JPH11228676A - Polyester resin and composition for powder coating, and powder coating by using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a polyester resin and a composition, for a powder coating, capable of providing the powder coating excellent in weather resistance and solvent resistance, and further to obtain the powder coating by using the polyester and the composition. SOLUTION: This polyester resin for a powder coating has 13-85 mg/g acid value and 0.15-0.40 dl/g intrinsic viscosity and is composed of constituents consisting essentially of isophthalic acid as an acid component, and ethylene glycol as an alcohol component. The polyester resin composition for the powder coating is obtained by compounding a β-hydroxyalkylamide-based hardening agent or a triglycidyl isocyanurate-based hardening agent with the polyester resin.

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 a powder coating capable of forming a powder coating excellent in weather resistance and solvent resistance, and a powder coating using the same. .

[0002]

2. Description of the Related Art Compared with conventional solvent-based paints, powder paints are non-polluting paints, can be used immediately after painting, do not require multiple layers of coating, are relatively inexpensive. In view of the fact that it can be recovered and used, it has been recognized that it has been rapidly growing in recent years as a paint for protective decoration of members such as building materials, home electric appliances, and automobile parts.

Heretofore, epoxy resin-based, acrylic resin-based, and polyester resin-based powder coatings have been mainly known. In particular, polyester resin-based powder coatings have a well-balanced coating film performance. Also known as paint.

In order to obtain a polyester resin powder coating having excellent weather resistance, it is necessary to improve the weather resistance of the polyester resin as a main component, and usually, the copolymerization ratio of the neopentyl glycol component is increased. Polyester resin is used. Since neopentyl glycol has no hydrogen bonded to the carbon at the β-position, it is known that polyester resins containing a large amount of this component have good weather resistance, but generally have poor solvent resistance. However, it is not suitable for applications that particularly require. So in this field,
With terephthalic acid and ethylene glycol as main components,
As the third component, a polyester resin obtained by copolymerizing a small amount of isophthalic acid has been used, but there is a problem that the weather resistance is not sufficient.

As described above, it is difficult to obtain a polyester resin which simultaneously satisfies both the weather resistance and the solvent resistance of the conventionally used polyester resin for powder coatings. A method is used in which a resin composition in which an acrylic resin having improved compatibility with the polyester resin is blended with a polyester resin having an increased content is used as a main component of the powder coating, but this method is an expensive acrylic resin. However, there is a problem that the paint cost is increased due to the use of the paint.

On the other hand, the present inventors have proposed to solve the above-mentioned problems by adding a blocked isocyanate resin to a polyester resin having a specific intrinsic viscosity and a hydroxyl value and containing isophthalic acid and ethylene glycol as main components. A method has been proposed in which a resin composition containing a curing agent is used as a main component of a powder coating (Kaihei 7-309933). However, in this method, since the blocked isocyanate is used, there has been a problem that the blocking agent volatilizes during baking of the powder coating, and the baking furnace and the environment are easily contaminated.

[0007]

DISCLOSURE OF THE INVENTION The present invention provides a polyester resin and a composition for a powder coating which can be formed into a powder coating excellent in weather resistance and solvent resistance, and a powder coating using the same. Is what you do.

[0008]

Means for Solving the Problems The present inventors have made intensive studies to solve the above problems, and as a result, have reached the present invention. That is, the gist of the present invention is as follows. (1) Acid value 13-85 mgKOH / g, intrinsic viscosity 0.15-0.40dl / g
A polyester resin for powder coatings, characterized by comprising isophthalic acid as an acid component and ethylene glycol as an alcohol component as main components. (2) A polyester resin composition for powder coatings, wherein a β-hydroxyalkylamide-based curing agent or a triglycidyl isocyanurate-based curing agent is blended with the polyester resin described in (1) above. (3) A powder coating using the polyester resin composition for powder coating according to (2).

[0009]

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

The polyester resin for powder coating of the present invention comprises:
It is necessary that the acid component is 13 to 85 mgKOH / g, the intrinsic viscosity is 0.15 to 0.40 dl / g, and the main components are isophthalic acid as an acid component and ethylene glycol as an alcohol component.

If the acid value of the polyester resin is less than 13 mgKOH / g, large irregularities tend to be formed on the surface of the coating film, and the smoothness tends to decrease. If the acid value exceeds 85 mgKOH / g, the mechanical strength of the coating film decreases. It tends to decrease. Further, when the intrinsic viscosity of the polyester resin is less than 0.15 dl / g, the anti-blocking property of the powder coating tends to decrease, and when the intrinsic viscosity exceeds 0.40 dl / g, the pulverization property of the resin tends to deteriorate. Become. Furthermore, if the ratio of isophthalic acid and ethylene glycol is low,
A polyester resin satisfying both weather resistance and solvent resistance cannot be obtained at the same time.

As the acid component of the polyester resin, isophthalic acid is mainly used, and its proportion is preferably at least 70 mol%, more preferably at least 80 mol%, and most preferably at least 90 mol% in the acid component. It is preferably at least mol%. If this ratio is less than 70 mol%, the weather resistance tends to decrease.

As the acid component, other dicarboxylic acids may be used in a small amount (less than 30 mol%) as long as the effects of the present invention are not impaired. Such dicarboxylic acids include terephthalic acid and phthalic anhydride. Examples include aromatic dicarboxylic acids such as acids, adipic acid, sebacic acid, azelaic acid, aliphatic dicarboxylic acids such as dodecanedicarboxylic acid, and alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid. Further, as long as the polyester resin is not gelled, a trivalent or higher polycarboxylic acid such as trimellitic acid, pyromellitic acid or trimesic acid may be used in combination.

As the alcohol component, ethylene glycol is mainly used, and its proportion is preferably at least 70 mol%, more preferably at least 80 mol%, most preferably at least 90 mol% in the alcohol component. It is preferable that If this ratio is less than 70 mol%, the solvent resistance tends to decrease.

As the alcohol component, other diols may be used in a small amount (less than 30 mol%) as long as the effects of the present invention are not impaired. Such diols include neopentyl glycol, diethylene glycol,
Aliphatic diols such as propylene glycol, 1,4-butanediol and 1,6-hexanediol, alicyclic diols such as 1,4-cyclohexanedimethanol and 1,4-cyclohexanediol, and ethylene oxide adducts of bisphenol A And aromatic diols such as ethylene oxide adduct of bisphenol S. Further, a trifunctional or higher functional polyol such as trimethylolpropane, glycerin, pentaerythritol or the like may be used in combination as long as the polyester resin is not gelled.

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

The polyester resin of the present invention is obtained by subjecting the above-mentioned acid component and alcohol component (including their ester-forming derivatives) to esterification or transesterification at a temperature of 150 to 260 ° C. by a conventional method. After
Under reduced pressure of about 13 hPa, 200-300 ° C, preferably 230-29
It can be prepared by a method in which a polycondensation reaction is carried out at a temperature of 0 ° C to obtain a polyester having a high degree of polymerization, and then a carboxylic acid is added to carry out a depolymerization reaction at 220 to 280 ° C.

After the esterification or transesterification reaction is carried out at a temperature of 150 to 260 ° C. by a conventional method, the reaction is carried out at a normal pressure or under a reduced pressure of about 50 to 100 hPa, preferably at 200 to 300 ° C.
It can also be prepared by a method of performing a polycondensation reaction at a temperature of 230 to 290 ° C. until a predetermined intrinsic viscosity and an acid value are obtained.

Examples of the carboxylic acid component used in the above depolymerization reaction include dicarboxylic acids such as isophthalic acid, phthalic acid and phthalic anhydride, and tri- or more functional groups such as trimellitic acid, trimellitic anhydride and pyromellitic acid. A polyvalent carboxylic acid is used.

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

Further, the polyester resin obtained by the above method preferably has a softening temperature in the range of 50 to 150 ° C. If the softening temperature is less than 50 ° C, the powdered resin tends to aggregate and form a lump, and the blocking resistance tends to decrease.If the softening temperature exceeds 150 ° C, it is necessary to increase the kneading temperature during paint production. The reaction between the resin and the curing agent proceeds during the kneading, and as a result, the smoothness and mechanical strength of the coating film tend to decrease.

In the polyester resin composition for powder coating of the present invention, a β-hydroxyalkylamide-based curing agent or a triglycidyl isocyanurate-based curing agent must be blended with the polyester resin. The type of these curing agents is not particularly limited, but examples of β-hydroxyalkylamide-based curing agents include Primid XL-552 manufactured by EMS. Further, the triglycidyl isocyanurate-based curing agent, for example,
Araldite PT-810 manufactured by Geigy Corporation is mentioned.

The compounding amount of the curing agent is suitably 0.8 to 1.2 equivalents, more preferably 1.0 equivalent, based on the acid value of the polyester resin.

The powder coating composition of the present invention is obtained by mixing the above-mentioned polyester resin composition for powder coating composition with a curing catalyst, a leveling agent, and other additives, if necessary, for example, a pigment such as titanium dioxide or carbon black. Can be prepared by melt-kneading at 70 to 150 ° C. using a kneader or a roll.

[0025]

Next, the present invention will be described in detail with reference to examples. In the examples, the characteristic values of the resin and the evaluation of the coating film performance were measured by the following methods. (a) Intrinsic viscosity The intrinsic viscosity of the polyester resin was determined by measuring at 20 ° C. using an equal weight mixture of phenol and ethane tetrachloride as a solvent. (b) Acid value 0.5 g of the polyester resin was dissolved in 50 ml of a mixed solvent of dioxane / distilled water = 10/1 (weight ratio), heated to reflux, and titrated with a 0.1 N methanol solution of potassium hydroxide. (c) Softening temperature Polyester resin pulverized to a size of 60 to 100 mesh is filled into a bottomed glass tube of 2.5 mm in diameter and 150 mm in length to a height of 30 mm, and the resin-filled part is immersed in an oil bath. 1 ℃ /
The temperature at which the temperature rises at a rate of one minute and the liquefaction begins is visually determined and defined as the softening temperature. (d) Specular glossiness at 60 degrees Determined according to JIS K 5400. (e) Impact resistance According to JIS K 5400, sandwich a coated steel plate between a shooting mold with a 1.27 cm diameter spherical surface and a cradle with a corresponding depression so that the coating film contacts the spherical surface, and from above A 1 kg weight was dropped vertically to determine the cracking height of the coating film. 30cm
Those that do not crack the coating film even when dropped from the above height pass. (f) Solvent resistance Xylene was dropped on the coating film, left for 2 hours, and then pressed with a nail to determine whether or not a trace remains. ：: No trace is left on the coating film. X: A trace remains on the coating film. (g) Accelerated weather resistance According to SK 5400, using a WEL-6-XS-HC-B-EC type sunshine weather meter (manufactured by Suga Test Instruments Co., Ltd.), the gloss retention (% ). Gloss retention rate
80% or more are acceptable.

Examples 1 to 6 and Comparative Examples 1 to 4 The starting compounds shown in Table 1 were placed in an esterification reactor, and subjected to an esterification reaction at 250 ° C. for 4 hours under a slight pressure (0.24 MPaG), and the resulting water was removed. An esterified product was prepared by removing it from the reaction system. After transferring the obtained esterified product to a polycondensation reaction vessel, as a catalyst, 2 × 10 ⁻⁴ mol of antimony trioxide / 1 mol of an acid component and 2 × 10 ⁻⁵ mol of tetrabutyl titanate / 1 mol of an acid component, and a stabilizer As triethyl phosphate 2x
10 ^-4 mol / 1 mol of acid component was added, and 280
A polycondensation reaction was performed at a temperature of 3 ° C. for 3 hours to obtain a polyester resin having an intrinsic viscosity of 0.45 dl / g. Subsequently, trimellitic acid and / or isophthalic acid were added to the polyester resin in the amounts (mol parts) shown in Table 1 and depolymerization was carried out at 250 ° C. for 2 hours under normal pressure. Was obtained. Next, Table 2 was added to the obtained polyester resin.
1.0 to the acid value of polyester resin
Double equivalents, curing catalysts shown in Table 2 (used only in Example 6 and Comparative Example 4), butyl polyacrylate-based leveling agent (Acronal 4F, manufactured by BSF Inc.), benzoin and rutile dioxide Titanium pigment (CR-90, manufactured by Ishihara Sangyo Co., Ltd.) was blended in the amount (parts by weight) shown in Table 2 and dry-blended with a Henschel mixer (Mitsui Miike Seisakusho, FM10B type). Made, PR-46
Melt-kneaded at 110 ° C using a
Classify with a mesh (106μm) wire mesh, average particle size about 50μm
Powder coating was obtained. The obtained powder coating material was electrostatically coated on a zinc phosphate treated steel plate and baked at 180 ° C. for 20 minutes.

Table 1 shows the blending of the raw materials, the type of depolymerizing agent and the characteristic value of the polyether resin, and Table 2 shows the blending of the paint and the evaluation results of the coating film performance.

[0028]

[Table 1]

[0029]

[Table 2]

Regarding the coating films obtained in Examples 1 to 6,
The 60 degree specular gloss, impact resistance, solvent resistance, and accelerated weather resistance were all good. On the other hand, in Comparative Example 1, the proportion of the isophthalic acid component in the used polyester resin was small (not the main component), so that the accelerated weather resistance of the coating film was poor. In Comparative Example 2, the solvent resistance of the coating film was inferior because the proportion of the ethylene glycol component in the used polyester resin was small (not the main component). In Comparative Example 3, since the limiting viscosity of the polyester resin used was too high, it was difficult to pulverize the resin, and a powder coating that could be used for the test could not be obtained. In Comparative Example 4, since the epi-bis type epoxy resin-based curing agent (Araldite AER-6003, manufactured by Ciba-Geigy) was used as the curing agent, the accelerated weather resistance of the coating film was poor.

[0031]

According to the present invention, it is possible to obtain a polyester resin and a composition for a powder coating capable of forming a powder coating excellent in weather resistance and solvent resistance, and a powder coating using the same. it can.

Claims (3)

[Claims] An acid value of 13 to 85 mgKOH / g and an intrinsic viscosity of 0.15
A polyester resin for powder coatings, wherein the polyester resin has a main component of isophthalic acid as an acid component and ethylene glycol as an alcohol component. 2. The polyester resin according to claim 1,
-A polyester resin composition for powder coatings containing a hydroxyalkylamide-based curing agent or a triglycidyl isocyanurate-based curing agent. 3. A powder coating using the polyester resin composition for powder coating according to claim 2.