Magnesium material surface treatment process and treatment agent set

Abstract

To provide a magnesium surface treatment process that can form a coating on magnesium materials that provides good appearance, corrosion resistance, and moisture resistance. [Solution] A magnesium material surface treatment process comprising: a pretreatment step of treating the magnesium material with a pretreatment agent; a chemical conversion step of chemically treating the magnesium material after the pretreatment step; and an anionic electrodeposition coating step of anionic electrodeposition coating the magnesium material after the chemical conversion step, wherein the pretreatment agent contains an amino group-containing compound and has a pH of 6.0 or more and less than 12.0; and the anionic electrodeposition coating step comprises an electrodeposition coating step of immersing the magnesium material in an anionic electrodeposition coating composition and applying a voltage to form an electrodeposited coating film, and a heat curing step of heating and curing the electrodeposited coating film formed in the electrodeposition coating step to form a cured electrodeposited coating film.

Description

Technical Field

[0001] The present disclosure relates to a surface treatment process for magnesium materials and a set of treatment agents.

Background Art

[0002] Electrophoretic coating is a coating method in which an object to be coated is immersed in an electrophoretic coating composition and a voltage is applied to deposit a coating film on the surface of the object to be coated. This method can coat even the details of an object to be coated having a complex shape, and can be coated automatically and continuously. Therefore, electrophoretic coating is widely used as an undercoat coating method for objects to be coated having a large and complex shape, such as automobile bodies, industrial machines, construction machines, and metal parts of fixed structures. Furthermore, electrophoretic coating can provide high corrosion resistance to the object to be coated and also has an excellent protective effect on the object to be coated. In addition, since the electrophoretic coating composition is an aqueous coating composition, it can reduce the environmental load compared to a solvent-based coating composition.

[0003] Examples of electrophoretic coating include cationic electrophoretic coating and anionic electrophoretic coating. Anionic electrophoretic coating is used, for example, as a coating method that imparts excellent corrosion resistance to materials such as aluminum materials (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In recent years, magnesium or magnesium alloys (magnesium materials) have been considered as alternatives to aluminum in various products such as home appliances, office automation equipment, mobile devices, and automotive parts, due to their light weight, high recyclability, and abundant resources. On the other hand, magnesium is a reactive metal and therefore easily corroded, creating a need for surface treatments such as chemical conversion treatment and / or painting to improve the corrosion resistance of magnesium materials. Furthermore, aesthetics are particularly important in the casings of mobile devices. However, when attempting to surface treat magnesium materials, the resulting chemical conversion film can be uneven, and the appearance, corrosion resistance, moisture resistance, and other durability of the resulting coating have not been sufficient.

[0006] This disclosure has been made in view of the above, and aims to provide a magnesium material surface treatment process that can form a coating film that imparts good appearance, corrosion resistance, and moisture resistance to magnesium materials. [Means for solving the problem]

[0007] (1) The present disclosure relates to a process for surface-treating a magnesium material, comprising: a pretreatment step of treating the magnesium material with a pretreatment agent; a chemical conversion step of chemically converting the magnesium material after the pretreatment step; and an anionic electrodeposition coating step of anionic electrodeposition coating the magnesium material after the chemical conversion step, wherein the pretreatment agent contains an amino group-containing compound and has a pH of 6.0 or more and less than 12.0; the chemical conversion agent contains a zirconium compound and an amino group-containing compound; and the anionic electrodeposition coating step comprises the magnesium material in an anionic electrodeposition coating composition. The present invention relates to a magnesium material surface treatment process comprising: an electrodeposition coating step of immersing the material and applying a voltage to form an electrodeposited coating film; and a heat curing step of heating and curing the electrodeposited coating film formed in the electrodeposition coating step to form a cured electrodeposited coating film, wherein the anionic electrodeposition coating composition comprises a film-forming resin (A) and a curing agent (B), the film-forming resin (A) comprises an acrylic resin having carboxyl groups and hydroxyl groups, having a weight-average molecular weight of 5,000 to 100,000 and a hydroxyl value of 30 to 200 mgKOH / g, and the heat curing step having a heating temperature of 110 to 230°C.

[0008] (2) The magnesium material surface treatment process according to (1), wherein the curing agent (B) is at least one selected from the group consisting of amino resins and blocked isocyanate compounds.

[0009] (3) The magnesium material surface treatment process according to (1) or (2), wherein the anionic electrodeposition coating composition further comprises a gloss modifier (C).

[0010] (4) The magnesium material surface treatment process according to any one of (1) to (3), wherein the anionic electrodeposition coating composition further comprises a pigment (D).

[0011] (5) The magnesium material surface treatment process according to any one of (1) to (4), wherein the amino group-containing compound is at least one selected from the group consisting of amino group-containing alkoxysilane compounds and polymers having allylamine units, and the amino group-containing compound is contained in a concentration range of 50 ppm by mass or more and 1,500 ppm by mass or less as solid content relative to the total mass of the pretreatment agent.

[0012] (6) The magnesium material surface treatment process according to any one of (1) to (5), wherein the amino group-containing compound contained in the chemical treatment agent and the amino group-containing compound contained in the pretreatment agent are of the same type.

[0013] (7) A magnesium material surface treatment process according to any one of (1) to (6), wherein, following the pretreatment step, the pretreated magnesium material is chemically treated by the chemical conversion step without going through any other steps.

[0014] (8) The magnesium material surface treatment process according to any one of (1) to (7), wherein the amino group-containing compound is an amino group-containing alkoxysilane compound.

[0015] (9) The magnesium material surface treatment process according to (8), wherein the ratio of the solid content mass of the amino group-containing alkoxysilane compound to the total solid content mass of the pretreatment agent is 95% or more.

[0016] (10) The magnesium material surface treatment process according to any one of (1) to (9), wherein the pretreatment agent does not contain an epoxy group-containing silane compound.

[0017] (11) The present disclosure also relates to a treatment agent set used in a magnesium material surface treatment process described in any of (1) to (10), the treatment agent set comprising: a pretreatment agent used in the pretreatment step; a chemical conversion treatment agent used in the chemical conversion treatment step; and an anionic electrodeposition coating composition used in the anionic electrodeposition coating step. [Effects of the Invention]

[0018] According to the present disclosure, a magnesium material surface treatment process capable of forming a coating film that imparts good appearance, corrosion resistance, and moisture resistance to a magnesium material can be provided.

Embodiments for Carrying out the Invention

[0019] Hereinafter, embodiments of the present disclosure will be described. The present disclosure is not limited to the descriptions of the following embodiments.

[0020] The magnesium material surface treatment process according to this embodiment includes a pretreatment step, a chemical conversion treatment step, and an anion electrodeposition coating step in this order. The magnesium material to be treated in the magnesium material surface treatment process includes magnesium alone and magnesium alloys. Since the magnesium material surface treatment process according to this embodiment can suppress the reactivity of the magnesium material and uniformize the chemical conversion film reaction in the pretreatment step, the effects of the present disclosure are preferably exhibited for the highly reactive magnesium material as described above.

[0021] <Pretreatment Step> The pretreatment step is a step of treating a magnesium material with a pretreatment agent. The pretreatment agent contains an amino group-containing compound. The amino group-containing compound is preferably at least one selected from the group consisting of an amino group-containing alkoxysilane compound and a polymer having an allylamine unit. The amino group-containing compound is more preferably an amino group-containing alkoxysilane compound. By containing an amino group-containing alkoxysilane compound in the pretreatment agent, the effect of suppressing the reactivity of the magnesium material and uniformizing the chemical conversion film reaction can be more preferably obtained.

[0022] An amino group-containing alkoxysilane compound is a silane compound having an amino group and an alkoxy group in the molecule. The amino group-containing alkoxysilane compound has, for example, at least one alkyl chain in the molecule, the alkyl chain is bonded to the bond of the silicon atom and has at least one amino group, and the functional group bonded to the remaining bonds of the silicon atom is an alkoxy group.

[0023] The amino group-containing alkoxysilane compound is not particularly limited, and examples thereof include N-2(aminoethyl)3-aminopropylmethyldimethoxysilane, N-2(aminoethyl)3-aminopropyltrimethoxysilane, N-2(aminoethyl)3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-triethoxysilyl-N-(1,3-dimethyl-butylidene)propylamine, N-phenyl-3-aminopropyltrimethoxysilane, N,N-bis[3-(trimethoxysilyl)propyl]ethylenediamine, and the like.

[0024] As the above amino group-containing alkoxysilane compound, commercially available products can be used. Examples of commercially available products include KBM-602, KBM-603, KBE-603, KBM-903, KBE-9103, KBM-573 (all manufactured by Shin-Etsu Chemical Co., Ltd.), and the like.

[0025] The amino group-containing alkoxysilane compound may be a hydrolyzate. The hydrolyzate of the amino group-containing alkoxysilane compound can be produced by a conventionally known method, for example, a method of dissolving the amino group-containing alkoxysilane compound in ion-exchanged water and adjusting it to be acidic with an arbitrary acid. As the hydrolyzate of the amino group-containing alkoxysilane compound, commercially available products such as KBP-90 (manufactured by Shin-Etsu Chemical Co., Ltd.) can also be used. The amino group-containing alkoxysilane compound may be a hydrolysis condensate.

[0026] The ratio of the solid content of the amino group-containing alkoxysilane compound to the total solid content of the pretreatment agent is preferably 95% or more. More preferably, the above ratio is 98% or more, and may be 100%.

[0027] A polymer having an allylamine unit is a polymer that contains at least a segment derived from allylamine or a segment derived from diallylamine (hereinafter, these may be referred to as "allylamine segment" and "diallylamine segment," respectively). The allylamine segment and the diallylamine segment may be in the form of a quaternary nucleotide. A polymer having an allylamine unit may have only allylamine segments or diallylamine segments in its structure, or it may contain other segments. Furthermore, each of the aforementioned segments may independently have a counterion. A polymer having an allylamine unit may be a homopolymer or a copolymer. Preferably, a polymer having an allylamine unit is composed of only allylamine units, only diallylamine units, or allylamine units and diallylamine units.

[0028] The allylamine segment has, for example, the structure shown in formula (2) below.

[0029] [ka]

[0030] The allylamine segment may have an anionic counterion similar to that of the diallylamine segment described below.

[0031] The diallylamine segment has a heterocyclic structure represented by the following formula (1a) or (1b).

[0032] [ka]

[0033] R in formulas (1a) and (1b) 1 The group represents hydrogen, an alkyl group, or an aralkyl group. Examples of alkyl groups include unsubstituted alkyl groups having 1 to 10 carbon atoms, and more preferably unsubstituted alkyl groups having 1 to 6 carbon atoms. Specific examples of alkyl groups include methyl, ethyl, propyl, butyl, pentyl, and hexyl groups. The aralkyl group is preferably an aralkyl group having 7 to 11 carbon atoms. Examples of aralkyl groups having 7 to 11 carbon atoms include benzyl, phenylethyl, phenylpropyl, phenylbutyl, and naphthylmethyl groups.

[0034] The polymer having the allylamine unit is preferably an acid addition salt having an anionic counterion to the ammonium cation. The dissociation constant pKa of the acid forming the acid addition salt is preferably in the range of -3.7 to 4.8. In this specification, the dissociation constant pKa of the acid refers to the value at 25°C with water as the solvent. Examples of diallylamine segments constituting the polymer having the allylamine unit which is the acid addition salt are represented by the following general formulas (1c) and (1d).

[0035] [ka]

[0036] R in the above formulas (1c) and (1d) 2 and R 3 These independently represent hydrogen, alkyl groups, or aralkyl groups, and D - This indicates a monovalent anion.

[0037] The anionic counterion is not particularly limited, but examples include monovalent anions such as formate ions, acetate ions, benzoate ions and other carboxylate ions, chloride ions, sulfate ions, sulfamate ions, and nitrate ions. Acids that form acid addition salts include organic acids such as formic acid, acetic acid, and benzoic acid, and inorganic acids such as hydrochloric acid, sulfuric acid, sulfamic acid, and nitric acid.

[0038] A polymer having an allylamine unit may have other segments besides those mentioned above, but it is preferable that it contains a total of 50 mol% or more of the above-mentioned allylamine segment and diallylamine segment as segments. The allylamine segment and diallylamine segment constituting the polymer having an allylamine unit may be of only one type, or two or more types may be combined. The polymer having an allylamine unit is preferably a polyallylamine polymer composed only of allylamine segments, a polydiallylamine polymer composed only of diallylamine segments, a copolymer composed only of allylamine segments and diallylamine segments, or a polydiallylamine polymer composed only of diallylamine segments.

[0039] Other segments in polymers containing an allylamine unit, besides the allylamine segment and the diallylamine segment, are not particularly limited, but include, for example, segments derived from sulfur dioxide (sulfonyl group), segments derived from unsaturated compounds having a hydroxyl group such as 2-hydroxyethyl (meth)acrylate, segments derived from (meth)acrylic monomers having a primary amino group, segments derived from N,N-dialkylaminoalkyl (meth)acrylate and its salts or quaternary compounds, N,N-dialkylaminoalkyl (meth)acrylamide and its salts or quaternary compounds, vinylimidazole and its salts or quaternary compounds, vinylpyridine and its salts or quaternary compounds, N-alkylallylamine and its salts, N,N-dialkylallylamine and its salts, N-alkyldiallylamine and its salts or quaternary compounds, etc., alkyl (meth)acrylate esters such as methyl (meth)acrylate and ethyl (meth)acrylate, vinyl carboxylates such as vinyl acetate and vinyl propionate, unsaturated acids, etc.

[0040] The weight-average molecular weight of the polymer having allylamine units is preferably 500 to 500,000, and more preferably 5,000 to 100,000. The weight-average molecular weight can be measured, for example, by gel permeation chromatography (GPC).

[0041] The polymer having the allylamine unit may be modified to the extent that it does not impair the objective of the present invention. For example, some of the amino groups of the polymer having the allylamine unit may be modified by methods such as acetylation, or it may be crosslinked with a crosslinking agent to the extent that it does not affect solubility.

[0042] The method for preparing polymers having allylamine units is not particularly limited, but for example, a mixture of monomers, which may include alkyldiallylamine and other components as needed, can be radically polymerized in a suitable solvent in the presence of a radical polymerization initiator. Polymerization conditions can be appropriately selected from those known to those skilled in the art.

[0043] The amino group-containing compound is preferably included in the pretreatment agent at a concentration range of 50 ppm to 1,500 ppm by mass as solid content relative to the total mass of the pretreatment agent, and more preferably at a concentration range of 200 ppm to 1,000 ppm by mass.

[0044] The pretreatment agent has a pH of 6.0 or higher and less than 12.0. This prevents rust formation and unwanted etching before chemical conversion treatment. The pH of the pretreatment agent is preferably 6.0 or higher and 11.0 or lower, and more preferably 6.0 or higher and 10.0 or lower. The pH of the pretreatment agent can be measured using a commercially available pH meter. The pH of the pretreatment agent can be adjusted with a pH adjusting agent such as nitric acid or ammonia water.

[0045] The pretreatment agent according to this embodiment may contain components other than those listed above. For example, it may contain silicon-containing compounds other than the amino group-containing alkoxysilane compounds mentioned above, rust inhibitors such as amine compounds and benzotriazole, surfactants, pH adjusters, etc. Furthermore, when pretreating magnesium material with the pretreatment agent, metal components may inevitably be mixed into the pretreatment agent.

[0046] The pretreatment agent is preferably free of epoxy group-containing silane compounds. The epoxy group-containing silane compounds are not particularly limited and include, for example, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropyldimethylmethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylethyldiethoxysilane, 3-glycidoxypropyldiethylethoxysilane, 3-glycidoxypropyltriethoxysilane, and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.

[0047] In the pretreatment step, there are no particular limitations on the method of contacting the magnesium material with the pretreatment agent, and known methods can be used. Examples include immersion, spraying, and roll coating. The treatment temperature in the pretreatment step can be in the range of 5 to 40°C, and the treatment time can be in the range of 30 seconds to 5 minutes.

[0048] <Chemical treatment process> The chemical conversion treatment process involves contacting a magnesium material that has undergone a pretreatment process with a chemical conversion treatment agent to form a chemical conversion film on its surface. The chemical conversion treatment agent includes, for example, a metal component, fluorine, and an amino group-containing compound. The metal component is a chemical conversion film-forming component and is, for example, at least one selected from the group consisting of zirconium, titanium, and hafnium. It is preferable that the metal component includes zirconium.

[0049] The zirconium compounds that serve as the source of the zirconium are not particularly limited, but examples include alkali metal fluorozirconates such as K2ZrF6, zirconhydrofluoric acid (H2ZrF6), ammonium hexazirconate ((NH4)2ZrF6), ammonium zirconium carbonate ((NH4)2ZrO(CO3)2), tetraalkylammonium-modified zirconium, zirconium fluoride, and zirconium oxide.

[0050] The source of the titanium is not particularly limited, but examples include alkali metal fluorotitanates, fluorotitanates such as (NH4)2TiF6, fluorotitanic acids such as H2TiF6, titanium fluoride, and titanium oxide.

[0051] The source of the aforementioned hafnium is not particularly limited, but examples include fluorohafnate acids such as H2HfF6 and hafnium fluoride.

[0052] The content of the metal component is preferably 10 to 10,000 ppm by mass in terms of metal elements, relative to the total mass of the chemical treatment agent (total mass including solids and volatiles of the chemical treatment agent; the same applies hereinafter). The content of the metal component is preferably 50 to 2,000 ppm by mass, and more preferably 100 to 1,000 ppm by mass, in terms of metal elements.

[0053] Fluorine has the function of etching the surface of magnesium material. The source of fluorine is not particularly limited, but examples include fluorides such as hydrofluoric acid, ammonium fluoride, boric acid fluoride, ammonium hydrogen fluoride, sodium fluoride, and sodium hydrogen fluoride. As for complex fluorides, examples include hexafluorosilicates, and specific examples include hydrofluorosilica, zinc hydrofluorosilica, manganese hydrofluorosilica, magnesium hydrofluorosilica, nickel hydrofluorosilica, iron hydrofluorosilica, and calcium hydrofluorosilica. Furthermore, fluorine-containing compounds such as alkali metal fluorozirconates, which were exemplified as sources of metal components, can serve as both sources of metal components and sources of fluorine.

[0054] The fluorine concentration is preferably 10 to 12,500 ppm by mass, and more preferably 125 to 1,250 ppm by mass, relative to the total mass of the chemical treatment agent, in terms of fluorine element. Methods for measuring the fluorine concentration include, for example, quantitative analysis by ion chromatography.

[0055] Examples of amino group-containing compounds include those similar to those contained in the pretreatment agent described above. The content of the amino group-containing compound is preferably 25 to 5,000 ppm by mass in terms of solid content relative to the total mass of the chemical treatment agent. More preferably, the content of the amino group-containing compound is 50 to 2,500 ppm by mass in terms of solid content, and even more preferably 50 to 600 ppm by mass.

[0056] The chemical treatment agent contains an amino group-containing compound, and it is preferable that the amino group-containing compound contained in the chemical treatment agent is the same type of compound as the amino group-containing compound contained in the pretreatment agent. Here, "same type" means that both the amino group-containing compound contained in the chemical treatment agent and the amino group-containing compound contained in the pretreatment agent are amino group-containing alkoxysilane compounds, or both are polymers having allylamine units. This preferably provides an effect of homogenizing the chemical conversion film reaction, thereby improving the effects of this disclosure, such as desirable corrosion resistance, coating adhesion, and appearance. Furthermore, being the same type of compound is also preferable from a manufacturing standpoint. It is even more preferable that the amino group-containing compound contained in the chemical treatment agent and the amino group-containing compound contained in the pretreatment agent are the same, as this further enhances the aforementioned effects.

[0057] The chemical treatment agent may contain components other than those listed above. For example, it may contain polymers other than diallylamine polymers having allylamine units, polyallylamine resins, polyvinylamine resins, polydiallylamine resins, urethane resins, acrylic resins, polyester resins, natural polymer derivatives such as chitin / chitosan derivatives and cellulose derivatives. It may also contain silane coupling agents other than the amino group-containing compounds, metal components other than those listed above such as aluminum, copper, zinc, magnesium, calcium, gallium, indium, manganese, iron, cobalt, nickel, and chromium, and oxidizing agents such as nitric acid, nitrite, hydrochloric acid, bromate, chloric acid, hydrogen peroxide, HMnO4 and HVO3, and salts thereof.

[0058] The chemical treatment agent is preferably substantially free of phosphate ions. In this specification, "substantially free of phosphate ions" means that phosphate ions are not present to such an extent that they act as a component in the chemical treatment agent.

[0059] The pH of the chemical treatment agent is preferably 2.0 to 7.0. When the target substrate is magnesium, the pH is more preferably 5.0 to 7.0, and when other metal species are the target substrate, the pH is more preferably 3.0 to 5.0. Acidic compounds such as nitric acid and sulfuric acid, and basic compounds such as sodium hydroxide, potassium hydroxide, and ammonia can be used to adjust the pH.

[0060] In the chemical treatment process, the method of contacting the magnesium material with the chemical treatment agent is not particularly limited, and known methods can be used. Examples include immersion, spraying, and roll coating. The treatment temperature in the chemical treatment process can be in the range of 15 to 70°C, and is preferably in the range of 30 to 50°C. The treatment time in the chemical treatment process can be in the range of 5 to 1200 seconds, and is preferably in the range of 30 to 120 seconds.

[0061] The chemical conversion treatment process is preferably a process in which the magnesium material, which has been pre-treated by the pre-treatment process, is chemically treated without going through other processes such as washing or drying. This can improve the rust prevention and coating adhesion of the edges. Note that the other processes refer to intentionally performed processes such as washing the surface of the magnesium material, contact with chemicals, or heating or cooling, and do not refer to unavoidable processes such as leaving the magnesium material for a predetermined time after the pre-treatment process.

[0062] <Anionic electrodeposition coating process> The anionic electrodeposition coating process involves immersing a magnesium material that has undergone a chemical conversion treatment process in an anionic electrodeposition coating composition and applying a voltage to form an anionic electrodeposition coating film on the surface of the magnesium material. The anionic electrodeposition coating composition comprises a coating film-forming resin (A) and a curing agent (B). Preferably, the anionic electrodeposition coating composition further comprises a gloss modifier (C), a pigment (D), and a curing catalyst, as needed.

[0063] The film-forming resin (A) is an acrylic resin having carboxyl groups and hydroxyl groups. Examples of such acrylic resins include acrylic resins obtained by radical polymerization of monomers using a carboxyl group-containing radical polymerizable unsaturated monomer (a-1) and a hydroxyl group-containing radical polymerizable unsaturated monomer (a-2), and optionally other radical polymerizable unsaturated monomers (a-3).

[0064] A carboxyl group-containing radical polymerizable unsaturated monomer (a-1) is a compound having at least one carboxyl group and at least one polymerizable unsaturated bond in one molecule. Examples of carboxyl group-containing radical polymerizable unsaturated monomers (a-1) include vinyl polymerizable α,β-unsaturated fatty acids such as (meth)acrylic acid, itaconic acid, maleic acid, maleic anhydride, fumaric acid, maleic acid monoester, itaconic acid monoester, crotonic acid, and citraconic acid, caprolactone-modified carboxyl group-containing (meth)acrylic monomers, and mixtures thereof. It is preferable to use at least one selected from the group consisting of acrylic acid and methacrylic acid as the carboxyl group-containing radical polymerizable unsaturated monomer (a-1). In this specification, (meth)acrylic acid refers to either acrylic acid or methacrylic acid.

[0065] Hydroxyl group-containing radical polymerizable unsaturated monomers (a-2) are compounds having at least one hydroxyl group and at least one polymerizable unsaturated bond in one molecule. Examples of hydroxyl group-containing radical polymerizable unsaturated monomers (a-2) include hydroxyalkyl (meth)acrylates such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and hydroxybutyl (meth)acrylate; polyalkylene glycols (meth)acrylates such as polyethylene glycol (meth)acrylate and polypropylene glycol (meth)acrylate; and reaction products of these hydroxyl group-containing acrylic monomers with lactone compounds such as β-propiolactone, dimethylpropiolactone, butyrolactone, γ-valerolactone, γ-caprolactone, γ-capryloractone, γ-laurylolactone, ε-caprolactone, and δ-caprolactone. Commercially available products may be used as such reaction products, for example, Praxel FM1 (manufactured by Daicel Corporation, trade name, caprolactone-modified (meth)acrylate hydroxyesters), Praxel FM2 (same as above), Praxel FM3 (same as above), Praxel FA1 (same as above), Praxel FA2 (same as above), Praxel FA3 (same as above), etc.

[0066] Other radical polymerizable unsaturated monomers (a-3) are monomers other than the carboxyl group-containing radical polymerizable unsaturated monomer (a-1) and the hydroxyl group-containing radical polymerizable unsaturated monomer (a-2) described above, and are compounds having at least one radical polymerizable unsaturated bond in one molecule. Examples of other radical polymerizable unsaturated monomers (a-3) include C1-8 alkyl esters or C3-8 cycloalkyl esters of (meth)acrylic acid such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, octyl (meth)acrylate, lauryl (meth)acrylate, and cyclohexyl (meth)acrylate; styrene, α-methylstyrene, vinylitol Examples include aromatic polymerizable monomers such as ene; (meth)acrylamides and their derivatives such as (meth)acrylamide, N-butoxymethyl(meth)acrylamide, and N-methylol(meth)acrylamide; (meth)acrylonitrile compounds; and alkoxysilyl group-containing polymerizable monomers such as γ-(meth)acryloxypropyltrimethoxysilane, γ-(meth)acryloxypropylmethyldimethoxysilane, γ-(meth)acryloxypropyltriethoxysilane, and vinyltrimethoxysilane.

[0067] As a method for radical copolymerizing the monomers (a-1), (a-2), and (a-3), solution polymerization methods, emulsion polymerization methods, etc., commonly used by those skilled in the art can be used. In the preparation of the acrylic resin, it is preferable to use the carboxyl group-containing radical polymerizable unsaturated monomer (a-1) in an amount of preferably 3 to 30% by mass, more preferably 4 to 20% by mass, of the total mass of monomers; the hydroxyl group-containing radical polymerizable unsaturated monomer (a-2) in an amount of preferably 3 to 40% by mass, more preferably 5 to 30% by mass, of the total mass of monomers; and the other radical polymerizable unsaturated monomer (a-3) in an amount of preferably 30 to 90% by mass, more preferably 40 to 85% by mass, of the total mass of monomers.

[0068] The acrylic resin preferably has an acid value of 15 to 150 mgKOH / g, and more preferably 30 to 80 mgKOH / g. When the acid value of the acrylic resin is 15 mgKOH / g or higher, the water dispersibility of the resin is enhanced, and a uniform paint can be produced. When the acid value is 150 mgKOH / g or lower, there are advantages such as improved corrosion resistance and acid resistance of the cured coating film.

[0069] The acrylic resin has a hydroxyl value of 30 to 200 mgKOH / g. Preferably, the hydroxyl value is 40 to 150 mgKOH / g. When the hydroxyl value of the acrylic resin is 30 mgKOH / g or higher, the curing reaction occurs sufficiently, and the original coating performance is obtained. When it is 200 mgKOH / g or lower, there are advantages such as no unreacted hydroxyl groups remaining in the coating film, thus not reducing corrosion resistance, acid resistance, etc. In this specification, acid value and hydroxyl value represent solid content acid value and solid content hydroxyl value, respectively, and can be measured by the method described in JIS K 0070.

[0070] The acrylic resin has a weight-average molecular weight (Mw) of 5,000 to 100,000. Preferably, the weight-average molecular weight (Mw) is 10,000 to 50,000. When the weight-average molecular weight (Mw) of the acrylic resin is 5,000 or more, there are advantages such as improved coating film performance, including corrosion resistance and acid resistance. When it is 100,000 or less, there are advantages such as improved flowability of the electrodeposited coating and the acquisition of a cured electrodeposited coating with a good coating appearance. In this specification, the weight-average molecular weight (Mw) is the polystyrene equivalent value measured by gel permeation chromatography (GPC).

[0071] In the anionic electrodeposition coating compositions of this disclosure, it is preferable that the acrylic resin is used as a water-soluble or water-dispersible resin by neutralizing the carboxyl group with a basic substance (e.g., triethylamine, dimethylethanolamine, ammonia, etc.). In such neutralization of the acrylic resin, the neutralization rate is preferably 30 to 100%, and more preferably 50 to 80%. By having a neutralization rate within this range, the acrylic resin can be well dispersed in the anionic electrodeposition coating composition.

[0072] In the anionic electrodeposition coating composition of this disclosure, the content of the acrylic resin is preferably 50 to 80% by mass with respect to 100% by mass of the total resin solids content of the coating film-forming resin (A) and the curing agent (B). A content of 50% by mass or more enhances chemical resistance such as acid resistance and alkali resistance, as well as corrosion resistance. A content of 80% by mass or less ensures that the electrodeposited coating film hardens sufficiently, resulting in the desired coating film performance.

[0073] The anionic electrodeposition coating composition of this disclosure may contain, as necessary, other film-forming resins as the film-forming resin (A), in addition to the acrylic resin. Examples of other film-forming resins include polyester resins, urethane resins, epoxy resins, butadiene resins, phenolic resins, xylene resins, and the like. Epoxy resins are preferred as the other film-forming resins from the viewpoint of improving the corrosion resistance of the cured electrodeposition coating. When such other film-forming resins are used, their content is preferably less than 20% by mass, and more preferably less than 15% by mass, relative to the resin solids content in the coating composition.

[0074] The epoxy resin used as the other film-forming resin is preferably one having at least two epoxy groups in one molecule. Specifically, examples include epibis epoxy resin and those obtained by extending the chain with diols, dicarboxylic acids, diamines, etc.; epoxidized polybutadiene; novolac phenol type polyepoxy resin; novolac cresol type polyepoxy resin; polyglycidyl acrylate; polyglycidyl ether of aliphatic polyol or polyether polyol; and polyglycidyl ester of polybasic carboxylic acid.

[0075] The curing agent (B) is preferably at least one selected from the group consisting of amino resins and blocked isocyanate compounds.

[0076] Amino resins are condensates obtained by modifying condensates of amino compounds such as melamine, urea, and benzoguanamine with aldehyde compounds such as formaldehyde and acetaldehyde using lower alcohols such as methanol, ethanol, propanol, and butanol. Specific examples of such amino resins include fully alkyl-type methyl / butyl mixed etherified melamine resins, methylol-group-type methyl / butyl mixed etherified melamine resins, imino-type methyl / butyl mixed etherified melamine resins, fully alkyl-type methylated melamine resins, and imino-group-type methylated melamine resins.

[0077] Commercially available amino resins may be used. Examples of commercially available products include fully alkyl methyl / butyl mixed etherified melamine resins such as Cymel 232, Cymel 235, Cymel 236, Cymel 238, and Cymel 285-100; imino-type methyl / butyl mixed etherified melamine resins such as Cymel 202, Cymel 212, and Cymel 254; fully alkyl methylated melamine resins such as Cymel 300, Cymel 301, Cymel 303LF, and Cymel 350; and imino-type methylated melamine resins such as Cymel 325, Cymel 327, Cymel 703, Cymel 254, and Mycoat 212 (all manufactured by Ornex Japan Co., Ltd.), and Yuban 20SE60 (manufactured by Mitsui Chemicals, Inc., a butyl etherified melamine resin).

[0078] Preferably, the blocked isocyanate compound is obtained by reacting a blocking agent with at least one selected from the group consisting of the following 1) to 3): 1) aliphatic diisocyanates such as trimethylene diisocyanate and hexamethylene diisocyanate, and alicyclic diisocyanates such as isophorone diisocyanate; 2) bifunctional or more polyisocyanates obtained by reacting the diisocyanates with polyhydric alcohols such as ethylene glycol, trimethylolpropane, and pentol; and 3) isocyanurate bond-containing trifunctional isocyanates obtained by reacting 3 moles of the diisocyanates from 1).

[0079] Preferably used as blocking agents include, for example, monohydric alkyl (or aromatic) alcohols such as n-butanol, n-hexyl alcohol, 2-ethylhexanol, lauryl alcohol, phenolcarbinol, and methylphenylcarbinol; cellosolves such as ethylene glycol monohexyl ether and ethylene glycol mono-2-ethylhexyl ether; polyether-type terminal diols such as polyethylene glycol, polypropylene glycol, and polytetramethylene ether glycolphenol; polyester-type terminal polyols obtained from diols such as ethylene glycol, propylene glycol, and 1,4-butanediol, and dicarboxylic acids such as oxalic acid, succinic acid, adipic acid, suberic acid, and sebacic acid; phenols such as para-t-butylphenol and cresol; oximes such as dimethyl ketoxime, methyl ethyl ketoxime, methyl isobutyl ketoxime, methyl amyl ketoxime, and cyclohexanone oxime; and lactams represented by ε-caprolactam and γ-butyrolactam.

[0080] Specific examples of commercially available polyisocyanate compounds include Bahijur VPLS2186 (manufactured by Sumika Covestro Urethane Co., Ltd.).

[0081] A mixture of the amino resin and the blocked isocyanate compound may be used as the curing agent (B). It is more preferable to use the amino resin as the curing agent (B) in order to effectively obtain the effects of this disclosure.

[0082] In the anionic electrodeposition coating composition of this disclosure, the content of the curing agent (B) is preferably 20 to 50% by mass relative to 100% by mass of the total resin solids content of the coating film-forming resin (A) and the curing agent (B). When the content is 20% by mass or more, the curing reaction proceeds sufficiently and the desired coating performance is obtained. When the content is 50% by mass or less, the adhesion and flexibility of the coating film are enhanced.

[0083] The anionic electrodeposition coating composition in this disclosure may optionally contain a gloss modifier (C). Examples of the gloss modifier (C) include wax, silica particles, resin beads, and the like.

[0084] The wax is an aqueous dispersion of one or more waxes selected from the group consisting of natural waxes and polyolefin waxes. Specific examples of natural waxes include wood wax, carnauba wax, petroleum-based microcrystalline wax, paraffin wax, and mineral-based montan wax. Specific examples of polyolefin waxes include polyethylene, polypropylene, oxidized polyethylene, oxidized polypropylene, chlorided polyethylene, chlorinated polypropylene, and other polyolefin waxes.

[0085] Examples of methods for preparing the aqueous dispersion of the wax include, for example, a method of dissolving the wax in a hydrophilic organic solvent and then mechanically dispersing it in an aqueous solvent; a method of dispersing the wax in an aqueous solvent using a surfactant or a polymer emulsifier; and a method of reacting the wax with an α,β-unsaturated carboxylic acid to introduce carboxyl groups, and then emulsifying and dispersing the introduced carboxyl groups in an aqueous solvent by neutralizing the introduced carboxyl groups with an organic amine or an inorganic base. In these preparation methods, it is preferable to use polyethylene, polypropylene, oxidized polyethylene, oxidized polypropylene, etc., as the wax.

[0086] The wax is not particularly limited, but examples include the HI-DISPER® series from Gifu Cerac Co., Ltd., the AQUACER® series and AQUAMAT® series from Big Chemie Japan Co., Ltd., the ChemiPearl W® series from Mitsui Chemicals, and the Arrowbase® series from Unitika Corporation. The silica particles are not particularly limited, but may be manufactured by either a wet or dry method. Examples of silica particles include silica particles with an untreated surface, silica particles with an organic surface, and organic solvent-dispersible colloidal silica.

[0087] The average particle diameter of the silica particles is preferably 1 μm to 20 μm, more preferably 2 μm to 17 μm, for example, 2 μm to 15 μm or 2.5 μm to 15 μm. In this specification, the average particle diameter refers to the volume-average particle diameter (D50) obtained by conventional measuring instruments such as laser scattering or diffraction.

[0088] Commercially available silica particles may be used. Examples of commercially available products include the Silicia series such as Silicia 710, Silicia 740, and Silicia 550 (all manufactured by Fuji Silicia Chemical Co., Ltd.), the Mizukasil series such as Mizukasil P-73 (manufactured by Mizusawa Chemical Industry Co., Ltd.), the Nipseal and Nipgel series such as Nipseal E-200A and Nipsgel AZ-6A0 (all manufactured by Tosoh Silica Co., Ltd.), and the GASIL series such as GASIL HP270 and GASIL HP395 (all manufactured by PQ Corporation).

[0089] Examples of resins constituting the resin beads include acrylic resin, urethane resin, polyester resin, polyamide resin, polystyrene resin, polyethylene resin, melamine resin, urea resin, fluororesin, and polyacrylonitrile resin. Furthermore, "particulate" refers to particulate, spherical, or hollow spherical particles. The average particle size of the resin beads is preferably 1 μm or more and 20 μm or less, and may be, for example, 2 μm or more and 15 μm or less, 2.5 μm or more and 15 μm or less, or 5 μm or more and 10 μm or less.

[0090] Commercially available resin beads may be used. Examples of commercially available acrylic resin beads include Gantzpearl GM-0801 (manufactured by Aica Kogyo Co., Ltd.). Examples of commercially available urea resin beads include Pergo Pack M4 (manufactured by Lonza Co., Ltd.).

[0091] The gloss modifier (C) preferably contains at least one of wax, silica particles, and resin beads. This makes it possible to give the formed anionically cured electrodeposited coating a desirable matte appearance.

[0092] The gloss modifier (C) is preferably present in an amount of 2 to 20 parts by mass per 100 parts by mass of the resin solids content of the anionic electrodeposition coating composition. The content is more preferably 3 to 20 parts by mass, and even more preferably 4 to 19 parts by mass. In this specification, "resin solids content of the anionic electrodeposition coating composition" refers to the resin solids content of the film-forming resin contained in the electrodeposition coating composition, and specifically refers to the resin solids content of the film-forming resin (A) and the curing agent (B).

[0093] The aforementioned anionic electrodeposition coating composition may optionally contain a pigment. Examples of pigments include coloring pigments and luminous pigments.

[0094] Examples of the aforementioned coloring pigments include inorganic pigments such as titanium dioxide, carbon black, graphite, iron oxide, and cold dust; organic pigments such as phthalocyanine blue, phthalocyanine green, quinacridone, perylene, anthrapyrimidine, carbazole violet, anthrapyridine, azo orange, flavanthron yellow, isoindoline yellow, azo yellow, induthron blue, dibromanzathron red, perylene red, azo red, quinacridone red, benzimidazolon yellow, and anthraquinone red; and aluminum powder, alumina powder, bronze powder, copper powder, tin powder, zinc powder, iron phosphide, and finely atomized titanium. These may be used individually or in combination of two or more.

[0095] Examples of the aforementioned luminous pigments include foil pigments such as aluminum foil, bronze foil, tin foil, gold foil, silver foil, titanium metal foil, stainless steel foil, nickel-copper alloy foil, and foil-like phthalocyanine blue. These may be used individually or in combination of two or more.

[0096] The pigment (D) may be used alone or in combination of two or more types. Preferably, the pigment (D) is contained in an anionic electrodeposition coating composition in an amount of 0 to 60 parts by mass per 100 parts by mass of resin solids.

[0097] The anionic electrodeposition coating composition in this disclosure may be a clear coating containing a film-forming resin (A) and a curing agent (B) among the above components. Alternatively, it may be a matte coating containing a film-forming resin (A), a curing agent (B), and a gloss modifier (C). Alternatively, it may be a color clear coating or a colored coating containing a film-forming resin (A), a curing agent (B), and a pigment (D). Alternatively, it may be a color matte coating containing a film-forming resin (A), a curing agent (B), a gloss modifier (C), and a pigment (D).

[0098] The anionic electrodeposition coating composition in this disclosure preferably further comprises a curing catalyst (E). Examples of curing catalysts (E) include sulfonic acid catalysts such as n-butylbenzenesulfonic acid, amylbenzenesulfonic acid, octylbenzenesulfonic acid, dodecylbenzenesulfonic acid, octadecylbenzenesulfonic acid, dibutylbenzenesulfonic acid, i-propylnaphthalenesulfonic acid, p-toluenesulfonic acid, dodecylnaphthalenesulfonic acid, dinonylnaphthalenesulfonic acid, dinonylnaphthalenedisulfonic acid, and amine neutralized products of these sulfonic acid catalysts; tin compound catalysts such as dioctyl tin dilaurate, dioctyl tin dibenzoate, and dibutyl tin dibenzoate; and the like.

[0099] It is more preferable to use the sulfonic acid catalyst as the curing catalyst (E), and even more preferable to use one or more selected from the group consisting of dodecylbenzenesulfonic acid, p-toluenesulfonic acid, dodecylnaphthalenesulfonic acid, dinonylnaphthalenesulfonic acid, and dinonylnaphthalenedisulfonic acid. In the anionic electrodeposition coating composition of this disclosure, by using such a curing catalyst (E), the heating temperature in the heat curing step can be set to relatively low heating conditions, such as 100 to 160°C, preferably 110 to 160°C. Furthermore, even if the heating temperature in the heat curing step is relatively low as described above, there is an advantage in that a cured electrodeposition coating film with good performance such as scratch resistance can be formed.

[0100] The amount of curing catalyst (E) contained in the anionic electrodeposition coating composition is preferably 0.05 to 10 parts by mass, more preferably 0.1 to 5 parts by mass, and even more preferably 0.2 to 4 parts by mass, based on 100 parts by mass of the total solid content of the coating resin (A) and crosslinking agent (B). By using within the above range, a cured electrodeposition coating film with good performance such as scratch resistance can be formed.

[0101] (Other ingredients) The anionic electrodeposition coating composition in this disclosure is an aqueous coating composition containing water as the main solvent. On the other hand, the anionic electrodeposition coating composition in this disclosure may optionally contain an organic solvent. Specific examples of organic solvents include alcohols such as methanol, isopropanol, ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, and methoxypropanol; ethers such as ethylene glycol monobutyl ether, propylene glycol monobutyl ether, and diethylene glycol monobutyl ether; ketones such as acetylacetone; esters such as ethylene glycol monoethyl ether acetate; and hexane. These organic solvents may be used individually, or two or more may be used in combination. However, from the viewpoint of VOC emission regulations, it is preferable to use as little organic solvent as possible.

[0102] The anionic electrodeposition coating compositions in this disclosure may optionally include other additives known in the art, such as pigments other than pigment (D) (extender pigments, rust inhibitors), film-forming aids, drying retardants, viscosity modifiers, preservatives, antifungal agents, antiseptics, defoaming agents, light stabilizers (e.g., hindered amine-based light stabilizers), antioxidants, ultraviolet absorbers, pH adjusters, etc.

[0103] The pigments other than pigment (D) that may be included in the anionic electrodeposition coating composition in this disclosure are not particularly limited and include, for example, extender pigments such as barium sulfate, talc, kaolin, calcium carbonate, and barium sulfate; phosphomolybthenate-based rust inhibitors such as aluminum zinc phosphomolybthenate, zinc phosphomolybthenate, and calcium phosphomolybthenate, and rust inhibitors such as molybthenate-based rust inhibitors and phosphate-based rust inhibitors; and the like.

[0104] (Anionic pigment dispersion paste) When incorporating pigments into an anionic electrodeposition coating composition, it is preferable to prepare the pigments in the form of a pigment dispersion paste beforehand, from the viewpoint of ease of dispersibility. An anionic pigment dispersion paste can be prepared by dispersing the pigments in an anionic pigment dispersion resin. As the anionic pigment dispersion resin, for example, a modified acrylic resin prepared using acrylic acid esters, acrylic acid, and azonitrile compounds can be used. An anionic pigment dispersion paste can be prepared by mixing the anionic pigment dispersion resin, pigment, aqueous medium, and a neutralizing base as needed, and then dispersing the mixture using a commonly used dispersion device such as a ball mill or sand grind mill until the particle size of the pigments in the mixture reaches a predetermined uniform particle size. Examples of neutralizing bases include ammonia; organic amines such as diethylamine, ethylethanolamine, diethanolamine, monoethanolamine, monopropanolamine, isopropanolamine, ethylaminoethylamine, hydroxyethylamine, diethylenetriamine, and triethylamine; and basic compounds such as alkali metal hydroxides such as sodium hydroxide and potassium hydroxide. Generally, anionic pigment dispersion pastes are prepared to have a solid content of 20-70% by mass, preferably 25-65% by mass.

[0105] As the anionic pigment dispersion paste, commercially available anionic coloring pastes may be used. Examples of commercially available products include Emakol NS Ochre 4622, Emakol Black 3929 (manufactured by Sanyo Shikiso Co., Ltd.), NAF5002 White, NAF1053 Blue, and NAF1032 Red (manufactured by Dainichi Seika Kogyo Co., Ltd.).

[0106] (Method for preparing anionic electrodeposition coating composition) The anionic electrodeposition coating composition in this disclosure can be prepared by dispersing the film-forming resin (A), curing agent (B), gloss modifier (C), pigment (D), curing catalyst, and optionally an anionic pigment dispersion paste in an aqueous medium. The aqueous medium is water, or a mixture of water and the aforementioned organic solvent. Deionized water is preferred as the water. A neutralizing base may also be used as needed.

[0107] The amount of neutralizing base used should preferably be sufficient to neutralize at least 30%, more preferably 50-120%, of the anionic groups (carboxyl groups) present in the film-forming resin (A). The pH of the anionic electrodeposition coating composition may also be adjusted using the neutralizing base. The pH of the anionic electrodeposition coating composition is preferably 7.0-9.0, and more preferably 7.0-8.5.

[0108] The anionic electrodeposition coating process of this disclosure includes an electrodeposition coating step of immersing an object to be coated in an anionic electrodeposition coating composition and applying a voltage to form an electrodeposition coating film, and a heat curing step of heating and curing the electrodeposition coating film formed in the electrodeposition coating step to form a cured electrodeposition coating film.

[0109] The electrodeposition coating process involves immersing the object to be coated as the anode in an anionic electrodeposition coating composition, and then applying a voltage of typically 10 to 300V between the anode and the cathode. A voltage of 50 to 150V is preferred. The coating temperature of the anionic electrodeposition coating composition during electrodeposition is preferably 10 to 40°C, and more preferably 20 to 30°C. The time for applying the voltage can be arbitrarily selected according to the electrodeposition coating conditions, for example, 10 seconds to 5 minutes, and preferably 30 seconds to 2 minutes. By applying the voltage, an electrodeposited coating film is formed on the surface of the object to be coated. The formed electrodeposited coating film may be washed with water if necessary.

[0110] In the heat curing process, the electrodeposited coating film formed in the painting process is heated, causing the electrodeposited coating film to harden and a cured electrodeposited coating film to be obtained. The heating temperature in the heat curing process is 110 to 230°C.

[0111] The heating time for the electrodeposited coating in the heat curing process can be appropriately selected depending on the size of the object to be coated and the heating temperature. The heating time is, for example, 5 to 60 minutes, preferably 10 to 30 minutes.

[0112] The thickness of the formed cured electrodeposited coating film is preferably 5 to 30 μm, and more preferably 10 to 25 μm.

[0113] (Other processes) The magnesium material surface treatment process according to this embodiment may include steps other than those described above. For example, it may include an alkaline degreasing step to degrease the surface of the magnesium material before the pretreatment step, or an acid etching step and a desmutting step as needed after the alkaline degreasing step and before the pretreatment step. It may also include a post-chemical treatment water washing step after the chemical treatment step and before the painting step.

[0114] The alkaline degreasing process involves applying an alkaline degreasing agent, such as a phosphorus-free and nitrogen-free degreasing cleaning solution, to the surface of the magnesium material by methods such as spraying or immersion, to remove oil adhering to the surface of the magnesium material. A preliminary degreasing treatment may be performed before the alkaline degreasing process.

[0115] The acid etching process involves contacting the surface of a magnesium material with an acidic aqueous solution by methods such as spraying or immersion. Examples of acidic aqueous solutions include inorganic acids such as phosphoric acid, nitric acid, sulfuric acid, hydrofluoric acid, and hydrofluorosilicic acid, as well as organic acids such as oxalic acid and acetic acid. These may be used individually or in combination of two or more.

[0116] The desmutting process involves removing the smut adhering to the magnesium material surface during the acid etching process and stabilizing the magnesium material surface by coating it with hydroxide. The desmutting process can be carried out using an alkaline aqueous solution. The alkaline compound used in the alkaline aqueous solution is not particularly limited and can include, for example, compounds such as sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate, and ammonia.

[0117] The acid etching process and the desmutting process may be repeated multiple times in this order. Furthermore, a water rinse may be performed after each process.

[0118] The post-chemical treatment rinsing process is carried out by one or more spray treatments or immersion rinsing, within a range that does not affect the adhesion and corrosion resistance after painting. The final rinsing treatment is preferably performed with deionized water or pure water. After the post-chemical treatment rinsing process, a drying step for the chemically treated metal may be provided as needed.

[0119] (Magnesium material) The magnesium material relating to this disclosure includes pure magnesium or magnesium alloys. The magnesium has a density of 1.8 g / cm³. 3 Aluminum, which has the lowest density among currently used metal materials and is widely used in various applications as a lightweighting material for metals, has a density of 2.7 g / cm³. 3 It is also only 2 / 3 the size of aluminum alloy. Furthermore, magnesium alloy has almost the same density as carbon fiber reinforced plastic (CFRP), and is also strong, highly recyclable, and abundant in resources. For these reasons, magnesium alloy has recently attracted attention as a lightweight material to replace aluminum alloy and is being used in a wide range of fields. Consequently, magnesium alloy is being applied to home appliances, office automation equipment, mobile devices, automobile parts, etc. Specifically, to electronic devices such as cameras, PCs, TVs, and smartphones, as well as doorknobs, kitchen components, and bicycle parts. In recent years, one of the drawbacks of magnesium alloy, its high flammability, has been addressed by developing flame-retardant magnesium alloys with increased ignition temperatures through the addition of calcium, and their application to large structural components, particularly components for high-speed transport vehicles such as Shinkansen bullet trains, is being considered.

[0120] Examples of magnesium alloys include Mg-Al-Zn alloys, Mg-Zn alloys, Mg-Al-Zn-Mn alloys, Mg-RE (rare earth element) alloys, and Y-added alloys. Specific examples of the above alloys include Al-containing magnesium alloys such as AZ31, AZ31B, AZ61, AZ91, AZ91D, AM50, AM60, and AM60B, as specified in SAE (Society of Automotive Engineers) J465. Here, "AZ" and "AM" indicate the added metal elements; "A" stands for aluminum, "M" for manganese, and "Z" for zinc. The numbers following these notations indicate the proportion of these added elements; for example, AZ91 contains 9% aluminum and 1% zinc. [Examples]

[0121] The contents of this disclosure will be described in more detail below based on the examples. The contents of this disclosure are not limited to the descriptions of the following examples. In the examples, "parts," "%," and "ppm" are on a mass basis unless otherwise specified.

[0122] (Manufacturing Example 1) Preparation of coating resin (A) A 2L reaction vessel equipped with a stirrer, condenser, nitrogen inlet tube, and a thermometer connected to a temperature controller was charged with 560 parts by mass of isopropyl alcohol and 140 parts by mass of ethylene glycol monobutyl ether as solvents, and heated to 80°C under a nitrogen atmosphere. In this reaction vessel, a mixed solution of 35 parts by mass of acrylic acid, 133 parts by mass of 2-hydroxyethyl methacrylate, 385 parts by mass of methyl methacrylate, 21 parts by mass of ethyl acrylate, 35 parts by mass of n-butyl acrylate, 91 parts by mass of 2-ethylhexyl acrylate, and 63 parts by mass of dimethyl 2,2'-azobis(2-methylpropionate) as an initiator was added dropwise at a constant rate over 3 hours, and then held at 80°C for 4 hours to obtain acrylic resin (A-1) as a coating resin (A) (acid value: 38 mg KOH / g, hydroxyl value: 80 mg KOH / g, weight-average molecular weight: 5,000, solid content concentration: 50% by mass).

[0123] (Manufacturing examples 2-7) Acrylic resins (A-2) to (A-7) were prepared in the same manner as in Production Example 1, except that the monomer species and amounts were changed as shown in Table 1. The characteristic values ​​of each resin, such as the solids content hydroxyl value, are shown in Table 1.

[0124] [Table 1]

[0125] The initiators used in the above-mentioned manufacturing process are as follows: (Initiator) • Dimethyl 2,2'-azobis(2-methylpropionate): Manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. • Azobisbutyrillonitrile: Manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.

[0126] (Example 1) Preparation of anionic electrodeposition coating composition 1 520 parts by mass of the acrylic resin (A-1) prepared in Production Example 1, 140 parts by mass of Cymel 235 (a melamine resin) as a curing agent (B-1), and 6 parts by mass of triethylamine were mixed. The resulting mixture was diluted to a solid content of 10% using deionized water to obtain anionic electrodeposition coating composition 1.

[0127] Anionic electrodeposition coating compositions for other examples and comparative examples were prepared in the same manner as anionic electrodeposition coating composition 1, except that the types and amounts of each component were changed as shown in Tables 2 and 3. Note that the amounts of each component refer to the amounts in their natural state, including volatile components such as solvents.

[0128] The components used in the anionic electrodeposition coating composition are as follows: (B) Hardener (B-1) Cymel 235; fully alkyl methyl / butyl mixed etherified melamine resin, manufactured by Ornex Japan, solid content concentration: 100% by mass (B-2) Bahijur VPLS2186; Blocked isocyanate compound, manufactured by Sumika Covestro Urethane Co., Ltd., Solid content concentration: 70% by mass (C) Gloss adjuster (C-1) NipSeal E200A; Silica, manufactured by Tosoh Silica Co., Ltd., Solid content concentration: 100% by mass (C-2) Gantzpearl GM0801; Acrylic resin beads, manufactured by Aica Kogyo Co., Ltd., Solid content concentration: 100% by mass (D) Pigment (D-1) NAF5002 White; Aqueous dispersion of titanium dioxide, manufactured by Dainichi Seika Kogyo Co., Ltd., Pigment concentration: 65% by mass (D-2) Emacol Black 3929; Aqueous dispersion of carbon black, manufactured by Sanyo Shikkei Co., Ltd., Pigment concentration: 26% by mass

[0129] As the magnesium material, magnesium alloy AZ91B (50mm x 100mm) was used and subjected to degreasing and surface treatment (pretreatment, chemical conversion treatment) under the following conditions.

[0130] (Degreasing process 1) As a degreasing treatment, the magnesium material was immersed in 2% by mass of "Surf Cleaner EC90" (manufactured by Nippon Paint Surf Chemicals Co., Ltd.; degreasing agent) at 40°C for 2 minutes. Following degreasing, the material was sprayed with tap water for 30 seconds as a rinsing treatment.

[0131] (Pre-treatment step 1) The magnesium material, after the degreasing treatment, was pretreated by immersion using a pretreatment agent adjusted to contain 500 ppm by mass of amino group-containing compound A1 and have a pH of 10. Specifically, the temperature of the pretreatment agent was adjusted to 25°C, and the magnesium material was immersed for 60 seconds. Ammonia water or nitric acid was used to adjust the pH of the pretreatment agent.

[0132] (Chemical treatment process 1) The magnesium material, after the aforementioned pretreatment, was subjected to a chemical conversion treatment by immersion using a chemical conversion agent mainly composed of zircon hydrofluoric acid, adjusted to have a Zr concentration of 500 ppm by mass, a concentration of amino group-containing compound A1 of 800 ppm by mass, and a pH of 6.2. Specifically, the temperature of the chemical conversion agent was adjusted to 35°C, and the magnesium material was immersed for 120 seconds. Sodium hydroxide was used to adjust the pH of the chemical conversion agent.

[0133] The components used in the pretreatment agent and chemical treatment agent are as follows: (Amino group-containing compound) A1: KBM-603; N-2-(aminoethyl)-3-aminopropyltrimethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd., active ingredient concentration: 100% by mass A2:PAA-D19-HCl; Allylamine hydrochloride / diallylamine hydrochloride copolymer, manufactured by Nitto Boseki Medical Co., Ltd., weight-average molecular weight: 40,000, solid content concentration: 21% by mass A3: KBM-903; 3-aminopropyltrimethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd., active ingredient concentration: 100% by mass

[0134] (Chemical treatment agent (main component)) Zr: A chemical treatment agent containing zirconhydrofluoric acid as its main component.

[0135] (Anionic electrodeposition coating process 1) The magnesium material after the chemical conversion treatment was immersed in the prepared anionic electrodeposition coating composition, and a DC voltage of 80-200V was applied for 2.5 minutes to electrodeposit the coating so that the cured film thickness was 20 μm. The resulting electrodeposited coating was heated and dried at 180°C for 20 minutes to obtain an electrodeposited coating plate having a cured electrodeposited coating. The obtained electrodeposited coating plate was evaluated according to the following criteria. The evaluation results are shown in Tables 2 and 3 below.

[0136] For the other examples and comparative examples besides Example 1, the electrodeposited coated boards used for evaluation in Tables 2 and 3 were obtained under the conditions shown below. (Degreasing process) Degreasing treatments according to other examples and comparative examples were performed in the same manner as in the degreasing treatment step 1 described above.

[0137] (Pre-treatment process) Except for changing the type, concentration, and pH of the amino group-containing compound and the pretreatment agent as shown in Tables 2 and 3, the pretreatment for the other examples and comparative examples was carried out in the same manner as in pretreatment step 1. Note that no pretreatment was performed for Comparative Examples 5 and 10.

[0138] (Chemical treatment process) Except for changing the type and concentration of the amino group-containing compound as shown in Tables 2 and 3, the chemical conversion treatment for the other examples and comparative examples was carried out in the same manner as in chemical conversion treatment step 1. Note that comparative examples 9 and 10 did not undergo chemical conversion treatment.

[0139] (Anionic electrodeposition coating process) Using the prepared anionic electrodeposition coating composition, electrodeposition coating was performed in the same manner as in the anionic electrodeposition coating step 1, and the heating temperature was set to the temperatures shown in Tables 2 and 3 to obtain coated plates having cured electrodeposition coating films according to other examples and comparative examples.

[0140] [Table 2]

[0141] [Table 3]

[0142] (Evaluation of coating appearance) The paint film appearance of the painted boards for each example and comparative example immediately after painting was evaluated visually according to the following evaluation criteria, considering factors such as paint repellency, unevenness, and transparency. A circle (○) was considered a passing grade in all cases.

[0143] (Evaluation Criteria) <Hajiki> ○: No errors were observed at all. △: No or fewer misses are observed. ×: Four or more instances of the markings are observed. <Village> ○: No inconsistencies were observed at all. △: Slight unevenness is observed. ×: Unevenness is visible throughout. <Transparency> ○: No cloudiness is observed at all. △: Slight overcasting is observed. ×: Significant turbidity is observed throughout.

[0144] (Pencil hardness test) The pencil hardness of painted boards was measured in accordance with JIS K 5600-5-4. Specifically, pencils (Mitsubishi Pencil Co., Ltd.: Mitsubishi UNI (6B-5B-4B-3B-2B-HB-FH-2H-3H-4H-5H-6H) for scratch hardness testing by the Japan Paint Inspection Association) were pressed onto the surface of the painted boards at a scratching angle of 45° and with a load of 750g, and moved around. The presence or absence of paint film defects caused by the pencil lead was visually observed. Two types of paint film defects were evaluated: 1) plastic deformation, which creates a permanent indentation in the paint film but does not result in cohesive failure, and 2) cohesive failure, which is visible to the naked eye as scratches or fractures where the paint film material has been removed from the surface. For example, in the test using an H pencil, if no such paint film defects occurred, it was judged to be H or higher. The test was performed twice, and if the results of the two tests differed, the test was repeated and the evaluation was performed in the same manner, starting from one level lower.

[0145] (Evaluation Criteria) <Plastic deformation> A score of H or higher was considered a passing grade. <Aggregate failure> A score of 3H or higher was considered a passing grade.

[0146] (Moisture resistance (HCT)) The coated panels obtained in the examples and comparative examples were left to stand for 96 hours in a constant temperature and humidity test chamber at a temperature of 60°C ± 3°C and a humidity of 95%. After the test, the condition of the coating (dissolution, blistering, cracking, chipping, and peeling) was evaluated visually according to the following evaluation criteria. ○ was considered a pass.

[0147] (Evaluation Criteria) ○: No dissolution, blistering, cracking, chipping, or peeling of the coating film was observed. ×: Dissolution, blistering, cracking, chipping, or peeling is observed in the coating.

[0148] (Corrosion resistance (Salt spray test (SST))) The painted boards obtained in the examples and comparative examples were subjected to a salt spray test (SST) for 48 hours using a salt spray tester ST-11L (manufactured by Suga Test Instruments Co., Ltd.) in accordance with the neutral salt spray resistance test method described in JIS K 5600-7-1 (JIS Z 2371). After the test, the condition of rust and blistering on the flat surface, and the presence or absence of rust, blistering, discoloration, and corrosion of the substrate on the edges were visually evaluated according to the following evaluation criteria. A circle (○) was considered a pass for the flat surface, and a score of 3 or higher was considered a pass for the edges.

[0149] (Evaluation Criteria) <Plane part> ○: No rust or blistering observed. △: Slight rust and blistering are present. ×: Rust and blistering are clearly visible. <Edge section> 4 points: No rust or blistering observed. 3 points: Slight discoloration is observed. Points 2: White rust spots, discoloration, and blistering are observed. 1 point: The base material is corroded and damaged.

[0150] The results shown in Table 2 confirm that magnesium materials subjected to the pretreatment, chemical conversion treatment, and electrodeposition coating according to each example exhibited good corrosion resistance, moisture resistance, and coating appearance. As shown in Table 3, Comparative Example 1 was an example in which the weight-average molecular weight of the acrylic resin (A) used to form the coating film was less than 5,000, and the coating film appearance (repellency), pencil hardness, moisture resistance, and corrosion resistance were not sufficiently satisfactory. Comparative Example 2 is an example in which the acrylic resin (A), which is the film-forming resin, has a hydroxyl value of less than 30, and the film appearance (unevenness), pencil hardness, moisture resistance, and corrosion resistance were not sufficiently satisfactory. Comparative Examples 3 and 4 were examples where the heating temperature in the heat curing step of the electrodeposition coating process was less than 110°C, and the moisture resistance and corrosion resistance were not sufficiently satisfactory. Comparative Example 5 lacked a pretreatment step, and therefore did not fully satisfy the requirements for pencil hardness (plastic deformation), moisture resistance, and corrosion resistance. Comparative Examples 6 and 7 were cases where the pH of the pretreatment agent exceeded 12.0, and the coating appearance, pencil hardness, moisture resistance, and corrosion resistance were not sufficiently satisfactory. Comparative Example 8 was an example lacking an amino group-containing compound in the chemical treatment agent, and therefore did not provide satisfactory moisture resistance and corrosion resistance. Comparative Example 9 lacked a chemical conversion treatment process, and the coating film appearance, pencil hardness, moisture resistance, and corrosion resistance were not sufficiently satisfactory. Comparative Example 10 lacked a pretreatment step and a chemical conversion treatment step, and the coating film appearance, pencil hardness, moisture resistance, and corrosion resistance were not sufficiently satisfactory.

Claims

1. A process for surface treating magnesium materials, A pretreatment step in which the magnesium material is treated with a pretreatment agent, A chemical treatment step in which the magnesium material that has undergone the above pretreatment step is chemically treated with a chemical treatment agent, The process includes an anionic electrodeposition coating step in which the magnesium material that has undergone the chemical conversion treatment step is anionic electrodeposition coated, The aforementioned pretreatment agent contains an amino group-containing compound and has a pH of 6.0 or higher and less than 12.

0. The aforementioned chemical treatment agent comprises a zirconium compound and an amino group-containing compound. The anionic electrodeposition coating process includes an electrodeposition coating step of immersing the magnesium material in an anionic electrodeposition coating composition and applying a voltage to form an electrodeposition coating film, and a heat curing step of heating and curing the electrodeposition coating film formed in the electrodeposition coating step to form a cured electrodeposition coating film. The anionic electrodeposition coating composition comprises a film-forming resin (A) and a curing agent (B), The aforementioned coating-forming resin (A) comprises an acrylic resin having carboxyl groups and hydroxyl groups, has a weight-average molecular weight of 5,000 to 100,000, and a hydroxyl value of 30 to 200 mgKOH / g. The aforementioned heat curing step involves a heating temperature of 110 to 230°C. Magnesium material surface treatment process.

2. The magnesium material surface treatment process according to claim 1, wherein the curing agent (B) is at least one selected from the group consisting of amino resins and blocked isocyanate compounds.

3. The magnesium material surface treatment process according to claim 1, wherein the anionic electrodeposition coating composition further comprises a gloss modifier (C).

4. The magnesium material surface treatment process according to any one of claims 1 to 3, wherein the anionic electrodeposition coating composition further comprises a pigment (D).

5. The amino group-containing compound is at least one selected from the group consisting of amino group-containing alkoxysilane compounds and polymers having an allylamine unit. The magnesium material surface treatment process according to any one of claims 1 to 3, wherein the amino group-containing compound is contained in a concentration range of 50 ppm by mass or more and 1,500 ppm by mass or less as solid content relative to the total mass of the pretreatment agent.

6. The magnesium material surface treatment process according to claim 5, wherein the amino group-containing compound contained in the chemical treatment agent and the amino group-containing compound contained in the pretreatment agent are of the same type.

7. A magnesium material surface treatment process according to any one of claims 1 to 3, wherein, following the pretreatment step, the pretreated magnesium material is chemically treated by the chemical conversion treatment step without going through any other steps.

8. The magnesium material surface treatment process according to any one of claims 1 to 3, wherein the amino group-containing compound is an amino group-containing alkoxysilane compound.

9. The magnesium material surface treatment process according to claim 8, wherein the ratio of the solid content mass of the amino group-containing alkoxysilane compound to the total solid content mass of the pretreatment agent is 95% or more.

10. The magnesium material surface treatment process according to any one of claims 1 to 3, wherein the pretreatment agent does not contain an epoxy group-containing silane compound.

11. A treatment agent set used in a magnesium material surface treatment process according to any one of claims 1 to 3, The pretreatment agent used in the aforementioned pretreatment step, The chemical treatment agent used in the aforementioned chemical treatment process, A treatment agent set comprising the anionic electrodeposition coating composition used in the anionic electrodeposition coating process.

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