JP2007167839A - Hydrophilic hollow fiber membrane and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydrophilic hollow fiber membrane consisting of polyvinylidene fluoride having physical strength and high-level separation performance and a method suitable for manufacturing the hydrophilic hollow fiber membrane. <P>SOLUTION: The hydrophilic hollow fiber membrane is formed from polyvinylidene fluoride and characterized in that the ratio of C-F bonds to C-H bonds, which exist on the surface of the hydrophilic hollow fiber membrane and are measured by XPS (X-ray photoelectron spectroscopy), is 0.6-0.9, the ratio of the O element content to the F element content, which exist on the surface of the hydrophilic hollow fiber membrane and are measured by XPS, is 0.15-0.67 and the hydrophilic hollow fiber membrane has ≥40 mN/m penetrating/wetting tension. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technique related to a hydrophilic hollow fiber membrane. More specifically, the present invention relates to a hollow fiber membrane made of a hydrophilic vinylidene fluoride polymer and a method for producing the hollow fiber membrane.

  A “hollow fiber membrane” is often used when performing separation (filtration) removal of unnecessary substances in liquid, dialysis, degassing of dissolved gas in liquid, concentration of liquid, and the like. This hollow fiber membrane is a tube-like or straw-like filament membrane having a cavity inside, and is usually designed to have an outer diameter of about 1.5 mm or less, and is generally in the form of a membrane module in which many are bundled. Used.

  This hollow fiber membrane is required to have excellent performance in separation characteristics (filtration characteristics), chemical resistance, physical strength, permeability, and the like. For this reason, research and development on the material side has been conventionally performed. Hollow fiber membranes made of hydrophilic polymer materials (for example, cellulosic membranes) are less susceptible to membrane contamination by organic substances typified by humic substances due to their hydrophilicity, while they are resistant to acid and alkali chemicals. Is scarce.

For this reason, by introducing hydrophilic functional groups (for example, hydroxyl groups, carboxyl groups, etc.) to the surface of hydrophobic polymer materials with excellent chemical resistance to make them hydrophilic, chemical resistance and water permeability performance by suppressing membrane contamination can be achieved. Research and development is progressing to achieve maintenance. A typical example of this hydrophobic polymer material is poly vinylidene difluoride (abbreviation PVDF, structural formula-[CF ₂ CH ₂ ] n-).

  Here, Patent Document 1 discloses a technique for hydrophilizing a porous film made of a vinylidene fluoride polymer by treating with an alkaline aqueous solution. Patent Document 2 discloses a technique of hydrophilizing a vinylidene fluoride polymer by performing an alkali treatment after an alkali treatment.

  Further, Patent Document 3 discloses that a porous vinylidene fluoride polymer porous membrane is obtained by impregnating an aqueous solution solvent into pores of a porous membrane made of a vinylidene fluoride polymer and then treating with a strong alkaline aqueous solution containing an oxidizing agent. A technique for obtaining the above is disclosed. In the example shown in Patent Document 3, a 40 wt% aqueous potassium hydroxide solution containing 3.0 wt% potassium permanganate is used. In this technology, the double bond formed on the vinylidene fluoride polymer molecule by the action of strong alkali can be instantly oxidized by the action of an oxidizing agent to introduce polar groups, resulting in excessive double bonds that cause browning It is said that the occurrence of Patent Document 4 discloses a similar technique.

Further, in Patent Document 5, the ratio of the hydrogen atom-carbon atom bond of the fluorine atom-carbon atom bond on the film surface obtained by XPS (X-ray photoelectron spectroscopy) measurement is 0.5 or less, and the ozone treatment is performed. A microporous membrane made of a vinylidene fluoride polymer is disclosed, and it is described that the hydrophilicity is excellent when the XPS measurement value is 0.5 or less.
JP-A-58-93734. JP-A-5-317663. JP-A-63-172745. JP-A-1-75542. JP-A-6-343843.

  The hydrophilic hollow fiber membrane composed of the vinylidene fluoride polymer disclosed in the above-mentioned prior art document is discolored (browned or blackened) due to the formation of carbon-carbon double bonds in the hydrophilization process, although to a different extent. )) And a reduction in physical strength (strength, elongation) during the hydrophilization process.

  Therefore, the main object of the present invention is to solve the technical problems and to provide a hydrophilic hollow fiber membrane made of a vinylidene fluoride polymer having a high degree of separation performance and a suitable production method thereof.

  The present inventors have conducted research for many years on hydrophilization treatment of vinylidene fluoride polymers. As a result, the process and conditions of the hydrophilization treatment are devised to control the predetermined chemical bonding state involving carbon atoms on the film surface, thereby providing the desired osmotic wet tension, breaking elongation, and tensile strength. It has been found that a hydrophilic hollow fiber membrane having new physical properties can be provided.

  In particular, when a carbon-carbon double bond is formed by subjecting a vinylidene fluoride polymer to an alkali treatment, molecular chain breakage also occurs in the course of dehydrofluorination, resulting in a break elongation and tensile strength. Newly discovered that the physical strength (mechanical properties) that can be specified will decrease, and based on this, the oxidation treatment is performed while controlling the decrease in elongation at break and tensile strength in the alkali treatment process as much as possible. A new method has been found that can achieve the necessary and sufficient hydrophilization.

  In the present invention, first, a ratio of C—F bonds to C—H bonds on a film surface formed from a vinylidene fluoride polymer and measured by (1) XPS (X-ray photoelectron spectroscopy) is 0.6 to 0. .9, (2) The ratio of the O element content on the film surface measured by XPS (X-ray photoelectron spectroscopy) to the F element content is 0.15 to 0.67, (3) Osmotic wetting tension 40 mN / m or more, providing a hydrophilic hollow fiber membrane comprising all of these (1) to (3), and further having a breaking elongation of 40% or more and a tensile strength of 7.5 MPa or more. A hollow fiber membrane is provided. And in this invention, in order not to lose a hydrophilic effect by chemical | medical immersion, it is 3 days at 23 degreeC in the mixed aqueous solution of sodium hypochlorite and 1 weight% sodium hydroxide with an effective chlorine concentration of 5,000 ppm. Provided is a hydrophilic hollow fiber membrane in which the osmotic wetting tension after immersion is 40 mN / m or more. The use of the hydrophilic hollow fiber membrane having such physical properties is various, but one example is suitable as a water treatment application.

  Next, the present invention provides a suitable production method capable of obtaining the above-described hydrophilic hollow fiber membrane having physical properties. Specifically, a method for producing a hydrophilic hollow fiber membrane is first provided in which a hollow fiber membrane made of a vinylidene fluoride polymer is first subjected to a weak alkali treatment and then subjected to an oxidation treatment.

  In the weak alkali treatment, the breaking elongation and the decrease in tensile strength of the hollow fiber membrane are controlled by dehydrofluorinating the vinylidene fluoride polymer surface to gently form a carbon-carbon double bond. In the oxidation treatment, the carbon-carbon double bond appropriately formed by the weak alkali treatment is finally hydroxylated (hydroxyl group addition) to make the film surface hydrophilic. As described above, in the present invention, since the carbon-carbon double bond formation can be delicately controlled by the weak alkali treatment, the effect of suppressing the membrane contamination is also considered with respect to the degree of hydrophilization by the oxidation treatment. It becomes possible to control while.

  In this production method, the weak alkali treatment is particularly performed on a hollow fiber membrane made of a vinylidene fluoride polymer that has been previously stretched. By performing the weak alkali treatment step on the hollow fiber membrane made of the vinylidene fluoride polymer that has been subjected to the stretching treatment, and then the subsequent oxidation treatment, the strength required for the water treatment membrane can be realized.

  The hydrophilic hollow fiber membrane according to the present invention is excellent in penetrating wetting tension, breaking elongation, and tensile strength. Furthermore, the hydrophilic effect is not lost even by chemical immersion.

  Further, the method for producing a hydrophilic hollow fiber membrane according to the present invention prevents the occurrence of discoloration (browning or blackening) associated with the formation of a carbon-carbon double bond in the hydrophilization process, while in the hydrophilization process. It is possible to reliably produce a hydrophilic hollow fiber membrane made of a vinylidene fluoride polymer having a high separation performance while preventing a decrease in physical strength due to decomposition of the resin structure.

(Vinylidene fluoride polymer)
In the present invention, as the vinylidene fluoride polymer, a homopolymer of vinylidene fluoride, that is, a copolymer of polyvinylidene fluoride, another copolymerizable monomer, or a mixture thereof is used. As the monomer copolymerizable with the vinylidene fluoride polymer, one or more of tetrafluoroethylene, hexafluoropropylene, ethylene trifluoride, ethylene trifluoride chloride, vinyl fluoride and the like can be used. The vinylidene fluoride polymer preferably contains 70 mol% or more of vinylidene fluoride as a structural unit. Among these, it is preferable to use a homopolymer composed of 100 mol% of vinylidene fluoride because of its high mechanical strength.

(Hollow fiber membrane made of vinylidene fluoride polymer)
A hollow fiber membrane made of such a vinylidene fluoride polymer is produced by a known method. As a general feature of the produced hollow fiber membrane, the porosity is 55 to 90%, preferably 60 to 85. %, Particularly preferably 65 to 80%, and the film thickness is usually in the range of about 5 to 800 μm, preferably 50 to 600 μm, particularly preferably 150 to 500 μm. The outer diameter is about 0.3 to 3 mm, particularly about 1 to 3 mm. Even if the hollow fiber membrane made of such a vinylidene fluoride polymer is subjected to weak alkali treatment and oxidation treatment, the general characteristics are not changed.

(Wet treatment)
When the hollow fiber membrane made of the vinylidene fluoride polymer produced by the above method is subjected to weak alkali treatment with an alkaline aqueous solution, the hollow fiber membrane made of the vinylidene fluoride polymer is difficult to wet with the alkaline aqueous solution. It is preferable to carry out. For example, the hollow fiber membrane made of the vinylidene fluoride polymer is immersed in an alcohol such as methanol or ethanol that can be wetted, and then replaced with water, so that the entire surface of the hollow fiber membrane is wetted with water. be able to.

(Weak alkali treatment)
Examples of the alkali used in the present invention include alkali metal hydroxides such as sodium hydroxide and potassium hydroxide, alkaline earth metal hydroxides such as magnesium hydroxide and calcium hydroxide, or alkali metals or alkaline earth metal alkoxides. And organic amines such as trimethylamine and triethylamine. When these alkalis are liquid, they can be used for treatment as they are. Even in the case of a solid or liquid, it can be dissolved in water, alcohol such as methanol or ethanol, and the solution can be used for the treatment. In the case where these alkaline solutions can wet the hollow fiber membrane made of vinylidene fluoride polymer, the above-described wetting treatment may be omitted.

  The weak alkali treatment conditions refer to conditions under which the penetration wet tension of the hollow fiber membrane after the weak alkali treatment is in the range of 37 to 40 mN / m. In the alkali treatment in which the osmotic wet tension is less than 37 mN / m, the amount of carbon-carbon double bonds formed is insufficient, and as a result, sufficient hydrophilicity cannot be imparted even if oxidation treatment is performed. On the other hand, the alkali treatment in which the penetrating wetting tension exceeds 40 mN / m is not suitable as a film for water treatment because the strength and elongation are remarkably lowered.

(Oxidation treatment)
As a preferred example of the oxidation treatment in this production method, it is selected from potassium permanganate (KMnO ₄ ), sodium hypochlorite (NaClO), formic acid (HCOOOH), and concentrated sulfuric acid (H ₂ SO ₄ ). A method using at least one oxidizing agent can be proposed. Potassium permanganate is 0.1 to 5% by weight, sodium hypochlorite is 1 to 12% effective chlorine concentration, formic acid is 5 to 40% by weight, and concentrated sulfuric acid is 20 to 97% by weight. It is preferable to process.

  In the weak alkali treatment and the oxidation treatment, it is possible to appropriately select both treatments in one step or in two steps or more based on the characteristics of the chemicals used in each treatment. The employed oxidation treatment (sulfuric acid addition and hydration reaction) is performed as a step separated from the weak alkali treatment step.

In addition, the oxidation treatment process of the present invention is not limited to the above-mentioned method. For example, a hydroxyl group is added to a carbon-carbon double bond (cis addition) by a Milas reaction using OsO ₄ (osmium tetroxide). Alternatively, a method of trans-adding a hydroxyl group from m-chloroperbenzoic acid (a kind of peracid) can also be employed.

  The hydrophilic hollow fiber membrane comprising the vinylidene fluoride polymer of the present invention obtained through the series of steps described above is (1) C—F bond C—H on the membrane surface measured by XPS (X-ray photoelectron spectroscopy). Ratio of bonds to 0.6 to 0.9, preferably 0.65 to 0.8, (2) F element content of O element content on film surface measured by XPS (X-ray photoelectron spectroscopy) Is 0.15-0.67, preferably 0.2-0.55, more preferably 0.2-0.3, (3) penetrating wetting tension of 40 mN / m or more, preferably 42-60 mN / m. It is. That is, all of these (1) to (3) are satisfied. As a result, it is possible to effectively suppress film contamination with respect to organic substances in water treatment. More specifically, it is possible to effectively increase the flux maintenance rate indicating the maintenance performance of water permeability in river water filtration.

  The hydrophilic hollow fiber membrane obtained by the present invention is characterized by having a breaking elongation of 40% or more, preferably 45 to 100%, and a strength of 7.5 MPa or more, preferably 8 to 15 MPa.

  Furthermore, the hydrophilic hollow fiber membrane obtained by the present invention is also characterized in that the hydrophilic effect is not lost by chemical immersion. More specifically, this property is that the osmotic wet tension after being immersed in a mixed aqueous solution of sodium hypochlorite having an effective chlorine concentration of 5,000 ppm and 1 wt% sodium hydroxide at 23 ° C. for 3 days is 40 mN / m or more. It is expressed by that. Thereby, the film | membrane contamination inhibitory effect with respect to organic substance can be maintained over a long term in uses, such as water treatment which performs chemical cleaning using the said chemical | drug | medicine. More specifically, the flux maintenance factor can be kept high over a long period of time.

  Examples of the present invention will be described below in comparison with comparative examples. The scope of the present invention is not construed narrowly by the following examples. The characteristics described in this specification, including the following description, are based on measured values by the following method.

(Weight average molecular weight of vinylidene fluoride polymer)
“Weight average molecular weight (Mw) of vinylidene fluoride polymer” was measured using ShodexKD-806M manufactured by Showa Denko Co., Ltd. on the column and ShodexKD- G ”, NMP was used as a solvent, and the molecular weight was measured in terms of polystyrene by gel permeation chromatography (GPC) at a temperature of 40 ° C. and a flow rate of 10 mL / min.

(Weight average molecular weight of polyvinyl alcohol resin (PVA))
The “weight average molecular weight (Mw) of polyvinyl alcohol resin (PVA)” is calculated using Shodex KF-606M for the column and Shodex KF-606M for the pre-column using a GPC device (Shodex GPC-104) manufactured by Showa Denko. ShodexKF-G ", hexafluoropropanol (HFIP) was used as a solvent, and the molecular weight was measured as a polymethyl methacrylate equivalent molecular weight by gel permeation chromatography (GPC) method at a temperature of 40 ° C and a flow rate of 0.6 mL / min.

(XPS)
“XPS (X-ray Photoelectron Spectroscopy)” performs non-destructive analysis of the state of the extreme surface by detecting and analyzing the photoelectron peaks unique to the elements generated by irradiation with soft X-rays. It is an analytical measurement method that can. This XPS is adopted for specifying the chemical structure on the membrane surface of the hydrophilic hollow fiber membrane according to the present invention. For the measurement, Quantera SXM (manufactured by Physical Electronics) was used. Measurement was performed under the conditions of a measurement area of 100 μm and a detection depth of about 4 to 5 nm (photoelectron extraction angle of 45 degrees) using monochromatic AlKα radiation (1486.6 eV) as a radiation source. By dividing the peak area value (B) in the bond energy (eV) between atoms to be compared with the peak area value (A) in the bond energy (eV) between specific atoms obtained by this measurement method, the ratio value ( B / A) is obtained. Further, the ratio value (D / C) is obtained by dividing the peak area (D) of the element to be compared by the peak area (C) of the specific element. More specifically, in the present invention, the ratio of the C—F bond (a) on the film surface to the C—H bond (b) (a / b), the O element content (c) on the film surface, and the F element content. A ratio (c / d) to the amount (d) was determined, and a suitable hydrophilic state on the membrane surface was specified by a numerical range of this ratio.

(Osmotic wet tension)
“Osmotic wetting tension” is adopted as a parameter that allows the hydrophilic state of the membrane surface to be known. In the present invention, water and ethanol are mixed at different ratios, and ethanol aqueous solutions having different surface tensions are prepared. A hollow cut into a length of 5 mm in the ethanol aqueous solution in an atmosphere at a temperature of 25 ° C. and a relative humidity of 50%. The surface tension of the aqueous ethanol solution in which the hollow fiber membrane was gently floated and the hollow fiber membrane sinked 100 mm or more below the water surface within 1 minute was defined as the penetration wet tension of the hollow fiber membrane. The relationship between ethanol concentration and surface tension was referred to the Chemical Industry Handbook (Maruzen Co., Ltd., revised 5th edition).

(Penetration wetting tension after immersion in aqueous solution of sodium hypochlorite and sodium hydroxide)
After immersing the hollow fiber membrane in a mixed aqueous solution of sodium hypochlorite having an effective chlorine concentration of 5,000 ppm and 1% by weight sodium hydroxide at 23 ° C. for 3 days, the permeation wetting tension was measured by the above method.

(Elongation at break and tensile strength)
“Elongation at break” is the elongation relative to the initial length when a tensile force is applied to the material, and “tensile strength” is the tensile force applied to the material. It is the maximum tensile stress until it breaks, and all are parameters for specifying the physical strength of the hollow fiber membrane according to the present invention. In the present invention, using a tensile tester (“RTM-100” manufactured by Toyo Baldwin Co., Ltd.) in an atmosphere at a temperature of 23 ° C. and a relative humidity of 50% under conditions of an initial sample length of 20 mm and a crosshead speed of 40 mm / min. The measured value is used.

(Porosity)
The apparent volume V (cm ³ ) of the hollow fiber membrane is calculated by measuring the length, outer diameter and inner diameter of the hollow fiber membrane, and the weight W (g) of the hollow fiber membrane is further measured. Thus, the porosity was obtained. In Equation 1, ρ is the density of polyvinylidene fluoride (1.78 g / cm ³ ).

(Pure water flux)
First, the sample hollow fiber membrane was immersed in ethanol for 15 minutes, then immersed in pure water for 15 minutes and wetted, and then using the apparatus shown in FIG. The hollow fiber membrane was attached so that both ends were taken out of the pressure vessel as lead portions. The length of the lead-out portion (the portion where filtration is not performed and the joint portion with the pressure vessel) was 50 mm at both ends. After filling the pressure vessel with pure water (water temperature 25 ° C.) so that the hollow fiber membrane was sufficiently immersed in the supplied water until the measurement was completed, filtration was performed while maintaining the pressure vessel at a pressure of 100 KPa. The obtained amount of water per day (m ³ / day) was divided by the membrane area (m ² ) (= outer diameter × π × test length L) of the hollow fiber membrane to obtain a pure water flux. The unit is m / day (m ³ / m ² / day).

(Flux maintenance rate).
Polyaluminum chloride as a flocculant was added to the Koisegawa river water collected in Ishioka City, Ibaraki Prefecture at a concentration of 10 ppm, stirred, then allowed to stand for 6 hours, and then a filtration test was conducted using the supernatant as the feed water. Contamination was evaluated. The turbidity of the feed water is 1.0N. T.A. U and chromaticity were 5.6 degrees. First, the sample hollow fiber membrane was immersed in ethanol for 15 minutes, then immersed in pure water for 15 minutes and wetted, and then the test length (the length of the portion to be filtered) was 400 mm using the apparatus shown in FIG. A hollow fiber membrane was attached so that both ends were taken out of the pressure vessel as a lead-out portion. The length of the lead-out portion (the portion where filtration is not performed and the joint portion with the pressure vessel) was 50 mm at both ends. After filling the pressure vessel with pure water (water temperature 25 ° C.) so that the hollow fiber membrane was sufficiently immersed in the supplied water until the end of measurement, filtration was performed while maintaining the pressure vessel at a pressure of 50 kPa. After the start of filtration, the weight of filtered water that flowed out from both ends during the first minute was taken as the initial water permeability. Next, instead of pure water, supply water (water temperature 25 ° C.) is filled in the pressure vessel so that the hollow fiber membrane is sufficiently immersed in the supply water until the end of the measurement, and then the pressure vessel is maintained at a pressure of 50 kPa. Filtration was performed until the filtration amount per unit membrane area became 0.3 m ³ / m ² . When the amount of filtration per unit membrane area became 0.3 m ³ / m ² , the weight of the filtered water that flowed out from both ends per minute was defined as the amount of water permeation at 0.3 m ³ / m ² . From the initial water permeability and the water permeability at 0.3 m ³ / m ² , the flux maintenance factor was calculated by Equation 2.

(Average pore diameter)
Based on ASTM F316-86 and ASTM E1294-89, average pore diameter was measured by a half dry method using “Palm Porometer CFP-200AEX” manufactured by Porous Materials, Inc. Perfluoropolyester (trade name “Galwick”) was used as a test solution.

(Maximum hole diameter)
Based on ASTM F316-86 and ASTM E1294-89, the maximum pore size was measured by the bubble point method using “Palm Porometer CFP-200AEX” manufactured by Porous Materials, Inc. Perfluoropolyester (trade name “Galwick”) was used as a test solution.

Example 1
(1) Film formation.
Polyvinylidene fluoride (PVDF) (powder) having a weight average molecular weight (Mw) of 4.12 × 10 ⁵ and polyvinylidene fluoride (PVDF) (powder) for crystal property modification having an Mw of 9.36 × 10 ⁵ Were mixed using a Henschel mixer in proportions of 95% by weight and 5% by weight, respectively, to obtain a mixture A having an Mw of 4.38 × 10 ⁵ .

  Next, adipic acid-based polyester plasticizer ("PN-150" manufactured by Asahi Denka Kogyo Co., Ltd.) as the aliphatic polyester and N-methylpyrrolidone (NMP) as the solvent, 72.5 wt% / 27.5 wt% The mixture B was obtained by stirring and mixing at room temperature.

  Using a co-rotating meshing twin screw extruder (“BT-30” manufactured by Plastics Engineering Laboratory Co., Ltd., screw diameter 30 mm, L / D = 48), powder provided at a position 80 mm from the most upstream part of the cylinder The mixture A is supplied from the supply unit, and the mixture B heated to a temperature of 160 ° C. from the liquid supply unit provided at a position 480 mm from the most upstream part of the cylinder is mixed A / mixture B = 35.7 / 64.3 ( The mixture was kneaded at a barrel temperature of 220 ° C., and the kneaded product was extruded into a hollow fiber form at a discharge rate of 16.6 g / min from a nozzle having a circular slit having an outer diameter of 6 mm and an inner diameter of 4 mm. At this time, air was injected into the hollow portion of the yarn at a flow rate of 9.5 ml / min from a vent provided in the center of the nozzle.

  The extruded mixture is maintained in a molten state at a temperature of 40 ° C. and has a liquid surface at a position 280 mm away from the nozzle (ie, an air gap of 280 mm), and is cooled and solidified (in the liquid) Was taken up at a take-up speed of 11 m / min, and was wound around a case having a circumference of about 1 m to obtain a first intermediate formed body.

  Next, the first intermediate molded body is immersed in dichloromethane at room temperature for 30 minutes while being vibrated, and then the dichloromethane is replaced with a new one and immersed again under the same conditions to extract the aliphatic polyester and the solvent. Subsequently, heating was 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.

  Next, the second intermediate formed body is passed through a 60 ° C. water bath at a first roll speed of 12.5 m / min, and the second roll speed is set to 23.1 m / min in the longitudinal direction. The film was stretched 1.85 times. Next, 8% relaxation treatment was performed in water by passing through water controlled at a temperature of 90 ° C. and dropping the third roll speed to 21.3 m / min. Furthermore, 4% relaxation treatment was performed in the dry heat bath tank by passing it through a dry heat bath tank (2.0 m long) controlled at a space temperature of 140 ° C. and dropping the fourth roll speed to 21.4 m / min. It was. This was wound up to obtain a polyvinylidene fluoride porous hollow fiber membrane (third molded body).

The obtained hollow fiber membrane has an outer diameter of 1.35 mm, an inner diameter of 0.85 mm, a film thickness of 0.25 mm, a porosity of 71%, and a pure water flux of 38 m ³ / m ² / day (100 kPa, L = 200 mm), 35 m ³ / m ² / day (100 kPa, L = 800 mm), average pore diameter of 0.11 μm by half dry method, maximum pore diameter of 0.19 μm by bubble point method, tensile strength of 11 MPa, elongation at break of 85%, The physical properties were 34mN / m.

(2) Alkali treatment.
The obtained hollow fiber membrane was immersed in ethanol for 15 minutes, then immersed in pure water for 15 minutes and wet-treated, then immersed in a 1% by weight aqueous sodium hydroxide solution at 70 ° C. for 1 hour, washed and dried.

(3) Oxidant treatment.
The obtained alkali-treated hollow fiber membrane was immersed in ethanol for 15 minutes, then immersed in pure water for 15 minutes and wet treated, then immersed in 97 wt% sulfuric acid at room temperature for 10 minutes, washed with water and dried.

The obtained hollow fiber membrane has an outer diameter of 1.35 mm, an inner diameter of 0.85 mm, a film thickness of 0.25 mm, a porosity of 71%, and a pure water flux of 47 m ³ / m ² / day (100 kPa, L = 800 mm), an average pore size of 0.13 μm by the half dry method, a maximum pore size of 0.22 μm by the bubble point method, a tensile strength of 10.0 MPa, a breaking elongation of 75%, and an osmotic wetting tension of 45 mN / m.

(Example 2)
A hollow fiber membrane was obtained in the same manner as in Example 1 except that the alkali treatment of Example 1 was performed by immersing in a 5 wt% aqueous sodium hydroxide solution at 70 ° C. for 30 minutes.

(Example 3)
A hollow fiber membrane was obtained in the same manner as in Example 1 except that the oxidizing agent treatment was performed by immersing in a 1 wt% aqueous potassium permanganate solution at room temperature for 10 minutes.

Example 4
A hollow fiber membrane was obtained in the same manner as in Example 1 except that the oxidant treatment was performed by immersing in an aqueous solution of sodium hypochlorite having an effective chlorine concentration of 10% at room temperature for 8 hours.

(Example 5)
A hollow fiber membrane was obtained in the same manner as in Example 2 except that the stretching treatment and the relaxation treatment were not performed.

(Comparative Example 1)
A hollow fiber membrane was obtained in the same manner as in Example 1 except that the alkali treatment and the oxidizing agent treatment were not performed.

(Comparative Example 2)
A hollow fiber membrane was obtained in the same manner as in Example 1 except that the oxidizing agent treatment was not performed.

(Comparative Example 3)
A hollow fiber membrane was obtained in the same manner as in Example 1 except that the alkali treatment was performed by immersing in a 20 wt% aqueous sodium hydroxide solution at 80 ° C. for 3 hours.

(Comparative Example 4)
A hollow fiber membrane was obtained in the same manner as in Example 1 except that the alkali treatment was performed by immersing in a 10 wt% aqueous sodium hydroxide solution at 25 ° C for 10 minutes.

(Comparative Example 5).
A hollow fiber membrane was obtained in the same manner as in Example 1 except that the alkali treatment was performed by immersing in a 10 wt% aqueous sodium hydroxide solution at 70 ° C. for 10 minutes.

(Comparative Example 6)
Main polyvinylidene fluoride (PVDF) (powder) having a weight average molecular weight (Mw) of 4.12 × 10 ⁵ and polyvinylidene fluoride (PVDF) (powder) for crystal property modification having an Mw of 9.36 × 10 ⁵ And 95% by weight of polyvinyl alcohol resin (manufactured by Nihon Vinegar Bipoval Co., Ltd., “J Poval JMR-150L”, PVA having an average saponification degree of 22 mol%) (powder, average particle size: about 1080 μm) Mixing was performed using a Henschel mixer at a ratio of 5 wt% and 8.6 wt% to obtain a mixture A.

  Adipic acid polyester plasticizer ("PN-150" manufactured by Asahi Denka Kogyo Co., Ltd.) as the aliphatic polyester and N-methylpyrrolidone (NMP) as the solvent in a ratio of 82.5 wt% / 17.5 wt% The mixture B was obtained by stirring and mixing at room temperature.

  Using a co-rotating meshing twin screw extruder (“BT-30” manufactured by Plastics Engineering Laboratory Co., Ltd., screw diameter 30 mm, L / D = 48), powder provided at a position 80 mm from the most upstream part of the cylinder The mixture A is supplied from the supply unit, and the mixture B heated to a temperature of 160 ° C. from the liquid supply unit provided at a position 480 mm from the most upstream part of the cylinder is mixed A / mixture B = 35.7 / 64.3 ( The kneaded material was extruded at a discharge rate of 11.8 g / min from a nozzle having a circular slit with an outer diameter of 5 mm and an inner diameter of 3.5 mm. At this time, air was injected into the hollow portion of the yarn at a flow rate of 4.0 ml / min from a vent provided in the center of the nozzle.

  The extruded mixture is maintained in a molten state at a temperature of 40 ° C. and has a liquid surface at a position 280 mm away from the nozzle (that is, an air gap of 280 mm) and is cooled and solidified (in the liquid) (Residence time: about 7 seconds) After being taken up at a take-up speed of 5 m / min, this was wound around a case having a circumference of about 1 m to obtain a first intermediate molded body.

  Next, the first intermediate molded body is immersed in dichloromethane at room temperature for 30 minutes while being vibrated, and then the dichloromethane is replaced with a new one and immersed again under the same conditions to extract the aliphatic polyester and the solvent. Subsequently, heating was 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.

  Next, the second intermediate formed body is passed through a 60 ° C. water bath at a first roll speed of 12.5 m / min, and the second roll speed is set to 22.5 m / min in the longitudinal direction. The film was stretched 1.8 times. Next, 5% relaxation treatment was performed in the dichloromethane solution by passing through a dichloromethane solution controlled to a temperature of 5 ° C. and dropping the third roll speed to 21.4 m / min.

  Furthermore, 5% relaxation treatment was performed in the dry heat bath tank by passing it through a dry heat bath tank (2.0 m long) controlled at a space temperature of 140 ° C. and reducing the fourth roll speed to 20.3 m / min. went. This was wound up to obtain a polyvinylidene fluoride porous hollow fiber membrane (third molded body).

  The raw material compositions, film forming conditions, alkali / oxidation treatment conditions, and physical property measured values for Examples 1 to 5 and Comparative Examples 1 to 6 are summarized in the following “Table 1”.

  As can be seen from the results shown in the above-mentioned “Table 1”, the polyvinylidene fluoride hollow fiber membranes (Examples 1 to 5) subjected to weak alkali treatment and oxidation treatment are excellent in osmotic wetting tension and elongation at break. Degree and tensile strength also show sufficient values.

  On the other hand, in Comparative Example 1 in which neither weak alkali treatment nor oxidation treatment was performed, the penetrating wetting tension remained at 35 mN / m, which is outside the scope of the present invention. Next, in Comparative Example 2 in which only the weak alkali treatment was performed, the penetrating wetting tension remained at 38 mN / m, which is outside the scope of the present invention.

  Comparative Example 3 in which the strong alkali treatment and the concentrated sulfuric acid treatment were performed was insufficient in the elongation at break, and was outside the scope of the present invention.

  Next, in Comparative Example 4 in which the alkali treatment was performed with a 10% by weight aqueous sodium hydroxide solution and immersed at 25 ° C. for 10 minutes, the osmotic wet tension remained at 38 mN / m, which was outside the scope of the present invention. As in Comparative Example 4, it was found that when excessive weak alkali conditions were employed, the desired hydrophilicity (penetration wetting tension of 40 mN / m or more) could not be achieved.

  On the other hand, in Comparative Example 5 in which the temperature of the alkali treatment was changed to 70 ° C., it became a strong alkali condition, and hydrophilicity could be achieved, but elongation could not be achieved. Comparative Example 6 is an example of polyvinylidene fluoride blended with partially saponified polyvinyl alcohol. In such an example, although the hydrophilicity is improved, polyvinyl alcohol has no chemical resistance, and after the chemical immersion, the original The problem of returning to hydrophilicity arises.

  The hydrophilic hollow fiber membrane according to the present invention is used in the field of water treatment, for example, separation (filtration) removal of unnecessary substances in liquid, dialysis, degassing of dissolved gas in liquid, concentration of liquid, pure water for electronic industry. It can be used in fields such as manufacturing and sterilization of water during pharmaceutical manufacturing. In particular, the hydrophilic hollow fiber membrane according to the present invention is suitable for fields such as membrane filtration treatment technology during the production of clean water using river water, lake water, groundwater, etc., and membrane filtration treatment technology such as sewage and wastewater. Available.

  In addition, the production method according to the present invention can be used as a production technique for a hydrophilic hollow fiber membrane made of a vinylidene fluoride polymer having sufficient strength and high separation performance.

It is a structure of the apparatus which measures a pure water flux.

Claims (7)

A hydrophilic hollow fiber membrane formed from a vinylidene fluoride polymer and comprising all of the following (1) to (3).
(1) The ratio of C—F bonds to C—H bonds on the film surface measured by XPS (X-ray photoelectron spectroscopy) is 0.6 to 0.9.
(2) The ratio of the O element content on the film surface measured by XPS (X-ray photoelectron spectroscopy) to the F element content is 0.15 to 0.67.
(3) Penetration wetting tension of 40 mN / m or more.   The hydrophilic hollow fiber membrane according to claim 1, which has a breaking elongation of 40% or more and a tensile strength of 7.5 MPa or more.   The osmotic wetting tension after being immersed in a mixed aqueous solution of sodium hypochlorite having an effective chlorine concentration of 5,000 ppm and 1 wt% sodium hydroxide at 23 ° C for 3 days is 40 mN / m or more. 3. The hydrophilic hollow fiber membrane according to 1 or 2.   The hydrophilic hollow fiber membrane according to claim 1, which is used for water treatment.   A method for producing a hydrophilic hollow fiber membrane, comprising subjecting a hollow fiber membrane to a weak alkali treatment from a vinylidene fluoride polymer, followed by an oxidation treatment.   6. The method for producing a hydrophilic hollow fiber membrane according to claim 5, wherein the hollow fiber membrane is stretched before the weak alkali treatment.   The hydrophilic property according to claim 5 or 6, wherein at least one oxidizing agent selected from potassium permanganate, sodium hypochlorite, performic acid, and concentrated sulfuric acid is used in the oxidation treatment. A method for producing a hollow fiber membrane.

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