JPS61266442A - Production of porous fluorinated polyolefin article - Google Patents

Abstract

PURPOSE:To obtain the titled porous article having excellent resistance to heat and chemicals, suitable for use as a microfilter and having a uniform pore structure, by deaerating a porous polyolefin article having a three- dimensional network structure in vacuum and fluorinating it. CONSTITUTION:A porous polyolefin article having a three-dimensional structure having an average pore size of 0.01-1mu and a void content of 30-95%, composed of fibers having an average diameter of 1mu or below, obtd. by mixing a fine inorg. powder and an org. liquid with a polyolefin resin, melt-molding the mixture and extracting the fine inorg. powder and the org. liquid, is deaerated under reduced pressure of 0.5X10<-1>mmHg or below for at least 10min. Fluorine gas under a pressure of 1-300mmHg and optionally, inert gas such as N2 or Ar are added (repeatedly several times) thereto to thereby bring the article into, contact with it for 1min-24hr in total, whereby the article is fluorinated to such an extent that a degree of fluorination reaches at least 40%.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a porous fluorinated polyolefin material and a method for producing the same. More specifically, the present invention is directed to a fluorinated polyolefin porous material having extremely excellent heat resistance and chemical resistance and having a uniform pore structure, which is suitable as a microfilter for refining various chemicals used particularly in semiconductor manufacturing processes. and a method for advantageously manufacturing the same.

Background of the Invention In recent years, with the rapid increase in demand for semiconductors, there has been an increase in the demand for products with excellent heat and chemical resistance for refining chemicals such as hot concentrated sulfuric acid, hot concentrated nitric acid, and hot phosphoric acid used in the semiconductor manufacturing process. The demand for microfilters is also increasing significantly. Conventionally, such microfilters have been made of porous membranes with a pore size of 1μ or less made of polytetrafluoroethylene (hereinafter abbreviated as PTFE) resin, which has excellent heat resistance and chemical resistance. (For example, r GORE-
Tl! :

However, since PTFK resin has poor processability, the shape of the molded product is limited, and a porous body with a uniform pore structure cannot be obtained, and productivity is low and cost is high. This method has disadvantages such as the high cost of the porous material.

Problems to be Solved by the Invention The object of the present invention is to overcome these drawbacks and to provide a microfilter that has excellent heat resistance and chemical resistance, and is particularly suitable as a microfilter for purifying various chemicals used in semiconductor manufacturing processes. The object of the present invention is to provide an inexpensive porous body having a uniform pore structure.

Means for Solving the Problems The present inventors discovered that polyolefins have excellent processability;
Focusing on the fact that a porous material with a uniform pore structure can be produced easily and at low cost, as a result of intensive research, we introduced fluorine gas into a polyolefin porous material with a specific structure to fluorinate the polyolefin. By doing so, they discovered that the above object could be achieved, and based on this knowledge, they completed the present invention.

That is, the present invention is characterized in that it has a three-dimensional network structure composed of fibers with an average thickness of 1 μm or less, has an average pore diameter of 0.01 to 1 μm, and is fluorinated to a degree of fluorination of 404 or more. It is an object of the present invention to provide a porous fluorinated polyolefin material. Such a fluorinated polyolefin porous material has an average pore diameter of 0 and is composed of fibers with an average diameter of 1 μm or less.
．． It can be produced by degassing a polyolefin porous body having a three-dimensional network structure of 0.01 to 1 μm under reduced pressure, and then introducing fluorine gas into the porous body under reduced pressure to fluorinate the polyolefin.

By the way, regarding fluorination treatment technology for molded products made of polyolefin resin, it has already been used industrially to modify the surface of molded products such as films. Fluorination treatment has also been attempted (UK Patent No. 710,523). However, this method requires a very long fluorination treatment (several days) in order to fluorinate the inside of the molded product, resulting in low productivity and is not suitable for industrial implementation.

On the other hand, according to the present invention, a polyolefin porous material having a three-dimensional network structure composed of fibers with an average thickness of 1 μm or less is fluorinated in a specific method, thereby making it possible to fluorinate the material in an extremely short time (several minutes to several minutes). The inside of the resin can be almost completely fluorinated in just a few hours), and the shape of the three-dimensional network structure is maintained essentially as is, while the heat resistance and chemical resistance are as excellent as those of porous PTFE membranes. You can get one with

In the present invention, polyolefin is used as the material for the porous body, but this polyolefin is not only inexpensive, but also has good processability and can easily provide a uniform porous body. Examples of such materials include polyethylene, polypropylene, polybutene, poly-4-
Methylpentene-1, ethylene-propylene copolymer,
Or ethylene-tetrafluoroethylene copolymer,
Examples include copolymers made of olefins and fluorine-based monomers, such as ethylene-chlorotrifluoroethylene copolymers. Among these.

In particular, polyethylene is suitable because it is inexpensive, easy to fluorinate, and so on.

In the present invention, the polyolefin porous body having a three-dimensional network structure composed of fibers having an average thickness of 1 μm or less is used.

This three-dimensional network structure refers to a porous structure in which a network structure made of resin is observed on the surface of the porous body and in cross sections in each direction, and refers to a so-called sponge structure having communicating pores. Such a three-dimensional structure has excellent strength as a porous body, and when this porous body is used for a filter, it has an excellent particulate removal effect.

Further, the fibers constituting the network structure refer to the network resin portion surrounding the holes, and are expressed as fibers for convenience, but there are no particular restrictions on their shape.

As long as it forms a three-dimensional network structure, other than fibrous shapes, thin film shapes, nodular shapes, and even irregularly shaped materials may be used.

In the present invention, the average thickness of the fibers constituting the network is 1 μm.
It is necessary that the following is true. If the thickness exceeds 1 μm, the fluorination treatment will take a long time and productivity will decrease. Furthermore, from the viewpoint of productivity and strength of the porous body, 0.01 to 0
．． Preferably, it is in the range of 5μ. The thickness of the fibers can be determined by observing the surface and cross section of the porous body using an electron microscope.
This value is the average thickness of the fibers in each part.

Moreover, the average pore diameter of the polyolefin porous material is 0.01 to
It is selected within the range of 1μ, preferably 0.05 to 0.5μ. If the average pore diameter is less than 0.01μ, there is a large resistance to the diffusion of fluorine gas into the porous body during fluorination treatment, and treatment spots are likely to occur, and when the porous body is used as a microfilter, Low permeability is not desirable. On the other hand, if it exceeds 1μ, the particle removal rate will be low when used as a microfilter, which is not preferable.

Furthermore, the porosity of the porous body is desirably in the range of 30 to 95%, more preferably in the range of 50 to 90%. If the porosity is less than 30, the permeability will be undesirably low when the porous body is used as a microfilter, and if it exceeds 95, the strength of the porous body will be undesirable.

The porous polyolefin material with a uniform pore structure used in the present invention can be obtained by, for example, mixing inorganic fine powder, organic liquid, and polyolefin resin, melt-molding the mixture, and extracting the inorganic fine powder and organic liquid from this molded product. (Japanese Unexamined Patent Publication No. 55-131028).

In the present invention, the polyolefin is fluorinated by bringing the polyolefin porous body into contact with fluorine gas. Regarding the fluorination treatment using this contact method, for example, a method is known in which fluorination is carried out by flowing fluorine gas at normal pressure onto the surface of the molded product (British Patent No. 710,523), but according to this method, , it takes time for the fluorine gas to diffuse into the porous body, and unevenness of fluorination occurs on the surface and inside of the porous body, and it takes a long time to sufficiently fluorinate the entire porous body. Undesirable.

In contrast, the present invention employs a method in which a porous polyolefin material is degassed under reduced pressure and then fluorine gas is introduced into the porous material under reduced pressure, and the porous material can be fluorinated uniformly and in a short time. In the present invention, in order to perform a particularly uniform fluorination treatment, the fluorination treatment is repeated several times using a low concentration fluorine gas, rather than one time fluorination treatment using a high concentration fluorine gas. is advantageous. Regarding the concentration of this fluorine gas, the pressure is 1 to 30 (lIIH
It is preferably in the range of g, especially in the range of 10 to 100,100 l. If the pressure is less than 1 ml Hg, the fluorination treatment will take a long time, and if it exceeds 30 ml Hg, side reactions such as resin deterioration will occur, which is not preferable.
If desired, fluorine gas may be mixed with an inert gas such as nitrogen, helium, or argon.
001 mHg, preferably 10-100 m11!
Selected within Hg range.

Further, the contact time between the polyolefin porous body and the fluorine gas depends on the concentration of the fluorine gas, but it is desirable that the combined contact time is in the range of 1 minute to 24 hours, particularly 30 minutes to 10 hours. If this contact time is less than 1 minute, the degree of fluorination will not be sufficient and uniform treatment will be difficult;
If it exceeds 4 hours, it will be disadvantageous in terms of productivity.

During such fluorination treatment, the presence of oxygen causes side reactions such as deterioration and coloring of the resin. Therefore, in the present invention, the porous polyolefin material is degassed under reduced pressure before introducing fluorine gas. conduct.

This vacuum degassing is carried out at a vacuum degree of 5×10 11Hg or less for 10 minutes or more, preferably 30 minutes or more.

Further, the oxygen concentration in the fluorine gas or in the mixed gas of fluorine gas and inert gas is preferably 10% or less, particularly 2 min or less. Further, the temperature of the fluorination treatment is preferably 50° C. or lower, particularly 30° C. or lower in order to prevent side reactions such as resin deterioration. If necessary, the porous body may be subjected to fluorination treatment while being cooled.

Unreacted fluorine gas after the fluorination treatment is removed from the porous body by degassing under reduced pressure and further washing with water.

The degree of fluorination of the polyolefin porous body fluorinated in this manner is indicated by the degree of fluorination determined by the following formula from the elemental composition of the fluorinated polyolefin.

For example, a fluorinated polyolefin having an elemental ratio of 1 carbon atom to 2 fluorine atoms has a degree of fluorination of 1
00 I regret it. Note that the elemental composition of the fluorinated polyolefin is determined by elemental analysis.

For example, "Polymer Analysis No Ndoptsuk" (edited by the Japan Society of Analytical Chemistry, published by Breakfast Shoten), pages 106 and 294 (
(1985). In addition, if the elemental composition of the polyolefin before fluorination treatment is known, the elemental composition of this fluorinated polyolefin is determined by assuming that the fluorine atoms are replaced with the same number of hydrogen atoms by fluorination. It can be roughly determined easily by weight measurement.

In the present invention, the degree of fluorination must be 40% or higher, preferably 70% or higher, and more preferably 80% or higher. If the degree of fluorination is less than 40%, the heat resistance and chemical resistance of the fluorinated polyolefin porous body will be low.

By the way, when used as a filter, it is generally used as a filtration device in the form of a module in which a filter made of a porous body is integrated with a housing and an adhesive. In this case, it is also possible to create a module using a polyolefin porous material and then subject this module to a fluorination treatment to fluorinate the polyolefin porous material.

Examples of the shape of the porous body of the present invention include a film shape, a hollow fiber shape, a tube shape, a pipe shape, a rod shape, and the like. The fluorinated polyethylene porous material of the present invention has a uniform pore structure, and has excellent heat resistance and chemical resistance comparable to that of a PTFE porous material. In addition, it is inexpensive, and by using this porous material as a microfilter, it can be used for heat-resistant and resistant materials such as filter purification of hot concentrated sulfuric acid, hot nitric acid, hot phosphoric acid, etc. It has become possible to carry out filtration and purification under extremely harsh chemical conditions with high precision and at low cost.

Example Next, the present invention will be explained in more detail with reference to Examples.

In addition, each physical property of the porous body was measured according to the following method.

(1) Average pore diameter (μ) The pore diameter was measured on the surface and cross section of the sample using an electron microscope and averaged.

(2) Maximum pore diameter (μ) Measured by bubble point method according to ASTM F-316.

(3) Porosity (regret) It was calculated using the following formula.

However, the pore volume was determined by subtracting the weight of only the porous body from the weight of the porous body whose pores were filled with water.

Example High-density polyethylene (manufactured by Asahi Kasei Corporation, Santic@S)
-360) 20.0% by weight, 56.4% by weight of dioctyl phthalate, and 23.6% by weight of finely divided silica were mixed in a mixer and then ground in a pulverizer. After melt-extruding this raw material into a hollow fiber shape using an extruder and a hollow nozzle,
It was cooled and taken away. The hollow fibers were immersed in 1.1.1-) dichloroethane to extract and remove dioctyl phthalate, washed with a 40% by weight aqueous sodium hydroxide solution and water, and further dried to obtain a polyethylene hollow fiber porous body. This porous body has an inner diameter Q of 7 am and a film thickness of 250
It was a uniform porous body that grew a three-dimensional network structure with an average pore diameter of 0.15 μ, a maximum pore diameter of 0.30 μ, and a porosity of 70 μ, and the thickness of the fibers constituting the network was 0.12 μ.

This polyethylene hollow fiber porous material was placed in a reaction vessel (inner diameter 2 (
1+m, length 30011m) K insert, I x 10-'
After degassing for 30 minutes at a vacuum level of 111Hg, fluorine gas was introduced into the reaction vessel to a concentration of 3Q111Hg for 20 minutes.
The reaction was carried out at ℃ for 30 minutes. Next, after degassing, fluorine gas was introduced at 3011 Hgt and reacted for 30 minutes, which was repeated 9 times. The contact time between the porous body and the fluorine gas was 5 hours. Next, after degassing and introducing nitrogen gas, the porous body was taken out of the reaction vessel, washed with water, and dried to obtain a fluorinated polyolefin hollow fiber porous body. This fluorinated polyolefin porous body has an inner diameter Q, 7 n
, film thickness 250μ, average pore diameter 0015μ, maximum pore diameter 0.3
0μ, porosity is 70, and the thickness of the fibers making up the net is 0.
It is a uniform porous body with a three-dimensional network structure of 12μ,
The degree of fluorination was 98.

This fluorinated polyolefin porous body was heated at 250°C for 10
There was no substantial change even after hours of heat exposure;
There was no substantial change even after immersion in 98% concentrated sulfuric acid for 10 days, and the heat resistance and chemical resistance were good.

For comparison, when a polyethylene hollow fiber porous material before fluorination treatment was exposed to heat at 250°C, it instantly melted and was significantly deformed, causing the pores to disappear; It melted and was significantly deformed, the pores disappeared, and it turned black and became extremely brittle.

Example 2 The same raw materials as in Example 1 were melt-extruded into a film using an extruder and a flat die, and the same operations as in Example 1 were carried out to obtain a polyethylene film-like porous body.

This porous material has a thickness of 300μ, an average pore diameter of 0.15μ, a maximum pore diameter of 0.30μ, a porosity of 70, and a three-dimensional network structure with a thickness of 0° and 12μ for the fibers that make up the network. Met.

This polyethylene film-like porous material is placed in a reaction container,
After degassing for 30 minutes at a vacuum level of 1X10,000 IHg, fluorine gas was introduced into one reaction vessel to a concentration of 80 mmHg and reacted at 20°C for 30 minutes. Next, after degassing, fluorine gas was introduced to a concentration of 80 mmHg. The operation of reacting for 30 minutes was repeated three times. The contact time between the porous body and the fluorine gas was approximately 2 hours. Next, after degassing and introducing nitrogen gas, the porous body was taken out from the reaction vessel, washed with water, and dried to obtain a fluorinated polyolefin film-like porous body.

This fluorinated polyolefin porous body has a film thickness of 300μ,
Average pore rotation 15μ, maximum pore diameter 0.30μ, porosity 70%
It was a uniform porous body having a three-dimensional network structure in which the thickness of the fibers constituting the network was 0.12 μm, and the degree of fluorination was 96.

% of this fluorinated polyolefin porous material at 250℃
There was no substantial change after 0 hours of heat exposure;
There was no substantial change even after 10 days of immersion in 98% concentrated sulfuric acid at °C, and the heat resistance and chemical resistance were good.

Comparative Example Three polyethylene film-like porous materials were stacked closely together as in Example 2, except that the film thickness was 100 μm.
The film thickness was the same as that of Example 2) and was placed in a reaction vessel. First, 1 atm nitrogen gas was flowed into the reaction vessel for 1 hour at a flow rate of 40 cc/min, and then a 1 atm mixed fluorine gas consisting of a fluorine gas partial pressure of 80 Hg and a nitrogen gas partial pressure of 6801111 Hg was flowed into the reaction vessel for 2 hours at a flow rate of 43 cc/min. It was passed to. Then,
After flowing 1 atm nitrogen gas into the reaction vessel at a flow rate of 4 Qcc/min for 1 hour, the porous body was taken out from the reaction vessel, washed with water, and dried to obtain a fluorinated polyolefin porous body.

When the degree of fluorination of this fluorinated polyolefin porous material was measured, the film-like porous material in the center layer was 5.
It was very low.

From these results, we found that the fluorination method, in which fluorine gas at normal pressure is brought into contact with the surface of the porous material while flowing it (-- however, it takes time for the fluorine gas to diffuse into the inside of the porous material, and it takes a long time to fully fluorinate the entire porous material. It takes time to find out what is undesirable.

Claims (1)

[Claims] 1. An average pore size of 0, composed of fibers with an average thickness of 1μ or less.
．． A porous fluorinated polyolefin material having a three-dimensional network structure of 0.01 to 1 μm and fluorinated to a degree of fluorination of 40% or more. 2 An average pore diameter of 0.2 made up of fibers with an average thickness of 1μ or less.
A polyolefin porous body having a three-dimensional network structure of 0.01 to 1 μm is degassed under reduced pressure, and then fluorine gas is introduced into the porous body under reduced pressure to fluorinate the porous body until the degree of fluorination reaches 40% or more. A method for producing a porous fluorinated polyolefin material.