JP2012192348A - Crystalline polymer microporous film, method for manufacturing the same, and filtration filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a crystalline polymer microporous film having a minute pore diameter, capable of efficiently catching a fine particle of several tens of nanometer size, having a high flow rate, being high in the uniformity of the thickness distribution of each layer in a width direction and the uniformity of the filtration performance distribution, and being reduced in the leakage in large area use; and to provide a method for manufacturing the crystalline polymer microporous film, and a filtration filter.SOLUTION: The method for manufacturing the crystalline polymer microporous film includes: a sheet-like molding formation process for forming a sheet-like molding by incising a cylindrical molding, in which a layer containing a first crystallizable polymer and a layer containing a second crystallizable polymer are laminated, in a central axis direction of the cylindrical molding; an unheated film formation process for forming an unheated film by rolling the sheet-like molding with pressure; a symmetrical heating process for forming a symmetrical heating film by heating the unheated film symmetrically; and a drawing process for drawing the symmetrical heating film.

Description

  The present invention relates to a filter for filtration, a crystalline polymer microporous membrane suitable for the filter for filtration, and a preferred production method thereof.

Conventionally, microporous membranes have been widely used for filtration filters and the like. Examples of the material for such a microporous membrane include cellulose ester (see Patent Document 1), aliphatic polyamide (see Patent Document 2), polyfluorocarbon (see Patent Document 3), polypropylene (see Patent Document 4), and the like. It has been known.
These microporous membranes are used for filtration and sterilization of electronic industrial cleaning water, pharmaceutical water, pharmaceutical manufacturing process water, food water, etc., and their use and usage have been increasing in recent years. A highly porous microporous membrane has attracted attention. Among these, a microporous film made of a crystalline polymer has excellent chemical resistance, and in particular, a crystalline polymer microporous material made of polytetrafluoroethylene (hereinafter sometimes referred to as “PTFE”). Since the film is excellent in heat resistance and chemical resistance, the growth of the demand is remarkable.

In such a crystalline polymer microporous membrane, a preform formed by laminating a polytetrafluoroethylene (PTFE) polymer layer and a modified polytetrafluoroethylene (PTFE) copolymer layer is rolled, and the temperature is equal to or higher than the melting point of the fired body. It is proposed that a multilayer film composed of a filtration layer having a small average pore diameter and a support layer having a large average pore diameter can be produced by stretching after heating in (see Patent Documents 5 and 6). According to these proposals, it is disclosed that even a very thin filtration layer can be formed, and a multilayer film in which layer interfaces are completely integrated is disclosed.
However, in these proposals, detailed heat treatment conditions are not described, and it is difficult to produce a film having a minute pore size. Moreover, since the thickness of the layer containing a crystalline polymer having a low melting point is not specified, there is a problem that it is difficult to produce a filter exhibiting desired performance (high flow rate).

In addition, in order to capture fine particles efficiently, layers made of crystalline polymers having different number average molecular weights are laminated, and in each layer, pores whose pore diameter continuously changes in the thickness direction are formed. A film has been proposed (see Patent Document 7).
However, in this proposal, the melting point of the crystalline polymer is not taken into consideration, and if a crystalline polymer having a low melting point is used, tear propagation or the like occurs, and fine particles having a small pore size and a size of several tens of nm are efficiently obtained. It is difficult to produce a crystalline polymer microporous membrane with a multi-layer structure that can be captured. Moreover, since it is necessary to provide a temperature gradient in the heating step in the method for producing a crystalline polymer microporous membrane, there is a problem that stable and efficient production is difficult.

  Therefore, a low melting crystalline polymer that is difficult to be formed into a film in a single layer due to tear propagation etc. is layered with a high melting crystalline polymer, so that the low melting crystalline polymer layer is not damaged. Crystalline polymer microporous membrane having a large pore diameter and capable of efficiently capturing fine particles of several tens of nanometers in a high flow rate, a method for producing the crystalline polymer microporous membrane, and a filter for filtration The current situation is that there is a strong demand for rapid development.

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-A-3-179038 JP-A-3-179039 JP 2009-61363 A

  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 fine pore diameter, can efficiently capture fine particles having a size of several tens of nanometers, has a high flow rate, and further has a uniform thickness distribution of each layer in the width direction and It is an object to provide a crystalline polymer microporous membrane with high uniformity of filtration performance distribution and reduced leakage when used in a large area, a method for producing a crystalline polymer microporous membrane, and a filter for filtration. To do.

Means for solving the problems are as follows. That is,
<1> A sheet-like molded body obtained by cutting a cylindrical molded body in which a layer containing a first crystalline polymer and a layer containing a second crystalline polymer are laminated in the central axis direction of the cylindrical molded body Forming a sheet-like molded body to form
An unheated film forming step of forming an unheated film by rolling the sheet-like molded body;
A symmetrical heating step of symmetrically heating the unheated film to form a symmetrical heated film;
A method for producing a crystalline polymer microporous membrane, comprising: a stretching step of stretching the symmetric heating film.
<2> The method for producing a crystalline polymer microporous film according to <1>, wherein the cylindrical molded body is formed by extrusion of a multilayer paste.
<3> The method for producing a crystalline polymer microporous film according to <2>, wherein the cylindrical molded body is formed by extrusion of a multilayer paste using an extrusion device having a cylindrical drawn portion.
<4> Multi-layer paste extrusion includes a cylindrical preform body charging portion, a cylindrical throttle portion connected to the preform molding portion, and a fan connecting the preform molding portion and the throttle portion. The manufacturing method of the crystalline-polymer microporous film | membrane as described in said <3> using the apparatus which has a part.
<5> In the above <4>, the drawing ratio of the extrusion device is a ratio (C / D) between the cross-sectional area C of the preformed body charging portion and the minimum cross-sectional area D of the drawn portion, and is 10 to 4,000. A method for producing the crystalline polymer microporous membrane described.
<6> The above-mentioned <1> to <5, wherein the cylindrical molded body is a cylindrical molded body in which a layer containing the first crystalline polymer and a layer containing the second crystalline polymer are concentrically stacked. > Is a method for producing a crystalline polymer microporous film.
<7> The DSC chart obtained by measuring the second crystalline polymer with a differential scanning calorimeter has one peak and a shoulder portion on the high temperature side or low temperature side of the peak,
When having a peak on the low temperature side and a high temperature side shoulder on the high temperature side of the peak, symmetrical heating of the unheated film is performed at a temperature higher than the peak temperature on the low temperature side,
When the peak is on the high temperature side and the low temperature side shoulder portion is on the low temperature side of the peak, the symmetric heating of the unheated film is performed at a temperature higher than the temperature of the low temperature side shoulder portion. A method for producing a crystalline polymer microporous membrane according to any one of the above.
<8> The method for producing a crystalline polymer microporous film according to any one of <1> to <7>, wherein the unheated film is symmetrically heated at a temperature not higher than the melting point of the first crystalline polymer.
<9> The maximum thickness A of the layer containing the second crystalline polymer is thinner than the maximum thickness B of the layer containing the first crystalline polymer, and satisfies the following formula: A / B ≦ 1/2 The method for producing a crystalline polymer microporous film according to any one of <1> to <8>.
<10> The method for producing a crystalline polymer microporous film according to <9>, wherein the following formula, A / B ≦ 1/3 is satisfied.
<11> A crystalline polymer fine layer composed of two or more layers in which a layer containing a first crystalline polymer and a layer containing a second crystalline polymer are laminated and a plurality of pores communicating in the thickness direction are formed. A porous membrane,
The melting point of the first crystalline polymer is higher than the melting point of the second crystalline polymer;
At least one layer in the crystalline polymer microporous membrane has a plurality of pores having a constant average pore diameter in at least a part in the thickness direction of the crystalline polymer microporous membrane,
The crystalline polymer microporous membrane is characterized in that the thickness variation rate in the width direction of at least one layer in the crystalline polymer microporous membrane is 14% or less.
<12> The crystalline polymer microporous film according to <11>, wherein the thickness variation rate is 10% or less.
<13> The crystalline polymer microporous membrane according to <11> to <12>, wherein the variation rate of the average flow pore size in the width direction of the crystalline polymer microporous membrane is 13% or less.
<14> The crystalline polymer microporous membrane according to <13>, wherein the variation rate of the average flow pore size is 9% or less.
<15> The crystalline polymer according to any one of <11> to <14>, including two layers including a first crystalline polymer and a layer including a second crystalline polymer between the two layers. It is a microporous membrane.
<16> The maximum thickness A of the layer containing the second crystalline polymer is thinner than the maximum thickness B of the layer containing the first crystalline polymer, and satisfies the following formula: A / B ≦ 1/2 The crystalline polymer microporous membrane according to any one of 11 to <15>.
<17> The crystalline polymer microporous membrane according to <16>, which satisfies the following formula: A / B ≦ 1/3.
<18> The crystalline polymer microporous membrane according to any one of <11> to <17>, wherein the thickness of the layer containing the second crystalline polymer is 0.1 μm to 50 μm.
<19> The crystalline polymer microporous membrane according to any one of <11> to <18>, wherein the first crystalline polymer is at least one of polytetrafluoroethylene and a polytetrafluoroethylene copolymer. It is.
<20> The crystalline polymer microporous membrane according to any one of <11> to <19>, wherein the second crystalline polymer is at least one of polytetrafluoroethylene and a polytetrafluoroethylene copolymer. It is.
<21> The above <19> to <20>, wherein the polytetrafluoroethylene copolymer contains at least two selected from tetrafluoroethylene, perfluoroalkyl vinyl ether, hexafluoropropylene, and chlorotrifluoroethylene The crystalline polymer microporous film described in 1.
<22> A filtration filter comprising the crystalline polymer microporous membrane according to any one of <11> to <21>.
<23> area of the crystalline polymer microporous membrane ^is a filtration filter according to the a 0.04m ² ~10m 2 <22>.
<24> The filtration filter according to any one of <22> to <23>, which is a cartridge filter.
<25> The filter for filtration according to <22> to <24>, wherein the layer containing the second crystalline polymer having a low melting point in the crystalline polymer microporous membrane is disposed so as to be close to the outlet side.

  In addition to being able to efficiently capture fine particles with a small pore size and several tens of nanometers in size, in addition to the high flow rate, the uniformity of the thickness distribution of each layer in the width direction and the uniformity of the filtration performance distribution It is possible to provide a crystalline polymer microporous membrane, a method for producing a crystalline polymer microporous membrane, and a filter for filtration, which have a high leakage and reduced leakage when used in a large area.

FIG. 1 is a schematic view showing an example of a crystalline polymer microporous membrane having a two-layer structure according to the present invention. FIG. 2 is a schematic view showing an example of a crystalline polymer microporous film having a two-layer structure of a comparative example. FIG. 3 is a schematic diagram showing an example of a crystalline polymer microporous film having a three-layer structure according to the present invention. FIG. 4 is a schematic view showing an example of a crystalline polymer microporous film having a three-layer structure of a comparative example. FIG. 5 is a diagram showing an example of the steps of the method for producing a crystalline polymer microporous membrane of the present invention. FIG. 6 is a diagram showing an example of a sheet-like molded body forming step of the method for producing a crystalline polymer microporous membrane of the present invention. FIG. 7 is a cross-sectional view showing an example of a cylindrical molded body. FIG. 8 is a diagram showing another example of the sheet-like formed body forming step of the method for producing a crystalline polymer microporous membrane of the present invention. FIG. 9 is a cross-sectional view showing another example of a cylindrical molded body. FIG. 10 is a diagram illustrating a structure of a general pleated filter element before being assembled into the housing. FIG. 11 is a view showing the structure of a general filter element before being assembled in the housing of the capsule filter cartridge. FIG. 12 is a view showing the structure of a general capsule filter cartridge integrated with a housing. FIG. 13 is a DSC chart showing an example of the second crystalline polymer (low melting crystalline polymer). FIG. 14 is a DSC chart showing another example of the second crystalline polymer (low melting crystalline polymer). FIG. 15 is a DSC chart showing another example of the second crystalline polymer (low melting crystalline polymer).

(Crystalline polymer microporous membrane)
The crystalline polymer microporous membrane of the present invention has at least a layer containing a first crystalline polymer and a layer containing a second crystalline polymer, and if necessary, other layers. It has.
The melting point of the first crystalline polymer is higher than the melting point of the second crystalline polymer, and the first crystalline polymer may be referred to as a “high-melting crystalline polymer”. The crystalline polymer may be referred to as a “low melting crystalline polymer”.
Here, the melting point indicates a peak position of a DSC chart obtained by measurement with a differential scanning calorimeter, and when it has two peaks, or when it has one peak and one shoulder portion. The higher peak intensity is defined as the melting point.

  At least one layer in the crystalline polymer microporous membrane has a plurality of pores having a constant average pore diameter in at least a part in the thickness direction of the crystalline polymer microporous membrane.

The crystalline polymer microporous membrane is a laminate. “Laminated body” means a “laminated structure” formed by laminating two or more layers containing a crystalline polymer, and means not a “single layer structure”.
The “laminated structure” can be clearly distinguished from a “single layer structure” having no boundary by having a boundary between a layer containing a crystalline polymer and a layer containing another crystalline polymer. Here, the boundary between the layer containing the crystalline polymer and the layer containing the other crystalline polymer is, for example, a cut surface obtained by freezing the crystalline polymer microporous film in the thickness direction and cutting it. It can detect by observing with a microscope (SEM).

The thickness variation rate in the width direction of at least one layer in the crystalline polymer microporous film is 14% or less, preferably 10% or less, and more preferably 8% or less.
When the thickness variation rate exceeds 14%, the filtration performance varies, and the yield when using a large area may be deteriorated. When the thickness variation rate is within the preferable range, it is advantageous in terms of uniformity of thickness distribution of each layer in the width direction, uniformity of filtration performance distribution, fine particle capturing ability, and leakage reduction when using a large area.
Here, the thickness variation rate in the width direction refers to the thickness of each layer in the width direction (for example, the thickness of each section obtained by dividing the crystalline polymer microporous film into n equal parts in the width direction). It is represented by the ratio of its standard deviation to the mean value. The thickness of each layer can be measured by freezing and cleaving the crystalline polymer microporous film in the width direction and performing cross-sectional observation with an optical microscope or a scanning electron microscope (SEM).
When the average value (average thickness) of the n pieces of thickness data (X ₁ , X ₂ ,... X _n ) is Xm and the standard deviation is Sx, the thickness variation rate Vx can be calculated by the following formula (1).
Thickness variation rate (%): Vx = Sx / Xm × 100 (1)

  The structure of the crystalline polymer microporous membrane is not particularly limited as long as it is two or more layers, and can be appropriately selected according to the purpose. However, the first crystalline polymer having two or more layers (high melting point) A crystalline polymer microporous film comprising a layer containing a crystalline polymer) and a layer containing a second crystalline polymer (a low melting crystalline polymer) is preferred, and two layers of the first crystalline polymer (A high-melting crystalline polymer) and one layer of the second crystalline polymer (low-layer) interposed between the two layers of the first crystalline polymer (high-melting crystalline polymer). A three-layer structure having a layer containing a crystalline polymer having a melting point is more preferable. By adopting such a three-layer structure, the second crystalline polymer having the smallest diameter that most affects the trapped particle diameter (the layer containing a crystalline polymer having a low melting point) is subjected to physical destruction factors such as friction and scratching. It is possible to protect it from being trapped and to stabilize the capture performance.

In the microporous film having the three-layer structure, the thickness of the layer containing the first crystalline polymer (high melting crystalline polymer) of one layer is the second crystalline polymer (low melting crystalline polymer). The thickness of the layer containing the first crystalline polymer (high-melting crystalline polymer) of the other layer that is thicker than the thickness of the containing layer contains the second crystalline polymer (low-melting crystalline polymer) It is preferably thicker than the thickness of the layer.
By arranging the layer containing the second crystalline polymer (crystalline polymer having a low melting point) close to the outlet side (outlet side) of the filtrate, fine particles having a size of several tens of nm can be captured efficiently. It is preferable in that the filtration efficiency can be improved.

In the present invention, a plurality of pores communicating in the thickness direction of the crystalline polymer microporous membrane are formed, and at least one layer in the crystalline polymer microporous membrane is formed of the crystalline polymer microporous membrane. At least part of the thickness direction has a plurality of holes having a constant average hole diameter. Thereby, fine particles can be captured efficiently.
It can be confirmed by observing with the optical microscope or scanning electron microscope (SEM) that the “a plurality of holes communicating in the thickness direction” are formed.

“The at least one layer in the crystalline polymer microporous membrane has a plurality of pores having a constant average pore diameter in at least a part in the thickness direction of the crystalline polymer microporous membrane” means that the horizontal axis When the distance t (corresponding to the depth from the front surface) in the thickness direction from the front surface of the crystalline polymer microporous membrane is taken, and the average pore diameter D of the hole portion is taken on the vertical axis, 1) A graph from the front surface (t = 0) to the back surface (t = thickness) is drawn with one continuous line for each crystalline polymer layer (continuous), and the slope of the graph (dD / Dt) is substantially 0 (zero).
Here, “substantially 0” includes about ± 10% from the average value, and does not include monotonic increase and monotonic decrease.

Here, as shown in FIG. 1, the average pore diameters of the holes 101b and 102b in the crystalline polymer microporous film of the present invention having a two-layer structure in which the layers 101 and 102 containing the crystalline polymer are laminated are both crystalline. The average pore diameter of the crystalline polymer microporous membrane as a whole changes (decreases in steps) in the thickness direction of the crystalline polymer microporous membrane.
On the other hand, as shown in FIG. 2, the average pore diameters of the holes 101a and 102a in the crystalline polymer microporous film of the comparative example of the two-layer structure in which the layers 101 and 102 containing the crystalline polymer are laminated are both The crystalline polymer microporous film changes (continuously decreases) in the thickness direction, and the average pore diameter of the crystalline polymer microporous film as a whole changes (decreases in steps).

In addition, as shown in FIG. 3, the average pore diameter of the holes 101b, 102b, 103b in the crystalline polymer microporous membrane of the present invention having a three-layer structure in which the layers 101, 102, 103 containing the crystalline polymer are laminated is Both are constant in the thickness direction of the crystalline polymer microporous membrane, and the entire crystalline polymer microporous membrane has a portion in which the average pore diameter changes stepwise in the thickness direction.
On the other hand, as shown in FIG. 4, the average pore diameter of the holes 101a, 102a, 103a in the crystalline polymer microporous film of the comparative example of the three-layer structure in which the layers 101, 102, 103 containing the crystalline polymer are laminated. Are both changed in the thickness direction of the crystalline polymer microporous membrane (continuously decreased), and the entire crystalline polymer microporous membrane is changed in the thickness direction (decrease in steps). is doing.

It is preferable that a crystalline polymer microporous film formed by laminating three or more layers containing a crystalline polymer has a layer containing a low melting crystalline polymer having the smallest maximum average pore diameter of the pores. As a result, the layer containing the crystalline polymer having the smallest average pore diameter that most affects the trapped particle diameter can be protected from physical destruction factors such as friction and scratching, and the trapping performance can be stabilized. It can be manufactured stably.
Here, as shown in FIG. 3, in the pores 101b, 102b, and 103b in the three-layered crystalline polymer microporous film in which the layers 101, 102, and 103 containing the crystalline polymer are laminated, the maximum average of the pores A layer 102 containing a low melting crystalline polymer having the smallest maximum average pore diameter Lm2 among the pore diameters Lm1, Lm2, and Lm3 is present inside the crystalline polymer microporous membrane.

The average pore diameter of the pores in the layer containing the second crystalline polymer is preferably 1 μm or less, and more preferably 0.5 μm or less. If the average pore size of the pores of the layer containing the second crystalline polymer is larger than 1 μm, there is a possibility that dust in the liquid such as fine particles cannot be sufficiently captured.
The average pore diameter of the pores in the layer containing the first crystalline polymer is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 0.001 μm to 500 μm, preferably 0.002 μm to 250 μm is more preferable, and 0.005 μm to 100 μm is still more preferable.

  Here, the average pore diameter of the holes is obtained by, for example, taking a photograph of the film surface or film cross-section with a scanning electron microscope (SEM photograph, magnification 1,000 to 100,000 times), and subjecting the obtained photograph to image processing. Obtain an image consisting only of crystalline polymer fibers by incorporating it into the 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). The average pore diameter can be obtained by calculating the image.

The average flow pore size of the crystalline polymer microporous membrane is preferably less than 200 nm and more preferably 150 nm or less. The average flow pore size is preferably 0.001 μm or more. If the average flow pore size is 200 nm or more, dust in the liquid such as fine particles may not be sufficiently captured. If the average flow pore size is less than 0.001 μm, a sufficient flow rate may not be obtained.
Here, the average flow hole diameter is a hole diameter obtained from the intersection of 1/2 in the dry state and air flow in the wet state is referred to as an average flow hole diameter, and is determined by, for example, a half dry method (ASTM E1294-89). . Specifically, up to 15 nm can be measured with a 500 psi high pressure palm porometer (manufactured by PMI), and 15 nm or less can be measured with a nano palm porometer (manufactured by PMI).

Further, the variation rate of the average flow pore size in the width direction of at least one layer in the crystalline polymer microporous membrane is not particularly limited and can be appropriately selected according to the purpose, but is preferably 13% or less. 9% or less is more preferable, and 7.5% or less is particularly preferable.
If the variation rate of the average flow pore diameter exceeds 13%, the filtration performance varies, and the yield rate when using a large area may be deteriorated. When the variation rate of the average flow pore diameter is within the more preferable range, the thickness distribution uniformity in each layer in the width direction, the filtration performance distribution uniformity, the particulate trapping property, and the leakage reduction when using a large area. It is advantageous.
The variation rate of the average flow pore diameter is the average flow pore diameter of each section obtained by dividing the crystalline polymer microporous membrane into n equal parts in the width direction, and the ratio of the standard deviation to the average value of the average flow pore diameter. expressed.
When the average value of the _n average flow pore diameter data (Y ₁ , Y ₂ ,... Y _n ) is Ym and the standard deviation is Sy, the variation rate Vy of the average flow pore diameter can be calculated by the following equation (2). .
Fluctuation rate of average flow hole diameter (%): Vy = Sy / Ym × 100 (2)

-Crystalline polymer-
The “crystalline polymer” is not particularly limited as long as it is 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. Can be appropriately selected according to the purpose. 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.

The crystalline polymer is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include polyalkylene, polyester, polyamide, polyether, liquid crystalline polymer, and the like. 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, and the like. Among these, polyalkylene (for example, polyethylene and polypropylene) is preferable from the viewpoint of chemical resistance and handleability, 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 preferable in terms 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. Preference is given to using fluoroethylene.

  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-106, polyflon PTFE F-201, polyflon PTFE F-205, polyflon PTFE F-208, polyflon PTFE F-301, F-302, and lubron L. -2, L-5 (all manufactured by Daikin Industries, Ltd.); Teflon (registered trademark) PTFE 6-J, Teflon (registered trademark) PTFE 62XT, Teflon (registered trademark) PTFE 6C-J, Teflon (manufactured by company) Registered trademark) PTFE 640-J (both manufactured by Mitsui DuPont Fluorochemical Co., Ltd.), and the like. Among these, F-104, F-106, F-205, F201, L-5, CD1, CD141, CD126, CD123, 6-J are preferable, and F-106, F-205, F-201, CD1, CD126, CD123, and 6-J are more preferable, and F-106, F-205, CD126, and CD123 are particularly preferable.

There is no restriction | limiting in particular as glass transition temperature of the said crystalline polymer, Although it can select suitably according to the objective, -100 to 400 degreeC is preferable and -90 to 350 degreeC is more preferable.
There is no restriction | limiting in particular as a weight average molecular weight of the said crystalline polymer, Although it can select suitably according to the objective, 1,000-100,000,000 are preferable.
The number average molecular weight of each crystalline polymer is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 500 to 50,000,000, more preferably 1,000 to 25,000,000. preferable.
Here, the number average molecular weight can be measured, for example, by gel permeation chromatography (GPC). However, since PTFE is insoluble in a solvent, crystallization heat (ΔHc: cal / g) measurement by DSC measurement is performed, and a relational expression: Mn = 2.1 × 10 ¹⁰ × ΔHc ^−5.16 is used. It is preferable to calculate.

<Layer containing first crystalline polymer (high melting crystalline polymer)>
The layer containing the first crystalline polymer (high melting crystalline polymer) is not particularly limited as long as it contains the first crystalline polymer (high melting crystalline polymer), and is appropriately selected according to the purpose. can do.
The thickness variation rate in the width direction of the layer containing the first crystalline polymer (crystalline polymer having a high melting point) is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 14% or less. 10% or less is more preferable, and 8% or less is particularly preferable.
When the thickness variation rate exceeds 14%, the filtration performance varies, and the yield rate when using a large area may deteriorate. When the thickness variation rate is within the more preferable range, it is advantageous in terms of uniformity of thickness distribution of each layer in the width direction, uniformity of filtration performance distribution, particulate trapping property, and leakage reduction when using a large area. .

The maximum thickness of the layer containing the first crystalline polymer (high melting crystalline polymer) is larger than the maximum thickness of the layer containing the second crystalline polymer (low melting crystalline polymer). Thereby, the flow rate of the crystalline polymer microporous membrane can be improved.
Here, the “maximum thickness” means the maximum value of the thickness of each layer. For example, a layer containing a first crystalline polymer (high melting crystalline polymer) with a thickness of 20 μm, a layer containing a first crystalline polymer (high melting crystalline polymer) with a thickness of 15 μm, and a thickness In the case of a crystalline polymer microporous membrane having a 10 μm first crystalline polymer (high melting crystalline polymer) layer, the first crystalline polymer (high melting crystalline polymer) layer The maximum thickness is 20 μm, and a layer containing a second crystalline polymer (low melting crystalline polymer) with a thickness of 20 μm and a second crystalline polymer (low melting crystalline polymer) with a thickness of 15 μm In the case of a crystalline polymer microporous membrane having a layer containing and a layer containing a second crystalline polymer (low melting crystalline polymer) having a thickness of 10 μm, the second crystalline polymer (low melting crystalline Of the layer containing the polymer) The thickness becomes 20μm.
There is no restriction | limiting in particular as thickness of the layer containing said 1st crystalline polymer (high melting crystalline polymer), Although it can select suitably according to the objective, 1.0 micrometer-100 micrometers are preferable. 25 μm to 75 μm is more preferable, and 1.5 μm to 50 μm is particularly preferable.
When the thickness of the layer containing the first crystalline polymer (crystalline polymer having a high melting point) is less than 1.0 μm, the layer containing the crystalline polymer having a low melting point is affected by friction and scratching and is stable. In some cases, the fine particle capturing ability cannot be maintained, and when it exceeds 100 μm, a sufficient flow rate may not be obtained. In addition, it is advantageous in terms of fine particle capturing property and flow rate when the thickness of the layer containing the first crystalline polymer (crystalline polymer having a high melting point) is within the particularly preferable range.

When the crystalline polymer microporous film has a two-layer structure, the thickness of the layer containing the first crystalline polymer (high-melting crystalline polymer) and the second crystalline polymer (low-melting crystalline polymer) ) Is preferably 10,000: 1 to 1.2: 1, more preferably 5,000: 1 to 1.25: 1, and 1,000: 1 to 1.5. Is particularly preferred.
If the ratio is more than 10,000: 1, the thickness of the layer containing the low melting crystalline polymer may not be precisely controlled, and if less than 1.2: 1, the low melting crystalline The layer containing the polymer may be affected by friction and scratching, and may not be able to maintain a stable particulate capturing property. In addition, it is advantageous in terms of thickness control and fine particle capturing property that the ratio is within the particularly preferable range.

The crystalline polymer microporous membrane has a three-layer structure (two layers of a first crystalline polymer (a high melting crystalline polymer) and two layers of a first crystalline polymer (a high melting point crystal). A layer containing the first crystalline polymer (high-melting crystalline polymer) in the case of one layer of the second crystalline polymer (low-melting crystalline polymer) interposed between the layers containing the crystalline polymer) Is preferably 5,000: 1 to 1.2: 1, more preferably 2,500: 1 to 1.2: 1, and the thickness of the layer containing the second crystalline polymer (low melting crystalline polymer). 1.25: 1 is more preferable, and 1,000: 1 to 1.5: 1 is particularly preferable.
If the ratio is more than 5,000: 1, the thickness of the layer containing the low melting crystalline polymer may not be precisely controlled, and if it is less than 1.2: 1, the low melting crystalline The layer containing the polymer may be affected by friction and scratching, and may not be able to maintain a stable particulate capturing property. In addition, it is advantageous in terms of thickness control and fine particle capturing property that the ratio is within the particularly preferable range.
The thickness of the other one layer (the other layer not having the maximum thickness) of the two layers containing the first crystalline polymer (high melting crystalline polymer) is not particularly limited. Although it can select suitably according to it, it is preferable that it is more than the thickness of the layer containing said 2nd crystalline polymer.
If the thickness of the layer containing the second crystalline polymer is exceeded, the flow rate may not be sufficient. In addition, it is further advantageous at the point of the flow volume that the said thickness is in the said especially preferable range.

-First crystalline polymer (crystalline polymer with high melting point)-
The first crystalline polymer (high melting crystalline polymer) is not particularly limited as long as it is a crystalline polymer having a melting point higher than that of a low melting crystalline polymer described later, and is appropriately selected according to the purpose. However, in terms of chemical resistance, polytetrafluoroethylene (PTFE) and polytetrafluoroethylene copolymer are preferable.
The polytetrafluoroethylene copolymer is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include tetrafluoroethylene / trifluorochloroethylene copolymer, tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer. Binary copolymers such as polymers, tetrafluoroethylene / ethylene copolymers, tetrafluoroethylene / hexafluoropropylene copolymers, and tetrafluoroethylene / ethylene copolymers, or copolymers of ternary or higher Examples thereof include a copolymer composed of at least one polymer selected from a coalescence. Among these, a polytetrafluoroethylene copolymer containing at least two selected from tetrafluoroethylene, perfluoroalkyl vinyl ether, hexafluoropropylene, and chlorotrifluoroethylene is particularly preferable.

The melting point of the first crystalline polymer (high melting crystalline polymer) is not particularly limited as long as it is higher than the melting point of the second crystalline polymer (low melting crystalline polymer) described later, and depends on the purpose. The melting point of the second crystalline polymer (low melting crystalline polymer) is preferably 1 ° C. or higher, more preferably 3 ° C. or higher.
If the melting point of the first crystalline polymer (high melting crystalline polymer) is lower than the melting point of the second crystalline polymer (low melting crystalline polymer), a sufficient flow rate cannot be obtained, and filtration is performed. Efficiency may be significantly reduced.
The melting point of the crystalline polymer means the temperature of the peak of the endothermic curve that appears when measured by, for example, a differential scanning calorimeter (DSC).

<Layer containing second crystalline polymer (low melting crystalline polymer)>
The layer containing the second crystalline polymer (low melting crystalline polymer) is not particularly limited as long as it contains the second crystalline polymer (low melting crystalline polymer), and is appropriately selected according to the purpose. be able to.
The thickness variation rate in the width direction of the layer containing the second crystalline polymer (low melting crystalline polymer) is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 14% or less. 10% or less is more preferable, and 8% or less is particularly preferable.
When the thickness variation rate exceeds 14%, the filtration performance varies, and the yield rate when using a large area may deteriorate. When the thickness variation rate is within the more preferable range, it is advantageous in terms of uniformity of thickness distribution of each layer in the width direction, uniformity of filtration performance distribution, particulate trapping property, and leakage reduction when using a large area. .

The thickness of the layer containing the second crystalline polymer (low melting crystalline polymer) is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 0.1 μm to 50 μm. 1 μm to 25 μm is more preferable. If the thickness is less than 0.1 μm, the hole diameter of the hole portion cannot be reduced, and the in-plane uniformity of the hole diameter may be lost. If the thickness exceeds 50 μm, the flow rate cannot be increased. is there. On the other hand, when the thickness of the layer containing the second crystalline polymer (low melting crystalline polymer) is within the particularly preferred range, it is advantageous in terms of in-plane uniformity of pore diameter and flow rate.
According to the crystalline polymer microporous membrane of the present invention, the uniformity of the thickness distribution in the width direction of each layer and the uniformity of the filtration performance distribution in the width direction of the crystalline polymer microporous membrane can be achieved. In the held state, the thickness of the layer containing the second crystalline polymer (low melting crystalline polymer) can be reduced.

The maximum thickness A of the layer containing the second crystalline polymer (low melting crystalline polymer) is thinner than the maximum thickness B of the layer containing the first crystalline polymer (high melting crystalline polymer), It is preferable to satisfy the following formula, A / B ≦ 1/2, and it is more preferable to satisfy the following formula, A / B ≦ 1/3. When the A / B is 1/2 or more, the layer containing the crystalline polymer having a low melting point may be affected by friction and scratching, and stable fine particle capturing properties may not be maintained. When it is within the particularly preferable range, it is advantageous in terms of fine particle capturing ability.
When the thickness of the layer containing the crystalline polymer having a low melting point is reduced, the flow rate characteristics are improved while the fine particle capturing rate is lowered. On the contrary, when the thickness of the layer containing the low melting crystalline polymer is increased, the flow rate characteristic is lowered, but the fine particle capturing rate is improved.
When an intermediate layer containing both the high-melting crystalline polymer and the low-melting crystalline polymer is present at the interface between the layers, the intermediate layer includes the first crystalline polymer (high-melting crystalline Polymer) and the layer containing the second crystalline polymer (low melting crystalline polymer).

-Second crystalline polymer (low melting crystalline polymer)-
The second crystalline polymer (low melting crystalline polymer) is not particularly limited as long as the melting point is lower than that of the first crystalline polymer (high melting crystalline polymer). However, polytetrafluoroethylene (PTFE) and polytetrafluoroethylene copolymer are preferable from the viewpoint of chemical resistance.
There is no restriction | limiting in particular as said polytetrafluoroethylene copolymer, According to the objective, it can select suitably, For example, the thing similar to a said 1st crystalline polymer can be used.

  The total thickness of the crystalline polymer microporous membrane 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 200 μm, and particularly preferably 10 μm to 100 μm. .

It is preferable that the layer containing at least the second crystalline polymer in the crystalline polymer microporous film has a microstructure including at least fibrils, and the microstructure includes a node.
The fibril means a fiber that is spun between particles or into particles when a mechanical force is applied between two fused crystalline polymer particles.
The average major axis length of the fibril is preferably 1 μm or less, and more preferably 0.5 μm or less. When the average major axis length exceeds 1 μm, there is a possibility that dust in the liquid such as fine particles cannot be sufficiently captured.
The nodules (nodes) are clusters of primary particles of crystalline polymer, and the average minor axis length (average diameter) of the clusters is larger than the average minor axis length (average diameter) of the fibrils, and the average diameter is The thickness is preferably 0.1 μm or more, and more preferably 0.2 μm or more. If the average diameter is less than 0.1 μm, sufficient film strength may not be obtained.

  The layer containing at least the second crystalline polymer in the crystalline polymer microporous membrane “has a microstructure containing at least fibrils” and the diameter of the node is the thickness of the crystalline polymer microporous membrane. A cross section in the direction is taken with a scanning electron microscope (SEM photograph, magnification 1,000 to 100,000 times). This cross-sectional SEM photograph 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), and it becomes a nodule and a fibril. By separating, an image consisting only of nodules and an image consisting only of fibrils are obtained. By randomly selecting 100 images from this image and performing arithmetic processing, the average long axis length of the fibrils and the average diameter of the nodes can be measured.

(Method for producing crystalline polymer microporous membrane)
The method for producing a crystalline polymer microporous membrane of the present invention includes at least a sheet-like molded body forming step, an unheated film forming step, a symmetrical heating step, and a stretching step, and further surface modification as necessary. It includes other processes such as processes.

<Sheet-shaped molded body forming step>
The sheet-like molded body forming step includes a cylindrical shape in which a layer containing a first crystalline polymer (high melting crystalline polymer) and a layer containing a second crystalline polymer (low melting crystalline polymer) are laminated. This is a step of cutting a molded body in the central axis direction of the cylindrical molded body to form a sheet-shaped molded body.
The first crystalline polymer (high melting crystalline polymer) and the second crystalline polymer (low melting crystalline polymer) having different melting points are not particularly limited and may be appropriately selected according to the purpose. Can be used.

First, a cylindrical molded body is produced by laminating two or more mixtures (pastes) in which each crystalline polymer is mixed with an extrusion aid, and the cylindrical molded body is cut in the central axis direction to form a sheet-shaped molded body. Is made.
There is no restriction | limiting in particular as a shape of the said cylindrical molded object, According to the objective, it can select suitably, For example, a cylindrical shape, an elliptical cylinder shape, the polygonal cylinder shape which has a corner angle, etc. are mentioned. Among these, the cylindrical shape is in terms of uniform thickness distribution in the width direction of each layer of the obtained crystalline polymer microporous membrane and uniform filtration performance distribution in the width direction of the crystalline polymer microporous membrane. preferable.
The tubular molded body is not particularly limited and can be appropriately formed by a known method according to the purpose, but is preferably formed by multilayer paste extrusion, and an extrusion apparatus having a tubular squeezed portion is used. More preferably, it is formed by extrusion of the used multilayer paste. The cylindrical molded body is preferably a cylindrical molded body in which a layer containing the first crystalline polymer and a layer containing the second crystalline polymer are stacked concentrically. The paste extrusion is preferably performed at a temperature of 19 ° C to 200 ° C.

The extrusion apparatus used for extruding the multi-layer paste includes a cylindrical preform forming part, a cylindrical throttle connected to the preform charging part, and the preform charging part and the throttle part. And a multi-layer paste extrusion apparatus shown in FIG. 5, for example.
The ratio of the cross-sectional area of the preformed body input portion and the minimum cross-sectional area of the drawn portion in the extrusion apparatus is referred to as a drawing ratio (sometimes referred to as “Reduction Ratio (RR)” or “reduction ratio”). The drawing ratio is represented by the ratio (C / D) between the cross-sectional area C of the preformed body charging portion and the minimum cross-sectional area D of the drawn portion.
There is no restriction | limiting in particular as drawing ratio in the said extrusion apparatus, Although it can select suitably according to the objective, 5-4,000 are preferable, 8-500 are more preferable, and 10-200 are especially preferable. If the squeezing ratio is less than 5, the primary particles of the crystalline polymer may not be bound and the shape of the resulting cylindrical molded body may not be maintained. If it exceeds 4,000, the crystalline polymer is primary. Particles may collapse and become difficult to fibrillate. On the other hand, when the drawing ratio is within the particularly preferable range, it is advantageous in that the primary particles of the crystalline polymer are bound at an appropriate ratio and easily fibrillated, and a microporous film can be easily formed by stretching.
As the extrusion aid used in the multilayer paste extrusion, a liquid lubricant is preferably used, and examples thereof 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 15 to 30 parts by mass with respect to 100 parts by mass of the crystalline polymer.

Here, with reference to FIGS. 5-9, an example of the manufacturing method of the crystalline polymer microporous film | membrane of this invention is demonstrated.
As shown in FIGS. 6 and 7, the first layer 3 including the fine powder 1 of PTFE, the second layer 4 including the fine powder 2 of PTFE, and the third layer 5 including the fine powder 1 of PTFE are included. A cylindrical molded body 6 having a three-layer structure is produced. FIG. 6 is a view showing an example of a sheet-like formed body forming step of the method for producing a crystalline polymer microporous membrane of the present invention, and FIG. 7 shows an example of a cylindrical formed body. It is sectional drawing in the surface orthogonal to the central axis of a molded object.
Each of these layers is a paste 1 in which a liquid lubricant such as solvent naphtha or white oil is added 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. And from paste 2. Moreover, the paste which forms a 1st layer and a 3rd layer may be mutually the same, and may differ. The amount of the liquid lubricant used is not particularly limited and varies depending on the type, molding conditions, etc., and cannot be specified unconditionally, but is in the range of 15 to 35 parts by mass with respect to 100 parts by mass of the fine powder of PTFE. It is preferable that a coloring agent or the like can be added as necessary.
Also, as shown in FIGS. 8 and 9, a cylindrical molded body 6 having a two-layer structure including a first layer 3 containing PTFE fine powder 1 and a second layer 4 containing PTFE fine powder 2 may be produced. it can. FIG. 8 is a diagram showing an example of a sheet-like molded body forming step of the method for producing a crystalline polymer microporous membrane of the present invention, and FIG. 9 shows an example of a cylindrical molded body. It is sectional drawing in the surface orthogonal to the central axis of a molded object.

  First, the paste 1 containing the fine powder 1 of PTFE for forming the first layer and the fine PTFE for forming the second layer in the lower mold 8 in the multilayer paste extrusion apparatus 7 shown in FIG. The paste 2 containing the powder 2 and the paste 1 containing the PTFE fine powder 1 for forming the third layer are spread concentrically, and then the upper mold 9 is pressed in the direction of the arrow. As a result, a cylindrical preform is formed in which three layers of the first layer 3, the second layer 4, and the third layer 5 are concentrically stacked.

Next, after the obtained cylindrical preform is stored in the preform input part (cylinder part) of the multilayer paste extrusion apparatus 7 shown in FIG. 5, it is pressed by a pressurizing means (not shown) in the direction of the arrow. Press to. 5 is a cylindrical shape in which the inner diameter of the outer frame in the cross section in the direction perpendicular to the axis is 85 mm and the outer diameter of the inner frame is 40 mm, for example. The outer frame has an inner diameter of 66 mm and the inner frame has an outer diameter of 62 mm.
In this way, the first layer 3, the second layer 4, and the third layer 5 are completely integrated, and as shown in FIGS. 6 and 7, a multi-layer polytetrafluoroethylene cylinder in which each layer has a uniform thickness. A shaped molded body 5 is molded. As shown in FIG. 6, the cylindrical molded body 5 is cut in the central axis (AA ′ axis) direction to form a sheet-shaped molded body 10. It has been confirmed by a stereomicroscope that the thickness composition ratio of each layer of the sheet-like molded body is substantially the same as the thickness composition ratio of each layer of the preform.

<Unheated film formation process>
The unheated film forming step is a step of rolling the sheet-like formed body to form two or more layers of unheated films.

The sheet-like molded body is then rolled to form a film. Rolling can be performed, for example, by calendaring with a calender roll at a speed of 5 m / min. The rolling temperature can usually be set to 19 ° C to 380 ° C. Thereafter, the extrusion aid is removed by heating the film to form a multilayer crystalline polymer unheated film. Although the heating temperature at this time can be suitably selected according to the kind of extrusion adjuvant to be used, 40 to 400 degreeC is preferable and 60 to 350 degreeC is more preferable. For example, when removing solvent naphtha using polytetrafluoroethylene, 150 ° C. to 280 ° C. is preferable, and 180 ° C. to 260 ° 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 multilayer crystalline polymer unheated film thus produced can be appropriately adjusted according to the thickness of the crystalline polymer microporous film to be finally produced, and depends on the subsequent stretching step. It is necessary to adjust in consideration of a decrease in thickness.
In addition, when manufacturing the said multilayer crystalline polymer unheated film, the matter described in "Polyfuron handbook" (Daikin Kogyo Co., Ltd. issue, 1983 revision) can be employ | adopted suitably.

<Symmetric heating process>
The symmetrical heating step is a step of forming a symmetrical heated film by symmetrically heating the obtained unheated film.
The symmetrical heating is performed by laminating a layer containing the first crystalline polymer (high melting crystalline polymer) and a layer containing the second crystalline polymer (low melting crystalline polymer). The entire unheated film is not particularly limited as long as it can be uniformly and uniformly heated without a temperature difference between one surface of the unheated film and the opposite surface, and can be appropriately selected according to the purpose. Examples include baths, hot air heaters, furnaces, roll heating, IR heating, and the like. Among these, a salt bath is particularly preferable from the viewpoint that it is possible to suppress variation in heating when the entire unheated film is heated.

In the DSC chart obtained by measuring the second crystalline polymer (low melting crystalline polymer) with a differential scanning calorimeter, it has one peak and a shoulder on the high temperature side or low temperature side of the peak. When the peak is on the low temperature side and the high temperature shoulder portion is on the high temperature side of the peak, it is preferable that the unheated film is symmetrically heated at a temperature higher than the peak temperature on the low temperature side. When the symmetric heating is performed at a temperature lower than the peak temperature on the low temperature side, the pore diameter is not sufficiently reduced, and the fine particle capturing property may be lowered.
In the DSC chart obtained by measuring the second crystalline polymer (low melting crystalline polymer) with a differential scanning calorimeter, it has one peak and a shoulder on the high temperature side or low temperature side of the peak. When the peak is on the high temperature side and the low temperature shoulder portion is on the low temperature side of the peak, it is preferable that the unheated film is heated symmetrically at a temperature higher than the temperature of the low temperature shoulder portion. When the symmetrical heating is performed at a temperature lower than the temperature of the low-temperature side shoulder portion, the pore diameter is not sufficiently reduced, and the fine particle capturing property may be lowered.
In addition, it is preferable from the viewpoint of increasing the flow rate that the unheated film is symmetrically heated at a temperature not higher than the melting point of the first crystalline polymer (high melting crystalline polymer). The temperature of the peak position corresponding to the melting point of the high-melting crystalline polymer is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 343 ° C to 350 ° C.

In the DSC chart obtained by measuring the second crystalline polymer (low melting crystalline polymer) with a differential scanning calorimeter, as shown in FIG. 13, the peak T ₂ on the low temperature side and the high temperature of the peak Those having a high temperature side shoulder T ₁ on the side, and those having a peak T ₃ on the high temperature side and a low temperature side shoulder T ₄ on the low temperature side of the peak as shown in FIG. Accordingly, the symmetric heating of the unheated film is performed at a temperature higher than the peak T _{2 in} FIG. 13 or a temperature higher than the low-temperature side shoulder T _{4 in} FIG. 14, thereby forming a plurality of short fibrils and nodes (nodes). A crystalline polymer microporous membrane with a layer structure is obtained.
As shown in FIG. 15, when the second crystalline polymer (low melting crystalline polymer) has two peaks, a low temperature side peak T ₅ and a high temperature side peak T ₆ , symmetric heating of the unheated film is preferably performed at a temperature higher than the low temperature side peak temperature T _5.

Specifically, in the DSC chart obtained by measuring with the differential scanning calorimeter of the second crystalline polymer, as shown in FIG. 13, the peak T ₂ on the low temperature side and the high temperature on the high temperature side of the peak. when having side shoulder portion T _1, the lower limit value of the temperature of heating symmetrically the unheated film is a temperature higher than the peak T _2, the upper limit value corresponds to a high melting point of the crystalline polymer melting point peak The temperature of the position is preferred.
Further, in the DSC chart of the second crystalline polymer, as shown in FIG. 14, when the peak T ₃ is on the high temperature side and the low temperature side shoulder T ₄ is on the low temperature side of the peak, the unheated the lower limit of the temperature of the film symmetrically heated is a temperature higher than the low temperature-side shoulder portion T _4, the upper limit is preferably at a temperature of a peak position corresponding to the high melting point of the crystalline polymer melting point.
In addition, in the DSC chart of the second crystalline polymer, as shown in FIG. 15, in the case of having two peaks of a low temperature side peak T ₅ and a high temperature side peak T ₆ , the unheated film is heated symmetrically. the lower limit of the temperature at which, the a low-temperature side peak temperature T ₅ temperature higher than the upper limit value is preferably a temperature of a peak position corresponding to the high melting point of the crystalline polymer melting point.

<Extension process>
The said extending process is a process of extending | stretching the symmetrical heating film of the state heated by the said symmetrical heating process.
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 1.2 times to 50 times, more preferably 1.5 times to 40 times, and particularly preferably 2.0 times to 10 times. The longitudinal stretching temperature is preferably 35 ° C to 330 ° C, more preferably 45 ° C to 320 ° C, and particularly preferably 55 ° C to 310 ° C.
The stretching ratio in the width direction is preferably 1.2 times to 50 times, more preferably 1.5 times to 40 times, still more preferably 2.0 times to 30 times, and particularly preferably 2.5 times to 10 times. . The stretching temperature in the width direction is preferably 35 ° C to 330 ° C, more preferably 45 ° C to 320 ° C, and particularly preferably 60 ° C to 310 ° C.
The area stretching ratio is preferably 1.5 times to 2,500 times, more preferably 2 times to 2,000 times, and particularly preferably 2.5 times to 100 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 higher than the stretching temperature and lower than the melting point of the crystalline polymer.
When the crystalline polymer is a fluororesin such as PTFE, it is preferable to heat at a melting point or higher.

<< Surface modification process >>
The surface modification step is a step of modifying the surface of at least a part of the crystalline polymer microporous membrane.
At least a part of the crystalline polymer microporous membrane includes not only the exposed surface of the crystalline polymer microporous membrane but also the periphery of the pore and the inside of the pore.

  The surface modification method is not particularly limited and may be appropriately selected depending on the intended purpose. For example, (1) a method of laser irradiation after impregnation with a hydrogen peroxide solution or an aqueous solution of a water-soluble solvent (Japanese Patent Application Laid-Open No. Hei 7). -3048888, etc.), (2) a method of irradiating with radiation, plasma or the like (see JP 2003-151571 A, etc.), (3) chemical etching treatment (see JP 2007-154153 A, etc.), (4) A method of coating with a crosslinking material (see JP-A-8-283447, etc.), (5) a method of coating with a polymerization material (see JP-A-2000-235849, etc.), and the like.

  The crystalline polymer microporous membrane of the present invention has a fine pore diameter, can efficiently capture fine particles of several tens of nanometers, has a high flow rate, and has a uniform thickness distribution of each layer in the width direction. High uniformity of filtration performance distribution and reduced leakage when using large areas, so it can be used for various applications that require filtration, but it is particularly suitable for use as a filter for filtration described below. Can do.

(Filter for filtration)
The filtration filter of the present invention is characterized by using the crystalline polymer microporous membrane of the present invention.
As the area of the crystalline polymer microporous membrane of the cartridge ^filter, preferably 0.04 m 2 through 10m ^2, more preferably ^{0.1m 2 ~5m 2, 1.3m 2 ~5m} 2 is particularly preferred. Moreover, it is preferable that the filter for filtration of this invention is a cartridge filter.
In the microparticle complementarity test, the conventional crystalline polymer microporous membrane is not a problem when used in a small area (less than 200 mm × 200 mm = 0.04 m ² ), but when used in a large area (for example, 1 cartridge = At 1.3 m ² ), leakage occurs at a rate of 1% to 10%. In contrast, the crystalline polymer microporous membrane of the present invention has a uniform layer thickness by suppressing variations in the width direction (particularly variations near both ends) that cause non-uniformity in the layer thickness. Leakage can be reduced even when the area is used.

When the crystalline polymer microporous membrane of the present invention is used as a filter for filtration, it is arranged so that the position of the layer containing the crystalline polymer having a low melting point is close to the outlet side (outlet side) of the filtrate. By doing so, fine particles of several tens of nanometers can be efficiently captured.
In addition, since the crystalline polymer microporous membrane of the present invention has a large specific surface area, 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 is preferably processed and formed into a pleated shape. Processing into pleats has the advantage that the effective surface area used to filter the filter per cartridge can be increased.

  Here, FIG. 10 is a development view showing a structure of an element exchange type pleated filter cartridge element. The microfiltration membrane 113 is folded and folded around a core 115 having a large number of liquid collection ports while being sandwiched by two membrane supports 112 and 114. On the outside, there is an outer cover 111 that protects the microfiltration membrane. Microfiltration membranes are sealed at both ends of the cylinder by end plates 116a and 116b. The end plate is in contact with a seal portion of a filter housing (not shown) through a gasket 117. The filtered liquid is collected from the core collection port and discharged from the fluid outlet 118.

A capsule pleated filter cartridge is shown in FIGS.
FIG. 11 is a development 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 22 is folded and folded around a filter element core 27 having a large number of liquid collection ports, sandwiched between two supports 21 and 23. There is a filter element cover 26 on the outside to protect the microfiltration membrane. A microfiltration membrane is sealed at both ends of the cylinder by an upper end plate 24 and a lower end plate 25.
FIG. 12 shows the structure of a capsule pleated filter cartridge in which a filter element is integrated in a housing. The filter element 30 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 28. The liquid enters the housing from the liquid inlet nozzle, passes through the filter medium 29, is collected from the liquid collection port of the filter element core 27, and is discharged from the liquid outlet nozzle 34. The housing base and the housing cover are usually heat-sealed in a liquid-tight manner at the welding portion 37.

  FIG. 11 shows an example in which the lower end plate and the housing base are sealed through an O-ring. However, the sealing between the lower end plate and the housing base may be performed by heat fusion or an adhesive. Alternatively, the seal between the housing base and the housing cover can be made by using an adhesive in addition to heat sealing. 10 to 12 are specific examples of the microfiltration filter cartridge, and the present invention is not limited to these drawings.

  The filter for filtration using the crystalline polymer microporous membrane of the present invention has high uniformity of thickness distribution and filtration performance distribution of each layer in the width direction of the crystalline polymer microporous membrane. When the porous membrane is used in a large area, the yield can be improved and leakage can be reduced. In addition, the filter for filtration using the crystalline polymer microporous membrane of the present invention has such a feature that the filtration function is high and the life is long, so that the filtration device can be compactly assembled. In the conventional filtration apparatus, a large number of filtration units are used in series 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 series 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 filtration filter of the present invention is suitably used for microfiltration of gases, liquids, etc., for example, filtration of corrosive gas, various gases used in the semiconductor industry, washing water for electronics industry, pharmaceutical water, pharmaceutical manufacture Widely used in process water, food water filtration, sterilization, high temperature filtration, reactive chemical filtration, wire coating materials, catheters, artificial blood vessels, anti-adhesion membranes, cell culture scaffolds, insulating membranes, fuel cell separators, etc. it can.

  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>
-Production of cylindrical molded body-
Polytetrafluoroethylene fine powder as a high melting crystalline polymer (Daikin Kogyo Co., Ltd., “F106”, melting point 346 ° C.) 100 parts by mass, as an extrusion aid, hydrocarbon oil (Esso Oil Co., Ltd., “ Isopar H ")) 23 parts by weight was added. This was designated as paste 1.
Polytetrafluoroethylene fine powder as a low melting crystalline polymer (Daikin Kogyo Co., Ltd., “F205”, melting point 341 ° C.) 100 parts by mass, as an extrusion aid, hydrocarbon oil (Esso Oil Co., Ltd., “ Isopar H ")) 20 parts by weight was added. This was designated as paste 2.
FIG. 13 shows a DSC chart of this fine powder of polytetrafluoroethylene (“F205” manufactured by Daikin Industries, Ltd.). From the results shown in FIG. 13, the polytetrafluoroethylene fine powder “F205” has one peak with a high-temperature shoulder portion (T ₁ ) of 341 ° C. and a low-temperature peak (T ₂ ) of 338 ° C. It was found to have two shoulders.
Next, in the concentric multilayer paste extrusion apparatus shown in FIG. 5, the cross-sectional area ratio of paste 1 and paste 2 (from the outside, paste 1 / paste 2 / paste 1) is 3/1/1. A cylindrical molded body having a three-layer concentric cylindrical structure was laid down and pressed in a cylindrical mold.

Here, the melting points of the high-melting crystalline polymer and the low-melting crystalline polymer were measured as follows.
--Measuring method of melting point--
The melting point of the crystalline polymer was measured from a DSC chart using DSC7200 manufactured by SII. Specifically, a sample to be measured was weighed about several mg to 10 mg, put in an aluminum pan, and simply sealed, and then measured at a rate of 10 ° C./min. Melting | fusing point shows the peak position of the chart, and when it has two peaks, or when it has one peak and one shoulder part, the temperature with the higher peak intensity was made into melting | fusing point.

−Preparation of sheet-shaped molded body−
The prepared preform was extruded and a concentric multilayer paste was extruded into a cylindrical shape. Note that the cylinder part (preliminary molded body injection part) of the concentric multilayer paste extrusion apparatus shown in FIG. 5 has a cylindrical shape with an inner diameter of the outer frame of 85 mm and an outer diameter of the inner frame of 40 mm in the cross section perpendicular to the axis. , And an aperture portion (cylindrical shape having an inner frame inner diameter of 66 mm and an inner frame outer diameter of 62 mm), and the aperture ratio is 11. The obtained cylindrical molded body was cut in the central axis direction of the molded body to obtain a sheet-shaped molded body.

-Production of unheated film-
The obtained sheet-like molded body was calendered with a calender roll heated to 60 ° C. to produce a multilayer polytetrafluoroethylene film. The obtained multilayer polytetrafluoroethylene film was passed through a hot air drying oven at 250 ° C. to remove the extrusion aid, and the multilayer polytetrafluoroethylene unheated film having an average thickness of 100 μm, an average width of 250 mm, and a specific gravity of 1.45. Was made.

-Production of symmetrical heating film-
The obtained multilayer polytetrafluoroethylene unheated film was heated for 50 seconds in a salt bath (mixed salt of potassium nitrate and sodium nitrate was used as the molten salt) kept at 344 ° C. higher than the peak (T ₂ ). Thus, a symmetrical heating film was produced.

-Fabrication of crystalline polymer microporous membrane-
The obtained symmetrically heated film was stretched between rolls 3 times in the longitudinal direction at 250 ° C. and once wound up on a winding roll. Thereafter, both ends were sandwiched between clips and stretched 3 times in the width direction at 250 ° C. Thereafter, heat setting was performed at 370 ° C. Thus, the crystalline polymer microporous membrane of Example 1 was produced.

  In the obtained crystalline polymer microporous membrane, having a plurality of pores in which the average pore diameter is constant (not changed) in the thickness direction of each layer freezes and cleaves the microporous membrane. It confirmed by performing cross-sectional observation with an electron microscope (SEM) (JSM-6360, JEOL company make). As a result, it was found that the crystalline polymer microporous membrane of Example 1 had a plurality of pores in which the average pore diameter was constant (not changed) in all three layers.

<Evaluation>
Next, for the prepared crystalline polymer microporous membrane of Example 1, confirmation of “a plurality of pores communicating in the thickness direction was formed” and measurement of the thickness of each layer were performed as follows. went. The results are shown in Table 1.

<< Confirmation that "a plurality of holes communicating in the thickness direction are formed">>
The fact that “a plurality of pores communicating in the thickness direction was formed” was obtained by freezing and cleaving the crystalline polymer microporous membrane of Example 1 and scanning electron microscope (SEM) (JSM-6360, manufactured by JEOL). ) Was confirmed by observing the cross section.

<< Measurement of thickness distribution of each layer in width direction >>
The crystalline polymer microporous membrane of Example 1 was frozen and cut, and the thickness of each layer was measured by observing a cross section with a scanning electron microscope (SEM) (JSM-6360, manufactured by JEOL). Specifically, the thickness of each section obtained by dividing the crystalline polymer microporous membrane into 100 equal parts in the width direction is measured, and the width direction of 100 pieces of thickness data (X ₁ , X ₂ ,... X ₁₀₀ ). The average value (average thickness) Xm of was obtained. Further, the thickness variation rate Vx was obtained by the following formula (1). The results are shown in Table 1.
Thickness variation rate (%): Vx = Sx / Xm × 100 (1)
(Wherein, Xm represents an average value (average thickness) of n pieces of thickness data (X ₁ , X ₂ ,... X _n ), and Sx represents a standard deviation of the n pieces of thickness data.)

<< Measurement of average flow pore size distribution in width direction >>
For the crystalline polymer microporous membrane of Example 1, the average flow pore size was measured using a palm porometer (manufactured by PMI). Specifically, the crystalline polymer microporous membrane is equally divided into squares with a side of 20 mm in the width direction, the average flow pore diameter of each part is measured, and 20 average flow pore diameter data (Y ₁ , Y ₂ ,... -The average value Ym in the width direction of Y ₂₀ ) was determined. Further, the fluctuation rate Vy of the average flow hole diameter was obtained by the following formula (2). The results are shown in Table 2.
Fluctuation rate of average flow hole diameter (%): Vy = Sy / Ym × 100 (2)
(Wherein, Ym is an average value of _n average flow rate pore diameter data (Y ₁ , Y ₂ ,... Y _n ), and Sy is a standard deviation of n average flow rate pore size data.)

<< filtration test >>
Next, a filtration test was performed on the crystalline polymer microporous membrane of Example 1. First, an aqueous solution containing 1 ppm of polystyrene latex (weight average particle diameter 0.05 μm) was filtered at a differential pressure of 100 kPa. Table 2 shows the results of the capture rate calculated from the difference between the concentration of the stock solution and the concentration of the filtrate.

<< Flow test >>
Next, a flow rate test was performed on the crystalline polymer microporous membrane of Example 1. Specifically, the permeation amount per unit area (m ² ) / unit time (min) when isopropyl alcohol (IPA) was flowed at a differential pressure of 100 kPa was defined as a flow rate (L · m ⁻² · min ⁻¹ ). . The results are shown in Table 2.

(Example 2)
In Example 1, a cylindrical molded body having a three-layer concentric cylindrical structure in which the cross-sectional area ratio (from the outside, paste 1 / paste 2 / paste 1) is 3/1/1 is the cross-sectional area ratio (from the outside, paste 1 The paste of Example 2 was prepared in the same manner as in Example 1 except that a cylindrical formed body having a two-layer concentric cylindrical structure was prepared by laying in a cylindrical shape and applying pressure so that the paste 2) was 4/1. A porous polymer microporous membrane was prepared and evaluated. The results are shown in Tables 1 and 2.
In addition, it was confirmed in the same manner as in Example 1 that the plurality of pores having a constant average pore diameter in the thickness direction of each layer in the obtained crystalline polymer microporous membrane was confirmed. Was found to have a plurality of holes that are constant.

(Example 3)
In Example 1, a cylindrical molded body having a three-layer concentric cylindrical structure in which the cross-sectional area ratio (from the outside, paste 1 / paste 2 / paste 1) is 3/1/1 is the cross-sectional area ratio (from the outside, paste 1 / Paste 2 / Paste 1) Except that a cylindrical molded body having a three-layer concentric cylindrical structure was prepared by laying in a cylindrical shape and applying pressure so that the ratio was 10/1/3, The crystalline polymer microporous membrane of Example 3 was prepared and evaluated. The results are shown in Tables 1 and 2.
Further, it was confirmed in the same manner as in Example 1 that the plurality of pores having a constant average pore diameter in the thickness direction of each layer in the obtained crystalline polymer microporous membrane was confirmed. Was found to have a plurality of holes that are constant.

Example 4
In Example 1, instead of polytetrafluoroethylene fine powder (“F106” manufactured by Daikin Industries, Ltd.) as a high melting crystalline polymer, polytetrafluoroethylene fine powder as a high melting crystalline polymer A crystalline polymer microporous membrane of Example 4 was produced and evaluated in the same manner as in Example 1 except that Asahi Glass Co., Ltd., CD123, melting point 346 ° C. was used. The results are shown in Tables 1 and 2.
Further, it was confirmed in the same manner as in Example 1 that the plurality of pores having a constant average pore diameter in the thickness direction of each layer in the obtained crystalline polymer microporous membrane was confirmed. Was found to have a plurality of holes that are constant.

(Example 5)
In Example 1, instead of using F205 manufactured by Daikin Industries, Ltd. as a low melting crystalline polymer, multi-layer polytetrafluoroethylene using CD126 (melting point: 341 ° C.) manufactured by Asahi Glass Co., Ltd. as a low melting crystalline polymer. A salt bath in which an unheated film was prepared and the obtained multilayer polytetrafluoroethylene unheated film was kept at 341 ° C. higher than the low-temperature shoulder (T ₄ ) (as molten salt, a mixture of potassium nitrate and sodium nitrate) The crystalline polymer microporous membrane of Example 5 was prepared and evaluated in the same manner as in Example 1 except that a symmetric heating film was prepared by heating for 50 seconds using a salt). did. The results are shown in Tables 1 and 2.
A DSC chart of CD126 manufactured by Asahi Glass Co., Ltd. as a low melting crystalline polymer is shown in FIG. From the results of FIG. 14, it was found that CD126 manufactured by Asahi Glass Co., Ltd. as a low melting crystalline polymer has a low temperature side shoulder (T ₄ ) 336 ° C. and a high temperature side peak (T ₃ ) 341 ° C.
Further, it was confirmed in the same manner as in Example 1 that the plurality of pores having a constant average pore diameter in the thickness direction of each layer in the obtained crystalline polymer microporous membrane was confirmed. Was found to have a plurality of holes that are constant.

(Comparative Example 1)
In Example 1, the unheated film was replaced with the polytetrafluoroethylene multilayer unheated film prepared by the following procedure, and the heating temperature of the polytetrafluoroethylene multilayer unheated film was the low temperature side peak (T ₂ ) at 338 ° C. A crystalline polymer microporous membrane of Comparative Example 1 was produced in the same manner as in Example 1 except that this was performed.

-Preparation of preform-
Paste 1 and paste 2 in Example 1 were spread and pressed in a square mold so that the average thickness ratio (paste 1 / paste 2 / paste 1) was 3/1/1, and three layers were formed. A rectangular column shaped preform was formed.

-Production of unheated film-
The prepared preform was inserted into a square cylinder of a paste extrusion mold, and a multilayer paste was extruded into a sheet shape. This was calendered with a calender roll heated to 60 ° C. to produce a multilayer polytetrafluoroethylene film. The obtained multilayer polytetrafluoroethylene film was passed through a hot air drying oven at 250 ° C. to remove the extrusion aid, and the multilayer polytetrafluoroethylene unheated film having an average thickness of 100 μm, an average width of 250 mm, and a specific gravity of 1.45. Was made.
In the thickness direction of each layer in the obtained crystalline polymer microporous membrane, it was confirmed in the same manner as in Example 1 that the average pore diameter was constant without change. Was found to have a plurality of holes that were constant without change.

(Comparative Example 2)
In Comparative Example 1, instead of using F205 manufactured by Daikin Industries, Ltd. as a low melting crystalline polymer, multi-layer polytetrafluoroethylene using CD126 (melting point: 341 ° C.) manufactured by Asahi Glass Co., Ltd. as a low melting crystalline polymer. Comparative Example 2 was prepared in the same manner as Comparative Example 1 except that an unheated film was prepared and the obtained multilayer polytetrafluoroethylene unheated film was performed at a temperature (T ₄ ) of 336 ° C. on the low-temperature side shoulder. A crystalline polymer microporous membrane was prepared.
In the thickness direction of each layer in the obtained crystalline polymer microporous membrane, it was confirmed in the same manner as in Example 1 that the average pore diameter was constant without change. Was found to have a plurality of holes that were constant without change.

(Comparative Example 3)
-Production of cylindrical molded body-
Polytetrafluoroethylene fine powder with a number average molecular weight of 1 million as a crystalline polymer (Asahi Glass Co., Ltd., “Fluon PTFE CD1”, melting point 339 ° C.) 100 parts by mass, as an extrusion aid, hydrocarbon oil (Esso Oil Co., Ltd.) 27 parts by mass of “Isopar H” produced by the company was added. This was designated as paste 3.
Similarly, polytetrafluoroethylene fine powder (Asahi Glass Co., Ltd., “Fluon PTFE CD123”, melting point 346 ° C.) having a number average molecular weight of 10 million is added to 100 parts by mass of hydrocarbon oil (Esso Oil Co., Ltd.) as an extrusion aid. 27 parts by mass, manufactured by “Isopar H”) was added. This was designated as paste 4.
Next, cylindrical gold in the concentric multilayer paste extrusion apparatus shown in FIG. 5 is used so that the thickness ratio of paste 3 and paste 4 (paste 3 / paste 4 / paste 3) is 3/1/1. The mold was spread and pressed to form a cylindrical molded body having a three-layer concentric cylindrical structure.

−Preparation of sheet-shaped molded body−
The produced cylindrical molded body was subjected to paste extrusion, and a concentric multilayer paste was extruded into a cylindrical shape. The obtained cylindrical molded body was cut in the central axis direction of the molded body to obtain a sheet-shaped molded body.

-Production of unheated film-
The produced sheet-like molded body was inserted into a cylinder of a paste extrusion mold, and a multilayer paste was extruded into a sheet shape. This was calendered with a calender roll heated to 60 ° C. to produce a multilayer polytetrafluoroethylene film. The resulting multilayer polytetrafluoroethylene film was passed through a hot air drying oven at 250 ° C. to remove the extrusion aid, and the multilayer polytetrafluoroethylene unheated having an average thickness of 100 μm, an average width of 250 mm, and a specific gravity of 1.55 A film was prepared.

-Production of semi-heated film-
The back surface (paste 4 side) of the obtained multilayer polytetrafluoroethylene unheated film was heated with a near-infrared ray with a halogen heater with a built-in tungsten filament at a film surface temperature of 345 ° C. for 1 minute to form a half-heated film. Produced.

-Fabrication of crystalline polymer microporous membrane-
The obtained semi-heated film was stretched between rolls by 12.5 times in the longitudinal direction at 270 ° C. and once wound on a take-up 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 crystalline polymer microporous film of Comparative Example 3 was produced.
It was found that in the obtained crystalline polymer microporous membrane, there were a plurality of pores whose average pore diameter varied continuously or discontinuously in the thickness direction of each layer.

(Comparative Example 4)
-Production of cylindrical molded body-
The paste 2 in Example 1 was laid alone in a cylindrical mold in a concentric multilayer paste extrusion apparatus shown in FIG. 5 and pressed to obtain a cylindrical molded body having a cylindrical structure.

−Preparation of sheet-shaped molded body−
The produced cylindrical molded body was subjected to paste extrusion, and a concentric multilayer paste was extruded into a cylindrical shape. This was calendered with a calender roll heated to 60 ° C. to produce a single-layer polytetrafluoroethylene film. When the obtained single layer polytetrafluoroethylene film is passed through a hot air drying oven at 250 ° C. to remove the extrusion aid and wind up, tearing occurs in the middle, and the single layer polytetrafluoroethylene unheated stably. A film could not be produced.

  From this result, in Examples 1-5 of this invention, it turned out that the thickness fluctuation rate of the width direction in each layer is low, Therefore, the uniformity of the thickness distribution in the width direction is high. It was also found that the variation rate of the average flow pore size in the width direction in the crystalline polymer microporous membrane was low, and thus the uniformity of the filtration performance distribution in the width direction was high.

(Example 6)
-Filter cartridge-
The crystalline polymer microporous membrane of Example 1 was laminated as follows, pleated to a pleat width of 12.5 mm (pleat width = 220 mm), and 230 folds were taken and rolled into a cylindrical shape. The seam is welded with an impulse sealer. The cylinder was cut off at both ends of 15 mm, and the cut surfaces were thermally welded to a polypropylene end plate to complete an element exchange type filter cartridge.
−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 Crystalline polymer microporous membrane of Example 1
Thickness: about 0.07 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

(Examples 7 to 10)
In Example 6, in place of the crystalline polymer microporous membrane of Example 1, the crystalline polymer microporous membrane of Examples 2 to 5 was used, respectively. The filter cartridges of Examples 7-10 were prepared.

<Evaluation>
<< Fine particle capture test when using large area >>
About 100 filter cartridges of Examples 6 to 10, an aqueous solution containing 1 ppm of polystyrene fine particles (average particle size 0.05 μm) was filtered at a differential pressure of 100 kPa, and the presence or absence of fine particle leakage was examined. The results are shown in Table 3.

  Since the filter cartridges of Examples 6 to 10 of the present invention use the crystalline polymer microporous membranes of Examples 1 to 5 of the present invention, fine particles having a minute pore size and a size of several tens of nm are efficiently used. It was possible to capture well, the flow rate was high, the uniformity of the thickness distribution of each layer in the width direction and the uniformity of the filtration performance distribution were high, and leakage when using a large area was reduced.

  The crystalline polymer microporous membrane of the present invention and a filter for filtration using the same can be used in various situations where filtration is required, and is suitably used for microfiltration of gases, liquids, etc. Filtration of corrosive gases, various gases used in the semiconductor industry, electronic industry cleaning water, pharmaceutical water, pharmaceutical manufacturing process water, food water filtration, sterilization, high temperature filtration, reactive chemical filtration, wire coating It can be widely used for materials, catheters, artificial blood vessels, adhesion prevention membranes, cell culture scaffolds, insulating membranes, fuel cell separators, and the like.

DESCRIPTION OF SYMBOLS 3 1st layer 4 2nd layer 5 3rd layer 6 Cylindrical molded object 7 Concentric circular multilayer paste extrusion apparatus 8 Lower mold 9 Upper mold 10 Sheet-shaped molded body 21 Primary side support 22 Microfiltration membrane 23 Secondary side Support 24 Upper end plate 25 Lower end plate 26 Filter element cover 27 Filter element core 28 O-ring 29 Filter media 30 Filter element 31 Housing cover 32 Housing base 33 Liquid inlet nozzle 34 Liquid outlet nozzle 35 Air vent 36 Drain 37 Welding part 101, 102, 103 Crystalline polymer layer 101a, 102a, 103a Hole 101b, 102b, 103b Hole 111 Perimeter cover 112 Membrane support 113 Microfiltration membrane 114 Membrane support 115 Core 116a, 116b End Plate 117 Gasket 118 Liquid outlet

Claims (16)

A tubular molded body in which a layer containing the first crystalline polymer and a layer containing the second crystalline polymer are laminated is cut in the central axis direction of the cylindrical molded body to form a sheet-shaped molded body. A sheet-like molded body forming step;
An unheated film forming step of forming an unheated film by rolling the sheet-like molded body;
A symmetrical heating step of symmetrically heating the unheated film to form a symmetrical heated film;
A method for producing a crystalline polymer microporous membrane, comprising: a stretching step of stretching the symmetric heating film.   The method for producing a crystalline polymer microporous film according to claim 1, wherein the cylindrical molded body is formed by extrusion of a multilayer paste.   The method for producing a crystalline polymer microporous film according to claim 2, wherein the cylindrical molded body is formed by extrusion of a multilayer paste using an extrusion apparatus having a cylindrical drawn portion. In the DSC chart obtained by measuring the second crystalline polymer with a differential scanning calorimeter, it has one peak and a shoulder on the high temperature side or low temperature side of the peak,
When having a peak on the low temperature side and a high temperature side shoulder on the high temperature side of the peak, symmetrical heating of the unheated film is performed at a temperature higher than the peak temperature on the low temperature side,
When it has a peak on the high temperature side and a low temperature side shoulder portion on the low temperature side of the peak, the symmetrical heating of the unheated film is performed at a temperature higher than the temperature of the low temperature side shoulder portion. A method for producing the crystalline polymer microporous membrane described.   The method for producing a crystalline polymer microporous membrane according to any one of claims 1 to 4, wherein the unheated film is symmetrically heated at a temperature not higher than the melting point of the first crystalline polymer. A crystalline polymer microporous membrane comprising two or more layers in which a layer containing a first crystalline polymer and a layer containing a second crystalline polymer are laminated and a plurality of pores communicating in the thickness direction are formed Because
The melting point of the first crystalline polymer is higher than the melting point of the second crystalline polymer;
At least one layer in the crystalline polymer microporous membrane has a plurality of pores having a constant average pore diameter in at least a part in the thickness direction of the crystalline polymer microporous membrane,
A crystalline polymer microporous membrane having a thickness variation rate in the width direction of at least one layer of the crystalline polymer microporous membrane of 14% or less.   The crystalline polymer microporous membrane according to claim 6, wherein the variation rate of the average flow pore size in the width direction of the crystalline polymer microporous membrane is 13% or less.   The crystalline polymer microporous membrane according to any one of claims 6 to 7, comprising two layers containing a first crystalline polymer and a layer containing a second crystalline polymer between the two layers.   The maximum thickness A of the layer containing the second crystalline polymer is thinner than the maximum thickness B of the layer containing the first crystalline polymer, and satisfies the following formula: A / B ≦ 1/2. The crystalline polymer microporous membrane according to any one of the above.   The crystalline polymer microporous membrane according to claim 9, satisfying the following formula: A / B ≦ 1/3.   The crystalline polymer microporous membrane according to any one of claims 6 to 10, wherein the thickness of the layer containing the second crystalline polymer is 0.1 µm to 50 µm.   The crystalline polymer microporous membrane according to any one of claims 6 to 11, wherein the first crystalline polymer is at least one of polytetrafluoroethylene and a polytetrafluoroethylene copolymer.   The crystalline polymer microporous membrane according to any one of claims 6 to 12, wherein the second crystalline polymer is at least one of polytetrafluoroethylene and a polytetrafluoroethylene copolymer.   A filter for filtration, comprising the crystalline polymer microporous membrane according to claim 6. Area of the crystalline polymer microporous ^membrane, filtration filter according to claim 14 which is 0.04 m 2 through 10m ^2.   The filter for filtration according to any one of claims 14 to 15, which is a cartridge filter.