JPH03149271A - Thermosetting solvent-base paint composition having good adhesiveness - Google Patents

Abstract

PURPOSE:To improve the resistance to acid rain, the durability, the appearance of a coating film, and the adhesiveness by using two specified acrylic copolymers and a quaternary phosphonium salt as constituents. CONSTITUTION:A monomer having an acid radical (e.g. acrylic acid) is reacted with other copolymerizable monomer [e.g. methyl (meth)acrylate] to give an acrylic copolymer (A) having ao acid value of 30-150 KOH mg/g, a number- average molecular weight of 3,500 to 20,000, and a glass transition point of 0 deg.C or lower. An epoxy monomer (e.g. glycidyl methacrylate) is reacted with a hydroxylated monomer (e.g. hydroxyethyl acrylate) and other copolymerizable monomer to give an acrylic copolymer (B) having an epoxy equivalent of 200-1,000g/eq., a hydroxyl number of 4-40 KOH mg/g, a number-average molecular weight of 5,000 or lower, and a glass transition point of 50 deg.C or lower. 0.01-3 pts.wt. quaternary phosphonium salt (C) (e.g. methyltrioctylphosphonium dimethyl phosphate) is incorporated into 100 pts.wt. mixture of A and B at an equivalent ratio of the acid radical to the epoxy group of (1:0.5) to (0.5:1).

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, the clear paint composition is used in a painting system in which a base coat containing colored pigments and metallic pigments is applied, a clear top coat is applied on top of the base coat using 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 various purposes and has excellent acid resistance, coating film appearance, weather resistance, recodeability, etc.

[Conventional technology]

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

In recent years, in order to satisfy these demands, a two-coat system in which a clear coat is applied on a base coat containing a pigment has been frequently used. Conventionally, acrylic-melamine thermosetting solvent-based paints have been frequently used as clear coat paints. However, acrylic and melamine resin paints
It does not have sufficient resistance to acid rain, causing blistering, whitening, rain stains, etc., and lacks durability.

On the other hand, JP-A-62-087288, JP-A-1-1
39653, JP-A-1-139654, JP-A-1-13
A thermosetting solvent-based coating composition based on a curing reaction between an acid group and an epoxy group such as 9655 has been proposed.

[Problem to be solved by the invention]

The above-mentioned thermosetting solvent-based paint compositions based mainly on the curing reaction of acid groups and epoxy groups have no problems with acid rain resistance, durability, appearance, etc., but they do not cause any problems with paint film defects that occur when painting new cars. When performing full-scale repairs, there was a problem in that the adhesiveness of the base coat paint and the glue coat was poor.

[Means to solve the problem]

The present inventors have developed a clear coating composition for top coating in a wet-on-wet coating method on a base coat, using a conventional thermosetting solvent-based coating composition based on a curing reaction between acid groups and epoxy groups. As a result of extensive research into a thermosetting solvent-based coating composition that maintains sufficient rain resistance, durability, and coating film appearance, and has excellent adhesion to paint and glue coats in repair lines, the present invention was completed.

That is, the present invention comprises (,1) a monomer having an acid group and other copolymerizable monomers with an acid value of 30 to 150 KOHmg/g,
An acrylic copolymer with a number average molecular weight of 3.500 to 20.000, (b) consisting of a monomer having an epoxy group, a monomer having a hydroxyl group, and other copolymerizable monomers ,
Epoxy equivalent weight is 200-1,000 g/eQ, hydroxyl number is 4-40 KOHmg/g, number average molecular weight is 5. An acrylic copolymer and a (c1J-class phosphonium salt) having a molecular weight of less than
1 and (a) and (relative to 100 parts by weight of the total amount of bl)
This is a thermosetting solvent-based coating composition with good adhesion, comprising 0.01 to 3 parts by weight of c).

In the present invention, preferred examples of the monomer having an acid group used in the acrylic copolymer (al) include acrylic acid and methacrylic acid, and further examples include maleic acid, maleic anhydride, itaconic acid, and monomers thereof. Examples include esterified products, and one or more of these can be used.

Copolymerizable monomers 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 (
meth)acrylate, cyclohexyl(meth)acrylate, benzyl(meth)acrylate, phenyl(meth)acrylate, hydroxyethyl(meth)acrylate, hydroxypropyl(meth)acrylate, hydroxybutyl(meth)acrylate, 1,4-butanediol mono (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)
Esters of acrylic acid and methacrylic acid, such as acrylates, can be used. 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, methylolmethacrylamide, vinyl chloride, propylene, ethylene, C, ~C,. α-olefins and the like can be mentioned.

The amount of the monomer having an acid group is limited so that the acid value of acrylic copolymer (al) is 30 to 150 Komg/g.When the acid value is less than 30KOHmg/g,
Curability is insufficient, solvent resistance is poor, and acid value is 150KO.
If it exceeds hg/g, the solubility in the solvent will be poor and the stability of the paint will be poor, such as the formation of precipitates in the paint, making it impractical as a solvent-based paint. The preferred acid value range is 5
0 to 120 KOHmg/g, more preferably 70 to
toOKOH+ag/g. In addition, the acid value is resin t
It is expressed by the number of H in OH required to neutralize g, and the unit is KOHmg/g.

The number average molecular weight was obtained by measuring polystyrene using GPC as a standard. Number average molecular weight is 3.50
0-20. Must be Goo, 3.50
When it is less than 0, solvent resistance is poor, it is easily scratched by brushes during car washing, water resistance is poor, and durability in maintaining good coating film quality is poor.

In addition, in wet-on-wet painting with a base coat, the base coat and clear coat may mix, resulting in glossy pixelation and poor paint film appearance.

If the number average molecular weight is greater than 20.000, the nonvolatile content during coating will be low and the appearance of the coating will be poor.

The preferred number average molecular weight is s, ooo ~ 20.000
, more preferably in the range of 5.500 to 20.000.

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

The copolymer having an acid group must be an acrylic copolymer; if another polymer, such as a polyester resin having an acid group, is used in place of the acrylic copolymer group (a), , its acid resistance is poor, and rain stains occur due to acid rain, making it impractical.

Acrylic copolymer (a) can be synthesized by a conventional method, and can be produced by any known polymerization method such as solution polymerization method, suspension polymerization method, bulk polymerization method, emulsion type method, etc. . At that time, as a polymerization initiator, azobisisobutyronitrile, 4,4'-azobis(4-cyanopentaic acid), penzoyl peroxide, t-butylperoxy-2-
Ethylhexanoate, cumene hydroperoxide, potassium persulfate, hydrogen peroxide, 2,2°-
Azobis[2-methyl-N-(2-hydroxyethyl)
Pouf-ropiamide], etc. can be used, and dodecyl mercaptan, mercaptoethanol, α-methylstyrene dimer, etc. can be used as a chain transfer agent, if necessary.

Examples of the monomer having an epoxy group used for the acrylic copolymer color in the present invention include glycidyl methacrylate, glycidyl acrylate, methylglycidyl methacrylate, methylglycidyl acrylate, and acrylic glycidyl ether. One or more types of these can be used.

In the present invention, the acrylic copolymer (a monomer having a hydroxyl group used in bl) is preferably hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, or hydroxyl methacrylate. Propyl ester, acrylic acid hydroxybutyl ester, methacrylic acid hydroxybutyl ester, etc.
These can be used alone or in combination of two or more.

As other copolymerizable monomers, all those exemplified as 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 200-1.000 g/eq. Epoxy equivalent is 1.00
If it exceeds 0 g/eq, the curing properties will be insufficient and the solvent resistance will be poor. Also, the epoxy equivalent is 200 g/eq
If it is less than that, the surface of the coating film will not be smooth and a desirable coating quality cannot be obtained. Note that the epoxy equivalent is expressed in grams of resin per Ig equivalent of the epoxy group. The unit is g/eq.

The monomer having a hydroxyl group has a hydroxyl value of 4 to 40 Koumg/g of the acrylic copolymer (b).
-l 〇 - Limit the amount used. When the hydroxyl value is less than 4 KOHmg/g, the adhesive coating properties with the base coat paint during repair are poor. Hydroxyl number is 40
If it exceeds KOHmg/g, there are problems such as poor water resistance and acid resistance of the clear coating film.

The number average molecular weight of the acrylic copolymer (b) needs to be 5.000 or less. However, the number average molecular weight is 5
If it is less than 00, reactivity increases, but it tends to be difficult to obtain a desired coating film. If it exceeds 5.000, the curing reaction with the acrylic copolymer (Al) 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 an acrylic copolymer (al) and an acrylic copolymer (b), that is, the acrylic copolymer (
If the number average molecular weight of bl is greater than 5.000, the viscosity of the uncured paint will increase significantly at the early stage of the crosslinking reaction.
It is presumed that this is to reduce the frequency of collision reactions between acid groups and epoxy groups in the subsequent crosslinking reaction. Preferably, an acrylic copolymer (the number average molecular weight of bl is equal to that of an acrylic copolymer (
It is desirable that it be lower than that of a). The acrylic copolymer (b) acts as a curing agent for the acrylic copolymer (a).

The glass transition point of the acrylic copolymer weight 1 is preferably 50°C or lower, more preferably -20°C to 40°C.

It is necessary to adjust the coating material so that the equivalent ratio of acid groups to epoxy groups in the acrylic copolymers (a) and (b) is 1:0.5 to G, 5:1. Outside this range, the solvent resistance and water resistance of the coating film will be poor.

Examples of the quaternary phosphonium salts of the present invention include methyltrioctylphosphonium dimethylphosphate, methyltributylphosphonium dimethylphosphate, methyltriphenylphosphonium dimethylphosphate, tetrabutylphosphonium acetate, benzyltriphenylphosphonium acetate, tetrabutylphosphonium bromide, and tetrabutylphosphonium. Chloride, tetrabutylphosphonium iodide, tetrall-phenylphosphonium bromide, tetraphenylphosphonium chloride, tetraphenylphosphonium iodide, benzyltriphenylphosphonium bromide, benzyltriphenylphosphonium chloride, benzyltriphenylphosphonium iodide, tetrabutylphosphonium hydroxide , tetraphenylphosphonium tetraphenylporate, and the like. Furthermore, there are monomers, polymers, and copolymers of p-styryldiphenylphosphonium bromide with monomers copolymerizable therewith. One or more quaternary phosphonium salts can also be used as a mixture. The quaternary phosphonium salt acts as a reaction catalyst between acid groups and epoxy groups. Furthermore, quaternary ammonium salts, tertiary amines, organic metal compounds, organic acid metal salts, imidazoles, Lewis acids, and boric acid esters can also be used in combination.

The quaternary phosphonium salt of (c) is (total amount of al and (b) 1
0.01 to 3 parts by weight relative to 0.00 parts by weight, and 0.01 to 3 parts by weight.
If the baking temperature is low (approximately 120 parts by weight)
When the baking temperature is around ℃), the solvent resistance and water resistance are poor.

If it exceeds 3 parts by weight, the viscosity of the paint increases during storage, resulting in poor stability and is not suitable for practical use.

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% by weight or more.

The coating composition of the present invention is formulated using an acrylic copolymer (a
), acrylic copolymer (b) and quaternary phosphonium salt (c), the equivalent ratio of acid groups in (a) to epoxy groups in (b) is 1:0.5 to 0.5:l. , cutlet (c)
is 0.01 to 100 parts by weight in total of (a) and (b).
It may be blended by a conventional method so that the amount is 3 parts by weight. Furthermore, if necessary, in addition to components (al, (b) and (c)), other commonly used components, such as viscosity modifiers such as organic montmorite, microgel, polyamide, and polyethylene wax, silicone, Surface conditioning agents of acrylic organic polymers, weathering stabilizers such as ultraviolet absorbers, melamine resins, blocked isocyanate resins, etc. may be blended.

Furthermore, a small amount of pigment may be added to the clear coat to add color to the clear coat to the extent that complete hiding properties are not achieved. 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% by weight or more of aromatic and aliphatic hydrocarbon solvents.

As the base coat paint, any paint that can be used in automobile painting can be used.

Base coat paints include resins, colorants, and metal pigments.
As the resin, acrylic-melamine resin type and polyester-melamine resin type are commonly used.

Metallic and colored pigments used in base coat paints include, for example, aluminum flakes, copper bronze flakes, and mica.

Coloring pigments include, for example, inorganic pigments, especially titanium dioxide,
Iron oxide, chromium oxide, lead chromate 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 flashing time may be left at room temperature for 1 to 10 minutes, or an appropriate heating step of about 80°C may be added.

After the base coat and clear coat have been applied to the object to be coated, after a setting time of about 5 to 20 minutes, the object to be coated is baked at about 100 DEG to 180 DEG C. for about 5 to 60 minutes. The thickness of a typical adhesive film is 20
~60μ.

The clear coat composition may be applied by conventional methods such as brushing, spraying, dipping, or dipping; however, spraying is preferred in order to provide an excellent coating appearance. It's a method. Examples of the spray coating method include an air atomization method and a bell atomization method.

〔Example〕

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

Reference Example 1 (Adjustment of acrylic copolymer having acid groups (Al)) After purging nitrogen into a four-necked flask equipped with a stirrer, thermometer, reflux condenser, and nitrogen inlet tube, the flask was filled with Sorbets #100 (Esso 85 parts of aromatic hydrocarbon, boiling point 150-177°C) and 15 parts of n-butanol were heated and heated to 100°C.The raw materials shown in Table 1 were added dropwise over 5 hours, and -1 F-1 flow and then held at 100°C for 6 hours to reduce the solid content to about 5.
0% by weight of acrylic copolymer with acid groups (al
) to (a-4) were obtained.

Reference Example 2 (Preparation of acrylic copolymer (b) having epoxy groups) After purging the same reaction apparatus as that used in Reference Example 1 with nitrogen, a flask was charged with Sorbets #lOO (manufactured by Esso, aromatic hydrocarbon , boiling point: 150 to 177°C), and heated to 140°C. The raw materials shown in Table 2 were added dropwise to this mixture over a period of 5 hours, and then heated at 100°C for 6 hours.
After holding for a period of time, 100.50 parts of Sorbets #100 was distilled off by heating under reduced pressure (~30 mg) to obtain an acrylic copolymer with epoxy groups (b-l) with a solid content of about 50% by weight.
) to (b-6) were obtained.

Reference Example 3 (3-1, Adjustment of base coat paint) (3-1-1, Adjustment of metallic base coat paint) 100 parts of xylene was charged in a 4-tube flask equipped with a stirrer, thermometer, and condenser, and heated to 100°C. did.

Here, 10 parts of styrene, 10 parts of methyl methacrylate,
30 parts of butyl acrylate, 3 parts of isobutyl acrylate
5 parts of 2-hydroxy methacrylate, 12 parts of methacrylic acid, and 2 parts of azobisbutyronitrile were mixed, added dropwise over 4 hours, and then kept at the same temperature for 6 hours to determine the solid content. Approximately 50% acrylic resin was obtained. 180 parts of this acrylic resin, Yuban 20311-
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.

The base coat paint composition obtained above was diluted with the following mixed solvent and the viscosity was adjusted to 725° C. for 13 seconds using a Ford Cup #4 to obtain a metallic base coat paint.

Ethyl acetate 15 parts toluene
40 part Sorbets #10
0 (manufactured by Esso) 35 parts cellulose acetate
Part 1O (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. .

Furthermore, Yuban 20Sl! Add 21.7 parts of -60, dilute with the following mixed solvent, and use a Ford Cup #4 for 13
The viscosity was adjusted to 725° C. to obtain a solid color base coat paint.

Toluene 60 parts Solvetz #100 (manufactured by Esso) 3-14n-butanol 10 parts Reference Example 4 (Preparation of clear coat paint) Clear coat paints were blended in the proportions shown in Table 3, and further 0.00 parts based on the resin solid content. 2% by weight Remix RL-4
(Leveling agent manufactured by Mitsui Toatsu Chemical Co., Ltd.) was added, stirred with a stirrer, Solbets #100.50 parts, Solbets #
The mixture was diluted with a mixed solvent of 150.50 parts (manufactured by Esso), and the viscosity was adjusted to 725° C. for 30 seconds using a Ford Cup #4 to obtain a clear coat paint.

Example 1 Acrylic copolymer (a-l), acrylic copolymer (
bl) and benzyltriphenylphosphonium chloride as the quaternary phosphonium salt (cl) were blended in the proportions shown in Table 3, and a clear coat paint 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.

23-Example 2.3.4, Comparative Examples 1 and 2.3.4 Similarly to Example 1, paints were prepared in the proportions shown in Table 3, and test plates were obtained in the same manner.

Example 5 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 coat paint prepared in (3-2) of Reference Example 3 to the same object as in Example 1 with air spray, let it set for 3 minutes, then 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.

Note that performance evaluation was performed as follows.

1) Visual appearance Those with excellent coating film appearance were rated ◎, and those with poor appearance were rated ×.

2) Acid resistance 40% by volume of ntsoa 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) Water resistance The coating film was immersed in warm water at 50° C. for 48 hours and then observed. Those with no abnormality were evaluated as ◎, and those with significant whitening and blisters were evaluated as X.

4) Apply wet-on-wet non-sand record base coat paint and clear coat paint, and after setting for 10 minutes,
The same base coat paint and clear coat paint were applied again in the same manner on the coating film cured by heating at ℃ for 20 minutes and cured by heating. After that, 10 rows are placed at 1m intervals.
After cutting with a cutter, adhesiveness between the layers was evaluated by peeling off with cellophane tape. The number of closely adhered gobbles after the tape was peeled off was displayed.

I Purple III Do I 1 1111 Ko1 1 Mouth, 1. [Effects of the Invention] As shown in Table 4, the thermosetting solvent-based coating composition of the present invention is excellent in visual appearance, acid resistance, durability, and non-sand recordability.

Claims (3)

[Claims] (1) (a) consisting of a monomer having an acid group and other copolymerizable monomers and having an acid value of 30 to 150 KOHmg/g;
An acrylic copolymer having a number average molecular weight of 3,500 to 20,000; (b) consisting of a monomer having an epoxy group, a monomer having a hydroxyl group, and other copolymerizable monomers; ,
Epoxy equivalent is 200-1,000g/eq, hydroxyl value is 4-40KOHmg/g, number average molecular weight is 5,
000 or less, and (c) a quaternary phosphonium salt, the equivalent ratio of the acid group (a) to the epoxy group (b) is 1:0.
5:1 to 0.5:1 and a thermosetting solvent-based coating composition with good adhesion, comprising 0.01 to 3 parts by weight of (c) to 100 parts by weight of the total amount of (a) and (b). (2) The glass transition point of the acrylic copolymer (a) is 50
The thermosetting solvent-based coating composition according to claim 1, which has a temperature of 0.degree. (3) The glass transition point of the acrylic copolymer (b) is 50
The thermosetting solvent-based coating composition according to claim 1, which has a temperature of 0.degree.