阅读说明：本技术 亲水性多孔膜及亲水性多孔膜的制造方法 (Hydrophilic porous membrane and method for producing hydrophilic porous membrane ) 是由 石井阳大 梅原健志 于 2020-02-25 设计创作，主要内容包括：本发明提供一种亲水性多孔膜及亲水性多孔膜的制造方法,所述亲水性多孔膜包含多孔膜及保持于上述多孔膜的羟烷基纤维素,其中,上述多孔膜的两个表面彼此的平均孔径不同,在上述亲水性多孔膜的厚度方向上分布的上述羟烷基纤维素在GPC中示出2个以上的检测强度的峰,上述峰中最晚检测出的峰的重均分子量Mw-(min)小于100,000,所述亲水性多孔膜的制造方法包括如下步骤：个别准备包含重均分子量较小的羟烷基纤维素的亲水化液和包含重均分子量较大的羟烷基纤维素的亲水化液,从多孔膜的两面分别进行涂布或从一面依次进行涂布。(The present invention provides a hydrophilic porous membrane comprising a porous membrane and hydroxyalkyl cellulose held by the porous membrane, wherein the average pore diameters of both surfaces of the porous membrane are different from each other, and the hydroxyalkyl cellulose is distributed in the thickness direction of the hydrophilic porous membrane, and a method for producing the hydrophilic porous membraneShows 2 or more peaks of detection intensity in GPC, and the weight average molecular weight Mw of the peak detected at the latest among the peaks min Less than 100,000, the method for manufacturing the hydrophilic porous membrane comprising the steps of: a hydrophilizing liquid containing a hydroxyalkyl cellulose having a small weight average molecular weight and a hydrophilizing liquid containing a hydroxyalkyl cellulose having a large weight average molecular weight are separately prepared and applied from both sides of the porous film or sequentially applied from one side.)

1. A hydrophilic porous membrane comprising a porous membrane and hydroxyalkyl cellulose retained in the porous membrane, wherein,

the two surfaces of the porous membrane have different average pore sizes from each other,

the hydroxyalkyl cellulose distributed in the thickness direction of the hydrophilic porous membrane shows 2 or more peaks of detection intensity in gel permeation chromatography,

the weight average molecular weight Mw of the latest detected peak among the peaks_minLess than 100,000.

2. The hydrophilic porous membrane according to claim 1, wherein,

when the hydrophilic porous membrane is divided into 2 parts A and B with an equal thickness from the surface side with a smaller average pore diameter in the thickness direction,

the detection intensity of the latest detected peak is larger in the gel permeation chromatogram of the hydroxyalkyl cellulose retained in the portion a than in the hydroxyalkyl cellulose retained in the portion B.

3. The hydrophilic porous membrane according to claim 2, wherein,

has a layered compact part with the smallest pore size in the inner part,

the pore diameter continuously increases from the dense site toward at least one membrane surface of the porous membrane in the thickness direction,

the dense site is located in the portion a.

4. The hydrophilic porous membrane according to claim 3, wherein,

the average pore diameter of the dense part is 0.01-5 μm.

5. The hydrophilic porous membrane according to any one of claims 1 to 4, wherein,

the weight average molecular weight Mw of the earliest detected peak among the peaks_maxThe following relationship is satisfied:

30,000≤Mw_max/d_max≤130,000

in the formula (d)_maxThe average pore diameter [ mu m ] of the surface on the side where the average pore diameter of the porous membrane is large]。

6. The hydrophilic porous membrane according to any one of claims 1 to 5, wherein,

the porous membrane comprises polyethersulfone or polysulfone.

7. The hydrophilic porous membrane according to any one of claims 1 to 6, wherein,

the hydroxyalkyl cellulose is hydroxypropyl cellulose.

8. The hydrophilic porous membrane according to any one of claims 1 to 7, wherein,

the total mass of the hydroxyalkyl cellulose is 0.02-3% by mass relative to the total mass of the porous film.

9. A method for producing a hydrophilic porous membrane comprising a porous membrane and hydroxyalkyl cellulose retained in the porous membrane, the production method comprising the steps of:

preparing two porous membranes with different surface average pore sizes;

coating a hydrophilizing liquid containing hydroxyalkyl cellulose having a large weight average molecular weight on the surface side of the porous membrane having a large average pore diameter; and

a hydrophilization solution containing hydroxyalkyl cellulose having a small weight average molecular weight is applied to the surface side of the porous membrane having a small average pore diameter.

10. A method for producing a hydrophilic porous membrane comprising a porous membrane and hydroxyalkyl cellulose retained in the porous membrane, the production method comprising the steps of:

preparing the porous membrane having different average pore diameters on both surfaces; and

the porous membrane is coated with a hydrophilizing liquid containing a hydroxyalkyl cellulose having a smaller weight average molecular weight on the surface side having a larger average pore diameter, and then coated with a hydrophilizing liquid containing a hydroxyalkyl cellulose having a larger weight average molecular weight on the same surface side.

11. The manufacturing method according to claim 9 or 10,

the smaller the weight average molecular weight is less than 100,000.

12. The manufacturing method according to any one of claims 9 to 11,

the concentration of the hydroxyalkyl cellulose in the hydrophilization solution containing hydroxyalkyl cellulose is 0.005 to 0.5 mass%.

Technical Field

The present invention relates to a hydrophilic porous membrane and a method for producing the hydrophilic porous membrane.

Background

Porous membranes made of polymers are industrially useful as filtration membranes for water purification and the like, and are also commercially available as pleated sleeves which are collected in a certain volume. Typically, integrity tests are performed on the filter cartridge in order to identify the presence or absence of defects such as pin holes or poor seals. In the integrity test, air pressure was applied and gas leakage was observed after water was passed through a filter membrane installed in a filter to fill pores with water. In this case, if the filter membrane is not wetted with water and has pores that are not blocked with water, gas leaks even if there is no defect when pressure is applied, and the presence or absence of a defect (integrity) cannot be determined. That is, if the filtration membrane is hydrophobic, it is difficult to accurately confirm the presence or absence of defects by an integrity test. Therefore, hydrophilization of porous membranes using hydrophilic polymers has been carried out.

Patent document 1 discloses a microfiltration porous membrane that is obtained by adding a hydrophilic polymer to a polyethersulfone membrane and that can be subjected to autoclave sterilization treatment. In the production of the microfiltration porous membrane described in patent document 1, hydroxypropyl cellulose having a molecular weight of 110,000 to 150,000 is used as the hydrophilic polymer.

Patent document 2 describes a method for pleating a filter in which a polyethersulfone membrane as an anisotropic porous membrane is hydrophilized with hydroxypropyl cellulose.

Prior art documents

Patent document

Patent document 1: japanese patent laid-open publication No. 2003-251152

Patent document 2: japanese laid-open patent publication No. 2006-116383

Disclosure of Invention

Technical problem to be solved by the invention

In the anisotropic porous film having a pore size distribution, hydrophilization of a portion having a small pore size is insufficient or clogging is easily caused, and the hydrophilization methods described in patent documents 1 and 2 still have room for improvement.

The invention provides a hydrophilic porous membrane and a method for producing the same. In particular, an object of the present invention is to provide a hydrophilic porous membrane that can pass an integrity test and has high water permeability when used as a filtration membrane of a filter cartridge, and a method for producing the same.

Means for solving the technical problem

The present inventors have conducted intensive studies to solve the above problems, and found that a hydrophilic porous membrane produced by using a combination of a hydroxyalkyl cellulose having a weight average molecular weight of less than 100,000 and a hydroxyalkyl cellulose having a larger weight average molecular weight provides accurate results by sufficient hydrophilicity in an integrity test, and has high water permeability, thereby solving the above problems.

Namely, the present invention provides the following <1> to <12 >.

<1> a hydrophilic porous membrane comprising a porous membrane and hydroxyalkyl cellulose retained on the porous membrane, wherein,

the two surfaces of the above porous film have different average pore diameters from each other,

the hydroxyalkyl cellulose distributed in the thickness direction of the hydrophilic porous membrane shows 2 or more peaks of detection intensity in gel permeation chromatography,

the weight average molecular weight Mw of the peak detected at the latest among the above peaks_minLess than 100,000.

<2> the hydrophilic porous membrane according to <1>, wherein,

when the hydrophilic porous membrane is divided into 2 parts A and B with a uniform thickness from the surface side having a small average pore diameter in the thickness direction,

the hydroxyalkyl cellulose retained in the portion a has a higher detection intensity of the peak detected at the latest in a gel permeation chromatogram than the hydroxyalkyl cellulose retained in the portion B.

<3> the hydrophilic porous membrane according to <2>, wherein,

has a layered compact part with the smallest pore size in the inner part,

the pore diameter continuously increases from the dense portion toward at least one membrane surface of the porous membrane in the thickness direction,

the dense site is located in the portion A.

<4> the hydrophilic porous membrane according to <3>, wherein,

the dense part has an average pore diameter of 0.01 to 5 μm.

<5> the hydrophilic porous membrane according to any one of <1> to <4>, wherein,

the weight average molecular weight Mw of the peak detected earliest among the above peaks_maxThe following relationship is satisfied:

30,000≤Mw_max/d_max≤130,000

in the formula (d)_maxThe average pore diameter [ μm ] of the surface on the side where the average pore diameter of the porous membrane is larger than that of the porous membrane]。

<6> the hydrophilic porous membrane according to any one of <1> to <5>, wherein,

the porous membrane contains polyethersulfone or polysulfone.

<7> the hydrophilic porous membrane according to any one of <1> to <6>, wherein,

the hydroxyalkyl cellulose is hydroxypropyl cellulose.

<8> the hydrophilic porous membrane according to any one of <1> to <7>, wherein,

the total mass of the hydroxyalkyl cellulose is 0.02 to 3% by mass relative to the total mass of the porous film.

<9> a method for producing a hydrophilic porous membrane comprising a porous membrane and hydroxyalkyl cellulose retained by the porous membrane, the method comprising the steps of:

preparing the porous film having different average pore diameters on both surfaces;

applying a hydrophilizing solution containing hydroxyalkyl cellulose having a large weight average molecular weight to the surface side of the porous membrane having a large average pore diameter; and

a hydrophilization solution containing hydroxyalkyl cellulose having a small weight average molecular weight is applied to the surface side of the porous membrane having a small average pore diameter.

<10> a method for producing a hydrophilic porous membrane comprising a porous membrane and hydroxyalkyl cellulose retained by the porous membrane, the method comprising the steps of:

preparing the porous film having different average pore diameters on both surfaces; and

the porous membrane is coated with a hydrophilizing solution containing a hydroxyalkyl cellulose having a small weight average molecular weight on the surface side having a large average pore diameter, and then coated with a hydrophilizing solution containing a hydroxyalkyl cellulose having a large weight average molecular weight on the same surface side.

<11> the production method according to <9> or <10>, wherein,

the smaller of the above weight average molecular weights is less than 100,000.

<12> the production method according to any one of <9> to <11>, wherein,

the concentration of the hydroxyalkyl cellulose in the hydrophilization solution containing hydroxyalkyl cellulose is 0.005 to 0.5 mass%.

Effects of the invention

The present invention provides a hydrophilic porous membrane and a method for producing the same. The hydrophilic porous membrane of the present invention can be defect-inspected by an integrity test of the filter cartridge and has high water permeability.

Drawings

Fig. 1 is a view showing a cross-sectional view (photograph) of a porous membrane used in an example of the present invention.

Detailed Description

The present invention will be described in detail below.

In the present specification, "-" is used in the meaning including numerical values described before and after the term "lower limit value" and numerical values described after and after the term "upper limit value".

< hydrophilic porous Membrane >

In the present specification, the hydrophilic porous membrane refers to a membrane in which a porous membrane as a base is hydrophilized. The hydrophilic porous membrane refers to a membrane in which hydrophilicity is increased by retaining hydroxyalkyl cellulose relative to a porous membrane as a substrate, and does not mean that the porous membrane as a substrate is completely hydrophobic.

The hydrophilic porous membrane is a membrane having a plurality of pores. The pores can be confirmed by, for example, a Scanning Electron Microscope (SEM) image or a Transmission Electron Microscope (TEM) image of the cross section of the film.

The hydrophilic porous membrane of the present invention comprises a porous membrane and hydroxyalkyl cellulose retained in the porous membrane.

The term "held in the porous membrane" means that the hydrophilic porous membrane is bonded to the porous membrane to such an extent that the hydrophilic porous membrane is not easily peeled off during storage or use. The porous membrane and the hydroxyalkyl cellulose may also be bonded to each other by, for example, hydrophobic interaction.

When the porous film to be a substrate is hydrophilized with hydroxyalkyl cellulose, the hydroxyalkyl cellulose is usually held in a state of covering at least a part of the outer surface of the porous film. In the present specification, the outer surface of the porous membrane refers to the membrane surface (front or back surface of the membrane) of the porous membrane and the surface of the porous membrane facing each pore inside the porous membrane (in the present specification, it may be referred to as "pore surface"). In the hydrophilic porous membrane of the present invention, the membrane surface (both the front surface and the back surface of the membrane) of the porous membrane is coated in the membrane thickness direction. In addition, the hydrophilic porous membrane of the present invention is preferably such that the surface of more fine pores is coated than in the prior art, and preferably the surface of substantially all fine pores is coated.

The hydrophilic porous membrane of the present invention may contain a portion that is not hydrophilized in the area direction. That is, the hydrophilic porous membrane of the present invention may have hydroxyalkyl cellulose held over the entire surface, or may have hydroxyalkyl cellulose held only in a part thereof. By being retained over the entire surface, hydrophilization of the entire porous film can be preferably achieved. Further, hydrophilization can be achieved within a necessary range by making use of the properties of the porous film as a base material by hydrophilizing only a portion where hydrophilicity is particularly required.

As an example of the hydrophilic porous membrane of the present invention that retains hydroxyalkyl cellulose only in a part of the area direction, a hydrophilic porous membrane that retains hydroxyalkyl cellulose only at both ends on the long side of a long sheet-like porous membrane is preferable. In the case of a porous membrane having a short side of 20 to 35cm, both ends on the long side may be, for example, a portion ranging from the edge of the long side of the hydrophilic porous membrane to 4cm, more preferably within 2cm, in the short side direction. When the porous membrane is used as a filtration membrane of a filter cartridge, a load is easily applied to both ends. That is, a long sheet-like porous film is pleated as necessary, wound into a cylindrical shape, and the aligned portions are sealed, and then both end portions of the cylindrical shape are welded to a plate called an end plate of a sleeve. When welded, the porous film is hydrophobized by application of heat and is susceptible to gas leakage caused by poor wettability in an integrity test. In particular, by increasing the hydrophilicity at both ends to which heat is applied by holding hydroxyalkyl cellulose, a hydrophilic porous membrane capable of preventing a decrease in hydrophilicity due to a sleeve production process can be obtained, and a filter cartridge that passes an integrity test can be produced using the hydrophilic porous membrane.

Therefore, as for the long sheet-like porous membrane, particularly, the long sheet-like porous membrane used as a filtration membrane of a filter cartridge preferably has hydroxyalkyl cellulose held at both ends at least on the long side.

[ porous film ]

(Structure of porous Membrane)

In the present specification, a porous membrane is a membrane that is a substrate of a hydrophilic porous membrane.

The porous film refers to a film having a plurality of pores. The pores can be confirmed by, for example, a Scanning Electron Microscope (SEM) image or a Transmission Electron Microscope (TEM) image of the cross section of the film.

In the hydrophilic porous membrane of the present invention, the average pore diameters of both surfaces (front and back surfaces) of the porous membrane are different from each other. The comparison of the average pore diameters of both surfaces is performed by comparing the average pore diameters of the regions closest to the front surface and the back surface of the membrane, respectively, in the comparison of the pore diameters in the thickness direction of the membrane described later.

The porous membrane in the hydrophilic porous membrane of the present invention has a structure having a pore size distribution in the thickness direction. The membrane has a structure (asymmetric structure) which is asymmetric in the thickness direction and has a pore size distribution such that the pore size on the front surface and the pore size on the back surface of the membrane are different. Examples of the asymmetric structure include a structure in which the pore diameter continuously increases in the thickness direction from one membrane surface toward the other membrane surface, a structure in which a layer-like dense site having the smallest pore diameter is provided inside one membrane surface, and the pore diameter continuously increases in the thickness direction from the dense site toward at least one membrane surface of the porous membrane.

The porous membrane used in the present invention preferably has a structure in which the average pore diameters of both surfaces of the porous membrane are different from each other and a layered dense site having the smallest pore diameter is provided inside. When the porous membrane is divided into 2 portions A, B having a uniform thickness in the thickness direction, the dense portion may be located in the portion a on the surface side having a small average pore diameter.

The term "having dense sites inside" as used herein means that the dense sites are not in contact with the surface of the membrane, and means that the dense sites are not partitions closest to either surface of the membrane when the pore diameters in the thickness direction of the membrane are compared as described below. By using a porous membrane having a structure in which dense sites are present inside, the permeability of a substance intended to permeate the porous membrane is less likely to decrease than when a porous membrane having the same dense sites in contact with the surface is used. Although not being bound by any theory, it is considered that the adsorption of other substances such as proteins is not easily caused by the dense site in the interior.

In the present specification, the average pore diameter of the porous membrane may be measured from a photograph of a cross section of the membrane obtained by an electron microscope. Specifically, a section for observation of a porous membrane was cut out from a porous membrane obtained by immersing a porous membrane in methanol and freezing the porous membrane in liquid nitrogen using a microtome (manufactured by Leica corporation, EM UC6), and a photograph of the cross section of the porous membrane was obtained by SEM photography (manufactured by Hitachi High-techniques corporation, SU8030 type FE-SEM) at 3000 magnifications.

The average pore diameter of the hydrophilic porous membrane can be made smaller than that of the porous membrane of the substrate by retaining the hydroxyalkyl cellulose, but can be generally approximated to be the same as the pore diameter of the porous membrane.

In this specification, when comparing the pore diameters of the membranes in the thickness direction, SEM photographs of the membrane cross-section were taken by dividing the membrane cross-section in the thickness direction of the membrane. The number of divisions can be appropriately selected according to the thickness of the film. The number of divisions was set to at least 5 or more, and for example, 20 parts of the membrane was divided from the surface having a small average pore diameter in a 200 μm thick membrane. At this time, 19 dividing lines obtained by dividing the cross section of each porous film into 20 parts in the thickness direction were drawn, and the holes (closed holes) intersecting or contacting with each dividing line were traced with a digitizer to have a circular diameter equivalent to the same area as the closed holes, and the average pore diameter of 50 continuous holes was determined. The size of the division width is a width in the thickness direction of the film, and does not mean a width in a photograph. In the comparison of the pore diameters in the thickness direction of the membrane, the pore diameters were compared as the average pore diameter of each partition. The average pore diameter of each partition may be, for example, an average of 50 pores in each partition in a membrane sectional view. The film cross-sectional illustration at this time can be obtained, for example, with a width of 80 μm (a distance of 80 μm in a direction parallel to the surface). In this case, for a partition in which the hole is large and 50 partitions cannot be measured, the number of the partitions that can be obtained may be measured. At this time, if the hole is large and cannot enter the partition, the size of the hole is measured in another partition.

The layer-like dense portion having the smallest pore diameter means a layer-like portion of the porous membrane corresponding to the partition having the smallest average pore diameter among the partitions of the membrane cross section. The dense sites are constituted of sites corresponding to 1 or more partitions having an average pore diameter within 1.1 times the smallest average pore diameter. The thickness of the dense part may be 0.5 to 50 μm, and preferably 0.5 to 30 μm. In the present specification, the average pore diameter of the dense part is preferably 0.01 to 5 μm, more preferably 0.02 to 3 μm, and still more preferably 0.05 to 1.4 μm.

The average pore size of the dense sites corresponds to the smallest pore size of the porous membrane. The minimum pore size of the porous membrane can also be determined by ASTM F316-86.

The minimum pore size of the porous membrane can be appropriately selected depending on the size of the object to be filtered.

In the porous membrane of the hydrophilic porous membrane of the present invention, the dense sites are located in a portion a on the side of a surface having a small average pore size (in the present specification, sometimes referred to as "surface X") when the porous membrane is divided into 2 portions with a uniform thickness in the thickness direction. That is, the dense portion is shifted from the central portion of the thickness of the porous membrane toward the surface X. Specifically, the dense portion is preferably located at a distance of 2 minutes or less, more preferably 3 minutes or less and 1 minute or less, and still more preferably 4 minutes or less and 1 minute or less from the surface X in the thickness of the porous film. The distance may be determined from the photograph of the cross section of the film.

In the porous film, the pore diameter may continuously increase from the dense portion toward at least one side surface in the thickness direction. In the porous membrane, the pore diameter may continuously increase from the dense portion toward the surface X in the thickness direction, the pore diameter may continuously increase from the dense portion toward the surface on the opposite side to the surface X in the thickness direction, or the pore diameter may continuously increase from the dense portion toward any one surface of the porous membrane in the thickness direction. Of these, the pore diameter preferably continuously increases at least from the dense site toward the surface on the opposite side to the surface X in the thickness direction, and more preferably also continuously increases from the dense site toward any surface of the porous membrane in the thickness direction. The phrase "the pore diameter continuously increases in the thickness direction" means that the difference in the average pore diameter between the partitions adjacent to each other in the thickness direction is 50% or less, preferably 40% or less, and more preferably 30% or less of the difference between the maximum average pore diameter (maximum pore diameter) and the minimum average pore diameter (minimum pore diameter). By "continuously increasing" is meant essentially a site where there is no decrease and an increase is uniform, but may occasionally produce a decrease. For example, when 2 partitions are combined from the surface, the average value of the combination uniformly increases (uniformly decreases from the surface toward the dense site), and it can be determined that "the pore diameter continuously increases from the dense site toward the surface of the membrane in the thickness direction".

The maximum pore diameter of the porous membrane is preferably 0.1 μm or more, more preferably more than 0.1 μm, and still more preferably more than 1.5 μm, and is preferably 25 μm or less, more preferably 23 μm or less, and still more preferably 21 μm or less. In the present specification, the average pore diameter of the partition having the largest average pore diameter among the partitions of the membrane cross section is defined as the maximum pore diameter of the porous membrane.

The ratio of the average pore diameter of the dense portion to the maximum pore diameter of the porous membrane (the ratio of the minimum pore diameter to the maximum pore diameter of the porous membrane, and the value obtained by dividing the maximum pore diameter by the minimum pore diameter, which may also be referred to as "anisotropic ratio" in the present specification) is preferably 3 or more, more preferably 4 or more, and further preferably 5 or more. The reason is to increase the average pore diameter except for the dense sites and to improve the substance permeability of the porous membrane. The anisotropy ratio is preferably 25 or less, and more preferably 20 or less. This is because the effect of the multistage filtration described above can be obtained efficiently in the range of the anisotropy ratio of 25 or less.

The partition in which the average pore diameter becomes the largest is preferably a partition closest to or adjoining either surface of the membrane.

In the partition closest to either surface of the membrane, the average pore diameter is preferably more than 0.05 μm and 25 μm or less, more preferably more than 0.08 μm and 23 μm or less, and still more preferably more than 0.1 μm and 21 μm or less. The ratio of the average pore diameter of the partition closest to any one surface of the membrane to the average pore diameter of the dense site is preferably 1.2 or more and 20 or less, more preferably 1.5 or more and 15 or less, and still more preferably 2 or more and 13 or less.

The thickness of the porous membrane is not particularly limited, but is preferably 10 to 1000 μm, more preferably 10 to 500 μm, and still more preferably 30 to 300 μm from the viewpoints of membrane strength, handling properties, and filtration performance.

The hydroxyalkyl cellulose is held, so that the thickness of the hydrophilic porous membrane can be larger than that of the porous membrane of the substrate, but is generally substantially the same as that of the porous membrane of the substrate.

(composition of porous Membrane)

The porous membrane contains a polymer. The porous membrane is preferably composed essentially of a polymer. The number average molecular weight (Mn) of the polymer is preferably 1,000 to 10,000,000, more preferably 5,000 to 1,000,000.

Examples of polymers include thermoplastic and thermosetting polymers. Specific examples of the polymer include polysulfone, sulfonated polysulfone, Polyethersulfone (PES), sulfonated polyethersulfone, cellulose acylate, nitrocellulose, polyacrylonitrile, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, saponified ethylene-vinyl acetate copolymer, polyvinyl alcohol, polycarbonate, organosiloxane-polycarbonate copolymer, polyester carbonate, organopolysiloxane, polyphenylene ether, polyamide, polyimide, polyamideimide, polybenzimidazole, ethylene-vinyl alcohol copolymer, Polytetrafluoroethylene (PTFE), polyethylene, polypropylene, polyvinyl fluoride, polyethylene terephthalate, 6-nylon, and polyvinylidene fluoride (PVDF). These may be homopolymers, copolymers, polymer blends, or polymer alloys from the viewpoints of solubility, optical properties, electrical properties, strength, elasticity, and the like.

Among these, polysulfone, polyethersulfone, PVDF, sulfonated polysulfone, sulfonated polyethersulfone, 6-nylon, and cellulose acylate are preferable, and polysulfone is more preferable.

The porous film may contain other components than the polymer as additives.

Examples of the additive include salt, metal salts of inorganic acids such as lithium chloride, sodium nitrate, potassium nitrate, sodium sulfate, and zinc chloride, metal salts of organic acids such as sodium acetate and sodium formate, polymers such as polyethylene glycol and polyvinylpyrrolidone, polymer electrolytes such as sodium polystyrene sulfonate and polyvinyl benzyl trimethyl ammonium chloride, and ionic surfactants such as sodium dioctyl sulfosuccinate and sodium alkylmethyltaurate. The additive may act as an expanding agent for the porous structure.

For example, when polysulfone or polyethersulfone is used as the polymer, the porous membrane preferably further contains polyvinylpyrrolidone. In this case, the polyvinylpyrrolidone may be in a state of being held in the porous film. Polysulfone or polyethersulfone, which is hydrophobic, is rendered hydrophilic by the inclusion of polyvinylpyrrolidone. Polyvinylpyrrolidone is added as a pore-forming agent to a solution for forming a polysulfone film or a polyethersulfone film as described in, for example, jp 64-34403 a. Most of the polyvinylpyrrolidone in the film-forming dope is dissolved in the solidification water and removed during the film-forming process, but a part of the polyvinylpyrrolidone remains on the film surface.

The porous film is preferably a film formed of one composition as a single layer, and is preferably not a multilayer laminated structure.

As a method for producing a porous film, reference can be made to Japanese patent application laid-open No. 63-141610, Japanese patent application laid-open No. 4-349927, Japanese patent application laid-open No. 4-68966, Japanese patent application laid-open No. 04-351645, Japanese patent application laid-open No. 2010-235808, and the like.

Commercially available porous films can be used. Examples thereof include Sumilite FS-1300 (manufactured by Sumitomo Bakelite Co., Ltd.), Micro PES 1FPH (manufactured by Membrana GmbH), Astropore (manufactured by polysulfone membrane, FUJIFILM Co., Ltd.), Durapore (manufactured by PVDF membrane, Merkmillipore Co., Ltd.), and Sartopore (manufactured by PES membrane, Sartorius Co., Ltd.).

[ hydroxyalkyl cellulose ]

The hydroxyalkyl cellulose in the hydrophilic porous membrane of the present invention is a hydrophilic polymer for hydrophilizing the porous membrane.

The hydrophobicity of the cellulose skeleton of the hydroxyalkyl cellulose contributes to hydrophobic interaction with the porous film as a base, and the hydrophilic property can be imparted to the porous film by the hydroxyl group or hydroxypropyl group of the side chain of the hydroxyalkyl cellulose while keeping the hydrophobic interaction with the porous film. Furthermore, since the hydroxyalkyl cellulose has a high intermolecular force, it is presumed that the molecules strongly interact with each other in the hydrophilic porous membrane and can maintain the form.

Furthermore, hydroxyalkyl cellulose is an ingredient that can be used as a food additive, and therefore, there is no need to rinse after manufacturing the filter cartridge. Therefore, a safe hydrophilic porous membrane with less process burden can be obtained.

The hydroxyalkyl cellulose distributed in the thickness direction in the hydrophilic porous membrane of the present invention shows 2 or more peaks of detection intensity in gel permeation chromatography, and the weight average molecular weight Mw of the peak detected at the latest among the peaks_minLess than 100,000. Specifically, when the hydrophilic porous membrane of the present invention is cut out in the entire thickness direction including the site to be hydrophilized and subjected to gel permeation chromatography of the hydroxyalkyl cellulose included therein, 2 or more peaks as described above are detected. Gel Permeation Chromatography (GPC) can be specifically measured according to the procedure and conditions described in examples of the present specification. The weight average molecular weight of each peak detected by GPC can be determined by a method known to those skilled in the art (for example, refer to sondinghei, "size exclusion chromatography", and copending publication (1991)).

Regarding the peaks observed in the above-mentioned gel permeation chromatography, from the viewpoint of hydrophilization matching with the pore diameter, the more the peaks are preferable, and it is preferable that the distribution of the weight average molecular weight is stepwise to such an extent that the peaks cannot be discriminated by a usual measurement. However, from the viewpoint of ease of obtaining hydroxyalkyl cellulose and the like, the peaks observed in the above-mentioned gel permeation chromatography are preferably 2 or 3, and more preferably 2.

The hydrophilic porous membrane of the present invention contains hydroxyalkyl cellulose showing a peak of weight average molecular weight of less than 100,000 in gel permeation chromatography, that is, hydroxyalkyl cellulose having weight average molecular weight of less than 100,000. By containing hydroxyalkyl cellulose having a weight average molecular weight of less than 100,000, the surface of the pores in the porous membrane at the site having a smaller pore diameter can also be hydrophilized. Furthermore, the hydroxyalkyl cellulose is not easy to agglomerate. Therefore, clogging due to hydroxyalkyl cellulose is hardly caused, and a decrease in water permeability of the hydrophilic porous membrane can be prevented.

The weight average molecular weight Mw of the hydroxyalkyl cellulose corresponding to the peak detected at the latest in the gel permeation chromatography_minThat is, the hydroxyalkyl cellulose having the lowest weight average molecular weight among the hydroxyalkyl celluloses contained in the hydrophilic porous membrane of the present invention preferably has a weight average molecular weight of 10,000 or more, more preferably 10,000 or more and 80,000 or less, and still more preferably 30,000 or more and 50,000 or less. By setting the content to 10,000 or more, the interaction between the hydroxyalkyl celluloses and the interaction between the hydroxyalkyl cellulose and the porous membrane can be made sufficient, and the hydroxyalkyl cellulose can be retained in the porous membrane.

The hydroxyalkyl cellulose distributed in the thickness direction in the hydrophilic porous membrane of the present invention further contains hydroxyalkyl cellulose showing a peak different from the above-described latest detected peak in a gel permeation chromatography, and having a weight average molecular weight of 100,000 or more. By containing the hydroxyalkyl cellulose having a large weight average molecular weight, the surface of the pores in the porous membrane at the site having a large pore diameter can be hydrophilized efficiently. The hydroxyalkyl cellulose having a weight average molecular weight of 100,000 or more has a weight average molecular weight of more preferably 100,000 or more and 2,500,000 or less, and further preferably 140,000 or more and 1,500,000 or less.

And, of the hydroxyalkyl celluloses having a weight average molecular weight of 100,000 or more, the hydroxyalkyl cellulose having the largest weight average molecular weight has the weight average molecular weight Mw_max(weight average molecular weight of the earliest peak among 2 or more peaks detected by GPC) and the average pore diameter d of the surface on the side where the pore diameter of the porous membrane is large_max[μm]The relationship (c) preferably satisfies the following. This makes it possible to efficiently hydrophilize the surface of the fine pores having a large pore diameter and prevent clogging.

30,000≤Mw_max/d_max≤130,000

Further, the following is more preferably satisfied.

80,000≤Mw_max/d_max≤110,000

From the following analysis, it was identified and confirmed that the surface of the fine pores in the sites having a small pore diameter was hydrophilized with the hydroxyalkyl cellulose having a small weight average molecular weight, and the surface of the fine pores in the sites having a large pore diameter was hydrophilized with the hydroxyalkyl cellulose having a large weight average molecular weight.

When the porous membrane is divided into 2 parts a and B in order of uniform thickness from the surface side having a smaller average pore diameter in the thickness direction, the detection intensity of the peak that is the latest among the 2 or more peaks in the detection time becomes larger in the gel permeation chromatography of the hydroxyalkyl cellulose held in the part a than in the part B. For example, although PSE20 used in the embodiment of the present application has a structure shown in a cross-sectional view in fig. 1, when it is equally divided into 2 parts in the thickness direction, the lower side becomes part a and the upper side becomes part B in fig. 1. As can be seen from fig. 1, part a has a generally dense site. In such an example, the hydroxyalkyl cellulose eluted from the portion a shows a smaller weight average molecular weight than the hydroxyalkyl cellulose eluted from the portion B.

The hydroxyalkyl cellulose is preferably a cellulose to which an alkylene oxide having 3 to 5 carbon atoms has been added. This is because the interaction between the porous membrane and the hydroxyalkyl cellulose and the hydrophilicity of the hydrophilic porous membrane obtained are obtained in a range preferable for practical use. Among these, hydroxypropyl cellulose in which propylene oxide (having 3 carbon atoms) is added to cellulose is most preferable. When the number of addition (degree of substitution) of alkylene oxide is large, hydrophilicity increases, whereas when the number of addition (degree of substitution) of alkylene oxide is small, hydrophilicity decreases. From this viewpoint, the molar substitution degree is preferably 1 or more, and more preferably 2 or more.

The content of the hydroxyalkyl cellulose in the portion where the hydroxyalkyl cellulose is held (the portion where the hydroxyalkyl cellulose permeates) is preferably 0.02 to 3% by mass, and more preferably 0.05 to 1.0% by mass, based on the mass of the hydrophilic porous membrane. The content of the hydroxyalkyl cellulose in the porous film can be determined by the method shown in the examples, for example.

[ method for producing hydrophilic porous film ]

The hydrophilic porous membrane can be produced by subjecting a porous membrane as a substrate to hydrophilization treatment with hydroxyalkyl cellulose. Specifically, the hydrophilic film can be produced by permeating a hydrophilizing liquid containing hydroxyalkyl cellulose into a porous film. The hydrophilized porous film may be further subjected to a cleaning treatment, a sterilization treatment, or the like.

(hydrophilizing solution)

The hydrophilizing liquid may be prepared as a solution containing hydroxyalkyl cellulose. The solvent is not particularly limited as long as it is water or a solvent having a property of being mixed with water. The solvent may be a mixed solvent of water and an organic solvent. When a mixed solvent of water and an organic solvent is used, the organic solvent is preferably at least 1 or more lower alcohols. Examples of the lower alcohol include alcohols having 5 or less carbon atoms such as methanol, ethanol, propanol, isopropanol, butanol, ethylene glycol, propylene glycol, and glycerol. The organic solvent is more preferably methanol, ethanol, or isopropanol, and still more preferably ethanol. The solvent of the hydrophilizing liquid is particularly preferably water.

The hydrophilizing liquid may contain a surfactant, a preservative, a film-curing agent such as polyphenol, and the like in addition to the hydroxyalkyl cellulose and the solvent.

(osmosis)

The method of permeating the hydrophilizing liquid into the porous membrane is not particularly limited, and examples thereof include a dipping method, a coating method, a transfer method, and a spraying method. The penetration is preferably performed so that the hydrophilizing liquid penetrates the entire thickness direction of the porous film at least at the site where the hydrophilization is performed. Among them, the dipping method or the coating method is preferable. This is because the hydrophilizing liquid can be efficiently permeated into the porous membrane. The method of penetrating the hydrophilizing liquid into the porous film is more preferably a coating method. This is because the hydroxyalkyl cellulose having an appropriate pore size can be efficiently permeated into the porous membrane.

Examples of the coating method include a method of coating a hydrophilizing liquid containing hydroxyalkyl cellulose having the above-mentioned weight average molecular weight distribution from one surface or both surfaces of a porous film, and a method of separately preparing a hydrophilizing liquid for each of hydroxyalkyl celluloses having different weight average molecular weights and separately coating the hydrophilizing liquid. In particular, by the latter method of preparing a hydrophilizing liquid for each weight average molecular weight, hydroxyalkyl cellulose having an appropriate pore size can be infiltrated into the porous film.

By applying a hydrophilizing liquid prepared for each weight average molecular weight to the porous membrane as in the following step 1 or 2, for example, the aggregation of the hydroxyalkyl cellulose can be prevented, and the clogging of the porous membrane due to the hydroxyalkyl cellulose can be prevented.

Step 1 (two-side coating)

The porous membrane is coated with a hydrophilizing liquid containing hydroxyalkyl cellulose having a large weight average molecular weight on the surface side having a large average pore diameter, and coated with a hydrophilizing liquid containing hydroxyalkyl cellulose having a small weight average molecular weight on the surface side having a small average pore diameter.

Step 2 (coating in sequence)

The hydroxyalkyl cellulose solution containing a smaller weight average molecular weight is coated on the surface side of the porous membrane having a larger average pore diameter, and then the hydroxyalkyl cellulose solution having a larger weight average molecular weight is coated on the same surface side.

The coating is preferably performed so that the hydrophilizing liquid penetrates the entire thickness direction of the porous film. When a plurality of hydrophilizing liquids are used for coating, the hydrophilizing liquids may be applied in their entirety and then allowed to permeate through the porous film in the thickness direction. When only a part of the porous film is coated, a coating method of coating a part to be coated with a hydrophilizing liquid can be performed. The application of the hydrophilizing liquid can be performed by a known method such as a method of immersing the hydrophilizing liquid in a sponge or cloth to bring the hydrophilizing liquid into contact with the surface of the porous film, bead coating, gravure coating, or wire bar coating.

In the impregnation method, the hydrophilization solution is impregnated into the porous film by impregnating the porous film into the hydrophilization solution. As the hydrophilizing liquid, a hydrophilizing liquid containing hydroxyalkyl cellulose having the above-mentioned weight average molecular weight distribution may be used. After the immersion, the porous film may be pulled up from the hydrophilizing liquid to remove the excess hydrophilizing liquid.

The impregnation can be carried out under pressure. The hydrophilizing liquid can be efficiently injected into each pore of the porous membrane by pressurization.

The dipping time or pressing time in the dipping treatment or pressing treatment is not particularly limited, and may be generally about 0.5 seconds to 1 minute, and preferably about 0.5 seconds to 30 seconds. The impregnation time can be shortened by selection of a solvent or the like.

The amount of hydroxyalkyl cellulose deposited can be appropriately adjusted depending on the time for which the porous membrane is immersed in the hydrophilizing solution and the concentration of hydroxyalkyl cellulose in the hydrophilizing solution.

(drying and heating)

After the hydrophilization liquid has permeated into the porous film, the solvent in the hydrophilization liquid is preferably removed by drying and volatilization. The drying method includes, but is not limited to, heating drying, air drying, and reduced-pressure drying, and preferably air drying or heating drying in view of the simplicity of the production process. Drying can be achieved by simple standing.

(cleaning)

After the above drying, washing is preferably performed using a washing solvent. This is because excess hydroxyalkyl cellulose and the like can be removed. Further, unnecessary components contained in the porous film of the raw material can be removed by washing. The cleaning method is not particularly limited, but the cleaning solvent may be removed by allowing the cleaning solvent to permeate the membrane surface and pore surface of the hydrophilic porous membrane by immersion or press-in method. Examples of the cleaning solvent include solvents exemplified as solvents for hydrophilization solutions. The penetration and removal of the cleaning solvent may be performed 2 or more times. In the washing 2 or more times, the washing solvent may be the same or different, but preferably different. The cleaning solvent used at the end of the cleaning is preferably water. Immersion in water is particularly preferred. This is for removing organic solvent components such as alcohol.

The washed hydrophilic porous membrane is dried again by the above-mentioned steps.

(Sterilization treatment)

As the sterilization treatment of the hydrophilic porous membrane, for example, a high-pressure steam sterilization treatment can be performed. It is particularly preferable to carry out the treatment by high-temperature and high-pressure steam using an autoclave. Generally, the plastic is sterilized by autoclaving with saturated steam for 10 to 30 minutes at about 110 to 140 ℃, but the hydrophilic porous membrane of the present invention can be sterilized under the same conditions. Examples of the autoclave used for the sterilization treatment include SS325 manufactured by TOMY SEIKO co.

< use of hydrophilic porous Membrane >

The hydrophilic porous membrane of the present invention can be used in various applications as a filtration membrane. The filtration membrane is suitable for separation, purification, recovery, concentration, and the like of a liquid containing or suspending various polymers, microorganisms, yeasts, and fine particles, and is particularly suitable for a case where it is necessary to separate fine particles from a liquid containing the fine particles to be filtered. For example, a filtration membrane can be used for separating fine particles from various suspensions, fermentation solutions, culture solutions, and the like containing fine particles, as well as from pigment suspensions and the like. Specifically, the hydrophilic porous membrane of the present invention can be used as a required microfiltration membrane in the production of pharmaceuticals in the pharmaceutical industry, the production of alcoholic beverages such as beer in the food industry, microfabrication in the field of electronics industry, the production of purified water, and the like.

When the hydrophilic porous membrane of the present invention having a pore size distribution is used as a filtration membrane, the portion having smaller pore sizes is disposed close to the outlet side (outlet side) of the filtrate to perform filtration, whereby fine particles can be efficiently captured. Further, since the hydrophilic porous membrane has a pore size distribution, the fine particles introduced from the surface thereof are removed by adsorption or adhesion before reaching the minimum pore size portion. Therefore, clogging is not likely to occur, and high filtration efficiency can be maintained for a long period of time.

The hydrophilic porous membrane of the present invention can be processed into a shape corresponding to the application and used for various applications. The shape of the hydrophilic porous membrane may be a flat membrane, a tubular shape, a hollow linear shape, a corrugated shape, a fibrous shape, a spherical particle shape, a crushed particle shape, a block continuous shape, or the like. The porous film may be processed into a shape corresponding to the application before hydrophilization treatment of the porous film, or may be processed into a shape corresponding to the application after hydrophilization treatment of the porous film.

The hydrophilic porous membrane may be attached to a sleeve that can be easily detached in a device used for various purposes. The hydrophilic porous membrane is preferably held in the cartridge in a form capable of functioning as a filtration membrane. The cartridge holding the hydrophilic porous membrane can be manufactured in the same manner as a known porous membrane cartridge, and for example, refer to WO2005/037413, japanese patent laid-open No. 2012-045524.

For example, the filter cartridge can be manufactured as follows.

The long hydrophilic porous membrane is pleated so as to form creases in the short side (width) direction. For example, typically sandwiched between 2 membrane holders and can be pleated by known methods. The film support may be a nonwoven fabric, woven fabric, mesh, or the like. The membrane holder serves to reinforce the filter membrane against filter pressure fluctuations while introducing liquid deep into the folds. The width of the crease may be, for example, 5mm to 25 mm. Rolling the pleated hydrophilic porous membrane into a cylindrical shape, and sealing the joint.

A cylindrical hydrophilic porous membrane is terminated on the end plate. The end capping may be performed by a known method depending on the material of the end plate. When a thermosetting epoxy resin is used for the end plate, a liquid of a prepared epoxy resin adhesive is poured into a casting mold to be precured, the viscosity of the adhesive is appropriately increased, and then one end surface of the cylindrical filter material is inserted into the epoxy adhesive and heated to be completely cured. When the material of the end plate is a thermoplastic resin such as polypropylene or polyester, a method of inserting one end surface of the cylindrical filter member into the resin immediately after the hot-melt resin is poured into the mold may be performed. On the other hand, only the sealing surface of the molded end plate may be brought into contact with a hot plate or an infrared heater may be irradiated to melt only the surface of the plate, and one end surface of the cylindrical filter medium may be pressed against the melted surface of the plate to be welded.

The assembled filter cartridge may be further used in a known cleaning process.

In addition, the hydroxyalkyl cellulose in the hydrophilic porous membrane may be partially or completely dissolved in a solvent used in a washing step or the like in the cartridge and removed.

Examples

The features of the present invention will be described in more detail below with reference to examples and comparative examples. The materials, the amounts used, the ratios, the contents of the processes, the processing steps, and the like shown in the following examples can be appropriately modified within the scope not departing from the gist of the present invention. Therefore, the scope of the present invention should not be construed as being limited to the specific examples shown below.

[ preparation of hydrophilizing solution ]

For hydroxypropyl cellulose, NIPPON SODA co., NISSO HPC H grade (molecular weight 100 ten thousand), M grade (molecular weight 70 ten thousand), SL grade (molecular weight 10 ten thousand) and SSL grade (molecular weight 4 ten thousand) manufactured by ltd. were used. For the hydroxyethyl cellulose, Sansho co, ltd, manufactured sanhe c M grade (molecular weight 72 ten thousand), L grade (molecular weight 9 ten thousand) were used. Any of the above was added to pure water to have a mass% concentration as shown in table 1, and stirred until completely dissolved. In table 1, in example 1 and comparative example 1, any 2 grades of the above were mixed and used, but the 2 grades were mixed at a mass ratio of 1: 1, and the concentrations shown in the table are the concentrations of the mixture.

[ production of hydrophilic porous film ]

The hydrophilic porous membranes of the examples and comparative examples were produced by the steps shown in table 1 using the porous membranes shown in table 1.

In Table 1, PSF is a polysulfone film PSE20 manufactured by FUJIFILM Corporation. PSE20 had a minimum pore size of 0.2 μm and a maximum pore size (average pore size of a surface having a large average pore size: d)_max) A structure of 7 μm, a thickness of 140 μm, and an asymmetric pore size distribution. Fig. 1 shows a sectional view. PSF2 was formed into a film by reference to example 1 of Japanese patent application laid-open No. 9-227714. Having a minimum pore diameter of 2 μm and a maximum pore diameter (average pore diameter of a surface having a large average pore diameter: d)_max) 20 μm, 180 μm thick and asymmetric pore size distribution. PES was a polyether sulfone membrane, Membrana TM200, manufactured by 3M company and having a minimum pore diameter of 0.3 μ M and a maximum pore diameter (average pore diameter of a surface having a large average pore diameter: d)_max) 10 μm, a thickness of 140 μm, and an asymmetric pore size distribution.

The hydroxyalkyl cellulose was infiltrated into the porous membrane by the procedure described in table 1. The procedure described in table 1 is as follows. In addition, coating was performed using Gieser.

Dipping: the porous membrane was immersed in a hydrophilizing liquid containing 2 kinds of hydroxyalkyl celluloses for 27 seconds continuously and then pulled up.

Two-sided coating (large and small): the porous membrane is coated with a hydrophilizing liquid containing hydroxyalkyl cellulose having a large weight average molecular weight on the surface side having a large average pore diameter, and coated with a hydrophilizing liquid containing hydroxyalkyl cellulose having a small weight average molecular weight on the surface side having a small average pore diameter.

Two-sided coating (size): the porous membrane is coated with a hydrophilizing liquid containing hydroxyalkyl cellulose having a small weight average molecular weight on the surface side having a large average pore diameter, and coated with a hydrophilizing liquid containing hydroxyalkyl cellulose having a large weight average molecular weight on the surface side having a small average pore diameter.

Coating in order (small and large): the porous membrane is coated with a hydrophilizing liquid containing a hydroxyalkyl cellulose having a small weight average molecular weight on the surface side having a large average pore diameter, and then coated with a hydrophilizing liquid containing a hydroxyalkyl cellulose having a large weight average molecular weight on the same surface side.

Coating in order (size): the porous membrane is coated with a hydrophilizing liquid containing a hydroxyalkyl cellulose having a large weight average molecular weight on the surface side having a large average pore diameter, and then coated with a hydrophilizing liquid containing a hydroxyalkyl cellulose having a small weight average molecular weight on the same surface side.

Each of the hydrophilic porous films after the above steps was heated and dried in an oven at 80 ℃ for 80 seconds.

For each of the hydrophilic porous films after drying, in order to remove the excess hydroxyalkyl cellulose, the film was immersed in pure water at 25 ℃ for 5 minutes and washed. Then, the mixture was dried at a temperature of 70 ℃ for 24 hours.

[ evaluation of weight average molecular weight ]

Each hydrophilic porous membrane was cut into 10cm × 10cm, and dissolved in DMF (N, N-dimethylformamide). After the dissolved liquid was freeze-dried, the dried product was dissolved in the eluent described below, and the weight average molecular weight of the hydroxyalkyl cellulose in the membrane was evaluated.

The weight average molecular weight was evaluated by GPC (gel permeation chromatography). The conditions were as follows.

Pullulan (P-82) was used as a molecular weight marker

An apparatus: HLC-8320GPC EcoSEC (Tosoh Corporation)

Column: ohpak KB-805 HQ (7.8 mmI.D.. times.30 cm)

Column: ohpak KB-804 HQ (7.8 mmI.D.. times.30 cm)

Column: ohpak SB-803 HQ (7.8 mmI.D.. times.30 cm)

Eluent: 0.1M NaNO₃

Column temperature: 40 deg.C

The number of peaks observed, the weight average molecular weight (Mw) of the earliest peak and the latest peak were determined_max、Mw_min) Shown in table 1.

[ hydroxyalkyl cellulose amount in porous Membrane ]

After cutting out 51 cm square porous membranes and measuring the mass, the membranes were immersed in 1ml of methanol for 30 minutes. The Liquid was evaluated using a Liquid Chromatograph (Liquid Chromatograph)/electrospray Detector (Cbarged Aerosol Detector) (LC/CAD). The conditions were as follows.

Standards: a solution (20/50/100ppm) obtained by dissolving a predetermined amount of hydroxyalkyl cellulose in methanol

An apparatus: ACQUITY UPLC H-Class manufactured by Waters corporation

Column: presto FF-C18150X 4.6mm

The detector: CAD (Corona Ultra RS, Thermo Fisher Scientific)

Eluent: … water solution A and … acetonitrile solution B

Elution conditions: 5-90% B (0-15min), 0.4ml/min, 37 deg.C

The amount of hydroxyalkyl cellulose in the porous film [ HAC content (mass%) in the film ] is calculated using the area ratio of the hydroxyalkyl cellulose peak detected at a holding time of 8.5 to 12.5 minutes at the time of measurement under the above conditions to the peak obtained in the standard sample.

[ distribution of hydroxyalkyl cellulose ]

Each of 2 hydrophilic porous membranes was cut at 20 cm. times.20 cm. These were cut out from the surface side having a large average pore diameter and the surface side having a small average pore diameter of the porous membrane to the center in the thickness direction, and the weight average molecular weight of the hydroxyalkyl cellulose eluted was evaluated by dissolving each in DMF. The portion on the side where the peak was detected at the latest detection time and the detection intensity was large (portion A: the surface side having a small average pore diameter; portion B: the surface side having a large average pore diameter) was confirmed. The same applies to "equal" in table 1.

[ integrity test ]

A filter cartridge (10 inches) was prepared from the hydrophilized film, and water was passed through the cartridge at 8L/min for 200 seconds, after which the water was drained. Subsequently, 150kPa air pressure was applied from the 1 st surface side, and the amount of air passing through the filter cartridge was measured, and it was determined as passed if it was 30mL/min or less, and as failed if it was more than 30 mL/min.

[ Water permeability ]

The water permeability was evaluated by applying a pressure of 100kPa to the hydrophilized porous film to permeate pure water. The volume of water flowing out through the membrane per unit area for 1 minute was measured and regarded as the water permeability (mL/min/cm)²)。