JP2764096B2 - Resin composition for powder coating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial application field) The present invention relates to a resin composition for powder coatings, which is characterized by the characteristics of a polyester resin coating film that is smooth, glossy, and excellent in strength, hardness, stain resistance, and the like. The present invention relates to a resin composition for a powder coating capable of providing an ideal coating film having the characteristics of an acrylic resin coating film having excellent weather resistance.

(Prior Art) In order to cover a metal surface and maintain protection and aesthetics over a long period of time, usually two or more coating films are usually required. From such a viewpoint, a resin having excellent adhesiveness and corrosion resistance has been used for a primer, and a resin having excellent weather resistance, stain resistance and hardness has been used for a top coat.

As for the coating method, the transition from two-coat two-bake (two-coat and two-bake) to two-coat one-bake is progressing, and considering energy saving, one-coat one-bake is the ideal method. Becomes

On the other hand, the demand for powder coatings is steadily increasing from the viewpoint of obtaining a coating film with good performance and being economical. However, since it is monolayer, that is, it is monofunctional, it cannot provide the performance of a coating film of two or more layers. There was a limit.

In view of this, there has been a demand for powder coatings that can provide coatings with better performance. From such a viewpoint, the characteristics of resin compositions for powder coatings composed of polyester resin and those for powder coatings composed of acrylic resin Research on resin compositions for polyester / acrylic / hybrid type powder coatings that combine the features of resin compositions has been actively conducted (Japanese Patent Publication No.
-1945).

(Problems to be Solved by the Invention) However, the conventional resin composition for polyester / acrylic / hybrid type powder coating is mainly a simple blend of polyester resin and acrylic resin.
If both resins with poor compatibility are blended, a smooth painted surface cannot be obtained. On the other hand, if both resins with good compatibility are blended, a coating film showing an intermediate performance between both resins can be obtained. It was not too much.

The present inventors have previously described Japanese Patent Application No. 62-272047 (Japanese Unexamined Patent Publication No.
No. 115969) combines the characteristics of a polyester resin coating, which is smooth, glossy, and excellent in strength with one coat and one bake, and the characteristics of an acrylic resin coating, which also has excellent hardness, stain resistance, and weather resistance. We have proposed a resin composition for powder coatings that can obtain a coated film. However, in recent years, a coating film having higher performance such as smoothness has been required, and the development of a composition satisfying such requirement has been desired.

The present invention meets such a demand, and the problem is that one coat and one bake combine the characteristics of a polyester resin coating film and the characteristics of an acrylic resin coating film, and provide higher performance such as smoothness. An object of the present invention is to provide a resin composition for a powder coating capable of obtaining a coating film.

(Means for Solving the Problems) In view of the present situation, the present inventors have, as described above, made a polyester-acrylic-hybrid type in which excellent coating properties such as smoothness can be obtained with one coat and one bake. Intensive research was conducted to provide a resin composition for powder coatings. As a result, it has been found that the above-mentioned problems can be achieved by blending a low melting point and crystalline aromatic polyester with the resin composition for powder coating proposed in the above-mentioned Japanese Patent Application No. 62-272047. Reached.

 That is, the gist of the present invention is as described below.

Amorphous polyester resin (A) having an average of 0.1 to 1.0 carboxyl groups in one molecule, a hydroxyl value of 10 to 100 and a softening point of 50 to 150 ° C, a hydroxyl value of 10 to 400, and a melting point of 50 to 125 ℃
Crystalline aromatic polyester resin (B), average 1
Has 0.1 to 4.0 glycidyl groups in the molecule and a hydroxyl value of 30
A composition (D) containing an acrylic resin (C) having a softening point of 50 to 150 ° C. and a copolymer obtained by reacting the polyester resin (A) with the acrylic resin (C);
A resin composition for a powder coating composition comprising 100 parts by weight of a resin composition (E) in which (A) to (D) satisfy the following ratio, and 5 to 50 parts by weight of a block polyisocyanate compound as a curing agent.

Polyester resin (A): 0 to 80% by weight Polyester resin (B): 2 to 30% by weight Acrylic resin (C): 0 to 80% by weight Composition (D): 98 to 1% by weight Hereinafter, the present invention is described in detail. Will be described.

The polyester resin (A) in the present invention has 0.1 to 1.0, preferably 0.1 to 1.0, carboxyl groups per molecule on average.
It has 15 to 0.6, and has a hydroxyl value of 10 to 100, preferably 20 to 50, and a softening point of 50 to 150 ° C, preferably 90 to 140 ° C.

If the number of carboxyl groups is less than 0.1 in one molecule on average, it will not react sufficiently with the acrylic resin (C) when preparing the composition (D) described below. Not only is the molecular weight of the coalescence too high, which lowers the smoothness of the coating film, but also causes, for example, gelling in the process of reacting the polyester resin (A) and the acrylic resin (C). On the other hand, if the hydroxyl value is less than 10, a sufficient cross-linking effect cannot be obtained after painting and baking, and the strength of the resulting coating film is insufficient. On the other hand, if it exceeds 100, the curing reaction proceeds too much and the coating film is smooth and glossy. Not only is not obtained, but also the flexibility of the coating film is impaired. If the softening point is lower than 50 ° C, a powder coating having good storage stability cannot be obtained. If the softening point is higher than 150 ° C, the flowability of the coating decreases and it is difficult to obtain a smooth coating film. The softening point is the temperature at which the sample is crushed into fine powder, packed in a glass capillary (2.6 mm in inner diameter, 5 mm in outer diameter), heated in an oil bath at 1 ° C / min, and started to liquefy. Is read with the naked eye.

Also, the use of an amorphous polyester resin (A) results in an extremely brittle coating film if both the polyester resin (A) and the polyester resin (B) described below are crystalline. It is. "Amorphous"
The distinction between “crystallinity” and “crystallinity” can be determined by the method described below.

Such a polyester resin (A) is a hydroxyl-rich polyester resin having a predetermined amount of a carboxyl group at a terminal, for example, a method of adding an acid anhydride to a part of the hydroxyl groups of a hydroxyl-containing polyester resin, or a method of polycondensation. It can be prepared by a method of controlling the reaction rate when producing a polyester resin by a reaction or the like.

In order to prepare such a polyester resin (A),
For example, terephthalic acid, isophthalic acid, phthalic acid, 1,4-
Aromatic dicarboxylic acids such as naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, diphenic acid, etc., as the main acid component, in an amount of 20 mol% or less With succinic, glutaric, adipic, pimelic, suberic, azelaic, sebacic, 1,9-nonanedicarboxylic, 1,10-decanedicarboxylic, 1,12-dodecanedicarboxylic, 1,2- Dodecanedicarboxylic acid, 1,2-octadecanedicarboxylic acid,
Aliphatic dicarboxylic acids such as eicosane dicarboxylic acid, unsaturated dicarboxylic acids such as maleic acid and fumaric acid, alicyclic dicarboxylic acids such as hexahydroterephthalic acid, hexahydroisophthalic acid and hexahydrophthalic acid, trimellitic acid, pyromellitic acid, etc. Or a lower alkyl ester and an anhydride thereof, or a hydroxycarboxylic acid such as malic acid, tartaric acid, 12-hydroxystearic acid, or paraoxybenzoic acid.

Examples of the alcohol component include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol,
1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,9-nonanediol, 1,10-decanediol, neopentyl glycol, spiroglycol, 1 1,4-cyclohexanedimethanol, 2,2,4-trimethylpentane-1,3-diol, trimethylolethane, trimethylolpropane, glycerin, pentaerythritol, hydrogenated bisphenol A, ethylene oxide addition of hydrogenated bisphenol A Propylene oxide adduct or the like.

Next, the polyester resin (B) in the present invention is a crystalline aromatic polyester obtained by appropriately combining the monomer components exemplified as the components of the polyester (A). As a typical example, polyhexamethylene terephthalate (having a melting point of 150 ° C), polyoctamethylene terephthalate (melting point 140 ° C), polydecamethylene terephthalate (melting point 125 ° C), polydecamethylene-2,6-naphthalate (melting point 135 ° C) and crystalline polyesters containing these as main components. . The hydroxyl value is adjusted to be 10 to 400, and has an endothermic peak due to melting in DSC (differential scanning calorimetry) or DTA (differential thermal analysis). ~ 150 ° C. The polyester (A) has no endothermic peak due to melting in DSC or DTA.

In the polyester resin (B), those having a hydroxyl value of less than 10 have a high molecular weight and tend to have reduced fluidity, and therefore are not suitable for the purpose of further improving the smoothness of the coating film. On the other hand, those with a low molecular weight having a hydroxyl value of more than 400 have good fluidity, but the blocking resistance of the powder coating tends to decrease. The melting point of the crystalline polyester resin is preferably from 50 to 150 ° C.
Those showing a sharp melting behavior at -120 ° C are preferred.
If the melting point is lower than 50 ° C, the blocking resistance of the powder coating is reduced, while if it is higher than 150 ° C, the effect of improving the smoothness of the coating film is not exhibited.

Next, the acrylic resin (C) in the present invention has 0.1 to 4, preferably 0.3 to 2 glycidyl groups in one molecule on average, and has a hydroxyl value of 30 to 150, preferably 50 to 120, It has a softening point of 50 to 150 ° C, preferably 90 to 140 ° C.

When the number of glycidyl groups is less than 0.1 in one molecule on average, the polyester resin (A) does not react sufficiently. On the other hand, when the number of glycidyl groups exceeds 4.0, not only the smoothness of the coating film tends to decrease, but also However, gelation may occur during the reaction between the polyester resin (A) and the acrylic resin (C), which is not preferable. On the other hand, if the hydroxyl value is less than 30, a sufficient crosslinking effect cannot be obtained and the coating strength is not sufficient, and if it exceeds 150, the curing reaction proceeds too much, making it difficult to obtain a smooth and glossy coating film.
If the softening point is lower than 50 ° C, powder coatings with good storage stability cannot be obtained. If the softening point is higher than 150 ° C, the fluidity of the coating decreases and a sufficiently smooth coating film cannot be obtained.

Such an acrylic resin (C) has a predetermined amount of a glycidyl group, and includes one or more hydroxyl group-containing monomers, one or two or more glycidyl group-containing monomers, One or two of other comonomer
It can be prepared by a known polymerization method such as solution polymerization, suspension polymerization, bulk polymerization or the like using the above species.

Examples of the hydroxyl group-containing monomer for preparing the acrylic resin include, for example, hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, 2-hydroxy-2-phenylethyl Acrylate, 2
-Hydroxy-2-phenylethyl methacrylate, allyl alcohol and the like can be used. Examples of the glycidyl group-containing monomer include glycidyl acrylate, glycidyl methacrylate, α-methyl glycidyl acrylate, α-methyl glycidyl methacrylate, β-methyl glycidyl acrylate, and β-methyl glycidyl methacrylate. Further, as other copolymer monomers, for example, acrylic acid, methacrylic acid, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-propyl acrylate, n-propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, n- Butyl acrylate, n-butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, octyl acrylate, octyl methacrylate, dodecyl acrylate, dodecyl methacrylate, benzyl acrylate, benzyl Methacrylate, dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate And methacrylic esters such as diethylaminoethyl acrylate and diethylaminoethyl methacrylate. Further, as other comonomer, for example, dialkyl fumarate,
Dialkyl itaconic acid, styrene, vinyltoluene, α-methylstyrene, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, methylolacrylamide, methylolmethacrylamide, vinyloxazoline, vinyl acetate, vinyl propionate, lauryl vinyl ether, halogen-containing vinyl Monomers, silicon-containing vinyl monomers, and the like.

Next, the composition (D) in the present invention contains a copolymer obtained by reacting the polyester resin (A) and the acrylic resin (C), and the copolymer (D) in the composition (D) The content of the copolymer varies depending on the weight ratio of the two resins and the distribution of the carboxyl groups in the polyester resin (A) and the glycidyl groups in the acrylic resin (C).
Usually, 0.5 to 20% by weight / weight of the composition (D) is preferable,
Particularly preferably, it is 2 to 10% by weight / composition (D). Therefore, when the content of the glycidyl group in the acrylic resin (C) is small and when the amount of the acrylic resin (C) is small, it is necessary to increase the reaction rate of the glycidyl group. On the other hand, when the content of the glycidyl group is large and the blending amount of the acrylic resin (C) is large, it is necessary to control the reaction rate of the glycidyl group and control the amount of the copolymer within a certain range. In particular, when more than one glycidyl group is contained in one molecule on average, the reaction rate of glycidyl groups is controlled so that the number of glycidyl groups involved in the reaction remains within one molecule on average. There is a need to.

It is difficult to isolate a copolymer of the polyester resin (A) and the acrylic resin (C) contained in the composition (D).
Therefore, the amount of such a copolymer can be calculated assuming that the glycidyl group in the acrylic resin (C) involved in the formation of the copolymer is contained in every molecule of the acrylic resin (C). It is a value calculated by multiplying the reaction rate. In the present invention, the amount of the copolymer is calculated as described above and used as a rough guide.

The above-mentioned copolymer is preferably a block copolymer. The copolymer of polyester and acrylic is formed by the reaction between the carboxyl group of the polyester resin (A) and the glycidyl group of the acrylic resin (C). Considering the freedom of combination of both resins or the freedom of blending. , The groups involved in the reaction of both resins are on average per molecule
It is preferably from 0.01 to 1.0, particularly preferably from 0.1 to 0.9.

The composition (D) contains the unreacted polyester (A) and the acrylic resin (C) as well as containing the copolymer obtained as described above. It is preferable that the polyester resin (A) and the acrylic resin (C) contained in the resin composition are the same as the polyester resin (A) and the acrylic resin (C) blended as the resin composition (E). No problem.

The composition (D) can be prepared, for example, as follows. That is, the polyester resin (A) and the acrylic resin (C) are mixed in a weight ratio of preferably 10 to 90:90 to 10, particularly preferably 30 to 70:70 to 30, and both the polyester and acrylic resin are melted. The conditions under which the carboxyl group of the polyester resin (A) and the glycidyl group of the acrylic resin (C) can selectively react, for example, from 120 to 180
At 100 ° C., preferably 140 to 160 ° C., for 1 to 100 minutes, preferably 10 to 60 minutes, in a reaction vessel under melt stirring, selecting a carboxyl group of polyester resin (A) and a glycidyl group of acrylic resin (C). To form a copolymer of the two. In addition,
Using a heating roll, a kneader, or the like instead of the above-mentioned reaction vessel, a copolymer of the two can be prepared by reacting under the same conditions as described above. However, if the above reaction is insufficient, preferable performance is exhibited. Hateful. To accelerate this reaction, for example, metal stearate, imidazole,
Of course, a catalyst such as a phosphorus compound may be mixed in both resins or one of them.

In the present invention, the resin composition (E) is obtained by blending the above resin components as follows.

Polyester resin (A): 0 to 80% by weight Polyester resin (B): 2 to 30% by weight Acrylic resin (C): 0 to 80% by weight Composition (D): 98 to 1% by weight Polyester (A) and acrylic Since the resin (C) is contained in the composition (D), it does not necessarily have to be added. When these components exceed 80%, the effect of adding the polyester resin (B) and the composition (D) is not exhibited. The mixing ratio of the polyester (B) in the resin composition (E) is 2 to 30% by weight, preferably 2 to 10% by weight. 2% by weight of polyester (B)
If the amount is less than 30% by weight, the powder coating tends to block. The composition ratio of the composition (D) in the resin composition (E) is 98 to 1% by weight, preferably 98 to 5% by weight. When the content of the composition (D) is less than 1% by weight, the copolymer in the composition (D) has insufficient compatibility with the polyester resin (A) and the acrylic resin (C). However, the smoothness of the coating film is not sufficient, and the toughness of the coating film is poor. 98% by weight
If the ratio exceeds the limit, the amount of the polyester (B) will be less than 2% by weight, and it will be difficult to achieve the object of the present invention.

In the present invention, a block polyisocyanate compound is used as a curing agent.

The block polyisocyanate compound is obtained by masking an isocyanate compound or a prepolymer having an isocyanate group with a blocking agent, and reacts with a hydroxyl group of a resin constituting the resin composition (E) to participate in crosslinking and curing. Anything can be used. Examples of the isocyanate compound include isophorone diisocyanate, hexamethylene diisocyanate, hydrogenated xylylene diisocyanate, dicyclohexylmethane diisocyanate, and isocyanate compounds having a dimer or trimer of a uretdione ring and an isocyanuric ring. Examples of the prepolymer include a prepolymer obtained by reacting the above isocyanate compound with ethylene glycol, diethylene glycol, trimethylolpropane, pentaerythritol, or the like. Examples of the blocking agent include lactams, phenols, alcohols, oximes, malonic esters, and acetylacetone.

The amount of the block polyisocyanate compound to be used is 5 to 50 parts by weight, preferably 10 to 30 parts by weight, based on 100 parts by weight of the resin composition (E). If the amount of the block polyisocyanate is less than 5 parts by weight, the composition is not sufficiently cured, and a coating film having sufficient strength cannot be obtained. On the other hand, when the amount exceeds 50 parts by weight, the blocking resistance of the obtained powder coating material decreases, which is not preferable.

The resin composition for powder coatings of the present invention may contain, for example, an epoxy resin in order to improve corrosion resistance, benzoin in order to suppress cracking of the coating film, and
In order to accelerate the curing reaction, additives such as a curing catalyst, a pigment, a leveling agent, and an antistatic agent can be blended.

The resin composition for a powder coating of the present invention can be produced by a conventional method such as, for example, dry-blending the above components with a Henschel mixer, melt-blending with an extruder, and then cooling, pulverizing, and classifying. it can.

 The measuring method of each characteristic in the present invention is as follows.

Measurement of glycidyl group 5 g of a sample is dissolved in 100 ml of chloroform, and the measurement is performed using the tetraethylammonium bromide / perchloric acid method.

Measurement of hydroxyl value 3 g of sample was dissolved in 50 ml of pyridine, and acetic anhydride was added.
The hydroxyl group is blocked by adding 5 ml of a 12% by volume pyridine solution, and excess acetic anhydride and acetic acid are determined by titration with an alcoholic KOH solution.

Measurement of carboxyl group A 500 mg sample is dissolved in 50 ml of dioxane, and this is directly titrated with an alcoholic KOH solution.

Measurement of softening point The sample is pulverized to a fine powder, packed in a glass capillary (inner diameter 2.6 mmφ, outer diameter 5 mmφ) and placed in an oil bath.
The temperature rises at ℃ / min, and the temperature at which liquefaction begins is visually determined,
read.

(Function) The resin composition for powder coating of the present invention comprises a polyester resin (A), a polyester (B), and a copolymer obtained by reacting the polyester resin (A) with the acrylic resin (C). The resin composition (E) obtained by blending the composition (D) is blended with a curing agent. Since the polyester (B) is a crystalline, aromatic polyester, the polyester (B) is blended. Accordingly, when the powder coating material is baked, if the polyester (B) reaches a temperature higher than its melting point during heating, the polyester (B) is rapidly dissolved and flows, and the flowability of the coating material is improved. On the other hand, after the completion of baking, the polyester (B) reacts with the block polyisocyanate compound like the polyester resin (A) and is incorporated into the coating, and the toughness of the coating is due to its high flexibility. It is estimated to contribute to the improvement of

(Examples) Next, the present invention will be described specifically with reference to examples, but the present invention is not limited thereto.

 In the examples, “parts” means “parts by weight”.

In the following, each property such as the performance of the coating film was evaluated as follows.

Smoothness Determine visually.

：: Extremely smooth, ○: Smooth, ×: Extremely glossy (60-degree specular reflectance) (%) Calculate the 60-degree specular reflectance (%) according to JIS-K-5400.

Erichsen strength (mm) Determined according to JIS-K-7777.

Impact resistance (cm) Du-Pont type impact resistance tester according to JIS-K-5400 (diameter:
1 / 2in.φ, load: 1kg).

Flexibility (2 mmφ bending) A bending test is performed at a bending diameter (curvature diameter) of 2 mmφ according to JIS-K-5400.

 ：: acceptable, ×: unacceptable Pencil hardness Determined according to JIS-K-5400.

Stain resistance Using a felt pen for writing impregnated with oil-based ink,
Apply oil-based ink, wipe off with methanol after standing for 24 hours, and determine residual contamination visually.

：: No trace, ×: Almost remaining Weather resistance (%) In accordance with JIS-K-5400, light irradiation was performed for 500 hours with a sunshine weather meter to determine the gloss retention.

The acid value represents the amount of the carboxyl group in KOHmg / g.

Reference Example 1 [Production Example of Polyester Resin (A-1)] The following raw materials were charged into a reaction vessel, an esterification reaction was performed at 250 ° C. for 5 hours, and a theoretical amount of water was removed from the system. Was added, and the reaction was carried out at 270 ° C for 5 hours while controlling the degree of vacuum at 20 mmHg. At 250 ° C, 9 parts of trimellitic anhydride was reacted to give a hydroxyl value of 36 and a softening point of 115.
℃, acid value 3, polyester resin with number average molecular weight 4200 (A-
1) was obtained. This resin has on average 0.17 carboxyl groups in one molecule.

Terephthalic acid 1162 parts Isophthalic acid 498 parts Ethylene glycol 186 parts Neopentyl glycol 1040 parts Trimethylolpropane 67 parts Reference example 2 [Production example of polyester resin (A-2)] The following raw materials are charged into a reaction vessel and heated at 250 ° C. After performing an esterification reaction and removing the theoretical amount of water out of the system, add 0.5 part of antimony trioxide and react under vacuum at 270 ° C for 4 hours to prepare a polyester resin with a high degree of polymerization of 100 to 150. did.
Next, the polyester resin having a high degree of polymerization was depolymerized using 54 parts of trimethylolpropane to obtain a hydroxyl value of 33 and a softening point of 1.
A polyester resin (A-2) having an acid value of 1.6 and a number average molecular weight of 5,200 at 25 ° C. was obtained.

This resin has an average of 0.15 carboxyl groups per molecule.

Terephthalic acid 1494 parts Adipic acid 146 parts Ethylene glycol 497 parts 1,4-cyclohexanedimethanol 721 parts Reference example 3 [Production example of polyester resin (B-1)] The following raw materials were charged into a reaction vessel, and the same as in Reference example 2 Thus, a polyester resin having a high polymerization degree of 100 to 150 was prepared. Next, the polyester resin having a high degree of polymerization was depolymerized using 27 parts of trimethylolpropane to obtain a hydroxyl value of 21,21.
A polyester resin (B-1) having a melting point of 130 ° C., an acid value of 2, and a number average molecular weight of 5,300 was obtained.

This resin has an average of 0.25 carboxyl groups per molecule.

Terephthalic acid 1496 parts Sebacic acid 455 parts 1,6-hexanediol 1727 parts Reference example 4 [Production example of polyester (B-2)] The following raw materials were charged into a reaction vessel, and an esterification reaction was carried out at 230 ° C to obtain a theoretical amount. After removing the water from the system, 0.7 parts of tetrabutyl titanate was added, and the mixture was heated at 245 ° C under a reduced pressure of 0.5 mmHg.
A polyester resin having the same high degree of polymerization as in Reference Example 3 was prepared. Next, this polyester resin was depolymerized using 12 parts of 1,6-hexanediol and 13 parts of trimethylolpropane, and had a hydroxyl value of 24, an acid value of 1, a melting point of 126 ° C. and a number average molecular weight of 53.
Thus, Compound (B-2) of Compound No. 00 was obtained.

Terephthalic acid 1010 parts 1,10-decanediol 1697 parts Reference Example 5 [Production example of acrylic resin (C-1)] Xylene 30 was placed in a reactor equipped with a stirrer and a reflux condenser.
A mixture of the following monomer, polymerization initiator and chain transfer regulator was added dropwise over 4 hours while heating and refluxing while adding 00 parts, and the mixture was further kept under reflux for 1 hour, and then cooled.
Add 5 parts of azobisisobutyronitrile and remove the remaining monomers outside the system at 80 to 100 ° C to complete the polymerization. Further, remove the solvent under reduced pressure to obtain a hydroxyl value of 47, a softening point of 110 ° C, and a number average. An acrylic resin (C-1) having a molecular weight of 4,700 and containing no glycidyl group was obtained.

Methyl methacrylate 400 parts n-butyl methacrylate 284 parts Hydroxyethyl methacrylate 156 parts Styrene 291 parts Azobisisobutyronitrile 50 parts n-dodecylmercaptan 2 parts Reference Example 6 [Production example of acrylic resin (C-2)] Hydroxyl value 77, softening point 105 ° C, glycidyl equivalent 5800, number average molecular weight in the same manner as in Reference Example 5
4,000 acrylic resins (C-2) were obtained.

This resin has an average of 0.7 glycidyl groups in one molecule.

Methyl methacrylate 600 parts n-butyl methacrylate 312 parts Hydroxypropyl methacrylate 230 parts Glycidyl methacrylate 25 parts Reference Example 7 [Production example of composition (D-1)] Polyester resin (A-2) and acrylic resin (C-
2) was mixed at a weight ratio of 70:30 and reacted at 170 ° C. for 1 hour to obtain a composition (D-1). The glycidyl equivalent of the composition (D-1) was 33,700, and the reaction rate of the glycidyl group was 42.6.
%Met.

Reference Example 8 [Production Example of Composition (D-2)] Polyester resin (A-1) and acrylic resin (C-
2) was mixed at a weight ratio of 70:30 and reacted at 150 ° C. for 30 minutes to obtain a composition (D-2). The glycidyl equivalent of the composition (D-2) was 29,700, and the reaction rate of the glycidyl group was 34.8%.
Met.

Examples 1 to 4, Comparative Examples 1 to 4 A resin composition was prepared with the components and compounding ratios shown in Table 1, and 40 parts of rutile-type titanium oxide [JR600E (manufactured by Teikoku Chemicals Co., Ltd.)] was used as a pigment. As a leveling agent, a polyacrylate ester leveling agent (Acronal 4F;
1 part) and melt-kneaded at 120 ° C for 3 minutes using a heating roll. After cooling and solidifying, pulverize and classify to obtain a particle size.
A powder coating of 105 μm or less was obtained. The curing agent used was a block polyisocyanate [Adduct B-1530 (manufactured by Huls)].

The resulting powder coating was applied to a 0.8 mm thick zinc phosphate treated steel sheet by electrostatic spraying to a thickness of about 50 μm.
Bake at 00 ° C for 20 minutes.

 Table 1 also shows the performance of the obtained coating films.

The resin composition for powder coating of Comparative Example 2 was difficult to pulverize, and could not be applied because the pulverized material was blocked.

In addition, as is clear from Table 1, Comparative Examples 1 and 4 have little or no amount of the polyester (B), and the coating film has insufficient flexibility and lacks smoothness. It was inferior to that of the example. However, when the amount of the polyester (B) is too large as in Comparative Example 2, the blocking resistance of the paint may be sacrificed. Comparative Example 3
As can be seen from the above, the resin composition for a powder coating not containing the composition (D) not only remarkably deteriorates the smoothness and gloss of the coating film but also lacks the toughness of the coating film.

As in Examples 1 to 4, from the resin composition for a powder coating satisfying the requirements of the present invention, a coating film excellent in smoothness, flexibility and other properties was obtained.

(Effect of the Invention) The resin composition for powder coating of the present invention has the characteristics of a polyester resin coating having smoothness, gloss, and excellent strength, and an acrylic resin coating having excellent hardness, stain resistance, and weather resistance. It is possible to provide a powder coating material that can be formed by a single coating and a single baking of an ideal coating film having the features described above.

Claims (1)

(57) [Claims] An amorphous polyester resin (A) having an average of 0.1 to 1.0 carboxyl groups in one molecule, a hydroxyl value of 10 to 100, and a softening point of 50 to 150 ° C. 400, melting point
50-150 ° C crystalline aromatic polyester resin (B),
On average 0.1 to 4.0 glycidyl groups per molecule,
A composition (D) containing an acrylic resin (C) having a hydroxyl value of 30 to 150 and a softening point of 50 to 150 ° C, and a copolymer obtained by reacting the polyester resin (A) with the acrylic resin (C). , (A) to (D) satisfy the following ratio: 100 parts by weight of a resin composition (E), and 5 to 50 parts by weight of a block polyisocyanate compound as a curing agent. . Polyester resin (A): 0 to 80% by weight Polyester resin (B): 2 to 30% by weight Acrylic resin (C): 0 to 80% by weight Composition (D): 98 to 1% by weight