JPH02673A - Powder coating composition - Google Patents

Abstract

PURPOSE:To obtain the present composition which can give a coating film improved in yellowing resistance, smoothness, etc., by mixing a polyester resin with a specified acrylic resin, a glycidyl compound and a uretedione compound. CONSTITUTION:20-90wt.% at least one monomer (a) selected from glycidyl (meth)acrylate and beta-methylglycidyl (meth)acrylate is polymerized with 80-10wt.% other vinyl monomers (b) to obtain a (beta-methyl)glycidyl group-containing acrylic resin (B) of a number-average MW of 300-6000. 70-95 pts.wt. polyester resin (A) of a number-average MW of 2000-6000, an acid value of 10-40, a hydroxyl value of 5-40, and a glass transition temperature of 55-70 deg.C is mixed with 4-24 pts.wt. component B, 1-6 pts.wt. glycidyl compound (C) of an MW of 100-298, 1-20 pts.wt. uretedione compound (D) and, optionally, a pigment, a metallic powder, a mica powder, a surface modifier, a catalyst, etc., (E).

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a powder coating that does not generate tar from the coating components during curing, has excellent yellowing resistance, and has smoothness and resistance to yellowing. # This relates to a powder coating composition that forms a coating film with excellent impact resistance, adhesion properties, 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 a powder coating comprising a carboxyl group-containing polyester resin and an acrylic resin containing a glycidyl group and/or β-methylglycidyl group is disclosed in Japanese Patent Application Laid-Open No. 56-136856. Disclosed in the official gazette.

Furthermore, as a material for improving the physical properties (especially impact resistance) and corrosion resistance of the resin composition for powder coatings, polyester resins having carboxyl groups and hydroxyl groups, polymers containing glycidyl groups and/or β-methylglycidyl groups, etc. A resin composition for a powder coating comprising a block isocyanate compound and a block isocyanate compound is disclosed in JP-A-60-120764.

[Problem to be solved by the invention]

However, the resin composition for powder coatings disclosed in JP-A-60-120764 has poor coating film smoothness in thin film thicknesses, and the blocking agents of block isocyanates 1 to 1 are used during coating curing. Because it dissociates and evaporates, tar from the blocking agent is generated in the baking oven, which may fall onto the painted product and cause the painted product to be defective, or the paint film to yellow easily.
Furthermore, there were other drawbacks such as the blocking agent gas being a pollution problem.

[Means to solve the problem]

The present inventors have solved these conventional problems and developed a powder coating composition that has excellent lubricity in thin coating films and does not cause yellowing of the coating film or generation of tar when the coating hardens. As a result of intensive research to obtain polyester resins having carboxyl groups and hydroxyl groups, acrylic resins containing glycidyl groups and/or β-methylglycidyl groups, and molecular weight of 1.
．． It has been discovered that the object can be achieved by a composition comprising a glycidyl group-containing compound of OO-298 and a bovine 1-dione compound, and the present invention has been completed.

That is, the present invention has an acid value of 10 to 40 and a hydroxyl value of 5.
~40, glass transition temperature (hereinafter referred to as Tg) is 55
~70°C and a number average molecular weight of 2000-6000
70 to 95 parts of polyester resin (A), glycidyl acrylate, glycidyl methacrylate, β
- 20 to 90% by weight of one or more monomers selected from the group consisting of methylglycidyl acrylate-1- and β-methylglycidyl methacrylate and 80 to 10% by weight of other vinyl monomers, and number average Molecular weight is ζ3
00-6000 glycidyl group and/or β-
4 acrylic resin (B) containing methylglycidyl group
-24 parts by weight, 1 to 6 parts by weight of a glycidyl group-containing compound (C) with a molecular weight of 100 to 298, and 1 to 20 parts by weight of a uretdione compound (D). .

The polyester 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 includes, for example, ,
Phthalic acid, trimellisic 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 be mentioned.

In addition, examples of polyhydric alcohol components include ethylene glycol, propanediol, butanediol, bentanediol, 2,6-hexanediol, neopentyl glycol, 2,2'diethylpropanediol, cyclohexanediol, trimethylolpropane,
Examples include 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.
9-W, FINDIC A-239-X, FINDIC A-239-Y (all trade names), and the like.

The acrylic resin (B) containing a glycidyl group and/or β-methylglycidyl group used in the present invention has monomers of 20 to 90% by weight, preferably 40 to 80% by weight.
and other vinyl monomers 80-10% by weight, preferably 60%
~20% by weight, and the number average molecular weight is ~300
6,000, preferably in the range of 500 to 5,000.

If the amount of monomer 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 durability becomes insufficient. Moreover, if it exceeds 90% by weight, the crosslinking density becomes too high and mechanical strength such as impact resistance and flexibility of the resulting coating film decreases, which is inappropriate.

In addition, if the number average molecular weight is less than 300, the resulting coating film will have insufficient mechanical strength such as impact resistance and flexibility, and smoke will be generated when the coating film is baked. Not only does this result in poor coating film appearance such as smoothness, but also poor compatibility between resins, and the crosslinking reaction does not proceed sufficiently, resulting in poor mechanical strength such as impact resistance and flexibility. Both cases are inappropriate, since the

This acrylic resin (B) contains a surface monomer,
Other vinyls that can be copolymerized with it! Examples of other copolymerizable vinyl monomers include styrene, methyl acrylate, ethyl acrylate-1-, n-butyl acrylate, and im-butyl acrylate-1. -, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate-1~, inbutyl methacrylate, cyclohexyl methacrylate-1~, cellosolve methacrylate, acrylonitrile, and acrylamide, but especially methyl methacrylate and cellosolve methacrylate. Ray-1 and the like are preferred because they have excellent compatibility with the polyester resin (A).

These are preferably present in an amount of 50 to 80% by weight in other vinyl monomers.

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

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

As such acrylic resin (B), for example, as commercial products, FINDIC A-229 and FINDIC A-229-30 manufactured by Inu Nippon Ink Chemical Industry Co., Ltd.
, FINDIC A-229-40 (both are trade names).

The glycidyl group-containing compound (C) used in the present invention is
]-~6 parts by weight is required; if this content is less than 1 part by weight, the resulting coating film will have poor smoothness, and if it exceeds 6 parts by weight, corrosion resistance will decrease. .

Examples of such a glycidyl group-containing compound (C) include diglycidyl terephthalate-1~, roseglycidyloxybenzoic acid glycidyl ester, and triglycidyl isocyanure-1~.

Typical uretdione compounds (D) used in the present invention include 1-lylene diisocyanes 1 to 1. Xylylene diisocyanate 1~, Isophorone diisocyanate 1
Examples include compounds having an aromatic, alicyclic or aliphatic iso-1-dione ring such as - and hexamethylene diisocyanate. Adak+-BF-ts4 manufactured by l s company
o (product name), etc.

If the amount of the uretdione compound (D) added to 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-mentioned four components, the powder coating composition of the present invention may optionally contain colored pigments (for example, titanium dioxide,
Inorganic pigments such as yellow iron oxide and carbon black, organic pigments such as phthalocyanine blue, phthalocyanine green, quinacridone red pigments, and inintrinon 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, and antifoaming agents; and catalysts such as organic tin compounds 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 can be uniformly applied to metals such as iron, aluminum, copper, zinc, or combinations thereof, such as stainless steel and brass, using a commercially available electrostatic powder coating machine. After that, it can be baked in a hot air oven, infrared oven, induction heating oven, etc. to form a good coating film.

〔Effect of the invention〕

The coating film obtained using the powder coating composition of the present invention is as follows.

Paint film appearance such as smoothness at thin film thickness, gloss, and resistance to 1
#Excellent plasticity, flexibility, corrosion resistance, and weather resistance,
It is industrially useful because it does not generate tar from the paint when it cures, and yellowing of the paint film is less likely to occur.

[Examples and comparative examples]

Next, examples and comparative examples of the present invention will be given and explained in more detail. In these examples, parts are by weight.

Examples 1-9. Comparative Examples 1 to 8 All components of the compositions of Examples 1 to 9 and Comparative Examples 1 to 8 shown in Table 1 were blended in a dry blender (manufactured by Mitsui Kakoki Co., Ltd., trade name Henschel Mixer) for about 1 minute. After uniformly mixing, the mixture is melt-kneaded using an extrusion kneader (Bus Co., Ltd., trade name Busco Kneader I R-46) at a temperature of 80 to 100°C, and after cooling, it is pulverized using a hammer-type impact pulverizer. did. Next, it was filtered through a 180-mesh wire mesh to obtain each powder coating.

The obtained powder coating was electrostatically coated onto a 0.8 mm thick iron plate treated with phosphorus and zinc, 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 9, the coating films obtained from the powder coating compositions of the present invention had excellent coating film outsideness, glossiness,
It has excellent impact resistance, flexibility, corrosion resistance, and weather resistance, and its performance (
It is free from tar and has excellent yellowing resistance.

On the other hand, the content of polyester resin (A) is 70
Comparative example 1 with less than 95 parts by weight has poor impact resistance, adhesion, corrosion resistance, and weather resistance, and comparative example 2 with more than 95 parts by weight has poor appearance, impact resistance, adhesion, and corrosion resistance. , poor weather resistance. Comparative Example 3 with an acrylic resin (B) content of less than 4 parts by weight and Comparative Example 4 with an acrylic resin (B) content of more than 24 parts by weight had poor coating film appearance, impact resistance, flexibility, corrosion resistance, and weather resistance. Inferior.

In addition, Comparative Example 5, which does not contain the glycidyl group-containing compound (C), which is an essential component of the present invention, has poor coating film appearance, and Comparative Example 6, in which the content of the glycidyl group-containing compound (C) exceeds 6 parts by weight, , poor impact resistance, pliability, corrosion resistance, and weather resistance. Comparative Example 7, in which the content of the uretdione compound (l) exceeds 20 parts by weight, was inferior in coating film appearance, impact resistance/16 properties, flexibility, corrosion resistance, and weather resistance, and the glycidyl group-containing compound (
C) is not blended and instead of the uretdione compound (D),
Comparative Example 8 using a blocked incyanate compound is
The appearance of the paint film is poor, there is a lot of tar, and the yellowing resistance is also poor.

Claims (1)

Scope of Claims: (A) An acid value of 10 to 40, a hydroxyl value of 5 to 40, a glass transition temperature of 55 to 70°C, and a number average molecular weight of 200
0 to 6000, and 70 to 95 parts by weight of (B) 20 to 90% by weight of one or more monomers selected from the group consisting of glycidyl acrylate, glycidyl methacrylate, β-methylglycidyl acrylate, and β-methylglycidyl methacrylate. An acrylic resin containing 80 to 10% by weight of other vinyl monomers and containing a glycidyl group and/or β-methylglycidyl group with a number average molecular weight of 300 to 6000.
24 parts by weight A powder coating composition comprising (C) 1 to 6 parts by weight of a glycidyl group-containing compound having a molecular weight of 100 to 298 and (D) a uretdione compound in a proportion of 1 to 20 parts by weight.