JPS5917746B2 - Composition for powder coating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a composition suitable for powder coating.

Powder coatings such as electrostatic coatings are general coatings. Compared to traditional coatings, they do not use solvents, so there are no pollution or hygiene problems, the performance of the coating is superior, there is less loss of raw materials, and it is easier to automate. Significantly developed. Polyolefins, epoxy resins, polyvinyl chloride resins, polyamide resins, polyacrylic resins, polyester resins, etc. are used as resins for powder coating. It is widely used because of its excellent properties, food hygiene, etc., and because it is inexpensive.

When using polyolefin for powder coating, it is more difficult to use than homopolymers such as polyethylene or polypropylene.
It is better to use copolymers such as ethylene-propylene copolymer, ethylene-butene copolymer, ethylene-vinyl acetate copolymer, propylene-ethylene copolymer, propylene-butene copolymer, etc. Flexibility, impact strength,
It has become clear that coatings with excellent flattening strength, stress and cracking resistance can be obtained.

However, when applying electrostatic coating, the adhesion of powder is good with homopolymers such as ethylene and propylene, but with copolymers such as those mentioned above, as shown in Figure 1. Only a coated layer with uneven powder adhesion is obtained, and even if this is further melted by heat treatment, a coating with an uneven surface as shown in FIG. 2 is obtained. Although polyolefin copolymers have excellent physical properties such as flexibility, impact resistance, flattening resistance, stress/cracking resistance, etc., the powder does not spread evenly onto the coated material. It was not often used for electrostatic painting because it did not adhere easily. The present inventors investigated ways to improve the electrostatic coating method using polyolefins, and found that when a composition is formed with a certain type of compound even if it is a copolymer of the above-mentioned polyolefins, the results shown in Figure 4 are as follows. It was discovered that a film with an excellent appearance could be obtained as shown in the figure.
We have arrived at the present invention. That is, in the present invention, powdered silica is contained in polyolefin powder and polyolefin powder is 0.
．． A powder coating composition comprising 0.01 to 10% by weight and an antioxidant. Polyolefins used in the method of the present invention include homopolymers such as low-density polyethylene, medium-density polyethylene, high-density polyethylene, polypropylene, poly-1-butene, poly-4-methyl-1-benzene, and ethylene-propylene. There are polyolefin copolymers such as copolymers, ethylene-butene copolymers, ethylene monovinyl acetate copolymers, propylene-ethylene copolymers, and propylene-butene copolymers, but copolymers are more common than homopolymers. is preferable.

Furthermore, in order to improve the adhesion between these polyolefins and metals, unsaturated carboxylic acids such as acrylic acid, maleic acid, maleic anhydride, or their anhydrides are added to the homopolymers or copolymers of these polyolefins. Modified polyolefins obtained by blending or graft polymerizing polyolefins, hydroxyl group-containing monomers such as vinyl alcohol, amino group-containing monomers such as acrylamine, amide group-containing monomers such as acrylamide and methacrylamide, or epoxies such as vinyl glycidyl ether. A modified polyolefin obtained by graft polymerization or copolymerization of a group-containing monomer may be used, or a polyolefin homopolymer or copolymer blended with the modified polyolefin obtained in this manner may be used.

Among these polyolefins, polyolefin copolymers, modified polyolefin copolymers, and polyolefin copolymers blended with modified polyolefins are particularly effective when used in the composition of the present invention, and have excellent physical properties of films. It is a combination. The polyolefin used as the composition of the present invention is in powder form, and the average particle size thereof is usually 10 to 300μ, preferably 50 to 200μ.

In general, methods for producing polyolefin powder include extracting the polyolefin directly from the reactor in powder form during polymerization, mechanically crushing polyolefin pellets, and dissolving polyolefin in a solvent at high temperature and then removing it from a poor solvent. In addition, there are methods such as precipitation, but polyolefin powder produced by any method can be used. The powdered silica used as the composition of the present invention has an average particle size of 10 μm or less, particularly preferably 0.1 μm or less.

The amount added is 0.01 to 10% by weight, preferably 0.05 to 0.5% by weight, based on the polyolefin powder. Further, as the antioxidant in the composition of the present invention, for example, 2,6-di-Tert-butyl-p-cresol, tetra-scratch [methylene (3,5-di-Tert-
butyl-4-hydroxy cinnamate)]methane, n
-octadecyl-3-(4/-hydroxy-3'・5'
-di-tert-butylphenyl)propionate, 1
・1-bis(4/-hydroxy-3/-Tert-butyl-5'-methylphenyl)-3-(4'hydroxy-
3'-Tert-butyl-5/-methylphenyl)butane, 4,4'-butylidene-bis(6tert-butyl-m-cresol), 1,3,5-trimethyl-2,4
・6-Tri(47-hydroxy-3'・5/-di-Te
Alkylphenol antioxidants such as rt-butyltolyl)benzene, thioether antioxidants such as dilaurylthiodipropionate, distearylthiodipropionate, laurylstearylthiodipropionate, etc. are used. However, among these, those having a melting point of 80°C or higher are preferred. The amount of antioxidant used is 0.01 to 1.0% by weight based on the polyolefin powder,
Preferably, 0.05 to 0.50% by weight is appropriate.

The composition of the present invention is suitable for powder coating methods, and is particularly effective when applied to electrostatic coating methods or improved methods thereof.

For example, even in cases where it is difficult to obtain a smooth coating layer due to uneven powder adhesion using conventional methods, such as copolymers of ethylene and α-olefin or copolymers of propylene and α-olefin, the composition of the present invention can be used. It has been found that a uniform coated layer can be obtained by forming the coating into a material, and a smooth coating with an excellent appearance can be obtained by melting. In order to obtain the effects of the present invention, it is necessary to coexist both powdered silica and an antioxidant in the polyolefin powder. For example, if powdered silica is not present, polyolefin powder cannot be uniformly deposited, and if an antioxidant is not present, a smooth coating cannot be obtained after melting. Of course, the composition of the present invention can also be applied to conventionally used homopolymers such as polyethylene and polypropylene. Furthermore, pigments, other inorganic fillers, and additives may be added to this composition depending on the purpose of use. Furthermore, if necessary, the composition of the present invention may be applied electrostatically after subjecting the object to a pretreatment such as primer treatment. Next, the composition of the present invention will be specifically explained using Examples. In addition,
In Examples and Comparative Examples, 50 mm x 150 mm
×0.8 mm bright steel plate test piece (manufactured by Japan Test Panel Co., Ltd.) was coated with an electrostatic powder coating device (Studio standard model made by Thermes Co., Ltd.) at a voltage of 60 K and a current of 1501 tA.
The powder was applied to each test piece under conditions of a primary air pressure of 0.5 kg/day and a secondary air pressure of 2 k9/d using a spray gun so that the amount of powder adhered to each test piece was 4.07 to 4.57.

The state of adhesion of the powder was determined by visual inspection. Those with no unevenness on the coated surface as shown in FIG. 3 were evaluated as good, and those with unevenness as shown in FIG. 1 were evaluated as poor. The test piece coated with powder in this way was heated for 20 minutes in an electric furnace kept at 200°C to perform melting treatment. The appearance of the film after melting treatment is determined by visual inspection. As shown in Figure 4, a test piece with no crater-shaped irregularities is considered good, and a specimen with crater-shaped irregularities as shown in Figure 2 is considered defective. And so. The physical properties of the film obtained by electrostatic coating method are determined by Erichsen test (JISZ-22
47).

Example 1 In a stainless steel autoclave with an internal volume of 31 cm, an ethylene-1-butene copolymer (
Melt index 10, density 0.925) 2007
and xylene 1/? was charged and dissolved at a temperature of 90 to 110° C. while performing electromagnetic induction stirring.

Thereafter, when 500 ml of methanol was added to the copolymer solution, the copolymer became powder and precipitated. This powder was separated, thoroughly washed with methanol, and then dried. The average particle size of the powder thus obtained was 100μ, and this powder was mixed with powdered silica with an average particle size of 10μ and tetra-scratch [methylene (3,5-diTe) as an antioxidant.
rt-butyl-4-hydroxyhydrocinnamate)]
Methane (manufactured by Ciba Kirkey Co., Ltd., trade name Irganox 1010) was added in an amount of 0.30% by weight to obtain a uniform composition. This composition was applied to the test specimen using the electrostatic coating device described above. As a result, this composition was uniformly adhered to the test piece as shown in FIG. 3, and the adhesion state was good. This test piece was melt-treated by the method described above. As shown in FIG. 4, the film after melting was uniform and smooth, with a thickness of 300 to 350 μm, and no irregularities were observed. As a result of the Erichsen test of this test piece, the Erichsen value was 8 mm or more. The physical properties of the film were good. Comparative Example 1 A test was conducted in exactly the same manner as in Example 1 except that only powdered silica was added without adding an antioxidant.

Although the adhesion of the powder to the test piece was good as in Example 1, the coating after melting had crater-like irregularities and had an unfavorable appearance. As a result of the Erichsen test of this film, the Erichsen value was 8 mm or more, and the physical properties of the film were good. Comparative Example 2 A test was conducted in the same manner as in Example 1 without adding either powdered silica or antioxidant.

Since the powder did not adhere uniformly to the test piece, the surface had many irregularities, and the adhesion state of the powder was not desirable as shown in FIG. The film after melting had many crater-like irregularities as shown in FIG. 2, and its appearance was poor. Comparative Example 3 A test was conducted in exactly the same manner as in Example 1 except that only the antioxidant was added without adding powdered silica.

Since the powder did not adhere uniformly to the test piece, the surface had many irregularities, and the state of adhesion of the powder was not desirable. After melting, the film had crater-like irregularities and had a poor appearance. Example 2 A stainless steel autoclave with an internal volume of 31 cm was charged with 200 V of propylene-ethylene copolymer (ethylene content 5 mol%, melt index 8, density 091) and xylene 11, and the same procedure as in Example 1 was carried out. processed by the method.

Powdered silica and 1,3,5-trimethyl-2,4,6-tri(4') as an antioxidant were added to the obtained copolymer powder.
-Hydroxy-3',5'-di-tert-butyltolyl)benzene (manufactured by Ciel Chemical Co., Ltd., trade name: Ionox 330) was added in an amount of 0.30% by weight to obtain a uniform composition.

This composition was applied to test specimens in the same manner as in Example 1.
As a result, this composition adhered uniformly to the test piece;
The state of adhesion was good. After melting this test piece, the coating was uniform and smooth, with a thickness of 300 to 300 mm.
It was 50μ. The result of the Erichsen test for this test piece is
The Erichsen value was 8 mm or more, and the physical properties of the film were excellent. Example 3 In a glass-lined autoclave completely purged with nitrogen, an ethylene-propylene-based compound was prepared using dry kerosene as a solvent and an Al/Ti-based solid Ziegler catalyst with a particle size of 5 μm as a catalyst. Polymerization was carried out.

After removing the solvent, the product was washed with methanol and dried, and the resulting product was in the form of a powder with a propylene content of 4 mol % and a melt index 101 density of 0.930. To this powdered copolymer, powdered silica with an average particle size of 8 mμ and 1,1-bis(4'-hydroxy-13'-
Tert-butyl-5/-methylphenyl)-3-(l
-Hydroxy-3/-Tert-butyl-5'-methylphenyl)butane (manufactured by Imperial Chemical Industries, trade name: Dopanol CA) at 0% each.
A uniform composition was obtained by adding 10% by weight and 0.30% by weight.

This composition was applied to test specimens in the same manner as in Example 1.
As a result, this composition adhered uniformly to the test piece;
The state of adhesion was good. After melting this test piece, the coating was smooth and had a thickness of 300 to 350 μm.
It was hot. As a result of the Erichsen test of this test piece, the Erichsen value was 8 mm or more, and the physical properties of the film were excellent.
Example 4 In a stainless steel autoclave with an internal volume of 2 f, ethylene-propylene copolymer (propylene content 4 mol%, melt index 10, density 0.930) 1007,
Toluene 11, maleic anhydride 0.4f7, and digyl peroxide 0.04f were charged and reacted at 120°C, and then cooled to precipitate the product as a powder.

The reaction product was separated separately, washed with acetone, and then dried. The powder thus obtained had a grafting rate of maleic anhydride of 0.1% by weight and a melt index of 8.
It was hot. Using this powder, powdered silica and an antioxidant were added to prepare a composition in exactly the same manner as in Example 1.
Electrostatic painting was performed. As a result, the coating state of the powder was good, and the surface of the coating after melting the test piece was uniform and smooth. The result of the Erichsen test for this test piece is
The Erichsen value was 8 or more, and the physical properties of the film were good. Example 5 Conducted using high-density ethylene homopolymer (manufactured by Mitsui Petrochemical Co., Ltd., trade name Hi-Zex 1300J, melt index 14, density 0.965) 1007, maleic anhydride 5.0 t, and digmyl peroxide 0.57 Grafting was carried out in the same manner as in Example 4 to obtain a modified polyethylene powder having a maleic anhydride grafting rate of 1.0% by weight and a melt index of 5.

Ethylene-propylene copolymer (propylene content 4
Mol%, melt index 10, density 0.930)
Average particle size 1 obtained by solution precipitation method using xylene as a solvent from
To a mixture of 90 parts by weight of 20μ powder and 10 parts by weight of modified polyethylene powder obtained by the above method, 0.30% by weight of powdered silica with an average particle size of 10μ and tetra-scratch [methylene ( 3.5-Ji Ter
t-Butyl-4-hydroxyhydrocinnamate)] Methane (manufactured by Ciba Kirkey, trade name: Irganox 1)
010) 0.30% by weight was added to make a homogeneous composition, which was electrostatically coated.

As a result, the coating state of the powder was good, and the surface of the coating after melting the test piece was uniform and smooth. As a result of the Erichsen test of this test piece, the Erichsen value is 8m
It was over m. The physical properties of the film were good. Comparative example
4 Ethylene-1-butene copolymer 10 used in Example 1
After adding 0.30 parts by weight of each of the powdered silica and antioxidant used in the examples to 0 parts by weight, the mixture was melt-kneaded and granulated using an extruder.

Next, the skeleton granules were mechanically pulverized into powder, and those of 80 mesh or more were sieved to obtain powder with an average particle size of 100 μm. The powder thus obtained was tested in exactly the same manner as in Example 1. Since the powder did not adhere uniformly to the test piece, the surface had many irregularities, and the adhesion state of the powder was not desirable.
After melting, the film had crater-like irregularities and had a poor appearance. Example 6 100 parts by weight of powder of high-density ethylene homopolymer (manufactured by Mitsui Petrochemical Industries, Ltd., trade name HIZEX 51300J, melt index 14, density 0.965) was added with 0.30% by weight of powdered silica, and 0.30% by weight of dilauryl thiodipropionate was added as an antioxidant to form a uniform composition, which was then electrostatically coated.

As a result, the coating state of the powder was good, and the surface of the coating after melting the test piece was uniform and smooth. As a result of the Erichsen test for this test piece, the Erichsen value was 8 m1I
It was over L. The physical properties of the film were good.

[Brief explanation of drawings]

FIG. 1 is a photograph of the appearance of a product coated with ethylene-1-butene copolymer powder by electrostatic coating.

Claims (1)

[Claims] 1. A powder coating composition comprising a polyolefin powder, 0.01 to 10% by weight of powdered silica based on the polyolefin powder, and an alkylphenol-based antioxidant and/or a thioether-based antioxidant.