JPH04328171A - Polyester resin composition for powder coating - Google Patents

Abstract

PURPOSE:To obtain a polyester resin composition, useful for powder coatings, capable of providing films, having high hardness and excellent in processability and fouling resistance. CONSTITUTION:A polyester resin composition is composed of 75-95 pts.wt. polyester resin, containing terephthalic acid and naphthalenedicarboxylic acid as a main acid component and ethylene glycol and neopentyl glycol as a main alcohol component, having 0.15-0.4dl/g intrinsic viscosity and 300-900g equiv./10<6>g hydroxyl value and 5-25 pts.wt. blocked isocyanate-based curing agent.

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 coatings.

0002

[Prior Art] Compared to conventional solvent-based paints, powder paints are non-polluting, can be used immediately after painting, do not require multiple layers of paint, and are relatively inexpensive. It has been recognized for its advantages such as the ability to be recycled and recovered and reused, and the demand for it as a protective and decorative paint for components such as home appliances, building materials, and automobile parts has rapidly increased in recent years.

Conventionally, painting of home appliances, etc. was done by processing steel plates.
Previously, this was done after forming, but in order to streamline the painting line and improve productivity, flat steel plates were painted and then processed.
There is a shift to a pre-coated molding method.

However, since pre-painted steel sheets are processed and formed into complicated shapes after being painted, the paint used for them is
It must provide a coating film with high hardness and excellent workability and stain resistance.

[0005] Thermosetting acrylic resin paints are mainly used for painting home appliances, especially products such as refrigerators and washing machines that require hard coatings and stain resistance. but,
Acrylic resin paints have poor workability when used in pre-coat coatings, and when softened to improve workability, the paint film lacks the hardness and stain resistance for practical use. .

Furthermore, paints based on polyester resins with a high degree of polymerization have excellent processability and have been put into practical use for coating home appliances, etc., but they have had the problem of insufficient coating hardness.

[0006]

[Problems to be Solved by the Invention] The present invention provides a polyester resin composition for powder coatings that eliminates these drawbacks and provides a coating film with high hardness and excellent processability and stain resistance. This is what I am trying to do.

[0007]

[Means for Solving the Problems] In order to achieve the above object, the present inventors have made extensive studies and found that it is advantageous to blend a blocked isocyanate curing agent into a specific polyester resin, and the present invention has been made. reached.

That is, the present invention has an intrinsic viscosity of 0.15 to 0.4 dl/g and a hydroxyl value of 300, which has terephthalic acid and naphthalene dicarboxylic acid as the main acid components and ethylene glycol and neopentyl glycol as the main alcohol components. The gist of this invention is a polyester resin composition for powder coatings comprising 75 to 95 parts by weight of a polyester resin of ~900 geq/106 g and 5 to 25 parts by weight of a blocked isocyanate curing agent.

In the present invention, the acid component constituting the polyester resin is mainly composed of terephthalic acid and naphthalene dicarboxylic acid, and preferably naphthalene dicarboxylic acid accounts for 5 to 50 mol % of the total acid component. If the proportion of naphthalene dicarboxylic acid is too small, the effect of increasing the hardness of the coating film will be poor, while if it is too large, impact resistance and processability will decrease.

[0010] As the naphthalenedicarboxylic acid, 2,6
-naphthalene dicarboxylic acid, 2,7-naphthalene dicarboxylic acid, 1,4-naphthalene dicarboxylic acid, etc. are used, but 2,6-naphthalene dicarboxylic acid is most preferred in terms of reactivity and the like.

The alcohol component is mainly composed of ethylene glycol and neopentyl glycol, and the appropriate molar ratio of ethylene glycol to neopentyl glycol is 20/80 to 80/20.

In addition to these, isophthalic acid, adipic acid,
Azelaic acid, sebacic acid, 1,4-cyclohexanedicarboxylic acid, γ-butyrolactone, ε-caprolactone, p-hydroxybenzoic acid, diethylene glycol, 1
, 2-propanediol, 1,5-pentanediol,
A bifunctional compound such as 1,6-hexanediol may be copolymerized in an amount of about 20 mol% or less of the acid component or alcohol component. Furthermore, trifunctional or higher functional compounds such as trimellitic acid, pyromellitic acid, trimesic acid, glycerin, trimethylolpropane, pentaerythritol, etc. may be copolymerized in a range of about 5% by weight or less (trifunctional or higher functional compounds may be copolymerized). If more than this is copolymerized, processability will decrease.)

The polyester resin of the present invention is produced by, for example, making a low polymer obtained by a transesterification method or a direct esterification method to a high molecular weight by a polycondensation reaction, and then carrying out a depolymerization reaction if necessary. Ru.

Polyester resin has an intrinsic viscosity of 0.15
~0.4dl/g, hydroxyl value 300-900geq/
It needs to be 106g.

[0015] The intrinsic viscosity of the polyester resin is 0.15d.
If it is less than 1/g, the hydroxyl value becomes large and the amount of curing agent used must be increased, which is not only economically disadvantageous, but also the blocking resistance of the paint deteriorates.
On the other hand, if it exceeds 0.4 dl/g, the crushability and the smoothness of the coating film will deteriorate.

[0016] Furthermore, the hydroxyl value of the polyester resin is 30.
If it is less than 0geq/106g, large irregularities will occur on the surface of the coating film and the smoothness will tend to decrease;
When it exceeds eq/106g, the mechanical strength of the coating film decreases.

In the composition of the present invention, the weight ratio of the polyester resin to the blocked isocyanate curing agent is 75/25 to 95/5, preferably 80/20 to 95/5.
It is necessary to make it 90/10. If the proportion of the curing agent is too small, the curing reaction will be insufficient, resulting in unsatisfactory coating performance, while if it is too large, the strength of the coating will decrease and the appearance of the coating will be poor. The amount of curing agent used is preferably such that the amount of functional groups approximately corresponds to the amount of hydroxyl groups in the polyester resin (0.8 to 1.2 equivalents).

As the blocked isocyanate curing agent, isophorone diisocyanate blocked with ε-caprolactam, such as B-1065 manufactured by Huls,
B-1530 etc. are used.

[0019] The composition of the present invention is blended with a spreading agent and pigments such as titanium dioxide, talc, carbon black, etc., as required, and is heated to 70 to 150% using a kneader or roll.
A powder coating can be obtained by kneading at °C and pulverizing.

[0020]

[Examples] Next, the present invention will be specifically explained with reference to Examples. In addition, the characteristic values and the performance of the coating film in the Examples were measured or evaluated by the following method. (1) Intrinsic viscosity Measured at 20°C using an equal weight mixture of phenol and tetrachloroethane as a solvent. (2) Hydroxyl value Determined by titration with a methanol solution of potassium hydroxide after acetylation. (3) Acid value Determined by dissolving in dioxane and titrating with a methanol solution of potassium hydroxide. (4) Smoothness The appearance of the coating film was visually evaluated. (5) 60° specular gloss Determined according to JIS K 5400. (6) Using a high-grade pencil specified in pencil hardness JIS S 6006,
Determined according to IS K 5400.

(7) Impact resistance Determined according to JIS K 5400. (8) Workability A coated steel plate was bent 180 degrees at a temperature of 0° C., and the occurrence of cracks at the bent portion was observed and evaluated using a 20x magnifying glass. In addition, IT means a thickness of 0.5 mm at the bending part.
This indicates that one plate is sandwiched between the two and bent. ○: No abnormality, △: Some cracks occurred, ×: Many cracks occurred. (9) Stain Resistance The coating film was smeared with oil-based ink, left for 24 hours, wiped off with methanol, and the degree of remaining stain was visually evaluated. ○: No contamination, △: Slight contamination, ×: Significant contamination.

Reference Examples 1 to 11 Terephthalic acid, 2,6-naphthalene dicarboxylic acid, isophthalic acid, adipic acid, ethylene glycol, neopentyl glycol and 1,6-hexanediol were used as raw materials in the amounts shown in Table 1 (by weight). part) into an esterification reaction tank, and the reaction temperature was gradually raised from 100°C to 250°C.
The esterification reaction was carried out at ℃ for 4 hours.

After transferring the obtained esterified product to a polycondensation reaction tank, 2×10 −4 mol of antimony trioxide/1 mol of acid component was added as a catalyst, and the pressure was reduced to below 0.5 Torr.
Polycondensation reaction was carried out at 280°C for 3 hours, and the intrinsic viscosity was 0.45.
A polyester of dl/g was obtained.

Next, trimethylolpropane, pentaerythritol, and glycerin as depolymerization components were added to this polyester in the amounts (parts by weight) shown in Table 1, and the mixture was heated at 270° C. for 1 hour under normal pressure in an inert atmosphere. A depolymerization reaction was carried out to obtain polyester resins A to K having the characteristic values shown in Table 1.

[0025]

[Table 1]

Examples 1 to 7 and Comparative Examples 1 to 4 Polyester resin and blocked isocyanate curing agent shown in Table 2: Hüls B-1530, pigment: 50 parts by weight of titanium dioxide, and spreading agent: BASF. Acronal 4F
After adding 1 part by weight and dry blending with an FM20B Henschel mixer (manufactured by Mitsui Miike Seisakusho),
The mixtures were melted and mixed at 120° C. using a mold co-kneader (manufactured by Busu Co., Ltd.), cooled and solidified, pulverized, and separated using a 145-mesh wire mesh to obtain a powder coating.

The obtained powder coating was electrostatically coated onto a zinc phosphate treated steel plate to a film thickness of 50 to 60 μm.
A coating film was formed by baking at 0° C. for 20 minutes. Table 2 shows the results of evaluating the performance of the coating film.

[0028]

[Table 2]

[0029]

Effects of the Invention According to the present invention, a polyester resin composition for powder coatings is provided which provides a coating film having high hardness and excellent processability and stain resistance.

Claims (2)

[Claims] Claim 1: A product containing terephthalic acid and naphthalene dicarboxylic acid as the main acid components and ethylene glycol and neopentyl glycol as the main alcohol components, with an intrinsic viscosity of 0.15 to 0.4 dl/g and a hydroxyl value of 300 to 300.
900geq/106g polyester resin 75-95
A polyester resin composition for powder coatings, comprising 5 parts by weight and 5 to 25 parts by weight of a blocked isocyanate curing agent. 2. The composition according to claim 1, wherein the polyester resin contains naphthalene dicarboxylic acid in an amount of 5 to 50 mol % of the total acid component.