JP5078729B2 - Crystalline polymer microporous membrane, method for producing the same, and filter for filtration - Google Patents

Description

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

Microporous membranes have been known for a long time, and are widely used for filtration filters and the like (see Non-Patent Document 1). Examples of such a microporous membrane include those manufactured using cellulose ester as a raw material (see Patent Documents 1 to 7), those manufactured using aliphatic polyamide as a raw material (see Patent Documents 8 to 14), and polyfluorocarbon. And the like (see Patent Documents 15 to 18) and those made of polypropylene (see Patent Document 19).
These microporous membranes are used for filtration and sterilization of electronic industrial cleaning water, pharmaceutical water, pharmaceutical manufacturing process water, food water, and the like. Therefore, highly reliable microporous membranes are attracting attention. Among these, a microporous film made of a crystalline polymer has excellent chemical resistance, and in particular, a microporous film made from polytetrafluoroethylene (PTFE) has excellent heat resistance and chemical resistance. The demand growth is remarkable.

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

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

US Pat. No. 1,421,341 US Pat. No. 3,133,132 US Pat. No. 2,944,017 Japanese Patent Publication No. 43-15698 Japanese Examined Patent Publication No. 45-3313 Japanese Examined Patent Publication No. 48-39586 Japanese Patent Publication No. 48-40050 US Pat. No. 2,783,894 US Pat. No. 3,408,315 US Pat. No. 4,340,479 US Pat. No. 4,340,480 U.S. Pat. No. 4,450,126 German Patent Invention No. 3,138,525 JP 58-37842 A US Pat. No. 4,196,070 US Pat. No. 4,340,482 JP 55-99934 A JP 58-91732 A West German Patent No. 3,003,400 Japanese Patent Publication No.55-6406 Japanese Examined Patent Publication No. 4-68966 JP-A-4-351645 JP 7-292144 A Published by R. Kesting “Synthetic Polymer Membrane”, McGraw Hill (McGrawHill)

  An object of the present invention is to solve the above-described problems and achieve the following objects. That is, the present invention can efficiently capture fine particles and has a crystalline polymer microporous membrane with a long filtration life, and a crystalline polymer microporous membrane that can efficiently produce the crystalline polymer microporous membrane. An object of the present invention is to provide a method for producing a porous membrane, and a filter for filtration using the crystalline polymer microporous membrane.

Means for solving the problems are as follows. That is,
<1> A crystalline polymer microporous film obtained by heating one surface of a film made of a crystalline polymer by infrared irradiation and stretching a semi-baked film in which a temperature gradient is formed in the thickness direction of the film. ,
The average pore diameter of the surface opposite to the infrared irradiation surface of the crystalline polymer microporous film is larger than the average pore diameter of the back surface, and the average pore diameter continuously changes from the front surface to the back surface. A crystalline polymer microporous membrane.
<2> The crystalline polymer microporous film according to <1>, wherein the infrared rays are far infrared rays.
<3> The crystalline polymer microporous membrane according to any one of <1> to <2>, wherein the crystalline polymer is polytetrafluoroethylene.
<4> The crystalline polymer microporous membrane according to any one of <1> to <3>, wherein the stretching is biaxial stretching.
<5> The above <1> to <4, wherein dD / dt on the surface of the crystalline polymer microporous membrane (where D represents an average pore diameter and t represents a distance in the thickness direction from the surface) is negative. > A crystalline polymer microporous membrane according to any one of the above.
<6> The crystalline polymer microporous film according to <5>, wherein dD / dt on the back surface of the film is larger than dD / dt on the surface of the crystalline polymer microporous film.
<7> The crystalline polymer microporous membrane according to any one of <1> to <6>, wherein the crystalline polymer microporous membrane has a single-layer structure in which the average pore size on the surface is larger than the average pore size on the back surface. is there.
<8> The crystalline polymer microporous film according to <7>, wherein a surface having an average pore diameter smaller than the average pore diameter on the surface and larger than the average pore diameter on the back surface exists in the crystalline polymer microporous film. It is a membrane.
<9> The crystalline polymer microporous membrane according to any one of <1> to <8>, wherein the average pore diameter continuously decreases from the front surface to the back surface of the crystalline polymer microporous membrane. .
<10> Crystalline polymer microporosity including at least an asymmetric heating step in which one surface of a film made of a crystalline polymer is heated by infrared irradiation to form a semi-baked film having a temperature gradient in the thickness direction of the film. A method for manufacturing a membrane, comprising:
The average pore diameter of the surface opposite to the infrared irradiation surface of the crystalline polymer microporous film is larger than the average pore diameter of the back surface, and the average pore diameter continuously changes from the front surface to the back surface. Is a method for producing a crystalline polymer microporous membrane.
<11> The method for producing a crystalline polymer microporous film according to <10>, wherein the infrared rays are far infrared rays.
<12> The method for producing a crystalline polymer microporous membrane according to any one of <10> to <11>, wherein the crystalline polymer is polytetrafluoroethylene.
<13> The method for producing a crystalline polymer microporous membrane according to any one of <10> to <12>, including a stretching step of stretching the semi-baked film in at least one direction.
<14> The method for producing a crystalline polymer microporous film according to any one of <10> to <13>, including a stretching step of stretching the semi-fired film in a biaxial direction.
<15> The crystalline polymer microporous membrane according to any one of <10> to <14>, wherein the asymmetric heating step is performed under a condition where more heat energy is supplied to the back surface of the film than the front surface. It is a manufacturing method.
<16> The method for producing a crystalline polymer microporous membrane according to any one of <10> to <15>, wherein the asymmetric heating step is continuously performed.
<17> The method for producing a crystalline polymer microporous membrane according to any one of <10> to <16>, wherein the asymmetric heating step is continuously performed by heating the back surface of the film and cooling the surface. It is.
<18> The method for producing a crystalline polymer microporous membrane according to any one of <10> to <17>, wherein the asymmetric heating step is intermittently performed.
<19> The crystalline polymer according to any one of <10> to <18>, wherein the asymmetric heating step is intermittently performed by intermittently heating and cooling the back surface of the film to suppress a temperature rise of the surface. This is a method for producing a microporous membrane.
<20> A filtration filter using the crystalline polymer microporous membrane according to any one of <1> to <9>.
<21> The filtration filter according to <20>, wherein the filter is processed into a pleated shape.
<22> The filter for filtration according to any one of <20> to <21>, wherein a surface side having a large pore size of the crystalline polymer microporous membrane is used as a filter surface of the filter.

The crystalline polymer microporous membrane of the present invention is obtained by heating one surface of a film made of a crystalline polymer by infrared irradiation and stretching a semi-baked film having a temperature gradient in the thickness direction of the film,
The average pore diameter of the surface opposite to the infrared irradiation surface of the crystalline polymer microporous film is larger than the average pore diameter of the back surface, and the average pore diameter continuously changes from the front surface to the back surface.
In the crystalline polymer microporous membrane of the present invention, fine particles can be captured efficiently over a long period of time, and since it has excellent heat resistance and chemical resistance, it has not been possible with conventional filters for filtration. It can also be applied to high-temperature filtration and reactive chemical filtration.

In the method for producing a crystalline polymer microporous membrane of the present invention, one surface of a crystalline polymer film is heated by infrared irradiation to form a semi-baked film having a temperature gradient in the thickness direction of the film. Including at least an asymmetric heating step,
The crystalline polymer microporous film is formed so that the average pore diameter on the surface opposite to the infrared irradiation surface is larger than the average pore diameter on the back surface, and the average pore diameter continuously changes from the front surface to the back surface. .
In the method for producing a crystalline polymer microporous membrane of the present invention, the microporous membrane of the present invention can be efficiently produced.

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

  In the present invention, the surface having the larger average pore diameter which is the opposite side of the infrared irradiation surface is referred to as the “front surface”, and the surface having the smaller average pore diameter which is the infrared irradiation surface is referred to as the “back surface”. Is merely a name given for convenience in order to make the description of the present invention easier to understand. Therefore, any surface of the unheated crystalline polymer film may be made “surface” after being irradiated with infrared rays and semi-baked.

  According to the present invention, the conventional problems can be solved, fine particles can be efficiently captured, and the crystalline polymer microporous membrane having a long filtration life and the crystalline polymer microporous membrane are efficiently produced. It is possible to provide a method for producing a crystalline polymer microporous membrane that can be used, and a filter for filtration using the crystalline polymer microporous membrane.

(Crystalline polymer microporous membrane and crystalline polymer microporous membrane production method)
The crystalline polymer microporous film of the present invention is formed by heating one surface of a film made of a crystalline polymer by infrared irradiation and stretching a semi-fired film in which a temperature gradient is formed in the thickness direction of the film.
In the method for producing a crystalline polymer microporous membrane of the present invention, one surface of a crystalline polymer film is heated by infrared irradiation to form a semi-baked film having a temperature gradient in the thickness direction of the film. It includes at least an asymmetric heating step, and includes a crystalline polymer film preparation step, a stretching step, and other steps as necessary.
In the present invention, the average pore diameter of the surface opposite to the infrared irradiation surface of the crystalline polymer microporous film is larger than the average pore diameter of the back surface, and the average pore diameter continuously changes from the front surface to the back surface. ing.
Hereinafter, the crystalline polymer microporous membrane and the method for producing the crystalline polymer microporous membrane of the present invention will be described in detail.

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

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

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

One feature of the crystalline polymer microporous film of the present invention is that the average pore diameter on the surface opposite to the infrared irradiation surface is larger than the average pore diameter on the back surface.
The crystalline polymer microporous membrane has a thickness of “10”, an average pore diameter in the thickness portion “1” in the depth direction from the surface is P1, and an average pore diameter in the thickness portion of “9” is P2. P1 / P2 is preferably 2 to 10,000, and more preferably 3 to 100.
Further, the crystalline polymer microporous membrane has a ratio of the average pore diameter of the front and back surfaces (surface / back surface ratio) of preferably 5 to 30 times, more preferably 10 to 25 times, and more preferably 15 to 20 times. Further preferred.

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

  In addition to the above characteristics, the crystalline polymer microporous membrane of the present invention further has an aspect in which the average pore diameter continuously changes from the front surface to the back surface (first aspect), and in addition to the above characteristics. Furthermore, both of the embodiments (second embodiment) having a single layer structure are included. By further adding these additional features, the filter life can be effectively improved.

  In the first aspect, “the average pore diameter is continuously changing from the front surface to the back surface” means that the horizontal axis is the distance d in the thickness direction from the surface (corresponding to the depth from the surface), When the average pore diameter D is taken on the vertical axis, this means that the graph is drawn with one continuous line. The graph from the front surface (d = 0) to the back surface (d = film thickness) may consist of only a negative slope area (dD / dt <0), or a negative slope area and a slope. May be a mixture of regions having zero (dD / dt = 0), or a region having a negative slope and a positive region (dD / dt> 0). Preferably, the region is composed only of a negative slope region (dD / dt <0), or a negative slope region and a zero slope region (dD / dt = 0) are mixed. More preferably, it is composed of only a negative slope region (dD / dt <0).

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

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

  The crystalline polymer microporous membrane of the present invention preferably has both the features of the first embodiment and the features of the second embodiment. That is, it is preferable that the average pore diameter on the surface of the film is larger than the average pore diameter on the back surface, the average pore diameter continuously changes from the front surface to the back surface, and a single layer structure. With such a microporous membrane, fine particles can be captured more efficiently when filtration is performed from the surface side, the filtration life can be greatly improved, and it can be easily and inexpensively manufactured. it can.

  The film thickness of the crystalline polymer microporous membrane of the present invention is preferably 1 μm to 300 μm, more preferably 5 μm to 100 μm, and still more preferably 10 μm to 80 μm.

<Method for producing crystalline polymer microporous membrane>
The method for producing a crystalline polymer microporous membrane of the present invention includes at least an asymmetric heating step, and further includes a crystalline polymer film production step, a stretching step, and other steps as necessary.

-Crystalline polymer film production process-
There is no restriction | limiting in particular as a kind of crystalline polymer raw material used when manufacturing the unheated crystalline film which consists of crystalline polymers, The crystalline polymer mentioned above can be used preferably. Among these, polyethylene or a crystalline polymer in which a hydrogen atom is substituted with a fluorine atom is used, and polytetrafluoroethylene (PTFE) is particularly preferable.
The crystalline polymer used as a raw material preferably has a number average molecular weight of 500 to 50,000,000, more preferably 1,000 to 10,000,000.
As the crystalline polymer used as a raw material, polyethylene is preferable, and for example, polytetrafluoroethylene can be used. As polytetrafluoroethylene, polytetrafluoroethylene produced by an emulsion polymerization method can be usually used, and preferably a finely divided polytetrafluoroethylene obtained by coagulating an aqueous dispersion obtained by emulsion polymerization. Fluoroethylene is used.
The number average molecular weight of polytetrafluoroethylene used as a raw material is preferably 2.5 million to 10 million, more preferably 3 million to 10 million.
There is no restriction | limiting in particular as said polytetrafluoroethylene, According to the objective, it can select suitably, A commercial item can be used. Examples of the commercially available products include polyflon PTFE F-104, polyflon PTFE F-201, polyflon PTFE F-205, polyflon PTFE F-207, polyflon PTFE F-301 (all manufactured by Daikin Industries, Ltd.); Fluon PTFE CD1, Fluon PTFE CD141, Fluon PTFE CD145, Fluon PTFE CD123, Fluon PTFE CD076, Fluon PTFE CD090 (all manufactured by Asahi Glass Co., Ltd.); Teflon (registered trademark) PTFE 6-J, Teflon (registered trademark) TFElon (Registered Trademark) PTFE 6C-J, Teflon (Registered Trademark) PTFE 640-J (all manufactured by Mitsui DuPont Fluorochemical Co., Ltd.), and the like. Among these, F-104, CD1, CD141, CD145, CD123, 6-J are preferable, F-104, CD1, CD123, 6-J are more preferable, and CD123 is particularly preferable.

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

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

-Asymmetric heating process-
The asymmetric heating step is a step of forming a semi-baked film in which one surface of a film made of a crystalline polymer is heated by infrared irradiation to form a temperature gradient in the thickness direction of the film.
Here, the semi-firing means that the crystalline polymer is heat-treated at a temperature not lower than the melting point of the heated body and not higher than the melting point of the unheated body + 15 ° C.
In the present invention, an unheated crystalline polymer means one that has not been subjected to an asymmetric heat treatment. Moreover, the heating body of a crystalline polymer means what was heat-processed at the temperature more than melting | fusing point of an unheated body.
The melting point of the crystalline polymer means the temperature of the peak of the endothermic curve that appears when an unheated crystalline polymer is measured with a differential scanning calorimeter. The melting point of the heated body and the melting point of the unheated body vary depending on the kind of the crystalline polymer and the average molecular weight, but are preferably 50 ° C to 450 ° C, more preferably 80 ° C to 400 ° C.
Such a temperature can be considered as follows. For example, in the case of polytetrafluoroethylene, the melting point of the heated body is about 324 ° C., and the melting point of the unheated body is about 345 ° C. Therefore, in the case of a polytetrafluoroethylene film, the temperature is preferably 327 ° C. to 360 ° C., more preferably 335 ° C. to 350 ° C., for example, heating to a temperature of 345 ° C. The semi-fired body is in a state where a melting point of about 324 ° C. and a melting point of about 345 ° C. are mixed.

The semi-baking is performed by heating one surface of a film made of a crystalline polymer by infrared irradiation. Thereby, the heating temperature can be controlled asymmetrically in the thickness direction, and the crystalline polymer microporous membrane of the present invention can be easily produced.
Moreover, as a temperature gradient in the thickness direction of the film, the temperature difference between the front surface and the back surface is preferably 30 ° C. or more, and more preferably 50 ° C. or more.

There is no restriction | limiting in particular as said infrared irradiation, According to the objective, it can select suitably.
The general definition of the infrared can be referred to “practical infrared” (Human and History, published in 1992). In the present invention, the infrared ray means an electromagnetic wave having a wavelength of 0.74 μm to 1,000 μm, of which a wavelength range of 0.74 μm to 3 μm is a near infrared ray, and a wavelength range of 3 μm to 1,000 μm is far away. Infrared.
In the present invention, since it is preferable that there is a temperature difference between the front surface and the back surface of the unheated film, far infrared rays advantageous for heating the surface layer are preferably used.
The type of infrared device is not particularly limited as long as it can irradiate infrared rays having a target wavelength, and can be appropriately selected according to the purpose. In general, near infrared rays are bulbs (halogen lamps), far infrared rays are A heating element such as ceramic, quartz, or metal oxide surface can be used.
Moreover, if it is infrared irradiation, a semi-baking can be performed continuously by a flow operation industrially, and also temperature control and apparatus maintenance are easy. Moreover, since it is non-contact, it does not cause defects such as cleanness and fluff.
The film surface temperature by the infrared irradiation can be controlled by the output of the infrared irradiation apparatus, the distance between the infrared irradiation apparatus and the film surface, the irradiation time (conveying speed), and the atmospheric temperature, and is set to the temperature at which the above-mentioned semi-fired body is formed. However, it is preferably 327 ° C to 380 ° C, more preferably 335 ° C to 360 ° C. When the surface temperature is less than 327 ° C., the crystal state does not change, and the pore diameter may not be controlled. When the surface temperature exceeds 380 ° C., the entire film melts, and the shape is excessively deformed. Thermal decomposition may occur.
The irradiation time of the infrared rays is not particularly limited, and is a time necessary for the desired half-baking to sufficiently proceed, preferably 30 seconds to 120 seconds, more preferably 45 seconds to 90 seconds, and more preferably 60 seconds to 80 seconds is more preferable.

The infrared irradiation in the asymmetric heating step may be performed continuously, or may be performed intermittently after being divided into several times.
When the back surface of the film is continuously heated by infrared irradiation, the surface is preferably cooled simultaneously with the heating of the back surface in order to maintain a concentration gradient between the front and back surfaces of the film.
The method for cooling the surface is not particularly limited and may be appropriately selected depending on the purpose. For example, a method of blowing cold air, a method of contacting a refrigerant, a method of contacting a cooled material, cooling by cooling, etc. These methods can be used, and the method of bringing a coolant into contact with the surface of the film is not preferable because the surface of the contact is heated by far infrared rays.
Moreover, also when performing the said asymmetrical heating process intermittently, it is preferable to heat and cool the back surface of a film intermittently and to suppress the temperature rise of the surface.

-Stretching process-
The semi-baked film is then preferably stretched. Stretching is preferably performed in both the longitudinal direction and the width direction. Each of the longitudinal direction and the width direction may be sequentially stretched, or biaxially stretched simultaneously.
When sequentially stretching in the longitudinal direction and the width direction, respectively, it is preferable to first stretch in the longitudinal direction and then stretch in the width direction.
The stretching ratio in the longitudinal direction is preferably 4 times or more, more preferably 8 times or more, and still more preferably 10 times or more. The stretching temperature in the longitudinal direction is preferably 100 ° C to 300 ° C, more preferably 200 ° C to 300 ° C, and particularly preferably 270 ° C.
The stretching ratio in the width direction is preferably 10 to 100 times, more preferably 12 to 90 times, still more preferably 15 to 70 times, and particularly preferably 20 to 40 times. The stretching temperature in the width direction is preferably 100 ° C to 300 ° C, more preferably 200 ° C to 300 ° C, and particularly preferably 270 ° C.
The area stretch ratio is preferably 50 times or more, more preferably 75 times or more, and still more preferably 100 times or more. When stretching, the film may be preheated to a temperature below the stretching temperature.

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

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

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

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

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

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

  FIG. 2 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. In addition to heat sealing, the housing base and the housing cover can be sealed by using an adhesive. 1-3 are specific examples of the microfiltration filter cartridge, and the present invention is not limited to these drawings.

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

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

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

( Reference Example 1)
-Fabrication of crystalline polymer microporous membrane-
As a crystalline polymer, polytetrafluoroethylene fine powder having a number average molecular weight of 6,200,000 (Daikin Kogyo Co., Ltd., “Polyflon Fine Powder F104U”) is added to 100 parts by mass of hydrocarbon oil (Exxon Mobil Co., Ltd.) 27 parts by mass of “Isopar M”) was added, and paste extrusion was performed in a round bar shape. This was calendered at a speed of 50 m / min with a calender roll heated to 70 ° C. to produce a polytetrafluoroethylene film. This film was passed through a hot air drying oven at 250 ° C. to remove the extrusion aid, thereby producing a polytetrafluoroethylene film having an average thickness of 100 μm, an average width of 150 mm, and a specific gravity of 1.55.
One surface of the obtained polytetrafluoroethylene film was heated for 1 minute at a film surface temperature of 345 ° C. by a near infrared ray using a halogen heater with a built-in tungsten filament to produce a semi-baked film.

The obtained semi-baked film was stretched between rolls by 12.5 times in the longitudinal direction at 270 ° C., and once wound on a winding roll. Then, after preheating the film to 305 ° C., both ends were sandwiched between clips and stretched 30 times in the width direction at 270 ° C. Thereafter, heat setting was performed at 380 ° C. The area stretch ratio of the obtained stretched film was 260 times in terms of stretched area ratio. Thus, the polytetrafluoroethylene microporous membrane of Reference Example 1 was produced.

(Example 2)
-Fabrication of crystalline polymer microporous membrane-
Reference Example 1, one surface of a polytetrafluoroethylene film, except that using a Kanthal alloy wire heating element built quartz tube heater, and 1 minute Centrifuge infrared heating a film surface temperature of 345 ° C., the reference example 1 In the same manner as described above, the polytetrafluoroethylene microporous membrane of Example 2 was produced.

(Example 3)
-Fabrication of crystalline polymer microporous membrane-
In Reference Example 1, one side of the polytetrafluoroethylene film was heated in the same manner as in Reference Example 1 except that one side of the polytetrafluoroethylene film was heated at a film surface temperature of 345 ° C. for 1 minute using a ceramic heater. A polytetrafluoroethylene microporous membrane was prepared.

Example 4
-Fabrication of crystalline polymer microporous membrane-
In Reference Example 1, a cycle of heating one surface of a polytetrafluoroethylene film at a film surface temperature of 345 ° C. for 10 seconds using a ceramic heater and then allowing to cool at room temperature for 5 minutes is repeated 7 times, intermittently A polytetrafluoroethylene microporous membrane of Example 4 was produced in the same manner as in Reference Example 1, except that heating with far infrared rays was performed.

( Reference Example 5)
-Fabrication of crystalline polymer microporous membrane-
Polytetrafluoroethylene fine powder having a number average molecular weight of 10 million as a crystalline polymer (manufactured by Asahi Glass Co., Ltd., “Fluon
PTFE CD123 ") was added to 27 parts by mass of hydrocarbon oil (" Isoper H "manufactured by ExxonMobil Co., Ltd.) as an extrusion aid, and paste extrusion was performed in a sheet form (width 100 mm, film thickness 2 mm). This was calendered at a speed of 5 m / min with a calender roll heated to 60 ° C. to produce a polytetrafluoroethylene film. This film was passed through a hot air drying oven at 250 ° C. to remove the extrusion aid, and a polytetrafluoroethylene film having an average thickness of 120 μm, an average width of 100 mm, and a specific gravity of 1.55 was produced.
One surface of the obtained polytetrafluoroethylene film was heated for 1 minute at a film surface temperature of 345 ° C. by a near infrared ray using a halogen heater with a built-in tungsten filament to produce a semi-baked film.

The obtained semi-baked film was stretched between rolls 20 times in the longitudinal direction at 300 ° C., and then wound up on a take-up roll. Then, after preheating the film to 305 ° C., both ends were clipped and stretched 10 times in the width direction at 350 ° C. Thereafter, heat setting was performed at 380 ° C. The area stretch ratio of the obtained stretched film was 140 times in terms of stretched area ratio. Thus, the polytetrafluoroethylene microporous membrane of Reference Example 5 was produced.

( Reference Example 6)
As a crystalline polymer, 100 parts by mass of polytetrafluoroethylene fine powder having a number average molecular weight of 10 million (Asahi Glass Co., Ltd., “Fluon PTFE CD123”) and a hydrocarbon oil (ExxonMobil Co., Ltd. ”) 27 parts by mass was added, and paste extrusion was performed in a sheet form (width 100 mm, film thickness 2 mm). This was calendered at a speed of 5 m / min with a calender roll heated to 60 ° C. to produce a polytetrafluoroethylene film. This film was passed through a hot air drying oven at 250 ° C. to remove the extrusion aid, and a polytetrafluoroethylene film having an average thickness of 120 μm, an average width of 100 mm, and a specific gravity of 1.55 was produced.
One surface of the obtained polytetrafluoroethylene film was heated for 1 minute at a film surface temperature of 345 ° C. by a near infrared ray using a halogen heater with a built-in tungsten filament to produce a semi-baked film.

The obtained semi-baked film was stretched 20 times in the longitudinal direction and 10 times in the width direction at 250 ° C. using a simultaneous biaxial stretching machine. Thereafter, heat setting was performed at 380 ° C. The area stretch ratio of the obtained stretched film was 140 times in terms of stretched area ratio. Thus, the polytetrafluoroethylene microporous membrane of Reference Example 6 was produced.

( Reference Example 7)
-Fabrication of crystalline polymer microporous membrane-
Polytetrafluoroethylene fine powder having a number average molecular weight of 3 million as a crystalline polymer (manufactured by Mitsui DuPont Fluorochemical Co., Ltd., “Teflon (registered trademark) PTFE)
6-J ") 27 parts by mass of hydrocarbon oil (" Isoper G "manufactured by ExxonMobil Co., Ltd.) as an extrusion aid was added to 100 parts by mass, and paste extrusion was performed in a sheet form (width 150 mm, film thickness 2 mm). . This was calendered at a speed of 10 m / min with a calender roll heated to 60 ° C. to produce a polytetrafluoroethylene film. The film was passed through a hot air drying oven at 250 ° C. to remove the extrusion aid, and a polytetrafluoroethylene film having an average thickness of 80 μm, an average width of 150 mm, and a specific gravity of 1.55 was produced.
One surface of the obtained polytetrafluoroethylene film was heated for 1 minute at a film surface temperature of 345 ° C. by a near infrared ray using a halogen heater with a built-in tungsten filament to produce a semi-baked film.

The obtained semi-baked film was stretched between rolls 20 times in the longitudinal direction at 300 ° C., and then wound up on a take-up roll. Then, after preheating the film to 305 ° C., both ends were clipped and stretched 10 times in the width direction at 350 ° C. Thereafter, heat setting was performed at 380 ° C. The area stretch ratio of the obtained stretched film was 140 times in terms of stretched area ratio. Thus, the polytetrafluoroethylene microporous membrane of Reference Example 7 was produced.

(Comparative Example 1)
-Fabrication of crystalline polymer microporous membrane-
A polytetrafluoroethylene microporous membrane of Comparative Example 1 was prepared in the same manner as in Reference Example 1, except that both sides of the polytetrafluoroethylene film were heated at 345 ° C. for 1 minute using an oven in Reference Example 1. did.

Next, for each of the polytetrafluoroethylene microporous membranes of Reference Example 1, Examples 2 to 4, Reference Examples 5 to 7 and Comparative Example 1 that were produced, the microporous membrane is on the opposite side of the infrared irradiation surface. In order to confirm whether the average pore diameter on the surface is larger than the average pore diameter on the back surface and the average pore diameter continuously changes from the front surface to the back surface, the film thickness (average film thickness) is as follows. , And P1 / P2 were measured. The results are shown in Table 1.

<Film thickness (average film thickness)>
The thickness (average film thickness) of each of the polytetrafluoroethylene microporous membranes of Reference Example 1, Examples 2 to 4, Reference Examples 5 to 7 and Comparative Example 1 was measured using a dial-type thickness gauge (K402B, manufactured by Anritsu Corporation). It was measured. Arbitrary three places were measured and the average value was calculated.

<Measurement of P1 / P2>
About each polytetrafluoroethylene microporous film of Reference Example 1, Examples 2 to 4, Reference Examples 5 to 7, and Comparative Example 1, the film thickness of the microporous film was “10”, and the depth direction “ P1 / P2 was determined when the average pore diameter in the thickness portion of “1” was P1, and the average pore diameter of the thickness portion of “9” was P2.
Here, the average pore diameter of the microporous membrane was measured with a scanning electron microscope (Hitachi S-4000 type, vapor deposition was Hitachi E1030 type, both manufactured by Hitachi, Ltd.). Image processing apparatus (main body name: manufactured by Nippon Avionics Co., Ltd., TV image processor TVIP-4100II, control software name: manufactured by Ratok System Engineering Co., Ltd., TV image processor image command) 4198) to obtain an image consisting only of polytetrafluoroethylene fibers, and the average pore size was determined by subjecting the image to arithmetic processing.

From the results of Table 1, each of the microporous membranes of Reference Example 1, Examples 2 to 4, and Reference Examples 5 to 7 has an average pore diameter on the surface opposite to the infrared irradiation surface larger than the average pore diameter on the back surface. And it turned out that an average hole diameter is changing continuously from the surface to a back surface.
In contrast, in the microporous film of Comparative Example 1, the average pore diameter on the surface opposite to the infrared irradiation surface is substantially the same as the average pore diameter on the back surface, and the average pore diameter does not change from the front surface to the back surface. I understood that.

<Filtration test>
Next, a filtration test was performed on each of the microporous membranes of Reference Example 1, Examples 2 to 4, Reference Examples 5 to 7, and Comparative Example 1. First, an aqueous solution containing 0.01% by mass of polystyrene latex (average particle size 0.17 μm) was filtered with a differential pressure of 0.1 kg. The results are shown in Table 2.

From the results in Table 2, the microporous membrane of Comparative Example 1 was substantially clogged at 500 ml / cm ² .
In contrast, the microporous membranes of Reference Example 1, Examples 2 to 4, and Reference Examples 5 to 7 were found to have a significantly improved filtration life by using the microporous membrane of the present invention. . Particularly in Examples 2 to 4 using far infrared rays, filtration was possible up to 1500 ml / cm ² or more, and the effect of improving the filtration life was remarkable.

( Reference Example 8)
-Filter cartridge-
The PTFE microporous membrane of Reference Example 1 was laminated as shown below, pleated to a pleat width of 12.5 mm (pleated width = 220 mm), 230 folds were taken and rolled into a cylindrical shape, and the alignment was made. Weld the eyes 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
PTFE microporous membrane of filter media reference example 1 Thickness: about 0.05 mm, use 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
The filter cartridge of Reference Example 8 of the present invention is excellent in solvent resistance because it uses the crystalline polymer microporous film of Reference Example 1 of the present invention. Further, since the hole portion has an asymmetric structure, it has a long life with a large flow rate and hardly clogged.

  The crystalline polymer microporous membrane of the present invention and a filter for filtration using the same are capable of capturing fine particles efficiently over a long period of time, and are excellent in heat resistance and chemical resistance. It can be used in various situations. For example, it can be widely used for electronic industrial cleaning water, pharmaceutical water, pharmaceutical manufacturing process water, food water filtration, sterilization, high temperature filtration, reactive chemical filtration, and the like.

FIG. 1 is a diagram illustrating a structure of a general pleated filter element before being assembled in a housing. FIG. 2 is a view showing the structure of a general filter element before being assembled into the housing of the capsule filter cartridge. FIG. 3 is a view showing the structure of a general capsule filter cartridge integrated with a housing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Primary side support 2 Microfiltration membrane 3 Secondary side support 4 Upper end plate 5 Lower end plate 6 Filter element cover 7 Filter element core 8 O-ring 9 Filter media 10 Filter element 11 Housing cover 12 Housing base 13 Liquid inlet nozzle 14 Liquid Outlet nozzle 15 Air vent 16 Drain 17 Welding part 101 Outer cover 102 Membrane support 103 Microfiltration membrane 104 Membrane support 105 Core 106a, 106b End plate 107 Gasket 108 Liquid outlet

Claims (10)

A crystalline polymer microporous membrane formed by heating one surface of a film made of a crystalline polymer by far- infrared irradiation and stretching a semi-fired film in which a temperature gradient is formed in the thickness direction of the film,
The average pore diameter of the surface opposite to the far infrared irradiation surface of the crystalline polymer microporous film is larger than the average pore diameter of the back surface, and the average pore diameter continuously changes from the front surface to the back surface. A crystalline polymer microporous membrane characterized. The crystalline polymer microporous membrane according to claim 1, wherein the crystalline polymer is polytetrafluoroethylene. The crystalline polymer microporous membrane according to claim 1, wherein the stretching is biaxial stretching. A crystalline polymer microporous membrane comprising at least an asymmetric heating step in which one surface of a crystalline polymer film is heated by far-infrared irradiation to form a semi-baked film having a temperature gradient in the thickness direction of the film. A manufacturing method comprising:
The crystalline polymer microporous film is formed so that the average pore diameter of the surface opposite to the far-infrared irradiation surface of the crystalline polymer is larger than the average pore diameter of the back surface, and the average pore diameter continuously changes from the front surface to the back surface. A method for producing a crystalline polymer microporous membrane. The method for producing a crystalline polymer microporous membrane according to claim 4, wherein the crystalline polymer is polytetrafluoroethylene. The method for producing a crystalline polymer microporous membrane according to any one of claims 4 to 5, further comprising a stretching step of stretching the semi-baked film in at least one direction. The method for producing a crystalline polymer microporous membrane according to any one of claims 4 to 6, further comprising a stretching step of stretching the semi-fired film in a biaxial direction. A filter for filtration, comprising the crystalline polymer microporous membrane according to any one of claims 1 to 3. The filter for filtration according to claim 8, wherein the filter is processed and formed into a pleat shape. The filter for filtration according to any one of claims 8 to 9, wherein a surface side having a large pore size of the crystalline polymer microporous membrane is used as a filter surface of the filter.