JP2002317055A - Method for producing crosslinked fluororesin - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a crosslinked fluororesin, having a high efficiency and a low cost, for which a large-scale plant and equipment investment is not required and excessive operations such as molding, grinding of a burned body are not needed. SOLUTION: Fluororesin powder 25 scattered in a closed chamber 11 is irradiated with a prescribed dose of radioactive rays.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a crosslinked fluororesin, and more particularly to a method for producing a crosslinked fluororesin capable of performing a crosslinking operation at low cost.

[0002]

2. Description of the Related Art In order to improve the properties such as strength and elongation of a fluororesin, a powdery fluororesin is baked by heating and solidified into a mat having a small bulk density.
After irradiation, the modified fired body is pulverized and returned to a powder state, and is used as a molding material.

FIG. 4A summarizes the procedure. First, an unfired powder of PTFE (polytetrafluoroethylene) as a raw material is supplied to a fixed mat type.
Next, after baking by heating it to a temperature equal to or higher than its melting point, a crosslinking treatment based on radiation irradiation and cooling at an elevated temperature by irradiation is performed, and finally pulverization is performed.

FIG. 4 (b) shows an outline of an apparatus used in the cross-linking step, wherein 1 is an irradiation apparatus for ionizing radiation such as an electron beam, and 2 is an irradiation apparatus through an irradiation window 3. An irradiation chamber 4 installed below 1 is a carrier disposed so as to circulate in the irradiation chamber 2, and is composed of a conveyor 5 and a tray 6 suspended at a constant interval therefrom.

[0005] On the tray 6, a fired body 7 of PTFE powder which has been solidified in a mat shape in the process is placed.
The fired body 7 is irradiated with radiation when passing through the lower part of the irradiation window 3. The interior of the irradiation chamber 2 is set to a temperature slightly higher than the melting point of PTFE, and is placed in an oxygen-free state by nitrogen gas or the like in order to eliminate the influence of oxygen. It is configured to be cooled to the original temperature by the circulation of the gas by the fan.

In the above-described configuration, the fired body 7 is repeatedly circulated in the irradiation chamber 2 and receives irradiation each time it passes through the position of the irradiation window 3, thereby irradiating a predetermined dose of radiation. This method of setting the irradiation amount per one time to a low level and integrating a predetermined dose by repeating irradiation is evaluated and utilized as a method for producing a stable crosslinked fluororesin.

[0007]

However, according to the above-mentioned conventional method for producing a crosslinked fluororesin, for example, when an electron beam irradiator having an acceleration voltage of 800 kV is used as an irradiator, concrete for irradiation equipment and X-rays is used. Although a large investment is required for a protective wall or the like, the thickness of the applicable fired body 7 is only about 2 mm, and therefore, the production efficiency per unit weight is low, and the investment efficiency is low. The low cost necessitates high manufacturing costs.

In this manufacturing method, the temperature of the fired body 7 is increased by irradiation with radiation and the low thermal conductivity of PTFE (0.
25W / mK), the operation of the conveyor 5 must be performed at a low speed because of the cooling in consideration of
The low work efficiency due to this acts to increase the cost, and furthermore, the powdery nature of PT
The configuration of the process of once hardening the FE into the fired body 7 and crushing it again after irradiation with the radiation to return to the powder state is obviously uneconomical,
This will increase costs.

Accordingly, an object of the present invention is to provide a high-efficiency and low-cost method for producing a crosslinked fluororesin which does not require large-scale capital investment and does not require extra operations such as molding and pulverization of a fired body. Is to provide.

[0010]

Means for Solving the Problems In order to achieve the above object, the present invention provides a method for producing a crosslinked fluororesin in which the fluororesin is irradiated with radiation to crosslink the molecules of the fluororesin. It is intended to provide a method for producing a crosslinked fluororesin, wherein powder is scattered in a closed chamber, and the scattered fluororesin powder is irradiated with a predetermined dose of radiation.

In the present invention in which the powdery fluororesin is irradiated, the effective range required for the radiation is much smaller than that of the conventional production method, and therefore, crosslinking with low-level radiation is possible. Becomes This is because the average particle size of the fluororesin powder used for this kind of application is about 50 μm.
m, on the other hand, when the thickness of the fired body in the conventional manufacturing method is considered to be in the order of mm, it becomes naturally obvious.

[0012] In order to efficiently carry out the crosslinking with this low-level radiation, it is preferable to fly the fluororesin powder as close as possible to the irradiation window. Table 1 shows the range of an electron beam (energy level 280 kV) immediately after passing through a 15 μm-thick Ti irradiation window accelerated at 300 kV and passing through a substance. For example, in the case of a mixture of a PTFE powder and a gaseous substance, when the powder passes more than 7 mm from the irradiation window, the irradiation effect is lost.

[0013]

[Table 1]

Therefore, in practicing the present invention, it is preferable to comply with the above facts. The scattered form of the powder is not unevenly scattered, but is randomly (rotated) near the irradiation window. It is preferable that the sheet passes repeatedly. As a means for this, for example, a method of circulating the fluororesin powder together with the gas in the closed chamber by a stirring device such as a fan or a pulsator provided in a cylindrical closed chamber, or the method of mixing the fluororesin powder and the gas A method of circulating by mixing and blowing into a cylindrical closed chamber may be considered.

In practicing the present invention, the following mode is preferably adopted in order to efficiently supply the uncrosslinked fluororesin powder into the closed chamber and take out the crosslinked fluororesin powder from the closed chamber. That is, a plurality of sealed chambers are sequentially fed to the radiation irradiation position set at a predetermined position, and the fluororesin powder is supplied into the sealed chamber before being sent to the radiation irradiation position, and the irradiation is carried out from the closed chamber after the irradiation. It is preferable to form a line so that the fluororesin powder can be taken out, and to perform the operation continuously by repeating these operations.

[0016] The closed chambers may be sequentially fed into a plurality of closed chambers disposed on a turntable to a radiation irradiation position by rotating the turntable, or a plurality of closed chambers linearly arranged at predetermined intervals. A mode in which the closed chamber is sequentially sent to the radiation irradiation position and this operation is reciprocated can be considered. One closed chamber is provided with a supply port and a discharge port, and after supplying unirradiated fluororesin powder from the supply port and irradiating it, the operation of discharging the irradiated fluororesin powder from the discharge port may be repeated. preferable.

[0017]

Next, an embodiment of the method for producing a crosslinked fluororesin according to the present invention will be described. In FIG.
11 is a closed chamber, 12 is a 300 kV non-scanning electron beam irradiator with an accelerating voltage attached to the upper center of the closed chamber 11,
13 is a cathode for thermionic emission, 14 is a cathode 13
2 shows an irradiation window made of 15 μm thick Ti provided at a lower position of FIG. Reference numeral 15 denotes a connector. Heating power is supplied to the cathode 13 via the connector 15,
A high DC voltage is supplied between the cathode 13 and the irradiation window 14.

The closed chamber 11 comprises a cylindrical portion 17 and a conical portion 18 whose periphery is covered with a heat insulating material 16, and a pulsator 19 is provided at the bottom. 20 is a motor for rotating the pulsator 19, 21 is the cylindrical portion 1
7 and an electric heater provided on the outer periphery of the conical portion 18;
Reference numeral 2 denotes a nitrogen gas supply port formed on the top plate 23 above the closed chamber 11, and reference numeral 24 denotes the same.

The nitrogen gas is heated outside and supplied to the supply port 22.
It is further fed into the closed chamber 11 and is discharged from the discharge port 24 to the outside through a filter that does not allow the fluororesin powder to pass. The supply amount and the discharge amount of the nitrogen gas are set to be the same, thereby stabilizing the internal temperature and absorbing the expansion and contraction, and the products generated from the fluororesin accompanying the electron beam irradiation, for example, fluorine gas or various Fluorocarbon gases of molecular weight are eliminated.

The crosslinking in this embodiment is performed as follows. First, a predetermined amount of PTF is placed in the closed chamber 11.
The powder of E (average particle size: 50 μm) is accommodated, and the current of the electron beam irradiation device 12 is set to 5 mA. Further, taking into account that the total energy of the electron beam of 1.5 kWh is converted into heat, the output of the electric heater 21 is adjusted so as to maintain the crosslinking temperature of 340 ± 5 ° C. Adjust the gas temperature.

Next, the motor 20 is operated under the above conditions, and the pulsator 19 is rotated to agitate and scatter the PTFE powder. The scattered PTFE powder 25 develops a rapid movement as shown by an arrow C, and repeatedly passes near the irradiation window 14 with a certain probability while rotating individually.

On the other hand, during this time, an electron beam is output from the irradiation window 14 by the operation of the irradiation device 12 and scattered PTFE.
Irradiation is performed on the powder 25. Irradiation is performed by rotating each powder 2 based on the development movement of the powder 25 in the direction of arrow C.
After the irradiation dose reaches a predetermined level, the irradiation device 12, the motor 20, and the nitrogen gas supply device are stopped, whereby the predetermined cross-linking operation is completed.

The amount of PTFE powder stored in the closed chamber 11 is set to 5 kg when the inner volume of the closed chamber 11 is 50 l, for example.
A specific gravity of the powder / gas mixture of 0.1 g / cm3 is formed. The amount of electron beam absorption required for crosslinking of this PTFE powder is about 100 kGy, and the total amount of absorbed energy is 0.1 kGy.
It is equivalent to 14 kWh. This energy amount corresponds to about 10% of the total energy amount of 1.5 kWh when the irradiation device 12 having the above capacity is irradiated for one hour. The irradiation time of the electron beam in this embodiment is 1 hour or less.

According to the present embodiment carried out as described above, since the irradiation of the electron beam is performed in a state where the PTFE powder is scattered, the irradiation target becomes a fine powder of 50 μm, and therefore, the irradiation of the low level Cross-linking becomes possible. The effects obtained by the present embodiment, including the effects of this, are summarized as follows.

1. Since the fine powder is to be irradiated, it can be cross-linked with a low-level electron beam, and thus 300 k
Irradiation devices with V-class low accelerating voltage can be sufficiently used, and the irradiation devices can be procured at low cost.

2. The X-ray generation rate by-produced by the collision of the electron beam output from the irradiation apparatus of the 300 kV accelerating voltage class with the irradiation window is as low as about 0.8%. X-rays can be protected by plywood and iron plywood, so that the capital investment can be significantly reduced as compared with the conventional manufacturing method requiring a thick concrete protective wall.

3. Irradiation is performed not on the unit of mm but on the unit of μm, so that high-efficiency crosslinking can be performed in a short time. 4. Since the irradiation target is a powder, there is no need to perform any extra processing such as molding and pulverization of a fired body as in the related art, thereby improving the working efficiency and shortening the process by omitting the process.

5. The irradiation window attached to the irradiation device
The temperature rises due to electron beam irradiation, which raises the temperature of the atmosphere, causing a problem.However, since cross-linking with low-level electron beams is possible, the temperature rise of the irradiation window is small and the work is stabilized. be able to.

6. Since the powder to be irradiated is fine and is in a floating state in which it is scattered individually and is not interconnected like a fired body, the heat radiation of the irradiated body is good and the temperature control of the work is easy. 7. Since the fluororesin powder is placed in a flying state, the powder does not agglomerate, and becomes a high-quality crosslinked powder. 8. Since the electron beam does not come into contact with the atmosphere, no ozone countermeasures are required.

FIG. 2 shows another embodiment of the method for producing a crosslinked fluororesin according to the present invention (the same symbols as in FIG. 1 indicate the same parts as in FIG. 1). The feature of this embodiment is that three components 26 each having the enclosed chamber 11 of FIG. 1
2 is provided at a predetermined location, and the structure 26 is sequentially fed to the position of the irradiation device 12 by rotation of the turntable 27.

The component 26 is first supplied with a fluororesin powder into the closed chamber 11 at a position B, and circulated with heated nitrogen gas from a supply port 22 and a discharge port 24 at a position C to thereby form a closed chamber 11. After the inside is preheated, it is sent to the position D, where it is irradiated with an electron beam on the fluororesin powder 25 which is agitated and scattered under the same conditions as in FIG.

After the electron beam irradiation is completed, the constituent 26
It is sent to the position B, where the irradiated and crosslinked fluororesin powder is taken out of the closed chamber 11 and supplied again with the unirradiated fluororesin powder. Three components 26
Receive the treatments at the positions B to D in turn, whereby the predetermined crosslinking operation is continuously performed.

The top plate 23 of the closed chamber 11 is attached to columns 28 and 29 provided at positions C and D, and is attached to and detached from the closed chamber 11 by operations E and F. The reason why the top plate 23 is attached at the positions C and D is that these positions are the preheating and electron beam irradiation positions. Therefore, the top plate 23 at the position B where the fluororesin powder is taken in and out is unnecessary, and the closed chamber 11 at this position is left open.

The advantage of this embodiment resides in that the batch-type cross-linking operation can be carried out continuously. As a result, the operation becomes more efficient and the cross-linked fluororesin can be provided at lower cost. As a result of sequentially feeding the plurality of components 26, the fact that the fluororesin powder can be taken in and out by external setup that does not require equipment downtime is also beneficial, and this has a great effect.

FIG. 3 shows still another embodiment of the method for producing a crosslinked fluororesin according to the present invention. The same reference numerals as in FIG. 1 denote the same parts as in FIG. In this embodiment,
1 is formed by forming a transport mechanism of fluororesin powder using nitrogen gas as a transport medium between a supply port 22 and a discharge port 24 of nitrogen gas. It is characterized in that it supplies and discharges powder.

The raw material PTFE powder is supplied to a powder transfer device 31 directly connected to a nitrogen gas supply device 30, and a predetermined amount thereof is supplied into the closed chamber 11 via a cyclone separator 32. After the supply, the valve 33 is closed and the scattered powder 25 is irradiated with an electron beam of a predetermined dose in the same manner as in FIG.
The crosslinked powder in the closed chamber 11 is sent out to the cyclone separator 35 by the nitrogen gas supplied from the
The PTFE powder is separated and dispensed as a crosslinked powder. In addition, the nitrogen gas containing the decomposition product at the time of crosslinking is sent from the cyclone separator 35 to the waste gas treatment device 36 for treatment.

An advantage of this embodiment carried out as described above is that continuous crosslinking can be performed by a single closed chamber 11, and as a result, highly efficient production can be performed with low investment. Is possible, and a cross-linked fluororesin at lower cost can be provided. It is needless to say that the effects enumerated in the embodiment of FIG. 1 can be obtained in the case of the embodiment of FIGS.

[0038]

As described above, according to the method for producing a crosslinked fluororesin according to the present invention, since the crosslinking is carried out by irradiating the fluororesin powder scattered in the closed chamber with radiation, a low level of radiation is obtained. Cross-linking is possible,
Therefore, a high-efficiency and low-cost production of a crosslinked fluororesin that does not require large-scale capital investment and does not require extra operations such as molding and pulverization of a fired body.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an embodiment of a method for producing a crosslinked fluororesin according to the present invention, wherein (a) is a front view of an apparatus used, (b) is a side view, and (c) is (a). A-A cross-sectional view of FIG.

FIG. 2 is an explanatory view showing another embodiment of the method for producing a crosslinked fluororesin according to the present invention, wherein (a) is a plan view of an apparatus used, and (b) is an AA arrow of (a). FIG.

FIG. 3 is an explanatory view showing still another embodiment of the method for producing a crosslinked fluororesin according to the present invention.

FIG. 4 is an explanatory view showing a conventional method for producing a crosslinked fluororesin, wherein (a) shows the procedure, (b) shows an outline of an apparatus used, (i) is a front view, and (ii) is FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Closed room 12 Electron beam irradiation device 13 Cathode for generating thermoelectrons 14 Irradiation window 15 Connector 16 Insulation material 17 Cylindrical portion 18 Conical portion 19 Pulsator 20 Motor 21 Electric heater 22 Supply port 23 Top plate 24 Discharge port 25 Spraying powder 26 Structure Object 27 Turntable 28, 29 Column 30 Nitrogen gas supply device 31 Powder transport device 32, 35 Cyclone separator 33, 34 Valve 36 Waste gas treatment device

Claims (3)

[Claims] 1. A method for producing a cross-linked fluororesin, wherein the fluororesin is irradiated with radiation to cross-link the molecules of the fluororesin, wherein powder of the fluororesin is scattered in a closed chamber, and A method for producing a crosslinked fluororesin, which comprises irradiating a powder with a predetermined dose of radiation. 2. The step of irradiating the radiation includes sequentially feeding the fluororesin powder to an irradiation position set at a predetermined position, and supplying the fluororesin powder before being sent to the radiation irradiation position. A plurality of the closed chambers from which the fluororesin powder is taken out from the inside at a predetermined position apart from the irradiation position after receiving the irradiation of the predetermined dose by the radiation at the irradiation position. The method according to claim 1, wherein the method is carried out. 3. The step of irradiating the radiation is performed by repeatedly supplying and discharging from a supply port and a discharge port provided in the closed chamber to a predetermined amount of the fluororesin powder sequentially contained in the closed chamber. The method for producing a crosslinked fluororesin according to claim 1, wherein