JP2009013236A - Electrodeposition-coating composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrodeposition-coating composition capable of satisfying both excellent coated film smoothness and good corrosion resistance at its edge part. <P>SOLUTION: This composition is formed by mixing 2 kinds of cationic resin emulsions so as to have the lowest melt viscosities in the curing of their coated membranes, obtained by the logarithmic decrement measurement of the coated membranes by using a pendulum type viscoelasticity measuring instrument and the measuring temperatures in the lowest melt viscosity measurements, within prescribe ranges. The cationic resin emulsion A has ≤0.1 lowest melt viscosity in the curing of its coated membrane, and also the measuring temperature in the measurement of the lowest melt viscosity measurement is ≥160°C. The cationic resin emulsion B has ≥0.3 lowest melt viscosity in the curing of its coated membrane, and also the measuring temperature in the measurement of the lowest melt viscosity is ≤155°C. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a cationic electrodeposition coating composition that is widely applied to general steel sheets and has both excellent coating film smoothness and edge corrosion resistance.

  Cationic electrodeposition coating is generally used for the purpose of rust prevention of steel sheets, but in the case of an automobile outer plate where the electrodeposition coating is used as a lower layer coating and overcoating is applied to the lower coating, Good smoothness and high gloss are required for the appearance of the coating film. Since the smoothness of the final coating film is strongly influenced by the smoothness of the lower layer coating film, the smoothness of the electrodeposition coating film is required.

  In order to improve the smoothness of the electrodeposited coating film, the conventional electrodeposition coating has a technique of improving the flowability during baking (lowering the coating film melt viscosity during baking). There is a pendulum viscoelasticity measurement method as a viscosity measurement method at the time of baking a coating film. A conventional electrodeposition paint having good smoothness has a minimum melt viscosity of 0 obtained from logarithmic decay rate measurement by a pendulum viscoelasticity measurement method. .15 or less, and the temperature at that time is 160 ° C. or more.

  However, in such a conventional electrodeposition paint, surface tension acts on the edge of the steel sheet during baking and melting, and the edge portion is exposed, resulting in deterioration of the corrosion resistance of the edge portion.

  In electrodeposition coatings, in order to improve the edge corrosion resistance, it is generally known that increasing the viscosity at the time of melting improves the edge coverage and improves the corrosion resistance. No solution has been reached. For example, in the invention described in Patent Document 1, the corrosion resistance of the edge portion is improved by the type and amount of the pigment, but the method using the pigment has a large specific gravity of the pigment, so that the coating portion such as the horizontal portion and the vertical portion of the coated object is applied. The pigment concentration of the coating film differs depending on the type, and there is a problem that it is difficult to obtain stable edge corrosion resistance. In addition, the appearance quality of the horizontal portion is degraded. In the invention described in Patent Document 2, low-temperature curability is used to increase the melt viscosity and improve the corrosion resistance of the edge portion.

  In the case of an electrodeposition coating, the stability of the paint bath liquid is important because it is always managed by a method of replenishing the amount of paint used and consumed for painting, and the low-temperature curing component inevitably suffers from long-term stability. For this reason, it is difficult to obtain stable edge corrosion resistance and appearance quality.

  In the inventions described in Patent Documents 3 to 5, the melt viscosity of the electrodeposition paint is increased by using internally crosslinked fine resin particles. Many inventions that improve edge corrosion resistance using this technique have been devised, but the electrical characteristics (charged particle characteristics) of such crosslinked microparticles and other resin particles contained in the electrodeposition paint are different, Further, in order to obtain sufficient edge corrosion resistance, the ratio of the crosslinked microparticles increases, which often causes problems in appearance quality. In the inventions described in Patent Documents 6 and 7, the edge corrosion resistance is improved by a coating method, and the edge corrosion resistance is improved by performing electrodeposition coating twice. In the case of such a method, the coating process is complicated and the practicality is poor.

JP 63-62897 A JP 63-39972 A JP-A-63-63761 Japanese Patent Laid-Open No. 2-303831 Japanese Patent Laid-Open No. 2-305995 JP 2000-239576 A Japanese Patent Laid-Open No. 1-8291

  An object of the present invention is to provide an electrodeposition coating composition capable of achieving both excellent coating film smoothness and edge portion corrosion resistance.

In the present invention, the minimum melt viscosity at the time of curing the coating film determined from the logarithmic decay rate measurement of the coating film using a pendulum viscoelasticity measuring instrument is 0.1 or less, and the measurement temperature at the time of measuring the minimum melt viscosity is 160. A cationic resin emulsion A having a temperature of not lower than ° C.,
The minimum melt viscosity at the time of curing the coating film determined from the logarithmic decay rate measurement of the coating film using a pendulum type viscoelasticity measuring device is 0.3 or more, and the measurement temperature at the time of measuring the minimum melt viscosity is 155 ° C. or less. It is an electrodeposition coating composition characterized by containing cationic resin emulsion B.

  Further, the present invention is characterized in that the temperature at the time of measuring the minimum melt viscosity of the cationic resin emulsion A is 165 ° C. or more and the temperature at the time of measuring the minimum melt viscosity of the resin emulsion B is 150 ° C. or less. And

  Further, the present invention is characterized in that the ratio of the content of the cationic resin emulsion A and the cationic resin emulsion B is 95/5 to 50/50 in terms of solid content weight ratio A / B.

  Further, the present invention is characterized in that the ratio of the content of the cationic resin emulsion A and the cationic resin emulsion B is 95/5 to 70/30 in terms of solid content weight ratio A / B.

  According to the present invention, by using the cationic resin emulsion A and the cationic resin emulsion B such that the minimum melt viscosity during coating film curing and the measurement temperature during minimum melt viscosity measurement are within a predetermined range, Excellent film smoothness and edge corrosion resistance can be achieved without impairing coating film characteristics such as required performance, water resistance, chemical resistance, substrate adhesion, top coatability, and coating workability.

  Further, according to the present invention, the ratio of the content of the cationic resin emulsion A and the cationic resin emulsion B is preferably a solid content weight ratio A / B of 95/5 to 50/50, preferably 95/5 to 70/30 is more preferable.

  By setting the solid content weight ratio in the above range, the coating film smoothness and the edge corrosion resistance can be further improved.

The electrodeposition coating composition of the present invention comprises two types of cationic resin emulsions.
On the other hand, the cationic resin emulsion A has a minimum melt viscosity of 0.1 or less at the time of curing the coating film determined from logarithmic decay rate measurement of the coating film using a pendulum viscoelasticity measuring device, and the minimum melt viscosity measurement. The measured temperature at that time is 160 ° C or higher.

  The other cationic resin emulsion B has a minimum melt viscosity of 0.3 or more at the time of coating film curing determined from logarithmic decay rate measurement of the coating film using a pendulum viscoelasticity measuring device, and the minimum melt viscosity. The measurement temperature at the time of measurement is 155 ° C. or lower.

  By including these two types of cationic resin emulsions, various required performance, water resistance, chemical resistance, substrate adhesion, top coatability, coating workability, etc. that are usually required for electrodeposition coating compositions. Excellent film smoothness and edge portion corrosion resistance can be achieved at the same time without impairing the resistance.

Hereinafter, the electrodeposition coating composition of the present invention will be described in detail.
The cationic resin emulsion A contained in the electrodeposition coating composition of the present invention can be obtained by dispersing a base resin having a cationic group and a curing agent for curing the base resin in water.

  As the base resin, it is preferable to use a cationic epoxy resin in which an active hydrogen compound such as an amine is reacted with the epoxy ring of the epoxy resin, the epoxy group is opened, and a cationic group is introduced.

  As the curing agent, it is preferable to use a blocked polyisocyanate obtained by blocking the isocyanate group of the polyisocyanate.

  As a cationic epoxy resin which is a base resin of the cationic resin emulsion A, a cationic property imparted with flexibility by reacting a bisphenol type epoxy resin with a flexible modifier such as polyester polyol or polyether polyol. Examples thereof include a cationic epoxy resin imparted with flexibility by reacting an epoxy resin or a bisphenol type epoxy resin with a flexible epoxy, for example, an epoxy group-containing polyol.

  As the bisphenol type epoxy resin, Epicoat 828 (manufactured by Japan Epoxy Resin Co., Ltd., epoxy equivalent 184 to 194), Epicoat 1001 (manufactured by Japan Epoxy Resin Co., Ltd., epoxy equivalent 450 to 500), Epicoat 1002 (manufactured by Japan Epoxy Resin Co., Ltd.) In addition, commercially available products such as epoxy equivalents of 600 to 700) can also be used.

  Moreover, about flexible epoxy, for example, Glicier PP-300P (manufactured by Sanyo Kasei Kogyo Co., Ltd., Adeka Resin EP-4058 (manufactured by Asahi Denka Kogyo Co., Ltd.) can be used.

  In addition, these epoxy resins can be chain-extended using a reaction between an epoxy group and a diol or dicarboxylic acid.

  In introducing a cationic group into the epoxy resin used in the cationic resin emulsion A, a cationizing agent is used so that the cationic group becomes 0.3 to 4.0 meq / g after ring opening of the epoxy group. Is used. Further, it is desirable that the primary amino group occupies 5 to 50% of the cationic group.

  Examples of the cationizing agent include those capable of introducing a cationic group into the base resin, for example, primary amines such as aliphatic, alicyclic, and aromatic, secondary amines, acid salts of tertiary amines, and secondary sulfide acids. Examples include salts.

  Specific examples include butylamine, octylamine, diethylamine, dibutylamine, methylbutylamine, monoethanolamine, diethanolamine, N-methylethanolamine, triethylamine hydrochloride, N, N-dimethylethanolamine acetate, diethyl disulfide / acetic acid mixture, etc. In addition, there are secondary amines in which primary amines such as aminoethylethanolamine ketimine and diethylenetriamine diketimine are blocked. One or more amines selected from these may be used in combination.

  As the curing agent, various known block isocyanate type curing agents can be used. The polyisocyanate may be, for example, any of aliphatic, alicyclic, aromatic and aromatic-aliphatic. Adducts or prepolymers obtained by reacting polyisocyanates with polyhydric alcohols such as ethylene glycol, propylene glycol, trimethylolpropane and hexanetriol at an NCO / OH equivalent ratio of 2 or more are also used as blocked polyisocyanate curing agents. be able to. As the blocking agent, those usually used such as ε-caprolactam and butyl cellosolve can be used. As a usage-amount of a hardening | curing agent, it prepares so that the ratio of NCO group may become 30 to 80% with respect to the OH group of the epoxy which is a base.

  By using the base resin and the curing agent as shown above, as the characteristics of the cationic resin emulsion A, the minimum melt viscosity at the time of curing the coating film is 0.1 or less, and the measurement at the time of measuring the minimum melt viscosity The temperature can be 160 ° C. or higher, more preferably 165 ° C. or higher, the smoothness of the cured coating film can be ensured by the fluidity of the coating film, and other coating film properties can be secured. It is not limited.

  The cationic resin emulsion B contained in the electrodeposition coating composition of the present invention comprises a base resin having a cationic group and a curing agent or a gelling agent for curing the base resin, and these are dispersed in water. Obtained by.

  As the base resin, it is preferable to use a cationic epoxy resin in which an active hydrogen compound such as an amine is reacted with the epoxy ring of the bisphenol-type epoxy resin and the epoxy group is opened to introduce a cationic group.

  As the curing agent, a blocked polyisocyanate obtained by blocking the isocyanate group of the polyisocyanate can be used.

  The gelling agent may be an amine adduct of epoxidized polybutadiene containing two or more epoxy groups in one molecule and two or more α, β-ethylenically unsaturated groups. it can.

  Examples of the cationic epoxy resin that is a base resin of the cationic resin emulsion B include a cationic epoxy resin in which an active hydrogen-containing compound such as an amine is reacted with an epoxy group of a bisphenol type epoxy resin to introduce a cationic group. be able to.

  As the bisphenol type epoxy resin, commercially available products such as Epicoat 1004 (manufactured by Japan Epoxy Resin Co., Ltd., epoxy equivalent 875-975) and Epicoat 1007 (Japan Epoxy Resin Co., Ltd., epoxy equivalent 1750-2200) can also be used. In addition, an epoxy resin having a softening point of 70 ° C. or higher and an epoxy equivalent of 600 to 3000 can be used.

  As a cationizing agent for epoxy resin, those capable of introducing a cationic group into the resin, for example, primary amine such as aliphatic, alicyclic, aromatic, secondary amine, tertiary amine acid salt, secondary sulfide Examples include acid salts. Specifically, the cationizing agent exemplified in the cationic resin emulsion A can be used in the same manner.

  As the polyisocyanate blocking agent of the curing agent, a low-temperature dissociation blocking agent such as methyl ethyl ketoxime is preferable. However, if the curing start temperature of the base resin is 130 ° C. or less, preferably 110 ° C. or less, the type of polyisocyanate and the blocking agent It can be selected depending on the type and the presence or absence of a catalyst. As a usage-amount of a hardening | curing agent, it prepares so that the ratio of NCO group may become 30 to 80% with respect to the OH group of the epoxy which is a base.

  Examples of the gelling agent include derivatives of epoxidized polybutadiene containing two or more epoxy groups in one molecule, and derivatives containing two or more α, β-ethylenically unsaturated groups. . In order to improve stability, it is preferable to further react with a secondary amine. As the compound for introducing the α, β-ethylenically unsaturated group, acrylic acid or the like can be used. As the secondary amine, aliphatic amines such as dimethylamine and diethylamine, methylethanolamine and the like are preferable. The ratio of the content of the base resin and the gelling agent is preferably 80/20 to 60/40 by weight ratio.

  By using the base resin and the curing agent as shown above, as the characteristics of the cationic resin emulsion A, the minimum melt viscosity at the time of curing the coating film is 0.3 or more, and the minimum melt viscosity is measured. The measurement temperature can be 155 ° C. or lower, more preferably 150 ° C. or lower, and the corrosion resistance of the edge portion can be secured and the other coating film properties can be secured, but it is not limited thereto.

  In the synthesis of the base resin having a cationic group, the curing agent, the gelling agent, etc. used in the cationic resin emulsion A and the cationic resin emulsion B, the solvent is removed in a later step, It is preferable to carry out in the presence of an azeotropic organic solvent. Since most of the used organic solvent is removed, the solvent content during the reaction is not particularly limited, but is preferably about 20 to 40% by weight for easy handling of the resin and shortening the time required for the solvent removal step.

Next, the preparation method of the cationic resin emulsion A and the cationic resin emulsion B will be shown.
Actually, the cationic resin emulsion A and the cationic resin emulsion B are prepared separately, but the preparation method itself can be prepared by a similar method.

  After the base resin having a cationic group, a curing agent or a gelling agent, and if necessary, an emulsifier is mixed in a solvent and neutralized, the solid content of the resin composition is 20 to 40% by weight. Dilute with water to

  After dilution, the solvent in the composition is removed under normal pressure or reduced pressure. When the water is added, naturally the dispersion of the resin composition in water is insufficient, but the paint particles are stabilized in water by sufficient mixing in the azeotropic solvent removal.

  In addition, since the cationic resin emulsion B has low temperature reactivity, in order to ensure sufficient chemical stability in the coating liquid, the amount of solvent is 1% by weight or less in the state of coating use. It is preferable to adjust the amount of the solvent in the cationic resin emulsion A and the cationic resin emulsion B so as to be. More preferably, it is adjusted to 0.5% by weight or less.

  Here, the neutralizing agent used for the neutralization treatment is not particularly limited as long as it can neutralize the cationic epoxy resin, but it is preferable to use an organic acid such as formic acid, acetic acid, lactic acid, and sulfamic acid. In order to uniformly neutralize the base resin, the neutralizing agent is used at a concentration as low as possible, and is mixed so as to be 15 to 40 milliequivalents, preferably 20 to 30 milliequivalents with respect to 100 g of the resin solid content. .

  Cationic resin emulsion A and cationic resin emulsion B are mixed at a constant ratio. A preferable mixing ratio is 95/5 to 50/50, more preferably 95/5 to 70/30, and still more preferably 85/15 to 75/25 in terms of a solid content weight ratio A / B.

  The minimum melt viscosity of the electrodeposition coating film using a pendulum viscoelasticity measuring device and the measurement temperature at the time of viscosity measurement will be described.

For the pendulum viscoelasticity measuring device, for example, Leo Vibron DDV-OPA type manufactured by Toyo Baldwin Company is used. A pendulum having a weight of 22 g and an inertia moment of 859 g · cm ² is used. The temperature increase rate is measured at 20 ° C./min, and the viscosity value when the logarithmic decay rate is the lowest (λmin) is defined as the minimum melt viscosity, and the coating temperature at that time is defined as the measurement temperature at the time of measuring the minimum melt viscosity.

  Such measurement methods are also described in JP-A-2-303831, JP-A-2-305995 and the like.

  The cationic electrodeposition coating composition of the present invention containing these compositions may further contain, if necessary, conventional coating additives such as coloring pigments such as titanium oxide (titanium white), carbon black, bengara, and talc. Extender pigments such as calcium carbonate, mica, kaolin (clay), silica, rust preventive pigments such as aluminum phosphomolybdate, aluminum tripolyphosphate, aluminum phosphite, zinc phosphate, bismuth compound, curing catalyst, antifoaming agent, A repellency inhibitor, a rheology control agent, and the like can be contained. The pigment content is preferably in the range of 10 to 40% by weight in the coating film.

  The electrodeposition coating composition of the present invention can be applied to the surface of a desired material by a known electrodeposition coating method. Specifically, the solid content concentration of the coating is preferably 5 to 40% by weight, more preferably 15 to 25% by weight, the pH is adjusted to 5 to 8 depending on the amount of neutralizing acid used, and the bath temperature is 20%. Although it can coat on the conditions of -35 degreeC and a load voltage of 50-400V, it is not limited to this condition. The coated coating film is washed with water and then baked at a temperature of 130 to 200 ° C. for 5 to 20 minutes in a baking oven to obtain a cured coating film.

Hereinafter, examples and comparative examples of the present invention will be described.
As a basic composition, an amine-modified epoxy resin is used as a base resin, and a blocked polyisocyanate and a gelling agent are used as a curing agent. In addition, unless otherwise indicated, the numerical values, such as the compounding quantity in the following, represent a weight part and weight%.

[Production Example 1] Production of Cationic Base Resin A Using the raw materials shown in Table 1, a base resin used for the cationic resin emulsion A was produced by the method shown below, and this was used as the cationic base resin A. And

  Here, Glyciere PP-300P manufactured by Sanyo Chemical Industries, Ltd. was used as the raw material (1), and Epicoat 828 manufactured by Japan Epoxy Resin Co., Ltd. was used as the raw material (2).

  Raw materials (1), (2), (3), (4) were charged into a reaction vessel equipped with a stirrer, thermometer, and cooling tube, stirred and heated, and the temperature was raised from room temperature to 150 ° C. in 1 hour. Warm up. After holding at 150 ° C. for 6 hours, the raw material (5) was gradually added and cooled to 80 ° C. in 30 minutes. Next, the raw material (6) was added and the temperature was raised to 100 ° C. in 10 minutes. After maintaining at 100 ° C. for 2 hours, it was cooled to 80 ° C. in 10 minutes and taken out. The obtained amine-modified epoxy resin is referred to as “cationic base resin A”. Solid content concentration of the obtained cationic base resin A was 70.0%.

[Production Example 2] Production of Curing Agent A Using the raw materials shown in Table 2, a curing agent used for the cationic resin emulsion A is produced by the method shown below, and this is designated as curing agent A.

  Here, Nippon Polyurethane Industry Co., Ltd. Millionate MR-400 was used for the raw material (1).

  The raw materials (1) and (2) were charged into a reaction vessel equipped with a stirrer, a thermometer, and a cooling tube, and the mixture was stirred and heated, and the temperature was raised from room temperature to 100 ° C. in 30 minutes. Thereafter, while keeping the temperature in the reaction vessel at 100 ° C., a solution of the raw material (4) previously dissolved in the raw material (3) was charged over 1 hour and reacted at 100 ° C. for 2 hours. Subsequently, the same temperature was maintained, and the raw material (5) was dropped over 1 hour. After dropping, the raw material (5) was further maintained at 100 ° C. for 2 hours, and then cooled to 80 ° C. for 10 minutes and taken out. Let the obtained blocked polyisocyanate be the curing agent A. The solid content concentration of the resulting curing agent A was 65.0%.

[Production Example 3] Production of cationic resin emulsion A 100 parts of cationic base resin A obtained in Production Example 1, 40 parts of curing agent A obtained in Production Example 2, HN-120 (synthetic alcohol-based nonionic surfactant) , HLB14.2, manufactured by Sanyo Chemical Industries, Ltd.) was charged into a reaction vessel equipped with a stirrer, thermometer, cooler and decompression device. After mixing well, 4.5 parts of 50% lactic acid diluted with deionized water was added and stirred at 40-70 ° C. for 30 minutes, and then 85 parts of deionized water was added. A predetermined amount of solvent was removed at a pressure of 300 to 500 mmHg (gauge pressure) at about 70 ° C. Thereafter, 125.5 parts of deionized water was added to obtain an emulsion having a solid concentration of 31.5%. This is designated as cationic resin emulsion A.

  This cationic resin emulsion A had a minimum melt viscosity (minimum damping rate λmin) of 0.05, and a measurement temperature at the time of measuring the minimum melt viscosity was 168 ° C.

[Production Example 4] Production of Cationic Base Resin B Using the raw materials shown in Table 3, a base resin used for the cationic resin emulsion B of the present invention was produced by the method shown below, and this was converted into a cationic group. Agent resin B.

  Here, Epicoat 1004 manufactured by Japan Epoxy Resin Co., Ltd. was used as the raw material (1).

  Into a reaction vessel equipped with a thermometer, a stirrer and a reflux condenser, the raw materials (1) and (2) were charged and heated from room temperature for 30 minutes to dissolve the epoxy resin, then at 70 ° C. (3), then (4) was added, and after 2 hours of reaction at 100 ° C., (5) was further added. The obtained amine-modified epoxy resin is referred to as “cationic base resin B”. The resulting cationic base resin B had a solid content concentration of 55.0%.

[Production Example 5] Production of gelling agent B Using the raw materials shown in Table 4, a gelling agent used for the cationic resin emulsion B of the present invention was produced by the method shown below. To do.

Here, Ricon 657 manufactured by Sartomer was used as the raw material (1).
The raw materials (1), (2), and (3) were charged, and the temperature was raised from room temperature to 170 ° C. over 1 hour with stirring in a nitrogen gas stream, and maintained at 170 ° C. for 6 hours. Subsequently, it cooled to 120 degreeC in 30 minutes, (4) and (5) were thrown in, and the composition obtained by hold | maintaining at 120 degreeC for 4 hours was used as the gelatinizer B. The gelling agent B obtained had a solid content concentration of 75.0%.

[Production Example 6] Production of Curing Agent B Using the raw materials shown in Table 5, a curing agent used for the cationic resin emulsion B is produced by the method shown below, and this is designated as curing agent B.

  Raw materials (1) and (2) were charged into a reaction vessel equipped with a stirrer, a thermometer, and a cooling tube, stirred and heated, and heated from room temperature to 70 ° C. in 30 minutes. Thereafter, while keeping the temperature in the flask at 60 to 70 ° C., the raw material (3) was gradually added dropwise, and after reacting at 70 ° C. for 1.5 hours, (4) was added. Let the obtained blocked polyisocyanate be the curing agent B. The solid content was 65.0%.

[Production Example 7] Production of cationic resin emulsion B1 1000 parts of the cationic base resin B obtained in Production Example 4, 200 parts of the gelling agent B obtained in Production Example 5, HN-120 (synthetic alcohol type) 7 parts of a nonionic surfactant (HLB14.2, manufactured by Sanyo Chemical Industries, Ltd.) was charged into a reaction vessel equipped with a stirrer, thermometer, cooler and decompression device. After thorough mixing, 31.5 parts of 50% lactic acid diluted with deionized water was added and stirred at 40-60 ° C. for 30 minutes, and then 680 parts of deionized water was added. A predetermined amount of solvent was removed at a pressure of 100 to 400 mmHg (gauge pressure) at about 65 ° C. Thereafter, 1346.5 parts of deionized water was added to obtain an emulsion having a solid content concentration of 25.0%. This is designated as cationic resin emulsion B1.

  The obtained cationic resin emulsion B1 had a minimum melt viscosity (minimum damping rate λmin) of 0.33, and a measurement temperature at the time of measuring the minimum melt viscosity was 150 ° C.

[Production Example 8] Production of cationic resin emulsion B2 1000 parts of the cationic base resin B obtained in Production Example 4, 250 parts of the curing agent B obtained in Production Example 6, and HN-120 (synthetic alcohol-based nonion) 10 parts of a surfactant, HLB14.2, manufactured by Sanyo Chemical Industries, Ltd.) was charged into a reaction vessel equipped with a stirrer, thermometer, cooler and decompression device. After thorough mixing, 38.5 parts of 50% lactic acid diluted with deionized water was added and stirred at 50-65 ° C. for 30 minutes, and then 720 parts of deionized water was added. A predetermined amount of solvent was removed at a pressure of 100 to 400 mmHg (gauge pressure) at about 65 ° C. Thereafter, 1331 parts of deionized water was added to obtain an emulsion having a solid content of 25.0%. This is designated as cationic resin emulsion B2.

  This cationic resin emulsion B2 had a minimum melt viscosity (minimum damping rate λmin) of 0.37, and a measurement temperature at the time of measuring the minimum melt viscosity was 148 ° C.

[Production Example 9] Production of Cationic Base Resin C Using the raw materials shown in Table 6, a base resin used for the cationic resin emulsion C was produced by the method shown below, and this was used as the cationic base resin C. And

  Here, the raw material (1) is Glycier PP-300P manufactured by Sanyo Chemical Industries, Ltd., the raw material (2) is Epicoat 828 manufactured by Japan Epoxy Resin Co., Ltd., and the raw material (7) uses diethylenetriamine and diketimine of methyl isobutyl ketone. It was.

  Raw materials (1), (2), (3), and (4) are charged into a reaction vessel equipped with a stirrer, thermometer, and cooling tube, stirred, heated, and heated from room temperature to 150 ° C. in 1 hour. did. After holding at 150 ° C. for 6 hours, the raw material (5) was gradually added and cooled to 80 ° C. in 30 minutes. Next, the raw materials (6) and (7) were added and the temperature was raised to 100 ° C. in 10 minutes. After maintaining at 100 ° C. for 2 hours, it was cooled to 80 ° C. in 10 minutes and taken out. The obtained amine-modified epoxy resin is referred to as “cationic base resin C”. The solid content concentration of the obtained cationic base resin C was 70.0%.

[Production Example 10] Production of Cationic Resin Emulsion C 100 parts of cationic base resin C obtained in Production Example 9, 20 parts of curing agent A obtained in Production Example 2, and 20 parts of curing agent B obtained in Production Example 6 , 0.5 part of HN-120 (synthetic alcohol-based nonionic surfactant, HLB14.2, manufactured by Sanyo Chemical Industries, Ltd.) was charged into a reaction vessel equipped with a stirrer, thermometer, cooler and decompression device. . After mixing well, 4.5 parts of 50% lactic acid diluted with deionized water was added and stirred at 40-70 ° C. for 30 minutes, and then 85 parts of deionized water was added. A predetermined amount of solvent was removed at a pressure of 300 to 500 mmHg (gauge pressure) at about 70 ° C. Thereafter, 125.5 parts of deionized water was added to obtain an emulsion having a solid content of 31.5%. This is designated as cationic resin emulsion C.

  This cationic resin emulsion C had a minimum melt viscosity (minimum damping ratio λmin) of 0.15 and a measurement temperature during recording of 157 ° C. The obtained cationic resin emulsion C has physical properties such that the minimum melt viscosity and the measurement temperature at the time of measuring the minimum melt viscosity deviate from any of the ranges of the cationic emulsion A and the cationic emulsion B. It is.

[Production Example 11]
Separately prepared pigment dispersion resin (amine-modified epoxy resin), acetic acid, deionized water, diethylene glycol monobutyl ether, carbon black, titanium oxide, kaolin, dibutyltin oxide, and rust preventive pigment are thoroughly stirred with a dissolver and then granulated with a horizontal sand mill. A pigment paste was obtained by dispersing until the gauge particle size became 10 μm or less.

[Preparation of electrodeposition paint]
Examples 1-5 Comparative Examples 1-8
Table 7 (Examples 1 to 5) and Table 8 (Comparative Examples) were prepared using the cationic resin emulsion A, the cationic resin emulsions B1 and B2, the cationic resin emulsion C, the pigment paste, and others prepared above. 1-4) and the electrodeposition coating liquid prepared in the ratio as shown in Table 9 (Comparative Examples 5-8) were obtained.

[Test plate production method and test method]
After baking, using the electrodeposition coating liquid obtained above as a cathode with a carbon electrode as an anode and a degreased cold rolled steel sheet (manufactured by Partec Co., Ltd., 0.8 × 70 × 150 mm, degreasing and zinc phosphate treatment) The electrodeposition coating was performed under the condition that the film thickness of the film was 15 to 18 μm. After electrodeposition coating, it was washed with deionized water and baked at 170 ° C. for 20 minutes. The evaluation results of the coating film performance are shown in Table 7 (Examples 1 to 5), Table 8 (Comparative Examples 1 to 4), and Table 9 (Comparative Examples 5 to 8), respectively.

[Paint appearance evaluation]
(Surface roughness)
Arithmetic mean roughness Ra was measured using a surface roughness meter. It shows that smoothness is so favorable that Ra is small.

(Visual evaluation)
Moreover, the smooth state of the surface by visual observation was also evaluated. The evaluation criteria were ◎: best, ○: good, Δ: somewhat bad, x: bad.

[Cutter blade rust evaluation]
(Number of rust)
A knife cutter blade (OLFA model number LB-10K) was degreased and then coated with zinc phosphate, and the number of rust portions generated at the edge portion in a salt spray test 168 hours was measured.

(Visual evaluation)
Moreover, the rust state of the surface by visual observation was also evaluated. The evaluation criteria were as follows: ◎: almost no rust, ○: slightly rust, Δ: slightly rust, ×: almost rust.

  Since Comparative Example 1 uses only the cationic resin emulsion A, the coating film smoothness was obtained, but rust was generated at the edge portion. In Comparative Example 2, the RC agent was added to the cationic resin emulsion A to increase the viscosity. As a result, although the corrosion resistance of the edge portion was improved from Comparative Example 1, the smoothness of the coating film was greatly deteriorated. In Comparative Example 3, only the cationic resin emulsion C was used and the coating film smoothness was good, but rust was generated at the edge portion. In Comparative Example 4, since only the cationic resin emulsion B1 was used, the corrosion resistance of the edge portion was obtained, but the surface roughness was large and the surface state was poor. Since Comparative Example 5 uses only the cationic resin emulsion B2, the corrosion resistance of the edge portion was obtained, but the surface roughness was large and the surface state was poor.

  In Comparative Example 6, the cationic resin emulsion A and the cationic resin emulsion C were mixed, and the coating film smoothness was obtained, but rust was generated at the edge portion. In Comparative Example 7, the cationic resin emulsion B1 and the cationic resin emulsion C were mixed, and the corrosion resistance of the edge portion was obtained, but the surface roughness was large and the surface state was slightly poor. In Comparative Example 8, the cationic resin emulsion B2 and the cationic resin emulsion C were mixed, and the corrosion resistance of the edge portion was obtained, but the surface roughness was large and the surface state was poor.

  In contrast to these comparative examples, Examples 1-4 were good in both coating film smoothness and edge portion corrosion resistance by mixing cationic resin emulsion A and cationic resin emulsion B. In particular, Examples 2 and 3 were excellent in evaluation, and it was found that more preferable coating properties can be obtained by setting the solid content weight ratio A / B in the range of 85/15 to 75/25.

Claims (4)

The minimum melt viscosity at the time of curing the coating film determined from the logarithmic decay rate measurement of the coating film using a pendulum viscoelasticity measuring instrument is 0.1 or less, and the measurement temperature at the time of measuring the minimum melt viscosity is 160 ° C. or more. A cationic resin emulsion A;
The minimum melt viscosity at the time of curing the coating film determined from the logarithmic decay rate measurement of the coating film using a pendulum type viscoelasticity measuring device is 0.3 or more, and the measurement temperature at the time of measuring the minimum melt viscosity is 155 ° C. or less. An electrodeposition coating composition comprising a cationic resin emulsion B.   The temperature at the time of the minimum melt viscosity measurement of the cationic resin emulsion A is 165 ° C or higher, and the temperature at the time of the minimum melt viscosity measurement of the resin emulsion B is 150 ° C or lower. The electrodeposition coating composition as described.   The ratio of the content of the cationic resin emulsion A and the cationic resin emulsion B is 95/5 to 50/50 as a solid content weight ratio A / B. Electrodeposition paint composition.   The ratio of the content of the cationic resin emulsion A and the cationic resin emulsion B is 95/5 to 70/30 as a solid content weight ratio A / B. Electrodeposition paint composition.