Cationic electrodeposition coating composition and method for producing cationic electrodeposition coating composition

Abstract

Provided is a cationic electrodeposition coating composition having good low-temperature curability and capable of maintaining coating film properties such as corrosion resistance.　The cationic electrodeposition coating composition comprises an aminated epoxy resin (A) and a polyisocyanate curing agent (B), wherein the polyisocyanate curing agent (B) includes a blocked polyisocyanate compound (B1) of a polyisocyanate compound selected from the group consisting of a multimer of 1,5-pentamethylene diisocyanate and 1,5-pentamethylene diisocyanate.

Description

Cationic electrodeposition coating composition and method for producing cationic electrodeposition coating composition

[0001] The present invention relates to a cationic electrodeposition coating composition and a method for producing the cationic electrodeposition coating composition.

[0002] Cationic electrodeposition coating compositions are widely used as primer coatings to impart corrosion resistance to industrial products such as automobiles. Cationic electrodeposition coating compositions are generally aqueous coating compositions containing an amino group-containing epoxy resin and a polyisocyanate curing agent, and because they are aqueous compositions, they have the advantage of being environmentally friendly.

[0003] In recent years, with the further increase in awareness of environmental issues, low-temperature curing properties are also required for water-based coating compositions. For example, WO2019 / 039467 (Patent Document 1) describes that low-temperature curing properties can be improved in cationic electrodeposition coating compositions by using emulsion particles containing a Michael addition reaction donor component and emulsion particles containing a Michael addition reaction acceptor component.

[0004] WO2019 / 039467

[0005] An object of the present invention is to provide a cationic electrodeposition coating composition which has good low-temperature curing properties and is capable of maintaining coating film properties such as corrosion resistance.

[0006] In order to solve the above problems, the present invention provides the following aspects. [1] A cationic electrodeposition coating composition comprising an aminated epoxy resin (A) and a polyisocyanate curing agent (B), wherein the polyisocyanate curing agent (B) comprises a blocked polyisocyanate compound (B1) of a polyisocyanate compound selected from the group consisting of 1,5-pentamethylene diisocyanate and a polymer of 1,5-pentamethylene diisocyanate, and wherein the equivalent ratio NCO / OH of the hydroxyl group equivalent of the aminated epoxy resin (A) to the isocyanate group equivalent of the polyisocyanate curing agent (B) is 0.5 or more and less than 3.1. [2] The cationic electrodeposition coating composition according to [1], wherein the blocking agent used in preparing the blocked polyisocyanate compound (B1) comprises one or more compounds selected from the group consisting of oxime compounds, pyrazole compounds, imidazole compounds, and triazole compounds. [3] The cationic electrodeposition coating composition according to [1] or [2], wherein a coating film of the aminated epoxy resin emulsion, which is a mixture of the aminated epoxy resin (A) and the polyisocyanate curing agent (B), cured at 135°C for 25 minutes has a Tg of 65°C or higher and 95°C or lower as determined by dynamic viscoelasticity measurement. [4] A method for producing a cationic electrodeposition coating composition, comprising the following steps: a step of preparing a blocked polyisocyanate compound (B1); and a step of mixing a polyisocyanate curing agent (B) containing the blocked polyisocyanate compound (B1) and an aminated epoxy resin (A) to prepare an aminated epoxy resin emulsion, wherein the blocked polyisocyanate compound (B1) is prepared by blocking a polyisocyanate compound selected from the group consisting of 1,5-pentamethylene diisocyanate and a polymer of 1,5-pentamethylene diisocyanate with a blocking agent, and the blocking agent comprises one or more compounds selected from the group consisting of oxime compounds, pyrazole compounds, imidazole compounds, and triazole compounds.

[0007] In the present invention, the polyisocyanate curing agent (B) contains a blocked polyisocyanate compound (B1) of a polyisocyanate compound selected from the group consisting of 1,5-pentamethylene diisocyanate and 1,5-pentamethylene diisocyanate polymers, and the equivalent ratio NCO / OH of the hydroxyl group equivalent of the aminated epoxy resin (A) to the isocyanate group equivalent of the polyisocyanate curing agent (B) is 0.5 or more and less than 3.1, which has the advantages of ensuring coating film properties such as corrosion resistance and exhibiting good low-temperature curing properties.

[0008] The cationic electrodeposition coating composition of the present disclosure comprises an aminated epoxy resin (A) and a polyisocyanate curing agent (B), wherein the polyisocyanate curing agent (B) comprises a blocked polyisocyanate compound (B1) of a polyisocyanate compound selected from the group consisting of 1,5-pentamethylene diisocyanate and polymers thereof, and wherein the equivalent ratio NCO / OH of the hydroxyl group equivalent of the aminated epoxy resin (A) to the isocyanate group equivalent of the polyisocyanate curing agent (B) is 0.5 or more and less than 3.1. Each requirement will be explained below.

[0009] Aminated Epoxy Resin (A) The aminated epoxy resin (A) is a film-forming resin. In the aminated epoxy resin (A), at least one oxirane ring (also referred to as an "epoxy group") of the epoxy resin is aminated. The aminated epoxy resin (A) is preferably contained in the electrodeposition coating composition in the form of a resin emulsion together with the polyisocyanate curing agent (B).

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

[0011] The number average molecular weight of the aminated epoxy resin (A) is a value calculated as a styrene homopolymer, measured by gel permeation chromatography.

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

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

[0014] The aminated epoxy resin (A) may have a hydroxyl group, and the hydroxyl value of the aminated epoxy resin (A) is, for example, 150 mgKOH / g or more and 650 mgKOH / g or less. When the hydroxyl value is 150 mgKOH / g or more, the curability of the coating composition is enhanced and the appearance of the coating film is improved. When the hydroxyl value is 650 mgKOH / g or less, the amount of hydroxyl groups remaining in the cured electrodeposition coating is appropriate, and the water resistance of the coating film is easily improved. In one embodiment, the hydroxyl value of the aminated epoxy resin (A) is 150 mgKOH / g or more, 180 mgKOH / g or more, 200 mgKOH / g or more, 250 mgKOH / g or more, 300 mgKOH / g or more, 350 mgKOH / g or more, 400 mgKOH / g or more, 450 mgKOH / g or more, 500 mgKOH / g or more, 550 mgKOH / g or more, or 600 mgKOH / g or more. In another embodiment, the hydroxyl value of the aminated epoxy resin (A) component is 650 mgKOH / g or less, 600 mgKOH / g or less, 550 mgKOH / g or less, 500 mgKOH / g or less, 450 mgKOH / g or less, 400 mgKOH / g or less, 350 mgKOH / g or less, 300 mgKOH / g or less, 250 mgKOH / g or less, or 200 mgKOH / g or less. In yet another embodiment, the hydroxyl value of component (A) is 180 to 300 mgKOH / g.

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

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

[0017] The coating composition may contain multiple aminated epoxy resins (A) with different amine values ​​and / or hydroxyl values. In this case, the average amine value and average hydroxyl value calculated based on the mass ratio of the multiple aminated epoxy resins (A) preferably fall within the above-mentioned ranges. In particular, the multiple aminated epoxy resins (A) preferably include an aminated epoxy resin having an amine value of 20 to 50 mgKOH / g and a hydroxyl value of 50 to 300 mgKOH / g, and an aminated epoxy resin having an amine value of 50 to 200 mgKOH / g and a hydroxyl value of 200 to 500 mgKOH / g. This makes the core of the emulsion more hydrophobic and the shell more hydrophilic, thereby further improving the rust prevention properties of the coated object.

[0018] The aminated epoxy resin (A) can be obtained by reacting the epoxy group of the above-mentioned epoxy resin with an amine compound.

[0019] (Epoxy Resin) The epoxy resin that is the starting material for the aminated epoxy resin (A) is, for example, a polyphenol polyglycidyl ether type epoxy resin, which is a reaction product of a polycyclic phenol compound and epichlorohydrin. Examples of the polycyclic phenol compound include bisphenol A, bisphenol F, bisphenol S, phenol novolac, and cresol novolac. In this specification, the term "polyphenol polyglycidyl ether type epoxy resin" includes a state in which a polyphenol polyglycidyl ether type epoxy resin and a polycyclic phenol compound are alternately and continuously reacted to each other to extend the chain.

[0020] The epoxy resin may be a resin obtained by subjecting a portion of the epoxy resin to a chain extension reaction before modification with an amine compound. For example, bifunctional polyester polyols, polyether polyols, dibasic carboxylic acids, etc. can be used for the chain extension reaction. Examples of the polyether polyol include polyols having polyethylene oxide groups and polyols having polypropylene oxide groups. For example, when a chain extension reaction is performed using a polyol having polypropylene oxide groups, a polypropylene oxide group-containing epoxy resin is obtained. The content of the polypropylene oxide group-containing epoxy resin is preferably 1 to 40 parts by mass, more preferably 15 to 25 parts by mass, per 100 parts by mass of the epoxy resin. Examples of epoxy resins similar to the polypropylene oxide group-containing epoxy resin include epoxy resins obtained by chain extension reaction of polyphenol polyglycidyl ether epoxy resins, polycyclic phenol compounds, and polypropylene oxide group-containing epoxy resins.

[0021] The aminated epoxy resin (A) can be obtained by reacting the epoxy groups of the epoxy resin with an amine compound. The epoxy groups of the epoxy resin are all consumed by the reaction with the amine compound, and substantially no epoxy groups remain in the molecules of the aminated epoxy resin (A).

[0022] (Amine Compound) As the amine compound, an amine compound generally used in producing aminated epoxy resins is used. Examples of commonly used amine compounds include primary amines such as butylamine, octylamine, and monoethanolamine; secondary amines such as diethylamine, dibutylamine, methylbutylamine, diethanolamine, and N-methylethanolamine; and complex amines such as diethylenetriamine. The primary amines can form ketimine groups using ketone compounds, thereby controlling the reaction through so-called blocking. Usable amine compounds having a ketimine or diketimine group include the ketimine of aminoethylethanolamine and the diketimine of diethylenetriamine. Examples of ketone compounds that generate ketimine groups include methyl isopropyl ketone (MIPK), diisobutyl ketone (DIBK), methyl isobutyl ketone (MIBK), diethyl ketone (DEK), ethyl butyl ketone (EBK), ethyl propyl ketone (EPK), dipropyl ketone (DPK), and methyl ethyl ketone (MEK), with methyl isobutyl ketone (MIBK) being preferred. Tertiary amines may also be used as amine compounds, and specific examples thereof include triethylamine, N,N-dimethylbenzylamine, and N,N-dimethylethanolamine. These amines may be used alone or in combination of two or more.

[0023] During the conversion to amination, the amine compound is preferably used in an amount of 0.9 to 1.2 equivalents per equivalent of epoxy groups in the raw material epoxy resin. The reaction conditions for the conversion to amination can be appropriately selected depending on the reaction scale, etc. For example, the reaction may be carried out at 80°C to 150°C for 0.1 to 5 hours, or at 120°C to 150°C for 0.5 to 3 hours.

[0024] In one embodiment of the present invention, an amine compound having at least one of a primary amino group, a secondary amino group, and a tertiary amino group, excluding ketimine (including diketimine), is used as the amine compound that modifies the oxirane ring (also referred to as an "epoxy group") of the epoxy resin.

[0025] When it is necessary to narrowly control the molecular weight distribution of an aminated epoxy resin, particularly when it is necessary to control the molecular weight distribution to 2.7 or less, selecting a specific amine compound has the advantage of facilitating control. Specific examples of such embodiments include a combination of two amine compounds, a primary amine and a secondary amine, in which the primary amine has the formula: NH2-(CH2)n-NR11R12 (1) (in formula (1), R11 and R12 are the same or different and represent an alkyl group of 1 to 6 carbon atoms which may have a terminal hydroxyl group, and n is an integer of 2 to 4), and the secondary amine has the formula: R13R14NH (2) (in formula (2), R13 and R14 represent an alkyl group of 1 to 4 carbon atoms which has a terminal hydroxyl group). When these amine compounds are used, the primary amino group of the primary amine first reacts with the epoxy resin and is consumed, leaving only the secondary amino group, which reacts with the epoxy group of the epoxy resin, so the reaction proceeds evenly without any difference in reactivity, making it possible to control the molecular weight distribution. It is possible that the tertiary amino group present in the primary amine or the tertiary amino group produced by the reaction of the secondary amino group also reacts with the epoxy group to form a quaternary ammonium group, but this reaction is thought to occur infrequently.

[0026] The primary amine has the formula (1) above, and R11 and R12 are specifically methyl, ethyl, propyl, or butyl, and may have a terminal hydroxyl group. Furthermore, n is 2 to 4, preferably 3. Specific examples of the primary amine include aminopropyldiethanolamine, dimethylaminopropanediamine, diethylaminopropanediamine, and dibutylaminopropanediamine. The secondary amine is a secondary amine having the formula (2) above, in which R13 and R14 are bonded to a nitrogen atom, and both R13 and R14 have an alkyl group having 1 to 4 carbon atoms and a hydroxyl group. Specific examples of the secondary amine include dimethanolamine and diethanolamine.

[0027] In another embodiment of the present invention, the amine compound used for the amination may include an amine compound having a ketimine group or a diketimine group.

[0028] The coating composition may optionally contain an aminated resin other than the aminated epoxy resin (A), such as an aminated acrylic resin or an aminated polyester resin. The coating composition may also contain a film-forming resin other than the above aminated resin. Examples of other film-forming resins include hydroxyl-containing acrylic resins, hydroxyl-containing polyester resins, urethane resins, butadiene resins, phenolic resins, and xylene resins. Of the film-forming resins contained in the coating composition that react with a curing agent to form a coating film, 80% by mass or more, even 90% by mass or more, and particularly 100% by mass may be constituted by the aminated epoxy resin.

[0029] In one embodiment, the combined use of an aminated epoxy resin and an aminated acrylic resin has the advantage of improving the weather resistance of the electrodeposition coating film. The aminated acrylic resin (B) can be prepared by copolymerizing an amino group-containing acrylic monomer, a hydroxyl group-containing acrylic monomer, and other ethylenically unsaturated monomers. Alternatively, the aminated acrylic resin (B) can be prepared by copolymerizing an epoxy group-containing acrylic monomer instead of the amino group-containing acrylic monomer with a hydroxyl group-containing acrylic monomer and other ethylenically unsaturated monomers, and then ring-opening the epoxy groups of the resulting copolymer with an amine.

[0030] Polyisocyanate Curing Agent (B) The polyisocyanate curing agent (B) (hereinafter sometimes simply referred to as curing agent (B)) is a component that reacts preferentially with the amine groups of the aminated epoxy resin (A) and then with the hydroxyl groups, thereby curing the aminated epoxy resin (A) and forming an electrodeposition coating film. The polyisocyanate curing agent (B) of the present disclosure contains a blocked polyisocyanate compound (B1) of a polyisocyanate compound selected from the group consisting of 1,5-pentamethylene diisocyanate and 1,5-pentamethylene diisocyanate polymers. This configuration has the advantage of ensuring good coating film properties, such as corrosion resistance, of the electrodeposition coating film, while also achieving good low-temperature curing properties.

[0031] The use of blocked polyisocyanates of hexamethylene diisocyanate and / or its multimers as the polyisocyanate curing agent (B) has been investigated. For example, blocked polyisocyanates of hexamethylene diisocyanate and / or its multimers can impart flexibility to electrodeposition coating films and improve properties such as chipping resistance. However, while blocked polyisocyanates of hexamethylene diisocyanate and / or its multimers can impart flexibility, they have sometimes exhibited poor corrosion resistance as a trade-off. In the present invention, the inventors have found through experiments that the use of 1,5-pentamethylene diisocyanate and / or its multimers can solve the problem of balancing flexibility with other properties such as corrosion resistance and further improve low-temperature curing properties, leading to the completion of the present invention.

[0032] In addition to the above advantages, the use of 1,5-pentamethylene diisocyanate and / or its polymer has the advantage of being a biomass-derived raw material (non-fossil raw material) and thus reducing the environmental load.

[0033] Examples of the 1,5-pentamethylene diisocyanate polymers include isocyanurates, adducts, biuret-type compounds, uretdione compounds, allophanates, and prepolymers having an isocyanate residue of 1,5-pentamethylene diisocyanate. Examples of the 1,5-pentamethylene diisocyanate prepolymers include prepolymers (adducts) obtained by reacting 1,5-pentamethylene diisocyanate with polyhydric alcohols such as ethylene glycol, propylene glycol, trimethylolpropane, and hexanetriol at an NCO / OH ratio of 2 or more.

[0034] The blocked polyisocyanate compound (B1) can be prepared by blocking a polyisocyanate compound selected from the group consisting of 1,5-pentamethylene diisocyanate and polymers thereof with a blocking agent. Examples of blocking agents include monohydric alkyl (or aromatic) alcohol compounds such as n-butanol, n-hexyl alcohol, 2-ethylhexanol, lauryl alcohol, phenol carbinol, and methylphenyl carbinol; cellosolve compounds such as ethylene glycol monohexyl ether and ethylene glycol mono 2-ethylhexyl ether; polyether-type both-terminal diol compounds such as polyethylene glycol, polypropylene glycol, and polytetramethylene ether glycol phenol; polyester-type both-terminal polyol compounds obtained from diols such as ethylene glycol, propylene glycol, and 1,4-butanediol and dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, suberic acid, and sebacic acid; phenol compounds such as para-t-butylphenol and cresol; oxime compounds such as dimethyl ketoxime, methyl ethyl ketoxime, methyl isobutyl ketoxime, methyl amyl ketoxime, and cyclohexanone oxime; and pyrazole compounds such as 3,5-dimethylpyrazole. Examples include imidazole compounds such as 2-ethyl-4-methylimidazole; and lactam compounds such as ε-caprolactam and γ-butyrolactam.

[0035] The blocking agent used in the preparation of the blocked polyisocyanate compound (B1) is preferably one or more selected from the group consisting of oxime compounds, pyrazole compounds, imidazole compounds, and triazole compounds, and more preferably a blocking agent containing an oxime compound. The use of such a blocking agent in the preparation of the blocked polyisocyanate compound (B1) has the advantages of ensuring good low-temperature curing properties and maintaining a favorable balance of the physical properties of the resulting electrodeposition coating film.

[0036] The polyisocyanate curing agent (B) of the present disclosure may contain, in addition to the blocked polyisocyanate compound (B1), other blocked polyisocyanate compounds. The other blocked polyisocyanate compounds can be prepared by blocking a polyisocyanate compound other than 1,5-pentamethylene diisocyanate and its polymers with a blocking agent. The blocking agents described above can be used as the blocking agent.

[0037] Examples of polyisocyanate compounds other than 1,5-pentamethylene diisocyanate and its polymers include aliphatic polyisocyanate compounds having 3 to 12 carbon atoms, such as hexamethylene diisocyanate (including trimer), 2,2,4-trimethylhexane diisocyanate, and lysine diisocyanate; Alicyclic polyisocyanate compounds such as 1,4-cyclohexane diisocyanate (CDI), isophorone diisocyanate (IPDI), 4,4'-dicyclohexylmethane diisocyanate (hydrogenated MDI), methylcyclohexane diisocyanate, isopropylidenedicyclohexyl-4,4'-diisocyanate, 1,3-diisocyanatomethylcyclohexane (hydrogenated XDI), hydrogenated TDI, 2,5- or 2,6-bis(isocyanatomethyl)-bicyclo[2.2.1]heptane (also known as norbornane diisocyanate); Examples of the diisocyanate include aromatic polyisocyanate compounds such as tolylene diisocyanate (TDI), diphenylmethane-4,4'-diisocyanate (MDI), polymethylene polyphenyl polyisocyanate (MDI polymer, polymeric MDI), p-phenylene diisocyanate, and naphthalene diisocyanate; aliphatic polyisocyanate compounds having an aromatic ring such as xylylene diisocyanate (XDI) and tetramethylxylylene diisocyanate (TMXDI); and modified products of these diisocyanates (urethane compounds, carbodiimides, uretdione, uretoimine, biuret, isocyanurate modified products, etc.).

[0038] The polyisocyanate curing agent (B) of the present disclosure may contain, in addition to the blocked polyisocyanate compound (B1), other blocked polyisocyanate compounds. In one embodiment, the polyisocyanate curing agent (B) contains the blocked polyisocyanate compound (B1) and a blocked polyisocyanate compound of an aromatic polyisocyanate compound. In the above embodiment, the mass ratio of the blocked polyisocyanate compound (B1) to the blocked polyisocyanate compound of the aromatic polyisocyanate compound, expressed as the mass ratio of (B1) / other blocked polyisocyanate compound, may be 5 / 95 to 95 / 5, 20 / 80 to 80 / 20, or 30 / 70 to 70 / 30.

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

[0040] The ratio NCO / OH of the hydroxyl group equivalent of the aminated epoxy resin (A) to the isocyanate group equivalent of the polyisocyanate curing agent (B) is preferably 0.5 or more and less than 3.1. The isocyanate group equivalent is the equivalent of the free isocyanate group generated and cured by dissociation of the blocking agent during heat curing, and the hydroxyl group equivalent of the aminated epoxy resin (A) is the equivalent of the hydroxyl group reacting with the isocyanate group. The lower limit of the equivalent ratio is more preferably 0.6 or more, and the upper limit is more preferably 2.8 or less. By maintaining the equivalent ratio NCO / OH within the above range, there is an advantage in that the physical properties of the electrodeposition coating film, such as corrosion resistance, can be further improved.

[0041] The coating composition may contain a curing agent other than the polyisocyanate curing agent (B) as needed. Examples of other curing agents include organic curing agents such as melamine resins or phenolic resins, silane coupling agents, and metal curing agents. Of all the curing agents contained in the coating composition, 80% by mass or more, even 90% by mass or more, and particularly 100% by mass may be the polyisocyanate curing agent (B).

[0042] Mixture (Resin Emulsion) of Aminated Epoxy Resin (A) and Polyisocyanate Curing Agent (B) The cationic electrodeposition coating composition of the present invention is preferably characterized in that the aminated epoxy resin (A) and polyisocyanate curing agent (B) are mixed to form an aminated epoxy resin emulsion, which is then cured (heat cured at 135°C for 25 minutes) to form a cured coating film having a Tg of 65°C or higher and 95°C or lower, as determined by dynamic viscoelasticity measurement. Dynamic Tg is measured by applying a time-varying (oscillating) strain or stress to a sample and measuring the resulting stress or strain. This differs from the conventional Tg (glass transition temperature, also known as static glass transition temperature), which is measured by applying a constant strain or stress that does not change with time. The dynamic glass transition temperature (dynamic Tg) is not significantly different from the static glass transition temperature Tg (static Tg), but differs in that a time-varying strain or stress is applied. The dynamic Tg is preferably in the range of 70° C. to 90° C., more preferably 75° C. to 85° C. If the dynamic Tg of a coating film formed from an aminated epoxy resin emulsion is lower than 65° C., the coating film will be too soft, whereas if the dynamic Tg exceeds 95° C., the coating film will be hard and brittle.

[0043] The dynamic Tg described herein can be obtained by subjecting a measurement sample to a method similar to that used for measuring Tg using conventional dynamic viscoelasticity. A specific measurement method that can be used in the present invention involves peeling a cured electrodeposition coating film formed on a substrate using mercury, cutting the film, and then performing dynamic viscoelasticity measurements on the prepared measurement sample. In this method, the prepared measurement sample is subjected to vibration at a frequency of 11 Hz at a temperature rise rate of 2°C per minute in a temperature range from room temperature to 200°C, and its viscoelasticity is measured. The ratio (tan δ) of the loss modulus (E″) to the storage modulus (E′) thus measured is measured, and the dynamic Tg is determined as the temperature at which tan δ peaks when the tan δ is plotted against temperature. Examples of devices for performing the dynamic viscoelasticity measurement include a dynamic viscoelasticity measuring device (Rheogel-E4000, manufactured by UBM Corporation).

[0044] Other Components The cationic electrodeposition coating composition of the present disclosure may contain components other than those described above, as necessary. Examples of other components include pigments, curing catalysts, and additives.

[0045] <Pigment> The pigment is a pigment commonly used in coating compositions. Examples of pigments include color pigments such as titanium white (titanium dioxide), carbon black, and red iron oxide; extender pigments such as kaolin, talc, aluminum silicate, calcium carbonate, mica, and clay; and rust-preventive pigments such as iron phosphate, aluminum phosphate, calcium phosphate, aluminum tripolyphosphate, aluminum phosphomolybdate, and aluminum zinc phosphomolybdate. The coating composition may contain an extender pigment, which can further improve edge rust prevention.

[0046] The solid content of the coating composition refers to all components contained in the coating composition that remain in solid form even after removal of the solvent, specifically, the solid components contained in the coating composition, such as the aminated epoxy resin (A), the polyisocyanate curing agent (B), and the pigment, pigment dispersing resin, and additives that are optionally contained.

[0047] Pigments are usually added to coating compositions as a pigment dispersion paste comprising a pigment dispersing resin and a pigment.

[0048] (Pigment Dispersion Resin) The pigment dispersion resin is a resin for dispersing pigments. Examples of the pigment dispersion resin include pigment dispersion resins having a cationic group, such as modified epoxy resins having at least one group selected from a quaternary ammonium group, a tertiary sulfonium group, and a primary amino group. Specific examples of the pigment dispersion resin include quaternary ammonium group-containing epoxy resins and tertiary sulfonium group-containing epoxy resins. Examples of the aqueous solvent include ion-exchanged water and ion-exchanged water containing a small amount of alcohol.

[0049] (Curing Catalyst) The coating composition may contain a curing catalyst. The curing catalyst is not particularly limited, and those known in the coating field can be used. Examples of curing catalysts include organotin compounds and bismuth compounds. Examples of organotin compounds include dibutyltin oxide, dioctyltin oxide, dioctyltin dilaurate, dibutyltin dilaurate, dioctyltin dilaurate, dibutyltin diacetate, dibutyltin dibenzoate, and dioctyltin dibenzoate. Examples of bismuth compounds include bismuth oxide, bismuth hydroxide, bismuth subsalicylate, and bismuth subnitrate. In a preferred embodiment of the cationic electrodeposition coating composition of the present disclosure, a curing catalyst containing a bismuth compound can be used.

[0050] From the viewpoint of environmental load, the content of the curing catalyst (particularly, the organotin compound) may be 0.5 mass % or less, or 0.25 mass % or less, of the solid content of the coating composition.

[0051] (Metal Nitrite) The coating composition may further contain a metal nitrite. The metal nitrite can further improve edge rust prevention. As the metal nitrite, a nitrite of an alkali metal or a nitrite of an alkaline earth metal is preferred, and a nitrite of an alkaline earth metal is more preferred. Examples of the metal nitrite include calcium nitrite, sodium nitrite, potassium nitrite, magnesium nitrite, strontium nitrite, barium nitrite, and zinc nitrite.

[0052] The content of the metal nitrite is, for example, 0.001% by mass or more and 0.2% by mass or less in terms of the metal element of the metal component relative to the total mass of the coating film-forming resin and the curing agent.

[0053] (Additives, etc.) The coating composition may contain additives commonly used in the coating field, such as organic solvents, surfactants such as drying inhibitors and antifoaming agents, viscosity modifiers such as acrylic resin microparticles, anti-repellent agents, and inorganic rust inhibitors, as needed. Examples of organic solvents include ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, ethylene glycol monoethylhexyl ether, propylene glycol monobutyl ether, dipropylene glycol monobutyl ether, and propylene glycol monophenyl ether. Examples of inorganic rust inhibitors include vanadium salts, copper salts, iron salts, manganese salts, magnesium salts, and calcium salts.

[0054] Furthermore, in addition to the above, known auxiliary complexing agents, buffering agents, smoothing agents, stress relaxation agents, glossing agents, semi-glossing agents, antioxidants, ultraviolet absorbers, etc. may be included depending on the purpose.

[0055] <Preparation of Cationic Electrodeposition Coating Composition> The coating composition can be obtained by first preparing the blocked polyisocyanate compound (B1) as described above, and then mixing a resin emulsion containing a coating film-forming resin (typically an aminated epoxy resin (A)) and a curing agent (typically a polyisocyanate curing agent (B)), a pigment dispersion paste containing a pigment, and optional additives, by a commonly used method, to prepare a resin emulsion.

[0056] (Preparation of Resin Emulsion) In one embodiment of the preparation of the resin emulsion, the aminated epoxy resin (A) and, if necessary, other film-forming resins, and the polyisocyanate curing agent (B) and, if necessary, other curing agents are each dissolved in an organic solvent to prepare a solution, and these solutions are mixed and then neutralized with a neutralizing acid.

[0057] Examples of the neutralizing acid include organic acids such as methanesulfonic acid, sulfamic acid, lactic acid, dimethylolpropionic acid, formic acid, acetic acid, etc. The neutralizing acid may be one or more selected from the group consisting of formic acid, acetic acid, and lactic acid.

[0058] The solid content of the resin emulsion may be, for example, 25% by mass or more and 50% by mass or less, or 35% by mass or more and 45% by mass or less, based on the total amount of the resin emulsion. The solid content of the resin emulsion refers to all components contained in the resin emulsion that remain in solid form even after removal of the solvent. Specifically, the solid content of the resin emulsion refers to the aminated epoxy resin (A), the blocked polyisocyanate curing agent (B), and other solid components added as needed, contained in the resin emulsion.

[0059] The amount of neutralizing acid used, expressed as the equivalent ratio of the neutralizing acid to the equivalent of the amino groups in the aminated epoxy resin, may be 10% or more and 100% or less, or 20% or more and 70% or less. Hereinafter, the equivalent ratio of the neutralizing acid to the equivalent of the amino groups in the aminated epoxy resin will be referred to as the neutralization rate. A neutralization rate of 10% or more ensures affinity for water and improves water dispersibility.

[0060] (Method for preparing pigment dispersion paste) The pigment dispersion paste is prepared by mixing a pigment dispersion resin and a pigment. The solid content mass of the pigment dispersion resin in the pigment dispersion paste is not particularly limited, and may be, for example, 20 parts by mass or more and 100 parts by mass or less per 100 parts by mass of the pigment.

[0061] The solid content mass of the pigment dispersion paste is, for example, 40% by mass or more and 70% by mass or less, and may be 50% by mass or more and 60% by mass or less.

[0062] The solid content of the pigment dispersion paste refers to all components contained in the pigment dispersion paste that remain solid even after removal of the solvent, specifically, the pigment dispersion resin, pigment, and other solid components added as needed.

[0063] [Method for producing an electrodeposition-coated article] An electrodeposition coating film is formed by electrodeposition coating an article using a coating composition. An electrodeposition-coated article having an electrodeposition coating film is produced by a method comprising the steps of immersing the article in the cationic electrodeposition coating composition according to this embodiment, applying a voltage between the article and a counter electrode to form an uncured electrodeposition coating film on the article, and heating the coating film at a temperature of 75°C or higher and 200°C or lower to obtain a cured electrodeposition coating film.

[0064] As described above, the cationic electrodeposition coating composition contains the aminated epoxy resin (A), the polyisocyanate curing agent (B), and optionally pigments, additives, etc.

[0065] (1) Formation of an uncured electrodeposition coating film After immersing a substrate in a cationic electrodeposition coating composition, a voltage is applied between the substrate as a cathode and a counter electrode (anode), resulting in the deposition of an uncured electrodeposition coating film on the substrate.

[0066] (Application Conditions) The voltage is, for example, 50 V or more and 450 V or less. The bath liquid temperature is, for example, 10° C. or more and 45° C. or less. The time for applying the voltage is not particularly limited, and is, for example, 2 minutes or more and 5 minutes or less.

[0067] (Substrate) The material of the substrate is not particularly limited as long as it is electrically conductive. The shape of the substrate is also not particularly limited, and it may be flat or have a complex three-dimensional shape. Examples of substrates include cold-rolled steel sheets, hot-rolled steel sheets, stainless steel, electrogalvanized steel sheets, hot-dip galvanized steel sheets, zinc-aluminum alloy-plated steel sheets, zinc-iron alloy-plated steel sheets, zinc-magnesium alloy-plated steel sheets, zinc-aluminum-magnesium alloy-plated steel sheets, aluminum-plated steel sheets, aluminum-silicon alloy-plated steel sheets, tin-plated steel sheets, and those that have been subjected to a chemical conversion treatment (e.g., a surface treatment using a phosphate, zirconium salt, or the like). When performing a chemical conversion treatment with a phosphate, the substrate may be surface-conditioned with a zinc-, titanium-, or manganese-based surface conditioner prior to the chemical conversion treatment. This makes the crystals of the zinc phosphate coating denser.

[0068] (2) Curing of Electrodeposition Coating Film The formed uncured electrodeposition coating film is washed with water, if necessary, and then heated at a temperature of 75° C. to 200° C. This causes a curing reaction to occur, resulting in a cured electrodeposition coating film.

[0069] (Curing Conditions) The curing temperature may be 100° C. or higher, or may be 110° C. or higher. The curing temperature may be, for example, 180° C. or lower, or may be 150° C. or lower. The heating time is not particularly limited, and is, for example, 10 to 30 minutes.

[0070] (Electrodeposition Coated Article) An electrodeposition coated article comprises a substrate and a cured electrodeposition coating film formed on the substrate from the cationic electrodeposition coating composition described above.

[0071] From the viewpoint of rust prevention, the thickness of the cured electrodeposition coating film may be 5 μm or more and 60 μm or less. The thickness of the cured electrodeposition coating film may be 10 μm or more. The thickness of the cured electrodeposition coating film may be 25 μm or less.

[0072] The cationic electrodeposition coating composition of the present disclosure has the advantage that it can ensure coating film properties such as corrosion resistance and also achieve low-temperature curing properties by using, as the polyisocyanate curing agent (B), a curing agent containing a blocked polyisocyanate compound (B1) selected from the group consisting of 1,5-pentamethylene diisocyanate and 1,5-pentamethylene diisocyanate polymers. The cationic electrodeposition coating composition of the present disclosure can be suitably used in coating applications in which the formation of an intermediate coating film and / or a top coating film, which are generally formed on an electrodeposition coating film, is omitted, such as the coating of specific parts or components of an automobile body.

[0073] The present invention will be described in more detail with reference to the following examples, but is not limited thereto. In the examples, "parts" and "%" are by weight unless otherwise specified.

[0074] Production Example 1: Production of aminated epoxy resin (A) 92 parts of methyl isobutyl ketone, 940 parts of bisphenol A epoxy resin (trade name: DER-331J, manufactured by Dow Chemical Company), 382 parts of bisphenol A, 63 parts of octylic acid, and 2 parts of dimethylbenzylamine were added, and the temperature inside the reaction vessel was maintained at 140°C. The reaction was allowed to proceed until the epoxy equivalent reached 1145 g / eq. The reaction vessel was then cooled to 120°C. Next, a mixture of 78 parts of diethylenetriamine diketimine (a methyl isobutyl ketone solution with a solids content of 73%) and 92 parts of diethanolamine was added, and the reaction was allowed to proceed at 120°C for 1 hour, yielding aminated epoxy resin (A) (cation-modified epoxy resin). This resin had a number average molecular weight of 2,560, an amine value of 56 mgKOH / g, and a hydroxyl value of 186 mgKOH / g.

[0075] Production Example 2-1 Production of Blocked Polyisocyanate Curing Agent (Curing Agent B1-1) 1,540 parts of 1,5-pentamethylene diisocyanate (PDI) and 732 parts of MIBK were charged into a reaction vessel and heated to 60°C. A solution of 346 parts of trimethylolpropane in 1,067 parts of MEK oxime was added dropwise to the vessel at 60°C over 2 hours. After further heating at 75°C for 4 hours, it was confirmed that absorption due to isocyanate groups had disappeared in IR spectrum measurement. After allowing the mixture to cool, 101 parts of MIBK was added to obtain a blocked polyisocyanate curing agent (B1-1) with a solids content of 78%. The NCO equivalent of this blocked polyisocyanate curing agent was 148.

[0076] Production Example 2-2: Production of Blocked Polyisocyanate Curing Agent (Curing Agent B1-2) 143.3 parts of an isocyanurate of 1,5-pentamethylene diisocyanate and 24 parts of MIBK were charged into a reaction vessel and heated to 60°C. 75 parts of methyl ethyl ketoxime (MEK oxime) was added dropwise over 2 hours. After further heating at 70°C for 2 hours, IR spectroscopy confirmed that absorption due to isocyanate groups had disappeared. 36 parts of butyl cellosolve was then added to obtain a blocked polyisocyanate curing agent (B1-2) with a solids content of 78%. The NCO equivalent of this blocked polyisocyanate curing agent was 256.

[0077] Production Example 2-3: Production of Blocked Polyisocyanate Curing Agent (Curing Agent B1-3) 1,340 parts of 4,4'-diphenylmethane diisocyanate and 277 parts of MIBK were charged into a reaction vessel and heated to 80°C, after which a solution of 226 parts of ε-caprolactam in 944 parts of butyl cellosolve was added dropwise at 80°C over 2 hours. After further heating at 100°C for 4 hours, it was confirmed in IR spectrum measurement that absorption due to isocyanate groups had disappeared. After allowing to cool, 349 parts of MIBK was added to obtain a blocked polyisocyanate curing agent (B1-3) (solids content 80%). The NCO equivalent of this blocked polyisocyanate curing agent was 251.

[0078] Production Example 2-4: Production of Blocked Polyisocyanate Curing Agent (Curing Agent B1-4) 1,680 parts of hexamethylene diisocyanate (HDI) and 732 parts of MIBK were charged into a reaction vessel and heated to 60°C. A solution of 346 parts of trimethylolpropane in 1,067 parts of MEK oxime was added dropwise to the reaction vessel at 60°C over 2 hours. After further heating at 75°C for 4 hours, it was confirmed that absorption due to isocyanate groups had disappeared in IR spectrum measurement. After allowing to cool, 140 parts of MIBK was added to obtain a blocked isocyanate curing agent (B1-4) with a solids content of 78%. The NCO equivalent of this blocked polyisocyanate curing agent was 155.

[0079] Production Example 2-5: Production of Blocked Polyisocyanate Curing Agent (Curing Agent B1-5) 165 parts of an isocyanurate of hexamethylene diisocyanate (trade name Sumidur N3300, manufactured by Sumika Bayer Urethane Co., Ltd.) and 24 parts of MIBK were charged into a reaction vessel and heated to 60°C. 75 parts of methyl ethyl ketoxime (MEK oxime) were added dropwise over 2 hours. After further heating at 70°C for 2 hours, IR spectroscopy confirmed that absorption due to isocyanate groups had disappeared. Thereafter, 44 parts of butyl cellosolve was added to obtain a blocked polyisocyanate curing agent (B1-5) with a solids content of 78%. The NCO equivalent of this blocked polyisocyanate curing agent was 281.

[0080] Production Example 2-6: Production of Blocked Polyisocyanate Curing Agent (Curing Agent B1-6) 1,540 parts of 1,5-pentamethylene diisocyanate (PDI) were charged into a reaction vessel and heated to 60°C. A solution of 346 parts of trimethylolpropane in 732 parts of MIBK was added dropwise to the vessel over 2 hours at 60°C. Then, 1,178 parts of 3,5-dimethylpyrazole were slowly added at a temperature of 60-70°C. After further heating at 70°C for 2 hours, IR spectroscopy confirmed that absorption due to isocyanate groups had disappeared. After allowing the mixture to cool, 132 parts of MIBK were added to obtain a blocked polyisocyanate curing agent (B1-6) with a solids content of 78%. The NCO equivalent of this blocked polyisocyanate curing agent was 153.

[0081] Production Example 2-7: Production of Blocked Polyisocyanate Curing Agent (Curing Agent B1-7) 143.3 parts of an isocyanurate of 1,5-pentamethylene diisocyanate and 24 parts of MIBK were charged into a reaction vessel and heated to 60°C. 83 parts of 3,5-dimethylpyrazole was slowly added thereto at a temperature of 60-70°C. After further heating at 70°C for 2 hours, IR spectroscopy confirmed that absorption due to isocyanate groups had disappeared. 40 parts of butyl cellosolve was then added to obtain a blocked polyisocyanate curing agent (curing agent B1-7) with a solids content of 78%. The NCO equivalent of this blocked polyisocyanate curing agent was 265.

[0082] Production Example 3: Preparation of Pigment Dispersion Resin 2,220 parts of isophorone diisocyanate and 342.1 parts of methyl isobutyl ketone were charged into a reaction vessel equipped with a stirrer, a cooling tube, a nitrogen inlet tube, and a thermometer. The temperature was raised to 50°C, and 2.2 parts of dibutyltin laurate was added. The temperature was raised to 60°C, and 878.7 parts of methyl ethyl ketone oxime was added. The mixture was then kept at 60°C for 1 hour, and it was confirmed that the NCO equivalent was 348. 890 parts of dimethylethanolamine was then added. The mixture was then kept at 60°C for 1 hour, and it was confirmed by IR that the NCO peak had disappeared. Next, while cooling so as not to exceed 60°C, 1,872.6 parts of 50% lactic acid and 495 parts of deionized water were added to obtain a quaternizing agent.

[0083] 870 parts of tolylene diisocyanate and 49.5 parts of methyl isobutyl ketone were charged into a separate reaction vessel. 667.2 parts of 2-ethylhexanol were added dropwise to the reaction vessel over 2.5 hours while cooling so that the temperature did not exceed 50°C. After completion of the dropwise addition, 35.5 parts of methyl isobutyl ketone were added and the mixture was kept warm for 30 minutes. Thereafter, it was confirmed that the NCO equivalent was 330 to 370, and a half-blocked polyisocyanate was obtained.

[0084] A reaction vessel equipped with a stirrer, a condenser, a nitrogen inlet tube, and a thermometer was charged with 940.0 parts of bisphenol A epoxy resin (trade name DER-331J, manufactured by The Dow Chemical Company) and 38.5 parts of methanol, followed by the addition of 0.1 parts of dibutyltin dilaurate. The mixture was heated to 50°C, and then 87.1 parts of tolylene diisocyanate was added. The mixture was further heated to 100°C, and 1.4 parts of N,N-dimethylbenzylamine was added. The mixture was then maintained at 130°C for 2 hours. At this time, methanol was fractionated using a fractionating column. The mixture was cooled to 115°C, and methyl isobutyl ketone was added until the solids concentration reached 90%. Subsequently, 270.3 parts of bisphenol A and 39.2 parts of 2-ethylhexanoic acid were added, followed by heating and stirring at 125°C for 2 hours. Subsequently, 516.4 parts of the half-blocked polyisocyanate was added dropwise over 30 minutes, followed by heating and stirring for 30 minutes. Furthermore, 1506 parts of polyoxyethylene bisphenol A ether was gradually added and dissolved therein. After cooling to 90°C, the quaternizing agent was added, and the temperature was maintained at 70 to 80°C. After confirming that the acid value was 2 or less, deionized water was added to obtain a pigment dispersion resin (resin solids content 30%).

[0085] Production Example 4: Preparation of pigment dispersion paste

[0120] 1,200 parts of the pigment dispersion resin obtained in Production Example 3, 3 parts of carbon black, 620 parts of kaolin, 500 parts of titanium dioxide, 70 parts of bismuth oxide, and 713 parts of deionized water were placed in a sand grinding mill and dispersed until the particle size reached 10 µm or less, thereby obtaining a pigment dispersion paste (solid content 50%).

[0086] Example 1 Preparation of Cationic Electrodeposition Coating Composition (Preparation of Aminated Epoxy Resin Emulsion) 400 parts (solids content) of the aminated epoxy resin (A) obtained in Production Example 1 and 600 parts (solids content) of the blocked polyisocyanate curing agent (B1-1) obtained in Production Example 2-1 were mixed, and ethylene glycol mono-2-ethylhexyl ether was added so that the amount was 3% based on the solids content. Next, formic acid was added to neutralize the mixture to a neutralization rate of 40%, and the mixture was slowly diluted with ion-exchanged water to obtain an aminated epoxy resin emulsion.

[0087] (Preparation of cationic electrodeposition coating composition) To a stainless steel container were added 1,666 parts of ion-exchanged water, 1,172 parts of the aminated epoxy resin emulsion prepared above, and 330 parts of the pigment dispersion paste obtained in Production Example 4. The mixture was then aged at 40°C for 16 hours to obtain a cationic electrodeposition coating composition.

[0088] [Examples 2 to 6] and [Comparative Examples 1 to 6] Cationic electrodeposition coating compositions were produced in the same manner as in Example 1, except that the type and amount of the blocked polyisocyanate curing agent were changed as shown in Table 1. Electrodeposition coated articles (single-layer coating films) were produced using the resulting cationic electrodeposition coating compositions in the same manner as in Example 1.

[0089] The cationic electrodeposition coating compositions prepared in the Examples and Comparative Examples were evaluated as follows, and the results are shown in the table below.

[0090] Preparation of Electrodeposition Coated Objects Cold-rolled steel sheets (JIS G3141, SPCC-SD) were prepared as substrates. These steel sheets were degreased by immersion in Surf Cleaner EC90 (manufactured by Nippon Paint Surf Chemicals) at 50°C for 2 minutes. Subsequently, they were immersed in Surfdyne EC3200 (manufactured by Nippon Paint Surf Chemicals, a zirconium conversion treatment agent) at 35°C for 90 seconds. Afterwards, they were rinsed with deionized water.

[0091] The viscosity of the cationic electrodeposition coating composition obtained above was adjusted by adding a required amount of 2-ethylhexyl glycol so that the thickness of the electrodeposition coating film after curing would be 20 μm. After all of the steel plates were immersed in the obtained cationic electrodeposition coating composition, voltage application was immediately initiated. The voltage was increased over 30 seconds, and after reaching 180 V, it was maintained for 150 seconds. This resulted in the deposition of an uncured electrodeposition coating film on the substrate. The resulting uncured electrodeposition coating film was heat-cured at 135°C for 25 minutes to obtain an electrodeposition-coated product having a cured electrodeposition coating film thickness of 20 μm. The resulting electrodeposition-coated product was evaluated for gel fraction (evaluation of low-mix curing ability), solvent rubbing property, and corrosion resistance as described below. The results are shown in Table 1. Table 1 also lists the equivalent ratio NCO / OH of the hydroxyl group equivalent of the aminated epoxy resin (A) and the isocyanate group equivalent of the polyisocyanate curing agent (B).

[0092] Evaluation of low-temperature curing properties (measurement of gel fraction) The electrodeposition coating film formed by the above procedure was placed in a Soxhlet extractor and extracted under acetone reflux conditions for 6 hours, and the gel fraction of the coating film was calculated according to the following formula: Gel fraction (%) = [mass after extraction (g) / mass before extraction (g)] x 100 The calculated gel fraction was evaluated according to the following criteria: ⊚: Gel fraction 95% or more ◯: Gel fraction 90% or more but less than 95% ×: Gel separation less than 90%

[0093] Evaluation of Solvent Resistance (Solvent Rubbing) A rubbing test was performed on the coating film of the cured electrodeposition coated plate using a cloth soaked in MIBK solvent with a load of 500 grams applied, and the condition of the coating film surface was observed. Evaluation was based on the following criteria: ○: The coating film surface did not dull after 30 back and forth rubbings. △: The coating film surface dulled after 20 back and forth rubbings. ×: The coating film surface dulled after 10 back and forth rubbings.

[0094] Corrosion Resistance (Salt-Solution Dipping Test (SDT)) A scratch was made with a knife in the coating film of a cured electrodeposition coated plate made of cold-rolled steel plate so that it reached the substrate, and the coated plate was immersed in 5% saline solution at 55°C for 240 hours. After that, tape was used to peel the plate and measure the peel width on both sides. The measured peel width was evaluated according to the following criteria. Evaluation criteria ○: Peel width less than 12 mm △: Peel width 12 mm or more but less than 14 mm ×: Peel width 14 mm or more

[0095] Measurement of Dynamic Tg of Cured Coating Film of Aminated Epoxy Resin Emulsion The aminated epoxy resin emulsions prepared in the Examples and Comparative Examples were electrodeposited onto tinplates for dynamic viscoelasticity measurement, and then baked and cured at 135°C for 25 minutes to obtain cured electrodeposited coating films. The resulting coating films were peeled off using mercury and cut to prepare measurement samples. Using a dynamic viscoelasticity measuring device (Rheogel-E4000, manufactured by UBM Corporation), the sample was vibrated from room temperature to 200°C at a rate of 2°C per minute and a frequency of 11 Hz to measure its viscoelasticity. The ratio (tan δ) of the loss modulus (E") to the storage modulus (E') was calculated, and the temperature at which this peak value was obtained was determined to determine the dynamic Tg.

[0096]

[0097] As is clear from the results in Table 1 above, cationic electrodeposition coating compositions (Examples 1 and 3) using a blocked product of 1,5-pentamethylene diisocyanate (Production Example 2-1) or a blocked product of the nurate form of 1,5-pentamethylene diisocyanate (Production Example 2-2) as a blocked isocyanate curing agent, and combinations of these with other blocked polyisocyanate compounds (blocked product of 4,4'-diphenylmethane diisocyanate in Production Example 2-3) (Examples 2 and 4) exhibit excellent gel fractions, solvent rubbing properties, and corrosion resistance. Examples 5 and 6 use a pyrazole compound (specifically, 3,5-dimethylpyrazole) as the blocking agent for the blocked polyisocyanate, and there is no change in performance even when the blocking agent is changed. On the other hand, Comparative Example 1 uses a blocked product of hexamethylene diisocyanate as the curing agent, and exhibits very poor gel fractions and corrosion resistance. Comparative Example 2, which combines a blocked product of 4,4'-diphenylmethane diisocyanate with a blocked product of hexamethylene diisocyanate, exhibits very poor gel fraction and solvent rubbing properties. Comparative Example 3, which uses a blocked product of hexamethylene diisocyanate isocyanurate as a curing agent, exhibits very poor gel fraction and corrosion resistance. Comparative Example 4, which uses a combination of a blocked product of 4,4'-diphenylmethane diisocyanate with a blocked product of hexamethylene diisocyanate isocyanurate as a curing agent, exhibits very poor gel fraction and solvent rubbing properties. Comparative Examples 5 and 6 exhibit poor performance because the NCO / OH ratio is not within the appropriate range. The dynamic Tg range of the cured coating film of the aminated epoxy resin emulsion is also too high in Comparative Example 5 and too low in Comparative Example 6.

[0098] The cationic electrodeposition coating composition of the present disclosure has the advantages of good low-temperature curing properties and of maintaining coating film properties such as corrosion resistance.The cationic electrodeposition coating composition of the present disclosure also has the advantage of being made from biomass-derived raw materials (non-fossil raw materials), thereby reducing the environmental impact.

Claims

1. A cationic electrodeposition coating composition comprising an aminated epoxy resin (A) and a polyisocyanate curing agent (B), wherein the polyisocyanate curing agent (B) contains a blocked polyisocyanate compound (B1) selected from the group consisting of 1,5-pentamethylene diisocyanate and multimers of 1,5-pentamethylene diisocyanate, and the equivalent ratio NCO / OH of the hydroxyl equivalent of the aminated epoxy resin (A) to the isocyanate group equivalent of the polyisocyanate curing agent (B) is 0.5 or more and less than 3.

1. Cationic electrodeposition coating composition.

2. The blocked agent used in the preparation of the blocked polyisocyanate compound (B1) contains one or more selected from the group consisting of oxime compounds, pyrazole compounds, imidazole compounds, and triazole compounds. The cationic electrodeposition coating composition according to claim 1.

3. The cured coating film of the aminated epoxy resin emulsion, which is a mixture of the aminated epoxy resin (A) and the polyisocyanate curing agent (B), at 135 ° C for 25 minutes has a Tg of 65 ° C or more and 95 ° C or less by dynamic viscoelasticity measurement. The cationic electrodeposition coating composition according to claim 1 or 2.

4. A method for producing a cationic electrodeposition coating composition, comprising the following steps: a step of preparing a blocked polyisocyanate compound (B1); and a step of mixing a polyisocyanate curing agent (B) containing the blocked polyisocyanate compound (B1) and an aminated epoxy resin (A) to prepare an aminated epoxy resin emulsion. The blocked polyisocyanate compound (B1) is prepared by blocking a polyisocyanate compound selected from the group consisting of 1,5-pentamethylene diisocyanate and multimers of 1,5-pentamethylene diisocyanate with a blocking agent, and the blocking agent contains one or more selected from the group consisting of oxime compounds, pyrazole compounds, imidazole compounds, and triazole compounds. Manufacturing method.

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