JP2005334776A - Method for forming multi-layer coating film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for forming a multi-layer coating film excellent in finishing appearance. <P>SOLUTION: The method for forming the multi-layer coating film includes a process of forming an uncured electrodeposition-coating film by electrodeposition-coating a material to be coated with a cation electrodeposition-coating material composition, a process of forming an uncured intermediate-coating film by coating the uncured electrodeposition-coating film with an intermediate-coating composition, and a process of simultaneously curing by baking the cured eletrodeposition-coating film and the intermediate-coating film. The material to be coated is a steel material having the surface of 0.3-0.9 μm in average roughness (Ra) at the center line in a roughness curve. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for forming a multilayer coating film having a good finished appearance.

  On the surface of a substrate such as an automobile, a plurality of coating films having various roles are formed to protect the substrate and at the same time give a beautiful appearance. Such a coating film is generally formed by baking and curing each coating layer one by one.

  However, in recent years, due to demands for energy saving and cost reduction, a method in which the next coating is applied by so-called wet-on-wet without baking and hardening, and then a plurality of layers are baking and hardening at a time is being adopted. As an example of such a method, after the electrodeposition coating is cured, the intermediate coating, top coating base and clear coating are applied wet-on-wet, and then the three uncured coatings are baked and cured at once. Three-coat / one-bake coating (also called three-wet coating) is considered the most feasible method. In addition, as another means for achieving the demand for energy saving and cost reduction, two-wet coating is also considered in which an intermediate coating is applied wet-on-wet without curing the electrodeposition coating after electrodeposition coating.

  By the way, in such coating, since there are few baking processes compared with the conventional process, it turned out that the surface state of a steel plate has a big influence on the external appearance of the obtained multilayer coating film.

  Japanese Patent Application Laid-Open No. 2003-253494 (Patent Document 1) discloses an outer plate portion of an automobile body that is composed of an oxide film-treated aluminum material or a dissimilar metal material in which an oxide film-treated aluminum material and a steel material are combined. Alternatively, in the inner plate portion, the surface roughness of the aluminum material to which the oxide film treatment is applied is Ra of 0.2 μm or less, and the aluminum material to which the oxide film treatment is applied contains magnesium and silica. JIS K-6000 series There is described a method for coating an automobile body, which is an aluminum alloy and the oxide film-treated aluminum material is coated with a thermosetting electrodeposition coating film. And it is described that a coating film excellent in finished appearance and coating film performance can be obtained. However, in the technique disclosed herein, the surface roughness of the aluminum material requires a high smoothness of Ra of 0.2 μm or less, and when Ra exceeds 0.2 μm, the oxide film treated aluminum material It is also described that the smoothness of the electrodeposition coating film to be coated is lowered.

JP-A-8-325796 (Patent Document 2) discloses a steel plate, an alloyed hot-dip galvanized layer provided thereon, and a coating weight of 1.0 to 5.0 g / An alloyed hot-dip galvanized steel sheet having an electrodeposition coating property, which is composed of an m ² phosphoric acid-based chemical conversion coating film, and the crushed (sliding) portion of the surface of the alloyed hot-dip galvanized layer has a total surface area. On the other hand, an alloyed hot-dip galvanized steel sheet is described in which the plating layer has a surface roughness Ra of 0.3 to 1.0 μm in excess of 5% and 80% or less. According to this, it is described that uneven appearance defects generated when electrodeposition coating is applied after chemical conversion treatment can be improved. However, the present invention is limited to a plating layer having a surface roughness Ra of 0.3 to 1.0 μm and a steel sheet plated. On the other hand, the present invention is not limited to a plated steel sheet. In the present invention, a steel plate that has been plated may be used, or a steel plate that has not been plated may be used. The present invention differs from the invention described in Patent Document 2 in that it focuses on the numerical range of the center line average roughness (Ra) of the roughness curve of the steel sheet regardless of the presence or absence of plating.

  Moreover, it is described that the invention described in Patent Document 2 relates to an alloyed hot-dip galvanized steel sheet excellent in electrodeposition coating properties. On the other hand, the present invention aims to save energy in the coating process from the viewpoint of global environment such as energy resource conservation in the automotive field where a multilayer coating film such as an electrodeposition coating film / intermediate coating film / top coating film is applied. Accordingly, the present invention provides a coating method in which the baking process is omitted. When the invention described in Patent Document 2 is used in a coating method in which such a baking step is omitted, it cannot be said that a sufficient coating film appearance is obtained. Moreover, patent document 2 does not contain any suggestion with respect to using for the coating method by which such a baking process was abbreviate | omitted.

JP 2003-253494 A JP-A-8-325796

  An object of the present invention is to solve the above-described problems of the prior art. More specifically, an object of the present invention is to provide a method capable of forming a multilayer coating film having a good finished appearance.

The present invention
A step of electrodepositing a cationic electrodeposition coating composition on an object to form an uncured electrodeposition coating film;
Applying the intermediate coating composition on the uncured electrodeposition coating film to form an uncured intermediate coating film, and simultaneously baking and curing the uncured electrodeposition coating film and the intermediate coating film Process,
A multilayer coating film forming method comprising:
The object to be coated is a method for forming a multilayer coating film, which is a steel material having a surface with a centerline average roughness (Ra) of a roughness curve of 0.3 to 0.9 μm. This achieves the above object.

Furthermore, the present invention provides
A step of electrodeposition coating a cationic electrodeposition coating composition on an object to form an electrodeposition coating, and heating and curing the obtained electrodeposition coating;
Applying an intermediate coating composition on the cured electrodeposition coating to form an uncured intermediate coating;
Applying an overcoating base coating composition on the uncured intermediate coating film to form an uncured top coating base film;
A step of applying an overcoat clear coating composition on an uncured topcoat base coating to form an uncured topcoat clearcoat; and an uncured intermediatecoat, topcoat basecoat and topcoat clear coat Simultaneously baking and curing,
A multilayer coating film forming method comprising:
There is also provided a method for forming a multilayer coating film, in which the article to be coated is a steel material having a surface with a centerline average roughness (Ra) of a roughness curve of 0.3 to 0.9 μm.

  These cationic electrodeposition coating compositions are preferably electrodeposition coating compositions containing a cationic epoxy resin and a blocked isocyanate curing agent.

  Furthermore, this invention also provides the coated steel material which has a multilayer coating film obtained by said multilayer coating-film formation method.

  By the method of the present invention, a multilayer coating film having a good finished appearance can be obtained regardless of the type of steel material and the presence or absence of plating treatment / chemical conversion treatment. By using this method, it is possible to form a multi-layer coating film by a coating method with little baking and curing, which meets the demand for energy saving and cost reduction.

Steel Material The coating film forming method of the present invention is characterized in that a steel material having a surface with a center line average roughness (Ra) of a roughness curve in a specific range is used. As used herein, the center line average roughness (Ra) of the roughness curve is a parameter defined in JIS B 0601. The center line average roughness (Ra) of the surface roughness curve of the steel material can be measured according to JIS B 0601 using, for example, an evaluation type surface roughness measuring machine manufactured by Mitutoyo Corporation.

  In the present invention, a steel sheet having a center line average roughness (Ra) of a roughness curve on the steel material surface of a lower limit of 0.3 μm and an upper limit of 0.9 μm is used. The upper limit of Ra on the surface of the steel material is more preferably 0.8 μm. When Ra on the surface of the steel material is less than 0.3 μm, a multilayer coating film appearance having higher smoothness can be obtained. However, the center line average roughness of the roughness curve on the steel material surface is actually 0. It is difficult to adjust a steel material having a surface of less than 3 μm with the current technology. Moreover, when an upper limit exceeds 0.9 micrometer, the smoothness of the surface of the obtained multilayer coating film will be inferior. Examples of a method for obtaining a steel material having an Ra value of 0.9 μm or less include a method of polishing the steel material surface by a known polishing method such as buffing, barrel rotation polishing, vibration barrel polishing, belt polishing, or blast polishing.

  The type of steel material to be painted is not particularly limited. Moreover, plating treatment or chemical conversion treatment may be performed on the surface of the steel material, or an untreated steel material that is not subjected to the treatment may be used. Examples of steel materials that can be used include cold-rolled steel sheets, hot-rolled steel sheets, stainless steel, electrogalvanized steel sheets, hot-dip galvanized steel sheets, zinc-aluminum alloy plated steel sheets, zinc-iron alloy plated steel sheets, zinc-magnesium alloy plated steel sheets, Zinc-aluminum-magnesium alloy plated steel sheets, aluminum-plated steel sheets, aluminum-silicon alloy-plated steel sheets, tin-based plated steel sheets, lead-tin alloy-plated steel sheets, chromium-plated steel sheets, and these steel sheets. Steel materials that have been treated are listed. As chemical conversion treatments that can be applied to steel sheets, phosphate treatment agents (such as zinc phosphate treatment agents, iron phosphate treatment agents, manganese phosphate treatment agents), phosphate alcohol treatment agents, chromic phosphate treatments Agent, sodium carbonate-based treating agent, chromate-based treating agent (chromic acid, dichromate, etc.), non-chromate-based treating agent (eg, zirconium-silane coupling agent-containing treating agent containing silane coupling agent, zirconium compound, etc.) And a chemical conversion treatment with a titanium-based treatment agent, a fluorine-based treatment agent, and the like.

  In the present invention, by using a steel material having a surface with Ra of 0.9 μm or less as the steel material to be coated, a multilayer having a good finished appearance regardless of the type of the steel material and the presence or absence of plating treatment / chemical conversion treatment It has come to find the feature that a coating film can be obtained. In this field, many methods for obtaining a multilayer coating film having a good finished appearance by changing the components and blending amounts of the electrodeposition coating composition and the like are provided. In addition to these techniques, it is possible to form a coating film having a better finished appearance by using the multilayer coating film forming method using a steel material having a specific surface shape according to the present invention.

  From the viewpoint of improving the finished appearance of the steel material, the type of the steel material is not limited as described above. However, in consideration of the durability of the coated steel material on which the coating film is formed, the hot-dip galvanized steel sheet, the electrogalvanized steel sheet, the zinc-aluminum alloy-based steel sheet, the zinc-iron alloy-based steel sheet, the zinc-magnesium alloy It is preferable to use a plated steel sheet, a zinc-aluminum-magnesium alloy plated steel sheet, stainless steel, an aluminum plated steel sheet, or the like.

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 blocked isocyanate curing agent, dispersed or dissolved in an aqueous solvent, neutralization Contains acid and organic solvent. The cationic electrodeposition coating composition may further contain a pigment.

Cationic Epoxy Resin The cationic epoxy resin used in the present invention includes an amine-modified epoxy resin. The cationic epoxy resin may be a known resin described in JP-A Nos. 54-4978 and 56-34186.

  Cationic epoxy resins typically open all of the epoxy rings of a bisphenol-type epoxy resin with an active hydrogen compound capable of introducing a cationic group, or some epoxy rings with other active hydrogen compounds. It is produced by opening the ring and opening the remaining epoxy ring with an active hydrogen compound capable of introducing a cationic group.

  A typical example of the bisphenol type epoxy resin is bisphenol A type or bisphenol F type epoxy resin. As the former commercial product, there are Epicoat 828 (manufactured by Yuka Shell Epoxy Co., Epoxy Equivalent 180-190), Epicoat 1001 (Same, Epoxy Equivalent 450-500), Epicoat 1010 (Same, Epoxy Equivalent 3000-4000), etc. Examples of the latter commercially available product include Epicoat 807 (same as above, epoxy equivalent 170).

  The following formula described in JP-A-5-306327

[Wherein R represents a residue excluding the glycidyloxy group of the diglycidyl epoxy compound, R ′ represents a residue excluding the isocyanate group of the diisocyanate compound, and n represents a positive integer. An oxazolidone ring-containing epoxy resin represented by the above formula may be used as the cationic epoxy resin. This is because a coating film having excellent heat resistance and corrosion resistance can be obtained.

  As a method for introducing an oxazolidone ring into an epoxy resin, for example, a blocked 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 a by-product lower alcohol is formed in the system. It is obtained by further distilling off.

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

  It is known that an epoxy resin containing an oxazolidone ring can be obtained by reacting a bifunctional epoxy resin with a diisocyanate blocked with a monoalcohol (ie, bisurethane). Specific examples and production methods of the oxazolidone ring-containing epoxy resin are described in, for example, paragraphs 0012 to 0047 of JP-A No. 2000-128959 and are publicly known.

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

  These epoxy resins are ring-opened with an active hydrogen compound so that an amine equivalent of 0.3 to 4.0 meq / g is obtained after ring opening, and more preferably 5 to 50% of them are occupied by primary amino groups. It is desirable to do.

  Active hydrogen compounds that can introduce a cationic group include primary amines, secondary amines, tertiary amine acid salts, sulfides and acid mixtures. In order to prepare a primary, secondary or / and tertiary amino group-containing epoxy resin, an acid salt of a primary amine, secondary amine or tertiary amine is used as an active hydrogen compound capable of introducing a cationic group.

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

Blocked isocyanate curing agent The polyisocyanate used for the preparation of the blocked isocyanate curing agent of the present invention refers to a compound having two or more isocyanate groups in one molecule. The polyisocyanate may be any of aliphatic, alicyclic, aromatic and aromatic-aliphatic, for example.

  Specific examples of polyisocyanates include aromatic diisocyanates such as tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), p-phenylene diisocyanate, and naphthalene diisocyanate; hexamethylene diisocyanate (HDI), 2,2,4- C3-C12 aliphatic diisocyanates such as trimethylhexane diisocyanate and lysine diisocyanate; 1,4-cyclohexane diisocyanate (CDI), isophorone diisocyanate (IPDI), 4,4′-dicyclohexylmethane diisocyanate (hydrogenated MDI) , Methylcyclohexane diisocyanate, isopropylidene dicyclohexyl-4,4'-diisocyanate, and 1,3-diisocyanatomethylcyclo Carbon such as xane (hydrogenated XDI), hydrogenated TDI, 2,5- or 2,6-bis (isocyanatomethyl) -bicyclo [2.2.1] heptane (also referred to as norbornane diisocyanate). Aliphatic diisocyanates having a number of 5 to 18; aliphatic diisocyanates having an aromatic ring such as xylylene diisocyanate (XDI) and tetramethylxylylene diisocyanate (TMXDI); modified products of these diisocyanates (urethanes, carbodiimides, Uretdione, uretonimine, burette and / or isocyanurate modified product); These may be used alone or in combination of two or more.

  Adducts or prepolymers obtained by reacting polyisocyanates with polyhydric alcohols such as ethylene glycol, propylene glycol, trimethylolpropane and hexanetriol at an NCO / OH ratio of 2 or more may also be used as the block isocyanate curing agent.

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

Pigment The cationic electrodeposition coating composition used in the method of the present invention may contain a commonly used pigment. Examples of pigments that can be used include commonly used inorganic pigments, for example colored pigments such as titanium white, carbon black and bengara; extender pigments such as kaolin, talc, aluminum silicate, calcium carbonate, mica and clay; Zinc phosphate, iron phosphate, aluminum phosphate, calcium phosphate, zinc phosphite, zinc cyanide, zinc oxide, aluminum tripolyphosphate, zinc molybdate, aluminum molybdate, calcium molybdate and aluminum phosphomolybdate, phosphomolybdic acid Examples include rust preventive pigments such as aluminum zinc.

  When a pigment is used as a component of an electrodeposition paint, generally, the pigment is dispersed in advance 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 in a single step in a low concentration uniform state used in the electrodeposition coating composition. Such a paste is generally called a pigment dispersion paste.

  The pigment dispersion paste is prepared by dispersing a pigment in an aqueous solvent together with a pigment dispersion resin varnish. 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 sulfonium group is generally used. 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 the pigment dispersion resin varnish and the pigment are mixed, the pigment is dispersed using a normal dispersing device such as a ball mill or a sand grind mill until the particle size of the pigment in the mixture reaches a predetermined uniform particle size. A dispersion paste can be obtained.

  In addition to the above components, the cationic electrodeposition coating composition contains an organotin compound such as dibutyltin laurate, dibutyltin oxide, dioctyltin oxide when it contains a dissociation catalyst for dissociating the blocking agent of the blocked isocyanate curing agent. Alternatively, amines such as N-methylmorpholine, metal acetates such as lead acetate, strontium, cobalt, and copper can be used. The concentration of the dissociation catalyst is 0.1 to 6 parts by mass with respect to 100 parts by mass of the total of the cationic epoxy resin and the blocked isocyanate curing agent in the cationic electrodeposition coating composition.

Preparation of Cationic Electrodeposition Coating Composition The cationic electrodeposition coating composition used in the present invention is prepared by dispersing the above-described catalyst, cationic epoxy resin, blocked isocyanate curing agent, and pigment dispersion paste in an aqueous solvent. Prepared. Further, the aqueous solvent usually contains a neutralizing acid in order to neutralize the cationic epoxy resin and improve the dispersibility of the binder resin emulsion. The neutralizing acid is an inorganic or organic acid such as hydrochloric acid, nitric acid, phosphoric acid, formic acid, acetic acid, lactic acid.

  The amount of neutralizing acid used is preferably in the range of a lower limit of 10 mg equivalent and an upper limit of 25 mg equivalent with respect to 100 g of binder resin solid content containing a cationic epoxy resin and a blocked isocyanate curing agent. 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. , The precipitation of the solid content of the paint is lowered and the throwing power is inferior.

  The cationic electrodeposition coating composition can be prepared by dispersing a cationic epoxy resin and a blocked isocyanate curing agent in an aqueous solvent. The amount of the blocked isocyanate curing agent is sufficient to react with active hydrogen-containing functional groups such as primary, secondary amino groups, hydroxyl groups, etc. in the cationic epoxy resin during curing to give a good cured coating film. Needed. The amount of the blocked isocyanate curing agent is preferably 90/10 to 50/50, more preferably 80/20, expressed as a weight ratio of the cationic epoxy resin to the blocked isocyanate curing agent (cationic epoxy resin / curing agent). It is in the range of ~ 65/35. By adjusting the solid content ratio between the cationic epoxy resin and the blocked 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.

  The organic solvent is necessary as a solvent when synthesizing resin components such as a cationic epoxy resin, a blocked isocyanate curing agent, and a pigment dispersion resin, and complicated operations are required for complete removal. Moreover, when the organic solvent is contained in binder resin, the fluidity | liquidity of the coating film at the time of film forming will be improved, and the smoothness of a coating film will improve.

  Examples of the organic solvent usually contained in the cationic electrodeposition coating composition include ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol monoethyl hexyl ether, propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, and propylene glycol monophenyl ether. Can be mentioned.

  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. An amino group-containing acrylic resin, an amino group-containing polyester resin, and the like may be included.

Electrodeposition coating formation

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

  The electrodeposition coating process is composed of a process of immersing an object to be coated in a cationic electrodeposition paint composition, and a process of applying a voltage between the object to be coated as a cathode and an anode to deposit a film. . Moreover, although the time which applies a voltage changes with electrodeposition conditions, generally it can be made into 2 to 4 minutes.

  The film thickness of the electrodeposition coating film is preferably 5 to 25 μm, more preferably 20 μm. When the film thickness is less than 5 μm, the rust prevention property is insufficient, and when it exceeds 25 μm, the paint is wasted.

  The electrodeposition coating film obtained as described above is cured or electrodeposited by baking at 120 to 260 ° C., preferably 140 to 220 ° C. for 10 to 30 minutes after completion of the electrodeposition process or after washing with water. A coating film is formed.

Multi-layer coating film forming method On the cured electrodeposition coating film obtained in this way, an intermediate coating composition, a solid color coating, a metallic coating or other top coating composition, a top coating clear coating composition, etc. Paint. Any coating composition generally known to those skilled in the art can be used as these coating compositions. These coating compositions can be applied by known coating methods such as electrostatic coating, spray coating, and roll coater coating. Coatings obtained with these coating compositions are 1 coat 1 bake (1C1B), 2 coat 1 bake (2C1B), 2 coat 2 bake (2C2B), 3 coat and 1 bake (3C1B, 3 wet paint) It can also be baked and cured by 3-coat 2-bake coating (3C2B) or the like.

Forming method of multi-layer coating film by three-coat / one-bake coating One of the coating methods to obtain multi-layer coating film, the coating-film forming method by three-coating / one-bake coating (3C1B) is useful in terms of energy saving. Specifically, the method includes the following steps: a step of electrodeposition-coating a cationic electrodeposition coating composition on an object to form an electrodeposition coating film, and heating and curing the obtained electrodeposition coating film; Applying the intermediate coating composition on the electrodeposition coating film to form an uncured intermediate coating film; applying the top coating base coating composition on the uncured intermediate coating film; Forming an uncured topcoat base film; applying a topcoat clear coating composition on the uncured topcoat base film to form an uncured topcoat clear film; and Coating film, top coating base coating and top coating Step of simultaneously baking and curing a clear coating. In this coating method, a multilayer coating film having a good finished appearance is obtained by using a steel material having a surface with a centerline average roughness (Ra) of a roughness curve of 0.3 to 0.9 μm as an object to be coated. Can be obtained.

  In the method for forming a multilayer coating film by such three-coat / one-bake coating (3C1B), the above-described cationic electrodeposition coating composition can be used as the cationic electrodeposition coating composition. As the intermediate coating composition, an intermediate coating resin component, a pigment, and an aqueous solvent and / or an organic solvent containing solvent can be used. The intermediate coating resin component is composed of an intermediate coating resin and, optionally, an intermediate coating curing agent. As the aqueous solvent and organic solvent, those exemplified in the above cationic electrodeposition coating composition can be used in the same manner.

  Examples of the intermediate coating resin include acrylic resin, polyester resin, polyurethane resin, alkyd resin, fluororesin, epoxy resin, and polyether resin. Of these resins, acrylic resins, polyester resins, and polyurethane resins are preferably used. These resins may be used alone or in combination of two or more.

  In general, the intermediate coating resin includes a curable type and a lacquer type, but a curable type is preferably used. When a curable type is used, an intermediate coating curing agent such as a melamine resin, a blocked isocyanate compound, an oxazoline compound, and a carbodiimide compound is used in combination with the intermediate coating resin. The intermediate coating paint curing agent can be included in the intermediate coating resin component to cause the curing reaction to proceed later under heating or at room temperature. Further, a curable type intermediate coating resin and a non-curable type resin can be used in combination.

  When an intermediate coating curing agent is included, the preferred weight ratio of the intermediate coating resin and the intermediate coating curing agent in the coating solid content is 90/10 to 50/50, more preferably 85/15 to 60/40. It is. If the amount of the intermediate coating material curing agent is so small that the weight ratio between the intermediate coating material resin and the intermediate coating material curing agent deviates from 90/10, sufficient crosslinking in the coating film may not be obtained. On the other hand, when the amount of the intermediate coating paint curing agent is so large that this ratio deviates from 50/50, the storage stability of the coating composition composition is lowered and the curing rate is increased, which may deteriorate the appearance of the coating film. There is.

  Examples of pigments contained in the intermediate coating composition include barita powder, precipitated barium sulfate, barium carbonate, gypsum, clay, silica, talc, magnesium carbonate, alumina white and other extender pigments, and colored pigments. Examples of coloring pigments include organic pigments such as azo lake pigments, phthalocyanine pigments, indico pigments, berylene pigments, quinophthalone pigments, dioxazine pigments, quinacridone pigments, isoindolinone pigments, metal complex pigments, and carbon black. Or inorganic pigments such as yellow lead, yellow iron oxide, bengara, and titanium dioxide. The amount of the pigment can be arbitrarily set according to the desired performance and hue. These pigments may be used alone or in combination of two or more.

  The pigment concentration (PWC) with respect to the solid content of the intermediate coating composition is preferably in the range of a lower limit of 10% by weight and an upper limit of 50% by weight. The upper limit is more preferably 30% by weight. The solid content concentration of the intermediate coating composition is preferably in the range of 35% by weight lower limit and 65% by weight upper limit.

  In addition to the above components, the intermediate coating composition comprises a polyamide wax which is a lubricating dispersion of an aliphatic amide, a polyethylene wax which is a colloidal dispersion mainly composed of oxidized polyethylene, a curing catalyst, an ultraviolet absorber, and an antioxidant. , Leveling agents, surface conditioners such as silicon and organic polymers, sagging inhibitors, thickeners, antifoaming agents, lubricants, crosslinkable polymer particles (microgels) and the like can be appropriately added. By blending these additives at a ratio of 15 parts by mass or less with respect to 100 parts by mass (solid content basis) of the intermediate coating resin component, the performance of the coating composition and the coating film can be improved.

  Such an intermediate coating composition can be prepared, for example, by a known method described in JP-A-2002-224613.

  As the topcoat base paint composition, a glitter paint composition or a solid paint composition containing a topcoat base resin component, a glitter pigment and / or a color pigment, an extender pigment and a solvent can be used. This topcoat base coating composition is of an aqueous or organic solvent type including an aqueous dispersion or an organic solvent dispersion.

  The topcoat base resin component contained in these topcoat base paint compositions is composed of a topcoat base paint resin and, if necessary, a topcoat base paint curing agent. The top coat base resin component (top coat base paint resin, top coat base paint curing agent), coloring pigment, extender pigment, various additives and solvent contained in the top coat base paint composition are those described in relation to the intermediate coat composition. Any of those described for the cationic electrodeposition coating composition can be used. Using the topcoat base resin component, a glittering pigment and optionally a colored pigment are dispersed in the glittering topcoat base coating composition, and a colored pigment is dispersed in the solid topcoat base coating composition.

  As the top coat base resin, at least one film-forming resin selected from acrylic resins, polyester resins, fluororesins, epoxy resins, polyurethane resins, polyether resins and modified resins thereof can be used. As the topcoat base paint curing agent, the above intermediate coating paint curing agent and etherified melamine resin can be used. The etherified melamine resin is obtained by etherifying melamine with an alcohol such as methanol or butanol. A preferred combination of the topcoat base paint resin and the topcoat base paint curing agent, which are the topcoat base resin components, includes an acrylic resin / melamine resin system. 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. Such a topcoat base coating composition can be prepared, for example, by a known method described in JP-A-2002-224613.

  The topcoat clear coating composition is formed from a clear coating composition containing a topcoat clear resin component, various additives and a solvent. The topcoat clear coating composition is an aqueous or organic solvent-based composition including an aqueous dispersion and an organic solvent dispersion.

  The topcoat clear resin component contained in these topcoat clear paint compositions comprises a topcoat clear paint resin and, if necessary, a topcoat clear paint curing agent. As the topcoat clear resin component (topcoat clear paint resin, topcoat clear paint curing agent), various additives, and organic solvents contained in the top coat clear paint composition, any of those described for the intermediate coat composition can be used. .

  A preferred combination of the topcoat clear coating resin, which is the topcoat clear resin component, and the topcoat clear paint curing agent is an acrylic resin / melamine resin system. 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. Such a topcoat clear coating composition can be prepared by a known method described in, for example, JP-A-2002-224613.

  In the method of forming a multi-layer coating film by three-coating / one-bake coating (3C1B), the method of electrodeposition coating a cationic electrodeposition coating composition and the method of heat-curing the obtained electrodeposition coating film are the above-mentioned electrodeposition coating methods Can be used. Examples of a method for forming an uncured intermediate coating film on the obtained cured electrodeposition coating film include a method of applying an intermediate coating composition using a spray method, a roll coater method, or the like. Specifically, as a painting method, an air electrostatic spray called “react gun” or a rotary atomization type called “micro / micro (μμ) bell”, “micro (μ) bell”, “metabell”, etc. It is preferable to apply using an electrostatic coating machine. Among these, it is particularly preferable to perform the coating using a rotary atomizing electrostatic coating machine.

  A preferable dry film thickness of the intermediate coating film is 5 to 80 μm, and more preferably 10 to 50 μm. In this three-coat / one-bake 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 top coat base coating film is formed, preheating may be performed at a temperature lower than the temperature used in the heat curing (baking) treatment.

  The topcoat base coating film is obtained by coating the topcoat base coating composition on the intermediate coating film. In three-coat / one-bake coating, the topcoat base coating composition is applied onto an uncured intermediate coating film by a wet-on-wet method. Although the coating method of top coat base coating composition is not specifically limited, The method illustrated as a coating method of the said intermediate coating composition can be mentioned. 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 enhanced by performing multi-stage coating by air electrostatic spraying, preferably two-stage coating. Or you may paint by the coating method which combined the air electrostatic spray and said rotary atomization type electrostatic coating machine.

  By forming this topcoat base coating film, design properties are imparted, and adhesion with the intermediate coating film formed in the previous process and adhesion with the topcoat clear coating film to be applied in the next process are ensured. Is done. The dry film thickness of the topcoat base coating film is preferably 5 to 50 μm, more preferably 10 to 30 μm per coat. After the formation of the topcoat base coating film, the process proceeds to the formation process of the topcoat clear coating film in the next step without being cured by heating. Before forming the top clear film, preheating may be performed at a temperature lower than the temperature used in the heat curing (baking) treatment.

  The top clear film is obtained by applying the top clear coating composition on the top base film. This topcoat clear coating composition is applied onto the uncured topcoat base coating film in a wet-on-wet manner.

  The method for forming the above-mentioned clear clear coating 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 clear clear coating film is preferably 20 to 50 μm per coat, and more preferably 25 to 40 μm. By forming an overcoat clear coating film, the topcoat base coating film is protected, and a sense of depth can be imparted to the resulting multilayer coating film.

  In the three-coat / one-bake coating which is one embodiment of the present invention, after forming a top clear film, three layers of an uncured intermediate coat, top coat base coat, and top clear film are formed. A multilayer coating film can be obtained by baking and curing at ˜160 ° C. for a predetermined time. In the method of the present invention, the intermediate coating composition, the topcoat base coating composition, and the topcoat clear coating composition are each applied wet-on-wet in this order. 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 by leaving or heating at room temperature to 100 ° C., which is lower than the temperature used in the heat curing (baking) treatment, for 1 to 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.

Method of forming a multilayer coating film by two-wet coating Another method of obtaining a multilayer coating film, which is useful in terms of energy saving, is to cure the electrodeposition coating film obtained as described above In this method, the intermediate coating composition is applied onto an uncured electrodeposition coating film and then heated to cross-link and cure both coating films together. Specifically, this two-wet coating includes the following steps: a step of electrodepositing a cationic electrodeposition coating composition on an object to form an uncured electrodeposition coating film; A step of applying an intermediate coating composition thereon to form an uncured intermediate coating film; and a step of baking and curing the uncured electrodeposition coating film and the intermediate coating film simultaneously. In this coating method, a multilayer coating film having a good finished appearance is obtained by using a steel material having a surface with a centerline average roughness (Ra) of a roughness curve of 0.3 to 0.9 μm as an object to be coated. Can be obtained.

  In such a method of forming a multilayer coating film by two-wet coating, the above-described cationic electrodeposition coating composition can be used as the cationic electrodeposition coating composition. As the intermediate coating composition, the above-described intermediate coating composition containing an intermediate coating resin component, a pigment, and an aqueous solvent and / or an organic solvent can be used. An intermediate coating composition suitable for use in this two-wet coating can be produced by a known method, for example, from JP-A No. 2003-266013.

  In the method of forming a multilayer coating film by two-wet coating, the above-mentioned electrodeposition coating method can be used as a method for electrodeposition coating a cationic electrodeposition coating composition. In the two-wet coating, the uncured electrodeposition coating film thus obtained is applied with an intermediate coating without performing a heat curing step. However, it is preferable to perform preheating before coating with the intermediate coating. The water in the uncured coating film is removed by preheating, and at the same time, the pores on the surface of the uncured coating film that occur during electrodeposition are closed, so that the finished appearance of the resulting multilayer coating film is good. Is preferable. This preheating is preferably performed for 1 to 10 minutes under conditions of a lower limit room temperature and an upper limit of 100 ° C.

  As a method for applying the intermediate coating composition to the uncured electrodeposition coating film, the above-mentioned method for applying the intermediate coating composition can be used. The uncured electrodeposition coating film and intermediate coating film thus obtained are heated at a temperature of 100 to 250 ° C., more preferably at a temperature of 130 to 180 ° C., for 5 to 60 minutes, more preferably 10 to 40 minutes. Thus, these coating films can be baked and cured simultaneously. On the cured multilayer coating film thus obtained, a top coat base coating composition, a top coat clear coating composition, and the like can be applied as necessary.

  The following examples further illustrate the present invention, but the present invention is not limited thereto. Unless otherwise specified, “parts” represents parts by weight.

Production Example 1 Preparation of cationic electrodeposition coating composition
Production Example 1-1 Production of amine-modified epoxy resin 2,4- / 2,6-tolylene diisocyanate (weight ratio = 8/2) was placed in a flask equipped with a stirrer, cooling tube, nitrogen introduction tube, thermometer and dropping funnel. ) 92 parts, methyl isobutyl ketone (hereinafter abbreviated as MIBK) 95 parts and dibutyltin dilaurate 0.5 part were charged. While stirring the reaction mixture, 21 parts of methanol was added dropwise. The reaction was started from room temperature and heated to 60 ° C. due to heat generation. Then, after continuing reaction for 30 minutes, 50 parts of ethylene glycol mono-2-ethylhexyl ether was dripped 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 to 65 ° C. and continued until absorption based on the isocyanate group disappeared in the measurement of IR spectrum.

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

  Subsequently, 61 parts of bisphenol A and 33 parts of octylic acid were added and reacted at 120 ° C., resulting in an epoxy equivalent of 1190. Thereafter, the reaction mixture was cooled, 11 parts of diethanolamine, 24 parts of N-ethylethanolamine and 25 parts of 79 wt% MIBK solution of ketimine product of aminoethylethanolamine were added and reacted at 110 ° C. for 2 hours. Then, it diluted with MIBK until it became 80% of non volatile matters, and obtained the amine modified epoxy resin (resin solid content 80%) whose glass transition temperature is 2 degreeC.

Production Example 1-2 Production of Blocked Isocyanate Curing Agent 1250 parts of diphenylmethane diisocyanate and 266.4 parts of MIBK were charged into a reaction vessel, which was heated to 80 ° C., and then 2.5 parts of dibutyltin dilaurate was added. A solution prepared by dissolving 226 parts of ε-caprolactam in 944 parts of butyl cellosolve was added dropwise at 80 ° C. over 2 hours. Further, after heating at 100 ° C. for 4 hours, in the IR spectrum measurement, it was confirmed that the absorption based on the isocyanate group had disappeared, and after standing to cool, MIBK 336.1 parts were added to block isocyanate curing with a glass transition temperature of 0 ° C. An agent was obtained.

Production Example 1-3 Production of Pigment Dispersing Resin First, 222.0 parts of isophorone diisocyanate (hereinafter abbreviated as IPDI) was placed in a reaction vessel equipped with a stirrer, a cooling tube, a nitrogen introduction tube, and a thermometer, and MIBK 39.1. Then, 0.2 part of hedibutyltin dilaurate was added. Then, after heating this to 50 degreeC, 131.5 parts of 2-ethylhexanol was dripped over 2 hours in dry nitrogen atmosphere, stirring. The reaction temperature was maintained at 50 ° C. by cooling appropriately. As a result, 2-ethylhexanol half-blocked IPDI (resin solid content: 90.0%) was obtained.

  Next, 87.2 parts of dimethylethanolamine, 117.6 parts of 75% aqueous lactic acid solution, and 39.2 parts of ethylene glycol monobutyl ether are added to a suitable reaction vessel in this order, and the mixture is stirred at 65 ° C. for about half an hour to form quaternization. An agent was prepared.

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

  The reaction mixture is kept at 110-120 ° C. for about 1 hour, then 463.4 parts of ethylene glycol monobutyl ether are added, the mixture is cooled to 85-95 ° C. and homogenized, and then the quaternizing agent 196 prepared above is used. 7 parts were added. After maintaining the reaction mixture at 85 to 95 ° C. until the acid value becomes 1, 964 parts of deionized water is added to finish quaternization in the epoxy-bisphenol A resin, and a pigment dispersion having a quaternary ammonium salt portion A resin was obtained (resin Tg = 5 ° C., resin solid content 50%).

Production Example 1-4 Production of Pigment Dispersion Paste 120 parts of pigment dispersing resin obtained in Production Example 1-4 in a sand grind mill, 2.0 parts of carbon black, 100.0 parts of kaolin, 80.0 parts of titanium dioxide, 18.0 parts of aluminum phosphomolybdate and 221.7 parts of ion-exchanged water were added and dispersed until the particle size became 10 μm or less to obtain a pigment dispersion paste (solid content 48%).

Production Example 1-5 Preparation of Cationic Electrodeposition Coating Composition Amine-modified epoxy resin obtained in Production Example 1-1 and the blocked isocyanate curing agent obtained in Production Example 1-2 at a solid content ratio of 80/20 Mixed to be uniform. Glacial acetic acid was added so that the milligram equivalent (MEQ (A)) of the acid per 100 g of resin solids was 30, and ion-exchanged water was slowly added to dilute. By removing MIBK under reduced pressure, an emulsion having a solid content of 36% was obtained.

  1500 parts of this emulsion and 540 parts of the pigment dispersion paste obtained in Production Example 1-4, 1920 parts of ion-exchanged water, 40 parts of 10% aqueous cerium acetate solution and 10 parts of dibutyltin oxide were mixed to obtain a solid content of 20 weight. % Cationic electrodeposition coating composition was obtained.

Production Example 2 Preparation of aqueous intermediate coating composition for two-wet coating
Production Example 2-1 Preparation of Acrylic Resin Solution 40.0 parts of dipropylene glycol methyl ether was added to a reaction vessel, and the temperature was raised to 130 ° C. while mixing and stirring in a nitrogen stream. Next, 100 parts of a monomer mixture (methacrylic acid, ethyl acrylate, 2-hydroxyethyl acrylate, methyl methacrylate, styrene, α-methylstyrene dimer (MSD-100, manufactured by Mitsui Chemicals)) and dipropylene glycol methyl ether 10 An initiator solution consisting of 0.0 part and 13 parts of tertiary butyl peroxy 2-ethylhexanoate was added dropwise to the reaction vessel in parallel over 3 hours. After completion of the dropping, aging was performed at the same temperature for 0.5 hours. Further, an initiator solution consisting of 5.0 parts of dipropylene glycol methyl ether and 0.3 part of tertiary butyl peroxy-2-ethylhexanoate was added dropwise to the reaction vessel over 0.5 hours. After completion of the dropping, aging was performed at the same temperature for 2 hours.

  After removing 11.11 parts of the solvent at 130 ° C. under reduced pressure (70 torr) using a solvent removal apparatus, 194.24 parts of deionized water and 8.82 parts of dimethylaminoethanol were added to obtain an acrylic resin solution. The resulting acrylic resin solution had a non-volatile content of 30.0%, a viscosity of 1000 centipoise (measured by one revolution of an E-type viscometer), a number average molecular weight = 3000, a weight average molecular weight = 9000, a solid content acid value = 56, The solid content hydroxyl value was 70, and the neutralization rate was 100%.

Production Example 2-2 Preparation of aqueous polyester resin solution for aqueous resin 176 parts of phthalic anhydride, 197 parts of isophthalic acid, 87 parts of adipic acid in a reaction vessel equipped with a nitrogen introduction tube, a stirrer, a temperature controller, a cooling tube and a decanter, 102 parts of trimethylolpropane, 272 parts of neopentyl glycol, 0.8 part of dibutyltin oxide and 17 parts of xylene were charged, and the temperature was raised to 200 ° C. over 2 hours after the reflux of xylene started. Meanwhile, water produced by the reaction was removed by azeotropy with xylene. When the acid value of the carboxylic acid reached 8, cool to 150 ° C., add 49 parts of trimellitic anhydride, cool to 60 ° C., add 46 parts of dimethylethanolamine and mix. 1137 parts of ion-exchanged water was added to obtain an aqueous polyester resin solution having a number average molecular weight of 2000, a solid content of 40%, a solid content acid value of 40, and a hydroxyl value of 100 by gel permeation chromatography measurement.

Production Example 2-3 Preparation of water-based intermediate coating composition for two wets 44.0 parts of the acrylic resin solution obtained in Production Example 2-1 and CR-97 (trade name, titanium dioxide manufactured by Ishihara Sangyo Co., Ltd.) 24. 5 parts, 12 parts of B-34 (trade name, precipitated barium sulfate manufactured by Sakai Chemical Co., Ltd.), 0.5 part of MA-100 (trade name, carbon black manufactured by Mitsubishi Chemical Corporation) and LMR-100 (trade name, Fuji Talc) A glass bead medium was added to 0.3 part of talc (manufactured by Kogyo Co., Ltd.), and the mixture was dispersed at room temperature for 1 hour to obtain a pigment dispersion composition having a particle size of 10 μm or less. Based on 84.0 parts of this pigment dispersion composition, 72.0 parts of aqueous polyester resin solution obtained in Production Example 2-2, Marquat 723 (trade name, melamine resin manufactured by Mitsui Cytec Co., Ltd., 100% by mass) ) 18 parts and 0.5 part of Surfinol 104E (trade name, Air Products Japan surface conditioner) were mixed and stirred and mixed with a disper for 10 minutes to obtain an aqueous intermediate coating composition. Water-based intermediate coating composition for two-wet coating was applied to Ford Cup No. 4 and diluted to 20 seconds at 20 ° C.

Production Example 3 Preparation of aqueous intermediate coating composition for 3C1B
Production Example 3-1 Preparation of Colored Pigment Paste Commercial Dispersant “Disperbyk 190” (by Big Chemie) 9.4 parts, ion-exchanged water 36.8 parts, rutile titanium dioxide 34.5 parts, barium sulfate 34.4 parts After 6 parts of talc were premixed, glass bead medium was added in a paint conditioner and mixed and dispersed at room temperature until the particle size became 5 μm or less to obtain a colored pigment paste.

Production Example 3-2 Production of Acrylic Emulsion Resin 35.75 parts of deionized water was added to a reaction vessel, and the temperature was raised to 80 ° C. while mixing and stirring in a nitrogen stream. Then, as an α, β-ethylenically unsaturated monomer mixture, styrene 10 parts, methyl methacrylate 24.02 parts, butyl acrylate 28.94 parts, ethyl acrylate 20.11 parts, acrylate 4-hydroxybutyl 15.40 Parts, methacrylic acid 1.53 parts, Aqualon HS-10 (polyoxyethylene alkylpropenyl phenyl ether sulfate ester, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), Adekaria soap NE-20 (Asahi Denka Co., Ltd.) 0. A monomer emulsion consisting of 5 parts and 50 parts deionized water and an initiator solution consisting of 0.30 parts ammonium persulfate and 15.0 parts deionized water were added dropwise to the reaction vessel in parallel over 2 hours. After completion of the dropping, aging was performed at the same temperature for 2 hours. Subsequently, it cooled to 40 degreeC and filtered with a 400 mesh filter, and obtained the acrylic emulsion resin of particle size 200nm, non-volatile content 50%, acid value 10, hydroxyl value 60, and weight average molecular weight 200000.

Production Example 3-3 Preparation of 3C1B aqueous intermediate coating composition 30 parts of the color pigment paste obtained in Production Example 3-1, 42 parts of the acrylic emulsion resin obtained in Production Example 3-2, Cymel 327 ( 28 parts of Mitsui Cytec Co., Ltd. (imino melamine resin) and 2.33 parts of Adecanol UH-814N (Asahi Denka Co., Ltd. thickener) were added to obtain an aqueous intermediate coating composition.

Example 1
Measurement of the center line average roughness (Ra) of the roughness curve of the steel material The surface of a hot-dip galvanized steel sheet (JIS G3302 standard product, 150 × 70 × 0.8 mm) used as a steel material is wiped with a cloth soaked with toluene, Degreased. With respect to this hot dip galvanized steel sheet, the Ra value of the surface to be coated was 0.63 μm when measured in advance by the following measuring method. The obtained results are shown in Table 2.

Measuring method of Ra value The Ra value of the steel before coating was measured using an evaluation type surface roughness measuring machine (manufactured by Mitutoyo, SURFTEST SJ-201P) in accordance with JIS-B0601. Measurement was performed 7 times using a sample with a 2.5 mm width cut-off (number of sections: 5), and an Ra value was obtained by an average of vertical erasure. In addition, these Ra values show that there are few unevenness | corrugations on the surface, and a coating-film external appearance is so favorable that a value is small.

Evaluation 1
Formation of multi-layer coating film by two-wet coating and evaluation of surface condition of multi-layer coating film obtained by two-wet coating Hot-dip galvanized steel sheet (JIS G3302 standard product, 150 x 70 x 0.8 mm) The cationic electrodeposition paint prepared in Example 1 was electrodeposited to a dry film thickness of 15 μm, washed with water, and preheated at 80 ° C. for 10 minutes. On this uncured electrodeposition coating surface, the water-based intermediate coating prepared in Production Example 2 was applied by air spraying to a dry film thickness of 30 μm, and the two-layer coating was heated at 150 ° C. for 30 minutes. And cured at the same time.

  By measuring the LW (measurement wavelength: 1300 to 12000 μm) and SW (measurement wavelength: 300 to 1200 μm), using Wave Scan (manufactured by BYK-Gardner) with respect to the finished appearance of the obtained multilayer coating film. Evaluation was performed. The obtained results are shown in Table 2. These numerical values indicate that the smaller the numerical value, the better the appearance.

Evaluation 2
Formation of multi-layer coating film by three-coat one-bake (3C1B) coating, and evaluation of the surface state of the multi-layer coating film obtained by hot-dip galvanized steel sheet (JIS G3302 standard product, 150 × 70 × 0.8 mm) The cationic electrodeposition coating material prepared according to Production Example 1 was electrodeposited to a dry film thickness of 15 μm, washed with water, and baked at 160 ° C. for 10 minutes. Next, the water-based intermediate coating prepared in Production Example 3 was applied by air spray coating to a dry film thickness of 20 μm, preheated at 80 ° C. for 5 minutes, and then water-based base coating (“AQUAREX AR- 2000 Base ”(manufactured by Nippon Paint Co., Ltd., acrylic resin / polyester resin / melamine resin-based paint) was applied by air spray coating to a dry film thickness of 13 μm, and preheated at 80 ° C. for 3 minutes. Further, a clear coating ("Mac Flow O-1800W-2 Clear" manufactured by Nippon Paint Co., Ltd., acrylic resin / polyester resin coating having a carboxylic acid epoxy group curing system) is applied to the coating plate by air spray coating to a dry film thickness of 40 μm. The three-layer coating film was heated at 140 ° C. for 30 minutes and cured at the same time. The aqueous intermediate coating, aqueous base coating, and clear coating were diluted and applied under the following conditions.
(Water-based intermediate coating) thinner: ion-exchanged water 40 seconds / NO. 4 Ford Cup / 20 ° C
(Water-based paint) Thinner: ion-exchanged water 45 seconds / NO. 4 Ford Cup / 20 ° C
(Clear paint) thinner: EEP (Ethoxyethyl propionate) / S-150 (Aromatic hydrocarbon solvent manufactured by Exxon) = 1/130 sec / NO. 4 Ford Cup / 20 ° C

  By measuring the LW (measurement wavelength: 1300 to 12000 μm) and SW (measurement wavelength: 300 to 1200 μm), using Wave Scan (manufactured by BYK-Gardner) with respect to the finished appearance of the obtained multilayer coating film. Evaluation was performed. The obtained results are shown in Table 2. These numerical values indicate that the smaller the numerical value, the better the appearance.

Example 2
A zinc phosphate treating agent having the following composition was prepared.

  The surface of a hot dip galvanized steel sheet (JIS G3302 standard product, 150 × 70 × 0.8 mm) was degreased by wiping with an alkaline cleaner (Surf Cleaner SD250; manufactured by Nippon Paint Co., Ltd.), then washed with water and dried. This steel plate was immersed in the zinc phosphate treating agent obtained above at 50 to 54 ° C. for 90 seconds to perform chemical conversion treatment. Subsequently, it was washed with water at room temperature for 15 seconds. The obtained steel plate was dried with hot air at 100 ° C. for 10 minutes to obtain a steel material.

  With respect to the obtained steel material, the Ra value of the surface to be coated was measured in the same manner as in Example 1. As a result, it was 0.76 μm. Then, evaluations 1 and 2 were performed in the same manner as in Example 1. The obtained results are shown in Table 2.

Example 3
2.5 g of Silaace S-330 (γ-aminopropyltriethoxysilane; manufactured by Chisso Corporation) was added to 1 liter of pure water and stirred at room temperature for 5 minutes, and then SNOWTEX N (water-dispersible silica; manufactured by Nissan Chemical Industries, Ltd.). ) Was added and stirred for 5 minutes. Further, zircozol AC-7 (zirconyl ammonium carbonate; manufactured by Daiichi Rare Element Co., Ltd.) was added to 2.5 g of zirconium ions, and 5.0 g of thiourea and phosphorus were added. Ammonium acid was added as phosphate ion so as to be 1.25 g and stirred for 5 minutes to obtain a zirconium-silane coupling agent-containing treatment agent.

The surface of a hot dip galvanized steel sheet (JIS G3302 standard product, 150 × 70 × 0.8 mm) was wiped with an alkaline cleaner (Surf Cleaner 155; manufactured by Nippon Paint Co., Ltd.), degreased and dried. This steel plate was coated with a bar coater # 3 to a coating weight of 55 mg / m ² and dried at a reaching plate temperature of 60 ° C. to obtain a steel material.

  With respect to the obtained steel material, the Ra value of the surface to be coated was measured in the same manner as in Example 1. As a result, it was 0.88 μm. Then, evaluations 1 and 2 were performed in the same manner as in Example 1. The obtained results are shown in Table 2.

Example 4
It carried out similarly to Example 1 except having used the cooling steel plate (JIS G3141 standard goods, 150x70x0.8 mm) as steel materials. In addition, about the steel material, when the Ra value of the surface to paint was measured similarly to Example 1, it was 0.72 micrometer. The obtained results are shown in Table 2.

Example 5
It carried out similarly to Example 2 except having used the cooling steel plate (JIS G3141 standard goods, 150x70x0.8 mm) as steel materials. In addition, about the steel material, when the Ra value of the surface to paint was measured similarly to Example 1, it was 0.79 micrometer. The obtained results are shown in Table 2.

Example 6
It carried out similarly to Example 3 except having used the cooling steel plate (JIS G3141 standard goods, 150x70x0.8 mm) as steel materials. In addition, about the steel material, when the Ra value of the surface to paint was measured similarly to Example 1, it was 0.84 micrometer. The obtained results are shown in Table 2.

Comparative Example 1
The same operation as in Example 1 was performed except that a steel material having an Ra value of 1.01 μm on the surface to be coated was used. The obtained results are shown in Table 3.

Comparative Example 2
The same operation as in Example 2 was performed except that a steel material having a Ra value of 0.95 μm on the surface to be coated was used. The obtained results are shown in Table 3.

Comparative Example 3
The same operation as in Example 3 was performed except that a steel material having an Ra value of 1.04 μm on the surface to be coated was used. The obtained results are shown in Table 3.

Comparative Example 4
It carried out similarly to Example 4 except having used the steel materials whose Ra value of the surface to paint is 1.00 micrometer. The obtained results are shown in Table 3.

Comparative Example 5
It carried out similarly to Example 5 except having used the steel material whose Ra value of the surface to paint is 1.09 micrometer. The obtained results are shown in Table 3.

Comparative Example 6
It carried out similarly to Example 6 except having used the steel materials whose Ra value of the surface to be coated is 1.00 μm. The obtained results are shown in Table 3.

In Table 2 and Table 3,
Types of steel materials SGC: Hot-dip galvanized steel sheet SPC: About cold-rolled steel sheet treatment agent None: No chemical conversion treatment Zinc phosphate chemical conversion treatment: Chemical conversion treatment with zinc phosphate treatment agent Zr-APS treatment: Zirconium-silane coupling agent contained Chemical conversion treatment with a treatment agent is shown.

  About the evaluation 1 (evaluation of the surface state of the multilayer coating film obtained by two-wet coating) shown by Table 2 and Table 3, it shows as a graph in FIG. In the graph of FIG. 1, the x axis is the numerical axis of Ra (μm) on the steel material surface, and the y axis is the numerical axis of Lw and Sw of the multilayer coating film. As is apparent from the graph, it can be seen that when the Ra value on the surface of the steel material before coating exceeds 0.9 μm, the surface state of the obtained multilayer coating film has deteriorated rapidly.

  The evaluation 2 shown in Table 2 and Table 3 (evaluation of the surface state of the multilayer coating film obtained by three-coating one-bake (3C1B) coating) is shown as a graph in FIG. In the graph of FIG. 2, the x axis is the numerical axis of Ra (μm) on the steel surface, and the y axis is the numerical axis of Lw and Sw of the multilayer coating film. As is apparent from the graph, it can be seen that when the Ra value on the surface of the steel material before coating exceeds 0.9 μm, the surface state of the obtained multilayer coating film has deteriorated rapidly.

  By the method of the present invention, a multilayer coating film having a good finished appearance can be obtained regardless of the type of steel material and the presence or absence of plating treatment / chemical conversion treatment. By using a coating film forming method using a steel material having a specific surface shape according to the present invention, and using an electrodeposition coating composition that can improve the finished appearance of the coating film together with this, it is even better. A coating film having a finished appearance can be formed.

It is a graph which shows the result of evaluation 1 of an Example and a comparative example. It is a graph which shows the result of evaluation 2 of an Example and a comparative example.

Claims (4)

A step of electrodepositing a cationic electrodeposition coating composition on an object to form an uncured electrodeposition coating;
Applying the intermediate coating composition on the uncured electrodeposition coating film to form an uncured intermediate coating film, and simultaneously baking and curing the uncured electrodeposition coating film and the intermediate coating film Process,
A multilayer coating film forming method comprising:
The object to be coated is a steel material having a surface with a centerline average roughness (Ra) of a roughness curve of 0.3 to 0.9 μm.
A method for forming a multilayer coating film. A step of electrodeposition coating a cationic electrodeposition coating composition on an object to form an electrodeposition coating, and heating and curing the obtained electrodeposition coating;
Applying an intermediate coating composition on the cured electrodeposition coating to form an uncured intermediate coating;
Applying an overcoating base coating composition on the uncured intermediate coating film to form an uncured top coating base film;
A step of applying an overcoat clear coating composition on an uncured topcoat base coating to form an uncured topcoat clearcoat; and an uncured intermediatecoat, topcoat basecoat and topcoat clear coat Simultaneously baking and curing,
A multilayer coating film forming method comprising:
The article to be coated is a steel material having a surface with a centerline average roughness (Ra) of a roughness curve of 0.3 to 0.9 μm.
A method for forming a multilayer coating film.   The method for forming a multilayer coating film according to claim 1 or 2, wherein the cationic electrodeposition coating composition is an electrodeposition coating composition containing a cationic epoxy resin and a blocked isocyanate curing agent. The coated steel material which has a multilayer coating film obtained by the multilayer coating-film formation method in any one of Claims 1-3.

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