JP2002348385A - Cross-linking method for fluororesin powder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cross-linking method for a fluororesin powder whereby a cross-linked powder having excellent fineness and homogeneity can be obtained while decreasing the loss of an auxiliary material for cross-linking by utilizing a liquid as the auxiliary material. SOLUTION: A fluororesin powder is dispersed in a liquid, and the resultant dispersion 17 is irradiated with an electron beam by using an electron beam radiation apparatus 11. A condenser 33 is connected to a storage tank 18 of the dispersion 17, and a noncondensing decomposition gas generated by the irradiation with an electron beam and the vapor of the liquid are introduced together into the condenser 33. The vapor of the liquid is condensed in the condenser and returned to the storage tank 18. The noncondensing decomposition gas collecting on the upper side of the passage 36 of the condenser 33 is sent into a treatment apparatus 42 for making an exhaust gas harmless, is made harmless, and is exhausted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cross-linking fluororesin powder, and more particularly to using a liquid as a cross-linking auxiliary material to impart excellent fineness and homogeneity to the obtained cross-linked powder. The present invention relates to a method of cross-linking fluororesin powder that can be performed and has low loss of auxiliary materials.

[0002]

2. Description of the Related Art In order to improve the properties such as the strength and elongation of a fluororesin, a powdery fluororesin is heated and calcined to irradiate radiation to a mat having a small bulk density.
After irradiation, the fired body is pulverized to return to the original powder state, and this is used as a molding material.

FIG. 4 shows an outline of an apparatus used in this method, wherein 1 is an irradiation apparatus for ionizing radiation such as an electron beam, and 2 is installed below the irradiation apparatus 1 through an irradiation window 3. Irradiated chamber 4 indicates a transporting body arranged to circulate in the irradiation chamber 2, and includes a conveyor 5 and a tray 6 suspended therefrom.
It is composed of

[0004] On a tray 6, a fired body 7 of a fluororesin powder solidified in a mat shape is placed.
When passing through the lower part of the irradiation window 3, it is irradiated with radiation. The interior of the irradiation chamber 2 is set at a temperature slightly higher than the melting point of the fluororesin, and is placed in an oxygen-free state by nitrogen gas or the like to eliminate the influence of oxygen. Is configured to be cooled to the original temperature by circulation of nitrogen gas by a fan.

[0005] In the above configuration, the fired body 7 is repeatedly circulated in the irradiation chamber 2, and is irradiated each time it passes through the position of the irradiation window 3, thereby being irradiated with a predetermined dose of radiation. This method of integrating a predetermined dose by repeating irradiation has been evaluated and utilized as a stable method of crosslinking fluororesin powder.

[0006]

However, according to the conventional method for crosslinking fluororesin powder, the fluororesin powder is coarsened by fusion and the ductility of each fused powder group is large. However, there is a problem that it is difficult to return to a fine and homogeneous original powder during pulverization after crosslinking.

[0007] Accordingly, an object of the present invention is to provide a crosslinked powder obtained by using a liquid as a cross-linking auxiliary material, thereby imparting excellent fineness and homogeneity to the fluororesin with a small amount of auxiliary material loss. An object of the present invention is to provide a method for crosslinking a powder.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a method for crosslinking fluororesin powder by irradiating the fluororesin powder with radiation, wherein the fluororesin powder is housed in a closed storage tank. By dispersing a fluororesin powder in a liquid heated to a crosslinking temperature of a fluororesin to be crosslinked, and irradiating the liquid with radiation through an irradiation window provided in the storage tank to the fluororesin powder. Fluorine gas or the like generated by irradiating the radiation in a condenser that absorbs a predetermined dose of radiation, is connected to the storage tank at a position higher than the liquid level of the liquid, and has a cooling wall for condensation formed in an internal passage. A non-condensable decomposition gas is introduced together with the vapor of the liquid, and the liquid condensed and generated from the vapor by contact with the condensing cooling wall is returned to the storage tank. There is provided a method of crosslinking the fluorine resin powder, characterized by discharging the non-condensable cracked gas accumulated above in serial condenser to the outside of the condenser.

Irradiation of the radiation in the present invention is preferably carried out in a state in which the fluororesin powder is carried, for example, by rotating the liquid in the liquid by imparting a fluidizing action to the liquid. In addition, radiation can be uniformly applied to the entire circumference of the fluororesin powder, and the crosslinking becomes more uniform.

As means for causing the liquid to flow, use of a stirrer or flowing of the liquid through a predetermined flow path can be considered. Particularly, in the latter method, the flow of the liquid is set to a turbulent state. It is preferred that the movement of the fluororesin powder is thereby increased. In addition, as the radiation, ionizing radiation such as an electron beam is preferable because it is easy to handle.

The liquid for dispersing the fluororesin powder is preferably a liquid that is stable at the crosslinking temperature, has no reactivity with the fluororesin, and has excellent radiation resistance. Specifically, biphenyl (C12 H10) and diphenyl ether (C12 H10 O)
(Hereinafter, referred to as liquid A).

The liquid for dispersing the powder preferably has a saturated vapor pressure higher than the atmospheric pressure. When such a liquid is used, the liquid is disposed outside the condenser (in many cases, detoxification of exhaust gas). The non-condensable gas can be smoothly discharged to the processing device) using the vapor pressure.
Liquid A is also suitable in this regard.

It is, of course, possible to use a liquid having a saturated vapor pressure lower than the atmospheric pressure. In this case, in order to smoothly discharge the non-condensable decomposition gas to the outside from the condenser,
It is preferable to apply a pressure such as nitrogen gas to the upper space of the storage tank and use this gas pressure as a part of the discharge pressure. Specific examples of this type of liquid include, for example, a diallyl alkyl liquid (hereinafter, referred to as liquid RP).

[0014]

Next, an embodiment of a method for crosslinking a fluororesin powder according to the present invention will be described. In FIG. 1A, 11 is an electron beam irradiation device, 12 is an electron beam deflecting device, 13 is a scanning horn, 14 is a horn 1 for transmitting an electron beam and for maintaining a vacuum in the scanning horn 13.
3 shows an irradiation window having a Ti foil configuration provided at the tip of No. 3.

Reference numeral 15 denotes a circulating device for circulating a liquid (hereinafter, referred to as a dispersion) in which a fluororesin powder is dispersed,
A dispersion channel 16 disposed immediately below the scanning horn 13, a closed storage tank 18 serving as a supply source of the dispersion 17, a dispersion 17
And a pipe 20 connecting them.

FIG. 1B shows a cross-sectional structure of the dispersion liquid flow path 16, which is provided so as to cover a metal gutter 22 having a groove 21 for flowing the dispersion liquid 17 and an upper part of the groove 21. The irradiation window 23 has a Ti foil structure. Reference numeral 24 denotes a holding metal fitting for fixing the irradiation window 23 to the metal gutter 22.
Reference numeral 5 denotes an outlet of the dispersion liquid 17.

The storage tank 18 includes a stirrer 26 for stirring the dispersion liquid 17, an electric heater 27 for keeping the dispersion liquid 17 at a constant temperature, a power supply 28, a pipe opening 29 serving as a material input section and a vacuum evacuation section, Insulation material 30 and circulating dispersion 1
7 is composed of a forward path 31 and a return path 32.

Reference numeral 33 denotes a condenser attached to a pipe 35 drawn out of an upper space 34 of the storage tank 18.
The cooling wall 3 for condensation is provided in the internal passage 36 having a diameter larger than
7 are formed, and the fins 38 provided on the outer surface of the wall surface 37 are configured to be cooled by a fan 39, whereby the wall surface 37 has a cooling function. 4
Reference numeral 0 denotes a blower pump attached to the pipe 35 via the valve 41 between the condenser 33 and the reference numeral 42 denotes an exhaust gas detoxification treatment apparatus attached to the end of the pipe 35.

Crosslinking of the fluororesin powder in this embodiment is performed as follows. First, liquid A, which is a secondary material for crosslinking, and polytetrafluoroethylene (PT)
After the powder of FE) is supplied into the storage tank 18 from the pipe port 29, a vacuum is drawn from the pipe port 29, thereby removing air.

Next, the dispersion liquid 17 is uniformly prepared by stirring with a stirrer 26, and the temperature of the dispersion liquid 17 is reduced with PTF by heating with an electric heater 27.
The temperature is raised to 340 ° C., which is the crosslinking temperature of E, the valve 43 is opened, and the pump 19 is operated.

As a result of the operation of the pump 19, the dispersion liquid 17 becomes
The liquid is supplied into the dispersion liquid flow path 16 through the pipe 20, flows in a turbulent state, and is irradiated with an electron beam of a predetermined dose from the electron beam irradiation device 11 in a flowing process. The PTFE powder present in the turbulent dispersion liquid 17 and thus rotating randomly, receives the electron beam uniformly over the entire circumference by this irradiation, and is contained in the dispersion liquid 17 and discharged from the flow path 16. You.

The discharged dispersion liquid 17 is returned to the storage tank 18, and after being stirred by the stirrer 26, is again supplied to the dispersion liquid flow path 16 through the above route, and is irradiated with the electron beam. Thereafter, this is repeated until the irradiation amount reaches a predetermined dose, and the electron beam irradiation device 11 is stopped when the target crosslinking level is reached.

After stopping the electron beam irradiation device 11, the valve 43
Is closed, the pump 19 is stopped, and the dispersion liquid 17 is discharged to the outside from the discharge part 44 at the bottom of the storage tank 18. After that, the discharged dispersion liquid 17 is sequentially subjected to washing and drying treatment, whereby a predetermined crosslinked powder is obtained.

During this time, the non-condensable decomposition gas such as a fluorine gas or a low molecular weight fluorinated hydrocarbon gas is generated from the PTFE powder by irradiation with the electron beam, and the vapor of the liquid A is dispersed from the dispersion liquid 17. Will occur. The non-condensable decomposition gas is a harmful substance. Therefore, it is not preferable to release the non-condensable decomposition gas directly into the atmosphere, and it is desired to perform a detoxification treatment before releasing the gas.

The decomposition gas and the vapor of the liquid A are difficult to separate, and in order to make the decomposition gas harmless, it is necessary to treat it together with the vapor of the liquid A as a cross-linking auxiliary material. Due to the high temperature, the amount of vapor generated from the liquid A is large. Therefore, treating and releasing the vapor indefinitely leads to a large loss of sub-materials, which is a great economic burden.

In this regard, according to the present embodiment, the storage tank 18
Since the condenser 33 is arranged at a position higher than the liquid level of the dispersion liquid 17 in the container and is connected to the storage tank 18 via the pipe 35, the non-condensable decomposition gas accumulated in the upper space 34 of the storage tank 18 The gas mixture of the vapor of the liquid A rises in the pipe 35 due to the vapor pressure of the liquid A, and is cooled by contacting the cooling wall 37 for condensation in the internal passage 36 of the condenser 33. As a result, the vapor of the liquid A contained in the mixed gas is condensed and liquefied, and the liquefied liquid A is
, And is returned to the storage tank 18 by gravity to be collected.

On the other hand, the non-condensable decomposition gas from which the vapor of the liquid A has been removed is collected above the internal passage 36 of the condenser 33 by the heat siphon effect. That is, due to the pressure difference generated due to the condensation of the vapor of the liquid A, the mixed gas of the vapor of the liquid A and the non-condensable decomposition gas is accelerated and moved upward from the lower portion. Collision between the obtained kinetic energy and the mixed gas rising from the lower portion causes the gas to collect above the passage 36. Therefore, if the valve 41 is opened at regular intervals, the non-condensable decomposition gas is discharged out of the condenser 33. Will be discharged.

The discharged non-condensable decomposition gas is sent to an exhaust gas detoxification device 42 via a blower pump 40,
After being rendered harmless here, it is released into the atmosphere. In addition, the amount of the liquid A discharged from the condenser 33 together with the non-condensable decomposition gas is insignificant, and its economic burden is negligibly small.

As described above, according to the present embodiment, it is possible to suppress the loss of the liquid A, which is the auxiliary material for crosslinking, and
The non-condensable decomposition gas can be separated and detoxified, and thus the cross-linking operation of the fluororesin powder can be performed under realistic conditions. Moreover, the obtained crosslinked powder does not require a pre-firing step and a subsequent pulverizing step unlike the conventional cross-linking method, so that uniform and fine high quality without coarsening can be provided. In addition,
In the above-described embodiment, it is possible to detect the degree of accumulation of the non-condensable decomposition gas in the passage 36 by measuring the temperature of the cooling wall 37 of the condenser 33. It is practical to open and close the valve 41 by using this method.

FIG. 2 shows the relationship between the temperature of the liquid A and the saturated vapor pressure, and also shows the viscosity at each temperature in comparison with normal-temperature water. According to this, PTFE
The liquid A has a vapor pressure of 4.6 M at a crosslinking temperature of 340 ° C.
Pa, while the viscosity is 0.17 mPa · s (１ ／ of the viscosity of room temperature water of 0.85 mPa · s). Therefore,
The heat siphon effect as described above can be sufficiently obtained, and at the same time, the permeability or wettability with respect to the PTFE powder is sufficient, and it can be said that the material is suitable as an auxiliary material liquid.

FIG. 3 shows another embodiment of the method for crosslinking a fluororesin powder according to the present invention. The difference from FIG. 1 is that a cooling heat exchanger 45 is attached to the return path 32 between the dispersion liquid flow path 16 and the storage tank 18, and further, the return path 32 is branched behind the heat exchanger 45, and the branched tip And the use of a liquid RP as a liquid for the auxiliary material. The same reference numerals as those in FIG.
It shows the same parts as in FIG.

In this embodiment, the dispersion liquid flow path 1
The dispersion liquid 17 that has exited 6 is cooled by a heat exchanger 45 in a portion that has been heated by electron beam irradiation, and then returned to the storage tank 18. Therefore, the dispersion liquid 17 supplied to the flow path 16 through the storage tank 18 and the pipe 20 is always maintained at a constant crosslinking temperature, whereby crosslinking under stable temperature conditions is performed. Will be done.

In the case of this embodiment using a liquid RP having a low saturated vapor pressure as shown in FIG. 2, the vapor of the liquid RP stored in the upper space 34 of the storage tank 18 and the non-condensable decomposition gas Is supplied into the condenser 33 by being purged by the supply of nitrogen gas into the storage tank 18 from the nitrogen gas supply device 46.

Accordingly, the liquid RP in the mixed gas is
Is condensed by coming into contact with the condensing cooling wall surface 37 and returns to the storage tank 18 by gravity, while the non-condensable decomposed gas is collected above the passage 36 of the condenser 33. The collected non-condensable decomposition gas is then sent into an exhaust gas detoxification treatment device 42 by opening a valve 41, where it is detoxified and released to the atmosphere.

In the above embodiment, the amount of the liquid RP sent to the detoxifying apparatus 42 is extremely small, and therefore, the loss of the liquid RP as a sub-material is suppressed, and the amount of the non-condensable decomposition gas is reduced. This embodiment is practical and useful in eliminating harm. Moreover, the obtained cross-linked PTFE powder is fine and homogeneous because it does not require pre-firing and post-crushing as in the conventional method, and can provide a high-quality cross-linked powder.

[0036]

As described above, according to the method for crosslinking a fluororesin powder according to the present invention, the fluororesin powder is dispersed in a liquid, and the dispersion is irradiated with a predetermined dose of radiation. In addition to cross-linking the powder, a condenser is connected to the dispersion liquid storage tank, and the non-condensable decomposition gas generated by irradiation is introduced with the liquid vapor to condense the liquid vapor and return it to the storage tank. On the other hand, the non-condensable decomposition gas accumulated above the condenser is discharged to the outside of the condenser, so that a uniform and fine crosslinked powder without coarsening can be provided, and the liquid as a cross-linking auxiliary material can be provided. Loss can be minimized.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an embodiment of a method for crosslinking a fluororesin powder according to the present invention, in which (a) is a schematic view of an apparatus used, and (b) is a cross-sectional view taken along line AA of (a). Show.

FIG. 2 is an explanatory diagram showing a relationship between vapor pressure and viscosity of a liquid used in an embodiment of the present invention and temperature.

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

4A and 4B are explanatory views showing a conventional method for crosslinking a fluororesin powder, wherein FIG. 4A is a front view and FIG. 4B is a side view.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Electron beam irradiation apparatus 12 Electron beam deflection apparatus 13 Scanning horn 14, 23 Irradiation window 15 Circulation device 16 Dispersion liquid flow path 17 Dispersion liquid 18 Storage tank 19 Pump 20, 35 Piping 21 Groove part 22 Metal gutter 24 Holding metal fitting 25 Exit 26 Stirrer Reference Signs List 27 electric heater 28 power supply 29 pipe mouth 30 heat insulating material 31 forward path 32 return path 33 condenser 34 upper space 36 internal passage 37 cooling wall surface for condensation 38 fin 39 fan 40 blower pump 41, 43 valve 42 waste gas detoxification processing unit 44 discharge unit 45 Cooling heat exchanger 46 Nitrogen gas supply device

Claims (2)

[Claims] 1. A method of crosslinking a fluororesin powder by irradiating radiation to the fluororesin powder, wherein the fluororesin powder is contained in a closed storage tank and heated in a liquid heated to the crosslinking temperature of the fluororesin to be crosslinked. By dispersing a fluororesin powder, a predetermined dose of radiation is absorbed by the fluororesin powder by irradiating the liquid with radiation through an irradiation window provided in the storage tank. The non-condensable decomposition gas such as fluorine gas generated by the irradiation of the radiation is introduced together with the liquid vapor into a condenser which is connected to the storage tank and has a cooling wall for condensation in an internal passage, While refluxing the liquid condensed and generated from the vapor by contact with the condensing cooling wall surface into the storage tank,
A method of cross-linking a fluororesin powder, comprising discharging the non-condensable decomposition gas accumulated in the condenser to the outside of the condenser. 2. The step of irradiating the radiation is performed in a state where the fluororesin powder is moved in the liquid by giving a fluid action such as stirring to the liquid. The method for crosslinking a fluororesin powder according to claim 1.