JPH01313573A - Powder coating composition - Google Patents

Abstract

PURPOSE:To obtain the title composition excellent in smoothness, impact resistance and weathering resistance and freed from problems of yellowing of coating film and deposition of resin during curing of a coating by constituting it from a polyester resin, a glycidyl acrylic resin and a low-MW epoxy compound. CONSTITUTION:This powder coating composition is prepared by mixing 70-95 pts.wt. polyester resin (of an acid value of 10-100, a Tg of 50-80 deg.C and number- average MW of 2000-8000, e.g., Finedic M-8900, a product of Dainippon Ink) with 5-30 pts.wt. acrylic resin (containing 20-60wt.% at least one monomer selected from glycidyl (meth)acrylate and beta-methylglycidyl (meth)acrylate and having a number-average MW of 500-6000) and 1-10 pts.wt. glycidyl compound (of an MW of 100-298, e.g., diglycidyl terephthalate).

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides powder coatings that do not generate tar from coating components during curing, have excellent yellowing resistance, and have smoothness, impact resistance,
The present invention relates to a powder coating composition that forms a coating film with excellent flexibility, stain resistance, 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 powder coating resin composition comprising a carboxyl group-containing polyester resin and a glycidyl group- and/or β-methylglycidyl group-containing acrylic resin is disclosed in JP-A-56-136856. has been disclosed.

In addition, a resin composition for powder coatings comprising a polyester resin having a carboxyl group and a hydroxyl group, a polymer containing a glycidyl group and/or β-methylglycidyl group, and a blocked isocyanate compound has been disclosed in JP-A-60
It is disclosed in Japanese Patent No. 120764.

Further, a powder coating composition comprising glycidyl butarate and a polyester resin containing a carboxyl group is disclosed in JP-A-59-108065.

[Problem to be solved by the invention]

However, the resin composition for powder coatings consisting of a carboxyl group-containing polyester resin and a glycidyl group- and/or β-methylglycidyl group-containing acrylic resin disclosed in JP-A-56-136856 has a phase difference between these two resins. Since it has poor solubility and the curing reaction between the carboxyl group and the glycidyl group and/or β-methylglycidyl group is rapid, it exhibits a rapid thickening phenomenon when heated. Therefore, when a powder coating resin composition having such a structure is applied and baked, the melt fluidity is insufficient, and the resulting cured coating film has the drawback of not exhibiting sufficient physical properties and appearance. It was something that I had.

In addition, the resin composition for powder coating disclosed in JP-A-60-120764 has excellent smoothness and r# impact resistance, but is inferior in weather resistance and stain resistance, and furthermore, when the coating is cured, The blocking agent of the blocked isocyanate dissociates, causing tar from the blocking agent to form inside the baking furnace.The tar falls from the furnace wall onto the painted product, resulting in defective painted products and the coating film becoming yellowed easily. In addition, there was a drawback that gas from the blocking agent was generated as a volatile by-product.

Furthermore, since the powder coating disclosed in JP-A-59-108065 uses difunctional diglycidyl terephthalate as a curing agent, the crosslinking density during curing is low, resulting in smoothness, impact resistance, and flexibility. Although it has excellent properties, it has the disadvantage of being inferior in stain resistance, corrosion resistance, weather resistance, etc.

[Means to solve the problem]

The present inventors solved these conventional problems.

As a result of intensive research to obtain a powder coating composition that has excellent smoothness, impact resistance, flexibility, and weather resistance, and does not cause yellowing of the coating film or generation of tar when the coating hardens, we have found that it contains a carboxyl group. Polyester resin, glycidyl group and/or β-
The present inventors have discovered that the object can be achieved with a composition consisting of acrylic toilet fat containing methylglycidyl groups and a compound containing low molecular weight glycidyl groups, and have completed the present invention.

That is, in the present invention, a polyester resin (A) having an acid value of 10 to 100, a glass transition temperature (hereinafter referred to as Tg) of 50 to 80°C, and a number average molecular weight of 2000 to 8000 is used in a 70 to 95 weight range. 20 to 6 parts, one or more monomers selected from the group consisting of glycidyl acrylate, glycidyl methacrylate, β-methylglycidyl acrylate, and β-methylglycidyl methacrylate.
Contains 0% by weight and has a number average molecular weight of 500 to 6000
The acrylic resin (B) containing a glycidyl group and/or β-methylglycidyl group is mixed with 5 to 30 parts by weight and the glycidyl group-containing compound (C) having a molecular weight of 100 to 298 is added to 1 to 10 parts by weight. A powder coating composition comprising:

The polyester resin (A) used in the present invention is.

It is a condensation product 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, trimellitic acid, pyromellitic acid, and Their anhydrides; terephthalic acid, isophthalic acid, methyl terephthalic acid, adipic acid, sebacic acid, succinic acid,
Examples include fumaric acid, β-oxypropionic acid, oxalic acid, and glutaric acid.

Examples of polyhydric alcohol components include ethylene glycol, propanediol, butanediol, bentanediol, ], 6-hexanediol, neopentyl glycol, 2,2'-diethylpropanediol, cyclohexanediol, trimethylolpropane, Examples include pentaerythritol.

As such polyester resin (A), for example, commercially available products include FINDIC M-8900 manufactured by Dainippon Ink and Chemicals Co., Ltd., Ester Resin ER-8200 and Ester Resin ER-8 manufactured by Nippon Ester Co., Ltd.
107 (both are product names).

When the content of the polyester resin (A) in the powder coating composition of the present invention is less than 70 parts by weight, the compatibility with the acrylic resin (B) becomes poor and the cross-sectional density becomes too high. The appearance of the paint film is poor, and is it durable? # Mechanical strength such as impact resistance and malleability also decreases. In addition, if it exceeds 95 parts by weight, the reactivity with the acrylic resin (B) will be insufficient, resulting in poor mechanical strength such as attack resistance and flexibility, as well as stain resistance and weather resistance. Become.

The monomer content of the acrylic resin (B) containing a glycidyl group and/or β-methylglycidyl group used in the present invention is 20 to 60% by weight, preferably 30 to 60% by weight.
It is 50% by weight. If this amount is less than 20% by weight, the compatibility with the polyester resin (A) will be poor,
Moreover, the reactivity with the polyester resin (A) is insufficient, resulting in poor coating film appearance and insufficient mechanical strength such as impact resistance and flexibility. Moreover, when it exceeds 60 double sliding parts, the crosslinking density becomes too high and the mechanical strength such as impact resistance and flexibility of the resulting coating film decreases, which is 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 its smoothness and sharpness, be inferior, but also the reaction will not proceed sufficiently, resulting in a decrease in mechanical strength such as impact resistance and flexibility. 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, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, There are monomers such as isobutyl methacrylate, cyclohexyl methacrylate, cellosolve methacrylate, and styrene, but methyl methacrylate and cellosolve methacrylate are particularly suitable because they have excellent compatibility with the polyester resin (A).

Furthermore, as a method for producing the acrylic resin (B), any well-known method can be employed, but the solution polymerization method is particularly optimal because it is easy to adjust the molecular weight.

Further, the powder coating composition of the present invention has a molecular weight of 100 to
It is necessary to contain 1 to 10 parts by weight of the glycidyl group-containing compound (C) of No. 298. If the content of the glycidyl group-containing compound (C) is less than 1 part by weight, the compatibility between the polyester resin (A) and the acrylic resin (B) will be insufficient.

Moreover, since the curing reaction is rapid, the appearance of the coating film is poor, mechanical strength such as WI impact resistance and flexibility is insufficient, and weather resistance is also poor. Moreover, if it exceeds 10 parts by weight, the crosslinking density during curing becomes too low, resulting in poor stain resistance, corrosion resistance, weather resistance, etc., which is not preferable.

That is, by containing 1 to 10 parts by weight of the glycidyl group-containing compound (C), the compatibility between the polyester resin (A) and the acrylic resin (B) is improved, and the curing reaction and crosslinking density are further controlled. Therefore, it is possible to obtain a coating film that is excellent in appearance, gloss, mechanical strength such as impact resistance and flexibility, as well as stain resistance, corrosion resistance, and weather resistance.

Examples of such a glycidyl group-containing compound (C) include terephthalic acid diglycidyl ester and p-oxybenzoic acid diglycidyl ester.

Examples include triglycidyl isocyanurate.

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, calcium carbonate, barium sulfate, and mica; Metal powders such as copper powder, stainless steel powder, and aluminum powder; surface conditioners, ultraviolet absorbers,
Additives such as thermal deterioration inhibitors and antifoaming agents can be added as appropriate.

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.

After uniformly coating metals such as iron, aluminum, copper, zinc, or their alloys, such as stainless steel and brass using a commercially available electrostatic powder coating machine, it is 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 is as follows.

It has excellent coating film appearance such as smoothness and sharpness, gloss, mechanical strength such as VR@ resistance and flexibility, stain resistance, corrosion resistance, and weather resistance, as well as the generation of tar from the paint when it cures. It is industrially useful because it has no yellowing and has very little yellowing of the paint film.

[Production Examples, Examples and Comparative Examples]

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

Production Example [Production of glycidyl group-containing acrylic resin (B)] A mixture consisting of 40 parts of glycidyl methacrylate, 20 parts of β-methylglycidyl methacrylate, 30 parts of methyl methacrylate, 10 parts of cellosolve methacrylate, and 0.5 part of t-butyl perbenzoate was prepared. was added dropwise to 100 parts of xylene heated to 155°C under pressure and polymerized, and then the xylene was removed and the number average molecular weight was 1.
0000 acrylic resin (B-1) was obtained.

Next, using the same amount of monomer as that used for the acrylic resin (B-1) except for changing the addition/preposition of t-butyl perbenzoate, from 1.0 parts to several parts of t-butyl perbenzoate, Acrylic resin (B-2) with an average molecular weight of 5000 was mixed with t-butyl perbenzoate 2,
From 0 parts, acrylic resin with number average molecular ff11500 (
B-3), and from 4.0 parts of t-butyl perbenzoate, acrylic resin (B-4) with a number average molecular weight of 500, t
-Butyl perbenzoate From 5.0 parts, an acrylic resin (B-5) having a number average molecular weight of 300 was obtained.

Examples 1-7. Comparative Examples 1 to 8 All components of the compositions of Examples 1 to 7 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 was melt-kneaded at a temperature of 80 to 100° C. using an extrusion kneader (Bus Co., Ltd., trade name Busco Kneader PR-46), and after cooling, it was pulverized using a hammer-type impact pulverizer. Next, the mixture was filtered 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 with a thickness of 0.8 mm and baked under the conditions shown in Table 2 to obtain each cured coating. The coating performance of the test pieces obtained is shown in Table 2.

As is clear from the results of Examples 1 to 7, the coating films obtained from the powder coating compositions of the present invention have excellent coating film appearance, gloss, impact resistance, flexibility, stain resistance, corrosion resistance, Excellent weather resistance,
It has no volatile matter (tar) and has excellent yellowing resistance.

On the other hand, the content of polyester resin (A) is 95
Comparative Example 1, which exceeds parts by weight, has impact resistance.

Comparative Example 2, which has poor ductility, stain resistance, corrosion resistance, and weather resistance, and has a polyester resin (A) content of less than 70 parts by weight, has poor paint film appearance, gloss, rtrN resistance, ductility, and corrosion resistance. inferior to

Comparative Example 3 in which the number average molecular weight of the acrylic resin (B) exceeds 6000 has poor coating film appearance, gloss, impact resistance, flexibility,
Acrylic resin (B) has poor stain resistance, corrosion resistance, and weather resistance.
Comparative bowl 4 with a number average molecular weight of less than 500 has a coating film appearance,
Endurance? #Strongness, flexibility.

Poor corrosion resistance.

Comparative Example 5, in which the content of the glycidyl group-containing compound (C) exceeds 10 parts by weight, is poor in stain resistance and weather resistance, and Comparative Example 6, in which the content of the glycidyl group-containing compound (C) is less than 1 part by weight, is poor. , poor paint film appearance, impact resistance, ductility, stain resistance, corrosion resistance, and weather resistance.

Also, JP-A No. 60-120764 Ml LuIJ
Comparative Example 7 using the shown blocked isocyanate compound had poor stain resistance and weather resistance, and had low volatile content (tar).
It also has poor yellowing resistance.

Furthermore, Comparative Example 8, which uses glycidyl phthalate and a polyester resin containing a carboxyl group, disclosed in JP-A-59-108065, is inferior in stain resistance, corrosion resistance, and weather resistance.

Claims (1)

[Claims] (A) An acid value of 10 to 100 and a glass transition temperature of 50 to 8
70 to 95 parts by weight of a polyester resin having a number average molecular weight of 2,000 to 8,000 at 0°C 5 to 30 parts by weight of an acrylic resin containing 20 to 60% by weight of the above monomers and a glycidyl group and/or β-methylglycidyl group with a number average molecular weight of 500 to 6000; A powder coating composition comprising a glycidyl group-containing compound of 1 to 10 parts by weight.