JPS5938322B2 - Microporous hollow fiber and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a longitudinally oriented hollow fiber having micropores in the fiber wall and having a high tensile strength, which is useful for purification and separation of gases, liquids, etc.

Another object of the present invention is to provide a method for producing high-strength microporous hollow fibers useful as materials for functional materials by melt spinning.

Further, the present invention is a method for producing hollow fibers that does not have to worry about residual solvent such as a solvent for dissolving and removing soluble components.

Conventionally, planar membranes having fine pores have been well known, and various techniques have been proposed for application to purification and separation of liquids, gases, etc., packaging that requires breathability, and the like.

However, if a flat membrane is used to separate and purify liquid or gas through a microporous membrane, it generally requires a larger occupied volume than the filtration area, making it difficult to downsize the device.

Further, in the method of manufacturing microporous hollow fibers by wet spinning, high strength fibers cannot be obtained.

In contrast, the microporous hollow fibers of the present invention have a significantly large surface area compared to the volume and provide a separation membrane with high efficiency per unit space and high strength.

On the other hand, various types of hollow fibers have been proposed in the past, and due to their texture, bulk, increased covering power, and improved heat insulation effect, they are used for clothing, futon cotton, kapok for life preservers, etc.

Recently, polyester hollow fibers have been used for separating gases such as hydrogen and helium.

However, there are no penetrating fine pores in the fiber walls of these hollow fibers, and therefore the permeation rate of gas and liquid inherent in the polymer is not changed in any way.

The microporous hollow fibers of the present invention are oriented in the length direction and have micropores that penetrate through the fiber walls, so they have a significantly higher permeation rate than the gas or liquid permeation rate that the polymer originally has. It has high strength.

Microporous fibers made of polyamide, polyester, and polyoxymethylene are also known (USP 35131
10,' (see JSP3551363), but these fiber forms are not hollow fibers and do not have the filtration properties of the fibers of the present invention.

In view of the above, the present inventors have arrived at the present invention as a result of various studies over many years.

That is, the present invention is a longitudinally oriented hollow fiber made of a thermoplastic crystalline polymer, which has penetrating micropores with an average pore diameter of 0.01 to 0.5 μ in the hollow fiber wall. , the amount of nitrogen permeation at 20°C in the fiber wall is 0.01 to 10
The present invention relates to a microporous hollow fiber having a value of 0cc, /cr/l·min·10αHg.

Furthermore, the present invention uses a spinneret for spinning polyolefin at a winding speed of 10 m and a draft ratio of 200 to 1 for 7 minutes or more.
500, melt-spun at 200 to 300°C for polypropylene and 180 to 280°C for polyethylene, heat-treated the resulting undrawn yarn as necessary, and
Birefringence value of 0-3 or more, high crystallinity and substantially 0.
Obtain an undrawn yarn that does not have through holes of 01 to 0.5 μm, and in the case of polypropylene, the undrawn yarn is heated at 80°C or lower by 5 to 100%.
After the cold stretching, hot stretching is carried out at 120 to 155°C by 20 to 450%, or in the case of polyethylene, the temperature is 10 to 80°C or less.
30-150% at 90-120°C after ~50% cold stretching
The result is a longitudinally oriented hollow fiber made of a thermoplastic crystalline polymer resulting from the stretching, and the pore size (average) produced in the hollow fiber wall by the stretching.
has penetrating micropores of 0.01 to 0.5μ, and the amount of nitrogen permeation through the fiber wall at 20°C is 0. '01-10
The present invention relates to a method for producing microporous hollow fibers having a value of occ/7.min.10 mg.

The present invention will be explained in more detail.

In the present invention, it is essential to use a polyolefin consisting of polyethylene or polypropylene as a starting polymer.

These polymers also contain stabilizers, UV absorbers, plasticizers,
Dyes, pigments, and crystal nucleating agents can be added as necessary.

Furthermore, the above-mentioned crystalline polymers may be blended with each other, and non-grade polymers such as elastomers and rubbers, and inorganic substances such as calcium carbonate may also be added to these crystalline polymers.

A preferred method for producing the microporous hollow fibers of the present invention is a method for obtaining hollow fibers by melt-spinning a melt of a crystalline polymer having fiber-forming properties through a spinneret, in which the diameter of the discharge opening of the annular slit of the spinneret is (outer diameter) is 0.2~2Qm
m, the width of the annular slit is 0.05 to 5 groups, the spinning temperature is 15 to 150 ° C higher than the melting point of the polymer,
Winding speed is l Q yn /min or more, draft ratio is 2
Melt-spun in the range of 00 to 1500 with an outer diameter of 2 mm or less,
Hollow fibers with a wall thickness of 100μ or less are made, heat treated at a temperature 10 to 100°C lower than the melting point of the polymer, and then stretched to an elongation of 500% or less by stage or multistage stretching to increase the pore size (average ) is a method for producing hollow fibers having penetrating micropores of 0.5μ or less in the fiber wall.

For melt spinning these crystalline polymers, a conventional melt spinning apparatus equipped with a screw, a gear pump, and a hollow spinneret is sufficient.

The polymer melted in a screw extruder or melting grid is sent to a hollow fiber spinning nozzle by a gear pump, spun into a spinning tube through an annular slit, solidified by cooling with cold air, and wound up in a winder.

An example of the hollow fiber spinneret of the present invention is shown in FIGS. 1 and 2.

It is preferable that the annular slit of the hollow fiber spinning die has a discharge opening diameter (outer diameter of the annular ring) a of 0.2 to 20 ml, and a width of the slit of 0.05 to 5 mm.

Even if the diameter of the discharge opening of the annular slit is too small or too large, increasing the draft ratio during spinning will increase the number of yarn breakages, making spinning difficult.

Furthermore, if the slit width is too narrow, the shear rate of the fluid polymer becomes too high, which tends to cause melt fractures, making it difficult to obtain uniform fibers, and increasing the number of thread breakages.

If the slit width is too wide, the resulting hollow fiber will have a large wall thickness, and even if the hollow fiber is stretched to form penetrating micropores in the fiber wall of the hollow fiber, if the wall thickness is too thick, the penetrating micropores will be formed. is less likely to occur.

It is advantageous to obtain micropores penetrated by hollow fibers having an outer diameter of 2 mm or less and a wall thickness of 100 μm or less, and for this purpose, the dimensions of the spinneret are preferably within the above ranges.

In addition, the shape of the circular slit of the spinneret for hollow fibers is not limited to a closed circular ring, but can be C-shaped (circular ring with a partially cut-out part), star-shaped, triangular, square, polygonal, or modified. There is no problem with anything that can be used to spin hollow fibers.

In this case, the discharge port diameter can be determined from the diameter calculated by converting the circumferential length into a circle.

Further, a hollow spinneret equipped with a gas supply pipe 1 for supplying gas to the hollow portion of the hollow fiber is also more preferable for producing the microporous hollow fiber.

When the spinneret has continuous slits in an annular shape, the gas may be supplied or sucked into the hollow part of the fiber by either natural suction or forced suction.

However, the outer diameter and wall thickness of the hollow fibers obtained vary depending on the amount of gas supplied to the hollow portion.

If the amount of gas supplied is too large, the fibers will swell into a lantern shape, which is undesirable.

The outer diameter of the resulting fibers is preferably smaller than the diameter of the spinneret outlet.

Moreover, if the amount of gas supplied is too small, the fibers will not be hollow fibers.

In the case of a C-type spinneret (see Fig. 1) with discontinuous slits (a system in which outside air is sucked in through cuts in the discharged polymer), gas is naturally sucked into the hollow part.

The polymer discharged from the spinneret has a draft ratio of 200 to 1.
It can be wound in the range of 500.

The draft ratio is the ratio between the winding speed and the linear speed at which the polymer is discharged from the spinneret, and is expressed by the following formula.

If the draft ratio is low, penetrating micropores will not occur even if the wound hollow fiber is drawn, and if the draft ratio is high, the tension applied to the yarn during spinning will exceed the melting point strength of the polymer, resulting in yarn breakage. When gas is forcibly inhaled into the hollow part of the generated hollow fibers during spinning, the preferable draft ratio for obtaining microporous hollow fibers becomes smaller than when gas is naturally inhaled.

Depending on the amount of gas inhaled, in the case of forced income, the draft ratio is 200 to 800, and in the case of natural inhalation, the draft ratio is 400.
~1500 is preferred.

The hollow fiber thus obtained has an outer diameter of 211! +1
! Hereinafter, the wall thickness is preferably 100 μm or less.

If the fibers are too thick, it will be difficult to maintain their shape, and they will likely collapse and flatten especially when external pressure is applied.

Furthermore, if the fiber is too thin, thread breakage is likely to occur during spinning, and when the microporous hollow fiber is used to pass gas or liquid through the hollow portion of the fiber, pressure loss tends to increase.

The outer diameter of the hollow fibers is preferably 10 to 500μ).

In addition, the relatively thinner the hollow fiber is, the easier it is to obtain penetrating micropores during stretching, and the thickness is preferably 5 to 60 μm.

The outer diameter and wall thickness of the hollow fiber can be easily measured by observing it using an optical microscope or a scanning electron microscope.

The winding speed of the hollow fiber is preferably 107 rL/- or more, preferably 50 to 1000 rL/- to achieve the above draft ratio.
0yx/mm is suitable.

Winding at a high speed also improves the orientation of the molecular chains of the polymer, which tends to generate micropores in the subsequent stretching process.

l Q m At a winding speed of 7M or less, the linear velocity of the polymer discharged from the spinneret becomes extremely slow in order to achieve the above draft ratio, and the freezing point of the yarn becomes too close to the spinneret, resulting in failure of spinning. It becomes stable.

In addition, the molecular orientation of the polymer is low, and even when the wound fibers are stretched, fewer micropores are generated.

In order to obtain more uniform fibers, it is effective to blow cold air onto the molten polymer yarn discharged from the spinneret.

The spinning temperature is preferably within a range of 15 to 150°C higher than the melting point of the polymer.

If good quality fibers can be obtained, the spinning temperature is preferably as low as possible.

For example, in the case of polypropylene, 200 to 300
°C, preferably 210 to 260 °C, in the case of high density polyethylene, 180 to 280 °C, preferably 200 to 2
The degree of molecular orientation of the hollow fibers obtained by spinning at a relatively low temperature of 50° C. and the high draft ratio is considerably higher than that of unoriented fibers.

If expressed using birefringence as an index of the degree of molecular orientation, it is 5X.
A value of 10<-3> or more is preferable; for example, for polypropylene hollow fibers, a value of 10*10<-3> or more is preferable.

This value can be determined in a conventional manner using a polarizing microscope.

The degree of crystallinity of the spun and wound hollow fiber is relatively high, but if it is still insufficient, the desired crystallization can be achieved by subjecting the fiber to tension or relaxation heat treatment within a temperature range of 10 to 100 degrees Celsius below the melting point of the polymer. reach the degree.

The degree of crystallinity can be determined from the values of crystal density and amorphous density [Co-authored by Seizo Okamura et al., "Introduction to Polymer Chemistry JP, 85 Kagaku Dojin (1973)]" based on the density determined from ASTM-D1505.

The degree of crystallinity may be 40% or more in the hollow fiber before drawing, but 50% or more is more preferable.

If the as-spun hollow fibers have not reached this state, their crystallinity can be increased by leaving them as they are or by heat-treating them.

For heat treatment, the heat treatment temperature is 120 to 160 °C for polypropylene and 90 to 13 °C for high density polyethylene.
It is 0℃.

The heat treatment time is preferably 10 seconds or more, preferably 20 seconds to 1 hour.

If the degree of crystallinity increases by leaving it at room temperature for several days, that is fine.

Micropores have not yet been formed in the hollow fiber in this state.

This hollow fiber exhibits significant elasticity.

Furthermore, if the hollow fibers are stretched, micropores will be formed.

The generation of micropores occurs only when the material is stretched beyond its yield point.

As the amount of stretching increases, the porosity significantly increases.

The size of the micropores varies slightly depending on the amount of stretching, but the pore diameter (average value) is 0.5 μ or less, and most of the pore diameters are 0.602 to 0.
．． It is 2μ.

In other words, unless stretched, this fiber is a normal hollow fiber.

Microporous hollow fibers are obtained only by stretching, and stretching is essential in the manufacturing conditions in order to obtain microporous hollow fibers.

If stretching at a temperature of 80°C or lower is cold stretching, and stretching at 80°C or higher is hot stretching, then in one-stage cold stretching, compared to the initial length,
It can be stretched up to an elongation of 200%, and further up to 500 in multi-stage stretching that combines cold stretching and hot stretching.

When stretched to a higher magnification, the fibers often break.

It is necessary to perform cold stretching until micropores are uniformly generated during stretching.

If hot stretching is performed first, the generation of micropores will be significantly less or no micropores will occur even after stretching.

In multi-stage stretching, it is necessary that the first stretching is cold stretching, and 5% or more, preferably 10 to 60%
If tether stretching is followed by hot stretching, the stretching ratio will increase compared to one-stage cold stretching, and the number of micropores will increase.

For polypropylene, the temperature is initially 5 to 100°C at a low temperature of 80°C or lower, preferably room temperature or 0°C or lower to -60°C.
%, preferably 10-60% cold stretching, followed by 20-450%, preferably 30-450% at 120-155°C.
300% hot stretching is required.

The stretching may be carried out in two stages or in multiple stages of two or more stages.

For polyethylene, the temperature is 80°C or less, preferably room temperature or 0°C.
Cold stretching for 10-50% at a low temperature of -60°C from below °C, followed by 30-150% at 90-120°C
It is necessary to carry out hot stretching to achieve a total stretching of 40 to 200%.

Cold stretching can also be carried out at a low temperature of -60°C or lower,
This is not economical to implement industrially.

The stretching speed can be in the range of 1 to 606%2.

Furthermore, by immersing the fibers in an organic solvent and stretching them during stretching, it is possible to increase the porosity and enlarge the pore diameter.

Dimensional stability of hollow fibers of any polymer can be improved by heat-setting at a temperature 10 to 100°C lower than the melting point of the polymer in a tensioned state or in a relaxed state of less than 25% of the total amount of stretching. .

For example, it is effective to heat set polypropylene at a temperature of 130 to 160°C and high-density polyethylene at a temperature of 100 to 130°C.

The heat setting time is preferably 3 seconds or more.

The microporous hollow fibers of the present invention can be easily obtained by the method described above, but the method is not limited thereto.

The microporous hollow fibers of the present invention are oriented in the length direction, and the orientation usually exhibits a birefringence value of 10XIO-3 or more.

And the average pore diameter is 0.02~0.2μ for most of the pores below 05μ.
It has micropores that penetrate through it.

The size of the micropores can be measured using a wood porosimeter.

In addition, the outer diameter of the microporous hollow fiber is 2 mm or less, and the wall thickness is 100 mm.
μ or less, the porosity of the fiber wall is usually 20-30%, sometimes as high as 50, and the amount of nitrogen gas permeation at 20°C is 0.0
It exhibits the characteristics of 1 to 100 squares/c11t -- 10CrILHg.

The microporous hollow fiber of the present invention is suitable for separating and filtering various substances by utilizing its characteristics.

Examples include, but are not limited to, applications in the food industry such as the removal of yeast in the beer manufacturing process, applications in pollution prevention such as filtration of various waste liquids, and applications in water purification and recycling. isn't it.

Furthermore, the fibers of the present invention can also be used to absorb or adsorb many substances into the fiber walls and/or hollow portions by utilizing the through-pores.

For example, microporous hollow fibers made of polyolefin are suitable as an oil catcher 1 for oil spread on the water surface or as a filler for an oil-water separator.

Furthermore, advanced functions can be imparted by proactively incorporating various substances into the hollow portions of the fibers and/or the micropores of the fiber walls.

For example, a substance with ion exchange ability or chelating ability may be incorporated to purify water or collect metals, or an artificial catalyst or natural enzyme may be filled and immobilized to serve as a catalyst for a reaction, a detection element, etc.
Can be used for medical materials.

In addition, a lasting effect can be obtained by filling the hollow part with insecticides and fragrances and volatilizing them through the micropores.

Furthermore, it can be filled with moisture absorbers, oxygen absorbers, liquid crystals, fertilizers, medicines, etc.

- Incorporation or filling of the above substances can be easily carried out by impregnating microporous hollow fibers with a liquid containing these substances, but it is also possible to use the impregnating process alone or by heat treatment after the impregnating process. Can be used after being encapsulated.

If the microporous hollow fiber of the present invention is heated, for example, polypropylene can be heated to about 160°C or higher, and high-density polyethylene can be heated to about 160°C or higher.
Since the micropores disappear at temperatures above 30° C., various substances can be sealed within the micropores and the hollow space by utilizing this.

The measurement method used in the present invention is shown below.

(1) Density: Measured at a temperature of 27°C according to ASTM-Dl 505.

(2) Melt index: Measured at 230° C. for polypropylene and 190° C. and 2.16 KP for polyethylene according to ASTM-D1238.

(3) Dimensions of hollow fiber: The cross section of the hollow fiber was determined by observing it at a magnification of 50 to 200 times using a biological microscope mold manufactured by Nippon Kogaku Kogyo Co., Ltd.

(4) Porosity and pore diameter: Measured using a water scissors porosimeter model 800 manufactured by Carlo Erba.

(5) Nitrogen permeation amount: 100 microporous hollow fibers are bundled in a U-shape, the cut ends of the fibers are hardened with epoxy resin, a part of the fibers is cut to align the fiber end faces, and from there, nitrogen flows inside the hollow fibers. By applying an internal pressure of 10 crfLHg, the unit amount of nitrogen permeating to the outside through the wall surface of the hollow fiber was determined.

(6) Birefringence Niolin Bus Optical Co., Ltd. polarizing microscope p
Measured using os.

(Strength and elongation: Using a universal tensile tester Tensilon UTM-3 manufactured by Toyo Soki Co., Ltd., yarn length 40 mm, test speed 20 mm 1
Measured in minutes.

The measured value is for the actual cross-sectional area excluding the hollow part.

Example 1 Isotactic polypropylene (melt index 1.0) was extruded using an extruder (screw diameter 2011111, L
/D 18, compression ratio 3.2) at a temperature of 250°C and a hollow spinneret (discharge diameter IQ
The fibers were spun using a circular slit with a slit width of 1 mm and a slit width of 1 mm.

It was wound up under the conditions of a discharge amount of 27 g/M, a discharge linear velocity of 0.13 m/m, a winding speed of 7 Qrn/min, and a draft ratio of 540.

Gas is supplied into the hollow fiber by natural suction.

The dimensions of the obtained hollow fibers were an outer diameter of 450μ and a wall thickness of 55μ.

The density was 0.892 gloc, the crystallinity was 48%, and the birefringence was 16 x 10-''.

When this hollow fiber is heat treated in a relaxed state at a temperature of 140°C for 5 minutes, the density is 0.911 g/(f, and the crystallinity is 70
%Became.

The birefringence increased to 24X10-s.

The crystallinity was determined using a crystal density of 0.936 g/cc and an amorphous density of 0.8509/cc.

The heat-treated hollow fibers were cold-stretched for 20% at a temperature of 10°C, and then thermally stretched for 30 to 300 degrees at a temperature of 145°C.

The total amount of stretching was 50 to 320 degrees.

This was heat-set under tension at 148° C. for 1 minute.

The hollow fibers thus obtained scattered light due to the micropores and were white in color.

This fiber easily absorbed ethyl alcohol.

When the amount of nitrogen permeation through this microporous hollow fiber was measured, it showed a significantly large value, and it was clear that there were fine pores that penetrated through the fiber.

Moreover, the results of measuring this microporous hollow fiber with a mercury porosimeter revealed that most of the pores had a pore diameter of 0.02 to 0.1 μ.

Table 1 shows changes in microporosity depending on unstretched and stretched amounts.

The breaking strength of the above-mentioned fiber 1-3 was 14 Ky/mx2, and the breaking elongation was 35%.

Comparative Example 1 After the hollow fiber spun in Example 1 was heat treated, the amount of nitrogen permeation and the porosity were measured without stretching, and both were zero.

Table 1 shows the results. Example 2 High-density polyethylene (melt index 0.23, density 0.953) was processed using an extruder (screw diameter 3Q+++m).
, L/D 25, compression ratio 3.5), and melted at a temperature of 230°C using a hollow spinneret (discharge port diameter 2 mm, slit width Q, 3 nm, discontinuous slit width Q, A 3 mm C-shaped slit) was used for spinning.

Discharge amount is 23 g/min, discharge linear velocity 1.5 Q m
/mir+, winding speed 12007n/m, draft ratio 8
It was wound with 00.

The dimensions of the obtained hollow fibers were 62μ in outer diameter and 12μ in wall thickness.

The birefringence was 21×10 −3 .

This hollow fiber was heat-treated at a temperature of 110°C for 1 minute, cold-stretched at 25°C for 30 inches, and then the second-stage drawing temperature was changed from room temperature to 1 minute.
The film was stretched by 50% at varying temperatures of 10°C.

The total amount of stretching was 80%. This was heat-set at 120° C. for 1 minute.

It was found that the obtained fibers easily absorbed ethyl alcohol and had open pores.

Most pore diameters are 0.0 when measured with a wood-tone porosimeter.
It was found that the thickness was distributed between 2 and 0.2μ.

The results are shown in Table 2.

Comparative Example 2 A hollow fiber spun and heat-treated under the same conditions as Example 2 was cold-stretched at 25°C by 30%, and then the second-stage stretching temperature was increased to 1.
It was stretched 50% at 25-135°C.

The total amount of stretching was 80%.

In this case, after the stretching was completed, heat setting was carried out for 1 minute at the same temperature as the stretching temperature.

The hollow fibers obtained were found to be transparent, did not absorb ethyl alcohol, and were free of pores.

The results are shown in Table 2.

[Brief explanation of drawings]

FIGS. 1 and 2 show an example of the discharge shape of a spinneret for spinning the fiber of the present invention.

Claims (1)

[Claims] 1. Polyolefin is melt-spun using a hollow fiber protection spinneret at a winding speed of 10 m/min or higher, a draft ratio of 200 to 1,500, and a temperature in the following range, and the resulting undrawn yarn is used as necessary. Heat treatment is performed to obtain an undrawn yarn having a birefringence value of 5X10-'' or more, a high degree of crystallinity, and substantially no through holes of 0.01 to 0.5μ, and the undrawn yarn is stretched under the following conditions. The result is a longitudinally oriented hollow fiber made of polyolefin resulting from the stretching, and penetrating fine pores with an average pore diameter of 0.01 to 0.5 μ generated by the stretching in the hollow fiber wall. and the permeation amount of nitrogen in the fiber wall at 20°C is 0.01 to 100 cc/c1.・ma
A method characterized in that it produces microporous hollow fibers with a value of n -10 cmHg. Spinning temperature: 200-300°C for polypropylene, 180-280°C for polyethylene.Stretching conditions: 5-100% cold stretching at 80°C for polypropylene, followed by 20-450% hot stretching at 120-155°C. Do this. In the case of polyethylene, after cold stretching of 10 to 50% below 80°C, hot stretching of 30 to 150% is carried out at 90 to 120°C.