JP2009061361A - Crystalline polymer microporous film, its manufacturing method, and filtration filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a crystalline polymer microporous film which can efficiently capture fine particles, is hardly clogged and has improved scratch resistance while keeping performance of capturing fine particles and has long filtration life and to provide a method for manufacturing the crystalline polymer microporous film with which the crystalline polymer microporous film can be efficiently manufactured and a filtration filter using the crystalline polymer microporous film. <P>SOLUTION: The crystalline polymer microporous film has a crystalline polymer layer which is composed of two or more crystalline polymers different from one another and has a single structure, and many pores each penetrating the crystalline polymer layer in the thickness direction. The composition ratio of the crystalline polymers changes in the thickness direction of the crystalline polymer layer and the average pore diameter of pores also changes in the thickness direction of the crystalline polymer layer. This crystalline polymer microporous film is used in the filtration filter. <P>COPYRIGHT: (C)2009,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 microporous membranes include those using cellulose ester as a raw material (see Patent Documents 1 to 7), those using aliphatic polyamide as a raw material (see Patent Documents 8 to 14), and polyfluorocarbon as a raw material. And the like (see Patent Documents 15 to 18) and those made of polypropylene (see Patent Document 19).
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, the microporous film made of a crystalline polymer has excellent chemical resistance, and in particular, the crystalline polymer microporosity using polytetrafluoroethylene (hereinafter sometimes referred to as “PTFE”) as a raw material. Since the film is excellent in heat resistance and chemical resistance, the growth of the demand is remarkable.

In general, the filterable amount per unit area of the microporous membrane is small (that is, the filtration life is short). For this reason, when industrially used, in order to increase the membrane area, it is necessary to use many filtration units in parallel, and from the viewpoint of cost reduction of the filtration process, the filtration life is increased. Is needed. For example, as a microporous membrane effective for reducing the flow rate due to clogging or the like, an asymmetric membrane is proposed in which the pore diameter gradually decreases from the inlet side toward the outlet side (see Patent Documents 20 and 21).
In addition, a polytetrafluoroethylene multilayer porous membrane comprising a filtration layer having a small pore size and a support layer having a pore size larger than the filtration layer (see Patent Document 22), polytetrafluoroethylene emulsion dispersion on a polytetrafluoroethylene sheet The thing which apply | coated the liquid and extended | stretched (refer patent document 23) etc. is proposed.

However, when trying to realize the asymmetric membranes of Patent Documents 20 and 21 using polytetrafluoroethylene, since the polytetrafluoroethylene is soluble only in a very special solvent, the pore diameter gradually decreases. A conductive film cannot be produced. Further, when filtration is performed using the obtained microporous membrane, there is a problem that the flow rate is reduced due to clogging or the like.
Further, according to Patent Documents 22 and 23, the problems in Patent Documents 20 and 21 can be reduced, but on the other hand, when applied and dried, cracks and defects are likely to occur in the microporous film. There is a problem. Moreover, since only the surface has a small pore diameter, there is a problem that a sufficient filtration life cannot be obtained.
However, Patent Documents 22 and 23 have a problem that cracks and defects are likely to occur in the microporous film when applied and dried. Furthermore, since only the surface has a small pore diameter, there is a problem that a sufficient filtration life cannot be obtained.

  Further, according to Patent Documents 24 and 25, a multi-layer sheet extrusion method can be used to produce a completely integrated filter layer having a small pore diameter and a support layer having a large pore diameter. There is a problem that clogging is likely to occur at (a portion where the pore diameter is discontinuous).

  Patent Document 26 proposes a method for producing an asymmetric pore diameter thin film by applying a temperature difference and a compressive force in the thickness direction of the tetrafluoroethylene resin thin film. However, in this proposal, since the heating temperature is as low as 250 ° C. to the melting point of the tetrafluoroethylene resin, it is impossible to form a hole having a desired shape.

  Accordingly, a crystalline polymer microporous membrane comprising a crystalline polymer layer having a single layer structure composed of two or more different crystalline polymers, capable of capturing fine particles efficiently, having no clogging, and having a long filtration life, and The present condition is that the manufacturing method and the prompt provision of the filter for filtration are desired.

US Pat. No. 1,421,341 US Pat. No. 3,133,132 US Pat. No. 2,944,017 Japanese Patent Publication No. 43-15698 Japanese Examined Patent Publication No. 45-3313 Japanese Examined Patent Publication No. 48-39586 Japanese Patent Publication No. 48-40050 US Pat. No. 2,783,894 US Pat. No. 3,408,315 U.S. Pat. No. 4,340,479 US Pat. No. 4,340,480 U.S. Pat. No. 4,450,126 German Patent Invention No. 3,138,525 JP 58-37842 A US Pat. No. 4,196,070 US Pat. No. 4,340,482 JP 55-99934 A JP 58-91732 A West German Patent No. 3,003,400 Japanese Patent Publication No.55-6406 Japanese Examined Patent Publication No. 4-68966 JP-A-4-351645 JP 7-292144 A JP-A-3-179038 JP-A-3-179039 Japanese Patent Publication No. 63-48562 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 includes a crystalline polymer layer having a single layer structure composed of two or more different crystalline polymers, and a large number of pores penetrating in the thickness direction of the crystalline polymer layer. By changing the composition ratio of the polymer in the thickness direction of the crystalline polymer layer and changing the average pore diameter of the pores in the thickness direction of the crystalline polymer layer, fine particles can be captured efficiently. A crystalline polymer microporous membrane that is free of clogging, can be filtered at a high flow rate, and has a long filtration life, and a crystalline polymer microporous membrane that can efficiently produce the crystalline polymer microporous membrane An object of the present invention is to provide a production method and a filter for filtration using the crystalline polymer microporous membrane.

Means for solving the problems are as follows. That is,
<1> A crystalline polymer microporous film having a crystalline polymer layer having a single layer structure composed of two or more different crystalline polymers, and a large number of pores penetrating in the thickness direction of the crystalline polymer layer. There,
Crystallinity characterized in that the composition ratio of the crystalline polymer changes in the thickness direction of the crystalline polymer layer, and the average pore diameter of the pores changes in the thickness direction of the crystalline polymer layer It is a polymer microporous membrane.
<2> The crystalline polymer microporous membrane according to <1>, wherein the change in average pore diameter in the pores is any one of continuous or discontinuous increase and continuous or discontinuous decrease. is there.
<3> The crystalline polymer microporous membrane according to any one of <1> to <2>, wherein a portion having a minimum average pore diameter is present in the crystalline polymer layer.
<4> The composition according to any one of <1> to <3>, wherein the change in the composition ratio of the crystalline polymer is any one of continuous or discontinuous increase and continuous or discontinuous decrease. It is a crystalline polymer microporous membrane.
<5> The crystalline polymer layer is composed of two or more crystalline polymers having different number average molecular weights, and the number average molecular weight of the crystalline polymer is changed in the thickness direction of the crystalline polymer layer <1> To <4>, the crystalline polymer microporous membrane.
<6> The crystalline polymer microporous membrane according to any one of <1> to <5>, wherein the crystalline polymer is polytetrafluoroethylene.
<7> Two or more types of crystalline polymer particles different from each other are spread in the mold one by one, the crystalline polymer particles are interfacially mixed and pressed to form a preform, and the preform is extruded. A crystalline polymer film production process for producing a crystalline polymer film,
A crystalline polymer microporous membrane comprising at least a stretching step of stretching the obtained crystalline polymer film.
<8> The crystalline polymer micropore according to <7>, including an asymmetric heating step in which one surface of the crystalline polymer film before stretching is heated to form a temperature gradient in the thickness direction of the crystalline polymer film. It is a manufacturing method of a conductive film.
<9> The method for producing a crystalline polymer microporous film according to any one of <7> to <8>, wherein the interfacial mixing is performed by applying vibration to the crystalline polymer particles.
<10> The method for producing a crystalline polymer microporous membrane according to any one of <7> to <9>, wherein the crystalline polymer particles have different number average molecular weights.
<11> The method for producing a crystalline polymer microporous membrane according to any one of <7> to <10>, wherein the crystalline polymer particles are polytetrafluoroethylene particles.
<12> The method for producing a crystalline polymer microporous membrane according to any one of <7> to <11>, wherein the stretching is uniaxial stretching.
<13> The method for producing a crystalline polymer microporous membrane according to any one of <7> to <11>, wherein the stretching is biaxial stretching.
<14> A filtration filter using the crystalline polymer microporous membrane according to any one of <1> to <6>.
<15> The filter for filtration according to <14>, wherein a surface of the pore portion of the crystalline polymer microporous membrane having a larger average pore diameter is used as a filter surface of the filter.

  The crystalline polymer microporous membrane of the present invention comprises a crystalline polymer layer having a single layer structure composed of two or more different crystalline polymers, and a large number of pores penetrating in the thickness direction of the crystalline polymer layer. And the composition ratio of the crystalline polymer changes in the thickness direction of the crystalline polymer layer, and the average pore diameter of the pores changes in the thickness direction of the crystalline polymer layer. It is possible to capture efficiently, there is no clogging, and the filtration life can be extended.

The method for producing a crystalline polymer microporous membrane of the present invention includes at least a crystalline polymer film production step and a stretching step.
In the method for producing a crystalline polymer microporous membrane of the present invention, in the crystalline polymer film preparation step, two or more different types of crystalline polymer particles are spread in a mold one by one, and the crystalline polymer particles Are interfacially mixed and pressed to form a preform, and the preform is extruded to produce a crystalline polymer film. In the stretching step, the obtained crystalline polymer film is stretched. As a result, the composition ratio of the crystalline polymer changes in the thickness direction of the crystalline polymer layer, and the average pore diameter of the pores changes in the thickness direction of the crystalline polymer layer, so that fine particles can be captured efficiently. It is possible to efficiently produce a crystalline polymer microporous membrane having no clogging and a long filtration life.

  Since the filter for filtration of the present invention uses the crystalline polymer microporous membrane of the present invention, it is possible to efficiently capture fine particles by performing filtration with the surface (surface) having a large average pore diameter as the inlet side. Can do. In addition, since the specific surface area is large, the effect that the fine particles are removed by adsorption or adhesion before reaching the minimum pore diameter portion is great, and the filtration life can be greatly improved.

  According to the present invention, a conventional problem can be solved, and a single-layered crystalline polymer layer composed of two or more different crystalline polymers and a large number of holes penetrating in the thickness direction of the crystalline polymer layer. And the composition ratio of the crystalline polymer is changed in the thickness direction of the crystalline polymer layer, and the average pore diameter of the pores is changed in the thickness direction of the crystalline polymer layer, whereby fine particles are obtained. A crystalline polymer microporous membrane that can be efficiently trapped, has no clogging, can be filtered at a high flow rate, and has a long filtration life, and can efficiently produce the crystalline polymer microporous membrane A method for producing a crystalline polymer microporous membrane, and a filter for filtration using the crystalline polymer microporous membrane can be provided.

(Crystalline polymer microporous membrane)
The crystalline polymer microporous membrane of the present invention comprises a crystalline polymer layer having a single layer structure composed of two or more different crystalline polymers, and a large number of pores penetrating in the thickness direction of the crystalline polymer layer. And other configurations as necessary.

The “single layer structure” means that there is no boundary between the crystalline polymer layer and the crystalline polymer layer, and includes those in which the boundary is removed from a laminate of two or more crystalline polymer layers. It is. Here, the presence / absence of a boundary between the crystalline polymer layer and the crystalline polymer layer is confirmed by, for example, a cut surface obtained by cutting the crystalline polymer microporous film in the thickness direction using an optical microscope or a scanning electron microscope (SEM). be able to.
The method for eliminating the boundary is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include a method in which powder at the interface (interlayer) is randomly diffused and mixed at the interface.

  In the present invention, the composition ratio of the crystalline polymer in the crystalline polymer layer of the single-layer structure is changed in the thickness direction of the crystalline polymer layer, and the average of the pores in the crystalline polymer layer of the single-layer structure The pore diameter changes in the thickness direction of the crystalline polymer layer. Thereby, fine particles can be captured efficiently, there is no clogging, and the filtration life can be extended.

"The composition ratio of the crystalline polymer is changing in the thickness direction of the crystalline polymer layer" means that at least two kinds of crystalline polymers constituting the crystalline polymer layer having a single layer structure are interfacially mixed and the composition It means that the ratio changes in the thickness direction of the crystalline polymer layer, resulting in a continuous gradient composition ratio. A partly discontinuous gradient composition ratio may be included.
Examples of the method for identifying the change in the composition ratio of the crystalline polymer include spectroscopic techniques (X-ray, ultraviolet (UV), visible light, infrared (IR)), NMR, MS spectrum, DSC, TG-DTA, Density, average molecular weight (number average molecular weight, mass average molecular weight, etc.), etc. can be used. Among these, it is preferable to mix two kinds of materials having different average molecular weights for the purpose of controlling the pore diameter, and in order to form a mixing ratio, it is straightforward to measure the average molecular weight from the point of view of the crystalline polymer. It is particularly preferred to use the number average molecular weight.
By these methods, the thickness direction of, for example, a preform, a sheet after extrusion, a sheet after rolling, a sheet after stretching, etc. in any step in the method for producing a crystalline polymer microporous membrane of the present invention The composition ratio in the thickness direction of the crystalline polymer can be determined by cross-sectional analysis (sampling, imaging, etc.) or etching treatment (dissolution, decomposition, cutting, etc.) from the front or back surface.

It is preferable that the change in the average pore diameter and the change in the composition ratio of the crystalline polymer in the pores are either continuously or discontinuously increased and continuously or discontinuously decreased.
The phrase “the average pore diameter of the pores changes in the thickness direction of the crystalline polymer layer” means that the horizontal axis indicates the distance d in the thickness direction from the front surface of the crystalline polymer microporous membrane (mainly (1) From the front surface (d = 0) to the back surface (d = film thickness) The graph is drawn with one continuous line (continuous), and the slope (dD / dt) of the graph is a negative area (decrease) or a positive slope (increase). If there is, the case where the inclination is 0 (zero) may be included. The case where the inclination is 0 (zero) in the entire microporous membrane (no change) is not included.
Among these, it is particularly preferable that the average pore diameter of the pores in the crystalline polymer layer has a continuously decreasing graph from the front surface to the back surface.

In addition, “the composition ratio of the crystalline polymer is changing in the thickness direction of the crystalline polymer layer” means that the horizontal axis indicates the distance d (in the thickness direction from the front surface of the crystalline polymer microporous membrane). (Corresponding to the depth from the front surface) and taking the composition ratio of the crystalline polymer on the vertical axis, (1) From the front surface (d = 0) to the back surface (d = film thickness) The graph up to this point is drawn with one continuous line (continuous), and the slope (dD / dt) of the graph is negative (decrease) or the slope is positive (increase). If it is continuous, the case where the inclination is 0 (zero) may be included. The case where the inclination is 0 (zero) in the entire microporous membrane (no change) is not included.
Among these, it is particularly preferable that the composition ratio of the crystalline polymer has a continuously decreasing graph from the front surface to the back surface.

  In the present invention, the surface of the crystalline polymer microporous membrane having the larger average pore diameter is referred to as “front surface”, and the surface having the smaller average pore diameter is referred to as “back surface”. However, this is merely a name given for convenience in order to make the description of the present invention easier to understand, and any surface may be a “back surface”.

Here, as shown in FIG. 1, the pore diameter of the hole 101a in the crystalline polymer microporous film of the present invention comprising the crystalline polymer layer 101 having a single layer structure changes in the thickness direction of the crystalline polymer layer (one As the whole crystalline polymer microporous membrane, the pore diameter of the pore 101a changes in the thickness direction (decreases in steps), and the pore diameter changes. The part which is carrying out is a taper shape.
On the other hand, as shown in FIG. 2, the pore diameters of the holes 102b and 103b in the conventional crystalline polymer microporous film having a two-layer structure in which the crystalline polymer layers 102 and 103 are laminated are all the crystalline polymers. It does not change in the thickness direction of the layer, and as a whole crystalline polymer microporous membrane, the pore diameter changes (decreases in steps) in the thickness direction.
Further, as shown in FIG. 3, in the crystalline polymer layer 104 having a single layer structure, the average pore diameter of the pores 104a changes in the thickness direction of the crystalline polymer layer (including a part that has not changed partially and is continuous). And the portion where the hole diameter is changed is tapered.
On the other hand, as shown in FIG. 4, the hole diameters of the holes 105b, 106b, 107b in the conventional crystalline polymer microporous film having a three-layer structure in which the crystalline polymer layers 105, 106, 107 are laminated are all The crystalline polymer layer does not change in the thickness direction, and when the entire crystalline polymer microporous film is viewed, there is a portion where the pore diameter changes stepwise in the thickness direction.

Further, in the crystalline polymer microporous membrane of the present invention, it is preferable that a portion having a minimum average pore diameter is present inside the crystalline polymer layer. Thereby, the crystalline polymer layer having the smallest diameter that most affects the trapped particle size can be protected from physical destruction factors such as friction and scratching, and the trapping performance can be stabilized.
For example, as shown in FIG. 3, a portion 104 c where the average pore diameter of the hole 104 a is minimum exists inside the crystalline polymer layer 104 having a single layer structure.

  Here, the average pore diameter of the hole is, for example, a photograph of the film surface (SEM photograph, magnification 1,000 times to ~) with a scanning electron microscope (Hitachi S-4000 type, vapor deposition is Hitachi E1030 type, both manufactured by Hitachi, Ltd.) 5,000 times) and the obtained photograph is processed 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 ) To obtain an image composed only of crystalline polymer fibers, and the average pore size is obtained by calculating the image.

-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 that 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.

The crystalline polymer is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include polyalkylenes, polyesters, polyamides, polyethers, and liquid crystalline polymers. Specific examples include polyethylene, Examples include polypropylene, nylon, polyacetal, polybutylene terephthalate, polyethylene terephthalate, syndiotactic polystyrene, polyphenylene sulfide, polyether ether ketone, wholly aromatic polyamide, wholly aromatic polyester, fluororesin, and polyether nitrile.
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. Alkylene is more preferred, and polytetrafluoroethylene (PTFE) is particularly preferred.
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, HDPE is particularly preferable from the viewpoint of crystallinity control.

  As the polytetrafluoroethylene, polytetrafluoroethylene produced by an emulsion polymerization method can be usually used, and a finely divided polytetrafluoroethylene obtained by coagulating an aqueous dispersion obtained by emulsion polymerization. It is preferred to use ethylene.

  There is no restriction | limiting in particular as said polytetrafluoroethylene, According to the objective, it can select suitably, A commercial item can be used. Examples of the commercially available products include polyflon PTFE F-104, polyflon PTFE F-201, polyflon PTFE F-205, polyflon PTFE F-207, polyflon PTFE F-301 (all manufactured by Daikin Industries, Ltd.); Fluon PTFE CD1, Fluon PTFE CD141, Fluon PTFE CD145, Fluon PTFE CD123, Fluon PTFE CD076, Fluon PTFE CD090 (all manufactured by Asahi Glass Co., Ltd.); Teflon (registered trademark) PTFE 6-J, Teflon (registered trademark) TFElon (Registered Trademark) PTFE 6C-J, Teflon (Registered Trademark) PTFE 640-J (all manufactured by Mitsui DuPont Fluorochemical Co., Ltd.), and the like. Among these, F-104, CD1, CD141, CD145, CD123, 6-J are preferable, F-104, CD1, CD123, 6-J are more preferable, and CD123 is particularly preferable.

The crystalline polymer layer is composed of two or more different crystalline polymers.
Here, “different from each other” means that the materials, number average molecular weights, crystallinity, etc. of two or more kinds of crystalline polymers contained in the crystalline polymer layer are different.
The material of each crystalline polymer may be the same material or different materials. When each crystalline polymer is the same material, the number average molecular weight and the degree of crystallinity Any one of the different crystalline polymers may be used.
Examples of the crystalline polymer of the different materials include a case where PTFE and polyethylene are used.
Examples of the crystalline polymer having different number average molecular weights include those having a difference in number average molecular weight of 1 million or more in the case of PTFE.
Examples of the crystalline polymer having a different crystallinity include those having a difference in crystallinity of 5% or more in the case of PTFE.
Here, the crystallinity can be measured by, for example, wide-angle X-ray diffraction, NMR, infrared (IR), DSC, density measurement, “Fluorine Resin Handbook” (Nikkan Kogyo Shimbun, edited by Takaomi Satokawa) 45 or the like.

Each of the crystalline polymers preferably has a glass transition temperature of 40 ° C to 400 ° C, more preferably 50 ° C to 350 ° C.
Each of the crystalline polymers preferably has a mass average molecular weight of 1,000 to 100,000,000.
The number average molecular weight of each crystalline polymer is preferably 500 to 50,000,000, more preferably 1,000 to 10,000,000.
Here, the number average molecular weight can be measured, for example, by gel permeation chromatography (GPC). However, since PTFE is insoluble in a solvent, the heat of crystallization (ΔHc: cal / g) is measured by DSC measurement and calculated using the relational expression: Mn = 2.1 × 10 ¹⁰ × ΔHc ^−5.16 It is preferable to do.

  The film thickness of the crystalline polymer microporous film having a single layer structure is preferably 1 μm to 300 μm, more preferably 5 μm to 100 μm, and still more preferably 10 μm to 80 μm.

(Method for producing crystalline polymer microporous membrane)
The method for producing a crystalline polymer microporous membrane of the present invention comprises at least a crystalline polymer film preparation step and a stretching step, and further comprises an asymmetric heating step and, if necessary, other steps.

-Crystalline polymer film production process-
In the crystalline polymer film production step, two or more types of crystalline polymer particles different from each other are spread in a mold one by one, the crystalline polymer particles are interfacially mixed and pressed to form a preform, This is a process for producing a crystalline polymer film by extruding a preform.
The different crystalline polymers can be appropriately selected from those described above according to the purpose, and it is preferable to use crystalline polymer particles having different number average molecular weights.

There is no restriction | limiting in particular in the said crystalline polymer film preparation process, It can carry out according to the well-known paste extrusion method.
First, a mixture (paste) obtained by mixing two different kinds of crystalline polymer particles with an extrusion aid is spread one by one in a mold, and the paste (crystalline polymer particles) is interfacially mixed.
As the extrusion aid, a liquid lubricant is preferably used. Specific examples include solvent naphtha and white oil. Moreover, a commercial item can be used as the extrusion aid, and a hydrocarbon oil such as “Isopar” manufactured by Esso Petroleum Corporation may be used as the commercial item. 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.
There is no restriction | limiting in particular as said interface mixing, According to the objective, it can select suitably, For example, it is preferable to give a vibration to a crystalline polymer particle. The vibration is preferably performed using a known vibrator and appropriately adjusting the vibration mode (vertical, horizontal, rotational, random, etc.), amplitude, speed, time, and the like.
Next, the interfacial mixed paste is pressurized to prepare a preform, and the preform is rolled by a paste extruder to prepare a crystalline polymer unheated film.

The paste extrusion is preferably performed at a temperature of 50 ° C to 80 ° C. There is no restriction | limiting in particular about extrusion shape, According to the objective, it can select suitably, Usually rod shape or rectangular shape is preferable. 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. Thereafter, the extrusion aid is removed by heating the film to form a crystalline polymer unheated film. Although the heating temperature at this time can be suitably selected according to the kind of crystalline polymer to be used, 40 to 400 degreeC is preferable and 60 to 350 degreeC is more preferable. For example, when polytetrafluoroethylene is used, it is preferably 150 ° C. to 280 ° C., more preferably 200 ° C. to 255 ° C. The heating can be performed by a method such as passing the film through a hot air drying furnace. The thickness of the crystalline polymer unheated film thus produced can be appropriately adjusted according to the thickness of the crystalline polymer microporous film to be finally produced.
In the production of the crystalline polymer unheated film, the items described in “Polyfluorocarbon Handbook” (issued by Daikin Industries, Ltd., revised in 1983) can be appropriately employed.

Here, with reference to FIGS. 5-8, an example of the manufacturing method of the crystalline polymer microporous film | membrane of this invention is demonstrated.
As shown in FIG. 7, a preform 10 comprising a crystalline polymer layer 6 having a single-layer structure in which two kinds of PTFE fine powders 1 and 2 are interfacially mixed to eliminate the boundary is produced.
The preform is prepared by adding a liquid lubricant such as solvent naphtha or white oil to a fine powder of PTFE produced by coagulating a PTFE emulsion polymerization aqueous dispersion having an average primary particle size of 0.2 μm to 0.4 μm. Obtained from paste 1 and paste 2. The amount of the liquid lubricant used varies depending on the type, molding conditions and the like, and is usually used in the range of 20 to 35 parts by mass with respect to 100 parts by mass of the fine powder of PTFE. Furthermore, a coloring agent etc. can also be added as needed.
First, a paste 1 containing PTFE fine powder 1 (white circles) for forming a first layer is laid in layers on the lower mold 8 in a box-shaped lower mold 8 as shown in FIG. The paste 2 containing the fine powder 2 (black circle) of PTFE for forming the second layer is spread on the first layer 4, and the second layer 5 is formed on the first layer 4. At this time, shake each paste well so that the powders do not stick to each other, and then spread.
Next, in a state where the powder can flow, the mold is vibrated with a test tube mixer (amplitude 5 mm, 150 rpm) to interfacially mix the powder of each layer (see FIG. 6). This interfacial mixing eliminates the boundary between the two layers (a single layer structure paste). Thereafter, the paste mixed at the interface was pressurized to form a preform 10 (see FIG. 7).
As described above, the preformed body 10 is obtained which is molded to a size that can be accommodated in the cylinder portion of the paste extrusion apparatus as shown in FIG.

Next, after storing the obtained preform 10 in the cylinder part of the paste extrusion apparatus shown in FIG. 8, it is pressed in the direction of the arrow by a pressurizing means (not shown). The cylinder part of the paste extrusion apparatus of FIG. 8 is, for example, a rectangle having a cross section in the direction perpendicular to the axis of 50 mm × 100 mm, and is composed of a nozzle 50 mm × 5 mm in which one of the cylinder parts is squeezed at the outlet part.
In this way, the polytetrafluoroethylene unheated film 15 having a single layer structure is formed.

-Stretching process-
The stretching step is a step of stretching the obtained crystalline polymer film.
The 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 4 to 100 times, more preferably 8 to 90 times, and still more preferably 10 to 80 times. The stretching temperature in the longitudinal direction is preferably 100 ° C to 300 ° C, more preferably 200 ° C to 290 ° C, and particularly preferably 250 ° C to 280 ° C.
The stretching ratio in the width direction is preferably 10 to 100 times, more preferably 12 to 90 times, still more preferably 15 to 70 times, and particularly preferably 20 to 40 times. The stretching temperature in the width direction is preferably 100 ° C to 300 ° C, more preferably 200 ° C to 290 ° C, and particularly preferably 250 ° C to 280 ° C.
The area stretch ratio is preferably 50 times to 300 times, more preferably 75 times to 280 times, and still more preferably 100 times to 260 times. When stretching is performed, the crystalline polymer film may be preheated to a temperature equal to or lower than the stretching temperature in advance.
In addition, after extending | stretching, heat setting can be performed as needed. The heat setting temperature is usually preferably not lower than the stretching temperature and lower than the melting point of the crystalline polymer.

-Asymmetric heating process-
The asymmetric heating step is a step of heating one surface of the crystalline polymer film before stretching to form a temperature gradient in the thickness direction of the crystalline polymer film.
Here, the asymmetric heating means that the crystalline polymer film is heat-treated at a temperature not lower than the melting point of the heated body and not higher than the melting point of the unheated body + 15 ° C.
In the present invention, the unheated body means one that has not been subjected to asymmetric heating treatment. The melting point of the unheated body means the temperature at the peak of the endothermic curve that appears when the unheated body is measured with a differential scanning calorimeter. The melting point of the heated body and the melting point of the unheated body vary depending on the kind of crystalline polymer, the number average molecular weight, etc., 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, in the case of polytetrafluoroethylene, the melting point of the heated body is about 324 ° C., and the melting point of the unheated body is about 345 ° C. Therefore, in the case of a polytetrafluoroethylene film, 324 ° C. to 360 ° C. is preferable for forming a semi-heated body in which a melting point of about 324 ° C. and a melting point of about 345 ° C. are mixed. 350 degreeC is more preferable, for example, it heats to the temperature of 345 degreeC.

  Regarding the supply of heat energy in the asymmetric heating step, either a method of continuously supplying energy or a method of supplying energy intermittently after being divided several times can be employed. According to the definition of the asymmetric heating, it is necessary to cause a temperature difference between the front surface and the back surface of the crystalline polymer film. As this method, the temperature of the back surface is supplied by intermittently supplying energy. The method of suppressing the rise can be used. On the other hand, in the case of continuous heating, in order to maintain this temperature gradient, a method of cooling the back surface simultaneously with the heating of the front surface can be used effectively.

There is no restriction | limiting in particular as the supply method of the said heat energy, According to the objective, it can select suitably, For example, (1) The method of spraying a hot air on a crystalline polymer film, (2) The crystalline polymer film is used as a heat medium. A method of contacting, (3) a method of bringing the crystalline polymer film into contact with a heating member, (4) a method of irradiating the crystalline polymer film with infrared rays, and (5) a method of heating the crystalline polymer film with electromagnetic waves such as microwaves. Etc. can be used. Among these, (3) a method of contacting the heating member and (4) a method of irradiating infrared rays are preferable.
The heating member (3) is preferably a heating roll. If it is a heating roll, asymmetric heating can be performed continuously in a flow operation industrially, and temperature control and maintenance of the apparatus are easy. The temperature of the heating roll can be set to the temperature at which the semi-heated body is used. The time for which the film is brought into contact with the heating roll is the time necessary for the target asymmetric heating to sufficiently proceed, preferably 30 seconds to 120 seconds, more preferably 45 seconds to 90 seconds, and more preferably 60 seconds to 80 seconds. Is more preferable.

There is no restriction | limiting in particular as infrared irradiation of said (4), According to the objective, it can select suitably.
The general definition of the infrared can be referred to “practical infrared” (Human and History, published in 1992). In the present invention, the infrared ray means an electromagnetic wave having a wavelength of 0.74 μm to 1,000 μm, of which a wavelength range of 0.74 μm to 3 μm is a near infrared ray, and a wavelength range of 3 μm to 1,000 μm is far away. Infrared.
In the present invention, since it is preferable that there is a temperature difference between the front surface and the back surface of the unheated body, far infrared rays advantageous for heating the surface layer are preferably used.
The type of 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.
In addition, if infrared irradiation is used, it is possible to perform asymmetric heating continuously in a flow operation industrially, and temperature control and maintenance of the apparatus are easy. Moreover, since it is non-contact, it does not cause defects such as cleanness and fluff.
The film surface temperature by the infrared irradiation can be controlled by the output of the infrared irradiation apparatus, the distance between the infrared irradiation apparatus and the film surface, the irradiation time (conveying speed), and the atmospheric temperature, and is set to the temperature at which the half-heated body is formed. However, 324 ° C to 380 ° C is preferable, and 335 ° C to 360 ° C is more preferable. When the surface temperature is less than 324 ° C., the crystal state does not change and the pore diameter control may not be possible. When the surface temperature exceeds 380 ° C., the crystalline polymer film melts and the shape is excessively deformed. Thermal decomposition of the crystalline polymer may occur.
The irradiation time of the infrared rays is not particularly limited, and is a time necessary for the target asymmetric heating to sufficiently proceed, preferably 30 seconds to 120 seconds, more preferably 45 seconds to 90 seconds, and 60 seconds to 80 seconds is more preferable.
The infrared irradiation in the asymmetric heating may be performed continuously, or may be performed intermittently after being divided into several times.

Further, as the temperature gradient in the thickness direction of the crystalline polymer film, the temperature difference between the front surface and the back surface is preferably 30 ° C. or more, and more preferably 50 ° C. or more.
When the back surface of the crystalline polymer film is continuously heated, a temperature gradient is maintained between the front surface and the back surface of the crystalline polymer film. It is preferable to cool.
The method for cooling the front surface is not particularly limited and may be appropriately selected depending on the purpose. For example, a method of blowing cold air, a method of contacting with a refrigerant, a method of contacting with a cooled material, or cooling. Various methods such as cooling by the method can be used, and the method of bringing the cooling member into contact with the surface of the film is not preferable because the surface of the contact object is heated by far infrared rays.
Moreover, also when performing the said asymmetrical heating process intermittently, it is preferable to heat and cool the back surface of a crystalline polymer film intermittently, and to suppress the temperature rise of a front surface.

  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 uses 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 carried out with the surface (surface having a large average pore diameter) as the inlet side. That is, the surface side having a large pore size is used as the filter surface of the filter. In this way, fine particles can be efficiently captured by performing filtration with the surface (surface) having a large average pore diameter 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 filtration filter of the present invention can be filtered at least 5 ml / cm ² · min or more when filtration is performed at a differential pressure of 0.1 kg / cm ² .
The filter for filtration of the present invention is preferably processed and formed into a pleated shape. Processing into a pleated shape has the advantage that the effective surface area used for filtering the filter per cartridge can be increased.

  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 polytetrafluoroethylene microporous membrane>
-Preparation of preform-
As a crystalline polymer, 100 parts by mass of polytetrafluoroethylene fine powder (Asahi Glass Co., Ltd., “Fluon PTFE CD1”) having a number average molecular weight of 1,000,000, and a hydrocarbon oil (Esso Oil Co., Ltd., “ Isopar M ”)) 27 parts by weight was added. This was designated as paste 1.
Similarly, 100 parts by mass of polytetrafluoroethylene fine powder having a number average molecular weight of 10 million (Asahi Glass Co., Ltd., “Fluon PTFE CD123”) and hydrocarbon oil (Esso Oil Co., Ltd. M ") 27 parts by weight were added. This was designated as paste 2.
Next, paste 1 and paste 2 were spread in a mold as shown in FIG. 5 so that the thickness ratio (paste 1 / paste 2) was 4/1 (in FIG. 5, paste 1 was 5). , Paste 2 is represented by 4). At this time, the pastes were thoroughly shaken and spread to prevent the powders from sticking to each other.
Next, in a state where the powder before pressurization was able to flow, the mold was vibrated for 1 minute with a test tube mixer (amplitude 5 mm, 150 rpm), and the powder of each layer was interfacially mixed (see FIG. 6). Thereafter, the paste mixed at the interface was pressurized to form a preform 10 (see FIG. 7).
In the subsequent processing, the paste 1 (5) side was the “front surface” and the paste 2 (4) side was the “back surface”.

For the purpose of investigating the distribution of the composition ratio of the crystalline polymer in the thickness direction of the obtained preform, the thickness of the preform is 20, and the number in the thickness portion in the depth direction 0 (that is, the surface layer) from the front surface. The average molecular weight is M0, the number average molecular weight in the thickness portion in the depth direction 1 is M1, the number average molecular weight in the thickness portion in the depth direction 20 is M20, and M0 to M20 are DSCs in the thickness direction of the preform. Measurement (10 mg sampling for each part) was performed, and the number average molecular weight of the crystalline polymer was determined using the following relational expression 1. The DSC measurement was performed using a differential scanning calorimeter (DSC7200, manufactured by SII).
<Relational expression 1>
Number average molecular weight (Mn) = 2.1 × 10 ¹⁰ × ΔHc− ^5.16
However, ΔHc represents DSC heat of crystallization (cal / g).
The number average molecular weight (Mn) at the depth (M0 to M20) from the surface layer was plotted based on the values of M0 to M20 determined as described above. The results are shown in FIG.
From the results shown in FIG. 9, in the crystalline polymer layer of the single-layer structure preform, the number average molecular weight of the crystalline polymer changes in the thickness direction of the crystalline polymer layer (including a part that has not changed partially and is continuous). From this, it was found that the preform had a continuous gradient composition ratio due to interfacial mixing.

-Production of unheated film-
The prepared preform 10 was inserted into a cylinder of a paste extrusion mold as shown in FIG. 8, and a multilayer paste was extruded into a sheet shape. This was calendered with a calender roll heated to 60 ° C. to produce a polytetrafluoroethylene film. The obtained polytetrafluoroethylene film was passed through a hot air drying furnace at 250 ° C. to remove the extrusion aid, and a polytetrafluoroethylene unheated film having an average thickness of 100 μm, an average width of 150 mm, and a specific gravity of 1.55 was produced. .

-Production of polytetrafluoroethylene microporous membrane-
The obtained polytetrafluoroethylene unheated film was stretched between rolls by 12.5 times in the longitudinal direction at 270 ° C., and once wound on a winding roll. Then, after preheating the film to 305 ° C., both ends were sandwiched between clips and stretched 30 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 260 times in terms of stretched area ratio. Thus, the polytetrafluoroethylene microporous membrane of Example 1 was produced.

(Example 2)
-Production of polytetrafluoroethylene microporous membrane-
In Example 1, except that the thickness ratio at the time of producing the preform was set to paste 1 / paste 2 / paste 1 = 3/1/1 from the front surface, A molded body was produced.
About the obtained preform, the number average molecular weight at the depth (M0 to M20) from the surface layer of the preform was plotted in the same manner as in Example 1. The results are shown in FIG.
From the results shown in FIG. 10, in the crystalline polymer layer of the single-layer structure preform, the number average molecular weight of the crystalline polymer changes in the thickness direction of the crystalline polymer layer (including the non-changed portion, continuously From this, it was found that the preform had a continuous gradient composition ratio.
Next, using the obtained preform, a polytetrafluoroethylene unheated film was produced in the same manner as in Example 1, and stretched in the same manner to obtain the polytetrafluoroethylene microporous membrane of Example 2. Produced.

(Example 3)
-Production of polytetrafluoroethylene microporous membrane-
Using the same preform as in Example 1, a polytetrafluoroethylene unheated film was produced in the same manner as in Example 1. In addition, it turned out that the preforming body of Example 3 is the same result as FIG. 9, and has a continuous gradient composition ratio.
Next, the back surface (side of paste 2) of the polytetrafluoroethylene unheated film is heated with a halogen heater with a built-in tungsten filament by near infrared rays at a film surface temperature of 345 ° C. for 1 minute to produce a semi-heated film. A polytetrafluoroethylene microporous membrane of Example 3 was produced in the same manner as in Example 1 except that the semi-heated film was stretched in the same manner as in Example 1.

(Comparative Example 1)
-Production of polytetrafluoroethylene microporous membrane-
In Example 1, a preform was produced in the same manner as in Example 1 except that the powder of each layer of the preform before pressing was not interfacial mixed.
About the obtained preform, the number average molecular weight at the depth (M0 to M20) from the surface layer of the preform was plotted in the same manner as in Example 1. The results are shown in FIG.
From the results shown in FIG. 11, in each crystalline polymer layer of the two-layered preform, the number average molecular weight of the crystalline polymer does not change in the thickness direction, and the number average molecular weight changes as a whole (intermittently). It was found that it was increasing.
Next, using the obtained preform, a multilayer polytetrafluoroethylene unheated film was prepared in the same manner as in Example 1, stretched in the same manner, and the multilayer polytetrafluoroethylene fine film of Comparative Example 1 was A porous membrane was prepared.

(Comparative Example 2)
-Production of polytetrafluoroethylene microporous membrane-
In Example 2, a preform was produced in the same manner as in Example 2 except that the powder of each layer of the preform before pressing was not interfacial mixed.
About the obtained preform, the number average molecular weight at the depth (M0 to M20) from the surface layer of the preform was plotted in the same manner as in Example 1. The results are shown in FIG.
From the results of FIG. 12, in each crystalline polymer layer of the three-layered preform, the number average molecular weight of the crystalline polymer does not change in the thickness direction, and the number average molecular weight is intermittent when viewed as a whole. I found it changing.
Next, using the obtained preform, a multilayer polytetrafluoroethylene unheated film was prepared in the same manner as in Example 1, stretched in the same manner, and the multilayer polytetrafluoroethylene fine film of Comparative Example 2 was A porous membrane was prepared.

  Next, for each of the prepared polytetrafluoroethylene microporous membranes of Examples 1 to 3 and Comparative Examples 1 and 2, the average thickness and the average pore diameter in the thickness direction from the front surface were as follows. Was measured.

<Measurement of average film thickness>
The 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-type thickness gauge (K402B, manufactured by Anritsu Corporation). In addition, arbitrary three places were measured and the average value was calculated | required. The results are shown in Table 1.

<Layer structure of microporous membrane>
The layer structures of the polytetrafluoroethylene microporous membranes of Examples 1 to 3 and Comparative Examples 1 to 2 were measured by SEM observation of cut surfaces cut in the thickness direction.
As a result, Examples 1 to 3 were found to have a single-layer structure with no interface in the microporous membrane. Moreover, it turned out that the comparative example 1 has one interface in a microporous film | membrane, and is a 2 layer structure. In addition, it was found that Comparative Example 2 has two interfaces in the microporous film and has a three-layer structure.

<Measurement of average pore diameter in thickness direction from front surface>
About each polytetrafluoroethylene microporous film | membrane of Examples 1-3 and Comparative Examples 1-2, the film thickness of a microporous film | membrane is set to 20, and 0 (namely, surface layer) part in the thickness direction from the front surface The average pore diameter at P0, the average pore diameter at 1 in the thickness direction as P1,..., The average pore diameter at 20 in the thickness direction as P20, and P0 to P20 were determined from SEM photographs of the film cross section. Here, the SEM photograph was taken with a scanning electron microscope (Hitachi S-4000 type, vapor deposition was Hitachi E1030 type, both manufactured by Hitachi, Ltd.), and the magnification was 1,000 to 5,000 times. An image consisting only of polytetrafluoroethylene fibers is taken into a processing device (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). The average pore diameter was obtained by computing the image.
Based on the values of P0 to P20 determined as described above, the average pore diameter (μm) at the distance (μm) in the thickness direction from the front surface was plotted. The results are shown in FIGS.

From the results of FIG. 13, in the polytetrafluoroethylene microporous membrane of Example 1, in the crystalline polymer layer having a single layer structure, the average pore diameter of the pores changed in the thickness direction of the crystalline polymer layer (partially changed). It was found that the pore diameter of the pores of the crystalline polymer microporous film as a whole changed (decreased in stages) in the thickness direction.
Further, from the results of FIG. 14, in the polytetrafluoroethylene microporous membrane of Example 2, in the crystalline polymer layer having a single layer structure, the average pore diameter of the pores changed in the thickness direction of the crystalline polymer layer (one In the entire crystalline polymer microporous membrane, the pore diameter changes in the thickness direction (decreases in steps). I found out. Moreover, it turned out that the site | part with the smallest largest average hole diameter of a hole exists in the inside of the crystalline polymer layer of a single layer structure.
Further, from the results of FIG. 15, in the polytetrafluoroethylene microporous membrane of Example 3, in the crystalline polymer layer having a single-layer structure, the average pore diameter of the pores changed in the thickness direction of the crystalline polymer layer (continuous It was found that it was decreasing.
In contrast, from the results of FIG. 16, the polytetrafluoroethylene microporous membrane of Comparative Example 1 is
In each crystalline polymer layer of the two-layered microporous membrane, the average pore diameter of the pores does not change in the thickness direction, and the number average molecular weight changes (decreases intermittently) as a whole. I understood that.
In addition, from the results of FIG. 17, in the polytetrafluoroethylene microporous membrane of Comparative Example 2, the average pore diameter of the pores changed in the thickness direction in each crystalline polymer layer of the microporous membrane having a three-layer structure. However, it was found that the number average molecular weight changed intermittently as a whole.

<Filtration test>
Next, the filtration test was done about each crystalline polymer microporous film | membrane of Examples 1-3 and Comparative Examples 1-2.
For Examples 1 and 2 and Comparative Examples 1 and 2, an aqueous solution containing 0.01% by mass of polystyrene fine particles (average particle size 3.0 μm) in accordance with the pore size of the layer having the minimum average pore size was set at a differential pressure of 0.00. Filtration was performed at 1 kg. About Example 3, it filtered by making the aqueous solution containing 0.01 mass% of polystyrene microparticles | fine-particles (average particle size 1.0 micrometer) into 0.1 kg of differential pressure | voltages. The results are shown in Table 2.

表２の結果から、比較例１及び比較例２の微孔性膜に対し、実施例１〜３の各微孔性膜は濾過寿命が大幅に改善されることが分かった。

From the results of Table 2, it was found that the filtration life of each of the microporous membranes of Examples 1 to 3 was significantly improved compared to the microporous membranes of Comparative Example 1 and Comparative Example 2.

  The crystalline polymer microporous membrane of the present invention and a filter for filtration using the same are capable of capturing fine particles efficiently over a long period of time, and are excellent in heat resistance and chemical resistance. Can be used in various situations, and is preferably used for microfiltration of gases, liquids, etc., for example, filtration of corrosive gases, various gases used in the semiconductor industry, washing water for electronics industry, pharmaceutical water It can be widely used for filtration of pharmaceutical production water, food water, etc., sterilization, high temperature filtration, filtration of reactive chemicals, and the like.

FIG. 1 is a schematic view showing an example of the crystalline polymer microporous membrane of the present invention. FIG. 2 is a schematic view showing an example of a conventional crystalline polymer microporous film having a two-layer structure. FIG. 3 is a schematic view showing an example of the crystalline polymer microporous membrane of the present invention. FIG. 4 is a schematic view showing an example of a conventional crystalline polymer microporous film having a three-layer structure. FIG. 5 is a diagram showing an example of the production process of the crystalline polymer microporous membrane of the present invention. FIG. 6 is a diagram showing another example of the production process of the crystalline polymer microporous membrane of the present invention. FIG. 7 is a diagram illustrating an example of a preform. FIG. 8 is a diagram showing another example of the production process of the crystalline polymer microporous membrane of the present invention. FIG. 9 is a graph showing the relationship between the number average molecular weight and the distance from the surface in the preform of Example 1. FIG. 10 is a graph showing the relationship between the number average molecular weight and the distance from the surface in the preformed body of Example 2. FIG. 11 is a graph showing the relationship between the number average molecular weight and the distance from the surface of the preform of Comparative Example 1. FIG. 12 is a graph showing the relationship between the number average molecular weight and the distance from the surface in the preform of Comparative Example 2. FIG. 13 is a graph showing the relationship between the average hole diameter of the holes and the distance from the surface in Example 1. FIG. 14 is a graph showing the relationship between the average hole diameter of the holes and the distance from the surface in Example 2. FIG. 15 is a graph showing the relationship between the average hole diameter of the holes and the distance from the surface in Example 3. FIG. 16 is a graph showing the relationship between the average hole diameter of the holes and the distance from the surface in Comparative Example 1. FIG. 17 is a graph showing the relationship between the average hole diameter of the holes and the distance from the surface in Comparative Example 2.

Explanation of symbols

4 First layer 5 Second layer 8 Lower mold 10 Preliminary body 15 Polytetrafluoroethylene unheated film 101, 104 Crystalline polymer layer (single layer)
102, 103, 105, 106, 107 Crystalline polymer layer (multilayer)
101a, 104a hole 102b, 103b, 105b, 106b, 107b hole

Claims (15)

A crystalline polymer microporous membrane having a crystalline polymer layer having a single layer structure composed of two or more different crystalline polymers, and a large number of pores penetrating in the thickness direction of the crystalline polymer layer,
Crystallinity characterized in that the composition ratio of the crystalline polymer changes in the thickness direction of the crystalline polymer layer, and the average pore diameter of the pores changes in the thickness direction of the crystalline polymer layer Polymer microporous membrane.   The crystalline polymer microporous membrane according to claim 1, wherein the change in average pore diameter in the pores is any one of continuous or non-continuous increase and continuous or non-continuous decrease.   The crystalline polymer microporous membrane according to any one of claims 1 to 2, wherein a portion having a minimum average pore diameter is present in the crystalline polymer layer.   The crystalline polymer microporosity according to any one of claims 1 to 3, wherein the change in the composition ratio of the crystalline polymer is any one of continuous or non-continuous increase and continuous or non-continuous decrease. film.   The crystalline polymer layer is composed of two or more crystalline polymers having different number average molecular weights, and the number average molecular weight of the crystalline polymer is changed in the thickness direction of the crystalline polymer layer. A crystalline polymer microporous membrane according to claim 1.   The crystalline polymer microporous membrane according to any one of claims 1 to 5, wherein the crystalline polymers are all polytetrafluoroethylene. Two or more different kinds of crystalline polymer particles different from each other are spread in the mold one by one, the crystalline polymer particles are interfacially mixed and pressed to form a preform, and the preform is extruded to form crystals. A crystalline polymer film production process for producing a crystalline polymer film;
A method for producing a crystalline polymer microporous membrane comprising at least a stretching step of stretching the obtained crystalline polymer film.   The production of a crystalline polymer microporous membrane according to claim 7, comprising an asymmetric heating step in which one side of the crystalline polymer film before stretching is heated to form a temperature gradient in the thickness direction of the crystalline polymer film. Method.   The method for producing a crystalline polymer microporous membrane according to any one of claims 7 to 8, wherein the interfacial mixing is performed by applying vibration to the crystalline polymer particles.   The method for producing a crystalline polymer microporous membrane according to any one of claims 7 to 9, wherein the crystalline polymer particles have different number average molecular weights.   The method for producing a crystalline polymer microporous membrane according to any one of claims 7 to 10, wherein the crystalline polymer particles are polytetrafluoroethylene particles.   The method for producing a crystalline polymer microporous membrane according to any one of claims 7 to 11, wherein the stretching is uniaxial stretching.   The method for producing a crystalline polymer microporous membrane according to any one of claims 7 to 11, wherein the stretching is biaxial stretching.   A filter for filtration, comprising the crystalline polymer microporous membrane according to any one of claims 1 to 6.   The filter for filtration according to claim 14, wherein a surface of the pore portion of the crystalline polymer microporous membrane having a larger average pore diameter is used as a filter surface of the filter.

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