Cationic electrodeposition coating material composition

Abstract

The present invention addresses the problem of providing a cationic electrodeposition coating material composition having excellent anti-corrosion properties and finishability on an edge portion and a flat portion of a coated article, and the coated article having such excellent coating film performance. As a solution, a cationic electrodeposition coating material composition is characterized in that, if the cationic electrodeposition coating material composition is electrodeposition-coated on a metal substance to be coated and the obtained uncured electrodeposition coating film is heat-dried, a storage modulus (G'), a loss modulus (G"), and a minimum value (G'min) of G' during the heat-drying step of the coating film satisfy specific numerical ranges. Furthermore, provided is the cationic electrodeposition coating material composition containing an amine-modified epoxy resin (A), a blocked polyisocyanate compound (B), and a viscosity modifier (C).

Description

Cationic electrodeposition coating composition

[0001] The present invention relates to a cationic electrodeposition coating composition and a method for forming a coating film using the cationic electrodeposition coating composition, characterized in that when the cationic electrodeposition coating composition is electrodeposited onto a metal substrate and the resulting uncured electrodeposition coating film is dried by heating, the storage modulus (G'), loss modulus (G"), and minimum value of G' (G'min) in the heat drying step of the coating film satisfy specific numerical ranges.

[0002] Cationic electrodeposition coating compositions have excellent coating workability and the coating films they form have good corrosion resistance, and therefore are widely used as primer coatings for conductive metal products such as automobile bodies, automobile parts, electrical equipment parts, and other equipment, which require these properties.

[0003] When a substrate has sharp edges, the coating film at the edges may become thin during heat curing, resulting in poor corrosion protection. Therefore, when coating substrates with edges, there is a need for a method to improve the corrosion protection of the edges.

[0004] Patent Document 1 discloses the inclusion of a polyacrylamide resin in an electrodeposition paint as a method for improving the rust resistance of edge portions. It is believed that the inclusion of this resin can control shrinkage caused by heating or inhibit the deterioration of edge coverage due to flow through interaction with the coating film components. However, the inclusion of a highly polar soluble resin can result in poor corrosion resistance on flat surfaces. Patent Documents 2 and 3 also disclose the inclusion of a cationic microgel dispersion (epoxy viscous agent) in an electrodeposition paint. The inclusion of this resin can inhibit the flow of the electrodeposition coating film due to thermal flow at edge portions, but under severe corrosion conditions, sufficient corrosion resistance at edge portions may not be achieved.

[0005] JP 2017-214572 A JP 2018-159032 A JP 7-268063 A

[0006] The problem to be solved by the invention is to provide a cationic electrodeposition coating composition and a coating film forming method which are excellent in corrosion resistance and finish on edge and flat surfaces.

[0007] As a result of extensive research into solving the above-mentioned problems, the inventors have found that the above-mentioned problems can be solved by a cationic electrodeposition coating composition, which is electrodeposited onto a metal substrate and the resulting uncured electrodeposition coating film is dried by heating, so that the storage modulus (G'), loss modulus (G"), and minimum value of G' in the heat drying step (G'min) of the coating film satisfy the following formulas (1) to (3), thereby completing the present invention: G'>1.05×G" ０．７ ...Equation (1) G'>60 (Pa) ...Equation (2) G'min<300 (Pa) ...Equation (3) That is, the present invention provides the following cationic electrodeposition coating composition and coated article obtained by the method for applying a cationic electrodeposition coating film. Item 1. A cationic electrodeposition coating composition characterized in that when the cationic electrodeposition coating composition is electrodeposited onto a metal substrate and the resulting uncured electrodeposition coating film is dried by heating, the storage modulus (G'), loss modulus (G"), and minimum value of G' in the heat drying step (G'min) of the coating film satisfy the following equations (1) to (3): G'>1.05×G" ０．７...Equation (1) G'>60 (Pa) ...Equation (2) G'min<300 (Pa) ...Equation (3) Item 2. The cationic electrodeposition coating composition according to Item 1, characterized in that it contains an amine-modified epoxy resin (A), a blocked polyisocyanate compound (B), and a viscosity modifier (C). Item 3. The cationic electrodeposition coating composition according to Item 2, characterized in that the amine-modified epoxy resin (A) is a reaction product of an epoxy resin and an amine compound. Item 4. The cationic electrodeposition coating composition according to Item 2 or 3, characterized in that the amine-modified epoxy resin (A) has a number-average molecular weight of 3,000 or more and a glass transition temperature of 100°C or less. Item 5. The cationic electrodeposition coating composition according to any one of Items 2 to 4, characterized in that the viscosity modifier (C) contains a cationic microgel (C-1). Item 6. The cationic electrodeposition coating composition according to Item 5, characterized in that the cationic microgel (C-1) contains a silane coupling agent as a constituent component. Item 7. The cationic electrodeposition coating composition according to any one of Items 2 to 6, wherein the viscosity modifier (C) comprises a (meth)acrylate-modified epoxy (C-2) and / or a hydroxy(meth)acrylate-blocked polyisocyanate compound (C-3). Item 8. The cationic electrodeposition coating composition according to any one of Items 2 to 7, further comprising a bismuth compound. Item 9. The cationic electrodeposition coating composition according to any one of Items 2 to 8, wherein the blocked polyisocyanate compound (B) is a reaction product of a polyisocyanate compound and a blocking agent, and the blocking agent comprises a diol compound having two hydroxyl groups with different reactivities. Item 10. A coating film forming method comprising electrodeposition-coating a metal substrate with the cationic electrodeposition coating composition according to any one of Items 1 to 9, and subsequently heating and drying the resulting uncured electrodeposition coating film.Item 11. A method for forming a coating film using a cationic electrodeposition coating composition, comprising electrodeposition coating a metal substrate with a cationic electrodeposition coating composition containing an amine-modified epoxy resin (A), a blocked polyisocyanate compound (B), and a viscosity modifier (C), and subsequently heating and drying the resulting uncured electrodeposition coating film, wherein the storage modulus (G'), loss modulus (G"), and minimum value of G' in the heating and drying step (G'min) of the electrodeposition coating film satisfy the following formulas (1) to (3): G'>1.05×G". ０．７ ...Formula (1) G'>60 (Pa) ...Formula (2) G'min<300 (Pa) ...Formula (3)

[0008] The cationic electrodeposition coating composition of the present invention has excellent corrosion resistance and finish on edges and flat surfaces, and exhibits good corrosion resistance on edges even under severe corrosive conditions. Automobile bodies coated with the product of the present invention are less susceptible to corrosion deterioration even when driven in an environment where snow-melting salt is sprayed.

[0009] 1 shows an example of viscoelasticity measurement (measured values ​​from 50° C. to 150° C.). 2 shows cross-sectional photographs of the edge portion (left photograph: exposed edge portion, right photograph: coated edge portion).

[0010] Hereinafter, embodiments for carrying out the present invention will be described in detail. It should be understood that the present invention is not limited to the following embodiments and includes various modified examples that are implemented within the scope of the present invention. In the present invention, the storage modulus (G') can also be abbreviated as "G'", the loss modulus (G") as "G", and the minimum value of G' in the heat drying step (G'min) as "G'min".

[0011] The cationic electrodeposition coating composition of the present invention is characterized in that when the cationic electrodeposition coating composition is electrodeposited onto a metal substrate and the resulting uncured electrodeposition coating film is dried by heating, the storage modulus (G'), loss modulus (G"), and minimum value of G' in the heat drying step (G'min) of the coating film satisfy the following formulas (1) to (3). In this specification, the units of G', G" and G'min are "Pa": G'>1.05×G" ０．７...Equation (1) G'>60 (Pa) ...Equation (2) G'min<300 (Pa) ...Equation (3) <Method of Measuring Viscoelasticity> The storage modulus (G') and loss modulus (G") (viscoelasticity measurement) can be measured using a rotational viscoelasticity measuring device. An example of such a measuring device is a viscoelasticity measuring device (manufactured by TA Instruments, trade name "ARES-G2"). In addition, in order to evaluate the curing property of a coating film during the heat drying process, measurements were carried out using the jig described in JP 2010-78444 A. The jig is a viscoelasticity measuring jig having a rotating shaft and a circular body attached concentrically to the tip of the rotating shaft, and the circular body has a cutout portion covering 60% of the projected area in the direction of the rotating shaft, i.e., the area of ​​the outer circumference of the projected circular body, and the diameter of the outer circumference is 40 mm and the inner diameter is 38 mm. Before measuring the viscoelasticity, the above-mentioned device was calibrated with a viscosity standard liquid (JS-100, manufactured by Nippon Grease) to ensure the correct viscosity.

[0012] Specific measurement conditions were as follows: first, a sample cationic electrodeposition coating composition was applied to a measurement cell of the viscoelasticity measuring device to a thickness of approximately 0.6 mm, and the jig was then placed on top of the coating and inserted into the sample to a depth of approximately 0.3 mm. The temperature was then raised from 50°C at a frequency of 1.0 Hz and a temperature increase rate of 15°C / min, and the storage modulus (G') and loss modulus (G") were measured between 50°C and 150°C, with the minimum storage modulus (G') between 50°C and 150°C being taken as G'min. Equations (1) and (2) can be said to be within the ranges when all measured values ​​of the storage modulus (G') and loss modulus (G") between 50°C and 150°C are within the ranges.

[0013] For example, Figure 1 is a graph showing an example of viscoelasticity measurement results (measured values). The measured values ​​of storage modulus (G') and loss modulus (G") between 50°C and 150°C are graphed, with the value at the top right being the value at 50°C and the value at the bottom left being the value at 150°C. The shaded area in Figure 1 is within the range that satisfies both formula (1) and formula (2).

[0014] According to the present invention, it is possible to achieve both corrosion resistance and finish quality in both edge and flat areas by adjusting the storage modulus (G'), loss modulus (G"), and minimum value of G' in the heat drying process (G'min) among the dynamic viscoelasticity of the uncured coating film applied in electrodeposition coating.

[0015] When the electrodeposition coating composition is applied to a substrate by electrodeposition and then heated, the coating film becomes fluid due to the heat, and then the curing reaction begins. In this process, the storage modulus (G') and loss modulus (G") of the uncured coating film before the start of the curing reaction, and the minimum value of G' (G'min) during the heat drying step, are controlled within specific ranges, thereby making it possible to achieve both corrosion resistance and finish quality at both edge and flat surfaces of the resulting cured coating film.

[0016] If the coating viscosity during the heat drying process is kept above a certain value, edge coverage is maintained, but problems arise with workability (poor film buildability and finish) and the occurrence of voids (air bubbles) in the cured coating (reduced rust prevention on general surfaces). On the other hand, if the viscosity of the coating is lowered to improve film buildability and suppress voids, the edges will not be covered. However, it has been discovered that edge coverage can be maintained by increasing the elasticity (G' is higher than G") even if the viscosity is lowered during the heat drying process. [Equation 1] Furthermore, it has been discovered that edge coverage is good when the storage modulus (G') is always above a certain value [Equation 2], but that finish (voids) and corrosion prevention will deteriorate unless the minimum value of the storage modulus (G') is below a certain value [Equation 3].

[0017] Examples of methods for adjusting the storage modulus (G') and loss modulus (G") include adding a viscosity modifier (C), adjusting the solids concentration, adjusting the molecular weight of the resin, adjusting the amount of functional groups in the resin, adjusting the glass transition temperature of the resin, and adjusting the pigment concentration. These methods can be used alone or in combination of two or more. Of these, adjustments can be made simply and effectively by using the viscosity modifier (C), the molecular weight and / or the glass transition temperature of the resin (A).

[0018] Cationic Electrodeposition Coating Composition The cationic electrodeposition coating composition of the present invention preferably contains an amine-modified epoxy resin (A), a blocked polyisocyanate compound (B), and a viscosity modifier (C), and preferably further contains a pigment dispersion paste.

[0019] Amine-Modified Epoxy Resin (A) The amine-modified epoxy resin (A) that can be used in the present invention is preferably a reaction product of an epoxy resin and an amine compound. Examples include (1) adducts of an epoxy resin with primary mono- and polyamines, secondary mono- and polyamines, or mixed primary and secondary polyamines (see, for example, U.S. Pat. No. 3,984,299); (2) adducts of an epoxy resin with secondary mono- and polyamines having a ketiminated primary amino group (see, for example, U.S. Pat. No. 4,017,438); and (3) reaction products obtained by etherification of an epoxy resin with a hydroxy compound having a ketiminated primary amino group (see, for example, JP-A-59-43013). Among these, it is preferable that the amine compound that reacts with the epoxy resin contains the ketiminated primary amine of (2) or (3) above.

[0020] The epoxy resin (A-1) used in the production of the above-mentioned amine-modified epoxy resin (A) is a compound having at least one, preferably two or more, epoxy groups per molecule, and suitably has a number average molecular weight of at least 300, preferably 400 to 6,000, more preferably 800 to 4,000, and an epoxy equivalent of at least 160, preferably 180 to 3,000, more preferably 400 to 2,000. Examples of such epoxy resins that can be used include those obtained by reacting a polyphenol compound with an epihalohydrin (e.g., epichlorohydrin).

[0021] Examples of the polyphenol compound used to form the epoxy resin include bis(4-hydroxyphenyl)-2,2-propane [bisphenol A], bis(4-hydroxyphenyl)methane [bisphenol F], bis(4-hydroxycyclohexyl)methane [hydrogenated bisphenol F], 2,2-bis(4-hydroxycyclohexyl)propane [hydrogenated bisphenol A], 4,4'-dihydroxybenzophenone, bis(4-hydroxyphenyl)-1,1-ethane, bis(4-hydroxyphenyl)-1,1-isobutane, bis(4-hydroxy-3-tert-butyl-phenyl)-2,2-propane, bis(2-hydroxynaphthyl)methane, tetra(4-hydroxyphenyl)-1,1,2,2-ethane, 4,4'-dihydroxydiphenyl sulfone, phenol novolac, and cresol novolac.

[0022] Among the epoxy resins obtained by the reaction of a polyphenol compound with an epihalohydrin, the epoxy resin of the following formula (1) derived from bisphenol A is preferred. Furthermore, it is also possible to use an epoxy resin which has been made high molecular weight and / or multifunctional by reacting the epoxy resin of the following formula (1) with a polyphenol compound, and among these, bisphenol A is preferred as the polyphenol compound.

[0023]

[0024] Here, n=0 to 8 is preferred.

[0025] Commercially available examples of such epoxy resins include those sold by Mitsubishi Chemical Corporation under the trade names "jER828EL," "jER1002," "jER1004," and "jER1007."

[0026] Furthermore, the epoxy resin (A-1) may be an epoxy resin containing a polyalkylene oxide chain in its resin skeleton. Typically, such an epoxy resin can be obtained by (α) reacting an epoxy resin having at least one, preferably two or more, epoxy groups with an alkylene oxide or polyalkylene oxide to introduce a polyalkylene oxide chain, or (β) reacting the polyphenol compound with a polyalkylene oxide having at least one, preferably two or more, epoxy groups to introduce a polyalkylene oxide chain. Alternatively, an epoxy resin already containing a polyalkylene oxide chain may be used (see, for example, JP-A-8-337750). The alkylene group in the polyalkylene oxide chain is preferably an alkylene group having 2 to 8 carbon atoms, more preferably an ethylene group, a propylene group, or a butylene group, with a propylene group being particularly preferred. From the viewpoint of improving paint stability, finish quality and corrosion resistance, the content of the polyalkylene oxide chain is suitably within the range of usually 1.0 to 15.0 mass%, preferably 2.0 to 9.5 mass%, more preferably 3.0 to 8.0 mass%, as the content of the polyalkylene oxide as a constituent component, based on the solids mass of the amine-modified epoxy resin.

[0027] Examples of the primary mono- and polyamines, secondary mono- and polyamines, or mixed primary and secondary polyamines used in the production of the amine-modified epoxy resin (A) above (1) include one or more of mono- or di-alkylamines such as monomethylamine, dimethylamine, monoethylamine, diethylamine, monoisopropylamine, diisopropylamine, monobutylamine, and dibutylamine; alkanolamines such as monoethanolamine, diethanolamine, mono(2-hydroxypropyl)amine, and monomethylaminoethanol; and alkylene polyamines such as ethylenediamine, propylenediamine, butylenediamine, hexamethylenediamine, diethylenetriamine, and triethylenetetramine.

[0028] Examples of the secondary mono- and polyamines having a ketiminated primary amino group used in the production of the amine-modified epoxy resin (A) described above in (2) include ketimines produced by reacting a ketone compound with, for example, diethylenetriamine, dipropylenetriamine, or the like, among the mixed primary and secondary polyamines used in the production of the amine-added epoxy resin described above in (1).

[0029] Examples of the hydroxy compound having a ketiminated primary amino group used in the production of the amine-modified epoxy resin (A) of (3) above include hydroxyl group-containing ketimines obtained by reacting a compound having a primary amino group and a hydroxyl group, such as monoethanolamine or mono(2-hydroxypropyl)amine, among the primary mono- and polyamines, secondary mono- and polyamines, or mixed primary and secondary polyamines used in the production of the amine-modified epoxy resin (A) of (1) above, with a ketone compound.

[0030] The amine value of such an amine-modified epoxy resin (A) is preferably in the range of 30 to 120 mg KOH / g resin solid content, more preferably 40 to 100 mg KOH / g resin solid content, from the viewpoint of improving water dispersibility and corrosion resistance.

[0031] Furthermore, the amine-modified epoxy resin (A) can be modified with a modifier, if necessary. Such a modifier is not particularly limited as long as it is a resin or compound reactive with the epoxy resin (A-1). For example, one or more of the following modifiers can be used: polyol, polyether polyol, polyester polyol, polyamidoamine, polycarboxylic acid, fatty acid, polyisocyanate compound, compound obtained by reacting a polyisocyanate compound, lactone compound such as ε-caprolactone, acrylic monomer, compound obtained by polymerizing an acrylic monomer, xylene formaldehyde compound, and epoxy compound. These modifiers can be used alone or in combination of two or more.

[0032] The addition reaction of the amine compound and the modifier to the epoxy resin (A-1) can usually be carried out in a suitable solvent at a temperature of about 80 to about 170°C, preferably about 90 to about 150°C, for about 1 to 6 hours, preferably about 1 to 5 hours.

[0033] Examples of the solvent include hydrocarbons such as toluene, xylene, cyclohexane, and n-hexane; esters such as methyl acetate, ethyl acetate, and butyl acetate; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and methyl amyl ketone; amides such as dimethylformamide and dimethylacetamide; alcohols such as methanol, ethanol, n-propanol, and isopropanol; ether alcohol compounds such as ethylene glycol monobutyl ether and diethylene glycol monoethyl ether; and mixtures thereof.

[0034] The proportion of the modifier used is not strictly limited and can be varied as appropriate depending on the application of the coating composition, etc. From the viewpoint of improving the finish and corrosion resistance, it is usually appropriate that the proportion be within the range of 0 to 50 mass %, preferably 3 to 30 mass %, and more preferably 6 to 20 mass %, based on the solids mass of the amine-modified epoxy resin.

[0035] Furthermore, from the viewpoint of edge corrosion resistance, if the number-average molecular weight of the amine-modified epoxy resin (A) is large (the lower limit is usually 2,000 or more, preferably 3,000 or more, and the upper limit is usually 5,000 or less, preferably 4,000 or less) and the glass transition temperature (Tg) is 100°C or less, G' increases quickly, preventing edge exposure, and the viscosity is low due to the influence of the glass transition temperature (Tg), thereby suppressing void (bubble) formation. Even if the molecular weight is large, if the glass transition temperature (Tg) is high, G' and viscosity will always be high, so that although the edge is covered, voids will form, which may result in a decrease in finish or corrosion resistance due to the voids.

[0036] In this specification, unless otherwise specified, the number average molecular weight and weight average molecular weight of the uncrosslinked resin are values ​​obtained by converting the retention time (retention volume) measured using gel permeation chromatography (GPC) into the molecular weight of polystyrene using the retention time (retention volume) of a standard polystyrene of known molecular weight measured under the same conditions. Specifically, as the gel permeation chromatography, "HLC8120GPC" (trade name, manufactured by Tosoh Corporation) was used, and four columns, "TSKgel G-4000HXL", "TSKgel G-3000HXL", "TSKgel G-2500HXL" and "TSKgel G-2000HXL" (trade names, all manufactured by Tosoh Corporation), were used. Measurements can be performed under the conditions of a mobile phase of dimethylformamide (containing 0.5% by mass of triethanolamine), a measurement temperature of 40 ° C, a flow rate of 1 mL / min, and a detector RI.

[0037] Blocked Polyisocyanate Compound (B) The blocked polyisocyanate compound (B) is a reaction product of a polyisocyanate compound and a blocking agent in approximately stoichiometric amounts. The polyisocyanate compound used in the blocked polyisocyanate compound (B) may be any known compound, and examples thereof include aromatic, aliphatic, or alicyclic polyisocyanate compounds such as tolylene diisocyanate, xylylene diisocyanate, phenylene diisocyanate, diphenylmethane-2,2'-diisocyanate, diphenylmethane-2,4'-diisocyanate, diphenylmethane-4,4'-diisocyanate, crude MDI [polymethylene polyphenylisocyanate], bis(isocyanatomethyl)cyclohexane, tetramethylene diisocyanate, hexamethylene diisocyanate, methylene diisocyanate, and isophorone diisocyanate; cyclized polymers or biuret products of these polyisocyanate compounds; or combinations thereof.

[0038] In particular, aromatic polyisocyanate compounds such as tolylene diisocyanate, xylylene diisocyanate, phenylene diisocyanate, diphenylmethane-2,4'-diisocyanate, diphenylmethane-4,4'-diisocyanate, crude MDI, etc. (preferably crude MDI, etc.) are more preferred for their anticorrosive properties.

[0039] On the other hand, the above-mentioned blocking agent is added to the isocyanate group of the polyisocyanate compound to block it, and the blocked polyisocyanate compound produced by the addition is stable at room temperature, but it is desirable that the blocking agent dissociates to regenerate free isocyanate groups when heated to the baking temperature of the coating film (usually about 100 to about 200°C).

[0040] Examples of the blocking agent used in the blocked polyisocyanate compound (B) include one or more of the following: oxime compounds such as methyl ethyl ketoxime and cyclohexanone oxime; phenolic compounds such as phenol, para-t-butylphenol, and cresol; alcohol compounds such as n-butanol, 2-ethylhexanol, phenyl carbinol, methylphenyl carbinol, ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, ethylene glycol, and propylene glycol; lactam compounds such as ε-caprolactam and γ-butyrolactam; and active methylene compounds such as dimethyl malonate, diethyl malonate, ethyl acetoacetate, methyl acetoacetate, and acetylacetone (preferably, alcohol compounds).

[0041] Among these, diol compound (b-1), which is a type of alcohol-based compound, is preferred from the viewpoints of curability (corrosion resistance and edge corrosion resistance) and storage stability. When the diol compound (b-1) has two hydroxyl groups with the same reactivity, the molecular weight increases, potentially resulting in a deterioration in finish quality. Therefore, it is preferable to contain a diol compound (b-2) having two hydroxyl groups with different reactivities. Examples of the diol compound (b-2) include at least one diol compound (b-2) selected from the group consisting of a primary hydroxyl group and a secondary hydroxyl group, a primary hydroxyl group and a tertiary hydroxyl group, and a secondary hydroxyl group and a tertiary hydroxyl group. Furthermore, in order to reduce loss on heating, the molecular weight of the blocking agent is preferably 300 or less, more preferably 200 or less, and even more preferably 150 or less. Specific examples include one or more of propylene glycol, 1,3-butanediol, 1,2-butanediol, 3-methyl-1,2-butanediol, 1,2-pentanediol, 1,4-pentanediol, 3-methyl-4,3-pentanediol, 3-methyl-4,5-pentanediol, 2,2,4-trimethyl-1,3-pentanediol, 1,5-hexanediol, and 1,4-hexanediol. Among these, diol compounds having a primary hydroxyl group and a secondary hydroxyl group are preferred, and propylene glycol is suitable from the viewpoints of curability of the blocked polyisocyanate, reduction of heat loss, and storage stability of the coating material. These diol compounds (b-2) typically react with the isocyanate group from the more reactive hydroxyl group to block the isocyanate group. The diol compound (b-2) can be used in combination with other blocking agents, and the content (mol %) of the diol compound (b-2) having two hydroxyl groups with different reactivities is preferably 50 mol % or more, more preferably 96 mol % or more, and even more preferably 100 mol %.

[0042] Viscosity Modifier (C) The viscosity modifier (C) that can be contained in the cationic electrodeposition coating composition of the present invention can be any known additive capable of adjusting viscosity, and can be, for example, one or more selected from the group consisting of cationic microgel (C-1), (meth)acrylate-modified epoxy (C-2), hydroxy(meth)acrylate-blocked polyisocyanate compound (C-3), inorganic particles (C-4), and polar polymer (C-5). Among these, it is preferable to contain at least one selected from cationic microgel (C-1), (meth)acrylate-modified epoxy (C-2), and hydroxy(meth)acrylate-blocked polyisocyanate compound (C-3).

[0043] The amount of the viscosity modifier (C) to be blended is usually 0.1 to 40 mass %, preferably 0.1 to 20 mass %, and more preferably 0.5 to 20 mass %, based on the total mass of the solid contents of the resin (A) and compound (B).

[0044] Cationic Microgel (C-1) The cationic microgel (C-1) is not particularly limited as long as it is a cationic resin-crosslinked particle. Specific examples include cationic epoxy resin crosslinked particles, acrylic resin crosslinked particles, urethane resin crosslinked particles, polyester resin crosslinked particles, and composite particles thereof. One type may be used alone, or two or more types may be used in combination.

[0045] The amount of the cationic microgel (C-1) to be blended is usually 0.1 to 40 mass %, preferably 0.1 to 20 mass %, more preferably 0.5 to 20 mass %, even more preferably 1 to 15 mass %, and particularly preferably 2 to 9 mass %, based on the total mass of the solid contents of the resin (A) and compound (B).

[0046] Crosslinked Epoxy Resin Particles (C-1-1) The crosslinked epoxy resin particles (C-1-1) have a number average molecular weight, measured under the following conditions, of usually less than 100,000, preferably 9,000 or less, and more preferably 5,000 or less as an upper limit, and usually 100 or more, preferably 150 or more, and more preferably 200 or more as a lower limit, which are suitable from the viewpoints of finish and corrosion resistance of edges.

[0047] <Method for measuring the number average molecular weight of crosslinked epoxy resin particles> The crosslinked epoxy resin particles (C-1-1) were diluted with N,N'-dimethylformamide to a concentration of 1% by mass solids and allowed to stand at room temperature for 24 hours. The insoluble components (crosslinked components) were then filtered out using a Myshori filter for GPC (pore size: 0.2 microns), and the number average molecular weight was measured using gel permeation chromatography (GPC) as described below. In gel permeation chromatography (GPC) measurements, the presence of insoluble components (crosslinked components that are not soluble in the solvent in this invention) can cause clogging in the apparatus and lead to malfunctions, so it is common to prepare samples by filtration using a filter.

[0048] <Gel permeation chromatography (GPC)> Apparatus: "HLC8120GPC" (trade name, manufactured by Tosoh Corporation) Column: Four columns: "TSKgel G-4000HXL", "TSKgel G-3000HXL", "TSKgel G-2500HXL", and "TSKgel G-2000HXL" (trade names, all manufactured by Tosoh Corporation) Mobile phase: N,N'-dimethylformamide Conditions: Measurement temperature 40°C, flow rate 1 mL / min Detector: RI

[0049] The number average molecular weight is a value obtained by converting the retention time (retention volume) measured using the above-mentioned gel permeation chromatography (GPC) into the molecular weight of polystyrene using the retention time (retention volume) of a standard polystyrene of known molecular weight measured under the same conditions.

[0050] Since the epoxy resin crosslinked particles (C-1-1) have poor finish properties when their molecular weight is increased, the peak area (polymer ratio) at molecular weights of 100,000 or more preferably accounts for less than 40%, more preferably less than 30%, of the total peak area in number-average molecular weight measurement data measured by gel permeation chromatography (GPC). In this specification, the peak area at molecular weights of 100,000 or more may be referred to as the "polymer ratio."

[0051] Furthermore, the proportion of the insoluble components in the epoxy resin crosslinked particles (C-1-1) is preferably 10% by mass or more, more preferably 10 to 90% by mass, even more preferably 10 to 60% by mass, and particularly preferably 15 to 45% by mass, from the viewpoints of corrosion resistance and finish quality at the edge and flat surfaces. If the insoluble components are too high, the finish quality deteriorates, while if the insoluble components are too low, the corrosion resistance at the edge deteriorates. Therefore, by keeping the proportion within this range, both corrosion resistance and finish quality at the edge can be achieved. The proportion of the insoluble components (crosslinked components) can be calculated by the following method.

[0052] <Method for Measuring the Proportion of Insoluble Components (Crosslinked Components)> The epoxy resin crosslinked particles (C-1-1) were diluted with N,N'-dimethylformamide to a solids concentration of 1% by mass and allowed to stand at room temperature for 24 hours. The insoluble components (crosslinked components) were then filtered using a GPC Myshori filter (pore size: 0.2 μm), and the insoluble residue was dried at 130°C for 3 hours to measure the solid mass of the residue. The proportion (mass %) of the insoluble components (crosslinked components) can be calculated using the following formula: Proportion (mass %) of Insoluble Components (Crosslinked Components) = A / B x 100, where A: solid mass of the filtration residue, and B: solid mass of the epoxy resin crosslinked particle (C-1-1) solution before filtration. The epoxy resin crosslinked particles (C-1-1) that can be used in the cationic electrodeposition coating composition of the present invention are not particularly limited, as long as they are cationic particles obtained by crosslinking an epoxy resin with a crosslinking agent. Here, the epoxy resin used as the raw material for the epoxy resin crosslinked particles (C-1-1) includes resins obtained by modifying epoxy resins, and also includes resins that do not have epoxy groups obtained by modifying epoxy groups. Examples of crosslinking agents include compounds having one or more (preferably two or more) reactive functional groups such as epoxy groups, isocyanate groups, alkoxysilyl groups, hydroxyl groups, carboxyl groups, and amino groups, and may have two or more types of reactive functional groups.

[0053] Examples of the crosslinked epoxy resin particles (C-1-1) include crosslinked epoxy resin particles obtained by reacting an epoxy resin with an amine compound to produce an amine-modified epoxy resin, neutralizing the amine-modified epoxy resin with an acid compound, dispersing the amine-modified epoxy resin in an aqueous solvent, and mixing and reacting the resulting dispersion with a crosslinking agent [e.g., a polyfunctional epoxy resin, an organosilicon compound (silane coupling agent), a polyisocyanate compound, etc.]. The crosslinking agent preferably contains an epoxy resin and / or an organosilicon compound (silane coupling agent), and more preferably contains an organosilicon compound (silane coupling agent) from the viewpoint of exhibiting viscoelasticity.

[0054] The reason why the organosilicon compound (silane coupling agent) has an effect on viscoelasticity is thought to be that during the heating and drying process, reactive functional groups such as alkoxysilyl groups remaining in the silane coupling agent react with primary amino groups, secondary amino groups, and / or hydroxyl groups of the amine-modified epoxy resin (A), resulting in a high molecular weight resin.

[0055] As one embodiment of the epoxy resin crosslinked particles (C-1-1), a production process is shown below, which includes the following steps: step (I) of producing an amine-modified epoxy resin obtained by reacting an epoxy resin with an amine compound; step (II) of neutralizing the amine-modified epoxy resin with an acid compound and dispersing the resultant in an aqueous solvent; and step (III) of mixing and reacting the resulting dispersion with a crosslinking agent containing a silane coupling agent to obtain the epoxy resin crosslinked particles.

[0056] <Step (I)> As the step of producing an amine-modified epoxy resin obtained by reacting an epoxy resin with an amine compound, the same production method as that for the amine-modified epoxy resin (A) described above can be used.

[0057] The epoxy resin may be the same as the epoxy resin (A-1) described above, and among these, an epoxy resin derived from bisphenol A is preferably used. Furthermore, an epoxy resin that has been made high molecular weight and / or multifunctional by reacting an epoxy resin with a polyphenol compound is preferably used, and the polyphenol compound is preferably bisphenol A. The number average molecular weight of the epoxy resin is preferably 400 to 5,000, and more preferably 700 to 3,000.

[0058] The amine compound may be any of the amine compounds listed above for the amine-modified epoxy resin (A), but it is particularly preferred to include a ketiminated amine compound, and particularly preferred to include a secondary mono- and polyamine having a ketiminated primary amino group. Examples of the secondary mono- and polyamine having a ketiminated primary amino group include ketiminated products of amine compounds represented by the following formula (2), specifically, diketiminated products of diethylenetriamine, dipropylenetriamine, dibutylenetriamine, bis(hexamethylene)triamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexaamine, and the like.

[0059] (In the formula, R １ and R ２ are hydrocarbon groups having 1 to 8 carbon atoms and may be different or the same. n is an integer of 1 to 5.) The ketiminated amine compound is contained in the amine compound in an amount of preferably 0.1 mol% or more and less than 80 mol%, more preferably 1 mol% or more and less than 50 mol%, even more preferably 2 mol% or more and less than 40 mol%, and particularly preferably 5 mol% or more and less than 30 mol%. In this specification, the content of the ketiminated amine compound may be referred to as the "ketimine compound content."

[0060] The ketiminized and blocked primary amino group of the amine compound is hydrolyzed in the water dispersion step (II) described below to reveal a primary amino group. Then, in step (III), the primary amino group reacts with the epoxy group of the epoxy compound, resulting in a polymerizing and / or crosslinking reaction. Therefore, by adjusting the amount of the amine compound within the above range, the molecular weight, particle size, and / or degree of crosslinking (proportion of insoluble components) of the epoxy resin crosslinked particles (C-1-1) can be optimized.

[0061] <Step (II)> The amine-modified epoxy resin obtained in step (I) above is subsequently neutralized with an acid compound and dispersed in an aqueous solvent to obtain a dispersion. Here, the aqueous solvent refers to a solvent containing water and other solvents that can be added as needed. Examples of other solvents include ester solvents, ketone solvents, amide solvents, alcohol solvents, and ether alcohol solvents, as well as mixtures thereof. Any known acid compound can be used as the acid compound without any particular restrictions. Among these, organic acids are preferred, with formic acid, lactic acid, acetic acid, or mixtures thereof being particularly preferred. The neutralization equivalent is preferably 0.2 to 1.5 equivalents of the acid compound per equivalent of amino group, more preferably 0.5 to 1.0 equivalents. In addition to the acid compound, additives such as emulsifiers may also be added.

[0062] The dispersion of the amine-modified epoxy resin in the aqueous solvent may be carried out by adding the aqueous solvent to the neutralized amine-modified epoxy resin while stirring, or by adding the neutralized amine-modified epoxy resin to the aqueous solvent while stirring, or by mixing the aqueous solvent and the neutralized amine-modified epoxy resin and then stirring. The dispersion temperature is preferably less than 100°C, more preferably 40 to 99°C, and even more preferably 50 to 95°C. The resin solids concentration of the dispersion is preferably 5 to 80% by mass, more preferably 10 to 50% by mass.

[0063] <Step (III)> The dispersion obtained in the above step (II) is subsequently mixed with a crosslinking agent containing a silane coupling agent, and further reacted to obtain cationic epoxy resin crosslinked particles (C-1-1). Furthermore, as the crosslinking agent, the silane coupling agent can be used in combination with other crosslinking agents (e.g., epoxy resins or polyisocyanate compounds). Examples of the silane coupling agent include amino group-containing silane coupling agents, epoxy group-containing silane coupling agents, (meth)acryloyl group-containing silane coupling agents, mercapto group-containing silane coupling agents, vinyl group-containing silane coupling agents, ureido group-containing silane coupling agents, sulfide group-containing silane coupling agents, and silane coupling agents having a cyclic anhydride structure. These silane coupling agents can be used alone or in combination of two or more.

[0064] Commercially available silane coupling agents include, for example, "KBM-1003" (vinyltrimethoxysilane), "KBM-1083" (7-octenyltrimethoxysilane), "KBM-303" (2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane), "KBM-403" (3-glycidoxypropyltrimethoxysilane), "KBM-4803" (8-glycidoxyoctyltrimethoxysilane), and "KBM-1403" (manufactured by Shin-Etsu Chemical Co., Ltd.). p-styryltrimethoxysilane), "KBM-503" (3-methacryloxypropyltrimethoxysilane), "KBM-5803" (8-methacryloxyoctyltrimethoxysilane), "KBM-5103" (3-acryloxypropyltrimethoxysilane), "KBM-603" (N-2-(aminoethyl)-3-aminopropyltrimethoxysilane), "KBM-903" (3-aminopropyltrimethoxysilane), "KBM-573" (N-phenyl- 3-aminopropyltrimethoxysilane), "KBM-575" (N-(vinylbenzyl)-2-aminoethyl-3-aminopropyltrimethoxysilane hydrochloride), "KBM-6803" (N-2-(aminoethyl)-8-aminooctyltrimethoxysilane), "KBM-9659" (tris-(trimethoxysilylpropyl)isocyanurate), "X-12-1290" (1,3-diallyl-5-(3-(trimethoxysilyl)propyl)-1,3,5-triisopropyltrimethoxysilane), dinane-2,4,6-trione), "KBM-803" (3-mercaptopropyltrimethoxysilane), "X-12-967C" (3-trimethoxysilylpropylsuccinic anhydride); "Sila-Ace S810" (3-mercaptopropyltrimethoxysilane) manufactured by Chisso Corporation; "SIM6473.5C" (mercaptomethyltrimethoxysilane) and "SIU9058.0" (N-(3-trimethoxysilylpropyl)urea) manufactured by Azmax Corporation.

[0065] In the reaction step, the reactive functional groups (e.g., primary amino groups) of the amine-modified epoxy resin from which the ketiminized blocks have been removed by hydrolysis react with the reactive functional groups (e.g., alkoxysilyl groups) of the silane coupling agent, which serves as the crosslinking agent, resulting in a polymerization and / or crosslinking reaction. The reactive functional group equivalent ratio between the amine-modified epoxy resin and the crosslinking agent is preferably 0.5 to 2.0 equivalents, more preferably 0.7 to 1.5 equivalents, of the crosslinking agent per equivalent of the amine-modified epoxy resin. The reaction temperature is preferably less than 100°C, more preferably 40 to 99°C, and even more preferably 50 to 95°C. Furthermore, during or after the polymerization and / or crosslinking reaction, a desolvation step can be performed by reducing the pressure at a temperature of 40 to 99°C.

[0066] Another embodiment of the silane coupling agent-containing crosslinked epoxy resin particles (C-1-1) may be crosslinked epoxy resin particles produced by a process other than the above steps (I) to (III).

[0067] The volume-average particle diameter of the crosslinked epoxy resin particles (C-1-1) is typically within the range of 10 nm to 1,000 nm, preferably greater than 15 nm, more preferably greater than 20 nm, even more preferably greater than 25 nm, and particularly preferably greater than 30 nm, from the viewpoints of corrosion resistance at the edges and flat surfaces, and finish quality. It is also preferably smaller than 800 nm, more preferably smaller than 700 nm, even more preferably smaller than 600 nm, and particularly preferably smaller than 500 nm. The volume-average particle diameter of the cationic microgel (C-1) can be measured using a laser diffraction / scattering measurement device, and the particle diameters herein were measured using a "Microtrac UPA250" (trade name, manufactured by Nikkiso Co., Ltd., particle size distribution measurement device). The amine value of the crosslinked cationic epoxy resin particles (C-1-1) is preferably within the range of 25 to 200 mgKOH / g, and more preferably within the range of 50 to 180 mgKOH / g. By adjusting the content within the above range, the dispersibility of the particles in the aqueous solvent and the water resistance of the coating film are excellent.

[0068] (Meth)acrylate-Modified Epoxy (C-2) The (meth)acrylate-modified epoxy (C-2) can be suitably used as long as it is an epoxy resin having at least one (meth)acryloyl group, and can be obtained, for example, by the following method (1) or (2). (1) It can be obtained by reacting the above-mentioned epoxy resin (A-1) with a compound having at least one reactive functional group and at least one (meth)acryloyl group. Examples of the reactive functional group include a carboxyl group and a primary or secondary amino group, with a carboxyl group being preferred. Specific examples of the compound having at least one reactive functional group and at least one (meth)acryloyl group include (meth)acrylic acid and aminoethyl (meth)acrylate. These can be used alone or in combination of two or more. (2) It can be obtained by reacting a hydroxyl group or a primary or secondary amino group of the above-mentioned amine-modified epoxy resin (A) with a compound having at least one reactive functional group and at least one (meth)acryloyl group. Examples of the reactive functional group include a glycidyl group and an isocyanate group. Specific examples of the compound having at least one reactive functional group and at least one (meth)acryloyl group include glycidyl (meth)acrylate and (meth)acryloyloxyethyl isocyanate. These can be used alone or in combination of two or more.

[0069] The reason why the (meth)acrylate-modified epoxy (C-2) has an effect on viscoelasticity is thought to be that during the heat drying process, a Michael addition reaction occurs between the (meth)acryloyl group of the (meth)acrylate-modified epoxy (C-2) and the primary amino group, secondary amino group, and / or hydroxyl group of the amine-modified epoxy resin (A), resulting in a high molecular weight resin.

[0070] When a (meth)acrylate-modified epoxy (C-2) is used as the viscosity modifier (C), it is preferable that the amine compound, which is a constituent of the amine-modified epoxy resin (A), contains a ketimine compound of a primary amine, from the viewpoint of the reactivity between the amine-modified epoxy resin and the viscosity modifier.

[0071] Hydroxy(meth)acrylate-blocked polyisocyanate compound (C-3) The hydroxy(meth)acrylate-blocked polyisocyanate compound (C-3) can be obtained by reacting a polyisocyanate compound with a hydroxy(meth)acrylate, and the polyisocyanate compounds listed above for the blocked polyisocyanate compound (B) can be suitably used as the polyisocyanate compound. Furthermore, any compound having at least one hydroxy group and at least one (meth)acryloyl group can be suitably used as the hydroxy(meth)acrylate. Examples include monoesters of (meth)acrylic acid with dihydric alcohols having 2 to 8 carbon atoms, such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate, as well as ε-caprolactone-modified products of the monoesters of (meth)acrylic acid with dihydric alcohols having 2 to 8 carbon atoms. These compounds can be used alone or in combination of two or more.

[0072] Furthermore, the hydroxy(meth)acrylate-blocked polyisocyanate compound (C-3) can be used in combination with the compounds listed as the blocking agents for the blocked polyisocyanate compound (B) as well as the above-mentioned hydroxy(meth)acrylates, as compounds that react with the isocyanate groups of the polyisocyanate compound. The ratio of the isocyanate groups of the polyisocyanate compound to the reactive groups (such as hydroxyl groups) that react with the isocyanate groups is usually 0.1 to 5.0, and preferably 0.5 to 2.0.

[0073] The reason why the hydroxy(meth)acrylate-blocked polyisocyanate compound (C-3) is effective in improving viscoelasticity is believed to be that during the heat drying process, a Michael addition reaction occurs between the (meth)acryloyl group of the hydroxy(meth)acrylate-blocked polyisocyanate compound (C-3) and the primary amino group, secondary amino group, and / or hydroxyl group of the amine-modified epoxy resin (A), resulting in a high molecular weight resin.

[0074] When the hydroxy(meth)acrylate-blocked polyisocyanate compound (C-3) is used as the viscosity modifier (C), it is preferable that the amine compound, which is a constituent of the amine-modified epoxy resin (A), contains a ketimine compound of a primary amine, from the viewpoint of the reactivity between the amine-modified epoxy resin and the viscosity modifier.

[0075] Inorganic Particles (C-4) Examples of the inorganic particles include silica and / or clay minerals, with silica being preferred.

[0076] The silica is generally a solid substance whose main component is silicon dioxide. Among them, silica obtained by mixing sodium silicate and acid using a so-called wet method is preferred, and examples of commercially available products include the Sylysia series available from Fuji Silysia Chemical. Metal ion-exchanged silica, in which metal ions are introduced into a silica support by ion exchange, can also be used preferably. Examples of the metal ions include calcium ions, magnesium ions, cobalt ions, nickel ions, and lithium ions.

[0077] The silica has excellent affinity with the amine-modified epoxy resin (A), and it is believed that the corrosion resistance of the edge portion is improved by the interaction between the silica and the polar groups of the amine-modified epoxy resin (A).

[0078] Clay minerals are the main component minerals that make up clay, and include layered silicate minerals (phyllosilicates), calcite, dolomite, feldspars, quartz, zeolites, and others with chain structures (attapulgite, sepiolite, etc.), fibrous structures (palygorskite, etc.), and those without a clear crystalline structure (allophane). The clay minerals preferably contain at least one clay mineral other than clay, and preferably use a combination of clay and at least one clay mineral other than clay. Note that "clay" refers to plate-like or layered clay primarily composed of silica, magnesium, iron, potassium, and sodium extracted from clay layers, and also includes refined clay. Refined clay is clay from which impurities have been dissolved and removed using acid or other methods. Kaolin clay, which contains kaolinite, is commonly used in paint applications.

[0079] The shape of the inorganic particles (C-4) is preferably at least one selected from the group consisting of spherical, plate-like, scale-like, layer-like, rod-like, chain-like, needle-like and fibrous shapes.

[0080] The inorganic particles (C-4) have an average particle size of preferably 0.1 to 30 μm, more preferably 0.2 to 20 μm, and even more preferably 0.4 to 10 μm. The average particle size can be measured by laser diffraction (volume basis).

[0081] Polar Polymer (C-5) The cationic electrodeposition coating composition of the present invention may contain a polar polymer (C-5).

[0082] The content of the polar polymer (C-5) is typically 0.1 to 40 mass%, preferably 0.1 to 20 mass%, more preferably 0.5 to 20 mass%, even more preferably 0.5 to 15 mass%, particularly preferably 0.5 to 10 mass%, and even more preferably 0.5 to 5 mass%, based on the total mass of the solid contents of the resin (A) and compound (B).

[0083] In this specification, the term "polymer" refers to a polymer formed by the polymerization (reaction) of two or more monomers. The weight-average molecular weight of the polar polymer (C-5) is, for example, 100 or more, preferably 500 or more, more preferably 1,000 to 10,000,000, even more preferably 2,000 to 8,000,000, and most preferably within the range of 3,000 to 5,000,000, from the viewpoints of viscosity development and water resistance.

[0084] The polar polymer (C-5) is a highly polar, high-molecular-weight compound having a polar functional group, such as at least one selected from the group consisting of amide group-containing resins, urea group-containing resins, urethane group-containing resins, polyvinyl alcohol, polyvinyl acetal, polyalkylene ethers, polycarbonates, polyester resins, acrylic resins, and polysaccharides, or a composite resin thereof. These can be used alone or in combination of two or more. Among these, amide group-containing resins and polyvinyl alcohol are preferred. Examples of the amide group-containing resin include polyamides, fatty acid amides, polyhydroxycarboxylic acid amides, polyvinylpyrrolidone, polyvinyl acetamide, polyvinyl formamide, poly-N-methylvinyl acetamide, and poly(meth)acrylamide. Furthermore, the polar functional group preferably contains at least one polar functional group selected from the group consisting of amino groups, sulfonic acid groups, carboxyl groups, phosphate groups, polyalkylene ether groups, amide groups, hydroxyl groups, ester groups, and epoxy groups.

[0085] The polar functional group concentration in the polar polymer (C-5) is usually 0.1 mmol / g or more, preferably 1 to 30 mmol / g, more preferably 2 to 25 mmol / g, even more preferably 5 to 23 mmol / g, and particularly preferably 6 to 20 mmol / g, from the viewpoints of viscosity development and throwing power.

[0086] In this specification, the polar functional group concentration is calculated by counting one polar functional group as one. For example, if one polymerizable unsaturated monomer has two polar functional groups, it is calculated as two.

[0087] Regarding the cationic electrodeposition coating composition, the blending ratio of the amine-modified epoxy resin (A) and the blocked polyisocyanate compound (B) in the cationic electrodeposition coating composition of the present invention is preferably within the range of 5 to 95 mass %, preferably 50 to 80 mass %, of component (A) and 5 to 95 mass %, preferably 20 to 50 mass %, of component (B), based on the total mass of the solid contents of the above components (A) and (B), in order to obtain coated articles with good paint stability and excellent finish and corrosion resistance. A ratio outside these ranges is undesirable, as it may impair either the above-mentioned paint properties or coating film performance.

[0088] The cationic electrodeposition coating composition of the present invention is not particularly limited, but is preferably a composition containing, for example, a resin emulsion (I) obtained by thoroughly mixing the resin (A) and compound (B) described above with various additives, such as a viscosity modifier (C), a surfactant, and a surface modifier, as needed, and then adding water to prepare a compounded resin, and a pigment paste (II) described below. The composition can be obtained by thoroughly mixing this with water, an organic solvent, a neutralizing agent, and the like. Any known organic acid can be used as the neutralizing agent without any particular limitation, and formic acid, lactic acid, or a mixture thereof is particularly preferred.

[0089] The viscosity modifier (C) may be mixed into the coating composition by, for example, incorporating it into the aqueous dispersion when producing the resin emulsion (I), incorporating it into the pigment dispersion paste together with the pigment and dispersing resin when producing the pigment dispersion paste (II), or adding it to the coating composition containing the resin emulsion (I) and the pigment paste (II) while stirring. Any of these methods can be suitably used, but it is preferable to incorporate it into the resin emulsion (I).

[0090] Examples of the shear type dispersing machine include mixers such as a Disper, a Homomixer, and a Planetary Mixer, and homogenizers (such as "Clearmix" manufactured by M Technique, "Filmix" and "High Shear Mixer" manufactured by PRIMIX, and "Abramix" and "Mixer" manufactured by Silverson), but are not limited to these.

[0091] The pigment dispersion paste (II) is a dispersion in which a pigment such as a color pigment, an anti-rust pigment, or an extender pigment is previously dispersed into fine particles. For example, the pigment dispersion paste can be prepared by blending a pigment dispersing resin, a neutralizing agent, and a pigment, and dispersing the mixture in a dispersion mixer using media such as a ball mill, a sand mill, or a pebble mill.

[0092] As the pigment dispersing resin, any known resin can be used without any particular limitation, and examples thereof include epoxy resins or acrylic resins having a hydroxyl group and a cationic group, surfactants, tertiary amine-type epoxy resins, quaternary ammonium salt-type epoxy resins, tertiary sulfonium salt-type epoxy resins, tertiary amine-type acrylic resins, quaternary ammonium salt-type acrylic resins, and tertiary sulfonium salt-type acrylic resins.

[0093] As the pigment, any known pigment can be used without any particular limitation, and for example, one or more of the following can be added: coloring pigments such as titanium oxide, carbon black, and red iron oxide; extender pigments such as clay, mica, baryta, calcium carbonate, and silica; and rust-preventive pigments such as aluminum phosphomolybdate, aluminum tripolyphosphate, and zinc oxide (zinc white).

[0094] Furthermore, to improve the curability of the coating film, it is preferable to include a bismuth compound as a curing catalyst. Examples of the bismuth compound include one or more of bismuth oxide, bismuth hydroxide, basic bismuth carbonate, bismuth nitrate, bismuth silicate, and organic acid bismuth. From an environmental perspective, it is preferable not to include organotin compounds such as dibutyltin dibenzoate, dioctyltin oxide, and dibutyltin oxide. By using the bismuth compound as a curing catalyst, it is possible to improve the curability of the coating film without including these organotin compounds. The amount of the pigment is preferably 1 to 100 parts by weight, particularly 10 to 50 parts by weight, per 100 parts by weight of the total resin solids of resin (A) and compound (B). When a bismuth compound is used as a curing catalyst, the amount of the bismuth compound is preferably 0.1 to 10 parts by weight, particularly 1 to 5 parts by weight, per 100 parts by weight of the total resin solids of resin (A) and compound (B).

[0095] The solid content of the cationic electrodeposition coating composition is suitably in the range of 5 to 40% by mass, preferably 15 to 25% by mass.

[0096] Coating Film Formation Method The present invention provides a method for forming a cationic electrodeposition coating film, which comprises the steps of immersing a metal substrate in an electrodeposition bath comprising the above-mentioned cationic electrodeposition coating composition, and passing a current through the metal substrate using it as a cathode.

[0097] The substrates to be coated with the cationic electrodeposition coating composition of the present invention include automobile bodies, motorcycle parts, household appliances, other appliances, etc., and are not particularly limited as long as they are made of metal.

[0098] Examples of metal steel sheets to be coated include cold-rolled steel sheets, galvannealed steel sheets, electrogalvanized steel sheets, zinc-iron two-layer electroplated steel sheets, organic composite plated steel sheets, Al materials, Mg materials, and the like, as well as these metal sheets whose surfaces have been cleaned as necessary by alkaline degreasing or the like, and then subjected to surface treatments such as phosphate conversion treatment, chromate treatment, zirconium chemical conversion treatment, etc.

[0099] The cationic electrodeposition coating composition can be applied to the surface of the desired substrate by cationic electrodeposition coating. The cationic electrodeposition method generally involves preparing a bath containing the cationic electrodeposition coating composition, which has been diluted with deionized water or the like to a solids concentration of about 5 to 40 mass%, preferably 10 to 25 mass%, and further adjusted to a pH of 4.0 to 9.0, preferably 5.5 to 7.0. The bath temperature is typically adjusted to 15 to 35°C, and the substrate is used as the cathode and energized one or more times (preferably once) at a load voltage of 100 to 400 V, preferably 150 to 350 V. After electrodeposition coating, the substrate is typically thoroughly washed with ultrafiltrate (UF filtrate), reverse osmosis water (RO water), industrial water, pure water, or the like to remove any excess cationic electrodeposition coating.

[0100] The thickness of the electrodeposition coating is not particularly limited, but can generally be within the range of 5 to 40 μm, preferably 10 to 35 μm, based on the dried coating. Heat drying of the coating is carried out by heating the electrodeposition coating using drying equipment such as an electric hot air dryer or a gas hot air dryer at a temperature of 110 to 200°C, preferably 140 to 180°C, at the surface temperature of the coated object, for 10 to 180 minutes, preferably 20 to 50 minutes. A cured coating can be obtained by the above-mentioned baking drying.

[0101] The present invention will be described in more detail below with reference to Production Examples, Examples, and Comparative Examples, but the present invention is not limited thereto. In each example, "parts" means parts by mass, and "%" means % by mass.

[0102] Preparation of Amine-Modified Epoxy Resin Preparation Example 1: 945 parts of "jER828EL" (trade name, manufactured by Japan Epoxy Resins Co., Ltd., epoxy resin, epoxy equivalent 190, number average molecular weight 350) were added to 388 parts of bisphenol A and 0.2 parts of dimethylbenzylamine in a flask equipped with a stirrer, thermometer, nitrogen inlet tube, and reflux condenser, and the mixture was allowed to react at 120°C until the epoxy equivalent reached 670. Next, 188 parts of Placcel 212CP was added, and the mixture was allowed to react at 120°C for 2 hours. Further, 350 parts of a ketimine compound of diethylenetriamine and methyl isobutyl ketone and 53 parts of diethanolamine were added, and the mixture was allowed to react at 120°C for 4 hours. Ethylene glycol monobutyl ether was then added to obtain an amine-modified epoxy resin (a-1) solution with a solids content of 80%. The amine-modified epoxy resin (a-1) had an amine value of 115 mg KOH / g, a number average molecular weight of 2,050, and a glass transition temperature of 90°C.

[0103] Production Example 2: 945 parts of "jER828EL" (trade name, manufactured by Japan Epoxy Resins Co., Ltd., epoxy resin, epoxy equivalent 190, number average molecular weight 350) was mixed with 388 parts of bisphenol A and 0.3 parts of dimethylbenzylamine in a flask equipped with a stirrer, thermometer, nitrogen inlet tube, and reflux condenser, and the mixture was allowed to react at 120°C until the epoxy equivalent reached 1050. Next, 188 parts of PLACCEL 212CP was added, and the mixture was allowed to react at 120°C for 2 hours. Further, 500 parts of a ketimine compound of diethylenetriamine and methyl isobutyl ketone was added, and the mixture was allowed to react at 120°C for 4 hours. Ethylene glycol monobutyl ether was then added to obtain an amine-modified epoxy resin (a-2) solution with a solids content of 80%. The amine-modified epoxy resin (a-2) had an amine value of 96 mgKOH / g, a number average molecular weight of 3100, and a glass transition temperature of 95°C.

[0104] Production Example 3: 990 parts of bisphenol A and 0.3 parts of dimethylbenzylamine were added to 1,870 parts of "jER828EL" (trade name, manufactured by Japan Epoxy Resins Co., Ltd., epoxy resin, epoxy equivalent 190, number average molecular weight 350) in a flask equipped with a stirrer, thermometer, nitrogen inlet tube, and reflux condenser, and the mixture was allowed to react at 120°C until an epoxy equivalent of 1,430 was reached. Next, 300 parts of a ketimine compound of diethylenetriamine and methyl isobutyl ketone and 100 parts of diethanolamine were added, and the mixture was allowed to react at 120°C for 4 hours. After that, ethylene glycol monobutyl ether was added to obtain an amine-modified epoxy resin (a-3) solution with a solids content of 80%. The amine-modified epoxy resin (a-3) had an amine value of 70 mgKOH / g, a number average molecular weight of 3,200, and a glass transition temperature of 105°C.

[0105] Production Example 4: 2,450 parts of "jER828EL" (trade name, manufactured by Japan Epoxy Resins Co., Ltd., epoxy resin, epoxy equivalent 190, number average molecular weight 350) were added to 1,370 parts of bisphenol A and 0.4 parts of dimethylbenzylamine in a flask equipped with a stirrer, thermometer, nitrogen inlet tube, and reflux condenser, and the mixture was allowed to react at 120°C until the epoxy equivalent reached 1,900. Next, 350 parts of a ketimine compound of diethylenetriamine and methyl isobutyl ketone and 80 parts of diethanolamine were added, and the mixture was allowed to react at 120°C for 4 hours. After that, ethylene glycol monobutyl ether was added to obtain an amine-modified epoxy resin (a-4) solution with a solids content of 80%. The amine-modified epoxy resin (a-4) had an amine value of 60 mgKOH / g, a number average molecular weight of 4,200, and a glass transition temperature of 110°C.

[0106] The glass transition temperature (Tg) of the above epoxy resin was measured under the following conditions.

[0107] <Measurement of Glass Transition Temperature (Tg)> The glass transition temperature (Tg) of the epoxy resin was measured after removing the solvent using a viscoelasticity measuring device (manufactured by TA Instruments, trade name "ARES-G2"). - Jig: Parallel plates with a diameter of 8 mm - Temperature decrease: 130°C to 50°C (5°C / min) - Frequency: 1 Hz - Strain: Varying from 1 to 60% (automatic control) - Torque: Varying from 0.1 to 23 g cm (automatic control) In the obtained viscoelasticity spectrum, the peak temperature of the loss tangent (tan δ) was taken as the glass transition temperature.

[0108] Production of Blocked Polyisocyanate Compound Production Example 5 270 parts of "Cosmonate M-200" (trade name, manufactured by Mitsui Chemicals, Inc., crude MDI, NCO group content 31.3%) and 127 parts of methyl isobutyl ketone were placed in a reaction vessel and heated to 70° C. 236 parts of ethylene glycol monobutyl ether was added dropwise thereto over 1 hour, and the temperature was then raised to 100° C. Sampling was performed over time while maintaining this temperature, and infrared absorption spectroscopy confirmed that the absorption of unreacted isocyanate groups had disappeared, yielding a blocked polyisocyanate compound (b-1) with a resin solids content of 80%.

[0109] Production Example 6: 152 parts of propylene glycol and 106 parts of methyl isobutyl ketone were placed in a reaction vessel and heated to 70°C. 270 parts of "Cosmonate M-200" (trade name, manufactured by Mitsui Chemicals, Inc., crude MDI, NCO group content 31.3%) was added dropwise to the mixture over 1 hour. While maintaining this temperature, the mixture was sampled over time, and infrared absorption spectroscopy confirmed that no absorption due to unreacted isocyanate remained, yielding a blocked polyisocyanate compound (b-2) with a solids content of 80%.

[0110] Preparation of Pigment Dispersion Resin Preparation Example 7: 450 parts of nonylphenol and 960 parts of "CNE195LB" (trade name, manufactured by Chang Chun Japan Co., Ltd., cresol-type novolac epoxy resin, glycidyl ether of novolac-type phenolic resin) were charged into a flask equipped with a stirrer, thermometer, dropping funnel, and reflux condenser, and the mixture was gradually heated with stirring to 160°C for reaction. Thereafter, 430 parts of ε-caprolactone was charged, and the mixture was heated to 170°C for reaction. Furthermore, 105 parts of diethanolamine and 124 parts of N-methylethanolamine were reacted, and after confirming that the epoxy value had reached 0, ethylene glycol monobutyl ether was added to adjust the solids content, yielding a pigment dispersion resin solution with a solids content of 60%.

[0111] Preparation of Pigment Dispersion Paste Preparation Example 8 8.3 parts (solids content: 5 parts) of the pigment dispersion resin containing a quaternary ammonium salt group and having a solids content of 60% obtained in Preparation Example 7, 21.5 parts of titanium oxide, 0.3 parts of carbon black, 2 parts of bismuth hydroxide, and 20.3 parts of deionized water were added and dispersed in a ball mill for 20 hours, thereby obtaining a pigment dispersion paste (p-1) having a solids content of 55%.

[0112] Preparation of Epoxy Resin Crosslinked Particles Preparation Example 9: 413 parts of "jER828EL" (trade name, manufactured by Japan Epoxy Resins Co., Ltd., epoxy resin, epoxy equivalent 190, number average molecular weight 350), 126 parts of bisphenol A, and 0.1 parts of dimethylbenzylamine were added to a reaction vessel equipped with a stirrer, thermometer, dropping funnel, and reflux condenser, and the temperature inside the reaction vessel was maintained at 160°C, allowing the reaction to proceed until the epoxy equivalent reached 490 g / mol. The temperature inside the reaction vessel was then cooled to 140°C, and 1.3 parts of dimethylbenzylamine was added to allow the reaction to proceed until the epoxy equivalent reached 890 g / mol. After that, 177 parts of methyl isobutyl ketone was added while the temperature inside the reaction vessel was cooled to 100°C. Next, a mixture of 44 parts of diethanolamine, 4 parts of N-methylethanolamine, and 35 parts of a diketimine compound of diethylenetriamine and methyl isobutyl ketone (ketimine compound content: 22 mol%) was added, and the reaction was carried out at 115°C for 1 hour, thereby obtaining an amino group-containing epoxy resin solution. 305 parts of the obtained amino group-containing epoxy resin solution was added to a new reaction vessel, and the temperature inside the reaction vessel was maintained at 90°C. Next, 26 parts of 88% lactic acid was added for acid neutralization, and 1,146 parts of deionized water was added for dilution and dispersion. Next, 24 parts of a jER828EL solution adjusted to an 80% solids content with propylene glycol monomethyl ether was added, and the reaction was carried out at 90°C for 3 hours. After that, methyl isobutyl ketone was removed under reduced pressure, and the mixture was diluted with deionized water to obtain a solution of epoxy resin crosslinked particles No. 1 with an 18% solids content. The obtained epoxy resin crosslinked particles No. 1 had a number average molecular weight (Note 1) of 1,000, a polymeric fraction (Note 2) of 10%, a proportion of insoluble components (Note 3) of 25% by mass, and a volume average particle diameter (Note 4) of 50 nm. (Note 1) Number average molecular weight: Crosslinked epoxy resin particles were diluted with N,N'-dimethylformamide to a solids concentration of 1% by mass and allowed to stand at room temperature for 24 hours. The insoluble components (crosslinked components) were then filtered out using a Myshori filter for GPC (pore size: 0.2 microns), and the number average molecular weight was measured using gel permeation chromatography (GPC) ["HLC8120GPC" (trade name, manufactured by Tosoh Corporation)]. (Note 2) Polymeric fraction (%): In the molecular weight measurement data, this refers to the ratio (%) of the peak area with a molecular weight of 100,000 or greater to the total peak area.(Note 3) Insoluble component ratio (mass %): The epoxy resin crosslinked particles were diluted with N,N'-dimethylformamide to a solids concentration of 1 mass % and allowed to stand at room temperature for 24 hours. The solution was then filtered through a GPC Myshori filter (pore size: 0.2 microns), and the insoluble component ratio (crosslinked component ratio) was calculated using the following formula: Insoluble component ratio (mass %) = A / B x 100 [A: solids mass of the filtration residue, B: mass of the epoxy resin crosslinked particle solution diluted to 1 mass % solids / 100]. (Note 4) Volume average particle diameter (nm): The epoxy resin crosslinked particles were measured using a "Microtrac UPA250" (trade name, manufactured by Nikkiso Co., Ltd., particle size distribution analyzer).

[0113] Production Example 10: 413 parts of "jER828EL" (trade name, manufactured by Japan Epoxy Resins Co., Ltd., epoxy resin, epoxy equivalent 190, number average molecular weight 350), 126 parts of bisphenol A, and 0.1 parts of dimethylbenzylamine were added to a reaction vessel equipped with a stirrer, thermometer, dropping funnel, and reflux condenser, and the temperature inside the reaction vessel was maintained at 160°C, allowing the reaction to proceed until the epoxy equivalent reached 490 g / mol. The temperature inside the reaction vessel was then cooled to 140°C, and 1.3 parts of dimethylbenzylamine was added to allow the reaction to proceed until the epoxy equivalent reached 890 g / mol. After that, 177 parts of methyl isobutyl ketone was added while the temperature inside the reaction vessel was cooled to 100°C. Next, a mixture of 44 parts of diethanolamine, 4 parts of N-methylethanolamine, and 35 parts of a diketimine compound of diethylenetriamine and methyl isobutyl ketone (ketimine compound content: 22 mol%) was added, and the reaction was carried out at 115°C for 1 hour, yielding an amino group-containing epoxy resin solution. 305 parts of the resulting amino group-containing epoxy resin solution was added to a new reaction vessel, and the temperature inside the reaction vessel was maintained at 90°C. Next, 26 parts of 88% lactic acid was added for acid neutralization, and 1,146 parts of deionized water was added for dilution and dispersion. Next, 12 parts of jER828EL solution adjusted to an 80% solids content with propylene glycol monomethyl ether and 12 parts of KBM-403 (3-glycidoxypropyltrimethoxysilane, molecular weight 236) were added, and the reaction was carried out at 90°C for 3 hours. After that, the methyl isobutyl ketone was removed under reduced pressure, and the mixture was diluted with deionized water to obtain a solution of crosslinked epoxy resin particles No. 2 with an 18% solids content. The resulting crosslinked epoxy resin particles No. No. 2 had a number average molecular weight (Note 1) of 1,000, a polymer ratio (Note 2) of 12%, an insoluble component ratio (Note 3) of 28% by mass, and a volume average particle diameter (Note 4) of 50 nm.

[0114] Preparation of (Meth)acrylate-Modified Epoxy Example 11: 1,200 parts of "jER828EL" (product name, manufactured by Japan Epoxy Resins Co., Ltd., epoxy resin, epoxy equivalent 190, number average molecular weight 350) were added to a flask equipped with a stirrer, thermometer, nitrogen inlet tube, and reflux condenser, along with 500 parts of bisphenol A and 0.2 parts of dimethylbenzylamine, and the mixture was allowed to react at 130°C until the epoxy equivalent reached 850. Next, 53 parts of diethanolamine, 108 parts of acrylic acid, 0.04 parts of p-benzoquinone, and 0.4 parts of tetrabutylammonium bromide were added at 100°C and allowed to react, followed by the addition of ethylene glycol monobutyl ether, to obtain a (meth)acrylate-modified epoxy solution with a solids content of 80%. The (meth)acrylate-modified epoxy had an amine value of 15 mg KOH / g and a number average molecular weight of 1,900.

[0115] Preparation of Hydroxy(meth)acrylate-Blocked Polyisocyanate Compound Preparation Example 12 Into a reaction vessel, 270 parts of "Cosmonate M-200" (trade name, manufactured by Mitsui Chemicals, Inc., crude MDI, NCO group content 31.3%), 127 parts of methyl isobutyl ketone, 0.05 parts of 4-tert-butylcatechol, and 0.004 parts of bismuth tris(2-ethylhexanoate) were added and the temperature was raised to 70°C. While constantly bubbling oxygen into the mixture, 35 parts of 2-hydroxyethyl acrylate was added dropwise over 1 hour, and the temperature was then raised to 100°C and the reaction was carried out at this temperature. Further, while maintaining the temperature at 100°C, 150 parts of ethylene glycol monobutyl ether was gradually added, and after infrared absorption spectroscopy was used to confirm that the absorption of unreacted isocyanate groups had disappeared, ethylene glycol monobutyl ether was added to obtain a hydroxy(meth)acrylate-blocked polyisocyanate compound solution with a solids content of 80%.

[0116] Preparation of Cationic Electrodeposition Coating Composition Example 1 87.5 parts (solids content: 70 parts) of the amine-modified epoxy resin (a-1) obtained in Preparation Example 1 and 37.5 parts (solids content: 30 parts) of the blocked polyisocyanate compound (b-2) obtained in Preparation Example 5 were mixed, and 13 parts of 10% acetic acid was added and stirred to homogeneity. Deionized water was then added dropwise over approximately 15 minutes with vigorous stirring to obtain an emulsion with a solids content of 34%. Next, 294 parts (solids content: 100 parts) of the above emulsion, 52.4 parts of the pigment dispersion paste (p-1) obtained in Preparation Example 8, 27.8 parts (solids content: 5 parts) of viscosity modifier (c-1-1) (epoxy resin crosslinked particles No. 1), and deionized water were added to prepare a cationic electrodeposition coating composition (X-1) with a solids content of 20%.

[0117] Examples 2 to 11 and Comparative Examples 1 to 3 Cationic electrodeposition coating compositions (X-2) to (X-14) were prepared in the same manner as in Example 1, except for the formulations shown in Table 1 below. The results of the evaluation tests described below are also shown in Table 1. The cationic electrodeposition coating composition of the present invention must pass all evaluations ("C" indicates failure).

[0118] The results of measuring the viscoelasticity of the electrodeposition coating film are shown in Table 1 below. The viscoelasticity was measured under the conditions of the "Method for measuring viscoelasticity" described in this specification. The meanings in the table are as follows: "G'>1.05 x G" ０．７ ": The measured G' value (Pa) is "1.05 x G" ０．７ " value was always higher than 60 (Pa), it was marked as "Good", otherwise it was marked as "Poor". - "G'>60 (Pa)": If the measured G' value (Pa) is always higher than 60 (Pa), it was marked as "Good", otherwise it was marked as "Poor". - "G'min<300 (Pa)": The measured G'min (minimum value of G') value (Pa).

[0119]

[0120] All blend amounts in the table are values ​​of solid content. The components in the table are as follows. Viscosity modifier (c-1-1): Epoxy resin crosslinked particles No. 1 (Production Example 9) Viscosity modifier (c-1-2): Epoxy resin crosslinked particles No. 2 (Production Example 10) Viscosity modifier (c-2): (meth)acrylate-modified epoxy (Production Example 11) Viscosity modifier (c-3): Hydroxy (meth)acrylate-blocked polyisocyanate compound (Production Example 12) Viscosity modifier (c-4): "Silisia 710" (trade name, manufactured by Fuji Silysia Chemical Ltd., silica, particle diameter 2.8 μm, specific surface area: 700 m ２ / g) Viscosity adjuster (c-5): Polyvinyl alcohol: saponification degree 88%, weight average molecular weight 180,000.

[0121] Evaluation Test <Edge Corrosion Resistance (48 Hours)> A test plate was prepared by electrodeposition coating a cutter blade (blade angle 20 degrees, length 10 cm, zinc phosphate treated) at a bath temperature of 28°C, adjusting the energization time, and forming a film thickness of 20 μm on the general surface. Next, this was subjected to a 48-hour salt spray resistance test in accordance with JIS Z-2371, and the edge portion at the tip of the cutter blade was evaluated according to the following criteria. The evaluation was performed with "A" and "B" as pass, and "C" as fail. A: No rust formation B: Number of rust particles less than 20 / 10 cm C: Number of rust particles 20 or more / 10 cm

[0122] Preparation of Test Plates Cold-rolled steel plates (150 mm (length) × 70 mm (width) × 0.8 mm (thickness)) that had been subjected to a chemical conversion treatment (manufactured by Nippon Parkerizing Co., Ltd., trade name "Palbond #3020", zinc phosphate treatment agent) were used as coating substrates, and were electrodeposited with each of the cationic electrodeposition paints obtained in the Examples and Comparative Examples so that the dry film thickness was 17 μm, and then baked and dried at 170° C. for 20 minutes to obtain test plates.

[0123] <Flat surface corrosion resistance> A cross-cut was made in the coating film with a cutter knife so as to reach the base material of the test plate, and this was subjected to a 35°C salt spray test for 840 hours in accordance with JIS Z-2371, and the rust and blister width on one side of the cut was evaluated according to the following criteria. "A" and "B" are pass ratings, and "C" is fail rating. A: The maximum width of the rust and blister was 2.0 mm or less on one side of the cut. B: The maximum width of the rust and blister was more than 2.0 mm and 3.0 mm or less on one side of the cut. C: The maximum width of the rust and blister was more than 3.0 mm on one side of the cut.

[0124] <Finish (Voids)> The cross section (1 mm x 17 μm) of the coating film of the obtained test plate was observed, and the number of voids (air bubbles) on the coating surface was visually counted. The evaluation was passed with "A" and "B", and failed with "C". A: No voids, good B: No large voids (1 μm or more), but one to three small voids (less than 1 μm) present C: At least one large void present, or four or more small voids present

Claims

1. A cationic electrodeposition coating composition, characterized in that when the cationic electrodeposition coating composition is electrodeposited onto a metal substrate and the resulting uncured electrodeposition coating film is dried by heating, the storage modulus (G'), loss modulus (G"), and minimum value of G' in the heat drying step (G'min) of the coating film satisfy the following formulas (1) to (3): G'>1.05×G" ０．７ ...Formula (1) G'>60 (Pa) ...Formula (2) G'min<300 (Pa) ...Formula (3) 2. The cationic electrodeposition coating composition according to claim 1, characterized in that the cationic electrodeposition coating composition contains an amine-modified epoxy resin (A), a blocked polyisocyanate compound (B), and a viscosity modifier (C).

3. The cationic electrodeposition coating composition according to claim 2, wherein the amine-modified epoxy resin (A) is a reaction product of an epoxy resin and an amine compound.

4. The cationic electrodeposition coating composition according to claim 2, wherein the amine-modified epoxy resin (A) has a number-average molecular weight of 3,000 or more and a glass transition temperature of 100°C or less.

5. The cationic electrodeposition coating composition according to claim 2, wherein the viscosity modifier (C) contains a cationic microgel (C-1).

6. The cationic electrodeposition coating composition according to claim 5, wherein the cationic microgel (C-1) contains a silane coupling agent as a constituent component.

7. A cationic electrodeposition coating composition according to claim 2, characterized in that the viscosity modifier (C) contains a (meth)acrylate-modified epoxy (C-2) and / or a hydroxy(meth)acrylate-blocked polyisocyanate compound (C-3).

8. The cationic electrodeposition coating composition according to claim 2, further comprising a bismuth compound.

9. The cationic electrodeposition coating composition according to claim 2, characterized in that the blocked polyisocyanate compound (B) is a reaction product of a polyisocyanate compound and a blocking agent, and the blocking agent contains a diol compound having two hydroxyl groups with different reactivities.

10. A method for forming a coating film, comprising electrodepositing the cationic electrodeposition coating composition according to any one of claims 1 to 9 onto a metal substrate, and then heating and drying the resulting uncured electrodeposition coating film.

11. A method for forming a coating film using a cationic electrodeposition coating composition, comprising electrodeposition coating a metal substrate with a cationic electrodeposition coating composition containing an amine-modified epoxy resin (A), a blocked polyisocyanate compound (B), and a viscosity modifier (C), and subsequently heat-drying the resulting uncured electrodeposition coating, wherein the storage modulus (G'), loss modulus (G"), and minimum value of G' (G'min) in the heat-drying step of the electrodeposition coating satisfy the following formulas (1) to (3): G'>1.05×G" ０．７ ...Formula (1) G'>60 (Pa) ...Formula (2) G'min<300 (Pa) ...Formula (3)

Images