JPS5857299B2 - Composite membrane manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for applying a thin polymer film uniformly on the surface of a porous material and
This is related to the formation of a shape with good reproducibility.

The two main goals for improving ultrafiltration membranes, reverse osmosis membranes, and gas permeation membranes are high separation efficiency and high flow rate.

Separation efficiency is determined by the pore size distribution of the membrane or the chemical interaction between the separation substance and the membrane material.

As for the droplet flow rate, it is determined by the thickness of the dense part of the membrane.

That is, the thickness of the membrane and the permeation flow rate are inversely proportional, and a high flow rate can be obtained by making the membrane thinner.

However, the thickness at which polymers can be formed into thin films and handled individually is at most a few microns, and it is difficult to handle films with a thickness smaller than this without damaging the film.

Therefore, in order to handle thin films with a thickness of several microns or less, it becomes necessary to fix the thin film to a support, but the support must be porous to avoid pressure loss.

When a solution containing a polymer is cast onto this porous material,
The solution cannot penetrate into the pores of the porous body and evaporate the solvent on the surface of the porous body to form a thin film.

The present inventor completed the present invention as a result of intensive research into a method for forming a uniform thin film on the surface of a porous body to overcome these difficulties.

That is, the present invention provides a composite membrane characterized in that a polymer solution is cast onto a plate, a porous substance is placed on the plate, and the solvent in the solution is evaporated through the pores of the porous substance. Regarding the manufacturing method.

The content of the invention will be explained in detail below.

A solution in which a polymer to be formed into a thin film is dissolved (referred to as a film-forming solution) is cast onto a flat plate with a smooth surface, and a porous material that is to become a support is formed on top of this by bubbles. Step 11: Allow the solvent in the film-forming solution to completely evaporate by leaving it to stand or in a dry air stream, and then peel the porous material from the flat plate. A porous material with a thin polymer film formed thereon is obtained.

The flat plate with a smooth surface used in the present invention may be, for example, a glass plate, a metal plate, a polymer plate, etc. Among these, the polymer plate must not swell or dissolve in the film forming solution. The polymer plate must be selected depending on the film forming solution, and examples include polyethylene, polypropylene, polyvinyl chloride, polyvinylidene chloride, polyethylene fluoride, polyvinylidene fluoride, and polyvinyl tetrafluoride. , cellulose mixed ester, etc. are effective.

The polymer dissolved in the film-forming solution can be selected arbitrarily; it does not need to be a single polymer, and may be a mixture of different polymers or a copolymer. No.

Further, the solvent in which the polymer is dissolved may be a single solvent or a mixed solvent as long as it dissolves the polymer.

The concentration of the film-forming solution is important because it is closely related to the thickness of the thin film that is ultimately formed, and it must be determined by considering the casting area and the desired thickness of the thin film. .

The porous material that will ultimately serve as a support for the thin film must also not swell or dissolve in the film-forming solution.

Examples of such porous materials include inorganic filters such as glass filters with polished surfaces, silver black filters, commonly used polyvinyl chloride,
There are □Clofilters made of nylon, polytetrafluoroethylene, polypropylene, cellulose mixed ester, etc.

It is desirable that the pore diameters of these porous materials be as uniform as possible, and the average pore diameter should not exceed twice the thickness of the thin polymer film formed on the surface, and preferably be approximately the same as that thickness. Something is hopeful.

The surface thin film of the composite membrane provided by the present invention can have a thickness of at least about 300 angstroms, and can be used as an ultrafiltration membrane, a reverse osmosis membrane, or a gas separation membrane.

Examples will be shown below for more specific explanation.

Example 1 A 0.1 polybenzene solution of polytetrahydrowalane was cast on a glass plate, and a polypropylene black filter (pore size 0.1 μm) was carefully placed on top of it so that no air bubbles remained. 1 inch Benzene was evaporated.

After 3 hours, the polypropylene microfilter on the glass plate was peeled off while the glass plate was immersed in methanol.

The peeled surface of the polypropylene microfilter shows red scattered light, and this composite membrane can withstand a pressure difference of 650 mmHg.
It was confirmed that methanol did not pass through the glass at all, and there were no pinholes.

The thickness of the surface thin film of this composite film is calculated to be about 2500 angstroms.

Example 2 0.05% of a block copolymer of 2-vinylpyridine and styrene (weight composition ratio 2:1) on a polyethylene plate
Cast the toluene solution, carefully place a polyvinyl tetrafluoride micron filter (pore size 0.2 μm) on top of the toluene solution so as not to create bubbles, and then carefully place a polyethylene plate after completely evaporating the toluene. The upper polytetrafluoroethylene microfilter was peeled off.

The peeled surface of the polytetrafluoroethylene microfilter turned red, and it was confirmed that there were no pinholes because there was virtually no permeation of methanol despite the pressure difference of 650 mmHg across this composite membrane.

The thickness of the surface thin film of this composite film was calculated to be 1800 angstroms.

Example 3 A 0.008% IIVF solution of polyvinylene carbonate was cast onto a polytetrafluoroethylene flat plate, covered with a silver filter (pore size 0.2 μm), and dried in dry nitrogen at 80°C ( After 28 hours), the silver filter was carefully peeled off from the polytetrafluoroethylene plate.

It was confirmed that this membrane did not allow any nitrogen gas to pass through it under a pressure difference of 650 MHg, and that a uniform thin film without pinholes was formed on the silver filter.

The calculated thickness of the polyvinylene carbonate on the silver filter was 600 angstroms.

Claims (1)

[Claims] 1. A method for producing a composite membrane, which comprises casting a polymer solution onto a plate, placing a porous substance on top of the plate, and evaporating the solvent in the solution through the pores of the porous substance.