JPH10324998A - Method for controlling oxidized film thickness in formation of anodically oxidized film of aluminum shape material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for easily controlling an anodically oxidized film thickness by a relatively simple method of decreasing the variations in the film thickness by positively utilizing the gaseous hydrogen generated at the time of anodic oxidation for controlling the film thickness and more particularly changing the form of CGF. SOLUTION: The anodically oxidized film thickness is controlled by controlling the surface temp. of the aluminum shape material 3 by utilizing the thermal diffusivity of the electrolyte by the flow of the bubbles of the gaseous hydrogen generated from a cathode at the time of the anodic oxidation of the aluminum shape material 3. More specifically, the sizes of the bubbles of the gaseous hydrogen flowing in the shape material direction and the stage of the density in the liquid, etc., are controlled by changing the micropore diameters of a barrier 4 disposed on the peripheral of the cathode 2 or the distribution and/or configuration form thereof, by which the sizes of the bubbles of the gaseous hydrogen and the state of the density in the liquid, etc., are partially controlled in accordance with the characteristics of the anodically oxidized film thickness distribution at the time of the current anodic oxidation. The surface temp. of the shape material is thereby controlled and the relatively easy control of the anodically oxidized film thickness is made possible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anodic oxide film (hereinafter abbreviated as a film) uniformly on an aluminum profile (hereinafter abbreviated as a profile) for building materials or the like by utilizing hydrogen gas generated from a cathode. In some cases). In this specification, the aluminum profile is a general term for aluminum or aluminum alloy profiles.

[0002]

2. Description of the Related Art In general, for a building material or the like, an anodizing treatment is performed in an electrolytic solution such as dilute sulfuric acid for the purpose of imparting decorative properties, corrosion resistance, etc., and an anodized film is formed on the surface. . In recent years, anodic oxidation composite coatings with an electrodeposition coating coating on the coating have become the mainstream.However, in the anodizing process, when processing long shapes in large quantities in large processing tanks, Due to various factors, there is a difference in the profile surface temperature, and as a result, the film thickness varies. Conventionally, as a countermeasure, a method of anodizing while spraying an electrolytic solution onto a shape material as an anode (Japanese Patent Publication No. 59-44400, Japanese Patent Publication No. 59-50758, Japanese Patent Application Laid-Open No. 55-79898,
JP-A-57-43996) or a method of anodizing while stirring an electrolytic solution with bubbles such as air (Japanese Patent Publication No. Sho 61-105).
No. 60, JP-A-55-54600, JP-A-55-11
No. 9199, JP-A-57-13196). In the former method, an electrolyte solution is used, and in the latter method, air bubbles are used. In each case, the surface temperature of the shaped material is made uniform to reduce the variation in film thickness. However,
Each of these methods requires equipment costs, frequently causes troubles during production, and has many problems from the viewpoint of equipment maintenance. For example, in the case of the former method, the piping from which the electrolytic solution is blown out is often damaged by the contact of the profile, and the maintenance thereof becomes very burdensome. As described above, it is hard to say that the conventional technology is necessarily linked to cost reduction.

On the other hand, during anodization, hydrogen gas is generated as fine bubbles at the cathode. This hydrogen gas bubble
If left undisturbed, it diffuses into the electrolyte and then rises to the electrolyte surface and bursts, generating mist. Since these mist significantly deteriorate the working environment, a barrier (Cathode Gas Filtration) that permeates the electrolyte but does not allow hydrogen gas bubbles to permeate.
ter, hereafter abbreviated as CGF) is attached to the entire surface of the cathode to suppress all diffusion of hydrogen gas into the electrolyte and to quickly evacuate the hydrogen gas to the outside of the system to prevent mist scattering. We have been (Japanese Patent Publication No. 58-4475)
9, JP-B-59-24199, JP-A-55-273
No. 8, JP-A-55-58390, JP-A-56-334
No. 69, JP-A-57-41397). In this case, since there is no agitation action on the electrolytic solution by the hydrogen gas bubbles, the temperature of the electrolytic solution at the upper portion of the processing tank increases, and accordingly, the film thickness at the upper portion of the profile tends to increase. Conversely, when the CGF is not attached due to restrictions on facilities, the upper portion of the profile becomes extremely thin due to the flow of the electrolyte produced by the hydrogen gas. There is a difference in the distribution tendency of the film thickness, but in all cases, the film is not evenly formed, so if a minimum film thickness is to be secured, an excessive current must be applied, and excessive power is consumed during anodization. At present, it is inevitable.

[0004]

As described above, the method of reducing the variation in the film thickness by spraying the electrolyte solution or stirring the electrolyte solution by bubbles such as air as described above is required in terms of cost and operation. There's a problem. On the other hand, CG
F is mainly used only for environmental measures, that is, only to quickly exhaust hydrogen gas that causes mist to the outside of the system. Until now, this hydrogen gas has been actively used for controlling the film thickness. No attempt has been made to do so. The present invention has been made in view of such prior art, and actively uses hydrogen gas generated during anodic oxidation for controlling the film thickness.
The purpose is to reduce variations in film thickness while suppressing the effects of mist. In particular, an object of the present invention is to provide a method for easily controlling the film thickness by a relatively simple method of changing the form of CGF.

[0005]

According to the present invention, in order to achieve the above object, the thermal diffusivity of an electrolytic solution due to the flow of bubbles of hydrogen gas generated from a cathode at the time of anodic oxidation of an aluminum material is utilized. The present invention provides a method for controlling the thickness of an oxide film when an anodic oxide film is formed on an aluminum shape, wherein the method controls the surface temperature of the profile and thereby controls the thickness of the anodic oxide film. More specifically, by controlling the state of the size of the bubbles of hydrogen gas flowing in the shape direction in the electrolyte solution, the density in the liquid, etc., for example, control is performed stepwise or stepwise in the vertical direction of the processing tank. In the case of an existing anodizing apparatus, or in the case of an existing anodizing apparatus, the size of the hydrogen gas bubbles partially corresponds to the current anodic oxidation film thickness distribution characteristics,
By controlling the state such as the liquid density, the surface temperature of the profile is controlled, and the thickness of the anodic oxide film is controlled. The state of hydrogen gas bubbles flowing in the shape direction, such as the size of bubbles in the liquid and the density in the liquid, can be controlled relatively easily by changing the size or distribution and / or arrangement of the micropores of the barrier provided around the cathode. Can be.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The presence of a variation in the film thickness generally means that the profile surface temperature during the anodic oxidation varies. In other words, the rate of film formation during anodization is temperature-dependent, and current flows more easily in areas where the surface temperature of the profile is high, so more current flows, resulting in a thicker film and conversely, the surface temperature of the profile The lower the part, the thinner the film. In the areas where a large amount of current flows, the surface temperature of the profile increases further due to Joule heat or oxidation reaction heat, causing a synergistic effect such that more current flows, and as a result, variations in the film thickness are amplified more and more. You. Factors that cause variations in the profile surface temperature are the electrolyte temperature around the profile and its flow (flow direction and strength) except for the edge effect of the current and the bias of the profile surface temperature due to the action of the surplus cathode. ) Is considered to be the main one. If heat is uniformly removed from a profile that generates heat uniformly, the profile surface temperature becomes uniform. For that purpose, it is necessary to make the temperature of the electrolytic solution in the processing tank and the flow of the solution to the profile as uniform as possible. In order to make the electrolyte temperature uniform, it is necessary to forcibly agitate the electrolyte solution, and to impart a uniform flow to the profile, it is necessary to cause a forced flow in the electrolyte solution. Even if the heat is generated uniformly, if the heat is not diffused uniformly from the shape due to the difference in electrolyte temperature and liquid flow around the shape, the surface temperature of the shape will be uneven In addition, the film thickness varies.

The present invention stirs the electrolytic solution by the flow of hydrogen gas bubbles generated on the cathode during anodization, controls the diffusion of hydrogen gas bubbles at that time, and utilizes the thermal diffusivity due to the flow of hydrogen gas bubbles. And the profile surface temperature is made uniform. Hereinafter, the method of the present invention will be described with reference to FIG. FIG. 1 schematically shows the anodizing apparatus and the flow of the electrolytic solution. In the drawing, reference numeral 1 denotes an anodizing tank, 2 denotes a cathode, 3 denotes an aluminum material (anode), 4 denotes a CGF, and 5 denotes a circulation pipe disposed near the bottom of the tank. Note that an exhaust hood (not shown) is provided above the cathode 2.

At the time of anodic oxidation, the shaped material generates heat due to Joule heat generated by the flow of electric current and heat of oxidation reaction accompanying the formation of an oxide film, and the temperature of the electrolytic solution L gradually rises. Therefore, the electrolyte solution overflowing from the upper part of the anodizing tank 1 is cooled to a predetermined temperature through a heat exchanger (not shown), and then is provided at the bottom of the tank via a circulation pipe 5 as shown by a solid line arrow in FIG. It is returned with a gentle flow and rises. In addition, profile 3
The flow of the electrolytic solution L by natural convection as shown by a broken arrow in FIG. At this time, the CG that does not allow bubbles of hydrogen gas to pass therethrough so as to cover the entire circumference of the cathode 2
When F4 is provided, the temperature of the electrolyte and the surface of the profile is
Are distributed so as to gradually rise from the bottom to the top. As a result, generally, as described above, the coating thickness gradually increases from the lower portion to the upper portion of the profile, and a large variation in the film thickness occurs at the lower portion and the upper portion of the profile (Comparative Example 1 described later).
And FIG. 3). Conversely, when no CGF is provided around the cathode 2, in addition to the problem of mist generation as described above, the flow of the electrolyte L that rises with the rise of the hydrogen gas bubbles is:
At the surface of the electrolytic solution, the fluid flows toward the profile, and the stirring action of the electrolytic solution at the upper portion of the profile increases, so that the surface temperature of the upper portion of the profile decreases. As a result, in general, the coating thickness gradually increases from the lower portion of the profile to the upper portion, but rapidly decreases at the upper portion of the profile (see Comparative Example 2 and FIG. 5).

Therefore, in the method of the present invention, hydrogen gas bubbles having a size and an amount (amount of hydrogen gas bubbles per unit volume of the electrolytic solution, that is, a liquid density) that do not significantly affect the generation of mist are formed. The heat of the profile is uniformly diffused by the flow (stirring) of the electrolytic solution L accompanying the diffusion of the hydrogen gas bubbles as shown by the hollow arrows in FIG. The purpose is to make the material surface temperature uniform and thereby obtain a uniform film thickness. That is, CG
The amount of diffusion of hydrogen gas bubbles into the electrolytic solution, and the amount of heat radiation from the profile by partially manipulating the diffusion, by changing the size of the fine pores of F4 or the form such as the distribution and arrangement of the pores. Control so that the profile surface temperature is uniform. Since the electrolyte is stirred by the diffusion of hydrogen gas bubbles, the temperature of the electrolyte becomes fairly uniform, and the increase in the temperature of the electrolyte at the top of the processing tank, which is seen when a CGF that does not diffuse hydrogen gas bubbles at all, is installed. Is suppressed.

The CGF does not hinder the permeation of the electrolyte, does not hinder the anodic oxidation, and has a CGF of hydrogen gas bubbles.
It is necessary to have fine pores capable of controlling the amount of diffusion from the glass. Although it varies depending on the material of the CGF and the pressure at which the hydrogen gas bubbles try to diffuse out of the CGF, diffusion of the hydrogen gas bubbles is almost hindered if the size of the micropores is about 0.005 mm or less, and about 0.5 mm. Is exceeded, the diffusion of hydrogen gas bubbles is hardly hindered. Micropore size from 0.005mm to 0.5
If it is between mm, the diffusion amount of the hydrogen gas bubbles changes according to the size. Rather than diffusing the hydrogen gas out of the CGF at all, using techniques such as changing the size of the micropores in the CGF or partially removing the CGF, the amount of hydrogen gas bubbles diffused into the electrolyte and the amount of liquid The medium density can be controlled. The present invention controls the diffusion amount of hydrogen gas bubbles and the density of the hydrogen gas in the liquid, thereby suppressing the variation in the surface temperature of the shaped material and achieving a uniform film thickness.

The material of the CGF may be a non-conductive material which is not affected by the electrolytic solution. For example, a synthetic resin fiber or a porous sintered material can be suitably used. As a method of attaching to the cathode, a method of attaching a bag-shaped thing to each cathode, a method of attaching a bag-shaped thing to several cathodes collectively, a method of inserting a sheet-shaped thing between the cathode and the shape,
There is a method in which the periphery of the cathode is used as a cathode chamber and isolated by a barrier.

When the thick film portion exists partially, that is, when the surface temperature of the profile of the portion is relatively higher than that of the other portion, the form of CGF is changed so as to diffuse hydrogen gas bubbles there. It is only necessary to select and lower the profile surface temperature. If the film thickness distribution of an existing production line has unique characteristics, it is possible to make the film thickness uniform by adjusting the CGF form according to the characteristics. For example, if there is a thick film portion in the center of the profile in the vertical direction, a CG that diffuses hydrogen gas so that the profile surface temperature at that portion is almost the same as other portions
What is necessary is just to select the form of F. As a method of changing the amount of diffusion of hydrogen gas outside the CGF in the vertical direction, a method of changing the size of the micropores of the CGF or a method of changing the distribution density of the micropores at the same size can be considered. A point to be noted here is the difference between the processing tanks in the vertical direction. Once hydrogen gas diffuses out of the CGF, it rises in the electrolyte without returning to the CGF. In other words, the hydrogen gas diffused from the upper part of the cathode substantially affects only the upper part of the section, but the hydrogen gas diffused from the lower part of the cathode affects not only the lower part of the section but also the central part and the upper part of the section. . On the other hand, in the CGF, since the amount of hydrogen gas in the
The pressure at which hydrogen gas tries to diffuse out of F is higher than in the lower part. In addition, since there is a difference in water pressure between the upper and lower processing tanks, there is also a difference in the size of hydrogen gas bubbles. As described above, due to the difference in the vertical direction of the processing tank, care must be taken when selecting the form of CGF.

[0013]

EXAMPLES Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples, but it goes without saying that the present invention is not limited to the following Examples. In each of the following examples and comparative examples, anodizing was performed in the anodizing tank 1 shown in FIG. The material used was an extruded 6063S aluminum alloy material (1,500 mm length), and eight different shapes were anodized in a dilute sulfuric acid bath at a time. Anodizing conditions were as follows: sulfuric acid concentration 19 w / v%, electrolyte temperature 21 ° C.
The current density was 1.3 A / dm ² and the anodic oxidation time was 30 minutes. The film thickness was measured using the eddy current film thickness meter.
In Form F, the film thickness at the same measurement position was measured (measurement points were 60 points). In addition, in FIG. 3, FIG. 5, FIG. 7, FIG. 9, FIG. 11, FIG.
Is the leftmost profile of the eight, "right" is the rightmost profile of the eight, "center" is the profile located at the center of the eight, "center (short)" is The measurement data of each of the profiles arranged in the central portion having half the length of the other profiles among the eight profiles is shown.

Comparative Example 1 FIG. 2 shows the CGF morphology (partial view) used, and FIG. 3 shows the obtained film thickness distribution. C that does not transmit hydrogen gas bubbles at all
When GF (mesh size (mesh mesh size, the same applies hereinafter) 0.001 mm) 4a was attached to all of the cathodes 2 and anodized, the upper part of the profile became thick.

Comparative Example 2 The form of the cathode used is shown in FIG. 4, and the distribution of the obtained film thickness is shown in FIG. When anodic oxidation was performed without attaching any CGF, the upper part of the profile became extremely thin.

Example 1 FIG. 6 shows the CGF morphology (partial view) used, and FIG. 7 shows the obtained film thickness distribution. CG that slightly permeates hydrogen gas bubbles
Anodization was performed in the same manner as in Comparative Example 1 except that F (mesh size: 0.05 mm) 4b was attached to all of the cathodes 2, and the thick film tendency at the upper part of the profile was slightly relaxed as compared with Comparative Example 1. Was.

Example 2 FIG. 8 shows the CGF morphology (partial view) used, and FIG. 9 shows the obtained film thickness distribution. CGF (mesh size 0.2 mm) 4c that transmits most hydrogen gas bubbles into cathode 2
When anodic oxidation was performed in the same manner as in Comparative Example 1 except that all were attached, the tendency of the thin film on the upper portion of the profile was slightly relaxed as compared with Comparative Example 2.

Example 3 FIG. 10 shows the CGF morphology (partial view) used, and FIG. 11 shows the obtained film thickness distribution. Comparative Example 1 except that CGF (mesh size 0.001 mm) 4a, which does not transmit hydrogen gas bubbles at all, was attached only to upper 2/3 of cathode 2.
When anodic oxidation was performed in the same manner as in
(Without GF), the film became slightly thick near the boundary between the presence and absence of CGF, but the tendency of thick film on the upper part of the profile as in Comparative Example 1 was almost completely eliminated.

Example 4 FIG. 12 shows the CGF morphology (partial view) used, and FIG. 13 shows the obtained film thickness distribution. Anodizing was performed in the same manner as in Comparative Example 1 except that CGF (mesh size 0.001 mm) 4a, which did not transmit hydrogen gas bubbles at all, was attached to the upper 2/3 of the cathode 2 and 1/3 of the total number. (The lower third of the cathode, which is 1/3 of the total number, has no CGF), and a relatively uniform coating thickness distribution was obtained.

Example 5 FIG. 14 shows the CGF morphology (partial view) used, and FIG. 15 shows the obtained film thickness distribution. The lower one-third is CGF (mesh size 0.2m) that almost transmits hydrogen gas bubbles.
m) 4c, CGF (mesh size 0.05 mm) 4b that is slightly transparent at the center 1/3, CGF (mesh size 0.001 mm) 4a that is completely transparent at the top 1/3
Anodizing was performed in the same manner as in Comparative Example 1 except that the CGF changed in the vertical direction was attached to the entire surface of the cathode 2 as described above, and a relatively uniform film thickness distribution was obtained. Table 1 below shows the standard deviation of the film thickness obtained in each of the above Examples and Comparative Examples.
Shown in

[Table 1]

[0021]

As described above, according to the method of the present invention,
By actively utilizing the diffusion of the hydrogen gas bubbles for controlling the film thickness, it is possible to reduce the variation in the film thickness and reduce the electric power during anodic oxidation. In particular, the method of controlling the size of hydrogen gas bubbles, liquid density, etc. by changing the form of CGF can be performed relatively easily, and also leads to reduction in variation in film thickness and, consequently, power reduction during anodic oxidation. Its industrial value is extremely large.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an anodizing apparatus used in each of Examples and Comparative Examples.

FIG. 2 is a partial morphological diagram of CGF used in Comparative Example 1.

FIG. 3 is a graph showing the results of measuring the film thickness obtained in Comparative Example 1 (the results of four of the eight films having the same shape).

FIG. 4 is a partial form view of a cathode used in Comparative Example 2.

FIG. 5 is a graph showing film thickness measurement results (four results of the same shape out of eight films) obtained in Comparative Example 2.

FIG. 6 is a partial morphological diagram of CGF used in Example 1.

FIG. 7 is a graph showing the results of measuring the film thickness obtained in Example 1 (the results of four of the eight films having the same shape).

FIG. 8 is a partial morphology diagram of CGF used in Example 2.

FIG. 9 is a graph showing the results of measuring the film thickness obtained in Example 2 (4 out of 8 films having the same shape).

FIG. 10 is a partial morphology diagram of CGF used in Example 3.

FIG. 11 is a graph showing film thickness measurement results (four results of the same shape out of eight films) obtained in Example 3.

FIG. 12 is a partial morphological diagram of CGF used in Example 4.

FIG. 13 is a graph showing film thickness measurement results (four results of the same shape out of eight films) obtained in Example 4.

FIG. 14 is a partial morphology diagram of CGF used in Example 5.

FIG. 15 is a graph showing the results of measuring the thickness of the film obtained in Example 5 (the results of four of the eight films having the same shape).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Anodizing tank 2 Cathode 3 Aluminum profile (anode) 4 CGF 5 Circulation pipe L Electrolyte

Claims (5)

[Claims] 1. A method for controlling the thickness of an anodic oxide film by controlling the surface temperature of an aluminum profile by utilizing the thermal diffusivity of an electrolytic solution caused by the flow of hydrogen gas bubbles generated from a cathode during anodization of the aluminum profile. A method for controlling the thickness of an oxide film when an anodic oxide film is formed on an aluminum material. 2. A method for controlling the surface temperature of a profile by controlling the size and density of a hydrogen gas flowing in an electrolytic solution toward the aluminum profile in the direction of the aluminum profile, thereby controlling the thickness of the anodic oxide film. Item 7. The method according to Item 1. 3. The shape of a hydrogen gas flowing in an electrolytic solution in the direction of an aluminum shape, such as the size and density of bubbles in the liquid, is controlled partially or stepwise in the vertical direction of the processing tank. The method according to claim 1, wherein the surface temperature is controlled and the thickness of the anodic oxide film is controlled. 4. A method of controlling the shape of a hydrogen gas flowing in the direction of an aluminum profile by partially controlling the size of bubbles, the density in a liquid, and the like of the hydrogen gas in accordance with the thickness distribution characteristics of the anodized film during anodization. The method according to claim 1, wherein the surface temperature is controlled and the thickness of the anodic oxide film is controlled. 5. The state of the size of hydrogen gas bubbles flowing in the direction of the aluminum material, such as the size and density in a liquid, is controlled by changing the size or the distribution and / or arrangement of the micropores of the barrier provided around the cathode. The method according to any one of claims 2 to 4.