JPH02284634A - Production of porous membrane of polytetrafluoroethylene resin and production of membrane separation apparatus with the same membrane - Google Patents

Abstract

PURPOSE:To obtain a porous membrane capable of being made effectively hydrophilic and ensuring satisfactory water permeability by heat-treating a molded body of a mixture of polytetrafluoroethylene resin dispersed in a liq. with a fiber forming polymer, removing the polymer and sticking a surfactant. CONSTITUTION:Polytetrafluoroethylene(PTFE) resin dispersed in a liq. is mixed with a fiber forming polymer such as viscose and this mixture is molded. The molded body is heat-treated at the m.p. of the PTFE resin or above, then the fiber forming polymer is removed. A surfactant having <=30dyn/cm surface tension at 25 deg.C when dissolved in water to 0.1wt.% concn. is then stuck. Since the resulting porous membrane is made effectively hydrophilic by the surfactant and water can be passed through the membrane only by applying a slight water pressure, a significant separating effect is produced.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for producing a new polytetrafluoroethylene resin porous membrane suitable for concentration and substance separation such as reverse osmosis, ultrafiltration, and microfiltration, and the use of the membrane. This paper relates to a method for manufacturing a membrane separation device.

(Prior art) Porous membranes such as cellulose acetate-based, polyethylene, polypropylene-based, polymethyl methacrylate-based, polyacrylonitrile-based, and polysulfone-based membranes have been used for reverse osmosis, ultrafiltration, microfiltration, etc. However,
It had drawbacks in permeation performance, mechanical strength, heat resistance, alkali resistance, acid resistance, solvent resistance, chemical resistance, etc.

From this point of view, mechanical strength, heat resistance, alkali resistance,
Polytetrafluoroethylene resins, which have excellent properties such as acid resistance, solvent resistance, and chemical resistance, have attracted attention, and the creation of porous membranes has been studied. For example, Special Publication No. 42-13560
No., JP-A-46-7284, JP-A-50-71759
A molded article made from an unsintered polytetrafluoroethylene resin mixture containing a liquid lubricant or an agglomerated mixture of a solid pore-forming agent and a resin dispersion, as described in No. So far, there have been examples in which membranes have been obtained using a method characterized by heating the membrane to a temperature of approximately 327°C or higher in a stretched state, but either the pore structure of the membrane is insufficiently controlled and the performance is low, or the membrane formation process is poor. There were problems in that it had poor properties and could only be formed with a thick film, and the hydrophilic effect was not sufficient, resulting in a large water pressure burden when water was passed through.

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

(Means for solving problems) The present invention has the following configuration.

(1) A homogeneous mixture obtained by mixing a polytetrafluoroethylene resin dispersion and a fiber-forming polymer is molded, and the resulting molded product is heat-treated at a temperature higher than the melting point of the resin. The coalescence was removed, and then 0.1% by weight (hereinafter w
The surface tension of an aqueous solution (abbreviated as t%) is 3 Q dyne
s/cm (25° C.) or less.

(2) A homogeneous mixture obtained by mixing a polytetrafluoroethylene resin dispersion and a fiber-forming polymer is molded, and the resulting molded product is heat-treated at a temperature higher than the melting point of the resin. A method for manufacturing a membrane separation device, which comprises removing coalescence and then performing a combination treatment of the following steps.

■The surface tension of 0.1wt% aqueous solution is 30 dynes/
A step of attaching a surfactant having a temperature of not more than cm (25° C.).

(2) The process of storing a porous polytetrafluoroethylene resin membrane in a case, forming a flow path through a protective membrane, and sealing and fixing the protective membrane and the end of the case with resin.

The present invention will be explained in detail below.

The surface tension of the surfactant aqueous solution used in the present invention is 30 d.
If it is higher than 7nes/am (25°C), the desired hydrophilic effect will not be sufficient. Therefore, 0. 1wt%
The surface tension of an aqueous solution is 30 d7nes/am (25℃
) or below, and depending on the material of the membrane, 2
It is preferably 5 dynes/cm (25°C) or less, and more preferably 20 dynes/cm (25°C) or less.

There are no other restrictions on surfactants; anionic,
The surfactants can be selected from cationic, amphoteric, and nonionic surfactants, and can be used alone or in combination. In particular, when heat resistance and chemical resistance are required, fluorinated surfactants, which are fluorocarbon compounds in which all or part of the hydrogen atoms in the hydrophobic group of the hydrocarbon surfactant are replaced with fluorine atoms, are preferred. .

In the present invention, the polytetrafluoroethylene resin porous membrane has a surface tension of 3°d7nes/c of a 0°1 wt% aqueous solution.
It is characterized by the adhesion of a surfactant with a temperature of less than Preferably, the agent is attached.

Therefore, as a method for adhesion, it is preferable to inject a solution of the surfactant into the porous structure inside the membrane. Specifically, it is preferable to immerse the membrane or module in the surfactant solution and reduce the pressure, or apply pressure with the module to pass the surfactant solution inside the membrane, and then dry it.

The amount of the surfactant used in the present invention varies depending on the type of polytetrafluoroethylene resin and surfactant used, so it cannot be determined in part, but it must be 0.001 wt% or more based on the weight of the membrane. Since there is no effect, the content is preferably 0.01 wt% or more, and more preferably 0.05 wt% or more.

On the other hand, when the amount of adhesion increases, the film becomes sticky,
Since powder may float on the surface of the membrane, the content is preferably 100wt% or less, preferably 5Qwt% or less, and even lO
More preferably, it is less than wt%.

The porous polytetrafluoroethylene resin membrane used in the present invention may be any membrane as long as it has a separation pore diameter of 0.01 to 2μ, but it is possible to downsize the device and reduce costs by increasing the effective area per unit volume. Hollow fiber membranes are preferable because they are economical, but in order to suppress the pressure loss in the hollow part of the hollow fiber membrane, the hollow ratio (the cross-sectional area of the hollow part relative to the total cross-sectional area of the membrane part and the hollow part) The higher the ratio (I), the better; it is 30% or more, preferably 35% or more, and even more preferably 40% or more.

The polytetrafluoroethylene resin in the present invention is
Tetrafluoroethylene homopolymer Single copolymer based on tetrafluoroethylene, such as tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and tetrafluoroethylene-ethylene copolymer Or a mixture thereof.

The polytetrafluoroethylene resin in the present invention is
Although it is used as an aqueous or organic dispersion, an aqueous dispersion obtained by emulsion polymerization in an aqueous medium containing a surfactant or a concentrate thereof is particularly preferable, and more specifically, a particle size of 1 μm or less is more preferable. A uniform dispersion of polytetrafluoroethylene resin particles of 0.8 μm or less is preferred.

The fiber-forming polymer in the present invention may be any polymer that can be made into fibers and forms a homogeneous mixture that can be molded by mixing with a polytetrafluoroethylene resin dispersion, but in the case of an aqueous dispersion, is preferably a viscose (cellulose xanthate-based), polyvinyl alcohol-based, or sodium alginate-based polymer alone or a mixture thereof.

The mixing ratio of the fiber-forming polymer to the polytetrafluoroethylene resin in the present invention varies depending on the type of fiber-forming polymer used, but is preferably 10 to 30
0 wt%, more preferably 30 to 200 wt%. If the mixing ratio of the fiber-forming polymer is less than 10 wt%, a porous membrane with an average pore diameter of o, oiμ or more cannot be obtained, and if it is more than 300 wt%, the mechanical strength of the membrane is low and is not practical.

In the present invention, when mixing the polytetrafluoroethylene resin dispersion and the fiber-forming polymer, additives may be mixed.

Any additive may be used as long as it can be removed by thermal decomposition, extraction, dissolution, radiolysis, etc., but examples include silicates such as silicate, aluminum silicate, and carbonates such as calcium carbonate and magnesium carbonate. Salts, phosphates such as sodium phosphate and calcium phosphate, hydrochlorides such as acetates, oxalates, ammonium chloride and sodium chloride, sulfates such as sodium sulfate and barium sulfate, nitrates, and weak acids such as perchlorates.・Strong acid salts, metal powders such as iron powder, metal oxides such as alumina, zirconia, and magnesium oxide, inorganic fine powders such as finely divided silicic acid, kaolin clay, and diatomaceous earth, polyamides, polyesters, polyolefins, polysulfones, and polyesters. Resin fine powder such as vinyl chloride, polyvinylidene fluoride, polyvinyl fluoride, silicone oil, hexafluoropropylenoxide oligomer, chlorotrifluoroethylene oligomer, phthalate esters, trimellitic acid esters, cepatic acid Select from heat-resistant organic substances such as esters, adipate esters, azelaic esters, phosphoric esters, etc.
Can be used alone or in combination.

The total amount of additives in the present invention varies depending on the type of additive, polytetrafluoroethylene resin, and fiber-forming polymer used, so it cannot be determined unconditionally, but it is 1000 wt for polytetrafluoroethylene resin. %
The content should preferably be below 1000 wt%, and if it exceeds 1000 wt%, the mechanical strength of the membrane will be low and not practical.

On the other hand, additives are preferable because they can further increase and adjust the pore structure, but the effect of addition is not seen unless the additive is IQwt% or more. 30-700 wt
The range of % is more preferable, and even more preferably 50 to 50
A range of 0 wt% is preferable.

In the present invention, a dispersant may be further mixed. Additives alone can cause agglomeration, which can clog filters and cause problems, and molded products may become uneven.
It is preferable to mix and use a dispersant when problems occur such as defects in the molded product.

Any dispersant may be used as long as it has the effect of suppressing agglomeration of additives, and can be selected from various commercially available surfactants, peptizers, and the like.

Examples of surfactants include anionic, cationic,
The optimal HLB surfactant can be selected from amphoteric surfactants and nonionic surfactants, and fluorine surfactants are also preferred.

The peptizer can be appropriately selected from free acid type or salt type, such as acrylic acid oligomers, acrylic acid copolymer oligomers, methacrylic acid oligomers, and methacrylic acid copolymer oligomers.

The amount of dispersant added in the present invention varies depending on the additive used, so it cannot be determined unconditionally, but the amount of O,
If the amount is less than 0.01 wt%, no effect of addition will be observed. 0.1
The range is more preferably 1 to 100 wt%, and even more preferably 1 to 50 wt%.

In the present invention, it is preferable to mix the polytetrafluoroethylene resin dispersion and the fiber-forming polymer at a temperature of 100°C or lower; if they are mixed at a temperature higher than 100°C, the resin particles and additives in the dispersion will aggregate. This may cause problems such as filter clogging during molding, causing problems, or non-uniformity of the molded product, or defects in the molded product. Furthermore, the temperature is preferably as low as 80°C or lower, 60°C or lower, and more preferably 40°C or lower.

The homogeneous mixture in the present invention may be any mixture as long as a molded product can be obtained, but the mixture has a viscosity of 10 to 1000 at the molding temperature.
A liquid of 0 poise is preferably used, more preferably a liquid of 100 to 5000 poise.

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

The molded product in the present invention is obtained by rolling, extrusion, or a combination of the two, and manufacturing of a sheet-like product or spinning of hollow fibers is selected depending on the shape of the desired molded product. However, hollow fiber spinning is preferred because it allows various molding conditions to be used and the structure of the molded product can be easily controlled.

For example, after casting the molding mixture onto a flat plate such as a glass plate or metal plate or a continuous belt, the molding mixture can be immersed in a coagulating liquid to solidify it, or the molding mixture can be extruded through a slit die for flat membranes and then directly or Either by passing it through the air and introducing it into a coagulating liquid to solidify it, or from a hollow fiber nozzle.
Either a non-coagulable or coagulable fluid is extruded through the core at the same time as the molding mixture and the fluid is introduced directly or once through the air into the coagulation liquid, or a coagulation liquid is extruded through the core at the same time as the molding mixture and directly introduced. Alternatively, it can be formed by passing through the air and introducing it into a non-solidifying fluid to solidify it. The non-coagulating fluid mentioned here may be any fluid as long as it does not have a coagulating effect, but it cannot be generalized because it depends on the type of fiber-forming polymer used, but examples include water, glycerin, ethylene glycol, and polyethylene. It can be appropriately selected from glycol, liquid paraffin, isopropyl myristate, freon, etc., mixed liquids thereof, air, nitrogen, and gases such as inert gases.

The temperature of the die cannot be specified because it greatly affects the spinning properties due to its relationship with the viscosity of the stock solution, but a temperature of 120° C. or lower is usually good. Furthermore, the temperature is preferably at least 20°C lower than the coagulating liquid temperature, and can prevent deterioration in spinning properties due to steam condensation on the die surface, which becomes noticeable when the distance between the die surface and the coagulating liquid surface is short. .

The conditions during air travel when the extruded molding mixture passes through the air and is introduced into the coagulation liquid vary depending on the size of the molded product, molding speed, etc. - Although they cannot be specified for boat fishing, The distance from the mouth surface to the point where the material is introduced into the coagulating liquid is preferably in the range of 02 to 200 cm from the viewpoint of molding stability. The ambient temperature is usually atmospheric temperature or indoor temperature, but depending on the case, it may be cooled.

Any coagulating liquid may be used as long as it is a non-solvent for the fiber-forming polymer of the present invention and has affinity and miscibility with the solvent of the molding mixture. Varies depending on the type, such as aqueous solutions of inorganic salts such as sodium sulfate, ammonium sulfate, zinc sulfate, potassium sulfate, zinc sulfate, copper sulfate, magnesium sulfate, aluminum sulfate, calcium chloride, magnesium chloride, zinc chloride, sulfuric acid, hydrochloric acid, nitric acid, acetic acid. , 17 oxalic acid, halonic acid, or a mixture thereof. Further, the temperature of the coagulating liquid has a large influence on 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 as long as the polytetrafluoroethylene resin particles can be fused together, such as in vacuum, air, nitrogen, oxygen, sulfur gas, helium gas, silicone oil, etc. It can be carried out in various atmospheres such as inside the room at a temperature higher than the melting point of the polytetrafluoroethylene resin. Furthermore, the molded product can be heat-treated under tension or without tension, and batch processing or continuous processing can also be selected. In addition, hoes (7) are processed in a free state without being fixed, stretched before heat treatment and fixed to the processing frame, or fixed to the processing frame under conditions with a fixed length or shrinkage rate, Alternatively, a method of continuous treatment under the conditions of stretching, constant length, shrinkage, or a combination thereof can also be adopted as appropriate.

In addition, stretching can be performed before, after, or during heat treatment, or can be performed in combination, but if the stretching ratio is too high, the shape of the pores as seen in a plane parallel to the membrane surface will be affected. Either it is impossible to obtain a membrane without orientation, or it is impossible to control the pore size, resulting in a membrane with low reliability in permeation performance.

Usually, the stretching ratio is 1-11-.3 times, and the stretching temperature can be appropriately selected within the range from room temperature to the heat treatment temperature, and stretching can also be carried out in two directions.

In the present invention, a porous membrane is formed by removing the fiber-forming polymer from the molded article after heat treatment, but the fiber-forming polymer referred to here may differ from the original one due to the heat treatment.

In the present invention, the fiber-forming polymer and optionally added additives can be removed from the heat-treated molded product by a dissolution method or a decomposition method using liquid, gas, heat, radiation, etc. , or a combination of these methods can be adopted, and can be carried out batchwise or continuously. It is also possible to carry out the process after incorporating the molded product into a module or element.

It depends on the type of fiber-forming polymer and additives used, so it cannot be said in part, but it is usually a mixture of acids such as sulfuric acid, nitric acid, hydrochloric acid, perchloric acid and hydrofluoric acid,
Alternatively, a method of immersing the heat-treated molded product in a liquid mainly composed of alkali such as thorium hydroxide or potassium hydroxide alone or in a mixture heated to a temperature in the range of room temperature to 200°C, or a module or element. A method of immersing or circulating this liquid after washing is easily used.

When removing the fiber-forming polymer after making it into a module or element, it is difficult to remove the fiber-forming polymer from the sealing part of the molded product and it remains, albeit in a small amount, especially if eluted matter is a problem. It is preferable to remove the fiber-forming polymer from only the ends of the heat-treated molded product before sealing.

Further, the membrane thus formed can be further subjected to a stretching treatment to change its permeability, mechanical strength, dimensional stability, etc. The stretching ratio is about 1°1 to 3 times,
The temperature is usually in the range from room temperature to the melting point of the polytetrafluoroethylene resin, but heat setting can also be carried out by applying a temperature after stretching.

When creating a membrane separation device using the porous polytetrafluoroethylene resin obtained in this way, a combination of the following steps is performed, but any one of them may be performed before or after.

The surface tension of 00.1 wt% aqueous solution is 30 drnes/
A step of attaching a surfactant having a temperature of not more than cm (25° C.).

(2) The process of storing a porous polytetrafluoroethylene resin membrane in a case, forming a flow path through a protective membrane, and sealing and fixing the protective membrane and the end of the case with resin.

The resin used to seal and fix the ends of the membrane and case mentioned above can be any resin that can be fixed by fusion by utilizing the difference in melting point of the membrane materials or by curing and fixing by chemical reaction such as crosslinking reaction. Often, fluororesin,
Preferable examples include olefin resins, imide resins, amide resins, ester resins, urethane resins, epoxy resins, and acrylonitrile resins.

In particular, in cases where very little eluate is required and heat resistance and chemical resistance are required, in addition to PTFE resin (melting point approximately 327°C), examples of materials that are actually being talked about include tetrafluorocarbon resin. Ethylene-perfluoroalkyl vinyl ether copolymer resin (melting point approximately 306°C), tetrafluoroethylene-hexafluoropropylene copolymer resin (
melting point approximately 270°C), tetrafluoroethylene-ethylene copolymer resin (melting point approximately 260°C), vinylidene fluoride polymer resin (melting point approximately 174°C), chlorotrifluoroethylene polymer resin (melting point approximately 211°C), etc. Fluororesin is preferable, and PTFE is more preferable.
membrane of the same resin (melting point: approx. 327°C), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin (melting point: approx. 306°C), or tetrafluoroethylene-hexafluoropropylene copolymer resin (melting point: approx. 306°C).
(melting point: approx. 270°C), a membrane of tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin (melting point: approx. 306°C) and a tetrafluoroethylene-hexafluoropropylene copolymer resin (melting point: approx. 270°C).
°C) combination is good.

The protective film and the resin for fixing the ends of the case may be used in any form such as pellets, powder, sheet, dispersion, or liquid.

There are no particular limitations on the method of sealing the protective film and the end of the case in the present invention, and any method such as heat fusion fixing or chemical reaction curing fixation such as crosslinking reaction may be used.Specifically, Heating the part or the whole using a heating iron, various heaters, oven, ultrasonic adhesive, etc.
Measures such as pressurization, depressurization, standing still, vibration, or application of centrifugal force can be carried out singly or in combination.

There are no restrictions on the shape of the module or element;
In the case of a hollow fiber membrane module or element, the fiber bundle is arranged straight and both ends are fixed with a seal, or the fiber bundle is bent into a U shape and the end of the bundle is fixed with a seal. is preferable from the viewpoint of ease of use.

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

In the membrane separation device obtained by the present invention, a plurality of membranes (hollow fiber membranes) 1 covered with a case protective cover 2 are arranged in a bundle, and the ends of the membranes 1 are connected to a housing sealing member 3 and a fixed resin. It is sealed and fixed by 4.

The polytetrafluoroethylene resin porous membrane obtained by the present invention can be used as a separation device such as a module or element for desalination of seawater, desalination, removal of bases, acids, etc. from industrial wastewater, and ultraviolet rays for use in the electronic industry. Manufacture of pure water and high purity chemicals, recovery of degreasing and electrocoating liquids, paper pulp waste liquid treatment, oil/water separation, oil emulsion separation, and other industrial wastewater treatment, separation and purification of fermentation products, and concentration of fruit and vegetable juices. , soybean processing, concentration in the food industry such as the sugar industry,
It is widely used in medical applications such as separation, purification, artificial kidneys, blood component separation, microfilters for bacterial isolation, pharmaceutical separation and purification, and biotechnology fields such as bioreactors.

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

(1) Membrane dimensions Measured using an optical microscope.

(2) Hollow ratio Measured using method (1) (7) Using the dimensions of the hollow fiber membrane, 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 expressed as a percentage (%) It was calculated by

(3) Measure the weight (W) of the membrane whose pores are filled with pure water using the porosity ethanol replacement method, the bone dry type 1 (Wo), and its volume (V), and calculate using the following formula. did.

(W-Wo) and the water permeability was calculated from the transmembrane pressure difference.

The hollow fiber membrane was made into a small module, water pressure was applied to the inside of the hollow fiber while maintaining the temperature at 37°C, and water permeability was calculated from the amount of water permeating through the membrane in a certain period of time, the effective membrane area, and the pressure difference between the membranes.

(5) Filtration performance of 200 ppm polystyrene latex particle dispersion Using a commercially available polystyrene latex particle dispersion, water permeability was measured by the method described in (4) above.

The particle rejection rate was calculated by measuring the concentration CO of the stock solution and the concentration C of the permeated solution using the following formula.

(Co-C)
1 part, barium sulfate (X-ray contrast agent Varitop, manufactured by Sakai Chemical Industry Co., Ltd.) 600 parts, silicone oil (5H-200 manufactured by Tomu Silicone Co., Ltd.) 30 parts, fluorine surfactant (manufactured by Sumitomo 3M Co., Ltd. FC- 129) 60 parts to 800 parts of purified water
A homogeneous stock solution was obtained by dissolving and mixing the mixture at 10°C. To this stock solution, 500 parts of an aqueous dispersion of polytetrafluoroethylene (D-2 manufactured by Daikin, solid content 61% by weight, surfactant 5.7% by weight) was added and stirred at 10°C to obtain a uniform stock solution. Obtained. The viscosity of this stock solution was about 2000 poise at 1.0°C. Transfer this stock solution from the hollow fiber nozzle to a nozzle temperature of 130°C.
Extrusion with a core liquid of approximately 10% by weight calcium chloride aqueous solution; -1 After traveling 5 cm in air, approximately 40% by weight
After being introduced into a coagulating solution of calcium chloride aqueous solution at about 40°C and coagulated, the hollow fiber was washed with water and wound at 20 m/min. A 1.0μ cut filter was used as a spinneret filter, and stable spinning was possible without any filter clogging. This hollow fiber membrane was placed in a hot air dryer and heated to 3
After heat treatment at 40°C for 30 minutes, the sample was left immersed in concentrated sulfuric acid to remove sodium alginate, silicone oil or modified products thereof, and barium sulfate.

The porosity of this hollow fiber membrane was about 60%, the dimensions of the obtained wet hollow fiber membrane were: inner diameter: about 500p, membrane thickness: about 110μ, and hollowness: about 48%. Next, the surface tension of a fluorine-based surfactant (Sumitomo 3M FC-129, 0.1 wt% aqueous solution (25°C) = 17 dynes/en+) is 0.1
The hollow fiber bundle was immersed in a wt % aqueous solution to sufficiently replace the pores in the membrane, the liquid was drained, and the fiber bundle was dried in a hot air dryer. The amount of fluorosurfactant deposited was approximately 0.08 wt% to polymer weight. This dried thread became transparent just by immersing it in water, and water flow through the membrane was immediately confirmed when pressure was applied. Water permeability with pure water: 2400m1/m-h
In the filtration evaluation of r-mrnHg, 200ppm polystyrene latex particle dispersion, water permeability = 940ml/n (-hr-nnmHg
, Rejection rate: ]-00%.

Comparative Example 1 Example 1. Dip the dry yarn in water before attaching the fluorine-based surfactant (Sumitomo 3M FC-129, 0.1% aqueous solution surface tension (25°C): 17 d7nes/cm) obtained in the same manner as above. However, the thread remained white. In addition, water permeability measurements showed that no water was observed to pass through the membrane even when the pressure was increased to 1 kg/al.

Comparative Example 2 The dried yarn of Comparative Example 1 was treated with a fluorine-based surfactant (FC-98, Q manufactured by Sumitomo 3M Co., Ltd., and the surface tension of a 1 wt % aqueous solution (2
5°C): 0.40 drnes/cm). 1wt
% aqueous solution under reduced pressure, but the pores in the membrane could not be replaced sufficiently, so after draining the liquid, the yarn bundle was dried in a hot air dryer and the amount of fluorosurfactant attached was measured. However, it was less than 0.001 wt% to polymer weight. The dried yarn was immersed in water, but the yarn remained white. Furthermore, water permeability measurements showed that no water was observed to pass through the membrane even when the pressure was increased to 1 kg/car.

Comparative Example 3 A hollow fiber membrane was produced in the same manner as in Example 1, except that the heat treatment temperature was 310°C. It was immersed in concentrated sulfuric acid overnight and then treated with sodium alginate and silicone oil or their modified components. When the substance and barium sulfate were removed, the hollow fiber membrane collapsed and could not maintain its shape.

Example 2 A 5Q mm tip end of a U-shaped bundle of 400 porous hollow fibers obtained in Example 1 after acid washing and water washing was gently injected into a tetrafluoroethylene-hexafluoropropylene copolymer (melting point 270). °C) aqueous dispersion (solids content 50
wt%, viscosity 20cp1 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, and then gently repeating this immersion-drying procedure five times. A resin film was evenly formed on the surface. Next, the periphery of the coating part of the yarn bundle was coated with tetrafluoroethylene-hexafluoropropylene copolymer (melting point: 270°C).
) film and stainless steel fixing jig,
The resin was melted by heating to 328° C. in an electric furnace, and the hollow fibers were bonded together without the inclusion of open air bubbles. Next, remove the fixing jig,
A PTFE housing sealing member is fitted into the hollow fiber bonding part, and tetrafluoroethylene-hexafluoropropylene copolymer (melting point 270°C) pellets are filled, and the sealing member is attached to the hollow fiber bundle by heating to 328°C in a vacuum atmosphere. was fixed. Next, one end of the hollow fiber bundle seal portion was sliced to obtain an element with an open hollow portion. This element was treated with a fluorosurfactant (FC-12 manufactured by Sumitomo 3M).
Surface tension of 9, 0, 1 wt% aqueous solution (25°C):
The element was immersed in a 0.1 wt % aqueous solution of 17d7nes/cm) to sufficiently replace the pores in the membrane, the liquid was drained, and the element was dried in a hot air dryer. The amount of the fluorosurfactant attached to the hollow fibers was about 0.7 wt % to the weight of the polymer. The hollow fibers of this element became transparent just by immersing them in water, and water flow through the membrane could be confirmed as soon as pressure was applied.

An air leak test was also conducted in a water-containing state, but no seal leakage was observed.

Comparative Example 4 A fluorine-based surfactant (FC-129 manufactured by Sumitomo 3M, 0.1 wt% aqueous solution (surface tension (25°C): 17d7nes/am) obtained in the same manner as in Example 2 was attached to the hollow fiber. The previous element was immersed in water, but the thread remained white.Also, no water flow was observed through the membrane even when water pressure was applied to 1 kg/cnr.

Comparative Example 5 The element of Comparative Example 4 was treated with a fluorine-based surfactant (Sumitomo 3M FC-98, surface tension of 0.1 wt% aqueous solution (25°C): 40 d7nes/cm) of 0.1
Although it was immersed in a wt% aqueous solution under reduced pressure, the pores in the membrane could not be replaced sufficiently, so the element was dried in a hot air dryer after draining the liquid, and the fluorosurfactant adhered to the hollow fibers. When the amount was measured, it was not even 0.001 wt% to polymer weight.

The hollow fibers of this element remained white even when immersed in water. Further, even when a water pressure of up to 1 kg/cnr was applied, no water flow was observed through the membrane.

(Effects of the invention) The polytetrafluoroethylene resin porous membrane of the present invention has
Because the surfactant is attached, the hydrophilic effect is large,
Water can be passed through the membrane by applying only a small amount of water pressure, and it has excellent separation effects because there is no water pressure burden when water passes through.

[Brief explanation 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 shown in FIG. 1. 1: Membrane (hollow fiber membrane) 2: Case protective cover 3: Housing seal member 4: Fixed resin

Claims (2)

[Claims] (1) A homogeneous mixture obtained by mixing a polytetrafluoroethylene resin dispersion and a fiber-forming polymer is molded, and the resulting molded product is heat-treated at a temperature higher than the melting point of the resin. A method for producing a porous polytetrafluoroethylene resin membrane, which comprises removing the coalescence, and then attaching a surfactant having a surface tension of 30 dynes/cm (25° C.) or less in a 0.1% aqueous solution. (2) A homogeneous mixture obtained by mixing a polytetrafluoroethylene resin dispersion and a fiber-forming polymer is molded, and the resulting molded product is heat-treated at a temperature higher than the melting point of the resin. A method for manufacturing a membrane separation device, which comprises removing coalescence and then performing a combination treatment of the following steps. [1] The surface tension of a 0.1% aqueous solution is 30 dynes
/cm (25°C) or less. [2] A step of storing a porous polytetrafluoroethylene resin membrane in a case, forming a flow path through the membrane, and sealing and fixing the membrane and the ends of the case with resin.