JPS6213996B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention particularly relates to a polyester-epoxy powder coating resin composition that can form a cured coating film with excellent weather resistance and stain resistance, and has improved skin irritation. A polyester/epoxy powder coating made by blending bisphenol A/diglycidyl ether with a carboxyl group-containing polyester resin is applied to an object and cured by heating.The coating film has excellent corrosion resistance and mechanical properties. Poor weather resistance, 2
After ~3 months of outdoor exposure, the luster disappears and a so-called yoking phenomenon occurs. In addition, polyester/epoxy powder coatings are made by blending p-oxybenzoic acid glycidyl ester ether as a curing agent with this carboxyl group-containing polyester resin.
Although it can form a cured coating film with excellent weather resistance, this p-oxybenzoic acid glycidyl ester ether tends to cause skin irritation and is an occupational health problem during powder coating manufacturing and powder coating. . Moreover, polyesters using this p-oxybenzoic acid glycidyl ester ether as a curing agent.
Epoxy powder coatings tend to block during storage, which is a pending problem that is difficult to solve simply by reducing the amount of the glycidyl ester ether curing agent. Body paints generally have poor stain resistance, and cannot be used in home appliances such as refrigerators or washing machines, which require particularly strict stain resistance, and their uses are naturally limited. However, as a result of intensive research aimed at improving the various drawbacks mentioned above, the present inventors have completed the present invention. That is, the inventors found that the acid value was 20 to 300 mg
Polyester resin 8 with KOH/g and a softening point (according to the ring and ball method; the same applies hereinafter) of 70 to 140°C
~93 parts by weight, and p-oxybenzoic acid diglycidyl ester ether and general formula (In the formula, R ₁ and R ₂ are a hydrogen atom or an alkyl group having 1 to 8 carbon atoms.) Obtained by an addition reaction with a heterocyclic compound represented by the formula, and having a glycidyl group at the end. , softening point 50~
The object of the present invention is to provide a resin composition for powder coating, which contains 92 to 7 parts by weight of an adduct at 150°C. Here, the above-mentioned polyester resin refers to a resin obtained by reacting a polyhydric alcohol component and a polybasic acid component under conditions such that carboxyl groups remain. To name a few, ethylene glycol, propylene glycol, 1,3-butanediol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, dipropylene glycol, 1,4-cyclohexanedimethanol, neopentyl glycol, Isopentyl glycol, bishydroxyethyl terephthalate, hydrogenated bisphenol A, ethylene oxide adduct of hydrogenated bisphenol A, trimethylolpropane, glycerin, pentaerythritol, 2,2,4-trimethylpentane-1,3-
diols or monoepoxy compounds, and on the other hand, typical polybasic acid components include terephthalic acid, isophthalic acid, phthalic acid,
Methyl terephthalic acid, trimellitic acid, pyromellitic acid, adipic acid, sebacic acid, succinic acid, maleic acid, fumaric acid, tetrahydrophthalic acid, methyltetrahydrophthalic acid, hexahydrophthalic acid or methylhexahydrophthalic acid, and these and polybasic acid anhydrides such as phthalic anhydride, trimellitic anhydride or pyromellitic anhydride. The polyester resin, which is the first component constituting the composition of the present invention, can be obtained by any known and commonly used method as long as the carboxyl group remains, but the most preferred method is There is a method as follows. First, a polyester containing hydroxyl groups and having a molecular weight of 1,000 to 30,000 is produced by reacting the above-mentioned polyhydric alcohols with polybasic acids or their reactive derivatives in such a proportion that the hydroxyl groups are in excess of the carboxyl groups. and then react with polybasic acid anhydride. Thus, the composition of the present invention has a suitable acid value and softening point, that is, an acid value in the range of 20 to 300, and a temperature of 70 to 140 °C, more preferably 100 to
Polyester resins with softening points in the range 130°C can be obtained. On the other hand, the adduct, which is the second component constituting the composition of the present invention, is an addition reaction product between p-oxybenzoic acid diglycidyl ester ether and the heterocyclic compound represented by the general formula []. Among these, p-oxybenzoic acid diglycidyl ester ether can be represented by the following general formula []. (In the formula, m is preferably 0 to 4.) First, in order to obtain p-oxybenzoic acid diglycidyl ester ether in which m is represented by 1 to 4 in the above general formula [], p-oxybenzoic acid diglycidyl ester ether in which m is represented by 0
- Oxybenzoic acid diglycidyl ester ether and p-oxybenzoic acid are combined, for example, with a quaternary ammonium salt such as triethylbenzylammonium chloride, a tertiary amine such as triethylamine or dimethylbenzylamine, or a The reaction may be carried out in the presence of a basic catalyst such as an alkylphosphine, and m can be adjusted to a desired value by appropriately adjusting the blending ratio of p-oxybenzoic acid diglycidyl ester ether and p-oxybenzoic acid. can be adjusted to the value of On the other hand, representative examples of the heterocyclic compounds represented by the general formula [] include hydantoin, 5,5-dimethylhydantoin, 5,5-diethylhydantoin, 5,5-dipropylhydantoin, 5, 5-dibutylhydantoin, 5,5
- Dipentylhydantoin, 5-methylhydantoin or 5-ethylhydantoin. The adduct, which is the second component of the composition of the present invention, can basically be represented by the following general formula [], [In the formula, n is preferably 1 to 10, and R is the formula (However, m in the formula is preferably 0 to 4.) R ₁ and R ₂ are a hydrogen atom or an alkyl group having 1 to 8 carbon atoms. ] The adduct is prepared in the presence of a basic catalyst as described above,
Easily produced by reacting the heterocyclic compound represented by the general formulas [] and [] with p-oxybenzoic acid diglycidyl ester ether at 100 to 200°C, preferably 130 to 180°C. By adjusting the blending ratio of both, n in the above general formula can be adjusted to a desired value, and thus the softening point suitable for the composition of the present invention is 50 to 150°C, More preferably, the temperature range is from 80 to 120°C, and an adduct having a glycidyl group at the end can be formed. The resin composition for powder coating according to the present invention contains 8 to 93 parts by weight and 92 to 7 parts by weight of the above-mentioned polyester resin and adduct, respectively. If the usage ratio of this additive is less than 7 parts by weight, the stain resistance, which is one of the features of the present invention, will be reduced, and if it exceeds 92 parts by weight, the weather resistance will be significantly reduced. Both are unfavorable. In addition, since the composition of the present invention has excellent curability by itself, the powder coating obtained from the composition of the present invention satisfies normal baking conditions, but it can be baked at lower temperatures or at lower temperatures. In order to cure in a shorter time, a curing accelerating catalyst such as a tertiary amine, an imidazole derivative, or a carboxylic acid metal salt can be added, if necessary. Among these curing accelerating catalysts, imidazole derivatives are particularly useful because they also have the effect of suppressing the formation of pinholes on the coating surface. To prepare a powder coating, the composition of the present invention is blended with a known and commonly used flow control agent, pigment or other filler, optionally a color scorch inhibitor or a curing accelerating catalyst as described above, and then melt-kneaded. A suitable method is to compact the material and then pulverize it. The powder coating thus obtained is applied to the object to be coated by a known and commonly used method such as fluidized dip coating or electrostatic spray coating at a temperature of 130°C or higher, preferably 160°C or higher.
When cured by baking at 230°C, it is possible to form a cured coating film that has excellent image clarity, corrosion resistance, and mechanical strength, as well as particularly excellent weather resistance and stain resistance. Unlike p-oxybenzoic acid diglycidyl ester ether, which tends to cause skin irritation, p-oxybenzoic acid diglycidyl ester ether derivative is not irritating to the skin, so it can be used safely in terms of occupational health, and it is also safe to use. The composition of the invention also has the advantage of excellent storage stability. Next, the present invention will be specifically explained using examples. All parts hereinafter are based on weight. Reference Example 1 (Example of Preparation of Polyester Resin) A mixture consisting of 1162 parts of neopentyl glycol, 1085 parts of dimethyl terephthalate and 1 part of zinc acetate was heated at 150°C for 1 hour while removing the generated methanol from the reaction system, and then After heating at 210°C for 2 hours, 780 parts of isophthalic acid and 1 part of dibutyltin oxide were added, and the mixture was further maintained at the same temperature for 4 hours, and then heated at 240°C for 10 hours. Thereafter, the temperature of the reaction mixture was lowered to 180°C, 312 parts of trimellitic anhydride was added, and the temperature was maintained for 3 hours until the softening point (according to the ring and ball method) was 118°C.
and a polyester resin having an acid value of 65 (hereinafter referred to as polyester resin 1),
It was then cooled and coarsely crushed. Reference Example 2 (same as above) The amounts of neopentyl glycol, dimethyl terephthalate and zinc acetate were 2049 parts and 1911 parts, respectively.
The same operation as in Reference Example 1 was repeated except that the mixture was heated at 210° C. for 2 hours, and then 67 parts of adipic acid, 1375 parts of terephthalic acid, and 1.5 parts of dibutyltin oxide were added. Thereafter, the same operation as in Reference Example 1 was repeated except that the amount of trimellitic anhydride was changed to 330 parts, and a polyester resin having a softening point of 126°C and an acid value of 35 (hereinafter referred to as This was obtained (referred to as polyester resin 2), cooled, and then coarsely crushed. Reference Example 3 (Preparation of adduct) A mixture consisting of 1000 parts of p-oxybenzoic acid diglycidyl ester ether having an epoxy equivalent of 150 and 206 parts of 5,5-dimethylhydantoin was heated to 160°C with stirring in a nitrogen gas atmosphere. As a result, an adduct (hereinafter referred to as adduct 1) having an epoxy equivalent of 450 and a softening point of 95° C. was obtained. Examples 1 and 2 and Comparative Example 1 After dry-blending the compositions shown in Table 1 (all amounts used are in parts), the mixture was blended using "Conider PR-46" manufactured by Buss, Switzerland. The mixture was melt-kneaded, pulverized, and passed through a 150-mesh wire mesh to obtain various white powder coatings. Next, this powder coating was individually applied to a zinc phosphate treated steel plate by electrostatic spraying and baked at 200°C for 15 minutes. The coating thickness of each of these coatings was approximately 60 microns, and the coating performance and storage stability of each coating were as shown in Table 1. Separately, Taisho Pharmaceutical
Using a test plaster sold by Co., Ltd., 10 people applied p-oxybenzoic acid diglycidyl ester ether, the adduct 1 obtained in Reference Example 3, and the powder coatings of Examples 1 and 2. It was brought into contact with the upper arm and peeled off after a certain period of time to determine the condition of the skin. As a result, in the case of p-oxybenzoic acid diglycidyl ester ether, all 10 people had redness and swelling at the contact area after 12 hours, and the skin irritation was significant, but in the case of other samples, after 48 hours had passed. However, no abnormalities were still observed.

【table】

【table】

[Table] Salt water resistance is determined by making a cut line with a knife on the sample coating surface, spraying 5% saline at 35℃ for 1000 hours, then attaching cellophane tape to the cut area and peeling it off. indicates the peeling width. In addition, stain resistance is determined by applying magic ink, wiping it with absorbent cotton soaked in benzene, and comparing and judging the degree of ink adhesion.

Claims (1)

[Scope of Claims] 1. Polyester resin having an acid value of 20 to 300 mgKOH/g and a softening point (ring and ball method) of 70 to 140°C 8
~93 parts by weight, and p-oxybenzoic acid diglycidyl ester ether and general formula (In the formula, R ₁ and R ₂ are a hydrogen atom or an alkyl group having 1 to 8 carbon atoms.) and 92 to 7 parts by weight of an adduct having a softening point (ring and ball method) of 50 to 150°C.