JP2002285391A - Electrodeposition coating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrodeposition coating method by which influence exerted on the environment can be reduced since VOC(volatile organic content) and metallic ion concentration are low, and the amount of the electrodeposition coating material to be used is also small. SOLUTION: The electrodeposition coating method includes: a stage where a lead-free cationic electrodeposition coating material composition having low VOC and metallic ion concentration is filled into an electrodeposition bath; a stage where the temperature of the electrodeposition coating material composition in the electrodeposition bath is controlled to the level equal to the glass transition temperature of a coating film to be electrodeposited on the material to be coated or to the range above the glass transition temperature by <=30 deg.C; a stage where the material to be coated is dipped into the electrodeposition coating material composition; and a stage where electrodeposition coating is performed with the material to be coated as the cathode to form a coating film on the surface of the material to be coated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrodeposition coating method and, more particularly, to an electrodeposition method using a high throwing power lead-free cationic electrodeposition coating composition having a low volatile organic content (VOC) and a low metal ion concentration. Related to painting method.

[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] On the other hand, in order to reduce coating costs, it is also desired to reduce the amount of paint used.

[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, it is necessary to improve the throwing power of the electrodeposition paint.

The cause of the decrease in throwing power is that the coating of the coating liquid is not insulated from the coating liquid due to the incomplete film formation of the binder resin deposited on the surface of the coating, and the electric resistance of the coating is low. Can be lowered. Therefore, in the cationic electrodeposition coating, in order to realize high throwing power, it is necessary to completely form the binder resin deposited on the surface of the object to be coated and to increase the electric resistance value of the coating film.

[0012]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems.
An object of the present invention is to provide an electrodeposition coating method capable of achieving a high throwing power with a small effect on the environment since the concentrations of OC and metal ions are low and the amount of the electrodeposition coating material used is small. .

[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 (VOC) of 1% by weight or less, a metal ion concentration of 500 ppm or less, and a neutralizing acid content of the binder resin solid content. A step of filling the electrodeposition bath with a lead-free cationic electrodeposition coating composition having an equivalent weight of 10 to 30 mg per 100 g; Adjusting the temperature to a temperature equal to the glass transition temperature (Tg) of the coating film to 30 ° C. above the glass transition temperature; immersing the coated object in the electrodeposition coating composition; As Forming an applied film on the surface of the object to be coated by performing electrodeposition under the temperature conditions of the electrodeposition bath adjusted as described above. Objective is achieved.

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]

DETAILED DESCRIPTION OF THE INVENTION The cationic electrodeposition coating composition contains various additives such as an aqueous medium, a binder resin, a neutralizing acid, an organic solvent, and a metal catalyst dispersed or dissolved in the aqueous medium. 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, an active hydrogen compound such as an amine is reacted with an epoxy ring of an epoxy resin as a cationic resin, and the epoxy group is opened to introduce a cationic group. It is preferable to use a cationic epoxy resin and use a blocked polyisocyanate in which an isocyanate group of the 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.

These epoxy resins may be modified with suitable resins such as polyester polyols, polyether polyols, and monofunctional alkylphenols. Further, the epoxy resin can be chain-extended by utilizing a reaction between an epoxy group and a diol or dicarboxylic acid.

[0025] These epoxy resins can be used after the ring-opening.
It is desirable to open the ring with an active hydrogen compound such that the amine equivalent is 4.0 meq / g, more preferably 5 to 50% of which is occupied by a primary amino group.

Examples of the active hydrogen compound into which a cationic group can be introduced include primary amine, secondary amine, and tertiary amine acid salts.
There are sulfide and acid mixtures. First grade used in the present invention,
In order to prepare a secondary or / and tertiary amino group-containing epoxy resin, a primary amine, a secondary amine and an acid salt of a tertiary amine are used as an active hydrogen compound capable of introducing a cationic group.

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

Blocked Isocyanate Curing Agent The polyisocyanate used in the blocked isocyanate curing agent 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 that is added to the polyisocyanate group and is stable at room temperature, but can regenerate a free isocyanate group when heated above 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.

The pigment electrodeposition coating composition generally contains a pigment as a colorant. The lead-free cationic electrodeposition coating composition used in the present invention also contains a commonly used pigment. Examples of such pigments include coloring pigments such as titanium white, carbon black and red iron oxide, extender pigments such as kaolin, talc, aluminum silicate, calcium carbonate, mica, clay and silica, zinc phosphate, iron phosphate, Rust preventive pigments such as aluminum phosphate, calcium phosphate, zinc phosphite, zinc cyanide, zinc oxide, aluminum tripolyphosphate, zinc molybdate, aluminum molybdate, calcium molybdate and aluminum phosphomolybdate, aluminum zinc phosphomolybdate And the like.

The pigment is generally contained in the coating composition in an amount of 1 to 35% by weight, preferably 15 to 30% by weight of the total solids of the electrodeposition coating composition.

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, since the pigment is in a powder form, it is difficult to disperse the pigment in a low concentration uniform state used in the electrodeposition coating composition 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 coating composition 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 distributed to the electrodeposition coating composition as eluates from pigments containing salts or metal ions in combination with a suitable 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 amount of the metal catalyst is adjusted so 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 Coating Composition The lead-free cationic electrodeposition coating composition used in the present invention is obtained by dispersing the above-mentioned metal catalyst, cationic epoxy resin, blocked isocyanate curing agent, and pigment dispersion paste in an aqueous medium. It is prepared by 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,
It is an inorganic or organic acid such as acetic acid or 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 sufficient to react with active hydrogen-containing functional groups such as primary and secondary amino groups and hydroxyl groups in the cationic epoxy resin at the time of curing to give a good cured coating film. And should generally be expressed as a weight ratio of solid content of the cationic epoxy resin to the blocked isocyanate curing agent of 90/10 to 50/50.
50, preferably in the range of 80/20 to 65/35.

The coating composition may 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 indispensable 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.

The organic solvent usually contained in the coating composition includes 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 of 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.

The lead-free cationic electrodeposition coating composition used in the present invention is electrodeposited on a substrate to form an electrodeposition coating film (uncured). The object to be coated is not particularly limited as long as it has electrical conductivity, and examples thereof include an iron plate, a steel plate, an aluminum plate, a surface-treated one thereof, and a molded product thereof.

The electrodeposition coating is usually carried out 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,
When the voltage exceeds 0 V, the coating film is destroyed and has an abnormal appearance. At the time of electrodeposition coating, the bath temperature of the coating composition is usually adjusted to 10 to 45 ° C.

The electrodeposition process includes (i) a process of immersing the object to be coated in the cationic electrodeposition coating composition, and (ii) a voltage is applied between the above-mentioned object to be used as a cathode and an anode to form a coating. Deposition process. 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 temperature of the electrodeposition bath is usually 10 to
It is adjusted to 45 ° C., but in the method of the present invention, a maximum of 60 ° C.
The T of the coating film to be electrodeposited on the object to be coated within a range of at least 10 ° C.
The temperature of the coating composition in the electrodeposition bath is determined on the basis of g. This is because even when the kind of the binder resin contained in the coating composition changes, the film formation of the binder resin deposited on the surface of the object to be coated is completely performed. Here, the temperature of the electrodeposition bath is 60 ° C.
When it exceeds, the change with time of the paint is large and it becomes difficult to maintain a predetermined quality. In addition, poor appearance such as drying unevenness also occurs. If the temperature is lower than 10 ° C., a normal electrodeposition coating film cannot be obtained.

Specifically, the temperature of the electrodeposition bath is adjusted within a range from a temperature equal to the Tg of the coating film to be coated on the substrate to 30 ° C. above the Tg. If the temperature of the electrodeposition bath is lower than the above Tg, the heat flow of the deposited coating film is not sufficient, the coating film is not uniformly coated, and the increase of the coating film resistance is hindered. When the temperature exceeds ℃, the viscosity of the deposited film is lowered more than necessary, which also prevents obtaining a high coating resistance.
The temperature of the electrodeposition bath is preferably 5 to 5 g above the Tg of the electrodeposited coating.
To 25 ° C, more preferably 10 to 20 ° C.

The term “Tg” as used in the present invention means a theoretical value calculated from the Tg of all resin components contained in the cationic electrodeposition coating composition. The calculation of Tg is performed according to the Fox equation. The Fox equation is shown below.

[0061]

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

[0062] 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 the glass transition of the resin with a differential scanning calorimeter is used.

The thickness of the electrodeposited film is preferably 10 to 20 μm. When the film thickness is less than 10 μm, the rust prevention property is insufficient, and when it exceeds 20 μm, the paint is wasted.

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 lead-free cationic electrodeposition coating composition used therein has a low VOC and metal ion concentration, a high throwing power, and requires a small amount of the coating itself. Therefore, the impact on the environment is small.

[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 A flask equipped with a stirrer, condenser, nitrogen inlet tube, thermometer and dropping funnel was charged with 92 parts of 2,4- / 2,6-tolylene diisocyanate (weight ratio = 8/2), methyl 95 parts of 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%).

Example 1 Production of Cationic Electrodeposition Coating Composition 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 20/50. / 30 to mix. Glacial acetic acid was added to this so that the milligram equivalent of acid (MEQ (A)) per 100 g of resin solid content was 30, and then ion-exchanged water was slowly added to dilute the mixture.
By removing MIBK under reduced pressure, the solid content was reduced to 36%.
% Emulsion 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, a cationic electrodeposition coating composition 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 composition was 10 ° C., the solvent amount (VOC) in the coating was 0.5%, 100g resin solids
The milligram equivalent of acid was 24.2, and the total concentration of eluted cerium ions and zinc ions was 390 ppm. The temperature of the electrodeposition coating bath was 30 ° C.

Example 2 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 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 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, a cationic electrodeposition coating composition was obtained. The Tg of the electrodeposited coating film (deposited film) calculated from each resin Tg of all the resin components of the cationic electrodeposition coating composition was 14 ° C., the amount of the solvent in the coating was 0.5%, and the solid content of the resin was 0.5%. The milligram equivalent of acid per 100 g was 25.5, and the total concentration of eluted cerium ions and zinc ions was 205 ppm. The temperature of the electrodeposition coating bath was 28 ° C.

Comparative Example 1 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 at a solid content ratio of 40/30/30 to be uniform. did. Thereafter, ethylene glycol-2-ethylhexyl ether was added so as to be 3% 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 5, 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, a cationic electrodeposition coating composition was obtained. The Tg of the electrodeposited coating film (precipitated film) calculated from each resin Tg of all the resin components of the cationic electrodeposition coating composition was 7 ° C., the solvent amount in the coating material was 0.9%, and the resin solid content was 0.9%. The milligram equivalent of acid per 100 g was 31.1, and the total concentration of eluted cerium ions and zinc ions was 590 ppm. The temperature of the electrodeposition coating bath was 30 ° C.

Comparative Example 2 In the same manner as in Example 1, the amine-modified epoxy resin obtained in Production Example 1 and the blocked isocyanate curing agent obtained in Production Example 4 were made uniform at a solid content ratio of 70/30. Mixed. Thereafter, ethylene glycol-2-ethylhexyl ether was added so as to be 3% 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 30, and then ion-exchanged water was slowly added for dilution. 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, 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, a cationic electrodeposition coating composition 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 composition was 1.5 ° C., the solvent amount in the coating material was 0.9%, The milligram equivalent of acid was 25.7 per 100 g of solids, and the total concentration of eluted cerium ions and zinc ions was 400 ppm.
The temperature of the electrodeposition coating bath was set at 33 ° C.

The following evaluation tests were performed on the cationic electrodeposition coating films obtained by baking the cationic electrodeposition coating compositions obtained in Examples and Comparative Examples. The results are shown in Table 1.

The throwing power was evaluated by the Ford pipe method. The evaluation criteria at that time were as follows.

：: Good throwing power (21 cm or more) ×: Poor throwing power (less than 21 cm)

Electrodeposition was performed on a cold-rolled steel sheet obtained by treating the saltwater-immersion corrosion-resistant cationic electrodeposition coating composition with zinc phosphate so that the thickness of the dried coating film became 20 μm. This was baked at 170 ° C. for 25 minutes, and the resulting cationic electrodeposition coating film was immersed in a 5% saline solution at 55 ° C. for 240 hours, and the cut portion was tape-peeled. The peel width on both sides of the cut portion was evaluated according to the following criteria.

：: <3 mm Δ: 3 to 6 mm ×:> 6 mm

The cationic electrodeposition paint obtained above was electrodeposited on a smooth untreated zinc phosphate steel sheet so as to have a dry film thickness of 20 μm.
The coated film was baked at 160 ° C. for 10 minutes, and the surface of the obtained coating film was measured with a surface roughness meter Surftest-211 (manufactured by Mitutoyo) on the basis of a cutoff of 0.8 mm and a scan length of 4 mm.
(Ra) was measured.

：: Ra value less than 0.2 μm ×: Ra value 0.2 μm or more

Stability of the electrodeposition coating composition The cationic electrodeposition coating composition was stored at 40 ° C. for 2 weeks, and then the filterability when sieved through a 380 mesh sieve was observed and evaluated according to the following criteria.

：: Can be filtered without any problem ×: Cannot be filtered

[0097]

[Table 1]

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Mitsuo Yamada 19-17 Ikedanakamachi, Neyagawa-shi, Osaka F-term in Nippon Paint Co., Ltd. (reference) 4J038 DB061 DB391 DG161 DG301 JA37 JB18 JC15 KA02 KA03 KA04 KA06 MA08 MA09 MA10 MA13 NA01 NA23 PA04 PB07 PC02

Claims (5)

[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.
Filling the electrodeposition bath with a lead-free cationic electrodeposition coating composition having a g equivalent weight; the temperature of the electrodeposition bath is in the range of 60 ° C. to 10 ° C. at the highest and the glass transition of the coating film electrodeposited on the object Adjusting the temperature to a range from a temperature equal to the temperature to 30 ° C. above the glass transition temperature; immersing the object to be coated in the electrodeposition coating composition;
And forming a coating film on the surface of the object to be coated by performing the electrodeposition under the temperature conditions of the electrodeposition bath adjusted as described above using the object as a cathode. 2. The method according to claim 1, wherein the temperature of the electrodeposition bath is 25 to 35 ° C. 3. The method according to claim 1, wherein the glass transition temperature of the coating film electrodeposited on the substrate is from 5 to 20 ° C. 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.