JPH0593028A - Resin composition for urethane coating - Google Patents

Abstract

PURPOSE:To provide the title composition excellent in the masking tape nature and clearness of the cured coating film therefrom, containing, as curing catalyst, a combination of each specific organotin compound and carboxylic acid compound at the specified ratio. CONSTITUTION:The objective composition containing, as curing catalyst, a combination of (A) an organotin compound of the formula (R1 and R2 are each 1-4C alkyl; R3 and R4 are each 8-18C alkyl) e.g. dibutyltin dilaurate) and (B) at least one kind of carboxylic acid compound selected from formic acid, acetic acid, propionic acid, butyric acid and (meth)acrylic acid at the weight ratio A/B=10-30. The component A is pref. incorporated at 0.005-0.1wt.% based on the total amount of the resin and curing agent in the present composition.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a resin composition for urethane coatings. More specifically, the present invention relates to a resin composition for urethane coating, which has both a masking tape property and a sharpness of a cured coating film.

[0002]

2. Description of the Related Art In resin compositions for urethane coatings, it is known in the art that the masking tape property and the image clarity of a cured coating film depend on the amount of a curing catalyst (for example, an organotin compound) compounded in the composition. Are well known in. However, the more the curing catalyst is added to accelerate the curing reaction, the better the masking tape property of the cured coating film (the more quickly the masking tape can be applied), but on the other hand, the clearness of the cured coating film is improved. The current situation is that these two performances cannot be achieved at the same time because of the decrease.

[0003]

DISCLOSURE OF THE INVENTION As a result of intensive studies in view of such circumstances, the present inventors have found that a specific amount of a specific carboxylic acid compound is contained in a resin composition for urethane coating containing an organotin compound as a curing catalyst. The present invention has been accomplished by finding that the compounding of the composition makes it possible to achieve both the masking tape property and the sharpness of the cured coating film.

[0004]

That is, the present invention provides an organotin compound (A) represented by the following general formula as a curing catalyst.

[Chemical 2] (However, R ₁ and R ₂ are an alkyl group having 1 to 4 carbon atoms, R ₃
And R ₄ represents an alkyl group having 8 to 18 carbon atoms) and one or more carboxylic acid compounds (B) selected from the group consisting of formic acid, acetic acid, propionic acid, butyric acid, acrylic acid and methacrylic acid, The weight ratio of (B) / (A) is 10
It relates to a resin composition for urethane coatings, characterized in that it is contained in an amount of 30 to 30.

In the present invention, the organotin compound (A) is represented by the following general formula.

[Chemical 3] (However, R ₁ and R ₂ are an alkyl group having 1 to 4 carbon atoms, R ₃
And R ₄ represents an alkyl group having 8 to 18 carbon atoms) As R ₁ and R ₂ , a methyl group, an ethyl group, an n-propyl group, an n-butyl group, and the like, and as R ₃ and R ₄ , 2 −
Ethylhexyl group, lauryl group, stearyl group,
I can list each. Of these, a compound (dibutyltin dilaurate) having n-butyl group for both R ₁ and R _{2 and} lauryl group for both R ₃ and R ₄ has excellent curing catalytic ability and can sufficiently accelerate the curing reaction even in a small amount. Therefore, it is particularly preferable. In the present invention, it is preferable that the organotin compound (A) is blended in an amount of 0.005 to 0.1% by weight based on the total amount of the resin and the curing agent in the resin composition for urethane coating, because the effect is high.

In the present invention, the carboxylic acid compound (B)
Is one or more selected from the group consisting of formic acid, acetic acid, propionic acid, butyric acid, acrylic acid and methacrylic acid. With the carboxylic acid compounds other than the above, the effect of the present invention, that is, the effect of achieving both the masking tape property of the cured coating film and the sharpness cannot be achieved. It should be noted that acetic acid and propionic acid are particularly suitable because they have a boiling point close to that of the coating solvent.

In the present invention, the weight ratio of (B) / (A) needs to be 10-30. If this ratio is less than 10, the cured coating film has poor image clarity, and the effect of the present invention cannot be achieved. On the other hand, when this ratio exceeds 30, the cured coating film is inferior in masking tape property and the effect of the present invention cannot be achieved. From the viewpoint of both effects, the weight ratio of (B) / (A) is 12 to
20 is preferable.

The resin composition for urethane coatings of the present invention contains a hydroxyl group-containing acrylic resin, polyester resin and the like as a resin component of the main component. The hydroxyl group-containing acrylic resin is typically obtained by appropriately combining (meth) acrylic acid alkyl ester, a hydroxyl group-containing monomer and, if necessary, other monomers, and polymerizing them by a conventionally known method.

Examples of alkyl (meth) acrylates include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate and sacrylic acid.
ec-butyl, tert-butyl acrylate, alkyl acrylates such as 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate. , Alkyl methacrylates such as sec-butyl methacrylate, tert-butyl methacrylate, 2-ethylhexyl methacrylate, and the like.

Examples of the hydroxyl group-containing monomer include 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate and the like.

Other examples of monomers include styrene,
Examples thereof include α-methylstyrene, chlorostyrene, vinyl acetate, methacrylic acid, acrylic acid, glycidyl methacrylate and glycidyl acrylate.

The (meth) acrylic acid alkyl ester, the hydroxyl group-containing monomer, and the other monomer used as required are used in an appropriate combination so that the glass transition temperature and the hydroxyl value of the acrylic resin are within the desired ranges. The other monomers are preferably used within 10% by weight based on all the monomers. These monomer mixtures are polymerized by a conventionally known method such as solution polymerization, suspension polymerization and emulsion polymerization. Among them, solution polymerization is particularly preferable because the polymer can be directly used as a coating resin. Solution polymerization is typically carried out in a solution of toluene, xylene or the like using a radical polymerization initiator such as azobisisobutyronitrile or benzoyl peroxide at a temperature of 80 to 130 ° C. The molecular weight of the acrylic resin can be adjusted by the compounding amount of the radical polymerization initiator and the polymerization temperature.

On the other hand, the hydroxyl group-containing polyester resin is typically obtained by condensation polymerization of a dibasic acid, a dihydric alcohol and a trihydric or higher polyhydric alcohol by a conventionally known method.

Examples of dibasic acids include phthalic acid, isophthalic acid, terephthalic acid, adipic acid and sebacic acid. Examples of the dihydric alcohol include ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, neopentyl glycol and the like. Examples of trihydric or higher polyhydric alcohols include glycerin, trimethylolpropane, pentaerythritol and the like.

These monomers are used in an appropriate combination so that the molecular weight, glass transition temperature and hydroxyl value of the polyester resin are within the desired ranges. Condensation polymerization typically involves heating these monomers to 180-250 ° C. in the presence of a catalyst such as dibutyltin oxide or in the absence of a catalyst,
It can be carried out while distilling off the condensation water.

The urethane coating resin composition of the present invention contains an isocyanate prepolymer as a curing agent. Examples of the isocyanate prepolymer, toluene diisocyanate, its trimethylolpropane adduct, its isocyanurate body, hexamethylene diisocyanate, its trimethylolpropane adduct, its isocyanurate body, its biuret body, isophorone diisocyanate,
The trimethylolpropane adduct, its isocyanurate body, xylylene diisocyanate, its trimethylolpropane adduct, etc. can be mentioned. Among these, the isocyanurate body of hexamethylene diisocyanate is particularly preferable because it does not easily turn yellow and has excellent weather resistance. The resin as the main agent and the curing agent are blended so that the molar ratio of hydroxyl group / isocyanate group is preferably 0.8 to 1.2, particularly preferably 0.9 to 1.1.

In the resin composition for urethane coating of the present invention, the mixture of the organic tin compound (A), the carboxylic acid compound (B), the main agent and the curing agent is treated with a suitable solvent such as toluene, xylene, butyl acetate or cellosolve acetate. It is diluted and adjusted.

If necessary, a cellulose derivative such as nitrocellulose or cellulose acetate butyrate may be added to the resin composition. Further, various color pigments, various mica, aluminum flakes and the like can be further added to the coating resin composition depending on the purpose. The coating resin composition can be applied to a suitable substrate and dried and cured at a temperature of approximately 5 to 80 ° C.

[0019]

In the present invention, the organotin compound (A) has the effect of promoting the curing reaction as a curing catalyst and, as a result, improving the masking tape property of the cured film. However, on the other hand, the organotin compound (A) also has a negative effect of reducing the clarity of the cured coating film. On the other hand, the carboxylic acid compound (B) temporarily suppresses the action of the organotin compound (A) as a curing catalyst in the initial stage of the curing reaction, and as a result, does not significantly reduce the masking tape property of the cured coating film. , Has the effect of improving the sharpness of the cured coating film. The carboxylic acid compound (B) is considered to gradually evaporate from the coating film together with the solvent as the curing reaction proceeds.

[0020]

EXAMPLES The present invention will be specifically described below with reference to examples. Example 1 A mixed monomer of 10 g of styrene, 14 g of 2-hydroxyethyl methacrylate and 76 g of isobutyl methacrylate was used as a polymerization initiator in a xylene solvent (1.8 g of 2,2′-azobisisobutyronitrile, di-t-butyl peroxide). Solution polymerization was carried out at 130 ° C. using 0.5 g) to obtain a resin solution (I). The nonvolatile content of the resin solution (I) is 55
% By weight. Xylene was removed from the resin solution (I), and the molecular weight of the resin (GPC (GPC) method, standard polystyrene conversion) and the glass transition temperature (DSC method) were measured. The number average molecular weight was 2,900 and the weight average molecular weight was 20,000.
The glass transition temperature was 24 ° C. Further, the hydroxyl value was calculated from the monomer composition during resin synthesis. The calculation was according to the following formula (1).

[Equation 1] Here, W ₀ ; total weight of monomers W; weight of 2-hydroxyethyl methacrylate M; molecular weight of 2-hydroxyethyl methacrylate, hydroxyl value was 60 mgKOH / g.

Resin solution (I) and curing agent Coronate EH
(Commercial name, isocyanurate of hexamethylene diisocyanate manufactured by Nippon Polyurethane Industry Co., Ltd., isocyanate group content 21.3% by weight) is blended so that the molar ratio of hydroxyl group / isocyanate group is 1 and further, the resin and the curing agent are mixed. A resin composition (I) for urethane coating was prepared by diluting with a mixed solvent of xylene, butyl acetate and cellosolve acetate so that the total amount was 50% by weight. At this time, 0.06% by weight of the curing catalyst dibutyltin dilaurate and 0.85% by weight of acetic acid were added to the total amount of the resin and the curing agent.

Next, using this resin composition for urethane coating (I), two coats having a film thickness of about 120 μm (film thickness after drying and curing of about 60 μm) were prepared with an applicator.
A curing reaction was performed at a temperature of 1 ° C., and one sheet was used for evaluation of the masking tape property of the cured coating film, and the other was used for evaluation of image clarity. As the substrate, a bonderite-treated steel plate (JIS G3141, manufactured by Nippon Test Panel Industry Co., Ltd.) was used. As for the masking tape, the masking tape No. 7
235 (trade name, manufactured by Nitto Denko Co., Ltd.) was used and evaluated by the shortest curing reaction time at 60 ° C. under which no tape sticking trace remained. The sharpness of the coating film was 60 by using an image clarity gloss meter DGM-30 type (manufactured by Murakami Color Research Laboratory Co., Ltd.).
Evaluation was performed after the curing reaction was performed at 60 ° C. for 60 minutes. The above evaluation results are summarized in Table 1 together with the amounts of the curing catalyst dibutyltin dilaurate and acetic acid blended.

Comparative Example 1 The procedure of Example 1 was repeated except that the amount of acetic acid was 1.9% by weight based on the total amount of the resin and the curing agent. Was evaluated. The evaluation results are shown in Table 1 together with the compounding amounts of the curing catalyst dibutyltin dilaurate and acetic acid.

Comparative Example 2 The procedure of Example 1 was repeated except that the content of acetic acid was 0.4% by weight based on the total amount of the resin and the curing agent. evaluated. The evaluation results are shown in Table 1 together with the compounding amounts of the curing catalyst dibutyltin dilaurate and acetic acid.

Comparative Example 3 The masking tape property and the clearness of the cured coating film were evaluated in the same manner as in Example 1 except that acetic acid was not added. The evaluation results are shown in Table 1 together with the blending amount of the curing catalyst dibutyltin dilaurate.

Comparative Example 4 In Example 1, no acetic acid was added and the curing catalyst dibutyltin dilaurate was added to 0.0 based on the total amount of the resin and the curing agent.
The masking tape property and the sharpness of the cured coating film were evaluated in the same manner except that 2% by weight was blended. The evaluation results are shown in Table 1 together with the blending amount of the curing catalyst dibutyltin dilaurate.

[0027]

[Table 1]

[0028]

EFFECT OF THE INVENTION The resin composition for urethane coatings according to the present invention is excellent in both masking tape properties and sharpness of the cured coating film (that is, these two properties can be compatible).

Claims (3)

[Claims] 1. An organotin compound (A) represented by the following general formula as a curing catalyst: (However, R ₁ and R ₂ are an alkyl group having 1 to 4 carbon atoms, R ₃
And R ₄ represents an alkyl group having 8 to 18 carbon atoms) and one or more carboxylic acid compounds (B) selected from the group consisting of formic acid, acetic acid, propionic acid, butyric acid, acrylic acid and methacrylic acid, The weight ratio of (B) / (A) is 10
A resin composition for urethane coatings, characterized in that it is contained in an amount of -30. 2. The resin composition for urethane coating according to claim 1, wherein the organotin compound (A) is dibutyltin dilaurate. 3. The carboxylic acid compound (B) is acetic acid and / or
Alternatively, the resin composition for urethane coating according to claim 1 or 2, which is propionic acid.