JPS61249503A - Hydrophilic polytetrafluoroethylene filter membrane and its production - Google Patents

Abstract

PURPOSE:To obtain the titled hydrophilic PTFE membrane having resistance to both heat and chemicals by cross-linking a fluorine surfactant on the PTFE membrane until the surfactant is made insoluble in aq. soln. CONSTITUTION:An anionic fluorine surfactant is coated on the surface of a PTFE filter membrane having narrow pore diameter distribution. At this time, the PTFE filter membrane is placed under 100-150mmHg reduced pressure and immersed in a dilute soln. of the fluorine surfactant to reduce the immersion time. After hydrophilicity is provided to the porous surface of the fluorine surfactant by the complete immersion, high-energy radiation rays are irradiated to make the fluorine surfactant insoluble in water. The reaction is preferably carried out under conditions where oxygen is substantially absent.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a hydrophilic polytetrafluoroethylene filtration membrane having excellent heat resistance and chemical resistance, and a method for manufacturing the same.

[Conventional technology and problems]

Although polytetrafluoroethylene (hereinafter referred to as PTFE) has excellent heat resistance and chemical resistance, it is water repellent, but it is difficult to apply it to water or strong acid/strong alkali aqueous solutions. It is also accompanied by For example, in order to impart hydrophilicity to a filter membrane made of PTFE,
071 or US Pat. No. 8,666,698, a method is known in which acrylic acid, 4-vinylpyridine, N-vinylpyrrolidone, etc. are grafted by a polymerization reaction using ionizing radiation or a polymerization catalyst. However, in theory, hydrophilization by these methods still lacks heat resistance and chemical resistance, and although graft polymerization progresses on the surface layer, it is difficult for grafting to progress inside, and in the end, homogeneous hydrophilicity is achieved. I can't do that. For example, US Patent No. 890,087 and 3,8
82,387, porous tetrafluoroethylene resin is impregnated with a surfactant, sharply etched with sodium-naphthalene, etc., and then a polymerizable upper layer is graft-polymerized to impart hydrophilicity. Are known. These methods can be applied uniformly when the pore size of the PTFE filtration membrane is large, such as felt, but on the other hand, as the pore size becomes smaller, the etching relief becomes uneven and the hydrophilicity becomes uneven. .

Polymer membranes made of hydrophilic materials can be used as dialysis membranes in addition to filtration membranes.
It is used as an ultrafiltration membrane, reverse osmosis membrane, etc. to separate substances in systems where water is present. This application requires a membrane with excellent solute rejection and mechanical strength in wet conditions. The most typical membrane is cellulose ester membrane, which is said to have excellent permeability and mechanical properties, but both properties need to be further improved for practical use. In particular, if the acidity or alkalinity is too strong, the cellulose ester membrane will be hydrolyzed, and if the pore size becomes small, the usable temperature limit will decrease.

On the other hand, a technology was developed in which a hydrocarbon surfactant was mixed into a film made of a water-insoluble polymer material and the surface was cross-linked by irradiating it with plasma.
924, but the membrane here is semi-permeable, specifically for application to reverse osmosis and ultrafiltration, and is not resistant to strong acids and strong alkalis as aimed at in the present invention. Not intended for application.

A PTFE material with excellent chemical resistance is used for the diaphragm of the electrolytic cell. In particular, in the electrolysis of alkali metal halides, chlorine, sodium hydroxide, etc. are generated, so a wetting method using a fluorinated surfactant has been developed. It is disclosed in Sho 56-130486. However, the fluorinated surfactant is brought into contact with the PTFE diaphragm, dried to inactivate it, and then reactivated by simply contacting it with an aqueous solution at the time of use. They are in contact simply due to chemical affinity, and the fluorinated surfactant has the disadvantage that it is easily desorbed because it does not undergo the water insolubilization escape process.

[Kth way to solve the problem]

As a result of intensive studies to address the shortcomings of the conventional technology, the present invention combines a fluorinated surfactant with excellent heat resistance and chemical resistance with a PTFE filtration membrane, and combines the fluorinated surfactant with a PTFE filtration membrane. The purpose is to provide a PTFE filtration membrane that has both heat resistance and chemical resistance by crosslinking it until it becomes insoluble in an aqueous solution. Therefore, an object of the present invention is to develop a hydrophilic PTFE filtration membrane useful for separating and purifying solid substances in expensive liquids in the pharmaceutical and food fields.

[Effect]

The PTFE filtration membrane used in the present invention is
It is necessary that the pore diameter distribution is narrow.

However, the fluorine-based surfactant used in the present invention is preferably an anionic type or a nonionic type, whereas a cationic type may have some problems in wettability and permeability.

Anionic types are particularly preferred for use in high-temperature atmospheres, and some maintain durability even at 250°C or 350°C.

Specifically, CF s (CF m )mCOOMe
(where m is 3 to 19 and Me is an alkali metal) carboxylates exhibit heat resistance up to about 250°C, and CFs (
CFs) mSOa Me sulfonate is durable up to about 850°C. The values of wettability and permeability vary somewhat depending on the value of km.

On the other hand, in terms of wettability, permeability, solubility, and water-solubilization crosslinking, a nonionic type, particularly a nonionic type having a structure consisting of an ethylene oxide adduct, is preferable.

A specific example of nonionic type is CFa(CFs)m(C
Hg CHs 0) nH (here m is 5 to 9, n is 6
~19), exhibiting high wettability and permeability,
It has the characteristic of being soluble in many types of solvents.

Fluorade FC is a commercially available anion type.
-95, FC-98, FC-129, Surflon S-1
11, S-113, Unidyne DS-101, DS-1
There is 1st grade, and the most nonionic type is Fluorade F.
C-170C, FC-430, FC-4311 Surflon S-141, S-145, Unidyne DS-401,
There are DS-402, etc., and it is relatively easy to select one from these.

The perfluorotetraalkyl group represented by CFs (CFs) m- is highly compatible with the porous surface of the PTFE filtration membrane.
The bond is quite strong due to the aals force, and if the water container is stored in an aqueous salt solution, it will maintain its hydrophilicity for a long period of time. However, if the fluorosurfactant is not cross-linked to the point where it becomes insoluble in an aqueous solution, most of the fluorosurfactant will diffuse into the water or aqueous solution due to long-term storage in water. PTFE
When the 27ff filtration membrane is dried, its wettability and permeability are greatly reduced, and the PTFE filtration membrane itself exhibits water repellency.

If the fluorosurfactant is crosslinked until it becomes insoluble in an aqueous solution as in the present invention, it will not diffuse even when stored in water for a long period of time, and the same hydrophilicity as the initial one can be maintained. .

The above characteristics make a noticeable difference when performing an operation called filtration. In other words, when sulfuric acid or sulfuric acid is filtered under pressure or reduced pressure through a PTFE filtration membrane that is not cross-linked with fluorosurfactant, when the liquid to be filtered is no longer in the filtration container, gases such as air are filtered out. It passes through the membrane, which greatly reduces hydrophilicity. Therefore, it is necessary to add the next liquid to be filtered while the liquid to be filtered remains in the filter container, making the entire operation complicated.

This tendency becomes even more pronounced when filtering a liquid that easily generates gas from the solution, such as hydrogen peroxide (H++Og), and when a small amount of filtration is performed, the generated gas fills the porous spaces of the filter membrane. occupies the water and becomes water repellent.

In contrast, the filtration membrane of the present invention maintains hydrophilicity even after the entire filtrate flows through the filtration container, and even when filtering a liquid that easily generates gas, such as 0 g of Hg, the filtration membrane does not create porous spaces due to the generated gas. The second generated gas and H808 can be used in their entirety at the same time.

Next, the manufacturing method will be explained in detail.

Tokuko Showa 60-384! P manufactured by methods such as
Although it is preferable to use a TFE filtration membrane, a PTFE filtration membrane with a somewhat wider pore size distribution can also be used. The porous surface of these PTFE filtration membranes is first coated with a fluorosurfactant.

For this purpose, the fluorosurfactant is diluted with a soluble liquid such as water or alcohol.

In addition to the above, diluting liquids include acetone, dimethylformamide, methyl cellosolve, carbon tetrachloride, and toluene, and two types may be used simultaneously. If the concentration after dilution is 5% by weight or more, the next step can be started immediately after dipping, but if it is less than 5% by weight, the immersion time is 1%.
It is necessary to make the time longer than 0 hours.

As a method to reduce the soaking time, the PTFE filtration membrane can be first placed under vacuum and then the diluted solution can be injected. It is most desirable to use a reduced pressure of 100 to 150 amH/H for this purpose, but it can be carried out at any pressure up to 760 amH/H. By using reduced pressure, the dilution concentration can be further lowered, and even if the concentration is 3% by weight, complete immersion can be achieved within 2 hours of immersion time. Mana α5% by weight
Even at low concentrations, complete immersion can be achieved by injecting under reduced pressure and setting the immersion time to 12 hours. Complete immersion here refers to a state in which the PTFE filtration membrane is dried after being immersed, and then brought into contact with water again so that the entire surface becomes completely transparent or translucent and exhibits hydrophilic properties.

Therefore, incomplete immersion means that some parts become transparent or translucent, but white spots that do not penetrate remain in other parts. The reason why complete immersion is achieved by increasing the immersion time is that time is required for the fluorine-based surfactant in the diluted solution to diffuse to completely cover the porous surface of the PTFE filtration membrane. It is estimated to be.

After confirming that complete immersion has been completed, high-energy radiation is irradiated to make the fluorosurfactant insoluble in water. Suitable forms of radiation include gamma radiation (particularly Co60), electron beams, and high energy plasmas. In the case of irradiation with gamma rays or electron beams, the presence of oxygen causes deterioration, particularly a significant decrease in mechanical strength, so it is desirable to carry out the irradiation in a state where oxygen is substantially absent.

One method for this licking is to completely immerse the PTFE filtration membrane in a diluted solution of fluorosurfactant with water, remove the excess, and then pack it in a bag with plastic film.
P T F E When the filtration membrane is irradiated while still wet, P
The presence of oxygen in the TFE filtration membrane can be reduced. For further completeness, the interior of the bag-like material may be replaced with nitrogen before irradiation.

The irradiation dose is 0.5 Mrad or more and is 3 Mrad.
The range of d is preferable; if it is less than 0.5 Mrad, the amount of reactions such as crosslinking will be insufficient, and the amount of water-insolubilized products produced will be small.

On the other hand, when it exceeds 8 Mrad, the mechanical strength decreases significantly.

On the other hand, water insolubilization treatment using plasma can also be performed. The energy of gamma rays and electron beams is high energy of 15 eV, but the electrons in non-equilibrium plasma are 1 to 2 eV, but a small amount of high-energy electrons are included, and the energy is 10 to 12 eV.
It extends to the range of V.

In order to confirm that these high-energy electrons have sufficient energy to make the fluorosurfactant water insolubilized, it is necessary to use PTFE when using this high-energy plasma.
? The filtration membrane is completely immersed in the fluorosurfactant, and then
Completely remove the diluting liquid and irradiate in a dry state.

The PTFE filtration membrane is fixed to a support, but when using a support that fixes only the periphery, it is convenient because the front and back sides can be irradiated at the same time, but when using a flat support, one side is treated and then the opposite side is treated. It is desirable to further irradiate the area. To perform irradiation with non-equilibrium plasma, the system must be irradiated with 1aIH.
/ or less, preferably θ, 6■HJ' or less, and a carrier gas containing hydrogen, for example, hydrogen,
It is preferable to use methane, water, etc., and gases such as helium, argon, nitrogen, etc., which are often used in general non-equilibrium plasma, are not preferable. This is because a carrier gas containing hydrogen efficiently makes the fluorosurfactant insoluble in water.

The invention will be further explained below by way of examples.

Example 1 Fluorobor FP-028 (PTFE filtration membrane manufactured by Sumitomo Electric)
was immersed for 20 minutes in a 5% by weight solution of Fluorade FC98 (potassium perfluoroalkylsulfonate, manufactured by A.M.). After 9 days of air drying, it was set in a Pelger type plasma device and the pressure inside the system was reduced to αl-H/. 0.5 m by supplying hydrogen gas at a flow rate of 1 cc (STP)/min
The pressure was adjusted to nHP, and plasma was generated with a radio wave output of 1156 MHz and 50 W. After 10 minutes of discharge, the Fluoropore was taken out and soaked in water and sulfuric acid (95%
), hydrochloric acid (37%), and nitric acid (C'lO%), the entire surface was penetrated.

Punch out a circular shape with a diameter of 47m5, attach it to a filtration device, and perform the filtration of the above strong acid by dividing the 0 strong acid into 100cc portions. When comparing the time required to filter 100cct, it was found that the two coincided.

Comparative Example 1 A film was formed under the same conditions as in Example 1 except that the carrier gas supplied to the plasma apparatus was changed to nitrogen. This membrane is only partially permeable to hydrochloric acid and nitric acid, and
However, water (sulfuric acid) does not penetrate the entire surface.

When 500 cc of sulfuric acid was repeatedly filtered five times for each 100 cc, the filtration time became longer with each repetition, and by the time the fifth and final filtration was completed, the permeability of sulfuric acid had significantly decreased through the membrane.

Example 2 Fluoropore FP-022 was immersed in a 5% by weight solution of Surflon S-111 (perfluoroalkyl carboxylate, manufactured by Asahi Glass) in a mixed solvent of 70% water and 30% isopropyl alcohol for 24 hours.

After removing the excess solution that has adhered to it, it is sealed in a PE bag while purging with nitrogen gas, and irradiated with a dose of 2 Mrad using a zero electron beam accelerator, and then washed and dried. This membrane has permeability to concentrated liquids such as sulfuric acid, nitric acid, and hydrochloric acid, and the same results as in Example 1 were obtained in the filtration experiment. (ethylene oxide adduct) in isopropyl alcohol at a concentration of 2% by weight.

Fluoropore FP-010t-100 amH was placed in a separable flask under reduced pressure, and then a solution of DS-401 was injected. Fluoropore F is removed from the solution immediately after the injection is completed.
Take out P-010 and dry the alcohol at a temperature of 90°C. Suspend and fix to the low-temperature plasma device so that both surfaces can be treated at the same time, and connect the piping so that water vapor at equilibrium with 40"C water can be supplied at the same time as nitrogen gas. The plasma was adjusted to 8 HJ' and excited at 50 W for 15 minutes. Fluoropore subjected to this treatment showed the same filtration properties against strong acids as in Example 1. Using a 2% by weight aqueous solution of ethylene oxide adduct),
It was impregnated into 70 Roboa FP-010 under reduced pressure of 50 μH/. After removing the excess solution, the same electron beam irradiation as in Example 2 was performed, but the same strong acid permeability and filtration properties as in Example 1 were not obtained.

Claims (10)

[Claims] (1) Hydrophilic polytetrafluoroethylene, characterized in that a fluorinated surfactant is laminated on the porous surface of a polytetrafluoroethylene filtration membrane, and the fluorinated surfactant is crosslinked until it becomes insoluble in an aqueous solution. ethylene filtration membrane (2) The hydrophilic polytetrafluoroethylene filtration membrane according to claim 1, wherein the fluorinated surfactant is anionic or nonionic. (3) Method for producing a hydrophilic polytetrafluoroethylene filtration membrane by applying a fluorinated surfactant solution to the porous surface of the polytetrafluoroethylene filtration membrane and irradiating it with high-energy radiation. (4) A method for producing a hydrophilic polytetrafluoroethylene filtration membrane according to claim 3, wherein the fluorinated surfactant is anionic or nonionic. (5) A method for producing a hydrophilic polytetrafluoroethylene filtration membrane according to claim 3, characterized in that the fluorinated surfactant is applied to the polytetrafluoroethylene filtration membrane under reduced pressure. (6) A method for producing a hydrophilic polytetrafluoroethylene filtration membrane according to claim 3, wherein the high-energy radiation is Co^6^0 gamma rays. (7) A method for producing a hydrophilic polytetrafluoroethylene filtration membrane according to claim 3, wherein the high-energy radiation is an electron beam. (8) A method for producing a hydrophilic polytetrafluoroethylene filtration membrane according to claim 3, characterized in that the high-energy radiation is non-equilibrium plasma. (9) Fluorinated surfactant is CF_3 (CF_2)_m
COOMe, CF_3(CF_2)_mSO_3Me or CF_3(CF_2)_m(CH_2-CH_2-
O)_nH (in the above formula, m is 3 to 19, n is 6 to 19,
The method for producing a hydrophilic polytetrafluoroethylene filtration membrane according to claim 4, wherein Me is Li, Na, or K. (10) Claim 6, characterized in that in high-energy radiation crosslinking using non-equilibrium plasma, a hydrogen-containing gas such as hydrogen, water, or methane is used as the carrier gas.
Method for producing a hydrophilic polytetrafluoroethylene filtration membrane according to item 7 or 8