JP3467450B2 - Porous membrane for dissolving hardly soluble gas and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a tubular porous membrane for dissolving a sparingly soluble gas such as ozone in a liquid and a method for producing the same.

[0002]

2. Description of the Related Art A liquid such as water in which a gas such as ozone or carbon dioxide is dissolved is used as a cleaning liquid.
For example, in a semiconductor manufacturing process, ozone-added ultrapure water is used in a wet cleaning process. Ozone-added ultrapure water is ultrapure water to which a very small amount (ppm order) of ozone is added. Ozone dissolved in ultrapure water acts as a clean and strong oxidizing agent, decomposes and removes residual organic substances such as surfactants on the silicon wafer, and forms a uniform and flat oxide film. Also, in the liquid crystal display manufacturing process, it is said that the efficiency of removing organic substances and resist residues can be improved by cleaning the glass substrate, cleaning after etching, cleaning after lapping, and the like.

As a method of dissolving gas in a liquid,
Conventionally, the following methods are known. A method of mechanically mixing a gas and a liquid. A method of bubbling gas in a liquid. A method of using a porous PTFE tube made of polytetrafluoroethylene (hereinafter abbreviated as PTFE). Among these methods, the mechanical mixing method has a problem that it is difficult to efficiently dissolve a certain amount of gas in a liquid, and furthermore, there is a problem that metal ions are mixed from a mixing device or parts. A liquid mixed with metal ions cannot be used for semiconductor or liquid crystal related applications that require high purity. In addition, the method of bubbling has a low gas dissolution efficiency, it is difficult to control the amount of gas dissolved, and there is a possibility that gas that has not dissolved during bubbling is released to the outside of the system, which may be bad. Further, also in the method using bubbling, there is a possibility that metal ions may be mixed from the device or part used.

On the other hand, in the method using the porous PTFE tube, the gas and the liquid to be treated are brought into contact with each other through the tubular porous PTFE membrane to form the porous PTFE.
Since the gas is dissolved in the liquid to be treated by utilizing the hydrophobicity and gas permeability of the E film, the problem of mixing of metal ions can be avoided. Moreover, the porous PTFE tube is
The film area per unit capacity can be increased by bundling a large number of modules into a module. The porous PTFE tube thus modularized is put into a container, and while the liquid is caused to flow in the tube, the gas is appropriately mixed in the container, for example, in the range of 5 to 15 vol%, and the container is supplied. By controlling the partial pressure of the gas in the liquid, while preventing bubbling of gas that permeates through the membrane into the liquid, according to Henry's law of gas dissolution, while controlling the amount of gas dissolved, the efficiency It is often said that it can dissolve gas.

By the way, in the single-wafer cleaning apparatus and the like adopted in semiconductor and liquid crystal cleaning, a high-pressure water source is used to enhance cleaning efficiency, and the gas dissolving module is required to have high water pressure resistance. It Of course, increasing the pressure of the gas on the outside of the tube can cancel the increase in water pressure inside the tube, but for that purpose, equipment for pressurizing the outside gas is required and the strength of the entire module is increased. Therefore, the cost of the module as a whole increases. Therefore, it is required that the tube itself has some strength and can withstand an increase in water pressure.

Therefore, for example, Japanese Patent Laid-Open No. 7-21388.
No. 0 publication discloses (a) a tubular membrane in which a porous PTFE film having a small pore size obtained by stretching a PTFE sheet on the outer periphery of a porous tube having a large pore size is laminated, and
(B) It has been proposed to use a tubular membrane formed by winding a porous PTFE film having a small pore size in an ozone dissolving module.

[0007]

However, the tubular membrane described in Japanese Patent Laid-Open No. 7-213880 has the following problems. That is, in the tubular membrane of (a) above, a porous tube having a large pore size is arranged inside the tube through which the liquid to be treated flows, and the porous PTFE film having a small pore size contributes to the contact between gas and liquid. Not not. Therefore, the reliability of the liquid to be treated with respect to the operating pressure is insufficient, and the liquid to be treated enters the inside of the film partially or entirely. The liquid to be treated that has entered the inside of the film is difficult to flow and becomes stagnant, and the ozone concentration rises locally, and as a result, ozone is constantly prevented from reaching the gas-liquid contact interface, The amount of ozone dissolved in the liquid to be processed flowing inside is extremely reduced. Further, due to hydraulic pressure, a part of the inner porous tube having a large pore size may be swollen and the outer porous PTFE film having a small pore size may be peeled off.

In addition, the porous P having a small pore size of the above (b)
The tubular membrane formed by winding TFE film is
In order to secure mechanical strength, it is necessary to laminate many times, and in order to ensure adhesion between layers, PFA or
Since it is necessary to interpose an adhesive such as FEP, the number of effective pores is reduced, the gas permeability including the collapse of the film is reduced, and the original characteristics of the porous PTFE film cannot be utilized. Further, there is a problem that both (a) and (b) are very troublesome to manufacture.

[0009]

Means for Solving the Problems The present invention has solved the above-mentioned problems and has sufficient reliability with respect to the working pressure of the liquid to be treated, the liquid to be treated does not enter the inside of the film, and is stable. An object of the present invention is to provide a tubular film capable of efficiently dissolving a gas such as ozone and a method for producing the tubular film. The sparingly soluble gas-dissolving tubular membrane of the present invention is a porous PTFE tube having a porosity of 10% or more and 40% or less and leakage of the tube.
The water pressure is 0.4 MPa or more . Generally, in gas absorption, the following formula is applied as a theoretical formula. Qa = Kov.A. (Ya-H (y) .Xa) lm Qa: Dissolution amount A: Effective membrane area (gas-liquid contact area) H (y): Henry's constant ya: Gas mole fraction in gas Xa: Liquid Gas mole fraction Kov in: Overall mass transfer coefficient According to the above equation, the dissolved amount of gas is proportional to the gas-liquid contact area. Therefore, the amount of dissolved gas should be proportional to the porosity. However, the present inventors have found that, in the case of PTFE porous, this theoretical formula is not applicable depending on the region, and the present invention has been completed. That is, if the porosity is lowered, the pore diameter is also decreased, and it is expected that the water leak pressure will increase. At the same time, if the porosity is lowered, the gas-liquid contact area is reduced and the gas dissolution amount is also lowered. It is normal to think. However, surprisingly, the porosity was 40%.
It was found that even if the content is smaller than 10%, if the content is 10% or more, no decrease in the amount of dissolved gas is observed. PTFE is
Since the water repellency is extremely strong, the amount of dissolved gas does not seem to be affected by the porosity as long as the air layer is widened at the gas-liquid contact interface to form continuous pores. In this way, it was found that a porous membrane having a large gas dissolving ability and a large water leakage can be obtained in the range of the preferable porosity of the PTFE porous membrane. The porous PTFE
The tube has a porosity of 10% or more and 40% by uniaxially stretching a PTFE tube extruded into a tubular shape at a stretching rate of 115% or more and 140% or less.
It has the following characteristics and a leak pressure of 0.4 MPa or more.
It can be a tube.

[0010]

EXAMPLES The contents of the present invention will be described with reference to examples and comparative examples. In both Examples and Comparative Examples, the following is common:
A PTFE tube was made. Asahi Glass Fluoropolymers PTFE fine powder CD123 · 1kg, 220g naphtha as a liquid lubricant was added and mixed uniformly,
After preforming at a pressure of 5 MPa, the paste was extruded into a tube shape with a paste extruder and then heated to remove naphtha.

Next, in the vertical cylindrical furnace, uniaxially stretched at a predetermined ratio in each of Examples and Comparative Examples, and then sintered in the same cylindrical furnace to the inner surface of the tube. Examples, comparative examples,
Table 1 shows the shape, drawing rate and porosity of each tube.
Shown in. For each tube, a tube with a sample effective length of 500 mm was used to apply water pressure to the tube at a pressurizing speed of 0.1 MPa / 30 sec in the atmosphere, and the pressure when water droplets were observed on the outer surface of the tube was leaked. The pressure was investigated, and the results are also shown in Table 1. Also,
Breaking pressure means the pressure to break within 1 minute.

[0012]

[Table 1]

As can be seen from Table 1, as in Examples 1 and 2, by setting the stretching ratio to 115% or more and 140% or less, the porous PTF having a porosity of 10% or more and 40% or less.
E-tube is obtained. When the gas pressure outside the tubes is atmospheric pressure, the leak pressure of these tubes is 0.4M.
It has a property of being Pa or more, and being assembled in a module to dissolve ozone in water in a tube and sufficiently effectively used for cleaning semiconductors and liquid crystals. On the other hand, Comparative Example 2,
As shown in 3, the stretch ratio is set to 150% and the porosity is set to 45.
% And 60%, the water leak pressure becomes 0.
3, which is as small as 0.15 MPa, which is insufficient for cleaning semiconductors and liquid crystals.

Next, the tubes of Examples and Comparative Examples were bundled into a module, and ozone gas was dissolved in water in the tubes under predetermined conditions. At this time, a housing having an outer diameter of 53 mm and a length of 550 mm was used, and a tube having an effective length of 450 mm was used as a tubular membrane in Example 1, 100 in Comparative Examples 1 and 2, and Example 2,
In Comparative Example 3, 50 pieces were used. Also, in the housing,
Ozone gas was supplied at a concentration of 200 g / Nm ³ at a gas pressure and atmospheric pressure at a gas flow rate of 0.25 liter / min.
The relationship between the water pressure in the tube and the dissolved ozone concentration (value one hour after starting the experiment) is as shown in FIG. 1, and in Examples 1 and 2, the water pressure was 0.1 to 0.4 MPa. In the range of, the dissolved ozone concentration was stable at 7 to 8 mg / L. On the other hand, as in Comparative Example 1, when the stretching ratio was 110% and the porosity was 5%, the dissolved ozone concentration was too low, and the cleaning effect could not be expected. Further, as in Comparative Examples 2 and 3, the stretching ratio was 150.
%, And the porosity increased to 45% and 60% are not suitable for cleaning semiconductors and liquid crystals because the water pressure stability is poor and the dissolved ozone concentration decreases with increasing water pressure.

[0015]

The porous PTFE tube having a porosity of 10% or more and 40% or less according to the present invention is obtained by extruding a PTFE tube into a tubular shape and stretching it at 115% or more and 14% or more.
It can be easily produced by substantially uniaxially stretching at 0% or less, the water leakage pressure is 0.4 MPa or more, and the gas pressure outside the tube remains at atmospheric pressure, even if the water pressure is increased. Of course, water does not leak from the water side to the gas side of the membrane, and ozone can be stably dissolved without the dissolution performance being lowered due to the infiltration of water into the membrane. Therefore, if this is assembled into an ozone dissolution module and ozone is dissolved in the water in the tube, it can be used sufficiently effectively for cleaning semiconductors and liquid crystals.

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between water pressure in a tube and ozone gas dissolved concentration in tubes of Examples and Comparative Examples.

[Explanation of symbols]

A Example 1 B Example 2 C Comparative Example 1 D Comparative Example 2 E Comparative Example 3

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI C02F 1/78 C02F 1/78 C08J 9/00 C08J 9/00 A (56) Reference JP-A-11-227087 (JP, A ) JP-A-10-174834 (JP, A) JP-B-42-13560 (JP, B1) (58) Fields investigated (Int.Cl. ⁷ , DB name) B01D 61/00-71/82 510 B01D 53 / 22 B01F 1/00

Claims (2)

(57) [Claims] 1. A porous PTFE tube having a porosity of 10% or more and 40% or less and a leakage of the tube.
A tubular membrane for dissolving a sparingly soluble gas , which has a water pressure of 0.4 MPa or more . 2. A paste extrusion molding method is used to mold a mixture of PTFE fine powder and a liquid lubricant into a tube shape, and after heating to remove the liquid lubricant, a stretching ratio of 115% or more and 140% or less. By uniaxially stretching the film , the porosity is 10% or more and 40% or less, and the leakage
A method for producing a hardly-soluble gas-dissolving tubular membrane, characterized in that the tube has a water pressure of 0.4 MPa or more .