JP2010082509A - Porous membrane - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a porous membrane having an excellent permeability and hydrophilicity in a membrane surface and hardly generating fouling. <P>SOLUTION: The porous membrane is prepared by heat-induction phase-separation with a crosslinked polyamide resin prepared by reacting a polyamide resin with a crosslinking agent, and the contact angle of the membrane surface against water is 90° or less. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a porous membrane used for filtration in the water treatment field, the medical field, the food industry field, and the like.

  In recent years, porous filtration membranes such as ultrafiltration membranes and microfiltration membranes have been used in many industrial fields such as water treatment fields such as drinking water production and water and sewage treatment, medical fields such as blood purification, and food industries. Advances have been made in the development of porous membranes with various pore sizes. A porous membrane having a pore size of nm to μm, which is frequently used as a porous filtration membrane, is often produced by utilizing phase separation of an organic polymer solution. Since this technique can be applied to many organic polymer compounds and is easily industrialized, it is currently the mainstream of industrial production methods for porous filtration membranes (hereinafter simply referred to as porous membranes).

  In the phase separation method, a fine polymer dense phase and a polymer dilute phase are generated from a uniform polymer solution (phase separation), and they are bonded to each other to grow, and the membrane skeleton (polymer rich phase) and pores Since a (polymer dilute phase) is formed, a porous film is obtained by removing pore components (such as a solvent) thereafter. Typically, there are two types, a non-solvent induced phase separation method (NIPS method) and a thermally induced phase separation method (TIPS method).

  The NIPS method is a method for producing a porous film by dissolving a polymer compound in a solvent having solubility even at room temperature and then discharging it into a non-solvent and depositing the polymer compound by liquid exchange between the solvent and the non-solvent. It is.

  In the TIPS method, a polymer compound is mixed at a high temperature using a solvent that does not dissolve the polymer compound at room temperature but dissolves at a high temperature, and the solution is discharged into air or water to cool the polymer compound. Is a method of producing a porous film by solidifying and then extracting and removing the solvent. The TIPS method can be applied to a crystalline polymer compound to which the NIPS method cannot be applied because there is no solvent that can be dissolved at room temperature, and the film strength can be increased by using the crystalline polymer compound. It becomes possible. There is an advantage that a film having a large pore diameter is not formed, and the film forming process is easily controlled because it is composed of only a polymer compound and a solvent. Further, a material having a high porosity and a sharp pore size distribution can be obtained.

  As a material for the porous membrane, generally, a polyolefin such as polyethylene or polypropylene, or a hydrophobic thermoplastic resin such as polyvinylidene fluoride is often used. This is because it is advantageous to use as the membrane material a hydrophobic resin that can exhibit strength even in water because the main application is filtration of aqueous liquids. However, when a hydrophobic resin is used as the membrane material, fouling occurs due to the adsorption of organic substances contained in the raw filter water, and the filtration performance decreases. For this reason, proposals have been made such as forming a film by blending a hydrophilic substance with a hydrophobic resin, or coating a hydrophilic substance on the surface of a film made of a hydrophobic material. It may be detached or peeled off from the surface, leaving the problem of reduced hydrophilicity. Although proposals have been made to form a film using a hydrophilic resin such as an ethylene-vinyl alcohol resin, the strength in water tends to be low because it is hydrophilic.

Therefore, it has been studied to use a polyamide-based resin having a relatively high hydrophilicity and a small decrease in strength in water. For example, Patent Document 1 proposes a separation membrane using a polyamide resin.
Special Table 2003-534908

  However, polyamide resins have few solvents with high affinity. In addition, it is necessary to use a resin having a high molecular weight in order to form a film by the thermally induced phase separation method, but the polyamide resin currently on the market does not have a sufficiently high molecular weight and the solution viscosity is insufficient. Therefore, it is necessary to increase the concentration of the resin, and it is difficult to obtain a sufficient porosity, so that there is a problem that a sufficient water permeability cannot be obtained.

  In view of the above problems, an object of the present invention is to provide a porous membrane that can obtain a sufficient amount of water permeation, has excellent membrane surface hydrophilicity, and hardly causes fouling.

  As a result of intensive studies, the present inventors have found that the above problems can be solved by using a crosslinked polyamide resin obtained by reacting a polyamide resin with a crosslinking agent, and have completed the present invention.

  That is, the porous membrane of the present invention is a porous membrane produced by a thermally induced phase separation method using a crosslinked polyamide resin obtained by reacting a polyamide resin and a crosslinking agent, and has a contact angle with water on the membrane surface. Is 90 ° or less.

  Since the porous membrane of the present invention uses a crosslinked polyamide resin having hydrophilicity, hydrophilicity can be expressed economically and stably on the membrane surface, and it has high resistance to fouling caused by organic matter. In addition, a sufficient porosity and a sufficient water permeability can be obtained.

Hereinafter, the present invention will be described in detail.
The porous membrane of the present invention is a porous membrane produced by a thermally induced phase separation method using a crosslinked polyamide resin obtained by reacting a polyamide resin and a crosslinking agent, and has a contact angle of 90 on water on the membrane surface. It is characterized by being less than °.

Since a cross-linked polyamide resin obtained by reacting a polyamide resin with a cross-linking agent is used, film forming properties can be ensured even when the porosity is increased and the water permeability is increased. The crosslinked polyamide resin preferably has a melting point of + 80 ° C. and a melt viscosity of 400 to 1200 Pa · s at a shear rate of 1000 s ⁻¹ .

  When the porous membrane has a contact angle with water on the membrane surface of more than 90 °, the organic matter contained in the raw filter water is likely to be adsorbed on the membrane, causing fouling of the membrane and reducing the filtration performance in a short time. The film is formed so as to be 90 ° or less. It is particularly preferable that the angle is 80 ° or less.

The porous membrane is also preferably formed so that the water permeability of pure water is 1000 L / atm / m ² / h or more. If the water permeation amount is less than 1000 L / atm / m ² / h, although separation performance is generally high, fouling is likely to occur due to organic matter contained in the treated raw water, which is not preferable. In addition, the amount of liquid that can be separated in a certain time is small, and in order to obtain the same water permeation amount, it is necessary to increase the membrane area.

  The polyamide resin used in the present invention is not particularly limited as long as it can be molded into a fiber shape, but the relative viscosity is preferably in the range of 2.0 to 4.5. If the relative viscosity is lower than 2.0, even if it is crosslinked with a crosslinking agent as a thermoplastic resin, the solution viscosity when dissolved in the solvent becomes too low to be formed into a hollow fiber membrane, If a large amount of a crosslinking agent is added to increase the viscosity, gelation may occur, which is not preferable. When the relative viscosity exceeds 4.5, the solution viscosity of the thermoplastic resin after crosslinking becomes too high, and it becomes difficult to control the phase separation, which is not preferable. Examples of polyamide resins that can be used include nylon 6, nylon 66, nylon 46, nylon 610, nylon 12, polymetaxylene adipamide and the like. Is preferred.

  The cross-linking agent used in the present invention is not particularly limited as long as it has a functional group capable of reacting with the polyamide resin. However, if there are too few functional groups capable of reacting, compatibility with the polyamide resin is inadequate. It becomes sufficient and the film forming property deteriorates. On the other hand, if the amount is too large, the reaction with the polyamide resin proceeds excessively, resulting in a remarkable increase in melt viscosity, which makes film formation difficult and causes gelation. The reactive functional group is preferably 300 to 6000 geq / t, more preferably 500 to 3000 geq / t.

  Glycidyl-based crosslinking agents, acid anhydride-based crosslinking agents, isocyanate-based crosslinking agents, and the like can be suitably used. Among these, glycidyl crosslinking agents and acid anhydride crosslinking agents that are highly reactive and hardly cause gelation are preferable. As the glycidyl-based crosslinking agent, a terpolymer of ethylene-acrylic acid ester-glycidyl methacrylate and a terpolymer of styrene-acrylic acid ester-glycidyl methacrylate are preferable, and as the acid anhydride-based crosslinking agent, An ethylene-acrylic acid ester-maleic anhydride copolymer is preferred.

  The addition ratio of the crosslinking agent to the polyamide resin is preferably 0.1 to 10% by mass. If it is less than 0.1% by mass, the thermoplastic resin after crosslinking does not have a film shape or the film strength becomes insufficient, which is not preferable. If it exceeds 10% by mass, it is difficult to control the phase separation, and a porous film cannot be formed, or a uniform film cannot be formed by gelation or the like, which is not preferable.

  The solvent used for film formation by the TIPS method is not particularly limited as long as it does not dissolve the thermoplastic resin produced by the crosslinking reaction at room temperature but dissolves at high temperature. Glycerin such as glycerin and diglycerin A glycol such as ethylene glycol, triethylene glycol or polyethylene glycol; a lactam such as caprolactam; a lactone such as caprolactone or butyrolactone. In particular, triethylene glycol having excellent affinity with the polyamide resin is preferable.

  The shape of the porous membrane can be a flat membrane or a hollow fiber membrane, and is shaped into a desired shape by a known technique such as casting, coating, spinning, and extrusion molding. From the viewpoint, a hollow fiber membrane shape is preferable.

  In order to produce a hollow fiber membrane-shaped porous membrane by the TIPS method, as shown in FIG. 1, a general apparatus used for dry and wet spinning can be used. In addition, as shown in FIG. 2, a spinneret having a double circular shape used when producing a core-sheath type composite fiber in melt spinning can be used.

  The above-mentioned thermoplastic resin and solvent are mixed at a high temperature to form a film-forming stock solution. A core inflow liquid for forming the hollow portion is prepared. As the core influent, a liquid is often used because the film forming stock solution is low in viscosity and can be spun even under difficult conditions, and the same solvent system as the film forming stock solution is used. The solution etc. which adjusted the coagulation | solidification power of the film forming stock solution by addition of a poor solvent are used. When the film-forming stock solution has a high viscosity and excellent spinnability, a gas such as an inert gas may be used.

  As shown in FIGS. 1 and 2, the film-forming stock solution L <b> 1 and the core inflow solution L <b> 2 are measured by the metering pumps 1 and 2 and sent to the spinneret 3. The resin solution L3 (film forming stock solution L1 + core inflow solution L2) discharged from the spinneret 3 is substantially dissolved in the coagulation bath 4 through the slight air gap, that is, the thermoplastic resin contained in the resin solution L3. It is introduced into a liquid such as water that is not allowed to cool and solidify. During the cooling and solidifying process of the resin solution L3, a thermally induced phase separation occurs to form a hollow fiber having a sea-island structure, and this hollow fiber is introduced into the washing bath 5 and a solvent and a core influent L2 that are island components of the sea-island structure. The solvent inside is removed with water or the like to form a hollow fiber-shaped porous film which is wound up by the winding device 6. In the spinneret 3, 7 is a core inflow (or gas) inflow hole, and 8 is a film-forming stock solution inflow hole.

  Hereinafter, the present invention will be specifically described by way of examples. Measurement and evaluation of characteristic values in the examples were performed as follows.

(A) Melt viscosity Using a capillary rheometer (manufactured by Shimadzu Corporation, CFT-500D, die diameter 1.0 mm × length 1.0 mm), the melt viscosity is measured at the melting point of the crosslinked polyamide resin + 80 ° C. The melt viscosity at a shear rate of 1000 s- ¹ was calculated.

(B) Contact angle After the dried hollow fiber membrane is halved in the fiber axis direction and flattened, the angle between the sample surface and the droplet (pure water) dropped on the surface is measured using an optical microscope. It measured in the stationary state.

(C) Relative viscosity Measured at a concentration of 1 g / deciliter and a temperature of 25 ° C. using 96% sulfuric acid as a solvent.

(D) Melting point of cross-linked polyamide resin Using a differential scanning calorimeter (DSC), the temperature of the endothermic peak when the temperature was raised in nitrogen at a heating rate of 10 ° C./min, cooled to room temperature, and then raised again. The temperature at the peak top was taken as the melting point.

(E) Water permeation amount In a device as shown in FIG. 3, a hollow fiber membrane 9 is cut into 10 to 20 cm and an injection needle having a diameter corresponding to the inner diameter is inserted into the hollow portions at both ends, and a predetermined time (h ), Pure water was passed through the liquid feed pump 10, and the volume of water that permeated through the membrane and stored in the tray 11 was measured, and this was defined as the permeated water amount (L). At this time, the inlet pressure gauge, the outlet pressure gauge 13, and the outlet valve 14 were used to measure the inlet pressure and the outlet pressure. Using the inner diameter (m), length (m), inlet pressure (atm), outlet pressure (atm), and permeate flow rate (L) of the hollow fiber membrane, the water permeation rate (L / atm / m ² / h) according to the following equation: )
Permeable water amount = permeated water amount / [2π × inner diameter × length × {(inlet pressure + outlet pressure) / 2} × time]

Example 1
1% by mass of an ethylene-acrylic acid ester-glycidyl methacrylate ternary copolymer (LOTADER AX8840, manufactured by Arkema) is added to a nylon 12 chip (Rilsan AECN0TL, manufactured by Arkema Co., Ltd., relative viscosity 2.25). It melt-kneaded at 260 degreeC using the type | mold extruder. The resulting crosslinked polyamide resin had a melting point of 180 ° C. and a melt viscosity at 260 ° C. of 650 Pa · s.

  30 parts by weight of this resin and 70 parts by weight of triethylene glycol (TEG) were kneaded at 270 ° C. for 8 minutes in a nitrogen atmosphere to prepare a film forming stock solution. TEG is used as the core inflow for forming the hollow part, and these film-forming stock solution and core inflow are sent to the spinneret via a metering pump using a batch-type extrusion apparatus, and 220 ° C., Extrusion was performed at a pressure of 0.2 MPa. A spinneret having a hole diameter of 1.58 mm outer diameter and 0.83 mm inner diameter was used.

  The extruded resin solution was put into a 40 ° C. water bath through an air gap of 0.5 cm to be cooled and solidified, and the hollow fiber formed thereby was wound at a winding speed of 20 m / min. This hollow fiber was immersed in water for a whole day and night, and the remaining solvent and core inflow were extracted to obtain a hollow fiber-like porous membrane. The obtained porous membrane had a contact angle of 67 °.

(Example 2)
3% by mass of an ethylene-acrylic acid ester-maleic anhydride terpolymer (Arkema, Bondine LX4110) was added to a nylon 12 chip (Rilsan AECN0TL, manufactured by Arkema Inc., relative viscosity 2.25). It melt-kneaded at 260 degreeC using the ruder type | mold extruder. The resulting crosslinked polyamide resin had a melting point of 180 ° C. and a melt viscosity at 260 ° C. of 570 Pa · s.

  28 parts by weight of this resin and 72 parts by weight of triethylene glycol (TEG) were kneaded at 270 ° C. for 8 minutes in a nitrogen atmosphere to prepare a film forming stock solution. TEG is used as the core inflow for forming the hollow part, and these film-forming stock solution and core inflow are sent to the spinneret via a metering pump using a batch-type extrusion apparatus, and 220 ° C., Extrusion was performed at a pressure of 0.2 MPa. A spinneret having a hole diameter of 1.58 mm outer diameter and 0.83 mm inner diameter was used.

  The extruded resin solution was put into a 40 ° C. water bath through an air gap of 0.5 cm to be cooled and solidified, and the hollow fiber formed thereby was wound at a winding speed of 20 m / min. This hollow fiber was immersed in water for a whole day and night, and the remaining solvent and core inflow were extracted to obtain a hollow fiber-like porous membrane. The obtained porous membrane had a contact angle of 70 °.

(Examples 3 to 4)
A hollow fiber-like porous membrane was produced in the same manner as in Example 1 except that the polyamide resin and the crosslinking agent were melt-kneaded at the ratio shown in Table 1. The contact angle of the obtained porous membrane is shown in Table 1.

(Example 5)
3% by mass of an ethylene-acrylic ester-glycidyl methacrylate ternary copolymer (Archema, LOTADAR AX8840) is added to a nylon 6 chip (Unitika, relative viscosity 3.53), and extruder extrusion The mixture was melt kneaded at 260 ° C. using a machine. The generated crosslinked polyamide resin had a melting point of 180 ° C. and a melt viscosity at 260 ° C. of 760 Pa · s.

  28 parts by weight of this resin and 75 parts by weight of polyethylene glycol (PEG 400) having a molecular weight of 400 were kneaded at 280 ° C. for 8 minutes in a nitrogen atmosphere to prepare a film forming stock solution. TEG is used for the core inflow for forming the hollow part, and these film-forming stock solution and core inflow are sent to the spinneret via a metering pump using a batch-type extruder, and the temperature is 230 ° C. And extruded at a pressure of 0.2 MPa. A spinneret having a hole diameter of 1.58 mm outer diameter and 0.83 mm inner diameter was used.

  The extruded resin solution was put into a 40 ° C. water bath through an air gap of 0.5 cm to be cooled and solidified, and the hollow fiber formed thereby was wound at a winding speed of 20 m / min. This hollow fiber was immersed in water for a whole day and night, and the remaining solvent and core inflow were extracted to obtain a hollow fiber-like porous membrane. The obtained porous membrane had a contact angle of 45 °.

(Example 6)
Example 5 except that 1% by mass of a styrene-acrylic acid ester-glycidyl methacrylate ternary copolymer (manufactured by BASF, JONCRYL ADR-4300S) was used as a crosslinking agent, and triethylene glycol (TEG) was used as a solvent. In the same manner, a hollow fiber-like porous membrane was produced. The obtained porous membrane had a contact angle of 50 °.

(Comparative Example 1)
30 parts by weight of nylon 12 chips (Rilsan AECN0TL, relative viscosity 2.25, manufactured by Arkema) and 70 parts by weight of triethylene glycol (TEG) are kneaded at 270 ° C. for 8 minutes using a biaxial melt kneader in a nitrogen atmosphere. Thus, a film forming stock solution was prepared. TEG was used as the core inflow for forming the hollow part, and these spinning stock solution and core inflow liquid were fed to the spinneret through a metering pump using a batch-type extruder, and were heated to 220 ° C. and 0.2 MPa. When the resin solution was extruded at a pressure of 1, the viscosity of the resin solution was too low to be formed into a hollow fiber membrane shape.

(Comparative Example 2)
The hollow fiber membrane was molded in the same manner as in Comparative Example 1 except that 40 parts by weight of a nylon 12 chip (Rilsan AECN0TL, relative viscosity 2.25, manufactured by Arkema) and 60 parts by weight of triethylene glycol (TEG) were used. went. The obtained hollow fiber membrane had few voids and did not have water permeability.

(Comparative Example 3)
15 mass% of an ethylene-acrylic acid ester-glycidyl methacrylate terpolymer (LOTADER AX8840 manufactured by Arkema) is added to a nylon 12 chip (Rilsan AECN0TL, manufactured by Arkema Co., Ltd., relative viscosity 2.25), and an extruder type It melt-kneaded at 260 degreeC using the extruder. The produced resin was gelled and difficult to dissolve in TEG used as a solvent.
The results of Examples 1 to 6 and Comparative Examples 1 to 3 are shown in Table 1.

It is a schematic process drawing which shows one embodiment which manufactures the porous membrane of this invention. It is a schematic diagram of the spinneret for manufacturing the porous membrane of FIG. It is the schematic of the apparatus which measures the water permeability of the hollow fiber membrane which is a porous membrane of this invention.

Explanation of symbols

3: Spinneret 4: Coagulation bath 5: Washing bath L1: Film forming solution L2: Core inflow solution L3: Resin solution

Claims (4)

A porous membrane produced by a thermally induced phase separation method using a crosslinked polyamide resin obtained by reacting a polyamide resin and a crosslinking agent, wherein the contact angle with respect to water on the membrane surface is 90 ° or less. Porous membrane.   The porous film according to claim 1, wherein the addition ratio of the crosslinking agent to the polyamide resin is 0.1 to 10% by mass.   The porous film according to claim 1 or 2, wherein the crosslinking agent is a glycidyl crosslinking agent and / or an acid anhydride crosslinking agent. The porous membrane according to any one of claims 1 to 3, wherein the crosslinked polyamide resin has a melt viscosity of 400 to 1200 Pa · s at a melting point of + 80 ° C and a shear rate of 1000 s ^-1 . .

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