium, calcium, iron, lead, magnesium, mercury, molybdenum, nickel, potassium, silver, titanium, or zinc. A preferred metal is zinc. The , β- ethylenically unsaturated carboxylic acid component of the salt (b) is generally selected among acrylic acid or methacrylic acid. Preferred metal salts (b) are zinc diacrylate or zinc dimethacrylate. The amount of metal salt (b) to be used in the compositions and methods of the present invention should be an amount effective to yield an improvement in adhesion of the composition to the substrate. Generally, the amount to be used should be an amount from about 0.5 parts to. about 40 parts per 100 parts of (al) + (a2) if it exists + (a3) . Preferably, amounts of from about l parts to about 10 parts are used. The salt (b) acts as a reactant or as a coreactant in a Michael addition. The amine cure epoxy coating composition of the present invention can be formulated with at least one additional constituent selected among solvents, fillers, reinforcing agents, dyes, pigments, dispersing acids, stabilizers and other additives depending upon the end use and desired properties. The compositions can be dissolved in and used from solvents, e.g., aromatic hydrocarbons, ethers, ether-esters, ether-alcohols, esters, alcohols, ketones and the like. However, because of their low viscosity, these compositions are particularly adaptable to being used with no solvents, i.e., at 100% solids. A preferred amine cure epoxy coating composition is a high solids or solventless acrylate modified coating composition, in other words a composition which has a low solvent content in the range of approximately 0 -25% by weight of said composition. The composition according to the present invention is intended for use in a two-component, ambient cure system, one of the component containing (al) and (a2) if it exists and the other component consisting in or containing (a3) , the metal salt (b) being blended into the former component, or it is intended for use in a one-component, high temperature bake system, an effective amount of (a3) in the form of a latent curing agent or of latent curing agents being blended into the mixture of the constituents (al) , (a2) if it exists, and the possible additional components, the metal salt (b) being also blended into said mixture. The latent curing agents shall release, by thermal effect (generally at a temperature higher than 80 * C), possibly in the presence of an accelerator, the amine functions required for the curing. Examples 3 and 4 of the present patent application illustrate this embodiment. The coating compositions of the present invention may be prepared for application in any conventional manner, and may be applied to the substrate by any conventional means such as dipping, spraying, roller coating or the like. The coating compositions may be utilized in a variety of settings such as paints, protective coatings, and the like. The term "substrate", as used herein, is intended to include metals, glass, rubbers or elastomers, plastics, polyesters, polyamides, polyacetals, and woven fabrics made of glass fibers or natural or synthetic organic fibers. Curable ■ compositions according to the present invention are useful as coatings and have the low viscosity and high cure speed of known high solids and solventlesε acrylate modified epoxy coatings. Moreover, cured compositions according to the present invention have improved adhesion properties to the substrates. The present invention relates also to a cured composition provided by curing the composition as defined above, and to a method for providing a curable composition comprising the steps of : (a) providing an amine cure epoxy coating composition as defined above ; and (b) adding an adhesion improving effective amount of a metal salt of an α, 3-ethylenically unsaturated carboxylic acid to the amine cure epoxy coating composition. The invention will be clarified further by a consideration of the following examples, which are intended to be purely exemplary, and in which all of the ingredients are expressed in parts by weight, unless otherwise noted. Example 1 (comparative) 50 grams of a coating consisting of 5 parts of titanium dioxide dispersed into 95 parts of diglycidyl ether of bisphenol A (available as EPON 828™ epoxy resin from Shell Oil Co.) was prepared.. This blend waε then reacted with 15 parts triethylenetetraa ine in a 100 ml disposable beaker. The coating was drawn down to a 0,381 mm (15 mil) dry film thickness using a wire wound rod and cured at 25'C (77'F). The time to gel was 50 minutes. The film exhibited a 100% loss of adhesion to cold-rolled steel using the cross-hatch adhesion method (ASTM D3359) . Example 2 50 grams of a coating consisting of 5 parts each of titanium dioxide and zinc diacrylate dispersed into 95 parts Epon 828 epoxy resin was prepared. This blend waε also reacted with 15 parts triethylenetetraamine in a 100 ml disposable beaker. This coating was drawn down and cured as in Example 1. The time to gel was 49 minutes. The film exhibited only a 40% loss of adhesion to cold-rolled steel using the cross-hatch method as in Example 1. Example 3 (comparative) 50 grams of a sealant formulation consisting of 40 parts of silicon dioxide dispersed into 44.2 parts diglycidyl ether of bis A (available as DER 331™ from Dow Chemical) epoxy resin, 11 parts 1,6 hexanediol diacrylate, 1.2 parts epoxy alamine adduct (available as ANCAMINE 2014AS™ from Air Products) and 3.6 parts of dicyanodiamide (available as AMICURE CG 1200™ from Air Products) was prepared. Thiε formulation was then applied to a 2,54 cm x 10,16 cm (l" x 4") strip of aluminum at approximately 3,17 mm (1/8") thickness. The specimens were baked at 163'C (325'F) for 20 minutes. Lap shear adhesion [2,54 cm x 2,54 cm (1" x 1") overlap)] waε tested following ASTM D1002. This formulation exhibited a Lap Shear Adhesion of 1,58 x 10 6 Pa (229 psi) to aluminum and 2,76 x 10 6 Pa (400 psi) to galvanized steel. Example 4 50 grams of a sealant formulation consisting of 40 parts silicon dioxide dispersed into 44.2 parts DER 331 epoxy resin, 8.25 parts 1,6 hexanediol diacrylate, 2.75 parts zinc diacrylate, 1.2 parts ANCAMINE 2014AS™ and 3.6 parts of AMICURE CG 1200™ was prepared. Lap Shear specimens were prepared and cured as in Example 3. This formulation exhibited a lap shear adhesion to aluminum of > 3.8 x 10 6 Pa (>550 psi) and 4.93 x 10 6 Pa (716 psi) to galvanized steel. It will be further understood that various changes in the details, materials, and arrangements of the parts which have been described and illustrated in order to explain the nature of thiε invention may be made by those skilled in the art without departing from the principle and scope of the invention as expressed in the following claims.

Claims: CLAIMS 1 - A curable coating composition comprising : (a) the constituents of an amine cure epoxy coating composition, which comprise : (al) at least one polyepoxide ; (a2) possibly at least one polyacrylate or polymethacrylate ester of a polyol ; and (a3) at least one curing agent of the amine type ; (b) an adhesion improving effective amount of at least a metal salt of an α, 3-ethylenically unsaturated carboxylic acid. 2 - The composition according to claim 1, characterized by the fact that the epoxide (al) is selected among glycidyl polyethers of polyhydric phenols, particularly being the diglycidyl ether of bisphenol A. 3 - The composition according to claim 1 or claim 2, characterized by the fact that the polyacrylate or polymethacrylate ester of a polyol (a2) is selected among the di- and polyacrylates and the di- and polymethacrylate of alkylene glycols, alkoxylene glycols, alicyclic glycols and higher polyols, such as ethylene glycol, triethylene glycol, tetraethylene glycol, tetramethylene glycol, hexanediol, trimethylolethane, trimethylolpropane, pentaerythritol, dipentaerythritol, tripentaerythritol, or mixtures of these with each other or with their partially esterified analogs. 4 - The composition according to anyone of claims 1 to 3, characterized by the fact that the curing agent (a3) is selected among aliphatic polyamines having at least 3 active amine hydrogen atoms per molecule. 5 - The composition according to anyone of claims 1 to 3, characterized by the fact that the curing agent (a3) is in the form of a latent curing agent, able to release, by thermal effect, possibly in the presence of an accelerator, the amine functions. 6 - The composition according to anyone of claims 1 to 5, characterized by the fact that the metal component of the metal salt (b) is aluminum, antimony, barium, cadmium, calcium, iron, lead, magnesium, mercury, molybdenum, nickel, potassium, silver, titanium, or zinc, and that the α,3-ethylenically unsaturated carboxylic acid component of the salt (b) is acrylic acid or methacrylic acid. 7 - The compoεition according to claim 6, characterized by the fact that the metal salt (b) is zinc diacrylate or zinc dimethacrylate. 8 - The compoεition according to anyone of claims 1 to 9, characterized by the fact that the adhesion improving effective amount of the metal salt (b) is 0.5 to 40 parts by weight, particularly, 1 to 10 parts by weight, per 100 parts of the constituents (al) + (a2) if it exists + (a3). 9 - The composition according to anyone of claims 1 to 8, characterized by the fact that the amine cure epoxy coating composition further comprises at least one additional constituent selected among solvents, fillers, reinforcing agents, dyes, pigments, dispersing acids, stabilizers and other additives depending upon the end use and desired properties. 10 - The composition according to anyone of claims 1 to 9, characterized by the fact that the amine cure epoxy coating composition has a solvent content in the range of 0 - 25% by weight of said composition. 11 - The composition according to anyone of claims 1 to 10, characterized by the fact that it iε intended for use in a two-component, ambient cure system, one of the component containing (al) and (a2) if it exists and the other component consisting in or containing (a3) , the metal salt (b) being blended into the former component. 12 - The composition according to anyone of claims 1 to 10, characterized by the fact that it is intended for use in a one-component, high temperature bake system, an effective amount of (a3) in the form of a latent curing agent or latent curing agents being blended into the mixture of the constituentε (al) , (a2) if it exists, and the posεible additional components, the metal salt (b) being also blended into said mixture. 13 - A cured composition provided by curing the composition as defined in anyone of claims 1 to 12. 14 - A method for providing a curable composition comprising the steps of : (a) providing an amine cure epoxy coating composition as defined in anyone of claims 1 to 12 ; and (b) adding an adhesion improving effective amount of a metal salt of an α,5-ethylenically unsaturated carboxylic acid to the amine cure epoxy coating composition.

Inventors: BAILEY MICHAEL A, CESKA GARY W, COSTIN C RICHARD, BAILEY, MICHAEL, A., CESKA, GARY, W., COSTIN, C., RICHARD
Applicants: CRAY VALLEY SA, SARTOMER CO INC, CRAY VALLEY S.A., SARTOMER COMPANY, INC.
Application year: 1996
Main classification: C08G59
IPC codes: C08G59, C08K5, C08L63, C09D4, C09D163