JPH11166154A - Polyester resin composition for powder coating material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester resin composition for powder coating materials which is free from any volatile component and gives a coating film showing high weathering resistance. SOLUTION: This composition is prepared by mixing a polyester resin for powder coating materials which has an acid component comprising isophthalic acid and an alcohol component based on neopentyl glycol, an acid value of 12-45 mgKOH/g and a limiting viscosity of 0.15-0.40 dl/g with a glycidyl ester curing agent having an epoxy equivalent of 200 g/eq or below.

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 coating film having good weather resistance.

[0002]

2. Description of the Related Art Compared to conventional solvent-based paints, powder paints are non-polluting paints, can be used immediately after painting, do not require multiple layers of coating, and are relatively inexpensive. For some reasons, there are advantages such as being able to collect and reuse the surplus during painting, and the demand for paints for home appliances and the like has been rapidly expanding in recent years.

[0003] As the powder coating, epoxy-based, epoxy-polyester hybrid-based, acrylic-based and polyester-based coatings are mainly known. In recent years, paints having good weather resistance have been demanded for reasons such as maintenance-free, and acrylic powder paints are known as having good weather resistance. However, acrylic powder paints are expensive and have extremely poor compatibility with other paints. If mixed with other paints, they may cause cissing, so the paint line must be isolated. there were.

[0004] Polyester-based powder coatings do not have such a problem, but have a problem that they are inferior in weather resistance to acrylic-based coatings. Therefore, development of polyester-based powder coatings having good weather resistance has been promoted. ing.

For example, Japanese Patent Application Laid-Open No. Hei 6-234941 discloses that a polyester resin for powder coatings containing isophthalic acid as an acid component, neopentyl glycol as an alcohol component, and having a hydroxyl group as a terminal group is mainly used. A polyester resin composition for powder coating containing an isocyanate-based curing agent is disclosed. However, the powder coating using this has a problem in terms of the environment, such as the blocking agent volatilizing when baking is performed after coating and contaminates the baking furnace.

To solve this problem, Japanese Patent Application Laid-Open No.
No. 166104 discloses an epoxy obtained from bisphenol A and epichlorohydrin in a powder coating polyester resin having isophthalic acid as an acid component, neopentyl glycol as an alcohol component, and a carboxyl group as a terminal group. A polyester resin composition for powder coating containing a resin is disclosed. Powder coatings using this do not contain volatile components and have improved weather resistance, but have insufficient weather resistance for use in applications requiring a high degree of weather resistance.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a polyester resin composition for powder coatings which does not contain a volatile component and gives a coating film exhibiting high weather resistance.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. The gist of the present invention is to use isophthalic acid as an acid component and neopentyl glycol as an alcohol component as main components and have an acid value of 12 to 45. mgKOH / g, intrinsic viscosity
A polyester resin composition for powder coatings comprising a polyester resin for powder coatings of 0.15 to 0.40 dl / g and a glycidyl ester-based curing agent having an epoxy equivalent of 200 g / eq or less.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

The polyester resin of the present invention comprises isophthalic acid as an acid component, neopentyl glycol as an alcohol component, and an acid value of 12 to 45 m.
gKOH / g, with an intrinsic viscosity of 0.15 to 0.40 dl / g.

As the acid component of the polyester resin, isophthalic acid is mainly used, and its ratio is usually 70%.
Mol% or more, preferably 80 mol% or more, and most preferably 90 mol% or more.

A small amount (30 mol% or less) of another dicarboxylic acid may be used together with isophthalic acid. Examples of such dicarboxylic acids include aromatic dicarboxylic acids such as terephthalic acid, aliphatic dicarboxylic acids such as adipic acid, sebacic acid, azelaic acid and dodecane diacid, and alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid. Further, a trivalent or higher carboxylic acid such as trimellitic acid, pyromellitic acid and trimesic acid may be used in combination as long as the polyester resin is not gelled.

[0013] Neopentyl glycol is mainly used as the alcohol component.
Usually at least 70 mol%, preferably at least 80 mol%, optimally
90 mol% or more.

A small amount (30 mol% or less) of another diol may be used together with neopentyl glycol. Such diols include ethylene glycol, diethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, 1,4-cyclohexanediol,
Examples include an ethylene oxide adduct of bisphenol A. Further, a trihydric or higher alcohol such as trimethylolpropane, glycerin or pentaerythritol may be used in combination as long as the polyester resin is not gelled.

An oxycarboxylic acid such as 4-hydroxybenzoic acid and ε-caprolactone may be used in a small amount.

The polyester resin has the above-mentioned components.
(Including their ester-forming derivatives) as raw materials, and can be prepared by a conventional method for producing polyester.

The polyester resin has an acid value of 12 to 45 mg KOH
/ g and intrinsic viscosity of 0.15 to 0.40 dl / g.

When the acid value of the polyester resin is less than 12 mgKOH / g, the molecular weight is consequently increased, and large irregularities are formed on the surface of the coating film, and the smoothness tends to decrease.
If it exceeds gKOH / g, not only the mechanical strength of the coating film tends to decrease, but also the blending amount of the glycidyl ester-based curing agent needs to be increased, so that the weather resistance and the blocking resistance decrease.

The intrinsic viscosity of the polyester resin is 0.15
When the amount is less than dl / g, the blocking resistance of the resin composition may be deteriorated. On the other hand, when the amount exceeds 0.40 dl / g, the pulverizability is deteriorated. Particularly preferred are those having an intrinsic viscosity of 0.20 to 0.35.
dl / g.

Further, for use in powder coatings, the polyester resin preferably has a softening point in the range of 50 to 150 ° C. When the softening point is less than 50 ° C., the powdered resin is likely to be coagulated and solidified, and the blocking resistance tends to be poor,
On the other hand, if the temperature exceeds 150 ° C., the kneading temperature becomes high, and the reaction with the curing agent proceeds during the formation of the coating, and as a result, the smoothness and mechanical strength of the coating film tend to decrease.

The polyester resin composition of the present invention can be obtained by blending a glycidyl ester-based curing agent with the above polyester resin.

As the glycidyl ester-based curing agent, 1
Those having a number of glycidyl groups per molecule of 2 or more and an epoxy equivalent of 200 g / eq or less, preferably 130 to 200 g / eq, are used. If the epoxy equivalent exceeds 200 g / eq, the amount added must be increased, and the weather resistance and the blocking resistance will be reduced. The epoxy equivalent is 130 g /
Those less than eq are difficult to obtain commercially.

Specific examples of the glycidyl ester-based curing agent include diglycidyl terephthalate, triglycidyl trimellitate, diglycidyl phthalate, and diglycidyl cyclohexanesicarboxylate.

The amount of the glycidyl ester-based curing agent is
It is appropriate that the amount is approximately equivalent to the amount of the carboxyl group of the polyester resin (0.8 to 1.2 times equivalent).

To prepare the resin composition for powder coating, a polyester resin is blended with a glycidyl ester-based curing agent and, if necessary, a leveling agent, a pigment such as titanium dioxide, carbon black, and other additives. Knead at 70-150 ° C using a kneader or roll.

[0026]

Next, the present invention will be described specifically with reference to examples. In addition, the characteristic value of the polyester resin was measured by the following method. (1) Intrinsic viscosity It was measured at a temperature of 20 ° C. using an equal weight mixture of phenol and tetrachloroethane as a solvent. (2) Acid value 0.5 g of the polyester resin was dissolved in 50 ml of a mixed solvent of dioxane and distilled water at a weight ratio of 10/1, and the acid value was determined by titration with a 0.1 N methanol solution of potassium hydroxide. (3) Specular glossiness at 60 ° Determined according to JIS K 5400. (4) Impact resistance In accordance with JIS K 5400, sandwich the coated steel plate between the shooting platform having a spherical surface with a diameter of 1.27 cm and the receiving platform with a dent matching it so that the spherical surface of the coating film is in contact with it, and above it Was dropped vertically to determine the height at which the coating film breaks.
(If the value is 20 cm or more, the test is acceptable.) (5) Gloss retention (accelerated weathering resistance) WEL-6XS-HC-B / Ec type sunshine weather meter manufactured by Suga Test Equipment Co., Ltd. in accordance with JIS K 5400 It measured using. (700
The gloss retention after time irradiation was determined. If this value is 80% or more, it passes. )

REFERENCE EXAMPLE The raw material compounds shown in Table 1 were charged into the esterification reaction tank in the amounts (mol parts) shown in Table 1, and the temperature was gradually raised from 100 ° C. to 250 ° C. for 4 hours. Was done. After transferring the obtained esterified product to a polycondensation reaction tank, 4 × 10 ⁻⁴ mol of antimony trioxide / 1 mol of an acid component is added as a catalyst, the pressure is reduced to 0.4 hPa or less, and the polycondensation reaction is performed at 280 ° C. for 3 hours. Was carried out to obtain a polyester having an intrinsic viscosity of 0.45 dl / g. Next, the compound described in the column of "depolymerization" in Table 1 was added to the polyester in an amount (molar part) shown in Table 1, and a depolymerization reaction was performed at 250 ° C. for 2 hours in an inert atmosphere under normal pressure. Do
Polyester resins A to G having the characteristic values shown in Table 1 were obtained.

[0028]

[Table 1]

[0029] Examples 1-6, a curing agent to a polyester resin obtained in Comparative Example 1-3 Reference Example, 2-undecyl imidazole curing catalyst (made by Shikoku Corp. "Curezol C ₁₁ Z"), polyacrylate Leveling agent (BA
SF10 “Acronal 4F”), benzoin and rutile type titanium dioxide (“CR-90” manufactured by Ishihara Sangyo Co., Ltd.) were used in proportions to obtain the paint composition (parts by weight) shown in Table 2, and the FM10B Henschel mixer (Mitsui Miike Seisakusho) Dry blending) and using a PR-46 type co-kneader (Buss).
After melting and kneading at ℃, cooling and pulverizing, 140 mesh wire mesh
(0 to 106 μm) to obtain a powder coating. The obtained powder coating was electrostatically coated on a zinc phosphate-treated steel sheet so as to have a thickness of 50 μm, and baked at 190 ° C. for 20 minutes. Table 2 shows the results of evaluating the coating film performance of this coated steel sheet. In Comparative Example 3, the intrinsic viscosity of the polyester resin was high, the pulverization of the resin was difficult, and a powder coating that could be used for the test was not obtained. In Table 2, the curing agent means the following. EX711 (manufactured by Nagase Chemical Industry Co., Ltd.): Diglycidyl terephthalate R-540 (manufactured by Mitsui Chemicals, Inc.): cyclohexanedicarboxylic acid diglycidyl ester YD-128 (manufactured by Toto Kasei Co., Ltd.): epoxy resin from bisphenol A and epichlorohydrin

[0030]

[Table 2]

[0031]

According to the present invention, no volatile component is contained,
Provided is a polyester resin composition for a powder coating, which provides a coating film exhibiting high weather resistance.

Claims (1)

[Claims] 1. An acid component comprising isophthalic acid as a main component and neopentyl glycol as an alcohol component having an acid value of 12 to 45 mgKOH / g and an intrinsic viscosity of 0.15 to 0.40 dl / g.
Epoxy equivalent of 20 for polyester resin for powder coating
A polyester resin composition for powder coatings containing a glycidyl ester-based curing agent of 0 g / eq or less.