JPH078548B2 - Polyvinylidene fluoride-based resin porous membrane and method for producing the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a novel polyvinylidene fluoride resin porous membrane suitable for concentration such as reverse osmosis, ultrafiltration and microfiltration, and substance separation, and a method for producing the same. .

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

From this point of view, mechanical strength, heat resistance, alkali resistance,
Polyvinylidene fluoride resins, which have excellent properties such as acid resistance, solvent resistance, and chemical resistance, have attracted attention, and formation of porous films has been studied. For example, JP-A-49-126572 and JP-A-SHO-5
0-35265, JP-A-52-11261, JP-A-52-154862, JP-A-55-66935, JP-A-55-69627, JP-A-55-99934
No. 5, JP-A-58-91732, JP-A-Sho 60-97001, and the like, tubes of JP-A-54-62273, JP-A-56-56202,
JP-A-58-91808, JP-A-58-98105, JP-A-59-16503
Although there are examples of hollow fiber membranes such as JP-A No. 60-216804 and JP-A No. 60-216804, no porous membranes with large pores can be obtained, or complicated stock solutions using a three-component mixed solvent containing additives. Since it is a system, it has drawbacks such as poor control of the porous structure of the permeable layer and low performance, or complicated film forming process.

(Problems to be Solved by the Invention) As a result of intensive investigations by the present inventors on a polyvinylidene fluoride resin porous membrane that does not have the above-mentioned drawbacks, the present invention has been accomplished.

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

(1) A porous polyvinylidene fluoride resin membrane having at least a five-layer structure in which at least three permeable layers having microporosity and a supporting layer having huge voids are interposed between the permeable layers.

(2) The polyvinylidene fluoride-based resin porous membrane according to claim 1, wherein the permeable layer is composed of micropores having an average pore diameter of 0.01 to 1 μm.

(3) The support layer has an average pore diameter of 1 to 20 on a plane parallel to the membrane surface.
The polyvinylidene fluoride resin porous membrane according to claim 1, wherein the porous membrane is a polyvinylidene fluoride resin.

(4) Polyvinylidene fluoride resin characterized in that when a polyvinylidene fluoride resin is dissolved in a solvent containing dimethylsulfoxide as a main component to form a film, the both surfaces are brought into contact with a liquid having a coagulating action to coagulate. Manufacturing method of porous membrane.

The permeable layer referred to in the present invention has a large number of micropores having an average pore size of 0.01 to 1 μm, and the thickness thereof is 10 μm or less, preferably 5 μm or less. The size and number of the pores of the permeable layer and the thickness of the permeable layer are important factors involved in the water permeability and the solute rejection rate of the membrane, but in the present invention, this permeable layer is described below on both surfaces of the membrane and inside. Due to the characteristic structure that there are at least three layers with the supporting layer interposed, the inner permeable layer can be made thin and the water permeability is high, and there is no difference in the permeation performance regardless of which side of the membrane the stock solution flows through. Is excellent. Further, there is also a feature that a highly reliable sharp fractionation characteristic can be obtained by filtering at least three times. In addition, even if there is a defect in the permeable layer on the side of the undiluted solution during use, the remaining at least two permeable layers exhibit excellent permeation performance, thus ensuring safety and reliability. Excellent,
Moreover, there is an effect that the usage period is significantly extended.

The support layer referred to in the present invention has a large number of pores having an average pore diameter of 1 to 20μ on a plane parallel to the membrane surface, and is continuous with the permeable layer and plays a role of bearing the mechanical strength of the membrane. There is. The pores of the support layer do not necessarily have to have an isotropic shape, but may have a shape elongated in the thickness direction of the film and having a major axis length of 20 μm or more. The thickness of the support layer is thicker than that of the transmissive layer, and is at least 3 times or more, preferably 5 times or more.

The polyvinylidene fluoride resin in the present invention is a vinylidene fluoride homopolymer, and, for example, a vinylidene fluoride-tetrafluoroethylene copolymer, a vinylidene fluoride-hexafluoropropylene copolymer, an ethylene-tetrafluoroethylene copolymer. Random vinylidene fluoride such as polymer, block copolymer, etc., or a mixture thereof containing 70% by weight or more of vinylidene fluoride in the resin, but containing 80% or more of vinylidene fluoride in the resin Is preferred.

Next, dimethylsulfoxide (DMSO), which is the main component of the solvent preferably used in the present invention, has a suitable affinity with the resin, and therefore has good film-forming properties and spinnability, and is a liquid with coagulation action on both sides. By bringing them into contact with each other to solidify, a membrane having a multilayer structure composed of the microporous permeable layer of the present invention and a supporting layer containing giant voids can be easily obtained. In addition, in the same process, by adjusting the film forming conditions (eg, concentration of the stock solution, temperature, coagulation bath composition, temperature) or additives to the solvent, a uniform and wide pore size separation membrane from the reverse osmosis membrane to the microfiltration membrane can be obtained. Can be easily obtained.

When a solvent having a higher affinity for DMSO than DMSO, for example, dimethylacetamide, N-methylpyrrolidone, dimethylformamide, trimethylphosphate, etc., is used as a solvent main component, a separation membrane having such a wide range of performance, particularly It is difficult to easily obtain an ultrafiltration membrane or a microfiltration membrane having a large pore size. In addition, DM
When a solvent having only lower solubility than SO, for example, dioxane, tetrahydrofuran, methyl ethyl ketone, etc., is used as a solvent main component, film forming and spinnability are poor,
It is difficult to obtain the target membrane performance. In addition, DMSO is infinitely soluble in water, can be easily removed by washing with water after film formation, spinning, and has extremely low toxicity compared to other solvents,
It has excellent properties in terms of the safety of the product when it is used in the work environment or for medical purposes.

Furthermore, when preparing a membrane-forming stock solution, water, formamide, alcohols (butanol, propanol, ethylene glycol, glycerin, etc.), urea, calcium chloride, etc. are used to control the pore size according to the purpose of the separation membrane. It is also a preferable method to add a non-solvent or a surfactant such as polyoxyethylene ether lauryl alcohol or isooctylphenoxypolyethoxyethanol. Among these, glycerin is a particularly preferable additive when the separation membrane having a large addition effect and a uniform pore size is formed and the yarn is formed. The proportion of the additive in this solvent system is preferably 5 to 30% by weight in order to obtain a good film forming property of DMSO and a film having a wide range of separation characteristics without losing the spinnability.

The concentration of the resin in the membrane-forming solution, the spinning solution, varies depending on the type of solvent used, the membrane-forming method, the spinning method, the pore size of the target separation membrane, and the like, but is usually 5 to 35% by weight, and preferably 10% by weight.
Is in the range of up to 30% by weight.

The membrane formation of the present invention includes not only the production of a flat membrane but also the spinning into a hollow fiber and the like, but it is essential that both surfaces are contacted with a liquid having a coagulation action to coagulate, and only by this method The porous membrane of the present invention is obtained. For example,
The stock solution is extruded from the slit and introduced into the coagulation bath directly or once in the air to coagulate from both sides, or the coagulation solution is extruded from the hollow fiber die to the core at the same time as the stock solution and passed directly or once The film can be formed by introducing it into the coagulating liquid and coagulating from both sides.

The spinneret temperature cannot be specified because it greatly affects the spinnability due to the relationship with the viscosity of the stock solution, but
It is preferably 20 ° C. or lower. In this temperature range, there is also an effect of preventing deterioration of the spinnability due to condensation of steam on the die surface, which becomes remarkable when the distance between the die surface and the coagulating liquid surface is short.

When the extruded stock solution is once introduced into the coagulation solution through the air, the conditions during air running vary depending on the size of the film, the film forming speed, etc. Alternatively, the distance from the surface of the die to the introduction into the coagulating liquid is usually preferably in the range of 0.2 to 200 cm from the viewpoint of stability of film formation. The ambient temperature is usually atmospheric temperature or room temperature, but in some cases, cooling may be performed. In addition, it is also possible to adjust the humidity appropriately to finely control the membrane performance.

The coagulating liquid may be any as long as it is a non-solvent of the resin of the present invention and has an affinity and compatibility with the solvent of the stock solution, but generally, water, aliphatic lower alcohols, or their A mixture or a mixture of these coagulation liquids and a solvent is preferably used.

The temperature of the coagulating liquid has a great influence on the permeability of the membrane, and generally a membrane having high water permeability on the high temperature side is obtained, and it is usually carried out at around 0 to 98 ° C.

The porous membrane of the present invention can be used by drying,
It is preferable to form and store the film in a water-containing state or a wet state without being dried from the coagulation bath, and the permeation performance and mechanical properties are not significantly changed for a long period of time. In order to keep it in a wet state, it is sufficient to attach a suitable wetting agent such as hydrous glycerin, ethylene glycol, polyethylene glycol, and various surfactants.

Furthermore, the permeation performance, mechanical strength, dimensional stability, etc. of the membrane can be changed by heat treatment after the membrane formation. Heat treatment is performed under tension or without tension, and the temperature is usually 50 to 110.
C. It is preferably in the range of 70 to 90.degree.

Further, the permeation performance, mechanical strength, dimensional stability, etc. of the membrane can be changed by stretching treatment after the membrane formation. The draw ratio is about 1.1 to 3 times, and the temperature is usually 50 to 110 ° C, preferably 70.
The temperature is in the range of up to 90 ° C, but the heat treatment and the stretching treatment can be performed simultaneously.

The polyvinylidene fluoride resin porous membrane according to the present invention,
Desalination of seawater, desalination, removal of bases and acids in industrial wastewater, production of ultrapure water for the electronic industry, production of high-purity chemicals, degreasing liquid, recovery of electrodeposition coating liquid, waste paper pulp treatment , Industrial water treatment such as oil water separation, oil emulsion separation, separation and purification of fermentation products, concentration of fruit juice and vegetable juice, soybean treatment, concentration in food industry such as sugar industry, separation, purification, artificial kidney, separation of blood components , Widely used in the field of biotechnology such as bioreactor, medical applications such as microfilter for bacterial separation, pharmaceutical separation and purification.

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

(Example) (1) Dimension of film It measured using the optical microscope.

(2) Pore size of the film It was performed by scanning electron microscope (Akashi Seisakusho α-9) photograph observation.

(3) Water permeability Insert the hollow fiber membrane into a glass case with holes for reflux liquid at both ends, make a small module using a commercially available potting agent, and keep it at 37 ° C inside the hollow fiber. The water permeation performance was calculated from the amount of water that permeates outward through the membrane under water pressure, the effective membrane area, and the transmembrane pressure difference.

(4) Overperformance with 5% albumin aqueous solution Using a stock solution prepared using commercially available bovine albumin, water permeability was measured by the method of (3) above.

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

Example 1 Vinylidene fluoride resin (Kynar 4 manufactured by Penwalt, Inc., USA)
60) Add 200 parts to 1000 parts of dimethyl sulfoxide to obtain 8
It was dissolved at 0 ° C to obtain a uniform stock solution having a polymer concentration of 16.7% by weight. The stock solution viscosity (50 ° C) was about 30 poise. This stock solution is extruded from a hollow fiber die at a die temperature of 40 ° C together with a core solution of an aqueous solution containing 70% by weight of dimethylsulfoxide, allowed to run for 5 cm in air, and then at about 50 ° C consisting of an aqueous solution containing about 10% by weight of dimethylsulfoxide. The hollow fiber was passed through the coagulating liquid to solidify from both the inner surface and the outer surface of the hollow fiber, washed with water, attached with glycerin, and wound at 20 m / min. The inner diameter of this hollow fiber was about 490μ, and the film thickness was about 60μ. A permeation layer having an average pore size of about 0.2μ or less and a thickness of about 1μ on the inner surface of the membrane, a permeation layer having an average pore size of about 0.1μ or less and a thickness of about 1μ on the outer surface of the membrane, and an average pore size of about 0.1μ inside the membrane. μ or less, thickness about 2
There is a permeable layer of μ, sandwiched between these permeable layers, the average pore size in the plane parallel to the membrane surface is 5 to 10 μ, and the major axis length is 10 to 20 μ. There is a support layer of 5
Layer structure is observed.

When the performance of the membrane was evaluated using this membrane as a small module, the water permeability of pure water: 90 ml / m ² · hr · mmHg, the permeation performance with a 5% albumin aqueous solution was water permeability: 40 ml / m ² · hr.・ MmHg,
Albumin inhibition rate: About 95%.

Example 2 Vinylidene fluoride resin (Kynar 4 manufactured by Penwalt, Inc., USA)
60) 200 parts was added to a solvent prepared by adding 1000 parts of dimethyl sulfoxide to 100 parts of glycerin (10 wt% to dimethyl sulfoxide) and dissolved at 80 ° C to obtain a uniform stock solution having a polymer concentration of 15.4 wt%. The stock solution viscosity (50 ° C) was about 55 poise. This stock solution is extruded from a hollow fiber die at a die temperature of 40 ° C together with a core solution of an aqueous solution containing 70% by weight of dimethylsulfoxide, allowed to run for 5 cm in air, and then at about 50 ° C consisting of an aqueous solution containing about 10% by weight of dimethylsulfoxide. The hollow fiber was passed through the coagulating liquid to solidify from both the inner surface and the outer surface of the hollow fiber, washed with water, attached with glycerin, and wound at 20 m / min. The inner diameter of this hollow fiber is about 465μ, and the film thickness is about 50μ.
Met. The structure of this film is shown in FIGS. 1, 2 and 3. The inner surface of the membrane has an average pore diameter of about 0.2μ or less and a thickness of about 1μ permeation layer 1a, the outer surface of the membrane has an average pore diameter of about 0.1μ or less, a thickness of about 1μ permeation layer 1b, and the inside of the membrane has an average pore diameter of about 0.1μ. There is a permeable layer 1c having a thickness of less than or equal to μ and a thickness of about 2μ, and sandwiched between the permeable layers 1a, 1b and 1c, the average pore diameter in the plane parallel to the membrane surface is 5 to 10μ,
Approximately 20μ and 25 thick, including giant voids with a major axis length of 10-15μ
A five-layer structure in which μ supporting layers 2a and 2b were present was observed.

When this membrane was used as a small module and the performance of the membrane was evaluated, the water permeability of pure water: 2400 ml / m ² · hr · mmHg, 5% albumin aqueous solution, the water permeability: 120 ml / m ² · hr・ MmH
g, albumin inhibition rate: about 70%.

Example 3 Permeability of pure water obtained by washing out with water in Example 2: 2400 ml / m ² · hr
The mmHg wet film was replaced with ethanol and then dried. Next, after dipping this dry film in ethanol, the water permeability was measured by substituting with water and found to be 2430 ml / m ² · h.
It was r · mmHg and maintained 100% water permeability. As a result, it was confirmed that water permeability can be exhibited by the above method even when the membrane is dried.

Example 4 The same stock solution as in Example 2 was applied to the hollow fiber spinneret at a spinneret temperature of 40 ° C.
After extruding with the core liquid of water by 5 cm and running in air for 5 cm, it is passed through a coagulating liquid of about 50 ° C consisting of an aqueous solution containing about 10% by weight of dimethyl sulfoxide to coagulate from both the inner and outer surfaces of the hollow fiber. After washing, wash with water, attach glycerin,
The hollow fiber was wound at 20 m / min. The inner diameter of this hollow fiber is about 4
It was 85μ and the film thickness was about 62μ. The structure of this film is shown in FIG.
This is shown in FIGS. 5 and 6. Mean pore size on the inner surface of the membrane is about 0.2μ
Below, a permeable layer 1a with a thickness of about 0.5μ, an average pore diameter of about 0.1μ or less on the outer surface of the membrane, a permeable layer 1b with a thickness of about 0.5μ, an average pore diameter of about 0.1μ or less, a thickness of about 1μ There is a permeable layer 1c, sandwiched between those permeable layers 1a, 1b, 1c, the average pore diameter in the plane parallel to the membrane surface is about 10μ, including a giant void with a major axis length of about 35μ,
Support layer 2 with a thickness of about 12μ, including giant voids with a thickness of about 48μ, an average pore size of about 6μ on a plane parallel to the membrane surface, and a major axis length of about 10μ.
A 5-layer structure in which a and 2b were present was observed.

When this membrane was used as a small module and the performance of the membrane was evaluated, the water permeability of pure water: 690 ml / m ² · hr · mmHg, 5% albumin aqueous solution, water permeability: 55 ml / m ² · hr・ MmH
g, albumin inhibition rate: about 94%.

Comparative Example 1 Vinylidene fluoride resin (Kynar 4 manufactured by Penwalt, Inc., USA)
60) 200 parts to 600 parts of dimethylacetamide with an average molecular weight
200 parts of polyethylene glycol (90 parts) was added to the solvent and dissolved at 80 ° C. for 8 hours to obtain a stock solution having a polymer concentration of 22.5% by weight. This stock solution is passed through the hollow fiber die and the die temperature is 60 ° C
Then, extruded with a core liquid of water, after running in the air for 5 cm, after passing through a coagulating liquid of about 70 ° C composed of an aqueous solution containing about 10% by weight of dimethylacetamide for coagulation, washing with water and attaching glycerin, The hollow fiber was wound at 20 m / min. Since the undiluted solution was slightly non-uniform, the spinnability was slightly inferior, and tears occasionally occurred in a part of the hollow fiber membrane. The inner diameter of this hollow fiber was about 470μ, and the film thickness was about 53μ. The structure of this membrane consists of a permeable layer with an average pore size of about 0.2μ or less and a thickness of about 0.5μ on both inner and outer surfaces, and a single support layer containing huge voids inside the permeable layer. It was a structure.

(Effect of the Invention) The polyvinylidene fluoride resin porous membrane of the present invention has a porous layer having an average pore diameter of 0.01 to 1 μm and has a permeable layer that controls the permeation property, and has at least three layers on both surfaces and inside the membrane. , Having at least a five-layer structure in which a supporting layer for retaining the mechanical strength of the membrane, which contains a giant void having an average pore diameter of 1 to 20 μm in a plane parallel to the membrane surface, is interposed between the permeable layers. The inner permeation layer can be made thin, the water permeability is high, and there is no difference in permeation performance regardless of which side of the membrane the stock solution is flowed through, which is practically excellent. Further, there is also a feature that a highly reliable sharp fractionation characteristic can be obtained by filtering at least three times. In addition, even if there is a defect in the permeable layer on the side of the stock solution during use, the remaining at least two permeable layers exhibit excellent permeation performance, so that safety and reliability can be improved. It is a film with high heat resistance and chemical resistance.
It is characterized by a long usage period. Moreover, by using dimethylsulfoxide as a main component, which has an appropriate affinity for the resin of the present invention, the membrane forming process is also simple, and it is possible to easily obtain a separation membrane with a wide pore size by adjusting the conditions or additives. You can

[Brief description of drawings]

FIG. 1 shows a scanning electron micrograph (magnification: 4000 times) showing the shape of fibers on the inner surface of the polyvinylidene fluoride resin porous hollow fiber membrane obtained in Example 2 of the present invention. FIG. 2 shows a scanning electron micrograph (magnification: 800) showing the shape of fibers in the cross section of the polyvinylidene fluoride resin porous hollow fiber membrane obtained in Example 2 of the present invention. FIG. 3 is a scanning electron micrograph (magnification: 4000 times) showing the shape of fibers on the outer surface of the polyvinylidene fluoride resin porous hollow fiber membrane obtained in Example 2 of the present invention. FIG. 4 is a scanning electron micrograph (magnification: 4000 times) showing the shape of fibers on the inner surface of the polyvinylidene fluoride resin porous hollow fiber membrane obtained in Example 3 of the present invention. FIG. 5 shows a scanning electron micrograph (magnification: 800 times) showing the shape of fibers in the cross section of the polyvinylidene fluoride resin porous hollow fiber membrane obtained in Example 3 of the present invention. FIG. 6 shows a scanning electron micrograph (magnification: 4000 times) showing the shape of fibers on the outer surface of the polyvinylidene fluoride resin porous hollow fiber membrane obtained in Example 3 of the present invention. 1a, 1b, 1c: Transmission layer 2a, 2b, 2c: Support layer

Claims (4)

[Claims] 1. A porous polyvinylidene fluoride resin membrane having at least a five-layer structure in which at least three permeable layers having microporosity and a supporting layer having a huge void are interposed between the permeable layers. 2. The polyvinylidene fluoride resin porous membrane according to claim 1, wherein the permeable layer is composed of micropores having an average pore diameter of 0.01 to 1 μm. 3. The polyvinylidene fluoride-based resin porous membrane according to claim 1, wherein the support layer is composed of pores having an average pore diameter of 1 to 20 μm on a plane parallel to the membrane surface. . 4. When forming a film from a stock solution of a polyvinylidene fluoride resin dissolved in a solvent containing dimethylsulfoxide as a main component, both sides are brought into contact with a solution having a coagulating action to coagulate the polyvinylidene fluoride. -Based resin porous membrane manufacturing method.