JPS6283007A - Hydrophilic treatment of hollow yarn - Google Patents

Abstract

PURPOSE:To turn the micro bores inside the membrane and also the inner face of membrane hydrophilic and durable by carrying out the two-stage plasma treatment to treat the membrane in low temperature plasma with the gas which able to form the hydrophilic radical after the micro porous hollow yarn membrane being treated with the plasma polymerizable gas. CONSTITUTION:The micro porous hollow yarn membrane 3 made of hydrophobic polymer such as polyethylene and the like is placed in the belljar-type plasma treater 1, and is treated with the plasma polymerizable gas such as methane gas having gas pressure 10<-4>-1torr under the high-frequency electric discharge. After the said gas is exhausted, the activated gas, which is able to form the hydrophilic radical such as O<2> gas, is treated in the low temperature plasma having the activated gas pressure 10<-4>-1torr. The porous hollow yarn membrane treated with the two-stage plasma turns hydrophilic not only in its outer face but also in the micro bores inside the membrane and the entire inside of the membrane.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for making microporous hollow fiber membranes hydrophilic with excellent durability.

[Prior Art] Recently, hollow fiber membranes have been used for various separation processes. Hollow fiber membranes have the advantage of having a much larger membrane area than flat membranes. When hollow fiber membranes were initially developed, homogeneous hollow fiber membranes were mainly made of materials such as cellulose resins and silicone resins, but recently, microporous hollow fiber membranes made of polyolefin resins, etc. The microporous membrane has attracted attention because of its excellent separation performance due to its pore structure and because it is easy to manufacture.

However, when using microporous hollow fiber membranes made of polyolefin resins etc. for aqueous separation processes, it is necessary to allow water to pass through the fine pores of the hollow fiber membranes. In order to use this hollow fiber membrane, it is necessary to make it hydrophilic.

Conventionally, such hydrophilic treatment of polyolefin hollow fiber membranes has been carried out by, for example, immersing the hollow fiber membranes in a hydrophilic agent such as alcohol or a surfactant, or coating them with a hydrophilic compound. It had been. Although these hydrophilic treatment methods are extremely simple, the sustainability of hydrophilicity is poor, and while the hollow fiber membrane's fine pores retain their hydrophilicity while immersed in water, There is a problem in that once a hollow fiber membrane dries, its hydrophilicity is immediately lost, and it has been desired to develop a hydrophilic treatment method with excellent durability.

On the other hand, various methods are conventionally known as methods for making the surface of hydrophobic polymeric substances hydrophilic.

For example, a method of forming a hydrophilic group by ultraviolet irradiation in the air, a method of corona discharge treatment, a method of flame treatment,
Examples of methods include oxidizing chemical treatment, oxidizing gas treatment, plasma treatment, etc.
It is well known that, although all of these methods yield products with good hydrophilicity immediately after treatment, the hydrophilicity deteriorates over time.

- For example, according to the plasma treatment method disclosed in Japanese Patent Publication No. 58-14553, the surface of a plastic molded product is treated with low-temperature plasma of oxygen gas, and then treated with low-temperature plasma of carbon monoxide or argon. A method is shown. It has been reported that this method can stably make the surface of a plastic molded product hydrophilic and suppress the bleeding of the iT (Q31j agent) in the molded product. As described in the examples, the hydrophilicity still decreases over time, and is insufficient for hydrophilizing microporous hollow fiber membranes that require long hydrophilicity + iJI storage stability.

Furthermore, although normal plasma treatment methods can be applied to films, sheets, and molded bodies, microporous membranes with fibrils such as hollow fibers undergo fibril destruction, resulting in a significant drop in separation performance. It could not be applied to hydrophilization of hollow fiber membranes.

[Problems to be Solved by the Invention] As a result of intensive study on a durable hydrophilic treatment method for microporous hollow fiber membranes, the present inventors found that a crosslinked structure can be formed in microporous hollow fiber membranes. Through two-stage plasma treatment, gases are combined with plasma under specific conditions, and then low-temperature plasma treatment is performed under specific conditions using an active gas that forms hydrophilic groups.
Long-term durable hydrophilicity is achieved not only on the outer surface of the hollow fiber membrane, but also on the outer surface of the hollow fiber membrane.
The present inventors have discovered that the present invention can be applied to the surface of extremely fine pores in hollow fiber membranes and to the inner surface of hollow membranes.

The objective of the present invention is to provide a simple treatment method that imparts durable hydrophilization to all of the outer surface of a microporous hollow fiber membrane, the fine pores within the membrane, and the inner surface of the membrane. It is in.

[Last step L to solve the problem] That is, in the method for hydrophilizing a microporous hollow fiber membrane of the present invention, a microporous hollow fiber IIQ made of a hydrophobic polymer is heated at a gas pressure of lθ'' to I Lorr's plasma polymerizable gas to form a plasma polymerized membrane having a crosslinked structure on the hollow fiber membrane, and then the hollow fiber membrane is heated to a gas pressure of 10'' to I The method includes a process of processing in a low-temperature plasma of torr.

[Preferred IE for carrying out the invention] In the method for hydrophilizing a microporous hollow fiber membrane of the present invention, first, a specific plasma bonding method that can form a crosslinked structure in the microporous hollow fiber membrane is used. Perform plasma treatment in a gas atmosphere. Examples of the plasma polymerizable gas include carbon monoxide, carbon disulfide, or gases having 4 carbon atoms such as methane, ethane, ethylene, and acetylene.
The following gases such as hydrocarbons are preferably used because they can form a plasma-polymerized film having a high degree of cross-linking, and methane and carbon disulfide are particularly preferred because they form a cross-linked plasma-polymerized film with a high density.

Plasma polymerization using these plasma polymerizable gases is performed using lO
It is carried out in a low-temperature plasma under a pressure of 1 to 5 torr to form a plasma polymerized membrane on a microporous hollow fiber membrane. It is more preferable that the gas pressure is in the range of 10-3 to 3 torr.When the gas pressure exceeds Start, the crosslinking density in the plasma polymerized membrane decreases, and durable hydrophilic groups are formed on the surface of the hollow fiber membrane. On the contrary, when the gas pressure is less than 10'' tart, fibril destruction of the microporous hollow fiber membrane becomes significant.

To generate low-temperature plasma of plasma polymerizable gas,
between the electrodes, e.g. 13.58 MHz, 10-500
A power of about W may be applied. The polymerization time depends on the applied voltage, plasma gas concentration, the thickness of the hollow fiber membrane to be treated,
Processing j4. It is sufficient to polymerize for about 0.1 seconds to 5 minutes, although it varies depending on the method of supplying the treated hollow fiber membrane. If the polymerization time is too long, the fibrils of the microporous hollow fiber membrane may be cut or the hollow fibers may The pores in the thread membrane become blocked.

On the other hand, if the polymerization time is too short, the formation of a plasma polymerized film may not be sufficient. The preferred low temperature plasma polymerization time of the plasma polymerizable gas is in the range of 1 second to 30 seconds. Of course, prior to this plasma polymerization, the hollow fiber membrane to be treated may be subjected to cleaning, drying, etc.

Various methods can be appropriately adopted for the arrangement of hollow fiber membranes in the processing apparatus during plasma polymerization. For example, plasma polymerization may be carried out by leaving an appropriate amount of hollow fiber membranes in a scattered state in a plasma processing apparatus, or alternatively, a yarn feeding roll and a winding roll are arranged in a plasma processing apparatus. Plasma polymerization may be continuously performed on the hollow fiber membrane stretched linearly between the rolls while rotating these rolls.

Through this plasma polymerization, a high-density crosslinked plasma polymerized membrane is formed depending on the type of active gas used on the surface of the microporous hollow fiber membrane (including the pores and inner surface of the hollow fiber). The plasma polymerized membrane formed on the surface of a porous hollow fiber membrane is optimal depending on the material and purpose of the porous hollow fiber membrane, so use a plasma polymerizable gas that is suitable for the material and purpose. It is preferable to generate a crosslinked plasma polymerized film by

After performing low-temperature plasma polymerization using a plasma polymerizable gas as described in 1-, the introduction of the plasma polymerizable gas is stopped, and then the active gas that forms a hydrophilic group is vented to increase the pressure to 10'I~. I Torr, preferably 10-3 to 10'
Torr is adjusted and maintained, and plasma is generated according to the plasma generation method for the plasma polymerizable gas described above, and plasma processing is performed. The plasma treatment time at this time also varies depending on the applied voltage, etc., but generally it is 0.1 seconds to 1 second.
By processing for about a minute, it is sufficient [1 target is achieved,
More preferably, it is in the range of 1 second to 10 seconds.

If the pressure of the active gas exceeds 1 torr, sufficient hydrophilic groups will not be formed on the surface of the hollow fiber membrane, while if the gas pressure is less than 10" torr, the deterioration of the hollow fiber membrane and fibril destruction will be significant. Regarding the treatment time, if the treatment time is less than 0.1 seconds, sufficient hydrophilic groups will not be formed on the surface of the hollow fiber membrane, and conversely, if the treatment time is more than 1 minute, the previously formed plasma π gold film will be activated. It is removed by plasma or the fibrils of the microporous hollow fiber membrane are cut.

Active gases that form hydrophilic groups through plasma treatment include oxygen, nitrogen, ammonia, methylamine, dimethylamine, nitrogen monoxide, nitrogen dioxide, sulfur dioxide, hydrogen sulfide, and other gases that form excellent hydrophilic groups. Therefore, it is preferable,
These may be used in combination. Considering the ease of handling these gases, oxygen and ammonia are particularly preferred.

By the two-step treatment of plasma polymerization and plasma treatment described in I- below, it has become possible for the first time to impart hydrophilicity that is durable over time to hollow fiber membranes without causing fibril destruction.

Although it is generally known that plastic surfaces are made hydrophilic by plasma treatment with active gases such as oxygen and ammonia, it is also well recognized that the obtained hydrophilicity deteriorates over time. It is generally understood that the cause of hydrophilic deterioration over time is that hydrophilic groups formed on the plastic surface rotate and crawl into the interior of the plastic due to the microscopic slow motion of the polymer. However, if a high-density crosslinked plasma polymerized membrane is formed on the surface of the microporous hollow fiber membrane before plasma treatment with an active gas that forms hydrophilic groups, the hydrophilicity obtained in the second stage of plasma treatment can be improved. It has been found that it does not deteriorate over time. This is because a plasma-polymerized film of plasma-polymerizable gases such as father (disulfide) and methane successfully forms a high-density crosslinked film on the surface of a hydrophobic polymer mainly composed of hydrocarbon chains, and this forms on the plastic surface. This is thought to be because it functions to prevent the formed hydrophilic group from slipping in due to rotation.

Therefore, it is necessary to set the plasma interest rate condition of the first step plasma merging gas atmosphere within the above-mentioned range, and the object of the present invention cannot be achieved by processing under condition F outside of this condition range.

In addition, there are various plasma processing methods other than the above-mentioned methods. For example, low frequency, microwave, direct current, etc. can be used as the discharge frequency band, and the plasma generation mode also includes glow discharge, corona discharge, and spark discharge. , silent discharge, etc. In addition to external electrodes, the electrodes may also be internal electrodes, coil type, capacitive coupling, or inductive coupling.

However, no matter what method is adopted, it is necessary to select treatment conditions such that the pores of the microporous hollow fiber membrane to be treated are not deformed by the discharge heat.

There are no particular restrictions on the microporous hollow fiber membranes that can be subjected to plasma treatment, but especially hydrophobic crystalline membranes such as polyethylene, polypropylene, and polyester that are difficult to make durable and hydrophilic using other treatment methods. Microporous hollow fiber fibers obtained by cold-stretching a precursor obtained by melt-spinning molecules and, if necessary, hot-stretching and heat-setting, are suitable.

In particular, JP-A-57-1361 made of polyethylene
In the microporous hollow fiber membrane as disclosed in No. 14 and the microporous hollow fiber membrane as disclosed in Japanese Patent Publication No. 56-52123 made of polypropylene, various effects can be obtained by the above plasma treatment. There is almost no decrease in physical properties or chemical deterioration, making it a preferred hollow fiber membrane to be treated.

The microporous hollow fiber membrane made of polyethylene mentioned above has a laminated structure in which micropores are interconnected from the inner wall surface to the outer wall surface of the hollow membrane, and the porosity is 30 to 90% by volume. The micropores are (1) rectangular micropores formed by microfibrils arranged in the length direction and nodules connected approximately at right angles to the microfibrils, and (2) qz of the microfibrils. The average size J and the average length are du = 0.02~0.3, L = 0,5
~3,0 un, (3) the average length ZK of the nodule in the fiber length direction is ~0.1~1.0μ, (4) the average length of the short 1111-shaped micropores. width (TV and average length Zv dV/dM ~0.3~5, lv/dv =
It is specified by having a relationship between 3 and 50. Furthermore, it is preferable that the bubble point of the hollow fiber membrane in ethanol falls within the range of 1 to 20 kg/cm2.

In addition, the microporous hollow fiber membrane made of polypropylene described in -1- has a peripheral wall thickness of less than 40μ, and the peripheral wall has a pore radius distribution curve of a large number of interconnected micropores. It is specified by having at least one local maximum point within the range of 200-1200.

In the microporous hollow fiber membrane treated with plasma in this manner, durable hydrophilization is imparted not only to the outer surface but also to the fine pores within the membrane and the entire inner surface. Although it is naturally expected that the outer surface of the hollow fiber membrane will be made hydrophilic by plasma treatment, the hydrophilicity of the outer surface of the hollow fiber membrane after treatment is confirmed by measuring water retention.

The water retention capacity of a hollow fiber membrane can be determined by the following method. In this state, calculate the membrane area of the hollow fiber membrane, time, and water permeation rate per pressure.
Next, after draining the water in the module into a tank liquid, water is again supplied into the module after a certain period of time has elapsed, and the amount of water permeation is determined under almost the same conditions as the initial stage. The water permeation amount at this time is divided by the initial water permeation amount and expressed as a percentage, but for hollow systems with poor water retention, the same water permeation amount as the initial amount cannot be obtained.

In addition, plasma treatment can reduce the fine pores in the hollow fiber membrane and I+! 2. It is confirmed that the inner surface has been made hydrophilic by measuring the water permeability pressure of the hollow fiber membrane after treatment.

The permeation pressure is 1. For example, water is supplied by applying water pressure to the hollow part of a hollow fiber membrane whose one end is sealed.

It is determined as the water pressure when a constant amount of water begins to flow through the hollow fiber membrane.

[Effects of the Invention] According to the treatment method of the present invention, not only the outer surface of a microporous hollow fiber membrane made of a hydrophobic polymer but also the fine pores and inner surface of the membrane are treated. A microporous hollow fiber membrane made of a hydrophobic polymer that can easily impart durable hydrophilic properties to any substance, has a unique microstructure of pores, and has excellent separation performance. It has become possible to further expand the field of application.

[Example] Hereinafter, the present invention will be explained in more detail based on examples.

Example 1 A polyethylene hollow fiber (manufactured by Mitsubishi Rayon Co., Ltd., grade EHF-2707) with an average inner diameter of 270 μs, a porosity of 70%, and a bubble point of 2.2 kg/cm2 was used as a first fiber having a parallel plate inner electrode. It was installed in the Pelger-type plasma processing machine shown in the figure (distance between electrodes is 2 ha) in the state shown in FIG. 1. Under high frequency discharge of 13.5EIMHz, output 50W, methane gas pressure 1torr, 1
After processing for 0 seconds and exhausting the methane gas, 02 gas was introduced and the pressure of 02 gas was 0.01 to
rr, and a discharge output of 50 W was applied for 5 seconds.

After the obtained hollow fibers were left for one week, water permeability and water retention were measured, and the water permeability was 3.5 kg/cm2. Water retention measured after 4 hours was 99.8%. On the other hand, the permeability pressure of untreated hollow fiber EHF-2707 is 5.6k.
Water retention after 2.4 hours in g/am was 70%.

Furthermore, when the hollow fibers subjected to the above plasma treatment were left for 6 months and the water permeability and water retention properties were remeasured, the water permeability was 3. The water retention property after 2.4 hours was 100%, confirming that it had excellent durable hydrophilicity.

Example 2 The same hollow fiber EHF-2707 used in Example 1 was
The plasma processing apparatus was installed in a plasma processing apparatus manufactured so that it could continuously pass through a glass tube having a high-frequency inductively coupled steel tube of 13.58) Hlz shown in FIG. While the hollow fiber was passed continuously through the tube at a speed of 50 m/sec, the high frequency output was too high and the cs2 gas pressure was 0.01.
Processed with tarr. Since the discharge section is about 30 cm, the processing time is about 8 seconds.Next, after exhausting the C82 gas, NH3 gas is introduced, and the hollow fiber is moved in the opposite direction for 5 seconds.
High frequency output 100 while passing at a speed of cm/sec
W, N) +3 gas pressure 0. OO? Processed with torr.

The processing time is approximately 8 seconds.

The water permeability and water retention of the obtained hollow fibers after being left for one week were 18 kg/am 2.102% (after 4 hours), respectively. After the same sample was left for 6 months, the water permeability and water retention were re-measured and found to be 2.9 kg/cm each.
2 and 101% (after 4 hours), indicating excellent durable hydrophilicity.

Reference Example 1 An experiment similar to Example 1 was conducted on a polyethylene film, and the contact angle with water was measured after 1 week, 1 month, 3 months, and 6 months, and the results were 43.44, respectively.
．． It was 42.43 degrees.

Comparative Example 1 Using the same hollow fiber and plasma treatment machine as in Example 1,
The hollow fiber was treated at an output of 50 W and an O2 pressure of 0.4 torr for 10 minutes.

When the water permeability and water retention of this hollow fiber were measured after 6 months, the water permeability was 5.1·kg/cm and the water retention after 2.4 hours was poor at 75%. Furthermore, during the water permeability measurement, it was observed that pinholes were generated in the hollow fibers, and water spouted from the pinholes. On the other hand, when the surface of this hollow fiber was observed using an electron microscope, it was found that many fibrils were cut.

Comparative Example 2 Using the same hollow fiber and plasma treatment machine as in Example 1, the hollow fiber was first treated at an output of 150 W and a methane gas pressure of 2 torr.
After evaporating methane gas for 10 minutes, 02 gas was introduced, and treatment was performed for 10 minutes at 02 gas pressure of 2 torr and output of +50 W.

After the obtained hollow fibers were left for 6 months, water permeability and water retention were determined as Δ11. The permeability pressure was 5.6 kg/cm2, and the water retention after 4 hours was poor at 72%, and water gushing due to the generation of pinholes was observed during the permeability measurement. Furthermore, when the surface of the hollow fiber was observed using an electron microscope, it was found that many fibrils were cut.

[Brief explanation of drawings]

FIGS. 1 and 2 are schematic diagrams showing an example of a processing apparatus used in the plasma processing method of the present invention.

Claims (1)

[Scope of Claims] 1) A microporous hollow fiber membrane made of a hydrophobic polymer is treated in a plasma polymerizable gas with a gas pressure of 10^-^4 to 1 torr, and a crosslinked structure is formed on the hollow fiber membrane. A microporous membrane comprising the steps of: forming a plasma-polymerized membrane with Hydrophilic treatment method for hollow fiber membranes. 2) The hydrophilic treatment method according to claim 1, wherein the plasma polymerized film is formed in a low-temperature plasma of carbon monoxide, carbon disulfide, or a hydrocarbon having 4 or less carbon atoms. 3) The hydrophilic treatment method according to claim 2, wherein the plasma polymerized film is formed in a low-temperature plasma of methane or carbon disulfide. 4) The active gas according to claim 1, wherein the active gas is one or more selected from the group consisting of oxygen, nitrogen, ammonia, methylamine, dimethylamine, nitrogen monoxide, nitrogen dioxide, sulfur dioxide gas, and hydrogen sulfide. Hydrophilic treatment method. 5) The hydrophilic treatment method according to claim 4, wherein the active gas is oxygen or ammonia. 6) Plasma polymerization time during plasma polymerization film formation is 0.1
The hydrophilic treatment method according to claim 1, wherein the treatment time is in the range of seconds to 5 minutes. 7) The hydrophilic treatment method according to claim 1, wherein the treatment time in the low-temperature plasma using the active gas is in the range of 0.1 seconds to 1 minute.