JP2002037913A - Method for modifying porous ptfe film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To impregnate and fix a solution having low affinity for PTFE to a porous PTFE film without carrying out a time-consuming operation in which in order to impregnate a solution having low affinity for PTFE such as an aqueous solution of PVA into a porous PTFE film, the porous PTFE film is immersed in isopropyl alcohol once and then isopropyl alcohol is replaced with a solution having low affinity for PTFE. SOLUTION: The solution having low affinity for PTFE and a porous PTFE film are subjected to application of pressure/release of pressure repeatedly two or more times, the solution is impregnated into the porous film and successively the solution impregnated into the porous film is polymerized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for modifying a porous PTFE membrane.

[0002]

2. Description of the Related Art A porous membrane made of tetrafluoroethylene resin (PTFE) is a material having inherent properties such as chemical resistance and heat resistance, and high separation based on a uniform and fine porous structure. It is widely used in fields such as membrane filters and battery membranes because it has structural characteristics such as high permeability and high permeability based on high porosity. However, porous PTFE membranes are not suitable for aqueous separation applications.
Due to the inherent water repellency, water hardly permeates through the microporous structure, and a satisfactory separation function cannot be exhibited.

As a method for imparting hydrophilicity to a porous PTFE film, conventionally, for example, irradiation of energy such as an electron beam, surface modification of the porous PTFE film with an alkali metal, or porous PTFE film of a hydrophilic resin has been known. Various methods have been proposed, such as fixing the microporous structure of the membrane to the surface. In particular, a method of impregnating a porous PTFE membrane with polyvinyl alcohol (PVA) and then crosslinking the PVA is considered promising. That is, due to the hydrophilicity of PVA fixed to the porous PTFE membrane as described above, the porous PTFE membrane is easily wetted by water, and water easily penetrates into the microporous. With the PTFE membrane as it is, an aqueous solution can be easily filtered even at a low pressure at which almost no water permeates.

[0004]

A solution having a low affinity for PTFE, such as an aqueous solution of PVA, is used as a porous PTFE solution.
In order to impregnate the membrane, usually, a complicated operation such as first immersing the porous PTFE membrane in an isopropyl alcohol aqueous solution to impregnate the isopropyl alcohol, and then replacing the isopropyl alcohol with a PVA aqueous solution is performed. I have. With such a method, mass production is difficult.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for modifying a porous PTFE membrane which can be mass-produced without the above-mentioned complicated operation. A solution having low affinity for PTFE is added to a porous PT
Pressing / releasing operation is repeated twice or more with FE.
The solution is impregnated in a porous membrane, and subsequently, the solution or a part of the solution impregnated in the porous membrane is polymerized or crosslinked.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an example of an embodiment of the present invention, and the contents will be described with reference to the drawings. 1 is porous PTFE
At the membrane, it is fed between a pair of rolls abutted against each other.
The roll pair 2 is preferably configured such that one side is a metal roll and the other is a rubber roll. Then, the roll can be rotated at a required speed by a motor around an axis perpendicular to the paper surface. Although not shown, a solution supply port is provided at the end of the pair of rolls perpendicular to the plane of the paper, and the affinity for PTFE is such that a solution pool is formed at the top of the abutted roll pair. Low solution (eg PV
A aqueous solution). As shown in FIG. 1, a plurality of roll pairs are vertically arranged, and a solution pool is formed at the top of each pair. The porous PTFE membrane sequentially passes between these roll pairs. Thus, a solution having low affinity for PTFE, together with the porous PTFE membrane,
The pressurizing / releasing operation is repeated twice or more, and as a result, the solution is impregnated in the porous membrane. This method comprises providing a plurality of rolls in a container containing a solution having a low affinity for PTFE, passing the solution having a low affinity for PTFE onto the porous PTFE membrane through a porous PTFE membrane. Compared to the method of impregnating the membrane,
The solution volume is much smaller.

Subsequently, both surfaces of the porous PTFE film impregnated with a solution having a low affinity for PTFE are covered with a dummy sheet 3 in a sandwich shape. Irradiation causes the impregnated solution to polymerize or crosslink. In addition, PTF
When covering a porous PTFE membrane impregnated with a solution having low affinity for E with a dummy sheet in a sandwich form, adjusting the gap between the rolls to remove the impregnating solution attached to the surface of the porous PTFE Is also possible. The method of polymerization or crosslinking is not limited to ultraviolet irradiation, and other methods such as electron beam irradiation and heating can be used. The dummy sheet plays a role of preventing volatilization of the impregnated solution and preventing contact with oxygen, and as a result, promotes fixation of the solution by polymerization or crosslinking in the porous membrane. As the dummy sheet, a polypropylene sheet, an FEP sheet, or the like, which is excellent in chemical resistance, heat resistance, and ultraviolet transmittance, can be preferably used. After irradiating ultraviolet rays and polymerizing the impregnated solution, the dummy sheet is made of porous PTF.
The film is peeled off from the E film and is wound up by a winding roll 5.
The porous PTFE membrane in which the impregnated solution is fixed by polymerization or crosslinking is wound around another winding roll 6.

Examples of the solution having low affinity for PTFE include vinylpyridine and vinylpyrrolidone in addition to the above-mentioned PVA aqueous solution.
According to the method of the present invention, the porous PTFE membrane can be impregnated and fixed, and hydrophilicity and ion exchange ability can be imparted.

[0009]

As described above, according to the method of the present invention, once the porous P
A solution having a low affinity for PTFE can be obtained without dipping the TFE membrane and impregnating with isopropyl alcohol, and then replacing the isopropyl alcohol with a solution having low affinity for PTFE. Can be impregnated and fixed in a porous PTFE membrane.
It is effective for mass production of the modification of the TFE film.

[Brief description of the drawings]

FIG. 1 schematically shows a method of the present invention in which a solution having low affinity for PTFE is impregnated and immobilized on a porous PTFE membrane.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Porous PTFE film 2 Impregnation roll 3 Dummy sheet 4 Ultraviolet irradiation equipment 5 Dummy sheet take-up roll 6 Modified porous PTFE film take-up roll

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Atsushi Uno 950 Noda, Kazatori-cho, Sennan-gun, Osaka F-term in Sumitomo Electric Fine Polymer Co., Ltd. 4D006 MC30 NA41 NA42 4F073 AA02 AA12 AA13 BA17 BB04 CA45 EA01 4F074 AA39 AA42 CE15 CE17 CE26 CE54 CE84 DA47

Claims (6)

[Claims] 1. A solution having a low affinity for PTFE,
The operation of pressurizing / releasing the pressure is repeated twice or more together with the porous PTFE membrane to impregnate the solution into the porous membrane and then polymerize the solution impregnated in the porous membrane or a part of the solution. Or porous PTF characterized by crosslinking
Method for modifying E film. 2. A pressurizing / releasing operation that is repeated two or more times is performed between a plurality of pairs of rolls in which each pair of rolls is in contact and the solution is stored above each pair of rolls. 2. The method for modifying a porous PTFE membrane according to claim 1, wherein the porous PTFE membrane is passed sequentially. 3. A pressurizing / releasing operation that is repeated two or more times, wherein each pair of rolls is in contact with each other, and the solution is stored on top of each pair of rolls. The method for modifying a porous PTFE membrane according to claim 1, wherein the plurality of pairs of rolls are sequentially passed from bottom to top. 4. A solution having a low affinity for PTFE,
After impregnating in the porous PTFE membrane, the porous PTFE
Put a dummy sheet on both sides of the membrane in a sandwich shape,
The method for modifying a porous PTFE membrane according to claim 1, wherein the solution or a part of the solution impregnated in the porous membrane is polymerized or crosslinked in this state. 5. The method according to claim 4, wherein the dummy sheet is a polypropylene sheet or an FEP sheet. 6. The method for modifying a porous PTFE membrane according to claim 1, wherein the polymerization or crosslinking is ultraviolet polymerization or crosslinking.