JPS5825351B2 - powder coating composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermosetting powder coating composition that is stable and does not undergo solid phase reactions, particularly during storage.

Recently, in the field of synthetic resin paints, powder paints have been developed as paints that do not contain volatile components such as solvents or water.
It is attracting attention because it avoids air pollution caused by solvents and can save labor by allowing thick coatings to be applied in one coat.

Among these, thermosetting acrylic powder coatings are considered the most promising in terms of weather resistance, gloss, chemical resistance, solvent resistance, and mechanical strength, and various thermosetting acrylic resins for powder coatings are being developed. An attempt has been made (Special Publication No. 17844, 1973).

These have excellent weather resistance, gloss, chemical resistance, solvent resistance,
Although it is recognized that the powder has good mechanical strength, even if the flowability of the powder particles during baking is good in the early stage of production, if the storage temperature of the paint is high, During long-term storage, a curing reaction (solid phase reaction) progresses in the powder state.
This method has the disadvantage that the flowability of the powder particles during baking is significantly reduced, and the resulting coating film has poor smoothness and gloss.

As a result of continuing research to solve this problem, the inventor of the present invention further added one or more metal salts of fatty acids to a mixture of a glycidyl group-containing acrylic copolymer and a polycarboxylic acid compound. The inventors have discovered that the above-mentioned drawbacks can be solved by using the same method, and have arrived at the present invention.

That is, the present invention provides (A) glycidyl group-containing monomer 5
Ethylenically unsaturated monomers containing ~40% by weight and acrylic esters and/or methacrylic esters 95-6
(B) for 100 parts by weight of an acrylic copolymer copolymerized with 0% by weight and having a glass transition temperature in the range of 10 to 75°C and a number average molecular weight in the range of 1.500 to 30.000. 1 to 40 parts by weight of a polyhydric carboxylic acid compound, and (
C) 0.05 of one or more metal salts of fatty acids
A powder coating composition comprising 10 parts by weight is provided.

The acrylic copolymer, which is one component of the powder coating composition of the present invention, contains 5 to 40% by weight of a glycidyl group-containing monomer, and has a glass transition point of 1.500 to 1.500 at 10 to 75°C.
It is an acrylic copolymer with a number average molecular weight of 30,000.

If the content of the glycidyl group-containing monomer component in the acrylic copolymer (A) is less than 5% by weight of the total monomers, the coating film strength and metal adhesion will decrease, while if it exceeds 40% by weight. This is unsuitable because the smoothness of the painted surface deteriorates due to excessive curing reaction.

Furthermore, if the glass transition temperature of the acrylic copolymer is less than 10°C, the storage stability of the powder coating will decrease;
Exceeding this is inappropriate because the thermal fluidity decreases and the smoothness of the painted surface is impaired.

In addition, the number average molecular weight of the acrylic copolymer is 1.500
If it is less than 30,000, the strength and chemical resistance of the coating film and the storage stability of the paint will decrease, while if it exceeds 30,000, the smoothness of the painted surface will decrease, which is not preferable.

Examples of the glycidyl group-containing monomer used to provide a glycidyl group in the acrylic copolymer of the present invention include glycidyl ester of acrylic acid, methylglycidyl ester of acrylic acid, glycidyl ester of methacrylic acid, and glycidyl ester of methacrylic acid. Methyl glycidyl ester, glycidyl ether of allyl alcohol, methyl glycidyl ether of allyl alcohol, glycidyl ether of meta-allyl alcohol, methyl glycidyl ether of meta-allyl alcohol, N-glycidyl acrylic acid amide,
Examples include glycidyl vinyl sulfonate, and these can be used alone or as a mixture of two or more.

On the other hand, as monomers to be copolymerized with glycidyl group-containing monomers, for example, at the temperature during polymerization and crosstalk,
Monomers that have low reactivity with glycidyl groups and radically copolymerize with the above-mentioned glycidyl group-containing monomers, such as acrylic esters, methacrylic esters, and optionally other ethylenic non-monomers. Saturated monomers may be used alone or in mixtures.

Examples of esters of acrylic acid or methacrylic acid include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, and teracrylate.
t-butyl, cyclohexyl acrylate, acrylic acid 2
-Ethylhexyl, octyl acrylate, acrylic acid 2
-ethyl octyl, dodecyl acrylate, benzyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate,
n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, hexyl methacrylate,
Cyclohexyl methacrylate, 2-ethylhexyl methacrylate, octyl methacrylate, 2-ethyloctyl methacrylate, benzyl methacrylate, dodecyl methacrylate, phenyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-methacrylate -Hydroxyethyl, 2-hydroxypropyl methacrylate, etc.

Other ethylenically unsaturated monomers include fumaric acid dialkyl ester, itaconic acid dialkyl ester, styrene, vinyltoluene, α-methylstyrene, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, methylol acrylamide, alkoxymethylol. Examples include amide, vinyloxazoline, vinyl acetate, vinyl propionate, lauryl vinyl ether, and the like.

The above acrylic ester, methacrylic ester and other ethylenically unsaturated monomers can be used alone or as a mixture of two or more, and the proportion of the acrylic ester and/or methacrylic ester in the total copolymer is preferably 20 to 80% by weight.

Any known method can be used to produce the above acrylic copolymer, such as solution polymerization followed by solvent removal, or suspension polymerization followed by separation to collect the resulting copolymer. This method is simple.

On the other hand, examples of the polyvalent carboxylic acid compound (B) include glutaric acid, adipic acid, pimelic acid, speric acid,
Azelaic acid, sebacic acid, 1,12 dodecanedioic acid, 1
．． 20 Icosane 2 acid, citric acid, maleic acid, citraconic acid, itaconic acid, dalconic acid, fucuric acid, isophthalic acid, hexahydrophthalic acid, cyclohexene 1,2
Examples include polycarboxylic acids such as dicarboxylic acids.

It may also be a polyhydric carboxylic acid anhydride such as succinic anhydride, sebacic anhydride, phthalic anhydride, itaconic anhydride, trimellitic anhydride, etc. Also included are polymers with polyhydric carboxylic acids such as polyester resins, acrylic resins, or polyamide resins.

The polyhydric carboxylic acid compound (B) is used in a proportion of 1 to 40 parts by weight per 100 parts by weight of the acrylic copolymer,
If the amount used is less than 1 part by weight, the crosslinking reaction may not proceed sufficiently during baking, and if it exceeds 40 parts by weight, thermal fluidity may be insufficient in the baking process after applying the powder coating. It is unsuitable for this purpose as it is difficult to obtain a smooth painted surface.

In the metal salt of fatty acid (C), the cross-linking reaction hardly occurs in the heating cross-fertilization process during the production of powder coatings;
The obtained powder coating forms a smooth coating surface without inhibiting the flowability of the powder particles during baking, and has a smooth coating surface at the initial stage of production compared to a composition that does not contain the component (C). It is something that can maintain sex for a long time.

Examples of the metal salts of fatty acids in (C) above include octylic acid, lauric acid, palmitic acid, stearic acid,
There are higher fatty acids such as ricinoleic acid and 2-ethylhexoic acid, and salts of these with metals other than alkali metals such as magnesium, calcium, strontium, barium, zinc, aluminum, tin, and lead, such as zinc stearate and calcium stearate. , lead stearate, barium stearate, calcium laurate, zinc laurate, barium laurate, calcium ricinoleate, and the like.

The above (C) is used alone or as a mixture, and the amount thereof is usually 0.05 to 10 parts by weight, preferably 0.5 parts by weight.
-5.0 parts by weight is preferable (if it is less than 0.05 parts by weight, the desired effect of the present invention will not be achieved, while if it is more than 10 parts by weight, the smoothness of the coating film will be impaired, and the clear In the case of a coating film, it is not preferable because it impairs transparency.

The composition of the present invention includes resins such as epoxy, polyester, polyamide, various resins such as cellulose derivatives, pigments, fluidity regulators, antiblocking agents, ultraviolet absorbers,
One or more commonly used coating additives such as benzoin, antistatic agents, and antioxidants can be added as needed, and the powder coating can be put to practical use with or without additives. It is offered.

When manufacturing powder coatings, (5), (B), (C
)Three components and various resins, pigments, fluidity regulators as necessary,
After appropriately mixing an antiblocking agent, a UV absorber, benzoin, an antistatic agent, an antioxidant, etc., it is heated to 80 to 12
The mixture is thoroughly melted and mixed at about 0°C, cooled, and then ground to form a powder coating.

Regarding painting, the object to be coated is coated using well-known coating methods such as electrostatic spraying and fluidized dipping, and this is usually done in one step.
A powder coating film can be obtained by baking in a baking oven at 50 to 210°C.

Example (1) Production of acrylic copolymer Monomers, dispersant, polymerization initiator, chain transfer agent, and ion-exchanged water were added in the amounts shown in experiment numbers (a) to (c) in Table 1 below. Place it in a four-bottle flask equipped with a stirrer, reflux condenser, thermometer, and nitrogen inlet, replace the air in the flask with nitrogen, raise the temperature while stirring, and raise the temperature to 90°C while stirring.
The polymerization was completed for a certain period of time, and then cooled, and the precipitated pearl-like solid copolymer obtained by the polymerization was filtered and collected, and dried to obtain a solid acrylic copolymer.

(2) Production of powder coatings Solid acrylic copolymers (a) to (C) produced as described above under the temperature condition of 90°C using a heated roll were prepared as shown in Table-2.
Polycarboxylic acid compounds, one or more metal salts of fatty acids, pigments, and fluidity modifiers are melt-mixed in the amounts shown in Experiment Numbers (1) to (3), and after cooling, the mixture is pulverized using a pulverizer. The fractions that passed through a 100-mesh sieve were collected to obtain powder coatings of experiment numbers (1) to (3), respectively.

As a comparative example, in experiment numbers (4) to (6), Table -
A similar method was used except that the amounts of materials used were as shown in 2.

(3) Each powder coating of experiment numbers (1) to (6) shown in Powder Coating Evaluation Table-2,
According to each experiment number, using an electrostatic spray paint machine for powder coating, paint was applied to a satin steel plate of 08mrIL thickness treated with zinc phosphate to the film thickness shown in Table 3 at 180℃ x 3.
A test plate was obtained by baking for 0 minutes, and an evaluation test of the cured coating film was conducted for each item shown in Table 3 according to each experiment number, and the results are shown in Table 3.

In addition, each powder coating was left in a constant temperature and humidity chamber maintained at 40°C and a relative temperature of 70% for 7, 30, 90, and 180 days, and each coating was applied using the method described above. The surface smoothness and gloss (6σ gloss) were evaluated and the results are shown in Table 3.

The smoothness and gloss of the coating film were evaluated by observing and measuring the coating surface with a thickness of 50 μm.

The method for each evaluation test is as follows.

(1) Film thickness The thickness of the coating film was measured from the difference in magnetic force using an electromagnetic film thickness meter.

(2) Smoothness of painted surface According to JIS K-54006,1.

(3) Gloss of painted surface (60 degree specular reflectance) According to JIS K-54006,7.

(4) Mechanical strength (a) After placing the Erichsen-painted board in a constant temperature and humidity chamber at approximately 20°C and 75% RH for 1 hour, it was installed in an Erichsen tester with the painted surface facing outward, and the curvature radius was approximately 101n1rL. Push it out from the back side of the painted board using a punch with a
Expressed in numbers.

(b) Impact resistance According to JIS K-54006, 13, 3, B method.

(5) Gloss retention rate The gloss measurement method is based on JIS K-54006,7.

The gloss retention rate □□□ is calculated by the following formula, and this is defined as the gloss retention rate (to).

(6) Chemical resistance (a) 5% NaOH immersion A coated plate was immersed in a 5% NaOH aqueous solution for a predetermined period of time, and the state of blistering of the coating film was observed.

(b) 5% CH3CO0H immersion A coated plate was immersed in a 5% CH3CO0H aqueous solution for a predetermined period of time, and the state of blistering of the coating film was observed.

(7) Solvent Resistance A cloth was impregnated with toluene, and the coated surface was strongly rubbed back and forth with the cloth to determine the condition of the coated surface.

(100 times of rubbing)

Claims (1)

[Scope of Claims] 1(A) Copolymerizing 5 to 40% by weight of a glycidyl group-containing monomer and 95 to 60% by weight of an ethylenically unsaturated monomer containing an acrylic ester and/or a methacrylic ester. and a glass transition temperature in the range of 10 to 75°C and 15
(B) 1 to 40 parts by weight of a polyhydric carboxylic acid compound, and (C) one kind of metal salt of fatty acid or 0.2 types or more.
A powder coating composition comprising 05 to 10 parts by weight.