JPH11279450A - Composition for powder coating material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyurethane powder coating composition exhibiting sufficiently high curability at a low baking temperature compared with conventional powder coating material, e.g. at <=180 deg.C and giving a coating film having excellent appearance and quality. SOLUTION: This composition contains (1) one or more kinds of polyols selected from polyester polyol, acrylic polyol, fluorinated polyol, polycarbonate polyol, epoxy polyol and urethane polyol, (2) a uretdione group-containing addition polymerization compound composed of an alicyclic diisocyanate and (3) one or more kinds of curing catalysts selected from butyltin stearate, butyltin acetate, acetylacetone tin and dimethyltin oxide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a powder coating composition useful for coating metal plates and the like.

[0002]

2. Description of the Related Art At present, a polyurethane powder coating composition comprises, as a main component polyol and a curing agent, JP-B-61-31744.
The mainstream is a polyisocyanate composed of isophorone diisocyanate (hereinafter abbreviated as IPDI) as disclosed in JP-A No. 2000-163, in which the NCO group is blocked with a blocking agent such as ε-caprolactam.
However, such a paint has a problem in the working environment and the like because the blocking agent is scattered at the time of baking.

In order to solve the above problem, Japanese Patent Publication No. Sho 64
JP-A-5627, JP-B-2-16332 and the like disclose a polyuretdione-type curing agent comprising IPDI without using a blocking agent. Further, Japanese Unexamined Patent Publication No.
JP-A-239446 and JP-A-8-319439 disclose a polyuretdione-type curing agent comprising 4,4'-diisocyanatodicyclohexylmethane (hereinafter abbreviated as hydrogenated MDI) and the like. This is 2 moles of N
The uretdione ring formed between the CO groups can be dissociated into 2 moles of NCO groups again at the time of coating baking and react with the polyol, so that it can be used as a curing agent for powder coatings.

However, in a powder coating using these curing agents, a baking temperature of 180 ° C. or higher is required in order to obtain a gel fraction exhibiting sufficient mechanical properties and weather resistance as a coating film. There is a problem that coating cost increases. Therefore, from the viewpoint of cost, there has been a demand for a powder coating composition that uses a curing catalyst that cures at a low baking temperature and does not impair the appearance of a coating film.

[0005]

The object of the present invention is to provide a composition for a polyurethane powder coating which exhibits a sufficiently high gel fraction at a lower baking temperature than before and does not impair the appearance of the coating film. It is the purpose.

[0006]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that a polyurethane powder coating using a uretdione group-containing polyaddition compound composed of an alicyclic diisocyanate has a specific curing property. By adding a catalyst, it has been found that a powder coating composition having high curability at a baking temperature of 180 ° C. or less can be obtained,
The present invention has been completed.

That is, the present invention relates to a powder coating composition comprising: One or more polyols selected from polyester polyols, acrylic polyols, fluorine polyols, polycarbonate polyols, epoxy polyols, and urethane polyols.

A uretdione group-containing polyaddition compound comprising an alicyclic diisocyanate. One or more curing catalysts selected from butyltin stearate, butyltin acetate, acetylacetone tin, and dimethyltin oxide. Hereinafter, the present invention will be described in detail. As the polyol used in the present invention, polyester polyol, acrylic polyol, fluorine polyol,
There are polycarbonate polyols, epoxy polyols and urethane polyols.

As the polyester polyol, for example, succinic acid, adipic acid, sebacic acid, dimer acid,
Maleic anhydride, fumaric anhydride, isophthalic acid, terephthalic acid and other dicarboxylic acids selected from the group of carboxylic acids alone or in combination with ethylene glycol, propylene glycol, diethylene glycol, butylene glycol, neopentyl glycol, trimethylolpropane , Polyester polyol resins obtained by a condensation reaction with a polyhydric alcohol selected from the group of glycerin or the like alone or in a mixture, and poly such as obtained by ring-opening polymerization of ε-caprolactone using a polyhydric alcohol. Examples thereof include caprolactone, and esters of an aliphatic having a hydroxyl group and a polyhydric alcohol represented by castor oil.

[0010] As the acrylic polyol, one in the molecule
It can be obtained by copolymerizing a polymerizable monomer having two or more active hydrogens and a copolymerizable monomer. Such materials include, for example, acrylic acid-2
Acrylates having active hydrogen such as hydroxyethyl, 2-hydroxypropyl acrylate, 2-hydroxybutyl acrylate, methacrylic acid-2-
Methacrylates having active hydrogen such as hydroxyethyl, 2-hydroxypropyl methacrylate, and 2-hydroxybutyl methacrylate; or acrylate monoester or methacrylate monoester of glycerin, and trimethylolpropane Methyl acrylate, ethyl acrylate, isopropyl acrylate, acrylic acid, alone or in a mixture selected from the group of (meth) acrylates having polyvalent active hydrogen such as acrylate monoester or methacrylate monoester Acrylates such as -n-butyl, 2-ethylhexyl acrylate, methyl methacrylate,
Ethyl methacrylate, isopropyl methacrylate,
Methacrylic acid-n-butyl, isobutyl methacrylate, methacrylic acid-alone or a mixture selected from the group of methacrylates such as n-hexyl,
Acrylic acid, methacrylic acid, unsaturated carboxylic acids such as itaconic acid, acrylamide, N-methylol acrylamide, unsaturated amides such as diacetone acrylamide, and styrene, vinyl toluene, vinyl acetate,
Acrylic polyol resins obtained by polymerization in the presence or absence of a single or a mixture selected from the group of other polymerizable monomers such as acrylonitrile, and the like.

The fluorine polyol is, for example, a fluorine polyol obtained by copolymerizing a fluoroolefin or a fluorine-containing vinyl monomer and a hydroxyl-containing vinyl monomer as essential components with a vinyl monomer copolymerizable therewith. Kind. As the epoxy polyol, for example, novolak type, β-methyl epichlorohydrin type, cyclic oxirane type, glycidyl ether type, glycidyl ester type, glycol ether type, epoxidized aliphatic unsaturated compound, epoxidized aliphatic ester type,
Epoxy resins such as polycarboxylic acid ester type, aminoglycidyl type, and resorcinol type are exemplified.

As the polycarbonate polyol, for example, those obtained by a conventional method using an aromatic polyhydric alcohol such as bisphenol A or an aliphatic or alicyclic polyhydric alcohol such as 1,6-hexanediol as a raw material can be used. can give. The urethane polyol is, for example, a polymer formed by repeating an addition reaction between an aromatic, aliphatic, or alicyclic diisocyanate and a compound having active hydrogen, has a urethane bond in the polymer, and has a polymer side chain. And those having an OH group at the terminal.

As a guide for selecting the above polyol, a solid at room temperature and a hydroxyl value of 20 to 300 mg KOH /
g, acid value 10 mgKOH / g or less, glass transition temperature 4
0-80 ° C, weight average molecular weight 2000-80,000. The polyols described above can be used by being appropriately mixed. A uretdione group-containing polyaddition compound (hereinafter, referred to as an alicyclic diisocyanate) used in the present invention.
Referred to as a hardener)
JP-B-2-16332, JP-A-8-239446
And a preferable example is a polyuretdione-type curing agent composed of IPDI without using a blocking agent, for example, "Vestagon BF1540" (trademark) manufactured by Huls Co., Ltd. , "Bestagon BF1300" (trademark), "Bestagon BF1310" (trademark), "LS21" manufactured by Bayer AG
47 "(trademark) or a polyuretdione-type curing agent composed of hydrogenated MDI, for example," Cleran TP "manufactured by Bayer AG
LS2147 "(trademark).

Further, a polyuretdione type curing agent comprising norbornene diisocyanate (hereinafter abbreviated as NBDI), cyclohexyl diisocyanate (hereinafter referred to as CHDI)
), A hydrogenated xylylene diisocyanate (hereinafter abbreviated as hydrogenated XDI)
A polyuretdione-type curing agent composed of a hydrogenated (hydrogenated) aromatic diisocyanate, such as a polyuretdione-type curing agent, is also included. Furthermore, a polyuretdione composed of IPDI and hexamethylene diisocyanate (hereinafter, referred to as IPDI)
HDI) or a core duct,
Prepolymer or core duct of polyuretdione and HDI composed of hydrogenated MDI, prepolymer of polyuretdione and HDI composed of CHDI or core duct, prepolymer of polyuretdione and HDI composed of hydrogenated XDI or core duct, hydrogen And a prepolymer of polyuretdione and HDI comprising a fluorinated aromatic diisocyanate, or a core duct.

The uretdione group-containing polyaddition compound comprising an alicyclic diisocyanate used in the present invention is such that the uretdione ring is dissociated even at 180 ° C. or lower by the curing catalyst used in the present invention. Are crosslinked by a urethane reaction. The amount of the uretdione group-containing polyaddition compound (curing agent) composed of an alicyclic diisocyanate used in the present invention is preferably 5 to 100 parts by weight based on 100 parts by weight of the polyol described above. If the amount is less than 5 parts by weight, the crosslinking reaction is not always sufficient, and the weather resistance and mechanical properties of the coating film deteriorate, and
If the amount exceeds 0 parts by weight, an excessive curing agent remains, and the mechanical properties and the like of the coating film may decrease.

The curing catalyst used in the present invention is a catalyst capable of dissociating a uretdione ring at a low temperature and having an effect of promoting a urethane reaction between an NCO group formed after dissociation and an OH group in a polyol. It is. This gives 1
Under conditions of 80 ° C. or lower, high curability can be exhibited. Examples of the curing catalyst include the following.

As the butyltin stearate, specifically, dibutyltin distearate, for example, “SS-700” (trademark) manufactured by Tokyo Fine Chemical Co., Ltd .;
As the butyltin acetate system, specifically, dibutyltin diacetate, for example, "SCAT-8F" (trademark) manufactured by Sankyokisei Co., Ltd., tetrabutyldiacetoxydistannoxane, for example, Takeda Pharmaceutical Co., Ltd. Made "T
K-1 "(trademark), etc., tin acetylacetone, etc., and
And dimethyltin oxide. As a standard of high curability (gel fraction), at least 80%, these curing catalysts have an action of dissociating the uretdione ring at a low temperature.

The above-mentioned curing catalysts can be used by mixing them as appropriate. The amount of the curing catalyst used in the present invention is preferably 0.01 to 5 parts by weight, more preferably 0.01 to 5 parts by weight, based on 100 parts by weight of the polyol and 5 to 100 parts by weight of the uretdione group-containing polyaddition compound composed of an alicyclic diisocyanate. 0.1 to 2 parts by weight. When the curing catalyst is 0.0
If the amount is less than 1 part by weight, a sufficient effect is not exhibited as low-temperature curing, and the gel fraction may not be increased. On the other hand, if it exceeds 5 parts by weight, the gel fraction can be at least 80%, but it hardens before it melts and flows sufficiently during baking, so that the surface smoothness of the coating film, that is, the appearance may be reduced. is there.

The powder coating composition of the present invention comprises, in addition to the polyol and the uretdione group-containing polyaddition compound comprising an alicyclic diisocyanate, a curing catalyst, a pigment, a colorant, a surface smoothing agent, Inhibitor, foam inhibitor,
Various additives used in the technical field such as a photodeterioration inhibitor, an ultraviolet inhibitor, a pigment dispersant, a plasticizer, an antioxidant, and a salt damage inhibitor can be mixed and used.

An example of a method for preparing the powder coating composition of the present invention and an example of a coating method will be described. First, the polyol shown above, a uretdione group-containing polyaddition compound consisting of an alicyclic diisocyanate, and a curing catalyst are mixed once with a Henschel mixer or the like together with the above-mentioned additives such as pigments,
The mixture is melted and mixed in a temperature range of 80 to 140 ° C. by a multi-screw extruder and a kneader. After cooling, the powder coating raw material having a particle size of about 20 was cooled by a coarse pulverizer and a fine pulverizer.
Make powder of 0 μm or less.

As a general method of applying a powder coating, electrostatic coating using a spray gun is generally performed, but coating using a fluid immersion tank, spray coating, roll coating, curtain flow coating, or the like is also performed. After the powder coating composition is adhered to the object to be coated, a uniform coating film is formed on the object by heating and baking at a temperature of 180 ° C. or lower. Examples of the object to be coated mainly include a metal plate. As the metal plate, stainless steel plate, aluminum plate,
There are titanium plate, cold-rolled steel plate, galvanized steel plate, chromium-plated steel plate, nickel-plated steel plate, etc.If necessary, clean the metal surface by alkali degreasing, etc., and form the metal surface to improve the adhesion with the coating film. To process. Further, the metal plate may be a metal molded body that has been subjected to predetermined molding. Examples of the object to be coated other than the metal plate include concrete products, wood products, plastic products, and the like.

[0022]

Next, the present invention will be described in more detail by way of examples. The gel fraction was 160 to 180.
The coated plate baked at 20 ° C. was immersed in acetone at 20 ° C., taken out after 24 hours, and a value obtained by subtracting the weight of the titanium oxide pigment from the weight after drying at 100 ° C. for 1 hour, and the weight of the titanium oxide from the original weight. It was divided by the subtracted value and calculated as a percentage (%).

[0023]

Example 1 Polyester polyol (hydroxyl value = 34)
mgKOH / g, acid value = 1.1 mgKOH / g, glass transition temperature = 60 ° C., weight average molecular weight = 33000) 10
A uretdione group-containing polyaddition compound consisting of IPDI ("Vestagon BF1540" manufactured by Huls) is added to 0 parts by weight.
(Trademark), latent NCO% = 15.0%), 17.0 parts by weight (NCO / OH = 1.0 (molar ratio)) and titanium oxide in 5 parts
8 parts by weight, Modaflow powder (surface smoothing agent) 0.9
Parts by weight and 0.5 parts by weight of dibutyltin distearate (“SS-700” (trademark) manufactured by Tokyo Fine Chemical Co., Ltd.) as a curing catalyst were blended. This mixture was mixed once with a Henschel mixer, and then mixed with a twin screw extruder for 12 hours.
The mixture was melt-mixed at 0 ° C., and the resulting melt was cooled with a 10 ° C. pinch roller to obtain a powder coating composition.

The obtained composition for powder coating is pulverized by a coarse pulverizer and a fine pulverizer, and the powder sieved with 100 mesh is applied to a zinc phosphate-treated steel sheet by a spray gun type powder coating machine. Baking was performed at 160 ° C, 170 ° C, and 180 ° C. The result of measuring each gel fraction was as follows. Further, the appearance of the obtained coating film was good. 160 ° C 81% 170 ° C 84% 180 ° C 87%

[0025]

Example 2 Polyester polyol (hydroxyl value = 34)
mgKOH / g, acid value = 6 mgKOH / g, glass transition temperature = 59 ° C., weight average molecular weight = 25,000), 100 parts by weight of a uretdione group-containing polyaddition compound (IP Huster's “Bestagon BF1310” (trademark), Potential NCO% = 14.0%) 15.9 parts by weight (N
CO / OH = 1.0 (molar ratio), 58 parts by weight of titanium oxide, 0.9 part by weight of Modaflow powder (surface smoothing agent), and tetrabutyldiacetoxydistannoxane as a curing catalyst (Takeda Pharmaceutical Co., Ltd. "TK-1" (Trademark))
0.5 part by weight was blended. This mixture was once mixed with a Henschel mixer, then melt-mixed at 120 ° C. with a twin screw extruder, and the resulting melt was cooled with a 10 ° C. pinch roller to obtain a powder coating composition.

The obtained powder coating composition is pulverized by a coarse pulverizer and a fine pulverizer, and the powder sieved with 100 mesh is applied to a zinc phosphate-treated steel sheet by a spray gun type powder coating machine. Baking was performed at 160 ° C, 170 ° C, and 180 ° C. The result of measuring each gel fraction was as follows. Further, the appearance of the obtained coating film was good. 160 ° C 82% 170 ° C 87% 180 ° C 93%

[0027]

Example 3 Polyester polyol (hydroxyl value = 34)
mgKOH / g, acid value = 6 mgKOH / g, glass transition temperature = 59 ° C., weight average molecular weight = 25,000) 100 parts by weight of a uretdione group-containing polyaddition compound (IP Bayer, “LS2147” (trademark), N
17.6 parts by weight (NCO / OH = CO% = 15.5%)
1.0 (molar ratio)), 58 parts by weight of titanium oxide, 0.9 parts by weight of modaflow powder (surface smoothing agent), and tetrabutyldiacetoxydistannoxane (manufactured by Takeda Pharmaceutical Co., Ltd.) as a curing catalyst. TK-1 "(trademark) was added in an amount of 0.5 part by weight. This mixture was once mixed with a Henschel mixer, then melt-mixed at 120 ° C. with a twin screw extruder, and the resulting melt was cooled with a 10 ° C. pinch roller to obtain a powder coating composition.

The obtained powder coating composition is pulverized by a coarse pulverizer and a fine pulverizer, and the powder sieved with 100 mesh is applied to a zinc phosphate-treated steel sheet by a spray gun type powder coating machine. Baking was performed at 160 ° C, 170 ° C, and 180 ° C. The result of measuring each gel fraction was as follows. Further, the appearance of the obtained coating film was good. 160 ° C 80% 170 ° C 85% 180 ° C 90%

[0029]

Example 4 Polyester polyol (hydroxyl value = 30)
mgKOH / g, acid value = 0.5 mgKOH / g, glass transition temperature = 63 ° C., weight average molecular weight = 55000) 10
A uretdione group-containing polyaddition compound consisting of hydrogenated MDI ("Cleran TPLS214" manufactured by Bayer AG) was added to 0 parts by weight.
7 "(trademark), 15.0 parts by weight (NCO / OH = 1.0 (molar ratio)), 58 parts by weight of titanium oxide, and modaflow powder (surface smoothing agent) 0.9 parts by weight and 0.5 parts by weight of acetylacetone tin as a curing catalyst were blended. This mixture was once mixed with a Henschel mixer, then melt-mixed at 120 ° C. with a twin screw extruder, and the resulting melt was cooled with a 10 ° C. pinch roller to obtain a powder coating composition.

The obtained powder coating composition is pulverized by a coarse pulverizer and a fine pulverizer, and the powder sieved with 100 mesh is applied to a zinc phosphate-treated steel sheet by a spray gun type powder coating machine. Baking was performed at 160 ° C, 170 ° C, and 180 ° C. The result of measuring each gel fraction was as follows. Further, the appearance of the obtained coating film was good. 160 ° C 80% 170 ° C 85% 180 ° C 91%

[0031]

Example 5 Polyester polyol (hydroxyl value = 33)
mg KOH / g, acid value = 3 mg KOH / g, glass transition temperature = 64 ° C., weight average molecular weight = 26000) and 100 parts by weight of a uretdione group-containing polyaddition compound comprising hydrogenated MDI (“Cleran TPLS2147” manufactured by Bayer AG).
(Trademark), latent NCO% = 15.0%) 16.5 parts by weight (NCO / OH = 1.0 (molar ratio)) and titanium oxide 5
8 parts by weight, Modaflow powder (surface smoothing agent) 0.9
Parts by weight, dimethyltin oxide 0.5 as curing catalyst
Parts by weight were blended. This mixture was once mixed with a Henschel mixer, then melt-mixed at 120 ° C. with a twin screw extruder, and the resulting melt was cooled with a 10 ° C. pinch roller to obtain a powder coating composition.

The obtained powder coating composition was pulverized by a coarse pulverizer and a fine pulverizer, and the powder sieved with a 100 mesh was applied to a zinc phosphate-treated steel sheet by a spray gun type powder coating machine. Baking was performed at 160 ° C, 170 ° C, and 180 ° C. The result of measuring each gel fraction was as follows. Further, the appearance of the obtained coating film was good. 160 ° C 82% 170 ° C 86% 180 ° C 93%

[0033]

Example 6 Polyester polyol (hydroxyl value = 34)
mg KOH / g, acid value = 6 mg KOH / g, glass transition temperature = 59 ° C., weight average molecular weight = 25000) and 100 parts by weight of a uretdione group-containing polyaddition compound made of hydrogenated MDI (“Cleran TPLS2147” manufactured by Bayer AG).
(Trademark), latent NCO% = 15.0%), 17.0 parts by weight (NCO / OH = 1.0 (molar ratio)) and titanium oxide in 5 parts
8 parts by weight, Modaflow powder (surface smoothing agent) 0.9
Parts by weight and 0.5 parts by weight of tetrabutyldiacetoxydistannoxane ("TK-1" (trademark) manufactured by Takeda Pharmaceutical Co., Ltd.) as a curing catalyst were blended. This mixture was mixed once with a Henschel mixer, and then mixed with a twin screw extruder for 12 hours.
The mixture was melt-mixed at 0 ° C., and the resulting melt was cooled with a 10 ° C. pinch roller to obtain a powder coating composition.

The obtained powder coating composition was pulverized by a coarse pulverizer and a fine pulverizer, and the powder sieved with 100 mesh was applied to a zinc phosphate-treated steel sheet by a spray gun type powder coating machine. Baking was performed at 160 ° C, 170 ° C, and 180 ° C. The result of measuring each gel fraction was as follows. Further, the appearance of the obtained coating film was good. 160 ° C 80% 170 ° C 86% 180 ° C 92%

[0035]

Comparative Example 1 Polyester polyol (hydroxyl value = 30)
mgKOH / g, acid value = 0.5 mgKOH / g, glass transition temperature = 63 ° C., weight average molecular weight = 55000) 10
A uretdione group-containing polyaddition compound consisting of IPDI ("Vestagon BF1540" manufactured by Huls) is added to 0 parts by weight.
(Trademark), latent NCO% = 15.0%), 15.0 parts by weight (NCO / OH = 1.0 (molar ratio)) and titanium oxide in 5 parts
8 parts by weight, Modaflow powder (surface smoothing agent) 0.9
Parts by weight of dibutyltin dilaurate as a curing catalyst.
5 parts by weight were blended. This mixture was once mixed with a Henschel mixer, then melt-mixed at 120 ° C. with a twin-screw extruder, and the resulting melt was cooled with a 10 ° C. pinch roller to obtain a powder coating composition.

The obtained powder coating composition was pulverized by a coarse pulverizer and a fine pulverizer, and the powder sieved with a 100 mesh was applied to a zinc phosphate-treated steel plate by a spray gun type powder coating machine. Baking was performed at 160 ° C, 170 ° C, and 180 ° C. The result of measuring each gel fraction was as follows. The appearance of the obtained coating films was good, but all had low gel fractions.

160 ° C. 50% 170 ° C. 62% 180 ° C. 78%

[0038]

The powder coating composition of the present invention can be cured at a low temperature by using a specific curing catalyst for a uretdione group-containing polyaddition compound comprising a polyol and an alicyclic diisocyanate. I made it. The appearance of the obtained coating film is good, and the baking temperature can be lowered without impairing the quality of the coating film, so that the coating cost can be reduced.

Claims (1)

[Claims] 1. A composition for a powder coating, comprising: One or more polyols selected from polyester polyols, acrylic polyols, fluorine polyols, polycarbonate polyols, epoxy polyols, and urethane polyols. A uretdione group-containing polyaddition compound comprising an alicyclic diisocyanate. One or more curing catalysts selected from butyltin stearate, butyltin acetate, acetylacetone tin, and dimethyltin oxide.