JPH1160998A - Resin composition for powder coating and method for forming coating film using the composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject composition having excellent coating film appearance without lowering the antiblocking property by using a specific heat- dissociation resin wherein the lowering of molecular weight in melting is caused by reversible dissociation reaction. SOLUTION: This composition is composed of (A) a heat-dissociation resin produced by modifying (i) a resin having hydroxyl group and curable functional group with (ii) a diisocyanate compound having secondary isocyanate group and tertiary isocyanate group (preferably m-tetramethylxylylene diisocyanate) in such a manner as to bond 0.1-3 hydroxyl groups to the isocyanate group based on one molecule of the component (i) and (B) a curing agent. Preferably, the component (i) is e.g. 30-65 wt.% of an acrylic resin containing an ethylenic unsaturated monomer having a hydroxyl value of 10-100 mgKOH/g and containing epoxy group as the curable functional group and 70-35 wt.% of other ethylenic unsaturated monomer. When the component (i) is the above acrylic resin, the component B is preferably dodecanedicarboxylic acid.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a resin composition for powder coatings and a method for forming a coating film using the same.

[0002]

2. Description of the Related Art Powder coatings have attracted attention in recent years as environmentally safe coatings due to the small amount of solvent released into the atmosphere. Such powder coatings are those that form a coating film by the flow of resin or coating material during hot melting, but the resulting coating film is inferior in smoothness and has a specific defect called so-called rough surface, Since the appearance is generally inferior to that of solvent-based paints, they cannot be used in fields where the appearance of surfaces is important such as automobile bodies.

Therefore, in order to improve the appearance of the coating film,
A method of reducing the melt viscosity of the powder coating has been adopted.
This is performed by lowering the glass transition point (Tg) of the resin used or by lowering the molecular weight of the resin. However, when the Tg or the molecular weight is reduced, coalescence of the resin particles is likely to occur during storage, resulting in a decrease in blocking resistance. Therefore, development of a powder coating material having excellent blocking resistance, low viscosity at the time of melting, and excellent coating film appearance is desired.

[0004]

DISCLOSURE OF THE INVENTION In view of the above, the present invention has been made in view of the above, and provides a resin composition for a powder coating having an excellent appearance of a coating film without deteriorating blocking resistance, and forming a coating film using the same. The aim is to provide a method.

[0005]

Means for Solving the Problems The present inventors have conducted intensive studies on a resin having a sufficiently low viscosity at the time of melting without lowering the blocking resistance. The present invention provides a resin that can be sufficiently cured at the time of curing, that is, a resin that can be sufficiently cured at the time of curing, that is, a thermodissociable resin that undergoes a reversible dissociation reaction while being cured. It has been found that the object of the present invention can be achieved, and the present invention has been completed.

That is, the present invention provides a resin (a) having a hydroxyl group and a curable functional group such that 0.1 to 3.0 of the hydroxyl groups are bonded to an isocyanate group per molecule of the resin (a). The same or different 2 selected from the group consisting of secondary isocyanate groups and tertiary isocyanate groups
It is a resin composition for powder coatings comprising a heat dissociable resin (A) modified with a diisocyanate compound (b) having two isocyanate groups, and a curing agent (B).

[0007] The present invention also provides a step (1) of applying a base paint on an undercoated or intermediate-coated substrate, and a step of applying the resin composition for a powder coating on the substrate coated with the base paint. (2), and heating the substrate on which the base paint and the resin composition for powder coating are applied to form a base coating film and a coating film comprising the resin composition for powder coating. A method for forming a coating film, comprising a step (3) of curing. Hereinafter, the present invention will be described in detail.

The resin composition for powder coating of the present invention comprises a resin (A) having a hydroxyl group and a curable functional group, which is modified with a diisocyanate compound (b);
It consists of a curing agent (B). In the present specification, a curable functional group refers to a functional group capable of reacting with a curing agent to be blended. Resin (a) having a hydroxyl group and a curable functional group
Is not particularly limited as long as it is a thermosetting resin generally used for powder coatings, and examples thereof include an epoxy resin, an epoxy-polyester resin, a polyester resin, an acrylic resin, and an acrylic-polyester resin. . Above all, acrylic resin has good weather resistance, and polyester resin has good impact resistance.
It is preferable to use an acrylic resin or a polyester resin.

The acrylic resin is not particularly limited, but has a hydroxyl value of 10 to 100 mgKOH / g,
An acrylic resin (a-1) containing 30 to 65% by weight of an ethylenically unsaturated monomer having an epoxy group as a curable functional group and 70 to 35% by weight of another ethylenically unsaturated monomer is preferred. The hydroxyl value is 10 m
If it is less than gKOH / g, the modification with the diisocyanate compound (b) is not sufficient, and a decrease in viscosity during heating cannot be expected. If it exceeds 100 mgKOH / g, it becomes difficult to synthesize a thermally dissociable resin. More preferably, 20 to 8
0 mgKOH / g.

The acrylic resin (a-1) contains 30 to 65% by weight of an ethylenically unsaturated monomer having an epoxy group, and 70 to 3% of other ethylenically unsaturated monomers.
It consists of 5% by weight. When the content of the ethylenically unsaturated monomer having an epoxy group is less than 30% by weight,
If the curability is insufficient, and if it exceeds 65% by weight, the curing speed will be too fast, and the appearance will deteriorate. More preferably, it is 45 to 52% by weight.

The above-mentioned epoxy-containing ethylenically unsaturated monomer is not particularly restricted but includes, for example, glycidyl acrylate, glycidyl methacrylate, α-methylglycidyl acrylate, α-glycidyl methacrylate and the like. These may be used alone or in combination of two or more.

The above-mentioned other ethylenically unsaturated monomer is not particularly limited. When an ethylenically unsaturated monomer having a hydroxyl group is used, a hydroxyl group can be introduced into the acrylic resin (a-1).

The above-mentioned ethylenically unsaturated monomer having a hydroxyl group is not particularly limited as long as it is a compound having a hydroxyl group and a copolymerizable double bond and having a relatively low molecular weight of 18 or less, preferably 10 or less carbon atoms. Not, for example, F
A-1 (2-hydroxyethyl acrylate ε-caprolactone one-to-one adduct), 4-hydroxybutyl acrylate, 2-hydroxyethyl acrylate, 3-hydroxypropyl acrylate, 2-hydroxypropyl acrylate, FM-1 (2- Ε-caprolactone one-to-one adduct of hydroxyethyl methacrylate), 2,
Examples thereof include 4-hydroxybutyl methacrylate, 2-hydroxyethyl methacrylate, 3-hydroxypropyl methacrylate, and 2-hydroxypropyl methacrylate. These may be used alone,
Two or more kinds may be used in combination.

The other ethylenically unsaturated monomer may be any other copolymerizable ethylenically unsaturated monomer other than the above-mentioned hydroxyl-containing ethylenically unsaturated monomer, and these may be present together with the hydroxyl group. It may be one having a functional group capable of forming. Specifically, for example, methacrylic acid, α-methylstyrene, methyl acrylate, ethyl acrylate, 2-ethylhexyl acrylate, i-butyl acrylate, n-butyl acrylate, isobornyl acrylate, cyclohexyl acrylate, acrylonitrile, acrylamide, dimethylacrylamide , Methyl methacrylate, ethyl methacrylate, 2-ethylhexyl methacrylate, i
-Butyl methacrylate, n-butyl methacrylate,
Examples include isobornyl methacrylate, cyclohexyl methacrylate, lauryl methacrylate, t-butyl methacrylate, and methacrylamide. These may be used alone or in combination of two or more.

The acrylic resin (a-1) can be copolymerized by a conventional method by blending each of the above monomers using a polymerization initiator and a chain transfer agent.

In the above-mentioned copolymerization, when the above-mentioned ethylenically unsaturated monomer having a hydroxyl group is used, its amount is preferably 0.1 to 35% by weight based on the total monomer composition. If it is less than 0.1% by weight, the introduction of hydroxyl groups is insufficient, and if it exceeds 35% by weight, it becomes difficult to synthesize a thermally dissociable resin.

The polymerization initiator is not particularly limited.
Those commonly used in the synthesis of acrylic monomers can be used, for example, t-hexylperoxypivalate, t-butylperoxypivalate, 1,1,1
3,3-tetramethylbutylperoxy-2-ethylhexanoate, t-hexylperoxy-2-ethylhexanoate, t-butylperoxy-2-ethylhexanoate, benzoyl peroxide, t-hexyl Organic peroxide-based polymerization initiators such as peroxyisopropyl monocarbonate, dicumyl peroxide, di-t-butyl peroxide, t-butyl peroxy laurate, t-butyl cumyl peroxide; 2,2'-azo Bisisobutyronitrile, 2,2'-azobis-2-methylbutyronitrile, 2,2'-azobis-2,4-dimethylvaleronitrile, 1,1'-azobiscyclohexanecarbonitrile, dimethyl-2, 2'-azobisisobutyrate, 4,4'-azobis-4-cyanovaleric acid,
An azo-based polymerization initiator such as 2,2'-azobis- (2-aminopropane) dihydrochloride can be used.

The chain transfer agent is not particularly limited.
For example, α-methylstyrene dimer, normal octyl mercaptan, normal dodecyl mercaptan and the like can be mentioned.

The acrylic resin (a-1) may have a hydroxyl group introduced by using a hydroxyl group-containing polymerization initiator. When the ethylenically unsaturated monomer constituting the acrylic resin (a-1) is polymerized in the presence of the hydroxyl group-containing polymerization initiator, a hydroxyl group can be introduced into a terminal.
The ethylenically unsaturated monomer is not particularly limited, and includes, for example, those exemplified as the other ethylenically unsaturated monomers described above.

The hydroxyl group-containing polymerization initiator is not particularly restricted but includes, for example, 2,2-azobis @ 2-methyl-N
-[1,1-bis (hydroxymethyl) ethyl] propionamide}, 2,2-azobis [2-methyl-N-
(2-hydroxyethyl) propionamide].

By using the above-mentioned hydroxyl group-containing polymerization initiator,
When a hydroxyl group is introduced into the acrylic resin (a-1),
The hydroxyl group-containing polymerization initiator is used in an amount of 0.1% based on all monomers.
It is preferably added so as to be 1 to 25% by weight. If the amount is less than 0.1% by weight, the introduction of hydroxyl groups is insufficient, and if the amount exceeds 25% by weight, a synthetic side reaction such as induced decomposition of the hydroxyl group-containing polymerization initiator occurs to synthesize the designed resin. Can not do it. More preferably, 5-1
5% by weight.

The introduction of the hydroxyl group can also be carried out by polymerizing the ethylenically unsaturated monomer in the presence of a hydroxyl group-containing chain transfer agent. The hydroxyl-containing chain transfer agent is not particularly limited, and examples thereof include thioglycerol.

By using the above-mentioned hydroxyl group-containing chain transfer agent,
When a hydroxyl group is introduced into the acrylic resin (a-1),
The hydroxyl group-containing chain transfer agent is used in an amount of 0.1 to all monomers.
It is preferably added so as to be 1 to 25% by weight. If the amount is less than 0.1% by weight, the introduction of hydroxyl groups is insufficient. If the amount exceeds 25% by weight, side reactions such as induced decomposition of the hydroxyl group-containing chain transfer agent occur, and the designed resin is synthesized. Can not do it. More preferably, 5-1
5% by weight.

When a polyester resin is used as the resin (a) having a hydroxyl group and a curable functional group, the polyester resin has a hydroxyl value of 10 to 100 mg.
KOH / g polyester resin (a-2), hydroxyl value is 10-100 mgKOH / g, acid value is 10
100 mgKOH / g polyester resin (a-
3) is preferred.

The polyester resin (a-2) has a hydroxyl value of 10 to 100 mgKOH / g. 10mgK
If it is less than OH / g, the curing will be insufficient, and 100 mgK
If it exceeds OH / g, the appearance will deteriorate. More preferably, it is 30 to 80 mgKOH / g.

The polyester resin (a-2) is not particularly restricted but includes, for example, polyhydric alcohols such as ethylene glycol, propanediol, pentanediol, hexanediol, neopentyl glycol, trimethylolpropane and pentaerythritol; acid,
Examples thereof include those obtained by polymerizing an acid component such as terephthalic acid, isophthalic acid, phthalic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, or a carboxylic acid such as β-oxypropionic acid in a conventional manner.

The polyester resin (a-2) is subjected to, for example, a known polymerization method, for example, a transesterification reaction between the acid component and the polyol component, or a direct polyesterification of the acid component, followed by a melt polycondensation reaction. Can be prepared.

In the above polymerization reaction, a catalyst may be used. The catalyst is not particularly limited, for example, dibutyltin oxide, antimony trioxide, zinc acetate,
Manganese acetate, cobalt acetate, calcium acetate, lead acetate, tetrabutyl titanate, tetraisopropyl titanate and the like can be mentioned.

In the above polymerization reaction, the reaction conditions are appropriately selected according to the reaction method and the properties of the polyester resin to be prepared, but it is preferable to carry out the reaction at, for example, 200 to 250 ° C. for 4 to 10 hours.

In the above-mentioned polymerization reaction, the above-mentioned acid component and the above-mentioned polyol component may be essentially in a stoichiometric amount. For example, 1.0 to 1.3 of the above-mentioned polyol per 1 mol of the above-mentioned acid component. Mole is preferable, and the catalyst is used in an amount of 0.01 to 0.01 with respect to the total amount of the acid component and the polyol component.
0.5% by weight is preferred.

In the above-mentioned polymerization reaction, the above-mentioned acid component and the above-mentioned polyol component may be added in their entirety at the same time, respectively, or may be added plural times to carry out the polymerization.

The polyester resin (a-3) is obtained in the same manner as the polyester resin (a-2), but has an acid value of 10 to 100 mgKOH / g.
It is something that is. When it is less than 10 mgKOH / g,
Insufficient curing occurs, and when it exceeds 100 mgKOH / g, the appearance is reduced. More preferably, 30 to 80 m
gKOH / g.

In the present invention, the resin (a) having a hydroxyl group and a curable functional group is a diisocyanate such that 0.1 to 3.0 of the hydroxyl groups are bonded to an isocyanate group per molecule of the resin (a). Modified with compound (b). The resin (a) bonded to the isocyanate group
When the number of hydroxyl groups in the resin (a) is less than 0.1 per molecule, the effect of decreasing the viscosity by thermal dissociation cannot be exhibited,
If the number exceeds 3.0, gelation may be caused, so that the content is limited to the above range. Preferably, 1.0 to
2.0.

In order to make the number of hydroxyl groups in the resin (a) having the hydroxyl group and the curable functional group bonded to the isocyanate group 0.1 to 3.0 per molecule of the resin (a), for example, The mixing ratio of the resin (a) having a hydroxyl group and a curable functional group and the diisocyanate compound (b) is determined by the molar ratio of the hydroxyl group to the isocyanate group is (mol number of hydroxyl group) / (mol number of isocyanate group) = 10/1
The reaction may be performed so as to be 1 / 0.5.

The diisocyanate compound used in the present invention is a bifunctional compound having two isocyanate groups in the molecule. If it is trifunctional or more, the resulting heat dissociable resin (A) may be gelled. If it is monofunctional, the effect of lowering the viscosity due to a decrease in molecular weight cannot be obtained. Limited to sensory ones.

The diisocyanate compound (b) is
It has two identical or different isocyanate groups selected from the group consisting of a tertiary isocyanate group and a tertiary isocyanate group. When the isocyanate group is primary, since the steric hindrance is small, the reaction rate with the resin (a) having the hydroxyl group and the curable functional group at the time of melting is too fast, and it is difficult to sufficiently lower the molecular weight. is there.
Therefore, in the present invention, it is limited to those having a secondary isocyanate group or a tertiary isocyanate group in which the steric hindrance of the isocyanate group is moderate and the decomposition reaction rate at the time of melting is high.

The diisocyanate compound having a secondary isocyanate group is not particularly restricted but includes, for example, isophorone diisocyanate, 1,4-cyclohexylene diisocyanate, dicyclohexylmethane diisocyanate and the like. The diisocyanate compound having a tertiary isocyanate group is not particularly limited, and examples thereof include meta-tetramethylxylylene diisocyanate. Among them, in the present invention, a diisocyanate compound having a tertiary isocyanate group is preferable, and meta-tetramethylxylylene diisocyanate is more preferable.

The reaction between the resin (a) having a hydroxyl group and a curable functional group and the diisocyanate compound (b) can be carried out by a known method. The above reaction is
The reaction is performed at a temperature of room temperature to 200 ° C, preferably 50 to 150 ° C, more preferably 60 to 120 ° C. In the above reaction, a solvent and a catalyst may be used as necessary.

When a solvent is used in the above reaction, the solvent is not particularly restricted but includes, for example, aliphatic hydrocarbons such as pentane, hexane, heptane, petroleum ether and petroleum benzene; benzene, toluene, xylene and the like. Aromatic compounds such as cyclohexane, methylcyclohexane and decalin; Halogenated hydrocarbon compounds such as carbon tetrachloride, chloroform and 1,2-dichloroethane; ethyl ether, isopropyl ether and anisole Ethers such as benzene, dioxane and tetrahydrofuran; ketones such as acetone, methyl isobutyl ketone, methyl ethyl ketone, cyclohexanone, acetophenone and isophorone; esters based such as ethyl acetate and butyl acetate; acetonitrile and dimethyl sulfoxide De, and dimethyl formamide and the like.

The catalyst is not particularly restricted but includes, for example, dibutyltin dilaurate, bis (2-ethylhexanoate) tin, bis (2,4-pentanedionate) dichlorotin, and n-butyltris (2-ethylhexayl). Noate) tin, tin acetate, di-n-butylbis (2-
Ethyl hexanoate) tin, di-n-butyl bis (2,4-pentanedionate) tin, dioctyl dilauryl tin, tetra-n-butyl tin, tetra-n-octyl tin, 2,4-pentanedionate tin , A Lewis acid such as titanium tetraisopropoxide; a protic acid such as paratoluenesulfonic acid, phosphoric acid, methanesulfonic acid, sulfuric acid, or hydrochloric acid; triethylamine, tributylamine,
N-methylmorpholine, diazabicyclo [2,2,
2] Organic bases such as octane and N, N'-dimethylpiperazine; and inorganic bases such as lithium hydroxide, lithium hydride, sodium hydroxide, sodium hydride, potassium hydroxide and potassium t-butoxy. .

Among the thermally dissociable resins (A) obtained by the above reaction, the thermally dissociable resin (A) obtained by using an acrylic resin (a-1) as the resin (a) having a hydroxyl group and a curable functional group is used. A-1) has a number average molecular weight of 100
It is preferably from 0 to 60000. If it is less than 1000, the blocking resistance is reduced, and if it is more than 60000, the appearance is reduced. More preferably, 20
00 to 20000. More preferably, 2000 to
10,000.

The above-mentioned heat dissociable resin (A-1) preferably has a glass transition point (Tg) of 20 to 100 ° C.
When the temperature is lower than 20 ° C., the blocking resistance decreases, and when it exceeds 100 ° C., the appearance becomes poor. More preferably, the temperature is 25 to 70 ° C, still more preferably, 35 to 6 ° C.
0 ° C.

Of the above-mentioned heat-dissociable resin (A), a heat-dissociable resin (A-2) obtained by using a polyester resin (a-2) as the resin (a) having a hydroxyl group and a curable functional group. And the heat dissociable resin (A-3) obtained using the polyester resin (a-3) has a number average molecular weight of 1
It is preferably from 500 to 10,000. If it is less than 1500, the low molecular weight component of the resin after the modification reaction will increase, and the blocking resistance will decrease. If it exceeds 10,000, the resin flow property will decrease significantly, causing a deterioration in appearance.

The heat dissociable resins (A-2) and (A-
In 3), the glass transition point (Tg) is preferably 20 to 70 ° C. When the temperature is lower than 20 ° C., the blocking resistance decreases, and when it exceeds 70 ° C., the appearance becomes poor.
More preferably, it is 35 to 60 ° C.

The heat dissociable resin (A) may modify the remaining hydroxyl groups and other functional groups, if necessary, to make these groups other functional groups. For example, when the resin (a) having a hydroxyl group and a curable functional group is a polyester resin (a-3), the remaining hydroxyl groups can be reacted with an acid anhydride to introduce an acid group. The acid anhydride is not particularly limited, for example, succinic anhydride,
Examples thereof include phthalic anhydride, maleic anhydride, and hexahydrophthalic anhydride. The method for introducing the acid group is not particularly limited, and can be performed by a known method.

Since the resin (A) having a hydroxyl group and a curable functional group is crosslinked with the diisocyanate compound (b), the heat dissociable resin (A) has a large molecular weight, is solid at room temperature, and is heat-meltable. Occasionally, the molecular weight decreases due to the dissociation reaction, causing a decrease in viscosity. The decrease in the molecular weight during the heating and melting is due to the cleavage of the bond between the hydroxyl group and the diisocyanate group, which is caused by the reaction that is dissociated into the resin (a) having the hydroxyl group and the curable functional group and the diisocyanate compound (b). It is. This reaction is a reversible reaction. At a high temperature, the equilibrium moves in the direction of a decrease in molecular weight, and at a low temperature, the recombination between a hydroxyl group and a diisocyanate group is excellent, and the resin having the hydroxyl group and the curable functional group ( a) is a polymer in which the two are linked by the diisocyanate compound (b).

The resin composition for a powder coating of the present invention comprises the above-mentioned heat dissociable resin (A) and a curing agent (B). The curing agent (B) is appropriately selected depending on the type of the curable functional group of the heat dissociable resin (A) to be used. For example, when the heat dissociable resin (A) is the acrylic resin (a-
When the curing agent (B) is obtained by modifying 1),
It is preferable to use a polyvalent carboxylic acid (B-1).

The polyvalent carboxylic acid (B-1) is a compound having at least two carboxyl groups in the molecule. The polycarboxylic acid (B-1) is cross-linked by a ring-opening addition reaction of the carboxyl group to the epoxy group of the thermally dissociable resin (A-1) obtained by modifying the acrylic resin (a-1). This cures the heat dissociable resin (A-1).

The polycarboxylic acid (B-1) is not particularly restricted but includes, for example, succinic acid, adipic acid, sebacic acid, azelaic acid, decanedicarboxylic acid, dodecanedicarboxylic acid, hexadecanedicarboxylic acid, eicosandicarboxylic acid, Aliphatic dibasic acids such as tetraicosane dicarboxylic acid; tribasic acids such as butanetricarboxylic acid and citric acid; tetrabasic acids such as butanetetracarboxylic acid; aromatic polycarboxylic acids such as isophthalic acid and trimellitic acid; Alicyclic dibasic acids such as hydrophthalic acid, tetrahydrophthalic acid and cyclohexanedicarboxylic acid can be mentioned. Of these, dodecanedicarboxylic acid is preferred.

The heat dissociable resin (A-1) and the polycarboxylic acid (B-1) are combined with the heat dissociable resin (A-1).
Group contained in the polycarboxylic acid (B-1)
The molar ratio to the carboxyl groups contained in (molar number of epoxy groups) / (molar number of carboxyl groups) is 10/3 to 1
It is preferable to be blended so as to be 0/10. 10
When the ratio is less than / 3, the thermosetting property of the obtained resin composition for powder coating decreases, and when it exceeds 10/10, the gloss of the coating film decreases. More preferably, it is 10/5 to 10/8.

In the present invention, the heat dissociable resin (A)
Is a product obtained by modifying the polyester resin (a-2), a blocked isocyanate (B-2) having two or more isocyanate groups in the molecule may be used as the curing agent (B). preferable.

The above-mentioned blocked isocyanate (B-2) is not particularly limited, and examples thereof include those obtained by subjecting an isocyanate compound having two or more isocyanate groups in a molecule to a blocking agent to undergo an addition reaction by a known method. Can be. The isocyanate compound is not particularly limited. For example, trimers of tetramethylene diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, xylylene diisocyanate, hydrogenated xylylene diisocyanate, isophorone diisocyanate, and isophorone diisocyanate Compounds such as ethylene glycol, propylene glycol, trimethylolpropane, glycerin, sorbitol, ethylenediamine, monoethanolamine, diethanolamine, low molecular active hydrogen compounds such as triethanolamine; polyester polyols,
Examples thereof include a terminal isocyanate group-containing compound obtained by reacting with a polymer active hydrogen compound such as polyester polyols and polyamides.

The blocking agent is not particularly limited.
For example, phenols such as phenol, thiophenol, ethylphenol, methylphenol, cresol, xylenol, resorcinol, nitrophenol, and chlorophenol; oximes such as acetoxime, methylethylketoxime and cyclohexanone oxime; and methanol and ethanol, propanol and butanol Alcohols; halogen-substituted alcohols such as ethylene chlorohydrin and 1,3-dichloro-2-propanol;
Tertiary alcohols such as t-butanol, t-pentanol, and t-butanethiol; lactams such as ε-caprolactam, δ-valerolactam, γ-butyrolactam, β-propyllactam; aromatic amines; imides; Active methylene compounds; Mercaptans; Imines; Ureas;
Examples include diaryl compounds.

The blending amounts of the heat dissociable resin (A-2) and the blocked isocyanate (B-2) are 95 to 70% by weight of the heat dissociable resin (A-2) and the blocked isocyanate (B-2). ) 5 to 30% by weight. If the content of the heat dissociable resin (A-2) is less than 70% by weight, the transparency of the coating film is reduced, and the appearance is poor.
If the amount is more than 10% by weight, the curability decreases.

In the present invention, the heat dissociable resin (A)
Is a product obtained by modifying the polyester resin (a-3), it is preferable to use an epoxy compound (B-3) as the curing agent (B).

The epoxy compound (B-3) is not particularly limited, but has at least two epoxy groups in the molecule.
Glycidyl ether of bisphenol A, glycidyl ether of hydrogenated bisphenol A, diglycidyl ether of orthophthalic acid,
Diglycidyl isophthalate, diglycidyl terephthalate, glycidyl p-oxybenzoate, diglycidyl tetrahydrophthalate, diglycidyl hexahydrophthalate, diglycidyl succinate, diglycidyl adipate, sebacic acid Diglycidyl ester, ethylene glycol diglycidyl ester, propylene glycol diglycidyl ester, 1,4-butanediol diglycidyl ester, 1,6-hexanediol glycidyl ester, trimellitic acid triglycidyl ester,
Examples thereof include triglycidyl isocyanurate, hydroquinone diglycidyl ether, and an epoxy compound modified with an oligomer or polyester resin thereof.

The amounts of the heat dissociable resin (A-3) and the epoxy compound (B-3) are 95 to 70% by weight of the heat dissociable resin (A-3) and the epoxy compound (B
-3) It is preferably 5 to 30% by weight. When the content of the heat dissociable resin (A-3) is less than 70% by weight, the transparency of the coating film is reduced, and poor appearance is caused. When it exceeds 95% by weight, the curability is reduced.

The resin composition for a powder coating according to the present invention is characterized in that when the heat dissociable resin (A) is the heat dissociable resin (A-2) or the heat dissociable resin (A-3), A catalyst may be added. The curing catalyst is not particularly limited, and examples thereof include tin compounds such as dibutyltin dilaurate; and tertiary amine compounds such as benzyldiamine. The blending amount of the curing catalyst is determined based on the heat dissociable resin (A
-2) or 0.1 to 5 parts by weight based on 100 parts by weight of the heat dissociable resin (A-3).

The resin composition for powder coatings of the present invention may contain, if necessary, a dissociation catalyst, a pigment, a surface conditioner, an ultraviolet absorber,
Additives such as antioxidants, light stabilizers and antiblocking agents may be added.

[0060] The dissociation catalyst may be used as the heat dissociable resin (A).
Is added for the purpose of accelerating the dissociation reaction. The dissociation catalyst is not particularly limited, and includes, for example, a curing catalyst generally used for the reaction between a blocked isocyanate and a polyol. For example, dibutyltin dilaurate, bis (2-ethylhexanoate) tin, bis (2 , 4-pentanedionate) dichlorotin, n-butyltris (2-ethylhexanoate) tin, tin acetate, di-n
-Butylbis (2-ethylhexanoate) tin, di-
n-butylbis (2,4-pentanedionate) tin,
Dioctyl dilauryl tin, tetra-n-butyl tin,
Lewis acids such as tetra-n-octyltin, 2,4-pentanedionate tin and titanium tetraisopropoxide; protonic acids such as paratoluenesulfonic acid, phosphoric acid and methanesulfonic acid; triethylamine, tributylamine, N-methyl Morpholine, diazabicyclo [2,
Tertiary amines such as 2,2] octane and N, N'-dimethylpiperazine. The compounding amount of the dissociation catalyst is 100% of the blocked isocyanate (B-2).
0.1 to 10 parts by weight based on parts by weight is preferred.

The above-mentioned pigments are not particularly restricted but include, for example, extenders such as lead oxide, strontium chromate, carbon black, coal dust, titanium dioxide, phthalocyanine blue, talc and barium sulfate; cadmium yellow, cadmium red, chromium yellow and the like. And a metal pigment such as aluminum flake. The blending amount of the pigment is appropriately set, but usually is preferably 10 to 100 parts by weight based on 100 parts by weight of the heat dissociable resin (A).

The above-mentioned surface conditioner is used to promote the fusion of the paint particles during heating and to enhance the transparency of the resulting coating film. As the surface conditioner, it is preferable to use a resin having good compatibility with paint particles composed of the heat dissociable resin (A) and the curing agent (B). The above resin is not particularly limited, but has an SP value of 10.4.
１11.0 and a number average molecular weight of 2,500 to 9000
Is preferred.

When the SP value of the resin is within the above range,
Good compatibility with the paint particles. More preferably, it is 10.6-10.9. If the number average molecular weight of the above resin is less than 2500, the blocking resistance is reduced, and the surface conditioning effect becomes insufficient. If the number average molecular weight exceeds 9000, the smoothness of the resulting coating film is impaired. More preferably, it is 3000-7000.

Examples of the resin include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, t-butyl (meth) acrylate, Isobutyl (meth) acrylate, cyclohexyl (meth) acrylate,
Examples thereof include those obtained by polymerizing one or more of stearyl (meth) acrylate and lauryl (meth) acrylate.

The amount of the surface conditioner is preferably 0.1 to 4 parts by weight based on 100 parts by weight of the total amount of the heat dissociable resin (A) and the curing agent (B). If the amount is less than 0.1 part by weight, the smoothness of the obtained coating film is impaired, and if it exceeds 4 parts by weight, the blocking resistance is reduced. More preferably, it is 0.3 to 2 parts by weight.

The ultraviolet absorber, antioxidant and light stabilizer are used to improve the weather resistance of the resulting coating. The ultraviolet absorber is not particularly limited. For example, Tinuvin 328, Tinuvin 900, Tinuvin 327, Tinuvin 1130, Tinuvin CGL384
(All manufactured by Ciba-Geigy); Sea Soap 103 (Cipro Kasei); Sand bar (Sand). The antioxidant is not particularly limited. For example, Irganox 245, Irganox 2
59, Irganox 565, Irganox 101
0, Irganox 1035, Irganox 107
6, Irganox 1098 (all manufactured by Ciba-Geigy) and the like. The light stabilizer is not particularly limited, and may be, for example, SANOL LS-770, SANOL LS-144, SANOL LS-292, SANOL LS
-440 (all manufactured by Sankyo); Tinuvin CGL123
(Manufactured by Ciba-Geigy); Sunsover 3050 (manufactured by Sando).

The compounding amount of the ultraviolet absorber and the antioxidant is preferably 0.1 to 3 parts by weight based on 100 parts by weight of the heat dissociable resin (A).

The above antiblocking agent is not particularly limited, but it is preferable to use fine resin particles. As the resin fine particles, the average particle size is 0.01 to 10 μm
It is preferable that the glass transition point (Tg) is 50 to 150 ° C. and the SP value is 9 to 15.

The above resin fine particles have an average particle size of 0.01 μm.
If it is less than 10 μm, production is difficult, and if it exceeds 10 μm, particles for imparting blocking resistance adversely affect the appearance. More preferably, it is 0.03 to 3 μm. When the glass transition point (Tg) of the resin fine particles is less than 50 ° C., the effect of improving the blocking resistance is poor, and
If it exceeds 0 ° C., it is not practical. More preferably, 70
~ 120 ° C. If the SP value of the resin fine particles is outside the above-mentioned range, the compatibility with the paint particles is reduced, and the appearance is adversely affected. More preferably, it is 10-13.

The above antiblocking agent is usually added and mixed after preparing the resin composition for powder coating. The amount added at this time is not particularly limited, but usually,
0.0 parts by weight based on 100 parts by weight of the resin composition for powder coating.
5 to 20 parts by weight. If it is less than 0.05 parts by weight,
The effect of improving the blocking resistance is inferior, and if it exceeds 20 parts by weight, the appearance of the obtained coating film deteriorates. More preferably, it is 0.1 to 10 parts by weight.

The resin composition for powder coatings of the present invention may further contain, if necessary, a silicone compound for adjusting the appearance and fluidity, and may also add Aerosil as a fluidity modifier. Good.

The resin composition for powder coating of the present invention can be produced, for example, as follows. A thermally dissociable resin (A), a curing agent (B), and
If necessary, mix additives, melt-knead using a kneader or the like, cool and solidify, pulverize using a pulverizer such as an ultracentrifugal pulverizer, classify into powder . afterwards,
Further, if necessary, adding an anti-blocking agent,
By mixing, the resin composition for powder coating of the present invention is obtained.

The resin composition for powder coating of the present invention preferably has an average particle size of 5 to 60 μm. When the thickness is less than 5 μm, the blocking resistance decreases, and when the thickness exceeds 60 μm, the appearance decreases. More preferably, it is 7 to 50 μm.

The method for applying the resin composition for a powder coating of the present invention is not particularly limited, and a method usually used for applying a powder coating can be used. For example, a method of adhering a resin composition for powder coating to a preheated object to be coated, and melting the resin composition for powder coating by the heat of the object to be coated to form a uniform continuous film (spray method,
Fluid immersion method); a method in which the resin composition for powder coating is heated at the time of coating and adhered to the object to be coated in a molten state (spraying method, plasma method); After being attached to the object to be coated, a method of baking and drying (electrostatic coating method) and the like can be mentioned.

The object to be coated is not particularly limited, and includes, for example, wood; steel, aluminum, metal such as an alloy of steel and aluminum; glass, cloth, plastic,
Foams and the like can be mentioned. Among them, a substrate made of plastic, metal, or the like is preferable.

The resin composition for powder coating of the present invention is applied to a substrate such as the above substrate and then heated to 100 to 250 ° C., preferably 120 to 200 ° C., so that the surface is smooth and uniform. A cured coating can be obtained. The curing time is
Depends on the curing temperature, but it is 14 ~
45 minutes is preferred.

The thickness of the coating film formed from the resin composition for a powder coating of the present invention is appropriately selected according to the desired use, but is usually 20 to 120 μm, preferably 4 to 100 μm, after drying.
0 to 100 μm.

In the coating method of the present invention, a step (1) of applying a base paint on a base-coated or intermediate-coated substrate,
Step (2) of applying the resin composition for a powder coating of the present invention on the substrate to which the base coating is applied, and
The step (3) of curing the base coating film and the coating film composed of the resin composition for powder coating by heating the substrate coated with the base coating and the resin composition for powder coating.

The first step of the coating method of the present invention is a step of applying a base coating on a substrate which has been subjected to undercoating or intermediate coating.

The substrate is not particularly limited, and may be, for example, those exemplified above as the objects to be coated.

The base paint is not particularly limited.
For example, 5 to 40% by weight of an amide group-containing ethylenically unsaturated monomer, 3 to 15% by weight of an acid group-containing ethylenically unsaturated monomer, 10 to 40% by weight of a hydroxyl group-containing ethylenically unsaturated monomer, and the balance Number average molecular weight of 60 obtained by copolymerizing other ethylenically unsaturated monomers
A film-forming vinyl polymer 90 obtained by neutralizing at least a part of the acidic groups of the
10 to 10 parts by weight (solid content), and a diol having a terminal hydroxyl group and a molecular weight of 100 to 5000, a diisocyanate and a compound having at least one hydroxyl group in the molecule and having a hydrophilic group are subjected to isocyanate-rich conditions. 5 to 90 parts by weight (solid content) of a urethane group-containing aqueous dispersion obtained by dispersing a hydrophilic group-containing oligomer obtained by the reaction in step 1 in an aqueous medium containing at least one of a primary polyamine and a secondary polyamine And the like.

The thickness of the base coating film formed from the base paint is preferably 10 to 30 μm as a dry film thickness.

In the present invention, after passing through the above-mentioned step (2) of applying the resin composition for powder coating of the present invention on the substrate coated with the base coating, the base coating and the powder coating are applied. The base coating film and the coating film composed of the resin composition for a powder coating are simultaneously cured by a so-called two-coat one-bake method through a step (3) of heating the substrate on which the resin composition for powder coating is applied. The curing conditions are not particularly limited, but are preferably 100 to 250 ° C, preferably 120 to 200 ° C, and 15 to 45 minutes.

The resin composition for powder coating according to the present invention comprises a thermosetting resin (A) obtained by modifying a thermosetting resin (a) having a hydroxyl group and a curable functional group with a diisocyanate compound (b).
Is used, the viscosity can be sufficiently reduced at the time of heating and melting, and the coating film surface can be smoothed. In addition, since the change of the thermally dissociable resin (A) at the time of heating and melting is reversible, the resin is recombined at the time of forming a coating film, and thus has sufficient curability. Furthermore, since the heat dissociable resin (A) has a high glass transition point (Tg) and is a high molecular weight solid at room temperature, the resin composition for powder coatings of the present invention has excellent blocking resistance. .

The resin composition for a powder coating of the present invention can form a coating by a two-coat, one-bake method of curing simultaneously with the base coating, so that the number of steps for forming the coating is small and economical.

[0086]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

Synthesis Example 1 Synthesis of Hydroxyl-Containing Acrylic Resin Xylene 100 was placed in a reaction vessel equipped with a dropping funnel, a thermometer, a mantle heater, a cooling pipe, a stirrer, and a nitrogen introduction pipe.
A part by weight was charged and heated to 130 ° C. under a nitrogen stream. A monomer mixture of 45 parts by weight of glycidyl methacrylate, 20 parts by weight of styrene, 9.3 parts by weight of 2-hydroxyethyl methacrylate, 18.7 parts by weight of methyl methacrylate, 7 parts by weight of isobornyl methacrylate, and t-butyl peroxy- An initiator solution containing 15 parts by weight of 2-ethylhexanoate and 22 parts by weight of xylene was dropped at a constant speed over 3 hours using a dropping funnel. After holding for 30 minutes after the completion of the dropping, an initiator solution of 0.1 parts by weight of t-butylperoxy-2-ethylhexanoate and 10 parts by weight of xylene was dropped at a constant speed over 30 minutes using a dropping funnel. After the completion of the dropping, the mixture was held for another 1 hour, and the hydroxyl-containing acrylic resin A-
1 was obtained.

Synthesis Example 2 Synthesis of Hydroxy Group-Containing Acrylic Resin The amount of 2-hydroxyethyl methacryl was 7.7 parts by weight, the amount of methyl methacrylate was 21.3 parts by weight, and the amount of isobornyl methacrylate was 6 parts by weight. Parts by weight and the amount of the t-butyl peroxy-2-ethylhexanoate (initiator) was 11.5 parts by weight, except that the hydroxyl-containing acrylic resin A-
2 was obtained.

Synthesis Example 3 Synthesis of Hydroxyl-Containing Acrylic Resin 70 parts by weight of xylene was added to a reaction vessel equipped with a dropping funnel, a temperature control device, a mantle heater, a cooling pipe, a stirrer, and a nitrogen introduction pipe, and heated to 130 ° C. under a nitrogen stream. Heated.
A monomer mixture of 45 parts by weight of glycidyl methacrylate, 20 parts by weight of styrene, 8 parts by weight of isobutyl methacrylate, 27 parts by weight of methyl methacrylate, and VA-
An initiator solution of 7.5 parts by weight of 086 (manufactured by Wako Pure Chemical Industries, Ltd.) and 100 parts by weight of N-methylpyrrolidone was dropped at a constant speed over 3 hours using a dropping funnel. After completion of dropping, the mixture was held for 30 minutes, and then VA-086 (manufactured by Wako Pure Chemical Industries, Ltd.) over 30 minutes.
An initiator solution containing 1 part by weight of N-methylpyrrolidone and 10 parts by weight of N-methylpyrrolidone was added dropwise over 30 minutes, and the mixture was kept for 1 hour to obtain a hydroxyl group-containing acrylic resin A-3.

Synthesis Example 4 Synthesis of Hydroxyl Group-Containing Acrylic Resin 70 parts by weight of xylene was added to a reaction vessel equipped with a dropping funnel, a temperature control device, a mantle heater, a cooling pipe, a stirrer and a nitrogen introduction pipe, and heated to 130 ° C. under a nitrogen stream. Heated.
Glycidyl methacrylate 45 parts by weight, styrene 20 parts by weight, isobutyl methacrylate 8 parts by weight, methyl methacrylate 27 parts by weight, a monomer mixed solution of thioglycerol 5 parts by weight, and t-butyl peroxy-2-ethylhexanoate 3 parts by weight Then, an initiator solution of 20 parts by weight of xylene was dropped at a constant speed over 3 hours using a dropping funnel. After completion of dropping, after holding for 30 minutes, t-
An initiator solution of 0.1 part by weight of butyl baroxy-2-ethylhexanoate and 10 parts by weight of xylene was added dropwise over 30 minutes, and the mixture was further kept for 1 hour, and the hydroxyl group-containing acrylic resin A was added.
-4 was obtained.

[0091] Synthesis of Synthesis Example 5 thermal dissociation acrylic resin, a heating mantle, a reaction vessel equipped with a cooling tube, a stirrer and a nitrogen inlet tube, a hydroxyl group-containing acrylic resin A-
130 parts by weight of xylene varnish 1 (100 parts by weight of hydroxyl group-containing acrylic resin A-1), 8.7 parts by weight of meta-tetramethylxylylene diisocyanate (TMXDI),
After charging 0.02 parts by weight of dibutyltin dilaurate (DBTL) and heating to 60 ° C. under a nitrogen stream and reacting for 2 hours, xylene was removed by distillation under reduced pressure to obtain a Tg of 40 ° C.
A thermally dissociable acrylic resin T-1 having a number average molecular weight of 2710 and a weight average molecular weight of 14600 was obtained. The number of hydroxyl groups bonded to isocyanate groups in the obtained thermally dissociable acrylic resin T-1 was 1.6 per molecule. As for the melt viscosity of this heat dissociable acrylic resin T-1, the lowest melt viscosity value at 140 ° C. was 72 poise. Also, DB was used as a dissociation catalyst in 100 parts by weight of the thermally dissociable acrylic resin T-1.
When 3 parts by weight of TL was added, the lowest melt viscosity at 140 ° C. was 270 poise.

Tg was determined by measuring with a differential scanning calorimeter (DSC). The number average molecular weight and the weight average molecular weight were measured by gel permeation chromatography (G
PC) to obtain an average molecular weight in terms of polystyrene. The melt viscosity was determined by measuring the steady-state viscosity at 140 ° C. or 180 ° C. using an MR-3 liquid meter (manufactured by Rheology), and the lowest melt viscosity was defined as the lowest viscosity.

Synthesis Example 6 Synthesis of Thermally Dissociable Acrylic Resin Synthetic example except that hydroxyl-containing acrylic resin A-1 was changed to hydroxyl-containing acrylic resin A-2 and the amount of TMXDI was changed to 7.2 parts by weight. In the same manner as in 5, Tg45
° C, number average molecular weight 3130, weight average molecular weight 20700
Was obtained. In the obtained thermally dissociable acrylic resin T-2, the number of hydroxyl groups bonded to isocyanate groups was 1.6 per molecule. The melt viscosity of the thermally dissociable acrylic resin T-2 was such that the lowest melt viscosity value at 140 ° C. was 72 poise. Further, when 5 parts by weight of DBTL was added as a dissociation catalyst to 100 parts by weight of the thermally dissociable acrylic resin T-2, the melt viscosity was 140.
The lowest melt viscosity value at 180C was 180 poise.

Synthesis Example 7 Synthesis of Thermally Dissociable Acrylic Resin Synthetic example except that hydroxyl-containing acrylic resin A-1 was changed to hydroxyl-containing acrylic resin A-3 and the amount of TMXDI was changed to 16.1 parts by weight. In the same manner as in 5, Tg42
° C, number average molecular weight 3900, weight average molecular weight 13300
Was obtained. In the obtained thermally dissociable acrylic resin T-3, the number of hydroxyl groups bonded to isocyanate groups was 1.0 per molecule. As for the melt viscosity of the thermally dissociable acrylic resin T-3, the lowest melt viscosity value at 140 ° C. was 230 poise. Further, when 3 parts by weight of DBTL as a dissociation catalyst was added to 100 parts by weight of the thermally dissociable acrylic resin T-3, the melt viscosity was 140.
The minimum melt viscosity at ° C was 124 poise.

Synthesis Example 8 Synthesis of Thermally Dissociable Acrylic Resin Synthetic Example except that hydroxyl-containing acrylic resin A-1 was changed to hydroxyl-containing acrylic resin A-4 and the amount of TMXDI was changed to 11.3 parts by weight. In the same manner as in 5, Tg46
° C, number average molecular weight 4500, weight average molecular weight 16800
Was obtained. In the obtained thermally dissociable acrylic resin T-4, the number of hydroxyl groups bonded to isocyanate groups was 1.0 per molecule. As for the melt viscosity of this thermally dissociable acrylic resin T-4, the lowest melt viscosity value at 140 ° C. was 340 poise. Further, when 3 parts by weight of DBTL as a dissociation catalyst was added to 100 parts by weight of the thermally dissociable acrylic resin T-4, the melt viscosity was 140
The minimum melt viscosity at ℃ was 186 poise.

Synthesis Example 9 Comparative Acrylic Tree Containing Epoxy Group
63 parts by weight of xylene was charged into a reaction vessel equipped with a synthetic dropping funnel for fat, a thermometer, a mantle heater, a cooling tube, a stirrer, and a nitrogen introduction tube, and heated to 130 ° C. under a nitrogen stream. Glycidyl methacrylate 45 parts by weight, styrene 20 parts by weight,
Using a dropping funnel, a monomer mixture of 27 parts by weight of methyl methacrylate, 8 parts by weight of isobutyl methacrylate, and an initiator solution of 7.5 parts by weight of t-butyl peroxy-2-ethylhexanoate and 7 parts by weight of xylene. For 3 hours. After the dropping, after holding for 30 minutes,
t-butyl peroxy-2-ethylhexanoate
An initiator solution of 1 part by weight and 7 parts by weight of xylene was dropped at a constant speed over 30 minutes using a dropping funnel. After the completion of the dropwise addition, the mixture was held for another 1 hour, and then xylene was removed by distillation under reduced pressure to obtain an acrylic resin A-5 having a Tg of 52 ° C., a number average molecular weight of 3,100 and a weight average molecular weight of 6,110. As for the melt viscosity of the obtained acrylic resin A-5, the lowest melt viscosity value at 140 ° C. was 590 poise. In addition, acrylic resin A-
When 5 parts by weight of DBTL was added as a dissociation catalyst to 100 parts by weight of No. 5, the lowest melt viscosity at 140 ° C. was 370 poise.

Examples 1 to 8 and Comparative Examples 1 to 2 Each component was blended according to the composition shown in Table 1 and mixed.
The mixture was melt-kneaded using a buscon kneader (manufactured by Buss Corp.), extruded, and cooled to obtain a solid coating composition. This was centrifugally pulverized using an ultracentrifugal pulverizer (manufactured by Mitamura Riken Kogyo Co., Ltd.), and classified (150 mesh) to obtain resin compositions 1 to 10 for powder coatings.

[0098]

[Table 1]

Each of the obtained resin compositions for powder coating was evaluated for blocking resistance in the following manner. Blocking resistance Each of the resin compositions for powder coatings was placed in a 50-ml sample bottle, left at 30 ° C. for one week, taken out, and the state of aggregation was evaluated. ：: No aggregate is present. △: Aggregate is present, but cannot be picked up with fingers. △: A small amount of aggregate is present, but easily crushed. X: Aggregate is present, not crushed.

[0100]

[Table 2]

With respect to each of the resin compositions for powder coatings of Examples 1 to 8 and Comparative Examples 1 and 2, test plates were prepared and the appearance was evaluated as follows. The NSIC value of the appearance was obtained. A cationic electrodeposition paint (Powertop U-50, manufactured by Nippon Paint Co., Ltd.) and an intermediate coating paint (Oliger P-2, manufactured by Nippon Paint Co., Ltd.) were applied to a 0.8 mm thick phosphoric acid-treated plate, respectively, to a dry film thickness of 25 μm. After painting to 40μm,
Each of the resin compositions for powder coatings of coating numbers 1 to 10 was electrostatically coated so as to have a film thickness of 70 μm.
Baking was performed for 5 minutes to obtain test plates 1 to 10. The surface smoothness and gloss of the coating film were visually observed. The results are shown in Table 3. ：: Good ○ △: Smooth but small irregularities △: Round, irregularities can be confirmed △ ×: Irregularities and no gloss ×: Poor

Appearance (NSIC value) Each resin composition for powder coating was uniformly applied to an iron plate by an electrostatic coating method and baked at 140 ° C. for 20 minutes to form a coating film. The appearance of the obtained coating film was evaluated by NSIC value (%) measured by a mapping clarity measuring device (manufactured by Suga Test Instruments Co., Ltd.). The NSIC value was obtained by performing a Fourier spectrum analysis on a rectangular wave pattern image formed through reflection on the coating film surface using the optical system shown in FIG. The results are shown in Table 3. In FIG. 1, light emitted from a light source 1 passes through a condenser lens 2, a pattern 3, and a projection lens 4, is reflected on a coating surface of a coating object 5, and forms an image on a light receiving surface of a photodiode array 6. An imaging waveform was obtained. The light source 1 and the light receiving surface of the photodiode array 6
It was arranged at an angle θ with respect to the painted surface of the painted object 5.

[0103] Here, NSIC value, the fundamental frequency [nu ₀ and the sum of three times the power square root of frequency 3Nyu ₀ imaging waveform obtained by subtracting the baseline intensity b to emphasize the shape information {P ([nu ₀ ) ^1/2 + P (3ν ₀ ) ^1/2基準 normalized by a similar value {P (ν ₀ ) ^1/2 + P (3ν ₀ ) ^1/2 ｝ _BG for a black glass plate: NSIC = [{P (ν ₀ ) ^1/2 + P (3ν ₀ ) ^1/2 } /
{P (ν ₀ ) ^1/2 + P (3ν ₀ ) ^1/2 _{BG BG} ] × 100, which is representative of the skin texture of the image (distortion of shape from a rectangular mesh) as a seed.

Synthesis Example 10 Synthesis of Varnish A 1 L reaction vessel equipped with a stirrer, a temperature controller and a condenser was charged with 76 parts by weight of ethylene glycol monobutyl ether, and further 15 parts by weight of styrene, 63 parts by weight of methyl methacrylate, 48 parts by weight of ethyl methacrylate (HEMA), n-butyl acrylate 11
7 parts by weight, 27 parts by weight of methacrylic acid, acrylamide 3
61 parts by weight of a monomer solution comprising 0 parts by weight and 3 parts by weight of azobisisobutyronitrile were added, and the temperature was adjusted to 120 ° C. with stirring. After adding 245 parts by weight of the monomer solution in 3 hours, stirring was continued for 1 hour. Further, 28 parts by weight of dimethylethanolamine and 200 parts by weight of deionized water were added, and the volatile matter content was 50% and the number average molecular weight was 12,000.
Acrylic resin varnish was obtained. The hydroxyl value of the obtained acrylic resin varnish is 70 mgKOH / g, and the acid value is
It was 58 mgKOH / g.

Synthesis Example 11 Synthesis of hydrophilic group-containing oligomer
Forming a thermometer, equipped with a stirrer and condenser 1000ml
, 40.2 parts by weight of dimethylpropionic acid,
30 parts by weight of triethylamine, N-methylpyrrolidone 3
12 parts by weight were added and dissolved by heating at 90 ° C. Next, 290 parts by weight of isophorone diisocyanate and 70 parts by weight of polypropylene glycol (molecular weight: 1000) were added,
After stirring for 10 minutes, 1.03 parts by weight of DBTL was added, and 95
C., and reacted for 1 hour to obtain a hydrophilic group-containing oligomer (urethane prepolymer solution).

Synthesis Example 12 Preparation of Urethane Emulsion To a 5000 ml reaction vessel equipped with a thermometer, a stirrer, a condenser and a dropping funnel, 1775 parts by weight of deionized water and 9.2 parts by weight of hydrazine hydrate were added. The hydrophilic group-containing oligomer (urethane prepolymer solution) obtained in Synthesis Example 11 was added. Thereafter, stirring was continued for 30 minutes to obtain a urethane emulsion which was a cloudy and stable aqueous dispersion. The urethane emulsion obtained has an acid value of 1
It was 6.2 mgKOH / g, and the nonvolatile content was 33%.

Synthesis Example 13 Preparation of aqueous base coating composition Aluminum pigment paste (Alpaste 7160N,
30 parts by weight of Cymel 303 (methoxylated methylol melamine, manufactured by Mitsui Toatsu Co.) was added to 15 parts by weight of Al metal content (65%, manufactured by Toyo Aluminum Co., Ltd.) and uniformly mixed. Further, 2 parts by weight of isostearyl acid phosphate (Phoslex A-180L, manufactured by Sakai Chemical Industry Co., Ltd.) was uniformly mixed to obtain an aluminum pigment solution. Next, an aluminum pigment solution was added to 112 parts by weight of the acrylic resin varnish obtained in Synthesis Example 10 and uniformly dispersed.
43 parts by weight of the urethane emulsion obtained in 2 were uniformly dispersed to obtain an aqueous base coating composition.

Example 9 Test by 2 coats / 1 bake
The aqueous base coating composition obtained in Synthesis Example 13 was applied to an intermediate coated steel sheet in an environment of a temperature of 23 ° C. and a humidity of 85% by an air spray coating means at an interval of 1 minute at two stages at a dry film thickness of 20 μm. After preheating at 80 ° C. for 2 minutes, the resin composition for powder coating (paint No. 2) obtained in Example 2 was air-sprayed wet-on-wet in one stage to a dry film thickness of 60 μm. Painted. After setting for 7 minutes, the resulting painted plate was
The test plate 11 was prepared by baking at 30 ° C. for 30 minutes in a drier. As the intermediate coated steel sheet, a degreased polished mild steel sheet coated with an electrodeposition paint for automobiles and baked, followed by intermediate coating and baking in an intermediate coating line was used.
The appearance of the obtained test plate 11 was evaluated in the same manner as in Example 1, and the NSIC value was measured. The results are shown in Table 3.

Example 10 Trial by 2 coats / 1 bake
Preparation resin composition for powder coating of the test plate (coating No. 2), Example 4
A test plate 12 was obtained in the same manner as in Example 9 except that the resin composition for powder coating (paint No. 4) obtained in the above was used. The appearance of the obtained test plate 12 was evaluated in the same manner as in Example 1, and the NSIC value was measured. The results are shown in Table 3.

[0110]

[Table 3]

Synthesis Example 14 Synthesis of Polyester Resin Dimethyl terephthalate (DMTP) 36.7 was placed in a reaction vessel having a heating device, a stirrer, a nitrogen inlet tube and a fractionation tower.
Parts by weight, 42.1 parts by weight of neopentyl glycol (NPG) and 4.3 parts by weight of trimethylolpropane (TMP) were charged, and heating was started under dry nitrogen to melt the raw materials. Then, a transesterification reaction was performed at 130 to 210 ° C., and methanol was distilled off. The transesterification was continued at 210 ° C. Next, 31.6 parts by weight of terephthalic acid was added and a dehydration reaction was performed at 240 ° C. The reaction was completed when the acid value of the resin was 5.0 mgKOH / g, to obtain a polyester resin P-1. The obtained polyester resin P-1 is
The hydroxyl value was 50 mgKOH / g, and the number average molecular weight was 3,000.

Synthesis Example 15 Synthesis of Polyester Resin A polyester resin was synthesized in the same manner as in Synthesis Example 14 except that DMTP was 34.5 parts by weight, NPG was 31.8 parts by weight, and terephthalic acid was 34.5 parts by weight. Resin P-2 was obtained. The obtained polyester resin P-2 has a hydroxyl value of 4
5 mgKOH / g and number average molecular weight was 3500.

SYNTHESIS EXAMPLE 16 Heat-dissociable polyester resin
In a reaction vessel equipped with a synthesis thermometer, a mantle heater, a cooling pipe, a stirrer and a nitrogen introduction pipe, a hydroxyl value of 50 mgKOH / g was added.
100 parts by weight of a polyester resin P-1, 400 parts by weight of methyl ethyl ketone, 6.5 parts by weight of TMXDI and 0.2 parts by weight of DBTL were charged, and the mixture was heated at 60 ° C. under a nitrogen stream.
And reacted for 2 hours. After completion of the reaction, methyl ethyl ketone was removed by distillation under reduced pressure to obtain a thermally dissociable polyester resin PT-1 having a Tg of 44 ° C. and a number average molecular weight of 4,200. The obtained heat dissociable polyester resin PT-1 has a hydroxyl value of 33 mgKOH / g and a melt viscosity of 1 mgKOH / g.
The minimum melt viscosity value at 80 ° C. was 240 poise. The number of hydroxyl groups bonded to isocyanate groups in this heat-dissociable polyester resin PT-1 was 1.8 per molecule.

Synthesis Example 17 Synthesis of heat-dissociable polyester resin
Except that the synthetic polyester resin P-1 was changed to the polyester resin P-2 and 6.5 parts by weight of TMXDI was changed to 5.9 parts by weight, the thermal dissociation property of Tg of 46 ° C. and the number average molecular weight of 4510 was obtained in the same manner as in Synthesis Example 16. A polyester resin PT-2 was obtained. The obtained heat dissociable polyester resin PT-2 has a hydroxyl value of 30 mgKOH / g and a melt viscosity of 1 mgKOH / g.
The minimum melt viscosity value at 80 ° C. was 350 poise. The number of hydroxyl groups bonded to isocyanate groups in this heat-dissociable polyester resin PT-2 was 1.6 per molecule.

Synthesis Example 18 Synthesis of Comparative Polyester Resin A reactor equipped with a heating device, stirrer, nitrogen inlet tube and fractionating tower was charged with 32.3 parts by weight of DMTP, 12.21 parts by weight of NPG, 9.69 parts by weight of ethylene glycol, 13.85 parts by weight of 1,6-hexanediol, 0.05 parts by weight of DBTL, and 1.4 parts by weight of TMP were charged, and heating was started under dry nitrogen to melt the raw materials. Then 130-210 ° C
To carry out a transesterification reaction, and methanol was distilled off.
The transesterification was continued at 210 ° C. Next, 31.43 parts by weight of terephthalic acid was added and a dehydration reaction was performed at 240 ° C. The reaction was completed when the acid value of the resin was 2.0 mgKOH / g, to obtain a polyester resin P-3. The obtained polyester resin P-3 had a hydroxyl value of 36 mgKOH / g,
The number average molecular weight was 4,500. Further, Tg was 43 ° C. As for the melt viscosity of the obtained polyester resin P-3, the lowest melt viscosity value at 180 ° C. was 412 poise.

Examples 11 to 12 and Comparative Example 3 Each component was blended according to the blending composition shown in Table 4 and mixed with a drive render (Henschel mixer, manufactured by Mitsui Kakoki Co., Ltd.). The mixture was melt-kneaded, extruded, and cooled to obtain a solid coating composition. This was centrifugally pulverized using an ultracentrifugal pulverizer (manufactured by Mitamura Riken Kogyo Co., Ltd.) and classified (150 mesh) to obtain resin compositions 11 to 13 for powder coatings. Each of the obtained resin compositions for powder coatings was electrostatically coated on a zinc phosphate-treated copper plate having a thickness of 0.6 mm, and baked at 180 ° C. for 20 minutes. Using the obtained test plate, the appearance of the coating film was evaluated in the same manner as in Example 1. Moreover, evaluation of blocking resistance was performed in the same manner as in Example 1. Table 5 shows the results.

[0117]

[Table 4]

In Table 4, * 1 indicates a caprolactam block of isophorone diisocyanate (isocyanate equivalent 3
56, manufactured by Bayer AG), and * 2 is a surface conditioner (manufactured by Monsanto).

[0119]

[Table 5]

Synthesis Example 19 Carboxylic acid-terminated thermally dissociable poly
In a reaction vessel equipped with a synthetic thermometer for ester resin , a mantle heater, a cooling pipe, a stirrer, and a nitrogen inlet pipe, heat dissociable polyester resin P
100 parts by weight of T-1, 400 parts by weight of cyclohexanone, and 6 parts by weight of succinic anhydride were charged under a nitrogen stream.
The mixture was heated to 0 to 130 ° C. and reacted for 3 hours. After completion of the reaction, cyclohexanone was removed by distillation under reduced pressure, and a carboxylic acid-introduced thermodissociable polyester resin PTA-1 was introduced into the terminal.
I got The acid value of the obtained carboxylic acid-terminated thermally dissociable polyester resin PTA-1 was 33 mgKOH / g.

Synthesis Example 20 Carboxylic acid-terminated thermally dissociable poly
Synthetic ester resin Synthetic thermo-dissociable polyester resin PT-1 is referred to as thermo-dissociable polyester resin PT-, and 6 parts by weight of succinic anhydride is 5.5
A carboxylic acid-terminated thermally dissociable polyester resin PTA-2 was obtained in the same manner as in Synthesis Example 19 except that the amount was changed to parts by weight. The acid value of the obtained carboxylic acid-terminated thermally dissociable polyester resin PTA-2 was 27 mgKOH / g.

Synthesis Example 21 Carboxylic acid-terminated polyester
Synthesis of Resin The carboxylic acid-terminated polyester resin PA- was prepared in the same manner as in Synthesis Example 19, except that the heat-dissociable polyester resin PT-1 was changed to the polyester resin P-3 and 6 parts by weight of succinic anhydride was changed to 7 parts by weight. 1 was obtained. The acid value of the obtained carboxylic acid-terminated polyester resin PA-1 is 34 mg KOH
/ G.

Examples 13 to 14 and Comparative Example 4 Each component was blended in accordance with the blending composition shown in Table 6 and a drive render (Henschel mixer, manufactured by Mitsui Chemicals, Ltd.)
Then, the mixture was melt-kneaded using a buscon kneader (manufactured by Buss Corp.), extruded, and cooled to obtain a solid coating composition. This was centrifugally pulverized using an ultracentrifugal pulverizer (manufactured by Mitamura Riken Kogyo Co., Ltd.) and classified (150 mesh) to obtain resin compositions 14 to 16 for powder coatings. Each of the obtained resin compositions for powder coatings was electrostatically coated on a zinc phosphate-treated copper plate having a thickness of 0.6 mm, and baked at 180 ° C. for 20 minutes. Using the obtained test plate, the appearance of the coating film was evaluated in the same manner as in Example 1. In addition, evaluation of blocking resistance was performed in the same manner as in Example 1. The results are shown in Table 7.

[0124]

[Table 6]

In Table 6, * 3 indicates triglycidyl isocyanurate (manufactured by Nissan Chemical Industries, Ltd.), and * 4 indicates a surface conditioner (manufactured by Monsanto).

[0126]

[Table 7]

Table 7 shows that Examples 13 and 14 using the heat dissociable resin had better appearance and did not lower the blocking resistance as compared with Comparative Example 4. Was.

[0128]

As described above, the resin composition for powder coating of the present invention has the above-mentioned constitution, so that the appearance of the formed coating film can be improved without lowering the blocking resistance. It can also be used in fields where the appearance of a coating film surface is required, such as in an automobile body. Further, the coating method of the present invention can be performed by a two-coat one-bake method of simultaneously curing the base paint and the resin composition for a powder coating of the present invention, so that the coating does not go through a multi-step coating film forming process. Is very economical.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram illustrating an optical system in measuring an NSIC value.

Claims (16)

[Claims] 1. A resin (a) having a hydroxyl group and a curable functional group is used in an amount of 0.1 to 3.0 per molecule of the resin (a).
Such that the hydroxyl groups are bonded to isocyanate groups,
It comprises a heat dissociable resin (A) modified with a diisocyanate compound (b) having two identical or different isocyanate groups selected from the group consisting of a secondary isocyanate group and a tertiary isocyanate group, and a curing agent (B). A resin composition for a powder coating, comprising: 2. The resin composition for a powder coating according to claim 1, wherein the diisocyanate compound (b) is meta-tetramethylxylylene diisocyanate. 3. The composition according to claim 1, further comprising a tin compound as a dissociation catalyst in an amount of 0.1 to 10% by weight based on the total composition.
Or the resin composition for powder coating according to 2. 4. The resin (a) having a hydroxyl group and a curable functional group comprises 30 to 65% by weight of an ethylenically unsaturated monomer having an epoxy group and 70 to 35% by weight of another ethylenically unsaturated monomer. Has a hydroxyl value of 10
The acrylic resin (a-1) is 100 mgKOH / g, and the thermosetting resin (A) is the acrylic resin (a-
The heat dissociable resin (A-1) obtained by modifying 1) with a diisocyanate compound (b), and the curing agent (B) is a polycarboxylic acid (B-1). Resin composition for powder coating. 5. The heat dissociable resin (A-1) has a number average molecular weight of 1,000 to 60,000 and a glass transition point of 20.
The resin composition for a powder coating according to claim 4, wherein the temperature is from 100C to 100C. 6. The heat dissociable resin (A-1) and the polyvalent carboxylic acid (B-1) are: (mol number of epoxy group) / (mol number of carboxyl group) = 10/3 to 10 / The resin composition for a powder coating according to claim 4 or 5, which is blended so as to be 10. 7. The resin composition for powder coatings according to claim 4, wherein the acrylic resin (a-1) has a hydroxyl group introduced by copolymerization of a hydroxyl group-containing ethylenically unsaturated monomer. 8. The acrylic resin (a-1) is obtained by adding 0.1 to 20% by weight of a hydroxyl group-containing polymerization initiator to all monomers constituting the resin (a-1) and polymerizing the same. 7. The resin composition for a powder coating according to claim 4, wherein a hydroxyl group is introduced. 9. The acrylic resin (a-1) is obtained by adding 0.1 to 20% by weight of a hydroxyl group-containing chain transfer agent to all the monomers constituting the resin (a-1) and polymerizing the same. 7. The resin composition for a powder coating according to claim 4, wherein a hydroxyl group is introduced. 10. The resin (a) having a hydroxyl group and a curable functional group is a polyester resin (a-2) having a hydroxyl value of 10 to 100 mgKOH / g, and the thermally dissociable resin (A) is a polyester resin. Thermodissociable resin (A-) obtained by modifying resin (a-2) with diisocyanate compound (b)
2) and the curing agent (B) is a blocked isocyanate (B-2) having two or more isocyanate groups in the molecule.
The resin composition for a powder coating according to claim 1, 2, or 3. 11. The heat dissociable resin (A-2) has a number average molecular weight of 1500 to 20,000 and a glass transition point of 2
The resin composition for a powder coating according to claim 10, which is at 0 to 70C. 12. A thermally dissociable resin (A-2) of 95 to 70% by weight, and a blocked isocyanate (B-2) of 5 to 3%.
The resin composition for a powder coating according to claim 10 or 11, comprising 0% by weight. 13. The resin (a) having a hydroxyl group and a curable functional group is a polyester resin (a-3) having a hydroxyl value of 10 to 100 mgKOH / g and an acid value of 10 to 100 mgKOH / g, The heat dissociable resin (A) is a heat dissociable resin (A-3) obtained by modifying the polyester resin (a-3) with a diisocyanate compound (b), and the curing agent (B) has an epoxy group in the molecule. The resin composition for a powder coating according to claim 1, wherein the resin composition is an epoxy compound (B-3) having at least two of the following. 14. The heat dissociable resin (A-3) has a number average molecular weight of 1500 to 20,000 and a glass transition point of 2
The resin composition for a powder coating according to claim 13, which is at 0 to 70 ° C. 15. A thermally dissociable resin (A-3) of 95 to 70% by weight and an epoxy compound (B-3) of 5 to 30% by weight.
The resin composition for a powder coating according to claim 13, comprising: 16. The method according to claim 1, wherein a step (1) of applying a base paint on the undercoated or intermediate-coated substrate is performed. Step (2) of applying the resin composition for body coating, and heating the substrate on which the base coating and the resin composition for powder coating are applied, thereby forming a base coating film and the resin composition for powder coating. A method for forming a coating film, comprising a step (3) of curing a coating film made of an object.