JP2012144395A - Method of producing porous film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing a porous film having a shielding layer on its surface by a simple step which does not have the least effect on chemical and physical features of the porous film and eliminates the need for a specific apparatus and a vacuum step.SOLUTION: The method of producing the porous film includes: a step of forming the porous film on a base material; a step of forming on the support, a gel film that contains a condensation polymer of an inorganic oxide precursor; a step of obtaining a laminate by making the porous film formed on the base material adhere tightly to the gel film formed on the support; a step of hardening the gel film by heating the laminate; and a step of removing the support on the gel film thus hardened.

Description

  The present invention relates to a method for producing a porous membrane, and more particularly to a method for producing a porous membrane having a sealing layer.

  Porous membranes with a large number of pores inside can be made wide by controlling and imparting physical and chemical characteristics according to the purpose such as specific surface area, porosity, pore diameter, functionalization of pore surface, etc. Application to the field is progressing. Specifically, it is applied to fields such as a catalyst carrier membrane, a separation membrane, a humidity control membrane, an electrode, a low dielectric constant membrane, and an optical thin film. In particular, the pore diameter is an important parameter that determines the type of substance that can be introduced into the porous body in the case of a carrier, and the type of light that can be applied in the case of an optical thin film. In the 1990s, the development of mesoporous materials having a pore size in the meso region, which is intermediate between nano-size and micro-size, has advanced, and application studies of porous membranes have been accelerated.

  When using a porous film as an optical thin film, in addition to controlling the structure of the porous film and imparting optical functions, environmental stability is also important so that the desired optical properties can be stably exhibited even when the surrounding environment changes. . However, porous membranes have a specific surface area that is several orders of magnitude greater than non-porous membranes, so that the optical properties of porous membranes are sensitive due to adsorption and desorption of suspended molecules in the environment, including water molecules, to the pore surface. Change. Therefore, in order to guarantee environmental stability, the suppression of adsorption / desorption of floating molecules in the environment to the pore surface is a major issue.

  As a means for improving the environmental stability of the porous membrane, it is expected to be effective to form a sealing layer made of a non-porous material on the surface of the porous membrane. However, when forming the sealing layer, it is necessary to suppress as much as possible the material itself forming the sealing layer and the material used in the sealing layer forming process from entering the porous film. In addition, it is important to selectively form a sealing layer on the surface of the porous film without affecting the physical and chemical characteristics of the pores.

  As a technique for forming a sealing layer on the surface of the porous film, for example, in Patent Document 1 and Patent Document 2, the pores of the porous substrate are temporarily filled with an organic substance and then sealed on the surface of the porous film. A technique for forming a stop layer is disclosed. Non-Patent Document 1 and Non-Patent Document 2 report a technique for forming a sealing layer on the surface of a porous film by an atomic layer deposition method using plasma in combination.

JP 2004-352568 A JP 2007-45691 A

“J. AM. CHEM. SOC.”, Vol. 128, p. 11018, 2006 “Microelectronic Engineering”, Vol. 86, p. 2241, 2009

  The above document discloses a technique for forming a sealing layer on the surface of a porous film. When the techniques described in Patent Document 1 and Patent Document 2 are used, in order to prevent the sealing layer material from entering the inside of the porous film, the organic material is once filled in the pores over the entire surface of the porous film or the entire film. There is a need to. Therefore, when the surface of the pores in the porous membrane has been subjected to chemical modification in advance, the function that was initially expected is lost after the step of filling with different organic substances once and removing them again. There was a fear.

  Further, the techniques described in Non-Patent Document 1 and Non-Patent Document 2 enable strict film thickness control of the sealing layer and can form a very dense film. However, since a dedicated vacuum apparatus is required and the process is complicated and the film forming speed is low, the application uses are limited from the viewpoint of cost.

  As described above, in order to improve the environmental stability of the porous membrane, the sealing layer is formed on the surface of the porous membrane, and the chemical and physical characteristics of the porous membrane itself are not affected as much as possible and simple. It was a problem to form a sealing layer by a simple process.

  The present invention has been made in view of such background art, and forms a sealing layer on the surface of the porous membrane by a simple process without changing the physical and chemical properties of the porous membrane. The present invention provides a method for producing a porous membrane.

  A method for producing a porous membrane that solves the above problems includes a step of forming a porous membrane on a substrate, a step of forming a gel membrane containing a polycondensation polymer of an inorganic oxide precursor on a support, The porous film formed on the substrate and the gel film formed on the support are adhered to each other to obtain a laminate, and the gel film is cured by heating the laminate. And a step of removing the support on the cured gel film.

  According to the present invention, there is provided a method for producing a porous membrane capable of forming a sealing layer on the surface of the porous membrane by a simple process without changing the physical and chemical properties of the porous membrane. can do.

It is the schematic which shows one embodiment of the manufacturing method of the porous film of this invention. It is the schematic which shows the process of closely_contact | adhering a gel film and a porous film. It is a flowchart of the manufacturing method of the porous membrane of this invention.

The present invention relates to a method for producing a porous film having a sealing layer made of an inorganic oxide on the surface, and has the following steps.
(1) A step of forming a porous film on the substrate.
(2) The process of forming the gel film containing the condensation polymer of an inorganic oxide precursor on a support body.
(3) The process of obtaining the laminated body by making the porous film formed on the said base material, and the gel film formed on the said support body closely_contact | adhere.
(4) The process of heating the said laminated body and hardening | curing the said gel film to make it the sealing layer which consists of inorganic oxides.
(5) A step of removing the support on the sealing layer.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic view showing one embodiment of the method for producing a porous membrane of the present invention. In the figure, 1 is a substrate, 2 is a porous film, 3 is a support, 4 is a gel film containing a condensation polymer of an inorganic oxide precursor, 5 is a sealing layer made of an inorganic oxide, and 7 is a laminate. Indicates. Moreover, in FIG. 3, a series of processes are shown by a flowchart.

Process (1)
First, as shown in FIGS. 1A and 3, the step (1) of forming the porous film 2 on the substrate 1 will be described.

  The base material 1 is selected from materials and structures according to a device to be used, such as an optical lens, a display panel, and an electrode. The material is not particularly limited as long as it is a material having sufficient heat resistance and chemical resistance for each manufacturing process described later including the formation of a porous film. When the porous film is used for optical applications such as an antireflection film, the substrate 1 can be selected from quartz glass, borosilicate glass, and the like according to the application, performance, and cost. The substrate is not limited to a single composition, and another member may be formed on the surface of the substrate 1 in advance.

  Before forming the porous membrane 2, it is preferable that the surface of the substrate 1 is sufficiently washed with ultrapure water or the like in advance.

  A porous film 2 is formed on the substrate 1. The production method of the present invention can be particularly effectively applied to a porous membrane having a pore diameter of 1 nm or more. As the porous film 2, a mesoporous silica film in which pores having a pore diameter of 2 to 50 nm are formed in a continuous matrix of silica is particularly preferably used. The mesoporous silica film can be optically applied as a low-refractive index film that suppresses almost no light scattering derived from the pore diameter at wavelengths in the visible range.

  Hereinafter, a case where the porous film 2 is a mesoporous silica film will be described.

  The film thickness of the porous film 2 depends on the application, but is preferably in the range of 50 nm to 1 μm in order to maintain the film quality uniformity.

  The method for producing the mesoporous silica film is not particularly limited, and can be produced by appropriately selecting from known methods such as a sol-gel method, a hydrothermal method, and a gas phase method using an amphiphilic material as a template. The structure of the mesoporous silica film is not particularly limited, and a known structure can be used.

  As an example, a method for producing a mesoporous silica film using a sol-gel method using an amphiphilic material as a template will be described below.

  First, a sol solution is prepared. The specific material is composed of an amphiphilic material serving as a template for forming the void portion, a silica precursor material that is a raw material for forming the silica wall, an alcohol, an acid or base catalyst, and water. In addition to these materials, other additives may be added for the purpose of adjusting the film quality.

  As the amphiphilic material, a material that forms a molecular assembly such as an ionic surfactant or a nonionic surfactant is used. The amphiphilic material becomes a template for forming pores by removing by subsequent baking, and the kind and amount are appropriately selected depending on the structure of the required mesoporous silica film.

  Examples of the silica precursor material include those used when forming silica by a general sol-gel method. Of these, silicon alkoxide is preferably used because of its high reactivity and excellent dispersion uniformity in the sol solution. Specific examples of the silicon alkoxide include tetramethoxysilane, tetraethoxysilane, and tetrapropoxysilane.

  The alcohol is not particularly limited as long as it is compatible with the above amphiphilic material and silicon alkoxide, and methanol, ethanol, 2-propanol, 1-propanol and the like are used. These alcohols may be used singly or plural kinds may be mixed.

  An acid or base is used as a catalyst for hydrolyzing and dehydrating and condensing silicon alkoxide to form silica. Specifically, hydrochloric acid, acetic acid, nitric acid, sodium hydroxide, ammonia, and an aqueous solution thereof are used.

  Water necessary for the hydrolysis of the silicon alkoxide may be added in the form of the above-described aqueous catalyst solution, or water may be added separately. Alternatively, the water in the air may be taken in by stirring the sol solution in an open container.

  The sol solution obtained as described above is applied onto a substrate. There is no restriction | limiting in particular in a coating method, For example, general methods, such as a spin coat method, a dip coat method, and a spray coat method, are used.

  Next, the obtained coating film is dried. As a result, not only the unnecessary solvent evaporates, but also the condensation reaction of the silica wall proceeds to some extent. There is no particular limitation on the drying method, and heating using a hot plate or a drying furnace, standing for a predetermined time in a constant temperature bath, or the like can be applied. The optimum drying method may be selected according to the material to be used, the required structure, the efficiency of the drying process, and the like.

  The dried coating film is baked using an electric furnace or the like. In the temperature rising process in firing, the condensation reaction of the silica wall proceeds, and when the temperature reaches a certain temperature or higher, the amphiphilic material in the coating film is removed by firing to form pores. As a result, a mesoporous silica film having a high porosity is obtained as the porous film.

  In addition, the mesoporous silica film is given functionalities to the mesoporous silica film in advance depending on the application, such as chemical modification of the pore surface inside the film and introduction of functional molecules and / or functional nanoparticles inside the pores. May be.

Process (2)
Next, as shown in FIG. 1B and FIG. 3, the step (2) of forming the gel film 4 containing the condensation polymer of the inorganic oxide precursor on the support 3 will be described.

  The support 3 is a material that can form a gel film 4 containing a condensation polymer of an inorganic oxide precursor on the surface, and can easily remove the support itself by a support removal process described later. Can be used. The support is preferably a film made of an organic polymer material, and a plastic film having flexibility is particularly preferable. For example, acrylic, methacrylic, styrene, vinyl alcohol, vinyl acetate, polyamide, polyimide, polyamideimide, polyetherimide, polyester, polycarbonate, polysulfone, polythioether, polyethersal Hong-based, natural polymer-based, cellulose-based, olefin-based, ethylene-based, propylene-based, vinyl halide-based, vinylidene chloride-based, vinyl chloride-based plastic films can be used.

  When selecting the material of the support 3, it is necessary to have sufficient heat resistance in the gel film curing step described later. As an example, if the gel film 4 containing a silicon alkoxide polycondensation polymer is cured at a temperature of 100 ° C. over 20 hours, the support 3 is a material having at least a heat resistance greater than 100 ° C. Need to be selected from. In this case, specifically, polypropylene, polyvinylidene chloride, polycarbonate, phenol resin, melamine resin, epoxy resin, or the like may be selected as appropriate.

  The thickness of the support 3 is not particularly limited as long as it is selected in consideration of the operability in each manufacturing process of the present invention and the thickness that can be sufficiently removed in the removal process of the support 3 described later. When the support 3 is removed by baking, the thickness of the support 3 is preferably 10 μm to 500 μm.

  In order to facilitate the formation of the gel film 4, the surface of the support 3 may be subjected to physical and / or chemical treatment in advance. For example, performing UV ozone treatment on the surface of the support 3 to such an extent that the structure and surface shape of the support 3 itself are not significantly affected improves the film quality uniformity in the formation of the gel film 4. This is one of the effective methods.

  In order to determine the surface shape of the sealing layer 5 finally obtained, the surface of the support 3 desirably has a surface shape corresponding to the use of the porous membrane 2. For example, when the porous film 2 is used as an optical film, the surface of the sealing layer 5 is preferably flat in order to suppress scattering, and specifically, the surface roughness Ra is preferably 1 μm or less.

  Next, the gel film 4 containing the condensation polymer of the inorganic oxide precursor formed on the support 3 will be described.

  The gel film in the present invention refers to a film in which a sol solution containing an inorganic oxide precursor is developed into a film and a part or all of the solvent is evaporated. In the gel film 4, an inorganic oxide precursor which is a raw material for forming the sealing layer 5 is contained in a state in which intermolecular condensation polymerization has progressed.

  First, a sol solution that is the basis of the gel film 4 is prepared. The sol solution necessarily contains an inorganic oxide precursor material that is a raw material for forming the sealing layer 5, and further comprises alcohol, an acid or base catalyst, water, and other additives as necessary. As the inorganic oxide precursor material, an inorganic oxide precursor material used in a general sol-gel method can be used. For example, metal alkoxide, metal acetylacetonate, metal carboxylate, metal nitrate, metal oxychloride, metal chloride, silicon alkoxide, silicon chloride and the like are used.

  The alcohol is not particularly limited as long as it is compatible with the above-described inorganic oxide precursor substance and does not exhibit liquid repellency on the support 3. For example, methanol, ethanol, 2-propanol, 1-propanol, 1-butanol, 2-butanol and the like are used. These alcohols may be used singly or plural kinds may be mixed.

  An acid or base is used as a catalyst for hydrolyzing and dehydrating and condensing silicon alkoxide to form silica. Specifically, hydrochloric acid, acetic acid, nitric acid, sodium hydroxide, ammonia, and an aqueous solution thereof are used.

  Water necessary for the hydrolysis of the silicon alkoxide may be added in the form of the above-described aqueous catalyst solution, or water may be added separately. Alternatively, the water in the air may be taken in by stirring the sol solution in an open container.

  The gel film 4 is formed on the support 3 using the sol solution obtained as described above. There is no restriction | limiting in particular in the formation method of a gel film, A gel film is formed by the method suitable for achieving the film thickness and film quality of the sealing layer determined according to a use. For example, a spin coat method, a dip coat method, a spray coat method, or the like is used. When a plastic film is used as the support 3, if it is difficult to form the gel film 4 directly on the support 3 due to a lack of rigidity of the support 3, the support 3 is once changed to another rigidity. The gel film 4 may be formed after being fixed on a high substrate.

  In the gel film 4, it is desirable that various solvents contained in the sol solution are evaporated as much as possible. In order to remove these solvents from the gel film, the gel film may be dried by heating before moving to the next step. However, if the drying time is too long or the drying temperature is too high, the condensation polymerization of the inorganic oxide precursor will proceed too much, and the adhesion between the porous film and the gel film will deteriorate in the subsequent steps. There is a fear. Although this point depends on the material constituting the gel film 4 and the material constituting the porous film, for example, the absorption peak derived from the solvent and the absorption peak derived from the hydroxyl group in the infrared absorption spectrum of the gel film 4 are used as a guide. In addition, appropriate drying conditions and drying time may be determined.

Process (3)
Next, as shown in FIG. 1 (c) and FIG. 3, the surface of the porous film 2 formed on the substrate 1 and the condensation polymer of the inorganic oxide precursor formed on the support 3 are used. The process of obtaining the laminated body 7 by sticking the surface of the gel film 4 to be included will be described.

  The surface of the porous film 2 is preferably subjected to surface treatment such as UV ozone cleaning in advance. Thereby, the amount of hydroxyl groups exposed on the surface of the porous film 2 increases, and more covalent bonds are formed with the inorganic oxide precursor contained in the gel film 4 in the heating step described later. As a result, the adhesion between the porous layer 2 and the gel film 4 is increased.

  It is desirable that the gel film 4 is evaporated as much as possible as described above. As a result, the penetration of the solvent into the porous film 2 is suppressed when the gel film 4 is brought into close contact with the porous film 2. Thereby, the sealing layer can be formed on the surface of the porous membrane 2 without affecting the chemical and physical characteristics of the porous membrane itself as much as possible. Also, the surface of the gel film 4 may be subjected to surface treatment such as UV ozone cleaning in advance for the same reason as described above.

  The surface of the gel film 4 formed on the support 3 is brought into close contact with the surface of the porous film 2 whose surface has been sufficiently washed to obtain a laminate 7. The laminate 7 is composed of a structure in which a substrate 1 / porous membrane 2 / gel membrane 4 / support 3 are laminated. The environment in which this step is performed is preferably performed in a clean room or the like having a high air cleanliness in order to suppress foreign matter from entering the close contact interface. It is also an effective means for suppressing the entry of foreign matter into the adhesion interface portion by performing a charge removal process on the surfaces of the porous film 2 and the gel film 4 with a charge removal air gun or the like.

  When the gel film 4 formed on the support 3 is brought into close contact with the surface of the porous film 2, it is necessary to pay sufficient attention to contamination of air bubbles in addition to foreign substances. If the support 3 is a plastic substrate having flexibility, as shown in FIG. 2, air bubbles to the adhesion interface can be obtained by gradually bringing the porous film 2 into close contact with the end 6 of the gel film 4. Can be prevented.

Step (4)
Next, in FIGS. 1D and 3, the laminate 7 is heated at a temperature lower than the firing removal temperature of the support to cure the gel film 4 and convert it into a sealing layer 5 made of an inorganic oxide. The process to perform is demonstrated.

  In this step, in the state in which the shape of the support 3 is maintained, the condensation polymerization reaction of the inorganic oxide precursor material proceeds in the gel film 4 to harden the gel film 4, and the sealing layer made of the inorganic oxide 5 is formed. Therefore, as described above, when the support 3 is removed by baking, it is necessary to select a material having a baking removal temperature higher than the temperature necessary for curing the gel film 4 as the support 3.

  When the firing removal temperature of the support 3 is lower than the temperature necessary for curing the gel film 4, the firing removal of the support 3 proceeds in a state where the gel film 4 is not sufficiently cured with heating. As a result, the gel film 4 in which the condensation polymerization reaction has not sufficiently progressed may permeate from the surface of the porous film 2 to the inside. Further, in the absence of the support 3, when the condensation polymerization proceeds in the gel film 4, shrinkage in the in-plane direction increases, and as a result, cracks may occur in the sealing layer 5.

  The combination of the temperature necessary for the curing of the gel film 4 and the support 3 is selected in consideration of the type of inorganic oxide precursor material contained in the gel film 4, the time for curing, the atmosphere, etc. To do.

  In addition, if it is temperature as long as the support body 3 is not baked and removed, it is effective also from a viewpoint of time reduction in production to advance hardening as high temperature as possible.

  The sealing layer 5 made of an inorganic oxide obtained by curing the gel film 4 is selected depending on the purpose. For example, when forming an optically transparent sealing film, silica, titania, alumina, a composite thereof, or the like is used. Moreover, in order to function as an electrical element including the porous film 2, when providing the function as a transparent electrode to the sealing layer 5, titania, zinc oxide, indium oxide, tin oxide, and these composites Things are used. The sealing layer made of an inorganic oxide preferably contains at least one of silica, titania, alumina, zinc oxide, indium oxide, and tin oxide.

Process (5)
Next, a process of removing the support 3 on the sealing layer (on the cured gel film) will be described with reference to FIGS.

  In the step of removing the support, the support is removed by heating at a temperature higher than the firing removal temperature of the support, or the support is removed by dissolution with an organic solvent. As long as the sealing layer 5 is in a state of being hardened as compared with the state of the gel film, the method for removing the support 3 is not particularly limited. From the viewpoint of further promoting the curing of the sealing layer 5, a method of firing and removing the support 3 by firing in an oxygen atmosphere is desirable.

  However, if the support 3 is removed by firing at an excessively high temperature, the porous film 2 may be destroyed in the porous structure or cracks may be generated. For this reason, the firing removal treatment of the support 3 depends on the material constituting the porous membrane 2, but generally a temperature of 1000 ° C. or lower is desirable.

  When the support 3 is subjected to the firing removal treatment, the heating method is not particularly limited. For example, it may be left in an electric furnace and heated isotropically, or it may be left on a hot plate and heated from the substrate 1 side. Further, other oxidation methods such as UV ozone treatment may be used in combination.

  The step of curing the gel film 4 by heating to convert it into the sealing layer 5 made of an inorganic oxide and the step of removing the support 3 by firing need not necessarily be performed independently. If the order is such that the support 3 is removed after the hardening of the gel film 4 has progressed, it can be carried out by a single baking step. As an example, a case where the gel film 4 is made of a material containing a polycondensation polymer of silicon alkoxide and the support 3 is made of a film made of polyimide that can be removed by baking at 350 ° C. will be described. In the polycondensation reaction of silicon alkoxide, it is known that dehydration condensation proceeds and is further cured by heating at a temperature of 170 ° C. or higher even between adjacent silanol groups that have not progressed in dehydration condensation due to formation of hydrogen bonds. It has been. Therefore, by performing a heating process in an oxygen atmosphere in which the temperature is increased from room temperature to 400 ° C. at a heating rate of 0.5 ° C./min, the gel film 4 is cured at a stage exceeding 170 ° C. It converts into the sealing layer 5 which consists of. When further heated to exceed 350 ° C., the support 3 is gradually removed by firing.

  Moreover, it is preferable to use a combination of materials or a heating method that satisfies conditions such that the firing removal rate of the support 3 is sufficiently slower than the rate at which the gel film 4 is cured and converted into the sealing layer 5. I can do it. If it is this heating method, both hardening of a gel film and baking removal of a support body can be achieved by a single heating step as described above.

  When it is necessary to avoid the baking removal treatment of the support 3 such as the material constituting the porous membrane 2 or the heat resistance of the functional material separately introduced into the porous membrane 2 is low, an organic solvent is used. The support 3 may be dissolved and removed. The organic solvent used at this time is not particularly limited as long as it can dissolve the support 3. By the above-mentioned process, the polycondensation reaction is sufficiently advanced in the sealing layer 5, so that the organic solvent is prevented from penetrating into the porous film 2 in the dissolution and removal process of the support 3. Therefore, in the method of the present invention, even when the support 3 is removed using an organic solvent, changes in the physical and chemical characteristics of the porous membrane 2 are suppressed as much as possible.

Example 1
A sol solution was obtained by mixing and stirring 5.2 g of tetraalkoxysilane, 0.7 g of a block copolymer (Pluronic P123, manufactured by BASF), 10 g of ethanol, and 2.7 g of a 0.01 M hydrochloric acid aqueous solution. A sol solution was applied by a dip coating method onto a quartz substrate that had been cleaned with ultrapure water to obtain a coating film. Then, the mesoporous silica thin film was obtained by baking a board | substrate at 400 degreeC for 4 hours with an electric furnace.

  Further, 5.2 g of tetraalkoxysilane, 10 g of ethanol, and 2.7 g of 0.01 M hydrochloric acid aqueous solution were mixed and stirred to obtain a sol solution for a sealing layer. A sol solution for sealing layer was applied by spin coating on a polyimide film (support, fired removal temperature: 350 ° C., thickness 40 μm) subjected to ultrapure water washing to obtain a gel film. Note that the polyimide film was temporarily fixed on the glass plate only during spin coating.

  The surface of the mesoporous silica thin film was washed with a UV ozone cleaner for 5 minutes. Thereafter, the gel film formed on the polyimide film was carefully brought into close contact with the end portion so that air bubbles would not enter, and a laminate including quartz substrate / mesoporous silica thin film / gel film / support was obtained.

  Next, the laminate was placed in an electric furnace in an air atmosphere and heated to 200 ° C. at a rate of 1 ° C./min. After reaching 200 ° C., it was held for 1 hour, and the gel film was cured to obtain a sealing layer. Thereafter, the temperature was raised to 400 ° C. at a rate of 1 ° C./min. After reaching 400 ° C., the substrate was held for 24 hours, and the support was removed by baking. As described above, a mesoporous silica thin film having a sealing layer made of silica on the surface was obtained. This mesoporous silica thin film having a sealing layer on its surface has a function as an antireflection film, and its antireflection characteristics hardly changed even after exposure to an environment of 90% relative humidity for 100 hours.

(Example 2)
A laminate including quartz substrate / mesoporous silica thin film / gel film / support was obtained in the same manner as in Example 1.

  Next, the laminate was placed in an electric furnace in an air atmosphere, and the temperature was raised to 400 ° C. at a temperature raising rate of 0.5 ° C./min. After reaching 400 ° C., it was kept for 24 hours. As described above, a mesoporous silica thin film having a sealing layer made of silica on the surface was obtained. In this example, the gel film was cured and the support was baked and removed during one temperature raising process. As a result, a mesoporous silica thin film having a sealing layer on the surface similar to that described in Example 1 was obtained. was gotten.

(Example 3)
A laminate including quartz substrate / mesoporous silica thin film / gel film / support was obtained in the same manner as in Example 1 except that an acrylic resin film (thickness: 100 μm) was used as the support.

  Next, the laminate was placed in an electric furnace under a nitrogen atmosphere, and the temperature was raised to 100 ° C. at a rate of 1 ° C./min. After reaching 100 ° C., the gel film was cured for 20 hours to obtain a sealing layer. Then, the said laminated body was once taken out in air | atmosphere, and the support body was melt | dissolved and removed by immersing the surface acrylic resin film in acetone.

  In this example, a mesoporous silica thin film having a sealing layer on the surface similar to that described in Example 1 was obtained in a temperature environment of 100 ° C. or less by dissolving and removing the support.

Example 4
A mesoporous silica thin film was obtained on a quartz substrate by the same method as in Example 1.
Further, 2.6 g of titanium tetraisopropoxide, 20 g of 1-butanol, and 1.4 g of an 11M hydrochloric acid aqueous solution were mixed and stirred to obtain a sol solution for a sealing layer. A sol solution for sealing layer was applied by spin coating on a polyimide film (support, fired removal temperature: 350 ° C., thickness 40 μm) subjected to ultrapure water washing to obtain a gel film.

  The surface of the mesoporous silica thin film was subjected to a cleaning treatment for 5 minutes with a UV ozone cleaner. Thereafter, the gel film formed on the support was closely adhered from the end so that air bubbles would not enter, and a laminate including a quartz substrate, a mesoporous silica thin film, a gel film, and a support was obtained.

  Next, the laminate was placed in an electric furnace in an air atmosphere and heated to 200 ° C. at a rate of 1 ° C./min. After reaching 200 ° C., it was held for 1 hour, and the gel film was cured to obtain a sealing layer. Thereafter, the temperature was raised to 400 ° C. at a rate of 1 ° C./min. After reaching 400 ° C., the substrate was held for 24 hours, and the support was removed by baking. Thus, a mesoporous silica thin film having a sealing layer made of titania on the surface was obtained.

(Comparative Example 1)
A sol solution was obtained by mixing and stirring 5.2 g of tetraalkoxysilane, 0.7 g of a block copolymer (Pluronic P123, manufactured by BASF), 10 g of ethanol, and 2.7 g of a 0.01 M hydrochloric acid aqueous solution. A sol solution was applied by a dip coating method onto a quartz substrate that had been cleaned with ultrapure water to obtain a coating film. Then, the mesoporous silica thin film was obtained by baking a board | substrate at 400 degreeC for 4 hours with an electric furnace.

  The mesoporous silica thin film having no sealing layer on the surface had a function as an antireflection film, and the initial reflectance at a wavelength of 550 nm was 0.5%. However, the reflectivity increased to 1.0% after 100 hours exposure in an environment with a relative humidity of 90%. This is due to an increase in the refractive index of the mesoporous silica film due to the adsorption of water molecules inside the porous film.

  The method for producing a porous membrane of the present invention can form a sealing layer made of an inorganic oxide on the surface of the porous membrane without changing the physical and chemical properties of the porous membrane. It can be used in fields such as carrier membranes, separation membranes, humidity control membranes, electrodes, low dielectric constant membranes, and optical thin films.

DESCRIPTION OF SYMBOLS 1 Base material 2 Porous membrane 3 Support body 4 Gel film 5 Sealing layer 6 End part 7 Laminated body

Claims (8)

Forming a porous film on a substrate;
Forming a gel film containing a condensation polymer of an inorganic oxide precursor on a support;
A step of closely contacting the porous film formed on the substrate and the gel film formed on the support to obtain a laminate;
Curing the gel film by heating the laminate;
Removing the support on the cured gel film, and a method for producing a porous film.   The method for producing a porous film according to claim 1, wherein the step of curing the gel film cures the gel film by heating at a temperature lower than a firing removal temperature of the support.   The method for producing a porous membrane according to claim 1 or 2, wherein the step of removing the support removes the support by heating at a temperature higher than a firing removal temperature of the support. .   The method for producing a porous membrane according to claim 1 or 2, wherein in the step of removing the support, the support is removed by dissolution with an organic solvent.   The method for producing a porous film according to any one of claims 1 to 4, wherein the gel film is obtained by advancing condensation polymerization of the inorganic oxide precursor by a sol-gel method.   The method for producing a porous film according to any one of claims 1 to 5, wherein the porous film is a mesoporous silica film.   The method for producing a porous film according to any one of claims 1 to 6, wherein the inorganic oxide includes at least one of silica, titania, alumina, zinc oxide, indium oxide, and tin oxide.   The method for producing a porous film according to claim 1, wherein the support is a film containing an organic polymer material.

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