JPH0365439B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to surface treatment of aluminum or aluminum alloy, and in particular to nameplates attached to the surface of equipment for explaining how to use the equipment in telephones, measuring instruments, vending machines, electronic equipment, etc. This paper relates to surface treatment of aluminum plates used as [Prior Art] Nameplates have traditionally been used for public telephones, vending machines, etc., which are made of aluminum or its alloys, formed with an anodized film on the surface, and dyed with letters, figures, etc. There is. On such nameplates, the anodic oxide film is limited to a thickness of about 6 μm so as not to spoil the silvery white background color, so they are easily damaged. For example, in public telephones, coins can only damage the oxide film. It even spread to the board itself, and a few months after it was installed, the letters,
In many cases, the graphics become unreadable or the nameplate is damaged, resulting in an unsightly condition. For this reason, the base metal is made thicker and the anodic oxide film is made 30 to 60 μm thick.
Attempts have also been made to use so-called hard alumite produced to a thickness of . [Problems to be solved by the invention] However, in order to generate a thick anodic oxide film, it is necessary to apply a high voltage or immerse it in an alumite treatment solution for a long time, which may cause the oxide film to become “burned” or “rough”. The surface of the nameplate becomes dark gray or grayish-black, and even if the letters, figures, etc. are dyed, there is no contrast, making them unclear and difficult to read, or the dyeing becomes dark and the vividness of the colors is significantly impaired. However, the disadvantage is that the desired color cannot be obtained.
In addition, a thick oxide film is prone to cracks, and on the other hand, by making the oxide film thicker, the micropores on the surface are reduced and the amount of dye adsorption is reduced, and when exposed to sunlight, dyed surfaces such as letters and figures However, there are still problems with its practical use, as it easily discolors and fades, making it unreadable. The present invention satisfies the conflicting demands regarding dyeing property and surface hardness of the anodic oxide film on the aluminum surface, and provides an anodized film that is less susceptible to damage by coins, etc., and less likely to cause "burn" or "roughness." The present invention provides a method for surface treatment of aluminum to form a film. [Means for Solving the Problems] The present invention provides a method for anodizing the surface of aluminum or aluminum alloy, in which the surface is degreased and then a spherical abrasive material of 20 to 400 meshes is sprayed onto the surface. This is a method for surface treatment of aluminum, which is characterized in that the processed surface is then formed with an anodic oxide film having a thickness of 15 to 100 μm. In the present invention, the material that generates the anodic oxide film is aluminum or aluminum alloy,
Pure aluminum, which has little color change due to oxide film, is usually used, but from the viewpoint of hardness as a material, a corrosion-resistant aluminum alloy containing 2 to 5% magnesium is preferable. The shape of the aluminum material treated in the present invention is arbitrary; normally, when used for nameplates, a plate of the desired thickness is used, but for exterior members that require scratch resistance, and which can be honed as described below. If so, one molded into any shape can be used. In the following explanation, a nameplate will be explained. After degreasing an aluminum or aluminum alloy plate (hereinafter referred to as an aluminum plate or simply plate) to remove oil and fat adhering to the plate surface, polish it into a spherical shape with a desired particle size between 20 and 400 mesh using a Tyler standard sieve. A satin finish is applied to the surface of the board by honing, which involves blowing wood onto the surface of the board.
Glass beads are usually used as the spherical abrasive, but any abrasive can be used as long as it has a substantially spherical shape. In the honing process, an abrasive material and water are sprayed onto the aluminum plate at a pressure of 1 to 5 kg/cm ² from a nozzle placed at a distance of about 50 to 200 mm to create fine irregularities on the surface of the aluminum plate. The honed surface is etched with caustic alkali or the like to remove the oxide film on the surface to make the surface uniformly active, and the generated smut is removed by dissolving it in a 10% nitric acid solution, followed by the next anodizing treatment. I do. Anodic oxidation is performed by immersing the plate in a 15% sulfuric acid solution or a mixed solution of sulfuric acid and oxalic acid as an electrolyte, and applying an electrolytic voltage of 8 to 20 V and an electrolysis time of 15 to 90 minutes to form a layer of 15 to 25 μm thick on the surface of the plate. Generates an anodic oxide film. In addition to the above-mentioned normal alumite treatment, the method of generating an anodized film is to apply an electrolytic voltage of 22
Pulse alumite treatment can be applied in which a high voltage of ~26 V and a low voltage of 15 to 18 V are alternately applied in a rectangular waveform with a cycle of 60 to 90 seconds. '', the oxide film has little discoloration, the dyeing is clear, and the film has high hardness, so it is particularly advantageously applied to the anodic oxidation of the treatment method of the present invention. [Operations and Effects] In the method of the present invention, the reason why the surface of the aluminum plate is honed in advance prior to anodizing treatment imparts excellent scratch resistance to the oxide film is not necessarily clear, but the honing treatment The size of the particles of the abrasive used for this is related to the scratch resistance of the resulting oxide film, and those in the range of 20 to 400 mesh are used. If large particles of 20 mesh or less are used, the surface of the board will be severely roughened.
In addition to the reduced scratch resistance, the printability of the resist during dyeing is poor, and the resolution is reduced, making it difficult to express clear characters and figures. Furthermore, honing treatment using fine particles of 400 meshes or more does not provide any treatment effect, and the scratch resistance of the oxide film sharply decreases. This is shown by the following scratch resistance test results using coins. Figure 3 shows an overview of the coin scratch resistance tester, in which a sample plate 3 is pressed against a coin 2 with a constant load (5 kg).
When the coin 2 is pulled out in the direction of the arrow, the surface of the oxide film on the sample plate is scratched by the edge of the coin 2. Using coins made of the six types of materials with different hardness shown in Table 1, the oxide film 4 was
A state in which there was no scratch on the surface was defined as 0, a state in which the oxide film was completely damaged by the coin and peeled off, and a state in which the base metal was damaged to 5 was defined as 4, and the damage level was divided into three levels. The degree of damage to the film was expressed by summing up the degree of damage caused by the six types of coins.

〔Example〕

In the following examples, the strength of the anodic oxide film is demonstrated by a coin abrasion test. Figure 5 shows the outline of the coin abrasion test.
Place the coin 6 of H) on the sample plate 3 at an angle of 45°,
Coin 6 when load 7 (500g) is applied and sample plate 3 is reciprocated and the reciprocating friction is repeated 1000 times.
Measure the amount of wear (weight loss, mg). Example 1 80 each of pure aluminum plates (A1050) with a thickness of 2 mm
The mesh and 240 mesh glass beads wet-honed were anodized in a 15 W/V% sulfuric acid solution at a voltage of 12 V for 60 minutes to form an oxide film. The thickness of the produced film is 23~26μ
It was m. For comparison, anodic oxide films were formed on samples without honing in the same electrolytic bath, and coin abrasion tests were conducted on three types of samples. The results are shown in Figure 6. On honed plates, the coin wears significantly and the weight of the coin decreases compared to non-honed plates. The honed surface acted like a file and pulverized the edges of the coin, causing no damage at all, and any adhering coin powder could be easily removed by wiping it gently. On the other hand, the surface that has not been honed has scratches from the coin edges,
It could not be removed even by wiping. Example 2 The surface of the same material as in Example 1 was honed using 240 mesh glass beads, and an anodic oxide film of 21 to 24 μm was formed by pulse alumite treatment. Pulse alumite treatment is performed at a liquid temperature of 24℃.
Using 15W/V% sulfuric acid solution as electrolyte, at high voltage 22V.
Electrolysis was carried out for 25 minutes under electrolysis voltage with a rectangular waveform voltage for 10 seconds at a low voltage of 14 V for 60 seconds. The coin abrasion test results of the obtained oxide film are shown in FIG. 7 in comparison with the surface that was not honed. Examples 3 and 4 The same procedure as in Examples 1 and 2 was conducted using corrosion-resistant aluminum alloy A5052 as the material. The results of each coin abrasion test are shown in FIGS. 8 and 9.

[Brief explanation of drawings]

FIG. 1 shows the effect of the particle size of glass beads on the degree of damage to the oxide film during honing in the method of the present invention, and FIG. 2 shows the effect of the thickness of the oxide film. FIG. 3 shows an outline of the scratch resistance tester, and FIG. 4 is a diagram showing the criteria for determining the degree of damage in the scratch resistance test. FIG. 5 is a diagram explaining the outline of the coin abrasion test, and FIGS. 6 to 9 show the results of the coin abrasion test for various anodic oxide films. FIGS. 10 to 12 are micrographs showing the state of damage to the metal structure on the sample surface as a result of the scratch resistance test.

Claims (1)

[Claims] 1. In a method of anodizing the surface of aluminum or aluminum alloy, after degreasing the surface, a process is performed in which 20 to 400 meshes of spherical abrasive material is sprayed onto the surface, and then the processed surface is A method for surface treatment of aluminum, characterized by forming an anodic oxide film with a thickness of 15 to 100 μm. 2. The method according to claim 1, wherein the spherical abrasive material is a glass bead. 3. The method according to claim 1 or 2, wherein the anodization is carried out at an electrolysis voltage of 8 to 20V and an electrolysis time of 15 to 90 minutes. 4 Anodic oxidation, high voltage 22~26V, low voltage 15~
18V, high voltage connection period 55-65 seconds, repeat cycle
3. The method according to claim 1 or 2, which is carried out at an electrolytic voltage with a rectangular waveform voltage for 60 to 90 seconds.