JPH06327950A - Filtration membrane for liquid its production and filter used therefor - Google Patents

Abstract

PURPOSE:To obtain a filtration membrane for liquid having high hydrophilic property and excelling in durability, chemical resistance, pressure resistance and heat resistance without necessitating air vent operation, and to obtain a filter using the membrane by intermingling a part which is continuously hydrophobic from the surface to the rear of a membrane and a part which is continuously hydrophilic from the surface to the rear of the membrane. CONSTITUTION:Narrow pores of a porous membrane are impregnated with a compound solution. During the impregnation, the membrane is shielded by using a shielding means which is preferably formed into a fixed pattern and irradiated with ultraviolet rays, so a part of F atoms of high molecular polymer porosity is replaced with hydrophilic radicals in an exposed part, and as a result, a filter membrane for liquid 1 having a hydrophilic part 2 and a hydrophobic part 3 is obtained. As an ultraviolet ray source, for example, a low voltage mercury lamp is used. The irradiation time is set in consideration of various factors, such as output, an irradiation distance, kinds and concentrations of compound water solutions and the form of a film, but it is normally about 20-30sec. The area ratio of the hydrophobic part 3 to the whole is preferably <=30%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid filtration membrane for use in microfiltration and ultrafiltration of liquids such as chemicals, foods and water, a method for producing the same and a filtration device.

[0002]

2. Description of the Related Art In microfiltration and ultrafiltration of liquids such as chemicals, foods and water, the removal performance of fine particles, permeation flux of liquids, chemical resistance, pressure resistance, heat resistance, etc. are important selections of filtration membranes. Is a factor. Therefore, conventionally, a porous film made of a fluororesin such as polytetrafluoroethylene (hereinafter abbreviated as PTFE) or polyvinylidene fluoride, or a high molecular polymer such as polyethylene, polypropylene or polyolefin has been selected.

However, in recent years, the need for a hydrophilic film has further increased. That is, for example, in the semiconductor industry, silicon wafers are washed with nitric acid, hydrofluoric acid, sulfuric acid, etc., but when the chemicals are replaced after circulating cleaning, the chemicals are discharged to remove air from the filtration cartridge filter. Flows in. Therefore, the PT in the filter
When air is brought into contact with the surface of a hydrophobic membrane such as an FE membrane, the effect of hydrophilic treatment of the membrane with an organic solvent when the filter is attached disappears. Is drastically reduced. Therefore, there is a problem that the liquid having a low surface tension must be made hydrophilic again.

As a method for making the fluororesin porous material hydrophilic, a method of applying a surfactant, or JP-A-56-6
As described in Japanese Patent No. 3772, a water-soluble polymer such as polyvinyl alcohol or polyethylene glycol is impregnated into pores of a porous body, and the polymer is heat-treated,
Acetalization treatment, esterification treatment, dichromic acid treatment,
A method of making hydrophilic by irradiation with ionizing radiation is known. Further, as disclosed in Japanese Patent Application Laid-Open No. 2-196834, a method is known in which surface modification of a fluororesin is irradiated with an ArF laser to make it hydrophilic.

[0005]

However, even when filtration is carried out using the hydrophilic membrane of the prior art described above, if the generated bubbles are present on the membrane surface, the bubble point (the bubbles permeate the wet membrane). At a pressure below the pressure at which the liquid starts to flow, air bubbles occur because air bubbles do not pass through the membrane, and the liquid permeation flux decreases. Therefore, it was necessary to frequently perform the air bleeding operation. In particular, when a foaming chemical such as hydrogen peroxide was used, the liquid permeation flux was remarkably lowered, and it was necessary to operate extremely frequently. Also, the bubble point depends on the pore size, porosity, bending rate, film thickness, etc. of the membrane, but since it is several kg / cm ² higher than the normal filtration operation pressure, it is practically necessary to operate above the bubble point. In addition, there is a problem that the piping and the device are expensive because they have high pressure specifications.

In order to solve the above-mentioned conventional problems, the present invention provides
An object of the present invention is to provide a liquid filtration membrane having high hydrophilicity, excellent durability, chemical resistance, pressure resistance, and heat resistance, which does not require air bleeding operation, a method for producing the same, and a filtration device using the same. And

[0007]

In order to achieve the above-mentioned object, a liquid filtration membrane of the present invention is a liquid filtration membrane using a hydrophobic high molecular weight polymer porous membrane, wherein It is characterized in that a portion which is continuously hydrophobic and a portion which is continuously hydrophilic from the film front surface to the film rear surface are mixed.

In the above structure, it is preferable that the high molecular polymer porous film is a fluorine-based high molecular polymer porous film. Further, in the above structure, it is preferable that the hydrophobic portion and the hydrophilic portion are formed in a predetermined pattern.

Next, the method for producing a liquid filtration membrane of the present invention is as follows.
A method for producing a filtration membrane for liquid using a hydrophobic high molecular weight polymer porous membrane, wherein the binding energy with F atom is 539 k.
The method is characterized in that a solution of a compound having J / mol or more atoms and a hydrophilic group is brought into contact with the high molecular weight polymer porous membrane, and then a part of the porous membrane is shielded to be irradiated with ultraviolet rays.

Next, a liquid filtration device incorporating the liquid filtration membrane of the present invention is a liquid filtration membrane using a hydrophobic high molecular weight polymer porous membrane, which is continuous from the membrane surface to the membrane back surface. The filter membrane for liquid in which the hydrophobic portion and the hydrophilic portion continuously from the membrane surface to the membrane rear surface are mixed is installed in the container.

[0011]

According to the above-described structure of the present invention, a portion which is continuously hydrophobic from the film surface to the film back surface and a portion which is continuously hydrophilic from the film surface to the film back surface are mixed. As a result, it is possible to provide a liquid filtration membrane that has high hydrophilicity, excellent durability, chemical resistance, pressure resistance, and heat resistance, and does not require air bleeding operation, and a filtration device using the same.

In the above structure, by covering a part of the film with a shield and subjecting it to plasma treatment, UV graft treatment, electron beam graft treatment, or the like, only that portion is continuously hydrophobic from the film front surface to the film back surface. While holding
It can be made hydrophilic.

Further, in the above constitution, from the viewpoint of chemical resistance and heat resistance, the high molecular polymer porous film is particularly a fluoro high molecular polymer porous film such as polytetrafluoroethylene or polyvinylidene fluoride. May be desirable.

Further, as a method for forming the hydrophilic portion and the hydrophobic portion, for example, in the case of a fluoropolymer porous film, F is used.
By contacting a solution of a compound having an atom with a binding energy with an atom of 539 kJ / mol or more and a hydrophilic group with a macromolecular polymer porous film, shielding a part of the porous film and irradiating with ultraviolet rays. However, only that portion can be made hydrophilic while continuously maintaining hydrophobicity from the film surface to the film back surface.

In the above constitution, an aqueous solution of an aluminum compound having a hydrophilic group, a boron compound having a hydrophilic group, or a lithium compound having a hydrophilic group is preferable.

In the above structure, it is preferable that the ultraviolet light source is a low pressure mercury lamp.

[0017]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the invention is not limited thereto.

The inventor of the present invention shields a part of the porous membrane to make it hydrophilic, so that only that portion of the porous membrane continuously becomes hydrophobic from the front surface to the back surface of the membrane while being made hydrophilic.
The present invention found that a high molecular polymer porous film having high hydrophilicity, excellent durability, chemical resistance, solvent resistance, heat resistance, adhesiveness, etc., and which does not require air bleeding operation can be obtained. Has been completed.

That is, in the method for producing a filtration membrane for a hydrophilic liquid according to the present invention, in the case of a fluoropolymer porous membrane, the binding energy with an F atom has an atom of 539 kJ / mol or more. After the solution of the compound is brought into contact with the high molecular weight polymer porous membrane, a part of it is shielded and ultraviolet rays are irradiated. The area irradiated with light was the C—F bond of the fluororesin (539 kJ /
mol) is cut off. Since the F atom has a large electronegativity of 4.0, the presence of an atom having an electronegativity smaller than that of the C atom (2.5) prevents C—F recombination. In addition, the binding energy between the atom and the F atom is C—F bond (539
If it is higher than kJ / mol), re-cutting becomes difficult. Therefore, a part of the F atoms of the macromolecular polymer porous membrane is replaced with the hydrophilic functional group. Since the portion that has been shielded continues to retain hydrophobicity from the membrane surface to the membrane back surface, a liquid filtration membrane having a hydrophilic portion and a hydrophobic portion can be obtained.

In the present invention, the fluorine-containing polymer porous film is usually PTFE, but in addition, for example, tetrafluoroethylene-hexafluoropropylene copolymer, ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene. It may be composed of a perfluoroalkylvinyl ether copolymer, a vinyl fluoride resin, a vinylidene fluoride resin, a trifluoroethylene chloride resin, or the like.

This high molecular weight polymer porous film is
It may have any shape such as a tongue shape or a tube shape, and either a baked product or an unbaked product can be used. The porosity and the pore diameter can be variously set according to the application, but usually the former is 20 to 80% and the latter is about 0.01 to 10 μm.
Is.

The polymer porous membrane can be obtained by various methods. For example, a PTFE membrane is disclosed in Japanese Examined Patent Publication Sho 58-25.
332, Japanese Patent Publication No. 51-18991, Japanese Patent Publication No. 42-13560, etc., or a method using a foaming agent described in Japanese Patent Publication No. 42-4974. it can.

The compound used in the present invention has a binding energy with an F atom of 539 kJ / mol or more and an electronegativity of less than 2.5 (aluminum (binding energy with an F atom: 671 kJ / mol, Electronegativity is 1.
5), boron (745 kJ / mol, 2.0), calcium (560 kJ / mol, 1.0), barium (58)
1 kJ / mol, 1.2), lithium (580 kJ / m)
Compounds such as aluminum hydroxide, boric acid, ammonium borate, lithium hydroxide, calcium hydroxide, barium hydroxide, etc. having a sol. Further, an alkali salt such as sodium hydroxide or potassium hydroxide may be added to increase the solubility of the solute.

In the method of the present invention, first, in the case of a fluoropolymer porous film, the compound aqueous solution is impregnated into the pores thereof. The fluoropolymer macroporous film may be used after being immersed in an organic solvent or subjected to ultrasonic cleaning in an organic solvent.

The impregnation of the aqueous solution of the compound into the pores of the fluoropolymer macromolecular porous membrane can be carried out by various methods, but the following method is preferred in consideration of the hydrophobic nature of the film. It is a thing. (1) (a) An organic solvent (methanol, ethanol, acetone, isopropyl alcohol) having excellent compatibility with water and having a surface tension of 30 dyne / cm or less is used as the fluoropolymer porous film. Etc.), and the first step of impregnating the solvent in the film. (B) Next, the second step of immersing this in water and replacing the solvent with water (water is impregnated into the pores). (C) After that, the porous membrane is immersed in the compound solution and water is replaced with the aqueous solution (the aqueous solution is impregnated into the pores).
Third step.

A method of impregnation through the above three steps. (2) By mixing the compound in an organic solvent having a low surface tension as described above to prepare a solution having a concentration of 30 dyne / cm or less, and coating, spraying, or immersing the porous polymer on the fluoropolymer. A method of impregnating the solution in the pores of a fluoropolymer macroporous membrane.

By the method as described above, the compound solution can be impregnated into the pores of the porous membrane. When a part of the high molecular polymer porous F atom is replaced with a hydrophilic group when a part of it is irradiated with ultraviolet rays in the next step while being impregnated with the aqueous solution, the exposed part has a hydrophilic part and a hydrophobic part. A membrane can be obtained.

The ultraviolet light source may be a low pressure mercury lamp, a high pressure mercury lamp, a metal halide lamp, or the like, which uses a bright line with a photon energy of 539 kJ / mol or more, so that the C—F bond can be cleaved and replaced with a hydrophilic group. A low pressure mercury lamp can be preferably used. The irradiation time is set in consideration of various factors such as output, irradiation distance, type of compound aqueous solution, concentration, film shape, etc., but is usually about 20 seconds to 30 minutes.

The patterns of the hydrophilic part and the hydrophobic part are shown in FIG.
As shown in (i), it can be formed in a linear shape, an oblique line shape, a wavy line shape, a grid shape, a mosaic shape, a sea-island shape, a dot shape, or the like. Since the permeation flux decreases when the hydrophobic portion becomes large, the area ratio of the hydrophobic portion is preferably 30% or less of the whole. Further, it is desirable that the hydrophobic part is located at the upper part where bubbles are accumulated in the filtering device.

As described above, when the compound solution is impregnated into the pores of the porous film, the compound solution is shielded by the shielding means preferably formed in a certain pattern during the impregnation, and the compound is irradiated with ultraviolet rays,
In the exposed part, a part of the F atom of the polymer macromolecule is replaced with the hydrophilic group, so that the liquid filtration membrane 1 having the hydrophilic part 2 and the hydrophobic part 3 can be obtained.

Further, the cartridge filter obtained by processing the hydrophilic liquid filtration membrane obtained as described above into, for example, a disc shape or a pleat shape, adhering it to a support and incorporating it into a container. Alternatively, a filtration device such as a plate type module or a hollow fiber membrane module which is supported by a plate and a frame in a flat membrane state can be used.

The present invention will be described in more detail with reference to specific examples. (Example 1) Thickness 60 μm, pore diameter 0.1 μm, porosity 7
A PTFE porous membrane of 5% in length and width of 10 cm was immersed in methanol and water for 10 minutes each, and then in a compound aqueous solution for 10 minutes to impregnate the pores with the compound aqueous solution. Here, a 4.1% by weight aqueous boric acid solution was used as the compound aqueous solution. Place the thick paper (the pattern of Fig. 1 (e), the diameter of the white circles is about 0.5 cm, the spacing is about 2 cm) on the film in the state of being impregnated with the aqueous solution to shield the light and output 50 W.
After irradiating the low-pressure mercury lamp of No. 2 for 60 seconds, it was washed with pure water and dried to obtain a filter membrane for hydrophilic liquid, 1 part of which was hydrophobic. When this membrane was immersed in pure water, it quickly absorbed water except for the hydrophobic portion.
Furthermore, the surface analysis of the hydrophilized portion of this film by ESCA revealed that the O / C ratio before hydrophilization treatment was 0 (zero).
On the other hand, it was 0.18 after the hydrophilic treatment. Also, F /
Since the C values were 2.0 and 0.28, respectively, it could be confirmed that the F atom was replaced with the hydrophilic group. In addition, when a waveform analysis was performed, C of --CF ₂ -bond (292 eV) was observed.
When the number of atoms is 100, a -CO- bond (286e
V) was 81 and the —C═O (288 eV) bond was 18, confirming the presence of hydrophilic functional groups. Prior to treatment, these functional groups were absent.

This film was treated with hydrofluoric acid (50%) and hydrochloric acid (36%).
%) And sulfuric acid (97%) were kept hydrophilic even after 1 day of immersion at room temperature. Also, wash with ethanol and acetone,
It remained hydrophilic even after drying.

A pressure of 2 kg / c is applied to the hydrophilic liquid filtration membrane.
m²Under cyclic pressurization of NH_FourOH: H ₂O₂: H₂O =
When the solution of 1: 1: 5 was subjected to the permeation test, the initial permeation
Flux is 12.2 cm³/ Cm²/ Min, 30 minutes
After that, 12.0 cm³/ Cm₂It was / min.

(Comparative Example 1) Hydrophilization treatment was carried out in the same manner as in Example 1 except that shielding was not carried out to obtain a hydrophilization film having no hydrophobic portion. When the same evaluation experiment as in Example 1 was performed,
The initial permeation flux was 13.0 cm ³ / cm ² / min, but it did not permeate after 30 minutes.

(Example 2) The same pattern paper shield as in Example 1 was attached to a polypropylene film and set in the plasma processing apparatus, and adjusted to 0.8 Pa to 13.5.
The product of high frequency power density and processing time is 15.6W at 6MHz
-The surface was made hydrophilic by oxygen plasma treatment so that it became sec / cm ² . The same solution as in Example 1 was used, and the pressure was 0.
When subjected to a permeation test under a circulating pressure of ² kg / cm ^2, the solution permeated even after 30 minutes.

(Comparative Example 2) A hydrophilic treatment was carried out in the same manner as in Example 2 except that the shielding was not performed, and the hydrophilic membrane having no hydrophobic portion did not allow the solution to permeate after 30 minutes.

(Example 3) As in Example 1, a shield was attached to a polyethylene film, and an electron beam accelerator was used to
Under the conditions of an accelerating voltage of 2 million volts and a beam current of 20 milliamperes, an electron beam of 20 megarads is irradiated in the air, and then immersed in a 30 wt% methanol solution of methacrylic acid and graft polymerized at 70 ° C. went. When the same solution as in Example 1 was subjected to a permeation test under a circulating pressure of 0.2 kg / cm ² , the solution permeated even after 30 minutes.

(Comparative Example 3) A hydrophilic treatment was carried out in the same manner as in Example 3 except that the shielding was not performed. The solution did not permeate the hydrophilic membrane having no hydrophobic portion after 30 minutes.

[0040]

As described above, according to the present invention, a part of the high molecular polymer porous membrane is continuously hydrophobic from the membrane surface to the membrane back surface, has high hydrophilicity and excellent durability, Provided are a macromolecular polymer porous membrane which is excellent in chemical resistance, solvent resistance, heat resistance, adhesiveness, etc., and which does not require an operation for removing air generated in the process of filtering a liquid, and an apparatus incorporating the same. can do.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of patterns of a hydrophilic portion and a hydrophobic portion of a liquid filtration membrane according to an embodiment of the present invention.

[Explanation of symbols]

 1 Filter Membrane for Liquid 2 Hydrophilic Part 3 Hydrophobic Part

Claims (5)

[Claims] 1. A filtration membrane for liquid using a hydrophobic high molecular weight polymer porous membrane, wherein a hydrophobic portion is continuously provided from the membrane surface to the back surface and a membrane portion is continuously provided from the membrane surface to the back surface. A filtration membrane for liquid, wherein a hydrophilic portion is mixed. 2. The filtration membrane for liquid according to claim 1, wherein the high molecular polymer porous membrane is a fluorine-based high molecular polymer porous membrane. 3. The liquid filtration membrane according to claim 1, wherein the hydrophobic portion and the hydrophilic portion are formed in a predetermined pattern. 4. A method for producing a filtration membrane for liquid using a hydrophobic high molecular weight polymer porous membrane, which is a solution of an atom having a binding energy with an F atom of 539 kJ / mol or more and a compound having a hydrophilic group. Is contacted with the high molecular weight polymer porous membrane, and then a part of the porous membrane is shielded to be irradiated with ultraviolet rays. 5. A filtration membrane for liquid using a hydrophobic high molecular weight polymer porous membrane, wherein a hydrophobic portion is continuously provided from the membrane surface to the back surface and a membrane portion is continuously provided from the membrane surface to the back surface. A liquid filtration device in which a liquid filtration membrane in which a hydrophilic portion is mixed is mounted in a container.