JP2006083305A - Lead-free cationic electrodeposition coating composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lead-free cationic electrodeposition coating composition capable of obtaining a coated film having corrosion resistance equivalent to or higher than corrosion resistance in the case where a lead compound is used by using metal bismuth colloid particles instead of a lead compound as a corrosion resistance-imparting agent, excellent in long-term storage stability and further not using tin. <P>SOLUTION: The lead-free cationic electrodeposition coating composition comprises an oxazolidone ring-containing amine-modified epoxy resin and metal bismuth colloidal particles. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a lead-free cationic electrodeposition coating composition.

Electrodeposition coating can be applied to the details even if the object has a complicated shape, and it can be applied automatically and continuously. It is widely used as an undercoating method for objects to be coated that requires high rust prevention. Moreover, it is economical because the use efficiency of the paint is extremely high compared with other coating methods, and is widely used as an industrial coating method.

Conventionally, lead compounds such as lead chromate and basic lead silicate have been added to such electrodeposition paints used for electrodeposition coating as corrosion resistance imparting agents. However, in recent years, lead compounds have a negative impact on the environment, so there is a need to reduce the amount used. However, the electrodeposition paints have been made lead-free and lead-free, so that the coating performance, especially the corrosion resistance of the coating, is reduced. There is a problem that decreases.

A technique using a bismuth compound has been proposed as a corrosion resistance imparting agent instead of a lead compound. For example, an electrodeposition coating composition containing a hydroxide such as bismuth hydroxide and an organic tin compound has been proposed, and a lead compound can be obtained by adding a metal hydroxide such as bismuth hydroxide and an organic tin compound. It is disclosed that corrosion resistance equivalent to or better than that can be imparted (see, for example, Patent Document 1).

However, the technique disclosed here uses a soluble bismuth compound. When a soluble bismuth compound such as bismuth acetate is to be added to the paint, it is necessary to add an excess of acid in order to suppress precipitation as bismuth oxyacetate, bismuth oxide, etc. There is a problem that the metal base material which is the object to be coated is corroded due to the acid.

It is conceivable to use metal bismuth as a corrosion resistance imparting agent without using an excess of acid. However, since metal bismuth is insoluble, it is difficult to stably exist in the paint and handling is difficult. was there.

On the other hand, an aqueous paint containing colloidally dispersed metal bismuth is disclosed (Patent Document 2). However, what is mainly disclosed here is inferior in storage stability and contains tin.
Japanese Patent Laid-Open No. 5-140487 (second page) Japanese translation of PCT publication No. 2003-525970 (2nd page)

In view of the present situation, the present invention uses a metal bismuth colloidal particle instead of a lead compound as a corrosion resistance imparting agent, and can obtain a coating film having corrosion resistance equivalent to or higher than that when using a lead compound. An object of the present invention is to provide a lead-free cationic electrodeposition coating composition which is excellent in long-term storage stability and does not use tin.

The present invention is a lead-free cationic electrodeposition coating composition comprising an oxazolidone ring-containing amine-modified epoxy resin and metal bismuth colloidal particles.
In the lead-free cationic electrodeposition coating composition, the content of the metal bismuth colloidal particles is 0.1 to 1.5% by mass with respect to 100% by mass of the resin solid content of the lead-free cationic electrodeposition coating composition as metal conversion. It is preferable that
The metal bismuth colloidal particles preferably contain a polymer pigment dispersant.
The lead-free cationic electrodeposition coating composition preferably does not contain tin.
The present invention is described in detail below.

Although the lead-free cationic electrodeposition coating composition of the present invention is a lead-free cationic electrodeposition coating composition, the lead-free cationic electrodeposition coating composition is equal to or more than the case of using a cationic electrodeposition coating composition containing a lead compound. An electrodeposition coating film having corrosion resistance can be obtained. For this reason, the lead-free cationic electrodeposition coating composition of the present invention is preferable from the viewpoint of environmental protection.

The lead-free cationic electrodeposition coating composition is substantially free of lead and does not contain lead in an amount that adversely affects the environment. Specifically, the lead content in the lead-free cationic electrodeposition coating composition is 100 ppm or less, preferably 50 ppm or less.

The lead-free cationic electrodeposition coating composition of the present invention contains an oxazolidone ring-containing amine-modified epoxy resin and metal bismuth colloidal particles. That is, some conventional cationic electrodeposition coating compositions contain a soluble bismuth compound, but the lead-free cationic electrodeposition coating composition of the present invention contains metal bismuth colloidal particles. Usually, when metal bismuth is used, metal bismuth settles in the paint, and it is difficult to make it exist stably. For this reason, when metal bismuth is used, it is difficult to form an electrodeposition coating film containing a sufficient amount of metal bismuth by performing cationic electrodeposition coating. As a result, an electrode having sufficient corrosion resistance is obtained. A coated film cannot be obtained. On the other hand, since the lead-free cationic electrodeposition coating composition of the present invention contains metal bismuth colloidal particles, precipitation of the metal bismuth colloidal particles can be sufficiently suppressed in the coating, and metal bismuth can be stably added. Colloidal particles can be present. Therefore, when the lead-free cationic electrodeposition coating composition of the present invention is used, an electrodeposition coating film in which a sufficient amount of metal bismuth colloidal particles are uniformly dispersed can be formed by performing cationic electrodeposition coating. Can do. Therefore, the metal bismuth colloidal particles uniformly dispersed in the coating film sufficiently function as a corrosion resistance imparting agent, and as a result, an electrodeposition coating film having sufficient corrosion resistance can be obtained.

The lead-free cationic electrodeposition coating composition is excellent in long-term storage stability because it can sufficiently suppress the precipitation of metal bismuth colloid particles in the coating. Moreover, it is preferable that the said lead-free cationic electrodeposition coating composition is a thing which does not contain tin substantially, and is preferable also from an environmental viewpoint in this case. Here, “not containing tin substantially” means that the tin content is 50 ppm or less, particularly preferably 0 ppm.

The metal bismuth colloidal particles in the present invention are metal bismuth colloidal particles having an average particle diameter of, for example, 2 to 30 nm, and exist stably in the lead-free cationic electrodeposition coating composition. Since the lead-free cationic electrodeposition coating composition of the present invention contains metal bismuth colloidal particles, excellent corrosion resistance can be imparted to the resulting electrodeposition coating film. Further, since the metal bismuth colloidal particles are excellent in stability in the paint, an electrodeposition coating film in which the metal bismuth colloidal particles are uniform and sufficiently dispersed can be formed.

The metal bismuth colloidal particles can be obtained, for example, by the production method shown below.
The metal bismuth colloidal particles are obtained from a bismuth-containing compound.

The bismuth-containing compound is not particularly limited as long as it is a compound containing bismuth capable of supplying metal bismuth colloidal particles by dissolving in a solvent and reducing, for example, bismuth chloride, bismuth oxychloride, bromide Inorganic bismuth-containing compounds such as bismuth, bismuth silicate, bismuth hydroxide, bismuth trioxide, bismuth nitrate, bismuth nitrite, bismuth oxycarbonate; bismuth lactate, triphenyl bismuth, bismuth gallate, bismuth benzoate, bismuth citrate , Bismuth methoxyacetate, bismuth acetate, bismuth formate, bismuth 2,2-dimethylolpropionate, etc., for example, (basic) bismuth compounds such as bismuth oxide, bismuth hydroxide, basic bismuth carbonate, and organic acids Made by mixing and dispersing in an aqueous medium Organic bismuth-containing compound in the organic acid-modified bismuth (see International Publication No. WO99 / 31187) or the like that enables the like. Of these, bismuth chloride and bismuth nitrate are preferable from the viewpoint of solubility in water as a reaction solvent.

Examples of the organic acid include organic carboxylic acids such as formic acid, acetic acid, lactic acid, and propionic acid, and organic sulfonic acids such as amidosulfonic acid. Further, as the organic acid of the general formula _{^{R 1 CH (OR 2) (}} CH 2) in n COOH (wherein, ^{R 1} represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, ^{R 2} is hydrogen or C An aliphatic carboxylic acid represented by the formula 1-10, wherein n is 0 or 1.), for example, fatty acids such as hydroxyacetic acid, lactic acid, hydroxypropionic acid, etc. Aliphatic carboxylic acids such as methoxyacetic acid, ethoxyacetic acid, and 3-methoxypropionic acid.

The lead-free cationic electrodeposition coating composition of the present invention preferably contains metal bismuth in the form of a protective colloid. Thereby, metal bismuth colloidal particles can be made to exist more stably in the paint.

The protective colloid is not particularly limited as long as it has an action of stabilizing the hydrophobic colloid, for example, natural polymers such as cellulose, starch, and fibers; synthetic polymers such as polystyrene, nylon, and polyacetal; alumina, Complex oxides such as silica and clay minerals; surfactants, citric acid, salts of citric acid and the like can be used. In the present invention, it is particularly preferable to include a polymer pigment dispersant. Thereby, in the lead-free cationic electrodeposition coating composition of the present invention, the metal bismuth colloidal particles can be more stably present.

The polymer pigment dispersant is an amphiphilic copolymer in which a functional group having high affinity for the pigment surface is introduced into a high molecular weight polymer. This material is suitable as a dispersant for organic pigments or inorganic pigments because it has sufficient compatibility with resin compositions for paints and the like, and is usually used as a pigment dispersant in the production of pigment pastes. It is what.

The polymer pigment dispersant is considered to function to stabilize the production of metal colloid particles by reduction of the metal compound and the dispersion in the solvent after the production.
The number average molecular weight of the polymer pigment dispersant is preferably 1,000 to 1,000,000. If it is less than 1000, the dispersion stability may not be sufficient, and if it exceeds 1,000,000, the viscosity may be too high and handling may be difficult. More preferably, it is 2000-500,000, More preferably, it is 4000-500,000.

The polymer pigment dispersant is not particularly limited as long as it has the above-described properties, and examples thereof include those exemplified in JP-A-11-80647. As the polymer pigment dispersant, various types can be used, but commercially available ones can also be used. The polymer pigment dispersant is polar.

As the polymer pigment dispersant, various types can be used, but commercially available ones can also be used. Examples of the commercially available products include Dispersic R, Dispersic 154, Dispersic 180, Dispersic 187, Dispersic 184, Dispersic 190, Dispersic 191, Dispersic 192 (manufactured by BYK Chemie), Solsperse 20000, Solsperse 27000, Solsperse 12000, Solsperse 40000, Solsperse 41090, Solsperse HPA34 (manufactured by Abyssia), EFKA-450, EFKA-451, EFKA-452, EFKA-453, EFKA-4540, EFKA-4550, EFKA-1501, EFKA- 1502 (manufactured by Fuka Chemicals), Floren TG-720W, Floren TG-730W, Floren TG-740W, Flow Len TG-745W, Floren TG-750W, Floren G-700DMEA, Floren G-WK-10, Floren G-WK-13E (manufactured by Kyoeisha), Dispar Aid W-30, Dispar Aid W-39 (Made by Elementis) ), K-SPERSE XM2311 (manufactured by King), Neoletz BT-24, Neoletz BT-175 (manufactured by Zeneca), SMA1440H (manufactured by Atchem), Orotan 731DP, Orotan 963 (manufactured by Rohm and Haas), Yonelin (manufactured by Yoneyama Chemical), Sunspearl PS-2 (manufactured by Sanyo Kasei), Triton CF-10 (manufactured by Union Carbide), John Krill 678, John Krill 679, John Krill 683, John Krill 611, John Krill 680, John Kuril 682, Jonku Lil 52, Jonkrill 57, Jonkrill 60, Jonkrill 63, Jonkrill 70, Jonkrill HPD-71, Jonkrill 62 (Johnson Polymer) Surfinol CT-111 (Air Products), Addispar PW911, Addispar PB821 (made by Ajinomoto Co., Inc.) etc. can be mentioned. These may be used alone or in combination of two or more.

In the lead-free cationic electrodeposition coating composition of the present invention, the metal bismuth colloidal particles can be obtained by reducing the bismuth-containing compound, but the bismuth-containing compound is reduced in the presence of the polymer pigment dispersant. It is preferable to obtain it. Thereby, the obtained metal bismuth colloidal particle can be made to exist more stably in a coating material.

That is, the metal bismuth colloidal particles are obtained, for example, by dissolving the bismuth-containing compound in a solvent and reducing it to metal bismuth using a compound having a reducing action in the presence of a polymer pigment dispersant. Can do.

The solvent is not particularly limited as long as it can dissolve the bismuth-containing compound, and examples thereof include water, an acid, and an organic solvent.
It does not specifically limit as said acid, For example, hydrochloric acid, hydrobromic acid, hydroiodic acid, perchloric acid etc. can be mentioned.

It does not specifically limit as said organic solvent, For example, C1-C4 alcohol, such as methanol, ethanol, ethylene glycol, and methoxypropanol; Ketones, such as acetone; Esters, such as ethyl acetate, etc. are mentioned. The said solvent may be used independently and may use 2 or more types together. When the solvent is a mixture of water and an organic solvent, the organic solvent is preferably water-soluble, and examples thereof include acetone, methanol, ethanol, and ethylene glycol. In the present invention, when other components other than the polymer pigment dispersant and the metal bismuth colloid particles are removed by ultrafiltration or the like, methanol and ethanol are preferable because they are suitable for removal.

When an acid is used as the solvent, the acid solution preferably has a pH of 4 or less. If the pH exceeds 4, by-products such as bismuth oxide may be generated due to insufficient reduction when reducing bismuth ions, which is not preferable.

The bismuth-containing compound is preferably used so that the bismuth ion concentration in the solvent is 0.01 mol / l or more. If it is less than 0.01 mol / l, a sufficiently high concentration bismuth colloid solution may not be obtained. More preferably, it is 0.05 mol / l or more, More preferably, it is 0.07 mol / l or more.

The blending amount of the polymer pigment dispersant is preferably 5 parts by mass for the lower limit and 1000 parts by mass for the upper limit with respect to 100 parts by mass of the metal bismuth colloidal particles. When the amount is less than 5 parts by mass, the dispersibility of the metal bismuth colloidal particles is insufficient. When the amount exceeds 1000 parts by mass, the amount of the polymer pigment dispersant mixed in the binder resin increases when blended in the paint. In addition, problems such as physical properties are likely to occur. The lower limit is more preferably 20 parts by mass, and the upper limit is more preferably 200 parts by mass.

Examples of the method for reducing the bismuth ions to metal bismuth include a method of irradiating light with a high-pressure mercury lamp, a method of adding a compound having a reducing action, and the like. Of these, the method of adding a compound having a reducing action is advantageous in production because it does not require a special apparatus.

As the compound having the reducing action, various kinds of commonly used reducing agents can be used, for example, dithionite, sodium formaldehyde sulfoxylate (called Rongalite, which is a derivative of dithionite). And zinc formaldehyde sulfoxylate, citric acid, tartaric acid, ascorbic acid, malic acid, lithium borohydride, sodium aluminum hydride, dimethylamine borane, hydrazine, hypophosphorous acid, hydrosulfite, etc. . Among the above reducing agents, when using citric acid, tartaric acid, ascorbic acid, malic acid, which are relatively mild reducing agents, a solution of iron (II) sulfate, tin (II) chloride, titanium (III) chloride and Reduction ability can be improved by mixing and using together. Among the reducing agents, sodium formaldehyde sulfoxylate (Longalite) is more preferable from the viewpoint of safety and reaction efficiency.

The amount of the compound having a reducing action is preferably equal to or more than the amount necessary for reducing bismuth in the bismuth-containing compound. If the amount is less than this amount, reduction may be insufficient. Moreover, although an upper limit is not specifically limited, It is preferable that it is 30 times or less of the quantity required for reducing the bismuth in the said bismuth containing compound, and it is more preferable that it is 10 times or less.

When sodium formaldehyde sulfoxylate is used as the compound having the reducing action, the lower limit of 1.5 mol and the upper limit of 20 mol are preferable with respect to 1 mol of the bismuth-containing compound. When the amount is less than 1.5 mol, the reduction is not sufficiently performed, and when the amount exceeds 20 mol, the aggregation stability of the generated colloidal particles decreases. The lower limit is more preferably 3 mol, and the upper limit is more preferably 10 mol. Further, when using sodium formaldehyde sulfoxylate, iron (II) sulfate may be used in combination.

Also, when using sodium borohydride as the compound having the reducing action, the sodium borohydride is expensive and should be handled with care, but can be reduced at room temperature, There is no need to prepare a special light irradiation device.

When sodium borohydride is used as the compound having the reducing action, the addition amount of the sodium borohydride is preferably a lower limit of 1 mol and an upper limit of 50 mol with respect to 1 mol of the bismuth-containing compound. When the amount is less than 1 mol, the reduction is not sufficiently performed, and when the amount exceeds 50 mol, the stability of the generated colloidal particles is lowered and the particles tend to aggregate. The lower limit is more preferably 1.5 mol, and the upper limit is more preferably 10 mol.

When citric acid or a salt thereof is used as the compound having the reducing action, bismuth ions and the like can be reduced by heating to reflux in the presence of alcohol. The citric acid or a salt thereof has an advantage that it is very inexpensive and easily available. As the citric acid or a salt thereof, sodium citrate is preferably used.

When citric acid or a salt thereof is used as the compound having the reducing action, the lower limit of 1.5 mol and the upper limit of 50 mol are preferable with respect to 1 mol of the bismuth-containing compound. When the amount is less than 1.5 mol, the reduction is not sufficiently performed. When the amount exceeds 50 mol, the aggregation stability of the generated colloidal particles is lowered. The lower limit is more preferably 10 mol. Further, when citric acid or a salt thereof is used, iron (II) sulfate may be used in combination.

The method for adding the compound having the reducing action is not particularly limited, and can be performed, for example, after the addition of the polymer pigment dispersant. In this case, for example, the polymer pigment dispersant is first dissolved in a solvent. Furthermore, the reduction can be advanced by adding the remaining compound having the reducing action or the bismuth-containing compound to the solution obtained by dissolving either the compound having the reducing action or the bismuth-containing compound. it can. As a method of adding the compound having the reducing action, the polymer pigment dispersant and the compound having the reducing action may be mixed in advance, and the mixture may be added to the solution of the bismuth-containing compound. .

By the reduction, a solution containing metal bismuth colloidal particles having an average particle diameter of about 5 to 100 nm is obtained. The metal bismuth colloidal particles obtained here are those in which a polymer pigment dispersant is present as a protective colloid around the metal bismuth, so that the metal bismuth colloidal particles are stably present in the solvent. I think that the.
The solution after the reduction contains stabilized metal bismuth colloid particles using the above-described polymer pigment dispersant as a protective colloid, and becomes a metal bismuth colloid solution. The metal bismuth colloidal solution means a solution in which fine particles of metal bismuth are dispersed in a solvent and are visible as a solution.

In addition to the metal bismuth colloidal particles, the solution after the reduction includes excess polymer pigment dispersant, miscellaneous ions such as chloride ions derived from raw materials such as bismuth-containing compounds, salts generated by reduction, and sometimes reduction. These compounds include compounds having an action, and these miscellaneous ions, salts, and compounds having a reducing action may adversely affect the stability of the resulting metal bismuth colloidal solution, so it is desirable to remove them. For removal of these components, for example, a method such as centrifugation or ultrafiltration can be used.

By carrying out the above centrifugation, the metal bismuth colloidal particles are precipitated, but the unnecessary miscellaneous ions, the salt, the compound having a reducing action, and the excessive polymer pigment dispersant are dissolved in the supernatant liquid. By removing the liquid, these components can be removed. The removal effect of the metal bismuth colloidal particles remaining in this way can be enhanced by washing by adding a solvent and repeating the centrifugation.

The centrifugation is preferably performed at 1000 G or more. If it is less than 1000 G, it may be difficult to remove a part of the excessive polymer pigment dispersant. Centrifugation conditions differ depending on the particle diameter of the metal bismuth colloidal particles. For example, in order to precipitate particles having a particle diameter of the order of several nanometers, it is necessary to perform so-called ultracentrifugation conditions. Standard conditions include 3000 G, a lower limit of 5 minutes, and an upper limit of 60 minutes. The lower limit is more preferably 15 minutes, and the upper limit is more preferably 45 minutes.

In the centrifugation, the metal bismuth colloidal particles can be fractionated on the basis of the particle diameter by appropriately changing the above-described conditions of gravity acceleration, time and / or the number of operations. By the fractionation, the particle diameters of the metal bismuth colloidal particles can be made uniform to some extent.

The metal bismuth colloidal solution obtained by the above centrifugation is concentrated and usually takes a paste form. The concentration is generally preferably 80% or more by solid content. The upper limit is not particularly defined, but is 90% or less in consideration of ease of handling.

The ultrafiltration (UF) has a screen size smaller than that of a filtration membrane used for microfiltration (MF). Ultrafiltration is usually used for the purpose of separating high molecular weight substances and colloidal substances.

In the ultrafiltration, a substance to be separated usually has a diameter of 1 nm to 5 μm. By targeting the diameter, excess polymer pigment dispersant can be removed together with the unnecessary ions, salts and compounds having a reducing action. If it is less than 1 nm, unnecessary components may not be eliminated without passing through the filtration membrane, and if it exceeds 5 μm, most of the metal bismuth colloid particles pass through the filtration membrane, and the desired metal bismuth colloid solution cannot be obtained. There is a case.

The filtration membrane for ultrafiltration is not particularly limited, but usually, for example, a resin made of a resin such as polyacrylonitrile, vinyl chloride / acrylonitrile copolymer, polysulfone, polyimide, polyamide or the like is used. Of these, polyacrylonitrile and polysulfone are preferable, and polyacrylonitrile is more preferable. The ultrafiltration filtration membrane is preferably a filtration membrane that can be back-washed from the viewpoint of efficiently washing the filtration membrane that is usually performed after the ultrafiltration.

As the filtration membrane for ultrafiltration, those having a molecular weight cut-off of a lower limit of 3000 and an upper limit of 80000 are preferable. If it is less than 3000, excess polymer pigment dispersant or the like is not easily removed, and if it exceeds 80000, the metal bismuth colloid particles easily pass through the filtration membrane, so that the desired metal bismuth colloid solution is obtained. It may not be possible. The lower limit is more preferably 10,000, and the upper limit is more preferably 60000. The molecular weight cut off generally refers to the molecular weight of a polymer that passes through the pores of the ultrafiltration membrane and is excluded when the polymer solution is passed through the ultrafiltration membrane. Used to evaluate. The larger the molecular weight cut off, the larger the pore size of the filtration membrane.

The form of the ultrafiltration filtration module is not particularly limited, and examples thereof include a hollow fiber type module (also called a capillary module), a spiral module, a tubular module, a plate type module, and the like depending on the form of the filtration membrane. Is also preferably used in the present invention. Among these, since the time required for filtration can be shortened as the membrane area is large, a hollow fiber type module having a compact form for the filtration area is preferable from the viewpoint of efficiency. In addition, when the amount of the metal bismuth colloid solution to be treated is large, it is preferable to use one having a large number of ultrafiltration membranes to be used.

The ultrafiltration method is not particularly limited. For example, a conventionally known method is used. Usually, a solution containing the metal bismuth colloidal particles and the polymer pigment dispersant obtained by the above reaction is ultrafiltered. This is done by passing through a membrane, whereby the filtrate containing the above-mentioned miscellaneous ions, salt, compound having a reducing action and excess polymer pigment dispersant is eliminated. The ultrafiltration is usually repeated until the miscellaneous ions in the filtrate are removed below the desired concentration. At that time, it is preferable to add the same amount of solvent as the amount of filtrate removed in order to keep the concentration of the metal bismuth colloid solution to be treated constant. As the solvent added at this time, it is possible to replace the solvent of the metal bismuth colloidal solution by using a different type of solvent from that used at the time of reduction.

The ultrafiltration can be performed by a normal operation, for example, a so-called batch system. This batch method is a method in which the metal bismuth colloid solution to be treated is added as the ultrafiltration progresses. The ultrafiltration can be further performed to increase the solid content concentration after the miscellaneous ions are removed to a desired concentration or less.

The metal bismuth colloidal solution obtained by the centrifugal separation and the ultrafiltration is obtained by removing a part of the miscellaneous ions and excess polymer pigment dispersant, and this is the lead-free cationic electrodeposition coating material of the present invention. When used in the composition, the stability of the metal bismuth colloidal particles in the paint is more excellent, and the stability of the resulting paint is excellent over time. It can be used suitably and a favorable electrodeposition coating film can be formed.

In the lead-free cationic electrodeposition coating composition of the present invention, the content of the metal bismuth colloidal particles is a lower limit of 0.1% by mass with respect to the resin solid content of the lead-free cationic electrodeposition coating composition as metal. The upper limit is preferably 1.5% by mass. If it is less than 0.1% by mass, the resulting electrodeposition coating film may not have sufficient corrosion resistance. Even if it exceeds 1.5 mass%, the improvement of an effect is not seen but there exists a possibility that it may not be economical. The lower limit is more preferably 0.3% by mass. The upper limit is more preferably 1.0% by mass.

In the lead-free cationic electrodeposition coating composition of the present invention, when the metal bismuth colloidal particles contain a polymer pigment dispersant, the mass ratio of the polymer pigment dispersant to the metal bismuth (polymer pigment dispersion) The agent / metal bismuth) preferably has a lower limit of 1/9 and an upper limit of 9/1. If it is less than 1/9, the stability of the metal bismuth colloidal particles in the paint may be reduced. Even if it exceeds 9/1, the improvement of the effect is not observed and it is not economical, and the general performance of the obtained electrodeposition coating film may be deteriorated. The lower limit is more preferably 3/7, and the upper limit is more preferably 7/3.

In the lead-free cationic electrodeposition coating composition of the present invention, the method for blending the metal bismuth colloidal particles includes: (1) an electrodeposition coating composition containing a component other than the metal bismuth colloidal particles; (2) In the production of a pigment dispersion paste to be described later, a method in which the metal bismuth colloidal particles are further added and dispersed at the same time when the pigment is dispersed, and (3) an oxazolidone ring-containing amine-modified epoxy described later. Examples thereof include a method of adding a neutralizing acid to a mixture of a conductive resin such as a resin and a curing agent, further adding metal bismuth colloidal particles, and dispersing and emulsifying.

The lead-free cationic electrodeposition coating composition contains an oxazolidone ring-containing amine-modified epoxy resin. Thereby, the coating film which is excellent in heat resistance and corrosion resistance, and also excellent in impact resistance can be obtained, and low temperature curability can be improved.

The oxazolidone ring-containing amine-modified epoxy resin is an active hydrogen such that the primary amino group occupies 5 to 50% of the amine equivalent, so that an amine equivalent of 0.3 to 4.0 meq / g is obtained after ring opening. It is desirable to open the ring with a compound.

Examples of the active hydrogen compound capable of introducing a cationic group (amino 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.

Examples of acid salts of the primary amine, secondary amine, and tertiary amine include butylamine, octylamine, diethylamine, dibutylamine, methylbutylamine, monoethanolamine, diethanolamine, N-methylethanolamine, triethylamine hydrochloride, N, N -In addition to dimethylethanolamine acetate, diethyl disulfide / acetic acid mixture and the like, there are secondary amines blocked with primary amines such as ketimine of aminoethylethanolamine and diketimine of diethylenetriamine. These may be used alone or in combination of two or more.

The number average molecular weight of the oxazolidone ring-containing amine-modified epoxy resin is preferably a lower limit of 600 and an upper limit of 4000 by GPC analysis. If it is less than 600, the film-forming property may be insufficient, and if it exceeds 4000, emulsification and water-solubilization may be difficult.

The lead-free cationic electrodeposition coating composition of the present invention usually contains a curing agent. As said hardening | curing agent, the blocked isocyanate which is blocked, such as polyisocyanate, can be used, for example. The polyisocyanate used in the curing agent is 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.

Examples of the polyisocyanate 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-diisocyanatomethy Carbon such as cyclohexane (hydrogenated XDI), hydrogenated TDI, 2,5- or 2,6-bis (isocyanatomethyl) -bicyclo [2.2.1] heptane (also referred to as norbornane diisocyanate), and the like. Aliphatic diisocyanates having 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, uretoimine, burette and / or isocyanurate modified product); These may be used alone or in combination of two or more.

An adduct or prepolymer obtained by reacting the polyisocyanate with a polyhydric alcohol such as ethylene glycol, propylene glycol, trimethylolpropane, hexanetriol or the like at an NCO / OH ratio of 2 or more may also be used as a curing agent.

The polyisocyanate is preferably an aliphatic polyisocyanate or an alicyclic polyisocyanate. This is because the formed coating film has excellent weather resistance.

Examples of the aliphatic polyisocyanate or the alicyclic polyisocyanate include hexamethylene diisocyanate, hydrogenated TDI, hydrogenated MDI, hydrogenated XDI, IPDI, norbornane diisocyanate, their dimer (biuret), and trimer (isocyanate). Nurate) or the like.

The polyisocyanate is usually applied to a paint in a form reacted with a blocking agent. The blocking agent is added to a polyisocyanate group and is stable at room temperature, but can regenerate free isocyanate groups when heated to a temperature higher than the dissociation temperature.

As the polyisocyanate blocking agent, when low temperature curing (160 ° C. or lower) is desired, lactam blocking agents such as ε-caprolactam, δ-valerolactam, γ-butyrolactam, and β-propiolactam; formaldoxime It is preferable to use an oxime blocking agent such as acetoaldoxime, acetoxime, methyl ethyl ketoxime, diacetyl monooxime or cyclohexane oxime.

In the lead-free cationic electrodeposition coating composition of the present invention, the content of the binder containing the oxazolidone ring-containing amine-modified epoxy resin and the curing agent is 100% by mass of the total solid content of the lead-free cationic electrodeposition coating composition. The lower limit is preferably 25% by mass and the upper limit is preferably 90% by mass. The lower limit is more preferably 40% by mass, and the upper limit is more preferably 80% by mass.

The lead-free cationic electrodeposition coating composition of the present invention generally contains a pigment as a colorant. The above lead-free cationic electrodeposition coating composition can also contain a commonly used pigment.

The pigment is not particularly limited, and examples thereof include colored pigments such as titanium white, carbon black, and bengara; extender pigments such as kaolin, talc, aluminum silicate, calcium carbonate, mica, clay, and silica; zinc phosphate, phosphoric acid Protection such as iron, aluminum phosphate, calcium phosphate, zinc phosphite, zinc cyanide, zinc oxide, aluminum tripolyphosphate, zinc molybdate, aluminum molybdate, calcium molybdate, aluminum phosphomolybdate, zinc aluminum phosphomolybdate A rust pigment etc. can be mentioned.

In the lead-free cationic electrodeposition coating composition, the content of the pigment is a lower limit of 1% by mass, an upper limit of 35% by mass and the lower limit with respect to 100% by mass of the total solid content of the lead-free cationic electrodeposition coating composition. Is more preferably 15% by mass, and the upper limit is more preferably 30% by mass.

When the pigment is used as a component of a lead-free cationic electrodeposition coating composition, generally, the pigment is dispersed in an aqueous medium at a high concentration in advance to form a paste. This is because the pigment is in a powder form and it is difficult to disperse in one step in a low concentration uniform state used in the lead-free cationic electrodeposition coating composition. In general, such a paste is called a pigment dispersion paste.

The pigment dispersion paste is prepared by dispersing a pigment in an aqueous medium together with a pigment dispersion resin. 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 medium, ion-exchanged water or water containing a small amount of alcohol is used. Generally, the pigment dispersion resin is used at a solid content ratio of 5 to 40 parts by mass, and the pigment is used at a solid content ratio of 20 to 50 parts by mass.

The lead-free cationic electrodeposition coating composition of the present invention is prepared, for example, by dispersing the metal bismuth colloid particles, the oxazolidone ring-containing amine-modified epoxy resin, the curing agent and the pigment dispersion paste in an aqueous medium. The compounding method of the metal bismuth colloid particles at this time is as described above. Further, the aqueous medium usually contains a neutralizing agent in order to improve the dispersibility of the oxazolidone ring-containing amine-modified epoxy resin. The neutralizing agent is an inorganic acid or organic acid such as hydrochloric acid, nitric acid, phosphoric acid, formic acid, acetic acid, lactic acid. The content of the neutralizing agent is an amount that achieves a neutralization rate of at least 20%, preferably 30 to 60%.

The content of the curing agent reacts with active hydrogen-containing functional groups such as primary and / or secondary amino groups and hydroxyl groups in the oxazolidone ring-containing amine-modified epoxy resin at the time of curing to give a good cured coating film. In general, it is generally in the range of 90/10 to 50/50, preferably 80/20 to 65/35, expressed as a solid mass ratio of the oxazolidone ring-containing amine-modified epoxy resin to the curing agent.

The lead-free cationic electrodeposition coating composition is preferably substantially free of tin. Thereby, it can be set as a tin free coating composition. In the present invention, sufficient curability can be obtained without using tin compounds such as dibutyltin dilaurate and dibutyltin oxide which have been conventionally used as urethane cleavage catalysts.

The lead-free cationic electrodeposition coating composition of the present invention may contain conventional coating additives such as a water-miscible organic solvent, a surfactant, an antioxidant, and an ultraviolet absorber.

The lead-free cationic electrodeposition coating composition of the present invention can be electrodeposited onto an article to be coated by a method well known to those skilled in the art to form a cured coating film. The object to be coated when performing electrodeposition coating using the lead-free cationic electrodeposition coating composition is preferably a conductor that has been subjected to surface treatment such as zinc phosphate treatment in advance by dipping, spraying, or the like. However, the surface treatment may not be performed. In addition, the conductor is not particularly limited as long as it can become a cathode in performing electrodeposition coating, and a metal substrate is preferable.

As said metal base material, steel plates, such as a cold-rolled steel plate and a zinc nickel steel plate, can be mentioned. Further, the steel sheet may be a structure used for a specific application, such as the automobile body described above. The structure is formed by forming the metal material into a concavo-convex shape so as to be used for automobiles or other applications. The coated material obtained by the electrodeposition coating film forming method described above can be suitably used as a structure such as an automobile body.

The lead-free cationic electrodeposition coating composition of the present invention contains an oxazolidone ring-containing amine-modified epoxy resin and metal bismuth colloidal particles. Therefore, the coating film obtained by using the above lead-free cationic electrodeposition coating composition is obtained by uniformly and sufficiently dispersing metal bismuth colloidal particles, and as a result, a coating film having excellent corrosion resistance can be obtained. . Moreover, since the said metal bismuth colloidal particle exists stably in a paint for a long period of time, the coating film excellent in corrosion resistance can be obtained even after storing a paint for a long period of time. Moreover, even if it does not use the tin compound conventionally used as a urethane cleavage catalyst, a sufficient cured coating film can be obtained and it can be set as a tin free coating material. Furthermore, since it is lead-free, it is preferable from the viewpoint of the environment. Therefore, the lead-free cationic electrodeposition coating composition can be suitably used for automobiles, for example.

Since the lead-free cationic electrodeposition coating composition of the present invention has the above-described configuration, a coating film having corrosion resistance equivalent to or higher than that when a lead compound is used can be obtained. In addition, even if tin conventionally used as a curing catalyst is not used, it has sufficient curability immediately after preparation of the paint and after storage stability. Therefore, the lead-free cationic electrodeposition coating composition can be suitably used for automobiles, for example.

Examples The present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples. In the examples, “parts” means “parts by mass” unless otherwise specified.

Production Example 1 Production of Metal Bismuth Colloid Solution 500 g Kolben was charged with 300 g of 1N hydrochloric acid and 9.46 g of bismuth chloride, and stirred and dissolved in a 50 ° C. oil bath. After dissolution of bismuth chloride, the oil bath is removed, and 6.72 g of Dispersic 190 (manufactured by Big Chemie, 40% by mass of active ingredient, number average molecular weight by GPC analysis is 30000) is added to Kolben with stirring, and a 50 ° C. hot water bath The mixture was stirred and dissolved in the solution for 30 minutes, and then cooled to room temperature. Next, apart from the above Kolben, 23.11 g of sodium formaldehyde sulfoxylate dihydrate and 36.89 g of deionized water were stirred and dissolved in a 50 ° C. hot water bath, and the temperature of the resulting solution was obtained. Was added to Kolben instantaneously while stirring. The liquid turned black in an instant. Stirring was continued for 2 hours while maintaining the liquid temperature at 25 ° C., and a black metal bismuth colloidal solution was obtained.

Next, ultrafiltration module AHP1010 (manufactured by Asahi Kasei Co., Ltd .; molecular weight cut off 50000, number of membranes used 400), magnet pump, and 3 l stainless steel cup with tube connection port at the bottom are connected by a silicon tube, and ultrafiltration is performed. The device. The metal bismuth colloidal solution was put in a stainless steel cup, and 2 liters of water was added, and then ultrafiltration was performed by operating the pump. When the filtrate from the module became 2 liters after about 20 minutes, 2 liters of water was added to the stainless steel cup. Thereafter, the filtrate was confirmed to have a conductivity of 7 μS / cm or less, and concentrated until the amount of the mother liquor was 500 ml.

Subsequently, an ultrafiltration device comprising a 500 ml stainless cup, an ultrafiltration module AHP0013 (manufactured by Asahi Kasei Co., Ltd .; fractional molecular weight 50000, number of membranes used 100), a tube pump, and an aspirator was assembled. The mother liquor obtained previously was put into this stainless steel cup and concentrated to increase the solid content concentration. When the mother liquor reached about 100 ml, the pump was stopped and the concentration was terminated to obtain a metal bismuth colloidal solution having a solid content of 30%. The average particle diameter of the metal bismuth colloid particles in this solution obtained from the electron microscope observation was 25 nm. The composition of the obtained metal bismuth colloidal solution had a bismuth content of 14.2%, Dispersic 190 4.8%, and deionized water 77.4%. In addition, the said composition was calculated and calculated | required from the measurement result obtained with the differential thermal balance "TG-DTA" (made by Seiko Instruments Inc.).

Production Example 2 Production of oxazolidone ring-containing amine-modified epoxy resin To a flask equipped with a stirrer, a condenser tube, a nitrogen inlet tube, a thermometer and a dropping funnel, 2,4- / 2,6-tolylene diisocyanate (mass) Ratio = 8/2) 92 parts and 95 parts of methyl isobutyl ketone (hereinafter referred to as MIBK) were charged. While stirring the mixture, 21 parts of methanol was added.

The reaction started from room temperature, heated to 60 ° C. by exotherm, and then continued for 30 minutes, and then 57 parts of ethylene glycol mono-2-ethylhexyl ether was added dropwise through a dropping funnel. Furthermore, 42 parts of a bisphenol A-propylene oxide 5-mol adduct (trade name, Newpol BP-5P, manufactured by Sanyo Chemical Co., Ltd.) was added. 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 an epoxy equivalent 188 bisphenol A type epoxy resin (trade name DER-331J, manufactured by Dow Chemical Co., Ltd.) synthesized from bisphenol A and epichlorohydrin by a known method is added to the above reaction mixture and heated to 125 ° C. Warm up. Thereafter, 1.0 part of benzyldimethylamine was added and reacted at 130 ° C. until the epoxy equivalent was 410.

Subsequently, 87 parts of bisphenol A was added and reacted at 120 ° C. to give 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% 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 oxazolidone ring containing amine modified epoxy resin (resin solid content 80%).

Production Example 3 Production of Block Polyisocyanate Curing Agent In a flask similar to Production Example 2, 2,5- and 2,6-bis (isocyanatomethyl) -bicyclo [2.2.1] heptane (Mitsui) Toatsu Co., Ltd., isocyanate equivalent 103) 723 parts and MIBK 333 parts were charged. The resulting reaction mixture was heated to 80 ° C., and the reaction mixture was uniformly dissolved. Then, 610 parts of methyl ethyl ketoxime was added dropwise over 2 hours. After completion of the dropping, the reaction temperature was maintained at 80 ° C., and the reaction was continued until the absorption based on the isocyanate group disappeared in the measurement of IR spectrum to obtain a methyl ethyl ketoxime block polyisocyanate curing agent. (Resin solid content 80%)

Production example 4 Production of resin for pigment dispersion In a reaction vessel equipped with a stirrer, a cooling tube, a nitrogen introduction tube and a thermometer, 222.0 parts of isophorone diisocyanate (hereinafter referred to as IPDI) was placed and MIBK 39.1 was added. Diluted in portions. Thereafter, the temperature was raised to 50 ° C., and then 131.5 parts of 2-ethylhexanol was added dropwise over 2 hours in a dry nitrogen atmosphere while stirring. The reaction temperature was maintained at 50 ° C. by cooling appropriately. As a result, 2-ethylhexanol half-blocked IPDI was obtained.

Next, Epicoat 828 (bisphenol A type epoxy resin manufactured by Yuka Shell Epoxy Co., Ltd., epoxy equivalent 182-194) 376.0 parts, bisphenol A 114.0 parts and octylic acid 29.2 parts, stirring device, cooling tube, nitrogen introduction A reaction vessel equipped with a tube and a thermometer was charged. The reaction mixture was heated to 130 ° C. in a nitrogen atmosphere, 0.15 part of dimethylbenzylamine was added, and the mixture was reacted at 170 ° C. for 1 hour under an exothermic reaction, whereby a bisphenol A type epoxy resin having an epoxy equivalent of 649 was obtained. Obtained.

Subsequently, after cooling to 140 ° C., 396.8 parts of 2-ethylhexanol half-blocked IPDI prepared as described above was added, and the mixture was reacted at 140 ° C. for 1 hour. Next, 323.2 parts of ethylene glycol monobutyl ether was added for dilution, and the reaction mixture was cooled to 100 ° C. Then, 188.8 parts of a 78.3% MIBK solution of aminoethylethanolamine in methyl isobutyl monoketimine was added.

The mixture was kept at 110 ° C. for 1 hour, then cooled to 90 ° C., 360.0 parts of ion-exchanged water was added, and stirring was continued for another 30 minutes, whereby the ketiminate portion in the epoxy resin was converted into a primary amino acid. Converted into a group. Excess water and MIBK were removed from this mixture under reduced pressure, and then diluted with 588.1 parts of ethylene glycol monobutyl ether to obtain a pigment dispersing resin having a primary amino group. (Resin solid content 50%)

Production Example 5 Production of pigment dispersion paste 60 parts of pigment dispersion 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, 18.0 parts of aluminum phosphomolybdate and 251 parts of ion-exchanged water were added and dispersed until the particle size became 10 μm or less to obtain a pigment dispersion paste.

Example 1 Production of lead-free cationic electrodeposition coating composition 672 parts of the oxazolidone ring-containing amine-modified epoxy resin obtained in Production Example 2 and 209.1 parts of the curing agent prepared in Production Example 3 were used as solid components. After homogeneous mixing, ethylene glycol mono-2-ethylhexyl ether was added in an amount of 3% based on the solid content.

The acid that was insufficient to neutralize was adjusted to a neutralization rate of 41.7% (neutralization rate with respect to the cationic group of the resin) by adding formic acid, and further diluted with ion-exchanged water. Thereafter, MIBK was removed under reduced pressure until the solid content became 37.6%. Here, the metal bismuth colloid solution prepared in Production Example 1 was 1 in terms of bismuth metal amount with respect to the resin solid content in the paint. The main emulsion was prepared by gradually adding 0.0 wt%.

By mixing 979.5 parts of the obtained main emulsion, 284.0 parts of the pigment dispersion paste obtained in Production Example 5, and 1236.5 parts of ion-exchanged water, lead-free cationic electrodeposition having a solid content of 20.0% A coating composition was obtained.

Example 2
The electrodeposition paint obtained in Example 1 was stored at room temperature for 4 weeks and then evaluated for curability and corrosion resistance.

Example 3
A lead-free cationic electrodeposition coating composition was prepared in the same manner as in Example 1, except that the amount of bismuth metal was 0.5% by weight.

(Electrodeposition coating formation method)
A cold rolled steel sheet treated with phosphoric acid polymerization having a length of 15 cm, a width of 7 cm, and a thickness of 0.8 mm as a cathode was immersed in the bath of the lead-free cationic electrodeposition coating composition obtained in Examples 1 to 3, and electrodeposition coating was performed. And thoroughly washed with ion-exchanged water. This coated plate was baked at 160 ° C. for 10 minutes to obtain a cured coating film having a dry film thickness of 20 μm.

Comparative Example 1
A cationic electrodeposition coating composition was prepared in the same manner as in Example 1 except that the metal bismuth colloid solution was not contained, and a cured coating film was obtained in the same manner as in the electrodeposition coating film forming method.

Comparative Example 2
A cured coating film was obtained using “Power Top V-6” (Nihon Paint Co., Ltd., lead-containing cationic electrodeposition coating material) in the same manner as the above electrodeposition coating film forming method.

[Evaluation]
The cured coating films obtained in Examples and Comparative Examples were evaluated for corrosion resistance by MIBK rubbing (tin-free curability) and the following salt spray test. The results are shown in Table 1.

(Curable)
The coating film was rubbed 50 times with gauze soaked in MIBK, and the curability was determined by the surface state of the coating film. The evaluation criteria are as follows.
○: No change in coating film.
Δ: There are coating streaks.
×: Gauze is colored.

(Corrosion resistance)
The test piece having a cured coating film having a predetermined film thickness was subjected to a salt spray resistance test according to JIS K 5400 9.1. The test piece after 840 hours passed was washed with water and allowed to stand at room temperature for 2 hours, and then evaluated by the following method. A “cello tape” manufactured by Nichiban Co., Ltd. (cellophane adhesive tape, width 24 mm) was pressure-bonded to the surface of the coating film with a finger and peeled off vigorously. The width at which the coating film peeled from the cut part (maximum on one side) was measured with a tape. The evaluation criteria are as follows.
A: 0 mm ≦ peeling width <1.0 mm
○: 1.0 mm ≦ peeling width <2.0 mm
Δ: 2.0 mm ≦ peeling width <3.0 mm
×: Peel width ≧ 3.0 mm

From Table 1, the cured coating film obtained by the Example was excellent in sclerosis | hardenability and corrosion resistance compared with the cured coating film obtained by the coating material of the comparative example 1 which does not contain a metal colloid solution. Moreover, although it was dependent on the compounding quantity of a metal bismuth colloidal particle, when the coating material containing a lead compound was used (Comparative Example 2), the same curability and corrosion resistance were shown. In addition, bismuth metal colloidal particles exist stably and have their functions because they have been confirmed to be sufficiently curable without the use of tin, which has been used as a curing catalyst. It was confirmed that it was demonstrating.

Example 4
70 g of the metal bismuth colloid solution obtained in Production Example 1 was taken immediately after being put in 260.5 g of the main emulsion obtained during the production of Example 1 and after storage for 4 weeks at room temperature. It was shown in 2.

As can be seen from these electron micrographs, it was confirmed that the metal bismuth colloidal particles did not aggregate even for 4 weeks and existed stably. In addition, the electron micrograph which shows the presence state of the metal bismuth colloid in the cationic electrodeposition coating material obtained in Example 1 was shown in FIG.

The lead-free cationic electrodeposition coating composition of the present invention can be suitably applied to a substrate such as an automobile body.

The electron micrograph immediately after main emulsion addition in Example 4. FIG. The electron micrograph after storage for 4 weeks at room temperature in Example 4. 4 is an electron micrograph of the cationic electrodeposition paint obtained in Example 1. FIG.

Claims (4)

A lead-free cationic electrodeposition coating composition comprising an oxazolidone ring-containing amine-modified epoxy resin and metal bismuth colloidal particles. In the lead-free cationic electrodeposition coating composition, the content of the metal bismuth colloidal particles is 0.1 to 1.5% by mass with respect to 100% by mass of the resin solid content of the lead-free cationic electrodeposition coating composition in terms of metal. The lead-free cationic electrodeposition coating composition according to claim 1. The lead-free cationic electrodeposition coating composition according to claim 1 or 2, wherein the metal bismuth colloidal particles contain a polymer pigment dispersant. The lead-free cationic electrodeposition coating composition according to claim 1, 2, or 3, wherein the lead-free cationic electrodeposition coating composition contains substantially no tin.