JPH02102722A - Hollow yarn membrane - Google Patents

Abstract

PURPOSE:To obtain a hollow yarn membrane having low filtration resistance and ensuring a large amt. of permeated water by continuously changing pore diameter from the outer surface of a hollow yarn membrane to the inner surface and allowing a part having the min. pore diameter to exist at the middle part between the outer and inner surfaces. CONSTITUTION:A film-forming polymer such as polysulfone is dissolved in a mixture of plural kinds of solvents having different solvent powers to the polymer to produce a film-forming stock soln. This soln. is ejected from a spinning nozzle with n-hexane, etc., as an inner liq. in an atmosphere at about 0-60 deg.C and about 10-80% relative humidity and the ejected soln. is immersed in a solidifying bath such as water set under the nozzle at about 1-30cm interval. At this time, the space between the nozzle and the solidifying bath is enclosed with a cylindrical hood and air is allowed to flow at a certain speed in the hood. A layer having the min. pore diameter is formed in the resulting membrane by delicately regulating the rate of spinning, the interval between the spinning nozzle and the solidifying bath, the amt. of vapor of a bad solvent in the hood and the speed of air.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a hollow fiber membrane, and more specifically to a dry hollow fiber membrane with an anisotropic structure that has low transient resistance and high water permeability. .

(Prior art) Conventionally known membrane structures of hollow fibers include: ■The inner and outer surfaces of the hollow fiber are skin layers, and the inside of the membrane has a sponge-like or finger-shaped structure; for example, JP-A-Sho! 6-/Q570≠, JP-A-74-//j60ko, JP-A-5R-T3xiti, JP-A-Sho j1-//! 40/1. JP-A-Sho tO-2≠At/ko,
What is disclosed in JP-A-47-16μ≦O, ■ Either the inner surface or the outer surface has a dense skin layer, and the other surface is a microporous layer or a porous layer. film,
For example, JDURNAL OF APPLIEDPO
LYMER5CIENCE vol, J/, /jA(
15'77), JP-A-17-J Koj/j, JP-A-J! −
Examples include the membrane described in Gua 02 and the HP series membrane manufactured by Amicon.

(Problems to be Solved by the Invention) When these membranes are viewed from the perspective of transient resistance, the portion that provides the most resistance during filtration is the portion that has the smallest pore diameter. The porosity of the round pores formed on the surface of the membrane is low and is normally limited to a few t-cents to several tens of cents, 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. ■
This applies to the membrane structure of

However, the surface of this extremely thin dense layer is easily damaged during the hollow fiber spinning process and the subsequent module assembly process, and the slightest scratch can reveal coarse pores inside, resulting in a temporary loss of reliability. Become. As a countermeasure to this problem, 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.

(Means for Solving the Problems) The present inventors have conducted extensive research to overcome the above-mentioned drawbacks, and as a result they have arrived at the present invention. That is, the present invention is a hollow fiber membrane in which the pore diameter continuously changes from the outer surface to the inner surface 1 of the hollow fiber membrane, and the portion having the smallest pore diameter exists in the intermediate portion between the outer surface and the inner surface.

The pore diameter on the inner surface of this hollow fiber membrane gradually decreases toward the outside of the membrane, reaches its minimum midway between the outer and inner surfaces, and then gradually increases until it reaches the outer surface, which is a unique structure that has never been seen before. have. The structure as seen in an electron micrograph is shown in Figure 1.

Since the membrane of the present invention has a porosity ranging from rO% to rz%, the ratio between the internal membrane space and the skeleton portion is from rO% to rz%. Filtration resistance can be made extremely low. Another major feature is that the filtration resistance of the entire membrane can be lowered by increasing the pore diameters on the inner and outer surfaces, which have a lower aperture ratio, to reduce the filtration resistance. As a result, high water permeability can be obtained.

Another feature of the membrane of the present invention is that by having the minimum pore size layer inside the membrane, it is possible to protect the minimum pore size layer from scratches during the above-mentioned spinning process and module processing process.

Thus, a membrane with low transient resistance and high filtration reliability can be produced.

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, polyethersulfone, polyacrylonitrile, polyamide, polyimide, polyphenylene oxide, and the like.

In the present invention, among these, it is particularly preferable to use polysulfone and polyether sulfone as the film-forming polymer, and polymers represented by the following repeating units are preferable.

The production of the microporous membrane of the present invention involves using the above polymer as a good solvent,
A membrane-forming stock solution is prepared by dissolving it in a mixed solvent of a good solvent and a poor solvent or a mixture of multiple types of solvents with different degrees of solubility for the polymer, and the stock solution is discharged from a hollow fiber spinning nozzle. This is introduced into a coagulation bath to obtain a hollow fiber microporous membrane.

Coagulation baths include water, alcohols such as methanol, ethanol, and butanol. Anything that is not decomposed by polymer tm can be used, such as glycols such as ethylene glycol and diethylene glycol, glycerols such as glycerin, ethers, and aliphatic hydrocarbons such as n-hexane and n-hebutane. Preferred are water, alcohols, or a mixture of two or more of these liquids.

It is also possible to slow down the solidification rate by adding a solvent to these liquids. For example, n-methyl-cobyrolidone may be added to water in an amount of 0%. These coagulating liquids are used both as an external solution and an internal solution for the hollow fiber.

The temperature of the coagulating liquid is preferably 1≠o-ro°C. Good luck nO'
C-4o 'C3zBi. jO°C or more 1'cBo'
If it is less than c, the state of the hollow fiber surface is difficult to stabilize.

The spinning speed is preferably / ~ J 00 m 7inin, /
If it is less than m 2 /min, it will be difficult to balance the injection rate of the internal coagulating liquid for balancing the shape of the hollow fibers, making it impossible to obtain hollow fibers with a stable shape.

Moreover, if it exceeds 200 m 7 tnin, a hollow fiber having a stable shape cannot be obtained due to vibrations during transport of the thread.

The shape in which the portion having the minimum pore size layer of the present invention is present in the intermediate portion between the inner surface and the outer surface of the hollow fiber is due to the presence of a slag produced on the surface of the filamentous stock solution when the tube-forming stock solution passes through the coagulation bath 1 from the nozzle. An important technique is to appropriately adjust the amount of evaporation and the amount of moisture absorbed into the air. For example, the distance between the spinning nozzle and the coagulating liquid is 1 to 30 degrees, the internal liquid is n-hexane, the coagulating liquid is water, and the relative humidity is 71o to 6o'c [/(
This can be achieved by passing through a 7-40% atmosphere.

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.

In conventional hollow fiber membrane manufacturing methods, air travel time is often investigated for the purpose of forming a skin layer on the outer surface and finger-like pores m inside the membrane, but the hollow fiber membrane of the present invention A minimum pore size layer is formed inside the membrane by absorbing water from the outer surface of the membrane forming stock solution.

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 surface of the stock solution immediately after spinning absorbs the poor solvent, and phase separation of the polymer occurs only in the surface part. It is presumed that this is due to The characteristics of the present invention are to form phase separation only in a shallow part of the outer surface of the hollow fiber by finely adjusting the spinning speed, the distance between the spinning nozzle and the coagulating liquid, the poor solvent vapor source in the atmosphere between them, and the wind speed. It's about letting it happen. This FA adjustment technology made it possible to form a minimum pore size layer inside the membrane, which could not be achieved using conventional spinning methods.

(Example) Examples are shown below.

Examples 1-3 Polysulfone (AMOCOCo, P-3r.

O) 2.2% by weight, n-methyl-2-pyrrolidone Jr. %, polyvinylpyrrolidone 76%, Lic/,!
% by weight, a film-forming stock solution consisting of water double tS, kept at λt'C, and using hexane as the inner solution, the spinning orifice (inner diameter of the annular nozzle!, 01T11 outer diameter).

A coagulation bath of 2j'C (Om) is discharged from /jα under
water). The winding speed was fixed at Om/Sec, and the spinning was performed while changing the humidity of the atmosphere and the wind speed. Both of the obtained hollow fibers had an outer diameter of about 0.2 mm, and an inner diameter of about 0.2 mm.

The water permeability of the hollow fiber membrane obtained in Example / is /, λm//c
rIL2/min/kg/m2te, s+)ri. moreover'
The cross sections of the hollow fiber membranes of IIt Examples/~3 were observed with a scanning electron microscope, and the depths from the outer surface of the minimum pore size layer were measured, and the results are shown in Table/.

Example 911 A cross-sectional photograph of a hollow fiber spun in the same manner as in Example, except that the atmosphere was set to humidity aO% and wind speed of 3 m/min, using a membrane-forming stock solution with the same composition as in Example, is shown below. It is shown in Figure 1. It can be seen that a dense layer is formed in the middle part about 20 μm from the outer surface.

Comparative Example/FIG. 2 shows a surface photograph of a hollow fiber spun under the same conditions as in Example/, except that the membrane forming solution having the same composition as in Example/ was used and the atmospheric humidity was set to 0%. It can be seen that there is an outer surface skin layer. When the water permeability fi1 of the obtained hollow fiber was examined, it was 0. θ Hiroze/α2/min/yu/c! It was fL2.

table/

Claims (1)

[Claims] A hollow fiber membrane characterized in that the pore diameter gradually decreases from the outer surface of the hollow fiber toward the inside, and after reaching the minimum pore diameter inside, the pore diameter gradually increases again and opens on the inner surface.