UV crosslinking and heat curing combined electrodeposition solution

Abstract

The present invention aims to solve the problems of the prior art and provide an electrodeposited solution that can be electrodeposited onto a conductive substrate and form an electrodeposited coating with an excellent balance of corrosion resistance (weather resistance, solvent resistance, chemical resistance), high adhesion, and high hardness, as well as a conductive substrate with an electrodeposited coating using the said electrodeposited solution, and a method for forming an electrodeposited coating. [Means for solving the problem] An electrodeposition solution for UV crosslinking and heat curing that contains a specific cationic (meth)acrylic resin (A), a specific crosslinking agent (B), and a specific solvent (D), and an electrodeposition solution for UV crosslinking and heat curing that further contains a specific polymerization initiator (C).

Description

[Technical Field]

[0001] This invention relates to an electrodeposition solution that uses a combination of ultraviolet crosslinking and heat curing for electrodeposition coating of conductive substrates. [Background technology]

[0002] When excellent adhesion to structures is required, anionic electrodeposition is often used for anodizing, while cationic electrodeposition is commonly used for automobiles and other applications. However, as the shapes of objects to be coated become more complex, it is becoming increasingly difficult to form a uniform coating with sufficient coverage even on the walls of narrow recesses. In particular, conductive objects coated by 3D printers often have complex shapes and narrow recesses, so there is a growing demand for the development of electrodeposition coatings that offer significantly improved coverage and uniform curing film formation. Compositions for anionic electrodeposition coatings containing a specific water-soluble or water-dispersible vinyl copolymer, an amino resin, and an alkoxyamine, which have excellent coating stability, gloss stability, appearance, and weather resistance, have been investigated (Patent Document 1). Resin compositions for negative cationic electrodeposition photoresists for electrodeposition coatings containing a specific water-soluble or water-dispersible vinyl copolymer, a copolymerizable vinyl monomer having a specific amino group, a copolymerizable vinyl monomer other than those mentioned above, a polyfunctional acrylate having three or more vinyl groups in one molecule, a polyfunctional thiol, and a photopolymerization initiator, which have excellent coating stability and sensitivity, have also been investigated (Patent Document 2). However, a satisfactory product has yet to be obtained. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2006-111687 [Patent Document 2] Japanese Patent Publication No. 2016-126174 [Overview of the project] [Problems that the invention aims to solve]

[0004] The present invention aims to solve the problems of the prior art described above and to provide an electrodeposited solution that combines ultraviolet crosslinking and heat curing, which can be electrodeposited onto a conductive substrate and form an electrodeposited coating with an excellent balance of corrosion resistance (weather resistance, solvent resistance, chemical resistance), high adhesion, and high hardness; a conductive substrate with an electrodeposited coating using the same electrodeposited solution; and a method for forming an electrodeposited coating. [Means for solving the problem]

[0005] As a result of diligent research, the inventors have discovered that an ultraviolet crosslinking and heat-curing combined electrodeposition solution containing a specific cationic (meth)acrylic resin (A), a specific crosslinking agent (B), and a specific solvent (D), and an ultraviolet crosslinking and heat-curing combined electrodeposition solution further containing a specific polymerization initiator (C), can overcome the above-mentioned problems, leading to the present invention. Furthermore, the present invention is characterized by the following points. [1] A cationic electrodeposition solution applied to a conductive substrate, which is then heated and baked using ultraviolet irradiation and heating at a temperature of 170°C or higher and 200°C or lower, wherein The UV crosslinking and heat curing combined electrodeposition solution contains (meth)acrylic resin (A), a crosslinking agent (B), and a solvent (D). (Meth)acrylic resin (A) has a glass transition temperature of -15 to 5°C, contains hydroxyl groups, tertiary amino groups, and quaternary ammonium bases, and is water-soluble or water-dispersible. The quaternary ammonium base is a neutralized base consisting of a tertiary amino group and a neutralizing agent (E). The alkali value of (meth)acrylic resin (A) before neutralization is 10-40 mgKOH / g. The concentration of the tertiary amino group in (meth)acrylic resin (A) is 0.05 to 0.3 mmol / g. The concentration of the quaternary ammonium base in the (meth)acrylic resin (A) is 0.1 to 0.4 mmol / g. The crosslinking agent (B) contains at least an ultraviolet crosslinking agent (B1) and / or a thermal crosslinking agent (B2), UV crosslinking agent (B1) is a monomer having five or more (meth)acryloyl groups in one molecule. The thermal crosslinking agent (B2) is a compound that thermally crosslinks with the (meth)acrylic resin (A). Solvent (D) is an aqueous solvent containing an aqueous organic solvent and water. The content of (meth)acrylic resin (A) is 50-75% by mass of the total of (meth)acrylic resin (A) and crosslinking agent (B). The crosslinking agent (B) content is 15 to 35% by mass of the total. A combined UV crosslinking and heat curing type electrodeposition solution. [2] The UV crosslinking and heat curing combined electrodeposition solution further contains a polymerization initiator (C), The polymerization initiator (C) contains an ultraviolet polymerization initiator (C1) and / or a thermal polymerization initiator (C2), The content of polymerization initiator (C) is 1 to 7% by mass relative to the total. The UV crosslinking and heat curing combined electrodeposition solution described in [1] above. [3] A cationic electrodeposition solution applied to a conductive substrate, which is then heated and baked using ultraviolet irradiation and heating at a temperature of 110°C or higher and 200°C or lower, The UV crosslinking and heat curing combined electrodeposition solution contains (meth)acrylic resin (A), a crosslinking agent (B), a polymerization initiator (C), and a solvent (D). (Meth)acrylic resin (A) has a glass transition temperature of -10 to 15°C, contains hydroxyl groups, tertiary amino groups, and quaternary ammonium bases, and is water-soluble or water-dispersible. The quaternary ammonium base is a neutralized base consisting of a tertiary amino group and a neutralizing agent (E). The alkali value of (meth)acrylic resin (A) before neutralization is 15-40 mgKOH / g. The concentration of the tertiary amino group in (meth)acrylic resin (A) is 0.1 to 0.4 mmol / g. The concentration of the quaternary ammonium base in the (meth)acrylic resin (A) is 0.2 to 0.55 mmol / g. The crosslinking agent (B) contains at least an ultraviolet crosslinking agent (B1). The ultraviolet crosslinking agent (B1) is a monomer having five or more (meth)acryloyl groups in one molecule. The polymerization initiator (C) contains at least an ultraviolet polymerization initiator (C1). The solvent (D) is an aqueous solvent containing an aqueous organic solvent and water. The content of the (meth)acrylic resin (A) is 35 to 70% by mass in the total of the (meth)acrylic resin (A) and the crosslinking agent (B) contained in the ultraviolet crosslinking and heat baking type electrodeposition liquid. The content of the ultraviolet crosslinking agent (B1) is 20 to 60% by mass in the total. The content of the ultraviolet polymerization initiator (C1) is 1 to 7% by mass based on the total. An ultraviolet crosslinking and heat baking type electrodeposition liquid. [4] An ultraviolet crosslinking and heat baking type electrodeposition liquid which is cationically electrodeposited on a conductive object to be coated and is irradiated with ultraviolet rays and heat baked at a temperature of 70°C or higher and 200°C or lower. The ultraviolet crosslinking and heat baking type electrodeposition liquid contains a (meth)acrylic resin (A), a crosslinking agent (B), a polymerization initiator (C), and a solvent (D). The (meth)acrylic resin (A) has a glass transition temperature of 0 to 12°C, has a hydroxyl group, a tertiary amino group, and a quaternary ammonium base, and is water-soluble or water-dispersible. [[ID=二十二]]The quaternary ammonium base is a neutralized base composed of a tertiary amino group and a neutralizing agent (E). The alkali value of the (meth)acrylic resin (A) before neutralization is 15 to 40 mgKOH / g. The concentration of the tertiary amino group possessed by the (meth)acrylic resin (A) is 0.1 to 0.35 mmol / g. The concentration of the quaternary ammonium base possessed by the (meth)acrylic resin (A) is 0.2 to 0.45 mmol / g. The crosslinking agent (B) contains at least an ultraviolet crosslinking agent (B1). The ultraviolet crosslinking agent (B1) is a monomer having five or more (meth)acryloyl groups in one molecule. The polymerization initiator (C) contains at least an ultraviolet polymerization initiator (C1). The solvent (D) is an aqueous solvent containing an aqueous organic solvent and water. The content of the (meth)acrylic resin (A) is 40 to 50% by mass in the total of the (meth)acrylic resin (A) and the crosslinking agent (B). The content of the ultraviolet crosslinking agent (B1) is 40 to 50% by mass in the total. The content of the ultraviolet polymerization initiator (C1) is 1 to 7% by mass with respect to the total. Ultraviolet crosslinking and heat baking combined type electrodeposition liquid. [5] A conductive coated object with a baked electrodeposition coating film, produced using the ultraviolet crosslinking and heat baking combined type electrodeposition liquid according to any one of [1] to [4] above. [6] A method for forming a baked electrodeposition coating film, which forms a baked electrodeposition coating film on the surface of a conductive coated object by cationic electrodeposition coating using the ultraviolet crosslinking and heat baking combined type electrodeposition liquid according to any one of [1] to [4] above. The forming method includes the following steps (1) to (6) in this order, and includes the following steps (6), (7), and (8) in the order of (6), (7), (8) or (6), (8), (7). (1) A degreasing step for the surface of the conductive coated object. (2) A water washing step for the surface of the conductive coated object. (3) An immersion step of the conductive coated object into the ultraviolet crosslinking and heat baking combined type electrodeposition liquid. (4) A bubble removing step from the surface of the conductive coated object . (5) An electrodeposition coating film forming step on the surface of the conductive coated object. (6) A water washing and draining step for the electrodeposition coating film. (7) An ultraviolet irradiation step for the electrodeposition coating film. (8) A heat baking step for the electrodeposition coating film. Here, Step (3) includes a step of immersing the conductive coated object into the ultraviolet crosslinking and heat baking combined type electrodeposition liquid in a state where the surface is wetted with water. Step (4) includes a step of stirring the ultraviolet crosslinking and heat baking combined type electrodeposition liquid and moving the conductive coated object up and down. Step (5) includes the step of applying the UV crosslinking and heat baking combined electrodeposition solution while the stirring of the conductive object to be coated is stopped and the vertical movement of the conductive object is stopped. A method for forming a baked electrodeposition coating. [Effects of the Invention]

[0006] According to the present invention, an ultraviolet crosslinking and heat-baking combined electrodeposition solution can be electrodeposited onto a conductive substrate to form an electrodeposited coating film with an excellent balance of corrosion resistance (weather resistance, solvent resistance, chemical resistance), high adhesion, and high hardness. The present invention also provides a conductive substrate with an electrodeposited coating film using the ultraviolet crosslinking and heat-baking combined electrodeposition solution, and a method for forming an electrodeposited coating film. The UV crosslinking and heat curing combined electrodeposition solution of the present invention can form a coating film with good solvent resistance and adhesion to the surface of a conductive substrate at low cost, even if the conductive substrate has a complex shape, such as a structure formed by a 3D printer. Furthermore, by using heat curing in combination, a sufficiently cured coating film can be obtained even in intricate areas and deep parts of the coating film where UV light is difficult to irradiate sufficiently. [Modes for carrying out the invention]

[0007] The present invention will be described in more detail. <Electrodeposition solution using UV crosslinking and heat curing> The ultraviolet crosslinking and heat curing combined electrodeposition solution of the present invention contains a specific (meth)acrylic resin (A), a specific crosslinking agent (B), and a specific solvent (D), and may further contain a specific polymerization initiator (C).

[0008] The (meth)acrylic resin (A) preferably has a hydroxyl group, a tertiary amino group, and a quaternary ammonium base, and is preferably water-soluble or water-dispersible. The glass transition temperature (Tg) of the (meth)acrylic resin (A) is preferably -15 to 15°C, and more preferably -11 to 12°C.

[0009] Furthermore, it is preferable that the quaternary ammonium base is a neutralized base consisting of a tertiary amino group and a neutralizing agent (E). The alkali value of the (meth)acrylic resin (A) before neutralization is preferably 10 to 40 mg KOH / g, and more preferably 15 to 40 mg KOH / g. The concentration of tertiary amino groups in the (meth)acrylic resin (A) is preferably 0.05 to 0.4 mmol / g, and more preferably 0.1 to 0.3 mmol / g. The concentration of quaternary ammonium base in the (meth)acrylic resin (A) is preferably 0.1 to 0.55 mmol / g, and more preferably 0.15 to 0.45 mmol / g.

[0010] The crosslinking agent (B) preferably contains at least an ultraviolet crosslinking agent (B1) and / or a thermal crosslinking agent (B2), wherein the ultraviolet crosslinking agent (B1) is preferably a monomer having five or more (meth)acryloyl groups in one molecule, and the thermal crosslinking agent (B2) is preferably a compound that thermally crosslinks with the (meth)acrylic resin (A).

[0011] The polymerization initiator (C) preferably contains an ultraviolet polymerization initiator (C1) and / or a thermal polymerization initiator (C2).

[0012] The solvent (D) is preferably an aqueous solvent containing an aqueous organic solvent and water.

[0013] In the UV crosslinking and heat curing combined electrodeposition solution of the present invention, the total content of (meth)acrylic resin (A) and crosslinking agent (B) is preferably 5 to 20% by mass. Within this range, good handling properties and electrodeposition coating efficiency can be easily obtained. The content of (meth)acrylic resin (A) contained in the ultraviolet crosslinking and heat curing combined electrodeposition solution of the present invention is preferably 35 to 75% by mass, and more preferably 38 to 72% by mass, in the total of (meth)acrylic resin (A) and crosslinking agent (B). Furthermore, the content of the crosslinking agent (B) is preferably 15 to 60% by mass, and more preferably 25 to 59% by mass, in the total of the (meth)acrylic resin (A) and the crosslinking agent (B).

[0014] If the crosslinking agent (B) contains an ultraviolet crosslinking agent (B1), the content of the ultraviolet crosslinking agent (B1) is preferably 14 to 60% by mass, and more preferably 14 to 59% by mass, in the total of the (meth)acrylic resin (A) and the crosslinking agent (B). If the crosslinking agent (B) contains a thermal crosslinking agent (B2), the content of the thermal crosslinking agent (B2) is preferably 14 to 35% by mass, and more preferably 14 to 30% by mass, in the total of the (meth)acrylic resin (A) and the crosslinking agent (B).

[0015] When the ultraviolet crosslinking and heat curing combined electrodeposition solution of the present invention contains a polymerization initiator (C), the content of the polymerization initiator (C) is preferably 1 to 7% by mass, and more preferably 1 to 6% by mass, relative to the total of the (meth)acrylic resin (A) and the crosslinking agent (B).

[0016] When the polymerization initiator (C) contains an ultraviolet polymerization initiator (C1), the content of the ultraviolet polymerization initiator (C1) is preferably 1 to 7% by mass, and more preferably 2 to 6% by mass, relative to the total of the (meth)acrylic resin (A) and the crosslinking agent (B). When the polymerization initiator (C) contains a thermal polymerization initiator (C2), the content of the thermal polymerization initiator (C2) is preferably 0.5 to 7% by mass, and more preferably 1 to 2% by mass, relative to the total of the (meth)acrylic resin (A) and the crosslinking agent (B).

[0017] In the ultraviolet crosslinking and heat curing combined electrodeposition solution of the present invention, the mass ratio of (meth)acrylic resin (A) to crosslinking agent (B) is preferably 30 / 70 or more and 80 / 20 or less, and more preferably 40 / 60 or more and 75 / 25 or less. If the mass ratio of (meth)acrylic resin (A) / crosslinking agent (B) is smaller than the above range, the water dispersibility (water solubility or emulsification) of (meth)acrylic resin (A) and crosslinking agent (B) in the UV crosslinking and heat curing combined electrodeposition solution will decrease, making liquid separation and sedimentation more likely, and significantly increasing manufacturing costs. Also, if the mass ratio of (meth)acrylic resin (A) / crosslinking agent (B) is larger than the above range, the corrosion resistance (weather resistance, solvent resistance, chemical resistance), adhesion, and hardness of the electrodeposited coating film tend to be insufficient.

[0018] Furthermore, the UV crosslinking and heat curing combined electrodeposition solution of the present invention can be further enriched with various curing accelerators, water-dispersible pigments, dyes, fillers, light stabilizers, antioxidants, wetting agents, leveling agents, defoamers, surfactants, etc., to provide necessary coloring, improve workability during film formation, and impart various functions and design properties to the film.

[0019] The UV crosslinking and heat curing combined electrodeposition solution of the present invention may be a homogeneous solution or an emulsion, has excellent adhesion properties, and can uniformly electrodeposit coatings conductive substrates.

[0020] (Viscosity of electrodeposition solution used with UV crosslinking and heat curing) The viscosity of the UV crosslinking and heat-curing combined electrodeposition solution of the present invention, when measured at a rotation speed of 100 rpm using a B-type viscometer equipped with an L-type rotor and a low-viscosity adapter, is preferably between 1.50 mPa·s and 2.70 mPa·s. Within this range, good handling properties and electrodeposition coating efficiency can be easily obtained.

[0021] [Stability of electrodeposition solutions using UV crosslinking and heat curing] The ultraviolet crosslinking and heat curing combined electrodeposition solution of the present invention preferably does not undergo sedimentation separation during static storage. For example, it is preferable that when an electrodeposition solution using a combination of UV crosslinking and heat curing is placed in a transparent glass container and left to stand for 48 hours, no sedimentation separation is detected visually.

[0022] [Heat curing temperature for electrodeposition solutions using UV crosslinking and heat curing] The UV crosslinking and heat-curing combined electrodeposition solution of the present invention, by containing the above-mentioned specific components, can achieve corrosion resistance (weather resistance, solvent resistance, chemical resistance), high adhesion, and high hardness by crosslinking after electrodeposition coating by UV irradiation, and further by heat-curing at a temperature of 70 to 200°C for 8 minutes or more and 20 minutes or less.

[0023] Furthermore, the heating and baking temperature can be adjusted to 170-200°C, 110-200°C, or 70-200°C depending on the combination of the type and content of the (meth)acrylic resin (A), crosslinking agent (B), and polymerization initiator (C). Specifically, by limiting the glass transition temperature and alkali value of the (meth)acrylic resin (A) to a narrower range, heating and baking at lower temperatures becomes possible. Furthermore, by limiting the content of the crosslinking agent (B), particularly the UV crosslinking agent (B1), to a high range, it becomes possible to heat-bake at lower temperatures.

[0024] The UV crosslinking and heat-curing combined electrodeposition solution of the present invention contains the above-mentioned (meth)acrylic resin (A), crosslinking agent (B), and solvent (D), or the above-mentioned (meth)acrylic resin (A), crosslinking agent (B), polymerization initiator (C), and solvent (D) in the above-mentioned proportions, thereby making liquid separation and sedimentation less likely to occur, making it easier to suppress manufacturing costs, making cationic electrodeposition easier, and after UV irradiation crosslinking, by heating and curing at a temperature of 70 to 200°C for 8 minutes or more and 20 minutes or less, it becomes easier to obtain an electrodeposited coating film with a good balance of corrosion resistance (weather resistance, solvent resistance, chemical resistance), high adhesion, and high hardness.

[0025] [Electrodeposition solution for use with UV crosslinking and heat curing, suitable for curing at 170-200°C] In one aspect of the present invention, an ultraviolet crosslinking and heat-curing combined electrodeposition solution contains a specific (meth)acrylic resin (A), a specific crosslinking agent (B), and a specific solvent (D), and by heating and curing at 170-200°C for 8 minutes to 20 minutes after ultraviolet irradiation, it can have corrosion resistance (weather resistance, solvent resistance, chemical resistance), high adhesion, and high hardness.

[0026] The glass transition temperature of the (meth)acrylic resin (A) is preferably -15 to 5°C, and more preferably -11 to 5°C. Furthermore, the (meth)acrylic resin (A) preferably has a hydroxyl group, a tertiary amino group, and a quaternary ammonium base, and is preferably water-soluble or water-dispersible. The quaternary ammonium base is preferably a neutralized base consisting of a tertiary amino group and a neutralizing agent (E). The alkali value of the (meth)acrylic resin (A) before neutralization is preferably 10 to 40 mg KOH / g, and more preferably 15 to 30 mg KOH / g. The concentration of tertiary amino groups in the (meth)acrylic resin (A) is preferably 0.05 to 0.4 mmol / g, and more preferably 0.1 to 0.3 mmol / g. The concentration of quaternary ammonium base in the (meth)acrylic resin (A) is preferably 0.1 to 0.55 mmol / g, and more preferably 0.15 to 0.45 mmol / g.

[0027] The crosslinking agent (B) preferably contains at least an ultraviolet crosslinking agent (B1) and / or a thermal crosslinking agent (B2). The ultraviolet crosslinking agent (B1) is preferably a monomer having five or more (meth)acryloyl groups in one molecule, and the thermal crosslinking agent (B2) is preferably a compound that thermally crosslinks with the (meth)acrylic resin (A).

[0028] The polymerization initiator (C) preferably contains an ultraviolet polymerization initiator (C1) and / or a thermal polymerization initiator (C2). The solvent (D) is preferably an aqueous solvent containing an aqueous organic solvent and water.

[0029] The content of (meth)acrylic resin (A) contained in the UV crosslinking and heat curing combined electrodeposition solution of the present invention is preferably 50 to 75% by mass, and more preferably 65 to 72% by mass, in the total of (meth)acrylic resin (A) and crosslinking agent (B). The crosslinking agent (B) contained in the UV crosslinking and heat curing combined electrodeposition solution of the present invention is preferably 15 to 35% by mass, and more preferably 25 to 30% by mass, in the total of the (meth)acrylic resin (A) and the crosslinking agent (B). If the crosslinking agent (B) contains an ultraviolet crosslinking agent (B1), the content of the ultraviolet crosslinking agent (B1) is preferably 14 to 35% by mass, and more preferably 14 to 30% by mass, in the total of the (meth)acrylic resin (A) and the crosslinking agent (B). If the crosslinking agent (B) contains a thermal crosslinking agent (B2), the content of the thermal crosslinking agent (B2) is preferably 14 to 35% by mass, and more preferably 15 to 30% by mass, in the total of the (meth)acrylic resin (A) and the crosslinking agent (B). Furthermore, if the crosslinking agent (B) contains ultraviolet crosslinking agent (B1) and crosslinking agent (B2), the mass ratio of ultraviolet crosslinking agent (B1) to crosslinking agent (B2) is preferably 33 / 67 to 67 / 33, and more preferably 45 / 55 to 55 / 45. When the UV crosslinking and heat curing combined electrodeposition solution of the present invention contains a polymerization initiator (C), the content of the polymerization initiator (C) is preferably 1 to 7% by mass, and more preferably 2 to 6% by mass, relative to the total of the (meth)acrylic resin (A) and the crosslinking agent (B). Furthermore, if the polymerization initiator (C) contains an ultraviolet polymerization initiator (C1), the content of the ultraviolet polymerization initiator (C1) is preferably 1 to 7% by mass, and more preferably 2 to 5% by mass, relative to the total. If the polymerization initiator (C) contains a thermal polymerization initiator (C2), the content of the thermal polymerization initiator (C2) is preferably 1 to 7% by mass, and more preferably 0.5 to 2% by mass, relative to the total of the (meth)acrylic resin (A) and the crosslinking agent (B).

[0030] The UV crosslinking and heat-curing combined electrodeposition solution of the present invention contains the above-mentioned (meth)acrylic resin (A), crosslinking agent (B), and solvent (D), or the above-mentioned (meth)acrylic resin (A), crosslinking agent (B), polymerization initiator (C), and solvent (D) in the above-mentioned proportions, thereby making liquid separation and sedimentation less likely to occur, making it easier to suppress manufacturing costs, making cationic electrodeposition easier, and by heating and curing at 170-200°C for 8 minutes to 20 minutes after UV irradiation crosslinking, it becomes easier to obtain an electrodeposited coating film with a good balance of corrosion resistance (weather resistance, solvent resistance, chemical resistance), high adhesion, and high hardness.

[0031] [Electrodeposition solution for use with UV crosslinking and heat curing, suitable for curing at 110-200°C] In a different aspect of the present invention, the UV crosslinking and heat-curing combined electrodeposition solution contains a specific (meth)acrylic resin (A), a specific crosslinking agent (B), a specific polymerization initiator (C), and a specific solvent (D), and by heating and curing at 110-200°C for 8 minutes to 20 minutes after UV irradiation, it can have corrosion resistance (weather resistance, solvent resistance, chemical resistance), high adhesion, and high hardness.

[0032] The glass transition temperature of the (meth)acrylic resin (A) is preferably -10 to 15°C, and more preferably -1 to 12°C. Furthermore, the (meth)acrylic resin (A) preferably has a hydroxyl group, a tertiary amino group, and a quaternary ammonium base, and is preferably water-soluble or water-dispersible. The quaternary ammonium base is preferably a neutralized base consisting of a tertiary amino group and a neutralizing agent (E). The alkali value of the (meth)acrylic resin (A) before neutralization is preferably 15-40 mgKOH / g, and more preferably 20-40 mgKOH / g. The concentration of tertiary amino groups in the (meth)acrylic resin (A) is preferably 0.1 to 0.4 mmol / g, and more preferably 0.15 to 0.3 mmol / g. The concentration of quaternary ammonium base in the (meth)acrylic resin (A) is preferably 0.2 to 0.55 mmol / g, and more preferably 0.25 to 0.45 mmol / g.

[0033] The crosslinking agent (B) preferably contains at least an ultraviolet crosslinking agent (B1), and the ultraviolet crosslinking agent (B1) is preferably a monomer having five or more (meth)acryloyl groups in one molecule.

[0034] The polymerization initiator (C) preferably contains at least an ultraviolet polymerization initiator (C1). The solvent (D) is preferably an aqueous solvent containing an aqueous organic solvent and water.

[0035] The content of (meth)acrylic resin (A) contained in the ultraviolet crosslinking and heat curing combined electrodeposition solution of the present invention is preferably 35 to 70% by mass, and more preferably 38 to 69% by mass, in the total of (meth)acrylic resin (A) and crosslinking agent (B). The UV crosslinking agent (B1) contained in the UV crosslinking and heat curing combined electrodeposition solution of the present invention is preferably 20 to 60% by mass, and more preferably 25 to 59% by mass, in the total of the (meth)acrylic resin (A) and the crosslinking agent (B). The UV polymerization initiator (C1) contained in the UV crosslinking and heat curing combined electrodeposition solution of the present invention is preferably 1 to 7% by mass, and more preferably 2 to 5% by mass, relative to the total amount of (meth)acrylic resin (A) and crosslinking agent (B).

[0036] The UV crosslinking and heat-curing combined electrodeposition solution of the present invention contains the above-mentioned (meth)acrylic resin (A), crosslinking agent (B), polymerization initiator (C), and solvent (D) in the above-mentioned proportions, making it less prone to liquid separation and sedimentation, thus reducing manufacturing costs, facilitating cationic electrodeposition, and making it easier to obtain an electrodeposited coating film with a good balance of corrosion resistance (weather resistance, solvent resistance, chemical resistance), high adhesion, and high hardness by heating and curing at 110-200°C for 8 to 20 minutes after UV irradiation crosslinking.

[0037] [Electrodeposition solution for curing at 70-200°C, combining UV crosslinking and heat curing] In a further different embodiment, the UV crosslinking and heat-curing combined electrodeposition solution contains a specific (meth)acrylic resin (A), a specific crosslinking agent (B), a specific polymerization initiator (C), and a specific solvent (D), and by heating and curing at 70-200°C for 8 minutes to 20 minutes after UV irradiation, it can achieve corrosion resistance (weather resistance, solvent resistance, chemical resistance), high adhesion, and high hardness.

[0038] The glass transition temperature of the (meth)acrylic resin (A) is preferably 0 to 12°C, and more preferably 3 to 9°C. Furthermore, the (meth)acrylic resin (A) preferably has a hydroxyl group, a tertiary amino group, and a quaternary ammonium base, and is preferably water-soluble or water-dispersible. The quaternary ammonium base is preferably a neutralized base consisting of a tertiary amino group and a neutralizing agent (E). The alkali value of the (meth)acrylic resin (A) before neutralization is preferably 15-40 mgKOH / g, and more preferably 20-35 mgKOH / g. The concentration of tertiary amino groups in the (meth)acrylic resin (A) is preferably 0.1 to 0.35 mmol / g, and more preferably 0.15 to 0.25 mmol / g. The concentration of quaternary ammonium base in the (meth)acrylic resin (A) is preferably 0.2 to 0.45 mmol / g, and more preferably 0.25 to 0.35 mmol / g.

[0039] The crosslinking agent (B) preferably contains at least an ultraviolet crosslinking agent (B1). The UV crosslinking agent (B1) is preferably a monomer having five or more (meth)acryloyl groups in one molecule.

[0040] The polymerization initiator (C) preferably contains at least an ultraviolet polymerization initiator (C1). The solvent (D) is preferably an aqueous solvent containing an aqueous organic solvent and water.

[0041] The content of (meth)acrylic resin (A) contained in the UV crosslinking and heat curing combined electrodeposition solution of the present invention is preferably 40 to 50% by mass, and more preferably 45 to 50% by mass, in the total of (meth)acrylic resin (A) and crosslinking agent (B). The UV crosslinking agent (B1) contained in the UV crosslinking and heat curing combined electrodeposition solution of the present invention is preferably 40 to 50% by mass, and more preferably 45 to 49% by mass, in the total of the (meth)acrylic resin (A) and the crosslinking agent (B). The UV polymerization initiator (C1) contained in the UV crosslinking and heat curing combined electrodeposition solution of the present invention is preferably 1 to 7% by mass, and more preferably 1.5 to 6% by mass, relative to the total amount of (meth)acrylic resin (A) and crosslinking agent (B).

[0042] The UV crosslinking and heat-curing combined electrodeposition solution of the present invention contains the above-mentioned (meth)acrylic resin (A), crosslinking agent (B), polymerization initiator (C), and solvent (D) in the above-mentioned proportions, making it less prone to liquid separation and sedimentation, thus reducing manufacturing costs, facilitating cationic electrodeposition, and making it easier to obtain an electrodeposited coating film with a good balance of corrosion resistance (weather resistance, solvent resistance, chemical resistance), high adhesion, and high hardness by heating and curing at 70-200°C for 8 to 20 minutes after UV irradiation crosslinking.

[0043] <About each ingredient> [(Meth)acrylic resin (A)] The (meth)acrylic resin (A) in the present invention has a hydroxyl group and an electrodeposition functional group. Furthermore, the (meth)acrylic resin (A) has a structural portion derived from a (meth)acrylic monomer, a structural portion derived from a (meth)acrylic monomer having a hydroxyl group, and a structural portion derived from a (meth)acrylic monomer having an electrodeposition functional group, and may further have a structural portion derived from a polymerizable monomer having copolymerizable carbon-carbon unsaturated bond groups other than (meth)acrylic groups.

[0044] The mass fraction of the structural components derived from hydroxyl group-containing (meth)acrylic monomers in the (meth)acrylic resin (A) is preferably 2 to 25% by mass, and more preferably 5 to 15% by mass. If it is lower than the above range, the crosslinking reaction between the (meth)acrylic resin (A) and the crosslinking agent (B) tends to be difficult to carry out during the baking curing process of the electrodeposited coating film. If it is higher than the above range, the hydrophilicity tends to become too high, making the UV crosslinking and heat curing combined type electrodeposition solution prone to sedimentation separation.

[0045] Furthermore, the hydroxyl groups of the (meth)acrylic resin (A) can undergo a thermal crosslinking reaction with the functional groups of the thermal crosslinking agent (B2), thereby improving the corrosion resistance (weather resistance, solvent resistance, chemical resistance), adhesion, and hardness of the coating film made from an ultraviolet crosslinking and heat-curing electrodeposition solution.

[0046] The main skeleton of (meth)acrylic resin (A) is mainly formed by the copolymerization of (meth)acrylic groups of (meth)acrylic monomers, or by the copolymerization of (meth)acrylic groups of (meth)acrylic monomers with carbon-carbon unsaturated bond groups of other polymerizable monomers. Specific examples of carbon-carbon unsaturated bond groups other than (meth)acrylic groups include vinyl groups, allyl groups, αβ-unsaturated carbonyl groups, and one or more of these may copolymerize with (meth)acrylic groups.

[0047] Preferably, at least a portion of the functional groups of the (meth)acrylic resin (A) are neutralized by the neutralizing agent (E) to ionize and become bases, thereby improving water solubility or water dispersibility.

[0048] (Cationic electrodeposition (meth)acrylic resin (A)) The (meth)acrylic resin (A) for cationic electrodeposition preferably has a hydroxyl group, a tertiary amino group, and a quaternary ammonium base. The (meth)acrylic resin (A), having a tertiary amino group and a quaternary ammonium base, exhibits good water solubility or water dispersibility in solvent (D), which is an aqueous solvent, and can be used for cationic electrodeposition. Furthermore, the tertiary amino group or quaternary ammonium base of the (meth)acrylic resin (A) is preferably one having two alkyl groups with 1 to 4 carbon atoms.

[0049] The above-mentioned quaternary ammonium base is preferably a base formed by neutralizing at least a portion of the tertiary amino groups originally present in the (meth)acrylic resin (A) with a neutralizing agent (E), that is, a base consisting of the tertiary amino groups originally present in the (meth)acrylic resin (A) and the neutralizing agent (E). In the neutralized (meth)acrylic resin (A), the molar ratio of lactic acid to tertiary amino group is preferably 0.5 to 1.0, and more preferably 0.6 to 0.8. If the above molar ratio is smaller than the above range, the resin components of the water-soluble or water-dispersed electrodeposition solution are more likely to settle and separate. If the above molar ratio is larger than the above range, the resin components deposited by electrodeposition are more likely to redissolve, and dissolution is more likely to occur in the water washing process after electrodeposition.

[0050] To obtain the (meth)acrylic resin (A) having a hydroxyl group, a tertiary amino group, and a quaternary ammonium base as described above, it is preferable to synthesize a (meth)acrylic resin having a hydroxyl group and a tertiary amino group using, for example, a (meth)acrylic monomer, a (meth)acrylic monomer having a hydroxyl group, and a (meth)acrylic monomer having a tertiary amino group, and then neutralize a portion of the tertiary amino group using a neutralizing agent (E) to convert it into a quaternary ammonium base to obtain the (meth)acrylic resin (A).

[0051] The mass fraction of the structural components derived from the (meth)acrylic monomer having a tertiary amino group in the (meth)acrylic resin before neutralization is preferably 2 to 15% by mass, and more preferably 4 to 12% by mass. If it is lower than the above range, the water solubility of the (meth)acrylic resin (A) decreases, the particle size of the emulsion in the UV crosslinking / heat curing combined electrodeposition solution becomes too large, and sedimentation separation is likely to occur. If it is higher than the above range, adhesion tends to decrease.

[0052] The alkali value of the cation-electrodeposition (meth)acrylic resin (A) before neutralization is preferably 10 to 40 mg KOH / g, and more preferably 15 to 40 mg KOH / g. If the alkali value of the (meth)acrylic resin (A) before neutralization is within this range, a good UV crosslinking and heat curing combined electrodeposition solution can be produced. However, if it is below the above range, it becomes difficult to obtain sufficient water dispersibility, and if it is above the above range, water resistance tends to decrease, making it difficult to obtain sufficient coating performance.

[0053] Furthermore, it is preferable that the quaternary ammonium base is a neutralized base consisting of a tertiary amino group and a neutralizing agent (E). The alkali value of the (meth)acrylic resin (A) before neutralization is preferably 10 to 40 mg KOH / g, and more preferably 15 to 40 mg KOH / g. The concentration of tertiary amino groups in the (meth)acrylic resin (A) is preferably 0.05 to 0.4 mmol / g, and more preferably 0.1 to 0.3 mmol / g. The concentration of quaternary ammonium base in the (meth)acrylic resin (A) is preferably 0.1 to 0.55 mmol / g, and more preferably 0.15 to 0.45 mmol / g. By ensuring that the alkali value of the (meth)acrylic resin (A) before neutralization, and the concentrations of the tertiary amino groups and quaternary ammonium bases present in the (meth)acrylic resin (A) are within the above range, the UV crosslinking and heat curing combined electrodeposition solution of the present invention can exhibit excellent water solubility or water dispersibility, and electrodeposition properties.

[0054] (Alkali value) The alkali value is a value that indicates how many milligrams of KOH (potassium hydroxide) equivalent amino groups are present in (meth)acrylic resin (A) (the residue after heating of the (meth)acrylic resin (A) reaction solution). The alkalinity can be calculated using the following measurement method. 1 g of (meth)acrylic resin (A) before neutralization is accurately weighed, and 80 ml of butyl cellosolve is added to dissolve it and obtain a homogeneous solution. While stirring this homogeneous solution with a magnetic stirrer, 0.05 ml of 0.1 N hydrochloric acid with a known factor is added dropwise using a burette, and the amount added and the pH are recorded each time. Create a graph of the drip rate curve, with the drip rate on the horizontal axis and the pH value on the vertical axis. Then, the volume [mL] of 0.1N hydrochloric acid added at the neutralization point is read from the dropping curve. The neutralization point can be determined, for example, as the midpoint between the point in the obtained dropping curve where the change in pH value begins to increase sharply and the point where the change in pH value begins to decrease sharply. The alkali value is then calculated using the following formula. It is preferable to perform the measurement operation two or more times to obtain the average value of the alkali value. Alkali value [mgKOH / g] = (Volume of 0.1N hydrochloric acid added at the neutralization point [mL] × Hydrochloric acid factor [-] × 0.1 [mol / L] × 56.1 [gKOH / mol] × 100) / (Weight of (meth)acrylic resin (A) before neutralization [g])

[0055] The glass transition temperature (Tg) of the (meth)acrylic resin (A) is preferably -15 to 15°C, and more preferably -11 to 12°C. If it is lower than the above range, the electrodeposited coating film tends to flow more easily during the baking and curing process, resulting in a thinner and more uneven coating. If it is higher than the above range, the fluidity of the electrodeposited coating film is too low, which tends to result in poor surface smoothness of the electrodeposited coating film.

[0056] (Method for calculating Tg value) In the present invention, the Tg value of the (meth)acrylic resin (A) can be calculated using the following formula, with respect to the Tg values ​​of the homopolymer composed of each monomer used as a (co)polymerization raw material. 1 / Tg A =1 / Tg1×Wt1+1 / Tg2×Wt2+···+1 / Tg n ×Wt n Tg A Tg [absolute temperature (K)] of (meth)acrylic resin (A) Tg1, Tg2, ...Tg n :Tg [absolute temperature (K)] of homopolymers composed of each monomer. Wt1, Wt2, ...Wt n : Mass fraction of each monomer relative to the total amount The Tg of homopolymers composed of each monomer can be the values ​​listed in textbooks such as "Introduction to Synthetic Resins for Paints" (Polymers Publication Association, authored by Kyozo Kitaoka, Shin Polymer Library 7). When using two or more types of (meth)acrylic resins (A), the Tg and mass fraction of each (meth)acrylic resin (A) can be used to calculate the Tg.

[0057] The solubility parameter (SP) value of (meth)acrylic resin (A) is 10.5~11.5 (cal / cm³). 3 ) 0.5 This is preferable. If the solubility parameter value is within the above range, the (meth)acrylic resin (A) will have appropriate hydrophilicity and will easily exhibit excellent water solubility or water dispersibility, and the UV crosslinking and heat curing combined electrodeposition solution will be less prone to sedimentation separation. If the SP value is lower than the above range, the hydrophobicity tends to become too high, and if it is higher than the above range, the hydrophilicity tends to become too high. Therefore, electrodeposition solutions using UV crosslinking and heat curing are prone to sedimentation separation.

[0058] [(meth)acrylic monomers containing hydroxyl groups] Specific examples of (meth)acrylic monomers having a hydroxyl group include 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl acrylate, 3-hydroxypropyl methacrylate, 4-hydroxybutyl acrylate, 4-hydroxybutyl methacrylate, diethylene glycol monoacrylate, cyclohexanedimethanol monoacrylate, and cyclohexanedimethanol monomethacrylate. One or more monomers selected from this group can be used in combination.

[0059] Among the above, it is preferable to use one or more selected from the group consisting of 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl acrylate, 3-hydroxypropyl methacrylate, 4-hydroxybutyl acrylate, and 4-hydroxybutyl methacrylate, in that they have high reactivity with the thermal crosslinking agent (B2).

[0060] [(meth)acrylic monomers having a tertiary amino group] The tertiary amino group in the (meth)acrylic monomer having a tertiary amino group is preferably one having two alkyl groups with 1 to 4 carbon atoms. Specific examples of (meth)acrylic monomers having a tertiary amino group include 2-(dimethylamino)ethyl acrylate, 2-(diethylamino)ethyl acrylate, 2-(dimethylamino)ethyl methacrylate, and 2-(diethylamino)ethyl methacrylate, which are compounds that facilitate the preparation of electrodeposition emulsions in order to increase the water solubility of the copolymer. One or more of these compounds can be selected from the group and used in combination.

[0061] [Other (meth)acrylic monomers] Other monomers that do not have carboxyl groups and tertiary amino groups can be used as copolymerizing raw materials for (meth)acrylic resin (A).

[0062] Other specific examples of (meth)acrylic monomers include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-propyl acrylate, n-propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, n-butyl acrylate, n-butyl methacrylate, n-hexyl acrylate, n-hexyl methacrylate, n-heptyl acrylate, n-heptyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, and n-lauryl acrylate. Examples include methacrylate, lauryl methacrylate, stearyl acrylate, stearyl methacrylate, acrylonitrile, acrylamide, N-methoxymethylacrylamide, N-ethoxymethylacrylamide, N-n-butoxymethylacrylamide, N-isobutoxymethylacrylamide, N-methoxymethylmethacrylamide, N-ethoxymethylmethacrylamide, N-n-butoxymethylmethacrylamide, N-isobutoxymethylmethacrylamide, etc., and one or more selected from this group can be used in combination.

[0063] Among the above, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, n-propyl acrylate, n-propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, n-butyl acrylate, n-butyl methacrylate, n-hexyl acrylate, n-hexyl methacrylate, n-heptyl acrylate, n-heptyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, acrylonitrile, and acrylamide are preferred in terms of the ease of obtaining raw materials.

[0064] [Other copolymerizable polymerizable monomers having carbon-carbon unsaturated bond groups] Other specific examples of polymerizable monomers having copolymerizable carbon-carbon unsaturated bond groups include styrene, α-methylstyrene, α-chlorostyrene, vinyltoluene, vinyl acetate, etc., and one or more selected from this group can be used in combination. Among the above, using styrene is preferable in terms of the ease of obtaining the raw materials.

[0065] (Meth) Acrylic resin (A) synthesis method (Meth)acrylic resin (A) is preferably synthesized by (co)polymerizing polymerizable carbon-carbon unsaturated groups in various aqueous solvents using raw material monomers such as monomers having polymerizable carbon-carbon unsaturated groups and tertiary amino groups, monomers having polymerizable carbon-carbon unsaturated groups and hydroxyl groups, and other monomers having polymerizable carbon-carbon unsaturated groups. Various polymerization initiators can be used as needed.

[0066] Specific examples of aqueous solvents include water, alcohols, ethylene glycol ethers, and propylene glycol ethers. One or more solvents selected from this group can be used in combination, but the solvent is not limited to these. Among the above, isopropanol, ethylene glycol mono-n-butyl ether, and propylene glycol monomethyl ether are preferred.

[0067] When synthesizing (meth)acrylic resin (A), it is preferable to use a radical initiator as the polymerization initiator. Specific examples of the radical initiators mentioned above include dihalogen compounds, azo compounds, organic peroxides, and redox initiators. One or more of these can be selected and used in combination, but are not limited to these. Among the above, azo compounds are preferably used, and among azo compounds, 2,2'-azobisisobutyronitrile, 2,2'-azobisiso(2-methylbutyronitrile), and 2,2'-azobis(2,4-dimethylvaleronitrile) are preferably used.

[0068] Furthermore, it is preferable to add a neutralizing agent (E) to the reaction solution containing the synthesized (meth)acrylic resin (A) to convert the functional groups of the (meth)acrylic resin (A) into salts and ionize them. Adding the neutralizing agent (E) to a reaction solution containing (meth)acrylic resin (A) allows for higher concentrations of (meth)acrylic resin (A) and neutralizing agent (E) than adding it to an electrodeposition solution that uses both UV crosslinking and heat curing, thus enabling more efficient neutralization of (meth)acrylic resin (A).

[0069] [Crosslinking agent (B)] The crosslinking agent (B) may include an ultraviolet crosslinking agent (B1) that crosslinks by ultraviolet irradiation, and may further include a thermal crosslinking agent (B2) that crosslinks by heating.

[0070] (UV crosslinking agent (B1)) UV crosslinking agent (B1) is a compound having polymerizable carbon-carbon unsaturated bonding groups, and can be used in combination with one or more compounds having polymerizable carbon-carbon unsaturated bonding groups, allowing for (co)polymerization by crosslinking the polymerizable carbon-carbon unsaturated bonding groups of UV crosslinking agent (B1).

[0071] Examples of UV crosslinking agents (B1) include polyfunctional (meth)acrylates and (meth)acrylate oligomers.

[0072] Polyfunctional (meth)acrylates are preferably monomers having five or more (meth)acryloyl groups in one molecule. Specific examples of polyfunctional (meth)acrylates include dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate, and ethoxylated dipentaerythritol polyacrylate, which may be used individually or in combination of two or more.

[0073] Furthermore, specific examples of (meth)acrylate oligomers include urethane acrylate and polyester acrylate.

[0074] (Thermal crosslinking agent (B2)) The thermal crosslinking agent (B2) is preferably a compound that can be thermally crosslinked with the (meth)acrylic resin (A) by heating. The thermal crosslinking agent (B2) may be a compound having a functional group that reacts with hydroxyl groups or tertiary amino groups of the (meth)acrylic resin (A).

[0075] Specific examples of functional groups possessed by the thermal crosslinking agent (B2) include isocyanate groups, blocked isocyanate groups, alkylated methylol groups, etc. The thermal crosslinking agent (B2) may be a compound having one or more functional groups selected from the group consisting of these. Alternatively, the thermal crosslinking agent (B2) may be a mixture of one or more compounds. The thermal crosslinking agent (B2) may be a monomer having the above-mentioned functional group, or it may be a resin. Specific examples of resins include isocyanate resins and amino resins, which may be used individually or in combination of two or more.

[0076] For thermal crosslinking (B2) that can be used for 120°C heating and baking, a suitable option is one in which dimethylpyrazole, which dissociates at 120°C, is used as the blocking agent for the blocked isocyanate group. For use with 180°C heating and baking, a suitable thermal crosslinking agent (B2) is one that uses a thermal crosslinking agent (B2) for 120°C heating and baking, and also uses caprotactam as a blocking agent.

[0077] (Isocyanate resin) Isocyanate resins are resins that have two or more isocyanate groups in a single molecule. Blocked isocyanate resins are also included in the category of isocyanate resins.

[0078] The isocyanate resin may be an aromatic isocyanate resin, an aliphatic isocyanate resin, an alicyclic isocyanate resin, or their biuret derivatives, their isocyanurate derivatives, or an adduct derivative obtained by the reaction of trimethylolpropane with the above-mentioned isocyanate compound. Specific examples of isocyanate resins include tolylene diisocyanate, xylylene diisocyanate, phenylene diisocyanate, diphenylmethane-2,4'-diisocyanate, diphenylmethane-4,4'-diisocyanate, bis(isocyanatomethyl)cyclohexane, tetramethylene diisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate. Among the above, tetramethylene diisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate are preferred.

[0079] Blocked isocyanate resins are isocyanate resins in which the isocyanate groups are blocked (sealed, protected) by various blocking agents. Blocked isocyanate resins can be regenerated by heating, which dissociates the blocking agent and allows the isocyanate groups to react.

[0080] Examples of the above-mentioned blocking agents include lactam compounds such as ε-caprolactam and γ-butyrolactam, oxime compounds such as methyl ethyl ketoxime and cyclohexanone oxime, phenolic compounds such as phenol, para-t-butylphenol and cresol, pyrazole compounds such as 3,5-dimethylpyrazole and 3,5-diisopropylpyrazole, active methylene compounds such as diethyl malonate, acetate acetate and acetylacetone, aliphatic alcohols such as n-butanol and 2-ethylhexanol, aromatic alkyl alcohols such as phenylcarbinol and methylphenylcarbinol, and ether alcohol compounds such as ethylene glycol monobutyl ether and diethylene glycol monoethyl ether.

[0081] Specific examples of blocked isocyanate resins include 3,5-dimethylpyrazole-blocked hexamethylene diisocyanate trimer.

[0082] (Amino resin) Amino resins are a general term for resins obtained by the condensation reaction of compounds containing amino or amide groups, such as urea and melamine, with aldehydes, and it is preferable that they have two or more alkylated methylol groups in one molecule. Examples of amino resins include melamine resin, guanamine resin, benzoguanamine resin, urea resin, thiourea resin, and aniline-formaldehyde resin. One or more types selected from this group can be used in combination.

[0083] As for aldehydes, formaldehyde is mainly used, and through the reaction of an amino group or amide group with formaldehyde, formaldehyde is added to the nitrogen atom to produce a methylol compound (hydroxymethyl compound).

[0084] For example, some or more of the -NH2 groups are methylated to form methylol groups such as -NH-CH2-OH or -N(CH2-OH)2, and some or more of the methylol groups are further alkylated to form -NH-CH2-OR, -N(CH2-OR)2, or -N(CH2-OH)(CH2-OR). Among amino resins, melamine resin is preferred in terms of its ease of reaction with (meth)acrylic resin (A), and melamine resin having alkylated methylol groups, in which at least a portion of the methylol groups are alkylated with a lower alcohol, is more preferred.

[0085] As the lower alcohols mentioned above, it is preferable to use one or more selected from the group consisting of methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, etc. In other words, the alkylated methylol group is preferably one or more selected from the group consisting of methylated methylol group, ethylated methylol group, n-propylated methylol group, isopropylated methylol group, n-butylated methylol group, isobutylated methylol group, etc.

[0086] Among the above, lactam compounds, oxime compounds, or pyrazole compounds are preferred, more preferably ε-caprolactam, γ-butyrolactam, methyl ethyl ketoxime, cyclohexanone oxime, and 3,5-dimethylpyrazole.

[0087] [Polymerization initiator (C)] The polymerization initiator (C) may include an ultraviolet polymerization initiator (C1) that initiates a crosslinking reaction of polymerizable carbon-carbon unsaturated bond groups by ultraviolet irradiation, and may further include a thermal polymerization initiator (C2) that initiates a crosslinking reaction between the (meth)acrylic resin (A) and the thermal crosslinking agent (B2) by heating.

[0088] (UV polymerization initiator (C1)) Thioxanthones, benzophenones, α-aminoketones, and α-acylphosphine oxides can be used as UV polymerization initiators (C1). Specific examples of thioxanthones include 2,4-diethylthioxanthone and 2-isopropylthioxanthone, and one or more selected from this group can be used. Specific examples of α-aminoacetoketones include 2-methyl-1[4-(methylthio)phenyl]-2-monofolinopropan-1-one and 2-benzyl-2-(dimethylamino)-4'-morpholinobtyrophenone, and one or more selected from this group can be used.

[0089] (Thermal polymerization initiator (C2)) Azobis compounds and peroxide compounds can be used as the thermal polymerization initiator (C2). Specific examples of azobis compounds include 2,2'-azobis(2-methylbutyronitrile) and 2,2'-azobisisobutyronitrile, and one or more compounds selected from this group can be used.

[0090] Suitable thermal polymerization initiators (C2) for use in 120°C heating and baking include 2,2'-azobis(2-methylbutyronitrile) and 2,2'-azobisisobutyronitrile, which have a 10-hour half-life of 60-70°C. In addition to the thermal polymerization initiator (C2) for 120°C heating and baking, 1,1'-azobis(cyclohexane-1-carbonitride) can be used as a thermal polymerization initiator (C2) for 180°C heating and baking.

[0091] [Solvent (D)] Solvent (D) is an aqueous solvent capable of forming an aqueous solution or emulsion with (meth)acrylic resin (A) and crosslinking agent (B). Furthermore, it is preferable that the solvent (D) has a boiling point and volatility that allows it to be sufficiently removed from the coating during the heating and baking process. The solvent (D) preferably contains water and / or an aqueous organic solvent, and the aqueous organic solvent may be one type of aqueous organic solvent or a mixed solvent consisting of multiple types of aqueous organic solvents.

[0092] The content of the aqueous organic solvent in the UV crosslinking and heat curing combined electrodeposition solution is preferably 0.1% by mass or more and 5% by mass or less, and more preferably 2.0% by mass or more and 4.0% by mass or less. If it is lower than the above range, the film formation state during electrodeposition will be poor, and the surface shape of the electrodeposited coating will be uneven and the surface smoothness will be poor. If it is higher than the above range, the film thickness variation of the electrodeposited coating will be large.

[0093] (water) Deionized water is preferred as the water contained in solvent (D). When water with a high ion content is used, impurities mixed into the UV crosslinking and heat curing electrodeposition solution can easily generate gas during electrodeposition coating.

[0094] (Water-based organic solvents) The aqueous organic solvent is preferably one or more selected from the group consisting of alcohols, ethylene glycol ethers, and propylene glycol ethers. Alcohols, ethylene glycol ethers, and propylene glycol ethers exhibit excellent plasticization, solubility, and affinity with water for (meth)acrylic resins (A) and crosslinking agents (B).

[0095] Furthermore, alcohols, ethylene glycol ethers, and propylene glycol ethers can also be used as solvents when synthesizing (meth)acrylic resin (A), and it is preferable that the solvent used for synthesizing (meth)acrylic resin (A) and solvent (D) contain a common solvent. If the commonality between the two solvents is high, the reaction solution used when synthesizing (meth)acrylic resin (A) can be directly incorporated into the UV crosslinking / heat curing combined electrodeposition solution and used.

[0096] Specific examples of alcohols include methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, n-hexyl alcohol, 2-ethylhexyl alcohol, benzyl alcohol, etc. One or more alcohols selected from this group can be used in combination, but are not limited to these.

[0097] Specific examples of ethylene glycol ethers include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monon-propyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monon-butyl ether, ethylene glycol monoisobutyl ether, ethylene glycol monotertiary butyl ether, ethylene glycol monon-hexyl ether, ethylene glycol monon-octyl ether, and ethylene glycol mono-2-ethylhexyl ether. One or more of these can be selected from the group and used in combination, but are not limited to these.

[0098] Specific examples of propylene glycol ethers include propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monon-propyl ether, propylene glycol monoisopropyl ether, propylene glycol monon-butyl ether, propylene glycol monoisobutyl ether, propylene glycol monotertiary butyl ether, propylene glycol monon-hexyl ether, propylene glycol monon-octyl ether, and propylene glycol mono-2-ethylhexyl ether. One or more of these can be selected from the group and used in combination, but are not limited to these.

[0099] The solvent (D) in the UV crosslinking and heat curing combined electrodeposition solution of the present invention preferably contains isopropanol and propylene glycol monomethyl ether or ethylene glycol monon-butyl ether, mixed in a mass ratio of isopropanol / (propylene glycol monomethyl ether or ethylene glycol monon-butyl ether) of 0.1 to 3. The solvent used in the synthesis of (meth)acrylic resin (A) needs to have an excellent balance of reaction temperature, reflux temperature, solvent boiling point, and affinity for water. A mixture containing isopropanol or n-butanol and propylene glycol monomethyl ether or ethylene glycol mono-n-butyl ether in a mass ratio of 0.1 to 3 is preferably used. If the solvent (D) contained in the UV crosslinking and heat curing combined electrodeposition solution has a similar composition to the solvent used when synthesizing the (meth)acrylic resin (A), then the reaction solution used when synthesizing the (meth)acrylic resin (A) can be directly incorporated into the UV crosslinking and heat curing combined electrodeposition solution.

[0100] [Neutralizing agent (E)] The neutralizing agent (E) is a compound that neutralizes the functional groups of the (meth)acrylic resin (A), forming a salt and ionizing it.

[0101] For example, if the (meth)acrylic resin (A) has a tertiary amino group, it is preferable to use carboxylic acids as the neutralizing agent (E). Carboxylic acids neutralize the tertiary amino groups of the (meth)acrylic resin (A) to form salts, which are then ionized. This enhances the emulsifying or water-soluble properties of the (meth)acrylic resin (A) in the aqueous solvent (D), thereby improving the dispersibility of the (meth)acrylic resin (A).

[0102] Specific examples of carboxylic acids used as neutralizing agents (E) include organic acids such as formic acid, acetic acid, propionic acid, lactic acid, butyric acid, 2-ethylbutanoic acid, and octic acid, as well as sulfuric acid and phosphoric acid. Among these, acetic acid and lactic acid are particularly suitable. Carboxylic acids may be industrially synthesized products or plant-derived products, and may be used in aqueous solutions mixed with water. For example, a fermented lactic acid aqueous solution containing 88% L-form lactic acid produced from grains and 12% water may be used.

[0103] <Conductive coated material> Examples of conductive substrates to which the UV crosslinking and heat-curing combined electrodeposition solution of the present invention is applied include carbon fiber bundles, copper stranded wires, conductive mesh tubes, plain weave conductors, metal meshes, conductive substrates with complex shapes produced by 3D printers (e.g., metal machinery, general metal tools, metal ornaments, etc.), and plated objects on plastic. 3D printed conductive coated objects may have complex structures, such as lattice structures or truss structures, that are difficult to mold by conventional casting.

[0104] For molded objects with complex structures, conventional non-electrodeposition coating often results in very thin or uneven coatings, requiring multiple coats and drying cycles to achieve a thicker film. However, the UV crosslinking and heat-curing combined electrodeposition solution of the present invention can form a sufficiently thick and uniform coating on conductive substrates with complex structures in a single electrodeposition coating. Furthermore, even if there are areas on the conductive coated object that are not easily directly exposed to ultraviolet light, the corrosion resistance (weather resistance, solvent resistance, chemical resistance), adhesion, and hardness of the coating film made from an ultraviolet crosslinking and heat-curing combined electrodeposition solution can be improved by heat curing.

[0105] There are no particular limitations on the type of metal that constitutes the conductive coated object, but examples include aluminum, pure iron, stainless steel, copper, titanium, nickel alloys, etc., and it may include one or more types selected from the group consisting of these.

[0106] The surface of the conductive coated object may be polished by sandblasting, buffing, electrolytic polishing, etc., as needed. Furthermore, it is preferable that rust-preventive oil on the surface of the iron-based conductive coated object be removed before electrodeposition.

[0107] <Conductive coated material with electrodeposited coating> The conductive coated object with an electrodeposited coating of the present invention is a molded object in which an electrodeposited coating is formed by electrodepositing the ultraviolet crosslinking and heat-curing combined type electrodepositing solution of the present invention onto the surface of the conductive coated object, and the electrodeposited coating is crosslinked and cured by ultraviolet irradiation and then crosslinked and cured by heating and baked, thereby forming an electrodeposited coating. The electrodeposited coating has a balance of corrosion resistance (weather resistance, solvent resistance, chemical resistance), high adhesion, and high hardness.

[0108] (Thickness of electrodeposited coating) There are no particular limitations on the thickness of the electrodeposited coating film formed by UV crosslinking and heat baking on a conductive substrate; however, the UV crosslinking and heat baking combined electrodeposition solution of the present invention can form a baked electrodeposited coating film with a thickness of, for example, 3 to 50 μm on a conductive substrate with a complex structure.

[0109] (Adhesion of electrodeposited coating) The adhesion of electrodeposited coatings is affected by the surface condition of the conductive substrate, the composition of the UV crosslinking and heat-curing combined electrodeposition solution, the UV irradiation conditions, and the heat-curing conditions. The adhesion of a baked electrodeposited coating can be evaluated, for example, in accordance with JIS K 5600-5-6, by marking 10 x 10 = 100 grid squares on the electrodeposited coating formed on a conductive substrate, and then counting the number of squares that did not peel off and the number of missing squares after applying and peeling tape. It is preferable that all 100 squares do not peel off and that there are no missing squares.

[0110] (corrosion resistance) Conductive coated materials with electrodeposited coatings have improved corrosion resistance compared to conductive coated materials without electrodeposited coatings because of the baked electrodeposited coating on the surface. However, if the baked electrodeposited coating is uneven or has defects, corrosion will progress, and the resulting atomic hydrogen will penetrate and accumulate in the surface layer of the conductive coated material. As it gasifies, the surface will bulge in a disc-like shape, forming a blister.

[0111] Types of corrosion resistance include weather resistance to temperature and humidity, solvent resistance to solvents, and chemical resistance to active compounds such as acids, alkalis, and ions. Weather resistance can be evaluated, for example, by making cross-cuts in the electrodeposited coating formed on a conductive substrate in accordance with JIS K 5600-7-1, leaving it under the target temperature and humidity, and observing the change in the adhesion of the electrodeposited coating.

[0112] Solvent resistance can be evaluated, for example, by pressing a cotton ball containing methyl ethyl ketone (MEK) against the electrodeposited coating formed on a conductive coated object with a 1 kg load and rubbing it, then detecting defects such as scratches, peeling, or dissolution of the electrodeposited coating. Chemical resistance can be evaluated, for example, by cross-cutting the electrodeposited coating formed on a conductive substrate in accordance with JIS K 5600-7-1, spraying the target chemical (e.g., neutral salt water), leaving it to stand, and observing the change in the adhesion of the coating and the degree of blister formation.

[0113] <Method for forming electrodeposited coatings> The electrodeposition coating method using the UV crosslinking and heat-curing combined electrodeposition solution of the present invention can provide more thorough coating than air spray coating, and is less prone to paint dripping than simple dipping coating. The ultraviolet crosslinking and heat curing combined type electrodeposition solution of the present invention can form an electrodeposited coating film by, for example, the following electrodeposited coating film formation method. The electrodeposition coating method of the present invention includes the following steps (1) to (6) in this order, and preferably the following steps (6), (7), and (8) are included in the order of (6), (7), and (8), or (6), (8), and (7). (1) Degreasing process for the surface of the conductive coated object, (2) A water washing process for the surface of the conductive coated object, (3) Immersion step of the conductive object to be coated into the ultraviolet crosslinking and heat baking combined electrodeposition solution, (4) Steps to remove bubbles from the surface of the conductive coated object, (5) Process of forming an electrodeposited coating on the surface of a conductive object to be coated, (6) Washing and draining process of the electrodeposited coating, (7) Ultraviolet irradiation process of electrodeposited coating film, (8) Heating and baking process of electrodeposited coating,

[0114] Details of each step are as follows: (1) Degreasing process for the surface of the conductive coated object The surface of conductive objects to be coated may have oil or grease applied to prevent rust. In order to form a highly adhesive electrodeposited coating, it is preferable to remove this oil or grease by immersing it in a degreasing solution such as an organic solvent, acid, or alkali. The temperature of the degreasing solution is preferably 20-60°C, and more preferably 25-35°C. The immersion time is preferably 10 seconds to 5 minutes, and more preferably 10 seconds to 2 minutes. If the conductive coated object has a particularly complex structure, such as one fabricated with a 3D printer, it may similarly be further immersed in several types of degreasing solutions with different compositions.

[0115] (2) Washing process of the surface of the conductive coated object After the surface of the conductive coated object has been degreased, it is preferable to immerse or spray it in room temperature deionized water in a circulating water washing tank for 30 to 90 seconds, more preferably 45 to 75 seconds, and then wash it with water.

[0116] (3) Immersion process of conductive coated object in a combined ultraviolet crosslinking and heat baking electrodeposition solution The UV crosslinking and heat-curing combined electrodeposition solution into which conductive objects to be coated are immersed is preferably kept at 18-28°C, and more preferably at a constant temperature of 20-25°C, in order to stabilize its viscosity. It is preferable that conductive substrates to be immersed in an electrodeposition solution that combines UV crosslinking and heat curing be washed with water and immersed in a wet state in order to improve the adhesion of the electrodeposition solution to the surface. Furthermore, during immersion, it is preferable to immerse the conductive workpiece while stirring the UV crosslinking and heat-curing combined electrodeposition solution in the electrodeposition tank with a magnetic stirrer or the like, in order to improve the adhesion of the UV crosslinking and heat-curing combined electrodeposition solution to the surface of the conductive workpiece.

[0117] (4) Process to remove bubbles from the surface of the conductive coated object If air bubbles are present on the surface of a conductive substrate immersed in an electrodeposition solution that combines UV crosslinking and heat curing, the solution will not adhere well to the areas with bubbles. Therefore, it is preferable to remove the bubbles. To remove air bubbles, it is preferable to agitate the UV crosslinking and heat-curing combined electrodeposition solution in the electrodeposition tank while shaking the immersed conductive object to be coated up and down for 20 to 40 seconds, more preferably 25 to 35 seconds. By removing air bubbles, the entire surface of the conductive substrate can be uniformly coated with the UV crosslinking and heat-curing type electrodeposition solution.

[0118] (5) Process of forming an electrodeposited coating on the surface of a conductive object to be coated When applying the UV crosslinking and heat curing combined electrodeposition solution of the present invention to a conductive workpiece for cationic electrodeposition, the conductive workpiece is used as the cathode and the electrode as the anode. There are no particular restrictions on the electrode on the side that is not the conductive coated object, but it is preferable to use a stainless steel plate. Specifically, SUS304, SUS316, etc. are preferred types of stainless steel.

[0119] Furthermore, in order to obtain a uniform electrodeposited coating in a short time, it is preferable to stop stirring the UV crosslinking / heat baking combined electrodeposition solution and to stop the vertical movement of the conductive workpiece during application. Furthermore, after the application is complete, it is preferable to leave the conductive object to be coated in an ultraviolet crosslinking and heat-curing electrodeposition solution for 5 to 60 seconds, more preferably 8 to 30 seconds. This allows for the removal of any unstable layer remaining on the surface of the formed electrodeposited coating.

[0120] The UV crosslinking and heat curing combined electrodeposition solution of the present invention can be used for electrodeposition coating by either the constant current method or the constant voltage method. Generally, when forming an electrodeposited coating using the constant voltage method, the current value decreases or slows down as the electrodeposited coating's resistance increases due to the growth of the coating's thickness, thus reducing the rate of coating formation. Also, when forming an electrodeposited coating film by the constant current method, as the resistance of the electrodeposited coating film increases, the applied voltage increases, so that the current value can be maintained and the formation rate of the electrodeposited coating film can be maintained. However, in the case of the constant current method, the film thickness of the formed electrodeposited coating film is determined by the integrated value of the current density and the energization time. In the case of a conductive coated object with a complex shape, it is difficult to calculate or measure the surface area, so it is difficult to obtain the target film thickness. Therefore, for the ultraviolet crosslinking and heat baking combined type electrodeposition liquid of the present invention, it is preferable to form an electrodeposited coating film by the constant voltage method for a conductive coated object with a complex shape.

[0121] (Application conditions in the case of the constant voltage method) Although it depends on the resistance value of the conductive coated object, the target film thickness, etc., the applied voltage in the case of electrodeposition coating by the constant voltage method is preferably 80 to 200 volts, and the energization time is preferably 10 seconds to 3 minutes.

[0122] (Application conditions in the case of the constant current method) Although it depends on the resistance value of the conductive coated object, the target film thickness, etc., in the case of electrodeposition coating by the constant current method, the current density is preferably 0.02 to 0.60 A / dm 2 is preferable, and the energization time is preferably 1 to 3 minutes.

[0123] (6) Water washing and draining process of the electrodeposited coating film The conductive coated object with the produced electrodeposited coating film is preferably immersed in deionized water in a circulating water washing tank for 30 to 90 seconds, more preferably 45 to 75 seconds, after being pulled out from the ultraviolet crosslinking and heat baking combined type electrodeposition liquid, and it is preferable to wash with water. After being pulled out from the deionized water, it is drained at room temperature of 20 to 30 °C, preferably for 3 to 7 minutes, more preferably for 4 to 6 minutes, and then the water droplets on the surface of the coating film are removed by air blowing or the like, and the surface of the coating film is preferably dried at 50 to 70 °C, preferably for 1 to 5 minutes.

[0124] (7) Ultraviolet irradiation process of the electrodeposited coating film A conductive coated object with an electrodeposited coating can undergo ultraviolet crosslinking curing treatment of the electrodeposited coating by, for example, ultraviolet irradiation under the following conditions. UV wavelength: 300~500nm UV illuminance: 900~1500mJ / cm 2 UV exposure time: 7-20 minutes

[0125] (8) Heating and baking process of electrodeposited coating Conductive coated objects with electrodeposited coatings can be subjected to heat curing treatment by heating them in a hot air convection oven, far-infrared heater oven, etc. The heating temperature can be selected from 170-200°C, 110-200°C, or 70-200°C, depending on the composition of the UV crosslinking and heat-curing combined electrodeposition solution of the present invention. The heating time is preferably 8 to 20 minutes, and more preferably 10 to 15 minutes. [Examples]

[0126] The main raw materials and supplies used in the embodiments of this invention are as follows. <Ingredients> [polymerizable monomers] 2-dimethylaminoethyl methacrylate 2-hydroxyethyl acrylate 2-hydroxyethyl methacrylate ·styrene • 2-Ethylhexylacrylate • Ethyl acrylate n-butyl acrylate Methyl methacrylate

[0127] [UV crosslinking agent] • Polyfunctional acrylate 1: Manufactured by Toagosei Co., Ltd., Aronics M-400. A mixture of dipentaerythritol pentaacrylate and dipentaerythritol hexaacrylate.

[0128] [Thermal crosslinking agent] • Isocyanate resin solution 1: Lanxess Trixene BI 7982. Solution of 3,5-dimethylpyrazole-blocked hexamethylene diisocyanate trimer / propylene glycol monomethyl ether = mass ratio 70 / 30.

[0129] [UV polymerization initiator] • UV polymerization initiator 1: Omnirad907, a photopolymerization initiator manufactured by IGM Resins BV. 2-methyl-1[4-(methylthio)phenyl]-2-monophorinopropan-1-one. • UV polymerization initiator 2: Kayacure DETX-S, a photopolymerization initiator manufactured by Nippon Kayaku Co., Ltd. 2,4-Diethylthioxanthone. [Thermal polymerization initiator] • Thermal polymerization initiator 1: 2,2'-azobis(2-methylbutyronitrile)

[0130] [Neutralizing agent] • Fermented lactic acid aqueous solution 1: Contains 88% L-form lactic acid produced from grains and 12% water. [solvent] • Deionized water: Water produced using ion exchange resin or RO membrane (reverse osmosis membrane). Conductivity of 1 μS / cm or less.

[0131] <Example of synthesis> [Synthesis of (meth)acrylic resin (A1)] (Flask preparation) The following compounds were placed in a 3-liter four-necked flask equipped with a stirrer, reflux condenser, dropping funnel, and nitrogen inlet tube, and the mixture was heated to 90°C and refluxed. Isopropyl alcohol 5 parts by mass 15 parts by mass of propylene glycol monomethyl ether

[0132] (First batch) A mixture of the following compounds was placed in a dropping funnel and added dropwise to the flask over 120 minutes to allow the reaction to proceed. After the addition was complete, the mixture was stirred at 90°C for 30 minutes to allow the reaction to continue. Isopropyl alcohol 5 parts by mass 15 parts by mass of propylene glycol monomethyl ether 7 parts by mass of 2-dimethylaminoethyl methacrylate 15 parts by mass of 2-hydroxyethyl acrylate 10 parts by mass of styrene 10 parts by mass of 2-ethylhexyl acrylate 15 parts by mass of ethyl acrylate n-butyl acrylate 15 parts by mass 28 parts by mass of methyl methacrylate 2,2'-Azobis(2-methylbutyronitrile) 1 part by mass

[0133] (Second batch preparation) Furthermore, a mixture of the following compounds was added dropwise, and the reaction was continued by stirring at 90°C for 30 minutes after the addition was complete. 7 parts by mass of propylene glycol monomethyl ether Azobisisobutyronitrile 0.2 parts by mass

[0134] (Third batch) Furthermore, a mixture of the following compounds was added dropwise, and the reaction was continued by stirring at 90°C for another 30 minutes after the dropwise addition was complete. 2 parts by mass of propylene glycol monomethyl ether Azobisisobutyronitrile 0.2 parts by mass

[0135] (Fourth batch of brewing) After 30 minutes, the mixture of the following compounds was added dropwise, and the reaction was continued by stirring at 90°C for another 120 minutes after the addition was complete. 2 parts by mass of propylene glycol monomethyl ether Azobisisobutyronitrile 0.2 parts by mass

[0136] (Fifth batch of brewing) The reaction was carried out by stirring at 90°C for 120 minutes, then cooled, and the following compound was added dropwise to the contents at 70°C to neutralize and obtain copolymer (A1) reaction solution. Fermented lactic acid aqueous solution: 2.73 parts by mass

[0137] The copolymer (A1) obtained by removing the solvent from the reaction solution of the resulting copolymer (A1) had a Tg of 1.3°C and an alkali value of 24.98 mgKOH / gNV.

[0138] [(Meth)acrylic resin (A2)~(A4) synthesis] The raw materials were selected according to the information in Table 1, and the reaction solutions for (meth)acrylic resins (A2) to (A10) were obtained by the same procedure as for (meth)acrylic resin (A1) and evaluated in the same manner.

[0139] <Evaluation Method> [Calculation of glass transition temperature of (meth)acrylic resin (A)] The Tg of (meth)acrylic resin (A) was calculated using the following formula, the Tg of the homopolymer composed of each monomer, and the mass fraction of each monomer. 1 / Tg A =1 / Tg1×Wt1+1 / Tg2×Wt2+···+1 / Tg n ×Wt n Tg A Tg [absolute temperature K] of (meth)acrylic resin (A) Tg1, Tg2, ...Tg n :Tg [absolute temperature K] of homopolymers composed of each monomer Wt1, Wt2, ...Wt n : Mass fraction of each monomer relative to the total amount The Tg of the homopolymer composed of each monomer is as follows: • 2-Hydroxyethyl acrylate: 258K (-15℃) • 2-Hydroxyethyl methacrylate: 328K (55℃) Ethyl acrylate: 251K (-22℃) n-butyl acrylate: 219K (-54℃) • 2-Ethylhexyl acrylate: 188K (-85℃) Methyl methacrylate: 378K (105℃) 2-Dimethylaminoethyl methacrylate: 291K (18℃) Styrene: 373K (100℃)

[0140] [Measurement of alkalinity] The reaction solution of (meth)acrylic resins (A1) to (A10) before adding the neutralizing agent (F) was heated to remove the solvent and obtain (meth)acrylic resin (A) before neutralization. One g of the (meth)acrylic resin (A) obtained before neutralization was accurately weighed, and 80 ml of butyl cellosolve was added to dissolve it and obtain a homogeneous solution. While stirring this homogeneous solution with a magnetic stirrer, 0.05 ml of 0.1 N hydrochloric acid with a known factor was added dropwise using a burette, and the amount added and the pH were recorded each time. A dropping curve graph was created with the amount added on the x-axis and the pH value on the y-axis. A parallel tangent line and a median line parallel to the obtained dropping curve were drawn, and the point where the median line intersects the dropping curve was defined as the neutralization point. The amount of 0.1N hydrochloric acid dropped at this neutralization point [mL] was read from the graph. The alkali value was then calculated using the following formula. The measurement procedure was performed twice, and the average value of the alkalinity was calculated. Alkali value [mgKOH / g] = (Volume of 0.1N hydrochloric acid added [mL] × Hydrochloric acid factor [-] × 0.1 [mol / L] × 56.1 [gKOH / mol] × 100) / (Weight of (meth)acrylic resin (A) before neutralization [g])

[0141] [Table 1]

[0142] <<Example A: Electrodeposition solution for UV irradiation + 170~200℃ curing>> [Example A1] The (meth)acrylic resin (A4) reaction solution obtained above, polyfunctional acrylate 1, UV polymerization initiator 1, UV polymerization initiator 2, and UV polymerization initiator 3 were mixed and stirred in the following proportions. (Meth)acrylic resin (A) reaction solution A1: 90 parts by mass Polyfunctional acrylate 1 25.34 parts by mass UV polymerization initiator 1: 2.98 parts by mass UV polymerization initiator 2: 0.74 parts by mass Propylene glycol monomethyl ether 11.17 parts by mass Then, while continuing to stir, the following mass parts of deionized water were added to obtain an ultraviolet crosslinking and heat curing combined electrodeposition solution with a heating residue of 10% by mass. Deionized water: 734.72 parts by mass

[0143] Using the UV crosslinking and heat curing combined electrodeposition solution obtained above, an electrodeposited coating film was formed on the surface of a metal plate by the following procedure, and various evaluations were performed. (1) Degreasing process for the surface of the conductive coated object First, the copper plate to be used as the cathode was degreased by immersing it in acetone at approximately 25°C for 15 seconds, and then pickled by immersing it in a 10% sulfuric acid solution at approximately 25°C for 10 seconds. (2) Washing process of the surface of the conductive coated object The conductive object to be coated was immersed in deionized water at room temperature and rinsed by agitating it up and down for 60 seconds. (3) Immersion step of the conductive object to be coated into the ultraviolet crosslinking and heat baking combined electrodeposition solution, The UV crosslinking and heat-curing combined electrodeposition solution prepared above was poured into a 1L beaker and heated to 24°C, and the cathode and anode were immersed in it. (4) Process to remove bubbles from the surface of the conductive coated object While stirring the UV crosslinking and heat curing electrodeposition solution in a 1L beaker, the immersed conductive workpiece was shaken up and down for 30 seconds to remove air bubbles adhering to the surface of the conductive workpiece and allow the surface of the conductive workpiece to adhere to the curing electrodeposition solution. (5) Process of forming an electrodeposited coating on the surface of a conductive object to be coated Using the constant voltage method and cationic electrodeposition method under the following conditions, an ultraviolet crosslinking and heat-curing combined electrodeposition solution was electrodeposited onto the cathode surface for approximately 15 seconds to achieve a coating thickness of 10 ± 1 μm after curing. Cathode: Tough pitch copper plate C-1100. 50mm x 50mm x 0.2mm thick. Anode: SUS304 plate 70 x 200 mm x 0.5 mm thick. Applied voltage: 120V (6) Washing and draining process of the electrodeposited coating The electrodeposited copper sheets were removed, thoroughly washed with running water, the excess liquid was removed with compressed air, and then dried in a forced-air circulating oven at 60°C for 1 minute to obtain electrodeposited copper sheets. Two electrodeposited copper sheets were prepared. (7) Ultraviolet irradiation process of electrodeposited coating film The electrodeposited coating on the copper plate with electrodeposited coating was treated with a UV-LED irradiator (wavelength 365nm, illuminance 438mW / cm²). 2 Using ), the light was irradiated for 0.8 seconds, resulting in an ultraviolet light intensity of 350 mJ / cm². 2 It was irradiated. (8) Heating and baking process of electrodeposited coating The electrodeposited copper plate was placed in a forced-air circulating oven and heated and baked. Three different heating and curing conditions were used to obtain hardened copper plates with electrodeposited coatings for each condition. 180℃ for 10 minutes 120℃ for 10 minutes 80℃ for 10 minutes Then, the electrodeposited coating thickness, solvent resistance, and electrodeposited coating adhesion were evaluated for each copper plate after heating and baking.

[0144] <Evaluation Method> [Electrodeposition coating thickness] The thickness of the electrodeposited coating on the copper plate after heating and baking was measured using an eddy current film thickness gauge (Fisher DUALSCOPE FMP40), and it was confirmed that the coating thickness was 10 ± 1 μm.

[0145] [Settling and Separation Resistance] The UV crosslinking and heat-curing combined electrodeposition solution was placed in a transparent glass test tube, and after standing for 48 hours, the presence or absence of sedimentation separation was detected visually. The meanings of the symbols in the table are as follows: ○: No sedimentation △: Slight subsidence observed ×: Subsidence present

[0146] [Solvent resistance] A cotton ball containing methyl ethyl ketone (MEK) was pressed against the electrodeposited coating on a copper plate with a 1 kg load and moved back and forth up to 100 times until the electrodeposited coating dissolved. The presence or absence of dissolution of the coating was checked every 20 times, and the appearance of the electrodeposited coating and the coating retention rate (film thickness at the time of dissolution detection / initial film thickness × 100 [%]) were recorded to determine whether the coating was good or bad. The meanings of the symbols in the table are as follows: 〇: Good ×: Bad

[0147] [Adhesion of electrodeposited coating] In accordance with JIS K 5600-5-6, 10 x 10 = 100 grid squares were engraved into an electrodeposited coating on a copper plate. The number of squares that remained intact without peeling or chipping after being applied and removed with tape was then counted.

[0148] [Examples A2-A8, B1-B8, C1-C3, Comparative Examples 1-5] According to the instructions in Tables 2-4, an electrodeposition solution using a combination of ultraviolet crosslinking and heat curing was prepared in the same manner as in Example A1. An electrodeposited coating film was formed on the surface of a copper plate, and the copper plate with the electrodeposited coating film after heat curing was obtained by ultraviolet irradiation and heat curing, and evaluated in the same manner.

[0149] [Table 2]

[0150] [Table 3]

[0151] [Table 4]

[0152] [Summary of Results] As described above, the UV crosslinking and heat-curing combined electrodeposition solution of Example A, which contains 50-75% by mass of (meth)acrylic resin (A) with a Tg of -15 to 5°C and an alkali value of 10-40 mgKOH / g, and 15-35% by mass of a crosslinking agent (B), showed excellent solvent resistance and electrodeposited film adhesion after UV irradiation and heat curing at 180°C.

[0153] Furthermore, the UV crosslinking and heat-curing combined electrodeposition solution of Example B, which contains 35-70% by mass of (meth)acrylic resin (A) with a narrower range of Tg (-10-15°C) and alkali value (15-40 mgKOH / g), a larger amount of UV crosslinking agent (B1) (20-60% by mass), and UV polymerization initiator (C1) (1-7% by mass), showed excellent solvent resistance and electrodeposition film adhesion under both UV irradiation and heat-curing conditions of 120°C and 180°C.

[0154] Furthermore, the UV crosslinking and heat-curing combined electrodeposition solution of Example C, which contains 40-50% by mass of (meth)acrylic resin (A) with a Tg limited to an even narrower range of 0-12°C and alkali value of 15-40 mgKOH / g, an even larger amount of UV crosslinking agent (B1) (40-50% by mass), and UV polymerization initiator (C1) (1-7% by mass), showed excellent solvent resistance and electrodeposition film adhesion under UV irradiation and any of the heat-curing conditions of 180°C, 120°C, and 180°C.

[0155] However, the electrodeposition solutions of Comparative Examples 1 and 2, which contained (meth)acrylic resin (A) with a Tg of 20°C or higher, and the electrodeposition solutions of Comparative Examples 3 to 5, in which the content of (meth)acrylic resin (A), crosslinking agent (B), and polymerization initiator (C) did not meet the requirements of the present invention, showed poor solvent resistance and / or electrodeposition film adhesion under any of the UV irradiation and heating / baking conditions of 80°C, 120°C, and 180°C. [Industrial applicability]

[0156] The UV crosslinking and heat curing combined electrodeposition solution of the present invention can form a coating film with good solvent resistance and adhesion to the surface of conductive substrates inexpensively by electrodeposition coating, even on structures with complex shapes formed by a 3D printer, or on woven or knitted carbon fiber fabrics with intricate fibers. Furthermore, by combining heat curing, a sufficiently cured coating film can be obtained even in intricate areas and deep parts of the coating film where UV light is difficult to irradiate sufficiently.

Claims

1. A cationic electrodeposition solution is used to coat a conductive substrate, followed by UV irradiation and heating and baking at a temperature of 170°C or higher and 200°C or lower. The UV crosslinking and heat curing combined electrodeposition solution contains (meth)acrylic resin (A), a crosslinking agent (B), and a solvent (D). (Meth)acrylic resin (A) has a glass transition temperature of -15 to 5°C, contains hydroxyl groups, tertiary amino groups, and quaternary ammonium bases, and is water-soluble or water-dispersible. The quaternary ammonium base is a neutralized base consisting of a tertiary amino group and a neutralizing agent (E). The alkali value of (meth)acrylic resin (A) before neutralization is 10 to 40 mg KOH / g. The concentration of the tertiary amino group in the (meth)acrylic resin (A) is 0.05 to 0.3 mmol / g. The concentration of the quaternary ammonium base in the (meth)acrylic resin (A) is 0.1 to 0.4 mmol / g. The crosslinking agent (B) contains at least an ultraviolet crosslinking agent (B1) and / or a thermal crosslinking agent (B2), The UV crosslinking agent (B1) is a monomer having five or more (meth)acryloyl groups in one molecule. The thermal crosslinking agent (B2) is a compound that thermally crosslinks with the (meth)acrylic resin (A). Solvent (D) is an aqueous solvent containing an aqueous organic solvent and water. The content of (meth)acrylic resin (A) is 50 to 75% by mass of the total amount of (meth)acrylic resin (A) and crosslinking agent (B). The content of the crosslinking agent (B) is 15 to 35% by mass in the total. An electrodeposition solution that combines UV crosslinking and heat curing.

2. The aforementioned UV crosslinking and heat curing combined electrodeposition solution further contains a polymerization initiator (C), The polymerization initiator (C) contains an ultraviolet polymerization initiator (C1) and / or a thermal polymerization initiator (C2), The content of polymerization initiator (C) is 1 to 7% by mass relative to the total. The electrodeposition solution for combined UV crosslinking and heat curing according to claim 1.

3. A cationic electrodeposition solution is used to coat a conductive substrate, followed by UV irradiation and heating and baking at a temperature of 110°C or higher and 200°C or lower. The UV crosslinking and heat curing combined electrodeposition solution contains (meth)acrylic resin (A), a crosslinking agent (B), a polymerization initiator (C), and a solvent (D). (Meth)acrylic resin (A) has a glass transition temperature of -10 to 15°C, contains hydroxyl groups, tertiary amino groups, and quaternary ammonium bases, and is water-soluble or water-dispersible. The quaternary ammonium base is a neutralized base consisting of a tertiary amino group and a neutralizing agent (E). The alkali value of the (meth)acrylic resin (A) before neutralization is 15 to 40 mg KOH / g. The concentration of the tertiary amino group in the (meth)acrylic resin (A) is 0.1 to 0.4 mmol / g. The concentration of the quaternary ammonium base in the (meth)acrylic resin (A) is 0.2 to 0.55 mmol / g. Crosslinking agent (B) contains at least ultraviolet crosslinking agent (B1), The UV crosslinking agent (B1) is a monomer having five or more (meth)acryloyl groups in one molecule. The polymerization initiator (C) contains at least an ultraviolet polymerization initiator (C1), Solvent (D) is an aqueous solvent containing an aqueous organic solvent and water. The content of (meth)acrylic resin (A) is 35 to 70% by mass of the total amount of (meth)acrylic resin (A) and crosslinking agent (B) contained in the UV crosslinking and heat curing combined electrodeposition solution. The content of the UV crosslinking agent (B1) is 20 to 60% by mass in the total. The content of the ultraviolet polymerization initiator (C1) is 1 to 7% by mass relative to the total. An electrodeposition solution that combines UV crosslinking and heat curing.

4. A cationic electrodeposition solution is used to coat a conductive substrate, followed by UV irradiation and heating and baking at a temperature of 70°C or higher and 200°C or lower. The UV crosslinking and heat curing combined electrodeposition solution contains (meth)acrylic resin (A), a crosslinking agent (B), a polymerization initiator (C), and a solvent (D). (Meth)acrylic resin (A) has a glass transition temperature of 0 to 12°C, contains hydroxyl groups, tertiary amino groups, and quaternary ammonium bases, and is water-soluble or water-dispersible. The quaternary ammonium base is a neutralized base consisting of a tertiary amino group and a neutralizing agent (E). The alkali value of the (meth)acrylic resin (A) before neutralization is 15 to 40 mg KOH / g. The concentration of the tertiary amino group in the (meth)acrylic resin (A) is 0.1 to 0.35 mmol / g. The concentration of the quaternary ammonium base in the (meth)acrylic resin (A) is 0.2 to 0.45 mmol / g. Crosslinking agent (B) contains at least ultraviolet crosslinking agent (B1), The UV crosslinking agent (B1) is a monomer having five or more (meth)acryloyl groups in one molecule. The polymerization initiator (C) contains at least an ultraviolet polymerization initiator (C1), Solvent (D) is an aqueous solvent containing an aqueous organic solvent and water. The content of (meth)acrylic resin (A) is 40 to 50% by mass in the total of (meth)acrylic resin (A) and crosslinking agent (B). The content of the UV crosslinking agent (B1) is 40 to 50% by mass in the total. The content of the ultraviolet polymerization initiator (C1) is 1 to 7% by mass relative to the total. An electrodeposition solution that combines UV crosslinking and heat curing.

5. A conductive coated workpiece with a baked electrodeposited coating, manufactured using an ultraviolet crosslinking and heat baking combined type electrodeposition solution described in any one of claims 1 to 4.

6. A method for forming a baked electrodeposited coating film, comprising forming a baked electrodeposited coating film on the surface of a conductive workpiece by cationic electrodeposition coating using an ultraviolet crosslinking and heat baking combined type electrodeposition solution described in any one of claims 1 to 4, The forming method includes the following steps (1) to (6) in this order, and the following steps (6), (7), and (8) in the order of (6), (7), and (8), or in the order of (6), (8), and (7). (1) Degreasing step for the surface of the conductive object to be coated, (2) A water washing step for the surface of the conductive coated object, (3) Immersion step of the conductive object to be coated into the ultraviolet crosslinking and heat baking combined electrodeposition solution, (4) Steps to remove bubbles from the surface of the conductive coated object, (5) Steps to form an electrodeposited coating on the surface of the conductive object to be coated, (6) Washing and draining process of the electrodeposited coating film, (7) Ultraviolet irradiation step of the electrodeposited coating film, (8) Heating and baking process of the electrodeposited coating film, Here, Step (3) includes immersing the conductive object to be coated in the ultraviolet crosslinking and heat curing combined electrodeposition solution while its surface is wet with water. Step (4) includes stirring the UV crosslinking and heat baking combined electrodeposition solution and moving the conductive object to be coated up and down. Step (5) includes the step of applying the UV crosslinking and heat baking combined electrodeposition solution while the stirring of the conductive object to be coated is stopped and the vertical movement of the conductive object is stopped. A method for forming a baked electrodeposition coating.

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