JPS62221401A - Porous hollow yarn made of polyethylene - Google Patents

Abstract

PURPOSE:To obtain porous hollow yarn which is capable of high-pressure vapor sterilization and excellent in heat resistance by regulating m.p. of hollow yarn produced in a stretch opening method to a specified temp. and regulating degree of shrinkage in the lengthwise direction of yarn at high-pressure vapor sterilization temp. to a specified proportion and below. CONSTITUTION:High-density polyethylene is used as a raw material and spun in the temp. range within a temp. range of m.p. to about 50 deg.C above mp. at about >=100 draft ratio and cooled and thereafter subjected to annealing treatment at about 90-125 deg.C. This nonstretched raw yarn is subjected to low stretching at about <=50 deg.C and one-stage or multistage thermal stretching is successively performed at about 90-125 deg.C and thereafter one-stage or multistage thermal setting is performed. In this case, thermal setting temp. is regulated to about 125 deg.C to 130 deg.C and degree of relaxation is regulated to 20-50% and thereby the following porous hollow yarn made of polyethylene is obtained wherein m.p. is between 130 deg.C and 150 deg.C and degree of shrinkage in the lengthwise direction of yarn under nonextension at 121 deg.C is <=10%.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a hollow fiber membrane used in a medical plasma separator, a cancer filter for sterilization with a certain I/%l, and more specifically, The present invention relates to a porous hollow fiber obtained by a stretching method using polyethylene, which is flexible in high-pressure steam sterilization, and has excellent heat resistance that can be used for applications such as high-temperature water filtration.

(Prior art) Porous hollow fibers made of polyethylene produced by the stretching method are disclosed in, for example, JP-A-52-137026 and JP-A-57-42919.
, JP-A-57-66114, and the like.

Unlike the phase conversion method in which a solvent and additives are added to the polymer, the stretch hole method does not require a solvent or additives, and therefore is useful as a highly safe method, especially in medical applications. Ethylene oxide gas sterilization is generally used to sterilize the hollow fibers obtained by this method. However, this sterilization method has drawbacks such as concerns about side effects due to residual gas and inability to be applied to water-filled separators. Furthermore, as another sterilization method, gamma ray sterilization is considered, but it is not suitable because it generates eluates and degrades performance due to deterioration and decomposition of the polymer. Therefore, an autoclave sterilization method that does not have these drawbacks is an excellent method. However, porous hollow fibers made of polyethylene have not been put to practical use so far. In other words, the possibility of high-pressure steam sterilization of polyethylene porous hollow fibers by the stretched pore method is suggested in JP-A-57-84702, and in JP-A-60-25.
No. 7804 discloses improvement in heat resistance by radiation irradiation.

(Problems to be Solved by the Invention) JP-A-57-84702 describes that high-pressure steam sterilization at 110°C±10°C is possible. However, the United States Pharmacopeia (Chapter XXI) states that autoclaving is
o, 15 minutes as the standard, and "sterilization, sterilization, and magnetic shielding technology for microorganisms" (Sanitation Technology Society, 1981) states that 15 minutes is the standard.
It is stated that it should be sterilized at 21°C for 15 minutes. Therefore, a temperature range of 110'C±10°C is insufficient for practical use.

Furthermore, when the present inventors created a separator using the hollow fibers obtained under the conditions described in JP-A-57-84702 and performed high-pressure steam sterilization at 121°C 12O, the hollow fibers Cutting occurred and no usable product was obtained. Note that high-pressure steam sterilization was performed at 121° C. for 20 minutes in accordance with the standards of the Japanese Pharmacopoeia.

On the other hand, the method disclosed in JP-A No. 60-257804 is a method of crosslinking polyethylene by irradiation with radiation to improve heat resistance.

Although this method does improve heat resistance, the treatment requires a high radiation dose of 10 Mrad or more, which can cause decomposition of the material, generation of eluates, or coloring of the material. There are concerns about this and it is inappropriate, especially in the medical field. Furthermore, there is a problem in that large-scale equipment is required for industrial implementation. The purpose of the present invention is to solve these problems and
The object of the present invention is to provide a porous hollow fiber made of polyethylene that can be sterilized with high-pressure steam at a temperature of 0.degree.

(Means for solving the problem) Polyethylene porous hollow fibers produced by the stretched pore method are first manufactured by using high-density polyethylene with high crystallinity as a raw material, as shown in JP-A-57-42919, for example. This is melt-spun under high draft and shaped into hollow fibers, and then annealed to grow crystals to obtain undrawn hollow fibers.

Subsequently, the crystals are cleaved by cold stretching in the filament length direction.

It is a porous hollow fiber whose gaps have been expanded by rough hot stretching. Therefore, the obtained hollow fibers have high crystallinity and
It is thought that heat treatment in a temperature range lower than the crystal melting point may maintain the pore structure. However, crystallization is not 100%, and due to the pore opening principle,
Tension in the fiber length direction is required during stretching, and the resulting hollow fibers therefore have residual internal strain within their structure.

Therefore, in a high-temperature atmosphere, the residual internal strain acts as a contraction force, causing problems such as cutting of the hollow fibers, deformation of the adhesive, and peeling of the adhesive surface.

As a result of intensive studies on this point, the present inventors have solved these problems with a porous hollow fiber having the following characteristics. Namely.

The gist of the present invention is to provide a porous hollow fiber having an average permeation pore diameter of 0.01 to 2 gm obtained by a stretching pore method, the melting point of which is 130°C or more and less than 150°C, and a fiber under no tension at 121°C. The shrinkage rate in the longitudinal direction is 10% or less. Here, the contraction rate in the yarn length direction under no tension at 121°C (hereinafter referred to as "shrinkage rate at 121°C") is:
This is an index indicating the magnitude of the residual internal strain described above, and is the most important condition in the present invention. Also, 121'0
The shrinkage rate is the criterion used to indicate resistance to autoclaving. The shrinkage rate of the hollow fiber at 121'O according to JP-A-57-84702 mentioned above was 22%.
The present inventors investigated the relationship between the shrinkage rate of porous hollow fibers at 121°C and the high-pressure steam sterilization resistance of the separator at 121°C for 20 minutes, and found that the shrinkage rate at 121°C was 10%.
A separator that can be sterilized in 121'0120 minutes can be obtained if the following conditions are met, and more preferably, a satisfactory separator can be obtained with no deterioration in performance when the shrinkage rate at 121°C is 7% or less. I figured it out.

(Embodiments and Effects) In the present invention, the permeation average pore diameter is a value determined from the Hagen-Boiseuille equation. Here, η is viscosity, t is pore length (film thickness), J is water permeability, Pr is porosity, and Δp is differential pressure. If the pore size is less than 0 and the OI is less than JLm, the obtained plasma protein concentration will be small, making it unsuitable for the field of application aimed at by the present invention, and if it exceeds 2 gm, leakage of blood cells or hemolysis will occur, making it unsuitable. A more preferable pore size range is 0.1 to 0.
．． 6 gm, and within this range, good plasma separation can be obtained with little deterioration over time due to blood cell penetration into the membrane surface or protein clogging.

Next, the melting point of the hollow fiber of the present invention indicates the temperature of the melting point of the crystal determined by a conventional method using DSC.

The melting point of 1306C or higher and lower than 150C indicates that the hollow fibers are made of general high-density polyethylene that has not undergone any special treatment such as crosslinking.

It is more preferable that the hollow fiber of the present invention has the following requirements, namely, a porosity of 0.50 to 0.75,
Water permeability is 5-30n/rrr *hr *mmHg
, and the water permeability per porosity is 0.111rrf
It is more than r・mmHg. Here, the porosity is a value obtained from measurement of the apparent density of hollow fibers. 0
．． If it is less than 50, the filtration capacity is small and clogging occurs easily;
If it exceeds 75, the strength of the hollow fiber decreases, which is undesirable.
Water permeability is the rate at which pure water passes from the inside of a hollow fiber under certain conditions, and is used as an indicator of membrane performance.

Here, water permeability 51/rrfm h r * mmHg
If it is less than that, the plasma separation rate will be insufficient in plasma separation and is not preferable.

Roughly speaking, the amount of water permeation per porosity is the value obtained by dividing the amount of water permeation described above by the porosity, and is considered to be an index indicating the effective use of pores. Hollow fibers produced by the stretched hole method have a structure oriented in the fiber length direction, so they have high tensile strength, but are prone to bending, bending, crushing, and hollow flattened parts. If a permeable layer with the same porosity could be obtained, this drawback would be improved. In polyethylene hollow fibers produced by the conventional stretching hole method, 0. IJL/m″・hr*m
Although only those with a value of less than m'Hg were known, the hollow fiber of the present invention with a value of more than O,li/rn'*hremmHg has become possible for the first time to provide a hollow fiber with excellent permeability and ease of handling.

Next, a method for measuring physical property values used in the present invention will be described.

(1) Shrinkage ratio Using a high-pressure steam sterilizer (Toyo Seisakusho model 5VS-20), process the hollow fiber (length 1) at 121°C for 20 minutes, cool it thoroughly, and then reduce the length to lz). was measured using a differential scanning calorimeter (hereinafter referred to as DSC) [D
T-30 type] at a heating rate of 10"C!/min, and the temperature was determined as the top temperature of the resulting melting peak.

(3) Porosity: Obtain the apparent volume from the outer and inner diameters and lengths of the hollow fibers, and further calculate the apparent density (ρ1) from the weight, where ρ is calculated from the following formula. is the density of raw polyethylene.

(4) Water permeability A mini-module with an effective length of 13 cm and hollow fiber ends opened at both ends was made by bundling 50 hollow fibers and bonding and solidifying both ends. The permeation time of 15 mJl of pure water was measured under pressure and calculated as the amount per inner diameter standard.

The hollow fiber of the present invention is manufactured, for example, by the following method.

(1) Made of high-density polyethylene with a density of 0.95 or more, preferably 0.96 or more, (2) Draft ratio of 10 in the temperature range of melting point to melting point + 50°C
After cooling the spinning at a temperature of 0 or higher, (3) annealing at 90°C to 125°C, (4) 50°C
Cold stretching at a temperature of 10-50% at a temperature below ℃, followed by a total stretching ratio of 300-700 at a temperature of 90-125℃
%, one-stage or multi-stage hot stretching, (5) temperature of 125°C or higher and lower than 130°C, relaxation rate 20
% to 50%, preferably 30% to 50%, single or multi-stage heat setting is performed.

Here, the relaxation described in the present invention is a means of loosening the hollow fiber in the length direction and reducing its internal strain. For example, using a hollow fiber supply roll and a take-up roll, the take-up roll speed (Ri) is This is done by lowering the roll speed (R2). In addition, the relaxation rate refers to the degree of relaxation in the above-mentioned method, and especially the heat setting conditions are extremely important in realizing the hollow fiber of the present invention.

The conventionally known heat set temperature is 100°C to 125°C.
(Japanese Unexamined Patent Publication No. 57-66114), but in the present invention, 1
The porous hollow fiber of the present invention can be obtained by using the limited conditions of 25° C. or higher and 130° C. or lower and a high relaxation rate of 20% to 50%. To explain in more detail the method for manufacturing the hollow fiber of the present invention, the raw material polyethylene has a density of 0.95 or more, preferably 0.96 or more.
Although the melt index is not particularly limited, it is preferably 1 to 10 on spinning. This raw material polyethylene is melt-extruded using a double tubular spinneret at a temperature between the melting point and the melting point +50°C to form a hollow shape, and is spun under a high draft with a draft ratio of 100 or more to obtain an unprocessed yarn. Next, this untreated yarn is annealed in a 90° 0-125° C. heating bath to obtain an undrawn yarn in which crystals have grown.

This undrawn yarn is cold-stretched between rolls by 10-50% at 50°C or lower to cleave the crystals, and then hot-stretched in one stage or in multiple stages to a total stretching amount of 300-700%. By this, a porous body having hollow fiber walls continuous from the inner surface to the outer surface is obtained. The temperature of this hot stretching greatly affects the open pore state of the membrane, and is usually 90-125°C. If the temperature is lower than this, a sufficient porous body cannot be obtained;
Further, if the temperature is higher than this range, problems such as thread breakage may occur during the stretching operation.Successively after the hot stretching operation, a heat setting treatment, which is an important point of the present invention, is performed to impart heat resistance. The heat setting temperature is 25°C and less than 25°C and 30°C. 1
At temperatures below 25°C, a shrinkage rate of 10% or less at 121°C cannot be obtained, and at temperatures above 130°C, the hollow fibers become thinner and transparent, the cross-sectional dimensions become more uneven, and the transmission performance decreases. Although the undesirable heating means is not specified, it is convenient to use homogenized hot air with sufficient temperature control. Although the heating time is not particularly limited, a range of 1 second or more and 1 minute or less is considered to be a range that provides both uniformity of treatment and industrial practicality. At the same time, an important factor is to moderate, 20% to 50%, preferably 30% to
A relaxation rate of 50% is used. Below 20%, L 2 t
"It is not possible to obtain a shrinkage ratio of less than 10% at c.
% or more is practically difficult. Heat setting may be done in one stage or in multiple stages, but from the viewpoint of uniformity of setting, heat setting is performed in 2 to 3 stages.
Multi-stage processing is preferred. The porous hollow fiber membrane according to the present invention is suitable for use in the separation of blood cells and plasma or in sterile filtration, and is also effective in fields where microfiltration is generally used. In particular, it is made of polyethylene, which has excellent chemical resistance, and has improved heat resistance, so it can be used for precision filtration of semiconductor process chemicals, electric power, process water treatment at nuclear facilities, and surface treatment wastewater. It is effectively used for processing, concentration and purification of products in the pharmaceutical and food fields. The present invention will be explained below with reference to Examples.

(Example 1) High density polyethylene (ρ=o, 9sa, MI=5.5.
Using Hi-ZEX-2208J) as raw material, using a hollow double spinneret, polymer extrusion rate 16g/min, hollow N2 amount 23m
Jl/min, spinning speed 200m/min, spinning draft ratio 3400
It was melt-spun.

The obtained hollow fibers were annealed in an oven at 115° C. for 2 hours to obtain undrawn fibers.

Using this undrawn yarn, cold drawing, hot drawing, and heat setting were successively performed. That is, after cold stretching of 30% at room temperature, followed by two-stage hot stretching of 200% at 102°C and 43% at 115°C, the speed between the rolls was adjusted in an air heating tank at 128°C. A two-stage heat set was performed by adjustment.

A porous hollow fiber was obtained at a relaxation rate of 27% in the first stage and 17% in the second stage, a total of 40%, and the shrinkage rate at 121° C. of the hollow fiber was measured. First, the hollow fiber was moistened with ethanol, then replaced with water, and cut into a length of 20 cm. This was placed in an autoclave while keeping it hydrated for 12 hours.
Heat treatment was performed at 1° C. for 20 minutes. After cooling, the length was measured and the shrinkage rate was found to be 6.5%. The hollow fiber has an inner diameter of 378 gm, a membrane pressure of 49 gm, and a porosity of 0.68.
The water permeability was io, 3 fL/m'*hr, 11 mmHg. Water permeability per porosity is 0.151/rrfahr
*mrnHg, permeation average pore diameter was 0.18 Bm. The peak melting point of the hollow fiber by DSC was 133°C. This hollow fiber had excellent straightness and was easy to handle. In addition, this hollow fiber was extracted with water at 70°C for 1 hour,
I measured the eluate, but it was not detected at all.

Using 1,700 hollow fibers, they were inserted into a polycarbonate container and both ends were adhesively fixed with urethane to produce a plasma separator with an effective length of 13 cm. After making it hydrophilic with 70% ethanol, it was thoroughly washed with pure water and left in a hydrated state for 12 hours.
High-pressure steam sterilization was performed at 1° C. for 20 minutes. No abnormality was observed in the appearance of the separator after sterilization, and no deformation was observed in the adhesive part. Filling water was replaced with physiological saline, Ht40
% of fresh bovine blood was poured, and no blood cells leaked.
At a blood flow rate of 60 mJL/min, a plasma flow rate of 13 mJL/min was obtained. Moreover, no hemolysis was observed in the obtained plasma.

(Example 2) After opening the holes by stretching in the same manner as in Example 1, two-stage heat setting was performed at 128° C., with the first stage at 32% and the second stage at 26%, for a total of 50%. The obtained hollow fiber has a temperature of 121'C! Te (7)
Shrinkage rate 3.0%, inner diameter 386Bm, membrane thickness 51gm, porosity 0.63, water permeability 10, 417m' fist hr・m
mHg, the permeation average pore diameter was 0°20 lm, and the water permeation amount per porosity was 0.17 cross/m''·hr·mmHg.

When a separator was manufactured in the same manner as in Example 1 and bovine blood was passed through it, there was no leakage of blood cells, a plasma flow rate of 12 mJL/min was obtained when the blood flow rate was 60 mJL/min, and no hemolysis was observed.

(Comparative Example 1) After spinning and drawing in the same manner as in Example 1, 128
The temperature was set to ℃. The obtained hollow fiber had an inner diameter of 370
gm, membrane thickness 48 gm, porosity 0°77, water permeability 7.1
1/m''*hr@mmHg, and the average permeation pore diameter is 0.
15Bm, water permeability per porosity is 0.09u/ln'・h
It was r*mmHg. In addition, hollow fibers are prone to bending and flattening, and the shrinkage rate at 121"O is 19%.
A separator was manufactured in the same manner as in Example 1, and the temperature was 121℃.
When high-pressure steam sterilization was performed for 120 minutes, dents were observed in the polyurethane portion of the adhesive, and breakage of the hollow fibers was also observed.

(Example 3) Using the plasma separator produced in Example 1, the whole was evacuated in a pressure-resistant stainless steel container, then filled with degassed water, and
A pressure of 0 kg/Crn' was applied to moisten the membrane pores. This plasma separator was autoclaved at 121°C for 20 minutes.
No breakage of the hollow fibers was observed. Furthermore, when cow blood with 36% Ht was poured, there was no leakage of blood cells, and the blood flow was 5H6.
At 0 ml/min, a plasma flow rate of 18 mA/min was obtained.

The permeability of plasma proteins was as high as 95%.

(Example 4) After spinning and drawing in the same manner as in Example 1, the set temperature was set to 125.
A one-stage heat setting was performed at a relaxation rate of 30% at .degree. C. to obtain a porous hollow fiber.

This hollow fiber has an inner diameter of 362u, m, an Ili thickness of 50=m,
Porosity 0.69. Water permeability 10.2jL/rn"*hr
* mmHg, and water permeability per porosity is 0°154
17rn's hre mmHg. Also 1
The shrinkage rate during high-pressure steam sterilization of 21” Cl2O is 7°0
%, and the water permeability after sterilization is 9.7 min/rn'eh
There was almost no change in r cloudy mmHg.

(Example 5) Under the spinning conditions of Example 1, the polymer discharge amount was set to 14.
An undrawn hollow fiber was obtained by performing the same spinning and annealing treatment except that the amount of hollow N2 was 5 g/min and the amount of hollow N2 was 20 m1/min.

After cold-stretching this hollow fiber by 30% at room temperature,
Hot stretching was performed at 104°C to 200%, and at 115°C to 43%, and further, i! 1m at 128℃, the first
A two-stage heat setting was performed with a first stage of 19% and a second stage of 14% and a total relaxation rate of 30%. When the inner diameter of the obtained hollow fiber was measured at 20 points, the average value was 326 x m, the difference between the maximum fi value and the minimum value was 19 m, the 2-layer thickness was 48 Bm, and the porosity was 0.67.
, water permeability 1tO, 51/nf * h r * mmHg
, water permeability per porosity is 0.161L/rn”*hr*
mmHg, permeation average pore diameter is 0.18 pm, 121”O
The shrinkage rate is .

It was 3.7%.

(Comparative Example 2) After spinning and drawing under the same conditions as in Example 5, a hollow fiber was obtained by setting the temperature in the heat setting condition to 131"0. This hollow fiber had a heat shrinkage rate of 1.3%. Although it showed a good value, the inner diameter was small at an average of 283 ILm.

In addition, the difference between the maximum value and the minimum value was 15 full m, which was a large variation in the cross-sectional diameter. Also, 7! iThe amount of water is 4,6
The value decreased to 41/ln'e h r * mmHg, which was not practical.

(Effects of the Invention) The polyethylene porous hollow fiber of the present invention has a WA structure and exhibits excellent heat resistance without impairing performance.
High-pressure steam sterilization at 121°C for 20 minutes is possible. Therefore, it can be safely used in plasma separators and sterilization filters, and is extremely useful.

Claims (2)

[Claims] (1) The average permeation pore diameter obtained by the stretching pore method is 0.0
The melting point of porous hollow fibers of 1 to 2 μm is 130
A porous hollow fiber made of polyethylene, characterized in that the temperature is at least 150°C and the shrinkage rate in the fiber length direction under no tension at 121°C is 10% or less. (2) Porosity is 0.50-0.75, water permeability is 5-30
1/m^2*hr*mmHg, and a water permeability per porosity of 0.1 l/m^2*hr*mmHg or more, according to claim 1.