JP3249053B2 - One-component low-temperature curing clear coating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has excellent durability and water resistance and is also flexible, so that it is used as a coating material for automobile bumpers and the like, and is used as a top coating for a base coat layer formed on the surface of a material. Regarding improvement.

[0002]

2. Description of the Related Art In recent years, acid rain caused by environmental pollution has become a problem. For cars running outdoors,
It is particularly important to solve this problem, and automotive paints used for plastic materials such as bumpers and steel plates for bodies are all excellent in acid resistance, and the coating does not deteriorate even if acid rain adheres to the surface. Is required. The most frequently used automotive coatings at present are those that cure by melamine crosslinking. Since melamine resin is decomposed by acid, it cannot be said that the acid resistance is sufficient.

[0003] With respect to paints for automobile bumpers, the obtained coating film must have flexibility in terms of the function of the bumper, so that the glass transition temperature of the coating film is usually set low. For this reason, there is a problem that the paint for bumpers is easily stained as compared with the paint for steel plates, and is more difficult to remove. In order to improve the stain resistance of the paint for bumpers, a method of raising the glass transition temperature of the coating film and hardening the coating film is conceivable, but then the flexibility, that is, the flexibility is reduced. This causes another problem that the coating film is cracked. As described above, in a bumper paint, stain resistance and flexibility are contradictory properties. Therefore, it is desired that both of these properties be compatible.

[0004]

Japanese Patent Publication No. 4-508 discloses a coating composition containing an acrylic resin, a polyalkylene glycol resin, an amino resin and a blocked isocyanate which satisfies the basic properties of a bumper paint. Things are listed. This coating composition has a resin component composed of a combination of an acrylic resin and a polyalkylene glycol resin, and has excellent properties such as weather resistance and water resistance, and can form a coating film having good hardness. The stain resistance and acid resistance are not sufficient. in this case,
It is thought that the polyalkylene glycol resin acting as a softening agent and contained as an essential component in the coating composition reduces stain resistance and acid resistance.

[0005] Japanese Patent Application Laid-Open (JP-A) No. 1-158079 discloses a coating composition which contains an acrylic copolymer and a melamine resin as essential components and may contain a blocked isocyanate as a coating material for bumpers. This paint is baked and cured at high temperatures. In automotive applications,
After coating, a method of baking and curing the coating film at a high temperature is performed. However, baking at a low temperature of about 120 ° C. is required because plastic materials for bumpers and the like have low heat resistance. However, the above known coatings are
When baking is performed at a low temperature, curing becomes insufficient, so that stain resistance and acid resistance decrease.

Although it is for metal, Japanese Patent Laid-Open No.
No. 6483 describes an automotive metal paint containing an organotin monocarboxylate as a blocked isocyanate dissociation catalyst. Further, Japanese Patent Application Laid-Open No. 7-258599
In the publication, a coating material for a steel sheet containing an inorganic catalyst as a blocked isocyanate dissociation catalyst is described. In this case, since the inorganic catalyst is insoluble in the solvent, it cannot be used as a clear coating requiring transparency. These steel plate paints, like the plastic paints described above, are insufficiently cured when baked at low temperatures,
The stain resistance and acid resistance decrease.

[0007] As described above, none of the prior arts is sufficient to cure sufficiently even when baked at a low temperature to secure stain resistance and acid resistance. Under such circumstances, development of automotive paints that are sufficiently cured by low-temperature baking and are excellent in stain resistance and acid resistance are expected. The problem to be solved by the present invention is that even when baked at a low temperature, it hardens sufficiently, without impairing flexibility.
An object of the present invention is to provide a one-component low-temperature curing type clear coating material capable of forming a cured coating film having excellent stain resistance and acid resistance.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted various experiments to solve the above problems, and as a result, have found that the physical properties of the cured coating film and the flexibility, stain resistance, and acid resistance are not improved. The inventors have obtained the knowledge that there is a correlation between the two, and the knowledge that, when a blocked isocyanate dissociation catalyst having a specific structure is used, curing can be sufficiently performed even when baking is performed at a low temperature.

That is, the one-component low-temperature curing clear coating composition of the present invention comprises a resin component containing an acrylic polyol having a hydroxyl value of 60 to 200 KOH mg / g, hexamethylene diisopropane.
Cyanate block and / or isophoronedi
Including a cross-linking agent that may contain a melamine resin as an essential component with a blocked isocyanate that is a blocked isocyanate, and a blocked isocyanate dissociation catalyst comprising at least bis (dibutyltin) maleate,
The weight ratio of the blocked isocyanate and the melamine resin is block isocyanate / melamine resin = 100.
/ 0 to 30/70, and the glass transition temperature of the cured coating film obtained from the paint is 50 to 65 ° C.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The one-pack low-temperature curing clear coating composition of the present invention contains a resin component, a crosslinking agent and a blocked isocyanate dissociation catalyst. Hereinafter, each component of the clear paint will be described in detail. [Resin Component] The resin component used in the present invention contains an acrylic polyol having a hydroxyl value of 60 to 200 KOH mg / g as an essential component. Acrylic polyol is an alternative to the combination of acrylic resin and polyalkylene glycol resin used in the prior art, and is excellent in softness.

The acrylic polyol has a hydroxyl value of 6
There is no particular limitation as long as it is in the range of 0 to 200 KOHmg / g. The acrylic polyol is a polymer having a structural unit derived from an acrylic monomer (A) having a hydroxyl group as an essential component. The acrylic monomer (B) having a carboxyl group and the acrylic monomer are appropriately used. Acrylic monomer (C) having an ester group copolymerizable with (A) and (B)
Alternatively, the copolymer may further include a structural unit derived from a monomer such as a vinyl monomer (D) other than an acryl-based monomer, and the type of the structural unit constituting the polymer is particularly limited. There is no.

Examples of the acrylic monomer (A) having a hydroxyl group include 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate,
Examples thereof include 4-hydroxybutyl (meth) acrylate and 2-hydroxyethyl (meth) acrylate, and their ε-caprolactone adducts. Only one type may be used, or two or more types may be used in combination as necessary. May be.

The acrylic monomer (B) having a carboxyl group includes, for example, (meth) acrylic acid and the like, and may be used alone or, if necessary, in combination of two or more. Good. Examples of the acrylic monomer (C) having an ester group include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, and (meth) acrylic acid. Lauryl and the like can be mentioned, and only one kind or two or more kinds may be used in combination as needed.

Examples of the vinyl monomer (D) include styrene and the like, and only one kind may be used or two or more kinds may be used in combination as needed. The acrylic polyol is appropriately selected from the above acrylic monomers (A) to (C) and the vinyl monomer (D),
It is obtained by polymerizing. The hydroxyl value of the acrylic polyol is in the range of 60 to 200 KOH mg / g, preferably 70 to 160 KOH mg / g. When the hydroxyl value is less than 60 KOHmg / g, acid resistance and stain resistance become insufficient. In addition, the hydroxyl value is 200K
If it exceeds OH mg / g, the flexibility may decrease. [Crosslinking Agent] The crosslinking agent used in the present invention contains a blocked isocyanate as an essential component and may further contain a melamine resin. The crosslinking agent regulates the strength of the coating film.

[0015] As blocked isocyanate, a non-yellowing type polyisocyanate of F hexamethylene diisocyanate and / or Isohoronji <br/> isocyanate DOO, acetone oxime, methylethyl ketone oxime, ethyl acetoacetate is reacted with a blocking agent such as acetylacetone to give Blocked product is used. Use these
That is, ing as weather resistance is excellent.

The present invention relates to a one-component, low-temperature-curable clear coating, which is required to have transparency. Therefore, when a blocked product of an aromatic isocyanate such as tolylene diisocyanate is used as a cross-linking agent, the paint is undesirably yellowed. As the melamine resin, for example, methyl etherified melamine, ethyl etherified melamine,
Examples thereof include alkyl etherified melamines such as butyl etherified melamine, and the like, and only one type may be used, or two or more types may be used in combination as necessary.

The weight ratio of the blocked isocyanate and the melamine resin blended as the crosslinking agent is 100/0 to 30/70, and preferably 50/50 to 30/70. If the weight ratio is less than 30/70, the proportion of the melamine resin in the entire cross-linking agent increases, which is not preferable because acid resistance and stain resistance decrease.

The mixing ratio of the cross-linking agent contained in the one-component low-temperature curing type clear coating material is not particularly limited. For example, it is preferably 20 parts by weight based on 100 parts by weight of the resin component.
-40 parts by weight, more preferably 25-35 parts by weight. If the compounding ratio of the crosslinking agent is too small, it will not be cured sufficiently, and the acid resistance and stain resistance will be reduced. On the other hand, if it is too large, the flexibility may decrease.

[0019] The cross-linking agent, the blocked isocyanate Ya
Other than melamine resin, it may be one containing other agents benzoguanamine. [Blocked Isocyanate Dissociation Catalyst] Since the cross-linking agent used in the present invention essentially comprises a blocked isocyanate, the one-component low-temperature curing clear coating composition contains at least a blocked isocyanate dissociation catalyst comprising bis (dibutyltin) maleate .

[0020] By using bi scan (dibutyltin) Maree bets, a coating of one-liquid low-temperature curing type clear paint 1
Baking can be performed in a low temperature range of 10 to 120 ° C., and the compatibility with the resin component is improved, so that the appearance of the coated film after baking is improved.

The mixing ratio of the blocked isocyanate dissociation catalyst contained in the one-component low-temperature curing clear coating composition is not particularly limited, but is, for example, preferably 1 to 3 parts by weight with respect to 100 parts by weight of the resin component. . If the proportion of the blocked isocyanate dissociation catalyst is too small, the composition is not sufficiently cured, and the acid resistance and stain resistance are reduced. On the other hand, if it is too large, the appearance may decrease. [Other components] One-component low-temperature-curable clear coating materials include, as required, a melamine resin curing catalyst such as paratoluenesulfonic acid and dodecylbenzenesulfonic acid; an ultraviolet absorber such as benzotriazole; An agent can be compounded. The mixing ratio of these additives in the paint is not particularly limited and can be appropriately selected. [One-component low-temperature curing type clear coating material] The one-component low-temperature curing type clear coating material is obtained by mixing the resin component, the crosslinking agent and the blocked isocyanate dissociation catalyst described in detail above. If necessary, other components may be further mixed.

The glass transition temperature of the cured coating film obtained from the one-component low-temperature curing type clear coating material is 50 to 65 ° C. If the glass transition temperature of the cured coating film is less than 50 ° C., the acid resistance and stain resistance are not sufficient. On the other hand, if the glass transition temperature exceeds 65 ° C., cracks occur in the coating film, and the flexibility deteriorates, which is not preferable. The one-component low-temperature-curable clear coating is usually used for overcoating the base coat layer by a wet-on-wet method. There is no particular limitation on the method of overcoating the clear paint. The clear paint may be used after being diluted with a solvent or the like in advance. The base coat layer is formed by painting the surface of a base material with a base paint.

After overcoating with a clear paint, the overcoated surface can be baked to cure the coating. When the baking temperature is as low as 110 to 120 ° C.,
The coating film can be sufficiently cured, the work efficiency is high,
A plastic material is preferable because heat resistance is not impaired.

[0024]

The present invention will be described in more detail with reference to the following Examples and Comparative Examples. However, the present invention is not limited to the following Examples. First,
In Production Examples 1-2 and Comparative Production Examples 1-2, acrylic polyols A-D were produced. Hereinafter, “parts” means “parts by weight”. (Production Examples 1-2 and Comparative Production Examples 1-2) 100 parts of Solvesso # 100 (solvent naphtha, exxon) was charged as a solvent into a flask equipped with a stirrer, a temperature controller and a condenser, and heated while stirring. And the solvent temperature was raised to 100 ° C. Subsequently, the copolymer components shown in Table 1 (total of 101 parts) were each added dropwise over 2 hours.
Thereafter, polymerization was carried out at 100 ° C. for 4 hours to produce acrylic polyols A to D having a hydroxyl value shown in Table 1.

[0025]

[Table 1]

(Examples 1 to 3 and Comparative Examples 1 to 5) Table 2
Were mixed to produce clear paints 1 to 3 and comparative clear paints 1 to 5. The obtained (comparative) clear paint was evaluated as follows. The surface of the bumper polypropylene material is wipe-cleaned with tap water, and a primer (RB195-1, manufactured by Nippon Bee Chemical Co., Ltd.) is applied.
It was painted with a thickness of 0 μm and baked at 120 ° C. for 5 minutes. Next, a base paint (R-331, manufactured by Nippon Bee Chemical Co., Ltd.) was applied to the surface of the baked primer by 15 μm.
To form a base coat layer. The base coat layer was wet-on-wet, coated with the clear paint prepared above (comparative) to a thickness of 25 μm, and
Bake at 20 ° C. for 20 minutes to cure. The physical properties of each of the obtained cured coating films were evaluated by the following evaluation methods.

<Evaluation Method> Glass transition temperature (Tg) of cured coating film The glass transition temperature was measured using Rheospectra 9002-DVE (manufactured by Rheology Co., Ltd.). 2. Acid resistance Artificial acid rain was dropped on the surface of the cured coating film and left in a gradient oven (manufactured by BYK) at 70 ° C. for 30 minutes.
After washing with water, the surface roughness was measured with a surface roughness meter (manufactured by Toyo Seimitsu Co., Ltd.).
Those exceeding 5 μm were judged as x.

3. Stain resistance The cured coating film was exposed outdoors for 6 months, and then stains attached to the cured coating film were wiped off with tap water. Those that could be washed off were evaluated as ○, and those with remaining stains were evaluated as x. 4. Flexibility After the cured coating film was left overnight at 20 ° C., it was bent at 90 °, and the case where no crack was generated in the cured film was evaluated as “O”, and the case where crack was generated in the cured film was evaluated as “X”.

[0029]

[Table 2]

* 1 Isobutylated melamine (Uban 1
65, manufactured by Mitsui Toatsu Chemical Co., Ltd.) * 2 Methyl ethyl ketone oxime block of hexamethylene diisocyanate trimer * 3 Methyl ethyl ketone oxime block of isophorone diisocyanate * 4 Bis (dibutyltin) maleate <Evaluation results> In Examples 1 to 3, In any case, the Tg of the cured coating film is in the range of 50 to 65 ° C., and is excellent in acid resistance, stain resistance and flexibility. On the other hand, in Comparative Example 1, since the acrylic polyol having a hydroxyl value of less than 60 KOHmg / g was used, the acid resistance and the stain resistance were poor.
In Comparative Example 2, since an acrylic polyol having a hydroxyl value exceeding 200 KOH mg / g was used, the flexibility was inferior. In Comparative Example 3, since the Tg was lower than 50 ° C., the acid resistance and the stain resistance were poor. In Comparative Example 4, Tg
Is over 65 ° C., so that the flexibility is poor. In Comparative Example 5, since no blocked isocyanate dissociation catalyst was used, curing was not sufficient, and acid resistance and stain resistance were poor.

[0031]

EFFECT OF THE INVENTION The one-part low-temperature curing type clear coating composition of the present invention has excellent weather resistance and water resistance, has good adhesion to plastic materials and has flexibility, and is sufficiently cured even when baked at a low temperature. However, a cured coating film having excellent stain resistance and acid resistance can be formed without deteriorating the flexibility. Therefore, the one-pack low-temperature-curable clear coating material of the present invention is particularly excellent for coating applications such as automobile bumpers.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C09D 175/04

Claims (1)

(57) [Claims] 1. A resin component containing an acrylic polyol having a hydroxyl value of 60 to 200 KOH mg / g, hexamethylenediyl
Socyanate block and / or isophorone di
A crosslinking agent which may contain a melamine resin as an essential component, which is a blocked isocyanate which is an isocyanate-blocked product , and a blocked isocyanate dissociation catalyst comprising at least bis (dibutyltin) maleate, wherein the weight ratio of the blocked isocyanate and the melamine resin is Block isocyanate / melamine resin = 1
A one-component low-temperature curing type clear coating material which satisfies 00/0 to 30/70 and has a glass transition temperature of 50 to 65 ° C. of a cured coating film obtained from the coating material.