Corrosion resisting method and method for forming magnesium substrate and mold release material layer

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to an anticorrosion method for forming a titania film on the surface of a substrate made of magnesium or an alloy thereof, a method for adding an anticorrosion / photocatalytic function, and a method for forming a magnesium substrate and a release material layer.

【0002】

[Conventional technology]

Conventionally, magnesium (Mg) or an alloy containing magnesium (collectively, "magnesium alloy" is hereinafter referred to as "magnesium alloy") because it has a small specific gravity (about 1.75 to 2.0) and is excellent in processability, strength, and cosmeticity. It has a wide range of uses such as clothing, medical equipment, building materials, decorative decoration materials, building hardware, aircraft, automobile parts, etc. However, magnesium alloys have difficulty in corrosion resistance, and are usually used by the heavy chromium acid method or the selenic acid method. Although surface treatment is applied, there is a problem that the number of processing steps increases. It is also considered to apply a synthetic resin coating called the HAE method, but the adhesiveness between the substrate and the resin coating is not sufficient. It cannot be said that there is a problem in terms of reliability. On the other hand, the number of petrochemical products is increasing, and complex contamination of harmful organic compounds is becoming a problem inside and outside the living environment. As a means to solve this, oxidative decomposition by a photocatalytic semiconductor is used. Attention is being paid to its use. For example, it has been proposed to support a photocatalyst semiconductor on the surface of a substrate constituting an apparatus or facility, and oxidatively decompose harmful organic substances adhering to the photocatalyst semiconductor by the photocatalyst semiconductor, and it has been put into practical use. Therefore, in order to protect the surface of the Mg alloy substrate, it is conceivable to form a titania film and add a photocatalyst function to decompose organic compounds and inorganic gases by ultraviolet excitation of the titania film.

【0003】

[Problems to be Solved by the Invention]

However, when a titania film is simply provided on the surface of a substrate made of an Mg alloy, since a small amount of iron is contained in the substrate, the corrosion resistance is lowered and a sufficient anticorrosion effect cannot be obtained, and the titania film and the substrate are not obtained. There is a drawback that the adhesion with is reduced. That is, in order to form a photocatalytic functional layer on the surface of the substrate, a solution containing a photocatalytic semiconductor is usually applied to the surface of the substrate, and then 300 ° C. in the air to improve adhesion to the substrate and enhance photocatalytic activity. Sintering is performed at a temperature of more than C or 500 ° C or less, but the conventional method causes a problem that a film cannot be firmly formed on the surface of the substrate. Further, the magnesium alloy member is manufactured by, for example, a so-called die casting method in which a molten magnesium alloy is injected into a mold (usually made of steel). An oil-based mixed material (molding material) such as a fatty acid ester is applied to the inner surface (cavity surface) of the mold. However, in this method, it is necessary to apply a mold release material for each casting cycle, and since oily components remain on the surface of the casting, operations such as cleaning and blasting are required to remove them.

【0004】

Therefore, an object of the present invention is to provide an anticorrosion method capable of forming a titania film on the surface of a substrate without impairing cosmetic properties. Another object of the present invention is to provide a magnesium substrate having excellent cosmetic properties and a high anticorrosion effect. Another object of the present invention is to provide a method capable of forming a mold release material layer having photocatalytic activity on the inner surface of a mold used for casting a magnesium alloy casting.

【0005】

[Means for solving problems]

In order to achieve the above object, in the first invention, an amorphous titanium peroxide aqueous solution is applied to the surface of a substrate made of Mg or an alloy thereof, and heated at a temperature of less than 200 ° C. to form a transparent titania film. We adopted the technical means of forming. The titania film thus obtained is a film in which titanium peroxide particles having a particle size of 2 to 10 nm are laminated, and is firmly formed on the surface of the substrate by the strong adhesive force of the peroxo group of titanium peroxide. .. Under these heating conditions, titanium oxide has not yet transferred to the anatase type, which has a photocatalytic function, so the surface of the titania film is coated with or plated with an inorganic paint containing an organic polymer resin or Si compound as the main component. Thereby, a film having a higher degree of anticorrosion performance can be formed. In order to achieve the above object, in the second invention, an aqueous solution containing amorphous titanium peroxide and / or anatase type titanium oxide is applied to the surface of a substrate made of Mg or an alloy thereof, and the temperature is 200 ° C. or higher. We adopted the technical means of heating at a temperature of 800 ° C or less. Since the amorphous peroxidation is transferred to the anatase type under these heating conditions, a photocatalytic function can be added to the titania film. In the third invention, in a method of forming a mold release material layer on the inner surface of a mold for casting a molten metal made of Mg or an alloy thereof, an aqueous solution containing amorphous titanium peroxide or anatase type titanium oxide on the inner surface of the mold. Is applied, so that a mold release material layer having photocatalytic activity can be formed on the inner surface of the mold.

【0006】

BEST MODE FOR CARRYING OUT THE INVENTION

The details of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view of a substrate on which a titania film is formed according to an embodiment of the present invention. In the substrate on which the titania film shown in FIG. 1 is formed, a titania film 2 having a thickness of 0.1 to 2 μm is formed on the surface of the substrate 1. If the thickness of the titania film is thinner than 0.1 μm, a sufficient anticorrosion effect cannot be obtained, and if the thickness is thicker than 2 μm, the titania film is easily peeled off. As a material for forming the above substrate 1, an alloy containing Mg or Mg and Al, Zn or the like (Mg-Al type, Mg-Al-Zn type, Mg-Mn type or the like) can be used. Collectively, these are referred to as "Mg alloy substrates". An aqueous solution containing amorphous titanium peroxide or a viscous aqueous solution is applied to the surface of an Mg alloy substrate by a spray method, a dip method, a spin coating method, etc., dried at room temperature, and then heat-dried at a temperature of less than 200 ° C. As a result, an Mg substrate having an amorphous titania film can be obtained. However, if the heating temperature is low, the film formation time becomes long, so it is preferable to heat at 70 ° C. or higher. In this case, the amorphous titanium peroxide does not crystallize at a temperature of less than 200 ° C. Therefore, due to the strong fixing effect of the peroxo group, the adhesion to the substrate is excellent, and a uniform and flat transparent titania film can be formed. ..

【0007】

Next, as shown in FIG. 2, on the surface of the titania film 2 formed on the above substrate 1, an organic polymer resin such as acrylic, polyester, vinyl chloride or fluorine, silica or a compound thereof or siloxane By forming an inorganic paint containing a crosslinked product or a coating film 3 such as plating (Cu-Ni-Cr plating, electroless Ni plating, etc.), a decorative base material having higher anticorrosion performance can be obtained. The coating film can be formed by a known method such as brush coating, spray coating, or electrostatic coating, and an economically superior method may be selected among these. These Mg alloy substrates can be used, for example, for building hardware, fittings, interior / exterior materials, curtain walls, eyeglasses, watches, accessories and the like.

【0008】

In the present invention, as shown in FIG. 3, an amorphous type titanium peroxide or a mixed sol or an aqueous solution of the anatase type titanium oxide is applied to the surface of the Mg alloy substrate by a spray method, a dip method, a spin coating method or the like. By heating and drying at 200 ° C. or higher, an Mg alloy substrate 1 in which an anatase-type titania film 2'having a photocatalytic function is formed can be obtained. However, if the heating temperature is too high, the crystal structure of titanium oxide becomes a rutile type, so it is preferable to heat at 500 ° C. or lower. In FIGS. 1 to 3 and FIG. 4 described later, white circles indicate amorphous titanium peroxide and black circles indicate anatase type titanium oxide. Photocatalytic performance refers to the formation of a photocatalytic semiconductor metal such as anatase-type titanium oxide on the surface of a substrate, and the excitation wavelength (TiO) on the surface of the film.₂In the case of, active radical species are generated when exposed to electromagnetic waves of 360 to 380 nm or less, and have a purification function by redox decomposition of organic compounds and inorganic gases. This enables an Mg alloy substrate having mudproofing, deodorizing, antibacterial functions and the like. This Mg alloy substrate can be used for, for example, medical / dental instruments, vehicles, aircrafts, automobiles, electric appliances, machine tools, tools, etc., in addition to the above-mentioned applications.

【0009】

As shown in FIG. 4, the film-forming method of the present invention can also be applied to a mold for producing a casting of Mg or an alloy thereof. For example, an amorphous titanium peroxide aqueous solution is applied to the inner surface (cavity forming surface) 5 of a steel mold 4 by a spray method, air-dried, and then a molten Mg alloy is cast to obtain 500 amorphous titanium peroxides. The mold release material layer 6 made of a titania film having photocatalytic activity is formed by heating to about 600 ° C. The crystal structure of amorphous titanium peroxide is transferred to anatase-type titanium oxide by heating at 200 ° C or higher, but it still functions as a release material.

【0010】

The amorphous titanium peroxide sol used in the present invention can be prepared, for example, as follows. Titanium tetrachloride TiCl₄50% solution (Sumitomo Systics Co., Ltd.) diluted 70 times with distilled water and ammonium hydroxide NH₄A 25% solution of OH (Takasugi Pharmaceutical Co., Ltd.) diluted 10-fold with distilled water is mixed at a volume ratio of 7: 1 to carry out a neutralization reaction. After the neutralization reaction, adjust the pH to 6.5 to 6.8, leave it for a while, and then discard the supernatant. Remaining Ti (OH)₄Add about 4 times the amount of distilled water in the gel, stir well and leave. Check with silver nitrate and repeat washing with water until no chlorine ions are detected in the supernatant. Finally, discard the supernatant and leave only the gel. In some cases, dehydration can be performed by centrifugation. This pale bluish white Ti (OH)₄To 3,600 ml, 210 ml of 35% hydrogen peroxide solution is added in two portions every 30 minutes, and the mixture is stirred at about 5 ° C overnight to obtain about 2,500 ml of a yellow transparent amorphous titanium peroxide sol. In the above steps, if heat generation is not suppressed, water-insoluble substances such as metatitanic acid may precipitate. Therefore, it is desirable to suppress heat generation in all steps.

【0011】

Furthermore, the above amorphous titanium peroxide sol has Pt, Ag, Rh, and RuO for functional complementation such as antifungal sterilization.₂, Nb, Cu, Sn, NiO particles are mixed in a small amount, or zeolite, silica (silicon dioxide), alumina, zinc oxide, magnesium oxide are added to improve the decomposition performance by redox. , Inorganic materials such as rutyl-type titanium oxide and zirconium phosphate, or various activated carbons, porous phenol resins and melamine resins can be mixed in one or more.

【0012】

[Experimental example]

(Example 1) Amorphous titanium peroxide aqueous solution (0.84 wt%) 0.7 g / 100 cm on the surface of the Mg alloy substrate²Spray (wet state). Then, after drying at room temperature, it was heated in the air (100 ° C × 1 hr).

【0013】

(Examples 2 and 3) Heating was performed under the same conditions as in Example 1 except that the heating temperature was set to 150 ° C (Example 2). A titania film was formed under the same conditions as in Example 2 except that the heating temperature was set to 190 ° C (Example 3).

【0014】

(Example 4) Heating was performed under the same conditions as in Example 1 except that the heating temperature was set to 60 ° C (Example 4).

【0015】

(Example 5) Almofus type titanium peroxide aqueous solution (0.84 wt%): Anatase type titanium oxide aqueous solution (0.84 w%): Colloidal silica aqueous solution (0.84 wt%) is mixed at a ratio of 7: 3: 0.1 to the Mg plate. 0.7g / 100cm on the surface²Spray (wet state). Then, after drying at room temperature, it was dried by heating in the air (230 ° C × 30 min) to form a titania film.

【0016】

(Examples 6 to 8) Heating was performed under the same conditions as in Example 5 except that the heating temperature was set to 300 ° C (Example 6). In addition, heating was performed under the same conditions as in Example 5 except that the heating temperature was set to 400 ° C (Example 7). In addition, heating was performed under the same conditions as in Example 6 except that the heating temperature was set to 480 ° C (Example 8).

【0017】

(Example 9) Heating was performed under the same conditions as in Example 5 except that the heating temperature was set to 550 ° C.

【0018】

(Examples 10 to 13) 1.4 g / 100 cm of special modified polyester resin paint is applied to the surface of the Mg alloy substrate obtained through the same steps as in Examples 1 to 3.²It was applied in a (wet state) application amount and air-dried.

【0019】

(Evaluation) When the corrosion resistance of the above 13 types of Mg alloy substrates was evaluated, those of Examples 1 to 3 and 5 to 13 showed good corrosion resistance, but those of Example 4 were inferior in corrosion resistance. In Example 4, the heating temperature was low and the adhesion between the titania film and the substrate was inferior. Furthermore, stains (20-fold diluted Pilot red ink) are artificially attached to the above 5 types of Mg alloy substrates (Examples 5 to 9), and 360 nm ultraviolet light is irradiated with black light 30. As a result of visually observing the surface after 1 minute, it was confirmed that the Mg alloy substrates of Examples 5 to 8 were decomposed. However, the Mg alloy substrate of Example 9 was insufficiently decomposed.

【0020】

The X-ray diffraction pattern of the titania film formed at different drying temperatures in Examples 1 and 5 was measured. The results are shown in FIGS. 5 and 6. From both figures, at temperatures below 200 ° C (150 ° C), almost no crystal face pattern appears, and it is composed of amorphous titania, and the heating temperature is 200 ° C or higher (300 ° C, 450 °). In C), an anatase-type crystal plane appears, and it can be seen that it is composed of crystalline titania. The substrates of Examples 10 to 13 have white cosmetic properties, have excellent adhesion between the resin and the titania film, and can be obtained without any problem in terms of anticorrosion performance.

【0021】

[Effect of the invention]

According to the present invention, since a transparent titania film is provided on the surface of a magnesium alloy or a substrate made of the alloy, a magnesium alloy member having excellent cosmetic properties and high corrosion resistance can be obtained. Further, according to the present invention, since the inner surface of the Mg alloy casting mold is coated with amorphous titanium peroxide or a sol containing the amorphous titanium peroxide and anatase type titanium oxide, a release material layer having photocatalytic activity can be formed.

[Simple explanation of drawings]

[Figure 1]

It is sectional drawing of the substrate which concerns on one Example of this invention.

[Figure 2]

It is sectional drawing of the substrate which concerns on other Examples of this invention.

[Fig. 3]

It is sectional drawing of the substrate which concerns on other Examples of this invention.

[Fig. 4]

It is sectional drawing of the mold which concerns on other Examples of this invention.

[Fig. 5]

It is an X-ray diffraction pattern of the titania film by heating temperature which formed the film by using the amorphous type titanium peroxide which concerns on one Example of this invention as a main raw material.

[Fig. 6]

It is an X-ray diffraction pattern of the titania film by heating temperature which formed the film by using the amorphous type titanium peroxide and the anatase type titanium oxide as the main raw materials according to another Example of this invention.

[Explanation of symbols]

1 substrate, 2 titania film