JP2009120892A - Self-supported film of alumina by anodization and production method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thick self-supported film of alumina formed by anodization, and to provide a production method therefor. <P>SOLUTION: The self-supported film 1 of alumina formed by anodization has a film thickness (t) of 230 μm or more, and is provided with nanoholes 2 having aspect ratios of 10,000 or more. The thick self-supported film 1 of alumina formed by anodization can be produced by keeping a temperature on the film surface to 10°C or lower while the anodic oxide film is formed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an anodized alumina free-standing film and a method for manufacturing the same, and more particularly to a thick-film anodized alumina free-standing film and a method for manufacturing the same.

  When aluminum is electrochemically anodized, an alumina film is formed on the surface. Among these alumina films, those having a porous structure (generally composed of upright holes formed perpendicular to the substrate when the film is grown on the substrate surface) are called anodized. It is well known as one of surface treatment techniques for pure aluminum or aluminum alloys for the purpose of improving corrosion resistance and wear resistance, and for decorating with various colors.

  The thickness of the anodized alumina film becomes a constant value as the processing time elapses. This is because the generated anodized alumina film is subjected to a chemical dissolution action to balance the growth rate of the anodized alumina film and the chemical dissolution rate. It is important that this chemical dissolution rate depends on the processing temperature, which is one of the control factors. That is, the temperature rise due to Joule heat generated in the processed material according to the voltage and current density during the anodizing treatment greatly affects the chemical dissolution rate of the anodized alumina film. Therefore, when anodizing is performed in a treatment tank at a constant temperature, a part of this Joule heat is removed through the surface of the treatment object, so that the temperature of the treatment liquid sufficiently away from the treatment object surface is approximately the above. Although it is maintained at a constant temperature, the temperature of the treatment liquid in the vicinity of the surface of the treatment object increases. As the temperature of the treatment liquid rises, the anodized alumina film is subjected to a steady chemical dissolving action immediately after the start of anodization.

Therefore, in order to obtain a thicker anodized alumina film would relatively as fast as possible than chemical dissolution rate within the anodic oxidation treatment time t _s it is sufficient to produce an anodized alumina film. As the method, the chemical dissolution rate can be reduced, the anodized alumina film formation rate can be increased, or a combination of both can be dealt with. By the way, in order to perform anodization at a high speed under a constant temperature, it is necessary to anodize at a high current density in accordance with Faraday's law of electrolysis.

  However, if anodic oxidation is performed at a high current density for speeding up film growth, a local current concentration phenomenon called burning tends to occur. When this burning phenomenon occurs, the thickness of the anodized alumina film becomes non-uniform, the structure is abnormal, and an appearance defect such as partial burning of the anodized alumina film is caused. For this reason, there is a limit to the current density that can be applied industrially, and there is a limit to increasing the speed of anodization. In other words, there is a certain limit (limit film thickness) in the thickness of the film that can be formed by anodic oxidation.

  Conventionally, a technique for avoiding the burning phenomenon has been studied (see, for example, Patent Document 1). In Patent Document 1, a relational expression between the electrolytic current density and the oxide film where burning occurs is reported, and the burning phenomenon during anodic oxidation occurs with a smaller film thickness as the electrolytic current density increases. Further, Patent Document 1 proposes a fast anodic oxidation method (Hoshino method) that takes into consideration the prevention of the occurrence of burning based on the relationship between the electrolysis current density and the electrolysis time derived from the above relational expression (burning curve).

Conventionally, theoretical analysis and experimental investigation have been made on the limit film thickness based on the burn occurrence curve proposed in Patent Document 1 (see, for example, Non-Patent Document 1). According to Non-Patent Document 1, the limit film thickness d _l when anodizing aluminum with sulfuric acid as an electrolytic solution (sulfuric acid bath treatment) is expressed by the following equation in theoretical analysis.
^{_{d l = SB s {1 +}} 3ki 0 3/2 (t s -t 0) / SB s} / i 0 1/2
Here, S is a safety factor, B _s is the burn constant, k is the formation constant of the anodized alumina film, i ₀ is the initial current density, and t ₀ is the initial constant current electrolysis time. The burn constant B _s is a constant determined by the temperature and concentration of the electrolyte and the material of aluminum.

According to Non-Patent Document 1, when the theoretical value obtained from the above equation is compared with the experimental result, the film thickness increases almost along the theoretical value at the beginning of the anodic oxidation. It is shown that the difference between and increases. In this case, a dusting phenomenon occurs in which a fine fiber bundle (powder) is generated on the surface of the anodized alumina film. The time to reach the maximum film thickness is shorter than the theoretical value of the film dissolution time t _s. This is thought to be because the temperature of the test piece increased due to Joule heat generated during anodization.

  Therefore, it is reported in Non-Patent Document 1 that the thickness of the anodized alumina film that is actually obtained remains at about 70% of the theoretical value. For example, when sulfuric acid is used as the electrolytic solution and the temperature of the electrolytic solution is 20 ° C., the theoretical value of the thickness of the anodized alumina film is 280 μm, whereas the actually obtained thickness is 230 μm at most.

  Patent Document 1 reports an example in which a coating having a thickness of 200 μm was obtained at high speed by the Hoshino method. Further, the practical application of the Hoshino method has been proposed (see, for example, Patent Document 2). Specifically, the electrolytic bath circulation vertical ejection using the ejection nozzle to the object to be processed, the initial current density A high-speed anodizing method to which reduction control is applied has been proposed mainly as a method for producing a thick film for a short time. However, Patent Document 2 only reports an example in which a film having a thickness of at most 50 μm was obtained.

  On the other hand, several studies have been made on the formation of a thick anodized alumina film (see, for example, Patent Document 3, Non-Patent Document 2, and Non-Patent Document 3).

  In Patent Document 3, a surface treatment method capable of forming a 300 to 500 μm film on the surface of an aluminum material by applying a high voltage of a treatment voltage of 100 to 200 V using a treatment liquid containing nickel sulfate in sulfuric acid. Has been proposed. In addition, properties such as hardness, heat resistance, abrasion resistance, and antibacterial properties have been reported. In the confirmation test of these properties, a sample having a coating of 100 μm or less by polishing is used. In addition, detailed information (for example, hole diameter, tissue uniformity, uprightness, etc.) regarding the upright holes is not disclosed.

  Non-Patent Document 2 describes a report example in 1904 that a hard alumite film having a thickness of 300 μm was formed by a special method of water-cooling the inner surface of an aluminum pipe in sulfuric acid solution. The coating is not flat. Moreover, the experimental result which obtained the hard alumite film | membrane with a maximum thickness of 670 micrometers by the constant current method in an oxalic acid solution is described. However, due to remelting due to the length of the contact liquid time, and a burning phenomenon due to local current concentration, the limit film thickness as a practical good structure is described as about 400 μm. In addition, detailed information (for example, hole diameter, tissue uniformity, uprightness, etc.) regarding the upright holes is not disclosed.

Non-Patent Document 3 introduces an anodized alumina film having a thickness of about 2 mm produced by 100 V constant voltage electrolysis in an oxalic acid solution. It has been reported that a large crack is generated at the edge portion as the film grows, and that the average growth rate of the film thickness is as small as 2.5 μm / hr. In addition, detailed information (for example, hole diameter, tissue uniformity, uprightness, etc.) regarding the upright holes is not disclosed.
Japanese Patent Publication No. 60-23196 JP-A-11-236696 International Publication WO 2004/067807 Pamphlet Shigeo Hoshino “How thick is the Al surface coating? (Exploring its limitations)”, ARS Conference Lecture Proceedings Vol.2 (1985), p.13-18 Seto Tomita “How thick an anodized film can be”, ARS Conference Lecture Proceedings Vol.3 (1986), p.46-48 Hideki Masuda, Nobuyoshi Baba “Creating 2mm thick oxalate alumite”, Proceedings of ARS Conference Lecture Vol.9 (1992), p.70

As a conventional technical common sense, based on the theory of the above limit thickness d _l, thickening of the anodized alumina film beyond the limits thickness was considered not easy. Conventionally, it has been considered that when an anodized alumina film is formed using a sulfuric acid-based treatment solution, an upright hole having a small diameter that is effective in aiming to form an upright hole having a high aspect ratio can be formed. However, the film thickness of the anodized alumina film formed using a sulfuric acid-based treatment solution is 230 μm at most as a free-standing film even if the base aluminum can be removed. For example, special equipment is required for partial cutting. It is difficult to handle because it is difficult to post-process. Therefore, in the prior art, there is no mention of a self-supporting film of anodized alumina using a sulfuric acid-based treatment liquid.

  The aspect ratio generally refers to the ratio of the long side to the short side, but here refers to the ratio of the alumina film thickness to the diameter of the upright holes. An anodized alumina self-supporting film is an alumina single film that can be handled without holding a support (especially the base aluminum), and has a film thickness of 230 μm, more preferably 300 μm or more. Yes, having a bending strength of 100 MPa or more and an Hv hardness of 400 or more.

  As described above, the thickness of the anodized alumina film increases with the reaction amount, that is, the total coulomb amount (current value × time) in principle according to Faraday's law of electrolysis. At the same time, however, the anodized alumina coating dissolves over time at a dissolution rate depending on the processing temperature. Therefore, in order to increase the film thickness of the anodized alumina film under certain processing conditions, it is necessary that the film growth rate in the film thickness direction is faster than the film dissolution rate in the processing bath. When the film growth rate and the film dissolution rate are balanced, the critical film thickness under the processing conditions is determined.

  The film growth rate is proportional to the total amount of coulomb per unit time. That is, the higher the processing voltage, the higher the film growth rate. On the other hand, the dissolution rate of the oxide film increases with increasing temperature. The cause of the temperature rise is not only the temperature control ability of the treatment tank, but is also greatly affected by the temperature rise due to Joule heat generated during the anodizing treatment. How efficiently the temperature rise of the anodized alumina film itself due to Joule heat can be suppressed is important for thick film formation and film growth rate increase.

  On the other hand, the porous anodized alumina film has upright holes with nanoscale diameters (called nanoholes, and nm-level holes with high uniformity in diameter distribution are formed in a direction perpendicular to the film thickness) It is known that the diameter thereof has a positive correlation with the processing voltage. That is, the higher the processing voltage, the larger the nanohole diameter. Therefore, in order to form an anodized alumina film having a small nanohole diameter that is effective in aiming at a high aspect ratio, the processing voltage must be reduced. However, since the current value follows Ohm's law, when the treatment voltage is reduced, the Joule heat generated by the reaction is reduced, but the total coulomb amount per unit time is also reduced, so that the film growth rate becomes extremely slow.

  Thus, at present, it has a thin nanohole diameter (φ50 nm or less, aspect ratio is 10,000 or more), has good surface properties (smooth and flat, has no fine cracks), and has excellent heat resistance ( There is no method for easily producing a single thick film (at least 230 μm or more, preferably 300 μm or more) of a flat anodized alumina film. Naturally, it is a single thick film with a large thickness, accompanied by structural deformations of upright holes (for example, diameter change in the extending direction, through / non-through holes, composite with 3D network structure, etc.) Is not possible with the prior art.

  Therefore, a main object of the present invention is to provide a thick anodized alumina free-standing film and a method for manufacturing the same.

  The anodized alumina free-standing film according to the present invention has a film thickness of 230 μm or more, preferably 300 μm or more. In this case, it is an anodized alumina self-supporting film having a thickness of 230 μm or more, preferably 300 μm or more, which exceeds the conventionally considered limit film thickness, and has a bending strength of 100 MPa and Hv hardness of 400 or more. Withstand handling more than enough. Furthermore, such an anodized alumina self-supporting membrane has a porous space composed of a nano-level porous structure, so that it has a separation function for a passing substance such as a filter or into a nano-level porous space. It can be suitably used for multipurpose applications such as a hybrid function self-supporting film by filling each functional substance (for example, magnetic substance, phosphor, conductor, etc.).

  Preferably, the anodized alumina free-standing film is formed with upright holes having an aspect ratio of 10,000 or more. Here, an upright hole is a hole formed perpendicular to the substrate when an anodized alumina film is grown on the surface of an aluminum-based substrate, and is a hole formed in the thickness direction of the self-standing film. An upright hole is a nanohole having a nanoscale (for example, 50 nm or less) diameter. An upright hole having an aspect ratio of 10,000 or more is a characteristic obtained by making the thickness of an anodized alumina self-supporting film of 230 μm, preferably 300 μm or more, compatible with nanoholes formed as an internal structure of the self-supporting film. Therefore, an upright hole having an aspect ratio of 10,000 or more cannot be easily obtained by the conventional method. Also, the greater the aspect ratio, the greater the surface area in the upright holes. Therefore, when the functional substance is filled in the upright holes, the reactivity of the functional substance is improved (for example, the reactivity such as adsorptivity is equivalent to the higher the fine particles). The target effect can be increased.

  Preferably, the upright hole has a diameter that changes in the extending direction. In this case, the diameter of the upright hole is enlarged or reduced in the middle of the extending direction of the upright hole (that is, the thickness direction of the self-standing film). Therefore, if the diameter of the upright hole is arbitrarily adjusted, for example, when a self-supporting membrane is used as a filter, operations such as changing the permeability of the gas component, separation of the passing substance, shielding, and retention are possible. Such a change in diameter of the upright hole can be formed by changing the diameter when the upright hole is formed. Alternatively, the diameter can be changed by post-processing even after the upright holes are formed.

  The change in the diameter of the upright hole is not limited to one place in the extending direction, and the diameter is changed in a plurality of places in the extending direction, or the diameter is changed in one of the end portions of the upright hole. There may be. The change in the diameter of the upright hole may be continuous, stepwise expansion or reduction, or a combination of these. The diameter once expanded along the extending direction is reduced again. It may be changed in any way according to the application. When the anodized alumina free-standing film is thin, even if the diameter of the upright hole changes, the length of the upright hole at each diameter is small. The volume (effective volume) of the upright holes that can contribute to is small. On the other hand, since the effective volume of the self-supporting film having a large film thickness is remarkably large, the reactivity with the change in the diameter of the upright hole is excellent with respect to the permeability of the gas component and the operation of the passing material.

  In addition, when the diameter is increased afterwards by post-processing after the formation of the upright holes, the interval between the upright holes becomes narrow at the portion where the diameter of the upright holes is enlarged, and the wall structure volume between the upright holes is reduced. The strength of the self-supporting film is reduced. However, the anodized alumina free-standing film having a film thickness of 230 μm or more has a higher bending strength than a thin film of the same area due to an increase in the effective wall texture volume between the upright holes due to the thick film thickness. However, the appropriate thickness of the anodized alumina film and the enlarged diameter of the upright holes may be adjusted in accordance with the required bending strength according to the application.

  In the above-mentioned anodized alumina free-standing film, the upright holes preferably penetrate the anodized alumina free-standing film. In this case, the use of an anodized alumina self-supporting film having a thickness of 230 μm or more, preferably 300 μm or more, and a through-hole having an aspect ratio of 10,000 or more expands the application as a hybrid function self-supporting film. For example, not only for applications that require a separation function such as a filter, but also a reactive filter combined with the above-mentioned functional substance (for example, magnetic substance, phosphor, conductor, etc.), various functional films, or It can be used for applications such as utilizing the spectral characteristics of the anodized alumina film and the interaction between nanospaces and nanofillers. Such a structure can be manufactured by subjecting the free-standing film to appropriate post-processing (for example, wet melting, machining, or electron beam irradiation).

  Also preferably, the upright hole has a bottom. Thus, the self-supporting film can also be used as an anodized alumina self-supporting film having non-through-type upright holes in which the upright holes do not penetrate the self-supporting film in the thickness direction. In this case, it becomes possible to expand to a multipurpose application such as a hybrid function free-standing film in the same manner as described above by filling a nano-level porous space with a functional substance (for example, a magnetic material, a phosphor, a conductor, etc.).

  Preferably, the anodized alumina free-standing film has a three-dimensional network structure layer formed on one or both of the film surfaces. In this case, a three-dimensional network structure layer having a higher porosity than the portion where the upright holes are formed can be formed on at least one of the film surfaces. For example, when a self-supporting membrane is used as a filter, if the catalyst is filled in the three-dimensional network structure layer, the amount of catalyst filling becomes larger because of the higher porosity, providing a high-performance and long-life filter, etc. can do.

  Conventionally, in an anodized alumina film in which upright holes are formed, while maintaining a state with a large aspect ratio, when producing a composite structure that combines structures with different void volumes in a specific region or surface layer in the thickness direction, There was only a technique for forming an upright hole with a smaller diameter or expanding an upright hole in the vicinity of the surface (Note that if the hole diameter is expanded over the entire length of the upright hole by post-processing after forming the oxide film, the aspect ratio becomes small. Become).

  Conventionally, however, the emphasis has been on forming an anodized alumina film as a surface treatment rather than producing an anodized alumina free-standing film having a thick film as in the present invention. In order to form an anodized alumina film as a surface treatment, production in a relatively short time is desirable, and therefore, a maximum voltage with a high growth rate is selected. Therefore, the structure adjustment for reducing the hole diameter in the thickness direction reduces the voltage. That is, the diameter of the upright hole becomes smaller corresponding to the processing voltage, and a structure with an increased void volume cannot be formed. Moreover, since the upright holes are originally small in diameter, even if the hole diameter is adjusted, the change rate of the void volume is small, and the passage efficiency of the substance passing through the upright holes is not preferable. In addition, in the hole diameter expansion, the hole diameter expansion near the end face or the hole diameter expansion over the entire length of the upright holes can be considered, but since the wall thickness between the upright holes becomes thin, any thin film thickness leads to a decrease in strength. Problems arise.

  In contrast, the three-dimensional network structure layer of the present invention has a basic structure in which a thick film can be designed to maintain a region requiring a high aspect ratio. Can be formed as a structure having a high porosity.

  The manufacturing method of the anodized alumina self-supporting film according to the present invention includes a step of preparing a substrate containing aluminum. Moreover, the process of forming an anodized alumina film | membrane by applying a voltage to a board | substrate, maintaining a film | membrane surface temperature at 10 degrees C or less is provided. Moreover, the process of removing the board | substrate residual part which is not anodized from the anodized alumina membrane | film | coat formed in the surface of a board | substrate is provided.

  In this case, the surface temperature of the anodized alumina film can be set to 10 ° C. or less as an anodic oxidation condition. In this way, since the Joule heat can be efficiently removed from the anodized alumina film surface by lowering the temperature, the film dissolution rate that inhibits substantial film growth when this film is formed on the substrate surface, Can be slower. As a result, since the dissolution amount of the film is reduced, the film growth rate exceeds the film dissolution rate, and a thick film is achieved. Then, an anodized alumina self-supporting film having a film thickness of 230 μm or more that exceeds the conventionally considered limit film thickness and having good surface flatness can be manufactured with good reproducibility.

  It should be noted that the temperature controlled to 10 ° C. or lower here is the temperature of the anodized alumina film surface, not the bath temperature (temperature of the treatment liquid). Moreover, the temperature of the anodized alumina film surface is desirably 7 ° C. or less, more desirably 5 ° C. or less, and further desirably 0 ° C. or less. However, when the temperature is lowered, it is important that the treatment liquid does not freeze on the film surface. When freezing, various non-reactive anti-icing agents such as ethylene glycol may be added to lower the freezing point of the treatment liquid.

  Then, the Joule heat generated by the anodizing reaction at the film growth interface (boundary surface between the anodized alumina film and the base aluminum) moving in the depth (thickness) direction from the initial film surface is in contact with the treatment liquid. The amount of heat per time exhausted by the thermal gradient based on the temperature difference between the film surface side and the film growth interface increases as the temperature of the film surface decreases. Therefore, the surface temperature of the anodized alumina film in contact with the treatment liquid is constantly lowered, and the film dissolution rate is reduced. Therefore, as a result, the film growth rate becomes higher than the film dissolution rate, so that the film thickness of the anodized alumina film can be made larger.

  Preferably, in the method for producing the anodized alumina self-supporting film, in the step of forming the anodized alumina film, the treatment liquid is sprayed on the surface of the substrate from an oblique direction. In this case, a mechanism that can preferentially inject in the oblique direction with respect to the surface of the target substrate is used, and a jet of the processing liquid controlled and maintained at a temperature equal to or lower than a control value of a predetermined processing liquid temperature is You can hit it. As a result, the Joule heat generated on the film surface can be forcibly and efficiently eliminated, so that the film surface temperature can be maintained at 10 ° C. or lower, and the film growth rate is relatively higher than the film dissolution rate. You can speed up.

  As a mechanism for injecting the processing liquid in an oblique direction with respect to the surface of the substrate, for example, a predetermined bundle of nozzle bundles aligned in one direction or a predetermined flow from the row of tubes arranged along the sample shape obliquely to the sample surface A forced jet nozzle or the like in which a plurality of injection holes capable of providing the same is formed can be used. In addition, the temperature control of the film surface of the anodized alumina film can be performed by managing the temperature of the treatment liquid sprayed onto the substrate surface. Further, the treatment liquid injection can be selected from steady injection, pulse injection, time difference injection (shifting the injection timing from each injection hole, including random injection), and the like.

  In addition, in the prior art, there is one that forcibly injects the processing liquid in the vertical direction toward the sample surface in order to exhaust Joule heat immediately above the sample surface (see, for example, Patent Document 2), but the cooling efficiency is not sufficient. Absent. That is, there is a distance between the ejection nozzle and the sample surface, turbulence is likely to occur on the sample surface, and a back flow (back pressure flow) perpendicular to the surface is generated, so that the direct cooling effect on the sample surface is reduced. It is. In addition, since the ejection nozzle is arranged between the sample surface and the counter cathode, it becomes an obstacle to the electric field distribution.

  On the other hand, in the structure of the present invention in which the processing liquid is sprayed on the surface of the substrate from an oblique direction, it is not necessary to install an ejection nozzle between the sample surface and the counter cathode, and the flow of the processing liquid is not affected. Since no pressure flow is generated, the cooling capacity loss is small. Further, the processing liquid can be ejected from a position closer to the substrate surface. Therefore, Joule heat from the sample surface side can be efficiently exhausted.

  Preferably, in the method for producing an anodized alumina self-supporting film, in the step of forming the anodized alumina film, only one surface of the substrate surface is brought into contact with the treatment liquid (that is, other than forming the anodized alumina film on the substrate surface). The portion is hermetically isolated from the processing solution), and a uniform current distribution is formed in the portion of the surface of the substrate that is in contact with the processing solution. As current supply to the substrate that is the object to be processed, for example, if the structure is such that the ridge line and back surface of the substrate are hermetically sealed with a mechanical seal or the like, and the electrodes are evenly provided on the back surface, the back surface and the electrode portion connected thereto Can be completely shielded from the processing liquid, local current concentration can be prevented, and a uniform current distribution can be formed in a portion (effective surface) in contact with the processing liquid on the substrate surface.

  In this case, since a uniform current distribution is formed on a predetermined effective surface that is in contact with the processing liquid on one side of the substrate surface, it is possible to grow a uniform anodized alumina film without burning. . For this reason, since the stress concentration location generated by the local change in film thickness is eliminated on the surface of the anodized alumina film, it is possible to prevent the occurrence of surface cracks, which is a problem in increasing the film thickness. Furthermore, by applying the oblique jet described above, bubbles on the sample surface that are generated during the anodizing reaction and inhibit film growth at the contact point can be forcibly removed, so that the ridgeline of the effective surface is also very smooth. Can be made. As a result, a stable anodized alumina free-standing film can be manufactured with good reproducibility.

  Further, since a uniform anodized alumina film can be grown, the upright holes grow so as to extend in a direction perpendicular to one surface of the surface of the substrate. The obtained self-supporting film has through-hole nanoholes penetrating the self-supporting film by applying appropriate post-processing to the surface of the self-supporting film on the side that is fixed to the surface of the substrate remaining portion as the anodized alumina film. Can also be formed easily.

  In general, since the initial surface properties of the sample are inherited as they are in the anodizing treatment, in some cases, surface undulations having irregularities of various sizes may remain on the surface of the anodized alumina film. In the anodic oxidation treatment of the present invention, although the microscopic irregularities corresponding to the rolling stripes remain on the film formed by the anodizing treatment at the roughness level of the rolling stripes found in ordinary cold rolled materials, the nanoholes are on the entire surface. As long as it is formed and does not have an original shape that induces a unique notch effect, it can be used without self-occurring microcracks. However, a smoother fine surface is required depending on application development. In this case, the surface property (roughness) of the substrate before processing is mirror-polished (for example, chemical polishing, buff polishing, electrolytic polishing, etc.) to produce an anodized thick film having a very excellent smooth surface. be able to.

  Preferably, in the method for producing the anodized alumina free-standing film, the concentration of dissolved aluminum in the treatment liquid is 75 mg / ml or less in the step of forming the anodized alumina film. In this case, the anodic oxidation process can be performed with stable quality by restricting and controlling the dissolved aluminum concentration. For example, according to the literature ("latest surface treatment technology overview", latest surface treatment technology overview editorial committee, published by Sangyo Service Center Co., Ltd. (1987)), 3.5 g / l is described as the control value in surface coating treatment. However, in the present invention, the allowable range of the molten aluminum temperature of the treatment liquid can be greatly increased.

Preferably, in the step of forming the anodized alumina film, an inert gas is introduced into the treatment liquid. In this case, an inert gas (for example, N ₂ gas, Ar gas, etc.) can be introduced into the processing solution by, for example, bubbling during the formation process of the anodized alumina film. The dissolved oxygen increases during the anodizing treatment. However, if the dissolved oxygen increases too much, the anodizing reaction is suppressed, so that the thick film growth is delayed and the film quality is deteriorated. Since the dissolved oxygen can be forcibly removed or suppressed (in accordance with Sievert's law) by introducing the inert gas, it is possible to suppress the inhibition of the anodic oxidation reaction.

  Preferably, the method further includes a step of locally masking the substrate before the step of forming the anodized alumina film. In this case, an anodized alumina film can be formed only in a predetermined region (selected region) by local masking. Therefore, an anodized alumina self-supporting film having any special shape can be easily produced by forming a seal type or mask having a special shape (for example, star shape). As the masking material, it is preferable to use a material having durability against the treatment liquid and having non-hydrophilicity, insulation, and heat resistance, such as a fluorine-based resin and a silicone-based resin. In addition, when aiming at a precise shape, the masking which applied the resist pattern by the photolithographic method can also be used.

  Preferably, the method further includes a step of forming an upright hole penetrating the anodized alumina free-standing film by performing a post-treatment on the anodized alumina free-standing film after the step of removing the remaining portion of the substrate. In this case, the bottom wall of the upright hole on the side in contact with the substrate is removed by subjecting the free-standing film to an appropriate post-processing (for example, mechanical processing such as wet melting, polishing, or electron beam irradiation). Therefore, a penetrating upright hole that penetrates the self-supporting film can be easily manufactured. By using an anodized alumina self-supporting film having a thickness of 230 μm, preferably 300 μm or more and a through-hole having an aspect ratio of 10,000 or more, the use of the self-supporting film is further expanded.

  In order to form a through-type upright hole, prior to the step of removing the remaining portion of the substrate, an anodized alumina film between the growth tip portion of the upright hole and the remaining portion of the substrate (that is, the bottom wall of the upright hole) A step of removing may be provided. For example, the anodized alumina film can be dissolved and removed by a chemical method. At this time, regarding the voltage applied to form the anodized alumina film, if the voltage immediately before releasing the voltage load is made extremely small, the anodized alumina film to be removed for the formation of the through-type upright hole The thickness can be reduced. Therefore, it becomes easy to remove the anodized alumina film at this portion, so that the production efficiency can be improved.

  Preferably, the method for producing an anodized alumina self-supporting film further includes a step of expanding the diameter of the upright holes formed in the anodized alumina self-supporting film after the step of removing the remaining portion of the substrate. In this case, the diameter of the upright hole can be expanded (pore widening) by wet melting performed as a post-processing on the self-supporting film. If the temperature of the solution is high, the amount of dissolution increases and the pore size increases. Therefore, the diameter of the upright hole can be arbitrarily changed by changing the temperature of the solution and the treatment time.

  Preferably, in the step of forming the anodized alumina film, the voltage applied to the substrate is adjusted, or the substrate is immersed in the processing liquid and the holding temperature of the processing liquid is increased in a state where the voltage load is released. The diameter of at least a part of the upright holes formed in the anodized alumina free-standing film is changed. In this case, the diameter of the upright hole may be continuous or intermittent in one or a plurality of places in the middle of the extending direction of the upright hole (thickness direction of the self-standing film) or in the entire length in the extending direction of the upright hole. Further, even a configuration in which these are combined can be enlarged or reduced. Note that when the voltage is increased, the diameter of the upright holes is enlarged and the interval between the adjacent upright holes is narrowed, so that the wall texture volume between the upright holes is reduced. However, the anodized alumina free-standing film having a film thickness of 230 μm or more has a higher bending strength than a thin film of the same area due to an increase in the effective wall texture volume between the upright holes due to the thick film thickness. Therefore, even if the wall tissue volume is reduced, there is no problem in the strength of the free-standing film.

  Preferably, in the step of preparing the substrate, a substrate having a groove profile pattern with a predetermined shape formed on the surface of the substrate is prepared. In the step of forming the anodized alumina film, an anodized alumina film is formed on the surface of the substrate on which the groove profile pattern having a concave shape is formed, so that the anodization can be easily cut and separated along the groove profile pattern. Manufactures self-supporting alumina film. In this case, the workability of the anodized alumina free-standing film can be improved.

  The anodized alumina self-supporting film of the present invention has a film thickness of 230 μm, preferably 300 μm or more, which exceeds the conventionally considered limit film thickness, and can withstand handling sufficiently as a single film. Deployment is possible.

  Embodiments of the present invention will be described below with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated.

  FIG. 1 is a perspective view of an anodized alumina self-supporting film of the present invention. As shown in FIG. 1, nanoholes 2 as upright holes are formed in the anodized alumina free-standing film 1. The film thickness t of the anodized alumina free-standing film 1 is 230 μm or more. The nanohole 2 is formed in the thickness direction of the anodized alumina free-standing film 1 and penetrates the anodized alumina free-standing film 1. The diameter of the nanohole 2 is 50 nm or less, and can be arbitrarily selected depending on the practical use. For example, the hole diameter may be 10 nm to 30 nm.

  The aspect ratio of the nanohole 2 having a pore diameter of 50 nm or less penetrating the anodic alumina self-supporting film 1 having a thickness of 230 μm or more can be at least 10,000. That is, by adjusting the combination of the thickness of the anodic oxide alumina free-standing film 1 and the diameter of the nanohole 2, the aspect ratio of the nanohole 2 can be 10,000 or more. For example, when the film thickness is 230 nm, the condition that the pore diameter is 23 nm or less is selected. When the pore diameter is 50 nm, the film thickness is 500 μm or more, so that the aspect ratio of the nanohole 2 can be arbitrarily adjusted according to the application. it can.

  As described above, the aspect ratio generally refers to the ratio of the long side to the short side, but here, the diameter of the nanohole 2 (that is, the shortest distance from the edge to the opposite edge on the opening surface of the nanohole 2 (opening width) )) And the depth (that is, the length in the extending direction and is equal to the film thickness of the anodized alumina self-supporting film 1 in a nanohole penetrating the anodized alumina self-supporting film 1).

  FIG. 2 is a schematic cross-sectional view showing Modification 1 of the anodized alumina free-standing film. As shown in FIG. 2, nanoholes each having a large diameter portion 12 b and a small diameter portion 12 a are formed in the anodized alumina free-standing film 11. The diameter of the nanohole changes in the middle of the extending direction (that is, the thickness direction of the anodized alumina free-standing film 11). The growth direction of the anodized alumina free-standing film 11 is indicated by an arrow 19. The diameter of the nanohole is enlarged during the process of growing the anodized alumina free-standing film 11. The nanohole has a bottom 13 in the large diameter portion 12b. That is, in the anodized alumina free-standing film 11 shown in FIG. 2, the nanohole is formed as a non-penetrating type that does not penetrate the anodized alumina free-standing film 11 in the thickness direction.

  Note that FIG. 2 shows a one-to-one case of a small-diameter nanohole (small-diameter portion 12a) and a large-diameter nanohole (large-diameter portion 12b). As a modification, for example, the anodizing voltage is greatly changed. In some cases, a plurality of small-diameter nanoholes are connected to one large-diameter nanohole during the growth process.

  FIG. 17 is a diagram showing an example of nanoholes whose diameter changes in the extending direction, and the initial DC pulse voltage is 8 V in a state where the bath temperature is maintained at 10 ° C. in a 1 mol / l sulfuric acid treatment solution. It is the photograph which shows the cross-sectional structure | tissue of the anodic oxidation alumina self-supporting film | membrane obtained by applying this voltage and raising pressure | voltage after that to 25V. As shown in FIG. 17, the diameter of the nanohole formed when the processing voltage is as small as 8V is small. On the other hand, after boosting to 25 V, the diameter of the nanohole is relatively large. That is, it can be seen that in the anodized alumina free-standing film produced by changing the processing voltage, the diameter of the upright hole (nanohole) changes after the voltage change.

  FIG. 3 is a schematic cross-sectional view showing Modification 2 of the anodized alumina free-standing film. As shown in FIG. 3, nanoholes having large diameter portions 22 a and small diameter portions 22 b are formed in the anodized alumina free-standing film 21. The large diameter portion 22a is a portion having a relatively large diameter in the nanohole. The small diameter portion 22b is a portion having a relatively small diameter in the nanohole. The diameter of the nanohole changes in the middle of the extending direction (that is, the thickness direction of the anodized alumina free-standing film 21). The growth direction of the anodized alumina free-standing film 21 is indicated by an arrow 29. The diameter of the nanohole is reduced during the process of growing the anodic alumina self-supporting film 21. That is, the nanohole is formed so that the plurality of small diameter portions 22b are connected to one large diameter portion 22a. The nanoholes are formed so as to penetrate the anodized alumina free-standing film 21 in the thickness direction, but can be selected according to the use and may remain non-penetrating.

  FIG. 4 is a schematic cross-sectional view showing Modification 3 of the anodized alumina free-standing film. As shown in FIG. 4, a nanohole 32 having a bottom 33 is formed in the anodized alumina free-standing film 31. A three-dimensional network structure layer 35 is formed on the film surface 34 of the anodized alumina free-standing film 31. In the three-dimensional network structure layer 35, a large number of fine holes are three-dimensionally formed in alumina, and a plurality of holes are connected to each other so that the fine alumina is intertwined in a three-dimensional network. A structure linked to is formed. Therefore, the three-dimensional network structure layer 35 has a higher porosity than the portion where the nanoholes 32 are formed. If the catalyst is filled in the three-dimensional network structure layer 35 having a high porosity, the filling rate can be further increased.

  FIG. 18 is a diagram illustrating an example of a three-dimensional network structure layer. This is an example in which the three-dimensional network structure layer 35 formed on the surface of the anodized alumina free-standing film 31 shown in FIG. 4 is observed by SEM (Scanning Electron Microscope). As shown in FIG. 18, the three-dimensional network structure layer is a structure in which thin alumina structures are connected so as to be entangled with each other in a three-dimensional network, and has a large porosity. Such a three-dimensional network structure layer is formed by, for example, forming an anodized alumina self-supporting film by applying a 25 V direct-current pulse voltage in a 1 mol / l sulfuric acid treatment solution maintained at 10 ° C., and subsequently setting the treatment temperature to 20 ° C. It can be formed on the surface layer by carrying out the same treatment by raising the temperature.

  FIG. 5 is a schematic cross-sectional view showing Modification 4 of the anodized alumina free-standing film. As shown in FIG. 5, a three-dimensional network structure layer 45 is formed on the film surfaces 44 and 44 of the anodized alumina free-standing film 41. As described above, the three-dimensional network structure layer 45 is formed on both of the film surfaces, and the nanoholes 42 may be formed to communicate with the three-dimensional network structure layer 45.

  Next, a method for producing an anodized alumina free-standing film will be described. FIG. 6 is a schematic diagram showing an outline of an anodized alumina film forming apparatus. As shown in FIG. 6, the anodized alumina film forming apparatus includes an electrolytic cell 101. A non-consumable electrode 104 and a substrate holder 105 are provided inside the electrolytic cell 101. A substrate 103 to be processed on which an anodized alumina film is to be formed on the surface 103 a is fixed to a substrate holder 105. The anode side of the variable DC power source 102 is electrically connected to the substrate holder 105, and the cathode side is electrically connected to the non-consumable electrode 104. The surface 103 a of the substrate 103 and the non-consumable electrode 104 are arranged to face each other inside the electrolytic cell 101. The variable DC power supply 102 may be a normal DC power supply, a DC pulse power supply, or an AC power supply. The waveform may be any shape such as a square, a triangle, a sine wave, or a composite waveform thereof, and is a specification in which the voltage is variable in a range of at least 0 V to 100 V, preferably 0 V to 30 V. It is desirable to be.

  The electrolytic bath 101 is filled with a processing liquid 106. As the treatment liquid 106, for example, sulfuric acid having a concentration of 1 mol / l is used. As the treatment liquid 106, sulfuric acid having a concentration of 0.5 mol / l or more and 10 mol / l or less can be used. The treatment liquid 106 basically does not require an additive. For example, when the treatment temperature is lowered, a non-reactive anti-icing agent for lowering the freezing point of the treatment liquid is added to avoid freezing. In some cases, an appropriate additive may be added for adjustment. In addition, a cooling jet nozzle 111 as a cooling member for forcibly cooling the substrate 103 and the anodized alumina film is disposed at a position close to the substrate 103 inside the electrolytic cell 101. Further, an inert gas introduction device 107 and a temperature measuring body 108 for measuring the temperature of the surface 103a of the substrate 103 and the film surface of the anodized alumina film to be formed are provided inside the electrolytic cell 101. Yes.

  The substrate holder 105 has a structure in which only the surface 103 a of the substrate 103 is brought into contact with the processing liquid 106. On the other hand, the back surface opposite to the front surface 103a is formed by, for example, arranging a mechanical seal using a resin insulator so as to cover the outer peripheral ridge line portion of the substrate 103 and the contact portion between the back surface and the substrate holder 105. Airtightness is maintained. That is, the substrate holder 105 has a structure in which the back surface of the substrate 103 is isolated from the processing liquid 106 and the back surface is not brought into contact with the processing liquid 106. Therefore, the anode on the back surface side of the substrate 103 has a structure in which a uniform current distribution is formed in a portion of the front surface 103a that is in contact with the processing liquid 106 and local abnormal current concentration can be avoided. For this reason, no discontinuous film thickness occurs on the surface of the anodized alumina film, so that local stress concentration points can be eliminated and the occurrence of surface cracks can be prevented.

  6 is maintained in a relative directional relationship (for example, the substrate 103 and the non-consumable electrode 104 face each other and the cooling jet nozzle 111 is inclined with respect to the substrate 103). In this case, the surface 103a of the substrate 103 may be installed in either the vertical or horizontal direction. However, in the anodic oxidation process, reactive gas bubbles (mainly hydrogen) are generated on the surface 103 a of the substrate 103, and therefore, when the substrate 103 is inclined, the bubbles may move along the substrate 103. is there. In that case, since the poor contact with the processing liquid 106 occurs at the bubble contact portion, the film quality may be locally degraded. Further, bubbles may accumulate between the upper portion of the substrate holder 105 and the substrate 103 for maintaining airtightness. Therefore, it is preferable that the surface 103a of the substrate 103 is directed upward as shown in FIG.

  FIG. 7 is a process flow diagram showing a method for producing an anodized alumina free-standing film. With reference to FIG. 7, each process of the manufacturing method of an anodized alumina self-supporting film | membrane is demonstrated. First, in the step (S10), a substrate 103, which is pure aluminum or an aluminum alloy (for example, an Al—Mn alloy, an Al—Mg alloy, an Al—Mg—Si alloy, etc.) as an object to be processed, is prepared. The substrate 103 is fixed to the substrate holder 105 in the electrolytic cell 101.

  Next, in step (S20), the substrate 103 is anodized to form an anodized alumina film on the surface 103a of the substrate 103. The anodized alumina film is formed in a direction perpendicular to the substrate surface at a film growth rate of about 10 to 20 μm / hr. As described above, sulfuric acid is used for the treatment liquid. In order not to change the diameter of the nanohole, it is desirable to load a constant voltage. However, a constant current load condition may be used, and a pulse voltage or an AC power supply may be used. The waveform may be loaded with an arbitrary shape such as a square, a triangle, a sin wave, or a composite waveform thereof. When the treatment voltage is high, the nanohole diameter becomes large. However, when a range of 15 V or more and 30 V or less is applied as a desirable voltage for forming a self-supporting film, the hole diameter can be set to 20 to 30 nm.

  If the treatment voltage is changed during the anodizing treatment, the nanohole diameter can be easily changed. That is, the processing voltage can be properly used according to the aim of the structure of the anodized alumina free-standing film. If the processing voltage is increased, the nanohole diameter is increased, and if the processing voltage is decreased, the nanohole diameter is decreased. By changing the treatment voltage a plurality of times or continuously, it is possible to enlarge or reduce the nanohole diameter at a plurality of locations in the extending direction of the nanohole or continuously. This method is advantageous in terms of cost and quality control compared to batch processing because continuous processing is possible as a manufacturing process.

  In addition, as an application of the above-described method for changing the nanohole diameter, the substrate 103 with the anodized alumina film formed on the surface 103a is immersed in the processing liquid, and the holding temperature of the processing liquid is raised in a state where the voltage load is released. be able to. If it does in this way, the nanohole diameter currently formed in the anodized alumina membrane | film | coat can be expanded over the surface or full length. Further, when the processing temperature is continuously returned to the predetermined temperature and the voltage load is resumed, the subsequent film growth resumes. In this way, it is possible to change the nanohole diameter in the extending direction partially or over the entire length, and similarly, since continuous processing is possible, it is an advantageous method in terms of cost and quality control. .

  Note that during the anodizing process, the processing liquid is sprayed to the substrate 103 from an oblique direction close to the substrate 103 via the cooling jet nozzle 111 disposed in the vicinity of the substrate 103. FIG. 8 is a schematic diagram showing the arrangement of the cooling jet nozzles with respect to the substrate. The cooling jet nozzle 111 is a nozzle bundle aligned in one direction that can inject the processing liquid onto the surface 103a of the substrate 103 from one direction. The cooling jet nozzle 111 is disposed so that the opening at the tip of the cooling jet nozzle 111 faces the surface 103 a and the injection direction of the processing liquid is oblique with respect to the substrate 103. In FIG. 8, the nozzle bundles are aligned in the same direction, but may be arranged in a fan shape toward the center of the surface 103 a of the substrate 103.

  Note that the mechanism for injecting the treatment liquid is not limited to the cooling jet nozzle 111. FIG. 9 is a schematic diagram showing a modification of the cooling jet nozzle. The cooling jet nozzle 121 shown in FIG. 9 has a mother pipe having a shape along the shape of the outer periphery of the substrate 103 (in this case, an annular shape is shown, but an arched partial annular shape may be used). A plurality of injection holes are connected to the mother pipe. The injection holes are arranged so as to be oblique to the central portion of the substrate 103 with respect to the substrate 103, and are formed so that a predetermined flux can be given from a plurality of directions toward the surface 103a of the substrate 103. ing. If the cooling jet nozzle 121 is used, a more uniform anodized alumina film can be formed.

  Since the cooling jet nozzles 111 and 121 spray the processing liquid onto the surface 103a of the substrate 103 or the film surface of the formed anodized alumina film, Joule heat generated on the film surface by anodization can be forcibly eliminated. The temperature of the film surface is maintained at 10 ° C. or lower. By controlling the temperature of the treatment liquid sprayed onto the substrate surface, the temperature of the film surface of the anodized alumina film can be controlled. Note that it is preferable to control the temperature of the treatment liquid sprayed onto the substrate surface so that the temperature is kept below the bath temperature. For example, if the temperature of the treatment liquid sprayed onto the substrate surface is maintained at 10 ° C. or lower, the temperature of the film surface of the anodized alumina film can be maintained at 10 ° C. or lower. Note that the temperature of the sprayed processing liquid is preferably lower than the bath temperature because the exhaust heat effect is increased, and the temperature of the processing liquid may be a temperature at which the processing liquid does not freeze in the nozzle. As a result, the film dissolution rate is reduced, so that the film growth rate exceeds the film dissolution rate, and the film thickness can be increased.

  In this way, by performing anodizing treatment for a predetermined time while maintaining the film surface temperature at 10 ° C. or lower, an anodized alumina having a film thickness of 230 μm or more, preferably 300 μm or more exceeding the limit film thickness conventionally considered. A film can be produced. FIG. 10 is a schematic cross-sectional view showing a state where an anodized alumina film is formed on the substrate surface. A state is shown in which an anodized alumina film 141 having a nanohole 142 having a bottom 143 formed therein is formed on the surface of the substrate 103. At the tip of nanohole growth at the bottom 143, aluminum contained in the substrate 103 reacts with oxygen, and nanohole formation proceeds through formation of a thin dense anodized alumina film 141 (called a barrier layer). A nanohole 142 extending in the extending direction is generated.

  Next, in step (S30), the substrate remaining portion of the substrate 103 that has not been anodized is removed. For example, by selectively dissolving and removing the residual portion of the substrate with a chemical solution such as methanol bromide, removing the residual portion of the substrate by machining, or peeling the anodized alumina film from the residual portion of the substrate by an electrochemical reaction. The part can be removed. And an anodized alumina film | membrane becomes a single original standing film | membrane which can hold | maintain and handle a shape without a support body. FIG. 11 is a schematic cross-sectional view showing the anodized alumina free-standing film from which the substrate remaining portion has been removed.

  Next, post-processing is performed in step (S40). For example, the nanohole 2 shown in FIG. 1 is obtained by subjecting the anodized alumina free-standing film shown in FIG. 11 to wet melting, machining, electron beam irradiation, etc., and removing the non-penetrating film surface portion on the bottom 143 side of the nanohole 142. Can be formed as an anodized alumina free-standing film 1 penetrating in the thickness direction of the film. In addition, for example, the anodized alumina free-standing film shown in FIG. 11 can be wet-dissolved, and the diameter of the nanohole 142 can be enlarged (pore widening). At this time, if the temperature of the solution is high, the amount of dissolution per unit time increases and the pore size increases, and therefore the pore size of the nanoholes can be changed by appropriately combining the temperature of the solution and the treatment time. it can. Furthermore, if masking or the like is used in combination, not only the entire region but also a part of the region can be penetrated or not penetrated depending on the application.

  FIG. 19 is a diagram showing an example in which the above-described post-treatment is performed on the anodized alumina free-standing film. FIG. 19A shows the non-penetration of the anodized alumina self-supporting film of FIG. 11 on the substrate 103 side after the substrate 103 is removed (that is, the anodized alumina self-supporting film on the bottom wall side of the nanohole 142). It is a photograph showing the surface. FIG. 19 (b) is a photograph showing the same surface of the anodized alumina free-standing film after performing penetration as post-processing.

  FIG. 19A shows an anodized alumina film formed by applying a 25 V direct-current pulse current load with an anodized alumina film having a surface temperature of 10 ° C. and a treatment solution of 1 mol / l sulfuric acid, and then removing the aluminum base substrate. The side interface is shown. As schematically shown in FIGS. 10 and 11, the end surface forms a closed pore structure. That is, non-throughright upright holes are formed in the anodized alumina free-standing film. Then, this end surface was immersed in 1 mol / L sulfuric acid at 20 ° C. for 4 hours (wet treatment), and the resulting surface texture is shown in FIG. 19A and 19B, an upright hole (nanohole) that was clearly closed was opened, and an anodized alumina free-standing film in which a through hole was formed was obtained.

  FIG. 20 is a diagram showing an upright hole diameter enlargement process (pore widening) as another example of post-processing the anodized alumina free-standing film. In this post-processing, the surface of the anodized alumina free-standing film shown in FIG. 10 or the surface on which the above-described penetration processing is performed after the substrate 103 is removed is a processing target. FIGS. 20A and 20B are photographs of the same surface of the anodized alumina free-standing film before and after the post-treatment.

  FIG. 20A is a photograph of the surface structure of an anodized alumina film obtained by anodizing pure aluminum in a sulfuric acid solution at 10 ° C. and 1 mol / l under a load of 25 V DC pulse voltage. . During the anodizing process, the cooling jet is applied and controlled so that the film surface temperature does not exceed 10 ° C. Upright holes are observed on the membrane surface. Thereafter, the anodized alumina film is placed in a 1 mol / l sulfuric acid treatment solution at 20 ° C. for 40 minutes in a state in which the electric field load is released in order to perform the diameter expansion process (pore widening) by wet melting. Soaked. As a result, as shown in FIG. 20B, an anodized alumina self-supporting film in which the diameter of the open upright holes was clearly increased could be obtained.

  In addition, as a post-treatment, an electrolytic treatment or a one-sided or double-sided immersion treatment in a treatment solution causes a structural change such as a dissolution and reprecipitation reaction of the surface layer, and a three-dimensional network is formed on the surface layer of the anodized alumina free-standing film A structural layer can be formed. By doing so, it is possible to obtain the anodic oxide alumina free-standing films 31 and 41 in which the three-dimensional network structure layers 35 and 45 shown in FIGS. 4 and 5 are formed. The three-dimensional network structure layers 35 and 45 have a larger porosity than the portions where the nanoholes 32 and 42 are formed inside the anodized alumina free-standing films 31 and 41. Therefore, for example, when the anodized alumina free-standing film is filled with a catalyst and used, the filling rate can be further increased.

  Note that the three-dimensional network structure layer can also be formed by changing the processing conditions when performing the anodizing treatment (that is, removing from the anodizing treatment condition range in which good upright holes are formed). For example, when the anodizing temperature is maintained at 10 ° C., the three-dimensional network structure layer can be formed by raising the processing temperature to 20 ° C. If the processing conditions are changed at the beginning or end of the anodizing treatment, a three-dimensional network structure layer can be formed on only one side or both sides of the anodized alumina free-standing film.

  By the manufacturing method described above, an anodized alumina self-supporting film having a film thickness of 230 μm or more, preferably 300 μm or more, can be easily manufactured with good reproducibility. Since a sulfuric acid-based liquid is used as the treatment liquid, a preferable voltage condition when performing the anodizing treatment can be as low as 15 to 30V. Therefore, the nanohole diameter can be made as small as 20 to 30 nm, and the aspect ratio of the nanohole can be made 10,000 or more.

  On the other hand, when an anodized alumina film is formed using an oxalic acid-based treatment solution, stable production as an anodized alumina free-standing film has not been developed, and the anodized alumina film is used as a film on the surface of a support. It was used. In addition, since the treatment voltage generally used in the oxalic acid-based treatment liquid is as high as 100 V or more, the nanohole diameter cannot be reduced to 50 nm or less. Therefore, the aspect ratio of the nanohole is small. That is, nanoholes having a small pore diameter cannot be formed unless sulfuric acid is used as a treatment liquid. Furthermore, since dilute sulfuric acid is inexpensive and easy to handle, there is an advantage that sulfuric acid is industrially advantageous over oxalic acid.

  Hereinafter, modified examples of the method for producing the anodized alumina free-standing film will be described. FIG. 12 is a schematic diagram of a step of forming a groove profile pattern on the anodized alumina free-standing film. As shown in FIG. 12A, a substrate 203 on which a groove profile pattern is formed is prepared as a substrate before anodic oxidation. Here, the groove profile pattern can be easily formed by selecting an appropriate method according to the width, depth, length, concave shape, and pattern shape of the groove, such as mechanical cutting, embossing, and laser processing. it can. As shown in FIG. 12B, an anodized alumina film 241 is formed by anodizing the surface of the substrate 203. Then, if the substrate 203 is removed, as shown in FIG. 12C, an anodized alumina self-supporting film 241 in which the concave shape along the groove profile pattern is directly reflected on the surface is obtained.

  The anodized alumina free-standing film 241 produced in this way can be easily cut along the groove profile pattern (for example, well by hand bending or the like) as shown in FIG. Further, separation into the anodized alumina free-standing films 241a, 241b, and 241c is possible. Therefore, the workability of the anodized alumina free-standing film can be improved in the same manner as the method for producing a special-shaped anodized alumina free-standing film by local masking described later. In addition, as an anodized alumina free-standing film having various groove profile patterns on the surface as it is without cutting or separating, for example, by forming a conductive material on the groove portion on the groove profile pattern by vapor deposition or plating It can also be applied to circuit boards having a hybrid function.

  FIG. 13 is a schematic view showing a substrate for producing a specially shaped anodized alumina free-standing film. Conventionally, to produce a specially shaped filter, the filter can be handled by combining it with a porous substrate having a pore size larger than the effective pore size of the filter having the target function. become. In the present invention, although it is a single unique standing film having a high aspect ratio, it is possible to easily produce a specially shaped anodized alumina free-standing film without performing mechanical processing or the like in a subsequent process.

  14 is a schematic cross-sectional view showing a cross section taken along line XIV-XIV shown in FIG. FIG. 15 is a perspective view showing a special-shaped anodized alumina free-standing film. As shown in FIGS. 13 and 14, the substrate 303 is provided with a star-shaped local masking 313 which is an example of an arbitrary planar shape. The local masking 313 is used by adhering a fluorine-based resin, a silicone-based resin sheet or the like that is easy to process and excellent in durability, for example. Moreover, when aiming at a precise shape, the masking which applied the resist pattern by the photolithographic method can also be used. By anodizing such a substrate 303, an anodized alumina film can be formed in a predetermined selected region.

  FIG. 16 is a flowchart showing a method for manufacturing an anodized alumina free-standing film when the substrate shown in FIG. 13 is used. After the substrate is prepared in the step (S10), the substrate 303 having the local masking 313 shown in FIG. 13 is prepared by forming a seal mold or a mask on the substrate in the step (S11). Using this, the anodic oxidation in step (S20) and the removal of the substrate in (S30) are performed, and further post-processing such as formation of through holes and enlargement of the hole diameter is performed in step (S40). The star-shaped anodized alumina free-standing film 343 shown can be easily manufactured. It goes without saying that the above-described manufacturing method can produce an anodic oxidized alumina free-standing film having any shape, not limited to a star shape.

  Embodiment 1 of the present invention will be described below. Using the method for producing an anodized alumina self-supporting film of the present invention, samples were prepared by changing the film surface temperature, and an experiment was conducted to clarify the film thickness of each sample and the aspect ratio of the upright holes formed in each sample. I did it. The treatment solution was sulfuric acid with a concentration of 1 mol / l, and the treatment voltage was 25 V DC pulse voltage load, and an anodization treatment was performed for 25 hours. When the anodized alumina film surface temperature is 20 ° C., 17 ° C., 15 ° C., 10 ° C. and 5 ° C., the film thickness, the average upright hole diameter, the value of the aspect ratio, and the aspect ratio based on the aspect ratio of 10,000 The relative ratio is shown in Table 1.

  From Table 1, when the surface temperature of the anodized alumina film is 10 ° C. or less, an anodized alumina free-standing film having a film thickness exceeding 230 μm, which has been considered as a conventional limit film thickness, is obtained, and the aspect ratio is 10,000. It was shown that an anodized alumina self-supporting film having the above-described upright holes can be obtained. Moreover, it shows in Table 2 about the characteristic example of the obtained anodic oxidation alumina self-supporting film | membrane.

  From Table 2, it was also confirmed that the anodized alumina free-standing film obtained according to the present invention has handleable bending strength and hardness (Hv), and high-temperature heat resistance.

  In Example 2, an experiment was conducted to confirm the effect of a cooling jet nozzle that injects a treatment liquid from an oblique direction onto the surface of the substrate during the formation of the anodized alumina film. The temperature (bath temperature) of the processing liquid in the electric field tank can be controlled by circulating the processing liquid in the electric field tank on which the substrate to be anodized is fixed. The cooling jet nozzle is installed in a circulation system in which the treatment liquid in the electric field tank is branched, and the circulation system is provided with a cooling pump, and the treatment liquid at a temperature further cooled than the bath temperature is supplied to the substrate. It was supposed to be able to spray on the surface.

  Using such an apparatus, the surface temperature of the anodized alumina film was measured when the bath temperature was 8 ° C. and the temperature of the treatment liquid sprayed on the surface of the substrate was 8 ° C., 5 ° C., and 3 ° C. As a comparative example, the surface temperature of the anodized alumina film was measured when the bath temperature was 14.8 ° C. and 8 ° C. without using a cooling jet nozzle. The results are shown in Table 3.

  From Table 3, when maintaining the bath temperature at 10 ° C. or lower, which is a temperature necessary for forming an anodized alumina self-supporting film having a film thickness exceeding 230 μm, anodization is performed by applying injection by a cooling jet nozzle. It was shown that the temperature difference between the surface temperature of the alumina coating and the bath temperature can be 3 ° C. or less. In addition, the temperature difference is further reduced by lowering the temperature of the processing liquid sprayed onto the substrate, indicating that the cooling ability of the cooling jet nozzle is excellent. In addition, it is thought that it is easy to further improve the cooling ability if the jetting ability is increased.

  In Example 3, an experiment was performed to confirm the influence of the dissolved aluminum concentration in the treatment liquid. As anodizing conditions, sulfuric acid having a concentration of 1 mol / l was used, and a 25 V DC pulse load was applied at a bath temperature of 10 ° C. Comparison was made with respect to the gloss and surface texture of the outermost surface of the anodized alumina film after the anodizing treatment under the respective conditions of the dissolved aluminum concentration of 15, 50, 76, 100, and 150 mg / ml. The results are shown in Table 4.

  From Table 4, when the dissolved aluminum concentration exceeds 75 mg / ml, the gloss of the anodized alumina film is gradually not observed, and the surface structure becomes a three-dimensional network structure in the matte region, and good upright holes are not formed. It was shown that That is, it was shown that an anodized alumina self-supporting film in which good upright holes are formed can be produced by setting the molten aluminum temperature of the treatment liquid to 75 mg / ml or less.

In Example 4, an experiment was conducted to confirm the effect of introducing an inert gas during the formation of the anodized alumina film. As the anodizing condition, 25 V DC pulse was applied using sulfuric acid having a concentration of 1 mol / l. Gas bubbles were generated in the treatment liquid by introducing N ₂ gas into the treatment liquid through the spherical porous material. Under these conditions, the film gloss and surface texture of the outermost surface of the anodized alumina film after the anodizing treatment at the bath temperatures of 8 ° C. and 10 ° C. were compared. Further, as a comparative example, a case where inert gas bubbling was not applied was also compared. The results are shown in Table 5.

  From Table 5, when the bath temperature was set to 10 ° C. under conditions where there was no inert gas bubbling, the gloss of the anodized alumina film was not observed on a part of the surface, and the surface texture was poor in the non-glossy region. On the other hand, as a result of stabilizing the anodic oxidation reaction by applying inert gas bubbling, it was shown that a good anodic alumina free-standing film can be formed without altering the upright holes even when the processing temperature is around 10 ° C. .

  The embodiments and examples disclosed herein are illustrative in all respects and should not be construed as being restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a perspective view of the anodized alumina free-standing film of this invention. It is a cross-sectional schematic diagram which shows the modification 1 of an anodized alumina self-supporting film | membrane. It is a cross-sectional schematic diagram which shows the modification 2 of the anodized alumina self-supporting film | membrane. It is a cross-sectional schematic diagram which shows the modification 3 of the anodized alumina self-supporting film | membrane. It is a cross-sectional schematic diagram which shows the modification 4 of the anodized alumina self-supporting film | membrane. It is a schematic diagram which shows the outline of an anodized alumina film forming apparatus. It is a process flow figure showing a manufacturing method of an anodized alumina self-supporting film. It is a schematic diagram which shows arrangement | positioning of the cooling jet nozzle with respect to a board | substrate. It is a schematic diagram which shows the modification of a cooling jet nozzle. It is a cross-sectional schematic diagram which shows the state in which the anodic oxidation alumina membrane | film | coat was formed in the board | substrate surface. It is a cross-sectional schematic diagram which shows the anodized alumina self-supporting film | membrane from which the board | substrate was removed. It is a schematic diagram of the process of forming a groove profile pattern in an anodized alumina free-standing film. It is a schematic diagram which shows the board | substrate for manufacturing the anodic oxidation alumina self-supporting film | membrane of a special shape. It is a cross-sectional schematic diagram which shows the cross section in the XIV-XIV line | wire shown in FIG. It is a perspective view which shows the anodic oxidation alumina self-supporting film | membrane of a special shape. It is a flowchart which shows the manufacturing method of the anodic oxidation alumina self-supporting film | membrane in the case of using the board | substrate shown in FIG. It is a figure which shows the example of the nanohole from which the diameter is changing in the middle of the extension direction. It is a figure which shows the example of a three-dimensional network structure layer. It is a figure which shows the example which performs a post-process to an anodized alumina self-supporting film | membrane. It is a figure which shows the other example which performs a post-process to an anodized alumina self-supporting film | membrane.

Explanation of symbols

  1,11,21,31,41 Anodized alumina free-standing film, 2,32,42 nanohole, 12a, 22a small diameter part, 12b, 22a large diameter part, 13, 33, 43 bottom part, 19, 29, 39, 49 arrow , 34, 44 Film surface, 35, 45 Three-dimensional network structure layer, 101 Electrolysis tank, 102 Variable DC power supply, 103 Substrate, 103a Surface, 104 Non-consumable electrode, 105 Substrate holder, 106 Treatment liquid, 107 Introduction of inert gas Apparatus, 108 Temperature sensor, 111, 121 Cooling jet nozzle, 141, 241 Anodized alumina coating, 142 Nanohole, 143 Bottom, 203, 303 Substrate, 241a, 241b, 241c, 343 Anodized alumina free-standing film, 313 Local masking .

Claims (17)

  An anodized alumina free-standing film having a film thickness of 230 μm or more, preferably 300 μm or more.   The anodized alumina self-supporting film according to claim 1, wherein an upright hole having an aspect ratio of 10,000 or more is formed.   The anodized alumina self-supporting film according to claim 2, wherein the diameter of the upright hole changes in the middle of the extending direction.   The anodized alumina self-supporting film according to claim 2 or 3, wherein the upright hole penetrates the anodized alumina self-supporting film.   The anodized alumina self-supporting film according to claim 2 or 3, wherein the upright hole has a bottom.   The anodized alumina self-supporting film according to any one of claims 1 to 5, wherein a three-dimensional network structure layer is formed on one of the film surfaces.   The anodized alumina self-supporting film according to any one of claims 1 to 4, wherein a three-dimensional network structure layer is formed on both of the film surfaces. A method for producing an anodized alumina free-standing film,
Preparing a substrate containing aluminum;
Forming an anodized alumina film by applying a voltage to the substrate while maintaining the film surface temperature at 10 ° C. or lower;
And a step of removing a remaining portion of the substrate that has not been anodized from the anodized alumina film formed on the surface of the substrate.   The method for producing an anodized alumina self-supporting film according to claim 8, wherein in the step of forming the anodized alumina film, a treatment liquid is sprayed on the surface of the substrate from an oblique direction.   The step of forming the anodized alumina film comprises contacting only one surface of the surface of the substrate with a processing solution, and forming a uniform current distribution in a portion of the surface of the substrate that is in contact with the processing solution. A method for producing an anodized alumina self-supporting film according to claim 8 or claim 9.   The method for producing an anodized alumina free-standing film according to any one of claims 8 to 10, wherein in the step of forming the anodized alumina film, the concentration of dissolved aluminum in the treatment liquid is 75 mg / ml or less.   The method for producing an anodized alumina self-supporting film according to any one of claims 8 to 11, wherein an inert gas is introduced into the treatment liquid in the step of forming the anodized alumina film.   The method for producing an anodized alumina self-supporting film according to any one of claims 8 to 12, further comprising a step of performing local masking on the substrate before the step of forming the anodized alumina film.   14. The method of claim 8, further comprising a step of forming an upright hole penetrating the anodized alumina free-standing film by performing post-treatment on the anodized alumina free-standing film after the step of removing the remaining portion of the substrate. The manufacturing method of the anodic oxidation alumina self-supporting film | membrane in any one of.   The anodic oxidation according to any one of claims 8 to 14, further comprising a step of expanding the diameter of an upright hole formed in the anodized alumina self-supporting film after the step of removing the remaining portion of the substrate. A method for producing an alumina self-supporting film.   In the step of forming the anodized alumina film, the voltage applied to the substrate is adjusted, or the substrate is immersed in the processing solution and the holding temperature of the processing solution is increased in a state where the voltage load is released. The method for producing an anodized alumina self-supporting film according to any one of claims 8 to 15, wherein a diameter of at least a part of the upright holes formed in the anodized alumina self-supporting film is changed. In the step of preparing the substrate, a substrate having a groove profile pattern of a predetermined shape formed on the surface of the substrate is prepared,
In the step of forming the anodized alumina film, the anodized alumina film can be easily cut and separated along the groove profile pattern by forming the anodized alumina film on the surface of the substrate on which the groove profile pattern is formed. The method for producing an anodized alumina self-supporting film according to any one of claims 8 to 16, wherein the self-supporting film is produced.