JP2007314690A - Water-based coating composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To control deposition ability of a resin deposited by electrodeposition in a method for attaining a pretreatment process and an electrodeposition process in the electrodeposition coating using the same electrodeposition bath by solely changing a voltage. <P>SOLUTION: The water-based coating composition comprises (A) a rare earth metal compound, (B) a base resin having amino group and (C) a curing agent. The base resin (B) has 50-120 total amine value (converted on KOH mg/1g resin solid component) included in the resin and 15-50 amine value based on primary amino group. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an aqueous coating composition. In particular, the present invention is a water-based coating composition that can perform 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 in one step. About.

  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 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, 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 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.

  The present inventors have already developed a water-based coating composition that can realize integration of 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. Has been proposed.

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. Even if this composition is applied to the method of Patent Document 3, compared with the current two-step process consisting of pretreatment and electrodeposition coating, for the purpose of obtaining a multilayer coating film having equivalent performance, Not always enough.
JP-A-8-53637 JP-A-8-53638 JP 2000-63710 A

  In view of the above-mentioned present situation, the present invention further provides a method for achieving the pretreatment step and the electrodeposition coating step in the electrodeposition coating proposed by the present inventors only by changing the voltage in the same electrodeposition coating bath. The purpose of this study is to control the precipitation of the resin deposited by electrodeposition.

The present inventors have found that the control of the depositability of the resin deposited by electrodeposition can be achieved by controlling the amine value of the resin.
That is, the present invention contains a rare earth metal compound (A), a base resin (B) having an amino group, and a curing agent (C), and the base resin (B) having an amino group is contained in the resin. Provided is an aqueous coating composition having an amine value of 50 to 120 (mg in terms of KOH / 1 g resin solid content) and an amine value based on a primary amino group of 15 to 50.

The rare earth metal compound (A) is a compound containing at least one rare earth metal selected from the group consisting of ytterbium (Yb), yttrium (Y), neodymium (Nd), and praseodymium (Pr). A water-based coating composition.
More preferably, the rare earth metal compound (A) is an aqueous coating composition characterized by being an ytterbium (Yb) compound.

Here, the rare earth metal compound (A) 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.
Furthermore, it is more preferable that a zinc (Zn) compound (D) is contained, and the blending weight ratio of the rare earth metal compound (A) and the zinc (Zn) compound (D) to the coating composition is 1:20 to It is preferably 20: 1.

  According to the present invention, by adjusting the amine value of the base resin (B) having an amino group (the amine value based on the total amine value and the primary amino group) within a predetermined range, the deposition property or electrodeposition of the base resin can be achieved. Therefore, the deposition of the electrolytic product by the rare earth metal compound occurs preferentially under a low voltage, and a deposited film of a rare earth metal having high corrosion resistance is formed under the low voltage. Thereafter, when the voltage is increased, precipitation of the base resin (B) having amino groups occurs, and as a result, an electrodeposition coating mainly composed of the resin is formed. As a result, the rare earth metal deposition coating and the resin deposition coating are formed. A multilayer coating film is formed, and an electrodeposition coating film with extremely high corrosion resistance is formed.

  When the aqueous coating composition of the present invention is used, the cathodic electrolytic treatment (pretreatment step) and the electrodeposition coating step are carried out practically and continuously by energizing at an applied voltage of at least two stages, and Provided is an aqueous coating composition that is optimal for carrying out a method for forming a multilayer coating film that is efficiently integrated. 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.).

Hereinafter, the aqueous coating composition of the present invention will be described in detail.
Ingredient (A)
The rare earth metal compound (A) contained in the aqueous coating composition of the present invention is an ytterbium (Yb) compound, yttrium (Y), neodymium (Nd) compound, or praseodymium (Pr) compound, and is another rare earth metal. It has been found that compared with cerium (Ce), the electrolytic deposition property in the pretreatment step is high, and a coating film with better corrosion resistance can be obtained by the above-mentioned multilayer coating film forming method.

  The ytterbium (Yb) compound has the highest electrolytic depositability among these rare earth metal compounds, and when it is contained in the aqueous coating composition, a pretreatment film having the best base adhesion can be obtained.

As the rare earth metal compound (A), 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.

  Preferred rare earth metal compounds (A) include, for example, ytterbium formate, yttrium formate, neodymium formate, praseodymium formate, ytterbium acetate, yttrium acetate, neodymium acetate, praseodymium acetate, ytterbium lactate, yttrium lactate, neodymium lactate, praseodymium lactate, and the like. Acid salts; inorganic acid salts or inorganic compounds such as ytterbium nitrate, yttrium nitrate, neodymium nitrate, praseodymium nitrate, ytterbium amidosulfate, yttrium amidosulfate, neodymium amidosulfate, praseodymium amidosulfate, and the like. Of these, ytterbium (Yb) compounds are more preferred.

  By using these, a chemical conversion film having an excellent anticorrosive property equivalent to or higher than that of the conventional “zinc phosphate film” can be obtained.

[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。]
で示されるオキサゾリドン環含有するエポキシ樹脂をカチオン変性エポキシ樹脂として用いてもよい。耐熱性及び耐食性に優れた塗膜が得られるからである。 Ingredient (B)
The base resin (B) having an amino group used in the aqueous coating composition of the present invention is a cation-modified epoxy resin obtained by modifying an oxirane ring in a resin skeleton with an organic amine compound. Generally, a cation-modified epoxy resin is produced by opening a ring of an oxirane ring in a starting material resin molecule by a reaction with an amine such as a primary amine, secondary amine, or tertiary amine acid salt. A typical example of the starting material resin is a polyphenol polyglycidyl ether type epoxy resin which is a reaction product of a polycyclic phenol compound such as bisphenol A, bisphenol F, bisphenol S, phenol novolak, cresol novolak, and epichlorohydrin. Examples of other starting material resins include the following formula described in JP-A-5-306327.

[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. ]
An epoxy resin containing an oxazolidone ring represented by formula (1) may be used as the cation-modified epoxy resin. This is because a coating film having excellent heat resistance and corrosion resistance can be obtained.

  The starting material resin can be used by extending the chain with a bifunctional polyester polyol, polyether polyol, bisphenol, dibasic carboxylic acid or the like before the oxirane ring-opening reaction with amines.

  Similarly, prior to the ring-opening reaction of the epoxy ring with amines, 2-ethylhexanol, nonylphenol, ethylene glycol mono-monomer for some epoxy rings for the purpose of adjusting the molecular weight or amine equivalent and improving heat flow. Monohydroxy compounds such as 2-ethylhexyl ether and propylene glycol mono-2-ethylhexyl ether can also be added and used.

  Examples of amines that can be used for opening an oxirane ring and introducing an amino group include primary, secondary, and tertiary amine salts as described above. A secondary monoamine compound is preferably used for controlling the addition reaction. This secondary monoamine compound mainly undergoes an addition reaction with a part of epoxy groups present in the resin 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, it is preferable that at least one secondary amine having at least one primary hydroxyl group in one molecule is contained. 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 of secondary amines having at least one primary hydroxyl group in one molecule include 2- (methylamino) ethanol, 2- (ethylamino) ethanol, 4- (methylamino) butanol, 4- (ethyl Amino) butanol, diethanolamine, dibutanolamine and the like.

  In addition, the secondary monoamine may contain a dialkylamine 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 diphenylamine, dibenzylamine or secondary amines containing ketimine-blocked primary amino groups such as aminoethylethanolamine / methylisobutylketimine, diethylenetriamine / methylisobutyldiketimine Can be used. In order to prepare an aqueous coating material from a synthetic resin after introduction into the resin, these can be easily hydrolyzed when dissolved or dispersed in an aqueous medium to produce the required amount of primary amino groups.
These amines must be reacted with at least an equivalent amount relative to the oxirane ring in order to open all the oxirane rings.

Further, as a method for imparting a cationic functional group to be introduced into the resin, a predetermined amount of a tertiary amine acid salt such as triethylamine acid salt or N, N-dimethylethanolamine acid salt is added separately from the addition reaction of these secondary monoamines. A part of the quaternary ammonium base may be introduced into the resin skeleton as required.
Furthermore, a primary amine may be partially introduced as a chain extender for adjusting the molecular weight of the synthetic resin.

  The cation-modified epoxy resin preferably has a number average molecular weight of 1,500 to 5,000, more preferably 1,600 to 3,000. When the number average molecular weight is less than 1,500, 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, and it may be difficult to handle in the 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.

  The cation-modified epoxy resin is preferably molecularly designed such that the hydroxyl value (mg / g resin solid content in terms of KOH) 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 cation-modified epoxy resin is preferably molecularly designed so that the total amine value (mg in terms of KOH / g resin solid content) is in the range of 50 to 120. The total amine value in this case means the total amount of amine values from primary to tertiary amine in the resin. If the amine value is less than 50, emulsification dispersion failure in the aqueous medium due to the acid neutralization is caused. On the other hand, if the amine value exceeds 120, water resistance decreases as a result of excess amino groups remaining in the coating film after curing. There is. The total amine value is preferably 60 to 100 (KOH equivalent mg / g resin solid content), more preferably 70 to 105 (KOH equivalent mg / g resin solid content).

  Furthermore, the cation-modified epoxy resin preferably has an amine value based on a primary amino group of 15 to 50 (mg / g resin solid content in terms of KOH). In the present invention, the amine value based on the primary amino group in the cation-modified epoxy resin is thus adjusted in the range of 15 to 50, and the electrodeposition property from the cation-modified epoxy resin in the electrodeposition coating process is controlled. Thus, it has been found that the electrolytic product can be deposited selectively from the rare earth metal compound in the pretreatment step. As a result, it was possible to form a multilayer coating film having the desired high corrosion resistance. When the amine value is out of the above range, the performance tends to decrease rapidly.

  The adjustment of the amine value based on the primary amino group in the synthetic resin can be easily achieved by adjusting the amount of the ketimine block primary amino group-containing secondary amine added to the resin.

  If the amine value based on the primary amino group is less than 15, the precipitation property becomes too high, and as a result, the precipitation of the resin may overlap with the precipitation of ytterbium (Yb) in the pretreatment step. As a result, the corrosion resistance of the multilayer coating film becomes insufficient. On the other hand, if it exceeds 50, the precipitation properties are excessively lowered, and as a result, electrodeposition coating efficiency (Coulomb efficiency) and throwing power are lowered, and at the same time, there is a risk of causing defects such as the occurrence of gas pin skin on the coating film.

  As described above, in the water-based coating composition of the present invention, the most ideal process is achieved by a combination of the rare earth metal compound having high precipitation during pretreatment electrolysis and the cation-modified epoxy resin whose precipitation is controlled by the resin amine value. Integration has been realized, and it has become possible to form a multilayer coating film having high corrosion resistance equivalent to or higher than the current process.

Ingredient (C)
The curing agent (C) in the present invention may be of any kind as long as each resin component can be cured at the time of heating, and among them, a block polyisocyanate suitable as a curing agent for an electrodeposition resin. Is 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 sealant 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 and ethylene glycol mono-2-ethylhexyl ether; polyether-type double-end diols such as polyethylene glycol, polypropylene glycol and polytetramethylene ether glycol phenol; ethylene glycol, propylene glycol, 1,4-butanediol and the like Polyester-type double-ended polyols obtained from diols of the above and dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, suberic acid, sebacic acid; para-t-butylphenol; Phenols such as resol; dimethyl ketoxime, methyl ethyl ketoxime, methyl isobutyl ketoxime, methyl amyl ketoxime, oximes such as cyclohexanone oxime, and ε- caprolactam, lactams typified by γ- butyrolactam is preferably used. In particular, the sealants of oximes and lactams dissociate at a low temperature, and therefore are suitable from the viewpoint of resin curability when co-baking with an intermediate coating film in a subsequent step.

  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 denaturing reaction with the resin components.

  The blending ratio of the block polyisocyanate to the base resin (B) having an amino group differs depending on the degree of crosslinking required for the purpose of use of the cured coating film, but the coating film properties and intermediate coating compatibility are different. Considering the solid content, the range of 15 to 40% by weight is preferable. If the blending ratio is less than 15% by weight, the coating film may be poorly cured. As a result, the physical properties of the coating film such as mechanical strength may be lowered, and the coating film may be damaged by paint thinner during intermediate coating. May invite. On the other hand, if it exceeds 40% by weight, it may be excessively cured, resulting in poor coating properties such as impact resistance. In addition, block polyisocyanate may be used in combination of two or more kinds for convenience of coating film physical properties, degree of curing and adjustment of curing temperature.

  The base resin (B) having an amino group is obtained by converting an amino group in the resin to an appropriate amount of an inorganic acid such as hydrochloric acid, nitric acid, hypophosphorous acid, or an organic acid such as formic acid, acetic acid, lactic acid, sulfamic acid, acetylglycine acid. It is prepared by neutralizing with an acid and emulsifying and dispersing in water as a cationized emulsion. Moreover, when emulsifying and dispersing, emulsion particles are usually formed containing the curing agent (C) as a core and (B) a base resin containing an amino group as a shell.

  The average particle diameter of the emulsion particles is 0.01 to 0.5 μm, preferably 0.02 to 0.3 μm, more preferably 0.05 to 0.2 μm. When 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 fixed amount of electricity is lowered. 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 (D)
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 (A). 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 (A) 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 (A) and the zinc compound (D) are preferably water-soluble or water-dispersible compounds.

(A) When the zinc compound (D) is used in addition to the rare earth compound, it is preferable that the weight ratio of rare earth metal: 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 (A) 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 (A) contained in the aqueous coating composition is a total of 0.05 to 10% by weight in terms of the rare earth metal based on 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. (A) The metal equivalent amount of the rare earth metal, the metal equivalent amount of the rare earth metal compound (A) 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 (A), the rare earth metal compound (A), or the rare earth metal compound (A) and the zinc compound (D) into the aqueous coating composition is not particularly limited. It can be performed in the same manner as the dispersion method. For example, a rare earth metal compound (A) 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. Moreover, when using a water-soluble rare earth metal compound and a water-soluble zinc compound as a rare earth metal compound (A) and a zinc compound (D), you may add as it is after preparing the resin emulsion for coating materials. 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).

In the aqueous coating composition used in the coating method of the present invention, such as a pigment, it 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 (A) 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 coatings because they have high concealability 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 (A), the (D) copper compound, and the (E) zinc compound.
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) constitutes an electrodeposition coating film containing a pigment dispersion resin in addition to the base resin (B) having the amino group, which is the main resin of the aqueous paint, and the curing agent (C). The total solid content of all resin binders 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 copper ions in the coating composition and the base resin emulsion 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 (A), an electrolysis product of a rare earth metal compound (A), 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. Then, in the pretreatment step, by applying a voltage of less than 50 V to perform cathodic electrolysis on the object to be coated, the electrolytic reaction product of the rare earth metal compound (A), the rare earth metal compound (A) 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 more, the precipitation of the base resin (B) and the curing agent (C) having an amino group, which is a paint vehicle, rather than the precipitation of the composite metal hydroxide becomes remarkable. This is not preferable because it is contrary to the purpose of film formation.

  As the applied voltage in the pretreatment step that enables the selective deposition of the electrolytic reaction product of the rare earth metal compound (A), the electrolytic reaction product of the rare earth metal compound (A) and the zinc compound (D), a preferable range is 1 to 1. 40V, and a more preferable range is 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.

By precipitating the precipitation amount of the rare earth metal compound (A) or the electrolytic reaction product of the rare earth metal compound (A) and the zinc compound (D) in the pretreatment to 5 mg / m ² or more, the rust prevention is specifically high. A film can be formed. A preferable precipitation amount is 10 to 1,000 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.

  In this case, rare earth metal ions that easily react with hydroxide ions are ytterbium (Yb) ion, yttrium (Y) ion, neodymium (Nd) ion, and praseodymium (Pr), which are more than cerium (Ce). It has a higher reactivity and tends to easily form a hydroxide of the corresponding metal. Among these, ytterbium (Yb) was found to have the highest reactivity.

  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 including the zinc compound (D) in the aqueous coating composition, it is possible to deposit a rare-earth alkali-zinc composite compound having poor alkali solubility 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.

  In addition, in the electrolysis conditions of the pretreatment step of the present invention, the pretreatment rust film is mainly formed preferentially, and the electrodeposition coating film is formed by precipitation of the base resin (B) having an amino group and the curing agent (C). The formation of is very advantageous because it tends to be suppressed.

  In the electrodeposition coating process of the present invention, the applied voltage is increased to 50 to 450 V, preferably 100 to 400 V, so that (B) a base resin having a cationic group and a curing agent (C), which is a paint vehicle, and The corresponding pigment 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 deteriorated. Moreover, excessive treatment time is not preferable because it may cause a significant decrease in 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.

  The following examples further illustrate the present invention, but the present invention is not limited thereto. In the examples, “parts” and “%” are based on weight unless otherwise specified.

Production Example 1 (Production of base resin having amino group)
In a reaction vessel equipped with a stirrer, decanter, nitrogen inlet tube, thermometer and dropping funnel, 2400 parts of bisphenol A type epoxy resin (trade name DER-331J, manufactured by Dow Chemical Company) with an epoxy equivalent of 188, 141 parts of methanol, methyl isobutyl 168 parts of ketone and 0.5 part of dibutyltin dilaurate were charged and stirred at 40 ° C. to uniformly dissolve, and then 320 parts of 2,4- / 2,6-tolylene diisocyanate (80/20 weight ratio mixture) was added. When dripped 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 diglycidyl ether type epoxy resin containing a plurality of oxazolidone rings in the 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.

  Further, 644 parts of methyl isobutyl ketone, 413 parts of 2-ethylhexanoic acid, and 341 parts of bisphenol A were added, the temperature in the system was kept at 120 ° C., and the reaction was continued until the epoxy equivalent reached 840. Cooled to ° C.

  Subsequently, a mixture of 148 parts of N-methylethanolamine, 386 parts of di (2-ethylhexyl) amine and 205 parts of diethylenetriamine diketimine (a methyl isobutyl ketone solution having a solid content of 73%) 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 total amine value was 70, the amine value was 15 based on the primary amino group, and the hydroxyl value was 160.

Production Example 2 (Production of base resin having amino group)
In a reaction vessel equipped with a stirrer, decanter, nitrogen inlet tube, thermometer and dropping funnel, 2400 parts of bisphenol A type epoxy resin (trade name DER-331J, manufactured by Dow Chemical Company) with an epoxy equivalent of 188, 141 parts of methanol, methyl isobutyl 168 parts of ketone and 0.5 part of dibutyltin dilaurate were charged and stirred at 40 ° C. to uniformly dissolve, and then 320 parts of 2,4- / 2,6-tolylene diisocyanate (80/20 weight ratio mixture) was added. When dripped 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 diglycidyl ether type epoxy resin containing a plurality of oxazolidone rings in the 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.

  Further, 644 parts of methyl isobutyl ketone, 413 parts of 2-ethylhexanoic acid, and 341 parts of bisphenol A were added, the temperature in the system was kept at 120 ° C., and the reaction was continued until the epoxy equivalent reached 840. Cooled to ° C.

  Subsequently, a mixture of 148 parts of N-methylethanolamine, 234 parts of di (2-ethylhexyl) amine and 430 parts of diethylenetriamine diketimine (methyl isobutyl ketone solution having a solid content of 73%) was added and reacted at 120 ° C. for 1 hour. Thereafter, the resultant was diluted with 283 parts of methyl isobutyl ketone to obtain a resin varnish for water-based paint having a solid content of 80% by weight. The number average molecular weight of this resin was 1,860, the total amine value was 88, the amine value was 32 based on the primary amino group, and the hydroxyl value was 161.

Production Example 3 (Production of base resin having amino group)
In a reaction vessel equipped with a stirrer, decanter, nitrogen inlet tube, thermometer and dropping funnel, 2400 parts of bisphenol A type epoxy resin (trade name DER-331J, manufactured by Dow Chemical Company) with an epoxy equivalent of 188, 141 parts of methanol, methyl isobutyl 168 parts of ketone and 0.5 part of dibutyltin dilaurate were charged and stirred at 40 ° C. to uniformly dissolve, and then 320 parts of 2,4- / 2,6-tolylene diisocyanate (80/20 weight ratio mixture) was added. When dripped 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 diglycidyl ether type epoxy resin containing a plurality of oxazolidone rings in the 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.

Further, 644 parts of methyl isobutyl ketone, 413 parts of 2-ethylhexanoic acid, and 341 parts of bisphenol A were added, the temperature in the system was kept at 120 ° C., and the reaction was continued until the epoxy equivalent reached 840. Cooled to ° C.
Subsequently, a mixture of 148 parts of N-methylethanolamine, 39 parts of di (2-ethylhexyl) amine and 664 parts of diethylenetriamine diketimine (a methyl isobutyl ketone solution having a solid content of 73%) was added and reacted at 120 ° C. for 1 hour. Thereafter, it was diluted with 214 parts of methyl isobutyl ketone to obtain a resin varnish for aqueous paint having a solid content of 80% by weight. The number average molecular weight of this resin was 1,880, the total amine value was 104, the amine value was 50 based on the primary amino group, and the hydroxyl value was 162.

Comparative Production Example 1 (Production of base resin having amino group)
In a flask equipped with a stirrer, cooler, nitrogen injection tube, thermometer and dropping funnel, 92 g of 2,4- / 2,6-tolylene diisocyanate (weight ratio = 8/2), 95 g of methyl isobutyl ketone and dibutyltin dilaurate 0.5 g was added, and 21 g of methanol was further added dropwise with stirring. The reaction started from room temperature and was heated to 60 ° C. due to heat generation. Then, after continuing reaction for 30 minutes, 57 g of ethylene glycol mono-2-ethylhexyl ether was dripped from the dropping funnel, and also 42 g of bisphenol A-propylene oxide 5 mol adducts were added. The reaction was carried out mainly in the range of 60 ° C. to 65 ° C. and continued until the isocyanate group disappeared while measuring the IR spectrum. Next, 365 g of an epoxy resin having an epoxy equivalent of 188 synthesized from bisphenol A and epichlorohydrin was added, and the temperature was raised to 125 ° C. Thereafter, 1.0 g of benzyldimethylamine was added and reacted at 130 ° C. until the epoxy equivalent was 410. Subsequently, when 87 g of bisphenol A was added to the reaction vessel and reacted at 120 ° C., the epoxy equivalent was 1190. Thereafter, the reaction mixture was cooled, 11 g of diethanolamine, 24 g of N-methylethanolamine, and 25 g of a ketimine product of aminoethylethanolamine (79% by weight methyl isobutyl ketone solution) were added and reacted at 110 ° C. for 2 hours. Then, it diluted with methyl isobutyl ketone until it became 80 weight% of non volatile matters, and the base resin containing an oxazolidone ring was obtained. The number average molecular weight of this resin was 1750, total amine value 56, amine value 10 based on primary amino groups, and hydroxyl value 160.

Comparative Production Example 2 (Production of base resin having amino group)
In a reaction vessel equipped with a stirrer, decanter, nitrogen inlet tube, thermometer and dropping funnel, 2400 parts of bisphenol A type epoxy resin (trade name DER-331J, manufactured by Dow Chemical Company) with an epoxy equivalent of 188, 141 parts of methanol, methyl isobutyl 168 parts of ketone and 0.5 part of dibutyltin dilaurate were charged and stirred at 40 ° C. to uniformly dissolve, and then 320 parts of 2,4- / 2,6-tolylene diisocyanate (80/20 weight ratio mixture) was added. When dripped 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 diglycidyl ether type epoxy resin containing a plurality of oxazolidone rings in the 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.

Further, 634 parts of methyl isobutyl ketone, 413 parts of 2-ethylhexanoic acid, and 341 parts of bisphenol A were added, the temperature in the system was kept at 120 ° C., and the reaction was continued until the epoxy equivalent reached 840. Cooled to ° C.
Next, a mixture of 148 parts of N-methylethanolamine and 729 parts of diethylenetriamine diketimine (a methyl isobutyl ketone solution having a solid content of 73%) was added and allowed to react at 120 ° C. for 1 hour to obtain an aqueous coating resin having a solid content of 80% by weight. A varnish was obtained. The number average molecular weight of this resin was 1,890, the total amine value was 109, the amine value was 55 based on the primary amino group, and the hydroxyl value was 164.

Comparative Production Example 3 (Production of a base resin having an amino group)
In a reaction vessel equipped with a stirrer, decanter, nitrogen inlet tube, thermometer and dropping funnel, 2400 parts of bisphenol A type epoxy resin (trade name DER-331J, manufactured by Dow Chemical Company) with an epoxy equivalent of 188, 141 parts of methanol, methyl isobutyl 168 parts of ketone and 0.5 part of dibutyltin dilaurate were charged and stirred at 40 ° C. to uniformly dissolve, and then 320 parts of 2,4- / 2,6-tolylene diisocyanate (80/20 weight ratio mixture) was added. When dripped 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 diglycidyl ether type epoxy resin containing a plurality of oxazolidone rings in the 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.

  Further, 522 parts of methyl isobutyl ketone, 300 parts of 2-ethylhexanoic acid, and 230 parts of bisphenol A were added, the temperature in the system was kept at 120 ° C., and the reaction was continued until the epoxy equivalent reached 500. Cooled to ° C.

  Subsequently, a mixture of 148 parts of N-methylethanolamine, 622 parts of di (2-ethylhexyl) amine, and 700 parts of diethylenetriamine diketimine (a methyl isobutyl ketone solution having a solid content of 73%) was added and reacted at 120 ° C. for 1 hour. Then, it diluted with 252 parts of methyl isobutyl ketone, and obtained the resin varnish for water-based paints of solid content 80weight%. The number average molecular weight of this resin was 1,900, the total amine value was 130, the amine value was 48 based on primary amino groups, and the hydroxyl value was 152.

Production Example 4 (Production of blocked 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 Examples 5 to 7 (Production of Resin Emulsion with Resin for Water-Based Paint of Production Examples 1 to 3)
After adding 357 parts of the block polyisocyanate curing agent produced in Production Example 4 and 20 parts of acetic acid to 1,250 parts of each aqueous coating resin obtained in Production Examples 1, 2, and 3, ion-exchanged water After dilution to a non-volatile content of 32%, the solution was concentrated to a non-volatile content of 36% under reduced pressure to obtain aqueous emulsions (hereinafter referred to as E1, E2, and E3) mainly composed of a cation-modified epoxy resin.

Comparative Production Examples 4 to 6 (Production of Resin Emulsion with Resin for Water-Based Paints of Comparative Production Examples 1 to 3)
After adding 357 parts of the block polyisocyanate curing agent produced in Production Example 4 and 20 parts of acetic acid to 1,250 parts of each aqueous coating resin obtained in Comparative Production Examples 1, 2 and 3, ion-exchanged water Was diluted to a non-volatile content of 32%, and then concentrated under reduced pressure to a non-volatile content of 36% to obtain an aqueous emulsion mainly composed of a cation-modified epoxy resin (hereinafter referred to as E4, E5 and E6).
To make the resin varnish for water-based paints E1 to E6 easy to understand, the results are summarized in Table 1 as follows.

Examples and Comparative Examples (Preparation of aqueous coating composition)
Clear coating compositions (solid content concentration of all 20%) were prepared using various cationic resin emulsions (E1 to E6) and deionized water obtained in Production Examples 5 to 7 and Comparative Production Examples 4 to 6. 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.

  Since rare earth metal compounds, or rare earth metal compounds and zinc compounds, are water-soluble acetates or nitrates, they are directly added to the aqueous coating composition and adjusted to the addition amount (% by weight) as a metal shown in Table 1. Each water-based coating composition was prepared. The combinations of the above various materials are shown in Tables 2 to 5 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 2 to 5, 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 7-10, Comparative Examples 7-10), after converting a rare earth metal compound into a metal amount and changing to 0.3 wt%, 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 2 to 5 show the corrosion resistance test results of the multilayer coating films prepared from the respective 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 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 numerical values in the table are weights converted to metal amounts.

It shows below about the procedure of the evaluation test of Tables 2-5.
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 960 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 the 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.

  It comprises at least a rare earth metal compound (A), a base resin (B) having an amino group, and a curing agent (C). The base resin (B) having the amino group has a total amine value of 50 to 120 contained in the resin. A water-based coating composition having an amine value based on a primary amino group of 15 to 50 (mg in terms of KOH / 1 g of resin solid content).

  As is apparent from Tables 2 to 5, the total amine value of the present invention is 50 to 120 (mg in terms of KOH / 1 g resin solid content), and the amine value based on the primary amino group is 15 to 50. A multilayer coating film obtained from an aqueous coating composition using an amino group-containing base resin as a binder is obtained from an aqueous coating composition using an amine-modified epoxy resin whose amine value is not within the above-mentioned appropriate range. It was confirmed that it has excellent corrosion resistance compared to the multilayer coating film.

  Moreover, it was confirmed that the combination of the ytterbium (Yb) compound and the zinc (Zn) compound has the best corrosion resistance in the type of rare earth metal compound (Example 7).

The aqueous coating 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 the same aqueous coating 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 (6)

  The base resin (B) containing a rare earth metal compound (A), an amino group-containing base resin (B) and a curing agent (C) has a total amine value of 50 to 120 contained in the resin. A water-based coating composition having an amine value based on a primary amino group of 15 to 50 (mg in terms of KOH / 1 g of resin solid content).   2. The rare earth metal compound (A) is a compound containing at least one rare earth metal selected from the group consisting of ytterbium (Yb), yttrium (Y), neodymium (Nd), and praseodymium (Pr). Water-based paint composition.   The aqueous coating composition according to claim 1, wherein the rare earth metal compound (A) is an ytterbium (Yb) compound.   The aqueous coating composition according to claim 1, wherein the rare earth metal compound (A) is 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 coating.   Furthermore, the aqueous coating composition in any one of Claims 1-4 containing a zinc (Zn) compound (D). The water-based coating composition according to claim 5, wherein a blending weight ratio (A / D) of the rare earth metal compound (A) and the zinc (Zn) compound (D) is 1:20 to 20: 1.