JP3168036B2 - Large-pore porous polyethylene hollow fiber membrane, method for producing the same, and hydrophilic porous polyethylene hollow fiber membrane - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a porous polyethylene hollow fiber membrane having a large pore size and a high porosity, which is suitable for fields requiring extremely high filtration flux, such as microfiltration and air purification. The present invention relates to a production method and a hydrophilic porous polyethylene hollow fiber membrane.

[0002]

2. Description of the Related Art A porous hollow fiber membrane made of polyethylene in which strip-shaped micropores are laminated has been known, and details thereof are disclosed, for example, in JP-B-63-35726 and JP-B-6-76.
It is disclosed in JP-A-3-42006. The former has a melt index value of 1 to 15 and a density of 0.960 g / cm.
Using a high-density polyethylene of ³ or more, the spinning draft is melt-spun in the range of 1,000 to 10,000, and then cold-drawn at a drawing speed of 50% or more per second, and then
Thermal stretching in a temperature range of 125 ° C. to give a total stretching amount of 40
The porous hollow fiber membrane obtained at 0% to 700% has characteristic strip-shaped micropores, the average pore diameter of the micropores measured by a mercury porosimeter is 0.5 μm to 2 μm, and the porosity is It is disclosed that the rejection to blue dextran is less than 90%. However, the average pore diameter of the micropores of the porous hollow fiber membrane disclosed in the example is only at most 0.82 μm. Also, Japanese Patent Publication No. Sho 63-42006 discloses that 5 cm to 30 cm
A porous hollow fiber obtained by melt spinning with a spinning draft exceeding 2,000 in a state where a spinning cylinder of cm is installed and having a total drawing amount of 100% to 400% has a water permeability of 100 to 2000 l / m ² · hr · 760 mmHg. It is disclosed to have an amount and a permeability to human serum albumin of 30% or more, and a rejection to blue dextran of 90% or more. That is, the latter provides a hollow fiber membrane having micropores having a smaller pore diameter than the former.

Japanese Patent Application Laid-Open No. 61-86902 discloses that a pore diameter obtained by a stretch opening method is 0.1 to 1.0 μm.
m porous hollow fiber membranes are disclosed. The feature of this porous hollow fiber membrane is that the microfibrils arranged in the fiber length direction are substantially cut. That is, in spite of the fact that the microfibrils are cut and the strip-shaped micropores are enlarged in width and larger in diameter, in reality, only pores with a diameter of up to 1.0 μm are obtained. is there.

Further, Japanese Patent Application Laid-Open No. 61-271003 discloses a hydrophilic composite porous membrane comprising a porous structure matrix composed of a polyolefin and an ethylene-vinyl alcohol copolymer coating layer. In the claims, the average pore diameter of the fine pores is 0.02 to 4.0.
There is a description that it is μm. However, the technology disclosed in this hydrophilic composite porous membrane is disclosed in JP-B-63-35726 and JP-A-61-61926 regarding the pore size.
It does not exceed the technical level of JP-A-86902 at all, and the average pore size of the hollow fiber obtained in the example is 0.25 to 0.70 μm.

[0005] Thus, in the prior art, the average pore size is 1.
A polyethylene porous hollow fiber membrane having strip-shaped micropores exceeding 0 μm was not obtained.

[0006] Generally, porous membranes are roughly classified into hydrophilic membranes and hydrophobic membranes depending on the characteristics of the material. As examples of the hydrophilic porous membrane, cellulose, cellulose derivatives, polyvinyl alcohol, ethylene-vinyl alcohol copolymer and the like are known. The feature of the hydrophilic porous membrane is that the pore surface of the membrane is hydrophilic, so that the membrane is easily wetted by water, and the aqueous solution can be filtered without any special pretreatment.

However, hydrophilic membranes have the disadvantage that the mechanical strength when wetted and the swelling due to water are large, and when dried from a wet state, the membrane performance is reduced.
It has the disadvantage that it is easily deteriorated.

[0008] On the other hand, since the hydrophobic porous membrane is hydrophobic, it is difficult to transmit water as it is, and a hydrophilic treatment is required to transmit a hydrophilic liquid such as water. In particular, various methods for hydrophilization by surface modification of polyolefins have been studied.However, for hydrophilization of porous membranes with complicated surface shapes, simple methods for hydrophilization of film-like materials with a smooth surface are used. Cannot be applied to

As a method for hydrophilizing a polyolefin porous membrane, the entire surface including the micropores of the polyolefin porous membrane is wet-treated with an organic solvent such as alcohol or ketone having good compatibility with water. An organic solvent wetting / water replacement method in which an organic solvent is replaced with water, a physical adsorption method in which a hydrophilic substance such as polyethylene glycol or a surfactant is adsorbed on the surface of the porous membrane to impart hydrophilicity to the porous membrane ( JP-A-54-153873 and JP-A-59-24732.
Japanese Patent Application Laid-open No. Sho 5 (1994), or a method of irradiating radiation while keeping a hydrophilic monomer on the surface of a porous film.
Chemical surface modification methods such as a method of plasma-treating a porous structure of a hydrophobic resin (Japanese Patent Application Laid-Open No. 56-157737) are known.

[0010] However, in the organic solvent wetting / water replacement method, once water in the pores escapes during storage or use, the portion returns to hydrophobic and cannot pass through water. It needs to be filled with water, and handling is complicated. The physical adsorption method is simple in operation, but is not necessarily a sufficient hydrophilization method because a hydrophilic substance is desorbed over a long period of use. In addition, in the conventional chemical surface modification method, in both cases of the method of irradiating radiation and the method of plasma treatment, it is difficult to uniformly hydrophilize in the film thickness direction, and when the film is thick or the film is hollow fiber-shaped. If the entire surface in the film thickness direction is subjected to a hydrophilic treatment, the porous membrane substrate is damaged and mechanical strength is inevitably reduced.

Further, it has been proposed that a hydrophobic porous membrane is previously subjected to a hydrophilization treatment with a saponified product of an ethylene-vinyl acetate copolymer, that is, an ethylene-vinyl alcohol copolymer (JP-A-61-125408). No., JP 6
1-271003). Also, after blending and melt-spinning two different polymers, a stretching treatment is performed to cleave the interface between the different polymers to form microporous porous hollow fibers, and to hydrolyze the side chain groups present in the constituent polymers. It has been proposed to produce a hydrophilic porous hollow fiber having a pore surface made hydrophilic by post-treatments such as decomposition and sulfonation (JP-A-55-137208).

Further, there has been proposed a porous membrane in which a hydrophilic polymer is firmly held on the pore surface of a polyolefin porous membrane, and a method for producing the same (JP-A-63-19).
No. 0602). The details of the technology are as follows: a hydrophilic cross-linked polymer composed of monomers containing diacetone acrylamide and a cross-linkable monomer is held on at least a part of the pore surface of the polyolefin porous membrane. In addition, this is a production method in which a monomer containing diacetone acrylamide and a crosslinkable monomer is heated and polymerized while being held on at least a part of the pore surfaces of the polyolefin porous membrane.

However, all of these methods use a conventionally known polyolefin porous membrane as a starting material, so that their performance is insufficient for applications requiring a high permeation flow rate. That is, in order to obtain a hydrophilic porous membrane having a high permeation flow rate, it was necessary to consider hydrophilization including increasing the pore diameter and increasing the porosity of the hydrophobic porous membrane.

[0014]

In the field of microfiltration and air purification, an extremely high filtration flux is required, and membranes and nonwoven fabrics having micron-order pores opened with high porosity are used. I have. As described in JP-B-63-35726, a porous hollow fiber having strip-shaped micropores has a large gas permeation amount and liquid permeation rate, and has a structure in which strip-shaped micropores are stacked. In addition, it has a feature that clogging is unlikely to occur. However, such hollow fibers having strip-shaped micropores still perform well in sterile dustless air filters, dust filters for various gases, filters for sterile water, etc., which require extremely high filtration flux and low pressure loss. Is insufficient. The reason is that the pore diameter is still small and the porosity is low for application to such fields.

On the other hand, the hydrophilization treatment with an alcohol or a surfactant is a temporary hydrophilization, and if the hydrophilization treatment agent is used for filtration or the like while being attached to the porous membrane, the alcohol or the surfactant becomes Since the water is transferred to and contaminates purified water, it is necessary to sufficiently wash and remove these hydrophilizing agents before filtration. In addition, when dried in such a state, the membrane surface returns to hydrophobic. Therefore, once the hydrophilic treatment is performed, the hydrophilic agent is replaced with water, and the pore surface of the porous membrane is always kept in contact with water. Has the problem of having to do so.

In the method described in Japanese Patent Application Laid-Open No. 56-33833, permanent hydrophilicity is achieved because a group exhibiting hydrophilicity is chemically fixed to the porous membrane. Since it is necessary to irradiate with radiation, large-scale equipment is required, and the stability of the process is not sufficient.
There is also a risk that the film material may be damaged, and there is a problem that the operation and management of the processing steps are difficult.

In addition, fibers obtained by melt-spinning and drawing a blend of different polymers described in JP-A-55-137208 to be porous generally have a low porosity. Further, post-treatments such as hydrolysis and sulfonation for hydrophilization are required, and there is a problem that the process becomes complicated.

Further, even if the technique of JP-A-56-38333 is applied to the hollow fiber membrane of JP-B-63-35726, only a hydrophilic hollow fiber membrane having a submicron pore diameter can be obtained.

The technology disclosed in Japanese Patent Application Laid-Open Nos. 61-125408 and 61-271003 for the hydrophilic composite porous membrane is disclosed in JP-B-63-35726 described above. The average pore size of the hollow fibers obtained in the examples is 0.25 to 0.70 μm.

Furthermore, Japanese Patent Application Laid-Open No. 63-190602 discloses that a hydrophilic cross-linked polymer composed of monomers containing diacetone acrylamide and a cross-linkable monomer is held on the pore surface of a porous polyolefin membrane. 1 is a disclosed hydrophilic porous hollow fiber membrane.

However, a porous membrane having a crosslinkable polymer held on the pore surface of such strip-shaped micropores is
Performance is still insufficient for filtration of aqueous solutions and suspensions requiring extremely high filtration flux and low pressure loss, production of hydrophobicity for use in the electronics industry, sterilization of raw water for pharmaceutical production, and the like.
The reason is that the pore diameter is still small and the porosity is low for application to such fields. If the membrane structure is composed of a lamination of strip-shaped micropores with excellent filtration efficiency, and if a porous hollow fiber with a large pore size and high porosity can be given permanent hydrophilicity, energy saving and ultra-clean The contribution to cutting-edge industrial fields such as creation of a safe environment is extremely large.

Under these circumstances, the present inventors have developed a porous polyethylene hollow fiber membrane and a permanent hydrophilicity which can achieve a high porosity, a large pore diameter and a large air permeability with a structure in which strip-shaped micropores are stacked. As a result of intensive studies to obtain a porous polyethylene hollow fiber membrane having a high porosity and a large pore diameter, the present invention was achieved.

[0023]

The gist of the present invention is to provide a porous hollow fiber membrane made of polyethylene, which is formed by being surrounded by microfibrils arranged in the fiber length direction and a knot portion made of a stack dramella. The strip-shaped micropores have a laminated structure in which the micropores communicate with each other from the inner wall surface of the hollow fiber membrane to the outer wall surface. The average pore diameter of the micropores measured by a mercury porosimeter exceeds 2 μm and is 10 μm or less, and the porosity is 75% to 95
%, The amount of air permeated is 8 × 10 ⁵ liter / m ² · hr · 0.
A large-pore-diameter porous polyethylene hollow fiber membrane having a diameter of 5 atm or more.

The present invention also provides a method of spinning a high molecular weight polyethylene having an MI value of 0.05 to 5.5 at a temperature 20 to 150 ° C. higher than the melting point of the polymer by using a hollow fiber nozzle.
After melt spinning with a draft of 5 to 5000 , the obtained undrawn yarn is annealed at 100 to 130 ° C for 30 minutes or more , and then cold drawn at 40 ° C or less at a rate of 40% or more per second , and then for 1 second. The present invention is to produce a large-pore-diameter porous polyethylene hollow fiber membrane having the above-mentioned characteristics, which is thermally stretched at a rate of 10% or less per unit area and a total stretch amount is 750 to 2500%.

Further, the present invention provides a hydrophilic porous polyethylene obtained by holding a saponified ethylene-vinyl acetate copolymer on at least a part of the surface of the micropores of the large-pore porous polyethylene hollow fiber membrane described above. In the hollow fiber membrane.

Still further, the present invention provides a hydrophilic polymer obtained by polymerizing a monomer containing diacetone acrylamide and a crosslinkable monomer on at least a part of the surface of the micropores of the large-pore porous polyethylene hollow fiber membrane described above. And a hydrophilicized porous polyethylene hollow fiber membrane holding a hydrophilic crosslinked polymer.

Hereinafter, the present invention will be described in more detail.

The polyethylene used in the present invention is preferably a high-density polyethylene having few branches.
The density according to the measurement method indicated by ASTM D-1505 is preferably at least 0.960 g / cm ³ or more, more preferably 0.965 g / cm ³ or more. Melt shaping this polyethylene under specific conditions,
Further, by stretching under specific conditions, a porous hollow fiber membrane having a large pore diameter in which the micropores are connected to each other from the inner wall surface to the outer wall surface of the hollow fiber can be obtained.

The MI value of the polyethylene used in the present invention is preferably in the range of 0.05 to 6.0. MI value is a value measured by ASTM D-1238,
More preferably, it is in the range of 0.1 to 5.5. When a polyethylene having an MI value exceeding 6.0 is used, 750 is used.
% Or more, and it is difficult to obtain a porous hollow fiber membrane having a large pore diameter and a high porosity according to the present invention. In addition, polyethylene having an MI value of less than 0.05 has too high a melt viscosity, making stable spinning difficult. It is one of the important points of the present invention to employ polyethylene having a high molecular weight as long as stable spinning is possible.

In the present invention, the specific high-density polyethylene is melt-spun using a nozzle for producing a hollow fiber,
A highly oriented crystalline undrawn hollow fiber is produced. It is desirable that the nozzle has a double pipe structure with less uneven thickness, but a nozzle having a horseshoe shape or another structure may be used. In a nozzle having a double pipe structure, the gas supplied to maintain the hollow form inside the hollow fiber may be supplied by natural suction or forced suction.

In order to stably obtain the porous hollow fiber membrane of the present invention, the spinning temperature is 20 to 150 ° C. below the melting point of the polymer.
It is desirable to set the temperature in a high range. When spinning is performed at a temperature lower than this temperature range, melting of the polymer is incomplete, melt fracture is likely to occur, and stability in the stretching step is reduced. Conversely, when spinning is performed in a temperature range higher than this temperature range, it is difficult to increase the pore diameter and the porosity of the porous hollow fiber membrane.

The polymer discharged at an appropriate spinning temperature is:
It is desirable to take the spinning draft in the range of 5 to 5000. When the spinning draft exceeds 5000, an undrawn hollow fiber capable of performing a total drawing of 750% or more cannot be obtained. If the spinning draft is less than 5, a highly oriented undrawn hollow fiber cannot be obtained, and it is impossible to make the drawing porous.

The undrawn hollow fiber thus obtained is an undrawn hollow fiber highly oriented in the fiber axis direction, and has an inner diameter of 10%.
The thickness is about 0 to 2000 μm, and the thickness is about 15 to 800 μm. This undrawn hollow fiber is subjected to a heat treatment under a temperature condition of 100 to 130 ° C, more preferably 115 to 130 ° C, and is subjected to drawing. The required heat treatment (annealing) time is 30 minutes or more. By this annealing treatment, the crystal structure becomes more complete, and the elastic recovery at 50% elongation is at least 50%.

In the production method of the present invention, the stretching is performed by two-stage stretching in which hot stretching is performed after cold stretching. In the cold stretching, it is preferable to fix the stretching point in order to break down the crystal structure and uniformly generate microcraze, and it is desirable to perform the cold stretching at a high stretching speed of 40% or more per second. Further, in order to break the crystal structure without relaxing it and to generate microcraze, the cold stretching temperature is desirably 40 ° C. or less.

After performing cold stretching of about 5 to 150% in this way, hot stretching is performed in a temperature range of 100 to 130 ° C. If the hot stretching temperature exceeds this range, the hollow fiber membrane becomes transparent, and it is difficult to obtain a desired porous structure. If the temperature is lower than 100 ° C., the porous structure becomes fine and the porosity decreases, and the desired large fineness is obtained. A product having a pore size cannot be obtained. Furthermore, the deformation rate during hot stretching is 10% per second.
The following are extremely important points of the present invention. At deformation rates above 10%, it is virtually impossible to achieve a total stretch of 750% or more. Total stretching amount is 7
It needs to be 50% to 2500%. If the stretching exceeds 2500%, yarn breakage during stretching frequently occurs, and the process stability is undesirably reduced. At a total stretching amount of less than 750%, a porous structure is formed, but a hollow fiber membrane having a large pore size and a high porosity according to the present invention cannot be obtained. Porosity of 7
In order to make it 5% or more, 750% or more, preferably 10% or more.
A total stretching amount of more than 00%, more preferably 1200% or more is required.

The term "deformation speed" as used in the present invention refers to a value obtained by dividing the amount of stretching (%) in a stretching section by the time (seconds) during which the yarn passes through the stretching section.

The obtained porous hollow fiber membrane has a substantially morphological stability secured by thermal drawing, and does not necessarily require a heat setting step for fixing the porous structure. However, the heat setting may be performed at a constant length under tension or with contraction as needed in the same temperature range as the above-mentioned hot stretching temperature.

The thus obtained porous polyethylene hollow fiber membrane having a large pore diameter has an average pore diameter of fine pores as measured by a mercury porosimeter of more than 2 μm and 10 μm or less, and a porosity of 7 μm.
5% to 95%, air permeability 8 × 10 ⁵ liter / m ² ·
hr. 0.5 atm or more. In addition, it has a characteristic strip-shaped micropore formed by being surrounded by microfibrils arranged in the fiber length direction and a knot portion made of a stack dramella, and this micropore is formed by the inner wall surface of the hollow fiber from the wall surface. And has a structure in which these minute holes are stacked. The average length of the microfibrils is more than 3 μm and not more than 15 μm.

FIG. 1 is a scanning electron micrograph of the large-pore-diameter porous polyethylene hollow fiber membrane of the present invention obtained in Example 1 described later. The average pore size measured by a mercury porosimeter was 2.7 μm. FIG. 2 is a scanning electron micrograph of the polyethylene hollow fiber membrane of the prior art obtained in Comparative Example 2, having an average pore diameter of 0.5 μm, and having a pore diameter much larger than that of the large pore porous polyethylene hollow fiber membrane of FIG. It is small. FIG. 3 is a schematic diagram of a pore structure drawn for easy understanding of the photograph of FIG. In this figure, 1 is a microfibril, 2 is a knot portion made of a stack dramella, and 3 is a strip-shaped micropore.

The saponified ethylene-vinyl acetate copolymer (ethylene-vinyl alcohol copolymer) used in the hydrophilized porous hollow fiber membrane of the present invention may be any type of copolymer such as random, block, or graft. The copolymer may be in the form of a coal, but the ethylene content of the copolymer is preferably in the range of 20 to 70 mol%. When the ethylene content is less than 20 mol%, the adhesion of the polymer to polyethylene is low, and the surface of the micropores of the porous film and the thin film layer are undesirably separated. If it exceeds 70 mol%, the hydrophilicity of the thin film layer is lost, which is not preferable. In particular, 25 to 50 mol% is preferable because the balance between the adhesiveness and the hydrophilicity is good. Ethylene-
It is considered that the vinyl alcohol-based copolymer has good adhesiveness because it contains ethylene having a common structure with polyethylene serving as a matrix as a constituent component.

The surface of at least a part of the porous membrane in which the hydrophilic copolymer is retained in the hydrophilic porous membrane of the present invention means a part or all of the pore surface and the outer surface. That is, it is sufficient that the polymer is held so that the hydrophilicity is substantially improved, and the polymer does not necessarily need to be held on all surfaces.

The term "retained" means that the polymer is firmly bonded or physically adhered to the pore surface to such an extent that the polymer is not easily detached during storage or use. Therefore, the polymer may be chemically bonded to the surface of the pore, the polymer may be closely adhered by an anchor effect, or microfibrils or nodules forming strip-shaped micropores may be formed. The polymer may be tightly cross-linked so as to cover the parts and the like, or these holding states may be mixed.

As described above, the holding state of the hydrophilic cross-linked polymer on the wall surface forming the micropores of the raw material hollow fiber can take any of the above-mentioned states. However, the hydrophilic porous membrane that physically holds the polymer on the wall surface without chemical bonding, such as an anchor effect or close crosslinking, has a lower mechanical strength than the raw material hollow fiber that is the base material. This is particularly preferable because there is almost no change in the micropore structure.

In the hydrophilic porous hollow fiber membrane of the present invention, the hydrophilic copolymer is firmly held so as to surround the microfibrils forming the strip-shaped micropores.

The hydrophilic porous polyethylene hollow fiber membrane having a large pore size and a high porosity according to the present invention is characterized in that the micropores of the porous polyethylene hollow fiber membrane are formed by mixing a water-miscible organic solvent alone or a mixture of the solvent and water. It is obtained by treating with an ethylene-vinyl alcohol copolymer solution dissolved in a solvent.

The treatment with the ethylene-vinyl alcohol copolymer solution includes a step of dipping or coating the copolymer solution in the micropores of the polyethylene porous hollow fiber membrane, and a step subsequent to the step. A drying step of evaporating and removing the solvent.

The organic solvent for dissolving the ethylene-vinyl alcohol copolymer is a water-miscible organic solvent. Examples of preferred organic solvents include methanol, ethanol,
n-propanol, isopropanol, sec-butanol, t-butanol, alcohols such as cyclohexanol, ethylene glycol, propylene glycol, polyhydric alcohols such as glycerin, tetrahydrofuran,
Examples include dioxane, dimethylformamide, dimethylsulfoxide, dimethylacetamide, formamide, ethylene chlorohydrin and the like. Among them, ethanol and dimethyl sulfoxide are particularly preferable because of good solubility of the ethylene-vinyl alcohol copolymer and low toxicity.

These organic solvents can be used alone or in a mixed solvent system, and a mixed solvent system with water is particularly preferable. The ethylene-vinyl alcohol copolymer is composed of a non-polar and hydrophobic ethylene moiety and a polar and hydrophilic vinyl alcohol moiety, but is dissolved in a strongly polar solvent system and coated on a non-polar polyethylene. In this case, it is considered that the nonpolar ethylene portion is localized on the polyethylene side, and the polar vinyl alcohol portion is likely to be localized on the surface. This phenomenon is a preferable phenomenon because the adhesion between the thin film layer and the surface of the micropores is improved, and the hydrophilicity of the surface of the thin film layer is improved. It is preferable to add water to the above-mentioned organic solvent to form a mixed solvent system because the polarity of the solvent becomes stronger and the above-mentioned phenomenon is accelerated. The proportion of water to be mixed is preferably large within a range that does not inhibit the solubility of the ethylene-vinyl alcohol copolymer.The proportion varies depending on the ethylene content of the copolymer, the temperature of the solvent, and the like. A preferred range is 60% by weight. The concentration of the copolymer used can be any concentration suitable for forming a thin film on the surface of the micropores, and for example, a concentration of about 0.1 to 5% by weight is suitable. The hydrophilization treatment may be completed by one treatment, but may be repeated several times at a relatively low concentration.

The temperature of the copolymer solution is not particularly limited, but a higher temperature is generally preferred because the copolymer has better solubility and lowers the viscosity of the solution.
A range up to 00 ° C is preferred. The hydrophilic treatment time is preferably in the range of several seconds to several tens of minutes. The removal of the solvent retained inside the pores of the porous membrane can be performed by vacuum drying, hot air drying, or the like. The degree of drying may be a temperature at which the hydrophilized porous membrane is not deformed by heat, and is preferably 130 ° C. or less.

The hydrophilic polyethylene porous hollow fiber membrane of the present invention is prepared by, for example, applying a solvent containing an ethylene-vinyl acetate copolymer to at least a part of the wall surface forming the micropores of the polyethylene porous hollow fiber membrane. After the deposition, the solvent is removed by drying, or immersed in a coagulation solvent solution of the ethylene-vinyl acetate copolymer to form a thin film of a water-insoluble organic polymer by performing a rapid coagulation treatment. It can also be obtained by saponifying the ethylene-vinyl acetate copolymer and drying it.

Since the ethylene chain of the ethylene-vinyl acetate copolymer has an excellent affinity for the polyethylene porous hollow fiber membrane, the ethylene-vinyl acetate copolymer thin film is made of fine pores of the polyethylene porous hollow fiber membrane. Strongly adheres to the surface. However, when the ethylene content of the ethylene-vinyl acetate copolymer increases, the adhesiveness improves, but the hydrophilicity decreases, so that the vinyl acetate content of the ethylene-vinyl acetate copolymer is 20 mol% or more. preferable. Ethylene-
The ethylene-vinyl acetate copolymer concentration of the solution containing the vinyl acetate copolymer is preferably 1 to 5% by weight. If the amount is less than 1% by weight, the ethylene-vinyl acetate copolymer is not preferable because sufficient hydrophilicity cannot be obtained after the saponification treatment. On the other hand, if it exceeds 5% by weight, the micropores of the porous polyethylene hollow fiber membrane become small, and the filtration performance is undesirably reduced.

These water-insoluble organic polymer thin films are formed as uniformly as possible on the wall surface of the porous hollow fiber membrane where the micropores are formed, and the adhesion amount is minimized. It is preferable to minimize the closing of the micropores.

The saponification treatment can be carried out, for example, by heating in an aqueous alkali solution such as sodium hydroxide for a certain period of time to convert the acetyl group of the vinyl acetate portion into a hydroxyl group.

Further, in the hydrophilic porous hollow fiber membrane of the present invention, which holds a hydrophilic crosslinked polymer obtained by polymerizing monomers containing diacetone acrylamide and a crosslinkable monomer, the hydrophilic crosslinked polymer is retained. At least a part of the wall surface forming the micropores of the raw material hollow fiber to be used refers to a part or all of the wall surface forming the micropores. That is, the polymer is applied to the wall surface of the micropores to such an extent that a permeation flow rate that does not hinder the use of the micropores of the porous membrane through water by the normally used transmembrane pressure is obtained. It is sufficient that the wall is held, and it is not always necessary that the entire wall surface forming the micropores is covered with the polymer. The polymer may or may not be held on the outer surface of the porous membrane.

In the present invention, the hydrophilic porous film composed of monomers containing diacetone acrylamide and a crosslinkable monomer is formed on the wall surface of the porous polyethylene hollow fiber membrane having a large pore diameter and high porosity, where the fine pores are formed. Retains cross-linked polymers, which are compared to other polymers,
(1) can be held firmly against polyethylene;
(2) that it can be maintained substantially uniformly over almost the entire wall surface forming the micropores of the polyethylene porous hollow fiber membrane, (3) that it has an appropriate hydrophilicity, and (4) that it has moderate hydrophilicity.
Due to being substantially water-insoluble.

The hydrophilic cross-linked polymer obtained by polymerizing monomers containing diacetone acrylamide and a cross-linkable monomer contains diacetone acrylamide as a monomer component in an amount of 50% by weight or more and contains a cross-linkable monomer. It is a crosslinked polymer composed of a non-crosslinkable monomer as a monomer component in addition to these.

As the crosslinkable monomer, a monomer having two or more polymerizable unsaturated bonds such as a vinyl bond and an allyl bond copolymerizable with diacetone acrylamide, or having one polymerizable unsaturated bond, and A monomer having at least one functional group capable of forming a chemical bond by a condensation reaction or the like and having a common good solvent with diacetone acrylamide is exemplified. Examples thereof include N, N-methylenebisacrylamide, N-hydroxymethyl (meth) acrylamide, triallyl cyanurate, triallyl isocyanurate, divinylbenzene,
2,2-bis (4-methacryloyloxypolyethoxyphenyl) propane, ethylenedi (meth) acrylate,
Polyethylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, trimethylolethanetri (meth) acrylate, butanediol di (meth) acrylate, hexanediol di (meth) acrylate, Diallyl phthalate, 1,3,5-
Triacryloylhexanehydroxy-s-triazine and the like.

The non-crosslinkable monomer is a monomer having one polymerizable unsaturated bond such as a vinyl bond or an allyl bond copolymerizable with diacetone acrylamide, and a good solvent common to diacetone acrylamide. And a monomer having the same. Examples thereof include dimethyl acrylamide, vinyl pyrrolidone, acrylic acid, methacrylic acid, hydroxyethyl methacrylate, styrene sulfonic acid, sodium styrene sulfonate, sodium sulfoethyl methacrylate, vinyl pyridine, vinyl methyl ether and the like.

Hereinafter, such crosslinkable monomers and non-crosslinkable monomers used together with diacetone acrylamide are collectively referred to as copolymerizable monomers.

The composition ratio of diacetone acrylamide to form a hydrophilic crosslinked polymer and the crosslinkable monomer is preferably from 0.3 to 100 parts by weight of the crosslinkable monomer to 100 parts by weight of diacetone acrylamide.
More preferably, the amount is 0.5 to 80 parts by weight. Also,
The composition ratio with the copolymerizable monomer is such that the copolymerizable monomer is 0.3 to 11 based on 100 parts by weight of diacetone acrylamide.
It is preferably 0 parts by weight, more preferably 0.5 to 100 parts by weight.

In the present invention, the polymer held on at least a part of the wall surface forming the micropores of the polyethylene porous hollow fiber membrane having a large pore size and high porosity is a crosslinked polymer. This polymer has the advantage that the degree of swelling in water is small and there is no danger of closing micropores, and the stability of the polymer is good and the amount of components eluted in water is extremely small. Therefore, the hydrophilized porous membrane of the present invention is effective in the field of water treatment or blood treatment where a trace amount of eluted components becomes a problem. On the other hand, a diacetone acrylamide-based polymer having no cross-linked structure swells in water to block micropores, and dissolves in a small amount of water to become an eluted component. The porous membrane holding the coalescence may cause various problems during use.

Further, as the degree of hydrophilicity of the polymer increases,
Since the water permeability of the hydrophilized porous membrane is good and water is uniformly transmitted from the entire membrane surface in a short time at the start of use,
As a crosslinkable monomer that forms a hydrophilic crosslinked polymer,
It is preferable that the water-soluble crosslinkable monomer has a sufficient degree of hydrophilicity.

Such a water-soluble crosslinkable monomer includes:
It is a crosslinkable monomer having a solubility in water at 30 ° C. of 1.0 g / dl or more, and examples thereof include N-hydroxymethylacrylamide, N-hydroxymethylmethacrylamide, and N, N′-methylenebisacrylamide. Can be.

The amount of the hydrophilic cross-linked polymer retained on at least a part of the wall surface forming the micropores of the polyethylene porous hollow fiber membrane of the present invention depends on the porosity of the polyethylene porous hollow fiber membrane, Although it depends on the pore diameter, it is about 0.5 to 100% by weight based on the weight of the polyethylene porous hollow fiber membrane.
It is preferred that it is about. If the amount of retained polymer is less than this range, sufficient hydrophilicity cannot be imparted to the porous hollow fiber membrane, and even if the amount exceeds this range, the hydrophilicity of the porous hollow fiber membrane is further improved. Instead, the pore volume may be reduced and the water permeability may be reduced. The retention amount of the polymer is more preferably about 0.5 to 50% by weight, and particularly preferably about 1 to 30% by weight.

As a method for holding the hydrophilic cross-linked polymer on at least a part of the wall surface forming the micropores of the polyethylene porous hollow fiber membrane, diacetone acrylamide and an appropriate solvent such as an organic solvent or water are used. A method in which a solution in which the aforementioned copolymerizable monomers (hereinafter referred to as "monomers") and a polymerization initiator are dissolved is prepared, and a raw material hollow fiber is immersed in the solution, or a membrane module is manufactured using the raw material hollow fiber. After that, a method of impregnating the raw material hollow fiber with the monomer solution by, for example, pressing the solution into the raw material hollow fiber, and then volatilizing and removing the solvent can be adopted. By using a solution of the monomers diluted with the solvent, the monomers can be adhered almost uniformly over the entire porous hollow fiber membrane without closing the micropores of the porous hollow fiber membrane. Further, the amount of the attached monomers can be adjusted by changing the concentration of the monomers in the solution or the impregnation time of the solution.

The solvent is removed in a state where these monomers are retained on at least a part of the wall surface forming the micropores of the raw material hollow fiber, and then polymerized to form a polyethylene porous hollow. The hydrophilic cross-linked polymer can be retained on at least a part of the wall surface of the fibrous membrane where the micropores are formed.

As a solvent for preparing the above solution, water or an organic solvent having a lower boiling point than the monomers and capable of dissolving the monomers is used. When a polymerization initiator is added, It is preferable to use a solvent that can also dissolve the polymerization initiator. Examples of such organic solvents include alcohols such as methanol, ethanol, propanol, and isopropanol; ketones such as acetone, methyl ethyl ketone and methyl isobutyl ketone; ethers such as tetrahydrofuran and dioxane; and ethyl acetate. The boiling point of the organic solvent is not particularly limited, but is preferably 100 ° C. or lower, more preferably 80 ° C. or lower, in consideration of easy removal of the solvent before the polymerization step.

Since the surface of the polyethylene porous hollow fiber membrane is hydrophobic, particularly when water is used as a solvent, when the aqueous solution containing the monomer penetrates into the pores, the monomers are hydrophilically dispersed on the pore surface. Since the functional group is easily oriented and adsorbed toward the outside, if this state is fixed by polymerization, hydrophilicity can be imparted extremely efficiently. When water is used as the solvent, the porous hollow fiber membrane can be brought into direct contact with the solution.However, the wall surface of the porous hollow fiber membrane where the micropores are formed in advance with alcohols or ketones is wet-treated. After that, the solution can be contacted.

When an organic solvent is used as the solvent,
There are advantages such as that the solution permeates into the micropores of the raw material hollow fiber in a short time and that the solvent can be easily removed from the micropores.

Even when the polymerization is carried out in a state where the monomers are randomly oriented on the surface of the pores without utilizing the above-mentioned orientational adsorption, the formed hydrophilic cross-linked polymer has a degree of hydrophilicity as compared with polyethylene. Is larger, the wall surface forming the micropores holding the polymer is relatively hydrophilic compared to the wall surface forming the micropores not holding the polymer. Thus, a polyethylene porous hollow fiber membrane having hydrophilicity can be obtained.

The necessity of the polymerization initiator depends on the polymerization method. In the case of a thermal polymerization method or a photopolymerization method, a polymerization initiator is used.
In the case of the radiation polymerization method, no polymerization initiator is required.

In the case of the thermal polymerization method, various peroxides, azo compounds and redox initiators known as radical polymerization initiators can be used. As an example,
2,2'-azobisisobutyronitrile, 2,2'-azobiscyclopropylpropionitrile, 2,2'-azobis-2,4-dimethylvaleronitrile, 2,2'-
Azo compounds such as azobis-2,3,3-trimethylbutyronitrile; acetyl peroxide, propionyl peroxide, butyryl peroxide, isobutyryl peroxide, succinyl peroxide, benzoyl peroxide, benzoyl isobutyryl peroxide, β -Allyloxypropionyl peroxide,
Peroxides such as hexanoyl peroxide, 3-bromobenzoyl peroxide, bis- (4-t-butylcyclohexyl) peroxydicarbonate; and persulfates such as potassium persulfate and ammonium persulfate.

Particularly when water is used as the solvent, a water-soluble polymerization initiator such as azobisisobutyramide,
Although 4'-azobis-4-dianopentanoic acid is preferred, the water-insoluble polymerization initiator can be dispersed in water even if a water-insoluble polymerization initiator is used because the monomers themselves have surface activity. Can be used.

Examples of the polymerization initiator for the photopolymerization method include benzophenone, benzoin methyl ether, benzyldimethyl ketal, fluorenone, 4-bromobenzophenone, 4-chlorobenzophenone, methyl O-benzoin benzoate, benzoyl peroxide, anthraquinone, and biacetyl. And uranyl nitrate. It is also possible to use these in an appropriate combination.

The composition of the monomer and the solvent in the solution may be appropriately selected in consideration of the type of the solvent, the target amount of the polymer to be retained, and the like. 10,000 parts by weight is preferred, and 200 to
More preferably, it is 5000 parts by weight.

The polymerization initiator is used in an amount of 100
0.001 to 100 parts by weight with respect to parts by weight is preferable,
It is more preferably 0.01 to 30 parts by weight, and 0.1 to 30 parts by weight.
Particularly preferred is 1 to 20 parts by weight.

When the amount of the solvent exceeds the above range with respect to the monomers, the amount of the monomers retained on the wall surface forming the micropores of the porous hollow fiber membrane is too small, and a sufficient amount of weight It is not possible to keep the coalesced, and if it is less than the above range, it is difficult to control the amount of the polymer held, and the amount of the polymer held on the wall or inside the micropores forming the micropores is reduced. It is not preferable because the number of pores is so large that micropores may be blocked.

The immersion time or press-fitting time when immersing or press-fitting the raw material hollow fiber using these solutions is about 0.5 seconds to 30 minutes, and the wettability to the raw material hollow fiber is good. The use of a solution can be performed in a shorter time.

As described above, the polyethylene porous hollow fiber membrane in which the monomer containing a polymerization initiator is optionally held on the wall surface having at least a part of the micropores is surrounded by excess liquid around the polyethylene. Is removed and, if necessary, the solvent inside the micropores is removed by evaporation, and then the process proceeds to the next polymerization step.

If the temperature at the time of evaporating and removing the solvent is too high, the polymerization partially proceeds while the solvent remains, and the inside of the micropores other than the wall forming the micropores of the porous hollow fiber membrane is formed. In this case, polymerization occurs, and as a result, some of the micropores may be closed, which is not preferable. In view of this, the temperature at the time of removing the solvent is preferably 10 to 40 ° C.

In producing the hydrophilized porous membrane of the present invention, polymerization methods such as a thermal polymerization method, a photopolymerization method, a radiation polymerization method, and a plasma polymerization method can be employed.

In the case of the thermal polymerization method, the polymerization temperature is not lower than the decomposition temperature of the polymerization catalyst and not higher than the temperature at which the membrane structure of the polyethylene porous hollow fiber membrane is not changed and the membrane substrate is not damaged. Is desirable, usually 30
Temperatures of １００100 ° C. can be employed. The heating time depends on the type of the polymerization initiator and the heating temperature, but is usually 1 minute to 5 hours, more preferably 15 minutes to 3 hours in the batch method. In the continuous method, polymerization can be performed in a shorter time because of high heat transfer efficiency, and the heating time is usually 10 seconds to 60 minutes.
Preferably, it is 20 seconds to 10 minutes.

In the case of the photopolymerization method, ultraviolet light or visible light can be used as a light source for light irradiation, and a low-pressure mercury lamp, high-pressure mercury lamp, xenon lamp, arc lamp, or the like can be used as an ultraviolet light source.

As a light irradiation condition, for example, when a mercury lamp is used as a light source, irradiation is performed at a power of 10 to 300 W / cm from a distance of 10 to 50 cm for 0.5 to 300 seconds to obtain a light of 0.001 to 10 joule / cm. ² , preferably 0.05 to 1 joule / cm ² energy is applied.

When the irradiation intensity is low, it is difficult to achieve sufficient hydrophilicity, and when the irradiation intensity is high, the polyethylene porous hollow fiber membrane is significantly damaged. Is preferably selected.

The radiation polymerization can be carried out, for example, by irradiating an electron beam at a temperature of 120 ° C. or lower, preferably 100 ° C. or lower, with an electron beam irradiator at about 10 to 50 Mrad.

In the case of these polymerizations, if oxygen is present in the atmosphere, the polymerization reaction is significantly inhibited. Therefore, the polymerization is carried out in an inert gas atmosphere such as a nitrogen atmosphere or in a state substantially free of oxygen such as a vacuum. It is desirable.

In producing the hydrophilic cross-linked polymer, the cross-linking reaction may be carried out simultaneously with the polymerization reaction, or the cross-linking may be performed after the formation of the copolymer. Further, the crosslinking reaction by condensation may be carried out by utilizing heat of polymerization reaction, or may be carried out by heating.

In particular, when a cross-linking reaction by condensation is used, an uncross-linked copolymer of diacetone acrylamide and a cross-linkable monomer prepared in advance is dissolved in a solution, and then the micropores of the polyethylene porous hollow fiber membrane are removed. A method in which the film is held on the formed wall surface and a crosslinking reaction is performed in that state may be used. In this case, the molecular weight of the uncrosslinked copolymer is 1 to
The molecular weight is preferably 500,000. If the molecular weight is too large, it is difficult to make the copolymer penetrate into the micropores of the polyethylene porous hollow fiber membrane, which is not preferable. Molecular weight 5
More preferably, it is up to 300,000.

In producing the hydrophilic porous hollow fiber membrane of the present invention, various polymerization methods can be employed as described above, but the method using thermal energy is most preferable. When thermal energy is used, the porous hollow fiber membrane can be heated to a uniform temperature up to the minute pores, so that the polymer is uniformly polymerized on the wall surface on which all the pores holding the monomers are formed And without changing the structure of the membrane by setting the polymerization temperature appropriately,
In addition, there is an advantage that the polymerization can be performed without deteriorating the membrane substrate. On the other hand, when light energy is used, it is difficult for light to sufficiently reach the micropores of the porous hollow fiber membrane due to light scattering. There is a problem, and also when using radiation energy, there is a problem that the deterioration of the membrane substrate is apt to proceed. Therefore, when using these polymerization methods, it is necessary to carefully select polymerization conditions that do not deteriorate the membrane substrate.

The monomers held on the wall surface forming the micropores of the raw hollow fiber and the uncrosslinked copolymer are polymerized / crosslinked or crosslinked on the surface of the porous membrane by these polymerization techniques. Therefore, at least a part of the wall surface forming the micropores of the porous hollow fiber membrane is coated with these polymers.

After the formation of the hydrophilic cross-linked polymer, unreacted monomer and free monomer existing around the wall surface forming the micropores of the porous hollow fiber membrane are removed by a dipping method or a press-fitting method using an appropriate solvent. It is desirable to remove unnecessary components such as the removed polymer. As the solvent, water, an organic solvent, or a mixed solvent thereof can be used alone or in combination.

The hydrophilized porous hollow fiber membrane of the present invention can be produced in this manner. As a particularly preferred method, a monomer containing diacetone acrylamide and a water-soluble crosslinkable monomer and a polymerization initiator are used. And a method of heating and polymerizing the polyethylene porous hollow fiber membrane while holding it on the wall surface where at least a part of the micropores are formed.

When a water-soluble crosslinking monomer is used as the copolymerizable monomer, swelling of the polymer in water is suppressed,
The amount of the eluted portion can be further reduced, and the hydrophilic porous hollow fiber membrane exhibits excellent water permeability.

Further, the hydrophilic porous hollow fiber membrane produced by the heat polymerization method is characterized in that there is no unevenness in the holding state of the polymer in the thickness direction and there is almost no damage to the membrane substrate.

Although the respective steps have been described separately, when manufacturing the hydrophilic porous hollow fiber membrane of the present invention, the hydrophilic porous hollow fiber membrane is coated on the wall surface of the polyethylene porous hollow fiber membrane where the micropores are formed. Retention of monomers, solvent removal, polymerization,
Washing and the like after polymerization can be performed almost continuously.

[0097]

The present invention will be specifically described below with reference to examples. The measuring method was as follows. 1. Measurement of Hollow Fiber Membrane (1) Air Permeation Amount: A module was manufactured by bundling 50 porous hollow fibers in a U-shape and solidifying the hollow openings with urethane resin. The length of the resin-embedded portion was 2.5 cm, and the effective length of the hollow fiber was 5 cm. Air is injected into the hollow fiber of this module.
A pressure of 5 atm was applied at 25 ° C., and the permeation amount of air passing through the wall surface of the hollow fiber to the outside was determined. The membrane area was based on the inner diameter. (2) Elastic recovery rate: Measured at a yarn length of 2 cm and a test speed of 1 cm / min using Tensilon UTM-II manufactured by Toyo Baldwin Co., Ltd., and determined by the following equation.

[0098]

(Equation 1) (3) Average length of microfibrils: measured from electron micrographs. 2. Measurement of hydrophilic porous hollow fiber membrane "water penetration pressure", "water permeability of alcohol hydrophilization" and "water permeability after polymer retention" is the effective membrane area, each with a test membrane module of 163cm ² It was measured by the following method. The solubility of N-hydroxymethylacrylamide, N, N'-methylenebisacrylamide and triallyl isocyanurate used in the examples in water at 30 ° C was 197 g / dl, 3 g / dl and 0.1 g / dl, respectively.
1 g / dl. (1) Permeability: 25 ° C. water is supplied from one side of the test membrane module (inside of the hollow fiber in the case of a hollow fiber membrane) at a rate of 0.1 kg / cm ² every minute while increasing the water pressure, and integrated. The water pressure when the amount of permeated water reaches 30 ml and 50 ml is measured. Subsequently, the water pressure was plotted on the horizontal axis or the amount of permeated water was plotted on the vertical axis, and the pressure value at the point where a straight line connecting the plotted points intersects the horizontal axis was determined as the water pressure. (2) Water permeability by alcohol hydrophilization method: Ethanol was injected at a flow rate of 25 ml / min for 15 minutes from one of the test membrane modules not subjected to hydrophilization treatment (in the case of hollow fiber membrane, inside the hollow fiber membrane). After sufficiently moistening the inside of the pores of the porous membrane with ethanol, water was added at a flow rate of 100 ml / min for 15 minutes.
The mixture is allowed to flow for minutes, and the ethanol present inside the pores is replaced with water. Subsequently, water at 25 ° C. was flowed from one of the test membrane modules (the inside of the hollow fiber in the case of the hollow fiber membrane) to reduce the transmembrane pressure to 50%.
The amount of permeated water at mmHg was measured, and the water permeability (liter / m ² · hr · mmHg) was determined from the measured value. (3) Retention amount of polymer: The nitrogen content was measured by elemental analysis, and it was assumed that this nitrogen was derived only from the polymer and a polymer having the same composition ratio as the monomer composition ratio was formed. The weight% of the hydrophilic cross-linked polymer held with respect to the unit weight of the polyethylene porous hollow fiber membrane was calculated. (4) Evaluation of coating state of pore surface: JIS K6768
The porous membrane was immersed in a standard solution for wetting test (blue) having a surface tension of 54 dyn / cm described in (1971) for 1 minute and then air-dried. The cross section of the porous membrane was observed under an optical microscope and colored. The distribution state of the polymer thus obtained was examined. (5) Cumulative elution rate: The porous hollow fiber membrane is immersed in hot water of 65 ° C. 10 times its weight, and the total organic carbon content in the hot water is measured at regular intervals. Assuming that the total amount of organic carbon is derived only from the hydrophilic cross-linked polymer having the composition ratio assumed in the above (3), the integrated elution amount was calculated, and the integrated elution ratio with respect to the polymer retention amount before the elution treatment was calculated. (% By weight). (6) Water permeability after holding the polymer: a pressure of 2 kg / cm ² from one of the test membrane modules (in the case of the hollow fiber membrane, inside the hollow fiber membrane) made of the porous hollow fiber membrane holding the polymer. Of water for 3 hours, water at 25 ° C. was flowed from one side of the test membrane module, and the amount of permeated water at a transmembrane pressure difference of 50 mmHg was measured. From the value, the water permeability (liter / m ² · hr) was measured.・
mmHg).

Example 1 High-density polyethylene having a density of 0.968 g / cm ³ and a melt index of 0.7 (NOVATE manufactured by Mitsubishi Chemical Corporation)
C BU 007U) using a spinneret for hollow fiber shaping having a discharge port diameter of 16 mm, an annular slit width of 2.5 mm, and a discharge cross-sectional area of 1.06 cm ² , a spinning temperature of 180 ° C., and a discharge rate of 32.
Spinning at 1cm / min, temperature at 25 ° C, speed at 4.0m / min
It was cooled by countercurrent cooling air of sec. and wound up by a spinning draft 234 at a winding speed of 75 m / min. The dimensions of the obtained undrawn hollow fiber were such that the inner diameter was 570 μm and the film thickness was 173 μm.

The undrawn hollow fiber was treated at 125 ° C. for 24 hours.
Heat treatment was performed at a constant length. The elastic recovery of this undrawn hollow fiber is 7
2%. Subsequently, the film is stretched 110% at a deformation rate of 160% per second at room temperature, and then deformed in a heating box heated to 118 ° C. until the total stretching amount becomes 1350% (that is, the total stretching ratio is 14.5 times). The inside of the roller was stretched so that the speed was 3.5% per second, and a porous hollow fiber membrane was continuously produced. The obtained porous polyethylene hollow fiber membrane was stretched 14.5 times with respect to the unstretched fiber, the inner diameter was 500 µm, the film thickness was 150 µm, and the porosity was 86%. The average pore diameter measured with a mercury porosimeter was 2.7 μm, and the air permeation amount was 140 × 10 ⁴ liter / m ² hr 0.5 atm.

Observation with a scanning electron microscope revealed that there were numerous characteristic strip-shaped micropores, and the average length of the microfibrils was 7.5 μm. FIG. 1 is a scanning electron micrograph showing a typical porous structure of the outer surface of the porous polyethylene hollow fiber membrane.

Example 2 High-density polyethylene having a density of 0.968 g / cm ³ and a melt index of 5.5 (HI, manufactured by Mitsui Petrochemical Industries, Ltd.)
ZEX 2200J) has a double pipe structure with a discharge port diameter of 25 mm and an annular slit width of 1.5 mm, and a discharge sectional area of 0.2 mm.
Using a 754 cm ² spinneret for hollow fiber molding, a spinning temperature of 1
The fiber is spun at 65 ° C. and a discharge linear speed of 10.5 cm / min, cooled with countercurrent cooling air at a temperature of 25 ° C. and a speed of 3.0 m / sec.
The film was wound by a spinning draft 2860 at a winding speed of 300 m / min. The dimensions of the obtained undrawn hollow fiber have an inner diameter of 250 μm.
m, and the film thickness was 35 μm.

The undrawn hollow fiber was heated at 120 ° C. for 24 hours.
Heat treatment was performed at a constant length. The elastic recovery of this undrawn hollow fiber is 7
3%. Subsequently, the film is stretched at room temperature by 80% at a deformation rate of 160% per second, and then, in a heating box heated to 125 ° C., the deformation rate becomes 7.0% per second until the total stretching amount becomes 800%. Then, heat stretching was performed for 40 seconds in a heating box heated to 125 ° C. to continuously produce a porous hollow fiber membrane. The obtained porous polyethylene hollow fiber membrane was stretched 9.0 times with respect to the undrawn yarn, had an inner diameter of 240 μm, a thickness of 30 μm, and a porosity of 82%. The average pore size measured by a mercury porosimeter was 2.1 μm, and the air permeation amount was 91 × 10 ⁴ liter / m ² hr 0.5 atm. Observation with a scanning electron microscope revealed that there were numerous characteristic micropores, and the average length of the microfibrils was 3.8 μm.

Example 3 Density: 0.969 g / cm ³ , Melt Index: 0.35
High density polyethylene (NOVAT manufactured by Mitsubishi Chemical Corporation)
EC BU 004U) using a spinneret for hollow fiber shaping having a discharge port diameter of 16 mm, an annular slit width of 2.5 mm, and a discharge cross-sectional area of 1.06 cm ² , at a spinning temperature of 230 ° C. and a discharge speed of 2
Spin at 8.0 cm / min, temperature 25 ° C, speed 4.0
Cooling with countercurrent cooling air of m / sec, winding speed 50m / min
And wound with a spinning draft 179. The dimensions of the obtained undrawn hollow fiber were such that the inner diameter was 583 μm and the film thickness was 168 μm.

The undrawn hollow fiber was heated at 125 ° C. for 24 hours.
Heat treatment was performed at a constant length. The elastic recovery of this undrawn hollow fiber is 7
It was 0%. Subsequently, after stretching 120% at room temperature at a deformation rate of 160% per second, the deformation rate is 2.8% per second until the total stretching amount is 1900% in a heating box heated to 120 ° C. , And the production of a porous hollow fiber membrane was continuously performed. The obtained porous polyethylene hollow fiber membrane was stretched 20 times with respect to the unstretched fiber, the inner diameter was 475 μm, the thickness was 130 μm, and the porosity was 89%. The average pore size measured with a mercury porosimeter was 5.1 μm and the air permeation was 290 × 1.
0 was ⁴ l / m ² · hr · 0.5atm.

Observation with a scanning electron microscope revealed that a number of characteristic strip-shaped micropores existed, and the average length of the microfibrils was 11.5 μm.

Comparative Example 1 High-density polyethylene having a density of 0.968 g / cm ³ and a melt index of 6.7 (NOVATE manufactured by Mitsubishi Chemical Corporation)
A hollow fiber was spun under exactly the same conditions as in Example 2 except that CJV 070S) was used. The dimensions of the obtained undrawn hollow fiber were 240 μm in inner diameter and 32 μm in film thickness.

This undrawn hollow fiber was heat-treated under the same conditions as in Example 2 and drawn. However, the yarn was frequently broken by hot drawing, and uniform drawing with a total drawing amount of 750% was impossible.

Comparative Example 2 The same undrawn yarn as in Comparative Example 1 was heat-treated under the same conditions as in Example 2 and drawn so that the total drawn amount was 400%. The resulting porous polyethylene hollow fiber membrane has an inner diameter of 205 μm.
m, and the film thickness was 25 μm. The porosity is 69%, the average pore size measured by a mercury intrusion porosimeter is 0.5 μm, and the air permeability is 24 × 10 ⁴ liter / m ² · hr · 0.5.
atm.

FIG. 2 is a scanning electron micrograph showing a typical porous structure of the outer surface of the porous polyethylene hollow fiber membrane.

Example 4 High-density polyethylene having a density of 0.970 g / cm ³ and a melt index of 0.7 (NOVATE manufactured by Mitsubishi Kasei Corporation)
CBU007U) using a spinneret for hollow fiber shaping having a discharge port diameter of 16 mm, an annular slit width of 2.5 mm, and a discharge cross-sectional area of 1.45 cm ² , a spinning temperature of 180 ° C. and a discharge rate of 12.2 cm /
The fiber was cooled by countercurrent cooling air having a temperature of 25 ° C. and a speed of 3.0 m / sec, and was wound by a spinning draft 328 at a winding speed of 40 m / min. The dimensions of the obtained undrawn hollow fiber had an inner diameter of 580 μm and a film thickness of 178 μm.

The undrawn hollow fiber was heated at 125 ° C. for 24 hours.
Heat treatment was performed at a constant length. The elastic recovery of this undrawn hollow fiber is 7
3%. Subsequently, the film was stretched at room temperature by 120% at a stretching speed of 200% per second, and then, in a heating furnace heated to 118 ° C., the deformation rate was set to 2.5% per second and the total stretching amount was 1%.
The inside of the roller was stretched to 400% to continuously produce a porous hollow fiber membrane.

The obtained porous polyethylene hollow fiber membrane was stretched 15.0 times with respect to the undrawn yarn, and had an inner diameter of 5
The film thickness was 05 μm, the film thickness was 155 μm, and the porosity was 87%. The average pore size measured with a mercury porosimeter is 2.7
μm, the air permeation amount is 140 × 10 ⁴ liters / m ² · h
r · 0.5 atm. Observation with a scanning electron microscope revealed that there were numerous characteristic strip-shaped micropores, and the average length of the microfibrils was 7.5 μm.

On the other hand, an ethylene-vinyl alcohol copolymer having an ethylene content of 33 mol% (Soarnol E manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) was dissolved by heating in a 75% by volume aqueous ethanol solution to obtain a 1% by weight solution. The temperature of this solution was maintained at 50 ° C., and the polyethylene porous hollow fiber membrane was immersed in the solution and left for 5 minutes. Then, after removing the excess copolymer solution, it was dried in a hot air dryer at 50 ° C. for 2 hours.

The obtained hydrophilic porous hollow fiber membrane having a large pore diameter and a high porosity had good wettability with water, easily wetted when immersed in water, and showed water permeability without special treatment. The 50 hollow hollow fiber membranes were bundled in a U-shape and housed in a housing, and the ends of the hollow fiber membranes were fixed to the housing with resin, and the water permeability was measured. The water permeability was 55 l / m ² · hr.
-It was mmHg and showed excellent water permeability. Further, drying and wetting were repeated 10 times, but no decrease in water permeability and no change in mechanical properties were observed.

Example 5 Ethylene-vinyl acetate copolymer (composition ratio 55:45) 3
After immersing a large-pore-diameter, high-porosity polyethylene porous hollow fiber membrane obtained in the same manner as in Example 4 for 30 seconds in a solution at 25 ° C. obtained by dissolving parts by weight of 97 parts by weight of toluene. After drying at 50 ° C. for 3 hours using a vacuum dryer, the solvent was removed.

Next, 10 g of sodium hydroxide was immersed in an aqueous alkali solution in 1 liter of water.
After performing saponification treatment for a period of time, it was washed with water and dried to obtain a hydrophilic polyethylene porous hollow fiber membrane.

The 50 hollow fiber membranes were bundled in a U-shape, and the ends of the hollow fiber membranes were fixed to the housing with resin, and the water permeability was measured. The water permeability was 50 l / m ² · hr · mmHg. And showed excellent water permeability. Drying and wetting were repeated 10 times, but no decrease in water permeability and no change in mechanical properties were observed.

Example 6 High-density polyethylene having a density of 0.970 g / cm ³ and a melt index of 0.7 (NOVATE manufactured by Mitsubishi Chemical Corporation)
C BU 007U), using a spinneret for hollow fiber shaping having a discharge port diameter of 16 mm, an annular slit width of 2.5 mm, and a discharge cross section of 1.45 cm ² , a spinning temperature of 180 ° C. and a discharge speed of 1
Spin at 2.2 cm / min, temperature 25 ° C, speed 3.0
/ Sec countercurrent cooling air, take-up speed 40m / min,
It was wound by a spinning draft 328. The dimensions of the obtained undrawn hollow fiber had an inner diameter of 580 μm and a film thickness of 178 μm.

The undrawn hollow fiber was heated at 125 ° C. for 24 hours.
Heat treatment was performed at a constant length. The elastic recovery of this undrawn hollow fiber is 7
3%. Subsequently, after stretching 100% at a deformation rate of 200% per second in a greenhouse, in a heating furnace heated to 118 ° C. until the total stretching amount becomes 1400% (that is, the total stretching ratio becomes 15.0 times). The inside of the roller was stretched so that the deformation speed became 2.5% per second, and a porous hollow fiber membrane was produced continuously. The obtained porous polyethylene hollow fiber membrane was stretched 15.0 times with respect to the undrawn hollow fiber, and had an inner diameter of 505 µm and a thickness of 155 µm.
The average pore size measured with a mercury porosimeter is 3.2 μm
And the air permeation amount is 190 × 10 ⁴ liters / m ² · hr ·
The porosity was 0.5 atm and the porosity was 87%. Observation with a scanning electron microscope revealed that there were numerous characteristic strip-shaped micropores, and the average length of the microfibrils was 7.5 μm. The water permeation pressure is 3.2 kg / cm ² , and the water permeability by the alcohol hydrophilization method is 55 l / m ² · hr · mm.
Hg.

The resulting polyethylene porous hollow fiber membrane having a large pore diameter and a high porosity was treated with diacetone acrylamide 1
It was immersed in a treatment solution consisting of 00 parts, 5 parts of N-hydroxymethylacrylamide, 1 part of benzoyl peroxide and 1000 parts of acetone for 10 seconds, taken out in nitrogen and air-dried for 5 minutes. Subsequently, the porous film was heat-treated at 65 ° C. for 60 minutes in a nitrogen atmosphere, and then immersed in a mixed solvent of water / ethanol = 50/50 (parts) for 10 minutes.
Further, unnecessary components were washed and removed by ultrasonic cleaning in warm water for 2 minutes. Next, the solvent is removed by hot air drying,
A polyethylene porous hollow fiber membrane holding the polymer was obtained. The water permeation pressure, water permeability, retained amount of polymer, integrated elution rate and the like of this porous hollow fiber membrane were measured, and the results are shown in Table 1.

The water permeability of the obtained hydrophilic polyethylene porous hollow fiber membrane was good. Observation with a scanning electron microscope showed that almost all of the wall surface of the polyethylene porous hollow fiber membrane forming micropores was observed. Approximately the polymer was retained over a period of time. From the measurement of the integrated dissolution rate, 24
It was found that there was substantially no eluted component after the time.

Examples 7 to 9 The amounts of N-hydroxymethylacrylamide shown in Table 1 were used as the crosslinkable monomers, and the other conditions were the same as in Example 6 to hold the polymer in the polyethylene porous hollow fiber membrane. I let it.

The performance of the thus obtained hydrophilic hollow polyethylene porous hollow fiber membrane was evaluated, and the results shown in Table 1 were obtained.

Example 10 A polyethylene porous hollow fiber membrane obtained in the same manner as in Example 6 was treated with diacetone acrylamide 10
0 parts, a solution consisting of 5 parts of N, N'-methylenebisacrylamide, 5 parts of 2,2'-azobisisobutyronitrile and 800 parts of acetone, and heat treatment conditions at 65 ° C. for 60 minutes, A polyethylene porous hollow fiber membrane holding a polymer was obtained in the same manner as in Example 6, and its performance was evaluated. The results shown in Table 1 were obtained.

When the coated state of the hydrophilic cross-linked polymer was observed, it was found that the polymer was held substantially uniformly over almost the entire wall surface forming the micropores. In addition, it was found from the measurement of the integrated dissolution rate that there was substantially no dissolution component after 24 hours.

Example 11 A high-density polyethylene having a density of 0.968 g / cm ³ and a melt index of 5.5 (HI, manufactured by Mitsui Petrochemical Industries, Ltd.)
ZEX2200J) using a spinneret for hollow fiber shaping having a discharge diameter of 25 mm, an annular slit width of 1.5 mm, and a discharge cross-sectional area of 1.11 cm ² , at a spinning temperature of 165 ° C. and a discharge linear speed of 1.
Spin at 0.5 cm / min, temperature at 25 ° C, speed at 3.0
/ Sec with countercurrent cooling air, winding speed 280m / min
And wound with a spinning draft 2667. The dimensions of the obtained undrawn hollow fiber were such that the inner diameter was 250 μm and the film thickness was 35 μm.

This undrawn hollow fiber was heat-treated at 125 ° C. for 25 hours at a constant length. The elastic recovery of this undrawn hollow fiber was 72%. Subsequently, the film is stretched at room temperature by 80% at a deformation rate of 160% per second, and then, in a heating furnace heated to 120 ° C., the deformation rate becomes 2.0% per second until the total stretching amount becomes 800%. Then, heat stretching was performed for 40 seconds in a heated heating furnace to continuously produce a porous hollow fiber membrane. The obtained porous polyethylene hollow fiber membrane has a weight of 9.0 with respect to the undrawn hollow fiber.
Stretched twice, the inner diameter is 240 μm, and the film thickness is 30 μm.
m. The average pore size measured by a mercury porosimeter was 2.1 μm, and the air permeation amount was 92 × 10 ⁴ liter / m ^2.
-Hr. 0.5 atm, porosity was 80%. Observation with a scanning electron microscope revealed that there were a myriad of characteristic microvoids, and the average length of the microfibrils was 3.8 μm.
m. The water permeation pressure is 3.7 kg / cm ² , and the water permeability by the alcohol hydrophilization method is 36 l / m ² · h.
r · mmHg.

The obtained polyethylene porous hollow fiber membrane having a large pore size and a high porosity was treated as a treatment solution with 100 parts of diacetone acrylamide, 5 parts of N-hydroxymethylacrylamide, 10 parts of benzoyl peroxide and 330 parts of methyl ethyl ketone. And a heat treatment condition of 60 ° C. for 60 minutes was used, and the other conditions were exactly the same as in Example 6 to obtain a polyethylene porous hollow fiber membrane holding a polymer, and its performance was evaluated. The results are shown in Table 1.

When the coated state of the hydrophilic cross-linked polymer was observed, it was found that the polymer was maintained substantially uniformly over almost the entire wall surface forming the micropores. Also, the measurement of the integrated dissolution rate revealed that there was substantially no dissolution component after 24 hours.

Examples 12 to 14 The amounts of N-hydroxymethylacrylamide shown in Table 1 were used as the crosslinkable monomers, and the other conditions were the same as in Example 11, except that the polymer was applied to the polyethylene porous hollow fiber membrane. Was held.

The performance of the hydrophilic polyethylene porous hollow fiber membrane thus obtained was evaluated, and the results shown in Table 1 were obtained.

Example 15 A polymer was retained on a polyethylene porous hollow fiber membrane in the same manner as in Example 6 except that 5 parts of triallyl isocyanurate was used as a crosslinking monomer. The performance of the thus obtained hydrophilic polyethylene porous hollow fiber membrane was evaluated, and the results shown in Table 1 were obtained. Observation of the coated state of the hydrophilic cross-linked polymer revealed that the polymer was maintained substantially uniformly over almost the entire wall surface forming the micropores.

Example 16 Using a solution composed of 100 parts of diacetone acrylamide, 1 part of divinylbenzene, 0.3 part of benzoyl peroxide and 450 parts of methyl ethyl ketone, the immersion time was 3 seconds, and the polymerization was carried out at 70 ° C. for 60 minutes under thermal polymerization conditions. The polymer was held on the polyethylene porous hollow fiber membrane in exactly the same manner as in Example 6 except for the above conditions.

The performance of the polyethylene porous hollow fiber membrane was evaluated, and the results shown in Table 1 were obtained. Observation of the coated state of the hydrophilic cross-linked polymer revealed that the wall surface of the polyethylene porous hollow fiber membrane forming the micropores was held almost uniformly over almost the entire surface. From the measurement of the integrated dissolution rate,
It was found that there was substantially no eluted component after 24 hours.

Examples 17 to 20 Density: 0.969 g / cm ³ , melt index: 0.35
High density polyethylene (NOVAT manufactured by Mitsubishi Chemical Corporation)
EC BU 004U) using a spinneret for hollow fiber shaping having a discharge opening diameter of 16 mm, an annular slit width of 2.5 mm, and a discharge cross-sectional area of 1.06 cm ² , at a spinning temperature of 230 ° C. and a discharge speed of 2
Spin at 8.0 cm / min, temperature 25 ° C, speed 4.0
/ Sec countercurrent cooling air, take-up speed 50m / min,
It was wound up by a spinning draft 179. The dimensions of the obtained undrawn hollow fiber were 585 μm in inner diameter and 168 μm in film thickness.

The undrawn hollow fiber was heated at 125 ° C. for 24 hours.
Heat treatment was performed at a constant length. The elastic recovery of this undrawn hollow fiber is 7
4%. Subsequently, after stretching in a greenhouse by 140% at a deformation rate of 180% per second, stretching in a roller is performed in a heating furnace heated to 120 ° C. so that the deformation rate becomes 2.6% per second. 11 to become 1900%
The film was relaxed and set in a heating furnace at 8 ° C. to continuously produce a porous hollow fiber membrane. The obtained porous polyethylene hollow fiber membrane is stretched 20 times with respect to the undrawn hollow fiber,
The inner diameter was 475 μm, and the film thickness was 130 μm. The average pore size measured by a mercury porosimeter was 5.1 μm, and the air permeation amount was 290 × 10 ⁴ liters / m ² hr 0.5 a.
tm, and the porosity was 89%. When observed with a scanning electron microscope, there are countless characteristic strip-shaped micropores,
The average length of the microfibrils was 11.5 μm.

The obtained polyethylene porous hollow fiber membrane having a large pore diameter and a high porosity was continuously supplied at a speed of 2 m / min, and immersed in a solution tank having a length of 10 cm to obtain a membrane having a diameter of 2 cm.
The adhered liquid was removed and dried in a pipe 1 having a length of 4 m, and then heated in a pipe 2 having a diameter of 2 cm and a length of 3 m to polymerize the monomers.

The compositions of the solutions were as follows: 100 parts of diacetone acrylamide, 0.5 parts of N-hydroxymethylacrylamide, bis- (4-t-butylcyclohexyl) peroxydicarbonate and 660 parts of acetone in the amounts shown in Table 1. did. Room temperature nitrogen in pipe 1 and heated nitrogen at 80 ° C in pipe 2 at 3 liters / mi
n shed.

Subsequently, this polyethylene porous hollow fiber membrane was placed in a 50 cm long tank containing a mixed solvent of water / ethanol = 50/50 (parts) and a 1.5 m long tank overflowed with hot water at 60 ° C. It was washed by passing through a water tank, and further dried in a hot air atmosphere to obtain a hydrophilic polyethylene porous hollow fiber membrane of the present invention.

The performance of the obtained hydrophilic porous hollow fiber membrane was evaluated, and the results shown in Table 1 were obtained. Observation of the coated state of the hydrophilic cross-linked polymer revealed that the polymer was held almost uniformly over almost the entire wall surface forming the polyethylene hollow fiber membrane.

[0142]

[Table 1]

[0143]

The large-pore-diameter porous polyethylene hollow fiber membrane of the present invention has a large pore diameter and a high porosity, so that it is suitable for liquid microfiltration, air cleaning, and the like. It allows for the design of compact modules and systems. In addition, since it is manufactured by a melt spinning method that does not use any solvent or the like, it is an extremely clean material and does not contaminate the filtration medium at all.

Further, the hydrophilicized polyethylene hollow fiber membrane of the present invention has excellent hydrophilicity, exhibits good water permeability even without pretreatment for hydrophilization with ethanol or the like, and almost no decrease in filtration performance is observed. I can't. Further, since the hydrophilic substance is firmly held on the surface of the micropores, the amount of the eluted components is extremely small. Therefore, the hydrophilic polyethylene porous hollow fiber membrane of the present invention can be used in the field of water treatment including high-temperature treatment, and its practical effect is extremely large.

[Brief description of the drawings]

FIG. 1 is a scanning electron micrograph showing a fiber structure on the outer surface of a large-pore-diameter porous polyethylene hollow fiber membrane of the present invention.

FIG. 2 is a scanning electron micrograph instead of a drawing showing the fiber structure of the outer surface of a conventional porous polyethylene hollow fiber membrane.

FIG. 3 shows strip-shaped micropores formed between microfibrils of a large-pore-diameter porous polyethylene hollow fiber membrane of the present invention and a knot formed of a stack dramella; FIG. 3 is a schematic view showing a laminated structure communicating with each other.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Microfibril 2 Nodule 3 Strip-shaped minute hole

────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kenji Kondo 20-1, Miyukicho, Otake City, Hiroshima Pref. Central Research Laboratory of Mitsubishi Rayon Co., Ltd. (56) References JP-B-63-35726 (JP, B2) (58) ) Surveyed field (Int.Cl. ⁷ , DB name) B01D 71/00-71/82

Claims (8)

(57) [Claims] 1. A polymer having an MI value of 0.05 to 5.5.
A porous hollow fiber membrane made of the amount of polyethylene, and microfibrils arranged in a fiber length direction, the strip-like micro-pores formed by being surrounded by the nodules consisting of stacked lamellae, than the hollow fiber inner wall It has a laminated structure mutually communicating with the outer wall surface, and the average pore diameter of the fine pores measured by a mercury porosimeter is more than 2 μm and 10 μm or less, and the porosity is 75% or more.
95%, air permeability 8 × 10 ⁵ l / m ² · hr.
A large-pore-diameter porous polyethylene hollow fiber membrane characterized by being 0.5 atm or more. 2. The microfibril has an average length of 3.0.
2. The large-pore-diameter porous polyethylene hollow fiber membrane according to claim 1, having a thickness of more than 15 μm and more than 15 μm. 3. An MI value of 0.1 using a hollow fiber production nozzle .
High-molecular-weight polyethylene having a molecular weight of
At a temperature 20 to 150 ° C. higher than the melting point, the spinning draft 5
Melt spinning at 5000 , the resulting unstretched yarn is 100 ~
After annealing at 130 ° C for 30 minutes or more , 40 ° C or less
Cold stretched at least 40% of the speed per second under, then 1
Thermal stretching at a rate of 10% or less per second, and a total stretching amount of 75 %
The method according to claim 1, wherein the content is 0 to 2500%. 4. A hydrophilized porous polyethylene hollow fiber obtained by retaining a saponified ethylene-vinyl acetate copolymer on at least a part of the surface of the micropores of the large pore porous polyethylene hollow fiber membrane according to claim 1. film. 5. The hydrophilized porous polyethylene hollow fiber membrane according to claim 4, wherein the saponified ethylene-vinyl acetate copolymer is physically retained. 6. A hydrophilic crosslinked polymer obtained by polymerizing a monomer containing diacetone acrylamide and a crosslinkable monomer on at least a part of the surface of the micropores of the large-pore porous polyethylene hollow fiber membrane according to claim 1. A hydrophilized porous polyethylene hollow fiber membrane holding the coalesced. 7. The hydrophilicized porous polyethylene hollow fiber membrane according to claim 6, wherein the hydrophilic cross-linked polymer is physically held. 8. The hydrophilic porous polyethylene hollow fiber membrane according to claim 6, wherein the crosslinkable monomer is a water-soluble crosslinkable monomer.