JPH073057A - Method for producing hydrophilic fluororesin film - Google Patents

Abstract

(57) [Abstract] [Purpose] In the presence of a specific compound, the fluorine resin film is irradiated with ultraviolet rays to replace the fluorine atom with a hydrophilic group, resulting in high hydrophilicity and excellent durability and chemical resistance. , A hydrophilic fluororesin film excellent in solvent resistance, heat resistance, etc. is manufactured at low cost. [Structure] A fluororesin film is contacted with or impregnated with a solution of a compound having a binding atom with a fluorine atom of 128 kcal / mol or more and a compound having a hydrophilic group, and then irradiated with ultraviolet rays to remove one of the fluorine atoms of the fluororesin film. A hydrophilic fluororesin film is obtained by substituting parts with hydrophilic functional groups. The compound is preferably an aluminum compound, a boron compound or a lithium compound, and the ultraviolet light source is preferably a low pressure mercury lamp.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing a hydrophilic fluororesin film. More specifically, it relates to a method for producing a hydrophilic fluororesin film that can be used in a filtration membrane for liquids used for microfiltration or ultrafiltration of liquids such as chemicals, foods and water, filtration devices and the like.

[0002]

2. Description of the Related Art In microfiltration and ultrafiltration of liquids such as chemicals, foods and water, fine particles removal performance, liquid permeation flux, chemical resistance, pressure resistance, heat resistance, etc. are important choices for filtration membranes. Is a factor. Conventionally, a porous film made of a fluororesin such as polytetrafluoroethylene (hereinafter abbreviated as PTFE) or polyvinylidene fluoride, or a 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 exchanged after circulating cleaning, the chemicals are discharged to remove air from the filtration cartridge filter. Flows in.

Therefore, air comes into contact with the surface of the hydrophobic membrane such as the PTFE membrane in the filter, and the effect of hydrophilic treatment of the membrane with an organic solvent when the filter is attached disappears.
Then, when the chemical is introduced, the liquid permeation flux 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 body hydrophilic,
A method of applying a surfactant or JP-A-56-637.
No. 72, a water-soluble polymer such as polyvinyl alcohol or polyethylene glycol is impregnated into the pores of a porous body, and the polymer is heat-treated, acetalized, esterified, heavy chromium. A method of making hydrophilic by acid treatment, irradiation of ionizing radiation, etc. is known.

Further, as disclosed in Japanese Patent Laid-Open No. 2-196834, there is known a method of irradiating an surface of a fluororesin with an ArF laser to make it hydrophilic.

[0007]

However, the method of applying the surfactant has a problem in that the surfactant does not adhere sufficiently to the porous body and is easily removed, so that the hydrophilicity is difficult to be maintained.

Further, in the method described in JP-A-56-63772, the irradiation of radiation causes decomposition and deterioration of the porous body, resulting in a marked decrease in mechanical strength. Further, the heat treatment, acetalization, and esterification make a part of the water-soluble polymer hydrophobic, so that there is a problem that the hydrophilicity is lowered.

Further, Japanese Unexamined Patent Publication (Kokai) No. 2-196834 describes surface modification by an excimer laser, but hydrophilization inside the fluororesin was insufficient.

In order to solve the above-mentioned problems of the prior art, the present invention is excellent in hydrophilicity and durability thereof, excellent in chemical resistance, pressure resistance, heat resistance and the like, and hydrophilic in that it can be manufactured at low cost. It is an object to provide a method for producing a fluororesin film.

[0011]

In order to achieve the above object, the method for producing a hydrophilic fluororesin film of the present invention comprises:
The binding energy with the fluorine atom is 128 kcal / mo
In the presence of a compound having 1 or more atoms and a hydrophilic group, the fluororesin film is irradiated with ultraviolet rays to be hydrophilized. That is, the C—F bond of the fluororesin (128 kcal / m 2
ol). At this time, as described later, the binding energy with the F atom is the C—F binding energy (128 kca).
The presence of atoms of 1 / mol or more causes the cleaved fluorine atom to bond with the atom and be trapped. Since the fluorine atom has a high electronegativity of 4.0, the recombination between C and F can be prevented by allowing an atom having an electronegativity smaller than that of a carbon atom (electronegativity: 2.5) to exist. The bond energy between the atom and the fluorine atom is C—F bond (128 kcal / mo).
Since it is higher than l), it is less likely to be cut again. Therefore, a part of the fluorine atoms of the fluororesin film can be replaced with the hydrophilic functional group.

In the above structure, when not only the surface of the film but also the inside of the film is made hydrophilic, the fluororesin film is preferably a porous fluororesin film. Further, in the above structure, the compound is preferably an aluminum compound, a boron compound or a lithium compound.

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

[0014]

According to the production method of the present invention, the hydrophilic fluororesin film can be produced efficiently and rationally. That is, a hydrophilic fluororesin film can be obtained at low cost without the need for vacuum operation such as electric discharge treatment.

Further, according to the preferred constitution of the present invention in which the fluororesin film is a porous fluororesin film, it is possible to provide a hydrophilic fluororesin film which is more excellent in hydrophilicity and durability.

Further, according to the preferable constitution of the present invention in which the compound is an aluminum compound, a boron compound or a lithium compound, a hydrophilic fluororesin film further excellent in hydrophilicity and durability can be obtained.

Further, according to the preferable constitution of the present invention in which the ultraviolet light source is a low pressure mercury lamp, it is possible to obtain a hydrophilic fluororesin film which is more excellent in hydrophilicity and durability.

Further, the hydrophilic fluororesin film obtained by the production method of the present invention is processed into, for example, a disc shape or a pleated shape, adhered to a support, and incorporated in a container, or in a flat film state. A filtration device such as a plate type module or a hollow fiber membrane module supported by a plate and a frame can be used.

The hydrophilic film obtained by the production method of the present invention can also be applied to a battery separator or the like. Further, the hydrophilic film provided by the production method of the present invention has increased adhesiveness, and thus can be applied to a heat-resistant adhesive tape or the like.

[0020]

EXAMPLES The present invention will be described in more detail with reference to the following examples. The present inventors, as a result of various studies, in the presence of a compound having a specific atom and a hydrophilic group, by irradiating the fluororesin film with ultraviolet rays, a part of the fluorine atoms of the fluororesin film is treated with a hydrophilic functional group. Replaced. And
It was found that the film has high hydrophilicity, excellent durability, and also excellent chemical resistance, solvent resistance, heat resistance, adhesiveness, etc., and completed the present invention.

The film used in the present invention is not particularly limited as long as it is made of a fluororesin, and is usually made of PTFE. Also, other fluororesins such as tetrafluoroethylene-hexafluoropropylene copolymer, ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, vinyl fluoride resin, vinylidene fluoride resin. , A trifluorochloroethylene resin or the like.

The film may have any shape such as a sheet shape or a tube shape, and either a baked product or an unbaked product may be used. When the film is porous, the porosity and the nominal pore diameter of the pores can be set variously according to the application, but normally, the porosity is preferably 20 to 80% and the nominal pore diameter is preferably about 0.01 to 10 μm.

The porous fluororesin film can be obtained by various methods. For example, a PTFE porous film is disclosed in Japanese Patent Publication No. 58-25332 and Japanese Patent Publication No. 51-1.
It can be obtained by the stretching method described in Japanese Patent Publication No. 8991, Japanese Patent Publication No. 42-13560, etc., or the method using a foaming agent described in Japanese Patent Publication No. 42-4974.

The compound used in the present invention has a binding energy with a fluorine atom of 128 kcal / mol or more and an electronegativity of less than 2.5 (a binding energy with a fluorine atom: 158 kcal / mo.
1, electronegativity: 1.5), boron (183 kcal /
mol, 2.0), calcium (134 kcal / mo)
1, 1.0), barium (139 kcal / mol,
0.9), lithium (139 kcal / mol, 1.
Compounds such as aluminum hydroxide, boric acid, ammonium borate, lithium hydroxide, calcium hydroxide and barium hydroxide having atoms such as 0) can be used.
In the present invention, aqueous solutions of these compounds are preferably used. Further, an alkali salt such as sodium hydroxide or potassium hydroxide may be added to increase the solubility of the solute.

In the present invention, the method of allowing the above compound to be present includes a method of contacting the fluororesin film with an aqueous solution of the above compound, preferably by impregnation or coating.

In the method of the present invention, first, in the case of a porous fluororesin film, the compound aqueous solution is impregnated into the pores thereof. The porous fluororesin film is immersed in an organic solvent,
Alternatively, a product obtained by performing ultrasonic cleaning in an organic solvent may be used.

The impregnation of the aqueous solution of the compound into the pores of the porous fluororesin film can be carried out by various methods, but it is preferable to adopt the following method in consideration of the fact that this film is hydrophobic. . (1) An organic solvent (methanol, ethanol, acetone, ether) having excellent compatibility with water and having a surface tension of 30 dyne / cm or less is used as the porous fluororesin film (a).
The first step of immersing the film in a solvent by immersing it in isopropyl alcohol or the like). (B) Next, the second step of immersing this in water to replace the solvent with water (water is impregnated into the pores). (C) Then, the third step of immersing the film in the compound solution and substituting water for the aqueous solution (impregnating the aqueous solution in the pores). The method of impregnating through the above three steps.

(2) The compound is mixed with an organic solvent having a low surface tension as described above to prepare a solution having a concentration of 30 dyne / cm or less, which is applied or sprayed on a fluororesin film.
Alternatively, a method of impregnating the solution into the pores of the fluororesin film by immersing the fluororesin film.

By the method as described above, the compound solution can be impregnated into the pores of the porous body.

When the ultraviolet ray in the next step is irradiated during the impregnation of the aqueous solution, a part of the fluorine atoms of the fluororesin film is replaced with the hydrophilic group. By using a bright line with a photon energy of 128 kcal / mol or more such as a low-pressure mercury lamp, a high-pressure mercury lamp, a YAG laser (fourth harmonic), or a metal halide lamp as an ultraviolet light source, it is possible to cut the C—F bond and replace it with a hydrophilic group. However, it is particularly preferable to use a low pressure mercury lamp. The irradiation time is set in consideration of various factors such as output, irradiation distance, type of compound aqueous solution, concentration, film shape and thickness, but is usually about 20 seconds to 30 minutes.

In the case of a non-porous film, it can be hydrophilized by bringing it into contact with the solution by floating it in a compound solution, immersing it, placing the solution on the film, or irradiating it with ultraviolet rays.

The present invention will be described in more detail with reference to specific examples. Example 1 A PTFE porous film having a thickness of 60 μm, a nominal pore size of 0.1 μm, a porosity of 75%, and a length and width of 10 cm was immersed in methanol and water for 10 minutes respectively, and further immersed in a compound aqueous solution for 10 minutes. The compound aqueous solution was impregnated into the pores. Here, a 4.1 wt% boric acid aqueous solution was used as the compound aqueous solution. Output 50 when impregnated with an aqueous solution
After being irradiated with a low pressure mercury lamp of W for 60 seconds, it was washed with pure water and dried to obtain a hydrophilic fluororesin film.

When this film was immersed in pure water, it immediately absorbed water. Furthermore, this film is ESCA (elec
Surface analysis by tron spectroscopy for chemical analysis showed that the O / C ratio before hydrophilization was 0.
On the other hand, it was 0.18 after the hydrophilic treatment. Also, F /
Since the values of C were 2.0 and 0.28, respectively, it could be confirmed that the fluorine atom was substituted with the hydrophilic group. Moreover, it was performed waveform analysis, -CF ₂ - bond (292 eV)
When the number of carbon atoms of is 100, a -CO- bond (28
6eV) was 81 and the —C═O (288eV) bond was 18, confirming the presence of a hydrophilic functional group. Prior to treatment, these functional groups were absent.

This film was treated with hydrofluoric acid (50% by weight),
After being soaked in hydrochloric acid (36% by weight) and sulfuric acid (97% by weight) at room temperature for 1 day, it was kept hydrophilic even after washing with water and drying. Further, the hydrophilicity was maintained even after washing with ethanol and acetone and drying.

This hydrophilic fluororesin film is applied with a pressure difference of 2
When subjected to a water permeability test at 35 mmHg, the permeation flux of pure water was 3.7 cm ³ / cm ² / min. The film not subjected to the hydrophilic treatment was 0 because it did not get wet with pure water, and the pure water permeation flux measured after the film was wet with ethanol was 3.7 cm ³ / cm ² / min. Therefore, no reduction in the permeation flux of the film due to the hydrophilic treatment was observed.

Tetraethoxysilane was brought into contact with this hydrophilic fluororesin film, washed, and observed with an X-ray microanalyzer. As a result, it was confirmed that Si atoms were present in the pores of the porous body and that they were hydrophilized. did.

Example 2 As in Example 1, ultraviolet rays were irradiated by a low pressure mercury lamp in the same manner except that a 2N aqueous lithium hydroxide solution was used as the compound solution. The obtained film absorbed water when immersed in pure water even after being washed and dried. The membrane performance was almost the same as in Example 1.

Example 3 As in Example 1, a mixed aqueous solution of 1N aluminum hydroxide and 1N sodium hydroxide was used as a compound solution, and ultraviolet rays were irradiated by a low pressure mercury lamp in the same manner. At this time, the film impregnated with the solution was immersed in the aqueous solution, and ultraviolet irradiation was performed using a low pressure mercury lamp with an output of 100 W or a high pressure mercury lamp with a power of 2 kW. Each of the obtained films absorbed water when immersed in pure water even after being washed and dried. Further, the respective membrane performances were almost the same as in Example 1.

Comparative Example UV irradiation was carried out in the same manner as in Example 1 except that the PTFE porous film was used and the compound solution was not used. The obtained film was not hydrophilized even when immersed in pure water after washing and drying.

Example 4 A non-porous PTFE film (manufactured by Nitto Denko Corporation, trade name Nitoflon tape, No. 900, 38 μm thick) was floated on the same compound solution as in Example 1 and irradiated with ultraviolet rays. . The contact angle of the obtained film with pure water is 5
It became 5 ° and was hydrophilic. It was 120 ° before hydrophilization.

A double-sided adhesive tape (manufactured by Nitto Denko Corporation, product number No. 500) was attached to the contact surface side with the hydrophilized solution, and the adhesive strength by the 180 ° peeling method (JIS Z
0237) was 13 times that before irradiation.

[0042]

As described above, according to the production method of the present invention, the hydrophilic fluororesin film can be produced efficiently and rationally. That is, a hydrophilic fluororesin film can be obtained at low cost without the need for vacuum operation such as electric discharge treatment.

When the fluororesin film is a porous fluororesin film, the inside of the film can be made hydrophilic, and a hydrophilic fluororesin film excellent in hydrophilicity and durability can be provided.

When the compound is an aluminum compound, a boron compound or a lithium compound, it is possible to obtain a hydrophilic fluororesin film which is more excellent in hydrophilicity and durability.

If the ultraviolet light source is a low pressure mercury lamp,
Further, a hydrophilic fluororesin film having excellent hydrophilicity and durability can be obtained. Further, the hydrophilic fluororesin film obtained by the production method of the present invention is, for example, processed into a disk shape, a pleated shape and adhered to a support, and a cartridge filter incorporated in a container or a plate in a flat film state. A filtration device such as a plate type module or a hollow fiber membrane module supported by a frame can be used.

The hydrophilic film obtained by the production method of the present invention can also be applied to a battery separator or the like. Further, the hydrophilic film provided by the production method of the present invention has increased adhesiveness, and thus can be applied to a heat-resistant adhesive tape or the like.

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] July 28, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0030

[Correction method] Change

[Correction content]

When the ultraviolet ray in the next step is irradiated during the impregnation of the aqueous solution, a part of the fluorine atoms of the fluororesin film is replaced with the hydrophilic group. The ultraviolet light source has a photon energy of 128 kca such as a low-pressure mercury lamp, a high-pressure mercury lamp, a YAG laser (fourth harmonic), a metal halide lamp , and an excimer lamp.
By using a bright line of 1 / mol or more, the C—F bond can be cleaved and replaced with a hydrophilic group, but it is particularly preferable to use a low pressure mercury lamp. Irradiation time is output, irradiation distance,
It is set in consideration of various factors such as the type and concentration of the compound aqueous solution, the shape of the film, the thickness, etc., but usually about 20 seconds to 30 seconds
Minutes.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Shuji Yano 1-2 1-2 Shimohozumi, Ibaraki City, Osaka Prefecture Nitto Denko Corporation

Claims (4)

[Claims] 1. The binding energy with a fluorine atom is 128.
A method for producing a hydrophilic fluororesin film, which comprises irradiating a fluororesin film with ultraviolet rays to make it hydrophilic in the presence of a compound having at least kcal / mol atoms and a hydrophilic group. 2. The method for producing a hydrophilic fluororesin film according to claim 1, wherein the fluororesin film is a porous fluororesin film. 3. The method for producing a hydrophilic fluororesin film according to claim 1, wherein the compound is an aluminum compound, a boron compound or a lithium compound. 4. The low-pressure mercury lamp as the ultraviolet light source.
5. The method for producing the hydrophilic fluororesin film according to.