JP2002282773A - Method of forming multilayered film and multilayered film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of forming a multilayered film, which is capable of providing a 3 coat film having high throwing power even in a 3 coat 1 base coating system using a water paint and providing the 3 coat film having the same film performance such as appearance and corrosion resistance as that obtained by the conventional 3 coat 3 bake coating system. SOLUTION: In the method of forming the multilayered film by forming an unhardened water based intermediate coating film, water based film and clear film by wet-on-wet system on a hardened cationic delectrodeposition film and after that, hardening by heating at the same time, a lead free cationic electrodeposition having low volatile organic component content(VOC) and low metallic ion concentration is used as the cationic electrodeposition coating material and one prepared by dispersing a film forming resin solution with a nonionic dispersing agent and/or a catonic dispersing agent in water is used as the intermediate coating material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a laminated coating film, and more particularly, to a method using a high throwing power lead-free cationic electrodeposition coating material having a low volatile organic content (VOC) and a low metal ion concentration. The present invention relates to a method for forming a laminated coating film having excellent appearance.

[0002]

2. Description of the Related Art In recent years, in the field of paints, especially in the field of automobile coating, resource saving, cost saving and environmental burden (VOC and HOC) have been observed.
(APs, etc.) In order to solve the problem of reduction, shortening of the coating process is strongly demanded. That is, in the conventional automobile coating finishing procedure, the electrodeposition coating, the intermediate coating, and the topcoat have been performed by a three-coat three-bake coating method in which the coating is baked after each coating. After baking the electrodeposition coating film, the three coating processes of intermediate coating, base coating and clear coating are performed on the wet coating on a wet basis, and a three-wet coating system for baking these wet coating films collectively is performed. It is required to reduce the number of baking steps and to maintain the same appearance and corrosion resistance as a three-coat film obtained by a conventional three-coat three-bake coating method.

In particular, when a conventional electrodeposition paint is used in a three-coat, one-bake coating method, the electrodeposition paint does not have perfect throwing power. It was thick and uneconomical. Furthermore, when the smoothness of the electrodeposition coating film is poor, the smoothness of the intermediate coating film formed thereon is reduced. In addition, when a conventional intermediate coating or base coating is used, there is a drawback in that the obtained coating film is incompatible with the coating film, and inconveniences such as reversal occur, resulting in inferior finished appearance.

[0004] Further, in order to effectively reduce the environmental burden, it is preferable to perform the coating step with a water-based coating.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to provide an economical method by a three-coat one-bake coating method using an aqueous paint for an intermediate coating and a top coating. It is an object of the present invention to provide a method for forming a laminated coating film capable of providing a three-coat film having excellent coatability and a coating appearance such as a finished appearance and corrosion resistance, which is equivalent to a conventional three-coat three-bake coating method.

[0006]

According to the present invention, an electrodeposition coating is formed on the surface of an object to be coated by an electrodeposition coating method using a cationic electrodeposition coating, and this is heated and cured to form a cured electrodeposition coating. Forming an uncured intermediate coating by applying an aqueous intermediate coating over the cured electrodeposition coating (I)
I), a step of applying an aqueous base paint on the uncured intermediate coating film to form an uncured base coating film (III), and applying a clear paint on the uncured base coating film Forming a uncoated clear coating film (IV), and simultaneously heating and curing the uncured intermediate coating film, base coating film and clear coating film (V). In the method, the cationic electrodeposition coating composition is an aqueous medium, a binder resin containing a cationic epoxy resin and a blocked isocyanate curing agent dispersed or dissolved in the aqueous medium, and a neutralization for neutralizing the cationic epoxy resin. It contains an 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 ppm.
And the amount of the neutralizing acid is 100
A lead-free cationic electrodeposition coating material having an equivalent weight of 10 to 30 mg per g, wherein the aqueous intermediate coating material is obtained by dispersing a coating film forming resin solution in water with a nonionic dispersant and / or a cationic dispersant. It is intended to provide a method for forming a laminated coating film characterized by containing the above, thereby achieving the above object.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The coating film forming method of the present invention comprises a step (I) of forming a cured electrodeposition coating film by applying an electrodeposition coating material on an object to be coated and then heating and curing to form a cured electrodeposition coating film. Step (II) of applying an aqueous intermediate coating on the coating to form an uncured intermediate coating, applying an aqueous base coating on the intermediate coating to form an uncured Step of forming base coating film (II
I), a step (IV) of applying a clear coating on the base coating film to form an uncured clear coating film, and forming an uncured intermediate coating film, a base coating film and a clear coating film. At the same time, it includes a step (V) of heating and curing to obtain a laminated coating film.

Step (I) In the present invention, the step (I) is to form an electrodeposition coating film by applying an electrodeposition coating material on an object to be coated and then curing by heating.

Lead-free cationic electrodeposition coating composition The electrodeposition coating composition of the present invention comprises an aqueous medium, a binder resin containing a cationic epoxy resin and a blocked isocyanate curing agent, and a cationic epoxy resin dispersed or dissolved in the aqueous medium. Containing a neutralizing acid, an organic solvent, and a metal catalyst, a volatile organic content 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. 10 to 100 g
It is a lead-free cationic electrodeposition paint having an equivalent weight of 30 mg. That is, 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.

[0010] 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.

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.

The cationic epoxy resin includes an epoxy resin modified with an amine. This cationic epoxy resin is disclosed in JP-A-54-4978 and JP-A-56-34.
For example, a known resin described in JP-A-186 or the like may be used.

[0013] 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.

The blocked isocyanate curing agent is obtained by adding a blocking agent to polyisocyanate. The 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 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 electrodeposition paint generally contains a pigment as a colorant. However, it is preferable that the lead-free cationic electrodeposition paint used in the present invention does not contain a coloring pigment. This is because the throwing power of the electrodeposition 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) between the pigment contained in the paint and the resin solid content is 1/9 or less. If the amount of the pigment in the coating exceeds 1/9 by weight with respect to the solid content of the resin, the throwing power of the electrodeposition coating decreases, and the amount of the coating increases, which is uneconomical.

Examples of the pigment which may be contained in the lead-free cationic electrodeposition coating used in 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.

However, for example, lead-based rust preventive pigments such as basic lead silicate, basic lead sulfate, lead tin and cyanamide lead are not used, or even if they are used, they are diluted paints (added to the electrodeposition bath). Should be used in such an amount that the lead ion concentration in the quenched state) is 50 ppm or less, preferably 20 ppm or less. When the lead ion concentration is high, it is not only harmful to the environment but also the smoothness of the coating film may be reduced.

When a pigment is used as a component of an electrodeposition paint,
Generally, a pigment is 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.

The lead-free cationic electrodeposition coating composition used in the present invention contains a metal catalyst for improving the corrosion resistance of the coating film as a metal ion. 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 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.

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. Also,
Usually, the aqueous medium contains a neutralizing acid to neutralize the cationic epoxy resin and improve the dispersibility of the binder resin emulsion. Neutralizing acids are inorganic or organic acids such as hydrochloric, nitric, phosphoric, formic, acetic, lactic acids.

When the amount of the neutralizing acid contained in the paint is increased, the neutralization ratio of the cationic epoxy resin is increased, the affinity of the binder resin particles for the aqueous medium is increased, and the dispersion stability is increased. 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 material is small, the neutralization rate of the cationic epoxy resin decreases, and the affinity of the binder resin particles for the aqueous medium decreases.
Dispersion stability is reduced. 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 paint, it is preferable to reduce the amount of neutralizing acid contained in the paint 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 m per 100 g of the binder resin solid content contained in the paint.
It is represented by the number of g equivalents and is indicated as MEQ (A).

The amount of the blocked isocyanate curing agent is sufficient to give a good cured coating by reacting with the active hydrogen-containing functional groups such as primary and secondary amino groups and hydroxyl groups in the cationic epoxy resin during curing. 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 can contain tin compounds such as dibutyltin dilaurate and dibutyltin oxide, and conventional urethane cleavage catalysts. Since substantially no lead is contained, the amount is preferably 0.1 to 5% by weight of the resin solids.

The 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.

Organic solvents usually contained in coatings include ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol mono2
-Ethylhexyl ether, propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, 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, and an ultraviolet absorber.

The electrocoating film forming method in the electrodeposition coating film formation method of Step (I), electrodeposition coating and electrodeposition coating film of lead-free cationic electrodeposition coating described above to a coating object (uncured) To form 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.

In the electrodeposition coating, first, a lead-free cationic electrodeposition coating material is filled in an electrodeposition tank, and a voltage of 50 to 450 V is usually applied between the electrode and the anode while the object to be coated is immersed in the coating material as a cathode. Perform by applying. 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.

The electrodeposition process includes (i) a process of immersing an object to be coated in a cationic electrodeposition paint, and (ii) a process in which the object is used as a cathode.
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 paint is usually 10 to 45
Adjusted to ° C.

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. The uncured cationic electrodeposition film thus obtained is set after the electrodeposition process is completed, as it is or after washing with water. After completion of the electrodeposition process,
0-260 ° C, preferably 160-220 ° C, 10-
Cure by baking for 30 minutes.

Step (II) In the present invention, the step (II) comprises the steps of:
An aqueous intermediate coating is applied to form an uncured intermediate coating film.

The aqueous intermediate coating used in the aqueous intermediate coating step (II) conceals the base,
It is applied in order to ensure surface smoothness (improve appearance) after overcoating and to impart physical properties of a coating film such as impact resistance and chipping resistance. The aqueous intermediate coating composition can be obtained by dispersing a film-forming resin solution in a hydrophilic medium such as water or alcohol.

The coating film forming resin solution is one which is dispersed in water by a nonionic dispersant and / or a cationic dispersant. When an aqueous intermediate coating containing an anionic dispersant was applied, a basic substance such as an amine present as a counter ion of the anionic functional group was contained in the coating film, so that the coating film was heated to cure. In some cases, the basic substance undergoes a chemical change or a color forming substance is formed, and the coating film turns yellow. In addition, the basic substance that evaporates from the uncured intermediate coating film is trapped inside the clear coating film formed in step (IV), and the clear coating film also turns yellow. Properties and design are reduced.

In the aqueous intermediate coating composition, the above-mentioned yellowing of the coating film can be suppressed by using a nonionic dispersant and / or a cationic dispersant to disperse the resin solution for forming the coating film in water. Can be. That is, when a nonionic dispersant having a nonionic functional group is used, the nonionic functional group does not need to form a salt with an amine or the like.
No volatile basic substances are present as counterions and no yellowing of the coating occurs. When using a cationic dispersant having a cationic functional group, -COO present as a counter ion of the cationic functional group ^- anion having an acidic group such as will not cause yellowing of the paint film.

The nonionic dispersant and the cationic dispersant are not particularly limited as long as they can disperse the coating film forming resin solution in water, and include a surfactant and a dispersing resin. The nonionic dispersant and the cationic dispersant need only have a structure containing a portion having an affinity for the film-forming resin solution and a hydrophilic group, and the surfactant and the dispersant are strictly distinguished. It is not necessary.

The nonionic dispersant has a nonionic hydrophilic group, but the present invention does not exclude a nonionic dispersant having a cationic functional group in the molecule.

The nonionic dispersant is not particularly restricted but includes, for example, polyoxyalkylene alkyl ethers such as polyoxyethylene lauryl ether, polyoxyethylene oleyl ether and polyoxyethylene stearyl ether; polyoxyethylene alkyl phenyl ether; Polyoxyalkylene ethers and / or fatty acid esters of sorbitan such as ethylene sorbitan stearate; oxyalkylene copolymers such as oxyethylene oxypropylene block copolymer; glycerin polyoxyalkylene ethers and / or fatty acid esters such as polyoxyethylene glyceride And the like. Among them, polyoxyalkylene alkyl ethers are preferable, and polyoxyethylene lauryl ether, polyoxyethylene oleyl ether, and polyoxyethylene stearyl ether are more preferable.

As the nonionic dispersant, a commercially available nonionic surfactant can be used.
For example, New Call 1120, New Call 1820
(Both manufactured by Nippon Emulsifier Co., Ltd.) and the like. As the nonionic dispersing agent, for example, a nonionic dispersing resin in which a nonionic functional group such as a hydroxyl group, an oxyethylene group, or an amide group is introduced into the resin can also be used.

The cationic dispersant has a cationic functional group which is ionized in water to become an organic cation. In the present invention, the cationic dispersant excludes those further having a nonionic functional group in the molecule. is not. The cationic dispersant may have a counter ion. Examples of the counter ion include inorganic acids such as hydrochloric acid, nitric acid, and phosphoric acid; formic acid,
Examples thereof include those derived from organic acids such as acetic acid, lactic acid, sulfamic acid, and acetylglycinic acid.

The cationic dispersant is not particularly restricted but includes, for example, alkyltrimethylammonium chloride; polyoxyethylenealkylamine and the like. Commercially available cationic surfactants can also be used as the cationic dispersant, and commercially available products include, for example, Adecamine 4MAC-30, Adecamine LDM
(Above, manufactured by Asahi Denka Co., Ltd.) and the like.

As the cationic dispersing agent, for example, a cationic dispersing resin into which a cationic functional group such as an amino group, an imino group or a hydrazino group is introduced can be used.

When a surfactant is used as a nonionic or cationic dispersant, the hydrophilic-lipophilic balance (HLB) is used.
Is preferably 6 or more. If it is less than 6, the hydrophilicity becomes too low, and the film-forming resin solution may not be sufficiently dispersed. More preferably, it is 12 or more.

When a dispersing resin is used as a nonionic or cationic dispersing agent, the number average molecular weight is 400 to 200.
00 is preferred. If it is less than 400, the dispersion of the coating film forming resin solution may be insufficient,
When it exceeds 00, the fluidity of the obtained resin solution decreases,
Handling may be difficult. More preferably, it is 600 to 10,000.

The nonionic and cationic dispersants may be used alone or in combination of two or more, and may be used in combination. The content of the nonionic dispersant and / or the cationic dispersant is 2 to 50% by weight based on the solid content based on the total amount of the coating film forming resin solution and the content of the nonionic dispersant and / or the cationic dispersant. %. If the amount is less than 2% by weight, the dispersion of the coating film forming resin solution becomes insufficient, and the dispersion stability may be reduced. If the amount exceeds 50% by weight, the physical properties of the obtained coating film may be reduced. More preferably, it is 2 to 40% by weight.

In the present specification, the coating film forming resin solution is not particularly limited as long as it is water-dispersible with a nonionic dispersant and / or a cationic dispersing agent. A curing agent and / or pigment may be included.

The film-forming resin is not particularly restricted but includes, for example, acrylic resins; polyester resins; alkyd resins; modified alkyd resins such as epoxy-modified, rosin-modified and phenolic resins; polyurethane resins; olefin resins; Resins used in ordinary solvent-type paints can be mentioned, and one or more of these can be used.

Preferred film-forming resins are solvent-type thermosetting resins having anionic functional groups. For example, an acrylic resin, a polyester resin, a polyurethane resin, an alkyd resin, a vinyl acetate resin, and the like can be given. Above all, from the viewpoint of water resistance and weather resistance, acrylic resin,
Polyester resins are preferred.

The anionic functional group is not particularly limited as long as it can form a counter ion with a volatile basic substance, and examples thereof include a carboxyl group, a sulfonic group, and a phosphate group. .

These anionic functional groups can be introduced by, for example, copolymerizing a monomer component containing a monomer having these anionic functional groups to produce a film-forming resin. Examples of the monomer having a carboxyl group include (meth) acrylic acid, crotonic acid, ethyl acrylic acid, propyl acrylic acid, isopropyl acrylic acid, itaconic acid, maleic anhydride, and fumaric acid. Examples of the monomer having a sulfonic acid group include t-
Butyl acrylamide sulfonic acid; The anionic functional group may also be introduced after producing the film-forming resin. Part of the anionic functional group is preferably a carboxyl group.

The film-forming resin may further contain, if necessary, a cationic functional group such as an amino group, an imino group and a hydrazino group.
And / or a nonionic functional group such as a hydroxyl group, an amide group, or a polyoxyethylene group. The cationic functional group and the nonionic functional group can be introduced by producing a film-forming resin by copolymerizing with a monomer having these functional groups and, if desired, other monomers. These functional groups can be introduced after the production of the film-forming resin. Among these functional groups, a nonionic functional group is preferably contained from the viewpoint of curability. Monomers having an anionic functional group, a cationic functional group and a nonionic functional group and other monomers,
One or two or more can be used respectively.

The film-forming resin has an acid value of 5 to 100 (mg
(KOH / g resin). If it is less than 5, the adhesion of the coating film may be poor and the curing may be poor. If it exceeds 100, the hydrophilicity may be too high and the water resistance of the coating film may deteriorate. More preferably, it is 30 to 70.

When the coating film forming resin contains a hydroxyl group, it preferably has a hydroxyl value of 30 to 150. If it is less than 30, curing failure may occur, and 1
If it exceeds 50, excessive hydroxyl groups may remain in the coating film after curing, resulting in poor water resistance. More preferably, 5
It is 0-100.

The coating film forming resin has a number average molecular weight of 1,000.
It is preferable that it is ~ 30000. If it is less than 1,000, physical properties such as solvent resistance of the cured coating film may be inferior, and if it exceeds 30,000, since the viscosity of the resin solution is high, it is difficult to handle in operation such as emulsification and dispersion of the obtained resin. Not only that, the appearance of the resulting coating film may be significantly reduced. More preferably, it is 2000 to 20000.

The method for producing the film-forming resin is not particularly limited, and can be appropriately selected depending on the kind and properties of the desired film-forming resin. Examples thereof include a melt polymerization method, a transesterification method, and an interface method. Conventionally known production methods such as a polymerization method and a solution polymerization method can be used.

The film-forming resin is usually an amino resin and / or
Alternatively, it is used in combination with a curing agent such as a blocked isocyanate resin. A combination of an acrylic resin and / or a polyester resin and a melamine resin is preferred from the viewpoint of pigment dispersibility and workability. One or more curing agents can be used.

As used herein, the term “volatile basic substance” means a basic substance having a boiling point of 300 ° C. or lower. Volatile basic substances are those used for neutralization of the film-forming resin, and include, for example, nitrogen-containing basic substances. Examples of the nitrogen-containing basic substance include:
Inorganic basic substances and organic basic substances can be mentioned. Examples of the inorganic basic substance include ammonia and the like. Examples of the organic basic substance include a C1-20 linear or branched alkyl group-containing 1 such as methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, isopropylamine, diisopropylamine, and dimethyldodecylamine. To tertiary amines; C such as monoethanolamine, diethanolamine and 2-amino-2-methylpropanol;
1-20 linear or branched hydroxyalkyl group-containing tertiary amines; C1-20 linear or branched alkyl groups such as dimethylethanolamine, diethylethanolamine and the like; C1-C20 substituted or unsubstituted chain polyamines such as diethylenetriamine, triethylenetetramine, etc .; morpholine, N-methylmorpholine, N-ethylmorpholine, etc. C1-20 substituted or unsubstituted cyclic monoamines; amines such as C1-20 substituted or unsubstituted cyclic polyamines such as piperazine, N-methylpiperazine, N-ethylpiperazine and N, N-dimethylpiperazine. One or more volatile basic substances can be used.

The volatile basic substance is preferably an amine, more preferably a C1-20 linear or branched alkyl group and / or a C1-20 linear or branched alkyl group. And tertiary amines containing a hydroxyalkyl group, more preferably triethylamine and dimethylethanolamine.

The amount of the volatile basic substance is not particularly limited as long as it is an amount sufficient to neutralize the film-forming resin. Therefore, the neutralization ratio is preferably 120% or less. 12
If it exceeds 0%, the coating unit area of the volatile basic substance contained in the uncured intermediate coating film and the uncured base coating film is 1
The total amount per mm ² cannot be reduced to 7 × 10 ⁻⁶ mmol or less, and the resulting coating film may be yellowed.

In the present invention, if the film-forming resin having an anionic functional group can be stably dispersed, the use of an aqueous intermediate coating composition containing no volatile basic substance is not excluded. Absent.

The aqueous intermediate coating preferably contains an elastomer. By containing an elastomer, flexibility can be imparted to the obtained intermediate coating film, and impact resistance and chipping resistance can be improved. Furthermore, as described above, since the resin layer having the same physical properties as the elastomer is formed on the side of the electrodeposition coating film which comes into contact with the air, the adhesion between the electrodeposition coating film and the intermediate coating film is formed. As a result, impact resistance and chipping resistance can be drastically improved.

The elastomer preferably has a designed glass transition temperature of -110 to 10 ° C. If it exceeds 10 ° C, the resulting coating film will be inferior in flexibility and impact resistance, and if it is lower than -110 ° C, it is actually difficult to prepare it. More preferably, it is -100 to -10C. The design glass transition temperature can be determined by calculation from the blending amount of the raw materials when producing the elastomer.

Specific examples of the elastomer include a homopolymer of a conjugated diene monomer such as butadiene, isoprene and chloroprene, or a conjugated diene monomer and ethylene, propylene, ethylidene, norbornene, dicyclopentadiene, 4-hexadiene, vinyl acetate, vinyl chloride, styrene, acrylonitrile, isobutylene, (meth) acrylic acid (ester), and other random or block copolymers; polyurethanes synthesized by polyaddition reaction of diisocyanate and diol Thermoplastic elastomer; dimethyl terephthalate,
Polyester thermoplastic elastomer synthesized from 1,4-butanediol, poly (tetramethylene) glycol, etc. by transesterification and polycondensation; transesterification and polymerization using lactam, dicarboxylic acid, polyetherdiol as raw materials Examples thereof include a polyamide-based thermoplastic elastomer synthesized by a condensation reaction.

The elastomer can be stably present in the aqueous intermediate coating by using a water-dispersed one or a water-soluble one. As a method of dispersing in water, for example, a dispersant such as a dispersing resin and a surfactant can be separately applied and emulsified and dispersed in an aqueous medium. Alternatively, it can be carried out by introducing a functional group such as a reactive group and a polar group into the elastomer and then as it is or in a form capable of being self-emulsified and dispersed in an aqueous medium by a neutralizing agent.

When the functional group is a cationic group such as an amine, an inorganic acid such as hydrochloric acid, nitric acid and phosphoric acid; and an organic acid such as formic acid, acetic acid, lactic acid, sulfamic acid and acetylglycinic acid can be used as the neutralizing agent. Acids can be mentioned. On the other hand, when the functional group is an anionic group such as a carboxyl group, an inorganic base such as ammonia; methylamine, dimethylamine, triethylamine, monoethanolamine, diethanolamine, N-methylethanolamine, triethylamine, N, Organic bases such as primary, secondary and tertiary amine salts such as N-dimethylethanolamine, morpholine and piperazine can be mentioned. As the dispersing resin and the surfactant, those conventionally used as dispersing agents can be used.

While only one type of elastomer can be used, two or more types may be used in order to balance the performance of the coating film.

The aqueous intermediate coating composition may contain a curing agent when it is necessary to cure the elastomer during the formation of the coating. The curing agent is not particularly limited, and examples thereof include an amino resin and / or a blocked isocyanate resin. Melamine resins are preferred from the viewpoint of pigment dispersibility and workability.

The content of the elastomer with respect to the solid content of the resin in the aqueous intermediate coating composition is preferably 20 to 100% by weight based on the solid content. If the amount is less than 20% by weight, the flexibility and chipping resistance of the obtained coating film are reduced. More preferably, it is 30 to 100% by weight. The resin solids refers to the total solids of the elastomer and other optional film-forming resins and curing agents added.

The aqueous intermediate coating usually contains a pigment. In the aqueous intermediate coating, those exemplified in the electrodeposition coating can be mentioned, to improve the weather resistance,
From the viewpoint of ensuring concealing properties, a coloring pigment is preferable. Especially titanium dioxide is excellent in white color hiding,
Moreover, it is more preferable because it is inexpensive. It can be a standard gray water-based intermediate coating with carbon black and titanium dioxide as the main pigments as the pigment, or a so-called color that combines a set gray that combines lightness or hue with a top coating and various colored pigments An aqueous intermediate coating can also be used.

The pigment is used in the aqueous intermediate coating composition in a ratio of the weight of the pigment to the total weight of the pigment and the resin solids (P
WC) is preferably 10 to 60% by weight. 1
If the amount is less than 0% by weight, the concealing property may be reduced due to insufficient pigment. If the amount exceeds 60% by weight, the viscosity at the time of curing is increased due to an excessive amount of the pigment, whereby the flowability is reduced and the appearance of the coating film may be reduced. The pigment can be previously dispersed in a generally used pigment dispersion resin, and after adjusting the pigment dispersion paste, an appropriate amount can be blended in preparing the aqueous intermediate coating composition.

The aqueous intermediate coating material is, for example, a film-forming resin which has been made water-soluble, water-dispersed or emulsified as it is or neutralized with a volatile basic substance, a curing agent,
It can be prepared by mixing an elastomer and a pigment dispersion paste in a hydrophilic medium. The aqueous intermediate coating further includes an ultraviolet absorber, an antioxidant, an antifoaming agent, a surface conditioner,
An additive component such as an anti-bake agent can be added.

The method for forming the intermediate coating film is not particularly limited as to the method of applying the intermediate coating film on the electrodeposition coating film obtained in the step (I). For example, an air electrostatic coating commonly called “react gun” is used. Spraying: Spraying can be performed by using a rotary atomizing type electrostatic coating machine called "micro-micro (μ) bell", "micro (μ) bell", "meta bell" or the like. Preferably, a method using a rotary atomization type electrostatic coating machine or the like is used.

The dry thickness of the intermediate coating film varies depending on the application, but is preferably 5 to 50 μm. If it is less than 5 μm, the base cannot be concealed and the film may be cut off, and if it is more than 50 μm, the sharpness may be reduced, or irregularities may occur at the time of coating, or defects such as flow may occur. The content of the volatile basic substance in the coating film is too large, and the total amount of the volatile basic substance contained in the uncured intermediate coating film and the uncured base coating film is calculated as the unit area of the coating film. It cannot be less than 7 × 10 ⁻⁶ mmol per 1 mm ^2, and the yellowing of the cured coating film may not be sufficiently suppressed.

Step (III) In the present invention, the step (III) comprises the steps of:
A base paint is applied to form an uncured base coating film.

Aqueous Base Coating In the present invention, the aqueous base coating is not particularly limited, and examples thereof include those comprising a film-forming resin, a curing agent, a pigment and other additives. The film-forming resin is not particularly limited, and examples thereof include an acrylic resin, a polyester resin, an alkyd resin, an epoxy resin, and a urethane resin. These are used in combination with a curing agent such as an amino resin and / or a blocked isocyanate resin. Can be A combination of an acrylic resin and / or a polyester resin and a melamine resin is preferred from the viewpoint of pigment dispersibility and workability.

The aqueous base paint can be used as a metallic base paint by adding a glittering pigment, or by blending a coloring pigment such as red, blue or black and / or an extender pigment without blending the glittering pigment. Can be used as a solid base paint.

The brilliant pigment is not particularly limited, and may be, for example, an uncolored or colored metallic brilliant such as a metal or an alloy, a mixture thereof, interference mica powder, colored mica powder,
Examples include white mica powder, graphite, and colorless colored flat pigments. A non-colored or colored metallic brilliant material such as a metal or an alloy, and a mixture thereof are preferable since a coating film having excellent dispersibility and high transparency can be formed. Specific examples of the metal include aluminum,
Examples thereof include aluminum oxide, copper, zinc, iron, nickel, and tin.

The shape of the brilliant pigment is not particularly limited, and may be colored. For example, the average particle size (D ₅₀ )
Is 2 to 50 μm, and a scale-like one having a thickness of 0.1 to 5 μm is preferable. Those having an average particle size in the range of 10 to 35 μm are excellent in glitter and are more preferable.

The pigment concentration (P
WC) is generally less than or equal to 23% by weight. When the content exceeds 23% by weight, the appearance of the coating film is deteriorated. Preferably, 0.01
To 20% by weight, more preferably 0.01 to 18% by weight.
% By weight.

As the pigments other than the glitter pigments, the coloring pigments and extenders described in the electrodeposition paints can be used. As the pigment, one or a combination of two or more of a bright pigment, a coloring pigment and an extender pigment can be used. The pigment concentration (PWC) in the base paint, including glitter pigments and all other pigments, is generally 0.1 to 50% by weight, preferably 0.5 to 40% by weight, Preferably it is 1 to 30% by weight. 5
When the content exceeds 0% by weight, the appearance of the coating film is deteriorated.

As the base paint, other additives to be used and a method for preparing the base paint include those exemplified for the aqueous intermediate coating.

Method of Forming Base Coating Film The base coating material is applied on the uncured intermediate coating film formed as described above to form an uncured base coating film.
Examples of the coating method include the methods exemplified when applying the aqueous intermediate coating composition. When the base paint is applied to an automobile body or the like, in order to enhance the design, multi-stage painting by air electrostatic spray, preferably two-stage painting, or air electrostatic spray and the above rotation It is preferable to carry out by a coating method in combination with an atomizing type electrostatic coating machine.

The dry film thickness of the base coating film varies depending on the application, but is preferably from 5 to 35 μm. Exceeding the upper limit may result in poor clarity and / or inconveniences such as unevenness and flow during coating. Below the lower limit, color unevenness may occur.

Step (IV) In the step (IV), a clear paint is applied on the uncured base coating film formed as described above to form an uncured clear coating film.

The clear coating film can be used to smooth the unevenness and flicker of the base coating film caused by the glittering pigment when using a metallic base coating containing a glittering pigment as the base coating. It is formed to protect. The clear coating is not particularly limited, and examples thereof include coatings formed of a coating film forming resin, a curing agent, and other additives.

The film-forming resin is not particularly restricted but includes, for example, acrylic resins, polyester resins, epoxy resins, urethane resins and the like, which are used in combination with a curing agent such as an amino resin and / or a blocked isocyanate resin. Can be It is preferable to use a combination of an acrylic resin and / or a polyester resin and an amino resin, or an acrylic resin and / or a polyester resin having a carboxylic acid / epoxy curing system, from the viewpoint of transparency or acid etching resistance.

As the clear coating, the base coating described above is applied in an uncured state after coating, and a viscosity controlling agent is contained as an additive in order to prevent adaptation, inversion or sagging between layers. Is preferred. The addition amount of the viscosity control agent is 0.01 to 10 parts by weight, preferably 0.02 to 8 parts by weight, per 100 parts by weight of the resin solid content of the clear paint.
Parts by weight, more preferably 0.03 to 6 parts by weight. 1
If the amount exceeds 0 parts by weight, the appearance deteriorates, and if the amount is less than 0.1 parts by weight, the effect of controlling the viscosity cannot be obtained, which causes a problem such as sagging.

The coating form of the clear coating may be any of an organic solvent type, an aqueous type (water-soluble, water-dispersible, emulsion), a non-aqueous dispersion type, and a powder type.
A curing catalyst, a surface conditioner and the like can be used.

Method for Forming Clear Coating Film The preparation method and the coating method of the clear paint can be carried out according to a conventional method. The dry film thickness of the clear coating film varies depending on the application, but is 10 to 70 μm.
When the dry film thickness exceeds the upper limit, the sharpness is reduced,
Problems such as unevenness and flow may occur at the time of coating, and if it is below the lower limit, the appearance may be deteriorated.

In the present invention, the formation of the uncoated, base and clear coatings in each of the steps (II) to (IV) in the uncured state means that the intermediate coating, the base coating and the clear coating are wet-on.・ It means to paint in this order with wet. In the present specification, the term “uncured” is a concept including, for example, a state after preheating. As preheat, after application, for example,
This is a step of leaving or heating at room temperature to less than 100 ° C. for 1 to 10 minutes. For the purpose of obtaining a good finished appearance, it is preferable to perform preheating after applying the aqueous intermediate coating and after applying the aqueous base coating.

Step (V) In step (V), the intermediate coating film, the base coating film and the clear coating film are simultaneously heated and cured to obtain a multilayer coating film.
By performing the heating and curing at a temperature of 110 to 180 ° C, preferably 120 to 160 ° C, a cured coating film having a high degree of crosslinking can be obtained. If it exceeds 180 ° C., the coating film becomes hard and brittle, and if it is lower than 110 ° C., curing is not sufficient. The curing time varies depending on the curing temperature.
A temperature of 0 to 160 ° C. for 10 to 60 minutes is suitable.

The film thickness of the multilayer coating film obtained by the coating film forming method of the present invention is usually 30 to 300 μm, preferably 5 to 300 μm.
0 to 250 μm. If it exceeds 300 μm, the physical properties of the film such as a thermal cycle decrease, and if it is less than 30 μm, the strength of the film itself decreases.

[0113]

According to the above-mentioned steps (II) to (IV), the intermediate coating, the base coating and the clear coating are applied on the electrodeposition coating film obtained in the step (I) by wet-on-wet. In the so-called 3 wet coating in which the intermediate coating film, the base coating film and the clear coating film are simultaneously baked in the step (V), a high throwing power is achieved, and the conventional electrodeposition coating, intermediate coating and top coating are achieved. Can be obtained with excellent finish appearance and film performance such as corrosion resistance comparable to a laminated film obtained by a three-coat three-bake method of baking and hardening each.

Further, by this three-wet coating, the baking step of the intermediate coating paint can be omitted from the conventional three-coat three-bake method, and since the paint is water-based, the process can be shortened, cost can be reduced, and energy consumption can be reduced. It is possible to construct a new coating system that aims to reduce the amount and environmental load.

[0115]

EXAMPLES The present invention will be described in detail with reference to specific examples, but the present invention is not limited to the following examples. Parts and% mean parts by weight and% by weight, respectively.

Preparation Example 1 (Preparation of Material for Electrodeposition Coating) 1-1 (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 92 parts of-/ 2,6-tolylene diisocyanate (weight ratio = 8/2), 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, after continuing the reaction for 30 minutes, 57 parts of ethylene glycol mono-2-ethylhexyl ether was added dropwise from the dropping funnel.
Further, 42 parts of a bisphenol A-propylene oxide 5 mol adduct was added to the reaction mixture. The reaction is mainly 6
The measurement was performed in the range of 0 to 65 ° C, and the measurement 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%).

1-2 (Production of 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.

1-3 (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. MIBK3
After dilution with 9.1 parts, 0.2 parts of dibutyltin dilaurate was added thereto. 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.

Then, 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 was kept at 110 to 120 ° C. for about 1 hour, and then 1390.2 parts of ethylene glycol monobutyl ether was added. The mixture was cooled to 85 to 95 ° C., homogenized, and then the quaternary solution prepared above was 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%). %).

1-4 (Production of Pigment Dispersion Paste) In a sand grind mill, 120 parts of the pigment dispersion resin obtained in Production Example 3, 2.0 parts of carbon black, and 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%).

Preparation Example 2 ( Preparation of aqueous intermediate coating) 2-1 (Preparation of solvent-type polyester resin) In a reaction vessel, 200.0 parts of isophthalic acid and 1 phthalic anhydride were added.
79.0 parts, adipic acid 176.0 parts, trimethylolpropane 150.0 parts, neopentyl glycol 29
5.0 parts, 2.0 parts of dibutyltin oxide were charged,
After heating in a nitrogen stream to melt the raw materials, the temperature was gradually raised to 170 ° C. while mixing and stirring. Thereafter, the mixture was subjected to dehydration transesterification while raising the temperature to 220 ° C. over a further 3 hours. When the acid value reached 10, the mixture was cooled to 150 ° C. Further, 114.0 parts of hexahydrophthalic acid was added and reacted for 1 hour to complete the reaction. Further, after cooling to 100 ° C., 112.0 parts of butyl cellosolve was added to obtain a polyester resin. The obtained polyester resin is
Resin solid content 70%, solid content acid value 50, hydroxyl value 65, G
The number average molecular weight obtained by PC was 10,000.

2-2 (Polyester resin emulsion 1)
Preparation of Newcol 1120 (polyoxyethylene lauryl ether, H) as a nonionic surfactant in ion-exchanged water
After dispersing 33.4 parts of LB16.4 (manufactured by Nippon Emulsifier Co.) and 6 parts of ethylene glycol mono-n-hexyl cellosolve, the polyester resin 11 obtained in 2-1 was dispersed.
By dropping 1.1 parts into the above dispersion while stirring, a polyester resin emulsion 1 coated with a nonionic surfactant having a nonvolatile content of 47.5% was obtained.

2-3 (Polyester resin emulsion 2)
After dispersing 55.7 parts of the cationic dispersion resin obtained in Preparation Example 2-2 and 6 parts of ethylene glycol mono-n-hexyl cellosolve in ion-exchanged water, the polyester obtained in 2-1 was obtained. 111.1 parts of the resin were dropped into the dispersion while stirring, to obtain a polyester resin emulsion 2 coated with a cationic dispersion resin having a nonvolatile content of 47.5%.

2-4 (Preparation of Pigment Dispersion Paste 2) 8 parts of Disperbyk 190 (manufactured by BYK Japan KK) as a pigment dispersion resin, 29 parts of ion-exchanged water, 31 parts of rutile type titanium dioxide, 31 parts of barium sulfate, and 1 part of talc After pre-mixing, add a glass bead medium in a paint conditioner, mix and disperse at room temperature for 1 hour,
Pigment dispersed paste 2 having a particle size of 5 μm or less was obtained.

2-5 (Preparation of Aqueous Intermediate Coating) Polyester resin emulsions 1 and 2 obtained in 2-3 and 2-4, pigment dispersion paste 2 obtained in 2-5,
Further, hexamethoxymethylol melamine (HMMM, trade name: Cymel 235, manufactured by Mitsui Cytec Co., Ltd.) was blended as a melamine resin so as to have a solid content as shown in Table 1, to obtain an aqueous intermediate coating material-1.

Preparation Example 3 ( Preparation of Waterborne Intermediate Paint) 2-3 and 2-4 of Preparation Example 2
And the pigment dispersion paste 2 obtained in 2-5 of Preparation Example 2 and hexamethoxymethylol melamine (HMMM, trade name: Cymel 235, manufactured by Mitsui Cytec Co., Ltd.) as a melamine resin Was mixed so as to have a solid content as shown in Table 1 to obtain an aqueous intermediate coating material-2.

[0131]

[Table 1]

Preparation Example 4 ( Preparation of aqueous base paint) 4-1 (Preparation of water-soluble acrylic resin) Dipropylene glycol methyl ether 2 was placed in a reaction vessel.
3.9 parts and propylene glycol methyl ether 1
6.1 parts were added and mixed and stirred in a nitrogen stream for 120 minutes.
The temperature was raised to ° C. Then, 54.5 parts of ethyl acrylate,
A mixed solution of 12.5 parts of methyl methacrylate, 14.7 parts of 2-hydroxyethyl acrylate, 10.0 parts of styrene and 8.5 parts of methacrylic acid, 10.0 parts of dipropylene glycol methyl ether and t-butyl par Oxy-
An initiator solution consisting of 2.0 parts of 2-ethylhexanoate was dropped into the reaction vessel in parallel over 3 hours. After completion of the dropping, aging was performed at the same temperature for 0.5 hour.

Further, an initiator solution consisting of 5.0 parts of dipropylene glycol methyl ether and 0.3 parts of t-butylperoxy-2-ethylhexanoate was added dropwise to the reaction vessel over 0.5 hour. After completion of dropping, aging was performed at the same temperature for 1 hour.

Next, the solvent was removed at 70 Torr.
After distilling off 16.1 parts of the solvent at 110 ° C. under reduced pressure, 22 mg of dimethylethanolamine (DMEA) per 1 g of resin solid content and ion-exchanged water were added to obtain a nonvolatile content of 3%.
A water-soluble acrylic resin having an acid value of 1%, an acid value of solid content of 56, a hydroxyl value of 70 and a number average molecular weight of 10,000 obtained by GPC was obtained.

4-2-1 (Preparation of Pigment Dispersion Paste 3) 100.0 parts of the water-soluble acrylic resin obtained in 4-1, 28.9 parts of ion-exchanged water, and 0.1% of dimethylaminoethanol.
3 parts, Degussa Carbon FW-285 (made by Degussa AG)
Pigment-dispersed paste 3 having a particle size of 5 μm or less was obtained in the same manner as in 2-5 of Preparation Example 2 except for using 5.1 parts.

4-2-2 (Preparation of Pigment Dispersion Paste 4) Using 67.0 parts of the water-soluble acrylic resin obtained in 4-1, 23.2 parts of ion-exchanged water, and 67.0 parts of rutile-type titanium dioxide Other than that described above, in the same manner as in 2-5 of Preparation Example 2,
A pigment dispersion paste 4 having a particle size of 5 μm or less was obtained.

4-3-1 (Preparation of aqueous base coating material 1) 118.8 parts of the water-soluble acrylic resin obtained in 4-1
The pigment-dispersed paste 3 obtained in -2-1 was used in 134.3.
In addition, 29.1 parts of Cymel 204 (manufactured by Mitsui Cytec) as a melamine resin and 161.3 parts of ion-exchanged water were blended to obtain an aqueous base paint 1.

4-3-2 (Preparation of aqueous base paint 2) Water-soluble acrylic resin obtained in 4-1, Cymel 204
(Melamine resin, manufactured by Mitsui Cytec) and 4-2-2
Using the pigment dispersion paste 4 obtained in the above, the solid content was blended so as to be as follows, whereby an aqueous base paint 2 was obtained.

[0139]

[Table 2]

[0140] were uniformly mixed in a 70/30 and a blocked isocyanate curing agent obtained in amine-modified epoxy resin and 1-2 obtained in 1-1 of Example 1 Preparation Example 1 at a solid content ratio. Thereafter, ethylene glycol-2-ethylhexyl ether was added so as to be 2% by weight based on the solid content. To this, milligram equivalent of acid per 100 g of resin solids (MEQ
Glacial acetic acid was added so that (A)) was 18, and ion-exchanged water was slowly added to dilute the mixture. MIB under reduced pressure
By removing K, an emulsion having a solid content of 36% was obtained.

To 2222 parts of this emulsion, 1759 parts of ion-exchanged water, 19 parts of a 10% cerium acetate aqueous solution and 16 parts of dibutyltin oxide were mixed to give a solid content of 2 parts.
0% by weight of the cationic electrodeposition coating composition-1 was obtained. The cationic electrodeposition coating composition contains substantially no pigment,
Solvent content (VOC) in paint is 0.4%, resin solids 10
The milligram equivalent of acid per 0 g is 20.4, and the total concentration of eluted cerium ion and zinc ion is 190 pp
m.

Using this, electrodeposition coating was applied to a zinc phosphate-treated dull steel sheet at a voltage such that the electrodeposition coating film thickness after baking became 15 μm, followed by baking at 170 ° C. for 20 minutes.

On the obtained coating film, the aqueous intermediate coating material obtained in Preparation Example 2 was dried by air spray to have a dry film thickness of 20%.
It was coated to a thickness of μm and preheated at 80 ° C. for 5 minutes. Thereafter, the aqueous base paint 1 obtained in Preparation Example 3
Was applied by air spray coating so as to have a dry film thickness of 18 μm, and preheated at 80 ° C. for 5 minutes. Further, Macflow O-180 is used as a clear paint on the coated plate.
After applying 1W clear (manufactured by Nippon Paint Co., Ltd.) by air spray coating so that the dry film thickness becomes 35 μm, 14
Bake at 0 ° C. for 30 minutes.

Example 2 In the same manner as in Example 1, the amine-modified epoxy resin obtained in 1-1 of Preparation Example 1 and the blocked isocyanate curing agent obtained in 1-2 were mixed at a solid content ratio of 70/30. Mix to make uniform. 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 100 g of resin solid content was 24, and ion-exchanged water was added slowly to dilute. MIB under reduced pressure
By removing K, an emulsion having a solid content of 36% was obtained.

1960 parts of this emulsion, 197 parts of the pigment-dispersed paste obtained in 1-4 of Preparation Example 1, 1805 parts of ion-exchanged water and 38% aqueous 10% cerium acetate solution
Was mixed with 14.5 parts of dibutyltin oxide to obtain a cationic electrodeposition coating composition-2 having a solid content of 20% by weight. In the cationic electrodeposition coating composition, the ratio of the pigment to the resin solid content is 1/10, and the amount of the solvent in the coating is 0.9.
%, The milligram equivalent of acid per 100 g of resin solid content is 2
5.2. The total concentration of eluted cerium ions and zinc ions was 420 ppm.

Using this, an electrodeposition coating film was obtained under the same conditions as in Example 1. Thereafter, a coating film was formed in the same manner as in Example 1 for intermediate coating, base coating, and clear coating.

Example 3 The electrodeposition coating film obtained in Example 1 was used.
Except that the intermediate coating material-2 was used in the same manner as in Example 1 to perform intermediate coating, base coating, and clear coating to form a coating film.

Comparative Example 1 In the same manner as in Example 1, the amine-modified epoxy resin obtained in 1-1 of Preparation Example 1 and the blocked isocyanate curing agent obtained in 1-2 were mixed in a solid content ratio of 70/30. And mixed to make it uniform. 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 100 g of resin solid content was 35, and ion-exchanged water was slowly added to dilute the mixture. M under reduced pressure
By removing the IBK, 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 1-4 of Preparation Example 1, 1901 parts of ion-exchanged water and 57% of a 10% cerium acetate aqueous solution
Was mixed with 9 parts of dibutyltin oxide to obtain a cationic electrodeposition coating composition-3 having a solid content of 20% by weight. In the cationic electrodeposition coating composition, the ratio between the pigment and the resin solid content was 1/3, the solvent amount in the coating material was 1.5%, and the milligram equivalent of acid per 100 g of the resin solid content was 30.3, which was eluted. The total concentration of cerium and zinc ions is 61
It was 0 ppm.

Using this, an electrodeposition coating film was obtained under the same conditions as in Example 1. Thereafter, a coating film was formed in the same manner as in Example 1 for intermediate coating, base coating, and clear coating.

Comparative Example 2 2222 parts of the emulsion obtained in Comparative Example 1, 1778 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 2 parts.
0% by weight of the cationic electrodeposition coating composition-4 was obtained. The cationic electrodeposition coating composition contains substantially no pigment,
The amount of solvent in the paint was 0.2%, the milligram equivalent of acid per 100 g of resin solid content was 34.7, and the total concentration of eluted cerium ions and zinc ions was 590 ppm.

Using this, an electrodeposition coating film was obtained under the same conditions as in Example 1. With respect to the subsequent intermediate coating, base coating, and clear coating, a coating film was formed in the same manner as in Example 3.

Evaluation method (1) Evaluation of electrodeposition paint The cationic electrodeposition paint obtained in each of Examples and Comparative Examples and the cationic electrodeposition coating film obtained by baking were subjected to the following evaluation tests. 3 is shown.

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

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

Stability of the electrodeposition paint The cationic electrodeposition paint was stored at 40 ° C. for 2 weeks,
The filterability when sifted through a 0-mesh sieve was observed and evaluated according to the following criteria.

：: Filterable without any problem ×: Filterable

(2) Evaluation of cured films of electrodeposition coating, intermediate coating, base coating and clear coating The appearance of the obtained coating film was evaluated by SW value of Wavescan manufactured by Big Chemie. Table 3 shows the obtained results. A smaller value indicates a better result.

[0163]

[Table 3]

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C25D 13/06 C25D 13/06 E 13/10 13/10 BA (72) Inventor Mitsuo Yamada Neyagawa, Osaka 19-17 Ikeda-Nakamachi, Japan F-term (reference) in Nippon Paint Co., Ltd. EB55 EB56 EC11 EC31 EC37 EC52 EC54 EC60

Claims (16)

[Claims] 1. A step of forming an electrodeposited coating film on the surface of an object to be coated by an electrodeposition coating method using a cationic electrodeposition coating material, and heating and curing the electrodeposited coating film to form a cured electrodeposition coating film, Applying an aqueous intermediate coating on the cured electrodeposition coating to form an uncured intermediate coating (II), applying an aqueous base coating on the uncured intermediate coating,
Step (III) of forming an uncured base coating, Step (IV) of applying a clear paint on the uncured base coating to form an uncured clear coating, and uncured intermediate coating A step (V) of simultaneously heating and curing the coating film, the base coating film and the clear coating film, wherein the cationic electrodeposition coating material is dispersed in an aqueous medium, an aqueous medium, or Dissolved, a binder resin containing a cationic epoxy resin and a blocked isocyanate curing agent, a neutralizing acid for neutralizing the cationic epoxy resin, an organic solvent,
It contains a metal catalyst, has a volatile organic content of 1% by weight or less, a metal ion concentration of 500 ppm or less, and an amount of neutralizing acid of 10% based on 100 g of a binder resin solid content.
A lead-free cationic electrodeposition paint having an equivalent weight of about 30 mg, wherein the aqueous intermediate coating contains a film-forming resin solution dispersed in water with a nonionic dispersant and / or a cationic dispersant. To form a laminated coating film. 2. The method according to claim 1, further comprising a step of performing preheating after the step (II). 3. The coating film forming method according to claim 1, further comprising a step of performing preheating after the step (III). 4. The multilayer coating film 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. Forming method. 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 composition further contains a pigment, and the weight ratio between the pigment contained in the coating composition and the resin solid content is 1%.
The method according to any one of claims 1 to 5, wherein the ratio is not more than / 9. 7. The method for forming a laminated coating film according to claim 1, wherein the film-forming resin of the aqueous intermediate coating composition is a polyester resin. 8. The method for forming a laminated coating film according to claim 1, wherein the resin solution for forming a coating film of the aqueous intermediate coating composition further contains a curing agent. 9. The amount of the nonionic dispersant and / or the cationic dispersant contained in the aqueous intermediate coating composition is based on the total amount of the film-forming resin solution and the nonionic dispersant and / or the cationic dispersant. The method according to any one of claims 1 to 8, wherein the content is 2 to 50% by weight on a solid basis. 10. The film-forming resin of the aqueous intermediate coating composition has a number average molecular weight of 1,000 to 30,000.
10. The method for forming a laminated coating film according to any one of the above items 9. 11. The method for forming a laminated coating film according to claim 1, wherein the resin solution for forming a coating film of the aqueous intermediate coating composition further contains a pigment. 12. Before the step (V), the total amount of the volatile basic substances contained in the uncured intermediate coating film and the uncured base coating film is 7 × / mm ^{2 of the} coating film unit area.
The method according to claim 1, wherein the amount is 10 ⁻⁶ mmol or less. 13. The method according to claim 1, wherein the aqueous intermediate coating composition further contains an elastomer. 14. The method according to claim 13, wherein the elastomer is water-dispersed or water-soluble. 15. The method according to claim 13, wherein the amount of the elastomer contained in the aqueous intermediate coating composition is 20 to 100% by weight based on the solid content of the resin in the aqueous intermediate coating composition. 16. A multilayer coating film formed by the multilayer coating film forming method according to any one of claims 1 to 15.