JPH0372925A - Porous membrane and its manufacturing method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a water-based porous membrane suitable for medical and industrial filtration, separation, etc., and a method for producing the same.

(Prior art) Porous membranes are used for medical purposes such as plasma separation, infusion filtration, plasma protein separation, and the production of sterile water.
It is used for the production of C cleaning water, food processing water, and purification of water for other processes, and in recent years, it has also been used in large quantities in water purifiers for home use, restaurants, etc. In these applications, if foreign substances are leached from the porous membrane material, the safety will be reduced or the quality of purified water or aqueous solution will be degraded, so there is a demand for a membrane that does not have to worry about such leaching.

By the way, various materials and porous structures have been proposed as porous membranes, but among them, crystalline thermoplastic polymers are melted and shaped into hollow fibers, tubes, or films. This is stretched at a relatively low temperature to generate crazes in the amorphous regions between the crystals, and then further hot-stretched to form a porous structure in the molten excipient. Because it is not used, it is attracting attention as a membrane suitable for applications where elution of impurities or compounds is undesirable. Such hollow fiber membranes are described in JP-A-52-137026, JP-A-57-42919, JP-A-57-66114, etc., and such flat membranes are described in σ8F 3679538.
This method is disclosed in Japanese Patent Publication No. 55-32531, etc.

Since the porous membrane obtained by this method is made of only polyolefin or fluorinated polyolefin and is essentially hydrophobic, it is difficult to remove aqueous liquids such as aqueous solutions. Therefore, such porous membranes are usually used for filtration of aqueous liquids after being treated with a hydrophilic agent such as Acor μ or a surfactant.

In addition, as a method of making a hydrophobic membrane hydrophilic, the hydrophobic membrane is coated with a hydrophilic 14-hydrocarbon monomer such as acrylic acid, methacrylic acid, or vinyl acetate, and then irradiated with ionizing radiation of about 1 to 10 megarads. A method of chemical fixation by
It is disclosed in Japanese Patent No. 6-38353.

In addition, after blending two different polymers and melt-spinning, a stretching treatment is performed to cleave the interface between the different polymers to form a microporous hollow fiber, and the side chain groups present in the constituent polymers are hydrated. JP-A-55-137208 discloses a method for producing hydrophilic porous hollow fibers whose pore surfaces are made hydrophilic by post-treatments such as decomposition and sulfonation.

(Problem to be solved by the invention) The hydrophilic treatment using Aμcol or a surfactant is a temporary hydrophilic treatment, and moreover, the casing 1 in which the hydrophilic treatment agent is attached to the porous membrane can be used for filtration, etc. When used, alcohol/L' alcohol and surfactants migrate to purified water and contaminate it, so it is necessary to thoroughly wash and remove these hydrophilic agents before filtration. In addition, when dried in this condition, the membrane surface returns to hydrophobicity, so once the hydrophilic treatment is performed, the hydrophilic agent is replaced with water, and the pore surface of the porous membrane is constantly kept in contact with water. There are problems that must be addressed.

Furthermore, in the method described in JP-A No. 56-18353, permanent hydrophilicity is achieved because groups that exhibit hydrophilicity are chemically fixed to the porous membrane, but irradiation with ionizing radiation This requires large-scale equipment, the stability of the process is not sufficient, there is a risk of damaging the membrane material, and there are problems in that the operation and management of the treatment process is difficult. .

Furthermore, the fibers described in JP-A-55-137208, which are made porous by melt-spinning and drawing a blend of different polymers, generally have a small porosity. In addition, post-treatments such as hydrolysis and sulfonation are required to make them hydrophilic, which also poses the problem of complicating the process.

In view of this situation, the inventors of the present invention have conducted intensive studies on polyolefin porous membranes that have permanent hydrophilicity suitable for aqueous liquid treatment and can be manufactured by an industrially advantageous method, and as a result, have arrived at the present invention. did.

[Means to solve the problem]

The gist of the present invention is suitable for a porous membrane consisting of a hydrophilic copolymer X and a polyolefin Y having monomer units A and ethylene units B as main components represented by the following formula (1). After melt-shaping a blend of a hydrophilic copolymer X whose main components are monomer units A and ethylene units B represented by the above formula and a polyolefin Y, the melt-shape molded product is placed in a vacuum or in an incubator. The method of producing a porous membrane includes heat treatment in an active gas medium at a temperature below the melting point of polyolefin Y for 1 hour or more, followed by stretching treatment to make it porous.

Examples of the polyolefin that is a component of the porous membrane of the present invention include polyethylene, polypropylene, poly3-methylbutene-1, poly4-methyρpentene-1, and copolymers thereof.

The value of n in the monolayer unit A in the hydrophilic copolymer x constituting the porous membrane of the present invention is preferably in the range of 2 to 9.
The bar ranges from 4 to 9.

Regarding this hydrophilic copolymer X, although the composition ratio of both components A and B is not particularly limited, it is preferable that the ratio of component A is in the range of 80 to 10% by weight for the following reasons. That is, if the content of the five components is less than 104, the porous membrane will not exhibit sufficient hydrophilicity, while if the content exceeds 80, the hydrophilic copolymer itself tends to contain a large amount of ultra-low molecular weight substances. Therefore, the hydrophilic copolymer is easily eluted from the porous membrane in which this copolymer and the polyolefin are blended. still,
In order for the porous membrane to exhibit sufficient hydrophilicity, the proportion of component A is preferably 15 to 70% by weight, and 20 to 6% by weight.
Particularly preferred is a 5 weight drop.

It can be obtained by the present aqueous copolymer used in the present invention or by a method in which maleic acid and ethylene are copolymerized, and then boria μ kylene glycol μ is added thereto.

It can also be produced by copolymerizing ethylene with a monomer consisting of an ethylenically unsaturated carboxylic acid containing a hydrophilic copolymer or boria μ-kylene glycol μ,
In this method, the generation of low molecular weight products is unavoidable due to the low reactivity of both components, and it is difficult to increase the content of ethylenically unsaturated carboxylic acids that die during co-electrolysis and coalescence. This method is not a preferred method because it is difficult to obtain a copolymer with a sufficient proportion of hydrophilic components.

The hydrophilic copolymer X basically consists of two components, A and B, but it may contain other components as long as they do not inhibit the hydrophilicity of the porous membrane. As such a third component, ethylenically unsaturated power µbonic acid ester µ
Alternatively, 0 ethylenically unsaturated monomer units such as ethylenically unsaturated vinyl μ Esthe μ can be mentioned, and component C is about 1 to 40 parts by weight with respect to a total of 100 parts by weight of the two components A and B. Preferably, it may be a copolymer containing about 1 to 10 polymers.

In the porous membrane of the present invention, the content ratio of hydrophilic copolymer A percentage can be determined. Generally, when the content of hydrophilic components in the hydrophilic copolymer X is large, X is added to the porous membrane.
Porous membranes exhibit sufficient hydrophilicity even with a small content of
When the content of hrt, min is small, it is necessary to increase the content of X in the porous membrane in order for the porous membrane to exhibit sufficient hydrophilicity.

In addition, when the porous membrane is a porous membrane produced by melt-forming or stretching, blending a large amount of hydrophilic copolymer On the other hand, if the hydrophilic copolymer The amount of blending of X and Y can be determined by taking into account the fact that it is unlikely to be inhibited.

Further, in the case of a porous membrane obtained by this method, the content of polyolefin Y in the porous membrane is preferably about 95 to 100 sat. If the content of polyolefin is less than this range, it becomes difficult to sufficiently grow lamellar crystals in the melt-shaped material, and a film with an excellent porous structure tends to be obtained.

The porosity, pore diameter, membrane thickness, etc. of the porous membrane of the present invention are not particularly limited.
The film thickness may be about 200 μm. Further, when the membrane is in the form of a hollow fiber, the inner diameter may be about 50 to 2000 μm.

In addition, the porous structure may be any structure in which pores are three-dimensionally interconnected, and blend polymers with a structure made porous by melt-forming and subsequent stretching may also be used. Examples include those having a structure obtained by a method of melt-forming and then extraction treatment. However, considering the mechanical strength of the porous membrane and the delay in increasing the pressure drop due to the clogging of the membrane, it is necessary to consider the mechanical strength of the porous membrane and the delay in increasing the pressure drop due to the clogging of the membrane. A porous membrane having a structure in which spaces are connected is preferable.

Next, a method for manufacturing the porous membrane of the present invention will be explained.

The porous membrane of the present invention can be manufactured by various methods including a wet film forming method and a film forming method combining melt-forming and extraction, but considering that it can be manufactured at low cost on an industrial scale, etc. It is preferable to manufacture by a so-called stretching method that combines melt-forming and stretching to make the film porous.

The film forming method using the stretching method will be explained below.

The above-mentioned polyolefin and hydrophilic copolymer can be blended sufficiently uniformly, but the blending methods include blending the above-mentioned polymers in a blender such as a V-type blender, or melting them in a melt extruder. Examples include a method of blending and then pelletizing.

This blended polymer is then melt cast using a conventional film or hollow fiber melt extruder. A double front type or a horseshoe type can be used as the spinning nozzle μ for hollow fibers, and in the former case, a shaped product with less uneven thickness can be obtained. Further, as the film extruder, either a T die type or a double front type die can be used. If a double-front die is used, a cylindrical film is obtained, in which case the subsequent stretching process can be carried out up to the cylindrical die. In addition, by adjusting the amount of internal air blown during film molding, it is possible to mold a film with a thickness and width depending on the purpose.

The extrusion temperature suitable for stably obtaining the unstretched melt-shaped material for obtaining the porous membrane of the present invention depends on the type of polymer used, the method index, the discharge rate employed, the cooling conditions, the winding speed, etc. The thickness and width of the desired molded product may be set appropriately within a range that can stably ensure the desired thickness and width, taking into account the conditions. It is molded at a temperature not exceeding 100°C higher than the melting point.

The unstretched melt-shaped material obtained by molding at a temperature below the lower limit of this temperature range is highly oriented, but the maximum amount of stretching becomes low when it is made to be stretched and porous in the subsequent stretching process. , is not preferred because it becomes difficult to obtain a sufficiently high porosity. Conversely, molding at a temperature exceeding the upper limit of the above temperature range is also undesirable since it is difficult to obtain a high porosity.

In the case of hollow fibers, the spinning draft is preferably 10 to 10,000, and 1000 to 1
It is more preferable to set it to 0000. The spinning draft is 1
If it is less than 0, the formation of a single crystal structure will be insufficient, and therefore it will be difficult to form a good porous structure even in the subsequent stretching process. f# Undrawn hollow fiber obtained by melt spinning has an inner diameter of 50 to 2000 μm and a film thickness of 10 to 200 μm.
Although it is preferable that the size is μm, the size may be outside this range if necessary.

Further, in the case of a tubular or flat molded product, it is preferable to take it off at a draft of 1 to 5,000, and more preferably to break it at a draft of 10 to 2,000. Fiμ to be taken away
It is preferable to rapidly cool the mold immediately after the die so that it can be stably taken up by the first roller it comes into contact with after exiting the die, and it is preferable to use an air knife or other cooling device.

The thus obtained unstretched molded product is subjected to an annealing μ treatment for one hour or more in a constant length or relaxed state at a temperature below Tm in order to increase its crystallinity. The longer the processing time, the better, but considering the economical
The time is preferably about 3 to 48 hours, preferably about 3 to 48 hours.

In addition, if such a long-time annealing process is performed in air, the hydrophilic copolymer changes in quality during that time, so in the present invention, a method of performing annealing process in an inert gas or vacuum is adopted. .

The annealed product is made porous by stretching, and a stretching method that combines cold stretching and hot stretching is usually employed. That is, first, D (Tm-220°C) ~ (TIII
I-80°C), preferably (Tm-160°C) ~
It is cold stretched at a temperature in the range of (1m-90°C), and then hot stretched at a temperature in the range of (Tm-60°C) to (τrn-5°C).

These cold stretching and hot stretching may be multistage stretching of two or more stages.

In these stretching processes, the crystal interfaces of the highly oriented crystalline unstretched molded product are exfoliated in the cold stretching process, and a microvoid laminated structure is developed by the thermoplastic stretching in the subsequent hot stretching process. How uniformly microcracking can be generated during the initial cold stretching is a major technical point in ensuring the homogeneity of the porous structure and the stability of the manufacturing process.

Note that if the hot stretching temperature is higher than the above upper limit, the stretched product becomes transparent and the desired porous structure cannot be obtained. When the hot stretching temperature is lower than the above lower limit, it is not preferable because the lower the temperature, the lower the porosity.

The stretching amount for cold stretching and hot stretching may be appropriately set according to the quality performance such as the porosity of the porous membrane, but it is preferable that the stretching amount for cold stretching is 5 to 100 mm. , the total stretching amount including cold stretching and hot stretching is 151) to 7
It is preferable to set the amount of hot stretching so as to correspond to 004.

If the total stretching amount exceeds 7004, the shaped material will frequently break during stretching, which is dangerous. The porous polyolefin thus obtained has almost the stability of its shape by hot stretching, but if necessary (Tm -60°C) ~
Heat setting may be performed at a temperature of (Tm -5° C.) under tension or under relaxed conditions. The temperature of this cold stretching and hot stretching,
By changing the magnification etc., porous membranes with various pore diameters and porosity can be obtained.

(Example) The present invention will be further explained below using Examples. In the Examples, mA crystallinity of blend polymer Xc =
(integral value of total diffraction intensity - integral value of diffraction intensity of amorphous part)
/The integrated value of the total diffraction intensity and the degree of crystal alignment were determined using a wide-angle x #1 diffractometer (110
) The half width of the distribution of the diffraction intensity in the fiber axis direction or the film MD direction was determined using the following formula.

Crystal alignment degree” (H(tt.) / (180-H(tt.)
. )) Xtoo (regret) However, H (IIQ): (1
10) Surface half-width Example 1 Acrylic acid and ethylene were copolymerized using an autoclave-type reactor with an internal volume of 2 tons, and the resulting copolymer was dissolved in xylene to form polyethylene glyco-A/ (n = 7
9) were reacted.

The content value (elemental analysis method) of polyethylene glycol maleate in the obtained copolymer was 55% by weight, and [η] was Q and 15 when measured in xylene at 75°C.

Next, this ethylene copolymer and the density cL965f/cm
A self-contained, air-introducing nozzle made of high-density polyethylene (manufactured by Mitsubishi Yuka ■28cm) with a two-way tube structure with a circular tube slit width of 55m, a spinning temperature of 170℃, and a spinning draft. 3400 at a spinning speed of 200 m/min and wound.

The obtained undrawn yarn was heat-treated at 120° C. for 24 hours under a constant length in a nitrogen atmosphere. The crystallinity of this undrawn yarn is 60%
The degree of crystal orientation was 694.

This undrawn yarn was cold-stretched at 25°C for 804 degrees, and then hot-stretched in a heating box having a length of 2W1 heated to 115°C until the total amount of stretching was 400 degrees. Further, relaxation heat setting was carried out in a heating box having a length of 2 m heated to the same temperature so that the total stretching amount was 500 mm.

The obtained porous hollow fiber had an inner diameter of 265 μm and a membrane thickness of 52
μm, porosity: 584, and water permeability pressure (water pressure when water permeates uniformly from the inside to the outside of the hollow fiber) was α2/−. Furthermore, the weight loss rate after immersion in water for 24 hours was α006'
It was l.

Comparative Example 1 Porous hollow fibers were obtained in the same manner as in Example 1 using high-density polyethylene (Mitsubishi Yuka IM Mitsubishi Polyethylene JX-20) with a length of 96,597 cm. 285 μm, film thickness 58 pm, porosity 72
cIJ,! The water pressure was 4.9 kg/ass.

(Effects of the invention) The porous @ membrane of the present invention is a porous membrane endowed with permanent hydrophilicity, and is used as a separation membrane in Type A fields including medical, food industry, and drinking water applications. can. In addition, in the case of a porous membrane having a porous structure in which the spaces formed by lamellae and a large number of fibrils μ connecting between the membranes are connected from one surface to the other surface of the membrane, the length as a whole is Due to the high degree of orientation, the membrane has excellent mechanical strength, and has a three-dimensionally connected network pore structure, which has the effect of delaying the clogging of the membrane during use. .

According to the production method of the present invention, hydrophilicity can be imparted to a porous polyolefin membrane in a simple manner, and a hydrophilic porous membrane can be obtained without using solvents, additives, or the like.

Claims (1)

[Scope of Claims] 1) A porous membrane comprising a hydrophilic copolymer X and a polyolefin Y whose main components are monomer units A and ethylene units B represented by the following formula (1). ▲There are mathematical formulas, chemical formulas, tables, etc.▼(1) (However, R_1 and R￥・2: hydrogen or methyl group n: 2
~9) 2) Claim 1, wherein the weight composition ratio X/Y of the hydrophilic copolymer X and the polyolefin Y is in the range of 5/95 to 50/50.
The porous membrane described. 3) The weight composition ratio of A/B in the hydrophilic copolymer X is 80/
The porous membrane according to claim 1 or 2, which has a molecular weight in the range of 20 to 10/90. 4) The porous membrane according to any one of claims 1 to 3, wherein the pore structure is a structure in which spaces surrounded by lamellae and a large number of longitudinally arranged fibrils connecting the lamellae are connected. 5) Claims 1 to 5, wherein the polyolefin Y is polyethylene.
Porous membrane according to 4. 6) After melt-shaping a blend of a hydrophilic copolymer X mainly composed of monomer units A and ethylene units B represented by the following formula (1) and a polyolefin Y, the melt-shape product is A method for producing a porous membrane, which comprises heat-treating in vacuum or in an inert gas medium at a temperature below the melting point of polyolefin Y for 1 hour or more, and then stretching to make it porous. ▲There are mathematical formulas, chemical formulas, tables, etc.▼(1) (However, R_1 and R_2: hydrogen or methyl group n: 2~
9) 7) The method for producing a porous membrane according to claim 6, wherein the weight composition ratio X/Y of the hydrophilic copolymer X and the polyolefin Y is in the range of 5/95 to 50/50. 8) The weight composition ratio of A/B in the hydrophilic copolymer X is 80/
The method for producing a porous membrane according to claim 6 or 7, wherein the porous membrane has a molecular weight in the range of 20 to 10/90.