JPS6150108B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a resin composition that forms a powder coating that has extremely excellent mechanical strength and corrosion resistance, and also has good gloss, sharpness, and smoothness. It is known to use a combination of a vinyl polymer having a glycidyl group or a hydroxyl group and various curing agents in powder coatings. However, coating films obtained using these known resin compositions are inferior in mechanical strength or corrosion resistance compared to coating films using compositions whose main components are polyester or epoxy resins, due to the structure of the resin. considered to be a fundamental flaw. Furthermore, since powder coatings do not contain solvents, in order to obtain a smooth coating film, melting and smoothing is required before crosslinking and curing during heating, and for this purpose, the resin used must have as narrow a molecular weight distribution as possible. It is necessary that there be. For example, as such a powder coating,
The smaller the ratio of weight average molecular weight/number average molecular weight of the polymer as described in Publication No. 29838, the more preferable it is, that is, 1.7 to 1.8 is suitable, and the maximum is considered to be 2.1, and it is exclusively used for high molecular weight products with narrow molecular weight distribution. Progress has been made in the development of polymers that do not contain many substances. As a result of intensive research, the present inventors have found that polymers with specific compositions and specific molecular weights and molecular weight distributions have good coating film appearance even when the ratio of weight average molecular weight/number average molecular weight is 2.1 or more; In the above, it was discovered that the mechanical strength and corrosion resistance of the coating film were dramatically improved, and the present invention was achieved. That is, the present invention provides (1) 10 to 80% by weight of styrene (hereinafter expressed as %), (2) 0% of methacrylic acid methyl ester.
~50%, (3) dialkyl ester of unsaturated aliphatic dibasic acid and/or (meth)acrylic acid alkyl ester having 2 or more carbon atoms of alkyl group 3~50%,
(4) Comprising 5 to 40% of (meth)acrylic acid (β-methyl)glycidyl ester and/or acrylic acid hydroxyalkyl ester with a softening point of 80 to
A resin composition for powder coatings comprising a vinyl polymer at 140°C, with a number average molecular weight of 3,000 to 10,000, a weight average molecular weight of 20,000 to 50,000, and a ratio of number average molecular weight to weight average molecular weight of 1:2.8 to 1:10. It is intended to provide something. Styrene, which is the first raw material of the polymer used in the present invention, improves the storage stability of powder coatings, the smoothness and sharpness of the coating film, and when used in combination with maleic acid and fumaric acid ester, the coating film It is a raw material that significantly improves the mechanical strength of. Its usage is
If it is less than 10%, the storage stability and smoothness of the coating film will be insufficient, and if it exceeds 80%, the weather resistance of the coating film will be poor. It is. The second raw material, methacrylic acid methyl ester, is a raw material to improve the hardness and stain resistance of the coating film. If the amount used exceeds 50%, the smoothness of the coating film will be poor, so it is usually less than 50%. Preferably it is 30% or less. The third raw material, dialkyl ester of unsaturated aliphatic dibasic acid and alkyl ester of acrylic acid, is a raw material that improves the smoothness, gloss, adhesion, mechanical strength, and corrosion resistance of the coating film in a well-balanced manner. Examples of dialkyl esters of unsaturated aliphatic dibasic acids include dialkyl maleates, dialkyl fumarates, dialkyl itaconates, and alkyl esters of (meth)acrylic acid in which the alkyl group has 2 or more carbon atoms. Examples include ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. Among these esters, maleic ester,
Fumaric acid ester is preferable because it has the advantage of significantly improving the mechanical strength of the coating film when used in combination with styrene. If the amount of these esters used is less than 3%, the above effect will be insufficient, and if it exceeds 50%, the stain resistance will be poor. be. The fourth raw material, (β-methyl)glycidyl (meth)acrylate and hydroxyalkyl ester of (meth)acrylic acid, is a crosslinking raw material for improving the mechanical strength of the coating film. (β-methyl)
Examples of glycidyl (meth)acrylate include glycidyl (meth)acrylate and β-methylglycidyl (meth)acrylate, and examples of hydroxyalkyl esters of (meth)acrylic acid include 2-hydroxyethyl (meth)acrylate.
Acrylate, 2-hydroxypropyl (meth)
Examples include acrylate, 4-hydroxybutyl (meth)acrylate, and the like. If the amount of these esters used is less than 5%, the mechanical strength of the coating film will not be sufficient, and if it exceeds 40%, the smoothness of the coating will be poor, so it is usually 5 to 40%, preferably 15%. ~
A range of 30% is appropriate. It is advantageous if the proportion of β-methyl type in the amount of glycidyl ester used is 1/3 or more, since a coating film with particularly excellent smoothness can be obtained. In addition to the above-mentioned raw material monomers, the following monomers may be used in small amounts in a range that does not impair the characteristics of the present invention. Examples include (meth)acrylamide vinyl chloride, vinyl acetate, substituted styrene, and (meth)acrylonitrile. The polymer in the present invention can be obtained by polymerizing the monomers in a predetermined proportion by a well-known method such as a solution polymerization method, a bulk polymerization method, or a suspension polymerization method. Such polymers may be a mixture of two or more. The softening point of such polymers is 80℃
If the number average molecular weight is less than 3,000, the weight average molecular weight is less than 20,000, or the ratio of number average molecular weight to weight average molecular weight is less than 1:2.8, the mechanical strength and corrosion resistance of the coating film will be insufficient, and it will soften. If the point is over 140℃, the number average molecular weight is over 10,000, the weight average molecular weight is over 50,000, and the ratio of number average molecular weight to weight average molecular weight is over 1:10, the smoothness of the coating will be poor, so it is normal. Softening point: 80~140℃, number average molecular weight: 3000~10000, weight average molecular weight: 20000~
50000, the ratio of number average molecular weight to weight average molecular weight is 1:2.5 to 1:10, preferably the softening point is 90 to 120°C,
Number average molecular weight 4000-9000, weight average molecular weight 25000
40,000, and the ratio of number average molecular weight to weight average molecular weight is suitably in the range of 1:2.8 to 1:5. The composition of the present invention is made by blending various curing agents with the above-mentioned polymer, and when the functional group of the polymer is a glycidyl group, the curing agent to be blended includes:
Examples include polyhydric carboxy compounds, polyhydric phenols, and in the case of hydroxy groups, examples include amino resins such as hexamethoxymethylmelamine and tetrabutoxybenzoguanamine, blocked polyisocyanates, and N-acyl polylactam compounds. The amount of the curing agent used is usually 5 to 30 parts, preferably 8 to 20 parts, per 70 to 95 parts by weight of the polymer (as shown below). Various catalysts that promote the curing reaction can be added to such compositions as necessary, and the coating films obtained using the compositions of the present invention have extremely excellent mechanical strength,
Although it has corrosion resistance, as is well known, an epoxy resin can also be added for the purpose of improving corrosion resistance. Furthermore, for the purpose of preventing craters and improving the smoothness of the coating film, a polymer of acrylic acid long-chain alkyl ester and a fluorine compound may also be blended. Powder coatings can be prepared by any known method. The resulting powder coating can be applied by any known method such as electrostatic spraying or fluidized dipping. The present invention will be explained below based on examples. In addition, parts in the examples mean parts by weight. Example 1 40 parts of styrene, 20 parts of methyl methacrylate, 10 parts of di-n-butyl fumarate, 10 parts of n-butyl acrylate, 15 parts of β-methylglycidyl methacrylate, 5 parts of glycidyl methacrylate, 2 parts of azobisisobutyronitrile 1 part of benzoyl peroxide was added dropwise over 4 hours to a mixture of 70 parts of toluene and 30 parts of n-butanol heated to 100°C, and the reaction was continued for an additional 10 hours.
The solvent was removed with Hg until no solvent was distilled out to obtain a solid polymer. The resulting polymer has a softening point of 114
℃, number average molecular weight 8600, weight average molecular weight 32000,
The ratio of weight average molecular weight to number average molecular weight was 3.7.
13 parts of decanedicarboxylic acid is added to 87 parts of this vinyl polymer.
1 part, 30 parts of titanium oxide, 4 parts of Epiclon 1050 (an epoxy resin made by Dainippon Ink), and 1 part of Modaflow (a fluidity regulator made by Monsanto) were mixed, melted and kneaded in an extruder, and then ground into 200 mesh. The amount that passed through the wire mesh was applied to a zinc phosphate treated steel plate by electrostatic spraying and baked at 190°C for 20 minutes. Table 1 shows the physical properties of the coating film obtained. Comparative Example 1 In Example 1, n-butyl acrylate 10
15 parts of β-methylglycidyl methacrylate and 5 parts of glycidyl methacrylate were replaced with 18 parts of n-butyl acrylate and 12 parts of methacrylic acid to obtain a solid polymer. To 60 parts of this polymer, 40 parts of Epiclon 2050 (Dainippon Ink & Chemicals, epoxy resin, epoxy equivalent: about 600), 30 parts of titanium oxide, and 1 part of Modaflow were added, and a coating film was obtained in the same manner as in Example 1. Ta. Its physical properties are shown in Table 1. Comparative Example 2 In Example 1, methyl methacrylate 20
10 parts of di-n-butyl fumarate and 10 parts of n-butyl acrylate to 25 parts of methyl methacrylate.
1 part, 0 parts of di-n-butyl fumarate and 15 parts of n-butyl acrylate to obtain a solid polymer. Thereafter, a coating film was obtained in the same manner as in Example 1. Its physical properties are shown in Table 1. Example 2 In the same manner as in Example 1, 50 parts of styrene, 10 parts of dimethyl maleate, and 15 parts of n-butyl acrylate were added.
parts, 20 parts of β-methylglycidyl methacrylate,
Polymerize using 5 parts of glycidyl methacrylate to obtain a softening point of 113°C, a number average molecular weight of 7200, a weight average molecular weight of 29000, and a ratio of weight average molecular weight to number average molecular weight.
A polymer of 4.0 was obtained. Using this, a coating film was obtained in the same manner as in Example 1. The physical properties of the coating film are shown in Table 1. Example 3 A product with a softening point of 116 was prepared in exactly the same manner as in Example 2 except that the same amount of 2-hydroxyethyl methacrylate was used instead of glycidyl methacrylate.
℃, number average molecular weight 8100, weight average molecular weight 33000,
A polymer having a weight average molecular weight to number average molecular weight ratio of 4.1 was obtained. Using this, a coating film was obtained in the same manner as in Example 1. The physical properties of the coating film are shown in Table 1. Example 4 To 83 parts of the vinyl polymer obtained in Example 3, 4 parts of Epiclon 1050 (bisphenol type epoxy resin manufactured by Dainippon Ink Co., Ltd.) and 13 parts of decanedicarboxylic acid were added.
A coating film was obtained in the same manner as in Example 1 by blending 1 part of hexamethoxymethyl melamine, 30 parts of titanium oxide, and 1 part of Modaflow.

[Table] Comparative example Styrene 40 parts, Methyl methacrylate 20
10 parts of n-butyl methacrylate, 20 parts of glycidyl methacrylate, 4 parts of azobisisobutyronitrile as a polymerization initiator, and 1 part of tert-butyl perbenzoate, except that the softening point was 108°C in the same manner as in Example 1. A polymer having a weight average molecular weight/number average molecular weight of 1.8/1 was obtained. A coating film was obtained using the polymer. The coating film had poor mechanical strength, especially bending resistance (cracking occurred even at φ=10 mm), and salt spray resistance.

Claims (1)

[Scope of Claims] 1 (1) Styrene 10 to 80% by weight (2) Methacrylic acid methyl ester 0 to 50% by weight (3) Dialkyl ester of unsaturated aliphatic dibasic acid and/or carbon number of alkyl group 2 (4) (meth)acrylic acid (β-methyl)glycidyl ester and/or hydroxyalkyl ester of (meth)acrylic acid 5 to 40% by weight, softening Point 80-140℃, number average molecular weight 3000
~10000, weight average molecular weight 20000~50000, ratio of number average molecular weight to weight average molecular weight 1:2.8~1:
A resin composition for powder coatings comprising 10 vinyl polymers.