WO2012043672A1

WO2012043672A1 - Porous polyethylene hollow-fiber membrane, cartridge for water purifier, and hollow-fiber membrane module

Info

Publication number: WO2012043672A1
Application number: PCT/JP2011/072267
Authority: WO
Inventors: 規孝柴田
Original assignee: 三菱レイヨン株式会社
Priority date: 2010-09-29
Filing date: 2011-09-28
Publication date: 2012-04-05
Also published as: JPWO2012043672A1; JP6003057B2; KR101536836B1; KR20130064812A; CN103228341B; CN103228341A

Abstract

The purpose of the present invention is to provide a porous polyethylene hollow-fiber membrane which uses a resin composition containing polyethylene and having excellent fluidity, and which retains excellent film quality and stiffness, and has high permeability and excellent filtering characteristics, and also to provide a hollow-fiber membrane module and a water purifier cartridge equipped with the porous polyethylene hollow-fiber membrane. The porous polyethylene hollow-fiber membrane is formed from a resin composition which contains polyethylene and has excellent fluidity, and the average pore-diameter in the hollow-fiber membrane is 0.1-0.5μm; the pore-diameter distribution in a region ± 0.05 μm from the average pore-diameter is at least 70% of the total pore-diameter distribution; the metal flow rate measured in accordance with JIS K7210 code D is 0.1-0.9g/10 minutes, and the metal flow rate measured in accordance with code G is 50-100g/10 minutes, with the FRR ratio (G/D) thereof being 50-100; and the density is 0.962-0.968g/cm³. Also provided are a hollow-fiber membrane module and a water purifier cartridge equipped with the porous polyethylene hollow-fiber membrane

Description

Polyethylene porous hollow fiber membrane, cartridge for water purifier, and hollow fiber membrane module

The present invention relates to a polyethylene porous hollow fiber membrane, and a water purifier cartridge and a hollow fiber membrane module comprising the polyethylene porous hollow fiber membrane.
This application claims priority on September 29, 2010 based on Japanese Patent Application No. 2010-218043 filed in Japan, the contents of which are incorporated herein by reference.

Polyethylene porous hollow fiber membranes are widely used as separation and selective permeation of various substances, separators and the like. As a method for producing a polyethylene porous hollow fiber membrane, for example, a method is known in which high-density polyethylene is spun while applying an appropriate draft, and then subjected to heat treatment and stretching to obtain a porous hollow fiber membrane. (Patent Documents 1 to 3).
In addition, as polyethylene, high-density polyethylene having a melt flow rate (MFRD) measured in accordance with JIS K7210 code D of 0.1 to 1 g / 10 minutes is used, and spinning is performed while applying an appropriate draft. A method of performing heat treatment and stretching after obtaining a yarn having excellent orientation is known (Patent Document 4). That is, after shaping polyethylene under specific spinning conditions, annealing treatment is performed to form a lamellar laminated crystal (stacked lamellar) in the film wall of the shaped product. Next, by stretching the shaped product, a porous hollow fiber membrane is obtained in which the lamella laminated crystals are grown while the stacked lamellas are separated. Since the hollow fiber membrane has the specific porous structure as described above, it has excellent mechanical strength. Furthermore, it is excellent in that no solvent is used in the production process.

In the porous hollow fiber membrane having a homogeneous structure as described above, in order to increase the water permeability, it is conceivable to make the porous hollow fiber membrane thinner. However, when the film thickness is reduced, the mechanical strength of the porous hollow fiber membrane is insufficient, and sufficient pressure resistance cannot be maintained particularly when the porosity is increased. Conversely, when the film thickness is increased, the mechanical strength of the porous hollow fiber membrane is increased, but the water permeability is decreased.

In order to obtain a porous hollow fiber membrane having a high mechanical strength and a large water permeability, it is conceivable to improve the material strength and rigidity of polyethylene as a membrane material. However, when the proportion of the high molecular weight component of polyethylene is increased to improve the rigidity, the MFRD is lowered, and thus the moldability is lowered, for example, the spinning speed at the time of melt spinning is lowered. On the other hand, when the proportion of the low molecular weight component is increased in order to obtain excellent moldability, it is necessary to increase the film thickness particularly in order to maintain pressure resistance, and sufficient filtration characteristics cannot be maintained.

Japanese Patent Laid-Open No. 52-137026 JP-A-57-66114 Japanese Patent Publication No. 63-42006 JP-A-6-277475

The present invention comprises a polyethylene porous hollow fiber membrane that is formed of a resin composition having excellent moldability, retains excellent rigidity, has a large water permeability, and has excellent filtration characteristics, and the polyethylene porous hollow fiber membrane. It aims at provision of the cartridge for water purifiers, and a hollow fiber membrane module.

The present invention employs the following configuration in order to solve the above problems.
[1] Polyethylene porous hollow having an average pore size of 0.1 to 0.5 μm and a pore size distribution in the region of ± 0.05 μm from the average pore size of 70% or more of the total pore size distribution Yarn membrane.
[2] The polyethylene porous hollow fiber membrane according to [1], which is formed of a resin composition containing polyethylene that satisfies the following requirements (a) to (d).
(A) The melt flow rate (MFRD) measured according to JIS K7210 code D is 0.1 to 0.9 g / 10 min.
(B) The melt flow rate (MFRG) measured in accordance with JIS K7210 code G is 50 to 100 g / 10 min.
(C) The ratio FRR (G / D) (= MFRG / MFRD) of the MFRD and the MFRG is 50-100.
(D) The density is 0.962 to 0.968 g / cm ³ .
[3] The polyethylene porous hollow fiber membrane according to the above [1] or [2], wherein the ratio Mw / Mn of the mass average molecular weight Mw to the number average molecular weight Mn in the polyethylene is 8.0 to 12.0.
[4] The polyethylene porous hollow fiber membrane according to any one of [1] to [3], wherein the polyethylene has an environmental stress crack resistance measured in accordance with JIS K6760 of 10 to 50 hours.
[5] The above [1] to [3], wherein the polyethylene has an amount of a component having a molecular weight of 1,000 or less of 2.0% by mass or less and an amount of a component having a molecular weight of 1,000,000 or more is 1.5 to 3.0% by mass. The polyethylene porous hollow fiber membrane according to any one of the above.
[6] The polyethylene porous hollow fiber membrane according to any one of the above [1] to [5], wherein the inner surface and the outer surface of the hollow fiber membrane are hydrophilized with a hydrophilic copolymer.
[7] The polyethylene porous hollow fiber membrane according to [6], wherein the hydrophilic copolymer is an ethylene-vinyl alcohol copolymer.
[8] A water purifier cartridge comprising the polyethylene porous hollow fiber membrane according to any one of [1] to [7].
[9] A hollow fiber membrane module comprising the polyethylene porous hollow fiber membrane according to any one of [1] to [7].
[10] The polyethylene porous hollow fiber membrane according to any one of [1] to [7], wherein the average flow pore size is 0.1 to 0.5 μm, and the pore size variation is 100% or less. .

The polyethylene porous hollow fiber membrane of the present invention is formed of a resin composition having excellent moldability, maintains excellent rigidity, has a large amount of water permeability, and is excellent in filtration characteristics.
Moreover, this invention provides the cartridge for water purifiers and hollow fiber membrane module which comprise the said polyethylene porous hollow fiber membrane.

Pore size distribution of the polyethylene porous hollow fiber membrane of the present invention

<Polyethylene porous hollow fiber membrane>
The polyethylene porous hollow fiber membrane of the present invention (hereinafter referred to as “the present hollow fiber membrane”) is a resin composition containing polyethylene that satisfies the following requirements (a) to (d) (hereinafter “the present resin composition”). It is a porous hollow fiber membrane formed by.
(A) Melt flow rate (hereinafter referred to as “MFRD”) measured in accordance with JIS K7210 code D (measurement temperature: 190 ° C., load: 2.16 kg) is 0.1 to 0.9 g / 10 min. It is.
(B) The melt flow rate (hereinafter referred to as “MFRG”) measured according to JIS K7210 code G (measurement temperature: 190 ° C., load: 21.6 kg) is 50 to 100 g / 10 min.
(C) The ratio FRR (G / D) (= MFRG / MFRD) of the MFRD and the MFRG is 50-100.
(D) The density is 0.962 to 0.968 g / cm ³ .

If the MFRD of polyethylene is 0.1 g / 10 min or more, the melt viscosity is not too high and the molding range capable of improving the crystal orientation is increased. Moreover, it is applicable also to the field | area where size reduction, such as a water purifier, is requested | required. If the MFRD of polyethylene is 0.9 g / 10 min or less, the melt viscosity is not too small, and the crystal orientation is improved by increasing the draft ratio. Therefore, the present hollow fiber membrane that has been sufficiently made porous by stretching during production can be obtained. Further, the rigidity can be improved, and the permeation performance can be improved by reducing the film thickness and increasing the porosity.

If the MFRG of polyethylene is 50 g / 10 min or more, excellent high-speed moldability can be obtained. When the MFRG of polyethylene is 100 g / 10 min or less, good environmental stress crack resistance (hereinafter referred to as “ESCR”) can be obtained. Here, high-speed moldability is the same conditions, lower the extruder load, how far the discharge speed can be increased, and how much the molding temperature can be lowered within the same range of the extruder load, It is a characteristic evaluated by judging.
The MFRG of polyethylene is preferably 60 to 90 g / 10 minutes.

The ratio FRR (G / D) of MFRG and MFRD of polyethylene generally has a correlation with the molecular weight distribution, and tends to increase as the molecular weight distribution becomes wider.
When the FRR (G / D) of polyethylene is 50 or more, the load on the extruder during molding does not become too high, and the high-speed moldability is excellent. Also, excellent stress crack resistance is obtained. If the FRR (G / D) of polyethylene is 100 or less, this hollow fiber membrane having high impact strength can be obtained. The FRR (G / D) of polyethylene is preferably 60-80.
When a hollow fiber membrane is formed by a melt drawing method, spinning is often performed at a lower temperature than ordinary extrusion molding from the viewpoint of improving crystal orientation. Since this condition is a condition in which the extruder is easily loaded, it is necessary to improve the fluidity of the molecule. When FRR (G / D) is within the above range, the crystal orientation can be improved while improving the flow of molecules. Therefore, not only the uniformity of the membrane pore diameter is increased, but the porosity is also increased.

When the density of polyethylene is 0.962 g / cm ² or more, the amount of low crystal components is small, the porosity is increased, and sufficient transmission performance is obtained. If the density of polyethylene is 0.968 g / cm ³ or less, ESCR of 20 hours or more is maintained.
The density is measured by a method based on JIS K7112 (ASTM D1505).

The ratio Mw / Mn between the weight average molecular weight (hereinafter referred to as “Mw”) and the number average molecular weight (hereinafter referred to as “Mn”) of polyethylene is preferably 8.0 to 12.0. When Mw / Mn is 8.0 or more, the ESCR is improved by increasing the amount of the high molecular weight component. If Mw / Mn is 12.0 or less, low molecular weight components such as wax are reduced, and it is easy to suppress dissolution of the low molecular weight components in water in drinking water applications such as water purifiers and waterworks. Moreover, the rigidity of this hollow fiber membrane improves because molecular weight distribution becomes narrow.

The polyethylene ratio Mw / Mn is calculated from measurement by high-temperature gel permeation chromatography (hereinafter referred to as “high-temperature GPC”). High-temperature GPC refers to GPC that performs measurement in a state in which a sample is heated and dissolved. The ratio Mw / Mn is calculated using a calibration curve created using polystyrene as a standard sample in the measurement by high temperature GPC.
Examples of the measuring apparatus include trade names “150-GPC”, “Alliance GPCV 2000” (manufactured by Waters).

The amount of a component having a molecular weight of 1000 or less (hereinafter referred to as “FL”) in polyethylene is preferably 0.1 to 2.0% by mass, preferably 0.2 to 1.0 is more preferable, and 0.3 to 0.7 is particularly preferable. FL is a so-called low molecular weight component among polyethylene components. If it is 0.1 mass% or more, it contributes to an improvement in a softness | flexibility, and if it is 2.0 mass% or less, an odor does not become a problem and it is suitable also for application to a food use etc.

The amount of a component having a molecular weight of 1,000,000 or more in polyethylene (hereinafter referred to as “FH”) is preferably 1.5 to 3.0% by mass with respect to 100% by mass of the total copolymer constituting the polyethylene, To 3.0 is more preferable, and 2.5 to 3.0 is particularly preferable. If the FH is 1.5% by mass or more, the amount of the high molecular weight component increases, so that long-term characteristics such as stress crack resistance and ESCR are improved. When FH is 3% by mass or less, sufficient fluidity can be easily obtained at the time of molding, so that an unmelted gel is hardly generated, and a non-porous portion contrary to the intention at the time of stretching is hardly generated.
FL and FH are obtained from the same high temperature GPC as the ratio Mw / Mn described above. That is, in the molecular weight distribution chart obtained by measurement by high temperature GPC, FL is obtained from the ratio of the area of the molecular weight portion of 1000 or less to the area of the entire molecular weight distribution. Similarly, FH is calculated | required from the ratio of the area of the part of molecular weight 1 million or more with respect to the area of the whole molecular weight distribution.

The ESCR (environmental stress crack resistance) of polyethylene is preferably 10 to 50 hours, more preferably 15 to 40 hours, and particularly preferably 15 to 30 hours. When the ESCR is 10 hours or longer, the present hollow fiber membrane that is difficult to break even when stress is applied can be obtained. Further, when the porous structure (stretching) is performed so that cracks are generated between the crystal components during production, the hollow fiber membrane is hardly broken. If the ESCR is 50 hours or less, the density is improved and the crystallinity is also improved, so that the openability is improved and good pores are formed.
The ESCR of polyethylene is measured by a constant strain environmental stress crack test according to JIS K6760. ESCR is the time when the probability of occurrence of cracks due to environmental stress is 50%.

As the polyethylene contained in the present resin composition, polyethylene having a short number of short branched chains is particularly preferable from the viewpoint of pore opening properties. The MFRD, MFRG, and molecular weight of polyethylene can be adjusted, for example, by using a molecular weight regulator such as hydrogen during the production of polyethylene.
Examples of commercially available polyethylene products include trade names “H6670B” and “H6430BM” (above, manufactured by SCG Chemical).

The resin composition is preferably a composition containing polyethylene as a main component. The composition mainly composed of polyethylene is a composition having a polyethylene content of 50% by mass or more. The polyethylene content in the polyethylene-based composition is preferably 80% by mass or more, more preferably 90% by mass or more, and particularly preferably 100% by mass with respect to 100% by mass of the resin composition.

Examples of other polymer components other than polyethylene contained in the resin composition include other olefinic monomers such as polypropylene.
When this resin composition contains other polymer components other than polyethylene, MFRD, MFRG, FRR (G / D), density, Mw / Mn, ESCR, FL and FH in all polymers containing them are It is preferable to be within the range.

In addition, a small amount of additives, fillers and the like may be added to the resin composition as long as the effects of the present invention are not impaired.
Examples of the additive include an antioxidant, a lubricant, and a nucleating agent that increases the crystallization speed and improves the moldability.
Examples of the antioxidant include hindered phenolic antioxidants such as trade names “IRGANOX1076” and “IRGANOX1010” (manufactured by Ciba Specialty Chemicals).
Examples of the lubricant include calcium stearate and magnesium stearate. The amount of lubricant added is preferably 800 ppm or less, more preferably 600 ppm or less, and even more preferably 300 ppm or less.
Examples of the nucleating agent include pigments such as titanium oxide.
Examples of the additive include an antistatic agent, a light stabilizer, an ultraviolet absorber, an antifogging agent, and an organic peroxide.

Examples of the filler include talc, silica, carbon, mica, calcium carbonate, magnesium carbonate, and wood powder. Moreover, you may add a titanium oxide and an organic pigment with a masterbatch as needed.

The hollow fiber membrane may be a hollow fiber membrane formed by a single membrane or a composite hollow fiber membrane formed by a composite membrane in which a plurality of membranes are laminated.
The thickness of the hollow fiber membrane is not particularly limited, but the hollow fiber membrane outer diameter is preferably 100 to 2000 μm. If the outer diameter of the hollow fiber membrane is 100 μm or more, a gap between the hollow fiber membranes can be easily obtained at the time of manufacturing a hollow fiber membrane module or the like, and a potting resin can easily enter between the hollow fiber membranes. If the outer diameter of the hollow fiber membrane is 2000 μm or less, the size of the entire module can be reduced even when a hollow fiber membrane module using a large number of hollow fiber membranes is manufactured. As a result, the volume of the potting process portion is also reduced, and it is easy to suppress a decrease in dimensional accuracy due to the shrinkage of the potting resin during the potting process.

The porosity of the hollow fiber membrane is preferably 30 to 80% by volume with respect to 100% by volume of the entire hollow fiber membrane. If the porosity is 30% by volume or more, the amount of water permeability tends to increase, and excellent filtration characteristics can be easily obtained. When the porosity is 80% by volume or less, mechanical strength such as pressure resistance is improved.
The size of the pores of the present hollow fiber membrane is not particularly limited as long as sufficient filtration characteristics and mechanical strength are satisfied.

In the present hollow fiber membrane, the membrane surface (inner surface and outer surface) is preferably hydrophilized with a hydrophilic polymer.
The hydrophilic copolymer is a copolymer obtained by copolymerizing a monomer mixture containing 20 mol% or more of ethylene and 10 mol% or more of a hydrophilic monomer. The hydrophilic copolymer may be any type of copolymer such as a random copolymer, a block copolymer, or a graft copolymer.
When the ethylene content in the hydrophilic copolymer is 20 mol% or more, the affinity of the hydrophilic copolymer for the hollow fiber membrane is increased, and the hydrophilic copolymer can be sufficiently coated. Therefore, the membrane surface of the present hollow fiber membrane can be sufficiently hydrophilized.

Examples of the hydrophilic monomer include vinyl compounds such as vinyl alcohol, (meth) acrylic acid and salts thereof, hydroxyethyl (meth) acrylate, polyethylene glycol (meth) acrylic ester, vinyl pyrrolidone, and acrylamide. Of these, vinyl alcohol is particularly preferable.
Only 1 type may be used for a hydrophilic monomer and it may use 2 or more types together.

The hydrophilic copolymer may contain a third component other than ethylene and the hydrophilic monomer.
Examples of the third component include vinyl acetate, (meth) acrylic acid ester, vinyl alcohol fatty acid ester, vinyl alcohol formalized product or butyral product.

The coating amount of the hydrophilic copolymer is preferably 3 to 30% by mass and more preferably 7 to 15% by mass with respect to 100% by mass of the present hollow fiber membrane. When the coating amount of the hydrophilic copolymer is 3% by mass or more, the affinity of the hollow fiber membrane with water is improved and the water permeability is improved. If the coating amount of the hydrophilic copolymer is 30% by mass or less, it is easy to suppress the pores of the hollow fiber membrane from being blocked by the hydrophilic copolymer, and the water permeability is improved.

In the pore diameter distribution of the hollow fiber membrane, it is preferable that the distribution is narrow. Specifically, if the average pore size ± 0.05 μm is 70% or more, not only the fractionation performance becomes sharp, but also the existence ratio of very small pore sizes that do not contribute to the water permeability decreases, so the entire membrane is filtered. There is an effect of reducing resistance, and as a result, water permeability is improved.
In addition, the average pore diameter of ± 0.05 μm is less than 70% of the entire pore diameter distribution, that is, the ratio of the ultrafine pore diameter is 15% or more of the whole, thereby increasing the filtration resistance of the entire membrane, thereby increasing the water permeability. Decreases.

(Production method)
The hollow fiber membrane can be produced, for example, by a method having the following spinning process, stretching process and permanent hydrophilization process.
Spinning step: A step of spinning the resin composition to obtain an unstretched hollow fiber membrane precursor.
Stretching step: A step of stretching a hollow fiber membrane precursor and making it porous to obtain a porous hollow fiber membrane.
Permanent hydrophilic step: A step of imparting permanent hydrophilicity to the membrane surface of the porous hollow fiber membrane.

Spinning process:
For example, using a composite nozzle base in which a plurality of annular discharge ports are arranged concentrically, the resin composition is extruded from the nozzle base, and cooled and solidified in an unstretched state while appropriately adjusting the extrusion speed and the winding speed. To do. Thereby, an unstretched hollow fiber membrane precursor is obtained.
The discharge temperature of the resin composition is not less than the melting point of the polymer used such as polyethylene, and is preferably 10 to 100 ° C. higher than the melting point. The discharged material is preferably taken up at a take-up speed of 0.1 to 3 m / sec in an atmosphere of 10 to 40 ° C.

Stretching process:
The unstretched hollow fiber membrane precursor obtained by melt spinning is subjected to a constant length heat treatment (annealing treatment) at a temperature equal to or lower than the melting point before stretching.
The constant-length heat treatment is preferably performed at 105 to 120 ° C. for 8 to 16 hours. If the temperature is 105 ° C. or higher, this hollow fiber membrane with good quality can be easily obtained. If temperature is 120 degrees C or less, sufficient elongation will be easy to be obtained, stability at the time of extending | stretching will improve, and extending | stretching by high magnification will become easy. Further, if the treatment time is 8 hours or more, the present hollow fiber membrane having good quality can be easily obtained.

The stretching is preferably two-stage stretching in which hot stretching is performed subsequent to cold stretching or multi-stage stretching in which hot stretching is divided into two or more multi-stages following cold stretching. Furthermore, in order to obtain the dimensional stability of the porous hollow fiber membrane obtained by the stretching, heat setting is performed in a state where the porous hollow fiber membrane is slightly relaxed under a constant length or within a range of 40% or less. Do.
The stretching is preferably slow stretching.
Cold drawing is a process of causing microcracking by causing structural breakdown of the film at a relatively low temperature. The temperature of cold drawing is in the range from 0 ° C. to a temperature lower than the melting point of the polymer used by 50 ° C. or more (for example, 0 to 80 ° C. when the polymer in the resin composition is only polyethylene). It is preferable to carry out at a low temperature. When cold drawing is performed at a temperature exceeding the above range, the occurrence of microcracking is reduced and the pores may be reduced.

Hot stretching is a process in which micro cracks generated by cold stretching are expanded to form pores. The heat stretching is preferably performed at a relatively high temperature, but is performed at a temperature not exceeding the melting point of the polymer used.
The heat draw ratio may be appropriately selected depending on the target pore diameter, and is preferably 3 to 7 times the length of the hollow fiber membrane precursor before drawing from the viewpoint of process stability.
It is preferable that the heat stretching is a multi-stage stretching of two or more stages. By setting it as multistage stretching, it becomes easy to form a pore, suppressing that a thread diameter becomes too thin at the time of extending | stretching.
Moreover, it is preferable to perform heat stretching at low speed. If it is low speed drawing, it becomes easy to form pores while suppressing the yarn diameter from becoming too thin during drawing.
In order to effectively perform heat setting, the heat setting temperature is preferably not less than the stretching temperature and not more than the melting temperature.

Permanent hydrophilization process:
As a method for coating the hydrophilic copolymer, for example, after immersing the hollow fiber membrane in a solution in which the hydrophilic copolymer is dissolved in a solvent (hereinafter referred to as “copolymer solution”), The method of drying is mentioned. The method of immersing the hollow fiber membrane in the copolymer solution may be a method of immersing twice or more in the copolymer solution of the same concentration, and immersing twice or more using solutions having different concentrations. The method of performing may be sufficient.

As the solvent, a water-miscible organic solvent is preferable.
Examples of the water-miscible organic solvent include alcohols such as methanol, ethanol, N-propanol and isopropyl alcohol, dimethyl sulfoxide, dimethylformamide and the like. These solvents may be used alone or in combination of two or more. These solvents are preferably mixed with water from the viewpoint of improving the solubility of the hydrophilic copolymer.
In addition, when drying this hollow fiber membrane coated with a hydrophilic copolymer, the boiling point is low because of the ease of creating a vapor-containing atmosphere of the solvent, that is, the low vapor pressure of the solvent and the low toxicity to the human body. It is particularly preferable to use a mixed solvent of alcohol (for example, methanol, ethanol, isopropyl alcohol, etc.) of less than 100 ° C. and water.

The mixing ratio of the water-miscible organic solvent and water may be in a range that does not decrease the water permeability of the hollow fiber membrane and does not excessively decrease the solubility of the hydrophilic copolymer. Specifically, although it varies depending on the type of hydrophilic copolymer used, when ethanol is used as the organic solvent, the ethanol / water ratio is preferably 90/10 to 30/70 (volume%).

The content of the hydrophilic copolymer in the copolymer solution is preferably 0.1 to 10% by mass, and 0.5 to 5% by mass with respect to 100% by mass as the total of the solvent and the hydrophilic copolymer. More preferred. When the content of the hydrophilic copolymer is 0.1% by mass or more, it becomes easy to uniformly coat the hydrophilic copolymer on the hollow fiber membrane. If the content of the hydrophilic copolymer is 10% by mass or less, it is easy to suppress the viscosity of the copolymer solution from becoming too large, and the pores of the hollow fiber membrane are blocked with the hydrophilic copolymer. It is easy to suppress that.

The higher the temperature of the copolymer solution at the time of the immersion treatment, the lower the viscosity, and the better the permeability of the solution into the hollow fiber membrane. Moreover, it is preferable that it is below the boiling point of a copolymer solution from the point which can perform an immersion process stably.
The immersion treatment time varies depending on the film thickness, pore diameter, and porosity of the hollow fiber membrane to be immersed, but is preferably in the range of several seconds to several minutes.

Before the hollow fiber membrane is dried after being immersed in the copolymer solution, the organic solvent vapor is contained in an amount of 3% by volume or more, and the temperature is within the range from room temperature to the boiling point of the solvent. A setting process for allowing the hollow fiber membrane to stay for at least 30 seconds is performed.
The purpose of the treatment is (1) to prevent pore clogging by forming a hydrophilic copolymer film on the surface of the nodule portion of the microfibril and stack lamella constituting the hollow fiber membrane. (2) To bind microfibrils to increase the diameter of slit-shaped pores to form elliptical pores, thereby increasing the amount of water permeation and increasing the affinity with treated water.

Examples of the drying treatment of the hollow fiber membrane after the setting treatment include known drying methods such as vacuum drying and hot air drying.
The drying temperature may be a temperature range in which the hollow fiber membrane is not deformed by heat. For example, in the case of the present hollow fiber membrane made of polyethylene, the drying temperature is preferably 120 ° C. or less, particularly preferably 40 to 70 ° C.

In addition, the manufacturing method of this hollow fiber membrane is not limited to the above-mentioned method. For example, a method that does not perform the permanent hydrophilization step may be used.

<Water purifier cartridge>
The cartridge for water purifier of this invention is a module which comprises this hollow fiber membrane mentioned above. The cartridge for water purifier of the present invention has the same form as a known cartridge for water purifier, except that this hollow fiber membrane is used.
For example, a cartridge for a faucet direct connection type water purifier, a cut ridge for a pitcher type water purifier, a cartridge for a stationary water purifier used by being installed on a sink, and a cartridge for an under-sink type water purifier installed in a storage space under the sink .

<Hollow fiber membrane module>
The hollow fiber membrane module of the present invention is a module comprising the above-described hollow fiber membrane. The hollow fiber membrane module of the present invention has the same form as a known hollow fiber membrane module, except that this hollow fiber membrane is used.
For example, a hollow fiber membrane module of a known form in which several hundreds of the present hollow fiber membranes are bundled and inserted into a cylindrical housing and the composite hollow fiber membranes are sealed with a sealing material (potting resin). .

Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples. However, the present invention is not limited by the following description.
(Melt flow rate (MFR))
For MFR of polyethylene, MFRD (unit: g / 10 minutes) was measured according to JIS K7210 code D (measurement temperature: 190 ° C., load: 2.16 kg), and JIS K7210 code G (measurement temperature). : MFRG (unit: g / 10 min) was measured based on 190 ° C. and load: 21.6 kg).
Moreover, FRR (G / D) (= MFRG / MFRD) was calculated | required from those measurement results.

(density)
The density (unit: kg / m ³ ) of polyethylene was measured according to JIS K7112.

(Ratio Mw / Mn)
The ratio Mw / Mn of polyethylene was calculated by obtaining Mw and Mn from calibration curves obtained by measurement by GPC (high temperature GPC) under the following conditions. The calibration curve was calculated in a third order by measuring a standard sample of polystyrene and using a polyethylene conversion constant (0.48). The columns used were the following three columns connected in series.
Measurement condition:
Measuring device: “150-GPC” (manufactured by Waters)
Column: “Shodex GPC AT-807 / S” (manufactured by Showa Denko) (1), “Tosoh TSK-GEL GMH6-HT” (manufactured by Tosoh) (2)
Solvent: 1,2,4-trichlorobenzene Column temperature: 140 ° C
Sample concentration: 0.05% by mass (injection amount: 500 μL)
Flow rate: 1.0 mL / min Sample dissolution temperature: 160 ° C.
Sample dissolution time: 2.5 hours

For polyethylene, when a shoulder peak is observed in the molecular weight distribution chart measured by the high temperature GPC, Mw and Mn of each component such as a low molecular weight component and a high molecular weight component are approximated by a Gaussian distribution, and The blending ratio of these components was calculated.

(FL, FH)
The component amount (FL) (unit: mass%) having a molecular weight of 1000 or less and the component amount (FH) (unit: mass%) having a molecular weight of 1,000,000 or more are calculated by measuring the molecular weight distribution by high-temperature GPC under the following conditions. did. That is, in the molecular weight distribution chart obtained by measurement by high-temperature GPC under the following conditions, the ratio of the area of the molecular weight portion of 1000 or less, or the ratio of the area of the molecular weight portion of 1 million or more to the total area of the molecular weight distribution, FL and FH were calculated. The columns used were the following three columns connected in series.
Measurement condition:
Measuring device: “Alliance GPCV 2000” (manufactured by Waters)
Column: “AT-807S” (manufactured by Showa Denko) (1), “GMHHR-H (S) HT” (manufactured by Tosoh) (2)
Solvent: 1,2,4-trichlorobenzene Column temperature: 140 ° C
Sample concentration: 20 mg / solvent 10 mL
Flow rate: 1.0 mL / min Sample dissolution temperature: 140 ° C.
Sample dissolution time: 1 hour

(ESCR)
The ESCR (environmental stress crack resistance, unit: time) of polyethylene was measured by a constant strain environmental stress cracking test according to JIS K6760. As a test solution, a 10% by mass aqueous solution of “Igepal CO-630” (manufactured by Rhodia Nikka Co., Ltd.) was used. The time when the probability of occurrence of cracks due to environmental stress was 50% was measured and used as the ESCR value.

(Coating amount of hydrophilic copolymer)
The coating amount W (unit: mass%) of the hydrophilic copolymer was calculated according to the following formula.
W = (XY) / Y × 100
However, in the formula, X is the dry membrane mass (unit: g) after the hydrophilization treatment, and Y is the dry mass (unit: g) of the hollow fiber membrane before the treatment.

(Water permeability)
The amount of water permeation (unit: m ³ / m ² · hour · MPa) of the obtained hollow fiber membrane is such that the hollow fiber membranes are bundled in a U shape and the ends of the hollow fiber membranes are solidified with urethane resin, and the effective membrane area A hollow fiber membrane module of 70 to 90 cm ² was produced, and ion exchange water was filtered at a differential pressure of 0.1 MPa, and the water permeability at that time was measured.

(Bubble point, porosity, pore size distribution)
The obtained hollow fiber membranes are bundled in a U shape, and the ends of the hollow fiber membranes are solidified with urethane resin to produce a hollow fiber membrane module having an effective membrane area of about 50 m ^2. The sample was immersed in ethanol having a concentration of 95% or more so that the portion of was completely immersed. After suctioning 100 mL or more of ethanol from inside the hollow fiber membrane so that the porous inside of the hollow fiber membrane is sufficiently wetted with ethanol, nitrogen is fed into the hollow fiber membrane while being immersed, in increments of 1 kPa every 10 seconds. The air pressure was increased. Bubbles were generated from almost the entire surface of the hollow fiber membrane, and the nitrogen pressure when the interval between the bubbles was within 1 mm was taken as the bubble point (BP). The relationship between the bubble point P (pressure) and the average pore diameter is as represented by the following formula.
P = 2σ cos θ / r
In the formula, σ is the surface tension of ethanol, θ is the contact angle between ethanol and the hollow fiber membrane, and r is the average pore radius.
The porosity (unit: volume%) was measured using a mercury porosimeter 221 type (manufactured by Carlo Elba).
The pore size distribution and the average pore size of the hollow fiber membranes are fluorine based on the PMI palm porosimeter PMI palm porometer CFP-1200AE (porous material automatic pore size distribution measuring system) based on the bubble point method (ASTM F316-86). The measurement was carried out using Surfactant Fluorinert FC-72 (manufactured by 3M) as a measurement solvent.
The pore diameter (μm) of the polyethylene porous hollow fiber membrane and the ratio (%) in the pore diameter distribution are shown in FIG. Further, an average pore diameter range of ± 0.05 μm that most influenced the flow rate was calculated by integration from the measured pore diameter distribution.

(Average flow hole diameter)
The average flow pore size was measured with a Palm Porometer CFP-1200AE (a porous material automatic pore size distribution measuring system) manufactured by PMI in accordance with ASTM F316-86.
(Opening diameter variation)
The pore size variation is measured by a PMI palm porometer CFP-1200AE (porous material automatic pore size distribution measurement system) according to ASTM F316-86, and the cumulative flow rate is 100%. The maximum pore diameter was 5%, and the minimum pore diameter was 95%.
Opening hole diameter variation (%) = [(5% maximum hole diameter−95% minimum hole diameter) / average flow hole diameter] × 100

[Example 1]
As a resin composition, a high-density polyethylene (trade name “H6670B” manufactured by SCG Chemical, density 0.966 g / cm ³ , MFRD: 0.7 g / 10 minutes) produced by a three-stage continuous polymerization method using a Ziegler-type catalyst. , MFRG: 54 g / 10 min, FRR (G / D) = 77, FL: 0.38 mass%, FH: 2.64 mass%, Mw / Mn = 8.8, ESCR: 20 hours).
Moreover, about the said high density polyethylene, three components which approximated the chart of the molecular weight distribution measured by high temperature GPC by Gaussian distribution were as follows. The chart had one shoulder peak at around 1 million molecular weight and around 5000 molecular weight.
1) Mn: 1.99 × 10 ⁴ Mw: 1.09 × 10 ⁵ Mixing ratio: 88%
2) Mn: 2.76 × 10 ³ Mw: 5.25 × 10 ³ Mixing ratio: 6%
3) Mn: 7.52 × 10 ⁵ Mw: 9.74 × 10 ⁵ Mixing ratio: 6%

Spinning process:
Using the resin composition, melt spinning was performed at a discharge temperature of 170 ° C. and a winding speed of 70 m / min using a hollow fiber manufacturing nozzle in which annular discharge ports were arranged concentrically. Further, the yarn was wound around the yarn discharged from the nozzle while uniformly flowing cooling air at a temperature of 20 ° C. and a wind speed of 0.5 m / sec to obtain an unstretched composite hollow fiber membrane precursor.

Stretching process:
The obtained unstretched composite hollow fiber membrane precursor was annealed by being placed in air at 115 ° C. for 16 hours while being wound around a bobbin. The composite hollow fiber membrane precursor after the annealing treatment was cold-stretched 1.5 times between rollers kept at 30 ° C., and subsequently the maximum stretch amount was 6.0 in a heating furnace heated to 117 ° C. The film is stretched between rollers so as to be doubled, and further relaxed by 20% in a heating furnace heated to 118 ° C., so that the total stretch ratio at the time of winding (the ratio relative to the unstretched composite hollow fiber membrane precursor) ) Was multiplied by 5 to obtain a polyethylene porous hollow fiber membrane.

Permanent hydrophilization process:
Next, an ethylene-vinyl alcohol copolymer having an ethylene content of 32 mol% (trade name “Soarnol DC3203”, manufactured by Nippon Synthetic Chemical Co., Ltd.) is mixed into a 70 ° C. ethanol / water = 40/60 (volume%) mixed solution. 1.5% by mass was dissolved to prepare a copolymer solution. After immersing the hollow fiber membrane in the copolymer solution for 30 seconds, the hollow fiber membrane was pulled up, and a part of the copolymer solution excessively adhered to the surface of the hollow fiber membrane was squeezed out by a guide. Subsequently, the hollow fiber membrane was raised at an angle of 90 ° in an atmosphere having an ethanol vapor concentration of 40% by volume and 60 ° C., and was allowed to stay for 80 seconds, so that the hydrophilic polymer was also applied to the pore inner surface of the hollow fiber membrane. Uniformly adhered. Thereafter, the solvent was removed by drying with hot air at 70 ° C. The adhesion rate of the ethylene-vinyl alcohol copolymer after drying was 10.5% by mass with respect to 100% by mass of the hollow fiber membrane.
When the obtained polyethylene porous hollow fiber membrane was observed with a scanning electron microscope, the inner and outer surfaces and the microporous inner surface of the polyethylene porous hollow fiber membrane were uniformly covered with a thin film of an ethylene-vinyl alcohol copolymer. It was broken.
Moreover, the bubble point which shows the hole diameter of a film | membrane was 122 kPa. The porosity was 73.5% by volume.
When a fluorosurfactant Fluorinert FC-72 (manufactured by 3M) was measured with a palm porosimeter manufactured by PMI as a measuring solvent, it occupied the total pore size distribution in a pore size range of average pore size 0.3123 μm and average pore size ± 0.05 μm. The film had a sharp pore size distribution such that the ratio was 85.5%.

[Example 2]
As a resin composition, a high-density polyethylene (trade name “H6430BM” manufactured by SCG Chemical Co., density: 0.966 g / cm ³ , MFRD: 0.4 g / kg) manufactured by a three-stage continuous polymerization method using a Ziegler-type catalyst. 10 minutes, MFRG: 30 g / 10 minutes, FRR (G / D) = 75, FL: 0.66 mass%, FH: 3.00 mass%, Mw / Mn = 12, ESCR: 25 hours).
Moreover, about the said high density polyethylene, three components which approximated the chart of the molecular weight distribution measured by high temperature GPC by Gaussian distribution were as follows. The chart had one shoulder peak at around 1 million molecular weight and around 5000 molecular weight.
1) Mn: 2.81 × 10 ³ Mw: 6.57 × 10 ³ Mixing ratio: 9%
2) Mn: 2.24 × 10 ⁴ Mw: 1.15 × 10 ⁵ Mixing ratio: 84%
3) Mn: 4.68 × 10 ⁵ Mw: 9.40 × 10 ⁵ Mixing ratio: 7%

A polyethylene porous hollow fiber membrane hollow fiber membrane was obtained in the same manner as in Example 1 except that the resin composition was used and the winding speed in melt spinning was 40 m / min. Moreover, the permanent hydrophilization process similar to Example 1 was performed. The adhesion rate of the ethylene-vinyl alcohol copolymer was 10.5% by mass relative to 100% by mass of the hollow fiber membrane.
When the obtained polyethylene porous hollow fiber membrane was observed with a scanning electron microscope, the inner and outer surfaces of the polyethylene porous hollow fiber membrane and the inner surface of the micropore were uniformly covered with a thin film of an ethylene-vinyl alcohol copolymer. It was.
Moreover, the bubble point which shows the hole diameter of a film | membrane was 127 kPa. The porosity was 73.8% by volume.
When a fluorosurfactant Fluorinert FC-72 (manufactured by 3M) was measured with a palm porosimeter manufactured by PMI as a measuring solvent, it occupied the total pore size distribution in the pore size range of average pore size 0.3155 μm and average pore size ± 0.05 μm. The film had a sharp pore size distribution such that the ratio was 87.3%.

[Comparative Example 1]
As a resin composition, high density polyethylene (trade name “HY540” manufactured by Nippon Polyethylene Co., Ltd., density 0.960 g / cm ³ , MFRD: 1.0 g / 10 min, MFRG, manufactured by slurry polymerization using a Ziegler type catalyst. : 45 g / 10 min, FRR (G / D) = 45, FL: 0.37 mass%, FH: 1.07 mass%, Mn: 1.8 × 10 ⁴ , Mw: 1.18 × 10 ⁵ , Mw /Mn=6.6, ESCR: 100 hours).
For the high-density polyethylene, no shoulder peak or the like was observed in the molecular weight distribution measured by high-temperature GPC in the vicinity of a molecular weight of 1,000,000.

Spinning process:
An unstretched composite hollow fiber membrane precursor was obtained by melt spinning as in Example 1 except that the resin composition was used and the discharge temperature was 180 ° C.
Stretching process:
The obtained unstretched composite hollow fiber membrane precursor was annealed by being placed in air at 115 ° C. for 16 hours while being wound around a bobbin. The hollow fiber membrane after the annealing treatment is cold-drawn 1.5 times between rollers kept at 30 ° C., and then the maximum drawing amount is 6.0 times in a heating furnace heated to 117 ° C. As described above, the film is stretched between rollers and relaxed at a constant length in a heating furnace heated to 118 ° C., so that the total draw ratio during winding (the ratio relative to the unstretched composite hollow fiber membrane precursor) is 6 times. Thus, a polyethylene porous hollow fiber membrane was obtained.
Permanent hydrophilization process:
A permanent hydrophilic treatment was performed in the same manner as in Example 1.

When the obtained polyethylene porous hollow fiber membrane was observed with a scanning electron microscope, the inner and outer surfaces and the microporous inner surface of the polyethylene porous hollow fiber membrane were uniformly covered with a thin film of an ethylene-vinyl alcohol copolymer. It was broken.
The bubble point indicating the pore size of the membrane was 132 kPa. The porosity was 71.3% by volume.
When a fluorosurfactant Fluorinert FC-72 (manufactured by 3M) was measured with a palm porosimeter manufactured by PMI as a measuring solvent, it occupied the total pore size distribution in a pore size range of average pore size 0.3813 μm and average pore size ± 0.05 μm. As a proportion of 58%, the membrane had a wider pore size distribution than the example.
Table 1 shows the results of evaluating the water permeability of the polyethylene porous hollow fiber membrane obtained in each example.

As shown in Table 1, in Examples 1 and 2 which are the polyethylene porous hollow fiber membranes of the present invention, the water permeability was large and the filtration characteristics were excellent. Further, the resin composition used had sufficient fluidity and excellent moldability. Further, since the amount of the low molecular weight component is not increased in order to improve moldability, excellent rigidity is maintained.
Further, the polyethylene porous hollow fiber membrane of Example 2 had a higher porosity than the polyethylene porous hollow fiber membrane of Example 1, had a large water permeability, and was excellent in filtration characteristics.

On the other hand, the polyethylene porous hollow fiber membrane of Comparative Example 1 using polyethylene whose density is too low has a remarkably low water permeability and inferior filtration characteristics.

In Example 1 which is the polyethylene porous hollow fiber membrane of the present invention, the average pore diameter is 0.3123, and the ratio of the average pore diameter in the pore diameter range of ± 0.05 μm to the total pore diameter distribution is as high as 85.5%. Results are shown. Further, in Example 2 which is the polyethylene porous hollow fiber membrane of the present invention, the average pore diameter is 0.3155, and the ratio of the average pore diameter within the pore diameter range of ± 0.05 μm to the total pore diameter distribution is 87.3%. And showed high results.
On the other hand, in Comparative Example 1 using polyethylene whose density is too low, the average pore diameter of the polyethylene porous hollow fiber membrane was 0.3813, but the ratio of the average pore diameter to the total pore diameter distribution in the pore diameter range of ± 0.05 μm Was as low as 58.0%.

Since the polyethylene porous hollow fiber membrane of the present invention is excellent in filtration characteristics and membrane strength, it can be suitably used for filtration of a wide variety of liquids to be treated.

Claims

A polyethylene porous hollow fiber membrane having an average pore size of 0.1 to 0.5 μm and a pore size distribution in a range of ± 0.05 μm from the average pore size of 70% or more of the total pore size distribution.
2. The polyethylene porous hollow fiber membrane according to claim 1, formed of a resin composition containing polyethylene that satisfies the following requirements (a) to (d).
(A) The melt flow rate (MFRD) measured according to JIS K7210 code D is 0.1 to 0.9 g / 10 min.
(B) The melt flow rate (MFRG) measured in accordance with JIS K7210 code G is 50 to 100 g / 10 min.
(C) The ratio FRR (G / D) (= MFRG / MFRD) of the MFRD and the MFRG is 50-100.
(D) The density is 0.962 to 0.968 g / cm 3 .
3. The polyethylene porous hollow fiber membrane according to claim 1, wherein a ratio Mw / Mn of the mass average molecular weight Mw and the number average molecular weight Mn in the polyethylene is 8.0 to 12.0.
The polyethylene porous hollow fiber membrane according to any one of claims 1 to 3, wherein the polyethylene has an environmental stress crack resistance measured in accordance with JIS K6760 of 10 to 50 hours.
The amount of a component having a molecular weight of 1,000 or less in the polyethylene is 2.0% by mass or less, and the amount of a component having a molecular weight of 1,000,000 or more is 1.5 to 3.0% by mass. The polyethylene porous hollow fiber membrane described.
The polyethylene porous hollow fiber membrane according to any one of claims 1 to 5, wherein the inner surface and the outer surface of the hollow fiber membrane are hydrophilized with a hydrophilic copolymer.
The polyethylene porous hollow fiber membrane according to claim 6, wherein the hydrophilic copolymer is an ethylene-vinyl alcohol copolymer.
A water purifier cartridge comprising the polyethylene porous hollow fiber membrane according to any one of claims 1 to 7.
A hollow fiber membrane module comprising the polyethylene porous hollow fiber membrane according to any one of claims 1 to 7.
The polyethylene porous hollow fiber membrane according to any one of claims 1 to 7, wherein the average flow pore size is 0.1 to 0.5 µm and the variation in pore size is 100% or less.