JPS6123818B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a thermosetting resin composition for powder coatings that forms a smooth coating film with excellent gloss, weather resistance, physical and chemical properties, etc., and has good storage stability. It is related to. Such thermosetting resin compositions for powder coatings, which are a combination of a known hydroxyl group-containing vinyl copolymer and a curing agent, have a structure with short distances between crosslinks. The physical performance of cured coatings also tends to be poor, and for this reason, curing agents with long distances between their functional groups have been required. Since it is not solid, powder coatings obtained therefrom have the disadvantage of being susceptible to blocking during storage. Attempts have also been made to improve the physical performance of these hydroxyl group-containing vinyl copolymers by lowering their glass transition point, but this has had little effect, and in order to obtain the full effect, the glass transition point has to be extreme. Conversely, when the point was lowered, the powder coating obtained began to block during storage, making it impossible to put it to practical use. However, as a result of intensive research in view of these points, the present inventors found that by adding a lactone compound to a hydroxyl group-containing vinyl copolymer, a physical The present invention was developed based on the discovery that the performance can be improved. That is, in the present invention, the softening point and number average molecular weight obtained by adding lactone to a hydroxyl group-containing vinyl copolymer as the first component are 80 to 80, respectively.
On the other hand, the polymer is 150℃ and 3000-15000
The object of the present invention is to provide a thermosetting resin composition for powder coatings, which contains as a second component a curing agent having a functional group that reacts with the hydroxyl groups present in the copolymer; By ring-opening addition of a lactone compound to the hydroxyl groups in the copolymer, the distance between crosslinks in the cured coating film becomes longer, resulting in a marked improvement in physical performance and a decrease in the softening point of the copolymer. Since the amount is so small, the storage stability as a powder coating is practically unchanged. Here, examples of the lactone compound include β-propiolactone, β- or γ-butyrolactone, pivalolactone, γ- or δ-
These include valerolactone and ε-caprolactone. The hydroxyl group-containing vinyl copolymer is obtained by polymerizing hydroxyl group-containing vinyl monomers as described below by a well-known method such as solution polymerization, bulk polymerization, or suspension polymerization. Examples include mono(meth)acrylic esters and monocrotonic esters of polyhydric alcohols, allyl alcohol, and monoallyl ethers of polyhydric alcohols. Here, examples of the polyhydric alcohol include dihydric alcohols such as ethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 1,6-hexanediol, There are polyhydric alcohols such as glycerin, trimethylolpropane, trimethylolethane, and pentaerythritol, but fumaric acid dihydroxyethyl ester, fumaric acid butyl hydroxyethyl ester, etc. can also be used. In addition, styrene, substituted styrene; esters of alcohols having 2 to 8 carbon atoms and unsaturated monobasic acids such as methacrylic acid, acrylic acid, and crotonic acid; maleic acid; Acids, esters with unsaturated dibasic acids such as itaconic acid, especially diesters; vinyl acetate; (meth)acrylonitrile, etc., and furthermore (meth)acrylic acid; pinyl monomers such as glycidyl (meth)acrylate cannot be used together. This is not a hindrance. The polymer, which is the first component of the composition of the present invention, is capable of adding a lactone compound to the vinyl copolymer thus obtained, in other words, to the hydroxyl groups present in the copolymer. Of course, it may be carried out after the formation of the hydroxyl group-containing monomer, or it may be carried out on the hydroxyl group-containing monomer during the copolymerization to obtain the copolymer, or before the copolymerization. It is also possible to add a catalyst to accelerate the process. Thus, a lactone-modified vinyl copolymer having a hydroxyl group in the molecule and having a softening point of 80 to 150°C and a number average molecular weight of 3,000 to 15,000 is finally obtained. Typical compounds (curing agents) having a functional group that reacts with the hydroxyl groups of such polymers include blocked polyisocyanate compounds and amino resins. Here, the term "blocked polyisocyanate compound" refers to a compound obtained by reacting polyisocyanate or an adduct of it with a polyhydric alcohol with a blocking agent to block free isocyanate groups. Examples of the polyisocyanate include isophorone diisocyanate, Tetramethylene diisocyanate, hexamethylene diisocyanate, lysine diisocyanate, xylylene diisocyanate, etc. are included; examples of the polyhydric alcohols include trimethylolpropane, glycerin, and ethylene glycol; and examples of the blocking agents include methanol, Examples include ethanol, ε-caprolactam, 2-pyrrolidone, acetoxime, and phenol. On the other hand, the amino resin refers to methylolated amino compounds such as methylolated melamine, methylolated urea, and methylolated benzoguanamine obtained by reacting formaldehyde with amino compounds such as melamine, urea, and benzoguanamine, and alkyl ether compounds thereof. These resins are commonly referred to as melamine resins, urea resins, and benzoguanamine resins. In the present invention, when a block polyisocyanate compound is used as the curing agent, the ratio is 5 to 50 parts by weight, more preferably 10 to 50 parts by weight of the block polyisocyanate compound to 50 to 95 parts by weight of the polymer. ~30 parts by weight. On the other hand, when using the amino resin as a curing agent, the proportion used is 85 to 97 parts by weight of the polymer,
3 to 15 parts by weight of amino resin, more preferably 5 to 15 parts by weight
The amount is 10 parts by weight. To the composition of the present invention having the above-mentioned structure, a blocking agent dissociation catalyst such as various amines or metal compounds can be added, if necessary, for the purpose of promoting the curing reaction. For this purpose, epoxy resins, cellulose derivatives, polymers of acrylic acid long-chain alkyl esters, and fluorine compounds may also be blended. Powder coatings can be prepared using the composition of the present invention by any known method. The obtained powder coating can be applied by any known method such as electrostatic spraying or fluidized dipping. Next, the present invention will be explained in detail according to examples. In the following, all parts mean parts by weight unless otherwise specified. Example 1 20 parts of β-hydroxyethyl methacrylate, 35 parts of styrene, 27.5 parts of methyl methacrylate, 4 parts of azobisisobutyronitrile and 1 part of benzoyl peroxide were added for 4 hours to 100 parts of xylene heated to 110°C. After continuing the reaction for an additional 10 hours, the temperature was raised to 125°C and ε-
17.5 parts of caprolactone and acetylacetone zinc salt
0.0175 part was added and the reaction was continued for 6 hours. Next, the solvent was removed at 200° C. and 1 mmHg until no more solvent was distilled out, to obtain a solid polymer. The polymer thus obtained had a softening point and a molecular weight of 118°C and 6500, respectively. Thereafter, 100 parts of this vinyl polymer was added with "Cleran U" (manufactured by Bayer AG, West Germany, ε-caprolactone block compound of isophorone diisocyanate adduct; isocyanate group content =
25 parts of titanium oxide (11.5% by weight), 50 parts of titanium oxide, "Modaflow" (flow regulator manufactured by Monsanto, USA)
After adding and mixing 10 parts and 1.0 part of dibutyltin dilaurate, the mixture was melt-kneaded in an extruder, then crushed, and an excess of 200 mesh wire mesh was applied to a mild steel plate by electrostatic spraying. The thus obtained coating was baked at 200°C for 20 minutes. Example 2 26.2 parts of styrene and ε-caprolactone
26.3 parts and acetylacetone zinc salt
The same operation as in Example 1 was repeated except for changing to 0.0263 parts, and the softening point and molecular weight were each 109.
A polymer with a temperature of 6000°C was obtained. Thereafter, the same procedure as in Example 1 was carried out to obtain a coating film. Example 3 25 parts of β-hydroxyethyl methacrylate, 25.6 parts of styrene, and ε-caprolactone
21.9 parts and acetylacetone zinc salt
The same operation as in Example 1 was repeated except for changing to 0.0219 parts, and the softening point and molecular weight were respectively
A polymer having a temperature of 112°C and 6200°C was obtained. Thereafter, the same procedure as in Example 1 was carried out to obtain a coating film. The performance of the coating film obtained in each of the above examples and the storage stability of the coating material are summarized in Table 1. In addition, weather resistance indicates the reflection gloss retention rate at 60℃ after one year of exposure in Bangkok, Thailand, UV resistance indicates the color difference after 48 hours of ultraviolet irradiation, and storage stability indicates one month at 35 degrees. Shows the state after storage. 【table】

Claims (1)

[Claims] 1 The softening point obtained by adding a lactone compound to a hydroxyl group-containing vinyl copolymer is 80 to 150℃.
A thermosetting resin composition for a powder coating comprising a polymer having a number average molecular weight of 3,000 to 15,000 and a curing agent having a functional group that reacts with a hydroxyl group.