JPS6340226B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a novel and useful resin composition for powder coatings, and more specifically, it contains a specified polyester and a (β-methyl)glycidyl group-containing vinyl polymer as essential components. The present invention relates to a composition comprising the following. Conventional powder coatings that combine a carboxyl group-containing polyester resin and an acrylic resin have poor compatibility between the two resins, and as a result, the cured coating film does not have sufficient physical properties. Since the appearance of the coating film is also poor, no one that can be put to practical use has yet been found. However, as a result of intensive research in view of these actual circumstances, the present inventors found that (beta-methyl) glycidyl group-containing vinyl polymers with a specific molecular weight and modified with a monobasic acid (hereinafter referred to simply as " When using a glycidyl group-containing vinyl polymer) as a curing agent for the polyester resin,
The present invention was completed by discovering a resin composition for powder coatings that has excellent not only compatibility but also the physical properties, appearance, and weather resistance of the resulting coating film. That is, the present invention has an acid value of 20 to 200 mgKOH/g.
The polyester (A) has a softening point (ring and ball method) of 80 to 150°C and a number average molecular weight of 1000 to 10000.
60 to 97% by weight and 3 to 40% by weight of a (β-methyl)glycidyl group-containing vinyl polymer (B) having a number average molecular weight of 300 to 5000 modified with a monobasic acid as essential components. The present invention provides a resin composition for powder coatings comprising: Here, the polyester (A) which is the first component of the composition of the present invention has an acid value of 20 to 200 mgKOH/
g, preferably 25 to 70 mgKOH/g, and a softening point (ring and ball method) of 80 to 150°C, preferably 100 to 130°C.
, and the number average molecular weight is within the range of 1000 to 10000, preferably 2000 to 5000, and as long as it is within this range, it may have a branched structure or a linear structure. But that's fine. There are no particular restrictions on the method for producing the polyester (A), and well-known and commonly used methods can be applied as they are, and the acid component and alcohol component are both well-known and commonly used dibasic acids and tribasic acids. The above polybasic acids can be used, as well as dihydric alcohols, trihydric alcohols and higher polyhydric alcohols. Therefore, to list only typical acid components and alcohol components, first, terephthalic acid,
Isophthalic acid, phthalic acid, methyl terephthalic acid,
trimellitic acid, pyromellitic acid and their anhydrides; or adipic acid, sebacic acid, succinic acid, maleic acid, fumaric acid, tetophhydrophthalic acid, methyl-tetophhydrophthalic acid, hexahydrophthalic acid, methyl-hexahydrophthalic acid and their anhydrides, while alcohol components include ethylene glycol, propylene glycol, 1,3-butanediol, 1,4-
Butanediol, 1,6-hexanediol, neopentyl glycol, bishydroxyethyl terephthalate, hydrogenated bisphenol A, ethylene oxide or propylene oxide adduct of hydrogenated bisphenol A, trimethylolethane, trimethylolpropane, glycerin ,
pentaerythritol and 2,2,4-trimethylpentane-1,3-diol, and monoepoxy compounds can also be used as one of the glycol components. On the other hand, the glycidyl group-containing vinyl polymer (B) modified with the monobasic acid described above, which is the second component of the composition of the present invention, has a number average molecular weight in the range of 300 to 5000, preferably 500 to 3000. (β-methyl)glycidyl (meth)acrylate from 20 to 99
% by weight, preferably 40-78% by weight, and 0-50% by weight of other vinyl monomers, preferably 20-40% by weight.
% by weight, monobasic acid 1-30% by weight, preferably 2-30% by weight
It is obtained from 20% by weight. There are no particular restrictions on the method of modifying glycidyl group-containing vinyl polymers with monobasic acids, and methods include methods in which (β-methyl)glycidyl (meth)acrylate and monobasic acid are esterified and polymerized in advance, Sometimes, (β-methyl)glycidyl (meth)acrylate and a monobasic acid are allowed to coexist and esterification and polymerization are carried out simultaneously, or even after the completion of polymerization, a monobasic acid is added to effect esterification. is applicable. If the molecular weight of such a polymer is lower than 300, the mechanical strength of the resulting coating film will be insufficient, and smoke will be emitted when the coating film is baked; In either case, it is unsuitable because not only will the film quality or smoothness be poor, but the compatibility between the resins will also be poor, and the crosslinking reaction will not proceed sufficiently, resulting in poor coating film strength. be. In addition, if the amount of (β-methyl)glycidyl (meth)acrylate is less than 20% by weight,
Since the compatibility with the polyester (A) deteriorates and the reaction with the polyester (A) becomes insufficient, a good cured coating film cannot be obtained. Such (β-methyl)glycidyl (meth)acrylates include glycidyl acrylate, glycidyl methacrylate, β-methylglycidyl acrylate, and β-methylglycidyl methacrylate. For this (β-methyl)glycidyl (meth)acrylate, vinyl monomers that may be used as copolymerization components include styrene,
Typical examples include (meth)acrylic acid ester, fumaric acid diester, acrylonitrile, acrylamide, etc. Among these (meth)acrylic acid esters, methyl methacrylate and cellosolve methacrylate are particularly suitable for polyester (A).
This is particularly preferred because of its excellent compatibility with It goes without saying that in addition to this, any material can be used as long as it can be copolymerized with the glycidyl (meth)acrylate. In addition, the monobasic acid used to modify the glycidyl group-containing vinyl polymer is also a component to improve the compatibility with the polyester (A), and if the amount is less than 1% by weight, the effect of its introduction is On the other hand, if it exceeds 30% by weight, the weather resistance of the resulting coating film will be poor, so it is unsuitable. Any of aromatic, aliphatic, or alicyclic acids can be used as the monobasic acid, but aliphatic monobasic acids are particularly preferred in terms of the smoothness, gloss, and sharpness of the coating film. preferable. Examples of monobasic acids include benzoic acid, paratertiary butylbenzoic acid and hydrogenated products thereof, caproic acid, capric acid, lauric acid, myristic acid,
Examples include palmitic acid, stearic acid, arachidic acid, behenic acid, and isomers in which these alkyl groups are branched. Furthermore, even if it is a polybasic acid, it is of course possible to use a monobasic acid obtained by esterification or etherification with one carboxyl group remaining. There are no particular restrictions on the method for producing the polymer (B), and well-known and commonly used methods can be applied as they are, but a solution polymerization method is particularly recommended because the molecular weight can be easily adjusted. The resin composition of the present invention contains each of the above-mentioned polyesters (A) and a glycidyl group-containing vinyl polymer (B) modified with a monobasic acid, and the ratio of these two components used is , 60-97 parts and 3-
40 parts, preferably 70-90 parts and 10-30 parts. The composition of the invention thus obtained contains pigments or other fillers, flow modifiers such as 2-ethylhexyl acrylate polymers or silicones, optionally various catalysts such as amines, imidazole or metal soaps, or other additions. It is then mixed with an extruder, etc., and then pulverized to form a powder coating. As a powder coating method, known methods such as electrostatic coating or fluidized dip coating can be employed. Next, the present invention will be specifically explained with reference to Examples, where all parts are by weight. Reference Example 1 (Polyester Preparation Example) A mixture consisting of 2049 parts of neopentyl glycol, 1911 parts of dimethyl terephthalate, and 1.1 parts of zinc acetate was gradually heated to 210°C while removing the generated methanol from the system. 67 parts of adipic acid, 1375 parts of terephthalic acid, and 1.5 parts of dimethyl oxide were added, and the temperature was raised to 240°C over 10 hours.
Thereafter, the temperature of the reaction product was lowered to 180°C, and 330 parts of trimellitic anhydride was added to obtain a polyester having an acid value of 35, a softening point of 126°C, and a number average molecular weight of 3000. This is referred to as "polyester (A-1)". Reference Example 2 (same as above) A mixture consisting of 951 parts of neopentyl glycol, 566 parts of ethylene glycol, 1836 parts of dimethyl terephthalate, and 1.8 parts of zinc acetate was gradually heated to 210°C while removing the generated methanol from the system. Later, 1570 parts of isophthalic acid and 2 parts of dibutyltin oxide were added, and the temperature was raised to 240°C over 10 hours.
Further, the reaction was continued at the same temperature to achieve an acid value of 25 and a softening point of
A polyester having a temperature of 105°C and a number average molecular weight of 3,700 was obtained. This is referred to as "polyester (A-2)". Reference Example 3 (Preparation example of glycidyl group-containing vinyl polymer modified with monobasic acid) β-methylglycidyl methacrylate 15 parts Glycidyl methacrylate 40 parts Methyl methacrylate 40 parts t-butyl perbenzoate 1 part and cumene hydroperoxide 0.5 After dropping the mixture into 100 parts of xylene and 5 parts of 2,2-diethylhexanoic acid under pressure at 150°C to polymerize, the xylene was removed, resulting in polymerization with a number average molecular weight of 1500 and an epoxy equivalent of 290. I got something. This is referred to as "polymer (B-1)". Reference Example 4 (same as above) 20 parts of β-methylglycidyl methacrylate 40 parts of glycidyl methacrylate 35 parts of cellosolve methacrylate A mixture of 2 parts of t-butyl perpenzoate was mixed with 100 parts of xylene at 155°C and
After polymerization by dropping into 5 parts of 2-diethylhexanoic acid and removing xylene, the number average molecular weight was 1300.
A polymer having an epoxy equivalent of 270 was obtained. This is referred to as "polymer (B-2)". Example 1 Polyester (A-1) obtained in Reference Example 1
85 parts and the polymer (B-1) obtained in Reference Example 3.
15 parts, plus 50 parts of titanium oxide and 1 part of "Acronal 4F" (flow regulator manufactured by Bayer, West Germany)
The mixture was mixed using an extruder, cooled, and crushed to obtain a powder coating. Next, this paint was applied to a mild steel plate and baked at 180°C for 20 minutes to obtain a paint film. Example 2 Polyester (A-2) obtained in Reference Example 2
89 parts and the polymer (B-1) obtained in Reference Example 4.
A coating film was obtained in the same manner as in Example 1, except that 11 parts were used. Example 3 Except for using 83 parts of the polyester (A-1) of Reference Example 1 and 17 parts of the polymer (B-2) of Reference Example 4,
A coating film was obtained in the same manner as in Example 1. Table 1 summarizes the performance of the coating films obtained in each example.
It had excellent weather resistance.

【table】

The gloss retention rate is shown in [Table].

Claims (1)

[Claims] 1 (A) An acid value of 20 to 200 mgKOH/g and a softening point of
80~150℃ and number average molecular weight 1000~
10,000 polyester (60-97% by weight) and (B) a number average molecular weight of 300-97% modified with a monobasic acid.
1. A resin composition for a powder coating, comprising 3 to 40% by weight of a vinyl polymer containing a glycidyl group or a β-methylglycidyl group of 5,000 as an essential component.