JPH01313544A - Modification of porous fluororesin tube - Google Patents

Abstract

PURPOSE:To make it possible to modify a porous fluororesin tube efficiently and economically by irradiating the tube in a state containing a hydrophilic monomer on the surface with a radiation in an inert gas atmosphere in a specified polymer tube or pipe. CONSTITUTION:A porous fluororesin tube (a) of a pore diameter of 0.02-100mum and a void volume of 95-96% (e.g., a tetrafluoroethylene resin tube) is immersed in an aqueous solution (b) containing 5-90wt.% hydrophilic monomer (e.g., acrylamide) to obtain component A comprising component (a) having component (b) on the surface. Component A and an inert gas (B) are inserted into a polymer (e.g., PE) tube or pipe (C) having at least oxygen barrier property and desirably excelling in radiation resistance, irradiated with a radiation at a dose of 0.1-12Mrad, and optionally subjected to graft polymerization at 30-120 deg.C for several min to 10hr.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for modifying a porous fluororesin tube,
More specifically, the present invention relates to a method of modifying the surface of a porous fluororesin tube by irradiating it with radiation while efficiently blocking oxygen gas to graft-polymerize a hydrophilic monomer.

[Conventional technology]

Fluororesins such as tetrafluoroethylene resin are water-repellent, and their porous membranes allow gases to pass through them easily, but liquid water does not. , liquid-liquid separation, gas-liquid reaction or separation, and many other applications. For example, there are gas-liquid exchange members such as gas-liquid reaction devices and diffuser tubes that utilize the hydrophobicity and gas permeability of porous polytetrafluoroethylene resin tubes.

However, due to its water repellency, porous membranes made of fluororesin such as tetrafluoroethylene resin are used in the application fields of hydrophilic polymer membranes, such as filtration membranes, dialysis membranes, ultrafiltration membranes, reverse osmosis membranes, etc. Difficulties have been associated with its application to material separation in systems. Therefore, there are expectations for technological development to make the surface (including the pore surface) of a fluororesin porous membrane hydrophilic. Furthermore, only the surface of the fluororesin porous membrane is made hydrophilic while the hydrophobicity in the thickness direction (inside the pores) is maintained.
Alternatively, functionality can be further enhanced by making only one of the surfaces hydrophilic. However, there were many difficulties in making the porous fluororesin membrane parent.

By the way, conventionally, several methods have already been studied for modifying a fluororesin and making it hydrophilic by graft polymerizing a hydrophilic monomer by irradiation with radiation.

For example, research is being conducted to make tetrafluoroethylene resin hydrophilic by irradiating it with radiation and using the generated radicals to advance the grafting reaction of hydrophilic membrane polymers. Tetrafluoroethylene resin easily generates radicals when irradiated with gamma rays, and if other monomers are present, it undergoes graft polymerization, but when hydrophilic monomers are graft polymerized, selectively permeable membranes with various performances can be obtained. It will be done.

For example, Shapiro et al. irradiated a tetrafluoroethylene resin film (non-porous membrane) with gamma rays in an aqueous solution of monomers such as acrylic acid and methacrylic acid, and performed graft polymerization of these seven polymers. ing. (Po1
7+wer Engineering And 5ci
ence.

vol, 20. No. 3, 202.1980) By graft polymerizing styrene onto an ethyl tetrafluoride L/7 resin film and sulfonating this, a strongly acidic membrane is obtained, and this membrane exhibits performance as a reverse osmosis membrane. Graft polymerization of acrylic acid or methacrylic acid yields weakly acidic membranes, which also have good properties as reverse osmosis membranes. Grafting with 4-vinylpyridine results in a weakly basic membrane.

Furthermore, Hayashi et al. irradiated tetrafluoroethylene resin with gamma rays in the coexistence of N-vinylpyrrolidone to obtain a craft polymer thereof. (Osaka Institute of Technology Quarterly Report, vol. 3
5. No. 2.117.1984) A neutral hydrophilic film is obtained by craft polymerizing N-vinylpyrrolidone on a tetrafluoroethylene resin film.

In both of these methods, irradiation is performed in the presence of a hydrophilic monomer.

On the other hand, EL-Sayed et al. irradiated a tetrafluoroethylene resin film (non-porous membrane) with gamma rays in advance, and then used vinyl acetate, N-vinylpyrrolidone, acrylic acid, 4-vinylpyridine, etc. A graft polymerization reaction is carried out by adding a solution of various hydrophilic monomers such as methyl methacrylate. (Journal of A
pplied Polymer 5c1ence.

(vol. 28.3117.1981) However, the conventional technology for making tetrafluoroethylene resin into a parent tree through the grafting reaction of a hydrophilic membrane tube is related to a non-porous membrane, and the pore surface of a porous fluororesin membrane tube For example, many problems must be solved in order to prevent the pores of a porous tube from becoming cold and to efficiently modify the surface to make it hydrophilic using a graft polymer. There must be.

Furthermore, fluororesins, especially tetrafluoroethylene resins (PTFE)
) is decomposed by γ-ray irradiation, resulting in the scission of the main chain and the detachment of fluorine atoms, which easily generates radicals, which makes it possible to perform graft polymerization. It is also easy to decompose, and it is difficult to carry out graft polymerization while controlling this decomposition. On the other hand, when a fluororesin is irradiated with radiation in a state where oxygen is blocked and excluded, the 1-decomposition reaction is suppressed. Therefore, in order to make the surface of a fluororesin porous tube hydrophilic by graft-polymerizing a hydrophilic membrane by irradiating it with radiation, it is necessary to block oxygen during and after the irradiation.

Therefore, the present inventors irradiated the fluororesin porous tube with radiation in an atmosphere in which oxygen gas (air) was replaced with an inert gas such as nitrogen scum or carbon dioxide gas, and the hydrophilic membrane tube was removed from the fluororesin resin. Research has been carried out on a method of graft polymerization on the surface of a porous tube, but this method requires replacing the entire device or the entire space where the irradiated object enters with inert gas, resulting in the following problems: was there.

That is, since a large amount of nitrogen gas, carbon dioxide gas, etc. is required to replace the air with inert gas, there is a problem in economic efficiency. Furthermore, if a large amount of these scum leaks out of the device, there is a risk of suffocation to the worker. This problem is a serious problem when modifying porous fluororesin tubes on an industrial scale.

[Problem to be solved by the invention]

An object of the present invention is to provide a method for modifying the pore surface of a porous fluororesin tube by irradiating the tube with radiation and craft polymerizing a hydrophilic upper layer. The objective is to efficiently and economically replace air with inert gas.

Another object of the present invention is to carry out the above-mentioned modification method safely by improved means.

As a result of intensive research to overcome the problems of the above-mentioned prior art, the present inventors have found that a polymer tube or pipe that has at least # elementary gas barrier properties and preferably has excellent radiation resistance. By irradiating radiation with a porous fluororesin tube and inert residue introduced,
The inventors have discovered that a porous fluororesin tube can be modified economically and safely, and have completed the present invention based on this knowledge.

[Means to solve the problem]

That is, the gist of the present invention is to provide a method for modifying the pore surface of a porous fluororesin tube by irradiating the tube with radiation and graft polymerizing a hydrophilic monomer, which has at least oxygen gas barrier properties. death,
A modification of a porous fluororesin tube, characterized in that radiation is irradiated with the porous fluororesin tube and an inert gas introduced into a polymer tube or pipe preferably having excellent radiation resistance. The quality is in the method.

Each component of the present invention will be explained in detail below.

(Fluororesin porous tube) The fluororesin used in the present invention includes ethylene-tetrafluoroethylene copolymer, vinylidene fluoride resin, trifluorochloroethylene resin, tetrafluoroethylene resin, and copolymers thereof. Among them, tetrafluoroethylene resin is particularly preferred.

The porous fluororesin tube used in the present invention is one in which the fluororesin forms a matrix and has a space inside, and the space extends from the front surface to the back surface of the membrane. Such porous fluororesin tubes can be produced by, for example, a method in which a tubular unsintered body obtained by paste extrusion of tetrafluoroethylene resin is stretched at a temperature below its melting point, and then sintered (Japanese Patent Publication No. It can be obtained by various methods such as No. 13560 Publication%i).

The fluororesin porous tube used in the present invention has 1. These fluororesin porous tubes, which may be produced by any production method or commercially available products, may have micropore sizes of 0.02 to 100g depending on the production conditions.
m, usually in the range of 0.1 to 10 ALm, and the porosity can be increased to a maximum of about 95 to 96%, but those with high porosity and high mechanical strength are preferably used. .

(Craft Polymerization Method) Fluororesins such as tetrafluoroethylene resin are highly sensitive to radiation, and decomposition reactions and crosslinking reactions occur when exposed to gamma rays. In particular, in tetrafluoroethylene resin, irradiation with gamma rays causes cleavage of the main chain or detachment of fluorine atoms to generate radicals. In this way, fluororesins such as tetrafluoroethylene resins easily generate radicals when irradiated with gamma rays, and if other monomers are present, they undergo graft polymerization. When a hydrophilic polymer is graft-polymerized onto a porous resin tube, its surface is modified and a permselective porous tube with various properties can be obtained.

Examples of the graft polymerization method in the present invention include the following various methods.

(+) Fluororesin generates radicals when irradiated with gamma rays, but the generated radicals are easily annihilated. Therefore, if a hydrophilic layer is present on the surface of the porous fluororesin tube during irradiation, fluorine This is effective because the radicals generated in the resin immediately react with the hydrophilic monomer. Therefore,
There is a method of irradiating the surface of a porous fluororesin tube with radiation while bringing a hydrophilic top layer into contact with the surface of the porous fluororesin tube by immersing it in a hydrophilic monomer solution or coating it with a hydrophilic monomer.

(2) There is a method in which a porous fluororesin tube is irradiated with gamma rays in advance and then immersed in a solution of a hydrophilic monomer or coated with a hydrophilic monomer to carry out graft polymerization.

(3) Graft polymerization reaction is carried out by irradiating radiation with a relatively small amount of hydrophilic supernatant present on the surface of the porous fluororesin tube, and then immersing it in a solution of hydrophilic supernatant. Alternatively, there is a method of continuing graft polymerization by applying a hydrophilic monomer and utilizing the remaining active sites of Kraft M.

(4) There is a method in which a hydrophilic monomer is present only on the outer surface or only on the inner surface of the porous fluororesin tube, and graft polymerization is carried out only on either surface.

Radiation irradiation can be performed using gamma rays or electron beams using Co as a radiation source. Fluororesin is easily decomposed by irradiation with ionizing radiation, but the decomposition reaction is reduced under conditions that exclude oxygen from the air, so place the fluororesin porous tube in an inert gas atmosphere such as nitrogen gas. Perform irradiation. In the present invention, a porous fluororesin tube or a porous fluororesin tube brought into contact with a hydrophilic aqueous solution is inserted into a polymer tube or a polymer pipe with oxygen barrier properties, and the polymer tube or Inert gas such as nitrogen gas or carbon dioxide gas is introduced into the polymer pipe to replace oxygen (air) before irradiation with radiation.

Polymer tubes or pipes must be oxygen barrier, such as polyethylene or ethylene-
It can be formed from various polymeric materials such as vinyl acetate copolymer. Among these, materials with excellent radiation resistance such as polyethylene are desirable.

Although rare gases such as helium and neon can be used as the inert gas, it is usually preferable to use nitrogen gas or carbon dioxide gas from an economic point of view. Therefore, in the present invention, nitrogen gas or carbon dioxide gas is preferably used. This is called an inert gas.

radiation&! The amount can be appropriately selected depending on the type of hydrophilic monomer, the size of the fluororesin porous tube, etc., but it is usually in the range of 0.1-12 Mrad that the grafting reaction can be carried out without deteriorating the fluororesin porous tube. This is preferable because it can be done. Further, after the radiation irradiation, a graft polymerization reaction is carried out at a temperature of 30 to 120° C. for several minutes to about 10 hours if necessary.

After the reaction is complete, take out the fluororesin porous tube and
Unreacted monomers and non-grafted hydrophilic polymers are thoroughly extracted and removed by washing with water or warm water.

(Hydrophilic Monomer) Examples of the hydrophilic monomer used in the present invention include acrylic acid, methacrylic acid, N-vinylpyrrolidone,
Examples include N-vinylpyridine, methyl methacrylate, and acrylamide. These seven potions may be used alone or in combination.

The aqueous solution containing these seven polymers has a monomer concentration of 5 to
A 90% by weight solution is used, preferably from 10 to 80% by weight. Use clean water such as distilled water or deionized water.

(Reforming method) In the present invention, it has at least oxygen gas barrier property,
Preferably, the fluoropolymer tube and inert gas are introduced into a highly radiation-resistant polymer tube or polymer pipe, and then radiation is irradiated to graft-polymerize the hydrophilic monomer to form the fluoropolymer porous resin. The features of the present invention will be specifically explained in comparison with conventional methods.

FIG. 1 is a schematic diagram showing the conventional method. The fluororesin porous tube (3) is irradiated with radiation (2) from the radiation irradiator (1) while being wound up from the feeder (7) to the winder (4). These devices are surrounded by a housing (5);
It is filled with an inert gas (6) such as nitrogen gas. Although not shown, the fluororesin porous tube is brought into contact with a hydrophilic monomer in advance, or is brought into contact with a hydrophilic monomer after being irradiated with radiation. The conventional method requires a large amount of inert gas, which is not only uneconomical, but also poses a risk of causing unexpected accidents such as suffocation of workers due to the leakage of a large amount of inert gas.

In contrast, FIG. 2 schematically shows the method of the present invention. The difference in terms of wood quality from the conventional method is that the winding machine and the feeding machine are each surrounded by a small housing (13, 16), and a polymer tube or pipe with oxygen barrier properties is inserted between them.
14) to connect. The air inside them is replaced with an inert gas such as nitrogen or carbon dioxide. The porous fluororesin tube (10) is wound up from a feeder through a polymer tube or pipe to a winder.

According to the method of the present invention, in which the radiation (9) is irradiated from the radiation irradiator (8) while passing through the polymer tube or polymer pipe, the housing can be made smaller, and the Since inert gas is passed through the molecular pipe, the amount of inert gas used can be greatly reduced. Furthermore, the risk of waste leakage can be reduced, and safety can be greatly improved.

FIG. 3 is a diagram showing an embodiment of the present invention. Supply m(2
7) and winding a (20) are each surrounded by small housings (22, 29), and oxygen-barrier polymer tubes or polymer pipes (26) are extended from each housing, and each end is hydrophilic. into a reaction tank (23) containing a monomer solution (24). The fluororesin porous tube (25) is passed through a polymer tube or a polymer pipe from a feeder to a winder and wound through a radiation irradiator (1).
8) by radiation (19). Each housing and polymer tube or pipe is filled with inert gas.

The fluororesin porous tube that has been irradiated with radiation comes into contact with a hydrophilic monomer in a reaction tank, and a graft polymerization reaction takes place. Note that, although not shown, if a lid is provided on the top of one reaction tank, leakage of inert gas can be more effectively prevented.

In the present invention, surface modification refers to modification of only the surface portion of the porous fluororesin tube, or modification of the surface portion and the surface portion inside the pores.The surface portion refers to the modification of the outer surface or the inner surface of the porous fluororesin tube. In order to modify only the inner surface, which may be only one of the inner surfaces, it is sufficient to introduce the seven-mer reaction solution only into the inside of the tube.

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited to these Examples.

Example A porous tube of tetrafluoroethylene resin was modified using the apparatus shown in FIG.

The polymer tube shown in Figure 3 has an outer diameter of 5 mm and an inner diameter of 4 mm.
mm polyethylene tube (melt index 2
．． 0, density 0.92). In addition, the fluororesin porous tube (25) has an outer diameter of 2.8 mm and an inner diameter of 2.0 mm.
A polytetrafluoroethylene resin porous tube with a porosity of 60% and an average pore diameter of 0.45 mm (manufactured by Susumu'Ifki Kogyo Co., Ltd., Boa-Fron Tube) was used. The inside of each housing and polyethylene tube is replaced with nitrogen gas, and the radiation source is removed while the porous tetrafluoroethylene resin tube is passed from the feeder (27) through the polyethylene tube, passed through the reaction tank (23), and wound up on the winding machine. (18) as acceleration voltage I M
It was irradiated with an electron beam of 1M rad. The reaction tank was filled with 50% by weight aqueous solutions (24) of various hydrophilic monomers shown in Table 1. The porous tetrafluoroethylene resin tube irradiated with electron beams was immersed in an aqueous hydrophilic monomer solution in a reaction tank, and a kraft polymerization reaction was carried out at about 90 to 100°C for 6 minutes.

After the reaction, the tube was placed in running water for 2 hours at 80°C.
The non-grafted polymer and unreacted supernatant were extracted for 2 hours in hot water with thorough stirring. Thereafter, the tube was vacuum dried at 60°C overnight. Water spread well on the surface of the obtained tube, showing hydrophilicity.

Next, Table 1 shows the types of hydrophilic polymers, reaction conditions, and grafting rates.

Table 1 (Note) The graft ratio was determined from the following formula based on the weight of the tube before and after the reaction.

In addition, copper pipes of the same diameter (outer diameter 5 mm, inner diameter 4 mm)
), but the grafting rate was 0%.
[Effect of the invention] As explained above, conventionally, in order to obtain a fluororesin porous tube whose surface has been made hydrophilic by graft polymerization of hydrophilic heptamers, it is necessary to remove oxygen during and after radiation irradiation. To do this, the entire device or the entire space where the irradiated object enters had to be replaced with a large amount of inert gas. However, by the method of the present invention, it is possible to minimize the size of the space 6n into which the fluorine tree perforated tube is inserted during irradiation, and as a result, the equipment can be simplified and the amount of inert gas used can be greatly reduced. It was possible to reduce the number of Also, the reduction of inert gas emissions can improve the safety of the working environment. therefore,
The industrial significance of the present invention is extremely large.

[Brief explanation of the drawing]

No. 11 is a cross-sectional view F@ of a conventional method, and No. 212 is a schematic cross-sectional view showing a method of the present invention. Further, FIG. 3 is a schematic cross-sectional view showing an embodiment of the present invention. 1.8.18 ... Radiation irradiator 2.9. Ill
...Radiation 3.10.25... Fluororesin porous tube 4.1
1,20... Winder 5.13.1B, 22.29... Housing 8, +
2.35, 21.28... Inert gas atmosphere? ,1
7.27... Fluororesin porous tube feeder 14.
28... Polymer tube or pipe 23...
・Reaction tank 24...Hydrophilic monomer solution

Claims (1)

[Claims] In a method of modifying the pore surface of a porous fluororesin tube by irradiating the tube with radiation and graft polymerizing a hydrophilic monomer, the porous fluororesin tube has at least oxygen gas barrier properties and preferably has radiation resistance. A method for modifying a porous fluororesin tube, which comprises irradiating the porous fluororesin tube and an inert gas into a superior polymer tube or pipe with radiation.