KR102144485B1 - Magnesium-based metallic member and process for producing magnesium-based metallic member - Google Patents

Abstract

It provides a magnesium-based metal member capable of reducing deterioration of a coating film and maintaining a metallic texture, and a method of manufacturing the same. The magnesium-based metal member includes a substrate made of a magnesium-based metal and a transparent coating film formed on the surface of the substrate. The coating film includes a transparent anticorrosive film formed on the surface of the substrate, and one or more transparent coating films formed on the anticorrosive film and made of a resin. The coating film has at least one weather-resistant layer to which an ultraviolet absorber is added.

Description

A magnesium-based metal member, and a method of manufacturing a magnesium-based metal member {MAGNESIUM-BASED METALLIC MEMBER AND PROCESS FOR PRODUCING MAGNESIUM-BASED METALLIC MEMBER}

The present invention relates to a magnesium-based metal member comprising a substrate made of a magnesium-based metal, a transparent coating film formed on the surface of the substrate, and a method for manufacturing the same.

Since magnesium alloys have excellent properties such as light weight and high specific strength, they are used in various members such as cases of portable electric and electronic devices such as mobile phones and notebook personal computers. In recent years, there is a demand for a magnesium alloy member such as the case to have a metallic texture to produce a sense of quality.

On the other hand, since magnesium is an active metal, it is easily corroded, and in a magnesium alloy member, a coating layer having corrosion resistance is formed on the surface of the substrate.

For example, Patent Literature 1 discloses a magnesium alloy member in which a metal texture is improved by subjecting the surface of a substrate made of a magnesium alloy to fine irregularities such as diamond cutting, and forming a transparent coating layer on the surface of the substrate. In addition, it is described that this coating layer has a multilayer structure including an anticorrosive layer formed by an anticorrosive treatment (chemical conversion treatment or anodizing treatment) and a coating layer formed thereon of a resin such as an acrylic resin.

Patent Document 1: Japanese Patent Publication No. 2009-120877

In the magnesium alloy member comprising the above-described transparent coating layer, it is required to maintain the metallic texture over a long period of time.

The present invention has been made in view of the above circumstances, and one of its objects is to provide a magnesium-based metal member capable of maintaining a metallic texture over a long period of time with little deterioration of a coating film, and a method of manufacturing the same.

The magnesium-based metal member of the present invention includes a substrate made of a magnesium-based metal and a transparent coating film formed on the surface of the substrate. The coating film includes a transparent anticorrosive film formed on the surface of the substrate, and one or more transparent coating films formed on the anticorrosive film and made of a resin. And, the coating film has at least one weather-resistant layer to which an ultraviolet absorber is added to the resin.

According to the magnesium-based metal (hereinafter, simply referred to as “Mg-based metal”) member of the present invention, the coating film has at least one weather-resistant layer, thereby suppressing aging deterioration due to ultraviolet rays of the resin forming the coating film. can do. In other words, by imparting weather resistance to the coating film, yellowing of the coating film, reduction of gloss, cracking, peeling, and deterioration such as blasting due to ultraviolet rays is small, and transparency and adhesion of the coating film can be secured over a long period of time, and the metal texture can be maintained. have. In addition, in the present invention, the Mg-based metal is a metal containing Mg as a main component, and the Mg-based metal contains pure Mg and Mg alloy.

Examples of the resin for forming the coating film include an epoxy resin, an acrylic resin, a urethane resin, a polyester resin, and a fluororesin, and these resins may be used alone or in combination of two or more. For example, when the coating film has a multilayer structure of two or more layers, it is also possible to change the resin for forming each layer. Further, each layer may be formed by coating a paint in which two or more types of resins are mixed. The coating film may be colored and transparent, but if it is colorless and transparent, it is easy to feel the color tone and atmosphere of the Mg-based metal substrate itself. In the present invention, since both the anticorrosive film and the coating film are transparent films, the metallic texture of the substrate itself can be felt. In addition, in the present invention, "transparent" means that the substrate has a degree of transparency that can be visually confirmed.

As an aspect of the magnesium-based metal member of the present invention, a coating film made of an epoxy resin is mentioned.

Conventional magnesium alloy members use acrylic resin to form a single coating layer, but acrylic resin has low adhesion to the Mg-based metal substrate (anticorrosive film), and the coating layer may be peeled off by prolonged use. There is. When the coating layer is peeled off, corrosion resistance is lowered, and the metal texture is damaged by corrosion of the substrate. According to the above configuration of the present invention, since the coating film formed on the anticorrosive film is formed of an epoxy resin, the adhesion of the coating film to the substrate (anticorrosive film) can be improved.

As another aspect of the magnesium-based metal member of the present invention, the coating film includes an innermost layer formed directly on the anticorrosive film, and at least one outer layer formed on the innermost layer, and the innermost layer is made of an epoxy resin. have.

According to the above configuration of the present invention, since the coating film has a multilayer structure of at least two or more layers including an innermost layer and an outer layer, and the innermost layer is formed of an epoxy resin, the adhesion of the coating film to the substrate (anticorrosive film) can be improved. have.

In addition, in the present invention, the epoxy resin is a resin containing an epoxy resin as a main component, and an epoxy resin is obtained by adding other resins such as acrylic resins, polyester resins or modified resins thereof, or a curing agent. Also good.

As the epoxy resin, bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol AD type epoxy resin, bisphenol S type epoxy resin, brominated bisphenol A type epoxy resin, hydrogenated bisphenol A type epoxy resin, and the like can be used. Among the epoxy resins, phosphoric acid-modified epoxy resins having more excellent adhesion to the substrate (anticorrosive film) are suitable. The phosphoric acid-modified epoxy resin can be obtained by reacting a phosphoric acid compound with a bisphenol-type epoxy resin. In this case, the bisphenol type epoxy resin to be used is not particularly limited, and the above bisphenol type epoxy resin can be used. Among the above-described bisphenol type epoxy resins, bisphenol A type epoxy resins are preferable.

As the phosphoric acid compound, phosphoric acids having two or more hydroxyl groups bonded to the phosphorus atom are used. Specifically, in addition to orthophosphoric acid or phosphonic acid, condensed phosphoric acid such as metaphosphoric acid, pyrophosphoric acid or tripolyphosphoric acid, monomethylphosphoric acid or mono Orthophosphoric acid esters, such as butyl phosphoric acid, monooctyl phosphoric acid, and monophenyl phosphoric acid, etc. are mentioned.

As the curing agent added to the epoxy resin, it is preferable to use a melamine compound or an isocyanate compound having good adhesion to the anticorrosive film. Methoxylated methylolmelamine, butoxylated methylolmelamine, etc. are used as the melamine compound. As the isocyanate compound, tolylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, or the like, or a resin obtained by biuret modification, adduct modification, or isocyanurate modification of these isocyanates is used. It is more preferable that the isocyanate compound is a blocked isocyanate compound in which an isocyanate group is blocked by a blocking agent. This is because isocyanate groups are easy to react, and if the coating composition is left at room temperature for a long time, the reaction gradually proceeds, and there is a fear that the properties of the composition may change.

Examples of the blocking agent include oximes such as methyl ethyl ketooxime, acetoxime, cyclohexanone oxime, acetophenone oxime, and benzophenone oxime; phenols such as m-cresol and xylenol; Alcohols such as butanol, 2-ethylhexanol, cyclohexanol, and ethylene glycol monoethyl ether; lactams such as ε-caprolactam, δ-valerolactam, and γ-butyrolactam; Diketones such as diethyl malonate and acetoacetic acid ester; Mercaptans such as thiophenol; Urea such as thioyoic acid; Imidazoles; Carbamic acids; And the like may be mentioned. Among them, oximes, phenols, alcohols, lactams, and diketones are preferable.

After coating the epoxy resin, a hard coating film can be formed by curing by a curing method such as hot baking or ultraviolet irradiation.

Compared to acrylic resins, epoxy-based resins have high adhesion to the base material (anticorrosive film) of Mg-based metals, but on the other hand, they have low weather resistance and are easily deteriorated by ultraviolet rays, so it is difficult to maintain transparency and adhesion over a long period of time. . However, in the present invention, when at least one layer of the coating film (if the coating film is a single layer itself) is a weather-resistant layer, deterioration due to ultraviolet rays of the coating film itself or the epoxy resin forming the innermost layer can be suppressed. , Transparency and adhesion can be maintained over a long period of time. As will be described later, it is also possible to add an ultraviolet absorber to the epoxy resin forming the innermost layer to make the innermost layer itself a weather-resistant layer.

In the above-described aspect in which the coating film includes an innermost layer and at least one outer layer, at least one of the outer layers is made of an acrylic resin.

When at least one of the outer layers is formed of an acrylic resin, abrasion resistance such as chipping resistance and scratch resistance can be imparted to the coating film. In particular, when the innermost layer in the coating film is formed of an epoxy resin and the outermost layer is formed of an acrylic resin, it is possible to achieve both adhesion and abrasion resistance of the coating film. After painting, the acrylic resin can be cured by a curing method such as hot baking or ultraviolet irradiation.

In the present invention, the acrylic resin is a resin containing an acrylic resin as a main component, and may be obtained by adding other resins such as fluororesin, polyester resin, urethane resin, modified urethane resin, or a curing agent to the acrylic resin. good. When the coating film has a multilayer structure, it is preferable that the outermost layer is made of an acrylic resin.

Acrylic resin can be obtained by polymerizing an acrylic monomer using a polymerization initiator, and a modified acrylic resin is also included. Examples of acrylic monomers include methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, hexyl acrylate, octyl acrylate, lauryl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, iso methacrylate Alkyl esters of acrylic acid or methacrylic acid such as propyl, butyl methacrylate, hexyl methacrylate, octyl methacrylate, and lauryl methacrylate; Alkoxyalkyl esters of acrylic acid or methacrylic acid, such as methoxyethyl acrylate, methoxyethyl methacrylate, methoxybutyl acrylate, methoxybutyl methacrylate, ethoxybutyl acrylate, and ethoxybutyl methacrylate; Alkenyl esters of acrylic acid or methacrylic acid such as allyl acrylate and allyl methacrylate; Hydroxyalkyl esters of acrylic acid or methacrylic acid such as hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, hydroxypropyl acrylate, and hydroxypropyl methacrylate ; Alkenyloxyalkyl esters of acrylic acid or methacrylic acid such as allyloxyethyl acrylate and allyloxyethyl methacrylate; Acrylamide, acrylonitrile, methacrylonitrile, acrylic acid, methacrylic acid, and the like. These may be used alone or in combination of two or more. As the acrylic monomer, methacrylic acids excellent in transparency are preferable, and methyl methacrylate is particularly suitable. In addition, you may use other vinyl monomers together with such an acrylic monomer. Other vinyl monomers include vinyl aromatic compounds such as styrene, α-methylstyrene, vinyltoluene, and p-chlorostyrene; Olefin compounds such as butadiene, isoprene, and chloroprene; Vinyl acetate, allyl alcohol, maleic acid, and the like.

Examples of the polymerization initiator include peroxides such as benzoyl peroxide and t-butylperoxy-2ethylhexanoate; Azo compounds, such as azobisisobutyronitrile and azobisdimethylvaleronitrile, are used.

As the curing agent added to the acrylic resin, it is preferable to use a melamine compound or an isocyanate compound having good adhesion to the innermost layer (eg, epoxy resin). Methoxylated methylolmelamine, butoxylated methylolmelamine, etc. are used as the melamine compound. As the isocyanate compound, tolylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, or the like, or a resin obtained by biuret modification, adduct modification, or isocyanurate modification of these isocyanates is used.

The polymerization method of the acrylic monomer is not particularly limited, and a solution polymerization method, an emulsion polymerization method, a bulk polymerization method, or the like can be used.

The glass transition temperature (Tg) of the acrylic resin to be used is preferably -60°C or more and 90°C or less. When Tg is -60°C or higher, the moisture resistance and hot water resistance of the coating film or layer formed of acrylic resin are good, and when Tg is 90°C or less, the reattachability of the coating film or layer formed of acrylic resin is good.

In the above-described aspect in which the coating film includes an innermost layer and at least one outer layer, each of at least one of the outer layers and the innermost layer is a weather resistant layer in which an ultraviolet absorber is added to a resin.

According to this configuration, since the innermost layer itself is a weather-resistant layer in which an ultraviolet absorber is added to the resin, and at least one of the outer layers is a weather-resistant layer, the innermost layer (e.g., epoxy resin) is reliably protected from deterioration by ultraviolet rays. It can protect, and transparency and adhesion can be sufficiently maintained over a long period of time.

In the above aspect in which the coating film includes an innermost layer and at least one outer layer, the thickness of the innermost layer is 5 µm or more and 50 µm or less, and the thickness of the outer layer is 5 µm or more and 100 µm or less.

When the thickness of the innermost layer (eg, epoxy resin) is 5 μm or more and 50 μm or less, adhesion and corrosion resistance can be sufficiently obtained. Further, when the thickness of the outer layer is 5 µm or more and 100 µm or less, sufficient corrosion resistance can be obtained. In addition, when each layer of the innermost layer and the outer layer is too thick, there is a fear that transparency may decrease or adhesion may decrease.

As an aspect of the magnesium-based metal member of the present invention, the anticorrosive film is a zirconium oxide chemical conversion film.

The anticorrosive film is formed on the surface of the base material of the Mg-based metal, imparts corrosion resistance to the base material, or contributes to improvement of coating adhesion. The anticorrosive film can be formed by performing an anticorrosive treatment such as chemical conversion treatment or anodization treatment. Examples of the chemical conversion treatment include zirconium chemical conversion treatment, chromate treatment, manganese chemical conversion treatment, and phosphoric acid conversion treatment.

Among them, the zirconium oxide chemical conversion film formed by the zirconium oxide chemical conversion treatment, which is one of the zirconium chemical conversion treatments, contains zirconium oxide as a main component and has strong resistance to acids and alkalis. Further, the zirconium oxide chemical conversion coating can improve the adhesion to the coating film, and the coating adhesion can be further improved by blending a resin or a coupling agent. In addition, the zirconium oxide chemical conversion coating has high transparency and is easy to increase the metal texture compared to the coating of a compound such as phosphate formed by a phosphoric acid chemical conversion treatment.

In the above aspect where the anticorrosive film is a zirconium oxide chemical conversion film, the zirconium oxide chemical conversion film contains zirconium 10 mg/m2 or more and 150 mg/m2 or less and has a thickness of 10 nm or more.

When the zirconium content in the zirconium oxide chemical film is 10 mg/m 2 or more and 150 mg/m 2 or less, and the thickness is 10 nm or more, acid resistance, alkali resistance and adhesion can be sufficiently obtained. A more preferable thickness of the zirconium oxide chemical conversion film is 20 nm or more. In addition, if the thickness of the zirconium oxide chemical conversion film is too thick, the upper limit is preferably set to 1 µm or less, since transparency or adhesion decreases.

As one embodiment of the magnesium-based metal member of the present invention, an ultraviolet absorber is an organic ultraviolet absorber.

The ultraviolet absorber is required to have an absorption characteristic in the ultraviolet region of 290 to 380 nm, which degrades the resin (especially, an epoxy resin) most, and not to have an absorption characteristic in the visible region. Both organic and inorganic can be used for the ultraviolet absorber. Examples of the organic absorbent include benzophenone-based, benzotriazole-based, hydroxyanilide-based, cyanoacrylate-based, triazine-based, and the like. On the other hand, examples of the inorganic water absorbing agent include particulate titanium oxide, zinc oxide, iron oxide, and cerium oxide. The ultraviolet absorber may be used singly or in combination of two or more of the above-listed absorbers, but it is adjusted so as to satisfy the above characteristics. The organic water absorbing agent is preferable from the viewpoint of high transparency compared to the inorganic water absorbing agent.

When using an organic ultraviolet absorber, it is required to select it in consideration of the heat resistance and durability of the absorber. The heat resistance should be such that the absorbent is not decomposed by heat when forming a coating film and when the resin is coated and fired, and the durability should be such that the UV absorption effect does not deteriorate even when exposed to UV rays for a long period of time. As a commercial item of an organic ultraviolet absorber, TINUVIN (registered trademark) 479, TINUVIN928, TINUVIN405, etc. manufactured by Shiba Japan (now BASF Japan) can be used. In addition, as long as the same effect is obtained, the same can be used.

In the case of using an inorganic ultraviolet absorber, in order to increase transparency, it is required to suppress scattering of visible light. Specifically, the particle size is refined (for example, the average particle diameter (the median diameter (D50) corresponding to 50% of the cumulative distribution on a volume basis is about 0.01 to 0.05 μm)), and the refractive index of each layer constituting the coating film As a commercial item of the inorganic ultraviolet absorber, for example, NANOBYK (registered trademark)-3812, NANOBYK-3821, NANOBYK-3841, NANOBYK-3842 manufactured by BYK-Chemie can be used.

Further, the amount of the ultraviolet absorber to be added is, for example, 0.01 to 20 parts by mass, preferably 0.5 to 10 parts by mass, particularly preferably 1 to 5 parts by mass in the case of an organic absorbent, per 100 parts by mass of the resin solid content. In addition, by adding a light stabilizer (HALS: Hindered Amine Light Stabilizer) in addition to the ultraviolet absorber, durability (weather resistance) can be further improved. The amount of the photostabilizer added is preferably 0 to 3.0 parts by mass, for example, based on 100 parts by mass of the resin solid content. Each addition amount of the ultraviolet absorber and the light stabilizer may be appropriately adjusted within a range that does not impair the transparency of the coating film.

Commercially available products of light stabilizer (HALS) include, for example, "SANOL (registered trademark) LS770, LS765" manufactured by Sankyo Lifetech, "TINUVIN 144" manufactured by Shiba Japan, and "Adekastave (registered trademark) manufactured by ADEKA. LA-57, LA-62, LA-63, LA-67, LA-68, LA-82, etc. can be used. When firing a resin (paint) at high temperature, TINUVIN123 is particularly suitably used.

As one embodiment of the magnesium-based metal member of the present invention, a thing in which fine uneven processing is applied to at least a part of the surface of the substrate is mentioned.

Metal texture can be improved by performing fine uneven processing on at least a part of the surface of the Mg-based metal substrate. Examples of the fine uneven processing include at least one of cutting processing, grinding processing, spray processing, and corrosion processing using an acid. Specifically, at least one of hairline processing, diamond cutting processing, spin cutting processing, shot blast processing, and etching processing may be mentioned. These processings may be used alone or in combination of two or more. The fine uneven processing may be performed only on a part of the surface of the base material, or may be performed on the entire surface.

As one embodiment of the magnesium-based metal member of the present invention, a magnesium-based metal is a magnesium alloy containing 3% by mass or more of aluminum.

Examples of the Mg alloy include those of various compositions containing an additive element (the balance: Mg and impurities). Among them, Mg-Al-based alloys containing Al as an additive element are preferable in terms of excellent mechanical properties such as corrosion resistance and strength. As the Al content increases, mechanical properties such as corrosion resistance and strength tend to improve. Therefore, it is preferable to contain 3 mass% or more of Al, and it is more preferable to contain 7.3 mass% or more. However, when the Al content exceeds 12% by mass, the plastic workability may be deteriorated, so the upper limit is preferably 12% by mass. In particular, it is preferable that the Al content is 11% by mass or less and 8.3 to 9.5% by mass.

As an additive element other than Al, selected from Zn, Mn, Si, Be, Ca, Sr, Y, Cu, Ag, Sn, Ni, Au, Li, Zr, Ce, and rare earth elements (excluding Y and Ce) At least one element is mentioned. In the case of containing such an additional element, the total content is preferably 0.01 to 10% by mass, more preferably 0.1 to 5% by mass. Among these additional elements, at least one element selected from Si, Sn, Y, Ce, Ca and rare earth elements (excluding Y and Ce) is 0.001 mass% or more in total, preferably 0.1 to 5 mass in total. When it contains %, heat resistance and flame retardance are improved. Further, in the case of a rare earth element, it is preferable to contain at least 0.1% by mass, and among them, it is preferable to contain at least 0.5% by mass of Y. Examples of impurities include Fe and the like.

As a specific composition of the MgAl-based alloy, for example, AZ-based alloy (MgAlZn-based alloy, Zn: 0.2 to 1.5% by mass), AM-based alloy (MgAlMn-based alloy, Mn: 0.15 to 0.5% by mass), MgAlRE ( Rare-earth element)-based alloys, AX-based alloys (MgAlCa-based alloys, Ca: 0.2 to 6.0 mass%), and AJ-based alloys (MgAlSr-based alloys, Sr: 0.2 to 7.0 mass%), and the like. In particular, MgAl-based alloys containing 8.3 to 9.5% by mass of Al and 0.5 to 1.5% by mass of Zn, typically AZ91, have high specific strength even compared to other AZ-based alloys, and have excellent corrosion resistance and impact resistance. desirable.

On the other hand, the manufacturing method of a magnesium-based metal member of the present invention is a manufacturing method of forming a transparent coating film on the surface of a substrate made of a magnesium-based metal, and includes the following steps.

Anticorrosive process of forming a transparent anticorrosive film on the surface of the substrate by subjecting the substrate to an anticorrosive treatment.

A painting process in which a resin is coated on the anticorrosive film to form one or more transparent coating films.

And in the painting process, as a coating film, at least one weather resistant layer in which an ultraviolet absorber is added to the resin is formed.

As an embodiment of the manufacturing method of the present invention, in the coating step, at least one layer of the coating film is formed of an epoxy resin to which an ultraviolet absorber is added.

As an aspect of the manufacturing method of the present invention, in the coating step, as a coating film, an innermost layer immediately above the anticorrosive film and at least one outer layer above the innermost layer are formed as a coating film. And, in the painting process, the innermost layer is formed of an epoxy resin, at least one of the outer layers is formed of an acrylic resin, and at least one layer of the innermost layer and the outer layer is formed as a weather resistant layer in which an ultraviolet absorber is added to the resin. have.

According to the method of manufacturing an Mg-based metal member of the present invention, it is possible to manufacture the Mg-based metal member of the present invention, which is less deteriorated in the coating film and can maintain the metal texture over a long period of time.

As a means for coating the resin (paint), known means such as spray coating or electrodeposition coating can be employed. Further, after coating the resin, it is cured by firing, whereby the coating film can be firmly formed.

In addition to the above-described steps, a surface treatment step of performing surface treatment such as degreasing, etching, desmuting, and surface adjustment to the base material may be performed as necessary before the anticorrosive step of performing an anticorrosive treatment on the base material.

In the magnesium-based metal member of the present invention, since the coating film has at least one weather resistant layer, the coating film is less deteriorated and the metallic texture can be maintained over a long period of time. In addition, the method of manufacturing a magnesium-based metal member of the present invention can produce the magnesium-based metal member of the present invention.

In particular, when at least one layer constituting the coating film is made of an epoxy resin, the water resistance of the coating film can be improved. In addition, since the innermost layer is made of an epoxy resin containing a phosphoric acid-modified epoxy resin as a main component, and the outer layer is made of an acrylic resin, in addition to the above effects, corrosion resistance and hardness of the coating film can be improved.

The Mg-based metal member of the present invention was produced and evaluated.

[Example 1]

A rolled plate of an Mg alloy equivalent to AZ91 (Mg 9.0% Al, 1.0% Zn) was prepared, and this was cut into appropriate sizes to obtain a plurality of substrates. Then, after the substrate was subjected to a degreasing treatment as a surface treatment, the substrate was subjected to a zirconium oxide chemical conversion treatment as an anticorrosive treatment to form a zirconium oxide chemical conversion film serving as an anticorrosive film on the surface of the substrate. The degreasing treatment and chemical conversion treatment were performed under the following conditions, respectively.

(Degreasing treatment)

Under agitation of 10% KOH and 0.2% solution of nonionic surfactant, 60℃, 10 minutes

(Mars treatment)

Under agitation of zirconium-containing chemical conversion treatment agent, 35°C, 1 minute

When the surface of the substrate on which the zirconium oxide chemical conversion film was formed was observed with the naked eye, the zirconium oxide chemical conversion film was almost colorless and transparent. Further, when the content of zirconium contained in the zirconium oxide chemical conversion film was measured using a fluorescence X-ray analyzer, the zirconium content in the zirconium oxide chemical conversion film was about 45 mg/m2.

Paint A or paint B shown in Table 1 was spray-coated on the anticorrosive film (zirconium oxide chemical conversion film) formed on the surface of the substrate, and baking was performed at 150° C. for 20 minutes to form a coating film made of an epoxy resin or an acrylic resin. .

Coating film formation paint Paint A Paint B Epoxy paint Acrylic paint Resin composition Phosphoric acid modified epoxy resin/block isocyanate compound Acrylic resin/isocyanate compound Exterior transparent transparent product name "MG Net P-2 Shitanuri Clean" manufactured by Origin Denki Co., Ltd. ``Econnet EY'' manufactured by Origin Denki Co., Ltd.

In this example, the coating material A and the coating material B with and without an ultraviolet absorber, respectively, were used. TINUVIN928 was used as the ultraviolet absorber, and the amount of the ultraviolet absorber added was 1.8 parts by mass based on 100 parts by mass of the resin solid content. Then, the Mg-based metal members of Samples No. 1-1 to No. 1-4 shown in Table 2 were prepared in which a coating film including an anticorrosive film and a coating film was formed on the surface of the Mg alloy substrate.

When the thickness of each of the formed anticorrosive film and coating film was measured, the thickness of the anticorrosive film was 20 nm, and the thickness of the coating film was 10 μm. In addition, for each thickness, the cross section of the substrate on which the anticorrosive film and the coated film were formed was observed with a scanning electron microscope (SEM), and measured at 10 points each within the observation field of view, and made the average value.

Sample No. Paint used Addition of UV absorber 1-1 Paint A none 1-2 Paint A has exist 1-3 Paint B none 1-4 Paint B has exist

Regarding the Mg-based metal members of samples No.1-1 to No.1-4, when the external appearance (substrate surface) was visually observed, the coating film was colorless and transparent, and had an excellent metallic texture.

Next, for the Mg-based metal members of samples No.1-1 to No.1-4, the adhesion test, corrosion resistance test (salt spray test and artificial sweat test), water resistance test, pencil hardness test, and weather resistance shown below. It evaluated by conducting a test. The results are shown in Table 3.

<Adhesion test>

The adhesion test was performed in accordance with the test method specified in JIS K5600, 5,6:1999 (general test method for paint, mechanical properties of coated film, adhesion (cross-cut method)). In this test, incisions reaching the base material were placed in the coating film on the surface of the Mg-based metal member at intervals of 1 mm in length and width, and a 10×10 grid pattern was formed, and then an adhesive tape was adhered and peeled off the grid pattern. And evaluated the adhesion of the coating film (coating film). Then, whether peeling (peeling) occurred in the grid cells was visually inspected, and the number of peeled cells was counted. If no peeling was observed in all the cells (100), it was evaluated that the adhesion of the coating film was good. In Table 3, if the evaluation of adhesion is good (the number of cells without peeling is 100), ○ if it is slightly defective (the number of cells without peeling is 70 or more) is △, and if it is defective (the number of cells without peeling) Less than 70) was denoted by x, and (number of cells without peeling/number of all cells) was indicated in parentheses.

In addition, the evaluation of the adhesion was performed according to the primary adhesion to be tested as it is after the manufacture of the Mg-based metal member, and the secondary adhesion to be performed after each of the salt spray test, artificial sweat test, and water resistance test described later.

<Corrosion resistance test>

(Salt spray test)

The salt spray test was performed according to the test method specified in JIS Z 2371:2000 (salt spray test method). In this test, an aqueous sodium chloride solution (brine) was sprayed onto the Mg-based metal member under the conditions shown below, and the corrosion resistance was evaluated. After the test, the appearance was visually inspected to see if corrosion of the substrate or discoloration or swelling occurred in the coating film, and if such abnormality was not observed and there was no change, the corrosion resistance by the salt spray test was evaluated to be good.

<Salt spray test conditions>

Salt water concentration: 5% by mass

Test temperature: 35℃

Test time: 100 hours

Further, after the salt spray test, the above-described adhesion test was performed to evaluate the secondary adhesion.

(Artificial sweat test)

In the artificial sweat test, the Mg-based metal member was immersed in the artificial sweat solution under the conditions shown below, and the corrosion resistance was evaluated. After the test, the appearance was visually inspected to see if corrosion of the base material or discoloration or swelling occurred in the coating film, and if such an abnormality was not observed and there was no change, the corrosion resistance by the artificial sweat test was evaluated to be good.

<Artificial sweat test conditions>

Artificial sweat solution: acidic solution adjusted to pH 4.0 by adding acetic acid and disodium phosphate to aqueous sodium chloride solution

Test temperature: 40℃

Test time: 120 hours

Further, after the artificial sweat test, the above-described adhesion test was performed to evaluate the secondary adhesion.

<Water resistance test>

In the water resistance test, the Mg-based metal member was immersed in hot water at 60°C for 9 hours, and the water resistance was evaluated. Take out the Mg-based metal member from hot water, remove moisture from the surface of the coating film, and leave it to stand until the surface temperature reaches room temperature (about 25°C), and then corrosion on the substrate, discoloration, swelling, cracking, peeling, etc. The appearance was visually inspected to see if such an abnormality was observed, and if such an abnormality was not observed and there was no change, the corrosion resistance by the artificial sweat test was evaluated to be good.

In addition, after the water resistance test, the above-described adhesion test was performed to evaluate the secondary adhesion.

<Pencil hardness test>

The pencil hardness test was performed in accordance with the test method specified in JIS K5600, 5, 4: 1999 (general paint test method, mechanical properties of coated film, scratch hardness (pencil method)). In this test, using a Uni (registered trademark) pencil manufactured by Mitsubishi Enpitsu Co., Ltd., a load of 750 g was applied and the hardness of the pencil was evaluated as the hardest pencil that did not generate a mark when scratched.

<Weather resistance test>

The weather resistance test was performed in accordance with the test method specified in JIS K5600 7-7:2008 (general coating test method, long-term durability of coating film, accelerated weather resistance and accelerated light resistance (xenon lamp method)). In this test, xenon arc light was irradiated to the Mg-based metal member under the conditions shown below to evaluate its weather resistance. After the test, the appearance of the coating film (coating film) was visually inspected for deterioration such as yellowing, and if such deterioration was not observed and there was no change, the weather resistance was evaluated to be good.

<Weather test conditions>

Irradiance: 60 W/㎡

Test temperature: 63℃

Wet cycle: continuous operation operation, 18 minutes (wet time)/102 minutes (dry period), 50% relative humidity during drying

Test time: 200 hours

Sample No. in which the coating film was formed of an epoxy resin (phosphoric acid-modified epoxy resin). 1-1, No. Among 1-2, in sample No.1-1 in which no ultraviolet absorber was added to the resin, yellowing was observed on the coating film after the weather resistance test, and the design properties and metal texture were impaired. On the other hand, sample No. in which an ultraviolet absorber was added to the resin. In 1-2, deterioration of yellowing was not observed in the coating film even after the weather resistance test, the transparency of the coating film was sufficiently ensured, and the metallic texture was maintained.

Sample No. in which acrylic resin was used as the resin for forming the coating film. 1-3 and No. In 1-4, the influence on the weather resistance due to the addition of the ultraviolet absorber was not very visible, but the secondary adhesiveness after the water resistance test was inferior compared to the case where an epoxy resin was used.

[Example 2]

In the same manner as in Example 1, a base material of an Mg alloy corresponding to AZ91 was prepared, and a zirconium oxide chemical conversion film serving as an anticorrosive film was formed on the surface of the base material.

After coating the paint A or paint B shown in Table 4 on the anticorrosive film (zirconium oxide chemical conversion film) formed on the surface of the substrate, paint C shown in Table 4 on each of them, and made of an epoxy resin or an acrylic resin. A coating film having a two-layer structure including an innermost layer and an outer layer made of an acrylic resin was formed. The coating of the innermost layer and the coating of the outer layer were performed under the following conditions, respectively.

(Painting of the innermost layer)

After spray painting the coating for forming the innermost layer, it is fired at 150°C for 20 minutes.

(Painting of the outer layer)

Formation of outer layer After spray painting the paint, sintering at 150°C for 20 minutes

Paint for forming the innermost layer Paint for outer layer formation Paint A Paint B Paint C Epoxy paint Acrylic paint Acrylic paint Resin composition Phosphoric acid modified epoxy resin/block isocyanate compound Acrylic resin/isocyanate compound Acrylic resin/melamine compound Exterior transparent transparent transparent
product name ``MG Net P-2 Shitanuri Clean'' manufactured by Origin Denki Co., Ltd. ``Econnet EY'' manufactured by Origin Denki Co., Ltd. ``MG Net T Uwanuri Clean'' manufactured by Origin Denki Co., Ltd.

In this example, the coating material A or the coating material C with or without an ultraviolet absorber was used. Paint B was used to which no ultraviolet absorber was added. As the ultraviolet absorber, the same TINUVIN928 as in Example 1 was used, and the amount of the ultraviolet absorber added was 1.8 parts by mass based on 100 parts by mass of the resin solid content. In addition, the sample No. shown in Table 5 was formed on the surface of the Mg alloy substrate, in which a coating film containing an anticorrosive film and a coating film was formed. 2-1∼No. 2-4, No. 2-6 and No. Mg-based metal members of 2-7 were prepared.

In the same manner as in Example 1, the thickness of each of the formed anti-corrosive film and coating film (inner layer and outer layer) was measured. The thickness of the anti-corrosive film was 20 nm, and the thickness of the innermost layer and the outer layer was 10 μm, respectively, The thickness of the entire coating film was 20 µm.

In addition, as a separate sample, sample No. 1 except that diamond cut processing was performed as fine irregularities on the surface of the Mg alloy substrate. In the same manner as in 2-2, sample No. shown in Table 5 was performed. 2-5 Mg-based metal members were prepared. The diamond cutting process was performed by a commercially available diamond cutting machine, and in this example, it was performed on the entire surface of the substrate surface. Diamond cutting was performed under the following conditions.

(Diamond cut processing)

Processing radius: 50 mm, depth: 0.02 mm (20 ㎛), pitch: 0.05 mm

Sample No.
Coating
On the surface of the substrate
Fine irregularities processing Innermost layer Outer layer Paint used Addition of UV absorber Paint used Addition of UV absorber 2-1 Paint A none Paint C none none 2-2 Paint A none Paint C has exist none 2-3 Paint A has exist Paint C has exist none 2-4 Paint A has exist Paint C none none 2-5 Paint A none Paint C has exist Diamond cut 2-6 Paint B none Paint C none none 2-7 Paint B none Paint C has exist none

Sample No. 2-1∼No. When the appearance (substrate surface) of the Mg-based metal members 2-7 was visually observed, the coating film was colorless and transparent, and had an excellent metallic texture.

Next, sample No. 2-1∼No. The Mg-based metal members of 2-7 were evaluated in the same manner as in Example 1.

The results are shown in Table 6.

Sample No. in which the innermost layer was formed of an epoxy resin. 2-1∼No. In 2-5, the ultraviolet absorber was not added to either the forming resin of the innermost layer and the outer layer, and the sample No. In 2-1, yellowing was observed in the innermost layer (epoxy resin) after the weather resistance test, and the design properties and metal texture were damaged. On the other hand, either of the innermost layer and the outer layer was sample No. 2, which was a weather-resistant layer in which an ultraviolet absorber was added to the forming resin. 2-2∼No. In 2-5, deterioration such as yellowing was not observed in the coating film even after the weather resistance test, the transparency of the coating film was sufficiently ensured, and the metallic texture was maintained. In addition, sample No. 2-2∼No. 2-5 and sample No. From comparison with 2-1, adhesion, corrosion resistance, and water resistance were not decreased by adding an ultraviolet absorber to the resin forming the coating film (inner layer or outer layer).

Sample No. in which acrylic resin was used as the forming resin of the innermost layer. 2-6 and No. In 2-7, as compared with the case of using an epoxy resin, discoloration was observed after a corrosion resistance test (salt spray test and artificial sweat test) or after a water resistance test, or secondary adhesion after an artificial sweat test or water resistance test was inferior.

In addition, the present invention is not limited to the above-described embodiment, and can be appropriately changed within a range not departing from the gist of the present invention. For example, the composition of the Mg alloy, the type of the anticorrosive film, the type or thickness of the resin forming the coating film (the innermost layer and the outer layer), the number of layers of the outer layer, and the like can be appropriately changed. In addition, in the present invention, when the demand for corrosion resistance is low, or when corrosion resistance can be secured by thickening the coating film, it is not necessary to provide an anticorrosive film.

The Mg-based metal member of the present invention can be suitably used in a field in which designability is particularly required, such as cases for portable electric and electronic devices such as mobile phones and notebook personal computers, and interior products for transportation equipment.

Although the present invention has been described in detail with reference to specific embodiments, it is clear to those skilled in the art that various changes and corrections can be added without departing from the spirit and scope of the present invention.

This application is based on the Japanese patent application (Japanese Patent Application No. 2013-090657) of the application on April 23, 2013, The content is taken in here as a reference.

Claims (16)

A magnesium-based metal member comprising a substrate made of a magnesium-based metal and a transparent coating film formed on the surface of the substrate,
The coating film is
A transparent anticorrosive film formed on the surface of the substrate,
It is formed on the anticorrosive film and comprises one or more layers of transparent coating film made of a resin,
The coating film is formed directly on the anticorrosive film and includes an innermost layer made of an epoxy resin, and at least one outer layer formed on the innermost layer,
The coating film has at least one weather-resistant layer in which an ultraviolet absorber is added to the resin,
The anticorrosive film is a zirconium oxide chemical film,
The epoxy resin constituting the epoxy resin is a magnesium-based metal member that is a phosphoric acid-modified epoxy resin. delete The magnesium-based metal member according to claim 1, wherein at least one layer of the outer layer is made of an acrylic resin. The magnesium-based metal member according to claim 1, wherein at least one layer of the outer layer and the innermost layer are weather-resistant layers in which an ultraviolet absorber is added to a resin, respectively. The method according to claim 1, wherein the innermost layer has a thickness of 5 µm or more and 50 µm or less,
The thickness of the outer layer is 5 μm or more and 100 μm or less. The magnesium-based metal member according to claim 1, wherein the coating film is made of an epoxy-based resin. delete delete The magnesium-based metal member according to claim 1, wherein the zirconium oxide chemical conversion film contains zirconium from 10 mg/m2 to 150 mg/m2 and has a thickness of 10 nm or more. The magnesium-based metal member according to claim 1, wherein the ultraviolet absorber is an organic ultraviolet absorber. The magnesium-based metal member according to claim 1, wherein at least a part of the surface of the base material is subjected to fine uneven processing. The magnesium-based metal member according to claim 11, wherein the uneven processing is at least one of hairline processing, diamond cutting processing, spin cutting processing, shot blast processing, and etching processing. The magnesium-based metal member according to claim 1, wherein the magnesium-based metal is a magnesium alloy containing 3% by mass or more of aluminum. A method for manufacturing a magnesium-based metal member for forming a transparent coating film on the surface of a substrate made of a magnesium-based metal,
An anticorrosive process of forming a transparent anticorrosive film on the surface of the substrate by performing an anticorrosive treatment on the substrate,
A coating process of coating a resin on the anticorrosive film to form one or more transparent coating films,
In the anticorrosive process, a zirconium oxide chemical conversion treatment is performed as the anticorrosive treatment to form a zirconium oxide chemical conversion film serving as the anticorrosive film,
In the painting process, as the coating film, an innermost layer made of an epoxy resin and at least one outer layer is formed on the innermost layer directly on the anticorrosive film,
The epoxy resin constituting the epoxy resin is a phosphoric acid-modified epoxy resin,
In the coating step, a method for producing a magnesium-based metal member, wherein at least one weather-resistant layer is formed by adding an ultraviolet absorber to a resin as a coating film. delete delete