JPH0312225A - Hydrophilic porous film and its manufacture - Google Patents

Abstract

PURPOSE:To manufacture a subject film of hydrophilic properties, easy to handle and useful for water treatment field and the like without lowering water permeation performance by adhering a copolymer containing three components, ethylene, vinyl alcohol and one other component each of specified volumes. CONSTITUTION:A copolymer composed of three components or more in the range of 0.125-0.75 of b/(a+b) when the content of ethylene is specified at least 20mol% or more, the content of vinyl alcohol ((b)mol%) is at least 10mol% or more and the content of one component or more other than ethylene or vinyl alcohol (preferably vinyl acetate) is (a)mol% is retained on the micro-pore surfaces at least partially on a polyolefin porous film to manufacture a hydrophilic porous film. As the process of adhering this copolymer on the surface of said porous film the immersing process in which the copolymer is preferably dissolved in a mixed solvent composed of ethanol and water, made in the state of solvent, adhered, dried and fixed on the surface is preferred.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a hydrophilized polyolefin porous membrane used in water treatment fields such as water purification and industrial fields, and a method for producing the same.

(Prior Art) Polyolefin porous membranes are used in a variety of industrial fields such as the medical field, semiconductor field, and water purification system due to the chemical stability of their substrates.

However, the polyolefin porous membrane is hydrophobic, and it is impossible for an aqueous liquid to pass through it as it is.Therefore, in order to allow an aqueous liquid to pass through it, it is necessary to make the polyolefin porous membrane hydrophilic.

As a method for converting polyolefin porous membranes into water, there is a
Select the hydrophilic agent from the viewpoint of hydrophobic-hydrophilic balance,
A method of forming a thin M of ethylene-vinyl acedate copolymer on a polyolefin porous membrane and then saponifying it for the purpose of imparting adhesive properties and permanent hydrophilicity to the polyolefin porous membrane ( Japanese Patent Publication No. 61-125
408) and a method of coating with an ethylene-vinyl alcohol copolymer (Japanese Unexamined Patent Publication No. 61-271005) have been proposed.

[Problem that the invention attempts to solve]

However, in the former method, the process is complicated because the ethylene-vinyl acetate-1 copolymer is attached to the poly-1/fin porous membrane and then saponified to convert the vinyl acetate into vinyl alcohol. In particular, there is a problem in that the reaction products and alkaline solution remaining in the vicinity of the porous pores must be sufficiently washed away. In the case of the latter method, ethylene-vinyl alcohol is mixed with a water-miscible organic solvent and water.
Dissolved polyolefin porous 'J! Hydrophilicity can be imparted simply by adhering and drying the copolymer, but when using ethanol as a water-miscible organic solvent, it is necessary to maintain the copolymer at a temperature higher than SaC or to remove it from the outside. There was a problem in terms of workability. In addition, when using dimethyl sulfoxide as a water-miscible organic solvent, it is possible to process at room temperature, but dimethyl sulfoxide has a lower vapor pressure than ethanol and requires a longer drying process to remove the solvent. It is very difficult to remove dimethyl sulfoxide incorporated into the copolymer, and even if sufficient drying is performed, dimethyl sulfoxide may remain. When used in a water purifier for drinking water, dimethyl sulfoxide is eluted during filtration, that is, into the drinking water, which poses a safety problem.

The purpose of the present invention is to provide a polyolefin porous membrane that is a thin film of a hydrophilic polymer that does not require any special pretreatment, can be easily handled at around room temperature, is permanent, and is safe in terms of eluates. The present invention provides a hydrophilized poly first/fin porous IL' membrane held on the micropore surface of the present invention, and a method for producing the same.

(Rounding means to solve problems) The gist of the present invention is that the content of ethyl alcohol is at least 20 moles or more, and the amount of i(b mole)Q...' containing hinyl alcohol is at least 10 moles. b when the mole is 6 or more, and the vinyl alcohol content is ethyl/1% or more, and the vinyl alcohol content is mol.
A copolymer consisting of three or more components in which / (e, 10b) is in the range of α125 = 0.75 is retained on the surface of at least a portion of the pores of the 17th fin porous membrane. Further, the polyolefin porous membrane is treated with a core copolymer bath solution by dissolving the copolymer in a solvent miscible with a water-miscible organic solvent and water, and then drying. There is a method for producing a hydrophilic porous membrane characterized by:

The polyolefin material constituting the polyolefin porous membrane of the present invention is mainly composed of one or more monomers selected from the group consisting of ethylene, propylene, 4-methyl-1-pentene, and 5-methyl-1-butene. Polymers or copolymers (8) These include fluorine compounds.

The porous membrane of the present invention can be in any form, such as a hollow fiber membrane, a flat membrane, or a tubular membrane, and can have various pore sizes depending on the purpose. As a preferable example, the film thickness is about 20 to 200 μm,
Porosity is about 20-904, pore diameter is 0.01-
Examples include those with a diameter of about 5 μm.

Porous membranes can be made with pores that can be obtained by various methods, including melt-forming and stretching, or melt-forming by mixing inorganic substances or esters, and then extracting the contaminants. Among them, porous membranes obtained by a method of melt-forming and then stretching (stretching method) are preferred because they have a large porosity, have little performance deterioration due to clogging, and do not contain contaminants. is preferred. A porous membrane produced by the stretching method is a porous membrane having a pore structure in which slit-shaped micro spaces (pores) formed by microfibrils, nodes, and K are three-dimensionally interconnected.
For example, Japanese Patent Publication No. 56-52125, Japanese Patent Publication No. 57-4
It can be manufactured by the method described in Japanese Patent No. 2919 and the like.

Further, as for the shape of the porous membrane, a hollow fiber type is preferable because the membrane area per unit volume is large.

In the hydrophilized porous membrane trap of the present invention, at least a portion of the surface of the porous membrane on which the copolymer is retained refers to the pore surface and a portion or all of the outer surface. That is, it is sufficient that the copolymer is held in such a way that its hydrophilicity is substantially improved.
It is not necessary that the copolymer be retained on all surfaces.

Retained means that the copolymer is firmly bonded or adhered to the pore surface to such an extent that it does not easily come off during storage or use.

In particular, if a porous membrane made porous by the above-mentioned stretching method is used, the copolymer can be firmly held by wrapping the microfibrils. The copolymer consisting of 5 or more components including an adhesion alcohol may be any type of copolymer such as random, block, or graft. If the ethylene content in the copolymer is less than 20 molar percentages, the adhesion of the copolymer to the polyolefin is generally insufficient and peeling may occur, which is not preferred.

In addition, if the vinyl alcohol content is less than 10 molar units, the polyolefin porous membrane will not exhibit sufficient hydrophilicity, which is undesirable.On the other hand, in order to develop even better hydrophilicity, it is particularly preferable to adjust the vinyl alcohol content to 20 molar units or more. preferable.

By the way, the method of adhering the copolymer to the pore surface and outer surface of the polyolefin porous membrane is not particularly limited, and may include a method of spraying the copolymer solution with an air gun, a roll coater or a calendar. Among them, a dipping method is particularly suitable for uniformly fixing a thin film of the copolymer onto the pore surface of the polyolefin porous membrane.

In either method, the copolymer is used in the form of a solution, and from the viewpoint of workability, it is preferable to maintain the dissolved state at a temperature around room temperature. The term "near room temperature" as used herein refers to approximately 30°C to 10°C.

From this point of view, as a result of intensive studies on ethylene-vinyl alcohol copolymers, we found that the solubility properties of ethylene-vinyl alcohol copolymers change significantly when vinyl alcohol is added as a copolymer component in an amount greater than ethylene and vinyl alcohol. This book was based on the discovery that when the content of the components is within a specific range between the content of vinyl alcohol and the content of vinyl alcohol, the dissolution state can be maintained at around room temperature in a specific solvent, leading to the present invention.

That is, under the conditions that the ethylene content is 20 mol or more and the vinyl alcohol content (b mol 4) is 10 mol or more, when ethylene and bi% or more and the vinyl alcohol content is a mol width, b / (a-4 -b) to (Ll 25~(L
More preferably 11!5 than K in the 750 range
When the range is from 0 to (175), it is possible to maintain a dissolved state near room temperature.

Examples of compounds used as ethylene and vinyl alcohol include vinyl acetate, acrylic acid, methacrylic acid, acrylic esters, methacrylic esters, vinyl compounds in fatty acid esters of vinyl alcohol, and vinyl alcohol. Examples include marled or butyralized ones, and it is sufficient if one or more of these are contained, but a particularly preferred component is vinyl acetate.

As the solvent for the core copolymer used in the present invention, a mixed solvent of a water-miscible organic solvent and water is particularly preferable, and examples of the water-miscible organic solvent include alcohols such as methanol, ethanol, n-propanol, and isopropyl alcohol. , dimethyl sulfoxide, dimethyl formamide, etc., but ethanol is particularly preferred from the viewpoint of ease of solvent removal in the drying process and low toxicity to the human body. By using an ethanol/water miscible system as a solvent, the copolymer solution is stable even at room temperature and has excellent workability.

When the ratio 'b/(a + b) is outside the range of the present invention, the copolymer swells or dissolves in an ethanol/water miscible solvent when heated, but precipitates at room temperature, so it is preferable. The mixing ratio of ethanol and water is
The ethanol/water ratio may vary depending on the component ratio of the copolymer used, but the ethanol/water ratio may be 90/90 as long as it does not impede the permeability into the polyolefin and the solubility of the copolymer near room temperature. A vot width of 10 to 50,150 is preferred.

The concentration of the copolymer solution is usually about 01 to 10% by weight, preferably about 5 to 5% by weight. The concentration is [
If it is less than 1196, it is difficult to obtain a retaining layer with a uniform thickness, and if it exceeds 100 parts by weight, the solution viscosity will become too large and the polyolefin porous membrane will be adhered by clogging the micropores. This is not preferable because the filtration properties of the membrane deteriorate. In addition, in the present invention, as a method of attaching the copolymer solution, two copolymer solutions of the same concentration are used.
It may be carried out more than once, or it may be carried out two or more times using solutions with different concentrations.6 The amount of the copolymer retained on the polyolefin porous membrane as the base material is approximately 1% from the viewpoint of filtration properties.
-40 weight range, preferably 5-30 weight range.

The copolymer solution attached to the polyolefin porous membrane is
It can be dried by a known drying method such as vacuum drying or hot air drying. The drying temperature may be any temperature at which the polyolefin porous membrane does not undergo deformation due to heat, for example,
In the case of a polyethylene porous membrane, the copolymer can be uniformly fixed on the outer surface and the inner surface of the micropores of the porous membrane by heating and drying at a temperature of 120° C. or lower.

(Example) Hereinafter, the present invention will be explained by examples.

Examples 1 to 5 A saponification reaction of 20 t of ethylene-vinyl acetate copolymer was carried out in 500 methanol at 45° C. with stirring using a caustic soda catalyst (α12 t), and a poor solvent was added to precipitate the saponified product. Washed and dried. The ethylene content of the ethylene-vinyl acetate copolymer used was 27.5 mol, 30
It was 0 mole tatami mat 548 mole. By changing the saponification time, ethylene-vinyl alcohol-vinyl acetate copolymers having different content ratios of vinyl alcohol to vinyl acetate were obtained. The vinyl acetate content in the copolymer is J
Determined in accordance with Technical Standards 13K 6730.

1 part by weight of the copolymer was mixed with ethanol/water (70/50
vot4) Dissolved in 99 parts by weight under heating and heated to 25°C.
The stability of the solution was judged by its turbidity.

Polyethylene porous hollow fiber membrane (manufactured by San-ai Iyon ■, ff
1HIF-270T, inner diameter 270 pm, outer diameter 380μ
m) was immersed in the copolymer solution 11C for 5 minutes, and then heated to 60°C.
The solvent was removed by drying with hot air for 3 hours, and the amount of the copolymer retained was determined.

A membrane module with an effective membrane area of 70 cm was fabricated by bundling 100 of these hollow fiber membranes and hardening the ends with urethane resin.

A water pressure of 'kg/cIn' was applied to this membrane module to filter water, the amount of water permeated at that time was measured, and then 5 tons of water was permeated at a water pressure of 1 kg/α8 and then completely dried.This water filtration, After drying 10 times, water pressure 1k
The water permeability was measured at 1/cps"K.

The above results are shown in Table 1. Table 1 shows that the ethanol/aqueous solution of the copolymer is stable at room temperature, and the module exhibits high water permeability and is durable.

In any of the Examples, the copolymer was applied to the entire surface of the fl pores of the hollow fiber membrane. It stuck evenly.

Examples 6 to 8 Using the copolymer used in Example 3, 1ir-J14 solutions of the copolymer were prepared by changing the mixing ratio of ethanol/water, and allowed to cool to about 30°C. Membrane modules were manufactured by the method described in Examples 1 to 5, and the amount of water permeation was measured.6 As shown in Table 2, the solution was stable even when the mixing ratio of ethanol/water was changed, and showed high water permeability. .

Table 2 Comparative Example 1 The same method as in Example 1 was carried out using an ethylene-vinyl acetate copolymer with an ethylene content of 30 mol. 1-functional ethylene content of 30 mol, vinyl alcohol 59.7 mol 4 (b) ,
Vinyl acetate 1 α 3 mol 4 (a), b/(a-+1)
A copolymer of -a85 was obtained. This copolymer was dissolved in a mixed solvent of ethanol/water (90/10.80/20.7, respectively).
0/30.60/40 or 50/50 vol
4) was dissolved under heating to a concentration of 1 wt. 4, and allowed to cool to around room temperature. Even in the ethanol/water solvent system of bt", there was a clouding phenomenon, and precipitation of the copolymer was observed. However, the stability of the solution at room temperature was not observed.

Comparative Example 2 Ethylene-vinyl alcohol copolymer with an ethylene content of 27.6 mol and a saponification rate of 99 or higher (b/
(a + b) = 099 or more) to ethanol/water (
75/25 vol4) K After heating and dissolving the copolymer at 70°C so that 1 weight is 1, when it is left to cool, the solution starts to become cloudy at a temperature lower than the liquid temperature of 50°C, and 3
At 0°C, complete cloudiness occurred and precipitation of the copolymer was observed.

(Effects of the Invention) The hydrophilized porous membrane of the present invention has good water wettability, and even after repeated water permeation drying, no decrease in water permeability is observed, making it a porous membrane endowed with durable hydrophilic properties. be. Further, in the method of the present invention, since a hydrophilic agent having good solution stability at room temperature is used, the hydrophilic treatment of the polyolefin porous membrane can be uniformly and reliably performed.

Claims (1)

[Scope of Claims] 1) When the ethylene content is at least 20 mol% or more, the vinyl alcohol content (b mol%) is at least 10 mol% or more, and the content of components other than ethylene and vinyl alcohol is a mol%. b/(a+b) of Q125~
1. A hydrophilic porous membrane comprising a copolymer comprising three or more components having a molecular weight of 0.75 or more and held on the surface of at least some pores of a polyolefin porous membrane. 2) The hydrophilized porous membrane according to claim 1, wherein the polyolefin porous membrane is made porous by a stretching method. 3) The hydrophilized porous membrane according to claim 2, wherein the component other than ethylene and vinyl alcohol in the copolymer is vinyl acetate. 4) b/(a+b) where the ethylene content is at least 20 mol% or more, the vinyl alcohol content (b mol%) is at least 10 mol% or more, and the content of components other than ethylene and vinyl alcohol is a mol%. is 0.125
A copolymer consisting of three or more components in the range of ~0.75 is dissolved in a mixed solvent of a water-miscible organic solvent and water, and a polyolefin porous membrane is treated with the copolymer solution and then dried. Characteristic manufacturing method of hydrophilic porous membrane. 5) The method according to claim 4, wherein the water-miscible organic solvent is ethanol.