JPS6325805B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a dry semipermeable membrane having permselectivity.

In detail, a semipermeable membrane in a wet state with permselectivity (hereinafter referred to as a wet membrane) manufactured by a wet casting method is a semipermeable membrane in a dry state that is convenient for processing, storage, transportation, etc. while maintaining its performance. (hereinafter referred to as a dry film).

In recent years, technology for separating, purifying, and concentrating substances using semipermeable membranes, such as ultrafiltration, reverse osmosis, precision filtration, dialysis,
Electrodialysis is an energy-saving technology that is widely used in seawater desalination, the production of ultrapure water essential in the medical, pharmaceutical, and electronic industries, recovery of valuables, concentration of various solutions, hemofiltration, dialysis, etc. It is being used.

In order to be able to be applied to a wide range of purposes, research and development is actively being conducted on the development of various new semipermeable membrane materials and the modification of semipermeable membranes using existing materials. It has important value as one of the modification methods.

As a manufacturing method for semipermeable membranes used for various purposes such as those mentioned above, a membrane-forming solution in which a polymer substance serving as a semipermeable membrane material is dissolved in a solvent and a swelling agent to form a porous structure is used to form a thin film or a membrane-forming solution. Hollow fibers or cylindrical shapes are cast, the solvent is evaporated in air for a certain period of time, and then immersed in water for a certain period of time to gel.
It is generally known that the membrane grade is then determined by heat treatment in warm water.

Semipermeable membranes produced in this way typically have a
% of water, and this water plays an important role in maintaining the separation and water permeability properties of the semipermeable membrane.

When moisture is lost in a semipermeable membrane in such a wet state, the semipermeable membrane not only loses its function as a semipermeable membrane, but also loses its porosity as the moisture dissipates further and dries. The tissue changes to a homogeneous state, and the size of the semipermeable membrane begins to shrink. Moreover, this change is irreversible and occurs in a relatively short period of time, depending on the atmospheric conditions, which is a fatal drawback of wet membranes.

Therefore, the semipermeable membrane must always be stored in water or in air with sufficient humidity, and must be processed by some means to prevent it from drying out.

Furthermore, it goes without saying that careful consideration must be given to the packaging for storing and transporting modules made from processed and molded semipermeable membranes in order to maintain a moist state.

As a means of alleviating the above-mentioned disadvantages, it has been proposed to handle semipermeable membranes in a dry state, and modules for artificial dialysis are already on the market due to the need to perform sterile operations and maintain sterile conditions. Most of the products on the market use dry membranes.

For example, a method for manufacturing a dry film by immersing a wet film in various solutions is disclosed in JP-A-47-
11662, JP 48-6033, JP 50-35033, JP 56-7602, etc. are publicly known;
11662, a semipermeable membrane made of cellulose acetate is immersed in a mixed aqueous solution of a polyhydric alcohol having 1 to 3 carbon atoms in the molecule and an organic carboxylic acid having 1 to 3 carbon atoms in the molecule. A method of replacing the water contained in the mixture with the mixture and then drying it was disclosed in the Japanese Patent Publication Publication No. 1973-
6033 describes a method in which a water-miscible organic solvent is applied to a cellulose membrane in the first step, and then a non-polar organic solvent is contacted in the second step, followed by drying. There is a method in which acetyl cellulose membrane is immersed in an aqueous solution of a polyethylene glycol nonionic surfactant, heat-treated at a temperature of 60°C or higher, and then dried. A method is shown in which the material is soaked in liquefied carbon dioxide gas and then dried.

However, in all of these methods, the strength of the membrane after treatment is drastically reduced, making it difficult to process it into modules, and the solute used as the immersion liquid remains in the semipermeable membrane forever, limiting its use. It also has drawbacks such as requiring special equipment.

Therefore, the present inventors conducted intensive studies to develop a method for producing a dry membrane free from the above-mentioned problems, and as a result, completed the invention as described below.

The present invention deals with membranes that are generally used for the purpose of treating aqueous liquids, from industrially used ultrafiltration membranes, reverse osmosis membranes, microfiltration membranes, etc. to membranes used for medical purposes, in a dry state. The semipermeable membrane is modified by immersing a wet membrane made by the general manufacturing method described above in an aqueous lactate solution, more specifically, an aqueous sodium lactate solution. separation function,
The purpose is to be able to dry without impairing water permeability or causing dimensional deformation.

According to this method, reaction products caused by urethane adhesives are not detected, and since sodium lactate is sometimes used as one of the components of injections, there is no problem with safety for living organisms. The dry film obtained by the present invention is highly effective not only for general industrial use but also for use in the medical and pharmaceutical field in particular.

The present invention will be described in detail below, including examples. In the present invention, the concentration of sodium lactate in the sodium lactate aqueous solution used in the dipping treatment when turning a wet film into a dry film is not particularly limited, but is suitably 5 to 70% by weight, preferably 10% by weight. ~50% by weight is preferred.

If the sodium lactate concentration is less than 5% by weight, the strength of the dried membrane after treatment will be weak and the membrane performance will also deteriorate, making it impossible to put it to practical use. On the other hand, if it exceeds 70% by weight, the viscosity of the sodium lactate aqueous solution will increase, making handling difficult and causing problems such as it takes time to remove water from the membrane in the drying process after dipping. . Furthermore, if the content of sodium lactate in the dry film is high, it will easily absorb moisture from the air, causing problems such as difficulty in adhesion in subsequent processing steps.

In order to produce a dry membrane with selective permselectivity according to the present invention, a membrane forming solution is cast, immersed in water and coagulated to obtain a wet membrane containing a large amount of water inside. After immersing the film in a sodium lactate aqueous solution of a predetermined concentration, the water in the film is removed by heating, blowing air, etc.

The membrane material used in the present invention is not particularly limited, and any material can be used, and the application of the semipermeable membrane is not limited either, such as for hemodialysis, Possible applications include precision filtration for plasma separation, ultrafiltration, and reverse osmosis. Further, any shape of the membrane can be used, such as a flat membrane, a tubular membrane, or a hollow fiber membrane.

The present invention will be explained below with reference to Examples.

In addition, the ultrafiltration rate (hereinafter abbreviated as UFR) here refers to the ultrafiltration rate under a pressure of 0.5Kg/cm ² G.
The water permeation amount per minute per 1 m ² of membrane area is expressed in ml, and the solute rejection rate is defined by the following formula.

Solute exclusion rate (%) = solute concentration in filtrate/solute concentration in stock solution used for evaluation x 100 Example 1 A membrane was formed using the membrane forming method described in the specification of JP-A-134608-1980. A wet ultrafiltration membrane made of cellulose acetate was immersed for 30 minutes in an aqueous solution at room temperature consisting of 30% by weight of sodium lactate and 70% by weight of water, and then dried for 1 hour in a hot air dryer at 50°C. The obtained membrane was immersed in water again, and after returning to a wet membrane, 2000ppm
using a phosphate buffer containing ovalbumin of
When the UFR and ovalbumin elimination rate were measured under a pressure of 0.5 Kg/cm ² G, UFR810
ml/m ² ·min, ovalbumin exclusion rate was 99.9%. Incidentally, the membrane performance of the wet membrane before immersion treatment with an aqueous sodium lactate solution was measured under the same conditions as UFR810ml/m ² ·min, ovalbumin rejection rate.
99.9%, confirming that the membrane performance was maintained even after immersion and drying treatment with an aqueous sodium lactate solution.

For comparison, the tensile strength of the dried membrane used in this example was compared with that of a dried membrane immersed in a 30% glycerin aqueous solution and dried under the same conditions. As a result, the former exhibited 1.7 times the strength of the latter.

Comparative Example 1 When the wet membrane shown in Example 1 was dried in the same manner as in Example 1 without being immersed in an aqueous sodium lactate solution and the membrane performance was measured, the UFR was 0, indicating that the membrane performance was not maintained. Ta.

Example 2 The procedure of Example 1 was repeated except that a polysulfone wet ultrafiltration membrane obtained by the membrane manufacturing method described in Japanese Patent Application No. 121286/1986 was used, and the following results were obtained. The dried semipermeable membrane has a UFR780ml/
^m2・min, ovalbumin exclusion rate is 99.2%, and the untreated membrane has a UFR of 820ml/ ^m2・min, ovalbumin exclusion rate is 99.2%, and the performance is maintained. It was confirmed that this method can also be applied to membranes.

Comparative Example 2 Membrane performance was measured by drying as in Example 2 without immersing it in a sodium lactate aqueous solution.
UFR was 0 and membrane performance was not maintained.

Example 3 The same procedure as Example 1 was carried out except that a wet ultrafiltration membrane made of polyacrylonitrile-polyvinylpyrrolidone copolymer obtained by the membrane forming method shown in JP-A No. 49-122479 was used, and the following procedure was carried out. Got the results. The dry treated membrane has a UFR of 970 ml/m ² ·min and an ovalbumin exclusion rate of 99.9%, and the untreated membrane has a UFR of 910 ml/m 2 ·min.
m ² ·min, the ovalbumin exclusion rate was 99.8%, and the performance was maintained, confirming that the present invention can also be applied to the semipermeable membrane made of the above-mentioned polyacrylonitrile-polyvinylpyrrolidone copolymer.

Comparative Example 3 Membrane performance was measured by drying as in Example 3 without immersing it in a sodium lactate aqueous solution.
UFR was 0 and membrane performance was not maintained.

Claims (1)

[Claims] 1. When drying a wet semipermeable membrane having an asymmetric structure obtained by casting a polymer solution and immersing it in water to form a hydrogel, the semipermeable membrane is soaked in a lactate aqueous solution. A method for producing a dry semipermeable membrane, which comprises soaking and then drying. 2 Lactate concentration in lactate aqueous solution is 5 to 70% by weight
The method for producing a dry semipermeable membrane according to claim 1, wherein the amount is preferably 10 to 50% by weight. 3. The method for producing a dry semipermeable membrane according to claim 1, wherein the lactate is sodium lactate.