JPS63258672A - Formation of film by two-coating and one-baking coating - Google Patents

Abstract

PURPOSE:To prevent color mixture and to improve brightness or the like by applying the coloring paint I contg. a vehicle wherein specified oil-free polyester resin and a cross-linking agent are blended at a specified rate, and thereafter applying coloring paint II having composition different from the paint I. CONSTITUTION:Coloring paint I contg. resin composition consisting of 85-60pts. wt. oil-free polyester resin having 10-11.5 soluble parameter at a ratio of solid content of resin and 15-40pts.wt. cross-linking agent as a vehicle is prepared, and this is applied on a material to be coated. Separately coloring paint II contg. resin component consisting of 85-50pts.wt. oil-free polyester resin having 9.5-10.5 soluble parameter at a ratio of solid content of resin wherein the difference of soluble parameter between it and the above-mentioned resin is 0.2-1.5 and 15-50pts.wt. cross-linking agent as the vehicle is prepared. Furthermore this is applied on the coated film of the above-mentioned paint I and thereafter heated and cured to form a film resulting from a two-coating and one-baking coating system.

Description

[Detailed Description of the Invention] Technical Field The present invention relates to a method for forming a coating film using a two-coat, one-bake coating system, and more particularly, to a two-coat coating method of a colored coating containing an oil-free polyester resin and an alkoxylated melamine-polmaldehyde resin as a vehicle. The present invention relates to a method for forming a coating film with excellent appearance in one bake coating.

When applying multiple coats of conventional technology paint, the first coat is usually applied;
Drying or dry baking requires a lot of man-hours because the next paint is applied afterwards and drying or dry baking is performed, so the first paint is applied and while it is still wet, the second paint is applied and finally dried. Two-coat, one-bake painting that involves baking is attracting attention.

However, in such a coating method, mixing of both paints tends to occur during application or heat curing, so
In the case of solid colors, it is extremely difficult to select the paint, and the first
The only paints that have been put into practical use are coating a metallic base paint, then applying a clear paint, and then curing with heat. Moreover, even in the metallic base coat-clear coat system, the technology of adding cellulose ester to the base coat to improve drying properties (for example, Japanese Patent Publication No. 38005/1973) is too ineffective in preventing repelling and denting that cause abnormalities in the appearance of the paint film. technology to lower the solubility parameter of the solvent in clear coat paints (
For example, in Japanese Patent Publication No. 53-35580, most of the solvent evaporates when the paint is applied, so the effect is small; Tokuko Sho 58-444
No. 30) is more effective and more practical than the first two, but the resin is limited to acrylic, and the technology is for base coats and clear coats, so it cannot be applied to solid color paints. be. In the paint field, paints that use polyester resin as a vehicle have high hardness and excellent solvent resistance, so they are particularly useful for metal coatings, interior coatings for automobiles, etc. With solid colors, it is particularly difficult to obtain stability between the eyebrows, and no effective two-coat, one-bake painting method using colored paints has yet been found.

Problems to be Solved by the Invention Accordingly, the present invention is a polyester-based coating composition, which is capable of two-coat one-bake coating in which another colored coating is applied on top of a colored coating and then cured by heating, and which improves the appearance. There is a strong demand for a coating film forming method that can provide an excellent coating film, particularly in the automobile industry and other fields, and it is an object of the present invention to meet this problem.

Means for Solving the Problems According to the present invention, the above object is achieved by: (A) 85 to 60 parts by weight of an oil-free polyester resin having a solubility parameter of 10 to 11.5 in terms of resin solid content (B) Crosslinking agent
Colored paint (I) containing as a vehicle a resin composition containing 15 to 40 parts by weight for a total of 100 parts by weight
Then, the resin solid content ratio is <C) solubility parameter is within the range of 9.5 to 10.5, and the difference from the solubility parameter of (A) resin is 0.
．． Oil-free polyester resin with a rating of 2 to 1.5
85-50 parts by weight (D) Crosslinking agent 1
2-coat 1 characterized in that a colored paint (II) containing as a vehicle a resin composition containing 5 to 50 parts by weight for a total of 100 parts by weight is applied and then heated and cured.
This is achieved by a coating film formation method using a bake coating system.

Comparatively low molecular weight compounds of so-called oil-free polyester resins obtained by polycondensation of polybasic acids and polyhydric alcohols, such as those with a number average molecular weight of up to about 3,000, are combined with a crosslinking agent in the form of a fess and baked to harden. It is used as a resin vehicle for paints. The solubility parameter of such oil-free polyester resin is usually 10 to
It shows a high value of 11.5. In addition, the solubility parameter (δ
Sp) Hani, W, 5IJH, J, M, C0RBETT
; Journal of Applied Polym
ers 5science 12.2359 (1968
) (6 formula %) (where mJ: low Sp solvent, mh: high sp solvent, δ: solubility parameter, ■=molecular weight at cloudy point), and is a quantitative expression of the polarity of a substance.

In the present invention, first, 85 to 65 parts by weight of this ordinary oil-free polyester resin in terms of resin solid content as the colored paint (I) is added to the substrate or the intermediate coated substrate;
A colored paint containing as a vehicle a resin composition containing 15 to 40 parts by weight of a crosslinking agent for a total of 100 parts by weight is applied. Therefore, the oil-free polyester resin used in this paint (I) has a solubility parameter of 10 to 1.
1.5, and its number average molecular weight is usually 1,
It is preferable that it is 000-3,000.゛Crosslinking agents include blocked polyisocyanates, alkoxylated melamine formaldehyde resins (alkoxylated products of condensates of melamine and formaldehyde or paraformaldehyde, such as methoxylated methylolmelamine, imbutoxylated methylolmelamine, n-butoxylated methylolmelamine) etc., and at least one of them is used.

In the present invention, a resin composition is used in which the oil-free polyester resin is blended in a solid weight ratio of 85 to 65 parts by weight and the crosslinking agent is 15 to 40 parts by weight (total 100 parts by weight). This is because if the crosslinking agent is less than 15 parts by weight, the crosslinking density of the coating film will be low and a tough coating film cannot be obtained, and if it exceeds 40 parts by weight, the hydrolyzability and alkali resistance of the coating film will decrease, both of which are undesirable. It is from.

The coating material (I) may contain various solvents, colorants such as pigments and dyes, fillers, surface conditioners, and other coating additives in addition to the above-mentioned resin composition.

Colored paint (I) applied on top of this paint (I) in the present invention
I) is an oil-free polyester resin 85 to (C) having a solubility parameter within the range of 9.5 to 10.5 and a difference from the solubility parameter of the (containing) resin of 0.2 to 1.5. 50 parts by weight and 15 to 50 parts by weight of crosslinking agent, total 10
This is a colored paint containing a resin composition as a vehicle in a proportion of 0 parts by weight. As already mentioned, the solubility parameter of oil-free polyester resin for ordinary paints is 10.
11.5, but we have applied coatings based on such resins based on oil-free polyester resins with different values of solubility parameters than the polyester resins of paint (I). When applying the paint, mixing of the resins and thus color mixing is avoided; this effect is achieved when the solubility parameters of both resins differ by 0.2 to 1.
From the viewpoint of appearance such as gloss and sharpness, the solubility parameter of the oil-free polyester resin of paint (II) is preferably within the range of 9.5 to 10.5, and the most effective The solubility parameter of the oil-free polyester resin of paint (I) is 0.2 to 1.5.
It was found that the low value should be determined within the range of 9.5 to 10.5, which was an important basis for the present invention.

If the difference in the solubility parameters of the oil-free polyester resins of paint (I) and paint (II) is less than 0.2, color mixing of the two will occur for the purpose of the present invention in which both are colored paints.
No improvement in appearance can be obtained, and it is impractical for the difference to exceed 1.5 at best if it is large. It has also been found that the difference in solubility parameters is preferably between 0.4 and 1.0. Since the solubility parameter is also proportional to the surface tension of the paint, the solubility parameter of the resin of paint (II) that forms the surface coating is generally lower, ranging from 9.5 to 9.5.
It is advantageous in terms of coating film gloss and image clarity that it is determined within the range of 10.5 and preferably lower than that of the resin of paint (I). Paint (II) to form a surface coating layer
) Therefore, it is preferable that the oil-free polyester resin used in
~2000, hydroxyl value 80-210, acid value 5-3
0 oil-free polyester is recommended as preferred. Such a resin may contain, for example, alicyclic polybasic acid and aromatic polybasic acid in a ratio of 10:90 to 80 as polybasic acid components.
: Used at a molar ratio of 20, and a mixture of dihydric alcohol and trihydric alcohol as a polyhydric alcohol component.
; R2 and R4 are each CH3 or C21+5: R
3 is H or CH3), C) I20H C211, -C-R5 ■ H2O11 (wherein, R5 is C2■ or C4H9>) Contains 10 to 35% by weight of the resin weight The trihydric alcohol is obtained by polycondensation of trimethylolethane and/or trimethylolpropane.In order to further improve the curability, an alicyclic polybasic acid is first used as the above-mentioned polybasic acid. After reacting with a polyhydric alcohol, aromatic polybasic acids, especially those that exhibit a half-equivalent point potential of 1350 mV or more by non-aqueous potentiometric titration in a state capable of developing a resin acid value, such as phthalic anhydride and isophthalic acid. , terephthalic acid, trimellitic anhydride, pyromellitic anhydride, etc. are subsequently added and the reaction is continued (Japanese Patent Application No. 154209/1989). It is preferable to use an oil-free polyester resin based on an aromatic polybasic acid that exhibits a half-equivalent point potential of −350 mV or more by water potentiometric titration.

In the present invention, the paint (II) contains 85 to 50 parts by weight of an oil-free polyester resin characterized by the solubility parameters as described above and 15 to 50 parts by weight of a crosslinking agent (total 1
00 parts by weight) is used as a vehicle. As crosslinking agents, the same compounds as mentioned for paint (I) are used. In the paint (II), as the oil-free polyester resin, a resin having a relatively high hydroxyl value as mentioned above is preferably selected, so the proportion of the crosslinking agent is somewhat higher than that of the paint (I), and the oil-free polyester resin is 85 to 85. 50 weight 1 part to crosslinking agent 1
It is desirable that the proportion is selected from 5 to 50 parts by weight.

However, if the amount of the crosslinking agent is less than 15 parts by weight, sufficient crosslinking density cannot be obtained, and if it exceeds 50 parts by weight, the hydrolyzability and alkali resistance of the coating film will decrease. The coating material (II) may also contain various solvents, colorants such as pigments or dyes, fillers, surface conditioners, and other arbitrary coating additives in addition to the above-mentioned resin composition.

The above paint (I) and paint (II) are applied using a normal coating method.
For example, by diluting it to a predetermined viscosity and sequentially applying it by spray painting, and then subjecting it to heat curing treatment, it is possible to obtain a good coating film appearance, that is, a coating film with no color mixture and excellent gloss and image clarity. In the film forming method of the present invention, for example, a black top coat is applied over a gray intermediate coat, or a colored paint layer of color H is provided on a colored paint layer of color (■), and a two-coat, one-bake coating system is used to improve the appearance. Because it is possible to obtain an extremely good coating film,
It is extremely useful in fields such as metal painting and automobile painting.

The present invention will be explained below with reference to Examples. Parts and percentages are by weight unless otherwise specified.

Example 1 (Avf1 fat) Trimethylolpropane 22
3 parts of neopentyl glycol, 319 parts of neopentyl glycol, and 188 parts of 1.6-hexanediol were charged, heated and melted at 80 to 100'C, and when stirring became possible, stirring was started.
Furthermore, 707 parts of isophthalic acid, 155 parts of adipic acid, and 0.8 parts of dibutyltin oxide are added, and the temperature is raised to 160°C. When condensed water begins to form, water is distilled out of the system, kept at 160 to 170°C for 1 hour, and then raised to 210°C over 4 hours.

When the temperature reaches 210°C, 30 parts of xylene is gradually added into the flask, and the condensation reaction is continued by the xylene reflux method. When the resin acid value reaches 1O10, the reaction is terminated and the mixture is cooled. After cooling, 570 parts of xylene was added, and the non-volatile content was 70.4%.
Gardner viscosity X-Y at 25°C, resin acid value 10,
4. Resin solution I having a solubility parameter (SP value) of 10.7 was obtained.

Example 2 ε-caprolactone was added to 974 parts of resin solid content of Example 1.
46 parts were added and reacted at 150°C. During the reaction, the amount of unreacted ε-caprolactone was monitored using IR, and the reaction rate was 98%.
At the point above, the reaction was terminated and the mixture was cooled. After cooling, 480 parts of xylene was added, and the nonvolatile content was 70.2%, and the viscosity was V-
A resin solution (■) having W, a resin acid value of 9.0, and a solubility parameter of 1005 was obtained.

Examples 3 to 5 and Comparative Examples 1 to 3 Based on the charging compositions shown in Table 1, resin solutions 1 to 5 and 1 to 3 were obtained in the same manner as in Example 1. The resin property values of these resin solutions are shown in Table 1.

According to the above Examples 1 to 5 and Comparative Examples 1 to 3, various (A
) resin was synthesized.

(Left below) (Note 1) HPN...Hydroxybivaleic acid neopentyl glycol ester Example 6 (Cffl fat) In a four-loaf flask equipped with a heating device, a stirrer, a thermometer, a nitrogen introduction tube, and a cooling tube, Hexahydrophthalic anhydride 1
50.3 parts of trimethylolpropane, 85.3 parts of hydroxypivalic acid neopentyl glycol ester (HP N ), 322.4 parts of neopentyl glycol, 161.4 parts of neopentyl glycol, and 0.5 parts of dibutyltin oxide were charged and heated. did. Once the raw materials have melted and can be stirred, start stirring and gradually raise the temperature from 180℃ to 230℃ over 3 hours.

At this time, while distilling the generated condensation water out of the system,
After keeping warm at ℃ and reacting until the resin acid value reached 2.0, it was heated to 80℃.
Cooled to . Furthermore, 376.5 parts of isophthalic acid was added and heated again. The temperature was raised from 190°C to 210°C over 2 hours, and the temperature was raised to 210°C while distilling the generated condensed water out of the system.
Continue the reaction at °C. Resin acid value 10. After reacting to O, it was cooled and diluted with 428 parts of xylene to reduce the non-volatile content to 69.
A resin solution A having a Gardner viscosity of 8% and a Gardner viscosity of TU at 25° C. was obtained.

The solubility parameter (SP value) of this resin solution A is 9.7
Met. Furthermore, as a result of non-aqueous potentiometric titration using pyridine as a solvent and tetrabutylammonium hydroxide (methanol/benzene = 1/10 solution) as a titration reagent, it was found that there were two inflection points; Half-equivalent point potential -3
00 mV (which comes from isophthalic acid),
It was confirmed that it accounted for 80 mol% of all carboxyl groups.

Example 7 246.4 parts of hexahydrophthalic anhydride, 264.5 parts of isophthalic acid, 185 parts of trimethylolpropane HP
257.6 parts of N and 0.5 parts of dibutyltin oxide were charged and reacted in the same manner as in Example 6. The reaction was completed at a resin acid value of 2.0 by keeping the temperature at 230°C, and after cooling to 80°C, 21.1 parts of phthalic anhydride was further added, and the reaction was carried out at 150°C for 1 hour. Diluted with 335 parts of xylene and non-volatile content 75.1. Gardner viscosity at 25°C X-Y, S
P value 10.0, half-equivalent point potential -290mV, -290m
A resin solution B containing 80 mol% of carboxyl groups exhibiting V was obtained.

Example 8 Hexahydrophthalic anhydride 31g, 2 parts, isophthalic acid 146.4 parts, trimethylolpropane 212.7 parts,
1-(PN 319.6 parts, dibutyltin oxide 0
．． 5 parts were charged and the reaction was carried out in the same manner as in Example 6. 230
The reaction was completed at a resin acid value of 5.0 by keeping warm at ℃, and after cooling to 80℃, tetrachlorophthalic anhydride was added to 25.5.
of xylene and reacted at 150″C for 1 hour.
Diluted with 35 parts, nonvolatile content 75, Gardner viscosity u at 8.25°C, sp value! 0.0, half-equivalent point potential -1
50 mol% of carboxyl groups exhibiting 20 mV and 120 mV
Obtain a resin solution C.

Examples 9 to 15 Resin solutions D-J were obtained in the same manner as in Example 6 based on the charging composition shown in Table 2. However, isophthalic acid and phthalic anhydride were post-reacted in the same manner as in Example 6. Table 2 shows the resin property values of these resin solutions.

Comparative Examples 4 to 6 Based on the charging composition shown in Table 2, all raw materials were charged, reacted in the same manner as in Example 6, cooled to a resin acid value of 1010, and diluted with xylene to obtain resin solutions V to X. . Table 2 shows the resin property values of these resin solutions.

Various C
The resin was synthesized.

(Left below) (Note 1) HPN...Hydroxypivalic acid neopentyl glycol ester (Note 2) EHD...2-ethyl-1,3-hexanediol 2
H5 +10 C112-CI -Cll-C112-CH2
-CI+ 3H (Note 3) DEPD...2,2-diethyl-1,3-propanediol 2H5 HOCH2-C-CH20H Amount C2H2 (Note 4) BEPD...-2-n-butyl-2-ethyl-1 ,3-
Propanediol C211.

HOC112-C-CI 2011 -C4Hg (Note 5) TMPD...2,2.4-)-tumethyl-1,3-bentanediol (blank below) Example I6 Using the resin solution I obtained in Example 1 A dispersed gray intermediate coating paint was prepared based on the following formulation.

Solid content of polyester resin ■ 21.9 parts Melamine resin solid content (Kneepan 2ON-60, manufactured by Mitsui Toatsu Co., Ltd.) 9.4 parts Titanium R820 (manufactured by Sakai Chemical Co., Ltd.) 32 parts Mitsubishi Carbon MA-100 (manufactured by Mitsubishi Kasei Co., Ltd.) ) 0.12 parts Butyl cellosolve 5, θ parts Toluene 5.0 parts This paint is polyester resin/melamine resin = 70/30 <solid content weight ratio).

Subsequently, using the resin solution A obtained in Example 6, a dispersed black top paint (paint for automobile aluminum sash window frames) was prepared based on the following formulation.

Solid content of polyester resin A 24.0 parts Melamine resin solid content (?IMEL 1130-254J, manufactured by Mitsui Cyanamid Co., Ltd.) 16.0 parts Epoxy resin (EP-01)
50 varnish, non-volatile content 50%, manufactured by Yuka Shell)
4.1 part Mitsubishi Carbon MA-1001, 8 parts Titanium R8206 parts Shinkasha Red Y RT-759D (manufactured by Ciba Geigy) 0.5 parts Tsurupetz 100 (manufactured by Esso Standard Oil Co., Ltd., aromatic hydrocarbon solvent) 3.0 Partial butyl acetate ester
6.0 parts This paint has a polyester resin/melamine resin ratio of 60/40 (solid content weight ratio).

The resulting gray intermediate coat and black top coat were mixed with xylene/
Butyl acetate = 70/31) (weight ratio) The viscosity of each at 20°C in a mixed solvent is Ford Cup #4
The intermediate coating was diluted to give a dry film thickness of 40 μm on a coating film that had been cationically electrodeposited on a polished mild steel plate that had undergone chemical conversion treatment. After setting for 7 minutes, apply a black top coat to a dry film thickness of lθμ.
Apply stepwise coating to obtain 6 film thicknesses of approximately 5μ increments from 35μ to 35μ, and bake at 140°C for 30 minutes. Table 3 shows the results of evaluation of this cured coating film in terms of intermediate coat/top coat color mixing prevention film thickness (μ), top coat thickness of 30 μm, skin of the paint film, pencil hardness, water resistance, and alkali resistance.

Examples 17 to 25 and Comparative Examples 7 to 12 Based on the gray intermediate coating formulation and black top coating formulation of Example 16, Al! Each paint was prepared using L resin and C resin in the combinations shown in Table 3, and an intermediate coat/top coat was applied in the same manner as in Example 16.
Bake at 0℃ for 30 minutes.

Regarding these cured coatings, the intermediate coating/top coating has a thick μ
), and the results of evaluating the skin, pencil hardness, water resistance, and alkali resistance of the 30 μm topcoat film are shown in Table 3.

(Margin below) (Note 6) Intermediate/top coat color mixture prevention film thickness (μ) The minimum film thickness (μ) of the top coat that prevents the gray color of the intermediate coat from mixing with the black color of the top coat. Determine the film thickness (μ) and indicate the film thickness (μ).

(Note 7) Repellency and dents on the surface of the skin coating were evaluated using the following criteria.

○...No repelling or denting Δ...Some repelling or denting ×...Many repelling or denting Poor skin (Note 8) Water resistance The following is the condition of the painted surface after immersion in warm water at 40°C for IO days. It was evaluated based on the following criteria.

O... No abnormalities △... Some blisters occur ×... Blisters occur, gloss and sink (Note 9) Alkali resistance N/10 Dropped onto the coating film of NaOH aqueous solution and left at room temperature for 24 hours, then It was evaluated based on the following criteria.

O...No spot marks, no discoloration △...Spot marks, slight discoloration ×...Spot marks, significant discoloration Patent application agent

Claims (8)

[Claims] (1) Contains (A) 85 to 60 parts by weight of an oil-free polyester resin with a solubility parameter of 10 to 11.5 (B) 15 to 40 parts by weight of a crosslinking agent in a ratio of resin solid content of 100 parts by weight in total. A colored paint (I) containing a resin composition as a vehicle is applied, and then (C) the solubility parameter is within the range of 9.5 to 10.5 in terms of resin solid content, and (A) the resin is dissolved. The difference from the gender parameter is 0.
．． Oil-free polyester resin 85 that is 2 to 1.5
A colored paint (II) containing as a vehicle a resin composition containing ~50 parts by weight (D) and 15 to 50 parts by weight of a crosslinking agent for a total of 100 parts by weight is applied, and then heated and cured. A coating film formation method using a 2-coat, 1-bake coating system. (2) The method according to claim 1, wherein the crosslinking agent (B) is an alkoxylated melamine formaldehyde resin. (3) The method according to claim 1, wherein the solubility parameter of the resin (C) is 0.2 to 1.5 smaller than the solubility parameter of the resin (A). (4) (A) The resin has a number average molecular weight of 1,000 to 3,00
The method according to claim 1, wherein the oil-free polyester resin has an oil-free polyester resin of 0. (5) (C) The resin has a number average molecular weight of 700 to 2,000,
The method according to claim 1, which is an oil-free polyester resin having a hydroxyl value of 80 to 210 and an acid value of 5 to 30. (6) (C) The resin is an oil-free polyester resin consisting of a polybasic acid component and a polyhydric alcohol component, and the polybasic acid component is 10:90 to 8 of alicyclic polybasic acid and aromatic polybasic acid.
Consisting of a 0:20 molar ratio mixture, the polyhydric alcohol component is 2
It is a mixture of alcohol and trihydric alcohol, and the dihydric alcohol has formulas, ▲mathematical formulas, chemical formulas, tables, etc.▼ (In the formula, R_1 is H or CH_3; R_2 and R_4
are CH_3 or C_2H_5; R_3 is H or CH_3), ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ (In the formula, R_5 is C_2H_5 or C_4H_9)
, HO-(CH_2)_9-OH, ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ and ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ At least one of the compounds represented by
The method according to claim 5, containing 35% by weight. (7) (C) Claim 6 based on an aromatic polybasic acid in which 10 to 100 mol% of the carboxyl groups expressing the resin acid value of the resin exhibit a half-equivalent point potential of −350 mV or more by non-aqueous potentiometric titration. The method described in section. (8) The method according to claim 1, wherein the crosslinking agent (D) is an alkoxylated melamine formaldehyde resin.