JP2012057035A - Coating method of cationic electrodeposition paint composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coating method of a cationic electrodeposition paint composition that secures throwing power equivalent to electrodeposition coating on a conventional phosphate chemical conversion film and further exhibits excellent rust prevention properties while maintaining electrodeposition coating workability on a nonphosphorylated chemical conversion film of a reduced environmental load and cost type.SOLUTION: The coating method uses the cationic electrodeposition paint composition containing: (A) a cationic amine-modified epoxy resin (a base) which is obtained by cationizing an amine-modified epoxy resin obtained by the reaction of an epoxy resin with an amine; (B) a blocked polyisocyanate (a curing agent); and (C) a metal salt obtained from lactic acid and a transition metal.

Description

  The present invention provides a cation capable of exhibiting excellent throwing power and rust prevention properties on a non-phosphate treated film typified by a metal oxide film, which is one of automotive steel sheet treatments with low environmental burden and cost burden. The present invention relates to a coating method for a conductive electrodeposition coating composition.

  Electrodeposition coating has better throwing power and less environmental pollution compared to air spray coating and electrostatic spray coating for automobile body and its parts, and parts with a bag structure such as electric appliances. Therefore, it has been widely put to practical use as a primer coating. In order to exhibit the excellent throwing power and rust prevention properties of this electrodeposition coating, it is a common practice to perform a phosphate chemical conversion treatment as a base treatment for the steel sheet.

  On the other hand, the phosphate chemical conversion treatment requires a degreasing step, a water washing step, and a surface conditioning step before the treatment, and a water washing step and a drying step after the treatment. The number of steps is very large and complicated. This is a cost burden. In addition, the phosphate chemical conversion treatment requires not only continuous management of the treatment liquid, but also the size of environmental loads such as sludge treatment and wastewater treatment is a problem.

  Therefore, in recent years, an alternative treatment film for phosphate chemical conversion treatment for automobile steel sheets has been studied mainly for the purpose of reducing the environmental load and the number of pretreatment steps. For example, Patent Documents 1 and 2 propose a method of treating a steel sheet surface with a metal chemical conversion treatment agent containing zirconium ions, titanium ions, and fluorine ions. Patent Document 3 proposes a surface treatment method in which electrolytic treatment is performed with an aqueous surface treatment liquid containing a zirconium compound, a titanium compound, a calcium compound, a magnesium compound, and a strontium compound. Patent Document 4 proposes a method of forming a continuous film by electrolytic treatment in a treatment composition containing a nitrate of a rare earth metal compound. Further, Patent Document 5 proposes a base treatment agent containing a titanium compound.

  However, on the surface treatment film of these patent documents, compared with the conventional phosphate chemical conversion treatment, film resistance is less likely to occur during electrodeposition coating, and as a result, the film thickness of the automobile body outer plate increases. Thus, there is a problem that the film thickness of the inner plate is lowered and the throwing power is lowered. In Patent Documents 1 and 5, there is a description of epoxy-based cationic electrodeposition coating, but there is no special device for improving throwing power. Therefore, it has only been used for some parts so far and is complicated. This is one of the factors that hinder the development of automobile bodies and the like with various shapes.

Patent Document 6 proposes an electrodeposition coating composition containing a zirconium salt of an organic acid represented by the chemical formula ZrO (C _n H _2n-1 O ₂ ) ₂ , but this is merely rust-proof. This is a technique for improving the rust prevention property of an untreated steel sheet.

JP 2004-43913 A JP 2006-219691 A JP 2004-190121 A JP 2007-238998 A JP 2002-275691 A JP 2009-46628 A

  The present invention was devised in order to solve the problems of the prior art. The purpose of the present invention was to maintain the electrodeposition coating workability on the non-phosphate-based treatment film with reduced environmental load and cost. To provide a coating method of a cationic electrodeposition coating composition that ensures a throwing power equivalent to that of conventional electrodeposition coating on a phosphate chemical conversion coating and further exhibits excellent rust prevention properties It is in.

  One of the major factors governing throwing power during electrodeposition coating is a rapid increase in film resistance of the deposited coating. On the conventional phosphate chemical conversion coating, the energization point is subdivided by the rectifying effect of the non-conductive phosphate crystal particles densely arranged on the material, so that the material coating of the deposited coating can be performed. Proceeds quickly and develops coating resistance. On the other hand, since the rectifying effect does not work on the non-phosphate surface treatment film without such inorganic crystal particles, the energization point becomes sparse and the onset of coating film resistance is delayed. As a result, the film thickness of the outer plate portion increases, and the current concentrates on the outer plate portion, so that the arrival of current to the inner plate portion is delayed, and the film thickness of the inner plate portion is decreased. The present invention can overcome such problems and improve throwing power on the non-phosphate-based treatment film.

That is, the present invention has the following configurations (1) to (3).
(1) (A) a cationic amine-modified epoxy resin (base) obtained by cationizing an amine-modified epoxy resin obtained by reacting an amine with an epoxy resin, (B) a blocked polyisocyanate (curing agent), and (C) ) A coating method characterized by using a cationic electrodeposition coating composition containing a metal salt obtained from lactic acid and a transition metal.
(2) The epoxy resin of (A) cationic amine-modified epoxy resin (base) is an epoxy resin obtained by reacting glycidyl ether of polyol, glycidyl ether of dihydric phenol and dihydric phenol. The coating method according to (1).
(3) The coating method according to (1) or (2), wherein the transition metal constituting the metal salt (C) is zirconium or titanium.

  According to the method for coating a cationic electrodeposition coating composition of the present invention, not only on a conventional phosphate chemical conversion coating film, but also on a non-phosphate coating film having a high effect of reducing environmental and cost burdens. Circumstance can be expressed. Therefore, this non-phosphate surface treatment can be performed even for a shape having a complicated bag structure such as an automobile body.

  The reason why the above-mentioned effects can be obtained is that the deposited electrodeposition coating film is densely formed by the action of the metal salt obtained from lactic acid and transition metal even on the non-phosphate treatment film where the coating film resistance is hardly exhibited. This is considered to be achieved by accelerating the expression of the coating film resistance, accelerating the formation of the coating film on the outer plate portion, and quickly reaching the current to the inner plate portion of the bag structure.

A panel for assembling a box-like structure for evaluating throwing power. It is a perspective view which shows an example of the box-shaped structure for throwing power evaluation. It is a side view which shows an example of the box-shaped structure for throwing power evaluation. It is explanatory drawing which shows the coating method for throwing power evaluation.

  The cationic electrodeposition coating composition used in the coating method of the present invention comprises (A) a cationic amine-modified epoxy resin (base), (B) a blocked polyisocyanate (curing agent), and (C) a transition with lactic acid. It contains a metal salt obtained from a metal.

[(A) Cationic amine-modified epoxy resin (base)]
(A) The cationic amine-modified epoxy resin (base) is a cationized amine-modified epoxy resin obtained by reacting an amine with an epoxy resin having at least one, preferably two or more epoxy groups in one molecule. Is.

  About the epoxy resin before making it react with an amine, Preferably it is an epoxy resin which has two epoxy groups in 1 molecule on the average, The epoxy equivalent is 400-3000, Especially 500-1500 are preferable. The main component constituting the epoxy resin is glycidyl ether of dihydric phenol. Examples of the dihydric phenol include resorcin, hydroquinone, 2,2-bis- (4-hydroxyphenyl) -propane, 4,4′-dihydroxybenzophenone, 1,1-bis- (4-hydroxyphenyl) -methane, 1, 1-bis- (4-hydroxyphenyl) -ethane, 4,4′-dihydroxybiphenyl and the like can be mentioned, but 2,2-bis- (4-hydroxyphenyl) -propane, so-called bisphenol A is particularly preferable. is there.

  More preferably, a glycidyl ether such as polyol, polyalkylene polyol, polyalkylphenol or the like can be added as a flexible modifier, and the modification rate is preferably 1 to 50%, more preferably 5 to 35%. . As the introduction method, these flexible glycidyl ethers are reacted with an excess of the above dihydric phenol to obtain an initial condensate, and then the chain length is extended to the target molecular weight by reaction with the divalent phenol glycidyl ether. Although the method of doing is illustrated as a thing with favorable reaction efficiency, it is not limited to this.

  Examples of the glycidyl ether of the polyol include ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, 1,6-hexanediol diglycidyl ether, neopentyl glycol diglycidyl ether, diethylene glycol diglycidyl ether, triethylene glycol diglycidyl ether, 1 , 4-cyclohexanediol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, polytetramethylene glycol diglycidyl ether, or a mixture thereof.

  Examples of the divalent phenol glycidyl ether include resorcin diglycidyl ether, hydroquinone diglycidyl ether, bisphenol A diglycidyl ether, 4,4'-dihydroxybenzophenone diglycidyl ether, 1,1-bis- (4-hydroxyphenyl). ) -Methane diglycidyl ether, 1,1-bis- (4-hydroxyphenyl) -ethane diglycidyl ether, 4,4′-dihydroxybiphenyl diglycidyl ether, or a mixture thereof.

  Examples of the dihydric phenol include resorcin, hydroquinone, bisphenol A, 4,4′-dihydroxybenzophenone, 1,1-bis- (4-hydroxyphenyl) -methane, 1,1- (2,4′-dihydroxy. Phenyl) -methane, 1,1-bis- (4-hydroxyphenyl) -ethane, 4,4′-dihydroxybiphenyl, and the like, or a mixture thereof.

  As amines to be reacted with the epoxy resin, methylamine, ethylamine, n-propylamine, isopropylamine, monoethanolamine, diethylamine, diethanolamine, N-methylethanolamine, N-ethylethanolamine, ethylenediamine, diethylenetriamine, hydroxyethyl Examples thereof include aminoethylamine, ethylaminoethylamine, methylaminopropylamine, dimethylaminopropylamine and the like, or a mixture thereof. In the reaction between the epoxy resin and the amine, the primary amino group may be blocked by reacting with a ketone in advance, and then the remaining active hydrogen may be reacted with the epoxy group.

  The reaction of the diglycidyl ether of polyol, the diglycidyl ether of dihydric phenol and the dihydric phenol can be carried out in a melt without a solvent, but can also be carried out in a system to which a small amount of solvent is added. The solvent is not particularly limited as long as it does not react with the epoxy group. The reaction temperature is suitably 80 to 180 ° C. The amination in which an amine is reacted with an epoxy group can be carried out in a solvent or a melt without a solvent, and the reaction temperature is suitably 50 to 150 ° C.

  In addition, a specific method for cationization of the amine-modified epoxy resin can be performed by neutralizing the amino group with a protonic acid, and particularly preferable acids include formic acid, lactic acid, acetic acid, methanesulfonic acid, propion. There are acids, citric acid, malic acid, sulfamic acid and the like or mixtures thereof.

[(B) Blocked polyisocyanate (curing agent)]
(B) The blocked polyisocyanate (curing agent) is a reaction product of a polyisocyanate and a blocking agent, and the polyisocyanate is an aromatic or aliphatic (including alicyclic) polyisocyanate. Examples include 2,4- or 2,6-tolylene diisocyanate and mixtures thereof, p-phenylene diisocyanate, diphenylmethane-4,4′-diisocyanate, polymethylene polyphenyl diisocyanate, tetramethylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate. 1,3 or 1,4-bis- (isocyanatomethyl) -cyclohexane, dicyclohexylmethane-4,4′-diisocyanate, bis- (isocyanatomethyl) -norbornane, 3 or 4-isocyanatomethyl-1-methylcyclohexyl isocyanate, m- or p-xylylene diisocyanate, m- or p-tetramethylxylylene diisocyanate, Modified or isocyanurate modified, or a part of the isocyanate group of the above isocyanate, ethylene glycol, propylene glycol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, triethylene glycol, 1,4-cyclohexanediol Such as low molecular diols such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polylactone diols such as polylactone diols, polyisocyanates linked by polyols such as trimethylol ethane, trimethylol propane, pentaerythritol, or mixtures thereof. Can do.

  Examples of the blocking agent include aliphatic alcohol compounds such as methanol, ethanol, n-butanol and 2-ethylhexanol, cellosolve compounds such as ethylene glycol monobutyl ether and ethylene glycol monohexyl ether, diethylene glycol monoethyl ether and diethylene glycol monobutyl ether. Carbitol compounds, oxime compounds such as acetone oxime, methyl ethyl ketone oxime and cyclohexanone oxime, lactam compounds such as ε-caprolactam, phenol compounds such as phenol, cresol and xylenol, active methylene such as ethyl acetoacetate and diethyl malonate Mention may be made of group-containing compounds.

  The reaction between the polyisocyanate and the blocking agent can be carried out in a solvent or in a melt. Solvents used for the reaction include solvents that do not react with polyisocyanates, such as ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclopentanone, cyclohexane, and isophorone, and aromatics such as benzene, toluene, xylene, chlorobenzene, and nitrobenzene. Examples thereof include hydrocarbons, cyclic ethers such as tetrahydrofuran, and halogenated hydrocarbons such as chloroform. Although it does not specifically limit about reaction temperature, Preferably it is 30-150 degreeC.

[(C) Metal salt obtained from lactic acid and transition metal]
Examples of transition metals used in metal salts obtained from (C) lactic acid and transition metals include scandium, titanium, vanadium, yttrium, zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, and particularly titanium. Zirconium is preferred, with zirconium being more preferred. Commercially available titanium lactate can be used, and specific examples include Olga-Tix TC-310 or TC-315 manufactured by Matsumoto Fine Chemical Co., Ltd.

  Zirconium carbonate is preferred as the zirconium compound used in the production of zirconium lactate. The reaction ratio of zirconium carbonate and lactic acid can be variously selected. For example, 1 mol of lactic acid is mixed with 1 mol of zirconium carbonate, more preferably 1 to 3 mol, and (A) a cationic property. A paste obtained by kneading and reacting with an amine-modified epoxy resin (base) is preferably used as a lactate salt of zirconium. If the amount of lactic acid is less than 1 mol, the effect of improving throwing power is not sufficient, and if it exceeds 5 mol, there is a possibility that the electrodeposition coating workability may be deteriorated due to excessive acid.

  The content of the metal salt obtained from (C) lactic acid and a transition metal used in the cationic electrodeposition coating composition is not particularly limited, but is preferably 0.1 with respect to 100 parts by weight of the total resin solid content in the coating composition. -5.0 parts by weight. The content ratio of (A) cationic amine-modified epoxy resin (base) and (B) blocked polyisocyanate (curing agent) in the coating composition is 90 to 40/10 to 60 in terms of solid content, Preferably it is 85-40 / 15-60, More preferably, it is 80-55 / 20-45.

  In addition to the above components (A), (B) and (C), the cationic electrodeposition coating composition may further include a usual paint additive, for example, a color pigment such as titanium white, carbon black, bengara, etc. , Kaolin, talc, aluminum silicate, calcium carbonate, mica, clay, silica and other extender pigments, zinc phosphate, iron phosphate, aluminum phosphate, calcium phosphate, zinc cyanide, zinc oxide, aluminum tripolyphosphate, zinc molybdate, Additives such as rust preventive pigments such as aluminum molybdate, calcium molybdate, and bismuth compounds, antifoaming agents, repellency inhibitors, aqueous solvents, curing catalysts, and the like can be contained. In addition, other resins such as an acrylic resin, a polyester resin, a urethane resin, and a butadiene resin can be contained.

[Preparation of electrodeposition coating composition]
The method for preparing the cationic electrodeposition coating composition is not particularly limited. For example, (A) a cationic amine-modified epoxy resin (base) and (B) a blocked polyisocyanate (curing agent) are charged into a reaction vessel. After stirring and mixing well, an acid is added to cationize the amino group of the amine-modified epoxy resin, and water is added to prepare an aqueous resin dispersion. On the other hand, (A) a cationic amine-modified epoxy resin After adding acid and water to (base) to produce a water-soluble vehicle, (C) metal salt obtained from lactic acid and transition metal, and if necessary, coloring pigment, extender pigment and additives, It is possible to prepare a pigment paste by dispersing to a required particle size with a disperser such as a sand mill and mixing the resin aqueous dispersion and the pigment paste thus obtained together with water. Kill.

[Electrodeposition coating method]
The cationic electrodeposition coating composition used in the coating method of the present invention is usually in a state of being dispersed in water. Specifically, the solid content concentration of the coating is preferably about 5 to 40% by weight, More preferably, the coating material can be coated as a cathode under conditions of 15 to 25% by weight, pH adjusted to 5 to 8, bath temperature of 15 to 35 ° C., and load voltage of 100 to 450V. Even if electrodeposition coating is performed below, the object can be sufficiently achieved. After the coated object is washed with water, a cured coating film can be obtained by baking at 100 to 200 ° C. for 10 to 30 minutes in a baking oven. As for the object to be coated, it can be selected widely from zinc phosphate chemical conversion treated steel sheet, zirconium metal oxide film treated steel sheet, untreated steel sheet, hot dip galvanized steel sheet, etc. In the non-phosphate-treated steel sheet, high throwing power that cannot be obtained by the conventional electrodeposition coating method is secured, and at the same time, excellent rust prevention is secured. Although the film thickness of the coating film obtained from the coating method of this invention is not restrict | limited in particular, 5-60 micrometers in a cured coating film, Preferably 10-40 micrometers is suitable.

  The excellent effects of the cationic electrodeposition coating composition of the present invention will be shown below by Examples, but the present invention is not limited to these.

[Production of amine-modified epoxy resin A1]
Using the raw materials shown in Table 1, an amine-modified epoxy resin A1 was produced by the method shown below. Raw materials (1), (2), (3), and (4) were charged into a four-necked flask equipped with a stirrer, a thermometer, and a cooling tube, and the temperature was raised to 150 ° C. by stirring and heating. After maintaining at 150 ° C. for 3 hours, the raw material (5) was gradually added and cooled to 80 ° C. Next, the raw material (6) was charged and the temperature was raised to 100 ° C. After holding at 100 ° C. for 2 hours, it was cooled to 80 ° C. and taken out. The resulting amine-modified epoxy resin A1 had a solid content of 70%.

[Production of amine-modified epoxy resin A2]
Using the raw materials shown in Table 2, the amine-modified epoxy resin A2 of the present invention was produced by the method shown below. Raw materials (1), (2), and (3) were charged into a four-necked flask equipped with a stirrer, a thermometer, and a cooling tube, and the temperature was raised to 150 ° C. by stirring and heating. After maintaining at 150 ° C. for 3 hours, the raw material (4) was gradually added and cooled to 80 ° C. Next, the raw material (5) was charged and the temperature was raised to 100 ° C. After holding at 100 ° C. for 2 hours, it was cooled to 80 ° C. and taken out. The resulting amine-modified epoxy resin A2 had a solid content of 70%.

[Production of blocked polyisocyanate B]
Using the raw materials shown in Table 3, blocked isocyanate B was produced by the method shown below. Raw materials (1) and (2) were charged into a four-necked flask equipped with a stirrer, a thermometer, and a cooling tube, and the temperature was raised to 100 ° C. by stirring and heating. Thereafter, a solution of the raw material (4) previously dissolved in the raw material (3) was charged over 1 hour while keeping the temperature in the flask at 100 ° C., and reacted at 100 ° C. for 2 hours. Next, the raw material (5) was added dropwise over 1 hour while maintaining the same temperature. After the addition, the material (5) was further maintained at 100 ° C. for 2 hours, and then cooled to 80 ° C. and taken out. The obtained blocked polyisocyanate B had a solid content of 75%.

[Production of Zirconate Lactate-Containing Paste C]
Using the raw materials shown in Table 4, a zirconium lactate-containing paste C was prepared by the following method. The raw materials (1), (2), (3), and (4) were sufficiently stirred with a dissolver, and then dispersed in a horizontal sand mill for 2 hours while maintaining a temperature of 35 to 50 ° C., and a zirconium lactate having a grain gauge particle size of 10 μm or less. A containing paste C was obtained.

[Preparation of resin aqueous dispersion]
Amine-modified epoxy resin A1 or A2, blocked polyisocyanate B, diethylene glycol monobutyl ether, formic acid, and deionized water were charged into a reaction vessel equipped with a stirrer, thermometer, cooler, and decompression device. After sufficiently stirring and mixing these, the solvent is removed under a reduced pressure of −300 to −600 mmHg (gauge pressure), and then deionized water is added to be used in Examples 1 to 6 and Comparative Examples 1 and 2. A resin aqueous dispersion was obtained. Table 5 shows the compounding amounts of the components of each resin water dispersion.

[Preparation of pigment paste]
Amine-modified epoxy resin A1, formic acid, deionized water, carbon black, titanium oxide, kaolin, and bismuth hydroxide are blended in the amounts shown in Table 5, and after sufficiently stirring with a dissolver, the particle gauge particle size becomes 10 μm or less with a horizontal sand mill. The pigment paste used in Examples 1 to 6 and Comparative Examples 1 and 2 was obtained.

[Preparation of electrodeposition paint]
Examples 1 to 6 and Comparative Examples 1 and 2 were prepared by blending the above-mentioned resin water dispersion, pigment paste, and titanium lactate or zirconium lactate-containing paste C shown in Table 5 in the amounts shown in Table 5. An electrodeposition paint was obtained.

[Evaluation of coating film performance]
Using the electrodeposition paints of Examples 1 to 6 and Comparative Examples 1 and 2 prepared above, according to the test plate production method shown below, each test plate was produced, and the paint and coating film were produced according to the following evaluation method. The performance evaluation was performed.

[Test plate preparation method]
Using the electrodeposition paint obtained above, a cold rolled steel sheet (made by Nihon Parkerizing Co., Ltd., 0.8 ×) with a stainless steel plate as an anode and a zirconium-based metal oxide film treatment that is a non-phosphate treatment is applied. 70 × 150 mm) or a cold-rolled steel sheet (0.8 × 70 × 150 mm, manufactured by Partec Co., Ltd.) treated with zinc phosphate as the cathode, and the coating temperature 30 so that the coating film thickness after baking is 15 μm. Electrodeposition coating was performed at a temperature of 150 ° C. and a coating voltage of 150 to 300 V, washed with water, and baked at 170 ° C. for 20 minutes. The details of the preparation of the test plate for evaluating throwing power are described in the section (2) Throwing property below.

[Evaluation methods]
(1) Coating film resistance value The above-mentioned cold-rolled steel sheet panel (SPCC-SD) subjected to zirconium-based metal oxide film treatment or zinc phosphate treatment as a non-phosphate treatment film is used to adhere the back surface to a cloth. Masking was performed with a tape or the like, and electrodeposition coating was performed at a constant coating voltage and coating time such that a film thickness of 15 μm was obtained.
R = V × S × (1 / Af−1 / Ai)
In the formula, R: coating film resistance (kΩ · cm ² )
V: Voltage between electrodes (V)
Ai: Initial current value (A)
Af: Final current value (A)
S: Area to be coated (cm ² )

(2) Throwing property Throwing property was evaluated by painting on a box-shaped structure produced using four panels. That is, as shown in FIG. 1, a non-phosphate treatment is applied to a panel (a) having an 8 mm diameter through hole at a position 50 mm from the bottom of the panel and 35 mm from both sides, and a panel (b) having no hole. Using the above-mentioned cold-rolled steel sheet panel (SPCC-SD) subjected to zirconium-based metal oxide film treatment or zinc phosphate treatment as a film, a box-shaped structure combined as shown in FIGS. 2 and 3 was produced. (A to G planes in order from the counter electrode side, and the non-counter electrode side is referred to as the H plane). As shown in FIG. 4, this box-like structure is immersed in an electrodeposition coating container, and the box-like structure is used as a cathode and the counter electrode plate is used as an anode. Painted. After painting, the box-shaped structure was disassembled, each panel was washed with water, baked at 170 ° C. for 20 minutes, and the film thickness from the A surface to the H surface was measured. The throwing power is evaluated by the ratio of the G-plane film thickness to the A-plane film thickness (G / A). The larger this value, the better the throwing power.

(3) Salt spray resistance A scratch that reaches the substrate on the electrodeposition coating film is put on a non-phosphate treated test plate with a cutter knife, and the rust width is measured after 840 hours under 35 ° C., 5 wt% salt spray. did. The smaller the rust width, the better the performance.

(4) Salt water immersion test A test plate with non-phosphate treatment was immersed in salt water at 50 ° C. and 5% by weight for 840 hours, then washed with water and air-dried so that the cellophane adhesive tape does not contain bubbles on the entire test surface. After pasting, the tape was peeled off, and the ratio of the coating film peeling area to the whole test surface was measured. The smaller the peeled area, the better the performance.

  Table 6 shows the coating performance evaluation results of Examples 1 to 6 and Comparative Examples 1 and 2.

  As is apparent from the results of Table 6, Examples 1 to 6 using lactic acid and zirconium or titanium metal salt were performed on a zirconium-based metal oxide film (non-phosphate-based) -treated film or on a zinc phosphate-treated film. In any of the cases, it was confirmed that the throwing power and the antirust property were superior to those of Comparative Examples 1 and 2.

  The cationic electrodeposition coating composition of the present invention can be applied not only on a conventional phosphate-treated film, but also on a non-phosphate-based film, with excellent paint throwing power and rust resistance. It is possible to provide film quality and can therefore be used favorably for automotive parts with many complex bag structures.

Claims (3)

  (A) a cationic amine-modified epoxy resin (base) obtained by cationizing an amine-modified epoxy resin obtained by reacting an amine with an epoxy resin, (B) a blocked polyisocyanate (curing agent), and (C) lactic acid A coating method comprising using a cationic electrodeposition coating composition containing a metal salt obtained from a transition metal.   (A) The cationic amine-modified epoxy resin (base) epoxy resin is an epoxy resin obtained by reacting a glycidyl ether of a polyol, a glycidyl ether of a dihydric phenol, and a dihydric phenol. Item 2. The coating method according to Item 1.   (C) The coating method according to claim 1 or 2, wherein the transition metal constituting the metal salt is zirconium or titanium.