JPH0711169A - Polyester resin composition for powder coating material - Google Patents

Abstract

PURPOSE:To obtain the subject compsn. which gives a smooth coating film while maintaining mechanical strengths. CONSTITUTION:This resin compsn. is obtd. by adding an alcohol mixture comprising 70-99.5wt.% dihydric alcohol and 30-0.5wt.% monohydric alcohol to a polyester formed from an arom. dicarboxylic acid component and an aliph. diol component to depolymerize the polyester and compounding the resulting polyester having a number average mol.wt. of 2,500-7,000 and a hydroxyl value of 10-35mgKOH/g with an isocyanate-based curative.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a polyester resin composition for powder coating.

[0002]

2. Description of the Related Art Powder paints are relatively inexpensive as compared with conventional solvent-based paints because they are pollution-free, can be used immediately after painting, do not require multi-layer overcoating. In addition, it has a number of advantages such as the ability to collect and use paint, and in recent years demand has expanded rapidly. As the powder coating material, various types such as polyester type, epoxy type and acrylic type are known. In particular, polyester resin powder coatings are known as well-balanced coatings with excellent weather resistance, chemical resistance, mechanical strength, etc., and are used in many fields including home appliances, building materials, and automobile parts. There is. However, the powder coating material is inferior to the solvent type coating material in terms of the smoothness of the coating film surface under the present circumstances.

Conventionally, as a method for improving the smoothness of the coating film surface of a powder coating, the average molecular weight of the polyester resin which is the main component of the coating is decreased to lower the melt viscosity, or the amount of functional groups is reduced. A method of lowering the crosslink density has been adopted. However, these methods have a fatal defect that the mechanical strength of the coating film is remarkably lowered due to the decrease in the strength of the polyester resin itself.

[0004]

DISCLOSURE OF THE INVENTION The present invention is intended to provide a polyester resin composition for powder coatings, which provides a coating film having good smoothness while maintaining mechanical strength.

[0005]

Means for Solving the Problems As a result of earnest research for solving the above problems, the present inventors have found that a polyester resin having a specific molecular weight and a hydroxyl value obtained by depolymerizing polyester by a specific method. It has been found that this object can be achieved by the combination of the above with an isocyanate-based curing agent, and has reached the present invention.

That is, the present invention provides a polyester comprising an aromatic dicarboxylic acid component and an aliphatic diol component.
70-99.5% by weight of monohydric alcohol and 30-0.5 monohydric alcohol
The number average molecular weight obtained by depolymerization by adding alcohol consisting of 1% by weight is 2500 to 7,000, and the hydroxyl value is 10 to 35 mgK.
The gist of the present invention is a polyester resin composition for powder coating, which comprises an OH / g polyester resin mixed with an isocyanate curing agent.

The present invention will be described in detail below. As the aromatic dicarboxylic acid component constituting the polyester resin, those mainly composed of terephthalic acid and / or isophthalic acid are preferable, and if necessary, 5-sodium sulfoisophthalic acid, 2,6-naphthalenedicarboxylic acid, You may use together other dicarboxylic acids, such as adipic acid and sebacic acid.

As the diol component, those mainly composed of neopentyl glycol and ethylene glycol are preferable, and if necessary, diethylene glycol,
Propylene glycol, 1,4-butanediol, 1,6-
Hexanediol, 1,4-cyclohexanedimethanol, 1,4-cyclohexanediol, bisphenol A
And a small amount of triglyceride or higher alcohol such as glycerin, trimethylolpropane and pentaerythritol may be used in combination.

Furthermore, together with the acid component and the diol component,
A hydroxycarboxylic acid such as p-hydroxybenzoic acid or tartaric acid may be used in combination.

The polyester resin used in the present invention is a polyester having a high degree of polymerization by carrying out an esterification or transesterification reaction from the above raw material components (including an ester-forming derivative) by a conventional method and then performing a polycondensation reaction. After that, it is obtained by adding a dihydric alcohol and a monohydric alcohol and depolymerizing.

The alcohol added during depolymerization is
Neopentyl glycol, diethylene glycol, ethylene glycol, etc. are preferably used as the dihydric alcohol, and stearyl alcohol, nonadecanol, eicosanol, etc. are preferably used as the monohydric alcohol.

The alcohol added during depolymerization is 70 to 99.5% by weight of dihydric alcohol and 30 to 0.5% of monohydric alcohol.
It is necessary to make it to be the weight%. If the amount of the monohydric alcohol exceeds 30% by weight, the curing reaction will be delayed, and the mechanical strength of the coating film will be significantly reduced. On the other hand, if it is less than 0.5% by weight, the melt viscosity will be high and the curing reaction will be too fast. The smoothness of the coating film is impaired.

The polyester resin has a number average molecular weight of 2,500.
Must be in the range of ~ 7000, 4000-55
00 is preferable. When the number average molecular weight is less than 2500, the polyester resin becomes brittle and the mechanical strength of the coating film decreases, while when it exceeds 7,000, the melt viscosity becomes too high, and the smoothness of the coating film is impaired.

The polyester resin has a hydroxyl value of 10
Must be ~ 35 mg KOH / g. If the hydroxyl value is less than 10 mgKOH / g, the smoothness and mechanical strength of the coating film are low, and if it exceeds 35 mgKOH / g, the mechanical strength of the coating film is low, which is not preferable.

In order to obtain a coating film having good smoothness while maintaining the mechanical strength, the alcohol component added during depolymerization, the number average molecular weight of the polyester and the hydroxyl value are appropriately selected within the scope of the present invention. do it. For example, the alcohol component added during depolymerization is 95% by weight of dihydric alcohol, 1
A preferable result is obtained when the amount of the hydric alcohol is 5% by weight, the number average molecular weight of the polyester is 4500, and the hydroxyl value is about 20 mgKOH / g.

As the curing agent, which is one component of the resin composition of the present invention, an isocyanate type is used, and specifically, the following compounds are preferably used.

(A) Blocked isocyanate compound,
For example, ε-caprolactam-blocked isophorone diisocyanate (B 1530 manufactured by Huls, Cleran UI manufactured by Bayer) and the like. (B) an internal blocked isocyanate compound, for example,
A uretdione ring-bonded internally blocked isocyanate compound (BF 1540 manufactured by Huls) and the like.

The compounding amount of the curing agent is preferably in the range of 0.5 to 1.5 times equivalent, preferably 0.8 to 1.20 times equivalent of the amount of hydroxyl groups of the polyester resin.

The resin composition for powder coating material of the present invention comprises a polyester resin satisfying the above conditions and a curing agent, and if necessary, a leveling agent generally used, pigments such as titanium dioxide and carbon black, and other components. Add additives,
It can be prepared by kneading with a heatable kneader or roll at 70 to 130 ° C.

[0020]

EXAMPLES Next, the present invention will be specifically described with reference to Examples and Comparative Examples. The resin properties and coating film performance in the examples are obtained by the methods described below. (a) Number average molecular weight It was determined by gel permeation chromatography. (b) Hydroxyl value 3 g of polyester and 0.6 ml of acetic anhydride were added to 50 ml of pyridine to acetylate the polyester, which was then titrated with a 1/2 normal potassium hydroxide methanol solution. (c) 60 degree specular gloss Measured according to JIS K 5400. (d) Smoothness The state of the coating film was visually observed and evaluated in the following two stages. ◯: Same level as the coating film of solvent-based paint (melamine alkyd type, Amylak 1000 manufactured by Kansai Paint Co., Ltd.) B: Inferior to the coating film of the solvent type paint. (e) Impact resistance: Measured according to JIS K 5400. (Diameter 1/2 inch, 500
g) (f) Blocking resistance After the coating composition was left in a thermostat at 40 ° C for 1 week, the state of lump formation was evaluated according to the following three grades. ◯: No lump was generated. Δ: A lump is generated, but the lump cannot be gripped by hand. X: The lump can be grasped by hand.

Reference Examples 1 to 10 The raw material compounds shown in Table 1 were placed in a stainless steel reaction can equipped with a stirring blade in the amounts (parts by weight) shown in Table 1 and gradually heated from 100 ° C to 250 ° C. The mixture was heated and stirred for 4 hours, and the produced water was continuously removed from the reaction system. The obtained esterification reaction product was transferred to a polycondensation reactor, 5.84 g of antimony trioxide was added as a polycondensation reaction catalyst, and the polycondensation reaction was carried out at 280 ° C for 3 hours while maintaining the degree of vacuum at 0.5 mmHg or less. Viscosity 0.45
Of polyester was obtained. Then, the depolymerizing agent shown in Table 1 was added to this polyester in the amount (parts by weight) shown in Table 1, and the depolymerization reaction was carried out by heating at 270 ° C. for 1 hour under normal pressure in a nitrogen gas atmosphere, Polyesters having a number average molecular weight and a hydroxyl value shown in Table 1 were obtained.

[0022]

[Table 1]

Examples 1 to 10 and Comparative Examples 1 to 5 Polyester resins 1 to 10 (numbers correspond to reference example numbers)
, Curing agent; B 1530, Clelan UI or BF 1540, Acronal 4F (Busuf's butyl polyacrylate leveling agent), benzoin and titanium dioxide in the amounts shown in Table 2 (parts by weight), FM 10B type Henschel mixer
PR-46 after dry blending with Mitsui Miike Seisakusho
Using a model co-kneader (manufactured by Buss Co.), the mixture was melt-kneaded at 110 ° C., cooled, pulverized, and then classified with a 145 mesh sieve to obtain a powder coating material. The obtained powder coating material was electrostatically coated on a zinc phosphate-treated steel sheet to a film thickness of 50 to 60 μm, and baked at 190 ° C. for 20 minutes. The results of evaluation of coating film performance are shown in Table 3.

[0024]

[Table 2]

[0025]

[Table 3]

[0026]

EFFECTS OF THE INVENTION According to the present invention, there is provided a polyester resin composition for powder coating, which provides a coating film having the same level of smoothness as the coating film of a solvent type coating composition while maintaining the mechanical strength.

Claims (1)

[Claims] 1. A polyester comprising an aromatic dicarboxylic acid component and an aliphatic diol component is added to a dihydric alcohol 70-9.
Polyester resin having a number average molecular weight of 2500-7000 and a hydroxyl value of 10-35 mgKOH / g obtained by depolymerization by adding an alcohol consisting of 9.5% by weight and 30-0.5% by weight of a monohydric alcohol to an isocyanate type. A polyester resin composition for a powder coating, which contains a curing agent.