JPH0198672A - Powder coating composition - Google Patents

Abstract

PURPOSE:To make it possible to form a powder coating composition excellent in smoothness, impact resistance, corrosion inhibition, etc. and free from yellowness of film, by mixing a specified polyester with an acrylic resin containing a glycidyl group and/or a beta-methylglycidyl group and a uretedione compound. CONSTITUTION:A composition comprises 70-95pts.wt. polyester resin having an acid value of 10-30, a hydroxyl value of 5-40, a glass transition temperature of 55-70 deg.C, a number-average MW of 2,000-6,000, 5-30pts.wt. acrylic resin containing a glycidyl group and/or a beta-methylglycidyl group and having a number-average MW of 500-6,000 and containing 20-60wt.% at least one monomer selected from among glycidyl acrylate, glycidyl methacrylate, beta- methylglycidyl acrylate and beta-methylglycidyl methacrylate, and 1-20pts.wt. uretedione compound.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a powder coating that, when cured, does not generate tar from the coating components, has excellent yellowing resistance, and has smoothness, impact resistance, The present invention relates to a powder coating composition that forms a coating film with excellent flexibility, corrosion resistance, weather resistance, etc.

[Conventional technology]

Powder coatings are used for general metal coatings due to their advantages of being non-polluting, resource-saving, and labor-saving, and are used for home appliances such as washing machines, refrigerators, and air conditioners where smoothness and corrosion resistance are important, as well as for home appliances that require corrosion resistance and weather resistance. It is widely used in important road materials such as bridges, railings, gates, and fences.

As an example of a powder coating, a resin composition for powder coating consisting of a polyester resin having a carboxyl group and a hydroxyl group, a polymer containing a glycidyl group and/or a β-methylglycidyl group, and a blocked isocyanate compound is disclosed in Japanese Patent Publication No. It is disclosed in Publication No. 60-120764.

[Problem that the invention seeks to solve]

However, although this resin composition for powder coatings has excellent smoothness, impact resistance, and weather resistance, the blocking agent of the blocked isocyanate dissociates during the coating curing, and the blocking agent causes tar in the baking oven. There are drawbacks such as generation and falling on painted products, resulting in defective painted products, yellowing of the paint film, and pollution problems caused by the gas of the blocking agent.

[Means for solving problems]

The present inventors solved these conventional problems and achieved smoothness and
As a result of intensive research in order to obtain a powder coating composition that has excellent impact resistance, flexibility, corrosion resistance, weather resistance, etc., and does not cause yellowing of the coating film or generation of tar when the coating hardens, we have found that carboxyl groups and hydroxyl groups With a composition consisting of a polyester resin having
The inventors have discovered that the object can be achieved and have completed the present invention.

That is, the present invention has an acid value of 10 to 30 and a hydroxyl value of 5.
~40. Glass transition temperature (hereinafter referred to as Tg) is 55
70 to 95 parts by weight of a polyester resin (A) having a temperature of ~70°C and a number average molecular weight of 2000 to 6000, and glycidyl acrylate.

20 to 60 of one or more monomers selected from the group consisting of glycidyl methacrylate, β-methylglycidyl acrylate, and β-methylglycidyl methacrylate.
5 to 30 parts by weight of an acrylic resin (B) containing a glycidyl group and/or β-methylglycidyl group and having a number average molecular weight of 500 to 6000 and 1 to 20 parts by weight of a uretdione compound (C). A powder coating composition comprising:

The polyethyl resin (A) used in the present invention is a condensate of a polyester-formable carboxylic acid mainly composed of terephthalic acid and a polyhydric alcohol mainly composed of ethylene glycol, and the carboxylic acid component is 1 For example,
Phthalic acid, trimellitic acid, pyromellitic acid and their anhydrides; terephthalic acid, isophthalic acid, methylterephthalic acid, adipic acid, sebacic acid, succinic acid, fumaric acid, β-oxypropionic acid, oxalic acid, glutaric acid, etc. can give.

Further, as the polyhydric alcohol component, for example.

Ethylene glycol, propanediol, butanediol, bentanediol, 1,6-hexanediol,
Examples include neopentyl glycol, 2,2'-diethylpropanediol, cyclohexanediol, trimethylolpropane, and pentaerythritol.

“ As such polyester resin (A), for example, as commercial products, FINDIC A-239-J and FINDIC A-23 manufactured by Dainippon Ink and Chemicals Co., Ltd.
Examples include 9-W, FINDIC A-239-X, and 7 FINDIC A-239-Y (all trade names).

Glycidyl group and/or β- used in the present invention
The monomer content of the acrylic resin (B) containing a methylglycidyl group is 20 to 60% by weight, preferably 40% by weight.
~50% by weight. If this amount is less than 20% by weight, the compatibility with the polyester resin (A) will be poor and the reaction with the polyester resin (A) will be insufficient, resulting in poor coating film appearance. , mechanical strength such as impact resistance and flexibility becomes insufficient. Also, 60% by weight
If it exceeds , the crosslinking density becomes too high.

Mechanical strength such as impact resistance and flexibility of the resulting coating film is reduced, making it unsuitable.

If the number average molecular weight of the acrylic resin (B) is less than 500, the resulting coating film will have insufficient mechanical strength such as impact resistance and flexibility, and if it exceeds 6000,
In either case, not only will the appearance of the resulting coating film, such as smoothness and sharpness, be inferior, but also the mechanical strength, such as impact resistance and flexibility, will be reduced because one reaction will not proceed sufficiently. is also inappropriate.

This acrylic resin (B) contains the monomer and
It is obtained by copolymerizing it with a copolymerizable monomer, and examples of the copolymerizable monomer include methyl acrylate.

There are monomers such as ethyl acrylate, normal butyl acrylate, isobutyl acrylate, methyl methacrylate, ethyl methacrylate, normal butyl methacrylate, isobutyl methacrylate, cyclohexyl methacrylate, cellosolve methacrylate, and styrene. It is suitable because it has excellent compatibility with resin (A).

Furthermore, as a manufacturing method of acrylic resin (B).

Although any well-known method can be employed, the solution polymerization method is particularly suitable because it is easy to adjust the molecular weight.

Typical uretdione compounds (C) used in the present invention include aromatic compounds such as tolylene diisocyanate, xylylene diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate;
Examples include compounds having a uretdione ring of alicyclic or aliphatic isocyanate, specifically 1, for example, Hii
Examples include Adduct BF-1540 (trade name) manufactured by LS.

If the amount of the uretdione compound (C) contained in the powder coating composition of the present invention is less than 1 part by weight, the resulting coating film will have insufficient mechanical strength such as impact resistance and flexibility;
If it exceeds 20 parts by weight, mechanical strength such as impact resistance and flexibility, corrosion resistance, weather resistance, etc. will be poor.

In addition to the above three components, the powder coating composition of the present invention may optionally contain coloring pigments (e.g., titanium dioxide, red iron,
Inorganic pigments such as yellow iron oxide and carbon black, organic pigments such as phthalocyanine blue, phthalocyanine green, quinacridone red pigments, and isoindolinone yellow pigments): extender pigments such as talc, silica, and calcium carbonate; metals such as aluminum powder Powder; mica powder; additives such as surface conditioners, ultraviolet absorbers, heat deterioration inhibitors, antifoaming agents, etc.; catalysts such as organic tin compounds, etc. can be appropriately blended.

The powder coating composition of the present invention can be produced by a method similar to known powder coating production methods.

The powder coating composition produced as described above is as follows.

Metals such as iron, aluminum, copper, zinc, or their alloys, such as stainless steel and brass, are coated uniformly using a commercially available electrostatic powder coating machine, and then baked in a hot air oven, infrared oven, induction heating oven, etc. It is possible to form a good coating film.

〔Effect of the invention〕

The coating film obtained using the powder coating composition of the present invention has excellent coating appearance such as smoothness and sharpness, mechanical strength such as gloss, impact resistance, and flexibility, corrosion resistance, and weather resistance. ,
It is industrially useful because it does not generate tar from the paint when it cures, and the yellowing of the paint film is very low.

[Production Examples, Examples and Comparative Examples]

Next, I will give a production example, an example, and a comparative example of the present invention,
This will be explained in more detail. In these examples, parts are by weight.

Production example [Production of glycidyl group-containing acrylic resin (B)] From 40 parts of glycidyl methacrylate, 20 parts of β-methylglycidyl methacrylate, 30 parts of methyl methacrylate, 10 parts of cellosolve methacrylate, and 0.5 parts of t-butylbarbenzoate. This mixture was added dropwise to 100 parts of xylene heated to 155° C. under pressure, and after polymerization, the xylene was removed to obtain an acrylic resin (B-1) having a number average molecular weight of 10,000.

Next, except for changing the amount of t-butyl perbenzoate added, the same amount of monomers as that used for the acrylic resin (B-1) was used, and from 1.0 part of t-butyl perbenzoate, the number average molecular weight 5000 acrylic resin (B-2), t-butyl perbenzoate 2.
From 0 parts, acrylic resin with a number average molecular weight of 1500 (B
-3), acrylic resin (B-4) with a number average molecular weight of 500 from 4.0 parts of t-butyl perbenzoate, and t-
An acrylic resin (B-5) having a number average molecular weight of 300 was obtained from 5.0 parts of butyl perbenzoate.

Examples 1-4. Comparative Examples 1 to 5 All components of the compositions of Examples 1 to 4 and Comparative IS1 to 5 shown in Table 1 were mixed in a dry blender (manufactured by Mitsui Kakoki Co., Ltd.,
After uniformly mixing for about 1 minute using a Henschel mixer (trade name), the mixture was mixed uniformly for about 1 minute, and then mixed using an extrusion kneader (trade name:
The zero-order product was melt-kneaded using Busco Kneader PR-48 (trade name, manufactured by Busu Co., Ltd.), cooled, and finely pulverized using a hammer-type impact crusher.

It was passed through a 150-mesh wire mesh to obtain each powder coating.

The obtained powder coating was electrostatically coated onto a zinc phosphate-treated iron plate having a thickness of 0 and 8 i+m, and baked under the conditions shown in Table 2 to obtain each cured coating film.

The coating performance of the obtained test pieces is shown in Table 2.

As is clear from the results of Examples 1 to 4, the coating film obtained from the powder coating composition of the present invention has excellent coating appearance, gloss, impact resistance, flexibility, corrosion resistance, and weather resistance. There is no residual tar (stain) and it has excellent yellowing resistance.

On the other hand, the content of polyester resin (A) is 70
Comparative Example 1 containing less than parts by weight had poor impact resistance and flexibility;
Comparative Example 2, in which the acrylic resin (B) has a number average molecular weight of less than 500, has poor impact resistance, flexibility, and corrosion resistance, and Comparative Example 3, in which the acrylic resin (B) has a number average molecular weight of more than 6,000.
is the appearance of the paint film.

Poor gloss, impact resistance, flexibility, and corrosion resistance.

In addition, Comparative Example 4 in which the content of the uretdione compound (C) exceeds 20 parts by weight has poor impact resistance, flexibility, corrosion resistance, and weather resistance. Comparative Example 5 using the blocked isocyanate compound disclosed in Japanese Patent No. 60-120764 has a large amount of resin (tar) and is poor in yellowing resistance.

Claims (1)

[Scope of Claims] Essential components include (A) an acid value of 10 to 30, a hydroxyl value of 5 to 40, a glass transition temperature of 55 to 70°C, and a number average molecular weight of 200;
70 to 95 parts by weight of a polyester resin having a molecular weight of 0 to 6,000 (B) 20 to 60 parts by weight of one or more monomers selected from the group consisting of glycidyl acrylate, glycidyl methacrylate, β-methylglycidyl acrylate, and β-methylglycidyl methacrylate. 5 to 30 parts by weight of an acrylic resin containing a glycidyl group and/or β-methylglycidyl group and having a number average molecular weight of 500 to 6,000 and 1 to 20 parts by weight of (C) a uretdione compound. A powder coating composition consisting of.