Paint composition, electrodeposition paint composition, painting method, and method for producing painted article

Abstract

A paint composition contains a resin (A) having a donor component of a Michael addition reaction and a curing agent (B) having an acceptor component of the Michael addition reaction. The curing agent (B) contains a reaction product of a furan ring-containing compound (b1) and a maleimide group-containing compound (b2).

Description

Coating Composition, Electrodeposition Coating Composition, Coating Method, and Method for Producing Coated Article

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

[0002] Electrodeposition coatings are widely used in fields such as automotive parts and home appliances because they can form a uniform coating film on members with complex shapes. Conventionally, in the curing process of such electrodeposition coatings, to impart curability at low temperatures, oxime blocking technology that uses a compound protected by oxime groups and Michael addition curing technology that utilizes a Michael addition reaction have been proposed.

[0003] In oxime blocking technology, heating causes elimination of the oxime groups and expression of reactive groups, thereby allowing the curing reaction to proceed. On the other hand, in Michael addition curing technology, an addition reaction between an active hydrogen compound and an unsaturated compound in the coating is utilized to form a crosslinked structure (for example, Patent Document 1).

[0004] WO2019 / 039467 Specification

[0005] However, even with these technologies, constant heating is required to allow the curing reaction to proceed sufficiently, and achieving complete low-temperature curing is not easy. In addition, when an oxime blocked compound is used, management of by-products accompanying the elimination reaction and control of the reaction rate become issues. Furthermore, when the Michael addition reaction is utilized, it is necessary to incorporate highly reactive components into the coating, which results in issues such as decreased storage stability of the coating and deterioration during long-term storage.

[0006] As described above, conventional low-temperature curing technologies still have room for improvement in achieving both a reduction in curing temperature and stability of the coating. Additionally, a catalyst may be required to achieve low-temperature curing, which also poses issues from the perspective of cost and catalyst residue.

[0007] An object of the present disclosure is to provide a coating composition that achieves both low-temperature curability and storage stability.

[0008] To solve the above-mentioned problems, one aspect of the present disclosure is a paint composition comprising a resin (A) having a donor component for a Michael addition reaction and a curing agent (B) having an acceptor component for the Michael addition reaction, wherein the curing agent (B) contains a reaction product of a furan ring-containing compound (b1) and a maleimide group-containing compound (b2).

[0009] According to one aspect of this disclosure, a coating composition that achieves both low-temperature curability and storage stability can be provided.

[0010] The embodiments of this disclosure will be described in detail below.

[0011] <Coating composition>

[0012] The coating composition of this disclosure contains a resin (A) having a donor component for the Michael addition reaction and a curing agent (B) having an acceptor component for the Michael addition reaction.

[0013] <<Resin (A)>> Resin (A) is a resin having a donor component for the Michael addition reaction. Here, "donor component for the Michael addition reaction" means an active hydrogen group that can be used in the Michael addition reaction, and examples of active hydrogen groups include an active methylene group, a primary amino group and / or a secondary amino group, a thiol group (mercapto group), and a hydroxyl group.

[0014] The resin (A) may have one or more (preferably more than one) active hydrogen groups in one molecule, and from the viewpoint of low-temperature curability and storage stability, it is preferable that the active hydrogen groups include at least one of an active methylene group and a primary amino group and / or a secondary amino group.

[0015] As resin (A), a compound containing active hydrogen groups in which the resin skeleton is resin (i.e., a resin containing active hydrogen groups) can be suitably used. Examples include modified resins obtained by adding a compound containing active hydrogen groups to acrylic resin, polyester resin, epoxy resin, polyamide resin, etc.

[0016] In particular, from the viewpoint of achieving both suitability for cationic electrodeposition coating and function as a donor component for the Michael addition reaction, an active hydrogen group-modified epoxy resin having amino groups is preferred as resin (A), more preferably having primary and / or secondary amino groups, and especially preferably an epoxy resin having primary amino groups. By using such an epoxy resin (A1) having primary amino groups, the progress of the Michael addition reaction is improved, efficient crosslinking is possible even under low temperature conditions, and low-temperature curability and finish quality are improved.

[0017] <<<Epoxy Resin (A1)>>> Epoxy resin (A1) is an epoxy resin having a primary amino group. Epoxy resin (A1) can be obtained as an adduct of epoxy resin with a primary monoamine and / or primary polyamine, a secondary monoamine and / or secondary polyamine, or a mixed polyamine of a primary amine and a secondary amine.

[0018] Examples of amines used in the above addition include mono- or di-alkylamines, alkanolamines, and alkylene polyamines. Specific examples include monoethanolamine, diethanolamine, ethylenediamine, diethylenetriamine, and triethylenetetramine.

[0019] Furthermore, examples of epoxy resins used as raw materials for epoxy resin (A1) include those having at least one epoxy group (preferably two or more) in one molecule. For example, epoxy resins obtained by the reaction of a polyphenol compound with an epihalohydrin can be used.

[0020] Examples of polyphenol compounds include bisphenol A, bisphenol F, phenol novolac, and cresol novolac.

[0021] In the production of the epoxy resin (A1) described above, the addition reaction of amines and other elements to the epoxy resin can be carried out, for example, in a solvent at a temperature of approximately 80 to 170°C for about 1 to 6 hours.

[0022] <<Curing Agent (B)>> Curing agent (B) is a curing agent having an acceptor component for the Michael addition reaction. Curing agent (B) contains a compound having an unsaturated bond that can react with active hydrogen groups (e.g., primary amino groups, secondary amino groups, active methylene groups, thiol groups, hydroxyl groups, etc.) contained in resin (A).

[0023] One embodiment of the curing agent (B) contains a reaction product of a furan ring-containing compound (b1) and a maleimide group-containing compound (b2) (hereinafter, also sometimes referred to as a "blocked maleimide group-containing compound").

[0024] The furan ring-containing compound (b1) and the maleimide group-containing compound (b2) can form an addition product, for example, through a Diels-Alder reaction. This allows for suppression of reactivity during paint storage, while the reaction can proceed and curing can be accelerated upon heating, thus contributing to achieving both low-temperature curing properties and storage stability.

[0025] <<<Furan ring-containing compound (b1)>>> The furan ring-containing compound (b1) is not particularly limited as long as it is a compound having a furan ring. Examples of furan ring-containing compounds (b1) include furans such as furan, 2-methylfuran, and 2,5-dimethylfuran; furfuryl group-containing compounds such as furfuryl alcohol, furfurylamine, furfuryl mercaptan, and furfuryl glycidyl ether; and furfural.

[0026] The furan ring-containing compound (b1) can be used with the maleimide group-containing compound (b2) in an equivalent ratio that allows for addition reaction (for example, in a range where the number of moles of the furan ring and the number of moles of the maleimide group are roughly equal to or in excess).

[0027] <<<Maleimide group-containing compound (b2)>>> The maleimide group-containing compound (b2) is not particularly limited as long as it is a compound having a maleimide group (-N-CO-CH=CH-CO-). Examples of maleimide group-containing compounds (b2) include compounds having one or more (preferably two or more) maleimide groups in one molecule.

[0028] As an example of a maleimide group-containing compound (b2), the compound represented by the following formula (1) can be used. In formula (1), X1 and X2 are organic groups, and n is an integer of 1 or more.

[0029]

[0030] Furthermore, the maleimide group-containing compound (b2) is not limited to the compound represented by formula (1) above, but a resin having a maleimide group (maleimide resin) can also be used. Examples of maleimide resins include resins composed of (meth)acrylic resins, polyester resins, epoxy resins, etc., that have a maleimide group, in which a maleimide group is introduced into the resin skeleton or side chains.

[0031] The reaction product of a furan ring-containing compound (b1) and a maleimide group-containing compound (b2) can be obtained, for example, by mixing the two in a solvent or without a solvent and reacting them at approximately 20 to 120°C (for example, approximately 50 to 90°C) for a predetermined time. The progress of the reaction can be tracked, for example, by infrared absorption spectroscopy. After the reaction, the product can be diluted with a solvent as needed and used in a solution form that is easily incorporated into paints.

[0032] By using a reaction product of a furan ring-containing compound (b1) and a maleimide group-containing compound (b2) represented by the above formula (1) as the curing agent (B), the curing reaction can be advanced by heating after the formation of the coating film, and curing can be obtained at a relatively low temperature. Furthermore, in one aspect of this disclosure, sufficient curability can be obtained at a low temperature even without using or reducing the amount of isocyanate dissociation catalysts (e.g., bismuth catalysts) that have been conventionally used in cationic electrodeposition coatings.

[0033] Another embodiment of the curing agent (B) contains a compound represented by the following formula (2). In formula (2), R1 and R2 are organic groups or hydrogen atoms, and n is an integer of 1 or more.

[0034]

[0035] The compound represented by formula (2) above (hereinafter also referred to as "curing agent (B1)"), used as an alternative embodiment of curing agent (B), has an unsaturated bond site shown in formula (2), and this unsaturated bond site can function as an acceptor component in a Michael addition reaction. Curing agent (B1) can form a crosslinked structure by an addition reaction with active hydrogen groups contained in resin (A).

[0036] The curing agent (B1) can be obtained, for example, as a reaction product obtained by reacting a resin having a maleimide group (hereinafter referred to as maleimide resin) with a furan ring-containing compound (b1) such as furfuryl alcohol.

[0037] As a specific example of the curing agent (B1), the reaction product of maleimide resin and furfuryl alcohol can be used, as shown in formula (3) below.

[0038]

[0039] In the production of the curing agent (B1), for example, a reaction product suitable for paint formulation (such as a blocked maleimide group-containing compound) can be obtained by mixing maleimide resin and a furan ring-containing compound such as furfuryl alcohol in a desired equivalence ratio and reacting them by heating and stirring. By using the curing agent (B1), reactivity is suppressed during storage, and the reaction can be accelerated by heating after the formation of the coating film, thus contributing to achieving both low-temperature curability and storage stability.

[0040] In addition to components (A) and (B), the paint composition of this disclosure may optionally contain a pigment dispersion paste, a solvent such as water or an organic solvent, a neutralizing agent, a surfactant, a surface modifier, a thickener, an anti-settling agent, an ultraviolet absorber, a light stabilizer, an antifoaming agent, a dissociation catalyst, a plasticizer, and the like.

[0041] Pigment dispersion paste is a paste in which pigments such as coloring pigments, rust-preventive pigments, and extender pigments are pre-dispersed into fine particles. Pigment dispersion paste can be prepared, for example, by blending a pigment dispersion resin, a neutralizing agent, a solvent, and a pigment, and then dispersing them in a dispersion mixer such as a ball mill, sand mill, or pebble mill.

[0042] The pigment is not particularly limited, and examples thereof include coloring pigments such as titanium dioxide, zinc oxide, zinc phosphate, aluminum phosphate, zinc molybdate, calcium molybdate, Prussian blue, ultramarine blue, cobalt blue, copper phthalocyanine blue, indanthrone blue, synthetic yellow iron oxide, transparent iron oxide (yellow), bismuth vanadate, titanium yellow, zinc yellow, monoazo yellow, isoindolinone yellow, metal complex azo yellow, quinophthalone yellow, benzimidazolone yellow, iron oxide red, monoazo red, quinacridone red, azo lake (Mn salt), quinacridone magenta, anthanthrone orange, dianthraquinonyl red, perylene maroon, perylene red, diketopyrrolopyrrole chrome vermilion, chlorinated phthalocyanine green, brominated phthalocyanine green, pyrazolone orange, benzimidazolone orange, dioxazine violet, and perylene violet; extender pigments such as baryta powder, barium sulfate, barium carbonate, calcium carbonate, gypsum, clay, white carbon, diatomaceous earth, talc, magnesium carbonate, alumina white, gloss white, and mica powder; and rust-preventive pigments such as aluminum phosphomolybdate, aluminum tripolyphosphate, and zinc oxide (zinc white).

[0043] As the solvent, water, organic solvents and the like can be appropriately used, with water being preferred. Examples of the organic 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 iso-propanol; ether alcohol compounds such as ethylene glycol monobutyl ether, diethylene glycol monoethyl ether and propylene glycol monomethyl ether; and mixtures of the foregoing.

[0044] When coating is performed using the coating composition of the present disclosure, methods such as brush coating, roller coating, dipping coating, bar coater coating, applicator coating, curtain coating, spray coating, rotary atomization coating, and electrodeposition coating can be used.

[0045] There is no particular limitation on the film thickness of the coating film obtained by coating using the coating composition of the present disclosure. For example, the film thickness based on the dried coating film can be in the range of 5 to 60 µm, preferably 8 to 50 µm, and more preferably 10 to 40 µm.

[0046] In addition, baking and drying of the coating film (hereinafter also referred to as "heat curing") can be performed by heating the coating film using drying equipment such as an electric hot air dryer or a gas hot air dryer at a surface temperature of the coated object of 80 to 140°C, preferably 100 to 135°C, more preferably 100 to 120°C, for a time of 3 to 180 minutes, preferably 10 to 50 minutes. Here, the range of 80 to 140°C represents a suitable baking temperature range generally applicable to the coating composition of the present disclosure, and exemplifies a typical range particularly when low-temperature curability is emphasized.

[0047] In particular, the range of 100 to 120°C is a suitable temperature range from the viewpoint that sufficient curability can be exhibited even under low-temperature conditions of 120°C or lower, and deterioration of finishing properties can be suppressed even after long-term storage. That is, the coating composition of the present disclosure can promote a sufficient crosslinking reaction even under curing temperature conditions lower than conventional ones, and thus can contribute to reduction of energy consumption and manufacturing cost.

[0048] Examples of substrates to be coated with the coating composition of the present disclosure include automobile bodies, automobile parts, two-wheeled vehicle parts, household appliances, and other equipment. There is no particular limitation on the material of the substrate, and examples thereof include metals, plastics, inorganic materials, wood, and fiber materials. In the case of metal materials, for example, those obtained by cleaning the surface such as alkali degreasing as necessary, and then performing surface treatment such as phosphate chemical conversion treatment or chromate treatment as necessary can be used, and the substrate may also be one that has been coated with an undercoat paint or the like.

[0049] A coated article can be obtained by coating the coating composition of the present disclosure onto the aforementioned substrate.

[0050] <Electrodeposition Coating Composition> The coating composition of this disclosure can be used as an electrodeposition coating composition for cationic electrodeposition coating (hereinafter sometimes referred to as a cationic electrodeposition coating composition). Cationic electrodeposition coating is a coating method in which a metal part (object to be coated) is immersed in a water-soluble coating solution and a direct current is passed through it, thereby electrically attracting and adhering the coating to the object to be coated, with the object to be coated acting as the cathode.

[0051] The cationic electrodeposition coating composition contains the above-mentioned resin (A) and curing agent (B). The blending ratio of (A) and (B) in the cationic electrodeposition coating composition of this disclosure is preferably such that, based on the total amount of resin solids in the coating composition, the resin (A) having a donor component for the Michael addition reaction is preferably 30 to 98% by mass, more preferably 40 to 97% by mass, and even more preferably 50 to 96% by mass, while the curing agent (B) is preferably 1 to 60% by mass, more preferably 2 to 58% by mass, and even more preferably 3 to 56% by mass. By adopting such a blending ratio, the balance between reactivity and storage stability is optimized, and low-temperature curability and the stability of the coating film appearance are maintained even after long-term storage.

[0052] The method for producing a cationic electrodeposition coating composition is not particularly limited, but for example, in addition to (A) and (B) above, various additives such as surfactants and surface modifiers may be mixed thoroughly to form a compounded resin, which is then dispersed in water, and then epoxy resin crosslinked particles, pigment dispersion paste, water or organic solvent, neutralizing agent, surfactant, etc. are thoroughly mixed in to obtain the composition. As the neutralizing agent, an organic acid may be used, and formic acid, lactic acid, or a mixture thereof is preferred.

[0053] Pigment dispersion paste is a paste in which pigments such as coloring pigments, rust-preventive pigments, and extender pigments are pre-dispersed into fine particles. For example, pigment dispersion paste can be prepared by blending a pigment dispersion resin, a neutralizing agent, and a pigment, and then dispersing them in a dispersion mixer such as a ball mill, sand mill, or pebble mill.

[0054] Examples of resins for pigment dispersion include epoxy resins and acrylic resins having hydroxyl groups and cationic groups, such as 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.

[0055] Examples of the above-mentioned pigments that can be added include coloring pigments such as titanium dioxide, carbon black, and red iron oxide; extender pigments such as clay, mica, barita, calcium carbonate, and silica; and rust-preventive pigments such as aluminum phosphomolybdate, aluminum tripolyphosphate, and zinc oxide (zinc oxide).

[0056] As a solvent, water or organic solvents can be used as appropriate, but water is preferred. Examples of organic solvents 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 iso-propanol; ether alcohol compounds such as ethylene glycol monobutyl ether, diethylene glycol monoethyl ether, and propylene glycol monomethyl ether; or mixtures thereof.

[0057] Furthermore, the electrodeposition coating composition of this disclosure does not necessarily have to contain a bismuth catalyst and / or a tin catalyst. The electrodeposition coating composition of this disclosure may contain a catalyst as needed, but because it utilizes a specific reaction using maleimide and a furan ring, it is advantageous in terms of environmental impact and safety because it can cure sufficiently at low temperatures even without containing isocyanate dissociation catalysts (e.g., bismuth catalysts, tin catalysts) that have been conventionally used in cationic electrodeposition coatings. In other words, by using a composition that does not contain such catalysts or reduces the amount used, catalyst-derived side reactions and degradation over time can be suppressed, and the long-term storage stability of the coating is further improved.

[0058] <Painting Method> The painting method of this disclosure comprises the step of immersing an object to be painted in an electrodeposition paint bath consisting of the above-mentioned electrodeposition paint composition and performing electrodeposition painting.

[0059] The substrate to which the electrodeposition coating composition is applied is a metal. The substrate is not particularly limited and can be, for example, an automobile body, a motorcycle part, household appliances, or other equipment.

[0060] Examples of metal sheets to be coated include cold-rolled steel sheets, alloyed hot-dip galvanized steel sheets, electro-galvanized steel sheets, electro-galvanized zinc-iron double-layer plated steel sheets, organic composite plated steel sheets, Al material, Mg material, etc., as well as metal sheets that have been cleaned by alkaline degreasing or other means as needed, followed by surface treatments such as phosphate chlorination or chromate treatment.

[0061] Cationic electrodeposition coating compositions can be applied to the surface of a desired substrate by cationic electrodeposition coating. The cationic electrodeposition method involves using a bath containing a cationic electrodeposition coating composition that has been diluted with deionized water or the like to a solid content concentration of approximately 5 to 40% by mass, preferably 10 to 25% by mass, and whose pH has been adjusted to within the range of 4.0 to 9.0, preferably 5.5 to 7.0. The coating is then typically carried out by adjusting the bath temperature to 15 to 35°C and applying current with the substrate as the cathode under load voltage conditions of 100 to 400V, preferably 150 to 350V.

[0062] After electrodeposition coating, the workpiece is thoroughly washed with ultrafiltration solution (UF filtrate), reverse osmosis permeate (RO water), industrial water, or pure water to remove any excess cationic electrodeposition paint.

[0063] The thickness of the electrodeposited coating is not particularly limited, but for example, it can be in the range of 5 to 40 μm, preferably 10 to 30 μm, based on the dry coating. Furthermore, the baking (heat curing) of the coating is performed by heating the electrodeposited coating using drying equipment such as an electric hot air dryer or a gas hot air dryer at a temperature of 80 to 160°C, preferably 80 to 140°C, on the surface of the coated object, for a time of 10 to 180 minutes, preferably 20 to 50 minutes. A cured coating can be obtained by the above baking (heat curing).

[0064] The reason why the electrodeposited coating film temperature range of 80 to 160°C includes an upper limit of 160°C is that higher temperature conditions may be adopted depending on the equipment conditions in the electrodeposition coating process and the type of material to be coated. On the other hand, from the viewpoint of more favorably exhibiting the low-temperature curing properties that are the effect of this disclosure, a temperature range of 140°C or lower, and particularly 120°C or lower, is preferred.

[0065] The electrodeposition coating process may include a step of further heating and curing the coating film obtained at a temperature of 120°C or lower. Even at low temperatures of 120°C or lower, the crosslinking reaction proceeds due to the combination of resin (A) and curing agent (B), and a practically sufficient cured coating film can be formed.

[0066] <Method for manufacturing painted articles> The method for manufacturing painted articles according to the present disclosure includes a step of further heating and curing the coating film obtained in the electrodeposition coating step at a temperature of 140°C or lower.

[0067] In the electrodeposition coating process, the metal workpiece is immersed in an electrodeposition coating bath consisting of a cationic electrodeposition coating composition using the aforementioned coating method, and cationic electrodeposition coating is performed. As a result, a coating film of the cationic electrodeposition coating composition is formed on the surface of the metal workpiece.

[0068] In the heat curing step, the metal workpiece on which the coating film was formed in the electrodeposition coating step described above is heated and dried to harden the coating film on the metal workpiece. At this time, the heating temperature for heat curing is preferably 140°C or lower. The heating temperature for heat curing may also be 120°C or lower.

[0069] In the method for manufacturing a coated article according to the present disclosure, a coating film of a cationic electrodeposition coating composition is formed on the surface of the metal workpiece, resulting in a metal workpiece with excellent corrosion resistance at the edges and a good finish on the flat surface when heated at low temperatures.

[0070] Furthermore, even when the coating obtained in the electrodeposition coating process is heat-cured at a low temperature of 140°C or less, a metal substrate with excellent finish on flat surfaces can be obtained. Therefore, manufacturing costs during the production of coated articles can be reduced. In addition, the environmental impact of the production of coated articles can be reduced.

[0071] In particular, by using a composition that includes a reaction product of a furan ring-containing compound and a maleimide group-containing compound, reactivity can be suppressed during storage of the paint, and the reaction can be selectively allowed to proceed when heated, thus achieving a high degree of both low-temperature curing properties and storage stability.

[0072] Furthermore, by heat-curing the coating obtained in the electrodeposition coating process at a temperature of 120°C or lower, it is possible to achieve both low-temperature curability and good finish for the metal substrate, resulting in significant reductions in manufacturing costs and environmental impact. Moreover, the low temperature condition of 120°C or lower has technical significance in that it realizes a curing mechanism that does not depend on the high-temperature baking conditions that were previously required.

[0073] The present disclosure will be further described below with reference to examples, but the disclosure is not limited to these examples. In each example, "parts" refers to parts by mass, and "%" refers to mass percent. In addition, numbers without units in the table refer to mass percent. Furthermore, various tests and evaluations will be carried out according to the methods described below.

[0074] - Preparation of a curing agent (B) which is a reaction product of a furan ring-containing compound (b1) and a maleimide group-containing compound (b2) - [Preparation Example 1] In a flask equipped with a thermometer, a stirrer, and a reflux condenser, 10 parts of maleimide resin (manufactured by Nippon Kayaku Co., Ltd., MIR-3000-70MT) (maleimide group content: 23.9 mmol) were added to 2.6 parts of furfuryl alcohol (26.3 mmol), and the mixture was reacted at 70°C for 4 hours with stirring to produce a blocked maleimide group-containing compound (B-1) solution with a solid content of 74%.

[0075] Furthermore, "MIR-3000-70MT" is a resin having a maleimide group represented by the following formula (4), with a solid content of 70% and a maleimide equivalent of 293 g / eq per solid content.

[0076] (In equation (4), n is an integer between 1 and 5.)

[0077] [Production Example 2] A solution of a blocked maleimide group-containing compound (B-2) with a solid content of 74% was prepared in the same manner as in Production Example 1, except that 2.1 parts (26.3 mmol) of 2-methylfuran were used instead of 2.6 parts (26.3 mmol) of furfuryl alcohol.

[0078] [Production Example 3] A solution of a blocked maleimide group-containing compound (B-3) with a solid content of 74% was prepared in the same manner as in Production Example 1, except that 1.79 parts (26.3 mmol) of furan was used instead of 2.6 parts (26.3 mmol) of furfuryl alcohol.

[0079] - Production of Oxime Blocked Isocyanate Compounds - [Production Example 4] 267 parts of Cosmonate M-200 (trade name, manufactured by Mitsui Chemicals, crude MDI, NCO group content 31.3%) and 110 parts of methyl isobutyl ketone were added to a reaction vessel and the temperature was raised to 60°C. 154 parts of methyl ethyl ketoxime were added dropwise over 1 hour, and the temperature was then raised to 80°C. While maintaining this temperature, samples were taken over time, and infrared absorption spectroscopy was used to confirm that the absorption of unreacted isocyanate groups had disappeared, thereby producing a blocked polyisocyanate composition (P) solution with a resin solids content of 74%.

[0080] - Production of resin (A) having a donor component for the Michael addition reaction - [Production Example 5] In a flask equipped with a thermometer, a stirrer, and a reflux condenser, 577 parts of bisphenol A type epoxy resin (manufactured by Mitsubishi Chemical Corporation, JER828EL ("JER" is a registered trademark), epoxy equivalent 190 g / eq), 123 parts of bisphenol A, 86 parts of octic acid, and 10 parts of methyl isobutyl ketone were mixed and heated to 100°C to dissolve. Then, 0.3 parts of tetrabutylammonium bromide and 10 parts of methyl isobutyl ketone were added and the mixture was reacted at 160°C until the epoxy equivalent was 576. Then, 55 parts of methyl isobutyl ketone were added and the mixture was cooled to 120°C, and 1.6 parts of dimethylbenzylamine and 10 parts of methyl isobutyl ketone were added and the mixture was reacted at 120°C until the epoxy equivalent was 920. Then, the mixture was cooled to 110°C and 32 parts of diethanolamine and 2.5 parts of methyl isobutyl ketone were added. After 30 minutes, 115 parts of methyl isobutyl ketonate of diethylenetriamine and 2.5 parts of methyl isobutyl ketone were added, and the reaction was maintained at 120°C. After confirming that no epoxy groups had reacted and remained, methyl isobutyl ketone was added to adjust the solid content, yielding an amino group-containing modified epoxy resin (A-1) with a solid content of 75%. The weight-average molecular weight of this resin determined by GPC was 2600, and the amount of primary amino groups was theoretically 52.24 mgKOH / g.

[0081] - Manufacturing of Pigment Dispersion Resin - [Manufacturing Example 6] In a flask equipped with a stirrer, thermometer, dropping funnel, and reflux condenser, 1010 parts of epoxy resin (manufactured by Mitsubishi Chemical Corporation, JER828EL ("JER" is a registered trademark), epoxy equivalent 190, number average molecular weight 350) were added, along with 390 parts of bisphenol A, 240 parts of polycaprolactone diol (manufactured by Daicel Chemical Industries, Ltd., Praxel 212, weight average molecular weight approximately 1250), and 0.2 parts of dimethylbenzylamine. The mixture was reacted at 130°C until the epoxy equivalent was approximately 1090. Next, 134 parts of dimethylethanolamine and 150 parts of a 90% aqueous lactic acid solution were added, and the mixture was reacted at 90°C until the epoxy groups disappeared. Then, propylene glycol monomethyl ether was added to adjust the solid content, and a pigment dispersion resin containing a quaternary ammonium base with a solid content of 60% was obtained.

[0082] - Production of Pigment Dispersion Paste - [Production Example 7] 8.3 parts (5 parts solids) of pigment dispersion resin containing a quaternary ammonium base with a solid content of 60% obtained in Production Example 6, 14.5 parts of titanium dioxide, 7 parts of purified clay, 0.3 parts of carbon black, and 20.3 parts of deionized water were added and dispersed in a ball mill for 20 hours to obtain a pigment dispersion paste (Q-1) with a solid content of 55%.

[0083] [Production Example 8] A pigment dispersion paste (Q-2) was obtained in the same manner as in Production Example 7, except that 2 parts of bismuth hydroxide were added as a catalyst to adjust the amount of deionized water to a solid content of 55%.

[0084] - Manufacture of Cationic Electrodeposition Coating Composition - [Example 1] 98.6 parts (74 parts solids) of the 75% amino group-containing epoxy resin (A-1) solution obtained in Production Example 5 and 35.1 parts (26.0 parts solids) of the 74% blocked maleimide group-containing compound (B-1) solution obtained in Production Example 1 as a curing agent were mixed. Then 17.2 parts of 10% acetic acid were added and the mixture was uniformly stirred. Deionized water was then added while vigorously stirring to adjust the solid content and obtain an emulsion with a solid content of 26%. Next, 384 parts (100 parts solids) of the 26% solids emulsion, 52.4 parts (28.8 parts solids) of the 55% solids pigment dispersion paste obtained in Production Example 7, and deionized water were added to adjust the solid content and produce a cationic electrodeposition coating (X-1) with a solid content of 20%.

[0085] [Examples 2-7 and Comparative Examples 1-2] Cationic electrodeposition coating compositions (X-2) to (X-9) were prepared in the same manner as in Example 1, except that the formulation was as shown in Table 1 below.

[0086] Furthermore, the results of the evaluation tests (low-temperature hardening properties, storage stability) described later are shown in Table 1.

[0087]

[0088] (Preparation of test plates) Cold-rolled steel sheets (150 mm (length) x 70 mm (width) x 0.8 mm (thickness)) were prepared by chemical conversion treatment with zinc phosphate treatment agent (Palbond #3020, manufactured by Nippon Parkerizing Co., Ltd. ("Palbond" is a registered trademark)). Two of these cold-rolled steel sheets were prepared for each sample, and two were electrodeposited using the respective cationic electrodeposition coatings obtained in the examples and comparative examples to achieve a dry film thickness of 15 μm. The test plates were then baked and dried at 110°C for 20 minutes or at 130°C for 20 minutes.

[0089] <Low-temperature curing properties (gel fraction)> The curing properties (gel fraction) at 110°C or 130°C were evaluated from the obtained test plates. The evaluation was based on the following criteria, with A and B being passable and C being failing.

[0090] [Evaluation Criteria] A: Gel fraction is 80% or more B: Gel fraction is 60% or more and less than 80% C: Gel fraction is less than 60%

[0091] <Storage Stability (Finish after Storage)> The obtained cationic electrodeposition coating was placed in a sealed container and stored at 40°C for 30 days. Next, a cold-rolled steel sheet (150 mm (length) x 70 mm (width) x 0.8 mm (thickness)) that had been chemically treated with zinc phosphate treatment agent (Palbond #3020, manufactured by Nippon Parkerizing Co., Ltd. ("Palbond" is a registered trademark)) was used as the substrate for electrodeposition coating with the stored cationic electrodeposition coating to a dry film thickness of 17 μm, and the sheet was baked and dried at 110°C for 20 minutes to obtain a test plate. Furthermore, the surface roughness value (Ra) of the obtained test plate was measured using a surface roughness meter (Surftest 301, manufactured by Mitutoyo ("Surftest" is a registered trademark)) with a cutoff of 0.8 mm, and evaluated according to the following criteria. The evaluation was as follows: A to B were considered acceptable, and C was considered unacceptable.

[0092] [Evaluation Criteria] A: Surface roughness value (Ra) is less than 0.25 B: Surface roughness value (Ra) is 0.25 or more and less than 0.3 C: Surface roughness value (Ra) is 0.3 or more

[0093] Table 1 shows that in Examples 1 to 7, both low-temperature curability and storage stability were good. In contrast, Comparative Example 1 showed poor results in all aspects, and while Comparative Example 2 showed good curability at 130°C, it exhibited poor low-temperature curability at 110°C and poor storage stability.

[0094] These results show that a paint composition containing a resin (A) having a donor component for the Michael addition reaction and a curing agent (B) having an acceptor component for the Michael addition reaction, wherein the curing agent (B) contains a reaction product of a furan ring-containing compound and a maleimide group-containing compound, achieves both low-temperature curability and storage stability. Furthermore, it was found that a paint composition containing a resin (A) having a donor component for the Michael addition reaction and a curing agent (B) having an acceptor component for the Michael addition reaction, wherein the curing agent (B) contains a compound represented by the following formula (2), also achieves both low-temperature curability and storage stability.

[0095] The embodiments disclosed above include, for example, the following aspects:

[0096] <1> A paint composition comprising a resin (A) having a donor component for a Michael addition reaction and a curing agent (B) having an acceptor component for the Michael addition reaction, wherein the curing agent (B) contains a reaction product of a furan ring-containing compound (b1) and a maleimide group-containing compound (b2).

[0097] <2> The paint composition according to <1>, wherein the maleimide group-containing compound (b2) is a compound represented by the following formula (1).

[0098] (In formula (1), X1 and X2 are organic groups, and n is an integer of 1 or more.)

[0099] <3> A paint composition comprising a resin (A) having a donor component for a Michael addition reaction and a curing agent (B) having an acceptor component for the Michael addition reaction, wherein the curing agent (B) contains a compound represented by the following formula (2).

[0100] (In formula (2), R1 and R2 are organic groups or hydrogen atoms. n is an integer of 1 or more.)

[0101] <4> The paint composition according to any one of <1> to <3>, wherein the resin (A) is an epoxy resin (A1) having a primary amino group.

[0102] <5> The paint composition according to any one of <1> to <4>, wherein the paint composition contains 30 to 98% by mass of the resin (A) and 1 to 60% by mass of the curing agent (B), based on the total amount of resin solids in the paint composition.

[0103] <6> An electrodeposition coating composition wherein the coating composition described in any one of <1> to <5> is an electrodeposition coating composition for cationic electrodeposition coating.

[0104] <7> The electrodeposition coating composition according to <6>, wherein the electrodeposition coating composition does not contain a bismuth catalyst and / or a tin catalyst.

[0105] <8> A painting method comprising the step of immersing an object to be painted in an electrodeposition paint bath consisting of the electrodeposition paint composition described in <6> or <7> above, and performing electrodeposition painting.

[0106] <9> The painting method according to <8>, further comprising the step of heating and curing the coating film obtained in the electrodeposition coating step at a temperature of 140°C or lower.

[0107] <10> The painting method according to <8>, further comprising the step of heating and curing the coating film obtained in the electrodeposition coating step at a temperature of 120°C or lower.

[0108] <11> A method for manufacturing a painted article, comprising the step of forming a coating film by the coating method described in any one of <8> to <10> above.

[0109] Although embodiments of the present invention have been described above, the present invention is not limited to any particular embodiment, and various modifications and changes are possible within the scope of the invention as described in the claims.

[0110] This application claims priority under U.S. Provisional Application No. 63 / 776480, filed on 24 March 2025, which is incorporated herein by reference in its entirety.

Claims

1. A paint composition comprising a resin (A) having a donor component for a Michael addition reaction and a curing agent (B) having an acceptor component for the Michael addition reaction, wherein the curing agent (B) contains a reaction product of a furan ring-containing compound (b1) and a maleimide group-containing compound (b2).

2. The paint composition according to claim 1, wherein the maleimide group-containing compound (b2) is a compound represented by the following formula (1). (In formula (1), X1 and X2 are organic groups, and n is an integer of 1 or more.) 3. A paint composition comprising a resin (A) having a donor component for a Michael addition reaction and a curing agent (B) having an acceptor component for the Michael addition reaction, wherein the curing agent (B) contains a compound represented by the following formula (2). (In formula (2), R1 and R2 are organic groups or hydrogen atoms. n is an integer of 1 or more.) 4. The paint composition according to claim 1 or 3, wherein the resin (A) is an epoxy resin (A1) having a primary amino group.

5. The paint composition according to claim 1 or 3, wherein the paint composition contains 30 to 98% by mass of the resin (A) and 1 to 60% by mass of the curing agent (B), based on the total amount of resin solids in the paint composition.

6. An electrodeposition coating composition wherein the coating composition according to claim 1 or 3 is an electrodeposition coating composition for cationic electrodeposition coating.

7. The electrodeposition coating composition according to claim 6, wherein the electrodeposition coating composition does not contain a bismuth catalyst and / or a tin catalyst.

8. A painting method comprising the step of immersing an object to be painted in an electrodeposition paint bath consisting of the electrodeposition paint composition described in claim 6, and performing electrodeposition painting.

9. The coating method according to claim 8, further comprising the step of heating and curing the coating film obtained in the electrodeposition coating step at a temperature of 140°C or lower.

10. The coating method according to claim 8, further comprising the step of heating and curing the coating film obtained in the electrodeposition coating step at a temperature of 120°C or lower.

11. A method for manufacturing a painted article, comprising the step of forming a coating film by the coating method described in claim 8.

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