JP2741379B2 - Paint for clear coat - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an abrasion resistance and a gloss when exposed outdoors, which are used in a field where a high degree of aesthetics and performance are required such as a coating film of an automobile body. The present invention relates to a clear coat paint that forms a coating film having excellent retention and stain resistance.

[Conventional technology]

In vehicle body coating, after electrodeposition coating and intermediate coating, a base coat paint containing a colorant such as a coloring pigment or a metallic pigment and a top coat clear coat paint are applied in a wet-on-wet manner. A so-called two-coat / one-bake system in which multiple coatings are applied and both coatings are simultaneously heated and cured is generally employed.

In recent years, in the field of the automobile industry, there has been a problem of durability of a coating film, particularly, deterioration of the coating film appearance due to scratches. The surface of the coating film, which is finished in a two-coat / one-bake method using a base coating material of a dark color such as black, navy blue, or red, and a coating material for a clear coat, has scratches caused by a car wash brush, sand particles soaring during traveling, and the like. Easy to stand out. Especially,
There is a strong demand for a solution to the problem of scratches caused by a car wash brush of an automatic car washer both in Japan and overseas.

As a solution to such a problem, it has been proposed to impart abrasion resistance by forming a hard coat using a UV-based or silicone-based paint, but the balance of acid resistance, repairability, weather resistance, etc. has been proposed. It was difficult to form a good coating.

[Problems to be solved by the invention]

An object of the present invention is to provide a two-coat, one-baked coating film that maintains the properties of an acrylic amino-based thermosetting coating, such as weather resistance and water resistance, and is excellent in acid resistance and abrasion resistance. It is an object of the present invention to provide a clear coat paint capable of forming a clear coat.

[Means for solving the problem]

That is, the clear coat paint of the present invention is a clear coat paint used in a coating system in which a base coat paint containing a coloring agent is applied, and then the clear coat paint is repeatedly applied, and then heated and cured to obtain a coating film. Then, the clear coating composition is represented by the following general formula (I): (Wherein, R ¹ represents a hydrogen atom or a methyl group, and m is 3 to
An integer of 5 and n is an integer of 1 to 6. ) A hydroxyl group-containing (meth) acrylate represented by the formula 10
(B) General formula (II) (Wherein R ² represents a hydrogen atom or a methyl group, and R ³ represents an alkylene group having 2 to 10 carbon atoms.)
And (c) other vinyl monomers copolymerizable therewith.
Acrylic copolymer (A) having a hydroxyl value of 60 to 160 mgKOH / g, an acid value of 0 to 40 mgKOH / g and a glass transition temperature of -50 to 40 ° C obtained by copolymerizing 80% by weight, and a curing agent of 20 to 60% by weight, containing an alkyl etherified melamine resin (B) and a blocked polyisocyanate (C) as a curing agent, and a content of a component (C) of 40% by weight. Is not exceeded.

[Action]

The acrylic copolymer (A) used in the clear coating composition of the present invention has the general formula (I) (Wherein, R ¹ represents a hydrogen atom or a methyl group, and m is 3 to
An integer of 5 and n is an integer of 1 to 6. The hydroxyl group-containing (meth) acrylic acid ester (a) represented by the formula (1) is used as an essential component in terms of scratch resistance.
Specific examples of the hydroxyl group-containing (meth) acrylate (a) include 2-hydroxyethyl methacrylate ε-
1 mol adduct of caprolactone, 2 mol adduct of ε-caprolactone of 2-hydroxyethyl methacrylate, 2-
Ε-caprolactone 1 of hydroxyethyl acrylate
Molar adduct, ε- of 2-hydroxyethyl acrylate
An adduct of 2-hydroxyethyl (meth) acrylate and an organic lactone such as a caprolactone 2 mol adduct may be used, and two or more of these may be used in combination.

Hydroxyl-containing (meth) acrylic acid ester (a)
Used in an amount of 5050% by weight. If it is less than 10% by weight, the abrasion resistance is not sufficiently improved, and if it exceeds 50% by weight, the hardness of the coating film is lowered and the water resistance is also undesirably lowered.

General formula (II) (Wherein, R ² represents a hydrogen atom or a methyl group, and R ³ represents an alkylene group having 2 to 10 carbon atoms.) The hydroxyl group-containing (meth) acrylate (b) represented by the formula: ) The acrylic copolymer (A) is contained in an amount such that the hydroxyl value of the acrylic copolymer (A) is 60 to 160 mgKOH / g in combination with the acrylic ester (a).
Specific examples of the hydroxyl group-containing (meth) acrylate (b) include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate,
Examples include hydroxyalkyl (meth) acrylates such as -hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, and 6-hydroxyhexyl (meth) acrylate, and two or more of these may be used in combination.

The other vinyl monomer (c) copolymerizable with the components (a) and (b) is used in an amount ranging from 30 to 80% by weight. That is, the acrylic copolymer (A) is used so that the glass transition temperature of the produced acrylic copolymer (A) is -50 to 40 ° C and the acid value is 0 to 40 mgKOH / g within a range that does not impair the scratch resistance which is a feature of the present invention. Can be Specific examples of the vinyl monomer (c) include styrene derivatives such as styrene, α-methylstyrene and vinyl toluene; polymerizable unsaturated nitriles such as acrylonitrile and methacrylonitrile; vinyl esters such as vinyl acetate vinyl propionate; N-methoxymethyl (meth) acrylamide, N-butoxymethyl (meth)
N-alkoxy-substituted amides such as acrylamide; epoxy group-containing monomers such as glycidyl (meth) acrylate, (meth) allyl glycidyl ether, and metaglycidyl (meth) acrylate; dimethylaminoethyl (meth) acrylic acid, diethylaminoethyl ( Basic monomers such as (meth) acrylic acid; (meth) acrylic acid,
Carboxyl group-containing vinyl monomers such as itaconic acid, fumaric acid, crotonic acid, maleic acid, monomethyl itaconate, monobutyl itaconate, and 2-sulfoethyl (meth) acrylate; methyl (meth) acrylate, ethyl (meth) acrylate, Meth) propyl acrylate,
Butyl (meth) acrylate, amyl (meth) acrylate, cyclohexyl (meth) acrylate, phenyl (meth) acrylate, benzyl (meth) acrylate
Examples thereof include 2-ethylhexyl acrylate, lauryl (meth) acrylate, tridecyl (meth) acrylate, and stearyl (meth) acrylate.

Acrylic copolymer (A) comprising these components
As the polymerization method of, can be obtained by any method such as a solution polymerization method, a bulk polymerization method, an emulsion polymerization method,
In particular, it is preferable to employ a solution polymerization method.

In the case of the solution polymerization method, a mixture of the monomers is copolymerized in the presence of an organic solvent and a polymerization initiator. As the organic solvent, a commonly used organic solvent such as isopropyl alcohol, n-butanol, toluene and xylene may be used, and a polymerization initiator such as azobisisobutyronitrile, benzoyl peroxide, cumene hydroperoxide, etc. Agent. If necessary, a chain transfer agent such as 2-mercaptoethanol or n-dodecylmercaptan may be used.

The clear coat paint of the present invention contains 40 to 80% by weight of the acrylic copolymer (A) thus obtained. If it is less than 40% by weight, the abrasion resistance is insufficiently improved, and if it exceeds 80% by weight, the crosslinked density of the cured coating film is low, and the water resistance and solvent resistance become insufficient.

The acrylic copolymer (A) has a hydroxyl value of
It is required that the acid value be 60 to 160 mgKOH / g, the acid value be 0 to 40 mgKOH / g, and the glass transition temperature be -50 to 40 ° C. When the hydroxyl value is lower than the above range, the reaction between the acrylic copolymer (A) and the alkyl etherified melamine resin and the blocked polyisocyanate becomes insufficient, and a coating film having excellent scratch resistance cannot be obtained. . If the hydroxyl value exceeds the above range, physical properties such as water resistance and acid resistance become insufficient. On the other hand, when the acid value exceeds the above range, the cosmetic properties of the coating film are reduced. Further, when the glass transition temperature is lower than −50 ° C., the hardness of the cured coating film becomes insufficient, and when it exceeds 40 ° C., the scratch resistance becomes insufficient.

The coating material for a clear coat of the present invention comprises a curing agent comprising an alkyl etherified melamine resin (B) and a blocked polyisocyanate (C), wherein the component (C) comprises 40% by weight.
In an amount not exceeding 20 to 60% by weight. If the amount is less than 20% by weight, the feature of the present invention that the abrasion resistance is improved cannot be sufficiently exhibited. On the other hand, if the content exceeds 60% by weight, the cured coating film becomes brittle, and the acid resistance further decreases, which is not preferable.

Specific examples of the alkyletherified melamine resin (B) include those obtained by methylolating aminotriazine and alkyletherifying it with cyclohexanol or an alkanol having 1 to 6 carbon atoms, and more specifically, butyletherified melamine. Resins, methyl etherified melamine resins, and butyl methyl mixed etherified melamine resins. Specific examples of butyl etherified melamine resin include Uban 20SE (manufactured by Mitsui Toatsu Chemicals, Inc.) and Super Petcamine (manufactured by Dainippon Ink and Chemicals, Inc.). Specific examples of methyl etherified melamine resin include Cymel (Manufactured by Mitsui Cyanamid Co., Ltd.). The preferred amount of the alkyl etherified melamine resin (B) is 20 to
50% by weight.

A block polyisocyanate (C) is added to the clear coat paint of the present invention for the purpose of further improving acid resistance and scratch resistance. As block polyisocyanate (C), isophorone diisocyanate, 1,6-
Hexamethylene diisocyanate, polyisocyanate such as tolylene diisocyanate phenol, ethyl acetoacetate, cyclohexanol, ε-caprolactam,
Blocked with acetoxime, diisobutyl ketone oxime, etc., for example, Coronate 2507 and Coronate DC-2535 manufactured by Nippon Polyurethane Co., Ltd., Takenate B-815N and Takenate B-820NSU manufactured by Takeda Pharmaceutical Co., Ltd.
And the like. Block polyisocyanate (C)
Is preferably not more than 40% by weight, and the total amount with the alkyl etherified melamine resin (B) is preferably 30 to 50% by weight. If the block polyisocyanate (C) exceeds 40% by weight, the cured coating film becomes brittle, the flexibility is reduced, and the scratch resistance is also reduced.

In addition, the clear coating paint of the present invention includes an external acid catalyst represented by paratoluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid, dinonylnaphthalenedisulfonic acid, or a neutralized product of these amines, etc. It may be used as a catalyst for the etherified melamine resin (B).

The clear coat paint of the present invention containing the above components (A) to (C) is usually used after being diluted with an organic solvent for dilution so as to have an appropriate viscosity. Examples of the organic diluting solvent include aromatic petroleum derivatives xylene, sorbetso # 100 (Esso), ketone-based 2-heptanone (Eastman), and the like.

Examples of the resin system serving as a vehicle of the base paint used together with the clear coat paint of the present invention include a thermosetting acrylic melamine resin system and a thermosetting alkyd melamine resin system. For example, in the case of an acrylic melamine resin base coat paint, a film-forming acrylic resin having a functional group capable of reacting with an amino resin, a volatile organic liquid diluent, and a curing agent dissolved in the organic liquid diluent. A composition comprising a certain amino resin, a luminous agent such as aluminum paste, mica, and flaky iron oxide; an organic pigment such as titanium oxide, carbon black, and quinacridone;
Non-acrylic resins such as epoxy resins and cellulose resins; auxiliary additives such as surface conditioners, ultraviolet absorbers, antioxidants, and anti-settling agents;
It is configured by adding a general compounding method.

〔Example〕

Hereinafter, the present invention will be described more specifically with reference to examples. In addition, "part" means "part by weight".

Production Example of Acrylic Copolymer Included in Base Coating Paint A reaction vessel equipped with a stirrer, a temperature controller and a condenser was charged with 40 parts of toluene and 10 parts of n-butanol. Heat the contents of the reaction vessel with stirring to a temperature of 10
Increased to 0 ° C. Next, 101.5 parts of a solution consisting of 5 parts of styrene, 2 parts of methacrylic acid, 35 parts of methyl methacrylate, 46 parts of ethyl acrylate, 12 parts of 2-hydroxyethyl acrylate and 1.5 parts of benzoyl peroxide were added dropwise over 4 hours, and then benzoyl peroxide was added. A solution consisting of 0.6 part and 20 parts of toluene was added dropwise over 30 minutes. The reaction solution was stirred and heated at 100 ° C. for another 2 hours to increase the conversion to resin, and then 30 parts of toluene was added to terminate the reaction. The obtained acrylic copolymer solution (nonvolatile content 50%) is referred to as acrylic resin varnish (D). The weight-average molecular weight of this acrylic copolymer was measured by gel-verification chromatography and found to be 70,000.

Example of Production of Base Coating Paint Each amount of each material shown in Table 1 was placed in a stainless steel container, and after sufficiently stirring, the viscosity was adjusted with a mixed solvent for dilution, and the base coating paints B-1 and B-2 were prepared. Was manufactured.

Production Example of Acrylic Copolymer (A) Included in Clear Coating Coating A seven-component mixture having a monomer composition shown in Table 2 was subjected to a polymerization reaction according to the following procedure. mixer,
In a reaction vessel equipped with a temperature controller and a condenser,
First, 53.3 parts of Solvesso # 100 (Esso) were charged and heated with stirring to raise the temperature to 140 ° C. Next, 100 parts of each monomer mixture shown in Table 2 and 1 part of azobisisobutyronitrile and 5 parts of t-butylperoxyisopropyl carbonate were added dropwise over 3 hours. Next, 0.1 parts of azobisisobutyronitrile was added four times at 30 minute intervals. After stirring and heating at 140 ° C. for another 2 hours to increase the conversion to resin, 13.3 parts of n-butanol was added to terminate the reaction.

The hydroxyl value and acid value of each of the obtained acrylic copolymers (P-1 to P-8), and the viscosity and nonvolatile content of the copolymer solution were as shown in Table 2.

Example A-1 and Comparative Examples A-2 to A-4 Four types of clear coat paints were produced by using the respective acrylic copolymer solutions described above and by blending the paints shown in Table 3.

Formation of coating film and evaluation thereof A cationic electrodeposition paint for automobiles was applied to a bonderite # 144 dull steel plate (manufactured by Nippon Test Panel Co., Ltd.).
Bake at 180 ° C for 30 minutes. Next, an aminoalkyd-based intermediate coating was applied and baked at 160 ° C. for 30 minutes, and then the coating was sanded and dried. The base coat paint shown in Table 1 and the clear coat paint shown in Table 3 were overcoated with the combination shown in Table 4 by a wet-on-wet method on this coating film. This recoating was performed as follows. First, a base coat paint is applied on the intermediate coat so that the dry film thickness becomes 20-30 μm.
After leaving for 30 minutes, apply the clear coating
It was painted to a thickness of μm. After leaving the undried coated film at room temperature for 10 minutes, the film was baked in a hot air dryer at 140 ° C. for 25 minutes to form a coated film.

Table 4 shows the results of evaluation of various coating properties such as scratch resistance of each of the coating films obtained in this manner.

As is clear from the results, when the clear coat paint of the present invention was used, a coating film having excellent performance in gloss, scratch resistance, hardness, gasoline resistance, warm water resistance, weather resistance, etc. was obtained. Can be

[Effect of the Invention] The clear coat paint of the present invention has excellent scratch resistance,
Since it forms a coating film having properties such as acid gloss, gasoline resistance, hot water resistance, and weather resistance, it is extremely useful as a coating for automobile bodies.

Claims (1)

(57) [Claims] (1) General formula (I) (Wherein, R ¹ represents a hydrogen atom or a methyl group, and m is 3 to
And n is an integer of 1 to 6. ) A hydroxyl group-containing (meth) acrylate represented by the formula:
50% by weight, (b) general formula (II) (Wherein, R ² represents a hydrogen atom or a methyl group, and R ³ represents an alkylene group having 2 to 10 carbon atoms.)
40% by weight, and (c) other vinyl monomers copolymerizable therewith.
Acrylic copolymer (A) having a hydroxyl value of 60 to 160 mgKOH / g, an acid value of 0 to 40 mgKOH / g and a glass transition temperature of -50 to 40 ° C obtained by copolymerizing 80% by weight and 20 to 60% by weight of a curing agent, and contains an alkyl etherified melamine resin (B) and a blocked polyisocyanate (C) as a curing agent, and the content of the component (C) is 40% by weight. Paint for a clear coat, not exceeding