JP2009119416A - Microfiltration filter and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a microfiltration filter which can effectively remove a solid component coexisting in fluid to be filtered and a gelatinous component having a particle size substantially smaller than the pore size of a filtration film of the lowermost stream side filtration film for removing the solid component by disposing only one sheet of microporous film made of a crystalline polymer having an asymmetric porous structure, can improve flux and life by reducing film thickness, thereby, can be used even for large equipment, can reduce the number of times of replacement of a cartridge to reduce expenses and time required for maintenance and can improve the yield when being used for semiconductor manufacturing processes, and to provide a manufacturing method thereof. <P>SOLUTION: The microfiltration filter is assembled by laminating the microporous film of monolayer structure made of a crystalline polymer having asymmetric porous structure and a polyolefin filtration layer. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a microfiltration filter and a method for producing the same, and more particularly to a microfiltration filter for effectively removing a component to be filtered from a fluid to be filtered containing a gel component and a method for producing the same.

  Since the photoresist in the manufacturing process contains a solid component and a gel component, it must be removed. In general, a filter element using PTFE (polytetrafluoroethylene, ie, polytetrafluoroethylene) as a filter membrane material is effective for filtering solid foreign matters, but in order to remove gel-like components, it is necessary to make the pore diameter extremely fine. Since a large operating pressure is required at the time of filtration, the filtration efficiency was lowered. On the other hand, it is known that filter elements made of polyolefin filtration membranes are effective for filtering gel-like foreign substances. For this reason, conventionally, by using a filter element made of PTFE as a filter membrane material and a filter element made of a polyolefin filter membrane material typified by polyethylene, respectively, the photoresist is subjected to multi-stage filtration. The solid component and the gel component are removed.

  As described above, since the foreign matters in the photoresist are removed by multi-stage filtration, the filtration process must be complicated. For this reason, it is difficult not only to maintain and inspect the filtration apparatus but also to improve the filtration efficiency.

  Further, the PTFE filtration layer is formed by laminating a plurality of PTFE filtration membranes, and among the plurality of PTFE filtration membranes, at least a pair of PTFE filtration membranes is a multilayer filter element having a different pore diameter for each PTFE filtration membrane. (For example, Patent Document 1).

However, this multilayer filter element has to be laminated with a plurality of PTFE filtration membranes, resulting in problems such as a large film thickness, a low flow rate, and a short life.
In addition, since it is necessary to laminate a plurality of PTFE filtration membranes in this laminated filter element, there is a concern about peeling of the PTFE filtration membrane, and there is a problem of durability.

JP 2001-340732 A

  An object of the present invention is to solve the conventional problems and achieve the following objects. That is, the present invention provides a solid component mixed in the fluid to be filtered and the most downstream filtration membrane for removing the solid component by providing only one microporous membrane made of a crystalline polymer having an asymmetric pore structure. The gel-like component having a diameter substantially smaller than the pore diameter can be effectively removed, the film thickness can be reduced and the flow rate and life can be improved. An object of the present invention is to provide a microfiltration filter that can reduce the number of replacements and reduce maintenance costs and time, and can improve yield by using it in a semiconductor manufacturing process, and a manufacturing method thereof. .

  The gel component having a diameter substantially smaller than the pore diameter of the most downstream filtration membrane for removing the solid component is equal to or smaller than the diameter at which the gel component can be deformed and passed through the pore diameter of the most downstream filtration membrane for solid component removal. The pore diameter is measured by the bubble point test method of JIS K 3832 microfiltration membrane element and module, and the pore diameter measured by the bubble point when bubbles from the entire surface of the filter are recognized, that is, In practice, this means the average pore diameter.

  As long as the fluid to be filtered processed by the microfiltration filter is a fluid containing a solid component and a gel component having a diameter substantially smaller than the pore size of the most downstream filtration membrane for removing the solid component, It is not limited to resist.

Means for solving the problems are as follows. That is,
<1> A microfiltration filter in which a microporous membrane having a single layer structure made of a crystalline polymer having an asymmetric pore structure and a polyolefin filtration layer are laminated and incorporated.
<2> The microfiltration filter according to <1>, wherein the microporous membrane is disposed on the upstream side with respect to the flow of the fluid to be filtered, and the polyolefin filtration layer is disposed on the downstream side with respect to the flow of the fluid to be filtered.
<3> The microfiltration filter according to any one of <1> to <2>, wherein the crystalline polymer is polytetrafluoroethylene.
<4> The above <1> to <3>, wherein the microporous membrane has an average pore size on the surface of the membrane larger than the average pore size on the back surface, and the average pore size continuously changes from the front surface to the back surface. The microfiltration filter according to any one of the above.
<5> The microfiltration membrane according to <4>, wherein the surface of the microporous membrane is disposed upstream with respect to the flow of the fluid to be filtered, and the back surface of the microporous membrane is disposed downstream with respect to the flow of the fluid to be filtered. It is.
<6> The method for producing a microfiltration filter according to any one of <1> to <5>, wherein the back surface of the unfired film is heated to form a temperature gradient in the thickness direction of the microporous film. It is a manufacturing method of the microfiltration filter characterized by including a baking process.

According to the present invention, the conventional problems can be solved and the object can be achieved, and the gel component is contained only by providing one microporous film made of a crystalline polymer having an asymmetric pore structure. Effectively removes the components to be filtered from the fluid to be filtered, thus reducing the film thickness and improving the flow rate and lifespan, so that it can be applied to large facilities and the number of cartridge replacements is reduced. Thus, it is possible to provide a microfiltration filter that can reduce the cost and time required for maintenance, and can improve the yield when used in a semiconductor manufacturing process, and a manufacturing method thereof.
Moreover, since the microfiltration filter of this invention has the characteristics that a filtration function is high and it is long-life, a filtration apparatus can be put together compactly. 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 microfiltration filter of the present invention is used, the number of filtration units used in parallel is greatly increased. Can be reduced.

  Hereinafter, the microfiltration filter of the present invention and the manufacturing method thereof will be described.

(Microfiltration filter)
The microfiltration filter includes a microporous membrane having a single layer structure and a polyolefin filtration layer, and further includes other films (membranes) appropriately selected as necessary.

  In the microfiltration filter, it is preferable that the microporous membrane is disposed upstream with respect to the flow of the fluid to be filtered, and the polyolefin filtration layer is disposed downstream with respect to the flow of the fluid to be filtered. The surface with the larger hole diameter is disposed on the upstream side, and the back surface with the smaller hole diameter is disposed on the downstream side.

  In addition, the microporous membrane and the polyolefin filtration layer are preferably arranged so that the pore diameter decreases continuously and / or stepwise from the upstream side to the downstream side with respect to the flow of the fluid to be filtered. In the microfiltration filter having such a configuration, the solid component and the gel component in the fluid to be filtered can be simultaneously filtered, and the operating pressure during filtration can be greatly reduced.

  Furthermore, the microfiltration filter of the present invention may be processed into a pleated cartridge or a flat membrane laminated cartridge, but is preferably processed into a pleated shape. Processing into a pleated shape has the advantage that the effective surface area used for filtering the filter per cartridge can be increased.

<Microporous membrane>
The microporous membrane is not particularly limited as long as it is made of a crystalline polymer having an asymmetric pore structure, and can be appropriately selected according to the purpose. The crystalline polymer is polytetrafluoroethylene. It is preferable.

One feature of the microporous membrane is that the average pore diameter on the front surface is larger than the average pore diameter on the back surface. The average pore diameter here is measured by the following method. That is, a film surface photograph (SEM photograph, magnification 1,000 to 5,000 times) is taken with a scanning electron microscope (Hitachi S-4000 type, vapor deposition is Hitachi E1030 type), and the obtained photograph is used as an image processing apparatus. (Main body name: Nippon Avionics Co., Ltd. TV image processor TVIP-4100II, control software name: Ratok System Engineering Co., Ltd. TV image processor image command 4198) to obtain an image consisting only of fibers and compute the image By doing so, the average pore diameter is obtained.
In the microporous membrane, the ratio of the average pore diameter of the front surface and the back surface (surface / back surface ratio) is preferably 5 to 30 times, more preferably 10 to 25 times, and 15 to 20 times. Is more preferable.

  In the present application, the surface having the larger average pore diameter is referred to as “front surface”, and the surface having the smaller average pore diameter is referred to as “back surface”, but this is for convenience of explanation of the present invention. It's just a name given to. Therefore, any surface of the unsintered crystalline polymer film used in the manufacturing method described later may be made “surface” after semi-firing.

  In addition to the above characteristics, the microporous membrane 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. In addition, both of the aspects (second aspect) characterized by a single layer structure are also 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 a distance d (corresponding to the depth from the surface) in the thickness direction 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, the region is composed only of a negative slope region (dD / dt <0).

  It is preferable that at least the surface of the film is included in the region having a negative inclination. In the region where the slope is negative (dD / dt <0), the slope may always be constant or different. For example, when the microporous film is composed only of a negative slope region (dD / dt <0), the dD / dt on the back surface of the film is larger than the dD / dt on the film surface. Can do. 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” referred to 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 microporous membrane preferably has both the features of the first aspect and the second aspect. 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 microporous membrane is preferably 1 to 300 μm, more preferably 5 to 100 μm, and further preferably 10 to 80 μm.

  In particular, when the microporous membrane has a membrane surface thickness of 10, an average pore diameter in the depth direction 1 portion from the surface is P1, and a pore diameter of 9 is P2, P1 / P2 is 2 to 10, Is preferably in the range of 000, and more preferably in the range of 3 to 100.

  Since the microporous membrane has a large specific surface area, fine particles introduced from the surface thereof are removed by adsorption or adhesion before reaching the minimum pore diameter portion. Therefore, clogging hardly occurs and high filtration efficiency can be maintained over a long period of time.

<< Crystalline polymer >>
The crystalline polymer represents 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 a resin exhibits 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.
Examples of such crystalline polymers include polyalkylenes, polyesters, polyamides, polyethers, liquid crystalline polymers, polyethylene, polypropylene, nylon, polyacetal, polybutylene terephthalate, polyethylene terephthalate, syndiotactic polystyrene, Examples thereof include polyphenylene sulfide, polyether ether ketone, wholly aromatic polyamide, wholly aromatic polyester, fluororesin, and polyether nitrile.
Among them, in the present invention, from the viewpoint of chemical resistance and handling properties, polyalkylenes (for example, polyethylene and polyethylene), in particular, fluorine-based polysiloxanes in which hydrogen atoms of the alkylene group are partially or completely substituted by fluorine atoms. Alkylene is preferably used, and polytetrafluoroethylene is particularly preferably used among them.
In the case of polyethylene, it is well known that the density changes depending on the degree of branching. Usually, those having a high degree of branching and low crystallinity are classified as low density polyethylene (LDPE), and those having a low degree of branching and high crystallinity are classified as high density polyethylene (HDPE). Can also be used. Of these, HDPE is preferred from the viewpoint of crystallinity control.

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

<< Method for Producing Microporous Membrane >>
Next, a method for producing the microporous membrane will be described. In the following, description will be made with specific reference to preferable manufacturing steps of the microporous membrane, but the microporous membrane is not limited to those manufactured by these specific manufacturing methods. Absent.

In producing the microporous membrane, it is preferable to produce a crystalline polymer unfired film first.
The kind of the crystalline polymer raw material used when producing the crystalline polymer green film is not particularly limited, and the above-described crystalline polymer can be preferably used. In particular, polyethylene or a crystalline polymer in which a hydrogen atom is substituted with a fluorine atom is used, and polytetrafluoroethylene is particularly preferably used.
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.
In particular, in the method for producing the microporous membrane, 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 usually 2,500,000 to 10,000,000, preferably 3,000,000 to 8,000,000. A polytetrafluoroethylene raw material sold in the market as a polytetrafluoroethylene raw material may be appropriately selected and used. For example, “Polyflon Fine Powder F104U” manufactured by Daikin Industries, Ltd. can be preferably used.

  In the present invention, it is preferable to prepare a film by preparing a mixture obtained by mixing a 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 Petroleum Corporation sold in the market may be used. The extrusion aid is preferably used in an amount of 20 to 30 parts by mass with respect to 100 parts by mass of the crystalline polymer.

  Paste extrusion is usually performed at 50 to 80 ° C. The extrusion shape is not particularly limited, but usually it is preferably a rod shape. 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 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 usually 40 to 400 ° C, preferably 60 to 350 ° C. In particular, when tetrafluoroethylene is used, the temperature is usually set to 150 to 280 ° C, preferably 200 to 255 ° C. The heating can be performed by a method such as passing the film through a hot air drying furnace. The thickness of the crystalline polymer unfired film thus produced is appropriately adjusted according to the thickness of the microporous film made of the crystalline polymer to be finally produced. When stretching is performed in a later step, 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 matters described in Polyflon Handbook (Daikin Co., Ltd., revised in 1983) can be appropriately employed.

In the method for producing the microporous film, the crystalline polymer green film is semi-fired. In the present application, 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 application, an unsintered body of a crystalline polymer means one not subjected to a heat treatment for firing. The melting point means the temperature of the peak of the endothermic curve 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, etc., but are usually 50 to 450 ° C., preferably 80 to 400 ° C.
Such a temperature can be considered as follows. That is, for example, in the case of polytetrafluoroethylene, the sintered body has a melting point of about 324 ° C. and the unfired body has a melting point of about 345 ° C. Therefore, in the case of a polytetrafluoroethylene film, it is heated to a temperature of about 327 to 360 ° C, preferably 335 to 350 ° C, for example, 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.

  Semi-baking is performed by a method in which thermal energy is applied to the surface of the unfired film to form a temperature gradient in the thickness direction of the film and / or a method in which more thermal energy is supplied to the surface of the film than the back surface. By performing the semi-firing under such conditions, the degree of firing can be controlled asymmetrically in the thickness direction, and the microporous film made of the crystalline polymer according to the first aspect of the present invention is easily produced. be able to. Regarding the degree of firing here, reference can be made to the description of JP-A-5-202217.

  Further, as the temperature gradient in the thickness direction of the film, the temperature difference between the front surface and the back surface is 30 ° C. or higher, preferably 50 ° C. or higher.

  Regarding the supply of thermal energy, either a method of supplying continuously during the process of the present invention or a method of supplying energy intermittently divided into several times can be adopted. According to the definition of the semi-baking step, it is necessary to cause a difference in temperature between the front and back of the film surface. As this method, a method of suppressing temperature increase on the back surface by supplying energy intermittently can be used. . On the other hand, in the case of continuous heating, in order to maintain this temperature gradient, a method of cooling the back surface simultaneously with the heating of the front surface can be used effectively.

  As a method for supplying thermal energy, various methods such as a method of blowing hot air, a method of contacting with a heating medium, a method of contacting with a heated material, a method of irradiating heat rays, heating by electromagnetic waves such as microwaves can be used. This method is not particularly limited, but is preferably performed by bringing a heated product into contact with the surface of the film. It is particularly preferable to select a heating roll as the heated product. If it is a heating roll, the semi-firing can be carried out continuously in a flow operation industrially, and temperature control and maintenance of the apparatus are easy. The temperature of the heating roll can be set to the temperature at which the semi-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.

  Conversely, when carrying out the step of cooling the back surface, various methods such as a method of blowing cold air, a method of contacting with a refrigerant, a method of contacting with a cooled material, and cooling by standing cooling can be used. Although this method is not particularly limited, it is preferably performed by bringing a coolant into contact with the surface of the film. It is particularly preferable to select a cooling roll as the cooling object. If it is a cooling roll, like the heating of the surface, the semi-firing can be carried out continuously in a flow operation industrially, and the temperature control and the maintenance of the apparatus 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 the time necessary for the intended half-firing to sufficiently proceed, and is usually 30 seconds to 120 seconds, assuming that the film is simultaneously performed with the heating step. Preferably, it is 45 seconds to 90 seconds, and more preferably 60 seconds to 80 seconds.

  The surface material of the heating and cooling rolls can be stainless steel, which is generally excellent in durability, and particularly SUS316. In the production method of the present invention, the surface of the film is preferably brought into contact with the heating and cooling rolls, but a roller set at a temperature lower than that of the heating and cooling rolls may be brought into contact with the back surface of the film. For example, a roller maintained at room temperature may be pressed from the back side of the film to fit the film to the heating roll. Moreover, you may make the back surface of a film contact a guide roll before or after making it contact with a heating roll.

  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.

  In the case of sequentially stretching in the longitudinal direction and the width direction, it is preferable to first stretch in the longitudinal direction and then stretch in the width direction. The draw ratio in the longitudinal direction is usually 4 to 100 times, preferably 8 to 90 times, more preferably 10 to 80 times. The stretching temperature in the longitudinal direction is usually 100 ° C to 300 ° C, preferably 200 ° C to 290 ° C, more preferably 250 ° C to 280 ° C. The draw ratio in the width direction is usually 10 to 100 times, preferably 12 to 90 times, more preferably 15 to 70 times, and particularly preferably 20 to 40 times. The stretching temperature in the width direction is usually 100 ° C to 300 ° C, preferably 200 ° C to 290 ° C, more preferably 250 ° C to 280 ° C. The area stretch ratio is usually 50 to 300 times, preferably 75 to 280 times, more preferably 100 to 260 times. When stretching, the film may be preheated to a temperature below the stretching temperature.

After stretching, heat setting can be performed as necessary. The heat setting temperature is usually higher than the stretching temperature and lower than the melting point of the crystalline polymer fired body.
Moreover, after heat setting, it can hydrophilize as needed. The hydrophilization is performed, for example, by immersing a microporous film previously impregnated with ethanol in hydrogen peroxide water and irradiating ArF excimer laser light (193 nm) from above the pulled microporous film.

-Hydrophilization process-
The hydrophilization step is a step of hydrophilizing the stretched film.
Examples of the hydrophilization treatment include (1) a treatment in which a stretched film is impregnated with an aqueous solution of hydrogen peroxide or a water-soluble organic solvent and then irradiated with an ultraviolet laser, and (2) a chemical etching treatment. It is done.

Examples of the water-soluble organic solvent that can be used for the treatment of irradiating an ultraviolet laser after impregnating the stretched film of (1) with an aqueous solution of hydrogen peroxide or a water-soluble organic solvent include ethers (for example, tetrahydrofuran). 1,4-dioxane, ethylene glycol monoalkyl ether, ethylene glycol dialkyl ether, diethylene glycol monoalkyl ether and diethylene glycol dialkyl ether), ketones (for example, acetone, methyl ethyl ketone, cyclohexanone, diacetyl and acetylacetone, etc.), alcohols (methanol) , Ethanol, propanol, hexyl alcohol, ethylene glycol, isopropyl alcohol, butanol, ethylene chlorohydrin, glycerin, etc.), aldehydes (for example, Acetaldehyde, propionaldehyde, etc.), amines (e.g., triethylamine, piperidine, etc.) and esters (e.g., methyl acetate, ethyl acetate, etc.) and the like.
Of these, ketones are preferred, acetone and methyl ethyl ketone are more preferred, and acetone is particularly preferred. The concentration of the hydrogen peroxide solution or water-soluble organic solvent at the stage of impregnating the crystalline polymer microporous membrane varies slightly depending on the material of the crystalline polymer microporous membrane and the size of the pores. In the case, it is preferably 85% by mass to 100% by mass. The concentration of the hydrogen peroxide solution or the water-soluble organic solvent in the crystalline polymer microporous film upon irradiation with ultraviolet laser light is preferably 0.1 to 10 as the absorbance at the wavelength of the ultraviolet laser light to be used. For example, in the case of acetone, when KrF is used as a light source, it corresponds to 0.05 mass% to 5 mass%. The absorbance is preferably 0.1 to 6, and more preferably 0.5 to 5. When irradiating a crystalline polymer microporous film containing hydrogen peroxide solution or water-soluble organic solvent adjusted to this concentration range with ultraviolet laser light, the hydrophilicity that should already be satisfied with a considerably lower irradiation dose than before. Effect can be obtained.

  In general, when a water-soluble organic solvent having a boiling point of 50 ° C. to 100 ° C. is used, the hydrophilization treatment efficiency by ultraviolet laser irradiation is high and the solvent removal after the hydrophilization treatment is easy, but the boiling point is 100 When a water-soluble organic solvent having a temperature higher than 0 ° C. is used, it is difficult to remove the water-soluble organic solvent after the hydrophilic treatment.

Crystalline polymer impregnated with water-soluble organic solvent in order to obtain a uniform and high hydrophilization effect when irradiating the crystalline polymer microporous membrane impregnated with water-soluble organic solvent with ultraviolet laser light The polymer microporous membrane is impregnated with water, and the concentration of the water-soluble organic solvent aqueous solution in the crystalline polymer microporous membrane is 0.1 to 10, preferably 0.1, at the wavelength of the ultraviolet laser light to be used. -6, particularly preferably adjusted to 0.5-5. When the absorbance is lower than 0.1, it may be difficult to obtain a sufficient hydrophilization effect. When the absorbance is higher than 10, absorption of light energy by the aqueous solution increases, and sufficient hydrophilicity to the inside of the micropores is obtained. May be difficult.
In order to adjust the concentration of the water-soluble organic solvent aqueous solution in the crystalline polymer microporous membrane, it is preferable to immerse in a very low concentration aqueous solution of the same water-soluble organic solvent.
Here, the absorbance means an amount defined by the following formula.
Absorbance ≡log ₁₀ (I ₀ / I) = εcd
Where ε is the extinction coefficient of the water-soluble organic solvent, c is the concentration of the aqueous water-soluble organic solvent solution (mol / dm ³ ), d is the transmitted light path length (cm), I ₀ is the light transmission intensity of the solvent alone, and I is It represents the light transmission intensity of the solution. In the present invention, the concentration at which the absorbance is x means a concentration at which the absorbance is x when d is measured in a measurement cell having 1 cm. However, if the concentration is so high that the amount of transmitted light is too small when d is 1 cm and it is difficult to measure the absorbance, the absorbance obtained by multiplying the absorbance obtained by using a measuring cell with d of 0.2 cm is 5 times. It was.

The method for impregnating the crystalline polymer microporous membrane with the aqueous solution of hydrogen peroxide or water-soluble organic solvent is not particularly limited and may be appropriately selected depending on the intended purpose. A method or the like may be appropriately employed depending on the form or size of the crystalline polymer microporous membrane, but an immersion method is common.
The impregnation temperature of the hydrogen peroxide solution or the water-soluble organic solvent or an aqueous solution thereof is preferably 10 ° C. to 40 ° C. from the viewpoint of the diffusion rate of the aqueous solution into the micropores of the crystalline polymer microporous membrane. When the impregnation temperature is lower than 10 ° C, a relatively long time is required to sufficiently diffuse the aqueous solution into the micropores. When the impregnation temperature is higher than 40 ° C, the evaporation rate of the water-soluble organic solvent is increased. It is not preferable.

The crystalline polymer microporous membrane subjected to the impregnation treatment is subjected to the following ultraviolet laser light irradiation treatment after adjusting the concentration of the impregnated hydrogen peroxide solution or water-soluble organic solvent to the above range.
As the ultraviolet laser light, those having a wavelength of 190 nm to 400 nm or less are preferable, and examples include argon ion laser light, krypton ion laser light, N ₂ laser light, dye laser light, and excimer laser light. Is preferred. Among these, KrF excimer laser light (wavelength: 248 nm), ArF excimer laser light (wavelength: 193 nm), and XeCl excimer laser light (308 nm) that can stably obtain a high output for a long time are particularly preferable.
The excimer laser light irradiation is usually performed at room temperature in the air, but is preferably performed in a nitrogen atmosphere. The irradiation conditions of excimer laser light depend on the type of fluororesin and the desired degree of surface modification, but general irradiation conditions are as follows.
・ Fluence: 10 mJ / cm ² / pulse or more ・ Incoming energy: 0.1 J / cm ² or more

Particularly suitable irradiation conditions for KrF excimer laser light, ArF excimer laser light, and XeCl excimer laser light are as follows.
KrF fluence: 50 to 500 mJ / cm ² / pulse incident energy: 0.25 to 10.0 J / cm ²
ArF fluence: 10 to 500 mJ / cm ² / pulse incident energy: 0.1 to 10.0 J / cm ²
XeCl fluence: 50 to 600 mJ / cm ² / pulse incident energy: 3.0 to 100 J / cm ²

Examples of the chemical etching treatment (2) include an oxidative decomposition treatment in which an alkali metal is used to modify the fluororesin constituting the crystalline polymer microporous membrane and remove the modified portion.
The oxidative decomposition treatment is performed using, for example, an organic alkali metal solution. When the crystalline polymer microporous film is subjected to a chemical etching treatment with an organic alkali metal solution, the surface is modified to impart hydrophilicity, and a browned layer (brown layer) is formed. This brown layer is composed of sodium fluoride, a decomposition product of a fluororesin having a carbon-carbon double bond, a polymer of these with naphthalene, anthracene, etc., but these are separated into the filtrate by dropping, decomposition, elution or the like. Since it may mix, it is preferable to remove. These can be removed by oxidative decomposition with hydrogen peroxide, sodium hypochlorite, ozone, or the like.

The chemical etching treatment can be performed using an organic alkali metal solution or the like, and specifically, can be performed by immersing a crystalline polymer microporous film in the organic alkali metal solution. In this case, since the chemical etching process is performed from the surface side of the crystalline polymer microporous film, it is possible to perform the chemical etching process only on the vicinity of both surfaces of the film. However, in order to further increase the water retention of the film, it is preferable to perform a chemical etching treatment not only near both surfaces but also inside the crystalline polymer microporous film. Even when the chemical etching treatment is applied to the inside of the crystalline polymer microporous membrane, the function as a separation membrane is not significantly lowered.
Examples of the organic alkali metal solution used for the chemical etching treatment include an organic solvent solution such as methyllithium, a metal sodium-naphthalene complex, a metal sodium-anthracene complex in tetrahydrofuran, a metal sodium-liquid ammonia solution, and the like. Among these, a solution of a complex with metal sodium having naphthalene as an aromatic anion radical is generally widely used. However, in order to perform chemical etching treatment to the inside of the crystalline polymer microporous film, benzophenone is used. Anthracene and biphenyl are preferably used as aromatic anion radicals.

<Polyolefin filtration layer>
The polyolefin filtration layer is constituted by a polyolefin filtration membrane. In addition, the said polyolefin filtration layer can also be comprised with a single polyolefin filtration membrane.

  As the polyolefin filtration membrane, a porous membrane and / or a microporous membrane formed from a polyolefin such as polypropylene, polyethylene having a low molecular weight to an ultra high molecular weight and polyethylene mixed with them can be applied. It has the property of capturing the gel component more effectively than the crystalline polymer microporous membrane.

  Moreover, the polyolefin filtration membrane can apply the thin film by the phase-separation method, or the thin film by the extending | stretching method, and can make a hole diameter into 0.1-1.0 micrometer.

  Moreover, a plurality of polyolefin filtration membranes made of polyolefin as a filtration membrane material are laminated to constitute a polyolefin filtration layer, and at least a pair of polyolefin filtration membranes among the plurality of polyolefin filtration membranes have different pore sizes for each polyolefin filtration membrane. It can be constituted as follows. At this time, of the at least one pair of polyolefin filtration membranes, the polyolefin filtration membrane having the larger pore diameter is arranged on the upstream side with respect to the flow of the fluid to be filtered, and the polyolefin filtration membrane having the smaller pore diameter with respect to the flow of the fluid to be filtered. It is desirable to arrange on the downstream side.

<Other films (membranes)>
The other film (film) is not particularly limited as long as the effects of the present invention are not impaired, and can be appropriately selected depending on the purpose. For example, you may arrange | position a nonwoven fabric in the upstream and downstream of a polyolefin filtration layer regarding the flow of to-be-filtered fluid.

  The non-woven fabric has a density gradient that increases from the upstream side to the downstream side of the fluid to be filtered (that has a reduced porosity gradient), that has a smaller fiber diameter, A fiber having a small fiber diameter while maintaining a suitable constant value is suitable, but a fiber having a uniform density and a thin fiber diameter, or a fiber having a constant fiber diameter can also be applied.

(Manufacturing method of microfiltration filter)
There is no particular limitation as long as it includes a semi-baking step of heating the back surface of the unfired film and forming a temperature gradient in the thickness direction of the microporous film, and can be appropriately selected according to the purpose, for example, Examples thereof include a stretching step for stretching the semi-baked film, a heat fixing step for heat fixing the stretched film, a hydrophilization step for hydrophilizing the heat fixed film, a cartridge processing step, and the like.

  Hereinafter, the present invention will be described specifically by way of examples. However, the present invention is not limited to this example.

Example 1
Polytetrafluoroethylene fine powder having a number average molecular weight of 6,200,000 (“Polyflon Fine Powder F104U” manufactured by Daikin Industries, Ltd.) and hydrocarbon oil (“Isopar M” manufactured by Esso Oil Co., Ltd.) as an extrusion aid. 27 parts by mass were added, paste extrusion was performed in a round bar shape, and this was calendered at a rate of 50 m / min with a calender roll heated to 70 ° C. to obtain 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 obtained.
The obtained unbaked film was baked for 1 minute with a roll (surface material: SUS316) heated to 345 ° C. to obtain a semi-baked film.

  The obtained semi-baked film was stretched between rolls 10 times in the longitudinal direction at 250 ° C. and once wound on a winding roll. Then, after preheating the film to 290 ° C., both ends were sandwiched between clips and stretched 20 times in the width direction at 250 ° C. Thereafter, heat setting was performed at 380 ° C. The area stretch ratio of the film was 180 times in terms of stretched area ratio. A polytetrafluoroethylene microporous membrane was produced by the above method.

(Cartridge processing)
A polypropylene non-woven fabric (Mitsui Petrochemical Syntex PK-110) is arranged on the primary side (upstream side), and the polytetrafluoroethylene microporous membrane is arranged on the secondary side (downstream side) of the polypropylene non-woven fabric. A polyethylene microporous membrane as a polyolefin filtration layer (manufactured by Akzo Nobel, pore diameter 0.1 μm, thickness 75 μm, porosity 61%) is provided on the secondary side (downstream side) of the polytetrafluoroethylene microporous membrane. The polypropylene non-woven fabric (Mitsui Petrochemical Syntex PK-110) was placed on the secondary side (downstream side), pleated and incorporated into a 10-inch pleated cartridge.

(Comparative Example 1)
As a polytetrafluoroethylene microporous membrane to be incorporated into a cartridge, a polytetrafluoroethylene microporous membrane produced in the same manner as in Example 1 was used instead of semi-firing using a roll in the production of a 345 ° C. oven. A membrane was used.

(Comparative Example 2)
Two (two types) polytetrafluoroethylene microporous membranes were used as the polytetrafluoroethylene microporous membranes to be incorporated into the cartridge. The first polytetrafluoroethylene microporous film disposed on the upstream side has an average pore diameter of 5.0 μm and a film thickness of 50 μm, and the second polytetrafluoroethylene microporous film disposed on the downstream side is The average pore diameter was 0.1 μm, and the film thickness was 50 μm.

(Evaluation)
In Example 1 and Comparative Example 1, when the film surface thickness of the microporous membrane was 10, the average pore diameter in the portion in the depth direction 1 from the surface was P1, and the pore diameter in the portion 9 was P2.
When P1 / P2 in each example was compared, Example 1 was P1 / P2 = 4.5. On the other hand, Comparative Example 1 was not an asymmetric film because P1 / P2 = 0.95 because semi-firing treatment by single-sided heating was not performed. Further, the minimum pore diameter portions of Example 1 and Comparative Example 1 were both 0.1 μm in pore diameter.

(Filtration life test)
The test liquid that is a fluid to be filtered was prepared by dissolving a phenol resin in toluene and adjusting the viscosity to about 15 mPa · s (15 cP).
In order to evaluate the filtration life of the cartridge (microfiltration filter), the test solution was filtered at a differential pressure of 0.1 kg / cm ² and the amount of filtration until clogging was measured. As a result, the cartridges (microfiltration filter) of Comparative Example 1 and Comparative Example 2 were substantially clogged at 50 ml / cm ² and 70 ml / cm ² , respectively, whereas the cartridge of Example 1 (microfiltration filter). Can be filtered up to 200 ml / cm ² , and it was demonstrated that the filter life was significantly improved by using the cartridge of Example 1 (microfiltration filter).
Moreover, in order to evaluate the cleanliness of the test liquid (filtrate) after filtration, the filtrate was filtered with a Nuclepore membrane having a pore diameter of 0.05 μm, and the amount of filtration per fixed time was measured. Example 1 and Comparative Example 1 There was almost no difference between the two cartridges (microfiltration filters), and both were clean.
Further, in order to evaluate the filtration flow rate of the cartridge (microfiltration filter) in the same test, the initial flow rate was evaluated. The cartridges (microfiltration filter) of Comparative Example 1 and Comparative Example 2 were each 50 ml / cm ^2. while there was a minute and 60 ml / cm ² · min, the cartridge (microfiltration filter) example 1 is 100 ml / cm ² · min, demonstrated that filtration flow to organic solvents is significantly improved It was done.

Further, in the cartridge (microfiltration filter) of Example 1 of the present invention, the thickness of the polytetrafluoroethylene microporous membrane, which is thin and difficult to handle, does not have to be laminated, and the polytetrafluoroethylene microporous membrane is 2 It can be produced more economically than the cartridge (microfiltration filter) of Comparative Example 2 using two sheets (two types).

Claims (6)

  A microfiltration filter incorporating a single-layer microporous membrane made of a crystalline polymer having an asymmetric pore structure and a polyolefin filtration layer.   The microfiltration filter according to claim 1, wherein the microporous membrane is disposed on the upstream side with respect to the flow of the fluid to be filtered, and the polyolefin filtration layer is disposed on the downstream side with respect to the flow of the fluid to be filtered.   The microfiltration filter according to claim 1, wherein the crystalline polymer is polytetrafluoroethylene.   The microporous membrane according to any one of claims 1 to 3, wherein the average pore size on the surface of the membrane is larger than the average pore size on the back surface, and the average pore size continuously changes from the front surface to the back surface. Microfiltration filter.   5. The microfiltration filter according to claim 4, wherein the surface of the microporous membrane is disposed on the upstream side with respect to the flow of the fluid to be filtered, and the back surface of the microporous membrane is disposed on the downstream side with respect to the flow of the fluid to be filtered.   It is a manufacturing method of the microfiltration filter in any one of Claim 1 to 5, Comprising: It includes the semi-baking process of heating the back surface of an unbaked film and forming a temperature gradient in the thickness direction of a microporous film. The manufacturing method of the microfiltration filter characterized.