JP5348517B2 - Separation membrane element and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separation membrane element made up of a porous fluororesin membrane which shows high filtration treatment capacity to an aqueous solution and is almost free from the deterioration of the treatment capacity, even in case a fluororesin membrane filter is exposed to a gas and the aqueous solution easily apt to be mingled with air bubbles, a dissolved gas, etc., is filtered, and to provide a method for easily manufacturing the separation membrane element. <P>SOLUTION: This separation membrane element is composed of a porous fluororesin membrane made up of an outer layer with not more than 70 kPa bubble point and an inner layer with not less than a 90 kPa bubble point. In addition, both surfaces of the porous fluororesin membrane with not less than the 90 kPa bubble point, are treated by the chemical etching process or surface roughening process with the help of a physical means. The manufacturing method of the separation membrane element is to perform the chemical etching treatment to both surfaces of the porous fluororesin membrane, following the arrangement of a plurality of pipes formed of the porous fluororesin membrane with not less than 90 kPa bubble point in a module case. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention is a separation membrane element that constitutes a filtration system suitable for removing fine particles by filtering an aqueous liquid (a solution comprising a solvent containing water as a main component; hereinafter referred to as “aqueous solution”). And a material using a fluororesin porous membrane as a material. The present invention also relates to a method for producing the separation membrane element.

  A porous membrane made of a fluororesin, particularly polytetrafluoroethylene (hereinafter referred to as “PTFE”), has a material characteristic inherent to the fluororesin itself, such as chemical resistance and heat resistance, and is uniform. In addition, it has structural features such as high resolution based on a fine porous structure and high permeability based on high porosity.

  In addition, since the fluororesin porous membrane is extremely flexible, when it is used as a separation membrane element, a processing method of folding it into a pleat shape, a processing of wrapping around a porous support and forming a plurality of bundles The filtration area can be easily increased by a method or the like.

  However, the fluororesin porous membrane is inherently water-repellent, and there is a problem that the aqueous solution hardly permeates through the fine porous structure when no treatment is performed. Therefore, a treatment for hydrophilizing the fluororesin porous membrane is performed.

  For example, Japanese Patent Publication No. 53-21270 (Patent Document 1) discloses a method of fixing a hydrophilic resin such as polyvinyl alcohol to the surface of a fine porous structure of a PTFE porous membrane by means such as adsorption or coating. Proposed. However, the film manufactured by this method cannot fully utilize the excellent properties of PTFE such as heat resistance and chemical resistance. In addition, the porosity and pore diameter of the original PTFE porous membrane may change due to the coating, which causes a problem in use as a separation membrane element.

  Also known is a method of improving hydrophilicity (wetting) by introducing a hydrophilic group into the surface of the porous PTFE membrane by a plasma beam. However, this method also has a problem that chemical resistance and heat resistance are lowered.

  A method of replacing water with an organic solvent that is soluble in water, for example, alcohol such as ethanol or isopropanol (IPA) without impregnating such treatment, after impregnating the porous structure of the fluororesin porous membrane. Also, hydrophilicity is imparted and water can easily pass therethrough.

However, the porous fluororesin membrane that has been subjected to this treatment is dried again when exposed to gas or with bubbles or dissolved gas mixed in the aqueous solution. As a result, treatment of the separation membrane element made of this membrane is performed. Ability is reduced. In particular, when used for filtration of a liquid that generates decomposition gas such as a wafer cleaning solution containing hydrochloric acid or hydrogen peroxide, or a foamable liquid, the processing capability of the separation membrane element is likely to decrease (Non-patent Document 1).
Japanese Patent Publication No.53-21270 Green Technology, June 1996, page 59

  In order to restore the processing capability of the separation membrane element, it is necessary to impregnate the porous body again with alcohol or the like and then replace it with water. During this operation, it is necessary to stop the operation of the separation membrane element, and a complicated operation is required to prevent mixing of alcohol or the like into the filtration system. Therefore, there has been a demand for a separation membrane element that has a small reduction in processing capability even when it is in contact with gas or when an aqueous solution in which bubbles or dissolved gases are likely to be mixed is filtered.

  The present invention is a separation membrane element made of a porous fluororesin membrane, which has a high treatment capacity when filtering an aqueous solution, and when the fluororesin membrane comes into contact with gas, bubbles, dissolved gas, etc. are mixed. It is an object of the present invention to provide a separation membrane element with a small reduction in processing capacity even when an easy aqueous solution is filtered. Another object of the present invention is to provide a method for easily producing the separation membrane element.

  The present inventors diligently investigated the ease of drying of the fluororesin porous membrane, and obtained the knowledge that the size of the bubble point in the fluororesin porous membrane is related to the ease of drying of the membrane. . Moreover, the knowledge that it became difficult to dry both surfaces of a fluororesin porous membrane by carrying out a chemical etching process and a roughening process was acquired. Then, by forming a separation membrane element using a fluororesin porous membrane having a bubble point on the outer layer side smaller than that on the inner layer side, or a fluororesin porous membrane whose both surfaces are chemically etched or roughened The inventors have found that the above-mentioned problems can be achieved and completed the present invention.

  The invention according to claim 1 is a separation membrane element comprising a fluororesin porous membrane comprising an outer layer having a bubble point of 70 kPa or less and an inner layer having a bubble point of 90 kPa or more.

  As a result of the study, the present inventor has found that in a fluororesin porous membrane, when the bubble point is small, it is difficult to dry, and conversely, when the bubble point is large, it is easy to dry. A porous layer (outer layer) with a small bubble point is arranged on both surface sides of the fluororesin porous membrane to make the membrane difficult to dry, and the bubble point is large inside (in the thickness direction) of the membrane. By using a porous fluororesin membrane that has a porous layer (inner layer) and retains high separation performance, the treatment capacity for filtering aqueous solution is high, and when the fluororesin membrane touches gas, It has been found that even when an aqueous solution in which dissolved gas or the like is likely to be mixed is filtered, a separation membrane element with a small reduction in processing capability (that is, high water retention) can be obtained.

  The porous membrane constituting the separation membrane element of the present invention has an inner layer (the inner part in the thickness direction of the membrane) with a bubble point of 90 kPa or more inside, and a bubble point of 70 kPa or less on both surface sides. It is characterized by having an outer layer (portion on the surface side of the film). This is because the bubble point is 70 kPa or less when the film is formed of only the porous layer constituting the outer layer, and the porous layer constituting the inner layer is formed. It means that the bubble point when a film is formed with only a quality layer is 90 kPa or more. Therefore, the porous layer forming both surface sides and the porous layer forming the inside thereof are different in easiness of drying.

  Here, the bubble point specifically means an IPA bubble point, and is a value measured by ASTM F316.

  When the porous membrane constituting the separation membrane element of the present invention does not have a layer having a bubble point of 90 kPa or more, the function as a separation membrane becomes insufficient and high separation ability is not maintained. On the other hand, when the bubble points on both surface sides (outer layers) exceed 70 kPa, the effect of suppressing drying, that is, water retention is not sufficient.

  In this way, a layer with a small bubble point with excellent water retention is arranged on both surface sides, and a layer with a large bubble point that functions as a separation membrane is placed inside, so it touches gas or mixes in aqueous solution Even if air bubbles or dissolved gas are attached, it becomes difficult to dry and high separation ability can be maintained, and a suitable separation membrane element can be provided. In addition, since a bubble point becomes small, so that a hole diameter is large, it is thought that the porous hole diameter which comprises an outer layer is larger than the porous hole diameter of an inner layer.

  Further, the layer having a bubble point of 70 kPa or less needs to be formed not only on one side of the film but also on the outer surface on both sides. When it is formed on only one side, the other surface side is easy to dry, so the effect of suppressing drying (water retention) is small, and the object of the present invention is not achieved.

  This fluororesin porous membrane is obtained, for example, by laminating a fluororesin porous membrane having a bubble point of 70 kPa or less on both surfaces of the fluororesin porous membrane having a bubble point of 90 kPa or more (claim) Item 2). This laminated film can be obtained by heating to above the melting point of these materials (in the case of PTFE, 327 ° C. or higher) and integrating them in a state where the distance between the two films is fixed.

  The fluororesin porous membrane having a bubble point of 90 kPa or more and the fluororesin porous membrane having a bubble point of 70 kPa or less, for example, after sintering a fluororesin fine particle to produce a fluororesin membrane, This fluororesin film can be obtained by stretching in a uniaxial or biaxial direction. As described in Japanese Examined Patent Publication No. 42-013560, the degree of porosity of the fluororesin film can be adjusted according to the stretching conditions. Therefore, the size of a predetermined bubble point is adjusted by changing the stretching conditions. be able to.

  In addition, the film | membrane laminated | stacked on both surface side may have a mutually different bubble point within the restriction | limiting that each bubble point is 70 kPa or less. Each of the inner fluororesin porous film having a bubble point of 90 kPa or more and the fluororesin porous film on both surfaces having a bubble point of 70 kPa or less may be a film in which two or more films are laminated. Good.

  Further, another porous film may be sandwiched between the inner film and the film laminated on both surface sides, and these may be overlapped and integrated. For example, a film having a structure in which a multilayer porous film is further laminated may be formed so that the bubble points are sequentially reduced from the inner side toward the both surface sides.

  In view of the function as the separation membrane, the porous membrane serving as the inner layer is more preferably one having a bubble point of 100 kPa or more. In view of the effect of suppressing drying, the porous layer on both surface sides, that is, the porous film serving as the outer layer, more preferably has a bubble point of 50 kPa or less.

  The invention according to claim 3 is a separation membrane element comprising a fluororesin porous membrane in which a chemical etching process is performed on both surfaces of a fluororesin porous membrane having a bubble point of 90 kPa or more.

  By subjecting a porous fluororesin membrane with a high bubble point, that is, a membrane having excellent function as a separation membrane, to perform a chemical etching treatment, it is possible to obtain a porous membrane having excellent separation performance and excellent water retention. A suitable separation membrane element can be provided using this membrane. That is, by performing a chemical etching treatment, the high hydrophobicity of the fluororesin porous membrane surface is weakened and the affinity with water is increased.

  As the chemical etching treatment, the fluororesin constituting the porous membrane is modified with an alkali metal, for example, using an organic alkali metal solution, and the modified portion (brown layer) is removed as necessary. Processing. The modification with an alkali metal is considered to be a reaction for extracting a fluorine atom of a fluororesin with an alkali metal.

  Examples of the organic alkali metal solution include an organic solvent solution such as methyllithium, metal sodium-naphthalene complex, metal sodium-anthracene complex tetrahydrofuran, and the like, a metal sodium-liquid ammonia solution, and the like. Among them, an organic alkali metal solution using benzophenone, anthracene, or biphenyl as an aromatic anion radical is preferable for the following reason (claim 4).

  A porous fluororesin film having a high bubble point is a porous film having a small pore diameter, but when the pore diameter is small, it becomes easy to dry, and thus higher water retention is required. In order to obtain higher water retention, it is preferable to perform chemical etching treatment to the inside of the pores of the porous membrane. However, the smaller the pore size, the more difficult the chemical etching process is performed to the inside of the pores of the porous membrane. Therefore, the present inventor further examined the conditions and method for performing chemical etching treatment to the inside of the pores of the membrane even when the pore size of the porous membrane is small. As a result, the organic alkali metal solution using benzophenone, anthracene, and biphenyl as the aromatic anion radical is more porous than the solution of the complex with sodium metal, which is a widely used naphthalene aromatic aromatic anion radical. It has been found that chemical etching can be easily performed to the inside.

  The chemical etching treatment using the organic alkali metal solution can be performed, for example, by immersing the fluororesin porous membrane in the organic alkali metal solution. In this case, since the chemical etching process is performed from the surface side of the porous film, it is possible to perform the chemical etching process only in the vicinity of both surfaces of the film. In order to increase it, it is preferable to perform chemical etching treatment to the inside of the pores of the porous membrane. Even if the chemical etching process is performed to the inside of the pores of the porous membrane, the decrease in the function as the separation membrane is small.

  When the fluororesin porous membrane is subjected to oxidative decomposition 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 be mixed, it is desirable to remove it. The present inventor has found that water retention is maintained even after the brown layer is decomposed and removed. These removals can be performed by oxidative decomposition with hydrogen peroxide, sodium hypochlorite, ozone, or the like.

  Furthermore, the present inventors have found that the lithium complex solution of benzophenone, unlike other complex solutions, has a stable reaction in the chemical etching treatment, such as the very surface of the film or the very surface of the wall in the hole, and so on. Because it reacts only with fluorine on the very surface, it does not become a violent reaction like etching that scrapes off the fluororesin, but conversely, the reaction can be easily controlled, and the uniformity of the reaction is very industrial. I found it easy to use.

  In addition, in the chemical etching process using a benzophenone lithium complex solution, a brown layer is not formed, so that a reduction process using hydrogen peroxide or the like after the process described later is unnecessary, and the cost can be reduced, which is also preferable in this respect. .

  The chemical etching treatment is a reaction of extracting a fluorine atom of the fluororesin with an alkali metal, but the effect of hydrophilization may be unstable. In particular, when a benzophenone lithium complex solution is used, it tends to be unstable. However, the effect of hydrophilization can be stably maintained by a very simple method of grafting a reactive monomer on a portion where fluorine atoms have been extracted by chemical etching.

  Specifically, the fluororesin porous membrane subjected to the chemical etching treatment is immersed in a stock solution or an aqueous solution of an acrylic monomer, and the monomer and the treated surface are brought into contact with each other. The monomer reacts with the radical portion from which the fluorine atom on the surface of the fluororesin is extracted to bond to form a hydrophilic graft chain. When a graft chain is formed, a decrease in hydrophilicity is suppressed. Examples of acrylic monomers include acrylic monomers such as acrylic acid, and methacrylic monomers such as methyl methacrylate and glycidyl methacrylate.

  The invention according to claim 5 is characterized by comprising a fluororesin porous membrane having a roughening treatment by physical means on both surfaces of a fluororesin porous membrane having a bubble point of 90 kPa or more. It is a membrane element. By subjecting both surfaces of a fluororesin porous membrane with a bubble point of 90 kPa or more to surface roughening by physical means, both surfaces can be formed at low cost with excellent water-retaining properties that are difficult to dry. can do. Examples of the roughening treatment by physical means include polishing with a file, sandblast, etc., surface etching with a plasma beam, etc., flame treatment, and the like.

  The fluororesin in the present invention means a polymer containing fluorine, and includes elastomers such as fluororubber in addition to resins such as PTFE and polytrifluoroethylene. Among these, a PTFE porous membrane is preferable because it has excellent chemical resistance and heat resistance as properties inherent to PTFE, and further has structurally superior characteristics such as high separation and high permeability. ).

  The PTFE porous membrane is not particularly limited as long as it is a membrane having PTFE as a main component and a fine porous structure. Further, the thickness, pore diameter and the like of the fluororesin porous membrane are not particularly limited as long as the bubbling point satisfies the scope of the present invention, and are appropriately determined according to the required permeability and mechanical strength.

  The porous membrane is used as a separation membrane element after its shape is processed by a known method so that the membrane area per unit volume is increased. For example, it is processed into a known shape such as a tubular module, a hollow fiber module, a pleat module, a spiral module, a plate & frame, and used.

  Here, the method shown as a pleated module is a method in which a fluororesin porous membrane is folded and used in a pleated form. As a method shown as a tubular module, the surface of a porous tube is covered with a fluororesin porous membrane. A method of bundling a plurality of pieces is exemplified. Also, a method of sealing a plurality of porous fluororesin porous membranes by overlapping a plurality of fluororesin porous membranes at intervals is also possible.

  As described above, by processing the shape of the fluororesin porous membrane and using it as a separation membrane element, the membrane area per volume, that is, the filtration area can be increased. It can be performed.

  Invention of Claim 7 is a manufacturing method of the separation membrane element of Claim 3 or Claim 4, Comprising: After providing the fluororesin porous membrane whose bubble point is 90 kPa or more in a module case, A method for producing a separation membrane element, characterized in that chemical etching treatment is performed on both surfaces of the fluororesin porous membrane.

  Here, the method for providing the fluororesin porous membrane in the module case is performed in the same manner as the method for installing the fluororesin porous membrane in the separation membrane element. That is, a plurality of fluororesin porous membranes are overlapped at intervals to seal between adjacent fluororesin porous membranes, and the fluororesin porous membranes are folded into a pleat shape to form a tubular fluororesin porous It is provided in the module case by a method of bundling a plurality of membranes, for example, a porous tube whose surface is covered with a fluororesin porous membrane. Therefore, the fluororesin porous membrane within the same volume is arranged and molded so as to function efficiently when used as a separation membrane element.

  The manufacturing method of claim 7 makes it possible to efficiently perform the chemical etching treatment of the fluororesin porous membrane by utilizing the large area of the membrane per volume. After providing the fluororesin porous membrane as described above, an organic alkali metal solution is introduced in the same flow path as that of the treatment liquid and non-treatment liquid when used as a separation membrane element, The inner and outer sides of the film are contacted with an organic alkali metal solution and a chemical etching process is performed, but since the area of the film per volume is large, without worrying about the occurrence of processing unevenness and the processing time at once. A large amount of chemical etching can be performed.

  In addition, when this method is performed, the metal case and other resins other than the fluororesin porous membrane in the filtration system such as the module case are also in contact with the organic alkali metal solution. Does not react. Alternatively, it is easy to select an organic alkali metal solution that does not react with a portion other than the fluororesin porous membrane in the filtration system. Therefore, this part does not deteriorate these parts. That is, this method focuses on the fact that the organic alkali metal solution specifically reacts only with the fluororesin and does not react with metals or other resins.

  The separation membrane element of the present invention can increase the treatment capacity when filtering an aqueous solution by a method of substituting with water after being immersed in alcohol or the like, and has excellent characteristics such as high separation ability and high permeability. Even when the fluororesin film is in contact with gas or when filtering an aqueous solution in which bubbles, dissolved gas or the like is likely to be mixed, the processing capacity is hardly lowered. This separation membrane element can be easily manufactured by the manufacturing method of the present invention.

  Next, the best mode for carrying out the present invention will be specifically described. In addition, this invention is not limited to this form, It can change into another form, unless the meaning of this invention is impaired.

  1 to 4 are schematic sectional views showing structural examples of the separation membrane element (module) of the present invention. In the example of the separation membrane element shown below, any one of the membranes defined in claim 1, 3 or 5 is used as the fluororesin porous membrane.

  1 and 2 show a separation membrane element having a structure in which a plurality of fluororesin porous membranes formed into a tubular shape are bundled. FIG. 1 shows a cross section taken along a plane parallel to the length direction of the tube, and FIG. 2 shows a cross section taken along a plane perpendicular to the length direction of the tube. In the figure, 1 represents a fluororesin porous membrane formed into a tubular shape. For example, a surface of a ceramic tube is formed by spirally winding a strip of a fluororesin porous membrane around the surface of a porous ceramic tube. Can be mentioned.

  The tubular fluororesin porous membrane 1 is composed of a plurality (seven in FIG. 2), and both end portions thereof are converged, sealed by a fixing portion 2, fixed, and integrated. Reference numerals 3 and 3 ′ in FIG. 1 denote an inlet and an outlet of the liquid to be treated, that is, an aqueous solution to be filtered, respectively. Reference numerals 4 and 4 ′ in FIG. 1 denote an inlet and an outlet of a processing liquid, that is, a filtered aqueous solution, respectively. In FIG. 2 and FIGS. 3 and 4 to be described later, the illustration of the inlet 4 or the outlet 4 'is omitted.

  In this example, the liquid to be treated and the liquid to be treated are circulated, and by setting the pressure on the liquid to be treated to be higher than the pressure on the liquid to be treated, a part of the liquid to be treated is transmitted to the liquid to be treated. Is filtered. A separation membrane element having a structure in which at least one of the outlets 3 ′ and 4 ′ is not provided, that is, a structure that does not circulate may be used. Moreover, 3 and 3 'in FIG. 1 can be used as the inlet and outlet of the processing liquid, respectively, and 4 and 4' in FIG. 1 can be used as the inlet and outlet of the liquid to be processed, respectively. .

  FIG. 3 shows a separation membrane element made of a porous fluororesin porous membrane, similar to the separation membrane element of FIG. 2, but differs in that the cross-sectional shape of the tube is not circular but rectangular. Thus, the term “tubular” includes not only a circular cross-sectional shape but also other shapes.

  FIG. 4 shows a separation membrane element having a structure in which a plurality of fluororesin porous membranes are overlapped at intervals to seal between adjacent fluororesin porous membranes. It is a schematic cross section cut along a plane perpendicular to the line. In FIG. 4, the same kind of members are represented by the same numbers as in FIGS. 1 and 2, so that 1 is a fluororesin porous membrane, but this fluororesin porous membrane 1 has a flat plate shape. As shown in FIG. 4, a plurality (six in the example of this figure) are overlaid. The adjacent porous fluororesin membranes 1 are sealed with a sealing tool 5, and the liquid to be treated is introduced into the cavity formed by the sealing tool 5 and the two fluororesin porous films 1. And filtration is performed.

  In addition, about the example of FIG. 4, the schematic cross section cut | disconnected by the surface perpendicular | vertical to a film | membrane and parallel to the flow of a process liquid and a to-be-processed liquid is represented by the same cross-sectional view as FIG.

Production Example 1
On both surface sides of a PTFE porous membrane having a bubble point of 120 kPa and a thickness of 30 μm (a porous membrane made of expanded PTFE, a pore diameter of 0.2 μm, trade name: Poeflon HP-020-30, manufactured by Sumitomo Electric Fine Polymer Co., Ltd.) In a state where a PTFE porous membrane having a bubble point of 15 kPa and a thickness of 100 μm (a porous membrane made of expanded PTFE, a pore diameter of 5 μm, trade name: Poeflon WP-500-100, manufactured by Sumitomo Electric Fine Polymer Co., Ltd.) is stacked and fixed A PTFE porous membrane was obtained by heating and integrating at 340 ° C. for 20 minutes.

Production Example 2
On both surface sides of a PTFE porous membrane having a bubble point of 120 kPa and a thickness of 30 μm (a porous membrane made of expanded PTFE, a pore diameter of 0.2 μm, trade name: Poeflon HP-020-30, manufactured by Sumitomo Electric Fine Polymer Co., Ltd.) In a state in which a PTFE porous membrane having a bubble point of 40 kPa and a thickness of 100 μm (a porous membrane made of expanded PTFE, a pore diameter of 1 μm, trade name: Poeflon WP-100-100, manufactured by Sumitomo Electric Fine Polymer Co., Ltd.) is stacked and fixed The porous PTFE membrane was obtained by heating and integration at 340 ° C. for 20 minutes.

Production Example 3
Both sides of a PTFE porous membrane having a bubble point of 120 kPa and a thickness of 30 μm (a porous membrane made of expanded PTFE, a pore diameter of 0.2 μm, trade name: Poeflon HP-020-30, manufactured by Sumitomo Electric Fine Polymer Co., Ltd.) A PTFE porous membrane was obtained by polishing with a paper file.

Production Example 4
PTFE porous membrane with a bubble point of 120 kPa and a thickness of 30 μm (a porous membrane made of expanded PTFE, pore diameter of 0.2 μm, trade name: Poeflon HP-020-30, manufactured by Sumitomo Electric Fine Polymer Co., Ltd.) is made of polypropylene so as not to shrink. The sample was fixed on a jig and immersed in a metal sodium-naphthalene complex solution (trade name: Tetra Etch, manufactured by Junkosha Co., Ltd.) for 0.5 seconds, and then washed with IPA and then distilled water. At this time, since the surface of the porous membrane was browned, it was further immersed in hydrogen peroxide solution having a concentration of 30% at 80 ° C. for 24 hours to decompose and remove the brown portion to obtain a PTFE porous membrane.

Production Example 5
A PTFE porous membrane was obtained in the same manner as in Example 4 except that the time for immersion in the metal sodium-naphthalene complex solution was changed from 0.5 second to 2 seconds.

Comparative production example 1
A PTFE porous membrane having a bubble point of 120 kPa and a thickness of 30 μm (a porous membrane made of expanded PTFE, a pore diameter of 0.2 μm, trade name: Poeflon HP-020-30, manufactured by Sumitomo Electric Fine Polymer Co., Ltd.) itself was used.

Comparative production example 2
Bubble points on both sides of a PTFE porous membrane with a bubble point of 120 kPa and a thickness of 30 μm (a porous membrane made of expanded PTFE, a pore size of 0.2 μm, trade name: Poeflon HP-020-30, manufactured by Sumitomo Electric Fine Polymer Co., Ltd.) In a state where 80 kPa, 30 μm thick PTFE porous membrane (a porous membrane made of expanded PTFE, pore diameter 0.45 μm, trade name: Poeflon HP-045-30, manufactured by Sumitomo Electric Fine Polymer Co., Ltd.) is overlaid and fixed. A PTFE porous membrane was obtained by heating and integrating at 340 ° C. for 20 minutes.

Comparative production example 3
Bubble point 120 kPa, 30 μm thick PTFE porous membrane (Porous membrane made of expanded PTFE, pore diameter 0.2 μm, trade name: Poaflon HP-020-30, manufactured by Sumitomo Electric Fine Polymer Co., Ltd.) In a state in which a PTFE porous membrane having a point of 15 kPa and a thickness of 100 μm (a porous membrane made of expanded PTFE, a pore diameter of 5 μm, a trade name: Poeflon WP-500-100, manufactured by Sumitomo Electric Fine Polymer Co., Ltd.) The porous PTFE membrane was obtained by heating and integration at 340 ° C. for 20 minutes.

Comparative production example 4
Only one side of a PTFE porous membrane having a bubble point of 120 kPa and a thickness of 30 μm (a porous membrane made of expanded PTFE, a pore size of 0.2 μm, trade name: Poeflon HP-020-30, manufactured by Sumitomo Electric Fine Polymer Co., Ltd.) A PTFE porous membrane was obtained by polishing with a numbered paper file.

  The PTFE porous membranes obtained in the above production examples and comparative production examples all repel water even if they were immersed in water as they were, and did not absorb water.

  The PTFE porous membranes obtained in the above production examples and comparative production examples were punched into a 47 mm diameter disk to prepare test specimens as models of separation membrane elements. The specimen is fixed to the filter holder, and the IPA flow rate is measured through IPA at a pressure of 50 kPa, and then the specimen is immersed in pure water stored in a beaker to replace IPA with pure water.

  Next, the test body is taken out from pure water and exposed to the outside air for 1 minute. When the porous membrane dries, the membrane changes from a wet translucent state to a dry whitish color. Again, fix to the dry filter holder and immediately pass pure water at a pressure of 50 kPa and measure the water flow rate.

  The ease of drying can be quantitatively expressed by the ratio of the IPA flow rate and the water flow rate obtained in this way. That is, the ratio of the water flow rate to the IPA flow rate is extremely low in the membrane that is easy to dry, whereas the ratio of the water flow rate to the IPA flow rate is high in the membrane that is difficult to dry. The measurement results are shown in Table 1. Table 1 also shows the IPA bubble point of each PTFE porous membrane measured by the following method (indicated as IPA-BP).

  IPA bubble point measurement method: Measured by ASTM F316. That is, when impregnated with isopropanol and filling the pores of the tube wall with isopropanol and then gradually applying air pressure from one surface, the pressure is the first time that bubbles emerge from the opposite surface.

  From the results of Examples 1 to 5, the lowering of the water flow rate can be suppressed by applying a film with a low bubble point, chemical etching, or roughening treatment to both surfaces of the PTFE porous film. It is clear that water retention is maintained (drying is suppressed), and it can be seen that a suitable separation membrane element can be obtained by using these PTFE porous membranes.

  On the other hand, when such a treatment was not performed (Comparative Example 1), when the bubble point of the film attached to both surfaces exceeded the range of the present invention (70 kPa or less) (Comparative Example 2), the above treatment was performed. When applied to only one side (Comparative Examples 3 and 4), excellent water retention is not obtained, indicating that there is a problem as a separation membrane element.

  Reference examples 1 to 4 are described below.

(Reference Example 1)
A PTFE porous membrane having a bubble point of 180 kPa and a thickness of 30 μm (a porous membrane made of expanded PTFE, a pore diameter of 0.1 μm, trade name: Poreflon HP-010-30, manufactured by Sumitomo Electric Fine Polymer Co., Ltd.) itself was used.

(Reference Example 2)
A PTFE porous membrane having a bubble point of 80 kPa and a thickness of 30 μm (a porous membrane made of expanded PTFE, a pore diameter of 0.45 μm, trade name: Poeflon HP-045-30, manufactured by Sumitomo Electric Fine Polymer Co., Ltd.) itself was used.

(Reference Example 3)
A PTFE porous membrane having a bubble point of 40 kPa and a thickness of 100 μm (a porous membrane made of expanded PTFE, a pore diameter of 1.0 μm, trade name: Poreflon WP-100-100, manufactured by Sumitomo Electric Fine Polymer Co., Ltd.) itself was used.

(Reference Example 4)
A PTFE porous membrane having a bubble point of 15 kPa and a thickness of 100 μm (a porous membrane made of expanded PTFE, a pore diameter of 5.0 μm, trade name: Poeflon WP-500-100, manufactured by Sumitomo Electric Fine Polymer Co., Ltd.) itself was used.

  The PTFE porous membrane of each reference example was also measured in the same manner as in the examples and comparative examples, and the results are shown in Table 2. In Reference Examples 2 to 4, the water flow rate / IPA flow rate is excellent, but these are inferior to the fluororesin porous membrane used in the above examples in terms of the fine particle capturing function of the separation membrane. .

It is a schematic cross section explaining an example of the separation membrane element of the present invention. It is a schematic cross section explaining an example of the separation membrane element of the present invention. It is a schematic cross section explaining another example of the separation membrane element of the present invention. It is a schematic cross section explaining another example of the separation membrane element of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fluororesin porous membrane 2 Fixing part 3 Process liquid inlet 3 'Process liquid outlet 4 Process liquid inlet 4' Process liquid outlet 5 Sealing tool

Claims (2)

The inner layer is a separation membrane element composed of a fluororesin porous membrane having an IPA bubble point of 90 kPa or more, and the fluororesin porous membrane is made of polytetrafluoroethylene, and benzophenone and anthracene are formed on both surfaces thereof. Or, when a chemical etching treatment is performed by oxidative decomposition treatment with an organic alkali metal solution using biphenyl as an aromatic anion radical , and a browned layer is formed by the chemical etching treatment, the browned layer Is removed by oxidative decomposition, and the fluororesin porous membrane is wetted with IPA through IPA at a pressure of 50 kPa, and the IPA flow rate is measured. Thereafter, the fluororesin porous membrane is immersed in pure water to obtain IPA. After replacing the water with pure water, it was exposed to the outside air for 1 minute, dried, and then at a pressure of 50 kPa. When measuring the water flow rate through the water, the separation membrane element ratio the IPA flow rate of the water flow rate is equal to or is 0.26 or more. The method for manufacturing a separation membrane element according to claim 1, wherein a plurality of tubes made of a fluororesin porous membrane having an IPA bubble point of 90 kPa or more are provided in the module case, and then both of the fluororesin porous membranes are provided. When the surface is subjected to an oxidative decomposition treatment with an organic alkali metal solution using benzophenone, anthracene or biphenyl as an aromatic anion radical, a chemical etching treatment is performed, and a browned layer is formed by the chemical etching treatment. A method for producing a separation membrane element, wherein the browned layer is removed by oxidative decomposition.

Images