JPH0259030A - Heat-resistant hydrophilicity imparted porous membrane and preparation thereof - Google Patents

Abstract

PURPOSE:To impart hydrophilicity and heat resistance to a membrane by successively holding a crosslinked polymer composed of a polymerizable monomer and divinylbenzene and a hydrophilic crosslinked polymer containing a hydrophilic monomer and a crosslinkable monomer to the surface of a porous membrane made of a synthetic resin. CONSTITUTION:A crosslinked polymer consisting of one or more kind of a polymerizable monomer composed of styrene and alpha-methylstyrene and divinylbenze, and a hydrophilic crosslinked polymer containing a hydrophilic monomer and a crosslinkable monomer is successively held on at least a part of the surface of a porous membrane composed of polyethylene or polypropylene and thermally polymerized to obtain a heat-resistant hydrophilic porous membrane. As the hydrophilic monomer, diacetone acrylamide and a monomer having two carboxy groups are used. By this method, heat resistance and hydrophilicity can be imparted to the porous polyethylene or polypropylene porous membrane.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a porous membrane for precision filtration that has excellent hydrophilicity and heat resistance, and a method for producing the same.

[Conventional technology]

With the development of industry in recent years, separation membranes of various degrees Celsius have been used in the water purification field, blood treatment field, air purification field, food industry field, etc. For example, microfiltration membranes are used to obtain highly purified water or highly clean air. Among these, precision filtration membranes made of polyolefins such as polyethylene are particularly widely used because they are inexpensive, have excellent chemical properties, and have excellent membrane properties such as strength, elongation, and flexibility.

The scope of application of precision filtration membranes is increasing more and more, and use at high temperatures of, for example, about 80 to 95°C is strongly desired. On the other hand, depending on the use of the microfiltration membrane, it is not acceptable for the membrane itself to be contaminated with microorganisms such as bacteria and mold, and in that case, it must be sterilized by some method.

Sterilization methods include ethylene oxide, formalin, hydrogen peroxide, radiation such as gamma rays, and steam heating, but steam heating is the most desirable method in terms of effectiveness and simplicity. Normally 121℃
A condition of approximately 30 minutes is adopted.

However, porous membranes made of polyolefins such as polyethylene have significant thermal shrinkage, and when these porous membranes are heat-treated or used at high temperatures, their morphology changes and water or air permeability is extremely reduced, resulting in separation. Its function as a membrane decreases.

Furthermore, since this porous membrane is hydrophobic, water cannot pass through it as it is.

In order to improve the heat resistance of polyolefin porous membranes, JP-A-62-33878 proposes a method in which a heat-resistant polymer thin film having a crosslinked structure is formed on the surface of a polyolefin hollow fiber membrane. Also, JP-A-56-5
Japanese Patent No. 7836 proposes a polyethylene porous membrane in which sulfone groups are introduced to impart hydrophilicity.

[The problem that the invention seeks to solve]

However, in the heat-resistant polyolefin hollow fiber membrane described in JP-A-62-33878, the heat resistance of the polymer thin film itself is insufficient.

Furthermore, although the polyethylene porous membrane described in JP-A-56-57836 has hydrophilic properties, it does not have sufficient heat resistance.

An object of the present invention is to provide a porous membrane made of polyethylene or polypropylene that is hydrophilic and has excellent heat resistance and can be subjected to steam sterilization, and a method for producing the same.

[Means to solve the problem]

The gist of the present invention is that styrene, α, etc.
- Holding a crosslinked polymer consisting of a polymerizable monomer of 1 fM or more consisting of methylstyrene and divinylbenzene, and further holding a hydrophilic crosslinked polymer consisting of monomers containing a hydrophilic monomer and a crosslinking monomer thereon. Surface 1 is a thermally hydrophilized porous membrane formed by coating, and the porous membrane is made of polyethylene or polypropylene. Thermal polymerization is carried out in a state in which a heptamer containing a synthetic monomer and divinylbenzene is held, and then monomers containing a hydrophilic monomer and a crosslinking monomer are held on at least a part of the surface of the porous membrane. The present invention provides a method for producing a heat-resistant hydrophilic porous membrane, which is thermally polymerized in a state where the membrane is heated.

In the present invention, the porous membrane can be in any form such as a hollow fiber membrane, a flat membrane, or a tubular membrane, and can have various pore diameters depending on the application, but is preferred. For example, the membrane thickness is approximately 20 to 200 μm, the porosity is approximately 20 to 90%, and the water permeability is 0.001 to 101/m-hr-m by alcohol hydrophilization method.
Examples include those having a pore size of about 1 Hp and a pore diameter of about 0.01 to 5 μm.

Such porous membranes include porous membranes obtained by various methods, including melt-forming and stretching methods, and methods of melt-forming and extracting the stretched material by mixing inorganic substances or esters. Porous membranes with a porous structure can be used, but porous membranes obtained by a method of melt-forming and then stretching are preferably used because they have a large porosity and are less susceptible to deterioration in performance due to clogging. A porous membrane produced by the method of stretching after shaping is a porous membrane having a pore structure in which slit-like micro spaces (pores) formed by micron ipril and knots communicate with each other three-dimensionally. Yes, for example, Japanese Patent Publication No. 5652123, Japanese Patent Application Laid-Open No. 57-4291
It can be manufactured by the method described in Publication No. 9 and the like.

Note that, as the form of the porous membrane, a hollow fiber type is preferably used because the membrane area per unit volume is large.

In the porous membrane of the present invention, a heat-resistant cross-linked polymer composed of a monomer such as styrene and divinylbenzene is retained in the first layer, and a hydrophilic cross-linked polymer is retained in the second layer. It is something.

Hereinafter, the former will be referred to as a thermophilic crosslinked polymer, the latter will be referred to as a hydrophilic crosslinked polymer, and both will be referred to as a crosslinked polymer.

In the porous membrane of the present invention, the bridges and ① combinations are maintained.

jl? l] Including, it is sufficient that the crosslinked polymer is retained so that the thermal properties and hydrophilicity are improved, and it is not necessary that the crosslinked polymer is retained on all surfaces. do not have.

Although the length of the crosslinked polymer retained on the surface depends on the porosity and pore diameter of the porous membrane, it is preferably about 5 to 80 Mk% based on the weight of the porous membrane. If the amount of cross-linked polymer retained is less than this range, it will not be possible to impart sufficient heat resistance and hydrophilicity to the porous membrane, and if it exceeds this range, the pore volume will decrease and the fluid permeation performance will deteriorate. This is not preferable because it may cause a decrease in

The retained amount of the crosslinked polymer is preferably about 10 to 703% (more preferably about 15 to 60% by weight, and particularly preferably about 31%). ] [The C ratio is not particularly limited, and the target heat resistance,
It can be selected as appropriate to achieve hydrophilicity.

Retained means that the cross-linked polymer is tightly bound to the pore surface to the extent that it does not easily detach during storage or use. The cross-linked polymer may be chemically bonded to the micropores (or the cross-linked polymer may be tightly attached to the micropores by an anchor effect), or the cross-linked polymer may be attached to the microfibrils or nodules that form the slit-like pores. The combination may be crosslinked or cross-linked, and these holding states may be mixed.

In this way polyethylene or polyglopylene porous T) fat 11. Retention state of the crosslinked polymer on the six faces of the hole
The heat-resistant and hydrophilic porous film, which has a physical property on the pore surface through anchoring effects and adhesive cross-linking without chemical bonding, has a deterioration in mechanical strength compared to porous wood membranes. IP and +fK are preferable because there is almost no change in porosity or pore size.

The composition ratio of the polymerizable monomer and divinylbenzene is not particularly limited, as long as the amount of divinylbenzene is approximately 2'N and the amount is 9 or more.

The hydrophilic cross-linked polymer is a system containing a hydrophilic monomer as a polymer component and having 3 crosslinkable polymers.
In addition to these, the monomer component may contain a non-crosslinked polymer.

Known hydrophilic hexamers can be used, but preferred ones include diacetone acrylamide, acid anhydrides such as maleic anhydride, itaconic anhydride, and hymic anhydride, maleic esters, fumaric esters, etc. Examples include monomer monomers having two esterified carboxyl groups (hereinafter referred to as "carboxy monomers"). Note that these acid anhydrides and ester compounds can be easily changed into a structure having a carboxyl group by hydrolysis, and therefore can impart hydrophilicity to the crosslinked polymer.

Examples of crosslinkable monomers include monomers having two or more polymerizable unsaturated bonds such as vinyl bonds and allyl bonds that can be copolymerized with hydrophilic monomers, or monomers that have one of the monomerizable unsaturated bonds and can be copolymerized with hydrophilic monomers by condensation reaction, etc. List monomers that have at least one functional group capable of forming a chemical bond and that share a good solvent with hydrophilic monomers. Examples include N, N'-methylenebisacrylamide, N -Hydroxymethyl(meth)acrylamide, triallyl(iso)cyanurate, divinylbenzene, 2,2-bis(4-methacryloyloxypolyethoxyphenyl)furopane, ethylene di(meth)acrylate, polyethylene glycol di(meth)acrylate, tri- methylolpropane tri(meth)acrylate,
Penquerythritol tetra(meth)acrylate, trimethylolethane tri(meth)acrylate, butanediol di(meth)acrylate, hexanedimer di(meth)acrylate, diallyl phthalate, 1.3.
Examples include 5-triacryloylhexanehydro-3-triazine.

In addition, as the non-crosslinking monomer, together with the hydrophilic monomer, 1
A monomer having one unsaturated bond such as a vinyl bond or an allyl bond that can be combined with a hydrophilic monomer and a good solvent in common with the hydrophilic monomer can be selected. For example, dimethyl acrylamide, vinylpyrrolidone,
Examples include (meth)acrylic acid, hydroxyethyl methacrylate, styrene sulfonic acid, sodium styrene sulfonate, sodium sulfoethyl methacrylate, vinylpyridine, vinyl methyl ether, and the like.

Hereinafter, such crosslinkable monomers and non-crosslinkable monomers will be collectively referred to as copolymerizable monomers.

The composition ratio of the hydrophilic monomer to the copolymerizable heptamer that forms the hydrophilic crosslinked polymer is 0.5 to 30011 parts (approximately 'u parts) per 100 parts by weight of the hydrophilic hetamine. is preferred.

In the present invention, since the polymer retained on the pore surface of the polyethylene or polypropylene porous membrane is a crosslinked polymer, the stability of the polymer is good, and the amount of components eluted in water is extremely small. There is an advantage. Therefore, the porous membrane is effective in the water treatment field, bovine blood purification field, etc., where a thorough amount of eluted components is a problem.

Next, a method for producing a porous membrane imparted with heat resistance and hydrophilicity according to the present invention will be explained. Although the crosslinked polymer will be explained below simply as a crosslinked polymer, both the heat resistant crosslinked polymer and the hydrophilic crosslinked polymer can be held on the surface of the porous membrane by the same method.

In the present invention, various methods can be used to retain the crosslinked polymer on the pore surface of the porous membrane. For example, monomers or The solution can be prepared by preparing a solution in which a polymerization initiator is dissolved and immersing the porous membrane in the solution, or by press-fitting the solution into the porous membrane after manufacturing a membrane module using the porous membrane. A method can be adopted in which a porous membrane is impregnated with monomers and then the solvent is removed by evaporation.By using a solution diluted with a solvent, the monomers can be applied almost uniformly throughout the porous membrane without clogging the pores of the porous membrane. Furthermore, the amount of monomers attached can be adjusted by changing the concentration of monomers in the solution and the immersion time.

When preparing the above solution, use an organic solvent that has a boiling point lower than that of the monomers and is capable of dissolving the monomers, or, if a polymerization initiator is added, a polymerization initiator. It is preferable to use a solvent that can dissolve it.

Such organic solvents include methanol, ethanol,
Furopanol, Influopanol caustic alcohols,
You can use ketones such as acetone, methyl ether ketone, and methyl isobutyl ketone, ethers such as tetrahydrofuran and dioxane, ethyl acetate, and chloroform.

The boiling point of organic solvents is particularly limited to 7'; however, considering the ease of solvent removal before the polymerization process, it is approximately 10
Preferably, the temperature is below 0°C, more preferably about 80°C or below.

The composition of the monomers and the solvent in the solution may be selected appropriately taking into account the type of solvent and the target retention i of the crosslinked polymer, and the proportion of the solvent is 5 parts by weight per 100 parts by weight of the monomers.
As long as it is about 0 to 10,000 parts by weight <200 to 500
It is more preferable that the amount is about ox parts by weight.

When dipping or press-fitting a porous membrane using these solutions, the dipping time or press-fitting time is approximately 0.
It takes about 5 seconds to 30 minutes, and it can be carried out in a shorter time when a solution with better wetting properties for the porous membrane is used.

In this way, the monomers or even the polymerization initiator can be removed by evaporation of the surrounding excess liquid, and if necessary, the solvent inside the pores can be removed by evaporation. After that, it is transferred to the next polymerization step.

If the temperature during evaporation of the solvent is too high, polymerization will partially proceed while the solvent remains, and polymerization will occur inside the pores of the porous membrane instead of on the pore surface, resulting in some of the pores being removed. This is not preferable since the pores may be blocked, and in consideration of this, the temperature during solvent removal is preferably about 10 to 50°C.

In the present invention, thermal polymerization method, photopolymerization method, radiation polymerization method,
A polymerization method such as the plasma 1 method can be employed, and known polymerization initiators can be used.

In the case of a thermal polymerization method, the degree of rationality is preferably higher than the decomposition temperature of the above-mentioned 1-polymer initiator and lower than the temperature that does not change the membrane structure of the porous membrane and damage the membrane substrate, Usually, a temperature of about 30 to 100°C can be employed. The heating time depends on the type of initiator and the heating temperature, but in a batch method it is usually about 1 minute to 5 hours, more preferably about 15 minutes to 3 hours. or,
In the continuous method, the heat transfer efficiency is high, so that the heating can be carried out in a shorter time, and the heating time is usually about 10 seconds to 60 minutes, more preferably about 20 seconds to 10 minutes.

In the case of the photopolymerization method, ultraviolet rays or visible light can be used as the light source for light irradiation, and the ultraviolet ray sources include low-pressure mercury lamps,
High-pressure mercury lamps, xenon lamps, arc lamps, etc. can be used.

As for the light irradiation conditions, for example, when using a mercury lamp as a light source, the input should be about 10 to 300 W/cra and 10 to 300 W/cra.
By irradiating for about 0.5 to 300 seconds from a distance of about 50z, it is possible to achieve a radiation density of about 0.001 to 1 Ojou16/(m'', preferably about 0.05 to 1J Ouel/C).
A condition of irradiating energy of about Yn'' is adopted.

In the case of radiation polymerization, for example, an electron beam irradiation device is used, and 1
This can be carried out by irradiating electron beams at a temperature of about 10 to 50 Mrad at a temperature of 20° C. or lower, more preferably 100° C. or lower.

In addition, during these polymerizations, the presence of oxygen in the atmosphere will significantly inhibit the polymerization reaction, so it is best to carry out the polymerization in an inert gas atmosphere such as a nitrogen atmosphere, or in a state in which oxygen is substantially absent, such as in a vacuum. desirable.

In the present invention, various polymerization methods can be employed as described above, but a method using thermal energy is most preferred. When using thermal energy, the pores of the porous membrane can be heated to a uniform temperature, so monomers can be uniformly polymerized on all pore surfaces where monomers are held, and the polymerization temperature can be maintained evenly. By appropriately setting , there is an advantage that the combination can be carried out without changing the structure of the membrane or deteriorating the membrane substrate. On the other hand, when using light energy, there is a problem that light scattering makes it difficult for light to reach the pores of a porous membrane, and that increasing the intensity of light irradiation tends to cause deterioration of the membrane substrate. Also, when using radiation energy, there is a problem in that the membrane substrate tends to deteriorate. Therefore, when employing these polymerization methods, it is necessary to carefully select polymerization conditions that will not deteriorate the membrane substrate.

Since the monomers held on the surface of the porous membrane are polymerized and crosslinked by these polymerization techniques, at least a portion of the surface of the porous membrane is coated with these crosslinked polymers.

After the crosslinked polymer is produced, unreacted monomers and free polymers existing around the pore surface and outer surface of the porous membrane are removed by dipping or press injection using an appropriate cleaning solvent as necessary. It is desirable to remove the components.

By such a method, first the heat-resistant crosslinked polymer is retained, and then the hydrophilic crosslinked polymer is retained.

When the hydrophilic crosslinked polymer is composed of a carboxy monomer, the hydrophilic crosslinked polymer is hydrolyzed to introduce carboxyl groups and impart hydrophilicity. In order to uniformly hydrolyze the hydrophilic crosslinked polymer held on the pore surface of the porous membrane, a heating method is preferable, but in that case, the thermal and chemical stability of the polyolefin and the held crosslinked polymer is Gender becomes an issue. For this reason, for example, it is preferable to immerse the porous membrane in a solution in which an alkaline substance is dissolved in a solvent system with low surface tension to form a dicarboxylic acid salt. Examples of the alkaline substance include alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, and lithium hydroxide, carbonates, and ammonia, and the concentration may be about 0.1 to 2N. Further, as a solvent, methanol, ethanol, inflobanol, or a mixed solution of these and water can be used. The immersion time may be 5 minutes or more.

〔Example〕

The present invention will be specifically explained below using Examples.

In addition, in the examples, porous membranes in which slit-like spaces (pores) formed by microfibrils obtained by bath melting and stretching and knots are three-dimensionally connected are used as porous membranes. was used.

The amount of the crosslinked polymer retained was determined by a dissolution fractionation method in which the porous membrane was dissolved under reflux of boiling xylene and expressed as weight % with respect to the porous membrane. The heat shrinkage rate was measured by treating the porous membrane in steam at 121'C for 30 minutes and using the length before treatment as a reference. In addition, the water permeability in the alcohol hydrophilization method and the water permeability and water permeability after retaining the crosslinked polymer are determined by the effective membrane area of 16
The measurement was carried out using a 3 cm" test membrane module according to the following method.

(1) Water permeability test using alcohol hydrophilization method Pressurize ethanol from one side of the membrane module (inside the hollow fiber membrane in the case of a hollow fiber membrane) at a flow rate of 25 d/tnln for 15 minutes to test the inside of the pores of the porous membrane. After thoroughly moistening with ethanol until
, the ethanol present inside the pores is replaced by water. Next, water at 25°C was poured from one side of the test membrane module (inside the hollow fiber in the case of a hollow fiber) until the transmembrane pressure difference reached 50 H/H.
Measure the amount of permeated water at , and calculate the water permeability (1/
Find m・hr−Ryu H7).

(2) Water permeability after retaining cross-linked polymer Water at a pressure of 2 kg 7 cm" was applied from one side of the test membrane module (inside of the hollow fiber membrane in the case of a hollow fiber membrane) made of a porous membrane retaining cross-linked polymer. was injected for 3 hours, water at 25°C was poured from one side of the test membrane module, the amount of permeated water was measured at a transmembrane pressure of 50 snH/, and the water permeability (J/m-hr-mHp) was calculated from that value. demand.

(3) Water permeability test Supplying water at 25°C from one side of the membrane module (inside of the hollow fiber in the case of a hollow fiber membrane) while increasing the water pressure at a rate of 0.1 kg/cm every minute, Cumulative water permeability is 30
Measure the water pressure when it reaches 1d and 501. Next, the water pressure is plotted on the horizontal axis and the amount of permeated water is plotted on the vertical axis, and the pressure value at the point where the straight line connecting the two plotted points intersects with the horizontal axis is determined, and that value is taken as the permeable pressure.

Examples 1 to 5 Porous membrane: porosity 65%, membrane thickness 70 μm, elongation at break 67%, heat shrinkage rate 41%, water permeability pressure 12.5 kJ/c
m”, water permeability by alcohol hydrophilization method is 1.21/
A polyethylene porous membrane of rrl.hr' IXHJII was used.

This porous membrane was immersed for 10 seconds in an acetone solution containing styrene, divinylbenzene, and 0.2TLi% benzoyl peroxide at the concentrations shown in Table 1, and then left at room temperature for 3 hours.
The mixture was air-dried for 0 minutes to volatilize acetone, and then heated in a nitrogen atmosphere at 60° C. for 60 minutes to polymerize the heptamers, thereby obtaining a porous IX membrane in which a heat-resistant crosslinked polymer was retained on the pore surface.

Subsequently, diacetone acrylamide at the concentration shown in Table 1,
10% in acetone solution containing N-hydroxymethylacrylamide and 0.2% N benzoyl peroxide.
After being immersed for seconds, it was taken out into nitrogen and air-dried for 5 minutes. Subsequently, this porous membrane was heated at 60°C for 60 minutes in a nitrogen atmosphere.
Heat treated for minutes, then water/ethanol 6/50
(Part) Unnecessary components were washed and removed by immersing the sample in a mixed solvent for 10 minutes and then ultrasonically cleaning it in warm water for 2 minutes.

Next, the solvent was removed by hot air drying to obtain a porous membrane in which the crosslinked polymer was retained.

The polymer retention amount, breaking elongation, water permeability, water permeability pressure and heat shrinkage rate of the porous membrane thus obtained were measured.
Shown in the table. Furthermore, when the condensed water of the water vapor used to measure the heating shrinkage rate was evaluated using UV absorbance, no eluted components were detected.

Examples 6 to 8 Using the same porous membrane as in Example 1, heat-resistant crosslinked polymers were retained in the same manner as in Examples 1 to 3. Subsequently, maleic anhydride, divinylbenzene and o at the concentrations shown in Table 1,
After immersing it in an acetone solution containing 2 mt% benzoyl peroxide for 10 seconds, it was air-dried at room temperature for 30 minutes to volatilize the acetone, and then heated in a nitrogen atmosphere at 60°C for 60 minutes to polymerize the monomers. A porous membrane was obtained in which a crosslinked polymer was retained on the pore surface. Subsequently, these porous membranes were hydroxylated.) They were immersed in an ethanol solution with an IJium concentration of 0.1 N for 3 hours, and then washed in running water for 30 minutes.

The properties of the porous membrane thus obtained were measured and are shown in Table 1. Further, when the condensed water of the water vapor used for measuring the heat shrinkage rate was evaluated using a UV absorption photometer, no eluted components were detected.

Examples 9 and 10 As a porous membrane, the porosity was 70%, the membrane thickness was 55 μm, and the inner diameter was 2
70 μm, breaking elongation 43%, heat shrinkage 45%, water permeability 5. A porous hollow fiber membrane made of polyethylene having a water permeability of 4.51/i-hr-111H/ by an alcohol hydrophilization method was used.

While continuously supplying this porous membrane, styrene and divinylbenzene at the concentrations shown in Table 1 and a concentration of 0.2:3 ('
After immersing for 12 seconds in an acetone solution containing M% bis-(4-1-butylcyclohexyl)beroxydicarbonate ((11 Nouri Co., Ltd.!!! Berkadox 16)), One seven-mer was run for 100 minutes in a heating box at 85°C with nitrogen flowing at a flow rate.
A porous membrane with a heat-resistant crosslinked polymer retained on the pore surface was obtained. Subsequently, while continuously feeding this porous membrane, diacetone acrylamide, N-hydroxymethyl acrylamide at the concentrations shown in Table 1, and bis-(4-t-butylcyclohexyl) peroxycarbonate (at a concentration of 0.2 Nt%) were added. VARCADOX 1 manufactured by Kayaku Nouri Co., Ltd.
6) After being immersed in an acetone solution for 12 seconds,
The acetone was air-dried by running for 1 minute in a box with nitrogen flowing at a flow rate of 1017 min, then 3 / / m1
The heptamers were polymerized by running for 2 minutes in a heated box at 80° C. through which nitrogen was flowing at a flow rate of n. Next, this hollow fiber membrane was washed by running it in a tank containing a mixed solvent of water/ethanol = 50,750 parts for 1 minute, then running it in a water tank with overflowing hot water at 60°C for 5 minutes, and then running it in a hot air atmosphere. The heat-resistant hydrophilized porous membrane of the present invention was obtained by drying the membrane.

The properties of the porous membrane thus obtained are shown in Table 1.

Example 11 Styrene and divinylbenzene were polymerized in the same manner as in Example 10 using the same porous membrane as in Example 10. Subsequently, this porous membrane was continuously fed with divinylbenzene at the concentrations shown in Table 1, maleic anhydride, and a concentration of 0.2.
! i% of bis=(4-t-butylcyclohexyl) peroxydicarbonate (Parryoku Dox 16 manufactured by Kayaku Nouri Co., Ltd.) was immersed in an acetone solution for 12 seconds, and then nitrogen was added at a flow rate of 31/min. ℃8
The mixture was run in a heated box at 5° C. for 5 minutes to polymerize the heptamers to obtain a porous membrane in which the crosslinked polymer was retained on the pore surface.

These porous membranes were then treated with sodium hydroxide at a concentration of 0.
．． The porous membrane of the present invention was obtained by immersing it in a 5N ethanol/water (95/5 vol. 1%) mixed solution for 5 minutes and washing it in water for 30 minutes.

The properties of the porous membrane thus obtained are shown in Table 1.

Example 12 In Example 11, di-n-butyl 7malate was used in the amount shown in Table 1 in place of maleic anhydride (b'), and the rest was the same as in Example 11. I got the result.

Comparative Example 1 A porous membrane holding a crosslinked polymer of styrene and divinylbenzene was obtained in the same manner as in Example 1, and its characteristics were evaluated.
Obtained the results in the table. The permeability pressure of this membrane is 10 kg/crn
”It was very thick.

Comparative Example 2 A porous membrane in which a hydrophilic crosslinked polymer was retained was obtained in the same manner as in Example 1 except that the step of retaining the heat resistant crosslinked polymer in Example 1 was not carried out. This porous membrane had a low permeability pressure, but a high heat shrinkage rate of 25%.

〔Effect of the invention〕

The porous membrane of the present invention has hydrophilic properties and has significantly lower water permeability pressure than untreated polyethylene or polypropylene porous membranes. Furthermore, even after steam treatment at 121° C., the shrinkage rate is small (there is almost no change in shape) and it has excellent heat resistance.

According to the method of the present invention, heat resistance and hydrophilicity can be imparted to a polyethylene or polypropylene porous membrane.

The porous membrane of the present invention can be applied to membrane separation applications that require steam sterilization, such as in the medical, food, and fermentation industries.
It can be applied to high-temperature water treatment such as polysaccharide purification and condensate treatment at power plants. It can also be applied to cell culture, non-preneant chromatography, and protein adsorption.

Claims (1)

[Scope of Claims] 1) A crosslinked polymer consisting of one or more polymerizable monomers consisting of styrene or α-methylstyrene and divinylbenzene is retained on the surface of at least a portion of a porous membrane consisting of polyethylene or polypropylene. A heat-resistant, hydrophilic porous membrane further comprising a hydrophilic crosslinked polymer made of monomers including a hydrophilic monomer and a crosslinkable monomer. 2) The heat-resistant hydrophilized porous membrane according to claim 1, wherein the hydrophilic monomer is diacetone acrylamide. 3) The heat-resistant hydrophilic porous membrane according to claim 1, wherein the hydrophilic monomer is a monomer having two carboxyl groups. 4) thermally polymerizing one or more polymerizable monomers such as styrene and α-methylstyrene and monomers containing divinylbenzene while retaining them on the surface of at least a portion of a porous membrane made of polyethylene or polypropylene;
A method for producing a heat-resistant hydrophilic porous membrane, which comprises then thermally polymerizing monomers including a hydrophilic monomer and a crosslinking monomer while retaining them on at least a portion of the surface of the porous membrane.