Cationic electrodeposition coating composition, electrodeposition coated product, and method for producing electrodeposition coated product

Abstract

The purpose of the present invention is to provide a cationic electrodeposition coating composition capable of exhibiting high rust prevention properties even without subjecting a coated product to chemical conversion treatment.　The present invention provides a cationic electrodeposition coating composition containing (A) an aminated epoxy resin and (B) a niobium compound. The (B) niobium compound can be niobium oxide sol or niobium oxide colloidal particles obtained by stabilizing niobium oxide sol. The cationic electrodeposition coating composition according to the present invention may further contain: (C) a blocked polyisocyanate curing agent; (D) a rust preventive auxiliary agent selected from the group consisting of silica, a silane coupling agent, a titanium coupling agent, and a mixture thereof; (E) a phosphoric acid compound; or (F) a polyamidine compound. The present invention also provides a coated product obtained by using the cationic electrodeposition coating composition. The present invention further provides a coating method using the cationic electrodeposition coating composition.

Description

Cationic electrodeposition coating composition, electrodeposition coated article, and method for producing electrodeposition coated article

[0001] The present invention relates to a cationic electrodeposition coating composition, an electrodeposition-coated article, and a method for producing an electrodeposition-coated article.

[0002] Cationic electrodeposition paints are widely used as primers to impart rust prevention to industrial products such as automobiles. Typically, substrates to be coated with cationic electrodeposition paints are subjected to a chemical conversion treatment, then immersed in an electrodeposition paint bath, and then painted by passing an electric current through the substrate, which serves as the cathode. From the standpoint of process simplification and resource conservation, it has been considered to apply cationic electrodeposition paint directly to substrates without chemical conversion treatment. However, substrates that are not chemically treated tend to have insufficient rust prevention even when subjected to cationic electrodeposition coating.

[0003] Japanese Patent Application Laid-Open No. 2005-36261

[0004] An object of the present invention is to provide a cationic electrodeposition coating composition which can exhibit high rust prevention properties without the need for chemical conversion treatment of the substrate.

[0005] In order to solve the above problems, the present invention provides the following aspects. [1] A cationic electrodeposition coating composition containing an aminated epoxy resin (A) and a niobium compound (B). [2] The cationic electrodeposition coating composition according to [1], wherein the niobium compound (B) is niobium oxide sol or niobium oxide colloidal particles obtained by stabilizing niobium oxide sol. [3] The cationic electrodeposition coating composition according to [1] or [2], further containing a blocked polyisocyanate curing agent (C). [4] The cationic electrodeposition coating composition according to [1] or [2], further containing a rust prevention adjuvant (D) selected from the group consisting of silica, silane coupling agents, titanium coupling agents, and mixtures thereof. [5] The cationic electrodeposition coating composition according to [1] or [2], further containing a phosphoric acid compound (E). [6] The cationic electrodeposition coating composition according to [1] or [2], further containing a polyamidine compound (F). [7] The polyamidine compound has the following general formula: (In the formula, R １ and R ２are each independently a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms, and X is an anion.) [8] The cationic electrodeposition coating composition according to [1] or [2], further containing a pigment (G). [9] The cationic electrodeposition coating composition according to [1] or [2], further containing a curing catalyst (H).

[10] The cationic electrodeposition coating composition according to [1] or [2], which is applied to a galvanized steel sheet, a cold-rolled steel sheet, or an aluminum substrate without chemical conversion treatment.

[11] An electrodeposition-coated article comprising: a substrate; and an electrodeposition coating film formed on the substrate using the cationic electrodeposition coating composition according to [1] or [2].

[12] A method for producing an electrodeposition coated article, comprising the steps of: immersing an article to be coated in the cationic electrodeposition coating composition according to [1] or [2], and then applying a voltage between the article to be coated and a counter electrode to form an uncured electrodeposition coating film on the article to be coated; and heating the uncured electrodeposition coating film at a temperature of 75°C or higher and 200°C or lower to obtain a cured electrodeposition coating film.

[0006] According to the present invention, by incorporating a niobium oxide compound (particularly niobium oxide sol or niobium oxide colloidal particles obtained by stabilizing niobium oxide with citric acid or a salt thereof) into a cationic electrodeposition coating composition, it is possible to perform cationic electrodeposition coating on a substrate (particularly a galvanized steel sheet or an aluminum substrate) without subjecting the substrate to a chemical conversion treatment, thereby forming a coating film having high rust prevention properties. Furthermore, it is possible to provide an electrodeposition-coated article using the cationic electrodeposition coating composition of the present invention and a method for producing the same.

[0007] The cationic electrodeposition coating composition of the present invention is believed to exhibit rust prevention properties by depositing a metal (specifically, niobium) on a metal substrate when the metal substrate is immersed in a bath of the electrodeposition coating composition. This metal deposition can occur even without applying current to the cationic electrodeposition bath, and it is believed that metal deposition is further accelerated when applying current to the cationic electrodeposition bath with the substrate as the cathode. More specifically, high rust prevention effects can be obtained on substrates such as galvanized steel sheets, cold-rolled steel sheets, or aluminum substrates without chemical conversion treatment or current application.

[0008] [Cationic Electrodeposition Coating Composition] The cationic electrodeposition coating composition according to this embodiment (hereinafter sometimes simply referred to as the coating composition) contains an aminated epoxy resin (A) and a niobium compound (B). The cationic electrodeposition coating composition of the present invention further contains a blocked polyisocyanate curing agent (C), a rust prevention auxiliary agent (D) such as silica, a silane coupling agent, a titanium coupling agent, or a mixture thereof, a phosphate compound (E), a polyamidine compound (F), a pigment (G), or a curing catalyst (H), etc. Each of these components is described below.

[0009] <Amino-substituted epoxy resin (A)> The aminated epoxy resin (A) is a film-forming resin. The aminated epoxy resin is contained in the cationic electrodeposition coating composition in the form of a resin emulsion. In the aminated epoxy resin (A), at least one oxirane ring (also referred to as an "epoxy group") of the epoxy resin is aminated.

[0010] The number average molecular weight of the aminated epoxy resin (A) is, for example, 1,000 or more and 7,000 or less. When the number average molecular weight is 1,000 or more, the rust prevention and solvent resistance of the resulting cured electrodeposition coating film are likely to be improved. When the number average molecular weight is 7,000 or less, the viscosity of the aminated epoxy resin (A) is easily adjusted, allowing for smooth synthesis, and in addition, the resulting aminated epoxy resin (A) is easily emulsified and dispersed. The number average molecular weight of the aminated epoxy resin (A) may be 1,500 or more and 4,000 or less.

[0011] The number average molecular weight is a value calculated as a styrene homopolymer, measured by gel permeation chromatography.

[0012] The amine value of the aminated epoxy resin (A) is, for example, 20 mgKOH / g or more and 100 mgKOH / g or less. When the amine value of the aminated epoxy resin (A) is 20 mgKOH / g or more, the stability of the emulsion dispersion of the aminated epoxy resin (A) in the coating composition is good. When the amine value is 100 mgKOH / g or less, the amount of amino groups in the cured electrodeposition coating film is appropriate, and a decrease in the water resistance of the coating film is suppressed. The amine value of the aminated epoxy resin (A) may be 20 mgKOH / g or more and 80 mgKOH / g or less.

[0013] The amine value can be determined in accordance with ASTM D2073 by the following method. (1) Accurately weigh out 500 mg of aminated epoxy resin into a 200 ml Erlenmeyer flask. (2) Add approximately 50 ml of glacial acetic acid and dissolve uniformly. (3) Add 5 to 6 drops of indicator (methyl violet solution) and stir uniformly. (4) Titrate with 0.1 N perchloric acid / acetic acid solution, and the endpoint is the point at which the color turns bright green. (The above steps (3) and (4) can also be replaced with potentiometric titration.)

[0014] The hydroxyl value of the aminated epoxy resin (A) is, for example, 150 mgKOH / g or more and 650 mgKOH / g or less. When the hydroxyl value is 150 mgKOH / g or more, the curability of the coating composition is enhanced and the appearance of the coating film is improved. When the hydroxyl value is 650 mgKOH / g or less, the amount of hydroxyl groups remaining in the cured electrodeposition coating film becomes appropriate, and the water resistance of the coating film is easily improved. The hydroxyl value of the aminated epoxy resin may be 150 mgKOH / g or more and 400 mgKOH / g or less.

[0015] The hydroxyl value can be determined by the neutralization titration method described in JIS K 0070 using an aqueous potassium hydroxide solution.

[0016] In particular, when the number average molecular weight of the aminated epoxy resin (A) is within the range of 1,000 to 7,000, the amine value is 20 to 100 mgKOH / g, and the hydroxyl value is 150 to 650 mgKOH / g (preferably 150 to 400 mgKOH / g), the rust prevention properties of the coated object are more likely to be improved.

[0017] The coating composition may contain multiple aminated epoxy resins (A) with different amine values ​​and / or hydroxyl values. In this case, the average amine value and average hydroxyl value calculated based on the mass ratio of the multiple aminated epoxy resins (A) preferably fall within the above-mentioned ranges. In particular, the multiple aminated epoxy resins (A) preferably contain two types of aminated epoxy resins: a first aminated epoxy resin having an amine value of 20 to 50 mgKOH / g and a hydroxyl value of 50 to 300 mgKOH / g, and a second aminated epoxy resin having an amine value of 50 to 200 mgKOH / g and a hydroxyl value of 200 to 500 mgKOH / g. The difference in amine value between the first and second aminated epoxy resins is preferably 10 to 100 mgKOH / g, and the difference in hydroxyl value is preferably 10 to 300 mgKOH / g. This makes the core of the emulsion more hydrophobic and the shell more hydrophilic, making it easier to improve the rust prevention properties of the coated object.

[0018] The aminated epoxy resin (A) can be obtained by modifying the oxirane ring (also referred to as the "epoxy group") of an epoxy resin with an amine compound. As the amine compound, it is preferable to use an amine compound having at least one of a primary amino group, a secondary amino group, and a tertiary amino group, excluding ketimines (including diketimines).

[0019] During the conversion to amination, the amine compound is preferably used in an amount of 0.9 to 1.2 equivalents per equivalent of epoxy groups in the raw material epoxy resin. The reaction conditions for the conversion to amination can be appropriately selected depending on the reaction scale, etc. For example, the reaction may be carried out at 80°C to 150°C for 0.1 to 5 hours, or at 120°C to 150°C for 0.5 to 3 hours.

[0020] (Epoxy Resin) The epoxy resin that is the starting material for the aminated epoxy resin (A) is, for example, a polyphenol polyglycidyl ether type epoxy resin, which is a reaction product of a polycyclic phenol compound and epichlorohydrin. Examples of the polycyclic phenol compound include bisphenol A, bisphenol F, bisphenol S, phenol novolac, and cresol novolac. In this specification, the term "polyphenol polyglycidyl ether type epoxy resin" includes a state in which a polyphenol polyglycidyl ether type epoxy resin and a polycyclic phenol compound are alternately and continuously reacted to each other to extend the chain.

[0021] When modifying an epoxy resin with an amine compound, it is preferable to use an epoxy resin obtained by a chain extension reaction of a polyphenol polyglycidyl ether epoxy resin and a polycyclic phenol compound. The conditions for the chain extension reaction are not particularly limited and can be selected appropriately depending on the stirring device used, the reaction scale, etc. Reaction conditions can be, for example, 85 to 180°C and 0.1 to 8 hours. More preferably, the reaction conditions can be 100 to 150°C and 2 to 8 hours. The stirring device used is not particularly limited, and stirring devices commonly used in the coatings field can be used.

[0022] In addition to the above, the epoxy resin may include the oxazolidone ring-containing epoxy resin described in JP-A-5-306327. These epoxy resins can be prepared by reacting epichlorohydrin with a diisocyanate compound or a bis-urethane compound obtained by blocking the isocyanate group of a diisocyanate compound with a lower alcohol such as methanol or ethanol.

[0023] The epoxy resin may be a resin obtained by subjecting a portion of the epoxy resin to a chain extension reaction before modification with an amine compound. For example, bifunctional polyester polyols, polyether polyols, dibasic carboxylic acids, etc. can be used for the chain extension reaction. Examples of the polyether polyol include polyols having polyethylene oxide groups and polyols having polypropylene oxide groups. For example, when a chain extension reaction is performed using a polyol having polypropylene oxide groups, a polypropylene oxide group-containing epoxy resin is obtained. The content of the polypropylene oxide group-containing epoxy resin is preferably 1 to 40 parts by mass, more preferably 15 to 25 parts by mass, per 100 parts by mass of the epoxy resin. Examples of epoxy resins similar to the polypropylene oxide group-containing epoxy resin include epoxy resins obtained by chain extension reaction of polyphenol polyglycidyl ether epoxy resins, polycyclic phenol compounds, and polypropylene oxide group-containing epoxy resins.

[0024] The aminated epoxy resin (A) can be obtained by reacting the epoxy groups of the epoxy resin with an amine compound. The epoxy groups of the epoxy resin are all consumed by the reaction with the amine compound, and substantially no epoxy groups remain in the molecules of the aminated epoxy resin (A).

[0025] (Amine Compound) Examples of amine compounds other than ketimines that can be used to amine the epoxy resin include primary amines such as butylamine, octylamine, and monoethanolamine; secondary amines such as diethylamine, dibutylamine, methylbutylamine, diethanolamine, and N-methylethanolamine; tertiary amines such as triethylamine, N,N-dimethylbenzylamine, and N,N-dimethylethanolamine; complex amines such as diethylenetriamine; diamines having a primary amino group and a tertiary amino group such as N,N-dimethyl-1,3-propanediamine and N,N-dimethylethylenediamine; and diamines having a primary amino group, a tertiary amino group, and a hydroxyl group such as N-(3-aminopropyl)diethanolamine. A single amine compound may be used alone, or two or more may be used in combination. In particular, the use of a diamine having a hydroxyl group tends to improve the adhesion and curability of the coating film.

[0026] In the amine compound, the number of primary amino groups is not particularly limited, as long as it is one or two or more. In particular, from the viewpoint of reaction control, the number of primary amino groups is preferably one. The number of hydroxyl groups is also not particularly limited, as long as it is one or two or more.

[0027] (Other Film-Forming Resins) The cationic electrodeposition coating composition may contain, as necessary, an aminated resin other than the aminated epoxy resin (A), such as an aminated acrylic resin or an aminated polyester resin. The coating composition may also contain another film-forming resin other than the above aminated resin. Examples of other film-forming resins include hydroxyl-containing acrylic resins, hydroxyl-containing polyester resins, urethane resins, butadiene resins, phenolic resins, and xylene resins. Of all the curable resins contained in the coating composition, 80% by mass or more, even 90% by mass or more, and particularly 100% by mass may be the aminated epoxy resin (A).

[0028] <Niobium Compound (B)> The niobium compound may be any compound containing niobium, but niobium oxide is generally used. In particular, niobium oxide sol is easily available. The niobium oxide sol is not particularly limited, and examples thereof include those produced by known methods described in Japanese Patent No. 2849799 and the like. Niobium oxide sol produced by Taki Chemical Co., Ltd. can also be used.

[0029] Examples of methods for producing the niobium oxide sol include dissolving niobium oxide in hydrofluoric acid, adding the resulting solution to aqueous ammonia, filtering and washing to obtain a niobium hydroxide slurry, adding oxalic acid dihydrate and then water, and allowing the reaction to proceed under reflux with stirring to obtain a uniform solution of niobium oxide colloidal particles. Citric acid or a salt thereof is then added, followed by stirring and mixing. If necessary, a basic compound such as ammonia may be added to the resulting niobium oxide sol to adjust the pH to a desired level. Whether a uniform niobium oxide colloidal particle solution has been obtained can be determined by the color of the slurry; a bluish color indicates a uniform state.

[0030] The niobium oxide sol that can be used in the cationic electrodeposition coating composition of the present invention may be a niobium oxide sol solution stabilized with oxalic acid that has been further stabilized by adding citric acid. The cationic electrodeposition coating composition of the present invention can be prepared by diluting the niobium oxide sol to the required concentration or by mixing other components, as needed, and remains stable for extended periods after preparation without causing thickening, gelation, precipitation, or the like. The key point is that the niobium oxide sol used in the cationic electrodeposition coating composition of the present invention is highly stabilized with citric acid or a salt thereof, and the amount of oxalic acid or a salt thereof added during the preparation of the niobium oxide sol is not particularly limited. This is advantageous in that the stability of the niobium oxide colloidal particles is not reduced even when mixed with other components contained in the cationic electrodeposition coating composition of the present invention, such as a blocked polyisocyanate curing agent (C), a rust prevention auxiliary (D) such as silica, a silane coupling agent, a titanium coupling agent, or a mixture thereof, a phosphate compound (E), a polyamidine compound (F), a pigment (G), or a curing catalyst (H).

[0031] The amount of citric acid or a salt thereof added to the cationic electrodeposition coating composition of the present invention is preferably within the range of a molar ratio of 0.02 (lower limit) to 1.0 (upper limit) relative to Nb in the cationic electrodeposition coating composition. If the amount of citric acid or a salt thereof added is less than 0.02 (in molar ratio), stability when other components are added will be insufficient, whereas if it exceeds 1.0, the stabilizing effect commensurate with the amount added will no longer be obtained, which is uneconomical.

[0032] The niobium oxide colloidal particles preferably have an average particle size of 100 nm or less. The smaller the average particle size, the more stable and dense a niobium oxide treatment coating film is formed, and therefore rust prevention can be stably imparted to the substrate. The average particle size of the niobium oxide colloidal particles can be measured using a particle size distribution measuring device that uses dynamic scattered light, such as a NICOMP Model-370 (manufactured by PACIFIC SCIENTIFIC).

[0033] The cationic electrodeposition coating composition of the present invention is a coating composition in which the niobium oxide colloidal particles are mixed with the Nb in the colloidal particles by the addition of Nb２ O ５ When calculated as 1% by mass or more, the content is preferably 1% by mass or more relative to the total nonvolatile content of the cationic electrodeposition coating composition. If the content is less than 1% by mass, sufficient rust prevention properties cannot be obtained, which is not preferable. The lower limit of the content is more preferably 2% by mass, and even more preferably 3% by mass. The upper limit of the content is more preferably 30% by mass, and even more preferably 15% by mass.

[0034] <Blocked Polyisocyanate Curing Agent (C)> A blocked polyisocyanate curing agent (C) (hereinafter sometimes simply referred to as curing agent (C)) may also be incorporated into the cationic electrodeposition coating composition. In cationic electrodeposition coatings, the blocked polyisocyanate curing agent (C) usually reacts with reactive groups (specifically, hydroxyl groups or amino groups) in the aminated epoxy resin (A), which is a coating film-forming component, to form a cured coating film. However, even without the blocked polyisocyanate curing agent (C), the cationic electrodeposition coating composition of the present invention can be used as a lacquer-like coating film formation method (coating film formation without an active curing reaction) in which niobium is precipitated on a metal substrate (particularly, a galvanized steel sheet, a cold-rolled steel sheet, or an aluminum substrate), and then the aminated epoxy resin is further precipitated to form a coating film. Therefore, the blocked polyisocyanate curing agent (C) is described as an additive. Usually, cationic electrodeposition coating compositions contain a blocked polyisocyanate curing agent (C) and are often actively cured by heating.

[0035] The blocked polyisocyanate curing agent (C) can be prepared by blocking a polyisocyanate with a capping agent.

[0036] Examples of polyisocyanates include aliphatic diisocyanates such as hexamethylene diisocyanate (including trimer), tetramethylene diisocyanate, and trimethylhexamethylene diisocyanate; alicyclic polyisocyanates such as isophorone diisocyanate and 4,4'-methylenebis(cyclohexyl isocyanate); and aromatic diisocyanates such as 4,4'-diphenylmethane diisocyanate, tolylene diisocyanate, and xylylene diisocyanate.

[0037] Preferred examples of the sealant include monohydric alkyl (or aromatic) alcohols such as n-butanol, n-hexyl alcohol, 2-ethylhexanol, lauryl alcohol, phenol carbinol, and methylphenyl carbinol; cellosolves such as ethylene glycol monohexyl ether and ethylene glycol mono-2-ethylhexyl ether; polyether-type both-terminal diols such as polyethylene glycol, polypropylene glycol, and polytetramethylene ether glycol phenol; polyester-type both-terminal polyols obtained from diols such as ethylene glycol, propylene glycol, and 1,4-butanediol and dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, suberic acid, and sebacic acid; phenols such as para-t-butylphenol and cresol; oximes such as dimethyl ketoxime, methyl ethyl ketoxime, methyl isobutyl ketoxime, methyl amyl ketoxime, and cyclohexanone oxime; and lactams represented by ε-caprolactam and γ-butyrolactam.

[0038] The blocked polyisocyanate curing agent (C) preferably has a blocking rate of 100%, which improves the storage stability of the coating composition.

[0039] The content of the curing agent (typically, a blocked polyisocyanate curing agent (C)) is set taking into consideration the amount, structure, etc. of the film-forming resin (typically, an aminated epoxy resin (A)). Specifically, a sufficient amount of curing agent is used to react with the active hydrogen-containing functional groups, such as primary amino groups, secondary amino groups, and hydroxyl groups, possessed by the film-forming resin. The curing agent is blended, for example, so that the solids mass ratio of the film-forming resin to the curing agent (film-forming resin / curing agent) is 90 / 10 to 50 / 50, more preferably 80 / 20 to 65 / 35. The fluidity and curing speed of the coating composition are controlled by the solids mass ratio of the film-forming resin to the curing agent.

[0040] The cationic electrodeposition coating composition may contain a curing agent other than the blocked polyisocyanate curing agent (C) as necessary. Examples of other curing agents include organic curing agents such as melamine resins or phenolic resins, and silane coupling agents, which are rust prevention aids explained as component (D) below. Of all the curing agents contained in the cationic electrodeposition coating composition, 80 mass % or more, even 90 mass % or more, and particularly 100 mass % may be the blocked polyisocyanate curing agent (C).

[0041] <Anti-rust auxiliary (D) selected from the group consisting of silica, silane coupling agents, titanium coupling agents, and mixtures thereof> The cationic electrodeposition coating composition of the present invention may contain an anti-rust auxiliary (D) selected from the group consisting of silica, silane coupling agents, titanium coupling agents, and mixtures thereof. These are used in combination with the niobium compound (B) to synergistically improve the anti-rust performance, so they are considered as anti-rust auxiliary. Examples of silica include normal water-dispersible silica.

[0042] The water-dispersible silica is not particularly limited, and examples thereof include spherical silica, chain silica, and aluminum-modified silica, each containing little impurities such as sodium. The spherical silica is not particularly limited, and examples thereof include colloidal silica such as "Snowtex N," "Snowtex O," "Snowtex OXS," and "Snowtex UP" (all manufactured by Nissan Chemical Industries, Ltd.), and fumed silica such as "Aerosil" (manufactured by Nippon Aerosil Co., Ltd.). The chain silica is not particularly limited, and examples thereof include silica gel such as "Snowtex PS-M" and "Snowtex PS-MO" (both manufactured by Nissan Chemical Industries, Ltd.). The aluminum-modified silica is exemplified by commercially available silica gel such as "Adelite AT-20A" (manufactured by Asahi Denka Kogyo Co., Ltd.).

[0043] When the cationic electrodeposition coating composition of the present invention contains the above-mentioned water-dispersible silica, the SiO ２ The content is preferably 30% by mass or less based on the total nonvolatile content in the cationic electrodeposition coating composition. If it exceeds 30% by mass, the coating becomes brittle and the rust prevention properties decrease. The upper limit is more preferably 30% by mass, and even more preferably 3% by mass.

[0044] Silane coupling agents and titanium coupling agents are preferred in that they can improve adhesion to metal surfaces, and further act as crosslinking agents for the aminated epoxy resin (A), thereby improving corrosion resistance.

[0045] The silane coupling agent is not particularly limited, and examples thereof include vinyl methoxysilane, vinyl trimethoxysilane, vinyl ethoxysilane, vinyl triethoxysilane, 3-aminopropyl triethoxysilane, 3-glycidoxypropyl trimethoxysilane, 3-methacryloxypropyl trimethoxysilane, 3-mercaptopropyl trimethoxysilane, N-(1,3-dimethylbutylidene)-3-(triethoxysilyl)-1-propanamine, N,N'-bis[3-(trimethoxysilyl)propyl]ethylenediamine, N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane, and N-(β-aminoethyl)-γ-aminopropyl Examples of the silane include 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, and N-[2-(vinylbenzylamino)ethyl]-3-aminopropyltrimethoxysilane.

[0046] Among these, particularly preferred silane coupling agents include vinyl methoxy silane, vinyl ethoxy silane, 3-aminopropyl triethoxy silane, 3-glycidoxypropyl trimethoxy silane, 3-methacryloxypropyl trimethoxy silane, 3-mercaptopropyl trimethoxy silane, N-(1,3-dimethylbutylidene)-3-(triethoxysilyl)-1-propanamine, and N,N'-bis[3-(trimethoxysilyl)propyl]ethylenediamine. The above silane coupling agents may be used alone or in combination of two or more.

[0047] The titanium coupling agent is not particularly limited, and examples thereof include isopropyl triisostearoyl titanate, isopropyl tri-n-dodecylbenzenesulfonyl titanate, isopropyl tris(dioctylpyrophosphate)titanate, tetraisopropyl bis(dioctylphosphite)titanate, tetraoctyl bis(ditridecylphosphite)titanate, tetra(2,2-diallyloxymethyl-1-butyl)bis(di-tridecyl)phosphite titanate, bis(dioctylpyrophosphate)oxyacetate titanate, bis(dioctylpyrophosphate)ethylene titanate, isopropyl trioctanoyl titanate, isopropyl dimethacryloylisostearoyl titanate, isopropyl isostearoyl diacryl titanate, isopropyl tri(dioctylphosphate)titanate, and isopropyl tricumylphenyl Titanate, isopropyl tri(N-aminoethyl-aminoethyl)titanate, tetraisopropyl titanate, tetra normal butyl titanate, butyl titanate dimer, tetrakis(2-ethylhexyl)titanate, tetrastearyl titanate, tetramethyl titanate, diethoxybis(acetylacetonato)titanium, diisopropylbis(acetylacetonato)titanium, diisopropoxybis(ethylacetoacetate)titanium, isopropoxy(2-ethyl-1,3-hexanediolato)titanium, di(2-ethylhexoxy)bis(2-ethyl-1,3-hexanediolato)titanium, di-n-butoxybis(triethanolaminato)titanium, tetraacetylacetonate titanium, hydroxybis(lactato)titanium, dicumylphenyloxyacetate titanate, diisostearoylethylene titanate, and the like.

[0048] As the titanium coupling agent, commercially available products can be used, for example, KR-TTS, KR-46B, KR-55, KR-41B, KR-38S, KR-138S, KR-238S, 338X, KR44, KR9SA, etc., which are the PLENACT series manufactured by Ajinomoto Fine-Techno Co., Ltd.; TA-10, T, etc., which are the ORGATIX series manufactured by Matsumoto Fine Chemical Co., Ltd. A-25, TA-22, TA-30, TC-100, TC-200, TC-401, TC-750, etc.; and A-1, B-1, TOT, TST, TAA, TAT, TLA, TOG, TBSTA, A-10, TBT, B-2, B-4, B-7, B-10, TBSTA-400, TTS, TOA-30, TSDMA, TTAB, TTOP, etc., manufactured by Nippon Soda Co., Ltd.

[0049] When the cationic electrodeposition coating composition of the present invention contains the above-mentioned silane coupling agent or titanium coupling agent (sometimes simply referred to as "coupling agent"), the content of the silane coupling agent or titanium coupling agent is preferably within the range of a lower limit of 0.5% by mass and an upper limit of 30% by mass, based on the total nonvolatile content of the cationic electrodeposition coating composition. If the content of the coupling agent is less than 0.5% by mass, the rust prevention auxiliary function may be insufficient, while if it exceeds 30% by mass, the effect of addition becomes saturated, making it uneconomical, and gelation, thickening, etc. of the composition may occur, reducing the liquid stability, which is not preferred. The lower limit is more preferably 1% by mass, and the upper limit is more preferably 20% by mass.

[0050] <Phosphate Compound (E)> The cationic electrodeposition coating composition of the present invention preferably contains a phosphate compound (E). The phosphate compound contained in the cationic electrodeposition coating composition of the present invention forms a metal phosphate on the surface of the substrate, thereby further improving the rust prevention properties of the surface treatment film.

[0051] The phosphate compound is not particularly limited as long as it is a compound that can form phosphate ions in water, and examples thereof include phosphoric acids (e.g., phosphorous acid, hypophosphorous acid, organic phosphoric acid, organic phosphorous acid, phosphoric acid, phosphonic acid, etc.); phosphate salts (e.g., Na ３ P.O. ４ , Na２ HPO ４ , NaH ２ P.O. ４ , zinc phosphate, etc.); condensed phosphoric acids (for example, condensed phosphoric acid, polyphosphoric acid, metaphosphoric acid, pyrophosphoric acid, ultraphosphoric acid, etc.) or salts thereof.

[0052] When the cationic electrodeposition coating composition of the present invention contains the above-mentioned phosphate compound, the content of the phosphate compound in the cationic electrodeposition coating composition is preferably within the range of a lower limit of 0.1 mass% and an upper limit of 20 mass% based on the total solids of the cationic electrodeposition coating composition. If the content is less than 0.1 mass%, the effect of improving corrosion resistance may be insufficient, while if it exceeds 20 mass%, excessive etching of the zinc-plated steel sheet or gelation of the composition may occur, which is not preferable. The lower limit is more preferably 0.5 mass%, and the upper limit is more preferably 10 mass%.

[0053] <Polyamidine Compound (F)> The polyamidine compound (F) is added to improve the corrosion resistance of the edge portion of the metal substrate. Specifically, the polyamidine compound (F) is a cyclic polyamidine compound represented by the following general formula (I): (In the formula, R １ and R ２ are each independently a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms, and X is an anion.

[0054] Such polyamidine compounds having a cyclic structure are easily deposited on the edge because they have an electric charge, and further increase the viscosity of the cationic electrodeposition coating composition, which is thought to improve the edge rust prevention properties.

[0055] R １ and R ２ may each independently be a hydrogen atom. X is, for example, a halogen ion. Examples of the halogen ion include F － , Cl － ,Br － , I － Among them, halogen ions are Cl because they are easily available. － It may be.

[0056] The cyclic polyamidine compound can be synthesized, for example, by hydrolyzing a copolymer of N-vinylcarboxylic acid amide and unsaturated nitrile in the presence of acid. During the hydrolysis in the presence of acid, the amide group derived from the N-vinylcarboxylic acid amide is hydrolyzed and reacts with the cyano group of the unsaturated nitrile to form a cyclic amidine skeleton.

[0057] Examples of N-vinylcarboxylic acid amides include N-vinylacetamide, N-vinyl-N-methylacetamide, N-vinylformamide, N-methyl-N-vinylformamide, N-vinylpropionic acid amide, and N-vinylbutyric acid amide. These may be used alone or in combination of two or more.

[0058] The unsaturated nitrile may have, for example, 3 to 18 carbon atoms, or 3 to 9 carbon atoms. Specific examples of the unsaturated nitrile include acrylonitrile; α-alkyl acrylonitriles such as methacrylonitrile and ethacrylonitrile; fumaronitrile; and α-halogeno acrylonitriles such as α-chloro acrylonitrile and α-bromo acrylonitrile. These may be used alone or in combination of two or more.

[0059] The acid used for the hydrolysis is, for example, a strong inorganic acid, and specific examples thereof include hydrochloric acid, nitric acid, and p-toluenesulfonic acid.

[0060] The cyclic polyamidine compound may be a partial hydrolysis product of a copolymer of N-vinylcarboxylic acid amide and an unsaturated nitrile. Therefore, the cyclic polyamidine compound may be a copolymer of the above-mentioned structural unit (I) and, for example, a copolymer of the following two general formulas: (In the above two formulas, R １ , R ２ and R ３are each independently a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms.) When these structural units (II) and (III) are arranged as shown in the following chemical formula, hydrolysis gives the amidine structure of the structural unit (I): (In the formula, R １ , R ２ and R ３ are each independently a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms.

[0061] The number average molecular weight of the cyclic polyamidine compound is, for example, 50,000 or more. This allows a small amount to be used to obtain the effect of improving edge rust prevention. The number average molecular weight of the cyclic polyamidine compound may be 80,000 or more, 100,000 or more, or 300,000 or more. The number average molecular weight of the cyclic polyamidine compound may be 4,000,000 or less, 3,500,000 or less, 3,200,000 or less, or 3,000,000 or less. In one aspect, the number average molecular weight of the cyclic polyamidine compound may be 50,000 or more and 4,000,000 or less, or 80,000 or more and 3,200,000 or less.

[0062] The solid content mass of the polyamidine compound (F) may be 20 ppm or more of the solid content mass of the cationic electrodeposition coating composition. The solid content mass of the polyamidine compound (F) may be 1,200 ppm or less. Even with such a small amount of polyamidine compound (F) added, the effect of improving edge rust prevention can be obtained. The solid content mass of the polyamidine compound (F) may be 23 ppm or more, 25 ppm or more, or 50 ppm or more. The solid content mass of the polyamidine compound (F) may be 1,000 ppm or less, 700 ppm or less, or 200 ppm or less. In one embodiment, the solids mass of the polyamidine compound (F) is 20 ppm or more and 1,200 ppm or less, and may be 25 ppm or more and 1,000 ppm or less, 25 ppm or more and 700 ppm or less, or 50 ppm or more and 200 ppm or less.

[0063] <Pigment (G)> The pigment is a pigment that is generally used in cationic electrodeposition coating compositions. Examples of pigments include color pigments such as titanium white (titanium dioxide), zinc oxide, carbon black, and red iron oxide; extender pigments such as kaolin (for example, calcined kaolin), talc, aluminum silicate, calcium carbonate, mica, and clay; and rust-preventive pigments such as iron phosphate, aluminum phosphate, calcium phosphate, aluminum tripolyphosphate, aluminum phosphomolybdate, and aluminum zinc phosphomolybdate. The coating composition may contain an extender pigment, as this can further improve edge rust prevention.

[0064] The solid content of a cationic electrodeposition coating composition refers to all components contained in the coating composition that remain in solid form even after removal of the solvent. The pigment is usually added to the cationic electrodeposition coating composition as a pigment dispersion paste containing a pigment dispersing resin and the pigment.

[0065] (Pigment Dispersion Resin) The pigment dispersion resin is a resin for dispersing pigments. Examples of the pigment dispersion resin include pigment dispersion resins having a cationic group, such as modified epoxy resins having at least one group selected from a quaternary ammonium group, a tertiary sulfonium group, and a primary amino group. Specific examples of the pigment dispersion resin include quaternary ammonium group-containing epoxy resins and tertiary sulfonium group-containing epoxy resins. Examples of the aqueous solvent include ion-exchanged water and ion-exchanged water containing a small amount of alcohol.

[0066] <Curing catalyst (H)> The cationic electrodeposition coating composition may contain a curing catalyst. There are no particular limitations on the curing catalyst, and those known in the coating field can be used. Examples of curing catalysts include organotin compounds and bismuth compounds. Examples of organotin compounds include dibutyltin oxide, dioctyltin oxide, dioctyltin dilaurate, dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin diacetate, dibutyltin dibenzoate, and dioctyltin dibenzoate. Examples of bismuth compounds include bismuth oxide, bismuth hydroxide, bismuth subsalicylate, and bismuth subnitrate.

[0067] From the viewpoint of environmental load, the content of the curing catalyst (particularly, the organotin compound) may be 0.5 mass % or less, or 0.25 mass % or less, of the solid content of the coating composition.

[0068] <Other Components> The coating composition may contain additives commonly used in the coating field, such as organic solvents, surfactants such as drying inhibitors and antifoaming agents, viscosity modifiers such as acrylic resin microparticles, anti-repellent agents, and inorganic rust inhibitors, as needed. Examples of organic solvents include ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol monoethylhexyl ether, propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, and propylene glycol monophenyl ether. Examples of inorganic rust inhibitors include vanadium salts, copper salts, iron salts, manganese salts, magnesium salts, and calcium salts.

[0069] Furthermore, in addition to the above, known auxiliary complexing agents, buffering agents, smoothing agents, stress relaxation agents, glossing agents, semi-glossing agents, antioxidants, ultraviolet absorbers, etc. may be included depending on the purpose.

[0070] <Preparation of Cationic Electrodeposition Coating Composition> The coating composition is prepared by mixing a coating film-forming resin (typically, an aminated epoxy resin (A)), a niobium compound (B), and, if necessary, other additive components, specifically, a blocked polyisocyanate curing agent (C), a rust-preventive auxiliary such as silica, a silane coupling agent, a titanium coupling agent, or a mixture thereof (D), a phosphoric acid compound (E), a polyamidine compound (F), a pigment (G), or a curing catalyst (H), etc., by a commonly used method.

[0071] The other components and additive components may be added to the resin emulsion, may be added to the pigment dispersion paste, or may be added during or after mixing of the resin emulsion and the pigment dispersion paste.

[0072] (Preparation of Resin Emulsion) The resin emulsion can be prepared by dissolving the aminated epoxy resin (A) and other film-forming resins, and the blocked polyisocyanate curing agent (C) and other curing agents in an organic solvent to prepare solutions, mixing these solutions, and then neutralizing the mixture with a neutralizing acid.

[0073] Examples of the neutralizing acid include organic acids such as methanesulfonic acid, sulfamic acid, lactic acid, dimethylolpropionic acid, formic acid, acetic acid, etc. The neutralizing acid may be one or more selected from the group consisting of formic acid, acetic acid, and lactic acid.

[0074] The solid content of the resin emulsion may be, for example, 25% by mass or more and 50% by mass or less, or 35% by mass or more and 45% by mass or less, based on the total amount of the resin emulsion. The solid content of the resin emulsion refers to all components contained in the resin emulsion that remain in solid form even after removal of the solvent. Specifically, the solid content of the resin emulsion refers to the aminated epoxy resin (A), the blocked polyisocyanate curing agent (C), and other solid components added as needed, contained in the resin emulsion.

[0075] The amount of neutralizing acid used, expressed as the equivalent ratio of the neutralizing acid to the equivalent of the amino groups in the aminated epoxy resin, may be 10% or more and 100% or less, or 20% or more and 70% or less. Hereinafter, the equivalent ratio of the neutralizing acid to the equivalent of the amino groups in the aminated epoxy resin will be referred to as the neutralization rate. A neutralization rate of 10% or more ensures affinity for water and improves water dispersibility.

[0076] (Method for preparing pigment dispersion paste) The pigment dispersion paste is prepared by mixing a pigment dispersion resin, a solid substance such as a pigment (in the present invention, any one of the niobium compound (B), the rust prevention aid (D), the phosphate compound (E), the pigment (G), and the curing catalyst (H), or a mixture thereof), and, if necessary, a polyamidine compound (F). The solid content by mass of the pigment dispersion resin in the pigment dispersion paste is not particularly limited, and may be, for example, 20 parts by mass or more and 100 parts by mass or less per 100 parts by mass of the pigment.

[0077] The solid content mass of the pigment dispersion paste is, for example, 40% by mass or more and 70% by mass or less, and may be 50% by mass or more and 60% by mass or less.

[0078] The solid content of the pigment dispersion paste refers to all components contained in the pigment dispersion paste that remain solid even after removal of the solvent, specifically, the pigment dispersion resin, pigment, and other solid components added as needed.

[0079] [Method for producing an electrodeposition-coated article] An electrodeposition coating film is formed by electrodeposition coating an article using a coating composition. An electrodeposition-coated article having an electrodeposition coating film is produced by a method (production method 1) comprising the steps of immersing the article in the cationic electrodeposition coating composition according to this embodiment, applying a voltage between the article and a counter electrode to form an uncured electrodeposition coating film on the article, and heating the coating film at a temperature of 75°C or higher and 200°C or lower to obtain a cured electrodeposition coating film.

[0080] As described above, the cationic electrodeposition coating composition contains the aminated epoxy resin (A), the niobium compound (B), and, if necessary, additive components (blocked polyisocyanate curing agent (C), rust prevention auxiliary agent (D), phosphate compound (E), polyamidine compound (F), pigment (G), curing catalyst (H), or a combination thereof).

[0081] (1) Formation of an uncured electrodeposition coating film After immersing a substrate in a cationic electrodeposition coating composition, a voltage is applied between the substrate as a cathode and a counter electrode (anode), resulting in the deposition of an uncured electrodeposition coating film on the substrate.

[0082] (Application Conditions) The voltage is, for example, 50 V or more and 450 V or less. The bath liquid temperature is, for example, 10° C. or more and 45° C. or less. The time for applying the voltage is not particularly limited, and is, for example, 2 minutes or more and 5 minutes or less.

[0083] (Substrate) The material of the substrate is not particularly limited as long as it is electrically conductive. The shape of the substrate is also not particularly limited, and it may be flat or have a complex three-dimensional shape. Examples of substrates 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, and tin-plated steel sheets, as well as those that have undergone chemical conversion treatment (e.g., surface treatment using phosphate, zirconium salt, etc.). When chemically treating with phosphate, the substrate may be surface-conditioned with a zinc-, titanium-, or manganese-based surface conditioner prior to chemical conversion treatment. This results in denser crystals in the zinc phosphate coating. In the present invention, substrates that have not undergone chemical conversion treatment, particularly zinc-plated steel sheets and aluminum substrates, can be used as is without chemical conversion treatment. By using the material without chemical conversion treatment, the chemical conversion treatment step can be omitted, which is very advantageous.

[0084] (2) Curing of Electrodeposition Coating Film The formed uncured electrodeposition coating film is washed with water, if necessary, and then heated at a temperature of 75° C. to 200° C. This causes a curing reaction to occur, resulting in a cured electrodeposition coating film.

[0085] (Curing Conditions) The curing temperature may be 100° C. or higher, or may be 110° C. or higher. The curing temperature may be, for example, 180° C. or lower, or may be 150° C. or lower. The heating time is not particularly limited, and is, for example, 10 to 30 minutes.

[0086] [Electrodeposition-coated product] An electrodeposition-coated product has a substrate and an electrodeposition coating film formed on the substrate using the cationic electrodeposition coating composition described above. The electrodeposition coating film is cured. The electrodeposition-coated product is produced, for example, by the method described above. The electrodeposition-coated product has excellent rust prevention properties. The electrodeposition-coated product also has a good appearance.

[0087] From the viewpoint of rust prevention, the thickness of the cured electrodeposition coating film may be 5 μm or more and 60 μm or less. The thickness of the cured electrodeposition coating film may be 10 μm or more. The thickness of the cured electrodeposition coating film may be 25 μm or less.

[0088] The present invention will be described in more detail with reference to the following examples, but is not limited thereto. In the examples, "parts" and "%" are by weight unless otherwise specified.

[0089] [Production Example 1] Production of aminated epoxy resin (A1) 26 parts of butyl cellosolve, 940 parts of bisphenol A-type epoxy resin (trade name DER-331J, manufactured by The Dow Chemical Company), 380 parts of bisphenol A, 58 parts of phenol, and 2 parts of dimethylbenzylamine were added to a reaction vessel, and the internal temperature was maintained at 120°C. The reaction was continued until the epoxy equivalent reached 1,100 g / eq, and then the reaction vessel was cooled to a temperature of 110°C. 60 parts of diethanolamine (DETA), 20 parts of N-methylethanolamine (MMA), and 85 parts of diethylenetriamine diketimine (diketimine: methyl isobutyl ketone solution with a solids content of 73%) were added, and the mixture was allowed to react at 140°C for 1 hour to obtain an aminated epoxy resin.

[0090] [Production Example 2] Production of aminated epoxy resin (A2) 198 parts by mass of DER-331J (diglycidyl ether of bisphenol A, manufactured by The Dow Chemical Company) and 108 parts by mass of bisphenol A were placed in a reaction vessel equipped with a stirrer, a condenser, a nitrogen inlet tube, and a thermometer, and dissolved in 45.7 parts by mass of DPnB (propylene glycol monobutyl ether) and 56.5 parts by mass of methyl isobutyl ketone (MIBK). 0.8 parts by mass of dimethylbenzylamine was added, and the reaction was continued at 120°C until the epoxy equivalent reached 4,000, yielding an aminated epoxy resin having a bisphenol skeleton as a raw material. After completion of the reaction, 62.5 parts by mass of DPnB and 34.9 parts by mass of ketimine were added, and the mixture was allowed to react at 120°C for 1 hour to obtain aminated epoxy resin (A2) having a bisphenol skeleton.

[0091] The obtained aminated epoxy resin had a number average molecular weight of 6000. The obtained amine-modified epoxy resin (A2) was added to a mixed liquid of 5.2 parts by mass of 90% acetic acid and 482.5 parts by mass of ion-exchanged water and thoroughly stirred, and then 163.3 parts by mass of the mixture of MIBK and water was distilled off under reduced pressure at 50°C to obtain a water dispersion of aminated epoxy resin (A2) (solid content concentration: 38% by mass).

[0092] [Production Example 3] Production of Blocked Polyisocyanate Curing Agent (C) 1,370 parts of polymethylene polyphenyl polyisocyanate (polymeric MDI) and 732 parts of methyl isobutyl ketone (MIBK) were charged into a reaction vessel and heated to 60°C. 300 parts of butyl diglycol ether and butyl cellosolve 1,330 were added dropwise at 60°C over 2 hours. After further heating at 75°C for 4 hours, IR spectroscopy confirmed that absorption due to isocyanate groups had disappeared. After allowing to cool, 27 parts of MIBK was added to obtain blocked polyisocyanate curing agent (C).

[0093] [Production Example 4] Preparation of pigment dispersion resin 2,220 parts of isophorone diisocyanate and 342.1 parts of methyl isobutyl ketone were charged into a reaction vessel equipped with a stirrer, a cooling tube, a nitrogen inlet tube, and a thermometer. The temperature was raised to 50°C, and 2.2 parts of dibutyltin laurate was added. The temperature was raised to 60°C, and 878.7 parts of methyl ethyl ketone oxime was added. The mixture was then kept at 60°C for 1 hour, and it was confirmed that the NCO equivalent was 348. 890 parts of dimethylethanolamine was then added. The mixture was then kept at 60°C for 1 hour, and it was confirmed by IR that the NCO peak had disappeared. Next, while cooling so as not to exceed 60°C, 1,872.6 parts of 50% lactic acid and 495 parts of deionized water were added to obtain a quaternizing agent.

[0094] 870 parts of tolylene diisocyanate and 49.5 parts of methyl isobutyl ketone were charged into a separate reaction vessel. 667.2 parts of 2-ethylhexanol were added dropwise to the reaction vessel over 2.5 hours while cooling so that the temperature did not exceed 50°C. After completion of the dropwise addition, 35.5 parts of methyl isobutyl ketone were added and the mixture was kept warm for 30 minutes. Thereafter, it was confirmed that the NCO equivalent was 330 to 370, and a half-blocked polyisocyanate was obtained.

[0095] A reaction vessel equipped with a stirrer, a condenser, a nitrogen inlet tube, and a thermometer was charged with 940.0 parts of bisphenol A epoxy resin (trade name DER-331J, manufactured by The Dow Chemical Company) and 38.5 parts of methanol, followed by the addition of 0.1 parts of dibutyltin dilaurate. The mixture was heated to 50°C, and then 87.1 parts of tolylene diisocyanate was added. The mixture was further heated to 100°C, and 1.4 parts of N,N-dimethylbenzylamine was added. The mixture was then maintained at 130°C for 2 hours. At this time, methanol was fractionated using a fractionating column. The mixture was cooled to 115°C, and methyl isobutyl ketone was added until the solids concentration reached 90%. Subsequently, 270.3 parts of bisphenol A and 39.2 parts of 2-ethylhexanoic acid were added, followed by heating and stirring at 125°C for 2 hours. Subsequently, 516.4 parts of the half-blocked polyisocyanate was added dropwise over 30 minutes, followed by heating and stirring for 30 minutes. Furthermore, 1506 parts of polyoxyethylene bisphenol A ether was gradually added and dissolved therein. After cooling to 90°C, the quaternizing agent was added, and the temperature was maintained at 70 to 80°C. After confirming that the acid value was 2 or less, a pigment dispersion resin (resin solids content 30%) was obtained.

[0096] Preparation Example 1: Preparation of Pigment Dispersion Paste A 116.7 parts of ion-exchanged water, 15.7 parts of 50% lactic acid aqueous solution, and 20.3 parts of bismuth oxide were mixed and stirred in a sand mill. 169.4 parts of the pigment dispersion resin obtained in Production Example 4 and 0.7 parts of a polyoxyalkylene-type nonionic surfactant were added to the mixture, and the mixture was stirred at 60°C for 1 hour using a dissolver at 3,000 rpm. Next, 338.7 parts of the pigment dispersion resin were added and stirred, followed by the addition of 6.8 parts of zinc oxide pigment, 67.7 parts of carbon black, and 264.1 parts of calcined kaolin. The mixture was dispersed in a sand mill at 40°C for 20 minutes at 1,800 rpm until the particle size reached 10 μm or less, yielding a pigment paste A with a solids concentration of 53% by mass.

[0097] [Preparation Example 2] Preparation of Pigment Dispersion Paste B 117 parts of ion-exchanged water, 15.7 parts of 50% lactic acid aqueous solution, and 20.3 parts of bismuth oxide were stirred and mixed in a sand mill. 169.4 parts of the pigment dispersion resin obtained in Preparation Example 4 and 0.7 parts of a polyoxyalkylene-type nonionic surfactant were added to the mixture, and the mixture was stirred at 60°C for 1 hour using a dissolver at 3,000 rpm. Next, 338.7 parts of the pigment dispersion resin were added and stirred, followed by the addition of 6.8 parts of zinc oxide pigment, 67.7 parts of carbon, 237.7 parts of calcined kaolin, and 26.4 parts of pigment silica. The mixture was dispersed in a sand mill at 40°C for 20 minutes at 1,800 rpm until the particle size reached 10 μm or less, yielding a pigment paste B with a solids concentration of 53% by mass.

[0098] Preparation Example 3: Preparation of Pigment Dispersion Paste C 117 parts of ion-exchanged water, 15.7 parts of 50% lactic acid aqueous solution, and 20.3 parts of bismuth oxide were stirred and mixed in a sand mill. 169.4 parts of the pigment dispersion resin obtained in Preparation Example 4 and 0.7 parts of a polyoxyalkylene-type nonionic surfactant were added to the mixture, and the mixture was stirred at 3,000 rpm with a dissolver at 60°C for 1 hour. Next, 338.7 parts of the pigment dispersion resin was added and stirred. 6.8 parts of zinc oxide pigment, 67.7 parts of carbon, 237.7 parts of calcined kaolin, and 26.4 parts of a zinc phosphate-based rust-preventive pigment (product name LF Bousei PW-2, manufactured by Kikuchi Color Co., Ltd.) were then added and dispersed in a sand mill at 40°C for 20 minutes at 1,800 rpm until the particle size reached 10 μm or less, yielding Pigment Paste B with a solids concentration of 53% by mass.

[0099] Example 1 Preparation of Resin Emulsion 450 parts (solids content) of the aminated epoxy resin (A1) obtained in Production Example 1 and 240 parts (solids content) of the blocked polyisocyanate curing agent (C) obtained in Production Example 2 were mixed, and ethylene glycol mono-2-ethylhexyl ether was added thereto so that the amount was 0.7% (4.5 parts) based on the solids content. Next, acetic acid was added to neutralize the mixture to a neutralization rate of 45%, and the mixture was slowly diluted with ion-exchanged water to obtain a resin emulsion.

[0100] (Production of Cationic Electrodeposition Coating Composition) Into a stainless steel container, 654.4 parts of ion-exchanged water, 687.8 parts of emulsion of amine-modified epoxy resin (A1), 157.8 parts of pigment dispersion paste, and niobium oxide sol (Nb ２ O ５ ; 6%, average particle size 5 nm, pH 8, NH ３ / Niobium oxide (Nb ２ O ５ ) (molar ratio=0.5 to 1.5, manufactured by Taki Chemical Co., Ltd.) was added and mixed, and then aged at 40° C. for 16 hours to obtain cationic electrodeposition coating composition A1.

[0101] (2) Preparation of electrodeposition coated objects Cold-rolled steel sheets, galvanized steel sheets, and aluminum substrates were degreased by immersion in Surf Cleaner EC90 (manufactured by Nippon Paint Co., Ltd.) at 50° C. for 2 minutes, followed by rinsing with deionized water.

[0102] To cationic electrodeposition coating composition A1, a required amount of ethylene glycol monohexyl ether was added so that the thickness of the electrodeposition coating film after curing would be 20 μm. Then, a galvanized steel sheet and an aluminum substrate were immersed, and a voltage was applied under the conditions of increasing the pressure for 30 seconds, and once the voltage reached the voltage conditions specified in each example, maintaining the voltage for 150 seconds, thereby depositing an uncured electrodeposition coating film on the substrate. The resulting uncured electrodeposition coating film was heat-cured at 160° C. for 15 minutes, yielding an electrodeposition-coated product having a cured electrodeposition coating film thickness of 20 μm.

[0103] The resulting coated objects (cold-rolled steel sheet, galvanized steel sheet, and aluminum substrate) were subjected to corrosion tests (cyclic corrosion tests) and evaluated for appearance using the methods described below. The results are shown in Table 1. Table 1 also lists the amounts of the components used (expressed as mass %). In Table 1, "appearance" was evaluated for both the galvanized steel sheet and the aluminum substrate, but the results were the same, so they are not listed separately for each coated object.

[0104] <Cycle Corrosion Test (CCT)> Using both a zinc-plated steel sheet and an aluminum substrate, which were electrodeposition-coated products, cross-cut scratches were made with a knife in the coating film of the cured electrodeposition-coated sheet so as to reach the substrate, and 100 cycles of JASO M609-91 "Corrosion Test Method for Automotive Materials" were performed. After that, the occurrence of rust and blisters from the cross-cut area was observed, and the corrosion resistance in accordance with an actual corrosive environment was evaluated for both the zinc-plated steel sheet and the aluminum substrate. The evaluation criteria were as follows: Evaluation criteria 5: The maximum width of the rust or blister is less than 7.5 mm from the cut part (both sides). No blisters other than the cut part. 4: The maximum width of the rust or blister is 5 mm to less than 6 mm from the cut part (both sides). Blisters are present other than the cut part. 3: The maximum width of the rust or blister is 6 mm to less than 10 mm from the cut part (both sides). 2: The maximum width of the rust or blister is 10 mm to less than 12.5 mm from the cut part (both sides). 1: The maximum width of the rust or blister is 12.5 mm or more from the cut part (both sides). A pass is 3 or above.

[0105] <Appearance> The arithmetic mean roughness (Ra) of the roughness curve of the cured electrodeposition coating was measured using an evaluation type surface roughness measuring instrument (SURFTEST SJ-201P, manufactured by Mitsutoyo Corporation) according to a method conforming to JIS-B0601. Seven measurements were made using a sample with a 2.5 mm wide cutoff (5 sections), and the Ra value (μm) was obtained by averaging the top and bottom erase results. The smaller the Ra value, the less unevenness there is and the better the coating appearance. 5: When Ra is less than 0.2 μm 4: When Ra is 0.2 μm or more but less than 0.3 μm 3: When Ra is 0.3 μm or more but less than 0.4 μm 2: When Ra is 0.4 μm or more but less than 0.5 μm 1: When Ra is 0.5 μm or more.

[0106] Example 2: A cationic electrodeposition coating composition was prepared in the same manner as in Example 1, and electrodeposition-coated products were produced by electrodeposition-coating a galvanized steel sheet and an aluminum substrate. The galvanized steel sheet and aluminum substrate were degreased by immersion in Surf Cleaner EC90 (Nippon Paint Surf Chemicals) for 2 minutes at 50°C, surface-conditioned by immersion in Surf Fine GL1 (Nippon Paint Surf Chemicals) for 30 seconds at room temperature, and then immersed in Surfdyne SD-5000 (Nippon Paint Surf Chemicals), a zinc phosphate conversion treatment solution, for 2 minutes at 40°C. The resulting electrodeposition-coated products were then subjected to a cyclic corrosion test and evaluated for appearance in the same manner as in Example 1. The results are shown in Table 1.

[0107] [Example 3] In the same manner as in Example 1, cationic electrodeposition coating compositions were prepared in the amounts shown in Table 1 and applied to zinc-plated steel sheets and aluminum substrates to produce electrodeposition-coated articles. The resulting electrodeposition-coated articles were subjected to a cyclic corrosion test and evaluated for appearance in the same manner as in Example 1. Example 3 is an experiment that did not contain pigment (G). The results are shown in Table 1.

[0108] Examples 4 to 10 In the same manner as in Example 1, cationic electrodeposition coating compositions were prepared in the amounts shown in Table 1 and applied to zinc-plated steel sheets and aluminum substrates to produce electrodeposition-coated products. The resulting electrodeposition-coated products were subjected to a cyclic corrosion test and evaluated for appearance in the same manner as in Example 1. The results are shown in Table 1. Example 11 To the composition of Example 1, a 2% aqueous solution of polyamidine compound (F) (Himloc ZP-700, manufactured by Hymo Co., Ltd., number-average molecular weight 3,000,000, partial hydrolyzate of acrylonitrile / N-vinylformamide copolymer) was further added so that the solid content was 0.1 parts by mass of the cationic electrodeposition coating composition. This was then applied to the substrates shown in Table 1 to produce electrodeposition-coated products. The resulting electrodeposition-coated products were subjected to a cyclic corrosion test and evaluated for appearance in the same manner as in Example 1. The results are shown in Table 1.

[0109] Comparative Examples 1 to 4 Cationic electrodeposition coating compositions were obtained in the same manner as in Example 1, except that the niobium compound (B) was not added and the components shown in Table 1 were used instead. The resulting cationic electrodeposition coating compositions were applied to a galvanized steel sheet and an aluminum substrate to produce electrodeposition-coated articles. Comparative Examples 1 and 2 are examples corresponding to Examples 1 and 2 that do not contain a niobium compound. Comparative Example 3 is an example in which a compound containing vanadium was used instead of a niobium compound, and Comparative Example 4 is an example in which a compound containing yttrium was used. The resulting electrodeposition-coated articles were subjected to a cyclic corrosion test and evaluated for appearance in the same manner as in Example 1. The results are shown in Table 1.

[0110]

[0111] The components used in Table 1 are as follows: Niobium oxide colloidal particles: Niobium oxide colloidal particle water dispersion (Nb ２ O ５10%, average particle size: 2000 nm). Silane coupling agent: KBM403, 3-glycidoxypropyltrimethoxysilane; manufactured by Shin-Etsu Chemical Co., Ltd. Silica: Sylysia 550 (silicon dioxide (amorphous); manufactured by Fuji Silysia Chemical Ltd.) Titanium coupling agent: Orgatix TC400 (titanium triethanolamine; Ti; 10.4%; solid content equivalent); manufactured by Matsumoto Fine Chemical Co., Ltd. Phosphonic acid: reagent. Zinc phosphate-based rust preventive pigment: LF Bousei P-W-2 (zinc phosphate); manufactured by Kikuchi Color Co., Ltd. Polyamidine compound (F): Himoloc ZP-700, number average molecular weight 3,000,000, partial hydrolyzate of acrylonitrile / N-vinylformamide copolymer, ratio of structural unit (I) to structural unit (I + II): (I) / (I + II) = 30-40% (molar ratio); manufactured by Hymo Co., Ltd. In the chemical formula of structural unit (I), R １ and R ２ Both are hydrogen, and X represents chlorine. Ammonium metavanadate (V; 43.6%): Reagent. Yttrium nitrate: Reagent.

[0112] All of the cationic electrodeposition coating compositions of the Examples achieved a rating of 3 or higher in the cyclic corrosion test, demonstrating high rust prevention. Comparative Example 1, like Example 1, does not contain a niobium compound, and poor values ​​were observed in the cyclic corrosion test, particularly on galvanized steel sheets. Comparative Example 2 used a zinc phosphate treatment (rust prevention treatment) for the pretreatment of the substrate, and therefore demonstrated excellent rust prevention performance on both galvanized steel sheets and aluminum substrates. Comparative Examples 3 and 4 used a vanadium-containing compound or an yttrium-containing compound instead of a niobium compound, but did not achieve excellent rust prevention performance on these metals.

[0113] The cationic electrodeposition coating composition of the present invention provides a coating film that is excellent in rust prevention and appearance.

Claims

1. A cationic electrodeposition coating composition comprising an aminated epoxy resin (A) and a niobium compound (B).

2. The cationic electrodeposition coating composition according to claim 1, wherein the niobium compound (B) is a niobium oxide sol or niobium oxide colloidal particles obtained by stabilizing a niobium oxide sol.

3. The cationic electrodeposition coating composition according to claim 1 or 2, further comprising a blocked polyisocyanate curing agent (C).

4. The cationic electrodeposition coating composition according to claim 1 or 2, further comprising (D) a rust-preventive auxiliary selected from the group consisting of silica, a silane coupling agent, a titanium coupling agent and mixtures thereof.

5. The cationic electrodeposition coating composition according to claim 1 or 2, further comprising a phosphoric acid compound (E).

6. The cationic electrodeposition coating composition according to claim 1 or 2, further comprising a polyamidine compound (F).

7. The polyamidine compound has the following general formula: (In the formula, R １ and R ２ are each independently a hydrogen atom or a hydrocarbon group having 1 to 3 carbon atoms, and X is an anion.

8. The cationic electrodeposition coating composition according to claim 1 or 2, further comprising a pigment (G).

9. The cationic electrodeposition coating composition according to claim 1 or 2, further comprising a curing catalyst (H).

10. The cationic electrocoating composition according to claim 1 or 2, which is applied to a galvanized steel sheet, a cold-rolled steel sheet or an aluminum substrate without chemical conversion treatment.

11. An electrocoated article comprising: a substrate; and an electrocoating film formed on the substrate from the cationic electrocoating composition according to claim 1 or 2.

12. A method for producing an electrodeposition coated object, comprising the steps of: immersing an object to be coated in the cationic electrodeposition coating composition according to claim 1 or 2, applying a voltage between the object to be coated and a counter electrode to form an uncured electrodeposition coating film on the object to be coated; and heating the uncured electrodeposition coating film at a temperature of 75°C or higher and 200°C or lower to obtain a cured electrodeposition coating film.

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