JPH02133608A - Porous polyolefin hollow fiber - Google Patents

Abstract

PURPOSE:To provide the title fiber having a specific porous structure, excellent in safety and hygiene and mechanical strength characteristics, suitable in filtration and separation for medical or industrial applications, consisting of a blend polymer comprising a polyolefin and hydrophilic polyolefin. CONSTITUTION:The objective hollow fiber consisting of a blend polymer comprising (A) 95-40wt.% of a polyolefin (e.g., PE, PP) and (B) 5-60wt.% of a hydrophilic polyolefin (e.g., a copolymer from ethylene and vinyl alcohol; pref. >=70 in contact angle to water when determined in the form of a film). This fiber is such that its peripheral wall part, from the outer wall surface to the inner one, represents a porous structure made up of communicating spaces surrounded, over the entire range, by lamellae and numerous fibrils mutually connecting said lamellae.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a hydrophilic porous hollow fiber suitable for medical and industrial filtration, separation, etc.

(Prior Art) Separation using polymer membranes has been widely used in the past, and polymer membranes made of various materials have been developed.

Among them, crystalline thermoplastic surface M is melt-spun into hollow 11All fibers, which are stretched at a relatively low temperature to generate crazes in the amorphous regions between crystalline lamellae, and preferably, this is further hot-stretched. Hollow fibers with a porous structure formed on the peripheral wall of the hollow fibers do not require additives or solvents to form micropores, so they are attracting attention as hollow fibers that are suitable for applications where impurities or compounds should not be leached into the system. has been done.

As a manufacturing method for such hollow fibers, Japanese Patent Application Laid-Open No. 52-13702
6, JP-A-57-42919, JP-A-57
It is disclosed in Publication No.-6611-1 and the like. The porous hollow fibers obtained by this method are made only of polyolefin or fluorinated polyolefin, and the material is woody and hydrophobic.
Therefore, as it is, extremely large pressure is required for filtering aqueous liquids such as aqueous solutions, which is not practical. Therefore, when used for filtration of aqueous liquids, it is treated with a wood-enhancing agent such as alcohol or a surfactant.

Also, 2f! After blending and melt-spinning different polymers, the interface between the different polymers is stretched and the interface between the different polymers is cleaved, so that at least a part of the wall surface of the continuous micropores communicating from the outer wall surface to the inner wall surface of the hollow fiber peripheral wall is different from the others. A microporous hollow woven fabric with a heterogeneous tt micropore wall surface composed of different types of polymers having properties is formed, and by post-treatment such as hydrolysis and sulfonation of the side tn groups present in the constituent polymers. JP-A-55-137208 discloses a method for producing wood-philic porous hollow fibers whose pore surfaces are made hydrophilic.

(Problems to be solved by the invention) Porous membranes are used for medical purposes such as blood sputum separation, infusion filtration, plasma protein separation, and production of plain water, and for industrial purposes such as IC.
It is used for cleaning, manufacturing water for food processing, and purifying water for other processes, and in recent years, it has also been used in large quantities in water purifiers for homes, restaurants, etc. All of these applications are water-based processes, and the elution of foreign substances from the porous membrane material is undesirable because it may lead to a decrease in safety, ice making, or the quality of the aqueous solution. It is requested.

On the other hand, hollow fibers made by melt-spinning polyolefin polymers and making them porous by low elongation are excellent because they do not use extraction additives or solvents, so there is no need to worry about elution when using membranes. Hydrophilic treatment is necessary, and treatment with alcohol or surfactant is only temporary hydrophilic treatment, and furthermore, if used for filtration, etc. with the hydrophilic treatment, the alcohol and surfactant will transfer to ice making. These hydrophilizing agents must be thoroughly washed and removed before filtration, as the membrane surface will return to hydrophobicity if it dries under these conditions, so it must be replaced with water after hydrophilization. The problem is that it must be kept in contact with water at all times.

In addition, the fiber made porous by melt-spinning and drawing a blend of different polymers described in JP-A-55-137203 generates a nose in the amorphous portion between the lamellae. Rather than forming fibrils, it cleaves the interface between different polymers, and therefore, compared to generating I-nozzes in the amorphous part between the lamellae and forming them into fibrils, it is difficult to form fibrils within the pores. The surface area is small, and the pore size is affected by the blended state of different types of polymers. There is also the problem of large splinters.Additionally, post-treatments such as hydrolysis and sulfonation are required to make the wood parent, making the process complicated.

(Means for Solving the Problem) As a result of intensive studies in view of the t2 situation, the inventors of the present invention have developed a method of generating crazes in the amorphous portion between the lamellae using polyolefin and using a melt spinning and drawing process. In order to utilize the excellent properties of porous hollow fibers obtained by making them porous, and to develop a technology that can produce porous hollow fibers with permanent hydrophilic properties suitable for aqueous liquid treatment in an industrially advantageous manner. As a result of intensive studies, we have arrived at the present invention (1).

That is, the gist of the present invention is 95-40% by weight of polyolefin.
A porous hollow fiber made of a blended polymer comprising 5 to 60% of a hydrophilic polyolefin, wherein the hollow fiber has a plurality of lamellae connecting the lamellae over the entire area from the outer wall surface to the inner wall surface. A porous polyolefin hollow fiber characterized by having a porous structure in which spaces surrounded by fibrils communicate with each other.

Polyolefins used in the present invention include polyethylene, polypropylene, poly3-methylbutene to 1
, poly-4-methylpentene-1, and the like. or,
In the present invention, the hydrophilic polyolefin to be blended with the polyolefin is preferably a polyolefin modified so that the contact angle with water is 80° or less, and is preferably 70° or less when measured using dough as a film. More preferably, it is a polyolefin modified in the following manner. Examples of such modified polymers include those in which hydroxyl groups, carboxyl groups, amino groups, sulfonic acid groups, polyoxyethylene groups, etc. are bonded to the molecular chains of various polyolefins, including ethylene and vinyl alcohol. Examples include copolymers of ethylene and vinyl acetate, copolymers of ethylene and maleic anhydride, copolymers of ethylene and polyoxyethylene chemically bonded, and metal ion crosslinked polyolefins.

Here, the reason why we limited the polymers to be blended with polyolefins to hydrophilic polyolefins is that when the above-mentioned polyolefins are blended with polyolefins, good affinity can be obtained between the two, and stiffness can be removed by melt spinning. The formation of a highly oriented, highly crystalline lamellar structure on the peripheral wall of the undrawn hollow fibers obtained by the process is not significantly inhibited, and furthermore, it is difficult to create a wound at the blend polymer interface, so it is different from the case where a polyolefin monopolymer is used. A similar collapsed porous membrane structure is obtained, and since it has a woody group, it has permanent hydrophilicity and can easily permeate water and moisture.
In addition, since the pores are the spaces around the fibrils, even if one location becomes clogged, it can be easily bypassed, so it has an excellent feature of virtually no clogging. The mixing ratio of this polyolefin and hydrophilic polyolefin is 95 to 40% by weight of polyolefin and 5 to 6% by weight of hydrophilic polyolefin.
It must be 0% by weight. This is because when highly wood-philic hydrophilic polyolefins are used, wood-philic properties can be achieved with a relatively small amount of blending, and conversely, when such hydrophilic polyolefins are blended in large amounts, lamellar crystals form. It tends to inhibit the formation of polyolefins, making it difficult to obtain a good porous structure, and in the case of products that have relatively low wood-philicity and have more of the characteristics of polyolefins, conversely, it is difficult to obtain a good porous structure. In order to achieve this, it is necessary to blend a relatively large amount, and furthermore, blending in a large amount does not inhibit the formation of lamellar crystals. The mixing ratio of polyolefin and wood-loving polyolefin is polyolefin 90-5
0% by weight and preferably 10 to 50% by weight of the hydrophilic polyolefin. If the proportion of polyolefin is less than the above-mentioned lower limit, it tends to be difficult to obtain a sufficiently uniform porous structure, which is not preferable, and if it exceeds the above-mentioned upper limit, hydrophilicity becomes insufficient, which is not preferable.

The porous structure of the porous hollow fibers of the present invention is created by stretching undrawn hollow fibers obtained by spinning a crystalline polymer, and stretching the folded molecules between the lamellae of the undrawn fibers to form fibrils. Since the structure is obtained by cleavage, a large number of fibrils arranged in the longitudinal direction of the fibers connecting the lamellae becomes a space, and this structure becomes a hollow tAIi.
It is connected from the outer wall surface to the inner wall surface of the peripheral wall portion of the fin.

The method for producing porous fibers of the present invention will be explained below.

First, the above-mentioned polyolefin and wood-loving polyolefin are blended, but this blend needs to be sufficiently uniform.The above-mentioned polymers are either blended in advance using a blender such as a V-type blender, or melted using a melt extruder. Preferably, the blended and pelletized mixture is passed through an extruder for melt spinning.

Next, this blended polymer is melt-spun using a nozzle for hollow fibers, and a nozzle for hollow fibers having a double tube structure is preferably used because it has less uneven thickness. Of course, as for the nozzle for hollow fibers, other types such as the hollow type can also be used.

The spinning temperature for melt spinning is determined by considering the type of polymer used, the melt index, the discharge rate used, the cooling strip '4, the winding speed, etc., to stabilize the inner diameter and film thickness of the target hollow fiber. It may be set as appropriate within the range that can be ensured, and usually the temperature is 20°C higher than the melting point (hereinafter referred to as mp, 1) of the polymer with a higher melting point among the polymers to be blended.
The spinning may be carried out at a temperature higher than 100° C. and not exceeding 100° C. higher than the melting point (mp, ). If the yarn is spun at a temperature lower than the lower limit of this temperature range, the resulting undrawn yarn will be highly oriented, but the maximum draw ratio will be low when the drawing process is performed in the later drawing step to make it porous. This is not preferable because it becomes difficult to obtain sufficient porosity.

On the other hand, spinning at a temperature exceeding the upper limit of the above temperature range is also not preferred because it is difficult to obtain a high porosity.

In order to achieve highly oriented and highly crystallized undrawn material obtained by melt spinning, the spinning draft is preferably from 100 to 10,000, more preferably from 1,000 to toooo. If the spinning draft is less than 100, the formation of a lamellar crystal structure will be insufficient, and therefore it will be difficult to form a good porous structure of 8Q even through the subsequent drawing process. The undrawn yarn obtained by melt spinning has a hollow inner diameter of 5
Although it is preferable that the film thickness is 0 to 2000 μm5 and 10 to 200 μm, a method outside this range 111 may be used if necessary.

The undrawn hollow fibers obtained in this way may be drawn as they are, but in order to enhance oriented crystallization, the temperature should be controlled at a constant temperature of mp+1 or less and within a range that does not substantially damage the structure of the undrawn yarn. It may be stretched after being annealed in a stretched or relaxed state.

The porous hollow fiber of the present invention is obtained by stretching the unstretched system thus obtained to make it porous, and the stretching temperature is below mptl-ao°C and mp.

-220°C or higher, preferably -160°C to m p
Cold stretching at H-90°C, then rllpu60°C~
Preferably, this is carried out in combination with hot stretching at mpn-5°C. The hot stretching may be a multi-stage stretching of two or more stages. If the hot stretching temperature is higher than the above upper limit, the desired porous structure cannot be obtained. When the hot stretching temperature is lower than the above lower limit, it is not preferable or undesirable because the lower the temperature, the lower the porosity.

The magnification of cold stretching and hot stretching depends on the porosity of the porous hollow fiber, etc.
Although it should be set appropriately depending on the desired quality performance, the stretching ratio in cold stretching is preferably 10 to 100%, and the stretching ratio in hot stretching is such that the total stretching amount of cold stretching and hot stretching is 150%. It is preferable to set it to 900%. If the total stretching amount exceeds 700%, it is not preferable because thread breakage occurs frequently during stretching. The porous polyolefin fibers obtained in this way are almost stable in shape by hot drawing, but if necessary,
mp, (Heat set 1 under tension or in a relaxed state at a temperature of -5°C. According to the study by the present inventors,
The porosity varies depending on the temperature and magnification of this cold stretching and hot stretching.
It is possible to appropriately achieve the desired quality performance of the porous fibers (9), such as the rejection rate in filtration.

(Example) The present invention will be further explained below using an example. In the example, the crystallinity of the blend polymer was calculated by integrating the diffraction intensity in all directions using a wide-angle X-ray diffraction device, and using the following formula. I asked for it.

Crystallinity χ. -(integral value of total diffraction intensity - integral value of diffraction intensity of amorphous part)/integral value of total diffraction intensity Also, the degree of crystal alignment is determined using a wide-angle X-ray diffractometer.The fiber axis of the diffraction intensity of the (110) plane The half value of the distribution in the direction was determined using the following formula.

Crystal alignment degree = (Ht+to+ / (180-H(1
1111) xtoO (%) However, HNI. +: Half value of (110) plane Also, the contact angle with water in the film state was measured by a known method using a Kyowa Contact Angle Meter manufactured by Kyowa Kagaku ■.

Example 1 High-density polyethylene (density 0, 968 g/cm')
HIZEX 2200J (manufactured by Yoi Petrochemical ■) and a cross-linked product of polyethylene and acrylic acid copolymer with zinc ions (manufactured by Mitsui Polychemical ■, HiSeishin-1 F02. Contact angle with water in film state: 69°). Blend with a V-type blender at a ratio of 1=1, and after drying, the outlet diameter is 2.
Using a hollow fiber manufacturing nozzle with a double tube structure of 8 mm and a circular tube slit width of 3.5 mm, air is introduced in a self-contained manner, the spinning temperature is 170°C, the spinning draft is 3400, and the spinning speed is 20.
The yarn was spun at 0 m/r+in and wound.

The obtained undrawn yarn was heated to t2oJ! at 115°C. ;Heat-treated under a short distance. The degree of crystallinity of this undrawn yarn was 62%, and the degree of crystal orientation was 75%. This undrawn yarn was heated to 80% at 25°C.
Cold stretching was carried out, and then the length 2 was heated to 115°C.
Hot stretching was carried out in a heated pile of 500 m until the total stretching ratio reached 520%. Furthermore, in a heating pile of 2 m length heated to the same temperature, the total stretching ratio is 400% by relaxing heat cera!・I did the following.

The obtained porous hollow fiber had an inner diameter of 270 μm and a membrane thickness of 51 μm.
m, porosity 62%, and water permeability pressure (water pressure when water permeates uniformly from the surface of the hollow fiber) 1.1 kg 7 cm2.

Example 2 High-density polyethylene with a density of 0 and 968 g/cm3 and a crosslinked product of a copolymer of polyethylene and acrylic acid using zinc ions were blended at a ratio of 1:1 using a V-type blender.
High-density polyethylene with a density of 0.968 g/cm3 (Mitsui Petrochemical A-Kasei Hi-ZEX 2) is used instead of the dried one.
200J) and an ethylene-vinyl alcohol copolymer (manufactured by Nippon Gosei Kagaku FM, contact angle with water on Soarnol D1 film 56°) were extruded at a ratio of 7=3 using an extruder and dried. The same procedure as in Example 1 was carried out except for using the following. The degree of crystallinity of the undrawn hollow fibers after heat treatment was 68%, and the degree of crystal orientation was 82%.

The porous hollow fiber obtained after stretching and heat setting has an inner diameter of 28
0 μm, membrane thickness 55 μm, porosity 65%, water permeability 1,
5 kg/cm".

Comparative Example 1 High-density polyethylene with a density of 0 and 9683/cm' and a crosslinked product of a copolymer of polyethylene and acrylic acid with zinc ions were blended in a ratio of 1=1 in a ■ type blender,
High-density polyethylene with a density of 0°968 g/cm' (Hizex 2 manufactured by Mitsui Petrochemicals) can be used instead of dried polyethylene.
A porous hollow fiber was obtained in the same manner as in Example 1, except that 200J) was used. The obtained porous hollow fiber has an inner diameter of 285
μm'n, membrane thickness 58μm, porosity 72%, water permeability 4゜9
J/c+++'.

(Effects of the Invention) The hollow fiber of the present invention is a hollow fiber membrane that is highly reliable in terms of safety and hygiene because it can be produced without using any solvent or extraction additive. Moreover, it has superior strength properties compared to membranes made using conventional wet or extraction methods.
In addition, since the peripheral wall of the hollow fiber has a porous structure in which spaces formed by lamellae and a large number of fibrils connecting between the lamellae are connected throughout from the outer wall surface to the inner wall surface, clogging is prevented. Moreover, since it is based on polyolefin and is blended with hydrophilic polyolefin, it has permanent wood-philicity, making it suitable for treating aqueous liquids in medical trenches, food industries, etc. It has excellent performance.

Claims (1)

[Scope of Claims] 1) A porous hollow fiber made of a blend polymer consisting of 95 to 40% by weight of polyolefin and 5 to 60% by weight of hydrophilic polyolefin, wherein the peripheral wall of the hollow fiber extends from the outer wall surface to the inner wall surface. A porous polyolefin hollow fiber characterized in that it has a porous structure in which spaces formed by encircling lamellae and a large number of fibrils connecting the lamellae are connected throughout. 2) The porous polyolefin hollow fiber according to claim 1, wherein the hydrophilic polyolefin has a contact angle with water of 80° or less when measured in a film state.