JPH08318212A - Paint composition and coating method thereof and coated material obtained by coating paint composition - Google Patents

Abstract

PURPOSE: To provide a top coating paint composition advantageous in cost by which a paint film having excellent paint film performance is formed even in a low temperature baking condition. CONSTITUTION: A top coating paint is provided by adding an acid catalyst such as p-toluenesulfonic acid (p-TSA) to one package thermosetting type base paint such as a melamine-acrylic resin paint as a base paint 2. Further, a top coating paint is provided by using a low temperature hardening type clear paint such as a two package type urethane paint as a clear paint 3.

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 an overcoat in multi-layer coating such as automobile coating, a coating method therefor, and a coated article obtained by applying the same.

[0002]

2. Description of the Related Art Conventionally, as a color base paint and a clear paint in a topcoat paint for automobiles, those in which the binder resin components constituting the matrix are the same system are 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 base paint and a clear paint, which are two-component urethane-based paints, 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 less.

In such coating of resin parts and the like, since the heat resistant temperature of the base material is low, it is not possible to use a high temperature baking type coating such as melamine-acrylic coating, and an expensive two-component urethane coating. It was necessary to paint using the above. Further, since it is necessary to separately coat the outer panel portion of the automobile and the resin component under different baking and drying conditions by using another type of coating material, there is a problem in terms of productivity.

Japanese Patent Application Laid-Open No. 59-191766 proposes that an organic basic catalyst is added to a thermosetting coating material to achieve low temperature curing. Further, for example, Japanese Patent Laid-Open No. 61-
As shown in Japanese Patent No. 285273, it is known to add an acid catalyst to a high solid type thermosetting coating material, and further, JP-A-6-134392 discloses a thermosetting coating material with a relatively high temperature. It has been proposed to coat a resin product by adding a large amount of a catalyst. Thus, when a catalyst is added to the thermosetting coating material, the curing reaction of the coating material is accelerated, and particularly when a relatively large amount of a catalyst is added, baking and drying can be performed at a sufficiently low temperature, so that the resin parts, etc. It is possible to apply a thermosetting coating material such as a melamine-acrylic type to an object having poor heat resistance.

However, when using the catalyst,
It is known that a different type of crosslinking reaction proceeds preferentially from the case where no catalyst is used.The difference in the crosslinking structure in such a finished coating film, and the influence of the catalyst components remaining in the finished coating film, etc. Therefore, in general, when a catalyst is used, various properties such as weather resistance and strength of the obtained coating film are deteriorated as compared with the case where a catalyst is not used. Therefore, it is not possible to obtain an automotive topcoat having satisfactory coating performance by simply using a thermosetting coating containing a catalyst.

In JP-A-2-68173, a high solid coating containing a standard amount of an acid catalyst is coated with a high solid coating containing a less than the standard amount of wet catalyst on a wet-on-wet basis. It has been proposed to obtain an excellent coating film. However, in this technology,
The baking and drying temperature cannot be lowered, and it is difficult to apply it to resin parts and the like.

[0007]

SUMMARY OF THE INVENTION Accordingly, the object of the present invention is to provide a coating composition suitable for use as a top coating in a multi-layer coating such as automobile coating, a coating method therefor, and a coated article obtained by applying the coating composition. It is what Furthermore, the present invention provides a top coating composition which is capable of forming a coating having good coating performance even under low temperature baking and drying conditions, and is also advantageous in terms of cost, a coating method therefor, and a coated article obtained by applying the same. It is intended to be provided.

[0008]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventors have added an acid catalyst to a one-component thermosetting base coating which is a high temperature baking type coating to form an upper layer. It was found that by applying a low temperature curing type paint such as a two-component urethane paint as the clear paint to be applied to the substrate, a coated product having sufficient coating performance can be obtained even under baking and drying conditions at a low temperature of 80 ° C. or lower. It came to.

That is, in the topcoat paint of the present invention which solves the above problems, a one-component thermosetting base paint to which an acid catalyst is added is used as a base paint, and a low temperature curing type clear paint is used as a clear paint. It is a feature.

The present invention also provides a top coating composition in which the one-component thermosetting base coating composition uses a polyester resin or an acrylic resin as the base resin of the binder. Further, the present invention shows a top coating material in which the low temperature curing type clear coating material is a two-component urethane resin coating material. The present invention also provides that the acid catalyst is
It shows a top-coat paint which is one or more compounds selected from the group consisting of p-toluenesulfonic acid, dinonylnaphthalenesulfonic acid, dinonylnaphthalenedisulfonic acid, dodecylbenzenedisulfonic acid and these amine blocks. is there. The present invention further provides a topcoat paint in which the amount of the acid catalyst added is in an amount of 1 to 10% by weight based on the binder solid content of the one-component thermosetting base paint.

The above-mentioned problem is also a method of applying the above-mentioned top coating composition, wherein the base coating composition is applied to an object to be coated,
Then, the clear paint is applied wet-on-wet, and then baked and dried at a temperature of 60 to 160 ° C., preferably 70 to 80 ° C. to achieve a coating method.

Further, the above object can also be achieved by an exterior part for an automobile, characterized by being coated with the above-mentioned top coating material according to the present invention.

[0013]

As described above, in the present invention, as the base paint, a one-component thermosetting base paint such as melamine-acrylic base paint to which an acid catalyst is added is used, and a clear paint applied on the upper layer thereof. For example, a low temperature curing type clear paint such as a two-component urethane paint is used.
It is a combination of different binder resin components in the base paint and the clear paint.

The top coating composition of the present invention has the effect of promoting the curing reaction by the added acid catalyst in the base coating composition.
Moreover, since the clear paint is originally a composition that can be baked at a low temperature, for example, 80
It can be cured with good adhesion even under low-temperature baking and drying conditions such as ℃ or less, and can be sufficiently applied to an object to be coated having poor heat resistance such as resin parts.

FIG. 1 schematically shows the constitution of a top coating film obtained by applying the top coating composition of the present invention. In the top coating film formed on the article to be coated 1, although the acid catalyst remains in the base coating film 2,
This base paint coating film 2 is not directly exposed to the external atmosphere, and a stable clear paint coating film 3 containing substantially no acid catalyst such as a two-component urethane paint is formed thereover. In addition, the top coating film has excellent durability such as weather resistance.

Further, in the present invention, since a one-component thermosetting coating material such as melamine-acrylic coating material is used as the base coating material, the conventional resin parts using urethane coating material as the base coating material, etc. Compared with the above-mentioned coating, it is advantageous in terms of material cost, and since the one-liquid type is used, the construction of the coating apparatus can be simplified and the coating quality control in the coating line can be reduced.

Further, according to the coating method of the present invention, in order to use the above-mentioned top coating according to the present invention which is inexpensive in cost and less dependent on the baking conditions, a resin plate such as a steel plate outer plate and a bumper is used. It is possible to paint with the same paint, and it is also possible to bake the outer plate and resin parts at the same time.Reducing the coating cost by sharing the paint, sharing and shortening the coating line, etc. Is possible.
In addition, the exterior parts of automobiles that have been painted in this way are
Despite being cheap in cost, it has excellent coating appearance, adhesion, and weather resistance, and does not have problems such as thermal deformation caused by coating baking drying process even for resin parts etc. By using, the matching of the color tone of the outer plate and the resin component becomes good.

Hereinafter, the present invention will be described in more detail based on the embodiments. In the top coat paint of the present invention, the base paint is a one-component thermosetting base paint to which an acid catalyst is added.

Various kinds of acid catalysts can be used, but preferably organic sulfonic acid compounds, particularly p-toluenesulfonic acid (p-TSA), dinonylnaphthalenesulfonic acid (DNNSA), di- Aromatic sulfonic acids such as nonylnaphthalenedisulfonic acid (DNDDSA), dodecylbenzenedisulfonic acid (DDBSA), and amine blocked products thereof are preferable, and amine blocked products thereof are most preferable, and p-TSA is most preferable.
And DNNSA.

The amount of such an acid catalyst to be added is not particularly limited as it depends on the type of the one-component thermosetting base paint as will be described later, but is generally one component. The amount is preferably 1 to 10% by weight, more preferably 2 to 3% by weight, based on the binder resin solid content of the thermosetting thermosetting base coating material. If the amount added is less than 1% by weight, the base coating film may not be sufficiently cured under low temperature baking conditions such as 80 ° C. or lower, and as a result, poor adhesion may occur. 10% by weight
If it exceeds, the water absorption of the acid catalyst may make it easier for water to accumulate in the coating film, resulting in the possibility of blistering (swelling).

On the other hand, in the one-part thermosetting base coating composition to which such an acid catalyst is added, the binder resin thereof has a relatively low activity with the base resin containing at least one or more crosslinkable functional groups. Some include a cross-linking agent component and a modified resin component that is included as necessary, or one that includes a base resin containing a self-crosslinking functional group and a modifying component that is included as necessary. Then, the base resin generally classified as an amino-alkyd resin paint, an oil-free alkyd resin paint (narrowly defined “polyester resin” paint) and the like is a polyester resin, and is generally classified as a thermosetting acrylic resin paint. The base resin is typically an acrylic resin.

As such a one-component thermosetting base coating composition, a commercially available one can be used or by adjusting it to an appropriate composition. The top coating composition of the present invention can be used for automobile coating. In the embodiment used for use, the baking and drying conditions are 120 to 140 ° C. and 20 to 30 without addition of the acid catalyst as described above.
It is desirable to select one that can be set to about a minute.
Some commercially available products already have an acid catalyst added to their coating composition (for example, a certain non-aqueous dispersion (NAD) type product). When the base coating material of the top coating composition of the present invention is used, the acid catalyst may be added in an amount within the above range in addition to the amount of the acid catalyst originally added.

As the amino resin which is a cross-linking agent component in the above-mentioned amino-alkyd resin paint, melamine resin, benzoguanamine resin, urea resin and the like are used.
Some of these are etherified with lower alcohols having about 1 to 4 carbon atoms, and as the topcoat paint for automobiles, those containing etherified melamine, especially butoxylated melamine as a main component are preferable. On the other hand, as the alkyd resin, depending on the length of the modified oil (or fatty acid), from the ultra-short oil with an oil length of about 30 to the ultra-long oil with an oil length of about 70, and depending on the type of the oil (or fatty acid), it may be dry or non-dry. Up to dryness, also, rosin, phenol, epoxy, isocyanate, depending on the presence or absence of a modified resin component such as silicone, various things are included, any of which can be used, as an automotive topcoat, Semi-drying 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 and combination of polybasic acids such as phthalic acid, isophthalic acid, terephthalic acid and adipic acid and polyhydric alcohols such as glycerin, pentaerythritol, ethylene glycol and neopentyl glycol. There are various types depending on the difference in the ratio and the type and compounding ratio of the amino resin that is the crosslinking agent component to be combined, and any of them can be used, but they are suitable for the baking and drying conditions as described above. It is desirable to be one. 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, but it is preferable to use a melamine resin as the top coating for automobiles.

The base resin in the thermosetting acrylic resin coating 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 and an N-alkylmethylol group (meta). ) Acrylic copolymer, which is used for the polymerization, such as methacrylic acid lower alkyl ester (methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, etc.), styrene, vinyltoluene, etc. Hard monomers of, for example, alkyl acrylates (methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, etc.), higher alkyl methacrylates (n-hexyl methacrylate, Soft such as lauryl methacrylate) Monomers and, for example, acrylic acid, methacrylic acid, itaconic acid, maleic acid, maleic anhydride, hydroxyethyl methacrylate, hydroxypropyl methacrylate, acrylamide, methacrylamide, glycidyl acrylate, glycidyl methacrylate, dimethylamino for introducing the functional group. Due to various combinations with functional monomers such as ethylmethacrylate and t-butylaminoethylmethacrylate, and differences in the compounding ratio, there exist various compounds having different characteristics. Furthermore, amino resin, epoxy resin, alkyd resin,
Some are modified with a modifying component such as a silicone resin.
On the other hand, as the cross-linking agent component, an amino resin such as melamine resin, benzoguanamine resin and urea resin, an alkyd resin, a vinyl resin, a blocked isocyanate compound, an epoxy resin or the like may be used alone or in an appropriate combination depending on the functional group of the base resin. used. Further, for example, in the case where the base resin is an acrylic copolymer having a self-crosslinking functional group such as N-alkylmethylol group, there is a coating composition containing no crosslinking agent component.

Although any of these thermosetting acrylic resin coating materials can be used in the present invention, in the embodiment in which the top coating material of the present invention is used for automobile coating, among these, a crosslinkable functional group is used. It is preferable to use a base resin component mainly composed of a hydroxyl group, an N-methylol group, an N-alkylmethylol group or the like as a group,
Furthermore, in consideration of price and availability, amide-
Acrylic resin paints, more preferably melamine-acrylic paints are preferred. In addition, 1% of this melamine-acrylic paint
The embodiment used as a liquid thermosetting base paint is the most preferred embodiment of the present invention. On the other hand, those mainly composed of a crosslinkable functional group epoxy group have a high coating cost and have some problems in storage stability, and those mainly composed of a carboxyl group as a crosslinkable functional group will be described later. In many cases, the effect of lowering the baking and drying conditions due to the addition of various acid catalysts is not sufficiently exhibited, and therefore those having an extremely large number of these functional groups are not very desirable.

The composition conditions such as the compounding ratio of the base resin and the cross-linking agent component in the various one-component thermosetting base coating materials as described above depend on the kind of the binder used, particularly the base resin. It cannot be unconditionally specified because it varies depending on the number of moles of the crosslinkable functional group and the number of reactive groups in the crosslinking agent, but the number of moles of the reactive group with respect to the number of moles of the crosslinkable functional group is at least approximately equivalent or more. It can be appropriately adjusted within the above-mentioned predetermined dry baking conditions (without addition of an acid catalyst), the glossiness of the coating film obtained, and high performance. For example, in a melamine-alkyd resin coating, the alkyd resin and melamine resin have a compounding ratio of about 6/4 to 8.5 / 1.5, and in a melamine-acrylic resin coating, an alkyd resin and a melamine resin. Is 6/4 to 8.5 / 1.5
The mixing ratio is about the same.

Further, in the one-component thermosetting base coating,
Pigments (including metal paste, mica powder, etc.), diluting solvents (including reactive diluting solvents) or dispersion media, and other stabilizers, antioxidants, and UV absorbers for exhibiting a solid or metallic predetermined color Additives such as agents and viscosity modifiers are added as necessary. Further, the one-component thermosetting base coating material may be any one 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 composition of the present invention, the clear coating composition applied to the upper layer of the base coating composition is a low temperature curable composition, preferably 2 to 70 ° C.
As long as it exhibits at least sufficient curability under baking and drying conditions such as 0 to 30 minutes and satisfies various properties such as glossiness, weather resistance, and hardness suitable for the outermost surface layer in multilayer coating, The type is not particularly limited, and a lacquer-based paint that uses a thermoplastic resin such as an acrylic lacquer-based paint as a binder resin to cure by volatilization drying of a solvent, or a catalyst-curable polyurethane paint, a polyol-curable polyurethane paint, an acrylic- Silicone-based paints, alkyd-silicone-based paints, oil-free alkyd-silicone-based paints, unsaturated polyester paints, etc., which are cross-linked and cured using a relatively highly active crosslinking agent or catalyst (typically a two-component paint)
Among these, a two-component polyurethane coating material, particularly a polyol-curable polyurethane coating material, is preferable.

The polyol-curable polyurethane coating material is a coating material in which a hydroxyl group of a polyol such as a polyester-based or polyether-based resin or a (meth) acrylic resin having a hydroxyl group is chemically reacted with an isocyanate prepolymer and cured by a urethane bond. . The polyol component may be any of them, but in view of adhesion to the base paint, the same system as the base paint is preferable, and for example, from the viewpoint of organic solvent resistance, a polyester system is preferable. From the viewpoints of alkali resistance and water resistance, polyether-based ones are preferable, and from the viewpoints of stain resistance and quick-drying, (meth) acrylic-based ones are preferable, and the isocyanate prepolymer is, for example, tolylene diisocyanate (TDI). ), 4,4′-diphenylmethane diisocyanate (MDI), etc. yellowing type (providing high hardness),
Non-yellowing type such as xylylene diisocyanate (XDI), hexamethylene diisocyanate (HMDI), lysine diisocyanate methyl ester (LDI), isophorone diisocyanate (IPDI), hydrogenated TDI (H ₆ TDI), hydrogenated MDI (H ₁₂ MDI) Various materials such as (providing high elasticity) configured by using an isocyanate simple substance as a raw material may be used.

Further, in the low temperature curing type clear paint, a diluent solvent (including a reactive diluent solvent) and other additives such as a stabilizer, an antioxidant, an ultraviolet absorber and a viscosity modifier may be added if necessary. Has been added. Further, this low temperature curing type clear coating material may be in any form such as a general solution type or a high solid type, but among them, in particular,
A general solution type is preferable.

Since the top coating composition of the present invention has the composition as described above, it has a low dependency on baking conditions and can be cured under a relatively wide range of baking and drying conditions including a low temperature range. The top coating composition of the present invention is 2 coat 2 bake,
Alternatively, dry-on-wet 2 coat 1 bake may be used, but wet-on-wet 2 coat 1 bake is preferable.

In the coating method of the present invention, the above base coating is applied to an object to be coated such as a steel plate such as an automobile body outer panel or a metal part or a resin part such as a resin bumper by using the above-mentioned top coating composition of the present invention. And then apply the clear paint wet-on-wet, then 60-
It is baked and dried 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, poor adhesion is likely to occur. Baking occurs and the durability of the coating film, for example, poor weather resistance occurs. Further, if baking and drying are performed at a temperature of 70 to 80 ° C., it is possible to perform coating on a resin component having a problem in heat resistance without causing thermal deformation or the like, and Simultaneous baking and drying with a steel plate outer plate is also possible.

In the coating method of the present invention, the baking and drying time is not specified unconditionally because it depends on the dry baking temperature to be set, the coating film thickness, etc., but it is, for example, a low temperature of about 60 to 80 ° C. 2 under baking conditions
About 0 to 30 minutes, and about 5 to 15 minutes is suitable under high temperature baking conditions of about 140 to 160 ° C.

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

The constitution of pretreatment, undercoating, intermediate coating and the like of the object to be coated which is carried out prior to the coating method of the present invention is arbitrary and can be appropriately selected and carried out by a conventionally known method. Further, the top coating composition or coating method of the present invention,
The present invention is not limited to coating of exterior parts of automobile bodies such as outer panels of automobile bodies and bumpers, but can be applied to painting in various fields.

[0038]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. Example 1 A 70 × 120 mm size ABS test piece (Sumitomo Bakelite) was pretreated with isopropyl alcohol, and subsequently used as a top coat paint in a color base paint for steel plate SPM-80 (manufactured by Nippon Paint Co., Ltd., one-pack acrylic-melamine). (Based paint), 1% by weight of p-TSA as an acid catalyst is added to the solid content of the binder resin of the paint, and then wet-on-wet as a clear paint, a two-component urethane paint R254 (Nippon Bee Chemical Co., Ltd.) Made)
Was coated and baked at 80 ° C. for 20 minutes for drying. The coating films were 15 μm and 35 μm, respectively. Then, the initial adhesion, moisture resistance, and weather resistance of the coating film obtained under the following conditions were examined. The results obtained are shown in Table 1.

Example 2 Coating was carried out under the same conditions as in Example 1 except that the addition amount of the acid catalyst in Example 1 was changed to 2% by weight, and the performance of the resulting coating film was compared with that in Example 1. I checked it as well. The results obtained are shown in Table 1.

Example 3 Coating was carried out under the same conditions as in Example 1 except that the addition amount of the acid catalyst in Example 1 was changed to 3% by weight, and the performance of the resulting coating film was compared with that in Example 1. I checked it as well. The results obtained are shown in Table 1.

Example 4 Coating was carried out under the same conditions as in Example 1 except that the addition amount of the acid catalyst in Example 1 was changed to 5% by weight, and the performance of the resulting coating film was compared with that in Example 1. I checked it as well. The results obtained are shown in Table 1.

Example 5 Coating was carried out under the same conditions as in Example 1 except that the addition amount of the acid catalyst in Example 1 was changed to 10% by weight, and the performance of the resulting coating film was compared with that in Example 1. I checked it as well. The results obtained are shown in Table 1.

Example 6 Example 1 was repeated except that the color base paint SPM-80 for steel plate was changed to the color base paint R-305 for bumper (manufactured by Nippon Bee Chemical Co., Ltd., one-component acrylic-melamine type paint).
Coating was carried out under the same conditions as above, and the performance of the obtained coating film was examined in the same manner as in Example 1. The results obtained are shown in Table 1.

Example 7 Coating was carried out under the same conditions as in Example 2 except that the color base paint for steel plate SPM-80 was changed to the color base paint for bumpers R-305, and the performance of the resulting coating film was carried out. It investigated like Example 1. The results obtained are shown in Table 1.

Example 8 Coating was carried out under the same conditions as in Example 3 except that the color base paint SPM-80 for steel sheet was changed to the color base paint R-305 for bumpers, and the performance of the obtained coating film was carried out. It investigated like Example 1. The results obtained are shown in Table 1.

Example 9 Coating was carried out under the same conditions as in Example 4 except that the color base paint SPM-80 for steel sheet was changed to the color base paint R-305 for bumpers, and the performance of the obtained coating film was carried out. It investigated like Example 1. The results obtained are shown in Table 1.

Example 10 Coating was performed under the same conditions as in Example 5 except that the color base coating SPM-80 for steel sheet was changed to the color base coating R-305 for bumper, and the performance of the obtained coating film was implemented. It investigated like Example 1. The results obtained are shown in Table 1.

Reference Example 1 Coating was carried out under the same conditions as in Example 1 except that the amount of acid catalyst added in Example 1 was changed to 0.5% by weight, and the performance of the resulting coating film was evaluated as in Example 1. It investigated like 1. The results obtained are shown in Table 1.

Reference Example 2 Coating was carried out under the same conditions as in Example 1 except that the addition amount of the acid catalyst in Example 1 was changed to 11% by weight, and the performance of the resulting coating film was compared with that in Example 1. I checked it as well. The results obtained are shown in Table 1.

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, and the performance of the resulting coating film was evaluated as in Example 1. Same as above. The results obtained are shown in Table 1.

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, and the performance of the resulting coating film was evaluated as in Example 1. Same as above. The results obtained are shown in Table 1.

< Coating film performance test method > The performance test of the coating films obtained in Examples and Reference Examples was carried out according to the following method.

1. Initial Adhesion It was carried out based on the cross-cut adhesion test of JIS K-5400 6.15. The evaluation was made on the basis of ◯: no problem, ×: peeling occurred.

2. Appearance of coating film It was carried out based on JIS K-5400 6.1. The evaluation was made on the basis of ◯: no problem, ×: abnormal occurrence of blister and the like.

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

4. Weather resistance 300 by sunshine weatherometer (SWOM)
After a time test and leaving at room temperature for 24 hours, the appearance and adhesion of the coating film were evaluated by the same method as described above.

[0057]

[Table 1]

[0058]

As described above, the topcoat paint of the present invention uses a one-component thermosetting base paint to which an acid catalyst is added as a base paint, and a low temperature curing as a clear paint to be applied as an upper layer. Since it uses a type clear paint, it can be cured with good adhesion even under low temperature baking and drying conditions, such as 80 ° C or less, and is sufficiently applied to objects with poor heat resistance such as resin parts. It is possible, and the resulting top coat film has excellent durability such as weather resistance and is advantageous in terms of cost.

Further, according to the coating method of the present invention, in order to use the top coating according to the present invention which is inexpensive in cost and less dependent on the baking conditions as described above, a resin plate part such as a steel plate outer plate and a bumper is used. It is possible to paint with the same paint, and it is also possible to bake the outer plate and resin parts at the same time.Reducing the coating cost by sharing the paint, sharing and shortening the coating line, etc. Is possible.

Further, since the automobile exterior parts of the present invention are coated with the above-mentioned top coating material,
Despite being cheap in cost, it has excellent coating appearance, adhesion, and weather resistance, and does not have problems such as thermal deformation caused by coating baking drying process even for resin parts etc. By using, the matching of the color tone of the outer plate and the resin component becomes good.

[Brief description of drawings]

FIG. 1 schematically shows a coating film structure obtained by applying a top coat of the present invention.

[Explanation of symbols]

 1 Object to be coated 2 Color base coating 3 Clear coating

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masahiko Yamanaka 2 Takara-cho, Kanagawa-ku, Yokohama-shi, Kanagawa Nissan Motor Co., Ltd.

Claims (8)

[Claims] 1. A topcoat paint comprising a base paint and a clear paint used in multi-layer coating, wherein a base liquid paint is a one-component thermosetting base paint to which an acid catalyst is added, and a clear paint is low temperature curing. Top coat paint characterized by using mold clear paint. 2. The topcoat paint according to claim 1, wherein the one-component thermosetting base paint uses a polyester resin or an acrylic resin as a base resin of its 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 acid catalyst is selected from the group consisting of p-toluenesulfonic acid, dinonylnaphthalenesulfonic acid, dinonylnaphthalenedisulfonic acid, dodecylbenzenedisulfonic acid and amine block products thereof.
Or 2 or more compounds, The topcoat paint in any one of Claims 1-3. 5. The addition amount of the acid catalyst is 1 to 1 with respect to the binder resin solid content of the one-component thermosetting base coating material.
The topcoat paint according to any one of claims 1 to 4, which is an amount of 0% by weight. 6. The method of applying a top-coat paint according to claim 1, wherein the base paint is applied to an object to be coated, then the clear paint is applied wet-on-wet, and then 60 to 160. A coating method characterized by baking and drying at a temperature of ℃. 7. The coating method according to claim 6, wherein the baking and drying temperature is 70 to 80 ° C. 8. An exterior component for an automobile, which is coated with the topcoat paint according to any one of claims 1 to 5.