JP2012192308A - Crystallizable polymer microporous membrane and method for manufacturing the same, and filtration film and filtration device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a crystallizable polymer microporous membrane suitable for manufacturing a filtration filter adoptable in a high-flux and high-strength filtration device, capable of preventing inner layers from breaking, superior in structural stability, having a minute pore diameter, capable of efficiently catching fine particles of tens of nm size, and flexible in performance design, and to provide an efficient method for manufacturing the same, and a filtration filter and a filtration device.SOLUTION: The method for manufacturing the crystallizable polymer microporous membrane includes: a laminated body forming step of forming a laminated body by extruding and rolling a preformed laminated body in a longitudinal direction, the preformed laminated body being prepared such that both surfaces of a second crystallizable polymer sheet layer are covered with a first crystallizable polymer, and a pair of opposite end surfaces of the second crystallizable polymer sheet layer in the longitudinal direction is covered with the first crystallizable polymer sheet layer; a symmetrical heating step of symmetrically heating the laminated body; and a stretching step of stretching the laminated body.

Description

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

  Microporous membranes have been known for a long time, but in recent years, their use and usage have been reduced as filtration filters used for filtration and sterilization of electronic industrial cleaning water, pharmaceutical water, pharmaceutical manufacturing process water, food water, etc. A highly reliable microporous membrane is drawing attention.

  Examples of the material of such a microporous membrane include cellulose ester (for example, see Patent Document 1), aliphatic polyamide (for example, see Patent Document 2), polyfluorocarbon (for example, see Patent Document 3), polypropylene ( For example, Patent Document 4), polytetrafluoroethylene (hereinafter sometimes referred to as “PTFE”) (see, for example, Patent Documents 5 and 6), and the like are known. Among these, the crystalline polymer microporous membrane using PTFE as a raw material is excellent in heat resistance and chemical resistance, and therefore, the growth in demand is remarkable.

As a crystalline polymer microporous film made of PTFE as a raw material, for example, a preform formed by laminating a homopolytetrafluoroethylene polymer and a modified polytetrafluoroethylene copolymer is rolled and stretched to obtain a small size. It has been proposed that a microporous membrane comprising a filtration layer having an average pore size and a support layer having a large average pore size is produced (see, for example, Patent Documents 5 and 6).
However, in these proposals, a material having a lower melting point than the material used for the support layer is used as the material of the filtration layer, and it can be expected that the pore diameter of the filtration layer can be effectively reduced as the melting point difference increases. Thus, the polytetrafluoroethylene polymer or the modified polytetrafluoroethylene polymer having a low melting point has a drawback that it is inferior in strength when not heated. Therefore, using these polymers as materials, producing a preform with the end face of the filtration layer (inner layer) exposed, extruding the preform and rolling it with a rolling roll, Due to the external force applied to the filter layer, there is a problem in that the entire membrane breaks due to cracks and breaks caused by the material of the filtration layer. In addition, in order to prevent the inner layer from starting to break, there is a problem that the design of the layer thickness and position is restricted and it is difficult to freely design the performance.

  Therefore, it is possible to prevent breakage in the inner layer, to have excellent structural stability, to have fine pore size, to efficiently capture fine particles of tens of nanometers, and to be able to design performance freely. Rapid development of a filter for filtration used in a filtration device having a high flow rate and high strength using the polymer microporous membrane, an efficient production method thereof, and these crystalline polymer microporous membranes The current situation is strongly demanded.

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 Japanese Patent Laid-Open No. 03-179038 Japanese Patent Laid-Open No. 03-179039

  An object of the present invention is to solve the above-described problems and achieve the following objects. That is, the present invention is suitable for producing a filter for filtration used in a filtration device having a high flow rate and high strength, can prevent breakage in the inner layer, has excellent structural stability, and has a fine pore diameter. A crystalline polymer microporous membrane that can efficiently capture fine particles of a size of several tens of nanometers and can be freely designed for performance, an efficient manufacturing method thereof, a filter for filtration, and a filtration device For the purpose.

As a result of intensive studies by the present inventors in order to solve the above-mentioned problems, both the first crystalline polymer sheet layer 4 as shown in FIG. When a material having a low melting point is used as the second crystalline polymer in the laminated preform 10 coated with, the second preform is extruded with the rolling roll 20 after the laminated preform is extruded. It was found that the break 16 occurred from the pair of end faces 5B in the length direction of the crystalline polymer sheet layer.
Therefore, as shown in FIG. 4, the second crystalline polymer sheet layer is covered with a pair of opposing end faces 5B in the longitudinal direction by using the first crystalline polymer, whereby the second crystalline polymer sheet layer is coated with the second crystalline polymer sheet layer. Can prevent breakage in the crystalline polymer sheet layer, has excellent structural stability, has a fine pore size, can efficiently capture fine particles of several tens of nanometers, and can be freely designed for performance It was found that a porous polymer microporous membrane was produced.
Further, the inventors of the present invention provide an efficient method for producing the crystalline polymer microporous membrane, and a high flow rate and high strength filtration device using the crystalline polymer microporous membrane. The filter used for filtration was discovered.

The present invention is based on the above findings by the present inventors, and means for solving the above problems are as follows. That is,
<1> A pair of lengthwise end faces facing each other in the second crystalline polymer sheet layer, the first crystalline polymer sheet layer covering both surfaces of the second crystalline polymer sheet layer However, the laminate preform formed by coating the first crystalline polymer sheet layer is extruded in the length direction and rolled to form a laminate, and the laminate is heated symmetrically. It is a manufacturing method of the crystalline polymer microporous film | membrane characterized by including the symmetrical heating process and the extending process which extends | stretches the said laminated body.
In the laminated body forming step, the laminated preform is extruded and rolled to form a laminated body. At this time, in the second crystalline polymer sheet layer of the laminated preform, a pair of opposing end faces in the length direction are covered with the first crystalline polymer sheet layer. When the molded body is extruded and rolled in the length direction, the second crystalline polymer sheet layer does not break. Next, in the symmetrical heating step, the laminate is heated symmetrically. In the stretching step, the laminate is stretched. As a result, a crystalline polymer microporous membrane is produced.
<2> The method for producing a crystalline polymer microporous film according to <1>, wherein the thicknesses of the two first crystalline polymer sheet layers covering both surfaces of the second crystalline polymer sheet layer are different from each other. .
<3> The crystal according to any one of <1> to <2>, wherein at least one layer in the laminate has a plurality of holes having a constant average pore diameter in at least a part of the laminate in the thickness direction. Is a method for producing a porous polymer microporous membrane.
<4> The crystallinity according to any one of <1> to <3>, wherein at least the second crystalline polymer sheet layer in the laminate has a microstructure including at least a fibril having an average major axis length of 1 μm or less. This is a method for producing a polymer microporous membrane.
<5> Any one of <1> to <4>, wherein the first crystalline polymer contained in the first crystalline polymer sheet layer is any one of polytetrafluoroethylene and a polytetrafluoroethylene copolymer. The method for producing a crystalline polymer microporous membrane described in 1.
<6> Any one of <1> to <5>, wherein the second crystalline polymer contained in the second crystalline polymer sheet layer is any one of polytetrafluoroethylene and a polytetrafluoroethylene copolymer. The method for producing a crystalline polymer microporous membrane described in 1.
<7> The polytetrafluoroethylene copolymer is a copolymer obtained by copolymerizing at least two selected from tetrafluoroethylene, perfluoroalkyl vinyl ether, hexafluoropropylene, and chlorotrifluoroethylene <6>. The method for producing a crystalline polymer microporous film according to 6>.
<8> 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, and the peak on the low temperature side. When the high temperature side shoulder portion is present on the high temperature side of the peak, symmetrical heating of the laminate is performed at a temperature higher than the peak temperature on the low temperature side, and the peak is on the high temperature side and the low temperature side shoulder portion is on the low temperature side of the peak. In the case, the method for producing a crystalline polymer microporous film according to any one of <1> to <7>, wherein the symmetric heating of the laminate is performed at a temperature higher than the temperature of the low temperature shoulder portion.
<9> The method for producing a crystalline polymer microporous membrane according to any one of <1> to <8>, wherein the laminated body is subjected to symmetrical heating at a temperature not higher than the melting point of the first crystalline polymer.
<10> A crystalline polymer microporous membrane produced by the method for producing a crystalline polymer microporous membrane according to any one of <1> to <9>.
<11> A filtration filter using the crystalline polymer microporous membrane according to <10>.
<12> A filtration device having an inlet, an outlet, and the filtration filter according to <11>, wherein the second crystalline polymer sheet in the filtration filter is disposed in the vicinity of the outlet. It is a filtration device.

  According to the present invention, the conventional problems can be solved, the object can be achieved, and it is suitable for producing a filter for filtration used in a filtration device having a high flow rate and high strength. Crystalline polymer microporous membrane that can prevent breakage, has excellent structural stability, has a fine pore size, can efficiently capture fine particles of several tens of nanometers, and can be freely designed for performance And the efficient manufacturing method, the filter for filtration, and the filtration apparatus can be provided.

FIG. 1 is a diagram showing an example of steps of a method for producing a crystalline polymer microporous membrane of the present invention. FIG. 2 is a diagram showing an example of another process of the method for producing a crystalline polymer microporous membrane of the present invention. FIG. 3 is a diagram showing an example of another process of the method for producing a crystalline polymer microporous membrane of the present invention. FIG. 4 is a diagram showing an example of a preform. FIG. 5 is a diagram showing an example of another process of the method for producing a crystalline polymer microporous membrane of the present invention. FIG. 6 is a schematic view showing an example of a crystalline polymer microporous film having a three-layer structure according to the present invention. FIG. 7 is a diagram showing an example of film breakage in a crystalline polymer microporous film. FIG. 8 is a diagram illustrating an example of a structure of a general pleated filter element before being assembled in the housing. FIG. 9 is a diagram illustrating an example of a structure of a general filter element before being assembled in the housing of the capsule filter cartridge. FIG. 10 is a diagram illustrating an example of a structure of a general capsule filter cartridge integrated with a housing. FIG. 11 is a diagram showing an example of a DSC chart of the second crystalline polymer (a low melting crystalline polymer). FIG. 12 is a diagram showing an example of a DSC chart of the second crystalline polymer (low melting crystalline polymer). FIG. 13 is a diagram showing an example of a DSC chart of the second crystalline polymer (crystalline polymer having a low melting point).

(Method for producing crystalline polymer microporous membrane)
The method for producing a crystalline polymer microporous membrane of the present invention includes a laminate forming step, a symmetrical heating step, and a stretching step, and further includes other steps as necessary.

<Laminated body formation process>
The laminated body forming step is a step of forming a laminated body by extruding and rolling the laminated preform.

  As the structure of the laminated preform, the first crystalline polymer sheet layer covers both surfaces (upper and lower bottom surfaces, surfaces perpendicular to the thickness direction) of the second crystalline polymer sheet layer, and In the second crystalline polymer sheet layer, a pair of lengthwise end faces (a pair of lengthwise and thickness faces facing each other) facing each other are covered with the first crystalline polymer sheet layer. If it is the structure which becomes, there will be no restriction | limiting in particular, According to the objective, it can select suitably, For example, laminated structures, such as a 3 layer structure and a 5 layer structure, are mentioned.

  In the second crystalline polymer sheet layer of the laminated preform, the pair of longitudinal end faces facing each other is not particularly limited and may be appropriately selected depending on the purpose. It is preferable that they are parallel. In the case where the laminated preform is circular or polygonal, the pair of end surfaces may be opposed to each other even if they are not substantially parallel. The crystalline polymer sheet layer may be coated so as not to be exposed. In addition, as shown in FIG. 4, the pair of end surfaces 5 </ b> B may have a structure that is covered so as not to be exposed by the first crystalline polymer sheet layer 4.

  There is no restriction | limiting in particular as a method of producing the said lamination | stacking preforming body, According to the objective, it can select suitably, For example, (1) As shown in FIG. Only the first paste 4A composed of the first crystalline polymer (sometimes referred to as “a high-melting crystalline polymer”) and other components is placed on the outer side 1 vertically separated, and the mold 8 And the second crystalline polymer (sometimes referred to as a “low-melting crystalline polymer”) on the inner layer 2 vertically divided by the metal plate 6 and on the layer made of the first paste 4A. After laminating the layer made of the second paste 5A made of other components and laminating the layer made of the first paste 4A, the metal plate 6 is taken out and pressed to produce a laminated preform. (2) As shown in FIG. A mold 8 having a substantially prismatic core rod 3 in the center is filled with the first paste 4A composed of the first crystalline polymer and other components, and the core rod 3 is pulled out. A method of producing a laminated preform by filling the cavity with the second paste 5A comprising the second crystalline polymer and other components and then applying pressure (3) as shown in FIG. In addition, as a first layer, a layer made of the first paste 4A composed of the first crystalline polymer and other components, and as a second layer, the second crystalline polymer and other components. As a layer made of the second paste 5A and a third layer, the layers made of the first paste 4A are sequentially laminated and pressed, and then the second paste 5A in the obtained preform is pressed. The first page is further formed above and below the large exposed surface. Providing a layer of a coat layer 4A, by pressurizing again, a method of making a multilayer preform, and the like.

  There is no restriction | limiting in particular as a metal mold | die used when producing the said lamination | stacking preforming body, According to the objective, it can select suitably, For example, a metal mold | die for plastics, a press metal mold | die, a die casting metal mold | die, a casting metal mold | die And forging dies.

The thickness of the first crystalline polymer sheet layer covering the end face is not particularly limited and can be appropriately selected according to the purpose. However, when the PTFE is used, it is preferably 2 mm or more, more preferably 3 mm or more. It is preferably 5 mm or more.
In the case of using the PTFE, if the thickness of the first crystalline polymer sheet layer covering the end face is less than 2 mm, a large rupture is triggered by a small tear generated at the time of deformation when rolling the laminated preform. May occur, and stable film formation may be difficult. On the other hand, if it is 2 mm or more, even if a single material having low tensile strength is used as the second crystalline polymer, it is continuous without causing breakage or breakage of the end portion even when a large deformation by rolling or stretching is applied. This is advantageous in that a film can be formed.
The upper limit of the thickness of the first crystalline polymer sheet layer covering the end face is not particularly defined, but if the thickness of the first crystalline polymer sheet layer covering the end face is excessively wide, a microporous film is formed. Since the area that can be effectively used decreases, the area can be appropriately set in consideration of the entire width of the laminate.

The average thickness of the laminated preform is set in accordance with an extrusion method or a rolling method described later. In other words, when it is set in accordance with the extrusion method, it is produced in accordance with the dimensions of the preformed body input part of the extrusion device, and when it is set in accordance with the rolling method, it is generally shaped according to the inlet shape of the rolling device. Is determined.
The average thickness of the laminated preform is not particularly limited and may be appropriately selected depending on the purpose. If a known example is shown, the preform may be set in accordance with an extrusion method. The average thickness of the preform is, for example, 5 cm to 10 cm, and the average thickness of the preform in the case of being set in accordance with the rolling method is, for example, 0.5 cm to 5 cm.

The outer dimension of the laminated preform is not particularly limited and can be appropriately selected according to the purpose, and is set in accordance with an extrusion method or a rolling method described later. When designing a square, 50 mm square to 150 mm square is preferable.
If the outer dimension of the laminated preform is too small, there will be a problem in the dimensional accuracy of the layer structure, and if it is too large, positional unevenness will occur in the pressure applied to the material due to the wall resistance at the time of preforming. is there. When designing the cross section of the laminated preform to be rectangular, as in the case of designing to a square, if the outer dimension is too small, there will be a problem in the dimensional accuracy of the layer structure, and if it is too large, Positional unevenness may occur in the pressure applied to the material due to wall resistance.

The crystalline polymers used for the first crystalline polymer sheet layer and the second crystalline polymer sheet layer may be the same or different.
The crystalline polymer is not particularly limited and may be appropriately selected depending on the intended purpose.However, the crystalline polymer is regularly aligned with a crystalline region in which long chain molecules are regularly aligned in the molecular structure. A polymer in which non-crystalline regions are mixed is preferable. Such polymers exhibit crystallinity by physical treatment. For example, when a polyethylene film is stretched by an external force, a phenomenon occurs in which a transparent film becomes cloudy at first. The above phenomenon originates from the fact that the molecular arrangement in the polymer is aligned in one direction by an external force, and crystallinity is developed.

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 crystal polymer, and the like. Polypropylene, polytetrafluoroethylene, polytetrafluoroethylene copolymer, nylon, polyacetal, polybutylene terephthalate, polyethylene terephthalate, syndiotactic polystyrene, polyphenylene sulfide, polyether ether ketone, wholly aromatic polyamide, wholly aromatic polyester, A fluororesin, polyether nitrile, etc. are mentioned. These may be used individually by 1 type and may use 2 or more types together.
Among these, polytetrafluoroethylene and polytetrafluoroethylene co-polymers are easy to obtain powdery products having high crystallinity, have high solvent resistance and heat resistance, and can be suitably used for various applications. Polymers are preferred.

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.
The polytetrafluoroethylene copolymer is not particularly limited and may be appropriately selected depending on the intended purpose. For example, the polytetrafluoroethylene copolymer is selected from tetrafluoroethylene, perfluoroalkyl vinyl ether, hexafluoropropylene, and chlorotrifluoroethylene. A copolymer containing at least two types is exemplified.

There is no restriction | limiting in particular as melting | fusing point of the said crystalline polymer, Although it can select suitably according to the objective, Melting | fusing point of the said 1st crystalline polymer is 1 rather than melting | fusing point of the said 2nd crystalline polymer. It is preferably higher by at least ° C, more preferably by at least 3 ° C.
If the melting point of the first crystalline polymer is lower than the melting point of the second crystalline polymer, a sufficient flow rate cannot be obtained, and the filtration efficiency may be significantly reduced.
The melting point indicates the peak position of the DSC chart obtained by measuring with a differential scanning calorimeter, and when it has two peaks, or when it has one peak and one shoulder, The higher peak intensity is defined as the melting point.

There is no restriction | limiting in particular as temperature of the endothermic peak position in the DSC chart applicable to melting | fusing point of said 1st crystalline polymer, Although it can select suitably according to the objective, 343 to 350 degreeC is preferable.
The temperature of the endothermic peak position in the DSC chart corresponding to the melting point of the second crystalline polymer is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 320 ° C to 338 ° C.

There is no restriction | limiting in particular as a form of the said crystalline polymer, According to the objective, it can select suitably, For example, a powder form, a particulate form, etc. are mentioned.
There is no restriction | limiting in particular as an average particle diameter at the time of setting it as the powder form of the said crystalline polymer, and a particulate form, Although it can select suitably according to the objective, 0.2 micrometer-0.4 micrometer are 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 and 10,000-10,000,000 are More preferred. The weight average molecular weight can be measured, for example, by gel permeation chromatography (GPC).

The number average molecular weight of the 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. . The number average molecular weight can be measured by, for example, gel permeation chromatography (GPC). However, since PTFE is insoluble in a solvent, the crystallization heat [ΔHc: cal / g] by DSC measurement is used. It is preferable to perform measurement and calculate using the relational expression: Mn = 2.1 × 10 ¹⁰ × ΔHc ^−5.16 .

There is no restriction | limiting in particular as said crystalline polymer, What was synthesize | combined suitably may be used and a commercial item may be used.
Examples of the commercially available products include polytetrafluoroethylene (manufactured by Daikin Industries, Ltd., trade names “Polyflon PTFE”, product names “F-104”, “F-106”, “F-201”, “F-205”). ”,“ F-208 ”,“ F-301 ”,“ F-302 ”, trade names“ Lublon ”, product numbers“ L-2 ”,“ L-5 ”), polytetrafluoroethylene (Asahi Glass Co., Ltd.) , Product name “Fluon (registered trademark) PTFE”, product type “CD1”, “CD141”, “CD145”, “CD123”, “CD076”, “CD090”, “CD126”), polytetrafluoroethylene (Mitsui DuPont) Fluorochemical Co., Ltd., trade name “Teflon (registered trademark) PTFE”, brand names “6-J”, “6C-J”, “62XT”, “640-J”) The
Among these, polytetrafluoroethylene (manufactured by Daikin Industries, trade name “Polyflon PTFE”, product name “F-106”) is preferable in that it is easy to obtain a molded product having a relatively low molding pressure and excellent strength. In terms of pore diameter refinement after stretching, polytetrafluoroethylene (manufactured by Daikin Industries, Ltd., trade name “Polyflon PTFE”, product name “F-205”, product name “Lebron”, product name “L-5”. ) Is preferred.

  There is no restriction | limiting in particular as said other component, According to the objective, it can select suitably, For example, liquid lubricants, such as solvent naphtha and white oil which are extrusion adjuvants, are mentioned. There is no restriction | limiting in particular as a commercial item of the said extrusion adjuvant, According to the objective, it can select suitably, For example, hydrocarbon oil (The Esso Petroleum Corporation make, brand name "Isopar") etc. are mentioned. There is no restriction | limiting in particular as addition amount of the said extrudate agent, Although it can select suitably according to the objective, It is preferable to add 15-30 mass parts with respect to 100 mass parts of said crystalline polymers. .

As a method of extruding the laminated preform, as shown in FIG. 5, a pair of lengthwise end faces facing each other in the second crystalline polymer sheet layer 4 is the first crystalline polymer. If it is the method of extruding the said lamination | stacking preforming body 10 coat | covered with the sheet layer 5 in a length direction, there will be no restriction | limiting in particular, According to the objective, it can select suitably, For example, as shown in FIG. The method of extruding the said lamination | stacking preformed object using an extrusion die is mentioned. In addition, the said length direction is coat | covered with the said 1st crystalline polymer sheet layer, and says the extrusion direction of the said laminated preform.
The temperature at which the laminated preform is extruded is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 19 ° C to 200 ° C.

There is no restriction | limiting in particular as a method of rolling the said lamination | stacking preformed body, According to the objective, it can select suitably, For example, the method of calendaring by the speed | rate of 5 m / min with a calender roll is mentioned.
There is no restriction | limiting in particular as temperature which rolls the said laminated preform, Although it can select suitably according to the objective, It can set to 19 to 380 degreeC.

  There is no restriction | limiting in particular as a method of forming the said laminated body, According to the objective, it can select suitably, For example, it describes in "Polyfuron handbook" (Daikin Kogyo Co., Ltd. issue, 1983 revision). The laminate can be formed by appropriately adopting the matters.

  The structure of the laminate is not particularly limited and may be appropriately selected depending on the purpose. For example, at least one layer in the laminate has an average pore diameter in at least a part in the thickness direction of the laminate. A laminated structure having a plurality of holes that are constant may be mentioned.

  A method for confirming that the laminate has a laminated structure is not particularly limited and may be appropriately selected depending on the purpose. For example, a cut surface obtained by freezing and cutting the laminate in the thickness direction is optical. It can be performed by observing with a microscope or a scanning electron microscope (SEM) and confirming whether or not there is a boundary between the first crystalline polymer sheet layer and the second crystalline polymer sheet layer.

  The thickness of the laminate is not particularly limited and can be appropriately selected depending on the purpose. For example, it can be appropriately adjusted according to the thickness of the crystalline polymer microporous film to be finally produced. The thickness can be adjusted in consideration of a decrease in thickness due to a subsequent stretching step.

<Symmetric heating process>
The said heating process is a process of symmetrically heating the obtained laminated body.
By performing the symmetric heating, a microporous membrane having a fine structure including short fibrils having an average major axis length of 1 μm or less is obtained, the pore diameter of the microporous membrane is reduced, and smaller fine particles are efficiently captured. A crystalline polymer microporous membrane that can be obtained is obtained.

  The structure of the laminate obtained by the symmetrical heating is not particularly limited and may be appropriately selected depending on the intended purpose. At least the second crystalline polymer sheet layer has an average major axis length of 1 μm. The microstructure preferably contains at least the following fibrils.

  The fibrils of the laminate obtained by symmetrical heating are fibers that are spun between particles or into particles when mechanical force is applied between two fused crystalline polymer particles. The average long axis length of the fibrils is preferably 1 μm or less, and more preferably 0.5 μm or less. If the average major axis length exceeds 1 μm, dust in the liquid such as fine particles may not be sufficiently captured.

  The nodules (nodes) of the laminate obtained by the symmetrical heating are clusters of primary particles of a crystalline polymer, and the average minor axis length (average diameter) of the nodules is the average minor axis of the fibrils. If it is longer than the length (average diameter), there is no particular limitation and it can be appropriately selected according to the purpose. However, the average diameter of the nodules is preferably 0.1 μm or more, 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 method of symmetric heating is not particularly limited as long as the laminate can be uniformly and uniformly heated, and can be appropriately selected according to the purpose. For example, heating with a salt bath, a hot air heater, a furnace, a roll, an IR, or the like. The method of doing is mentioned. Among these, the method of heating with a salt bath is preferable in that variation in heating when heating the entire laminate can be suppressed.

The temperature at the time of the symmetrical heating is not particularly limited and can be appropriately selected depending on the purpose. The DSC chart obtained by measuring the second crystalline polymer with a differential scanning calorimeter In the case of having a shoulder on one peak and the high temperature side or low temperature side of the peak and having a peak on the low temperature side and a high temperature side shoulder on the high temperature side of the peak, the symmetrical heating of the laminate is performed at a low temperature. It is preferable to carry out at a temperature higher than the peak temperature on the side, and when the peak is on the high temperature side and the low temperature side shoulder is on the low temperature side of the peak, the symmetrical heating of the laminate is higher than the temperature of the low temperature side shoulder. It is preferable to carry out at temperature.
Moreover, it is preferable to carry out symmetrical heating at the temperature below the said melting | fusing point of a said 1st crystalline polymer at the point of high flow volume.
When the symmetrical heating is performed at a temperature deviating from a preferable temperature, the pore diameter may not be sufficiently reduced, and the fine particle capturing property may be lowered.

Here, the laminated body used at the time of symmetrical heating and the temperature at the time of symmetrical heating will be described with reference to FIGS.
The laminate for the symmetrical heating is not particularly limited and can be appropriately selected according to the purpose. In the DSC chart obtained by measuring with a differential scanning calorimeter, as shown in FIG. The second crystalline polymer having the peak T ₂ on the low temperature side and the high temperature side shoulder T ₁ on the high temperature side of the peak, or the peak T ₃ on the high temperature side and the low temperature side of the peak as shown in FIG. cold side shoulder portion second obtained by using the crystalline polymer laminate having of T ₄ is preferred.
As the temperature in the symmetrical heating is not particularly limited and may be appropriately selected depending on the purpose, for example, a temperature higher than the peak T ₂ in FIG. 11, a temperature higher than the low temperature-side shoulder portion T ₄ in FIG. 12 In this way, a crystalline polymer microporous film having a multi-layer structure composed of short fibrils and nodes is obtained. As shown in FIG. 13, when the second crystalline polymer has two peaks, a low temperature side peak T ₅ and a high temperature side peak T ₆ , the laminated body is subjected to symmetrical heating. it is preferably performed at a temperature higher than the low temperature side peak temperature T _5.

<Extension process>
The said extending process is a process of extending the laminated body obtained by the said rolling process. By stretching the laminate obtained by the rolling step, a crystalline polymer microporous membrane having a high trapping property and a high flow rate can be produced by making the laminate no-node and finer fibrils.

  There is no restriction | limiting in particular as the said extending | stretching method, Although it can select suitably according to the objective, The method of extending | stretching about both a longitudinal direction and the width direction is preferable, and performing each extending | stretching sequentially about a longitudinal direction and the width direction, respectively. In such a case, a method in which stretching in the longitudinal direction is performed first and then stretching in the width direction is more preferable. The stretching may be performed sequentially in the longitudinal direction and the width direction, or may be performed biaxially at the same time.

The stretching ratio in the longitudinal direction in the stretching step is not particularly limited and may be appropriately selected depending on the purpose, but is preferably 1.2 times to 50 times, more preferably 1.5 times to 40 times, 2 to 10 times is particularly preferable.
There is no restriction | limiting in particular as the extending | stretching temperature of the longitudinal direction in the said extending process, Although it can select suitably according to the objective, 35 to 330 degreeC is preferable, 45 to 320 degreeC is more preferable, 55 to 310 degreeC. ° C is particularly preferred.

There is no restriction | limiting in particular as the draw ratio of the width direction in the said extending process, Although it can select suitably according to the objective, 1.2 times-50 times are preferable, 1.5 times-40 times are more preferable, 2.0 times to 10 times is particularly preferable.
There is no restriction | limiting in particular as the extending | stretching temperature of the width direction in the said extending process, Although it can select suitably according to the objective, 35 to 330 degreeC is preferable, 45 to 320 degreeC is more preferable, 60 to 310 degreeC. ° C is particularly preferred.

  The area stretching ratio in the stretching step is not particularly limited and can be appropriately selected according to the purpose, but is preferably 1.5 to 2,500 times, more preferably 2 to 2,000 times, 2.5 to 100 times is particularly preferable. When the stretching is performed, the sheet made of the crystalline polymer may be preheated to a temperature equal to or lower than the stretching temperature in advance. In addition, after the said extending | stretching, heat setting can be performed as needed. The temperature for heat setting is not particularly limited and may be appropriately selected depending on the intended purpose. However, it is preferably performed at a temperature equal to or higher than the stretching temperature and lower than the melting point of the crystalline polymer. The crystalline polymer is a fluorine such as PTFE. In the case of a resin, it is preferably carried out at a melting point or higher.

<Other processes>
There is no restriction | limiting in particular as said other process, According to the objective, it can select suitably, For example, an extrusion adjuvant removal process, a surface modification process, etc. are mentioned.

-Extrusion aid removal process-
The extrusion auxiliary agent removing step is a step of removing the extrusion auxiliary agent by heating the sheet made of the crystalline polymer obtained by the rolling step.
There is no restriction | limiting in particular as heating temperature in the said extrusion adjuvant removal process, Although it can select suitably according to the kind of extrusion adjuvant to be used, 40 to 400 degreeC is preferable and 60 to 350 degreeC is more preferable. In the case where polytetrafluoroethylene is used as the crystalline polymer and solvent naphtha is used as the extrusion aid, the heating temperature in the extrusion aid removal step is preferably 150 ° C. to 280 ° C., preferably 180 ° C. to 260 ° C. More preferred.
Examples of the heating method in the extruding auxiliary agent removing step include a method of heating the sheet made of the crystalline polymer by passing it through a hot air drying furnace. The thickness of the sheet made of the crystalline polymer thus produced can be appropriately adjusted according to the thickness of the crystalline polymer microporous film to be finally produced, It is necessary to adjust in consideration of the decrease.

-Surface modification process-
The surface modification step is a step of surface modifying at least a part of the crystalline polymer microporous film obtained by the stretching step. In addition to the exposed surface of the crystalline polymer microporous membrane, at least a part of the crystalline polymer microporous membrane includes the periphery of the pore and the inside of the pore.
The method for modifying the surface is not particularly limited and may be appropriately selected depending on the intended purpose. For example, the surface modification may be performed by irradiating with a laser after impregnation with an aqueous solution of hydrogen peroxide or an aqueous solvent. (Refer to Japanese Patent Laid-Open No. 7-304888), a method for surface modification by irradiation with radiation and plasma (see Japanese Patent Laid-Open No. 2003-151571), a method for surface modification by chemical etching treatment (special No. 2007-154153), a method of surface modification by coating with a crosslinking material (see JP-A-8-283447), and a method of surface modification by coating with a polymerization material (JP-A 2000). -235849 gazette).

  Here, with reference to FIGS. 1-5, an example of the manufacturing method of the crystalline polymer microporous film | membrane of this invention is demonstrated. As described above, a laminated preform 10 including the first crystalline polymer sheet layer 4 and the second crystalline polymer sheet layer 5 as shown in FIG. 4 is produced by the method shown in FIGS. Is done. Next, after the obtained laminated preform 10 is stored in the cylinder portion of the extrusion device 9 shown in FIG. 5, it is pressed in the direction of the arrow by a pressurizing means (not shown). The cylinder part of the extrusion device 9 shown in FIG. 5 has, for example, a 50 mm × 100 mm rectangular cross section in the direction perpendicular to the axis, and is composed of a nozzle 50 mm × 5 mm in which one of the cylinder parts is narrowed at the outlet part. In this way, the first crystalline polymer sheet layer 4 and the second crystalline polymer sheet layer 5 are completely integrated, and a laminate (unheated film laminate) 15 in which each layer has a uniform thickness is obtained. Molded. The laminated polymer is heated symmetrically and then stretched to produce the crystalline polymer microporous membrane of the present invention.

  The method for producing a crystalline polymer microporous membrane of the present invention includes a step of covering a pair of opposing end faces in the length direction of the second crystalline polymer sheet with the first crystalline polymer sheet. Therefore, it is possible to prevent the entire film from being broken due to cracks and breaks generated from the end face, and a conventional crystalline polymer that cannot be formed alone (second crystalline polymer having a low melting point). It is a technique that makes it possible to form a film by using and to freely design the performance. In particular, the second crystalline polymer is a material having a peak on a relatively low temperature side, and such a material has a tendency to have a low melt viscosity and a small particle size at the same time. It can be suitably used as a material having a minute pore size.

(Crystalline polymer microporous membrane)
The crystalline polymer microporous membrane of the present invention is a microporous membrane produced by the method for producing a crystalline polymer microporous membrane.

  The structure of the crystalline polymer microporous film is not particularly limited as long as it is a laminated structure of the first crystalline polymer sheet layer and the second crystalline polymer sheet layer. Although it can be selected, it is preferable to have a laminated structure in which the thicknesses of the two first crystalline polymer sheet layers covering both surfaces of the second crystalline polymer sheet layer are different from each other. By adopting the laminated structure, it is possible to increase the thickness of the first crystalline polymer sheet layer having a large pore size on the primary side in filtration without changing the thickness of the microporous membrane, and thus having a small pore size. This is advantageous in that clogging of the second crystalline polymer sheet layer can be efficiently suppressed.

  The method for confirming that the crystalline polymer microporous membrane has a laminated structure is not particularly limited and can be appropriately selected depending on the purpose. For example, the crystalline polymer microporous membrane is arranged in the thickness direction. There is a method of detecting a section cut by freezing by observing it with an optical microscope or a scanning electron microscope (SEM).

The shape of the pores of the crystalline polymer microporous membrane is not particularly limited and may be appropriately selected depending on the purpose.For example, the crystalline polymer microporous membrane penetrates in the thickness direction of the crystalline polymer microporous membrane, Examples include a shape in which 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 of the crystalline polymer microporous membrane in the thickness direction. By adopting the shape of the hole, fine particles can be captured efficiently.
Here, at least one layer in the crystalline polymer microporous membrane is 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. 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 holes is taken on the vertical axis, (1 ) A graph from the front surface (t = 0) to the back surface (t = film 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). The substantially 0 (zero) includes about ± 10% from the average value and does not include monotonic increase and monotonic decrease.

  There is no restriction | limiting in particular as a method of confirming the shape of the hole part of the said crystalline polymer microporous film | membrane, According to the objective, it can select suitably, For example, observation with an optical microscope or a scanning electron microscope (SEM) The method of confirming the shape of a hole part by doing is mentioned.

The average pore diameter of the pores of the crystalline polymer microporous membrane is not particularly limited and can be appropriately selected depending on the purpose. For example, the average pore diameter of the pores in the first crystalline polymer sheet layer And the average pore diameter of the pores in the second crystalline polymer sheet layer have different average pore diameters.
There is no restriction | limiting in particular as an average hole diameter in the 1st crystalline polymer sheet layer of the said crystalline polymer microporous film | membrane, Although it can select suitably according to the objective, 1 micrometer or less is preferable. 5 μm or less is more preferable.
There is no restriction | limiting in particular as an average hole diameter of the hole part in the 2nd crystalline polymer sheet layer of the said crystalline polymer microporous film | membrane, Although it can select suitably according to the objective, 1 nm-200 nm are preferable, and 5 nm -150 nm is more preferable, and 10 nm to 100 nm is particularly preferable.

  The method for measuring the average pore diameter of the pores in the crystalline polymer microporous membrane is not particularly limited and can be appropriately selected according to the purpose. For example, the surface of the membrane or the cross section of the membrane can be selected with a scanning electron microscope. (SEM photograph, magnification: 1,000 to 100,000 times) and the resulting photograph is an image processing device (main body: Nippon Avionics Co., Ltd., trade name “TV Image Processor TVIP-4100II”, control software : Ratok System Engineering Co., Ltd., trade name “TV Image Processor Image Command 4198”) to obtain an image consisting only of crystalline polymer fibers, and processing the image to calculate the average pore diameter. It is done.

The average flow pore size in the crystalline polymer microporous membrane refers to the pore size determined from the intersection of 1/2 in the dry state and the air flow rate in the wet state.
The average flow pore size of the pores in the first crystalline polymer sheet layer 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 or less, 0 More preferably, it is 5 μm or less.
The average flow pore size of the pores in the second crystalline polymer sheet layer of the crystalline polymer microporous membrane is not particularly limited and can be appropriately selected according to the purpose, but is preferably 1 nm to 200 nm, 5 nm to 150 nm is more preferable, and 10 nm to 100 nm is particularly preferable.

  There is no restriction | limiting in particular as a method of measuring the average flow volume diameter of the hole part of the said crystalline polymer microporous film | membrane, According to the objective, it can select suitably, For example, by a half dry method (ASTM E1294-89) The method of measuring is mentioned. Specifically, when the average flow pore diameter exceeds 15 nm, it can be measured with a 500 psi high-pressure palm porometer (manufactured by PMI). When the average flow pore diameter is 15 nm or less, the nano palm porometer (Manufactured by PMI).

There is no restriction | limiting in particular as thickness of the said crystalline polymer microporous film | membrane, Although it can select suitably according to the objective, 1 micrometer-300 micrometers are preferable, 5 micrometers-200 micrometers are more preferable, 10 micrometers-100 micrometers are especially preferable.
When the thickness is in a particularly preferred range, the thickness of the microporous membrane can be reduced, which is advantageous in terms of flow rate. The method for measuring the thickness is not particularly limited and may be appropriately selected depending on the intended purpose. For example, the crystalline polymer microporous membrane is frozen and cleaved, and each layer is measured by a scanning electron microscope (SEM). By observing the cross section, the thickness of each layer can be measured.

There is no restriction | limiting in particular as thickness of the 1st crystalline polymer sheet layer in the said crystalline polymer microporous film | membrane, Although it can select suitably according to the objective, 2 micrometers-100 micrometers are preferable, and 5 micrometers-80 micrometers are more. 10 μm to 60 μm is particularly preferable.
If the thickness is less than 2 μm, the crystalline polymer sheet layer having a low melting point may be affected by friction and scratching, and may not be able to maintain stable fine particle capturing properties. If the thickness exceeds 100 μm, a sufficient flow rate can be obtained. It may not be possible. On the other hand, when the thickness is within the particularly preferable range, it is advantageous in terms of fine particle capturing ability and flow rate.

The thickness of the second crystalline polymer sheet layer in the crystalline polymer microporous membrane is not particularly limited and may be appropriately selected depending on the intended purpose, but is preferably 0.1 μm to 50 μm, preferably 0.1 μm -25 μm is more preferable, and 0.5 μm to 20 μm is particularly preferable.
When the thickness is less than 0.1 μm, the production of a uniform microporous membrane and the hole diameter of the hole portion cannot be reduced, and the in-plane uniformity of the hole diameter may be lost, and when the thickness exceeds 50 μm. , High flow rate may not be achieved. On the other hand, when the thickness is within the particularly preferable range, it is advantageous in terms of in-plane uniformity of pore diameter and flow rate.

When the maximum thickness of the first crystalline polymer sheet layer in the crystalline polymer microporous membrane is thicker than the maximum thickness of the second crystalline polymer sheet layer, the flow rate characteristic in the crystalline polymer microporous membrane is Although improved, the particulate capture rate decreases.
When the thickness of the second crystalline polymer sheet layer in the crystalline polymer microporous film is thicker than the maximum thickness of the first crystalline polymer sheet layer, the flow rate characteristic in the crystalline polymer microporous film is lowered. However, the fine particle capture rate is improved.

  Here, an example of the crystalline polymer microporous membrane of the present invention will be described with reference to FIG. As shown in FIG. 6, the crystalline polymer of the present invention having a three-layer structure in which a first crystalline polymer sheet layer 101, a second crystalline polymer sheet layer 102, and a first crystalline polymer sheet layer 103 are laminated. The average pore diameters of the pores 101b, 102b, and 103b in the microporous membrane are all constant without changing in the thickness direction of the laminate, and the average pore diameter of the entire crystalline polymer microporous membrane is stepwise in the thickness direction. There is a part that changes. The second crystalline polymer sheet layer 102 having the smallest maximum average pore diameter Lm2 among the maximum average pore diameters Lm1, Lm2, and Lm3 of the pores is present inside the crystalline polymer microporous film (laminate). is doing.

  The crystalline polymer microporous membrane of the present invention is excellent in structural stability, has a fine pore size, can efficiently capture fine particles having a size of several tens of nanometers, and has a high flow rate. It can be used for various applications, and can be particularly suitably used as a filter for filtration described below.

(Filter for filtration and filtration device)
The filtering filter of the present invention uses the crystalline polymer microporous membrane.
The filtration apparatus of this invention has an inlet, an outlet, and the said filter for filtration, and arrange | positions the 2nd crystalline polymer sheet in the said filter for filtration in the vicinity of the said outlet.
Since the filtration filter uses a crystalline polymer microporous membrane produced by stretching a sheet made of a crystalline polymer having flexibility at a high magnification, it has high pleat resistance. And since the specific surface area of the said crystalline polymer microporous film | membrane is large, the fine particle introduce | transduced from the surface is removed by adsorb | sucking or adhering before reaching | attaining a minimum pore diameter part. Therefore, clogging is unlikely to occur and high filtration efficiency can be maintained over a long period of time.

  The filter for filtration is not particularly limited and may be appropriately selected depending on the purpose. However, the second crystalline polymer sheet layer in the crystalline polymer microporous membrane is disposed on the outlet side of the filtrate (outlet). It is preferable that the fine particles having a size of several tens of nm can be efficiently captured and the filtration efficiency can be improved.

  There is no restriction | limiting in particular as a shape of the said filter for filtration, Although it can select suitably according to the objective, It is preferable to process and shape in a pleat shape. When the shape of the filter for filtration is the pleated shape, it is advantageous in that the effective surface area used for filtering the filter per cartridge can be increased.

Here, with reference to FIGS. 8-10, an example of the filter for filtration which can be used conveniently for the filtration apparatus of this invention is demonstrated.
8 to 10 are specific examples of the microfiltration filter cartridge, and the present invention is not limited to these drawings.

  FIG. 8 is a development view showing the structure of an element exchange type pleated filter cartridge element. The microfiltration membrane 113 is folded in a state of being sandwiched by two membrane supports 112 and 114, and is wound around a core 115 having a large number of liquid collection ports. 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.

  FIG. 9 is a development view of 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 by a primary support 21 and a secondary support 23 which are two supports. 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. 9 shows an example in which the lower end plate 25 and the housing base are sealed through the O-ring 28. The lower end plate 25 and the housing base are sealed by heat fusion or an adhesive. Sometimes. Alternatively, the seal between the housing base and the housing cover can be made by using an adhesive in addition to heat sealing.

  FIG. 10 is a view showing 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 32 and a housing cover 31. The lower end plate is sealed by a water collecting pipe (not shown) at the center of the housing base 32 through an O-ring. The liquid enters the housing from the liquid inlet nozzle 33, passes through the filter medium 29, is collected from the liquid collection port of the filter element core, and is discharged from the liquid outlet nozzle 34. The housing base 32 and the housing cover 31 are usually heat-sealed in a liquid-tight manner at the welding portion 37.

  Since the filter for filtration using the crystalline polymer microporous membrane of the present invention has such a characteristic that the filtration function is high and the life is long, it can be compactly assembled in the filtration device of the present invention. . 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
<Production of crystalline polymer microporous membrane>
-Laminate formation process-
Polytetrafluoroethylene fine powder as a first crystalline polymer (trade name “Polyflon F-106”, manufactured by Daikin Industries, Ltd.) 100 parts by mass, and hydrocarbon oil (Esso Oil Co., Ltd., product) as an extrusion aid 23 parts by weight of "Isopar H") was added. This was designated as paste 1.
As a second crystalline polymer, polytetrafluoroethylene fine powder (manufactured by Daikin Industries, Ltd., trade name “Lublon L-5”) 100 parts by mass, as an extrusion aid, hydrocarbon oil (manufactured by Esso Oil Co., Ltd., 23 parts by mass of “Isopar H” (trade name) was added. This was designated as paste 2.

As shown in FIG. 1, a portion having a width of 2 mm from a wall surface of a mold used for producing a laminated preform is divided vertically by a metal plate having a thickness of 0.3 mm, and a paste 1 is placed on the outer side 1 shown in FIG. Only the inner side 2 shown in FIG. 1 was laminated and spread so that the thickness ratio of the paste layer was (Paste 1) / (Paste 2) / (Paste 1) = 3/1/1.
And after extracting a metal plate, it pressurizes on the conditions of 0.5 Mpa, both surfaces of the 2nd crystalline polymer sheet layer are coat | covered with the 1st crystalline polymer sheet layer, and said 2nd crystalline property A rectangular laminated preform in which a pair of end faces facing each other in the polymer sheet layer were coated with the first crystalline polymer sheet layer was produced.
Next, it was inserted into a square cylinder of a paste extrusion mold in a direction substantially orthogonal to the pair of end faces in the laminated preform, and multilayer paste extrusion was performed in a sheet form.
This was calendered with a calender roll heated to 60 ° C. and rolled, and then passed through a hot air drying furnace at 250 ° C. to remove the extrusion aid, thereby producing a laminate having an average thickness of 100 μm and an average width of 150 mm.

-Symmetric heating process-
The laminate obtained by the laminate formation step was heated for 50 seconds with a salt bath kept at 341 ° C. to symmetrically heat the laminate.

-Stretching process-
The laminate obtained by the symmetrical heating process was stretched between rolls in the longitudinal direction at 300 ° C. in the longitudinal direction, wound once on a take-up roll, then sandwiched between both ends by clips, and 3 ° in the width direction at 300 ° C. Stretched twice. Thereafter, heat setting was performed at 320 ° C., and the crystalline polymer microporous membrane of Example 1 was produced.

(Example 2)
<Production of crystalline polymer microporous membrane>
In the [laminated body forming step] of Example 1, lamination is performed so that the thickness ratio of the paste layer on the inner side 2 shown in FIG. 1 is (Paste 1) / (Paste 2) / (Paste 1) = 8/1/1. In the same manner as in Example 1 except that a rectangular laminated preform having the first crystalline polymer sheet layer and the second crystalline polymer sheet layer was produced, an average thickness of 100 μm and an average A laminate having a width of 150 mm was formed, and the crystalline polymer microporous membrane of Example 2 was produced.

(Example 3)
<Production of crystalline polymer microporous membrane>
In the [laminated body forming step] of Example 1, as a second crystalline polymer, 100 parts by mass of a fine powder of polytetrafluoroethylene (manufactured by Daikin Industries, Ltd., “Polyflon F-205”) is used as an extrusion aid. 23 parts by mass of hydrocarbon oil (Esso Petroleum Co., Ltd., “Isopar H”) is added to form paste 3, and the thickness ratio of the paste layer on the inner side 2 shown in FIG. 1 is (paste 1) / (paste 3) / ( Paste 1) Except that it was laminated so as to be 2/2/1, and a rectangular laminated preform having a first crystalline polymer sheet layer and a second crystalline polymer sheet layer was produced. In the same manner as in Example 1, a laminate having an average thickness of 80 μm and an average width of 150 mm was formed, and the crystalline polymer microporous film of Example 3 was produced.

Example 4
<Production of crystalline polymer microporous membrane>
In the [Laminate Forming Step] of Example 3, lamination is performed so that the thickness ratio of the paste layer on the inner side 2 shown in FIG. 1 is (Paste 1) / (Paste 3) / (Paste 1) = 2/5/1. In the same manner as in Example 3 except that a rectangular laminated preform having the first crystalline polymer sheet layer and the second crystalline polymer sheet layer was produced, an average thickness of 80 μm and an average A laminate having a width of 150 mm was formed, and the crystalline polymer microporous membrane of Example 4 was produced.

(Example 5)
<Production of crystalline polymer microporous membrane>
A crystalline polymer of Example 5 was formed in the same manner as in Example 1 except that the salt bath temperature in Example 1 [Symmetric heating step] was 335 ° C., and a laminate having an average thickness of 100 μm and an average width of 150 mm was formed. A microporous membrane was produced.

(Comparative Example 1)
<Production of crystalline polymer microporous membrane>
In the [laminated body forming step] of Example 1, the thickness ratio of the paste layer on the inner side 2 shown in FIG. 1 is (paste 1) / (paste 2) without providing only the portion of the paste 1 on the outer side 1 shown in FIG. ) / (Paste 1) = 3/1/1 is used, and a rectangular laminated preform having a first crystalline polymer sheet layer and a second crystalline polymer sheet layer is used. An attempt was made to form a laminate, but when calendering, a film break 16 as shown in FIG. 7 occurred from the end, and a crystalline polymer microporous film could not be produced.

(Comparative Example 2)
<Production of crystalline polymer microporous membrane>
In the [laminated body forming step] of Example 1, the thickness ratio of the paste layer of the inner side 2 shown in FIG. 1 is (paste 1) / (paste 2) without providing only the portion of the paste 1 on the outer side 1 shown in FIG. ) / (Paste 1) = 8/1/1 Using a rectangular laminated preform having a first crystalline polymer sheet layer and a second crystalline polymer sheet layer Attempts were made to form a laminate, but as in Comparative Example 1, when the calendering was performed, a film break 16 as shown in FIG. 7 occurred from the end, and a crystalline polymer microporous film was produced. I could not.

(Comparative Example 3)
<Production of crystalline polymer microporous membrane>
In the [laminated body forming step] of Example 3, the thickness ratio of the paste layer on the inner side 2 shown in FIG. 1 is (paste 1) / (paste 3) without providing only the paste 1 on the outer side 1 shown in FIG. ) / (Paste 1) = 2/2/1, and a rectangular laminated preform having a first crystalline polymer sheet layer and a second crystalline polymer sheet layer is used. Although the formation of a laminate was attempted, as in Comparative Example 1, when calendering, the film was broken from the end as shown in FIG. 7 to produce a crystalline polymer microporous film. could not.

(Comparative Example 4)
<Production of crystalline polymer microporous membrane>
In the [Laminate Forming Step] of Example 4, the thickness ratio of the paste layer on the inner side 2 shown in FIG. 1 is (paste 1) / (paste 3) without providing only the paste 1 on the outer side 1 shown in FIG. ) / (Paste 1) = 2/5/1, and a rectangular laminated preform having a first crystalline polymer sheet layer and a second crystalline polymer sheet layer is used. Although the formation of a laminate was attempted, as in Comparative Example 1, when calendering, the film was broken from the end as shown in FIG. 7 to produce a crystalline polymer microporous film. could not.

(Comparative Example 5)
<Production of crystalline polymer microporous membrane>
In the [Laminate Forming Step] of Example 1, a rectangular preform was produced using only the paste 2. However, since the preform was very brittle, the extruded sheet could easily collapse and be calendered. It was not possible to produce a crystalline polymer microporous membrane.

(Comparative Example 6)
<Production of crystalline polymer microporous membrane>
In the [Laminate Forming Step] of Example 1, a rectangular preform was produced using only the paste 3, but the membrane was broken from the end during calendering to produce a crystalline polymer microporous membrane. I couldn't.

(Comparative Example 7)
<Production of crystalline polymer microporous membrane>
A single-layer body having an average thickness of 100 μm and an average width of 150 mm was formed in the same manner as in Example 1 except that a rectangular preform was produced using only the paste 1 in [Laminate Forming Step] of Example 1. A crystalline polymer microporous membrane of Comparative Example 7 was produced.

(Comparative Example 8)
<Production of crystalline polymer microporous membrane>
A single layer body having an average thickness of 80 μm and an average width of 150 mm was formed in the same manner as in Example 1 except that a rectangular preform was produced only with paste 1 in the [laminated body forming step] of Example 3. A crystalline polymer microporous membrane of Comparative Example 8 was produced.

(Comparative Example 9)
<Production of crystalline polymer microporous membrane>
In place of [Symmetric heating step] in Example 1, the side closer to the outside on the metal roll heated to 345 ° C. was brought into contact with the side close to the outside for 10 seconds, in the same manner as in Example 1, with an average thickness of 100 μm, A laminate having an average width of 150 mm was formed, and a crystalline polymer microporous membrane of Comparative Example 9 was produced.

(Evaluation)
<Measurement of DSC chart>
A differential scanning calorimeter (manufactured by Seiko Instruments Inc., DSC7200) was used to measure at a heating rate of 10 ° C./min, and the peak position on the chart was specified from the differential curve of the DSC chart. The peak positions on the high temperature side and low temperature side of each crystalline polymer used in Examples 1 to 7 and Comparative Examples 1 to 9 were specified. The results are shown in Table 1.

<Measurement of average thickness of crystalline polymer microporous membrane>
The crystalline polymer microporous membranes of Examples 1 to 5 and Comparative Examples 7 to 9 were frozen and cleaved, and a cross section was obtained using a scanning electron microscope (SEM) (manufactured by JEOL, product name “JSM-6360”). The average thickness was observed. The results are shown in Table 1.

<Measurement of fiber length of second crystalline polymer layer>
Observe the second crystalline polymer sheet layer in the crystalline polymer microporous membrane of Examples 1 to 4 and the first crystalline polymer sheet layer in the crystalline polymer microporous membrane of Comparative Examples 7 and 8. The fiber length was measured at 10 points from the image, and the values were averaged to obtain the fiber length. However, when the average value was less than 0.5 μm, “<0.5” was set. The results are shown in Table 1.

<Measurement of average flow pore size>
About the crystalline polymer microporous film | membrane of Examples 1-5 and Comparative Examples 7-9, the average flow volume diameter was measured using the palm porometer (made by PMI). The results are shown in Table 1.

<Flow test>
About the crystalline polymer microporous membranes of Examples 1 to 5 and Comparative Examples 7 to 9, per unit area (m ² ) when isopropyl alcohol (IPA) was flowed at a differential pressure of 100 kPa, and per unit time (min) The permeation amount was measured as a flow rate (L · m ⁻² · min ⁻¹ ), and a flow rate test was performed.

  The crystalline polymer microporous membranes of Examples 1 to 5 can prevent breakage in the inner layer, have excellent structural stability, have a fine pore diameter, and efficiently capture fine particles of several tens of nanometers It was found that performance design can be freely performed.

  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 1 Outer 2 Inner 3 Core rod 4 1st crystalline polymer sheet layer 4A 1st paste 5 2nd crystalline polymer sheet layer 5A 2nd paste 5B End face 6 Metal plate 8 Mold 9 Extruder 10 Lamination preliminary molding Body 15 Laminate (Unheated film laminate)
16 Break 20 Roll 21 Primary support 22 Microfiltration membrane 23 Secondary 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 37 Welding portion 101 First crystalline polymer sheet layer 102 Second crystalline polymer sheet layer 103 First crystalline polymer sheet layer 101b Hole portion 102b Hole portion 103b Hole portion 111 Outer peripheral cover 112 Membrane support 113 Microfiltration membrane 114 Membrane support 115 Core 116a End plate 116b End plate 117 Gasket 118 Liquid outlet Lm1 Maximum average hole in the hole Lm2 maximum average pore diameter of the maximum average pore diameter Lm3 hole of the hole

Claims (12)

The first crystalline polymer sheet layer covers both surfaces of the second crystalline polymer sheet layer, and the pair of longitudinal end faces facing each other in the second crystalline polymer sheet layer are A laminated body forming step in which a laminated preform formed by coating with the first crystalline polymer sheet layer is extruded in the length direction and rolled to form a laminated body;
A symmetrical heating step of symmetrically heating the laminate;
A stretching step of stretching the laminate;
A method for producing a crystalline polymer microporous membrane, comprising:   The method for producing a crystalline polymer microporous film according to claim 1, wherein the thicknesses of the two first crystalline polymer sheet layers covering both surfaces of the second crystalline polymer sheet layer are different from each other.   The crystalline polymer microporous membrane according to any one of claims 1 to 2, wherein at least one layer in the laminate has a plurality of pores having a constant average pore diameter in at least a part of the laminate in the thickness direction. Manufacturing method.   The crystalline polymer microporous membrane according to any one of claims 1 to 3, wherein at least the second crystalline polymer sheet layer in the laminate has a microstructure containing at least fibrils having an average major axis length of 1 µm or less. Production method.   The crystalline polymer according to any one of claims 1 to 4, wherein the first crystalline polymer contained in the first crystalline polymer sheet layer is one of polytetrafluoroethylene and a polytetrafluoroethylene copolymer. A method for producing a microporous membrane.   The crystalline polymer according to any one of claims 1 to 5, wherein the second crystalline polymer contained in the second crystalline polymer sheet layer is either polytetrafluoroethylene or a polytetrafluoroethylene copolymer. A method for producing a microporous membrane.   The polytetrafluoroethylene copolymer is a copolymer obtained by copolymerizing at least two selected from tetrafluoroethylene, perfluoroalkyl vinyl ether, hexafluoropropylene, and chlorotrifluoroethylene. A method for producing a crystalline polymer microporous membrane. The DSC chart obtained by measuring the second crystalline polymer with a differential scanning calorimeter 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 laminate is performed at a temperature higher than the peak temperature on the low temperature side,
The crystal according to any one of claims 1 to 7, wherein 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 symmetrical heating of the laminate is performed at a temperature higher than the temperature of the low temperature side shoulder portion. For producing porous polymer microporous membrane.   The method for producing a crystalline polymer microporous membrane according to any one of claims 1 to 8, wherein the laminated body is subjected to symmetrical heating at a temperature not higher than the melting point of the first crystalline polymer.   A crystalline polymer microporous membrane produced by the method for producing a crystalline polymer microporous membrane according to any one of claims 1 to 9.   A filter for filtration, comprising the crystalline polymer microporous membrane according to claim 10.   A filtration device comprising an inlet, an outlet, and the filtration filter according to claim 11, wherein the second crystalline polymer sheet in the filtration filter is disposed in the vicinity of the outlet. .