JPH05263019A - Polyester resin composition for matte powder coating - Google Patents

Abstract

PURPOSE:To obtain at low cost a polyester resin composition for use in a powder coating which gives a coating film having excellent weatherability and a completely matte surface. CONSTITUTION:This composition comprises 87-98 pts.wt. polyester resin (A) comprising an aromatic dicarboxylic acid unit and an aliphatic diol unit and having an intrinsic viscosity of 0.15-0.40dl/g and a hydroxyl value of 250-1,000geq/10<6>g, 13-2 pts.wt. tetramethoxymethylglycoluril hardener (B), and p-toluidine-2-sulfonic acid in an amount of 0.1-5.0 pts.wt. per 100 pts.wt. the sum of (A) and (B).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester resin composition for powder coating which gives a matte coating film.

[0002]

2. Description of the Related Art Epoxy resin-based, acrylic resin-based, and polyester resin-based powder coatings are mainly known as powder coatings. Among them, polyester powder coatings have a well-balanced coating performance. Known as having paint. 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 degree specular gloss of 90% or more). ) And semi matte (about 30-70%) or matte (30
% Or less) may be required, but the market for matte powder coatings has recently been rapidly growing.

Conventionally, as a method of preparing a matte powder coating, a method of adding a large amount of pigments having coarse particles or dry blending two kinds of powder coatings of polyester powder coating and acrylic powder coating A method (Japanese Patent Publication No. 61-19668) is known. 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 deteriorate. In addition, the method of dry blending two types of powder paints increases the number of blending processes in addition to the normal powder paint manufacturing process, and it is not possible to obtain a matte paint in one step of paint, resulting in paint manufacturing costs. However, there are problems such as non-uniformity of the blend and a change in the blending ratio during recovery and use.

[0004] In order to solve such problems, in JP-A-64-1770, a hydroxyl value of 1200geq / 10 ⁶ g or more polyester and hydroxyl value of 200~1000geq / 10 ⁶ g polyester and block A resin composition for a powder coating, which is composed of a deisocyanate curing agent and has a gelling time difference of 3 minutes or more between both polyesters, has been proposed. However, in a powder coating material using this resin composition for powder coating material, a blocked isocyanate-based curing agent having a functionality of 2 to 3 is used, and therefore a large amount of the curing agent must be blended, which is cost-effective. It is a disadvantage. Further, the above-mentioned methods are the only methods for obtaining a matte powder coating with a polyester resin having a hydroxyl group at the end.

[0005]

The present invention solves such problems and provides a polyester resin composition for matte powder coatings excellent in weather resistance at low cost without combining two kinds of polyester resins. It is what

[0006]

Means for Solving the Problems As a result of repeated studies to solve the above problems, the present inventors have found that a specific polyester resin, tetramethoxymethylglycoluril as a curing agent, and p-toluidine-2 as a curing catalyst. The inventors have found that this object can be achieved by combining sulfonic acids in a specific ratio, and arrived at the present invention.

That is, according to the present invention, the intrinsic viscosity of the aromatic dicarboxylic acid component and the aliphatic diol component is 0.15 to
Polyester resin A having 0.40 dl / g and hydroxyl value of 250 to 1000 geq / 10 ⁶ g, tetramethoxymethylglycoluril curing agent B and p-toluidine-2-sulfonic acid C,
Polyester resin for matte powder coating, in which A is 87 to 98 parts by weight, B is 13 to 2 parts by weight, and C is 0.1 to 5.0 parts by weight based on 100 parts by weight of the total of A and B. The subject matter is a composition.

The present invention will be described in detail below. In the resin composition of the present invention, terephthalic acid and isophthalic acid are mainly used as the aromatic dicarboxylic acid component constituting the polyester resin, and neopentyl glycol and ethylene glycol are mainly used as the aliphatic diol component, but if necessary, Acid components such as 5-sodium sulfoisophthalic acid, adipic acid, sebacic acid, trimellitic acid, pyromellitic acid, trimesic acid, diethylene glycol, propylene glycol, 1,4-butanediol, trimethylolpropane, 1,6- Alcohol components such as hexanediol, 1,4-cyclohexanedimethanol, 1,4-cyclohexanediol, bisphenol A, pentaerythritol, and glycerin, and hydroxycarboxylic acid components such as 4-hydroxybenzoic acid are used as copolymerization components. It may be.

The polyester resin in the present invention is produced, for example, by converting a low polymer obtained by a transesterification method or a direct esterification method to a high molecular weight by a polycondensation reaction and then performing a depolymerization reaction.

Polyester resin has an intrinsic viscosity of 0.15 to 0.
It is necessary to have 40 dl / g and a hydroxyl value of 250 to 1000 geq / 10 ⁶ g. The intrinsic viscosity of polyester resin is 0.15dl
If less than / g, the blocking resistance of the composition becomes poor,
On the other hand, when it exceeds 0.40 dl / g, the pulverizability and the smoothness of the coating film deteriorate. Particularly preferred ones have an intrinsic viscosity of 0.20 to 0.35 dl
/ g. In addition, the hydroxyl value of the polyester resin
When it exceeds 1000 geq / 10 ⁶ g, the mechanical strength of the coating film tends to decrease and the matting effect becomes insufficient. On the other hand, 25
If it is less than 0 geq / 10 ⁶ g, the surface of the coating film will be uneven and will have large irregularities, resulting in poor smoothness.

Tetramethoxymethylglycoluril used as a curing agent in the present invention is commercially available from American Cyanamid under the trade name of "POWDERLINK * 1174".

The ratio of polyester A to curing agent B is
It is necessary that the content of B is 87 to 98 parts by weight and that of B is 13 to 2 parts by weight. If the proportion of A is too large, the curing reaction will be insufficient and not only the mechanical strength will decrease, but also the matting effect will be insufficient. On the other hand, if the proportion of A is too small, the storage stability will decrease and the coating film appearance will also deteriorate. Preferably, A is 90 to 97 parts by weight and B is 10 to 3 parts by weight.

The amount of the curing agent used is approximately the same as the amount of hydroxyl groups in the polyester resin, preferably 0.8 to 1.2.
A range of double equivalents is suitable.

Further, p-toluidine-2-sulfonic acid C
The compounding amount of 0.1 is based on 100 parts by weight of the total amount of A and B.
~ 5.0 parts by weight is necessary. If the amount of C is too small, the effect as a curing catalyst does not substantially appear and a matte coating film is not obtained. On the contrary, if the amount is too large, not only the reaction promoting effect is saturated, but also the coating film becomes yellow. In order to obtain a matte coating film, it is necessary to use p-toluidine-2-sulfonic acid, and an organic sulfonic acid compound other than p-toluidine-2-sulfonic acid cannot obtain a matte coating film. ..

The polyester resin composition for a matte powder coating of the present invention uses the above polyester resin A, tetramethoxymethylglycoluril curing agent B and p-toluidine-2-sulfonic acid C in a kneader or roll. It can be prepared by kneading at 70 to 130 ° C.

If necessary, a leveling agent and other additives such as pigments such as titanium dioxide and carbon black can be added.

[0017]

EXAMPLES Next, the present invention will be specifically described with reference to Examples and Comparative Examples. The characteristic values were measured by the following methods. Intrinsic Viscosity An equal weight mixture of phenol and ethane tetrachloride was used as a solvent and measured at 20 ° C. Hydroxyl value After acetylation, it was determined by titration with a methanol solution of potassium hydroxide. The acid value was determined by dissolving in dioxane and titrating with a potassium hydroxide methanol solution. 60 degree gloss (specular glossiness) Obtained according to JIS K 5400. Smoothness The smoothness of the coating film was visually evaluated and evaluated according to the following two grades. ○: No unevenness on the surface ×: There are many uneven unevenness on the surface Impact resistance According to JIS K 5400, the height at which a sphere with a diameter of 1/2 inch and a weight of 1 kg is dropped vertically to destroy the coating film. I asked. Accelerated weather resistance Determined according to JIS K 5400. (200 hours) (○ indicates no abnormality.)

Reference example terephthalic acid, isophthalic acid, neopentyl glycol
(1), ethylene glycol, diethylene glycol and
1,6-hexanediol was charged in the esterification reaction tank in the amount (parts by weight) shown in Table 1, the reaction temperature was gradually raised from 100 ° C, and the esterification reaction was carried out at 250 ° C for 4 hours. After transferring the obtained esterification reaction product to the polycondensation reaction tank, 5.84 g of antimony trioxide (2 × 10 ⁻⁴ mol / 1 mol of acid component) was added as a catalyst, and the pressure was reduced to 0.5 Torr or less.
Polycondensation reaction was carried out at 80 ° C. for 3 hours to obtain a polyester having an intrinsic viscosity of 0.45 dl / g. Next, neopentyl glycol (2) and trimethylolpropane were added to this polyester in the amounts (parts by weight) shown in Table 1, and the depolymerization reaction was carried out at 270 ° C. for 1 hour under atmospheric pressure in an inert atmosphere. Polyesters 1 to 7 having the characteristic values shown in 1 were obtained.

[0019]

[Table 1]

Examples 1 to 8 and Comparative Examples 1 to 6 Polyester resin and curing agent obtained in Reference Example; POWDERLINK * 1174 manufactured by American Cyanamid, curing catalyst; p
-Toluidine-2-sulfonic acid or p-toluenesulfonic acid, a leveling agent; BASF's acronal 4F, benzoin and titanium dioxide are taken in the ratios shown in Tables 2 and 3, and an FM10B type Henschel mixer (Mitsui Miike Seisakusho)
After dry-blending with a PR-46 type co-kneader (manufactured by Buss), melt and knead at 110 ° C.
The powder coating was obtained by separating with a 5-mesh wire mesh. The powder coating thus obtained was coated on a zinc phosphate-treated steel sheet with a film thickness of 50-60 μm.
And then baked at 190 ° C for 20 minutes. The results of evaluating the performance of the coating film are shown in Tables 2 and 3.

[0021]

[Table 2]

[0022]

[Table 3]

[0023]

EFFECTS OF THE INVENTION According to the present invention, a polyester resin composition for a powder coating having excellent weather resistance and a completely matte coating surface can be easily obtained at low cost.

Claims (1)

[Claims] 1. A polyester resin A comprising an aromatic dicarboxylic acid component and an aliphatic diol component and having an intrinsic viscosity of 0.15 to 0.40 dl / g and a hydroxyl value of 250 to 1000 geq / 10 ⁶ g, and a tetramethoxymethylglycoluril curing agent. B and p-toluidine-2-sulfonic acid C, A is 87 to 98 parts by weight,
A polyester resin composition for a matte powder coating, characterized in that 13 to 2 parts by weight of B and 0.1 to 5.0 parts by weight of C are mixed with 100 parts by weight of the total of A and B.