JP2007314689A - Water-based paint composition - Google Patents

Abstract

（式中、Ｒはジグリシジルエポキシ化合物のグリシジルオキシ基を除いた残基、Ｒ’はジイソシアネート化合物からイソシアネート基を除いた残基、ｎは正の整数を意味する。）を有する、分子鎖中に複数のオキサゾリドン環を含有するジグリシジルエーテル型エポキシ樹脂；（ｂ）１価の活性水素化合物；（ｃ）２価の活性水素化合物；（ｄ）没食子酸および（ｅ）第２級モノアミン化合物を反応させて得られる、数平均分子量１，０００〜５，０００の樹脂であることを特徴とする水性塗料組成物。
【選択図】なし
The present invention provides an aqueous coating composition that is most suitable for a method for forming a multilayer coating film that shortens and integrates both steps of a chemical conversion treatment liquid and a cationic electrodeposition coating composition.
An aqueous coating composition containing (A) a gallic acid / amine-modified diglycidyl ether type epoxy resin, (B) a curing agent and (C) a rare earth metal compound, the gallic acid / amine-modified diglycidyl The ether type epoxy resin (A) is represented by the formula (a):

(Wherein R represents a residue obtained by removing a glycidyloxy group of a diglycidyl epoxy compound, R ′ represents a residue obtained by removing an isocyanate group from a diisocyanate compound, and n represents a positive integer). A diglycidyl ether type epoxy resin containing a plurality of oxazolidone rings; (b) a monovalent active hydrogen compound; (c) a divalent active hydrogen compound; (d) gallic acid and (e) a secondary monoamine compound. A water-based coating composition, which is a resin having a number average molecular weight of 1,000 to 5,000 obtained by reaction.
[Selection figure] None

Description

  The present invention relates to an aqueous coating composition. In particular, the present invention relates to an aqueous coating composition capable of integrating a pretreatment (base treatment) step before electrodeposition coating applied to a metal material, particularly an untreated cold-rolled steel sheet, and an electrodeposition coating step.

  An automobile body is manufactured by forming a metal material such as a cold-rolled steel plate or a galvanized steel plate, coating the metal formed product as an object to be coated, and then performing assembly or the like. In general, such metal molded products are subjected to rust prevention treatment such as zinc phosphate chemical conversion treatment before electrodeposition coating in order to impart adhesion to the electrodeposition coating film.

  Electrodeposition coating using a cationic electrodeposition coating composition is excellent in corrosion resistance and throwing power, and can form a uniform coating film. Therefore, it is widely used mainly for automobile bodies and primer for parts.

  However, in the conventional cationic electrodeposition coating composition, although it is possible to develop sufficient corrosion resistance by electrodeposition coating for a material in which a pretreatment such as zinc phosphate is applied to the coating object, When the pretreatment (chemical conversion treatment) of the coating is insufficient, there is a problem that it is difficult to ensure corrosion resistance.

  JP-A-8-53637 (Patent Document 1) discloses a cathode electrodeposition coating composition obtained by dispersing a hydrophilic film-forming resin having a cationic group and a curing agent in an aqueous medium containing a neutralizing agent. Based on the solid content of the paint, 0.1 to 20% by weight of at least one phosphomolybdate selected from an aluminum salt, a calcium salt and a zinc salt, and 0.01 to 2. A cathode electrodeposition coating composition containing 0% by weight is described. Thereby, it is described that the corrosion resistance with respect to the surface untreated cold-rolled steel sheet can be improved.

  JP-A-8-53638 (Patent Document 2) discloses a cathode electrodeposition coating composition in which a hydrophilic film-forming resin having a cationic group and a curing agent are dispersed in an aqueous medium containing a neutralizing agent. , Based on the solid content of the paint, characterized in that it contains a total of 0.01 to 2.0% by weight of copper compound and cerium compound as metal, and the weight ratio of copper / cerium as metal is 1/20 to 20/1. A cathodic electrodeposition coating composition is described. Similarly, it is described that the corrosion resistance with respect to the untreated cold-rolled steel sheet can be improved.

  However, in any coating using the above electrodeposition coating composition, one-step electrodeposition coating is performed by one-step electrodeposition coating under the condition of an applied voltage of 100 to 450V. Under such electrolysis and electrodeposition conditions, film formation with cerium or cerium-copper is insufficient. For this reason, none of the improvement levels of the corrosion resistance according to these inventions has exhibited the base adhesion comparable to the conventional chemical conversion treatment with the conventional phosphate, and has not reached the level of the corrosion resistance after electrodeposition coating.

  At present, in the pretreatment process and the electrodeposition coating process, the chemical conversion treatment liquid and the cationic electrodeposition coating composition, which are separate solutions, respectively, are in the pH range where the components contained in each liquid are stably dissolved or dispersed. Is different. Therefore, it is not easy to combine these steps. Furthermore, in electrodeposition coating, even if a small amount of the chemical conversion treatment agent is mixed, the coating efficiency, anticorrosion performance, and finished appearance are adversely affected. For this reason, it is necessary to carefully wash the object to be coated after pre-treatment and before electrodeposition coating. For this reason, pretreatment and electrodeposition coating require longer coating process facilities.

  Japanese Patent Application Laid-Open No. 2000-63710 (Patent Document 3) discloses an aqueous coating composition suitable for electrodeposition coating, in which rare earth metal compounds include yttrium (Y), neodymium (Nd), praseodymium ( A compound selected from the group consisting of Pr) and samarium (Sm) is disclosed.

However, even if an aqueous coating composition containing these rare earth metal compounds is applied to the above-mentioned multilayer coating film forming method, it has equivalent performance as compared with the current two-step process consisting of pretreatment and electrodeposition coating. For the purpose of obtaining a multilayer coating film, it was not always sufficient.
JP-A-8-53637 JP-A-8-53638 JP 2000-63710 A

  In the present invention, in view of the above-mentioned present situation, both processes are epoch-making in contrast to the conventional pretreatment and cationic electrodeposition coating using separate chemical conversion treatment liquid and cationic electrodeposition coating composition. An object of the present invention is to provide an aqueous coating composition that is optimal for a method for forming a multilayer coating film that is shortened and integrated into

（式中、Ｒはジグリシジルエポキシ化合物のグリシジルオキシ基を除いた残基、Ｒ’はジイソシアネート化合物からイソシアネート基を除いた残基、ｎは正の整数を意味する。）を有する、分子鎖中に複数のオキサゾリドン環を含有するジグリシジルエーテル型エポキシ樹脂；（ｂ）１価の活性水素化合物；（ｃ）２価の活性水素化合物；（ｄ）没食子酸および（ｅ）第２級モノアミン化合物を反応させて得られる、数平均分子量１，０００〜５，０００の樹脂であることを特徴とする水性塗料組成物に関するものである。 The present invention provides an aqueous coating composition containing at least (A) a gallic acid / amine-modified diglycidyl ether type epoxy resin, (B) a curing agent and (C) a rare earth metal compound, Glycidyl ether type epoxy resin (A), formula (a)

(Wherein R represents a residue obtained by removing a glycidyloxy group of a diglycidyl epoxy compound, R ′ represents a residue obtained by removing an isocyanate group from a diisocyanate compound, and n represents a positive integer). A diglycidyl ether type epoxy resin containing a plurality of oxazolidone rings; (b) a monovalent active hydrogen compound; (c) a divalent active hydrogen compound; (d) gallic acid and (e) a secondary monoamine compound. The present invention relates to a water-based coating composition characterized by being a resin having a number average molecular weight of 1,000 to 5,000 obtained by reaction.

  Moreover, the said (B) hardening | curing agent is related with the water-based coating composition characterized by being block polyisocyanate.

The rare earth metal compound (C) is a compound containing at least one rare earth metal selected from the group consisting of cerium (Ce), yttrium (Y), neodymium (Nd), praseodymium (Pr), and ytterbium (Yb). The present invention relates to an aqueous coating composition.
Here, the rare earth metal compound (C) is preferably contained in an amount of 0.05 to 10% by weight in terms of the rare earth metal based on the solid content of the paint.

  The aqueous coating composition of the present invention further preferably contains a zinc compound (D), and the blending weight ratio of the rare earth metal compound (C): zinc compound (D) is 1:20 to 20: 1. It is preferable.

  In the present invention, a cathodic electrolysis process (pretreatment process) and an electrodeposition coating process are practically divided and continuously performed by energizing at least two levels of applied voltage using a kind of water-based paint composition. And an optimum water-based coating composition for efficient integration. As a result, the conventional pretreatment such as chemical conversion treatment and the coating process consisting of electrodeposition coating can be greatly shortened, and compared with the coating film obtained by the conventional chemical conversion treatment and electrodeposition process. As a result, it is possible to obtain a multilayer coating film having the same excellent coating film adhesion and corrosion resistance (excellent performance with respect to salt spray, salt water immersion, and wet / dry cycle corrosion test, etc.).

  According to the method of the present invention, it is possible to reduce the pretreatment process (especially the chemical conversion treatment process) that has been conventionally performed before electrodeposition coating, or to greatly shorten the process even if chemical conversion treatment is performed ( That is, the processing time and the washing time can be shortened, and the technical effect is great. In addition, in the electrodeposition coating process, a low voltage application process for pretreatment is added, but since the pretreatment and the coating process can be continued only by changing the applied voltage, the low voltage application process The addition hardly affects the electrodeposition coating process substantially.

（式中、Ｒはジグリシジルエポキシ化合物のグリシジルオキシ基を除いた残基、Ｒ’はジイソシアネート化合物からイソシアネート基を除いた残基、ｎは正の整数を意味する。）を有する、分子鎖中に複数のオキサゾリドン環を含有するジグリシジルエーテル型エポキシ樹脂；（ｂ）１価の活性水素化合物；（ｃ）２価の活性水素化合物；（ｄ）没食子酸および（ｅ）第２級モノアミン化合物を反応させて得られる、数平均分子量１，０００〜５，０００の樹脂であり、従来の没食子酸を変性しないカチオン性樹脂を含むバインダーと比較してより防食性が極めて高く、上記複層塗膜形成方法によって、高耐食性能を有する塗膜を得ることができることを見出した。 Hereinafter, the aqueous coating composition of the present invention will be described in detail.
Ingredient (A)
The gallic acid / amine-modified diglycidyl ether type epoxy resin (A) contained in the aqueous coating composition of the present invention has the formula (a):

(Wherein R represents a residue obtained by removing a glycidyloxy group of a diglycidyl epoxy compound, R ′ represents a residue obtained by removing an isocyanate group from a diisocyanate compound, and n represents a positive integer). A diglycidyl ether type epoxy resin containing a plurality of oxazolidone rings; (b) a monovalent active hydrogen compound; (c) a divalent active hydrogen compound; (d) gallic acid and (e) a secondary monoamine compound. It is a resin having a number average molecular weight of 1,000 to 5,000 obtained by the reaction, and has an extremely high anticorrosion property compared to a conventional binder containing a cationic resin that does not denature gallic acid, and the above multilayer coating film It has been found that a coating film having high corrosion resistance can be obtained by the forming method.

（式中、Ｒはジグリシジルエポキシ化合物のグリシジルオキシ基を除いた残基、Ｒ’はジイソシアネート化合物からイソシアネート基を除いた残基、ｎは正の整数を意味する。）を有する、分子鎖中に複数のオキサゾリドン環を含有するジグリシジルエーテル型エポキシ樹脂に、（ｂ）１価の活性水素化合物と（ｃ）２価の活性水素化合物を出発樹脂（ａ）のエポキシ基に対して１未満の当量比で反応させて反応中間体（Ｘ）を得た後、さらに（ｄ）没食子酸および（ｅ）第２級モノアミン化合物を（ａ）、（ｂ）および（ｃ）の反応生成物中に残っているエポキシ基を開環するように該反応生成物に反応させることにより得られるものである。 The gallic acid / amine-modified diglycidyl ether type epoxy resin (A) used in the aqueous coating composition of the present invention has the formula (a):

(Wherein R represents a residue obtained by removing a glycidyloxy group of a diglycidyl epoxy compound, R ′ represents a residue obtained by removing an isocyanate group from a diisocyanate compound, and n represents a positive integer). In a diglycidyl ether type epoxy resin containing a plurality of oxazolidone rings, (b) a monovalent active hydrogen compound and (c) a divalent active hydrogen compound are less than 1 with respect to the epoxy group of the starting resin (a). After reacting at an equivalent ratio to obtain reaction intermediate (X), (d) gallic acid and (e) secondary monoamine compound were further added to the reaction products of (a), (b) and (c). It is obtained by reacting the reaction product so that the remaining epoxy group is ring-opened.

  The (b) monovalent active hydrogen compound is a monocarboxylic acid compound, a monoalcohol compound, a monophenol compound, or a monothiol compound.

Furthermore, the (c) divalent active hydrogen compound is a diol compound, a dicarboxylic acid compound, a bifunctional polyester polyol or a bifunctional polyether polyol.
A method for producing the above (A) gallic acid / amine-modified diglycidyl ether type epoxy resin will be described below.

  The (A) gallic acid / amine-modified diglycidyl ether type epoxy resin used in the aqueous coating composition of the present invention is basically produced by blending and reacting the components (a) to (e) described below. It is what is done. However, the reaction between gallic acid (component (d)) and epoxy resin (specifically, diglycidyl ether type epoxy resin (a) containing a plurality of oxazolidone rings in the molecular chain) Control as described below is required.

Ingredient (a)
Component (a) is a diglycidyl ether type epoxy resin containing a plurality of oxazolidone rings in the molecular chain, and is an epoxy compound containing two epoxy groups in one molecule. The epoxy compound of component (a) is one of the constituent elements constituting the basic skeleton of the resin of the present invention, and affects the anticorrosion property of the aqueous paint coating film comprising the resin composition. Therefore, in the present invention, it is extremely important that the component (a) is a diglycidyl ether type epoxy resin containing a plurality of oxazolidone rings in the molecular chain in the range of a number average molecular weight of 300 to 2,000. As described in JP-A-5-306327, a diglycidyl ether type epoxy resin containing a plurality of oxazolidone rings in a molecular chain is excellent in thermal fluidity even though the glass transition temperature of the resin is high. Therefore, a coating film excellent in heat resistance and corrosion resistance can be obtained without impairing the smoothness of the coating film.

  The diglycidyl ether type epoxy resin (component (a)) containing a plurality of oxazolidone rings in the molecular chain includes a method (I) of reacting a polyepoxy compound and a blocked diisocyanate compound, and an unblocked diisocyanate compound. There is a method (II) of reacting directly with a polyepoxy compound. Either method (I) or (II) can be employed, but method (II) is preferred because method (II) tends to cause side reactions such as trimerization of diisocyanate.

  Specifically, the polyepoxy compound is a bisphenol A type or bisphenol F type epoxy resin. As the former commercial product, Epicoat 828 (Oilized Shell Epoxy Co., Ltd., Epoxy Equivalent 180-190), Epicoat 1001 (Same, Epoxy Equivalent 450-500), Epicoat 1010 (Same, Epoxy Equivalent 3,000-4,000) The latter commercially available product includes Epicoat 807 (same as above, epoxy equivalent 170).

  In addition to bisphenol-type epoxy resins, polyglycidyl ethers of polyhydric alcohols such as ethylene glycol, 1,4-butanediol, 1,6-hexanediol, trimethylolpropane, pentaerythritol, polyethylene glycol, and aliphatic and alicyclic groups Alternatively, polyglycidyl esters of aromatic polycarboxylic acids can also be used.

  Examples of the diisocyanate compound include aromatic diisocyanates such as 4,4′-diphenylmethane diisocyanate (MDI), tolylene diisocyanate (TDI), and xylylene diisocyanate (XDI), hexamethylene diisocyanate (HMDI), isophorone diisocyanate (IPDI), 4, Aliphatic and cycloaliphatic diisocyanates such as 4'-methylenebis (cyclohexyl isocyanate), trimethylhexamethylene diisocyanate may be used.

  In the method (II), these diisocyanate compounds are directly reacted with a polyepoxy compound, but in the preferred method (I), a blocked diisocyanate obtained by blocking these diisocyanate compounds with a blocking agent is used. For this reason, after diisocyanate is blocked with a blocking agent in advance, it may be mixed with the epoxy compound and allowed to react, or the blocking agent is dissolved in the epoxy compound, and the isocyanate is added to generate blocked diisocyanate in the presence of the epoxy compound. Thereafter, an oxazolidone ring-containing epoxy resin can be synthesized.

  The blocking agents that can be used are well known in the art and include aliphatic alcohols such as methanol, ethanol, isopropanol, n-butanol, 2-ethylhexanol, ethylene glycol monobutyl ether, cyclohexanol; phenol, nitrophenol, ethylphenol Phenols such as; oximes such as methyl ethyl ketoxime; and lactams such as ε-caprolactam.

  An oxazolidone ring-containing epoxy resin having a plurality of oxazolidone rings in the chain and having a terminal epoxy group is obtained by reaction of diepoxy compound n + 1 with respect to n moles of block diisocyanate. The reaction temperature is preferably 60 ° C to 200 ° C. As the reaction proceeds, the diisocyanate compound blocking agent is regenerated, which may be allowed to exist in the system as it is, or may be removed out of the system using a decanter or the like.

  In the method for synthesizing a 2-oxazolidinone compound by a reaction between an epoxy compound and a carbamate (urethane), the reaction can proceed smoothly by using a tertiary amine as a catalyst. This principle can be advantageously applied to the reaction between a blocked isocyanate compound and a polyepoxy compound. Tertiary amines that can be used for this purpose include N, N-dimethylbenzylamine, triethylamine, N, N-dimethylcyclohexylamine, N, N, N ′, N′-tetramethylethylenediamine, N-methylmorpholine, 1 , 8-diazabicyclo [5.4.0] undecene, 1,4-diazabicyclo [2.2.2] octane, pyridine, quinoline, imidazole and the like.

  In addition to tertiary amines, di-n-butyltin dilaurate, stannous chloride, tin octenoate, dibutyltin oxide, dioctyltin oxide, 1,3-diacetoxytetrabutyl distanoxane, 1,3-dichlorotetra A tin compound such as butyl distanoxane and dibutyl dibutoxy tin may be used in combination.

  When the molecular weight of the diglycidyl ether type epoxy resin containing a plurality of oxazolidone rings in the molecular chain of the component (a) is less than 300, the molecular weight of the aqueous coating resin of the present invention, which is the final product, becomes excessively low. Further, mechanical properties such as the strength of the coating film formed by curing from the binder resin may be lowered. Also, if the molecular weight exceeds 2,000, the molecular weight of the aqueous coating resin of the present invention becomes excessively high, and as a result, the skin (appearance) of the coating film formed by curing due to the high viscosity during the heat flow of the binder resin is poor. There is a risk of inviting.

Ingredient (b)
The monovalent active hydrogen compound of component (b) is a monocarboxylic acid compound, monoalcohol compound, monophenol compound or monothiol compound. These are constituent elements for introducing an alkyl group into the resin of the present invention mainly by addition reaction with part of the epoxy group remaining in the component (a).

  When the resin of the present invention is dispersed in an aqueous medium, it imparts hydrophobicity based on the corresponding alkyl group in the molecule of component (b) and is based on a tertiary amino group introduced by component (e) described below. It is effective for imparting appropriate emulsifying dispersibility to resin molecules by balancing with hydrophilicity.

  Accordingly, the monocarboxylic acid compound, monoalcohol compound, monophenol compound or monothiol compound as component (b) preferably has an alkyl group of an appropriate size. The size of the alkyl group is preferably about 4 to 18 carbon atoms.

  Examples of component (b) include monocarboxylic acids such as n-butanoic acid, n-hexanoic acid, 2-ethylhexanoic acid, n-octylic acid, 2-ethyl 3-methyl 5,5′-dimethylhexanoic acid, Vegetable fatty acids such as coconut oil, soybean oil or linseed oil; mono-alcohols: n-butanol, n-hexanol, 2-ethylhexanol, n-octyl alcohol, n-stearyl alcohol, n-dodecyl alcohol, ethylene glycol monohexyl Ether, ethylene glycol mono-2-ethylhexyl ether; monophenol, nonylphenol; monothiols include t-dodecyl mercaptan, n-dodecyl mercaptan, n-stearyl mercaptan, and the like.

Ingredient (c)
The divalent active hydrogen compound of component (c) is necessary for forming a linear polymer that becomes the basic skeleton of the resin of the present invention by linking reaction with the epoxy compound of component (a). It is a component. Specifically, it is a diol compound, a dicarboxylic acid compound, a bifunctional polyester polyol or a bifunctional polyether polyol.

  Examples of component (c) include, as diol compounds, alkane diols such as ethylene glycol, 1,2-propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol; Alicyclic diols such as 2-cyclohexanediol and 1,4-cyclohexanediol; 4,4′-dihydroxydiphenyl-2,2-propane (bisphenol A), 4,4′-dihydroxydiphenyl-2,2-methane ( Aromatic diols such as bisphenol F), bis (4-hydroxyphenyl) sulfone (bisphenol S) or 1,3-dihydroxybenzene (resorcin); dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, dodecanedioic acid, dimer Acid, C18-C20 long chain aliphatic dicarboxylic acid, terminal Aliphatic dicarboxylic acid such as carboxyl group-modified butadiene-acrylonitrile copolymer; bifunctional polyester obtained by esterification reaction of aromatic dicarboxylic acid polycarboxylic acid such as phthalic acid, isophthalic acid, terephthalic acid or the like with polyol and polyol Polyol, bifunctional polyester polyol (molecular weight 300 to 3,000) such as bifunctional polycaprolactone polyol obtained by polymerization reaction of caprolactone using polyol as an initiator; and polyoxyethylene glycol, polyoxypropylene glycol, polyoxytetramethylene Examples thereof include bifunctional polyether polyols (molecular weight: 300 to 3,000) such as glycol and random or block copolymers thereof.

Ingredient (e)
Component (e) is a secondary monoamine compound. This secondary monoamine compound mainly undergoes an addition reaction with part of the epoxy group present in component (a) to introduce a tertiary amino group into the resin of the present invention. A tertiary amino group forms a hydrophilic group by neutralizing with an organic or inorganic acid, for example, and is a constituent element necessary for dispersing a resin in water.

  In this case, the component (e) preferably contains at least one secondary amine (e1) having at least one primary hydroxyl group in one molecule. This is because when the aqueous resin of the present invention forms an aqueous coating film, for example, it becomes a resin component that undergoes a cross-linking reaction with a cross-linking agent typified by a blocked isocyanate that is separately present in the coating composition. Examples thereof include 2- (methylamino) ethanol, 2- (ethylamino) ethanol, 4- (methylamino) butanol, 4- (ethylamino) butanol, diethanolamine, dibutanolamine and the like.

  In addition, the component (e) may contain a dialkylamine (e2) having an alkyl group having 2 to 18 carbon atoms in one molecule. Examples thereof include diethylamine, dipropylamine, dibutylamine, diisobutylamine, di-sec-butylamine, methylbutylamine, N-ethyl-1,2-dimethylpropylamine, N-methylhexylamine, dihexylamine, di-n- Examples include octylamine, di-2-ethylhexylamine, N-methylhexylamine, N-methyllaurylamine, N-ethyl-iso-amylamine, distearylamine and the like.

  Other secondary monoamines include secondary amines (e3) containing a ketimine block primary amino group such as diphenylamine, dibenzylamine or aminoethylethanolamine / methylisobutylketimine, diethylenetriamine / methylisobutyldiketimine. Can be used according to.

In addition to these components (e), a predetermined amount of a tertiary amine acid salt such as triethylamine acid salt or N, N-dimethylethanolamine acid is reacted, and a quaternary ammonium base is added to the resin skeleton as required. May be partially introduced.
Furthermore, a primary amine may be partially introduced as a chain extender for adjusting the molecular weight of the synthetic resin.

Ingredient (d)
Component (d) is gallic acid (1,3,5-trihydroxybenzoic acid), and this polyhydric phenol carboxylic acid compound is formed when, for example, an electrodeposition paint is formed on the resin of the present invention. It is a very important component in remarkably improving the anticorrosion property of the paint coating film.

  Gallic acid penetrates into rust composed of iron hydroxide, iron oxide, etc. generated on the surface of the steel material to be coated, forms rust and chelate with polyphenol (pyrogallol) hydroxyl group, stabilizes rust and rust. It is a useful compound derived from the hydrolysis product of the natural product tannin, which is widely known for its anti-corrosion action that prevents red rust due to the reduction action of the hydroxyl group and converts it into stable black rust.

  The present invention provides a resin production method for maximizing the effect of this useful compound. When the aqueous coating resin of the present invention is to be produced, for example, in the component (a) When the bifunctional epoxy compound and the trifunctional or higher polyhydric phenol compound in component (d) are reacted as they are, it is actually difficult to control the reaction because there is a concern that the reaction system may be significantly increased in viscosity or gelled. .

At the same time, many of the polyphenolic hydroxyl groups having the anticorrosion function are lost by the reaction, and the expected anticorrosion function may not be sufficiently exhibited.
Therefore, in order to avoid this problem, the present invention provides a novel manufacturing means for solving the above-mentioned problems in the manufacturing method. Next, the method for producing the resin of the present invention will be specifically described.

In the case where the process components (a) to (e) are reacted as resin constituents, (b) a monovalent active hydrogen compound and (b) a diglycidyl ether type epoxy resin containing a plurality of oxazolidone rings in the molecular chain. c) A reaction intermediate (X) is obtained by reacting a divalent active hydrogen compound with an epoxy group of the starting resin (a) at an equivalent ratio of less than 1 and extending the molecular chain length appropriately. In the synthesis step of this reaction intermediate, (d) gallic acid is not blended for the reasons described above.

Next, when (e) the secondary monoamine compound is reacted so as to open the epoxy group remaining in the reaction intermediate (X), (d) gallic acid is reacted simultaneously.
At that time, the reaction selectivity between the carboxyl group of gallic acid and the epoxy group of the resin is improved in a basic atmosphere accompanying the addition of the amine compound, and the reaction between the phenolic hydroxyl group of gallic acid and the epoxy group in the resin is improved. It was estimated that the reaction was suppressed, but it was found that a significant increase in viscosity and gelation of the reaction system were avoided.
At that time, it is preferable that (d) gallic acid and (e) secondary monoamine are blended so as to be approximately equivalent to the epoxy group in the reaction intermediate (X), and an addition reaction is performed.

  In carrying out the series of resin synthesis reactions described above, the epoxy equivalent of the diglycidyl ether type epoxy resin containing (a) a plurality of oxazolidone rings in the molecular chain as a starting material should be selected from 150 to 1,000. Is preferred. This is because the preferable average molecular weight range of the component (a) is 300 to 2,000 as described above.

  Next, (b) a monovalent active hydrogen compound and (c) a divalent active hydrogen compound are reacted with an epoxy group of the starting resin (a) at an equivalent ratio of less than 1 to obtain a reaction intermediate (X). However, the residual epoxy equivalent is preferably designed to be 500 to 3,000. If the epoxy equivalent of the reaction intermediate (X) is less than 500, the finished viscosity of the synthetic resin is too low, or if the epoxy equivalent exceeds 3,000, the finished viscosity of the synthetic resin is too high. It is not preferable in the design of the composition.

  Further, when (d) gallic acid and (e) a secondary monoamine are reacted with the reaction intermediate (X), 0.02 to (d) gallic acid is added per equivalent of epoxy group in the reaction intermediate (X). It is preferable to carry out the reaction at a ratio of 0.5 equivalent, preferably 0.05 to 0.3 equivalent. When the reaction equivalent of gallic acid is less than 0.05, the amount of addition modification of gallic acid is insufficient, so that the intended anticorrosive effect by gallic acid is lost. On the other hand, if it exceeds 0.5 equivalents, the reaction equivalent of (e) secondary amine is excessively reduced to less than 0.5 equivalents, and the water dispersibility of the finished synthetic resin is insufficient. The preparation of the coating composition may be impossible.

  In the method for producing a resin for water-based paints according to the present invention, the reaction is controlled by simultaneously modifying gallic acid during the amine modification after the formation of the reaction intermediate, and a plurality of hydroxyl groups of gallic acid and the epoxy group of the resin. It has been found that it is possible to practically prevent a defective phenomenon such as a significant increase in viscosity or gelation of the reaction system due to the reaction. At the same time, many of the polyphenolic hydroxyl groups having the anticorrosion function do not disappear due to the reaction, so that the expected anticorrosion function is fully expressed.

  Gallic acid is blended in the aqueous coating resin in an amount of 0.1 to 5% by weight, preferably 0.4 to 4% by weight, based on the solid content of the resin. When the amount of gallic acid exceeds the above upper limit, the hydrophilicity becomes high and the anticorrosion property is not exhibited.

  As described above, the resin for water-based paints of the present invention has extremely high corrosion resistance and heat resistance due to chelation by gallic acid modification and reduction in an alkaline atmosphere in addition to the inclusion of the oxazolidone ring in the epoxy base resin. Can be granted.

Gallic acid / amine modified diglycidyl ether type epoxy resin (A)
The resin of the component (A) of the aqueous coating composition of the present invention is an aqueous coating resin, that is, a gallic acid / amine-modified diglycidyl ether type epoxy resin (A), and has a number average molecular weight of 1,000 to 5,000. It is preferable to prepare so that it may become 1,200-4,000, More preferably, it may become 1,500-3,000. When the number average molecular weight is less than 1,000, physical properties such as solvent resistance and corrosion resistance of the cured coating film may be inferior. On the other hand, when it exceeds 5,000, it is difficult to control the viscosity of the resin solution and it is difficult to synthesize it, and it may be difficult to handle in operation such as emulsification dispersion of the obtained resin. Furthermore, because of its high viscosity, the flowability during heating and curing is poor, and the appearance of the coating film may be significantly impaired.

  It is preferable that the water-based coating resin is molecularly designed so that a hydroxyl value (mg Kg converted resin solid content) is in the range of 50 to 250. When the hydroxyl value is less than 50, the coating film is poorly cured. On the other hand, when it exceeds 250, water resistance may be deteriorated as a result of excess hydroxyl groups remaining in the coating film after curing. The hydroxyl number is preferably 60 to 240, more preferably 80 to 220.

  Moreover, it is preferable that the water-based coating resin is molecularly designed so that the amine value (KOH conversion mg / g resin solid content) is in the range of 40 to 150. If the amine value is less than 40, the acid neutralization causes poor emulsification and dispersion in an aqueous medium. On the other hand, if it exceeds 150, water resistance may decrease as a result of excess amino groups remaining in the coating film after curing. is there. A more preferred amine value is 50 to 120. A more preferred amine value is 50-100.

Ingredient (B)
The curing agent (B) in the present invention may be of any type as long as the resin component can be cured at the time of heating. Among them, a block polyisocyanate suitable as a curing agent for an electrodeposition resin is used. Recommended.

  Examples of the polyisocyanate that is a raw material of the block polyisocyanate include aliphatic diisocyanates such as hexamethylene diisocyanate (including trimer), tetramethylene diisocyanate, and trimethylhexamethylene diisocyanate, isophorone diisocyanate, 4,4′- Examples thereof include alicyclic polyisocyanates such as methylene bis (cyclohexyl isocyanate), and aromatic diisocyanates such as 4,4′-diphenylmethane diisocyanate, tolylene diisocyanate, and xylylene diisocyanate. The blocked polyisocyanate can be obtained by blocking these with an appropriate sealant.

  Examples of the sealing agent include monovalent alkyl (or aromatic) alcohols such as n-butanol, n-hexyl alcohol, 2-ethylhexanol, lauryl alcohol, phenol carbinol, and methylphenyl carbinol, ethylene glycol Cellosolves such as monohexyl ether, ethylene glycol mono 2-ethylhexyl ether, phenols such as phenol, para-t-butylphenol, cresol, dimethyl ketoxime, methyl ethyl ketoxime, methyl isobutyl ketoxime, methyl amyl ketoxime, cyclohexanone oxime, etc. Oximes and lactams represented by ε-caprolactam and γ-butyrolactam are preferably used. In particular, sealants for oximes and lactams are suitable from the viewpoint of low-temperature curability because they dissociate at low temperatures.

  It is desirable that the block polyisocyanate be blocked beforehand by using a sealing agent alone or by using a plurality of types. The blocking rate is preferably set to 100% in order to ensure the storage stability of the paint unless there is a purpose of reacting with the resin composition in advance.

  The gallic acid / amine-modified diglycidyl ether type epoxy resin (A) has an amino group in the resin with an appropriate amount of inorganic acid such as hydrochloric acid, nitric acid, hypophosphorous acid, formic acid, acetic acid, lactic acid, sulfamic acid, It is prepared by neutralizing with an organic acid such as acetylglycine acid and emulsifying and dispersing in water as a cationized emulsion. When emulsifying and dispersing, usually, emulsion particles containing (B) a curing agent as a core and (A) a gallic acid / amine-modified diglycidyl ether type epoxy resin as a shell are formed.

  The average particle diameter of the emulsion particles is 0.01 to 0.5 μm, preferably 0.02 to 0.3 μm, and more preferably 0.05 to 0.2 μm. If the average particle size is less than 0.01 μm, the neutralizing agent necessary for water-dispersing the resin component becomes excessive, and the electrodeposition efficiency per a certain amount of electricity decreases. On the other hand, when the average particle diameter exceeds 0.5 μm, the dispersibility of the particles is lowered, and therefore the storage stability of the electrodeposition paint is lowered, which is not preferable.

Ingredient (C)
The rare earth metal compound (C) contained in the aqueous coating composition used in the present invention is selected from the group consisting of cerium (Ce), yttrium (Y), neodymium (Nd), praseodymium (Pr), and ytterbium (Yb). Preferably, the compound contains at least one rare earth metal. Among these, more preferred rare earth metals are ytterbium (Yb), neodymium (Nd), and praseodymium (Pr). When the rare earth metal compound containing these rare earth metals is contained in the aqueous coating composition, a pretreatment film having excellent base adhesion can be obtained.

As the rare earth metal compound (C), a water-soluble or water-dispersible compound can be used. Especially, when using the water soluble compound whose solubility with respect to water is 1 g / dm < ³ > or more, since a high corrosion-resistant effect is acquired by use of a small amount, it is preferable. By using this, it is possible to obtain a coating film having an excellent anticorrosion property equal to or higher than that of a lead compound.

  Preferred rare earth metal compounds (C) include, for example, cerium formate, yttrium formate, praseodymium formate, ytterbium formate, cerium acetate, yttrium acetate, praseodymium acetate, neodymium acetate, ytterbium acetate, cerium lactate, yttrium lactate, ytterbium lactate, neodymium lactate Organic acid salts such as praseodymium lactate and ytterbium oxalate; inorganic acid salts or inorganic compounds such as cerium nitrate, yttrium nitrate, neodymium nitrate, samarium nitrate, ytterbium nitrate, praseodymium nitrate, neodymium amidosulfate and ytterbium amidosulfate Can do. It is more preferable to use a rare earth metal nitrate as the rare earth metal compound (C).

  The aqueous coating composition used in the multilayer coating film forming method of the present invention may further contain a zinc compound (D) in addition to the rare earth metal compound (C). Further, by including the zinc compound (D), it is possible to form a rare-earth alkali-zinc composite compound having poor alkali solubility as an electrolytic reaction product in the pretreatment step. For this reason, higher adhesion of the multilayer coating film and rust prevention after electrodeposition coating can be expressed.

  Examples of the zinc compound (D) intended to be used in combination with the rare earth metal compound (C) include water-soluble salts represented by carboxylate salts such as zinc formate and zinc acetate, and inorganic acid salts such as zinc nitrate and zinc sulfate. It is done. Furthermore, a composite compound of zinc oxide and condensed zinc phosphate that generates zinc ions in the coating composition, (poly) zinc phosphate, zinc phosphomolybdate, and the like can also be used. These zinc compounds can generally be used as pigments (water-dispersible compounds).

As described above, both the rare earth metal compound (C) and the zinc compound (D) are preferably water-soluble or water-dispersible compounds.
When the zinc compound (D) is used in addition to the rare earth compound (C), it is preferable that the weight ratio of the rare earth metal: copper or zinc is 1:20 to 20: 1.

  When the ratio of the weight of the rare earth metal to the weight of zinc exceeds the above range, the effect of improving the adhesion and corrosion resistance due to the formation of the composite compound may be reduced. In addition, the said weight ratio calculates the metal amount contained in each of rare earth metal compound (C) and zinc compound (D), and shows the weight ratio of the metal amount of each component.

  In the aqueous coating composition used in the present invention, the amount of the rare earth metal compound (C) contained in the aqueous coating composition is 0.05 to 10% in total in terms of the rare earth metal with respect to the solid content of the coating. It is.

  When the aqueous coating composition further contains a zinc compound (D), these metals are preferably included in a total amount of 0.05 to 10% by weight in terms of the amount of metal with respect to the solid content of the coating. When the metal conversion amount is less than 0.05% by weight, corrosion resistance based on sufficient base rust prevention may not be obtained. On the other hand, when the metal equivalent exceeds 10% by weight, the dispersion stability of the aqueous coating composition component, the smoothness of the electrodeposition coating film, and the water resistance may be lowered. The metal equivalent amount of the rare earth metal (C), the metal equivalent amount of the rare earth metal compound (C) and the zinc compound (D) is more preferably 0.08 to 8% by weight, still more preferably 0.1 to 5% by weight. %.

  The introduction of the rare earth metal compound (C), the rare earth metal compound (C) and the zinc compound (D) into the aqueous coating composition is not particularly limited, and should be performed in the same manner as a normal pigment dispersion method. Can do. For example, a rare earth metal compound (C) and a zinc compound (D) as required can be dispersed in a dispersion resin in advance to prepare a dispersion paste, and this dispersion paste can be blended into an aqueous coating composition. Further, when a water-soluble rare earth metal compound or a water-soluble zinc compound is used as the rare earth metal compound (C) or the zinc compound (D), it may be added as it is after the preparation of the resin emulsion for paint. In addition, as a resin for pigment dispersion, a general one for cationic electrodeposition coating (epoxy sulfonium salt type resin, epoxy type quaternary ammonium salt type resin, epoxy type tertiary amine type resin, acrylic type quaternary ammonium salt) Type resin).

Other components The water-based coating composition used in the coating method of the present invention is not necessarily a necessary component, but a pigment may be further blended depending on the purpose. However, the pigment here does not include the rare earth metal compound (C) and the zinc compound (D). As the pigment, any pigment that is usually used in paints can be used without particular limitation. Examples include pigments such as carbon black, titanium dioxide and graphite, extender pigments such as kaolin, aluminum silicate (clay), talc, calcium carbonate, and inorganic colloids (silica sol, alumina sol, titanium sol, zirconia sol, etc.), phosphorus Examples include heavy metal-free rust preventive pigments such as acid pigments (aluminum phosphomolybdate, (poly) zinc phosphate, calcium phosphate, etc.) and molybdate pigments (aluminum phosphomolybdate, zinc phosphomolybdate, etc.).

  Furthermore, silane coupling agents such as vinyltriethoxysilane and γ-methacryloxypropyltrimethoxysilane can also be used. When these inorganic colloids and silane coupling agents are used in combination, there is an advantage that the effect of improving the adhesion of the base coating film and the effect of improving the corrosion resistance as a result.

Among these, titanium dioxide, carbon black, aluminum silicate (clay), silica, aluminum phosphomolybdate, and zinc polyphosphate are particularly important as pigments used in the aqueous coating composition of the present invention. In particular, titanium dioxide and carbon black are most suitable for electrodeposition paints because they are highly concealed as color pigments and are inexpensive.
In addition, although the said pigment can also be used independently, it is common to use multiple types according to the objective.

  The weight ratio {P / (P + V)} of the pigment to the total weight (P + V) of the pigment (P) and the resin solid content (V) contained in the aqueous coating composition (hereinafter referred to as PWC) is: It is preferably in the range of 5 to 30% by weight. However, it is defined that the pigment here does not include the rare earth metal compound (C) and the zinc compound (D).

When the weight ratio is less than 5% by weight, the barrier property against corrosion factors such as water and oxygen on the coating film is excessively lowered due to insufficient pigment, and weather resistance and corrosion resistance at a practical level may not be exhibited.
However, if such inconvenience does not occur, the pigment concentration may be set to zero as much as possible, and a clear or nearly clear aqueous coating composition may be prepared and used in the present invention.
Further, if the weight ratio exceeds 30% by weight, it is necessary to pay attention because excessive pigment causes an increase in viscosity at the time of curing, resulting in a decrease in flowability and a marked deterioration in the appearance of the coating film.

  The resin solid content (V) is an electrodeposition including a pigment dispersion resin in addition to the (A) gallic acid / amine-modified diglycidyl ether type epoxy resin, which is a main resin of an aqueous paint, and (B) a curing agent. The total solid content of all resin binders constituting the coating film is shown.

Aqueous paint composition The aqueous paint composition is adjusted so that the total solid content is in the range of 5 to 40 wt%, preferably 10 to 25 wt%. An aqueous medium (water alone or a mixture of water and a hydrophilic organic solvent) is used to adjust the total solid concentration.

  Further, the pH of the aqueous coating composition is preferably 5 to 7, and more preferably 5.5 to 6.5. If the pH is less than 5, electrodeposition coating efficiency and film appearance may be lowered. If it exceeds 7, the stability of the rare earth metal ions and the base resin emulsion in the coating composition tends to be lowered. When the pH is high, the pH can be lowered using an inorganic acid such as nitric acid or sulfuric acid, or an organic acid such as formic acid or acetic acid. When the pH is low, the pH can be increased using an organic base such as amine or an inorganic base such as ammonia or sodium hydroxide. The pH can be adjusted by using these inorganic acids, organic acids, inorganic bases and organic bases in amounts as required. The type of acid and base used is not particularly limited.

  The aqueous coating composition used in the present invention preferably has a coating conductivity of 1,500 to 4,000 μS / cm. When the paint conductivity is less than 1,500 μS / cm, the effect obtained by the pretreatment process becomes insufficient, and the throwing power of the pretreatment film or the electrodeposition film may be insufficient. On the other hand, if it exceeds 4,000 μS / cm, the appearance of the pretreatment film or electrodeposition coating film may be deteriorated, which is not preferable. In the present specification, the term “pretreatment film” means that an electrolysis product of a rare earth metal compound (C), an electrolysis product of a rare earth metal compound (C), and a zinc compound (D) are deposited on an object to be coated. The film obtained by this.

The paint conductivity of the aqueous paint composition can be measured using a commercially available conductivity meter. Examples of the conductivity meter include CM-305 manufactured by Toa Denpa Kogyo Co., Ltd.
Further, a small amount of additives may be introduced into the coating composition. Examples of additives include UV absorbers, antioxidants, surfactants, coating surface smoothers, curing catalysts (dibutyltin oxide, dioctyltin dilaurate, dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin diacetate, dibutyltin And organic tin compounds such as dibenzoate or dioctyltin dibenzoate).

Multilayer coating film forming method The object to be coated is immersed in the aqueous coating composition of the present invention, and coating is performed by the following multilayer coating film forming method.
With the multilayer coating film forming method,
In the aqueous coating composition, a pretreatment step in which a voltage of less than 50 V is applied with the article to be coated as a cathode, and in the aqueous coating composition, a voltage of 50 to 450 V is applied with the article to be coated as a cathode. An electrodeposition step.

  Examples of the object to be coated include untreated metal materials such as cold rolled steel sheet, high strength steel, high tensile steel, cast iron, zinc and galvanized steel, aluminum and aluminum alloy. Among these, a cold-rolled steel sheet is a material that can obtain a particularly excellent corrosion resistance effect by the method of the present invention.

  The object to be coated is immersed in the aqueous coating composition of the present invention prepared by the above method as a cathode. In the pretreatment step, by applying a voltage of less than 50 V and cathodic electrolysis is performed on the article to be coated, the electrolytic reaction product of the rare earth metal compound (C), the rare earth metal compound (C) and zinc are mainly used. It has been found that the electrolytic reaction product of compound (D) can be deposited very preferentially.

  When the applied voltage is 50 V or higher, the precipitation of (A) gallic acid / amine-modified diglycidyl ether type epoxy resin and (B) curing agent, which is a paint vehicle, rather than the precipitation of the above composite metal hydroxide becomes remarkable. Therefore, it is not preferable because it is contrary to the purpose of forming the pretreatment film.

  Enables selective deposition of an electrolysis reaction product of the rare earth metal compound (C), an electrolysis reaction product of the rare earth metal compound (C), or an electrolysis reaction product of the rare earth metal compound (C) and the zinc compound (D). The applied voltage in the pretreatment step is preferably 1 to 40V, and more preferably 1 to 20V.

  In the pretreatment step, the bath temperature of the bath containing the aqueous coating composition is preferably adjusted to 15 to 35 ° C. It is preferable to perform the pretreatment step at the same temperature as the bath temperature normally used in the electrodeposition coating performed after the pretreatment step because of the relationship with the electrodeposition coating step continuously performed after the pretreatment step. It is.

The energization time in the pretreatment is usually 10 to 300 seconds, preferably 30 to 180 seconds.
If the treatment time is too short, the film is not formed, or even if it is formed, the thickness is insufficient, and the corrosion resistance may be inferior. If the energization time is too long, an appearance defect called matte burn or burnt sometimes occurs. In addition, an excessive treatment time is not preferable because the productivity may be extremely reduced.

The precipitating amount of the rare earth metal compound (C), the rare earth metal compound (C) and (D) copper compound, or the electrolytic reaction product of the rare earth metal compound (C) and zinc compound (D) is set to 0.0. By setting it to 01 mg / m ² or more, a specifically high rust preventive film can be formed. A preferable precipitation amount is 0.1 to 100 mg / m ² .

If it is less than 5 mg / m ² , the underlying adhesion due to the formed film is lowered, so that the necessary rust preventive properties are not exhibited. On the other hand, if it exceeds 1,000 mg / m ² , the surface smoothness of the film is impaired, and the appearance after the electrodeposition coating film formation may be deteriorated.

The mechanism by which the electrolytic product is precipitated by the pretreatment process of the present invention is considered as follows. Depending on the electrolysis conditions in the pretreatment step, dissolved oxygen, hydrogen ions, water and other chemical species in the bath are reduced on the metal surface of the cathode, and hydroxide ions (OH ⁻ ) are generated. The hydroxide ions generated on the surface of the metal to be treated first react with the rare earth metal ions in the vicinity of the metal surface, whereby a precipitate of the rare earth metal hydroxide is generated and deposited as a film on the metal surface.

  A film made of the rare earth metal hydroxide, which is an electrolytic product thus deposited, is particularly excellent in adhesion to the base material and the electrodeposition coating film, and at least in the baking and drying process after electrodeposition coating. It is considered that a part of the film changes from a rare earth hydroxide to a film made of oxide dehydrated and exhibits high corrosion resistance.

  Further, by further including the zinc compound (D) in the aqueous coating composition, it is possible to deposit a rare-earth alkali-zinc complex compound as an electrolytic reaction product. The composite compound thus obtained can exhibit higher adhesion of the resulting multilayer coating and corrosion resistance after electrodeposition coating.

  Moreover, in the electrolysis conditions of the pretreatment step of the present invention, the pretreatment rust film is mainly formed preferentially, and (A) precipitation of gallic acid / amine-modified diglycidyl ether type epoxy resin and (B) curing agent Since the formation of the electrodeposition coating film due to is apt to be suppressed, it is very convenient.

  In the electrodeposition coating step of the present invention, the applied voltage is increased to 50 to 450 V, preferably 100 to 400 V, so that (A) a gallic acid / amine-modified diglycidyl ether type epoxy resin and (B) curing are applied. Agents and optionally pigments can be preferentially deposited. If the applied voltage is less than 50 V, the precipitation of the vehicle component of the electrodeposition paint may be insufficient. On the other hand, when the applied voltage exceeds 450 V, the above-mentioned vehicle component is deposited in excess of an appropriate amount, and as a result, a film appearance that cannot be put into practical use may be exhibited.

  The energization time is 30 to 300 seconds, preferably 30 to 180 seconds. When the treatment time is shorter than 30 seconds, the electrodeposition coating film is not generated, or even if it is generated, the thickness is insufficient, so that the corrosion resistance may be inferior. Further, excessive treatment time is not preferable because it may cause extremely low productivity.

  By subjecting the uncured multilayer coating film thus obtained to a curing reaction at 120 to 200 ° C., preferably 140 to 180 ° C., an electrodeposition cured coating film having a high degree of crosslinking can be obtained. However, if it exceeds 200 ° C., the coating film becomes excessively hard and brittle, while if it is less than 120 ° C., curing is not sufficient, and film physical properties such as solvent resistance and film strength may be lowered.

  Hereinafter, the present invention will be described in more detail with reference to production examples, examples and comparative examples. In each example, “part” represents “part by weight”, and “%” represents “% by weight”.

Production Example 1 (Gallic acid / oxazolidone ring-modified aminated epoxy resin)
Production of component (a) In a reaction vessel equipped with a stirrer, decanter, nitrogen inlet tube, thermometer and dropping funnel, 2400 parts of bisphenol A type epoxy resin having an epoxy equivalent of 188 (trade name DER-331J, manufactured by Dow Chemical Co., Ltd.) After 141 parts of methanol, 168 parts of methyl isobutyl ketone and 0.5 part of dibutyltin dilaurate were charged and stirred at 40 ° C. to dissolve uniformly, 2,4- / 2,6-tolylene diisocyanate (80/20 wt. When 320 parts of a specific mixture) were added dropwise over 30 minutes, heat was generated and the temperature rose to 70 ° C. To this was added 5 parts of N, N-dimethylbenzylamine, the temperature in the system was raised to 120 ° C., and the reaction was continued at 120 ° C. for 3 hours until the epoxy equivalent reached 232 while distilling off methanol. a) A diglycidyl ether type epoxy resin containing a plurality of oxazolidone rings in the molecular chain was obtained. Also from the measurement, such as infrared absorption spectrum, oxazolidone ring (absorption wave; 1750 cm ^-1) in the resin was confirmed to have.

Production of reaction intermediate (X) (reaction of components (a) with (b) and (c))
To the component (a), 644 parts of methyl isobutyl ketone, component (b): 413 parts of 2-ethylhexanoic acid, and component (c): 341 parts of bisphenol A are added, and the temperature in the system is kept at 120 ° C. The reaction was continued until the epoxy equivalent reached 840, and then the system was cooled to 90 ° C.

Production of waterborne resin (reaction of reaction intermediate (X) with components (d) and (e))
Subsequently, component (d): 144 parts of gallic acid, component (e1): 142 parts of N-methylethanolamine, component (e2): 157 parts of di (2-ethylhexyl) amine, and component (e3): diethylenetriamine diketimine (solid A mixture of 197 parts of a methyl isobutyl ketone solution (min. 73%) was added and reacted at 120 ° C. for 1 hour. Then, it diluted with 145 parts of methyl isobutyl ketone, and obtained the resin varnish for water-based paints of 80 weight% of solid content. The number average molecular weight of this resin was 1,800, the amine value was 56, and the hydroxyl value was 180.

Comparative Production Example 1 ( Production of conventional amine-modified epoxy resin)
Production of component (a) In a reaction vessel equipped with a stirrer, decanter, nitrogen inlet tube, thermometer and dropping funnel, bisphenol A type epoxy resin having an epoxy equivalent of 188 (trade name DER-331J, manufactured by Dow Chemical Co., Ltd.) 2,400 Of methanol, 141 parts of methanol, 168 parts of methyl isobutyl ketone, and 0.5 part of dibutyltin dilaurate, and stirred at 40 ° C. to dissolve uniformly, then 2,4- / 2,6-tolylene diisocyanate (80 / When 20 parts by weight of the mixture (20 weight ratio mixture) was added dropwise over 30 minutes, heat was generated and the temperature rose to 70 ° C. To this was added 5 parts of N, N-dimethylbenzylamine, the temperature in the system was raised to 120 ° C., and the reaction was continued at 120 ° C. for 3 hours until the epoxy equivalent reached 232 while distilling off methanol. a) A diglycidyl ether type epoxy resin containing a plurality of oxazolidone rings in the molecular chain was obtained. Also from the measurement, such as infrared absorption spectrum, oxazolidone ring (absorption wave; 1750 cm ^-1) in the resin was confirmed to have.

Production of reaction intermediate (Y) (reaction of components (a) with (b) and (c))
To the component (a), 644 parts of methyl isobutyl ketone, component (b): 413 parts of 2-ethylhexanoic acid, and component (c): 341 parts of bisphenol A are added, and the temperature in the system is kept at 120 ° C. The reaction was continued until the epoxy equivalent reached 840, and then the system was cooled to 90 ° C.

Manufacture of resin for water-based paint (reaction between reaction intermediate (Y) and component (e))
Next, component (e1): N-methylethanolamine 148 parts, component (e2): di (2-ethylhexyl) amine 386 parts, and component (e3): diethylenetriamine diketimine (methyl isobutyl ketone solution with a solid content of 73%) 205 Part of the mixture was added and reacted at 120 ° C. for 1 hour. Thereafter, the resultant was diluted with 223 parts of methyl isobutyl ketone to obtain a resin varnish for an aqueous paint having a solid content of 80% by weight. The number average molecular weight of this resin was 1,840, the amine value was 70, and the hydroxyl value was 160.

Production Example 2 ( Production of Block Polyisocyanate Curing Agent)
After adding 222 parts of isophorone diisocyanate to a reaction vessel equipped with a stirrer, nitrogen introducing pipe, cooling pipe and thermometer, diluting with 56 parts of methyl isobutyl ketone, adding 0.2 part of butyltin laurate and raising the temperature to 50 ° C 17 parts of methyl ethyl ketoxime was added such that the temperature of the contents did not exceed 70 ° C. Then, the infrared absorption spectrum was kept at 70 ° C. for 1 hour until the absorption of the isocyanate residue substantially disappeared, and then diluted with 43 parts of n-butanol to obtain the target block polyisocyanate having a solid content of 70%.

Production Example 3 (Production of Resin Emulsion with Water-Based Paint Resin of Production Example 1)
After adding 357 parts of the block polyisocyanate curing agent produced in Production Example 2 and 20 parts of acetic acid to 1,250 parts of the aqueous coating resin obtained in Production Example 1, the non-volatile content is reduced to 32% with ion-exchanged water. After dilution, the solution was concentrated to 36% non-volatile content under reduced pressure to obtain an aqueous emulsion (hereinafter referred to as E1) mainly composed of a cation-modified epoxy resin.

Comparative Production Example 2 (Production of Resin Emulsion with Aqueous Paint Resin of Comparative Production Example 1)
After adding 357 parts of the block polyisocyanate curing agent produced in Production Example 2 and 20 parts of acetic acid to 1,250 parts of the resin for water-based paint obtained in Comparative Production Example 1, the non-volatile content is 32% with ion-exchanged water. After dilution to a non-volatile content of 36% under reduced pressure, an aqueous emulsion mainly composed of a cation-modified epoxy resin (hereinafter referred to as E2) was obtained.

Examples and Comparative Examples (Preparation of aqueous coating composition)
A clear coating composition (all solid content concentrations of 20%) was prepared using the various cationic resin emulsions (E1 to E2) and deionized water obtained in Production Example 2 and Comparative Production Example 2. In each paint, an emulsion emulsion paste of dibutyltin oxide was added as a hardening accelerator so that the amount of tin was 1.5% of the solid content of the paint.

  The rare earth metal compound, or the rare earth metal compound and the zinc compound are water-soluble in acetate or nitrate, so they are added directly to the water-based coating composition, so that the addition amount (% by weight) as a metal shown in Tables 1 to 4 Each aqueous coating composition was prepared by adjusting. The combinations of the above various materials are shown in Tables 1 to 4 below.

(Preparation of multilayer coating and corrosion resistance test)
In the preparation of each aqueous coating composition in Examples and Comparative Examples, as shown in Tables 1 to 4, each rare earth metal compound was included in an amount of 0.5% by weight in terms of metal amount. Moreover, when using a zinc compound together (Examples 6-10, Comparative Examples 6-10), after converting a rare earth metal compound into a metal amount and changing to 0.3% by weight, the zinc compound is further converted into a metal amount. 0.2% by weight was included. The aqueous coating composition thus obtained was poured into a bathtub, and a surface-untreated cold-rolled steel sheet was immersed as a cathode. Next, in all of the examples and comparative examples, the applied voltage was boosted in two stages, so that the pretreatment process (applied voltage 5 V, energization time 60 seconds) and the electrodeposition coating process (applied voltage 180 V, energization time 150 seconds). ) Was carried out continuously. After coating so that the dry film thickness of the electrodeposition coating film in an electrodeposition coating process might be 20 micrometers, it hardened | cured in 170 * 20 minutes and evaluated the coating film. Tables 1 to 4 show the corrosion resistance test results of the multilayer coating films prepared from the aqueous coating compositions of Examples and Comparative Examples.

（注）各成分配合：表中の数値は金属量に換算した重量である。

(Note) Composition of each component: The values in the table are weights converted to metal amounts.

（注）各成分配合：表中の数値は金属量に換算した重量である。

(Note) Composition of each component: The numerical values in the table are weights converted to metal amounts.

（注）各成分配合：表中の数値は金属量に換算した重量である。

(Note) Composition of each component: The values in the table are weights converted to metal amounts.

（注）各成分配合：表中の数値は金属量に換算した重量である。

(Note) Composition of each component: The values in the table are weights converted to metal amounts.

The procedure of the evaluation test in the table is shown below.
Corrosion resistance test / salt spray test: A salt spray test in accordance with JIS Z 2371 was performed on a coated plate with a crosscut reaching the substrate with a knife. The following items were evaluated at a test time of 840 hours.
-Blister evaluation: It evaluated by the blister state (number) of the coating surface in the whole evaluation board single side | surface after a test.
◎; Very little ○; Less △; Somewhat more ×; Many ・ Peeling evaluation: The evaluation plate after the test was washed with water and dried, and then the tape was peeled off, and evaluated by the maximum peel width on one side from the cut part (mm). .
◎: Less than 2 mm ○: Less than 2-3 mm △: Less than 3-6 mm ×: 6 mm or more

Measurement of paint conductivity In an electrodeposition bath containing 200 ml of the aqueous paint composition obtained in Examples and Comparative Examples, the conductivity was measured at 25 ° C. using a conductivity meter (CM-305, manufactured by Toa Denpa Kogyo Co., Ltd.). It was measured.

  As is clear from Tables 1 to 4, the multilayer coating film obtained from the aqueous coating composition using the gallic acid / amine-modified epoxy resin of the present invention as a binder used a conventional amine-modified epoxy resin that was opposed to each other. Compared with the multilayer coating film obtained by an aqueous coating composition, it was confirmed that it has superior corrosion resistance.

The water-based paint composition of the present invention is practically divided into a cathodic electrolysis process (pretreatment process) and an electrodeposition coating process by energizing at least two stages of applied voltage using a kind of water-based paint composition. In addition, the multi-layer coating film forming method that can be carried out continuously and efficiently integrates the pretreatment process and the electrodeposition coating process, and has a coating film adhesion and corrosion resistance superior to conventional ones. A coating film can be obtained.

Claims (4)

(A) An aqueous coating composition containing a gallic acid / amine-modified diglycidyl ether type epoxy resin, (B) a curing agent and (C) a rare earth metal compound, the gallic acid / amine modified diglycidyl ether type epoxy resin (A) is the formula (a)

(Wherein R represents a residue obtained by removing a glycidyloxy group of a diglycidyl epoxy compound, R ′ represents a residue obtained by removing an isocyanate group from a diisocyanate compound, and n represents a positive integer). A diglycidyl ether type epoxy resin containing a plurality of oxazolidone rings; (b) a monovalent active hydrogen compound; (c) a divalent active hydrogen compound; (d) gallic acid and (e) a secondary monoamine compound. A water-based coating composition, which is a resin having a number average molecular weight of 1,000 to 5,000 obtained by reaction.   The rare earth metal compound (C) is a compound containing at least one rare earth metal selected from the group consisting of cerium (Ce), yttrium (Y), neodymium (Nd), praseodymium (Pr) and ytterbium (Yb). An aqueous paint composition.   An aqueous coating composition comprising 0.05 to 10% by weight of the rare earth metal compound (C) in terms of rare earth metal based on the solid content of the coating. The aqueous coating composition further comprising a zinc compound (D), wherein the blending weight ratio of the rare earth metal compound (C): zinc compound is 1:20 to 20: 1.