JPS5814904A - Support sheet for liquid separation membrane and continuous preparation thereof - Google Patents

Abstract

PURPOSE:To prepare the support sheet of a reverse osmosis liquid separation membrance excellent in reinforcing effect, by a method wherein a membrane forming polymer solution is coated on one surface of a base fabric and a coagulating liquid is contacted with the coated surface and thereafter contacted with the uncoated surface thereof. CONSTITUTION:A base fabric 1 such as knitted fabric or a non-woven fabric comprising a polyamide or a polyester fiber is passed between a knife edge 2 and the support thereof and introduced into a coagulating liquid 5 through a space 9 to be taken up by a rotary drum 6. During this time, a solution 4 containing a polymer such as polysulfone or polysulfonamide is coated on the base fabric at the nip of the knife edge 2 and the support thereof and the speed of the base fabric is regulated so as to impregnate the base fabric 1 with the solution 4 during a time when the base fabric 1 is passed through the space 9. In the next stage, the base fabric 1 is conveyed through the coagulating liquid 5 so as to contact the one surface thereof with a smooth flat plate 7 in said coagulating liquid 5 to selectively coagulate from the coated surface side liquid 5 and support sheet of a reverse osmosis liquid separation membrane consisting of a microporous polymer membrane of which theaverage pore size is 50Angstrom -50mu and the void ratio is 50-90% and a support sheet can be prepared.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a support for a reverse osmosis liquid separation membrane that not only has a reinforcing effect on the membrane but also maintains its separation properties over a long period of time.゛Due to the remarkable development of liquid separation technology in recent years, it is now possible to desalinate seawater (for the production of drinking water and industrial water) due to its features such as the ability to perform selective separation with no oxidation.

Wastewater treatment (water reuse and pollution prevention), recovery of useful materials (recovery of useful materials from plating waste liquid and electrocoating waste liquid).

It has been put to practical use in a wide range of applications, including concentrating orange juice and milk.

For example, cellulose acetate, aromatic polyamide.

Membranes made of polyimide, polybenzimidazole, polyarylene oxide, polysulfonamide, tris(hydroxyalkyl)in cyanurate polymers, and the like are known. However, these are usually 100A-! 10
It is an ultra-thin film of 0μ, generally.

It has been reinforced with various supports and has been put into practical use as a membrane with a composite structure.

Conventionally, the water permeability (flux: Flu
x ) −, salt rejection ability (Rezek'/ E 7 2Rej
It is known that it affects the membrane life (in particular).

Publication No. 55-2154).

'On the other hand, according to the studies of the present inventors, when a base fabric provided with a support film made of a microporous polymer is used as a support, structural defects in the support film It has been found that the following problem arises due to this problem. Namely.

The following drawbacks have a major impact on separation membrane performance.

(1) Large voids occur near the laminated interface between the base fabric and the microporous polymer membrane.

(11) Microporous membranes were formed on both sides of the base fabric. As is clear from the optical micrographs in Figures 5 and 6, a support such as 0 (+), which forms a so-called sandwich-inch laminated structure, is formed at the laminated interface between the base fabric and the microporous membrane. This is because the coarse voids are easily crushed by pressurization, causing deformation and destruction of the separation membrane itself formed on the support.

Significantly reduces the durability of the liquid separation membrane. Also (11)
A support like this tends to form a double-skin structure, which increases the liquid permeation resistance as a liquid separation membrane, and the polymer leached to the back surface of the base fabric can be used in the film forming equipment for manufacturing the support. There is a problem that it contaminates the film and makes continuous film formation impossible.

The object of the present invention is to provide a support for a reverse osmosis separation membrane that does not have the above-mentioned drawbacks. That is, the present invention has the following configuration.

- (1) A support membrane consisting of a base fabric and a microporous polymer.

In the integrally laminated support sheet, a part of the support membrane penetrates into the base fabric, and the microporous pore diameter is substantially in the range of 50λ to 50μ, from the base fabric side. It gradually becomes smaller, and the porosity of the support membrane is 50 to 90.
1. A support sheet for a liquid separation membrane, characterized in that:

(2. A support sheet for a liquid separation membrane according to claim 1, wherein the liquid separation membrane is a reverse osmosis separation membrane.

(3) Apply a film-forming polymer solution to one side of the base fabric.

1. A method for continuously producing a support sheet for a liquid separation membrane, characterized in that during wet coagulation, the coagulating liquid is first brought into contact with the coated surface and then brought into contact with the non-coated surface.

(4) In claim 6, the coated base fabric is introduced into the coagulation liquid, and in the introduction section, ``a parallel surface to the base fabric is provided close to the non-coated surface; A method for continuously producing a support sheet for a liquid separation membrane, characterized in that the wet coagulation is carried out continuously while maintaining a gas phase between both parallel surfaces.

By adopting such a configuration, 1. Even under high pressure in reverse osmosis separation, it is possible to obtain a support sheet that exhibits little or no morphological change.

The base fabric constituting the support of the present invention includes polyamide,
There are knitted fabrics and nonwoven fabrics made of various known fibers such as polyester, polyolefin, polyacrylic, and polyvinyl alcohol-based fibers. For example, polyester taffeta, satin and non-woven fabrics.

Vinylon nonwoven fabric and the like are advantageous in terms of durability. The conditions that the base fabric must have are smoothness and appropriate breathability.

Rigidity, chemical resistance, etc. are important, and are determined comprehensively depending on the application.

In addition, the microporous polymer membrane constituting the support and the
There are polysulfone, polysulfonamide, polyvinylidene fluoride, polyvinyl alcohol, polyacrylonitrile, etc., but it is preferable to use a polysulfone-based microporous membrane. The pore size is larger. So-called asymmetric porous membrane.

In particular, the ultra-thin film formed on the support is approximately 0.1μ or less, and in order to reduce liquid permeation resistance, the average pore diameter is approximately 50A to 0.1μ, and the porosity of the support film is 60
~80 units is good.

The support of the present invention is not one in which the support film and the base fabric are simply laminated together, but has a structure in which the support film penetrates into the inside of the base fabric over the entire surface of the support membrane and is integrated. It is preferable from the aspect.

A feature of the present invention is that in such a support structure, there are substantially no coarse voids with a pore diameter of about 50 μm, preferably more than about 50 μm, in the boundary layer. The performance of the liquid separation membrane is constant and 0.
It does not degrade easily against mechanical deformation and long-term liquid separation operation.

It is particularly useful for reverse osmosis liquid separation membranes that are operated for long periods under high pressures of 501 cg/m2 or higher. Hereinafter, a method for producing a support for a liquid separation membrane according to the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a schematic cross-sectional view showing one example of the manufacturing process of the composite sheet for liquid separation of the present invention.

In Figure 1, 1 is the base fabric and 2 is the knife.

6 is a knife support, 4 is a polymer solution, 5 is a coagulation bath, 6 is a rotating drum, 7 is a smooth plate, 8 is a winding device (
)-19 (not shown) is a space. The base material 1 is composed of a knife 2 and its support 6 and has a diameter of about 100 to 50.
It is introduced into the coagulation bath 5 through a space 9 through a gap of 0 micron, and is wound up via a nine-rotation drum 6. During this process, it is introduced into the gap formed by the knife blade 2 and its support 6. Before the polymer solution 4 is applied to the surface of the base fabric 1, it is coagulated in a coagulation bath 5.

A microporous polymer membrane is formed. In this case, first, a certain period of time is provided before contact with the coagulation liquid in order to infiltrate the polymer solution into the base fabric and create an integrated structure of the base fabric and the microporous membrane layer. , it is necessary to

It goes without saying that this penetration time varies depending on the properties of the polymer solution used, the base fabric, etc., but it also depends on the shape of the device, especially the shape of the knife 2, the smoothness of the support base 6, its length, and the overall shape. The film forming speed (cloth supply speed) is determined in consideration, and in most cases it is within a few seconds.

The second important thing is that in order to selectively perform the initial coagulation of the polymer solution applied to the base fabric from the side of the coated surface, as shown in Figure 1, the coagulant is applied to the non-coated side of the base fabric. It is necessary to provide a smooth plate 7 to prevent the penetration of water. That is, by providing this smooth plate 7, coagulation from the non-coated surface is prevented for a certain period of time.

Coagulates selectively from the side of the coated surface. As a result, gas can diffuse smoothly from the non-coated surface.

This is because the formation of a plurality of continuous coarse voids of 50 microns or more in the membrane portion in contact with the base fabric is completely suppressed.

Conditions for preventing coagulation of the polymer solution from the non-coated surface at 1:0 vary depending on the type of polymer solution, concentration, coating film thickness, coagulation speed, etc., but the length of the gas layer formed by the smooth plate 7:
! 0 is preferably a value close to (v x t) where tsθC is 1 hour of coagulation from the polymer surface and Van/8eC is the film forming speed.

For example, when forming a polysulfone microporous membrane, the preferred conditions are a coating liquid viscosity of about 3 poise, a base fabric with appropriate air permeability (air permeability when air is blown at a rate of 50 cc/sθC per area of 12.2 When the resistance is 10-10 or more in the water column and 1 to 10 in the space.

It takes 2 to 4 seconds to penetrate into the base fabric and about 6 seconds to coagulate, so at a film forming rate of 5 to 20 an/sec, 1=20
~50c! n is sufficient.

Further, it is also possible to use a drum as an example of a device that combines the functions of the support stand 6 and the smooth plate 7. In this case, the adhesion between the base fabric and the drum surface is high in the above-mentioned apparatus, and it is difficult for gas to escape from the base fabric interface. Therefore, in order to obtain an integrated structure, it is desirable to provide an uneven or corrugated surface on the drum surface so that the gas can be easily removed.

The support sheet of the liquid separation membrane thus obtained is:

A part of the microporous polymer membrane penetrates into the base fabric, and the pore diameter of the micropores is substantially in the range of 501 to 50μ, gradually decreasing from the base fabric side.

In addition, the porosity of the supporting membrane is 50 to 90, and the performance of the reverse osmosis separation membrane on which a semi-permeable ultra-thin membrane is provided is greatly improved. It is more preferable if the void ratio is 60 to 80%. If the porosity exceeds 90%, the strength of the support membrane will be poor, and if it is less than 50%, the resistance to liquid passage will become excessive, which is not preferable.

Figures 2 to 4 are optical micrographs (100 times magnified) showing examples of cross sections of the present invention and conventional composite sheets, respectively. Figure 2 is a cross-sectional micrograph of a composite sheet produced by delaying the infiltration of the coagulating liquid from the non-coated surface according to the composite sheet manufacturing method of the present invention. (Fig. 2A is satin; Fig. 2B, Fig. 3, and Fig. 4 are nonwoven fabrics) 10. At the interface between the porous membrane 11 and the porous membrane portion 12 in contact with this interface, there are no large continuous voids having a pore diameter of approximately 50 μm or more. Further, FIG. 3 shows an example in which the coating liquid permeates into the base fabric sufficiently and the effect of retarding solidification on the non-coated surface is observed, but the effect is not sufficient. In other words, it can be seen that in the conventional method, the penetration of the coating solution is insufficient, and the penetration of the coagulant from the non-coated surface is not suppressed at all.

Examples are shown below.

Example 1 Polysulfone (U, p-3500 manufactured by COC) was dissolved in dimethylformamide and formed into a film on 16 cast liquids. The cross-sectional micrograph of the support sheet obtained at a running speed of 12 cm/sec, a gas phase angle of 6 cm, a coagulant of water, and a back-side coagulation delay time of about 2 seconds shows that the base sheet is as shown in Figure 2. There are few or only 20 voids in the boundary layer with the fabric.
~60μ or less.

The albumin exclusion rate of this microporous membrane was 95 or more, the average surface pore diameter was 5008 or less, the average internal pore diameter by mercury porosimetry was 0.1 μm, and the porosity was 72 μm.

Comparative example 1 The smooth plate 7 of Example 1 was removed, and the rest was obtained.

As a result of evaluation of durability over time (change over time at 40° C. for 500 hours), the structure of Example 1 showed less change over time and was superior. , Permeated water concentration (ppm) The membrane structures are shown before (A) and after (B) evaluation, respectively.

It is clear that the deformation of the membrane of the invention is very small.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing one uniform process for manufacturing a support sheet for a liquid separation membrane of the present invention, and FIGS. 2 to 4 show a support sheet for a liquid separation membrane of the present invention and conventional supports, respectively. FIG. 2 is a micrograph (100x magnification) showing the cross-sectional structure of a body sheet and a schematic cross-sectional view thereof. Figures 5 and 6 are cross-sectional micrographs showing the deformation of the membrane as a result of pressure evaluation.

Claims (1)

[Claims] (1) A support film in which a base fabric and a support film made of a porous polymer are laminated together, and a part of the support film permeates into the base fabric. and the pore diameter of the micropores is substantially in the range of 50λ to 50μ, gradually decreasing from the base fabric side, and the porosity of the support membrane is 50 to 90μ. Separation membrane support sheet. (2Y In claim 1, the support sheet for a liquid separation membrane in which the bulk separation membrane is a reverse osmosis separation membrane. (3) A membrane-forming polymer solution is applied to one side of the base fabric. Wet process. A continuous method for producing a support sheet for a liquid separation membrane, characterized in that during coagulation and solidification, the coagulation liquid is first brought into contact with the coated surface and then brought into contact with the non-coated surface. (4) Patent Claim In the range item 3, the coated base fabric is introduced into the coagulating liquid, and in the introduction part, a parallel surface to the base fabric is provided close to the non-coated surface, and a space between the two parallel surfaces is provided. 1. A method for continuously producing a support sheet for a liquid separation membrane, characterized in that the wet coagulation is carried out continuously while maintaining a gas phase.