JP3385755B2 - Hydrophilic membrane and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrophilizing membrane obtained by retaining a vinyl acetal copolymer containing a vinyl acetal unit and a hydrophilic monomer unit on a hydrophobic porous membrane.

[0002]

2. Description of the Related Art Hydrophobic porous membranes represented by polyolefins have advantages such as high chemical stability and are used in fields such as separation and purification of water or aqueous solutions, treatment, and medical fields. . However, since it has a poor affinity with water as it is, it must be hydrophilized in advance when it is used for treating water or an aqueous solution. As a method for hydrophilizing the hydrophobic porous membrane, for example, alcohol,
There is a method in which the outer surface of the hydrophobic porous membrane and the inner surfaces of the fine pores are wet-treated with an organic solvent such as a ketone, and then the organic solvent is replaced with water. In addition, there is also a method of hydrophilization by holding a hydrophilizing agent such as a water-soluble hydrophilic polymer or a surfactant on the surface of the hydrophobic porous membrane.

[0003]

However, in the method of hydrophilizing with an organic solvent, it is necessary to keep the hydrophobic porous membrane in a wet state at all times, and the maintenance thereof is complicated. Further, in the method of hydrophilizing with a water-soluble hydrophilic polymer, the hydrophilizing agent held on the surface of the pores dissolves in water, and the porous membrane in such a state loses hydrophilicity once dried, It is not preferable in such applications. The hydrophilic method using a surfactant has a problem that it is likely to be eluted into water and that it is easily assimilated by various bacteria. The present invention aims to solve these problems.

[0004]

Means for Solving the Problems As a method for improving these problems, the present inventors have found that a polymer having a hydrophilic portion, having an affinity for a membrane component resin, and having a hydrophobic property. A compound that does not easily elute into the water to be treated when retained on the porous membrane is selected in consideration of the hydrophilic-hydrophobic balance, and the method for adhering and retaining it on the surface of the micropores of the porous membrane is earnestly studied. As a result, the present invention has been completed.

According to the present invention, in a membrane made of a hydrophobic thermoplastic resin having at least a part of fine pores communicating from one side to the other side, hydrophilic monomer units are contained in an amount of 35 to 90.
The present invention relates to a hydrophilized film characterized in that a water-insoluble vinyl acetal-based copolymer containing mol% is adhered and held on at least a part of the film having the fine pores to impart hydrophilicity. Furthermore, in communication with the other side from the one surface prior to applying the hydrophilic
Hydrophobic thermoplastic with at least some micropores in it
Even if a film made of resin is applied with a water pressure of 1 kg / cm ² ,
A film but does not transmit, the hydrophobic thermoplastic resin is poly <br/> ethylene, polypropylene, polyfluoroethylene, polyacrylonitrile, polyethylene terephthalate, polysulfone, at least one substance selected from polyamide and polyimide, or 2 The vinyl acetal-based copolymer, which is a copolymer of two or more kinds or a mixture of two or more kinds, has 1 to 6 carbon atoms in the alkyl group of the vinyl acetal ring, and the vinyl acetal copolymer is a single kind or two or more kinds. Of the vinyl acetal-based copolymer, wherein the vinyl group of the vinyl acetal ring has a methyl group, an ethyl group, a normal propyl group, an isopropyl group, and a phenyl group, and a hydrophilic monomer unit of 35 ~ 90 moles
% Including water-insoluble vinyl acetal copolymer alcohols, ketones, aromatic solvents, or a mixed solvent thereof, or a material obtained by dissolving in a water solvent with the immersion liquid, communicating from one surface to another surface Hydrophobic with fine pores
A film made of a thermoplastic resin is immersed, and a method for producing a hydrophilic film, characterized in that the vinyl acetal-based copolymer is adhered to and held in at least a part of the fine pores, wherein the solvent is methyl alcohol or ethyl alcohol. , A mixture of two or more of isopropyl alcohol and acetone, or a water-containing solvent thereof, wherein the vinyl acetal-based copolymer has a vinyl acetal ring whose alkyl group has 1 to 6 carbon atoms, and the vinyl acetal copolymer Method for producing a hydrophilic film in which the polymer is a single or a mixture of two or more and the alkyl group of the vinyl acetal ring of the vinyl acetal copolymer is a methyl group, an ethyl group, a normal propyl group, an isopropyl group and a phenyl group Regarding

As the hydrophobic porous membrane in the present invention,
Any form such as a hollow fiber membrane, a flat membrane, or a tubular membrane can be used. The material of the hydrophobic porous membrane is the above-mentioned monomer or copolymer such as polyethylene.

The vinyl acetal copolymer used in the present invention is represented by the following general formula:

[Chemical 1] In the formula, R = C _{1 to} C ₆ alkyl group and phenyl group, preferably CH ₃ , C ₂ H ₅ , C ₃ H ₇ and C ₆ H ₅ , and 1 + m = 10 to 65 mol%, n = 35. ~ 90 mol%
Is. If n, which is the hydrophilic monomer unit, is less than 35 mol%, sufficient hydrophilicity cannot be imparted, and if it exceeds 90 wt%, the polymer becomes water-soluble, which is not preferable.

A vinyl acetal-based copolymer is used as a single or mixed solvent of alcohol-based, acetone-based and aromatic-based solvents, or a water-containing solvent thereof, preferably one or two of methyl alcohol, ethyl alcohol, isopropyl alcohol or acetone. A dipping solution is prepared by dissolving it in a mixture of at least one kind or a hydrous material thereof. The concentration of the immersion liquid is preferably 0.5 to 5% by weight. When the immersion liquid has a high viscosity at room temperature, the immersion treatment can be performed by appropriately heating to reduce the viscosity of the immersion liquid. Next, the hydrophobic porous membrane is dipped, and the solution is sufficiently spread even in the through-holes of the membrane, and then dried to remove the solvent. As a drying means, an ordinary method such as air drying, reduced pressure drying, and heat drying can be appropriately used depending on the type of solvent.

The carrying rate showing the amount of the hydrophilizing agent on the membrane is expressed by the following formula, and the carrying rate of the hydrophilizing agent in the present invention is 5 to 40.
Weight percent is preferred. Carrying rate (% by weight) = [amount of hydrophilizing agent (g) / weight of hydrophobic yarn (g)] × 100

[0010]

EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples.

Example 1 2 parts by weight of a vinyl acetal copolymer having 72 mol% of a hydrophilic monomer part was mixed with 100 parts of ethanol-water (90:10).
A polypropylene porous hollow fiber membrane [manufactured by Ube Industries, Ltd., average pore diameter 0.3 μm]
m, porosity 70%] was immersed for 30 seconds. Then, the solvent was removed by air drying to obtain a hydrophilic film having a supporting rate of 25% by weight. 100 of the hydrophilically treated hollow fiber membranes were bundled and the ends were fixed with urethane resin to prepare a membrane module having an effective area of 100 cm ² . Water pressure of 1kg for this membrane module
/ Over cm ² where the water was filtered, water permeation rate is 60c
It was c / m ² · min and showed excellent water permeability. Further, even after passing 5 liters of water at a water pressure of 1 kg / cm ² and completely drying the membrane module, no decrease in water permeability was observed.

COMPARATIVE EXAMPLE 1 A polypropylene porous hollow fiber membrane similar to that used in Example 1 was used to prepare a membrane module similar to that of Example 1 without hydrophilizing the same, and water was filtered. I tried, but the water did not penetrate at all.

Comparative Example 2 A membrane module was evaluated in the same manner as in Example 1 except that a vinyl acetal copolymer having a hydrophilic monomer portion of 30 mol% was used, but no water was permeated. .

Example 2 The immersion liquid used in Example 1 was kept at 60 ° C. and subjected to the same hydrophilic treatment as in Example 1. As a result of water permeability evaluation by the same membrane module as in Example 1, 65 cc / m ² · min
The water permeability of

[0015]

EFFECT OF THE INVENTION The hydrophilized polyolefin porous membrane of the present invention is a porous membrane having durable hydrophilicity with no decrease in water permeability even when the porous membrane is dried after filtration. .

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) B01D 67/00-71/82 510 C02F 1/44

Claims (9)

(57) [Claims] 1. A film made of a hydrophobic thermoplastic resin having at least a part of micropores communicating from one surface to the other surface, and containing 35 to 90 mol% of hydrophilic monomer units.
A hydrophilic film, wherein a water-insoluble vinyl acetal-based copolymer is attached and held on at least a part of the film having the fine pores to impart hydrophilicity thereto. 2. From one surface before imparting hydrophilicity to the other surface.
Hydrophobic heat with through holes at least in part
A film made of plastic resin is applied with a water pressure of 1 kg / cm ^2.
A membrane that is impermeable to water even if
The hydrophilicized film described. 3. The hydrophobic thermoplastic resin is at least one substance selected from polyethylene, polypropylene, polyfluoroethylene, polyacrylonitrile, polyethylene terephthalate, polysulfone, polyamide and polyimide, or two or more copolymers or 2. The hydrophilic film according to claim 1, which is a mixture of two or more kinds. 4. The vinyl acetal-based copolymer, wherein the alkyl group of the vinyl acetal ring has 1 to 6 carbon atoms, and the vinyl acetal copolymer is used alone or as a mixture of two or more kinds. Hydrophilized film of either. 5. The hydrophilized film according to claim 1, wherein the alkyl group of the vinyl acetal ring of the vinyl acetal copolymer is a methyl group, an ethyl group, a normal propyl group, an isopropyl group or a phenyl group. 6. Containing 35 to 90 mol% of a hydrophilic monomer unit.
No water-insoluble vinyl acetal copolymer alcohols, ketones, aromatic solvents, or a mixed solvent thereof,
Alternatively, a solution obtained by dissolving it in a water-containing solvent is used as an immersion liquid, and a film made of a hydrophobic thermoplastic resin having fine pores communicating from one side to the other side is immersed, and the vinyl acetal is at least partially contained in the fine pores. A method for producing a hydrophilic film, characterized in that a base copolymer is attached and held. 7. The method for producing a hydrophilized film according to claim 6, wherein the solvent is one or a mixture of two or more of methyl alcohol, ethyl alcohol, isopropyl alcohol and acetone, or a water-containing solvent thereof. 8. The vinyl acetal-based copolymer, wherein the vinyl group of the vinyl acetal ring has 1 to 6 carbon atoms, and the vinyl acetal copolymer is used alone or as a mixture of two or more kinds. A method for producing a hydrophilic film according to any one of 1. 9. The method for producing a hydrophilic film according to claim 8, wherein the alkyl group of the vinyl acetal ring of the vinyl acetal copolymer is a methyl group, an ethyl group, a normal propyl group, an isopropyl group or a phenyl group.