JPH05103959A - Large-pore-diameter porous polypropylene hollow-fiber membrane, its production and hydrophilic porous polypropylene hollow-fiber membrane - Google Patents

Abstract

PURPOSE:To provide a porous PP hollow-fiber membrane wherein strip-shaped micropores are laminated, having high porosity and a large pore diameter and capable of permeating a large amt. of air and a large-pore-diameter porous PP hollow-fiber membrane having durable hydrophilicity and high porosity. CONSTITUTION:The strip-shaped micropores surrounded by the knots consisting of the microfibrils arranged in the longitudinal direction of the fiber and stacked lamellae are laminated and intercommunicated from the inner wall surface of the hollow fiber toward the outer wall surface to form a laminated structure. The average pore diameter of the micropores of the large-pore-diameter PP hollow-fiber membrane measured by a mercury porosimeter is controlled to 1-10mum, the porosity to 70-95% and the amt. of air to be permeated to >=4X10<5>l/ m.hr.0.5atm. The membrane is obtained by melt-spinning PP, annealing the undrawn fiber obtained under specified conditions, cold-drawing and then hot- drawing the annealed fiber.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a porous polypropylene hollow fiber membrane having a large pore size and high porosity, which is suitable for fields requiring extremely high filtration flux such as microfiltration and air purification. The present invention relates to a method for producing the same and a hydrophilized porous polypropylene hollow fiber membrane.

[0002]

2. Description of the Related Art A porous hollow fiber membrane made of polypropylene in which strip-shaped micropores are laminated has been conventionally known, and the details of the technique are described in, for example, JP-A-52-15627 and JP-A-2-2849. It is disclosed in the publication. For the former, polypropylene is melt-spun at a spinning temperature of 210 to 270 ° C. and a spinning draft of 180 to 600, and then 155
30 ~ 200% below 110 ℃ after heat treatment below ℃
By stretching and then heat-treating again at a temperature of 155 ° C. or lower at a temperature above the heat treatment temperature, there are characteristic strip-shaped micropores, and the distribution curve of the pore radius of the micropores is 200
Disclosed is a technique for producing a porous hollow fiber having at least one local maximum in the range of ~ 1200 angstrom. For the latter, melt-spun polypropylene hollow fibers are drawn in liquid nitrogen and then at high temperature (110-110).
155 ° C.), or melt-spun polypropylene hollow fibers at high temperature (120-145).
(100 ° C to 700%) and stretched at 115 to 155 ° C.
The pore diameter measured by the bubble point method for forming strip-shaped micropores is 0.1 to 0.1 by the method of performing heat treatment in
A 1.0 μm porous polypropylene hollow fiber membrane is disclosed.

Thus, in the prior art, the average pore size is 1 μm.
A polypropylene porous hollow fiber membrane having strip-shaped micropores exceeding m has not been obtained.

Generally, the porous membrane is roughly classified into a hydrophilic membrane and a hydrophobic membrane depending on the characteristics of the material. Known examples of hydrophilic porous membranes include cellulose, cellulose derivatives, polyvinyl alcohol, and ethylene-vinyl alcohol copolymer. The characteristic feature of the hydrophilic porous membrane is that the surface of the pores of the membrane is hydrophilic, so that it is easily wet with water and the aqueous solution can be filtered without any special pretreatment.

However, the hydrophilic membrane has the drawbacks of low mechanical strength when wet, large swelling with water, and the like, and when dried from a wet state, the membrane performance deteriorates.
It has the drawback of being easily deteriorated.

On the other hand, since the hydrophobic porous membrane is hydrophobic, it is difficult to allow water to permeate as it is, and a hydrophilic treatment is necessary in order to permeate a hydrophilic liquid such as water. In particular, various methods have been investigated for the hydrophilization method by modifying the surface of polyolefin, but for the hydrophilization of a porous film with a complicated surface shape, a simple hydrophilization method for a film-like material with a smooth surface is used. Cannot be applied to.

As a method of hydrophilizing the polyolefin porous membrane, the entire surface including the fine pores of the polyolefin porous membrane is wet-treated with an organic solvent having good compatibility with water, such as alcohol or ketone, and then An organic solvent wetting / water replacement method in which an organic solvent is replaced with water, and 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-54-153872, JP-A-59-24732
Or a method of irradiating with radiation while the hydrophilic monomer is held on the surface of the porous film (Japanese Patent Laid-Open No. Sho 5).
6-38333) and a method of plasma-treating a porous structure of a hydrophobic resin (JP-A-56-157437).

However, in the organic solvent wetting / water substitution method, once water in the pores escapes during storage or use, that portion returns to hydrophobic and cannot pass through the water, so that it is always around the porous membrane. It is necessary to fill it with water, and handling is complicated. Although the physical adsorption method is easy to operate, it cannot be said to be a sufficient hydrophilic method because the hydrophilic substance is desorbed during long-term use. Further, in the conventional chemical surface modification method, it is difficult to uniformly hydrophilize the film in the film thickness direction in both the method of irradiating radiation and the method of plasma treatment, and when the film is thick or when the film is hollow fiber-like. Further, when it was attempted to make the hydrophilic treatment almost uniform in the entire film thickness direction, there were problems such as damage to the porous membrane substrate and a decrease in mechanical strength being unavoidable.

Further, it has been proposed that the hydrophobic porous membrane is previously hydrophilized with a saponification product of an ethylene-vinyl acetate copolymer, that is, an ethylene-vinyl alcohol copolymer (Japanese Patent Laid-Open No. 61-125408). Publication, JP-A-61
-271003).

Further, two different polymers are blended and melt-spun, and then subjected to a stretching treatment to cleave the interface of the different polymers to form a microporous hollow fiber, and a side chain existing in the constituent polymer. It has been proposed to produce hydrophilic porous hollow fibers whose pores are hydrophilized by post-treatment such as hydrolysis of groups and sulfonation (JP-A-55-55).
137208).

Further, a porous membrane in which a hydrophilic polymer is firmly held on the surface of the pores of the polyolefin porous membrane and a method for producing the same have been proposed (JP-A-63-19).
0602 publication). For details of the technique, a hydrophilic porous membrane in which a hydrophilic cross-linked polymer composed of monomers containing diacetone acrylamide and a cross-linkable monomer is retained on the surface of at least some pores of the polyolefin porous membrane. In addition, it is a production method in which monomers containing diacetone acrylamide and a crosslinkable monomer are heated and polymerized while being held on the surface of at least some of the pores of the polyolefin porous membrane.

[0012]

However, since any of the methods uses a conventionally known polyolefin porous membrane as a starting material, the performance is insufficient for applications requiring a high permeation flow rate. That is, in order to obtain a hydrophilized porous membrane having a high permeation flow rate, the pore size of the micropores of the hydrophobic porous membrane should be increased,
It was necessary to consider hydrophilization including high porosity.

In the fields of microfiltration and air purification, extremely high filtration flux is required, and membranes and non-woven fabrics in which micron-order pores are opened with high porosity are used. Porous hollow fibers with strip-shaped micropores are disclosed in Japanese Examined Patent Publication No. 6
As described in Japanese Patent Laid-Open No. 3-35726, the gas permeation amount and the liquid permeation amount are large, and it has a feature that clogging is unlikely to occur due to the structure in which strip-shaped minute holes are laminated. However, such a hollow fiber having strip-shaped micropores still has performance as a sterile dust-free air filter requiring extremely high filtration flux and low pressure loss, a dust filter for various gases, and a filter for sterile water. Is insufficient. The reason is that the pore size is still small and the porosity is low for application in such fields.

On the other hand, the hydrophilizing treatment with alcohol or a surfactant is a temporary hydrophilizing treatment. Moreover, if the hydrophilizing agent is used for filtration or the like with the hydrophilizing agent attached to the porous membrane, the alcohol or the surfactant is removed. Since it migrates to purified water and contaminates it, it is necessary to sufficiently wash and remove these hydrophilizing agents before filtration. In addition, since the membrane surface returns to hydrophobic when dried in such a state, after once hydrophilizing treatment, the hydrophilizing agent should be replaced with water, and the pore surface of the porous membrane should always be in contact with water. It has the problem of having to be.

Further, in the method described in JP-A-56-38333, since the hydrophilic group is chemically fixed to the porous membrane, permanent hydrophilization is achieved, but ionization is performed. Since it is necessary to irradiate with radiation, large-scale equipment is required, and it cannot be said that the process stability is sufficient.
There is also a risk that the membrane material may be damaged and it is difficult to operate and manage the treatment process.

Fibers obtained by melt spinning and drawing a blend of different polymers described in JP-A-55-137208 to make them porous generally have a low porosity. Furthermore, there is also a problem that the post-treatment such as hydrolysis or sulfonation for making hydrophilic is necessary, and 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 hydrophilized hollow fiber membrane having a submicron pore size can be obtained. Further, JP-A-61-225408 and JP-A-6-125408.
The technology disclosed in the hydrophilic composite porous membrane of JP-A 1-271003 is related to the pore size as described in JP-B-63-3.
It does not exceed the state of the art disclosed in Japanese Patent No. 5726, and the average fiber diameter of the hollow fibers obtained in the examples is 0.25 to 0.70 μm.

Further, JP-A-63-190602 discloses that a hydrophilic cross-linked polymer composed of monomers containing diacetone acrylamide and a cross-linking monomer is held on the pore surface of a polyolefin porous membrane. It is the disclosed hydrophilic porous membrane.

However, such a porous membrane having a crosslinkable polymer retained on the surface of the pores of the strip-shaped micropores is
Performance is still insufficient for filtration of aqueous solutions and suspensions that require extremely high filtration flux and low pressure loss, production of pure water for the electronic industry, disinfection of raw water for pharmaceutical production, etc. ..
The reason is that the pore size is still small and the porosity is low for application in such fields. If the structure of the membrane is a laminated structure of strip-shaped micropores with excellent filtration efficiency, and if it is possible to impart permanent hydrophilicity to a porous hollow fiber with a large pore size and high porosity, it will be energy-saving and ultra-clean. It is extremely important to contribute to cutting-edge industrial fields such as the creation of a unique environment.

Under these circumstances, the inventors of the present invention have provided a porous polypropylene hollow fiber membrane and a permanent hydrophilicity capable of achieving a high porosity, a large pore diameter and a large air permeation rate in a structure in which strip-shaped micropores are laminated. The present invention has been accomplished as a result of intensive research to obtain a porous polypropylene hollow fiber membrane having a high porosity and a large pore size.

[0021]

That is, the present invention is a porous hollow fiber membrane made of polypropylene, which is formed by being surrounded by microfibrils arranged in the fiber length direction and a knotted portion made of a stacked lamella. The strip-shaped micropores have a laminated structure in which they communicate with each other from the inner wall surface to the outer wall surface of the hollow fiber, and the average pore diameter of the micropores measured by a mercury porosimeter is more than 1 μm and 10 μm or less, and the porosity is 70% ~
95%, air permeation rate 4 × 10 ⁵ liters / m ² · hr
A large-pore porous polypropylene hollow fiber membrane characterized by having 0.5 atm or more.

The present invention also relates to a porous hollow structure in which polypropylene is melt-spun using a hollow fiber producing nozzle, the obtained undrawn yarn is annealed, cold drawn, and then hot drawn to make it porous. In the method for producing a yarn, the undrawn yarn is annealed at a temperature of 120 to 165 ° C. for 30 minutes.
For 10 minutes or more, the deformation rate during hot stretching is 10% per second.
The following is the method for producing a large-pore porous polypropylene hollow fiber membrane, characterized in that the total stretching amount is 700% to 2500%.

The present invention further provides a hydrophilized porous polypropylene in which a saponified ethylene-vinyl acetate copolymer is retained on at least a part of the surface of the micropores of the large-pore porous polypropylene hollow fiber membrane described above. It is a hollow fiber membrane.

Still another aspect of the present invention is a hydrophilic property obtained by polymerizing monomers containing diacetone acrylamide and a crosslinkable monomer on at least a part of the surface of the micropores of the large-pore porous polypropylene hollow fiber membrane described above. A hydrophilized porous polypropylene hollow fiber membrane which holds a crosslinked polymer.

[0025]

The present invention will be described in more detail below.

The polypropylene used in the present invention is
It is preferably isotactic or syndiotactic polypropylene. By melt-molding this polypropylene under specific conditions and then stretching it under specific conditions, micropores with a relatively large pore size are interconnected from the inner wall surface of the hollow fiber to the outer wall surface of the hollow fiber membrane. Is obtained.

The MI value of the polypropylene used in the present invention is preferably in the range of 0.1 to 10. MI value is A
It is a value measured by STMD-1238, and more preferably in the range of 0.3 to 8. When polypropylene having an MI value of more than 10 is used, it is difficult to stably draw it to a total draw ratio of 700% or more, and the porous hollow fiber of the present invention has a large pore diameter and a high porosity. It is difficult to obtain a film. In addition, polypropylene having an MI value of less than 0.1 has a too high melt viscosity, which makes stable spinning difficult. It is one of the important points of the present invention to employ polypropylene having a high molecular weight in the range where stable spinning is possible.

In the present invention, the polypropylene as described above is melt-spun using a nozzle for producing a hollow fiber to produce a highly oriented crystalline unstretched hollow fiber. It is desirable that the nozzle has a double pipe structure because the uneven thickness is small, but a nozzle having a horseshoe shape or any other structure may be used. In the double-tube structure nozzle, the gas to be supplied to the inside of the hollow fiber to maintain the hollow form may be either 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. above the melting point of the polymer.
It is desirable to set the temperature in a high range. When spinning is performed in a temperature range lower than this temperature range, the melting of the polymer is incomplete, melt fracture easily occurs, and the stability in the drawing step decreases. On the contrary, when spinning is performed in a temperature range higher than this temperature range, it becomes difficult to increase the pore size and the porosity of the porous hollow fiber membrane.

The polymer discharged at the appropriate spinning temperature is
It is desirable to collect the fiber in the spinning draft range of 5 to 5000. If the spinning draft exceeds 5000, an unstretched hollow fiber capable of 700% or more total stretching cannot be obtained. If the spinning draft is less than 5, highly oriented unstretched hollow fibers cannot be obtained, and stretched porosity cannot be achieved.

The unstretched hollow fiber thus obtained is a highly stretched unstretched hollow fiber having an inner diameter of 10
The thickness is 0 to 2000 μm, and the film thickness is about 15 to 800 μm. This unstretched hollow fiber is heat-treated under a temperature condition of 120 to 165 ° C, more preferably 130 to 155 ° C, and then stretched. The necessary heat treatment (annealing) time is 30 minutes or more. By this annealing treatment, the crystal structure becomes more complete, and the elastic recovery rate at 50% elongation reaches 50% or more.

In the production method of the present invention, the stretching is carried out by two-stage stretching in which cold stretching is followed by hot stretching. In cold stretching, it is preferable to fix the stretching point in order to destroy the crystal structure and uniformly generate microcrazes, and it is desirable to carry out cold stretching at a high stretching speed of 40% or more in deformation rate per second. Further, the cold stretching temperature is preferably 80 ° C. or lower in order to break the crystal structure without relaxing it and generate microclades.

After the cold stretching of about 5 to 150% is carried out in this manner, the hot stretching is carried out in the temperature range of 120 to 165 ° C. When the hot drawing temperature exceeds this range, the hollow fiber becomes transparent, and it is difficult to obtain a desired porous structure.
If the temperature is lower than 120 ° C., the porous structure becomes fine and the porosity decreases, so that a target having a large 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 a deformation rate of more than 10%, it is virtually impossible to achieve a total stretch of 700% or more. Total stretching amount is 7
It is necessary to set it to 00% to 2500%. In the case where the stretching exceeds 2500%, yarn breakage frequently occurs during the stretching and the process stability decreases, which is not desirable. Although a porous structure is formed with a total stretching amount of less than 700%, the hollow fiber membrane of the present invention having a large pore diameter and a high porosity cannot be obtained. Porosity 7
To achieve 0% or more, 700% or more, preferably 10%
A total stretch of 00% or more is essential.

The deformation rate referred to in the present invention means a value obtained by dividing the amount of drawing (%) in the drawing section by the time (seconds) during which the yarn passes through the drawing section.

The obtained porous hollow fiber membrane has a substantially morphological stability ensured by hot drawing, and does not necessarily require a heat setting step for fixing the porous structure. However, heat setting may be performed under tension in a fixed length or while shrinking in the same temperature range as the above-mentioned hot stretching temperature, if necessary.

In the thus obtained porous polypropylene
The hollow fiber membrane is the flatness of the micropores measured with a mercury porosimeter.
Uniform pore diameter exceeding 1 μm and 10 μm or less, preferably 1.2
μm to 10 μm, porosity 70% to 95%, air permeation
The amount is 4 × 10^Five Liter / m ² ・ Hr ・ 0.5atm or less
Above. In addition, microfibrils arranged in the fiber length direction
It is formed by being surrounded by a joint and a node made of stacked dramera.
There is a characteristic strip-shaped micropore that is
These small holes communicate with each other from the inner wall surface to the outer wall surface.
Has a laminated structure. Flat of microfibril
The average length is more than 1 μm and 15 μm or less.

The hydrophilized porous hollow fiber membrane of the first type of the present invention is an ethylene-vinyl acetate copolymer having at least a part of the inner surface of the micropores of the large-pore porous polypropylene hollow fiber membrane having the above-mentioned characteristics. It can be obtained by holding a saponified polymer (hereinafter, simply referred to as “saponified product”). In the hydrophilized porous hollow fiber membrane of the present invention, the porous polypropylene hollow fiber membrane material as a substrate has a large pore size and porosity, and without impairing the characteristics such as sufficiently high mechanical strength, The retention of the saponified product imparts good hydrophilicity. Therefore, the hydrophilized porous membrane of the present invention has excellent permeability to an aqueous liquid, and is particularly suitable for high flow rate treatment. In addition, since the porous polypropylene hollow fiber membrane has a unique membrane structure composed of the above-mentioned strip-shaped minute pores, it has an advantage that clogging is unlikely to occur.

In the hydrophilized porous hollow fiber membrane of the present invention,
At least a part of the surface of the micropores of the raw material porous hollow fiber membrane in which the polymer is retained means a part or all of the wall surface forming the micropores. That is, the polymer is retained on the wall surface of the micropores to such an extent that the permeation flow rate that does not hinder the use of water through the micropores of the porous membrane due to the transmembrane pressure difference that is normally used. It suffices if all the wall surfaces forming the micropores are not necessarily covered with the polymer. Further, the polymer may or may not be retained on the outer surface of the porous membrane.

The term "retained" means that the polymer is firmly bonded or adhered to the wall surface forming the micropores so that the polymer is not easily detached during storage or use.
Therefore, the polymer may be chemically bonded to the wall surface, the polymer may be adhered to the wall surface by an anchor effect, and the microfibrils or knots forming strip-shaped micropores may be wrapped. The polymer may be adhered and crosslinked, or these retention states may be mixed.

As described above, the polymer may be held on the wall surface of the raw material hollow fiber membrane forming the micropores in any of the above states. However, the hydrophilized porous membrane that is physically held on the wall surface such as the anchor effect and adhesive cross-linking without chemically bonding the polymer has a higher mechanical strength than the raw material hollow fiber membrane that is the base material. It is particularly preferable because there is almost no deterioration or change in the micropore structure.

In the present invention, as a method of retaining the saponified product on at least a part of the inner surface of the micropores of the porous polypropylene hollow fiber membrane as the base material, for example, A method of directly supplying into the pores to hold it, a method of supplying the ethylene-vinyl acetate copolymer into the micropores of the porous polypropylene hollow fiber membrane and holding it, and then saponifying it can be used. ..

As the ethylene-vinyl acetate copolymer used to form the saponified product, various types such as random type, block type, and graft type can be used. The saponified type is also the ethylene-vinyl acetate copolymer type. Dependent.
The ethylene-vinyl acetate copolymer is basically formed from ethylene and vinyl acetate, but other monomer components may be mixed within a range that does not impair desired properties.

The content of ethylene units in the ethylene-vinyl acetate copolymer is important for obtaining good adhesion of the ethylene-vinyl acetate copolymer and its saponified product to polypropylene. Therefore, the content thereof is preferably 20 mol% or more. That is, when the content of the ethylene unit is less than 20 mol%, when the ethylene-vinyl acetate copolymer or a saponified product thereof is attached to the inner surface of the micropores of the porous polypropylene hollow fiber membrane, it is attached to the deposit. It is not preferable because good adhesion cannot be obtained and peeling of adhered substances easily occurs. On the other hand, if the content of ethylene units is too large, the saponified product finally obtained cannot provide good hydrophilicity to the porous polypropylene hollow fiber membrane, which is not preferable. Therefore, the content of ethylene units is preferably 70 mol% or less.
Considering a better balance between adhesion and hydrophilicity, the content of ethylene units is particularly preferably in the range of 25 to 50 mol%.

Saponification of the ethylene-vinyl acetate copolymer can be carried out by a known method such as heat treatment in an alkaline aqueous solution such as sodium hydroxide for a required time.
By this saponification treatment, the acetyl group in the vinyl acetate portion is converted into a hydroxyl group, and the copolymer is given good hydrophilicity. In order to impart sufficient hydrophilicity to the porous hollow fiber membrane, the saponification degree is preferably 60 mol% or more.

In the present invention, in order to directly retain the saponified product on a part of the inner surface of the microvoids of the porous hollow fiber membrane, a holding solution containing the saponified product is applied to the substrate by a method such as dipping or coating. A method of supplying at least into the micropores of the hollow fiber membrane to evaporate and remove the solvent of the solution, and a holding solution containing a saponified product by dipping, coating, etc. Inside, and further dipping this in a coagulant solution of the saponified product to rapidly solidify it at least on the inner surface of the micropores and dry it.
It can be done by etc.

The holding solution can be prepared by dissolving the saponified product in a solvent capable of dissolving the saponified product. As the solvent, a water-miscible organic solvent or a mixture of a water-miscible organic solvent and water can be used. Examples of the water-miscible organic solvent include alcohols such as methanol, ethanol, n-propanol, isopropanol, sec-butanol, t-butanol and cyclohexanol; ethylene glycol,
Examples thereof include polyhydric alcohols such as propylene glycol and glycerin; tetrahydrofuran, dioxane, dimethylformamide, dimethylsulfoxide, dimethylacetamide, formamide, ethylene chlorohydrin and the like, and one kind or a combination of two or more kinds thereof can be used. Of these, ethanol and dimethyl sulfoxide are particularly preferable because they have good solubility of saponified products and low toxicity.

As the solvent, a mixture of water-miscible organic solvent and water is particularly preferable for the following reasons. That is, the saponified product is composed of non-polar and hydrophobic ethylene units and polar and hydrophilic vinyl acetate units (including those in which the acetyl group is converted to a hydroxyl group by saponification). When a non-polar polypropylene base material is coated in the state of being dissolved in a highly polar solvent system, non-polar ethylene units are localized on the surface of the polypropylene base material side in the saponified thin film layer that is formed. However, it is considered that polar vinyl acetate units are likely to be localized on the surface (opposite the polypropylene base material) facing this. This phenomenon is a preferable phenomenon because the adhesion between the thin film layer and the polypropylene constituting the surface of the micropores is improved, and the hydrophilicity of the surface of the thin film layer held on the surface of the micropores is improved. Therefore, it is preferable to use a mixture of water and an organic solvent as the solvent of the above holding solution because the polarity of the solvent becomes stronger and this phenomenon is promoted. The proportion of water to be mixed is preferably larger within a range that does not inhibit the solubility of the saponified product,
Although the ratio varies depending on the concentration of the saponified product, the content of the ethylene portion thereof, the treatment temperature, etc., a preferable range is, for example, 5 to 60% by weight.

The concentration of the saponified product in the holding solution is set to a level necessary to obtain the desired hydrophilic effect, and is selected in consideration of the physical properties of the porous polypropylene hollow fiber membrane as the base material, For example, it is preferably used in the range of 0.1 to 5.0% by weight. The treatment such as dipping or coating the porous polypropylene hollow fiber membrane in the holding solution may be completed in a single treatment, but may be performed several times using a holding solution having a relatively low saponification concentration. You can do it separately. If the saponified product concentration exceeds 5.0% by weight,
There is a case where the amount of the saponified substance attached becomes too large and the diameter of the micropores of the porous polypropylene hollow fiber membrane as the base material is narrowed to reduce the liquid permeation performance, which is not preferable. The temperature of the holding solution is not particularly limited, but a higher temperature is generally preferable because the saponified product has better solubility and the viscosity of the solution is lowered, and for example, a range from room temperature to 100 ° C. is preferable. The immersion time in the case of the immersion treatment is preferably in the range of several seconds to several tens of minutes. The solvent can be removed from the holding solution held in the micropores of the porous polypropylene hollow fiber membrane as the substrate by vacuum drying, hot air drying or the like. The degree of drying may be any temperature as long as the base material is not deformed by heat, and is preferably 130 ° C. or lower.

Next, a method in which the ethylene-vinyl acetate copolymer is first retained on at least a part of the inner surface of the micropores of the porous polypropylene hollow fiber membrane as the substrate and then saponified An example will be described.

The ethylene-vinyl acetate copolymer can be held on the substrate by the same method as the method mentioned above for directly holding the saponified product, or the like. The content of ethylene units and vinyl acetate units in the ethylene-vinyl acetate copolymer is preferably set within the range described above. As the solvent of the holding solution of ethylene-vinyl acetate copolymer, those for preparing the holding solution of the above-mentioned saponified product, halogenated hydrocarbons, aromatic hydrocarbons and the like can be used, in particular, A mixture of water and an organic solvent is preferred for the same reasons as in the saponified product. The concentration of ethylene-vinyl acetate copolymer in the holding solution is
For example, it is preferably 1.0 to 5.0% by weight. Treatments such as dipping and coating for holding the ethylene-vinyl acetate copolymer may be completed once, or may be performed several times using a holding liquid having a relatively low concentration. . When it is completed once, less than 1.0% by weight is not preferable because sufficient hydrophilicity cannot be obtained after saponification treatment. Further, when it exceeds 5.0% by weight, the diameter of the micropores of the porous polypropylene hollow fiber membrane as the base material is narrowed,
It is not preferable because the liquid permeation performance is often reduced.

By thus saponifying the hollow fiber membrane holding the ethylene-vinyl acetate copolymer, the hydrophilic porous hollow fiber membrane of the present invention can be obtained. This saponification treatment can be carried out, for example, by subjecting the hollow fiber membrane holding the ethylene-vinyl acetate copolymer to heat treatment in an alkaline aqueous solution such as an aqueous sodium hydroxide solution for a required time.

The saponification of the saponified product on the surface of the micropores of the hollow fiber membrane by the various methods described above is carried out as uniformly as possible on the inner surface of the micropores of the porous polypropylene hollow fiber membrane as the substrate. Moreover, it is preferable to keep the amount of retention to a minimum, and to reduce the reduction of the pore size and the blockage of the micropores of the hollow fiber membrane due to the retention as much as possible.

The second type of hydrophilized porous polypropylene hollow fiber membrane of the present invention is crosslinkable with diacetone acrylamide on at least a part of the micropore surface of the large-pore porous polypropylene hollow fiber membrane described above. It holds a hydrophilic cross-linked polymer obtained by polymerizing monomers including monomers.

In this hydrophilized porous polypropylene hollow fiber membrane, diacetone acrylamide and a cross-linking monomer are provided on the wall surface of the polypropylene porous hollow fiber membrane having a large pore size and a high porosity, which forms fine pores. A hydrophilic cross-linked polymer composed of monomers contained therein is retained, but this polymer is capable of firmly retaining (1) polypropylene, compared with other polymers, and (2) polypropylene porous hollow fiber. This is because it can be held almost uniformly over almost the entire wall surface forming the micropores of the membrane, (3) it has appropriate hydrophilicity, and (4) it is substantially water-insoluble.

The hydrophilic cross-linked polymer obtained by polymerizing monomers containing diacetone acrylamide and a cross-linking monomer contains diacetone acrylamide as a monomer component in an amount of 50% by weight or more and also contains a cross-linking monomer. It is a crosslinked polymer obtained from the system, and as the monomer component, a non-crosslinkable monomer may be contained in addition to these.

As the crosslinkable monomer, a monomer having two or more polymerizable unsaturated bonds such as vinyl bond and allyl bond which are copolymerizable with diacetone acrylamide, or 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 good solvent in common with diacetone acrylamide can be mentioned. Examples thereof include N, N'-methylenebisacrylamide, N-hydroxymethyl (meth) acrylamide, triallyl cyanurate, triallyl isocyanurate, divinylbenzene, 2,2-bis (4-methacryloyloxypolyethoxyphenyl). ) Propane, ethylene di (meth) acrylate, polyethylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, trimethylolethane tri (meth) acrylate, butanediol di (meth) acrylate , Hexanediol di (meth) acrylate, diallyl phthalate, 1,3,5-triacryloylhexahydro-s-
Examples include triazine and the like.

The non-crosslinking monomer is a monomer having one polymerizable unsaturated bond such as vinyl bond or allyl bond which is copolymerizable with diacetone acrylamide, and is a good solvent common to diacetone acrylamide. The monomer which has is mentioned. 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 a crosslinkable monomer and a non-crosslinkable monomer used together with diacetone acrylamide are collectively referred to as a copolymerizable monomer.

The composition ratio of diacetone acrylamide to form a hydrophilic cross-linked polymer and the cross-linking monomer is preferably 0.3 to 100 parts by weight of the cross-linking monomer with respect to 100 parts by weight of diacetone acrylamide,
It is more preferably 0.5 to 80 parts by weight. Also,
The compositional ratio of the copolymerizable monomer to the copolymerizable monomer is 100 parts by weight of diacetone acrylamide.
It is preferably 3 to 110 parts by weight, and 0.5 to 10 parts by weight.
It is more preferably 0 part by weight.

In the present invention, since the polymer retained on at least a part of the wall surface forming the micropores of the polypropylene porous hollow fiber membrane having a large pore diameter and a high porosity is a crosslinked polymer, this weight The coalescence has the advantages that the degree of swelling in water is small and there is no risk of blocking micropores, and that the stability of the polymer is good and the amount of elution component in water is extremely small. Therefore, the hydrophilized porous membrane of the present invention is effective in the fields of water treatment, blood treatment, and the like, where a small amount of eluted components is a problem. On the other hand, a diacetone acrylamide-based polymer having no cross-linked structure swells in water to block micropores, and a small amount of it dissolves in water to become an elution component. A porous membrane holding such a polymer may cause various problems during use.

The greater the degree of hydrophilicity of the polymer,
The water permeability of the hydrophilized porous membrane is good, and at the beginning of use, water uniformly permeates from the entire membrane surface in a short time.
As the crosslinkable monomer that produces a hydrophilic crosslinked polymer,
It is preferable that the water-soluble crosslinking monomer has a sufficient degree of hydrophilicity.

Such a water-soluble crosslinkable monomer is
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. it can.

The amount of the hydrophilic cross-linked polymer retained on at least a part of the wall surface forming the micropores of the polypropylene porous hollow fiber membrane of the present invention having a large pore size and a high porosity is the polypropylene porosity. Although it depends on the porosity and pore diameter of the porous hollow fiber membrane, it is preferably about 0.5 to 100% by weight based on the weight of the polypropylene porous hollow fiber membrane. If the amount of polymer retained is less than this range, sufficient hydrophilicity cannot be imparted to the porous hollow fiber membrane, and even if it exceeds this range, the hydrophilicity of the porous hollow fiber membrane is further improved. Instead, the pore volume may rather decrease and the water permeability may decrease. Polymer retention is 0.5-5
It is more preferably about 0% by weight, particularly preferably about 1 to 30% by weight.

Various methods can be adopted as a method for holding the hydrophilic cross-linked polymer on at least a part of the wall surface of the polypropylene porous hollow fiber membrane forming the fine pores. For example, a solution in which diacetone acrylamide and the above-mentioned copolymerizable monomer (hereinafter, referred to as “monomers”) and a polymerization initiator are dissolved in a suitable solvent such as an organic solvent or water is prepared, and a raw hollow fiber membrane is prepared. After impregnating the raw material hollow fiber membrane with the solution of the monomers by a method of immersing in the solution, or a method of producing a membrane module with the raw material hollow fiber membrane and then pressing this solution into the raw material hollow fiber membrane, A method of volatilizing and removing the solvent can be adopted. By using the solution of the monomers diluted with the solvent, the monomers can be attached almost uniformly over the entire porous hollow fiber membrane without blocking the micropores of the porous hollow fiber membrane. In addition, the adhesion amount of the monomers can be adjusted by changing the concentration of the monomers in the solution and the impregnation time of the solution.

In this way, the solvent is removed while the monomers are retained on at least a part of the wall surface of the raw material hollow fiber membrane forming the micropores, and then the polymerization is carried out to obtain a polypropylene porous material. The hydrophilic crosslinked polymer can be retained on at least a part of the wall surface of the hollow fiber membrane in which the micropores are formed.

As the 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 the polymerization initiator is added, it is preferable to use a solvent that can also dissolve the polymerization initiator. Examples of such an organic solvent 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. Although the boiling point of the organic solvent is not particularly limited, it is preferably 100 ° C. or lower in consideration of easy removal of the solvent before the polymerization step, and 80
It is more preferable that the temperature is not higher than ° C.

Since the surface of the polypropylene porous hollow fiber membrane is hydrophobic, when water is used as the solvent, the monomers are hydrophilic on the surface of the pores when the aqueous solution containing the monomers permeates into the pores. Since the functional group is easily oriented and adsorbed outward, 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, but the wall surface of the porous hollow fiber membrane where micropores are previously formed is wetted with alcohols or ketones. After that, the solution can be contacted.

Further, when an organic solvent is used as the solvent, the solution is advantageous in that it penetrates into the micropores of the raw material hollow fiber membrane in a short time, and the solvent can be easily removed from the micropores. There is.

Even when the monomers are polymerized in a state where they are randomly oriented on the surface of the pores without utilizing the oriented adsorption, the formed hydrophilic cross-linked polymer is more hydrophilic than polypropylene. Due to the large degree, the wall surface forming the micropores in which the polymer is retained is relatively hydrophilic as compared with the wall surface forming the micropores in which the polymer is not retained. Therefore, a polypropylene porous hollow fiber membrane having hydrophilicity can be obtained.

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

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-based compounds such as azobis-2,3,3-trimethylbutyronitrile; acetyl peroxide, propionyl peroxide, butyryl peroxide, isobutyryl peroxide, succinyl peroxide, benzoyl peroxide, benzoylisobutyryl peroxide, β -Allyloxypropionyl peroxide,
Examples thereof include hexanoyl peroxide, 3-bromobenzoyl peroxide, bis- (4-t-butylcyclohexyl) peroxydicarbonate, and other peroxides; potassium persulfate, ammonium persulfate, and other persulfates; and the like. ..

Especially when water is used as a solvent, a water-soluble polymerization initiator such as azobisisobutyramidine, 4,
4′-azobis-4-cyanopentanoic acid is preferred, but the above-mentioned water-insoluble polymerization initiator is used because even the water-insoluble polymerization initiator can be dispersed in water because the monomers themselves have surface activity. You can also

As the polymerization initiator in the case of the photopolymerization method, benzophenone, benzoin methyl ether, benzyl dimethyl ketal, fluorenone, 4-bromobenzophenone, 4-chlorobenzophenone, methyl O-benzoylbenzoate, benzoyl peroxide, anthraquinone, biacetyl are used. , Uranyl nitrate and the like. It is also possible to use these in an appropriate combination.

The ratio of the monomers to the solvent in the solution may be appropriately selected in consideration of the kind of the solvent and the target amount of the polymer to be retained. The weight part is preferably 200 to
It is more preferably 5000 parts by weight.

The polymerization initiator is preferably 0.001 to 100 parts by weight with respect to 100 parts by weight of monomers,
It is more preferably 0.01 to 30 parts by weight,
It is particularly preferably 1 to 20 parts by weight.

When the amount of the solvent with respect to the monomers exceeds the above range, the amount of the monomers retained on the wall surface forming the micropores of the porous hollow fiber membrane is too small to obtain a sufficient amount of the polymer. If the amount of the polymer cannot be retained, and if it is less than the above range, it is difficult to control the amount of the polymer retained, and the amount of the polymer retained on the wall surface forming the micropores or inside the micropores increases. This is not preferable because it may cause the blockage of the micropores.

The dipping time or the press-fitting time when dipping or press-fitting the raw material hollow fiber using these solutions is about 0.5 seconds to 30 minutes, and the wetting property for the raw material hollow fiber is good. When using a solution, it can be carried out in a shorter time.

In this way, the polypropylene porous hollow fiber membrane in which the monomers optionally containing a polymerization initiator are held on the wall surface forming at least some of the micropores is The liquid is removed, and if necessary, the solvent inside the micropores is removed by evaporation, and then transferred to the next polymerization step.

If the temperature at the time of evaporation and removal of the solvent is too high, the polymerization partially proceeds while the solvent remains, and the inside of the micropores that are not the wall surface forming the micropores of the porous hollow fiber membrane. Polymerization may occur, and as a result, some of the micropores may be clogged, which is not preferable. Considering this, the temperature during solvent removal is preferably 10 to 40 ° C.

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

In the case of the thermal polymerization method, the polymerization temperature is not lower than the decomposition temperature of the polymerization initiator, and is not higher than the decomposition temperature of the polypropylene porous hollow fiber membrane and does not damage the membrane substrate. It is desirable to use a temperature of 30 to 100 ° C. The heating time depends on the kind 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. Further, in the continuous method, since the heat transfer efficiency is high, the polymerization can be performed in a short time, and the heating time is usually 10 seconds to 6 seconds.
It is 0 minutes, preferably 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, a high pressure mercury lamp, a xenon lamp, an arc lamp or the like can be used as an ultraviolet ray source.

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

At a low irradiation intensity, it is difficult to achieve sufficient hydrophilicity, and at a high irradiation intensity, the polypropylene porous hollow fiber membrane is greatly damaged. Careful selection is preferred.

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

During these polymerizations, the presence of oxygen in the atmosphere significantly inhibits the polymerization reaction. Therefore, the polymerization is carried out in an atmosphere of an inert gas such as nitrogen or in a state where oxygen is substantially absent in a vacuum. It is desirable to let

When forming the hydrophilic crosslinked polymer, the crosslinking reaction may be carried out simultaneously with the polymerization reaction, or the copolymer may be once formed and then crosslinked. Also,
The crosslinking reaction by condensation may be carried out by utilizing the heat of polymerization reaction or may be carried out by heating.

In particular, when utilizing a crosslinking reaction by condensation, an uncrosslinked copolymer of diacetone acrylamide and a crosslinking monomer prepared in advance is dissolved in a solvent, and then the micropores of the polypropylene porous hollow fiber membrane are removed. You may use the method of making it hold | maintain on the formed wall surface and carrying out a crosslinking reaction in the state. In this case, the molecular weight of the uncrosslinked copolymer is 1
It is preferably from 500,000, and when the molecular weight is too large, it is difficult to allow the copolymer to enter inside the micropores of the polypropylene porous hollow fiber membrane, which is not preferable. More preferably, the molecular weight is 5 to 300,000.

In producing the hydrophilic porous hollow fiber membrane of the present invention, various polymerization methods can be adopted as described above, but the method using heat energy is most preferable. When using thermal energy, the micropores of the porous hollow fiber membrane can be heated to a uniform temperature, so that all the micropores holding the monomers are uniformly polymerized on the wall. And without changing the structure of the membrane by appropriately setting the polymerization temperature,
Moreover, there is an advantage that polymerization can be carried out without degrading the membrane substrate. On the other hand, when light energy is used, it is difficult for light to reach the microscopic pores of the porous hollow fiber membrane due to light scattering, and deterioration of the membrane substrate tends to progress when the light irradiation intensity is increased. There is a problem, and also when utilizing radiation energy, there is a problem that the deterioration of the membrane substrate easily progresses. Therefore, when adopting these polymerization methods, it is necessary to carefully select the polymerization conditions that do not deteriorate the membrane substrate.

The monomers and the above-mentioned uncrosslinked copolymer retained on the wall surface of the raw hollow fiber membrane forming the micropores are polymerized or crosslinked on the surface of the porous membrane by these polymerization methods. Because of the crosslinking, at least a part of the wall surface forming the micropores of the porous hollow fiber membrane is covered with these polymers.

After the hydrophilic cross-linked polymer is produced, unreacted monomers and free radicals existing around the wall surface forming the microscopic pores of the porous hollow fiber membrane are dipped by an immersion method or a press-fitting method using a suitable solvent. It is desirable to remove unnecessary components such as the 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, but as a particularly preferred method, a monomer containing diacetone acrylamide and a water-soluble crosslinkable monomer and a polymerization initiator are used. The method may be a method in which the polypropylene porous hollow fiber membrane is heated and polymerized while being held on the wall surface forming at least some of the micropores.

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

Further, the hydrophilized porous hollow membrane produced by the heat polymerization method is characterized in that there is no unevenness in the state of retention of the polymer in the thickness direction, and the membrane substrate is hardly damaged.

Although the respective steps have been separately described above, in the production of the hydrophilized porous hollow fiber membrane of the present invention, the polypropylene porous hollow fiber membrane is formed on the wall surface forming fine pores. It is also possible to carry out holding of monomers and the like, removal of solvent, polymerization, washing after polymerization, etc. almost continuously.

[0096]

EXAMPLES The present invention will be specifically described below with reference to examples. The measuring method was based on the method shown below. 1. Measurement of Hollow Fiber Membrane (1) Air Permeation Amount: 50 porous hollow fiber membranes were bundled in a U-shape and the hollow openings were solidified with urethane resin to produce a module. The length of the resin-embedded portion was 2.5 cm, and the effective length of the hollow fiber was 5 cm. Air was applied to the inside of the hollow fiber membrane of this module at a pressure of 0.5 atm at 25 ° C., and the amount of permeation of air passing through the wall surface of the hollow fiber membrane to the outside was determined. The membrane area was based on the inner diameter. (2) Elastic recovery rate: Tensilon UTM-II type manufactured by Toyo Baldwin Co., Ltd., yarn length 2 cm, test speed 1 cm / m
It was measured by in and determined by the following formula.

[0097]

[Equation 1] (3) Average length of microfibrils: Measured from electron micrographs. 2. Measurement of Hydrophilized Porous Hollow Fiber Membrane "Permeability", "Water Permeability in Alcohol Hydrophilization Method" and "Water Permeability after Retaining Polymer" were measured using a test membrane module with an effective membrane area of 163 cm ^2. It was measured by the following method. The solubilities of N-hydroxymethyl acrylamide, N, N'-methylenebisacrylamide and triallyl isocyanurate used in the examples in water at 30 ° C. are 197 g / dl, 3 g / dl and 0.1 g / dl, respectively. (1) Water permeability: 0.1 kg / cm ² per minute from one side of the test membrane module (inside the hollow fiber membrane in the case of the hollow fiber membrane)
Water at 25 ° C. is supplied while increasing the water pressure at the ratio, and the water pressure when the accumulated permeated water amount becomes 30 ml and 50 ml is measured. Subsequently, 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 the straight line connecting the two plotted points intersects the horizontal axis was determined and used as the water permeation pressure. (2) Water permeability in alcohol hydrophilization method: Ethanol was pressed into one of the test membrane modules not subjected to hydrophilization treatment (in the hollow fiber membrane, inside the hollow fiber membrane) at a flow rate of 25 ml / min for 15 minutes. After sufficiently moistening the inside of the pores of the porous membrane with ethanol, water is caused to flow at a flow rate of 100 ml / min for 15 minutes to replace the ethanol existing inside the pores with water. Subsequently, water at 25 ° C. was caused to flow from one of the test membrane modules (inside the hollow fiber membrane in the case of a hollow fiber membrane) to measure the amount of permeated water at a transmembrane pressure difference of 50 mmHg, and from that value, the water permeability (liter / liter / m ² · hr · mmHg) was determined. (3) Amount of retained polymer: 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 crosslinked polymer retained per unit weight of the polyethylene porous hollow fiber membrane was calculated. (4) Evaluation of coating state on pore surface: JISK6768
The porous membrane was immersed in a standard solution (blue) for wetting test with a surface tension of 54 dyn / cm described in (1971) for 1 minute and then air-dried, and the cross-section of the porous membrane was observed by an optical microscope and colored. The distribution of the polymer was investigated. (5) Cumulative elution rate: The porous hollow fiber membrane is immersed in 10 times its weight of warm water at 65 ° C, and the total amount of organic carbon in the warm water is measured at regular intervals. The integrated elution amount was calculated assuming that the total amount of organic carbon was derived only from the hydrophilic cross-linked polymer having the composition ratio assumed in (3) above, and the integrated elution rate with respect to the polymer retention amount before the elution treatment was calculated. (Wt%) was determined. (6) Water Permeability after Retaining Polymer: Pressure of 2 kg / cm ² from one side (inside the hollow fiber membrane in the case of a hollow fiber membrane) of a test membrane module made of a porous hollow fiber membrane retaining a polymer.
After injecting water for 3 hours, water at 25 ° C. is flowed from one side of the module of the test membrane to measure the amount of permeated water at a transmembrane pressure difference of 50 mmHg, and from the value, the water permeability (liter / liter /
m ² · hr · mmHg) was determined.

Example 1 Polypropylene having a melt index of 3 (UBE Polypro YK121, trade name, manufactured by Ube Industries, Ltd.) has a discharge port diameter of 17.5 mm, an annular slit width of 1.5 mm and a discharge cross-sectional area of 0.75 cm ^2. Using the hollow-fiber forming spinneret for spinning, the spinning temperature was 200 ° C., the linear spinning speed was 9.24 cm / min, and the spinning was performed at a winding speed of 40 m / min and a spinning draft 433. The dimension of the obtained unstretched hollow fiber has an inner diameter of 545.
The thickness was 72 μm.

This unstretched hollow fiber was heated at 150 ° C. for 24 hours,
Heat treatment was performed at a fixed length. The elastic recovery rate of this unstretched hollow fiber is 9
It was 2.5%. 200% per second at room temperature
After stretching 40% at a deformation rate of 1, the deformation rate becomes 2.8% per second until the total stretching amount becomes 1100% (that is, the total stretching ratio is 12 times) in a heating box heated at 155 ° C. Thus, the inside of the roller was stretched to continuously produce a porous hollow fiber membrane.

The obtained porous polypropylene hollow fiber was drawn 12 times as large as the undrawn yarn, and the inner diameter was 430.
μm, the film thickness was 57 μm, and the porosity was 81%.
The average pore size measured with a mercury porosimeter is 1.8 μm, and the air permeation rate is 190 × 10 ⁴ liters / m ² · hr ·
It was 0.5 atm. Observation with a scanning electron microscope revealed that a number of characteristic strip-shaped micropores were present and the average length of microfibrils was 4.1 μm.

Example 2 A polypropylene having a melt index of 0.8 (UBE Polypro B101H, trade name, manufactured by Ube Industries, Ltd.) having a double pipe structure with a discharge port diameter of 17.5 mm and an annular slit width of 1.5 mm was used. Using a spinneret for hollow fiber shaping having a discharge cross-sectional area of 0.75 cm ² , spinning was carried out at a spinning temperature of 220 ° C. and a discharge linear velocity of 9.24 cm / min, and a winding speed was 20 m / mi.
n, and was wound in a spinning draft 216. The obtained unstretched hollow fiber had an inner diameter of 610 μm and a film thickness of 83 μm.

This unstretched hollow fiber was heated at 150 ° C. for 24 hours,
Heat treatment was performed at a fixed length. The elastic recovery rate of this unstretched hollow fiber is 9
It was 1%. Then, 35% stretched at a deformation rate of 200% per second at 40 ° C, and then the deformation rate becomes 0.5% per second until the total stretched amount becomes 1900% in a heating box heated at 155 ° C. As described above, the inter-roller stretching was performed, and heat setting was further performed for 60 seconds in a heating box heated to 155 ° C. to continuously produce a porous hollow fiber membrane.

The obtained porous polypropylene hollow fiber is
It is drawn 20 times more than the undrawn yarn and has an inner diameter of 54
The thickness was 0 μm, the film thickness was 73 μm, and the porosity was 88%. Average pore size measured by mercury porosimeter is 3.5μ
m, the air permeation rate is 380 × 10 ⁴ liters / m ² · h
It was r · 0.5 atm. Observation with a scanning electron microscope revealed that numerous characteristic micropores were present and the average length of the microfibrils was 7.5 μm.

Comparative Example 1 A polypropylene having a melt index of 3 (UBE Polypro YK121, trade name, manufactured by Ube Industries, Ltd.) was used to spin a hollow fiber under exactly the same conditions as in Example 1. The dimensions of the obtained undrawn yarn were such that the inner diameter was 553 μm and the film thickness was 76 μm.

This unstretched hollow fiber was heat-treated and stretched under the same conditions as in Example 1 except that the total stretching amount was 550%, and a porous hollow fiber was continuously produced. The average pore diameter measured by
Those having a size of more than μm could not be obtained.

Comparative Example 2 A hollow fiber was spun in exactly the same conditions as in Example 1 except that polypropylene having a melt index of 15 (UBE Polypro J115G, trade name, manufactured by Ube Industries, Ltd.) was used. The dimensions of the obtained undrawn yarn have an inner diameter of 580 μm and a film thickness of 78.
was μm. This unstretched hollow fiber has a total stretching amount of 600%
Heat treatment and drawing were carried out under the same conditions as in Example 1 except for the above. However, thermal drawing frequently caused yarn breakage and uniform drawing was impossible. Example 3 A polypropylene having a melt index of 3 (UBE Polypro YK121, trade name, manufactured by Ube Industries, Ltd.) having a discharge port diameter of 17.5 mm, an annular slit width of 1.5 mm, and a discharge cross-sectional area of 0.75 cm ^{2 is} a hollow fiber. Using a spinneret for shaping, spinning was carried out at a spinning temperature of 200 ° C., a discharge linear velocity of 9.24 cm / min, and a winding speed of 45 m / min and a spinning draft 489. The undrawn hollow fiber obtained had an inner diameter of 540
and the film thickness was 72 μm.

This unstretched hollow fiber was heated at 150 ° C. for 24 hours,
Heat treatment was performed at a fixed length. The elastic recovery rate of this unstretched hollow fiber is 9
It was 2.5%. Then, at room temperature, 200% per second
After stretching 40% at a deformation rate of 1, the deformation rate becomes 2.8% per second until the total stretching amount becomes 1100% (that is, the total stretching ratio is 12 times) in a heating box heated at 155 ° C. Thus, the inside of the roller was stretched to continuously produce a porous hollow fiber membrane.

The obtained porous polypropylene hollow fiber membrane was stretched 12 times with respect to the unstretched yarn, and the inner diameter was 43.
The thickness was 0 μm, the film thickness was 59 μm, and the porosity was 80%. The average pore diameter measured by a mercury porosimeter was 1.7 μm, and the air permeation amount was 105 × 10 ⁴ liter / m ² · hr · 0.5 atm. When the cross-sectional structure was analyzed with a scanning electron microscope, there were a myriad of characteristic strip-shaped micropores, and a laminated structure in which these micropores were interconnected from the inner wall surface of the hollow fiber membrane to the outer wall surface was confirmed, The average length of the microfibril was 3.7 μm.

On the other hand, ethylene-vinyl alcohol copolymer containing 33 mol% of ethylene (trade name: Soarnol E, saponified product of ethylene-vinyl acetate copolymer, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) was added to a 75% by volume aqueous ethanol solution. It was heated and dissolved to obtain a 1.0 wt% solution. The temperature of this solution is 50
The temperature was maintained at 0 ° C., the porous polypropylene hollow fiber membrane obtained above was immersed in this, and left for 5 minutes. The hollow fiber membrane was pulled out from the solution, excess solution was removed, and then dried in a hot air dryer at 50 ° C. for 2 hours.

The obtained porous hollow fiber membrane had a large pore size and a high porosity, and retained a saponified ethylene-vinyl acetate copolymer, and thus had good hydrophilicity. .. When this porous hollow fiber membrane was soaked in water, it was easily wet and showed good water permeability as it was without any special treatment. Fifty of the porous hollow fiber membranes are bundled in a U shape and housed in a housing, and the end portions of each porous hollow fiber membrane are fixed in the housing with resin in an open state. The area in contact with the outer wall surface and the area in which the end of each porous hollow fiber membrane was opened were liquid-tightly partitioned, and the amount of water permeation was measured to be 36 liters / m ² · hr · mm.
It was Hg and showed excellent water permeability. Further, this porous hollow fiber membrane was alternately subjected to a drying treatment and a wetting treatment with water 10 times each, but no decrease in water permeability or change in properties such as mechanical strength was observed. Example 4 Ethylene-vinyl acetate copolymer (composition ratio 55:45) 3
The polypropylene porous hollow fiber membrane obtained in the same manner as in Example 1 was immersed in a solution of 25 parts by weight dissolved in 97 parts by weight of toluene at 25 ° C. for 30 seconds, and then vacuum dried at 50 ° C. for 3 days. After drying for an hour, the solvent was removed.

Then, 10 g of sodium hydroxide was immersed in an alkaline aqueous solution prepared by dissolving 1 liter of water, and the mixture was stirred at 70 ° C. for 1 hour.
After saponification for a period of time, it was washed with water and dried to obtain a hydrophilic polypropylene porous hollow fiber membrane.

Example 3 using 50 porous hollow fiber membranes
The water permeability was measured by fixing it in the housing in the same manner as above, and the water permeability was 32 liters / m ² · hr · mmHg.
And showed excellent water permeability. Further, as in Example 3, the dry treatment and the wet treatment were alternately repeated 10 times on the porous hollow fiber membrane, but no decrease in water permeability or changes in properties such as mechanical strength were observed.

Example 5 A polypropylene having a melt index of 3 (UBE Polypro YK121, trade name, manufactured by Ube Industries, Ltd.) having a discharge port diameter of 17.5 mm, an annular slit width of 1.5 mm and a discharge cross-sectional area of 0.75 cm 2 is used. Using a hollow fiber shaping spinneret, spinning was performed at a spinning temperature of 215 ° C., a discharge linear velocity of 9.24 cm / min, and a winding speed of 50 m / min and a draft 543. The undrawn hollow fiber obtained has an inner diameter of 360
and the film thickness was 65 μm.

The unstretched hollow fiber was heated at 150 ° C. for 24 hours,
Heat treatment was performed at a fixed length. The elastic recovery rate of this unstretched hollow fiber is 9
It was 2.5%. 200% per second at room temperature
After stretching 40% at a deformation rate of 1, the deformation rate becomes 2.8% per second until the total stretching amount reaches 1000% (that is, the total stretching ratio is 11 times) in a heating box heated at 155 ° C. Thus, the inside of the roller was stretched to continuously produce a porous hollow fiber membrane.

The obtained porous polypropylene hollow fiber membrane was stretched 11 times with respect to the unstretched yarn and had an inner diameter of 30.
The thickness was 0 μm, the film thickness was 57 μm, and the porosity was 82%. Average pore size measured by mercury porosimeter is 1.7μ
Air permeation rate is 95 × 10 ⁴ liters / m ² · hr · m
It was 0.5 atm. Observation with a scanning electron microscope revealed that a number of characteristic strip-shaped micropores were present, and the average length of the microfibrils was 3.7 μm. In addition, water permeability by alcohol hydrophilization method is 39 l / m ² · hr
-It was mmHg.

The obtained polypropylene porous hollow membrane having a large pore size and a high porosity was replaced with diacetone acrylamide 1
After dipping for 12 seconds in a treatment solution consisting of 00 parts, 5 parts of N-hydroxymethylacrylamide, 1 part of benzoyl peroxide and 1000 parts of acetone, it was taken out in nitrogen and air dried for 5 minutes. Subsequently, this porous membrane is heat-treated in a nitrogen atmosphere at 65 ° C. for 60 minutes, then immersed in a mixed solvent of water / ethanol = 50/50 (parts) for 10 minutes, and further ultrasonically washed in warm water for 2 minutes. The unnecessary components were washed and removed by. Next, the solvent was removed by hot air drying to obtain a polypropylene porous hollow fiber membrane in which the polymer was retained. The water permeation pressure, water permeation rate, polymer retention, cumulative elution rate, etc. of this porous hollow fiber membrane were measured and the results are shown in Table 1.

The hydrophilic polypropylene porous hollow fiber membrane obtained had good water permeability, and the observation of the coating state of the hydrophilic cross-linked polymer revealed that the polypropylene porous hollow fiber membrane had fine pores. The polymer was held almost uniformly over almost the entire wall surface. In addition, from the measurement of the integrated dissolution rate, it was found that there was substantially no dissolved component after 24 hours.

Examples 6 to 8 The amount of N-hydroxymethylacrylamide shown in Table 1 was used as the crosslinkable monomer, and other conditions were the same as in Example 5 except that the polymer was retained in the polypropylene porous hollow fiber membrane. Let

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

Example 9 A polypropylene porous hollow fiber membrane obtained in the same manner as in Example 1 was treated with diacetone acrylamide 1 as a treatment solution.
A solution consisting of 00 parts, 5 parts of N, N'-methylenebisacrylamide and 5 parts of 2,2'-azobisisobutyronitrile and 800 parts of acetone was used, and the heat treatment condition was 65 ° C. for 60 minutes. In the same manner as in Example 5, a hydrophilic polypropylene porous hollow fiber membrane holding a polymer was obtained, its performance was evaluated, and the results in Table 1 were obtained.

Observation of the coated state of the hydrophilic crosslinked polymer showed that the polymer was held almost uniformly over almost the entire wall surface forming the micropores. Further, it was found from the measurement of the integrated dissolution rate that there was substantially no dissolved component after 24 hours.

Example 10 A solution consisting of 100 parts of diacetone acrylamide, 1 part of divinylbenzene, 0.3 part of benzoyl peroxide and 450 parts of methyl ethyl ketone was used for immersion time of 3 seconds and thermal polymerization conditions of 70 ° C. for 60 minutes. The other conditions were exactly the same as in Example 5, and the polymer was retained on the polypropylene porous hollow fiber membrane.

The performance of this hydrophilic polypropylene porous hollow fiber membrane was evaluated and the results shown in Table 1 were obtained. When the coated state of the hydrophilic cross-linked polymer was observed, the polymer was retained almost uniformly over the entire wall surface of the polypropylene porous hollow fiber membrane forming the micropores. From the measurement of the integrated dissolution rate, it was found that there was substantially no dissolved component after 24 hours.

[0124]

[Table 1]

[0125]

EFFECT OF THE INVENTION The large-pore porous polypropylene hollow fiber membrane of the present invention is suitable for microfiltration of liquids, air purification, and the like, because it has large pores with small pores and high porosity, and is extremely compact. It enables various modules and system design. Further, since it is produced by the melt spinning method without using any solvent, it is an extremely clean material and never contaminates the fluid to be treated.

Further, the hydrophilic polypropylene porous hollow fiber membrane of the present invention has excellent hydrophilicity and shows good hydrophilicity without pretreatment for hydrophilicity treatment with ethanol or the like, resulting in no deterioration in filtration performance. Hardly recognized. Moreover, since the hydrophilic substance is firmly held on the surface of the micropores, the amount of the eluted component is extremely small. Therefore, the hydrophilic polypropylene 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.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location C08J 9/36 CES 7148-4F D01D 5/24 B 7199-3B D01F 6/06 A 7199-3B / / B29K 23:00 C08L 23:10 (72) Inventor Kenji Kondo 20-1 Miyukicho, Otake City, Hiroshima Prefecture Mitsubishi Rayon Co., Ltd. Central Research Laboratory

Claims (8)

[Claims] 1. A porous hollow fiber membrane made of polypropylene, comprising microfibrils arranged in the fiber length direction,
The average pore diameter of the micropores measured by a mercury porosimeter has a laminated structure in which strip-shaped micropores surrounded by the nodes made of stacked lamellae communicate with each other from the inner wall surface of the hollow fiber to the outer wall surface. Is more than 1 μm and 10 μm or less,
A large-pore porous polypropylene hollow fiber membrane having a porosity of 70% to 95% and an air permeability of 4 × 10 ⁵ liter / m ² · hr · 0.5 atm or more. 2. The average length of microfibrils is 1 μm.
The large-pore porous polypropylene hollow fiber membrane according to claim 1, having a diameter of more than 15 and not more than 15 μm. 3. A method for producing a porous hollow fiber, which is obtained by melt-spinning polypropylene using a hollow fiber producing nozzle, annealing the resulting undrawn yarn, cold-drawing it, and then hot-drawing it to make it porous. In the method, the undrawn yarn is annealed at a temperature of 120 to 165 ° C. for 30 minutes or more, and the deformation rate during hot drawing is 10% or less per second,
The method for producing a large-pore porous polypropylene hollow fiber membrane according to claim 1, wherein the total stretching amount is 700% to 2500%. 4. A hydrophilized porous polypropylene hollow obtained by holding a saponified ethylene-vinyl acetate copolymer on at least a part of the micropore surface of the large-pore porous polypropylene hollow fiber membrane according to claim 1. Thread film. 5. The hydrophilized porous polypropylene hollow fiber membrane according to claim 4, wherein a saponified product of an ethylene-vinyl acetate copolymer is physically retained. 6. A hydrophilic cross-linked polymer obtained by polymerizing monomers containing diacetone acrylamide and a cross-linking monomer on at least a part of the micropore surface of the large-pore porous polypropylene hollow fiber membrane according to claim 1. A hydrophilized porous polypropylene hollow fiber membrane that holds 7. The hydrophilized porous polypropylene hollow fiber membrane according to claim 6, wherein the hydrophilic crosslinked polymer is physically retained. 8. The hydrophilized porous polypropylene hollow fiber membrane according to claim 6, wherein the crosslinkable monomer is a water-soluble crosslinkable monomer.