JPS6054115B2 - How to paint a car body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention prevents the paint film applied to the surface of an automobile body from being damaged by flying collisions with pebbles, gravel, rock salt, frozen snowpack, etc. while the automobile is running. The present invention also relates to a method of painting an automobile body, which makes the damaged part noticeable even when the vehicle is damaged, and which makes it possible to maintain the beauty of the exterior of the vehicle body.

By the way, car body painting is generally done with an undercoat (
Baking) 1st coat painting - (baking) 1st coat painting 1 (baking)
This process is carried out using the following process.

The top coat is composed of various solid colors or metallic colors, while the undercoat and intermediate coat are painted in a single color such as clay color or rust color. Conventionally, in order to prevent the paint film from being damaged by stones thrown up by the wheels while driving (i.e. stone chipping), a method of applying stone chipping primer or rocker panel primer was used. .

The purpose of these stone chipping primers or rocker panel primers 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 and the like collide with the paint film at a shallow angle, causing scratches (that is, peeling) between the intermediate and top coats. Because the colors of the intermediate and top coats are different, the scars are noticeable, making the car body look very unsightly, and resulting in a significant drop in product value. As mentioned above, the stone chipping primer or rocker panel primer has been shown to be effective as a measure to prevent scratches that reach the base material, but it is not effective as a measure to maintain the aesthetic appearance of the car body caused by the peeling phenomenon. I couldn't say it was enough.

The present inventors have overcome the drawbacks of the above-mentioned prior art, discovered a coating method that has good peeling resistance, and can maintain the beauty of the outside of the vehicle body even if peeling occurs, and have developed the present invention. It has come to completion.

That is, the present invention provides a method for painting an automobile body in which a primer coating film is formed on the automobile body, then an intermediate coating coating film is formed, and a top coating coating film is further formed on the automobile body. The color between the intermediate coat film and the top coat film is the same or similar to that of the top coat film, and the resulting paint film has a glass transition temperature of 15 to 50 C.
An automobile body characterized by forming an oil-free alkyd resin-based paint film containing (a) an oil-free alkyd resin, (b) a binder component consisting of an aminoaldehyde resin, and (c) a pigment as essential components. Regarding the painting method.

The oil-free alkyd resin paint used in the present invention has (a) an oil-free alkyd resin, (b) a binder component consisting of an aminoaldehyde resin, and (C) a pigment as essential components.

The oil-free alkyd resin can be produced by any known method. For example, polyhydric alcohols such as neopentyl glycol, ethylene glycol, hexanediol, diethylene glycol, propylene glycol, dipropylene glycol, pentanediol, trimethylpentanediol, trimethylolpropane, glycerin, pentaerythritol, cyclohexanedimethanol, phthalic acid, and isophthalic acid. acids, polybasic acids such as terephthalic acid, adipic acid, sebacic acid, etaconic acid, azelaic acid, and maleic acid, generally at a temperature of 18
It can be produced by carrying out a condensation polymerization reaction at 0 to 250°C for about 5 to 1 hour. In addition, the glass transition temperature of oil-free alkyd resin paint coating film I is 15 to 50°C.
This can be obtained by using a dihydric alcohol as at least a part of the polyhydric alcohol, and using an aliphatic dibasic acid as at least a part of the polybasic acid.

In addition, oil-free alkyd resin has an acid value of 10 or less and a hydroxyl value of 100 to 20C)s number average molecular weight of 2000 to 600.
What are the reaction conditions so that it becomes 0? Arrange.

If the acid value exceeds 10, the paint tends to thicken, the stability deteriorates, and wrinkles tend to occur when wet ● on ● wet coating is applied on the intermediate coating film, which is undesirable. Further, if the hydroxyl value is less than 10, the adhesion of the coating film will be poor, and if it exceeds 200, the water resistance etc. of the coating film will be poor, so both are not preferred. Further, if the number average molecular weight is less than 200, the coating film becomes brittle, and if it exceeds 6,000, the coating workability deteriorates, so both are not preferred. Furthermore, as the crosslinking agent for the oil-free alkyd resin, an aminoaldehyde resin can be used.

Typical examples of the aminoaldehyde resin include melamine formaldehyde resin, urea formaldehyde resin, and benzoguanamine formaldehyde resin. Further, as the crosslinking agent, a part of the aminoaldehyde resin may be replaced with a blocked isocyanate compound.

This blocked isocyanate compound is an aromatic, aliphatic or alicyclic polyisocyanate such as tolylene diisocyanate, metaphenylene diisocyanate, xylylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, or a combination of these polyisocyanates and a polyhydric alcohol. The free isocyanate groups are eliminated by reacting the isocyanate groups of the adducts with blocking agents such as lactams such as prolactam, monoalcohols, and oximes such as methyl ethyl ketoxime. As the pigment, it is possible to use pigments that are usually used for automobiles and have the same color or a similar color to the top coat, but it is particularly preferable to use the same pigment as the top coat.

The weight ratio (in terms of solid content) of the oil-free alkyd resin, crosslinking agent, and pigment is usually 100:20 to 65:5.
~55 is appropriate.

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, and acetic acid. Organic solvents such as esters and ethers such as ethyl and ethylene glycol monobutyl ether; extender pigments such as clay, calcium carbonate, talc, silica, alumina, and various types such as leveling agents, anti-sagging agents, surfactants, and ultraviolet absorbers. Auxiliary agents can be added as necessary.

The oil-free alkyd resin paint used in the present invention has a glass transition temperature of 15 to 5 when formed into a coating film.
A temperature of 0°C is required. Glass transition temperature is 5C
) If the value exceeds 15C, the effect of mitigating the destructive force when pebbles etc. collide becomes smaller, and the peeling resistance deteriorates.
If the temperature is below ℃, not only will water resistance and humidity resistance deteriorate,
Both are unfavorable because they tend to cause the prister phenomenon. In addition, although an oil-free alkyd resin paint is used in the present invention, if an oil-modified alkyd resin paint is used instead, the paint film will have poor weather resistance and the top coat will not block sunlight sufficiently. The deterioration of the coating film progresses due to sunlight reaching the lower layer, and the adhesion between the two coating films decreases, which tends to cause defects such as blister and delamination. On the other hand, since the oil-free alkyd resin paint has excellent weather resistance, there is almost no risk of causing the above-mentioned defects. Next, the coating method will be explained. The means for forming an undercoat film on an automobile body, then forming an intermediate coat film, and further forming a top coat film can be performed in exactly the same manner as known methods.

That is, a car body that has been chemically treated is coated by means such as electrodeposition coating or dipping coating, and baked to form an undercoat film with a film thickness of about 15 to 25 μm, and then oil-free alkyd-amino aldehyde resin paint or epoxy resin paint is applied. Apply ester melamine resin paint etc. using air spray or airless spray and bake.
Form an intermediate coating film with a film thickness of approximately 25 to 40 μm, then apply oil-free alkyd resin-based or acrylic resin-based solvent-based, water-based, or powder-based paint using air spray or airless spray, and bake. , to form a top coat film with a film thickness of approximately 30 to 40 μm. It should be noted that the resin used for the intermediate coating is the same as the resin used for the oil-free alkyd resin paint that is coated on top of it to improve adhesion between the coatings and stone chipping resistance. Particularly desirable from a gender perspective.

Further, the top coat may be either solid color or metallic color, but in the case of metallic color, it is desirable to further coat with clear paint.

In the present invention, after the intermediate coating is applied and set, the oil-free alkyd resin paint is applied only to areas susceptible to stone chipping, such as the tip of the hood and around the tire house, using air spray or airless spray. After setting, the intermediate coat film and the oil-free alkyd resin paint film are baked at the same time, usually at 120 to 180 C for 15 to 30 minutes.

Thereafter, a top coat film is formed by the above-mentioned known method.
Therefore, parts of an automobile body that are susceptible to stone chipping require an additional process of painting and setting the oil-free alkyd resin paint than other parts. The film thickness of the oil-free alkyd resin paint film is suitably 15 to 30 microns; if it is less than 15 microns, the anti-peeling effect will be reduced, and if it exceeds 30 microns, the paint film is likely to sag or wrinkle.

As explained above, the coating film obtained by the coating method of the present invention has good peeling resistance, and the glass transition temperature of the oil-free alkyd resin paint film is lower than the glass transition temperature of the ordinary intermediate coating film (approximately 70 to 90 ℃), so
This is especially effective in cold regions where roads are covered with a mixture of rock salt and gravel to prevent ice.

Furthermore, in the present invention, even if peeling occurs, an oil-free alkyd resin paint film of the same color or similar color is formed under the top coat, so the peeling phenomenon is not noticeable and the appearance of the car body is improved. It has the characteristic of being able to hold Next, the present invention will be explained in more detail with reference to Examples. In addition, in the example, 1
Parts and 1% are based on weight. The following oil-free alkyd resin paints and intermediate paints were used in Examples and Comparative Examples.

Oil-free alkyd resin paint (Paint A Note 0) l Oil-free alkyd resin Note 2) Varnish (solid content 60%) (1) Melamine resin varnish (solid content 60%) Note 3) 2-benzimidazolone orange 5 parts carbon black
0.6 parts iron oxide red
2j part Shinka Shared
0.4 parts butyl cellosolve 4 parts xylene 7 parts surface conditioner
0.0 Note 1 The resulting coating film is
Brown paint Note 2 with a glass transition temperature of 75°C (measured using a Pipelon viscoelasticity meter) containing polyhydric alcohols (neopentyl alcohol, trimethylolpropane, ethylene glycol, pentaerythritol) and polybasic acids (phthalate). acid, adipic acid)
Synthesized from hydroxyl value 128, acid value 5. Resin Note 3 Product Name 1 Super Beckamine L-117-60J (manufactured by Dainippon Ink & Chemicals Co., Ltd.) <Paint B> In the composition of Paint A, except for using the following oil-free alkyd resin , a brown paint with the same composition and the resulting coating film having a glass transition temperature of 45°C.

(Oil-free alkyd resin) Synthesized from polyhydric alcohol (neopentyl glycol, trimethylolpropane, 1,4-butanediol, ethylene glycol, pentaerythritol) and polybasic acid (phthalic acid, adipic acid), hydroxyl value 125 ．． Resin with acid value 5.2 and number average molecular weight 2500 (Coating C) The composition of Coating 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 23° C brown paint.

(Oil-free alkyd resin) Synthesized from polyhydric alcohol (neopentyl glycol, trimethylolpropane, 1,4-butanediol, ethylene glycol, pentaerythritol) and polybasic acid (phthalic acid, adipic acid), hydroxyl value 120 ．． Resin with an acid value of 5.2 and a number average molecular weight of 3000 (Paint D) The composition is the same as that of Paint A except that the following oil-free alkyd resin is used, and the resulting coating film has a glass transition temperature of 8°C brown color paint.

(Oil-free alkyd resin) Synthesized from polyhydric alcohols (neopentyl glycol, trimethylolpropane, 1,4-butanediol, ethylene glycol) and polybasic acids (phthalic acid, adipic acid, sebacic acid), with a hydroxyl value of 11. Resin with acid absorption value 4.5s and number average molecular weight 2800 (Paint E) In the composition of Paint A, the same oil-free alkyd resin varnish used in Paint B 5? , 15 parts of melamine resin varnish, blocked isocyanate compound [trade name: Takenate B-820-NS-U1, manufactured by Takeda Pharmaceutical Co., Ltd.] 1 m
Blau 7-color paint, which has the same composition except that the paint film obtained has a glass transition temperature of °C.

Intermediate paint (Intermediate paint A) Oil-free alkyd resin varnish Note 4) 40.5 parts Melamine resin varnish (solid content 60%) 13.5 parts Titanium oxide 32 J parts Carbon black 0.05 parts Butyl cellosolve
4 parts xylene
Part 9 Note 4: Uses the oil-free alkyd resin varnish used in Paint A above.

<Intermediate paint B> Intermediate paint A had the same composition except that the oil-free alkyd resin varnish used in paint B was used as the oil-free alkyd resin varnish.

Intermediate Paint C> Intermediate paint A had the same composition except that the oil-free alkyd resin varnish used in paint C was used as the oil-free alkyd resin varnish.

<Intermediate paint D> Intermediate paint A had the same composition except that the oil-free alkyd resin varnish used in paint D was used as the oil-free alkyd resin L resin varnish.

Example 1 A cationic electrodeposition paint [Komaron CED7OHJ (trade name, manufactured by Dainippon Toyo Co., Ltd.)] was applied by electrodeposition to a zinc phosphate-treated steel plate, and an undercoat film with a dry film thickness of 20 μm was formed by baking for 18Cf'Cl2O minutes. Obtained.

Next, apply intermediate paint B on top of it using air spray to a dry film thickness of approximately 35μ, and after setting it at room temperature for 2 minutes, apply paint B using air spray to a dry film thickness of approximately 20μ. It was coated over and over, set at room temperature for 2 minutes, and then baked at 150°C for two coats. Then apply brown metallic paint [1 Acrose #7300J (
Apply clear paint [1 Acrose #7100 (trade name, manufactured by Dainippon Toyo Co., Ltd.)] with air spray to a dry film thickness of approximately 35p, and after setting for 2 minutes at room temperature, clear paint [1 Acrose #7100 (trade name, manufactured by Dainippon Toyo Co., Ltd.) )] was coated with air spray to a dry film thickness of approximately 15μ, set at room temperature for 2 minutes, and then baked at 150°C for 2C.

Example 2 Coating was carried out in the same manner as in Example 1, except that intermediate coat C was used instead of intermediate coat B, and paint C was used instead of paint B.

Example 3 Painting was carried out in the same manner as in Example 1, except that paint E was used instead of paint B.

Comparative Example 1 Coating was carried out in the same manner as in Example 1 except that intermediate coat A was used instead of intermediate coat B, and paint A was used instead of paint B.

Comparative Example 2 Coating was carried out in the same manner as in Example 1, except that intermediate coating D was used instead of intermediate coating B, and coating D was used instead of coating B.

Comparative Example 3 Coating was carried out in the same manner as in Example 1 except that the coating step of paint B was omitted.

The coating films obtained in Examples 1 to 2 and Comparative Examples 1 to 3 were tested for peeling resistance and prister resistance, and the results are shown in Table 1.

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As is clear from Table 1 of the JLL discussion, the coating film obtained by the method of the present invention had good peeling resistance and blistering resistance.

On the other hand, in Comparative Example 1, in which a paint with a high glass transition temperature was used, the peeling resistance was poor, and on the contrary, in Comparative Example 2, in which a paint with a low glass transition temperature was used, the resistance to pre-starring was poor.

Claims (1)

[Claims] 1. In an automobile body painting method in which a base coat is formed, then an intermediate coat is formed, and then a top coat is formed, the tip of the hood, the area around the tire house, etc. are susceptible to stone chipping. The area between the intermediate coat film and the top coat film has the same color or similar color to the top coat film, and the glass transition temperature of the resulting paint film is 15 to 50 ° C.
A method for painting an automobile body, which comprises forming an oil-free alkyd resin paint film whose essential components are a) an oil-free alkyd resin, (b) a binder component consisting of an aminoaldehyde resin, and (c) a pigment.