JPH0576734A - Filtration film for liquid and filtering device using the same - Google Patents

Abstract

PURPOSE:To provide a filtration film for liquid, which is possible to use for precision filtration or ultrafiltration of liquid such as chemicals or water and free from deterioration of filtration rate, and a filtering device using the film. CONSTITUTION:The filtration film for liquid is made by forming a covering layer of a fluorine contained surface active agent having a structure expressed by a specific chemical formula at least on a narrow pores surface of a high molecular polymer porous film and has hydrophilic property.

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 used for microfiltration and ultrafiltration of liquids such as chemicals and water, and a filtration device using the same.

[0002]

2. Description of the Related Art In microfiltration and ultrafiltration of liquids such as chemicals and water, fine particle removal performance, liquid permeation flux,
Chemical resistance, pressure resistance, heat resistance, etc. are important selection factors for the filtration membrane. Therefore, conventionally, a porous film made of a fluororesin such as polytetrafluoroethylene (hereinafter abbreviated as PTFE) or a high molecular weight 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 in the filtration cartridge filter. Inflow. Therefore, PT in the filter
Since air comes into contact with the surface of a hydrophobic membrane such as an FE membrane and the effect of hydrophilic treatment of the membrane with an organic solvent or the like disappears, the liquid permeation flux decreases drastically when the chemical is introduced next time. for that reason,
There has been a problem that a liquid having a low surface tension has to be made hydrophilic again.

[0004]

Conventionally, chemical etching with a sodium-naphthalene complex has been performed to make the PTFE film hydrophilic. This treatment method is suitable for hydrophilizing the membrane surface, but when attempting to hydrophilize the inside, it has the disadvantages that it is non-uniform, the strength of the membrane deteriorates, and the pore size increases. It was Furthermore, since sodium is used, when used for semiconductor chemical filtration,
The elution becomes a big problem.

A method is known in which a fluorine-based surfactant is crosslinked to make it hydrophilic (for example, JP-A-61-295050).
No. 2, JP-A-61-249503), the surfactant disclosed therein has a single -CF ₃ end in the hydrophobic part, and therefore has a weak affinity for the membrane, and depending on such a surfactant, It could not be sufficiently hydrophilized, and the obtained film was not satisfactory.

[0006]

The present invention has been made in order to solve the problems of the prior art, and is a fluorine-based polymer having a specific structure at least on the surface of the pores of the high molecular weight polymer porous membrane. By chemically coating the surface-active agent, the hydrophobic membrane can retain the hydrophilicity without any particular cross-linking, and the permeation flux is maintained even when the liquid in the filtration device such as the cartridge filter is discharged. A filtration membrane for liquids that does not decrease, and a filtration device incorporating the same.

The high molecular weight polymer porous film of the present invention comprises
It is a hydrophobic film made of a fluororesin such as PTFE or polyvinylidene fluoride, or a polymer such as polyethylene or polypropylene, and PTFE is particularly preferable in terms of chemical resistance and heat resistance. Further, a membrane having a pore size of 0.01 to 1 μm, particularly 0.05 to 0.2 μm is preferably used.

The fluorosurfactant used as the coating layer in the present invention is represented by the following chemical formula 2.

[Chemical 2] (In the above formula, R is H, OH, COOH, or CH ₃ , m
Is 1 to 17, and n is 1 to 20. ) Has a structure represented by. Especially, part of ethylene oxide is OH
A surfactant substituted with a group or a COOH group is preferably used.

A specific example of such a fluorine-containing surfactant is represented by the following chemical formula 3.

[Chemical 3] There are things.

The method for coating the surface of the fine pores of the high molecular polymer porous membrane with the above-mentioned fluorine-containing surfactant is not particularly limited, but, for example, the above-mentioned fluorine-containing surfactant may be treated with an organic solvent. 1 to 10% by weight, preferably 1 to 5% by weight
After diluting with water, the high molecular polymer porous membrane can be coated by immersing it in the solution or by coating the solution and drying the membrane, and a hydrophilicized hydrophobic membrane can be easily obtained. .. The organic solvent used here is not particularly limited, but for example, acetone, ethanol, isopropyl alcohol, etc. are preferably used.

In the present invention, the obtained filtration membrane is further subjected to post-treatments such as plasma (H ₂ , O ₂ , N ₂ , Ar, etc.) irradiation, excimer laser irradiation, low-pressure mercury lamp irradiation, etc. It can be made hydrophilic.

In the present invention, as described above, the filtration membrane hydrophilized by adsorbing the fluorosurfactant to the pores by the chemical affinity is processed into, for example, a disc shape or a pleated shape and adhered to the support. Then, a cartridge filter incorporated in the container, a plate type module supporting a plate and a frame in a flat membrane state, a hollow fiber membrane module, or the like can be provided.

[0013]

According to the present invention, since at least the pore surface of the hydrophobic membrane can be hydrophilized, for example, in a filtration device such as a cartridge filter, even after the liquid has permeated, the membrane surface is left in the empty state. Since the liquid is retained, the hydrophilicity is maintained without air coming into contact with the inside. Therefore, even if the liquid in the filtering device is discharged,
It is possible to obtain a liquid filtration membrane without a reduction in permeation flux.

[0014]

【Example】

Example 1 A polytetrafluoroethylene porous membrane (manufactured by Nitto Denko Corporation, trade name NTF1111, nominal pore diameter 0.1 μm) was used as a fluorine-based surfactant having a structure of Chemical formula 4

[Chemical 4] Was immersed in 2.5% by weight of acetone solution, and after 30 minutes, the film was taken out and air-dried.

This membrane was cut into 10 cm ² and set in a cartridge type filtration device, and pure water was permeated by reducing the pressure on the permeate side to 235 mmHg, and the initial pure water permeation flux was 6.5.
It was cm ³ / (cm ² · min). As it was, 0.8 liter per 1 cm ^{2 of the} pure water was filtered, and then the membrane was taken out and the water was removed in a dryer at 60 ° C. for 15 minutes. Then, the pure water permeation flux did not change even if the pure water permeation flux was set again in the cartridge type filtration device and pure water was filtered under the same conditions as above. The latex inhibition rate was 98% when a 10 ppm aqueous solution of 0.102 μm latex was filtered under reduced pressure. In addition, ESCA analysis of the film surface confirmed that the ratio of F decreased and O increased. Furthermore, it was confirmed that this film remained hydrophilic even after immersion in a chemical such as NH ₄ F or HF.

Comparative Example 1 When tested in the same manner as in Example 1 except that no treatment with a fluorosurfactant was carried out, the initial pure water permeation flux was that water was not permeated because the membrane was hydrophobic. Then, after about 50 ml of ethanol was permeated through the membrane to make it hydrophilic, pure water was permeated under the same conditions to find that it was 7 cm ³ / (cm ² · min). The latex inhibition rate was 94%.
According to ESCA analysis, no other element was observed except that F showed twice the intensity of C.

Comparative Example 2 Surfactant having the structure of the following chemical formula 5

[Chemical 5] A filtration membrane was obtained and evaluated in the same manner as in Example 1 except that was used. The initial pure water flux of this membrane is 6.3 cm ³
It was / (cm ² · min), but when 0.3 l / cm ² · membrane was permeated with water and then dried, the membrane returned to hydrophobic and water was not permeated.

Example 2 The fluorine-based surfactant coating film obtained by the method of Example 1 was cut into a 20 cm square and held in the plasma irradiation apparatus at a distance of 5 cm from the electrode. After evacuating to 10 ^-5 torr, Ar gas was supplied at 10 cc (STP) / min, the chamber was kept at 5 × 10 ^-1 torr, plasma was generated at the output of 13.56 MH ₂ and 50 W, and the discharge was performed for 30 sec. After that, the film was taken out.

Regarding the performance of this membrane, the permeation performance was evaluated in the same manner as in Example 1, and the same result as in Example 1 was obtained. Regarding the chemical resistance, it was confirmed that the hydrophilicity was maintained even after 98% sulfuric acid immersion at room temperature.

Claims (3)

[Claims] 1. The following chemical formula 1 is provided on at least the pore surface of the high molecular polymer porous membrane. (In the above formula, R is H, OH, COOH, or CH ₃ , m
Is 1 to 17, and n is 1 to 20. A filtration membrane for liquids, characterized in that a coating layer of a fluorine-based surfactant having a structure represented by (4) is formed by chemical affinity and has hydrophilicity. 2. A liquid filtration membrane according to claim 1, which is further subjected to low temperature plasma irradiation, excimer laser irradiation or low pressure mercury lamp irradiation. 3. A liquid filtering device comprising the liquid filtering membrane according to claim 1 or 2 mounted in a container.