JP2017203189A - Method for coating cationic electrodeposition coating composition to coated matter subjected to zirconium chemical conversion treatment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for coating a cationic electrodeposition coating composition to a coated matter subjected to a zirconium chemical conversion treatment which can achieve all of throwing power, smoothness of a coating film, film thickness retention, and gas pinhole resistance, at high level.SOLUTION: A method for coating a cationic electrodeposition coating composition to a coated matter subjected to a zirconium chemical conversion treatment coats a cationic electrodeposition coating composition to the coated matter, which contains an amine-modified epoxy resin (A) and a block isocyanate curing agent (B) as components, has a coating film resistance (R3) when the film thickness after the coating film obtained by uniformly coated to the coated matter has been sintered reaches 3 μm of 10-200 kΩ cm, and a coating film resistance (R6) when the film thickness reaches 6 μm of 40-400 kΩ cm.SELECTED DRAWING: None

Description

  The present invention relates to a method for applying a cationic electrodeposition coating composition to a coated article that has undergone a zirconium conversion coating treatment. The present invention relates to a method for maintaining all of the smoothness of the film, the film thickness retention, and the gas pinhole resistance at a high level.

  Cationic electrodeposition coating is performed by immersing an object to be coated such as an automobile body in a cationic electrodeposition coating composition as a cathode and applying a voltage. This method is widely adopted as the most suitable method for the undercoating of an object to be coated such as an automobile body having a large and complicated shape.

  For the object to be coated made of a metal material, for example, a material subjected to a chemical conversion film treatment with zinc phosphate is used for the purpose of improving corrosion resistance. However, the chemical conversion film treatment with zinc phosphate uses a processing agent with extremely high reactivity, so that a lot of steps and labor are required for the treatment of the waste liquid, and there are big problems in terms of workability and cost. Yes.

  On the other hand, chemical conversion film treatment with a zirconium compound is used for the purpose of improving the corrosion resistance of the same substrate. The chemical conversion film treatment with a zirconium compound does not cause a problem like the chemical conversion film treatment with zinc phosphate described above, but the coated material subjected to such treatment has poor adhesion to the electrodeposition paint, and the chemical conversion treatment. Since the film thickness is thin, there has been a problem that throwing power performance (performance of forming a coating film to every corner of the object to be coated) is lowered.

On the other hand, in a method for applying a cationic electrodeposition coating composition to a coating object that has been subjected to a chemical conversion film treatment with a zirconium compound, a thickness of 15 μm formed by applying a voltage for 180 seconds at a coating temperature of 30 ° C. A method has been proposed in which the film resistance of the electrodeposition coating film is 900 to 1600 kΩ · cm ² (see Patent Document 1). This method is effective for improving throwing power, but there is room for improvement in terms of coating film smoothness, film thickness retention, and gas pinhole resistance.

JP 2010-95678 A

  The present invention was devised in view of the current state of the prior art, and the object of the present invention is to provide a throwing power in a method of coating a cationic electrodeposition coating composition on a coated article that has undergone a zirconium conversion coating treatment. Another object of the present invention is to provide a method capable of achieving all of the smoothness of the coating film, the film thickness retention, and the gas pinhole resistance at a high level.

  In order to achieve the above-mentioned object, the present inventors have intensively studied the conditions of a cationic electrodeposition coating composition suitable for use in coating a coated article that has undergone a zirconium conversion coating treatment. Among cationic electrodeposition coating compositions containing resin and blocked isocyanate curing agent resin as essential constituents, the coating resistance at the very beginning of the electrodeposition process with a thin electrodeposition coating is relatively low. By selecting and using a cationic electrodeposition coating composition satisfying that the increase in coating resistance at a very early stage of the electrodeposition process is within a specific range, the throwing power and smoothness of the coating are improved. The inventors have found that all of the properties, film thickness retention, and gas pinhole resistance can be maintained at a high level, and the present invention has been completed.

That is, the present invention has the following configurations (1) to (4).
(1) In a method of applying a cationic electrodeposition coating composition to an article subjected to a zirconium conversion coating treatment, an amine-modified epoxy resin (A) and a blocked isocyanate curing agent resin (B) are included as constituent components, and When the film thickness after baking of the coating film obtained by uniformly coating the coating material reaches 3 μm, the coating film resistance (R3) is 10 to 200 kΩ · cm ² and reaches 6 μm. A method comprising applying a cationic electrodeposition coating composition satisfying a coating film resistance (R6) of 40 to 400 kΩ · cm ² .
(2) Coating film resistance (when the film thickness after baking of the coating film obtained by uniformly applying the cationic electrodeposition coating composition on the object to be coated, calculated by the following formula, reaches 3 μm ( (3) The method according to (1), wherein the rate of increase in coating film resistance (R6) when reaching 6 μm from R3) is 50 to 700% / μm.
Increase rate (% / μm) = ((R6) / (R3)) × 100/3
(3) The method according to (1) or (2), wherein the cationic electrodeposition coating composition further comprises a pigment paste.
(4) The method according to any one of (1) to (3), wherein the object to be coated is an iron-based metal substrate, an aluminum-based metal substrate, or a zinc-based metal substrate.

  According to the coating method of the present invention, a cationic electrodeposition coating composition having a specific essential component and controlling the coating film resistance and the increase in the coating at a very early stage of the cationic electrodeposition process within a specific range is selected. Therefore, not only the wrapping property but also the smoothness of the coating film, the film thickness retention, and the gas pin resistance when the cationic electrodeposition coating composition is applied to the coated material subjected to the zirconium chemical conversion treatment. Hall property can also be maintained at a high level.

FIG. 1 is a schematic diagram illustrating a method for evaluating throwing power. FIG. 2 is a schematic diagram for explaining a throwing power evaluation method. FIG. 3 is a schematic diagram for explaining a throwing power evaluation method. FIG. 4 is a schematic diagram for explaining a throwing power evaluation method.

  In the coating method of the present invention, when a cationic electrodeposition coating composition is applied to an article subjected to zirconium conversion coating treatment, the electrodeposition process is extremely difficult among cationic electrodeposition coating compositions having specific components. It is characterized by selecting and using a cationic electrodeposition coating composition in which the coating film resistance and the increase of the coating in the initial stage are in a specific range. Hereinafter, the details of the method of the present invention will be described.

[Substrate of substrate]
The object to be coated by the coating method of the present invention is not particularly limited as long as it is a metal substrate that can be cationically electrodeposited. For example, an iron-based metal substrate, an aluminum-based metal substrate, or a zinc-based metal substrate. Can be used. According to the coating method of the present invention, the problems of throwing power, smoothness of the coating film, and film thickness retention that occur when the object to be coated is an iron-based metal substrate and an aluminum-based metal substrate are solved. These problems peculiar when the object to be coated is a zinc-based metal substrate and the problem of gas pinhole resistance can be solved.

[Zirconium conversion coating treatment]
In the coating method of the present invention, the article is preliminarily subjected to a zirconium conversion coating treatment, and a cationic electrodeposition coating is performed on the article subjected to the zirconium conversion coating treatment. Zirconium conversion coating treatment is a treatment in which a zirconium conversion treatment agent is brought into contact with the object to be coated to form a chemical conversion film on the surface of the object to be coated. In order to improve the corrosion resistance and film adhesion of the object to be coated. Applied.

  Zirconium conversion coating treatment is widely used today because it has less environmental impact than zinc phosphate conversion coating treatment. Various zirconium chemical conversion treatment agents have been proposed in the past, but in general, a fluorine-containing compound such as a zirconium-containing compound such as fluorinated zirconic acid or hydrofluoric acid for stabilizing the treatment liquid. A compound and other optional components are dissolved in water. Recently, a zirconium chemical conversion treatment agent that does not contain a fluorine-containing compound has also been proposed in response to a tendency to tighten regulations on the fluorine content in wastewater. In the present invention, not only these zirconium chemical conversion treatment agents but also any conventionally known zirconium chemical conversion treatment agents can be used.

By bringing such a zirconium chemical conversion treatment agent into contact with the object to be coated, a chemical conversion film is formed on the surface of the object to be coated. The method for bringing the zirconium chemical conversion treatment agent into contact with the article to be coated is not particularly limited, and generally includes an immersion method, a spray method, a roll coating method, a pouring method and the like. The processing temperature and processing time are also not particularly limited, and are generally 20 to 80 ° C. and 2 to 1000 seconds. The content of zirconium in the formed chemical conversion coating is generally 10 mg / m ^{2 to 1} g / m ² .

  Since the chemical conversion treatment film is thinner than the zinc phosphate chemical conversion treatment, the resistance of the chemical conversion treatment film itself is low. Therefore, in the zirconium chemical conversion treatment, the absolute value and increase of the coating resistance value in the initial stage of electrodeposition have a greater influence on the throwing power of the electrodeposition coating and the appearance of the coating. Based on this finding, the present invention proposes a range of coating resistance values in the initial stage of electrodeposition suitable as a cationic electrodeposition coating composition to be used for an article subjected to zirconium chemical conversion treatment.

  The cationic electrodeposition coating composition used in the coating method of the present invention comprises an amine-modified epoxy resin (A) and a blocked isocyanate curing agent resin (B) as essential components, and the coating composition at the very initial stage of the cationic electrodeposition process. The film resistance and its increase are selected from a specific range.

[Amine-modified epoxy resin (A)]
The amine-modified epoxy resin (A) is an epoxy resin modified with an amine, and its epoxy skeleton has an average of two epoxy groups per molecule and has a number average molecular weight of 400 to 2400, particularly 1000 to 1600. It is preferable that Specific examples include glycidyl ethers of polyphenols having two phenolic hydroxyl groups in one molecule, or polycondensates thereof. Preferred polyphenols include resorcin, hydroquinone, 2,2-bis- (4-hydroxy Phenyl) -propane, 4,4′-dihydroxybenzophenone, 1,1-bis- (4-hydroxyphenyl) -methane, 1,1-bis- (4-hydroxyphenyl) -ethane, 4,4′-dihydroxybiphenyl Among them, 2,2-bis- (4-hydroxyphenyl) -propane, so-called bisphenol A is particularly preferable. Furthermore, a glycidyl ether of a diol having two alcoholic hydroxyl groups in one molecule or a polycondensate thereof can be mentioned. Preferred diols include ethylene glycol, propylene glycol, 1,4-butanediol, 1,6- Examples include, but are not limited to, low molecular diols such as hexanediol, neopentyl glycol, diethylene glycol, triethylene glycol, and 1,4-cyclohexanediol, and oligomer diols such as polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. is not.

  Further, in order to adjust the amine-modified epoxy resin to a suitable molecular weight, it is necessary to cause the above compound to undergo a high molecular weight reaction with a linking agent. Preferred linking agents include the above polyphenols and dicarboxylic acids having two carboxyl groups in one molecule, such as succinic acid, adipic acid, azelaic acid, sebacic acid, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, isophthalic acid, Examples thereof include dimer acid, carboxyl group-containing butadiene polymer, and butadiene / acrylonitrile copolymer. The linking agent containing an amino group includes diamines such as ethylamine, n-propylamine, isopropylamine, n-butylamine, isobutylamine, monoethanolamine, dimethylaminopropylamine, diethylaminopropylamine, or hexamethylenediamine. Examples thereof include diamines obtained by secondaryizing each amino group with a monoepoxy compound. Further, a diisocyanate can be linked to a hydroxyl group generated by ring opening of an epoxy group. Particularly preferably, it can be achieved by a method in which the glycidyl ether of the polyphenol or the glycidyl ether of the diol or a mixture thereof is subjected to a ligation reaction with the polyphenol. is there.

  Epoxy ends are based on amination, but part of the epoxy group is added as necessary with a compound having one carboxyl group in one molecule or a compound having one phenolic hydroxyl group in one molecule. The basicity of the resin can be adjusted by reaction. Examples of the aminating agent include dimethylamine, diethylamine, dibutylamine, diethanolamine, N-methylethanolamine, N-ethylethanolamine, diketimine obtained by reacting a primary amino group of diethylenetriamine with a ketone, or a mixture thereof. it can. Particularly preferred is the case where alkanolamines having a hydroxyl group are used, and the reaction is preferably carried out at 50 to 130 ° C. without solvent or in the presence of a solvent.

[Block isocyanate curing agent resin (B)]
The blocked isocyanate curing agent resin (B) is composed of a polyisocyanate and a blocking agent that blocks the polyisocyanate. Polyisocyanates include 2,4- or 2,6-toluene 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- (isocyanatemethyl) -norbornane, 3- or 4-isocyanatomethyl-1-methyl Cyclohexyl isocyanate, m- or p-xylene diisocyanate, m- or p-tetramethylxylene diisocyanate, and Biuret-modified products or isocyanurate modified product of cyanate, and the like, but not limited thereto. These can be used alone or in a mixture.

  A part of the polyisocyanate can be reacted with a polyol. Examples thereof include ethylene glycol, propylene glycol, 1,6-hexanediol, neopentyl glycol, diethylene glycol, triethylene glycol, 1,4-cyclohexanediol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, polylactone diol, Examples include trimethylolethane, trimethylolpropane, pentaerythritol, or a mixture thereof.

  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, carbides such as diethylene glycol monoethyl ether and diethylene glycol monobutyl ether. Toll compounds, oxime compounds such as acetone oxime, methyl ethyl ketone oxime, cyclohexanone oxime, lactam compounds such as ε-caprolactam, phenol compounds such as phenol, cresol and xylenol, active methylene group-containing compounds such as ethyl acetoacetate and diethyl malonate Is mentioned.

  The reaction between the polyisocyanate and the blocking agent is preferably performed at 50 to 130 ° C. in the absence of a solvent or in the presence of a solvent that does not react with an isocyanate group.

  Although the weight ratio of the amine-modified epoxy resin (A) / block isocyanate curing agent resin (B) in the cationic electrodeposition coating composition used in the coating method of the present invention is not particularly limited, It is preferable that it is 55-75 / 45-25.

[Other ingredients]
The cationic electrodeposition coating composition used in the coating method of the present invention is a pigment paste, if desired, in addition to the essential components of the amine-modified epoxy resin (A) and the blocked isocyanate curing agent resin (B), Any known additive components such as plasticizers, surfactants, UV absorbers and antioxidants can be included.

  Pigment paste is a vehicle in which pigment dispersion resin is water-solubilized, and additives such as antifoaming agents, surfactants, and anti-fogging agents are blended as needed, with extender pigments, colored pigments, antirust pigments, curing catalyst pigments, etc. The mixture is mixed and the pigment is dispersed through a disperser.

  As the pigment dispersion resin, a tertiary amine type in which the amine-modified epoxy resin (A) is neutralized with formic acid, acetic acid, lactic acid, sulfamic acid, methanesulfonic acid, or the like, or a quaternary ammonium salt type in which the epoxy terminal is quaternized is used. it can. As extender pigments, kaolin, talc, aluminum silicate, calcium carbonate, mica, clay, silica, etc. can be used. As coloring pigments, carbon black, titanium white, bengara, etc. can be used. As anticorrosive pigments, phosphoric acid can be used. Zinc, iron phosphate, aluminum phosphate, calcium phosphate, aluminum tripolyphosphate, zinc molybdate, aluminum molybdate, calcium molybdate, bismuth compounds, etc. can be used, and tin compounds, bismuth compounds, etc. can be used as curing catalyst pigments .

  Although the weight ratio of the total resin weight (A + B) / pigment paste in the cationic electrodeposition coating composition used in the coating method of the present invention is not particularly limited, it is preferably 70-80 / 30-20.

  Formic acid, acetic acid, lactic acid, sulfamic acid, methanesulfonic acid, etc. are suitable as the neutralizing acid necessary for emulsifying the resin mixed with the amine-modified epoxy resin (A) and the blocked isocyanate curing agent resin (B). A mixture of these can also be used.

  The cationic electrodeposition coating composition used in the coating method of the present invention is obtained by diluting the emulsion with deionized water and optionally mixing the pigment paste with stirring. The solid content concentration of the coating composition is preferably adjusted to around 20%.

[Film resistance]
In the coating method of the present invention, a cationic electrodeposition coating composition having the above-described constituent components is applied to an article subjected to the zirconium conversion coating treatment. As the cationic electrodeposition coating composition, such an article to be coated is applied. The coating film resistance (R3) when the film thickness after baking of the coating film obtained by uniformly coating with respect to 3 μm reaches 10 to 200 kΩ · cm ² and the coating when the film thickness reaches 6 μm A film having a film resistance (R6) satisfying 40 to 400 kΩ · cm ² is selected and used. Furthermore, in the coating method of the present invention, when the film thickness after baking of the coating film obtained by uniformly coating the object to be coated reaches 6 μm from the coating film resistance (R3) when it reaches 3 μm. The coating film resistance (R6) increase rate (that is, the increase rate (% / μm) = ((R6) / (R3)) × 100/3) is selected to satisfy 50 to 700% / μm. And preferably used. The film resistance at film thicknesses of 3 μm and 6 μm corresponds to the film resistance at the very initial stage of the cationic electrodeposition process. The present inventor uses a cationic electrodeposition coating composition in which this very initial coating resistance is in a relatively low specific range, and further, this very early increase in coating resistance is in a specific range. As a result, it has been found that all of the throwing power, the smoothness of the coating film, the film thickness retaining property, and the gas pinhole resistance can be achieved at a high level in the coating on the object subjected to the zirconium conversion coating treatment.

In the present invention, the cationic electrodeposition coating composition used has a coating film resistance (R3) of 10 to 200 kΩ · cm ² , preferably 15 when the film thickness after baking of the coating film reaches 3 μm as described above. It is necessary to satisfy that it is ˜190 kΩ · cm ² , more preferably 15 to 180 kΩ · cm ² . When the coating film resistance (R3) when the film thickness reaches 3 μm is less than the above lower limit, the finally formed coating film generally tends to have poor circulation properties. On the other hand, when the coating film resistance (R3) when the film thickness reaches 3 μm exceeds the upper limit, the finally formed coating film is inferior in the smoothness of the coating film.

In the present invention, the cationic electrodeposition coating composition used has a coating film resistance (R6) of 40 to 400 kΩ · cm ² when the film thickness after baking of the coating film reaches 6 μm as described above, preferably Needs to satisfy the condition of 45 to 390 kΩ · cm ² , more preferably 50 to 380 kΩ · cm ² . When the coating film resistance (R6) when the film thickness reaches 6 μm is less than the lower limit, the finally formed coating film is inferior in throwing power. On the other hand, when the coating film resistance (R6) when the film thickness reaches 6 μm exceeds the above upper limit, the finally formed coating film has the smoothness of the coating film, the film thickness retention, and the (coating object) When Z is a zinc-based metal substrate, the gas pinhole resistance is poor.

Furthermore, in the present invention, the cationic electrodeposition coating composition to be used is calculated from the coating film resistance (R3) when the film thickness after baking of the coating film reaches 3 μm, calculated by the following formula as described above. The rate of increase in coating film resistance (R6) when reaching 6 μm is preferably 50 to 700% / μm, more preferably 55 to 600% / μm, and still more preferably 60 to 500% / μm. It is preferable to satisfy.
Increase rate (% / μm) = ((R6) / (R3)) × 100/3
Limiting the increase rate to less than the lower limit is extremely difficult in the initial stage of the electrodeposition process where the film thickness is thin as described above. On the other hand, if the increase rate exceeds the upper limit, the smoothness of the coating film, It tends to be inferior in film thickness retention and gas pinhole resistance.

  In order to actually use a cationic electrodeposition coating composition whose coating film resistance is in the above-mentioned range when the film thickness reaches 3 μm and 6 μm, adjust the physical property values of the uncured coating film that has been deposited. It is preferable to prepare a cationic electrodeposition coating composition that has been confirmed to satisfy the condition of coating film resistance in advance, and select and use it. Specifically, the hardness of the deposited coating, the viscoelasticity of the resin component of the deposited coating, the basicity, the type and amount of the solvent contained in the deposited coating, the pigment concentration of the deposited coating, etc. When the physical property value of the coating film in the state is adjusted, the coating film resistance fluctuates up and down. Therefore, it is possible to obtain a cationic electrodeposition coating material satisfying the coating film resistance condition by experimentally adjusting and checking these. .

  In these adjustments, generally, when the deposited coating is adjusted in a soft direction, the ionic substance easily moves in the deposited coating, the coating resistance is lowered, and conversely, the deposited coating is adjusted in a hard direction. Then, it becomes difficult for the ionic substance to move in the deposited coating film, and the coating film resistance tends to increase, and the viscoelasticity of the resin is low, the basicity is high, and the amount of the solvent is large. In addition, when the pigment concentration is adjusted in the lower direction, the resistance of the coating film is lowered. Conversely, the viscoelasticity of the resin is higher, the basicity is lower, the solvent amount is lower, and the pigment concentration is higher. When adjusted, the coating film resistance tends to increase. Therefore, the types and amounts of the components of the cationic electrodeposition coating composition are adjusted in consideration of these tendencies. In general, the hardness of the deposited coating film can be adjusted by the bath liquid temperature (26 to 32 ° C.), the glass transition point of the resin component, the amount of solvent, and the pigment concentration. The viscoelasticity of the resin can be generally adjusted by the bath liquid temperature (26 to 32 ° C.), the glass transition point of the resin component, and the molecular weight. Furthermore, the basicity of the resin can be generally adjusted by the amine species and amount of the amine-modified resin. In addition, generally the ratio of the increase in coating-film resistance by the increase in film thickness from 3 micrometers to 6 micrometers can be adjusted with the hardness of a precipitation coating film. However, these tendencies do not all follow this general trend, and may change with a multi-dimensional function, so fluctuations in coating resistance with actual changes in the type and amount of ingredients It is preferable to make adjustments after grasping the trends individually and specifically.

[Cation electrodeposition coating]
In the method of the present invention, the cationic electrodeposition coating may be performed by immersing the article to be coated in the cationic electrodeposition coating composition as a cathode and applying a voltage as usual. The conditions for electrodeposition coating are not particularly limited, but generally the applied voltage is about 50 to 500 V, and the energization time is about 30 seconds to 10 minutes. Moreover, it is preferable that the bath liquid temperature of the cationic electrodeposition coating composition to be used is about 26-32 degreeC. After electrodeposition coating, the object to be coated is washed with water to wash off any excess coating composition remaining on the surface. Thereafter, baking is performed to cure the coating film formed on the surface of the object to be coated. The film thickness after baking of the final coating film obtained by cationic electrodeposition coating is generally 5 to 100 μm.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited only to these Examples.

(Production of amine-modified epoxy resin A1)
An amine-modified epoxy resin A1 was produced according to the raw material composition described in Table 1. Specifically, the raw materials (1), (2), (3), and (4) are put into a 2 liter flask equipped with a stirrer, a thermometer, and a cooling pipe, and stirring is started. The mixture was kept warm for 3 hours, and then the raw material (5) was added and kept at 150 ° C. for 2 hours, and then cooled to 80 ° C. while gradually adding the raw material (6). Next, the raw materials (7), (8) and (9) were sequentially added, and kept at 100 ° C. for 4 hours to obtain an amine-modified epoxy resin A1 having a solid content of 85% by weight and a number average molecular weight of 1600.

(Production of amine-modified epoxy resin A2)
An amine-modified epoxy resin A2 was produced according to the raw material composition described in Table 2. Specifically, the raw materials (1), (2), (3), and (4) are put into a 2 liter flask equipped with a stirrer, a thermometer, and a cooling pipe, and stirring is started. The mixture was kept warm for 3 hours, and then the raw material (5) was added and kept at 150 ° C. for 2 hours, and then cooled to 80 ° C. while gradually adding the raw material (6). Next, the raw materials (7), (8) and (9) were sequentially added, and kept at 100 ° C. for 4 hours to obtain an amine-modified epoxy resin A2 having a solid content of 85% by weight and a number average molecular weight of 2200.

(Production of blocked isocyanate curing agent resin B1)
A blocked isocyanate curing agent resin B1 was produced according to the raw material composition described in Table 3. Specifically, the raw materials (1), (2), (3), (4) and (5) are put into a 2 liter flask equipped with a stirrer, a thermometer and a cooling pipe, and stirring is started. The temperature was raised while paying attention to heat generation, and the temperature was kept at 100 ° C. for 3 hours to obtain a blocked isocyanate curing agent resin B1 having a solid content of 85% by weight.

(Production of blocked isocyanate curing agent resin B2)
A blocked isocyanate curing agent resin B2 was produced according to the raw material composition described in Table 4. Specifically, the raw materials (1), (2), (3), (4), (5), (6) are charged into a 2 liter flask equipped with a stirrer, a thermometer, and a cooling pipe, Stirring was started, the temperature was raised while paying attention to heat generation, and the mixture was kept at 100 ° C. for 3 hours to obtain a blocked isocyanate curing agent resin B2 having a solid content of 85% by weight.

(Production of pigment dispersion resin P1)
Pigment dispersion resin P1 was manufactured according to the raw material composition shown in Table 5. Specifically, the raw materials (1), (2), (3), and (4) were put into a 2 liter flask equipped with a stirrer, a thermometer, a cooling pipe, and a decompression device, and stirring was started. After incubating at 150 ° C. for 4 hours, the mixture was cooled to 100 ° C. and the raw material (5) was charged. Further, after cooling to 50 ° C., the raw material (6) was added dropwise over 2 hours while maintaining the temperature at 50 ° C. while paying attention to heat generation. After keeping the temperature at 100 ° C. for 4 hours, the mixture was cooled to 90 ° C., depressurized (7) to remove the solvent, and the raw materials (8), (9), and (10) were sequentially added. The mixture was kept at 80 ° C. for 2 hours to obtain a pigment dispersion resin P1 having a solid content of 85% by weight.

(Production of pigment dispersion resin P2)
According to the raw material composition shown in Table 6, pigment dispersion resin P2 was produced. Specifically, in a 2 liter flask equipped with a stirrer, a thermometer, and a cooling pipe, raw materials (1), (2), (3), (4), (5), (6), (7) Was added and stirring was started. The temperature was raised while paying attention to heat generation, and the mixture was kept at 120 ° C. for 4 hours to obtain a pigment dispersion resin P2 having a solid content of 85% by weight.

(Manufacture of emulsion)
Emulsions E1 to E11 were produced according to the raw material composition described in Table 7. Specifically, in a 3 liter flask equipped with a stirrer, a thermometer, a cooling pipe and a decompression device, the raw materials (1), (2), (3), (4), (5), (6), (7), (8), (9), (10) were added and stirring was started. The temperature was raised to 80 ° C. and the pressure was reduced (11) to remove the solvent. Subsequently, the raw material (12) was gradually added to obtain emulsions E1 to E11 having a solid content of 35% by weight.

(Manufacture of pigment paste)
Pigment pastes D1 and D2 were produced according to the raw material composition described in Table 8. Specifically, the raw materials (1), (2), and (3) were put into a container, and stirring was started. Raw materials (4) and (5) were slowly added and dissolved. Next, the raw materials (6), (7), (8), (9), (10), and (11) are added and dispersed uniformly at room temperature for 1 hour with a horizontal sand mill until the particle size is 10 μm or less. Pigment pastes D1 and D2 having a solid content of 65% by weight were obtained.

(Manufacture of cationic electrodeposition coating composition)
Cationic electrodeposition coating compositions a to g used in Examples and cationic electrodeposition coating compositions h to k used in Comparative Examples were produced according to the formulations shown in Table 9. Specifically, each emulsion was weighed in a container, deionized water was added under stirring, and then each pigment paste was added to obtain each cationic electrodeposition coating composition having a solid content of 20% by weight. Table 9 also shows the characteristics (solid content, MEQ, total solvent amount) of each cationic electrodeposition coating composition.

(Preparation of the object to be coated)
Cold-rolled steel plates (SPC-SD), galvanized steel plates (GA), and 6000 series aluminum (Al) were prepared as the objects to be coated. All of these objects to be coated were manufactured by Nippon Test Panel Co., Ltd., and the size was 70 mm × 150 mm × 0.8 mm.

(Zirconium conversion coating treatment)
Next, zirconium conversion coating treatment was performed on these objects to be coated according to the following procedure.

A thermometer of the silane condensation reaction product, stirrer, were charged ethanol 200g, deionized water 200g with respect to the cooling tube, a 1 liter flask equipped with a nitrogen inlet device was subjected to stirring. While nitrogen was blown into the gas phase and stirring was continued, 110 g of 3-aminopropyltriethoxysilane and 10 g of bis (triethoxysilyl) ethane were added, and the temperature was raised to 60 ° C. after a uniform solution was obtained. After reacting at 60 ° C. for 6 hours, the fraction was removed and heated to 120 ° C. while boiling point was changed to propylene glycol monomethyl ether. Subsequently, after cooling to 60 degreeC, it concentrated by distillation under reduced pressure and the silane condensation reaction product of the 40% of non volatile matter solution was obtained.

Preparation of metal surface treatment composition Using the silane condensation reaction product obtained as described above, ammonium hexafluorozirconate and magnesium nitrate, the metal element equivalent concentration of zirconium is 100 ppm, the metal element equivalent of magnesium The metal surface treatment composition was prepared so that the concentration was 1000 ppm and the solid content concentration of the silane condensation reaction product was 200 ppm.

  Each coated object was immersed in a commercial degreasing solution at 40 ° C. for 2 minutes for degreasing treatment, and then subjected to a 30-second water washing treatment with tap water. Next, each coated object after the water washing treatment was immersed in a metal surface treatment composition adjusted to pH 4.0 and a temperature of 45 ° C. for 120 seconds. The pH was adjusted with nitric acid or ammonia. Each article to be coated after the immersion treatment was washed with tap water for 30 seconds and further subjected to a washing treatment with ion-exchanged water for 30 seconds. Subsequently, it dried at 80 degreeC for 5 minute (s) with the hot-air drying furnace, and obtained each to-be-coated object which performed the zirconium chemical conversion film process.

Examples 1-9 and Comparative Examples 1-4
The coating film when the film thickness reaches 3 μm and 6 μm by applying the cationic electrodeposition coating composition as shown in Table 9 as the cationic electrodeposition coating composition to the coated article subjected to the zirconium conversion coating treatment. Resistance was measured and the results are shown in Table 10. In addition, the specific measurement procedure of coating-film resistance is as follows.

[Film resistance]
The back surface of the article to be coated with zirconium conversion coating is masked with gum tape or the like. The electrode plate / coating object ratio is set to 1/4 and the distance between the electrodes is set to 150 mm, and the object to be coated is completely immersed in the cationic electrodeposition coating composition. Coating is performed in units of 1 second with a load voltage of 30 V under stirring, and the coating film resistance [kΩ · cm ² ] when the coating film reaches a predetermined thickness (3 μm and 6 μm) is obtained from the equation (1).
R = V × S × (1 / Af−1 / Ai) (1)
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 )

As is apparent from Table 10, Examples 1 to 9 all have a coating film resistance in the range of 18 to 182 kΩ · cm ^{2 at} a film thickness of 3 μm, and a coating film resistance at a film thickness of 6 μm from 52 to 395 kΩ · cm. ² and both are within the scope of the present invention. On the other hand, in any of Comparative Examples 1 to 4, at least one of the coating film resistances at a film thickness of 3 μm and 6 μm is outside the scope of the present invention.

  Next, using the cationic electrodeposition coating compositions of Examples 1 to 9 and Comparative Examples 1 to 4, the throwing power, the smoothness of the coating film, the film thickness retention, and the gas pinhole resistance are as follows. The properties (only the zinc-based metal substrate) were evaluated, and the results are shown in Table 11.

[Throwing power]
The throwing power was evaluated by the four-box method. That is, as shown in FIG. 1, zirconium conversion coating treatment was 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. As shown in FIGS. 2 and 3, a combination (in order from the counter electrode surface side, A surface, B surface, C surface... Non-counter electrode surface side is referred to as H surface), 4 sheets A box is used which is arranged in parallel with an interval of 20 mm with both sides and bottoms sealed with an insulator such as an adhesive tape. As shown in FIG. 4, the box is immersed in a cationic electrodeposition coating container containing the cationic electrodeposition coating composition of each example or comparative example, and the cationic electrodeposition coating composition enters the box only from each through hole. To do. Next, each of the objects to be coated is electrically connected and arranged so that the distance between the object to be coated (surface A) closest to the counter electrode and the counter electrode is 150 mm. Cathode electrodeposition coating was performed by applying a voltage with the box as a cathode and the counter electrode as an anode. The energization method may be a method of boosting to a predetermined voltage in 5 to 30 seconds (soft start) or normal energization, but this time, docan energization was adopted. After painting, the box is disassembled, each article to be coated is washed with water, baked at 170 ° C. for 20 minutes, and the film thickness from the A side to the H side is measured. The throwing power is evaluated based on the ratio (G / A) of the G-face film thickness (unit μm) to the A-face film thickness (unit μm), and the larger the value, the better the throwing power.
Immersion depth: 9 cm, load voltage: 200 V
Evaluation criteria ○: G / A is 55% or more Δ: G / A is 35% or more and less than 55% ×: G / A is less than 35%

[Smoothness of coating film]
Cathodic electrodeposition coating is performed on the article subjected to the zirconium conversion coating treatment at a coating voltage at which the film thickness of the cured coating film after baking is 20 μm. After washing with water, baking is performed at 170 ° C. for 20 minutes to obtain a cured coating film. About the obtained coating film, the smoothness (Ra) of a coating film is measured using the surface roughness meter SJ-301 by Mitutoyo Corporation.
Measurement conditions Cut-off: 2.5mm
Feeding speed: 0.5 mm / sec Evaluation criteria ○: Ra is 0.25 or less Δ: Ra is more than 0.25 and less than 0.31 ×: Ra is 0.31 or more

[Thickness retention]
A cationic electrodeposition coating composition aged at 30 ° C. when a cationic electrodeposition coating is performed on a substrate subjected to a zirconium conversion coating treatment under conditions of a load voltage of 200 V and an energization time of 3 minutes (30 seconds slow pressure increase). About a thing, the film thickness retention on the 7th day with respect to the film thickness on the 1st day after a bathing is evaluated.
Evaluation criteria ○: Film thickness retention 85% or more Δ: Film thickness retention 70% or more and less than 85% ×: Film thickness retention 70% or less

[Gas pinhole resistance]
Zinc-based plated steel sheet (GA) that has been subjected to zirconium conversion coating treatment with a load voltage of 230V and an energization time of 3 minutes (30 seconds slow pressure increase) is subjected to cationic electrodeposition coating, washed with water, and baked at 170 ° C for 20 minutes to cure. A coating film is obtained. About the obtained coating film, the number of generated gas pinholes is evaluated. In addition, since gas pinhole resistance is a phenomenon peculiar to a zinc-type metal base material, it did not evaluate with respect to an iron-type and aluminum-type metal base material.
Evaluation criteria ○: Gas pinholes do not occur in the coating film Δ: Number of gas pinholes in the coating film is 1 to 20 ×: Number of gas pinholes in the coating film is 21 or more

  As is apparent from Table 11, Examples 1 to 9 in which the coating film resistances at the film thicknesses of 3 μm and 6 μm are all within the scope of the present invention include throwing power, smoothness of the coating film, film thickness retention, and Excellent performance in gas pinhole resistance. On the other hand, Comparative Examples 1 to 4 in which at least one of the coating film resistances at the film thicknesses of 3 μm and 6 μm is outside the scope of the present invention, the throwing power, the smoothness of the coating film, the film thickness retention, and the resistance The performance of at least one of the gas pinhole properties was inferior.

  Since the method of the present invention uses a cationic electrodeposition coating composition in which the coating film resistance of the coating material in the very early stage of the cationic electrodeposition process is controlled within a specific range, On the other hand, the throwing power, the smoothness of the coating film, the film thickness retention and the gas pinhole resistance can be maintained at a high level, which is extremely useful.

Claims (4)

In a method of applying a cationic electrodeposition coating composition to an article subjected to a zirconium conversion coating treatment, an amine-modified epoxy resin (A) and a blocked isocyanate curing agent resin (B) are included as constituents, and the article is coated On the other hand, when the film thickness after baking of the coating film obtained by uniform coating reaches 3 μm, the coating film resistance (R3) is 10 to 200 kΩ · cm ² and the coating film when it reaches 6 μm. A method comprising applying a cationic electrodeposition coating composition satisfying a resistance (R6) of 40 to 400 kΩ · cm ² . From the coating film resistance (R3) when the film thickness after baking of the coating film obtained by uniformly coating the object to be coated with the cationic electrodeposition coating composition calculated by the following formula reaches 3 μm. The method according to claim 1, wherein an increase rate of the coating film resistance (R6) when reaching 6 μm is 50 to 700% / μm.
Increase rate (% / μm) = ((R6) / (R3)) × 100/3   The method according to claim 1 or 2, wherein the cationic electrodeposition coating composition further comprises a pigment paste.   The method according to claim 1, wherein the object to be coated is an iron-based metal substrate, an aluminum-based metal substrate, or a zinc-based metal substrate.