JPH0619063B2 - Resin composition for powder coating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Prior Art) Since powder coatings are pollution-free coatings and resource-saving coatings, their production and usage have been steadily increasing in recent years. Most of the domestic powder coatings, especially polyester powder coatings, are used in the field of aesthetics, and are often used in household appliances.

The former powder coating was characterized by being able to coat with one coat, and was mainly used as a heavy coating, but in recent years, due to cost reduction of coating and rapid development of film thickness control technology, Powder coatings have come to be coated with a film thickness of 20 to 30μ.

However, in the case of a coating material using a conventional powder coating resin, when such a coating thickness is applied, there is a drawback that the smoothness of the coating film is impaired.
For example, solvent-type paint is still used for the front door of refrigerators.

(Problems to be solved by the invention) To achieve powder coating in the field where smoothness of the coating film is particularly required, the polymerization degree of the conventional polyester resin for powder coating is lowered to improve the melt viscosity. However, if the smoothness of the coating film could be improved, the anti-blocking property of the coating material would deteriorate, and even if the entire coating device was cooled down, the friction during powder flow would be reduced. Due to such problems as fusion, it has not been possible to obtain a product with a quality that can be practically expanded to the part where smoothness is required.

Also, in US Pat. No. 4,442,270, terephthalic acid or isophthalic acid is used as the acid component and 1,6-
Molecular weight of hexanediol as an essential component 700-3000,
A polyester resin for powder coatings having a crystallinity of a hydroxyl value of 35 to 160 KOHmg / g is described. However, although powder coating using crystalline polyester resin improves the smoothness of the coating film in a thin film, insufficient hardness of the coating film related to resin composition, poor solvent resistance, etc. are not solved, and solvent At present, there is no quality paint that can be used as a substitute for mold paint.

Therefore, the object of the present invention is to be suitably used as a well-balanced powder coating having a beautiful appearance that can withstand a solvent-based coating and excellent coating performance even when it is used for coating a thin film. It is intended to provide a polyester resin composition for powder coating.

(Means for Solving Problems) As a result of earnest studies to achieve such an object, the present inventors have found that a polyester resin for powder coating which has been conventionally used has a specific crystalline polyester resin. The present invention has been completed by finding that a coating film having a well-balanced smoothness and coating film hardness can be obtained by adding a curing agent in a specific ratio.

That is, in the present invention, the acid component constituting the (A) polyester is mainly an aromatic dicarboxylic acid, the alcohol component is mainly an aliphatic glycol, the average degree of polymerization is 10 to 40, and the liquefaction temperature is 60 to 130.
℃, the terminal group is mainly hydroxyl group, the hydroxyl value is 20-50
At least 40 mol% of the acid component constituting the polyester (B) polyester is terephthalic acid and / or isophthalic acid, and 40 to 100 mol% of the alcohol component is 1,6- Hexanediol is a crystalline polyester resin with an average molecular weight of 700-6000 and a liquefaction temperature of 60-150 ℃ whose main end groups are hydroxyl groups, and (C) ε-caprolactam-blocked polyisocyanate. ), (B), and (C), the compounding ratio satisfies the following formula (I), and the effective isocyanate derived from (C) with respect to the total amount of free hydroxyl groups derived from (A) and (B). A gist of the polyester resin composition for powder coating is that the ratio of the amount of nato groups satisfies the following formula (II).

However, in the formula, a: weight of component (A) b: weight of component (B) NCO: equivalent number of effective isocyanate derived from component (C) (OH) _a : free amount derived from component (A) Equivalent Number of Hydroxyl Group (OH) _b : Equivalent Number of Free Hydroxyl Group Derived from Component (B) The amorphous polyester resin (A), which is one component of the resin composition for powder coating of the present invention, has an acid component Mainly aromatic dicarboxylic acids, diol components mainly aliphatic glycols, average degree of polymerization 10-40, liquefaction temperature 60-130 ℃, terminal groups mainly hydroxyl groups, hydroxyl value 20-50KOHmg /
g. If the average degree of polymerization is less than 10, the anti-blocking property of the paint will be poor, and if the average degree of polymerization exceeds 40, the melt viscosity of the paint will be too high and the smoothness of the coating film will be impaired. In addition, the pulverizability becomes poor and the workability becomes extremely poor. If the liquefaction temperature is less than 60 ° C, there will be a problem with the blocking properties when used as a paint.
If the temperature exceeds ℃, it takes a high temperature to form a paint, which causes a reaction with a curing agent, which may cause gelation or mix with a partially gelled paint depending on the paint conditions. In that case, they appear as foreign matter on the coating film, which is not preferable. If the hydroxyl group is less than 20 KOHmg / g, the gelling degree at the time of curing will be low and the physical properties of the coating film such as solvent resistance and hardness will deteriorate. It is economically unfavorable because the usage amount increases.

As the aromatic dicarboxylic acid component for producing the polyester resin (A), for example, one or more selected from terephthalic acid, isophthalic acid, phthalic acid, naphthalene dicarboxylic acid or their lower alkyl esters, and as an aliphatic glycol, , For example ethylene glycol,
1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, cyclohexanedimethanol, neopentyl glycol, etc. It is possible to use one or more selected from
In addition, if necessary, the amount of succinic acid, adipic acid, azelaic acid should be within the range that does not affect the blocking resistance of the powder coating, preferably 30 mol% or less, particularly preferably 20 mol% or less. It is possible to use an aliphatic dicarboxylic acid such as sebacic acid and / or an alicyclic dicarboxylic acid such as cyclohexanedicarboxylic acid.
Furthermore, even if a trivalent or higher polyvalent carboxylic acid such as trimellitic acid or pyromellitic acid, or a trivalent or higher polyvalent alcohol such as trimethanol propane or pentaerythritol is used as a branching component in an amount that does not cause gelation. Good. Examples of such amorphous polyester resin include Nippon Ester
There is a polyester resin "ER-6000 series" manufactured by Co., Ltd. that is commercially available.

The crystalline polyester resin (B), which is one component of the resin composition for powder coating of the present invention, has at least 40 mol% of the acid component being terephthalic acid and / or isophthalic acid, and 40 to 100 mol% of the diol component. Is 1,6-hexanediol, and the terminal group having an average molecular weight of 700 to 6000 and a liquefaction temperature of 60 to 150 ° C., preferably 80 to 120 ° C. is a hydroxyl group as a seed. When the total amount of terephthalic acid and isophthalic acid is less than 40 mol%, the obtained polyester resin becomes viscous and soft, while when the content of 1,6-hexanediol is less than 40 mol%, it is obtained. The polyester resin is not crystalline, and in any case, the resin composition is not preferable for powder coating. If the average molecular weight is less than 700, it will be difficult to completely separate free glycol during the production of polyester resin.
It is not preferable because it will be in a wet state or the hydroxyl value will be too high, so that a large amount of curing agent will have to be used. When the average molecular weight exceeds 6000, not only the viscosity at the time of melting becomes high but also the crystallinity becomes weak,
This results in a loss of the paint's blocking resistance. If the liquefaction temperature is too low, there is a high risk of blocking resistance and the risk of fusion during powder flow. Conversely, if the liquefaction temperature is too high, a reaction with the curing agent will occur during coating, which is not preferable. Further, the hydroxyl value is preferably 100 KOHmg / g or less in view of economy when used as a paint.

As the acid component other than terephthalic acid and isophthalic acid for producing the crystalline polyester resin (B), for example, saturated aliphatic dicarboxylic acid such as adipic acid, azelaic acid, sebacic acid can be used. As the diol component other than 1,6-hexanediol, for example, ethylene glycol, 1,4-butanediol, neopentyl glycol, 1,4-cyclohexanedimethanol can be used. Further, if necessary, a part of dicarboxylic acid and / or diol is used in an amount of 12 mol% or less, and trivalent or higher carboxylic acid such as trimellitic acid and pyromellitic acid, and trivalent such as trimethylolpropane and pentaerythritol. The above polyols may be used instead.

The curing agent, which is one component of the resin composition for powder coating of the present invention, is polyisocyanate (C) blocked with ε-caprolactam. As the polyisocyanate, for example, toluene diisocyanate, isophorone diisocyanate and the like are preferably used, and isophorone diisocyanate is particularly preferably used. Examples of such curing agents include trade names B-1065 and B-1530 manufactured by West Germany Huls.
The product name Clerant U-1 manufactured by Bayer Co., Ltd. is commercially available and can be suitably used.

(A), (B) and in the resin composition for powder coating of the present invention
The mixing ratios of the three components of (C) must satisfy the above formulas (I) and (II) at the same time. If the value of a / a + b in the above formula (I) is less than 0.4, the hardness and solvent resistance of the coating film will be poor when it is formed into a coating film, which is not preferable. Is inferior in smoothness and is not preferable. In addition, the above (I
When the ratio represented by the formula (I) is less than 0.5, the physical properties of the coating film do not appear, and when it exceeds 2.0, it is economically disadvantageous.

The resin composition for powder coating of the present invention comprises the above (A), (B) and
It can be prepared by taking the component (C) in the above proportions, then dry-blending it with a Henschel mixer (Mitsui Miike Seisakusho) or the like, and then melt-kneading it with a co-kneader or a three-roll mill.

When a powder coating material is produced using the resin composition of the present invention, commonly used fillers, colorants, flow regulators, curing catalysts and the like are used appropriately.

(Examples) Hereinafter, the present invention will be described more specifically with reference to Examples.

The resin characteristics and film-forming performance evaluation in the examples are obtained by the following methods.

(1) Liquefaction temperature The liquefaction temperature was measured by a hot plate melting point measuring device (Hot bench manufactured by Kofler).

(2) Hydroxyl value Acetylation reaction was performed and titrated with a KOH methanol solution.

(3) Average Molecular Weight Using gel permeation chromatography (Toyo Soda HLC-8000 type), tetrahydrofuran (TH
The polystyrene reduced number average molecular weight was measured using F) as a solvent.

(4) Glycol Copolymerization Ratio After alkali decomposition with 1N-KOH methanol solution, neutralization with terephthalic acid and measurement with gas chromatography.

(5) 60-degree specular reflectance Measured with a gloss meter V manufactured by Toyo Seiki Seisakusho according to JIS Z-8874.

(6) Erichsen According to JIS Z-2247, it was measured with an Erichsen type film strength tester manufactured by Toyo Seiki Seisakusho.

(7) Impact resistance Measured with a DuPont type impact tester at a 1/2 inch φ, 1 kg of impact.

(8) Xylene rubbing test The film surface was rubbed 50 times with gauze containing xylene, and it was evaluated in four grades of ◎ extremely good, ○ good, △ somewhat bad, and × bad depending on the degree of gloss of the coating film.

(9) Pencil hardness According to JIS K-5400, it was measured with a Mitsubishi pencil unit using a pencil hardness tester manufactured by Ueshima Seisakusho.

(10) Smoothness The smoothness of the film is ◎ extremely good, ○ good, △ a little bad, ×
It was evaluated on a four-grade scale.

Reference Examples 1 to 3 Terephthalic acid, 1,6-hexanediol, 1,4-butanediol, neopentyl glycol or trimethylolpropane were charged into a stainless steel reactor at the ratio shown in Table 1, and tetrabutyl titanate was used as a catalyst. After adding 0.1 part by weight of water to the outside of the reaction system at 240 to 250 ° C, the esterification reaction was carried out until the theoretical amount of water was distilled off, and the pressure was reduced to 100 ± 10 mmHg. While reacting for 5 hours, a polyester resin having the characteristic values shown in Table 2 was obtained.

Example 1 Polyester resin (A) [manufactured by Nippon Ester Co., Ltd., trade name E
R-6800, an amorphous polyester resin obtained by copolymerizing terephthalic acid and isophthalic acid as acid components, ethylene glycol as a diol component, and a small amount of trimethylolpropane.
Average weight 25, liquefaction temperature 79-82 ℃, hydroxyl value 32.0KOHmg /
g polyester resin] 50 parts by weight, polyester resin (B)
[Polyester resin (1) obtained in Reference Example 1] 32 parts by weight, hardener [isophorone diisocyanate blocked with ε-caprolactam] (trade name B-, manufactured by Huls, West Germany)
1065, NCO content 10.5 wt%) 18 parts by weight (NCO / OH
= 1.0), 1 part by weight of a leveling agent (manufactured by BASF, trade name Acronal 4F), 0.3 part by weight of a curing catalyst (dibutyltin dimaleate) and 50 parts by weight of titanium oxide (manufactured by Teikoku Kako, trade name JR-600E). After dry blending the parts with a Henschel mixer (Mitsui Miike Seisakusho, FM-20B type),
The mixture was melted and kneaded with a co-kneader (PR-46 type, manufactured by Buss).
After cooling and solidification, the powder was pulverized and classified with a wire mesh of 150 mesh to obtain a powder coating.

SPCC-SD by electrostatically spraying this powder coating
Steel plate is zinc phosphate treated 0.8mm thick, 70 size
It was applied to a test piece (mm x 150 mm) and baked at 200 ° C for 20 minutes to obtain a coating film with an average density of 30μ. This coating film was extremely smooth, had a 60 ° specular reflectance of 97%, Erichsen of 9 mm or more, body impact of 50 cm or more, xylene rubbing test, and pencil hardness of H to 2H.

Examples 2 to 4 and Comparative Examples 1 to 3 The same polyester resin (A), curing agent, leveling agent, curing catalyst and titanium oxide as those used in Example 1 and Reference Examples 1 and 2 as polyester resin (B). Alternatively, the polyester resin (1), (2) or (3) obtained in 3 or 3 was used in the proportions shown in Table 3 to form a paint in the same manner as in Example 1, and then Example 1
Painted in the same way. The physical properties of the coating film obtained are shown in Table 4.

Example 5, Comparative Example 4 As a polyester resin (A), trade name ER-6610 manufactured by Nippon Ester Co., Ltd. (terephthalic acid as an acid component, neopentyl glycol and ethylene glycol as a diol component, and a small amount of trimethyl roll propane) was used. Copolymerized amorphous polyester resin, average degree of polymerization 25, liquefaction temperature 85-88
℃, hydroxyl value 30.8KOHmg / g) as the polyester resin (B), the polyester resin (1) obtained in Reference Example 1 or 3 or
Using (3), the same curing agent, leveling agent, curing catalyst, and titanium oxide as those used in Example 1 were used, and these were compounded in the proportions shown in Table 3 and the same as in Example 1. It was made into a paint and then painted in the same manner as in Example 1. The coating properties obtained are shown in Table 4.

(Effects of the Invention) The resin composition for powder coating of the present invention has excellent coating film smoothness of conventional solvent-based coatings, excellent solvent resistance and high coating film of conventional powder coatings. It is a composition having sufficient performance to obtain a powder coating having hardness.

The powder coating material comprising the composition of the present invention is suitable for coating a thin film and therefore has great industrial significance.

Claims (1)

[Claims] 1. An acid component constituting (A) polyester is mainly an aromatic dicarboxylic acid, an alcohol component is mainly an aliphatic glycol, and an average degree of polymerization is 10 to 40 and a terminal group at a liquefaction temperature of 60 to 130 ° C. Amorphous polyester resin having mainly hydroxyl groups and a hydroxyl value of 20 to 50 KOHmg / g, and (B) at least 40 mol% of the acid component constituting the polyester is terephthalic acid and / or isophthalic acid, and the alcohol component Of crystalline polyester resin having an average molecular weight of 700 to 6000 and a liquefaction temperature of 60 to 150 ° C. whose end groups are mainly hydroxyl groups, and (C) ε-caprolactam. It consists of blocked polyisocyanate, and the compounding ratio of each component of (A), (B), (C) satisfies the following formula (I) and the amount of free hydroxyl groups derived from (A) and (B) Due to the (C) component of the sum Effective amount of a ratio of isocyanate groups is represented by the following formula (II) for powder coating polyester resin composition satisfying the to. 0.5 ≦ NCO / (OH) a + (OH) b ≦ 2.0 (II) (wherein a: weight of component (A) b: weight of component (B) NCO: effective isocyanate derived from component (C) Equivalent number of (OH) a: equivalent number of free hydroxyl groups derived from component (A) (OH) b: equivalent number of free hydroxyl groups derived from component (B)