JP2010172832A - Microporous film of crystalline polymer, method of producing the same, and filter for use in filtration - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a microporous film of a crystalline polymer with uniform mean pore-diameter distribution in a plane, capable of catching particles without allowing them to leak even upon using the same of a large area, free of clogging, having a high flow capacity, and having a long filtration life, a method of efficiently producing a microporous film of a crystalline polymer, and a filter for use in filtration that employs the microporous film of a crystalline polymer. <P>SOLUTION: The method of producing a microporous film of a crystalline polymer includes an asymmetrical heating process of heating one surface of an immobilized film made of a crystalline polymer using a heating means at a temperature not lower than the melting point of the calcined crystalline polymer while maintaining the film in a contactless state relative to the heating means to produce a half-calcined film wherein a temperature gradient is formed in the direction of the thickness of the film, and a stretching process of stretching the half calcined film. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a crystalline polymer microporous membrane having high filtration efficiency used for microfiltration of gas, liquid, etc., a method for producing the crystalline polymer microporous membrane, and a filter for filtration.

Microporous membranes have been known for a long time, and are widely used for filtration filters and the like (see Non-Patent Document 1). Examples of such a microporous membrane include those manufactured using cellulose ester as a raw material (see Patent Document 1 etc.), those manufactured using aliphatic polyamide as a raw material (see Patent Document 2 etc.), and polyfluorocarbon as a raw material. And the like (see Patent Document 3 etc.) and those made from polypropylene (see Patent Document 4).
These microporous membranes are used for filtration and sterilization of electronic industrial cleaning water, pharmaceutical water, pharmaceutical manufacturing process water, food water, and the like. Therefore, highly reliable microporous membranes are attracting attention. Among these, a microporous film made of a crystalline polymer is excellent in chemical resistance, and in particular, a microporous film made of polytetrafluoroethylene (PTFE) is excellent in heat resistance and chemical resistance. The demand growth is remarkable.

  Further, in Patent Document 5, in the manufacturing process of the PTFE porous membrane, by applying a compressive stress to the PTFE preform in a direction orthogonal to the direction of extruding and / or rolling the PTFE preform, the haze value is obtained. There has been proposed a PTFE porous membrane having a variation expressed by a variation rate of 20% or less. According to this proposal, the microporous structure of the PTFE porous membrane can be made uniform. However, the proposed PTFE porous membrane has a problem that it is not satisfactory in terms of flow rate and filtration life.

  Patent Document 6 discloses that the tape is stretched uniaxially at a temperature lower than the crystal melting point of the polytetrafluoroethylene component, and is increased by increasing the temperature of the tape to a temperature higher than the crystal melting point of the polytetrafluoroethylene component. There has been proposed a method for producing a porous polytetrafluoroethylene article comprising a step of fixing an amorphous tape and stretching in a direction perpendicular to the original stretching direction at a temperature exceeding the crystalline melting point of the polytetrafluoroethylene component. According to this proposal, the filtration flow rate can be increased. However, the above proposal has a problem that the filterable amount per unit area of the microporous membrane is reduced (that is, the filtration life is short).

Patent Document 7 proposes a method for producing a crystalline polymer microporous film including a semi-baking step in which thermal energy is applied to the surface of an unfired film and a temperature gradient is formed in the thickness direction of the film. . According to this proposal, multistage filtration is possible due to the asymmetric structure of the micropores, and the filtration life of the microporous membrane can be extended. However, in the proposed method for producing a microporous membrane, heating unevenness occurs, and as a result, the in-plane distribution of the average pore diameter of the obtained microporous membrane varies, and the small area (0.04 m ² or less) In the case of, there is almost no problem, but in the case of a large area (greater than 0.04 m ² ), there is a problem that particle leakage may occur.

  Therefore, the in-plane distribution of the average pore diameter is uniform, and even when used in a large area, particles can be captured without leakage, clogging, high flow rate, and long filtration life. There is a strong demand for further improvement and development of a polymer microporous membrane and a method for producing a crystalline polymer microporous membrane capable of efficiently producing the crystalline polymer microporous membrane. .

US Pat. No. 1,421,341 US Pat. No. 2,783,894 US Pat. No. 4,196,070 West German Patent No. 3,003,400 JP 2002-172316 A Japanese National Patent Publication No. 11-515036 JP 2007-332342 A

Published by R. Kesting “Synthetic Polymer Membrane”, McGraw Hill (McGrawHill)

  An object of the present invention is to solve the above-described problems and achieve the following objects. That is, the present invention has a uniform average pore diameter distribution, can capture particles without leakage even when used in a large area, has no clogging, has a high flow rate, and has a filtration life. Crystalline polymer microporous membrane having a long length, a method for producing a crystalline polymer microporous membrane capable of efficiently producing the crystalline polymer microporous membrane, and the crystalline polymer microporous membrane An object is to provide a filter for filtration.

Means for solving the problems are as follows. That is,
<1> One surface of a fixed film made of a crystalline polymer is heated by a heating means at a temperature equal to or higher than the melting point of the sintered body of the crystalline polymer in a non-contact state with the heating means, An asymmetric heating step of forming a semi-baked film having a temperature gradient in the thickness direction of the film;
A stretching step of stretching the semi-baked film;
It is a manufacturing method of the crystalline polymer microporous film | membrane characterized by including this.
In the method for producing a crystalline polymer microporous membrane according to <1>, a film made of a crystalline polymer is heated in the asymmetric heating step, and a semi-baked film having a temperature gradient in the thickness direction of the film is obtained. It is formed. At this time, since the film made of the crystalline polymer is heated and semi-baked in a fixed state, the film is heated and semi-fired without any unevenness in the surface. In the stretching step, the semi-baked film is stretched. As a result, a crystalline polymer microporous membrane having a uniform in-plane distribution of average pore diameter can be obtained.
<2> The method for producing a crystalline polymer microporous film according to <1>, wherein one whole surface of the film made of the crystalline polymer is fixed.
<3> In the film made of a crystalline polymer, the surface opposite to the surface heated by the heating means is fixed by a fixing means, and the fixing means has a plurality of holes formed on the surface, and the inside from the surface. The method for producing a crystalline polymer microporous membrane according to any one of <1> to <2>, wherein the crystalline polymer microporous membrane is any one of a belt and a roll that can be sucked together.
<4> The method for producing a crystalline polymer microporous membrane according to any one of <1> to <3>, wherein the crystalline polymer is polytetrafluoroethylene.
<5> The method for producing a crystalline polymer microporous membrane according to any one of <1> to <4>, wherein the stretching step stretches the semi-fired film in a uniaxial direction.
<6> The method for producing a crystalline polymer microporous film according to any one of <1> to <5>, wherein the stretching step stretches the semi-fired film in a biaxial direction.
<7> The method for producing a crystalline polymer microporous membrane according to any one of <1> to <6>, further including a hydrophilization step of hydrophilizing the stretched film.
<8> Manufactured by the method for producing a crystalline polymer microporous membrane according to any one of <1> to <7>, wherein an average pore diameter of one surface is larger than an average pore diameter of the other surface, and The crystalline polymer microporous membrane is characterized in that an average pore diameter continuously changes from the one surface to the other surface.
The crystalline polymer microporous membrane according to <8> is produced by the method for producing a crystalline polymer microporous membrane according to any one of <1> to <7>, and an average pore diameter on one surface However, since the average pore diameter is larger than the average pore diameter of the other surface and the average pore diameter continuously changes from the one surface to the other surface, the in-plane distribution of the average pore diameter is uniform and has a large area. Even when it is used in the process, particles can be captured without leakage, clogging is not caused, the flow rate is high, and the filtration life is long. Therefore, it is suitable for filtering a large amount of liquid industrially.
<9> The thickness of the crystalline polymer microporous film is X, the average pore diameter in the thickness portion in the depth direction X / 10 from the non-heated surface is P1, and the average pore diameter in the thickness portion in the depth direction 9X / 10 The crystalline polymer microporous membrane according to <8>, wherein P1 / P2 is 4.5 or more, where is P2.
<10> The crystalline polymer microporous membrane according to any one of <8> to <9>, wherein the in-plane variation of the average pore diameter is 20% or less.
<11> The crystalline polymer microporous membrane according to any one of <8> to <10>, wherein the area is greater than 0.04 m ² .
<12> A filtration filter using the crystalline polymer microporous membrane according to any one of <8> to <11>.
The filter for filtration according to <12> uses the crystalline polymer microporous film according to any one of <8> to <11>, so that even when used in a large area, the particles Can be captured without leakage, and fine particles can be captured efficiently. In addition, since the specific surface area is large, the effect of removing fine particles by adsorption or adhesion before reaching the minimum pore diameter portion is great, and the filtration life can be greatly improved.
<13> The filtration filter according to <12>, wherein the filter is processed into a pleated shape.
<14> The filter for filtration according to any one of <12> to <13>, wherein a surface side of the crystalline polymer microporous membrane having a large average pore diameter is used as a filter surface of the filter.

  According to the present invention, the above-described problems can be solved and the above-mentioned object can be achieved, the in-plane distribution of the average pore diameter is uniform, and the particles do not leak even when used in a large area. Crystalline polymer microporous membrane that can be captured, has no clogging, has a high flow rate, and has a long filtration life, and crystalline polymer microporous membrane that can efficiently produce the crystalline polymer microporous membrane And a filter for filtration using the crystalline polymer microporous membrane can be provided.

FIG. 1 is a diagram illustrating a structure of a general pleated filter element before being assembled in a housing. FIG. 2 is a view showing the structure of a general filter element before being assembled into the housing of the capsule filter cartridge. FIG. 3 is a view showing the structure of a general capsule filter cartridge integrated with a housing. FIG. 4 is a diagram illustrating the single-sided heating device according to the first embodiment. FIG. 5 is a diagram illustrating a single-sided heating apparatus according to the second embodiment.

(Crystalline polymer microporous membrane and method for producing crystalline polymer microporous membrane)
The method for producing a crystalline polymer microporous membrane of the present invention includes at least an asymmetric heating step and a stretching step, and further includes other steps such as a crystalline polymer film preparation step and a hydrophilization step as necessary. .
The crystalline polymer microporous membrane of the present invention is produced by the method for producing a crystalline polymer microporous membrane of the present invention.
Hereinafter, the details of the crystalline polymer microporous membrane of the present invention will be clarified through the description of the method for producing the crystalline polymer microporous membrane of the present invention.

  In the following description, a surface having a larger average pore diameter is referred to as a “non-heated surface”, and a surface having a smaller average pore diameter is referred to as a “heating surface”. This is merely a name given for convenience in order to make the description of the present invention easier to understand. Therefore, any surface of the unsintered crystalline polymer film may be heated to become a “heating surface” after semi-sintering.

<Crystalline polymer film production process>
The crystalline polymer film production step is a step of producing a film made of a crystalline polymer.

-Crystalline polymer-
In the present invention, the “crystalline polymer” means a polymer in which a crystalline region in which long chain molecules are regularly arranged in a molecular structure and an amorphous region that is not regularly arranged are mixed. Such polymers exhibit crystallinity by physical treatment. For example, when a polyethylene film is stretched by an external force, a phenomenon in which a transparent film becomes cloudy at first is recognized. This is because the crystallinity is expressed by aligning the molecular arrangement in the polymer in one direction by an external force.

There is no restriction | limiting in particular as said crystalline polymer, According to the objective, it can select suitably, For example, polyalkylene, polyester, polyamide, polyether, a liquid crystalline polymer etc. are mentioned. Specifically, polyethylene, polypropylene, nylon, polyacetal, polybutylene terephthalate, polyethylene terephthalate, syndiotactic polystyrene, polyphenylene sulfide, polyether ether ketone, wholly aromatic polyamide, wholly aromatic polyester, fluororesin, polyether nitrile , Etc.
Among these, from the viewpoint of chemical resistance and handleability, polyalkylene (for example, polyethylene and polypropylene) is preferable, and fluorine-based polyalkylene in which the hydrogen atoms of the alkylene group in the polyalkylene are partially or entirely substituted with fluorine atoms. Is more preferable, and polytetrafluoroethylene (PTFE) is particularly preferable.
The density of the polyethylene varies depending on the degree of branching, the degree of branching is high, and the degree of crystallization is low density polyethylene (LDPE), the degree of branching is low and the degree of crystallization is high density polyethylene (HDPE). Any of these can be used. Among these, polyethylene or a crystalline polymer in which a hydrogen atom is substituted with a fluorine atom is used, and polytetrafluoroethylene (PTFE) is particularly preferable.

The crystalline polymer preferably has a number average molecular weight of 500 to 50,000,000, more preferably 1,000 to 10,000,000.
As the crystalline polymer, polyethylene is preferable, and for example, polytetrafluoroethylene can be used. As polytetrafluoroethylene, polytetrafluoroethylene produced by an emulsion polymerization method can be usually used, and preferably a finely divided polytetrafluoroethylene obtained by coagulating an aqueous dispersion obtained by emulsion polymerization. Fluoroethylene is used.
The number average molecular weight of the polytetrafluoroethylene is preferably 2.5 million to 10 million, more preferably 3 million to 8 million.
There is no restriction | limiting in particular as said polytetrafluoroethylene raw material, You may select and use the polytetrafluoroethylene raw material currently marketed suitably. For example, “Polyflon Fine Powder F104U” manufactured by Daikin Industries, Ltd. is preferable.

  The crystalline polymer preferably has a glass transition temperature of 40 ° C to 400 ° C, more preferably 50 ° C to 350 ° C. The mass average molecular weight of the crystalline polymer is preferably 1,000 to 100,000,000. The number average molecular weight of the crystalline polymer is preferably 500 to 50,000,000, more preferably 1,000 to 10,000,000.

  The crystalline polymer film is preferably prepared by preparing a mixture obtained by mixing the polytetrafluoroethylene raw material with an extrusion aid, and extruding and rolling the mixture. As the extrusion aid, a liquid lubricant is preferably used, and specific examples thereof include solvent naphtha and white oil. As the extrusion aid, a hydrocarbon oil such as “Isopar” manufactured by Esso Oil Co., Ltd. sold in the market may be used. The addition amount of the extrusion aid is preferably 20 to 30 parts by mass with respect to 100 parts by mass of the crystalline polymer.

Paste extrusion is preferably performed at a temperature of 50 ° C to 80 ° C. There is no restriction | limiting in particular about extrusion shape, Although it can select suitably according to the objective, Usually, it is preferable to make it rod-shaped. The extrudate is then rolled into a film. Rolling can be performed, for example, by calendaring with a calendar roll at a speed of 50 m / min. The rolling temperature can usually be set to 50 ° C to 70 ° C. Then, it is preferable to remove the extrusion aid by heating the film to obtain a crystalline polymer unfired film. Although the heating temperature at this time can be suitably determined according to the kind of crystalline polymer to be used, it is preferably 40 ° C to 400 ° C, more preferably 60 ° C to 350 ° C. For example, when tetrafluoroethylene is used, 150 ° C. to 280 ° C. is preferable, and 200 ° C. to 255 ° C. is more preferable. The heating can be performed by a method such as passing the film through a hot air drying furnace. The thickness of the unsintered crystalline polymer film thus produced can be appropriately adjusted according to the thickness of the crystalline polymer microporous film to be finally produced, and is stretched in a later step. In some cases, it is necessary to adjust in consideration of a decrease in thickness due to stretching.
In the production of an unsintered crystalline polymer film, the items described in “Polyfluorocarbon Handbook” (published by Daikin Industries, Ltd., revised in 1983) can be appropriately employed.

-Asymmetric heating process-
In the asymmetric heating step, one surface of a fixed film made of a crystalline polymer is heated by a heating unit at a temperature equal to or higher than the melting point of the sintered body of the crystalline polymer in a non-contact state with the heating unit. Is a step of forming a semi-baked film having a temperature gradient in the thickness direction of the film. As a result, the film can be heated without uneven heating, the in-plane distribution of the average pore diameter of the obtained crystalline polymer microporous membrane is uniform, and asymmetric in the thickness direction of the crystalline polymer microporous membrane. The heating temperature can be controlled.

Here, the semi-firing means that the crystalline polymer is heat-treated at a temperature not lower than the melting point of the fired body and not higher than the melting point of the unfired body + 15 ° C.
In the present invention, an unsintered body of a crystalline polymer means one that has not been subjected to a heat treatment for firing. The melting point of the crystalline polymer means the temperature of the endothermic curve peak that appears when the unsintered crystalline polymer is measured with a differential scanning calorimeter. The melting point of the fired body and the melting point of the unfired body vary depending on the kind of crystalline polymer, the average molecular weight, and the like, but are preferably 50 ° C to 450 ° C, more preferably 80 ° C to 400 ° C.
Such a temperature can be considered as follows. For example, when the crystalline polymer is polytetrafluoroethylene, the sintered body has a melting point of about 324 ° C. and the green body has a melting point of about 345 ° C. Therefore, in the case of a polytetrafluoroethylene film, the temperature is preferably 327 ° C. to 360 ° C., more preferably 335 ° C. to 350 ° C., for example, heating to a temperature of 345 ° C. The semi-fired body is in a state where a melting point of about 324 ° C. and a melting point of about 345 ° C. are mixed.

In the semi-baking, one surface of a fixed film made of a crystalline polymer is heated by heating means at a temperature equal to or higher than the melting point of the fired body of the crystalline polymer in a non-contact state with the heating means. Do.
The entire surface of one surface of the crystalline polymer film is preferably fixed.
There is no restriction | limiting in particular as the fixing method of the one surface of the film which consists of said crystalline polymer, Although it can select suitably according to the objective, It is preferable to fix with the fixing means.
Further, the fixing surface of the film made of the crystalline polymer is not particularly limited and can be appropriately selected according to the purpose, but the surface opposite to the surface heated by the heating means described later is the fixing means. It is preferable to be fixed by.

--Fixing means--
The fixing means is not particularly limited and may be appropriately selected depending on the purpose, but a plurality of holes are formed on the surface, and any of a belt and a roll that can be sucked from the surface to the inside is preferable. A belt having a plurality of holes formed on the surface and capable of suction from the surface to the inside is more preferable.
The belt having a plurality of holes formed on the surface and capable of suction from the surface to the inside is not particularly limited and may be appropriately selected depending on the intended purpose, but a suction belt is preferable.
A roll having a plurality of holes formed on the surface and capable of suction from the surface to the inside is not particularly limited and may be appropriately selected depending on the intended purpose, but a suction roll is preferable.
The suction belt and the suction roll convey the film made of the crystalline polymer fixed to the surface by rotating while performing the suction. As a result, when the surface (heating surface) opposite to the fixed surface of the film made of the crystalline polymer is heated by a heating means described later, deformation of the film made of the crystalline polymer can be suppressed, and heating unevenness can be prevented. Can be prevented.

There is no restriction | limiting in particular as a structure of the said suction belt, According to the objective, it can select suitably, For example, the suction belt unit 41 etc. of FIG. 4 etc. are mentioned. The suction belt unit 41 includes a suction belt roll 45 at both inner ends, an endless belt 43 having a suction hole 42 on the surface, and a vacuum box 44 inside the endless belt 43. The inside of the endless belt 43 is decompressed by being sucked by a vacuum box 44, and the endless belt 43 fixes the film made of the crystalline polymer on the surface thereof while conveying the film made of the crystalline polymer. can do.
There is no restriction | limiting in particular as a structure of the said suction roll, According to the objective, it can select suitably, For example, the suction roll unit 51 of FIG. 5 etc. are mentioned. The suction roll unit 51 includes a roll 53 having a cavity that can be vacuum-loaded on the inside, a suction hole 52 on the surface, and a vacuum device (not shown) connected to the roll 53. The inside of the roll 53 is decompressed by being sucked by the vacuum device, and the roll 53 can fix the film made of the crystalline polymer on its surface while rotating.

  The material of the suction belt and the suction roll is not particularly limited and can be appropriately selected according to the purpose, but a material having durability at a temperature equal to or higher than the melting point of the sintered body of the crystalline polymer is preferable. For example, a metal etc. are mentioned. Suitable examples of the metal include SUS304H.

The shape of the cross section perpendicular to the axial direction of the suction holes of the suction belt and the suction roll is not particularly limited and can be appropriately selected according to the purpose. For example, hexagon, quadrilateral, circle, ellipse , A rectangle, a mesh, an indeterminate shape, and the like. Among these, a circle is preferable.
The maximum diameter of the suction belt and the suction hole of the suction roll is not particularly limited and may be appropriately selected depending on the purpose, but is preferably 0.1 mm to 10 mm, more preferably 0.2 mm to 7 mm, 0.3 mm to 5 mm is particularly preferable. When the maximum diameter of the suction holes of the suction belt and the suction roll is larger than 10 mm, the suction holes may remain on the crystalline polymer film.
The pitch of the suction holes of the suction belt and the suction roll (the average distance between the centers of the adjacent suction holes) is not particularly limited and may be appropriately selected depending on the intended purpose. Preferably, 1 mm to 40 mm is more preferable, and 5 mm to 20 mm is particularly preferable. When the pitch of the suction holes of the suction belt and the suction roll is less than 0.5 mm, the hole area ratio becomes too large, and the strength of the suction belt and the suction roll may be insufficient. The suction force may be weakened or air stagnation may occur easily.
There is no restriction | limiting in particular as how to arrange | position the suction hole of the said suction belt and a suction roll, According to the objective, it can select suitably.
There is no restriction | limiting in particular as the formation method of the suction hole of the said suction belt and a suction roll, According to the objective, it can select suitably, For example, the method of drilling with a drill etc. are mentioned.

There is no restriction | limiting in particular as an opening rate of the said suction belt and a suction roll, Although it can select suitably according to the objective, 0.01%-50% are preferable, 0.05%-20% are more Preferably, 0.1% to 10% is particularly preferable. When the aperture ratio of the suction belt and the suction roll is less than 0.01%, the suction force may be insufficient, and when it is more than 50%, the strength of the suction belt and the suction roll may be insufficient. is there.
In addition, the aperture ratio of the suction belt and the suction roll refers to the area occupied by the holes on the entire surface of the suction belt and the suction roll.

  The suction force of the suction belt and the suction roll is not particularly limited and can be appropriately selected according to the purpose. However, the difference between the atmospheric pressure and the internal pressure of the suction belt and the suction roll is 0. 0.5 KPa to 60 KPa is preferable, 1 KPa to 40 KPa is more preferable, and 3 KPa to 20 KPa is particularly preferable. If the difference between the atmospheric pressure and the internal pressure of the suction belt and the suction roll is less than 0.5 KPa, it may be difficult to fix the crystalline polymer film to the suction belt and the suction roll. If it is higher than 60 KPa, suction marks may be formed on the crystalline polymer film.

  It is preferable that the surface of the suction belt and the suction roll is processed so that a suction mark is not formed on the film made of the crystalline polymer. There is no restriction | limiting in particular as said process, According to the objective, it can select suitably, For example, it has a suction hole smaller than the suction hole of the said suction belt and the suction roll on the surface of the said suction belt and the suction roll. And covering with a layer.

There is no restriction | limiting in particular as a magnitude | size of the endless belt of the said suction belt, Although it can select suitably according to the objective, Perimeter 400mm-3,000mm are preferable, 500mm-2,000mm are more preferable, 600mm- 1,500 mm is particularly preferable. If the size of the endless belt is less than 400 mm, the contact area between the crystalline polymer film and the endless belt may be small, and uneven heating may occur. If the size is larger than 3,000 mm, the equipment becomes large. Too much. On the other hand, when the size of the belt is within a particularly preferable range, uneven heating can be prevented, and a crystalline polymer microporous film having a uniform in-plane distribution of average pore diameter can be obtained.
There is no restriction | limiting in particular as a magnitude | size of the roll for suction belts used for the said suction belt, According to the magnitude | size of a suction belt, it can select suitably.
There is no restriction | limiting in particular as a diameter of the roll of the said suction roll, Although it can select suitably according to the objective, 50 mm-700 mm are preferable, 100 mm-600 mm are more preferable, 150 mm-500 mm are especially preferable. When the diameter of the roll is less than 50 mm, the contact area between the film made of the crystalline polymer and the roll is small, and uneven heating may occur. When the diameter is greater than 700 mm, the equipment is too large. On the other hand, when the diameter of the roll is within a particularly preferable range, heating unevenness can be prevented, and a crystalline polymer microporous film having a uniform in-plane distribution of average pore diameter can be obtained.

-Heating means-
The heating means is not particularly limited as long as one surface of the film made of the crystalline polymer can be heated in a non-contact state, and can be appropriately selected according to the purpose. Is preferred.
By the heating, the heating temperature can be controlled asymmetrically in the thickness direction, and the crystalline polymer microporous membrane of the present invention can be easily produced.
Further, the temperature gradient in the thickness direction of the film made of the crystalline polymer is not particularly limited and may be appropriately selected depending on the intended purpose. However, the temperature difference between the heating surface and the non-heating surface is 30 ° C. or more. Is preferable, and 50 degreeC or more is more preferable.

There is no restriction | limiting in particular as said infrared irradiation, According to the objective, it can select suitably.
The general definition of the infrared ray can be referred to “practical infrared ray (Human and Historical Company, published in 1992). In the present invention, the infrared ray is an electromagnetic wave having a wavelength of 0.74 μm to 1,000 μm. Of which the wavelength range of 0.74 μm to 3 μm is the near infrared ray, and the wavelength range of 3 μm to 1,000 μm is the far infrared ray.
In the present invention, since it is preferable that there is a temperature difference between the heated surface and the non-heated surface of the film made of the crystalline polymer, far infrared rays that are advantageous for heating the surface layer are preferably used.
The type of the infrared device is not particularly limited as long as it can irradiate infrared rays having a target wavelength, and can be appropriately selected according to the purpose. In general, near infrared rays are bulbs (halogen lamps), far infrared rays are A heating element such as ceramic, quartz, or metal oxide surface can be used.
Moreover, if it is infrared irradiation, a semi-baking can be performed continuously by a flow operation industrially, and also temperature control and apparatus maintenance are easy. In addition, since the film is not in contact with the crystalline polymer film, it is clean and does not have fuzzy defects.
The heating surface temperature of the film made of the crystalline polymer by the infrared irradiation is not particularly limited as long as the semi-baked product can be obtained, and can be appropriately selected according to the purpose. Is preferable, and 335 degreeC-360 degreeC is more preferable. If the heating surface temperature is less than 327 ° C., the crystal state does not change, and the pore diameter may not be controlled. If the heating surface temperature exceeds 380 ° C., the shape of the film is excessively deformed by melting. Or thermal decomposition of the polymer may occur.
The method for controlling the heating surface temperature of the crystalline polymer film by the infrared irradiation is not particularly limited and can be appropriately selected according to the purpose. For example, the output of the infrared irradiation apparatus, the infrared irradiation apparatus and the above-mentioned It can be controlled by the distance from the heating surface of the film made of the crystalline polymer, the irradiation time (conveying speed), the ambient temperature, and the like.
There is no restriction | limiting in particular as said infrared irradiation time, The time required for the target semi-baking to fully advance can be selected suitably, However, 5 second-120 second are preferable, 10 second-90 second Is more preferable, and 20 seconds to 80 seconds is particularly preferable.

Infrared irradiation in the asymmetric heating step may be performed continuously, or may be performed intermittently after being divided several times.
When the infrared irradiation is performed continuously, it is preferable to cool the non-heated surface simultaneously with the heating of the heated surface in order to maintain a temperature gradient between the heated surface of the crystalline polymer film and the non-heated surface.
The method for cooling the non-heated surface is not particularly limited and may be appropriately selected depending on the purpose. Examples thereof include a method of blowing cold air, a method of contacting a refrigerant, a method of contacting a cooled material, and cooling. The method by etc. is mentioned.
Moreover, also when performing the said infrared irradiation intermittently, it is preferable to heat the heating surface of the film made of the crystalline polymer intermittently and cool the non-heating surface to suppress the temperature rise of the non-heating surface. .

-Stretching process-
The semi-baked film is then preferably stretched. Stretching is preferably performed in both the longitudinal direction and the width direction. Each of the longitudinal direction and the width direction may be sequentially stretched, or biaxially stretched simultaneously.
When sequentially stretching in the longitudinal direction and the width direction, respectively, it is preferable to first stretch in the longitudinal direction and then stretch in the width direction.
The stretching ratio in the longitudinal direction is preferably 3 to 100 times, more preferably 4 to 90 times, and particularly preferably 5 to 80 times. The stretching temperature in the longitudinal direction is preferably 100 ° C to 320 ° C, more preferably 200 ° C to 310 ° C, and particularly preferably 250 ° C to 300 ° C.
The stretching ratio in the width direction is preferably 3 to 100 times, more preferably 5 to 90 times, still more preferably 7 to 70 times, and particularly preferably 10 to 40 times. The stretching temperature in the width direction is preferably 100 ° C to 320 ° C, more preferably 200 ° C to 310 ° C, and particularly preferably 250 ° C to 300 ° C.
The area stretching ratio is preferably 10 times to 300 times, more preferably 20 times to 280 times, and particularly preferably 30 times to 200 times. When stretching, the film may be preheated to a temperature below the stretching temperature.

  In addition, after extending | stretching, heat setting can be performed as needed. The heat setting temperature is usually preferably not less than the stretching temperature and less than the melting point of the crystalline polymer fired body.

-Hydrophilization process-
The hydrophilization step is a step of hydrophilizing the stretched film.
Examples of the hydrophilization treatment include (1) treatment of irradiating an ultraviolet laser after impregnating a stretched film with ketones, and (2) chemical etching treatment.

  Examples of the water-soluble ketone that can be used for the treatment of irradiating an ultraviolet laser after impregnating the stretched film of (1) with a ketone include acetone and methyl ethyl ketone. Among these, acetone is particularly preferable. The concentration of the water-soluble ketone at the stage of impregnating the crystalline polymer microporous membrane varies slightly depending on the material of the crystalline polymer microporous membrane and the size of the pores. In the case of acetone and methyl ethyl ketone, preferably 85 It is mass%-100 mass%. The concentration of the water-soluble ketone in the crystalline polymer microporous membrane upon irradiation with ultraviolet laser light is preferably 0.1 to 10 as the absorbance at the wavelength of the ultraviolet laser light to be used. For example, in the case of acetone, when KrF is used as a light source, it corresponds to 0.05 mass% to 5 mass%. The absorbance is preferably 0.1 to 6, and more preferably 0.5 to 5. When the crystalline polymer microporous film containing a water-soluble ketone adjusted to this concentration range is irradiated with ultraviolet laser light, a satisfactory hydrophilizing effect can be obtained with a considerably lower irradiation dose than before.

  Generally, when a water-soluble ketone having a boiling point of 50 ° C. to 100 ° C. is used, the hydrophilization treatment efficiency by ultraviolet laser irradiation is high and the solvent removal after the hydrophilization treatment is easy, but the boiling point is 100 ° C. When a higher water-soluble ketone is used, it is difficult to remove the ketone after the hydrophilic treatment.

In the hydrophilic treatment by irradiating the crystalline polymer microporous membrane impregnated with water-soluble ketone with ultraviolet laser light, the crystalline polymer microporous membrane impregnated with water-soluble ketone is obtained in order to obtain a uniform and high hydrophilic treatment effect. The porous membrane is impregnated with water, and the water-soluble ketone aqueous solution concentration in the crystalline polymer microporous membrane is 0.1 to 10, preferably 0.1 to 6, at the wavelength of the ultraviolet laser beam used. Particularly preferably, it is adjusted to 0.5 to 5. When the absorbance is lower than 0.1, it may be difficult to obtain a sufficient hydrophilic treatment effect. When the absorbance is higher than 10, absorption of light energy by the aqueous solution increases, and sufficient hydrophilicity to the inside of the micropores is obtained. May be difficult.
As a method of impregnating water in order to adjust the concentration of the water-soluble ketone aqueous solution in the crystalline polymer microporous membrane, it is preferable to immerse in a very low concentration aqueous solution of the same ketone.
Here, the absorbance means an amount defined by the following formula.
Absorbance ≡log ₁₀ (I ₀ / I) = εcd
Where ε is the absorption coefficient of the ketone, c is the concentration of the aqueous ketone solution (mol / dm ³ ), d is the transmission optical path length (cm), I ₀ is the light transmission intensity of the solvent alone, and I is the light transmission intensity of the solution. Represents. In the present invention, the concentration at which the absorbance is x means a concentration at which the absorbance is x when d is measured in a measurement cell having 1 cm. However, if the concentration is so high that the amount of transmitted light is too small when d is 1 cm and it is difficult to measure the absorbance, the absorbance obtained by multiplying the absorbance obtained by using a measuring cell with d of 0.2 cm is 5 times. It was.

The method for impregnating the crystalline polymer microporous membrane with the aqueous solution of the water-soluble ketone is not particularly limited and may be appropriately selected according to the purpose. The dipping method, spraying method, coating method, etc. may be selected. A dipping method is common, although it may be adopted as appropriate depending on the form and dimensions of the microporous membrane.
The impregnation temperature of the water-soluble ketone or an aqueous solution thereof is preferably 10 ° C. to 40 ° C. from the viewpoint of the diffusion rate of the aqueous solution into the micropores of the crystalline polymer microporous membrane. When the impregnation temperature is lower than 10 ° C, a relatively long time is required to sufficiently diffuse the aqueous solution into the micropores. When the impregnation temperature is higher than 40 ° C, the evaporation rate of the water-soluble ketone increases. Is not preferable.

The crystalline polymer microporous membrane subjected to the impregnation treatment is subjected to the following ultraviolet laser light irradiation treatment after adjusting the concentration of the water-soluble ketone impregnated to the above range.
As the ultraviolet laser light, those having a wavelength of 190 nm to 400 nm or less are preferable, and examples include argon ion laser light, krypton ion laser light, N ₂ laser light, dye laser light, and excimer laser light. Is preferred. Among these, KrF excimer laser light (wavelength: 248 nm), ArF excimer laser light (wavelength: 193 nm), and XeCl excimer laser light (308 nm) that can stably obtain a high output for a long time are particularly preferable.
The excimer laser light irradiation is usually performed at room temperature in the air, but is preferably performed in a nitrogen atmosphere. The irradiation conditions of excimer laser light depend on the type of fluororesin and the desired degree of surface modification, but general irradiation conditions are as follows.
・ Fluence: 10 mJ / cm ² / pulse or more ・ Incoming energy: 0.1 J / cm ² or more

Particularly suitable irradiation conditions for KrF excimer laser light, ArF excimer laser light, and XeCl excimer laser light are as follows.
KrF fluence: 50 to 500 mJ / cm ² / pulse Incident energy: 0.25 to 3.0 J / cm ²
ArF fluence: 10 to 200 mJ / cm ² / pulse Incident energy: 0.1 to 3.0 J / cm ²
XeCl fluence: 50 to 500 mJ / cm ² / pulse Incident energy: 3.0 to 30.0 J / cm ²

Examples of the chemical etching treatment (2) include an oxidative decomposition treatment in which an alkali metal is used to modify the fluororesin constituting the crystalline polymer microporous membrane and remove the modified portion.
The oxidative decomposition treatment is performed using, for example, an organic alkali metal solution. When the crystalline polymer microporous film is subjected to a chemical etching treatment with an organic alkali metal solution, the surface is modified to impart hydrophilicity, and a browned layer (brown layer) is formed. This brown layer is composed of sodium fluoride, a decomposition product of a fluororesin having a carbon-carbon double bond, a polymer of these with naphthalene, anthracene, etc., but these are separated into the filtrate by dropping, decomposition, elution or the like. Since it may mix, it is preferable to remove. These can be removed by oxidative decomposition with hydrogen peroxide, sodium hypochlorite, ozone, or the like.

The chemical etching treatment can be performed using an organic alkali metal solution or the like, and specifically, can be performed by immersing a crystalline polymer microporous film in the organic alkali metal solution. In this case, since the chemical etching process is performed from the surface side of the crystalline polymer microporous film, it is possible to perform the chemical etching process only on the vicinity of both surfaces of the film. However, in order to further increase the water retention of the film, it is preferable to perform a chemical etching treatment not only near both surfaces but also inside the crystalline polymer microporous film. Even when the chemical etching treatment is applied to the inside of the crystalline polymer microporous membrane, the function as a separation membrane is not significantly lowered.
Examples of the organic alkali metal solution used for the chemical etching treatment include an organic solvent solution such as methyllithium, a metal sodium-naphthalene complex, a metal sodium-anthracene complex in tetrahydrofuran, a metal sodium-liquid ammonia solution, and the like. Among these, a solution of a complex with metal sodium having naphthalene as an aromatic anion radical is generally widely used. However, in order to perform chemical etching treatment to the inside of the crystalline polymer microporous film, benzophenone is used. Anthracene and biphenyl are preferably used as aromatic anion radicals.

<Crystalline polymer microporous membrane>
One feature of the crystalline polymer microporous membrane produced by the method for producing a crystalline polymer microporous membrane of the present invention is that the in-plane distribution of the average pore diameter is uniform.
Further, the in-plane variation of the average pore diameter of the crystalline polymer microporous membrane is preferably a variation rate of 20% or less, and more preferably 15% or less. When the variation rate exceeds 20%, the variation in pore diameter is too large, and the trapped particle diameter may increase.
Here, the in-plane distribution of the average pore diameter can be evaluated by the following method using a bubble point measurement value. A syringe holder with a diameter of 25 mm was used, IPA was used as the wetting liquid, and the initial bubble point value (corresponding to the maximum pore diameter) was taken as the measurement value. The microporous membrane is cut out into a square with a side of 400 mm, the inside of the square is divided into 100 equal parts with a square with a side of 40 mm, and bubble points are measured for each part to obtain an average value and a variation rate.
The rate of variation is represented by the ratio of the standard deviation to the average value of the measured values. When the average value of n pieces of data (X1, X2,... Xn) is Xm and the standard deviation is Sx, the variation rate Vx can be calculated by the following equation.
Fluctuation rate [%]; Vx = Sx / Xm × 100

One feature of the crystalline polymer microporous membrane of the present invention is that the average pore size of the non-heated surface is larger than the average pore size of the heated surface.
The crystalline polymer microporous membrane has a thickness of the crystalline polymer microporous membrane as X, an average pore diameter in the thickness direction X / 10 from the non-heated surface as P1, and a depth direction. When the average pore diameter of the 9X / 10 thickness portion is P2, P1 / P2 is preferably 2 to 10,000, more preferably 3 to 100, and particularly preferably 4.5 to 100.
The crystalline polymer microporous membrane preferably has a ratio of the average pore diameter between the non-heated surface and the heated surface (non-heated surface / heated surface ratio) of 5 to 30 times, more preferably 10 to 25 times. 15 to 20 times is more preferable.

  Here, the average pore diameter is, for example, a photograph of a film surface (SEM photograph, magnification 1,000 to 5,000 to 5,000 with a scanning electron microscope (Hitachi S-4000 type, vapor deposition is Hitachi E1030 type, both manufactured by Hitachi, Ltd.)). The image obtained is taken into an image processing apparatus (main body name: Nippon Avionics Co., Ltd., TV image processor TVIP-4100II, control software name: Ratok System Engineering Co., Ltd., TV image processor image command 4198). Thus, an average pore diameter is obtained by obtaining an image consisting only of crystalline polymer fibers and calculating the image.

  In the crystalline polymer microporous membrane of the present invention, in addition to the above-described features, the average pore diameter is continuously changed from the non-heated surface to the heated surface (first embodiment), and the above-mentioned features In addition to the features, both of the embodiments (second embodiment) having a single-layer structure are included. By further adding these additional features, the filter life can be effectively improved.

  In the first aspect, “the average pore diameter continuously changes from the non-heated surface to the heated surface” means that the horizontal axis indicates the distance d in the thickness direction from the non-heated surface (the depth from the surface). This means that the graph is drawn with one continuous line when the average pore diameter D is taken on the vertical axis. The graph from the non-heated surface (d = 0) to the heated surface (d = film thickness) may consist only of a negative slope region (dD / dt <0), or the slope is negative. A region and a region with zero inclination (dD / dt = 0) may be mixed, or a region with a negative inclination and a positive region (dD / dt> 0) may be mixed. . Preferably, the region is composed only of a negative slope region (dD / dt <0), or a negative slope region and a zero slope region (dD / dt = 0) are mixed. More preferably, it is composed of only a negative slope region (dD / dt <0).

  It is preferable that at least the non-heated surface of the film is included in the region where the inclination is negative. In the region where the slope is negative (dD / dt <0), the slope may be always constant or different. For example, if the crystalline polymer microporous membrane of the present invention consists only of a negative slope region (dD / dt <0), the dD on the heated surface of the membrane is higher than the dD / dt on the non-heated surface of the membrane. A mode in which / dt is large can be taken. Further, it is possible to adopt a mode in which dD / dt gradually increases (a mode in which the absolute value decreases) from the non-heated surface to the heated surface of the crystalline polymer microporous film.

  The “single layer structure” referred to in the second embodiment excludes a multilayer structure formed by bonding or laminating two or more layers. That is, the “single layer structure” in the second aspect means a structure having no boundary between layers existing in a multilayer structure. In the second aspect, it is preferable that a surface having an average pore size smaller than the average pore size of the non-heated surface and larger than the average pore size of the heated surface is present in the film.

  The crystalline polymer microporous membrane of the present invention preferably has both the features of the first embodiment and the features of the second embodiment. That is, the average pore diameter of the non-heated surface of the crystalline polymer microporous membrane is larger than the average pore diameter of the heated surface, the average pore diameter continuously changes from the non-heated surface to the heated surface, and Those having a layer structure are preferred. With such a crystalline polymer microporous membrane, fine particles can be captured more efficiently when filtration is performed from the non-heated surface side, the filtration life can be greatly improved, and it is easy and inexpensive. Can also be manufactured.

  The thickness of the crystalline polymer microporous membrane of the present invention is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 1 μm to 300 μm, more preferably 5 μm to 100 μm, and more preferably 10 μm to 80 μm. Particularly preferred.

The crystalline polymer microporous membrane of the present invention can capture particles without leakage even when used in a large area. Therefore, as the area of the crystalline polymer microporous membrane is not particularly limited and may be appropriately selected depending on the intended purpose, large 10 m ² is preferably less than 0.04 m ^2, 0.1 m ² or more 5m ² or less is more preferable.

  The crystalline polymer microporous membrane of the present invention can be used for various applications, and in particular, can be suitably used as a filter for filtration described below.

(Filter for filtration)
The filter for filtration of the present invention is characterized by using the crystalline polymer microporous membrane of the present invention.
When the crystalline polymer microporous membrane of the present invention is used as a filter for filtration, filtration is performed with the non-heated surface (surface having a large average pore diameter) as the inlet side. That is, the surface side with a large average pore diameter is used as the filter surface. In this way, fine particles can be efficiently captured by performing filtration with the surface having a large average pore diameter (non-heated surface) as the inlet side.
Further, since the crystalline polymer microporous membrane of the present invention has a large specific surface area, the fine particles introduced from the surface are removed by adsorption or adhesion before reaching the minimum pore diameter portion. Therefore, clogging is unlikely to occur and high filtration efficiency can be maintained over a long period of time.

The filter for filtration of the present invention can be at least 5 ml / cm ² · min or more when filtered with a differential pressure of 0.1 kg / cm ² .
As the shape of the filter for filtration of the present invention, a pleat type for folding the filtration membrane, a spiral type for filtering the filtration membrane, a frame-and-plate type for laminating disc-shaped filtration membranes, a filtration membrane, There is a tube type etc. which make it tubular. Among these, the pleated type is particularly preferable because the effective surface area used for filtering the filter per cartridge can be increased.
The filter cartridge is classified into an element exchange type filter cartridge in which only the filter element is replaced when the deteriorated filter membrane is replaced, and a capsule type filter cartridge in which the filter element is processed integrally with the filtration housing and made into a disposable type.

  Here, FIG. 1 is a development view showing the structure of an element exchange type pleated filter cartridge element. The microfiltration membrane 103 is folded in a state of being sandwiched by two membrane supports 102 and 104, and is wound around a core 105 having a large number of liquid collection ports. On the outside, there is an outer peripheral cover 101 that protects the microfiltration membrane. Microfiltration membranes are sealed at both ends of the cylinder by end plates 106a and 106b. The end plate is in contact with the seal portion of the filter housing (not shown) via the gasket 107. The filtered liquid is collected from the core collection port and discharged from the fluid outlet 108.

A capsule-type pleated filter cartridge is shown in FIGS.
FIG. 2 is a developed view showing the entire structure of the microfiltration membrane filter element before being assembled into the housing of the capsule filter cartridge. The microfiltration membrane 2 is folded in a sandwiched state by two supports 1 and 3 and is wound around a filter element core 7 having a large number of liquid collection ports. There is a filter element cover 6 on the outside to protect the microfiltration membrane. The microfiltration membrane is sealed by the upper end plate 4 and the lower end plate 5 at both ends of the cylinder.
FIG. 3 shows a structure of a capsule-type pleated filter cartridge in which a filter element is integrated in a housing. The filter element 10 is incorporated in a housing composed of a housing base and a housing cover. The lower end plate is sealed by a water collecting pipe (not shown) at the center of the housing base via an O-ring 8. The liquid enters the housing from the liquid inlet nozzle 13, passes through the filter medium 9, is collected from the liquid collection port of the filter element core 7, and is discharged from the liquid outlet nozzle 14. The housing base and the housing cover are usually heat-sealed in a liquid-tight manner at the welding portion 17.
In FIG. 3, “11” indicates a housing cover, “12” indicates a housing base, “15” indicates an air vent, and “16” indicates a drain.

  FIG. 2 shows an example in which the lower end plate and the housing base are sealed via the O-ring 8, but the lower end plate and the housing base may be sealed by heat fusion or an adhesive. . In addition to heat sealing, the housing base and the housing cover can be sealed by using an adhesive. 1-3 are specific examples of the microfiltration filter cartridge, and the present invention is not limited to these drawings.

  Since the filter for filtration using the crystalline polymer microporous membrane of the present invention has such a characteristic that the filtration function is high and the life is long, the filtration device can be compactly assembled. In the conventional filtration apparatus, a large number of filtration units are used in parallel to cope with the short filtration life. However, if the filtration filter of the present invention is used, the number of filtration units used in parallel is greatly increased. Can be reduced. Moreover, since the replacement period of the filter for filtration can be extended significantly, the cost and time required for maintenance can be reduced.

  The filter for filtration of the present invention can be used in various situations where filtration is required, and is preferably used for microfiltration of gases, liquids, etc., for example, corrosive gas, various types used in the semiconductor industry. It is used for filtration and sterilization of gas, etc., washing water for electronics industry, pharmaceutical water, pharmaceutical manufacturing process water, food water and the like. In particular, since the filter for filtration of the present invention is excellent in heat resistance and chemical resistance, it can be effectively used for high-temperature filtration and filtration of reactive chemicals that cannot be handled by conventional filter for filtration.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

Example 1
<Preparation of crystalline polymer microporous membrane>
100 parts by mass of polytetrafluoroethylene fine powder having a number average molecular weight of 6,200,000 (Daikin Kogyo Co., Ltd., “Polyflon Fine Powder F104U”), and hydrocarbon oil (Esso Oil Co., Ltd., “Isopar”) as an extrusion aid ) 27 parts by mass was added, and paste extrusion was performed in a round bar shape. This was calendered at a speed of 30 m / min with a calender roll heated to 60 ° C. to produce a polytetrafluoroethylene film. This film was passed through a hot air drying oven at 250 ° C. to remove the extrusion aid, and a polytetrafluoroethylene unfired film having an average thickness of 120 μm, an average width of 150 mm, and a specific gravity of 1.55 was produced.

  While fixing one surface of the obtained polytetrafluoroethylene film to the suction belt using the single-sided heating device shown in FIG. A semi-baked film was produced by heating at a temperature of 345 ° C. for 1 minute.

The structure of the single-sided heating apparatus of FIG. 4 is shown below.
・ Heater unit ("46" in Fig. 4)
Ten heaters (output: 1 KW, length: 300 mm) were arranged at intervals of 100 mm in the transport direction.
・ Suction belt unit (“41” in FIG. 4)
Suction hole (“42” in FIG. 4):
Hole diameter: 0.5 mm, center-to-center distance: MD 10 mm, TD 10 mm
Endless belt (“43” in FIG. 4):
Width: 300 mm, length: 2,100 mm, thickness: 0.2 mm, material: SUS304H, hole area ratio: 0.79%
Vacuum box (“44” in FIG. 4):
Length: 1,000mm, width: 280mm, suction power: 15KPa

  The obtained semi-baked film was stretched between rolls by 13 times in the longitudinal direction at 270 ° C., and then wound up on a take-up roll. Then, after preheating the film to 305 ° C., both ends were sandwiched between clips and stretched 12 times in the width direction at 270 ° C. Thereafter, heat setting was performed at 380 ° C. The area stretch ratio of the obtained stretched film was 120 times in terms of the stretch area ratio. Thus, the polytetrafluoroethylene microporous membrane of Example 1 was produced.

(Example 2)
A polytetrafluoroethylene microporous membrane of Example 2 was produced in the same manner as in Example 1 except that the single-sided heating device in Example 1 was changed to the single-sided heating device shown in FIG.

The structure of the single-sided heating apparatus of FIG. 5 is shown below.
・ Heater unit (“56” in FIG. 5)
Four heaters (output: 1 KW, length: 300 mm) were arranged at intervals of 100 mm in the transport direction.
・ Suction roll unit (“51” in FIG. 5)
Suction hole (“52” in FIG. 5):
Hole diameter: 0.5 mm, center-to-center distance: MD 10 mm, TD 10 mm
Roll (“53” in FIG. 5):
Diameter: 300 mm, Width: 280 mm, Material: SUS304H, Opening ratio: 0.79%, Suction force: 15 KPa

(Example 3)
In Example 1, after producing a stretched film, the polytetrafluoroethylene microporous membrane of Example 3 was produced in the same manner as in Example 1 except that the hydrophilic treatment shown below was performed.

-Hydrophilization treatment-
A stretched film previously impregnated with ethanol was immersed in hydrogen peroxide water having a concentration of 0.03% by mass (liquid temperature: 40 ° C.), and the fluence was 25 mJ / cm ² / from above the stretched film pulled up after 20 hours. A polytetrafluoroethylene microporous membrane made hydrophilic by irradiation with ArF excimer laser light (193 nm) under conditions of a pulse and an irradiation amount of 10 J / cm ² was produced.
The wettability of the microporous membrane was measured by using a wetting index standard solution defined in JIS K6768 after sufficiently washing with pure water and drying. That is, a series of mixed liquids whose surface tension changes in order is dropped onto the microporous film sequentially, and the highest surface tension of the mixed liquid determined to wet the microporous film is evaluated as a wetting index. did. As a result, the wetting index of the microporous membrane was 52 dyn / cm. This wetting index is significantly larger than the value of polytetrafluoroethylene microporous film not irradiated with ultraviolet laser light (less than 31 dyn / cm). From this result, it was found that the wettability of the fluorine surface was greatly improved by the hydrophilization treatment.

(Comparative Example 1)
A polytetrafluoroethylene microporous membrane of Comparative Example 1 was produced in the same manner as in Example 1 except that suction was not performed in the single-sided heating device of Example 1.

(Comparative Example 2)
A polytetrafluoroethylene microporous membrane of Comparative Example 2 was produced in the same manner as in Example 2 except that suction was not performed in the single-sided heating device of Example 2.

  Next, for each of the prepared polytetrafluoroethylene microporous membranes of Examples 1 to 3 and Comparative Examples 1 and 2, the average pore size of the non-heated surface of the microporous membrane is larger than the average pore size of the heated surface. In order to check whether the average pore diameter is continuously changing from the non-heated surface to the heated surface, the film thickness (average film thickness) and P1 / P2 are measured as follows. It was. The results are shown in Table 1.

<Film thickness (average film thickness)>
The thickness (average film thickness) of each of the polytetrafluoroethylene microporous membranes of Examples 1 to 3 and Comparative Examples 1 to 2 was measured with a dial thickness gauge (K402B, manufactured by Anritsu Corporation). Arbitrary three places were measured and the average value was calculated | required.

<Measurement of P1 / P2>
About each polytetrafluoroethylene microporous film | membrane of Examples 1-3 and Comparative Examples 1-2, the film thickness of this microporous film | membrane is set to X, The thickness part of the depth direction X / 10 from a non-heating surface P1 / P2 where P1 is the average pore diameter and the average pore diameter of the thickness portion in the depth direction 9X / 10 is P2.
Here, the average pore diameter of the polytetrafluoroethylene microporous membrane was measured with a scanning electron microscope (Hitachi S-4000 type, vapor deposition was Hitachi E1030 type, both manufactured by Hitachi, Ltd.). 1,000 times to 5,000 times) and the obtained photograph is an image processing apparatus (main body name: Nippon Avionics Co., Ltd., TV image processor TVIP-4100II, control software name: Ratok System Engineering Co., Ltd., TV An image processor image command 4198) was taken in to obtain an image consisting only of polytetrafluoroethylene fibers, and the average pore size was determined by calculating the image.

From the results of Table 1, in each of the polytetrafluoroethylene microporous membranes of Examples 1 to 3, the average pore diameter of the non-heated surface is larger than the average pore diameter of the heated surface, and the average from the non-heated surface to the heated surface It was found that the pore diameter changed continuously.
In contrast, in the polytetrafluoroethylene microporous membranes of Comparative Examples 1 and 2, the average pore size of the non-heated surface is larger than the average pore size of the heated surface, and the average pore size is continuous from the non-heated surface toward the heated surface. However, since single-sided heating was slightly unstable, the film thickness was slightly thicker than in Examples 1 to 3, and P1 / P2 was also small.

<Filtration life test>
About each polytetrafluoroethylene microporous film | membrane of Examples 1-3 and Comparative Examples 1-2, the filtration life test was done as follows.
For the measurement of the filtration life, a latex dispersion having a polydispersed particle size was used, and the filtration amount until the clogging was substantially carried out (L / m ² ) was evaluated. “Substantially clogging” in the present invention is defined as the time when the flow rate is reduced to ½ of the initial flow rate at a constant filtration pressure. The type of latex used in the latex dispersion used in this measurement is appropriately selected depending on the pore size of the membrane. As selection conditions, the particles contained in the liquid after filtration are 1 ppm or less, and the ratio of the average particle size of the latex to the pore size of the membrane is 1/5 to 5. Isopropanol was used as a dispersion medium, and the concentration was 100 ppm. The results are shown in Table 2.

From the results in Table 2, the polytetrafluoroethylene microporous membranes of Examples 1 to 3 were superior in filtration life to the polytetrafluoroethylene microporous membranes of Comparative Examples 1 and 2.

<Flow test>
About each polytetrafluoroethylene microporous film | membrane of Examples 1-3 and Comparative Examples 1-2, the flow rate test was done as follows.
The flow rate was measured according to JIS K3831 under the following conditions. The type of the test method was “Pressurized filtration test method”, and the sample was cut into a circle having a diameter of 13 mm and set in a stainless steel holder for measurement. Isopropanol was used as the test solution, and the time required to filter 100 mL of the test solution at a pressure of 100 KPa was measured, and the flow rate (L / min · m ² ) was calculated. The results are shown in Table 3.

From the results of Table 3, the flow rates of the polytetrafluoroethylene microporous membranes of Examples 1 to 3 were superior to the polytetrafluoroethylene microporous membranes of Comparative Examples 1 and 2.

<Measurement of pore size distribution>
For each of the polytetrafluoroethylene microporous membranes of Examples 1 to 3 and Comparative Examples 1 and 2, in-plane pore size distribution measurement was performed. The pore diameter was evaluated by the following method using bubble point measurement values. A syringe holder with a diameter of 25 mm was used, IPA was used as the wetting liquid, and the initial bubble point value (corresponding to the maximum pore diameter) was taken as the measurement value. Each of the microporous membranes was cut into a square with a side of 400 mm, and the inside of the square was equally divided into 100 with a square with a side of 40 mm, and bubble points were measured for each part to obtain an average value and a variation rate. The results are shown in Table 4.
The rate of variation is represented by the ratio of the standard deviation to the average value of the measured values. When the average value of n pieces of data (X1, X2,... Xn) is Xm and the standard deviation is Sx, the variation rate Vx can be calculated by the following equation.
Fluctuation rate [%]; Vx = Sx / Xm × 100

From the results of Table 4, in Examples 1 to 3, heating was performed uniformly by fixing one surface of the crystalline polymer film in the asymmetric heating step, and the in-plane variation of the average pore diameter after stretching was small. It was uniform and the effect of the present invention was confirmed.
On the other hand, in Comparative Examples 1 and 2, since the crystalline polymer film was not fixed in the asymmetric heating step, heating unevenness occurred and the in-plane variation of the average pore diameter after stretching was large.

Example 4
-Filter cartridge-
The polytetrafluoroethylene (PTFE) microporous membrane of Example 1 was laminated as follows, pleated to a pleat width of 12.5 mm (pleat width = 220 mm), and a pleat for 230 ridges was taken to form a cylinder. The seam was welded with an impulse sealer. Next, 15 mm at both ends of the cylinder were cut off, and the cut surfaces were thermally welded to a polypropylene end plate to produce an element exchange type filter cartridge (Example 4).
−Configuration−
Primary side net AET DELNET (RC-0707-20P)
Thickness: 0.13 mm, basis weight: 31 g / m ² , use area: about 1.3 m ²
Primary side non-woven fabric Syntex (PK-404N) manufactured by Mitsui Chemicals, Inc.
Thickness: 0.15 mm, working area: about 1.3 m ²
Filter medium PTFE microporous membrane of Example 1
Thickness: about 0.05 mm, working area: about 1.3 m ²
Secondary Net DELNET (RC-0707-20P) manufactured by AET
Thickness: 0.13 mm, basis weight: 31 g / m ² , use area: about 1.3 m ²

(Example 5)
A filter cartridge of Example 5 was produced in the same manner as in Example 4 except that the PTFE microporous membrane of Example 1 was changed to the PTFE microporous membrane of Example 2 in Example 4.

(Example 6)
A filter cartridge of Example 6 was produced in the same manner as in Example 4 except that the PTFE microporous membrane of Example 1 was changed to the PTFE microporous membrane of Example 3 in Example 4.

(Comparative Example 3)
A filter cartridge of Comparative Example 3 was produced in the same manner as in Example 4 except that the PTFE microporous membrane of Example 1 was changed to the PTFE microporous membrane of Comparative Example 1 in Example 4.

(Comparative Example 4)
A filter cartridge of Comparative Example 4 was produced in the same manner as in Example 4 except that the PTFE microporous membrane of Example 1 was changed to the PTFE microporous membrane of Comparative Example 2 in Example 4.

  Since the filter cartridges of Examples 4 to 6 of the present invention use the PTFE microporous membranes of Examples 1 to 3 of the present invention, they are excellent in solvent resistance. In addition, since the pores of the PTFE microporous membrane have an asymmetric structure, a large flow rate and clogging are difficult to occur, and the lifetime is long.

<Particle trapping test (large area: after cartridge processing)>
About 100 filter cartridges of Examples 4 to 6 and Comparative Examples 3 to 4, an aqueous solution containing 0.01% by mass of polystyrene fine particles (average particle size 0.9 μm) was filtered with a differential pressure of 0.1 kg, The presence or absence of particle leakage was evaluated. The results are shown in Table 5.

From the results of Table 5, in the filter cartridges of Examples 4 to 6, since the PTFE microporous membranes of Examples 1 to 3 that achieve highly uniform heating are used, the particle trapping variation is small. There was no leakage of particles, and even in a cartridge processing form requiring a large area, the particle capturing property was excellent.
On the other hand, in the filter cartridges of Comparative Examples 3 to 4, since the PTFE microporous film of Comparative Examples 1 and 2 in which unevenness in heating occurred is used, the particle trapping variation is relatively large and the large area is used. Occasionally, leakage of particles occurred, and the particle capturing ability was poor.

  The crystalline polymer microporous membrane of the present invention and the filter for filtration using the same have a uniform in-plane distribution of the average pore diameter, can capture fine particles efficiently over a long period of time, and have a resistance to particle trapping. Since the scratch resistance is improved and heat resistance and chemical resistance are excellent, it can be used in various situations where filtration is required, and is suitably used for microfiltration of gases, liquids, etc. Widely used for filtration of corrosive gases, various gases used in the semiconductor industry, washing water for electronics industry, pharmaceutical water, pharmaceutical manufacturing process water, food water, etc., sterilization, high temperature filtration, reactive chemical filtration, etc. be able to.

DESCRIPTION OF SYMBOLS 1 Primary side support 2 Microfiltration membrane 3 Secondary side support 4 Upper end plate 5 Lower end plate 6 Filter element cover 7 Filter element core 8 O-ring 9 Filter media 10 Filter element 11 Housing cover 12 Housing base 13 Liquid inlet nozzle 14 Liquid Outlet nozzle 15 Air vent 16 Drain 17 Welded part 41 Suction belt unit 42 Suction hole 43 Endless belt 44 Vacuum box 45 Suction belt roll 46 Heater unit 51 Suction roll unit 52 Suction hole 53 Roll 56 Heater unit 101 Outer cover 102 Film support 103 Microfiltration membrane 104 Membrane support 105 Core 106a, 106b End plate 107 Gasket 108 Body outlet

Claims (14)

The thickness of the film is fixed by heating one surface of the fixed film made of the crystalline polymer by heating means at a temperature equal to or higher than the melting point of the crystalline polymer fired body in a non-contact state with the heating means. An asymmetric heating step to form a semi-baked film having a temperature gradient in the direction;
A stretching step of stretching the semi-baked film;
A method for producing a crystalline polymer microporous membrane, comprising:   2. The method for producing a crystalline polymer microporous membrane according to claim 1, wherein one whole surface of the film made of the crystalline polymer is fixed.   In the film made of crystalline polymer, the surface opposite to the surface heated by the heating means is fixed by the fixing means, and the fixing means has a plurality of holes formed on the surface and can be sucked from the surface to the inside. The method for producing a crystalline polymer microporous membrane according to claim 1, wherein the method is any one of a belt and a roll.   The method for producing a crystalline polymer microporous membrane according to any one of claims 1 to 3, wherein the crystalline polymer is polytetrafluoroethylene.   The method for producing a crystalline polymer microporous membrane according to any one of claims 1 to 4, wherein the stretching step stretches the semi-fired film in a uniaxial direction.   The method for producing a crystalline polymer microporous membrane according to any one of claims 1 to 5, wherein the stretching step stretches the semi-fired film in the biaxial direction.   The method for producing a crystalline polymer microporous membrane according to any one of claims 1 to 6, further comprising a hydrophilization step of hydrophilizing the stretched film.   It is manufactured by the method for manufacturing a crystalline polymer microporous membrane according to any one of claims 1 to 7, wherein an average pore diameter of one surface is larger than an average pore diameter of the other surface, and the one surface A crystalline polymer microporous membrane characterized in that the average pore diameter continuously changes toward the other surface.   The thickness of the crystalline polymer microporous membrane is X, the average pore diameter in the thickness portion in the depth direction X / 10 from the non-heated surface is P1, and the average pore diameter in the thickness portion in the depth direction 9X / 10 is P2. The crystalline polymer microporous membrane according to claim 8, wherein P1 / P2 is 4.5 or more.   The crystalline polymer microporous membrane according to any one of claims 8 to 9, wherein the in-plane variation of the average pore diameter is a fluctuation rate of 20% or less. Crystalline polymer microporous membrane area according to any one of 0.04 m ² is greater than 8. 10.   A filter for filtration, comprising the crystalline polymer microporous membrane according to any one of claims 8 to 11.   The filter for filtration according to claim 12, wherein the filter is processed and formed into a pleated shape.   The filter for filtration according to any one of claims 12 to 13, wherein the surface side of the crystalline polymer microporous membrane having a larger average pore diameter is used as a filter surface of the filter.