JP2002285392A - Electrodeposition method - Google Patents

Abstract

[PROBLEMS] To reduce the effect on the environment due to low VOC and metal ion concentrations, and to minimize the difference in film thickness between the outer surface and the inner surface even if the amount of electrodeposition paint itself is small. And to provide an electrodeposition coating method which is further excellent in the smoothness of the outer surface. SOLUTION: A step of performing a first electrodeposition coating with a first lead-free cationic electrodeposition paint prepared such that the Tg of a coating film (electrodeposition coating film) to be electrodeposited on an object to be coated is low; Performing a second electrodeposition coating with a second lead-free cationic electrodeposition coating prepared so as to increase the Tg of a coating film to be electrodeposited on the object; and baking and curing the electrodeposition coating film. Electrodeposition method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electrodeposition coating method, and more particularly, to an electrodeposition coating method using a lead-free cationic electrodeposition coating material having a low volatile organic content (VOC) and a low metal ion concentration.

[0002]

2. Description of the Related Art Electrodeposition coating can be applied to even small objects having complicated shapes, and can be applied automatically and continuously. It has a complicated shape and is widely used as an undercoating method for an object requiring high rust prevention. In addition, the use efficiency of the paint is extremely high as compared with other coating methods, so it is economical and widely used as an industrial coating method. The cationic electrodeposition coating is performed by immersing the object to be coated as a cathode in the cationic electrodeposition coating and applying a voltage.

Heretofore, metal catalysts containing lead (such as a corrosion resistance imparting agent) have been added to electrodeposition paints in order to improve the corrosion resistance of the coating film. In recent years, since metal ions, particularly lead ions, have a bad influence on the environment, it has been required to reduce the amount of metal catalyst used in electrodeposition paints.

On the other hand, recently, as awareness of the environment has increased, developed countries have been moving toward regulating the amount of harmful air pollutants (HAPs). The electrodeposition paint contains a volatile organic solvent as a solvent for synthesizing a resin, and as a flow aid for an electrodeposition coating film or as a regulator of coating workability. Therefore, when the environmental regulation standards are strengthened, there is a fear that use becomes difficult.

[0005] Further, in order to further reduce the effect of the electrodeposition coating composition on the environment, it is desired to reduce the amount of the coating composition itself.

[0006] The deposition of a coating film in the process of cationic electrodeposition coating is due to an electrochemical reaction, and the coating film is deposited on the surface of an object to be coated by applying a voltage. Since the deposited coating has insulating properties, the electrical resistance of the coating increases as the deposition of the coating proceeds and the thickness of the deposited film increases in the coating process.

[0007] As a result, the deposition of the paint on the portion concerned is reduced, and instead, the deposition of the coating film on the undeposited portion starts. In this way, the paint solids are sequentially applied to the unapplied portions to complete the coating. In the present specification, the property that a coating film is sequentially formed on a non-adhered portion of a substrate is referred to as throwing power.

In the cationic electrodeposition coating, as described above, an insulating coating film is sequentially formed on the surface of the object to be coated, and thus has theoretically infinite throwing power. It should be possible to form a coating film uniformly on all parts of.

However, the voltage applied in the bath is weaker in the uncoated portion of the object to be coated than in the coated portion, so that the solid content of the coating is less likely to be deposited, and the throwing power of the electrodeposition coating is not necessarily sufficient. However, unevenness in film thickness occurs.

[0010] Cationic electrodeposition coating is usually used for undercoating and is performed mainly for the purpose of rust prevention and the like. Therefore, even in the case of an object having a complicated structure, the coating film is applied to all parts. It is necessary to make the film thickness more than a predetermined value. Therefore, if there is unevenness in the film thickness, the thick part is overpainted,
This means that the paint is used excessively. Therefore, in order to reduce the amount of paint used, the throwing power of the electrodeposition paint is improved, and furthermore, the electrodeposition coating film formed on the outer surface and the electrodeposition coating film formed on the inner surface of the object to be coated are improved. Needs to be reduced.

On the other hand, reducing the amount of paint used means that the film thickness is also reduced, resulting in poor smoothness, which has been a major problem for automotive coatings that require a high appearance.

[0012]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems.
Since the concentration of OC and metal ions is low, the influence on the environment is small, and even if the amount of the electrodeposition coating material itself is small, the difference in film thickness between the outer surface and the inner surface can be minimized, and the electrode has excellent outer surface smoothness. An object of the present invention is to provide a coating method.

[0013]

SUMMARY OF THE INVENTION The present invention is directed to an aqueous medium, a binder resin containing a cationic epoxy resin and a blocked isocyanate hardener dispersed or dissolved in an aqueous medium, and a method for neutralizing a cationic epoxy resin. Contains a neutralizing acid, an organic solvent, and a metal catalyst, has a volatile organic content of 1% by weight or less, and has a metal ion concentration of 500 pp.
m or less, and the amount of the neutralizing acid is 10
Using a lead-free cationic electrodeposition paint having a glass transition temperature of 0 ° C. or less, which is an equivalent of 10 to 30 mg to 0 g, and A first electrodeposition coating step of forming an electrodeposition coating film on a part of the surface of the substrate;
Aqueous medium, binder resin containing cationic epoxy resin and blocked isocyanate hardener dispersed or dissolved in aqueous medium, neutralizing acid for neutralizing cationic epoxy resin, organic solvent, metal catalyst The volatile organic content is 1% by weight or less, the metal ion concentration is 500 ppm or less, and the amount of the neutralizing acid is 10 to 30 mg equivalent to 100 g of the binder resin solids;
The glass transition temperature of the coating film electrodeposited on the object to be coated is 5 to 20 ° C.
A second electrodeposition coating step of forming an electrodeposition coating film on an unpainted portion of the object to be coated by an electrodeposition coating method using a lead-free cationic electrodeposition coating material, and baking and curing the electrodeposition coating film. The present invention provides an electrodeposition coating method comprising the steps of:

Here, "lead-free" means that it does not substantially contain lead, and means that it does not contain lead in an amount that adversely affects the environment. Specifically, it means that the lead compound concentration in the electrodeposition bath does not contain lead in an amount exceeding 50 ppm, preferably 20 ppm.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION A cationic electrodeposition coating composition comprises an aqueous medium,
Contains various additives dispersed or dissolved in an aqueous medium, such as a binder resin, a neutralizing acid, an organic solvent, and a metal catalyst. The binder resin contains a cationic resin having a functional group and a blocked isocyanate curing agent for curing the resin. As the aqueous medium, ion exchange water or the like is generally used.

In the lead-free cationic electrodeposition coating composition used in the present invention, a cationic resin obtained by reacting an active hydrogen compound such as an amine with an epoxy ring of an epoxy resin as a cationic resin and opening the epoxy group to introduce a cationic group. It is preferable to use an epoxy resin and use a blocked polyisocyanate in which an isocyanate group of a polyisocyanate is blocked as a blocked isocyanate curing agent.

Cationic Epoxy Resin The cationic epoxy resin includes an epoxy resin modified with an amine. This cationic epoxy resin is
Known resins described in JP-A-54-4978 and JP-A-56-34186 may be used.

[0018] The cationic epoxy resin is typically
All of the epoxy ring of the bisphenol type epoxy resin is opened with an active hydrogen compound capable of introducing a cationic group,
Alternatively, it is produced by opening a part of the epoxy ring with another active hydrogen compound and opening the remaining epoxy ring with an active hydrogen compound capable of introducing a cationic group.

A typical example of the bisphenol type epoxy resin is a bisphenol A type or bisphenol F type epoxy resin. The former commercial product is Epikote 828
(Yuika Shell Epoxy Co., epoxy equivalent 180 ~ 19
0), epicoat 1001 (same as above, epoxy equivalent 450-
500), Epicoat 1010 (same epoxy equivalent 30)
00-4000), and the latter commercially available products include Epicoat 807 (same as above, epoxy equivalent: 170).

JP-A-5-306327, No. 0004
An oxazolidone ring-containing epoxy resin as described in the formula in the paragraph, Chemical formula 3 may be used for the cationic epoxy resin. This is because a coating film having excellent heat resistance and corrosion resistance can be obtained.

As a method for introducing an oxazolidone ring into an epoxy resin, for example, a blocked polyisocyanate and a polyepoxide blocked with a lower alcohol such as methanol are heated and maintained in the presence of a basic catalyst to lower the by-product lower alcohol. It is obtained by distilling off from the system.

Particularly preferred epoxy resins are oxazolidone ring-containing epoxy resins. This is because a coating film having excellent heat resistance and corrosion resistance and also excellent impact resistance can be obtained.

It is known that the reaction of a bifunctional epoxy resin with a diisocyanate blocked with a monoalcohol (ie bisurethane) results in an epoxy resin containing an oxazolidone ring. Specific examples and production methods of this oxazolidone ring-containing epoxy resin are described, for example, in JP-A-2000-128959, 0012 to 0.
It is described in paragraph 047.

Blocked Isocyanate Curing Agent The blocked isocyanate curing agent is obtained by adding a blocking agent to polyisocyanate. Polyisocyanate is a compound having two or more isocyanate groups in one molecule. The polyisocyanate may be, for example, any of aliphatic, alicyclic, aromatic, and aromatic-aliphatic.

Specific examples of the polyisocyanate include aromatic diisocyanates such as tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), p-phenylene diisocyanate, and naphthalene diisocyanate; hexamethylene diisocyanate (HDI); Aliphatic diisocyanates having 3 to 12 carbon atoms, such as 1,4-trimethylhexane diisocyanate and lysine diisocyanate; 1,4-cyclohexane diisocyanate (CDI), isophorone diisocyanate (IPDI), 4,4'-dicyclohexylmethane diisocyanate (water MDI), methylcyclohexane diisocyanate, isopropylidene dicyclohexyl-4,4'-diisocyanate, and 1,3
-Diisocyanatomethylcyclohexane (hydrogenated XD
I), C5-C18 such as hydrogenated TDI, 2,5- or 2,6-bis (isocyanatomethyl) -bicyclo [2.2.1] heptane (also referred to as norbornane diisocyanate), and the like. Aliphatic diisocyanates having an aromatic ring such as xylylene diisocyanate (XDI) and tetramethyl xylylene diisocyanate (TMXDI); modified products of these diisocyanates (urethane compounds, carbodiimides, uretdione, uretimines, Viewlets and / or
Or isocyanurate modified product); These can be used alone or in combination of two or more.

The polyisocyanate is ethylene glycol, propylene glycol, trimethylolpropane,
Polyhydric alcohols such as hexanetriol and NCO / O
An adduct or prepolymer obtained by reacting at an H ratio of 2 or more may be used as a blocked isocyanate curing agent.

The blocking agent is one which is added to the polyisocyanate group and is stable at ordinary temperature but can regenerate free isocyanate group when heated to a temperature higher than the dissociation temperature.

As the blocking agent, a commonly used blocking agent such as ε-caprolactam and butyl cellosolve can be used. However, among these, many volatile blocking agents are regulated as targets of HAPs, and it is preferable to use the necessary minimum amount.

Pigment In general, the electrodeposition coating composition generally contains a pigment as a colorant. However, it is preferable that the lead-free cationic electrodeposition coating composition of the present invention does not contain a coloring pigment. This is because the throwing power of the paint is improved.

In order to impart corrosion resistance to the coating film, a rust preventive pigment or extender may be contained. However, the amount is such that the weight ratio (P / V) of the pigment and the resin solids contained in the coating composition is 1
/ 9 or less. If the amount of the pigment in the coating composition exceeds 1/9 by weight with respect to the solid content of the resin, the depositing property of the solid content of the coating decreases, and the throwing power decreases.

Examples of the pigment which may be contained in the lead-free cationic electrodeposition coating composition of the present invention include kaolin, talc,
Extenders such as aluminum silicate, calcium carbonate, mica, clay and silica, zinc phosphate, iron phosphate,
Aluminum phosphate, calcium phosphate, zinc phosphite, zinc cyanide, zinc oxide, aluminum tripolyphosphate, zinc molybdate, aluminum molybdate,
Rust preventing pigments such as calcium molybdate, aluminum phosphomolybdate, and aluminum zinc phosphomolybdate are included.

When a pigment-dispersed paste pigment is used as a component of an electrodeposition coating material, the pigment is generally dispersed in an aqueous medium at a high concentration in advance to form a paste.
This is because the pigment is in a powder form, and it is difficult to disperse the pigment in a low-concentration uniform state used in the electrodeposition paint in one step. Generally, such a paste is called a pigment dispersion paste.

The pigment dispersion paste is prepared by dispersing a pigment together with a pigment dispersion resin in an aqueous medium. As the pigment-dispersing resin, a cationic or nonionic low-molecular-weight surfactant or a cationic polymer such as a modified epoxy resin having a quaternary ammonium group and / or a tertiary sulfonium group is generally used. As the aqueous medium, ion exchange water, water containing a small amount of alcohols, or the like is used. Generally, the pigment dispersion resin is used at a solid content ratio of 5 to 40 parts by weight, and the pigment is used at a solid content ratio of 20 to 50 parts by weight.

Metal Catalyst The lead-free cationic electrodeposition paint used in the present invention contains a metal catalyst as a metal ion as a catalyst for improving the corrosion resistance of the coating film. As the metal ions, cerium ions, bismuth ions, copper ions, and zinc ions are preferable. These are incorporated into the electrodeposition paint as eluates from pigments containing salts or metal ions combined with an appropriate acid. The acid may be any one of inorganic acids and organic acids such as hydrochloric acid, nitric acid, phosphoric acid, formic acid, acetic acid and lactic acid which will be described later as neutralizing acids for neutralizing the cationic epoxy resin. The preferred acid is acetic acid.

The compounding amount of the metal catalyst is such that the metal ion concentration in the electrodeposition paint is 500 ppm or less. This is to reduce the impact on the environment. Preferably, the metal ion concentration in the electrodeposition paint is from 200 to 400 ppm. However, when a pigment is included in the coating composition, it is necessary to control within the above range in consideration of the amount of metal ions eluted from the pigment. Examples of metal ions eluted from the pigment include zinc ions, molybdenum ions, and aluminum ions.

The metal ion concentration in the electrodeposition paint is 500 pp
If it exceeds m, the effect on the environment will be large, and if the concentration of metal ions is high, the depositability of the coating film will also decrease, and the throwing power of the coating material will also decrease.
The metal ion concentration in the electrodeposition paint is measured by atomic absorption analysis of the supernatant obtained by centrifugation.

Electrodeposition paint The lead-free cationic electrodeposition paint used in the present invention is prepared by dispersing the above-mentioned metal catalyst, cationic epoxy resin, blocked isocyanate curing agent, and pigment dispersion paste in an aqueous medium. You. Usually, the aqueous medium contains a neutralizing acid to neutralize the cationic epoxy resin and improve the dispersibility of the binder resin emulsion. Neutralizing acid is hydrochloric acid, nitric acid, phosphoric acid, formic acid, acetic acid,
Inorganic or organic acids such as lactic acid.

When the amount of the neutralizing acid contained in the coating composition increases, the neutralization ratio of the cationic epoxy resin increases, the affinity of the binder resin particles for the aqueous medium increases, and the dispersion stability increases. This means that the binder resin hardly precipitates on the object to be coated at the time of electrodeposition coating, and the depositing property of the coating solids decreases.

Conversely, if the amount of the neutralizing acid contained in the coating composition is small, the neutralization rate of the cationic epoxy resin decreases, the affinity of the binder resin particles for the aqueous medium decreases, and the dispersion stability decreases. I do. This means that the binder resin easily precipitates on the object to be coated at the time of coating, and the deposition property of the coating solids increases.

Therefore, in order to improve the throwing power of the electrodeposition coating composition, it is preferable to reduce the amount of the neutralizing acid contained in the coating composition to suppress the neutralization ratio of the cationic epoxy resin to a low level.

Specifically, the amount of the neutralizing acid is 10 to 30 mg equivalent, preferably 15 to 25 mg equivalent, per 100 g of the solid content of the binder resin containing the cationic epoxy resin and the blocked isocyanate curing agent. If the amount of the neutralizing acid is less than 10 mg equivalent, the affinity for water is not sufficient, and it cannot be dispersed in water or is in a state of extremely lacking stability. If the amount exceeds 30 mg equivalent, the amount of electricity required for precipitation increases. However, the solidification of the paint is reduced, and the throwing power is inferior.

In the present specification, the amount of the neutralizing acid is represented by the number of mg equivalent relative to 100 g of the solid content of the binder resin contained in the coating composition, and is expressed as MEQ (A).

The amount of the blocked isocyanate curing agent is such that it reacts with active hydrogen-containing functional groups such as primary, secondary and / or tertiary amino groups and hydroxyl groups in the cationic epoxy resin at the time of curing to form a good cured coating film. Of the cationic epoxy resin to the blocked isocyanate hardener, typically 90 weight percent solids.
/ 10 to 50/50, preferably 80/20 to 65/3
5 range.

The coating composition can contain tin compounds such as dibutyltin dilaurate and dibutyltin oxide, and a conventional urethane cleavage catalyst. Since substantially no lead is contained, the amount is preferably 0.1 to 5% by weight of the resin solids.

An organic solvent is always required as a solvent when synthesizing resin components such as a cationic epoxy resin, a blocked isocyanate curing agent and a pigment dispersion resin, and requires a complicated operation to completely remove it. Further, when an organic solvent is contained in the binder resin, the fluidity of the coating film during film formation is improved, and the smoothness of the coating film is improved.

Organic solvents usually contained in the coating composition include ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol mono-2-ethylhexyl ether, propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, and propylene glycol monophenyl ether. And the like.

Therefore, conventionally, these organic solvents have not been completely removed from the resin component, and the VOC of the electrodeposition paint has been increased to some extent by adding an organic solvent separately, to about 1 to 5% by weight. Has been adjusted. Where VOC
The volatile organic content expressed by (volatile organic content) refers to an organic solvent having a boiling point of 250 ° C. or lower, and corresponds to those specifically listed above.

On the other hand, in the lead-free cationic electrodeposition coating composition of the present invention, the content of the organic solvent is preferably reduced as compared with the conventional one. This is to prevent adverse effects on the environment. Specifically, the VOC of the coating composition is 1% by weight or less, preferably 0.5 to 0.8% by weight, more preferably 0.2 to 0.5% by weight. If the VOC of the coating composition exceeds 1% by weight, the effect on the environment is increased, and the flow resistance of the coating film is reduced by improving the fluidity of the deposited coating film, so that the throwing power of the coating material is also reduced.

As a method for reducing the VOC to 1% by weight or less,
Organic solvents used for adjusting the viscosity during the reaction can be reduced by raising the reaction temperature and reacting with a low or no solvent. For the organic solvent which is absolutely necessary during the reaction, the content of volatile organic components in the final product can be reduced by using a solvent having a low boiling point so as to be recovered in a step such as solvent removal. The content of the organic solvent used for adjusting the viscosity at the time of coating can be reduced by lowering the viscosity of the resin, for example, by modification with a soft segment.

For the measurement of VOC, gas chromatography was carried out by an internal standard method, and VOC mixed as an organic solvent was measured.
It can be performed by measuring the amount of the component.

The coating composition may contain, in addition to the above, conventional coating additives such as a plasticizer, a surfactant, an antioxidant, an ultraviolet absorber, and a pigment.

Electrodeposition Method The electrodeposition method of the present invention is carried out by using the above-mentioned lead-free cationic electrodeposition paint. Then, the first electrodeposition coating step is performed with the first electrodeposition paint prepared so as to lower the Tg of the coating film (electrodeposition coating film) to be electrodeposited on the object to be coated, and The second electrodeposition coating step is performed on the second electrodeposition coating prepared so as to increase the Tg of the coating film to be formed, and an electrodeposition coating film is formed on the object to be coated. The first electrodeposition coating step and the second electrodeposition coating step may be performed using different electrodeposition tanks.

The Tg of the electrodeposition coating is a theoretical value calculated from the Tg of all the resin components contained in the cationic electrodeposition coating. The calculation of Tg is performed according to the Fox equation.
The Fox equation is shown below.

[0054]

1 / Tg = w ₁ / Tg ₁ + w ₂ / Tg ₂ +... +
w _n / Tg _n

[0055] In the formula, w _n is the weight percentage of n-th resin component, Tg _n is the glass transition temperature of the n-th resin component (where the unit is Kelvin.) It is. ]

As the Tg of all the resin components, a value measured by individually detecting a thermal change accompanying a glass transition of the resin with a differential scanning calorimeter is used.

The volatile organic content, the metal ion concentration, and the amount of neutralizing acid of the electrodeposition paint used in the first electrodeposition step and the second electrodeposition step are the same, but Tg is different. That is, the Tg of the electrodeposition coating film is the first Tg used in the first electrodeposition coating step.
In the case of an electrodeposition paint, the temperature is adjusted to 0 ° C or lower, preferably -20 to 0 ° C, more preferably -10 to 0 ° C. In the second electrodeposition paint used in the second electrodeposition coating step, the temperature is adjusted to 5 to 20 ° C, preferably 5 to 15 ° C. Those skilled in the art can adjust the Tg of the electrodeposition coating film by changing the composition of the binder resin contained in the electrodeposition coating material.

If the Tg of the electrodeposited coating film formed in the first electrodeposition coating step exceeds 0 ° C., the smoothness at less than 20 μ will be inferior. On the other hand, if the Tg of the electrodeposited coating film formed in the second electrodeposition coating step is less than 5 ° C., sufficient throwing power cannot be obtained, and the internal film thickness becomes less than 10 μ, resulting in poor anticorrosion properties. When the temperature exceeds ℃, the resin does not easily generate heat flow at the time of electrodeposition, and the formation of coating resistance, which is important for throwing power, is delayed, which also results in poor throwing power.

The object on which the coating film is formed is not particularly limited as long as it is conductive, and examples thereof include iron plates, steel plates, aluminum plates, surface-treated ones thereof, and molded products thereof. Can be mentioned.

In the first electrodeposition step and the second electrodeposition step, the electrodeposition coating is usually performed by applying a voltage of 50 to 450 V between the object to be coated as a cathode and the anode. If the applied voltage is less than 50 V, electrodeposition becomes insufficient, and if it exceeds 450 V, the coating film is broken and an abnormal appearance is obtained. During electrodeposition coating,
The bath temperature of the coating composition is usually adjusted to 10 to 45 ° C.

The electrodeposition process includes, in both the first electrodeposition coating step and the second electrodeposition coating step, (i) a step of immersing the object to be coated in the cationic electrodeposition paint, and (ii) a cathode of the object to be coated. And applying a voltage between the anode and the anode to deposit a film. The time for applying the voltage varies depending on the electrodeposition conditions, but can be generally 2 to 4 minutes.
At the time of electrodeposition coating, the bath temperature of the coating composition is usually 10 to 45.
Adjusted to ° C.

The film thickness of the electrodeposition coating film is adjusted so that the maximum thickness in the first electrodeposition coating step is 8 to 20 μm, preferably 10 to 15 μm. Further, the second electrodeposition coating step is performed so that the maximum film thickness is 8 to 15 μm, preferably 10 to 15 μm.

When the maximum thickness of the electrodeposition coating film obtained in the first electrodeposition coating step is less than 8 μm, the smoothness is poor, and
If it exceeds 20 μm, it becomes uneconomical. Further, if the maximum thickness of the electrodeposition coating film obtained in the second electrodeposition coating step is less than 8 μm, the anticorrosion property is inferior, and if it exceeds 15 μm, this is also uneconomical.

In this method, a coating film is formed mainly on the outer surface of the object to be coated in the first electrodeposition coating step, and a coating film is formed mainly on the inner surface of the object to be coated in the second electrodeposition coating step. As a result, the difference in film thickness between the electrodeposition coating film formed on the outer surface and the electrodeposition coating film formed on the inner surface of the object to be coated can be almost eliminated. Here, the outer surface portion refers to a portion visible from the outside of the object to be coated, and the inner surface portion refers to a portion inside the bag when the object to be coated is in a bag shape.

After completion of the electrodeposition process, the electrodeposited coating film obtained as described above is used as it is or after washing with water.
It is cured by baking at 60C, preferably 160-220C for 10-30 minutes.

[0066]

According to the electrodeposition coating method of the present invention, the total amount of the electrodeposition paint to be used is minimized, and the electrodeposition coating film formed on the outer surface of the object to be coated and the electrodeposition coating formed on the inner surface are reduced. Almost no difference in film thickness from the deposited coating film can be achieved.

[0067]

The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited thereto. In the examples,
“Parts” and “%” are based on weight unless otherwise specified.

Production Example 1 Production of Amine-Modified Epoxy Resin A flask equipped with a stirrer, cooling tube, nitrogen introduction tube, thermometer and dropping funnel was charged with 2,4- / 2,6-tolylene diisocyanate (weight ratio = 8 / 2) 92 parts, 95 parts of methyl isobutyl ketone (hereinafter abbreviated as MIBK) and 0.5 part of dibutyltin dilaurate were charged. While stirring the reaction mixture, 21 parts of methanol was added dropwise. The reaction was started at room temperature and heated to 60 ° C. due to exotherm. Then 30
After the reaction was continued for 2 minutes, ethylene glycol mono-2-
50 parts of ethylhexyl ether was dropped from the dropping funnel. Further, to the reaction mixture, 53 parts of a 5-mol bisphenol A-propylene oxide adduct was added. The reaction was carried out mainly in the range of 60 to 65 ° C., and was continued until the absorption based on the isocyanate group disappeared in the measurement of the IR spectrum.

Next, 365 parts of an epoxy resin having an epoxy equivalent of 188 synthesized from bisphenol A and epichlorohydrin by a known method was added to the reaction mixture, and the temperature was raised to 125 ° C. Thereafter, 1.0 part of benzyldimethylamine was added and reacted at 130 ° C. until the epoxy equivalent reached 410.

Subsequently, 61 parts of bisphenol A and 33 parts of octylic acid were added and reacted at 120 ° C.
The epoxy equivalent was 1190. Thereafter, the reaction mixture was cooled, 11 parts of diethanolamine, 24 parts of N-ethylethanolamine and 25 parts of a 79% by weight MIBK solution of a ketimine compound of aminoethylethanolamine were added, and the mixture was reacted at 110 ° C. for 2 hours. Thereafter, the mixture was diluted with MIBK until the nonvolatile content became 80%, and the glass transition temperature was 2%.
An amine-modified epoxy resin at 80 ° C. (resin solid content: 80%) was obtained.

Production Example 2 Production of Amine-Modified Epoxy Resin A flask equipped with a stirrer, cooling tube, nitrogen inlet tube, thermometer and dropping funnel was charged with 2,4- / 2,6-tolylene diisocyanate (weight ratio = 8 / 2) 92 parts, 95 parts of methyl isobutyl ketone (hereinafter abbreviated as MIBK) and 0.5 part of dibutyltin dilaurate were charged. While stirring the reaction mixture, 21 parts of methanol was added dropwise. The reaction was started at room temperature and heated to 60 ° C. due to exotherm. Then 30
After the reaction was continued for 2 minutes, ethylene glycol mono-2-
57 parts of ethylhexyl ether were dropped from the dropping funnel. Further, 42 parts of a bisphenol A-propylene oxide 5 mol adduct was added to the reaction mixture. The reaction was carried out mainly in the range of 60 to 65 ° C., and was continued until the absorption based on the isocyanate group disappeared in the measurement of the IR spectrum.

Next, 365 parts of an epoxy resin having an epoxy equivalent of 188 synthesized from bisphenol A and epichlorohydrin by a known method was added to the reaction mixture, and the temperature was raised to 125 ° C. Thereafter, 1.0 part of benzyldimethylamine was added and reacted at 130 ° C. until the epoxy equivalent reached 410.

Subsequently, when 87 parts of bisphenol A was added and reacted at 120 ° C., the epoxy equivalent was 1190
It became. Thereafter, the reaction mixture was cooled and 11 parts of diethanolamine, 24 parts of N-ethylethanolamine and 79 parts of ketimine compound of aminoethylethanolamine were obtained.
25 parts by weight of a MIBK solution was added and reacted at 110 ° C. for 2 hours. Thereafter, the mixture was diluted with MIBK until the nonvolatile content became 80% to obtain an amine-modified epoxy resin having a glass transition temperature of 22 ° C (resin solid content 80%).

Production Example 3 Production of a blocked isocyanate curing agent 1250 parts of diphenylmethane diisocyanate and M
266.4 parts of IBK were charged into a reaction vessel,
After heating to 2.5 parts, 2.5 parts of dibutyltin dilaurate were added. A solution prepared by dissolving 226 parts of ε-caprolactam in 944 parts of butyl cellosolve was dropped at 80 ° C over 2 hours. After further heating at 100 ° C. for 4 hours, I
In the measurement of the R spectrum, it was confirmed that the absorption based on the isocyanate group had disappeared.
6.1 parts were added to obtain a blocked isocyanate curing agent having a glass transition temperature of 0 ° C.

Production Example 4 Production of Pigment-Dispersed Resin First, 222.0 parts of isophorone diisocyanate (hereinafter abbreviated as IPDI) were placed in a reaction vessel equipped with a stirrer, a cooling pipe, a nitrogen introduction pipe, and a thermometer.
After dilution with 9.1 parts, here 0.2 part of heptbutyltin dilaurate was added. Thereafter, the temperature was raised to 50 ° C., and 131.5 parts of 2-ethylhexanol was added dropwise with stirring in a dry nitrogen atmosphere over 2 hours. The reaction temperature was maintained at 50 ° C. by cooling appropriately. As a result, 2-ethylhexanol half-blocked IPDI
(Resin solid content: 90.0%) was obtained.

Next, 87.2 parts of dimethylethanolamine and 117.6% aqueous lactic acid solution 117.6 were placed in a suitable reaction vessel.
Part and ethylene glycol monobutyl ether
2 parts were added in order and stirred at 65 ° C. for about half an hour to prepare a quaternizing agent.

Next, 710.0 parts of EPON 829 (bisphenol A type epoxy resin manufactured by Shell Chemical Company, epoxy equivalent: 193 to 203) and 289.6 parts of bisphenol A were charged into an appropriate reaction vessel. When heated to 150 to 160 ° C. in a nitrogen atmosphere, an initial exothermic reaction occurred. 150-16 reaction mixture
The reaction was carried out at 0 ° C. for about 1 hour, and then cooled to 120 ° C., and then 498.8 parts of the previously prepared 2-ethylhexanol half-blocked IPDI (MIBK solution) was added.

The reaction mixture is kept at 110-120 ° C. for about 1 hour, then 463.4 parts of ethylene glycol monobutyl ether are added and the mixture is cooled to 85-95 ° C.
After homogenization, 196.7 parts of the quaternizing agent prepared above was added. The reaction mixture is heated to 85 to 95 ° C. until the acid value becomes 1.
And then add 964 parts of deionized water to complete the quaternization of the epoxy-bisphenol A resin,
A pigment dispersing resin having a quaternary ammonium salt portion was obtained (resin Tg = 5 ° C., resin solid content 50%).

Production Example 5 Production of Pigment Dispersion Paste 120 parts of the pigment dispersing resin obtained in Production Example 4, 2.0 parts of carbon black, kaolin 10
0.0 parts, 80.0 parts of titanium dioxide, 18.0 parts of aluminum phosphomolybdate and 221.7 of ion-exchanged water
And dispersed until the particle size became 10 μm or less to obtain a pigment dispersion paste (solid content: 48%).

Production Example 6 Production of First Cationic Electrodeposition Paint The amine-modified epoxy resin obtained in Production Example 1 and Production Example 3
Was mixed with the blocked isocyanate curing agent obtained in the above at a solid content ratio of 70/30 to be uniform. Thereafter, a 6 mol ethylene oxide adduct of bisphenol A (Tg
= -40 ° C) to the solid content, and 10% by weight of ethylene glycol-2-ethylhexyl ether to the solid content, and 3% by weight to the solid content. Milligram equivalent of acid per 100 g of resin solid content (MEQ (A))
Glacial acetic acid was added so that the value was 30 and ion-exchanged water was slowly added to dilute the solution. By removing MIBK under reduced pressure, an emulsion having a solid content of 36% was obtained.

1500 parts of this emulsion and 540 parts of the pigment-dispersed paste obtained in Production Example 5, 1920 parts of ion-exchanged water, 40 parts of a 10% cerium acetate aqueous solution and 10 parts of dibutyltin oxide were mixed to give a solid content of 20 parts.
% By weight of the cationic electrodeposition paint was obtained. The Tg of the electrodeposition coating film (precipitated film) calculated from each resin Tg of all the resin components of the cationic electrodeposition coating material was −3 ° C., the solvent amount (VOC) in the coating material was 0.9%, and the The milligram equivalent of acid per 100 g of solid content was 24.7, and the total concentration of eluted cerium ions and zinc ions was 380 ppm.

Production Example 7 Production of Second Cationic Electrodeposition Coating The amine-modified epoxy resin obtained in Production Examples 1 and 2 and the blocked isocyanate curing agent obtained in Production Example 3 were mixed in a solid content ratio of 20 / The mixture was mixed to be uniform at 50/30. Glacial acetic acid was added to this so that the milligram equivalent of acid per 20 g of resin solid content was 20, and further, ion-exchanged water was slowly added for dilution. MIBK under reduced pressure
Was removed to obtain an emulsion having a solid content of 36%.

2220 parts of this emulsion, 1740 parts of ion-exchanged water, 40 parts of a 10% cerium acetate aqueous solution and 10 parts of dibutyltin oxide were mixed to obtain a cationic electrodeposition paint having a solid content of 20% by weight. The Tg of the electrodeposited coating film (precipitated film) calculated from each resin Tg of all the resin components of the cationic electrodeposition paint was 11 ° C., the solvent amount in the paint was 0.5%, and the resin solid content was 100 g. The milligram equivalent of the acid was 25.2, and the total concentration of eluted cerium ions and zinc ions was 200 ppm.

Production Example 8 Production of Second Cationic Electrodeposition Paint The amine-modified epoxy resin obtained in Production Example 2 and Production Example 3
Was mixed with the blocked isocyanate curing agent obtained in the above at a solid content ratio of 70/30 to be uniform. Glacial acetic acid was added to this so that the milligram equivalent of acid per 100 g of resin solid content was 25, and ion-exchanged water was slowly added to dilute. By removing MIBK under reduced pressure, an emulsion having a solid content of 36% was obtained.

1500 parts of this emulsion and 540 parts of the pigment-dispersed paste obtained in Production Example 5, 1940 parts of ion-exchanged water, 20 parts of a 10% cerium acetate aqueous solution and 10 parts of dibutyltin oxide were mixed to give a solid content of 20 parts.
% By weight of the cationic electrodeposition paint was obtained. The Tg of the electrodeposited coating film (precipitated film) calculated from each resin Tg of all the resin components of this cationic electrodeposition paint was 14 ° C., the amount of solvent in the paint was 0.5%, and the amount of resin solid content was 100 g. The milligram equivalent of the acid was 21.5, and the total concentration of eluted cerium ions and zinc ions was 205 ppm.

Example 1 First, as shown in FIG. 1, four zinc phosphate-treated steel sheets (JIS G 3141 SPCC-SD Surfdyne SD-5000 (manufactured by Nippon Paint Co., Ltd.)) 11 to 14 were set up. With interval 2
A box 10 was placed in parallel with Omm, and the lower part and the bottom face on both sides were sealed with an insulator such as a cloth adhesive tape.
In addition, the steel plates 11 to 13 other than the steel plate 14 have 8 mm
A through hole 15 of φ is provided.

4 liters of the first cationic electrodeposition paint obtained in Production Example 6 was transferred to a PVC container to form a first electrodeposition bath. As shown in FIG. 2, the box 10 was immersed in an electrodeposition coating container 20 containing an electrodeposition coating material 21 as an object to be coated. In this case, the paint 21 enters the box 10 only from each through hole 15.

The paint 21 was stirred with a magnetic stirrer (not shown). Then, the steel plates 11 to 14 were electrically connected, and the counter electrode 22 was arranged so that the distance from the closest steel plate 11 was 150 mm. Each steel plate 11 to 14 is a cathode,
A voltage was applied using the counter electrode 22 as an anode to perform cation electrodeposition coating on the steel sheet. The coating was performed at a bath temperature of 30 ° C. and an applied voltage of 170 V for 3 minutes.

Next, the second cationic electrodeposition paint obtained in Production Example 7 was transferred to a PVC container to form a second electrodeposition bath, and the box 10 was pulled out of the first electrodeposition bath. As shown in FIG. 2, it was immersed in the second electrodeposition bath. Then, electrodeposition coating was performed for 3 minutes at a bath liquid temperature of 30 ° C. and an applied voltage of 230 V.

Thereafter, the box 10 was taken out of the second electrodeposition bath, washed with water, and set for 10 minutes. Then, the film was put into a drying furnace set at 170 ° C. for 25 minutes and heated to cure the coating film. After the object to be cooled was air-cooled, the thickness of the anode side surface A of the steel plate 11 closest to the counter electrode 22 was measured as the thickness of the coating film formed on the outer surface of the object to be coated. The thickness of the anode side surface G was measured as the thickness of the coating film formed on the inner surface of the object to be coated. As a result, the thickness of the coating film formed on the outer surface A of the object to be coated was 15 μm.
The thickness of the coating film formed on the inner surface G was 12 μm.

At this time, the smoothness of the surface A was measured using a surface roughness meter Surftest-211 (manufactured by Mitutoyo).
In, _{R a} value was measured the surface roughness _{(R a)} at the standard cutoff 0.8mm and scan length 4mm is 0.12μ
m. The smaller the _Ra value, the smoother the value.

Example 2 A cured coating film was obtained in the same manner as in Example 1, except that the second cationic electrodeposition paint obtained in Production Example 8 was used. The thickness of the coating film formed on the outer surface A of the object to be coated is 13 μm
And the thickness of the coating film formed on the inner surface G was 11 μm. Further, the _Ra value of the A surface was 0.15 μm.

Comparative Example 1 The amine-modified epoxy resin obtained in Production Example 1 and Production Example 3
Was mixed with the blocked isocyanate curing agent obtained in the above at a solid content ratio of 70/30 to be uniform. Thereafter, ethylene glycol-2-ethylhexyl ether was added so as to be 5% by weight based on the solid content. Glacial acetic acid was added to this so that the milligram equivalent of acid per 100 g of resin solid content was 35, and ion-exchanged water was slowly added to dilute the mixture. By removing MIBK under reduced pressure,
An emulsion having a solid content of 36% was obtained.

1500 parts of this emulsion and 540 parts of the pigment-dispersed paste obtained in Production Example 6, 1900 parts of ion-exchanged water, 60 parts of a 10% cerium acetate aqueous solution and 10 parts of dibutyltin oxide were mixed to give a solid content of 20 parts.
% By weight of the cationic electrodeposition paint was obtained. The Tg of the electrodeposited coating film (precipitated film) calculated from each resin Tg of all the resin components of this cationic electrodeposition paint was 2 ° C., the amount of solvent in the paint was 1.1%, and The milligram equivalent of the acid was 29.7, and the total concentration of eluted cerium ions and zinc ions was 610 ppm.

As shown in FIG. 1, four zinc phosphate-treated steel sheets (Surdy Dyne SD-5000 (manufactured by Nippon Paint Co., Ltd.) of JIS G 3141 SPCC-SD) 11 to 14 were placed upright at an interval of 20 mm. To prepare a box 10 in which the lower part and the bottom part on both sides are sealed with an insulator such as cloth adhesive tape.

[0096] Four liters of the obtained cationic electrodeposition paint were transferred to a polyvinyl chloride container to form an electrodeposition bath. As shown in FIG. 2, the box 10 was immersed in an electrodeposition coating container 20 containing an electrodeposition coating material 21 as an object to be coated.

The paint 21 was stirred with a magnetic stirrer (not shown). Then, the steel plates 11 to 14 were electrically connected, and the counter electrode 22 was arranged so that the distance from the closest steel plate 11 was 150 mm. Each steel plate 11 to 14 is a cathode,
A voltage was applied using the counter electrode 22 as an anode to perform cation electrodeposition coating on the steel sheet. The coating was performed at a bath temperature of 30 ° C. and an applied voltage of 200 V for 3 minutes.

Thereafter, the box 10 was pulled out of the electrodeposition bath, washed with water, and set for 10 minutes. And 1
The film was put into a drying oven set at 70 ° C. for 25 minutes and heated to cure the coating film. After air-cooling the object, the counter electrode 22
The thickness of the anode side surface A of the steel plate 11 closest to the substrate was measured as the thickness of the coating film formed on the outer surface of the object to be coated, and the thickness of the anode side surface G of the steel plate 14 furthest to the counter electrode was measured. Was measured as the thickness of the coating film formed on the inner surface of the sample. As a result, the thickness of the coating film formed on the outer surface A of the object to be coated is 20 μm,
The thickness of the coating film formed on the inner surface G was 6 μm. In addition, the _Ra value of the A side was 0.21 μm.

Comparative Example 2 A cured coating film was obtained in the same manner as in Comparative Example 1 except that the applied voltage was changed to 260V. The thickness of the coating formed on the outer surface A of the substrate was 30 μm, and the thickness of the coating formed on the inner surface G was 12 μm. In addition, the _Ra value of the A surface is 0.1.
It was 19 μm.

Comparative Example 3 The first cationic electrodeposition paint obtained in Production Example 6 was used instead of the second cationic electrodeposition paint obtained in Production Example 7 (that is, the first cationic electrodeposition paint obtained in Production Example 6). The first electrodeposition coating is performed at 170 V for 3 minutes, and the second electrodeposition coating is also performed at 230 V for 3 minutes.
An article to be coated was obtained in the same manner as in Example 1 except that the coating was performed for one minute. The thickness of the coating film formed on the outer surface A of the substrate is 17 μm.
m, and the thickness of the coating film formed on the inner surface G was 5 μm. Further, the _Ra value of the A surface was 0.12 μm.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of a box used for evaluating throwing power.

FIG. 2 is a cross-sectional view schematically showing a method for evaluating throwing power.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Box, 11-14 ... Zinc phosphate processing steel plate, 15 ... Through-hole, 20 ... Electrodeposition coating container, 21 ... Electrodeposition paint, 22 ... Counter electrode.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4J038 DB001 DB381 DB391 DG302 KA03 KA04 KA08 MA08 MA10 MA13 NA03 NA14 NA27 PA04 PA19 PC02

Claims (6)

[Claims] An aqueous medium, a binder resin containing a cationic epoxy resin and a blocked isocyanate curing agent dispersed or dissolved in the aqueous medium, a neutralizing acid for neutralizing the cationic epoxy resin, an organic solvent, It contains a metal catalyst and has a volatile organic content of 1% by weight or less,
The metal ion concentration is 500 ppm or less, and the amount of the neutralizing acid is 10 to 30 m with respect to 100 g of the binder resin solid content.
g equivalent weight, using a lead-free cationic electrodeposition coating material having a glass transition temperature of 0 ° C. or less for a coating film to be electrodeposited on an object to be coated,
A first electrodeposition coating step of forming an electrodeposition coating film on a part of the surface of an object to be coated by an electrodeposition coating method; an aqueous medium, a cationic epoxy resin dispersed or dissolved in the aqueous medium, and a blocked isocyanate Contains a binder resin containing a curing agent, a neutralizing acid for neutralizing a cationic epoxy resin, an organic solvent, and a metal catalyst, and has a volatile organic content of 1% by weight.
Or less, the metal ion concentration is 500 ppm or less, the amount of the neutralizing acid is 10 to 30 mg equivalent relative to 100 g of the binder resin solid content, and the glass transition temperature of the coating film electrodeposited on the object to be coated is 5 or less. A second electrodeposition coating step of forming an electrodeposition coating on an unpainted portion of the object by an electrodeposition coating method using a lead-free cationic electrodeposition coating at -20 ° C; Baking and curing. 2. The method according to claim 1, wherein the first electrodeposition step and the second electrodeposition step are performed using different electrodeposition tanks. 3. The method according to claim 1, wherein the thickness of the electrodeposition coating film formed in the first electrodeposition coating step is 8 to 20 μm. 4. The method according to claim 1, wherein the metal ion is at least one selected from the group consisting of cerium ions, bismuth ions, copper ions, zinc ions, molybdenum ions, and aluminum ions. 5. The method according to claim 1, wherein the neutralizing acid is at least one selected from the group consisting of acetic acid, lactic acid, formic acid, and sulfamic acid. 6. The cationic electrodeposition coating used in the second electrodeposition step further comprises a pigment, and the weight ratio of the pigment contained in the coating composition to the resin solid content is 1/9 or less. Electrodeposition method.