WO2008015955A1

WO2008015955A1 - Method for forming multilayer coating film

Info

Publication number: WO2008015955A1
Application number: PCT/JP2007/064655
Authority: WO
Inventors: Naotaka Kitamura
Original assignee: Nippon Paint Co., Ltd.
Priority date: 2006-08-02
Filing date: 2007-07-26
Publication date: 2008-02-07
Also published as: TW200812710A; JPWO2008015955A1

Abstract

This invention provides a method for forming a multilayer coating film having a good finishing appearance which can reduce a burden on a coating equipment cost and an energy cost. The method for forming a multilayer coating film comprises an electrodeposition coating step of electrodepositing a cation electrodeposited coating composition to form an electrodepositon coated film and heat curing the electrodeposited coating film to form a cured electrodeposited coating film and a multilayer coating film forming step of coating a coating composition onto the cured electrodeposited coating film to form a multilayer coating film. In the cation electrodeposition coating composition, the density of a pigment contained in the solid content in the electrodeposition coating composition is 2 to 7% by weight. The pigment contains 95 to 100% by weight of titanium dioxide. The cured electrodeposition coating film has a lightness index L value of 55 or more in a film thickness of not less than 15 μm, and the cured electrodeposition coating film has a dried coating film specific gravity of 1.20 to 1.25.

Description

Specification

Multi-layer coating formation method

Technical field

TECHNICAL FIELD [0001] The present invention relates to a method for forming a multilayer coating film that can reduce the burden on coating equipment and energy costs, and has a good finishing power and good appearance.

Background art

[0002] Electrodeposition coating is a coating method performed by immersing an object to be coated in an electrodeposition coating composition and applying a voltage. In this method, even an object to be coated having a complicated shape can be applied to a thin part, and can be applied automatically and continuously. Widely used as an undercoating method for objects with shapes. Furthermore, electrodeposition coating can give the base material high anticorrosion properties and is excellent in protecting the base material.

[0003] In general, a large amount of pigment is added to an electrodeposition coating composition for the purpose of improving the hiding property or improving the physical properties of a coating film. These pigments are in a state of being dispersed in an aqueous medium in the coating composition. Since these pigments are generally inorganic pigments and have a high specific gravity, sedimentation tends to occur in the electrodeposition coating composition. For example, in a conventional electrodeposition coating composition, the pigment settles and aggregates when allowed to stand without stirring. In order to prevent such agglomeration, the electrodeposition tank and replenishment tank containing the electrodeposition coating composition must be constantly stirred, which is a burden on the equipment and energy costs of the painter. For this reason, by reducing the amount of pigment contained in the electrodeposition coating composition, a method may be taken to prevent sedimentation of the pigment and reduce the burden of equipment and energy costs. Reducing the pigment can also prevent the pigment from settling on the horizontal surface of the substrate, which is the object to be coated, and has the advantage that the appearance of the resulting electrodeposition coating is improved.

[0004] On the other hand, the role of coating is to provide a beautiful appearance in addition to protecting the substrate. In painting to obtain a beautiful appearance, a plurality of coating films having various roles are usually formed. Such a coating film is generally formed by baking and curing each coating film one by one. However, in recent years, due to demands for energy saving and cost reduction, a method of applying the next coating by so-called wet-on-wet without baking and curing after coating and then baking and curing multiple layers at once is being adopted. is there. As an example of this method, after the electrodeposition coating is cured, the intermediate coating, top coating base and top coating coating are applied wet-on-wet, and then three uncured coatings are baked at once. Curing, three coat 'one beta coating is considered. In addition, as another means to achieve the demand for energy saving and cost reduction, an intermediate coating composition is applied on a cured electrodeposition coating film that has been heat-cured and then cured by heating. Three-coat “two-beta” coating is also considered, in which the coating composition is applied in sequence and the uncured topcoat base coat and topcoat coater coat are heated and cured simultaneously. Furthermore, a method of top coating without applying intermediate coating after electrodeposition is also considered.

[0006] In such a coating with fewer baking processes than in the conventional process, the thickness of the intermediate coating film to be formed tends to be thinner than in the conventional process. When the thickness of the intermediate coating film is thin or when the intermediate coating film itself is not present, it has been found that the appearance and hue of the multilayer coating film that provides the concealability of the electrodeposition coating film are greatly affected. It was. The concealability of this electrodeposition coating film depends on the amount of pigment contained in the electrodeposition coating composition. An electrodeposition coating composition with a reduced amount of pigment is inferior in concealability, although it is excellent in preventing pigment settling. For this reason, it has been difficult to use an electrodeposition coating composition with a reduced amount of pigment for the above-mentioned three-coat 'one-bake coating, three-coat' two-beta coating and the like.

[0007] JP 2004-231989 (Patent Document 1) discloses that the pigment ash content in the cationic electrodeposition coating is 3 to 10% by weight, and the cation, based on the solid content of the cationic electrodeposition coating. Electrodeposition An environmentally-friendly electrodeposition coating method using a cationic electrodeposition paint having a solid content concentration of 5 to 12% by weight is described. However, the reduction of pigment ash content decreases the concealability of the electrodeposition coating film, so that the appearance of the resulting coating film is strongly influenced by the hue of the steel sheet. For this reason, when coating is performed using a steel plate with low brightness, the brightness of the resulting electrodeposition coating film also decreases, which ultimately affects the hue of the multilayer coating film.

JP-A-2002-126627 (Patent Document 2) discloses an aqueous intermediate coating on an electrodeposition coating film. Apply an aqueous base paint and a talya paint in sequence to form an uncured aqueous intermediate coat, an aqueous base coat and a talya coat, and simultaneously heat cure these films to obtain a multilayer coat. A method for forming a multilayer coating film, wherein the water-based intermediate coating and / or the water-based base coating is substantially free of pigments and volatile basic substances! /, And is obtained by predispersing a pigment dispersant. A method for forming a multi-layer coating film, characterized in that it contains a pigment dispersion paste obtained (Claim 1). By this method, the coating process can be shortened, the cost can be reduced and the environmental load can be reduced, and a multi-layer coating without yellowing can be formed. However, the film thickness of the intermediate coating film formed by this method may be thinner than the conventional one, and therefore the coating concealability may be inferior.

JP-A-2004-275971 (Patent Document 3) discloses a multilayer coating film in which an intermediate coating film, a base coating film, and a talya coating film are sequentially formed on a substrate on which an undercoating film has been formed. The intermediate coating film includes a white paint supply means for supplying a white paint with a variable supply amount and a black paint supply means for supplying a black paint with a variable supply amount. The white paint supply means and the black paint supply means are formed using an intermediate coating device connected to the rotary atomizing coating gun independently of each other. The paint describes a method for forming a multilayer coating film in which the pigment concentration (PWC) is 2 to 60% by mass, the non-volatile content is 35 to 60% by mass, and the viscosity of the paint is 0.03 to 0.3 Pa's. (Claim Do This Patent Document 3 describes a method for forming a multilayer coating film by two-coat 'one-beta coating. That the force S, while also tooth force, the relationship Nitsu V between brightness and multi-layer coating film of the cured electrodeposition coating film, Te is no description! /, A les.

[0010] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2004-231989

Patent Document 2: JP 2002-126627 A

Patent Document 3: Japanese Patent Application Laid-Open No. 2004-275971

Disclosure of the invention

Problems to be solved by the invention

[0011] An object of the present invention is to solve the above-described problems of the prior art. More specifically, the present invention relates to a method for forming a multi-layer coating film that can reduce the burden on painting equipment and energy costs, and has a good finish and appearance. Means for solving the problem

[0012] The present invention provides:

An electrodeposition coating process in which a cationic electrodeposition coating composition is electrodeposited to form an electrodeposition coating, and the resulting electrodeposition coating is cured by heating to obtain a cured electrodeposition coating;

Applying the coating composition on the obtained cured electrodeposition coating film to obtain a multilayer coating film, a multilayer coating film forming step,

A method for forming a multilayer coating film, comprising:

This cationic electrodeposition coating composition is a cationic electrodeposition coating composition in which the concentration of the pigment contained in the solid content of the electrodeposition coating composition is 2 to 7% by weight,

This pigment contains 95 to 100% titanium dioxide,

This cured electrodeposition coating film has a lightness index L value of 55 or more at a film thickness of 15 πι or more, and this cured electrodeposition coating film has a dry coating specific gravity of 1.20 to; 1.25.

A method for forming a multilayer coating film is provided, whereby the above object is achieved.

[0013] As one aspect of the present invention, the multilayer coating film forming step comprises

Applying an intermediate coating composition on the cured electrodeposition coating to form an uncured intermediate coating;

A step of applying an overcoating base coating composition on the obtained uncured intermediate coating film to form an uncured top coating base film;

A step of applying a top coat coating composition on the resulting uncured top coat base film to form an uncured top coat film; and

A heating step in which these uncured intermediate coating film, uncured topcoat base coating film, and uncured topcoat clear coating film are heated and cured simultaneously;

Including a multi-layer coating film forming method.

[0014] As another aspect of the present invention, the multilayer coating film forming step comprises

Applying the intermediate coating composition on the cured electrodeposition coating film to form an intermediate coating film, and heat-curing the obtained intermediate coating film to obtain a cured intermediate coating film;

A step of applying an overcoating base coating composition on the obtained intermediate cured coating film to form an uncured top coating base film, A step of applying a top coat coating composition on the resulting uncured top coat base film to form an uncured top coat film; and

A heating process for simultaneously heating and curing these uncured topcoat base coat and uncured topcoat film

Including a multi-layer coating film forming method.

[0015] In the above method, it is more preferable that the thickness of the cured intermediate coating film formed in the multilayer coating film forming step is 10 to 40 µm! /.

[0016] As another embodiment of the present invention, the multilayer coating film forming step comprises

Applying an overcoating base coating composition on the cured electrodeposition coating to form an uncured top-coating base coating;

A step of applying a talya coating composition on the obtained uncured topcoat base coating to form an uncured topcoat talya coating; and

Including a multi-layer coating film forming method.

[0017] As another embodiment of the present invention, the multilayer coating film forming step comprises

Applying a topcoat solid coating composition on the cured electrodeposition coating to form an uncured topcoat solid coating; and

A heating process for heating and curing this uncured topcoat solid coating film,

Including a multi-layer coating film forming method.

[0018] In the above-described method for simultaneously heating and curing the uncured intermediate coating film, the uncured top coating base film, and the uncured top coating film, the intermediate coating composition is an aqueous intermediate coating composition. The overcoating base coating composition is an aqueous topcoating base coating composition, or

It is preferable that the intermediate coating composition is a solvent intermediate coating composition, and the topcoat base coating composition is a solvent topcoat base coating composition.

[0019] The present invention further provides a multilayer coating film obtained by the above-described method for forming a multilayer coating film.

The invention's effect [0020] In the method of the present invention, the pigment concentration is 2 to 7% by weight, and the strength is low. Even though the thione electrodeposition coating composition is used, the type and configuration of the pigment are specified. Thus, it is possible to form a multilayer coating film having an excellent hue. Furthermore, even when a multilayer coating film is formed by a coating method such as the so-called three-coat 'one-beta coating method, which has few baking and curing processes, it has good concealment and also has excellent horizontal appearance. A membrane can be obtained. The coating film formed according to the present invention also has an advantage that the specific gravity is light, and can be used effectively for reducing the weight of the coated product. By using this method, it is possible to form a multi-layer coating film with excellent concealment, etc., by a coating method with less baking and curing in response to demands for energy saving and cost reduction.

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

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

Explanation of symbols

[0022] 10: box,

11 ~; 14: Zinc phosphate-treated steel sheet,

15: Through hole,

20: Electrodeposition coating container,

21: Electrodeposition paint,

22: Counter electrode.

BEST MODE FOR CARRYING OUT THE INVENTION

[0023] ¾ϋ

In the present invention, various base materials that can be energized, such as steel materials, can be used. In this case, the surface of the base material may be subjected to a plating treatment or a chemical conversion treatment, or may be an untreated base material that has not been applied. Examples of usable steel materials include cold-rolled steel sheets, hot-rolled steel sheets, stainless steel, electrogalvanized steel sheets, hot-dip galvanized steel sheets, zinc-aluminum alloy-based steel sheets, zinc-ferrous alloy-based steel sheets, zinc-magnesium composites. Gold plated steel sheet, zinc aluminum Magnesium alloy plated steel sheet, aluminum Steel, aluminum silicon alloy steel, tin steel, lead tin alloy steel, chromium steel, etc., and steels that have been subjected to chemical conversion treatment. Can be mentioned.

[0024] Cationic electrodeposition coating composition

The cationic electrodeposition coating composition used in the present invention comprises an aqueous solvent, a binder resin containing a cationic epoxy resin and a block isocyanate curing agent dispersed or dissolved in the aqueous solvent, a neutralizing acid, an organic solvent, Contains pigments.

[0025] 纖

The cationic electrodeposition coating composition used in the method of the present invention contains a pigment. The amount of the pigment is 2 to 7% by weight based on the solid content of the cationic electrodeposition coating composition. The amount of pigment contained in the cationic electrodeposition coating composition is 2 to 7% by weight based on the solid content of the cationic electrodeposition coating composition, thereby preventing precipitation of the pigment in the electrodeposition coating composition. can do. As a result, the stirring time of the electrodeposition tank can be reduced, and the burden on the painting equipment and energy costs can be reduced. Furthermore, it is possible to prevent sedimentation of the pigment onto the horizontal surface of the substrate that is the object to be coated during electrodeposition coating, and to improve the appearance of the resulting cured electrodeposition coating film on the horizontal surface. The amount of the pigment is preferably 3 to 5% by weight based on the solid content of the cationic electrodeposition coating composition.

Furthermore, in the electrodeposition coating composition of the present invention, 95 to 100% by weight of the pigment contained in the electrodeposition coating composition is titanium dioxide. By using a pigment containing 95 to 100% by weight of titanium dioxide, even if the amount of the pigment is 2 to 7% by weight relative to the solid content of the cationic electrodeposition coating composition, the resulting curing can be obtained. The lightness index L value of the electrodeposition coating can be maintained at 55 or higher. The amount of titanium dioxide contained in the pigment is more preferably 98 to 100% by weight. Particularly preferred is the case where only titanium dioxide is used as the pigment.

[0027] Examples of pigments that can be used in addition to titanium dioxide include commonly used inorganic pigments such as colored pigments such as carbon black and bengara; kaolin, talc, aluminum silicate, calcium carbonate, Extenders such as strength and clay; zinc phosphate, iron phosphate, aluminum phosphate, calcium phosphate, zinc phosphite, zinc cyanide, zinc oxide, tri And anti-mold pigments such as aluminum polyphosphate, zinc molybdate, aluminum molybdate, calcium molybdate, aluminum phosphomolybdate, and aluminum zinc phosphomolybdate.

[0028] When a pigment is used as a component of an electrodeposition paint, generally, the pigment is previously dispersed in an aqueous solvent at a high concentration to form a paste (pigment dispersion paste). This is because the pigment is in a powder form and it is difficult to disperse it in a single step in a low concentration uniform state used in the electrodeposition coating composition. In general, such a paste is called a pigment dispersion paste!

[0029] The pigment dispersion paste is prepared by dispersing a pigment together with a pigment dispersion resin in an aqueous solvent. As the pigment dispersion resin, a cationic polymer such as a cationic or nonionic low molecular weight surfactant or a modified epoxy resin having a quaternary ammonium group and / or a tertiary sulfone group is generally used. Use. As the aqueous solvent, ion-exchanged water or water containing a small amount of alcohol is used. In general, the pigment dispersion resin is used in an amount of 20 to 100 parts by mass with respect to 100 parts by mass of the pigment. After mixing the pigment dispersion resin and the pigment, the pigment dispersion is dispersed by using a normal dispersing device such as a ball mill or a sand grind mill until the pigment in the mixture has a predetermined uniform particle size. A paste can be obtained.

[0030] Cationic epoxy resin

The cationic epoxy resin includes an epoxy resin modified with ammine. Cationic epoxy resins typically have the ability to open all of the epoxy rings of bisphenol-type epoxy resins with active hydrogen compounds capable of introducing cationic groups, or some epoxy rings to other types. And the remaining epoxy ring is opened with an active hydrogen compound capable of introducing a cationic group.

[0031] A typical example of the bisphenol type epoxy resin is a bisphenol A type or bisphenol F type epoxy resin. As for the former commercial products, Epicoat 828 (manufactured by Yuka Shell Epoxy Co., Epoxy Equivalent 180 ~; 190), Epico 1001 (Equivalent Epoxy Equivalent 450 ~ 500), Epicote 1010 (Equipment Equivalent Equivalent 3000 ~ 4000), etc. Epicoat 807 (same as above, epoxy equivalent 170) is a commercial product of the latter.

[0032] These epoxy resins include polyester polyols, polyether polyols, and It may be modified with a suitable resin such as a monofunctional alkylphenol. Epoxy resins also have the ability to extend the chain using the reaction of epoxy groups with diols or dicarboxylic acids.

[0033] These epoxy resins are active hydrogen compounds such that after ring opening, an amine equivalent of 0.3-4 Omeq / g is obtained, and more preferably 5-50% of them are occupied by primary amino groups. It is desirable to open the ring at.

[0034] Examples of the active hydrogen compound into which a cationic group can be introduced include primary amines, secondary amines, tertiary amine acid salts, sulfides and acid mixtures. When an amine is used as the active hydrogen compound, an amine-modified epoxy resin having a tertiary amino group can be obtained by reacting an epoxy resin with a secondary amine. In addition, when an epoxy resin is reacted with a primary amine, an amine-modified epoxy resin having a secondary amino group is obtained. Furthermore, by using a compound having a primary amino group and a secondary amino group, it is possible to prepare an amine-modified epoxy resin having a primary amino group. Here, when preparing an amine-modified epoxy resin having a primary amino group using a compound having a primary amino group and a secondary amino group, the primary amino group of the compound is required before reacting with the epoxy resin. Can be prepared by blocking with a ketone to form a ketimine, which is introduced into the epoxy resin and then deblocked.

[0035] Specific examples of primary amine, secondary amine and ketimine include, for example, butyramine, otachinoreamine, jetinoreamine, dibutenoreamine, methinolevinoreamine, monoethanolanolamine, diethanolamine, N-methylethanolamine Mines, triethylamine hydrochloride, N, N-dimethylethanolamine acetate, jetyl disulfide 'acetic acid mixture. In addition, there are secondary amines with blocked primary amines, such as aminoethylethanolamine ketimine and diethylenetriamine diketimine. Two or more of these amines may be used in combination.

[0036] As the cationic epoxy resin, an oxazolidone ring-containing epoxy resin described in JP-A-5-306327 and known may be used. Japanese Patent Laid-Open No. 5-306327 is a basic application of US Patent No. 5276072, which is a priority application, and US Patent No. 5276072 is incorporated herein by reference. Epoxies on epoxy resin As a method for introducing a sazolidone ring, for example, a block isocyanate curing agent blocked with a lower alcohol such as methanol and a polyepoxide are heated and kept in the presence of a basic catalyst, and the by-product lower alcohol is introduced from the system. It can be obtained by distilling off. Specific examples and production methods of this oxazolidone ring-containing epoxy resin are described in, for example, paragraphs 0012 to 0047 of JP-A No. 2000-128959 and are publicly known. This Japanese Patent Laid-Open No. 2000-128959 is a basic application of US Pat. No. 6,664,345, which is a priority claim application, and this US Pat. No. 6,664,345 is incorporated herein by reference.

Yes

[0037] Block isocyanate curing agent

Polyisocyanates are used in the preparation of the block isocyanate curing agent. This polyisocyanate refers to a compound having two or more isocyanate groups in one molecule. Examples of the polyisocyanate include, for example, aliphatic / alicyclic, aromatic and aromatic-aliphatic, etc., and may be shifted! /.

[0038] Specific examples of polyisocyanates include aromatic diisocyanates such as tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), p-phenylene diisocyanate, and naphthalene diisocyanate. 1 to 4 aliphatic diisocyanates such as hexamethylene diisocyanate (HDI), 2,2,4-trimethylhexane diisocyanate, lysine diisocyanate and the like; -Cyclohexane diisocyanate (CDI), isophorone diisocyanate (IPDI), 4,4'-dicyclohexylenomethane diisocyanate (hydrogenated MDI), methylcyclohexane diisocyanate, isopropylidene Cyclohexyl, 4,4'-diisocyanate, and 1,3-diisocyanatomethylcyclohexane (hydrogenated XDI), hydrogenated TDI, 2,5- Aliphatic diisocyanates having 5 to 18 carbon atoms such as 2,6-bis (isocyanatomethyl) bibicyclo [2.2.1] heptane (also called norbornane diisocyanate); Aliphatic diisocyanates with aromatic rings such as cyanate (XDI) and tetramethylxylylene diisocyanate (TMXDI); modified products of these diisocyanates (urethanes, carpositimides, uretdiones, uretonimines, views) Lett and / or isocyanurate-modified product); These can be used alone or in combination of two or more. [0039] An adduct or prepolymer obtained by reacting a polyisocyanate with a polyhydric alcohol such as ethylene glycol, propylene glycol, trimethylolpropan or hexanetriol at an NCO / OH ratio of 2 or more is also cured with a block isocyanate. May be used in preparations.

[0040] The blocking agent is added to a polyisocyanate group and is stable at room temperature but can regenerate a free isocyanate group when heated to a temperature higher than the dissociation temperature.

[0041] Other ingredients

When the cationic electrodeposition coating composition contains a dissociation catalyst for dissociating the blocking agent of the block isocyanate curing agent in addition to the above components, dibutyltin laurate, dibutyltin oxide, dioctyltin oxide, etc. Organic tin compounds, amines such as N-methylmorpholine, and metal salts such as strontium, cobalt, and copper can be used. The concentration of the dissociation catalyst is 0 .;! To 6 parts by mass with respect to 100 parts by mass of the total of the force thione epoxy resin and the block isocyanate curing agent in the force thione electrodeposition coating composition.

[0042] Preparation of cationic lightning coating composition

The cationic electrodeposition coating composition used in the present invention is prepared by dispersing the above-described cationic epoxy resin, block isocyanate curing agent, and pigment dispersion paste in an aqueous solvent. Usually, the aqueous solvent is neutralized with a cationic epoxy resin to contain a neutralizing acid in order to improve the dispersibility of the binder resin emulsion. Neutralizing acids are inorganic or organic acids such as hydrochloric acid, nitric acid, phosphoric acid, formic acid, acetic acid, lactic acid.

[0043] The amount of the neutralizing acid used is preferably in the range of 10 to 25 mg equivalent to 100 g of the binder resin solid content containing the cationic epoxy resin and the block isocyanate hardener. The lower limit is more preferably 15 mg equivalent, and the upper limit is more preferably 20 mg equivalent. 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 stability is extremely poor. If the amount exceeds 25 mg equivalent, the amount of electricity required for precipitation increases. However, the precipitation of the solid content of the paint is lowered and the throwing power is inferior.

[0044] The amount of the block isocyanate curing agent reacts 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. A sufficient amount is required. The preferred amount of block isocyanate curing agent is 90/10 to 50/50 expressed as the weight ratio of cationic epoxy resin to block isocyanate curing agent (cationic epoxy resin / curing agent). More preferably, it is in the range of 80/20 to 65/35. By adjusting the solid content ratio between the cationic epoxy resin and the block isocyanate curing agent, the fluidity and curing speed of the coating film (deposition film) during film formation are improved, and the smoothness of the coating film is improved.

[0045] Examples of the organic solvent that is usually contained in the cationic electrodeposition coating composition include ethylene glycol monophenolatenore, ethyleneglycolenohexenoleatenore, ethyleneglycolenoethylenohexenoreethenole, propylene glycol Noremonobutinoreethenore, dipropylene glycolenoremonobutenoreatenore, propyleneglycolenomonomonoreinoatere and the like.

[0046] In addition to the above, the cationic electrodeposition coating composition may contain conventional coating additives such as a plasticizer, a surfactant, an antioxidant, and an ultraviolet absorber. Including amino group-containing acrylic resin, amino group-containing polyester resin, etc.

[0047] The solid content concentration of the cationic electrodeposition coating composition in the present invention is preferably 0.5 to 25% by weight. However, the cationic electrodeposition coating composition should be used when coating an object that has a solid content concentration of 0.5 to 7% by weight and requires high throwing power. You can include a conductivity control agent in the object! /. By including a conductivity control agent, throwing power can be improved. As the conductivity control agent that can be used, for example, an acid neutralized product of an amine-modified epoxy resin can be used. The acid neutralized product of an amine-modified epoxy resin can be prepared by first preparing an amine-modified epoxy resin and neutralizing it with an acid. The amine-modified epoxy resin can be prepared by opening the epoxy ring of the epoxy resin with an active hydrogen compound. Examples of the epoxy resin that can be used include nopolac type epoxy resins and bisphenol type epoxy resins. Examples of active hydrogen compounds include butynoleamine, octylamine, jetylamine, dibutylamine, methylbutyramine, monoethanolamine, diethanolamine, N-methylethanolamine, triethylamine hydrochloride, N, N-dimethylethanolamine acetate, jetyldis Rufuid 'acetic acid mixture and more aminoethyl ethano Lumamine ketimine, diethylenetriamine diketimine, and the like can be used. Then, when the epoxy ring of the epoxy resin is opened using the active hydrogen compound, the ring is opened so that the amine equivalent after the opening is 2.0 to 5. Omeq / g. As the neutralizing acid for neutralizing the amine-modified epoxy resin, inorganic acids and organic acids such as hydrochloric acid, nitric acid, phosphoric acid, formic acid, acetic acid, and lactic acid can be used. By adding an acid neutralized product of an amine-modified epoxy resin prepared using these materials to the electrodeposition coating composition, the conductivity of the electrodeposition coating composition can be adjusted to 1000 to 2000 S / cm. Thus, even when the solid content concentration of the electrodeposition coating composition is low, it is possible to ensure high throwing power.

[0048] Electrodeposition painting process

Electrodeposition is usually performed by applying a voltage of 50 to 450 V between the object to be coated as the cathode and the anode. If the applied voltage is less than 50V, electrodeposition may be insufficient, and if it exceeds 450V, the coating film may be destroyed and the appearance may be abnormal. During electrodeposition coating, the bath temperature of the coating composition is usually adjusted to 10 to 45 ° C.

[0049] The electrodeposition coating process includes a process of immersing an object to be coated in a cationic electrodeposition coating composition, and a process of applying a voltage between the object to be coated as a cathode and an anode to deposit a film. Composed. The time for applying the voltage varies depending on the electrodeposition conditions. In general, the force is 2 to 4 minutes.

[0050] The film thickness of the electrodeposition coating film is preferably 5 to 25 111, more preferably 20 m. The film thickness is 5

If it is less than in, the anti-mold property is insufficient, and if it exceeds 25 111, it will lead to waste of paint.

[0051] The electrodeposition coating film obtained as described above is 120 to 260 after the electrodeposition process, as it is or after being washed with water. C, preferably 140-220. With C, a cured electrodeposition coating is formed by baking for 10 to 30 minutes.

[0052] The cured electrodeposition coating film obtained by the present invention has a lightness index L value of 55 or more at a film thickness of 15 m or more. The electrodeposition coating composition used in the present invention can ensure a lightness index L value of 55 or more at a film thickness of 15 m or more of the cured electrodeposition coating film, although the pigment content is small. By forming a multilayer coating film using such a cured electrodeposition coating film, a good color that is not affected by the color of the substrate that is the object to be coated is obtained. It becomes possible to form a multilayer coating film having a phase. This lightness index L value is obtained in accordance with JIS Z 8722 and JIS Z 8730. Based on the tristimulus values X, Y, and Ζ values in the XYZ system measured by the transmission method in the wavelength range of 380 to 780 nm using the standard light C by the spectrophotometer, it is calculated according to the provisions of JIS standard Ζ 8730. This L value is called the brightness index in Hunter's color difference formula, and the greater the L value, the higher the whiteness.

[0053] In the present invention, by using an electrodeposition coating composition containing a pigment in which 95 to 100% by weight of the pigment is titanium dioxide in the pigment, the amount of the pigment is based on the solid content of the cationic electrodeposition coating composition. When the film thickness of the cured electrodeposition coating film is 15 m or more even though the weight is as low as 2 to 7% by weight! /, The curing electrodeposition coating film with a lightness index L value of 55 or more Can get. Furthermore, the cured electrodeposition coating film obtained according to the present invention has a lightness index of the cured electrodeposition coating film even when a substrate having a low brightness index such as a hot-dip galvanized steel sheet is used as an object to be coated. The number L has an advantage of 55 or more. In the present invention, the lightness index L value of 55 or more of the cured electrodeposition coating film can be secured when the film thickness is 15 in or more regardless of the color and material of the substrate. Electrodeposition coating in the present invention is particularly suitable as an undercoat for multilayer coating forming coatings with reduced coating thickness, such as three-coat 'one-beta coating, three-coat-two-beta coating, and intermediate coating-less coating. Yes.

[0054] The cured electrodeposition coating film obtained according to the present invention is also characterized in that the dry coating film has a specific gravity of 1.20 to 1.25. The amount of the pigment contained in the cationic electrodeposition coating composition is as low as 2 to 7% by weight based on the solid content of the cationic electrodeposition coating composition, and 95 to 100% by weight in the pigment. By using titanium dioxide, it is possible to achieve a dry coating specific gravity in the above range. Thus, the advantage of producing a cured electrodeposition coating film having a low specific gravity of the dried coating film is that the weight of the object to be coated can be reduced. For example, this weight reduction effect is more advantageous when painting an object having a large paint area, such as an automobile body. The specific gravity of the dried coating film can be determined according to JIS K 7112.

[0055] m ^

As an example of the method for forming a multilayer coating film of the present invention, an intermediate coating composition, a top coating base coating composition, and a top coating coating composition are sequentially applied onto a heat-cured cured electrodeposition coating film. Then, an uncured intermediate coating film, top coating base film, and top coating film are simultaneously heat-cured. This method is generally referred to as three-coat 'one beta coating (3C 1B). As another example of the method for forming a multilayer coating film of the present invention, an intermediate coating composition is applied on a heat-cured cured electrodeposition coating film and cured by heating, and then an overcoating base coating composition and a top coating film are applied. Examples thereof include a method in which coating compositions are sequentially applied, and an uncured top coat base coat and a top coat film are simultaneously heated and cured. This method is generally called three-coat 'two-beta coating (3C2B). As another example of the present invention, a method of top coating without applying an intermediate coating after electrodeposition coating, for example, a top coating base coating composition and a top coating tally coating composition on a heat-cured cured electrodeposition coating film In order to heat and cure the uncured base coat and topcoat coating at the same time (Two Coat One Beta Coat (2C1B)), and overcoating the cured solid electrodeposition paint Examples thereof include a method of applying the composition and heat-curing (one-coat 'one-beta coating (1C1B)).

[0056] Three-coat 'one-bake' painting

One of the coating methods for obtaining multi-layer coatings, the one-coat coating method that is useful in terms of energy saving, etc. The one-beta coating (3C1B) coating method specifically includes the following steps: : A step of applying an intermediate coating composition on a cured electrodeposition coating to form an uncured intermediate coating; applying an overcoating base coating composition on an uncured intermediate coating A step of forming an uncured topcoat film; a step of applying a topcoat coating composition on the uncured topcoat film to form an uncured topcoat film; and A heating process in which the cured intermediate coat, top coat base coat, and top coat film are heated and cured simultaneously.

[0057] Intermediate coating composition

In such a method for forming a multi-layer coating film by three-coat “one beta coating (3C1B)”, the intermediate coating composition may be an aqueous coating composition or a solvent-based coating composition. The components of the intermediate coating composition include an intermediate coating resin component, a pigment, and an aqueous solvent and / or an organic solvent. The intermediate coating resin component is composed of an intermediate coating resin and an intermediate coating curing agent. [0058] When the intermediate coating composition is water-based, it is preferable to blend a pigment dispersion paste obtained by dispersing the pigment and the pigment dispersant in advance! It is possible to use commercially available pigment dispersants. Commercially available products include, for example, Disperby k 190, Disperbyk 182 and Disperbyk 184 (all manufactured by Big Chemi), EFKAPO LYMER4550 (manufactured by EFKA), Sonoreth Nose 27000, Sonoreth Noose 41000, Sonoreth Nose 53095 (V, The difference is also made by Abyssia). The number average molecular weight of the pigment dispersant is preferably 1000 to 100,000. If it is less than 1000, sufficient dispersion stability may not be obtained, and if it exceeds 100,000, the viscosity may be too high and handling may be difficult. More preferably, it is 2000-50,000, More preferably, it is 4000-50,000.

[0059] The pigment dispersant is mixed and dispersed together with the pigment according to a known method to obtain a pigment dispersion paste. The blending ratio of the pigment dispersant in the pigment dispersion paste is preferably 1 to 20% by weight with respect to the solid content of the pigment dispersion paste. If it is less than 1% by weight, the pigment cannot be dispersed stably, and if it exceeds 20% by weight, the physical properties of the coating film may be inferior. Preferably, 5 to 15% by weight.

[0060] The pigment used in the intermediate coating composition is not particularly limited as long as it is a pigment used in a normal intermediate coating composition, but from the viewpoint of improving weather resistance and ensuring concealment. A color pigment is preferred. In particular, titanium dioxide is more preferable because it is excellent in white color concealment and has low strength and low cost.

[0061] Examples of pigments other than titanium dioxide include, for example, azochelate pigments, insoluble azo pigments, condensed azo pigments, phthalocyanine pigments, indigo pigments, perinone pigments, perylene pigments, dioxane pigments, and quinacridone. Organic pigments such as pigments, isoindolinone pigments, and metal complex pigments; inorganic pigments such as chrome yellow, yellow iron oxide, bengara, and carbon black. As the pigment, extender pigments such as calcium carbonate, barium sulfate, clay and talc may be used.

[0062] A standard gray-based intermediate coating with carbon black and titanium dioxide as the main pigments can be used as pigments, and a set gray or various colored pigments that combine brightness or hue with the top coating composition can be used. Use a so-called color intermediate coating in combination You can also.

[0063] In the intermediate coating composition, the pigment preferably has a weight ratio (PWC) of the pigment to the total weight of the pigment and the resin solid content of 10 to 60% by weight. If it is less than 10% by weight, the hiding property may be lowered due to insufficient pigment. When it exceeds 60 wt%, leading to viscosity increase during curing by Pigments excessive, the appearance of the coating film is child and the force ^s reduced flow resistance is reduced.

[0064] The aqueous intermediate coating composition can be prepared by mixing the pigment dispersion paste, the intermediate coating resin, and the intermediate curing agent. The content of the pigment dispersant in the aqueous intermediate coating is preferably from 0.5 to 10% by weight based on the solid content. If it is less than 5% by weight, the pigment dispersion stability may be inferior due to the small amount of the pigment dispersant. If it exceeds 10% by weight, the physical properties of the coating film may be inferior. Preferably, !! to 5% by weight.

[0065] The intermediate coating resin is not particularly limited, and examples thereof include acrylic resin, polyester resin, alkyd resin, epoxy resin, and urethane resin. Examples of the intermediate coating curing agent include melamine resin, amino resin, and block isocyanate curing agent. From the viewpoint of pigment dispersibility and workability, a combination of acrylic resin and / or polyester resin with melamine resin and / or block isocyanate resin is preferred. Each of the intermediate coating resin and the intermediate curing agent can be used alone, or two or more types can be used in order to balance the coating film performance.

[0066] When the intermediate coating composition is an aqueous intermediate coating composition, the intermediate coating resin is water-soluble, or a dispersing agent such as a dispersion resin or a surfactant is applied. By emulsifying and dispersing, it can be stably present in the aqueous intermediate coating. The water-based intermediate coating composition can further contain additive components such as an ultraviolet absorber, an antioxidant, an antifoaming agent, a surface conditioner, and an anti-fogging agent.

[0067] When the intermediate coating composition is a solvent intermediate coating composition, it can be prepared by stirring the intermediate coating resin, the intermediate curing agent and the pigment in an organic solvent. Preferred amounts of the above components are the same as above. Examples of organic solvents that can be used in the preparation of the solvent intermediate coating composition include aromatic solvents such as toluene and xylene. Ketone solvents such as methyl ethyl ketone, acetone, methyl isobutyl ketone, cyclohexanone, etc .; jetyl ether, isopropyl ether, tetrahydrofuran, dioxane, ethylene glyconoresin methino eleinoate, ethylene glycono retino enoenoate, jeti Ether solvents such as lenglycolinoresimethinoreethenore, diethyleneglycolenoretinoreetherenore, propylene glycol monomethyl ether, anisole, phenetol; ester solvents such as ethyl acetate, butyl acetate, isopropyl acetate, ethylene glycol diacetate Amide solvents such as dimethylformamide, jetylformamide, dimethyl sulfoxide and N-methylpyrrolidone; Cellosolv solvents such as lucose sorb; alcoholic solvents such as methanol, ethanol and propanol; halogen solvents such as dichloromethane, dichloroethane and chloroform; These solvents may be used alone or in combination. Further, in addition to the above components, if necessary, it is possible to include various additives well known by those skilled in the art, such as pigment dispersants, surface conditioners, viscosity control agents, ultraviolet absorbers, and antioxidants. Touch with S.

[0068] Topcoat base coating composition

The topcoat base coating composition includes a topcoat base resin component, a pigment, and a solvent. This overcoating base coating composition is of an aqueous type or a mixed lj type including an aqueous dispersion or an organic solvent dispersion.

[0069] When the topcoat base paint composition is an aqueous topcoat base paint composition, it can be prepared using a pigment dispersion paste in which a pigment is dispersed in advance using a pigment dispersant. As the pigment dispersant, those exemplified above for the aqueous intermediate coating composition can be used.

[0070] As the pigment contained in the topcoat base coating composition, the above-mentioned colored pigments and extender pigments can be used, and a glittering pigment can be blended and used as a metallic base paint. Further, coloring pigments such as red, blue, and black and / or extender pigments are blended without blending bright pigments and used as solid-type topcoat base coating compositions.

[0071] The luster pigment is not particularly limited, and may be, for example, an uncolored or non-colored metal or alloy In addition, a colored metallic luster material and a mixture thereof, interference my strength powder, colored my strength powder, white mica powder, graphite or colorless and flattened pigment can be used. Since it is excellent in dispersibility and can form a highly transparent coating film, an uncolored or colored metallic glitter material such as metal or alloy and a mixture thereof are preferred. Specific examples of the metal include aluminum, aluminum oxide, copper, zinc, iron, nickel, tin and the like.

[0072] The shape of the glitter pigment is not particularly limited and may be further colored. For example, the average particle diameter (D) is 2 to 50 111, and the thickness is 0.1 to 5 m. The scaly thing is

50

Good. Those having an average particle size in the range of 10 to 35 m are more preferable because of excellent glitter.

[0073] One or two or more of the above pigments can be used, and one or more of pigments, extender pigments, and flat pigments and glitter pigments can be used as necessary. Can be used in combination. When using a bright pigment, a paint film is formed using a color base paint composition containing a color pigment as a main component, and a paint film using a bright base paint composition containing a bright pigment as a main component thereon. It is also possible to form It is also possible to form a top coat film by such a method, and in the present invention, such an embodiment of top coat base film formation is also included.

[0074] The mixing ratio of the pigment dispersant in the pigment dispersion paste in the aqueous topcoat base coating composition is preferably 3 to 50% by weight based on the solid content of the pigment dispersion paste.

If it is less than 3% by weight, the pigment cannot be dispersed stably, and if it exceeds 50% by weight, the physical properties of the resulting coating film may be lowered.

[0075] The aqueous topcoat base coating composition can be prepared by mixing the pigment dispersion paste, the topcoat base resin and the topcoat base curing agent, which are the topcoat base resin components. The pigment concentration (PWC) in the top coating composition including the glitter pigment and all other pigments is generally 0.;! To 50% by weight, preferably 0.5 to 40%. % By weight, more preferably 1 to 30% by weight. If it exceeds 50% by weight, the coating film appearance may be deteriorated.

[0076] The content of the pigment dispersant in the aqueous topcoat base coating composition is preferably 1 to 20% by weight based on the solid content. If it is less than 1% by weight, the amount of the pigment dispersant is Due to the small amount, the dispersion stability of the pigment may be inferior. If it exceeds 20% by weight, the properties of the resulting coating film may be deteriorated.

[0077] The topcoat base resin and the topcoat base curing agent, which are the topcoat base resin components, and other additives are not particularly limited. For example, they can be used in intermediate coating compositions. . From the standpoint of pigment dispersibility and workability, the combination of the topcoat base resin and the topcoat base curing agent is preferably a combination of an acrylic resin and / or a polyester resin and a melamine resin.

[0078] The aqueous topcoat base coating composition can be prepared in the same manner as the aqueous intermediate coating composition. The solvent overcoating base coating composition can also be prepared in the same manner as the above-mentioned solvent intermediate coating composition.

[0079] Topcoat clear coating composition

The topcoat coating composition contains a topcoat resin component, various additives and a solvent. The top coat resin component contained in the top coat paint composition is composed of a top clear paint resin and optionally a top coat paint curing agent. As the top coat resin component (top coat paint resin, top coat paint curing agent), various additives, and organic solvents contained in the top coat composition, those described with respect to the above-mentioned middle coat composition! / Also, the deviation can be used.

[0080] A preferred combination and combination of the topcoat paint resin and the topcoat paint hardener that are the topcoat resin components is a combination of an acrylic resin and a melamine resin. In this case, the acrylic resin preferably has an acid value of 10 to 200, a hydroxyl value of 30 to 200, and a number average molecular weight of 2000 to 50000!

[0081] The top coat coating composition preferably contains a viscosity control agent as an additive since the top coat base coating composition is applied in an uncured state. By adding a viscosity control agent, it is possible to prevent the familiarity, inversion, or sagging of the coating layers. The addition amount of the viscosity control agent is preferably 0.01 to 10 parts by weight with respect to 100 parts by weight of the resin solid content of the top coat coating composition, and more preferably 0.02 to 8 parts by weight. It is particularly preferably 0.03 to 6 parts by weight. If it exceeds 10 parts by weight, the appearance of the coating film may be deteriorated. If it is less than 0.01 part by weight, the viscosity control effect will be reduced. It may not be obtained and may cause problems such as sagging.

[0082] The top coat coating composition may be any of a solvent type, an aqueous type (water-soluble, water-dispersible, emulsion), a non-aqueous dispersion type, and a powder type. The top coat coating composition may contain a curing catalyst, a surface conditioner and the like, if necessary, in addition to the above components. The top-coated talya coating composition can be formulated with the above-mentioned color pigments and glittering materials to such an extent that transparency is not impaired, and further includes curing accelerators, leveling agents, ultraviolet absorbers, light stabilizers and the like. Additives can be used.

[0083] The top coat coating composition can be prepared in the same manner as the water-based intermediate coating composition or the solvent intermediate coating composition. Further, the top coat coating composition can also be prepared by a known method described in, for example, JP-A No. 2002-224613. Further, as a powder top coat coating composition, for example, an acrylic resin or polyester resin having a hydroxyl group and a compound capable of reacting with this polymer compound, such as an amino resin, polyisocyanate, block isocyanate, etc. are combined. A combination of an acrylic resin having an epoxy group and a polyvalent carboxylic acid, a polyvalent carboxylic acid anhydride, etc., which does not substantially contain water or an organic solvent. .

[0084] Shelving

In the three-coat one-beta coating (3C1B) method for forming a multilayer coating, an uncured intermediate coating is formed on the cured electrodeposition coating obtained by the above method. Examples of a method for forming an uncured intermediate coating film include a method of applying an intermediate coating composition using a spray method, a roll coater method, or the like. Specific coating methods include air electrostatic sprays called “react guns” and rotary atomization type electrostatics called “micro” micro bells, “micro mouth” bells, and “meta bells”. It is preferable to paint using a coating machine. Of these, 1S is particularly preferable for coating using a rotary atomizing electrostatic coating machine.

[0085] A preferable dry film thickness of the intermediate coating film is generally 10 to 80 111, more preferably 10 to 50 111. However, in the three-coat 'One Beta coating (3C 1B), the dry film thickness of the intermediate coating film is preferably 10-40 μm, more preferably 15-30 μm! / ヽ. Three-coat · In one-beta coating, the dry film thickness of the intermediate coating film exceeds 40 m In such a case, there is a risk of sagging or wrinkling, and the appearance of the resulting multi-layer coating film may be inferior. On the other hand, when the dry film thickness is less than 10 m, the resulting multilayer coating film may be inferior in performance such as coating film appearance, hue, and chipping property.

[0086] In this three-coat 'one beta coating, after the intermediate coating film is formed, the process proceeds to the formation process of the topcoat base coating film in the next step without being heated and cured. In this case, before the overcoating base film is formed, it may be lower than the temperature used in the heat curing (baking) treatment! /, Or preheated at the temperature! /.

[0087] The topcoat base coating film is obtained by coating the topcoat base coating composition on the intermediate coating film. In the Three Coat One Beta coating, this topcoat base coating composition is applied onto an uncured intermediate coating by a wet-on-wet method. The method of applying the top coat base coating composition is not particularly limited! /, But examples thereof include the methods exemplified as the method of applying the intermediate coating composition. As a specific coating method when the top coating base coating composition is applied to an automobile body or the like, the design can be improved by performing multi-stage coating by air electrostatic spraying, preferably two-stage coating. Or you may paint by the coating method which combined air electrostatic spray and said rotary atomization type electrostatic coating machine.

[0088] By forming this topcoat base coating film, design properties are imparted, and adhesion with the intermediate coating film formed in the previous process is ensured, and the coating with the topcoat film coated in the next process is repeated. Adhesion is ensured. The dry film thickness of the top coat film is preferably 5 to 50 inches per coat, more preferably 10 to 30 111. After the top coat base film is formed, the process proceeds to the next top coat film forming process without heating and curing. Before forming the top coat film, preheating may be performed at a temperature lower than the temperature used in the heat curing (baking) process.

[0089] The top coat film is obtained by coating the top coat composition on the top base film. This top coat coating composition is applied on the uncured top coat base film in a wet-on-wet manner.

[0090] A method for forming the above-mentioned top coat film is not particularly limited, but a spray method, a roll coater method, and the like are preferable. The dry film thickness of the above top coat film is ₂ per coat. 0-50 111 are preferred, 25-40 111 are preferred. By forming the top coat film, the top coat base film is protected, and the depth S can be applied to the resulting multilayer film.

[0091] In the three-coat 'one-beta coating, which is one embodiment of the present invention, after forming the top coat film, an uncured intermediate coat film, a top coat base coat, and a top coat film are coated with three layers. 120-; 160. C, more preferably 140-; With C, it can be cured by heating for 25 to 35 minutes to obtain a multilayer coating. In this method, the intermediate coating composition, the top coating base coating composition, and the top coating composition are each coated in wet order on the wet. That is, an uncured coating film is sequentially formed. In the present invention, “uncured” means a state in which the film is not completely cured, and includes a state of a coating film that has been preheated. “Preheating” can be performed at room temperature to 100 ° C., which is lower than the temperature used in heat curing (baking) treatment, for 1 to 10 minutes, or by standing or heating for 10 minutes. By performing preheating after forming the intermediate coating film and after forming the topcoat base coating film, a coating film having a better finished appearance can be obtained.

[0092] In the three-coat 'one-beta coating (3C1B), as a combination of the intermediate coating composition and the top coating base coating composition to be used, the force used in combination with the aqueous intermediate coating composition and the aqueous top coating base coating composition; Alternatively, it is preferable to use a combination of a solvent intermediate coating composition and a solvent overcoating base coating composition. By using in such a combination, a multilayer coating film having a good finished appearance can be obtained. In the three-coat 'one-beta coating (3C1B) in the present invention, an aqueous intermediate coating composition, an aqueous top coating base coating composition, and a solvent top coating tally coating composition are used from the viewpoints of environmental protection and coating hygiene. Is the most preferred.

[0093] Method of forming a multilayer coating film by three-coat 'two-bake coating

In terms of energy saving, which is another method for obtaining a multi-layer coating film! /, The three-coat two-beta coating (3C2B) coating film formation method is specifically described below. The intermediate coating film is formed by applying the intermediate coating composition on the cured electrodeposition coating film, and the resulting intermediate coating film is cured by heating to obtain a cured intermediate coating film. Process; profit A step of applying an overcoating base coating composition on the cured intermediate coating film to form an uncured overcoating base coating film; Applying a rear coating composition to form an uncured top coat film; and heating step for simultaneously heating and curing these uncured top coat film and uncured top coat film.

[0094] In such a method of forming a multi-layer coating film by three coat two-to-beta coating (3C2B), it is possible to use the above-mentioned aqueous intermediate coating composition or solvent intermediate coating composition as the intermediate coating composition. . In addition, the above-mentioned water-based overcoating base coating composition or the solvent overcoating base coating composition can be used as the topcoating base coating composition, and the above-mentioned topcoat coating composition can be used as the overcoating clear coating composition. .

[0095] The preferable dry film thickness of the intermediate coating film is generally 10 to 80 111, more preferably 10 to 50 m. However, in the three-coat 'two-beta coating (3C2B), the dry coating thickness of the intermediate coating film is preferably 10 to 40 mm 111, more preferably 15 to 30 mm 111. If the dry film thickness of the intermediate coating film exceeds 4 (^ 111 in the three-coat 'two-beta coating, there is a risk of sagging, wrinkling, etc., resulting in poor appearance of the multilayer coating film. In addition, when the dry film thickness is less than 10πι, the resulting multilayer coating film may be inferior in performance such as coating film appearance, hue, and chipping property.

[0096] The multilayer coating film forming process in the three coat 'two-beta coating (3C2B) is a multilayer coating film in the three-coat' one beta coating (3C1B) except that it is heat-cured after the intermediate coating film is formed. It can be performed in the same manner as the forming step. The condition for heat curing the intermediate coating film is 100 to 250. The temperature of C, more preferably from 130 to 180; The conditions include heating at a temperature of C for 5 to 60 minutes, more preferably 30 to 40 minutes.

[0097] Method of forming a multilayer coating film by two-coat 'one-bake coating

The coating method by two-coat 'one beta coating (2C1B), which is another method of coating to obtain a multilayer coating film, specifically includes the following steps: on the cured electrodeposition coating film Applying a topcoat base coating composition to form an uncured topcoat base coating; applying a tarrier coating composition on the resulting uncured topcoat base coating to form an uncured topcoat Forming a talya coating; and A heating process in which the coating film and the uncured top coat film are heated and cured simultaneously.

[0098] In such a method for forming a multilayer coating film by two-coat 'one-beta coating (2C1B), the above-mentioned aqueous topcoat base paint composition or solvent topcoat base paint composition can be used as the topcoat base paint composition. The above-mentioned top coat coating composition can be used as the top coat coating composition.

[0099] In the two-coat one-beta coating (2C1B), the multilayer coating film forming step is performed except that the top coating base coating composition and the top coating film coating composition are applied without forming the intermediate coating film. It can be applied in the same way as the multi-layer coating formation process in Three-Coat One Beta Coating (3C1B).

[0100] One coat · One bake

The coating method by one-coat 'one-beta coating (1 C 1 B), which is another method for obtaining a multilayer coating film, specifically includes the following steps: Curing electrodeposition coating Applying an overcoating solid coating composition on the film to form an uncured topcoating solid coating; and heating to heat cure the uncured topcoating solid coating.

[0101] The top coating solid coating composition is not particularly limited. For example, in the case of an aqueous topcoat solid coating composition, a polymer compound that is soluble in water or dispersible in water, for example, an acrylic resin containing a hydroxyl group and a carboxyl group is neutralized with ammine or the like. Examples thereof include a combination of an acrylic resin aqueous solution and a resin that can react with the polymer compound, such as an amino resin or a block isocyanate resin that is soluble in water or dispersible in water.

[0102] Solvent-coated solid coating compositions include, for example, a polymer compound soluble in various organic solvents, such as an acrylic resin having a hydroxyl group, and a compound capable of reacting with the polymer compound, for example, And combinations of amino resins, polyisocyanates, block isocyanates, and the like.

[0103] The topcoat solid coating composition contains a pigment. As the pigment, a pigment that can be used in the above intermediate coating composition and / or the above top coating base coating composition can be used. For example, known inorganic or organic coloring pigments such as carbon black, phthalocyanine blue, and titanium dioxide. Is mentioned. The top coat solid paint composition is further an extender pigment. Further, additives such as a curing accelerator, a leveling agent, an ultraviolet absorber, and a light stabilizer may be included.

[0104] In the multi-layer coating film formation process in one-coat 'one-beta coating (1C1B), a multi-layer coating film is obtained by applying a top coating solid coating composition on a cured electrodeposition coating film and curing it by heating. That power S. For the formation of the top coat, it is preferable to perform spray coating so that the dry film thickness is 30 to 100 m. In addition, it can be applied multiple times, such as painting in two stages. The spray coating can be performed using an air spray coating machine, an airless spray coating machine, an air atomizing type or a rotary atomizing type electrostatic coating machine. Conditions for heating and curing the top-coated solid coating are 100 to 250 ° C, more preferably 130 to 180 ° C, and 5 to 60 minutes, more preferably 30 to 40 minutes. Can be mentioned. Example

[0105] The present invention will be described more specifically with reference to the following examples, but the present invention is not limited thereto. In the examples, “parts” and “%” are based on weight unless otherwise specified.

[0106] Production Example 1 Keying of Cationic Electrodeposition Coating Composition

Production Example 1 1 Preparation of Amine-modified Epoxy Resin

A flask equipped with a stirrer, condenser, nitrogen inlet tube, thermometer and dropping funnel was charged with 95 parts and dibutyltin dilaurate 0.5 parts. While stirring the reaction mixture, 21 parts of methanol was added dropwise. The reaction started from room temperature and was heated to 60 ° C by exotherm. Thereafter, the reaction was continued for 30 minutes, and then 50 parts of ethylene glycol mono-2-ethylhexyl ether was added dropwise from the dropping funnel. Further, 53 parts of a bisphenol A-propylene oxide 5 mol adduct was added to the reaction mixture. The reaction was mainly carried out in the range of 60-65 ° C, and continued until the absorption based on the isocyanate group disappeared in the IR spectrum measurement.

[0107] Next, an epoxy equivalent synthesized from bisphenol A and epichlorohydrin by a known method.

365 parts of 188 epoxy resin 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 an epoxy equivalent of 410 was reached.

[0108] Subsequently, 61 parts of bisphenolanol and 33 parts of octylic acid were added and reacted at 120 ° C. As a result, the epoxy equivalent was 1190. The reaction mixture is then cooled and 79 parts by weight of the ketimine product of 11 parts of diethylanolamine, 24 parts of Nethylethanolamine and aminoethylethanolamine! ^ 25 parts of the solution was added and reacted at 110 ° C for 2 hours. Thereafter, it was diluted with MIBK until the non-volatile content became 80% to obtain an amine-modified epoxy resin (resin solid content 80%).

[0109] Preparation Example 1 Preparation of 2 Block Isocyanate Curing Agent

A reactor was charged with 1250 parts of diphenylmethane diisocyanate and 4 parts of MIBK266. This was heated to 80 ° C, and 2.5 parts of dibutyltin dilaurate was added. Here, 226 parts of epsilon prolatatum were dissolved in 944 parts of butylcetone sorb, and dropped at 80 ° C. over 2 hours. After further heating at 100 ° C for 4 hours, in the IR spectrum measurement, it was confirmed that the absorption based on the isocyanate group disappeared, and after cooling, 1 part MIBK336.1 was added to block the glass transition temperature at 0 ° C. An isocyanate curing agent was obtained.

[0110] g 酉 ^

First, 220.0 parts of isophorone diisocyanate (hereinafter abbreviated as IPDI) was placed in a reaction vessel equipped with a stirrer, cooling pipe, nitrogen introduction pipe, and thermometer, and diluted with 39.1 parts. To this was added 0.2 part of dibutyltin dilaurate. Thereafter, the temperature was raised to 50 ° C., and 131.5 parts of 2-ethylhexanol was added dropwise over 2 hours under stirring in a dry nitrogen atmosphere. The reaction temperature was maintained at 50 ° C by cooling as appropriate. As a result, 2-ethyl hexanol nof-blocked IPDI (resin solid content: 90%) was obtained.

[0111] Next, in a suitable reaction vessel, 87.2 parts of dimethylolethanolanolamine, 75% aqueous lactic acid solution

117. 6 parts and 39.2 parts of ethylene glycol monobutyl ether were added in order, and the mixture was stirred at 65 ° C. for about half an hour to prepare a quaternizing agent.

[0112] Next, EPON 829 (Bisfenore A-type epoxy epoxies, epoxy equivalents 193-203, manufactured by Shell 'Chemical' Company) 710.0 咅 and bisphenolore A289. When charged in a container and heated to 150-160 ° C under a nitrogen atmosphere, an initial exothermic reaction occurred. The reaction mixture was allowed to react at 150-; 160 ° C for about 1 hour, then cooled to 120 ° C, and then 498.8 parts of 2-ethylhexanol half-blocked IPDI (MIBK solution) prepared previously was I got it. [0113] The reaction mixture is kept at 110-120 ° C for about 1 hour, then 463.4 parts of ethylene glycol monobutyl ether is added, the mixture is cooled to 85-95 ° C, homogenized and then prepared first. 196. 7 parts of the prepared quaternizing agent was added. After maintaining the reaction mixture at 85 to 95 ° C until the acid value becomes 1, add 964 parts of deionized water to finish quaternization in epoxy bisphenol A resin, and a pigment having a quaternary ammonium salt part A resin for dispersion was obtained (resin solid content 50%).

[0114] Preparation Example 1 4 Preparation of Pigment Dispersion Paste and Cationic Electrodeposition Coating Composition (1)

Add 100 parts of the pigment dispersion resin obtained in Production Example 1-3 in the sand grind mill, 100.0 parts of titanium dioxide and 10.0 parts of ion-exchanged water, and disperse until the particle size is 10 m or less. A paste was obtained (solid content 50%).

[0115] The amine-modified epoxy resin obtained in Production Example 1 1 and the block isocyanate curing agent obtained in Production Example 1 2 were mixed uniformly at a solid content ratio of 80/20. Glacial acetic acid was added to this so that the milligram equivalent (MEQ (A)) of the acid per 100 g of resin solid content was 30, and ion-exchanged water was slowly added to dilute. By removing MIBK under reduced pressure, an emulsion with a solid content of 36% was obtained.

[0116] 291 parts of this emulsion, 10 parts of the above pigment dispersion paste, 1890 parts of ion-exchanged water, 2.6 parts of 10% cerium acetate aqueous solution and 1.6 parts of dibutyltin oxide were mixed to obtain a solid content of 5% by weight. A cationic electrodeposition coating composition was obtained. The concentration of the pigment contained in the solid content of the cationic electrodeposition coating composition was 3% by weight. The solid content of the paint can be calculated as a percentage of the original mass of the residue after heating at 180 ° C for 30 minutes (conforming to JIS K5601).

[0117] Example 1 15 Preparation of pigment dispersion paste and cationic electrodeposition coating composition (2)

Put 100 parts of the pigment dispersion resin obtained in Production Example 1-3 in the sand grind mill, 98.0 parts of titanium dioxide, 2 parts of carbon black, and 10.0 parts of ion-exchanged water until the particle size is 10 m or less. Dispersion gave a pigment dispersion paste (solid content 50%).

[0118] The amine-modified epoxy resin obtained in Production Example 1 1 and the block isocyanate curing agent obtained in Production Example 1 2 were mixed uniformly at a solid content ratio of 80/20. Add glacial acetic acid to this so that the milligram equivalent (MEQ (A)) of acid per 100g of resin solids is 30, Further, ion exchange water was added slowly to dilute. By removing MIBK under reduced pressure, an emulsion with a solid content of 36% was obtained.

[0119] 291 parts of this emulsion, 10 parts of the above pigment dispersion paste, 1920 parts of ion-exchanged water, 2.6 parts of 10% cerium acetate aqueous solution and 1.6 parts of dibutyltin oxide were mixed to obtain a solid content of 5% by weight. A cationic electrodeposition coating composition was obtained. The concentration of the pigment contained in the solid content of the cationic electrodeposition coating composition was 3% by weight.

[0120] Preparation Example 1 6 Preparation of Pigment Dispersion Paste and Cationic Electrodeposition Coating Composition (3)

In a sand grind mill, 100 parts of the pigment dispersion resin obtained in Production Example 1-3, titanium dioxide

10.0 parts and 100.0 parts of ion-exchanged water were added and dispersed until the particle size became 10 m or less to obtain a pigment dispersion paste (solid content 50%).

[0121] The amine-modified epoxy resin obtained in Production Example 1 1 and the block isocyanate curing agent obtained in Production Example 1 2 were mixed so as to be uniform at a solid content ratio of 80/20. Glacial acetic acid was added to this so that the milligram equivalent (MEQ (A)) of the acid per 100 g of resin solid content was 30, and ion-exchanged water was slowly added to dilute. By removing MIBK under reduced pressure, an emulsion with a solid content of 36% was obtained.

[0122] 282 parts of this emulsion, 16 parts of the above pigment dispersion paste, 1892 parts of ion-exchanged water, 2.6 parts of 10% cerium acetate aqueous solution and 1.6 parts of dibutyltin oxide were mixed to obtain a solid content of 5% by weight. A cationic electrodeposition coating composition was obtained. The concentration of the pigment contained in the solid content of the cationic electrodeposition coating composition was 5% by weight.

[0123] Example 1 17 Preparation of pigment dispersion paste and cationic electrodeposition coating composition (4)

[0124] The amine-modified epoxy resin obtained in Production Example 1 1 and the block isocyanate curing agent obtained in Production Example 1 2 were mixed uniformly at a solid content ratio of 80/20. Glacial acetic acid was added to this so that the milligram equivalent (MEQ (A)) of the acid per 100 g of resin solid content was 30, and ion-exchanged water was slowly added to dilute. By removing MIBK under reduced pressure, an emulsion with a solid content of 36% was obtained. [0125] 272 parts of this emulsion, 23 parts of the above pigment dispersion paste, 1892 parts of ion-exchanged water, 2.6 parts of 10% cerium acetate aqueous solution and 1.5 parts of dibutyltin oxide were mixed to obtain a solid content of 5% by weight. A cationic electrodeposition coating composition was obtained. The concentration of the pigment contained in the solid content of the cationic electrodeposition coating composition was 7% by weight.

[0126] Example of preparation 1 8 Preparation of pigment dispersion paste and cationic electrodeposition coating composition (5)

[0127] The amine-modified epoxy resin obtained in Production Example 1 1 and the block isocyanate curing agent obtained in Production Example 1 2 were mixed uniformly at a solid content ratio of 80/20. Glacial acetic acid was added to this so that the milligram equivalent (MEQ (A)) of the acid per 100 g of resin solid content was 30, and ion-exchanged water was slowly added to dilute. By removing MIBK under reduced pressure, an emulsion with a solid content of 36% was obtained.

[0128] 1122 parts of this emulsion, 40 parts of the pigment dispersion paste, 811 parts of ion-exchanged water, 2.6 parts of 10% cerium acetate aqueous solution and 6.4 parts of dibutyltin oxide were mixed to obtain a solid content of 20% by weight. A cationic electrodeposition coating composition was obtained. The concentration of the pigment contained in the solid content of the cationic electrodeposition coating composition was 3% by weight.

[0129] i t lW Wholesale II

A flask equipped with a reflux condenser and a stirrer was charged with 295 parts of methylisoptyl ketone, 37.5 parts of methylethanolamine and 52.5 parts of diethanolamine, and kept at 100 ° C. with stirring. To this, 205 parts of cresol nopolac epoxy resin (product name: YDCN-7003, manufactured by Toto Kasei) was gradually added, and after the addition was completed, the mixture was reacted for 3 hours. The amine value (MEQ (B)) of the resulting amino-modified resin was measured and found to be 340 mmol / 100 g. The molecular weight was measured to be 2100.

[0130] To 140 parts of the amino-modified resin solution thus obtained, 5.5 parts of formic acid and 125.55 parts of deionized water were added and stirred for 30 minutes while maintaining at 80 ° C to remove the organic solvent under reduced pressure. As a result, a conductivity control agent having a solid content of 7.0% was obtained.

[0131] Preparation Example 1 10 Preparation of pigment dispersion paste and cationic electrodeposition coating composition (6) Add 100 parts of the pigment dispersion resin obtained in Production Example 1-3 in the sand grind mill, 100.0 parts of titanium dioxide and 10.0 parts of ion-exchanged water, and disperse until the particle size is 10 m or less. A paste was obtained (solid content 50%).

[0132] The amine-modified epoxy resin obtained in Production Example 1 1 and the block isocyanate curing agent obtained in Production Example 1 2 were mixed uniformly at a solid content ratio of 80/20. Glacial acetic acid was added to this so that the milligram equivalent (MEQ (A)) of the acid per 100 g of resin solid content was 30, and ion-exchanged water was slowly added to dilute. By removing MIBK under reduced pressure, an emulsion with a solid content of 36% was obtained.

[0133] 280 parts of this emulsion, 10 parts of the above pigment dispersion paste, 1845 parts of ion-exchanged water, 2.6 parts of 10% aqueous cerium acetate, 1.5 parts of dibutyltin oxide, and the electrical conductivity obtained in Production Example 19 A cationic electrodeposition coating composition having a solid content of 5% by weight was obtained by mixing 54 parts of a degree control agent. The concentration of the pigment contained in the solid content of the cationic electrodeposition coating composition was 3% by weight. Also, the conductivity of this cationic electrodeposition coating composition is 1000 S / cm.

[on i m ^-1 g 酉 ^ paste and cations

In a sand grind mill, 100 parts of the pigment dispersing resin obtained in Production Example 1-3, carbon black 1.0, moss phosphorus 40.0, titanium diacid titanium 50.0, linmolyp, anolynodenate 9 0 part and 100.0 part of ion-exchanged water were added and dispersed until the particle size became 10 m or less to obtain a pigment dispersion paste (solid content 50%).

[0135] The amine-modified epoxy resin obtained in Production Example 1 1 and the block isocyanate curing agent obtained in Production Example 1 2 were mixed uniformly at a solid content ratio of 80/20. Glacial acetic acid was added to this so that the milligram equivalent (MEQ (A)) of the acid per 100 g of resin solid content was 30, and ion-exchanged water was slowly added to dilute. By removing MIBK under reduced pressure, an emulsion with a solid content of 36% was obtained.

[0136] 199 parts of this emulsion, 76 parts of the above pigment dispersion paste, 1912 parts of ion-exchanged water, 2.6 parts of 10% cerium acetate aqueous solution and 1.3 parts of dibutyltin oxide were mixed to obtain a solid content of 5% by weight. A cationic electrodeposition coating composition was obtained. The concentration of the pigment contained in the solid content of the cationic electrodeposition coating composition was 23% by weight. Comparative Production Example 1 2 Preparation of Pigment Dispersion Paste and Cationic Electrodeposition Coating Composition (8) Production Example 1 The amine-modified epoxy resin obtained in 1 and the block isocyanate curing agent obtained in Production Example 1 2 The mixture was mixed uniformly at a solid content ratio of 80/20. Glacial acetic acid was added to this so that the milligram equivalent (MEQ (A)) of the acid per 100 g of resin solid content was 30, and ion-exchanged water was slowly added to dilute. By removing MIBK under reduced pressure, an emulsion with a solid content of 36% was obtained.

[0138] 304 parts of this emulsion, 1883 parts of ion-exchanged water, 2.6 parts of 10% cerium acetate aqueous solution and 1.6 parts of dibutyltin oxide were mixed to form a cationic electrodeposition coating composition having a solid content of 5% by weight. I got a thing.

[0139] i m ^-3 g 酉 ¾ Paste and cation

[0140] The amine-modified epoxy resin obtained in Production Example 1 1 and the block isocyanate curing agent obtained in Production Example 1 2 were mixed uniformly at a solid content ratio of 80/20. Glacial acetic acid was added to this so that the milligram equivalent (MEQ (A)) of the acid per 100 g of resin solid content was 30, and ion-exchanged water was slowly added to dilute. By removing MIBK under reduced pressure, an emulsion with a solid content of 36% was obtained.

[0141] 259 parts of this emulsion and 33 parts of the above pigment dispersion paste, 1895 parts of ion-exchanged water, 2.6 parts of 10% cerium acetate aqueous solution and 1.5 parts of dibutyltin oxide were mixed to obtain a solid content of 5% by weight. A cationic electrodeposition coating composition was obtained. The concentration of the pigment contained in the solid content of the cationic electrodeposition coating composition was 10% by weight.

[0142] Comparative Production Example 1 4 Preparation of pigment dispersion paste and cationic electrodeposition coating composition (10)

In a sand grind mill, add 100 parts of the pigment dispersion resin obtained in Production Example 1-3, 90.0 parts of titanium dioxide, 10.0 parts of carbon black and 10.0 parts of ion-exchanged water to a particle size of 10 mm or less. A pigment dispersion paste was obtained (solid content 50%).

[0143] The amine-modified epoxy resin obtained in Production Example 1 1 and the block isocyanate curing agent obtained in Production Example 1 2 were mixed so as to be uniform at a solid content ratio of 80/20. This is resin Glacial acetic acid was added to the mixture so that the milligram equivalent (MEQ (A)) of the acid per 30 g of solid content was 30 and further diluted with ion-exchanged water. By removing MIBK under reduced pressure, an emulsion with a solid content of 36% was obtained.

[0144] 291 parts of this emulsion, 10 parts of the above pigment dispersion paste, 1889 parts of ion-exchanged water, 2.6 parts of 10% cerium acetate aqueous solution and 1.6 parts of dibutyltin oxide were mixed to obtain a solid content of 5% by weight. A cationic electrodeposition coating composition was obtained. The concentration of the pigment contained in the solid content of the cationic electrodeposition coating composition was 3% by weight.

Comparative Production Example 1 5 Preparation of pigment dispersion paste and cationic electrodeposition coating composition (11)

[0146] The amine-modified epoxy resin obtained in Production Example 1 1 and the block isocyanate curing agent obtained in Production Example 1 2 were mixed so as to be uniform at a solid content ratio of 80/20. Glacial acetic acid was added to this so that the milligram equivalent (MEQ (A)) of the acid per 100 g of resin solid content was 30, and ion-exchanged water was slowly added to dilute. By removing MIBK under reduced pressure, an emulsion with a solid content of 36% was obtained.

[0147] 268 parts of this emulsion, 26 parts of the above pigment dispersion paste, 1893 parts of ion-exchanged water, 2.6 parts of 10% cerium acetate aqueous solution and 1.5 parts of dibutyltin oxide were mixed to obtain a solid content of 5% by weight. A cationic electrodeposition coating composition was obtained. The concentration of the pigment contained in the solid content of the cationic electrodeposition coating composition was 8% by weight.

[0148] Forging example 2 Key to water-based intermediate coating composition

Production Example 2 1 Preparation of water-soluble polyester shelf

Reaction vessel ί This is an isophthalenolic acid 200.0U, phthalenoic anhydride 179.0U, adipic acid 176.00U, trimethylolpropane 150 · 0 parts, neopentylglycol 295 · 0 parts, dibutyltin oxide 2 parts, in a nitrogen stream After heating and melting the raw material, the temperature was gradually raised to ¾170 ° C without mixing and stirring. Thereafter, the temperature was raised to 220 ° C. over 3 hours, and dehydration was carried out. When the acid value reached 10, it was cooled to 150 ° C. Further, 114.0 parts of hexahydrophthalic acid was added and reacted for 1 hour to complete the reaction. In addition, 10 After cooling to 0 ° C., 112.0 parts of butylceosolve was added to obtain a polyester resin. The obtained polyester resin had a solid content acid value of 50, a hydroxyl value of 65, and a weight average molecular weight of 10,000 obtained by GPC (gel permeation chromatography). This polyester resin was cooled to 60 ° C., and 80.0 parts of dimethylethanolamine and ion-exchanged water were added to obtain a polyester resin having a nonvolatile content of 50%.

[0149] Example 2—2 Production of polyester resin emulsion

New Coal 1120 (manufactured by Nippon Emulsifier Co., Ltd.) (33.4 parts) and ethylene glycol mono-n-hexylcetone sorb (6 parts) were dispersed in 94 parts of ion exchange water. The polyester resin was dropped into the previous dispersion while stirring 11.1.1 parts of the above polyester resin to obtain a polyester resin emulsion coated with a nonionic dispersant having a nonvolatile content of 47.5%.

[0150] Coloring ¾Manufacturing paste

Commercially available pigment dispersant Disperbyk 190 (Bic Chemi Co., Ltd .; solid content 40% by weight) 9.4 parts, ion exchange water 36.8 parts, rutile titanium dioxide 74.8 parts, carbon black 0.03 parts and oxidation After premixing 0.07 parts of iron yellow, glass beads medium was added in a paint conditioner and mixed and dispersed at room temperature until the particle size became 5 in or less to obtain a colored pigment paste. In the production of the pigment paste, the time required to reach a particle size of 5 m or less was 15 minutes.

[0151] 7 half-painting

121.2 parts of the colored paste obtained in Production Example 2-3, 28.8 parts of water-soluble polyester resin obtained in Production Example 2-1, 190.2 parts of polyester resin emulsion obtained in Production Example 2-2, Simel 235 (manufactured by Mitsui Cytec Co., Ltd.) 33.8 parts and 21.1 parts of ion-exchanged water were added and mixed and stirred to obtain an aqueous intermediate coating composition.

[0152] Forging Example 3 Keying of Solvent Intermediate Coating Composition

Production Example 3-1 Preparation of Polyester Shelf Solution

In a reaction vessel equipped with a thermometer, stirrer, temperature controller, reflux condenser, nitrogen inlet tube and fractionator, 258 parts of hexahydrophthalic anhydride, 184 parts of isophthalic acid, 213 parts of trimethylolprone, neo 180 parts of pentyl glycol, 72 parts of neopentyl glycol hydroxybivalate and cardiura (—10 (Versatic acid group manufactured by Shell Chemical Co., Ltd.) 94 parts of lysidyl ester were charged and heated to 180 ° C. After the above raw materials have melted and stirring is possible, 0.2 part of dibutyltin oxide is charged and stirring is started, and the reaction vessel is heated from 180 ° C to 220 ° C over a period of 3 hours at a constant rate of temperature rise. While maintaining the temperature, the condensed water produced was distilled out of the system. When the temperature reached 220 ° C, the mixture was kept warm for 1 hour with stirring, and 17 parts of xylene was gradually added as a refluxing solvent to further proceed the reaction. When the resin acid value reached 10, it was cooled to 150 ° C, and 182 parts of Plaxel M (Daicel Chemical Industries, Ltd. Until cooled. Further, 264 parts of xylene was added to obtain a polyester resin solution having a number average molecular weight of 1400, a solid content of 79% by weight, a hydroxyl value of 210, and an acid value of 8 by GPC measurement.

[0153] 7k

(a) Production of dispersion stable resin

A reaction vessel equipped with a thermometer, stirrer, temperature controller, reflux condenser and nitrogen inlet tube was charged with 90 parts of butyl acetate, 38.9 parts of methyl methacrylate, 38.8 parts of stearyl methacrylate, 3/8 clinoleic acid 2 —Hydroxyethinole 22 · and 20 parts of the monomer mixture consisting of 5.0 parts of Zeo'hi, Suisov, 'tyronitrinole with a calculated solubility parameter of 9.5 and stirring. While heating, the temperature was raised to 80 ° C. While refluxing, the remaining 85.0 parts of the above monomer mixture was added dropwise over 3 hours, and then a solution consisting of 0.5 parts of azobisisobutyronitrile and 10 parts of butyl acetate was added dropwise over 30 minutes. did. The reaction solution was further stirred and refluxed for 2 hours while maintaining the temperature at 80 ° C., and then the reaction was terminated to obtain a dispersion-stable resin solution having a number average molecular weight of 5600 and a solid content of 50% by weight as measured by GPC.

[0154] (b) Production of non-aqueous dispersion resin liquid

A reaction vessel equipped with a thermometer, a stirrer, a temperature controller, a reflux condenser and a nitrogen introduction tube was charged with 35 parts of butyl acetate and 60 parts of the resulting dispersion-stabilizing resin, and the temperature was raised to 100 ° C. Furthermore, from this, styrene 7.0, methacrylolic acid 1 · 8, methacrylolic acid methylolate 12 · 0, ethyl acrylate 8.5 parts, attalinoleic acid 2-hydroxyethylenole 40.7 parts and azobisisobutyronitrile 1.4 parts A monomer mixture having a solubility parameter of 11.8 determined by the following calculation was added dropwise over 3 hours, and then a solution consisting of 0.1 part of azobisisobutyronitrile and 1 part of butyl acetate was added. Added dropwise over 30 minutes. While stirring the reaction solution, After holding for 1 hour, dilute with butyl acetate to give a non-aqueous dispersion of liquid with an average particle size of 0.118 111, solid content of 40 wt%, viscosity at 25 ° C of 300 cps, glass transition temperature of 23 ° C, hydroxyl value of 162 Obtained.

[0155] Forging side 3-3 Keying of colored pigment paste

Production Example 3-1 The polyester resin solution obtained in 3-1 was used with respect to 328 parts of rutile titanium dioxide 981.7 parts, carbon black 0.39 parts, iron oxide yellow 0.92 parts, butyl acetate 159 parts and xylene 82. 1552 parts of glass beads were added and dispersed in a sand grind mill for 3 hours. When the particle size became 5 m or less with a grind gauge, the dispersion was terminated. After adding 81.8 parts of xylene, the mixture was stirred for about 10 minutes, and the glass beads were removed by filtration to obtain a pigment paste.

[0156] m- 吝 ιι width 'painting' painted words

83.1 parts of the colored paste obtained in Production Example 3-3, 21.0 parts of the polyester resin solution obtained in Production Example 3-1, 87.5 parts of the non-aqueous dispersion resin solution obtained in Production Example 3-2, Cymel 254 (Mitsui Cytec Co., Ltd.) 37.5 parts, PTMG1000 (Mitsubishi Chemical Co., Ltd.) 5. 2 parts were added and mixed and stirred to obtain an intermediate coating composition.

The cationic electrodeposition coating composition (1) obtained in Production Example 1-4 was applied to a zinc phosphate-treated hot-dip galvanized steel sheet (JIS G3302 standard product, 150 X 70 X 0.8 mm). Was electrodeposition coated so that the thickness was 15 m and baked at 160 ° C for 30 minutes to obtain a cured electrodeposition coating film.

[0158] On the obtained cured electrodeposition coating film, the aqueous intermediate coating composition prepared in Production Example 2 was applied for 20 m by air spray coating, and pre-heated at 80 ° C for 5 minutes, AQUALEX 2000 Pearl My Strength Base (water-based Pearl My Strength base coating composition manufactured by Nippon Paint Co., Ltd.) was applied with 13 πι by air spray coating and preheated at 80 ° C for 3 minutes. In addition, Mac Flow O-1800W-2 Talia (Nippon Paint's acid-epoxy-cured tarrier paint composition) was applied to the coated plate by air spray painting for 35 am and then baked at 140 ° C for 30 minutes. A test piece having a multilayer coating film was obtained. Water-based intermediate coating composition, aqueous top-coating base coating composition (AQUAREX AR-2000 base), and top-coating tarrier coating composition (Macflow O-1800W-2 Talia) were diluted and applied under the following conditions. . Thinner: ion-exchanged water, 40 seconds / No. 4 Ford cup / 20 ° C (water-based intermediate coating composition)

Thinner: Ion-exchanged water, 45 seconds / No. 4 Ford Cup / 20 ° C (Water-based topcoat composition)

Thinner: EEP (ethoxyethyl propionate) / S-150 (Aromatic hydrocarbon solvent made by Exxon) = 1/1, 30 seconds / No. 4 Ford cup / 20 ° C (Top coat coating composition) )

[0159] Measurement of specific gravity of dried electrodeposition coating film

A cationic electrodeposition coating composition was electrodeposited on a tin plate (JIS G3303 standard product, 150 X 70 X 0.3 mm) so that the dry coating film was 15 ΐη, and baked at 160 ° C for 30 minutes. The obtained substrate was immersed in mercury to release the coating film. The released coating was cut into 10 mm squares and used as test samples. With respect to this test sample, the dry film specific gravity was measured by a floatation / sink method specified in JIS K 7112, using a potassium iodide solution. Table 1 shows the results obtained.

[0160] Measurement of ffi ft ^ ffiMRa.)

The Ra value of the horizontal portion of the obtained cured electrodeposition coating film was measured using an evaluation type surface roughness measuring machine (SURFTEST SJ-201P, manufactured by Mitsutoyo) in accordance with JIS-B0601-2001. 2. The measurement was performed 7 times as a 5 mm width cut-off (number of sections: 5), and the Ra value was obtained by averaging the top and bottom. These Ra values indicate that the smaller the value, the better the appearance of the coating film with less irregularities on the surface.

[0161] Hardened lightning 'Lightness index of coating film Measurement of L value

About the hue of the obtained cured electrodeposition coating film, the lightness index L value was measured using a color difference meter (Minolta CR300, manufactured by Micareta).

[0162] Plum 'Hue evaluation of paint film

Using the color difference meter (Minolta CR300, manufactured by Mikareta Co., Ltd.), the L value, a value, and b value are side-colored for the hue of the resulting multilayer coating film, and Comparative Example 1 is the standard coating color (reference plate) I found ΔΕ. The results obtained are shown in Table 1. These values indicate that the smaller the difference between the values, the better the color difference from the reference plate. ΔΕ is obtained by the following equation. This ΔΕ If the value of exceeds 1, it is in a state where a clear hue change can be confirmed.

[0163] [Equation 1]

AE = ^ AL ² + Aa ² + Ab ²

[0164] The L value, the a value, and the b value are values obtained in accordance with JIS Z 8722 and JIS Z 8730. The L value is the brightness index in the Hunter's color difference formula, and the a and b values are called the chroma takeness index in the Hunter's color difference formula. In general, the lightness index L value has an upper limit of 100, and as the value increases, the hue of the substance to be measured increases in whiteness 1S, and as the value decreases, the blackness increases. The a-value, which is the chroma takeness index, means that when the value is negative, the greenness is increased in the hue of the substance to be measured, and when the value is positive, the redness is increased. The b value, which is the chromaticness index, means that when the value is negative, the hue of the substance to be measured increases blueness, and when it is positive, the yellowness increases.

[0165] Example 2

[0166] On the obtained cured electrodeposition coating film, the solvent intermediate coating composition prepared in Production Example 3 was applied by air spray coating for 20 inches and allowed to stand at room temperature for 10 minutes. Next, Superlac M-1300 Pearl My Strength Base (a melamine curable acrylic resin-based organic solvent-based top coating composition made by Nippon Paint Co., Ltd.) was applied to the object on which an uncured intermediate coating film was formed. After applying to m to obtain an uncured top coat film, it was left at room temperature for 20 minutes. In addition, Mac Flow O-1800W-2 Talia (Nippon Paint's acid epoxy curing type Talia paint composition) was applied to the coated plate by air spray coating for 35 am, and then baked at 140 ° C for 30 minutes. A test piece having a layer coating was obtained. In addition, the solvent intermediate coating composition, the solvent top coating base coating composition (Superlac M-1300 base), and the top coating composition (Macflow O-1800W-2 Talia) were diluted and applied under the following conditions. .

Thinner: Ethyl ethoxypropionate / xylene = 9/11, 19 seconds / No. 4 Ford Cup, twenty. C (Solvent intermediate coating composition)

Thinner: Toluene / Butyl acetate / Methylethylketone = 40/50/10, 15 seconds / No. 4 Ford Cup / 20 ° C (solvent top coating composition)

[0167] The obtained cured electrodeposition coating film and multilayer coating film were evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0168] Example 3

[0169] On the obtained cured electrodeposition coating film, a white intermediate coating composition Organa P-5 071 (a melamine curable polyester resin-based white intermediate coating composition manufactured by Nippon Paint Co., Ltd.) was dried. The film was coated with air spray so that the film thickness was 20 m, baked at 140 ° C for 30 minutes, and then cooled to obtain a substrate having a cured intermediate coating film. On the obtained substrate, Aqualex AR-2000 Pearl My Strength Base (water-based Pearl My Strength base coating composition manufactured by Nippon Paint Co., Ltd.) was applied by air spray coating 13 πι, and preheated at 80 ° C for 3 minutes. It was. Furthermore, after coating Mac Flow O-1800W-2 Talia (Nippon Paint's acid epoxy curing type Talia paint composition) on the coated plate by air spray coating for 35 am, baking was performed at 140 ° C for 30 minutes. A specimen was obtained. In addition, solvent intermediate coating composition (Olga P-5 071), water-based top coating composition (Aqualex 2000 base), and top coating composition (Macflow O-1800W-2 Talia) are diluted under the following conditions. And painted.

Thinner: EEP (Ethoxyethyl propionate) / xylene = 9/11, 19 seconds / No. 4 Ford power p / 20 ° C (solvent-coated coating composition)

Thinner: EEP (Ethoxyethyl propionate) / S-150 (Exon Aromatic Coal Hydrochloric acid solvent) = 1/1, 30 seconds / No. 4 Ford Cup / 20 ° C (Topcoat paint composition)

[0170] The obtained cured electrodeposition coating film and multilayer coating film were evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0171] Example 4

As the cationic electrodeposition coating composition, a cured electrodeposition coating film and a multilayer coating film were prepared in the same manner as in Example 1, except that the cationic electrodeposition coating composition (2) obtained from Production Example 15 was used. Obtained. These obtained coating films were evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0172] ^

As the cationic electrodeposition coating composition, a cured electrodeposition coating film and a multilayer coating film were prepared in the same manner as in Example 1 except that the cationic electrodeposition coating composition (3) obtained in Production Example 16 was used. Obtained. These obtained coating films were evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0173] rnmrne

A cured electrodeposition coating film and a multilayer coating film were prepared in the same manner as in Example 1 except that the cationic electrodeposition coating composition (4) obtained from Production Example 17 was used as the cationic electrodeposition coating composition. Obtained. These obtained coating films were evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0174] Example 7

As the cationic electrodeposition coating composition, a cured electrodeposition coating film and a multilayer coating film were prepared in the same manner as in Example 1, except that the cationic electrodeposition coating composition (5) obtained from Production Example 18 was used. Obtained. These obtained coating films were evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0175] Example 8

As the cationic electrodeposition coating composition, a cured electrodeposition coating film and a multilayer coating film were obtained in the same manner as in Example 1 except that the cationic electrodeposition coating composition obtained from Production Example 19) was used. It was. These obtained coating films were evaluated in the same manner as in Example 1. The result It is shown in Table 2.

[0176] Further, the throwing power was evaluated using the cationic electrodeposition coating composition (6) obtained in Production Example 19, and it was confirmed that the throwing power was also good. The evaluation of the messiness was performed as follows.

[0177] Evaluation of throwing power

The throwing power was evaluated by the so-called four-sheet box method. That is, as shown in FIG. 1, four zinc phosphate-treated steel plates (treated with JIS G3141 SPCC-SD, Surfdyne SD-5500 (made by Nippon Paint Co., Ltd.)) 11 to 14 were set up. In this state, a box 10 was prepared, which was arranged in parallel with an interval of 20 mm, and the bottom and bottom of both sides were sealed with an insulator such as cloth adhesive tape. The steel plates 11 to 13 other than the steel plate 14 are provided with through holes 15 of 8 mmφ at the bottom.

[0178] 4 liters of cationic electrodeposition paint was transferred to a vinyl chloride container to form a first electrodeposition bath. As shown in FIG. 2, the box 10 was immersed in an electrodeposition paint container 20 containing an electrodeposition paint 21 as an object to be coated. In this case, the paint 21 enters the box 10 only from each through hole 15.

[0179] Paint 21 was stirred with a magnetic stirrer (not shown). The steel plates 11 to 14 were electrically connected, and the counter electrode 22 was arranged so that the distance between the steel plate 11 and the steel plate 11 was 150 mm. Cathode electrodeposition coating was performed on steel rice with a voltage applied with each steel plate 11-; 14 as a cathode and the counter electrode 22 as an anode. The coating was performed by increasing the voltage until the film thickness of the coating film formed on the A side of the steel plate 11 reached 15 m within 5 seconds of application starting force, and then maintaining that voltage for 175 seconds in normal electrodeposition. .

[0180] Each steel plate after coating was washed with water, baked at 170 ° C for 25 minutes, air-cooled, and the film thickness of the coating film formed on the A surface of steel plate 11 closest to counter electrode 22 , The farthest from the counter electrode 22! /, And the film thickness of the coating film formed on the G surface of the steel plate 14 was measured, and the ratio (G / A value) of the film thickness (G surface) / film thickness (eight surfaces) The throwing power was evaluated. Generally, when this value exceeds 50%, it is good, and when this value is 50% or less, it can be judged as defective.

[0181] Comparative Example 1

As the cationic electrodeposition coating composition, a cured electrodeposition coating film and a multilayer coating were prepared in the same manner as in Example 1, except that the cationic electrodeposition coating composition (7) obtained in Comparative Production Example 11 was used. A membrane was obtained. These obtained coating films were evaluated in the same manner as in Example 1. The results are shown in Table 3. For the hue evaluation of the multilayer coating film, the evaluation results of Comparative Example 1 are used as a reference.

[0182] Comparative Example 2

As the cationic electrodeposition coating composition, a cured electrodeposition coating film and a multilayer coating film were prepared in the same manner as in Example 1 except that the cationic electrodeposition coating composition (8) obtained from Comparative Production Example 12 was used. Got. These obtained coating films were evaluated in the same manner as in Example 1. The results are shown in Table 3.

[0183] Comparative Example 3

As the cationic electrodeposition coating composition, a cured electrodeposition coating film and a multilayer coating film were prepared in the same manner as in Example 1 except that the cationic electrodeposition coating composition (9) obtained from Comparative Production Example 13 was used. Got. These obtained coating films were evaluated in the same manner as in Example 1. The results are shown in Table 3.

[0184] Comparative Example 4

As the cationic electrodeposition coating composition, a cured electrodeposition coating film and a multilayer coating film were obtained in the same manner as in Example 1 except that the cationic electrodeposition coating composition (10) obtained from Comparative Production Example 14 was used. Got. These obtained coating films were evaluated in the same manner as in Example 1. The results are shown in Table 3.

[0185] Comparative Example 5

The cured electrodeposition coating film and the multilayer coating film were the same as in Example 1 except that the cationic electrodeposition coating composition (11) obtained from Comparative Production Example 15 was used as the cationic electrodeposition coating composition. Got. These obtained coating films were evaluated in the same manner as in Example 1. The results are shown in Table 3.

[0186] [Table 1] Example Example Example Example Example 1 2 3 4 5 Titanium dioxide 100 100 100 98 100

Fee

Lingoliph "te" acid

Pair

Aluminum

Completion

Car-ho "Nuf" rack 2

Of pigments in solids

3.0 3.0 3.0 3.0 5.0 concentration (weight ⁰ I)

Of cured electrodeposition coating

1.21 1.21 1.21 1.21 1.22 Paint Hi Heavy

Of cured electrodeposition coating

57.6 57.6 57.6 56.2 58.0 Lightness index L value

Paint solids (wt ^_0/0) 5.0 5.0 5.0 5.0 5.0 cured electrodeposition coating film of R a

0.18 0.18 0.18 0.18 0.19 (horizontal plane)

3C1B 3C1B 3C2B 3C1B 3C1B Crane coating process (water tt / water (solvent / solution / water (aqueous / water / water) agent / lake) property / solvent) property / mixed D ft / lake) intermediate coating film Film thickness

20 20 20 20 20 (μm

To top coat-,-

13 13 13 13 13 Boat m)

△ L 0.09 0.08 0.07 -0.22 0.02 Multilayer coating △ a 0.06 0.07 0.06 0.04 0.10 Hue evaluation △ b -0.08 -0.05 -0.01 0.09 -0.05

ΔΕ 0.13 0.12 0.09 0.24 0.11

2]

Examples Examples Examples Examples

6 7 8 *

Titanium dioxide 100 100 100

Powerful!)

Fee

Lingoliph "te" acid

Pair

Aluminum

Completion

Kaho "Nuf" rack

Of pigments in solids

7.0 3.0 3.0

Concentration (weight ⁰ I)

Of cured electrodeposition coating

1.25 1.21 1.21

Paint Hi Heavy

Of cured electrodeposition coating

60.2 57.6 57.6

Lightness index L value

Paint solids (weight ^_0/0) 5.0 20 5.0

R a of cured electrodeposition coating

0.20 0.18 0.17

(Horizontal plane)

3C1B 3C1B 3C1B

Crane coating process (water tt / water (water tt / water property / water

14) / Lake) Sex / Solvent)

Film thickness of intermediate coating

20 20 20

(μm

To top coat-,-

13 13 13

Boat m)

△ L 0.10 0.08 0.10

△ a 0.11 0.12 0.08

Hue evaluation △ b -0.09 0.08 -0.06

ΔΕ 0.17 0.16 0.14

: The throwing power (G / A value) of the cationic electrodeposition coating composition in Example 8 was 66%, which was good.

[Table 3]

Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Titanium Dioxide 50 100 90 100 Kaolin 40

Fee

Linmorif 'te' aluminum acid

Pair 9

Nyum

Completion

Carphone; 7 1 10

Concentration of pigment in solids

23. 0 0 10. 0 3. 0 8. 0

(Weight ^_0/0)

Dry coating of cured electrodeposition coating

1. 40 1. 20 1. 30 1. 21 1. 27 Membrane specific gravity

Lightness finger of cured electrodeposition coating

56. 8 49. 6 73. 2 54. 0 64. 8 Number L value

Paint solids (wt%) 5. 0 5. 0 5. 0 5. 0 5. 0 R a of cured electrodeposition coating

0. 29 0. 17 0. 28 0. 18 0. 27 (horizontal plane)

3C1B 3C1B 3C1B 3C 1B 3C1B Multi-layer coating film formation process (water ft / water (aqueous / water (aqueous / water (aqueous / water (aqueous / water solvent)) property / solvent) property / solvent) property / solvent) property / solvent ) Middle coat ^,

20 20 20 20 20 (β m;

Topcoat 'film thickness

13 13 13 13 13 (m)

△ LL = 86. 79 * -1. 01 0. 28 -0. 77 0. 18 △ aa = 0. 56 * 0. 18 0. 06 0. 15 0. 14 Hue evaluation A bb = 0. 79 * 0. 11 0. 00 0. 18 0. 08

Δ Ε 1. 03 0. 29 0. 80 0. 24: In the hue evaluation of the multilayer coating film, the L value, a value, and b value of Comparative Example 1 were used as reference values, and values of each Example and Comparative Example were used. And the difference between the reference value.

As shown in Tables 1 and 2, the multi-layer coating film obtained in the example has a low concentration of the pigment contained in the cationic electrodeposition coating composition, which is about 12% of Comparative Example 1. Nevertheless, it can be seen that it has a hue comparable to that of Comparative Example 1. Furthermore, the cured electrodeposition coating films obtained by the examples also have a good horizontal appearance with a low Ra value. In addition, the cured electrodeposition coating film has an advantage that the specific gravity of the dried coating film is low. In addition, as in Example 8, the cationic electrodeposition coating composition containing the conductivity control agent shows good throwing power even though the coating solid content (wt%) is as low as 5 wt%. . On the other hand, the multilayer coating film obtained in Comparative Example 2 had a ΔΕ exceeding 1, and the hue of the multilayer coating film obtained in Comparative Example 1 was clearly different. This is because the effect of the color of the substrate itself is multi-layered because of the poor concealability of the coating film. This is because it also appeared on the coating film. Further, the cured electrodeposition coating films obtained in Comparative Examples 3 and 5 had a high Ra value, a poor horizontal appearance, and a high specific gravity of the dried coating film, as in Comparative Example 1. On the other hand, the multilayer coating film obtained in Comparative Example 4 was clearly different in hue from the multilayer coating film obtained in Comparative Example 1 where ΔΕ was as high as 0.80.

Industrial applicability

In the method of the present invention, a multilayer coating film having a lightness index L value of 55 or more and an excellent hue is formed despite the use of a cationic electrodeposition coating composition having a low pigment content. Can do. By using the method of the present invention, it is possible to form a multi-layer coating film excellent in concealing property and the like by a coating method with less baking and curing in response to demands for energy saving and cost reduction. Furthermore, the weight of the coated object can be reduced by the method of the present invention.

Claims

The scope of the claims

[1] An electrodeposition coating process in which a cationic electrodeposition coating composition is electrodeposited to form an electrodeposition coating, and the resulting electrodeposition coating is cured by heating to obtain a cured electrodeposition coating,

A method for forming a multilayer coating film, comprising:

The cationic electrodeposition coating composition is a cationic electrodeposition coating composition in which the concentration of the pigment contained in the solid content of the electrodeposition coating composition is 2 to 7% by weight,

The pigment contains 95-100% by weight of titanium dioxide,

The cured electrodeposition coating film has a lightness index L value of 55 or more at a film thickness of 15 m or more, and the cured electrodeposition coating film has a dry coating film specific gravity of 1.20 to; 1.25.

A method for forming a multilayer coating film.

[2] The multilayer coating film forming step includes:

A heating step of simultaneously heating and curing the uncured intermediate coating film, the uncured top coating base coating film, and the uncured top coating clear coating film,

The method for forming a multilayer coating film according to claim 1, comprising:

[3] The multilayer coating film forming step comprises:

A step of applying an overcoating base coating composition on the obtained intermediate cured coating film to form an uncured top coating base film,

On top of the resulting uncured topcoat base coating film, apply a topcoat coating composition. Forming an uncured top coat film, and

A heating step of simultaneously heating and curing the uncured topcoat base coating and the uncured topcoat film.

[4] The method for forming a multilayer coating film according to claim 2 or 3, wherein the thickness of the cured intermediate coating film formed in the multilayer coating film forming step is 10 to 40 ^ m.

[5] The multilayer coating film forming step includes:

[6] The multilayer coating film forming step includes:

A heating step of heating and curing the uncured topcoat solid coating film;

[7] The intermediate coating composition is an aqueous intermediate coating composition, and the topcoat base coating composition is an aqueous topcoat base composition, or

The intermediate coating composition is a solvent intermediate coating composition, and the topcoat base coating composition is a solvent topcoat base composition,

The method for forming a multilayer coating film according to claim 2.

[8] A multilayer coating film obtained by the multilayer coating film forming method according to any one of [1] to [7].