JPH0651850B2 - Resin composition for powder coating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a resin composition for powder coating which gives a matte or semi-matt coating film.

(Prior Art) Presently, as powder coatings, epoxy-based, acrylic-based, and polyester-based coatings are mainly known. Among them, polyester-based powder coatings, particularly isocyanate-cured coatings,
A powder coating composed mainly of hydroxyl-terminated polyester is known as a well-balanced coating having excellent weather resistance, corrosion resistance, and mechanical strength.

Currently, powder coatings are used in many fields such as home appliances, automobiles, and building materials, but when the coated surface requires gloss from an aesthetic point of view (60 ° specular gloss 90 to 100%).
Degree) and matte (about 30% or less) or semi-matte (30 ~
70%) may be required. Conventionally, as a method for preparing such a matte or semi-matte powder coating,
Known methods include adding a large amount of pigments having coarse particles, and dry blending two types of powder coatings, polyester powder coating and acrylic powder coating (Japanese Patent Publication No. 61-19668).

However, when a large amount of coarse particle pigment is added, there is a problem in that the smoothness and mechanical strength of the coating film decrease. In addition, the method of dry blending two types of powder coatings cannot obtain a matte or semi-matt coating in one step of coating, which increases the coating manufacturing cost and also causes non-uniform blending and recovery. There is a problem such as a change in the blend ratio during use.

(Problems to be Solved by the Invention) The present inventors have solved such problems and provided a matte or semi-matt coating film excellent in mechanical strength, and a powder that can be manufactured in a straight line. Polyester mainly composed of isophthalic acid and trimethylolpropane, terephthalic acid and / or isophthalic acid, ethylene glycol and / or neopentyl glycol or a component mainly composed of these for the purpose of providing a resin composition for paints Japanese Patent Application No. 61-300649 (Japanese Patent Application Laid-Open No. 63-157741), which has previously proposed a resin composition for powder coatings, which comprises a polyester composed of
issue).

However, among these compositions, the polyester mainly composed of isophthalic acid and trimethylolpropane has a low glass transition point of about 20 to 30 ° C, so that the powder is blocked during transportation or storage of the powder coating, especially in summer. Cause
There is a problem in that it may be inconvenient to handle.

The present invention solves such problems, provides a matte or semi-matt coating film having excellent mechanical strength, and further provides a resin composition for powder coatings which can be easily produced and has excellent blocking resistance. It is intended to be provided.

(Means for Solving Problems) As a result of repeated studies to develop a resin composition free from the above problems, the present inventors have formulated a specific polyester resin It was found that a resin composition for a matte or semi-matt powder coating, which gives a coating film excellent in mechanical strength, smoothness, and weather resistance without blocking even at high temperatures in summer, can be easily obtained, Came to.

That is, the present invention comprises an acid component mainly composed of terephthalic acid and / or isophthalic acid and an alcohol component mainly composed of trimethylolpropane and a glycol represented by the following general formula (I). The indicated glycol accounts for 5 to 50 mol% of the alcohol component and has a glass transition point of 35 to 70 ° C and is substantially non-gelling polyester.
Polyester (B) which is composed of (A), an acid component containing terephthalic acid and / or isophthalic acid as a main component and an alcohol component containing ethylene glycol and / or neopentyl glycol as a main component, and which is not substantially gelled (B) and a curing agent
(C) blended, polyester (A) and polyester
The gist of the present invention is a resin composition for powder coating composition in which the mixing ratio with (B) is 85:15 to 15:85 by weight.

(In the formula, R represents an alkylene group having 2 to 5 carbon atoms.) The carboxylic acid component of the polyester (A) which is one component of the resin composition of the present invention is mainly composed of terephthalic acid and / or isophthalic acid. However, if necessary, other polycarboxylic acid,
For example, aromatic dicarboxylic acids such as 2,6-naphthalenedicarboxylic acid, aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, alicyclic dicarboxylic acids, and in some cases trimellitic acid, pyromellitic acid, etc. A small amount of trivalent or higher carboxylic acid may be included. As the alcohol component, trimethylolpropane and the glycol represented by the general formula (I) are mainly used, but other polyhydric alcohols such as ethylene glycol, diethylene glycol and 1,2-propanediol may be used, if necessary. A small amount of aliphatic glycol such as neopentyl glycol or trivalent or higher glycol such as glycerin or pentaerythritol may be contained. Furthermore, it may contain a small amount of oxycarboxylic acid such as paraoxybenzoic acid and tartaric acid.

Here, as the glycol represented by the general formula (I), for example, one obtained by adding 1 mol of ethylene oxide to each of two hydroxyl groups of bisphenol S (hereinafter Bis-
Abbreviated as S-EO. ) Or similarly added with 1 mol of propylene oxide, and such glycol is 5 to 50 mol% of the alcohol component,
It should preferably account for 10 to 40 mol%. 5 mol%
If it is less than the above range, the glass transition point of the polyester is too low, and the blocking property in powder coating is poor. On the other hand, if it exceeds 50 mol%, the glass transition point of the polyester becomes too high, and the curing proceeds during kneading for the reason described below, which is not preferable.

The glass transition point of polyester (A) must be 35 to 70 ° C. If the glass transition temperature is less than 35 ° C, the powder coating will have poor blocking properties in a high temperature atmosphere. When the glass transition temperature exceeds 70 ° C (general formula
This corresponds to the case where the amount of glycol units shown in (I) is excessive. ), When the polyester resin and the curing agent are kneaded to form a coating material, it is necessary to raise the kneading temperature, and the curing proceeds during kneading, which is not preferable.

Further, the polyester (A) needs to be a polyester which is not substantially gelled. The "substantially non-gelling polyester" as used herein means one that can be crushed by a general crusher and has fluidity when melted. When it is substantially gelled, it is difficult to make it into a paint, and when it is made into a coating film, a uniform surface cannot be obtained.

The carboxylic acid component of the polyester (B) which is one component of the resin composition of the present invention is mainly composed of terephthalic acid and / or isophthalic acid, but other aromatic dicarboxylic acids such as 2,6-naphthalenedicarboxylic acid and , An aliphatic dicarboxylic acid such as succinic acid, adipic acid, and azelaic acid, and an alicyclic dicarboxylic acid can be used together as a copolymerization component in an optional amount. Further, as the alcohol component, ethylene glycol and neopentyl glycol are mainly used, but other aliphatic glycols such as diethylene glycol and 1,2-propanediol can be used.
Further, it does not substantially gel a trivalent or higher alcohol such as trimethylolethane, trimethylolpropane, glycerin or pentaerythritol and / or a trivalent or higher carboxylic acid such as trimellitic acid, pyromellitic acid or trimesic acid. It can be used in an amount within the range. The substantially non-gelled polyester is as described above, and the gelled one cannot be made into a paint. If necessary, it may contain an oxycarboxylic acid such as paraoxybenzoic acid or tartaric acid.

In the present invention, the hydroxyl value of polyester (A) is 1000 geq
It is preferably / 10 ⁶ g or more. If it is less than 1000 geq / 10 ⁶ g, it tends to be difficult to obtain a good matting effect.

The hydroxyl value of the polyester (B) is preferably in the range of 200 to 1000 geq / 10 ⁶ g. If less than 200geq / 10 ⁶ g,
The surface of the coating film tends to have large irregularities and the smoothness tends to decrease. When it exceeds 1000 geq / 10 ⁶ g, the mechanical strength of the coating film tends to decrease and the matting effect tends to be insufficient. is there.

The average degree of polymerization of the polyester (A) and the polyester (B) is preferably in the range of 4 to 50, which enables powderization.
Furthermore, since they are used for powder coatings, their softening points are 50-
It is preferably in the range of 150 ° C. If the softening point is less than 50 ° C, the powdered resin tends to aggregate and solidify, and the blocking resistance tends to be poor. The reaction with the curing agent progresses, and as a result, the smoothness and mechanical strength of the coating film tend to decrease.

In the resin composition of the present invention, the blending weight ratio of polyester (A) and polyester (B) is 85:15 to 15:85, preferably 40:60 to 20:80. If the blending ratio is outside this range, the matting effect is not sufficient.

Using the above-mentioned carboxylic acid and / or its alkyl ester and alcohol as raw materials, a known esterification reaction or transesterification reaction is carried out, and then, if necessary, a polycondensation reaction is carried out to produce a polyester (A) and a polyester (B ) Can be prepared.

The polyester (A) thus obtained and the polyester
70% of (B) and curing agent (C) using a kneader or roll
The resin composition for powder coating of the present invention can be obtained by kneading at 150 ° C.

As the curing agent (C), an isocyanate compound, a melamine compound, an acid anhydride or the like can be used, but an isocyanate compound, particularly a blocked isocyanate, is preferable from the viewpoint of the appearance of the coating film, low temperature curability and the like. Examples of the preferred blocked isocyanate include isophorone diisocyanate blocked with ε-caprolactam, such as B-1065 and B-1530 manufactured by Huls.
The amount of the curing agent (C) used is required to be a functional group amount substantially corresponding to the hydroxyl group amount of the polyester resin, and preferably in the range of 1.0: 0.8 to 1.0: 1.2.

If necessary, the resin composition of the present invention may contain pigments such as titanium oxide and carbon black, a curing catalyst, and other additives.

(Examples) Next, the present invention will be specifically described with reference to Examples and Comparative Examples.

The amounts of the compounds and the like in Tables 1 and 3 are parts by weight, and the characteristic values in the examples were measured by the methods described below.

Average degree of polymerization: determined by gel permeation chromatography.

Hydroxyl value: After acetylation, it was determined by titration with a potassium hydroxide solution.

Softening point: heated on a hot bench and visually determined.

Smoothness: The smoothness of the coating film was visually evaluated.

60 ° specular gloss; determined according to JIS K 5400.

Pencil hardness; determined according to JIS K 5400.

Accelerated weathering resistance; determined according to JIS K 5400 (200 hours) Glass transition point; Differential calorimeter (DSC manufactured by Seiko Instruments Inc.
-20 type) was used and the heating rate was 10 ° C / min.

Blocking property: A sample that has passed through a 145 mesh sieve is filled in a 10 cm x 3 cmφ test tube up to a height of 5 cm, left in a 40 ° C incubator for 72 hours, and then visually checked for blocking. Poor, no was judged as ◯.

Impact resistance: Determined according to JIS K 5400.

Bis-S-EO mol% in the alcohol component; quantified by gas chromatography.

Reference Examples 1 to 3 Preparation of Polyester (A) The compounds shown in Table 1 and 4.39 parts by weight of zinc acetate as a catalyst were placed in a stainless steel reaction can, heated to 230 ° C., and the produced water was continuously removed from the reaction system. Removed. Then, the degree of decompression
It was kept at 600 mmHg for 3 hours to obtain polyester resin 1, polyester resin 2 and polyester resin 3.

Reference Example 4 Preparation of Polyester (B) The compounds shown in Table 1 were placed in a stainless steel reaction vessel and
The resulting water was continuously removed from the reaction system by heating to ℃. Then, 5.84 parts by weight of antimony trioxide was added as a catalyst, and the polycondensation reaction was carried out at 280 ° C for 4 hours while maintaining the degree of vacuum at 0.5 mmHg or less to obtain a polyester resin with a high degree of polymerization.
The temperature was lowered to 270 ° C., 643 parts by weight of trimethylolpropane and 151 parts by weight of neopentyl glycol were added, and polyester resin 4 was obtained by a depolymerization reaction in a closed state.

Reference Example 5 Preparation of Polyester (B) The compounds shown in Table 1 were put in a stainless steel reaction vessel and
The resulting water was continuously removed from the reaction system by heating to ℃. Subsequently, 5.84 parts by weight of antimony trioxide was added as a catalyst, the degree of vacuum was maintained at 1.0 to 0.5 mmHg, and a polycondensation reaction was performed at 270 ° C. for 2 hours to obtain polyester resin 5.

Reference Examples 6 and 7 Reference Example 5 except that the compounds shown in Table 1 were used.
Polyester resin 6 and polyester resin 7 were obtained in the same manner as in.

The characteristic values of each polyester resin are as shown in Table 2.

Examples 1 to 6 and Comparative Examples 1 to 5 A polyester resin, a curing agent, a leveling agent, benzoin and titanium oxide shown in Table 3 were taken in the proportions shown in Table 3, and an FM 20 B type Henschel mixer (manufactured by Mitsui Miike Seisakusho) was used. ), Dry-blend with PR-46 type co-kneader (Bus Co., Ltd.), melt-knead at 100-130 ℃, cool and pulverize, and separate with 145-mesh wire net to obtain powder coating of 145-mesh or less. It was

The powder coating thus obtained was coated on a zinc phosphate-treated steel sheet with a film thickness of 50
It was electrostatically coated to a thickness of -60 µm and baked at 200 ° C for 20 minutes.

Each coating performance was evaluated and the results shown in Table 4 were obtained.

In Comparative Example 5, when the temperature of the cokneader was set to 145 ° C. because the polyester had a high melt viscosity, the curing reaction proceeded during the formation of a paint, and it was impossible to form a coating film.

As is clear from Table 4, in Comparative Examples 1 to 5, the properties of the polyesters (A) and (B) and other conditions were out of the ranges defined in the present invention, so that blocking properties, matting and semi-matting were obtained. In contrast to the poor effect, Examples 1 to 6 are excellent in blocking resistance, matting and semi-matting effects, and give good coatings with well-balanced mechanical strength and appearance.

Examples 7 to 8 Polyesters having the properties shown in Table 5 as in Reference Examples 1 to 3 except that the compounds shown in Table 5 were used in the amounts (parts by weight) shown in Table 5. Resin 8 and polyester resin 9 were obtained.

Using the polyester resins and additives shown in Table 6 in the amounts (parts by weight) shown in Table 6, powder coating materials were produced in the same manner as in Examples 1 to 6, and the performances of coating films were evaluated by coating. did.

The results are shown in Table 6.

(Effects of the Invention) When the resin composition of the present invention is used as a powder coating material, a matte or semi-matt coating film having excellent mechanical strength and appearance can be obtained, and the blocking resistance of the coating material is also improved. Since it is good, it is an excellent resin composition in terms of handling.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display area C09D 167/00 PLG 8933-4J 175/06 PHQ 8620-4J

Claims (4)

[Claims] 1. An acid component mainly composed of terephthalic acid and / or isophthalic acid and an alcohol component mainly composed of trimethylolpropane and a glycol represented by the following general formula (I), and represented by the general formula (I). Glycols account for 5 to 50 mol% of the alcohol component and have a glass transition point of 35 to
Substantially ungelled polyester at 70 ° C
Polyester (B) which is composed of (A), an acid component containing terephthalic acid and / or isophthalic acid as a main component and an alcohol component containing ethylene glycol and / or neopentyl glycol as a main component, and which is not substantially gelled (B) and a curing agent
(C) blended, polyester (A) and polyester
A resin composition for powder coating composition, wherein the blending ratio with (B) is 85:15 to 15:85 by weight. (In the formula, represents an alkylene group having 2 to 5 carbon atoms.) 2. The hydroxyl value of polyester (A) is 1000 geq / 10
⁶ g or more, the hydroxyl value of polyester (B) is 200-1000 geq
10. The resin composition according to claim 1, which is 10 ⁶ g. 3. The resin composition according to claim 1 or 2, wherein the weight ratio of the polyester (A) to the polyester (B) is 40:60 to 20:80. 4. The resin composition according to claim 1, wherein the curing agent is a blocked isocyanate.