JPS61133105A - Process for improving permeability of porous membrane - Google Patents

Abstract

PURPOSE:To obtain a porous membrane having improved permeation velocity for water and permeability for solute together with hydrophilized surface by filling pores of a crystalline high molecular porous membrane which have been opened after drawing with aq. soln. of a surface active agent and then drying the membrane. CONSTITUTION:Fine through holes are formed by drawing a high molecular formed body having >=20% crystallinity. The mean pore size of the formed body is 0.05-3mu. This porous membrane is immersed in an aq. soln. or aq. suspension contg. 0.001-10wt% surface active agent, and the surface active agent is filled in the pores. Necessary time for filling is several mins - several days. Then the water in the pores is removed by drying the membrane at ca.80 deg.C. The water is almost completely removed by drying for several tens mins - several days.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for improving the permeability of substances by enlarging the rate-determining pore diameter of the pores of a porous membrane.

(Prior art) In recent years, porous membranes made of polymer compounds have been widely used for filtering aqueous solutions or suspensions. It is used to sterilize raw water, and in the medical field to separate blood components and remove malignant particles from ascites.

Porous materials made of polymer compounds can be produced by wet film forming, after mixing additives such as plasticizers and melt-molding.
A melt phase inversion method for extracting and removing additives, a stretching hole opening method that can be used in the case of crystalline polymers, and the like are known.

In the stretch pore opening method, after melt-forming a crystalline polymer, cleavage is caused between crystal lamellae by cold stretching, the pores are enlarged by further stretching by jI%, and the structure is fixed by heat setting. is formed by fibrils oriented long and thin in the stretching direction and nodules connected at right angles to the fibrils. A continuous hole is formed that penetrates the surface. The porous membrane obtained by this method does not require additive extraction such as organic solvents or plasticizers during the manufacturing process, and there is no need to worry about residual additives leaching out during use. It is also useful as a highly safe porous membrane when used for medical purposes. However, since the porous membrane obtained by the stretching pore method has strip-shaped micropores oriented in the stretching direction, as is clear from the pore opening principle, the fibrils arranged in the stretching direction play the role of a screen.
Although each hole has a relatively large area at the end of the opening, it has the disadvantage that only one molecular weight cutoff can be obtained. In order to improve this drawback, a method has been proposed in which the pores of a porous membrane are filled with a liquid containing an organic solvent, the liquid is then removed, and then dried.
Disclosed in the issue.

However, since this method uses an organic solvent as a treatment agent, it has the problem that the greatest advantage of the stretch hole method, which is that no organic solvent is used in the manufacturing process, is negated.

(Means for Solving the Problems) The present inventors have made extensive studies to solve the above-mentioned drawbacks of porous membranes manufactured by the stretching pore method.

We have arrived at the present invention. That is, the present invention relates to a method for improving a porous membrane, which involves filling the pores of a porous membrane made of a crystalline polymer and produced by a stretched pore method with an aqueous solution or suspension containing a surfactant. After.

A method for improving the permeability of a porous membrane, which is characterized by drying the porous membrane. The rapid pore diameter is expanded and the molecular weight cutoff is improved. Since the surfactant used in the present invention is used in the form of an aqueous solution or suspension, it does not require an organic solvent and has the advantage of a stretched open-pore membrane that does not use an organic solvent during the manufacturing process. It is something that can be demonstrated to the fullest.

In addition, when using hydrophobic polymers as the material for porous membranes,
The treatment of the present invention also has the advantage that the pore surfaces are made hydrophilic, making it possible to pass an aqueous solution through the mouth without additional hydrophilization treatment even after drying.

(Functions and Effects) The crystalline polymer used in the present invention is a polymer that has crystallinity to the extent that the principle of the stretch aperture method can be applied, and specifically, in the form of a film or hollow fiber. at least 20%
As mentioned above, it is preferably a polymer that can have crystallinity of 50% or more.

Typical examples of the crystalline polymer of the present invention include polyethylene, polypropylene, poly-4-methylpentene-1
Polyolefins such as polyoxymethylene and some of them are used as oxyethylene J! 1! Random or block copolymers of polyoxymethylene substituted with m, polyvinylidene fluoride, polytetrafluoroethylene, polyphenylene oxide, polyphenylene sulfide, or aromatic polyesters such as polyethylene terephthalate and polybutylene terephthalate, nylon 6, nylon 66
, polyamides such as nylon 12, and the like, but polyethylene is particularly preferred because it has high crystallinity and is suitable for the stretching method.

The stretching pore opening method referred to in the present invention is a method of forming fine through holes by stretching a molded body made of a crystalline polymer, and is disclosed, for example, in Japanese Patent Publication No. 32531/1983. This method uses melt extrusion of crystalline polymers.
After forming into a film, hollow fiber, etc., annealing is performed as necessary to grow crystals, cold stretching is performed to cause cleavage between the crystal lamellae, rough hot stretching is performed to enlarge the pores, and then heat setting is performed. This method consists of a sequential process of fixing the structure. The porous membrane used in the present invention includes:
For example, film-like, hollow-fiber-like, etc. are mentioned, but hollow fiber-like ones are particularly preferable because they allow V-shaped construction of a small size and large membrane area.0 Average pore diameter of the pores of the porous membrane used in the present invention is not particularly limited, but the preferred range of average pore diameter is 0.05 in the state before applying the uninvented treatment.
~3. It is Ou.

If the average pore diameter is less than 0.05 g, there is no point in increasing the rate-determining pore diameter, and if the pore size is 3.0 g or more, it is difficult to
I can hardly get it.

The surfactant used in the present invention is at least one selected from anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants. Examples of anionic surfactants include fatty acid groups, higher alcohol sulfate salts, polyoxyethylene sulfate salts,
Examples of cationic surfactants include alkylbenzene sulfonates, alkyl phosphates, etc.
Examples of the amphoteric surfactants include alkyl amine salts, quaternary ammonium salts, polyoxyethylene alkyl amines, and examples of amphoteric surfactants include alkyl amino acid salts and alkyl betaines. Examples of nonionic surfactants include:
polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene fatty acid ester, polyhydric alcohol fatty acid ester ethylene oxide adduct, polyoxyethylene diethylene fatty acid amide,
Examples include fatty acid alkanolamides, ethylene oxide adducts of oils and fats, oxyethylene oxypropylene block polymers, fatty acid monoglycerides, sorbitan fatty acid esters, polio-bovine diethylene sorbitan fatty acid esters, and sucrose fat s esters.

Among these surfactants, nonionic surfactants have low toxicity and are preferred when the porous membrane is used for medical purposes. In the present invention, the surfactant is used in the form of an aqueous solution or a water-suspended solution, but it is preferable that it has some degree of solubility in water, and in the case of a nonionic surfactant, the HLB (hydrophilic-lipophilic balance) Preferably, the value is in the range of 5 to 1 day.

In the present invention, it is necessary to dry the porous membrane after filling the pores of the porous membrane with an aqueous solution or suspension containing a surfactant. Simply filling the pores with an aqueous solution or suspension containing a surfactant will not produce the effect of improving substance permeability of the present invention.

Further, the effects of the present invention cannot be obtained by simply filling water containing no surfactant and drying the water. Furthermore, if the same treatment as in the present invention is performed using a water-soluble, non-volatile liquid such as glycerin or polyethylene glycol 400, which has been conventionally known as a membrane wetting agent, instead of a surfactant, the substance (substance of the present invention) (improvement of permeability) cannot be obtained.

A detailed description of the invention is envisaged. That is, by filling the pores with an aqueous solution or suspension containing a surfactant, the surfactant migrates to the pore surface and covers the surface with exposed hydrophilic groups, making the surface hydrophilic. be converted into Water strongly interacts with the hydrophilized surface, but when the porous membrane is dried, the water that is removed acts strongly on the fibrils forming the pore surface due to its interfacial tension, causing mobility. It is presumed that by moving a certain fibril, the rate-limiting part of the pore (the part of the through-hole with the smallest diameter) expands, resulting in the effect of improving permeability. This is a phenomenon that is noticeable in porous membranes manufactured by the stretched pore method, and is thought to be due to the fact that the pores of the porous membrane have a strip-like structure surrounded by mobile fibrils. It will be done.

The content of the surfactant in the aqueous solution or aqueous suspension used in the present invention must be sufficient to at least coat the pore surfaces, and the preferred amount is o. oot~10% by weight. If the amount of surfactant is too large, the effect will not be much improved and it will be economically wasteful.In fact, if it is too large, the surfactant will remain as a solid in the pores after drying and may clog the pores. .

A more preferable surfactant content range is 0.01 to 5.
The weight is t. Surfactants that are not completely soluble in water can also be used in suspension, but the size of the suspended sJ particles must be smaller than the pore size. For this purpose, it is preferable to obtain sufficiently small particles by performing mechanical stirring, ultrasonic treatment, or the like. The aqueous solution or suspension of the surfactant may contain small amounts of water-soluble inorganic salts or water-soluble organic compounds.

Next, a specific method of the present invention will be explained. First, the pores of a porous membrane are filled with an aqueous solution or suspension containing a surfactant. As a filling method, it is sufficient to simply immerse the material in the liquid for a certain period of time, but in order to shorten the time, the air in the pores may be removed under vacuum and then immersed for a certain period of time.
1. It is also possible to heat the porous membrane to a temperature that does not deform it.

The time required for filling the liquid is from several minutes to several days.Next, the porous membrane is dried to remove water from the pores.

The porous membrane may be dried under no tension or under tension such as by fixing both ends with adhesive. Drying methods include, for example, blowing hot air or vacuum drying. However, the drying temperature should be kept at a level below which the porous membrane is not deformed by heat; for example, in the case of polyethylene, it is preferably about 80°C or below.

Further, the porous membrane may be dried only to the extent that moisture is almost completely removed, and the time required for this is several tens of minutes to several days.

Since the rate-determining pore diameter of the porous membrane treated by the method of the present invention is expanded, the water permeation rate is greatly improved, and the solute permeability is also dramatically improved. In addition, although the porous membrane improved by the method of the present invention is obtained as a dry membrane, one surface is also treated with wood at the same time, so even when a hydrophobic polymer such as polyethylene is used as the material, Unlike conventional porous membranes obtained by impregnating organic solvents and then drying them, this membrane does not require additional hydrophilic treatment and can be used as it is for oral filtration of aqueous solutions.

Next, the present invention will be explained with examples.

The various physical properties were measured using the following methods.

Average pore diameter (square) The pore diameter that indicates the pore volume at the pole of the total pore volume on the pore diameter-pore volume integral curve determined by a mercury porosimeter.

Water permeation rate (vertical ram” # tamHg) Measured using pure water at 25°C and differential pressure of 50+mHg.

Solute permeability (S(:) SC= (Cf/Go) 1% physiological saline was used.

(Example) High density polyethylene (density 0.988, MI value 5.
5° (trade name HIZEX 2208J) was spun using a circular double spinneret, the spinning lower was 155°C, and the spinning speed was 300 m/min.

The obtained hollow fibers were annealed at 115°C for 2 hours. Furthermore, this hollow fiber was subjected to 3D K stretching at room temperature, and then at 102°C.
The fibers were stretched by 350% #IK at a temperature of 100° C. and roughly heat-set at 110° C. to obtain porous polyethylene hollow fibers. The obtained hollow fiber had an inner diameter of 300 mm, a membrane thickness of 50 colors, and an average pore diameter of 0.30 mm. Bundle this hollow fiber.

Both ends were fixed with adhesive to create a module with a membrane area of 50 crrr'. This polyethylene porous hollow fiber module was immersed in an aqueous solution or suspension of various surfactants shown in Table 1 at 50° C. for 24 hours to fill the pores with the liquid. The module taken out from the liquid was subsequently dried in a vacuum dryer at room temperature for 24 hours. Polyethylene porous membrane (Example 1.2.4
-8) After making it hydrophilic by immersing it in ethanol, the permeation performance of the membrane is measured by the water permeation rate and blue dextran permeability (SC).
So, I evaluated it.

After the porous membrane of Example 3 was treated according to the present invention, it was immersed in water instead of ethanol, and its performance was measured. In Comparative Example 1, the performance was measured after being immersed in ethanol to make it hydrophilic without performing the treatment of the present invention. In Comparative Example 2, the membrane was immersed in ethanol to make it hydrophilic without performing the treatment of the present invention, then washed thoroughly with water, replacing the liquid filling the pores of the porous membrane with water, dried, and immersed in ethanol again to make it hydrophilic. The performance was then measured. In Comparative Example 3, the performance was measured after filling an aqueous surfactant suspension under the same conditions as in Example 1, immersing it in ethanol as it was without washing with water and drying it, and making it hydrophilic.

Comparative Example 4 is an example in which glycerin was used instead of a surfactant, and after immersing it in ethanol to make it parent wood according to the method of Comparative Example 2, replacing it with a glycerin aqueous solution, drying it, and then immersing it in ethanol again. The performance was measured after being immersed in water to make it hydrophilic.

The results are summarized in Table 1. As is clear from Table 1,
Compared to the porous membrane not treated according to the present invention shown in Comparative Example 1, the porous membrane treated according to the present invention has significantly improved water permeability and solute permeability. It was confirmed that the material was hydrophilized in the state of , and had sufficient permeability even without hydrophilic treatment with ethanol. Furthermore, as shown in Comparative Examples 2 and 3, no drying treatment was performed when filling with water without a surfactant and drying, or filling with an aqueous solution or aqueous suspension containing a surfactant. In some cases, no treatment effect was observed. Also, comparative example 4
As shown in , no treatment effect was observed when glycerin was used instead of a surfactant.

Claims (7)

[Claims] (1) After filling the pores of a porous membrane made of crystalline polymer and manufactured by the stretch pore method with an aqueous solution or aqueous suspension containing 0.001 to 10% by weight of a surfactant, A method for improving the permeability of a porous membrane, the method comprising drying the porous membrane. (2) The method according to claim 1, wherein the crystalline polymer is polyethylene. (3) The method according to any one of claims 1 to 2, using a porous membrane whose pores have an average pore diameter in the range of 0.05 to 3.0 μ. (4) The method according to any one of claims 1 to 3, wherein the surfactant is a nonionic surfactant. (5) The method according to claim 4, wherein the nonionic surfactant has an HLB of 5 to 18. (6) The method according to any one of claims 1 to 5, wherein the concentration of the aqueous solution or suspension containing the surfactant is 0.01 to 5% by weight. (7) The method according to any one of claims 1 to 5, wherein the porous membrane is in the form of a hollow fiber.