WO2020246550A1 - Porous membrane for membrane distillation - Google Patents

Porous membrane for membrane distillation Download PDF

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Publication number
WO2020246550A1
WO2020246550A1 PCT/JP2020/022159 JP2020022159W WO2020246550A1 WO 2020246550 A1 WO2020246550 A1 WO 2020246550A1 JP 2020022159 W JP2020022159 W JP 2020022159W WO 2020246550 A1 WO2020246550 A1 WO 2020246550A1
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Prior art keywords
membrane
ptfe
fibrous material
membrane distillation
porous membrane
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PCT/JP2020/022159
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French (fr)
Japanese (ja)
Inventor
櫻井　秀彦
北川　義幸
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東洋紡株式会社
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Priority to JP2020549729A priority Critical patent/JPWO2020246550A1/ja
Publication of WO2020246550A1 publication Critical patent/WO2020246550A1/en

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/10—Supported membranes; Membrane supports
    • B01D69/107—Organic support material
    • B01D69/1071—Woven, non-woven or net mesh
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D39/00—Filtering material for liquid or gaseous fluids
    • B01D39/14—Other self-supporting filtering material ; Other filtering material
    • B01D39/16—Other self-supporting filtering material ; Other filtering material of organic material, e.g. synthetic fibres
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/36—Pervaporation; Membrane distillation; Liquid permeation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/10—Supported membranes; Membrane supports
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/12—Composite membranes; Ultra-thin membranes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/12—Composite membranes; Ultra-thin membranes
    • B01D69/1213—Laminated layers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
    • B01D71/06—Organic material
    • B01D71/30—Polyalkenyl halides
    • B01D71/32—Polyalkenyl halides containing fluorine atoms
    • B01D71/36—Polytetrafluoroethene
    • D—TEXTILES; PAPER
    • D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
    • D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
    • D04H3/00—Non-woven fabrics formed wholly or mainly of yarns or like filamentary material of substantial length
    • D04H3/08—Non-woven fabrics formed wholly or mainly of yarns or like filamentary material of substantial length characterised by the method of strengthening or consolidating
    • D04H3/16—Non-woven fabrics formed wholly or mainly of yarns or like filamentary material of substantial length characterised by the method of strengthening or consolidating with bonds between thermoplastic filaments produced in association with filament formation, e.g. immediately following extrusion
    • D—TEXTILES; PAPER
    • D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
    • D06M—TREATMENT, NOT PROVIDED FOR ELSEWHERE IN CLASS D06, OF FIBRES, THREADS, YARNS, FABRICS, FEATHERS OR FIBROUS GOODS MADE FROM SUCH MATERIALS
    • D06M15/00—Treating fibres, threads, yarns, fabrics, or fibrous goods made from such materials, with macromolecular compounds; Such treatment combined with mechanical treatment
    • D06M15/19—Treating fibres, threads, yarns, fabrics, or fibrous goods made from such materials, with macromolecular compounds; Such treatment combined with mechanical treatment with synthetic macromolecular compounds
    • D06M15/21—Macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds
    • D06M15/244—Macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds of halogenated hydrocarbons
    • D06M15/256—Macromolecular compounds obtained by reactions only involving carbon-to-carbon unsaturated bonds of halogenated hydrocarbons containing fluorine

Definitions

  • the present invention relates to a porous membrane used for membrane distillation.
  • Membrane distillation involves contacting a separation membrane (permeable membrane) made of a hydrophobic material with a high-temperature liquid on one surface and a low-temperature liquid on the other surface directly or with an air layer provided between them to achieve a high vapor pressure. It is an operation to move steam from the high temperature side of the steam pressure to the low temperature side of the low vapor pressure by using the vapor pressure difference. Since membrane distillation utilizes the vapor pressure difference, it is not affected by the osmotic pressure difference between the two liquids.
  • the osmotic pressure of the liquid often becomes the limit of the concentration rate.
  • the reverse osmosis (RO) method which is widely used for desalination of seawater and wastewater treatment, is an operation of applying high pressure to a liquid and concentrating it, but the liquid has an osmotic pressure exceeding the pressure resistance of the membrane and the high pressure pump pressure. Cannot be concentrated. Therefore, in order to further concentrate the liquid having a high osmotic pressure, the evaporation method is often used in addition to the RO method.
  • the membrane distillation method utilizes the vapor pressure difference between two liquids with different temperatures, and does not require raising the temperature to the boiling point as in the general evaporation method. Therefore, the liquid can be concentrated to a high concentration with a relatively small temperature difference, and a heat source with a relatively low temperature such as exhaust heat or solar heat, which is difficult to use by the evaporation method, can be used, and it is necessary to lower the boiling point of the liquid by decompression. It has features such as no.
  • the properties required for a separation membrane in the membrane distillation method are hydrophobicity (liquid repellency) and diffusion permeability of water molecules (breathability). Insufficient hydrophobicity causes a decrease in the effective area due to clogging of condensed water and liquid penetration into the opposite surface. Further, when the porosity is small, the air permeability required for diffusion transmission becomes small. In order to improve the characteristics, it is necessary to have a structure that increases the porosity and an improvement in the liquid repellency that hinders liquid penetration even if the porosity is increased.
  • a porous body made of a particle molded body, a membrane, etc. has been conventionally used as the separation membrane, but the particle molded body obtained by bonding the particles to each other has a high packing density and low air permeability. Further, even in a PTFE membrane obtained by fibrillation by stretching a polytetrafluoroethylene (PTFE) film, the degree of freedom of the material and shape is small, and it is difficult to improve the liquid repellency and breathability of the material. It is an expensive material, and when applied to general applications, there is a problem that the finished film becomes expensive.
  • PTFE polytetrafluoroethylene
  • a relatively inexpensive hydrophobic film can be obtained by stretching a hydrocarbon-based polymer film such as polypropylene or polyethylene, or by fibrizing these polymers.
  • a hydrocarbon-based polymer film such as polypropylene or polyethylene
  • fibrizing these polymers the hydrophobicity of these hydrocarbon-based polymer films is insufficient, and when used in the membrane distillation method, the surface of the membrane pores becomes hydrophilic due to water vapor during long-term operation, and not only vapor but also liquid permeates. There's a problem.
  • a method of imparting a fiber shape by thermoplasticity or solvent solubility and further enhancing the liquid repellency has a method of mixing an additive having a perfluoro group in a resin (for example, Patent Document 5), a method of melt-spinning a thermoplastic fluororesin (for example, Patent Documents 6 and 7), and a perfluoro group.
  • an additive having a perfluoro group in a resin for example, Patent Document 5
  • a method of melt-spinning a thermoplastic fluororesin for example, Patent Documents 6 and 7
  • a perfluoro group examples thereof include a method of coating the surface with an emulsion processing agent (for example, Patent Document 8), a method of introducing a fluorine atom by substituting a hydrogen atom with plasma and fluorogas (for example, Patent Document 9), and the like. ..
  • fluorine-based resins and fluorine-based low-molecular-weight additives are suitable for melt spinning because hydrogen fluoride and carbonyl fluoride are observed as desorption of fluorine telomers and thermal decomposition products in an environment exceeding 320 ° C. Inappropriate. Further, in the introduction of fluorine atoms by fluorine gas or plasma treatment, it is necessary to strictly control the amount of oxygen and water in order to prevent leakage of fluorine gas and suppress hydrophilicity, and special equipment with high airtightness is required.
  • PFOA perfluorooctanoic acid
  • PFOS perfluorooctanesulfonic acid
  • a method of coating polytetrafluoroethylene by sputtering is also known, but it is difficult to obtain the required permeability resistance because the flying particles are unevenly distributed only on the outermost layer on the vapor deposition source side. There are concerns about decomposition of polytetrafluoroethylene and oxidation products.
  • the fluorine-containing acrylate-based processing agent generally used as a water-repellent and oil-repellent agent uses a short-chain perfluoro group of C 6 F 13 or less as a side chain so as to comply with PFOA and PFOS regulations.
  • Patent Document 10 a fluororesin which is made soluble and thermoplastic by amorphization and has a coating property is also known, but it is necessary to use a special monomer as the main skeleton, and the cost is extremely high. There is a problem of becoming.
  • Japanese Patent Publication Japanese Patent Publication "Japanese Patent Laid-Open No. 60-187305” Japanese Patent Publication "Japanese Patent Laid-Open No. 7-251036” Japanese Patent Publication "Japanese Patent Laid-Open No. 1-176404” Japanese Patent Publication "Japanese Patent Laid-Open No. 9-1143” Japanese Patent Publication "Japanese Patent Laid-Open No. 2009-6313” Japanese Patent Publication "Japanese Patent Laid-Open No. 2002-266219” Japanese Patent Publication "Japanese Patent Laid-Open No. 2007-18995" Japanese Patent Publication "Japanese Patent Laid-Open No. 2004-352976” Patent Gazette published in Japan "Special Table 2008-540856” International Publication "WO2009 / 104669"
  • the present invention solves the above-mentioned problems of conventionally known separation membranes, and an object of the present invention is to provide a novel separation membrane capable of achieving liquid repellency, breathability, and long-term operation stability.
  • the porous membrane for membrane distillation of the present invention has been completed as a result of diligent studies by the inventor in order to solve the above-mentioned problems. That is, the present invention is as follows. 1. 1. A porous membrane for membrane distillation, which is made of a fibrous material using a thermoplastic resin and in which polytetrafluoroethylene is supported on the surface of the fibrous material. 2. 2. The porous membrane for membrane distillation according to 1 above, wherein the fibrous material is a non-woven fabric obtained by the melt blown method. 3. 3. The porous membrane for membrane distillation according to 1 or 2 above, wherein the liquid repellency on the front and back is different.
  • the porous membrane for membrane distillation of the present embodiment is a fibrous material made of a thermoplastic resin, and polytetrafluoroethylene (PTFE) is supported on the surface thereof.
  • PTFE polytetrafluoroethylene
  • the fibrous material includes a fibrous material such as a woven or knitted fabric made of long fibers or short fibers, a non-woven fabric, a cotton-like material, or a fibrous material obtained from a stretched film, and includes a material, thickness, texture, and fiber diameter. It is possible to use a molded product according to the required characteristics. It is more preferable to use a non-woven fabric in order to obtain a structure having excellent water impermeability and breathability.
  • a method for obtaining a non-woven fabric a method of sheeting short fibers such as single component fibers, composite fibers such as core-sheath fibers and side-by-side fibers, and split fibers by carding, airlaid, wet papermaking method, etc.
  • Conventionally known methods such as a method of forming a sheet by a melt blown method, an electrospinning method, a force spinning method, or the like can be used.
  • Non-woven fabrics obtained by the melt blown method, electrospinning method, or force spinning method, which can easily obtain fineness and fineness, are preferable from the viewpoint of suppressing the penetration of droplets and effectively using them fused, and treatment of residual solvent is required.
  • the non-woven fabric obtained by the melt-blown method, the molten electrospinning method, and the molten force spinning method is more preferable, and the non-woven fabric obtained by the melt-blown method is particularly preferable. More preferably, it is a melt-blown non-woven fabric made of a thermoplastic resin having a melting point of 320 ° C. or lower.
  • the diameter of the fibers used in the fibrous material is preferably 0.001 to 100 ⁇ m, more preferably 0.005 to 20 ⁇ m, further preferably 0.01 to 10 ⁇ m, and 0.02 to 0.02 to 0.02 to 10 ⁇ m. It is particularly preferably 5 ⁇ m, and most preferably 0.03 to 3 ⁇ m.
  • the fiber diameter is larger than 100 ⁇ m, the fiber gap becomes large, so that the liquid barrier property is inferior in the porous membrane for membrane distillation.
  • the fiber diameter is smaller than 0.001 ⁇ m, the porous membrane distillation The air permeability of the membrane is reduced and it becomes difficult to impart pressure resistance.
  • the thickness of the fibrous material is preferably 0.01 to 10 mm, more preferably 0.02 to 5 mm, and even more preferably 0.05 to 3 mm.
  • the fibrous material itself may be changed in thickness to form a porous membrane for membrane distillation, or the fibrous material may be laminated in multiple layers to form a porous membrane for membrane distillation.
  • the fibrous material keeps the fiber gap constant. It is preferable to keep it within the range of.
  • d is the diameter of the fiber
  • ⁇ is the density of the polymer
  • ⁇ is the bulk density of the fibrous material.
  • the radius of water kinetics is a function of the diameter of the fiber and the bulk density of the fiber if the polymers are the same.
  • the hydraulic radius of the fibrous material of the present embodiment is preferably 0.1 ⁇ m to 40 ⁇ m, more preferably 0.3 ⁇ m to 20 ⁇ m, and even more preferably 0.5 ⁇ m to 10 ⁇ m.
  • the radius of water flow is larger than 40 ⁇ m, the barrier property of the liquid may decrease, and when it is smaller than 0.1 ⁇ m, the air permeability may decrease.
  • the fibrous material of the present embodiment may be a uniform product made of a single manufacturing method and a material, or may be a mixture made of two or more kinds of materials having different manufacturing methods, materials and fiber diameters.
  • the cross-sectional shape of the fiber is not limited to a circular shape, but a rectangular, star-shaped, clover-shaped or other irregular cross-sectional shape can also be preferably used.
  • the fibrous material of the present embodiment is not particularly limited, but is preferably a synthetic resin material having low hygroscopicity.
  • polyester, polycarbonate, polyamide, polyolefin, cyclic olefin, polyvinyl chloride, polyvinylidene chloride, polyphenylene sulfide, polyphenylene oxide, phenol resin and the like can be mentioned, among which polyethylene and polybutene can be mentioned.
  • Polyolefin, polymethylpentene, polystyrene, cyclic olefin and other polyolefins are preferable. It is a blended polymer obtained by mixing two or more different resin components, even if they have desired properties.
  • the synthetic resin conventionally known compounding agents and compounding compositions can be preferably used in order to suppress deterioration of the resin itself.
  • the compounding agent include various metal salts, antioxidants, light stabilizers, metal inactivating agents, and crystal nucleating agents.
  • the PTFE supported on the surface of the fibrous material is preferably low melting point PTFE having a melting point of 35 ° C. or higher and 320 ° C. or lower. Further, it is preferable that PTFE having a melting point of 60 ° C. or higher and 315 ° C. or lower is contained, and more preferably, PTFE of 80 ° C. or higher and 300 ° C. or lower is contained, and PTFE of 100 ° C. or higher and 290 ° C. or lower is contained. Is particularly preferred. As long as the melting point is in the above range, PTFE having a distribution in molecular weight may be used.
  • the reason for using low melting point PTFE with a melting point of 35 ° C or higher and 320 ° C or lower is (1) Since general PTFE has a melting point of 320 ° C. or higher, problems occur in deterioration and heat resistance of carriers (particularly synthetic polymers). (2)
  • the low melting point PTFE (minimum surface tension 13 mN / m or more and less than 17.5 mN / m) used in the present embodiment has a crystalline form or CF as compared with general PTFE (minimum surface tension 17.5 mN / m).
  • PTFE is evaporated at a temperature equal to or higher than the melting point and lower than the thermal decomposition temperature, cooled and solidified on the carrier, and if necessary, heat-treated at the melting point or higher of PTFE.
  • the method of immobilization can be mentioned by performing.
  • PTFE exhibits stability as a solid when used, has properties as a liquid and gas when heated, and can be preferably used as a material for a physical vapor deposition method (PVD method).
  • PVD method physical vapor deposition method
  • the PTFE used in the present embodiment has a melting point of 320 ° C. or lower, which is the thermal decomposition temperature, and the vapor deposition process can be performed by evaporating the temperature above the melting point.
  • the melting point at normal pressure (1 atm in the atmosphere) if it consists of n-C 10 F 22 , the melting point is 36 ° C, and if it consists of n-C 12 F 26 , the melting point is 76 ° C, from n-C 14 F 30.
  • the melting point is 103 ° C
  • the melting point is 125 ° C if it is composed of n-C 16 F 34
  • the melting point is 167 ° C if it is composed of n-C 20 F 42
  • n-C 24 F 50 When it has a melting point of 190 ° C. and n—C 31 F 64, it has a melting point of 219 ° C.
  • a method of vapor deposition a method is used in which vapor is generated by heating tetrafluoroethylene with various heat sources and deposited as droplets or crystals on the surface of the carrier kept at a lower temperature.
  • Such a method is preferably used regardless of whether it is a batch method in which the entire processed surface is processed at once, or a method in which the processed surfaces of different carriers are continuously processed by moving the carrier or the reaction vessel. ..
  • the vapor deposition process can be preferably carried out in any of pressure, normal pressure, reduced pressure, vacuum state and its pressure swing, atmosphere and atmosphere of an inert gas.
  • By reducing the pressure or setting the vacuum it is possible to improve the transpiration rate and reduce the transpiration temperature, and pressurize the transpiration to promote the precipitation of the transpiration.
  • a preferable adhesion state can be obtained according to the purpose by adjusting the carrying conditions of PTFE and the molecular weight.
  • a porous structure such as a fibrous material
  • the mean free path of molecules is large and PTFE is unevenly distributed on the carrier surface on the evaporation side, and in the case of low vacuum or normal pressure and pressure conditions. It is possible to improve the uniformity by wrapping around.
  • pressure swing and treatment with different processed surfaces (front and back) on the same carrier are also preferable methods.
  • PTFE is supported by a vapor deposition method, and by having one or more molecular weights, it is possible to utilize the difference in melting point and diffusion rate, and the amount of PTFE supported in the fiber layer thickness direction. And it is possible to easily provide a tilting function with respect to liquid repellency.
  • the PTFE supported on the fibrous material may have one molecular weight or two or more molecular weights according to the above-mentioned supporting conditions and the PTFE characteristics of the raw material. Good. That is, in the present embodiment, it is also preferable to use two or more kinds of PTFE to have a molecular weight distribution.
  • PTFE having one molecular weight may be mixed, or a mixture having a distribution in advance may be used.
  • low molecular weight PTFE liquefaction (registered trademark) V manufactured by Central Glass Co., Ltd. has a melting point range of 100 to 290 ° C.
  • peak temperature 270 ° C. peak temperature 270 ° C.
  • peak temperature 270 ° C. peak temperature 270 ° C.
  • It can be used as a source, and it is also preferable to heat the entire PTFE at 290 ° C. or higher and 320 ° C. or lower to liquefy it.
  • the simultaneous measurement of differential thermogravimetric mass will be described later.
  • the fibrous material may be heat-treated at room temperature or higher and melting point or lower during or after the vapor deposition process of PTFE.
  • the fibrous material is made of polypropylene, it is preferably heat-treated at 40 ° C. or higher and 140 ° C. or lower, more preferably 50 ° C. or higher and 140 ° C. or lower, and further preferably 60 ° C. or higher and 140 ° C. or lower. preferable.
  • the adhesiveness between the fibrous substance and PTFE is improved, the effect of stabilizing the electret by removing the low molecular weight substance and the released VOC component are reduced.
  • PTFE may be attached in a vapor state and then cooled and solidified, or may be attached as agglomerated liquid or solid particles.
  • the liquid repellency can be improved by forming the PTFE on the surface of the carrier to have a fine uneven structure.
  • the method of simultaneously supplying high melting point PTFE, organic, inorganic particles, liquid vapors of other species, and mist, which are condensed nuclei, to the atmosphere where the vapor of PTFE exists can also improve the adhesion rate and simultaneously support the condensed nuclei, and further, fibers. This is a preferable method because fine irregularities can be added to the shape.
  • the fine uneven structure is preferably finer than the droplet to be collected. This is because not only the increase in wet work due to the increase in surface area but also the presence of an air layer between the adhered particles and the carrier makes it possible to obtain a high liquid-repellent surface according to the Cassie-Baxter theory.
  • the liquid repellency obtained from the fibrous material of the present embodiment is characterized in that it can be arbitrarily adjusted according to the components contained in the raw water and the characteristics required for the required water pressure resistance. To do.
  • the surface tension test solution used by JIS K6768 and the AATCC118 method can be used.
  • the surface tension that gives permeation within 10 seconds, for example, as a typical value in PP melt blown, is preferably improved from 37 mN / m in the unprocessed state.
  • At least one surface is preferably 31 mN / m or less, more preferably 29 mN / m or less, further preferably 27 mN / m or less, and most preferably 25.4 mN / m or less. Since the penetration property into the porous carrier correlates with the capillary phenomenon derived from the contact angle, if the structures are the same, the relationship between the liquid repellency in the sheet shape and the hydrostatic pressure is derived.
  • porous membrane for membrane distillation of the present embodiment can be used not only as a single substance, but also as a laminate with other materials in order to impart functions for improving strength, transpiration, and practicality.
  • spunbonded non-woven fabric for example, spunbonded non-woven fabric, thermal-bonded non-woven fabric, net, structural support using urethane foam, glass filter, etc., surface processing to suppress the formation of biofilm and adhesion of substances contained in raw water, and processing sheet. It can be used as needed, such as laminating.
  • a hydrophilic material as another material to be laminated, it is expected that the liquid is easily supplied to the surface of the hydrophobic membrane and the permeation rate is increased.
  • sandwiching an ultrathin hydrophobic film whose strength cannot be maintained by itself between the porous membranes for membrane distillation of the present embodiment, it is possible to suppress the permeation of the liquid.
  • the two liquids having different temperatures can be brought into direct contact with the membrane surface made of a porous membrane for membrane distillation, or can be brought into indirect contact by providing an air layer between the membrane surface and the two liquids. ..
  • the direct contact can maximize the vapor pressure difference between the two liquids on both sides of the membrane.
  • the air layer between the membrane surface and the liquid can be provided on either the high temperature side or the low temperature side liquid, or can be provided on both sides.
  • Fiber diameter A scanning electron microscope was used to photograph the fibers forming the fibrous material at a magnification of 1000, and 30 fibers on the screen were randomly extracted using the obtained image to obtain the fiber diameter. The average was taken as the fiber diameter.
  • Thickness The thickness of the fibrous material was measured at 10 points using a dial thickness gauge 7301 manufactured by Mitutoyo, and the average value was taken as the thickness of the fibrous material.
  • Bulk Density The basis weight (g / m 2 ) of the fibrous material was obtained from the average weight of 10 samples obtained by cutting the dried fibrous material into 3 cm x 3 cm, and the thickness of the fibrous material obtained in (2). The teasing density was calculated.
  • test solution having a surface tension of 40 mN / m 50 ⁇ L of each was allowed to stand on the surface of the test sample with a micropipeter for microbial test, and the degree of penetration after 10 seconds was observed. After that, the degree of penetration was similarly observed in the order of a test solution having a surface tension of 39 mN / m, a test solution having a surface tension of 38 mN / m, a test solution having a surface tension of 26 mN / m, and a test solution having a surface tension of 25.4 mN / m.
  • the surface tension of the test solution having the smallest surface tension that was not absorbed was defined as the degree of oil repellency in the JIS K 6768 wet tension test solution. If there is a difference in the front and back states of the test material as a result of sequential measurement, the surface tension with the smaller surface tension is set as the oil repellency (the same applies to other oil repellency measurements thereafter). Is). When the test solution of 25.4 mN / m was non-permeated, the test result was set to 25.4 mN / m because there was no permeated test solution.
  • Example 1 Polypropylene non-woven fabric (fiber diameter 3.2 ⁇ m, thickness 0.25 mm, grain 42 g / m 2 , bulk density 0.12 g / cm 3 ) obtained by the melt blown method was applied to n-C 18 F 38 (melting point 149 ° C). It was immersed in a material dissolved in perfluorohexane to obtain a processed sheet (fibrous material) having a loading amount of 0.30 g / m 2 . The supported amount was 1% or less of the grain size, and the density of the fibrous polymer was 5.2 ⁇ m when the hydraulic radius was calculated using the polypropylene density of 0.95 g / cm 3 . The liquid repellency was 28 mN / m on both the front and back sides, and the pressure loss was 43 Pa. No film or blockage between the fibers was confirmed by microscopic observation.
  • Example 2 The same non-woven fabric as in Example 1 was attached to a constant temperature plate kept at 30 ° C. and installed on the ceiling of a reaction vessel made of cylindrical ceramic. A hot plate heated to 250 ° C. is installed on the bottom, and n-C 18 F 38 (melting point 149 ° C.) is evaporated from the metal boat to carry a processed sheet (fibrous material) with a loading capacity of 0.30 g / m 2 . ) Was obtained. The liquid repellency was 26 mN / m on the hot plate side and 31 mN / m on the ceiling side, and while both the front and back sides had liquid repellency, a processed sheet having a difference in liquid repellency was obtained. The pressure loss was 40 Pa. No film or blockage between the fibers was confirmed by microscopic observation.
  • a porous membrane for membrane distillation was prepared by stacking the four processed sheets, and the membrane distillation test was carried out in the same manner as in Example 1 by installing the porous membrane for membrane distillation. It was .9 L / m 2 / hr.
  • the NaCl concentration in the NaCl reservoir tank increased to 11.5% after 24 hours, but NaCl in the reservoir tank on the ion-exchanged water side was not detected. It is considered that the reason why the Lux higher than that of Example 1 was obtained is that the pressure loss of the processed sheet of Example 2 was smaller than that of the processed sheet of Example 1, and the transfer resistance of water vapor due to membrane distillation was small.
  • Example 2 when the porous membrane for membrane distillation after 24 hours was taken out and observed, although water droplets of the NaCl aqueous solution and the ion-exchanged water were attached to both sides of the membrane, they were repelled from the membrane surface. It was present, no liquid was observed inside the membrane, and it was in the same state as at the start of the experiment.
  • the NaCl concentration in the NaCl reservoir tank increased to 10.1% after 2 hours, increased to 10.2% after 6 hours, then gradually decreased, and reached 5% after 24 hours.
  • the NaCl concentration in the reservoir tank on the ion-exchanged water side was not detected until after 6 hours, but then increased to 5% after 24 hours.
  • the Lux and salt permeability were almost the same as those in Examples 1 and 2 until 2 hours later, but after that, Flux decreased and the salt permeability increased.
  • the porous membrane was taken out after 24 hours, it was observed that the aqueous NaCl solution was immersed in the porous membrane.
  • the porous membrane of Comparative Example 1 had high hydrophobicity and acted for membrane distillation, but the hydrophobicity decreased with the operation time, and after 6 hours, it did not work as a membrane distillation membrane. , It is considered that the NaCl aqueous solution and the ion-exchanged water were mixed.
  • Example 2 The same non-woven fabric as in Example 1 is immersed in a C6 acrylate water repellent oil repellent diluted with water and then squeezed with a mangle to support 0.3 g / m 2 to obtain a processed sheet (fibrous material). It was. However, it was difficult to allow the processing liquid to permeate the non-woven fabric, and as a result of microscopic observation, the surface was blocked. The liquid repellency of the front and back surfaces was higher than 24 mN / m, and the pressure loss was 75 Pa.
  • the porous membrane of Comparative Example 2 has high hydrophobicity, and although it acts for membrane distillation, the pressure loss is high, so that the vapor diffusion rate of membrane distillation decreases, and the hydrophobicity decreases with the operation time. After 12 hours, it did not work for membrane distillation, and it is considered that the NaCl aqueous solution and the ion-exchanged water were mixed. Therefore, it is considered that the C6 acrylate water-repellent oil-repellent agent is insufficient for long-term water-repellent retention of the porous film.
  • porous membrane for membrane distillation of the Examples can retain water repellency for a long period of time.
  • the porous membrane for membrane distillation of the present invention greatly contributes to the field of liquid separation membrane.

Abstract

The porous membrane for membrane distillation of the present invention comprises a fibrous object formed from a thermoplastic resin and polytetrafluoroethylene fixed to the surface of the fibrous object. Due to this, the porous membrane has improved liquid repellency and air permeability and has excellent stability over a long period.

Description

膜蒸留用多孔質膜Porous membrane for membrane distillation
　本発明は膜蒸留に用いられる多孔質膜に関する。 The present invention relates to a porous membrane used for membrane distillation.
　膜蒸留は、疎水性素材からなる分離膜（透過膜）の一方の面に高温の液体を、他方の面に低温の液体を、直接または間に空気層を設けて接することで、高い蒸気圧の高温側から低い蒸気圧の低温側へ、蒸気圧差を利用して蒸気を移動させる操作である。膜蒸留は、蒸気圧差を利用するため、二つの液体の浸透圧差の影響を受けることがない。 Membrane distillation involves contacting a separation membrane (permeable membrane) made of a hydrophobic material with a high-temperature liquid on one surface and a low-temperature liquid on the other surface directly or with an air layer provided between them to achieve a high vapor pressure. It is an operation to move steam from the high temperature side of the steam pressure to the low temperature side of the low vapor pressure by using the vapor pressure difference. Since membrane distillation utilizes the vapor pressure difference, it is not affected by the osmotic pressure difference between the two liquids.
　一般に、液体を濃縮する場合、液体の持つ浸透圧が濃縮率の限界となること多い。例えば、海水淡水化や排水処理に広く用いられている逆浸透（ＲＯ）法は、液体に高い圧力を賦与、濃縮する操作であるが、膜の耐圧や高圧ポンプ圧力を超える浸透圧を持つ液体を濃縮することはできない。そのため、高い浸透圧を持つ液体をさらに濃縮するためには、ＲＯ法に加えて、蒸発法が使用されることが多い。 In general, when concentrating a liquid, the osmotic pressure of the liquid often becomes the limit of the concentration rate. For example, the reverse osmosis (RO) method, which is widely used for desalination of seawater and wastewater treatment, is an operation of applying high pressure to a liquid and concentrating it, but the liquid has an osmotic pressure exceeding the pressure resistance of the membrane and the high pressure pump pressure. Cannot be concentrated. Therefore, in order to further concentrate the liquid having a high osmotic pressure, the evaporation method is often used in addition to the RO method.
　膜蒸留法は、温度の異なる二つの液体の蒸気圧差を利用し、一般の蒸発法のように沸点まで温度を上昇させることは必要としない。そのため、比較的小さな温度差で高い濃度まで液体を濃縮することができ、排熱や太陽熱など、蒸発法では利用が難しい比較的低い温度の熱源を利用でき、減圧により液体の沸点を下げる必要がないなどの特徴を有している。 The membrane distillation method utilizes the vapor pressure difference between two liquids with different temperatures, and does not require raising the temperature to the boiling point as in the general evaporation method. Therefore, the liquid can be concentrated to a high concentration with a relatively small temperature difference, and a heat source with a relatively low temperature such as exhaust heat or solar heat, which is difficult to use by the evaporation method, can be used, and it is necessary to lower the boiling point of the liquid by decompression. It has features such as no.
　また、分離膜を隔て一方を原料水、反対面を空間とした場合、拡散により移動した水分子を凝縮させることにより不揮発性のイオン分や固体物質を除去した純度の高い液体水が得られる。一方、原料水側では固体物質や不揮発成分の濃縮が行われる（例えば、特許文献１～４）。 Also, when one side is the raw water and the other side is the space separated by the separation membrane, high-purity liquid water from which non-volatile ions and solid substances have been removed can be obtained by condensing the water molecules that have moved by diffusion. On the other hand, on the raw water side, solid substances and non-volatile components are concentrated (for example, Patent Documents 1 to 4).
　膜蒸留法において分離膜に求められる特性は疎水性（撥液性）および水分子の拡散透過性（通気性）である。疎水性が不十分であると凝縮水閉塞による有効面積低下や反対面への液体浸透が生じる。また空隙率が小さい場合、拡散透過に必要な通気性が小さくなる。特性向上には空隙率を高める構造と、空隙率を高めても液体浸透を妨げる撥液性の向上とが必要である。 The properties required for a separation membrane in the membrane distillation method are hydrophobicity (liquid repellency) and diffusion permeability of water molecules (breathability). Insufficient hydrophobicity causes a decrease in the effective area due to clogging of condensed water and liquid penetration into the opposite surface. Further, when the porosity is small, the air permeability required for diffusion transmission becomes small. In order to improve the characteristics, it is necessary to have a structure that increases the porosity and an improvement in the liquid repellency that hinders liquid penetration even if the porosity is increased.
　分離膜には、粒子成形体、メンブレンなどからなる多孔質体が従来用いられているが、粒子同士の結合により得られる粒子成形体は充填密度が高く通気性が低い。またポリテトラフルオロエチレン（ＰＴＦＥ）フィルムの延伸によりフィブリル化して得られるＰＴＦＥメンブレンにおいても、素材や形状の自由度が小さく素材の撥液性と通気性を向上させることは困難であるとともに、ＰＴＦＥは高価な素材であり、一般的な用途に応用する際には、出来上がった膜が高価格となってしまう問題がある。 A porous body made of a particle molded body, a membrane, etc. has been conventionally used as the separation membrane, but the particle molded body obtained by bonding the particles to each other has a high packing density and low air permeability. Further, even in a PTFE membrane obtained by fibrillation by stretching a polytetrafluoroethylene (PTFE) film, the degree of freedom of the material and shape is small, and it is difficult to improve the liquid repellency and breathability of the material. It is an expensive material, and when applied to general applications, there is a problem that the finished film becomes expensive.
　比較的安価な疎水性膜は、ポリプロピレンやポリエチレンなどの炭化水素系ポリマーフィルムを延伸することや、これらのポリマーを繊維状化することで得られる。しかしながら、これらの炭化水素系ポリマー膜の疎水性は不十分であり、膜蒸留法に利用すると、長期運転時に水蒸気によって膜細孔表面が親水化してしまい、蒸気だけでなく液体も透過してしまう問題がある。 A relatively inexpensive hydrophobic film can be obtained by stretching a hydrocarbon-based polymer film such as polypropylene or polyethylene, or by fibrizing these polymers. However, the hydrophobicity of these hydrocarbon-based polymer films is insufficient, and when used in the membrane distillation method, the surface of the membrane pores becomes hydrophilic due to water vapor during long-term operation, and not only vapor but also liquid permeates. There's a problem.
　撥液性と通気性を向上させ、長期安定性を達成する方法としては、熱可塑性もしくは溶媒可溶性により繊維形状を与え、更に撥液性を高める方法が知られている。例えば、樹脂内にパーフルオロ基を有した添加剤を混合する方法（例えば、特許文献５）、熱可塑性フッ素樹脂を溶融紡糸する方法（例えば、特許文献６および７）、パーフルオロ基を有したエマルジョン加工剤で表面をコーティング処理する方法（例えば、特許文献８）、プラズマおよびフッ素ガスなどを用い水素原子を置換することによりフッ素原子を導入する方法（例えば、特許文献９）等が例示される。 As a method of improving liquid repellency and breathability and achieving long-term stability, a method of imparting a fiber shape by thermoplasticity or solvent solubility and further enhancing the liquid repellency is known. For example, it has a method of mixing an additive having a perfluoro group in a resin (for example, Patent Document 5), a method of melt-spinning a thermoplastic fluororesin (for example, Patent Documents 6 and 7), and a perfluoro group. Examples thereof include a method of coating the surface with an emulsion processing agent (for example, Patent Document 8), a method of introducing a fluorine atom by substituting a hydrogen atom with plasma and fluorogas (for example, Patent Document 9), and the like. ..
　しかしながら、フッ素系樹脂やフッ素系低分子添加剤は、３２０℃を超える環境下においてはフッ素テロマーの脱離や熱分解物としてフッ化水素やフッ化カルボニルなどの生成がみられるため溶融紡糸には不適である。また、フッ素ガスやプラズマ処理によるフッ素原子導入では、フッ素ガスの漏洩防止や親水化を抑制するために酸素、水分量管理を厳密に行う必要があり、気密性の高い特殊設備が必要となる。また、生体蓄積性の問題により、パーフルオロオクタン酸（ＰＦＯＡ）およびパーフルオロオクタンスルホン酸（ＰＦＯＳ）ならびにその塩、ならびにテロマーを生じる母物質の使用、ならびにその製造が禁止されており、これらの材料を添加したり、ランダムにフッ素－水素置換が生じたり、熱分解や酸化分解を生じたりする工程は好ましいとは言えない。 However, fluorine-based resins and fluorine-based low-molecular-weight additives are suitable for melt spinning because hydrogen fluoride and carbonyl fluoride are observed as desorption of fluorine telomers and thermal decomposition products in an environment exceeding 320 ° C. Inappropriate. Further, in the introduction of fluorine atoms by fluorine gas or plasma treatment, it is necessary to strictly control the amount of oxygen and water in order to prevent leakage of fluorine gas and suppress hydrophilicity, and special equipment with high airtightness is required. In addition, due to bioaccumulation problems, the use and production of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) and their salts, as well as the parent material that produces telomer, are prohibited, and these materials are prohibited. It cannot be said that the step of adding the above, randomly causing fluorine-hydrogen substitution, and causing thermal decomposition or oxidative decomposition is not preferable.
　また、スパッタリングによりポリテトラフルオロエチレンをコーティングする手法も知られているが、飛翔する粒子が蒸着源側の最表層にのみ偏在するため、必要とする耐浸透性を得ることが困難であるとともに、ポリテトラフルオロエチレンの分解や酸化生成物の懸念がある。 A method of coating polytetrafluoroethylene by sputtering is also known, but it is difficult to obtain the required permeability resistance because the flying particles are unevenly distributed only on the outermost layer on the vapor deposition source side. There are concerns about decomposition of polytetrafluoroethylene and oxidation products.
　また、一般的に撥水撥油剤として用いられる含フッ素アクリレート系加工剤は、ＰＦＯＡおよびＰＦＯＳ規制に対応させるようにＣ6Ｆ13以下の短鎖パーフルオロ基が側鎖として用いられるので、側鎖の耐加水分解性や効果の永続性に乏しいという耐久面、および、空隙率を維持したまま担体表面にコーティングさせる難いという加工面における課題がある。 In addition, the fluorine-containing acrylate-based processing agent generally used as a water-repellent and oil-repellent agent uses a short-chain perfluoro group of C 6 F 13 or less as a side chain so as to comply with PFOA and PFOS regulations. There are problems in terms of durability, which is poor in hydrolysis resistance and durability of the effect, and in terms of processing, which is difficult to coat the carrier surface while maintaining the porosity.
　また、アモルファス化により可溶性と熱可塑性を付与し、コーティング性を付与したフッ素系樹脂（例えば、特許文献１０）も知られているが、主骨格として特殊なモノマーを用いる必要があり、著しく高コストになるという問題がある。 Further, a fluororesin (for example, Patent Document 10) which is made soluble and thermoplastic by amorphization and has a coating property is also known, but it is necessary to use a special monomer as the main skeleton, and the cost is extremely high. There is a problem of becoming.
日本国公開特許公報「特開昭６０－１８７３０５」Japanese Patent Publication "Japanese Patent Laid-Open No. 60-187305" 日本国公開特許公報「特開平７－２５１０３６」Japanese Patent Publication "Japanese Patent Laid-Open No. 7-251036" 日本国公開特許公報「特開平１－１７６４０４」Japanese Patent Publication "Japanese Patent Laid-Open No. 1-176404" 日本国公開特許公報「特開平９－１１４３」Japanese Patent Publication "Japanese Patent Laid-Open No. 9-1143" 日本国公開特許公報「特開２００９－６３１３」Japanese Patent Publication "Japanese Patent Laid-Open No. 2009-6313" 日本国公開特許公報「特開２００２－２６６２１９」Japanese Patent Publication "Japanese Patent Laid-Open No. 2002-266219" 日本国公開特許公報「特開２００７－１８９９５」Japanese Patent Publication "Japanese Patent Laid-Open No. 2007-18995" 日本国公開特許公報「特開２００４－３５２９７６」Japanese Patent Publication "Japanese Patent Laid-Open No. 2004-352976" 日本国公表特許公報「特表２００８－５４０８５６」Patent Gazette published in Japan "Special Table 2008-540856" 国際公開公報「ＷＯ２００９／１０４６９９」International Publication "WO2009 / 104669"
　本発明は、上記の従来公知の分離膜の問題を解決するものであり、撥液性と通気性、および長期運転安定性を達成できる新規な分離膜を提供することを目的とする。 The present invention solves the above-mentioned problems of conventionally known separation membranes, and an object of the present invention is to provide a novel separation membrane capable of achieving liquid repellency, breathability, and long-term operation stability.
　本発明の膜蒸留用多孔質膜は前記の課題を解決するために、発明者が鋭意検討した結果完成するに到った。すなわち、本発明は下記の通りである。
　１．熱可塑性樹脂を用いた繊維状物から成り、当該繊維状物の表面にポリテトラフルオロエチレンが担持されていることを特徴とする膜蒸留用多孔質膜。
　２．前記繊維状物は、メルトブローン法により得られた不織布であることを特徴とする上記１に記載の膜蒸留用多孔質膜。
　３．表裏の撥液性に差異があることを特徴とする上記１または２に記載の膜蒸留用多孔質膜。 The porous membrane for membrane distillation of the present invention has been completed as a result of diligent studies by the inventor in order to solve the above-mentioned problems. That is, the present invention is as follows.
1. 1. A porous membrane for membrane distillation, which is made of a fibrous material using a thermoplastic resin and in which polytetrafluoroethylene is supported on the surface of the fibrous material.
2. 2. The porous membrane for membrane distillation according to 1 above, wherein the fibrous material is a non-woven fabric obtained by the melt blown method.
3. 3. The porous membrane for membrane distillation according to 1 or 2 above, wherein the liquid repellency on the front and back is different.
　本発明により、通気性および撥液性に優れた膜蒸留用多孔質膜を得ることが可能となる。 According to the present invention, it is possible to obtain a porous membrane for membrane distillation having excellent breathability and liquid repellency.
　以下に本発明の実施形態を例示するが、本発明の趣旨に従い最適な構成を選択することができる。 An embodiment of the present invention will be illustrated below, but the optimum configuration can be selected according to the gist of the present invention.
　本実施形態の膜蒸留用多孔質膜は、熱可塑性樹脂からなる繊維状物であり、表面にポリテトラフルオロエチレン（ＰＴＦＥ）が担持されてなる。 The porous membrane for membrane distillation of the present embodiment is a fibrous material made of a thermoplastic resin, and polytetrafluoroethylene (PTFE) is supported on the surface thereof.
　本実施形態において繊維状物とは、長繊維または短繊維からなる織編物、不織布、綿状物等の繊維状物や延伸フィルムから得られる繊維状物を含み、素材、厚み、目付、繊維径など必要特性に応じ成形したものを用いることができる。遮水性と通気性に優れた構造体を得るには不織布を用いることがより好ましい。 In the present embodiment, the fibrous material includes a fibrous material such as a woven or knitted fabric made of long fibers or short fibers, a non-woven fabric, a cotton-like material, or a fibrous material obtained from a stretched film, and includes a material, thickness, texture, and fiber diameter. It is possible to use a molded product according to the required characteristics. It is more preferable to use a non-woven fabric in order to obtain a structure having excellent water impermeability and breathability.
　不織布を得る方法としては、単成分繊維、芯鞘繊維やサイドバイサイド繊維といった複合繊維、分割繊維等の短繊維をカーディング、エアレイド、湿式抄紙法などによりシート化する方法、連続繊維をスパンボンド法、メルトブローン法、エレクトロスピニング法、フォーススピニング法などによりシート化する方法など、従来公知の方法を用いることが可能である。液滴の浸透を抑制し、融着した効果的に利用する観点から緻密で細繊度を容易に得られるメルトブローン法、エレクトロスピニング法やフォーススピニング法で得られる不織布が好ましく、残溶剤の処理を必要としない観点からメルトブローン法、溶融エレクトロスピニング法、溶融フォーススピニング法で得られる不織布がより好ましく、特に好ましくはメルトブローン法で得られる不織布である。さらに好ましくは融点３２０℃以下の熱可塑性樹脂からなるメルトブローン不織布である。 As a method for obtaining a non-woven fabric, a method of sheeting short fibers such as single component fibers, composite fibers such as core-sheath fibers and side-by-side fibers, and split fibers by carding, airlaid, wet papermaking method, etc. Conventionally known methods such as a method of forming a sheet by a melt blown method, an electrospinning method, a force spinning method, or the like can be used. Non-woven fabrics obtained by the melt blown method, electrospinning method, or force spinning method, which can easily obtain fineness and fineness, are preferable from the viewpoint of suppressing the penetration of droplets and effectively using them fused, and treatment of residual solvent is required. The non-woven fabric obtained by the melt-blown method, the molten electrospinning method, and the molten force spinning method is more preferable, and the non-woven fabric obtained by the melt-blown method is particularly preferable. More preferably, it is a melt-blown non-woven fabric made of a thermoplastic resin having a melting point of 320 ° C. or lower.
　繊維状物に用いられる繊維の直径は、０．００１～１００μｍであることが好ましく、０．００５～２０μｍであることがより好ましく、０．０１～１０μｍであることがさらに好ましく、０．０２～５μｍであることが特に好ましく、０．０３～３μｍであることが最も好ましい。繊維の直径が１００μｍよりも大きい場合には、繊維間隙が大きくなるため膜蒸留用多孔質膜において液体のバリア性に劣り、繊維の直径が０．００１μｍよりも小さい場合には膜蒸留用多孔質膜の通気性が低下するとともに耐圧性を与えることが困難となる。 The diameter of the fibers used in the fibrous material is preferably 0.001 to 100 μm, more preferably 0.005 to 20 μm, further preferably 0.01 to 10 μm, and 0.02 to 0.02 to 0.02 to 10 μm. It is particularly preferably 5 μm, and most preferably 0.03 to 3 μm. When the fiber diameter is larger than 100 μm, the fiber gap becomes large, so that the liquid barrier property is inferior in the porous membrane for membrane distillation. When the fiber diameter is smaller than 0.001 μm, the porous membrane distillation The air permeability of the membrane is reduced and it becomes difficult to impart pressure resistance.
　繊維状物の厚さは、０．０１～１０ｍｍであることが好ましく、０．０２～５ｍｍであることがより好ましく、０，０５～３ｍｍであることがさらに好ましい。厚さが１０ｍｍよりも大きいときは、膜蒸留用多孔質膜の蒸気の透過速度が低下することがあり、また厚さが０．０１ｍｍよりも小さいときは、膜蒸留用多孔質膜の強度が低下することがある。繊維状物はそのものの厚みを変化させて膜蒸留用多孔質膜を形成してもよいし、繊維状物を複層重ねて膜蒸留用多孔質膜を形成してもよい。 The thickness of the fibrous material is preferably 0.01 to 10 mm, more preferably 0.02 to 5 mm, and even more preferably 0.05 to 3 mm. When the thickness is larger than 10 mm, the vapor permeation rate of the porous membrane for membrane distillation may decrease, and when the thickness is smaller than 0.01 mm, the strength of the porous membrane for membrane distillation is high. May decrease. The fibrous material itself may be changed in thickness to form a porous membrane for membrane distillation, or the fibrous material may be laminated in multiple layers to form a porous membrane for membrane distillation.
　膜蒸留用多孔質膜は、それによって隔たれた２つの液体の温度差により生じる蒸気圧差を蒸気の移動の駆動力として利用し、液体そのものの移動を抑制するため、繊維状物は繊維間隙を一定の範囲に収めることが好ましい。繊維間隙を示すパラメーターとしては、以下の式（１）で定義される動水半径がある。
　動水半径＝繊維状物の細孔体積／繊維状物の細孔表面積＝ｄ／４ｘ（ρ／ω－１）　　　（１）
ここで、ｄは繊維の直径、ρはポリマーの密度、ωは繊維状物のかさ密度である。
　式（１）に示すように、動水半径は、ポリマーが同じであれば、繊維の直径と繊維物のかさ密度の関数となる。 In the porous membrane for membrane distillation, the vapor pressure difference caused by the temperature difference between the two liquids separated by the membrane is used as a driving force for the movement of the vapor, and the movement of the liquid itself is suppressed. Therefore, the fibrous material keeps the fiber gap constant. It is preferable to keep it within the range of. As a parameter indicating the fiber gap, there is a hydraulic radius defined by the following equation (1).
Radius of water flow = Volume of pores of fibrous material / Surface area of pores of fibrous material = d / 4x (ρ / ω-1) (1)
Here, d is the diameter of the fiber, ρ is the density of the polymer, and ω is the bulk density of the fibrous material.
As shown in the formula (1), the radius of water kinetics is a function of the diameter of the fiber and the bulk density of the fiber if the polymers are the same.
　本実施形態の繊維状物の動水半径は、０，１μm～４０μmであることが好ましく、０．３μｍ～２０μｍであることがより好ましく、０．５μｍ～１０μｍであることがさらに好ましい。動水半径が４０μｍよりも大きいときは、液体のバリア性が低下することがあり、０．１μｍよりも小さいときは、通気性が低下することがある。 The hydraulic radius of the fibrous material of the present embodiment is preferably 0.1 μm to 40 μm, more preferably 0.3 μm to 20 μm, and even more preferably 0.5 μm to 10 μm. When the radius of water flow is larger than 40 μm, the barrier property of the liquid may decrease, and when it is smaller than 0.1 μm, the air permeability may decrease.
　本実施形態の繊維状物は単独の製法、素材からなる均一物であってもよく、製法、素材および繊維径の異なる２種以上の素材を用いてなる混合物であってもよい。また、繊維の断面形状は円形のみならず、矩形、星型、クローバー状などの異形断面も好ましく用いることができる。 The fibrous material of the present embodiment may be a uniform product made of a single manufacturing method and a material, or may be a mixture made of two or more kinds of materials having different manufacturing methods, materials and fiber diameters. Further, the cross-sectional shape of the fiber is not limited to a circular shape, but a rectangular, star-shaped, clover-shaped or other irregular cross-sectional shape can also be preferably used.
　本実施形態の繊維状物は特に制限されないが、吸湿性の低い合成樹脂素材であることが好ましい。具体的には非フッ素系合成樹脂の場合にはポリエステル、ポリカーボネート、ポリアミド、ポリオレフィン、環状オレフィン、ポリ塩化ビニル、ポリ塩化ビニリデン、ポリフェニレンサルファイド、ポリフェニレンオキサイド、フェノール樹脂などが挙げられ、なかでもポリエチレン、ポリブテン、ポリプロピレン、ポリメチルペンテン、ポリスチレン、環状オレフィン等のポリオレフィンが好ましい。所望の特性がえられるものであれ2種以上の異なる樹脂成分を混合することにより得られるブレンドポリマーなどである。 The fibrous material of the present embodiment is not particularly limited, but is preferably a synthetic resin material having low hygroscopicity. Specifically, in the case of non-fluorinated synthetic resin, polyester, polycarbonate, polyamide, polyolefin, cyclic olefin, polyvinyl chloride, polyvinylidene chloride, polyphenylene sulfide, polyphenylene oxide, phenol resin and the like can be mentioned, among which polyethylene and polybutene can be mentioned. , Polyolefin, polymethylpentene, polystyrene, cyclic olefin and other polyolefins are preferable. It is a blended polymer obtained by mixing two or more different resin components, even if they have desired properties.
　上記合成樹脂には樹脂自体の劣化を抑制するために、従来公知の配合剤および配合組成を好ましく用いることができる。たとえば、配合剤としては各種金属塩、酸化防止剤、光安定化剤、金属不活性化剤、結晶核剤などを例示することができる。 For the synthetic resin, conventionally known compounding agents and compounding compositions can be preferably used in order to suppress deterioration of the resin itself. For example, examples of the compounding agent include various metal salts, antioxidants, light stabilizers, metal inactivating agents, and crystal nucleating agents.
　本実施の形態の膜蒸留用多孔質膜の疎水性向上のために、繊維状物の表面に担持されているＰＴＦＥは、融点３５℃以上３２０℃以下の低融点ＰＴＦＥが好ましい。さらに、融点６０℃以上３１５℃以下のＰＴＦＥが含まれていることが好ましく、８０℃以上３００℃以下のＰＴＦＥが含まれていることがより好ましく、１００℃以上２９０℃以下のＰＴＦＥが含まれていることが特に好ましい。融点が上記範囲であれば分子量に分布を有したＰＴＦＥでもよい。 In order to improve the hydrophobicity of the porous membrane for membrane distillation of the present embodiment, the PTFE supported on the surface of the fibrous material is preferably low melting point PTFE having a melting point of 35 ° C. or higher and 320 ° C. or lower. Further, it is preferable that PTFE having a melting point of 60 ° C. or higher and 315 ° C. or lower is contained, and more preferably, PTFE of 80 ° C. or higher and 300 ° C. or lower is contained, and PTFE of 100 ° C. or higher and 290 ° C. or lower is contained. Is particularly preferred. As long as the melting point is in the above range, PTFE having a distribution in molecular weight may be used.
　融点３５℃以上３２０℃以下の低融点ＰＴＦＥを用いる理由としては、
（１）一般的なＰＴＦＥは３２０℃以上の融点を持つため担体（とりわけ合成高分子）の劣化および耐熱性に問題が生じること、
（２）本実施形態で用いられる低融点ＰＴＦＥ（最小表面張力１３ｍＮ／ｍ以上１７．５ｍＮ／ｍ未満）は一般的なＰＴＦＥ（最小表面張力１７.５ｍＮ／ｍ）に比して結晶形やＣＦ３基末端密度により疎水性が高いこと、
（３）実用可能な温度範囲で融点および沸点を有しており、常圧、減圧、真空条件下で加熱することにより物理蒸着処理（ＰＶＤ処理）が可能なこと、
（４）付着成分の分子量や構造の制御が困難なプラズマ処理（炭化フッ素化）やスパッタリング処理と異なりＰＦＯＡやＰＦＯＳ規制の観点から有利であること、
（５）常温で固体であり結晶性を有しているため分子配向の変化による撥油性変化が抑制されること、
（６）明確な融点や流動性を有しているため溶融塗布が可能であること、
（７）炭化水素系の疎水性樹脂表面に対しても、界面活性剤を用いることなく濡れ性を発現すること、
などを例示することができる。 The reason for using low melting point PTFE with a melting point of 35 ° C or higher and 320 ° C or lower is
(1) Since general PTFE has a melting point of 320 ° C. or higher, problems occur in deterioration and heat resistance of carriers (particularly synthetic polymers).
(2) The low melting point PTFE (minimum surface tension 13 mN / m or more and less than 17.5 mN / m) used in the present embodiment has a crystalline form or CF as compared with general PTFE (minimum surface tension 17.5 mN / m). High hydrophobicity due to the density of 3 bases,
(3) It has a melting point and boiling point in a practical temperature range, and physical vapor deposition treatment (PVD treatment) can be performed by heating under normal pressure, reduced pressure, and vacuum conditions.
(4) It is advantageous from the viewpoint of PFOA and PFOS regulation unlike plasma treatment (fluorinated carbide) and sputtering treatment in which it is difficult to control the molecular weight and structure of the adhered component.
(5) Since it is solid at room temperature and has crystallinity, changes in oil repellency due to changes in molecular orientation are suppressed.
(6) Since it has a clear melting point and fluidity, it can be melt-coated.
(7) To develop wettability even on the surface of a hydrocarbon-based hydrophobic resin without using a surfactant.
Etc. can be exemplified.
　上記特性を利用し本実施形態にて用いられるＰＴＦＥの担持方法としては、例えば、ＰＴＦＥを融点以上熱分解温度以下の温度で蒸散させ担体上で冷却固化、必要に応じてＰＴＦＥの融点以上で熱処理を行うことで固定化する方法を挙げることができる。 As a method for supporting PTFE used in the present embodiment by utilizing the above characteristics, for example, PTFE is evaporated at a temperature equal to or higher than the melting point and lower than the thermal decomposition temperature, cooled and solidified on the carrier, and if necessary, heat-treated at the melting point or higher of PTFE. The method of immobilization can be mentioned by performing.
　ＰＴＦＥは、使用時には固体としての安定性を発現し、加熱時には液体および気体としての特性を有し物理蒸着法（ＰＶＤ法）の素材として好ましく用いることができる。ＰＴＦＥを熱分解温度以下で加熱することにより、ＰＴＦＥの構造を保持することができるため、分子量や構造の面で不定形なフッ素重合体が生じるプラズマ処理や高分子量ＰＴＦＥを原料とした高温での熱分解蒸着法に対し、有利な特徴である。 PTFE exhibits stability as a solid when used, has properties as a liquid and gas when heated, and can be preferably used as a material for a physical vapor deposition method (PVD method). By heating PTFE below the thermal decomposition temperature, the structure of PTFE can be maintained, so plasma treatment that produces an amorphous fluorine polymer in terms of molecular weight and structure, and high temperature using high molecular weight PTFE as a raw material This is an advantageous feature for the thermal decomposition vapor deposition method.
　本実施形態にて用いられるＰＴＦＥは、熱分解温度となる３２０℃以下に融点を有しており、融点以上の温度においては蒸散させることで蒸着加工を行うことが可能である。たとえば常圧（大気中１気圧）における融点に関し、ｎ－Ｃ10Ｆ22からなる場合には融点３６℃、ｎ－Ｃ12Ｆ26からなる場合には融点７６℃、ｎ－Ｃ14Ｆ30からなる場合には融点１０３℃、ｎ－Ｃ16Ｆ34からなる場合には融点１２５℃、ｎ－Ｃ20Ｆ42からなる場合には融点１６７℃、ｎ－Ｃ２４Ｆ５０、からなる場合には融点１９０℃、ｎ－Ｃ31Ｆ64からなる場合には融点２１９℃を有している。 The PTFE used in the present embodiment has a melting point of 320 ° C. or lower, which is the thermal decomposition temperature, and the vapor deposition process can be performed by evaporating the temperature above the melting point. For example, regarding the melting point at normal pressure (1 atm in the atmosphere), if it consists of n-C 10 F 22 , the melting point is 36 ° C, and if it consists of n-C 12 F 26 , the melting point is 76 ° C, from n-C 14 F 30. If the melting point is 103 ° C, the melting point is 125 ° C if it is composed of n-C 16 F 34 , the melting point is 167 ° C if it is composed of n-C 20 F 42, and if it is composed of n-C 24 F 50 . When it has a melting point of 190 ° C. and n—C 31 F 64, it has a melting point of 219 ° C.
　蒸着加工の手法としては、各種熱源によりテトラフルオロエチレンを加熱することで蒸気を発生させ、より低温に保持した担体表面に液滴または結晶として析出させる方法が用いられる。かかる手法は、加工面全体を一度に処理するバッチ法であっても、担体または反応槽を移動させることで、担体の異なる加工面を連続的に処理する方法のいずれであっても好ましく用いられる。 As a method of vapor deposition, a method is used in which vapor is generated by heating tetrafluoroethylene with various heat sources and deposited as droplets or crystals on the surface of the carrier kept at a lower temperature. Such a method is preferably used regardless of whether it is a batch method in which the entire processed surface is processed at once, or a method in which the processed surfaces of different carriers are continuously processed by moving the carrier or the reaction vessel. ..
　蒸着加工は加圧、常圧、減圧、真空状態およびその圧力のスイング、大気中および不活性ガスいずれの雰囲気においても好ましく実施することができる。減圧または真空状態とすることで、蒸散速度の向上および蒸散温度の低減が可能であり、加圧により蒸散物の析出を促進することができる。また、真空または不活性雰囲気とすることでＰＴＦＥや担体の酸化を抑制することが可能であるが、本実施形態では熱分解温度以下で低温処理が可能であるためコスト面で大気雰囲気を用いることも可能である。 The vapor deposition process can be preferably carried out in any of pressure, normal pressure, reduced pressure, vacuum state and its pressure swing, atmosphere and atmosphere of an inert gas. By reducing the pressure or setting the vacuum, it is possible to improve the transpiration rate and reduce the transpiration temperature, and pressurize the transpiration to promote the precipitation of the transpiration. Further, it is possible to suppress the oxidation of PTFE and the carrier by creating a vacuum or an inert atmosphere, but in the present embodiment, since low temperature treatment is possible at the thermal decomposition temperature or lower, the atmospheric atmosphere is used in terms of cost. Is also possible.
　本実施形態においては、ＰＴＦＥの担持条件ならびに分子量の調整により目的に応じて好ましい付着状態とすることができる。とりわけ、繊維状物などの多孔質構造体では、真空度が高い場合には、分子の平均自由工程が大きくＰＴＦＥは蒸散側の担体表面に偏在し、低真空または常圧、加圧条件の場合には回り込みによる均一性向上が可能となる。付着面を調整するために、同一担体において圧力のスイングや加工面（表裏）を変えた処理なども好ましい方法である。 In the present embodiment, a preferable adhesion state can be obtained according to the purpose by adjusting the carrying conditions of PTFE and the molecular weight. In particular, in a porous structure such as a fibrous material, when the degree of vacuum is high, the mean free path of molecules is large and PTFE is unevenly distributed on the carrier surface on the evaporation side, and in the case of low vacuum or normal pressure and pressure conditions. It is possible to improve the uniformity by wrapping around. In order to adjust the adhesion surface, pressure swing and treatment with different processed surfaces (front and back) on the same carrier are also preferable methods.
　特に本実施形態においてはＰＴＦＥが蒸着法により担持され、また１種もしくは２種以上の分子量を有することにより融点や拡散速度差を利用することが可能であり、繊維層厚み方向に対するＰＴＦＥの担持量および撥液性に関して傾斜機能を容易に与えることが可能である。 In particular, in the present embodiment, PTFE is supported by a vapor deposition method, and by having one or more molecular weights, it is possible to utilize the difference in melting point and diffusion rate, and the amount of PTFE supported in the fiber layer thickness direction. And it is possible to easily provide a tilting function with respect to liquid repellency.
　したがって、本実施形態においては、繊維状物に担持されているＰＴＦＥは上記の担持条件および原料となるＰＴＦＥ特性にしたがって、１つの分子量であっても、２つ以上の分子量を有していてもよい。すなわち、本実施形態では、２種以上のＰＴＦＥを用い分子量分布を持たせることも好ましい。本実施形態にて用いられるＰＴＦＥは、一つの分子量を有するＰＴＦＥを混合してもよいし、あらかじめ分布を有する混合物ものをもちいることもできる。市販混合物として、セントラル硝子株式会社製低分子量ＰＴＦＥセフラルルーブ（登録商標）Ｖにおいては、融点範囲として１００～２９０℃（ピーク温度２７０℃）を有しているため、１００℃以上で加熱することにより蒸着源として用いることが可能であり、ＰＴＦＥ全体が液状化する２９０℃以上３２０℃以下で加熱して用いることも好ましい。示差熱熱質量同時測定については、後述する。 Therefore, in the present embodiment, the PTFE supported on the fibrous material may have one molecular weight or two or more molecular weights according to the above-mentioned supporting conditions and the PTFE characteristics of the raw material. Good. That is, in the present embodiment, it is also preferable to use two or more kinds of PTFE to have a molecular weight distribution. As the PTFE used in the present embodiment, PTFE having one molecular weight may be mixed, or a mixture having a distribution in advance may be used. As a commercially available mixture, low molecular weight PTFE liquefaction (registered trademark) V manufactured by Central Glass Co., Ltd. has a melting point range of 100 to 290 ° C. (peak temperature 270 ° C.), and therefore is vapor-deposited by heating at 100 ° C. or higher. It can be used as a source, and it is also preferable to heat the entire PTFE at 290 ° C. or higher and 320 ° C. or lower to liquefy it. The simultaneous measurement of differential thermogravimetric mass will be described later.
　本実施形態においては、ＰＴＦＥの蒸着加工時または蒸着加工後に繊維状物（担体）を常温以上、融点以下にて加熱処理してもよい。例えば、繊維状物がポリプロピレンから成るものである場合においては、４０℃以上１４０℃以下にて加熱処理されることが好ましく、５０℃以上１４０℃以下がより好ましく、６０℃以上１４０℃以下がさらに好ましい。かかる処理により繊維状物とＰＴＥＦとの接着性向上、低分子量物の除去によるエレクトレットの安定化効果や遊離するＶＯＣ成分が低減される。具体的には蒸着加工時には蒸着槽温度、担体の冷却、加熱により調整することが可能であり、蒸着加工後に別途実施することも可能である。 In the present embodiment, the fibrous material (carrier) may be heat-treated at room temperature or higher and melting point or lower during or after the vapor deposition process of PTFE. For example, when the fibrous material is made of polypropylene, it is preferably heat-treated at 40 ° C. or higher and 140 ° C. or lower, more preferably 50 ° C. or higher and 140 ° C. or lower, and further preferably 60 ° C. or higher and 140 ° C. or lower. preferable. By such treatment, the adhesiveness between the fibrous substance and PTFE is improved, the effect of stabilizing the electret by removing the low molecular weight substance and the released VOC component are reduced. Specifically, it is possible to adjust the temperature of the vapor deposition tank, the cooling of the carrier, and the heating during the vapor deposition process, and it is also possible to separately carry out the process after the vapor deposition process.
　本実施形態においてはＰＴＦＥは蒸気の状態で付着させた後冷却固化させてもよいし、凝集させた液体や固体粒子として付着させてもよい。担体表面へのＰＴＦＥの担持を微細な凹凸構造とすることで撥液性を向上させることができる。ＰＴＦＥの蒸気が存在する雰囲気に凝縮核となる高融点ＰＴＦＥや有機、無機粒子、他種液体蒸気やミストを同時に供給する方法も、付着速度の向上や凝縮核へ担持が同時に行え、更には繊維状物に微細な凹凸を加えることができるため好ましい方法である。 In the present embodiment, PTFE may be attached in a vapor state and then cooled and solidified, or may be attached as agglomerated liquid or solid particles. The liquid repellency can be improved by forming the PTFE on the surface of the carrier to have a fine uneven structure. The method of simultaneously supplying high melting point PTFE, organic, inorganic particles, liquid vapors of other species, and mist, which are condensed nuclei, to the atmosphere where the vapor of PTFE exists can also improve the adhesion rate and simultaneously support the condensed nuclei, and further, fibers. This is a preferable method because fine irregularities can be added to the shape.
　前記微細な凹凸構造としては、捕集対象とする液滴よりも微細であることが好ましい。表面積の増加による濡れ仕事の増加のみならず、付着した粒子と担体の間に空気層が存在することで、Ｃａｓｓｉｅ－Ｂａｘｔｅｒ理論に沿った高い撥液表面を得ることができるためである。 The fine uneven structure is preferably finer than the droplet to be collected. This is because not only the increase in wet work due to the increase in surface area but also the presence of an air layer between the adhered particles and the carrier makes it possible to obtain a high liquid-repellent surface according to the Cassie-Baxter theory.
　本実施形態の繊維状物により得られる撥液性に関しては、原水に含まれる成分及び、必要とする耐水圧に必要とされる特性に応じて任意に調整することが可能であることを特徴とする。表面特性を確認するために、ＪＩＳ　Ｋ６７６８およびＡＡＴＣＣ１１８法により用いられる表面張力試験液を用いる事ができる。１０秒以内の浸透を与える表面張力として、たとえばＰＰメルトブローンにおける代表値としては無加工状態である３７ｍＮ／ｍよりも向上されてなることが好ましい。具体は少なくとも一面が３１ｍＮ／ｍ以下が好ましく、２９ｍＮ／ｍ以下がより好ましく、２７ｍＮ／ｍ以下がさらに好ましく、２５．４ｍＮ／ｍ以下が最も好ましい。多孔質担体への浸透特性は接触角に由来する毛細管現象と相関があるため、構造体が同一であればシート形状での撥液性と静水圧との関係が導かれる。 The liquid repellency obtained from the fibrous material of the present embodiment is characterized in that it can be arbitrarily adjusted according to the components contained in the raw water and the characteristics required for the required water pressure resistance. To do. In order to confirm the surface characteristics, the surface tension test solution used by JIS K6768 and the AATCC118 method can be used. The surface tension that gives permeation within 10 seconds, for example, as a typical value in PP melt blown, is preferably improved from 37 mN / m in the unprocessed state. Specifically, at least one surface is preferably 31 mN / m or less, more preferably 29 mN / m or less, further preferably 27 mN / m or less, and most preferably 25.4 mN / m or less. Since the penetration property into the porous carrier correlates with the capillary phenomenon derived from the contact angle, if the structures are the same, the relationship between the liquid repellency in the sheet shape and the hydrostatic pressure is derived.
　本実施形態の膜蒸留用多孔質膜は単体で用いるのみならず、強度や蒸散性向上及び実用性向上のための機能付与のため他材料と積層して用いることも可能である。 The porous membrane for membrane distillation of the present embodiment can be used not only as a single substance, but also as a laminate with other materials in order to impart functions for improving strength, transpiration, and practicality.
　例えば、スパンボンド不織布、サーマルボンド不織布、ネットならびに発泡ウレタンやガラスフィルターなどを利用した構造支持体、バイオフィルムの生成や原水に含まれる物質の付着を抑制するための表面加工ならびに、加工シートとの積層など必要に応じて用いることができる。例えば、積層する他材料として親水性の材料を使用することにより、疎水性膜の表面に液体が供給されやすくなり、透過速度が上がることが期待できる。また、本実施形態の膜蒸留用多孔質膜の間に、そのものだけでは強度を保つことができない極薄の疎水性フィルムを挟むことで、液体の透過を抑制することができる。
　本実施形態において、温度の異なる二つの液体は、膜蒸留用多孔質膜からなる膜面に直接接触させることも、膜面と二つの液体の間に空気層を設けて間接接触させることもできる。直接接触させることで、膜両面の二つの液体の蒸気圧差を最大化させることができる。また、膜面と二つの液体の間に空気層を設けることで、二つの液体間の熱伝導率を下げることができ、高い熱効率が得られる。膜面と液体の間の空気層は、高温側もしくは低温側液体のどちらかに設けることも、両側に設けることも可能である。 For example, spunbonded non-woven fabric, thermal-bonded non-woven fabric, net, structural support using urethane foam, glass filter, etc., surface processing to suppress the formation of biofilm and adhesion of substances contained in raw water, and processing sheet. It can be used as needed, such as laminating. For example, by using a hydrophilic material as another material to be laminated, it is expected that the liquid is easily supplied to the surface of the hydrophobic membrane and the permeation rate is increased. Further, by sandwiching an ultrathin hydrophobic film whose strength cannot be maintained by itself between the porous membranes for membrane distillation of the present embodiment, it is possible to suppress the permeation of the liquid.
In the present embodiment, the two liquids having different temperatures can be brought into direct contact with the membrane surface made of a porous membrane for membrane distillation, or can be brought into indirect contact by providing an air layer between the membrane surface and the two liquids. .. The direct contact can maximize the vapor pressure difference between the two liquids on both sides of the membrane. Further, by providing an air layer between the film surface and the two liquids, the thermal conductivity between the two liquids can be lowered, and high thermal efficiency can be obtained. The air layer between the membrane surface and the liquid can be provided on either the high temperature side or the low temperature side liquid, or can be provided on both sides.
　以下、本発明の実施例について説明する。初めに実施例及び比較例で作製した多孔質膜についての試験方法を下記に示す。 Hereinafter, examples of the present invention will be described. First, the test method for the porous membranes prepared in Examples and Comparative Examples is shown below.
（１）繊維径
　走査型電子顕微鏡を用いて繊維状物を形成する繊維を１０００倍にて撮影し、得られた画像を用い、画面中の繊維３０本をランダムに抽出し、その繊維直径の平均を繊維径とした。
（２）厚み
　ミツトヨ製ダイヤルシックネスゲージ７３０１を用いて繊維状物の厚みを１０か所測定し、その平均値を繊維状物の厚みとした。
（３）かさ密度
　乾燥させた繊維状物を３ｃｍｘ３ｃｍに切り出したサンプルを１０個の平均重量から、繊維状物の目付（ｇ／ｍ２）を求め、（２）で求めた繊維状物の厚みからかさ密度を計算した。
（４）融点
　ＰＴＦＥ原料もしくは加工済担体をアルミ製密閉パンに封入後、３００℃まで昇温、冷却することで、ブランクとの吸収熱量の差異として確認した。
（５）撥液度
　ＪＩＳ Ｋ　６７６８に定められた配合にて表面張力４０～２６ｍＮ／ｍの範囲にて１ｍＮ／ｍ間隔でぬれ張力試験液を１５種類調製し、別途２５．４ｍＮ／ｍのぬれ張力試験液を調整し、１６種類のぬれ張力試験液を準備した。そして、表面張力４０ｍＮ／ｍの試験液を用いて微生物試験用マイクロピペッターにて試験サンプル表面に５０μＬずつ静置し１０秒後の浸透度合いを観察した。その後、表面張力３９ｍＮ／ｍの試験液、表面張力３８ｍＮ／ｍの試験液、表面張力２６ｍＮ／ｍの試験液、表面張力２５．４ｍＮ／ｍの試験液の順に浸透度合いを同様に観察し、完全吸収されない最も表面張力の小さな試験液の表面張力をＪＩＳ Ｋ　６７６８ぬれ張力試験液での撥油度とした。なお、順次測定を行った結果、試験材料の表裏の状態に差異が生じる場合には、より表面張力の小さな方の表面張力を撥油度とした（以降の他の撥油度測定においても同様である）。また、２５．４ｍＮ／ｍの試験液が非浸透の場合は、浸透した試験液がないため、試験結果を２５．４ｍＮ／ｍとした。 (1) Fiber diameter A scanning electron microscope was used to photograph the fibers forming the fibrous material at a magnification of 1000, and 30 fibers on the screen were randomly extracted using the obtained image to obtain the fiber diameter. The average was taken as the fiber diameter.
(2) Thickness The thickness of the fibrous material was measured at 10 points using a dial thickness gauge 7301 manufactured by Mitutoyo, and the average value was taken as the thickness of the fibrous material.
(3) Bulk Density The basis weight (g / m 2 ) of the fibrous material was obtained from the average weight of 10 samples obtained by cutting the dried fibrous material into 3 cm x 3 cm, and the thickness of the fibrous material obtained in (2). The teasing density was calculated.
(4) Melting point The PTFE raw material or processed carrier was sealed in an aluminum sealed pan, then heated and cooled to 300 ° C., and confirmed as a difference in the amount of heat absorbed from the blank.
(5) Liquid repellency 15 types of wet tension test solutions were prepared at 1 mN / m intervals in the range of surface tension of 40 to 26 mN / m according to the formulation specified in JIS K 6768, and a separate wetness of 25.4 mN / m The tension test solution was adjusted, and 16 kinds of wet tension test solutions were prepared. Then, using a test solution having a surface tension of 40 mN / m, 50 μL of each was allowed to stand on the surface of the test sample with a micropipeter for microbial test, and the degree of penetration after 10 seconds was observed. After that, the degree of penetration was similarly observed in the order of a test solution having a surface tension of 39 mN / m, a test solution having a surface tension of 38 mN / m, a test solution having a surface tension of 26 mN / m, and a test solution having a surface tension of 25.4 mN / m. The surface tension of the test solution having the smallest surface tension that was not absorbed was defined as the degree of oil repellency in the JIS K 6768 wet tension test solution. If there is a difference in the front and back states of the test material as a result of sequential measurement, the surface tension with the smaller surface tension is set as the oil repellency (the same applies to other oil repellency measurements thereafter). Is). When the test solution of 25.4 mN / m was non-permeated, the test result was set to 25.4 mN / m because there was no permeated test solution.
（６）通気性（圧力損失）
　ＴＳＩ－８１３０型フィルターテスターを用い、風速１０ｃｍ／ｓにおける繊維状物の上下流の差圧を計測することで通気性の比較を行った。 (6) Breathability (pressure loss)
The air permeability was compared by measuring the differential pressure between the upstream and downstream of the fibrous material at a wind speed of 10 cm / s using a TSI-8130 type filter tester.
＜実施例１＞
　メルトブローン法により得られたポリプロピレン不織布（繊維径３．２μｍ、厚さ０．２５ｍｍ、目付４２ｇ／ｍ２、かさ密度０．１２ｇ／ｃｍ３）を、ｎ－Ｃ１８Ｆ３８（融点１４９℃）をパーフルオロヘキサンに溶解させたものに浸漬させ、０．３０ｇ／ｍ２の担持量の加工シート（繊維状物）を得た。担持量は目付の１％以下であり、繊維状物ポリマーの密度はポリプロピレンの密度０．９５ｇ／ｃｍ３を用いて動水半径を計算すると５．２μｍとなった。撥液度は表裏ともに２８ｍＮ／ｍ、圧力損失は４３Ｐａであった。顕微鏡観察において繊維間の皮膜や閉塞は確認されなかった。 <Example 1>
Polypropylene non-woven fabric (fiber diameter 3.2 μm, thickness 0.25 mm, grain 42 g / m 2 , bulk density 0.12 g / cm 3 ) obtained by the melt blown method was applied to n-C 18 F 38 (melting point 149 ° C). It was immersed in a material dissolved in perfluorohexane to obtain a processed sheet (fibrous material) having a loading amount of 0.30 g / m 2 . The supported amount was 1% or less of the grain size, and the density of the fibrous polymer was 5.2 μm when the hydraulic radius was calculated using the polypropylene density of 0.95 g / cm 3 . The liquid repellency was 28 mN / m on both the front and back sides, and the pressure loss was 43 Pa. No film or blockage between the fibers was confirmed by microscopic observation.
　上記得られた加工シートを４枚重ねて厚さ１ｍｍの膜蒸留用多孔質膜を作製し、膜面積１００ｃｍ２の膜蒸留用セルに設置した。膜の片側に８０℃に加熱した１０％ＮａＣｌ水溶液を１００ｍＬ／ｍｉｎの流量で、膜の他方には２０℃のイオン交換水を１００ｍＬ／ｍｉｎで供給した。出口から流出した液体は、それぞれ、初期体積５Ｌの定温リザーバータンクに戻して連続的に運転した。一定時間ごとにそれぞれのリザーバータンクの体積変化を測定、移動した水量を計算し、透過流束（Ｆｌｕｘ）を以下の式（２）により求めた。
　Ｆｌｕｘ（Ｌ／ｍ２／ｈｒ）＝ΔＶ÷Ａ÷Ｔ　　　（２）
ここでΔＶは単位時間当たりの体積変化（Ｌ）、Ａは膜面積（ｍ２）、Ｔは時間である。
　また、一定時間ごとにそれぞれのリザーバータンクの塩濃度を電気伝導度計を用いて測定した。 Four of the obtained processed sheets were stacked to prepare a 1 mm thick porous membrane for membrane distillation, which was placed in a membrane distillation cell having a membrane area of 100 cm 2 . A 10% NaCl aqueous solution heated to 80 ° C. was supplied to one side of the membrane at a flow rate of 100 mL / min, and ion-exchanged water at 20 ° C. was supplied to the other side of the membrane at 100 mL / min. The liquids flowing out from the outlets were returned to the constant temperature reservoir tank having an initial volume of 5 L and operated continuously. The volume change of each reservoir tank was measured at regular time intervals, the amount of water moved was calculated, and the permeated flux (Flux) was calculated by the following formula (2).
Flex (L / m 2 / hr) = ΔV ÷ A ÷ T (2)
Here, ΔV is the volume change (L) per unit time, A is the film area (m 2 ), and T is the time.
In addition, the salt concentration of each reservoir tank was measured at regular intervals using an electric conductivity meter.
　その結果、運転開始から２４時間後まで、Ｆｌｕｘは１．７Ｌ／ｍ２／ｈｒで一定であった。また、ＮａＣｌ側のリザーバータンク内のＮａＣｌ濃度は、初期１０％から、２４時間後に１０．８％に上昇したが、イオン交換水側のリザーバータンク内のＮａＣｌ濃度は、初期が０％であり、２４時間後もＮａＣｌは検出されなかった（検出感度１００ｐｐｍ）。２４時間後の膜蒸留用多孔質膜を取り出し観察したところ、膜の両側には、ＮａＣｌ水溶液とイオン交換水の水滴が付着しているものの、膜表面から弾かれるように存在し、膜内部には液体は観察されず、実験開始時と変わらない状態であった。 As a result, Flux was constant at 1.7 L / m 2 / hr from the start of operation to 24 hours later. In addition, the NaCl concentration in the reservoir tank on the NaCl side increased from 10% at the initial stage to 10.8% after 24 hours, but the NaCl concentration in the reservoir tank on the ion-exchanged water side was 0% at the initial stage. No NaCl was detected after 24 hours (detection sensitivity 100 ppm). When the porous membrane for membrane distillation after 24 hours was taken out and observed, water droplets of the NaCl aqueous solution and the ion-exchanged water were attached to both sides of the membrane, but they were present so as to be repelled from the membrane surface and inside the membrane. No liquid was observed, and the condition was the same as at the start of the experiment.
＜実施例２＞
　実施例１と同一の不織布を３０℃に保った恒温板に張り付け、円筒セラミック製の反応容器天井に設置した。底部に２５０℃に加熱した熱板を設置し、ｎ－Ｃ１８Ｆ３８（融点１４９℃）を金属性ボート上から蒸散させることで０．３０ｇ／ｍ２の担持量の加工シート（繊維状物）を得た。撥液性は熱板側が２６ｍＮ／ｍ、天井側が３１ｍＮ／ｍであり、表裏ともに撥液性を有している一方で、撥液性に差のある加工シートが得られた。圧力損失は４０Ｐａであった。顕微鏡観察において繊維間の皮膜や閉塞は確認されなかった。 <Example 2>
The same non-woven fabric as in Example 1 was attached to a constant temperature plate kept at 30 ° C. and installed on the ceiling of a reaction vessel made of cylindrical ceramic. A hot plate heated to 250 ° C. is installed on the bottom, and n-C 18 F 38 (melting point 149 ° C.) is evaporated from the metal boat to carry a processed sheet (fibrous material) with a loading capacity of 0.30 g / m 2 . ) Was obtained. The liquid repellency was 26 mN / m on the hot plate side and 31 mN / m on the ceiling side, and while both the front and back sides had liquid repellency, a processed sheet having a difference in liquid repellency was obtained. The pressure loss was 40 Pa. No film or blockage between the fibers was confirmed by microscopic observation.
　上記加工シート４枚を重ねて膜蒸留用多孔質膜を作製し、膜蒸留用セルに設置して実施例１と同様の膜蒸留テストを実施したところ、Ｆｌｕｘは運転開始から２４時間後まで１．９Ｌ／ｍ２／ｈｒであった。またＮａＣｌリザーバータンク内のＮａＣｌ濃度は２４時間後に１１．５％に上昇したが、イオン交換水側のリザーバータンク内のＮａＣｌは検出されなかった。実施例１より高いＦｌｕｘが得られた原因は、実施例２の加工シートの圧力損失が実施例１の加工シートよりも小さく、膜蒸留による水蒸気の移動抵抗が小さかったためと考えられる。実施例２においても、２４時間後の膜蒸留用多孔質膜を取り出し観察したところ、膜の両側には、ＮａＣｌ水溶液とイオン交換水の水滴が付着しているものの、膜表面から弾かれるように存在し、膜内部には液体は観察されず、実験開始時と変わらない状態であった。 A porous membrane for membrane distillation was prepared by stacking the four processed sheets, and the membrane distillation test was carried out in the same manner as in Example 1 by installing the porous membrane for membrane distillation. It was .9 L / m 2 / hr. The NaCl concentration in the NaCl reservoir tank increased to 11.5% after 24 hours, but NaCl in the reservoir tank on the ion-exchanged water side was not detected. It is considered that the reason why the Lux higher than that of Example 1 was obtained is that the pressure loss of the processed sheet of Example 2 was smaller than that of the processed sheet of Example 1, and the transfer resistance of water vapor due to membrane distillation was small. In Example 2, when the porous membrane for membrane distillation after 24 hours was taken out and observed, although water droplets of the NaCl aqueous solution and the ion-exchanged water were attached to both sides of the membrane, they were repelled from the membrane surface. It was present, no liquid was observed inside the membrane, and it was in the same state as at the start of the experiment.
＜比較例１＞
　実施例と１と同一の不織布のみ（繊維状物）を試験に用いた。撥液性は表裏とも３７ｍＮ／ｍであり、圧力損失は４２Ｐａであった。顕微鏡観察においては実施例１および２と同様であった。
　この繊維状物４枚を重ねて膜蒸留用多孔質膜を作製し、膜蒸留用セルに設置して実施例１と同様の膜蒸留テストを実施したところ、Ｆｌｕｘは運転開始時から２時間までは２．０Ｌ／ｍ２／ｈｒであったが、その後、Ｆｌｕｘは徐々に低下し、６時間後にゼロとなった。またＮａＣｌリザーバータンク内のＮａＣｌ濃度は２時間後に１０．１％に上昇、６時間後に１０．２％まで上昇の後、徐々に低下し、２４時間後は５％となった。イオン交換水側のリザーバータンク内のＮａＣｌ濃度は６時間後までは検出されなかったが、その後上昇し、２４時間後には５％となった。当初２時間後まではＦｌｕｘおよび塩透過率は実施例１、２とほぼ同等であったが、その後Ｆｌｕｘは低下し塩透過率は上昇した。２４時間後に多孔質膜を取り出したところ、多孔質膜内にＮａＣｌ水溶液が浸漬していることが観察された。運転開始初期には、比較例１の多孔質膜の疎水性が高く、膜蒸留用として作用していたが、運転時間と共に疎水性が低下し、６時間後には膜蒸留用膜としては働かず、ＮａＣｌ水溶液とイオン交換水が混じり合ったと考えられる。 <Comparative example 1>
Only the same non-woven fabric (fibrous material) as in Example 1 was used in the test. The liquid repellency was 37 mN / m on both the front and back sides, and the pressure loss was 42 Pa. In the microscopic observation, it was the same as in Examples 1 and 2.
A porous membrane for membrane distillation was prepared by stacking four of these fibrous materials, placed in a membrane distillation cell, and a membrane distillation test similar to that in Example 1 was carried out. As a result, Flux was used for up to 2 hours from the start of operation. Was 2.0 L / m 2 / hr, but then the Flex gradually decreased to zero after 6 hours. The NaCl concentration in the NaCl reservoir tank increased to 10.1% after 2 hours, increased to 10.2% after 6 hours, then gradually decreased, and reached 5% after 24 hours. The NaCl concentration in the reservoir tank on the ion-exchanged water side was not detected until after 6 hours, but then increased to 5% after 24 hours. Initially, the Lux and salt permeability were almost the same as those in Examples 1 and 2 until 2 hours later, but after that, Flux decreased and the salt permeability increased. When the porous membrane was taken out after 24 hours, it was observed that the aqueous NaCl solution was immersed in the porous membrane. At the beginning of the operation, the porous membrane of Comparative Example 1 had high hydrophobicity and acted for membrane distillation, but the hydrophobicity decreased with the operation time, and after 6 hours, it did not work as a membrane distillation membrane. , It is considered that the NaCl aqueous solution and the ion-exchanged water were mixed.
＜比較例２＞
　実施例１と同一の不織布を、Ｃ６系アクリレート撥水撥油剤を水で希釈したものに浸漬後にマングルで絞ることで、０．３ｇ／ｍ２の担持を行い加工シート（繊維状物）を得た。しかし加工液を不織布に浸透させることが困難であり、顕微鏡観察の結果表面が閉塞していた。表裏の撥液性は各々２４ｍＮ／ｍよりも高く、圧力損失は７５Ｐａであった。 <Comparative example 2>
The same non-woven fabric as in Example 1 is immersed in a C6 acrylate water repellent oil repellent diluted with water and then squeezed with a mangle to support 0.3 g / m 2 to obtain a processed sheet (fibrous material). It was. However, it was difficult to allow the processing liquid to permeate the non-woven fabric, and as a result of microscopic observation, the surface was blocked. The liquid repellency of the front and back surfaces was higher than 24 mN / m, and the pressure loss was 75 Pa.
　この加工シートを４枚を重ね膜蒸留用多孔質膜を作製し、膜蒸留用セルに設置して実施例１と同様の膜蒸留テストを実施したところ、Ｆｌｕｘは運転開始時から６時間までは１．２Ｌ／ｍ２／ｈｒであった。しかし、その後、Ｆｌｕｘは徐々に低下し、１２時間後にゼロとなった。またＮａＣｌリザーバータンク内のＮａＣｌ濃度は６時間後に１０．２％に上昇、１２時間後に１０．３％まで上昇の後、徐々に低下し、２４時間後は５％となった。イオン交換水側のリザーバータンク内のＮａＣｌ濃度は１２時間後までは検出されなかったが、その後上昇し、２４時間後には５％となった。当初６時間後までは塩透過率は実施例１、２と同等であったが、Ｆｌｕｘは実施例１、２より低く、その後Ｆｌｕｘは低下し塩透過率は上昇した。 Four of these processed sheets were laminated to prepare a porous membrane for membrane distillation, which was placed in a membrane distillation cell and subjected to the same membrane distillation test as in Example 1. For Lux, from the start of operation until 6 hours. It was 1.2 L / m 2 / hr. However, after that, Flux gradually decreased and became zero after 12 hours. The NaCl concentration in the NaCl reservoir tank increased to 10.2% after 6 hours, increased to 10.3% after 12 hours, then gradually decreased, and reached 5% after 24 hours. The NaCl concentration in the reservoir tank on the ion-exchanged water side was not detected until after 12 hours, but then increased to 5% after 24 hours. Initially, the salt permeability was equivalent to that of Examples 1 and 2 until 6 hours later, but Flux was lower than that of Examples 1 and 2, and then Flux decreased and the salt permeability increased.
　２４時間後に多孔質膜を取り出したところ、多孔質膜内にＮａＣｌ水溶液が浸漬していることが観察された。運転開始初期には、比較例２の多孔質膜の疎水性が高く、膜蒸留用として作用したものの圧力損失が高いため、膜蒸留の蒸気拡散速度が低下し、運転時間と共に疎水性が低下し、１２時間後には膜蒸留用としては働かず、ＮａＣｌ水溶液とイオン交換水が混じり合ったと考えられる。よって、Ｃ６系アクリレート撥水撥油剤は、多孔質膜の長期撥水性保持には不十分であると考えられる。 When the porous membrane was taken out after 24 hours, it was observed that the aqueous NaCl solution was immersed in the porous membrane. At the initial stage of the start of operation, the porous membrane of Comparative Example 2 has high hydrophobicity, and although it acts for membrane distillation, the pressure loss is high, so that the vapor diffusion rate of membrane distillation decreases, and the hydrophobicity decreases with the operation time. After 12 hours, it did not work for membrane distillation, and it is considered that the NaCl aqueous solution and the ion-exchanged water were mixed. Therefore, it is considered that the C6 acrylate water-repellent oil-repellent agent is insufficient for long-term water-repellent retention of the porous film.
　以上の実施例および比較例の結果より、実施例の膜蒸留用多孔膜は長期撥水性保持が可能であることが分かる。 From the results of the above Examples and Comparative Examples, it can be seen that the porous membrane for membrane distillation of the Examples can retain water repellency for a long period of time.
　本発明の膜蒸留用多孔質膜は、液体の分離膜の分野に多大に貢献する。
  The porous membrane for membrane distillation of the present invention greatly contributes to the field of liquid separation membrane.

Claims (3)

  1. 　熱可塑性樹脂を用いた繊維状物から成り、当該繊維状物の表面にポリテトラフルオロエチレンが担持されていることを特徴とする膜蒸留用多孔質膜。 A porous membrane for membrane distillation, which is composed of a fibrous material using a thermoplastic resin and is characterized in that polytetrafluoroethylene is supported on the surface of the fibrous material.
  2. 　前記繊維状物は、メルトブローン法により得られた不織布であることを特徴とする請求項１に記載の膜蒸留用多孔質膜。 The porous membrane for membrane distillation according to claim 1, wherein the fibrous material is a non-woven fabric obtained by the melt blown method.
  3. 　表裏の撥液性に差異があることを特徴とする請求項１または２に記載の膜蒸留用多孔質膜。
          The porous membrane for membrane distillation according to claim 1 or 2, wherein the liquid repellency of the front and back is different.
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