JPS6135233B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention particularly relates to an epoxy-polyester resin composition for powder coatings that forms a coating film with excellent weather resistance. As is well known, coating films obtained from so-called epoxy-polyester powder coatings containing bisphenol A glycidyl ether type epoxy resin and carboxyl group-containing polyester resin as resin components have excellent corrosion resistance and mechanical performance. However, due to its poor weather resistance, it had the drawback of significantly decreasing gloss and yellowing after short exposure. As a result of intensive research, the present inventors have discovered that the above drawbacks can be improved by containing bisphenol A nuclei and hydrogenated bisphenol A nuclei in a specific ratio in the epoxy resin chain, and have arrived at the present invention. be. The present invention is directed to an epoxy resin containing a bisphenol A nucleus and a hydrogenated bisphenol nucleus at a molar ratio of 5/95 to 40/60 in the same molecule, that is, in the molecular chain of the obtained epoxy resin, and a carboxyl group-containing The present invention relates to a resin composition for powder coatings comprising a polyester resin. A cured coating film for powder coatings made of such a composition not only has excellent weather resistance, but also has excellent corrosion resistance and mechanical properties inherent to epoxy/polyester systems. The molar ratio of bisphenol A nucleus and hydrogenated bisphenol A nucleus in the epoxy resin used is 5/95 to 4.
It is 0/60, more preferably in the range of 10/90 to 30/70. If the above molar ratio is smaller than 5/95, the blocking resistance and curing properties of the powder coating will be reduced, and if it is larger than 40/60, the weather resistance of the coating film will be reduced, so it is preferable. do not have. The ring and ball softening point of epoxy resin is 60~130℃
is suitable, and the epoxy equivalent is 500 to 3000
is appropriate. There is no restriction on the bonding mode of the main chain of the epoxy resin, and it may be only an ether bond, or an ester bond may be added to the ether bond. There are various methods for producing such epoxy resins.
There is. For example, a method of reacting a glycidyl ether type epoxy resin of hydrogenated bisphenol A with bisnol A or hydrogenated bisphenol A, a method of reacting a glycidyl ether type epoxy resin of hydrogenated bisphenol A, and a mixture of a glycidyl ether type epoxy resin of hydrogenated bisphenol A and a glycidyl ether type epoxy resin of bisphenol A. A method of reacting with bisphenol A or hydrogenated bisphenol A, gelling a mixture of a glycidyl ether type epoxy resin of hydrogenated bisphenol A and a glycidyl ether type epoxy resin of bisphenol A with a polyhydric carboxylic acid or polyhydric alcohol. There is a method in which the reaction is carried out with care, and a method in which the epoxy resin obtained by these methods is reacted with a polyhydric carboxylic acid or a polyhydric alcohol, taking care to avoid gelation. In these methods, a Lewis acid such as boron trifluoride is used as a catalyst when hydrogenated bisphenol A is used as a reaction component, and a basic compound is used in other cases. The carboxyl group-containing polyester resin refers to one having a large number of carboxyl groups. It may have a linear structure or a branched structure, but it has a branched structure because it contains a large number of carboxyl groups, especially a branched structure per molecule.
Those with a branched structure having 2.5 or more carboxyl groups are preferred. Regarding acid value, it is usually 20~
150KOHmg/g (unit omitted), more preferably 30-100, and ring and ball softening point 70-150
°C is appropriate. Any known method can be used to produce such polyester resins. Examples of acid raw materials that can be used include terephthalic acid, isophthalic acid, phthalic acid, methylphthalic acid, trimellitic acid, pyromellitic acid, adipic acid, sebacic acid,
Examples include succinic acid, maleic acid, fumaric acid, tetrahydrophthalic acid, methyltetrahydrophthalic acid, hexahydrophthalic acid, and reactive derivatives thereof. Examples of alcohol raw materials include 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, alkylene oxide adduct of hydrogenated bisphenol AA, trimethylolethane , trimethylolpropane, glycerin, pentaerythritol, 2,2,4-trimethylpentane-1,3-diol, etc.
Monoepoxy compounds can also be used as glycols. In order to obtain particularly favorable results, at least one aromatic polyhydric carboxylic acid should be used out of all the acid raw materials used.
70 mol%, and at least aliphatic polyhydric alcohol with 4 or more carbon atoms out of all alcohol raw materials used.
It is preferable to use 40 mol% of the polyhydric alcohol having a cyclohexane ring and 3 to 30 mol% of the polyhydric alcohol having a cyclohexane ring. The composition of the present invention is composed of the above-mentioned epoxy resin and polyester resin, and the blending ratio thereof is such that the equivalent ratio of oxirane group to carboxyl group is 0.5 to 2.0, preferably 0.6 to 1.5. is preferred. Such a composition has good curability and is cured at a temperature of 150°C or higher, preferably 160 to 230°C. However, in order to lower the heating temperature or shorten the heating time, a tertiary amine may be added as necessary. , imidazole derivatives, and carboxylic acid metal salt compounds can be added. In particular, the use of imidazole derivatives is very advantageous because pinholes can be suppressed even when coated thickly. Further, a blocked polyisocyanate compound can also be used as a curing agent in the composition. In order to prepare a powder coating material, a suitable method is to blend the composition of the present invention with a fluidity regulator, pigments and other fillers, additives, etc., melt-knead the composition, solidify it, and then finely pulverize it. The present invention will be explained below based on examples. Parts in the text indicate parts by weight. Synthesis of Epoxy Resin 1 From 900 parts of a hydrogenated bisphenol A diglycidyl ether type epoxy resin with an epoxy equivalent of 480 and 100 parts of Epiclon 850 (manufactured by Dainippon Ink Chemical Industries, bisphenol A diglycidyl ether type epoxy resin with an epoxy equivalent of 180). The mixture was diluted with bisphenol in the presence of 2 parts of N-methylmorpholine.
Reacted with A158 part at 120℃ for 3 hours, softening point 93
Epoxy resin 1 was obtained, having an epoxy equivalent of 1150° and a molar ratio of bisphenol A core to hydrogenated bisphenol A core of 26/74. Synthesis of Epoxy Resin 2 950 parts of the hydrogenated bisphenol type epoxy resin used in the preparation of Epoxy Resin 1 and Epicol
A mixture of 50 parts of N-850 was mixed with 100 parts of bisphenol A in the presence of 2 parts of N-methylmorpholine at 120°C.
After reacting for 2 hours, 37 parts of adipic acid was added and reacted for 2 hours at the same temperature, resulting in a softening point of 88°, epoxy equivalent of 1350, and a molar ratio of bisphenol A nucleus and hydrogenated bisphenol A nucleus of 16/84. Epoxy resin 2 was obtained. Synthesis of Polyester Resin 1 A mixture consisting of 1046 parts of neopentyl glycol, 119 parts of 1,4-cyclohexanedimethanol, 1000 parts of dimethyl terephthalate and 11 parts of zinc acetate was heated to 150°C while removing the methanol produced from the reaction system. After reacting at 210℃ for 2 hours, 47 parts of trimethylolpropane, terephthalic acid
800 parts and 1.5 parts of diptyltin oxide were added and reacted at the same temperature for 4 hours and at 240°C for 10 hours.
The temperature of the reaction mixture was then lowered to 180°C, 313 parts of trimellitic anhydride was added, and the mixture was reacted at the same temperature for 3 hours to obtain polyester resin 1 having a softening point of 125° and an acid value of 62. Synthesis of polyester resin 2 1777 parts of neopentyl glycol, 310 parts of 1,4-cyclohexanedimethanol, 70 parts of 1,6-hexanediol, 1830 parts of dimethyl terephthalate
A reaction was carried out in the same manner as in the synthesis of polyester resin 1 from 1,407 parts of terephthalic acid, and 316 parts of trimellitic anhydride to obtain a softening point of 120°C and an acid value of 42.
Polyester resin 2 was obtained. Example After dry-blending each component (the amount used is in parts) in the ratio shown in Table 1, it was melt-kneaded using a Co-kneader PR-46 manufactured by Buss, and then finely ground and passed through a 150-mesh wire mesh to produce a white powder. A powder coating was obtained. This paint was applied to a zinc phosphate treated steel plate by electrostatic spraying and baked at 180°C for 15 minutes. Film thickness approx.
The coating performance at 60 microns was as shown in Table 1. Comparative Example 1 In Example 1, the same amount of Epiclon 4050 (manufactured by Dainippon Ink Chemical Industry Co., Ltd.,
A powder coating and a cured coating film were obtained in the same manner using a glycidyl ether type epoxy resin of bisphenol A having an epoxy equivalent of 950. Table 1 shows the performance of the powder coatings and cured coatings obtained in each of the above examples.

[Table] 〓〓〓〓〓

[Table] 〓〓〓〓〓

Claims (1)

[Claims] 1. A resin composition for powder coatings comprising an epoxy resin containing a bisphenol A nucleus and a hydrogenated bisphenol A nucleus in the same molecule at a molar ratio of 5/95 to 40/60 and a carboxyl group-containing polyester resin. .