JPH04293939A - Modification of porous membrane - Google Patents

Abstract

PURPOSE:To obtain a functional porous membrane uniformly modified throughout the entire membrane by using an inert carrier gas in a process comprising irradiating a base porous membrane with an ionizing radiation to form free radicals thereon and treating the irradiated membrane with a monomer gas to fraft the monomer thereonto. CONSTITUTION:A base porous membrane 4 (e.g. a hollow yarn porous polyethylene membrane) irradiated with an ionizing radiation is set in a reactor 1, and an insert gas containing a monomer (e.g. glycidyl methacrylate) in a monomer tank 2 is forcibly sent through a recirculation pump 3 to the entire bundles of the base membranes to evenly feed the monomer thereto and to bring the membrane into contact with the formed free radicals. A functional porous membrane uniformly modified throughout the entire membrane 4 can be obtained is good reproducibility.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for synthesizing a multi-functional membrane by modifying a porous membrane, and particularly to a method for uniformly imparting functionality to the entire membrane. What is a multifunctional membrane?
After introducing a hydrophilic group, an ion exchange group, a chelate forming group, or an active precursor mainly into the inner surface of the pores of the porous membrane, the functional group or the monoclonal antibody,
It is obtained by introducing a ligand such as protein A, and it is not only a simple filtration based on particle size, but also a specific filter that utilizes the electrical, chemical properties, or biological affinity of the particles. It can be used for separation and purification.

To describe the present invention in more detail, it is applicable to hydrophilic membranes, ligand-immobilized membranes used in the separation and purification of enzymes and microbial cells in the pharmaceutical and fermentation fields, ion-exchange membranes used in the production of ultrapure water, and This relates to a method for manufacturing multifunctional membranes such as ion exchange membranes and chelate membranes used for purifying circulating water in nuclear power plants, etc., and has high water permeability,
This invention relates to a method for uniformly modifying a porous membrane in order to produce a high-performance composite functional membrane that has a high functional group introduction rate and excellent removal and trapping efficiency for fine particles, bacteria, and ions.

0003

[Prior Art] Examples of research on modification of porous membranes in which functionality is imparted by irradiating the porous membrane with radiation and bringing it into contact with monomers in the gas phase can be found, for example, in Journal of the Chemical Society of Japan, 1988 [2] p. 212
-216, Journal of the Seawater Society of Japan, 1989 [1] p. 3-1
1, described in Japanese Patent Application Laid-Open No. 64-30606. By adding functionality to porous membranes that have chemical durability, mechanical strength, and structural characteristics such as pore structure and shape that have excellent contact efficiency with liquids, we have created products with excellent durability and strength. It is possible to obtain a functional porous membrane that has structural characteristics suitable for purification and separation processes and also has functionality such as hydrophilic groups, ion exchange groups, and chelate forming groups.

However, the conventional techniques have the disadvantage that the graft polymerization reaction is not necessarily carried out uniformly over the entire porous membrane. In particular, when modularizing a hollow fiber-like porous membrane, it is preferable to react as a fiber bundle for each module, but in this case, especially when using monomers with low vapor pressure, the supply of the monomer is As a result, the amount of graft polymerization in the membrane at the center of the yarn bundle was significantly lower than that at the outer periphery, which was a major problem in production.

For example, in a film into which alcoholic hydroxyl groups are introduced as hydrophilic groups, if the amount of hydrophilic groups introduced is uneven, the surface of the hydrophobic base material remains exposed in some parts of the film. Therefore, bacteria removal, enzymes,
During protein separation, problems such as clogging due to the adhesion of foreign proteins, etc. may occur, resulting in a decrease in water permeability, and the target substance being hydrophobically adsorbed to the membrane, resulting in a decrease in its recovery rate. Are known.

[0006] Furthermore, in a membrane into which ion exchange groups have been introduced through a graft polymerization reaction, if the amount of ion exchange groups introduced is uneven within the membrane and there is a region where the density of ion exchange groups is low, liquid will flow from that region. Since the ions inside break through in a short time, high ion removal efficiency cannot be obtained. In order to overcome the above drawbacks, it is essential to uniformly introduce functional groups throughout the membrane.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to obtain a functional porous membrane in which the entire porous base membrane is uniformly modified.

[0008]

[Means for Solving the Problems] As a result of intensive research aimed at achieving the above object, the present inventors found that the object could be achieved by using an inert, monomer carrier gas. , we have completed the present invention. That is, the present invention uses an inert carrier gas in a porous membrane modification method in which a porous membrane is irradiated with ionizing radiation to generate radicals, and then treated with a monomer gas to graft-polymerize the monomer. This is a method for modifying a porous membrane characterized by the following.

That is, a porous base film irradiated with ionizing radiation is placed in a reactor, and an inert gas containing monomer is forced to flow to uniformly supply the monomer throughout the bundle of base films. By contacting with radicals, it is possible to suppress graft unevenness in the radial direction of the yarn bundle and obtain a uniform graft polymerized film with good reproducibility. FIG. 1 shows an apparatus used in the manufacturing method of the present invention. Carrier gas flow is one pass, and pump 3
However, with the circulation method, the carrier gas can be used efficiently, and the amount of graft polymerization can be determined over time by the amount of monomer decrease in the monomer tank. Therefore, it is a more desirable method.

The present invention will be explained in more detail below. The present invention is intended to solve the unevenness of graft polymerization by uniformizing the monomer feed rate throughout the yarn bundle. Conventional methods for supplying monomers in the gas phase in a vacuum system relied on the movement of monomers by diffusion, so a monomer pressure gradient always existed as a driving force for monomer movement. In the present invention, since the monomer is moved by the flow of the carrier gas, it is independent of the pressure gradient of the monomer, and it is possible to realize a state in which the pressure of the monomer is uniform throughout the entire yarn bundle.

Furthermore, by circulating a carrier gas at a constant temperature, it is possible to obtain the effect of keeping the entire yarn bundle at a constant temperature. Reaction heat is generated by the graft polymerization reaction, and when the temperature rises due to heat accumulation and the radicals are deactivated, especially in the center of the yarn bundle, the concentration of the radicals becomes uneven, which causes unevenness in the amount of graft polymerization. However, the present invention has been able to eliminate such causes.

[0012] According to the present invention, the monomer supply amount and temperature can be uniformly controlled throughout the yarn bundle, and the distribution of grafting reaction rates can be eliminated. On the other hand,
It has the characteristic that any functional side chain can be uniformly introduced. As the base film, polyolefins such as polyethylene, polypropylene, and ethylene-propylene copolymers, ethylene-tetrafluoroethylene copolymers, and ethylene are used because they require chemical resistance, heat resistance, and mechanical strength. - Olefins represented by chlorotrifluoroethylene copolymers - Halogenated olefin copolymers, halogenated polyolefins represented by polytetrafluoroethylene, polyvinylidene fluoride, polychlorotrifluoroethylene, etc., and polysulfones are suitable. .

[0013] With the aim of obtaining a membrane with high water permeability, high functional group introduction rate, and excellent removal and capture efficiency for fine particles, bacteria, and ions, we particularly examined the structure of the base membrane, and as a result, we found a three-dimensional network structure. 0.01 μm to 1
It has micropores of μm and an inner diameter of 0.1 mm to 10 m.
It has been found that a hollow fiber having a thickness of 0.02 mm to 5 mm is preferable.

[0014] If the pore size is 0.01 μm or less, high water permeability cannot be obtained, and if the pore size is 1 μm or more, the efficiency of trapping ions and the like decreases, and leakage thereof cannot be ignored. In order to ensure membrane area per unit volume and high processing capacity when modularized, hollow fibers with a small diameter are desired, and in order to obtain strength, a certain wall thickness is required. .

However, in terms of the usefulness of the present invention, the membrane shape is not limited to the above range. This effect is exhibited not only for membranes with smaller or larger pore diameters, thinner membranes with thinner membranes, thicker membranes with thicker membranes, and flat membranes as well as hollow fibers. The monomer used in the present invention may basically be a liquid or gas that can undergo radical polymerization and has a certain vapor pressure at the reaction temperature. In the case of a liquid, it is desirable to have a vapor pressure of 0.1 torr or more at the reaction temperature.

As the monomer, for example, if the purpose is to introduce an amino group, monomers such as N,N-diethylaminoethyl methacrylate, vinylpyridine, etc. are used, and if the purpose is to introduce a carboxylic acid group, monomers such as acrylic acid, methacrylic acid, etc. are used. Monomers can be used. In addition, introduction of hydroxyl groups using 2-hydroxyethyl methacrylate, introduction of hydroxyl groups by polymerizing vinyl acetate and then hydrolysis, glycidyl methacrylate, vinylbenzyl halide, acrylic acid or methacrylic acid halide, acrolein. It is possible to introduce an active functional group using the like, or to introduce a sulfonic acid group by graft polymerizing styrene and then sulfonation.

Any type of carrier gas may be used as long as it is inert to this type of reaction. Examples of the inert gas include argon, helium, and nitrogen. Furthermore, in polymerization reactions, the influence of deactivation of radicals by oxygen cannot be ignored in many cases, and the carrier gas preferably has an oxygen concentration of 20 ppm or less, particularly preferably 0.2 ppm or less.

Furthermore, if the flow rate of the carrier gas during the reaction is too small, the effect of removing the reaction heat will be insufficient, resulting in uneven grafting in the radial direction of the yarn bundle. 40ml per 1g of base film
A flow rate of /min or more is desirable. The effects of the present invention will be explained below using examples.

[0019]

【Example】

[0020]

Example 1 A hollow fiber porous membrane made of polyethylene was selected as the base membrane. The hollow fiber porous membrane has an inner diameter of 2 mm,
It has an outer diameter of 3 mm and an average pore diameter of 0.2 μm. Glycidyl methacrylate was selected as the monomer. Since glycidyl methacrylate has an epoxy group, it is possible to make it hydrophilic by introducing an alcoholic hydroxyl group through acid treatment after the graft polymerization reaction, and it is also possible to make it hydrophilic by introducing various ion exchange groups or chelate formation into the epoxy group. It is possible to introduce groups. Glycidyl methacrylate is a monomer that can be applied to many variations as a method for modifying porous membranes.

The hollow fiber porous membrane was irradiated with γ-rays of 100 KGy, and 100 irradiated porous membranes were bundled and placed in a reactor. The specifications of the reactor are shown in Figure 1. A gas cleaning bottle was used as a monomer tank (2) for storing monomer. The carrier gas has an oxygen concentration of 0.2pp.
Using less than m nitrogen, the monomer tank (2
) and then flowed into the reactor (1). The flow rate was 75 ml/min per gram of substrate film. The reactor (1) and monomer tank (2) were placed in a constant temperature bath, and the temperature was maintained at 40°C. After 8 hours of reaction, the yarn bundle was taken out from the reactor and 1
The membrane was washed and dried using ,1,1-trichloroethane. Next, the yarn bundle was divided into five parts from the center to the outer periphery, five samples were arbitrarily extracted from each part, and the grafting ratio was evaluated. What is the graft rate here?
It refers to the weight increase rate in the graft polymerization reaction when the weight of the base film is taken as 100. The experimental results are shown in Figure 2.

[0022]

Example 2 A hollow fiber porous membrane made of polyvinylidene fluoride was selected as the base membrane. The hollow fiber porous membrane has an inner diameter of 1 mm, an outer diameter of 1.5 mm, and an average pore diameter of 0.2 μm. As in Example 1, glycidyl methacrylate was selected as the monomer. For the hollow fiber porous membrane, 1
A bundle of 100 gamma rays of 0 KGy was irradiated, and a polymerization reaction was carried out in the same manner as in Example 1. The temperature of the constant temperature bath is kept at 40℃.
The reaction was run for 8 hours. After washing and drying the membrane, Example 1
A similar evaluation was made. The results are shown in Figure 3.

[0023]

[Comparative Example 1] The same hollow fiber porous membrane made of polyethylene and glycidyl methacrylate as used in Example 1 were used. 100KGy for a bundle of 100 hollow fiber porous membranes
It was irradiated with gamma rays and placed inside a reactor. The apparatus is shown in Figure 4. After freezing the monomer in the reactor (1),
The pressure inside the reactor (1) was reduced to 1 Torr or less, and the reactor was placed in a constant temperature bath. The temperature was maintained at 40°C and the reaction was carried out for 8 hours. After washing and drying the membrane in the same manner as in Example 1, the grafting rate was evaluated.

The results are shown in FIG. The graft reaction concentrates on the outer periphery of the yarn bundle, and the grafting rate inside the bundle is significantly lower than that on the outer periphery of the bundle.

[0025]

INDUSTRIAL APPLICABILITY The present invention is a method that can suppress graft treatment spots, which are a problem in production, and dramatically improve the uniformity of polymerization using a gas phase method. Functional porous membranes obtained by the gas-phase radiation graft polymerization method can be applied to hydrophilic porous membranes, adsorption membranes and chelate membranes for various ions, and affinity membranes used in biotechnology. In producing such a functional porous membrane, the most important point is that the distribution of functional groups within the membrane is uniform both microscopically and macroscopically. The present invention makes it possible to produce such an ideal functional porous membrane and is very useful.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an apparatus used in the manufacturing method of the present invention. The reactor 1 may be placed vertically, horizontally, or diagonally.

FIG. 2 is a graph showing the graft ratio distribution in the radial direction of the yarn bundle in Example 1.

FIG. 3 is a graph showing the graft ratio distribution in the radial direction of the yarn bundle in Example 2.

FIG. 4 is a schematic diagram showing an apparatus used in a conventional manufacturing method.

5 is a graph showing the graft ratio distribution in the radial direction of the yarn bundle in Comparative Example 1. FIG.

[Explanation of symbols]

1...Reactor 2... Monomer tank 3...Circulation pump 4... Thread bundle 5...Mesh-like support 6...Monomer

Claims (1)

[Claims] Claim 1: An inert carrier gas is used in a porous membrane modification method in which a porous membrane is irradiated with ionizing radiation to generate radicals, and then treated with a monomer gas to graft-polymerize the monomer. A method for modifying a porous membrane, characterized by: