JPH0765270B2 - Method for functionalizing hollow fiber membranes - Google Patents

Description

The present invention relates to a method for functionalizing a porous hollow fiber membrane.

In the present invention, the functionalization treatment includes hydrophilicity, antistaticity, biocompatibility, adsorption of specific substances such as dyes, proteins and lipids, antibacterial properties, high water repellency, etc. The functional monomer refers to a monomer having the ability to impart the above-mentioned function to the porous hollow fiber membrane when bound to the porous hollow fiber membrane.

[Conventional technology]

As hollow fiber membranes, membranes of various materials such as cellulose-based, polyolefin-based and polysulfone-based materials have been developed and used in the fields depending on the characteristics of each material.

However, as application development of membranes progresses, many applications are required to have multiple functions such as chemical resistance and hydrophilicity, biocompatibility and adsorption, hydrophilicity and antibacterial property, heat resistance and hydrophilicity.
There are no materials that satisfy both of these functions due to their inherent conflicting properties, or it is difficult to synthesize materials with specific multiple functions or to make hollow fiber membranes. Besides, there is an economical problem that the selection of materials for specific applications to form hollow fiber membranes does not provide a solid solution and the development cost is too high.

Therefore, functionalized surface treatment methods that impart new functions to existing microporous hollow fiber membranes have been actively investigated.

For example, as a method of imparting hydrophilicity to a polyolefin-based film, a method of applying a surfactant (JP-A-47-14269) is used.
JP-A-55-106239), and (meth) acrylic acid is graft-polymerized after irradiation with radiation such as γ-rays.

[Problems to be solved by the invention]

The former has the problem that the surfactant gradually falls off during use and elutes in the treatment liquid, while the latter is difficult to control the radiation source and is not suitable for general industrial use, or the radiation has high energy. Therefore, there is a problem that the hollow fiber membrane material is easily damaged. Further, the latter is formed as a microporous hollow fiber membrane in the space between the fibrils formed by multiple layers of fibrils laminated from the inner wall surface to the outer wall surface of the hollow fiber and nodes that fix both ends of the fibrils. When using micropores that are interconnected as spaces between the fibrils and penetrate from the inner wall surface to the outer wall surface of the hollow fiber, the fibrils that affect the fractionation characteristics of the membrane are cut off, and the membrane is exposed to high energy rays. However, it has a drawback that it is difficult to use because it is seriously damaged.

[Means for solving problems]

In view of the above circumstances, the present inventors have earnestly studied a method for functionalizing a microporous hollow fiber membrane, which is economical, has excellent productivity, is durable, and has little damage to the membrane. Reached

That is, the gist of the present invention is one or more polymers selected from the group consisting of functional monomers, photosensitizers and polyalkylene glycols, polyvinyl acetate or copolymers thereof, polyvinyl alcohol, acrylic resins, polyvinyl ethers, polyvinylpyrrolidone. In the method for functionalizing a hollow fiber membrane, a polyolefin-based microporous hollow fiber membrane is impregnated with a reaction solution containing a, and a cleaning treatment is performed after ultraviolet irradiation.

As the functional monomer used in the present invention, monomers having various functional groups can be used depending on the function to be imparted.

Hydrophilic, biocompatible, in order to impart antistatic properties, for example, -NH ₂ group, -OH group, -COOH group, OC ₂ H _{4 n} OH group, OC ₃
H _{6 m} OH, OC ₂ H _{4 n} OCH ₃ , OC ₂ H _{4 n} OC ₂ H ₅ groups, A monomer having a hydrophilic group such as —NCH ₃ ) ₂ group is used, and examples thereof include 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, acrylic acid, methacrylic acid, acrylamide, dimethylaminoethyl acrylate, N- Examples thereof include hydroxyethyl-N-methylacrylamide, N-hydroxymethylacrylamide, polyethylene glycol monoacrylate, polyethylene glycol monomethacrylate, polypropylene glycol monoacrylate, 2-methacryloyloxyethyl succinic acid, vinylpyrrolidone and vinylpyridine.

Further, dyes, proteins, to impart Aburano to adsorb lipids, etc. -SO ₃ H group, -SO ₃ Na group, a monomer having an -OSO ₃ Na group is used, examples of which 2-acrylamido - Two
-Methyl propane sulfonic acid, sulfoethyl acrylate, sulfopropyl acrylate, sulfophenyl acrylate, etc. can be mentioned, and in the case of imparting an antibacterial function as well as an adsorption function of dyes, proteins, lipids, etc., -N ⁺
A monomer having a CH ₃ ) ₃ · CH ₃ SO ₄ ⁻ group and a —N ⁺ CH ₃ ) ₃ Cl ⁻ group is used, and examples of such a monomer include acryloyloxytrimethylammonium chloride and trimethylaminoethyl methacrylate methylsulfate. Salt can be mentioned.

On the other hand, CF such as 3,3,3,2,2-pentafluoropropyl acrylate, 1,1,1,3,3,3-hexafluoropropyl methacrylate, 22,33,44,55-octafluoropentyl acrylate A monomer having a perfluoroalkyl group such as a _{2 n} F group gives a high degree of water repellency.

In addition, acryloyloxyethyl phosphite, methacryloyloxyethyl phosphite, etc. The monomer having is imparted with hydrophilicity and antistatic property.

These functional monomers can be used singly or in a mixed system of two or more kinds within a range having a function capable of being combined.

The functional monomer is preferably a monomer having an acryloyloxy group, a methacryloyloxy group or an acrylamide group as the polymerizable group, in consideration of the graft activity upon irradiation with ultraviolet rays.

As the photosensitizer used in the present invention, a photosensitizer that absorbs photons and is excited to extract hydrogen from the material forming the microporous hollow fiber membrane as a base material to form radical active sites on the base material is used. Examples of such a photosensitizer include benzophenone, 3,3 ′, 4,4′-benzophenone tetracarboxylic acid anhydride, 4,4′-dimethoxybenzophenone, 4-chlorobenzophenone, 2,4-dichlorobenzophenone, 4,
4'-dichlorobenzophenone, 4-fluorobenzophenone, 4-trifluoromethylbenzophenone, 4-methoxybenzophenone, 4-methylbenzophenone, 4,
Benzophenone-based photosensitizers such as 4′-dimethylbenzophenone, 4-cyanobenzophenone and o-benzoylbenzophenone, benzyl-based photosensitizers such as benzyl and dibenzyl ketone, 2-methylthioxanthone, 2 -Thioxanthone photosensitizers such as ethylthioxanthone, thioxanthone and 2-isopropylthioxanthone, anthraquinone photosensitizers such as anthraquinone, 2-ethylanthraquinone, 2-chloroanthraquinone and 2-t-butylanthraquinone, benzaldehyde, 4- Benzaldehyde photosensitizers such as methoxybenzaldehyde, 4-methylbenzaldehyde, 1-naphthaldehyde, 2,3
-Butanedione, dione-based photosensitizers such as 2,3-pentanedione, dibenzosuberone, methyl-o-benzoylbenzoate, 9-fluorenone, 3,4-benzofluorene, 1-acetylnaphthalene, benzanthrone, 9, Ten
-Phenanthrenequinone, 2-benzoylnaphthalene,
Examples thereof include 3,5-dimethylacetophenone and 4-bromoacetophenone.

Conventionally, a combination of a photosensitizer such as benzophenone, benzyl or 2-methylthioxanthone with a compound that easily releases hydrogen such as diethanolamine or diethylamine has been used as a photopolymerization initiator, and such a combination initiates polymerization. Radicals for generating the above are easily generated, but the radicals generated by exciting such a combination with light have a low hydrogen abstraction ability, and even if such a combination is used as the photosensitizer of the present invention, it is microporous. Radical active sites cannot be formed in the hollow fiber membrane, and even if a functional monomer coexists in the system, only a homopolymer is produced from the functional monomer and the microporous hollow fiber membrane cannot be functionalized. Therefore, as the photosensitizer of the present invention, a compound such as amine, which easily abstracts hydrogen, is used without coexisting.

There is no particular limitation on the material of the microporous hollow fiber membrane to be functionalized in the present invention, and ultrafiltration membrane, precision membrane, polyolefin such as polyethylene and polypropylene are relatively inexpensive materials, and the processing is It is preferable because it is easy and has excellent chemical resistance.

In addition, the structure of the microporous hollow fiber membrane is formed in the space between the fibrils, the micropores of which are formed by multiple layers of fibrils stacked from the inner wall surface to the outer wall surface of the hollow fiber and nodes that fix both ends of the fibrils. It is preferable that the micropores are interconnected as spaces between the fibrils and penetrate from the inner wall surface to the outer wall surface of the hollow fiber because a relatively small particle size can be prevented and the excess amount becomes large. Despite having a tendency to be damaged more easily than other structures, hydrogen is easily extracted from the hollow fiber membrane by the hydrogen abstraction type photosensitizer because the method of the present invention causes less damage. It is preferable because it is possible to easily form a radical active part to which a functional monomer can be grafted.

Such a hollow fiber membrane has the above-mentioned structure. (A) The average thickness ( _M ) and the average length ( _M ) of the fibrils are _M = 0.02-0.3μ _M = 0.5-3.0μ (B) The average length ( _K ) of the nodes in the fiber length direction is _K = 0.1 to 1.0 μ, and (c) the average width ( _V ) of the pores formed between the fibrils. And polyethylene having a porosity of 30 to 90 mol% such that the average length ( _V ) is _V / _V = 3 to 50, and the relationship between _V and _M is _V / _M = 0.3 to 5. Hollow fibers are shown as a preferred example.

Further, polypropylene hollow fibers as disclosed in JP-B-56-52123 are also preferably used.

The functionalization treatment of the hollow fiber membrane is possible even when treated in the same manner as in the method of the present invention using a reaction solution containing only the above-mentioned functional monomer and photosensitizer. Selected from the group consisting of polyalkylene glycol such as polypropylene glycol, polyvinyl acetate or vinyl acetate and (meth) acrylate, vinylpyrrolidone, copolymer of ethylene or unsaturated acid, polyvinyl alcohol, acrylic resin, polyvinyl ether, polyvinylpyrrolidone It was found that the coexistence of one or more types of polymers (hereinafter referred to as the adhesion-improving polymer) provides higher functionality than the case where they do not coexist. The amount of the adhesion improving polymer is preferably 1 to 300%, and more preferably 5 to 150%, based on the total weight of the functional monomer and the photosensitizer. If the amount of the adhesion improving polymer is less than 1%, the improvement in functionality is less than that in the case of more than 1%.
There is no further improvement in functionality compared to the case of 00%.

From the viewpoints of workability and adhesion, polyalkylene glycol, polyvinyl acetate or its copolymer, polyvinylpyrrolidone, and acrylic resin are preferably used as the above-mentioned adhesion improving polymer.

In the method of the present invention, the microporous hollow fiber membrane is impregnated with the reaction liquid containing the functional monomer as described above, the photosensitizer and the polymer A described above, but the functional monomer is a liquid at room temperature. When the photosensitizer and the polymer A are soluble in the functional monomer, only these can be used as the reaction solution, but when this system has a high viscosity at room temperature, the solubility of the photosensitizer is high. If it is not sufficient or if it is solid, the functional monomer, polymer A and the photosensitizer are dissolved in a solvent which can be used as a reaction solution. Examples of such a solvent include water, acetone, methyl ethyl ketone, ethyl acetate and the like.

The mixing ratio of the functional monomer and the photosensitizer is such that the molar ratio of the two is
It is preferably 1000 to 1/1 and more preferably 100 to 1.5 / 1. When the molar ratio of both is greater than 1000/1, the functionality is expressed, but the overspeed tends to decrease, and when the molar ratio is less than 1/1, the use efficiency of the photosensitizer deteriorates, The degree of polymerization of the grafted functional monomer does not sufficiently increase, and the functionality tends to be insufficiently exhibited.

For impregnation of the reaction solution into the microporous hollow fiber membrane, it is possible to apply the reaction solution to the hollow fiber in the form of a shower or curtain, and impregnate it, but it is more uniform to impregnate the reaction solution by the dipping method. It is preferable in that it can be caused. When the dipping method is used, it is possible to impregnate the hollow fiber with the reaction solution under pressure or under reduced pressure by reducing the size of the reaction solution impregnation tank through which the hollow fiber passes.

In the present invention, the microporous hollow fiber membrane impregnated with the reaction solution is irradiated with ultraviolet rays to carry out graft polymerization, and the graft ratio of the functional monomer to the hollow fiber membrane, that is, the functionality of the graft polymerization with respect to the weight of the hollow fiber membrane. The proportion of the monomer weight is preferably 0.1 to 100% by weight, more preferably 0.5 to 50% by weight. Graft ratio is 100% by weight
If it exceeds the above range, the functionality is not improved, but rather the overspeed is reduced. If the graft ratio is less than 0.1%, it is difficult to obtain sufficient functionality.

As a method for setting the graft ratio in a preferable range, the amount of functional monomer to be impregnated into the hollow fiber membrane, the ultraviolet irradiation energy, etc. are adjusted.

The functional monomer impregnation amount is preferably 0.1 to 500% by weight based on the weight of the hollow fiber, and the ultraviolet irradiation energy is 365 nm.
It is preferable to be 1 × 10 ^-3 ~10joule / cm ² as measured at a wavelength in the vicinity, and more preferably between ^{5 × 10 -2 ~1joule / cm 2} .

Considering the polymerization inhibitory effect of oxygen, the atmosphere during ultraviolet irradiation is preferably an inert gas such as carbon dioxide, nitrogen or helium.

Ultraviolet irradiation can use ultraviolet rays emitted from a xenon lamp, a low-pressure mercury lamp, a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, or the like. However, in view of productivity, the one having a high irradiation efficiency and a low calorific value is preferable. From this point, a high pressure mercury lamp with an electric input of about 10 W / cm to 300 W / cm is preferably used.

The time until the UV irradiation of the hollow fiber membrane impregnated with the reaction solution can be left for a long time in the case of a functional monomer with good adhesion to the hollow fiber membrane, but the functionality of poor adhesion is not a problem. When a monomer is used, the hollow fiber membrane of the substrate repels the functional monomer and the desired performance cannot be obtained. Especially when a polyolefin-based material such as polyethylene or polypropylene is used as the material for the hollow fiber membrane, it is easy to repel the functional monomer.
The irradiation with ultraviolet rays is preferably performed within 30 minutes, more preferably within 10 minutes.

The ultraviolet-irradiated microporous membrane is then washed to remove by-produced homopolymer, adhesion-improving polymer, photosensitizer and the like. For washing, a liquid which can dissolve or disperse a homopolymer of a functional monomer, a polymer for improving adhesion, a photosensitizer, and a decomposed product thereof as a washing solution and which does not substantially damage the hollow fiber is used. As the liquid, various solvents such as water and organic solvents can be used depending on the types of the functional monomer and the photosensitizer, and a surfactant, a wetting agent and the like may be added to improve the cleaning effect.

The washing may be extraction washing with the above washing solution, but it is preferable to apply ultrasonic waves during washing in order to improve washing efficiency and shorten washing time.

The intensity of ultrasonic waves is preferably adjusted so that the ultrasonic waves of 0.01 to 2.0 atm hit the hollow fiber, and more preferably 0.05 to 1.0 atm. If the ultrasonic wave intensity is less than the lower limit, the cleaning efficiency will not be improved, and if it exceeds the upper limit, the hollow fiber may be deteriorated.

It is preferable that the time from the end of UV irradiation to the washing does not exceed 30 minutes, more preferably within 10 minutes. If this time exceeds 30 minutes, you cannot wash effectively,
As a result, insufficient cleaning causes a decrease in the overspeed of the hollow fiber membrane, and the cleaning takes a long time.

〔Example〕

 Hereinafter, the present invention will be described in more detail with reference to examples.

The hydrophilicity, which is one of the functionalities, was evaluated using the following water permeation pressure.

Water Permeability Measurement Method A hollow fiber bundle was prepared in which one end was focused and fixed with a closed body, and the other end was focused and fixed with the opening of the hollow fiber end in an open state, and this was used as a test sample of water permeability. The hollow fiber bundle is visually observed while pressurizing water into the hollow fiber bundle from the opening end of the hollow fiber so that the pressure increases by 0,25 kg / cm ² every 30 seconds from 0 kg / cm ² . While the pressure is low, water does not come out from the side surface of the hollow fiber bundle, but when the pressure exceeds a certain pressure, the water begins to seep out, and when the pressure is further increased, the water comes out from the entire hollow fiber at a certain pressure or more. The pressure at which water starts to seep out from the entire hollow fiber is defined as the water permeation pressure of the hollow fiber.

The higher the hydrophilicity of the hollow fiber, the lower the water permeation pressure. Therefore, this water permeation pressure can be used as a measure of hydrophilicity.

Ultrasonic intensity Ultrasonic meter UTK-30 type (manufactured by Nippon Special Industries Co., Ltd.) was used for measurement.

Water Frax A mini-module having a membrane area of 20 cm ² was prepared using hollow fibers, and the hollow fibers were made hydrophilic by filling this module with ethyl alcohol, and after replacing the ethyl alcohol with water, 0.01-0.2 kg / cm ² The water pressure was applied to allow the water to pass, and the amount of permeated water per unit time under unit pressure was calculated.

Example 1 The micropores formed in the space between the fibrils are formed by the fibrils in which the micropores are stacked in layers from the inner wall surface to the outer wall surface of the hollow fiber and the nodes that fix both ends of the fibrils, and the micropores are formed between the fibrils. A microporous polyethylene hollow fiber, which is interconnected as a space and penetrates from the inner wall surface to the outer wall surface of the hollow fiber and which has the characteristics shown in the column of Example 1 in Table 1, acrylamide 142 g, benzophenone
A hollow fiber was impregnated with the reaction solution by slowly immersing it in a reaction solution consisting of 73 g, 50 g of polyvinyl acetate and 1000 g of acetone and pulling it up at a rate of 4 to 5 cm / sec. The amount of acrylamide attached to the hollow fibers was 60% by weight. Air dry this for 3 minutes
Ultraviolet rays were irradiated for 2 seconds in a nitrogen atmosphere using a 2 KW standard high pressure mercury lamp. The ultraviolet irradiation dose was 0.09 joule / cm ² . Then, while not exceeding 10 minutes after UV irradiation, ultrasonic waves are applied at an intensity of 0.4 atmosphere, and the hollow fibers are washed 4 times with a washing solution of acetic acid / water = 1/1 weight ratio, changing to fresh washing solution for 3 minutes each. did.

The results of examining the performance of the washed hollow fibers after air-drying overnight are shown in Table 1.

Incidentally, the performance of the hollow fiber before the treatment is shown in Reference Example 1 of Table 1.

Comparative Example 1 An experiment was conducted in the same manner as in Example 1 except that polyvinyl acetate was not used.

The results are shown in Table 1.

Comparative Example 2 An experiment was conducted in the same manner as in Example 1 except that benzophenone was not used.

As the result is clear from Table 1, acrylamide was not grafted, and no hydrophilizing effect was observed.

Comparative Example 3 The same procedure as in Example 1 was carried out except that benzophenone was not used and 20 Mrad of ionizing radiation was applied in a nitrogen atmosphere instead of UV irradiation.

The results are shown in Table 1. Although the graft content was 0.1% by weight, the breaking elongation and the breaking strength were significantly reduced.

Examples 2 and 3 The procedure of Example 1 was repeated, except that polyethylene hollow fibers having the same structure except that they had the properties shown in the columns of Examples 2 and 3 in Table 1 were used.

The performance of the obtained hollow fibers is shown in Table 1, and the performance of the untreated hollow fibers is shown in Reference Examples 2 and 3 of Table 1.

The amount of acrylamide deposited was 20% by weight in Example 2 and 5% by weight in Example 3.

Further, an experiment is shown in Table 1 as Comparative Examples 4 and 5 in the same manner as Comparative Example 1 except that the hollow fibers of Examples 2 and 3 were used.

As is clear from Table 1, the water permeation pressure is reduced by the treatment of the present invention.

In particular, it can be seen that the membrane of Example 1 has a large decrease in water permeation pressure and has an improved water flux.

Examples 4 to 6 have an average inner diameter of 270 μm, an average film thickness of 70 μm, and a porosity of 63%, and the fine pores are laminated in multiple layers from the inner wall surface to the outer wall surface of the hollow fiber and the node portion for fixing both ends of the fiber. Micro voids formed in the space between the fibrils formed by and are connected to each other as the space between the fibrils and penetrated from the inner wall surface to the outer wall surface of the hollow fiber,
Except that microporous polyethylene hollow fiber having the characteristics of _V / _M = 0.8 and _V / _V = 5 was used, the reaction solution had the composition shown in Table 2, and the ultrasonic intensity was 0.5 atm. Same as Example 1.

The amounts of the functional monomers (acrylamide, acrylic acid or 2-hydroxyethyl acrylate) attached after impregnating the reaction solution were 30% by weight, 30% by weight and 40% by weight, respectively.

The performance of the treated hollow fiber is shown in Table 2 together with the performance of the untreated hollow fiber (Reference Example 4).

Example 7 1100Å has a maximum distribution of hole radii of minute holes and has an average inner diameter
Microporous polypropylene hollow fiber with characteristics of 200μ, average film thickness 22μ, porosity 45%, acrylamide 71g, benzophenone 73g, polyvinyl acetate 50g and acetone 1000g.
An experiment was carried out in the same manner as in Example 1 using the reaction solution consisting of

The water permeation pressure and water flux of the untreated polypropylene hollow fiber were 20 kg / cm ² or more and 0.2 / hr ・ m ²・ mmHg, respectively.
The permeation pressure was improved to 13.1 kg / cm ² , and the water flux was 0.24.
/ hr · m ² · mmHg was shown.

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Claims (1)

[Claims] 1. A functional monomer, a photosensitizer and a polyalkylene glycol, polyvinyl acetate or a copolymer thereof,
1 selected from the group consisting of polyvinyl alcohol, acrylic resin, polyvinyl ether, and polyvinylpyrrolidone
A method for functionalizing a hollow fiber membrane, which comprises impregnating a polyolefin-based microporous hollow fiber membrane with a reaction liquid containing at least one polymer and performing a washing treatment after irradiation with ultraviolet rays.