KR19980057365A - Manufacturing method and powder coating composition of polyester resin - Google Patents

Abstract

The present invention relates to a method for preparing a polyester resin and a powder coating composition, and more particularly, to a crystalline polyester resin and bisphenol prepared by using a hydroxyl polyester prepolymer, a carboxyl polyester prepolymer, and a polyhydric alcohol. -A method for producing a polyester resin which is concealed even in a thin film with excellent dispersibility with pigments and excellent smoothness and clarity by mixing an epoxy resin mainly composed of Bisphenol-A as a curing agent and It relates to a powder coating composition containing.

Description

Manufacturing method and powder coating composition of polyester resin

The present invention relates to a method for preparing a polyester resin and a powder coating composition, and more particularly, to a crystalline polyester resin and bisphenol prepared by using a hydroxyl polyester prepolymer, a carboxyl polyester prepolymer, and a polyhydric alcohol. -A method for producing a polyester resin which is concealed even in a thin film with excellent dispersibility with pigments and excellent smoothness and clarity by mixing an epoxy resin mainly composed of Bisphenol-A as a curing agent and It relates to a powder coating composition containing.

In recent years, as the Green Round has emerged, international regulations have been strengthened in many aspects of the environment, including organic solvent emissions and working environment. Powder coating, deaerated paint, has been widely used and its marketability is highly appreciated. have.

Acidic polyester resins used in conventional thermosetting powder coatings are in an amorphous state and have a relatively high melt viscosity and poor dispersibility with pigments, resulting in a decrease in the appearance and smoothness of the coating film and thin film coating (30 μm). Poor appearance and there was a problem that the concealment is lowered. When the curing ability is reduced to improve the flowability of the polyester resin in the molten state, the appearance is improved and the concealment during thin film is improved, but the physical properties and the solvent resistance are deteriorated. In addition, if a thin film is formed by lowering the softening point of the paint and lowering the melt viscosity, the coating material is blocked during storage, resulting in deterioration of storage properties, so that the conventional hybrid powder coating is limited due to the above disadvantages. (US Pat. No. 4,094,721).

In general, in order to form a thin film, a good wettability and dispersibility with a pigment are required. To this end, the powder coating resin itself should have the following characteristics.

First, the resin itself must have excellent flowability. Low melt viscosity results in good flow behavior due to intermolecular attraction, which results in good wettability and dispersibility, and low molecular weight binders exhibit low melt viscosity.

Second, in order to form excellent flowability and smoothness, it must have a low melt viscosity within a range that does not affect the storage stability. To produce a resin with a lower melt viscosity, the resin itself must form a crystalline polymer. The crystalline polyester resins used in the present invention, having the above properties, exhibit lower melt viscosity than amorphous resins of similar molecular weight currently used.

Third, the molecular weight distribution should be a resin having a dense molecular weight distribution rather than evenly distributed from low to high molecular weight.

The high crystallization of the resin improves shelf life at room temperature and, when melted, forms faster physical properties, resulting in rapid impregnation of the pigment. When the intermolecular structure to facilitate the crystallization is symmetric (symmetric) structure is more favorable to crystallization, the more regular the condensation structure of the structure, the faster the crystallization rate. As a result, the crosslinking density and glass transition temperature are increased and the melt viscosity is lowered.

The thin powder coating should have all the physical properties, appearance, and concealment of the film thickness of 50 μm or more at the film thickness of 30 μm or less, and therefore should have a very low melt viscosity and thus have a minimum glass transition temperature to prevent deterioration of storage properties. Should have

In order to improve dispersibility with the pigment, a functional group having a polar group must be disposed at the polymer end, and these functional groups comprehensively wrap the pigment to improve pigment dispersion, thereby improving concealment of the coating film to a desired level.

In the present invention, a low molecular weight high crystalline oligomer having good physical properties and excellent thermal flow properties while having a storage property basically required to solve the problem of applying the conventional powder coating composition to a thin film and to impart the above-mentioned characteristics to the resin. The purpose of this is to make (Oligomer) and to make thin film by modifying the prepolymer.

Still another object of the present invention is to prepare a powder coating composition by mixing an epoxy resin with a crystalline polyester resin synthesized through a three-step manufacturing method, which is excellent in dispersibility with pigments and excellent in smoothness and sharpness. It is an object of the present invention to provide a powder coating composition capable of concealing.

The present invention is a method for producing a polyester resin for powder coating, a process of preparing a hydroxyl polyester prepolymer represented by the following formula (1) by reacting a mixture of an organic acid monomer mixture and an alcohol, an acid anhydride having 4 to 12 carbon atoms And a mixture of dihydric and trihydric alcohols to prepare a carboxyl polyester prepolymer represented by the following Chemical Formula 2, and a hydroxyl prepolymer represented by Chemical Formula 1, a carboxyl polyester prepolymer represented by Chemical Formula 2, and It characterized by consisting of a process of producing a crystalline polyester resin by polymerizing a divalent or higher polyacid mixture.

R in the above formulas is-(CH ₂ )-, phenyl or cyclohexyl group; R 'is-(CH ₂ ) _n -or an aromatic compound; n is an integer from 1 to 12.

In addition, the present invention is a powder coating composition consisting of a resin, a curing agent and an additive, 30 to 50% by weight of the crystalline polyester resin prepared above, diglycidyl ether bisphenol A type epoxy resin 20 to 50 of the equivalent 600 to 1,000 A powder coating composition comprising 20% by weight, 20% to 60% by weight of titanium dioxide, and 1 to 5% by weight of a curing catalyst and additives.

The present invention will be described in more detail as follows.

The crystalline polyester resin prepared by the production method of the present invention has a good balance of thermal behavior, melt viscosity, softening point and crosslinking, and excellent appearance, stable physical properties and dispersibility with pigments by appropriate selection of reaction conditions. Therefore, the powder coating composition having the main component thereof can be thin film coating even before and after 30 ㎛.

Scheme 1, Scheme 2 and Scheme 3 schematically illustrate the process of preparing the crystalline polyester resin of the present invention.

R in the above schemes is-(CH ₂ )-, phenyl or cyclohexyl group; R 'is-(CH ₂ ) _n -or an aromatic compound; n is an integer from 1 to 12.

Referring to the process of producing the crystalline polyester resin of the present invention in detail.

The first step is to prepare a hydroxyl prepolymer represented by the formula (1) using an organic acid monomer mixture consisting of a bifunctional carboxylic acid or an ester-forming derivative thereof and an alcohol mixture having 2 to 12 carbon atoms. The organic acid monomer mixture has 5 to 20% by weight of linear aliphatic monomer having 4 to 12 carbon atoms in the molecule and having two or more carboxyl groups, 60 to 90% by weight of para aromatic carboxylic acid, and 10% by weight of ortho or metaaromatic carboxylic acid. It consists of the following. The alcohol mixture is composed of alicyclic or aliphatic alcohols having 2 to 4 hydroxyls and 2 to 12 carbon atoms. The organic acid monomer mixture and the alcohol mixture were introduced in a reactor equipped with a stirrer, a thermometer, a nitrogen (inert gas) injector, and a cooler so that the equivalence ratio of (-OH) / (-COOH) was 1.1 to 1.5. The hydroxyl prepolymer represented by the formula (1) having a hydroxyl value (OH value) of 30 to 300, more preferably 30 to 150, is prepared while removing the condensed water.

In the second step, a low molecular weight carboxyl polyester prepolymer represented by Chemical Formula 2 is prepared by polymerizing an acid anhydride having 4 to 12 carbon atoms and an alcohol mixture. As the acid anhydride, one or two or more selected from acid anhydrides having 1 to 12 carbon atoms are used. As the alcohol mixture, an alcohol mixture containing hydroxy dimethylpropyl hydroxy dimethyl propenoate and a trivalent or higher alcohol among the alcohol compounds mentioned in step 1 as essential components is used. The acid anhydride and the alcohol mixture were heated and maintained at 150-180 ° C at an equivalence ratio of (-OH) / (-COOH) of 0.5 to 0.95, and the acid value (-COOH value) was 150 to 300 and the number average molecular weight was The carboxyl polyester prepolymer represented by the said Formula (2) which is 500-3000, More preferably, 500-1500 is manufactured. In this case, when reacted for a long time or reacted at the above temperature, the ring-opened anhydride group may recombine or condensed water may be generated, thereby not showing satisfactory physical properties.

The third step is 10 to 40 parts by weight of the carboxyl polyester prepolymer represented by the formula (2) prepared in the second step and a polyvalent polyvalent to 100 parts by weight of the hydroxyl prepolymer represented by the formula (1) prepared in the first step 5-20 parts by weight of the acid mixture is added to the mixture to increase the temperature, thereby preparing a crystalline polyester resin represented by Chemical Formula 3 as an object of the present invention. It is prepared to have 1 to 2 branched sites and 2 to 3 reactive carboxyl groups (-COOH). Remove the condensed water while reacting at 190 to 200 ℃, and increase the nitrogen to increase the degree of polymerization at the appropriate upper limit of the acid value or viscosity to be obtained to remove condensed water and unreacted substances (monomers) of the reaction system or to 100 to 200 mmHg. Reaction under reduced pressure removes condensed water and unreacted material.

The crystalline polyester resin represented by Chemical Formula 3 thus prepared has a final acid value (AV) of 30 to 300, preferably 50 to 150, a melt viscosity (175 ° C.) of 5,500 to 7,500 (CP), and a softening point ( ℃) is 100-120 degreeC, glass transition temperature (degreeC) is 40-70 degreeC, a number average molecular weight is 1,500-7,000, More preferably, it is 2,000-5,000.

In the three step process, the divalent or higher polyacid mixture is to give a branched site to the saturated polyester, thereby improving the appearance or chemical resistance of the coating film. When the amount of the divalent or higher polyacid mixture exceeds 20 parts by weight with respect to 100 parts by weight of the hydroxyl prepolymer represented by the formula (1), the crosslinking increases, the glass transition temperature and the softening point are increased, but the flexibility and the melt viscosity are decreased. When lowered and used below 5 parts by weight, the glass transition temperature and softening point are lowered, resulting in poor storage.

In addition, what is specifically considered in the three step process is the amount of the carboxyl polyester prepolymer represented by the formula (2). When the amount of the carboxyl polyester prepolymer represented by the formula (2) exceeds 40 parts by weight based on 100 parts by weight of the hydroxyl prepolymer represented by the formula (1), flowability and dispersibility with the pigment are improved, but deterioration of storage properties is feared. When it is used less than 10 parts by weight, the storage and mechanical properties are good, but the chemical resistance and flowability is lowered, the dispersibility with the pigment is also reduced, leading to a decrease in hiding when coating the thin film. Thus, considering the characteristics of each resin to maintain the appropriate balance to have more than complementary physical properties.

In the composition of the organic acid monomer mixture used in the preparation of the hydroxyl polyester represented by the formula (1), when the linear aliphatic monomer having two or more carboxyl groups is less than 5% by weight, the melt viscosity decreases to increase the flow rate, That is, when the appearance of the coating film is lowered and when used in excess of 20% by weight, the flowability is increased, but the glass transition temperature and the softening point are lowered, so that the storage property is lowered. The compound used at this time may be one or two or more selected from adipic acid, azeline acid, sebacic acid, succinic acid, glutaric acid, malonic acid, succinic acid, defic acid and pimalic acid.

When the para-aromatic carboxylic acid is used less than 60% by weight, the chemical resistance and chemical properties are lowered. When the para-aromatic carboxylic acid is used more than 90% by weight, the crystallinity is too high, leading to a decrease in mechanical properties and appearance. In addition, when the amount of the ortho or meta aromatic carboxylic acid is used in excess of 10% by weight has a detrimental effect on mechanical properties, crosslinking density and reactivity. The aromatic carboxylic acid having two or more reactive carboxyl groups or derivatives thereof may be selected from phthalic acid, phthalic anhydride, terephthalic acid, isophthalic acid, dimethyl terephthalate, dimethylisophthalate, trimellitic acid and trimellitic anhydride. It is preferable to select more than one type.

The alcohol compound is a cycloaliphatic or aliphatic alcohol having 2 to 4 hydroxyl groups and 2 to 12 carbon atoms, for example neopentyl glycol, hydroxy dimethylpropyl hydroxy dimethyl propenoate, ethylene glycol, diethylene Glycol, propylene glycol, dipropylene glycol, triethylene glycol, 1,3-butylene glycol, 1,4-butylene glycol, 1,6-hexanediol, 1,5-pentanol, trimethylolpropane, ditrimethylol One or two or more selected from propane, trimethylolethene, triethylolpropane, glycerin and pentaerythritol can be used.

The acid anhydride used in the second step, namely, the preparation of the carboxyl polyester prepolymer represented by Chemical Formula 2, is an alicyclic monomer such as methylhexahydrophthalic anhydride, hexahydrophthalic anhydride, succinic anhydride, tetrahydrophthalic anhydride, methyltetra One or two or more selected from hydrophthalic anhydride and methylendomethylenetetrahydrophthalic anhydride can be used.

The alcohol compound is selected from among the alcohols used in the step 1, but hydroxy dimethyl hydroxy dimethyl propenoate and ditrimethylol propanol in the trihydric or higher alcohol are essentially contained. DTMP, a tetrahydric alcohol, gives many hydroxy groups to the resin backbone to improve the dispersibility by increasing the degree of branching and increases the crystallinity of the resin with a single ester bond. If the content is more than 50% by weight in the alcohol compound, the flowability is increased, but storage deterioration is feared. If the content is less than 30% by weight, the flowability is feared. Gelatinized or the molecular weight is large, the crystalline oligomer can not be produced, if less than 20% by weight of the cross-linking density is low, there is a concern for storage properties.

As described above, the manufacturing process of the crystalline polyester resin according to the present invention comprises a three-step reaction as mentioned above. In the conventional two-step reaction, the resin structure becomes amorphous and the melt viscosity is high and flowability Due to this deterioration, no concealment was made during thin film coating. However, the three-step method of the present invention mentioned above introduced a high crystalline oligomer (carboxyl polyester) represented by Formula 2 as an intermediate to increase the crystallinity of the resin and lower the melt viscosity to develop a thin film type resin.

Powder coating compositions containing epoxy resin, titanium dioxide, a curing catalyst and other conventional additives in the crystalline polyester resin prepared above are also included in the present invention. The carboxyl group located at the terminal of the crystalline polyester resin represented by the formula (3) contained in the powder coating composition forms a solid and beautiful coating film by the ring-opening addition reaction as follows with the epoxy group of the epoxy resin, and the reaction is shown in Scheme 4. Indicated.

R in the above scheme is as defined above.

Next, look at the manufacturing process of the powder coating composition of the present invention.

30 to 50% by weight of the crystalline polyester resin represented by the general formula (3), 20 to 50% by weight of the diglycidyl ether bisphenol-A type epoxy resin equivalent to 600 to 1000, 20 to 60% by weight of titanium dioxide and a curing accelerator The powder coating composition of the present invention is prepared by mixing 1 to 5% by weight of an additive and passing it through an extruder.

The amount of the epoxy resin represented by the formula (E) to be contained during preparation of the powder coating composition according to the present invention is adjusted according to the acid value of the crystalline polyester resin represented by the formula (3) and the equivalent ratio of the epoxy resin. Curing accelerators include quaternary ammonium salts such as tetramethylammonium bromide or organotin compounds such as imidazoles and butyltin laurate. In addition, additives commonly used in powder coating, such as flow improvers, antioxidants, ultraviolet absorbers, and the like are added.

The powder coating prepared in this way has a low melt viscosity and good thermal flow when forming a coating film, and thus has good storage stability and good general physical properties at 35 to 40 ° C due to the necessary curing ability and sufficient glass transition temperature, such as solvent type. In addition, the thin film of 30 ± 5 ㎛ has excellent hiding power, appearance and gloss.

When explaining this invention based on a manufacture example and an Example, as follows, this Example of manufacture does not limit the scope of the present invention.

Production Example 1 hydroxyl polyester resin 1 (A-1)

It is a metal-based catalyst for an alcohol mixture of 1,500 g of terephthalic acid, 164 g of isophthalic acid, 117 g of adipic acid, 895 g of neopentyl glycol, 525 g of hydroxy dimethylpropyl hydroxy dimethyl propenoate, and 36 g of ethylene glycol. 4 g of butylchlorine dihydroxide (Fesket-4101, manufactured by MT) was added thereto, the temperature was raised to 250 ° C, and polymerization was carried out until no condensed water was produced. At this time, in order to remove the unreacted material and condensed water in the resin and to increase the degree of polymerization, an excess of nitrogen gas was added or the reaction was carried out under reduced pressure at 30 to 50 mmHg. The hydroxyl value of this prepolymer was 45, the acid value was 5, and the number average molecular weight was 1200.

Production Example 2 hydroxyl polyester resin 1 (A-2)

Alcohol mixture of organic acid monomer mixture of 1,000 g of terephthalic acid and 114 g of adipic acid and 600 g of neopentyl glycol, 350 g of hydroxy dimethylpropyl hydroxy dimethyl propenoate, 70 g of 1,6-hexanediol and 27 g of ditrimethylol propane To the catalyst was added 2 g of butylchlorine dihydroxide (Fesket-4101, manufactured by MT) as a catalyst, and the temperature was raised to 250 ° C until the condensation water was not produced. The hydroxyl value of this prepolymer was 50 and the number average molecular weight was 1,400.

Production Example 3 Hydroxyl Polyester Resin 1 (A-3)

1,200 g of terephthalic acid, 137 g of isophthalic acid, 179 g of adipic acid and 780 g of neopentyl glycol, 780 g of hydroxy dimethylpropyl hydroxy dimethyl propenoate, 74 g of diethylene glycol, and 40 g of trimethylolpropane 2.7 g of dibutyltin oxide was added to the mixture, and the temperature was raised to 250 ° C until the condensed water was not produced. The hydroxyl value of this prepolymer was 50 and the number average molecular weight was 1,200.

[Production Example 4] Hydroxyl Polyester Resin 1 (A-4)

Acetate 2.0 in an alcohol mixture of 800 g of dimethyl terephthalate, 80 g of adipic acid, an organic acid monomer mixture and 550 g of neopentyl glycol, 270 g of hydroxy dimethylpropyl hydroxy dimethyl propenoate, 50 g of ethylene glycol and 30 g of trimethylolpropane The reaction mixture was heated to 210 ° C. while removing methanol, cooled to 120 ° C., and then reacted with 50 g of succinic acid and 80 g of isophthalic acid, followed by 2.0 g of dimethyltin oxide. The hydroxyl value of this prepolymer was 55 and the number average molecular weight was 1,300.

Production Example 5 Carboxyl Polyester Resin 2 (B-1)

An acid anhydride mixture of 1,000 g of methylhexahydrophthalic anhydride, 150 g of succinic anhydride, 300 g of ditrimethylolpropane, 50 g of neopentyl glycol, and 350 g of hydroxy dimethylpropyl propenoate were charged and the anhydride group was completely ring-opened at 150 ° C. The reaction was continued until it was. The acid value of this resin was 170 mg KOH / g and the number average molecular weight was 600.

Production Example 6 Carboxyl Polyester Resin 2 (B-2)

An acid anhydride mixture of 900 g of hexahydrophthalic anhydride, 150 g of methyltetrahydrophthalic anhydride, 170 g of neopentyl glycol, 380 g of hydroxy dimethylpropyl hydroxy dimethyl propenoate and 155 g of trimethylol propane were added thereto, and Preparation Example 5 The reaction was carried out in the same manner as in. The acid value of this resin was 150 mg KOH / g and the number average molecular weight was 500.

Production Example 7 Carboxyl Polyester Resin 2 (B-3)

1,500 g of hexahydrophthalic anhydride, 350 g of succinic anhydride, an acid anhydride mixture of 70 g of tetrahydrophthalic anhydride, 452 g of ditrimethylol propane, 195 g of neopentyl glycol, 450 g of hydroxy dimethylpropyl hydroxy dimethyl propenoate 1.5 g of dimethyltin oxide was added to 85 g of butylethyl propane diol, and the reaction was carried out in the same manner as in Preparation Example 5. The acid value of this resin was 230 mgKOH / g and the number average molecular weight was 700.

[Manufacture example 8] Carboxyl Polyester Resin 2 (B-4)

Preparation Example 5 was added by adding 1.5 g of dibutyltin oxide to 1,200 g of methylhexahydrophthalic anhydride, 500 g of hexahydrophthalic anhydride, 500 g of tetrahydrophthalic anhydride, 600 g of ditrimethylol propane, and 542 g of neopentyl glycol. It was prepared in the same manner as. The acid value of this resin was 210 mgKOH / g and the number average molecular weight was 500.

[Examples 1 to 8]

The above-mentioned method by combining the polyester resins (Formula 1) prepared from Preparation Examples 1 to 4 and the polyester resins (Formula 2) prepared in Preparation Examples 5 to 8 with the polyacids described in Table 1 below A crystalline polyester resin (Formula 3) was prepared. As a catalyst, 0.1 wt% of butylchlorotin dihydroxide (Fesket-4101), which is a metal system, was added thereto, followed by polymerization to increase the temperature from 160 ° C to 230 ° C until no condensation water was produced.

division Example One 2 3 4 5 6 7 8 Hydroxyl prepolymer (1) (g) A-11000 A-11000 A-21000 A-21000 A-31000 A-31000 A-41000 A-41000 Carboxyl prepolymer (2) (g) B-1260 B-3280 B-2292 B-4270 B-1330 B-3225 B-2275 B-4285 Trimellitic anhydride (g) 50 75 50 101 78 66 67 88 Adipic acid (g) 30 25 - - 28 22 - 36 Isophthalic acid (g) - - - 18 - - - 28 Methyltetrahydrophthalic anhydride (g) 35 - 32 - 45 - 55 - Cyclohexanedicarboxylic acid (g) - - - 43 - 42 34 26 Number average molecular weight 2,100 2,300 2,000 2,500 2,350 2,250 2,250 2,500 Acid value (mgKOH / g) 71 67 75 72 77 61 69 67 Softening Point (℃) (mettler FP832 ℃ / min) 114 116 114 118 113 117 115 116

Comparative Example 1

Resin was prepared using the conventional two-step manufacturing method rather than the three-step manufacturing method used in the present invention by using the components composed of the same composition and content as in Example 1.

That is, in the same reactor as in Example 1, butyl, which is a metal-based catalyst, is an alcohol mixture consisting of neopentyl glycol, hydroxy dimethylpropyl hydroxy dimethyl propenoate, ethylene glycol, terephthalic acid, and adipic acid in one step. The prepolymer having a hydroxyl value (OH value) of 45 was prepared by raising the temperature to 230 ° C. using chlorotin dihydroxide (Fesket-4101) and subjected to two-step reaction to trimellitic anhydride and adipic acid. -4101 was added and the temperature was raised to 160-230 ° C to polymerize until no condensation water was produced, thereby preparing an acidic polyester resin leaving a carboxyl group at the terminal. The acid value of this resin was 69 mm KOH / g, the number average molecular weight was 2,000, and the softening point was 112 degreeC.

Comparative Example 2

Resin was prepared by the method of Comparative Example 1 in the same composition and content as the resin prepared in Example 2.

In one step, an alcohol mixture consisting of neopentyl glycol, hydroxy dimethylpropyl hydroxy dimethyl propenoate, glycol of 1,6-hexanediol, and ditrimethylol propane, and an acid mixture of terephthalic acid and adipic acid are catalyzed by a metal system. The prepolymer having a hydroxyl value (OH value) of 60 was prepared by raising the temperature to 230 ° C. using chlorotin dihydroxide (Fesket-4101), followed by two-step reaction to trimellitic anhydride and methyltetrahydrophthalic anhydride. Butylchlorotin dihydroxide (Fesket-4101), which is a metal system, was added as a catalyst, and the temperature was raised to 160-230 ° C., followed by polymerization until no condensation water was produced. It was. The acid value of this resin was 73 mmKOH / g, the number average molecular weight was 2,100, and the softening point was 110 degreeC.

Comparative Example 3

Resin was prepared in the same manner as in Comparative Example 1 in the same composition and content as the resin prepared in Example 2.

In one step, an alcohol mixture composed of neopentyl glycol, hydroxy dimethylpropyl hydroxy dimethyl propenoate and glycol of diethylene glycol trimethylol propane and an acid mixture of terephthalic acid, adipic acid and isophthalic acid are catalysts of a metal system, butylchlorotin. Dihydroxyl (Fesket-4101) was added thereto, the temperature was raised to 230 ° C, and polymerization was carried out until no condensation water was produced, thereby preparing an acidic polyester resin leaving a carboxyl group at the terminal. The acid value of this resin was 60 mm KOH / g, the number average molecular weight was 2,300, and the softening point was 112 degreeC.

Experimental Example Preparation of Powder Coating Composition

Using the resins of Examples 1 to 8 and Comparative Examples 1 to 3, the composition is blended in the composition shown in Table 2 below, and powder coating is prepared by using a conventional paint production method. Comparative Example 1 is a coating formulation of Example 1 of Table 2, Comparative Example 2 is a coating formulation of Example 3, Comparative Example 3 is a coating formulation of the coating formulation of Example 6 and coating and curing conditions Prepared in the same manner. That is, a 0.7 mm horseshoe sheet pretreated with zinc phosphate was cured at 200 ° C. for 10 minutes to prepare a coating having a thickness of 30 ± 5 μm.

Powder Coating Composition (Unit: g) division Example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 7 Example 8 Polyester resin 100 100 100 100 100 100 100 100 Epoxy resin N8020 ¹ 85 - - 85 90 - 85 - N8030 ¹ - 100 100 - - 90 - 100 Flow enhancer ² 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 Curing Accelerators ³ 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 Benzoin 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 UV absorbers ⁴ 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 Titanium dioxide 110 110 110 110 110 110 110 110 Note 1. Korea Chemical Products 2. PV-5, Bolsa Products 3. B-31, Shikokyu Kasei Co., Ltd. 4. Tinuvin-900, product of Shiba Gaiji

Test results of the coating properties using the resins of Examples 1 to 8 and Comparative Examples 1 to 3 are shown in Table 3 below.

1. C.R (Contrast Ratio Method)

2. ΔE value: lower value means better heat resistance

○: Good, △: Somewhat bad, X: Poor

division Example Comparative Example Condition One 2 3 4 5 6 7 One 2 3 Film thickness 29 32 32 30 34 31 28 30 32 34 30 ± 5 μm Exterior ○ ○ ○ ○ ○ ○ ○ × × ○ Concealment 98.1 98.1 98.3 98.2 98.5 98.1 98.2 94.6 95.1 96.4 CR method ¹ Polish 96 97 96 98 96 97 95 92 90 94 60。 Glossmeter Impact ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ 1kg / 30cm Erysen 7.0 7.0 7.0 7.0 7.0 7.0 7.0 7.0 7.0 7.0 Flexibility ○ ○ ○ ○ ○ ○ ○ × ○ × 3/16 Pencil hardness H 2H H 2H H H H 2H H F Storage stability ○ ○ ○ ○ ○ ○ ○ ○ ○ × 35 ℃ * 4 week Solvent resistance ○ ○ ○ ○ ○ ○ ○ × × × XL × 24hr deposition Acid resistance ○ ○ ○ ○ ○ ○ ○ × △ × 5% sulfuric acid (50hr) Alkali resistance ○ ○ ○ ○ ○ ○ ○ × △ × 5% NaOH Corrosion resistance ○ ○ ○ ○ ○ ○ ○ × △ × 5% NaCl Boiling water resistance ○ ○ ○ ○ ○ ○ ○ × △ × 100 ℃ × 2hr Heat resistance ΔE ² 1.3 1.58 1.36 1.74 1.52 1.33 1.47 2.09 1.76 2.21 210 ℃ × 1hr

As can be seen from the above results, when the powder coating composition was prepared by mixing an epoxy resin with a crystalline polyester resin and a curing agent prepared in a three-step method in the present invention, the amorphous polyester resin prepared in conventional two-step Compared to the powder coating composition used, it was found that excellent physical properties can be maintained while excellent concealment and excellent appearance at a coating thickness of 30 μm before and after.

Claims (13)

A method for producing a polyester resin for powder coating, comprising the steps of: preparing a hydroxyl polyester prepolymer represented by the following Chemical Formula 1 by polymerizing an organic acid monomer mixture and an alcohol mixture; A two-step process of preparing a carboxyl polyester prepolymer represented by Chemical Formula 2 by reacting a mixture of an acid anhydride having 4 to 12 carbon atoms with a divalent and trivalent alcohol; 3 to prepare a crystalline carboxylate polyester resin represented by the following formula (3) by adding a hydroxyl polyester prepolymer represented by the formula (1), a carboxyl polyester prepolymer represented by the formula (2) and a divalent or higher polyhydric acid mixture Step process; Method for producing a polyester resin, characterized in that consisting of. Formula 1 Formula 2 Formula 3 R in the above formulas is-(CH ₂ )-, phenyl or cyclohexyl group; R 'is-(CH ₂ ) _n -or an aromatic compound; n is an integer from 1 to 12. According to claim 1, wherein the mixture of the organic acid monomer in the first step 5 to 20% by weight of linear aliphatic monomer having 4 to 12 carbon atoms in the molecule and having two or more carboxyl groups, 60 to 90 para aromatic carboxylic acid A method for producing a polyester resin, characterized by using less than 10% by weight, ortho or metaaromatic carboxylic acid. The method of claim 2, wherein the ortho, meta or para aromatic carboxylic acid includes phthalic acid, phthalic anhydride, terephthalic acid, isophthalic acid, dimethyl terephthalate, dimethylisophthalate, trimellitic acid, trimellitic anhydride, and derivatives thereof. The manufacturing method of the polyester resin characterized by using 1 type (s) or 2 or more types selected from among. The alcohol mixture of claim 1, wherein the alcohol mixture contains at least 90% by weight of neopentyl glycol and hydroxy dimethylpropyl hydroxy dimethyl propenoate and at most 10% by weight of divalent or higher polyhydric alcohol. The manufacturing method of the polyester resin characterized by using what has become. The method of claim 4, wherein the divalent or higher polyhydric alcohol is ethylene glycol, diethylene glycol, 1,6-hexane diol, triethylene glycol, propylene glycol, dipropylene glycol, trimethylol propane, ditrimethylol propane, cyclo A method for producing a polyester resin, characterized by using one or two species selected from hexane dimethanol, 1,3-butylene glycol, and 1,4-butylene glycol. The hydroxyl polyester of claim 1, wherein the equivalent ratio of (-OH) / (-COOH) in the step 1 is reacted with 1.1 to 1.5, and the hydroxyl value (-OH) is 30 to 300. A method for producing a polyester resin, characterized by producing a prepolymer. The method of claim 1, wherein the acid anhydride in the two-step process contains 95% by weight or more of divalent or higher alicyclic acid and 5% by weight or less of linear aliphatic monomers. The divalent or higher alicyclic acid according to claim 7, wherein the aliphatic acid is one or more of methylhexahydrophthalic anhydride, hexahydrophthalic anhydride, succinic anhydride, tetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride and methylendomethylenetetrahydrophthalic anhydride. Or 2 or more types are used. The manufacturing method of the polyester resin characterized by the above-mentioned. The method of claim 1, wherein in the second step, the alcohol contains 30 to 50% by weight of hydroxy dimethylpropyl hydroxy dimethyl propenoate and 20 to 70% by weight of ditrimethylol propane. Way. According to claim 1, wherein the equivalent ratio (-OH) / (-COOH) of 0.5 to 0.95 in the step 2, the acid value (-COOH) is 150 to 300, the number average molecular weight is 500 to 3000 The carboxyl polyester prepolymer represented by the above is produced. The method according to claim 1, wherein in the step 3, 10 to 40 parts by weight of the carboxyl polyester prepolymer represented by Formula 2 and 5 to 20 parts by weight of a divalent polyacid mixture of 100 parts by weight of the hydroxyl polyester prepolymer represented by Formula 1 The manufacturing method of the polyester resin characterized by using a weight part. According to claim 1, wherein the crystalline polyester resin represented by the formula (3) prepared in step 3 has a reactive carboxyl group 2 to 3 at the terminal acid value 30 ~ 300 mg KOH / g, number average molecular weight 2000 ~ 5000 And a softening point becomes 100-120 degreeC, and glass transition temperature becomes 40-70 degreeC, The manufacturing method of the polyester resin characterized by the above-mentioned. In a powder coating composition comprising a polyester resin as a main component and a conventional powder coating additive, 30 to 50% by weight of the crystalline polyester resin represented by the following formula (3), and the equivalent 600 represented by the following formula (E) Powder coating composition characterized by containing 20-50 weight% of diglycidyl ether bisphenol-A epoxy resin of -1000. Formula 3 [Formula E] R and n in the above formula are as defined above.