JPH107944A - Polyester resin composition for powder coating material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester resin composition for powder coating material which can give semi-matte or matte coating films having good blocking resistance, reduced in the staining of an oven and weight loss when baked, and having excellent smoothness and strengths. SOLUTION: This composition comprises a non-gelled polyester A having an acid value of 70mgKOH/g or above, a non-gelled polyester B having an acid value of 10-50mgKOH/g, and a hydroxyalkylamide curing agent. The ratio of polyester A to polyester B is 70/30 to 10/90 be weight, and the difference (absolute value) in the gelation time between polyesters A and B is 3min or longer.

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 which gives a semi-matte or matte coating film.

[0002]

2. Description of the Related Art As powder coatings, epoxy resin, acrylic resin and polyester resin coatings are mainly known. Among them, polyester resin powder coatings are known.
It is known as a paint having a well-balanced coating performance.

[0003] Powder coatings are used in many fields such as home appliances, automobiles, building materials and the like, but the coating film is glossy from the aesthetic point of view (about 90 to 100% at 60 degree specular gloss). ,
Semi matte (also about 30-70%) and matte (also 30
% Or less) may be required.

Heretofore, methods for preparing such semi-matte or matte powder coatings include a method of adding a large amount of pigment having a coarse particle, a polyester resin powder coating and an acrylic resin powder coating. Method of dry blending
61-19668) and the like.

However, when a large amount of coarse pigment is added, there is a problem that the smoothness and strength of the coating film are reduced. In addition, the method of dry-blending two types of powder coatings cannot obtain a semi-matte or matte coating in one-step coating, which increases the coating production cost, and increases the non-uniformity and recovery of the blend. There are problems such as a change in the blending ratio during use.

[0006] In order to solve such problems, in JP-A-64-1770, a hydroxyl value of 1200geq / 10 ⁶ g or more polyesters, hydroxyl value of 200~1000geq / 10 ⁶ g polyester and block There has been proposed a resin composition for powder coatings comprising a polyisocyanate-based curing agent and having a difference in gelation time between both polyesters of 3 minutes or more.

However, since this resin composition uses a blocked isocyanate-based curing agent having 2 to 3 functions, a large amount of the curing agent must be added, which is disadvantageous in cost. Further, when the polyester resin and the blocked isocyanate-based curing agent react with each other, the blocking agent scatters and contaminates the baking furnace, and there is a problem that the weight is reduced by about 10%.

In order to solve this problem, for example,
Japanese Patent Application Laid-Open No. 5-186711 proposes a method using a polyfunctional curing agent such as a tetramethoxymethylglycoluril curing agent instead of the blocked isocyanate curing agent. However, this polyester resin composition has a problem in blocking resistance and the like.

[0009]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and has a good anti-blocking property, less contamination and weight loss of the furnace during baking, and a semi-matte excellent in smoothness and strength. It is another object of the present invention to provide a polyester resin composition for powder coating which gives a matte coating film.

[0010]

Means for Solving the Problems The present inventors have conducted studies to solve the above problems, and as a result, by combining two types of polyesters having a specific acid value with a hydroxylalkylamide-based curing agent, The inventors have found that this object is achieved, and have reached the present invention.

That is, the present invention relates to a non-gelled polyester A having an acid value of 70 mgKOH / g or more, and an acid value of 10 to 50 m
gKOH / g of non-gelled polyester B and hydroxylalkyl amide-based curing agent, polyester A
And a polyester B having a weight ratio of 70:30 to 10:90, and a difference (absolute value) in gel time between the polyester A and the polyester B being 3 minutes or more. The gist of the invention is a polyester resin composition.

In the present invention, the acid value and the gelation time are as follows:
It is a value obtained by the following method. (1) Acid value 0.5 g of a polyester resin is dissolved in a solution of 45 ml of dioxane and 5 ml of distilled water by heating, and the acid value is determined by titration with a 0.1 N methanol solution of potassium hydroxide. (2) Gelation time Functional group of polyester resin and hydroxylalkylamide curing agent (“Primid XL-552” manufactured by EMS-Chemie)
1.0 equivalent and 33% of rutile titanium dioxide powder
% By weight, and a curing curve is determined by a Brabender Plasticorder (manufactured by Brabender) at a sample weight of 90 g and a temperature of 170 ° C., and the time to the inflection point is defined as the gel time.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.

As the acid component constituting the polyesters A and B in the present invention, aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic anhydride, phthalic acid and naphthalenedicarboxylic acid are mainly used. Also, if necessary, aliphatic dicarboxylic acids such as adipic acid and succinic acid, and furthermore, monovalent carboxylic acids such as stearic acid and myristic acid, and trivalent or higher carboxylic acids such as trimellitic acid, pyromellitic acid and trimesic acid. An acid can be used in combination.

On the other hand, as the alcohol component constituting the polyesters A and B, neopentyl glycol and ethylene glycol are mainly used. If necessary, diethylene glycol, propylene glycol,
1,4-butanediol, trimethylolpropane, 1,6
-Hexanediol, 1,4-cyclohexanedimethanol, 1,4-cyclohexanediol, bisphenol A
Also, an ethylene oxide adduct of bisphenol S, pentaerythritol, glycerin and the like can be used in combination.

A hydroxycarboxylic acid component such as 4-hydroxybenzoic acid may be used in combination as a copolymer component.

In the polyester resin composition of the present invention, the acid value of polyester A is 70 mgKOH / g or more, preferably 120 to 280 mgKOH / g, and the acid value of polyester B is 10 to 50 mKOH / g.
It needs to be gKOH / g, preferably 20-40 mg KOH / g.

If the acid value of the polyester A is less than 70 mgKOH / g, the difference in acid value from the polyester B becomes small, so that it is difficult to obtain a good matting effect. When the acid value of the polyester B is less than 10 mgKOH / g, the melt viscosity of the polyester B becomes too high, so that large irregularities are generated on the surface of the coating film, the smoothness is reduced, and the curing reactivity is also slowed down. Therefore, the strength tends to decrease. On the other hand, when the acid value of the polyester B exceeds 50 mgKOH / g, the difference in the acid value from the polyester A becomes small, so that the matting effect becomes insufficient.

The ratio of polyester A to polyester B is 70:30 to 10:90 by weight, preferably 40:60 to 90:90.
20:80 is required. If the compounding ratio is out of this range, the matting effect becomes insufficient.

Further, polyester A and polyester B
It is necessary that the difference (absolute value) in the gelation time of the above is not less than 3 minutes, and if the difference is less than 3 minutes, the matting effect cannot be obtained. In order to obtain a high matte coating film (60% specular glossiness of not more than 20%), it is preferable to set it for 5 to 15 minutes.

In the present invention, the degree of matting can be controlled by the difference between the acid value of polyester A, the mixing ratio of polyesters A and B, and the gelation time. For example, the acid value of polyester A is 200 mgKOH / g,
When the mixing ratio of the polyesters A and B is 30:70, a semi-matte coating film having a 60 ° specular gloss of 50-60% with a gel time difference of 3-4 minutes can be obtained. About a minute
A matte film having a 60 ° specular gloss of about 20%, and if the same is applied for 6 minutes or more, a completely matte coating film having a 60 ° specular gloss of 10% or less can be obtained.

The polyesters A and B need to be substantially non-gelled polyesters. Here, the “polyester that is not substantially gelled” means a polyester that can be pulverized by a general pulverizer and can flow at the time of melting. It is difficult to form a coating with a gelled polyester, and a uniform coating film cannot be formed.

The polyesters A and B preferably have an intrinsic viscosity of 0.15 to 0.40 and a softening point of 50 to 150 ° C. When the intrinsic viscosity is less than 0.15, as a result, the softening point of the polyester resin becomes low, so that the blocking resistance tends to decrease. On the other hand, when the intrinsic viscosity is more than 0.40, the melt viscosity of the polyester resin becomes high, so that the smoothness of the coating film tends to decrease. In addition, softening point is 50
If the temperature is lower than ℃, the powdered polyester resin is likely to be coagulated and solidified, and the blocking resistance tends to be inferior. On the other hand, when the softening point exceeds 150 ° C., it is necessary to increase the temperature of the melt-kneading, and the reaction with the curing agent proceeds during the formation of the coating, and as a result, the smoothness and strength of the coating film tend to decrease. is there.

The polyesters A and B of the present invention are prepared by subjecting the above-mentioned carboxylic acid and / or its alkyl ester and alcohol to esterification reaction or transesterification reaction at 200 to 280 ° C. by a conventional method, and then 5 hPa or less. The polycondensation reaction is carried out at 200 to 300 ° C., preferably 230 to 290 ° C. under reduced pressure to obtain a polymer having a high degree of polymerization, followed by depolymerization with a small amount of a carboxylic acid component.

In the esterification reaction, transesterification reaction and polycondensation reaction, known reaction catalysts can be used.

Examples of the hydroxylalkylamide-based curing agent used as a curing agent in the present invention include those represented by the following general formula. "Primid XL-55" is available from EMS-Chemie.
2 "is commercially available under the trade name.

Embedded image Here, R ¹ represents hydrogen or an alkyl group, and R ² represents an alkylene group.

The compounding amount of the curing agent is preferably in the range of 0.6 to 1.2 equivalents, more preferably 1.0 equivalent, relative to the carboxyl group amount of the polyester resin.

The polyester resin composition for powder coating of the present invention comprises the above-mentioned polyesters A and B and a curing agent, and if necessary, a leveling agent and other additives such as titanium dioxide and carbon black. And kneading at 70 to 150 ° C. using a kneader or a roll.

[0029]

Next, the present invention will be described specifically with reference to examples and comparative examples. The characteristic values were measured by the following method. (a) Acid value It was determined by the method described above. (b) Intrinsic viscosity Measured at 20 ° C. using an equal weight mixture of phenol and ethane tetrachloride as a solvent. (c) Softening point It was heated on a hot bench and determined visually. (d) Gelation time It was determined by the method described above. (e) Blocking resistance A powdered paint was filled up to a height of 4 cm in a bottomed glass tube having a diameter of 3 cm and a height of 7 cm and left in a constant temperature bath at 40 ° C for 1 week.
The powder coating was taken out by turning the glass tube upside down, and the state of the coating was evaluated. ○: Not in bulk, ×: in bulk (f) Weight reduction rate The powder paint was electrostatically coated on a zinc phosphate-treated steel sheet so that the film thickness became 50 to 60 μm, and at 170 ° C. Bake for 20 minutes,
The ratio of the weight difference before and after baking to the weight before baking was determined. (g) Smoothness The smoothness of the coating film was visually evaluated. ：: good, ×: inferior (h) Specular glossiness at 60 ° Determined according to JIS K5400. (i) Impact resistance A sphere having a diameter of 1.27 cm and 500 g was vertically dropped according to JIS K 5400, and the breaking height of the coating film was determined. (If it is 10cm or more, it passes.)

Examples 1 to 7 and Comparative Examples 1 to 6 [Preparation of Polyester]
Was charged to the esterification reaction tank in the amount (mol part) shown in (1), the pressure was increased to 0.25 MPaG, the reaction temperature was gradually raised from 100 ° C., and the esterification reaction was performed at 250 ° C. for 4 hours. After transferring the obtained esterified product to a polycondensation reaction tank, antimony trioxide is added as a catalyst in an amount of 2 × 10 ⁻⁴ mol / acid component mol, the pressure is reduced to 0.4 hPa or less, and the polymerization is carried out at 280 ° C. for 4 hours. A condensation reaction was performed to obtain a polyester having an intrinsic viscosity of 0.45. Next, the compound shown in the column of depolymerization in Table 1 was added to the polyester in an amount (mol part) shown in Table 1, and a depolymerization reaction was performed at 250 ° C. for 2 hours under an atmospheric pressure in an inert gas atmosphere. Polyesters A1 to A3 and polyesters B1 to B5 having the characteristic values shown in Table 1 were obtained. Table 1 shows the characteristic values of each polyester resin.

[0031]

[Table 1]

[Preparation and Test of Powder Coating] Polyester resin, curing agent: "Primid XL-552" manufactured by EMS-Chemie, butyl polyacrylate-based leveling agent: Acronal 4F, benzoin and rutile type titanium dioxide manufactured by BASF: Take CR-90 manufactured by Ishihara Sangyo Co., Ltd. in the amounts (parts by weight) shown in Tables 2 and 3, and use a FM 10B Henschel mixer (Mitsui Miike Seisakusho).
After dry blending, melt-knead at 110 ° C using a PR-46 type co-kneader (manufactured by Buss), cool, pulverize,
A powder coating was obtained by separation with a wire mesh having a mesh size of 106 μm. The obtained powder coating is coated on a zinc phosphate treated steel sheet with a film thickness of 50-60μ.
m and baked at 170 ° C. for 20 minutes. Tables 2 and 3 show the results of evaluating the coating film performance.

[0033]

[Table 2]

[0034]

[Table 3]

The powder coatings obtained in Examples 1 to 7 have good blocking resistance, little weight loss at the time of baking, and have a matting effect, smoothness and strength (impact resistance).
Was excellent.

On the other hand, Comparative Examples 1 and 2 in which the proportion of polyester A is not appropriate, Comparative Example 4 in which the acid value of polyester B is large, Comparative Example 5 in which the difference in the gelation time between polyesters A and B is small, and Polyester A In Comparative Example 6 having a small acid value, no matte coating film was obtained. In Comparative Example 3 in which the acid value of polyester B was small, a coating film having good smoothness and strength (impact resistance) could not be obtained.

[0037]

According to the present invention, a powder which gives a semi-matte or matte coating film having good blocking resistance, little contamination of the furnace during baking and weight reduction, and excellent smoothness and strength. A polyester resin composition for body paint is provided.

Claims (1)

[Claims] 1. An ungelled polyester A having an acid value of 70 mg KOH / g or more, an ungelled polyester B having an acid value of 10 to 50 mg KOH / g, and a hydroxylalkylamide-based curing agent, wherein polyester A and polyester The ratio of B is 70:30 to 10:90 by weight, and the difference (absolute value) between the gel times of polyester A and polyester B is 3
A polyester resin composition for powder coating, wherein the composition is at least one minute.