JP2016023109A - Manufacturing method of phase-separated glass film, and manufacturing method of porous glass film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a phase-separated glass film by which the phase-separated glass film can be formed while suppressing composition change in base glass and which is excellent in reproducibility.SOLUTION: A manufacturing method of a phase-separated glass film includes: a film forming step of forming on a base material 10, a film 11 containing base glass powder bodies 12; a first heat treatment step of forming a base glass film 14 by performing heat treatment on the film 11 in an electric furnace; and a second heat treatment step of forming a phase-separated glass film 1 by performing heat treatment on the base glass film 14 to phase-separate the same. Further, the base glass powder bodies 12 include a volatile component that is volatilized in a temperature condition in the first heat treatment step, and the first heat treatment step is performed in a state in which a space into which the volatile component diffuses is restricted.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing a phase separation glass membrane and a method for producing a porous glass membrane.

  In recent years, attention has been focused on porous glass, and industrial applications such as an adsorbent, a microcarrier carrier, a separation membrane, and an optical material are expected to take advantage of its excellent characteristics. However, porous glass has many problems such as surface strength, porosity, and uniformity of pore diameter. In particular, when porous glass is used as an optical material, it is necessary to control the porosity of the porous layer in more detail for the purpose of suppressing light scattering and reflection.

  As a method for producing the porous glass relatively easily, there is a method utilizing the phase separation phenomenon of the glass itself. In particular, porous glass produced by utilizing the spinodal phase separation phenomenon of glass has a characteristic continuous porous structure that is uniformly controlled in a mesh shape, which is higher than other porous materials. It has the feature of having porosity. For this reason, porous glass having a spinodal type porous structure is a member that is highly expected from the viewpoint of industrial use.

  By the way, borosilicate glass using silica, boron oxide, alkali metal oxide or the like as a raw material is generally used as a base material of the porous glass utilizing the phase separation phenomenon. The molded borosilicate glass undergoes a phase separation phenomenon by performing a treatment (heat treatment) held at a constant temperature. Hereinafter, the above treatment (heat treatment) will be referred to as phase separation heat treatment. In the borosilicate glass subjected to the phase separation heat treatment, the non-silica rich phase, which is an acid-soluble component, is eluted by etching with an acidic solution. For this reason, the skeleton constituting the porous glass is mainly silica (silica-rich phase). The skeleton diameter, pore diameter, and porosity of the porous glass thus obtained are greatly affected by the glass composition, phase separation heat treatment temperature and time before the phase separation heat treatment. Furthermore, the skeleton, pore diameter, and porosity of the porous glass greatly affect the optical characteristics.

  On the other hand, since the phase separation phenomenon is a phenomenon that forms a nano-sized ultra-fine three-dimensional structure, it is very difficult to achieve selective etching to the inside of the glass, and uniform pores can be obtained. Have difficulty. One means for sufficiently promoting the selective etching and obtaining uniform pores is to make glass thin. However, when phase separation by heat treatment is performed on the thinned base glass, the surface accuracy of the glass deteriorates due to the movement of constituent elements during the phase separation, and it is difficult to obtain an excellent porous glass thin layer. I understood it. Although selective etching up to the inside of the glass proceeds favorably by making the glass into thin pieces, there is also a problem that the strength of the structure is reduced.

  Therefore, as one method for utilizing the unique surface characteristics of the spinodal phase-separated porous material, it is conceivable to form a thin film-like porous glass on the substrate. As a means for forming the thin film-like porous glass on the substrate, for example, a printing method can be mentioned. Specifically, a borosilicate glass as a base material is crushed to form a powder, and mixed with a resin to form a paste. The paste is printed on a base material and heat treated to form a glass film on the base material. Thereafter, a silica film and a non-silica rich phase are separated by performing phase separation heat treatment, and a porous film can be formed on the substrate by removing the non-silica rich phase by etching (Patent Document 1). reference).

JP 2013-33188 A

  However, since the method of Patent Document 1 has a process of forming a glass film by pulverizing a base glass once formed and performing a heat treatment again, a reheating step for fusing the pulverized glass at a high temperature is necessary. . Therefore inevitably, by boron or sodium is a volatile component contained in the glass body is volatilized and diffused from the glass body, there is a problem that the composition of the glass body is changed. Moreover, it has been confirmed that the volatilization of the volatile component becomes more prominent as the set temperature at the time of heat treatment becomes higher, and there is a trade-off relationship between removal of grain boundaries and suppression of volatilization. Furthermore, the phase change phenomenon cannot be expressed due to the composition change of the base glass due to the volatilization, so that the porous structure becomes insufficient and the low reflectance characteristic is not exhibited. On the other hand, due to the composition change of the base glass due to the volatilization, there is a problem that the silicon oxide contained in the base glass is crystallized and the crystallized silicon oxide becomes a foreign substance that affects the optical characteristics.

  The present invention is made in order to solve the above-described problems, and the object of the present invention is a phase-separated glass membrane that can be formed while suppressing variation in the composition of the base glass and has good reproducibility. It is to provide a manufacturing method.

The method for producing a phase-separated glass membrane according to the first aspect of the present invention comprises:
A film forming step of forming a film containing the base glass powder on the substrate;
A first heat treatment step of heat-treating the film in an electric furnace to form a base glass film;
A second heat treatment step for heat-treating the base glass film to phase-separate and form a phase-separated glass film,
The base glass powder contains a volatile component that volatilizes under the temperature conditions of the first heat treatment step,
The first heat treatment step is performed in a state where a space in which the volatile component diffuses is limited.

  ADVANTAGE OF THE INVENTION According to this invention, it can form, suppressing the composition fluctuation | variation of a base glass, Comprising: The manufacturing method of a phase-separation glass membrane with sufficient reproducibility can be provided.

It is a cross-sectional schematic diagram which shows the example of embodiment in the manufacturing method of the porous glass membrane of this invention. It is a figure which shows the frequency for every image density of the porous glass film which takes a spinodal type porous structure. It is a figure which shows the specific example of the definition of the skeleton diameter of the pore diameter which the porous glass membrane has, and the skeleton between pores. It is a cross-sectional schematic diagram which shows the example of the imaging device with which the optical member which has the porous glass film obtained with the manufacturing method of this invention was mounted. It is a figure which shows the optical microscope image of the base glass film | membrane A. It is a figure which shows the measurement result of the XPS measurement of the base glass film | membrane A. FIG. 6 is a view showing an optical microscope image of a base glass film B. It is a figure which shows the measurement result of the XPS measurement of the base glass film | membrane B.

The method for producing a phase-separated glass membrane of the present invention includes the following steps (1) to (3).
(1) Film forming step for forming a film containing base glass powder on a base material (2) First heat treatment step for forming a base glass film by heating the film in an electric furnace (3) Base glass A second heat treatment step for forming a phase-separated glass membrane by heat-treating the membrane, and the method for producing a porous glass membrane of the present invention also includes the steps (1) to (3), It has the process of following (4).
(4) Etching Step for Etching Phase-Separated Glass Film In the present invention, the base glass powder contains a volatile component that volatilizes under the temperature condition of the first heat treatment step (step (2)). In the present invention, the first heat treatment step (step (2)) is performed in a state where a space in which the volatile component diffuses is limited.

  In the production method of the present invention, after the base glass powder is applied on the base material, the space in which the volatile components diffuse is limited in the heat treatment (first heat treatment step) for forming the base glass film. As a result, volatile components contained in the base glass powder such as boron and sodium do not diffuse freely and remain in a specific space, so that a base glass film in which compositional deviation is suppressed can be formed. In addition, this base glass film forms a phase separation glass film by performing a phase separation heat treatment, and further forms a porous glass film by performing an etching process. Thereby, it is possible to obtain a phase-separated glass film or a porous glass film exhibiting a high transmittance without generating a large silicon oxide crystal of 1 μm or more in the film.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate. However, the present invention is not limited to the embodiments described below. Further, a well-known or publicly known technique in the technical field can be applied to a part that is not particularly illustrated in the drawings or a part that is not particularly described in the following description.

[Method for producing phase-separated glass membrane and porous glass membrane]
FIG. 1 is a schematic cross-sectional view showing an example of an embodiment in the method for producing a porous glass membrane of the present invention. Here, since the porous glass membrane (reference numeral 2 in FIG. 1 (e)) of the present invention is manufactured through the phase separation glass membrane 1 of FIG. 1 (d), FIG. 1 shows the phase separation glass of the present invention. It is also a figure which shows the example of embodiment in the manufacturing method of a film | membrane.

  Hereinafter, each manufacturing process will be described.

(1) Film formation process (FIG. 1A)
In order to manufacture the porous glass film of the present invention, first, a film 11 containing the base glass powder 12 is formed on the base material 10 (FIG. 1A).

(1-1) Substrate As the substrate 10 on which the film containing the base glass powder is provided, a substrate of any material can be used depending on the purpose. The material of the base material preferably contains a component of a porous glass film. When borosilicate glass is used, for example, quartz glass, quartz, sapphire and the like can be mentioned.

(1-2) Base Glass Powder Powdery base glass can be produced using a general glass manufacturing method. The material of the base glass is not particularly limited. For example, silicon oxide glass I (matrix glass composition: silicon oxide-boron oxide-alkali metal oxide), silicon oxide glass II (matrix glass composition: Silicon oxide-boron oxide-alkali metal oxide- (alkaline earth metal oxide, zinc oxide, aluminum oxide, zirconium oxide)), titanium oxide glass (matrix glass composition: silicon oxide-boron oxide-calcium oxide-magnesium oxide) -Aluminum oxide-titanium oxide) and the like. Among them, borosilicate glass of silicon oxide-boron oxide-alkali metal oxide is preferable.

When borosilicate glass is used as the base glass, the proportion of silicon oxide contained in the glass is preferably 55.0 wt% or more and 95.0 wt% or less, particularly 60.0 wt% or more and 85.0 wt% or less. preferable. By controlling the ratio of silicon oxide contained in the glass within the above range, it tends to be easy to obtain a phase-separated glass membrane and a porous glass membrane with high skeleton strength, and is useful when the strength of the glass membrane itself is required. It is. Moreover, it is preferable that a following formula ((alpha)) is satisfy | filled about the molar ratio of the boron and alkali component contained in glass.
0.25 <[Na / B] <0.4 (α)

  If the formula (α) is not satisfied, the film may be broken due to expansion or contraction of the film itself during the etching process.

  In the present invention, the base glass is used in a powder form, but a specific method for making the base glass into a powder form will be described later.

(1-3) Application / Film Formation of Film Containing Base Glass Powder Examples of a method for forming the film 11 including the base glass powder 12 include a printing method, a spin coating method, and a dip coating method. Hereinafter, a method using a general screen printing method will be described as a specific method for forming the film 11.

  In the screen printing method, since a paste-like substance containing a base glass powder is printed on a substrate or the like using a screen printer, preparation of the paste-like substance is essential.

  As a premise for preparing the pasty substance, the base glass of (1-1) is pulverized to form a base glass powder. The method for pulverization is not particularly limited, and a known pulverization method can be used. Examples of the pulverization method include a liquid phase pulverization method represented by a bead mill and a gas phase pulverization method represented by a jet mill.

  The particle size of the crushed base glass is appropriately controlled by the size of the plate used in screen printing and the design film thickness. However, when the particle size is large, the sedimentation is rapid when it is made into a paste, and it is difficult to maintain uniformity. Moreover, since it becomes difficult to form the printed film | membrane uniformly, it is preferable that the particle size of a base glass shall be 20 micrometers or less.

  When forming a film (coating film) containing the base glass powder, it is necessary to prepare a paste containing the base glass powder. This paste contains a thermoplastic resin, a plasticizer, a solvent and the like together with the base glass powder.

  The ratio of the base glass powder to be included in the paste when preparing the paste is desirably 30.0 wt% or more and 90.0 wt% or less, preferably 35.0 wt%, based on the total weight of the paste. % By weight or more and 70.0% by weight or less.

  The thermoplastic resin contained in the paste when preparing the paste is a component that increases the strength of the film formed by drying the paste and imparts flexibility to the film. As the thermoplastic resin, polybutyl methacrylate, polyvinyl butyral, polymethyl methacrylate, polyethyl methacrylate, ethyl cellulose and the like can be used. One type of these thermoplastic resins may be used alone, or a plurality of types may be mixed and used. Note that the thermoplastic resin contained in the paste functions as the binder 13 constituting the film 11 shown in FIG.

  The content of the thermoplastic resin contained in the paste is preferably 0.1% by weight or more and 30.0% by weight or less based on the total weight of the paste. When the content of the thermoplastic resin is smaller than 0.1% by weight, the strength of the film formed by drying the paste tends to be weakened. On the other hand, when the content of the thermoplastic resin is larger than 30.0% by weight, it is not preferable because a residual component of the resin tends to remain in the glass film when the glass film is formed.

  In the present invention, the paste may contain a plasticizer as appropriate. By adding a plasticizer, the drying speed of the paste can be controlled. Further, flexibility can be given to a film formed by drying the paste. Examples of the plasticizer included in the paste include butylbenzyl phthalate, dioctyl phthalate, diisooctyl phthalate, dicapryl phthalate, and dibutyl phthalate. These plasticizers may be used alone or in combination of two or more.

  When the plasticizer is included in the paste, the content is preferably 10.0% by weight or less based on the total weight of the paste.

  By the way, when preparing the paste, a solvent is appropriately used together with the thermoplastic resin. Examples of the solvent included in the paste include terpineol, diethylene glycol monobutyl ether acetate, 2,2,4-trimethyl-1,3-pentadiol monoisobutyrate, and the like. One of these solvents may be used alone, or a plurality of these solvents may be mixed and used.

  The content of the solvent contained in the paste is preferably 10.0% by weight or more and 90.0% by weight or less based on the total weight of the paste. If it is less than 10.0% by weight, it tends to be difficult to obtain a uniform film. Moreover, even if it exceeds 90.0% by weight, it tends to be difficult to obtain a uniform film.

  The paste can be prepared by kneading the above materials at a predetermined ratio.

  In this step, first, a paste is applied to any surface of the substrate 10 by screen printing. Thereafter, the solvent component of the paste is dried and removed. Thereby, the film | membrane 11 containing the base glass powder 12 shown by Fig.1 (a) can be formed on the base material 10. FIG. Further, in order to make the film 11 have a desired thickness, the base glass-containing paste may be applied and dried in an arbitrary number of times.

(2) First heat treatment step (FIGS. 1B and 1C)
Next, a first heat treatment is performed in the electric furnace on the film 11 including the base glass powder 12 applied and formed on a predetermined surface of the base material 10 (first heat treatment step). By this heat treatment, the film 11 is converted into the base glass film 14 (FIG. 1C). Here, this step is performed at a temperature at which the volatile component contained in the base glass powder 12 volatilizes and diffuses. In the present invention, the heat treatment is performed in a state where the space in which the volatile component diffuses is limited. In addition, limiting the space where the volatile component diffuses means a state in which most of the volatile component volatilized from the base glass powder 12 is kept in a predetermined space and is not diffused from the predetermined space to the outside. It is. That is, even if only a small part of the volatile component diffuses from the predetermined space to the outside, there is no particular problem as long as it is quantitatively small, and it is required to keep all the volatile component in a closed space. It is not a thing.

  As a specific method for limiting the space where the volatile component diffuses, for example, as shown in FIG. 1B, the container 20 is covered with the base material 10 on which the film 11 is provided, and the mouth of the container 20 is opened. Heat treatment is performed in contact with the ground. As a result, the inner glass part and the mouth part of the container 20 limit the space in which the volatile components that volatilize in this process can diffuse and convect, so that the composition glass is suppressed in composition deviation in the thickness direction. A film 14 can be formed.

  The material of the container 20 is not particularly limited as long as it does not cause diffusion of volatile components such as boron and sodium. However, a highly porous ceramic is not preferred. The porosity of the constituent material of the container 20 is preferably 2% or less. An example of a material that satisfies this porosity is quartz glass.

  In the present invention, the capacity of the container 20 is appropriately set based on the volume of the film 11 applied and formed on the substrate 10. In the present invention, the capacity of the container 20 is preferably 20000 times or less the total volume of the base glass powder 12 contained in the film 11.

  When heat treatment is performed in such a manner that the space surrounding the base material 10 on which the film 11 is provided by the container 20 or the like is limited, most of the volatilized boron and sodium do not diffuse outside the space. Can stay inside. For this reason, even if a high temperature treatment is performed, a certain amount or more of volatilization does not occur. In addition, since the heat treatment can be performed in a uniform state in the container 20, the base glass film 14 having a uniform composition can be obtained.

  By the way, when the boron content in the base glass powder 12 is reduced in the heat treatment step such as this step, the melting point of the glass rises, and there is a concern that the time required for flattening may be extended. Here, as in the present invention, if the volatilization and diffusion of volatile components can be suppressed, the glass melting point can be prevented from increasing, so that planarization can be performed in a short time. Moreover, since the surface area of the base glass film 14 is reduced by completing the planarization at an early stage, volatilization of volatile components can be further suppressed.

  In the present invention, the first heat treatment step is preferably performed at 700 ° C. or higher and 1100 ° C. or lower. The first heat treatment step is preferably performed in the range of 5 minutes to 1 hour.

(3) Second heat treatment step (phase separation step, FIG. 1 (d))
After the base glass film 14 flattened by the first heat treatment step is formed, a second heat treatment step is performed (FIG. 1D). This second heat treatment step is also called phase separation heat treatment.

  By this step, phase separation of the base glass film 14 is promoted, and a layer (phase separated glass film 1) divided into a silica-rich phase and a non-silica-rich phase is formed.

  In the present invention, the second heat treatment step is performed at a temperature lower than that of the first heat treatment step, and is preferably performed at 500 ° C. to 700 ° C. The second heat treatment step is usually performed within a range of 1 hour to 100 hours. However, the temperature condition and time condition of this step can be appropriately set according to the size of the non-silica rich phase to be obtained (corresponding to the pore diameter of the pores of the porous glass film 2). In order to suppress light scattering of the porous glass film 2 obtained through the steps described later, the pore diameter of the pores of the porous glass film 2 needs to be 50 nm or less, and this is realized. In addition, it is necessary to appropriately adjust the conditions for the phase separation heat treatment.

  Moreover, the temperature setting at the time of performing this process does not need to make it constant at predetermined temperature, and you may change preset temperature continuously and / or in steps within the suitable range mentioned above.

  Further, as already described, this step is performed at a temperature lower than that of the first heat treatment step. For this reason, this process may be performed in the process of cooling in the system performed after the first heat treatment process, or the substrate 10 is cooled to, for example, room temperature after the first heat treatment process. After that, heating may be performed again.

(4) Etching process (FIG. 1 (e))
The phase separation glass film 1 of the present invention is obtained by the second heat treatment step. In order to obtain the porous glass film 2 from the phase separation glass film 1, it is necessary to perform an etching process described below. Specifically, this etching treatment is a step of removing the non-silica rich phase of the phase separation glass film 1 by treating it with an aqueous solution. By this step, it is possible to obtain the porous glass film 2 composed only of the silica-rich phase (FIG. 1 (e)).

  The etching treatment (etching treatment for removing the non-silica rich phase) performed in this step is generally a treatment for eluting the non-silica rich phase, which is a water-soluble phase, by contacting with an aqueous solution. The means for bringing the aqueous solution into contact with the glass is generally a means for immersing the glass in the aqueous solution, but is not limited as long as the glass and the aqueous solution are in contact with each other, such as applying an aqueous solution to the glass. As the aqueous solution necessary for the etching treatment, it is possible to use an existing solution that can elute the non-silica rich phase, such as water, an acidic solution, or an alkaline solution. Moreover, you may select multiple types of processes made to contact these aqueous solutions according to a use.

  When etching the phase-separated glass film 1, in general, treatment with an acidic aqueous solution is performed from the viewpoint of a small load on the insoluble phase (silica-rich phase) and the degree of selective etching. Preferably used. By contacting an acidic aqueous solution with the phase-separated glass membrane 1, the non-silica-rich phase, which is an acid-soluble component, is eluted and removed, while the erosion of the silica-rich phase is relatively small, and thus high selective etching properties. Thus, this step can be performed.

  As acidic aqueous solution used at this process, inorganic acids, such as hydrochloric acid and nitric acid, are preferable, for example. In addition, the acidic aqueous solution used in this step is usually preferably used in a state (aqueous solution) appropriately diluted with water (solvent). The concentration of the acid solution is usually preferably set as appropriate within a range of 0.1 mol / L to 2.0 mol / L. In this step, the temperature of the acidic aqueous solution can be preferably in the range of room temperature to 100 ° C., and the time required for this step (treatment time) is preferably about 1 to 500 hours. can do.

  Depending on the glass composition of the phase-separated glass film 1, a silica layer (silica-rich phase) that inhibits etching is generated on the surface of the phase-separated glass film 1 obtained in the second heat treatment step on the order of several hundred nanometers. There is a case. In such a case, the silica layer present on the surface of the phase separation glass film 1 may be removed by polishing or alkali treatment.

(5) Water washing treatment After finishing the etching process, it is preferable to finally wash the substrate 10 with water. By washing with water, adhesion of residual components to the skeleton constituting the porous glass film 2 can be suppressed, and the porous glass film 2 having a higher porosity tends to be obtained. The temperature of the washing water used when washing with water is generally in the range of room temperature to 100 ° C. The time for washing with water can be appropriately determined according to the composition, size and the like of the target porous glass film 2, but it is usually preferably about 1 to 50 hours.

  In the present invention, (4) the etching step may be performed on the phase-separated glass film produced by the above-described production method, and the phase-separated glass film may be produced. You may purchase the base material in which the manufactured phase-separation glass membrane was formed. That is, the method for producing a porous glass film of the present invention comprises a step (etching) of preparing a phase separation glass film produced by the production method described above and etching the phase separation glass film to form a porous glass film. Process).

[Porous glass membrane]
Hereinafter, the porous glass film 2 manufactured by the manufacturing method of the present invention will be described.

  There are two types of phase separation: spinodal and binodal. The pores of the porous glass film 2 obtained by spinodal phase separation (the non-silica rich phase of the phase separation glass film 1) are through-holes connected from the surface to the inside. More specifically, the structure derived from spinodal phase separation, that is, the spinodal structure is an “ant's nest” -like structure in which pores are entangled three-dimensionally, and the silicon oxide skeleton is “nest”. The through hole corresponds to the “nesting hole”. On the other hand, the porous glass film 2 obtained by binodal type phase separation has a structure in which independent pores, which are pores surrounded by a closed surface close to a spherical shape, are discontinuously present in the skeleton of silicon oxide. The holes derived from the spinodal type phase separation and the holes derived from the binodal type phase separation can be judged and distinguished from the result of morphological observation by an electron microscope. Moreover, the aspect of phase separation can be controlled to be a spinodal type or a binodal type by appropriately controlling the composition of the base glass powder 12 and the temperature conditions when performing the second heat treatment step.

  The thickness of the porous glass film 2 is not particularly limited, but is preferably 200 nm or more and 50.0 μm or less, more preferably 500 nm or more and 20.0 μm or less, and particularly preferably 1.5 μm or more and 10.0 μm. It is as follows. When the thickness of the porous glass film 2 is smaller than 200 nm, the porous glass film 2 having a high surface strength and a high porosity (low refractive index) having an effect of suppressing the wavelength dependency of the reflectance cannot be obtained. Sometimes. On the other hand, when the thickness of the porous glass film 2 is larger than 50.0 μm, the influence of haze increases and it becomes difficult to handle as an optical member.

  Specifically, the thickness of the porous glass film 2 is set to, for example, an acceleration voltage of 5.0 kV using a scanning electron microscope (FE-SEMS-4800, manufactured by Hitachi, Ltd.). It can be obtained by taking an electron micrograph. More specifically, the thickness of the porous glass film 2 provided on the substrate 10 is measured at 30 points or more from the photographed image, and the average value is used.

  The ratio of the pores of the porous glass film 2, that is, the porosity is not particularly limited, but is preferably 30% by volume or more and 70% by volume or less, and more preferably 40% by volume or more and 60% by volume. It is as follows. If the porosity is less than 30% by volume, the advantage of the porousness cannot be fully utilized, and if the porosity is more than 70% by volume, the surface strength tends to decrease. Moreover, it is desirable that the porosity of the porous glass film 2 is continuously increased from the substrate 10 toward the surface side of the porous glass film 2.

  As a method for calculating the porosity, for example, processing for binarizing an image of an electron micrograph into a skeleton part and a hole part is performed. Specifically, a magnification of 100,000 times (in some cases 50,000 times) that allows easy observation of the density of the skeleton at an acceleration voltage of 5.0 kV using a scanning electron microscope (FE-SEM S-4800, manufactured by Hitachi, Ltd.) Then, the surface of the porous glass film 2 is observed. The observed image is stored as an image, and the porosity is obtained by graphing the SEM image at a frequency for each image density using image analysis software. FIG. 2 is a diagram showing the frequency for each image density of the porous glass film 2 having a spinodal porous structure. A peak portion (point A) indicated by a downward arrow in the image density in FIG. 2 indicates a skeleton portion located in front.

  When calculating the porosity using FIG. 2, the bright part (skeleton part) and the dark part (hole part) are binarized using white and black with an inflection point close to the peak position as a threshold value. . And the average value of all the images is taken about the ratio with respect to the area (the sum of the area of a white part and a black part) of the area of a black part. The average value obtained is taken as the porosity.

  The pore diameter of the porous glass film 2 is preferably 1 nm or more and 200 nm or less, and more preferably 5 nm or more and 100 nm or less. When the pore diameter is smaller than 1 nm, the characteristics of the porous structure cannot be fully utilized, and when the pore diameter is larger than 100 nm, the surface strength tends to decrease. However, the pore diameter is preferably smaller than the thickness of the porous glass film 2.

  The pore diameter here is defined as an average value of the minor diameters of the approximated ellipses obtained by approximating the pores appearing on the surface side of the porous glass film 2 with a plurality of ellipses. FIG. 3 is a diagram showing a specific example of the definition of the pore diameter of the porous glass film 2 and the skeleton diameter of the skeleton between the pores. For example, as shown in FIG. 3A, an electron micrograph of the surface of the porous glass film 2 is used, the pore 21 is approximated by a plurality of ellipses 22, and the minor axis 23 of each ellipse is It is obtained by calculating the average value. At least 30 or more pores 21 are measured, and the average value is obtained.

  The skeleton diameter of the porous glass film 2 is preferably 1 nm or more and 50 nm or less. When the skeleton diameter is larger than 50 nm, light scattering is conspicuous and the transmittance is greatly reduced. Moreover, when the average skeleton diameter is smaller than 1 nm, the strength of the porous glass film 2 tends to be small.

  The skeleton diameter here is defined as the average value of the short diameters of the approximated ellipses by approximating the skeleton that can be observed when the surface side of the porous glass film 2 is photographed with a plurality of ellipses. The For example, as shown in FIG. 3B, the skeleton 24 is approximated by a plurality of ellipses 25 using an electron micrograph obtained when the surface side of the porous glass film 2 is photographed. It is obtained by calculating the average value of the diameter 26. At least 30 points or more of the skeleton 24 are measured, and the average value is obtained.

  The pore diameter and skeleton diameter of the porous glass film 2 can be appropriately controlled depending on the material used as a raw material, heat treatment conditions for spinodal phase separation (various conditions for performing the second heat treatment step), and the like.

  The porous glass film 2 produced by the method of the present invention can be used as an optical member or one member constituting the optical member. The optical member having the porous glass film 2 can be mounted on an imaging device such as a digital camera or a digital video camera.

  FIG. 4 is a schematic cross-sectional view showing an example of an imaging device on which an optical member having a porous glass film obtained by the manufacturing method of the present invention is mounted. 4 is an imaging device for forming a subject image from a camera, specifically, a lens 32, on an imaging device 36 through an optical filter 33. The imaging device 3 shown in FIG. The imaging device 3 in FIG. 4 includes a main body 31 and a removable lens 32. When the imaging device 3 in FIG. 4 is an imaging device such as a digital single-lens reflex camera, photographing screens with various angles of view are obtained by replacing the photographing lens (lens 32) used for photographing with a lens having a different focal length. be able to. The main body 31 constituting the image pickup apparatus 3 in FIG. 4 includes an image pickup element 36, an infrared cut filter 35, a low-pass filter 33, and an optical member 34. Here, the optical member 34 includes the porous glass film 2 produced by the production method of the present invention. Further, since the optical member 34 includes the base material 10, it can also be used as the low-pass filter 33.

  4 is housed in a package (not shown), and the package holds the image sensor 36 in a sealed state with a cover glass (not shown). The image sensor 36 is connected to an image processing circuit 37, and information regarding a shadow image received by the image sensor 37 is converted into data by the image processing circuit 37. As the image pickup element 36, a CMOS element or a CCD element can be used.

  Further, a sealing structure (not shown) is provided between an optical filter such as the low-pass filter 33 and the infrared cut filter 35 and a cover glass (not shown). Although FIG. 4 shows an example in which both the low-pass filter 33 and the infrared cut filter 35 are provided as optical filters, either one may be omitted.

  In the optical member 34 including the porous glass film 2 formed according to the present invention, the substrate 10 is porous on the imaging element 36 side, and the porous glass film 2 is on the lens 32 side, that is, on the uppermost surface side of the optical filter. An embodiment in which the glass film 2 is disposed is preferable. In other words, the optical member 34 is disposed such that the porous glass film 2 is farther from the image sensor 36 than the base material 10.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not restrict | limited to the Example described below. First, what is used in Examples and Comparative Examples will be described.

(1) Base Material As the base material 10, a quartz glass base material (manufactured by Iiyama Special Glass Co., Ltd., softening point 1700 ° C., Young's modulus 72 GPa) was used. In addition, the used base material 10 cut | disconnects the plate-shaped member of thickness 0.5mm in the magnitude | size of 50 mm x 50 mm, and mirror-polished the surface.

(2) Preparation of base glass powder A mixed powder of silicon oxide powder, boron oxide, sodium carbonate, and aluminum oxide was put into a platinum crucible so that the charged composition was as follows, and in this crucible, It was melted at 1500 ° C. for 24 hours.
SiO ₂ : 64% by weight
B ₂ O ₃ : 27% by weight
Na ₂ O: 6% by weight
Al ₂ O ₃ : 3% by weight

  Next, the molten glass was cooled to 1300 ° C. and then poured into a graphite mold. Thereafter, the glass poured into the mold was allowed to cool in air for about 20 minutes, and then held in a slow cooling furnace at 500 ° C. for 5 hours. Next, block-shaped borate glass was obtained by cooling over 24 hours. Next, this borate glass was pulverized using a jet mill until the average particle size became 4.5 μm, whereby a base glass powder was obtained.

(3) Production of Glass Paste Glass paste was obtained by stirring and mixing the above raw materials.
Base glass powder: 60.0 parts by mass α-Terpineol: 44.0 parts by mass Ethylcellulose (registered trademark: ETHOCEL Std 200 (manufactured by Dow Chemical Company)): 2.0 parts by mass

[Example 1]
A phase-separated glass membrane and a porous glass membrane were produced according to the production process described in FIG.

(1) Film formation process (FIG. 1A)
A glass paste containing the base glass powder 12 and the binder 13 was applied onto the base material 10 by screen printing to form a film 11 (FIG. 1A). When performing this process, MT-320TV manufactured by Microtec Co., Ltd. was used as a printing machine, and a solid image of 30 mm × 30 mm of # 500 was used as a printing plate.

(2) First heat treatment step (FIGS. 1B and 1C)
Next, the substrate 10 on which the film 11 was formed was allowed to stand in a drying furnace at 100 ° C. for 10 minutes, and the solvent contained in the film 11 was dried. Next, the base material 10 on which the film 11 was formed was placed so as to be covered with a 70 mL crucible (container 20) made of quartz glass (FIG. 1 (b)). Here, the total volume of the glass powder is calculated as 36 × 10 ⁻¹⁰ m ³ from the coating area and the film thickness. On the other hand, the capacity of the crucible used (70 mL) is 19444 times the total volume of the glass powder. For this reason, the capacity of the crucible used (corresponding to the space where volatile components diffuse) is limited to 20000 times or less the total volume of the glass powder. Next, in a state in which the space where the volatile component of the base glass powder 12 diffuses was limited, the temperature was increased to 1000 ° C. at a temperature increase rate of 10 ° C./min, and then heat treatment was performed at this temperature (1000 ° C.) for 5 minutes. When performing this step, an electric muffle furnace (manufactured by Tokyo Glass Instruments Co., Ltd.) was used as a heating furnace. By this step, the base glass film 14 (base glass film A) was formed on the base material 10 (FIG. 1C). FIG. 5 is a view showing an optical microscope image of the base glass film A. FIG. As shown in FIG. 5, it can be seen that the base glass film (matrix glass film A) obtained in this step is free of bubbles and impurities and has a flat film.

  Next, the relationship between the thickness direction and the composition of the base glass film A was measured using an X-ray electron spectroscopy (XPS) apparatus (manufactured by ULVAC-PHI). FIG. 6 is a diagram showing measurement results of XPS measurement of the base glass film A. As shown in FIG. 6, in the base glass film A, a layer (modified layer) in which a large amount of Si is present is observed in the outermost layer (layer having a depth of about 50 nm from the surface). It can be seen that the composition of the base glass film 14 does not change at a depth of 100 nm or more. Therefore, it can be seen that the matrix glass film 14 obtained in this step has a uniform composition.

(3) Second heat treatment step (FIG. 1 (d))
The base material 10 on which the base glass film 14 produced in the above (2) was formed was heat-treated at 600 ° C. for 50 hours, thereby forming the phase-separated glass film 1 (FIG. 1D).

(4) Etching process (FIG. 1 (e))
Next, the altered layer present in the outermost layer of the phase separation glass membrane 1 is removed by polishing, and then the substrate on which the phase separation glass membrane 1 is formed in a 1.0 mol / L nitric acid aqueous solution heated to 80 ° C. 10 was immersed and allowed to stand at 80 ° C. for 24 hours. Subsequently, the base material 10 was immersed in distilled water heated to 80 ° C., and allowed to stand for 24 hours. Next, the base material 10 was taken out from distilled water and dried at room temperature for 12 hours to obtain a sample A, that is, the base material 10 on which the porous glass film 2 was formed (FIG. 1 (e)).

(5) Evaluation of porous film About the obtained sample A, the SEM image (electron micrograph) was image | photographed at the acceleration voltage of 5.0 kV using the scanning electron microscope (FE-SEMS-4800, Hitachi make). did. As a result, it was confirmed that the porous glass film 2 having a film thickness of 4.0 μm and a skeleton diameter of 15 nm was formed on the substrate 10.

  Next, the transmittance of Sample A was measured. Specifically, the transmittance is evaluated based on the absorption spectrum measured using a spectrophotometer (manufactured by JASCO Corporation, UV-visible spectrophotometer V-570 and automatic absolute reflectance measuring device ARM-500N). It was. As a result, it was found that the transmittance of Sample A was 90% or more.

[Comparative Example 1]
Example 1 (2) is the same as Example 1 except that the first heat treatment step was performed without using a quartz crucible and allowing the volatile components contained in the base glass powder 12 to freely diffuse. A base glass film B was produced by the method.

  FIG. 7 is a view showing an optical microscope image of the base glass film B. FIG. From FIG. 7, cracks and foreign matters were remarkably confirmed in the base glass film B. XPS measurement was also performed on the base glass film B. FIG. 8 is a diagram showing a measurement result of XPS measurement of the base glass film B. From FIG. 8, it can be seen that, unlike Example 1, the composition gently changes from the outermost layer (altered layer) to a point having a depth of 1.5 μm. This variation in composition seems to be because volatilization of boron always occurs without suppressing volatilization from within the glass in the first heat treatment step. Moreover, since the area | region where the composition has changed by volatilization is large, it is thought that the crack generate | occur | produced by the difference in the expansion coefficient of a glass film. In addition, it is considered that silicon oxide has crystallized due to composition variation.

  Since the phase-separated glass membrane and the porous glass membrane produced by the production method of the present invention are particularly excellent in permeability, for example, they can be used as optical members.

  1: phase separation glass membrane, 2: porous glass membrane, 10: base material, 11: membrane (glass powder membrane), 12: parent glass powder, 13: binder, 14: parent glass membrane, 20: container

Claims (6)

A film forming step of forming a film containing the base glass powder on the substrate;
A first heat treatment step of heat-treating the film in an electric furnace to form a base glass film;
A second heat treatment step for heat-treating the base glass film to phase-separate and form a phase-separated glass film,
The base glass powder contains a volatile component that volatilizes under the temperature conditions of the first heat treatment step,
The method for producing a phase-separated glass film, wherein the first heat treatment step is performed in a state where a space in which the volatile component diffuses is limited.   The method for producing a phase-separated glass film according to claim 1, wherein a space in which the volatile component diffuses is limited to 20000 times or less of a total volume of the base glass powder contained in the film.   3. The method for producing a phase-separated glass film according to claim 1, wherein, in the first heat treatment step, the film is heated to 700 ° C. or higher and 1100 ° C. or lower.   The base glass film is covered with a container in the electric furnace so that a space in which the volatile component diffuses is limited in the first heat treatment step. A method for producing a phase-separated glass membrane according to one item.   The method for producing a phase-separated glass membrane according to claim 4, wherein the porosity of the container is 2% or less. Preparing a phase separation glass produced by the method for producing a phase separation glass membrane according to any one of claims 1 to 3,
And a step of etching the phase-separated glass film to form a porous glass film. A method for producing a porous glass film, comprising:

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