JPH03213504A - Production of porous hollow fiber membrane - Google Patents

Abstract

PURPOSE:To obtain the title hollow fiber membrane capable of readily carrying out the control of membrane characteristics such as pore size of outer surface side without largely changing spinning state by passing a liquid layer with a specific gravity light more than and incompatible from a coagulating bath and then leading a discharge material into the coagulating bath. CONSTITUTION:A spinning dope, e.g. consisting of a membrane-forming polymer (e.g. polystyrene) and soluble organic solvent (e.g. dimethylacetamide) is discharged from a double cyclic nozzle. Then the dope is passed through a liquid layer (e.g. mechanical oil), preferably having 200-500cc stroke kinematic viscosity and 10-200mm depth and then discharged into a coagulating bath to provide the objective hollow fiber membrane. Thereby the time and the distance required from a discharge to contact with the coagulating bath can be extended without making the nozzle gap larger.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for producing a porous hollow fiber membrane.

More specifically, the present invention relates to a method for producing porous hollow fiber membranes that facilitates control of membrane performance.

[Prior art] and [Problem to be solved by the invention]
In a porous hollow fiber membrane obtained by a dry-wet spinning method in which a spinning stock solution is discharged from a double annular nozzle and then introduced into a coagulation bath and coagulated, the membrane performance is influenced by the membrane structure.

By the way, in the coagulation process of the spinning dope, when the spinning dope comes into contact with the coagulating liquid, the solvent starts to diffuse from the spinning dope and the coagulating liquid starts to diffuse into the spinning dope at the interface. At this time, since the coagulating liquid is a poor solvent for the polymer dissolved in the spinning dope, coagulation and coagulation of the polymer begin from the spinning dope-coagulating liquid interface, and generally the solvent of the spinning dope and the coagulating liquid The membrane structure is determined by the substitution rate of .

Therefore, in order to control the membrane performance, it is sufficient to adjust the rate of mutual diffusion between the spinning dope and the coagulating solution at the initial stage of contact, and this is possible to some extent depending on the composition of the spinning dope and the spinning speed.

However, in order to obtain membrane performance in a range that cannot be controlled by these conditions alone, it is necessary to adjust the composition and temperature of the coagulation bath. However, the coagulation bath generally has a large capacity, partly because it plays the role of a desolvation bath, and therefore it is difficult to adjust the large amount of coagulation bath to be contained therein.

Therefore, in the wet-dry spinning method, the spun hollow fibers are immersed in a coagulation bath, passed through a guide pipe into which a thickener such as a highly concentrated aqueous solution of glycerin is fed, and then passed through a coagulation bath. The present inventor has previously proposed a method for manufacturing porous hollow fiber membranes that facilitates control of membrane performance by contacting with
Publication No.). Although this method achieves the ultimate goal of facilitating control of membrane performance, there are problems in operability.

In addition, when a coagulable liquid is used as a core liquid and is discharged together with the spinning dope, the spatial distance between the spinning nozzle tip and the coagulation bath liquid level must be adjusted in order to delay the coagulation of the outer surface of the discharged material. Although it is effective to increase the nozzle gap, if the spatial distance is set to a size larger than the - chamber, the ejected material will stretch due to its own weight, and the hollow fiber membrane with a predetermined outer diameter will It becomes impossible to obtain the desired properties, and the phenomenon of thread breakage may even occur before solidification.

An object of the present invention is to provide a method for producing a porous hollow fiber membrane that does not cause problems in terms of operability and allows easy control of membrane performance.

[Means to solve the problem]

It is an object of the present invention to provide a wet-dry spinning method in which a spinning stock solution is discharged from a double annular nozzle and then introduced into a coagulation bath to be coagulated. This is achieved by a method of producing a porous hollow fiber membrane by disposing a layer, passing through the liquid layer, and then introducing the discharge into a coagulation chamber.

The step of discharging the spinning dope or a core liquid consisting of a coagulable liquid or a non-coagulable liquid from the double annular nozzle is carried out in a conventional manner. The film-forming polymer and its soluble organic solvent forming the spinning dope may be used, for example, in the following combinations, and a portion of the organic solvent may be replaced with a poor solvent.

[Polysulfone Dimethylacetamide, dimethylformamide Polyethersulfone Diethylacetamide, Diethylformamide, N-methylpyrrolidone, Morpholine, Triethylphosphate Polyacrylonitrile Dimethylacetamide, Dimethylformamide Aromatic polyamide Diethylacetamide, Diethylformamide Polyvinyl chloride
Dimethylacetamide, dimethylbormamide, diethylacetamide, diethylformamide, N-methylpyrrolidone, acetone polyvinylidene fluoride dimethylacetamide, dimethylformamide, triethyl phosphate cellulose acetate dimethylacetamide, dimethylformamide, acetone Generally, water or an aqueous liquid is used as the coagulation bath. In the method of the present invention, an immiscible liquid layer with a lighter specific gravity than the coagulation bath is placed above the coagulation bath, and the discharged material from the nozzle passes through this liquid layer before entering the coagulation bath. lead to,
Complete coagulation.

The liquid layer has a high viscosity such as machine oil or edible oil (kinematic viscosity of about 100 to 1000 centistokes, preferably about 20 centistokes).
0 to 500 centistokes), a liquid capable of slowing down the rate of desolvation from the spinning dope due to its viscosity;
Alternatively, a variety of liquids can be selected and used, such as silicone oil, which is chemically stable and has a variety of viscosities, thereby making it possible to precisely control the pore diameter. The depth of this liquid layer (passage distance) is generally about 10 to 200 mm, although it depends on the desired membrane structure.

〔Effect of the invention〕

According to the method of the present invention, the time and distance from discharge to contact with the coagulation bath can be reduced by passing the discharge from the spinning nozzle through a liquid layer that is incompatible with the coagulation bath prior to coagulation in the coagulation bath. , the nozzle gap can be lengthened without increasing the nozzle gap, and this allows the membrane structure of the porous hollow fiber membrane, especially the pore diameter on the outer surface side, to be adjusted without significantly changing other spinning conditions such as the spinning dope composition. Allows control.

Furthermore, the film structure can be controlled by forming this liquid layer with liquids of various viscosities or by changing its depth (passing distance).

〔Example〕

Next, the present invention will be explained with reference to examples.

Example Using double annular nozzles with diameters of 0.3 mm and 0.5 mm, 80 parts by weight of dimethylformamide and 2 parts of polysulfone were used.
0 parts by weight and polyethylene glycol (#6000)
A spinning stock solution consisting of 5 parts by weight was discharged together with a pure water core liquid, and a layer of silicone oil (kinematic viscosity 200 centistokes) was placed on a tap water coagulation bath (spatial distance between nozzle tip and liquid level 2).
0 mm, depth 100 mm) and then led into a coagulation bath, with an outer diameter of 0 and having 0.2 μm diameter pores on the outer surface side.
A porous hollow fiber membrane of 5 mm was obtained.

Comparative Example In the example, when the discharged product was directly introduced into a tap water coagulation bath without using a silicone oil layer, the outer diameter of the obtained porous hollow fiber membrane was 0.5 mm, but the outer diameter of the porous hollow fiber membrane was 0.5 mm. Pore diameter is 0
．． The diameter was as small as 0.05 μm or less.

In addition, the spatial distance between the nozzle tip and the coagulation bath liquid level was set to 20 mm.
If it is made larger, the ejected material will stretch under its own weight,
Thin hollow fibers with an outer diameter of 0.4 mm or less can be obtained, and if the spatial distance is further increased, the ejected material will break in the air.

Claims (1)

[Scope of Claims] 1. In the wet-dry spinning method in which the spinning dope is discharged from a double annular nozzle and then introduced into a coagulation bath and coagulated, there is a material in the upper part of the coagulation bath that is lighter in specific gravity than the coagulation bath and is incompatible with the spinning solution. 1. A method for producing a porous hollow fiber membrane, comprising disposing a liquid layer and introducing the discharged material into a coagulation bath after passing through the liquid layer. 2. The method for producing a porous hollow fiber membrane according to claim 1, wherein the core solution is discharged together with the spinning dope.