JPH08295728A - Polyester resin for powder coating material and composition - Google Patents

Abstract

PURPOSE: To provide a polyester for a powder coating material being excellent in adhesion to a solvent-based coating material, having good resistance to weathering, solvent and staining and used as a double coat on a solvent-based coating material. CONSTITUTION: This polyester resin mainly comprises an aromatic dicarboxylic acid component containing isophthalic acid and an aliphatic glycol containing neopentyl glycol, having an intrinsic viscosity of 0.15-0.40 and mainly terminated with hydroxyl groups, wherein the total of the rate of the isophthalic acid to the total acid component constituting the polyester and the rate of the neopentyl glycol to the total glycol constituting the polyester is 60mol% or above, and the molar ratio of the isophthalic acid to the neopentyl glycol is 30:70 to 70:30.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a powder coating which is excellent in adhesion to a solvent type coating and which is used as an overcoat with a solvent type coating having good weather resistance, solvent resistance and stain resistance. The present invention relates to polyester resin and composition.

[0002]

2. Description of the Related Art Compared with conventional solvent-based paints, powder paints have advantages such as low pollution, that they can be used immediately after painting, and that they are relatively inexpensive. Demand is rapidly expanding as a paint for protection of construction materials and decorative materials. Among them, polyester powder coating materials are known as coating materials having a balanced coating film performance.

Further, powder coating has a problem that it is difficult to change colors, and for the purpose of easily adjusting the color of the coating, a solvent of various colors is formed on the coating of the powder coating of the basic color. Overcoating with mold paint is performed.

By the way, the polyester resin used in the powder coating material is melted and kneaded by mixing the resin, the curing agent and various additives in the step of producing the coating material, so that the polyester resin must be kneaded at a temperature that does not react with the curing agent. However, the softening temperature of the resin is usually limited to 150 ° C. Further, in order to impart flexibility to the coating film after thermosetting, it is preferable to appropriately contain an aromatic component and an aliphatic component.

For these reasons, as the polyester resin for the thermosetting powder coating composition, polyethylene terephthalate copolymerized with a third component to lower the softening temperature is generally widely used. Various materials can be used as the third component, but neopentyl glycol is generally used for applications requiring weather resistance.

However, when polyethylene terephthalate is copolymerized with neopentyl glycol, weather resistance is improved, but solvent resistance and stain resistance tend to be lowered.

On the other hand, a polyester resin obtained by copolymerizing polyethylene terephthalate with isophthalic acid has been used for the purpose of improving weather resistance. However, a solvent type paint is overcoated on a coating film coated with a powder coating material. In that case, the interlayer adhesion is lowered, and the coating film of the solvent-based coating material overcoated tends to be easily peeled off. Therefore, this copolymerized polyester resin was unsuitable for powder coatings used for overcoating with solvent-based coatings.

As described above, it has heretofore been difficult to obtain a powder coating material which is excellent in adhesion to a solvent type coating material and which is excellent in weather resistance, solvent resistance and stain resistance.

[0009]

DISCLOSURE OF THE INVENTION The present invention provides a powder used for recoating with a solvent-based paint which has excellent adhesion to the solvent-based paint and has good weather resistance, solvent resistance and stain resistance. It is intended to provide polyester resins and compositions for paints.

[0010]

The inventors of the present invention have found that this object can be achieved by optimally selecting the constituent components of the polyester as a result of repeated studies for solving the above-mentioned problems. The invention was reached.

That is, the gist of the present invention is as follows. 1. An aromatic dicarboxylic acid component containing isophthalic acid and an aliphatic glycol containing neopentyl glycol as the main constituent components, and an intrinsic viscosity of 0.15 to 0.40 is a hydroxyl group-terminated polyester resin, which constitutes the polyester. The sum of the ratio of isophthalic acid to the acid component and the ratio of neopentyl glycol to all glycol components constituting the polyester is 60 mol% or more, and the molar ratio of isophthalic acid and neopentyl glycol is 30:70 to 70:
A polyester resin for powder coating used for overcoating with a solvent-based coating characterized by being 30. 2. A polyester resin composition for powder coating, which is used as an overcoat with a solvent-based coating prepared by blending the above polyester resin with an isocyanate curing agent.

The present invention will be described in detail below.

In the polyester resin of the present invention, the sum of the ratio of isophthalic acid to the total acid component of the polyester and the ratio of neopentyl glycol to the total glycol component of the polyester should be 60 mol% or more. Required, preferably 80 mol%
That is all. If this amount is less than 60 mol%, the weather resistance of the cured coating film will be deteriorated, which is not preferable.

The molar ratio of isophthalic acid, which is a constituent of the polyester resin, to neopentyl glycol is 3
It is necessary to be 0:70 to 70:30, preferably 4
It is 0:60 to 60:40. If the proportion of isophthalic acid is lower than this, the solvent resistance and stain resistance of the cured coating film will decrease, and conversely, if the proportion of isophthalic acid is higher than this, not only the adhesion to solvent-based paint will decrease, Mechanical strength such as impact resistance tends to decrease, which is not preferable.

In the present invention, it is necessary to use isophthalic acid and neopentyl glycol in combination, and this is the first time that the adhesiveness with solvent-based paint is excellent and
A polyester resin for powder coatings with good weather resistance, solvent resistance, and stain resistance.

In the polyester resin of the present invention, other dicarboxylic acid components used together with isophthalic acid include
Examples thereof include aromatic dicarboxylic acids such as terephthalic acid, phthalic anhydride, phthalic acid and naphthalenedicarboxylic acid, and aliphatic dicarboxylic acids such as adipic acid, sebacic acid and dodecanedioic acid. Of these, terephthalic acid is preferably used. In addition, a tricarboxylic or higher carboxylic acid component such as trimellitic acid or pyromellitic acid can be used in combination with the dicarboxylic acid component as long as the polyester resin is not gelled.

In the polyester resin of the present invention, other glycol components used in combination with neopentyl glycol include ethylene glycol, diethylene glycol, propylene glycol, 1,4-butanediol, 1,
Aliphatic glycols such as 6-hexanediol and 1,4-cyclohexanedimethanol can be mentioned, and among them, ethylene glycol is preferably used. Also,
A small amount of a diol having an aromatic group such as an ethylene oxide adduct of bisphenol A and an ethylene oxide adduct of bisphenol S can be used in combination, and further, together with a glycol component, trimethylol may be used within a range not causing gelation of the polyester resin. Trihydric or higher alcohol components such as propane, glycerin, and pentaerythritol can be used together.

If necessary, a small amount of an oxycarboxylic acid component 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 is in the range of 0.15 to 0.40 dl / g, preferably 0.20 to 0.35 dl / g. If the intrinsic viscosity is less than 0.15 dl / g, the blocking resistance of the resin and the resin composition is reduced, or the mechanical strength of the coating film tends to be reduced, and if the intrinsic viscosity exceeds 0.40 dl / g, The pulverizability of the resin tends to deteriorate.

The polyester resin of the present invention has a hydroxyl value in the range of 14 to 100 mgKOH / g, preferably 25 to 60 mgKOH / g. If the hydroxyl value is less than 14 mg KOH / g,
Large unevenness tends to occur on the surface of the coating material and the smoothness tends to decrease. When the hydroxyl value exceeds 100 mgKOH / g, the mechanical strength of the coating film 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 less than 50 ° C, the powdered resin or resin composition tends to agglomerate and solidify, and the blocking resistance tends to be poor, while if the softening temperature exceeds 150 ° C, during coating production. It is necessary to raise the kneading temperature of, and the reaction between the resin and the curing agent progresses during kneading, and as a result, the smoothness and mechanical strength of the coating film tend to decrease.

The polyester resin satisfying the above-mentioned conditions is prepared from isophthalic acid, neopentyl glycol and the above-mentioned acid component and alcohol component (including their ester-forming derivatives) as raw materials, and 200 to 28
After the esterification or transesterification reaction at a temperature of 0 ° C, a polycondensation reaction is performed at a temperature of 200 to 300 ° C, preferably 230 to 290 ° C under a reduced pressure of 5 hPa or less to obtain a polymer having a high degree of polymerization, and an alcohol. It can be prepared by a method of adding components to carry out a depolymerization reaction.

After conducting the esterification or transesterification reaction by a conventional method, the temperature is 200 to 300 ° C., preferably 220 to 280 ° C. under normal pressure or reduced pressure of about 50 to 100 hPa.
It can also be prepared by a method in which a polycondensation reaction is carried out until a predetermined intrinsic viscosity is reached.

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

The polyester resin of the present invention is made into a powder coating by blending a curing agent having a functional group which reacts with the hydroxyl group of the polyester resin. As the curing agent, an isocyanate curing agent, in particular, a blocked isocyanate curing agent that does not exhibit activity at a certain temperature or lower is preferably used.
As a specific example of such a curing agent, Hüls Co., which is an isophorone diisocyanate curing agent blocked with ε-caprolactam, "Vestagon B 1530" (trade name) or a blocking agent is not contained, and the isocyanate group is self-contained. The company's "Vestagon BF 1540" (trade name), which is a blocking isophorone diisocyanate-based curing agent, can be mentioned.

The amount of the curing agent used is approximately the same as the amount of hydroxyl groups in the polyester resin, preferably 0.6 to 1.2.
A range of double equivalents is suitable.

The resin composition for powder coating of the present invention can be prepared by kneading the above polyester resin and a curing agent at a temperature of 70 to 150 ° C. using a kneader or roll.

The resin composition of the present invention may contain, if necessary, known curing catalysts, leveling agents, other additives,
A pigment or the like can be added.

[0029]

EXAMPLES Next, the present invention will be described in detail with reference to Examples. The characteristic values and the like in the examples were obtained by the following methods. (a) Copolymerization Ratio of Isophthalic Acid (IPA Copolymerization Ratio) After methylating the resin, the amount of isophthalic acid was determined by gas chromatography and expressed in mol% based on all acid components. (b) Copolymerization Ratio of Neopentyl Glycol (NPG Copolymerization Ratio) After methylating the resin, the amount of neopentyl glycol was determined by gas chromatography and expressed as mol% based on all glycol components. (c) Intrinsic Viscosity An equal weight mixture of phenol and ethane tetrachloride was used as a solvent and measured at a temperature of 20 ° C. (d) Hydroxyl value The resin was acetylated with acetic anhydride and then titrated with a methanol solution of potassium hydroxide. (e) Softening temperature 60 to 100 mesh crushed resin 2.5m in diameter
The bottomed glass tube with a length of m and a length of 150 mm was filled to a height of 30 mm, the resin-filled portion was immersed in an oil bath, the temperature was raised at a rate of 1 ° C / min, and the temperature at which liquefaction began was visually determined The softening temperature was used. (f) Impact resistance: Measured according to JIS K 5400 using a ball with a diameter of 1/2 inch and 0.5 kg. Items with a size of 30 cm or more are indicated by ○, items with a size of less than 30 cm are indicated by ×
And (g) Solvent resistance After dripping xylene to the coating film and leaving it for 1 hour, the coating film surface was observed and judged. Those that did not change were rated as ◯, and those that had changes such as swelling and dissolution were rated as x. (h) Contamination resistance A line was drawn on the paint film with black, blue and red magic ink (oil felt pen made by Yoko Uchida Co., Ltd.), allowed to stand for 24 hours, and then wiped gently with a cloth impregnated with methanol three times to remove the line. Was observed and evaluated. 1 to 10 points for each color (the lower the score, the better)
When the total score of the three colors was 20 or less, it was evaluated as ◯, and when 21 or more were evaluated as x. (i) Accelerated weather resistance An accelerated weather resistance test was conducted according to JIS K 5400, and the gloss retention rate after 500 hours was determined and evaluated. Those with 50% or more were marked with ◯, and those with less than 50% were marked with x. (j) Adhesion with solvent-based paint Melatoite # 300 (Melamine-based solvent-based paint manufactured by Toupe Co., Ltd.) is applied to a coating film coated with powder paint so that the film thickness is 20 μm, and the temperature is 120 ° C for 20 minutes. After baking, JIS K 54
A cross-cut test was conducted according to 00 and evaluated. The solvent-free paint film with no peeling was rated as ◯, and the one with peeling was rated as x.

Examples 1 to 5 and Comparative Examples 1 to 3 The raw material compounds shown in Table 1 were used in the amounts shown in Table 1 (parts by mole).
Was charged into an esterification reaction tank at a pressure of 2532 hPaG and a temperature of 200.
The esterification reaction was carried out at ˜260 ° C. for 4 hours. After transferring the obtained esterified product to a polycondensation reaction tank, 4 × 10 ⁻⁴ mol of antimony trioxide / 1 mol of an acid component was added, the pressure was reduced to 0.4 hPa, and the polycondensation reaction was performed at 280 ° C. for 4 hours. Intrinsic viscosity 0.45
dl / g polyester was obtained. Next, the depolymerizing agent shown in Table 1 was added to this polyester in the amount shown in Table 1 (mole part).
, And depolymerize at 270 ° C for 1 hour under normal pressure.
Polyester resins having the characteristic values shown in Table 1 were obtained. In the obtained polyester resin, a blocked isocyanate curing agent: B 1530, BF 1540 manufactured by Huls, a dioctyl tin maleate curing catalyst: Stann OMF manufactured by Sansha Machine Synthesis, a butyl polyacrylate leveling agent: Acronal manufactured by Basuf 4F, epi-bis type epoxy resin: YD manufactured by Tohto Kasei Co., Ltd.
-014, benzoin and rutile titanium dioxide pigment: CR-90 manufactured by Ishihara Sangyo Co., Ltd. was added in the amount (parts by weight) shown in Table 1, and FM
After dry blending with a 10B Henschel mixer (Mitsui Miike Seisakusho), PR-46 type Co-Kneader (Bus)
Was melt-kneaded at 110 ° C., cooled, pulverized, and then classified with a 140-mesh wire net to obtain a powder coating material. The obtained powder coating material was electrostatically coated on a zinc phosphate-treated steel plate to a film thickness of 40 μm, and baked at 180 ° C. for 20 minutes. The results of evaluating the performance of the coating film are shown in Table 1.

In Table 1, compounds represented by abbreviations represent the following. IPA: isophthalic acid TPA: terephthalic acid EG: ethylene glycol HD: 1,6-hexanediol BA-EO: ethylene oxide 2 of bisphenol A
Molar adduct TMP: Trimethylolpropane GC: Glycerin NPG: Neopentyl glycol PETL: Pentaerythritol

[0032]

[Table 1]

[0033]

EFFECTS OF THE INVENTION According to the present invention, for powder coatings which are excellent in adhesion to solvent-based coatings, and are used for overcoating with solvent-based coatings having good weather resistance, solvent resistance and stain resistance. Polyester resins and compositions are provided.

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] September 5, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0029

[Correction method] Change

[Correction content]

[0029]

EXAMPLES Next, the present invention will be described in detail with reference to Examples. The characteristic values and the like in the examples were obtained by the following methods. (a) Copolymerization Ratio of Isophthalic Acid (IPA Copolymerization Ratio) After the resin was decomposed with methanol , the amount of isophthalic acid was determined by gas chromatography and expressed as mol% based on the total acid components. (b) Copolymerization Ratio of Neopentyl Glycol (NPG Copolymerization Ratio) After the resin was decomposed with methanol , the amount of neopentyl glycol was determined by gas chromatography and expressed as mol% based on the total glycol component. (c) Intrinsic Viscosity An equal weight mixture of phenol and ethane tetrachloride was used as a solvent and measured at a temperature of 20 ° C. (d) Hydroxyl value The resin was acetylated with acetic anhydride and then titrated with a methanol solution of potassium hydroxide. (e) Softening temperature 60 to 100 mesh crushed resin 2.5m in diameter
The bottomed glass tube with a length of m and a length of 150 mm was filled to a height of 30 mm, the resin-filled portion was immersed in an oil bath, the temperature was raised at a rate of 1 ° C / min, and the temperature at which liquefaction began was visually determined The softening temperature was used. (f) Impact resistance: Measured according to JIS K 5400 using a ball with a diameter of 1/2 inch and 0.5 kg. Items with a size of 30 cm or more are indicated by ○, items with a size of less than 30 cm are indicated by ×
And (g) Solvent resistance After dripping xylene to the coating film and leaving it for 1 hour, the coating film surface was observed and judged. Those that did not change were rated as ◯, and those that had changes such as swelling and dissolution were rated as x. (h) Contamination resistance A line was drawn on the paint film with black, blue and red magic ink (oil felt pen made by Yoko Uchida Co., Ltd.), allowed to stand for 24 hours, and then wiped gently with a cloth impregnated with methanol three times to remove the line. Was observed and evaluated. 1 to 10 points for each color (the lower the score, the better)
When the total score of the three colors was 20 or less, it was evaluated as ◯, and when 21 or more were evaluated as x. (i) Accelerated weather resistance An accelerated weather resistance test was conducted according to JIS K 5400, and the gloss retention rate after 500 hours was determined and evaluated. Those with 50% or more were marked with ◯, and those with less than 50% were marked with x. (j) Adhesion with solvent-based paint Melatoite # 300 (Melamine-based solvent-based paint manufactured by Toupe Co., Ltd.) is applied to a coating film coated with powder paint so that the film thickness is 20 μm, and the temperature is 120 ° C for 20 minutes. After baking, JIS K 54
A cross-cut test was conducted according to 00 and evaluated. The solvent-free paint film with no peeling was rated as ◯, and the one with peeling was rated as x.

Claims (2)

[Claims] 1. A polyester resin having an aromatic dicarboxylic acid component containing isophthalic acid and an aliphatic glycol containing neopentyl glycol as main constituents, and having an intrinsic viscosity of 0.15 to 0.40 and having a terminal hydroxyl group as a main component. The sum of the ratio of isophthalic acid to the total acid component of the polyester and the ratio of neopentyl glycol to the total glycol component of the polyester is 60 mol% or more, and the molar ratio of isophthalic acid and neopentyl glycol is
Polyester resin for powder coating used for overcoating with solvent-based coating, characterized in that it is 30:70 to 70:30. 2. A polyester resin composition for powder coating, which is used for overcoating with the solvent-based coating prepared by blending the polyester resin according to claim 1 with an isocyanate curing agent.