JP2008202112A - Microstructure and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a porus alumina membrane filter having excellent acid resistance, alkali resistance and excellent filtration rate, a microstructure suitable for the porus alumina membrane filter and a method of manufacturing the microstructure. <P>SOLUTION: The method of manufacturing the microstructure is carried out by applying (A) a treatment of forming an oxide film having micropores by an anodic oxidation treatment on the surface of an aluminum substrate and (B) a treatment of heating the oxide film formed in (A) at ≥50°C at least for 10 min in this order to obtain the microstructure having the micropores on the surface. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a microstructure and a manufacturing method thereof. The present invention also relates to a porous alumina membrane filter using the microstructure.

  Membrane filters put to practical use in the field of microfiltration include organic membrane filters and inorganic membrane filters, and organic membrane filters are widely used in practice. Many of these organic membrane filters do not have independent pores and have a relatively wide pore size distribution, so research to further improve the accuracy of separation of specific substances, which is the most important function of the filter, has been conducted. It is proceeding in various directions.

  In order to solve such problems, for example, in Non-Patent Document 1, etc., the organic film made of a polymer is irradiated with high energy particles generated from a nuclear reactor, and the tracks through which the particles have passed through the organic film are etched to form pores. A so-called track etching method is known. This track etching method can obtain independent pores with a narrow pore diameter distribution that are perpendicular to the organic film, but in order to avoid the generation of double holes due to the incidence of particles overlapping during track formation, There was a problem that the density, the so-called vacancy rate, could not be increased.

  On the other hand, as an inorganic membrane filter, a porous alumina membrane filter using an anodic oxide film of aluminum is known, as is known, for example, in Non-Patent Document 2. By anodizing aluminum in an acidic electrolyte, independent pores with a narrow pore size distribution are arranged with a high vacancy rate, so a membrane filter with a high filtration flow rate per hour can be manufactured at low cost. be able to.

  However, the porous alumina membrane filter does not have sufficient acid resistance and alkali resistance of the aluminum anodized film, and improvement is desired.

T.A. D. Block, Membrane Filtration, Sci. Tech, Inc. , Madison (1983) Hideki Masuda, “New Technology of Porous Membrane Using Anodization”, Altopia, July 1995

  Accordingly, the present invention provides a porous alumina membrane filter excellent in acid resistance and alkali resistance and excellent in filtration flow rate, a fine structure suitable for the porous alumina membrane filter, and a method for producing the fine structure. With the goal.

  As a result of intensive studies to achieve the above object, the present inventor completed the present invention by forming an anodized film having micropores and then heat-treating the anodized film.

That is, the present invention provides the following (i) to (iv).
(I) (A) a treatment for forming at least an oxide film having micropores on the surface of the aluminum substrate by anodic oxidation; and (B) at least the oxide film formed in (A) at a temperature of 50 ° C. or higher. Treatment for 10 minutes,
Is applied in this order to obtain a fine structure having micropores on the surface.
(Ii) In addition,
(C) The process which removes aluminum from the oxide film obtained by said (A), and (D) The process which penetrates the micropore of the oxide film obtained by said (A),
Are applied in this order, and then (B) is applied to obtain a microstructure having a micropore through-hole on the surface thereof.
(Iii) A fine structure obtained by the method for producing a fine structure according to (i) or (ii) above.
(Iv) a microstructure comprising an anodized aluminum film and having micropores,
In the anodized film, the S atom concentration is 3.2 wt% or less, the C atom concentration is 2.5 wt% or less, and the P atom concentration is 1.0 wt% or less. .
(V) The microstructure according to (iv), wherein the microstructure has a micropore through hole.
(Vi) The microstructure according to any one of (iii) to (v), wherein the pore diameter dispersion of the micropore is within 3% of the average diameter.
(Vii) The microstructure according to any one of the above (iii) to (vi), wherein the degree of ordering defined by the following formula (1) is 50% or more for the micropore.
Ordering degree (%) = B / A × 100 (1)
In the above formula (1), A represents the total number of micropores in the measurement range. B is centered on the center of gravity of one micropore, and when a circle with the shortest radius inscribed in the edge of another micropore is drawn, the center of gravity of the micropore other than the one micropore is placed inside the circle. This represents the number in the measurement range of the one micropore to be included.
(Viii) A porous alumina membrane filter using the microstructure according to any one of the above (iii) to (vii).

  According to the present invention, a porous alumina membrane filter excellent in acid resistance and alkali resistance and excellent in filtration flow rate can be obtained.

The present invention is described in detail below.
The manufacturing method of the microstructure of the present invention is as follows:
(A) At least a treatment for forming an oxide film having micropores by anodizing treatment on the surface of the aluminum substrate, and (B) The oxide film formed in (A) is heated at a temperature of 50 ° C. or higher for at least 10 minutes. Processing,
Are applied in this order to obtain a microstructure having a micropore on the surface.

<Aluminum substrate>
The aluminum substrate is not particularly limited. For example, a pure aluminum plate; an alloy plate containing aluminum as a main component and containing a small amount of foreign elements; a substrate obtained by depositing high-purity aluminum on low-purity aluminum (for example, recycled material); silicon Examples of the substrate include a substrate in which high purity aluminum is coated on the surface of a wafer, quartz, glass or the like by a method such as vapor deposition or sputtering; a resin substrate in which aluminum is laminated.

  Of the aluminum substrate, the surface on which the anodized film is provided by anodizing treatment preferably has an aluminum purity of 99.5% by mass or more, more preferably 99.9% by mass or more, and 99.99% by mass. % Or more is more preferable. When the aluminum purity is in the above range, the regularity of the micropore array is sufficient.

  The surface of the aluminum substrate is preferably subjected to degreasing and mirror finishing in advance.

  Moreover, it is preferable that the aluminum substrate is preliminarily subjected to heat treatment for the fine structure obtained by the present invention. The regularity of the pore arrangement is improved by the heat treatment.

<Heat treatment>
When heat treatment is performed, it is preferably performed at 200 to 350 ° C. for about 30 seconds to 2 minutes. Thereby, the regularity of the arrangement | sequence of the micropore produced | generated by the anodic oxidation process mentioned later improves.
The aluminum substrate after the heat treatment is preferably cooled rapidly. As a method of cooling, for example, a method of directly feeding into water or the like can be mentioned.

<Degreasing treatment>
Degreasing treatment uses acids, alkalis, organic solvents, etc. to dissolve and remove organic components such as dust, fat, and resin that adhere to the aluminum surface, and causes defects in each treatment described later due to the organic components. This is done for the purpose of preventing the occurrence of.
A conventionally known degreasing agent can be used for the degreasing treatment. Specifically, for example, various commercially available degreasing agents can be used by a predetermined method.

Especially, the following each method is illustrated suitably.
A method in which an organic solvent such as alcohol (for example, methanol), ketone, benzine, volatile oil or the like is brought into contact with the aluminum surface at room temperature (organic solvent method); a solution containing a surfactant such as soap or neutral detergent at a temperature from 80 to 80 A method in which the aluminum surface is contacted at a temperature up to ℃, and then washed with water (surfactant method); a sulfuric acid aqueous solution having a concentration of 10 to 200 g / L is brought into contact with the aluminum surface at a temperature from room temperature to 70 ° C for 30 to 80 seconds. Then, a method of washing with water; while a sodium hydroxide aqueous solution having a concentration of 5 to 20 g / L was brought into contact with the aluminum surface at room temperature for about 30 seconds, a direct current having a current density of 1 to 10 A / dm ² was passed with the aluminum surface as a cathode. And then neutralizing with a nitric acid aqueous solution having a concentration of 100 to 500 g / L; various known anodizing electrolytes are usually used. In while in contact with the aluminum surface, the aluminum surface by applying a direct current of a current density of 1 to 10 A / dm ² in the cathode, or a method of electrolysis by passing an alternating current; the alkaline aqueous solution in the concentration of 10 to 200 g / L A method of bringing the aluminum surface into contact at 40 to 50 ° C. for 15 to 60 seconds, and then neutralizing by contacting with an aqueous nitric acid solution having a concentration of 100 to 500 g / L; a surfactant, water or the like was mixed with light oil or kerosene. A method in which the emulsion is brought into contact with the aluminum surface at a temperature from room temperature to 50 ° C. and then washed with water (emulsion degreasing method); a mixed solution of sodium carbonate, phosphates, surfactants, etc. is brought to a temperature from room temperature to 50 ° C. The aluminum surface is brought into contact with the aluminum surface for 30 to 180 seconds and then washed with water (phosphate method).

  The degreasing treatment is preferably a method in which the fat on the aluminum surface can be removed while aluminum is hardly dissolved. In this respect, the organic solvent method, the surfactant method, the emulsion degreasing method, and the phosphate method are preferable.

<Mirror finish processing>
The mirror finishing process is performed to eliminate unevenness on the surface of the aluminum substrate and improve the uniformity and reproducibility of the particle forming process by an electrodeposition method or the like. Examples of the irregularities on the surface of the aluminum substrate include rolling stripes generated during rolling in the case where the aluminum substrate is manufactured through rolling.
In the present invention, the mirror finish is not particularly limited, and a conventionally known method can be used. Examples thereof include mechanical polishing, chemical polishing, and electrolytic polishing.

  Examples of mechanical polishing include a method of polishing with various commercially available polishing cloths, and a method of combining various commercially available abrasives (for example, diamond, alumina) and buffing. Specifically, a method in which the method using an abrasive is performed by changing the abrasive used from coarse particles to fine particles over time is preferably exemplified. In this case, the final polishing agent is preferably # 1500. Thereby, the glossiness can be 50% or more (in the case of rolled aluminum, both the rolling direction and the width direction are 50% or more).

As chemical polishing, for example, “Aluminum Handbook”, 6th edition, edited by Japan Aluminum Association, 2001, p. Various methods described in 164 to 165 may be mentioned.
Further, phosphoric acid - nitric acid method, Alupol I method, Alupol V method, Alcoa R5 _{method, H 3 PO 4 -CH 3 COOH} -Cu _{method, H 3 PO 4 -HNO 3 -CH} 3 COOH method are preferable. Of these, the phosphoric acid-nitric acid method, the H ₃ PO ₄ —CH ₃ COOH—Cu method, and the H ₃ PO ₄ —HNO ₃ —CH ₃ COOH method are preferable.
By chemical polishing, the glossiness can be made 70% or more (in the case of rolled aluminum, both the rolling direction and the width direction are 70% or more).

As electrolytic polishing, for example, “Aluminum Handbook”, 6th edition, edited by Japan Aluminum Association, 2001, p. Various methods described in 164 to 165 may be mentioned.
Moreover, the method described in US Pat. No. 2,708,655 is preferable.
“Practical Surface Technology”, vol. 33, no. 3, 1986, p. The method described in 32-38 is also preferably exemplified.
By electropolishing, the gloss can be 70% or more (in the case of rolled aluminum, both the rolling direction and the width direction are 70% or more).

  These methods can be used in appropriate combination. For example, a method of using an abrasive is preferably performed by changing the abrasive to be used from coarse particles to fine particles over time, and then performing electrolytic polishing.

By mirror finishing, for example, a surface having an average surface roughness R _{a of} 0.1 μm or less and a glossiness of 50% or more can be obtained. The average surface roughness _Ra is preferably 0.03 μm or less, and more preferably 0.02 μm or less. Further, the glossiness is preferably 70% or more, and more preferably 80% or more.
The glossiness is a regular reflectance obtained in accordance with JIS Z8741-1997 “Method 3 60 ° Specular Gloss” in the direction perpendicular to the rolling direction. Specifically, using a variable angle gloss meter (for example, VG-1D, manufactured by Nippon Denshoku Industries Co., Ltd.), when the regular reflectance is 70% or less, the incident reflection angle is 60 degrees and the regular reflectance is 70%. In the case of exceeding, the incident / reflection angle is 20 degrees.

<(A) Micropore formation treatment by anodic oxidation>
In the treatment (A), an aluminum substrate is anodized to form an oxide film having micropores on the surface of the aluminum substrate.
As the anodizing treatment, a conventionally known method can be used. Specifically, it is preferable to use the self-ordering method described later.
The self-ordering method is a method of improving the regularity by utilizing the property that the micropores of the anodized film are regularly arranged and removing the factors that disturb the regular arrangement. Specifically, high-purity aluminum is used, and an anodized film is formed at a low speed over a long period of time (for example, several hours to several tens of hours) at a voltage according to the type of the electrolytic solution.
In this method, since the pore diameter depends on the voltage, a desired pore diameter can be obtained to some extent by controlling the voltage.
In order to form the micropores by the self-ordering method, an anodizing process described later may be performed. Preferably, an anodizing process, a film removal process, and a re-anodizing process described later are performed in this order.

<Anodizing treatment>
The average flow rate during the anodizing treatment is preferably 0.5 to 20.0 m / min, more preferably 1.0 to 15.0 m / min, and 2.0 to 10.0 m / min. More preferably, it is min. By performing anodizing treatment at a flow rate in the above range, uniform and high regularity can be obtained.
Moreover, the method of flowing the electrolytic solution under the above-mentioned conditions is not particularly limited, but, for example, a method using a general stirring device such as a stirrer is used. It is preferable to use a stirrer that can control the stirring speed with a digital display because the average flow rate can be controlled. As such a stirring apparatus, for example, magnetic stirrer HS-50D manufactured by AS ONE can be mentioned.

  For the anodizing treatment, for example, a method of energizing an aluminum substrate as an anode in a solution having an acid concentration of 0.01 to 5 mol / L can be used. The solution used for the anodizing treatment is preferably an acid solution, more preferably sulfuric acid, phosphoric acid, chromic acid, oxalic acid, sulfamic acid, benzenesulfonic acid, amidosulfonic acid, etc., among which sulfuric acid, phosphoric acid, Oxalic acid is particularly preferred. These acids can be used alone or in combination of two or more.

The conditions for anodizing treatment vary depending on the electrolyte used, and thus cannot be determined in general. In general, however, the electrolyte concentration is 0.01 to 5 mol / L, the solution temperature is -10 to 30 ° C., and the current density. 0.01 to 20 A / dm ² , voltage 3 to 300 V, electrolysis time 0.5 to 30 hours are preferable, electrolyte concentration 0.05 to 3 mol / L, solution temperature −5 to 25 ° C., current density 0 0.05 to 15 A / dm ² , voltage 5 to 250 V, electrolysis time 1 to 25 hours is more preferable, electrolyte concentration 0.1 to 1 mol / L, solution temperature 0 to 20 ° C., current density 0.1 to More preferably, it is 10 A / dm ² , a voltage of 10 to 200 V, and an electrolysis time of 2 to 20 hours.

  The treatment time for the anodizing treatment is preferably 0.5 minutes to 16 hours, more preferably 1 minute to 12 hours, and further preferably 2 minutes to 8 hours.

  The anodizing treatment can be performed by changing the voltage intermittently or continuously in addition to being performed under a constant voltage. In this case, it is preferable to decrease the voltage sequentially. This makes it possible to reduce the resistance of the anodized film, and fine micropores are formed in the anodized film, which is preferable in terms of improving uniformity, particularly when sealing treatment is performed by electrodeposition. .

The thickness of the anodized film is preferably 0.1 to 2000 μm, more preferably 1 to 1000 μm, and still more preferably 10 to 500 μm.
The pore diameter of the micropore is preferably 0.01 to 0.5 μm.
The average pore density is preferably 50-1500 / μm ² .

In the range of 1 μm ² , the micropores preferably have a pore diameter dispersion within 3% of the average diameter, and more preferably within 2%. In addition, the average diameter and dispersion | distribution of a pore diameter can each be calculated | required by a following formula.
Average diameter: μ _x = (1 / n) ΣXi
Dispersion: σ ² = (1 / n) (ΣXi ² ) −μ _x ²
Dispersion / average diameter = σ / μ _x ≦ 0.03
Here, Xi is the pore diameter of one micropore measured in the range of 1 μm ² .

  The area ratio occupied by the micropores is preferably 20 to 50%. The area ratio occupied by the micropores is defined by the ratio of the total area of the micropore openings to the area of the aluminum surface.

  Further, at the interface between the anodized film and the aluminum substrate, the degree of ordering defined by the following formula (1) for the micropores is preferably 10% or more, more preferably 15% or more, and 20% The above is more preferable. Within the above range, the processing time of the regularization processing can be shortened, and as a result, the total processing time can be shortened.

  Ordering degree (%) = B / A × 100 (1)

  In the above formula (1), A represents the total number of micropores in the measurement range. B is centered on the center of gravity of one micropore, and when a circle with the shortest radius inscribed in the edge of another micropore is drawn, the center of gravity of the micropore other than the one micropore is placed inside the circle. This represents the number in the measurement range of the one micropore to be included.

  The method for calculating the degree of ordering of the micropores is the same as the method for calculating the degree of ordering of the micropores of the microstructure described later except that the degree of ordering at the interface between the anodized film and the aluminum substrate is used. . The degree of ordering at the interface between the anodized film and the aluminum substrate should be calculated after exposing the bottom of the micropore by, for example, dissolving the majority of the anodized film with a mixed aqueous solution of phosphoric acid and chromic acid. Can do.

<Film removal treatment>
After forming the anodized film on the surface of the aluminum substrate by anodizing treatment, a treatment for heating the anodized film described later may be performed immediately. However, after the anodizing treatment, film removal treatment and re-anodizing treatment are performed. After performing in this order, it is preferable to perform the process which heats an anodic oxide film.
In the film removal process, the anodized film formed on the surface of the aluminum substrate by the anodizing process is dissolved and removed.

  Since the anodic oxide film is more regular as it gets closer to the aluminum substrate, the anodic oxide film is removed once by this film removal treatment, and the bottom portion of the anodic oxide film remaining on the surface of the aluminum substrate is made the surface. It can be exposed to obtain regular depressions. Therefore, in the film removal treatment, aluminum is not dissolved, but only the anodized film made of alumina (aluminum oxide) is dissolved.

  Alumina solution includes chromium compound, nitric acid, phosphoric acid, zirconium compound, titanium compound, lithium salt, cerium salt, magnesium salt, sodium fluorosilicate, zinc fluoride, manganese compound, molybdenum compound, magnesium compound, barium compound and An aqueous solution containing at least one selected from the group consisting of simple halogens is preferred.

Specific examples of the chromium compound include chromium (III) oxide and anhydrous chromium (VI) acid.
Examples of the zirconium-based compound include zircon ammonium fluoride, zirconium fluoride, and zirconium chloride.
Examples of the titanium compound include titanium oxide and titanium sulfide.
Examples of the lithium salt include lithium fluoride and lithium chloride.
Examples of the cerium salt include cerium fluoride and cerium chloride.
Examples of the magnesium salt include magnesium sulfide.
Examples of the manganese compound include sodium permanganate and calcium permanganate.
Examples of the molybdenum compound include sodium molybdate.
Examples of magnesium compounds include magnesium fluoride pentahydrate.
Examples of barium compounds include barium oxide, barium acetate, barium carbonate, barium chlorate, barium chloride, barium fluoride, barium iodide, barium lactate, barium oxalate, barium perchlorate, barium selenate, selenite. Examples thereof include barium, barium stearate, barium sulfite, barium titanate, barium hydroxide, barium nitrate, and hydrates thereof. Among the barium compounds, barium oxide, barium acetate, and barium carbonate are preferable, and barium oxide is particularly preferable.
Examples of halogen alone include chlorine, fluorine, and bromine.

Among them, the alumina solution is preferably an aqueous solution containing an acid. Examples of the acid include sulfuric acid, phosphoric acid, nitric acid, hydrochloric acid, and the like, and a mixture of two or more acids may be used.
The acid concentration is preferably 0.01 mol / L or more, more preferably 0.05 mol / L or more, and still more preferably 0.1 mol / L or more. There is no particular upper limit, but generally it is preferably 10 mol / L or less, more preferably 5 mol / L or less. An unnecessarily high concentration is not economical, and if it is higher, the aluminum substrate may be dissolved.

  The alumina solution is preferably −10 ° C. or higher, more preferably −5 ° C. or higher, and still more preferably 0 ° C. or higher. In addition, since the starting point of ordering will be destroyed and disturbed if it processes using the boiling alumina solution, it is preferable to use it without boiling.

  The alumina solution dissolves alumina and does not dissolve aluminum. Here, the alumina solution may not dissolve aluminum substantially or may dissolve it slightly.

  The film removal treatment is performed by bringing the aluminum substrate on which the anodized film is formed into contact with the above-described alumina solution. The method of making it contact is not specifically limited, For example, the immersion method and the spray method are mentioned. Of these, the dipping method is preferred.

The dipping method is a treatment in which an aluminum substrate on which an anodized film is formed is dipped in the above-described alumina solution. Stirring during the dipping process is preferable because a uniform process is performed.
The dipping treatment time is preferably 10 minutes or longer, more preferably 1 hour or longer, and further preferably 3 hours or longer and 5 hours or longer.

<Re-anodizing treatment>
After removing the anodized film by removing the film to form regular depressions on the surface of the aluminum substrate, anodizing is performed again to form an anodized film with a higher degree of ordering of micropores. be able to.
A conventionally known method can be used for the anodizing treatment, but it is preferably performed under the same conditions as the above-described <anodic oxidation treatment>.
Also, a method of repeatedly turning on and off the current intermittently while keeping the DC voltage constant, and a method of repeatedly turning on and off the current while intermittently changing the DC voltage can be suitably used. According to these methods, fine micropores are generated in the anodic oxide film, which is preferable in that uniformity is improved particularly when sealing treatment is performed by electrodeposition.

When the anodized film is formed at a low temperature, the arrangement of micropores becomes regular and the pore diameter becomes uniform.
On the other hand, by performing the anodizing treatment at a relatively high temperature, the arrangement of the micropores can be disturbed, and the pore diameter variation can be made within a predetermined range. Also, the pore diameter variation can be controlled by the processing time.

The film thickness of the anodized film formed by the re-anodizing treatment is preferably 0.1 to 1000 μm, more preferably 1 to 500 μm, and still more preferably 10 to 500 μm.
The pore diameter of the micropore is preferably 0.01 to 0.5 μm.
The average pore density is preferably 50-1500 / μm ² .

As the treatment (A), the following steps (1) to (4) may be performed in this order to form an oxide film having micropores on the surface of the aluminum substrate.
(1) Step of forming an anodized film having micropores on the surface of the aluminum substrate by anodizing the surface of the aluminum substrate (2) Partially dissolving the anodized film using acid or alkali Step (3) Performing anodization to grow the micropores in the depth direction (4) Removing the anodized film above the inflection point of the cross-sectional shape of the micropores

Process (1)
In step (1), at least one surface of the aluminum substrate is anodized to form an anodized film having micropores on the surface of the aluminum substrate.
Step (1) can be carried out in the same procedure as the anodizing treatment described in paragraphs [0027] to [0038].
FIG. 1A shows a state in which the anodized film 14a having the micropores 16a is formed on the surface of the aluminum substrate 12a by the step (1).

Process (2)
In step (2), the anodized film formed in step (1) is partially dissolved using acid or alkali. The partial dissolution of the anodic oxide film does not completely dissolve the anodic oxide film formed in the step (1), but the micropores are formed on the aluminum substrate 12a as shown in FIG. This means that the surface of the anodized film 14a shown in FIG. 1A and the inside of the micropore 16a are partially dissolved so that the anodized film 14b having 16b remains.
Here, the dissolution amount of the anodized film is preferably 0.001 to 50% by mass of the entire anodized film, more preferably 0.005 to 30% by mass, and 0.01 to 15% by mass. More preferably. Within the above range, the irregular arrangement of the surface of the anodized film can be dissolved to increase the regularity of the arrangement of the micropores, and the anodized film can remain on the bottom of the micropores. Thus, the starting point of the anodizing treatment performed in the step (3) can be left.

  Step (2) is performed by bringing the anodized film formed on the aluminum substrate into contact with an acid aqueous solution or an alkali aqueous solution. The method of making it contact is not specifically limited, For example, the immersion method and the spray method are mentioned. Of these, the dipping method is preferred.

When an acid aqueous solution is used in step (2), it is preferable to use an aqueous solution of an inorganic acid such as sulfuric acid, phosphoric acid, nitric acid, hydrochloric acid, or a mixture thereof. Especially, the aqueous solution which does not contain chromic acid is preferable at the point which is excellent in safety | security. The concentration of the acid aqueous solution is preferably 0.01 to 1 mol / L. The temperature of the acid aqueous solution is preferably 25 to 60 ° C.
When an alkaline aqueous solution is used in step (2), it is preferable to use an aqueous solution of at least one alkali selected from the group consisting of sodium hydroxide, potassium hydroxide and lithium hydroxide. The concentration of the alkaline aqueous solution is preferably 0.01 to 1 mol / L. The temperature of the alkaline aqueous solution is preferably 20 to 35 ° C.
Specifically, for example, 0.5 mol / L, 40 ° C. phosphoric acid aqueous solution, 0.05 mol / L, 30 ° C. sodium hydroxide aqueous solution or 0.05 mol / L, 30 ° C. potassium hydroxide aqueous solution is suitable. Used.
The immersion time in the acid aqueous solution or alkali aqueous solution is preferably 8 to 120 minutes, more preferably 10 to 90 minutes, and still more preferably 15 to 60 minutes.

Step (3)
In step (3), the anodization process is again performed on the aluminum substrate in which the anodized film is partially dissolved in step (2) to grow micropores in the depth direction.
As shown in FIG. 1 (C), the oxidation reaction of the aluminum substrate 12a shown in FIG. 1 (B) proceeds by the anodizing treatment in the step (3), and the aluminum substrate 12b is more than the micropores 16b. An anodic oxide film 14c having micropores 16c grown in the depth direction is formed.

A conventionally known method can be used for the anodizing treatment, but it is preferably performed under the same conditions as the self-ordering method described above.
Also, a method of repeatedly turning on and off the current intermittently while keeping the DC voltage constant, and a method of repeatedly turning on and off the current while intermittently changing the DC voltage can be suitably used. According to these methods, fine micropores are generated in the anodic oxide film, which is preferable in that uniformity is improved particularly when sealing treatment is performed by electrodeposition.
In the above-described method of intermittently changing the voltage, it is preferable to decrease the voltage sequentially. As a result, the resistance of the anodized film can be lowered, and can be made uniform when the electrodeposition treatment is performed later.

  The amount of increase in the thickness of the anodized film is preferably from 0.1 to 100 μm, and more preferably from 0.5 to 50 μm. Within the above range, the regularity of the pore arrangement can be further increased.

Step (4)
In step (4), the anodized film above the inflection point 30 in the cross-sectional shape of the micropore 16c shown in FIG. As shown in FIG. 1C, the micropore formed by the self-ordering method has a substantially straight tube shape except for the upper portion of the micropore 16c. In other words, a portion (a deformed portion) 20 having a cross-sectional shape different from that of the remaining portion of the micropore 16c exists in the upper portion of the micropore 16c. In step (4), the anodized film above the inflection point 30 of the cross-sectional shape of the micropore 16c is removed in order to eliminate such a deformed portion 20 existing on the micropore 16c. Here, the inflection point 30 refers to a portion where the shape changes remarkably with respect to the main shape (here, substantially straight pipe shape) formed by the cross-sectional shape of the micropore 16c. In the cross-sectional shape of 16c, it refers to a portion where the continuity of the shape is lost with respect to the main shape (substantially straight pipe shape).
By removing the anodized film above the inflection point 30 of the cross-sectional shape of the micropore 16c, the entire micropore 16d has a substantially straight tube shape as shown in FIG.

  In step (4), the inflection point 30 of the cross-sectional shape of the micropore 16c is specified by photographing an FE-SEM of the anodized film 14c after the execution of the step (3) from the cross-sectional direction. The anodic oxide film above may be removed.

However, the deformed portion is generated in the micropore mainly when the anodized film 14a is newly formed on the aluminum substrate 12a as in the step (1). Therefore, in order to remove the anodic oxide film above the inflection point 30 of the cross-sectional shape of the micropore 16c and eliminate the deformed portion 20 above the micropore 16c, the anodic oxide film formed in the step (1) is used. May be removed in step (4).
As will be described later, when the step (3) and the step (4) are repeated twice or more, the deformed portion 30 is eliminated in the anodized film 14d after the step (4) is performed, and the cross-sectional shape of the micropore 16d Since the whole has a substantially straight pipe shape, a deformed portion is newly generated in the upper part of the micropore formed in the step (3) (step (3 ′)) performed after the step (4). Therefore, in the step (4) (step (4) ′) performed subsequent to the step (3 ′), it is necessary to remove the deformed portion newly formed on the micropore formed in the step (3 ′). . For this reason, in the step (4 ′), it is necessary to remove the anodized film above the inflection point of the micropore formed in the step (3 ′).

  In the step (4), the process for removing the anodic oxide film above the inflection point of the cross-sectional shape of the micropore 16c may be a polishing process such as mechanical polishing, chemical polishing, and electrolytic polishing. However, as in step (2), a treatment for dissolving the anodized film using an acid or an alkali is preferable. In this case, as shown in FIG. 1D, an anodic oxide film 14d having a thickness smaller than that of the anodic oxide film 14c shown in FIG. 1C is formed.

  In the step (4), when the anodized film is partially dissolved using acid or alkali, the dissolved amount of the anodized film is not particularly limited, and the total amount of the anodized film is not limited. It is preferable that it is 0.01-30 mass%, and it is more preferable that it is 0.1-15 mass%. Within the above range, the irregular portion of the surface arrangement of the anodized film can be dissolved, and the regularity of the arrangement of the micropores can be increased. Moreover, when performing a process (3) and a process (4) repeatedly 2 times or more, the starting point of the anodizing process in the process (3) implemented next can be left.

The above steps (3) and (4) are preferably repeated twice, because the regularity of the pore arrangement is high, more preferably three times or more, more preferably four times or more. Is more preferable.
When the above steps are repeated twice or more, the conditions of each step (3) and step (4) may be the same or different. From the viewpoint of improving the degree of ordering, the step (3) is preferably performed by changing the voltage every time. In this case, it is more preferable to gradually change to a high voltage condition from the viewpoint of improving the degree of ordering.

In the state shown in FIG. 1D, the average pore density is preferably 50 to 1500 / μm ² , and the area ratio occupied by the micropores is preferably 20 to 50%.

<(B) Heat treatment of anodized film formed in (A)>
The anodized film formed by the above procedure is heat-treated at a temperature of 50 ° C. or higher for at least 10 minutes. In order to perform this heat treatment, the aluminum substrate on which the anodized film is formed may be heated under the above conditions.
As a result of intensive studies, the inventors derived from the electrolytic solution used in the anodizing treatment, the alumina solution used in the film removal treatment, and the treatment solution used in the aluminum removal treatment and micropore penetration treatment described later. It has been found that when sulfuric acid is used as an acid solution, for example, SO ₄ ²⁻ , SO ₄ ²⁻ remains in the anodized film, which deteriorates the acid resistance and alkali resistance of the anodized film. .
By heating the anodic oxide film formed by the above procedure, the acid ions remaining in the anodic oxide film are removed. As a result, the acid resistance and alkali resistance of the anodized film are improved. The acid ions remaining in the anodic oxide film are dissolved in the water remaining in the anodic oxide film, and when the anodic oxide film is heated, the acid ions are evaporated together with the evaporation of the water remaining in the anodic oxide film. Is thought to be removed.

When the heating temperature is less than 50 ° C., the effect of removing the acid ions remaining in the anodized film cannot be sufficiently exhibited.
The heating temperature is preferably 150 ° C. or higher, more preferably 200 ° C. or higher, and further preferably 400 ° C. or higher.
However, if the heating temperature is too high, the aluminum substrate on which the anodized film is formed may be deformed by heat. Therefore, the heating temperature is preferably 800 ° C. or lower.

When the heating time is less than 10 minutes, the effect of removing the acid ions remaining in the anodized film cannot be sufficiently exhibited.
The heating time is preferably 15 minutes or longer, more preferably 30 minutes or longer, and even more preferably 1 hour or longer.
Heating for 10 hours or longer no longer contributes to the action of removing the acid ions remaining in the anodized film, which is not preferable from the viewpoint of yield and energy efficiency. Although depending on the heating temperature, when heated for 15 hours or longer, the aluminum substrate on which the anodized film is formed may be deformed by heat.

  The anodized film after heating is preferably cooled rapidly. As a method for cooling, for example, a method in which the fine structure is directly poured into water or the like can be mentioned.

When the fine structure is used as a porous alumina membrane filter, it is necessary that the micropores are penetrated, that is, the micropores are through holes.
When obtaining a microstructure having a micropore through hole, in the method for manufacturing a microstructure of the present invention,
(C) A treatment for removing aluminum from the oxide film obtained in the treatment (A), and (D) a treatment for penetrating the micropores of the oxide film obtained in the treatment (A).
Are applied in this order, and then the treatment (B) is preferably performed.

<(C) Aluminum removal treatment>
FIG. 2 is a partial cross-sectional view showing a state after the processing (A). As shown in FIG. 2, an anodic oxide film 14 having micropores 16 is formed on the surface of the aluminum substrate 12.
In the aluminum removal process, the aluminum substrate 12 is dissolved and removed from the state shown in FIG. FIG. 3 is a partial cross-sectional view showing the state after the main treatment, and shows a fine structure made of the anodized film 14 having the micropores 16.
Therefore, in the aluminum removal treatment, a treatment solution that does not dissolve alumina but dissolves aluminum is used.

The treatment liquid is not particularly limited as long as it does not dissolve alumina and dissolves aluminum. For example, an aqueous solution such as mercury chloride, bromine / methanol mixture, bromine / ethanol mixture, aqua regia, hydrochloric acid / copper chloride mixture, etc. Etc.
As a density | concentration, 0.01-10 mol / L is preferable and 0.05-5 mol / L is more preferable.
As processing temperature, -10 degreeC-80 degreeC are preferable, and 0 degreeC-60 degreeC is preferable.

  The aluminum removal treatment is performed by contacting with the treatment liquid described above. The method of making it contact is not specifically limited, For example, the immersion method and the spray method are mentioned. Of these, the dipping method is preferred. The contact time at this time is preferably 10 seconds to 5 hours, and more preferably 1 minute to 3 hours.

  The film thickness of the anodized film after the aluminum removal treatment is preferably 1 to 1000 μm, and more preferably 10 to 500 μm.

  After the aluminum removal treatment, the anodic oxide film 12 is washed with water before the treatment (D) described later. In order to suppress changes in the pore diameter of the micropores 16 due to hydration, the water washing treatment is preferably performed at 30 ° C. or lower.

<(D) Micropore penetration processing>
In the micropore penetrating treatment, the anodic oxide film 14 having the micropores 16 shown in FIG. 3 is immersed in an acid aqueous solution or an alkali aqueous solution to partially dissolve the anodic oxide film 14. Thereby, the anodic oxide film 14 at the bottom of the micropore 16 is removed, and the micropore 16 penetrates (a micropore through hole 18 is formed). FIG. 4 is a partial cross-sectional perspective view showing a state after the micropore penetrating process, and shows a fine structure made of the anodic oxide film 14 having the micropore through-hole 18.
In FIG. 4, all the micropores existing in the anodic oxide film 14 are the micropore through holes 18, but not all the micropores existing in the anodic oxide film may penetrate through the treatment (D). . However, when the microstructure of the present invention is used as a porous alumina membrane filter, it is preferable that 70% of the micropores present in the anodized film penetrate through the treatment (D).

When an acid aqueous solution is used for the micropore penetration treatment, it is preferable to use an aqueous solution of an inorganic acid such as sulfuric acid, phosphoric acid, nitric acid, hydrochloric acid, or a mixture thereof. The concentration of the acid aqueous solution is preferably 1 to 10% by mass. The temperature of the acid aqueous solution is preferably 25 to 40 ° C.
When an alkaline aqueous solution is used for the micropore penetration treatment, it is preferable to use an aqueous solution of at least one alkali selected from the group consisting of sodium hydroxide, potassium hydroxide and lithium hydroxide. The concentration of the alkaline aqueous solution is preferably 0.1 to 5% by mass. The temperature of the alkaline aqueous solution is preferably 20 to 35 ° C.
Specifically, for example, 50 g / L, 40 ° C. phosphoric acid aqueous solution, 0.5 g / L, 30 ° C. sodium hydroxide aqueous solution or 0.5 g / L, 30 ° C. potassium hydroxide aqueous solution is preferably used. .
The immersion time in the acid aqueous solution or alkali aqueous solution is preferably 8 to 120 minutes, more preferably 10 to 90 minutes, and still more preferably 15 to 60 minutes.

  The film thickness of the anodized film after the micropore penetration treatment is preferably 1-1000 μm, and more preferably 10-500 μm.

  After the micropore penetration treatment, the anodic oxide film 14 is washed with water before the treatment (B). In order to suppress a change in the pore diameter of the micropore through hole 18 due to hydration, the water washing treatment is preferably performed at 30 ° C. or lower.

By subjecting the aluminum substrate to at least the treatments (A) and (B) in this order, preferably, subjecting the aluminum substrate to the treatments (A), (C), (D) and (B) in this order. The resulting microstructure of the present invention is obtained by heating the anodic oxide film in the treatment (B), whereby the acid ions remaining in the anodic oxide film, that is, the electrolytic solution used in the anodic oxidation treatment, Since the alumina solution used for the treatment, as well as the acid ions derived from the treatment solution used in the aluminum removal treatment and micropore penetration treatment described later, are removed, the concentration of the acid ion-derived elements in the anodized film is significantly reduced. Has been.
The acid ions remaining in the anodized film vary depending on the type of acid used in various treatments such as anodizing treatment, but sulfuric acid, phosphoric acid or oxalic acid is particularly preferably used in the anodizing treatment. Therefore, the acid ions remaining in the anodized film are mainly SO ₄ ²⁻ , PO ₃ ²⁻ , and C ₂ H ₅ COO ⁻ . In the microstructure of the present invention, the concentration of these acid ion-derived elements in the anodized film is significantly reduced.
Specifically, in the microstructure of the present invention, the S atom concentration, the C atom concentration, and the P atom concentration in the anodized film are as follows.
S atom concentration: 3.2 wt% or less C atom concentration: 2.5 wt% or less P atom concentration: 1.0 wt% or less These atomic concentrations in the anodic oxide film are, for example, electron probe microanalysis (EPMA) or X-ray photoelectron spectroscopy. It can be measured by analysis (ESCA).

In the microstructure of the present invention, the micropores have a pore diameter dispersion within 3% of the average diameter, and more preferably within 2%, in the range of 1 μm ² . In addition, the average diameter and dispersion | distribution of a pore diameter can each be calculated | required by a following formula.
Average diameter: μ _x = (1 / n) ΣXi
Dispersion: σ ² = (1 / n) (ΣXi ² ) −μ _x ²
Dispersion / average diameter = σ / μ _x ≦ 0.03
Here, Xi is the pore diameter of one micropore measured in the range of 1 μm ² .

In the microstructure of the present invention, the degree of ordering defined by the following formula (1) is preferably 50% or more, more preferably 70%, and more preferably 80% or more for the micropores. Further preferred.
Ordering degree (%) = B / A × 100 (1)
In the above formula (1), A represents the total number of micropores in the measurement range. B is centered on the center of gravity of one micropore, and when a circle with the shortest radius inscribed in the edge of another micropore is drawn, the center of gravity of the micropore other than the one micropore is placed inside the circle. This represents the number in the measurement range of the one micropore to be included.

FIG. 5 is an explanatory diagram of a method for calculating the degree of ordering of pores. The above formula (1) will be described more specifically with reference to FIG.
The micropore 1 shown in FIG. 5A draws a circle 3 (inscribed in the micropore 2) having the shortest radius and centering on the center of gravity of the micropore 1 and inscribed in the edge of another micropore. In this case, the center of the circle 3 includes six centroids of micropores other than the micropore 1. Therefore, the micropore 1 is included in B.
The micropore 4 shown in FIG. 5 (B) draws a circle 6 (inscribed in the micropore 5) having the shortest radius and centering on the center of gravity of the micropore 4 and inscribed in the edge of the other micropore. In this case, the center of gravity of the micropores other than the micropores 4 is included inside the circle 6. Therefore, the micropore 4 is not included in B. In addition, the micropore 7 shown in FIG. 5B is centered on the center of gravity of the micropore 7 and has the shortest radius 9 inscribed in the edge of another micropore (inscribed in the micropore 8). Is drawn, the circle 9 includes seven centroids of micropores other than the micropore 7. Therefore, the micropore 7 is not included in B.

The microstructure of the present invention is suitable as a porous alumina membrane filter.
Moreover, the fine structure of the present invention can also carry organic compounds, inorganic compounds, metal fine particles, and the like in the micropores of the anodized film depending on the application.

  The present invention will be specifically described below with reference to examples. However, the present invention is not limited to these.

[Example 1]
1. Electropolishing treatment A high-purity aluminum substrate (manufactured by Sumitomo Light Metal Co., Ltd., purity 99.99 mass%, thickness 0.4 mm) is cut so that it can be anodized in an area of 10 cm square, and an electropolishing liquid having the following composition is used. The electropolishing treatment was performed under the conditions of a voltage of 25 V, a liquid temperature of 65 ° C., and a liquid flow rate of 3.0 m / min. The cathode was a carbon electrode, and GP0110-30R (manufactured by Takasago Seisakusho) was used as the power source. The flow rate of the electrolyte was measured using a vortex flow monitor FLM22-10PCW (manufactured by AS ONE).

<Electrolytic polishing liquid composition>
-660 mL of 85% by mass phosphoric acid (reagent manufactured by Wako Pure Chemical Industries, Ltd.)
・ Pure water 160mL
・ Sulfuric acid 150mL
・ Ethylene glycol 30mL

2. (A) Micropore formation treatment by anodic oxidation As the treatment (A), the steps (1) to (4) described above were performed in this order to form an oxide film having micropores on the surface of the aluminum substrate.
The polished sample obtained above was anodized with an electrolyte solution of 0.30 mol / L sulfuric acid for 1 hour under the conditions of a voltage of 25 V, a liquid temperature of 15 ° C., and a liquid flow rate of 3.0 m / min. Furthermore, the obtained sample was immersed for 20 minutes on 40 degreeC conditions using the mixed aqueous solution of 0.5 mol / L phosphoric acid.
After this treatment was repeated four times, re-anodization treatment was performed for 5 hours with an electrolyte solution of 0.30 mol / L sulfuric acid at a voltage of 25 V, a liquid temperature of 15 ° C., and a liquid flow rate of 3.0 m / min. Anodized film 14 in which micropores 16 are arranged in a straight tubular shape and in a honeycomb shape on the surface of aluminum substrate 12 shown in FIG. 2 is immersed in a mixed aqueous solution of L phosphoric acid at 40 ° C. for 20 minutes. Formed.
In both the anodizing treatment and the re-anodizing treatment, a stainless steel electrode was used as the cathode, and GP0110-30R (manufactured by Takasago Seisakusho) was used as the power source. In addition, NeoCool BD36 (manufactured by Yamato Kagaku Co.) was used as the cooling device, and Pair Stirrer PS-100 (manufactured by EYELA) was used as the stirring and heating device. The flow rate of the electrolyte was measured using a vortex flow monitor FLM22-10PCW (manufactured by AS ONE).

3. (C) Aluminum removal treatment The sample obtained above was immersed in an aqueous solution of mercury chloride having a concentration of 2 mol / L at 20 ° C. for 3 hours to dissolve and remove the aluminum substrate 12, and the micropores shown in FIG. A microstructure comprising an anodic oxide film 14 having 16 was prepared.

4). (D) Micropore penetrating treatment The sample obtained above is immersed in 5 mass% phosphoric acid at 30 ° C. for 30 minutes to penetrate the micropore, and the micropore through-hole 18 shown in FIG. A microstructure comprising an anodic oxide film 14 having

5. (B) Heat treatment The fine structure shown in FIG. 4 obtained above was heat-treated for 1 hour under the condition of a temperature of 400 ° C., and a sample of Example 1 was obtained.

[Example 2]
5. above. (B) A sample of Example 2 was obtained in the same manner as in Example 1 except that the temperature of the heat treatment was 200 ° C.

[Example 3]
5. above. (B) A sample of Example 2 was obtained in the same manner as in Example 1 except that the temperature of the heat treatment was 150 ° C.

[Example 4]
2. (A) Example 4 was carried out in the same manner as in Example 1 except that the electrolyte used in the micropore formation treatment by anodization was an electrolyte of 0.50 mol / L oxalic acid and the voltage was 40 V. Got a sample.

[Example 5]
2. (A) The electrolyte used in the micropore formation process by anodic oxidation is an electrolyte of 0.30 mol / L phosphoric acid, the voltage is 195 V, and the concentration of the phosphoric acid mixed aqueous solution used in the film removal process is 1.0 mol. A sample of Example 5 was obtained in the same manner as in Example 1 except that / L was used.

[Example 6]
5. above. (B) A sample of Example 6 was obtained in the same manner as in Example 3 except that the heat treatment time was 30 minutes.

[Example 7]
5. above. (B) A sample of Example 6 was obtained in the same manner as in Example 3 except that the heat treatment time was 10 hours.

[Comparative Example 1]
5. above. (B) A sample of Comparative Example 1 was obtained in the same manner as in Example 1 except that the heat treatment was omitted.

[Comparative Example 2]
5. above. (B) A sample of Comparative Example 2 was obtained in the same manner as in Example 4 except that the heat treatment was omitted.

[Comparative Example 3]
5. above. (B) A sample of Comparative Example 3 was obtained in the same manner as in Example 5 except that the heat treatment was omitted.

[Comparative Example 4]
5. above. (B) A sample of Comparative Example 4 was obtained in the same manner as in Example 1 except that the temperature of the heat treatment was 150 ° C. and the heating time was 5 minutes.

For the samples of Examples 1 to 7 and Comparative Examples 1 to 4, JEOL JXA-8800, acceleration voltage: 20 kV, irradiation current: 1 × 10 ⁻⁷ A, Dwell: 50 ms, probe system: 0 Magnification: S atom concentration, C atom concentration and P atom concentration in the anodized film were measured under the condition of 1000 times. The results are shown in Table 1.

Further, surface photographs (magnification 20000 times) of the samples of Examples 1 to 7 and Comparative Examples 1 to 4 were taken with FE-SEM, and the average diameter and the average diameter of 300 micropores in a 1 μm × 1 μm field of view were determined. The dispersion of the diameter was determined by the following formula, and the dispersion / average diameter was determined. The results are shown in Table 1.
Average diameter: μ _x = (1 / n) ΣXi
Dispersion: σ ² = (1 / n) (ΣXi ² ) −μ _x ²
Dispersion / average diameter = σ / μ _x
Here, Xi is the pore diameter of one micropore measured in the range of 1 μm ² .

Moreover, about the sample of Examples 1-7 and Comparative Examples 1-4, 300 micropores arbitrary in the 1 micrometer x 1 micrometer visual field of the surface photograph (magnification 20000 times) by FE-SEM are used, and a following formula ( The degree of ordering defined in 1) was obtained. The results are shown in Table 1.
Ordering degree (%) = B / A × 100 (1)
In the above formula (1), A represents the total number of micropores in the measurement range. B is centered on the center of gravity of one micropore, and when a circle with the shortest radius inscribed in the edge of another micropore is drawn, the center of gravity of the micropore other than the one micropore is placed inside the circle. This represents the number in the measurement range of the one micropore to be included.

  Moreover, the hydrochloric acid aqueous solution which adjusted the samples of Examples 1-7 and Comparative Examples 1-4 to pH = 0.05, 0.1, 1.0, 2.0, respectively, and pH = 11.0. The state of the sample after being immersed in a sodium hydroxide aqueous solution adjusted to 12.0 and 13.0, respectively, at 20 ° C. for 15 hours was observed with an FE-SEM. The results are shown in Table 1. In the table, ◯ indicates that there is no change before and after immersion, Δ indicates that a change is observed, and × indicates that the sample has been dissolved by immersion.

Moreover, the filtration characteristic as a porous alumina membrane filter of the samples of Examples 1 to 7 and Comparative Examples 1 to 4 was evaluated. Specifically, the filtration flow rate of 20 ° C. pure water with a driving pressure of 1.0 kgf · cm ⁻² and a filtration time of 0 to 100 minutes was determined. It can be said that the larger the value, the better the filtering characteristics as a filter. The results are shown in Table 1.

FIG. 1 is a schematic end view of an aluminum substrate and an anodized film formed on the aluminum substrate for explaining the method for producing a microstructure of the present invention. FIG. 2 is a partial cross-sectional view showing a state after the processing (A). FIG. 3 is a partial cross-sectional view showing a state after the processing (C). FIG. 4 is a partial cross-sectional view showing a state after the processing (D). FIG. 5 is an explanatory diagram of a method for calculating the degree of ordering of pores.

Explanation of symbols

1, 2, 4, 5, 7, 8 Micropore 3, 6, 9 Circle 12, 12a, 12b, Aluminum substrate 14, 14a, 14b, 14c, 14d Anodized film 16, 16a, 16b, 16c, 16d Micropore 18: Micropore through hole 20 Deformed portion 30 Inflection point

Claims (8)

(A) At least a treatment for forming an oxide film having micropores by anodizing treatment on the surface of the aluminum substrate, and (B) The oxide film formed in (A) is heated at a temperature of 50 ° C. or higher for at least 10 minutes. Processing,
Is applied in this order to obtain a fine structure having micropores on the surface. further,
(C) The process which removes aluminum from the oxide film obtained by said (A), and (D) The process which penetrates the micropore of the oxide film obtained by said (A),
2. The method for manufacturing a fine structure according to claim 1, wherein a fine structure having a micropore through hole is obtained on the surface by applying (B) after applying in this order.   A fine structure obtained by the method for producing a fine structure according to claim 1. A microstructure comprising an anodized aluminum film and having micropores,
In the anodized film, the S atom concentration is 3.2 wt% or less, the C atom concentration is 2.5 wt% or less, and the P atom concentration is 1.0 wt% or less. .   The microstructure according to claim 4, wherein the microstructure has a micropore through hole.   The microstructure according to any one of claims 3 to 5, wherein the pore diameter dispersion of the micropores is within 3% of the average diameter. The microstructure according to any one of claims 3 to 6, wherein the degree of ordering defined by the following formula (1) is 50% or more for the micropore.
Ordering degree (%) = B / A × 100 (1)
In the above formula (1), A represents the total number of micropores in the measurement range. B is centered on the center of gravity of one micropore, and when a circle with the shortest radius inscribed in the edge of another micropore is drawn, the center of gravity of the micropore other than the one micropore is placed inside the circle. This represents the number in the measurement range of the one micropore to be included.   A porous alumina membrane filter using the microstructure according to any one of claims 3 to 7.

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