JPH0211620B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing porous thermoplastic resin films.

[Background of the Invention] A porous thermoplastic resin film (porous thermoplastic resin film), which is composed of a film made of a polymeric material and having a large number of fine pores formed therein, is used, for example, in air purification, water treatment, etc. It is used in a variety of fields, including filtration membranes or separation membranes used in batteries, diaphragms used in electrolysis, and separation membranes used in artificial lungs or plasma separation.

A method for manufacturing a porous thermoplastic resin film is, for example, by forming a polymer material in which easily soluble substances are mixed and dispersed into a film, and then dissolving and removing the easily soluble substances with a solvent to form a large number of fine particles in the film. Methods of forming through holes are known.

In recent years, a method has also become common in which a thermoplastic crystalline polymer material is formed into a film, heat treated, and then stretched to generate pores in the film to create a porous body. It is becoming.

It is known that various polymer substances can be used as thermoplastic crystalline polymer materials used for such purposes, but in particular, polyolefins, fluorine-containing polymer compounds, polyamides,
Polyesters or copolymers similar to the above-mentioned polymer compounds are known. Among these, polypropylene (a propylene homopolymer or a copolymer of propylene and other monomers) and fluorine-containing polymer compounds are particularly popular for use in porous thermoplastic resin films due to their excellent strength and chemical resistance. It is considered to be an excellent polymeric material for manufacturing.

[Description and problems of the prior art] Porous thermoplastic resin films using polymeric materials and methods for producing the same are described, for example, in Japanese Patent Publication No. 1973-
Publication No. 40119, Special Publication No. 50-2176, Special Publication No. 1977
-Disclosed in Publication No. 32531, etc. In most of the porous thermoplastic resin films and their manufacturing methods disclosed in the above-mentioned publications, the molded thermoplastic resin film is first heat-treated and then processed at around room temperature or above the secondary transition temperature of the thermoplastic resin used. (For example, when polypropylene is used, it is stretched at a temperature of -40°C or higher) to generate pores to form a porous body, and then the formed pores are heat-treated again to heat-set. This is the main point.

Considering the intended use of the porous thermoplastic resin film, it is preferable that the fine pores are as homogeneous as possible and formed with a desired density (expressed as porosity). However, the porous thermoplastic resin film obtained by the above method has problems in that the average pore diameter is as small as 5000 Å or less, and the porosity is low. Therefore, the porous thermoplastic resin film obtained by the above method may be unsuitable for use as a separation membrane for plasma separation, for example, and its uses may be limited.

Generally, using known methods such as those mentioned above,
In order to obtain a porous thermoplastic resin film in which the fine pores formed are uniform and large and have a high porosity, the unstretched thermoplastic resin film used must have a high orientation or a high elastic recovery rate.
recovery) is necessary. Methods for preparing such an unstretched thermoplastic resin film include a method in which the film is formed under specific conditions, or a method in which the unstretched thermoplastic resin film is heat-treated to improve the degree of crystallinity. has been done. In other words, in the conventional method, in order to improve the quality of the porous thermoplastic resin film obtained, it was common to perform an operation to increase the crystallinity of the unstretched thermoplastic resin film in advance. Therefore, there has been a problem that the manufacturing process of the porous thermoplastic resin film tends to become complicated as a whole.

[Object of the Invention] An object of the present invention is to provide a method for producing a porous thermoplastic resin film having a high porosity, a large average pore diameter, and uniform pores. In particular, the present invention provides a method that even if an unstretched thermoplastic resin film made of a thermoplastic resin with a low elastic recovery rate or a low draft ratio is used, the porosity is high, the average pore diameter is large, and the pores formed are uniform. It is an object of the present invention to provide a method for producing a porous thermoplastic resin film.

[Summary of the Invention] The present invention provides a method for producing a porous thermoplastic resin film, which includes a step of forming a large number of fine pores in the film by stretching the thermoplastic resin film, the stretching step being performed using nitrogen, In a medium selected from the group consisting of oxygen, argon, carbon monoxide, methane and ethane, the stretching temperature is -70°C or lower, and the stretching temperature is 50°C below the freezing point of the medium and the boiling point of the medium. Provided is a method for producing a porous thermoplastic resin film, which is characterized in that it is carried out at a temperature below a high temperature.

The present invention also provides a method for producing a porous thermoplastic resin film, which includes a step of forming a large number of fine pores in the film by stretching the thermoplastic resin film, in which the stretching step includes: In a medium selected from the group consisting of nitrogen, oxygen, argon, carbon monoxide, methane and ethane, and at a stretching temperature of -70°C or less, from the freezing point of the medium to 50°C below the boiling point of the medium.
a step of stretching at a temperature below a high temperature; and () a step of hot stretching the film at a temperature 90 to 5° C. lower than the melting temperature of the thermoplastic resin after the stretching step at a cryogenic temperature; A method for producing a porous thermoplastic resin film is provided.

The present invention provides an excellent crazing effect that appears when a thermoplastic resin film such as polypropylene is stretched in a specific medium such as liquid nitrogen at extremely low temperatures. This function was completed based on the knowledge that even if the thermoplastic resin film does not have a high elastic recovery rate or draft ratio, it functions to become a porous thermoplastic resin film with excellent properties. In other words, in the present invention, the porosity is made using a specific medium under extremely low temperature conditions, so that it is difficult to produce porous thermoplastic resin films with particularly excellent properties using conventional methods. Even if a thermoplastic resin with a low recovery rate is used, uniform pores can be formed, and a porous thermoplastic resin film with a high porosity can be manufactured. Therefore, when producing an unstretched thermoplastic resin film, there is no particular need for complicated operations to improve its elastic recovery rate or draft ratio, unlike conventional methods.

[Detailed Description of the Invention] The present invention provides a thermoplastic resin in a specific medium.
It is necessary to stretch at a temperature of 70° C. or lower, and within a range from the freezing point of the medium to a temperature 50° C. higher than the boiling point of the medium (hereinafter also referred to as cryogenic stretching).

In the present invention, the conditions for making the material porous are completely different from those of conventional methods, so there is no particular restriction on the thermoplastic resin used. Examples of thermoplastic resins used include polyolefins (e.g., high-density polyethylene, polypropylene, poly(4-methyl-pentene-1), etc.), fluorine-containing polymer compounds (e.g., polybunylidene fluoride, ethylene, tetrafluorocarbon, etc.) ethylene copolymers, etc.), and these can be used alone or in combination. Polypropylene is particularly preferred as the thermoplastic resin of the present invention. However, in the present invention, polypropylene is not limited to a homopolymer of propylene, but also includes a homopolymer of propylene, a block copolymer of propylene and other monomers or oligomers, a block copolymer of propylene and other monomers or It contains a random copolymer with an oligomer. There are no restrictions on the other monomers or oligomers listed above as long as they can be copolymerized with propylene.
Examples include ethylene or oligomers derived from ethylene. In the present invention, the expression "polypropylene", which is not particularly limited, is a general term for the various types mentioned above.

Furthermore, the melt viscosity [melt flow index (MFI) or melt index (MI)] of the thermoplastic resin used does not need to be particularly limited as long as it can be formed into a film.
For example, when using polypropylene, considering the efficiency or productivity of film molding,
It is preferable to use one with an MFI of 0.5 to 40 g/10 minutes.

In addition, thermoplastic resins containing additives (materials) such as plasticizers, colorants, flame retardants, and fillers can also be used.

In the present invention, the above thermoplastic resin is first formed into an unstretched thermoplastic resin film according to a known film manufacturing method. Examples of film manufacturing methods that can be used include an inflation film molding method and a T-die film molding method. Molding conditions in such a molding method can be appropriately selected from known techniques. For example, the film forming temperature can be within a range of a temperature higher than the temperature at which the thermoplastic resin used can be discharged and lower than the thermal decomposition temperature of the resin. For example, when polypropylene is used, it is usually 170-300°C, preferably 190-270°C, and when high-density polyethylene is used, it is usually 150-300°C, preferably
160-270℃, poly(4-methyl-pentene-1)
When using ethylene/tetrafluoroethylene copolymer, the temperature is usually 260 to 330°C, preferably 270 to 300°C.
290 to 350℃, preferably 190 to 280℃, usually 190 to 280℃ when polyvinylidene fluoride is used.
The temperature is 300°C, preferably 190-280°C.

Furthermore, there is no particular limitation on the elastic recovery rate (or draft ratio) of the unstretched thermoplastic resin film obtained by molding. However, when an unstretched thermoplastic resin film with an elastic recovery rate (or draft ratio) of zero (%) or extremely low, that is, an unstretched thermoplastic resin film with extremely low crystal orientation, is used, Even when subjected to a stretching process at extremely low temperatures, it may be difficult to impart satisfactory properties to the resulting porous thermoplastic resin film. Therefore, it is preferable to set the molding conditions for the unstretched film in consideration of characteristics such as the porosity and the average diameter of the fine pores of the resulting porous thermoplastic resin film.

As mentioned above, there is no particular limit to the elastic recovery rate of the unstretched thermoplastic resin film, but for the above reasons, the elastic recovery rate of the unstretched thermoplastic resin film expressed by the following formula is
For example, when using polypropylene, the elastic recovery rate at 50% elongation at 25°C and 65% relative humidity is preferably 20% or more. Considering productivity and the like, a range of 30 to 95% is particularly preferable.

Elastic recovery rate (%) = [length when stretched - length after stretching] ÷ [length when stretched - length of original film]
×100 In addition, taking into consideration factors such as the above requirements and productivity, we also determined the draft ratio of the unstretched thermoplastic resin film used in the present invention (the take-up speed of the unstretched thermoplastic resin film and the discharge speed from the nozzle). The ratio (take-up speed/discharge speed) is preferably in the range of 10 to 6000 when polypropylene is used, for example.

The unstretched thermoplastic resin film may be heat treated before being subjected to the stretching process. By performing this heat treatment before stretching, the degree of crystallinity of the unstretched thermoplastic resin film can be increased, so that the properties of the porous thermoplastic resin film obtained by stretching are further improved.

The above heat treatment may cause the unstretched thermoplastic resin film to be
It is carried out by heating for 3 seconds or more in air heated to a temperature 5°C lower.

The stretching step in the present invention is performed in a medium selected from the group consisting of nitrogen, oxygen, argon, carbon monoxide, methane, and ethane, at a stretching temperature of -70°C or lower, and from the freezing point of the medium. It is necessary to conduct the reaction at a temperature that is 50° C. higher than the boiling point of the medium.

In the cryogenic stretching step of the present invention, the above-mentioned media can be used alone or in combination.

Examples of preferred stretching temperatures when using the above media are -209°C to -209°C when nitrogen is used.
Range of 146°C, -218°C to -218°C with oxygen
-132℃ range, when using argon, -
When using carbon monoxide, the range is -205°C to -141°C. When using methane, the range is -182°C to -111°C. When using ethane, the range is 189°C to -140°C. If it is, it is in the range of -183℃ to -70℃. When the stretching temperature is higher than -70° C., for example, when an unstretched film with a low elastic recovery rate is used, the effective rate of formation of pores by stretching becomes low. Note that, in the present invention, the term 50° C. higher than the boiling point or lower does not mean a temperature range that is lower than exactly 50° C. higher than the boiling point, but means a temperature approximately 50° C. higher than the boiling point or lower.

At such extremely low temperatures, the medium becomes liquid,
The medium is in a liquid/gaseous state or a gaseous state, and the stretching process of the present invention can be carried out even if the medium is in any of the above states.

It is presumed that the above-mentioned stretching according to the present invention occurs because a crazing effect appears when the medium is stretched at extremely low temperatures. In ordinary media other than those mentioned above, thermoplastic resin films become glassy at extremely low temperatures and are cut without elongation and no crazing action occurs.

The cryogenic stretching temperature of the present invention is -70°C or lower, from the freezing point to the boiling point of the medium used.
Although stretching can be carried out at a temperature lower than 50°C, it is generally recommended to carry out stretching at a temperature near the boiling point of the low-temperature liquid for manufacturing control and to maintain the properties of the resulting porous thermoplastic resin film. It is also advantageous in terms of

The stretching ratio in the above-mentioned cryogenic stretching process is generally 1 to 1 for the unstretched thermoplastic resin film.
The value is in the range of 200%. However, the preferred stretching ratio is in the range of 10 to 150%. At stretch ratios within these ranges, the number of through holes tends to increase as the stretch ratio increases, and by utilizing this tendency,
It is also possible to adjust the average pore diameter and porosity of the resulting porous thermoplastic resin film depending on the purpose.

The cryogenic stretching process described above can be repeated two or more times until the desired average pore diameter and porosity are obtained.

Unlike the conventional stretching process near room temperature, the thermoplastic resin film is made porous by using a stretching process under cooling at an extremely low temperature in a specific medium of the present invention. It works effectively even on thermoplastic resin films whose elastic recovery rate from strain is less than 40%, and the pores are uniform.
Moreover, an excellent porous thermoplastic resin film with high porosity can be obtained.

The thermoplastic resin film, which has been made porous through a stretching process at an extremely low temperature in the above-mentioned specific medium, is then
Preferably, it is subjected to a heat setting treatment. The main purpose of this heat setting treatment is heat setting to maintain the formed fine holes. This heat-setting process is performed by heating a porous thermoplastic resin film while maintaining its stretched state at an extremely low temperature in air heated to a temperature 20 to 5 degrees Celsius lower than the melting temperature of the thermoplastic resin used for at least 3 seconds. This is carried out by a method such as heating. The specific heating temperature is, for example,
When using polypropylene, usually
110-165℃, preferably 130-155℃, usually 70-125℃ when using high-density polyethylene
℃, preferably 80-120℃, poly(4-methyl-
When using pentene-1), usually
150-210℃, preferably 160-200℃, ethylene-
When using a tetrafluoroethylene copolymer, the temperature is usually 180 to 240°C, preferably 200 to 230°C.
°C, when using polyvinylidene fluoride,
Usually the temperature is 100 to 165°C, preferably 110 to 160°C. In addition, if the heating temperature is significantly higher than the upper limit of the listed temperature, the formed micropores may close, and if the heating temperature is significantly lower than the lower limit,
Alternatively, if the heating time is shorter than 3 seconds, heat fixation tends to be insufficient, the formed through holes may close later, and heat shrinkage tends to occur due to temperature changes during use. The cryogenic stretching and heat setting treatments described above can be repeated until a desired average pore diameter and porosity are obtained. That is, the temperature of the film can be returned to room temperature and subjected to a process including repeated cryogenic stretching (and heat setting treatment). By repeatedly performing cryogenic stretching, the number of through holes formed can be increased, and the average through hole diameter can be increased.

The porous thermoplastic resin film prepared as described above has a large average pore diameter and a high porosity and exhibits good properties. By applying it, its characteristics are further improved.

The hot stretching process of the thermoplastic resin film, which has been rendered porous through at least one stretching process at a cryogenic temperature, is carried out as follows. This hot stretching process is carried out mainly for the purpose of expanding the diameter of the fine holes formed at extremely low temperatures. This hot stretching process stretches the porous thermoplastic resin film below the melting temperature of the thermoplastic resin.
It is carried out by stretching in air heated to a temperature 90 to 5°C lower. For example, when using polypropylene film, increase the heating temperature to 80°C.
~160°C, preferably 110-155°C, typically 70-125°C when using high-density polyethylene,
Preferably from 80 to 120°C, and when poly(4-methyl-pentene-1) is used, usually from 150 to 120°C.
210°C, preferably 160-200°C, and when using ethylene-tetrafluoroethylene copolymer, usually 180-240°C, preferably 200-230°C
°C, when using polyvinylidene fluoride,
The temperature is usually set at 100 to 165°C, preferably 110 to 160°C. Note that if the heating temperature is higher than the upper limit of the above temperature, the formed micropores may close, and if the temperature is lower than the lower limit, the expansion of the pore diameter by stretching may be insufficient. There is.

The stretching ratio in this hot stretching process is usually 10 to 700%, preferably 50% to the film length (initial length) before being subjected to the cryogenic stretching process.
~550%. If the stretching ratio is lower than 10%, the expansion of the through holes may be insufficient;
If the temperature is higher, the film may be cut.

Note that this hot stretching step is performed alternately with the above-mentioned cryogenic stretching step, or after completing at least one cryogenic stretching step.

The film made porous by this stretching process is desirably subjected to a heat setting process between the stretching processes. The main purpose of this heat setting treatment is to heat set the through holes formed through the hot stretching process.

This heat-setting treatment is usually carried out by holding the porous thermoplastic resin film in the air for 3 seconds or more while maintaining its stretched state, at a temperature higher than the melting temperature of the thermoplastic resin used.
This is carried out by heating to a temperature 20 to 5 degrees Celsius lower. The specific heating temperature is, for example, usually 110 to 165°C, preferably 130 to 155°C when using polypropylene, and usually 70 to 125°C, preferably 80 to 120°C when using high density polyethylene.
℃, when poly(4-methyl-pentene-1) is used, usually 150 to 210℃, preferably 160 to 200℃
℃, usually 180 to 240℃ when using ethylene/tetrafluoroethylene copolymer, preferably
200-230℃, when polyvinylidene fluoride is used, usually 100-165℃, preferably 110-165℃
The temperature is 160℃.

It is desirable that this heat setting treatment be performed in the same manner on the film that has undergone all the stretching steps.

If the heating temperature is higher than the above upper limit temperature, the formed through holes may be closed. In addition, if the temperature is lower than the above lower limit temperature or the heating time is shorter than 3 seconds, heat fixation is likely to be insufficient, and the through holes will close later.
Furthermore, thermal shrinkage is likely to occur due to temperature changes during use.

Next, Examples and Comparative Examples of the present invention will be shown.

In addition, the water permeability shown in the following examples and comparative examples was determined according to the method specified in ASTM-F317.
The obtained porous film is made hydrophilic by immersing it in alcohol and a surfactant, and this hydrophilized porous film is mounted on a predetermined holder, and one side of the film is marked with the thickness of the film. It was determined by applying pressure in the direction and measuring the amount of water per unit time that permeated from the pressurized side of the film to the other side.

[Example 1] Polypropylene (product name: UBE-PP-J105G,
Made by Ube Industries, Ltd., MFI = 5g/10 minutes), diameter 50mm,
An unstretched polypropylene film was molded using an inflation molding machine equipped with an inflation molding die with a slit gap of 0.7 mm. In the molding operation, polypropylene is discharged while blowing air into a valve at a resin discharge temperature of 210°C and a blow ratio of 0.7, and room temperature air is blown onto the outer wall of the discharged film at a position 5 cm above the die. The mixture was soaked and cooled, and then taken off with a nip roll at a take-off speed of 36 m/min at a position 1.8 m above the die to form the desired unstretched polypropylene film.

The thickness of the obtained unstretched film was 10 μm. Furthermore, the elastic recovery rate of this film after 50% stretching was 31%.

This unstretched film was stretched by 10% of its initial length in liquid nitrogen (-195°C), and while maintaining this stretched state, it was heat-set in a heated air bath at 145°C for 10 minutes. . After heat setting, the stretched length is further stretched by 10% in liquid nitrogen.
While maintaining this stretched state, it was placed in an air bath at 145℃ for 10 days.
A porous polypropylene film was produced by heat setting for a minute.

The obtained porous polypropylene film was subjected to mercury intrusion method (measurement was carried out by CARLOERBA (Italy)).
This was done using POROSIMETRO SERIES 1500 manufactured by Manufacturer. The average pore diameter measured by
The diameter was 0.05 μm, and the porosity was 15.10%. The water permeability was 2.30 l/m ² ·min ·atmospheric pressure.

The surface and cross section of this porous polypropylene film were examined using a scanning electron microscope (manufactured by Hitachi, Ltd.: X-
650 (hereinafter the same), it was found that pores were formed almost uniformly on the surface of the film, and the pore diameters were also almost uniform over the entire surface. Further, when the cross section of this film was observed, it was confirmed that most of the holes formed were through holes that penetrated from one surface to the other surface.

[Comparative Example 1] Using the same apparatus as in Example 1, an unstretched polypropylene film was molded. The polypropylene used and the molding conditions are as follows.

Polypropylene UBE-PP-Y101J (Ube Industries, Ltd.)
MFI = 5 g/10 min Resin discharge temperature 210°C Take-up speed 36 m/min Blow ratio 0.70 The thickness of the obtained unstretched film was 10 μm. Furthermore, the elastic recovery rate of this film after 50% stretching was 31%.

Using this unstretched polypropylene film, stretching and heat setting were carried out in the same manner as in Example 1, except that instead of stretching in liquid nitrogen, stretching was carried out in air at room temperature (25°C). Ta.

When the surface and cross section of the obtained film were observed using a scanning microscope, no holes were found on the surface. Further, no evidence of hole formation was observed in the cross section.

[Example 2] Using the same apparatus as in Example 1, an unstretched polypropylene film was molded. The polypropylene used and the molding conditions are as follows.

Polypropylene UBE-PP-Y101J (Ube Industries, Ltd.)
MFI=1 g/10 min Resin discharge temperature 230°C Take-up speed 20 m/min Blow ratio 0.70 The thickness of the obtained unstretched film was 20 μm. Furthermore, the elastic recovery rate of this film after 50% stretching was 38%.

Using this unstretched polypropylene, a porous polypropylene film was produced in the same manner as in Example 1, except that stretching in liquid nitrogen and heat setting were repeated 16 times.

The average pore diameter of this porous polypropylene film measured by mercury intrusion method was 0.13μm, and the porosity was 50.2%.
It was hot. The water permeability was 6.50 l/m ² ·min ·atmospheric pressure.

When the surface and cross section of this porous polypropylene film were observed using a scanning electron microscope,
Holes are formed almost uniformly on the film surface,
The pore diameter was almost uniform throughout. Also,
When the cross section of this film was observed, it was confirmed that most of the holes formed were through holes that penetrated from one surface to the other surface.

[Example 3] Using the same apparatus as in Example 1, an unstretched polypropylene film was molded. The polypropylene used and the molding conditions are as follows.

Polypropylene UBE-PP-Y101J (Ube Industries, Ltd.)
MFI = 1 g/10 min Resin discharge temperature 210°C Take-up speed 36 m/min Blow ratio 0.70 The thickness of the obtained unstretched film was 10 μm. The elastic recovery rate of this film from 50% stretching is
It was 80%.

This film was stretched in liquid nitrogen and heat-set in the same manner as in Example 1, and then stretched in liquid nitrogen to the length in an air bath heated to 145°C. Stretched by 180%, and held at 145°C while maintaining this stretched state.
A porous polypropylene film was produced by heat setting in a heated air bath for 10 minutes.

The average pore diameter of the resulting porous polypropylene film measured by mercury intrusion method was 0.12 μm, and the porosity was 51.20%. In addition, the water permeability is 15.96l/ ^m2・
It was hot in minutes and atmospheric pressure.

When the surface and cross section of this porous polypropylene film were observed using a scanning electron microscope,
Holes are formed almost uniformly on the film surface,
The pore diameter was also almost uniform throughout. Also,
When the cross section of this film was observed, it was confirmed that most of the holes formed were through holes that penetrated from one surface to the other surface.

[Example 4] Using the same apparatus as in Example 1, an unstretched polypropylene film was molded. The polypropylene used and the molding conditions are as follows.

Polypropylene UBE-PP-Y101J (Ube Industries, Ltd.)
MFI = 1 g/10 min Resin discharge temperature 230°C Take-up speed 20 m/min Blow ratio 0.70 The thickness of the obtained unstretched film was 20 μm. Furthermore, the elastic recovery rate of this film after 50% stretching was 38%.

Using this film, stretching and heat setting, hot stretching, and heat setting were performed in the same manner as in Example 3, except that liquid nitrogen was replaced with argon and the stretching temperature was -180°C to produce a porous polypropylene film. did.

The average pore diameter of the resulting porous polypropylene film measured by mercury intrusion method was 0.13 μm, and the porosity was 53.20%. Also, the water permeability is 6.05l/ ^m2・
It was hot in minutes and atmospheric pressure.

When the surface and cross section of this porous polypropylene film were observed using a scanning electron microscope,
Holes are formed almost uniformly on the film surface,
The pore diameter was also almost uniform throughout. Also,
When the cross section of this film was observed, it was confirmed that most of the holes formed were through holes that penetrated from one surface to the other surface.

[Comparative Example 2] Using the same apparatus as in Example 1, an unstretched polypropylene film was molded. The polypropylene used and the molding conditions are as follows.

Polypropylene UBE-PP-Y101J (Ube Industries, Ltd.)
MFI = 1 g/10 min Resin discharge temperature 210°C Take-up speed 36 m/min Blow ratio 0.70 The thickness of the obtained unstretched film was 10 μm. The elastic recovery rate of this film from 50% stretching is
It was 80%.

Instead of stretching this film in liquid nitrogen in Example 1, an attempt was made to stretch the film at -195 DEG C. using helium gas, but the film was immediately cut and stretching could not be carried out.

[Comparative Example 3] Using the same apparatus as in Example 1, an unstretched polypropylene film was molded. The polypropylene used and the molding conditions are as follows.

Polypropylene UBE-PP-Y101J (Ube Industries, Ltd.)
MFI = 1 g/10 min Resin discharge temperature 210°C Take-up speed 36 m/min Blow ratio 0.70 The thickness of the obtained unstretched film was 10 μm. Moreover, the elastic recovery rate of this film after 50% stretching was 80%.

An attempt was made to stretch this film in air cooled to -60 DEG C. instead of stretching in liquid nitrogen as in Example 1, but the film was immediately cut and stretching could not be carried out.

[Example 5] Using the same apparatus as in Example 1, an unstretched polypropylene film was molded. The polypropylene used and the molding conditions are as follows.

Polypropylene UBE-PP-Y101J (Ube Industries, Ltd.)
MFI=1 g/10 min Resin discharge temperature 230°C Take-up speed 20 m/min Blow ratio 0.70 The thickness of the obtained unstretched film was 11 μm since the resin discharge amount was changed from Example 2. Also, the elastic recovery rate of this film from 50% stretching is
It was 32%.

Using this film, stretching in liquid nitrogen, heat setting, heat stretching, and heat setting were performed in the same manner as in Example 3 to produce a porous polypropylene film.

The average pore diameter of the resulting porous polypropylene film measured by mercury intrusion method was 0.59 μm, and the porosity was 19.40%. The water permeability was 5.67 l/m ² ·min ·atmospheric pressure.

When the surface and cross section of this porous polypropylene film were observed using a scanning electron microscope,
Holes are formed almost uniformly on the film surface,
The pore diameter was also almost uniform throughout. Also,
When the cross section of this film was observed, it was confirmed that most of the holes formed were through holes that penetrated from one surface to the other surface.

[Comparative Example 4] Using the same apparatus as in Example 1, an unstretched polypropylene film was molded. The polypropylene used and the molding conditions are as follows.

Polypropylene UBE-PP-Y101J (Ube Industries, Ltd.)
MFI = 1 g/10 min Resin discharge temperature 230°C Take-up speed 20 m/min Blow ratio 0.70 The thickness of the obtained unstretched film was the same as in Example 5, and the resin discharge amount was changed from Example 2. So
It was 11 μm. Furthermore, the elastic recovery rate of this film after 50% stretching was 32%.

Using this unstretched polypropylene film,
A stretched polypropylene film was obtained by carrying out stretching and heat setting in the same manner as in Example 3, except that instead of stretching in liquid nitrogen, stretching was carried out in air at room temperature (25°C).

An attempt was made to measure the average pore diameter and porosity of the obtained stretched polypropylene film, but it was not possible. However, the water permeability showed a value of 0.02 l/m ² ·min ·atmospheric pressure.

When the surface and cross section of this stretched film were observed with a scanning microscope, no holes were formed on the surface within the observed range. Similarly, no evidence of hole formation was observed in the cross section.

[Example 6] Using the same apparatus as in Example 1, an unstretched polypropylene film was molded. The polypropylene used and the molding conditions are as follows.

Polypropylene UBE-PP-Y101J (Ube Industries, Ltd.)
MFI = 1 g/10 min Resin discharge temperature 210°C Take-up speed 36 m/min Blow ratio 0.70 The thickness of the obtained unstretched film was 10 μm. Moreover, the elastic recovery rate of this film after 50% stretching was 80%.

The obtained film was heat-treated at 145° C. for 10 minutes without tension. The elastic recovery rate of the obtained film was improved to 87%.

Using this film, stretching in liquid nitrogen, heat setting, heat stretching, and heat setting were performed in the same manner as in Example 3 to produce a porous polypropylene film.

The average pore diameter of the resulting porous polypropylene film measured by mercury intrusion method was 0.14 μm, and the porosity was 54.60%. In addition, the water permeability is 23.18l/ ^m2・
It was hot in minutes and atmospheric pressure.

When the surface and cross section of this porous polypropylene film were observed using a scanning electron microscope,
Holes are formed almost uniformly on the film surface,
The pore diameter was also almost uniform throughout. Also,
When the cross section of this film was observed, it was confirmed that most of the holes formed were through holes that penetrated from one surface to the other surface.

[Comparative Example 5] Using the same apparatus as in Example 1, an unstretched polypropylene film was molded. The polypropylene used and the molding conditions are as follows.

Polypropylene UBE-PP-Y101J (Ube Industries, Ltd.)
MFI = 1 g/10 min Resin discharge temperature 210°C Take-up speed 36 m/min Blow ratio 0.70 The thickness of the obtained unstretched film was 10 μm. Moreover, the elastic recovery rate of this film after 50% stretching was 80%.

The obtained film was heat-treated at 145° C. for 10 minutes without tension. The elastic recovery rate of the obtained film was improved to 87%.

This film was stretched and heat-set in the same manner as in Example 3, except that the stretching in liquid nitrogen was replaced by stretching in air (25° C.) to produce a porous polypropylene film.

The average pore diameter of the resulting porous polypropylene film measured by mercury intrusion method was 0.07 μm, and the porosity was 41.50%. Also, the water permeability is 6.66l/ ^m2・
It was hot in minutes and atmospheric pressure.

Although the unstretched polypropylene used was the same as that used in Example 6, the average pore diameter, porosity, and water permeability of the obtained porous film were the same as those obtained in Example 6. The value was lower than that of quality polypropylene film. Furthermore, when the surface and cross section of the obtained porous polypropylene film were observed using a scanning electron microscope, it was found that pores were formed on the film surface, but when the cross section of the film was observed, pores penetrated from one surface to the other. There were fewer through holes compared to the film obtained in Example 6.

[Example 7] Using the same apparatus as in Example 1, an unstretched polypropylene film was molded. The polypropylene used and the molding conditions are as follows.

Polypropylene UBE-PP-Y101J (Ube Industries, Ltd.)
MFI = 1 g/10 min Resin discharge temperature 210°C Take-up speed 36 m/min Blow ratio 0.70 The thickness of the obtained unstretched film was 10 μm. Moreover, the elastic recovery rate of this film after 50% stretching was 80%.

Using this film, stretching and heat setting were carried out in the same manner as in Example 1, except that the stretching was carried out in liquid nitrogen at a stretching ratio of 20%.

This film was stretched in a heated air tank at 145°C to 160% of the length stretched in liquid nitrogen, and while maintaining this stretched state, it was heat-set in a heated air tank at 145°C for 10 minutes. A porous polypropylene film was prepared.

The average pore diameter of the resulting porous polypropylene film measured by mercury intrusion method was 0.14 μm, and the porosity was 56.00%. In addition, the water permeability is 17.30l/ ^m2・
It was hot in minutes and atmospheric pressure.

When the surface and cross section of this porous polypropylene film were observed using a scanning electron microscope,
Holes are formed almost uniformly on the film surface,
The pore diameter was also almost uniform throughout. Also,
When the cross section of this film was observed, it was confirmed that most of the holes formed were through holes that penetrated from one surface to the other surface.

[Example 8] Using the same apparatus as in Example 1, an unstretched polypropylene film was molded. The polypropylene used and the molding conditions are as follows.

Polypropylene UBE-PP-Y130G (Ube Industries)
Co., Ltd.) MFI = 30 g/10 min Resin discharge temperature 170°C Take-up speed 36 m/min Blow ratio 0.70 The thickness of the obtained unstretched film was 20 μm. Further, the elastic recovery rate of this film after 50% stretching was 30%.

The obtained film was heat-treated at 145° C. for 10 minutes without tension. The elastic recovery rate of the obtained film was improved to 72%.

This film was stretched in liquid nitrogen and heat-set in the same manner as in Example 1.

This film was stretched in a heated air tank at 145°C to 330% of the length stretched in liquid nitrogen, and while maintaining this stretched state, it was heat-set in a heated air tank at 145°C for 10 minutes. A porous polypropylene film was produced.

The average pore diameter of the resulting porous polypropylene film measured by mercury intrusion method was 0.98 μm, and the porosity was 65.30%. Also, the water permeability is 59.00l/
The temperature was ^m2・min・atmospheric pressure.

When the surface and cross section of this porous polypropylene film were observed using a scanning electron microscope,
Holes are formed almost uniformly on the film surface,
The pore diameter was also almost uniform throughout. Also,
When the cross section of this film was observed, it was confirmed that most of the holes formed were through holes that penetrated from one surface to the other surface.

[Example 9] Using the same apparatus as in Example 1, an unstretched polypropylene film was molded. The polypropylene used and the molding conditions are as follows.

Polypropylene UBE-PP-Y130G (Ube Industries)
Co., Ltd.) MFI = 30 g/10 min Resin discharge temperature 170°C Take-up speed 36 m/min Blow ratio 0.70 The thickness of the obtained unstretched film was 20 μm. Further, the elastic recovery rate of this film after 50% stretching was 30%.

The obtained film was heat-treated at 145° C. for 10 minutes without tension. The elastic recovery rate of the obtained film was improved to 72%.

Using this film, stretching in liquid nitrogen, heat setting, and hot stretching were performed in the same manner as in Example 3 to produce a porous polypropylene film.

The average pore diameter of the resulting porous polypropylene film measured by mercury intrusion method was 0.75 μm, and the porosity was 59.60%. In addition, the water permeability is 22.00l/ ^m2・
It was hot in minutes and atmospheric pressure.

When the surface and cross section of this porous polypropylene film were observed using a scanning electron microscope,
Holes are formed almost uniformly on the film surface,
The pore diameter was also almost uniform throughout. Also,
When the cross section of this film was observed, it was confirmed that most of the holes formed were through holes that penetrated from one surface to the other surface.

[Example 10] Using the same apparatus as in Example 1, an unstretched polypropylene film was molded. The polypropylene used and the molding conditions are as follows.

Polypropylene UBE-PP-Y130G (Ube Industries)
Co., Ltd.) MFI = 30 g/10 min Resin discharge temperature 170°C Take-up speed 36 m/min Blow ratio 0.70 The thickness of the obtained unstretched film was 20 μm. Further, the elastic recovery rate of this film after 50% stretching was 30%.

The obtained film was heat-treated at 145° C. for 10 minutes without tension. The elastic recovery rate of the obtained film was improved to 72%.

Using this film, the stretching rate in liquid nitrogen was
A porous polypropylene film was produced by carrying out stretching, heat setting, and hot stretching in the same manner as in Example 3, except that the polypropylene film was stretched by 20% and stretched once.

The average pore diameter of the resulting porous polypropylene film measured by mercury intrusion method was 0.70 μm, and the porosity was 57.20%. Also, the water permeability is 21.00l/ ^m2・
It was hot in minutes and atmospheric pressure.

When the surface and cross section of this porous polypropylene film were observed using a scanning electron microscope,
Holes are formed almost uniformly on the film surface,
The pore diameter was also almost uniform throughout. Also,
When the cross section of this film was observed, it was confirmed that most of the holes formed were through holes that penetrated from one surface to the other surface.

[Example 11] Using the same apparatus as in Example 1, an unstretched polypropylene film was molded. The polypropylene used and the molding conditions are as follows.

Polypropylene UBE-PP-Y109K (Ube Industries)
Co., Ltd.) MFI = 9 g/10 min Resin discharge temperature 200°C Take-up speed 36 m/min Blow ratio 0.70 The thickness of the obtained unstretched film was 20 μm. The elastic recovery rate of this film after 50% stretching was 41%.

The obtained film was heat-treated at 145° C. for 10 minutes without tension. The elastic recovery rate of the obtained film was improved to 73%.

Using this film, stretching in liquid nitrogen, heat setting, and hot stretching were performed in the same manner as in Example 3 to produce a porous polypropylene film.

The average pore diameter of the resulting porous polypropylene film measured by mercury intrusion method was 0.53 μm, and the porosity was 60.80%. The water permeability was 22.50 l/m ² ·min ·atmospheric pressure.

When the surface and cross section of this porous polypropylene film were observed using a scanning electron microscope,
Holes are formed almost uniformly on the film surface,
The pore diameter was also almost uniform throughout. Also,
When the cross section of this film was observed, it was confirmed that most of the holes formed were through holes that penetrated from one surface to the other surface.

Claims (1)

[Scope of Claims] 1. A method for producing a porous thermoplastic resin film, which includes a step of forming a large number of fine pores in a thermoplastic resin film by stretching the film, wherein the stretching step is performed using nitrogen, oxygen, In a medium selected from the group consisting of argon, carbon monoxide, methane and ethane, and the stretching temperature is -70°C or less, and the temperature is from the freezing point of the medium to 50°C higher than the boiling point of the medium. A method for producing a porous thermoplastic resin film, characterized in that it is carried out within the following range. 2. The method for producing a porous thermoplastic resin film according to claim 1, wherein the stretching step under cooling is repeated two or more times. 3. Claims characterized in that during the stretching process and after the final stretching process, the thermoplastic resin film is heat-set at a temperature 20 to 5°C lower than the melting temperature of the thermoplastic resin. 2. The method for producing a porous thermoplastic resin film according to item 2. 4. The method for producing a porous thermoplastic resin film according to any one of claims 1 to 3, wherein the thermoplastic resin is polypropylene. 5. A method for producing a porous thermoplastic resin film including a step of forming a large number of fine pores in the film by stretching the thermoplastic resin film, in which the stretching step comprises: () nitrogen, oxygen, argon; , in a medium selected from the group consisting of carbon monoxide, methane, and ethane, and the stretching temperature is -70°C or less, and the temperature is 50°C from the freezing point of the medium to the boiling point of the medium.
a step of stretching at a temperature below a high temperature; and () a step of hot stretching the film at a temperature 90 to 5° C. lower than the melting temperature of the thermoplastic resin after the stretching step at a cryogenic temperature; A method for producing a porous thermoplastic resin film comprising: 6. The method for producing a porous thermoplastic resin film according to claim 5, wherein the stretching step under cooling and the hot stretching step are each repeated two or more times. 7. A patent claim characterized in that the thermoplastic resin film is heat-set between each stretching process and after the final stretching process at a temperature 20 to 5°C lower than the melting temperature of the thermoplastic resin. A method for producing a porous thermoplastic resin film according to item 5 or 6. 8. The method for producing a porous thermoplastic resin film according to claim 5 or 6, wherein the thermoplastic resin is polypropylene.