JPH1085659A - Paint composition, its coating method and material coated with paint - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a coated material having sufficient coating film performance even by the baking and drying at a low temp. in an overcoat consisting of the two paints used in multilayer coating by using a one-pack thermosetting base paint as the base paint and a low-temp. curing clear paint excessively blended with a curing agent as the clear paint. SOLUTION: In an overcoat to be used in the multilayer coating of an automobile, etc., consisting of a base paint and a clear paint, a one-pack thermosetting base paint is used as the base paint and a low-temp. curing clear paint excessively blended with a curing agent as the clear paint. Further, a polyester or acrylic resin is used as the base resin of a binder in the one-pack thermosetting base paint, and a two-pack urethane resin paint is used as the clear paint. Besides, hexamethylene diisocyanate is used as the curing agent, and the amt. of the agent to be mixed is controlled in 1.1 to 2.3 molar ratio of NCO to OH.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating composition suitable for use as a top coating in multilayer coating such as automotive coating, a coating method therefor, and a coated product obtained by applying the coating method.

[0002]

2. Description of the Related Art Heretofore, as a color base paint and a clear paint in an automotive top coat, those having the same binder resin component constituting the matrix have been used. Generally, a melamine-acrylic base paint and a clear paint are applied to an automobile outer panel by a wet-on-wet method, and the coating film is cured at a baking and drying temperature of 140 ° C. or higher. A two-component urethane-based base paint and a clear paint are applied to parts and the like by a wet-on-wet method and baked at a baking and drying temperature of 80 ° C. or lower.

As described above, when coating resin parts and the like, since the heat-resistant temperature of the base material is low, a high-temperature baking type paint such as a melamine-acrylic paint cannot be used, and an expensive two-pack type urethane paint is used. It was necessary to paint using such as. Furthermore, since it is necessary to separately paint the automobile outer panel portion and the resin parts under different baking and drying conditions using another type of paint, there is a problem in terms of productivity.

It has been conventionally proposed to add a catalyst such as an organic basic catalyst or an acid catalyst to a thermosetting paint to achieve low-temperature curing. (For example, JP-A-59-191766,
JP-A-61-285273, JP-A-6-134392
issue). In this way, the addition of a catalyst to the thermosetting paint promotes the curing reaction of the paint. In particular, if a relatively large amount of catalyst is added, baking and drying can be performed at a sufficiently low temperature, and the resin component and the like can be dried. It is possible to apply a thermosetting paint such as a melamine-acrylic paint to an object having poor heat resistance.

However, under the use of a catalyst,
It is known that a different type of crosslinking reaction proceeds preferentially when a catalyst is not used, and such a difference in the cross-linking structure in the finished coating film and the influence of the catalyst components and the like remaining in the finished coating film. As a result, generally, when a catalyst is used, various properties such as weather resistance and strength of the obtained coating film are reduced as compared with the case where no catalyst is used. Therefore, a mere use of a thermosetting paint to which a catalyst has been added as described above cannot provide a top coat for automobiles having satisfactory coating performance.

Japanese Patent Application Laid-Open No. 2-68173 discloses a wet-on-wet coating of a high solid type paint containing a smaller amount of an acid catalyst on a high solid type paint containing a standard amount of an acid catalyst. It has been proposed to obtain an excellent coating film. However, in this technology,
The baking / drying temperature cannot be lowered, and it is difficult to apply to resin parts and the like.

In view of such problems of the prior art, the present inventors have added an acid catalyst to a one-component thermosetting base coating which is a high-temperature baking type coating to prepare a clear coating applied to the upper layer. An overcoating composition which is used as a low-temperature curable paint such as a two-component urethane paint was previously proposed (Japanese Patent Application No. 7-12 / 1995).
6738). This coating composition exhibits a very excellent effect that a coated product having sufficient coating film performance can be obtained even under baking and drying conditions at a low temperature of 80 ° C. or lower. However, since the amount of the acid catalyst added to the base paint is very small, it is difficult to add an accurate amount of the acid catalyst, and another problem remains that the paint stability after the addition of the acid catalyst is not sufficient.

[0008]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a coating composition suitable for use as a top coating in multilayer coating such as automobile coating, a coating method thereof, and a coated article obtained by applying the coating composition. It is assumed that. Further, the present invention provides a top coat composition and a coating method which can form a coating film having good coating performance even under low-temperature baking and drying conditions, and which is advantageous in cost, and a coated article obtained by applying the same. It is intended to provide. Further, the present invention provides a top coating composition, a method of applying the same, and a coated article obtained by applying the same, because the composition is excellent in terms of preparation of the coating composition and stability after preparation of the coating composition. It is intended for.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, have used a one-pack type thermosetting base paint which is a high-temperature baking type paint as a base paint, and formed an upper layer. By using a low-temperature curable paint such as a two-component urethane paint as the clear paint to be applied, and by adding an excessive amount of a curing agent to this low-temperature curable paint, a sufficient coating film can be obtained even under baking and drying conditions at a low temperature of 80 ° C. or less. The present inventors have found that a coated product having high performance can be obtained, and have reached the present invention.

[0010] That is, the top coat of the present invention which solves the above-mentioned problems is a top coat composed of a base paint and a clear paint used in multilayer coating, wherein a one-pack thermosetting base paint is used as the base paint. The present invention is characterized in that a low-temperature-curable clear paint containing an excessive amount of a curing agent is used as the clear paint.

[0011] The present invention also provides an overcoat paint wherein the one-component thermosetting base paint uses a polyester resin or an acrylic resin as a base resin of the binder. Furthermore, the present invention provides an overcoat paint, wherein the low-temperature-curable clear paint is a two-component urethane resin paint. The present invention also provides the curing agent,
1 shows a top coat which is hexamethylisocyanate. The present invention further provides an overcoat paint in which the blending amount of the curing agent in the clear paint is a molar ratio of NCO / OH ratio of 1.1 to 2.3.

[0012] The above object is also a method for applying the top coat paint, wherein the base paint is applied to an object to be coated,
Next, the above-mentioned clear paint is applied by wet-on-wet, and thereafter, the coating is performed by baking and drying at a temperature of 60 to 160 ° C, preferably 70 to 80 ° C.

[0013] The present invention also relates to a base coating composition of 15 to 20 µm.
m, showing the above coating method in which the clear paint is formed with a film thickness of 30 to 35 μm.

[0014] The above-mentioned object is further achieved by an automotive exterior part characterized by being coated with the above-mentioned top coat according to the present invention. The present invention further provides an automobile exterior part in which the automobile exterior part is made of resin.

[0015]

As described above, in the present invention, a one-component thermosetting base coating such as a melamine-acrylic coating is used as a base coating, and a two-component urethane is used as a clear coating applied thereon. The use of a low-temperature-curable clear paint such as a base paint is a combination of different binder resin components in the base paint and the clear paint.

In the topcoat paint of the present invention, the curing agent excessively added to the clear paint penetrates into the one-pack type color base paint, which is a high-temperature baking type paint applied to the lower layer, to bring about a curing reaction accelerating action. In addition, since clear paint is inherently a composition that can be baked at a low temperature, it must be cured with good adhesion and sufficient film performance even under low-temperature baking and drying conditions of, for example, 80 ° C or less, after being applied wet-on-wet. It can be sufficiently applied to an object having poor heat resistance such as a resin part.

Further, in the present invention, since a one-component thermosetting paint such as a melamine-acrylic paint is used as a base paint, a conventional resin component or the like which also uses a urethane paint as a base coating film. This is advantageous in terms of material cost as compared with the coating method, and the use of a one-component coating material simplifies the structure of the coating apparatus and reduces the quality control of the coating in the coating line.

In the present invention, since only an excessive amount of a curing agent is provided in a low-temperature curing type coating material as a clear coating material, it is necessary to finely control the addition amount, for example, when adding a catalyst. There is no difficulty in preparing the coating composition, and the coating composition is excellent in terms of stability after preparation.

Further, according to the coating method of the present invention, since the above-mentioned overcoating according to the present invention which is inexpensive and less dependent on baking conditions is used, resin parts such as steel plate outer plates and bumpers are used. Can be painted with a common paint, and it is also possible to bake the outer plate and resin parts at the same time, reducing the painting cost by sharing the paint and sharing and shortening the painting line. Becomes possible.
In addition, automotive exterior parts coated with such a coating,
Despite being inexpensive, it has excellent paint appearance, adhesion, and weather resistance, and has no defects such as thermal deformation due to the paint baking and drying process in resin parts. By using, the color matching between the outer plate and the resin component becomes good.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail based on embodiments.

The base paint used in the top coat of the present invention is a one-part thermosetting type.

The one-component thermosetting base coating composition that can be used in the present invention includes a base resin having at least one crosslinkable functional group, a crosslinker component having relatively low activity, There is a resin composed of a modified resin component included as needed, or a resin composed of a base resin containing a self-crosslinking functional group and a modified component contained as necessary. And, generally, amino-
Substrate resins classified as alkyd resin paints, oil-free alkyd resin paints ("polyester resin" paints in a narrow sense), etc. are polyester resins, and base resins generally classified as thermosetting acrylic resin paints are acrylic resins Typical are resins and the like.

The one-component thermosetting base paint can be used by using a commercially available one or by adjusting it to an appropriate composition. In the embodiment used for baking, the baking and drying conditions for baking and curing the base paint alone are 120 to 140 ° C and 20 to 140 ° C.
It is desirable to select one that can be set for about 30 minutes.

The amino resin which is a crosslinking agent component in the above-mentioned amino-alkyd resin paint includes melamine resin, benzoguanamine resin and urea resin.
Some are etherified with lower alcohols having about 1 to 4 carbon atoms, and as a top coating for automobiles, etherified melamine, particularly butoxylated melamine, is preferable. On the other hand, as the alkyd resin, depending on the length of the denatured oil (or fatty acid), from an ultra-short oil having an oil length of about 30 to an ultra-long oil having an oil length of about 70, and from the type of the oil (or fatty acid), it may be dry to immiscible. Up to dryness, rosin, phenol, epoxy, isocyanate, depending on the presence or absence of modified resin components such as silicone, etc., various things are included, any of which can be used, but as a top coating for automobiles, Semi-dry oil-modified short oil ~
It is preferable to use an ultra-short oil alkyd resin and a non-drying oil-modified short oil to ultra-short oil alkyd resin.

Also, as an oil-free alkyd resin paint, a combination or blend of a polybasic acid such as phthalic acid, isophthalic acid, terephthalic acid, and adipic acid with a polyhydric alcohol such as glycerin, pentaerythritol, ethylene glycol, and neopentyl glycol. There are various types depending on the difference in the ratio, and the type and the mixing ratio of the amino resin which is the cross-linking agent component to be combined, and any of them can be used, but it is suitable for the baking and drying conditions as described above. Desirably. As the amino resin, a melamine resin, a benzoguanamine resin, a urea resin, or the like can be used in the same manner as described above. However, a melamine resin is preferably used as the top coating for automotive coating.

The base resin in the thermosetting acrylic resin paint has a crosslinkable functional group such as a hydroxyl group, a carboxyl group, an epoxy group, an amide group, an imide group, an N-methylol group, an N-alkylmethylol group (meta- ) Acrylic copolymer, which is used for the polymerization, for example, lower alkyl methacrylate (methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, etc.), styrene, vinyltoluene, etc. And a hard monomer such as, for example, alkyl acrylate (methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, etc.), and higher alkyl methacrylate (n-hexyl methacrylate, Soft such as lauryl methacrylate) Monomers and for introducing the above functional groups, for example, acrylic acid, methacrylic acid, itaconic acid, maleic acid, maleic anhydride, hydroxyethyl methacrylate, hydroxypropyl methacrylate, acrylamide, methacrylamide, glycidyl acrylate, glycidyl methacrylate, dimethylamino Depending on the various combinations with functional monomers such as ethyl methacrylate, t-butylaminoethyl methacrylate, and the like, and the difference in the blending ratio, there are those having various characteristics. Furthermore, amino resin, epoxy resin, alkyd resin,
Some are modified with a modifying component such as silicone resin.
On the other hand, as a crosslinking agent component, depending on the functional group of the base resin, melamine resin, amino resin such as benzoguanamine resin and urea resin, alkyd resin, vinyl resin, block isocyanate compound, epoxy resin and the like are used alone or appropriately combined. used. Further, in the case of using an acrylic copolymer having a self-crosslinkable functional group such as an N-alkylmethylol group as a base resin, there is also a coating composition containing no crosslinking agent component.

Although any of these thermosetting acrylic resin coatings can be used in the present invention, in the embodiment in which the top coating of the present invention is used for automotive coating, among these, a crosslinkable functional coating is used. Hydroxyl, N-methylol group, those using a base resin component mainly composed of N-alkylmethylol group and the like as the group are preferable,
Furthermore, considering the price and availability, amide
Acrylic resin paints, more preferably melamine-acrylic paints, are preferred. In addition, this melamine-acrylic paint was
The embodiment used as a liquid thermosetting base coating is the most preferred embodiment in the present invention.

Further, in the one-component thermosetting base paint,
Pigments (including metal paste, mica powder, etc.), diluting solvents (including reactive diluting solvents) and dispersion media, and other stabilizers, antioxidants, and ultraviolet absorbers for exhibiting a predetermined solid or metallic color Additives such as agents and viscosity modifiers are added as needed. The one-component thermosetting base paint may be in any of a general solution type, a non-aqueous dispersion (NAD) type, a high solid type, and an aqueous dispersion type. Particularly, a general solution type is preferable.

On the other hand, in the top coating of the present invention, the clear coating applied to the upper layer of the base coating is a low-temperature curing coating to which a curing agent is excessively added.

The low-temperature-curable clear coating material preferably exhibits at least sufficient curability under baking and drying conditions of, for example, 70 to 80 ° C. for 20 to 30 minutes, and is suitable as the outermost surface layer in multilayer coating. The type is not particularly limited as long as it is a type that can be cured by a curing agent or a cross-linking agent that satisfies various properties such as glossiness, weather resistance, and hardness. For example, a polyol-curable polyurethane paint, acrylic-silicone Paints that use a relatively active curing agent such as lacquer-based paints, alkyd-silicone paints, oil-free alkyd-silicone paints, and unsaturated polyester paints (typically two-pack paints) Although it is possible, it is preferable to use a two-component polyurethane coating, particularly a polyol-curable polyurethane coating. It is.

The polyol-curable polyurethane coating is a coating which is cured by a urethane bond by chemically reacting a hydroxyl group of a polyol such as a polyester-based, polyether-based or (meth) acrylic resin having a hydroxyl group with an isocyanate prepolymer. .

The polyol component may be any one of them, but is preferably of the same type as the base coating in consideration of the adherence to the base coating. For example, from the viewpoint of organic solvent resistance, polyester-based is preferred. It is preferable to use a polyether type from the viewpoint of alkali resistance and water resistance, and a (meth) acryl type from the viewpoint of stain resistance and quick drying.

The curing agent to be added to such a low-temperature curing type paint is not particularly limited because it varies depending on the type of low-temperature curing type paint to be used. As isocyanates as curing agents used in various polyurethane coatings, tolylene diisocyanate (TDI), hexamethylene diisocyanate (HMDI), 4,4-diphenylmethane diisocyanate, 1,5-naphthalenediisocyanate,
Triphenylmethane triisocyanate, tolidine diisocyanate (TODI) xylene diisocyanate,
Examples thereof include dicyclohexylmethane diisocyanate and isophorone diisocyanate (IPDI), and hydrogenated products thereof can also be used. Of these, hexamethylene diisocyanate is particularly preferred.

The isocyanate prepolymer used in the polyol-curable polyurethane coating material may be any of various types composed of a simple isocyanate as a raw material as exemplified above.

In the present invention, however, the amount of the curing agent in the low-temperature-curable paint as a clear paint is excessive, that is, based on the number of moles of the crosslinkable functional group of the base resin of the low-temperature-curable paint. The number of moles of the reactive group of the curing agent must be at least equivalent.

Taking the case of a polyurethane coating as an example, the NCO / OH ratio (molar ratio)
For example, 1.1 to 2.3, more preferably 1.3 to 1.
It is desirable to be about 7. Here, when the NCO / OH ratio is less than 1.1, the color base coating film is not sufficiently cured, and as a result, poor adhesion may occur. On the other hand, when the NCO / OH ratio exceeds 2.3,
There is a high possibility that unreacted NCO reacts with water in the coating film to have water absorption. Therefore, moisture easily accumulates in the coating film, and as a result, problems such as blisters (bulging) occur.

Further, in the low-temperature curing type clear coating material, additives such as a diluting solvent (including a reactive diluting solvent) and other additives such as a stabilizer, an antioxidant, an ultraviolet absorber, and a viscosity modifier may be used, if necessary. Has been added. It is also possible to mix so-called color clear paints in the clear paint by blending pigments of the same or different kind with the pigments contained in the color base paint as long as the transparency is not impaired. In this case, it is desirable that the pigment incorporated in the clear paint has a smaller particle size than the pigment contained in the color base paint. The low-temperature-curable clear coating material may be in any form such as a general solution type or a high solid type, but among these, a general solution type is preferred.

Since the top coating composition of the present invention has the above-described composition, it has low dependence on baking conditions, and can be cured under a relatively wide range of baking and drying conditions including a low temperature range. The top coat of the present invention is 2 coats 2 bake,
Alternatively, two coats and one bake by dry-on-wet may be used, but preferably two coats and one bake by wet-on-wet.

The coating method of the present invention uses the above-mentioned top coating of the present invention to coat a base material such as a steel plate or a metal part such as an automobile body outer panel or a resin part such as a resin bumper with the base coating material. And then apply the clear paint by wet-on-wet,
Baking and drying are performed at a temperature of 160 ° C, preferably 70 to 80 ° C.

When the baking and drying temperature is lower than 60 ° C., the base coating film is not sufficiently cured, and as a result, there is a high possibility that poor adhesion may occur. Baking occurs and durability of the coating film, for example, poor weather resistance occurs. Further, if baking and drying is performed at a temperature of 70 to 80 ° C., coating can be performed without causing heat deformation or the like even on resin parts having a problem with heat resistance, and the resin parts and the like can be coated. Simultaneous baking and drying with a steel plate can also be performed.

In the coating method of the present invention, the baking drying time is not generally defined because it depends on the drying baking temperature to be set and the thickness of the coating film. 2 in baking conditions
About 5 to 15 minutes is appropriate under high temperature baking conditions of about 0 to 30 minutes and about 140 to 160 ° C.

The thicknesses of the base coating film and the clear coating film in the overcoating film thus obtained are as follows.
Although not particularly limited, for example, base coating film 1
The thickness is about 0 to 20 μm, and the clear coating film is about 30 to 40 μm.

The pretreatment of the object to be coated prior to the coating method of the present invention, and the structure of the undercoating layer such as undercoating and intermediate coating are optional, and can be appropriately selected by a conventionally known method. It is. Further, the top coat or coating method of the present invention is not limited to the coating of automobile body exterior parts such as automobile body outer panels and bumpers, but can be applied to painting in various fields.

[0044]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples.

Example 1 An ABS test piece (manufactured by Sumitomo Bakelite) having a size of 70 × 120 mm was pretreated with isopropyl alcohol. Subsequently, as a top coat, a color base paint for steel plate SPM-80 (manufactured by Nippon Paint, one-pack type) Acrylic-melamine-based paint) and wet-on-wet coating with a two-component urethane paint R254 (manufactured by Nippon Bee Chemical) whose NCO / OH ratio (molar ratio) was adjusted to 1.1 as a clear paint. Then, baking and drying were performed at 80 ° C. for 20 minutes. The coatings were 15 μm and 35 μm, respectively. Then, the initial adhesion, the appearance, the moisture resistance, and the weather resistance of the coating film obtained under the following conditions were examined. Table 1 shows the obtained results.

Example 2 The NCO / OH ratio of the clear paint in Example 1 was 1.5
Coating was carried out under the same conditions as in Example 1 except that the composition was changed to, and the performance of the obtained coating film was examined in the same manner as in Example 1.
Table 1 shows the obtained results.

Example 3 The NCO / OH ratio of the clear paint in Example 1 was 1.7.
Coating was carried out under the same conditions as in Example 1 except that the composition was changed to, and the performance of the obtained coating film was examined in the same manner as in Example 1.
Table 1 shows the obtained results.

Example 4 The NCO / OH ratio of the clear paint in Example 1 was 2.0.
Coating was carried out under the same conditions as in Example 1 except that the composition was changed to, and the performance of the obtained coating film was examined in the same manner as in Example 1.
Table 1 shows the obtained results.

Example 5 The NCO / OH ratio of the clear paint in Example 1 was 2.3.
Coating was carried out under the same conditions as in Example 1 except that the composition was changed to, and the performance of the obtained coating film was examined in the same manner as in Example 1.
Table 1 shows the obtained results.

Example 6 Example 1 was repeated except that the color base paint SPM-80 for steel plates was changed to a color base paint R-305 (manufactured by Nippon Bee Chemical Co., Ltd., one-pack acrylic-melamine paint) for bumpers.
The coating was performed under the same conditions as in Example 1 and the performance of the obtained coating film was examined in the same manner as in Example 1. Table 1 shows the obtained results.

Example 7 The coating was performed under the same conditions as in Example 2 except that the color base paint SPM-80 for steel plates was changed to the color base paint R-305 for bumpers, and the performance of the obtained coating film was evaluated. The examination was carried out in the same manner as in Example 1. Table 1 shows the obtained results.

Example 8 The coating was performed under the same conditions as in Example 3 except that the color base paint SPM-80 for steel plates was changed to the color base paint R-305 for bumpers, and the performance of the obtained coating film was evaluated. The examination was carried out in the same manner as in Example 1. Table 1 shows the obtained results.

Example 9 The coating was performed under the same conditions as in Example 4 except that the color base paint SPM-80 for steel plates was changed to the color base paint R-305 for bumpers, and the performance of the obtained coating film was evaluated. The examination was carried out in the same manner as in Example 1. Table 1 shows the obtained results.

Example 10 The coating was performed under the same conditions as in Example 5 except that the color base paint SPM-80 for steel plates was changed to the color base paint R-305 for bumpers, and the performance of the obtained coating film was evaluated. The examination was carried out in the same manner as in Example 1. Table 1 shows the obtained results.

Reference Example 1 The clear paint in Example 1 had an NCO / OH ratio of 1.0
Coating was carried out under the same conditions as in Example 1 except that the composition was changed to, and the performance of the obtained coating film was examined in the same manner as in Example 1.
Table 1 shows the obtained results.

Reference Example 2 The NCO / OH ratio of the clear paint in Example 1 was 2.4.
Coating was carried out under the same conditions as in Example 1 except that the composition was changed to, and the performance of the obtained coating film was examined in the same manner as in Example 1.
Table 1 shows the obtained results.

Reference Example 3 Coating was carried out under the same conditions as in Example 1 except that the baking and drying conditions in Example 1 were changed to 50 ° C. for 20 minutes. Was examined as well. Table 1 shows the obtained results.

REFERENCE EXAMPLE 4 Coating was carried out under the same conditions as in Example 1 except that the baking and drying conditions in Example 1 were changed to 170 ° C. for 20 minutes. Was examined as well. Table 1 shows the obtained results.

< Coating Film Performance Test Method > The coating films obtained in Examples and Reference Examples were tested for performance according to the following methods.

1. Initial Adhesion This was carried out based on the grid adhesion test of JIS K-5400 6.15. The evaluation was based on the following criteria: ○: no problem, x: peeling occurred.

[0061] 2. Appearance of coating film It was carried out based on JIS K-5400 6.1. The evaluation was based on the following criteria: ○: no problem, x: occurrence of abnormalities such as blisters.

3. Moisture resistance 12 in a constant temperature / humidity chamber in a humid atmosphere of 40 ° C and 90% RH.
After leaving for 0 hour and leaving at room temperature for 24 hours, the appearance and adhesion of the coating film were evaluated in the same manner as described above.

4. Weather resistance 300 with sunshine weatherometer (SWOM)
After performing a time test and leaving it to stand at room temperature for 24 hours, the appearance and adhesion of the coating film were evaluated in the same manner as described above.

[0064]

[Table 1]

[0065]

As described above, the overcoating composition of the present invention uses a one-component thermosetting base coating composition as a base coating composition, and a low-temperature curing composition containing an excessive amount of a curing agent as a clear coating composition applied to the upper layer. Because it uses a mold clear paint, it can be cured with good adhesion even under low-temperature baking and drying conditions of, for example, 80 ° C. or less, and can be sufficiently applied to substrates having poor heat resistance such as resin parts. It is possible, and the obtained overcoat film has excellent durability such as weather resistance and is advantageous in cost. Furthermore, the preparation of the coating composition also involves merely adding an excessive amount of the curing agent to the clear coating, and there is no difficulty such as the necessity of fine control of the addition amount. It is also excellent.

In addition, according to the coating method of the present invention, since the above-described top coating according to the present invention is inexpensive and has little dependence on baking conditions, resin parts such as steel plates and bumpers are used. Can be painted with a common paint, and it is also possible to bake the outer plate and resin parts at the same time, reducing the painting cost by sharing the paint and sharing and shortening the painting line. Becomes possible.

Further, since the automotive exterior parts of the present invention are coated with the above-mentioned top coat,
Despite being inexpensive, it has excellent paint appearance, adhesion, and weather resistance, and has no defects such as thermal deformation due to the paint baking and drying process in resin parts. By using, the color matching between the outer plate and the resin component becomes good.

Claims (10)

[Claims] An overcoating material comprising a base coating material and a clear coating material used in multilayer coating, wherein a one-component thermosetting base coating material is used as the base coating material, and a low-temperature curing agent containing an excessive amount of a curing agent as the clear coating material. Top coat paint characterized by using a mold clear paint. 2. The topcoat paint according to claim 1, wherein the one-part thermosetting base paint uses a polyester resin or an acrylic resin as a base resin of the binder. 3. The topcoat paint according to claim 1, wherein the low-temperature-curable clear paint is a two-component urethane resin paint. 4. The topcoat according to claim 1, wherein the curing agent is hexamethylene diisocyanate. 5. The compound according to claim 3, wherein the compounding amount of the curing agent in the clear coating material is such that the molar ratio of the NCO / OH ratio is 1.1 to 2.3. Topcoat paint. 6. The method for applying a top coat paint according to claim 1, wherein the base paint is applied to an object to be coated, and then the clear paint is applied wet-on-wet. A coating method characterized by baking and drying at a temperature of ° C. 7. The coating method according to claim 6, wherein the base paint is formed with a thickness of 15 to 20 μm and the clear paint is formed with a thickness of 30 to 35 μm. 8. The coating method according to claim 6, wherein the baking and drying temperature is 70 to 80 ° C. 9. An exterior part for an automobile, wherein the exterior part is coated with the top coating material according to claim 1. Description: 10. The vehicle exterior component according to claim 9, wherein the vehicle exterior component is made of resin.