JPH1017660A - Polyester resin for powder coating material and composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester resin for powder coating materials which can give coating films having good blocking resistance, sufficiently practicable strengths and excellent weather resistance and a composition thereof. SOLUTION: This invention provides a polyester resin for powder coating materials, having an intrinsic viscosity of 0.15-0.40dl/g and an acid value of 13-85mgKOH/g and made from an acid component comprising 70-99.7mol% isophthalic acid, 0.3-3mol% dimer acid and 0-29.7mol% terephthalic acid and an alcohol component based on neopentyl glycol and a composition prepared by mixing this resin with 1.5-12wt.% hydroxylalkylamide curing agent or triglycidyl isocyanurate 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 and a composition for powder coatings, which have good blocking resistance, give a coating film having practically sufficient strength and excellent weather resistance.

[0002]

2. Description of the Related Art In recent years, paints having good weather resistance have been demanded for reasons such as maintenance-free. Among powder coatings, acrylic resin-based coatings are known as having good weather resistance. However, acrylic resin-based powder coatings are expensive and have extremely poor compatibility with other coatings. If mixed with other coatings, they may cause cissing, so the coating line must be isolated. There was a problem.

[0003] Polyester resin-based powder coatings do not have such a problem, but generally have a problem of insufficient weather resistance, and polyester resins for powder coatings having improved weather resistance have been developed. .

For example, Japanese Patent Application Laid-Open No. Hei 6-234941 discloses an improved weather resistance in which isocyanate-based curing agent is blended with a polyester resin having isophthalic acid and neopentyl glycol as main constituents and a hydroxyl group as a terminal group. A polyester resin composition for powder coatings is disclosed.

However, the powder coating using the resin composition has a problem that the strength of the coating film is slightly insufficient in practical use. In order to solve this problem, there is a method of copolymerizing an aliphatic dicarboxylic acid or an aliphatic diol having a molecular weight of about 100 to 140, but in order to obtain a coating film having sufficient strength for practical use, these components must be used. Copolymerization must be performed in a large amount, so that the softening point of the resin is significantly reduced, and there is a problem that a blocking phenomenon in which the powder is aggregated is easily caused.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a polyester resin and a composition for a powder coating material having a good blocking resistance, a coating film having sufficient strength for practical use and excellent weather resistance. Things.

[0007]

Means for Solving the Problems The present inventors have made intensive studies to solve the above problems, and as a result, completed the present invention.

That is, the gist of the present invention is as follows. 1. Intrinsic viscosity 0.15-0.40dl / g, acid value 13-85mgKOH / g
A polyester resin of which 70 to 99.7 mol% of the total acid component constituting the polyester is isophthalic acid, 0.3 to 3 mol% is dimer acid, 0 to 29.7 mol% is terephthalic acid, and the alcohol component is neopentyl glycol. A polyester resin for powder coatings, characterized by being mainly composed of: 2. A polyester resin composition for powder coatings, comprising the above polyester resin and a hydroxyalkylamide-based curing agent or triglycidyl isocyanurate-based curing agent in an amount of 1.5 to 12% by weight.

[0009]

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

The polyester resin of the present invention has an acid component of 70 to 99.7 mol% of isophthalic acid and 0.3 to 3 mol% of dimer acid.
And 0 to 29.7 mol% of terephthalic acid, and the alcohol component is mainly composed of neopentyl glycol.

If the proportion of isophthalic acid in the acid component is smaller than the above range or the proportion of terephthalic acid is larger than the above range, sufficient weather resistance cannot be obtained. Further, if the proportion of the dimer acid is less than the above range, the strength of the coating film becomes insufficient, and if it is too large, the softening temperature of the polyester resin is lowered, and blocking tends to occur when the powder coating material is used, which is not preferable. . In order to simultaneously satisfy the strength and the blocking resistance, it is necessary that the copolymerization amount of the dimer acid is within the above range.

[0012] The dimer acid to be copolymerized includes 36 carbon atoms.
Are preferred. That is, a product obtained by dimerizing an unsaturated fatty acid having 18 carbon atoms such as linoleic acid and linolenic acid and having an unsaturated bond can be used as it is, but is preferably used after hydrogenation.

In the dimerization reaction of unsaturated fatty acids, monomers and trimers are formed together with the dimers, but the dimers are at least 94 mol% and the monomers are at most 2 mol%. , Trimers and the like are preferably used in an amount of 4 mol% or less. If the amount of the monomer is large, the reactivity decreases, and the degree of polymerization becomes difficult to increase.
If the amount of trimers is large, the resin becomes three-dimensional at the stage of resin production, and the smoothness of the coating film is impaired.

[0014] Dimer acid is commercially available from many companies, but those satisfying the above conditions include "Empol 1008" manufactured by Henkel Emery and "PRIP" manufactured by Unichema.
OL 1009 "and the like, and these may be used in combination.

A dicarboxylic acid such as (phthalic anhydride), naphthalenedicarboxylic acid, adipic acid, azelaic acid or cyclohexanedicarboxylic acid may be used in combination with the above dicarboxylic acid as long as the effects of the present invention are not impaired. . Also, as long as the polyester resin does not gel,
3 such as trimellitic acid, pyromellitic acid and trimesic acid
A carboxylic acid having a valency or higher may be used in combination.

As the glycol component, neopentyl glycol is mainly used, and its proportion is preferably at least 70 mol% of the glycol component. When the content of neopentyl glycol is less than 70 mol%, the weather resistance becomes insufficient.

Along with neopentyl glycol, ethylene glycol, diethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, bisphenol A are used as long as the effects of the present invention are not impaired. And a diol such as ethylene oxide adduct of bisphenol S and ethylene oxide adduct of bisphenol S. In addition, a trihydric or higher alcohol such as trimethylolpropane, glycerin, and pentaerythritol may be used in combination as long as the polyester resin is not gelled.

Further, a small amount of a hydroxycarboxylic acid such as 4-hydroxybenzoic acid or ε-caprolactone may be used in combination.

The polyester resin of the present invention has an intrinsic viscosity.
It should be 0.15 to 0.40 dl / g, preferably 0.20 to 0.35 dl / g. The limiting viscosity of polyester resin is 0.
If it is less than 15 dl / g, the softening temperature of the resin will decrease and the blocking resistance will decrease, or the strength of the coating film will tend to decrease.If it exceeds 0.40 dl / g, the crushability of the resin will increase. Tends to be worse.

The polyester resin of the present invention must have an acid value of 13 to 85 mgKOH / g, preferably 16 to 60 mgKOH / g. 13mg acid value of polyester resin
If it is less than KOH / g, there is a tendency for large unevenness to occur on the surface of the coating film and the smoothness tends to decrease.
The strength of the coating tends to decrease.

Further, the polyester resin of the present invention preferably has a softening temperature in the range of 50 to 150 ° C. If the softening temperature is lower than 50 ° C, the blocking resistance tends to be inferior, while if the softening temperature exceeds 150 ° C,
It is necessary to increase the kneading temperature during the production of the paint, and the reaction between the resin and the curing agent proceeds during kneading, and as a result, the smoothness and strength of the coating film tend to decrease.

The polyester resin of the present invention is obtained by subjecting the above-mentioned acid component and alcohol component (including their ester-forming derivatives) as raw materials to esterification or transesterification at a temperature of 200 to 280 ° C. by a conventional method. After 5hPa
Under the following reduced pressure, 200-300 ° C, preferably 230-290 ° C
The polyester can be prepared by a method of performing a polycondensation reaction at the above temperature to obtain a polyester having a high degree of polymerization, adding an acid component to the polyester, and performing a depolymerization reaction.

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

The polyester resin thus obtained is mixed with a curing agent having a functional group that reacts with a carboxyl group to form a resin composition for powder coating. In the present invention, hydroxy resin is used as the curing agent. An alkylamide-based curing agent or a triglycidyl isocyanurate-based curing agent is used. In addition, as a curing agent having a functional group that reacts with a carboxyl group, there is an epi-bis type epoxy resin. However, when an epi-bis type epoxy resin is used, the weather resistance of the coating material is significantly reduced.

Examples of the hydroxyalkylamide-based curing agent include "Primid XL-552" (trade name) manufactured by EMS-Chemie. As the triglycidyl isocyanurate-based curing agent, "ARALDITE PT 810" manufactured by Ciba Geigy is used.
(Product name).

The amount of the curing agent is from 1.5 to 12 of the resin composition.
Weight percent. 1.5% by weight of hardener
When the amount is less than the above, the strength of the coating film decreases, and when the amount is more than 12% by weight, the curing reaction becomes too fast, and the flowability decreases. The amount of the curing agent is selected so as to be in the range of the functional group amount corresponding to the carboxyl group of the polyester resin, preferably in the range of 0.8 to 1.2 times equivalent.

The polyester resin composition for powder coating of the present invention comprises the above-mentioned polyester resin and a curing agent, and if necessary, a curing catalyst, a leveling agent, and other additives, for example, pigments such as titanium dioxide. Can be prepared by kneading a mixture of the above at 70-150 ° C. using a kneader or a roll.

[0028]

Next, the present invention will be described in detail with reference to examples. The characteristic values and the like in the examples were measured or evaluated by the following methods. (a) Intrinsic viscosity Measured at a temperature of 20 ° C. using an equal weight mixture of phenol and ethane tetrachloride as a solvent. (b) Acid value The polyester resin was dissolved in a solution of dioxane and water at a weight ratio of 9/1, heated under reflux for 30 minutes, and then titrated with a potassium hydroxide methanol solution. (c) Softening temperature Resin crushed to a size of 60 to 100 mesh 2.5 m in diameter
m, filled into a bottomed glass tube with a height of 150 mm to a height of 30 mm, immersed the resin-filled part in an oil bath, heated at a rate of 1 ° C./min, and visually determined the temperature at which liquefaction started, The softening temperature was used. (d) Blocking resistance After the powder coating material 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 paint was taken out by turning the glass tube upside down and evaluated according to the state of the paint as follows. Good: There are no lumps in the paint. Poor: There are large aggregates in the paint. (e) Specular glossiness at 60 degrees Determined according to JIS K 5400. (f) Appearance of coating film It was visually evaluated as follows. Good: The coating film has few irregularities. Bad: The coating film has large irregularities. (g) Impact resistance Measured using a ball having a diameter of 1.27 cm and a weight of 1 kg according to JIS K 5400. (Even if the ball was dropped from a height of 20 cm or more, the coating was acceptable if there was no crack in the coating film.) (H) It was determined according to Erichsen JIS Z 2247. (Things that do not crack even when extruded by 5 mm or more are acceptable.) (I) Accelerated weathering resistance WEL-6XS-HC-B / Ec type sunshine weather meter (manufactured by Suga Test Instruments Co., Ltd.) in accordance with JIS K 5400 Using 10
The gloss retention after irradiation for 00 hours was determined. (If this value is 70% or more, it passes.)

Examples 1 to 6 and Comparative Examples 1 to 10 The starting compounds shown in Tables 1 and 2 were charged into an esterification reaction tank in the amounts (mol parts) shown in Tables 1 and 2 at a pressure of 0.
The esterification reaction was carried out at 05 to 1.5 MPa at a temperature of 200 to 260 ° C for 4 hours. After transferring the obtained esterified product to the polycondensation reaction tank, 4 × 10 ⁻⁴ mol of antimony trioxide / 1 mol of the acid component was added, the pressure was reduced to 0.4 hPa, and the polycondensation reaction was performed at 280 ° C. for 4 hours. A polyester having an intrinsic viscosity of 0.45 dl / g was obtained. Next, the depolymerizing agents shown in Tables 1 and 2 were added to the polyester in the amounts (mol parts) shown in Tables 1 and 2, and depolymerization was carried out at 250 ° C. for 2 hours under normal pressure. And the polyester resin of the characteristic value shown in Table 2 was obtained. Polyester resin, hydroxyalkylamide-based curing agent: "Primid XL-552" manufactured by EMS-Chemie or triglycidyl isocyanurate-based curing agent: "ARALDITE PT 810" manufactured by Ciba Geigy,
Curing catalyst: "ARALDITE DT-3126" manufactured by Ciba Geigy, butyl polyacrylate-based leveling agent: "Acronal 4F" manufactured by BASF, benzoin and rutile titanium dioxide pigment: "CR-90" manufactured by Ishihara Sangyo Co., Ltd. After blending in the amount (parts by weight) shown in Table 2 and dry blending with an FM 10B Henschel mixer (Mitsui Miike Seisakusho), PR-46
The mixture was melt-kneaded at 110 ° C. using a mold co-kneader (manufactured by Buss Co., Ltd.), cooled, pulverized, and then classified with a 140-mesh wire net to obtain a powder coating. The obtained powder coating was electrostatically coated on a zinc phosphate-treated steel sheet and baked at 180 ° C. for 20 minutes. Tables 1 and 2 show the results of evaluation of the blocking resistance of the paint and the performance of the coating film.

[0030]

[Table 1]

[0031]

[Table 2]

The powder coatings obtained in Examples 1 to 6 all had good blocking resistance, weather resistance and strength of the coating film.

On the other hand, in Comparative Examples 1 and 7, the copolymerization amount of the dimer acid was large, so that the blocking resistance was poor. In Comparative Examples 2 and 8, the dimer acid was not copolymerized, so that the impact resistance was low. Sex and Erichsen were low. In Comparative Example 3, the amount of dimer acid copolymerized was small, and thus Erichsen was low. In Comparative Example 4, the copolymerization amount of isophthalic acid was small, and the weather resistance was poor. Further, in Comparative Examples 5 and 9, since the amount of the curing agent was large, the appearance of the coating film was poor,
In Comparative Examples 6 and 10, since the amount of the curing agent was small, the impact resistance and Erichsen were low.

[0034]

According to the present invention, when a powder coating is prepared by using the resin of the present invention, it is possible to obtain a powder coating which has good blocking resistance and gives a coating film having sufficient strength and excellent weather resistance for practical use. .

Claims (2)

[Claims] 1. An intrinsic viscosity of 0.15 to 0.40 dl / g and an acid value of 13 to
85 mg KOH / g polyester resin, 70 to 99.7 mol% of all acid components constituting polyester is isophthalic acid,
A polyester resin for powder coatings, wherein 0.3 to 3 mol% is dimer acid, 0 to 29.7 mol% is terephthalic acid, and the alcohol component is mainly neopentyl glycol. 2. A polyester resin composition for powder coatings, comprising the polyester resin according to claim 1 and a hydroxyalkylamide-based curing agent or a triglycidyl isocyanurate-based curing agent in an amount of 1.5 to 12% by weight.