JP2006167681A - Method of forming multi-layer coating film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of forming a multi-layer coating film having a good finish appearance in the three-coat one-bake coating capable of saving energy and reducing costs. <P>SOLUTION: This method has a process of applying a cation electrodeposition coating composition to an article to be coated by electrodeposition to form an electrodeposition coating film and heat-hardening the obtained electrodeposition coating film, a process of applying an intermediate coating composition onto the hardened electrodeposition coating film to form an unhardened intermediate coating film, a process of applying a top-coat base coating composition onto the unhardened intermediate coating film to form an unhardened top-coat base coating film, a process of applying a top-coat clear coating composition onto the unhardened top-coat base coating film to form an unhardened top-coat clear coating film and a process of baking the three unhardened coating films to harden simultaneously. The electrodeposition coating film before heat-hardening has an arithmetic average roughness (Ra) of 0.3-4.0 μm 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. Moreover, the cured coating film which has a favorable external appearance is formed by making a coating film flow at the time of this baking hardening.

  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. A schematic process diagram of this coating process is shown in FIG. As a similar method, after the electrodeposition coating is cured, an intermediate coating is applied and cured, and then a top coating base and a clear coating are applied wet-on-wet, and then two uncured coatings are baked and cured at once. There are also three-coat and two-bake painting. A schematic process diagram of this painting process is shown in FIG.

  By the way, in three coats and one-bake coating as shown in the figure, the baking process is less than in the conventional process, so that the appearance of the multilayer coating film that can obtain the surface state of the cured electrodeposition coating film has a great influence. Has been found. As a method of improving the surface state of the cured electrodeposition coating film, it is known that the flowability at the time of melting is improved by lowering the melt viscosity at the time of heat curing of the electrodeposition coating film and the appearance of the electrodeposition coating film is improved. There is technology. However, lowering the melt viscosity also decreases the throwing power and may deteriorate the physical properties of the coating film.

  In JP 2002-224613 (Patent Document 1), the glass transition temperature of a cured electrodeposition coating film formed on a substrate by a cationic electrodeposition coating composition is 110 ° C. or more, and the surface roughness After forming a three-layer coating film by three-coating and one-bake coating on the electrodeposition coating film surface having a degree (Ra: arithmetic average roughness) of 0.3 μm or less, the three-layer coating film is simultaneously heated and cured. A multilayer coating formation method is described. In this document, the coating film appearance is evaluated only for the cured electrodeposition coating film, and does not include a description of the uncured electrodeposition coating film before heat curing.

JP 2002-224613 A

  An object of the present invention is to provide a method for forming a multilayer coating film having a good finished appearance in three-coat one-bake coating or three-coat two-bake coating capable of saving energy and reducing costs.

The present invention
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 electrodeposition coating film before heat-curing provides a multilayer coating film forming method having an arithmetic average roughness (Ra) of a roughness curve of 0.3 to 4.0 μm. Achieved.

The present invention also 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 the intermediate coating composition on the cured electrodeposition coating film to form an intermediate coating film, and heating and curing the obtained intermediate coating film;
Applying an overcoating base coating composition on the cured intermediate coating film to form an uncured top coating base film;
A step of applying an overcoat clear coating composition on the uncured topcoat base coating to form an uncured topcoat clearcoat, and baking and curing the uncured topcoat basecoat and topcoat clear coating simultaneously Process,
A multilayer coating film forming method comprising:
The electrodeposition coating film before heat-curing provides a multilayer coating film forming method having an arithmetic average roughness (Ra) of a roughness curve of 0.3 to 4.0 μm. Achieved.

  Furthermore, this invention also provides the multilayer coating film obtained by said multilayer coating-film formation method. In addition, the multilayer coating film in this specification has an electrodeposition coating film, an intermediate coating film, a top coating base coating film, and a top coating clear coating film.

  In the present invention, a technique for obtaining a coating film having a good appearance was found. By adjusting the surface state of the uncured electrodeposition coating film before heat-curing by the method of the present invention, it has a good appearance without adopting a technique for enhancing the flowability at the time of melting the electrodeposition coating film A cured electrodeposition coating film and a multilayer coating film having a good finished appearance can be formed. By the method of the present invention, a multilayer coating film having a good appearance can be obtained even in three-coat / one-bake coating or three-coat / two-bake coating with few baking steps. According to the present invention, energy required for baking and drying in the painting process can be saved, and energy saving and cost reduction can be achieved.

  In the present invention, the uncured electrodeposition coating film formed by electrodeposition coating has a cationic electrodeposition coating composition so that the arithmetic mean roughness (Ra) of the roughness curve has a lower limit of 0.3 μm and an upper limit of 4.0 μm. Adjust various components and contents contained in the product. The upper limit is preferably 3.5 μm. As used herein, the arithmetic mean roughness (Ra) of a roughness curve is a parameter defined in JIS B 0601. The arithmetic average roughness (Ra) of the roughness curve of the cured electrodeposition coating film should be measured according to JIS B 0601 using, for example, an evaluation type surface roughness measuring machine manufactured by Mitutoyo Corporation. Can do.

  When Ra of an uncured electrodeposition coating film exceeds 4.0 μm, the appearance of the multilayer coating film may be deteriorated. Further, the lower limit of Ra of 0.3 μm or less is difficult to achieve at the current technical level.

  For example, a binder resin containing a cationic epoxy resin and a blocked isocyanate curing agent may be used as a method for preparing a cationic electrodeposition coating composition from which an electrodeposition coating film having an arithmetic average roughness (Ra) of a roughness curve in the above range is obtained. Examples thereof include a method of adjusting the average particle size of the emulsion to 160 nm or less and the average particle size of the pigment-dispersed emulsion to 100 to 600 nm. Examples of the method for adjusting the average particle size of the binder resin emulsion include adjusting the amount of neutralized acid. As a method for adjusting the average particle diameter of the pigment-dispersed emulsion, for example, adjusting the pigment / dispersed resin ratio can be mentioned. Moreover, the smoothness of an electrodeposition coating film can be improved more by using the surface-treated steel sheet having a smaller surface roughness.

  Hereinafter, the coating object, the cationic electrodeposition coating composition, the intermediate coating composition, the top coating base coating composition, the top coating clear coating composition and the coating method thereof used in the multilayer coating film forming method of the present invention. Will be described sequentially.

Article to be coated as a coating objects used in the multilayer coating film forming method of the present invention, the electrodeposition coating includes any substrate that can be. Examples of such a substrate include iron, steel, aluminum, tin, zinc and the like, alloys containing these metals, and plating or vapor deposition products of these metals. Specific examples include car bodies and parts of automobiles such as passenger cars, trucks, motorcycles, and buses manufactured using these metal members. Conductive treatment was applied to resins such as polyethylene resin, polypropylene resin, ethylene-vinyl acetate copolymer resin, polyamide resin, acrylic resin, vinylidene chloride resin, polycarbonate resin, polyurethane resin, epoxy resin, and various FRPs. A plastic material can also be used as a substrate.

  In the multilayer coating film forming method of the present invention, the substrate may be used as it is, or pretreatment such as degreasing and chemical conversion treatment may be performed before electrodeposition coating.

Cationic electrodeposition coating composition The cationic electrodeposition coating composition used in the present invention comprises an aqueous solvent, a binder resin emulsion containing a cationic epoxy resin and a blocked isocyanate curing agent, dispersed or dissolved in an aqueous solvent, 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 a 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 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 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 the case where the cationic electrodeposition coating composition contains a dissociation catalyst for dissociating the blocking agent of the blocked isocyanate curing agent in addition to the components described above, an organic tin compound such as dibutyltin laurate, dibutyltin oxide, dioctyltin oxide, etc. 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 and coating of cationic electrodeposition coating composition The cationic electrodeposition coating composition used in the present invention disperses the catalyst, cationic epoxy resin, blocked isocyanate curing agent, and pigment dispersion paste described above in an aqueous solvent. It is prepared by. 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. Moreover, in this invention, the average particle diameter of a binder resin emulsion can be adjusted to a preferable range by using the quantity of this neutralizing acid in the said range.

  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. Moreover, the smoothness of an electrodeposition coating film can be improved more by using the surface-treated steel sheet having a smaller roughness.

  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 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 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. 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.

Intermediate Coating Composition The intermediate coating composition used in the present invention includes 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, 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.

  Examples of the acrylic resin include a copolymer of an acrylic monomer and another ethylenically unsaturated monomer. Acrylic monomers that can be used for the copolymerization include methyl, ethyl, propyl, n-butyl, i-butyl, t-butyl, 2-ethylhexyl, lauryl, phenyl, benzyl, 2-hydroxy of acrylic acid or methacrylic acid. Esterified compounds such as ethyl and 2-hydroxypropyl, ring-opening adducts of caprolactone of acrylic acid or 2-hydroxyethyl methacrylate, glycidyl acrylate, glycidyl methacrylate, acrylamide, methacrylamide and N-methylol acrylamide, polyvalent Examples include (meth) acrylic acid esters of alcohol. Examples of the other ethylenically unsaturated monomers copolymerizable with these include styrene, α-methylstyrene, itaconic acid, maleic acid, and vinyl acetate.

  Examples of the polyester resin include saturated polyester resins and unsaturated polyester resins, and examples include condensates obtained by heat condensation of polybasic acids and polyhydric alcohols. Examples of polybasic acids include saturated polybasic acids and unsaturated polybasic acids. Examples of saturated polybasic acids include succinic acid, adipic acid, azelaic acid, sebacic acid, hexahydrophthalic acid, 1,4- Examples of the unsaturated polybasic acid include maleic acid, maleic anhydride, fumaric acid, phthalic anhydride, terephthalic acid, and isophthalic acid. Examples of the polyhydric alcohol include dihydric alcohol and trihydric alcohol. Examples of the dihydric alcohol include ethylene glycol, diethylene glycol, neopentyl glycol, 1,5-pentanediol, and 1,6-hexanediol. Examples of the trihydric alcohol include glycerin and trimethylolpropane.

  Examples of the polyurethane resin include resins having a urethane bond obtained from various polyol components such as acrylic, polyester, polyether, and polycarbonate and a polyisocyanate compound. Examples of the polyisocyanate compound include 2,4-tolylene diisocyanate (2,4-TDI), 2,6-tolylene diisocyanate (2,6-TDI), and mixtures thereof (TDI), diphenylmethane-4,4 ′. Diisocyanate (4,4′-MDI), diphenylmethane-2,4′-diisocyanate (2,4′-MDI), and mixtures thereof (MDI), naphthalene-1,5-diisocyanate (NDI), 3,3 ′ -Dimethyl-4,4'-biphenylene diisocyanate (TODI), xylylene diisocyanate (XDI), dicyclohexylmethane diisocyanate (hydrogenated HDI), isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), hydrogenated xylylene diisocyanate (HX I), and the like can be given.

  As alkyd resins, the above polybasic acids and polyhydric alcohols are further reacted with modifying agents such as fats and oils / fatty acids (soybean oil, linseed oil, coconut oil, stearic acid, etc.) and natural resins (rosin, succinic acid, etc.). The obtained alkyd resin can be used.

  As the fluororesin, any of vinylidene fluoride resin, tetrafluoroethylene resin or a mixture thereof, a copolymer composed of a fluoroolefin and a hydroxy group-containing polymerizable compound and other copolymerizable vinyl compounds are copolymerized. Examples thereof include resins made of various fluorine-based copolymers obtained by the above process.

  Examples of the epoxy resin include a resin obtained by a reaction between bisphenol and epichlorohydrin. Examples of bisphenol include bisphenol A and F. Examples of the bisphenol type epoxy resin include Epicoat 828, Epicoat 1001, Epicoat 1004, Epicoat 1007, and Epicoat 1009 (all manufactured by Shell Chemical Co., Ltd.), and these are chain extended using an appropriate chain extender. It is also possible to use.

  The polyether resin is a polymer or copolymer having an ether bond, such as a polyoxyethylene-based polyether, a polyoxypropylene-based polyether, or a polyoxybutylene-based polyether, or an aromatic such as bisphenol A or bisphenol F. And a polyether resin having at least two hydroxyl groups per molecule, such as a polyether derived from an aromatic polyhydroxy compound. Also, the above polyether resin is reacted with polyvalent carboxylic acids such as succinic acid, adipic acid, sebacic acid, phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, or reactive derivatives such as these acid anhydrides. And carboxyl group-containing polyether resins obtained.

  The intermediate coating resin has an acid value of 3 to 200 and a hydroxyl value of 30 to 200, and preferably has a number average molecular weight of 500 to 50,000, in particular, an acid value of 3 to 200 and a hydroxyl value of 30 to 200, A preferable example is an acrylic resin having a number average molecular weight of 2,000 to 50,000, an acid value of 3 to 200, and a hydroxyl value of 30 to 200, and a polyester resin having a number average molecular weight of 500 to 20,000. When preparing the intermediate coating composition as an aqueous solution or aqueous dispersion, the acid value of the intermediate coating resin is preferably in the range of 10 to 200 and hydroxyl value of 30 to 200.

  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.

  The intermediate coating composition in the present invention contains a pigment. Examples of such pigments 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 concentration (PWC) of the pigment with respect to the solid content of the intermediate coating composition is preferably in the range of 10% by weight to 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 a lower limit of 35% by weight and an upper limit of 65% by weight. The lower limit is more preferably 40% by weight, and the upper limit is more preferably 60% by weight. When the lower limit of the solid content concentration is less than 35% by weight, a sagging phenomenon occurs during coating, which may reduce the finished appearance. On the other hand, when the upper limit exceeds 65% by weight, the flowability at the time of coating is lowered, and the finished appearance may be lowered.

  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.

Preparation of intermediate coating composition and coating intermediate coating composition can be prepared by dissolving or dispersing the above components in a solvent. Any solvent may be used as long as it dissolves or disperses the intermediate coating resin component, and an organic solvent and / or water can be used. Examples of the organic solvent include those usually used in the coating composition field. Examples include hydrocarbons such as toluene and xylene, ketones such as acetone and methyl ethyl ketone, esters such as ethyl acetate, butyl acetate, cellosolve acetate, and butyl cellosolve, and alcohols. When the use of an organic solvent is regulated from the viewpoint of the environment, it is preferable to use water. In this case, an appropriate amount of a hydrophilic organic solvent may be contained.

  The viscosity of the intermediate coating composition during coating is preferably adjusted to 10 to 30 seconds (Ford Cup # 4/20 ° C.) using the organic solvent and / or water and a mixture thereof. When the viscosity is lower than the above range, there is a possibility that the topcoat base coating film and the intermediate coating film formed in the next coating are mixed. On the other hand, if the viscosity exceeds the above range, it is difficult to handle the coating composition, and the coating film may solidify early, resulting in surface irregularities that cannot be covered or repaired by the next coating film. There is.

  The intermediate coating film is obtained by coating the intermediate coating composition on the cured electrodeposition coating film. By the formation of the intermediate coating film, the concealability of the electrodeposition coating film is improved, and chipping resistance is imparted. Furthermore, the adhesiveness with the topcoat base coating film reapplied in the next step is also improved.

  A method for forming the intermediate coating film is not particularly limited, but a spray method, a roll coater method and the like are preferable. Specifically, air electrostatic sprays called “react guns” are used, or rotary atomization type electrostatics called “micro-micro (μμ) bell”, “micro (μ) bell”, “metabell” etc. It can be painted using a 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 the three-coat / one-bake method, after the formation of the intermediate coating film, the process proceeds to the formation process of the top coating base coating film in the next process without heating and curing. 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. In the three-coat / two-bake method, after the intermediate coating film is formed, the intermediate coating film is heated and cured at 120 to 160 ° C., and the process proceeds to the formation process of the top coating base coating film in the next step.

Topcoat base paint composition The topcoat base paint composition used in the present invention comprises a topcoat base resin component, a glitter pigment and / or a color pigment, an extender pigment and a solvent, and a glitter paint composition or a solid paint composition. It is. 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. 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.

  Among the pigments contained in the above topcoat base coating composition, examples of the bright pigment include aluminum flake pigments, colored aluminum flake pigments, interference mica pigments, colored mica pigments, metal oxide-coated alumina flake pigments, and metal oxide coatings. Glass flake pigment, metal plated glass flake pigment, metal oxide coated glass flake pigment, metal oxide coated silica flake pigment, metal titanium flake pigment, graphite pigment, stainless steel flake pigment, plate-like iron oxide pigment, phthalocyanine flake pigment or hologram pigment Can be mentioned. In addition, when using the said luster pigment and / or a coloring pigment, 1-50% is preferable and, as for the total content (PWC) as the whole pigment, 5-30% is more preferable. If it is less than 1%, the designability is insufficient, and if it exceeds 50%, the appearance of the coating film may be deteriorated.

Preparation of Topcoat Base Coating Composition and Paint Topcoat Base Coating Composition is usually prepared by dissolving or dispersing the above components in a solvent. Any solvent may be used as long as it dissolves or disperses the topcoat base resin component, and an organic solvent and / or water can be used. Examples of the organic solvent include hydrocarbons such as toluene and xylene, ketones such as acetone and methyl ethyl ketone, esters such as ethyl acetate, butyl acetate, cellosolve acetate, and butyl cellosolve, and alcohols.

  It is desirable to adjust the viscosity of the topcoat base coating composition to 10 to 30 seconds at Ford Cup # 4/20 ° C. using a suitable diluent. When the viscosity is lower than the above range, there is a possibility that the clear top coating film and the top coating base film formed in the next coating are mixed. If the viscosity exceeds the above range, it is difficult to handle the coating composition, and the coating may solidify early, resulting in surface irregularities that cannot be covered or repaired by the next coating. is there.

  The topcoat base coating film is obtained by coating the topcoat base coating composition on the intermediate coating film. In the three-coat one-bake method, this topcoat base coating composition is applied onto an uncured intermediate coating film by a wet-on-wet method. In the three coat-to-bake method, the top coat base coating composition is applied onto the cured intermediate coat film. 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. When the top coating composition is applied to an automobile body or the like, it is possible to enhance the design 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.

Topcoat clear coating composition 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.

  From the standpoint of preventing acid rain and increasing the difference in solubility with the top coat film by wet-on-wetting and not disturbing the orientation of the glittering pigment in the top coat film, the clear paint composition described above is used. A clear coating composition containing a carboxyl group-containing polymer and an epoxy group-containing polymer described in JP-A-19315 is preferably used. In addition, these clear coating compositions can be added with color pigments, extender pigments, modifiers, ultraviolet absorbers, leveling agents, dispersants, antifoaming agents, etc., as necessary, as long as their transparency is not impaired. It is possible to mix an agent.

Preparation of topcoat clear coating composition and coating topcoat clear coating composition are prepared by dissolving or dispersing the above components in a solvent. Any solvent described above can be used as the solvent. The top clear film is obtained by applying the top clear 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 method, which is one aspect of the present invention, after forming the top clear film, three layers of the 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 120 to 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.

  In the three-coat-to-bake method, which is another embodiment of the present invention, an intermediate coating film is formed on the cured electrodeposition coating film, then heated and cured, and then a top coating base coating film and a top coating clear coating film are formed thereon. A two-layer coating film can be obtained by baking and curing two layers of an uncured topcoat base coating and topcoat clear coating at 120 to 160 ° C. for a predetermined time. Also in this method, preheating may be performed after the top coat base coating film is formed. By performing preheating, a coating film having a better finished appearance can be obtained.

  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 Production of amine-modified epoxy resin 2,4- / 2,6-tolylene diisocyanate (weight ratio = 8/2) 92 was placed in a flask equipped with a stirrer, a cooling tube, a nitrogen introducing tube, a thermometer and a dropping funnel. Part, 95 parts of methyl isobutyl ketone (hereinafter abbreviated as MIBK) and 0.5 part of dibutyltin dilaurate were charged. While stirring the reaction mixture, 21 parts of methanol was added dropwise. The reaction was started 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 2 Production of blocked isocyanate curing agent (1)
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. 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 had disappeared, and after standing to cool, MIBK 336.1 parts was added, and the glass transition temperature was 0 ° C. An agent was obtained.

Production Example 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 pipe, a nitrogen introduction pipe and a thermometer. After dilution, 0.2 part of heredibutyltin 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 4 Production of Pigment Dispersion Paste 120 parts of pigment dispersing resin obtained in Production Example 4 in a sand grind mill, 2.0 parts of carbon black, 100.0 parts of kaolin, 80.0 parts of titanium dioxide, aluminum phosphomolybdate 18.0 parts 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%).

Example 1
Production of Cationic Electrodeposition Composition and Formation of Electrodeposition Coating Film The amine-modified epoxy resin obtained in Production Example 1 and the blocked isocyanate curing agent obtained in Production Example 2 are uniformly at a solid content ratio of 80/20. It mixed so that it might become. 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. MIBK was removed under reduced pressure to obtain an emulsion having an average particle size of 70 nm and a solid content of 36%.

  1500 parts of this emulsion and 320 parts of pigment dispersion paste obtained in Production Example 4, 1660 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% by weight. A cationic electrodeposition coating composition was obtained. The milligram equivalent of acid per 100 g of resin solid content of this cationic electrodeposition coating composition was 24.2. The temperature of the electrodeposition coating bath was 30 ° C., and electrodeposition was applied to a surface-treated steel plate with a surface roughness Ra = 0.60 μm (cutoff value: 2.5 mm) to a film thickness of 15 μm. An electrodeposition coating film (A-1) was obtained.

Formation of cured electrodeposition coating film The obtained cationic electrodeposition coating film (A-1) was baked at 170 ° C. for 20 minutes to form a cured electrodeposition coating film.

Formation of intermediate coating film On the cured electrodeposition coating film , a polyester-melamine curing system intermediate coating composition ("OTO H-880", manufactured by Nippon Paint Co., Ltd.) is applied so that the dry film thickness is 20 μm. Coating was performed using a rotary atomizing electrostatic coating machine. In the three-coat two-bake (3C2B) method, the intermediate coating film was cured by baking at 140 ° C. for 30 minutes after coating. In the three-coat one-bake (3C1B) method, after the intermediate coating, preheating was performed at room temperature for 8 minutes to form an uncured intermediate coating film.

Formation of topcoat base coat and topcoat clear coat, and then on the uncured or cured intermediate coat face, an acrylic-melamine cured topcoat base coating composition ("OTO H-600", manufactured by Nippon Paint Co., Ltd.) The coating was applied so that the dry film thickness was 10 μm. After coating, it was preheated at room temperature for 7 minutes to form an uncured topcoat base coating film. Next, an acrylic acid-epoxy curable top coat clear coating composition (“MAC O-1600”, manufactured by Nippon Paint Co., Ltd.) was applied so that the dry film thickness was 35 μm. Subsequently, it baked for 30 minutes at the temperature of 140 degreeC, and obtained the multilayer coating film.

Measurement of arithmetic mean roughness (Ra) of roughness curve of uncured electrodeposition coating film Uncured electrodeposition coating film (A-1) obtained from the above electrodeposition coating composition was treated at 20 ° C. for 3 hours. I left it alone. Then, Ra value of this electrodeposition coating film (WET coating film) 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 averaging the top and bottom. The results are shown in Table 1.

  Moreover, the uncured electrodeposition coating film was baked at 170 ° C. for 20 minutes to form a cured electrodeposition coating film (DRY coating film). The arithmetic average roughness (Ra) of the roughness curve of this cured electrodeposition coating film was also measured in the same manner as described above. The results are shown in Table 1.

Appearance Evaluation of Multi-layer Coating Film The finished appearance of the multi-layer coating film after baking and curing obtained by the three-coat one-bake method (3C / 1B) or the three-coat two-bake method (3C / 2B) is expressed as Wave-scan DOI ( Measurement was performed using BYK-Gardner. Wa (measurement wavelength: 100 to 300 μm), Wb (measurement wavelength: 300 to 1000 μm), Wc (measurement wavelength: 1000 to 3000 μm), Wd (measurement wavelength: 3000 to 10,000 μm), and We (measurement wavelength: 10,000 μm to) Evaluation was performed from the values of Wa, Wc and Wd among the measured values. These values indicate that the smaller the numerical value, the better the appearance.

Example 2
The amine-modified epoxy resin obtained in Production Example 1 and the blocked isocyanate curing agent obtained in Production Example 2 were mixed so as to be uniform at a solid content ratio of 80/20. 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. MIBK was removed under reduced pressure to obtain an emulsion having an average particle size of 70 nm and a solid content of 36%.

  1500 parts of this emulsion and 320 parts of pigment dispersion paste obtained in Production Example 4, 1660 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% by weight. A cationic electrodeposition coating composition was obtained. The milligram equivalent of acid per 100 g of resin solid content of this cationic electrodeposition coating composition was 24.2. The temperature of the electrodeposition coating bath was 30 ° C., and electrodeposition was applied to a surface-treated steel plate with a surface roughness Ra = 0.90 μm (cutoff value: 2.5 mm) to a film thickness of 15 μm. An electrodeposition coating film (A-2) was obtained.

  In addition, the formation of the cured electrodeposition coating film was performed in the same manner as in Example 1 to obtain a multilayer coating film. Next, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

Example 3
The amine-modified epoxy resin obtained in Production Example 1 and the blocked isocyanate curing agent obtained in Production Example 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 35, and further ion-exchanged water was slowly added for dilution. By removing MIBK under reduced pressure, an emulsion having an average particle size of 38 nm and a solid content of 36% was obtained.

  1500 parts of this emulsion and 320 parts of pigment dispersion paste obtained in Production Example 4, 1660 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% by weight. A cationic electrodeposition coating composition was obtained. The milligram equivalent of acid per 100 g of resin solid content of this cationic electrodeposition coating composition was 26.5. The temperature of the electrodeposition coating bath was 30 ° C., and electrodeposition was applied to a surface-treated steel plate with a surface roughness Ra = 0.90 μm (cutoff value: 2.5 mm) to a film thickness of 15 μm. An electrodeposition coating film (A-3) was obtained.

  In addition, the formation of the cured electrodeposition coating film was performed in the same manner as in Example 1 to obtain a multilayer coating film. Next, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

Example 4
The amine-modified epoxy resin obtained in Production Example 1 and the blocked isocyanate curing agent obtained in Production Example 2 were mixed so as to be uniform at a solid content ratio of 70/30. 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. MIBK was removed under reduced pressure to obtain an emulsion having an average particle size of 92 nm and a solid content of 36%.

  1500 parts of this emulsion and 320 parts of pigment dispersion paste obtained in Production Example 4, 1660 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% by weight. A cationic electrodeposition coating composition was obtained. The milligram equivalent of acid per 100 g of resin solid content of this cationic electrodeposition coating composition was 24.2. The temperature of the electrodeposition coating bath was 30 ° C., and electrodeposition was applied to a surface-treated steel plate with a surface roughness Ra = 0.90 μm (cutoff value: 2.5 mm) to a film thickness of 15 μm. An electrodeposition coating film (A-4) was obtained.

  In addition, the formation of the cured electrodeposition coating film was performed in the same manner as in Example 1 to obtain a multilayer coating film. Next, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 1
The amine-modified epoxy resin obtained in Production Example 1 and the blocked isocyanate curing agent obtained in Production Example 2 were mixed so as to be uniform at a solid content ratio of 80/20. Glacial acetic acid was added so that the milligram equivalent (MEQ (A)) of the acid per 100 g of resin solid content was 25, and further ion-exchanged water was slowly added for dilution. By removing MIBK under reduced pressure, an emulsion having an average particle size of 125 nm and a solid content of 36% was obtained.

  1500 parts of this emulsion and 320 parts of pigment dispersion paste obtained in Production Example 4, 1660 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% by weight. A cationic electrodeposition coating composition was obtained. The milligram equivalent of acid per 100 g of resin solid content of this cationic electrodeposition coating composition was 23.3. The temperature of the electrodeposition coating bath was 30 ° C., and electrodeposition was applied to a surface-treated steel plate with a surface roughness Ra = 0.90 μm (cutoff value: 2.5 mm) to a film thickness of 15 μm. An electrodeposition coating film (B-1) was obtained.

  In addition, the formation of the cured electrodeposition coating film was performed in the same manner as in Example 1 to obtain a multilayer coating film. Next, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 2
The amine-modified epoxy resin obtained in Production Example 1 and the blocked isocyanate curing agent obtained in Production Example 2 were mixed so as to be uniform at a solid content ratio of 80/20. To this, glacial acetic acid was added so that the milligram equivalent (MEQ (A)) of the acid per 100 g of resin solid content was 20, and further ion-exchanged water was slowly added for dilution. MIBK was removed under reduced pressure to obtain an emulsion having an average particle size of 131 nm and a solid content of 36%.

  1500 parts of this emulsion and 320 parts of pigment dispersion paste obtained in Production Example 4, 1660 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% by weight. A cationic electrodeposition coating composition was obtained. The milligram equivalent of acid per 100 g of resin solid content of this cationic electrodeposition coating composition was 23.3. The temperature of the electrodeposition coating bath was 30 ° C., and electrodeposition was applied to a surface-treated steel plate with a surface roughness Ra = 0.90 μm (cutoff value: 2.5 mm) to a film thickness of 15 μm. An electrodeposition coating film (B-2) was obtained.

  In addition, the formation of the cured electrodeposition coating film was performed in the same manner as in Example 1 to obtain a multilayer coating film. Next, evaluation was performed in the same manner as in Example 1. The results are shown in Table 1.

  As is apparent from the results in Table 1, the electrodeposition coating film in which the surface state of the uncured electrodeposition coating film (Ra of the WET coating film) is within a specific range in Examples 1 to 4 is baked and cured. Even if it was made, Ra value was small and the surface state was favorable (refer Ra value of a DRY coating film). The multilayer coating film obtained by performing three-coat / one-bake coating or three-coat / two-bake coating on this cured electrodeposition coating film has low Wa, Wc, and Wd values and is attributed to the electrodeposition coating film. A good multilayer coating film having no poor coating appearance was obtained. On the other hand, Comparative Examples 1 and 2 had a coating film appearance defect due to the cured electrodeposition coating film, and a multilayer coating film having a good target appearance could not be formed.

  In the present invention, by the method of the present invention, even in coating by three-coat one-bake and three-coat two-bake with few baking steps, it is good without adopting a method for enhancing the flowability at the time of electrodeposition coating melting. A multilayer coating film having an appearance can be obtained. Therefore, energy required for baking and drying in the painting process can be saved, and energy saving and cost reduction can be achieved. The method of the present invention can be preferably used in fields where energy saving and good coating film appearance are required, such as automobile skins, motorcycle exteriors, container outer surfaces, coil coatings, and the home appliance industry. it can.

It is process drawing which shows the coating process of a three coat one bake typically. It is process drawing which shows the coating process of a three coat two bake typically.

Claims (3)

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 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 electrodeposition coating film before heat-curing has an arithmetic average roughness (Ra) of the roughness curve of 0.3 to 4.0 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 film, and heating and curing the obtained electrodeposition coating film;
Applying the intermediate coating composition on the cured electrodeposition coating film to form an intermediate coating film, and heating and curing the obtained intermediate coating film;
Applying an overcoating base coating composition on the cured 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 baking and curing the uncured topcoat basecoat and topcoat clear coating simultaneously Process,
A multilayer coating film forming method comprising:
The electrodeposition coating film before heat-curing has an arithmetic average roughness (Ra) of the roughness curve of 0.3 to 4.0 μm,
A method for forming a multilayer coating film. A multilayer coating film obtained by the multilayer coating film forming method according to claim 1 or 2.

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