JP3130996B2 - Large pore porous polypropylene hollow fiber membrane, method for producing the same, and hydrophilized porous polypropylene hollow fiber membrane - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a porous polypropylene hollow fiber membrane having a large pore size and a high porosity 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 hydrophilic 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 known, and details of the technology are described in, for example, JP-A-52-15627 and JP-A-2-2849. No. 6,086,045. In 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% at less than 110 ° C after heat treatment below 100 ° C
The film is stretched and then heat-treated at a temperature not lower than the above-mentioned heat treatment temperature and not higher than 155 ° C., thereby having characteristic strip-shaped fine pores and having a distribution curve of the pore radius of the fine pores.
A technique for producing a porous hollow fiber having at least one maximum point in the range of １1200 Å is disclosed. In the latter, a melt-spun polypropylene hollow fiber is stretched in liquid nitrogen, and then heated at a high temperature (110 to 110).
155 ° C.) or melt-spun polypropylene hollow fiber at a high temperature (120 to 145 ° C.).
° C) and stretched (100-700%), 115-155 ° C
The hole diameter measured by the bubble point method for forming a group of strip-shaped micropores is 0.1 to
A 1.0 μm porous polypropylene hollow fiber membrane is disclosed.

As described above, in the prior art, the average pore diameter is 1 μm.
A porous hollow fiber membrane made of polypropylene having strip-shaped micropores exceeding m was not obtained.

[0004] In general, 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 since the pore surface of the membrane is hydrophilic, it is easily wetted by water, and the filtration of the aqueous solution can be performed without any special pretreatment.

[0005] However, hydrophilic membranes have the disadvantage that the mechanical strength when wetted and the swelling due to water are large, and furthermore, when dried from a wet state, the membrane performance is reduced.
It has the disadvantage that it is easily deteriorated.

On the other hand, since the hydrophobic porous membrane is hydrophobic, it is difficult to permeate 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

[0007] As a method for hydrophilizing a polyolefin porous membrane, the entire surface of the polyolefin porous membrane including the micropores is wet-treated with an organic solvent having good compatibility with water, such as alcohol or ketone. 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.

[0008] However, in the organic solvent wet / 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). Gazette, JP 61
-271003).

Also, after blending two different polymers and melt-spinning, they are subjected to a stretching treatment to cleave the interface between the different polymers to form microporous porous hollow fibers, and the side chains existing in the constituent polymers. It has been proposed to produce hydrophilic porous hollow fibers in which the surface of the pores has been made hydrophilic by post-treatments such as group hydrolysis and sulfonation (Japanese Patent Application Laid-Open No. 55-1979).
137208).

Furthermore, 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 have been proposed (Japanese Patent Application Laid-Open No. 63-19 / 1988).
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.

[0012]

However, all of these methods use a conventionally known polyolefin porous membrane as a starting material, and therefore have insufficient performance 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 is necessary to increase the diameter of the micropores in the hydrophobic porous membrane,
It was necessary to consider hydrophilization including high porosity.

In the field of microfiltration and air purification, an extremely high filtration flux is required, and a membrane or nonwoven fabric having micron-order pores opened with a high porosity is used. Porous hollow fibers with strip-shaped micropores are disclosed in
As described in Japanese Patent Application Laid-Open No. 3-35726, the gas permeation amount and the liquid permeation amount are large, and because of the structure in which the strip-shaped micropores are stacked, clogging hardly occurs. 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 adhered 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.

Further, in the method described in JP-A-56-38333, permanent hydrophilicity is achieved because the 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. Further, Japanese Patent Application Laid-Open Nos. Sho 61-125408 and
The technology disclosed in Japanese Patent Application Laid-Open No. 1-271003 for a hydrophilic composite porous membrane is disclosed in
The average pore size of the hollow fiber obtained in the example is 0.25 to 0.70 μm, which does not exceed the technical level of 5726 and the like.

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. 3 is a disclosed hydrophilic porous 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 pure water for electronics industry, etc., and sterilization of raw water for pharmaceutical production. .
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 polypropylene 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 research to obtain a porous polypropylene hollow fiber membrane having a high porosity and a large pore size, the present invention has been achieved.

[0021]

That is, the present invention relates to a porous hollow fiber membrane made of polypropylene, which is formed by being surrounded by microfibrils arranged in the fiber length direction and nodes formed by a stack dramella. Has a laminated structure in which the strip-shaped micropores communicate with each other from the inner wall surface of the hollow fiber to the outer wall surface, 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 4 × 10 ⁵ l / m ² · hr
-A large-pore-diameter porous polypropylene hollow fiber membrane characterized by being 0.5 atm or more.

The present invention also relates to a porous hollow fiber which is prepared by melt-spinning polypropylene using a nozzle for producing hollow fibers, annealing the obtained undrawn yarn, cold-drawing, and then hot-drawing to make it porous. In the yarn manufacturing method, the undrawn yarn is annealed at a temperature of 120 to 165 ° C. for 30 minutes.
Min, and the deformation rate during hot stretching is 10% per second.
The following is a method for producing a large-pore-diameter porous polypropylene hollow fiber membrane, wherein the total stretching amount is 700% to 2500%.

Further, the present invention provides a hydrophilic porous polypropylene 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 polypropylene hollow fiber membrane described above. It is a hollow fiber membrane.

Still further, the present invention provides a hydrophilic polymer obtained by polymerizing a monomer containing diacetone acrylamide and a crosslinking monomer 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 hydrophilic porous polypropylene hollow fiber membrane holding a crosslinked polymer.

[0025]

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

The polypropylene used in the present invention is
Preferably, it is isotactic or syndiotactic polypropylene. This polypropylene is melt-molded under specific conditions and stretched under specific conditions to form porous hollow fiber membranes in which micropores with a relatively large pore diameter are interconnected from the inner wall surface to the outer wall surface of the hollow fiber. 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, more preferably in the range of 0.3 to 8. When a polypropylene having an MI value of more than 10 is used, it is difficult to stretch stably to a total stretching ratio of 700% or more, and the porous hollow fiber having a large pore size and a high porosity according to the present invention is used. It is difficult to obtain a film. On the other hand, polypropylene having an MI value of less than 0.1 has too high a melt viscosity, so that stable spinning is difficult. It is one of the important points of the present invention to employ a polypropylene having a high molecular weight as long as stable spinning is possible.

In the present invention, the above polypropylene is melt-spun using a nozzle for producing a hollow fiber to produce a highly oriented crystalline undrawn hollow fiber. The nozzle preferably has a double tube structure with less uneven thickness, but may have a horseshoe shape or another structure. In a nozzle having a double-tube structure, the supply of gas to be maintained inside the hollow fiber to maintain the hollow form may be 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 700% 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 120 to 165 ° C, more preferably 130 to 155 ° 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 80 ° C. or less.

After performing cold stretching of about 5 to 150% in this way, hot stretching is performed in a 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 is reduced, and a product having a desired large pore diameter 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 700% or more. Total stretching amount is 7
It is necessary to be 00% to 2500%. If the stretching exceeds 2500%, yarn breakage during stretching frequently occurs, and the process stability is undesirably reduced. With a total stretching amount of less than 700%, 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 0% or more, 700% or more, preferably 10% or more.
A total stretch of at least 00% is essential.

The deformation speed in the present invention refers to a value obtained by dividing the amount of stretching (%) in the stretching section by the time (second) that the yarn passes through the stretching section.

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

In the porous polypropylene thus obtained,
The hollow fiber membrane is composed of flat pores measured with a mercury porosimeter.
The pore size is more than 1 μm and 10 μm or less, preferably 1.2
μm to 10 μm, porosity 70% to 95%, air permeability
4 × 10^Five Liter / m ^Two ・ Hr ・ 0.5atm or less
Above. In addition, microfibrils arranged in the fiber length direction
And a node composed of stacked dramers.
Has a characteristic strip-shaped micropore, which is
These small holes communicate with each other from the inner wall to the outer wall.
Are laminated. Microfibril flat
The average length is more than 1 μm and not more than 15 μm.

The first type of hydrophilized porous hollow fiber membrane of the present invention is characterized in that at least a portion of the inner surface of the micropores of the large-pore porous polypropylene hollow fiber membrane having the above-mentioned properties is coated with ethylene-vinyl acetate. It can be obtained by retaining a saponified polymer (hereinafter simply referred to as "saponified product"). The hydrophilic porous hollow fiber membrane of the present invention has a large pore diameter and porosity of a porous polypropylene hollow fiber membrane material as a base material, and without impairing properties such as sufficiently high mechanical strength. Good hydrophilicity is imparted by holding the saponified compound. Therefore, the hydrophilized porous membrane of the present invention has excellent permeability for aqueous liquids, 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 micropores, there is an advantage that clogging hardly occurs.

In the hydrophilic 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 holding the polymer means a part or all of the wall surface forming the micropores. In other words, the polymer is held on 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 due to the normally used transmembrane pressure is obtained. It is sufficient that the entire wall surface forming the micropores is not necessarily covered with the polymer. Further, the polymer may or may not be held on the outer surface of the porous membrane.

The term "retained" means that the polymer is firmly bonded or adhered to the wall surface on which the micropores are formed, to such an extent 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 in close contact with the wall surface by an anchor effect, or wrap the microfibrils or nodes forming strip-shaped micropores. The polymer may be tightly cross-linked, or these holding states may be mixed.

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

In the present invention, as a method of retaining a saponified substance on at least a part of the inner surface of the micropores of the porous polypropylene hollow fiber membrane as a substrate, for example, A method of directly supplying and holding in the pores, a method of supplying and retaining the ethylene-vinyl acetate copolymer in the micropores of the porous polypropylene hollow fiber membrane, and saponifying the same can be used. .

As the ethylene-vinyl acetate copolymer used for the formation of the saponified product, various types such as random, block, and graft can be used, and the type of the saponified product is also the same as that of the ethylene-vinyl acetate copolymer. Dependent.
The ethylene-vinyl acetate copolymer is basically formed from ethylene and vinyl acetate, but other monomer components may be mixed as long as desired properties are not impaired.

The content of the ethylene unit 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, its content is preferably at least 20 mol%. 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 adhered to the inner surface of the micropores of the porous polypropylene hollow fiber membrane, the adhered substance may not be adhered. It is not preferable because good adhesion cannot be obtained and the adhered substance is easily peeled off. On the other hand, if the content of the ethylene unit is too large, the saponified product finally obtained cannot obtain a favorable effect of imparting hydrophilicity to the porous polypropylene hollow fiber membrane, which is not preferable. Therefore, the content of the ethylene unit is preferably set to 70 mol% or less.
In consideration of a better balance between adhesion and hydrophilicity, the content of ethylene units is particularly preferably in the range of 25 to 50 mol%.

The saponification of the ethylene-vinyl acetate copolymer can be carried out by a known method such as a heat treatment in an aqueous alkali solution such as sodium hydroxide for a required time.
By this saponification treatment, the acetyl group of the vinyl acetate moiety is converted to 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 at least 60 mol%.

In the present invention, in order to directly hold the saponified material on a part of the inner surface of the micropores of the porous hollow fiber membrane, the holding solution containing the saponified material is immersed or coated by a method such as dipping or coating. A method of supplying the solution into the at least micropores of the hollow fiber membrane and evaporating and removing the solvent of the solution; and a method of immersing and applying a holding solution containing a saponified substance to the micropores of the substrate hollow fiber membrane. And then dipped in a coagulant solution of the saponified product to rapidly solidify it on at least the inner surface of the micropores and dry it.
It can be performed by such as.

The holding solution can be prepared by dissolving a soap in a solvent capable of dissolving it. As the solvent, a water-miscible organic solvent, a mixture of a water-miscible organic solvent and water, and the like 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,
Polyhydric alcohols such as propylene glycol and glycerin; tetrahydrofuran, dioxane, dimethylformamide, dimethylsulfoxide, dimethylacetamide, formamide, ethylene chlorohydrin and the like, and one or more of these can be used in combination. Among them, ethanol and dimethyl sulfoxide are particularly preferable because of good solubility of the saponified product and low toxicity.

As the solvent, a mixture of a water-miscible organic solvent and water is particularly preferred for the following reasons. That is, the saponified product is composed of a non-polar and hydrophobic ethylene unit and a polar and hydrophilic vinyl acetate unit (including one whose acetyl group is converted to a hydroxyl group by saponification). When coated on a non-polar polypropylene substrate while dissolved in a highly polar solvent system, non-polar ethylene units are localized on the surface of the saponified thin film layer on the polypropylene substrate side However, it is considered that the polar vinyl acetate unit is likely to be localized on the surface opposite to this (the side opposite to the polypropylene substrate). 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 for the above-mentioned holding solution, since the polarity of the solvent is further increased and this phenomenon is promoted. The proportion of water to be mixed is preferably larger as long as the solubility of the saponified product is not impaired,
Although the ratio varies depending on the concentration of the saponified product, the content of the ethylene portion thereof, the treatment temperature, and the like, for example, a preferable range is 5 to 60% by weight.

The concentration of the saponified product in the holding solution is set to a level necessary for obtaining a desired hydrophilizing effect, and is selected in consideration of the physical properties of the porous polypropylene hollow fiber membrane as a substrate, and the like. For example, it is preferable to use it in the range of 0.1 to 5.0% by weight. The treatment such as immersion or application of the porous polypropylene hollow fiber membrane in the holding solution may be completed in one treatment, but may be completed several times using a relatively low concentration saponified holding solution. You may perform it separately. When the concentration of the saponified compound exceeds 5.0% by weight,
It is not preferable because 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 may be narrowed and the liquid permeability may be reduced. The temperature of the holding solution is not particularly limited, but generally, a higher temperature is preferable because the solubility of the saponified compound is better and the viscosity of the solution is reduced. For example, a temperature range from room temperature to 100 ° C. is preferable. The immersion time in the case of the immersion treatment is preferably in a range of several seconds to several tens of minutes. The removal of the solvent from the holding solution held in the micropores of the porous polypropylene hollow fiber membrane as the substrate can be performed by vacuum drying, hot air drying, or the like. The degree of drying may be a temperature at which the substrate is not deformed by heat, and is preferably 130 ° C. or less.

Next, a method in which an 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 a substrate, and then saponified. An example will be described.

The holding of the ethylene-vinyl acetate copolymer on the base material can be carried out by the same method as the method described above for directly holding the saponified product, and the like. The content of the ethylene unit and the vinyl acetate unit in the ethylene-vinyl acetate copolymer is preferably in the above-mentioned range. As the solvent for the solution for holding the ethylene-vinyl acetate copolymer, those for preparing the above-mentioned solution for holding the saponified product, halogenated hydrocarbons, aromatic hydrocarbons, and the like can be used. A mixture of water and an organic solvent is preferred for the same reasons as in the saponified product. The concentration of the ethylene-vinyl acetate copolymer in the holding solution is
For example, the content is preferably 1.0 to 5.0% by weight. The treatment such as immersion and coating for holding the ethylene-vinyl acetate copolymer may be completed in one step, or may be performed several times using a relatively low concentration holding liquid. . In the case where it is completed in one time, if it is less than 1.0% by weight, it is not preferable because sufficient hydrophilicity cannot be obtained after the saponification treatment. On the other hand, if it exceeds 5.0% by weight, the diameter of the micropores of the porous polypropylene hollow fiber membrane as the base material is reduced,
Liquid permeability is often reduced, which is not preferable.

By performing the saponification treatment on the hollow fiber membrane holding the ethylene-vinyl acetate copolymer as described above, the hydrophilic porous hollow fiber membrane of the present invention can be obtained. This saponification treatment can be performed, for example, by heating the hollow fiber membrane holding the ethylene-vinyl acetate copolymer in an aqueous alkali solution such as an aqueous sodium hydroxide solution for a required time.

The retention of the saponified substance on the surface of the micropores of the hollow fiber membrane by the above-described various methods is performed so that the saponified substance is as uniformly as possible on the inner surface of the micropores of the porous polypropylene hollow fiber membrane as a base material. In addition, it is preferable that the holding amount is kept to a minimum and the decrease in the pore diameter and the closing of the minute holes of the hollow fiber membrane due to the holding are minimized.

Further, the second type of hydrophilic porous polypropylene hollow fiber membrane of the present invention is characterized in that at least a part of the surface of the micropores of the large-pore porous polypropylene hollow fiber membrane is cross-linkable with diacetone acrylamide. It comprises a hydrophilic crosslinked polymer obtained by polymerizing monomers containing monomers.

In this hydrophilized porous polypropylene hollow fiber membrane, diacetone acrylamide and a crosslinkable monomer are coated on the wall surface of the porous porous hollow fiber membrane having a large pore size and high porosity, in which minute pores are formed. A hydrophilic cross-linked polymer consisting of monomers containing the polymer is retained. This polymer can be more strongly retained with respect to polypropylene than other polymers. (2) Polypropylene porous hollow fiber This is because the film can be maintained almost uniformly over almost the entire wall surface forming the micropores of the membrane, (3) it has a moderate hydrophilicity, and (4) it is substantially water-insoluble.

The hydrophilic crosslinked polymer obtained by polymerizing monomers containing diacetone acrylamide and a crosslinkable monomer contains diacetone acrylamide as a monomer component in an amount of 50% by weight or more and contains a crosslinkable monomer. It is a crosslinked polymer obtained from the system, and a non-crosslinkable monomer may be contained 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 or 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 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-
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 in combination 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 0.3 to 100 parts by weight of the crosslinkable monomer with respect to 100 parts by weight of diacetone acrylamide.
More preferably, the amount is 0.5 to 80 parts by weight. Also,
The composition ratio of the copolymerizable monomer to diacetone acrylamide was 100 parts by weight and the copolymerizable monomer was 0.1 part by weight.
It is preferably 3 to 110 parts by weight, and 0.5 to 10 parts by weight.
More preferably, it is 0 parts 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 size and high porosity is a crosslinked polymer, The merging 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. In contrast, a diacetone acrylamide-based polymer having no crosslinked structure swells in water to close micropores, and dissolves in a small amount of water to become an eluted component. There is a possibility that the porous membrane holding the various polymers 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 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 large-pore-diameter, high-porosity polypropylene porous hollow fiber membrane of the present invention is determined by the amount of the polypropylene 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 porous polypropylene hollow fiber membrane. 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 amount of polymer retained is 0.5 to 5
It is more preferably about 0% by weight, and particularly preferably about 1 to 30% by weight.

Various methods can be adopted as a method for retaining the hydrophilic cross-linked polymer on at least a part of the wall surface forming the micropores of the porous polypropylene hollow fiber membrane. For example, a solution prepared by dissolving diacetone acrylamide and the above-mentioned copolymerizable monomer (hereinafter, referred to as "monomers") and a polymerization initiator in an appropriate solvent such as an organic solvent or water is prepared, and the raw material hollow fiber membrane is prepared. After impregnating the raw material hollow fiber membrane with a solution of monomers by a method of dipping in the solution, or a method of manufacturing the membrane module with the raw material hollow fiber membrane and then pressing this solution into the raw material hollow fiber membrane, or the like, A method of 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, by changing the concentration of the monomers in the solution or the impregnation time of the solution, the amount of the attached monomers can be adjusted.

The solvent is removed while these monomers are retained on at least a part of the wall surface forming the micropores of the raw material hollow fiber membrane in this manner, and then the polymerization is carried out. The hydrophilic crosslinked polymer can be held on at least a part of the wall surface of the hollow fiber 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 adding a polymerization initiator, 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 in consideration of easy removal of the solvent before the polymerization step.
It is more preferable that the temperature is not higher than ° C.

Since the surface of the polypropylene 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 become hydrophilic 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, advantages such as the fact that the solution permeates the micropores of the raw material hollow fiber membrane in a short time and the solvent can be easily removed from the micropores are obtained. There is.

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 is more hydrophilic than polypropylene. Since the degree is large, the wall surface forming the micropores holding the polymer has a relatively hydrophilic property as compared with the wall surface forming the micropores not holding the polymer. Thus, a polypropylene 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-based compounds such as azobis-2,3,3-trimethylbutyronitrile; acetyl peroxide, propionyl peroxide, butyryl peroxide, isobutyryl peroxide, succinyl peroxide, benzoyl peroxide, benzoyl azobutyryl peroxide, β -Allyloxypropionyl peroxide,
Peroxides such as hexanoyl peroxide, 3-bromobenzoyl peroxide, and bis- (4-t-butylcyclohexyl) peroxydicarbonate; persulfates such as potassium persulfate and ammonium persulfate; .

Particularly when water is used as a solvent, a water-soluble polymerization initiator such as azobisisobutyramide,
Although 4'-azobis-4-cyanopentanoic acid is preferred, the above-mentioned water-insoluble polymerization initiator is used since the monomers themselves have surface activity and can be dispersed in water even if they are water-insoluble polymerization initiators. You can also.

Examples of the polymerization initiator for the photopolymerization method include benzophenone, benzoin methyl ether, benzyldimethyl ketal, fluorenone, 4-bromobenzophenone, 4-chlorobenzophenone, methyl O-benzoylbenzoate, benzoyl peroxide, anthraquinone, and biacetyl. And uranyl nitrate. Further, these can be used in an appropriate combination.

The ratio of the monomer to 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. Parts by weight are preferred, and 200 to
More preferably, it is 5000 parts by weight.

The polymerization initiator is preferably used in an amount of 0.001 to 100 parts by weight based on 100 parts by weight of the monomers.
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 with respect to the monomers exceeds the above range, the amount of the monomers held on the wall surface forming the micropores of the porous hollow fiber membrane is too small, and a sufficient amount of the polymer is not obtained. It is not possible to retain, and if it is less than the above range, it is difficult to control the amount of the retained polymer, and the amount of the polymer retained on the wall surface or inside the micropores forming the micropores increases. This is not preferable because it may cause micropores to be closed.

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.

In this way, the polypropylene porous hollow fiber membrane in which the monomers containing a polymerization initiator as required are retained on the wall surface forming at least a part of the micropores, the surrounding extraneous After the liquid is removed and the solvent inside the micropores is removed by evaporation if necessary, the process is moved 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 surface forming the micropores of the porous hollow fiber membrane is formed. In this case, the 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 hydrophilic porous membrane of the present invention, a polymerization method 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 initiator and not higher than the temperature at which the membrane structure of the porous polypropylene hollow fiber membrane is not changed and the membrane substrate is not damaged. Preferably, a temperature of 30 to 100 ° 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. Further, 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 6 seconds.
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, high-pressure mercury lamp, xenon lamp, arc lamp, or the like can be used as an ultraviolet light source.

As the light irradiation conditions, for example, when a mercury lamp is used as a light source, an input is set to 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 , preferably a condition of irradiating energy of 0.05 to 1 joule / cm ² is employed.

It is difficult to achieve sufficient hydrophilicity at a low irradiation intensity, and the polypropylene porous hollow fiber membrane is greatly damaged at a high irradiation intensity. It is preferable to choose carefully.

In the case of radiation polymerization, the irradiation can be carried out, for example, by irradiating an electron beam at a temperature of 120 ° C. or less, preferably 100 ° C. or less, with an electron beam irradiating device at about 10 to 50 Mrad.

During the polymerization, the presence of oxygen in the atmosphere significantly inhibits the polymerization reaction. Therefore, the polymerization is carried out in an inert gas atmosphere such as nitrogen or in a vacuum-free atmosphere. It is desirable to make it.

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 carried out after the formation of the copolymer. Also,
The cross-linking reaction by condensation may be performed using heat of polymerization reaction or may be performed by heating.

In particular, when a crosslinking reaction by condensation is used, a previously prepared uncrosslinked copolymer of diacetone acrylamide and a crosslinking monomer is dissolved in a solvent, and then the fine pores of the porous polypropylene 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
If the molecular weight is too large, it is difficult to make the copolymer penetrate into the micropores of the porous polypropylene hollow fiber membrane, which is not preferable. More preferably, the molecular weight is from 50,000 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 heat 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 pores of the porous hollow fiber membrane due to light scattering, and degradation of the membrane substrate tends to progress when the light irradiation intensity is increased. 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 employing these polymerization methods, it is necessary to carefully select polymerization conditions that do not degrade the membrane substrate.

The monomers and the uncrosslinked copolymer held on the wall surface forming the micropores of the raw hollow fiber membrane are polymerized, crosslinked or crosslinked on the porous membrane surface by these polymerization techniques. 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 formation of the hydrophilic cross-linked polymer, the unreacted monomer or free monomer existing around the wall surface forming the micropores of the porous hollow fiber membrane is 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.

[0092] The hydrophilized porous hollow fiber membrane of the present invention can be produced in this manner. As a particularly preferable method, a monomer containing diacetone acrylamide and a water-soluble crosslinking monomer and a polymerization initiator are used. And a method of heating and polymerizing the polypropylene 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 components can be further reduced, and the hydrophilic porous hollow fiber membrane exhibits excellent water permeability.

[0094] The hydrophilic porous hollow 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 above, when producing the hydrophilic porous hollow fiber membrane of the present invention, the hydrophilic porous hollow fiber membrane is coated on the wall surface forming the micropores of the polypropylene porous hollow fiber membrane. The retention of the monomers and the like, the removal of the solvent, the polymerization, and the washing after the polymerization can be performed almost continuously.

[0096]

The present invention will be described below in more detail with reference to examples. The measuring method was as follows. 1. Measurement of Hollow Fiber Membrane (1) Air Permeation: 50 porous hollow fiber membranes were bundled in a U-shape, and the hollow opening was 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 air permeating outside passing through the wall surface of the hollow fiber membrane was determined. The membrane area was based on the inner diameter. (2) Elastic recovery rate: using Tensilon UTM-II manufactured by Toyo Baldwin Co., Ltd., yarn length 2 cm, test speed 1 cm / m
In was measured by the following formula.

[0097]

(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 triallylisocyanurate in water at 30 ° C. used in the examples is 197 g / dl, 3 g / dl and 0.1 g / dl, respectively. (1) Permeability: 0.1 kg / cm ² every minute from one of the test membrane modules (in the case of a hollow fiber membrane, inside the hollow fiber membrane)
Is supplied at a temperature of 25 ° C. while increasing the water pressure at a rate of 1. The water pressure when the integrated permeated water amount becomes 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 (in the case of hollow fiber membrane, inside the hollow fiber membrane). After sufficiently wet the inside of the pores of the porous membrane with ethanol, water is flowed at a flow rate of 100 ml / min for 15 minutes to replace the ethanol present inside the pores with water. Subsequently, water at 25 ° C. was flowed from one of the test membrane modules (in the case of the hollow fiber membrane, inside the hollow fiber membrane), and the amount of permeated water at a transmembrane pressure difference of 50 mmHg was measured. m ² · hr · mmHg). (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, air-dried, and 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.
m ² · hr · mmHg).

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, a ring slit width of 1.5 mm, and a discharge cross-sectional area of 0.75 cm ^2. Was spun at a spinning temperature of 200 ° C. and a discharge linear speed of 9.24 cm / min, and wound up by a spinning draft 433 at a winding speed of 40 m / min. The dimension of the obtained undrawn hollow fiber is 545 in inner diameter.
μm and the film thickness was 72 μm.

The undrawn hollow fiber was heated at 150 ° C. for 24 hours.
Heat treatment was performed at a constant length. The elastic recovery of this undrawn hollow fiber is 9
2.5%. Followed by 200% per second at room temperature
After stretching at a deformation rate of 40%, the deformation rate becomes 2.8% per second until the total stretching amount reaches 1100% (that is, the total stretching ratio is 12 times) in a heating box heated to 155 ° C. As described above, the inside of the roller was drawn to continuously produce a porous hollow fiber membrane.

The obtained porous polypropylene hollow fiber was stretched 12 times with respect to the undrawn yarn, and had an inner diameter of 430.
μm, the film thickness was 57 μm, and the porosity was 81%.
The average pore size measured by a mercury porosimeter is 1.8 μm and the air permeation amount is 190 × 10 ⁴ liter / m ² · hr ·
It was 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 4.1 μm.

Example 2 Polypropylene having a melt index of 0.8 (UBE Polypro B101H, trade name, manufactured by Ube Industries, Ltd.) was used to form a double tube structure having a discharge port diameter of 17.5 mm and an annular slit width of 1.5 mm. It is spun at a spinning temperature of 220 ° C. at a discharge linear speed of 9.24 cm / min using a spinneret for hollow fiber shaping having a discharge cross-sectional area of 0.75 cm ² and a winding speed of 20 m / mi.
n, and was wound by a spinning draft 216. Regarding the dimensions of the obtained undrawn hollow fiber, the inner diameter was 610 μm and the film thickness was 83 μm.

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

[0103] The obtained porous polypropylene hollow fiber was
It is stretched 20 times with respect to the undrawn yarn, and the inner diameter is 54
The thickness was 0 μm, the film thickness was 73 μm, and the porosity was 88%. The average pore size measured with a mercury porosimeter is 3.5μ
m, air permeation is 380 × 10 ⁴ liters / m ² · h
r · 0.5 atm. Observation with a scanning electron microscope revealed that there were numerous characteristic microvoids, and the average length of the microfibrils was 7.5 μm.

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

This undrawn hollow fiber was heat-treated and drawn under the same conditions as in Example 1 except that the total drawing amount was 550%, and a continuous production of a porous hollow fiber was carried out. The average pore diameter measured in the step is 0.3 μm,
Those exceeding μm were not obtained.

Comparative Example 2 A hollow fiber was spun under 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 were such that the inner diameter was 580 μm and the film thickness was 78.
μm. This undrawn hollow fiber has a total drawing amount of 600%
The film was heat-treated and stretched under the same conditions as in Example 1, except that the yarn was frequently broken by thermal stretching, and uniform stretching was impossible. Example 3 Polypropylene having a melt index of 3 (UBE Polypro YK121, trade name, manufactured by Ube Industries, Ltd.) is a hollow fiber having a discharge port diameter of 17.5 mm, an annular slit width of 1.5 mm, and a discharge sectional area of 0.75 cm ² . Using a spinneret for shaping, spinning was performed at a spinning temperature of 200 ° C. and a discharge linear speed of 9.24 cm / min, and winding was performed at a winding speed of 45 m / min and a spinning draft 489. The dimensions of the obtained undrawn hollow fiber have an inner diameter of 540.
μm and the film thickness was 72 μm.

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

The obtained porous polypropylene hollow fiber membrane was stretched 12 times with respect to the undrawn yarn, and had an inner diameter of 43%.
The thickness was 0 μm, the film thickness was 59 μm, and the porosity was 80%. The average pore size 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, a number of characteristic strip-shaped micropores existed, and a laminated structure in which these micropores were mutually connected from the inner wall surface of the hollow fiber membrane to the outer wall surface was confirmed. The average length of the microfibrils was 3.7 μm.

On the other hand, ethylene-containing 33 mol% ethylene vinyl alcohol copolymer (trade name: Soarnol E, saponified ethylene-vinyl acetate copolymer, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) was converted into a 75% by volume aqueous ethanol solution. The mixture was dissolved by heating to obtain a 1.0% by weight solution. Raise the temperature of this solution to 50
C., and the porous polypropylene hollow fiber membrane obtained earlier was immersed therein and left for 5 minutes. After removing the hollow fiber membrane from the solution and removing the excess solution, it was dried in a hot air dryer at 50 ° C. for 2 hours.

The obtained porous hollow fiber membrane had a large pore diameter and a high porosity, and had good hydrophilicity because the saponified ethylene-vinyl acetate copolymer was retained. . When this porous hollow fiber membrane was immersed in water, it was easily wetted and showed good water permeability 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 of each porous hollow fiber membrane is fixed in the housing with a resin in an open state. A region in contact with the outer wall surface and a region where the end of each porous hollow fiber membrane is open were partitioned in a liquid-tight manner, and the amount of water permeation was measured. As a result, 36 l / m ² · hr · mm
Hg and excellent water permeability. Further, the drying treatment and the wetting treatment with water were alternately repeated 10 times on the porous hollow fiber membrane, 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 at 25 ° C. obtained by dissolving parts by weight in 97 parts by weight of toluene for 30 seconds. After drying for a time, the solvent was removed.

Next, the substrate was immersed in an aqueous alkali solution obtained by dissolving 10 g of sodium hydroxide in 1 liter of water.
After performing saponification treatment for a 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
When the amount of water permeation was measured while being fixed in the housing in the same manner as described above, the amount of water permeation was 32 l / m ² · hr · mmHg.
And showed excellent water permeability. Further, the drying treatment and the wetting treatment were alternately repeated 10 times for the porous hollow fiber membrane in the same manner as in Example 3, but no decrease in water permeability or change in properties such as mechanical strength was observed.

Example 5 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, a ring slit width of 1.5 mm, and a discharge sectional area of 0.75 cm 2 was used. Using a spinneret for hollow fiber shaping, spinning was performed at a spinning temperature of 215 ° C., a discharge linear speed of 9.24 cm / min, and winding was performed at a winding speed of 50 m / min and a spinning draft 543. The dimensions of the obtained undrawn hollow fiber have an inner diameter of 360.
μm, and the film thickness was 65 μm.

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

The obtained porous polypropylene hollow fiber membrane was stretched 11 times with respect to the undrawn yarn, and had an inner diameter of 30%.
The thickness was 0 μm, the film thickness was 57 μm, and the porosity was 82%. The average pore size measured with a mercury porosimeter is 1.7μ
m and air permeation rate is 95 × 10 ⁴ liters / m ² · hr ·
It was 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 3.7 μm. The water permeability by the alcohol hydrophilization method is 39 l / m ² · hr
-It was mmHg.

The obtained porous hollow polypropylene 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 12 seconds, taken out in nitrogen and air-dried for 5 minutes. Subsequently, the porous film is heat-treated at 65 ° C. for 60 minutes in a nitrogen atmosphere, then immersed in a mixed solvent of water / ethanol = 50/50 (parts) for 10 minutes, and further subjected to ultrasonic cleaning in warm water for 2 minutes. The unnecessary components were removed by washing. Next, the solvent was removed by hot air drying to obtain a porous polypropylene hollow fiber membrane holding the polymer. 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 polypropylene porous hollow fiber membrane was good, and the state of coating with the hydrophilic cross-linked polymer was observed. As a result, micropores were formed in the porous polypropylene hollow fiber membrane. The polymer was held almost uniformly over almost the entire wall surface. Also, the measurement of the integrated dissolution rate revealed that there was substantially no dissolution component after 24 hours.

Examples 6 to 8 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 5 to hold the polymer in the polypropylene hollow hollow fiber membrane. I let it.

The performance of the thus-obtained hydrophilic porous polypropylene hollow fiber membrane 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 used as a treatment solution for diacetone acrylamide 1
A solution consisting of 00 parts, 5 parts of N, N'-methylenebisacrylamide, 5 parts of 2,2'-azobisisobutyronitrile and 800 parts of acetone was used. The heat treatment was performed at 65 ° C. for 60 minutes. A hydrophilic polypropylene porous hollow fiber membrane holding a polymer was obtained in the same manner as in Example 5, 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 almost 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 10 Using 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, the immersion time was 3 seconds and the thermal polymerization conditions were 70 ° C. for 60 minutes. The polymer was held on a polypropylene porous hollow fiber membrane in exactly the same manner as in Example 5 except for the above conditions.

The performance of the hydrophilic polypropylene 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 of the porous hollow fiber membrane forming the micropores. From the measurement of the integrated dissolution rate, it was found that there was substantially no dissolution component after 24 hours.

[0124]

[Table 1]

[0125]

The porous polypropylene hollow fiber membrane of the present invention having a large pore size has a large pore size and a high porosity, so that it is suitable for liquid microfiltration or air purification, and is extremely compact. It enables a flexible module and system design. Further, since it is manufactured by a melt spinning method without using any solvent, it is an extremely clean material and does not contaminate the fluid to be processed at all.

Further, the hydrophilic polypropylene porous hollow fiber membrane of the present invention has excellent hydrophilicity, exhibits good hydrophilicity even without pre-hydrophilization treatment with ethanol or the like, and exhibits a decrease in filtration performance. Almost no. 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 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.

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Kenji Kondo 20-1, Miyukicho, Otake City, Hiroshima Prefecture Inside Mitsubishi Rayon Co., Ltd. (56) References JP-A-63-28406 (JP, A) JP-A-2-112404 (JP, A) JP-A-4-300318 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01D 71/00-71/42 D01F 6/06

Claims (8)

(57) [Claims] 1. A porous hollow fiber membrane made of polypropylene, comprising: microfibrils arranged in a fiber length direction;
It has a laminated structure in which strip-shaped micropores formed by being surrounded by the nodes composed of the stacked dramella communicate with each other from the inner wall surface of the hollow fiber to the outer wall surface, and the average pore diameter of the micropores measured by a mercury porosimeter Is more than 1 μm and 10 μm or less,
A large-pore-diameter porous polypropylene hollow fiber membrane having a porosity of 70% to 95% and an air permeation of 4 × 10 ⁵ liter / m ² · hr · 0.5 atm or more. 2. The microfibril has an average length of 1 μm.
2. The large-pore-diameter porous polypropylene hollow fiber membrane according to claim 1, wherein the diameter is larger than 15 μm. 3. Production of a porous hollow fiber which is obtained by melt-spinning polypropylene using a nozzle for producing a hollow fiber, annealing the obtained undrawn yarn, cold-drawing, and then hot-drawing to make it porous. In the method, the annealing treatment of the undrawn yarn is performed at a temperature of 120 to 165 ° C. for 30 minutes or more, and the deformation rate during hot drawing is set to 10% or less per second,
The method for producing a large-pore-diameter porous polypropylene hollow fiber membrane according to claim 1, wherein the total stretching amount is 700% to 2500%. 4. A hydrophilized porous polypropylene hollow 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 according to claim 1. Thread membrane. 5. The hollow fiber membrane of claim 4, wherein the saponified ethylene-vinyl acetate copolymer is physically retained. 6. A hydrophilic crosslinked polymer obtained by polymerizing a monomer containing diacetoneacrylamide and a crosslinkable monomer on at least a part of the surface of the micropores of the large-pore porous polypropylene hollow fiber membrane according to claim 1. And a hydrophilic porous polypropylene hollow fiber membrane. 7. The hydrophilic porous polypropylene hollow fiber membrane according to claim 6, wherein the hydrophilic cross-linked 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.