WO2004098796A1

WO2004098796A1 - Acrylic resin coating composition for metal surface

Info

Publication number: WO2004098796A1
Application number: PCT/US2004/013422
Authority: WO
Inventors: Jianhui Zhou; Qihua Xu
Original assignee: Lacks Enterprises, Inc.
Priority date: 2003-05-02
Filing date: 2004-04-30
Publication date: 2004-11-18
Also published as: WO2004098796B1

Abstract

An organic resin composition capable of forming a protective and/or decorative film coating on a chrome, nickel or other relatively inert metal surface is disclosed. The composition includes an organic solvent, an acrylic resin having tertiary amine groups, a first curing agent having at least one epoxy group and at least one hydrolyzable silyl group per molecule, and a second curing agent having at least two epoxy groups per molecule, or a curing agent having at least two epoxy groups and at least one hydrolyzable silyl group. The resulting coating is tenaciously adhered to relatively inert metal surfaces and exhibits good solvent resistance, water resistance, hardness, abrasion resistance and impact resistance.

Description

ACRYLIC RESIN COATING COMPOSITION FOR METAL SURFACE

FIELD OF THE INVENTION This invention relates to a coating composition that adheres tenaciously to metal surfaces and to a subsequently applied finish coating composition. BACKGROUND OF THE INVENTION

There has been an increased interest in the development of protective and/or decorative coatings for metals, especially metals that are resistant to oxidation and/or other reactions, such as nickel and chromium. In particular, there has been considerable interest in providing protective and/or decorative polymeric (organic) coatings on metal (e.g. , nickel or chrome) plated plastic (e.g., polycarbonate (PC), acrylonitrile-butadiene styrene (ABS) and PC/ABS blends) parts for automotive applications and for plumbing fixtures (e.g., facets, shower heads and the like).

However, it has been difficult to achieve good adhesion between an organic coating and a metal surface, especially a relatively inert metal surface such as a nickel or chromium surface. As a result, known organic coatings have not been able to meet the severe requirements and specifications for automotive and plumbing applications when they are applied to relatively inert metal surfaces (e.g., nickel or chrome). In particular, known coating compositions have not been able to pass thermal cycling, thermal shock, impact resistance and chemical resistance specifications for automotive applications or meet the stringent requirements for plumbing applications when they are applied to metals surfaces such as chrome or nickel surfaces.

The literature is replete with coating compositions that are alleged to be useful for forming a coating film on chromium and/or other metal surfaces. However, these compositions all have one or more deficiencies that prevent effective use in severe environments. In particular, the known coating compositions do not meet the automotive manufacturing specifications and are generally unsuitable for other severe applications such as plumbing components (i.e., facets, shower heads and the like), when applied to relatively inert metal surfaces. The known amine functionalized acrylic resin coating compositions alleged to exhibit improved properties generally include epoxy curing agents and/or curing agents having hydrolyzable silyl groups. However, none of the known compositions have the appropriate combination of resin and curing agents (cross-liking compounds) that are needed to achieve a combination of excellent adhesion with chrome, nickel or other relatively inert metal surfaces, good solvent resistance, good water resistance, hardness, abrasion resistance and impact resistance. Thus, improved coating compositions are needed for applications to chrome, nickel and other relatively inert metal surfaces of parts used in automotive, plumbing and other relatively severe applications. Japanese Patent Application Publication No. 05-255636 discloses a coating composition that is alleged to form a coating the exhibits excellent adhesion to chromium or nickel plating. The disclosed coating composition includes an acrylic resin having basic nitrogen, a compound having an epoxy group and a hydrolyzable silyl group in one molecule, and a compound having hydrolyzable silyl groups and/or silanol groups. Although this composition appears to achieve good adhesion to chrome surfaces and can pass thermal shock testing, the coating tends to whiten after water immersion testing, and is relatively brittle and unable to pass impact testing due to the relatively weak cross-link system. Thus, while this composition may represent an improvement over many other conventional coating compositions, it is not suitable for use on chrome surfaces of parts exposed to severe conditions, such as for automotive or plumbing applications.

Japanese Patent Application No. 06-287511 discloses a coating composition that allegedly can form a coating that exhibits excellent resistance to whitening by water, stain resistance, solvent resistance and chemical resistance. The disclosed coating composition includes an acrylic resin having at least one tertiary amino group, another acrylic resin having at least one hydroxyl group, an isocyanate compound, a compound having at least one epoxy group or both an epoxy group and a hydrolyzable silyl group, and a compound having a hydrolyzable silyl group and/or a silanol group. Although this composition appears to provide a coating that exhibits good toughness and chemical resistance, it does not exhibit sufficient adhesion to chrome or nickel surfaces for use in severe conditions such as automotive or plumbing applications.

Accordingly, there remains a need for a decorative and/or protective organic composition that forms a film coating that tenaciously adheres to chromium, nickel and other metal surfaces, and which is otherwise suitable for use in automotive components and other components exposed to severe conditions.

SUMMARY OF THE INVENTION An organic resin composition capable of forming a protective and/or decorative film coating on a chrome, nickel or other relatively inert metal surface, which tenaciously adheres to the surface, and exhibits good solvent resistance, water resistance, hardness, abrasion resistance, and impact resistance is provided. The composition comprises an organic solvent, an acrylic resin having tertiary amine groups, a first curing agent having at least one epoxy group and at least one hydrolyzable silyl group per molecule, and a second curing agent having at least two epoxy groups per molecule, or a curing agent having at least two epoxy groups and at least one hydrolyzable silyl group.

These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification and claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The coating compositions of this invention contain at least one acrylic polymer having tertiary amine groups. Suitable acrylic polymers having tertiary amine groups may be prepared using conventional polymerization techniques such as solution radical polymerization. Typical examples of solvents that may be utilized in the preparation of the acrylic polymer having tertiary amine groups using solution radical polymerization include various hydrocarbon solvents such as toluene, xylene, cyclohexane, n-hexane and octane; alcohols such as methanol, ethanol, iso-propanol, n-butanol, iso-butanol, sec-butanol, ethylene glycol monoethyl ether, ethylene glycol monoisopropyl ether and ethyleneglycol monobutyl ether; ester solvents such as methyl acetate, ethyl acetate, n- butyl acetate and amyl acetate; and ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone. These solvents may be used alone or in combination.

Conventional radical polymerization initiators may be utilized in solution radical polymerization. Examples of conventional initiators which may be employed include any of the various azo and peroxide initiators commonly employed in solution radical polymerization. A conventional chain transfer agent such as lauryl mercaptan, octyl mercaptan, dodecyl mercaptan, 2-mercaptoethanol, octyl thioglycolate, 3- mercaptopropionic acid and the like may be employed as needed or desired. In order to provide the required tertiary amine groups, the monomers used for the polymerization must include at least one polymerizable monomer having a tertiary amino group. Examples of suitable tertiary amino group-containing monomers include acrylic acid ester monomers and methacrylic acid ester monomers such as 2- dimethylaminoethyl methacrylate, 2-diemylamιnoethyl methacrylate, 3- dimethylaminopropyl methacrylate, 3-diethylaminopropyl methacrylate, N-(2- methacryloyloxyethyl) piperidine, N-(2-methyacryloyloxyethyl) pyrrolidine, N-(2- methacryloyloxyethyl) morpholine, acrylic acid ester analogs thereof and the like; aromatic monomers such as 4-(N,N-dimethylamino) styrene, 4-(N,N-diethylamino) styrene, and 4-vinylpyridine; methacrylamide and acrylamide monomers such as N-(2- dimethylaminoethyl) acrylamide, N-(3-dimethylaminopropyl) methacrylamide, the corresponding acrylamide analogs, and the like; and vinyl ether monomers such as 2- dmietylammoethyl vinyl ether, 2-diethylaminoethyl vinyl ether, 3-dimethylaminopropyl vinyl ether, 3-diethylaminopropyl vinyl ether, 4-dimethylaminobutyl vinyl ether and 6- dimethylaminohexyl vinyl ether.

Other monomers that may be employed during polymerization of the acrylic resin having tertiary arriine groups include radical polymerizable monomers capable of copolymerizing with the tertiary amino group-containing monomers. Examples include acrylic acid esters and methacrylic acid esters such as methylmethacrylate, ethylmethacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, iso-butyl methacrylate, tert-buyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, cyclohexyl methacrylate, benzyl methacrylate, 2-hydroxy ethyl methacrylate, 2-hydroxypropyl methacrylate, 2-hydroxybutyl methacrylate, 4- hydroxybutyl methacrylate, the aery late acid ester analogs thereof, and the like; vinyl esters such as vinyl acetate and vinyl benzoate; olefin halides such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, and chlorotrifluoroethylene; aromatic monomers such as styrene, alpha-methylstyrene, p-tert-butylstyrene and vinyl toluene; vinyl ethers such as ethyl vinyl ether, n-propyl vinyl ether, iso-butyl vinyl ether, 2-ethylhexyl vinyl ether, cyclohexyl vinyl ether, cyclopentyl vinyl ether, 2-hydroxy ethyl vinyl ether, 4- hydroxybutyl vinyl ether, and 6-hydroxyhexyl vinyl ether; acid monomers such as acrylic acid, methacrylic acid, maleic acid and itaconic acid. Other examples of monomers which may be employed include acrylamide, n-methylolacrylamide, di- acetonacrylamide, glycidyl methacrylate, and acrylonitrile.

A suitable amount of tertiary amino group-containing vinyl monomer (or repeat units in the polymer) is from about 1 mole percent to about 50 mole percent of the total monomers (or repeat units in the polymer) used to synthesize the polymer, and preferably from about 5 mole percent to about 25 mole percent. However, greater or lesser amounts of the tertiary amino group-containing monomers may be employed if desired, with the amount depending on the particular combination of monomers being employed and on the desired film properties.

In addition to the acrylic resin having tertiary amine groups, the coating compositions of this invention further comprise a first curing agent having at least one epoxy group and at least one hydrolyzable silyl group per molecule.

Examples of curing agents (cross-linking agents) having at least one epoxy group and at least one hydrolyzable silyl group per molecule include γ - glycidoxypropyltrimethoxysilane, γ -glycidoxypropyltriethoxysilane, γ - glycidoxypropylmethyldimethoxysilane, γ -glycidoxy- propylmethyldiethoxysilane, β- (3 ,4-epoxycyclohexyl) ethyltrimethoxysilane, β -(3 ,4-epoxy cyclohexyl) ethyltriethoxysilane, ?-(3,4-eρoxycyclohexyl) ethylmethyldiethoxysilane, γ- glycidoxypropyltriisopropenyloxysilane, and the like. In general, any compound having at least one epoxy group that can react with the tertiary amines of the acrylic polymer and at least one hydrolyzable silyl group may be suitable for use in the compositions of this invention.

In addition to the acrylic resin having tertiary amine groups and the first curing agent having at least one epoxy group and at least one hydrolyzable silyl group per molecule, the compositions of this invention also include a second curing agent having at least two epoxy groups per molecule. Examples of suitable epoxy curing agents include condensation products from epichlorohydrin and bisphenol A, such as cycloaliphatic bisepoxides, epoxydized polybutadienes formed by reaction of commercially available polybutadiene oils with peracids or organic acid/ water mixtures, epoxidation products of naturally occurring fats, oils, fatty acids derivatives, modified oils, epoxy-containing novolaks, glycidyl ethers of a polyhydric alcohol such as ethylene glycol diglycidyl ether, glycerol polyglycidyl ether, sorbitol polyglycidyl ether, trimethylolpropane polyglycidyl ether and pentaerythritol polyglycidyl ether and also suitable acrylate resins having attendant oxirane groups. Other suitable cross-linking agents having at least two epoxy groups include partially hydrolyzed and condensed γ -glycidoxyalkyltrialkoxysilane, reaction products of melamine resins with acrylamide with subsequent epoxidation of the acrylic double bond.

Alternatively, a curing agent having at least two epoxy groups and at least one hydrolyzable silyl group may be used to cross-link the acrylic polymer having tertiary amine groups. Such curing agents may be prepared from a γ - glycidoxyalkylalkoxysilane that has been partially hydrolyzed and condensed.

A suitable amount of curing agent which includes first curing agent and second curing agent is determined by the amount of tertiary amino-group hi the acrylic resin of this invention. For each tertiary amino-group in the acrylic resin of this invention, suitable total amount of epoxy group from the first curing agent and second during agent is 0.1 to 2.0, and preferably from 0.5 to 1.8. However, greater or lesser amount of curing agent maybe used depending on the particular formulation and desired film properties. The use of excessive amount of curing agent not only increases the cost, but also increases the brittleness of the coatings of this invention. While insufficient amount of curing agent will result in an insufficient cure and decrease the adhesion and other chemical and physical properties of the coatings of this invention.

The coating compositions of this invention are organic solvent based. Thus, it is generally unnecessary and undesirable to remove the solvent(s) used in the synthesis of the polymer. However, solvent may be removed to achieve a desired total solid content and/or to achieve desired Theological properties. Likewise, the same or different organic solvents may be added to lower the solids content and/or to decrease the viscosity of the coating. Organic based coating compositions are preferred for application to metal surfaces such as chrome plate.

The coating compositions of this invention may further contain various conventional coating additives and auxiliaries including a catalyst for encouraging hydrolysis and condensation, fillers such as ceramics, metals, and fibers; pigments and/or colorants, tinting agents, ultraviolet ray absorbers and/or stabilizers, leveling agents, etc.

The coating compositions of this invention may be utilized as either a primer coating composition for a subsequently applied organic coating, or as the sole coating composition for various substrates. While the coating compositions of this invention may be applied to generally any of a variety of substrates, including plastics, wood, ceramic, refractory and other materials, the coating compositions of this invention are particularly advantageous when applied to metal substrates due to the ability of the compositions to form film coatings that adhere tenaciously to metal surfaces. In particular, the coating compositions of this invention exhibit outstanding adhesion to chromium, nickel, stainless steel and other relatively inert surfaces as compared with conventional coating compositions, while also achieving excellent water resistance, chemical resistance, solvent resistance, abrasion resistance, impact resistance and hardness.

Non-limiting embodiments of the invention are described in greater detail in the following examples.

EXAMPLES Synthesis Example 1 - Preparation Of An Acrylic Resin Having Tertiary Amine Groups A round bottom flask having a capacity of one liter, and equipped with a stirrer, a thermometer, a nitrogen introduction pipe and a condenser, was charged with 135 grams of toluene and 90 grams of isobutyl alcohol. The flask was heated to 80°C. To the flask, a reactant mixture consisting of 169.7 grams of methyl methacrylate, 169.7 grams of butyl acrylate, 50.7 grams of dimethylaminoethyl methacrylate and 3.9 grams of 2,2'-azobisisobutyronitrile was introduced into the flask through a funnel over three hours in a nitrogen atmosphere. The flask was kept at 80 °C for one hour after monomer introduction to the flask was completed. A solution made from 2 grams of

2,2'-azobisisobutyronitrile and 96 grams of toluene was dropped over 30 minutes. Then the flask was further kept at 80 °C for three hours under stirring. A light amber colored acrylic resin having a weight average molecular weight of 20,000 was obtained in a solution comprising 50% non- volatile solids. The measured glass transition (T_g) of this resin was 3°C.

Synthesis Example 2 - Preparation Of An Acrylic Resin Having Tertiary Amine Groups

The same procedure in Synthesis Example 1 was followed except that the reactant mixture was replaced with 260 grams of methyl methacrylate, 78 grams of butyl acrylate, 50.7 grams of dimethylaminoethyl methacrylate and 4 grams of 2,2'- azobisisobutyronitrile. An acrylic resin having an average molecular weight of 20,000 was obtained in a solution comprising 50% non- volatile solids. The measured T_g of this polymer was 43 °C. Synthesis Example 3 - Preparation Of A Curing Agent Having At Least Two Epoxy Groups

A round bottom flask having a capacity of one liter and equipped with a stirrer, a thermometer, a nitrogen introduction pipe and a condenser was charged with 236 grams of f -glycidoxypropyltrimethoxy silane. To the flask, a mixture of 12 grams of purified water and one gram of diisopropylamine was introduced gradually through a funnel under agitation. The flask was then heated to 50 °C and kept for four hours under stirring. A partially hydrolyzed and condensed epoxy functional silane was obtained. Theoretically, the obtained epoxy silane has following structure: (R - Si)„ O „_₁ (OCH₃)_2;i_₁ here the "R" represents the group of (CH₂ CHO)CH₂ OCH₂ CH₂ CH₂ the estimated "n" value is 2.3 by measured average number molecular weight. Application Examples Application Example 1 A primer was formulated by mixing 320 grams of acrylic resin from synthesis

Example 1 with 15 grams of Silquest A 187 (OSI Specialties epoxy functional silane) and 30 grams of DER 331 (Dow Bis A-based epoxy resin). The mixture was further reduced to 14 seconds of Ford cup No. 4 by a solvent mixture containing 50 weight percent of methyl amyl ketone and 50 weight percent of methyl ethyl ketone for air gun spray application. The primer was applied to chromium plated ABS substrate and nickel-plated ABS substrate using a conventional air spray gun to 15 to 25 micron (dry film thickness), then topcoated with two component urethane basecoat TKPS6640 and two component urethane clear coat TKU2000C (both the products of PPC Industries, Inc.). The coated substrates were baked for one hour at 80 °C and aged three days before testing.

Application Example 2

Black flat monocoat paint was made by the following procedure: Mixing 360 grams of acrylic resin made in synthesis Example 2 with 9 grams of Cabot Monarch 1000, 30 grams of silica Lo-Vel HSF (Flatting agent, PPG Industries product), 15 grams of Microtalc MP-15-38 (Seegott Inc. product) and 2.4 grams of

BYK-161 (dispersion agent, BYK Chem product) in a stainless pot to form a mill base. The mill base was ground to 6 Hegman Grind using a media mil and was then reduced with 90 grams of toluene.

A black flat monocoat was formulated by mixing 460 grams of black past made above with 30 grams of Silquest A 187 (OSI Specialties epoxy functional silane), 15 grams of DER 331 (Dow Bis A-based epoxy resin) and 20 grams of DER 732 (Dow epoxy resin). The mixture was further reduced to 14 seconds of Ford cut No. 4 by a solvent mixture containing 50 weight percent of toluene and 50 weight percent of methyl ethyl ketone for air gun spray application.

The black flat monocoat was applied to chromium plated ABS substrate and nickel-plated ABS substrate respectively using a conventional air spray gun to 25 to 35 micron (dry film thickness). Th coated substrates were baked for one hour at 80 °C and aged three days before testing.

Application Example 3

A black flat monocoat was formulated by mixing 460 grams of black past made in application Example 2 with 39.7 grams of curing agent made in Synthesis Example 3,

1.6 grams of Tinuvin 292 and 3.2 grams of Tinuvin 1130 (both Ciba Speciality

Chemicals products). The mixture was further reduced to 14 seconds of Ford cup No. 4 by a solvent mixture containing 50 weight percent of toluene and 50 weight percent of methyl ethyl ketone for air gun spray application. The black flat monocoat was applied to chromium plated ABS substrate and nickel-plated ABS substrate respectively using a conventional air spray gun to 25 to 35 micron (dry film thickness). The coated substrates were baked for one hour at 80 °C and aged three days before testing.

Testing Results The test spacemen prepared in the application 1 to 3 were tested following the

Ford Motor specification ESB-M1J76-A and WSS-M2P180A for water resistance, humidity resistance, gasoline resistance thermal shock resistance and stone chip resistance.

The above coating compositions formed film coatings on chromium and nickel surfaces which exhibited outstanding adhesion with the substrates, in combination with other desirable properties, such as solvent resistance, water resistance, chemical resistance, hardness and impact resistance. More specifically, the coatings were able to meet the demanding quantitative specifications for exterior coatings on chrome and nickel.

The above description is considered that of the preferred embodiments only. Modifications of the invention will occur to those skilled in the art and to those who make or use the invention. Therefore, it is understood that the embodiments shown in the drawings and described above are merely for illustrative purposes and not intended to limit the scope of the invention, which is defined by the following claims as interpreted according to the principles of patent law, including the doctrine of equivalents.

Claims

The invention claimed is:

1. A coating composition comprising: an organic solvent; an acrylic resin having tertiary amine groups; a first curing agent having at least one epoxy group and at least one hydrolyzable silyl group per molecule; and a second curing agent having at least two epoxy groups per molecule.

2. The coating composition of claim 1, wherein the acrylic resin having tertiary amine groups is a copolymer of at least one alkyl acrylate or alkyl methacrylate and at least one dialklylaminoalkylene acrylate or dialkylaminoalkylene methacrylate.

3. The coating composition of claim 1, wherein the first curing agent is a γ - glycidoxyalkyltrialkoxysilane compound.

4. The coating composition of claim 1, wherein the second curing agent is a cycloaliphatic biepoxide.

5. The coating composition of claim 1, wherein the acrylic resin having tertiary amine groups is a copolymer in which from 1 mole percent to 50 mole percent of the repeat units have a tertiary amino group.

6. A coating composition comprising: an organic solvent; an acrylic resin having tertiary amine groups; and a curing agent having at least two epoxy groups and at least one hydrolyzable silyl group per molecule.

7. The coating composition of claim 6, wherein the curing agent is a partially hydrolyzed and condensed ^ -glycidoxyalkylalkoxy silane.

8. The coating composition of claim 6, wherein the acrylic resin having tertiary amine groups is a copolymer of at least one alkyl acrylate or alkyl methacrylate and at least one dialklylaminoalkylene acrylate or dialkylaminoalkylene methacrylate.

9. A process for applying a protective and/or decorative film coating on a metal surface, comprising: providing a coating composition containing an organic solvent, an acrylic resin having tertiary amine groups, a first curing agent having at least one epoxy group and at least one hydrolyzable silyl group per molecule, and a second curing agent having at least two epoxy groups per molecule; applying the coating composition to a meal surface; and drying the coating.

10. The process of claim 9, wherein the metal is chromium, nickel or stainless steel.

11. The process of claim 9, but requiring a curing agent having at least two epoxy groups and at least one hydrolyzable silyl group per molecule.

12. The process of claim 11, wherein the metal is chromium, nickel or stainless steel.

13. A process for applying a protective and/or decorative film coating on a metal surface, comprising: providing a coating composition containing an organic solvent, an acrylic resin having tertiary amine groups, and a curing agent having at least two epoxy groups and at least one hydrolyzable silyl group per molecule; applying the coating composition to a meal surface; and drying the coating.

14. The process of claim 13, wherein the metal is chromium, nickel or stainless steel.

15. The process of claim 13, but requiring a curing agent having at least two epoxy groups and at least one hydrolyzable silyl group per molecule.

16. The process of claim 13, wherein the metal is chromium, nickel or stainless steel.