JP2012012422A - Water-based coating composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a water-based coating composition having excellent storage quality which makes a polyester resin a binder, and can form a coating film excellent in physical properties.SOLUTION: The polyester resin (A) of the number-average molecular weight of 1000-20,000, which has a sulfonic acid group being an alkali metal salt in a molecule, is used as a binder, and thereby the water-based coating composition which excels in water dispersibility, has excellent storage quality, excels in coating film strength or coating film water resistance, and can form a coating film which can be utilized as an independent coating film can be obtained.

Description

  The present invention relates to an aqueous coating composition comprising a polyester resin having a sulfonic acid group which is an alkali metal salt in the molecule as a binder.

  In recent years, from the viewpoint of environmental protection, there is an increasing demand for water-based paints that emit less volatile organic compounds (VOC) into the atmosphere. Organic resins of various structures are used as binders in paints, but polyester resin is a typical resin that is often used because it is relatively inexpensive and has excellent physical properties such as flexibility and adhesion. is there. However, since the main chain is composed of an ester bond generated by condensation of acid and glycol, there is a drawback that hydrolysis tends to occur in an acidic atmosphere (generally pH 4 or less) or an alkaline atmosphere (generally pH 10 or more). When used as a binder for water-based paints, there were many cases where the storage stability was poor.

  As a typical method for using a polyester resin in a water-based paint, a method of using a relatively high acid value polyester resin having an acid value of 20 mgKOH / g or more by neutralizing with an organic amine as an aqueous dispersion, There is a method in which a polyester resin having a low acid value is forcibly made into an aqueous dispersion using a large amount of a surfactant.

  However, in the former case, a high acid value polyester resin often contains a large amount of free carboxylic acid and easily undergoes transesterification and hydrolysis, so that the molecular weight during storage and the viscosity of the coating are often reduced. In the latter case, since the emulsion is forcibly emulsified with a surfactant, the stability of the emulsified state, that is, the storage property is inferior as the polyester resin has a higher molecular weight. If a large amount of surfactant is used to compensate for this, the water resistance of the coating film is impaired. On the other hand, if a low molecular weight polyester resin that requires a relatively small amount of surfactant is used, the physical properties of the coating film, such as scratch resistance and impact resistance, which are greatly affected by the molecular weight, are impaired.

  It is conceivable to use sulfonic acid as an attempt to disperse the polyester resin in water using a functional group other than carboxylic acid.

  Conventionally, polyester resins having a sulfonic acid group are widely known, but mainly used for improving dyeability of polyester fibers. For example, in Patent Document 1, PET fiber copolymerized with a very small amount of 5-sodium sulfoisophthalic acid component exhibits good dyeability and fastness to both disperse dyes and cationic dyes, and has excellent mechanical properties and softness. It is disclosed that the polyester fiber has a good texture.

  However, it is not common to use a polyester resin having a sulfonic acid group as a binder for water-based paints.

  For example, in Patent Document 2, in a mixed aqueous solution or dispersion of a water-soluble or water-dispersible polyester resin copolymerized with a small amount of 5-sodium sulfoisophthalic acid and colloidal silica, a hydrophilic radical-polymerizable vinyl monomer and other Although a coating composition obtained by polymerizing a copolymerizable vinyl monomer is disclosed, it is mainly used as a coating agent for imparting ink jet printability to paper and film materials. When this material is used as a water-based paint, the strength of the formed coating film is low and its practicality is poor.

  Patent Document 3 discloses a copolyester derived from a sulfo derivative of a carboxylic acid selected from sulfoterephthalic acid and sulfoisophthalic acid as a water-soluble or water-dispersible organic binder, and optionally a melamine formaldehyde resin, an epoxy resin, and an isocyanate. A gas barrier coating agent is disclosed in which at least one crosslinking agent selected from aziridene, carbodiimide, urea formaldehyde, phenol resin, silanol and acid is combined. This is a water-soluble material that is required to contain an inorganic layered mineral and that exhibits a very high gas barrier property when applied to the surface of a polymer material such as PET, but does not impair recyclability. When the coating film strength or the water resistance of the coating film is required, it is necessary to overcoat the second different type of coating film.

JP-A-8-269820 JP-A-9-165552 Thus, an aqueous coating composition using a conventionally known sulfonic acid-containing polyester has an insufficient strength and physical properties, and an aqueous coating composition capable of forming a coating film that can be used as a single coating film is obtained. It was extremely difficult.

  An object of the present invention is to obtain a water-storing coating composition having good storability and capable of forming a coating film having excellent physical properties using a polyester resin as a binder.

  As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention obtained a polyester resin (A) having a number average molecular weight of 1000 to 20,000 having a sulfonic acid group as an alkali metal salt in the molecule. By using it as a binder, the present invention has found an aqueous coating composition that has excellent water dispersibility, good storage properties, excellent coating film strength and water resistance, and can form a coating film that can be used as a single coating film. It came to be completed.

Thus, the present invention comprises the following items.
1. A water-based paint composition comprising, as a binder, a polyester resin (A) having a sulfonic acid group which is an alkali metal salt in the molecule and having a number average molecular weight of 1000 to 20,000.
2. The composition of the polyester resin (A) is such that the acid component is (a) a dicarboxylic acid having a sulfonic acid group which is an alkali metal salt in the molecule: 1 to 5 mol%, (a) an aliphatic dicarboxylic acid or an alicyclic group Dicarboxylic acid: 24 to 49 mol%, (U) terephthalic acid: 0 to 5 mol% (e) Aromatic dicarboxylic acid other than terephthalic acid: 0 to 25 mol%, and the polyol component is The aliphatic or alicyclic diol having 4 or more carbon atoms, which may contain one carboxyl group, 35 to 60 mol%, (f) the aliphatic diol having 3 or less carbon atoms: 0 to 15 mol%, The water-based coating composition according to item 1, comprising: other than that, a trihydric or higher polyol: 0 to 25 mol%.
3. (A) The aqueous coating composition according to item 1 or 2, wherein the dicarboxylic acid having a sulfonic acid group which is an alkali metal salt in the molecule is sodium 5-sulfoisophthalate.
4). Item 4. The aqueous coating composition according to item 1 to item 3, wherein the acid value of the polyester resin (A) is 10 mg KOH / g or less.
5. Item 5. The aqueous coating composition according to any one of Items 1 to 4, further comprising a crosslinking agent (B) capable of reacting with the polyester resin (A).
6). Item 6. The aqueous coating composition according to any one of Items 1 to 5, wherein the liquid pH is in the range of 6 to 8.
7). Item obtained by coating the aqueous coating composition according to any one of Items 1 to 6.

ADVANTAGE OF THE INVENTION According to this invention, the water-based coating composition excellent in storage property and a coating-film physical property is provided. In particular, the water-based paint composition of the present invention uses very little organic amine, which has been used when water-dispersing polyester resins in the past, and therefore has very little environmental pollution, and the coating film formed is practical. In addition to being high, it has been clarified in the course of research, but the coating film formed is hydrophilic and has excellent stain resistance. The paint / coating according to the present invention is suitable for outdoor use.

The present invention will be described in more detail below.
Polyester resin
The polyester resin used in the present invention is produced by polycondensation of dicarboxylic acid and polyol, and can be produced by a known production method.

  The polyester resin used in the present invention can use a small amount of monocarboxylic acid or trivalent or higher polycarboxylic acid in addition to dicarboxylic acid as an acid raw material, but only dicarboxylic acid can be used as a coating material as an acid raw material. It is preferable from the viewpoint of physical properties of the coating film obtained. When a monocarboxylic acid is used in combination, a low molecular weight polyester oligomer may be produced as a by-product and the coating film may become brittle. When a tricarboxylic acid or higher polycarboxylic acid is used in combination, gelation may occur during production, and the acid value of the obtained resin may increase, resulting in poor storage properties.

  The polyester resin used in the present invention can use a small amount of monoalcohol or trihydric or higher polyol in addition to diol as a raw material, but when monoalcohol is used in combination, a low molecular weight polyester oligomer is produced as a by-product. The film may become brittle. When a large amount of a trivalent or higher polyol is used in combination, it may gel during production. However, it is easy to keep the acid value of the obtained resin low and storage problems are unlikely to occur.

Of the raw materials for the polyester resin used in the present invention, the following (A) to (E) can be used as the dicarboxylic acid component.
(A) Dicarboxylic acid having a sulfonic acid group which is an alkali metal salt in the molecule: for example, sulfoterephthalic acid, 5-sulfoisophthalic acid, 4-sulfophthalic acid, 4-sulfonaphthalene-2,7-dicarboxylic acid, 5 [[4-sulfophenoxy] isophthalic acid and other metal salts. Of these, 5-sulfoisophthalic acid sodium salt is particularly preferred.
(I) Aliphatic dicarboxylic acid: for example, adipic acid, sebacic acid, suberic acid, succinic acid, glutaric acid, maleic acid, chloromaleic acid, fumaric acid, dodecanedioic acid, pimelic acid, azelaic acid, itaconic acid, citraconic acid, Examples thereof include dicarboxylic acids such as dimer acid and acid anhydrides thereof.
(I) Alicyclic dicarboxylic acid: Examples thereof include dicarboxylic acids such as hexahydroisophthalic acid, hexahydroterephthalic acid, hexahydrophthalic acid and tetrahydrophthalic acid, and acid anhydrides thereof.
(C) Terephthalic acid.
(D) Aromatic dicarboxylic acids other than terephthalic acid: dicarboxylic acids such as isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, 4,4′-biphenyldicarboxylic acid, diphenylmethane-4,4′-dicarboxylic acid and acid anhydrides thereof Can be given.

  An equivalent polyester resin can also be obtained by replacing part or all of the raw carboxylic acid with its lower alkyl ester.

Of the raw materials for the polyester resin used in the present invention, the following (e) to (g) can be used as the polyol component.
(E) an aliphatic or alicyclic diol having 4 or more carbon atoms which may contain one carboxyl group in the molecule: for example, diethylene glycol, dipropylene glycol, butanediol, neopentyl glycol, hexanediol, 2-butyl-2 -Aliphatic diols such as ethyl-1,3-propanediol; Alicyclic diols such as 1,4-cyclohexanedimethanol and hydrogenated bisphenol A; One carboxyl group such as dimethylolpropionic acid and dimethylolbutanoic acid Examples include diols.
(F) Aliphatic diols having 3 or less carbon atoms: for example, ethylene glycol, propylene glycol, etc. (g) Other trivalent or higher polyols: glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, sorbitol Etc. Of these, trivalent polyols with less risk of gelation during production are preferred.

  The polyester resin used in the present invention is produced by using the above-mentioned raw materials (a) to (ki). Among them, (a) use of a dicarboxylic acid having a sulfonic acid group which is an alkali metal salt in the molecule. Is essential. The amount of dicarboxylic acid having a sulfonic acid group which is an alkali metal salt in the molecule is preferably in the range of 1 to 5 mol% based on the total amount of monomers used in the production of the polyester resin. When the amount is less than 1 mol%, the resin may not exhibit sufficient water dispersibility. When the amount exceeds 5 mol%, the hydrophilicity of the resin is high, so that the water resistance of the cured coating film when used in a paint becomes insufficient. There is a case.

  The mixing ratio of the acid monomers (a) to (e) other than (a) can be appropriately selected according to the purpose of use of the water-based paint, but from the viewpoint of balancing solubility, flexibility and water resistance. (I) 24 to 49 mol%, (c) 0 to 5 mol%, and (d) 0 to 25 mol% are balanced preferable ranges.

  The polyol components (e) to (g) are also soft and highly soluble components from the viewpoint that the physical properties of the resin affect the balance between solubility and flexibility and water resistance. (E) A carboxyl group in the molecule An aliphatic or alicyclic diol having 4 or more carbon atoms, which may contain one of the above, is 35 to 40 mol%, and is slightly hard and has a role of adjusting physical properties. (F) An aliphatic diol having 3 or less carbon atoms is 0 ˜15 mol%, the blending ratio of 0 to 25 mol% of the trivalent or higher polyol having the role of adjusting the molecular weight and the role of introducing the cross-linking functional group is a balanced preferable range. Even when (g) is 0 mol%, there is a crosslinkability because a hydroxyl group or a carboxyl group is present at the end of the polyester resin.

  The polyester resin used in the present invention preferably has a number average molecular weight in the range of 1000 to 20,000. When the number average molecular weight is less than 1000, a brittle coating film may be formed when a coating film is formed. On the other hand, when the number average molecular weight exceeds 20,000, the water dispersibility may be insufficient due to the entanglement of the resin, and the stability and storability of the water-based paint may be insufficient.

  Here, in this specification, the number average molecular weight (and weight average molecular weight) is the retention time measured using a gel permeation chromatograph (GPC), and the retention time of standard polystyrene whose molecular weight is known measured under the same conditions. It is the value calculated in terms of molecular weight. Specifically, “HLC8120GPC” (trade name, manufactured by Tosoh Corporation) is used as a gel permeation chromatograph, and “TSKgel G-4000HXL”, “TSKgel G-3000HXL”, “TSKgel G-2500HXL” are used as columns. ”And“ TSKgel G-2000HXL ”(trade names, all manufactured by Tosoh Corporation), a differential refractometer is used as a detector, mobile phase: tetrahydrofuran, measurement temperature: 40 ° C., flow rate: It can be measured under the condition of 1 mL / min.

  The polyester resin used in the present invention is characterized by exhibiting water dispersibility even when the acid value is low, and the acid value is preferably 10 (mgKOH / g) or less. If the acid value exceeds 10, the dispersion after water dispersion may become unstable and the resin may separate and settle. In order to prevent this, neutralization with a considerable amount of organic amine according to the acid value is sufficient, but organic amine is not preferable because it becomes VOC. Here, the acid value of the polyester resin is a numerical value when the mass of potassium hydroxide necessary for neutralizing the protonic acid contained in 1 g of the resin is expressed in mg, and the measurement is JIS K-2501-2003. Can be done based on.

  For producing the polyester resin used in the present invention, a known method such as a melting method or a solvent reflux dehydration method can be used. Further, an esterification catalyst (when the raw material is a carboxylic acid) or a transesterification catalyst (when the raw material is a carboxylic acid lower ester) can be used for the purpose of promoting the reaction during the production. Examples of these catalysts include dibutyltin oxide, antimony trioxide, zinc acetate, manganese acetate, cobalt acetate, calcium acetate, lead acetate, tetrabutyl titanate, tetraisopropyl titanate and the like.

  The polyester resin used in the present invention can be made into an aqueous dispersion by adding it to water as it is and stirring it. At this time, the aqueous dispersion in which the polyester resin is dispersed often becomes neutral to weakly acidic. The aqueous dispersion is stable as it is, but the liquid pH can be adjusted by adding a small amount of base.

  This pH adjustment may be performed immediately after the dispersion of the polyester resin, and if necessary, the pH may be adjusted after preparing an aqueous coating composition to which a crosslinking agent (and pigments, additives, etc.) is added. In addition, it is preferable that the liquid pH as the aqueous coating composition is in the range of 6-8. If the liquid pH is outside this range, the reaction between the polyester resin and the crosslinking agent is promoted, and the storability of the paint may be inferior.

Cross-linking agent
When the polyester resin of the present invention is used as an aqueous coating composition, a crosslinking agent can be added. When the polyester resin of the present invention has a hydroxyl group as a crosslinkable functional group, the crosslinking agent is not particularly limited as long as it is a compound having a functional group capable of reacting with a hydroxyl group. For example, the following melamine resin, polyisocyanate compound, Block polyisocyanate compounds and the like can be suitably used singly or in combination of two or more.

  Melamine resin: Specific examples of the melamine resin include di-, tri-, tetra-, penta-, hexa-methylol melamine and alkyl etherified products thereof with alcohol (alkyl includes, for example, methyl, ethyl, propyl, Isopropyl, butyl, isobutyl, 2-ethylhexyl and the like) and condensates thereof.

  Specific examples of the melamine resin include, for example, Cymel 303, Cymel 323, Cymel 325, Cymel 327, Cymel 350, Cymel 370, Cymel 380, Cymel 385, Cymel 212, Cymel 251, Cymel 254, Mymel manufactured by Nippon Cytec Industries, Ltd. Coat 776; Resin 735, Resimin 740, Resimin 741, Resimin 745, Resimin 746, Resimin 747 manufactured by Monsanto, Sumitomo Chemical Co., Ltd. Summar M55, Sumimar M30W, Summar M50W; Mitsui Chemicals, Inc., Uban 20SB Series etc. (all are trade names) can be mentioned.

  Among them, methyl / butyl (mixed) etherified melamine resin can be mentioned as a particularly preferred melamine resin. Specific examples of such melamine resins include Cymel 325, Cymel 327, Cymel 350, Cymel 212, Cymel 251 and My Coat 776 (trade name) manufactured by Nippon Cytec Industries.

  When a melamine resin is used as a crosslinking agent, sulfonic acids such as paratoluenesulfonic acid, dodecylbenzenesulfonic acid, dinonylnaphthalenesulfonic acid, and salts of these acids and amines can be used as catalysts.

  The melamine resins described above can be used alone or in combination of two or more.

  Polyisocyanate compound: a polyisocyanate compound having at least two free isocyanate groups in a molecule, for example, aliphatic polyisocyanates such as hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, dimer acid diisocyanate, and lysine diisocyanate; Burette type adducts, isocyanurate cycloadducts of these polyisocyanates; isophorone diisocyanate, 4,4′-methylenebis (cyclohexyl isocyanate), methylcyclohexane-2,4- (or-2,6-) diisocyanate, 1, 3- (or 1,4-) di (isocyanatomethyl) cyclohexane, 1,4-cyclohexane diisocyanate, 1,3-cyclopentane diisocyanate, 1 Alicyclic diisocyanates such as 2-cyclohexane diisocyanate and burette type adducts, isocyanurate cycloadducts of these polyisocyanates; xylylene diisocyanate, metaxylylene diisocyanate, tetramethyl xylylene diisocyanate, tolylene diisocyanate, 4, 4'-diphenylmethane diisocyanate, 1,5-naphthalene diisocyanate, 1,4-naphthalene diisocyanate, 4,4'-toluidine diisocyanate, 4,4'-diphenyl ether diisocyanate, (m- or p-) phenylene diisocyanate, 4,4 ' -Biphenylene diisocyanate, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, bis (4-isocyanatophenyl) sulfone, Aromatic diisocyanate compounds such as propylidenebis (4-phenylisocyanate) and burette-type adducts and isocyanurate cycloadducts of these polyisocyanates; triphenylmethane-4,4 ′, 4 ″ -triisocyanate, 1,3 , 5-triisocyanatobenzene, 2,4,6-triisocyanatotoluene, 4,4′-dimethyldiphenylmethane-2,2 ′, 5,5′-tetraisocyanate, etc. -Containing polyisocyanates and burette-type adducts and isocyanurate cycloadducts of these polyisocyanates; ethylene glycol, propylene glycol, 1,4-butylene glycol, dimethylolpropionic acid, polyalkylene glycol, trimethylol Urethane adducts obtained by reacting polyisocyanate compounds in excess ratio of isocyanate groups to hydroxyl groups of polyols such as propane and hexanetriol, burette type adducts, isocyanurate ring adducts, etc. of these polyisocyanates. Can be mentioned. These polyisocyanate compounds can be used alone or in combination of two or more.

  Blocked polyisocyanate compound: A compound obtained by blocking the isocyanate group of a polyisocyanate compound as exemplified above with a blocking agent. The blocking agent is a compound that temporarily blocks the free isocyanate group by reacting with the isocyanate group of the polyisocyanate compound, and the block polyisocyanate compound is usually, for example, 100 ° C. or higher, preferably 130 ° C. or higher. By heating, the blocking agent is released and the free isocyanate group is regenerated, and the blocked polyisocyanate compound can react with the hydroxyl group. Examples of the blocking agent include phenols such as phenol, cresol, xylenol, nitrophenol, ethylphenol, hydroxydiphenyl, butylphenol, isopropylphenol, nonylphenol, octylphenol, and hydroxybenzoic acid methyl; ε-caprolactam, δ-valerolactam, lactams such as γ-butyrolactam, β-propiolactam; aliphatic alcohols such as methanol, ethanol, propyl alcohol, butyl alcohol, amyl alcohol, lauryl alcohol; ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol mono Butyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, pro Len glycol monomethyl ether, ether systems such as methoxymethanol; benzyl alcohol; glycolic acid; glycolic acid ester systems such as methyl glycolate, ethyl glycolate, and butyl glycolate; lactic acid; lactate esters such as methyl lactate, ethyl lactate, and butyl lactate System; alcohol system such as methylol urea, methylol melamine, diacetone alcohol, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate; formamide oxime, acetamide oxime, acetoxime, methyl ethyl ketoxime, diacetyl monooxime, benzophenone oxime, cyclohexane oxime, etc. Active methyl such as dimethyl malonate, diethyl malonate, ethyl acetoacetate, methyl acetoacetate, acetylacetone Mercaptans such as butyl mercaptan, t-butyl mercaptan, hexyl mercaptan, t-dodecyl mercaptan, 2-mercaptobenzothiazole, thiophenol, methylthiophenol, ethylthiophenol; Acid amides such as acetic acid amide, stearic acid amide, benzamide; imides such as succinimide, phthalic acid imide, maleic acid imide; diphenylamine, phenylnaphthylamine, xylidine, N-phenylxylidine, carbazole, aniline, naphthylamine, butylamine Amines such as dimethyl, dibutylamine and butylphenylamine; imidazoles such as imidazole and 2-ethylimidazole; 3,5-dimethyl Pyrazoles such as razole; ureas such as urea, thiourea, ethylene urea, ethylene thiourea and diphenyl urea; carbamates such as phenyl N-phenylcarbamate; imines such as ethyleneimine and propyleneimine; sodium bisulfite And sulfites such as potassium bisulfite. These blocking agents can be used alone or in combination of two or more.

  Moreover, when using a polyisocyanate compound and a block polyisocyanate compound as a crosslinking agent, a catalyst for promoting urethanization reaction such as an organotin compound can be used.

  The water-based coating composition of the present invention becomes a coating film excellent in adhesion and durability, and can be suitably used in the field of outdoor coatings such as PCM coatings and building material coatings.

  The aqueous coating composition of the present invention uses a small amount of a resin such as cellulose acetate butyrate, epoxy resin, alkyd resin, acrylic resin in addition to a polyester resin having a sulfonic acid group which is an alkali metal salt in the molecule and a crosslinking agent. May be. Also, if necessary, additives such as solvents other than water, pigments, curing catalysts, UV absorbers, coating surface modifiers, antioxidants, fluidity modifiers, pigment dispersants, silane coupling agents, etc. It can be shown.

  Solvents other than water provide the effect of improving the smoothness of the coating film as a film-forming aid, such as hydrocarbon solvents such as xylene, octane and mineral spirits, ethyl acetate, n-butyl acetate, isobutyl acetate, methyl Ester solvents such as cellosolve acetate and butyl carbitol acetate, ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone and diisobutyl ketone, alcohol solvents such as methanol, ethanol, isopropanol, n-butanol, sec-butanol and isobutanol, n -Ether solvents such as butyl ether, dioxane, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, aromatic petroleum systems such as trade names Swazol 310, Swazol 1000, Swazol 1500 manufactured by Cosmo Oil Co., Ltd. Agents, and the like can be mentioned. These solvents can be used alone or in combination.

  Examples of the pigment that may be contained in the paint include organic pigments (for example, quinacridone compounds such as quinacridone, azo compounds such as pigment red, phthalocyanine compounds such as phthalocyanine blue and phthalocyanine green), inorganic pigments (for example, titanium oxide, Barium sulfate, calcium carbonate, barita, clay, silica, etc.), carbon pigments (carbon black), metallic powders (eg, aluminum, mica-like iron oxide, stainless steel, etc.), anti-rust pigments (eg, Bengala, strontium) Chromate).

  There are no particular restrictions on the base material on which the paint is applied. For example, a metal plate such as an aluminum plate or a steel plate, a plated steel plate on which the surface of the steel plate is plated with zinc, chromium, tin, aluminum, etc. It can be applied to various metal materials such as treated steel sheets chemically treated with acid, iron phosphate and zinc phosphate, polymer moldings such as polypropylene, ABS and FRP, and inorganic building materials such as gypsum board. In addition, a base paint may be applied to the surface of the material in advance.

  As a means for applying the paint, for example, roll coating, spray coating, brush coating, spray coating, or any method known per se can be used. The coating film thickness is usually about 1 to 50 microns for the cured coating, but it is not necessarily in this range.

  The coating film can be appropriately selected from room temperature drying to baking hardening depending on the purpose. For example, in the case of a PCM steel sheet, the coating film is generally about 150 to about 280 ° C., preferably about 180 ° C. to about 260 ° C., and about 20 Bake hardening is performed for ˜600 seconds, preferably about 30 to 300 seconds.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. Hereinafter, both “parts” and “%” are based on mass.

Manufacture of polyester resin (A)
Production Example 1
In a reaction apparatus equipped with a thermometer, a stirrer, a heating device and a rectifying column, 182 parts of 5-sulfoisophthalic acid sodium salt, 434 parts of 2-butyl-2-ethyl-1,3-propanediol, 1,6-hexane 959 parts of diol, 363 parts of methylolpropane, 396 parts of adipic acid, 225 parts of terephthalic acid, 835 parts of hexahydrophthalic anhydride and 0.7 part of monobutyltin oxide were charged. Subsequently, the content was gradually heated from 160 ° C. to 220 ° C. over 3 hours, and the condensed water produced through the rectification column was distilled off. After continuing the reaction at 220 ° C. for 90 minutes, the rectifying column was replaced with a water separator, and the temperature was raised to 230 ° C. About 165 parts of toluene was added to the contents, and toluene was also added to the water separator, and water and toluene were azeotroped to remove condensed water. 1 hour after the addition of toluene, acid value measurement was started, heating was stopped after confirming that the acid value was less than 5.0, toluene was removed under reduced pressure, and then cooled, and 660 parts of butyl cellosolve was added. It was. Thereafter, deionized water is added with stirring and the mixture is dispersed in water. A 1% aqueous dimethylethanolamine solution is added to adjust the pH, and an aqueous dispersion 1 of a polyester resin having an acid value of 5.0, a hydroxyl value of 120, and a number average molecular weight of 6000. Got. The obtained aqueous dispersion had a pH of 6.8 and a solid content of 50.0% by mass.
Production Examples 2-14
Polyester resin aqueous dispersions of Examples 2 to 9 and Comparative Examples 1 to 4 were obtained in the same manner as in Production Example 1 except that the raw materials shown in Tables 1 and 2 were used. The acid value, hydroxyl value, molecular weight, and pH of the aqueous dispersion after pH adjustment were also entered in the table. The solid content of the aqueous dispersion was 49.0% by mass to 51.0% by mass (not shown in the table).

Example 1
34.1 parts of “Cymel 370” (manufactured by Mitsui Cytec Co., Ltd., 88% water-soluble melamine resin solution) was added to 140.0 parts of the polyester aqueous dispersion obtained in Production Example 1 and mixed well. A composition was prepared.

Examples 2-10, Comparative Examples 1-4
The aqueous polyester compositions of Examples 2 to 10 and Comparative Examples 1 to 4 were prepared by mixing the polyester aqueous dispersion and the crosslinking agent with the formulation shown in Table 3 in the same procedure as in Example 1.

Performance test 1
Storage property: 180 g of the aqueous coating composition obtained in Examples and Comparative Examples was put in a wide-mouth mayonnaise bottle having an internal volume of 225 mL, sealed, and stored in a constant temperature room at 40 ° C. for 1 month, and the state after storage was evaluated. The evaluation results of this storage property are shown in the lower part of Table 3.

A: The content liquid is uniform and has the same or almost the same viscosity as the initial liquid.
○: The contents are slightly thickened but have sufficient fluidity.
(Triangle | delta): The content liquid is clearly thickened and lacks in fluidity | liquidity, or has isolate | separated into two layers.
X: The content liquid is remarkably thickened and hardly flows or gels.

Performance test 2
Creating test plates
Migaki mild steel plate (width 50 mm × length 100 mm × thickness 0.8 mm) The aqueous coating compositions of Examples 1 to 10 and Comparative Examples 1 to 4 had a dry coating thickness of 0.02 ± 0.002 mm. Then, air coating was performed, and after setting for 10 minutes at room temperature, test coating plates 1 to 14 were obtained by baking at 140 ° C. for 25 minutes in a hot air dryer.

  Each test coated plate was tested according to the following test method. Table 4 shows the obtained results.

Test method
Appearance of coating film: The coated plate was visually evaluated.
○: The coating film surface is smooth and glossy, and no discoloration due to baking is observed.
(Triangle | delta): Although the coating-film surface is smooth and glossy, slight thermal yellowing is recognized by baking.
X: The coating film surface is non-uniform and glossy, or significant yellowing due to baking is observed.

Impact resistance: Painted according to JIS K5600-5-3-6 (1999) DuPont impact resistance test under conditions of weight drop weight 500g, striker tip diameter 1/2 inch, drop weight height 50cm. An impact was given to the painted surface of the board. Then, a cellophane adhesive tape was applied to the part to which the impact on the coated surface was applied, and the peeled state of the coating film when the tape was instantaneously peeled was evaluated.
(Double-circle): The peeling of a coating film is not recognized by the coating surface.
○: Slight peeling of the coating film is observed on the coated surface.
X: Peeling of the coating film is considerably recognized on the coated surface.

  Water resistance: Each test plate was examined for appearance and adhesion after being immersed in deionized water at 40 ° C. for 48 hours. Adhesiveness evaluated the peeling after making a crosscut of a X mark with a cutter knife so that it might reach a substrate, sticking an adhesive cellophane tape on the crosscut part, and removing it rapidly.

○: No abnormality is observed at all.
Δ: Appearance abnormality such as blistering and blistering is not observed, but peeling is observed.

  X: Appearance abnormalities such as blistering and blistering and peeling are recognized.

Weather resistance: The gloss of each test plate conforms to JIS H 8602 5.12 (1992) (water spray time 12 minutes, black panel temperature 60 ° C.), and a carbon arc lamp type accelerated weather resistance tester Sunshine Weatherometer is used. Used to measure the time for the gloss retention to be less than 80% of the gloss before the exposure test. Furthermore, the coating film surface was observed visually.
A: Even after 1,500 hours, the gloss retention is 80% or more, and no crack occurs on the surface of the coating film.
◯: Time for gloss retention to be less than 80% or time for cracking to occur on coating film surface is 1,000 hours or more and less than 1,500 hours.
Δ: Time for gloss retention to be less than 80% or time for cracking on coating film surface is 500 hours or more and less than 1,000 hours.
X: Time for gloss retention to be less than 80% or time for cracking on coating film surface is less than 500 hours.

Claims (7)

  A water-based paint composition comprising, as a binder, a polyester resin (A) having a sulfonic acid group which is an alkali metal salt in the molecule and having a number average molecular weight of 1000 to 20,000.   The composition of the polyester resin (A) is such that the acid component is (a) a dicarboxylic acid having a sulfonic acid group which is an alkali metal salt in the molecule: 1 to 5 mol%, (a) an aliphatic dicarboxylic acid or an alicyclic group Dicarboxylic acid: 24 to 49 mol%, (U) terephthalic acid: 0 to 5 mol% (e) Aromatic dicarboxylic acid other than terephthalic acid: 0 to 25 mol%, and the polyol component is The aliphatic or alicyclic diol having 4 or more carbon atoms, which may contain one carboxyl group, 35 to 60 mol%, (f) the aliphatic diol having 3 or less carbon atoms: 0 to 15 mol%, The water-based coating composition according to claim 1, comprising: other polyols having a valence of 3 or more: 0 to 25 mol%.   (A) The aqueous coating composition according to claim 1 or 2, wherein the dicarboxylic acid having a sulfonic acid group which is an alkali metal salt in the molecule is sodium 5-sulfoisophthalate.   The aqueous coating composition according to claim 1, wherein the acid value of the polyester resin (A) is 10 mg KOH / g or less.   Furthermore, the water-based coating composition of any one of Claims 1-4 containing the crosslinking agent (B) which can react with a polyester resin (A).   The aqueous coating composition according to any one of claims 1 to 5, wherein the liquid pH is in the range of 6 to 8.   An article formed by applying the aqueous coating composition according to any one of claims 1 to 6.