JP3693072B2 - Electron beam irradiation device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electron beam irradiation apparatus that irradiates an object to be processed in the air (atmosphere with oxygen) and performs desired processing on the object to be processed.
[0002]
[Prior art]
In general, in an electron beam irradiation apparatus, thermoelectrons emitted from a linear filament are taken out as an electron beam, and after accelerating this electron beam in a vacuum space in an accelerating tube, it is taken out into an irradiation chamber through an irradiation window and irradiated. A desired process is performed by irradiating the object to be processed conveyed in the room. Here, an irradiation window part has window foil, a window frame, and the clamp board which hold | suppresses window foil from the irradiation chamber side. Conventionally, for example, when performing a curing treatment of a radiation curable resin applied to paper, a plastic film, or the like, an inert gas is flowed into the irradiation chamber to reduce the oxygen concentration to, for example, 300 ppm or less. This is because when there is a large amount of oxygen in the irradiation chamber, active oxygen is generated in the irradiation atmosphere in the irradiation chamber by irradiating an electron beam, and radicals generated in the irradiation object react with this oxygen, This is because the target reaction is hindered. Here, as the inert gas, nitrogen having a low cost is usually used. However, since it is necessary to always flow an inert gas, the equipment cost and the operation and maintenance cost become expensive. For this reason, when it is not necessary to set the irradiation chamber to an inert gas atmosphere, for example, when performing sterilization / sterilization processing or lamination processing, the irradiation chamber is air (atmosphere with oxygen) or low grade Processing is performed as an active gas atmosphere.
[0003]
[Problems to be solved by the invention]
However, when irradiating an electron beam in the atmosphere, corrosive gases such as ozone and nitrogen oxides are generated, and if moisture is contained in the atmosphere, the corrosive gas will be generated when the electron beam is irradiated. Reacts with water to form nitric acid (HNO ₃ ). For this reason, there has been a problem that nitric acid adheres to the structure located around the irradiation space in which the object to be processed is irradiated with the electron beam, and the structure is corroded. Particularly in such a structure, the clamp plate is made of brass, iron compound, or the like, and thus is easily corroded. Further, when the clamp plate is corroded and the generated corrosive substance flows and adheres to the window foil, the dose of the electron beam taken out through the window foil into the irradiation chamber is reduced, or a pinhole is made in the window foil. Furthermore, when such a corrosive substance adheres to the workpiece, the commercial value of the workpiece is reduced.
[0004]
The present invention has been made based on the above circumstances, and provides an electron beam irradiation apparatus capable of improving the corrosion resistance of a structure located around the irradiation space when an electron beam is irradiated in the atmosphere. It is intended to do.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, an invention according to claim 1 includes an electron beam generator that generates an electron beam, an irradiation chamber that performs a process of irradiating an object to be processed with the electron beam, and an inside of the electron beam generator. In an electron beam irradiation apparatus comprising a window foil for partitioning a vacuum atmosphere and an irradiation atmosphere in the irradiation chamber and extracting the electron beam into the irradiation chamber, the surface of the clamp plate that holds the window foil from the irradiation chamber side is an electron. It is characterized in that it is coated with a corrosion-resistant material that is a light element nitride or oxide that easily transmits light .
[0006]
The invention according to claim 2 for achieving the above object includes an electron beam generator that generates an electron beam, an irradiation chamber that performs a process of irradiating the object to be processed with the electron beam, and an electron beam generator in the electron beam generator. In an electron beam irradiation apparatus comprising a window foil for partitioning a vacuum atmosphere and an irradiation atmosphere in the irradiation chamber and taking out the electron beam into the irradiation chamber, an electron beam serves as a clamp plate that holds the window foil from the irradiation chamber side. It is characterized by being formed of a corrosion-resistant material that is a light element nitride or oxide that is easily permeable .
[0008]
[Action]
In the present invention, the surface of a structure located around the irradiation space is coated with a corrosion-resistant material, so that when an object is irradiated with an electron beam in the atmosphere, the corrosion resistance of the structure is improved. Can do. Here, a structure coated with a corrosion resistant material, it is most effective to the clamping plate. In particular, by covering the surface of the clamp plate, which is susceptible to corrosion, with corrosion-resistant materials, the generation of corrosive substances can be suppressed, so there is also a problem that the corrosive substances fall on the object to be processed and the commercial value of the object to be processed is lost. Very little. Instead of coating the surface of the structure located around the irradiation space with the corrosion resistant material, the structure located around the irradiation space may be formed of the corrosion resistant material.
[0009]
In addition, by using a light element nitride or oxide having a small specific gravity as the corrosion resistant material, generally, an electron beam is more easily transmitted through the light element material. Therefore, even if the corrosion resistant material covering the surface of the clamp plate is used, Even if corrosion occurs and the corrosive substance adheres to the window foil, the proportion of the electron beam absorbed by the corrosive substance can be kept small. For this reason, it becomes difficult to make a pinhole in a window foil, and the fall of the quantity of the electron beam taken out to an irradiation chamber can be prevented.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of an electron beam irradiation apparatus according to an embodiment of the present invention, FIG. 2 is a schematic circuit diagram of an electron beam generation unit of the electron beam irradiation apparatus, and FIG. FIG. 3B is a schematic plan view of the irradiation window portion, and FIG. 3B is a schematic sectional view of the irradiation window portion.
[0011]
The electron beam irradiation apparatus shown in FIG. 1 is used for various applications such as polymerization and crosslinking treatment on the surface of the object to be processed, sterilization treatment of the object to be processed, and the electron beam generator 10 and the irradiation chamber 20. And the irradiation window part 30 is provided.
The electron beam generator 10 includes a terminal 12 that generates an electron beam and an acceleration tube 14 that accelerates the electron beam generated at the terminal 12 in a vacuum space (acceleration space). Further, the inside of the electron beam generation unit 10 is 1.3 × 10 ⁻⁴ to 3 × 10 ⁻⁴ by a pump (not shown) in order to prevent electrons from colliding with gas molecules and losing energy and to prevent oxidation of the filament 12a. A vacuum of 1.3 × 10 ⁻⁵ Pa is maintained. The terminal 12 includes a linear filament 12a that emits thermoelectrons, a gun structure 12b that supports the filament 12a, and a grid 12c that controls thermoelectrons generated in the filament 12a.
[0012]
Further, as shown in FIG. 2, the electron beam generator 10 is applied with a heating power source 16a for heating the filament 12a to generate thermoelectrons, and a control for applying a voltage between the filament 12a and the grid 12c. A DC power source 16b for acceleration and an acceleration DC power source 16c for applying a voltage (acceleration voltage) between the grid 12c and the window foil 32 provided in the irradiation window portion 30 are provided.
[0013]
The irradiation chamber 20 includes an irradiation space 22 for irradiating an object with an electron beam. The object to be processed is moved from the left side to the right side in FIG. 1 by a conveying means (not shown) such as a conveyor in the irradiation chamber 20. A beam collector 24 is provided in the irradiation chamber 20 below the irradiation window 30. The beam collector 24 absorbs an electron beam that has penetrated the workpiece. The surroundings of the electron beam generator 10 and the irradiation chamber 20 are shielded from lead so that X-rays that are secondarily generated during electron beam irradiation do not leak to the outside.
[0014]
Further, the inside of the irradiation chamber 20 is set to an atmosphere such as an inert gas or the air according to the processing content. For example, when performing a curing treatment of a radiation curable resin applied to the surface of an object to be processed, the atmosphere in the irradiation chamber 20 is replaced with an inert gas such as nitrogen. This is because when oxygen is present in the irradiation chamber 20, radicals generated by irradiating an electron beam react with oxygen, thereby inhibiting the resin curing (polymerization) reaction. On the other hand, when performing sterilization / sterilization treatment, the irradiation atmosphere in the irradiation chamber 20 is set to the atmosphere (atmosphere with oxygen), the object to be treated is sterilized by an electron beam, and generated from oxygen by an electron beam. The sterilizing effect of ozone may also be used. In addition, when laminating, it is not necessary to make the irradiation atmosphere in the irradiation chamber 20 an inert atmosphere, so that the equipment cost for supplying a large amount of nitrogen gas and the operation and maintenance cost can be saved. The treatment is performed in the atmosphere.
[0015]
The irradiation window part 30 has the window foil 32 which consists of metal foil, the window frame 34, and the clamp board 36, as shown in FIG.1 and FIG.3 (a), (b). The window frame 34 and the clamp plate 36 serve to support the window foil 32, and the clamp plate 36 holds the window foil 32 from the irradiation chamber 20 side. In order to cool the window foil 32, the window frame 34 includes a water cooling channel (not shown) inside. In the window frame 34, a plurality of bars 34a having the same shape are arranged side by side, whereby a plurality of rectangular openings 34b are formed. And the window foil 32 is being fixed to the lower part of the window frame 34 with the clamp board 36 (In FIG.3 (b), it drew with the space | interval of the window foil 32, the window frame 34, and the clamp board 36). . As the material of the window frame 34, copper is used. On the other hand, as the material of the clamp plate 36, a substance having a thermal expansion coefficient comparable to that of the window frame 34, for example, brass or iron compound is used. The window foil 32 partitions the vacuum atmosphere in the electron beam generator 10 and the irradiation atmosphere in the irradiation chamber 20, and takes out an electron beam into the irradiation chamber 20 through the window foil 32. The metal used for the window foil 32 has a mechanical strength that can sufficiently maintain the vacuum atmosphere in the electron beam generator 10, has a small specific gravity and a small thickness so that the electron beam can be easily transmitted, and is heat resistant. It is desirable to have a superior quality. Usually, titanium (Ti) foil having a thickness of about 10 μm is used for ease of mechanical handling.
[0016]
When the heating power supply 16a heats the filament 12a through current, the filament 12a emits thermoelectrons, and these thermoelectrons are scattered in all directions by the control voltage of the control DC power supply 16b applied between the filament 12a and the grid 12c. Gravitate. Of these, only those passing through the grid 12c are effectively extracted as electron beams. The electron beam taken out from the grid 12c is accelerated in the acceleration space in the accelerating tube 14 by the acceleration voltage of the acceleration DC power supply 16c applied between the grid 12c and the window foil 32, and then the window foil. The object to be processed is irradiated through the irradiation chamber 20 below the irradiation window 30. Normally, the beam current is adjusted by setting the heating power supply 16a and the acceleration DC power supply 16c to predetermined values and making the control DC power supply 16b variable. In general, in an electron beam irradiation apparatus, the dose absorbed by an object is proportional to the beam current. For this reason, the absorbed dose of the electron beam can be adjusted by changing the beam current.
[0017]
By the way, when the irradiation atmosphere of the irradiation chamber 20 is the atmosphere (atmosphere with oxygen) and the electron beam is irradiated, the following problems occur. That is, when corrosive gas such as ozone and nitrogen oxide is generated and moisture is contained in the irradiation atmosphere, the corrosive gas reacts with water at the time of electron beam irradiation, and nitric acid (HNO ₃ ). It becomes. For this reason, nitric acid adheres to the structure located around the irradiation space 22 and the structure is corroded. Particularly in such a structure, the clamp plate 36 is made of brass, an iron compound, or the like, and thus is particularly easily corroded.
[0018]
Further, if a substance generated by corrosion of the structure, that is, a substance mainly composed of copper, iron or the like adheres to the window foil 32, it is difficult to take out an electron beam from the attached portion into the irradiation chamber 20. As a result, the output of the electron beam is reduced. In addition, the portion of the window foil 32 to which the corrosive substance is attached has heat, and finally, the pinhole is vacant in the window foil 32 and the inside of the electron beam generating unit 10 cannot be kept in vacuum, and the apparatus stops. The filament 12a is oxidized and cannot be used. FIG. 4 shows an electron beam penetration depth curve. Here, the horizontal axis of FIG. 4 represents the mass per unit area (surface density g / m ² ) of the substance, and the vertical axis of the figure represents the dose received on the surface of the substance irradiated with the electron beam as 100. It expresses the ratio of the dose received at the depth when%. Considering FIG. 4, since copper, iron, etc. have a large specific gravity, even if the thickness of the corroded material is several microns, the surface density corresponding to the horizontal axis of FIG. It can be seen that most of the electron beam is absorbed in the portion 32. Therefore, it is speculated that the phenomenon of pinholes in the window foil 32 may be caused by the conversion of the electron beam energy into heat.
[0019]
Therefore, in this embodiment, the surface of the structure located around the irradiation space 22 is covered with a corrosion-resistant material. In this embodiment, the structure covered with the corrosion-resistant material is the clamp plate 36 and the beam collector 24. The clamp plate 36 covers only the surface on the irradiation chamber 20 side, and the beam collector 24 covers the entire surface. Further, light element nitrides and oxides are used as the corrosion resistant material. Specifically, boron nitride (BN), silicon nitride (SiN), titanium nitride (TiN), alumina (Al ₂ O ₃ ), titanium oxide (TiO ₂ ), or the like is used. Here, the corrosion-resistant material is a light element substance, so that even if the substance corrodes and adheres to the window foil 32, a sufficient amount of electron beams can pass through the corrosive substance. It is to make it.
[0020]
Next, the present inventors conducted a test to confirm the corrosion resistance effect. In this test, two electron beam irradiation devices CB250 / 15 / 180L manufactured by Iwasaki Electric Co., Ltd. were used as electron beam irradiation devices. Further, a brass plate was used as the clamp plate 36, and the surface of the clamp plate 36 was not covered with one electron beam irradiation apparatus, and the surface of the clamp plate 36 was covered with a corrosion-resistant material in the other electron beam irradiation apparatus. Here, “BN Coat” manufactured by Odec Co., Ltd. was used as the corrosion resistant material. This BN coat is obtained by dissolving boron nitride in water. The BN coat was applied to the clamp plate 36 and then baked to coat the clamp plate 36 with boron nitride. By supplying air once passed through the water into the irradiation chamber 20 for both electron beam irradiation devices, setting the acceleration voltage to 150 kV, setting the beam current to 5 mA, and irradiating the electron beam A life test was conducted on both electron beam irradiation devices. In this test, the window foil 32 and the beam collector 24 were not coated.
[0021]
The result of this life test is shown in FIG. In the electron beam irradiation apparatus in which the coating treatment was not performed on the clamp plate 36, green and white corrosive substances were generated on the clamp plate 36 after one month. Then, after two months, the corrosive substance adhered to the window foil 32 and a hole was opened in the window foil 32, so that the electron beam irradiation apparatus could not operate. On the other hand, in the electron beam irradiation apparatus in which the clamp plate 36 was coated, no change occurred in the clamp plate 36 even after 6 months. After ten months, green pitting corrosion (corrosion distribution on the surface of the metal body is not uniform, and deep hole-shaped corrosion occurs partially) is observed in some places on the clamp plate 36. After two months, it was observed that the pitting corrosion had grown a little. Therefore, it was confirmed that the corrosion resistance is greatly improved by coating the clamp plate 36 with boron nitride.
[0022]
Further, the present inventors can take out an electron beam into the irradiation chamber 20 even when the corrosion-resistant material coated on the surface of the clamp plate 36 is corroded and the corrosive substance adheres to the window foil 32. A test was conducted to confirm the above. In this test, the surface of the window foil 32 was covered with a corrosion-resistant material, and it was examined whether or not an electron beam actually appeared in the irradiation chamber 20. Here, as the electron beam irradiation device, an electron beam irradiation device CB250 / 15 / 180L manufactured by Iwasaki Electric Co., Ltd. was used, and as a corrosion-resistant material, “BN Coat” manufactured by Odec Co., Ltd. was used. Then, the amount of transmission of the electron beam was measured using a dose film in the irradiation chamber 20 by changing the acceleration voltage of the electron beam in various ways. As a result, when the window foil 32 was coated with a corrosion-resistant material, the amount of transmission of the electron beam was attenuated as compared with the case where the window foil 32 was not coated, but the electron beam passed through the window foil 32. It was confirmed that it came out in the irradiation chamber 20.
[0023]
In the electron beam irradiation apparatus of the present embodiment, the surface of a structure located around the irradiation space is coated with a corrosion-resistant material, so that when an object is irradiated with an electron beam in the atmosphere, the structure Corrosion resistance can be improved. Here, it is most effective to use a clamp plate and a beam collector as the structure covered with the corrosion resistant material. In particular, by covering the surface of the clamp plate, which is susceptible to corrosion, with corrosion-resistant materials, the generation of corrosive substances can be suppressed, so there is also a problem that the corrosive substances fall on the object to be processed and the commercial value of the object to be processed is lost. Very little.
[0024]
In addition, by using a light element nitride or oxide having a small specific gravity as the corrosion resistant material, generally, an electron beam is more easily transmitted through the light element material. Therefore, even if the corrosion resistant material covering the surface of the clamp plate is used, Even if corrosion occurs and the corrosive substance adheres to the window foil, the rate at which the corrosive substance absorbs the electron beam can be kept small. For this reason, it becomes difficult to make a pinhole in a window foil, and the fall of the quantity of the electron beam taken out to an irradiation chamber can be prevented. Further, in the beam collector, the light element is easier to absorb the electron beam, so that there is an advantage that the electron beam can be absorbed efficiently as in the conventional case.
[0025]
In addition, this invention is not limited to said embodiment, A various deformation | transformation is possible within the range of the summary. For example, in the above-described embodiment, the case where the surface of the structure positioned around the irradiation space is covered with the corrosion-resistant material has been described. However, the structure itself may be formed of the corrosion-resistant material. In this case as well, it is presumed that the same effect as the above embodiment can be obtained. Further, an exhaust device may be provided in the irradiation chamber of the electron beam irradiation device to positively exhaust the gas generated in the irradiation space to the outside.
[0026]
【The invention's effect】
As described above, according to the first aspect of the present invention, when the surface of the structure located around the irradiation space is coated with the corrosion resistant material, the workpiece is irradiated with the electron beam in the atmosphere. An electron beam irradiation apparatus capable of improving the corrosion resistance of the structure can be provided.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an electron beam irradiation apparatus according to an embodiment of the present invention.
FIG. 2 is a schematic circuit diagram of an electron beam generator of the electron beam irradiation apparatus.
3A is a schematic plan view of an irradiation window portion of the electron beam irradiation apparatus, and FIG. 3B is a schematic cross-sectional view of the irradiation window portion.
FIG. 4 is a diagram showing the relationship between the surface density of a substance and the dose received by the thickness of the substance.
FIG. 5 is a diagram showing test results for corrosion resistance in the electron beam irradiation apparatus of the present embodiment and a conventional electron beam irradiation apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Electron beam generation part 12 Terminal 12a Filament 12b Gun structure 12c Grid 14 Acceleration tube 16a Heating power supply 16b Control direct current power supply 16c Acceleration direct current power supply 20 Irradiation room 22 Irradiation space 24 Beam collector 30 Irradiation window part 32 Window foil 34 Window Frame 34a Crosspiece 34b Opening 36 Clamp plate

Claims (2)

An electron beam generator that generates an electron beam, an irradiation chamber that performs a process of irradiating the object to be processed with the electron beam, a vacuum atmosphere in the electron beam generator and an irradiation atmosphere in the irradiation chamber, and the electron beam In the electron beam irradiation apparatus comprising a window foil for taking out the material into the irradiation chamber , the corrosion resistance is a light element nitride or oxide that easily transmits the electron beam through the surface of the clamp plate that holds the window foil from the irradiation chamber side. An electron beam irradiation apparatus characterized by being coated with a functional material. An electron beam generator that generates an electron beam, an irradiation chamber that performs a process of irradiating the object to be processed with the electron beam, a vacuum atmosphere in the electron beam generator and an irradiation atmosphere in the irradiation chamber, and the electron beam In the electron beam irradiation apparatus comprising a window foil for taking out the material into the irradiation chamber , a corrosion-resistant material that is a light element nitride or oxide that easily transmits an electron beam through a clamp plate that holds the window foil from the irradiation chamber side. An electron beam irradiation apparatus characterized in that it is formed by.

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