JP2001329069A - Manufacturing method of podery crosslinking polytetrafluoroethylene - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of powdery crosslinkable PTFE capable of easily crosslinking without aggregating PTFE powders. SOLUTION: A manufacturing method of powdery crosslinking polytetrafluoroethylene irradiates ionizing radiation by floating calcined polytetrafluoroethylene powder in gas of lower oxygen atmosphere heated at over the melting point of the calcined polytetrafluoroethylene to be crosslinked.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a crosslinked polytetrafluoroethylene (hereinafter referred to as a "crosslinkable polytetrafluoroethylene") capable of realizing sliding parts, sealing parts, packings, gaskets, containers and jigs for semiconductor production, etc. having excellent wear resistance and creep resistance. "Polytetrafluoroethylene" is referred to as "PTFE").

[0002]

2. Description of the Related Art PTFE has excellent low friction properties, heat resistance, electrical properties, chemical resistance and cleanliness (non-staining), and is widely used in various industrial and consumer applications.
However, PTFE has large wear and creep deformation in a sliding environment or a high temperature compression environment, and may not be used depending on the application. It is known that, when PTFE is irradiated with ionizing radiation at a temperature equal to or higher than the melting point of PTFE in a low-oxygen atmosphere gas and crosslinked, abrasion resistance, creep resistance, and radiation resistance can be improved. As a method for obtaining a PTFE molded body having a characteristic, there is a method of compression-molding a cross-linked PTFE powder into a predetermined shape alone or by mixing it with another polymer.

As a method of crosslinking PTFE powder, the applicant of the present invention has proposed a method of irradiating ionizing radiation by suspending PTFE powder in a low-oxygen atmosphere gas heated to a temperature higher than the melting point of the PTFE. (Japanese Patent Application No. 10-365292).

[0004]

However, PTFE has a transformation point around 19 ° C., and above this transformation point temperature, the aggregate of PTFE powder is apt to be flocculated with a slight pressure, and the above-mentioned is considered. In the method, there is a problem that the PTFE is easily aggregated in a portion where the airflow is slow in the irradiation container before the cross-linking reaction proceeds or in a process of being transported to the irradiation container.

Accordingly, it is an object of the present invention to provide a method for producing a powdery crosslinked PTFE which can easily perform a crosslinking treatment without agglomeration of the PTFE powder.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above-mentioned object, the present invention provides a method for producing a baked PTFE powder.
Powdered crosslinks P which are suspended in a low-oxygen atmosphere gas heated to a melting point of TFE or higher and irradiated with ionizing radiation to be crosslinked
Provided is a method for producing TFE. Since the PTFE powder heated and fired at a temperature equal to or higher than the melting point of PTFE is hardly agglomerated, the crosslinking treatment can be easily performed.

[0007]

DETAILED DESCRIPTION OF THE INVENTION In the present invention, a fired PTF is used.
Examples of the method for obtaining the E powder include a method in which the PTFE powder is directly baked, a method in which the PTFE powder is formed into a mat shape, and then fired at a temperature equal to or higher than the melting point of the PTFE. There are pulverizing methods, etc.
The latter method is preferred in consideration of the handling of the material.

In the crosslinking treatment of the calcined PTFE powder, the calcined PTFE powder and low-oxygen atmosphere gas are confined in a closed container, and ionizing radiation is applied while maintaining the temperature at or above the melting point of the calcined PTFE powder. This is done by: In this case, the PTFE powder generates heat in proportion to the absorbed dose of the PTFE powder, and excessive heating causes the breaking and decomposition of the molecular main chain, and also generates fluorine gas and various fluorine hydrocarbons. Therefore, the low oxygen atmosphere gas heated to the melting point of the burned PTFE or higher is continuously injected into the closed container, and at the same time, the same amount of the low oxygen atmosphere gas as the injection amount is continuously discharged through the filter. It is preferable to do so. In order to prevent the molecular main chain from being cut and decomposed due to excessive heating, the heating temperature is set to the firing temperature.
It is preferable to keep the melting point within the range of 10 to 30 ° C. higher than the melting point of TFE.

In the present invention, as ionizing radiation, γ-rays, electron beams and the like can be used. However, in the case of γ-rays, since the ability to penetrate an object is large, the size of particles is not substantially limited. It is preferable to use an electron beam for reasons such as difficulty in controlling the irradiation dose and handling the device. The electron beam is irradiated by the accelerating voltage (PTFE)
When the acceleration voltage is 800 kV, for example, the penetration depth into the mat-like fired PTFE having a bulk specific gravity of 0.5 is about 4 mm (when the relative dose is 70% or more). Since the coarse particles of PTFE move at random in all directions in the high-speed airflow of the atmosphere gas, if the shape is close to a sphere, the maximum particle size is twice the penetration depth of the electron beam, that is, up to about 8 mm. Will be done. However, the shape of the powder obtained by crushing after firing is complicated, and it is necessary to float the powder in an air current, so that it is preferable to set the powder to about 1 mm or less. The irradiation dose of the electron beam is preferably in the range of 1 kGy to 10 MGy.

[0010] Since the PTFE powder after irradiation crosslinking is coarsened by agglomeration, pulverization or the like is performed as necessary. The cross-linked PTFE powder has the characteristic of being easily pulverized, but the degree of pulverization is preferably not less than 5 μm because the degree of pulverization is too small to facilitate aggregation.

[0011]

FIG. 1 is a flow chart showing one embodiment of the method for producing a crosslinked PTFE powder of the present invention. The PTFE powder is formed into a mat shape by ram extrusion, the mat-shaped formed body is fired at a temperature equal to or higher than the melting point of PTFE, and the fired mat-shaped formed body is pulverized to obtain a fired PTFE powder. Subsequently, the calcined PTFE powder is charged into a container, suspended in a low-oxygen atmosphere gas heated at a temperature equal to or higher than the melting point of the calcined PTFE circulating at high speed, and irradiated with an electron beam to obtain a crosslinked PTFE powder. And then pulverized to a predetermined particle size to obtain a crosslinked PTFE fine powder.

FIG. 2 is an explanatory view of one embodiment for producing a fired PTFE powder. 1 is an air cylinder, 2 is an extrusion ram, 3 is a hopper, 4 is a PTFE powder, 5 is a molding cylinder, 6 is a PTFE mat-like molded body, 7 is a support roll,
8 is a firing chamber, 9 is an atmosphere gas generator, 10 is an atmosphere gas blower, 11 is a gas heating device, and 12 is fired PTFE.
13 is a cooling chamber, 14 is a cooling blower, 15 is a gas cooling device, and 16 is a crushing device.

An unfired PTFE powder 4 supplied to a hopper 3 is extruded by an extrusion ram 2 reciprocally driven by an air cylinder 1.
Thus, the PTFE mat-like molded body 6 is continuously molded by being pushed into the molding cylinder 5. This allows, for example,
A PTFE mat-shaped molded body 6 having a cross section thickness of 20 mm, a width of 200 mm and a bulk specific gravity of about 0.5 is obtained.

The PTFE mat-shaped molded body 6 is continuously fed into a firing chamber 8. The firing chamber 8 includes a plurality of support rolls 7, and the inside is filled with an atmosphere gas supplied from an atmosphere gas generator 9. The atmosphere gas is circulated through the atmosphere gas blower 10 and the heating device 11, so that the PTFE mat-shaped molded body is maintained at a firing temperature of 370 to 380 ° C.

The fired PTFE mat-like molded body 6 is
It is continuously fed into a cooling chamber 13 provided with a plurality of support rolls 7. The inside of the cooling chamber 13 is filled with the atmospheric gas supplied from the atmospheric gas generator 9. This atmospheric gas is circulated through a cooling blower 14 and a gas cooling device 15, and the PTFE mat-shaped molded body is cooled to 200 ° C. or lower in the cooling chamber 13.

The PTFE mat-shaped molded body 6 heated to a temperature higher than the firing temperature and then cooled is sent to a pulverizing device 16 and pulverized to a predetermined particle size to obtain a fired PTFE powder.

FIG. 3 is an explanatory view of one embodiment for producing a crosslinked PTFE powder. 17 is an irradiation bridge apparatus main body, 18 is a bottom conical cylindrical body, 19 is a cover plate, 20 is an impeller driving motor, 21 is a stirring impeller, 22 is a stirring blade, 23
Is a PTFE powder supply port, 24 is a PTFE powder extraction port, 25 is a storage hopper lower valve, 26 is PTFE
Powder storage hopper, 27 is the first cyclone side valve,
28 is a first cyclone separator, 29 is an electron beam irradiation window, 3
0 is a temperature sensor, 31 is an exhaust gas extraction port, 32 is a main body filter, 33 is a main body filter section valve, 34 is a suction fan, 35 is an exhaust gas treatment device, 36 is an electric heater,
37 is a heat insulating material, 38 is a storage hopper side valve, 39 is a second cyclone separator, 40 is a second cyclone side valve,
41 is a gas type PTFE powder conveying device, 42 is a second cyclone side filter, 43 is a second cyclone upper valve,
4 is a storage hopper side valve, 45 is a low-temperature atmosphere gas supply device, 46 is a high-temperature atmosphere gas valve, 47 is a high-temperature atmosphere gas supply device, 48 is a first cyclone filter, 49
Is a first cyclone upper valve, 50 is a first cyclone lower valve, and 51 is an electron beam irradiation device.

The main part of the irradiation crosslinking device main body 17 is a closed container in which a lid plate 19 is mounted on a bottom conical cylindrical body 18. A stirring impeller 21 that is rotated at a high speed by an impeller driving motor 20 is provided at a bottom portion thereof, and a stirring blade 22 is attached to an upper surface of the stirring impeller 21.
The mixture of the E powder 12 is agitated, and the PTFE powder 12 is suspended in the high-speed airflow.

On the side surface of the bottom conical cylinder 18, a supply port 23 for the uncrosslinked PTFE powder 12 and a crosslinked PTFE powder are provided.
A powder extraction port 24 is attached, the supply port 23 is connected to a PTFE powder storage hopper 26 via a storage hopper lower valve 25, and the extraction port 24 is connected to a first cyclone via a first cyclone side valve 27. It is connected to a separator 28. An electric heater 36 is attached to the outer surface of the bottom conical cylindrical body 18, and the entire outer surface of the sealed container is covered with a heat insulating material 37.

An electron beam irradiation window 29 made of Ti foil, a temperature sensor 30, and an exhaust gas extraction port 31 are attached to the cover plate 19. The exhaust gas extraction port 31 is connected to an exhaust gas treatment device 35 via a main body filter 32, a main body filter part valve 33, and a suction fan 34.

A second cyclone separator 39 is attached to the upper part of the PTFE powder storage hopper 26 via a storage hopper side valve 38. The second cyclone separator 39 is connected via a second cyclone side valve 40. Gas type P
It is connected to a TFE powder conveying device 41. The upper part of the second cyclone separator 39 is provided with a second cyclone-side filter 4.
2 and the suction fan 3 through the second cyclone side valve 43
4 and an exhaust gas treatment device 35. PTFE
The powder storage hopper 26 has a storage hopper side valve 4.
Low-temperature atmosphere gas supply device 4 with temperature adjustment function via 4
5 is connected. This low-temperature atmosphere gas supply device 45
Is supplied also to the gas-type PTFE powder conveying device 41. PTFE powder supply port 2
A high-temperature atmosphere gas supply device 47 is connected to 3 via a high-temperature atmosphere gas valve 46.

The upper part of the first cyclone separator 28 is connected to a suction fan 34 and an exhaust gas treatment device 35 via a first cyclone filter 48 and a first cyclone upper valve 49. A lower valve 50 for discharging crosslinked PTFE powder is attached to a lower portion of the first cyclone separator 28.

FIG. 4 is a sectional view taken along the line AA of FIG.
A stirring blade 22 is attached to the upper surface of the stirring impeller 21, and the entire outer surface of the bottom conical cylindrical body 18 is made of a heat insulating material 3.
7 covered.

FIG. 5 is a sectional view taken along the line BB of FIG.
The cover plate 19 around the electron beam irradiation window 29 is covered with a heat insulating material 37, and the cover plate 19 is provided with a temperature sensor 30 and an exhaust gas extraction port 31.

The procedure for crosslinking the PTFE powder with the apparatus shown in FIG. 3 will be described below.

The first cyclone side valve 27, the second cyclone side valve 40, the high-temperature atmosphere gas valve 46 and the first cyclone upper valve 49 are closed.

Opening all valves other than the valve closed above, operating the suction fan 34, and further filling the system with the atmosphere gas from the low-temperature atmosphere gas supply device 45 to purge the air, and then all the valves Close.

The storage hopper side valve 38, the second cyclone side valve 40 and the second cyclone upper valve 43
Is opened and the gas type PT is operated with the suction fan 34 operated.
A predetermined amount of uncrosslinked PTFE powder 1
2 through the cyclone separator 39 to the PTFE powder storage hopper 26 and then the second cyclone upper valve 4
Close 3.

The storage hopper lower valve 25, the main body filter part valve 33 and the storage hopper side valve 44 are opened, whereby the uncrosslinked PTFE powder 12 is put into the container of the bottom conical cylindrical body 18 together with the low-temperature atmosphere gas, and thereafter The valves 25, 33, and 44 are closed.

The impeller drive motor 20 is started, and the stirring impeller 21 is rotated at a high speed to float the PTFE powder in the gas stream.

The interior of the container is heated by the electric heater 36 while opening the high-temperature atmosphere gas valve 46 and injecting the high-temperature atmosphere gas. When the temperature detected by the temperature sensor 30 reaches a predetermined value (not less than the melting point of the fired PTFE), the electric heater 36
Is turned off, and the electron beam irradiation device 51 is operated to irradiate the PTFE powder with the electron beam through the electron beam irradiation window 29. In this process, the internal temperature is kept constant and the generated gas is removed while continuously injecting and continuously discharging fresh high-temperature atmosphere gas.

After irradiating the electron beam for a predetermined time,
The high-temperature atmosphere gas valve 46 is closed.

Storage hopper lower valve 25, first cyclone side valve 27, storage hopper side valve 4
4. Open the first cyclone upper valve 49 and the first cyclone lower valve 50, and discharge the crosslinked PTFE powder out of the container while injecting a low-temperature atmosphere gas. When the discharge is completed, the valve is closed and the motor for driving the impeller is stopped.

By repeating the above operations (1) to (3), the crosslinked PTFE powder can be mass-produced.

Crosslinked PTFE produced as described above
By pulverizing the powder using a conventional plastic pulverizer, a crosslinked PTFE powder for molding is obtained.

According to one embodiment of the method for producing a powdery crosslinked PTFE of the present invention, since the PTFE powder does not agglomerate, the three steps of calcination, crosslinking and pulverization are connected by an automatic powder conveying apparatus. Once the PTFE powder as the raw material is once introduced, the crosslinked PTFE powder can be automatically produced, and the high quality, low cost and high efficiency of the powdered crosslinked PTFE powder can be obtained.
It is possible to manufacture FE.

[0037]

According to the present invention described above, high-quality powdery PTFE can be produced at low cost and with high efficiency, and is extremely useful in industry.

[Brief description of the drawings]

FIG. 1 is a flowchart of one embodiment of a method for producing a powdery crosslinked PTFE of the present invention.

FIG. 2 is an explanatory view of a method for producing calcined PTFE in one embodiment of the method for producing powdery crosslinked PTFE of the present invention.

FIG. 3 is an explanatory view of a method for producing a crosslinked PTFE in one embodiment of the method for producing a powdery crosslinked PTFE of the present invention.

FIG. 4 is a sectional view taken along the line AA of FIG. 3;

FIG. 5 is a sectional view taken along the line BB in FIG. 3;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Air cylinder 2 Extrusion ram 3 Hopper 4 PTFE powder 5 Molding cylinder 6 PTFE mat-like molded object 7 Support roll 8 Firing room 9 Atmospheric gas generator 10 Atmospheric gas blower 11 Gas heating device 12 Firing PTFE powder 13 Cooling room 14 Cooling Blower 15 Gas cooling device 16 Crushing device 17 Irradiation crosslinking device main body 18 Bottom conical cylindrical body 19 Cover plate 20 Impeller drive motor 21 Stirring impeller 22 Stirring blade 23 PTFE powder supply port 24 PTFE powder extraction port 25 Lower part of storage hopper Valve 26 PTFE powder storage hopper 27 First cyclone side valve 28 First cyclone separator 29 Electron beam irradiation window 30 Temperature sensor 31 Exhaust gas extraction port 32 Main body filter 33 Main body filter section valve 34 Suction fan 35 Exhaust gas Controller 36 Electric heater 37 Insulation material 38 Storage hopper side valve 39 Second cyclone separator 40 Second cyclone side valve 41 Gas type PTFE powder transfer device 42 Second cyclone side filter 43 Second cyclone upper valve 44 Storage hopper side valve 45 Low-temperature atmosphere gas supply device 46 High-temperature atmosphere gas valve 47 High-temperature atmosphere gas supply device 48 First cyclone filter 49 First cyclone upper valve 50 First cyclone lower valve 51 Electron beam irradiation device

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroo Kusano 5-1-1 Hidaka-cho, Hitachi City, Ibaraki Prefecture Within Hitachi Cable Engineering Co., Ltd. (72) Inventor Takayasu Asai Hidaka-cho, Hitachi City, Ibaraki Prefecture 5-1-1, Hitachi Cable Co., Ltd. Hidaka Factory (72) Inventor Shigenori Nemoto 5-1-1, Hidaka-cho, Hitachi City, Ibaraki Prefecture F-term in Hidaka Factory, Hitachi Cable Co., Ltd. 4F070 AA24 DA41 DA46 GA04 GA07 GB02 GB03 GB04 HA03 HA04 HB02 HB04

Claims (4)

[Claims] 1. The method of claim 1, wherein the fired polytetrafluoroethylene powder is suspended in a low-oxygen atmosphere gas heated above the melting point of the fired polytetrafluoroethylene and irradiated with ionizing radiation for crosslinking. For producing powdery crosslinked polytetrafluoroethylene. 2. The fired polytetrafluoroethylene powder is formed by molding an unfired polytetrafluoroethylene powder into a mat shape, firing at a temperature equal to or higher than the melting point of the polytetrafluoroethylene. 2. A material obtained by pulverizing a calcined mat-like molded product.
A method for producing the powdery crosslinked polytetrafluoroethylene according to the above. 3. The fired polytetrafluoroethylene powder is suspended in a low-oxygen atmosphere gas heated above the melting point of the fired polytetrafluoroethylene circulating at a high speed in a closed container. 2. The method for crosslinking a powdery crosslinked polytetrafluoroethylene according to 1. 4. A low oxygen atmosphere gas heated above the melting point of the fired polytetrafluoroethylene is continuously injected into the closed vessel, and a low oxygen atmosphere gas having substantially the same amount as the injected amount is continuously injected. The method for crosslinking a powdery crosslinked polytetrafluoroethylene according to claim 3, wherein the low-oxygen atmosphere gas is circulated at a high speed in the closed container by discharging the gas.