JPS5850122B2 - Manufacturing method of composite semipermeable membrane - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for manufacturing a composite semipermeable membrane.

Generally, when a semipermeable membrane is interposed between a solution and a solvent and a pressure greater than osmotic pressure is applied to the solution side, the phenomenon in which the solvent on the solution side diffuses into the solvent side through the semipermeable membrane is called reverse osmosis.
Although they are used in a wide range of fields such as desalination of seawater and brine water and wastewater treatment, many conventional semipermeable membranes are still unsatisfactory in terms of water permeability, selective permeability, strength, durability, heat resistance, etc. In addition, various proposals have been made regarding the manufacturing method of semipermeable membranes, but there are many problems such as not being able to obtain a good semipermeable membrane unless the membrane forming conditions are strictly controlled. There was a problem.

Furthermore, semipermeable membranes are generally manufactured by using organic polymers as membrane materials and casting a membrane-forming solution consisting of organic solvents, water, swelling agents, etc.; Since solvents and expensive organic solvents such as N-methyl-2-pyrrolidone and N,N-dimethylacetamide are used, there are drawbacks such as harmful solvent vapors being generated during the manufacturing process and the products becoming expensive. there were.

The present invention has been made in consideration of the above points, and
It is an object of the present invention to provide a method for easily manufacturing a composite semipermeable membrane having high performance without requiring strict control of manufacturing conditions.

In the method for manufacturing a composite semipermeable membrane according to the present invention, one side of a porous support made of polytetrafluoroethylene or polysulfone is heated at an atmospheric pressure of 0.0005 to I Torr, and a product of processing power density and processing time of 0.01 to 50 W. Particularly, in the above-mentioned method, polyvinyl alcohol or polyvinyl acetate is partially saponified to form an insolubilized film on the treated surface in the presence of an insolubilizing catalyst. Alcohol or partially saponified polyvinyl acetate (hereinafter these may be collectively referred to as polyvinyl alcohol etc.)

) In order to form an insolubilized thin film on one side of a porous support, it is preferable to apply an aqueous solution containing polyvinyl alcohol or the like and its insolubilization catalyst to one side of the support and heat and dry it.

In the present invention, as the polymer material for forming the insolubilized film, as mentioned above, a partially saponified product to a substantially completely saponified product (saponification degree of about 98 mol φ) of polyvinyl acetate is used.
(above), that is, polyvinyl alcohol can be used, but polyvinyl alcohol is particularly preferably used.

When using partially saponified polyvinyl acetate, it is desirable to use one with a degree of saponification of 70 molar or more, taking into consideration its solubility in water and wetting to the porous support described below.

The degree of polymerization of polyvinyl alcohol and the like is not particularly limited, but in terms of viscosity, when made into a 4-weight polyhydric solution, one having a value of 3 to 100 centipoise (Brookfield viscometer) is preferably used.

The aqueous solution of polyvinyl alcohol etc. varies depending on the molecular weight of the polyvinyl alcohol etc., but usually 0.03~
3 weight rice cakes, preferably 0.1 to 1.0 weight rice cakes, are used.

Insolubilization catalyst such as polyvinyl alcohol and Citeha, usually,
Inorganic acids such as sulfuric acid and hydrochloric acid, organic acids such as p-1 luenesulfonic acid are used, and 0% is used in aqueous solutions such as polyvinyl alcohol.
．． 005 to 1.0 weight, preferably 0.03 to 0.5
Weight φ is added.

The porous support used in the present invention is made of polytetrafluoroethylene or polysulfone, and the surface on which the film is to be formed has been previously made hydrophilic by sputter etching.

A porous support made of polytetrafluoroethylene or polysulfone is a preferable support that forms a composite semipermeable membrane with excellent strength, heat resistance, durability, etc., but it does not have good wettability with aqueous solutions such as polyvinyl alcohol. If a film is formed thereon as is, film defects such as pinholes will occur.

Therefore, in the present invention, before forming a film, the surface on which the film is to be formed is subjected to sputter etching treatment to make it hydrophilic, and the film is formed on this treated surface.

In the above sputter etching process, the stability of discharge,
Sustainability depends on the atmospheric pressure and the distance between the electrodes, but from the practical standpoint of the processing equipment, the atmospheric pressure is between 0.0005 and I T
orr is appropriate, and under this atmospheric pressure, the product of processing power density and processing time is 0.01 to 50 W・sec/d1
Preferably, the porous support is subjected to sputter etching treatment to obtain an etching rate of 0.1 to 30 W·sec/d.

By treatment under such conditions, a porous support comprising polytetrafluoroethylene and polysulfone having hydrophilic properties suitable for use in the present invention can be obtained.

The power source used is a high frequency power of several hundred KHz to several tens of MHz, especially 13.56 MHz, which is the industrially allocated frequency in practice, and the distance between the electrodes is proportional to the reciprocal of the square root of the atmospheric pressure. For example, if the atmospheric pressure is 0.005 T
In the case of orr, it will be 30 mg+ or more.

In addition, atmospheric gases include inert gas, nitrogen, air,
Water vapor carbon dioxide gas etc. are used.

Porous polytetrafluoroethylene film 0, IT
When the polysulfone porous membrane was processed in an argon atmosphere of 0.03 W. Under an argon atmosphere of I Torr, the product of processing power density and processing time is 30 W・sec/d
The following table shows the wettability improvement effect in terms of contact angle with water when treated so that

In both cases, the advancing angle and receding angle with respect to water are significantly reduced, and as a result, the wetting of an aqueous solution such as polyvinyl alcohol to a porous support is improved, and when an insolubilized film is formed on a support according to the present invention, pinholes etc. A composite semipermeable membrane without defective parts can be obtained, and productivity and workability are also significantly improved.

In order to attach an aqueous solution containing polyvinyl alcohol etc. and an insolubilization catalyst to one side of a porous support, there is a method of casting the aqueous solution onto the support, leaving one side of the support still on the surface of the aqueous solution, However, the latter method is usually used for a simple method of contacting for several seconds to several tens of hours to deposit an aqueous solution of polyvinyl alcohol, etc. and an insolubilizing catalyst on one side of the support in the form of a thin film. A composite membrane can be obtained.

Note that the contact time is not particularly limited.

A support having an aqueous solution of polyvinyl alcohol or the like and an insolubilization catalyst adhered to one side is usually dried using a heating dryer or the like.
It is heated at a temperature of 80 to 240°C, preferably 105 to 210°C, for several minutes to several hours, preferably 3 to 60 minutes, thereby forming an insolubilized thin film of polyvinyl alcohol or the like.

In order to increase the water resistance or mechanical strength of the insolubilized thin film of polyvinyl alcohol etc. formed on the support, an inorganic crosslinking agent such as a boron compound, diisocyanate, diisocyanate, etc. is added to the aqueous solution of polyvinyl alcohol etc. in advance. Of course, appropriate modifications such as addition of an organic crosslinking agent such as aldehyde, radiation irradiation, or acetalization reaction after film formation may be performed.

In addition, in the present invention, when one side of the porous support is placed on the surface of an aqueous solution such as polyvinyl alcohol, an appropriate synthetic resin film or the like is placed on the other side of the support in advance to prevent the aqueous solution from adhering. Needless to say, it is possible to take measures such as adhering to the surface or applying an appropriate organic solvent for sealing, and then removing the film after forming the insolubilized film or removing the solvent.

As described above, in the method for producing a composite semipermeable membrane of the present invention, the membrane-forming surface of a porous support made of polytetrafluoroethylene or polysulfone is subjected to varnish etching treatment under predetermined conditions in advance to make it hydrophilic. An aqueous solution such as polyvinyl alcohol is attached to the treated surface and heated in the presence of an insolubilization catalyst to form a thin film and insolubilize it, so there are no film defects such as pinholes on the support, and there is no adhesion. A thin film with good properties can be formed, and thus a reverse osmosis membrane with excellent salt removal rate and water permeability can be obtained.

Furthermore, unlike conventional methods, the method of the present invention does not use low-boiling point or expensive organic solvents, so harmful solvent vapors are not generated during the manufacturing process, and furthermore, the casting of the film-forming solution is There is no need to strictly control gelation, heat treatment temperature, etc., and a high-performance composite semipermeable membrane can be easily produced.

In particular, when a porous support made of polytetrafluoroethylene is used as the support, it does not shrink during the reverse osmosis operation, so a composite semipermeable membrane with even better durability can be obtained.

Examples of the present invention are listed below.

Example 1 Average pore diameter 0.20μ, maximum pore diameter 0.28μ CAS TI
V) Measured with F316-70), one side of a polytetrafluoroethylene porous film with a thickness of about 150μ was coated with 0.
Under argon atmosphere of 1 Torr, processing power density IW/7
Sputter etching treatment was performed under conditions of a treatment time of 3 seconds.

Polyvinyl alcohol (Kuraray #117, degree of saponification 9865 mol%) 0.25 weight sulfuric acid 0.05% in aqueous solution
The sputter-etched side of the support was left standing at room temperature for 10 minutes on the surface of the aqueous solution added by weight,
Next, it was heated and dried at a temperature of 155° C. for 15 minutes, and then thoroughly washed with water.

Regarding the composite reverse osmosis membrane thus obtained, 0.5 weight of saline solution was used as the stock solution, and 40 Ky/
As a result of measuring the amount of water permeation through the membrane and the salt removal rate under conditions of crA and 25°C, the water permeation amount was 0.12 m3/d-field and the salt removal rate was 95.1%.

Comparative Example 1 A polyvinyl alcohol aqueous solution containing sulfuric acid was deposited on a porous polytetrafluoroethylene film that was not subjected to sputter etching in the same manner as in Example 1, and was dried by heating. The resulting insolubilized film had many pinholes and was not suitable for practical use.

Therefore, when a film was similarly formed using a 0.7 weight polyvinyl alcohol aqueous solution containing 0.05 weight weight sulfuric acid, an insolubilized film with relatively few pinholes was obtained.

When we selected a part without pinholes and measured the membrane properties, we found that the water permeability was 0.002 m3/m'day, and the salt removal rate was 91.
2%, not only was the salt removal rate inferior, but also the water permeation rate was extremely small, making it impossible to obtain a practical composite reverse osmosis membrane.

Example 2 Polysulfone (Union Carbide MP-1700)
) and 70 g of lithium nitrate to N-methyl-2-
A membrane forming solution prepared by dissolving 860 g of pyrrolidone was cast onto a glass plate, left to stand for 2 seconds at room temperature, and then immersed in water at 36°C to gel, resulting in a polysulfone porous membrane with a thickness of 150 μm. A support was obtained.

The surface side of this porous membrane, which has a dense layer called the skin layer, was heated to 0. Sputter etching treatment was carried out under the conditions of an argon atmosphere of ITorr, a processing power density of 10 W/lyA, and a processing time of 3 seconds.

The sputter etched surface was placed on the surface of a 0.3 weight aqueous solution of polyvinyl alcohol (Kuraray #217, degree of saponification 88 mol) to which 0.06% by weight of sulfuric acid was added at room temperature for 10 minutes. After being allowed to stand still, it was heated and dried at a temperature of 150° C. for 5 minutes.

The membrane properties of the thus obtained composite reverse osmosis membrane were measured under the same conditions as in Example 1, and the water permeability was 0.18.
On d/d-day, the salt removal rate was 92.8%.

Comparative Example 2 A polyvinyl alcohol insolubilized thin wire was formed in the same manner as in Example 2, except that a polysulfone porous membrane not subjected to sputter etching treatment was used.

The water permeability of this composite reverse osmosis membrane is 0.12 m'/yf・day,
The desalination rate was 28.9%, and due to the occurrence of pinholes,
There is a significant decrease in desalination rate.

Claims (1)

[Claims] 1 One side of a porous support made of polytetrafluoroethylene or polysulfone is heated to an atmospheric pressure of 0.0005 to I
Torr, product of processing power density and processing time 0.01 to 5
Manufacture of a composite semipermeable membrane characterized by subjecting it to sputter etching treatment under conditions of 0 W/sec/-, and forming an insolubilized membrane on the treated surface of partially saponified polyvinyl alcohol or polyvinyl acetate in the presence of an insolubilizing catalyst. Method. 2. The method for producing a composite semipermeable membrane according to claim 1, wherein the degree of saponification of the partially saponified polyvinyl acetate is 70 mol or more. 3. The method for producing a composite semipermeable membrane according to claim 1 or 2, wherein the insolubilization catalyst is an acid. 4. Claims characterized in that an aqueous solution containing polyvinyl alcohol or partially saponified polyvinyl acetate and an insolubilization catalyst is deposited on one side of a porous support and heated to form the polymer into an insolubilized membrane. A method for producing a composite semipermeable membrane according to any one of items 1 to 3. 5. The composite semipermeable membrane according to any one of claims 1 to 4, characterized in that the concentration of the partially saponified polyvinyl alcohol or polyvinyl acetate in an aqueous solution is 0.03 to 3 by weight. Production method.