JPH05156057A - Method for carrying out vapor phase graft reaction - Google Patents

Abstract

PURPOSE:To obtain a porous film having uniformly introduced functional groups and suitable as an ion absorbing film, etc., by subjecting a monomer to vapor phase graft polymerization by irradiating ionizing radiation onto the surface of a high polymer compound with a gradient dosage manner, using an inert gas as a carrier gas. CONSTITUTION:Polyethylene resin powder is preliminarily blended with silicic acid fine powder and dibutyl phthalate, etc., and the blend is extruded into a hollow fiber having 2mm inner diameter and 0.5mm thickness by a twin-screw extruder and immersed in 1,1,1-trichloroethane for 60min to extract dibutyl phthalate and further immersed in 40% aqueous solution of caustic soda kept at 60 deg.C to extract silicic acid fine powder. Thereby a hollow fiber-like porous film is formed. This porous film is packed in a vessel as bundles of 1mX100 pieces and the bundles are placed in an ionizing radiation irradiating device in a state where film bundles are inclined to radiation source (1). The ionizing radiation is irradiated onto the film bundles with a gradient irradiation dosage in an inert gas as a carrier gas to produce radical, and then a monomer is introduced into the device and is subjected to vapor phase graft reaction to uniformly introduce a functional group to the intrasurface of pores in the porous film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for uniformly introducing a functional group such as an ion exchange group or a hydrophilic group into the inner surface of pores of a porous membrane.

[0002]

2. Description of the Related Art A study example of surface modification of a porous membrane in which a porous membrane is irradiated with radiation and brought into contact with a gas phase monomer to introduce a functional group is described in, for example, Journal of the Chemical Society of Japan (1988) No.
2, p212-216, Journal of Japan Society of Sea Water (1989) N
o. 1, p3 to 11 and JP-A-64-30606. According to it, by introducing a functional group into a porous membrane that has chemical durability, mechanical strength, and has excellent contact efficiency with a liquid in terms of structural characteristics such as pore structure and shape, durability can be improved. It is possible to obtain a functional porous membrane that has excellent properties and strength, has structural characteristics suitable for purification and separation processes, and that has functional groups such as hydrophilic groups, ion-exchange groups, and chelate-forming groups on the membrane surface. ..

However, in the conventional technique in which a monomer is introduced into a reactor from a separately provided monomer tank to cause a graft reaction by utilizing only the vapor pressure of the monomer, the graft polymerization reaction is not always uniform over the entire porous membrane. There was a drawback that it was not done.

[0004] In particular, in the case of modularization using a hollow fiber-like porous membrane, the reaction as a bundle of yarns per module is preferable, but in this case, especially when a monomer having a low vapor pressure is used, the monomer is used. Is not sufficiently supplied, the graft ratio of the membrane in the central portion of the yarn bundle is significantly lower than that in the outer peripheral portion, which may cause a serious problem in production.

For example, in a case where an alcoholic hydroxyl group is introduced as a hydrophilic group and the amount of introduction of the hydrophilic group becomes non-uniform, the exposed portion of the hydrophobic substrate remains in the film. To do. Therefore, in the removal of bacteria and the separation of enzymes and proteins, for example, clogging occurs due to the attachment of proteins, etc., and the water permeability decreases, or the target substance is adsorbed to the membrane hydrophobically, and its recovery rate It is known that problems such as decrease in

Further, in a membrane having ion exchange groups introduced by a graft polymerization reaction, if the amount of ion exchange groups introduced is non-uniform in the membrane and there is a portion where the density of the ion exchange groups is low, the liquid is removed from that portion. Since the ions inside pass through in a short time, high ion removal efficiency cannot be obtained. In order to overcome the above drawbacks, it is an indispensable condition to uniformly introduce a functional group into the entire area of the film.

[0007]

DISCLOSURE OF THE INVENTION The present invention maintains high water permeability, removes fine particles and bacteria, recovers or removes specific ions such as cations, anions or complex ions, and removes specific proteins and enzymes. In order to synthesize a functional porous membrane that exhibits high performance in processes such as separation and purification, the objective is to uniformly immobilize functional groups over the entire porous substrate membrane.

[0008]

The present inventor has found that the object can be achieved by the following means as a result of earnest research to achieve the above-mentioned goal. That is, in the method of radiation graft polymerization of the surface of the polymer compound, the polymer compound is irradiated with ionizing radiation to generate radicals, and when the monomer is subjected to the gas phase graft reaction, an inert gas is used as a carrier gas, We have found a method of gas phase graft reaction characterized by grading the dose of ionizing radiation.

The present invention will be specifically described below.
Examples of the shape of the polymer compound used in the present invention include films, sheets, foams, fibers, particles, powders, and porous films. In particular, the porous membrane has a large surface area, and the effect of introducing a functional group is great.

As the material for the polymer compound used in the present invention, most of the materials currently on the market can be used, but for example, polyolefins such as polyethylene, polypropylene, and ethylene-propylene copolymers, ethylene. -4 Fluoroethylene copolymer, ethylene-
Olefin-halogenated olefin copolymers typified by chlorotrifluoroethylene copolymers, polytetrafluoroethylene, polyvinylidene fluoride, polyhalogenated olefins typified by polychlorotrifluoroethylene, cellulose (di- or tri- ) Acetate, polysulfone, polyamide and the like can be mentioned.

As the structure of the porous membrane, flat membranes (pleats, spirals), tubes, hollow fibers, etc. are used, but hollow fibers are particularly preferable. The average pore diameter of the porous membrane is preferably in the range of 0.01 μm to 5 μm. If it is smaller than this range, the water permeability is not sufficient for practical performance, and if it is larger than this range, there is a problem in functioning.

Although there are many methods for measuring the average pore size,
The present invention is based on the method described in ASTM F316-70, which is called an air flow method, and which is measured from the air permeation flux of a dry membrane and a wet membrane when the air pressure is changed. The porosity of the porous film is preferably in the range of 20% to 80%. Here, the porosity is measured by immersing the membrane in a liquid such as water in advance and then drying it, and measuring the weight change before and after that. When the porosity is outside the above range, it is not preferable in terms of permeation rate and mechanical properties.

The thickness of the porous film is preferably in the range of 10 μm to 5 mm. Below this range, problems occur in the mechanical strength of the membrane, and above this range, the water permeability is not practically sufficient. The pore structure of the porous film can be variously formed by a molding method. For example, polysulfone can be made into a three-dimensional network structure film by adopting a so-called wet method in which polysulfone is mixed with a solvent or the like and then discharged from a nozzle into a hollow fiber shape and molded with a coagulant or the like. In the case of polyolefin, it is possible to form a porous film by so-called stretching method, interfacial peeling method, etching radiation, etc., for example, Japanese Patent Publication No. 59-37292 and Japanese Patent Publication No. 40-957.
Those molded by the microphase separation method, the mixed extraction method, and the like disclosed in JP-B No. 47-17460 and JP-B No. 47-17460 are preferable in terms of practical performance in which functional groups are effectively used.

However, it should not be limited to this method. In particular, by using the porous film having the structure disclosed in Japanese Patent Laid-Open No. 55-131028, it is possible to achieve excellent functional performance that cannot be obtained by conventional techniques.
As the monomer, radical polymerization is basically possible, and a monomer having a constant vapor pressure at the reaction temperature may be used. Particularly, those having a vapor pressure of 0.1 torr or more at the reaction temperature are desirable.

Specifically, for example, if the purpose is to introduce an amino group, a monomer such as N, N-diethylaminoethyl methacrylate or vinyl pyridine is used; if the carboxylic acid group is introduced, acrylic acid, Monomers such as methacrylic acid can be used. Also, methacrylic acid 2
-Introduction of a hydroxyl group using hydroxyethyl; introduction of an active functional group using glycidyl methacrylate, vinylbenzyl halide, halide of acrylic acid or methacrylic acid, acrolein, etc .; and further by graft polymerization of styrene, followed by sulfonation For example, introduction of a sulfonic acid group can be performed.

Any carrier gas can be used as long as it is inert to the reaction. As an inert gas,
For example, argon, helium, nitrogen or the like can be used. In the polymerization reaction, the effect of deactivating radicals due to oxygen is often not negligible, and the carrier gas preferably has an oxygen concentration of 20 ppm or less.
0.2 ppm or less is preferable. The flow rate of the carrier gas is preferably 40 ml / min or more per 1 g of the base film. If the flow rate is too low, the effect of removing the reaction heat will be insufficient and graft unevenness will occur.

The ionizing radiation includes electron beams, γ rays, x
Rays are typical, but γ-rays, which have a high absorbed dose efficiency, are preferable. Regarding the dose of ionizing radiation, it is necessary to lower the dose to the polymer compound near the inlet of the monomer gas in the reactor and to increase the dose to the polymer compound near the outlet. is there. This is considered to be due to the following reasons. In the inside of the reactor, the introduced monomer reacts with the polymer compound at the inlet, so that the monomer concentration tends to be high at the inlet and low at the outlet.

That is, it is considered that the monomer concentration can be distributed in the reactor, and the graft ratio of each portion can be varied corresponding to the distribution of the monomer concentration. Therefore, lower the irradiation dose of ionizing radiation in the area where the monomer concentration is high,
Reducing the amount of radicals generated to reduce the reactivity, and increasing the irradiation dose of ionizing radiation in the portion where the monomer concentration is low, increasing the amount of radicals generated to increase the reactivity It is considered that a polymer compound having a uniform graft ratio can be obtained.

As a method of irradiating the ionizing radiation, the polymer compound is cooled down to a low temperature, and is inclined with respect to the radiation source as shown in FIG. As a method of cooling the polymer compound to a low temperature, for example, put the polymer compound in a container,
Place a cooling agent such as dry ice in the container to cool.
As a material of the container, a material having high heat retention and hard to shield radiation is preferable. In addition, the degree of inclination of irradiation dose is
If desired, the angle of inclination of the sample with respect to the source can be varied. The method of uniformly imparting functionality to the entire porous membrane of the present invention is very useful.

That is, in the composite functional film having this functionality, a hydrophilic group, an ion-exchange group, a chelate-forming group or an active precursor is introduced on the surface of the porous membrane and the inner surface of the pores. It can be obtained by introducing the functional group or a ligand such as a monoclonal antibody or protein A later, and not only simple filtration depending on the size of particles, but also the electrical and chemical characteristics of particles or biological It can be used for specific separation and purification using biological affinity.

The present invention will be described in more detail. In the fields of medicine and fermentation, enzymes, hydrophilic membranes used for separation and purification of cells, ligand-immobilized membranes, ion exchange membranes used for ultrapure production, or nuclear power. It can be applied to a method for producing a composite functional membrane used as an ion exchange membrane, a chelate membrane, etc. used for purification of circulating water in a power plant. Also; high water permeability, high functional group introduction rate, fine particles,
It can be applied to a method of uniformly introducing a functional side chain onto the inner surface of the pores of a porous substrate membrane in order to produce a high-performance composite functional membrane having excellent removal and trapping efficiency for bacteria and ions.

[0022]

The present invention is illustrated by the following examples, which do not limit the scope of the invention.

(Reference Example) ( Preparation of Porous Membrane Applied to the Present Invention ) Finely powdered silicic acid (manufactured by Nippon Aerosil Co., Ltd., trade name, Aerosil R-972) 2
2.1 parts by weight, dibutyl phthalate (DBP) 55.0
Parts by weight, polyethylene resin powder [Asahi Kasei Kogyo KK,
Trade name, SH-800 grade] After premixing 23.0 parts by weight of the composition, the inner diameter is 2 m with a 30 mm twin-screw extruder.
m, 0.5 mm thick hollow fiber extruded, 1, 1,
DBP was extracted by immersing it in 1-trichloroethane for 60 minutes. Further, the powdery silica was extruded by immersing it in a 40% aqueous solution of caustic soda at a temperature of 60 ° C. for about 20 minutes, washed with water, and dried (hereinafter referred to as a porous membrane (A)).

[Example 1] Hollow fiber-like porous membrane [porous membrane (A)] A bundle of 1 m x 100 pieces was placed in a polystyrene foam container, and dry ice was put together, and the temperature inside the container was -60. After confirming that the temperature is below ℃,
The container was installed as in Figure 1 so that it was inclined to the source of the rays, the reactor was inverted for half the total irradiation time and 20-50 KGy in the longitudinal direction as shown in Figure 2.
Was irradiated with γ-rays.

The membrane bundle irradiated with the γ-rays is fed to the reactor,
The entrance dose of glycidyl methacrylate, which is a monomer, is 20 KGy, which has a low irradiation dose, and the exit port of glycidyl methacrylate, which is a monomer, is a high irradiation dose, 50 KG.
Set y. Using this reactor as shown in FIG. 3, N ₂ gas saturated with glycidyl methacrylate as a monomer was introduced from the MD direction of the membrane at a flow rate of 100 L / min and reacted at 40 ° C. for 6 hours. It was
As a result, the variation in the reaction rate between the bundle-direction membranes is 2σ = 11.
%, And the variation in the reaction rate in the longitudinal direction of the film was 2σ = 20% (see FIG. 4).

The graft ratio was measured by a gravimetric method.
The unevenness of the graft ratio was obtained by statistical processing. That is, the porous membrane after the grafting reaction is divided into 10 equal parts in the lengthwise direction (for example, A, B, C ... of FIG. 4), and all the weights are measured respectively, and the weight is measured. The graft ratio was calculated from the change ratio of the above, and the standard deviation of the distribution was divided by the average graft ratio to obtain 2σ.

Comparative Example A hollow fiber porous membrane [porous membrane (A)] 1 m × 100 was uniformly irradiated with γ-rays of 40 KGy, and a reactor was set. N ₂ gas saturated with glycidyl methacrylate, which is a monomer, was introduced from the MD direction of the film at a flow rate of 100 L / min, and reacted at 40 ° C. for 6 hours. As a result, the variation in the reaction rate between the bundle-direction membranes is 2σ = 20%, and the variation in the reaction rate in the membrane longitudinal direction is 2%.
A result of σ = 45% was obtained (see FIG. 4). The graft ratio was measured by the gravimetric method. The unevenness of the graft ratio was obtained by weighing the weight of all the porous membranes and statistically processing them.

[0028]

INDUSTRIAL APPLICABILITY The present invention relates to a graft polymerization method using ionizing radiation, particularly in a gas phase method.
It is a novel production method capable of dramatically improving the performance of the obtained functional porous membrane. The functional porous membrane obtained by the radiation-induced graft polymerization method in the gas phase method can be applied to a hydrophilic porous membrane, an adsorption membrane for various ions, a chelate membrane, or an affinity membrane used in biotechnology.

The basis for producing such a functional porous film is that the distribution of the functional groups is microscopically and macroscopically uniform inside the film. The present invention is a method for producing such an ideal functional porous membrane,
The effect is tremendous.

[Brief description of drawings]

FIG. 1 is a schematic view showing a γ-ray irradiation method of the present invention.

FIG. 2 is a graph showing the result of γ-ray irradiation in Example 1.

FIG. 3 is a schematic view showing an apparatus used in the manufacturing method of the present invention. The reactor 1 may be placed vertically, horizontally, or diagonally.

FIG. 4 is a graph showing reaction rate distributions in the longitudinal direction of hollow fiber-shaped porous membranes in Example 1 and Comparative Example.

[Explanation of symbols]

 1 Monomer tank 2 Trap 3 Reactor 4 Hollow fiber porous membrane bundle 5 Circulation pump

Claims (1)

[Claims] 1. In a method of radiation graft polymerization on the surface of a polymer compound, the polymer compound is irradiated with ionizing radiation to generate radicals, and when a monomer is subjected to a gas phase graft reaction, an inert gas is used as a carrier gas. use,
Characterized by grading the dose of ionizing radiation,
Gas phase graft reaction method.