JP2002356647A - Lead-less cationic-electrodeposition paint composition and painting process - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an lead-less cationic-electrodeposition paint composition which contains low concentrations of VOC and metal ions and is environmental friendly because the small amount of the electrodeposition paint is required, and to provide an electrodeposition process using this. SOLUTION: The unleaded cationic-electrodeposition paint composition contains an aqueous medium, a binder resin which contains a cationic epoxy resin and a block isocyanate curing agent and is dispersed or dissolved in the aqueous medium, a neutralizing acid for neutralizing the cationic epoxy resin, an organic solvent and a metal catalyst. Its nonvolatile solid content is 22-35 wt.%. Its volatile organic content is not more than 1 wt.%. Its metal ion content is not more than 500 ppm. The amount of the neutralizing acid is 10-30 mg equivalent against 100 g of the resin solid content. The resistance of a 20 μm- thick film electrodeposited on a substrate is 1,000-1,500 kΩ/cm<2> .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[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. Further, the use efficiency of the paint is extremely high as compared with other coating methods, so that 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 an object to be coated 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 ionic groups, hydrated functional groups, and the like contained in the paint remain in the paint film to be formed, and these serve as a charge transfer medium. It is conceivable that the electric resistance value is reduced. Therefore, in the cationic electrodeposition coating, in order to realize high throwing power, it is necessary to eliminate such factors and increase the electric resistance value of the coating film.

Another cause of the decrease in throwing power is considered to be the low precipitation of the binder resin. The voltage applied to an unattached portion of the object to be coated is weak, and it is difficult for the solid content of the coating material to deposit on the object to be coated at the portion. In this case, if the precipitability of the binder resin from the coating emulsion to the object to be coated can be enhanced, the coating solids are precipitated even by a weak voltage applied to the non-adhered portion of the object to be coated, and all of the object to be coated are A coating film is uniformly formed on the portion.

Further, the conventional cationic electrodeposition coating composition comprises:
The non-volatile solid content was relatively low at about 20% by weight, and it was difficult to sufficiently enhance the precipitation property of the binder resin.

[0014]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems.
A high throwing power lead-free cationic electrodeposition coating composition having a low OC and metal ion concentration and a low effect on the environment because the amount of the electrodeposition coating material itself used is small, and an electrodeposition using the same. An object of the present invention is to provide a painting method.

[0015]

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 the aqueous medium, and a method for neutralizing the cationic epoxy resin. In a lead-free cationic electrodeposition coating composition containing a neutralizing acid, an organic solvent, and a metal catalyst, the nonvolatile solid content is 22 to 35% by weight, and the volatile organic content (VOC) is 1% by weight or less. Yes, the metal ion concentration is 500 ppm or less,
The amount of neutralizing acid is 1 to 100 g of binder resin solids.
0 to 30 mg equivalent, and a thickness of 10 to 2
The film resistance of the coating film deposited at 0 μm is 1000 to 1500
An object of the present invention is to provide a lead-free cationic electrodeposition coating composition having a kΩ / cm ² , which achieves the above object.

The present invention also provides an aqueous medium, a binder resin containing a cationic epoxy resin and a blocked isocyanate hardener dispersed or dissolved in the aqueous medium,
It contains a neutralizing acid for neutralizing a cationic epoxy resin, an organic solvent, and a metal catalyst, has a nonvolatile solid content of 22 to 35% by weight, a volatile organic content of 1% by weight or less, The ion concentration is 500 ppm or less, and the amount of the neutralizing acid is 10 to 3 with respect to 100 g of the binder resin solid content.
A step of immersing the object to be coated in a lead-free cationic electrodeposition coating composition having an equivalent weight of 0 mg;
m, a step of forming a coating film having a film resistance of 1000 to 1500 kΩ / cm ² , whereby the above object is achieved.

Here, "lead-free" means that it contains substantially no 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.

[0018]

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 of the present invention, a cation 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 a blocked polyisocyanate in which an isocyanate group of a polyisocyanate is blocked as a blocked isocyanate curing agent using a reactive epoxy resin.

Cationic Epoxy Resin The cationic epoxy resin used in the present invention includes an epoxy resin modified with an amine. This cationic epoxy resin is disclosed in JP-A-54-4978 and JP-A-56-3974.
A known resin described in, for example, Japanese Patent No. 4186 may be used.

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 reduce the by-produced 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.

[0027] 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.

These epoxy resins are used in a range of 0.3 to 0.3 after 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 capable of introducing a cationic group include primary amine, secondary amine and tertiary amine acid salt,
There are sulfide and acid mixtures. In order to prepare the primary, secondary and / or tertiary amino group-containing epoxy resin of the present invention, an acid salt of a primary amine, a secondary amine or a tertiary amine is used as an active hydrogen compound capable of introducing a cationic group. Used.

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 of the present invention is a compound having two isocyanate groups in one molecule.
Or more compounds. 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 normal 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.

Pigment-dispersed paste When a 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-dispersed paste is prepared by dispersing a pigment together with a pigment-dispersed 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 of 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 coating composition 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 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 of 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. 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, 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 will decrease, the affinity of the binder resin particles for the aqueous medium will decrease, and the dispersion stability will decrease. 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 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 the dispersion in water cannot be performed or the state is extremely lacking in stability. If the amount exceeds 30 mg equivalent, the amount of electricity required for precipitation increases. As a result, the precipitation of paint solids 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 during 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 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 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 a complicated operation is required 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 solvents usually contained in the coating composition include ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol monomer ethylhexyl ether, propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, propylene glycol monophenyl ether and the like. No.

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, the amount of the organic solvent used for adjusting the viscosity during the reaction is 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 the internal standard method, and VOC mixed as an organic solvent was measured.
It can be performed by measuring the amount of the component.

In the lead-free cationic electrodeposition coating composition of the present invention, the non-volatile solid content is adjusted to 22 to 35% by weight, preferably 24 to 27% by weight. This is in order to sufficiently enhance the solidification of the paint solids. When the non-volatile solid content of the coating composition is less than 22% by weight, the effect of enhancing the precipitation property is reduced irrespective of the conventional solid content concentration, and when it exceeds 35% by weight, coating workability such as uneven drying and secondary tare is deteriorated. However, this may cause coating film defects.

The increase in the non-volatile solid content of the coating composition may be carried out by increasing the amount of the solid component mixed in the aqueous medium. In addition, the measurement of the non-volatile solid content of the coating composition is as follows:
It can be performed by measuring the weight after drying a certain amount of the paint sample at 105 ° C. for 3 hours.

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

The lead-free cationic electrodeposition coating composition of the present invention is electrodeposited on an object to be coated 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 an object to be coated as a cathode and an 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 step includes (i) a step of immersing the object to be coated in the cationic electrodeposition coating composition, and (ii) a step of applying a voltage 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.

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. Further, the film resistance of the electrodeposition coating film is preferably 1000 to 1500 kΩ / cm ² at a film thickness of 10 to 20 μm. Film resistance of the coating film is in a state where no sufficient electrical resistivity can be obtained is less than 1000kΩ / cm ^2, a state in which poor throwing power, and the appearance of the coating film significantly inferior exceeds 1500kΩ / cm ² Become. The film resistance of the coating is preferably 1000 to 1300 kΩ / cm ² .

The film resistance of the electrodeposited film can be adjusted by controlling the amount and viscosity of the charge transfer medium of the deposited film.

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.

[0067]

The lead-free cationic electrodeposition coating composition of the present invention has a low VOC and metal ion concentration, a high throwing power, and requires a small amount of the coating itself, so that it has little effect on the environment.

[0068]

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 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 2 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.

Production Example 3 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 an appropriate 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 a suitable 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 to 120 ° C. for about 1 hour, and then 1390.2 parts of ethylene glycol monobutyl ether is added. The mixture is cooled to 85 to 95 ° C., homogenized, and then the quaternary mixture prepared above is prepared. 196.7 parts of the agent were added. The reaction mixture is brought to 85-9 until the acid value is 1.
After maintaining the temperature at 5 ° C., 37.0 parts of deionized water was added to complete the quaternization of the epoxy-bisphenol A resin to obtain a pigment dispersion resin having a quaternary ammonium salt portion (resin solid content of 50%). %).

Production Example 4 Production of Pigment Dispersion Paste 120 parts of the pigment dispersing resin obtained in Production Example 3, 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 The amine-modified epoxy resin obtained in Production Example 1 and Production Example 2
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 2% by weight based on the solid content. Milligram equivalent of acid per 100 g of resin solid content (MEQ (A))
Glacial acetic acid was added so that the solution became 24, 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.

To 2670 parts of this emulsion, 1310 parts of ion-exchanged water, 20 parts of a 10% cerium acetate aqueous solution and 15 parts of dibutyltin oxide were mixed to give a solid content of 2 parts.
4% by weight of a cationic electrodeposition coating composition was obtained. This cationic electrodeposition coating composition contains substantially no pigment, the solvent content (VOC) in the coating is 0.5%, and the resin solid content is 100 g.
The milligram equivalent of acid was 25.8, and the total concentration of eluted cerium ions and zinc ions was 210 ppm. The coating voltage of 20 μm at a bath temperature of 30 ° C. is 2
At 50 V, the coating resistance calculated from the residual current at the end of electrodeposition was 1000 kΩ / cm ² .

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 2 were made uniform at a solid content ratio of 70/30. Mixed. Thereafter, ethylene glycol-2-ethylhexyl ether was added so as to be 2% by weight based on the solid content. 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. By removing MIBK under reduced pressure, an emulsion having a solid content of 36% was obtained.

In 2670 parts of this emulsion, ion exchange
1310 parts of water replacement, 20 parts of a 10% cerium acetate aqueous solution and
And 15 parts of dibutyltin oxide to give a solid content of 3
0% by weight of the cationic electrodeposition coating composition was obtained. This katio
The electrodeposition coating composition contains substantially no pigment,
The amount of solvent in 0.5% of acid per 100g of resin solids
The milligram equivalent is 21.8, the eluted cerium ion
The total concentration of zinc and zinc ions was 200 ppm. Ma
The coating voltage of 20 μm at a bath temperature of 30 ° C. was 200 V,
The coating film resistance calculated from the residual current at the end of electrodeposition is 13
00kΩ / cm ^TwoMet.

Example 3 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 2 were made uniform at a solid content ratio of 70/30. Mixed. Thereafter, ethylene glycol-2-ethylhexyl ether was added so as to be 1% by weight based on the solid content. 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. By removing MIBK under reduced pressure, an emulsion having a solid content of 36% was obtained.

To 3330 parts of this emulsion, 650 parts of ion-exchanged water, 19 parts of a 10% cerium acetate aqueous solution and 15 parts of dibutyltin oxide were mixed to give a solid content of 34 parts.
By weight, a cationic electrodeposition coating composition was obtained. This cationic electrodeposition coating composition contains substantially no pigment, the amount of solvent in the coating is 0.3%, the milligram equivalent of acid per 100 g of resin solid content is 21.4, and cerium ion and zinc ion eluted Was 190 ppm. The coating voltage at 20 μm at a bath temperature of 30 ° C. was 300 V, and the coating resistance calculated from the residual current at the end of electrodeposition was 145.
It was 0 kΩ / cm ² .

[0084] Comparative Example Example 1 In a similar manner so as to be uniform and a block isocyanate curing agent obtained amine modified epoxy resin as in Preparation Example 2 obtained in Production Example 1 at a solid content ratio 70/30 mixture did. Thereafter, ethylene glycol-2-ethylhexyl ether was added so as to be 1% by weight based on the solid content. Glacial acetic acid was added to this so that the milligram equivalent of acid was 35 per 100 g of resin solids, and ion-exchanged water was added slowly to dilute. By removing MIBK under reduced pressure, an emulsion having a solid content of 36% was obtained.

1500 parts of this emulsion and 542 parts of the pigment-dispersed paste obtained in Production Example 4, 1901 parts of ion-exchanged water, 57 parts of a 10% cerium acetate aqueous solution and 9 parts of dibutyltin oxide were mixed to give a solid content of 20 parts. By weight, a cationic electrodeposition coating composition 1 was obtained. In the cationic electrodeposition coating composition, the ratio of the pigment to the resin solid content (P
/ V) is 1/3, the amount of solvent in the paint is 1.5%, the milligram equivalent of acid per 100 g of resin solids is 30.3, and the total concentration of eluted cerium and zinc ions is 61.
It was 0 ppm. The coating voltage at 20 μm at a bath temperature of 30 ° C. was 200 V, and the coating film resistance calculated from the residual current at the end of electrodeposition was 600 kΩ / cm ² .

The cationic electrodeposition coating films obtained by baking the cationic electrodeposition coating compositions obtained in Examples and Comparative Examples were subjected to the following evaluation tests, and 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) based on 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 sifted through a 380 mesh sieve was observed and evaluated according to the following criteria.

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

[0095]

[Table 1]

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Mitsuo Yamada 19-17 Ikedanakamachi, Neyagawa-shi, Osaka F-term in Nippon Paint Co., Ltd. 4J038 DB001 DB061 DB301 DB391 DG302 GA08 HA236 HA416 JA36 KA04 KA06 KA08 MA06 MA08 NA27 PA04

Claims (5)

[Claims] 1. An aqueous medium, a binder resin containing a cationic epoxy resin and a blocked isocyanate curing agent dispersed or dissolved in an aqueous medium, a neutralizing acid for neutralizing the cationic epoxy resin, an organic solvent, The lead-free cationic electrodeposition coating composition containing a metal catalyst has a nonvolatile solid content of 22 to 35% by weight, a volatile organic content of 1% by weight or less, and a metal ion concentration of 500% or less.
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 film resistance of the coating film electrodeposited to a thickness of 10 to 20 μm on the object to be coated is 1000 to 100 mg. A lead-free cationic electrodeposition coating composition having a viscosity of 1500 kΩ / cm ² . 2. The method according to claim 1, wherein the metal catalyst is cerium ion, bismuth ion, copper ion, zinc ion, molybdenum ion,
The lead-free cationic electrodeposition coating composition according to claim 1, which is at least one selected from the group consisting of aluminum ions. 3. The lead-free cationic electrodeposition coating composition 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. 4. The lead-free cationic electrodeposition coating composition according to claim 1, further comprising a pigment, wherein the weight ratio (P / V) between the pigment and the resin solids contained in the coating composition is 1/9 or less. object. 5. 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, has a non-volatile solid content of 22 to 35% by weight, a volatile organic content of 1% by weight or less, a metal ion concentration of 500 ppm or less, and a neutralizing acid amount of the binder resin solids. A step of immersing the object to be coated in a lead-free cationic electrodeposition coating composition having an equivalent weight of 10 to 30 mg per 100 g per minute; 10 to 20 μm in thickness, 100 in film resistance
Forming a coating film of 0 to 1500 kΩ / cm ² .