JPH0679659B2 - Method for producing porous polypropylene hollow fiber or film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a porous material composed of a polymer material, which is used as a means for separating various substances such as plasma separation, artificial lung or ultrafiltration in the medical field. The present invention relates to a method for producing a hollow fiber or a porous film.

[Conventional technology]

A method for producing a porous hollow fiber or a porous film, for example, a porous polypropylene hollow fiber or a porous polypropylene film, in which a large number of fine through holes are formed in a peripheral wall portion or a film of a hollow fiber made of a polymer material, has been conventionally used. Various known.

For example, after molding a polymer material in which an easily soluble substance is mixed and dispersed into a hollow fiber or film, the easily soluble substance is dissolved and removed by a solvent, and a large number of fine through holes are formed in the peripheral wall portion of the hollow fiber or the film. Methods of forming are known. In recent years, after molding a thermoplastic resin into a hollow fiber or film,
A method of forming a porous body by heat-treating this and then drawing it to form fine through holes in the peripheral wall portion of the hollow fiber or the film is also common. Polyolefins, polyamides, polyesters and similar copolymers are known as the thermoplastic resins used. Among them, polypropylene (a homopolymer of propylene or a copolymer of propylene and other monomers) is a moldable resin. It has excellent strength, chemical resistance, etc. and is excellent as a thermoplastic resin for porous hollow fibers or porous films.

Using polypropylene as a thermoplastic resin, the porous hollow fiber obtained by the stretching method and its manufacturing method, JP-A-52-15627, JP-A-52-137026,
JP-A-53-38715, JP-A-54-34418, JP-A-SHO
54-68414, JP 54-138623, JP 55-13
No. 14, JP-A-55-107505 and JP-A-57-5914. Most of the methods for producing porous polypropylene hollow fibers disclosed in these are, after first heat treating a spun undrawn polypropylene hollow fiber,
A glass transition temperature or higher and a temperature of 110 ° C. or lower, most of which is a temperature near room temperature, to form fine through holes, and then a stretching treatment is performed again at a temperature of 110 ° C. or higher, and then a heat treatment is performed again. This is a method of heat-fixing the porous body.

On the other hand, the porous thermoplastic resin film obtained by the stretching method and its manufacturing method are disclosed in, for example, Japanese Patent Publication No. 46-40119, Japanese Patent Publication No. 50-2176 and Japanese Patent Publication No. 55-32531. . Most of the porous thermoplastic resin films and their manufacturing methods disclosed in these are first heat treated after molding the thermoplastic resin film, and then at room temperature or at a temperature not lower than the second-order transition temperature of the thermoplastic resin used. A method is disclosed in which the fine through holes are formed by stretching treatment, and further, the fine through holes formed by the stretching treatment again at a higher temperature are heat-treated again and heat-set.

[Issues to be solved]

The conventional method for producing a porous polypropylene hollow fiber is to draw at around room temperature and then to draw again at a higher temperature (110 ° C or higher), and the drawing process has two stages, which makes the process complicated. It has become.

Further, in the above-mentioned conventional method, in order to improve the quality of the obtained porous polypropylene hollow fiber, it is necessary to previously perform a heat treatment for increasing the crystal orientation of the undrawn polypropylene hollow fiber. This heat treatment is also a factor that complicates the entire manufacturing process.

The porous polypropylene hollow fiber obtained by the conventional method is not always satisfactory for use in a field requiring a relatively large pore size such as a plasma separation membrane and has a problem in performance.

When a porous polypropylene hollow fiber is produced only by stretching at 110 ° C or lower, most of which is near room temperature, the number of steps required is small, but the diameter of fine pores formed is small and the density of fine pores (void (Which can be represented by a ratio), only small values can be obtained, and similarly to the above, it cannot be applied to a field requiring a relatively large through-hole diameter.

On the other hand, also in the porous polypropylene film, it is preferable that the fine pores are formed as homogeneously as possible and have a required density (which can be represented by a porosity). However, the porous polypropylene film obtained by the above method has the problems that the fine pores formed are inhomogeneous, the average pore diameter is as small as 5000 Å or less, and the porosity is also low. Therefore, the use of the porous polypropylene film obtained by the above method is limited, for example, it is not suitable for use as a separation membrane for plasma separation.

Further, in the conventional method, in order to improve the quality of the obtained porous polypropylene film, it is necessary to previously perform a heat treatment for increasing the crystal orientation of the unstretched polypropylene film. Therefore, as in the method of manufacturing the porous hollow fiber, there is a problem that the manufacturing process of the porous polypropylene film is complicated as a whole.

[Means for Solving the Problems]

The present invention is directed to specific temperature ranges, specific stretching strain rates,
The present invention relates to a method for producing a porous polypropylene hollow fiber or a porous polypropylene film by stretching an unstretched polypropylene hollow fiber or film at a strain rate of less than 5% / min in the final stage of the stretching step. According to the production method of the present invention, after stretching, even if no special treatment such as heat setting treatment or relaxation heat setting is performed, shrinkage due to subsequent heating does not substantially occur, the porosity is high, and the average permeability is high. Large pore size, and
It is possible to manufacture a porous polypropylene hollow fiber or film having uniform formed pores.

That is, the present invention is a method for producing a porous hollow fiber or film including a step of forming a large number of fine through holes in the peripheral wall portion of the hollow fiber by stretching the polypropylene hollow fiber or film, and the stretching step is 110 ℃ to 155 ℃, and 10
The present invention relates to a method for producing a porous polypropylene hollow fiber or film, which is less than 5% / min, and is performed at a drawing strain rate of less than 5% / min in the final stage of the drawing process.

In the present invention, since the conditions for the porosity thereof are completely different from the conventional method, the polypropylene used is not particularly limited, and a homopolymer of propylene and a block copolymer of propylene and another monomer or oligomer or a random copolymer. A copolymer or the like can be used. Additives such as a plasticizer, a colorant, a flame retardant, and a filler can be appropriately added to these polypropylenes as long as their properties are not impaired.

In the present invention, in the case of polypropylene hollow fiber, first,
The polypropylene is spun according to a known hollow fiber production method to obtain an unstretched polypropylene hollow fiber. The spinning conditions may be appropriately selected from known techniques. For example, the spinning temperature is not less than the temperature at which polypropylene can be discharged and not more than the thermal decomposition temperature of polypropylene, and is usually 170 to 300 ° C, preferably 190 to 270 ° C.
Further, there is no particular limitation on the draft ratio (ratio of the drawing speed of the undrawn yarn and the discharging speed from the nozzle: the drawing speed / the discharging speed) which is a guideline for crystal orientation. However, when an undrawn polypropylene hollow fiber having a draft ratio of 0 or extremely small, that is, unoriented or substantially non-oriented, is used, it is possible to obtain a porous material obtained by the drawing step of the present invention. It is difficult to give polypropylene hollow fibers satisfactory properties. Therefore, in consideration of characteristics such as average pore diameter and porosity of fine pores of the obtained porous polypropylene hollow fiber,
Considering factors such as productivity, the draft ratio of the undrawn polypropylene hollow fiber used in the present invention is preferably in the range of 10 to 6000.

In the case of a polypropylene film, first, an unstretched polypropylene film is molded using the above-mentioned polypropylene according to a known film manufacturing method. Examples of the film manufacturing method include an inflation molding method and a T-die molding method. The molding conditions in such a molding method can be selected from known techniques. For example, the film forming temperature can be a temperature within the range of not less than the temperature at which the polypropylene used can be discharged and not more than the thermal decomposition temperature of the polypropylene. Usually, it is 170 to 300 ° C, preferably 190 to 270 ° C.

Also, the elastic recovery rate (or draft ratio) of the unstretched polypropylene film obtained by molding is not particularly limited. However, when an unstretched polypropylene film having an elastic recovery rate of 0 to extremely low, that is, an unstretched polypropylene film having extremely low crystal orientation is used, the porosity obtained by the stretching step of the present invention can be obtained. It is difficult to give satisfactory characteristics to quality films. Therefore, it is desirable to set the molding conditions of the unstretched film in consideration of the properties such as the average pore diameter and the porosity of the fine pores of the obtained porous polypropylene film.

As described above, there is no particular limitation on the elastic recovery rate of the unstretched polypropylene film, but for the above reason, the unstretched polypropylene film represented by the following formula has a relative humidity of 65 ° C. of 25 ° C.
The elastic recovery rate at 50% elongation in% is preferably 20% or more. Further, in consideration of productivity and the like when an ordinary molding apparatus is used, the range of 30 to 95% is particularly preferable.

Elastic recovery rate (%) = [length after extension-length after extension] /
[Length at extension-length of original film] × 100 Further, in consideration of the above requirements and factors such as productivity, the draft ratio of the unstretched polypropylene film used in the present invention (unstretched thermoplastic resin). The ratio of the film take-up speed to the nozzle discharge speed: take-off speed / discharge speed is
It is desirable to be in the range of 10 to 6000.

The unstretched polypropylene hollow fiber or film may be heat treated before being subjected to the stretching step. By the heat treatment before the stretching, the crystallinity of the unstretched polypropylene hollow fiber or film can be enhanced, so that the properties of the porous polypropylene hollow fiber or film obtained by the stretching are further improved.

The above heat treatment is carried out by a method of heating an unstretched polypropylene hollow fiber or film in air heated to, for example, 100 to 155 ° C. for 3 seconds or more.

The stretching step of the present invention is 110 to 155 ° C., preferably 110 to 145.
The stretching strain rate is less than 10% / min in the temperature range of ° C, and particularly, the stretching strain rate is less than 5% / min in the final stage of the stretching process.

When the stretching is carried out at a temperature of less than 110 ° C., only those having a small pore diameter can be obtained, or the hollow fiber or film is cut at a small stretching ratio, and only those having a small porosity can be obtained.

Further, when the stretching is carried out at a temperature of 155 ° C. or higher, the diameter or width of the hollow fiber or film is reduced, polypropylene is melted or partially melted, and no through hole is formed, or only a small through hole is obtained. Sometimes there is not.

If the stretching strain rate is 10% / minute or more, only small holes may be obtained or no holes may be formed at all. Further, the diameter of the hollow fiber or the width of the film may be reduced.

The draw ratio can be changed according to the average pore diameter depending on the intended use of the intended porous polypropylene hollow fiber or film. The draw ratio is 100 to 700% relative to the initial length of the unstretched polypropylene hollow fiber or film, especially
The range of 150-600% is preferred.

If the draw ratio is higher than 700%, the hollow fiber or film may be cut.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Incidentally, the crimp shrinkage in the examples, the initial length of the hollow fiber or film under no load relative to the initial value of the hollow fiber or film under no load and the same after 24 hours of the hollow fiber or film. It is expressed as a percentage of the difference in length.

Example 1 Polypropylene (UBE-PP-F109K, trade name: manufactured by Ube Industries, Ltd., MFI = 9g / 10 minutes) is used with a nozzle for producing a hollow fiber equipped with a gas supply pipe having a diameter of 8 mm and an inner diameter of 7 mm. Then, spinning was performed under the conditions of a spinning temperature of 210 ° C., a take-up speed of 200 mm / min, and a draft ratio of 726. The polypropylene hollow fiber obtained is heat-treated in a heated air bath at 145 ° C for 30 minutes, then at a temperature of 140 ° C, 350% relative to the initial length, strain rate 8.33% / min, and final strain rate of stretching. Of 4.7% / min for 5 minutes to produce a porous polypropylene hollow fiber.

Mercury injection method [Measurement is made by CARLOERBA (Italy) POR
It was performed using OSIMETRO SERIES 1500] and the average pore diameter was 1.29 μm and the porosity was 68%. The crimp shrinkage of the obtained porous polypropylene hollow fiber after molding for 24 hours was 0.7%.

Example 2 An inflation molding machine equipped with an inflation molding die having a diameter of 50 mm and a slit gap of 0.7 mm, using polypropylene (UBE-PP-Y101J, trade name: Ube Industries, Ltd., MFI = 1 g / 10 minutes) To form an unstretched polypropylene film. Molding operation is carried out with polypropylene at a discharge temperature of 200 ° C, while blowing air into the valve so that the blow ratio is 0.7, and 5 cm above the die.
At room temperature, blow air at room temperature onto the outer wall surface of the film to cool it, then at a position of 1.8 m on the die, take it with a nip roll at a take-up speed of 35 m / min to form the target unstretched polypropylene film. did.

The thickness of the obtained unstretched film was 20 μm.
The elastic recovery rate from 50% elongation of this film was 38%.

This unstretched film was heated at a temperature of 140 ° C. at an initial length of 300%, a strain rate of 8.3% / min, and a final strain rate of 4.7% / min.
It was stretched for a minute to give a porous film.

The average pore diameter of the obtained porous polypropylene film is
It was 0.63 μm and the porosity was 68%. (Each measurement method is the same as in Example 1) The crimp contraction rate after 24 hours is 0.
It was 8%.

〔The invention's effect〕

According to the method for producing a porous polypropylene hollow fiber or film of the present invention, a heat treatment after stretching is not particularly required, and a porous hollow fiber or film having uniform fine pores can be obtained by a simple production process. Further, according to the method of the present invention,
A porous hollow fiber or film that can be applied to applications requiring a relatively large pore size such as plasma separation and has a sufficiently large porosity can be easily obtained.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location D01D 5/24 A 7199-3B D01F 6/06 A 7199-3B // B29K 23:00 B29L 7: 00

Claims (2)

[Claims] 1. A method for producing a porous polypropylene hollow fiber or film, which comprises the step of forming a large number of fine through holes in the peripheral wall portion of the hollow fiber by stretching the polypropylene hollow fiber or film. A method for producing a porous polypropylene hollow fiber or film, characterized in that the temperature is from ℃ to 155 ℃, and the stretching strain rate is less than 5% / min in the final stage of the stretching step, which is less than 10% / min. . 2. The method according to claim 1, wherein the polypropylene hollow fiber or film is heat-treated at a temperature in the range of 100 to 155 ° C. before being subjected to the stretching step.