JPH0734854B2 - Method for producing porous polytetrafluoroethylene resin membrane and method for producing a membrane separation apparatus using the membrane - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention uses a method for producing a novel polytetrafluoroethylene-based resin porous membrane suitable for concentration such as reverse osmosis, ultrafiltration and microfiltration, and substance separation, and the membrane. The present invention relates to a method of manufacturing a membrane separation device.

(Conventional technology) Conventionally, for reverse osmosis, ultrafiltration, microfiltration, etc., cellulose acetate type, polyethylene, polypropylene type,
Porous membranes such as polymethylmethacrylate type, polyacrylonitrile type, and polysulfone type have been used.
It has drawbacks such as permeability, mechanical strength, heat resistance, alkali resistance, acid resistance, solvent resistance, and chemical resistance.

From this point of view, mechanical strength, heat resistance, alkali resistance,
Polytetrafluoroethylene-based resins, which have excellent properties such as acid resistance, solvent resistance, and chemical resistance, have attracted attention and the formation of porous films has been studied. For example, an unsintered polytetrafluoroethylene resin mixture containing a liquid lubricant, as described in Japanese Patent Publication No. 42-13560, Japanese Patent Application Laid-Open No. 46-7284, and Japanese Patent Application Laid-Open No. 50-71759, or a solid A molded article from an agglomerated mixture of a pore-forming agent and a resin dispersion, an example obtained by a method characterized in that it is heated to about 327 ° C. or higher in a state of being stretched in at least one direction in a non-sintered state has been obtained so far. However, the control of the porous structure between them is insufficient and the performance is low, or the film forming property is poor and only a thick film can be made, and the effect of hydrophilization is not sufficient, so the water pressure during water passage is There was a problem that the burden was heavy.

(Problems to be Solved by the Invention) The present inventors have arrived at the present invention as a result of extensive studies on a polytetrafluoroethylene-based resin porous membrane that does not have the above-mentioned drawbacks and a membrane separation apparatus using the same.

(Means for Solving the Problems) The present invention has the following configurations.

(1) A uniform mixture obtained by mixing a polytetrafluoroethylene-based resin dispersion and a fiber-forming polymer is molded, and the obtained molded product is heat-treated at a temperature equal to or higher than the melting point of the resin to melt the resin particles. After forming the deposited structure, the fiber-forming polymer was removed, and then the surface tension of the 0.1 wt% aqueous solution was 30 dyn.
Fluorine-based surfactant below es / cm (25 ℃) is attached,
A method for producing a polytetrafluoroethylene-based resin porous membrane, which is characterized by being dried.

(2) A uniform mixture obtained by mixing the polytetrafluoroethylene-based resin dispersion and the fiber-forming polymer is molded, and the obtained molded product is heat-treated at a temperature higher than the melting point of the resin to melt the resin particles. A method for producing a membrane separation device, which comprises forming a deposited structure, removing a fiber-forming polymer, and then performing a combination treatment in the following steps.

A step of attaching a surfactant whose surface tension of a 0.1 wt% aqueous solution is 30 dynes / cm (25 ° C) or less.

A step of housing a polytetrafluoroethylene-based resin porous membrane in a case, forming a flow path through the membrane, and sealingly fixing the membrane and the end of the case with a resin.

The present invention will be described in detail below.

The surface tension of the aqueous surfactant solution used in the present invention is 30 dynes /
If it is higher than cm (25 ° C), the desired effect of hydrophilization is not sufficient. Therefore, the surface tension of a 0.1 wt% aqueous solution is 30 dyn.
It is indispensable to be es / cm (25 ° C) or less, preferably 25 dynes / cm (25 ° C) or less, and more preferably 20 dynes / cm (25 ° C) or less depending on the material of the membrane. Especially considering the conditions that require heat resistance and chemical resistance, it is a fluorocarbon surfactant that is a fluorocarbon compound in which all or part of the hydrogen atoms of the hydrophobic group of the hydrocarbon surfactant are replaced with fluorine atoms. There is a need.

The present invention is characterized in that a surfactant having a surface tension of a 0.1 wt% aqueous solution of 30 dynes / cm (25 ° C.) or less is attached to the polytetrafluoroethylene-based resin porous membrane, but only by applying pressure. In order to pass water, it is preferable that the surfactant is attached not only to the surface of the membrane but also to the porous structure inside the membrane.

Therefore, as a method of attachment, it is preferable to inject the solution of the surfactant into the porous structure inside the membrane. Specifically, a method is required in which the membrane or module is immersed in the surfactant solution to reduce the pressure, or the module is pressurized to pass the surfactant solution inside the membrane and then dried.

The adhesion amount of the surfactant used in the present invention varies depending on the type of the polytetrafluoroethylene-based resin and the surfactant used, and therefore cannot be generally stated.
No effect unless 0.001 wt% or more, preferably 0.01 wt
% Or more, more preferably 0.05 wt% or more.

On the other hand, when the amount of adhesion is large, the film becomes sticky,
Since powder may float on the surface of the film, 100 wt% or less is good,
It is preferably 50 wt% or less, and more preferably 10 wt% or less.

The polytetrafluoroethylene-based resin porous membrane of the present invention may be any as long as it has a separation pore diameter of 0.01 to 2 μ, but a large effective area per unit volume can be taken to reduce the size of the device and reduce the cost, which is economical. The hollow fiber membrane is preferable from the viewpoint that it is effective, but in order to suppress the pressure loss of the hollow portion in the hollow fiber membrane, the hollow ratio (the ratio of the cross-sectional area of the hollow portion to the total end area of the membrane portion and the hollow portion is I)
The higher the value, the better, 30% or more, preferably 35% or more, and more preferably 40% or more.

The polytetrafluoroethylene-based resin in the present invention is
Tetrafluoroethylene-based copolymers such as tetrafluoroethylene homopolymer, terrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and tetraflufluoroethylene-ethylene copolymer Either alone or as a mixture thereof.

The polytetrafluoroethylene-based resin in the present invention is
It is used as an aqueous or organic dispersion liquid, but an aqueous dispersion liquid obtained by emulsion polymerization in an aqueous medium containing a surfactant or a concentrated liquid thereof is particularly preferable, and more specifically, a particle diameter of 1 μm or less, more preferably A uniform dispersion of polytetrafluoroethylene-based resin particles having a particle size of 0.8 μm or less is preferable.

The fiber-forming polymer in the present invention may be any polymer as long as it is a polymer that can be formed into a fiber and is capable of being mixed with a polytetrafluoroethylene-based resin dispersion to form a uniform mixture, but in the case of an aqueous dispersion. Is preferably a viscose (sodium cellulose xanthate type), polyvinyl alcohol type, sodium alginate type polymer alone or a mixture thereof.

The mixing ratio of the fiber-forming polymer to the polytetrafluoroethylene-based resin in the present invention varies depending on the type of the fiber-forming polymer used, but is preferably 10 to 300 wt.
%, And more preferably 30 to 200 wt%. If the mixing ratio of the fiber-forming polymer is less than 10 wt%, the average pore size will be 0.
A porous film of 01 μ or more cannot be obtained, and if it exceeds 300 wt%, the mechanical strength of the film is low and it is not practical.

In the present invention, an additive may be mixed when the polytetrafluoroethylene resin dispersion and the fiber-forming polymer are mixed.

Any additive can be used as long as it can be removed by thermal decomposition, extraction, dissolution, radiolysis, etc., for example, silicates such as calcium silicate and aluminum silicate, carbonates such as calcium carbonate and magnesium carbonate. , Phosphates such as sodium phosphate, calcium phosphate, acetates, oxalates, ammonium chloride, hydrochlorides such as sodium chloride, sodium sulfate,
Sulfates such as barium sulfate, nitrates, weak acids and strong salts such as perchlorates, metal powder such as iron powder, alumina,
Metal oxides such as zirconia and magnesium oxide, fine powder silicic acid, kaolin clay, inorganic fine powder such as diatomaceous earth, polyamide series, polyester series, polyolefin series, polysulfone series, polyvinyl chloride series, polyvinylidene fluoride series, polyvinyl fluoride series , Resin fine powder such as, silicone oil, hexafluoropropylenoxide oligomer, chlorotrifluoroethylenoligomer, phthalic acid ester, trimellitic acid ester, sebacic acid ester, adipic acid ester, azelaic acid ester , Heat-resistant organic substances such as phosphoric acid esters, etc., and can be used alone or in combination.

The total amount of additives in the present invention, since it depends on the type of additives used, polytetrafluoroethylene-based resin and fiber-forming polymer can not be unequivocally stated, but 1000 wt% or less with respect to the polytetrafluoroethylene-based resin If it is more than 1000 wt%, the mechanical strength of the film is low and it is not practical. On the other hand, the addition of an additive is preferable because the porous structure can be further increased and adjusted, but the addition effect cannot be seen unless it is 10 wt% or more. The range of 30 to 700 wt% is more preferable, and the range of 50 to 500 wt% is more preferable.

In the present invention, a dispersant may be further mixed. When the additive alone is used, its agglomeration can be seen, causing filter clogging and causing troubles, and non-uniform moldings.
It is preferable to mix and use a dispersant in the case where a molded product has a defect or becomes a problem.

As the dispersant, any dispersant can be used as long as it has an effect of suppressing the aggregation of the additive, and it can be selected from various commercially available surfactants and peptizers.

As the surfactant, for example, anionic, cationic,
The optimum HLB surfactant can be selected from the amphoteric system and the nonionic system, and the fluorine-based surfactant is also preferable.

Examples of the deflocculant include acrylic acid oligomer, acrylic acid copolymer oligomer, methacrylic acid oligomer,
It can be appropriately selected from free acid type such as methacrylic acid copolymer oligomer or salt type.

The amount of the dispersant added in the present invention cannot be generally determined because it depends on the additive used, but it is 0.01% with respect to the additive.
If it is not more than wt%, the addition effect cannot be seen. 0.1-100 wt%
Is more preferable, and the range of 1 to 50 wt% is more preferable.

In the present invention, it is preferable to mix the polytetrafluoroethylene-based resin dispersion and the fiber-forming polymer at a temperature of 100 ° C. or lower, and when mixed at a temperature higher than 100 ° C., the resin particles and additives in the dispersion are aggregated. As a result, a filter may become clogged during molding to cause a trouble, the molded product may become uneven, or the molded product may be defective, which may cause a problem. Further, it is preferable that the temperature is as low as 80 ° C or lower and 60 ° C or lower, and more preferably 40 ° C or lower.

The homogeneous mixture in the present invention may be any as long as a molded product can be obtained, but a liquid having a viscosity of 10 to 10000 poise at the molding temperature is preferably used, and more preferably 100 to 5
A liquid of 000 poise is good.

The concentration of the polytetrafluoroethylene-based resin in the homogeneous mixture in the present invention varies depending on the type of the fiber-forming polymer and the additive used, the molding method, etc., but is usually 1 to 50 wt.
%, Preferably 5 to 30 wt%.

The molded product according to the present invention is a product obtained by a rolling process, an extrusion process, or a molding method in which both are combined, and the production of a sheet-like product or the spinning such as a hollow fiber is selected according to the shape of the desired molded product. However, the hollow fiber spinning is preferable because various molding conditions can be taken and the structure of the molded article can be easily controlled.

For example, after casting the molding mixture on a flat plate such as a glass plate or a metal plate or a continuous belt, it is immersed in a coagulating liquid to coagulate, or the molding mixture is extruded from a flat film slit mouthpiece, directly or Once introduced into the coagulating liquid through air to coagulate, or from the hollow fiber spinneret,
A non-coagulating or coagulating fluid is extruded onto the core at the same time as the molding mixture and is introduced directly or once into the coagulation liquid into the air, or the coagulation liquid is extruded onto the core at the same time as the molding mixture and directly. Alternatively, it can be molded by a method in which it is once passed through air and introduced into a non-solidifying fluid to solidify. The term "non-coagulable fluid" as used herein may be any as long as it does not have a coagulating action, but it cannot be unequivocally stated because it varies depending on the type of the fiber-forming polymer used.For example, water, glycerin, ethylene glycol, polyethylene Glycol, liquid paraffin, isopropyl alcohol, freon, and the like, a mixed liquid thereof, air, nitrogen, a gas such as an inert gas, and the like are appropriately selected and used.

The spinneret temperature cannot be specified because it has a great influence on the spinnability in relation to the viscosity of the stock solution, but a temperature of 120 ° C. or lower is usually good. Furthermore, it is preferable that the temperature is lower than the coagulating liquid temperature by 20 ° C. or more, and it is possible to prevent the deterioration of the spinnability due to the condensation of steam on the die surface which becomes remarkable when the distance between the die surface and the coagulating liquid surface is short. .

The conditions during air traveling when the extruded molding mixture is once guided through the air into the coagulating liquid are those that vary depending on the size of the molded product, the molding speed, etc., but cannot be generally specified. The distance from the surface of the die to the introduction into the coagulation liquid is usually preferably in the range of 0.2 to 200 cm from the viewpoint of molding stability. The ambient temperature is usually atmospheric temperature or room temperature, but in some cases, cooling may be performed.

The coagulating liquid may be any non-solvent of the fiber-forming polymer of the present invention, as long as it is compatible with and compatible with the solvent of the molding mixture, but of the fiber-forming polymer used. Depending on the type, for example, sodium sulfate, ammonium sulfate, zinc sulfate, potassium sulfate, zinc sulfate, copper sulfate, magnesium sulfate, aluminum sulfate, calcium chloride, magnesium chloride, zinc chloride and other inorganic salt aqueous solution, sulfuric acid, hydrochloric acid, nitric acid, acetic acid , An acid such as oxalic acid, boric acid, or a mixture thereof, and the like are used as appropriate. The temperature of the coagulating liquid has a great influence on the moldability, but it is usually carried out at around 0 to 98 ° C.

The heat treatment in the present invention may be performed under any conditions that allow the polytetrafluoroethylene-based resin particles to be fused to each other, such as vacuum, air, nitrogen, oxygen, sulfur gas, helium gas, and silicone oil. It can be carried out under various atmospheres such as inside at a temperature not lower than the melting point of the polytetrafluoroethylene-based resin. The molded product can be heat-treated under tension or without tension, and batch treatment or continuous treatment can be selected. In more detail, a method of processing in a free state without fixing, a method of stretching before heat treatment and fixing in a treatment frame, or a method of fixing treatment in a treatment frame under a condition with a fixed length or shrinkage ratio, or stretching,
A method of continuous treatment under the condition of either constant length or shrinkage or a combination thereof can also be appropriately adopted.

Further, the stretching can be performed before, after, and during the heat treatment, or can be performed in combination, but if the stretching ratio is too high, the shape of the pores seen in the plane parallel to the film surface is substantially increased. It is not possible to obtain a film with no orientation, or it is not possible to control the pore size, and only a film with low reliability of permeation performance can be obtained.

Usually, the stretching ratio is 1.1 to 3 times, the stretching temperature can be appropriately selected within the range of room temperature to the heat treatment temperature, and the stretching can be carried out in two directions.

In the present invention, the porous film is formed by removing the fiber-forming polymer from the molded product after the heat treatment, but the fiber-forming polymer here may be different from the original one by the heat treatment.

The method for removing the fiber-forming polymer and the additives optionally added from the molded product after the heat treatment in the present invention is a dissolution method, a decomposition method, or a method using liquid, gas, heat, radiation, or the like. A method in which these are combined can be adopted and can be carried out batchwise or continuously. It is also possible to incorporate the molded product into a module or an element before carrying out.

Since it depends on the type of the fiber-forming polymer and the type of the additive used, it cannot be generally stated, but usually, a single acid or a mixture of acids such as sulfuric acid, nitric acid, hydrochloric acid, perchloric acid and hydrofluoric acid, sodium hydroxide, or hydroxide. From a room temperature liquid containing a single or a mixture of alkalis such as potassium
A method of immersing the molded product after heat treatment while heating to a temperature in the range of 200 ° C, or a method of immersing in a liquid or circulating this liquid after forming a module or element is conveniently used.

When the fiber-forming polymer is removed after forming the module or element, the fiber-forming polymer in the seal portion of the molded product is difficult to remove but remains in a small amount. Prior to sealing, it is preferable to remove the fiber-forming polymer only from the end of the heat-treated molded product.

Further, the membrane thus formed can be further stretched to change the permeation performance, mechanical strength, dimensional stability, etc. of the membrane. The stretching ratio is about 1.1 to 3 times, and the temperature is usually in the range of room temperature to the melting point of the polytetrafluoroethylene-based resin, but the temperature after stretching can be applied to heat-set.

When a membrane separation device is produced using the polytetrafluoroethylene-based resin porous membrane obtained in this manner, a combination treatment of the following steps is performed, but either may be performed before or after.

A step of attaching a surfactant whose surface tension of a 0.1 wt% aqueous solution is 30 dynes / cm (25 ° C) or less.

A step of housing a polytetrafluoroethylene-based resin porous membrane in a case, forming a flow path through the membrane, and sealingly fixing the membrane and the end of the case with a resin.

The resin used to seal and fix the edges of the membrane and case described above can be any material that can be fused and fixed by utilizing the difference in the melting points of membrane materials, or can be cured and fixed by a chemical reaction such as a crosslinking reaction. Well, fluorinated resin,
Olefin resin, imide resin, amide resin, ester resin, urethane resin, epoxy resin, acrylonitrile resin, etc. are preferable.

In particular, when the amount of eluate is extremely small and heat resistance and chemical resistance are required, in addition to PTFE resin (melting point about 327 ° C), examples of commercially available materials include tetrafluoroethylene. -Perfluoroalkyl vinyl ether copolymer resin (melting point approx. 306 ° C), tetrafluoroethylene-hexafluoropropylene copolymer resin (melting point approx. 27
Fluorine-based resin such as tetrafluoroethylene-ethylene copolymer resin (melting point about 260 ℃), vinylidene fluoride polymer resin (melting point about 174 ℃), chlorotrifluoroethylene polymer resin (melting point about 211 ℃) Resins are preferred, and more preferably PTFE-based resins (melting point about 327).
(° C) film and the same resin, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin (melting point approx. 30
6 ° C) or a combination of tetrafluoroethylene-hexafluoropropylene copolymer resin (melting point approx. 270 ° C), a film of terrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin (melting point approx. 306 ° C) and tetrafluoroethylene- A combination of hexafluoropropylene copolymer resin (melting point about 270 ° C) is preferable.

The use form of the resin for fixing the film and the end of the case may be any of pellet, powder, sheet, dispersion, liquid, and the like.

There is no particular limitation on the method for sealing and fixing the membrane and the end portion of the case in the present invention, and any method such as heat fusion fixing or chemical reaction curing fixing such as crosslinking reaction may be used. Heating iron, various heaters, oven,
Means such as heating, pressurizing, depressurizing, leaving, applying vibration or centrifugal force to a part or the whole using an ultrasonic bonder or the like can be carried out individually or in combination.

There is no limit to the shape of the module or element,
In the case of a hollow fiber membrane module or element, the yarn bundle is straightly arranged and its both ends are sealed and fixed, or the ends of the yarn bundle formed by bending the yarn into a U shape are fixed and sealed. The thing of the thing is preferable from a point of the ease of use.

FIG. 1 is an external view showing an example of an element of a hollow fiber membrane separation device which is an example of the present invention, and FIG. 2 is a sectional view of the element of FIG.

In the membrane separating device obtained by the present invention, a plurality of membranes (hollow fiber membranes) 1 covered with a case protection cover 2 are arranged in a bundle, and the end portion of the membrane 1 has a housing sealing member 3 and a fixed resin. The seal is fixed by 4.

The polytetrafluoroethylene-based resin porous membrane obtained by the present invention is used as a separation device for modules or elements, for desalination of seawater, desalination, removal of bases, acids, etc. in industrial wastewater, and for the electronic industry. Production of pure water, high-purity chemicals, degreasing actual liquid, recovery of electrodeposition coating liquid, paper pulp waste liquid treatment, oil water separation, industrial wastewater treatment such as oil emulsion separation, separation and purification of fermentation products, fruit juice, vegetable juice Concentration, soybean treatment, concentration in the food industry such as sugar industry, separation, purification, artificial kidney, blood component separation, microfilter for bacterial separation, medical use such as pharmaceutical separation and purification, bioreactor and other biotechnology Widely used in fields.

Examples will be shown below, but the invention is not limited thereto.

(1) Film dimensions It was measured using an optical microscope.

(2) Hollow ratio Using the dimension of the hollow fiber membrane measured by the method of (1), the ratio of the cross-sectional area of the hollow part to the total cross-sectional area of the membrane part and the hollow part is calculated as a percentage (%). did.

(3) Porosity The weight (W), absolute dry weight (Wo) and its volume (V) of the membrane in which the pores were filled with pure water were measured using the ethanol substitution method, and calculated using the following formula. .

(W-Wo) x 100 / V (%) (4) Water permeability A flat membrane is installed in a commercially available cartridge and water pressure is applied while maintaining it at 37 ° C, and the amount of water that permeates the membrane in a certain time and the effective membrane area. And the water permeability was calculated from the transmembrane pressure difference.

Water pressure was applied to the inside of the hollow fiber while maintaining the hollow fiber membrane as a small module at 37 ° C, and the water permeability was calculated from the amount of water permeating through the membrane, the effective membrane area and the transmembrane pressure difference.

(5) Filtration performance of 200 ppm-polystyrene latex particle dispersion liquid The water permeability was measured by the method (4) using a commercially available polystyrene latex particle dispersion liquid.

The particle rejection rate was calculated by the following equation by measuring the stock solution concentration Co and the permeate concentration C.

(Co-C) x 100 / Co (%) (Example) Example 1 Sodium alginate (manufactured by Hanai Chemical Co., Ltd., 300 cps) 50 parts, barium sulfate (X-ray shadow enhancer Varitop, manufactured by Sakai Chemical Industry Co., Ltd.) 60
0 parts, silicone oil (Toray Silicone SH-2
00) 30 parts, fluorinated surfactant (Sumitomo 3M FC
-129) 60 parts was dissolved and mixed in 800 parts of purified water at 10 ° C to obtain a uniform stock solution. To this stock solution was added 500 parts of an aqueous dispersion of polytetrafluoroethylene (D-2 manufactured by Daikin Co., solid content 61% by weight, surfactant 5.7% by weight) and stirred at 10 ° C. to obtain a uniform stock solution. . The viscosity of this stock solution was about 2000 poise at 10 ° C. This stock solution is heated from the hollow fiber die to the die temperature of 10 ℃.
Then, it was extruded with a core liquid of about 10 wt% calcium chloride aqueous solution, run in air for 5 cm, then led to a coagulating liquid of about 40 wt% calcium chloride aqueous solution at about 40 ° C. to coagulate and then washed with water. The hollow fiber was wound at 20 m / min. A 10μ-cut filter was used as the spinneret filter, but spinning was stable without filter clogging. This hollow fiber membrane was placed in a hot air drier and heated to heat at 340 ° C. for 30 minutes, and then immersed in concentrated sulfuric acid and left to stand to remove sodium alginate and silicone oil or their modified products and barium sulfate.

The porosity of this hollow fiber membrane is about 60%, and the dimensions of the obtained wet hollow fiber membrane are: inner diameter: about 500μ, film thickness: about 110μ, hollowness: about 48
%Met. Fluorine-based surfactant (Sumitomo 3M FC-129, 0.1 wt% aqueous solution surface tension (25 ℃): 17dyn
The hollow fiber bundle was immersed in a 0.1 wt% aqueous solution (es / cm) to sufficiently replace the pores in the membrane, the liquid was cut off, and the yarn bundle was dried with a hot air dryer. Fluorine-based surfactant adhesion is about 0.08wt%
It was the weight of the polymer. This dried thread became transparent just by immersing it in water, and water was confirmed to pass through the membrane immediately after pressurization. Permeability is pure water and water permeability: 2400 ml / m ² · hr · mmH
In the filtration evaluation of g, 200ppm polystyrene latex particle dispersion liquid, latex with a particle diameter of 0.212μ has a water permeability of 940 ml / m ^2.
・ Hr ・ mmHg, rejection rate: 100%.

Comparative Example 1 Fluorine-based surfactant obtained in the same manner as in Example 1 (FC-129 manufactured by Sumitomo 3M Limited, surface tension of a 0.1% aqueous solution (25
(° C): 17 dynes / cm) The dry yarn before being deposited was immersed in water, but the yarn remained white. 1kg / cm for water permeability measurement
^No water flow through the membrane was observed even when pressure was increased to ² .

Comparative Example 2 The dried yarn of Comparative Example 1 was treated with a fluorosurfactant (Sumitomo 3M FC-98, surface tension of a 0.1 wt% aqueous solution (25 ° C.): 40 dy.
(nes / cm) was immersed in a 0.1 wt% aqueous solution under reduced pressure, but the pores of the membrane could not be replaced sufficiently, and after cutting the solution, the yarn bundle was dried with a hot air dryer to give a fluorine-based surface active agent. When the amount of the attached agent was measured, it was less than 0.001 wt% based on the weight of the polymer. The dry yarn was immersed in water, but the yarn remained white. In addition, water permeability was not observed through the membrane even when pressure was increased to 1 kg / cm ² .

Comparative Example 3 A hollow fiber membrane was prepared in the same manner as in Example 1 except that the heat treatment temperature was set to 310 ° C., and the hollow fiber membrane was immersed in concentrated sulfuric acid overnight and left to stand, soda alginate and silicone oil or their modification. When the substances and barium sulfate were removed, the hollow fiber membranes collapsed and the shape of the hollow fiber membrane could not be maintained.

Example 2 The tip portion 50 mm of a yarn bundle obtained by bundling 400 porous hollow fibers after acid washing and water washing obtained in Example 1 in a U-shape was gently mixed with a tetrafluoroethylene-hexafluoropropylene copolymer (melting point).
270 ℃) water-based dispersion (solid content 50wt%, viscosity 2
It is dipped in 0 cp, specific gravity 1.4) for 15 seconds and then dried at room temperature to form a thin film of resin on the hollow fiber surface. Then, this immersion drying procedure is gently repeated 5 times to make the resin evenly on the hollow fiber surface. Was formed. Next, tighten the area around the coating of the yarn bundle with a film of tetrafluoroethylene-hexafluoropropylene copolymer (melting point 270 ° C) and a stainless steel fixing jig, and heat to 328 ° C in an electric furnace to melt the resin. Then, the hollow fibers were bonded without the inclusion of open cells. Next, the fixing jig is removed, and a PTFE housing seal member is fitted into the hollow fiber adhesive portion, and a tetrafluoroethylene-hexafluoropropylene copolymer (melting point 270
C.) pellets were filled and heated to 328.degree. C. in a vacuum atmosphere to fix the seal member to the hollow fiber bundle. Next, one end of the hollow fiber bundle seal portion was sliced to form an element having an open hollow portion. Fluorine-based surfactant (Sumitomo 3M FC-129, surface tension of 0.1 wt% aqueous solution (25 ° C): 1
(7 dynes / cm) was soaked in a 0.1 wt% aqueous solution to sufficiently replace the pores in the membrane, the solution was cut off, and then the element was dried with a hot air dryer. The amount of the fluorosurfactant attached to the hollow fiber was about 0.7 wt% based on the weight of the polymer. The hollow fiber of this element became transparent just by immersing it in water, and it was possible to confirm water passage through the membrane immediately after pressurization. An air leak test was conducted in a water-containing state, but no seal leak was observed.

Comparative Example 4 Fluorine-based surfactant (FC-129 manufactured by Sumitomo 3M, 0.1 wt% aqueous solution, obtained in the same manner as in Example 2 (surface tension (25
(° C): 17 dynes / cm) was immersed in water before attaching the element to the hollow fiber, but the thread remained white. 1kg /
Water was not passed through the membrane even when water pressure was applied to cm ² .

Comparative Example 5 The element of Comparative Example 4 was used as a fluorine-based surfactant (FC-98 manufactured by Sumitomo 3M Limited, surface tension of a 0.1 wt% aqueous solution (25 ° C.):
40 dynes / cm) was dipped in a 0.1 wt% aqueous solution under reduced pressure.
The pores of the membrane could not be replaced sufficiently, the liquid was cut off, the element was dried with a hot air dryer, and the amount of fluorine surfactant adhering to the hollow fiber was measured to be 0.001 wt% vs. polymer weight. I never saw it. The hollow fibers of this element remained white upon immersion in water. In addition, no water flow through the membrane was observed even when water pressure was applied to 1 kg / cm ² .

(Effect of the invention) The polytetrafluoroethylene-based resin porous membrane of the present invention is
Since the surfactant is attached, the effect of hydrophilization is great,
Water can be passed through the membrane by applying a small amount of water pressure, and there is no water pressure burden when passing water, so it has an excellent separation effect.

[Brief description of drawings]

FIG. 1 is an external view showing an example of an element of a hollow fiber membrane module which is an example of an element of a membrane separation device according to the present invention, and FIG. 2 is a sectional view of the element of FIG. 1: Membrane (hollow fiber membrane) 2: Case protective cover 3: Housing sealing member 4: Fixed resin

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display part D01F 6/32 7199-3B (56) Reference JP-A-1-34407 (JP, A)

Claims (2)

[Claims] 1. A uniform mixture obtained by mixing a polytetrafluoroethylene-based resin dispersion and a fiber-forming polymer is molded, and the obtained molded product is heat-treated at a temperature not lower than the melting point of the resin to form resin particles. After forming a fused structure, the fiber-forming polymer was removed, and then a fluorosurfactant having a surface tension of 0.1 wt% aqueous solution of 30 dynes / cm (25 ° C) or less was attached and dried. A method for producing a polytetrafluoroethylene-based resin porous membrane, which comprises: 2. A uniform mixture obtained by mixing a polytetrafluoroethylene-based resin dispersion and a fiber-forming polymer is molded, and the molded product is heat-treated at a temperature not lower than the melting point of the resin to form resin particles. After forming the fused structure, the fiber-forming polymer is removed, and then a combination treatment of the following steps is carried out. A step of attaching a surfactant whose surface tension of a 0.1 wt% aqueous solution is 30 dynes / cm (25 ° C) or less. A step of housing a polytetrafluoroethylene-based resin porous membrane in a case, forming a flow path through the membrane, and sealingly fixing the membrane and the end of the case with a resin.