JPH04358529A - Heat-resistant hydrophilic porous membrane and preparation thereof - Google Patents

Abstract

PURPOSE:To adapt a porous membrane composed of polyolefin to a use necessary for heat, treatment such as steam sterilization in the medical industry, the food industry or the fermentation industry or a use at high temp. such as high temp. water treatment in the purification of polysaccharides or the condensed water treatment of a paper plant. CONSTITUTION:A crosslinkable monomer capable of forming a heat-resistant crosslinked polymer is polymerized and crosslinked on the surfaces of the pores of a polyolefin porous membrane and a saponified ethylene/vinyl acetate copolymer is further applied to said membrane for the purpose of hydrophilic treatment.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a porous membrane made of polyolefin that has excellent hydrophilicity and heat resistance and is suitable for precision filtration of aqueous liquids, and a method for producing the same.

0002

BACKGROUND OF THE INVENTION In recent years, with the development of industry, various separation membranes have been used in various fields such as water purification, blood treatment, air purification, and the food industry. For example, porous membranes made of polyolefins such as polyethylene are used as precision filtration membranes to obtain highly purified water or highly clean air. They are inexpensive, have excellent chemical resistance, and have physical properties such as strength, elongation, and flexibility. It is especially frequently used because it is excellent in terms of. The scope of application of precision filtration membranes is increasing, and use at high temperatures of about 80 to 95° C. is strongly desired, for example, in purification of condensate in nuclear power generation. On the other hand, depending on the application, such as when used in the food industry or blood processing, microfiltration membranes cannot be allowed to be contaminated with microorganisms such as bacteria or mold, and the membrane must not be sterilized. administered. Sterilization methods used include treatment with chemicals such as ethylene oxide, formalin, and hydrogen peroxide, irradiation with radiation such as gamma rays, and steam heating, which are effective and simple. The steam heating method, which usually employs conditions of about 121° C. for 30 minutes, is most useful.

However, porous membranes made of polyolefins such as polyethylene have significant thermal shrinkage, and when these porous membranes are heat-treated at high temperatures or used at high temperatures, their morphology changes and water or air permeability becomes extremely low. In many cases, the function as a separation membrane deteriorates.

On the other hand, since polyolefin porous membranes are hydrophobic, water cannot pass through them as they are, so when used for the treatment of aqueous liquids (water or water-based solutions), alcohol, etc. It is necessary to use the polyolefin porous membrane after making it hydrophilic using a hydrophilic agent, and the polyolefin porous membrane that has been made hydrophilic with alcohol etc. has problems such as losing its hydrophilicity once it is dried.

[0005] In an attempt to solve the problems of porous membranes made from these polyolefins, Japanese Patent Laid-Open No. 6
No. 2-33878 proposes a method for improving heat resistance by forming a heat-resistant polymer thin film having a crosslinked structure on the surface of a polyolefin hollow fiber membrane. Furthermore, as a method for imparting hydrophilicity, JP-A-56-57836 discloses a method of introducing sulfone groups into a polyethylene porous membrane to impart hydrophilicity, and JP-A-61-125408 discloses a method for imparting hydrophilicity to polyolefin porous membranes. After forming the ethylene-vinyl acetate copolymer on the inner surface of the micropores of the porous hollow fiber membrane,
A method of imparting hydrophilicity by saponification and a method of imparting hydrophilicity by retaining an ethylene-vinyl alcohol copolymer in a polyolefin porous membrane are proposed in JP-A-61-271003. ing.

[0006]

[Problems to be Solved by the Invention] However, these publications only disclose techniques for improving either hydrophilicity or heat resistance; The technique for applying it is unknown.

The object of the present invention is to provide a polyolefin porous membrane that has hydrophilicity suitable for treating aqueous liquids and heat resistance that enables heat treatment such as steam sterilization and use at high temperatures, and a method for producing the same. It is about providing.

[0008]

[Means for Solving the Problems] The heat-resistant hydrophilized porous membrane of the present invention comprises a polyolefin porous membrane, a heat-resistant crosslinked polymer held on the pore surface of the polyolefin porous membrane,
It is characterized by comprising a saponified product of ethylene-vinyl acetate copolymer held on the heat-resistant crosslinked polymer.

The polyolefin porous membrane used as a base material in the present invention includes polyethylene, polypropylene, a copolymer mainly composed of ethylene or propylene, or a fluorinated product thereof, poly-4-methyl-1-
Polyolefin polymers and copolymers such as pentene and poly-3-methyl-1-butene can be used.

As the polyolefin porous membrane, any form such as a hollow fiber membrane, flat membrane, or tubular membrane can be used, and membranes with various pore diameters can be used depending on the purpose. As a preferable example, the film thickness is approximately 20~
Approximately 200 μm, porosity is approximately 20 to 90%, water permeability by alcohol hydrophilization method is approximately 0.001 to 10 liters/m2・hr・mmHg, and average pore diameter is 0.
Examples include those having a diameter of about 0.01 to 5 μm.

[0011] The porous membrane has a pore structure obtained by various methods, including a method of melt-forming and then stretching, and a method of mixing inorganic substances or esters and extracting contaminants after melt-forming. Among them, a porous membrane obtained by a method of melt-forming and then stretching is preferably used because it has a large porosity and is less susceptible to deterioration in performance due to clogging. A porous membrane produced by melt-forming and then stretching is a porous membrane that has a pore structure in which slit-like micro spaces (pores) formed by microfibrils and knots are three-dimensionally interconnected. For example, it can be produced by the method described in Japanese Patent Publication No. 56-52123, Japanese Patent Application Laid-Open No. 57-42919, etc.

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

[0013] The amount of the heat-resistant crosslinked polymer retained on the pore surface depends on the type of crosslinking monomer, the porosity and pore diameter of the porous membrane, but it is preferably is about 5 to 50% by weight, more preferably 20 to 50% by weight.
It is considered to be a degree. If the amount of the heat-resistant crosslinked polymer retained is less than about 5% by weight, sufficient heat resistance cannot be imparted to the porous membrane, and even if it exceeds about 50% by weight, the heat resistance of the porous membrane will be reduced. This is not preferable because the pore volume may be reduced and the fluid permeation performance may be lowered without any improvement.

[0014] This heat-resistant crosslinked polymer is preferably retained on all of the pore surfaces of the porous polyolefin membrane, but it is not necessarily necessary that it is retained on all of the pore surfaces; It is sufficient that the pore size is such that water can pass therethrough depending on the transmembrane pressure difference used, and that the heat resistance is substantially improved. In addition,
The heat-resistant crosslinked polymer may be held so as to cover the surface of the pores of the porous membrane.

Examples of heat-resistant crosslinked polymers include trimethacrylates such as trimethylolpropane trimethacrylate and pentaerythritol trimethacrylate; tetramethacrylates such as pentaerythritol tetramethacrylate; ethylene glycol dimethacrylate;
, 3-butylene glycol dimethacrylate, triethylene glycol trimethacrylate, glycerol dimethacrylate; or crosslinked polymers obtained from crosslinkable monomers such as divinylbenzene. A combined crosslinked copolymer may also be used.

[0016] The saponified product of ethylene-vinyl acetate copolymer, which is further retained on the heat-resistant cross-linked polymer retained on the pore surface of the porous membrane, has a hydrophilicity imparting effect and an effect on the heat-resistant cross-linked polymer. An optimal composition is used in consideration of adhesion, but usually one with a saponification rate of about 60 mol% or more and an ethylene unit content of about 20 to 70 mol% can be used. Note that this saponified product may be directly retained on the surface of the pores of the porous membrane where the heat-resistant crosslinked polymer is not retained. The retained amount of this saponified material is determined as appropriate in consideration of the hydrophilicity and water permeability that should be imparted to the heat-resistant hydrophilic porous membrane;
It may be about 20% by weight, and more preferably about 2 to 15% by weight.

[0017] In the present invention, "retained" means that the heat-resistant crosslinked polymer or the above-mentioned saponified material is firmly bonded or adhered to a predetermined site to the extent that it does not easily detach during storage or use. However, these may be chemically bonded to a predetermined site, or may be closely attached to a predetermined site by an anchor effect, or may be held by a chemical bond or an anchor effect. In particular, if a porous membrane made porous by the above-mentioned stretching method is used,
A polymer is formed to wrap around the microfibrils,
Further, since the saponified material adheres thereon and can firmly hold them, it is preferable to use a porous membrane made porous by a stretching method.

Next, a method for manufacturing the porous membrane imparted with hydrophilicity and heat resistance according to the present invention will be described, but the manufacturing method is not limited to the following method. A typical manufacturing method includes a method in which a crosslinking monomer is polymerized while being retained on the pore surface of a polyolefin porous membrane, and then a saponified product of ethylene-vinyl acetate copolymer is further retained.

As a method for retaining the crosslinking monomer on the surface of the porous membrane, for example, a monomer solution in which the monomer is dissolved is prepared, and the porous membrane is immersed in the solution.
Alternatively, a method can be adopted in which the monomer solution is supplied into the pores of the porous membrane by pressurizing the monomer solution, and then the solvent is evaporated and removed from the porous membrane. The monomer solution may contain a polymerization initiator, a polymerization modifier, a stabilizer, etc. as necessary. By using a holding solution diluted with a solvent, the crosslinking monomer can be almost uniformly deposited over the entire porous membrane without blocking the pores of the porous membrane. Note that the amount of the crosslinkable monomer attached can be adjusted by changing the concentration of the crosslinkable monomer in the monomer solution and the immersion time.

[0020] As a solvent for preparing the monomer solution, an organic solvent having a boiling point lower than that of the crosslinking monomer and capable of dissolving the crosslinking monomer is used.
When using a polymerization initiator, it is preferable to use a solvent that can also dissolve these. Examples of such organic solvents include alcohols such as methanol, ethanol, propanol, and isopropanol; ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; ethers such as tetrahydrofuran and dioxane; ethyl acetate; and chloroform. . Although the boiling point of the organic solvent is not particularly limited, it is preferably about 100°C or less, more preferably about 80°C or less, considering that the solvent can be easily removed before and during the polymerization process.

[0021] The composition of the monomer solution may be appropriately selected in consideration of the type of solvent and the target amount of crosslinked polymer retained.
~10,000 parts by weight may be sufficient, and 200 to 500 parts by weight.
More preferably, it is about 0 parts by weight. When dipping or press-fitting a porous membrane using a monomer solution, the dipping time or press-fitting time is about 0.5 seconds to 30 minutes, and a monomer solution with good wetting properties for the porous membrane is used. The more you can do it, the faster it can be done. When the dipping treatment and the press-in treatment are completed, the excess monomer solution is removed from the porous membrane, and if necessary, the solvent of the monomer solution is evaporated from the porous membrane, and then the polymerization step is performed. Note that polymerization may be carried out simultaneously while removing the solvent. In this polymerization step, a heat-resistant crosslinked crosslinked polymer is formed and held there by a reaction between a crosslinkable monomer held on at least a portion of the surface of the porous pores and an optional polymerization initiator.

Various polymerization methods such as thermal polymerization, photopolymerization, and radiation polymerization can be used to polymerize the crosslinkable monomer, and known polymerization initiators can be used. In the case of photopolymerization, ultraviolet rays or visible light can be used as the light source for light irradiation.
Low-pressure mercury lamps, high-pressure mercury lamps, xenon lamps, arc lamps, etc. can be used. Furthermore, radiation polymerization can be carried out using, for example, an electron beam irradiation device. In the case of a thermal polymerization method, the polymerization temperature is desirably higher than the decomposition temperature of the polymerization initiator and lower than the temperature that does not change the membrane structure of the porous membrane and damage the membrane substrate; A temperature of about 30 to 100°C can be adopted. In addition, during these polymerizations, the presence of oxygen in the atmosphere will significantly inhibit the polymerization reaction, so it is preferable 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. . After the cross-linked polymer is formed, the pore surface and outer surface (in the case of hollow fiber membranes and tubular membranes, the inner surface It is desirable to remove unnecessary components such as unreacted monomers and liberated polymers present on the wall and outer wall surface.

The porous membrane holding the heat-resistant crosslinked polymer is then transferred to a step of holding a saponified product of ethylene-vinyl acetate copolymer. As the ethylene-vinyl acetate copolymer used to form the saponified product, various types such as random, block, and graft can be used, and the type of the saponified product also depends on the type of the ethylene-vinyl acetate copolymer. The ethylene-vinyl acetate copolymer is basically formed from ethylene and vinyl acetate, but other monomer components may be mixed within a range that does not impair the desired properties.

The content of ethylene units in the ethylene-vinyl acetate copolymer is determined in order to obtain good adhesion to the crosslinked polymer of the ethylene-vinyl acetate copolymer or its saponified product and to the pore surface of the porous membrane. This is important, and from the viewpoint of adhesion, its content is preferably 20 mol% or more. That is, if the content of ethylene units is less than 20 mol%, when the ethylene-vinyl acetate copolymer or its saponified product is applied, good adhesion to the deposit cannot be obtained, and the deposit may peel off. This is not preferable because it is more likely to occur. on the other hand,
If the content of ethylene units is too large, it is not preferable because the saponified product ultimately obtained will not have a good effect of imparting hydrophilicity to the porous membrane. Therefore, the content of ethylene units is preferably 70 mol% or less. Considering a better balance between adhesion and hydrophilicity, it is particularly preferable that the content of ethylene units is in the range of 25 to 50 mol%. In addition, the content of vinyl acetate units in the ethylene-vinyl acetate copolymer is preferably 20% by weight or more in order to obtain a good hydrophilicity imparting effect by the saponified product finally obtained, but the upper limit thereof is is preferably adjusted so that the content of ethylene units is within the above range.

The ethylene-vinyl acetate copolymer can be saponified by a known method such as heat treatment in an aqueous alkaline solution such as sodium hydroxide for a necessary period of time. This saponification treatment converts the acetyl group of the vinyl acetate moiety into a hydroxyl group, thereby imparting better hydrophilicity. The saponification rate may be about 60 mol% or more.

Retention of the saponified product can be carried out by directly retaining the saponified product or by retaining the ethylene-vinyl acetate copolymer and then saponifying it. In order to directly retain the saponified product, ① A method of supplying a retaining solution containing the saponified product into at least the pores of the base hollow fiber membrane by a method such as dipping or coating, and removing the solvent of the solution by evaporation. , and (2) supplying a retaining solution containing a saponified substance into the pores of the base hollow fiber membrane by dipping, coating, etc., and further immersing it in a coagulant solution of the saponified substance; rapidly solidifying at least on the inner surface of the pores;
This can be done by a method such as drying.

The holding solution can be prepared by dissolving the sapon in a solvent that can dissolve it. As the solvent, a water-miscible organic solvent or a mixture of a water-miscible organic solvent and water can be used. Examples of water-miscible organic solvents include alcohols such as methanol, ethanol, n-propanol, isopropanol, sec-butanol, t-butanol, and cyclohexanol; ethylene glycol,
Polyhydric alcohols such as propylene glycol and glycerin; examples include tetrahydrofuran, dioxane, dimethylformamide, dimethyl sulfoxide, dimethylacetamide, formamide, ethylene chlorohydrin, etc., and one type or a combination of two or more thereof can be used. Among these, ethanol and dimethyl sulfoxide are particularly preferred because they have good solubility in saponified products and low toxicity.

[0028] As the solvent, a mixture of a water-miscible organic solvent and water is particularly preferred for the following reasons. In other words, saponified products are composed of non-polar and hydrophobic ethylene units and polar and hydrophilic vinyl acetate units (including those whose acetyl groups have been converted to hydroxyl groups through saponification); Above, when this solution is dissolved in a highly polar solvent system and coated on a non-polar base material surface such as a pore surface made of a cross-linked polymer or polyolefin, the non-polar surface in the thin film layer of saponified material that is formed. It is thought that non-polar ethylene units are localized on the side surface, and polar vinyl acetate units are likely to be localized on the opposite surface (on the opposite side to the base material surface). This phenomenon occurs because the adhesion between the thin layer of saponified material and the crosslinked polymer or polypropylene that makes up the pore surface is improved, and the hydrophilicity of the surface of the thin layer of saponified material held on top of these is improved. This is a favorable phenomenon. Therefore, it is preferable to use a mixture of water and an organic solvent as the solvent for the above-mentioned holding solution, since this makes the polarity of the solvent stronger and promotes this phenomenon. The ratio of water to be mixed is preferably as large as possible within a range that does not inhibit the solubility of the saponified product, and the ratio varies depending on the concentration of the saponified product, the content of its ethylene moiety, the treatment temperature, etc., but for example, A preferable range is 60% by weight.

[0029] The concentration of the saponified substance in the above-mentioned holding solution is set to a level necessary to obtain the desired hydrophilic effect,
It is selected in consideration of the physical properties of the polyolefin porous membrane as a base material, and is preferably used in a range of 0.1 to 5.0% by weight, for example. The treatment by dipping or coating the porous membrane in the retention solution may be completed in one treatment, but it may be carried out in several steps using a retention solution with a relatively low concentration of saponified substances. It's okay. Note that the saponified product concentration is 5.
If it exceeds 0% by weight, the amount of saponified substances deposited becomes too large, which may narrow the diameter of the porous membrane as a base material and reduce liquid permeation performance, which is not preferable. The amount of saponified material retained is determined as appropriate by considering the hydrophilicity and water permeability that should be imparted to the heat-resistant hydrophilized porous membrane, but it is 1 to 20% by weight relative to the porous membrane before retaining the heat-resistant crosslinked polymer. %, and more preferably about 2 to 15% by weight.

[0030]Although the temperature of the holding solution is not particularly limited, generally the higher the temperature, the better the solubility of the saponified material is.
It is preferable because the viscosity of the solution also decreases, for example, from room temperature to 1
A range up to 00°C is preferred. In the case of dipping treatment, the dipping time is preferably in the range of several seconds to several tens of minutes. The solvent can be removed from the holding solution held in the pores of the porous polyolefin membrane as a base material by vacuum drying, hot air drying, or the like. The degree of drying may be at a temperature at which the base material is not deformed by heat, and is preferably 100° C. or lower.

On the other hand, saponification of the ethylene-vinyl acetate copolymer held in a porous membrane can be carried out, for example, by the following method.

First, ethylene- Retain vinyl acetate copolymer. The content of ethylene units and vinyl acetate units in the ethylene-vinyl acetate copolymer is preferably within the range described above. As the solvent for the solution for holding the ethylene-vinyl acetate copolymer, those for preparing the solution for holding the saponified product mentioned above can be used. The concentration of the ethylene-vinyl acetate copolymer in the holding solution is preferably 1.0 to 5.0% by weight, for example. Treatments such as dipping and coating for retaining the ethylene-vinyl acetate copolymer may be completed in one go, or may be carried out in several stages using a retaining liquid of relatively low concentration. . If the amount is less than 1.0% by weight, sufficient hydrophilicity cannot be obtained after the saponification treatment, so it is not preferable to complete the treatment at once. Moreover, if it exceeds 5.0% by weight, it is not preferable because it often narrows the diameter of the pores of the polyolefin porous membrane as a base material and reduces the liquid permeation performance. The amount of the ethylene-vinyl acetate copolymer retained is preferably adjusted so that the amount of the saponified product ultimately obtained falls within the range mentioned above.

By saponifying the porous membrane holding the ethylene-vinyl acetate copolymer in this manner, the heat-resistant hydrophilic porous membrane of the present invention can be obtained. This saponification treatment can be carried out, for example, by heating the porous membrane in an alkaline aqueous solution such as an aqueous sodium hydroxide solution for a necessary period of time. After the saponification treatment is completed, washing, deliquification, and drying steps are performed to obtain the heat-resistant hydrophilic porous membrane of the present invention. The drying temperature and time are set so as not to change the pore structure of the porous membrane.

Although each step has been explained separately above, in the present invention these steps can be performed continuously.

[0035]

[Examples] The present invention will be specifically explained below with reference to Examples. In addition, in the examples, porous membranes in which slit-like spaces (pores) formed by microfibrils and knots that are obtained by melt-forming and stretching are three-dimensionally connected are used as porous membranes. Using.

Example 1 A polyethylene porous hollow fiber membrane with an inner diameter of 270 μm, a membrane thickness of 79 μm, a porosity of 63%, a bubble point of 4.4 kg/cm2, and a water permeability of 1.5 liters/m2/hr/mmHg was threaded. It was fed into the monomer solution at a speed of 1 m/min and immersed for about 20 seconds. The composition of the monomer solution was 15 parts by weight of acrylic ester TMP (trade name, manufactured by Mitsubishi Rayon Co., Ltd., trimethylolpropane trimethacrylate), Pdx-16 (trade name, Kayaku Akzo (trade name)) as a polymerization initiator.
Co., Ltd.) and 8.5 parts by weight of acetone. Next, this hollow fiber membrane was kept in a nitrogen gas atmosphere at 80° C. for 6 minutes to remove acetone and polymerize the monomer. After the polymerization process, ethanol/
1 minute in water = 50/50 (weight ratio), then 60°C
Wash the hollow fiber membrane by immersing it in water for 5 minutes,
Further, it was dried for 4 minutes in an air atmosphere at 80°C.

[0037] The hollow fiber membrane in which the heat-resistant crosslinked polymer thus obtained was held on the pore surface was heated at a thread speed of 1 m/min.
Soarnol A4412 (trade name, manufactured by Nippon Gosei Kagaku Kogyo Co., Ltd., saponification rate of 98% or more, ethylene content 44 mol%), which is a saponified product of ethylene-vinyl acetate copolymer.1.
3 parts by weight, 75 parts by weight of ethanol, and 25 parts by weight of water so that the immersion time was 20 seconds, and then the sample was taken up into an atmosphere at 60° C. and left there for 4 minutes.

The obtained hollow fiber membrane exhibited the performance shown in Table 1. No. When the hollow fiber membrane was immersed in the 54 wet index test standard solution and the coloring state was observed with the naked eye, the entire membrane was almost uniformly stained blue.

Example 2 Acrylic ester TMP (20 parts by weight), Pdx-16
Polymerization was carried out in the same manner as in Example 1 using a monomer solution consisting of (0.2 parts by weight) and acetone (80 parts by weight). The hollow fiber membrane in which the obtained heat-resistant crosslinked polymer was retained on the pore surface was prepared by dissolving 3 parts by weight of ethylene-vinyl acetate copolymer (ethylene content: 44 mol%) in 97 parts by weight of toluene.
After immersing in a solution at 5℃ for 30 seconds, it was dried in a vacuum dryer for 50℃.
The solvent was removed by drying at °C for 30 hours. Next, this was immersed in an alkaline aqueous solution in which 10 g of sodium hydroxide was dissolved in 1 liter of water, saponified at 60°C for 1 hour, washed with water, and dried to make it heat-resistant and hydrophilic with the performance shown in Table 1. A porous membrane was obtained.

Example 3 Soarnol A4412 (1 part by weight), ethanol (75 parts by weight)
A heat-resistant, hydrophilized porous membrane having the performance shown in Table 1 was obtained in the same manner as in Example 1, except that a coating solution consisting of 25 parts by weight) and water (25 parts by weight) was used.

Example 4 A polyethylene porous hollow fiber membrane similar to that used in Example 1 was supplied into a monomer solution having the following composition at a yarn speed of 2 m/min and immersed for about 15 seconds. The composition of the monomer solution is as follows. Acrylic ester TMP
15 parts by weight Polymerization initiator V-70 (trade name, manufactured by Wako Pure Chemical Industries, Ltd.) 0.15 parts by weight Acetone

85 parts by weight Next, this hollow fiber membrane was kept in a nitrogen gas atmosphere at 45°C for 1 minute to remove acetone from the hollow fiber membrane, and then heated at 80°C.
The monomer was polymerized by remaining in the nitrogen gas atmosphere for 2 minutes. After the polymerization step, it was immersed in acetone at 25°C for 4 minutes, subjected to ultrasonic cleaning in that state, and then dried in an air atmosphere at 70°C for 4 minutes.

The hollow fiber membrane with the thus obtained heat-resistant crosslinked polymer retained on the pore surface was heated at a fiber speed of 2 m/min with Soarnol A4412 (1.3 parts by weight) and ethanol (7 parts by weight).
5 parts by weight) and water (25 parts by weight) for an immersion time of 15 seconds, and then lifted into an atmosphere at 60°C and left there for 4 minutes. A thread membrane was obtained.

Example 5 Acryester ED (trade name, manufactured by Mitsubishi Rayon Co., Ltd., ethylene glycol dimethacrylate) (1.5 parts by weight), V-70 (0.15 parts by weight) and acetone (85 parts by weight)
A heat-resistant, hydrophilized porous membrane having the performance shown in Table 1 was obtained in the same manner as in Example 4 except that a monomer solution of (parts by weight) was used.

Example 6 In Example 4, a polyethylene porous material with an inner diameter of 280 μm, a membrane thickness of 70 μm, a porosity of 71%, a bubble point of 2.2 kg/cm 2 , and a water permeability of 2.6 liters/m 2 ·hr · mmHg was used. Hollow fiber membrane (product name: EHF-410T,
Mitsubishi Rayon Co., Ltd.) was used, and Soarnol D2908 was used instead of Soarnol A4412 in the coating solution.
(trade name, manufactured by Nippon Gosei Kagaku Kogyo Co., Ltd., saponified product of ethylene-vinyl acetate copolymer) was prepared in the same manner as in Example 4, except that a heat-resistant hydrophilized porous membrane having the performance shown in Table 1 was used. Obtained.

Example 7 Polyethylene porous hollow fiber membrane (product) with an inner diameter of 270 μm, a membrane thickness of 55 μm, a porosity of 72%, a bubble point of 2.2 kg/cm2, and a water permeability of 4.0 liters/m2/hr/mmHg. A heat-resistant hydrophilized porous membrane having the performance shown in Table 1 was obtained in the same manner as in Example 4, except that a monomer solution having the following composition was used. Monomer solution composition Acryester TMP 7.5
Weight part Acryester ED 7
．． 5 parts by weight Polymerization initiator V-70
0.15 parts by weight acetone
85 parts by weight Example 8 Acryester TMP (15 parts by weight), polymerization initiator V-
Example 4 except that a monomer solution consisting of 70 (0.15 parts by weight), a polymerization degree regulator n-octyl mercaptan (manufactured by Wako Pure Chemical Industries, Ltd.) (0.075 parts by weight), and acetone (85 parts by weight) was used. A heat-resistant hydrophilized porous membrane having the performance shown in Table 1 was obtained in the same manner as in the above.

Comparative Example 1 The performance of the polyethylene porous hollow fiber membrane itself (untreated) used in Example 1 was tested, and the results shown in Table 1 were obtained. Comparative Example 2 In Example 1, the performance of the porous hollow fiber membrane in which the crosslinked polymer was retained before coating was tested, and the results shown in Table 1 were obtained. Comparative Example 3 A polyethylene porous membrane similar to that used in Example 1 was coated with Soarnol A4412 (1.3 parts by weight), ethanol (75 parts by weight), and water (25 parts by weight) at a yarn speed of 1 m/min.
The specimen was supplied into a coating solution consisting of the following for an immersion time of 20 seconds, and then taken up into an atmosphere at 60°C and left there for 4 minutes. The obtained hollow fiber membrane (in which retention of the crosslinked polymer was omitted) exhibited the performance shown in Table 1.

[0047]

[Table 1]

[0048]

[Effects of the Invention] The porous membrane of the present invention retains a heat-resistant crosslinked polymer and a saponified product of ethylene-vinyl acetate copolymer on the pore surface of the polyolefin porous membrane as a base material. It has hydrophilicity and heat resistance. For this reason, the present invention allows porous membranes made of polyolefin to be used in applications that require heat treatment such as steam sterilization in the medical, food, and fermentation industries, as well as in high-temperature water applications such as polysaccharide purification and condensate treatment in power plants. This makes it possible to apply it to applications that require use at high temperatures, such as processing.

Claims (3)

[Claims] 1. A polyolefin porous membrane, a heat-resistant crosslinked polymer held on the pore surface of the polyolefin porous membrane, and an ethylene-polymer held on the heat-resistant crosslinked polymer.
A heat-resistant hydrophilic porous membrane comprising a saponified vinyl acetate copolymer. [Claim 2] Claim 1, wherein the heat-resistant crosslinked polymer is a crosslinked polymer of trimethylolpropane trimethacrylate.
The heat-resistant hydrophilized porous membrane described in . 3. The method according to claim 1, wherein a crosslinkable monomer is crosslinked and polymerized on the pore surface of the polyolefin porous membrane, and then a saponified product of ethylene-vinyl acetate copolymer is held thereon. The method for producing the heat-resistant hydrophilic porous membrane described above.