JPH05148448A - Resin composition for thermosetting type coating material - Google Patents

Abstract

PURPOSE:To obtain a resin composition for a thermosetting type coating material capable of forming a coating film having high hardness, high processability and excellent durability on a metal plate such as steel plate. CONSTITUTION:In a resin composition for a thermosetting type coating material obtained by blending a polyester (I) with a cross-linking agent (II) composed of at least one of an isocyanate compound, an epoxy compound and an amino resin in a ratio of 0.01<=(II)/(I)<=0.7, the polyester (I) is one or more polyesters having molecular chain ends into which plural reactive groups are introduced by branching obtained by reacting a polyester (a) consisting essentially of a carboxylic acid containing an aromatic dicarboxylic acid as a carboxylic acid component and an aliphatic glycol as an alcohol component with a trifunctional carboxylic acid anhydride (b) and/or a hydroxyl group-containing monoepoxy compound (c) to characteristically give the resin composition for thermosetting type coating material.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin composition for paints, and more specifically, for a precoated steel sheet capable of giving a tough crosslinked coating film having both high hardness and high workability and excellent durability. And a resin composition for a thermosetting coating suitable for

[0002]

2. Description of the Related Art As thermosetting resin, many thermosetting resins such as epoxy resin, melamine alkyd resin, acrylic resin and polyurethane resin have been put to practical use. These are crosslinked for the purpose of imparting so-called durability such as solvent resistance, water resistance and weather resistance. However, if crosslinking is performed excessively, a hard coating film can be obtained, but the elongation of the coating film is significantly reduced, and only a hard and brittle coating film can be obtained. On the other hand, if the amount of cross-linking is reduced, the elongation of the coating film will not be lowered so much, but only the desired durability will be obtained and the hardness of the coating film will also be insufficient. Thus, it is very difficult to obtain a coating film that is hard and stretches well while maintaining durability.

As a field in which such characteristics are required, there is a resin for coating precoated steel sheet. In this application,
In addition to high coating hardness to prevent scratches and excellent processability to withstand various types of processing, stain resistance is the most important performance. However, if the workability is emphasized, the hardness becomes insufficient, and the use of the material is limited in some point. Among these, the best balance of performance at present is a system in which a high molecular weight linear polyester is crosslinked with a melamine resin, but since the polyester has a high molecular weight and is linear, Although the concentration is low and good workability can be provided, it must be said that it is still insufficient from the viewpoint of hardness and stain resistance. Therefore, a method of increasing the concentration of the reactive group by lowering the molecular weight of the polyester or taking a branched structure in the molecular chain by adding polycarboxylic acid, polyol or the like has been attempted. Although the stain resistance is improved, the molecular weight between cross-linking points becomes too short and the processability is lost. In addition, depending on the use of polycarboxylic acid, polyol, etc., gelation occurs when trying to increase the molecular weight, and therefore the concentration of reactive groups that can be introduced is limited.

[0004]

From such a situation,
Introducing a sufficient amount of reactive groups into the resin and performing sufficient crosslinking to impart excellent durability such as solvent resistance, water resistance, stain resistance, etc., while having an excellent balance of hardness and processability. It is extremely difficult to obtain a coating film, and the advent of a thermosetting coating resin capable of providing such a coating film is desired.

[0005]

Means for Solving the Problems As a result of intensive investigations by the present inventors, a method for obtaining a coating film having excellent hardness and durability while maintaining good processability of a high molecular weight linear polyester was obtained. The above object is achieved by a resin composition obtained by adding at least one of a block isocyanate compound, an epoxy compound, and an amino resin as a cross-linking agent to a polyester having a plurality of reactive groups introduced by branching at a molecular chain end. The present invention has been achieved and has reached the present invention.

That is, the present invention relates to polyester (I)
And a cross-linking agent (II) consisting of at least one of an isocyanate compound, an epoxy compound and an amino resin, 0.01 ≦
(II) / (I) ≤0.7 (weight ratio), which is a resin composition for thermosetting coating composition, wherein the polyester (I) contains an aromatic dicarboxylic acid as a carboxylic acid component. Molecular chain obtained by reacting contained carboxylic acid with polyester (a) mainly containing aliphatic glycol as an alcohol component and polycarboxylic acid anhydride (b) and / or monoepoxy compound (c) It is a resin composition for thermosetting coating material, characterized in that it is one or more kinds of polyester having a plurality of reactive groups introduced by branching at the terminal.

The carboxylic acid component of the polyester (a) used in the resin composition for thermosetting coating material of the present invention includes terephthalic acid, isophthalic acid, orthophthalic acid, and 1,5-
Aromatic dicarboxylic acids such as naphthalenedicarboxylic acid and 2,6-naphthalenedicarboxylic acid, p-oxybenzoic acid, p
-Aromatic oxycarboxylic acids such as (hydroxyethoxy) benzoic acid, succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid and other aliphatic dicarboxylic acids, fumaric acid, maleic acid, itaconic acid, hexahydro Examples include unsaturated aliphatic and alicyclic dicarboxylic acids such as phthalic acid and tetrahydrophthalic acid. If necessary,
A small amount of tri- and tetracarboxylic acids such as trimellitic acid, trimesic acid and pyromellitic acid may be contained.

The glycol component is, for example, ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6. -Hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol
2,2,4-trimethyl-1,3-pentanedio-
, 1,4-cyclohexane dimethanol, spiroglycol, 1,4-phenylene glycol, ethylene oxide adduct of 1,4-phenylene glycol, ethylene oxide adduct of bisphenol A and propylene Oxide adduct, ethylene oxide adduct of hydrogenated bisphenol A and propylene oxide adduct, polyethylene glycol, polypropylene glycol
And diol such as polytetramethylene glycol. If necessary, a small amount of triol and tetraol such as trimethylolethane, trimethylolpropane, glycerin, and pentaerythritol may be contained.

In the production of the polyester (a), the carboxylic acid component and the alcohol component may all be mixed at once, or may be added in portions as the reaction progresses. The polycondensation reaction may be carried out by a conventional transesterification method or an esterification method, or a combination of both methods, and the polymerization degree can be increased by pressurizing or depressurizing the system at an arbitrary stage.

The polyester (a) thus obtained must contain an aromatic dicarboxylic acid. It is difficult to obtain the excellent solvent resistance, water resistance, stain resistance, etc., which are the effects of the present invention, only with the aliphatic dicarboxylic acid. The content of the aromatic dicarboxylic acid component is 30 mol% or more, preferably 40 mol% or more, in the total carboxylic acid component.

Further, the polyester (a) is from 1,000 to
It has a molecular weight of 50,000. Preferably 1,000
-40,000, more preferably 2,000-30,
It is in the range of 000. Below a molecular weight of 1,000,
The coating film finally obtained does not have good flexibility, that is, processability, and when it exceeds 50,000, the concentration of the reactive group becomes too low, and the subsequent reaction does not proceed sufficiently to obtain the effect of the present invention. It gets harder. Although not particularly limited, in order to bring out the effect of the present invention sufficiently, it is desirable that the terminal group of the polyester (a) is a hydroxyl group. To obtain this, the glycol raw material may be used in excess with respect to the dicarboxylic acid raw material for synthesis. Also, polyester (a)
Is a hydroxyl group-terminated polyester
It may be a hydroxyl group-terminated polyester urethane obtained by reacting with a phenolic compound.

The polycarboxylic acid anhydride (b) of the present invention is a divalent or trivalent or more cyclic or linear acid anhydride such as aliphatic, alicyclic or aromatic.

Examples of the aliphatic polycarboxylic acid anhydride include acid anhydrides such as succinic acid, adipic acid, sebacic acid, azelaic acid, maleic acid and dodecanedioic acid.

As the alicyclic polycarboxylic acid anhydride, hexahydrohephthalic acid, methylhexahydrophthalic acid,
Tetrahydrophthalic acid, methyltetrahydrophthalic acid,
Examples thereof include acid anhydrides such as hymic acid, het acid, and 1,4-cyclohexanedicarboxylic acid.

Aromatic polycarboxylic acid anhydrides include terephthalic acid, isophthalic acid, orthophthalic acid, trimellitic acid, pyromellitic acid, benzophenonetetracarboxylic acid, ethylene glycol bistrimellitate, glyceryl toltrismellitate. And acid anhydrides such as biphenyltetracarboxylic acid and diphenylsulfonetetracarboxylic acid.

The divalent acid anhydride has a function of esterifying one hydroxyl group to give one carboxyl group.
The acid anhydride having a valence of at least one has a function of esterifying one hydroxyl group and imparting two or more carboxyl groups by branching at the molecular end. These polycarboxylic acid anhydrides (b) can be used alone or in combination.

Further, the monoepoxy compound (c) of the present invention
Is a compound having one epoxy group in the molecule, and specific examples thereof include ethylene oxide, propylene oxide, butylene oxide, octylene oxide, styrene oxide, cyclohexene oxide,
Oxides such as α-pinene oxide, methyl glycidyl ether, butyl glycidyl ether, alcohol glycidyl esters such as 2-ethylhexyl glycidyl ether, phenyl glycidyl ether, p-butylphenyl glycidyl ether -Glycidyl ethers of phenols such as ter and p-phenylphenylglycidyl ether
Ters, glycidyl benzoate, glycidyl acetate
Glycidyl esters such as glycidyl butyrate,
Further, glycidyl, 2-methylglycidyl, 3-
Examples thereof include epoxy compounds having a hydroxyl group such as propyloxirane methanol, 3-phenylglycidyl, and 2-methyl-3-phenylglycidyl.

The above-mentioned epoxy compound having no hydroxyl group undergoes an addition reaction in which the epoxy group is opened by one carboxyl group to form one hydroxyl group.

Since the epoxy compound having a hydroxyl group originally has a hydroxyl group in addition to the hydroxyl group generated in the same manner, two or more hydroxyl groups can be imparted by branching at the molecular end. These monoepoxy compounds (c) can be used alone or in combination.

The polyester (I) of the present invention is obtained by reacting the polyester (a) with the polycarboxylic acid anhydride (b) and / or the monoepoxy compound (c). As a first preferred embodiment for obtaining the polyester (I) of the present invention, the case where the polyester (a) is hydroxyl-terminated is shown. In this case, first, as a first reaction, at least the same number of polycarboxylic acid anhydrides (b) as the reactive hydroxyl groups of the polyester (a) are added, and the hydroxyl groups of the polyester (a) are subjected to an addition reaction. As a result, the hydroxyl group of the polyester (a) is esterified, and a product having a carboxyl group at the molecular end is obtained. When the carboxylic acid anhydride (b) having a valence of 3 or more is used here, the polyester of the present invention in which a plurality of reactive groups, that is, carboxyl groups are introduced at the molecular end by branching at the end of the molecular chain at this stage ( The equivalent of I) is obtained.

Then, as a second reaction, at least the same number of monoepoxy compounds as the carboxyl groups introduced into the polyester are subjected to an addition reaction. As a result, the carboxyl group reacts with the epoxy group to generate a hydroxyl group. When an epoxy compound having a hydroxyl group is used, even if a divalent carboxylic acid anhydride is used in the first reaction, a plurality of reactive groups, that is, hydroxyl groups, are attached to the molecular end at this stage due to branching of the molecular chain end. A product corresponding to the introduced polyester (I) of the present invention is obtained.

Further, if the number of reactive groups required at this stage is insufficient, then the polycarboxylic acid anhydride (b),
It is obvious that the desired number of reactive groups can be introduced by sequentially repeating the reaction such as the monoepoxy compound (c).

When the polyester (a) has a carboxyl group terminal, the first reaction is a monoepoxy compound, and the second reaction is a polycarboxylic acid anhydride. Polyester (I) of What is important here is that either a trivalent or higher carboxylic acid anhydride is used for the polycarboxylic acid anhydride (b) and / or a monoepoxy compound having a hydroxyl group is used for the monoepoxy compound (c). For example, it means that one or more polyesters (I) having a plurality of reactive groups introduced by branching at the molecular end of the present invention cannot be obtained. Of course, the polyester (a) to be used first may be one kind, or two or more kinds may be mixed, but the polycarboxylic acid anhydride (b) and the monoepoxy compound (c) may be used. It is desirable to avoid charging and reacting at the same time. This is because the reaction between the polycarboxylic acid anhydride (b) and the monoepoxy compound (c) proceeds preferentially and it becomes difficult to obtain the polyester (I) of the present invention.

These reactions can be carried out in the presence or absence of a solvent. Also, a suitable catalyst may be present. The polyester (I) of the present invention thus obtained has a plurality of reactive groups introduced by branching at the molecular ends. As is clear from the above,
The reactive group is a carboxyl group and / or a hydroxyl group.

The polyester (I) thus obtained is blended with a crosslinking agent (II) consisting of at least one of an isocyanate compound, an epoxy compound and an amino resin so as to satisfy the following formula. 0.01 ≦ crosslinking agent (II) / polyester (I) (weight ratio) <0.7 The crosslinking agent (II) is 0.01 to 0.7, preferably 0.05 to It is mixed in a ratio of 0.5 (weight ratio). If the blending ratio (weight ratio) does not reach 0.01, it is difficult to obtain excellent durability and hardness, and if it exceeds 0.7, the coating amount of the polyester (I) is small and the workability is excellent. Is difficult to obtain, which is not preferable.

Examples of the isocyanate compound of the present invention include aromatic, aliphatic, and araliphatic diisocyanates and polyisocyanates having a valence of 3 or more, which may be low molecular compounds or high molecular compounds. For example, tetramethylene diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, xylylene diisocyanate, hydrogenated Isocyanate compounds such as xylylene diisocyanate, isophorone diisocyanate, and isophorone diisocyanate trimer,
Alternatively, an excess amount of these isocyanate compounds and a low amount of ethylene glycol, propylene glycol, trimethylolpropane, glycerin, sorbitol, ethylenediamine, monoethanolamine, dietanolamine, triethanolamine, etc. Examples thereof include a terminal active isocyanate group-containing compound obtained by reacting a molecular active hydrogen compound or a high molecular weight active hydrogen compound such as various polyether polyols, polyester polyols and polyamides.

The isocyanate compound may be a blocked isocyanate. Examples of the isocyanate blocking agent include phenol and thiophenol.
, Methylthiophenol, ethylphenol, cresol, xylenol, resorcinol, nitrophenol
Phenol, such as chlorophenol and chlorophenol, oximes such as acetoxime, methylethylketoxime, cyclohexanone oxime, alcohols such as methanol, ethanol, propanol and butanol, ethylene chlorohydride Halogen-substituted alcohols such as phosphorus and 1,3-dichloro-2-propanol, tertiary alcohols such as t-butanol, t-pentanol and t-butanethiol,
Examples include lactams such as ε-caprolactam, δ-valerolactam, τ-putyrolactam, and β-propyllactam, and aromatic methylenes such as aromatic amines, imides, acetylacetone, acetoacetic ester, and malonic acid ethyl ester. Compounds, mercaptans, imines, ureas, diaryl compounds soda bisulfite and the like can also be mentioned. The blocked isocyanate is obtained by subjecting the above-mentioned isocyanate compound and an isocyanate blocking agent to an addition reaction by a conventionally known appropriate method.

Bisphenol A as an epoxy compound
Diglycidyl ether and its oligomer, hydrogenated bisphenol A diglycidyl ether and its oligomer, orthophthalic acid diglycidyl ester, isophthalic acid diglycidyl ester, terephthalic acid diglycidyl ester, p-oxybenzoic acid glycidyl ester ether , Tetrahydrophthalic acid diglycidyl ester, hexahydrophthalic acid diglycidyl ester, succinic acid diglycidyl ester, adipic acid diglycidyl ester, sebacic acid diglycidyl ester, ethylene glycol diglycidyl ether, propylene glyco-
Rudiglycidyl ether, 1,4-butanediol-diglycidyl ether, 1,6-hexanediol-diglycidyl ether, and polyalkylene glycol diglycidyl ethers, trimellitic acid triglycidyl ester, tri Glycidyl isocyanurate, 1,4-diglycidyloxybenzene, diglycidyl dimethylhydantoin, diglycidyl ethylene urea, diglycidyl propylene urea, glycerol polyglycidyl ether, trimethylolethane polyglycidyl ether, trimethyloyl Examples include polypropane polyglycidyl ether, pentaerythritol polyglycidyl ether, and polyglycidyl ether of glyceryl alkylene oxide adduct.

Examples of the amino resin include formaldehyde adducts such as urea, melamine and benzoguanamine, and alkylated products of alcohols having 1 to 6 carbon atoms.

These cross-linking agents (II) are used alone or in admixture of two or more. It is desirable to add a curing catalyst or an accelerator to these crosslinking agents (II).
A pigment, a solvent, an additive and the like can be added to the resin composition for thermosetting coating material of the present invention depending on the purpose and application.

As the pigment used in the coating composition of the present invention, various inorganic pigments and organic pigments used in the coloring material industry are usually used. Examples of the pigment include barite powder, precipitated barium sulfate, ground calcium carbonate, precipitated calcium carbonate, talc, clay, alumina white, white carbon glass and other extender pigments, lead white, zinc white, zinc sulfide, lithopone, and dioxide. White pigments such as titanium, blue pigments such as ultramarine blue, navy blue and cobalt blue, green pigments such as chromium oxide, viridian and chrome green, yellow lead, molybdenum
Yellow to orange to red pigments such as too orange, cadmium pigments, titanium ero, yellow iron oxide and red iron oxide, iron black, car
Black pigments such as bon black, metal powder pigments such as aluminum powder and bronze powder, red lead, lead suboxide powder, cyanamide lead,
M10, zinc chromate, strontium chromate
And anti-corrosion pigments such as zinc, zinc-free, cuprous oxide tripolyphosphate aluminum and the like. Examples of organic pigments include azo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, vat pigments, dyeing lake pigments, γ-Fe ₂ O ₃ , γ-Fe ₂ O ₃ and Fe ₃
O ₄ mixed crystal, CrO ₂ , cobalt ferrite, cobalt-coated iron oxide, barium ferrite, Fe-Co, Fe-
Magnetic powders such as Co-Ni, fillers such as glass fibers, carbon fibers and metal fibers are mentioned.

Examples of the solvent include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone, esters such as methyl acetate and ethyl acetate, tetrahydrofuran, dioxane, ethers such as ethylene glycol monoethyl ether, benzene and toluene. ,
Examples thereof include aromatic hydrocarbons such as xylene, aliphatic hydrocarbons such as hexane and heptane, alcohols such as methanol, ethanol and isopropyl alcohol, or a mixture thereof. The reaction solvent used during the synthesis of the polyester (I) of the present invention can be used as it is.

It is also possible to prepare an aqueous resin composition by using an aqueous medium. As the method for dissolving, dispersing and emulsifying the polyester (I) of the present invention in an aqueous medium, for example, in the case of the polyester (I) obtained by reacting in the absence of a solvent, (I) and a water-soluble organic compound are used. A method of mixing the compound with the compound at 50 to 150 ° C. in advance and adding water to the mixture to disperse the mixture by stirring, or conversely, a method of adding the mixture to water to disperse the mixture by stirring, or (I)
40 with water, water, and water-soluble organic compound if necessary
There is a method of stirring at ~ 120 ° C. In the case of polyester (I) obtained by reacting in a solvent, for example, (I)
Water and, if necessary, a water-soluble organic compound are added to the solution, the system is depressurized, and the solvent is removed from the system by azeotropic distillation. In the method for obtaining the aqueous resin composition of the polyester (I), an alkali or acid neutralizing agent, a surfactant and the like may be used, if necessary, and various polar groups are introduced into the polyester (I). You may keep it.

The water-soluble organic compound is an organic compound having a solubility of 20 g or more in 1 liter of water at 20 ° C., and specifically, it is an aliphatic or alicyclic alcohol, ether, ester or ketone compound. Yes, for example, methano-
Monohydric alcohols such as alcohol, ethanol, isopropanol and n-butanol, glycols such as ethylene glycol and propylene glycol, methyl cellosolve, ethyl cellosolve, n-butyl cellosolve and the like. Of the above, ethers such as dioxane and tetrahydrofuran, esters such as ethyl acetate, and ketones such as methyl ethyl ketone. These water-soluble organic compounds can be used alone or in combination of two or more. Among the above compounds, dispersibility in water, in view of coatability, ethanol, isopropanol, methyl cellosolve, butyl cellosolve,
Ethyl cellosolve is preferred.

Examples of the polar group include those represented by the following chemical formula 1.

[Chemical 1]

As additives, plasticizers, ultraviolet absorbers,
Antioxidant, stabilizer, desiccant, (dryer), antistatic agent, flame retardant, lubricant, dispersant, emulsifier, suspending agent, wetting agent, thickener, anti-sagging agent, antifreezing agent, color component Anti-reflective agent, anti-skin agent, anti-foaming agent, leveling agent, tackifier, anti-rust agent, anti-blocking agent, preservative, anti-mold agent,
Examples of the anti-algae agent include those selected and used according to the application.

The resin set for the thermosetting coating material of the present invention comprises a metal,
It is applied to various materials such as plastic, slates, gypsum, paper and wood. The thermosetting coating composition is also applied to the material used for the precoated steel sheet to form a cured coating film. Examples of the material include zinc iron plate, cold rolled steel plate, galvanized steel plate, aluminum plated steel plate, tin plate, tin-free steel plate, steel plate such as stainless steel plate, aluminum plate, etc., but the balance of various characteristics of precoat metal and Steel plates are preferred because of their excellent aesthetics. In order to impart adhesiveness and corrosion resistance to paints, those obtained by subjecting these materials to pretreatment such as crystalline phosphate treatment, amorphous chrome treatment, and composite oxide film treatment are also used. ..

The composition may be applied directly on the material, but a primer may be applied on the material and the composition may be applied thereon. When coating is performed using the composition, various conventionally known methods can be used. For example,
Examples include spray, roller coat, carten flow coat, knife edge coat and the like. Then usually 100
It is heat-cured at a temperature of 280 ° C to form a crosslinked coating film.

[0039]

The resin composition for a thermosetting coating material of the present invention uses a polyester having a plurality of reactive groups at the terminal of the molecular chain, unlike the conventionally known linear polyester. This makes it possible to introduce a sufficient amount of reactive groups into the resin,
It provides excellent durability such as solvent resistance, water resistance, and stain resistance, and can maintain good flexibility. That is, the hardness and workability of the cured coating film are excellent in balance. For this reason,
The thermosetting resin composition and the coating composition of the present invention can be used for various purposes by forming a coating agent, ink, coating material and the like. It is particularly useful as a coating material for precoated steel sheets.

[0040]

EXAMPLES Examples of the present invention will be described below. In the examples, "parts" means "parts by weight". (1) Synthesis example of raw material polyester (a) In an autoclave equipped with a thermometer and a stirrer, 437 parts of dimethyl terephthalate and 43 of dimethyl isophthalate.
7 parts, ethylene glycol 399 parts, neopentyl glycol 360 parts and tetraptoxy titanate 0.5
0 part was charged and transesterification was carried out by heating at 150 to 230 ° C. for 120 minutes. Then, the reaction system is heated to 25
After the temperature was raised to 0 ° C., the system pressure was gradually reduced to 45 mm after 10 mmHg, and the reaction was continued for another 60 minutes. The obtained polyester A had a molecular weight of 4,000, a hydroxyl value of 500 equivalent / 10 ⁶ g, and an acid value of 5 equivalent / 10 ⁶ g. Polyester B was obtained by the same production method. The molecular weights, hydroxyl values and acid values of polyesters A and B are summarized in Table 1.

Synthesis Example of Polyester (I) In a reaction vessel equipped with a thermometer, a stirrer and a reflux condenser,
400 parts of the polyester A obtained in (1) and 200 parts of Solvesso # 150 were charged and, after dissolution, 20 parts of succinic anhydride and 2 parts of 4-dimethylaminopyridine were added to obtain about 1
The reaction was carried out at 00 ° C. for 2 hours to obtain a carboxyl group-terminated polyester. Acid value of polyester at this stage is 480
The reaction was sufficiently advanced with an equivalent amount of 10 ⁶ g. Next, 15.1 parts of glycidyl was added and the reaction was carried out for 3 hours, after which 235.1 parts of cyclohexanone was added to dilute the system to obtain an acid value of 1 equivalent / 10 ⁶ g and a hydroxyl value of 940 equivalent / 10.
⁶ g of a polyester (I) -A solution having a solid content of 50% was obtained. Similarly, a solution of polyester (I) -B having a solid content concentration of 50% was obtained from polyester B. Table 2 shows the molecular weight, hydroxyl value and acid value of these polyesters.
Shown in.

Examples 1-3, Comparative Examples 1-3 100 parts of the above polyester (I) -A (solution 200
26 parts of polyisocyanate manufactured by Daicel Hurus Co., Ltd., IPDI-B1530, 0.1 part of dibutyltin dilaurate and 126 parts of titanium dioxide,
A white paint was prepared by dispersing. 0.5m thickness of this paint
It was applied on a galvanized steel sheet of m and baked and cured at 240 ° C. for 5 minutes to form a cured coating film having a thickness of 20 μm.
The performance of the coated steel sheet thus produced was evaluated by the following method.

Hardness Tested using Mitsubishi Pencil Uni, and expressed as hardness one rank below the lowest hardness at which scratches occur. It was tested by a bending test with a workability vise, and evaluated by the number of plates sandwiched between the minimum cracks. The surface state of the solvent resistant cured film was observed after rubbing 50 times with gauze containing xylene. ○: No abnormality. Δ: There is a tight feeling. X: The coating film peels off. After dipping the coated steel sheet in boiling water resistant boiling water, it was boiled for 2 hours, and the surface condition of the film was visually judged. ○: No abnormality. Δ: Slightly cloudy or slightly peeled off. X: Severely clouded or peeled. Contamination resistance Lines were drawn on the coated surface using three color magic inks of red, blue and black, left for 24 hours, wiped with gauze soaked with ethanol, and the line marks were evaluated. ◯: No trace remains. Δ: A trace remains slightly. X: Traces clearly remain.

Similarly, polyester (I) -B and a system in which (I) -A and (I) -B were blended at 50 parts / 50 parts were evaluated. Further, as comparative examples, polyesters A, B and A / B = 50/50 having no branch at the end of the molecular chain
(Part) The compounding system was evaluated. The compounding ratio of the coating material and the obtained coating film performance evaluation results are summarized in Table 3.

Example 4 40 parts of polyester (I) -A used above (80 parts of solution), 60 parts of polyester (I) -B (solution 12)
0 part) IPDI-B1530 16.2 parts, butylated melamine resin 12 parts, paratoluene sulfonic acid 0.
25 parts and 128 parts of titanium dioxide were added and dissolved / dispersed to prepare a white paint. Example 1 using this paint
A coated steel sheet was prepared in the same manner as in 1. and the performance was evaluated. The results were excellent performance such as hardness 2H, processability OT, solvent resistance ◯, water resistance ◯, and stain resistance ◯.

Example 5 In the same manner as in the synthesis example of the raw material polyester (a), terephthalic acid / isophthalic acid / adipic acid // neopentyl glycol / cyclohexanedimethanol = 35/35 /
30/50/50 (molar ratio) composition, molecular weight 950
0, hydroxyl value 210 equivalent / 10 ⁶ g, acid value 3 equivalent / 10
⁶ g of polyester C was obtained. Next, 400 parts of this polyester was charged into a kneader and melted under a nitrogen atmosphere, and then 16.1 parts of trimellitic anhydride was added to obtain 200
The reaction was carried out at ° C for about 30 minutes. The polyester (I) -C thus obtained has a molecular weight of 9400 and an acid value of 4
It was 30 equivalents / 10 ⁶ g. Next, 100 parts of polyester (I) -C was dissolved in 100 parts of cyclohexanone, and then 4.4 parts of tris (2,3-epoxypropyl) isocyanurate and 104 parts of titanium dioxide were added and dispersed to prepare a white paint. .. A coated steel sheet was produced in the same manner as in Example 1 using this coating material, and the performance was evaluated. As a result, hardness H, workability OT, solvent resistance ○, water resistance ○, stain resistance Δ to ○, and satisfactory performances were obtained. Had.

Example 6 In the same manner as in the synthesis example of the raw material polyester (a), terephthalic acid / isophthalic acid // diethylene glycol = 50.
/ 50/100 (molar ratio) composition, molecular weight 10,000
0, hydroxyl value 200 equivalent / 10 ⁶ g, acid value 5 equivalent / 10
⁶ g of polyester D was obtained. Then, polyester D was added to 100% in the same manner as in the synthesis example of polyester (I).
Parts, 2 parts of succinic anhydride and 1.6 parts of glycidol were reacted to obtain a solution of polyester (I) -D having a solid content concentration of 50%. Polyester (I) -D has a molecular weight of 1040
0, hydroxyl value 420 equivalent / 10 ⁶ g, acid value 2 equivalent / 10
It was ⁶ g. Polyester (I) used in Example 1
I to 40 parts of -A and 60 parts of polyester (I) -D
17.6 parts of PDI-B1530, 12 parts of butylated melamine resin, 0.25 parts of paratoluene sulfonic acid and 130 parts of titanium dioxide were added and dissolved / dispersed to prepare a white paint, and Example 1 A coated steel sheet was prepared in the same manner as above, and the performance was evaluated. The result is hardness 2H, workability O
T, solvent resistance o, water resistance o, stain resistance o were excellent performances.

[0048]

[Table 1]

[0049]

[Table 2]

[0050]

[Table 3]

[0051]

The resin composition for thermosetting coating material of the present invention comprises
Consisting of polyester (I) having multiple reactive groups due to branching at the end of the molecular chain and cross-linking agent (II), which can impart excellent durability such as solvent resistance, water resistance, and stain resistance, as well as excellent It is clear that it also has flexibility. Therefore, when the thermosetting resin of the present invention is applied to a pre-coated steel sheet, a pre-coated steel sheet having an unprecedented hardness / workability balance and various other properties can be obtained.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location C09D 175/04 PHQ 8620-4J (72) Inventor Nobuichi Kodera 1-2-1, Katata, Otsu, Shiga Prefecture No. 1 Toyobo Co., Ltd. Research Institute

Claims (1)

[Claims] 1. A cross-linking agent (II) comprising polyester (I) and at least one of an isocyanate compound, an epoxy compound, and an amino resin, 0.01 ≦ (II) / (I) ≦
A resin composition for a thermosetting coating composition, which is blended in a ratio of 0.7 (weight ratio), wherein the polyester (I) contains an aromatic dicarboxylic acid as a carboxylic acid component and an alcohol. Polyester (a) mainly composed of aliphatic glycol as a component and polycarboxylic acid anhydride (b)
And / or one or more polyesters having a plurality of reactive groups introduced by branching at a molecular chain terminal obtained by reacting with the monoepoxy compound (c), and a resin composition for thermosetting coating composition. object.