JPS6214903A - Process of turning hydrophobic microporous filter membrane hydrophilic - Google Patents

Abstract

PURPOSE:To turn the surface of hydrophobic, microporous filter membrane hydrophilic without damaging its physical characteristic by cross-linking the polymer after impregnating and applying the solution of hydrophobic polymer having the bond of ester on the side chains onto the said membrane, and treating to turn the membrane hydrophilic. CONSTITUTION:The hydrophobic polymer having bond of ester to the side chains of such substances as cellulose ester, vinyl acetate and the like is solved into the solvent, impregnated and applied onto the hydrophobic, microporous filter membrane. Non-solubility is achieved by reacting the cross-linking agent having the functional group over two numbers in the remaining OH or COOH group of hydrophobic polymer carrying bond of ester with the applied side chains. Next, saponification and glow discharge treatments are carried out to turn the said membrane hydrophilic.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for producing an aqueous microporous filtration membrane. More specifically, the present invention relates to a method for making a hydrophobic filtration membrane hydrophilic.

(Prior Art) Microporous filtration membranes have been known for a long time (for example, in Synthetic Polymer Membrane by R, Kesting).
c Polymer M e m b r a n e
, published by McGraw-Hill)
Widely used in filtration layer filters, etc. Microporous filtration membranes are described, for example, in U.S. Pat.
．． 133. No. 132, No. 2,944,017, Special Publication No. 15698-1970, Special Publication No. 33313-1977,
As described in No. 48-39586, No. 48-40050, etc., products manufactured using cellulose acetate as a raw material 1. U.S. Patent No. 2,783,894, 3
, 408.315, 4,340゜479, 4,
No. 340,480, No. 4,450,126, German Patent DE 3,138.525, JP-A-58-37842
U.S. Patent No. 4.196.070, which is manufactured using aliphatic polyamide as a raw material as described in U.S. Patent No. 4.196.070.
No. 4,203,847, No. 4,203.848, No. 4,340.482, JP 48-12871, JP 49-126572, JP 55-9993
No. 4, those manufactured using polyvinylidene fluoride as a raw material as described in JP-A-58-91732, etc., JP-A-54-26283, JP-A-56-154, etc.
No. 051, JP-A-56-86941, JP-A-56-1
There are those using polysulfone as a raw material, as described in German Patent No. 0L33003400, etc., and those using polypropylene as a raw material, as described in German Patent No. 0L33003400. These microporous filtration membranes are used in electronic industry cleaning water,
It is used for sterilization filtration and particulate filtration of medical water, process water for pharmaceutical manufacturing, food water, etc., and its applications and usage have expanded in recent years.

These membranes are generally manufactured by the following method. That is, it is dissolved in a good solvent for the polymer, a mixed solvent of a good solvent and a poor solvent, or a mixture of two or more solvents having different solubility for the polymer. This polymer solution is cast onto a suitable support, and immediately or after a certain period of time, the cast membrane is immersed in a coagulation tank filled with a suitable non-solvent for the polymer, followed by a washing process and then dried. Ru. The membrane thus formed has an average pore diameter of 0°01μ.
It has micropores from 5μ to 5μ and can be used for fluid filtration.

(Problems to be Solved by the Invention) However, since many of the polymers for these microporous filtration membranes are hydrophobic polymers, it is difficult to use these microporous filtration membranes to filter water. Water is also repelled and cannot be filtered properly. Therefore, in order to improve the hydrophilicity of the microporous filtration membrane, it is common practice to add a surfactant, a polyhydric alcohol such as glycerin or ethylene glycol, etc. to the microporous filtration membrane. However, when hydrophilicity is imparted to the microporous filtration membrane by such a method, there is a drawback that these additives dissolve into the filtrate during filtration and contaminate the filtrate.

Therefore, various methods as described below have been disclosed in the past in order to solve these drawbacks.

Another method for making a hydrophobic microporous filtration membrane hydrophilic is a method in which a microporous filtration membrane made of polysulfone is sputter-etched in a vacuum discharge atmosphere (Japanese Unexamined Patent Publication No. 58-3).
No. 5862). However, this method has disadvantages in that the microporous filtration membrane becomes colored after the hydrophilic treatment and its mechanical strength is significantly reduced.

JP-A-50-32198 discloses a method in which an epoxy resin layer is formed on a microporous filtration membrane made of a fluororesin, and then this epoxy resin layer is made hydrophilic by sulfonation or nitration. has been done. However, since concentrated sulfuric acid or concentrated nitric acid is used during sulfonation and nitration, not only the epoxy resin but also the microporous filtration membrane itself deteriorates, resulting in a decrease in mechanical strength and discoloration of the microporous filtration membrane. There was a drawback.

JP-A-53-80378 discloses a method of reacting polyalkylene oxide in the presence of a base. However, the microporous filtration membrane made hydrophilic by this method has the disadvantage that polyalkylene oxide is eluted into the filtrate, albeit gradually.

Japanese Patent Publication No. 56-16187 discloses a method of applying a water-soluble polymer to a hydrophobic microporous filtration membrane by dip coating, and then making it water-insoluble by electron beam irradiation, heating crystallization, and chemical reaction with formaldehyde or glyoxal. There is. However, this method has the disadvantage that the insolubilized polymer is eluted under somewhat harsh conditions, such as sterilization using hot water at 80°C or saturated steam at 121°C.

Therefore, a first object of the present invention is to provide a method for making a microporous filtration membrane made of a hydrophobic polymer hydrophilic.

A second object of the present invention is to provide a method for imparting hydrophilicity to the surface of a microporous filtration membrane made of a hydrophobic polymer without deteriorating the performance of the microporous filtration membrane. .

A further object of the present invention is to provide a method for producing biologically safe microporous filtration membranes for water filtration.

(Means for solving the problem) The above solution is to dissolve a hydrophobic polymer having an ester bond in its side chain in its solvent, apply this solution to a hydrophobic microporous filtration membrane, and then apply it to the vagina. This was achieved by a method of making a hydrophobic microporous filtration membrane hydrophilic, which is characterized by chemically crosslinking a polymer to make it insolubilized and then performing a hydrophilic treatment.

Examples of the hydrophobic polymer having an ester bond in the side chain used in the present invention include vinyl polymers such as polyvinyl acetate, polymethyl methacrylate, or polyethyl acrylate, cellulose acetate, cellulose nitrate,
Examples include cellulose esters such as cellulose propionate and cellulose butyl acetate. Particularly preferred are cellulose esters and vinyl acetate.

In the present invention, these polymers are dissolved in the solvent and impregnated onto a previously prepared hydrophobic microporous filtration membrane. In this case, since both the microporous filtration membrane and the applied polymer are hydrophobic, the adhesion between them is good.

In this way, the hydrophobic polymer having an ester bond in the side chain coated on the microporous filtration membrane is insolubilized by cross-linking the OH residue or C0OH residue of the polymer with a functional group of divalent or higher valence. This is achieved by reacting the agents.

The crosslinking agent that can be used in the present invention is a polyfunctional compound having a divalent or higher functional group as represented by the following general formula.

General formula % Formula %) Here, n is an integer of 2 or more. R represents a linking group, and A represents a functional group shown below.

-N=C=○, -N=C=S, -C=C=O1-5O2CH=CH2, -COCH=CH2, -CH2C
H2X, -CH2,CH20SO3-1-CH2
CH2SSO3-1 -NHCH2CH2oso3-1 -C-X.

I ;1 -502X, -NHCCH2X.

-0CH2X, -COCH=CHX.

-3O2CH=CHX.

■ -CONHCH20H, -NHCH20H.

-NHCH20-, 5iX2, 5i(OH)2 However, in the above, X represents a halogen atom.

In the general formula, the linking group R represents a substituted or unsubstituted alkyl, alkenyl, or aryl group having a valence of two or more.

Specific examples of such divalent linking groups include (-CH2+ -CH2CH2- ml m2 -O(-CH2CH20+), where D is 10-1-S -1-C
Represents OO-2-OCO-1-CON-, p, ml, m
2 represents an integer from 0 to 10.

R1 represents a hydrogen atom or an alkyl group.

Specific examples of trivalent linking groups include -C0-N-C
H2COO- 13O2N-CH2Coo- H2O- CH3CH2C-CH20- H2O- 0-CH2CH2-0- 0=P-0-CH2CH2-0- 0-CH2CH2-0- where p represents an integer.

Specific examples of crosslinking agents that can be used in the present invention are shown below.

l II Eight Na C.N. 0.

C2H5-OC-0-COC2H5, In the present invention, these crosslinking agents and a hydrophobic polymer having an ester bond in the side chain are added to a solvent that does not dissolve the microporous filtration membrane in an amount of 0.1% to 20% by weight. The solution is dissolved within a range of 100% and applied to the microporous filtration membrane by impregnation. The solvent for dissolving the crosslinking agent and the hydrophobic polymer having an ester bond in the side chain is
Although it varies depending on the type of hydrophobic polymer having an ester bond, chlorinated hydrocarbons such as methylene chloride and ethylene chloride, ketones such as acetone and methyl ethyl ketone, and esters such as ethyl acetate and methyl formate are often used. In this case, the ratio of the hydrophobic polymer having an ester bond in the side chain and the crosslinking agent is 100 in terms of equivalent ratio.
In the present invention, the crosslinking reaction is caused by drying and heat curing at a temperature of 60° C. or higher.

In the present invention, it is also possible to coat a microporous filtration membrane with a hydrophobic polymer having an ester bond in its side chain, dry it, and then impregnate it with a crosslinking agent and then crosslink it by heating. The former is preferable from the viewpoint of process simplification and uniform crosslinking. In the above application, the degree of saponification required for a hydrophobic polymer having an ester bond in its side chain is 0.1% or more. If the degree of saponification becomes too high, for example, vinyl polymers tend to dissolve or swell in hot water (which is undesirable), and cellulose esters become insoluble in solvents, making coating difficult. Therefore, the preferred saponification degree varies depending on the type of polymer used, but for example, in the case of polyvinyl acetate, a saponification degree of 0.1% to 70% is preferred, and a saponification degree of 5% to 40% is particularly preferred. Cellulose acetate preferably has a saponification degree of 2% to 40%, particularly preferably 5% to 35%.

After a hydrophobic polymer having an ester bond in a side chain is applied onto a hydrophobic microporous membrane as described above and crosslinked to make it insoluble, a hydrophilic treatment is performed in the present invention. Methods for hydrophilic treatment in this case include glow discharge treatment, corona discharge treatment, dry treatment such as ozone treatment, and saponification treatment with acid or alkali. Treatment is preferred.

In the case of glow discharge treatment, JP-A-59-186604
of air or inert gas as described in No.
0.1 to 10,000 W −s in an atmosphere of 0.01 to 20 Torr
e c −crl (product of processing power density and processing time)
The purpose can be achieved by processing.

On the other hand, preferred saponification liquids include aqueous solutions containing 6% by weight or less of alkali metal hydroxides (e.g., NaOH, KOH, L1OH), or -valent alcohols (e.g., methanol,
(ethanol, isopropanol or tertiary butanol) f4 liquid or a mixed solution of water and alcohol. Particularly preferred is an alkali solution of 0.5% to 3% by weight.

The treatment time can be appropriately selected depending on the concentration and type of alkali used and the type of applied hydrophobic polymer having an ester bond in its side chain.

For example, when a 2% by weight NaOH aqueous solution at 23° C. is used, a treatment time of 0.5 to 15 minutes is appropriate for cellulose acetate, and a treatment time of 10 seconds to 2 minutes is appropriate for polyvinyl acetate.

(Function) If a hydrophobic polymer having an ester bond in the side chain is coated on the surface of a hydrophobic microporous filtration membrane in this way, and then chemically crosslinked and then subjected to hydrophilic treatment, the produced Even when the hydrophilic microporous filtration membrane is sterilized with hot water at 80° C. or saturated steam at 121° C., it produces almost no eluate and does not impair biological safety. In addition, since the hydrophilic treatment such as saponification of the present invention requires comparatively mild conditions, only the surface can be treated without deteriorating the physical properties such as the mechanical strength of the initially hydrophobic microporous membrane. It can be made hydrophilic. Furthermore, since the initial hydrophobic microporous glands and the hydrophilic membrane on the surface are essentially hydrophobic polymers, the adhesion between the two at the interface is good, and this can be achieved to the extent that it is possible in the present invention. It is not damaged even by hydrophilic treatment.

(Effects of the Invention) According to the method of the present invention, only the surface can be made hydrophilic without impairing physical properties such as mechanical strength, although it is an extremely easy method.

Furthermore, the obtained microporous membrane has extremely high biological safety, making the present invention extremely meaningful.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited thereto.

(Example) Example 1 100 g of polysulfone (trade name Needel P-3500) consisting of repeating units of 1° was mixed with 35 g of dimethylformamide
0 g, and 130 g of polyethylene glycol having an average molecular weight of 3,000 was added and also dissolved. This solution was cast onto a glass plate, and then the glass plate was immersed in water at 20°C.

The solidified membrane with micropores formed therein was further washed with water and then dried.

Even when the resulting membrane was gently floated on the surface of water, it exhibited perfect hydrophobicity and did not absorb any water.

Example 2 15% by weight of polyvinylidene fluoride (KF100O manufactured by Kureha Chemical Co., Ltd.) and 70% by weight of dimethylacetamide were mixed and dissolved, and polyoxyethylene sorbitan monoole (Ig) was added to 100g of this polymer solution. Next, this solution was cast onto a glass plate and immediately immersed in a tank filled with methanol to solidify it.

When the resulting membrane was gently floated on the surface of water, it exhibited complete hydrophobicity and did not absorb any water.

Example 3 40 g of polyvinyl acetate with a degree of saponification of 10% and Ig of hexamethylene diisocyanate were dissolved in 11 parts of methyl acetate. The polysulfone microporous filtration membrane used in Example 1 was immersed in this solution, and then heated for 10 minutes in an air constant temperature bath at 120°C. Then NaOH 1% by weight, methanol 1ON
%, treated in a solution of 89% water at 40°C for 2 minutes,
After neutralization with wt% acetic acid, the mixture was washed with water and dried.

When the microporous filtration membrane thus prepared was floated on the surface of water, it was found to be so hydrophilic that water almost instantaneously absorbed into the pores in the membrane. Further, no eluate was detected even when the sample was subjected to hot water treatment at 121°C in a pressure cooker.

Example 4 10 g of polyvinyl acetate with a degree of saponification of 35% and 0.5 g of diglycidyl ethylene glycol were dissolved in 11 methanol. The polyvinylidene fluoride microporous filtration membrane used in Example 2 was immersed in this solution, and then heated for 10 minutes in an air constant temperature bath at 135°C.

Thereafter, it was treated in a 2% by weight NaOH aqueous solution at 20° C. for 1 minute, neutralized with 1% by weight acetic acid, and then washed with water and dried.

When the microporous filtration membrane thus prepared was floated on the surface of water, it was found to be so hydrophilic that water almost instantaneously absorbed into the pores in the membrane. Further, no eluate was detected even when the sample was subjected to hot water treatment at 121°C in a pressure cooker.

Example 5 20 g of cellulose acetate having a degree of acetylation of 54% and 1 g of tolylene diisocyanate were dissolved in 11 acetone. The polysulfone microporous membrane used in Example 1 was immersed in this solution, and then heated for 10 minutes in an air constant temperature bath at 120°C. Then NaOH 1% by weight, methanol 10% by weight, water 89%
The sample was saponified in a 1% by weight solution at 40°C for 20 minutes, neutralized with 1% by weight acetic acid, washed with water and dried.

When the microporous membrane prepared in this way is floated on the water surface,
The membrane was so hydrophilic that water almost instantly absorbed into the pores in the membrane. Further, no eluate was detected even when the sample was subjected to hot water treatment at 121°C in a pressure cooker.

Example 6 Cellulose nitrate IQg with a degree of nitrification of 12% and 2.5 g of diglycidyl ethylene glycol were dissolved in 11 methanol. The polyvinylidene fluoride microporous filtration membrane used in Example 2 was immersed in this solution, and then heated for 10 minutes in an air constant temperature bath at 135°C. Thereafter, it was treated in a 2% by weight NaOH aqueous solution at 20° C. for 10 minutes, neutralized with 1% by weight acetic acid, and then washed with water and dried.

When the microporous filtration membrane thus prepared was floated on the surface of water, it was found to be so hydrophilic that water almost instantaneously absorbed into the pores in the membrane. Further, no eluate was detected even when the sample was subjected to hot water treatment at 121°C in a pressure cooker.

Example 7 20 g of cellulose acetate with a degree of acetylation of 54% and 1 g of hexamethylene diisocyanate were dissolved in IJ acetone. The polysulfone microporous filtration membrane used in Example 1 was immersed in this solution, and then heated for 10 minutes in an air constant temperature bath at 120°C. Thereafter, in air at 0°5 Torr, the frequency 1
A glow discharge treatment of 00KH2 was performed.

When the microporous filtration membrane thus prepared was floated on the surface of water, it was found to be so hydrophilic that water almost instantaneously absorbed into the pores in the membrane. Further, no eluate was detected even after hot water treatment at 121'C in a pressure cooker.

Claims (1)

[Claims] 1) A hydrophobic polymer having an ester bond in a side chain is dissolved in the solvent, and a hydrophobic microporous filtration membrane is impregnated with this solution, and then the hydrophobic polymer is chemically crosslinked. 1. A method for making a hydrophobic microporous filtration membrane hydrophilic, the method comprising making it insolubilized by the following steps and then performing a hydrophilic treatment. 2) The method for making a hydrophobic microporous filtration membrane hydrophilic according to claim 1, wherein the hydrophilic treatment is a saponification reaction. 3) The method for making a hydrophobic microporous filtration membrane hydrophilic according to claim 1, wherein the hydrophilic treatment is glow discharge. 4) Hydrophobic micropores according to any one of claims 1 to 3, wherein the hydrophobic polymer having an ester bond in a side chain is cellulose ester or polyvinyl acetate. A method for making a filtration membrane hydrophilic.