JPS5844430B2 - Coating film formation method using 2-coat 1-bake coating system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming a coating film with excellent coating appearance and exposure weather resistance in a two-coat one-bake coating system.

Conventionally, two-coat, one-bake coating systems have been widely used for top coating of vehicles such as passenger cars as they provide excellent coating film appearance quality.

However, in recent years, it has been required to provide coating films with not only excellent coating appearance quality but also excellent weather resistance.

In order to improve the quality of the appearance of the paint film, the conventional method for meeting such demands is to apply the first coat (hereinafter sometimes referred to as a base coat) at an internal temperature of two coats.

) to speed up the drying of the base coat and the second coat (hereinafter sometimes referred to as clear coat).

In order to eliminate miscibility at any interface, cellulose ester is added to the base paint (see Japanese Patent Publication No. 49-38005), or the solubility parameter of the solvent of the clear paint is lowered (see Japanese Patent Publication No. 53-35580). It has been known.

On the other hand, when it comes to improving weather resistance, clear paints
■ Addition of compounds with ultraviolet absorption ability, ■ Use of resins obtained by polymerizing (or addition condensation) compounds containing groups with ultraviolet absorption ability, Addition of C antioxidants, ■ Addition of light stabilizers, or these combinations are known.

According to the present inventors, the deterioration of paint films due to exposure is extremely significant, in addition to the deterioration caused by photo-oxidation caused by light (including ultraviolet rays), as well as the deterioration due to the water resistance of the paint film due to rain, dew condensation, moisture absorption, etc. I found that it was working.

In order to improve the water resistance of a paint film, the following methods are generally used: ■ Increase the crosslinking density of the paint film, ■ Decrease the concentration of unreacted hydrophilic functional groups in the paint film, and ■ Decrease the water-soluble substances in the paint film. Possible methods include:

However, with respect to water resistance, which is discussed as the exposure weather resistance of a paint film, long-term water resistance performance of the paint film becomes a problem, and a method slightly different from the above three methods is required.

In other words, it has become clear that the hydrolysis reaction progresses considerably in paint films that are exposed over time, and that suppressing this hydrolysis reaction is an important point in improving weather resistance. , suppressing water diffusion, ■ Ease of hydrolysis of a paint film is correlated with an increase in carboxyl group concentration in the paint film, so suppressing this carboxyl group concentration, ■
It has been found that excessive initial crosslink density is rather unfavorable in terms of water resistance, since hydrolysis of the coating film is most likely to occur at the crosslinked portions.

In addition, peeling and clutching phenomena are likely to occur as weather resistance abnormalities of the coating film in a two-coat, one-bake coating system.

It has been found that the peeling phenomenon is likely to occur when water that has passed through the clear coating is absorbed by the coating, induces decomposition reactions such as hydrolysis, and reduces the cohesive force of the coating.

In addition, it is known that the crank phenomenon occurs when internal strain due to heat or volumetric contraction is applied to a paint film, and the elongation rate of the paint film itself exceeds the rate of elongation. Since the higher the value, the less likely the crack phenomenon will appear,
It has been found that by setting the coating film to an appropriate glass transition temperature range in consideration of the balance with water resistance, it is possible to improve the weather resistance of the coating film without impairing its appearance.

Based on the above findings, the present inventors have completed a coating film forming method in a two-coat, one-bake coating system that can provide a coating film with excellent coating appearance and exposure and weather resistance.

That is, the present invention is a coating film forming method using a two-coat, one-bake coating system, in which a base coating containing the following resin composition (a) is first applied, and then a clear coating containing the following resin composition (b) is applied. This method is characterized by applying a paint and then heating and curing it.

(XA) (1) Add the ethylenic monomer having a hydroxyl group in an amount that gives the resin solid content a hydroxyl value of 40 to 80, (2) Add the carboxyl group-containing ethylenic monomer to the resin solid content in an amount that gives an acid value of 5 to 25. and (3) other ethylenic monomers that can be copolymerized with 1) and (2) above in a total of 100 parts (parts by weight, the same applies hereinafter) with a glass transition temperature of 20 to 20. Vinyl multi-component copolymer 8 at 50°C and solubility parameter 10.3-11.5
5 to 60 parts of the crosslinking component (B), and 15 to 40 parts of the crosslinking component (B) in a total of 100 parts.

(I:I)(Q(4) Aromatic vinyl monomer (0-
40 parts) and/or carbon number 8 as an alcohol component
40 to 80 parts of an acrylic acid or methacrylic acid ester monomer (0 to 80 parts) having the above alkyl group, (5) an ethylenic monomer having a hydroxyl group in an amount that gives a hydroxyl value of 50 to 90 in the resin solid content. , (6) ethylenic monomer having a carboxyl group in an amount such that the acid value of the resin solid content is 5 to 25, and (7) other ethylenic monomer that can be copolymerized with the above (4) to (6) to 50%. A vinyl multi-component copolymer having a glass transition temperature of 10 to 45°C obtained by polymerization in a proportion of 100 parts or less in a total of 80 to 60 parts.
parts, and 0 alkoxylated melamine formaldehyde condensate 20
-40 parts in a total of 100 parts.

(a) Regarding the base paint used in the present invention: First, as the ethylenic monomer (1) having a hydroxyl group for constituting the vinyl multi-component copolymer (4), specifically, hydroxyethyl acrylate, acrylic hydroxypropyl acid, hydroxybutyl acrylate, hydroxymethyl methacrylate, hydroxyethyl methacrylate,
Examples include hydroxypropyl methacrylate, hydroxybutyl methacrylate, N-methylolacrylamide, allyl alcohol, and the like.

This monomer (1) is used in the monomer blending Zoo portion of the vinyl multi-component copolymer (A) in an amount such that the hydroxyl value of the resin solid content of the resulting polymer is from 40 to 80.

When the hydroxyl value is less than 40, the crosslinking density of the coating film is low and its water resistance is low.

If it exceeds 80, the number of hydrophilic groups increases rapidly when the coating film undergoes hydrolysis due to exposure (and its water resistance becomes poor).

Next, ethylenic monomer (2) having a carboxyl group
Specific examples include acrylic acid, methacrylic acid, crotonic acid, ethacrylic acid, propylacrylic acid, isopropylacrylic acid, itaconic acid, maleic anhydride, fumaric acid, and the like.

C1 This monomer (2) is used in an amount such that the resin solid content of the resulting polymer has an acid value of 5 to 25 in 100 parts of the monomer blend of the vinyl multi-component copolymer (A).

If the acid value is less than 5, the coating film will be insufficiently cured and its water resistance will be low.

If it exceeds 25, the coating film is susceptible to hydrolysis and its water resistance is low.

Next, as other ethylenic monomers (3), specifically, acrylic acid alkyl esters (methyl acrylate,
Ethyl acrylate, isopropyl acrylate, n-propyl acrylate, n-butyl acrylate, t acrylate
-butyl, 2-ethylhexyl acrylate, n-octyl acrylate, lauryl acrylate, etc.), methacrylic acid alkyl esters (methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-propyl methacrylate, n-butyl methacrylate, Isobutyl methacrylate, t-butyl methacrylate, methacrylic acid 2
- Ethylhexyl, n-octyl methacrylate, lauryl methacrylate, stearyl methacrylate, tridecyl methacrylate, etc.), addition reaction products of fat and oil fatty acids with acrylic acid or methacrylic acid ester monomers having an oxirane structure (e.g. nistearic acid and glycidyl methacrylate) addition reaction products), addition reaction products of oxirane compounds containing C8 or higher alkyl groups and acrylic acid or methacrylic acid (e.g., Japanese Patent No. 583185, Japanese Patent No. 609)
No. 322), styrene, α-methylstyrene, o-1f
Rustyrene, m-methylstyrene, p-methylstyrene, p tert 7” styrene, benzyl acrylate, benzyl methacrylate, itaconate ester (
Examples include dimethyl itaconate), maleic esters (dimethyl maleate, etc.), fumaric esters (dimethyl fumarate, etc.), acrylonitrile, methacrylatetrile, vinyl acetate, and the like.

The target vinyl multi-component copolymer diagram is based on the above three monomers (
It can be obtained by blending 1 or more of 1) to 3) in a predetermined ratio (total ioo parts) and polymerizing in a conventional manner.

For example, it can be obtained by mixing a monomer blend with a known polymerization catalyst, dropping the mixture into a reaction vessel containing a solvent heated to a polymerizable temperature, and aging the mixture.

The vinyl multi-component copolymer (A) thus obtained needs to have a glass transition temperature of 20 to 50°C.

If the temperature is lower than 20°C, water Q will easily diffuse into the coating film, and the coating film will likely peel off due to exposure.

If the temperature exceeds 50°C, the elongation rate of the coating film decreases and the cracking phenomenon of the clear coating film increases.

Note that the above glass transition temperatures are T and G. Fox: B
ull Am, Phys Soc,,l/163
．． 123 (1956) formula: 1/Tg-ΣWn/T
gn (Tg: glass transition temperature of copolymer, Wn:
It can be determined by the glass transition temperature of a homopolymer of n monomers).

The glass transition temperature of homopolymers is described, for example, in "Handbook of Polymer Materials", pages 1275 to 1283.

Further, the vinyl multi-component copolymer (4) has a solubility parameter of 10.3 to 11.5 (preferably 10.5 to 1).
1.3).

If it is less than 10.3, mixing with the clear paint will occur and the finished appearance of the paint film will deteriorate.

If it exceeds 11.5, the water resistance of the coating film will deteriorate and the weather resistance will be impaired.

Note that the above solubility parameter (δsp) + iK, W.

SUH, J, M, CORBETT: Journal
ofApplied Polymer 5cien
ce, 12.2359 ('68) formula: δ8p=(
Vml・δml+fshik・δmh )/(j instigation■+/
■E) (ml: low Sp solvent, mh: high Sp solvent, δ: solubility parameter, V: molecular volume at cloudy point).

Specifically, the crosslinking component (B) used in combination with the vinyl multi-component copolymer (A) includes blocked polyisocyanate, alkoxylated melamine formaldehyde condensate (condensation of melamine and formaldehyde or paraformaldehyde) (e.g., methoxylated methylolmelamine, imbutoxylated methylolmelamine, n-butoxylated methylolmelamine)
etc., and at least one of these is used.

In the present invention, the resin composition (a) includes the above component A and B.
It is obtained by blending the components at a ratio of 85 to 60 parts of the former and 15 to 40 parts of the latter (100 parts in total) based on the resin solid content.

If the latter is less than 15 parts, the bridge density of the coating film will not increase, and if it exceeds 40 parts, the coating film will be easily hydrolyzed and the finished appearance of the coating film will also deteriorate.

In the base paint of the present invention, the above resin composition (a)
In addition, various solvents, metal powders such as aluminum powder, pigments,
Colorants such as dyes, fillers, surface conditioners (e.g. silicone-based,
acrylic resin), etc.

Any of the known pigments and dyes can be used as the coloring agent, such as metal oxides, metal hydroxides, metal powders, metal sulfides, sulfates, carbonates, and chromium, which are commonly used for paints. Salts such as acid lead, organic pigments and organic dyes, etc. are used.

Fillers such as silica and talc are also used.

(b) Regarding the clear paint used in the present invention: First, a vinyl multi-component copolymer (aromatic vinyl monomer for composing q) (specifically, styrene, α-methylstyrene, 0-methylstyrene) , m-methylstyrene,
p-methylstyrene, p-tert-butylstyrene,
Examples include benzyl acrylate and benzyl methacrylate.

In addition, examples of the acrylic acid or methacrylic acid ester monomer (4'') having an alkyl group having 8 or more carbon atoms as an alcohol component include 2-ethylhexyl acrylate, n-octyl acrylate, lauryl acrylate, and methacrylic acid. 2-ethylhexyl, methacrylic acid n
-Octyl, lauryl methacrylate, stearyl methacrylate, tridecyl methacrylate, addition reaction product of oil or fat fatty acid and acrylic acid or methacrylic acid ester monomer having an oxirane structure (e.g. addition reaction product of nistearic acid and glycidyl methacrylate), C8 or higher Examples include addition reaction products of an oxirane compound containing an alkyl group with acrylic acid or methacrylic acid (eg, Japanese Patent Nos. 583185 and 609322).

The above two types of monomers (4') (the four may be used either alone or in combination, and are used in a proportion of 40 to 80 parts in 100 parts of the monomer blend of the vinyl multi-component copolymer (C)) do.

If it is less than 40 parts, the water absorption and water diffusion of the coating film will increase.

If it exceeds 80 parts, polymerizability deteriorates, it is difficult to obtain a uniform copolymer, and coating film performance deteriorates.

In addition, if the aromatic vinyl monomer (4 parts) exceeds 40 parts, the light resistance of the coating film will decrease.

Preferably, the monomers (4) are monomers (4 parts of styrene (15-30 parts) and monomers (4") (
30-65 parts) may be used in a proportion of 60-80 parts.

Next, an ethylenic monomer (5) having a hydroxyl group
Specific examples thereof include those exemplified in the above-mentioned monomer (1).

This monomer (5) has a hydroxyl value of 50 to 90. It is preferably used in an amount of 60 to 80.

When the hydroxyl value is less than 50, the crosslinking density of the coating film is low and its water resistance is low.

When it exceeds 90, when the coating film undergoes hydrolysis due to exposure, the rate of increase in hydrophilic groups is rapid, resulting in poor water resistance.

Next, ethylenic monomer (6) having a carboxyl group
Specific examples include those exemplified in the above-mentioned monomer (2).

This monomer (6) is used in an amount such that the resin solid content of the obtained polymer has an acid value of 5 to 25 in 100 parts of the monomer blend of the vinyl multi-component copolymer (q).

If the acid value is less than 5, the coating film will be insufficiently cured and its water resistance will be low.

If it exceeds 25, the coating film is susceptible to hydrolysis and its water resistance is low.

Next, regarding other ethylenic monomers (7), specifically, acrylic acid or methacrylic acid esters (methyl acrylate, ethyl acrylate, impropyl acrylate, n-propyl acrylate, n-butyl acrylate,
t-butyl acrylate, methyl methacrylate, ethyl methacrylate, inpropyl methacrylate, n-propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate), itaconic acid ester (itaconic acid) dimethyl, etc.), maleic acid esters (dimethyl maleate, etc.), fumaric acid esters (dimethyl fumaric acid, etc.), acrylonitrile, methacrylonitrile, vinyl acetate, and the like.

This monomer (7) is used in a proportion of 10 to 45° C. parts of the vinyl multi-component copolymer (C1 monomer blend).

If it exceeds 50 parts, the balance between glass transition temperature and water resistance will be lost.

The desired vinyl multi-component copolymer (q is a combination of the above-mentioned four or five monomers (4) to (7) in a predetermined proportion (total 100 parts) using one or more of the above-mentioned four or five monomers (4) to (7)). It can be obtained in the same manner as polymerization mA).

The vinyl multi-component copolymer (q) thus obtained must have a glass transition temperature of 10 to 45°C.

When the temperature is less than 10°C, water easily diffuses into the coating film, and exposure to the coating film tends to cause a decrease in gloss and peeling of the coating film.

When the temperature exceeds 45°C, the elongation rate of the coating film is low and cracks are likely to appear.

The alkoxylated melamine formaldehyde condensate 0 used in combination with such a vinyl multi-component copolymer (q) is an alkoxylated product of a condensate of melamine and formaldehyde or paraformaldehyde, such as methoxylated methylol melamine, imbutoxylated methylol melamine, etc. , n-butoxylated methylolmelamine, etc., and at least one of these is used.

In the present invention, the resin composition (b) includes the above C component and D.
It is obtained by blending the components at a ratio of 80 to 60 parts of the former and 20 to 40 parts of the latter (total ioo parts) based on the resin solid content.

If the latter is less than 20 parts, the crosslink density of the coating film will not increase, and if it exceeds 40 parts, the coating film will be easily hydrolyzed.

In the clear paint of the present invention, the above resin composition (b)
In addition, it may contain the aforementioned various solvents, surface conditioners, ultraviolet absorbers, light stabilizers, and the like.

Conventional techniques may be employed to form a coating film in two coats and one bake using the base paint and clear paint having the above formulations.

For example, each paint is diluted with a diluting solvent to a predetermined viscosity, and the base paint is spray applied to a film thickness of 20 μm.
After setting for about 3 minutes, apply clear paint to a thickness of 30 μm.
Simply apply the coating by spray coating, set for about 5 minutes, and then bake at a predetermined temperature for a predetermined time.

The coating film obtained in this way is the conventionally known 2-coat 1 coating film.
Compared to baked-on coatings, it has a good coating appearance and excellent performance, especially in terms of exposure and weather resistance.

Next, the present invention will be specifically explained with reference to Examples and Comparative Examples.

Note that % means weight % and ratio means weight ratio.

Examples 1 to 4 and Comparative Examples 1 to 7 Ingredient A: (Example 1) Kyjirol 3201, n-butanol 80F, methacrylic acid in a 2J separable colben equipped with a reflux condenser, dropping funnel, thermometer and stirring blade. 280 g of methyl, 384 g of ethyl acrylate, 1282 g of 2-hydroxyethyl methacrylate, and 8 tons of methacrylic acid were charged at 110°C.
Kijiroru 320 while maintaining that temperature.
r1n-butanol 80? , azobisin butyronitrile l and lauryl mercaptan 2f? The mixed solution** was lowered in a continuous manner for 3 hours, and after the dropwise addition was completed, it was kept for 2 hours.
The reaction has ended.

Resin solid content 50%. According to the above synthesis conditions, the following 1st
Various A components were synthesized using the monomer formulations shown in the table.

Component B: Used n-butylated methylolmelamine (Knee Buff 20SE60J manufactured by Mitsui Toatsu Co., Ltd., resin solid content 60%).

140 parts of the above component A, 50 parts of component B, aluminum pigment (“Alpaste #1123NJ” manufactured by Toyo Aluminum Co., Ltd.) 2
2 parts and 30 parts of pheasant roll, and the mixture 242 parts
part of mixed solvent (toluene/isobutanol/ethylene glycol monoethyl acetate = 60/20/20)
The mixture was diluted to 13 seconds (20° C.) using a /F64 Ford Cup and used as a base paint.

Examples 5 to 15 and Comparative Examples 8 to 17 Component C: (Example 5) Kijiroll 4402 and
-Butanol 160f? After charging and raising the temperature to 120°C, styrene 240y, 2-ethylhexyl methacrylate 1605', methyl methacrylate 85-6f, n-butyl methacrylate 76.8F, n-butyl acrylate 12
01, meta**hydroxyethyl acrylate 111.25
', methacrylic acid 6.4r and azobisisobutyronitrile 16f? A mixed solution consisting of Kijirole 50F and benzoyl peroxide 11 was poured down isocratically through a dropping funnel for 3 hours, and after 30 minutes of ripening time, a mixed solution consisting of Kijirole 50F and Benzoyl Peroxide 11 was allowed to flow down, followed by aging for 2 hours, and then 150 parts of Kijirole. The reaction was terminated.

Resin solid content 50%. According to the above synthesis conditions, the following second
Various C components were synthesized using the monomer formulations shown in the table.

Component D: n-butoxylated methylolmelamine (Kneepan 208E60J manufactured by Mitsui Toatsu) was used.

The above C component and D component were blended so that the resin solid content ratio was 70/30, and diluted with a Kijiroll/I64 Ford cup for 25 seconds (20° C.) to obtain a clear paint.

The base paints prepared in Examples 1 to 4 and Comparative Examples 1 to 7 were applied to intermediate coated steel plates, and then Examples 5 to 15 and Comparative Examples 8 to 16 were applied.
The clear paint prepared in step 1 was sprayed in two stages at intervals of 2 minutes, and then at intervals of 3 minutes, in a water washing booth at a temperature of 23°C and humidity of 85%, so that the dry film thickness was 20μ for the former and 30μ for the latter. The latter was spray-painted in a wet-on manner in one stage, and the coated plate was then baked in a dryer at 140° C. for 30 minutes to prepare a test plate.

The intermediate coated steel plate used was a polished mild steel plate that had been degreased and chemically treated and coated with automotive electrodeposition paint and intermediate coat paint on a line.

The finished appearance of each of the above test plates was evaluated.

The results are shown in Table 3.

The evaluation was rated ○ if the 60 degree gloss was 90 or more, and × if it was less than 90.

In addition, each of the above test plates was tested using a sunshine weather meter (manufactured by Suga Test Instruments) (600 hours of irradiation) and then a wet tester (500 hours of irradiation).
One cycle is to conduct the test at 0°C, 98% relative humidity, 96 hours), and this cycle is repeated to detect abnormalities in the appearance of the paint film (
Cracking, peeling, and reduction in gloss) were evaluated.

The results are shown in Table 3. In addition, for evaluation of paint film peeling, remove water droplets from the surface of the test plate taken out from the wet tester, dry it at room temperature for 30 minutes, and then make a cross cut on the painted surface.
Adhesive tape was attached to the cut surface, and when the adhesive tape was peeled off, the coating film remained.

○ indicates no abnormality, and × indicates peeling of the paint film.

Crank evaluation is based on visual appearance: ○ indicates no abnormality;
× indicates that cracks were observed on the painted surface.

Regarding the gloss evaluation, ◯ indicates that no significant loss of gloss was observed by visual inspection, and × indicates that significant loss of gloss was observed.

Examples 16-18 and Comparative Examples 17-20 First paint A
The components synthesized in Example 1 were used as clear paint C.
Test plates were obtained in the same manner as in the previous example, except that the components synthesized in Example 5 were used in the proportions shown in Table 4 below, and the test results are shown in Table 5. show.

Claims (1)

[Claims] A method for forming a coating film using a 12-coat, one-bake coating system, in which a coating material containing the following resin composition (a) is first applied, and then a clear coating material containing the following resin composition (b) is applied. A method characterized by applying and then heating and curing. (B) (A) (1) The ethylenic monomer having a hydroxyl group has a hydroxyl value of 40 to 80 in the resin solid content.
(2) an amount of the ethylenic monomer having a carboxyl group that gives the acid value of the resin solid content of 5 to 25, and (3) other ethylenic monomers that can be copolymerized with (1) and (2) above. A glass transition temperature of 20 to 50°C and a solubility parameter of 10.
3-11.5 vinyl multi-component copolymer 85-60 parts by weight,
and (B) a resin composition containing 15 to 40 parts by weight of a crosslinking component for a total of 100 parts by weight. (B) (C) (4) Aromatic vinyl monomer (0 to 4
0 parts by weight) and/or 40 to 80 acrylic acid or methacrylic acid ester monomers (0 to 80 parts by weight) having an alkyl group having 8 or more carbon atoms as an alcohol component.
parts by weight, (5) an amount of ethylenic monomer having a hydroxyl group to give a hydroxyl value of 50 to 90 in the resin solids, (6) an amount of ethylenic monomer having a carboxyl group to give an acid value of 5 to 25 in the resin solids. and (7) a glass transition temperature of 10 to 45 obtained by polymerizing other ethylenic monomers that can be copolymerized with (4) to (6) above in a proportion of 50 parts by weight or less for a total of 100 parts by weight. ℃ vinyl multi-component copolymer 80~
60 parts by weight, and 20 to 40 parts by weight of a 0-alkoxylated melamine formaldehyde condensate in a total proportion of 100 parts by weight. 2. The method of item 1 above, wherein component (A) has a hydroxyl value of 50 to 75. 3. The method of item 1 above, wherein component (B) is an alkoxylated melamine formaldehyde condensate. 4. The method of item 3 above, wherein the alkoxylated melamine formaldehyde condensate is a butoxylated melamine formaldehyde condensate. The method according to item 1 above, wherein component 5(C) has a glass transition temperature of 20 to 35°C. 6. The method of item 1 above, wherein the paint containing the resin composition (a) contains metal powder.