JPH0311821B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to a method for forming a coating film that is excellent in long-term durability and has a clear color without fading. In recent years, a two-coat, one-bake method has been widely adopted for painting automobile bodies and the like in order to shorten the painting process. In addition, vivid and deep solid colors have come to be preferred as hues for paint films.
Therefore, red, orange, yellow, green, or blue organic pigments have come to be used as coloring pigments for paints. However, since organic pigments generally have very low hiding power, the lack of hiding power is compensated for by using organic pigments at high concentrations, but when such high concentrations of organic pigments are used in paints, color fading occurs. There was a problem with the increased risk. To solve this problem, a two-coat one-bake method has been known in which a paint containing an organic pigment (base coat) is applied and then a transparent clear paint (top coat) is applied. However, with this method, reversal of the colored pigments is likely to occur, and therefore, in order to ensure the finished appearance and quality of the coating film, it was necessary to change the composition and molecular weight of the synthetic resins used in the base coat and top coat.
Therefore, due to the difference in expansion rate and contraction rate between the two coating films, it was inevitable that cracks and peeling would occur in the coating film, resulting in problems in long-term durability. Furthermore, in order to solve the problem of discoloration, a method has been proposed in which a colored semitransparent top coat layer is formed on a colored base coat layer by a two-coat, one-bake method. However, even in this method, the reversal phenomenon caused by the difference in pigment concentration between the base coat and top coat cannot be completely resolved by changing the composition or molecular weight of the synthetic resin in both layers, or by adding a surface conditioning agent. It was not possible to prevent this, and as a result, scratchy skin often occurred, causing problems in the smoothness of the coating film. In view of the above-mentioned current situation, the inventors of the present invention have arrived at the present invention as a result of intensive studies on a method for forming a coating film with excellent long-term durability, no fading, and sharpness. That is, the present invention applies the pigment weight concentration [the weight ratio of the pigment to the film-forming solid content (hereinafter referred to as PWC Colored paint A containing approximately 10 to 30% of the coloring paint A is applied.
A method for forming a coating film in which a colored semi-transparent coating B is applied over and over while the coating film is in a semi-dry state, and both of the formed coating films are dried simultaneously, the constituent components of the colored coating A and the colored semi-transparent coating B are The synthetic resins are the same, and the pigments used in colored semi-transparent paint B consist of colored pigments mainly consisting of organic coloring pigments with a PWC of about 1 to 10% and transparent pigments with a PWC of about 5 to 50%. , and the total PWC of the colored pigment and the transparent pigment is greater than or equal to the PWC of the colored paint A. The method of the present invention has the effect of significantly improving the discoloration properties of the coating film, since the concentration of the coloring pigment on the surface of the coating film is lower than that of the conventional one-coat, one-bake solid paint. In addition,
To prevent paint film destruction such as cracking and peeling caused by the difference in synthetic resins used for the base coat and top coat of the conventional 2-coat, 1-bake method, which have a negative impact on long-term durability, and to reverse color pigments. A remarkable effect can be obtained in improving the initial quality of the coating film, such as the occurrence of scratchy skin on the coating surface. As the colored paint A used in the present invention, dark solid paint films commonly used for automobiles and the like can be used as they are. That is,
The colored paint A is a synthetic resin such as an acrylic-urethane resin system, an acrylic-amino resin system, an alkyd-amino resin system, a polyester-amino resin system, or a polyester-urethane resin system; a coloring pigment; toluol, xylol, ethanol, butanol,
It consists of a solvent such as cellosolve and butyl acetate; and a small amount of additives such as an ultraviolet absorber, a surface conditioner, and a plasticizer. As the coloring pigment, an organic coloring pigment is used in an amount of about 10 to 30% PWC in order to give the coating film clarity.
Incidentally, as a coloring pigment, an inorganic coloring pigment such as titanium oxide, carbon black, or Bengara may be substituted with an organic coloring pigment in an amount of less than half, depending on the hue. It should be noted that if the PWC is less than 10%, the hiding power will not be sufficient, and if it exceeds 30%, the viscosity of the paint will increase and the painting workability will deteriorate, so both are not preferred. The organic coloring pigments include azo pigments, phthalocyanine pigments, basic dye lakes, acid dye lakes, anthraquinone pigments, perylene pigments, perinone pigments, thioindigo pigments, quinacridone pigments, and dioxazine pigments. , isoindolinone pigments, quinophthalone pigments, azomethine azo pigments, and the like. The same synthetic resin as the colored paint A is used for the colored semi-transparent paint B used in the present invention. By using the same synthetic resin in this way, the compatibility between the top coat and the base coat is improved, so it is possible to prevent the phenomenon of destruction between the coating films that often occurs in conventional coating methods. As the colored pigment used in the above-mentioned colored translucent paint B, the same organic coloring pigment as the above-mentioned colored paint A or a material mainly composed of organic coloring pigments can be used. The color pigment has a PWC of about 1, depending on the hue.
~10% is appropriate. When the PWC is less than 1%, the color shading due to the difference in film thickness becomes more noticeable;
If it exceeds 10%, discoloration tends to occur, which is not preferable. In addition, as the transparent pigment used in the colored semi-transparent paint B, barium sulfate, calcium carbonate, etc. with a particle size of 0.1μ or less can be used, but in the present invention, sulfuric acid with an average primary particle size of 0.05μ or less can be used. Barium (hereinafter referred to as ultrafine barium sulfate) is preferred. Such ultrafine barium sulfate particles are extremely transparent and exist between colored pigment particles to prevent agglomeration of colored pigments, thereby contributing to improving dispersion stability and making it possible to obtain a clear and glossy coating film. The above transparent pigment suitably has a PWC of 5 to 50%. If the PWC is less than 5%, the color pigments in the base coat tend to reverse, while if it exceeds 50%, the coating film becomes brittle, so both are unfavorable. In addition, the total PWC of colored pigments and transparent pigments is the PWC of colored paint A to prevent reversal of colored pigments.
It is necessary to do more than that. In the method of the present invention, surface treatment,
Colored paint A is applied to the surface of the workpiece that has been subjected to surface treatment such as applying a primer using a normal painting method such as air spray, airless spray, electrostatic spray, etc. to a dry film thickness of approximately 15 to 40μ. do. Next, let it stand for about 1 to 10 minutes, and while the paint film is still in an undried state, apply semi-transparent paint B to a dry film thickness of about 15 to 100 ml.
Apply to a thickness of 30μ. Next, the coating is left to stand for about 1 to 20 minutes, and both coating films are simultaneously dried at room temperature or by heating. As described above, by the method of the present invention, it is possible to obtain a coating film that is clear and does not fade in color and has long-term durability and is resistant to destruction between the top coat and the base coat. Hereinafter, the present invention will be explained in more detail with reference to Examples. Note that both "parts" and "%" are based on weight. Example 1 A base coat, transparent pigment dispersion base, translucent top coat, and diluent thinner having the following formulations were prepared in advance before painting. <Composition>...Base coat Thioindigo maroon Note 1) 8 parts Bengara 2 parts Alkyd resin Note 2) 36 parts Melamine resin solution Note 3) 25 parts Xylol 29 parts (PWC of color pigment = 16.4%) <Composition>... Transparent pigment dispersion base Barium sulfate Note 4) 40 parts Alkyd resin Note 2) 21 parts Melamine resin solution Note 3) 15 parts Xylol 24 parts (PWC of colored pigment = 57.1%) <Blend>... Translucent top coat Blend 100 parts Blend 400 parts Alkyd resin Note 2) 120 parts Melamine resin solution Note 3) 85 parts Xylene 95 parts (PWC of colored pigment = 2.0%, PWC of transparent pigment = 31.2%) <Formulation>... Diluting thinner Solbetsuso #100 80 parts Butyl cellosolve 15 parts n-butanol 5 parts Note 1) "Chromophthalbord-RS" (trade name manufactured by Ciba Geigy) Note 2) Coconut oil modified alkyd resin with oil length 19, acid value 7, number average molecular weight 3500 Note 3) "Yuban" 20SE” (trade name manufactured by Mitsui Toatsu Chemical Co., Ltd.) [Solid content 60%] Note 4) “BF-20” (trade name manufactured by Onahama Sakai Chemical Co., Ltd.)
[Average primary particle size 0.05μ] The formulation was diluted with a viscosity of 25 seconds/20℃ (Food Cup #4), and a cationic electrodeposition coating (20μ) and an amino alkyd resin intermediate coating (30μ) were applied. Air spray paint on the applied mild steel plate to a dry thickness of 20μ, and after setting for 3 minutes, dilute the formulation with a viscosity of 25 seconds / 20℃
(Food Cup #4) Dry film thickness
Repeat coating with air spray to make it 20μ, 7
After setting for a minute, it was baked at 150°C for 20 minutes. Comparative Example 1 A coating film was formed under exactly the same conditions as in Example 1, except that barium sulfate was not blended, the alkyd resin was 44 parts, and the melamine resin solution was 32 parts. Comparative Example 2 In the formulation, the organic pigment in the formulation was further added.
A coating film was formed under the same conditions as in Example 1, except that 115 parts of the pigment was added and the PWC of the colored pigment was 19.9%. Example 2 A base coat, a transparent pigment dispersion base, a translucent top coat, and a diluent thinner having the following formulations were each prepared in advance before painting. <Formulation> Base coat Perylene pigment Note 5) 16 parts Bengara 2 parts Titanium oxide 1 part Acrylic resin solution Note 6) 51 parts Melamine resin solution Note 7) 20 parts Xylol 10 parts (PWC of coloring pigment = 28.5%) <Blend>...Transparent pigment dispersion base Barium sulfate Note 8) 35 parts Acrylic resin solution Note 6) 38 parts Melamine resin solution Note 7) 15 parts Xylol 12 parts (PWC of colored pigment = 49.6%) <Blend>...Semi Transparent top coat Mixture 100 parts Mixture 550 parts Acrylic resin solution Note 6) 285 parts Melamine resin solution Note 7) 113 parts (PWC of colored pigment = 2.6%, PWC of transparent pigment = 26.7%) <Formulation>... Dilution thinner Solvetsuso # 100 80 parts Butyl cellosolve 15 parts n-butanol 5 parts Note 5) "Variogenredo L3910HD" (trade name manufactured by BASF) Note 6) "Kotakus SB-302" (trade name manufactured by Toray Industries) [Solid content 70%] Note 7) Same as note 3) Note 8) Same as note 4) Dilute the formulation and make the viscosity 27 seconds/20℃ (foed cup #4) with a cationic electrodeposition coating (20μ) and an amino alkyd resin intermediate coating. Air spray paint on a mild steel plate coated with a film (30μ) so that the dry film thickness is 20μ, and after setting for 3 minutes, dilute the formulation with a viscosity of 27 seconds/20℃.
The dry film thickness of the paint made with (Food Cup #4)
Repeat coating with air spray to make it 20μ, 7
After setting for a minute, it was baked at 150°C for 20 minutes. Comparative Example 3 A paint diluted with the formulation of Example 2 was air-sprayed to a dry film thickness of 40μ,
After setting for 7 minutes, it was baked at 150°C for 20 minutes. Comparative Example 4 Perylene pigment 16 in the formulation of Example 2
1 part, Bengara, 1 part of titanium oxide, 16 parts of Thioindigo Maroon, and 3 parts of Bengara were used, but the same paint was diluted with the same formulation, and the viscosity was 25 seconds/20°C (Food Cup #4). This was air-sprayed onto a mild steel plate that had been coated with a cationic electrodeposition coating (20μ) and an amino alkyd resin intermediate coating (30μ) to a dry film thickness of 20μ. After setting for 3 minutes, the formulation of Example 1 was diluted to a viscosity of 25.
The paint was coated with air spray at a temperature of 20°C/20°C (Food Cup #4) to a dry film thickness of 20μ, and after setting for 7 minutes, it was baked at 150°C for 20 minutes. The test plates obtained in Examples 1 to 2 and Comparative Examples 1 to 4 were tested for gloss, smoothness, discoloration, and durability of the coating film, and the results are shown in Table 1.

【table】

[Table] As is clear from Table 1, it can be seen that excellent coating films can be obtained by the method of the present invention. On the other hand, in the coating film obtained from Comparative Example 1 in which the pigment content of the top coat was reduced, the colored pigments caused a reversal phenomenon, and the gloss and skin smoothness were poor, and the durability was also poor. Furthermore, the coating films obtained in Comparative Examples 2 and 3, in which the top coat coloring pigment was used in excess, showed significant discoloration. Furthermore, the coating film obtained in Comparative Example 4 in which the synthetic resins of the top coat and base coat were changed had poor durability.

Claims (1)

[Scope of Claims] 1. A colored paint A having a pigment weight concentration of approximately 10 to 30% of a coloring pigment mainly composed of an organic coloring pigment is applied onto an object to be coated, and the coating film of the colored paint A is not dried. In the method of forming a paint film in which colored transparent paint B is applied over and over again while the paint is still in the state, and both coats are dried at the same time, the synthetic resins that are the constituent components of colored paint A and colored semi-transparent paint B are the same. The pigment used in the colored translucent paint B consists of a colored pigment mainly consisting of an organic coloring pigment with a pigment weight concentration of about 1 to 10%, and a transparent pigment with a pigment weight concentration of about 5 to 50%, and is colored. A method for forming a coating film, characterized in that the total pigment weight concentration of the pigment and the transparent pigment is greater than or equal to the pigment weight concentration of the colored paint A. 2 The above transparent pigment has an average particle size of primary particles.
2. The method for forming a coating film according to claim 1, wherein the coating material is barium sulfate having a particle size of 0.05μ or less.