JPH01218607A - Filtration membrane and its production - Google Patents

Abstract

PURPOSE:To obtain a membrane of superior selectivity and permeability, having ultrafine penetrating pores in high density and uniformly, by carrying out an anodic oxidation treatment on both faces of a highly pure aluminum foil to form anodic oxide films having a large number of fine pores and then by applying an electrolytic etching treatment to it. CONSTITUTION:A filtration membrane is produced by carrying out an anodic oxidation treatment on both faces of a highly pure (99.9% or more) aluminum foil with an electrolytic solution of such as sulfuric acid or oxalic acid to form anodic oxide films (ca. 0.1-10mum in thickness) having a large number of fine pores and then by applying an electrolytic etching treatment to it. By this treatment, etching proceeds from the fine pores of the anodic oxide film, the nuclei of etching, and fine etch pits penetrating the foil are formed, which give the foil a separability for fine foreign particles. Moreover, if a monomolecular film of polysiloxane polymer is supported on this membrane, for example, a uniform supporting membrane for gas separation can be formed, because surface diameters of etch pits are so small and uniform.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a filtration membrane used for purposes such as purification, purification, or separation of gases, liquids, or mixtures thereof from solids, particularly as a filter element. The present invention relates to a method for manufacturing a filtration membrane using porous electrolytically etched foil.

Conventional technologies and issues Conventionally, filtration membranes for the above-mentioned purposes have been
For example, organic filtration membranes made of polymeric materials such as cellulose acetate, cellulose acetate, polysulfone, and polyolefin are most commonly used. However, these organic filtration membranes have poor heat resistance and cannot be subjected to heat sterilization treatment, and also have problems with chemical resistance, solvent resistance, oil resistance, etc., and their uses are limited.

On the other hand, as filtration membranes with excellent heat resistance, those made of porous bodies of inorganic materials such as Vycor glass, carbon tubes, and silica/alumina ceramics are known. The body is used a lot.

However, in the case of filtration membranes made of these inorganic materials, the pore diameter is not uniform, and the direction of the pores that perform the filtration function does not match the flow direction of the fluid, resulting in poor fluid permeation properties. It is difficult to manufacture a filtration membrane while freely controlling the pore size in order to obtain a filtration membrane with a uniform micropore size, and there are problems such as the difficulty in manufacturing a filtration membrane with a uniform micropore size, which also limits its use. It was something.

Recently, filtration membranes using aluminum foil have been stabilized by etching high-purity aluminum foil to form through-etched pits with the required pore size, and by forming an anodic oxide film or hydroxide film on the surface. (For example, Japanese Patent Application Laid-Open No. 62-30
No. 511).

However, since the pores to perform the filtration function are formed as etched pits, the pore size can be controlled to a certain degree with some degree of freedom. In the range of When used as a support for a gas separation membrane to be condensed, there is a problem in that a supporting membrane for separation cannot be uniformly formed. That is,”
For bipedal oxygen separation, for example, 0
Siloxane-based polymer monomolecular films, which are reported to have a dissolution rate of 2/1 in 02/N2, are used in an accumulated and composite manner. Since the pore diameters are large, especially in the surface area of the foil, and have large variations, there has been a problem that the monomolecular membrane for oxygen separation has poor supporting properties and cannot be uniformly formed.

On the other hand, recently, porous aluminum has been used as a filtration membrane that can selectively block the passage of extremely fine foreign particles and has excellent properties such as gas permeability, heat resistance, and chemical resistance. The use of anodic oxide films is attracting attention.

However, since such anodic oxide films are originally brittle and breakable, it has been difficult to manufacture them into large films that can be used industrially.

In order to solve these problems, a filtration membrane has recently been proposed in which a porous aluminum foil or thin plate, which can function as a back-up layer, is laminated on one side of an anodic oxide film. The proposal is published in Japanese Unexamined Patent Publication No. 62-1.291.0
As seen in Publication No. 6, this conventionally proposed filtration membrane forms an anodic oxide film on one side of an aluminum foil or thin plate, and connects the fine pores of the oxide film to the aluminum substrate from the other side using photolithography technology. A large number of communicating pores are formed. For this reason, especially in the above-mentioned photolithography process, it is necessary to carry out a series of multiple steps such as oxidation → photoresist coating → masking-exposure → development → etching and photoresist removal, and process control is also complicated, resulting in poor manufacturing efficiency and poor production efficiency. However, there were some problems such as high costs.

Against this backdrop, the present inventors previously proposed a method for manufacturing a filtration membrane using an anodized film using electrolytically etched aluminum foil as a reinforcing material (Japanese Patent Application No. 62-21).
No. 9884). This manufacturing method involves electrolytically etching high-purity aluminum foil from one side as the first step.
A large number of etching pits are formed with a depth just up to the depth of the foil, and then, as a second step, the opposite side of the foil is anodized to form an anodized film having a large number of micropores as a filter element. After this formation, the final third step is to perform a penetration treatment in which the etching pits are immersed in a soluble treatment solution to communicate with the fine pores of the anodic oxide film. However, when using this method, it is difficult to control the depth of the etching pit I to a depth just before penetrating the foil in the first electrolytic etching step, and a penetrating portion of the etching pit occurs in the negative part. This has led to the discovery of a new problem in industrial production, which is the great difficulty of process control.

Therefore, it is an object of the present invention to further solve this problem and to obtain a filtration membrane having extremely fine through-holes at a high density and uniformity and having excellent selectivity and permeability.

Means for Solving the Problems This invention first performs anodic oxidation treatment on both sides of a high-purity aluminum foil, and uses the fine pores of the oxide film as etching nuclei in the subsequent electrolytic etching treatment to uniformly and oxidize the foil. The main feature is that fine penetrating etching pits are formed at high density.

That is, the present invention uses high purity aluminum foil of 99.9% or more, anodizes both sides of the foil to form an anodic oxide film having a large number of micropores, and then electrolytically etches the foil to form an anodic oxide film having a large number of micropores. This method of manufacturing a filtration membrane is characterized by forming uniform and fine penetrating etching pits using the micropores of the anodic oxide film as etching nuclei.

The reason why we use high-purity aluminum foil with a purity of 99.9% or higher is to ensure that the etching pits formed by electrolytic etching are formed in a direction perpendicular to the foil surface. This is to avoid impeding the formation or growth of the pits due to the presence of impurities. Most preferably purity is 99.
It is preferable to use 99% or more.

Also, its thickness is O,! It is preferable to use a material with a thickness of 5 mm or less, and in particular, a material with a thickness of approximately O, lt nm is preferably used.

As the first manufacturing step, both surfaces of the aluminum foil are anodized to form a porous anodic oxide film on the illuminated surface. This anodic oxidation treatment is performed as an electrolyte
30wt% sulfuric acid, 1-5wt% oxalic acid, 5-30wt
Using any bath selected from % phosphoric acid, 1 to 10 wt % chromic acid, and mixed acid baths thereof, the bath temperature is about 10 to 50 °C (sulfuric acid bath 10 to 30 °C, oxalic acid bath 10 to 50 °C) according to a conventional method. Electrolytic treatment is performed in a 40°C phosphoric acid bath (10 to 50°C) and a chromic acid bath (10 to 50°C). Further, this electrolytic treatment may be performed using any of direct current, alternating current, alternating current, and pulsed current. Further, the same electrolysis may be performed by -membrane electrolysis, or may be performed in multiple stages of two or more stages,
In this case, the first-stage electrolytic treatment is a normal electrolytic treatment until an oxide film of a predetermined thickness is obtained, and the second-stage electrolytic treatment is performed at a constant voltage that is rapidly lowered to a value within a predetermined range from the voltage applied during the first-stage electrolytic treatment. Advantageously, this is carried out by electrolytic treatment.

By the above anodizing treatment, both sides of the aluminum foil have a thickness of 0. A porous anodic oxide film of 1 to 10 μm is formed. By changing the anodic oxidation treatment conditions, the fine pores of this film can be created with a pore diameter of 100 to 2000 and an area ratio of 4.5.
It can be freely controlled within the range of ~40%.

Next, as a second step, the aluminum foil on which anodized films have been formed on both sides in the first step is subjected to an electrolytic etching treatment using a direct current in an aqueous solution containing chlorine ions according to a conventional method. By this electrolytic etching treatment, etching progresses using the fine pores of the anodic oxide film on both sides of the aluminum foil as etching nuclei, and the desired filtration membrane is obtained by forming fine penetrating etching pits that penetrate the foil. Can be done.

Of course, this filtration membrane can be put to practical use as a high-performance membrane with the ability to separate extremely fine foreign particles, but it can also be used for gas separation, such as when separating nitrogen from air to increase oxygen concentration. In applications, bipedal etched foil filtration membranes are used as supports for gas separation carrier membranes. In this case, one side of the support is subjected to a treatment to support a gas separation support membrane, for example, to support a polysiloxane polymer monomolecular film. The thinner the support membrane is, the better the gas permeability will be, but the mechanical strength of the membrane itself will be lower. Therefore, in order to avoid damage while maintaining good permeability, it is desirable that the etching pits functioning as permeation holes on the support side be as small and uniform as possible, especially in the diameter of the holes on the back side. In this sense, the etched aluminum foil according to the present invention is suitable in that fine through-etched pits can be formed uniformly and densely.

Examples Example 1 An annealed aluminum foil made of AlN99 aluminum material and having a width of 100 mm, a length of 200 mm, and a thickness of 0.1 mm (
1) is used as a material, and as a first step, both sides are subjected to anodizing treatment under the following electrolytic conditions, thereby forming an anodic oxide film (2
) was obtained (Fig. 1).

(Anodizing treatment conditions) Liquid composition: 15wt% sulfuric acid solution Temperature: 20±1°C Electrolytic conditions: DC 1.5A/d7dX5 minutesNext, as the second step electrolytic etching treatment, the above-mentioned anodized aluminum foil was Both surfaces were electrolytically treated under the following conditions to obtain the desired filtration membrane (A) having a large number of through-etching pits (4) that penetrated the foil using the micropores (3) of the anodic oxide film as etching nuclei.

(Electrolytic etching treatment conditions) Liquid composition: 5wt% HCQ+ 0, 1wt% H2C204 liquid Temperature: 70±2°C Current density: D, C15A/d processing time: 100 seconds Example 2 Anodizing treatment was performed as follows. A filtration membrane (A) was obtained in the same manner as in Example 1 except for the above steps.

(Anodizing treatment conditions) Liquid composition: 15wt% sulfuric acid solution Temperature: 20±1°C Electrolysis method: Multi-stage electrolysis Electrolysis conditions: First stage, DC IA/d bottom x 5 minutes Second stage, constant voltage several times at a lower voltage than the first stage Electrolysis (Final 2V) The anodic oxide film on the surface of the aluminum foil obtained by the above anodic oxidation treatment had a barrier film with a thickness of about 20 μm.

Example 3 A filtration membrane (A) was obtained in the same manner as in Example 1, except that the anodic oxidation treatment was performed as follows.

(Anodizing treatment conditions) Liquid composition + 3vt% oxalic acid solution Temperature: 30±1°C Electrolysis conditions: DC I A/d 7Itx 5 minutes The anodic oxide film formed by the above anodizing treatment has a thickness of approximately 1.5 μm.
It was from m.

Example 4 A filtration membrane (A) was obtained in the same manner as in Example 1, except that the anodic oxidation treatment was performed as follows.

(Anodizing treatment conditions) Liquid composition: 10 wt% phosphoric acid solution Temperature: 30±1°C Electrolytic conditions: DC constant voltage 10 Vxl□min The anodic oxide film formed by the above anodizing treatment has a thickness of approximately 0.5 μm. It was something.

Comparative Example 1 The same aluminum foil as in Example 1 was subjected to the same electrolytic etching treatment as in the second step of Example 1 without being anodized, as schematically shown in Figure 3. A filtration membrane (B) having a large number of etched pits (4) through the aluminum foil (11) was obtained. The etched pits (14) of this filtration membrane (B) had an irregular pore diameter, and in particular had enlarged portions (14a) of irregular pore diameter on the surface.

Comparative Example 2 After electrolytic etching was performed in the same manner as in Comparative Example 1, electrolytic treatment was further performed as a pore size reduction treatment under the following conditions to obtain a filtration membrane.

(Pore size reduction treatment) Liquid composition: 15vt% sulfuric acid solution Temperature: 25°C Electrolysis conditions: DC 1. OA/dTIIX 5 minutes [Comparative evaluation] Each of the filtration membranes obtained in Examples 1 to 4 and the comparative example above was used as a sample, and each sample was supported with a polysiloxane polymer monomolecular film as a gas separation support membrane (5). In addition to investigating the gas permeation characteristics by incorporating it into a gas permeation device, we also investigated the support processability of the support membrane. The results are shown in Table 1 below.

[Margin below]

Table 1 (Note) Supporting processability was evaluated as follows.

O: As shown in FIG. 2, the supporting film was formed uniformly and without defects.

×2 As shown in Figure 3, film defects such as tears and defects were observed in the supporting film.

As shown in Table 1 above, the examples of the present invention exhibited good and stable gas permeation properties both before and after the supporting treatment of the supported film, and as in the comparative example, defects in the supported film caused adverse effects on the permeation properties. It was confirmed that no significant changes occurred and that excellent separation function could be achieved.

Effects of the Invention According to the present invention, it is possible to obtain a filtration membrane that is originally made of aluminum and has excellent physical properties such as heat resistance, chemical resistance, and oil resistance. By having fluid circulation holes including micropores and etched pits extending perpendicularly to the thickness direction of the foil, a filtration membrane with excellent fluid permeation properties can be obtained.

In particular, before electrolytic etching, anodizing is performed to form a porous anodic oxide film on both sides of the foil, which prevents surface dissolution during the etching stage.
By using the fine pores of the anodic oxide film as etching nuclei, uniform and fine penetrating etching pits can be formed at a high density. Therefore, the amount of the anodic oxide film is substantially reduced.
- Pores can be made to function as filter elements, and pores with a required pore size can be uniformly formed depending on the purpose of use in manufacturing, and in particular, extremely fine foreign particles with extremely fine pores can be formed. It becomes possible to manufacture a filtration membrane that can be effectively used for the separation of

Furthermore, since the present invention can be carried out in combination with both electrolytic etching and anodic oxidation using simple surface treatment techniques as main steps, manufacturing is simple, and it is possible to carry out the manufacturing process in accordance with the above-mentioned JP-A-62 Compared to a manufacturing method that uses photolithography technology, which itself requires a combination of multiple steps, as shown in '-129106,
It is possible to manufacture a filtration membrane having uniform pores of arbitrary pore size at a low cost with much better productivity.

Furthermore, the aluminum foil used as the raw material is first anodized on both sides in the first step, and then electrolytically etched on both sides in the second step to penetrate the micropores of the anodic oxide film. Compared to the above-mentioned manufacturing method previously proposed by the present inventors, the number of steps can be reduced and process management can be simplified, and manufacturing efficiency and yield can be improved.

Further, in claim 2, it is advantageous in that an anodized film having uniform and fine pores in a high density distribution can be formed by anodizing treatment, and in claim 3,
It suppresses the surface dissolution of the foil during the etching process and enables reliable formation of through-etching pits grown from micropores.

Furthermore, the filtration membranes according to claims 4 and 5 do not cause film defects in the supporting membrane for gas separation, and have excellent durability and 1F.
It can be used for gas separation, especially oxygen separation, with excellent properties.

[Brief explanation of the drawing]

Figures 1 and 2 show the manufacturing method of a filtration membrane according to the present invention in the order of steps, with Figure 1 showing the state at the end of the anodizing process, and Figure 2 showing the state after the electrolytic etching process is completed. FIG. 2 is a schematic cross-sectional view showing the state in which the supporting film is supported. FIG. 3 is a schematic cross-sectional view showing a filtration membrane formed only by etching treatment after being treated with a supported membrane. (1)... Aluminum foil, (2)... Anodized film, (3)... Fine pores, (4)... Penetration etching pits, (5)... Support film. that's all

Claims (1)

[Claims] (1) Using high purity aluminum foil of 99.9% or more,
After anodic oxidation treatment is performed on both sides to form an anodic oxide film having many micropores, an electrolytic etching treatment is performed to form uniform and fine penetrating etching pits using the micropores of the anodic oxide film as etching nuclei. 1. A method for manufacturing a filtration membrane, characterized by forming a filtration membrane. (2) Manufacturing the filtration membrane according to claim (1), wherein the anodizing treatment is performed using an electrolytic solution containing one or more selected from sulfuric acid, oxalic acid, phosphoric acid, and chromic acid. Method. (3) The method for manufacturing a filtration membrane according to claim (1) or (2), wherein the anodic oxide film is formed to have a thickness in the range of 0.1 to 10 μm. (4) A filtration membrane comprising a supporting membrane for gas separation formed on one side of an aluminum foil in which through-etched pits are formed according to claim (1). (5) The filtration membrane according to claim (4), wherein the gas separation support membrane comprises a polysiloxane polymer monolayer.