JPS5891808A - Preparation of porous film of hollow filament - Google Patents

Abstract

PURPOSE:To obtain the titled porous film useful as artificial organs, etc., having improved heat resistance, showing high permeability, by adding an alcohol and an ester to a solution of polyvinylidene fluoride resin to give a stock solution, spinning it, extracting and removing the additives. CONSTITUTION:A copolymer comprising >=50wt% (poly)vinylidene fluoride is dissolved in a solvent such as dimethylformamide, etc., 5-30wt% 5-8C water-insoluble alcohol and/or 7-44 ester are added to the solution, to give a stock solution for making a film. The stock solution is extruded from a nozzle for hollow filament, the solvent is partially evaporated at a proper space distance, and the stock solution is coagulated in a coagulating bath comprising an aqueous solution containing a solvent for the vinylidene fluoride resin, to give a hollow filament. Th additives are extracted with an organic solvent such as methanol, to make it porous.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a polyvinylidene heptadide hollow fiber porous membrane having a large permeation rate. More specifically, it has high mechanical strength, heat resistance, and chemical resistance.
The present invention relates to a method for producing a polyvinylidene 7tride hollow fiber porous membrane having a large permeation rate.

BACKGROUND ART Polymer porous membranes using a variety of materials have been manufactured and used as reverse osmosis membranes and ultra-permeability membranes.

Their applications include desalination of shrubs, seawater, recovery of electrocoating liquids, treatment of pulp waste liquid, separation of oil and water, concentration of fruit juice, etc. in the food industry, artificial kidneys, and purification and separation of pharmaceuticals.

The range of applications for porous polymer membranes is expanding, and applications under increasingly harsh conditions are rapidly increasing. For example, treatment of strong alkali or strong acid solutions, treatment of organic solvents at high temperatures, sterilization with hypochlorous acid, etc. In order to carry out these treatments without problems, a porous polymer membrane having alkali resistance, acid resistance, heat resistance, solvent resistance, etc. is required.

Considering the recent technology for forming porous polymer membranes, acetic acid cellulose membranes can produce wide porous membranes and are used in reverse osmosis membranes, artificial kidneys, etc.; alkalinity,
Acid resistance etc. are not satisfactory.

Although polyacrylonitrile porous membranes have been improved in terms of solvent resistance, alkali resistance, acid resistance, etc., they are not sufficient. Polysulfone porous membranes have much better alkali resistance and acid resistance, but are still unsatisfactory in terms of solvent resistance.

Various porous membranes that improve the above points and have even better heat resistance, alkali resistance, acid resistance, solvent resistance, and high permeability are being studied, and one of them is poly7
There is a porous membrane using vinylidene tsulfide resin.

Generally, as a method for manufacturing porous membranes from thermoplastic resin,
(1) A method using various foaming agents, (2) A method of forming a film by mixing inorganic or organic fine powder that can be extracted with water or a solvent, and extracting the fine powder after molding. (8) A method that uses a bath agent or a foaming agent. Make a thermoplastic resin gel using M agent, and perform wet membrane formation by removing the bath agent and plasticizer from it. (4) Molding the thermoplastic resin in a bath and obtaining a porous membrane by extraction or stretching. There are methods such as bath melt film forming method (5) neutron irradiation method. Among these membrane forming methods, the wet membrane forming method provides a porous membrane with high permeability.

For example, JP-A-52-154862 and JP-A-52-
112!61, etc., there is a film forming method using acetone as the main solvent and a dispersant and a non-solvent. This is a film-forming method that utilizes phase separation due to evaporation of acetone, and it is difficult to control the evaporation rate of acetone, resulting in poor reproducibility. Furthermore, the porosity can be reduced by the method disclosed in JP-A-49-126572 and JP-A-50-35265, in which the polyvinylidene fluoride resin is dissolved in a slow-drying solvent and a quick-drying bath agent, and then immersed in a non-solvent. Only porous membranes with a small amount of permeation can be obtained. As described above, at present, a satisfactory polyvinylidene fluoride porous membrane has not been obtained even in the form of a flat membrane.

On the other hand, in the case of forming a hollow fiber porous membrane, the conditions that can be controlled are limited compared to flat membranes, and the pore size and permeation amount are generally reduced. In the method for manufacturing hollow fiber membranes using a wet method, the time for evaporation of the solvent in the air after discharging the solution is 10 seconds or less,
I can't make it long. In addition, the coagulating liquid penetrates quickly, and phase separation tends to be underdeveloped.

In addition, the membrane thickness and hollow fiber inner diameter are mutually related to the discharge rate and internal liquid volume, and cannot be adjusted independently.Furthermore, these are related to pore formation, and compared to flat membranes, Pore diameter and permeation amount tend to become smaller.

For example, JP-A-51-1370! ! No. 6 discloses a method for producing a hollow fiber porous membrane by melt spinning polyvinylidene heptadide, but the porosity and permeation rate are low. Furthermore, JP-A-56-56-5a discloses a method for producing a hollow fiber porous membrane by wet spinning polyvinylidene heptadide, which improves porosity and water permeability. Yes, but the value is not necessarily satisfactory.

In order to solve these problems, the present inventors have intensively studied the manufacturing method of a hollow fiber porous membrane. As a result, the present inventors have developed a non-water-soluble membrane in which polyvinylidene fluoride resin is dissolved in a solvent and uniformly mixed with the resin solution. A dope containing additives is discharged into a coagulation bath containing a solvent for the resin to form hollow fibers, and then the water-insoluble additives are extracted, resulting in improved porosity and permeation. It has been found that it is possible to obtain a hollow fiber porous membrane.

Consider a spinning process in which a polyvinylidene heptadide resin is dissolved in a solvent and a water-insoluble additive that is uniformly mixed with the resin solution is added thereto. When the hollow fibers enter the coagulation bath, the resin begins to coagulate, but the additives do not exit the hollow fibers and begin to aggregate within the hollow fibers, and do not contribute to the coagulation of the resin until they come into contact with the extraction solvent. It is thought that aggregation progresses accordingly.

It is presumed that during this time, the resin phase constituting the pores is strengthened, and the pores develop significantly. By then extracting the water-insoluble additive, an excellent hollow fiber porous membrane can be obtained. Furthermore, the porosity can be controlled by selecting additives with appropriate molecular weights.

The polyvinylidene heptadide resin used in the present invention is a copolymer containing polyvinylidene heptatide, vinylidene fluoride, and vinylidene fluoride as main components, and a monomer copolymerizable with this, The copolymerizable monomers include vinyl fluoride, trichlorethylene, tetrachloroethylene, 70%
Rochlorovinylidene, monofluorotrifluoroethylene,
It is selected from fluorine-containing olefins such as hexa70ropropylene, and olefins such as ethylene and propylene. A polyvinylidene fluoride resin containing 50% by weight or more (all percentages hereinafter refer to weight%) of vinylidene fluoride, preferably 80% or more, is dissolved in a solvent for the resin and uniformly mixed with the resin solution. A dope solution is prepared by mixing wastewater-soluble additives. Examples of solvents for the resin include dimethylformamide, diethylformamide, dimethylacetamide, diethylacetamide, tetramethylurea, tetraethylurea, N-methylpyrrolidone, trimethylphosphate, Examples include triethyl phosphate, dimethyl sulfoxide and mixtures thereof. The amount of solvent added is usually 30 to 70%, preferably 40 to 60%.

Water-insoluble (water-insoluble means 2) that mixes uniformly with the resin solution.
Additives with a water solubility of 5% or less at 0°C are monohydric alcohols having 5 to 18 carbon atoms, typically haamyl alcohol, 2-ethylhexyl alcohol, nonyl alcohol, etc. Examples include alcohol, lauryl alcohol, myristyl alcohol, cetyl alcohol, stearyl alcohol, and oleyl alcohol. Among esters, esters having 7 to 44 carbon atoms are monoesters of monobasic acid and some alcohol, such as isoamyl acetate, 2-ethylhexyl acetate, octyl acetate, nonyl acetate, stearyl acetate, oleyl acetate, and methyl acetate. , methyl caprylate, methyl laurate, methyl myristate, methyl palmitate, methyl stearate, methyl oleate, oleyl laurate, oleyl stearate, oleyl oleate, as diesters, diptyl oxalate, diptyl tartrate, dioctyl adipate. , dioctyl sepatate, aromatic esters such as methyl benzoate, ethyl benzoate, propyl benzoate, butyl benzoate, dimethyl 7-talate, 7
Diethyl talate, diptyl 7 talate, 7 tal! ! A typical example is 2-ethylhexyl. Preferably an alcohol having 12 to 18 carbon atoms, 12 to 1 carbon atoms
It is an ester of a higher fatty acid and a higher alcohol, and an aromatic ester. If the molecular weight of the additive is small, it is not sufficient to improve the porosity, and if it is too large, the compatibility with the resin solution will be poor. The amount added to the resin solution is 5% to 30%, preferably 10% to 25%.

The concentration of polyvinylidene fluoride resin in the dope is 10% to 40%, preferably 15% to 30%.

The process of spinning hollow fibers using the dope liquid prepared above is to discharge the dope from the hollow fiber nozzle, evaporate part of the bath medium at an appropriate distance, and then spin the dope using vinylidene fluoride. After coagulating in a coagulation chamber consisting of an aqueous solution containing a resin solvent to form hollow fibers, the additives are extracted with an organic solvent, and then washed with water and wound up. Stretch if necessary.

In order to obtain porous hollow fibers, it is necessary to adjust various conditions, and in addition to the dope solution adjustment conditions already mentioned, dope solution temperature, solvent evaporation time, spatial distance, coagulation bath composition, coagulation bath temperature, stretching Adjustment of magnification etc. is required. More specifically, the doping temperature is 30°C to 100°C, and the spatial distance is O11 to
1, coagulation bath temperature 20℃~60℃, stretching ratio 0.8
It is desirable to adjust it to 2.0 times to 2.0 times. Here, the coagulation bath composition influences the formation of the porous membrane, and the solvent for dissolving the polyvinylidene fluoride resin should be 10% to 70%, preferably 20% to
It is preferable to use an aqueous solution containing 50%. By mixing a bath agent for the resin during coagulation, the solidification rate of the resin can be adjusted, and by increasing the bath agent concentration in the coagulation, the number of through holes can be increased and the amount of permeation can be increased. can. If the solvent concentration is too low, coagulation of the hollow fiber surface will be accelerated and the porous structure will be reduced. Also, if the concentration is too high, coagulation will be slow, making it difficult to form hollow fibers.

The organic solvent for extracting the additive is preferably a water-soluble alcohol, ketone, etc., and methanol, ethanol, isopropanol, acetone, methyl ethyl ketone, etc. can be used.

According to the present invention, it is possible to obtain a hollow fiber porous membrane that has excellent heat resistance, alkali resistance, acid resistance, and solvent resistance, and exhibits high permeability. Applications of such porous membranes include waste liquid treatment, chemical filtration, separation in the food industry, artificial organs,
In particular, it can be applied as a support for an artificial lung, an artificial kidney, or a composite separation membrane.

14th Patent Applicant: Toyobo Co., Ltd. 11-

Claims (1)

[Scope of Claims] (1) Vinylidene heptatide or a copolymer containing at least 60% by weight of vinylidene heptatide is dissolved in a solvent, and water-insoluble alcohols and/or esters are further dissolved in the solvent. A hollow fiber porous membrane characterized in that the membrane-forming stock solution is added to form a membrane-forming stock solution, the film-forming stock solution is spun to form hollow fibers, and the above-mentioned additives are extracted with an organic solvent to make it porous. manufacturing method. (2) Alcohol as an additive has a carbon number of 6 to 18
The method according to claim 1, wherein the monoalcohol is (8) The method according to claim 1, wherein the ester as an additive is a monoester, diester, aromatic monoester, aromatic diester, or aromatic triester having 7 to 44 carbon atoms.