JPS6186908A - Treatment for making hollow yarn hydrophilic - Google Patents

Abstract

PURPOSE:To impart durable hydrophilicity to all of the outer surface, fine pores and inner surface of a hydrophobic microporous hollow yarn membrane by applying low temp. plasma treatment to said membrane by using active gas for forming a hydrophylic group before using inert gas. CONSTITUTION:Low temp. plasma treatment using active gas capable of forming a hydrophilic group is applied to a microporous hollow yarn membrane comprising a hydrophobic polymer. As the active gas, nitrogen-containing gas such as N2, NH3, CH3NH2, NO or NO2, oxygen-containing gas such as O2 or CO2 or sulfur-containing gas such as SO2 or H2S is used under pressure of 10<-4>-1torr. Next, low temp. plasma treatment is performed under pressure of 10<-4>-1torr by using inert gas. A treatment time is pref. about 1-10sec in both treatments.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for treating a microporous hollow fiber membrane with wood to provide excellent durability.

[Prior Art] Recently, hollow fiber membranes have been used for various separation processes. One advantage of hollow fiber membranes is that they can have 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 this microporous hollow fiber 1112 made of polyolefin resin or the like for an aqueous separation process, it is necessary to allow water to pass through the fine pores of the hollow fiber membrane. First, it is necessary to use this hollow fiber IIQ after being subjected to a hydrophilic treatment.

Conventionally, such polyolefin-based hollow fiber membranes have been subjected to parenterization treatment using, for example, alcohol for hollow fiber +12.

This was done by immersing it in a wood-loving agent such as a surfactant or coating it with a hydrophilic compound. Although these hydrophilic treatment methods are extremely easy to carry out, they lack long-lasting hydrophilicity, and while immersed in water, the wood-philicity of the fine M11 holes in the entire thread remains However, there is a problem that when the hollow fiber membrane dries, its wood-philicity is immediately lost, and it has been desired to develop a hydrophilic treatment method with excellent durability.

Various methods have been known for hydrophilic treatment of the surface of a self-hydrolytic, t:1 molecule substance.

For example, a method of forming hydrophilic groups by irradiating ultraviolet rays in the air,
Examples of methods include corona discharge treatment, flame treatment, oxidizing chemical treatment, oxidizing gas treatment, and plasma treatment. It is well known that although good plants can be obtained, their parentness 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 acid (ζ scum) and then treated with low-temperature plasma of -carbon or argon. This method has been shown to stably achieve hydrophilization of the surface of the plastic molded product and suppression of bleed of the 11f/fJj agent in the molded product. In such a method, as described in the example in 1.1, the wood-philicity decreases over time, and the long-term storage stability of hydrophilicity decreases with age. There is no difference in making the microporous hollow fibers 11 hydrophilic, which is required.

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. This method could not be applied to parent wood of hollow fiber membranes.

[Problems to be Solved by the Invention] As a result of intensive study on the durable parent wood-forming processing power υ of microporous hollow fibers, the present inventors found that the activity of forming parent wood, ( By a two-stage treatment of low temperature plasma treatment under specified conditions of gas followed by low temperature plasma treatment under specified conditions of inert gas.

The long-lasting and hydrophilic property is achieved by making not only the outer surface of the hollow fiber membrane hydrophilic, but also the extremely fine pore surface within the hollow fiber membrane and the inner surface of the hollow fiber membrane. This discovery led to the completion of the present invention.

The uninvented target is the outer surface of the microporous hollow fiber membrane, 11A.
The object of the present invention is to provide a simple treatment method that imparts durable wood parentification to all of the fine pores and inner surface of the wood.

[Structure of the Invention] In other words, the method for hydrophilizing a microporous hollow fiber membrane of the present invention is to treat a microporous hollow fiber membrane made of a hydrophobic polymer under a gas pressure of lO°'' of an active gas that forms hydrophilic groups. ~l toor
5. Then, the hollow fiber 119 is treated in a low-temperature plasma of an inert gas at a gas pressure of lO'4 to 1 toor.

[Optimum Mode for Carrying Out the Invention] In the method for hydrophilizing a microporous hollow fiber membrane of the present invention, first, a microporous hollow fiber membrane is treated with parent wood, an active casing capable of forming ( treated with low-temperature plasma.

1; Pathological waste includes nitrogen, ammonia, methylamine, dimethylamine, -nitrogen-containing thread waste such as nitrogen oxide, nitrogen dioxide; oxygen, -acid-containing thread gas such as carbon oxide, [9 thread gas;
Active gases such as +llxJtM dregs, nitrogen-containing thread dregs such as hydrogen sulfide, etc. are preferably used.

The treatment of this active residue with plasma takes 104 to 1 t.
This is carried out by generating low-temperature plasma of active scum at a pressure F of orr and leaving hollow fiber +1Q in this plasma atmosphere, thereby forming hydrophilic groups on the surface of hollow fiber 1. Since the pressure of the active gas is not suitable for cleaning the surface of the plastic molded product, the pressure of the active gas should be set to conditions that facilitate the formation of hydrophilic groups, i.e., 10-3 to 10'.
A pressure range of torr is more preferred.

Activated capacitance: If the force exceeds 1 tart, there is sufficient hydrophilicity on the surface of the hollow fiber), (If the force is not formed and, conversely, the gas pressure is not 104 torr), (If the force exceeds 1 tart, the fibrils of the hollow fibers of the material are destroyed or not. Become chopsticks.

In order to generate a low-temperature plasma of active scum, it is sufficient to apply a power of about 10 to 500 W at, for example, 13.56 MHz between the electrodes. The treatment time depends on the applied voltage, plasma gas concentration, membrane size of the hollow fiber membrane to be treated,
Although it varies depending on the treated fabric, the method of supplying the treated hollow fibers, etc., it is sufficient to process for about 0.1 seconds to 1 minute.
If the treatment time is too long, the fibrils of the microporous hollow fibers may be cut. On the other hand, if the processing time is too short, parent tree formation may not be sufficient. The preferred active gas low temperature plasma treatment time ranges from 1 second to 10 seconds.

Of course, prior to this active gas plasma treatment, the hollow fibers 11 to be treated may be subjected to cleaning, drying, etc.

Various methods can be used as appropriate to arrange the hollow fiber membranes in the processing apparatus during plasma processing. For example, the hollow fibers 11 may be placed in a plasma processing apparatus with appropriate 5B dispersed therein, and plasma processing may be carried out.
Alternatively, a yarn feeding roll and a yarn winding roll are disposed in the plasma processing apparatus, and while these rolls are rotated, plasma is continuously applied to the medium yarn stretched linearly between the rolls. Processing may be performed.

By treating this active residue with plasma, the surface of the microporous hollow fiber membrane (including the pores and inner surface of the fiber)
Activated plasma acts on the surface17, and depending on the type of active P1 residue used on the surface, water M), I;, ,
Calhono sulfonate (, amine 7), cis-sulfonic acid group, etc.), I; is produced. The hydrophilic layer formed on the surface of the porous hollow fiber (11Q) depends on the use of the porous hollow fiber (11Q), so the hydrophilic layer formed on the surface of the porous hollow fiber (11Q) is determined by using an active gas ligature suitable for that purpose. It is better to generate

After performing low-temperature plasma treatment using an active gas that forms hydrophilic groups as described in I-1, the introduction of the active gas is stopped.
2. Next, vent inert gas to increase the pressure to 104~1Too.
r, preferably 10-'-10-'Toor, and generate plasma according to the plasma generation method for the active gas described above to perform plasma processing. The plasma treatment time at this time also varies depending on the applied pressure, etc., but generally the purpose is sufficiently achieved by treating the culm for 0.1 seconds to 1 minute, but more preferably 1 second to 10 minutes. It is in the range of seconds.

In this second step, plasma treatment under specific processing conditions under an inert gas atmosphere makes it possible for the first time to impart wood-philic properties to hollow fibers that are durable over time without causing fibril destruction. Ta.

= Q2 It is well known that plasma treatment with active gases such as acid and ammonia makes the surface of plastics woody, but it is also well recognized that the woody property obtained deteriorates over time. This is where I am. It is generally understood that the cause of hydrophilic deterioration over time is that hydrophilic groups formed on the plastic surface rotate and sink into the interior of the plastic due to the micro-interlocking of polymers.

However, if the second stage of plasma processing in an inert gas atmosphere is performed under specific plasma processing conditions, surprisingly, the first stage of plasma processing is 11? It has been found that the hydrophilicity obtained by this method does not deteriorate over time. This is probably because under certain conditions, the plasma treatment with an inert gas successfully forms crosslinks on the plastic surface, which serves as an opportunity to prevent the rotation of the hydrophilic molecules formed on the plastic surface.

Therefore, it is necessary to set the plasma processing conditions of the inert gas atmosphere F in the second stage within the above-mentioned range, and depending on the processing under conditions outside this range,
” target is not achieved. For example, the pressure of inert gas is l t
If it exceeds orr, energy sufficient to crosslink the plastic surface cannot be obtained, while if the gas pressure is less than 10°' torr, deterioration of the base material and fibril destruction will become noticeable. Regarding the treatment time, if the treatment time is less than 0.61 seconds, no crosslinking effect will be obtained on the plastic surface, and conversely, if the treatment time is more than 1 minute, the previously formed wood-philic groups may be removed by the inert gas plasma. , the fibrils of microporous hollow fibers may be cut.

It should be noted that there are various plasma processing methods other than the method described in 1. For example, low frequency, microwave, direct current, etc. can be used as the radiant frequency band.

Plasma generation modes include glow discharge and corona discharge.
, spark discharge, silent discharge, etc. Also'
In addition to external electrodes, the electrodes may be internal electrodes, coil types, etc., capacitively coupled or inductively coupled. 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.

The inert gas used in the second treatment step of the method of the invention includes helium, neon, 7-Rugone, etc.
One or more of these gases can be used.

There are no particular restrictions on the microporous hollow fiber membranes that can be subjected to plasma treatment, but especially hydrophobic crystals such as polyethylene, polypropylene, polyester, etc., which are difficult to form into durable fibers using other treatment methods. Microporous hollow fiber fibers obtained by cold-stretching a precursor obtained by preventing melting of a polypropylene polymer and, if necessary, hot-stretching and heat-setting, are suitable.

In particular, JP-A-57-6611 made of polyethylene
In the case of the microporous hollow fiber 11 disclosed in No. 4, even when subjected to the plasma treatment mentioned above, there were no observed decreases in various physical properties and almost no chemical deterioration, making it one of the preferred treatment targets.
It is a thread membrane. This microporous hollow fiber membrane made of polyethylene has a laminated structure in which micropores are reciprocally connected from the inner wall surface to the outer wall surface of the hollow membrane.
0 to 90% by volume, the micropores are (1) strip-shaped micropores formed by microfibrils arranged in the fiber length direction and nodules connected almost at right angles to the microfibrils; 2) Average size a of the microfibrils. and the average length of the head is d, = 0.02~0.3 p, mu = 0.5~3.
It is 0p.

(3) The average length of the knot in the fiber length direction is
0.1-1.0, (4) Average width & average length of the strip-shaped micropores = 0.3-5. It is specified by having a relationship of Tv/dv=3 to 50. Furthermore, the bubble point of hollow fiber ■Q in ethanol is 1 to 20 kg/cm2.
It is preferable that the value falls within the range of .

In the microporous hollow fiber membrane treated with plasma in this manner, not only the outer surface but also the fine pores within the membrane and the entire inner surface are made durable and hydrophilic. This is confirmed by the following 411 constant. Is it naturally expected that the outer surface of the hollow fiber 11 becomes wood-philic due to plasma treatment?The wood-philic nature of the outer surface of the hollow fiber membrane after treatment was confirmed by measuring water retention. be done.

The water retention capacity of a hollow fiber membrane can be determined by the following method. For example, a module containing a hollow fiber membrane is created, and by passing ethanol and then water through this module, the inside of the module is completely replaced with water. Tosui et al. 1
, find. Next, after draining the water in the module, after a certain period of time, a slight water pressure is applied from one side of the hollow fiber membrane to determine water permeability: 11. The amount of water permeation at this time is divided by the initial amount of water permeation and expressed in 100%, or hollow fibers with poor water retention cannot obtain water permeation Xlt equivalent to the initial amount.

Furthermore, it is confirmed that the fine pores and inner surface of the hollow fiber membrane are made hydrophilic by the plasma treatment by measuring the water permeability pressure of the hollow fiber membrane after the treatment. The water permeability pressure is determined, for example, by applying water pressure from one side of the hollow fiber membrane, and as the water pressure when water starts flowing out through the hollow fiber membrane at a constant level of water H and X.

[Effects of the Invention] According to the treatment method of the present invention, not only the outer surface but also the fine pores and inner surface of the microporous hollow fibers made of hydrophobic polymers are treated. It is made of a hydrophobic polymer that has a unique microstructure of pores and has excellent separation performance. It has become possible to further expand the application fields of microporous hollow fiber membranes.

[Examples of the Invention] The present invention will be described in more detail below with reference to Examples.

Example 1 A polyethylene hollow fiber (manufactured by Mitsubishi Rayon Co., Ltd., grade EHF-2707) with an average inner diameter of 2701 LII, a porosity of 70%, and a bubble point of 2.2 kg/am' was used with parallel f-plate internal electrodes. The sample was placed in a Pelger-type plasma processing machine (distance between electrodes 20 cm) as shown in FIG. 1. Under high frequency discharge of 13.5EtMHz, output 50W and 02 pressure 0.01torr,
After exhausting the 0 and 02 gases, the process was carried out for 5 seconds.

5 at a pressure of 0.01 torr with Ar gas and a discharge output of 50 W.
Processed for seconds.

After the obtained hollow fibers were left for one week, water permeability and water retention were measured, and the water permeability was 3.1 kg, and the water retention measured after 4 hours was 99%. On the other hand, the permeability pressure of untreated hollow fiber EHF-2707 is 5.6 kg,
Water retention after 4 hours was 70%.

Furthermore, the hollow fibers subjected to the plasma treatment described in 1- were left for 6 months, and the water permeability pressure and water retention property were remeasured. showed 101%, indicating that it had excellent durable wood-parenting properties.

Example 2 The same hollow fiber EHF-270T used in Example 1 was
The plasma processing apparatus was installed in a plasma processing apparatus manufactured so that the 13.58 MHz high frequency inductively coupled steel tube shown in FIG. 2 could be passed continuously through a glass tube. While the hollow fiber was continuously passed through the tube at a speed of 5 crm/sec, a high frequency output of 100 W, NH, and gas pressure of 0.
007 torr. The discharge section is approximately 30cm
Therefore, the processing time is about 6 seconds.6 Then,
After exhausting the NH3 gas, rotate the hollow fiber in the opposite direction for 5 a.
High frequency output 100W while passing at a speed of m/see,
Processing was performed at an Ar gas pressure of 0.007 torr. The processing time is approximately 6 seconds.

The water permeability and water retention of the obtained hollow fibers after being left for one week were 2.8 kg/crn'' and 102% (after 4 hours), respectively.After the same sample was left for 6 months, the sewage pressure and When we re-measured the water retention capacity, it was 2.7 kg/cm.
' and 88% (after 4 hours), indicating excellent durable parent wood properties.

Reference Example 1 The same experiment as in 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.
．． It was 43.43 degrees.

Comparative Example 1 Using the same hollow fiber and plasma treatment machine as in Example 1, the hollow fiber was heated at an output of 50 W and 0. The treatment was performed at a pressure of 0.4 torr for 10 minutes.

When the water permeability pressure and water retention property of this hollow fiber after 6 months were summed up by a:11, the water permeation pressure was 4.5 kg/cm', and the water retention property after 4 hours was 75%, which was poor. Additionally, during water permeability measurements, it was observed that pinholes had occurred in the hollow fibers, and water spewed out from the pinholes.On the other hand, when the surface of the hollow fibers was observed with an electron microscope, many fibrils were broken. It turned out that

Comparative Example 2 Using the same hollow fiber and plasma treatment device as in Example 1, the hollow fiber was first heated to 1 at an output of 150 W, O, and a pressure of 2 torr.
After processing for 0 minutes and then exhausting the O2 gas,
The sample was treated with r-scum at a pressure of 2 torr and an output of 150 W for to minutes.

The obtained hollow fibers were allowed to stand for 6 months, and then their water permeability and water retention were measured. The permeability pressure was 4.7 kg/crrr', and the water retention after 4 hours was poor at 78%, and jetting of water due to pinholes was observed during the permeability measurement.

In addition, when observing the surface of the hollow fiber with an electronic WJ microscope, we found that
It was found that many fibrils were cut.

[Brief explanation of the drawing]

FIGS. 1 and 2 are schematic diagrams showing an example of a processing apparatus used in the plasma processing method of the present invention. 1: Vacuum container 2 Two electrodes 3: Hollow fiber 4: Raw material gas supply pipe 5: Deaeration pipe
6: High frequency circuit 7: Yarn winding roll 8: Yarn feeding roll Patent applicant Tamabishi Rayon Co., Ltd. Figure 1 Figure 2

Claims (1)

[Claims] 1) A microporous hollow fiber membrane made of a hydrophobic polymer is heated to a gas pressure of 10^-^4 to 1too of an active gas that forms hydrophilic groups.
A method for hydrophilizing a microporous hollow fiber membrane, comprising the steps of treating the hollow fiber membrane in a low temperature plasma of an inert gas pressure of 10^-^4 to 1 toor. 2) The processing method according to claim 1, wherein the processing times in the two low-temperature plasmas are both in the range of 0.1 seconds to 1 minute. 3) The processing method according to claim 1 or 2, wherein the gas pressures in the two low-temperature plasmas are both in the range of 10^-^3 to 10^-^1 toor.