JPS62279806A - Composite sheet and its production - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION 3. DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a composite membrane suitable for separation and filtration operations in ultrafiltration zones. Ultrafiltration is performed at 20 nm or less l nm (
The generally accepted definition is that filtration retains all molecules or particles in the size range up to nm: nanometers = 10°J. Another way to express this filtration range is to convert molecular size to molecular weight. According to this standard, filtration retains species within the molecular weight range of 300,000 or less.

The main requirements for ultrafiltration membranes are as follows: (a) They must be available in suitable sizes and shapes. Must be strong enough to withstand accidental damage.

(b) To withstand chemicals and heat that may be encountered during filtration operations.

In this respect, inorganic films are generally superior to organic films.

The pore size should be as uniform as possible. Again, modern polymeric organic ultrafiltration membranes have fairly broad pore size distributions, as a result of which their selectivity is low and their molecular weight fractionation is not sharp.

) be substantially and ideally completely free of cracks or pinholes;

(e) Regarding the pore size, it should have a high flux (that is, a large volume of fluid that passes through a unit area per unit time) to allow the door plate to pass through quickly.

This property not only requires a large number of 9 pores per unit area, but also requires that the length of the narrow pores be as short as possible.

US Pat. No. 3,944,658 describes a sol-gel process for making porous alumina products. Aluminum alkoxide is hydrolyzed in water and made into a colloidal solution with acid to form a colorless and transparent sol.

This sol is turned into a gel, and this gel is dried and fired to form a porous alumina product. Although it is stated that the sol can be applied as a coating to porous ceramic materials,
This is not described in further detail.

JP-A-60-180979 describes a method for producing a ceramic membrane for separating condensed (or condensed) components. A porous support substrate structure is repeatedly impregnated with alumina sol, dried and fired to form approximately 1πm (nanometers).
A product having micropores with a diameter of or above is obtained.

Lee Nurse CA-F of Twaente University of Technology in the Netherlands;
LeenαcLγS) et al. published a series of papers on alumina films produced by the sol-gel method in ``Journal of Colloid and Interface Science J Vol. 105 (May 1985). Month 1
The article on pages 27-39 describes the formation of composite membranes by applying an alumina sol to a porous alpha-alumina carrier. The support is immersed in the sol for a short time, typically 0.5 seconds, withdrawn, dried and calcined.

The thickness of the fired layer varies from 3 to 8 microns, but crack-free films are only obtained with layers below 5 microns. The thinnest layers can only be obtained with very short immersion times, and for such short times there is little control over the thickness and it is highly variable (
In other words, the fluctuation is about plus or minus 0.5 microns). Significant impregnation of the carrier by the sol generally occurs during impregnation.

“Journal of Membrane Science” No. 2
Volume 4 (1985), pages 246-260 and 261-
The article on page 270 describes the use of the composite membrane as described above in experiments to measure the permeability and ultrafiltration and superfiltration properties of the pure alpha form of composite @. The sol-gel films tested ranged from 2.5 to 55 after firing.
L41) at a micron thickness, resulting in generally low fluxes (flow rate/unit area/unit time).

There were some pinholes in those films, and as a result, the flux was weak when isolated.

Thus, the products described in these articles would not be suitable for use as ultrafiltration membranes.

It is an object of the present invention to overcome these problems and provide a composite membrane suitable for use in ultrafiltration.

In one aspect, the present invention provides a composite sheet comprising a porous anodized aluminum membrane and a microporous inorganic film overlying one surface of the membrane, wherein the microporous inorganic film has substantially uniform pores. A composite sheet is provided having dimensions and characterized as being substantially free of cracks and pinholes. The porous inorganic membrane may be an alumina membrane, preferably a porous anodic aluminum membrane, and these may be symmetrical or asymmetrical. The porous inorganic membrane has a thickness of 5 to 100 on the surface where the films overlap.
Preferably it has an average pore diameter of Lm (nanometers). Preferably, the microporous inorganic film has a substantially uniform thickness of 0.01 to 2.0 microns.

In another aspect, the invention provides a porous inorganic membrane:
Before applying a colloidal sol of an inorganic substance or a polymer to become an inorganic substance, a solution of the vomit is applied to one surface of the membrane to form a gel layer on the surface; and the gel is dried and heated,
converting the gel into a microporous film having a thickness of 0.01 to 2.0 microns and substantially uniform pore size and substantially free of cracks and pinholes. provide. Preferably, the surface of the membrane is pretreated with a silicate, borate or phosphate solution.

Conventional anodized aluminum membranes are symmetrical and have generally cylindrical pores that run straight through them.

Although such membranes are suitable for use in the present invention, particular advantages are obtained if the membrane is asymmetric.

A suitable asymmetric porous anodized aluminum membrane is described in EP 1788]1. The membrane has a system of relatively large pores extending inwardly from the first surface and a system of relatively small pores extending inwardly from the second surface. The larger pores are 01-10
0 microns long, with a diameter of a few + nm (nanometers) to 2 microns at its inner end, and the smaller pores are at least 2 nm (nanometers), preferably 5 to 2 microns long. 1100z, L or may have a substantially uniform minimum diameter that is less than half the diameter of the larger pore. Such an anodized film can be made to any desired thickness to provide adequate mechanical strength to the composite film. Anodic oxide films have a considerable number of pores per unit area, and these extend approximately at right angles to the surface on which the pores are formed.

The smallest diameter region of the smaller pores is at or near the second surface of the membrane.

The inorganic membrane may be a refractory membrane. Overlying one side of the membrane is a microporous film of inorganic material, which may be a refractory, such as a ceramic oxide.

These include oxides of aluminium, titanium, zirconium, silicon, mental, cerium, hafnium, yttrium, thorium, soot, kermaninium, indium, vanadium, niobium, iron, chromium, cobalt, boron and combinations thereof. sell.

The thickness of the microporous film is preferably substantially uniform across the surface of the membrane, between 0.001 and 20 microns,
In particular, it is preferably 0.03 to 0.05 microns. The thicker the microporous film, the lower the liquid flux obtainable with it in the ultra-E range, and for this reason the preferred maximum limit (thickness) is set at 2 microns.

The microporous film contains pores of substantially uniform pore size and is substantially free of cracks and pinholes. The average pore size is preferably between 05 and 30 nm, especially between 1 and 4 sm (nanometers), and there are preferably substantially no pores larger than twice the average pore size.

In the method of the present invention, a colloidal sol of an inorganic substance (eg, a ceramic oxide) or a solution of a polymer precursor that becomes an inorganic substance (eg, a metal oxide) is applied to one or both sides of the membrane. The colloidal sol is derived from inorganic oxide powder (for example, oxides of the various elements mentioned above) by a known method. More preferably, the colloidal sol or polymer solution is derived by hydrolysis of metal alkoxides. For example, boehmite sol is described in U.S. Patent No. 3,944.6.
It is made using the procedure described in No. 58 Specification Rose. According to this operation, aluminum alkoxide is heated at 80°C.
It is hydrolyzed in excess water kept at room temperature and then precipitated with acid to form a clear, colorless sol. This sol is composed of colloidal particles of stable crystalline aluminum oxide hydrate [At0(OH)] dispersed in an aqueous phase. Sols made in this way typically have At2
0. It contains an aluminum number of about 30 fi'/l, expressed as 1000 ml, which can be adjusted once as desired for coating by dilution with water or evaporation. The coating has an aluminum number concentration of up to 190 g/l, preferably flIO? /l~9°?
It can be carried out with a sol having a concentration of aluminum number (expressed as At2o) of /1. As another example, -Ti-0
-Ti-polymer solution was prepared using a linker (J.

Br1n & gr) and Bahlint 7 (M, S, Har
It can also be made by a similar operation to that described in the article by John Rington ("Solar Energy Materials", Vol. 5 (1981), pp. 159-178).

In the known procedure, titanium alkoxides are partially hydrolyzed in an alcoholic solution at room temperature in the presence of a hostile catalyst.
A stable 17'1-0-Ti polymer solution is formed. Solutions made in this way are typically T i O
Approximately 10 to 3 o expressed as x? /l, which can be adjusted once desired for coating by evaporation of the solvent or dilution with alcohol. The above-mentioned sol or solution can be applied to the anodized membrane in a freshly concentrated state, or it can be applied after aging to increase its viscosity. Control of film thickness in composite membranes is achieved in part by controlling the concentration and viscosity of the sol before application.

Prior to deposition of the sol, it is preferred to pre-treat the membrane (in particular an anodized aluminum membrane) by immersing it in a silicate, phosphate or borate solution. The effect of such pretreatment is to enable the subsequently formed gel layer to more easily and substantially completely cover the membrane than without pretreatment. Although the mechanism by which this desirable effect is exerted is not completely understood, it is believed that the pretreatment improves the "wetting" properties of the membrane surface, allowing the membrane to deposit or react with the surface. This forms a layer that easily accepts the sol and promotes its gelation. Sol'g! i is (in preferred order) an alkali metal metasilicate, such as sodium metasilicate; an alkali metal triphosphate (especially pentasodium triphosphate); or an alkali metal borate, such as disodium tetraborate; It can be an aqueous solution. Its concentration is from about 1% (by weight) to saturation 1, typically 3-5% by weight. Temperature is 10-3
It may be at ambient temperature, such as 0°C. The immersion time of the membrane in the solution will generally range from 1 second to 10 minutes, typically around 5 seconds. The soaking time must be adjusted, in relation to other operational variables, to be sufficient to modify (denature) the surface of the membrane, reduce the pore diameter, or completely eliminate the pores. The time should not be so long as to deposit large amounts of material to the extent that it closes. Following soaking, the membrane is rinsed in distilled water.

Adding a surfactant to the sol before application facilitates the formation of a thin, uniform gel layer. “Nonidet” (Non1d)
et; trademark; octylphenyl ethylene oquinde concentrate sold by BDH Chemicals), or [
Methocel J (trademark; Dow
Addition of a nonionic surfactant, such as methylcellulose polymer (available from Chemical Co., Ltd.), typically at a concentration of 0.1 to 1 part by weight, provides a thinner and more uniform gel layer than without the addition.

Furthermore, the formation of thin, uniform films is facilitated by the nature of the porous 8-layer membrane. In the case of anodized aluminum films, the surface is smooth and substantially free of large defects, resulting in a thin, uniform, defect-free coating. In the case of deposition of aqueous boehmite sol onto asymmetric anodized films, the pore size of the surface of the film in contact with the sol can be smaller than the crystal size of the boehmite particles in the sol, resulting in No or little sol penetration into the membrane occurs during deposition.

A thin, uniform gel film can be formed on the second surface of the anodic blur film by depositing a concentrated sol and then air drying.

A variety of methods can be used to apply the sol to the membrane, such as brushing, spray coating, dipping, spin coating, electrophoresis, and thermophoresis.

The coating can be applied using the knee-on roll method.

The anodized film is suspended vertically to allow excess sol to run off and spraying is continued until complete coverage of the film is achieved.

To create a spin-coated composite, the membrane is mounted horizontally on the platen of a commercially available spin-coating device. A predetermined amount of concentrated sol is applied to the surface of the membrane and allowed to remain on the surface for a predetermined period of time (typically up to 60 seconds). Excess sol is removed by rotating the membrane, typically at a speed of 200-2000 rpm. The thickness of the gel film is controlled by the concentration and aging of the sol, the residence time of the sol on the membrane surface, and the rotation speed and time.

The freshly coated membrane is then heated to convert the gel membrane into a microporous refractory film. For example, upon heating, the boehmite gel layer becomes mechanically stable gamma At, 03
It becomes a skeletal remains. Heating conditions are not a requirement for the present invention and may be conventional as long as they avoid thermal shock that could cause cracks or pinhole formation. A typical thermal operation schedule for a boehmite gel layer is
(α) Heating to 200'C at a rate of 50°C/hour, then incubating at 200'C for 15 minutes, then (b12
Heat the waste to 450°C at a rate of 00°C/hour, then 1
Hold constant temperature for 5 minutes and cool to room temperature at a rate of (C) 150°C/hour. The first heating operation schedule part to 200°C is set to remove absorbed water;
A second heating step to 450°C removes bound water and converts the gas/ma At0OHf gun-7At20°. This conversion occurs at temperatures of 390°C or higher. Considerable shrinkage of the film occurs during the heating operation. For films of large thickness to which the present invention is concerned, aggregation a occurs predominately in the direction perpendicular to the plane of the film (ie, the film becomes thinner). For thick films, shrinkage can occur in the plane of the film and can lead to cracking.

One advantage of using membranes with small pores (at least small pores at the surface where the microporous film overlaps) is that the thin film can be used without sagging or rupturing, allowing excessive penetration of film material into the pores. , can be cross-linked on top of the pores.

Membranes with pores of average diameter between 5 and 100 nm are preferred for this reason. However, for certain applications it may be preferable to apply a sol/gel layer to the larger pore surface (or even both surfaces) of an asymmetric membrane. It has been found that if the coating is applied to the larger pore surface, the penetration of the sol (into the pores) is still substantially limited by the confining effect of the smaller pores on the opposite surface. Alternatively, membranes such as anodized aluminum membranes or tape cast membranes (which may have large pores or which may not have been pretreated with silica salts or other solutions) may be used. It is also possible to achieve complete coverage by applying two or more consecutive sol/gel applications to form a film that also has the desired microporous structure. Therefore, a first aqueous sol is applied to the membrane, optionally dried and heated, and a second sol (aqueous or alcoholic) is applied to the gel or microporous film thus obtained. , the resulting gel can be dried and heated. This method is particularly suitable for positive axillary membranes with parallel pores or for large pore surfaces of asymmetric membranes. The waist is completely covered by two overlapping microporous films. The films can have the same or different pore sizes and are preferably free of cracks and pinholes.

In order to prevent the penetration of the sol or polymer solution into the pores of the membrane, it is possible to increase its viscosity. This requires only the addition of a relatively viscous miscible organic liquid. Alternatively, relatively viscous polymers with relatively high boiling points, e.g.
A polymer, such as polyvinyl alcohol, or a polyol, such as ethylene glycol, polyglycerol, is added to a colloidal sol (or my polymeric precursor) and then boiled to dissolve some of the low viscosity liquid (e.g. water). Or it can be removed entirely, but without destroying the colloidal dispersion of the inorganic material.

The composite membrane in FIG. 1 comprises a porous anodized aluminum membrane and a microporous ceramic oxide film 10. The porous membrane is asymmetric by having a relatively large pore system 12 extending inwardly from the first surface 14 and a relatively small pore system 16 extending inwardly from the twentieth surface 18. be. The large pore system is interconnected with the small pore system at 20. This drawing is not drawn to exact scale. The anodized layer is typically 30 microns thick; the porous layer may be 0.3 microns thick.

Figure 2 represents the pore size distribution in a composite ultrafiltration membrane measured using a combination of multi-point BIT gas adsorption isometry (up to 150λ) and mercury pore measurements (200-1000λ). . 12.5 (125λ) and 7 in Figure 2
The pores with a radius of 6 mm (760 λ) are from the anodized film carrier. Gamma alumina films have a narrow pore size distribution with an apparent average pore radius of about 2 tLm. However, the pores are actually slit-shaped (as expected from EET analysis) rather than cylindrical. Therefore, the pore diameter of about 4 nm obtained using the EET analysis method is larger than the actual slit width (2.7?Lm) that can be directly observed and measured using a transmission electron microscope.

It is this dimension, the slit width, that determines the functionality of the layer in ultrafiltration operations.

Experimental operation (alumina coating) The preparation and concentration of the boehmite sol is described below.

In a typical experiment, a boehmite sol was made by adding aluminum sec-butoxide (1 mol) to deionized water (1,8 t) heated to a temperature above 80°C. The mixture was stirred vigorously and maintained at 90°C.

One hour after addition of the alkoxide, nitric acid (0.07 mol) was added to turn the sol into a colloidal solution. The sol was kept at boiling in an open reactor for about 2 hours to evaporate most of the sec-butanol, and then refluxed for an additional 16 hours at 90'C with a reed to give a clear, colorless sol. Maintained.

Some typical properties of such a sol were measured and found to be as follows.

#degree 29.8? /1O) At20゜pH4,
00 Conductivity 2.20m% (21°C) Viscosity
The pH value and viscosity of the 5 centipoise (21°C) sol remained constant over a period of one month when it was stored at room temperature (21°C).

The thus produced boehmite sol containing 3020 At203 per 1 is evaporated by boiling in air to 190? It can be a concentrated sol containing up to At,03. Or diluted by adding water to 10? / can also be the following. The sol can be used for coating in a freshly shrunken state,
Alternatively, the coating may be performed after aging to increase the viscosity. At203' of υ622 for 1t month! The aging process of the sol shrunk at room temperature (21°C) was as follows.

0 3.72 5.11 510
3.80 4.48 620 3.83
4.70 730 3.83 4
．． ．． 448 All measurements were performed at 21°C.

The porous membrane used in the following examples is European Patent No. 178831.
Porous hot water anodized aluminum recycle as described in the specification of No. This material has an asymmetric pore structure, with a system of relatively large pores extending inward from one side and a system of relatively small pores extending inward from the other side, both of which are interconnected. has.

The membrane was used in the form of a 14Crn x 14 cm x 30 micron sheet. Typical internal dimensions of this are an asymmetric layer thickness of about O,S microns, a large pore average diameter of 150 nm,
The average diameter of the small pores was 25 nm. Example 1.2
and 4, the membrane was pretreated by immersing it in a saturated (5%) solution of sodium metasilicate, then rinsing with distilled water, and drying in air (but not in Examples 3 and 5). (not processed).

The invention is further illustrated by the following examples.

Example 1 62? /l A t20s 1itu K, viscosity 5c
A 3-day aged boehmite sol with p (21 °C) and conductivity of 50 mmho (21 °C) was applied to the anode using a spin-coating method using a sol residence time of 30 seconds, a spin speed of 500 rpm, and a spin time of 30 seconds. 14 of oxide film carrier
It was deposited onto a pretreated sheet of Cm x 14 cm. covered a
The support was heated to 200'C4 at (cL 150°C/hr) and held isothermally at this temperature for 1 hour, heated to 450°C at tb+50'C/hr and held isothermally at this temperature for 1 hour, and (cL 150°C This operation resulted in a uniform gamma At,O, coating of 0.4 micron thickness and a 0.01111/min/c at 110 kPa.
A composite ultrafiltration membrane was obtained exhibiting a pure water permeability of m''.

Example 2゜45? A 140 x 14 cm pretreated sheet of vertically suspended anodized film carrier was completely coated with an unaged boehmite sol having a concentration of 5 cp/l, a viscosity of 5 cp, and a conductivity of 3.22 mmho (21 °C). Spray coated until achieved. Excess sol was drained from the carrier. Heating at 450° C. using the same heating rate as in Example 1 resulted in a composite ultrafiltration membrane exhibiting a coating thickness of 0.3 microns and a pure water permeability of 0.014 m/min/cm” at 110 kPa. Ta.

Example 3 At of 621/l, 03 @ degree, viscosity 5 cp 4 electric power 5,
An unaged sol (5++
+l), 30 seconds of sol residence time by spin coating on the 14CrnX14cIn sheet of anodized film,
Deposition was performed using a spin speed of 500 rpm and a spin time of 30 seconds. 4 using the same heating rate as Example 1.
Heating at 50'C resulted in a woven ultrafiltration membrane with a thin, uniform gamma At203 coating of 0.07 microns thick. This example shows that a much thinner film can be obtained through the use of a wetting agent.

The flow rates (permeability) described in Examples 1 to 3 were measured as follows. The flow rates for distilled and deionized pure water at a pressure of 2 x 105 Fai were determined by Amicon (A
Measurements were made on a composite ultrafiltration membrane with a diameter of 25mm or 43mm using a stirred cell (Model 8050).The measurement of flow rate was carried out 20 minutes after the feed water reached normal pressure. Typical pure water fluxes for some of the other composite membranes according to the invention fired at 450° C. are shown in the table below.

A O,062,70,(14 5B O,432,70,014CO,28
2,70,026 Preparation of Polymer Solutions Derived from Titanium Alkoxides, Partially Hydrolyzed, Titanium Alkoxides Deposited on Porous Refractory Supports and Calcined to Give Microporous Films of Titania Fully Described Below .

In a typical experiment, a polymer solution was prepared by adding titanium inopropoxide (0,012 mol) to 50 Cf isopropanol under anhydrous conditions at room temperature. Deionized water (0,017 mol)'f! : was added to another 50 CC of isopropanol at room temperature. This water/alcohol bath was added dropwise to the alkoxide/alcohol solution at room temperature with stirring. Partial hydrolysis and polymerization of the alkoxide occurred. Adding an acid catalyst, typically HNO3 (0,006 mol) to the solution,
A colloidal solution was obtained. 10 expressed as TiO2
? A clear solution was obtained with a titanium number concentration of /l and a viscosity of 3 cp (21° C.).

The titanium polymer solution prepared in this way is T i O
30 expressed as 2? / can be concentrated to titanium numbers above, but it is preferred to use a titanium number concentration of 10 f/l expressed as TiO2 for film deposition.

The following examples illustrate the inventiveness of titania coatings.

Example 5 10? A freshly prepared polymeric solution having a T602ra degree of /l and a viscosity of 3-r:p was applied by spin coating to 14 cm of an unpretreated anodized aluminum film.
It was deposited on a sheet of InX 14 cm. Double coating was done. 5 seconds residence time, 500 rp for each coating process
A spin speed of m and a spin time of 30 seconds were used.

The membrane was heated as described below.

(α) Heat the sword to 200℃ at 20℃/hour, then 10℃
Hold isothermally (200°C) for 1 min, heat to 400°C at 150°C/hr, then hold at 400°C for 1 min, and cool to room temperature at 200°C/hr.

This operation results in a uniform TiO2 coating of approximately 0.01 micron thickness and 0.01 flll/min/c at 110 kPa.
A composite ultrafiltration membrane with a pure water permeability of IrL2 was obtained.

Example 6 This example illustrates the advantageous effects obtained by pre-treating the membrane.

A sheet of anode sensitized membrane carrier with dimensions 14 L: ln x 14 cm was mixed with various solutions such as 5 weight % sodium metasilicate aqueous solution, 5 weight % pentasodium triphosphate aqueous solution, or 5 weight % disodium tetraborate aqueous solution. It was immersed in water solution for 5 seconds at room temperature. Following this soaking, the membrane sheet was thoroughly rinsed with distilled water, dried in air, and then dried for 30 min. /l concentration of boehmite sol with a residence time of 5 seconds and 500τpm
Spin coating was performed using a spin speed of . The effectiveness of this pretreatment was monitored by direct visual observation of the coverage of the gel after the coating operation. This is because the uncovered areas of the film exhibited a different contrast than the covered areas when illuminated with white light. Use of the pretreatments listed in this example resulted in improved gel coverage of the membrane compared to untreated membranes.

Example 7 A 14zX14Crn sheet of pretreated anodized film '1 was attached to the platen of a commercially available spin coating machine and spun at 100 rpm. Concentration 27.5? /1 boehmite solution was deposited on the rotating membrane by brushing,
It was then spun for 30 seconds at 500 rpm. Example 1
Heating at 450° C. using the same heating schedule as described above resulted in a composite ultrafiltration membrane with a thin and uniform At203 coating. Using a scanning electron microscope, 30 m of the membrane
The thickness of the coating was measured at intervals of 5 rrrrn along a cross section of length m.

Over a length of 20 mm, the thickness is 0.13-0.14
The percentage varied between 8% and 8%. The remaining if): m length part had a thickness of 0.23 microns;
The thickness of is caused by the Vlasov edge effect during brush coating. When this composite ultrafiltration membrane was observed with an oblique scanning electron microscope at the same time as the thickness measurement described above, it was found that there were no cracks or pinholes in the coating.

For ultrafiltration, the composite membrane of the present invention has the following advantages over prior art ceramic oxide materials:

(b) The flux (flow rate) is significantly higher for equivalent pore sizes. This is due to the ability of the processing techniques described here to deposit uniform and very thin gel films. brought from.

(-The film of the present invention has a more uniform thickness and a smoother, defect-free surface free of larger pinholes and cracks.
In the present invention, it is substantially 5% or less compared to 0%. This provides reproducible flow rates. Very thin films reaching 0.07 microns or less are possible, and sol penetration into the asymmetric side of the anodized film carrier is negligible.

Example 8゜Untreated 14c of anodized film! A sheet of rLX14crn, with an unaged boehmite solution at a concentration of 451/l, 50
Spin coated for 30 seconds at 0 rpm.

Heating at 450'C produces a uniform A of 062 microns thick.
resulted in a t203 coating. When the surface of the coating was observed using a scanning microscope, it was found that 1
It was found that there were less than 5 pinholes with submicron dimensions. There were no pinholes larger than 1 micron in some areas. “Journal of Membrane Science Ji Vol. 24 (1985) No. 245-260
In Page Lgenars et al., several membranes (with dimensions as large as 910 microns) spread over a 10 m2 membrane surface area.
5) reported the coexistence of pinholes, but did not mention the coexistence of smaller pinholes.

78f trichlorethylene, 322 ethanol, 3
．． 8y corn oil, 8.42 polyvinyl butyral,
and 14.2? 165? in a liquid system containing polyethylene glycol. Alumina and 0.42? of magnesia was made into slurry. This slurry was tape cast into a 173 mm wide film on a glass substrate. This was dried in air to produce a flexible tape with a thickness of 0.141 mm. Cut a disk with a diameter of 26 cities from the tape,
Partial sintering produced a porous ceramic material with an average pore size of 03 μm. These discs were pretreated by immersion for 5 seconds in a 5% solution of total sodium metasilicate;
Concentration 15, in which water was previously replaced with diethylene glycol /l of viscous boehmite sol. This water replacement increased the viscosity by adding 100 mg of diethylene glycol to 50 ml of sol having a concentration of 30y7t, then boiling and evaporating to a volume of xooml. The coated porous material was heated at 450° C. for 1 hour to convert the gel layer into a stable gamma At203 film. This film contained pores with a slit width of 4.27 Lm.

Lacking 3 Q? An aqueous boehmite sol with a concentration of /l was deposited on the first sol-gel layer by total spray method.

Then, it was heated at 450°C for 1 hour, and the pore slit width was 2.8.
A nm stable gamma At203 film was generated.

The composite ultraviolet ray obtained in this way has a total coating thickness of 1 μm and 110 kPaVc or 0.0
It showed a pure water flux (permeation flow rate) of 16 ntl 1 min/cm 2 .

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of a composite membrane according to one embodiment of the present invention. FIG. 2 is a graph of pore size distribution (vertical axis) plotted against pore radius (horizontal). 10: Microporous inorganic film 12: Relatively thick (・Porous inorganic film) 16:
Relatively small pore system (porous inorganic membrane) (5 people included), 5L water chamber

Claims (27)

[Claims] (1) A composite sheet consisting of a porous inorganic membrane and a microporous inorganic film overlapping one surface of the membrane, wherein the surface where the porous inorganic membrane overlaps the film has a
A composite sheet having an average pore size of 100 nm and characterized in that the microporous inorganic film has a substantially uniform pore size and is substantially free of cracks and pinholes. (2) A composite sheet consisting of a porous inorganic membrane and a microporous inorganic film overlapping one surface of the membrane, where the microporous inorganic film has a thickness of 0.01 to 2.0 microns. and a composite sheet having substantially uniform pore size and being substantially free of cracks and pinholes. (3) A composite sheet consisting of a porous anodized aluminum film and a microporous inorganic film overlapping one surface of the film, wherein the microporous inorganic film has substantially uniform pore size. A composite sheet characterized by being substantially free of cracks and pinholes. (4) The composite sheet according to claim 1 or 2, wherein the porous inorganic membrane is an alumina membrane. (5) The composite sheet according to claim 4, wherein the alumina film is an anodized aluminum film. (6) The anodized aluminum film is asymmetrical because it has a relatively large pore system extending inward from the first surface and a relatively small pore system extending inward from the second surface. 6. A composite sheet according to claim 3 or 5, wherein the large pore system is interconnected with the small pore system and with the microporous inorganic membrane overlying the second side. (7) The composite sheet according to any one of claims 1 and 3 to 6, wherein the microporous inorganic film has a thickness of 0.01 to 2.0 microns. (8) The composite sheet according to any one of claims 1 to 7, wherein the microporous inorganic film is a metal oxide. (9) The composite sheet according to claim 8, wherein the microporous inorganic film is gamma alumina. (10) The average pore size of the microporous inorganic film is 0.5~
The composite sheet according to any one of claims 1 to 9, which has a thickness of 30 nm. (11) Prepare a porous inorganic membrane having an average pore size of 5 to 100 nm on one surface; apply a colloidal sol of an inorganic substance or a solution of a polymer precursor that becomes an inorganic substance to the above surface; forming a gel layer on; and drying and heating the gel to convert the gel into a microporous inorganic film having substantially uniform pore size and substantially free of cracks and pinholes; A method for manufacturing a composite sheet consisting of. (12) Prepare a porous inorganic membrane; apply a colloidal sol of an inorganic substance or a solution of a polymer precursor that becomes an inorganic substance to one surface of the membrane to form a gel layer on the surface; and the gel drying and heating to transform the gel into a microporous film having a thickness of 0.1 to 2.0 microns and substantially uniform pore size and substantially free of cracks and pinholes; A method for manufacturing a composite sheet consisting of. (13) Prepare a porous anodic aluminum oxide film; apply a colloidal sol of an inorganic substance or a solution of a polymer precursor that becomes an inorganic substance to one surface of the film to form a gel layer on the surface; and A method of making a composite sheet comprising drying and heating the gel to convert the gel into a microporous inorganic film having substantially uniform pore size and substantially free of cracks and pinholes. (14) Prepare a porous inorganic membrane; one surface of the membrane is impregnated with a solution of silicate, borate, or phosphate; and a colloidal sol of an inorganic substance or a solution of a polymer precursor that becomes an inorganic substance is added to the above solution. applied to a pretreated surface to form a gel layer on the surface; and the gel is dried and heated to form a microscopic layer with substantially uniform pore size and substantially free of cracks and pinholes. A method for manufacturing composite sheets consisting of converting the gel into a porous inorganic film. (15) Prepare a porous inorganic membrane and a colloidal sol of an inorganic substance or a solution of a polymer precursor that will become an inorganic substance; increase the viscosity of the sol or solution by adding a relatively viscous miscible organic liquid. applying the more viscous sol or solution to one surface of the membrane to form a gel layer on the surface; and drying and heating the gel to form a substantially uniform pore size; A method of making a composite sheet comprising converting the gel into a microporous inorganic film substantially free of cracks and pinholes. (16) The method according to any one of claims 11, 12, 14, and 15, wherein the porous inorganic film is an anodized aluminum film. (17) The porous anodized aluminum film is asymmetric by having a relatively large pore system extending inwardly from the first surface and a relatively small pore system extending inwardly from the second surface. 17. The method of claim 16, wherein the large pore system is interconnected with the small pore system, and the colloidal sol or solution is applied to the second surface. (18) The method according to any one of claims 11 to 13 and 15, wherein the porous inorganic membrane is an alumina membrane, and the surface thereof is pretreated with a solution of silicate, borate, or phosphate. . (19) A patent for pre-treating a porous membrane by contacting it with an aqueous solution of a silicate, borate or phosphate having a concentration of at least 1% by weight at a temperature of 0 to 50°C for 1 second to 10 minutes. A method according to claim 14 or 16. (20) The method according to any one of claims 11 to 19, wherein the colloidal sol is a sol of a refractory metal oxide, or the solution is a solution of a polymer precursor that becomes a metal oxide. (21) The method according to claim 20, wherein the colloidal sol is a boehmite sol obtained by hydrolyzing aluminum alkoxide. (22) The method according to claim 20, wherein the solution of the polymer precursor that becomes the metal oxide is a solution obtained by partial hydrolysis of titanium alkoxide. (23) The method according to any one of claims 11 to 22, wherein the colloidal sol or solution contains a surfactant. (24) The method according to any one of claims 11 to 23, wherein the colloidal sol or solution is applied to the porous membrane by an aerosol method. (25) The method according to any one of claims 11 to 23, wherein the colloidal sol or solution is applied to the porous membrane by a spin coating method. (26) The method according to any one of claims 11 to 25, which is used for manufacturing a composite sheet according to any one of claims 1 to 10. (27) A filter comprising the composite sheet according to any one of claims 1 to 10.