JPS6119661B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a thermosetting resin composition for powder coatings that forms a coating film with significantly improved adhesion after boiling without impairing the inherent excellent properties of a thermosetting vinyl resin composition. The present invention relates to a synthetic resin composition. Powder coatings using thermosetting vinyl resin compositions have been widely used in recent years for decorative coatings and the like because they form coatings with particularly excellent weather resistance. However, when the molecular weight of the vinyl resin used therein is relatively high, the melt viscosity is high, resulting in a drawback that the smoothness, gloss, and sharpness of the coating film are poor. Although this drawback can be improved by lowering the molecular weight and softening point of the vinyl resin, the physical performance of the coating film after boiling is inferior. In view of these points, the present inventors continued intensive research and found that by blending paraoxybenzoic acid glycidyl ester ether into a thermosetting vinyl resin composition, the original excellent properties of the vinyl resin composition were improved. It has been found that deficiencies in the physical performance of powder coating films after boiling can be improved without detriment. What is the thermosetting vinyl resin composition mentioned here?
A substance that can be used for thermosetting powder coatings.
Its ring and ball softening point is usually 80 to 150°C. There are two types of them: vinyl resins which are themselves self-crosslinking, and compositions consisting of vinyl resins and a hardening agent that can be crosslinked by reaction with a hardening agent. The vinyl resin used therein has a number average molecular weight of 3,000 to 15,000. A self-crosslinking vinyl resin is one having a self-crosslinking functional group such as a butoxymethylamide group in its molecule. Vinyl resins that can be crosslinked when used in combination with a curing agent are vinyl resins that have functional groups reactive with the curing agent, such as hydroxyl groups, carboxyl groups, and glycidyl groups. When the functional group is a hydroxyl group, there are, for example, amino resins such as hexamethoxymethylmelamine and tetrabutoxybenzoguanamine, blocked polyisocyanates, etc. When the functional group is a carboxyl group, there are, for example, epoxy resins, and when the functional group is a glycidyl group, there are, for example, polyhydric carboxylic acids, There are polyvalent phenols, etc. When a curing agent is used, it is suitable that its usage ratio does not exceed half the amount (weight ratio) of the thermosetting vinyl resin composition. Paraoxybenzoic acid glycidyl ester ether is obtained from the reaction of paraoxybenzoic acid and epihalohydrin, and has the general formula (However, n indicates 0 or an integer.) However, it is preferable that n does not exceed 10 at most. Since this paraoxybenzoic acid glycidyl ester ether acts as a modifier in the composition of the present invention, it is not necessarily necessary to participate in the crosslinking and curing reaction, but if it accounts for a high proportion of the entire composition. It is suitable for this to be involved in the crosslinking and curing reaction of the thermosetting vinyl resin composition. For this purpose, it is preferable to introduce a functional group reactive with the glycidyl group, such as a carboxyl group or an amino group, into the thermosetting vinyl resin composition to be blended. The blending ratio of paraoxybenzoic acid glycidyl ester ether is based on the thermosetting vinyl resin composition.
The amount is in the range of 1 to 15 parts, preferably 2 to 10 parts, per 100 parts by weight (as shown below). In this case, if the blending ratio is less than 1 part, the effects of the present invention cannot be fully achieved, while if it is more than 25 parts, the weather resistance of the coating film will be reduced, which is not preferred. In order to accelerate the crosslinking and curing reaction, a well-known catalyst may be appropriately added to the composition of the present invention, and a long chain acrylic acid as a fluidity regulator can be added to prevent the formation of craters on the coating surface and to improve smoothness. Alkyl ester polymers, fluorine compounds, etc. can be added. Any known method can be used to produce a powder coating from the composition of the present invention. A coating film with excellent performance can be obtained by applying the resulting powder coating by a well-known method such as an electrostatic spray method or a fluidized dipping method and then baking it. The present invention will be explained below based on examples. Example 1 40 parts of styrene, 20 parts of n-butyl methacrylate
100 parts of a mixture of 15 parts of dibutyl fumarate, 10 parts of glycidyl methacrylate and 15 parts of β-methylglycidyl methacrylate, 4 parts of azobisisobutyronitrile and 1 part of benzoyl peroxide.
100 parts of toluene heated to 100° C. and then gradually added dropwise to 100 parts of toluene, which was then maintained at the same temperature for an additional 10 hours. The resulting reaction product was desolvented at 200° C. and 1 mmHg to obtain a vinyl resin having a softening point of 108° C. and a number average molecular weight of 7,500. To 85 parts of this resin, 15 parts of decanedicarboxylic acid, 30 parts of titanium oxide, 1 part of Modaflow (flow control agent manufactured by Monsanto, an acrylic acid long chain alkyl ester polymer), and paraoxybenzoic acid glycidyl ester ether with an epoxy equivalent of 130 were added. 5 parts were added and mixed, melted and kneaded using an extruder, and pulverized. The amount that passed through 200 mesh wire mesh was applied to a mild steel plate by electrostatic spraying, and baked at 130°C for 20 minutes. Example 2 The total amount of paraoxybenzoic acid glycidyl ester ether used in Example 1 was changed to an epoxy equivalent of 165
A coating film was obtained in the same manner as in Example 1, except that 2 parts of paraoxybenzoic acid glycidyl ester ether was used. Example 3 40 parts of styrene, 15 parts of methyl methacrylate,
Using 100 parts of a mixture of 30 parts of n-butyl methacrylate and 15 parts of β-hydroxyethyl methacrylate, the softening point was 113° C. in the same manner as in Example 1.
A vinyl resin with a number average molecular weight of 8000 was obtained. This resin
To 85 parts, 15 parts of Kleran U1 (blocked isocyanate manufactured by Bayer), 50 parts of titanium oxide, 1 part of Modaflow, 1 part of dibutyltin oxide, and 5 parts of paraoxybenzoic acid glycidyl ester ether with an epoxy equivalent of 130 were added, and the following examples were prepared. The powder coating obtained in the same manner as in 1 was applied to a mild steel plate by electrostatic spraying and baked at 200°C for 20 minutes. Example 4 The total amount of paraoxybenzoic acid glycidyl ester ether used in Example 3 was converted to an epoxy equivalent of 165
A coating film was obtained in the same manner as in Example 3, except that 3 parts of paraoxybenzoic acid glycidyl ester ether was used. After immersing the specimens obtained in each of the above examples in boiling water for 2 hours,
The physical performance of the coating after standing at 23°C for 2 hours at % relative humidity is shown in the table below. 【table】

Claims (1)

[Claims] 1. A thermosetting resin composition for powder coating, comprising 100 parts by weight of a thermosetting vinyl resin composition and 1 to 15 parts by weight of paraoxybenzoic acid glycidyl ester ether.