JPH02102721A - Production of hollow yarn membrane - Google Patents

Abstract

PURPOSE:To produce a hollow yarn membrane having low filtration resistance by ejecting a film-forming stock soln. from a hollow yarn spinning nozzle and by drawing the resulting hollow yarn in a solidifying bath to cleave a skin layer formed on the outer surface of the hollow yarn. CONSTITUTION:When a polymer such as polysulfone or polyether sulfone is dissolved in a solvent, formed into hollow yarn and immersed in a solidifying liq. such as water or alcohol, the hollow yarn is drawn in the solidifying liq. By this drawing, a skin layer formed on the outer surface of the hollow yarn is cleaved to increase the surface porosity but the inner pore diameter deciding layer undergoes no change. The filtration resistance of the resulting membrane is reduced while maintaining the separating performance and the rate of permeability is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for manufacturing hollow fiber membranes. More specifically, the present invention relates to a method for manufacturing a hollow fiber membrane that has a high water permeability rate.

(Prior Art) The membrane structure of a conventionally known hollow fiber membrane is: (1) The inner and outer surfaces of the hollow fiber are skin layers, and the inside of the membrane has a spongy or finger-shaped structure, for example, JP-A-4-10! 708, JP-A-14-//Jt02, JP-A-5R-isλ///, JP-A-5R-tijtO/I! , Japanese Patent Publication No. 1.0-. 1 ut
r/2, JP-A-61-/6≠602! /C Disclosed: ■ Membranes in which either the inner or outer surface has a skin layer and the other surface is a microporous or porous layer, such as JOURNAL OF APPLID
E POLYMER8CIENCE vol,! /
, /j& (/ri77)K, and the HP series membrane manufactured by Amicon.

(Problems to be Solved by the Invention) When looking at these membranes from the perspective of transient resistance, the part that provides the most resistance during filtration is the part with the smallest pore diameter (corresponding to the skin layer in the above 2). The pores formed on the surface of the membrane have a low porosity, usually at a limit of e-cent to several ten percent, and therefore forming a portion with the minimum pore diameter on the surface is extremely disadvantageous in terms of filtration resistance. For this reason, conventional efforts have been made to reduce the filtration resistance through membrane structures such as making the minimum pore size layer formed on the surface extremely thin and forming coarse voids inside the membrane.

The membrane structure (2) corresponds to this. However, this extremely thin surface dense layer is easily damaged during the hollow fiber spinning process and the subsequent module assembly process, and the slightest abrasion reveals coarse pores inside, impairing the reliability of filtration. As a countermeasure against this, type 2 membranes with dense layers on both the inner and outer surfaces have been devised, but this membrane has the disadvantage of high filtration resistance due to the dense layers on both the inner and outer surfaces of the membrane, resulting in high water permeability. I couldn't get the quantity.

(Means for Solving the Problems) The present inventors have conducted extensive research to overcome the above-mentioned drawbacks, and as a result, have arrived at the present invention. That is, in a method for manufacturing a hollow fiber membrane, which includes a step of forming a solution in which a polymer is dissolved in a solvent into a hollow shape and then immersing it in a coagulating liquid, the hollow fiber is stretched in the coagulating liquid so that only the outer surface of the hollow fiber is formed. A method for manufacturing a hollow fiber membrane is characterized in that the hollow fiber membrane is cleaved, and a method for manufacturing a hollow fiber membrane is characterized in that a portion of the hollow fiber having the minimum pore size is present in an intermediate portion between the outer surface and the inner surface.

That is, the present invention discharges a membrane-forming stock solution from a hollow fiber spinning nozzle and stretches the hollow fiber in a coagulation bath, thereby cleaving the skin layer formed on the outer surface of the hollow fiber and increasing the surface porosity.
The present invention provides a method for producing a hollow fiber membrane in which the filtration resistance generated on the surface of a membrane removal membrane for filtration is reduced.

Conventional hollow fibers have a skin layer on the outer and inner surfaces as shown in Example V above, and this skin layer is the pore size determining layer, that is, the layer that exhibits the minimum pore size, so when drawing is performed, the skin layer is Cleavage occurs, drastically reducing separation performance. However, in the membrane of the present invention, the pore size determining layer is present in the intermediate portion between the outer surface and the inner surface of the membrane, so even if the outer surface of the membrane is cleaved by stretching, the internal pore size determining layer does not undergo any change. . Therefore, the water permeation rate can be improved while maintaining the separation performance of the membrane.

The polymer used in the present invention is not particularly limited, and can be selected depending on the use of the porous membrane and other purposes. Examples of such polymers include cellulose acetate, nitrocellulose, polysulfone, sulfonated polysulfone polyether sulfone, polyacrylonitrile, polyamide, polyimide, polyphenylene oxide, and the like.

In the present invention, it is particularly preferable to use polysulfone and/or polyethersulfone as the membrane-forming polymer, and a polymer represented by a repeating unit of or is preferable.

The microporous membrane of the present invention is manufactured by using the above polymer.

Good solvent, ■, mixed solvent of good bath solvent and poor solvent, or ■.

A membrane-forming stock solution is prepared by dissolving the polymer in a mixture of multiple types of solvents with different degrees of solubility, and the stock solution is discharged from a hollow fiber spinning nozzle and then introduced into a coagulation bath to form a hollow fiber microporous solution. Obtain a membrane.

Coagulation baths include water, alcohols such as methanol, ethanol, and butanol. Anything that does not dissolve the polymer can be used, such as glycol ethers such as ethylene glycol and diethylene glycol, aliphatic hydrocarbons such as n-hexane and n-hebutane, and glycerols such as glycerin. Preferred are water, alcohols, or a mixed liquid of at least three types of these liquids.

It is also possible to slow down the solidification rate by adding a solvent to these liquids. For example, n-methyl-2-pyrrolidone 77X may be added to water. These coagulating liquids are also used as internal solutions for hollow fibers.

The temperature of the coagulating liquid is preferably 1≠o-to'c. Preferably 0°
C-60°C is good. If the temperature is higher than 0C or lower than QoC, the condition of the outer surface of the hollow fibers is difficult to stabilize.

The membrane-forming stock solution discharged from the hollow fiber spinning nozzle is introduced into a coagulation bath with a draft ratio of 1. J-stretched. The stretching distance is 4LOOH/min or less, preferably 2017m/min.
A stable surface condition can be maintained as follows.

Immediately after the membrane forming solution enters the coagulation bath, a skin layer is formed on the surface of the hollow fiber, and the skin layer is cleaved by subsequent stretching, resulting in a hollow fiber having large openings IE on the surface.

When spinning hollow fibers, stretching in a coagulation bath has often been done in the past, but it has been considered important to prevent the surface from splitting. This is because conventional hollow fiber membranes have a surface skin layer with a minimum pore size, and considering that cleavage increases the minimum pore size, this was natural.

However, in the membrane of the present invention, the minimum pore size is not formed on either the inner or outer surfaces, but is formed in the intermediate portion between the inner and outer surfaces, so surface cleavage does not have any effect on the minimum pore size.

An important point for the success of the present invention is to appropriately control the amount of solvent evaporation that occurs on the surface of the filamentous stock solution and the amount of moisture absorbed in the air when the film-forming stock solution discharged from the cap passes between the cap and the coagulation bath. It's about adjusting. For example, the distance between the spinning nozzle and the coagulating liquid is l~JOQR, the internal liquid is n-hexane, the coagulating liquid is water, and the temperature is O~to oc relative humidity lO.
This can be achieved by passing through an atmosphere of ~10%. At this time, a stable hollow fiber can be formed by surrounding the space between the nozzle and the coagulating liquid with a cylindrical hood and flowing the coagulating liquid at a constant wind speed.

The reason why the part with the smallest pore size is formed in the middle part from the inner surface to the outer surface is not clear, but the outer surface of the raw solution immediately after spinning absorbs the poor solvent, and phase separation of the polymer occurs only in the outer surface part. It is presumed that this is due to the occurrence of this phenomenon.

In the membrane of the present invention, even if the surface is cleaved and the pore size becomes large, the layer that determines the minimum pore size of the membrane remains inside, so the filtration performance is improved.
In particular, it has excellent features that do not affect particle capture performance.

〔Example〕

Examples are shown below.

Examples: 22% by weight of polysulfone (AMOCOCo, P-3100), 60% of n-methyl-cobyro171', polyvinylpyrrolidone l! A mixed solution of hexane and n-methyl-2-pyrrolidone (/:/) was discharged from the spinning orifice into the dope solution consisting of %, LiCl 2%, and water 2%. ).During this time, spinning was performed with the humidity of the atmosphere at %, the wind speed at 1.-m/min, and the discharge speed at 1j/0?rL/mjn.
A hollow fiber was formed at a winding speed of 9 J OWL/min.

FIG. 1 shows a photograph of the cross section of the hollow fiber observed with a scanning electron microscope (J00x magnification). Although the outer surface of the hollow fiber is cleaved, it can be seen that a dense layer is formed in the intermediate portion between the outer surface and the inner surface.

Comparative Example Using a film forming stock solution with the same composition as in the example, the humidity of the atmosphere was set to 0.
In the case of hollow fibers spun under the same conditions except for %, a skin layer was formed on the surface, and surface cleavage due to draft in the coagulation bath destroyed the minimum pore size layer on the outer surface.

Table I shows the diameter o, io? The results of comparing the capture performance of latex in μm are shown.

Table D

Claims (2)

[Claims] (1) In a method for manufacturing a hollow fiber membrane, which comprises a step of forming a solution in which a polymer is dissolved in a solvent into a hollow shape and then immersing it in a coagulation liquid, the hollow fiber is stretched in the coagulation liquid so that only the outer surface of the hollow fiber is formed. A method for producing a hollow fiber membrane, which comprises cleaving the membrane. (2) The method for producing a hollow fiber membrane according to claim 1, wherein the portion of the hollow fiber membrane having the minimum pore size is present in an intermediate portion between the outer surface and the inner surface.