JP2009119411A - Crystalline polymer microporous film, method of manufacturing the same and filter for filtration - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a crystalline polymer microporous film which has a uniform in-plane distribution of average pore size, can efficiently catch fine particles, has a long filtration life and can be used for large equipment by using a higher flux film, to provide a method of manufacturing the crystalline polymer microporous film capable of efficiently manufacturing the crystalline polymer microporous film, and to provide a filter for filtration using the crystalline polymer microporous film. <P>SOLUTION: The method of manufacturing the crystalline polymer microporous film comprises: an asymmetric heating process of heating one side surface of a film made of a crystalline polymer while causing the surface to contact with a heating roller having a temperature distribution (maximum temperature-minimum temperature) in the roller width direction of 5°C or less to form a semi-calcined film in which a temperature gradient is formed in the thickness direction of the film; and a stretching process of stretching the semi-calcined film. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a crystalline polymer microporous membrane with good filtration efficiency used for microfiltration of liquids, gases, etc., a method for producing the crystalline polymer microporous membrane, and a filter for filtration.

Microporous membranes have been known for a long time, and are widely used for filtration filters and the like (see Non-Patent Document 1). Examples of such a microporous membrane include those manufactured using cellulose ester as a raw material (see Patent 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.

  Further, in Patent Document 24, in the production process of the PTFE porous membrane, by applying a compressive stress to the PTFE preform in a direction orthogonal to the direction of extruding and / or rolling the PTFE preform, There has been proposed a PTFE porous membrane having a variation expressed by a variation rate of 20% or less. According to this proposal, the microporous structure of the PTFE porous membrane can be made uniform. However, this proposed PTFE porous membrane does not have sufficiently satisfactory performance in terms of flow rate and filtration life, and further improvement and development are desired at present.

US Pat. No. 1,421,341 US Pat. No. 3,133,132 US Pat. No. 2,944,017 Japanese Patent Publication No. 43-15698 Japanese Examined Patent Publication No. 45-3313 Japanese Examined Patent Publication No. 48-39586 Japanese Patent Publication No. 48-40050 US Pat. No. 2,783,894 US Pat. No. 3,408,315 U.S. Pat. No. 4,340,479 US Pat. No. 4,340,480 U.S. Pat. No. 4,450,126 German Patent Invention No. 3,138,525 JP 58-37842 A US Pat. No. 4,196,070 US Pat. No. 4,340,482 JP 55-99934 A JP 58-91732 A West German Patent No. 3,003,400 Japanese Patent Publication No.55-6406 Japanese Examined Patent Publication No. 4-68966 JP-A-4-351645 JP 7-292144 A JP 2002-172316 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 provides a crystalline polymer microporous membrane that has a uniform in-plane distribution of average pore diameter, can capture fine particles efficiently, has a long filtration life, and can be used in large facilities by increasing the flow rate. And a method for producing a crystalline polymer microporous membrane capable of efficiently producing the crystalline polymer microporous membrane, and a filter for filtration using the crystalline polymer microporous membrane. And

Means for solving the problems are as follows. That is,
<1> By heating one surface of a film made of a crystalline polymer in contact with a heating roll having a temperature distribution (maximum temperature-minimum temperature) of 5 ° C. or less in the width direction of the roll, the thickness of the film An asymmetric heating step to form a semi-baked film having a temperature gradient in the direction;
A stretching step of stretching the semi-baked film;
It is a manufacturing method of the crystalline polymer microporous film | membrane characterized by including this.
<2> The method for producing a crystalline polymer microporous film according to <1>, wherein the heating roll is an induction heating roll.
<3> The method for producing a crystalline polymer microporous membrane according to any one of <1> to <2>, wherein the crystalline polymer is polytetrafluoroethylene.
<4> The method for producing a crystalline polymer microporous film according to any one of <1> to <3>, wherein the stretching step stretches the semi-fired film in a uniaxial direction.
<5> The method for producing a crystalline polymer microporous film according to any one of <1> to <3>, wherein the stretching step stretches the semi-fired film in a biaxial direction.
<6> Manufactured by the method for producing a crystalline microporous membrane according to any one of <1> to <5>, wherein an average pore diameter of one surface is larger than an average pore diameter of the other surface, and A crystalline polymer microporous membrane characterized in that the average pore diameter continuously changes from one surface to the other surface.
<7> The crystalline polymer microporous film according to <6>, wherein the in-plane variation of the average pore diameter is 20% or less.
<8> A filtration filter using the crystalline polymer microporous membrane according to any one of <6> to <7>.
<9> The filtration filter according to <8>, wherein the filter is processed and formed into a pleated shape.
<10> The filter for filtration according to any one of <8> to <9>, wherein a surface having a large average pore diameter of the crystalline polymer microporous membrane is used as a filter surface of the filter.

In the method for producing a crystalline polymer microporous membrane of the present invention, one surface of a film made of a crystalline polymer is applied to a heating roll having a temperature distribution in the roll width direction (maximum temperature-minimum temperature) of 5 ° C. or less. An asymmetric heating step of forming a semi-baked film having a temperature gradient in the thickness direction of the film by contacting and heating;
Stretching step of stretching the semi-baked film.
In the method for producing a crystalline polymer microporous membrane of the present invention, by performing the asymmetric heating step and the stretching step, the in-plane distribution of the average pore diameter is uniform, and fine particles can be captured efficiently, A crystalline polymer microporous membrane that has a long filtration life and can be used in a large facility by increasing the flow rate can be efficiently produced.

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

  According to the present invention, conventional problems can be solved, the in-plane distribution of the average pore diameter is uniform, fine particles can be captured efficiently, the filtration life is long, and the flow rate is increased so that it can be used for large facilities. Crystalline polymer microporous membrane, crystalline polymer microporous membrane production method capable of efficiently producing crystalline polymer microporous membrane, and crystalline polymer microporous membrane A filter for filtration can be provided.

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

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

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

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

There is no restriction | limiting in particular as said crystalline polymer, According to the objective, it can select suitably, For example, polyalkylene, polyester, polyamide, polyether, a liquid crystalline polymer etc. are mentioned. Specifically, polyethylene, polypropylene, nylon, polyacetal, polybutylene terephthalate, polyethylene terephthalate, syndiotactic polystyrene, polyphenylene sulfide, polyether ether ketone, wholly aromatic polyamide, wholly aromatic polyester, fluororesin, polyether nitrile , Etc.
Among these, from the viewpoint of chemical resistance and handleability, polyalkylene (for example, polyethylene and polypropylene) is preferable, and fluorine-based polyalkylene in which the hydrogen atoms of the alkylene group in the polyalkylene are partially or entirely substituted with fluorine atoms. 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, 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, and more preferably 3 million to 8 million.
There is no restriction | limiting in particular as said polytetrafluoroethylene raw material, You may select and use the polytetrafluoroethylene raw material currently marketed suitably. For example, “Polyflon Fine Powder F104U” manufactured by Daikin Industries, Ltd. is preferable.

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

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

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

-Asymmetric heating process-
In the asymmetric heating step, one surface of a film made of a crystalline polymer is heated by bringing it into contact with a heating roll having a temperature distribution in the width direction of the roll (maximum temperature-minimum temperature) of 5 ° C. or less. This is a step of forming a semi-baked film having a temperature gradient in the thickness direction of the film. As a result, the heating state of the film becomes uniform, the in-plane distribution of the average pore diameter of the resulting crystalline polymer microporous membrane becomes uniform, and the heating temperature is controlled asymmetrically in the thickness direction of the crystalline polymer microporous membrane. can do.

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

The semi-baking is performed by bringing one surface (heating surface) of a film made of a crystalline polymer into contact with a heating roll having a temperature distribution (maximum temperature-minimum temperature) of 5 ° C. or less in the width direction of the roll. .
The temperature distribution (maximum temperature-minimum temperature) is preferably 2 ° C. or less, and most preferably 0 ° C. When the temperature distribution exceeds 5 ° C., the heating state of the film becomes nonuniform, and the average pore diameter of the resulting crystalline polymer microporous membrane may become nonuniform.
The temperature distribution of the heating roll is, for example, the maximum temperature portion and the minimum temperature portion in the width direction in a steady state of the roll (a state in which the temperature variation for 10 seconds is within 1 ° C. in the temperature measurement at intervals of 0.1 seconds). The temperature difference can be measured using, for example, infrared thermography.

The heating roll is not particularly limited as long as the temperature distribution (maximum temperature-minimum temperature) in the width direction of the roll is 5 ° C. or less, and can be appropriately selected according to the purpose. For example, an induction heating roll is preferable. Used for.
In the induction heating roll, the roll shell generates induction heat by a coil inside the roll. Specifically, when an alternating current is supplied to the induction coil, a magnetic flux is generated in the coil. An induced current is induced inside the roll shell (outer cylinder) facing the coil by the action of the magnetic flux, and the roll itself self-heats (induced heat generation) due to the resistance heat. Unlike other indirect heating such as oil circulation type and hot water circulation type, the roll itself generates heat directly, so that high-temperature heat energy can be efficiently obtained as required.
Moreover, the roll surface can hold | maintain temperature with high precision uniformly in the width direction and the circumferential direction by the heat pipe mechanism.
As such an induction heating roll, a commercially available product can be used, for example, an induction heating metal roll mounted on a Yuri Roll Co., Ltd. "Induction Heating Method High Temperature High Speed Calendar Machine (installed in Yuri Roll Co., Ltd.)", etc. Is mentioned.

Further, as the temperature gradient in the thickness direction of the film made of a crystalline polymer, the temperature difference between the non-heated surface and the heated surface is preferably 30 ° C. or higher, and more preferably 50 ° C. or higher.
The temperature of the heating roll can be set to the temperature at which the semi-fired body is formed. The time for which the film is brought into contact with the heating roll is the time necessary for the target half-baking to sufficiently proceed, and is usually 30 seconds to 120 seconds, preferably 45 seconds to 90 seconds, more preferably 60 seconds to 80 seconds.

The heating in the asymmetric heating step may be performed continuously, or may be performed intermittently by dividing into several times.
When the heating surface of the film is continuously heated, it is preferable to cool the non-heating surface simultaneously with the heating of the heating surface in order to maintain a temperature gradient between the heating surface and the non-heating surface of the film.
The method for cooling the non-heated surface is not particularly limited and may be appropriately selected depending on the purpose. For example, a method of blowing cold air, a method of contacting with a refrigerant, a method of contacting with a cooled material, or by cooling. Various methods such as cooling can be used, and it is preferably performed by bringing a cooling material into contact with the non-heated surface of the film. As the cooling object, it is particularly preferable to select a cooling roll as the cooling object. If it is a cooling roll, like the heating of a heating surface, it can carry out an industrial semi-baking continuously by a flow operation | work, and also temperature control and apparatus maintenance are easy. The temperature of the cooling roll can be set so as to cause a difference from the temperature at which the semi-fired body is formed. The time for which the film is brought into contact with the cooling roll is a time required for the intended half-baking to sufficiently proceed, and is usually 30 seconds to 120 seconds, assuming that the film is simultaneously performed with the heating step. The time is preferably 45 seconds to 90 seconds, more preferably 60 seconds to 80 seconds.
In the production method of the present invention, the non-heated surface of the film is preferably brought into contact with the heating and cooling roll, but a roller set at a temperature lower than that of the heating and cooling roll may be brought into contact with the heating surface of the film. Absent. For example, a roller maintained at room temperature may be pressed from the film heating surface to fit the film to the heating roll. Moreover, you may make the heating surface of a film contact a guide roll before or after making it contact with a heating roll.
Moreover, also when performing the said asymmetrical heating process intermittently, it is preferable to suppress the temperature rise of a non-heating surface by heating the heating surface of a film intermittently and cooling a non-heating surface.

-Stretching process-
The semi-baked film is then preferably stretched. Stretching is preferably performed in both the longitudinal direction and the width direction. Each of the longitudinal direction and the width direction may be sequentially stretched, or biaxially stretched simultaneously.
When sequentially stretching in the longitudinal direction and the width direction, respectively, it is preferable to first stretch in the longitudinal direction and then stretch in the width direction.
The stretching ratio in the longitudinal direction is preferably 4 to 100 times, more preferably 8 to 90 times, and still more preferably 10 to 80 times. The stretching temperature in the longitudinal direction is preferably 100 ° C to 300 ° C, more preferably 200 ° C to 290 ° C, and particularly preferably 250 ° C to 280 ° C.
The stretching ratio in the width direction is preferably 10 to 100 times, more preferably 12 to 90 times, still more preferably 15 to 70 times, and particularly preferably 20 to 40 times. The stretching temperature in the width direction is preferably 100 ° C to 300 ° C, more preferably 200 ° C to 290 ° C, and particularly preferably 250 ° C to 280 ° C.
The area stretch ratio is preferably 50 times to 300 times, more preferably 75 times to 280 times, and still more preferably 100 times to 260 times. When stretching, 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 higher than the stretching temperature and lower than the melting point of the crystalline polymer fired body.

<Crystalline polymer microporous membrane>
One feature of the crystalline polymer microporous membrane produced by the method for producing a crystalline polymer microporous membrane of the present invention is that the in-plane distribution of the average pore diameter is uniform.
Further, the in-plane variation of the average pore diameter of the crystalline polymer microporous membrane is preferably 20% or less, more preferably 15% or less. When the variation rate exceeds 20%, the variation in pore diameter is too large, and the trapped particle diameter may increase.
Here, the in-plane distribution of the average pore diameter can be evaluated by the following method using a bubble point measurement value. A syringe holder with a diameter of 13 mm was used, IPA was used as the wetting liquid, and the initial bubble point value (corresponding to the maximum pore diameter) was taken as the measurement value. The microporous membrane is cut out into a square with a side of 200 mm, the inside of the square is divided into 100 equal parts with a square with a side of 20 mm, and bubble points are measured for each part to obtain an average value and a variation rate.
The rate of variation is represented by the ratio of the standard deviation to the average value of the measured values. When the average value of n pieces of data (X1, X2,... Xn) is Xm and the standard deviation is Sx, the variation rate Vx can be calculated by the following equation.
Fluctuation rate [%]; Vx = Sx / Xm × 100

One feature of the crystalline polymer microporous membrane of the present invention is that the average pore size of the non-heated surface is larger than the average pore size of the heated surface.
The crystalline polymer microporous membrane has a thickness of “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.
The crystalline polymer microporous membrane preferably has a ratio of the average pore diameter between the non-heated surface and the heated surface (non-heated surface / heated surface ratio) of 5 to 30 times, more preferably 10 to 25 times. 15 to 20 times is more preferable.

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

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

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

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

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

  The 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.

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

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

The 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.

Example 1
<Preparation of crystalline polymer microporous membrane>
-Production of semi-baked film-
100 parts by mass of polytetrafluoroethylene fine powder (Daikin Industries, Ltd., “Polyflon Fine Powder F104U”) having a number average molecular weight of 6.2 million, and hydrocarbon oil (Esso Petroleum Corporation, “Isopar”) as an extrusion aid ) 27 parts by mass was added, and paste extrusion was performed in a round bar shape. This was calendered at a speed of 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, and a polytetrafluoroethylene unfired film having an average thickness of 100 μm, an average width of 150 mm, and a specific gravity of 1.55 was produced.
A heated roll in which one surface (heated surface) of the obtained polytetrafluoroethylene unfired film was heated to 345 ° C. (“Induction heat generation type high temperature high speed calender machine (installed in Yuri Roll Co., Ltd.)” manufactured by Yuri Roll Co., Ltd. A semi-baked film was prepared by heating for 1 minute with an induction heat generating metal roll mounted on the substrate. When the temperature distribution in the width direction in the steady state of the heating roll used at this time (the temperature variation of 10 seconds in the temperature measurement at intervals of 0.1 seconds is within 1 ° C.) was measured by infrared thermography, the maximum temperature region was measured. And the temperature difference between the minimum temperature region was 1.0 ° C.

  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 20 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 200 times in terms of stretched area ratio. Thus, the polytetrafluoroethylene microporous membrane of Example 1 was produced.

(Example 2)
In Example 1, the polytetrafluoroethylene microporous membrane of Example 2 was produced in the same manner as in Example 1 except that the temperature difference between the maximum temperature part and the minimum temperature part of the heating roll was 3 ° C. did.

(Comparative Example 1)
-Fabrication of crystalline polymer microporous membrane-
In Example 1, a polytetrafluoroethylene microporous membrane of Comparative Example 1 was produced in the same manner as in Example 1 except that the heating roll was changed to the oil circulation type. When the temperature distribution in the width direction in the steady state of the roll used at this time was measured by infrared thermography, the temperature difference between the maximum temperature portion and the minimum temperature portion was 7.0 ° C.

(Comparative Example 2)
In Example 1, a polytetrafluoroethylene microporous membrane of Comparative Example 2 was produced in the same manner as in Example 1 except that an oven at 345 ° C. was used instead of the heating roll.

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

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

<Measurement of P1 / P2>
About each polytetrafluoroethylene microporous film | membrane of Examples 1-2 and Comparative Examples 1-2, the film thickness of a microporous film | membrane is set to "10" in the thickness part of the depth direction "1" from a non-heating surface. P1 / P2 was determined when the average pore diameter was P1 and the average pore diameter of the thickness portion of “9” was P2.
Here, the average pore size of the PTFE microporous membrane was measured with a scanning electron microscope (Hitachi S-4000 type, vapor deposition was Hitachi E1030 type, both manufactured by Hitachi, Ltd.) and a photograph of the membrane surface (SEM photograph, magnification 1,000). 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), an image consisting only of polytetrafluoroethylene fibers was obtained, and the average pore size was determined by processing the image.

From the results of Table 1, in each of the PTFE microporous membranes of Examples 1-2 and Comparative Examples 1-2, the average pore size of the non-heated surface is larger than the average pore size of the heated surface, and from the non-heated surface to the heated surface. It was found that the average pore diameter continuously changed.
In contrast, in the PTFE microporous membrane of Comparative Example 2, the average pore diameter of the non-heated surface is substantially the same as the average pore diameter of the heated surface, and the average pore diameter does not change from the non-heated surface toward the heated surface. I understood.

<Filtration test>
Next, the filtration test was done about each PTFE microporous membrane of Examples 1-2 and Comparative Examples 1-2. First, an aqueous solution containing 0.01% by mass of polystyrene latex (average particle size 0.17 μm) was filtered at a differential pressure of 0.1 kg / cm ² . The results are shown in Table 2.

From the results of Table 2, the PTFE microporous membrane of Comparative Example ² was substantially clogged at 500 ml / cm ² .
On the other hand, it was found that the PTFE microporous membranes of Examples 1 and 2 and Comparative Example 1 can be filtered up to 1200 ml / cm ² , and the filtration life is greatly improved.

<Measurement of pore size distribution>
In-plane pore size distribution measurement was performed on the PTFE microporous membranes of Examples 1-2 and Comparative Examples 1-2. The pore diameter was evaluated by a bubble point measurement value by the following method. A syringe holder with a diameter of 13 mm was used, IPA was used as the wetting liquid, and the initial bubble point value (corresponding to the maximum pore diameter) was taken as the measurement value. The microporous membrane was cut into a square with a side of 200 mm, and the inside of the square was divided into 100 equal parts with a square with a side of 20 mm, and bubble points were measured for each part to obtain an average value and a variation rate. The results are shown in Table 3.
The rate of variation is represented by the ratio of the standard deviation to the average value of the measured values. When the average value of n pieces of data (X1, X2,... Xn) is Xm and the standard deviation is Sx, the variation rate Vx can be calculated by the following equation.
Fluctuation rate [%]; Vx = Sx / Xm × 100

From the results of Table 3, in Examples 1 and 2, by using a heating roll having a uniform temperature distribution, semi-firing by heating is uniformly performed, and the in-plane variation of the average pore diameter after stretching is small and uniform, The effect of the present invention was confirmed. On the other hand, in Comparative Example 1, since the temperature distribution of the roll was non-uniform, the semi-firing by heating was non-uniform, and the in-plane variation of the average pore diameter after stretching was large.

<Particle capture ability test>
About each microporous film | membrane of Examples 1-2 and Comparative Examples 1-2, the aqueous solution containing 0.01 mass% of polystyrene microparticles | fine-particles (average particle size 0.9 micrometer) is filtered as a differential pressure of 0.1 kg / cm < ² >. Went. The presence or absence of particle leakage was evaluated. The results are shown in Table 4.

From the results of Table 4, since the PTFE microporous membranes of Examples 1 and 2 had small variation in average pore diameter, there was no particle leakage and excellent particle capturing ability. On the other hand, the PTFE microporous membrane of Comparative Example 1 had a large average pore size variation, and therefore had particle leakage and poor particle capturing ability.

(Example 3)
-Filter cartridge-
The PTFE microporous membrane of Example 1 was sandwiched between two polypropylene non-woven fabrics, pleated to a pleat width of 10.5 mm, 138 folds were taken and rounded into a cylindrical shape, and the seam was impulse sealer Weld with. Both ends of the cylinder were cut off by 2 mm, and the cut surfaces were heat welded to a polypropylene end plate to finish an element exchange type filter cartridge.
The filter cartridge of the present invention is excellent in solvent resistance because the built-in crystalline polymer microporous film uses a crystalline polymer. Further, since the in-plane distribution of the average pore diameter is uniform and the hole portion has an asymmetric structure, the flow rate is large and clogging is not likely to occur, resulting in a long life.

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

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)

One surface of a film made of a crystalline polymer is heated in contact with a heating roll having a temperature distribution (maximum temperature-minimum temperature) of 5 ° C. or less in the width direction of the roll, whereby the temperature in the thickness direction of the film is increased. An asymmetric heating step to form a semi-baked film with a gradient;
A stretching step of stretching the semi-baked film;
A method for producing a crystalline polymer microporous membrane, comprising:   The method for producing a crystalline polymer microporous membrane according to claim 1, wherein the heating roll is an induction heating roll.   The method for producing a crystalline polymer microporous membrane according to claim 1, wherein the crystalline polymer is polytetrafluoroethylene.   The method for producing a crystalline polymer microporous membrane according to any one of claims 1 to 3, wherein the stretching step stretches the semi-fired film in a uniaxial direction.   The method for producing a crystalline polymer microporous membrane according to any one of claims 1 to 3, wherein the stretching step stretches the semi-fired film in the biaxial direction.   6. A method for producing a crystalline microporous membrane according to claim 1, wherein an average pore diameter of one surface is larger than an average pore diameter of the other surface, and said one surface is A crystalline polymer microporous membrane characterized in that the average pore diameter continuously changes toward the surface.   The crystalline polymer microporous membrane according to claim 6, wherein the in-plane variation of the average pore diameter is 20% or less.   A filtration filter comprising the crystalline polymer microporous membrane according to any one of claims 6 to 7.   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 of the crystalline polymer microporous membrane having a large average pore diameter is used as a filter surface of the filter.