JPS5919151B2 - Thermosetting resin composition for powder coatings - Google Patents

Description

Detailed Description of the Invention The present invention forms a coating film that is smooth and has excellent gloss, sharpness, weather resistance, physical and chemical performance, etc., as well as good storage stability and extremely low odor during baking. The present invention relates to a thermosetting resin composition for powder coatings.

Since powder coatings do not contain solvents, their coatings have the drawback of being inferior in smoothness, gloss, and sharpness compared to solvent-based coatings. This drawback is especially noticeable in the case of vinyl powder coatings, but it can be improved to some extent by lowering the molecular weight and softening point of the vinyl polymer. But then,
Specific properties required for powder coatings include stability against blocking during storage, stain resistance of the coating film, metal adhesion,
This results in the inconvenience that mechanical strength and the like are reduced. As described above, in the case of vinyl powder coatings, it is extremely difficult to incorporate various performances in a well-balanced manner, and therefore a specific vinyl polymer must be used depending on the application. In addition, in the glycidyl group-containing vinyl polymer, in order to satisfy various performances such as weather resistance and physical properties of the coating film, the raw material monomer contains at least 30% by weight or more of (meth)acrylic acid alkyl ester, preferably 50% by weight.
However, when baked, these vinyl polymers emit a strange odor caused by alkyl (meth)acrylates, which is completely contradictory to the non-polluting advantage of powder coatings, and their use has been discouraged. has reached its limit. In view of the above, the present inventors continued intensive research and found that a polymer having a specific monomer composition, molecular weight, and softening point is used in a combination of a glycidyl group-containing vinyl copolymer and a polyvalent carboxy compound. The inventors have discovered that the above-mentioned problems can be solved, and have arrived at the present invention.

The present invention provides glycidyl ester of (meth)acrylic acid 1
0 to 40% by weight (hereinafter expressed in %), styrene 20 to 80%
%, dialkyl ester of aliphatic unsaturated dibasic acid 3-4
Softening point (ring and ball method) of 5 to 30% of an ester mixture in which more than half of the weight is methyl methacrylate and less than half is alkyl acrylate.
Provided is a thermosetting resin composition for powder coatings comprising a copolymer having a number average molecular weight of 3,000 to 15,000 at 0 to 150°C (hereinafter simply abbreviated as polymer) and a polyhydric carboxy compound. It is. No. 1 of the polymer used in the present invention. The glycidyl ester of (meth)acrylic acid, which is one raw material, refers to glycidyl (meth)acrylate and β-methylglycidyl (meth)acrylate.

These glycidyl esters are crosslinkable raw materials for improving the mechanical strength of the coating film. Regarding the amount used, if it is less than 10%, the mechanical strength of the coating film will not be sufficient, and if it exceeds 40%, the smoothness of the coating film will be poor, so it is usually 10 to 40%, preferably. A range of 15 to 30% is suitable. 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. Styrene, which is the second raw material, is a raw material for improving the storage stability, coating film smoothness, and image clarity of the powder coating.

If the amount used is less than 20%, 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. ~6
A range of 0% is appropriate. The dialkyl ester of aliphatic unsaturated dibasic acid, which is the third raw material, does not cause any unpleasant odor during baking and improves the smoothness, gloss, adhesion, mechanical strength, etc. of the coating film in a well-balanced manner. Even in systems where a large amount of styrene is used, it has the effect of significantly improving weather resistance, perhaps by shortening the styrene chains in the copolymer, and also improves adhesion after boiling and salt resistance. It is a raw material that improves water sprayability and also significantly improves the adhesion of repair coatings.

Examples of dialkyl esters of unsaturated dibasic acids include dialkyl maleates, dialkyl fumarates, dialkyl itaconates, etc. These esters have an alkyl group having 1 to 4 carbon atoms. preferable. If the amount of ester used is less than 3%, the above effects will be insufficient, and if it exceeds 40%, the stain resistance will be poor, so the appropriate range is usually 3 to 40%, preferably 10 to 30%. Furthermore, from the viewpoint of copolymerizability, it is desirable that the amount used does not exceed the amount of styrene used. Examples of the acrylic acid alkyl ester as the fourth raw material include methyl acrylate, ethyl acrylate, isopropyl acrylate, butyl acrylate, pentyl acrylate, 2-ethyl-\xyl acrylate, cecyl acrylate, lauryl acrylate, stearyl acrylate, etc. .

Methyl methacrylate used in combination with these has the effect of significantly improving the stain resistance and hardness of the coating film, and its usage amount is 50% or more, preferably 60 to 90% of the ester mixture. On the other hand, acrylic acid alkyl ester has the effect of mainly reinforcing the physical strength of the coating film, and its usage amount is 50% or less of the ester mixture, preferably 10 to 40%.
Among the acrylic acid alkyl esters, n-butyl acrylate is preferred because it has the effect of improving the sharpness and gloss of the coating film in addition to reinforcing the physical strength in a small amount.
The polymer used in the present invention is prepared by using a predetermined proportion of the above-mentioned monomers and by a well-known method such as a solution polymerization method, a bulk polymerization method, a suspension polymerization method, etc., and has a softening point (ring and ball method) of 80 to 150°C and a molecular weight (number It can be obtained by polymerizing until the average) is in the range of 3,000 to 15,000.

Examples of polyvalent carboxy compounds that are curing agents for such polymers include maleic acid, fumaric acid, succinic acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, brassylic acid, phthalic acid,
Polyhydric carboxylic acids such as trimellitic acid, pyromellitic acid, etc. can be used.

Among these, those with long carbon chains have the advantage of producing less smoke during baking. Also, as a polyvalent carboxy compound,
It is also possible to use a polyester resin having two or more carboxyl groups, a mixture of a polyester resin having two or more hydroxyl groups and an acid anhydride that produces such a polyester resin upon baking. Furthermore, polymers of unsaturated acids such as (meth)acrylic acid and fumaric acid can also be used. The composition of the present invention is composed of the above-mentioned polymer and a polyvalent carboxy compound, and the ratio of the number of glycidyl groups to carboxyl groups in the polymer ranges from 1:5 to 5:1. is appropriate.

Further, when the ratio is expressed as a polymerization ratio, the amount of the polyvalent carboxy compound is usually 5 to 30 parts, preferably 8 to 20 parts, per 70 to 90 parts by weight of the polymer (described below). If necessary, catalysts such as various amines and acids can be added to the composition of the present invention to accelerate the curing reaction, and polymers of epoxy resins, cellulose derivatives, and long-chain alkyl acrylic esters can be added for the purpose of modification. , fluorine compounds can 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. Example 1 10 parts of β-methylglycidyl methacrylate, 15 parts of glycidyl acrylate, 45 parts of styrene, 10 parts of di-n-butyl maleate, 7 parts of di-n-butyl fumarate, 10 parts of methyl methacrylate, 3 parts of n-butyl acrylate, 3 parts of azobisisobutyronitrile, 1 part of benzoyl peroxide, 0.5 parts of kyumene hydroperoxide
was added dropwise over 4 hours into a mixture of 70 parts of toluene and 30 parts of n-butanol heated to 105°C, and the reaction was continued for an additional 10 hours. A solid polymer was obtained.

The obtained polymer had a softening point of 102°C and a number average molecular weight of 7.0.
It was 00. To 100 parts of this vinyl polymer, 15 parts of decanedicarboxylic acid, 50 parts of titanium oxide, and 1 part of ModaFlo (flow control agent manufactured by Monsanto) were added, mixed, melt-kneaded in an extruder, and then finely pulverized. The amount that passed through the wire mesh was applied to a mild steel plate by electrostatic spraying. The coated material was baked at 200° C. for 20 minutes to obtain a coating film. Example 2 In the same manner as in Example 1, the softening point was determined from 18 parts of β-methylglycidyl methacrylate, 12 parts of glycidyl methacrylate, 50 parts of styrene, 5 parts of di-n-butyl fumarate, 12 parts of methyl methacrylate, and 3 parts of n-butyl acrylate. A polymer with a number average molecular weight of 6,500 was obtained at 118°C.

Using this, a coating film was obtained in the same manner as in Example 1. Example 3 In the same manner as in Example 1, the softening point was determined from 15 parts of β-methylglycidyl methacrylate, 5 parts of glycidyl methacrylate, 45 parts of styrene, 10 parts of di-n-butyl fumarate, 20 parts of methyl methacrylate, and 5 parts of n-butyl acrylate. A polymer with a molecular weight of 7,000 was obtained at 110°C.

A coating film was obtained in the same manner as in Example 1 using 13 parts of decanedicarboxylic acid with respect to 100 parts of this polymer. Table 1 shows the performance of the powder coatings and coating films obtained in each of the above examples.

Claims (1)

[Claims] 1 Glycidyl ester of (meth)acrylic acid 10-4
0% by weight, 20-80% by weight of styrene, 3-40% by weight of dialkyl esters of aliphatic unsaturated dibasic acids, and at least 50%, preferably 60-90% by weight of methacrylic acid methyl ester, 50% Below, preferably 10
Polymerized 5-30% by weight ester mixture of ~40% acrylic acid alkyl ester, softening point 80-1
A thermosetting resin composition for a powder coating comprising a copolymer having a number average molecular weight of 3,000 to 15,000 at 50°C and a polyvalent carboxy compound.