JPH01139655A - Thermosetting solvent-type paint composition - Google Patents

Abstract

PURPOSE:To obtain the title composition having excellent acid resistance, solvent resistance, water resistance, gasohol resistance and coating film appearance and suitable as a clear paint for automobile, by compounding an acrylic copolymer containing acid group, an acrylic copolymer containing epoxy group and an amino resin. CONSTITUTION:The objective composition is produced by compounding (A) an acrylic copolymer composed of an acid group-containing monomer and other copolymerizable monomer and having an acid value of 30-150mgKOH/g, a hydroxyl value of >=5KOHmg/g and a number-average molecular weight of >=3,500 with (B) an acrylic copolymer composed of an epoxy group-containing monomer and other copolymerizable monomer and having an epoxy equivalent of 200-1,000g/eq and a number-average molecular weight of <=5,000 and (C) an amino resin. The equivalent ratio of the acid group of the component A to the epoxy group of the component B is 1:0.5-0.5:1 and the amount of the component C is 1-20wt.% based on the sum of the components A-C.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a clear paint composition for top coating, which is applied onto a base coat by a wet-on-wet method.

More specifically, in painting automobile bodies, a clear paint composition is used in a coating system in which a base coat containing a colored pigment or a metallic pigment is applied, a clear top coat is applied thereon by a wet-on-wet method, and the coating is simultaneously baked. The present invention relates to a thermosetting solvent-based coating composition that is suitable for use in the industry and has excellent acid resistance, solvent resistance, water resistance, gasohol resistance, and coating film appearance.

[Conventional technology and its problems]

Strong demands for automotive paints include high appearance quality and high durability.

In recent years, in order to satisfy these demands, a two-coat method in which a clear coat is applied on a base coat containing a pigment has been frequently used. Conventional clear coat paints include:
Acrylic-melamine thermosetting solvent-based paints are often used. However, acrylic melamine paints do not meet the requirements for appearance quality, mainly gloss, and they also lack resistance to acid rain, causing rain stains, and lack durability. are doing. .

In addition, although the urethane-based clear coats used in some areas have a high appearance quality, they are inconvenient to handle because they are a two-component type that requires the hardening agent to be mixed immediately before use, and they are resistant to acid rain. It also has the disadvantage of lacking in sexuality.

Acrylic powder coatings that employ a curing reaction between acid groups and epoxy groups have also been attempted, but they suffer from poor appearance quality and high baking temperatures, typically over 160°C. There are drawbacks.

Furthermore, as described in JP-A No. 56-24074, acrylic powder coatings use dicarboxylic acids as a curing agent component, but these have poor solvent solubility, and as solvent-based coatings, deposits may form in the coating. It cannot be applied due to stability problems such as occurrence of.

[Means for solving problems]

In view of the fact that the conventional technology has not reached a sufficient level in terms of appearance quality and durability regarding clear paint compositions for top coats that are applied on a base coat by a wet-on-wet method, the present inventors have made efforts to As a result of research, thermosetting solvent-based coating compositions using acrylic copolymers with acid groups, acrylic copolymers with epoxy groups, and amino resins have excellent appearance quality, and have excellent acid resistance. It has excellent durability, such as reducing the occurrence of rain stains and being resistant to scratches from car wash brushes, and is also resistant to solvents, water, and gasohol, which is gasoline used as a fuel that contains a small amount of methanol, and is weather resistant. sex,
It was discovered that it is also excellent in various physical properties, leading to the present invention.

That is, the present invention comprises (a) a monomer having an acid group, a monomer having a hydroxyl group, and other copolymerizable monomers, and having an acid value of 30 to 15.
0 mgKOH/g or more, hydroxyl value 5 KOHmg/
(b) an acrylic copolymer having an epoxy group-containing monomer and other copolymerizable monomers, and an epoxy equivalent of 200 to 1000 g.
/eq, consisting of an acrylic copolymer with a number average molecular weight of 5000 or less, and (c) an amino resin, in which the acid group of (a) and the epoxy group of (b) are 1:0.5~o,
At an equivalent ratio of s:1, the amino resin of (c) is (a), (
b) 1 to 20% by weight based on the total of (c).

Preferred examples of monomers having acid groups used in the acrylic copolymer (a) in the present invention include acrylic acid and methacrylic acid, and further examples include maleic acid, maleic anhydride, itaconic acid, and their like. Examples include monoesterified products, and one or more of these can be used.

In addition, as a monomer having a hydroxyl group, hydroxyethyl (
meth)acrylate, hydroxypropyl(meth)acrylate, hydroxybutyl(meth)acrylate, 1
．． Examples include 4-butanediol mono (meth)acrylate, ε-caprolactone adduct of hydroxyethyl (meth)acrylate, ethylene and propylene adduct of hydroxyethyl (meth)acrylate, and one or more of these can be used. .

Examples of monomers that can covalently exist include methyl (meth)acrylate, ethyl (meth)acrylate, and propyl (meth)acrylate.
Acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, stearyl (meth)acrylate, tridecyl (
Acrylic acid and methacrylic acid esters such as meth)acrylate, cyclohexyl(meth)acrylate, benzyl(meth)acrylate, phenyl(meth)acrylate, dimethylaminoethyl(meth)acrylate, and diethylaminoethyl(meth)acrylate. Can be used. Note that, for example, methyl (meth)acrylate refers to methyl methacrylate and methyl acrylate. Other copolymerizable monomers include styrene, α-methylstyrene, vinyltoluene, acrylonitrile, methacrylnitrile, vinyl acetate, vinyl propionate, acrylamide, methacrylamide, methylolacrylamide, methylolmethacrinoamide,
Vinyl chloride, propylene, ethylene, α of C1-C2°
-Olefins and the like.

The amount of the monomer having an acid group is limited so that the acid value of the acrylic copolymer (a) is 30 to 150. When the acid value is less than 30, curing properties are insufficient and solvent resistance is poor.
If the acid value exceeds 150, the solubility in solvents will be poor, and the stability of the paint will be poor, such as the formation of precipitates, making it impractical as a solvent-based paint.The preferred acid value range is 50 to 120, and Preferably it is 70-100. The acid value is expressed by the number of KOH required to neutralize 1 g of resin, and the unit is KOH+wg/g.

The hydroxyl value of the acrylic copolymer (a) needs to be 5 or more. If the hydroxyl value is less than 5, the crosslinking reaction between the acrylic resin and the amino resin will be insufficient, resulting in poor gasohol resistance of the coating film. The preferred range of hydroxyl value is 5 to 130.
, more preferably from 5 to 100.

The number average molecular weight was obtained by measuring polystyrene using GPC as a standard. Number average molecular weight is 350
It needs to be 0 or more, and if it is less than 3500, it will have poor solvent resistance, will be easily scratched by brushes during car washes, etc., will have poor water resistance, and will not have enough durability to maintain good paint film quality. inferior in sex. Also wet with base coat.
In on-wet painting, the base coat and clear coat mix, resulting in glossy pixelation and poor paint film appearance. A preferred number average molecular weight ranges from more than 5,000 to 20,000, more preferably from more than 5,500 to 20,000.

The glass transition point of the acrylic copolymer (a) is 50°C
The temperature is preferably below, and more preferably -20°C to 40°C.

The copolymer having acid groups must be an acrylic copolymer; if another polymer, for example a polyester resin having acid groups, is used in place of the acrylic copolymer (a), , it has poor acid resistance and causes rain stains due to acid rain, making it impractical.

Acrylic copolymer (a) can be synthesized by conventional methods, and can be produced by any known polymerization method such as solution polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, etc. . At that time, as a polymerization initiator, azobisisobutyronitrile, 4,4°-azobis(4-cyanopentaic acid), benzoyl peroxide, t-butylperoxy-2-
Ethylhexanoate, cumene hydroperoxide, potassium versalphate, hydrogen peroxide, 2.2゛-
Azobis[2-methyl-N~(2-hydroxyethyl)
propioamide], etc., and, if necessary, dodecyl mercaptan, mercaptoethanol, α-methylstyrene dimer, etc. can be used as a chain transfer agent.

In the present invention, examples of the monomer having an epoxy group used in the acrylic copolymer Cb> include glycidyl methacrylate, glycidyl acrylate, methylglycidyl methacrylate, methylglycidyl acrylate, and allyl glycidyl ether. As copolymerizable monomers in which 111 or more of these can be used, all of the exemplified copolymerizable monomers described in (a) of the acrylic copolymer can be used. In addition, the acrylic polymer (b) can be synthesized by a conventional method in the same manner as the acrylic copolymer (a), using the polymerization method described for the acrylic copolymer (a) and a polymerization initiator, if necessary. It can be produced using a chain transfer agent.

The monomer having an epoxy group is an acrylic polymer (b)
The amount used is limited so that the epoxy equivalent of is 200 to 1000. If the epoxy equivalent exceeds 1000, curing properties will be insufficient and solvent resistance will be poor. In addition, the epoxy equivalent is 200
If it is smaller, the surface of the coating film will not be smooth, making it impossible to obtain desirable coating film quality. The epoxy equivalent is expressed in grams of resin per 1 gram equivalent of epoxy group. The unit is g/eq.

The number average molecular weight of the acrylic copolymer (b) needs to be 5,000 or less. If it exceeds 5,000, the curing reaction with the acrylic copolymer (a) during baking will not proceed sufficiently, resulting in poor solvent resistance. This is thought to be because the present invention uses a crosslinking reaction between polymers composed of the acrylic copolymer (a) and the acrylic copolymer (b), that is, the acrylic copolymer (b) When the number average molecular weight exceeds 5,000, the viscosity of the uncured paint increases significantly in the early stage of the crosslinking reaction, which is presumed to reduce the frequency of collision reactions between acid groups and epoxy groups in the subsequent crosslinking reaction.

Preferably, the number average molecular weight of the acrylic copolymer (b) is lower than that of the acrylic copolymer (a). The acrylic copolymer (b) acts as a curing agent for the acrylic copolymer (a).

The glass transition point of the acrylic copolymer (b) is preferably 50°C or lower, more preferably -20°C to 40°C.

In the present invention, the crosslinking reaction during baking of the paint is mainly a reaction between the acid groups of the acrylic copolymer (a) and the epoxy groups of the acrylic copolymer (b), but amino resins also participate in the crosslinking reaction. Participate. That is, it is a curing agent component that reacts with the hydroxyl groups contained in the acrylic copolymer (a) and the hydroxyl groups generated by the reaction between the acid groups and the epoxy groups. Furthermore, the reaction with the hydroxyl groups mainly contained in the acrylic copolymer (a) from the initial stage of the curing reaction forms a coating film with a high crosslinking density and improves resistance to low-molecular substances such as gasohol. It is presumed to work as an auxiliary curing agent.

The amino resin (C) in the present invention includes melamine,
A resin synthesized from formaldehyde and at least one of urea, benzoguanamine, glycoluril, etc., in which part or all of the methylol groups are removed with a lower alcohol such as methanol, ethanol, propatool, isopropanol, butanol, isobutanol, etc. An alkyl ether is used.

In the present invention, the amino resin is an acrylic copolymer (a)
, 1 to 20% by weight based on the total of the acrylic copolymer (b) and the amino resin (c).

If it is less than 1% by weight, the crosslinking density of the cured coating film will be insufficient, resulting in poor gasohol resistance. Moreover, if it exceeds 20% by weight, acid resistance will be poor.

It is necessary to adjust the paint so that the acid groups and epoxy groups of the acrylic copolymers (a) and (b) have an equivalent ratio of 1:0.5 to 0.5:l. Outside this range, the solvent resistance and water resistance of the coating film will be poor.

Examples of solvents that can be used in the thermosetting solvent-based paint of the present invention include aliphatic hydrocarbons such as hexane and heptane, aromatic hydrocarbons such as toluene and xylene, and mainly aliphatic hydrocarbons, but some Petroleum fractions of various boiling point ranges containing aromatic hydrocarbons, butyl acetate,
Esters such as ethylene glycol diacetate, 2-ethoxyethyl acetate, ketones such as acetone and methyl isobutyl ketone, and alcohols such as butyl alcohol may also be used. Preferably, the content of aliphatic hydrocarbons and aromatic hydrocarbons is 50% or more.

The coating composition of the present invention is formulated using an acrylic copolymer (a
) and the epoxy groups of the acrylic copolymer (b) in an equivalent ratio of 1:0.5 to 0.5:1, and the amino resin (
They may be blended in a conventional manner so that c) accounts for 1 to 20% by weight of the total of (a), (b), and (c). Furthermore, if necessary, in addition to the acrylic copolymer (a) and acrylic copolymer (b) components, other commonly used components such as organic montmorillonite, microgel, polyamide, and viscosity modifiers such as polyethylene wax may be added. It is also possible to blend agents, silicone, acrylic organic polymer surface conditioning agents, ultraviolet absorbers, melamine resins, blocked isocyanate resins, etc.Furthermore, a small amount of pigment may be blended into the clear coat to achieve complete concealment. It may be colored to such an extent that this does not occur. The resulting clear coat composition is adjusted to a predetermined viscosity using a suitable solvent as a thinner. In this case, it is preferable to use 50% or more of aromatic and aliphatic hydrocarbon solvents.

As the base coat coating composition, any composition that can be used in automobile coating can be used.

Basecoat coating compositions include a resin and a pigment, which is a coloring agent. Useful resin compositions include acrylic-melamine, polyester (alkyd)-melamine, water-soluble acrylic-melamine, and acrylic polyol and polyester polyol-polymer. Examples include valent incyanate systems, acrylic emulsions, and acrylic lacquers. Further, the clear coat resin of the present invention may be used as a base coat resin composition.

Metallic pigments and colored pigments used in the base coat paint composition include, for example, aluminum flakes, copper bronze flakes, and mica. 6 Colored pigments include, for example, 81R-free materials, especially titanium dioxide, iron oxide, chromium oxide, chromium Acid lead and carbon black, and organic pigments include phthalocyanine blue and phthalocyanine green.

Further, the base coat coating composition may further contain conventional additives such as surfactants, flow control agents, thixotropic agents, microgels, ultraviolet absorbers, catalysts, and the like. Furthermore, a cellulose resin can also be blended.

As a method for using the coating composition of the present invention as a clear coat, the following methods can be typically exemplified.

After the base coat is applied to the substrate, a flash period is allowed and the clear coat is applied. The flash time is a setting time of about 5 to 20 minutes after the base coat and clear coat have been applied to the object to be coated. After the coating time, the object to be coated will be about 100-18
Bake at 0°C for about 10-60 minutes. - The thickness of the rear film for boat fishing is 20 to 60μ.

The clear coat composition may be applied by conventional methods such as brush coating, spray coating, dipping coating, or dipping coating, but spray coating is preferred in order to provide an excellent coating appearance. Examples of the spray coating method include an air atomization method, a vesicle atomization method, and the like.

〔Example〕

The following reference examples, examples, and comparative examples are for explaining the present invention, and in the description, "1 part" and "1%" are by weight unless otherwise specified.

Reference Example 1 (Preparation of acrylic copolymer (a) having acid groups) After purging nitrogen into a four-bottle flask equipped with a stirrer, thermometer, reflux condenser, and nitrogen conduit, Tsurpetz 100 ( Manufactured by Esso, aromatic hydrocarbon, boiling point 1
50 to 177°C) and 15 parts of n-butanol were added and heated to 100°C. The raw materials listed in Table 1 were added dropwise over 5 hours, and then heated at 100°C for 6 hours.
By holding for a period of time, acrylic copolymers (a-1) to (a-8) having acid groups with a solid content of about 50% were obtained.

Reference Example 2 (Preparation of acrylic copolymer (b) having epoxy groups) After purging the same reactor as that used in Reference Example 1 with nitrogen, a flask was charged with Tsurpetz 11100 (manufactured by Esso, aromatic hydrocarbon, 150 parts of boiling point: 150-177°C) were charged, and the temperature was raised to 140°C. The raw materials listed in Table 2 were added dropwise over a period of 5 hours, and then 100%
After holding at °C for 6 hours, 50 parts of Tsurpets #100 was distilled off by heating under reduced pressure (~30a+mg) to obtain an epoxy group-containing acrylic copolymer (b-
1) to (b-7) were obtained.

Reference Example 3 (3-1, Adjustment of base coat paint) (3-1-1, Adjustment of metallic base coat paint) 100 parts of Kijiroll was placed in a 4-tube flask equipped with a stirrer, thermometer, and condenser, and heated to 100"C. 10 parts of styrene and 10 parts of methyl methacrylate were heated.
30 parts of butyl acrylate, 35 parts of isobutyl acrylate, 12 parts of 2-hydroxy methacrylate, 3 parts of methacrylic acid, and 2 parts of azobisbutyronitrile were mixed and added dropwise over 4 hours. Holding at temperature for 6 hours yielded an acrylic resin with approximately 50% solids. 180 parts of this acrylic resin, knee pants 203E-
60 (butylated melamine resin, manufactured by Mitsui Toatsu Chemical Co., Ltd., solid content 60%) 37.5 parts, aluminum paste 716ON (
(manufactured by Toyo Aluminum Co., Ltd.) were stirred and mixed using a stirrer.

(3-1-2, Preparation of metallic base coat material) Metallic base coats were blended as shown below and stirred and mixed using a stirrer to obtain a base coat paint composition.

Acrylic 107 parts copolymer (a
-3) 30 parts acrylic copolymer produced in Reference Example 2 (
b-1) Kneepan 205E-609, 3 parts Aluminum paste 716ON 10.3 parts (manufactured by Toyo Aluminum Co., Ltd.) The base coat paint composition obtained in (3-1-1) and (3-1-2) above was mixed as follows. Ford C diluted with solvent
The viscosity was adjusted to 13 seconds/25°C at uppH4 to obtain a metallic base coat paint.

Ethyl acetate 15 parts toluene
40 parts Tsurupets +1100 (
(manufactured by Esso) 35 parts cellulose acetate
10 parts (3-2, Preparation of solid color base coat paint) A solid color base coat paint was blended as follows.

For the base synthesized in (3-1-1) 60.7 parts Acrylic resin (solid content 50%) Titanium oxide CR-90 (manufactured by Ishihara Sangyo Co., Ltd.) 52 parts Pigment was dispersed in the above formulation using a paint shaker for 1 hour. .

Further, 21.7 parts of Kneepan 205E-60 was added, and the mixture was diluted with the following mixed solvent and the viscosity was adjusted to 13 seconds/25°C using Ford Cup pH4 to obtain a solid color base coat paint.

Toluene 60 parts Trupetz 11100 (manufactured by Esso) 30 parts n-butanol
10 parts Reference Example 4 (Adjustment of clear coat paint) Clear coat paints were blended in the proportions shown in Table 3, and 0.2% by weight of Remix RL-4 was added to the resin solid content.
(Leveling agent made by Mitsui Toatsu Chemical Co., Ltd.) was added, stirred with a stirrer, 1110050 parts of Tsurupetz, 1 part of Tsurupetz.
The mixture was diluted with a mixed solvent of 15,050 parts (manufactured by Esso), and the viscosity was adjusted to 30 seconds/25°C using a Ford Cup 4 to obtain a clear coat paint.

Example 1 Acrylic copolymer (a-1), acrylic copolymer (b-1) and amino resin (C) (kneepan 2ON-
60) were blended in the proportions shown in Table 3, and Clear Two 1 composition was prepared by the method shown in Reference Example 4.

The metallic base coat paint prepared in (3-1-1) of Reference Example 3 was coated with cationic electrodeposition paint on a steel plate for an automobile body, and after being applied with air spray to the baked object, after setting for 3 minutes, After applying the above clear coat paint wet-on-wet and setting it for 10 minutes,
A test plate was obtained by heating at 140°C for 20 minutes. The clear film thickness and coating performance are shown in Table 4.

Examples 2.5.6, Comparative Examples 1 to 4 Similarly to Example 1, paints were prepared in the proportions shown in Table 3, and test plates were obtained in the same manner.

Example 3 In the same manner as in Example 1, clear coat paints were prepared in the proportions shown in Table 3.

After applying the solid color base material 11 prepared in Reference Example 3 (3-2) to the same object as in Example 1 using air spray, and letting it set for 3 minutes, apply the above clear coat paint wet-on-wet. After setting for 10 minutes, the test plate was heated at 140°C for 20 minutes. The clear film thickness and coating performance are shown in Table 4.

Example 4 In the same manner as in Example 1, clear coat paints were prepared in the proportions shown in Table 3.

After applying the metallic base coat paint prepared in (3-1-2) of Reference Example 3 to the same object as in Example 1 in the same manner as in Example 3, a clear paint was applied and baked using the same method, and a test plate was prepared. Obtained. The clear film thickness and coating performance are shown in the table below.
4.

Note that performance evaluation was performed as follows.

1) Visual appearance Appearance of the coating film is excellent. ◎1. Inferior items were marked as ×.

2) Acid resistance 40vol% H2SO4 was dropped onto the coating film, left at 50°C for 5 hours, and then wiped off and observed. Those with no traces were evaluated as ◎, and those with traces were evaluated as ×.

3) The coating surface was rubbed back and forth 50 times with gauze impregnated with solvent-resistant Kijiroru, and then observed. Those with no traces were evaluated as ◎, those with some traces as O, and those with traces as ×.

4) Gasohol resistance The coating film was immersed in gasoline containing 50% methanol at room temperature for 2 hours and then observed. Those with no abnormality in the coating film were rated ◎, and those with blistering and cracking in the coating film were rated ×.

5) Scratch Resistance The paint film surface was moved back and forth 1000 times with a car wash brush and the paint film was observed after cleaning. Those with no traces were evaluated with ◎, those with some traces were evaluated with Δ, and those with traces were evaluated with ×.

6) Weather Resistance After testing for 3000 hours with a Nanshine weather meter, the gloss retention rate was displayed.

Claims (1)

[Scope of Claims] (a) Consisting of a monomer having an acid group, a monomer having a hydroxyl group, and other copolymerizable monomers, and having an acid value of 30 to 15
0mgKOH/g or more, an acrylic copolymer with a hydroxyl value of 5KOHmg/g or more, and a number average molecular weight of 3500 or more; (b) a monomer having an epoxy group and other copolymerizable monomers; , epoxy equivalent is 200-1000g
/eq, consisting of an acrylic copolymer having a number average molecular weight of 5000 or less, and (c) an amino resin, in which the acid group of (a) and the epoxy group of (b) are in a ratio of 1:0.5 to 0.
In an equivalent ratio of 5:1, the amino resin of (c) is combined with (a), (b)
), 1 to 20% by weight based on the total of (c).