JPH07118575A - Powder coating polyester resin composition - Google Patents

Abstract

PURPOSE:To obtain a powder coating polyester resin compsn. capable of forming a coating film excellent in weatherability, boiling water resistance and salt spray resistance. CONSTITUTION:A powder coating polyester resin compsn. comprises 85-98 pts.wt. polyester resin having an intrinsic viscosity of 0.15 to 0.40 and a hydroxyl no. of 10 to 70mg.KOH/g and prepd. from an acid component mainly comprising terephthalic acid and/or isophthalic acid and further comprising 0.01-0.15mol%., based on the acid component, isophthalic acid having a metal sulfonate group, and an alcohol component mainly comprising an aliph. diol; and 2-15 pts.wt. tetramethoxymethyl glycoluril curing agent.

Description

Detailed Description of the Invention

[0001]

The present invention is capable of low temperature baking,
The present invention relates to a polyester resin composition for powder coatings, which has good weather resistance, boiling water resistance and salt water spray 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 multi-layer coating, and are relatively inexpensive. It has been recognized that there are advantages such as being able to be collected and reused, and in recent years, the demand has rapidly expanded as a protective and decorative paint for members such as household electric appliances, building materials, and automobile parts.

As the powder coating material, various types such as polyester type, epoxy type, acrylic type and the like are known. In particular, the polyester type is heavily used as a coating which gives a well-balanced coating film. Among them, it is known that a polyester-based powder coating material containing a tetramethoxymethylglycoluril curing agent can be baked at a low temperature and is inexpensive as a coating material. However, the powder coating of the type curable with a tetramethoxymethylglycoluril curing agent has a problem that the adhesion is poor after boiling water treatment and salt spray treatment.

Conventionally, a method of blending an epoxy resin has been known as a method of improving the adhesion after boiling water treatment or salt spray treatment. However, there is a problem that the weather resistance and the mechanical strength are lowered by blending the epoxy resin.

[0005]

The present invention solves the above problems and has a polyester resin composition which has excellent weather resistance, boiling water resistance and salt water spray resistance and gives a powder coating which can be baked at a low temperature. It aims to provide goods at low cost.

[0006]

Means for Solving the Problems As a result of repeated studies to solve the above problems, the present inventors have introduced an isophthalic acid component containing a small amount of a metal salt sulfonate group into a constituent component of a polyester resin. It has been found that this object can be achieved by the above, and has reached the present invention.

That is, the gist of the present invention is mainly composed of terephthalic acid and / or isophthalic acid, and 0.01 to 0.
15 mol% is composed of an acid component which is isophthalic acid having a metal salt sulfonate group and an alcohol component which is mainly an aliphatic diol, and has an intrinsic viscosity of 0.15 to 0.40 and a hydroxyl value of 10
A polyester resin composition for powder coatings, which comprises 85 to 98 parts by weight of a polyester resin of 70 mgKOH / g and 2 to 15 parts by weight of a tetramethoxymethylglycoluril curing agent.

The present invention will be described in detail below. In the present invention, the acid component constituting the polyester resin is mainly terephthalic acid and / or isophthalic acid, and 0.01 to 0.15 mol% of the acid component is isophthalic acid having a metal salt sulfonate group, If necessary, adipic acid, sebacic acid, trimellitic acid, pyromellitic acid, trimesic acid and the like can be used in combination. On the other hand, as the alcohol component, those having an aliphatic diol as a main component are used, neopentyl glycol and ethylene glycol are preferable, and diethylene glycol, propylene glycol, 1,4-butanediol, trimethylolpropane, 1, if necessary. 6-hexanediol, 1,4-cyclohexanedimethanol, 1,4-cyclohexanediol, bisphenol A, pentaerythritol, glycerin and the like can be used in combination. Further, a hydroxycarboxylic acid component such as 4-hydroxybenzoic acid may be used in combination.

As the isophthalic acid having a metal salt sulfonate group (hereinafter abbreviated as SIP), 5-sodium sulfoisophthalic acid, 5-potassium sulfoisophthalic acid and 5-lithium sulfoisophthalic acid are preferably used.
It may be used as an ester-forming derivative such as dimethyl ester or diethylene glycol ester.

The amount of SIP is required to be 0.01 to 0.15 mol% of the total acid component, and preferably 0.05 to 0.10 mol%. If this amount is less than 0.01 mol%, no effect is recognized in improving the adhesion after boiling water treatment or salt spray treatment. On the other hand, if this amount exceeds 0.15 mol%, the smoothness of the coating film will deteriorate.

The intrinsic viscosity of polyester resin is 0.
It is necessary to have a hydroxyl value of 15 to 0.40 and a hydroxyl value of 10 to 70 mg KOH / g. When the intrinsic viscosity of the polyester resin is less than 0.15, not only the mechanical strength of the coating film is lowered, but also the glass transition temperature of the polyester resin is lowered, resulting in poor blocking resistance of the composition. On the other hand, when the intrinsic viscosity exceeds 0.40, the strength of the polyester resin becomes too strong, and the melt viscosity also increases, so that the pulverizability and the smoothness of the coating film deteriorate. Particularly preferred are those having an intrinsic viscosity of 0.20 to 0.35. If the hydroxyl value of the polyester resin is less than 10 mgKOH / g, the number of cross-linking points between the polyester resin and the tetramethoxymethylglycoluril curing agent will be small and the mechanical strength will be reduced. On the other hand, when the hydroxyl value exceeds 70 mgKOH / g, the molecular weight of the polyester resin is remarkably decreased, and as a result, the mechanical strength of the coating film tends to be decreased, which is not preferable. Particularly preferred are those having a hydroxyl value of 15 to 35 mg KOH / g.

The polyester resin used in the present invention can be produced by a conventional method. That is, it can be produced by carrying out an esterification or transesterification reaction, a polycondensation reaction to obtain a polyester having a high degree of polymerization, and then, if necessary, depolymerizing with a small amount of an alcohol component. And SIP can be introduced at any stage of the above reaction.

The tetramethoxymethylglycoluril used as a curing agent in the present invention may be, for example, one commercially available from American Cyanamid under the trade name of "POWDERLINK * 1174".

The ratio of the polyester resin to the curing agent should be 85 to 98 parts by weight of the polyester resin and 2 to 15 parts by weight of the curing agent, preferably the polyester resin.
90 to 97 parts by weight and 3 to 10 parts by weight of the curing agent. If the proportion of the curing agent is too small, the curing reaction will be insufficient and the mechanical strength will decrease. On the other hand, if the proportion of the curing agent is too large, the blocking resistance decreases and the coating film appearance also deteriorates. In addition, the compounding amount of the curing agent is preferably in the range of 0.8 to 1.2 times equivalent to the amount of the hydroxyl group of the polyester resin in the above range, and particularly preferably 1.0 times equivalent.

The polyester resin composition for powder coatings of the present invention contains the above polyester resin, a curing agent and, if necessary, a leveling agent and other additives such as a pigment such as titanium dioxide or carbon black in a kneader or a kneader. It can be prepared by kneading using a roll at 70 to 130 ° C.

[0016]

The reason why the boiling water resistance and salt spray resistance are improved by introducing the SIP component into the polyester resin has not been fully clarified, but the degree of adhesion between the metal salt sulfonate group and the article to be coated is very strong. It is presumed that this is due to the fact.

[0017]

EXAMPLES The present invention will be described in detail with reference to examples. The characteristic values were measured by the following methods. (1) Intrinsic Viscosity An equal weight mixture of phenol and ethane tetrachloride was used as a solvent and measured at 20 ° C. Hydroxyl value (2) 50 g of pyridine, 3 g of polyester resin, acetic anhydride
After 0.6 ml was added for acetylation, titration was performed with a 0.5 N potassium hydroxide methanol solution to obtain the value. (3) Acid value Dissolve 1 g of polyester resin in 50 ml of dioxane and add 0.1
It was determined by titration with a specified methanol solution of potassium hydroxide. (4) Smoothness The smoothness of the coating film was visually evaluated in the following three grades. ◯: Good Δ: Slightly inferior ×: Inferior (5) 60-degree specular gloss Measured according to JIS K 5400 7.6. (6) Impact resistance In accordance with JIS K 5400, 8.3.2, a ball with a diameter of 1/2 inch and 1 kg was dropped vertically to determine the height at which the coating film breaks. (7) Blocking resistance The state of the coating material after observing the powder coating material in an atmosphere of 40 ° C for 1 week was observed and evaluated according to the following three grades. ◯: Not lumpy. Δ: It is lumpy, but cannot be grabbed. X: A lump can be grabbed. (8) Boiling water resistance A test (2 hours) was carried out according to JIS K 5400 8.20, and then the remaining number was determined according to JIS K 5400 8.5.2. (100 pieces in 1 mm width) In addition, when the remaining number was 100, it was regarded as a pass. (9) Salt spray resistance The peel width on one side was determined according to JIS K 5400, 9.1. (500 hours) The peeling width on one side was 1.0 mm or less. (10) Accelerated weathering resistance Determined according to JIS K 5400 9.8.1. (200 hours)

Reference Example The raw material compounds shown in Table 1 were charged in the esterification reaction tank in the amounts (mol parts) shown in Table 1, the temperature was gradually raised from 100 ° C., and the esterification reaction was carried out at 250 ° C. for 4 hours. I went. After transferring the obtained esterification reaction product to a polycondensation reaction tank, 2 × 10 ⁻⁴ mol of antimony trioxide / mol of acid component was added as a polycondensation reaction catalyst, the pressure was reduced to 0.5 torr or less, and the temperature was adjusted to 3 at 280 ° C. A polycondensation reaction was carried out for a time to obtain a polyester having an intrinsic viscosity of 0.45. Then, the depolymerizing agent shown in Table 1 was added to this polyester in an amount (mol part) shown in Table 1, and the depolymerization reaction was carried out at 270 ° C. for 1 hour under atmospheric pressure in an inert gas atmosphere.
Polyester resins Nos. 1 to 11 having the characteristic values shown in Table 1 were obtained.

[0019]

[Table 1]

Examples 1 to 5 and Comparative Examples 1 to 6 Polyester resins and curing agents obtained in Reference Examples; POWDERLINK * 1174 manufactured by American Cyanamid, leveling agent; Acronal 4F (butyl polyacrylate based leveling manufactured by BASF) Agent), curing catalyst; POWDERLINK * MTSI made by American Cyanamid, benzoin and titanium dioxide are taken in the amounts (parts by weight) shown in Table 2 and dry-blended with an FM 10B type Henschel mixer (Mitsui Miike Seisakusho). PR-46 type co-kneader (manufactured by Buss) using 110 ℃
After melt kneading, cooling and pulverizing, separation was performed with a wire mesh of 145 mesh 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 then baked at the temperature shown in Table 2 for 20 minutes. Table 2 shows the evaluation results of the coating film performance.

[0021]

[Table 2]

[0022]

EFFECTS OF THE INVENTION According to the present invention, a polyester resin composition for powder coatings which gives a coating film excellent in weather resistance, boiling water resistance and salt water spray resistance can be obtained at low cost.

Claims (1)

[Claims] 1. An acid component mainly comprising terephthalic acid and / or isophthalic acid, and 0.01 to 0.15 mol% of the acid component is isophthalic acid having a metal salt sulfonate group, and an alcohol component mainly comprising an aliphatic diol. A polyester resin composition for powder coating, comprising 85 to 98 parts by weight of a polyester resin having an intrinsic viscosity of 0.15 to 0.40 and a hydroxyl value of 10 to 70 mgKOH / g and 2 to 15 parts by weight of a tetramethoxymethylglycoluril curing agent.