JPH0249153B2 - JIDOSHASHATAINOTOSOHOHO - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for coating an automobile body to obtain a coating film that is smooth, highly colored, and highly glossy and has excellent peeling resistance. The conventional method of painting automobile bodies is undercoat painting.
It was common to use the following steps: (baking) - intermediate coating - (baking) - topcoat - (baking). The top coat is composed of various solid colors, but the undercoat and intermediate coat are painted in a single color such as gray or rust color. In addition, to prevent pebbles, gravel, rock salt, snow blocks, etc. thrown up by the wheels from hitting the car body while driving and damaging the paint film (i.e. stone chipping),
The method used was to paint with a stone chipping primer or a rock panel primer.
In this way, the purpose of the primer is to prevent scratches from reaching the base steel plate of the vehicle body, thereby preventing the occurrence of rust. However, there are many cases where pebbles, etc. collide with the paint film at a shallow angle, causing scratches (i.e. peeling) between the intermediate and top coats.In such cases, there is no particular problem in terms of rust prevention, but Because the colors of the paint film and the top coat were different, the scratches were noticeable, making the car body look very unsightly and significantly reducing its product value. As mentioned above, the stone chipping primer or rocker panel primer was found to be effective in preventing scratches that reach the substrate; however,
This was an incomplete measure to maintain the aesthetic appearance of the car body caused by the peeling phenomenon. Additionally, in topcoat paints, organic coloring pigments are usually used to obtain a deep-colored coating, but organic coloring pigments generally have poor dispersibility in vehicles, making it difficult to obtain a clear and glossy coating. It was hot. The present inventors have overcome the drawbacks of the prior art,
It has good peeling resistance, and even if peeling occurs as described above, it will not be noticeable.
It is possible to maintain the aesthetic appearance of the vehicle body,
Furthermore, we have discovered a method for painting automobile bodies with a high-grade finish that can provide a highly colored, high-gloss, and smooth coating film, and have completed the present invention. That is, the present invention provides a method for painting an automobile body in which an undercoat film is formed on an automobile body, then a colored intermediate coat film is formed, and a colored top coat film is further formed, wherein the colored intermediate coat film is formed on the colored intermediate coat film. Same color or similar color to the film, and glass transition temperature 15~
(a) oil-free alkyd resin and (b) at 60°C.
A binder component consisting of aminoaldehyde resin and
(c) An oil-free alkyd resin paint film containing a colored pigment as an essential component, and the colored top coat contains ultrafine barium sulfuric acid with an average particle size of 0.08μ or less in the solid content of the top coat. The present invention provides a method for painting an automobile body, characterized in that the top coat film contains 3 to 20% by weight. The oil-free alkyd resin paint used in the present invention to form the colored intermediate coating film has as essential components a binder component consisting of an oil-free alkyd resin and an aminoaldehyde resin, and a colored pigment. The oil-free alkyd resin is produced by a known method, and there are no particular limitations on the production method. For example, polyhydric alcohols such as neopentyl glycol, ethylene glycol, hexanediol, diethylene glycol, propylene glycol, dipropylene glycol, pentanediol, trimethylpentanediol, trimethylolpropane, glycerin, pentaerythritol, cyclohexanedimethanol, and phthalic acid; isophthalic acid, terphthalic acid,
It is appropriately selected from polythermal acids such as adipic acid, sebacic acid, itaconic acid, azelaic acid, and maleic acid, and is produced by condensation polymerization reaction at a temperature of 180 to 250°C for about 5 to 12 hours as known. . In addition, in order to make the glass transition temperature of the oil-free alkyd resin paint film 15 to 60°C, at least a portion of the polyhydric alcohol should be dihydric alcohol, and the polybasic acid should be dihydric alcohol. The use of an aliphatic dibasic acid at least in part is adopted. In addition, oil-free alkyd resin has an acid value of 10 or less, a hydroxyl value of 100 to 200, and a number average molecular weight of 2000 to 6000.
Adjust the reaction conditions so that In the above, if the acid value exceeds 10, the coating tends to thicken and becomes less stable, which is not preferable. Further, if the hydroxyl value is less than 100, the adhesion of the coating film will be poor, whereas if it exceeds 200, the water resistance etc. of the coating film will be poor, which is not preferable. Also, the number average molecular weight
If it is less than 2,000, the coating film becomes brittle, while if it exceeds 6,000, painting workability deteriorates, so both are not preferred. As a crosslinking agent for the oil-free alkyd resin, aminoaldehyde resins such as melamine formaldehyde resin, urea formaldehyde resin, and benzoguanamine formaldehyde resin can be used. Moreover, a blocked isocyanate compound can also be used in combination. The blocking isocyanate compounds include aromatic, aliphatic or alicyclic polyisocyanates such as tolylene diisocyanate, metaphenylene diisocyanate, xylylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, or polyvalent polyisocyanates with these polyisocyanates. Examples include those obtained by reacting isocyanate groups such as alcohol adducts with blocking agents such as lactams such as caprolactam, monoalcohols, and oximes such as methyl ethyl ketoxime to eliminate free isocyanate groups. In addition, the coloring pigment used in the present invention should be selected to have the same or similar color as the top coat, and inorganic coloring pigments such as titanium oxide and iron oxide, which are usually used for automobiles, and carbon Organic coloring pigments such as black and phthalocyanine blue can be used. The weight ratio of the oil-free alkyd resin, crosslinking agent, and coloring pigment explained above is usually 100:20 to 100:20.
A range of 65:1 to 55 is suitable. Other components constituting the oil-free alkyd resin paint used in the present invention include hydrocarbons such as xylene and solvent naphtha, alcohols such as methyl alcohol and butyl alcohol, ketones such as methyl isobutyl ketone, Organic solvents such as esters and ethers such as ethyl acetate and ethylene glycol monobutyl ether; extender pigments such as clay, calcium carbonate, talc, silica, and alumina; and various auxiliaries such as leveling agents, anti-sagging agents, and surfactants. , can be added as necessary. The oil-free alkyd resin paint used in the present invention must have a glass transition temperature of 15 to 60°C when formed into a coating film. In the above, if the glass transition temperature exceeds 60℃,
The effect of mitigating the destructive force when a pebble or the like collides with it decreases, and the peeling resistance deteriorates. Conversely, 15℃
If it is less than this, not only will water resistance and moisture resistance deteriorate, but also blister phenomenon will occur more easily, so it is not preferable in any case. In addition, lowering the glass transition temperature not only improves peeling resistance as mentioned above, but also has the effect of making it possible to obtain a smooth coating film due to the synergistic effect with the ultrafine barium sulfate blended in the top coat. have In the present invention, the top coating includes solvent-based coatings,
Water-dispersed paints and other paints that have been commonly used as paints for automobiles can be used. That is,
It can be used without any particular restrictions on the form of the paint. The top coating further contains 3 to 20% by weight of ultrafine barium sulfate whose primary particle average diameter is 0.08μ or less based on the solid content of the paint.
It contains. The ultrafine barium sulfate has a conventional particle size of 0.1 to 1μ.
Carbon black, phthalocyanine-based, quinacridone-based, benzimidazolone-based, anthraquinone-based,
It is possible to stably disperse organic coloring pigments such as quinophthalone-based, anthrapyrimidine-based, and naphthol-based pigments. The mechanism by which the dispersion stability of organic color pigments is improved by blending ultrafine barium sulfate is not clear. Perhaps ultrafine barium sulfate is adsorbed onto the surface of organic color pigments due to differences in surface potential, or is interposed between organic color pigments and causes steric hindrance between the organic color pigments.
It is believed that this prevents the organic color pigment from re-agglomerating. Therefore, since the ultrafine barium sulfate is transparent and can stably disperse organic coloring pigments, the resulting top coat film is highly colored and has a high gloss. In the present invention, if the amount of ultrafine barium sulfate is less than the above range, the above-mentioned effects cannot be obtained, and if it is in excess, the coating film becomes brittle and the gloss of the coating film decreases. The case is also unfavorable. Furthermore, if the particle size of the ultrafine barium sulfate is larger than the above range, the above effects cannot be obtained. For example, conventional barium sulfate having a particle size of 0.1 to 1 μm is not preferable because it causes a decrease in the gloss of the coating film, white blurring, etc. As mentioned above, there is no particular restriction on the form of the top coat paint, such as solvent type or water dispersion type, but the essential components other than ultrafine barium sulfate are mainly resin, color pigment, and solvent (or dispersion medium). . As the resin, those conventionally used as top coatings for automobiles can be used as they are, such as baking types such as acrylic-melamine type and oil-free alkyd-melamine type, and lacquer types such as acrylic-urethane and polyester-urethane. Further, as the coloring pigment, the organic coloring pigments mentioned above can be typically used, and inorganic coloring pigments may also be used in combination, but when taking into consideration the high chromaticity of the coating film, when carbon black is used, Not less than 80% by weight of all colored pigments; if other organic colored pigments are used, at least 40% by weight of all colored pigments
The above should be blended. In addition, solvents that are commonly used for paints include hydrocarbons such as toluene and xylene, alcohols such as methanol and butanol, ketones such as methyl ethyl ketone and acetone, and esters such as methyl acetate and cellosolve acetate. Can be used. In the present invention, various other additives such as plasticizers, leveling agents, and ultraviolet absorbers can be added as necessary. Note that it is preferable not to include commonly used extender pigments such as calcium carbonate, magnesium carbonate, talc, and silica, since they reduce the various effects mentioned above of ultrafine barium sulfate. The blending ratio of resin, color pigment, and solvent in the top coat varies depending on the type of paint, but is usually in the range of 100:1 to 100:1.
The ratio is 15:80 to 300) [by weight], and the top coat used in the present invention is one in which ultrafine barium sulfate is blended therein. In particular, the hidden pay film thickness (measured according to JIS K-5400-6.2) of the top coat used in the present invention is 30~
80μ is suitable. In the above case, if the thickness of the hidden payload film is smaller than the above range, the concentration of the coloring pigment in the resin will inevitably increase in highly chromatic coating, and the phenomenon of chocking and color fading will easily occur. On the other hand, if it is too large, color unevenness tends to occur due to the difference in film thickness, so both are unfavorable. The method for producing the top coating used in the present invention includes, for example, adding ultrafine barium sulfate to a mill base rich in organic coloring pigments, using a sand grinder,
The most preferable method is to sufficiently knead and disperse near the primary particles using a dispersing machine such as a ball mill, then add other coating components and mix with a disperser, but the method is not limited thereto. Next, the painting method will be explained. The method is not particularly unusual. That is, first, an undercoat film is formed on the automobile body (in the case where a monochromatic paint film is subsequently formed, the coating layer up to that film layer is treated as the undercoat film in the present invention), and then the necessary After forming an intermediate coat of a single color such as a gray color or a dark color, which is generally done according to the conventional method, a colored intermediate coat is formed, and then areas where dust has adhered or defective areas of the paint film such as repellency or sagging are removed. After sanding, a colored top coat is applied. To explain in more detail, first, the car body that has been chemically treated is painted by means such as electrodeposition coating or dip coating, and then baked.
Forms an undercoat film with a film thickness of approximately 15 to 25 μm. Then, if necessary, the single color intermediate coating such as oil-free alkyd-melamine resin paint, oil-modified alkyd-melamine resin paint, or epoxy ester-melamine resin paint is applied by means such as air spray or airless spray, and baked. , forms an intermediate coating film with a film thickness of approximately 20 to 40μ. Next, the above-mentioned colored intermediate coating (oil-free alkyd resin paint) is applied by means such as air spray or airless spray, and baked.
Forms a colored intermediate coating film with a film thickness of approximately 15 to 40μ. In addition, when applying a monochromatic coating film as described above, it and the colored intermediate coating film can be baked and cured simultaneously in a wet-on-wet method. Next, if there are any defects in the paint film, sand them with #360 to #500 water-resistant abrasive paper (JIS R-6253), etc., and then apply a top coat using air spray or airless spray, etc., and bake the film to a thickness of approx. twenty five~
Forms a 40μ colored top coat. The effects achieved by the coating method of the present invention described above are as follows. It has good peeling resistance, and even if peeling occurs, it will not be noticeable and the beautiful appearance of the vehicle body can be maintained. Furthermore, it is possible to obtain a smooth, highly colored, and highly glossy coating film with no polishing marks. Hereinafter, the present invention will be explained in more detail with reference to Examples. In the examples, "parts" and "%" are based on weight. The following colored intermediate coatings and colored top coatings were used in Examples and Comparative Examples. Colored intermediate paint (Paint A) Note 1) Oil-free alkyd resin Note 2) Varnish (solid content 60%) 64.3 parts Melamine resin varnish (solid content 60%) Note 3)
21.5 parts Carbon black 0.03 parts Phthalocyanine blue 1.1 parts Titanium oxide 2.0 parts Xylene 7.0 parts Butyl cellosolve 4.0 parts Surface conditioner 0.07 parts Note 1 The resulting coating film is blue with a glass transition temperature of 45°C (measured with a Vibron viscoelasticity meter) System intermediate coating film Note 2 Polyhydric alcohol (neopentyl glycol, trimethylolpropane, 1,4-butanediol, ethylene glycol, pentaerythritol) and polybasic acid (phthalic acid, adipic acid)
A resin with a hydroxyl value of 125, an acid value of 5.2, and a number average molecular weight of 2500, synthesized from *3 "Super Betsukamine L-117-60" (trade name manufactured by Dainippon Ink & Chemicals Co., Ltd.) <Paint B> Composition of paint A The product has the same composition except that the following oil-free alkyd resin is used,
The resulting paint film is a blue intermediate coating with a glass transition temperature of 23°C. 《Oil-free alkyd resin》 Polyhydric alcohol (neopentyl glycol, trimethylolpropane, 1.4-butanediol,
A resin with a hydroxyl value of 120, an acid value of 5.2, and a number average molecular weight of 3000 synthesized from polybasic acids (ethylene glycol, pentaerythritol) and polybasic acids (phthalic acid, adipic acid) (Paint C) Oil-free alkyd in the composition of Paint A Oil-free alkyd resin varnish instead of 64.3 parts of resin varnish and 21.5 parts of melamine resin varnish.
55.7 parts, melamine resin varnish 16.1 parts, blocking isocyanate ["Takenate B-820-NS-U"]
(Trade name manufactured by Takeda Pharmaceutical Co., Ltd.) A blue intermediate coating with the same composition except that 14.0 parts is used, and the resulting coating film has a glass transition temperature of 43°C. <Paint D> A blue intermediate coating having the same composition as Paint A except that the following oil-free alkyd resin is used, and the resulting coating film has a glass transition temperature of 75°C. [Oil-free alkyd resin] Synthesized from polyhydric alcohols (neopentyl alcohol, trimethylolpropane, ethylene glycol, pentaerythritol) and polybasic acids (phthalic acid, adipic acid), with a hydroxyl value of 128 and an acid value.
5.0, a resin with a number average molecular weight of 2500 (Paint E) The composition of Paint A is the same except that the following oil-free alkyd resin is used, and the resulting coating film has a glass transition temperature of 8°C. Blue intermediate paint. 《Oil-free alkyd resin》 Polyhydric alcohol (neopentyl glycol, trimethylolpropane, 1.4-butanediol,
Hydroxyl value synthesized from ethylene glycol) and polybasic acids (phthalic acid, adipic acid, sebamic acid)
116, acid value 4.5, number average molecular weight 2800 resin (Paint F) Note 4) Oil-free alkyd resin varnish (solid content 60%) 59.3 parts Melamine resin varnish (solid content 60%) 25.5 parts Carbon black 1.0 part Iron oxide Red 0.2 parts Iron oxide yellow 2.0 parts Xylene 8.0 parts Butyl cellosolve 4.0 parts Surface conditioner 0.05 parts Note 4 The resulting coating film is a black intermediate coating film with a glass transition temperature of 45°C, and is made of oil-free alkyd resin varnish and melamine resin. Use the same varnish as paint A.

【table】

[Table] Example 1 Cationic electrodeposition paint [“Emaron CED 70H” (trade name, manufactured by Dainippon Toyo Co., Ltd.)] on zinc phosphate treated steel sheet
Electrodeposition coating, baking at 180℃ for 20 minutes, dry film thickness
A 20μ primer coating was obtained. Next was a gray oil-free alkyd resin paint [“Delikon Medium”
"MD-1" (trade name, manufactured by Dainippon Toyo Co., Ltd.)] was coated with air spray and baked at 150°C for 20 minutes to obtain a coating film with a dry film thickness of 25 μm. Next, apply paint A using air spray,
Baking was performed at 150°C for 20 minutes to obtain a blue intermediate coating film with a dry film thickness of 25 μm. Next, water sand with #400 water-resistant abrasive paper, drain and dry, then apply paint A again using air spray and bake at 150℃ for 20 minutes to obtain a dry film thickness of 30μ.
A blue topcoat film was obtained. Examples 2 to 5 and Comparative Examples 1 to 8 Painting was carried out in the same manner as in Example 1, except that the colored intermediate coating and colored top coating were used in the combinations shown in Table 1. In addition, in Comparative Example 8, the colored intermediate coating film was omitted. The coating films obtained in Examples 1 to 5 and Comparative Examples 1 to 8 were tested for peeling resistance, blister resistance, coating film roughness, and smoothness, and the results are shown in the lower part of the table.

【table】

[Table] As is clear from Table 1, the coating film performance, coating appearance, etc. obtained by the method of the present invention were good. On the other hand, Comparative Examples 1 and 7, which used a colored intermediate coating with a high glass transition temperature, were somewhat inferior in peeling resistance and smoothness of the coated surface, whereas Comparative Example 2, which used a colored intermediate coating with a low glass transition temperature, , Comparative Examples 3, 5, 6, which used colored topcoat paints that had poor blister resistance and did not contain ultrafine barium sulfate.
Comparative Example 4, which used a colored top coat containing an excessive amount of ultrafine barium sulfate, also had low gloss and poor coating surface roughness. Ta.

Claims (1)

[Scope of Claims] 1. A coating method for forming an undercoat film, then a colored intermediate coat film, and then a colored top coat film on an automobile body, wherein the colored intermediate coat film has the same color or a similar color to the colored top coat film. and glass transition temperature 15~60℃
It is an oil-free alkyd resin-based paint coating whose essential components are (a) an oil-free alkyd resin, (b) a binder component consisting of an aminoaldehyde resin, and (c) a colored pigment, and the above-mentioned colored topcoat. The coating film contains 3 to 20% of ultrafine barium sulfate with an average particle size of 0.08 μ or less in the solid content of the top coat.
1. A method for painting an automobile body, characterized in that the coating film is a top coat coating film containing % by weight.