WO2007125709A1

WO2007125709A1 - Porous water treatment membrane made of vinylidene fluoride-based resin with little contamination and method of producing the same

Info

Publication number: WO2007125709A1
Application number: PCT/JP2007/056363
Authority: WO
Inventors: Toshiya Mizuno; Yasushi Ebihara; Yasuhiro Tada; Kenichi Suzuki; Takeo Takahashi
Original assignee: Kureha Corporation
Priority date: 2006-04-25
Filing date: 2007-03-27
Publication date: 2007-11-08
Also published as: JP2007313491A

Abstract

A porous water treatment membrane with little contamination which is a porous membrane made of a vinylidene fluoride-based resin wherein the outer surface has been selectively hydrophilized. This porous water treatment membrane made of a vinylidene fluoride-based resin is characterized by: (a) showing little membrane contamination during filtration (i.e., having a high flux retention rate); (b) the little contamination properties being maintained after repeated washing with a chemical (i.e., a high tolerance to chemical-washing); and (c) having a favorable mechanical strength.

Description

Low-contamination vinylidene fluoride resin porous water treatment membrane and method for producing the same

[0001] The present invention relates to the resistance of water treatment membranes made of polyvinylidene fluoride resin used as microfiltration membranes for sterilization of water and sewage, contamination purification, aqueous chemical treatment, or pure water production. Concerning improvement of pollution.

Background art

As a water treatment membrane as described above, a synthetic resin-based porous membrane has been conventionally used. These porous membranes used as water treatment membranes have an appropriate porosity, pore size and pore size distribution suitable for removal and separation of fine particles to be removed, and a sufficient breaking point for mechanical strength during use. It is required to have stress, pressure resistance, elongation at break, chemical resistance to the liquid to be treated or backwashing after use and ozone treatment.

[0003] Since vinylidene fluoride resin is excellent in weather resistance, chemical resistance, heat resistance, strength, etc., application to these water treatment membranes is being studied. However, while the vinylidene fluoride resin has the above-mentioned excellent characteristics, it is a hydrophobic resin, so that during the drainage operation, organic matter contained in the treated water is However, there is a problem that the water permeability is difficult to recover even after regeneration treatment by physical cleaning such as backwashing or air scrubbing.

[0004] On the other hand, in order to improve the problems associated with hydrophobicity while taking advantage of the strength, weather resistance, etc. of the vinylidene fluoride resin-based water treatment membrane, There have also been some proposals to make the porous porous membrane hydrophilic (for example, Patent Documents 1 to 5 below).

[0005] For example, a polyvinylidene fluoride-based porous resin membrane can be hydrophilized by treating it with an alkali solution (Patent Document 1) or by further treating with ozone after the alkali solution treatment (Patent Document 2). Proposed. By such a treatment, the hydrophilic property of the polyvinylidene fluoride resin porous membrane is improved with certainty, but at the same time, there is a drawback that mechanical properties such as high elongation are remarkably lowered.

[0006] In addition, a polyvinylidene fluoride-based porous resin membrane is formed by dissolving a hydrophilic resin such as polybutyl alcohol. It has also been proposed to make it hydrophilic by immersing it in a liquid and forming a coating film (Patent Document 3), or by subjecting a hydrophilic monomer to a draft polymerization (Patent Document 4). However, the hydrophilic resin coating film or graft film formed in this way does not necessarily have good adhesion to the polyvinylidene fluoride resin porous film, and physical washing such as backwashing and air scrubbing is not possible. Poor durability for cleaning, low chemical resistance, poor durability including regeneration treatment, and formation of paint film or graft membrane reduces pore size, or pore connectivity If it is hindered and the water permeability capacity decreases, there is a drawback.

[0007] In addition, it has also been proposed that a hydrophilic resin such as polybulualcohol is mixed with a vinylidene fluoride resin to make the matrix resin itself forming a porous film hydrophilic (patent). Reference 5). However, a porous membrane made of a matrix resin mixed with a hydrophilic resin, which has a poor affinity for the vinylidene fluoride resin, which is a hydrophobic resin, prevents a decrease in mechanical strength. In addition, since the chemical resistance of the hydrophilic resin is small, the durability against chemical cleaning (drug cleaning durability) also decreases.

[0008] As described above, the conventional fluoride fluoride has been improved satisfactorily as a hydrophobic coagulant by hydrophilization while maintaining durability and mechanical properties including regeneration treatment with chemicals and the like. The reality is that a porous water treatment membrane made of redene-based rosin has not been obtained.

Patent Document 1: Japanese Patent Publication No. 62-17614

Patent Document 2: Japanese Patent No. 3242983

Patent Document 3: Japanese Patent Laid-Open No. 3-178429

Patent Document 4: Japanese Patent Laid-Open No. 2003-268152

Patent Document 5: Japanese Patent No. 3200095.

[0009] Disclosure of the Invention

In view of the above circumstances, the main objects of the present invention are (i) low membrane contamination during filtration operation (low contamination), and (mouth) maintained after chemical cleaning in which low contamination is repeated ( High (drug washing durability) and (c) Good mechanical strength (Polyvinylidene fluoride resin porous membrane retains the original mechanical strength well), Vinylidene fluoride resin porous water treatment membrane And to provide an efficient manufacturing method.

That is, the low-contamination porous water treatment membrane of the present invention is a flat film made of vinylidene fluoride resin. It is a porous membrane in the form of a membrane or a hollow fiber membrane, and its outer surface is selectively hydrophilized. Here, the outer surface of the porous film refers to at least one of the two main surfaces facing each other across the film thickness, and the surface (inner surface) of the fine pores distributed in the film thickness. This is an exception. However, it does not completely eliminate the surface of micropores that exist from the outer surface to a limited depth. Preferably, the degree of selectivity of hydrophilization on the outer surface is defined by the thickness of the hydrophilization layer (preferably, the wetting index) described later.

[0011] The present inventors will make a few additional comments on how the present inventors have studied for the above-mentioned purpose and arrived at the polyvinylidene fluoride-based resin porous water treatment membrane of the present invention.

[0012] Conventionally, hydrophobic hydrophobic resin porous membranes have been considered to easily adhere to membrane dirt components because they have a small electrical repulsive force with membrane dirt components. Attempts have been made to increase the electric repulsive force with the film dirt component to reduce the film dirt. On the other hand, membrane dirt components contained in raw water are deposited on the outer surface of the membrane on the raw water supply side (forming a cake layer) and adhered to the surface of micropores distributed in the film thickness, reducing the pore size. Some of them cause clogging of pores, all of which are thought to cause an increase in filtration resistance (decrease in water permeability). For this reason, even in the case of aiming at low contamination, the hydrophilization treatment to the hydrophobic resin porous membrane has been carried out exclusively on the entire surface including the microporous surface (for example, Patent Document 5).

[0013] The inventors of the present invention have fundamentally studied a membrane fouling mechanism as a water treatment membrane of a polyvinylidene fluoride resin porous membrane, and as a result, a change in filtration characteristics over time (due to reduction and regeneration). For the recovery of filtration characteristics, etc., the pores distributed in the thickness direction that form the porous membrane do not contribute uniformly, but deposit mainly on the outer surface of the raw water supply side and the outer surface. We found that the cake layer was dominant.

[0014] Furthermore, as a result of investigating the reduction of membrane fouling by hydrophilizing a polyvinylidene fluoride resin porous membrane, consolidation of the cake layer to be deposited (for example, cake filtration theory) The cake filtration resistance coefficient in the equation (Ruth equation) was found to be significantly reduced. The cake layer is mainly composed of fine particles to be removed, fungi, high molecular weight humic substances, etc., trapped on the outer surface and deposited in layers. The finding that it also affects the wearability was a new discovery.

[0015] When the hydrophilization treatment was performed on the pyridene fluoride resin porous membrane with a strong force, however, the mechanical strength of the porous membrane after the treatment was lowered, resulting in a problem.

[0016] Through various tests, the present inventors have determined that the outer surface of the polyvinylidene fluoride-based rosin porous membrane does not uniformly hydrophilize the outer surface and the inner microporous surface. If selectively hydrophilized, porous water treatment made of polyvinylidene fluoride resin, a hydrophilic resin that does not cause problems such as a decrease in mechanical strength due to uniform hydrophilization. We have found that many of the membrane problems can be improved and have reached the present invention.

[0017] Further, the inventors of the present invention, for efficient production of the above-described low-contamination porous water treatment membrane, used a contact treatment liquid for hydrophilization as a polyvinylidene fluoride resinous porous membrane. It has also been found that it is effective to selectively act on the outer surface of the film. That is, in the method for producing a low-contamination porous water treatment membrane of the present invention, a flat membrane or hollow fiber membrane-like porous membrane made of a vinylidene fluoride resin is hydrophilized by contact with a hydrophilization treatment liquid. In this case, the outer surface of the porous membrane is selectively hydrophilized.

Brief Description of Drawings

FIG. 1 is a schematic explanatory view of a water permeability measuring device used for evaluating the water treatment performance of hollow fiber porous membranes obtained in Examples and Comparative Examples.

BEST MODE FOR CARRYING OUT THE INVENTION

[0019] The low-contamination water treatment membrane of the present invention is generally produced by treating the outer surface of a hydrophobic polyvinylidene fluoride resin porous membrane produced by various production methods according to the method of the present invention. Can be built. For example, the method of selectively hydrophilizing the outer surface according to the present invention is applied to a flat membrane or hollow fiber membrane porous membrane made of vinylidene fluoride resin formed by the following method. A low-contamination porous water treatment membrane can be obtained.

[0020] (1) An organic liquid such as decyl phthalate and hydrophobic silica are mixed as inorganic fine powder with vinylidene fluoride resin, and after melt molding, the organic liquid and hydrophobic silica are extracted. A method for producing a vinylidene fluoride resin porous membrane that forms pores after extraction (JP-A-3-215535, etc.).

[0021] (2) Although it is a solvent for vinylidene fluoride resin such as dimethyl sulfoxide, it is compared. A solution in which the concentration of vinylidene fluoride resin is 5 to 35% by weight is extruded into a coagulation liquid containing water as the main component and coagulated. (For example, Japanese Patent Publication No. 7-8548). At this time, in order to control the pore distribution of the resulting porous membrane, a small amount of water, a non-solvent such as alcohols (for example, glycerin) is preferably added to the solvent.

[0022] (3) Extraction that does not dissolve polyvinylidene fluoride resin after melt mixing and film formation after adding plasticizer and good solvent to vinylidene fluoride resin having improved crystal characteristics A method in which the plasticizer and good solvent are extracted with a liquid to make it porous, and stretching is performed before and after extraction or after Z (for example, WO2005Z099879A1). By preferentially cooling one of the two outer surfaces for cooling during film formation, an inclined pore size distribution with an increased pore size is generated on the one outer surface force and the other outer surface, and a hollow fiber-like porous membrane is formed. When forming, a hollow fiber porous membrane having a generally increased pore size distribution toward the inner outer surface is obtained on the outer outer surface force generally on the raw water supply side.

[0023] As described above, in order to obtain the low-contamination porous water treatment membrane of the present invention by selective hydrophilization of the outer surface, the polyvinylidene fluoride resin porous membrane to which selective hydrophilization is applied is applied. In this sense, it is preferable that the membrane has an inclined pore size distribution in the thickness direction, and it is preferable to use a polyvinylidene fluoride-based resin porous membrane obtained by the method (3).

[0024] By having an inclined pore size distribution, it has a small pore size for reliably removing fine particles to be removed, and a film thickness that is somewhat large for ensuring mechanical strength, Great water permeability can be achieved.

[0025] In a porous membrane having an inclined pore size distribution, whether the feed surface of the raw water is large or small, and the side of the raw water is different from that of the dirt component or fine particles to be removed is determined. It is arbitrarily determined empirically or experimentally after considering factors such as chemical composition, particle size (ie, raw water quality), filtration conditions, and washing conditions (ie, operating conditions). The pore size is small in river water, lake water, ground water, or raw water (including MBR: activated sludge membrane filtration method) that is biologically treated from sewage, industrial wastewater, or livestock wastewater! It is preferable to supply raw water from the side.

[0026] The selective hydrophilization of the outer surface is effective in the part where membrane contamination is most likely to occur. The hole on the outer surface to which water is supplied has a small hole diameter! In a porous membrane having a slanted pore size distribution, when supplying side force raw water having a small pore size, it is inevitably effective to selectively hydrophilicize the outer surface on the side having a small pore size. When the raw water is supplied from the side with the larger pore diameter, factors such as the quality of the raw water and the operating conditions should be taken into consideration to determine whether the outer surface is selectively hydrophilized to the gap between the large and small pores. The empirical above is arbitrarily determined experimentally. Preferably, the outer surface to which raw water is supplied is selectively hydrophilized.

[0027] Although the above methods (1) to (3) are offset, a flat membrane-like porous membrane can be produced. For flat membranes and hollow fiber membranes, it is desirable to have a misalignment. U, heel! /, Etc., hollow fiber membranes are generally preferred in order to enable large-capacity processing with small-capacity modules. Therefore, it can be said that a flat membrane that has a simple module structure and is easy to remove dust is preferable for treatment of sewage / drainage including fiber waste such as hair and warax.

[0028] Hereinafter, the hollow fiber-like low-contamination porous material is obtained by selectively hydrophilizing the outer surface subsequent to each step of the method for producing a vinylidene fluoride-based porous resin membrane by the method (3). The process of the preferable one aspect | mode of this invention method which manufactures a water treatment membrane is demonstrated sequentially.

[0029] (Vinylidene fluoride resin)

In the present invention, it is preferable to use a vinylidene fluoride resin having a weight average molecular weight (Mw) of 200,000 to 600,000 as the main film material. When the Mw is 200,000 or less, the mechanical strength of the obtained porous film becomes small. When the Mw is 600,000 or more, the phase separation structure between the vinylidene fluoride resin and the plasticizer becomes excessively fine, and the water permeability when the obtained hollow fiber porous membrane is used as a microfiltration membrane is small. descend.

In the present invention, as the vinylidene fluoride-based resin, homopolymers of vinylidene fluoride, that is, poly (vinylidene fluoride) and other copolymerizable with vinylidene fluoride can be used. Copolymers with monomers or mixtures thereof are used. As the monomer copolymerizable with vinylidene fluoride, one or two or more of tetrafluoroethylene, hexafluoropropylene, trifluoride styrene, trifluoride salt, ethylene, butyl fluoride, etc. may be used. it can. The vinylidene fluoride resin preferably contains 70 mol% or more of vinylidene fluoride as a structural unit. Among them, it has a high mechanical strength and is composed of 100% by mole of vinylidene fluoride. It is preferable to use a polymer.

[0031] The above-described relatively high molecular weight vinylidene fluoride resin can be obtained by emulsion polymerization or suspension polymerization, particularly preferably suspension polymerization.

[0032] In addition to having a relatively large molecular weight of 200,000 to 600,000, as described above, the vinylidene fluoride resin forming the hollow fiber porous membrane of the present invention has a DSC measurement. The difference between the original melting point Tm2 (° C) and the crystallization temperature Tc (° C) due to Tm2—Tc is less than 32 ° C, preferably less than 30 ° C. At this time, it is preferable to have crystal characteristics that suppress the growth of spherical crystals and promote the formation of a network structure.

[0033] Here, the original melting point Tm2 (° C) of the resin is the melting point Tml (° C) measured by subjecting the obtained sample resin or the resin forming the porous film to the temperature rising process by DSC as it is. C) is distinct. In other words, generally available vinylidene fluoride-based resin has a melting point Tml (different from the original melting point Tm2 (° C) due to the heat and mechanical history received during its production process or thermoforming process. The melting point Tm2 (° C) of the above-described fluoride-redene resin is determined by subjecting the obtained sample resin to a predetermined temperature increase / decrease cycle. And the melting point (endothermic peak temperature associated with crystal melting) found again in the DSC temperature rise process after removing the mechanical history, and details of the measurement method are described in the description of Examples below. List in advance.

[0034] The condition of Tm 2-1 ^ ≤32, which represents the crystallization temperature of vinylidene fluoride resin preferably used in the present invention, can be achieved even if the reduction of 1¾12 is caused by copolymerization, for example. However, in this case, there is a case where the chemical resistance of the resulting porous film tends to be lowered. Accordingly, in a preferred embodiment of the present invention, 70 to 98% by weight of a vinylidene fluoride resin having a weight average molecular weight (Mw) of 150,000 to 600,000 is used as a matrix (mainly) resin. The Mw was 1.8 times or more, preferably 2 times or more and 1.2 million or less, obtained by adding 2 to 30% by weight of a high molecular weight vinylidene fluoride resin for crystal property modification. A vinylidene fluoride-based resin mixture is used. According to such a method, the crystallization temperature Tc can be significantly increased without changing the crystal melting point of the matrix resin alone (preferably represented by Tm2 within the range of 170 to 180 ° C.). More specifically, by increasing Tc, the outer surface force of the hollow fiber membrane formed by melt extrusion is preferential. During cooling, it is possible to accelerate the solidification of the vinylidene fluoride-based resin from the inside of the film, which is slower than the film surface, to the inner surface, thereby suppressing the growth of spherical particles. Tc is preferably 143 ° C or higher.

[0035] When the Mw of the high molecular weight vinyl fluoride-redene resin is less than 1.8 times the Mw of the matrix resin, it is difficult to sufficiently suppress the formation of the spherical particle structure. In some cases, it is difficult to disperse uniformly in the matrix resin.

[0036] If the amount of the high molecular weight vinylidene fluoride resin is less than 2% by weight, the effect of suppressing the formation of the spherical particle structure is not sufficient. On the other hand, if it exceeds 30% by weight, the vinylidene fluoride type resin is added. There is a tendency that the phase separation structure of the resin and the plasticizer becomes excessively fine and the water permeability of the membrane decreases.

[0037] According to a preferred embodiment of the present invention, a raw material for film formation is obtained by adding a plasticizer and a good solvent of vinylidene fluoride resin to the above-mentioned vinylidene fluoride resin. Form a composition.

[0038] (Plasticizer)

The hollow fiber porous membrane of the present invention is mainly formed of the above-mentioned vinylidene fluoride resin, but for its production, in addition to the above-mentioned vinylidene fluoride resin, at least its plastics are used. It is preferable to use an agent as a pore-forming agent. As the plasticizer, generally, an aliphatic polyester including a dibasic acid and a glycolic acid, for example, an adipic acid-based polyester such as adipic acid monopropylene glycol-based, adipic acid 1,3-butylene glycol-based, or the like; And azelaic acid polyesters such as azelaic acid-propylene glycol type and azelaic acid 1,3 butylene glycol type.

[0039] (good solvent)

In order to form the hollow fiber membrane of the present invention through melt extrusion with a relatively low viscosity, it is preferable to use a good solvent of vinylidene fluoride resin in addition to the plasticizer. As the good solvent, a solvent capable of dissolving vinylidene fluoride resin in a temperature range of 20 to 250 ° C. is used. For example, N-methylpyrrolidone, dimethylformamide, dimethylacetamide, dimethylsulfoxide, methylethyl Ketone, acetone, tetrahydrofuran, dioxane, ethyl acetate, propylene carbonate, cyclohexane, methyl isobutyl ketone , Dimethyl phthalate, and mixed solvents thereof. Of these, N-methylpyrrolidone (NMP) is preferred for its stability at high temperatures.

[0040] (Composition)

The raw material composition for forming a hollow fiber membrane is preferably 100 to 300 parts by weight of a plasticizer and a good solvent for vinylidene fluoride resin in a total amount of 100 parts by weight of vinylidene fluoride resin. Parts by weight, more preferably 140 to 220 parts by weight, and the ratio of the good solvent is 12.5 to 35% by weight, more preferably 15.0 to 32.5% by weight and mixed. Can be obtained.

[0041] When the total amount of the plasticizer and the good solvent is too small, the viscosity of the composition at the time of melt extrusion becomes excessive, and when it is too large, the viscosity is excessively decreased. In either case, it is difficult to obtain a porous hollow fiber having a homogeneous and moderately high porosity, and thus filtration performance (water permeability). In addition, when the proportion of the good solvent in the total amount of both is less than 12.5% by weight, it is difficult to obtain a uniform pore diameter effect. On the other hand, if the proportion of the good solvent exceeds 35% by weight, the crystallization of the resin in the cooling bath becomes insufficient, the yarn tends to be crushed, and the formation of the hollow fiber itself becomes difficult.

[0042] The raw material composition for producing the hollow fiber membrane used in the present invention contains various stabilizers and a small amount of additives such as a granular filler in addition to the plasticizer and good solvent described above. However, it is preferable not to include a fibrous reinforcing material. Including fibrous reinforcing material, in addition to unstable mixing and melt extrusion, the control of inner and outer diameters and wall thickness controls the strength and balances water permeability and microfiltration performance. This is because it becomes difficult to obtain a hollow fiber porous membrane. Therefore, for the hollow fiber porous membrane product obtained by the present invention, “substantially only the strength of vinylidene fluoride-based resin” means that the porous film is not only in the form of polyvinylidene-based resin. In addition to residual plasticizers and good solvents that are small or near the detection limit, optional stabilizers or small amounts of granular filler may be included, but no fibrous reinforcement is included.

[0043] (Mixing & melt extrusion)

The melt-extruded composition is generally formed into a film by extrusion through a hollow nozzle cover at a temperature of 140 to 270 ° C, preferably 150 to 200 ° C. Therefore, as long as a homogeneous composition in the above temperature range is finally obtained, the mixture of the vinylidene fluoride resin, the plasticizer and the good solvent is mixed. In addition, the molten form is arbitrary. According to one preferred embodiment for obtaining such a composition, a biaxial kneading extruder is used (preferably also having a mixture power of the main resin and the crystal characteristic modifying resin). -The redene-based resin is supplied from the upstream side of the extruder, and a mixture of a plasticizer and a good solvent is supplied downstream and is made into a homogeneous mixture before being discharged through the extruder. This twin-screw extruder can be controlled independently by dividing it into a plurality of blocks along its longitudinal direction, and appropriate temperature adjustment is made according to the contents of the passing material at each part. In order to obtain a hollow fiber porous membrane having a large wall thickness and cross-sectional area, it is effective to increase the melt extrusion speed, which is the raw material discharge amount per length (m) of the melt-extruded material. The melt extrusion speed is preferably 2.0 to 0. OgZm, more preferably 2.5 to 9. OgZm, and particularly preferably 2.5 to 6. OgZm. 2. If it is less than OgZm, the durability of the resulting film will be reduced, and if it exceeds 10. OgZm, the melt-extruded product may be crushed, making it impossible to form a hollow part.

[0044] Next, the melt-extruded hollow fiber membrane is introduced into a cooling bath, and the outer surface force is preferentially cooled to solidify and form a film. At that time, a hollow fiber membrane having an expanded diameter is obtained by cooling while injecting an inert gas such as air or nitrogen into the hollow portion of the hollow fiber membrane material. This is advantageous for obtaining a hollow fiber porous membrane with a small reduction in water permeability (WO2005Z03700A). In addition, obtaining a hollow fiber membrane whose diameter has been expanded by blowing an inert gas into the hollow portion is larger than that of simply increasing the thickness of the hollow fiber membrane to be produced. And is preferable for obtaining a hollow fiber membrane having good bending resistance. The inert gas injection rate as the feed rate per length (m) of the melt-extruded material is 0.7 to 6.8 ml / m, more preferably 1.2 to 3. Oml / m, especially 1 4 to 2. Oml / m range force S Preferred. If it is less than 7 mlZm, the inner diameter of the hollow portion becomes small, and the water permeability decreases due to flow resistance. If it exceeds 6.8 ml / m, the melt-extruded membrane may be punctured.

[0045] The larger the elapsed time (air gap passage time = air gap Z melt extrusion take-off speed) until entering the inert liquid bath after extrusion, the more uneven the yarn diameter (inner / outer diameter) due to yarn fluctuation in the longitudinal direction. However, it has the effect of suppressing the formation failure of the hollow fiber porous membrane due to thread crushing, and stabilizing the yarn diameter in order to gently reduce the yarn diameter and thickness while blowing inert gas. 0 seconds or more, especially 2.0 to 7.0 seconds is preferred Yes.

[0046] As the cooling liquid, a liquid that is inert (that is, non-solvent and non-reactive) with respect to vinylidene fluoride-based resin, preferably water, is generally used. In some cases, a good solvent for vinylidene fluoride resin (similar to that contained in the melt-extruded composition described above) that is compatible with an inert liquid (preferably NMP compatible with water) is cooled. When mixed in a proportion of 30 to 90% by weight, preferably 40 to 80% by weight in the liquid, the pore diameter on the outer surface side of the finally obtained hollow fiber porous membrane is increased, and air scrubbing It is also possible to obtain a hollow fiber porous membrane having a minimum pore size layer inside the membrane which is advantageous for regeneration (WO2004Z081109A1 report). The temperature after cooling is 0 to 120 ° C, and a wide temperature range force can be selected, but it is preferably 5 to 100 ° C, particularly preferably 10 to 80 ° C.

[0047] (Extraction)

The cooled and solidified film is then introduced into the extract bath and subjected to extraction removal of the plasticizer and good solvent. The extract is not particularly limited as long as it does not dissolve the polyvinylidene fluoride-based resin but can dissolve the plasticizer or good solvent. For example, polar solvents having a boiling point of about 30 to 100 ° C. such as methanol and isopropyl alcohol for alcohols and dichloromethane and 1,1,1-trichloroethane for chlorinated hydrocarbons are suitable.

[0048] (stretching)

It is preferable to stretch the hollow fiber membrane before and / or after the extraction of the plasticizer to increase the porosity and pore diameter and improve the strength. In general, the hollow fiber membrane is preferably stretched uniaxially in the longitudinal direction of the hollow fiber membrane by a pair of rollers having different peripheral speeds. This is because, in order to harmonize the porosity and the strong elongation of the vinylidene fluoride resin hollow fiber porous membrane of the present invention, the stretched fibril (fiber) portion and the unstretched node ( This is because it has been found that a fine structure in which sections) appear alternately is preferable. Stretching is a powerful means for adjusting the thickness when obtaining a large cross-sectional area hollow fiber membrane according to the present invention, and is also effective for obtaining a high-strength hollow fiber membrane. The draw ratio is suitably about 1.2 to 4.0 times, particularly about 1.4 to 3.0 times. If the draw ratio is too low, the relaxation ratio cannot be increased, and it is difficult to obtain the effect of improving the water permeability due to the relaxation. On the other hand, when the draw ratio is excessive, the tendency of the hollow fiber membrane to break increases. The stretching temperature is preferably 25 to 90 ° C, particularly 45 to 80 ° C. . If the stretching temperature is too low, the stretching becomes non-uniform and the hollow fiber membrane is easily broken. On the other hand, if the stretching temperature is too high, the pores will not advance even if the stretching ratio is increased, and even if the stretching is relaxed, it is difficult to obtain the effect of improving the water permeability. In order to improve the stretching operability, heat treatment is performed in advance at a temperature in the range of 80 to 160 ° C., preferably 100 to 140 ° C. for 1 second to 18000 seconds, preferably 3 seconds to 3600 seconds, to improve the crystallinity. Also preferred to increase.

[0049] (relaxation treatment)

The hollow fiber membrane after the stretching treatment is preferably subjected to relaxation treatment. The relaxation is preferably performed in at least two stages in a non-wetting atmosphere with respect to the vinylidene fluoride resin (PCTZJP2006Z318026 specification). The non-wetting atmosphere is a non-wetting liquid, typically water or air, that has a surface tension (JIS K6768) that is greater than the wetting tension of vinylidene fluoride resin near room temperature. It is composed of almost all gases, especially non-condensable gases near room temperature, or vapors of the non-wetting liquid. In order to achieve a large relaxation effect at a relatively low temperature for a short time, treatment with a non-wetting liquid with a large heat capacity and heat transfer coefficient (wet heat treatment) is preferably used, but if the relaxation treatment temperature is raised, A treatment in a heated gas (or steam) (dry heat treatment) is also preferably used. 25 ~ 100 ° C, especially 50 ~ 100 ° C underwater heat treatment and Z or 80 ~ 160 ° C in terms of giving good permeability and good working environment through a large relaxation rate Dry heat treatment with air (or water vapor) is preferably used. In particular, a two-stage relaxation treatment in which the first-stage relaxation is a wet heat treatment in water and the second-stage relaxation is a wet heat treatment in water or a dry heat treatment in air (or water vapor) is preferably used.

[0050] The relaxation treatment in each stage is performed by stretching the previously obtained non-wetting, preferably heated atmosphere, disposed between the upstream roller and the downstream roller, the peripheral speed of which is gradually reduced. It is obtained by passing through a hollow fiber porous membrane. (1 (downstream roller circumferential speed Z upstream roller circumferential speed)) The relaxation rate determined by X 100 (%) is preferably 2 to 20% at each stage, and the total relaxation rate is preferably about 4 to 30%. If the relaxation rate at each stage is less than 2%, it is difficult to obtain the desired effect of improving water permeability, which means that the meaning of multistage relaxation is insufficient. The same applies when the total relaxation rate is less than 4%. On the other hand, each stage relaxation rate exceeding 20%, or total relaxation rate exceeding 30%, is difficult to achieve the force depending on the draw ratio in the previous process, or even if realized, the water permeability can be improved. It is preferable because the fruit is saturated or is reduced.

[0051] The relaxation processing time in each stage may be short or long as long as a desired relaxation rate is obtained. In general, the force is about 5 seconds to 1 minute.

[0052] The effect of the above-described multistage relaxation treatment is a remarkable effect in that the water permeability of the obtained hollow fiber porous membrane is increased, but the pore size distribution does not change so much and the porosity tends to slightly decrease. . The thickness of the hollow fiber membrane slightly increases, and the inner diameter and outer diameter tend to increase.

[0053] After the above-described multistage relaxation treatment, heat treatment with a relaxation rate of 0%, that is, heat setting treatment may be performed.

[0054] (Selective hydrophilization of outer surface)

The outer surface of the polyvinylidene fluoride resin porous membrane obtained as described above (in the above, the manufacturing method is detailed for hollow fiber membranes, but flat membranes are of course! /) Is selectively hydrophilized (that is, preferential hydrophilization of the outer surface and the inner pore surface of the porous membrane with respect to the outer surface).

[0055] Selective hydrophilization of the outer surface can be basically achieved by any method as long as a desired effect is obtained. For example, the outer surface is oxidized on the outer surface, or is exposed to an outer surface such as ultraviolet rays or electron beams. Irradiation and the like are conceivable, but in order to impart a higher degree of hydrophilicity to the outer surface, a method of selectively acting a hydrophilization treatment liquid on the outer surface of the porous membrane is preferred according to the method of the present invention.

[0056] Examples of the hydrophilization treatment liquid include an organic solvent solution of a water-insoluble hydrophilic resin such as polyvinyl alcohol having a low saponification degree, or an organic solvent-based graft reaction liquid containing a hydrophilic monomer such as hydroxypropyl acrylate. Although it is conceivable, preferably, an aqueous hydrophilization treatment solution such as an alkaline aqueous solution alone as employed in Patent Documents 1 and 2 alone, more preferably an aqueous hydrophilization treatment solution such as an alkaline aqueous solution and an oxidant are sequentially treated. Is adopted. However, in order to perform hydrophilicity by bringing an aqueous hydrophilic treatment liquid such as an alkaline aqueous solution into contact with the hydrophobic hydrophobic vinylidene fluoride resin porous membrane, the aqueous polyvinylidene fluoride resin porous membrane is aqueous. Hydrophilic treatment It is necessary to give wettability to the liquid. In Patent Documents 1 and 2, for this purpose, prior to the alkaline aqueous solution treatment, immersion treatment in a water-miscible liquid such as ethanol that makes the polyvinylidene fluoride-based porous membrane wettable with the alkaline aqueous solution is performed. But this The inner surface of the vinylidene fluoride-based rosin porous membrane (that is, the inner pore surface) becomes wettable to the hydrophilization treatment liquid, and selective hydrophilization of the outer surface which is the object of the present invention cannot be achieved.

[0057] Therefore, in the method of the present invention, the wettability is improved on the outer surface of the porous membrane by the hydrophilic treatment liquid prior to the contact with the hydrophilic treatment liquid of the vinylidene fluoride-based rosin porous membrane. Process. Specific methods include selective oxidation of the outer surface of the above-mentioned polyvinylidene fluoride resin porous membrane; irradiation with ultraviolet rays; irradiation with ionizing radiation such as an electron beam; ethanol, N-methylbidonidone (NMP) It is also possible to selectively apply a water-miscible liquid that wets the vinylidene fluoride-based resin, such as, to the outer surface of the porous membrane. However, application of a wettability improving liquid having a surface tension of 25 to 45 mNZm (including the case of immersion) is preferable in order to give selective coating properties to the outer surface of the biridene fluoride resin porous membrane. If the surface tension is less than 25 mNZm, it may be difficult to selectively apply the wettability improving liquid to the outer surface because the penetration rate into the P VDF porous membrane is too high. If the surface tension exceeds 45 mNZm, It may be difficult to evenly apply the wettability improving liquid to the outer surface due to galling (insufficient wettability or permeability to the PVDF porous membrane).

[0058] In particular, the use of a surfactant solution obtained by adding a surfactant to water (that is, an aqueous solution of a surfactant or an aqueous homogeneous dispersion) is preferred as a wettability improving solution. There are no particular limitations on the type of surfactant, and for ionic surfactants, carboxylic acid types such as aliphatic monocarboxylates, sulfonic acid types such as alkylbenzene sulfonates, sulfuric acids such as alkyl sulfates, etc. Ester type, phosphate ester type such as alkyl phosphate salt; For cationic surfactants, amine salt type such as alkylamine salt, quaternary ammonium salt type such as alkyltrimethyl ammonium salt; For ionic surfactants, ester type such as glycerin fatty acid ester, ether type such as polyoxyethylene alkyl ether, ester ether type such as polyethylene glycol fatty acid ester; for amphoteric surfactant, N, N dimethyl-N —Carboxybetaine type such as alkylaminoacetic acid betaine, 2-alkyl 1 hydroxyethyl carbo Examples include glycine type such as xymethylimidazolium-umbetaine.

[0059] The surfactant preferably has an HLB (hydrophilic / lipophilic balance) of 8 or more. If the HLB is less than 8, the surfactant does not disperse in water, resulting in uniform wettability improvement and And hydrophilic treatment becomes difficult. Particularly preferably used surfactants include nonionic surfactants having an HLB of 8 to 20, and further 10 to 18 or ionic (cion, cationic and amphoteric) surfactants. However, nonionic surfactants are preferred.

[0060] In many cases, it is preferable to apply the wettability improving liquid (and the hydrophilization treatment liquid described later) to the outer surface of the porous film by batch or continuous immersion of the porous film. This immersion treatment is a double-sided coating treatment for flat membranes and a single-sided coating treatment for hollow fiber membranes. The flat membrane batch dipping treatment is performed by dipping the layers cut into appropriate sizes, and the hollow fiber membrane batch dipping treatment is performed by dipping the hollow fiber membrane bundled by bobbin winding or caulking. . In the case of a flat membrane and a hollow fiber membrane, the continuous treatment is performed by continuously immersing a long porous membrane in the treatment liquid. When selectively applying only to one side of the flat membrane, spraying of the treatment liquid is also preferably used.

[0061] There is no particular restriction on the viscosity of the wettability improving liquid! /, But depending on the application method of the wettability improving liquid, the permeation rate is moderately slowed by making the wettability improving liquid high viscosity, Alternatively, the penetration rate can be increased by lowering the viscosity.

[0062] There is no particular limitation on the temperature of the wettability improving liquid! /, But depending on the method of applying the wettability improving liquid, the permeation rate is moderately slowed by lowering the wettability improving liquid, Alternatively, the permeation rate can be increased by increasing the temperature. In this way, the viscosity and temperature of the wettability improving liquid act in opposite directions, and can be controlled complementarily to adjust the penetration rate of the wettability improving liquid.

[0063] Next, a contact (coating or dipping) treatment with a hydrophilization treatment liquid is performed on the porous film whose wettability with the hydrophilization treatment liquid is selectively improved on the outer surface.

[0064] As described above, the hydrophilic treatment solution is preferably an alkaline aqueous solution (preferably pH 9 to 13, particularly ρΗ 11 to 13), or more preferably an alkaline aqueous solution and an acidic agent. The combination by processing is performed. Examples of the alkali include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide; alkaline earth metal hydroxides such as magnesium hydroxide and calcium hydroxide; or alkali metal or alkaline earth Metal alkoxides; organic amines such as trimethylamine and triethylamine. Oxidizing agents include potassium permanganate (KMnO), sodium hypochlorite (NaC10),

Four

Examples include aqueous solutions of performic acid (HCOOOH) and concentrated sulfuric acid (H 2 SO 4). For example,

twenty four

It is preferable to treat with an aqueous solution in the range of 0.1 to 5% by weight for potassium permanganate, effective chlorine concentration of 12 to 12% by weight for sodium hypochlorite, and 20 to 97% by weight for concentrated sulfuric acid. In the case of formic acid, for example, 97% by weight of formic acid and 30% by weight of peroxyhydrogen water are mixed in a ratio of 20-80% formic acid and 80-20% by weight of peroxyhydrogen water. Then, a performic acid aqueous solution produced by the reaction can be used.

[0065] These hydrophilization treatment liquids can change the hydrophilization effect, particularly the hydrophilization layer wetting index described later, by appropriately changing the temperature in the range of 5 to 80 ° C. Further, by raising the temperature, the treatment time (contact time) for obtaining the desired hydrophilization treatment effect can be shortened. That is, both the concentration and temperature of the hydrophilization treatment liquid have the effect of increasing the hydrophilization rate by increasing, and can be complementarily controlled.

[0066] The state in which the outer surface of the porous membrane of the present invention is selectively hydrophilized is quantitatively expressed by two parameters of the hydrophilized layer thickness and the wetting index. First, the measurement method for these parameters is explained.

[0067] (Hydrophilic layer thickness)

Water 90 wt%: Ethanol 10 wt% mixed water Z Ethanol mixture solution 0.1 parts by weight of red dye ("Cation Red" manufactured by Kiwa Chemical Industry Co., Ltd.) dissolved in 100 parts by weight A dye solution was prepared. In this dye solution, a hollow fiber porous membrane cut to a length of 10 mm (or a flat porous membrane cut to a length of lOmm x width of 5 mm) is immersed for 1 minute, and then the porous membrane is taken out and immediately attached to the outer surface. The sample was cut off with a filter paper, and then the sample was cut in a direction perpendicular to the length at a position approximately in the middle of the length. The exposed sample cross-section was observed, and the outer surface force was also measured through a microscope for the distance that the dye solution entered. The penetration distance was measured at 4 locations equally divided in the circumferential direction (or 4 locations equally divided in the width direction), and the average value was taken as the hydrophilic layer thickness.

[0068] (Hydrophilic layer wetting index)

Water 100% by weight: Ethanol 0% by weight Water 90% by weight: Ethanol Reduce the water mixing ratio to 10% by weight in increments of 2.5% by weight. A dye solution was prepared by dissolving 0.1 part by weight of a red dye ("Kiyu Thion Red" manufactured by Kiwa Chemical Industry Co., Ltd.) with respect to 100 parts by weight of the mixture. The porous film was immersed in the same manner as in the method for measuring the thickness of the hydrophilic layer using the dye solution strength in which the water mixing ratio was 100% by weight, and the penetration distance of the dye solution was measured. The mixing ratio of water when the infiltration distance is 50% or more of the hydrophilized layer thickness for the first time (that is, the maximum concentration of water that can wet the outer surface force of the hydrophilized layer more than half the thickness (wt% )) Was measured as the hydrophilicity layer wetting index. If the water mixing ratio is 80% by weight or less, it will not be suitable as a test solution for measuring the degree of hydrophilicity because it will be hydrophilized and penetrate into the PVDF porous membrane.

[0069] According to the measurement of the thickness of the hydrophilic layer, the polyvinylidene fluoride-based porous membrane of the present invention has a hydrophilic layer thickness of 2 from the outer surface, which is the average outer surface pore diameter by SEM observation. It is characterized by being not less than twice, preferably not less than 5 times, more preferably not less than 10 times, and a film thickness of 1Z2 or less, preferably 1Z3 or less, more preferably 1Z4. If the hydrophilized layer thickness is less than twice the outer surface pore diameter, low contamination is not sufficiently exhibited. On the other hand, if the thickness exceeds 1Z2, the mechanical strength of the membrane decreases. The absolute thickness of the hydrophilic layer is preferably 0.5 to 200; ζ ΐη, more preferably 1 to: LOO / z m or 2 to 60 / ζ πι. In order to stabilize the surface hydrophilizing effect and to reduce the mechanical strength reduction accompanying the surface hydrophilization as much as possible, it is particularly preferable that the thickness of the hydrophilizing layer is in the range of 5 to 15 m. In order to stably provide such an optimum hydrophilized layer thickness, it is necessary to apply the wettability improving liquid to the porous membrane surface layer prior to the contact with the hydrophilic treatment liquid. It is preferable to reduce the immersion time dependency of the immersion depth. For this purpose, it is particularly preferable to use a wettability improving liquid having a surface tension of 34 to 45 mNZm. The optimum surface tension range of this wettability improving liquid is the value when the average pore diameter (SEM method) on the outer surface of the porous membrane to which the wettability improving liquid is to be applied is around 0.20 μm. In response to the decrease, each should be increased or decreased slightly.

[0070] Further, according to the measurement of the hydrophilic layer wetting index described above, the hydrophilic layer wetting index of the porous membrane of the present invention is preferably 90% by weight or more, more preferably 95% by weight or more, and most preferably 100% by weight. %. If the wetting index of the hydrophilic layer is less than 90% by weight, low contamination may not be sufficiently exhibited. [0071] As described above, the hydrophilized vinylidene fluoride-based rosin porous membrane after contact with a hydrophilic treatment solution, preferably an alkaline aqueous solution, more preferably an alkaline aqueous solution and an oxidizing agent solution, is further washed with water. By drying, the low-contamination porous water treatment membrane of the present invention is obtained.

[0072] (Vinylidene fluoride-based porous resin membrane)

The typical physical properties other than the outer surface selective hydrophilicity of the low-contamination vinylidene fluoride-based rosin porous water treatment membrane of the present invention are listed. The film thickness is 0.05 to L: 5 mm, preferably 0.1 to: Lmm, more preferably 0.15 to 0.5 mm (in the case of a hollow fiber membrane, the outer diameter is 0.3 to 4 mm, preferably 0.6 to 3.5 mm, more preferably l to 3 mm) The porosity (v) is 50 to 90%, preferably 60 to 85%, more preferably 65 to 80%, the tensile strength is 7 MPa or more, preferably 8 MPa or more, the elongation at break is 20% or more, Preferably 30% or more, the average pore diameter is 0.01 to 1 μm, preferably 0.5 to 0.5 / ζ πι, more preferably 0.1 to 0.2 / ζ πι, the maximum diameter 02 ~ 3 / zm, preferably 0.1 ~ 1 111, more preferably 0.15 ~ 0.5 m, pure water flux (water permeability) (test length L = 800mm, drainage pressure difference) = 100kPa) Force S30mZday or more, preferably 35mZ day or more, more preferably 40mZday or more, inclined hole . Raw water supply side outer surface pore size Z opposing outer surface side hole diameter ratio in the distribution layer is preferably 1Z20~1Z1 5, more preferably 1Z. 10 to: LZ2, and the like.

[0073] [Example]

Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. Among the characteristics described in this specification, including the following description, those other than the above-described hydrophilic layer thickness and wetting index are mainly based on the measured values by the following method.

[0074] (Weight average molecular weight (Mw))

A GPC device “GPC-900” manufactured by JASCO Corporation was used, “Shode x KD—806M” manufactured by Showa Denko Co., Ltd. as a column, “Shodex KD—G” used as a precolumn, NMP as a solvent, and a temperature of 40. The molecular weight was measured as a polystyrene-equivalent molecular weight by gel permeation chromatography (GPC) method at C, flow rate of lOmLZ.

[0075] (Crystal melting point Tml, Tm2 and crystallization temperature Tc)

Using a differential scanning calorimeter DSC7 manufactured by Perkin Elma Co., Ltd. Set in a constant cell, raise the temperature from 30 ° C to 250 ° C at a rate of 30 ° C to 10 ° CZ in a nitrogen gas atmosphere, then hold at 250 ° C for 1 minute, then 250 ° C The DSC curve was obtained by lowering the temperature to 30 ° C at a rate of 10 ° CZ. In the DSC curve, the endothermic peak velocity in the temperature rising process was defined as the melting point Tml (° C), and the exothermic peak temperature in the temperature decreasing process was defined as the crystallization temperature Tc (° C). Subsequently, after maintaining at a temperature of 30 ° C for 1 minute, the temperature was raised again from 30 ° C to 250 ° C at a rate of 10 ° CZ, and the DSC curve was measured. The endothermic peak temperature in the reheated DSC curve was defined as the original resin melting point Tm2 (° C) that defines the crystal characteristics of the vinylidene fluoride resin of the present invention.

[0076] (Porosity)

The apparent volume V (cm ³ ) of the porous membrane was calculated, the weight W (g) of the porous membrane was measured, and the porosity was calculated from the following formula:

[Number 1]

Porosity (%) = (1— WZ (VX p)) X 100

p: Specific gravity of PVDF (= 1. 78g / cm ³ ) ₀

[0077] (Maximum pore size (Pmax), Average pore size (Pm) and Minimum pore size (Pmin))

It was determined by the bubble point Z half-dry method (measurement method of maximum pore size Pmax and pore size distribution suitable for porous membranes, especially hollow fiber porous membranes as defined in ASTM-F316-86 and ASTM · E 1294-86). More specifically, in the bubble point method, pressurized air with gradually increasing pressure is fed into a hollow fiber porous membrane sample immersed in the test solution, and the first bubble generation point (bubble point) from the test solution is measured. Air pressure force Obtain the maximum pore size Pmax (m) of the sample membrane. In the half-dry method, the wetting flow rate curve (WET FLOW CURVE) when the hollow fiber porous membrane sample is wet with the test solution and the dry flow rate curve (DRY FL OW CURVE) with a 1Z2 slope curve (HALF DRY) Calculate the average pore size Pm m) of the sample membrane from the air pressure at the point where it intersects with (CURVE). In addition, the hole diameter obtained from the air pressure at the coincidence point between the wet flow curve and the dry flow curve was determined as the minimum hole diameter Pmin (m). The values stated in this document are “Palm Porometer CFP-2000AEXJ” manufactured by Porous Materials, Inc. as the measuring instrument, and perfluoropolyester (trade name “Galwick”) as the test solution. Based on the measurement results of the hollow fiber membrane samples. [0078] (Measurement of outer surface average pore diameter by SEM observation)

Using a scanning electron microscope (SEM), the outer and inner outer surfaces of the hollow fiber porous membrane were photographed at an observation magnification of 5000 times. The obtained SEM photograph (observation range is about 19 m square) was binarized using the image processing device “nexus New Qube Version4.01” manufactured by Nexus, and the polymer phase and voids were In the observation range, the equivalent circle diameter D (the diameter of the circle when the area is assumed to be given as a circle) of all the voids equal to or larger than the minimum pore diameter Pmin obtained by the half-dry method within the observation range and its The number n was measured, and the number average value (= ∑nDZ∑n) was defined as the average pore diameter of each outer surface. Excluding voids with D less than the minimum pore size Pmin by the half-dry method, these are not effective voids for filtration that form communication holes (for example, irregularities in the resin phase). is there.

[0079] (Tensile strength and elongation at break)

Using a tensile tester (“RTM-100” manufactured by Toyo Baldwin) under the conditions of an initial sample length of 100 mm and a crosshead speed of 200 mmZ in an atmosphere at a temperature of 23 ° C and a relative humidity of 50%. .

[0080] (Pure water flux (water permeability))

Sample length L (see Fig. 1) = 800 mm sample hollow fiber porous membrane was immersed in ethanol for 15 minutes, then immersed in pure water for 15 minutes, wetted, and measured at a water temperature of 25 ° C and a differential pressure of lOOkPa for 1 day Per unit water permeability (m ³ Zday) was obtained by dividing by the membrane area (m ² ) of the hollow fiber porous membrane (= calculated as outer diameter X π X test length L). The unit is mZday (= mm ² · day).

[0081] (Flux (water permeability) maintenance rate)

Add the polysalt salt aluminum as a flocculant to the Koisegawa river water collected in Ishioka-ken, Ibaraki Prefecture at a concentration of lOOppm, stir, then let stand for 6 hours, and then conduct a filtration test using the supernatant as the feed water The durability against the decrease in water permeability due to clogging was evaluated. The turbidity of the feed water is 1.2 N. TU (nephelometric turbidity unit; equivalent to the turbidity of water containing kaolin concentration of 0.72 (= 1. 2 X O. 6) mgZL) and chromaticity is 5.7 degrees (Corresponding to the chromaticity of 1L water containing 5.7mL of chromaticity standard solution (containing 1mg of platinum and 0.5mg of cobalt in 1mL)) [0082] First, the sample hollow fiber porous membrane was immersed in ethanol for 15 minutes, then immersed in pure water for 15 minutes and wetted, and then the sample hollow fiber was made to have a test length L force of OOmm using the apparatus shown in FIG. A hollow hollow fiber was attached, and both ends were taken out of the pressure vessel as drawers. The length of the drawer (the part where filtration is not performed, including the joint with the pressure vessel) was set to 50 mm at each end. Fill the pressure-resistant container with pure water (water temperature 25 ° C) so that the porous hollow fiber is sufficiently immersed in the pure water until the end of the measurement, and then filter while maintaining the pressure in the pressure-resistant container at 50 kPa. went. The weight (g) of filtered water that flowed out at both ends during the first minute after the start of filtration was taken as the initial water permeability.

[0083] Next, after filling the pressure vessel with supply water (water temperature 25 ° C) instead of pure water so that the porous hollow fiber is sufficiently immersed in the supply water until the end of the measurement, the pressure vessel Filtration was performed until the filtration amount per unit membrane area became 0.3 m ³ / m ² while maintaining the pressure at 50 kPa. When the filtration rate per unit membrane area reaches 0.3 m ³ Zm ² , the weight of water flowing out from both ends (drawers) per minute is set to 0.3 m ³ Zm ² , and The flatness (permeability) retention rate was calculated using the formula:

[Equation 2]

Flux maintenance rate (%)

= (0. 3m ³ Zm ² water permeability (g)) / (initial water permeability (g)) X 100.

[0084] (Drug wash durability)

After immersing the sample hollow fiber porous membrane in ethanol for 15 minutes, then in pure water for 15 minutes and then moistening, it contains sodium hypochlorite (NaCIO) at an effective chlorine concentration of 5000 ppm. It was immersed in an aqueous solution containing (NaOH) at a concentration of 1% by weight for 96 hours, and then washed with running water for 12 hours. The flux retention rate of this hollow fiber porous membrane was measured in the same manner as the measurement of the above-mentioned flatness retention rate, and it was evaluated whether the hydrophilization effect was maintained after immersion with the above mixed solution.

[0085] <Chenic acid resistant aqueous solution>

The sample hollow fiber porous membrane was immersed in ethanol for 15 minutes, then immersed in pure water for 15 minutes and wetted, then immersed in an aqueous solution containing 3% by weight of citrate for 96 hours, and then with running water. Washed with water for 12 hours. The flux maintenance factor of the hollow fiber porous membrane was measured in the same manner as the flux maintenance factor, and it was evaluated whether or not the hydrophilization effect was maintained even after immersion with the citrate aqueous solution.

[0086] (Method for measuring surfactant dispersed particle diameter)

Using a particle size distribution analyzer (“N4 plus” manufactured by Beckman Coulter), the temperature is 23 ° C, the scattering angle is 90 degrees, the measurement time is 100 seconds, Z times, the number of repetitions is 10, and the analysis mode is the monodisperse mode. The surfactant particle size distribution (range: 3ηπ! To 3000 nm) in the surfactant solution was measured under the conditions, and the average particle size was defined as the surfactant dispersed particle size.

[0087] (Surface tension measurement)

The surface tension of the wet treatment solution at a temperature of 25 ° C. was measured by a ring method in accordance with JIS-K3362 using a Duny surface tension tester.

[0088] (Production Example 1 of vinylidene fluoride-based rosin hollow fiber porous membrane)

Polyvinylidene fluoride (PVDF) (powder) with a weight average molecular weight (Mw) of 4. 12 X 10 ⁵ and polyvinylidene fluoride (PVDF) for crystal property modification with Mw of 9. 36 X 10 ⁵ (Powder) was mixed using a Henschel mixer in proportions of 95% by weight and 5% by weight, respectively, to obtain a PVDF mixture having Mw of 4.38 × 10 ⁵ .

[0089] Adipic acid polyester plasticizer ("PN-150" manufactured by Asahi Denka Kogyo Co., Ltd.) as the aliphatic polyester and N-methylpyrrolidone (NMP) as the solvent, 82.5 wt. ⁰ / oZl 7 The mixture was stirred and mixed at room temperature at a ratio of 5% by weight to obtain a liquid agent (plasticizer / solvent) mixture.

[0090] Using the same direction of rotation, a twin screw extruder (“BT-30” manufactured by Plastics Engineering Laboratory Co., Ltd., screw diameter 30 mm, LZD = 48) is positioned 80 mm from the most upstream part of the cylinder. The supplied powder supply force also supplies the PVDF mixture, and the cylinder uppermost flow force is the liquid supply (plasticizer + solvent) mixture heated to 160 ° C from the liquid supply provided at the position of 480mm. Z liquid mixture = 35. 7 / 64.3 (% by weight) is supplied and kneaded at a barrel temperature of 220 ° C. The kneaded product is discharged from a nozzle with a circular slit with an outer diameter of 7 mm and an inner diameter of 5 mm. 16. Extruded into a hollow fiber at 6 gZ. At this time, air with a vent hole provided at the center of the nozzle was injected into the hollow portion of the yarn at a flow rate of 12.4 mLZ.

[0091] The extruded mixture is maintained in a molten state at a temperature of 40 ° C and from the nozzle 28 It was led into a water cooling bath with a water surface at a distance of Omm (ie, air gap of 280 mm), cooled and solidified (residence time in the cooling bath: about 2.7 seconds), and taken up at a take-up speed of l lmZ Thereafter, this was scraped off into a force force having a circumference of about lm to obtain a first intermediate molded body.

[0092] Next, the first intermediate molded body was immersed in dichloromethane at room temperature for 30 minutes while being vibrated, and then the dichloromethane was replaced with a new one and immersed again under the same conditions to remove the plasticizer and the solvent. Extraction was then performed in an oven at a temperature of 120 ° C. for 1 hour to remove dichloromethane and heat treatment was performed to obtain a second intermediate molded body.

[0093] Next, the second intermediate compact is passed through a 60 ° C water bath with a first roll speed of 20. OmZ and a second roll speed of 37. OmZ. Thus, the film was stretched 1.85 times in the longitudinal direction. Next, the sample was passed through a warm water bath controlled at a temperature of 90 ° C., and the third roll speed was lowered to 34. OmZ, thereby performing 8% relaxation treatment in warm water. Furthermore, 4% relaxation treatment was performed in the dry heat bath by passing it through a dry heat bath (2. Om length) controlled at a space temperature of 140 ° C and dropping the fourth roll speed to 32.7 mZ. It was. This was wound up to obtain a PVDF hollow fiber porous membrane (third molded body). When the obtained PVDF hollow fiber porous membrane was observed with a scanning electron microscope (SEM), it was found that the pore size distribution from the inside to the inside / outside surface and its vicinity was larger than that of the outside and outside surface. Was confirmed.

[0094] (Production Example 2 of Vinylidene Fluoride-Based Resin Hollow Fiber Porous Membrane)

Using the same raw materials (resin, plasticizer and solvent) as in Production Example 1 above, changing the conditions such as lowering the take-off speed of the melt extrudate as described below, the outer diameter compared to Production Example 1 In addition, a thick vinylidene fluoride resin hollow fiber porous membrane was produced.

That is, the same PVDF mixture and liquid agent (plasticizer + solvent) mixture as in Production Example 1 were supplied using the same co-rotating twining twin screw extruder as in Production Example 1, and the same as in Production Example 1. Furthermore, the take-off speed of the melt extrudate with nozzle force was reduced to 4.8 mZ and extruded into a hollow fiber shape. At this time, air with a vent hole provided at the center of the nozzle was injected into the middle of the yarn at a flow rate of 8. OmLZ.

[0096] The extruded mixture is maintained in a molten state, maintained at a temperature of 40 ° C, and has a water surface at a position 28 Omm away from the nozzle (that is, an air gap of 280 mm). (Elapsed time to enter the cooling bath: 3.5 seconds, staying in the cooling bath After taking up at a take-up speed of 4.8 mZ, it was scraped into a force force with a circumference of about lm to obtain a first intermediate molded body.

[0097] Next, the first intermediate molded body was immersed in dichloromethane at room temperature for 30 minutes while being vibrated, and then the dichloromethane was replaced with a new one and immersed again under the same conditions to remove the plasticizer and the solvent. Extraction was then performed in an oven at a temperature of 120 ° C. for 1 hour to remove dichloromethane and heat treatment was performed to obtain a second intermediate molded body.

[0098] Next, the second intermediate formed body was passed through a 60 ° C water bath with a first roll speed of 20. OmZ, and the second roll speed was 37. OmZ. Stretched 1.85 times in the longitudinal direction. Next, the sample was passed through a warm water bath controlled at a temperature of 90 ° C., and the third roll speed was reduced to 3 4. OmZ, thereby performing 8% relaxation treatment in warm water. Furthermore, 4% relaxation treatment was performed in the dry heat tank by passing it through a dry heat tank (2. Om length) controlled to a space temperature of 140 ° C and dropping the fourth roll speed to 32.7 mZ. . This was wound up to obtain a polyvinylidene fluoride hollow fiber porous membrane (third molded body). When the obtained PVDF hollow fiber porous membrane was observed with a scanning electron microscope (SEM), it was found that there was an inclined pore size distribution with a large pore size on the inner outer surface and in the vicinity compared to the outer outer surface and in the vicinity. Certainly f * i¾.

[0099] The PVDF hollow fiber porous membranes obtained in Production Examples 1 and 2 are subjected to an outer surface selective hydrophilization treatment according to the present invention as follows, whereby the low-contamination porous membrane of the present invention is used. A water treatment membrane was obtained, and a porous water treatment membrane for comparison was obtained, and physical properties, drainage performance, flux maintenance rate, etc. were evaluated. The outline of the hydrophilization treatment and physical property measurement 'evaluation results are summarized in Table 2 (Examples) and Table 3 (Comparative Examples) below.

[0100] (Example 1)

The hollow fiber membrane obtained in Production Example 1 was cut to a length of 2 m and wound into a casserole with a circumference of about 220 mm, and glycerin fatty acid ester as a surfactant ("SY Glyster ML-310" manufactured by Sakamoto Pharmaceutical Co., Ltd.) After immersing HLB = 10.3) in 200 ml of emulsion aqueous solution (surface tension 30.9 mNZm) dissolved in pure water at a concentration of 0.5% by weight at a temperature of 25 ° C for 30 minutes, immediately add sodium hydroxide concentration 5 It was immersed in 200 ml of an alkaline aqueous solution dissolved in pure water at a weight percent for 12 hours at a temperature of 70 ° C., and then the taken-out hollow fiber membrane was washed with running water for 1 hour. Next, formic acid (9 7%) and hydrogen peroxide solution (30%) were mixed in 200 ml of a mixed solution (= formic acid (HCOOOH) aqueous solution) mixed at a normal temperature in a weight ratio of 70:30 and immersed for 4 hours. The temperature of the mixture at this time rose to 60 ° C due to the reaction exotherm. The removed hollow fiber membrane is washed with running water for 1 hour and then dried in a vacuum dryer maintained at a temperature of 40 ° C for 12 hours to obtain a PVDF hollow fiber membrane whose outer surface is selectively hydrophilized. It was.

[0101] (Example 2)

A PVDF hollow fiber membrane having a selectively hydrophilized outer surface was obtained in the same manner as in Example 1 except that a surfactant aqueous solution (surface tension 32.7 mNZm) having a concentration reduced to 0.1% by weight was used. .

[0102] (Example 3)

A PVDF hollow fiber membrane having a selectively hydrophilized outer surface was obtained in the same manner as in Example 1 except that the immersion time in the alkaline aqueous solution was shortened to 2 hours.

[0103] (Example 4)

A PVDF hollow fiber membrane having a selectively hydrophilized outer surface was obtained in the same manner as in Example 2 except that the immersion time in the alkaline aqueous solution was shortened to 2 hours.

[Example 5]

A PVDF hollow fiber membrane having a selectively hydrophilized outer surface was obtained in the same manner as in Example 1 except that the hollow fiber membrane obtained in Production Example 2 was used.

[0105] (Example 6)

A PVDF hollow fiber membrane having a selectively hydrophilized outer surface was obtained in the same manner as in Example 5 except that the immersion time in the alkaline aqueous solution was reduced to 30 minutes.

[Example 7]

A PVDF hollow fiber membrane having an outer surface selectively hydrophilized was obtained in the same manner as in Example 6 except that the concentration of the aqueous alkali solution was increased to 30% by weight.

[Example 8]

The hollow fiber membrane obtained in Production Example 1 was fed out at a line speed of 0.1 mZ, and surfactants (such as Lion's “Chaimmy V Quick”, sodium alkyl ether sulfate, etc.) 36% surfactant component) dissolved in pure water at a concentration of 0.5% by weight The solution is allowed to pass through a surfactant solution (bath time 25 minutes), then passed through a 5% aqueous sodium hydroxide solution maintained at a temperature of 85 ° C (bath time 25 minutes), It was passed through a washing bath (resting time 100 minutes) and scraped off with force. The wound wiped hollow fiber membrane is immersed in a mixed solution (= formic acid aqueous solution) in which formic acid (97%) and hydrogen peroxide solution (30%) are mixed at a weight ratio of 70:30 at room temperature. Soaked for 2 hours. The temperature of the mixture at this time rose to 60 ° C due to the reaction exotherm. The removed hollow fiber membrane was washed with running water for 1 hour and then dried for 12 hours in a vacuum dryer maintained at a temperature of 40 ° C. to obtain a PVDF hollow fiber membrane whose outer surface was selectively hydrophilized. . The surfactant solution had a surface tension of 28.9 mN Zm, the surfactant solution was a transparent aqueous solution, and the surfactant dispersed particle size was below the measurement limit (3 nm).

[Example 9]

A PVDF hollow fiber membrane having a selectively hydrophilized outer surface was obtained in the same manner as in Example 8 except that the bathing time of the surfactant solution was changed to 1 minute and the concentration of sodium hydroxide aqueous solution was changed to 20%. It was.

[Example 10]

The line speed was 0.86 mZ, the surfactant solution bathing time was 3 minutes, the sodium hydroxide aqueous solution concentration was 40%, the sodium hydroxide aqueous solution bathing time was 3 minutes, and the washing bath bathing time was 12 minutes. A PVDF hollow fiber membrane having an outer surface selectively hydrophilized was obtained in the same manner as in Example 8 except that the time was changed to minutes.

[0110] (Example 11)

The hollow fiber membrane obtained in Production Example 2 was fed out at a line speed of 0.86 mZ, and a surfactant (“SY Glyster MO-3S” manufactured by Sakamoto Yakuhin Kogyo Co., Ltd., HLB = 8.8) was added at 0.5 weight. The solution is allowed to pass through an aqueous solution of emeraldil dissolved in pure water at a concentration of 2% (resting time: 2.9 minutes), and then passed through a 40% strength by weight aqueous sodium hydroxide solution maintained at a temperature of 85 ° C (resting time 2). 9 minutes), then passed through a water bath (lag time 11.6 minutes) and wound onto a bobbin. The wound bobbin-wound hollow fiber membrane was immersed in an aqueous solution of 12% by weight sodium hypochlorite at room temperature and immersed for 24 hours. The removed hollow fiber membrane is washed with running water for 24 hours, and then dried for 12 hours in a vacuum dryer maintained at a temperature of 40 ° C to selectively select the outer surface. A hydrophilic PVDF hollow fiber membrane was obtained. The surfactant solution had a surface tension of 34.9 mNZm, and the surfactant solution was a cloudy emulsion-like aqueous solution.

[Example 12]

A PVDF hollow fiber membrane having an outer surface selectively hydrophilized was obtained in the same manner as in Example 11 except that “SY Glyster MO 7SJ” manufactured by Sakamoto Pharmaceutical Co., Ltd. was used as the surfactant. The HLB value of the agent was 12.9, the surface tension of the surfactant solution was 36.2 mN Zm, and the surfactant solution was a cloudy emeraldion-like aqueous solution.

[0112] The relationship between the immersion time of the hollow fiber membrane in the surfactant solution used in Examples 11 and 12 above and the thickness of the hydrophilic layer in the finally obtained hollow fiber membrane is as shown in Table 1 below. It can be seen that these surfactant liquids are excellent as wettability improving liquids for thinning and uniformly hydrophilizing the vicinity of the outer surface:

[table 1]

[0113] (Comparative Examples 1 and 2)

The PVDF hollow fiber membranes obtained in Production Examples 1 and 2 were evaluated as they were.

[0114] (Comparative Example 3)

In Example 1, the same treatment as in Example 1 was performed except that the surfactant emulsion was changed to an aqueous solution and immersed in ethanol (surface tension 22. OmNZm) for 15 minutes. As a result, a PVDF porous membrane in which all layers were hydrophilized was obtained.

[0115] (Comparative Example 4)

In Example 3, the surfactant was immersed in ethanol for 15 minutes instead of the emulsion aqueous solution, and the concentration of the sodium hydroxide aqueous solution was changed from 5% by weight to 1% by weight. The same treatment as in Example 3 was performed except that. As a result, a porous PVDF membrane was obtained in which all layers were hydrophilized.

The hydrophilization treatment conditions and the evaluation results of the obtained porous water treatment membranes according to the above examples and comparative examples are summarized in Tables 2 and 3 below.

[Table 2]

* 1: Water secondary sub--(NaCIO) concentration (overlapping W

Table 3]

Industrial applicability

As can be seen from the results of Table 2 (Example) and Table 3 (Comparative Example), according to the present invention, the outer surface of the polyvinylidene fluoride resin porous membrane is selectively hydrophilized. (I) Less membrane contamination during filtration (high flux retention), (mouth) low contamination is maintained after repeated chemical cleaning (high, chemical cleaning durability), and (C) A vinylidene fluoride resin porous water treatment membrane having good mechanical strength (maintaining the original mechanical strength of the vinylidene fluoride resin porous membrane) and an efficient production method thereof. Provided.

Claims

The scope of the claims

[I] A low-contamination porous water treatment membrane comprising a porous membrane made of vinyl fluoride-redene-based resin, the outer surface of which is selectively hydrophilized.

2. The water treatment membrane according to claim 1, wherein the porous membrane has a hollow fiber shape.

[3] The water treatment membrane according to claim 1 or 2, wherein, of the two main outer surfaces sandwiching the thickness, the outer surface to which raw water is supplied is selectively hydrophilized.

[4] The water treatment membrane according to any one of claims 1 to 3, wherein the water treatment membrane is hydrophilized from the outer surface to a depth not less than twice the average pore diameter of the outer surface and not more than 1Z2 of the film thickness.

[5] The water treatment membrane according to claim 4, which is hydrophilized from the outer surface to a depth of 5 to 15 m.

6. The water treatment membrane according to any one of claims 1 to 5, wherein the porous membrane has an inclined pore size distribution over its thickness direction.

7. The water treatment membrane according to claim 6, wherein, of the two main outer surfaces sandwiching the thickness, the average pore diameter of the outer surface on the raw water supply side is smaller than the average pore diameter of the opposing outer surface.

[8] The water treatment membrane according to any one of [1] to [7], wherein a pure water permeation rate is 30 mZday or more, a tensile strength is 7 MPa or more, and a breaking elongation is 20% or more.

[9] A low-contamination porous water treatment membrane that selectively hydrophilizes the outer surface of a porous membrane when the porous membrane made of a vinylidene fluoride resin is hydrophilized by contact with a hydrophilization treatment liquid Manufacturing method.

[10] The method of claim 9, wherein the hydrophilization treatment liquid is an aqueous liquid, and the wettability improvement treatment with the hydrophilization treatment liquid is selectively performed on the outer surface of the porous membrane prior to the hydrophilic treatment of the porous membrane. The manufacturing method as described.

11. The production method according to claim 10, wherein the wettability improving treatment is selective application of the wettability improving liquid to the outer surface of the porous film.

[12] The production method according to claim 11, wherein the wettability improving liquid has a surface tension (JIS K3362) of 25 to 45 mNZm.

13. The production method according to claim 11, wherein the wettability improving liquid has a surface tension of 34 to 45 mNZm.

[14] The production method according to any one of [11] to [13], wherein the wettability improving liquid is an aqueous surfactant solution.

15. The production method according to claim 14, wherein the surfactant is an ionic surfactant! /! Is a nonionic surfactant having an HLB (hydrophilic lipophilic balance) of 8 to 20.

16. The production method according to claim 14, wherein the surfactant is a nonionic surfactant having an HLB of 8 to 20.

[17] The production method according to any one of [9] to [16], wherein the hydrophilization solution is an alkaline aqueous solution.

18. The production method according to claim 17, wherein the outer surface of the porous membrane after the contact treatment with the alkaline aqueous solution is contacted with an oxidizing agent.