JP7071714B2 - Electron beam sterilization method - Google Patents

Description

The present invention relates to an electron beam sterilization method for sterilizing and sterilizing foods, medical supplies and the like by irradiating them with an electron beam.

By irradiating foods and medical supplies with radiation such as gamma rays, X-rays, and electron beams, foods and medical supplies are sterilized and sterilized.
Since the above-mentioned radiation has a penetrating power, it can be sterilized after packaging an object to be irradiated such as a target food or medical supplies. Therefore, in general, an object to be irradiated to be irradiated is sterilized by radiation in a shipping state housed in a container such as a cardboard box or a container.

Patent Document 1 describes a sterilization method in which food is housed in a packaging material and the food is irradiated with radiation through the packaging material, and the packaging material for irradiation is less likely to generate odor even when irradiated with radiation. There is a disclosure about.

Further, Patent Document 2 is a method of sterilizing a container by irradiating a container containing food with an electron beam, which is a shielding means for partially shielding the electron beam from a portion of the container having a large irradiation dose ratio. Disclosed is a method of irradiating a container with a substantially uniform dose by irradiating the electron beam from above the shielding means.

Patent Document 3 describes a tomography means for photographing a tomographic image in the irradiation direction to acquire the density distribution of the irradiated object, and a variation in the dose distribution of the irradiated radiation in the irradiated object based on the density distribution. Disclosed is an irradiation device having an irradiation condition determining means for determining irradiation conditions so as to suppress the irradiation to a predetermined reference width or less, and controlling the irradiation means to perform irradiation according to the irradiation conditions. ing.

JP-A-2010-159398 Japanese Unexamined Patent Publication No. 8-151021 Japanese Unexamined Patent Publication No. 2000-167029

When irradiating, it is generally necessary to adjust the irradiation dose and irradiation time to apply the required absorbed dose to the irradiated object. If the substance density of the irradiated object is not uniform, the absorbed dose in the irradiated object becomes non-uniform, and a uniform sterilization / sterilization effect cannot be obtained.
This problem becomes remarkable in the case of electron beam irradiation having a lower transmittance than gamma rays and X-rays. When the irradiation variation becomes large, the maximum dose specified for the irradiated object may be exceeded or the minimum dose may be exceeded. If the dose exceeds the maximum dose, deterioration due to radiation will occur, and the expected sterilization / sterilization effect below the minimum dose cannot be obtained.
Further, although the electron beam has substance permeability, its penetrating power is weak and the penetrating distance is short. Therefore, when a thick object to be irradiated is irradiated with an electron beam from one direction, the absorbed dose in the object to be irradiated becomes non-uniform.
The method described in Patent Document 3 is not a simple method because the apparatus becomes large-scale.

Conventionally, for a thick irradiated object, the absorbed dose in the irradiated object is made uniform by irradiating the two facing surfaces such as the upper and lower surfaces with an electron beam.
However, as shown in FIG. 10, when there is a region B having a high bulk density of the irradiated object in the container 2, when a sufficient absorbed dose is applied to the region B having a high bulk density, the region A having a low bulk density A. Is given an electron beam in excess of the maximum allowable dose, which is not preferable.
Further, when there is a region C in the container 2 in which the irradiation of the electron beam is desired to be avoided, it is difficult to reduce the irradiation of the electron beam to the region C by the method of irradiating the two facing surfaces such as the upper and lower surfaces with the electron beam. ..

An object of the present invention is to provide an electron beam sterilization method for equalizing the absorbed dose in an irradiated object.

The present invention for solving the above problems is an electron beam sterilization method as described below.
It is an electron beam sterilization method that sterilizes or sterilizes an object to be irradiated with an electron beam.
The electron beam should be applied to the object to be irradiated from at least two directions.
An irradiation dose adjusting plate having an area SA in which a shielding material for shielding an electron beam is arranged and an area SB in which the shielding material is not arranged is arranged between the electron beam extraction window of the electron beam irradiator and the irradiated object. ,
An electron beam sterilization method comprising irradiating an object to be irradiated with an electron beam through the irradiation dose adjusting plate.

By adopting the electron beam sterilization method of the present invention, the absorbed dose in the irradiated object can be made uniform.

It is a figure which shows an example of the irradiated object in the electron beam sterilization method of this invention. It is a figure which shows an example of the method of sterilizing the irradiated object shown in FIG. 1 with an electron beam. It is a figure which shows one Embodiment of the irradiation dose adjustment plate in this invention. It is a figure which shows the other embodiment of the irradiation dose adjustment plate in this invention. It is a figure which shows the other embodiment of the irradiation dose adjustment plate in this invention. It is a figure which shows the other embodiment of the irradiation dose adjustment plate in this invention. It is a figure which shows one embodiment of the sterilization method of this invention. FIG. 7A is a front view of the electron beam irradiating device, and FIG. 7B is a side view of the electron beam irradiating device. It is a figure which shows the other embodiment of the sterilization method of this invention. It is a figure which shows an example of the operation of the irradiation dose adjustment plate support transport means in the embodiment shown in FIG. It is a figure which shows the conventional electron beam irradiation method.

The present invention relates to the following electron beam sterilization method (1), but other embodiments include the following embodiments (2) to (7), which will also be described below.
(1) An electron beam sterilization method in which an object to be irradiated is irradiated with an electron beam to sterilize or sterilize the object.
The electron beam should be applied to the object to be irradiated from at least two directions.
An irradiation dose adjusting plate having an area SA in which a shielding material for shielding an electron beam is arranged and an area SB in which the shielding material is not arranged is arranged between the electron beam extraction window of the electron beam irradiator and the irradiated object. ,
An electron beam sterilization method in which an electron beam is irradiated to an irradiated object through the irradiation dose adjusting plate.
(2) The electron beam sterilization method according to (1) above, wherein the irradiated object is irradiated with an electron beam from two directions.
(3) The irradiation dose adjusting plate is an irradiation dose adjusting plate in which the metal material in the region corresponding to the region SB is removed from the metal plate and the region SA is formed by the remaining metal material. Alternatively, the electron beam sterilization method according to (2).
(4) The irradiation dose adjusting plate uses a plurality of metal plates as the shielding material, the region in which the plurality of metal plates are arranged is designated as the region SA, and the region in which the metal plates are not arranged is designated as the region SB. The electron beam sterilization method according to (1) or (2) above, which is an irradiation dose adjusting plate.
(5) The irradiation dose adjusting plate uses a plurality of metal tiles as the shielding material, the region in which the plurality of metal tiles are arranged is referred to as the region SA, and the region in which the metal tiles are not arranged is referred to as the region SB. The electron beam sterilization method according to (1) or (2) above, which is an irradiation dose adjusting plate.
(6) The irradiation dose adjusting plate comprises a plurality of metal spheres as the shielding material and a sieve having a mesh that does not allow the metal spheres to pass through, and a region in which the plurality of metal spheres are arranged in the mesh of the sieve is formed. The electron beam sterilization method according to (1) or (2) above, which is an irradiation dose adjusting plate in which the region SA is defined as the region SA and the region in which the metal sphere is not arranged is defined as the region SB.
(7) Any one of (1) to (6) above, wherein the irradiation dose adjusting plate is placed on the surface to be irradiated with the electron beam of the irradiated object or the container containing the irradiated object. The electron beam sterilization method described in.
(8) The irradiation dose adjusting plate is supported between the electron beam extraction window of the electron beam irradiator and the irradiated object, and the irradiation dose adjusting plate is transported at the same speed as the transport speed of the irradiated object. The electron beam sterilization method according to any one of (1) to (6) above, which uses an irradiation dose adjusting plate support transport means.
(9) Before irradiating the irradiated object with an electron beam, imaging is performed by irradiating the irradiated object with X-rays, and the arrangement of the shielding material on the irradiation dose adjusting plate is determined based on the obtained information. The electron beam sterilization method according to any one of (1) to (8) above.

First, an outline of the electron beam irradiation device that can be used in the embodiment of the present invention will be described with reference to FIGS. 7A and 7B.
FIG. 7A is a front view of the electron beam irradiating device 30, and FIG. 7B is a side view of the electron beam irradiating device 30.
The electron beam irradiating device 30 transports the device main body 11 that irradiates the container 2 containing the irradiated object 1 with the electron beam E, and the container 2 containing the irradiated object 1 arranged below the device main body 11. Includes device 12.
The apparatus main body 11 includes an electron gun 13 that generates electrons, an accelerating tube 14 that accelerates the electrons generated by the electron gun 13 downward, an electromagnet 15 that scans an electron beam from the accelerating tube 14 in a horizontal plane, and an electromagnet 15. It is provided with a scan horn 16 that emits the electron beam E scanned in 1 downward. At the lower part of the scan horn 16, an electron beam extraction window 17 for taking out the electron beam E downward is provided.

When the above-mentioned electron beam irradiation device 30 is used, there are three parameters that can adjust the absorbed dose of the irradiated object 1, and the parameters are the movement of the conveyor of the transport device 12 that conveys the irradiated object 1. Velocity, electron beam energy and current values.
However, if these parameters are only adjusted, the absorbed dose in the irradiated object becomes non-uniform when the substance density of the irradiated object is not uniform, and a uniform sterilization / sterilization effect cannot be obtained.

In the present embodiment, the image of the irradiated object 1 is performed in advance to acquire information on the bulk density (filling degree) of the material constituting the irradiated object 1. In the imaging, the irradiated object 1 is scanned with X-rays, and the distribution of the bulk density in the irradiated object 1 is grasped from the transmitted amount of the transmitted X-rays. Then, a low dose is given by irradiating a region with a low bulk density with a small amount of electron beam, and a higher dose is given by irradiating a region with a high bulk density with a larger amount of electron beam. do.
As the imaging, two-dimensional imaging may be performed or three-dimensional imaging may be performed depending on the shape and arrangement of the irradiated object 1 in the container 2.
If the material of the irradiated object 1 and the arrangement of the irradiated object 1 in the container 2 are known, it is not necessary to perform imaging.
Further, in the following, the region in the container 2 in which the bulk density of the irradiated object 1 is large and a high dose needs to be applied is referred to as a priority irradiation region B, and the region in the container 2 where the bulk density is small and a low dose needs to be applied is referred to. It may be referred to as a non-focused irradiation area A.

Next, in the present embodiment, the irradiation dose adjusting plate 20 in which the shielding material is arranged in the region corresponding to the non-priority irradiation region A is arranged between the electron beam irradiation device 30 and the container 2 accommodating the irradiated object 1. The irradiated object 1 is irradiated with an electron beam through the irradiation dose adjusting plate 20.
The irradiation dose adjusting plate 20 arranges a shielding material that shields the electron beam in the region of the irradiation dose adjusting plate (referred to as “region SA”) corresponding to the non-priority irradiation region of the irradiated object 1. As a result, the region (referred to as “region SB”) of the irradiation dose adjusting plate corresponding to the focused irradiation region B of the irradiated object 1 in the irradiation dose adjusting plate 20 is formed.
As the shielding material for the electron beam E, a metal plate such as an aluminum plate or a plastic plate can be used.
By selecting and adjusting the material and structure of the shielding material, it is possible to allow a part of the electron beam to pass through or to completely block the electron beam.

Hereinafter, embodiments of the electron beam sterilization method of the present invention will be described with reference to FIGS. 1 and 2.
In FIG. 1, the irradiated object housed in the container 2 has a non-focused irradiation region A and a focused irradiation region B. The focused irradiation region B is determined by an imaging process performed in advance.
FIG. 2 is a diagram showing a state in which the surface Fa of the container 2 is irradiated with the electron beam E, and the surface Fb of the container 2 is irradiated with the electron beam E.
It is not necessary to irradiate the container 2 with the electron beam E from two directions at the same time. First, the electron beam E is irradiated to the surface Fa of the container 2 from one direction, and then the container is rotated 90 degrees to rotate the surface of the container 2. Fb may be irradiated with an electron beam.
Further, in order to ensure that the high dose is absorbed in the focused irradiation region B and the low dose is absorbed in the non-focused irradiation region A, in the present embodiment, as shown in FIG. 2, an electron beam is formed on the surface Fa of the container 2. When E is irradiated, the irradiation dose adjusting plate 20 is arranged on the surface Fa, and when the surface Fb of the container 2 is irradiated with the electron beam E, the irradiation dose adjusting plate 20 is placed on the surface Fb. Deploy.

Next, the irradiation dose adjusting plate 20 will be described.
The irradiation dose adjusting plate 20 has a metal plate 3 which is an electron beam shielding material for reducing the irradiation dose in the non-priority irradiation region A. The metal plate 3 is arranged in the area of the surface of the container 2 corresponding to the non-focused irradiation region A of the irradiated object, whereby the opening in which the metal plate 3 is not arranged on the surface of the container corresponding to the focused irradiation region B. 10 is formed.
As a result, the electron beam E that is not shielded by the electron beam shielding material is irradiated to the focused irradiation region B from two directions through the opening 10, so that a large absorbed dose is given to the irradiated object in the focused irradiation region B. Will be done. On the other hand, the non-focused irradiation region A is irradiated with a low-dose electron beam E transmitted through the metal plate 3.
Further, in the region C where irradiation of the high dose electron beam shown in FIG. 2 is desired to be avoided, the electron beam transmitted through the metal plate 3 and the electron beam passing through the priority irradiation region B are irradiated from two directions. Its absorbed dose is low. Further, since the region D in which the irradiation of the high-dose electron beam shown in FIG. 2 is desired to be avoided is irradiated with the electron beam transmitted through the metal plate 3 from two directions, the absorbed dose is further reduced.

Next, an embodiment of the irradiation dose adjusting plate 20 will be described.
FIG. 3A is a diagram showing a state in which the irradiated object 1 is housed in the container 2.
The portion indicated by reference numeral A in FIG. 3A is the non-focused irradiation region, and the portion indicated by reference numeral B is the focused irradiation region.
FIG. 3B is a diagram showing an irradiation dose adjusting plate 20. In the irradiation dose adjusting plate 20, a plurality of metal plates 3 are arranged in the region SA corresponding to the non-focused irradiation region A in the container 2, and an opening is formed in the region SB corresponding to the focused irradiation region B in the container 2. It is made to be.
By combining a plurality of metal plates having different lengths and widths, it is possible to form openings corresponding to the focused irradiation regions having various shapes.

FIG. 4A shows an irradiation dose adjusting plate in which the metal material of the region SB corresponding to the priority irradiation region B in the container 2 is removed from the metal plate 5 to form the opening 10, and the region SA is formed by the remaining metal material. 20 is shown.
FIG. 4B shows an irradiation dose adjusting plate 20 used when a plurality of focused irradiation regions B in the container 2 are present at intervals, and an opening is provided in the region SB of the irradiation dose adjusting plate 20 corresponding to the focused irradiation region B. 10 is formed.
A high dose is applied to the focused irradiation region B corresponding to the opening 10, and a low dose is applied to the non-focused irradiation region A corresponding to the portion other than the opening 10.
As a method for partially removing the metal material from the metal plate 5, a method by die cutting, a method by etching, or the like can be adopted.

FIG. 5 shows an example in which a metal tile 6 is used as a shielding material.
By using a plurality of metal tiles 6 and arranging the metal tiles 6 in the region SA in the frame 4 corresponding to the non-focused irradiation region A, the opening 10 is formed at the position corresponding to the region SB. be.
By combining metal tiles 6 having the same shape or different shapes, an opening 10 that follows the shape of the priority irradiation region B can be formed.

FIG. 6 shows an example in which a metal ball 7 is used as a shielding material.
The metal balls 7 are held by a sieve 8 having a mesh that does not allow the metal balls 7 to pass through.
A plurality of metal balls 7 are arranged in a mesh of a sieve to form a region SA, and a region in which the metal balls 7 are not arranged is referred to as a region SB. By using a metal ball 7 having a small shape, it is possible to form an opening 10 that follows the shape of the focused irradiation region. Further, since the metal ball 7 can be easily removed, the irradiation dose adjusting plate 20 can be easily manufactured.

FIG. 7 shows an embodiment of the electron beam sterilization method of the present invention.
In the present embodiment, the irradiation dose adjusting plate 20 is placed on the surface of the container 2 to which the electron beam is irradiated. By placing the irradiation dose adjusting plate 20 on the surface of the container 2 irradiated with the electron beam, a low dose is applied to the non-priority irradiation region A corresponding to the region SA of the irradiation dose adjusting plate 20, and the region SB is irradiated with a low dose. The corresponding priority irradiation area B is irradiated with a high dose, and sterilization / sterilization treatment is performed.
Further, the case where the irradiated object 1 is not housed in the container 2. When the irradiation dose adjusting plate 20 can be placed on the surface irradiated with the electron beam of the irradiated object 1, the irradiation dose adjusting plate 20 is placed on the surface irradiated with the electron beam of the irradiated object 1. May be.

FIG. 8 shows another embodiment of the electron beam sterilization method of the present invention.
In this embodiment, the irradiation dose adjusting plate 20 supports the irradiation dose adjusting plate 20 between the electron beam extraction window of the electron beam irradiation device 30 and the container 2, and the irradiation dose adjusting plate 20 is at the same speed as the transport speed of the container 2. The irradiation dose adjusting plate support transport means 21 for transporting 20 is used.
The irradiation dose adjusting plate supporting and transporting means 21 supports a plurality of irradiation dose adjusting plates 20 at intervals, transports the irradiation dose adjusting plate 20 to the irradiation surface of the container 2 along the loop path, and transfers the irradiation dose adjusting plate 20 to the irradiation surface of the container 2. Move at the same speed. As a result, the low-dose electron beam that has passed through the region SA of the irradiation dose adjusting plate 20 is irradiated to the non-focused irradiation region A of the irradiated object, and the high-dose electron beam that has passed through the region SB is the focused irradiation of the irradiated object. Area B is irradiated.

As another embodiment, as shown in FIG. 9, the irradiation dose adjusting plate support / transport means 21 is reciprocated between the inlet a and the outlet b of the electron beam irradiation region of the electron beam irradiation device 30 at the position of a. The irradiation dose adjusting plate 20 may be arranged so as to cover the upper surface of the container 2, and when the container 2 reaches the position b, the irradiation dose adjusting plate 20 may be returned to the position a.

1 Irradiated object 2 Container 3, 5 Metal plate 4 Frame 6 Metal tile 7 Metal ball 8 Sieve 10 Opening 11 Electron beam irradiation device device body 12 Conveyor device 13 Electron gun 14 Acceleration tube 15 Electromagnet 16 Scanhorn 17 Electron beam Extraction window 20 Irradiation dose adjustment plate 21 Irradiation dose adjustment plate Supporting and transporting means 30 Electron beam irradiation device E Electron beam A Non-focused irradiation area B Focused irradiation area C, D Areas where irradiation should be avoided Fa, Fb Container surface SA Area SA
SB area SB

Claims (5)

An irradiation dose adjusting plate having an area SA in which a shielding material for shielding an electron beam is arranged and an area SB in which the shielding material is not arranged is arranged between the electron beam extraction window of the electron beam irradiator and the irradiated object. death,
An electron beam sterilization method for sterilizing or sterilizing an irradiated object by irradiating the irradiated object with an electron beam from at least two directions through the irradiation dose adjusting plate.
The irradiation dose adjusting plate is composed of a plurality of metal spheres as a shielding material and a sieve having a mesh that does not allow the metal spheres to pass through, and a region in which the plurality of metal spheres are arranged in the mesh of the sieve is defined as the region SA. An electron beam sterilization method comprising an irradiation dose adjusting plate in which a region in which the metal sphere is not arranged is defined as the region SB . The electron beam sterilization method according to claim 1, wherein the irradiated object is irradiated with an electron beam from two directions. The electron beam sterilization method according to claim 1 or 2 , wherein the irradiation dose adjusting plate is placed on a surface to be irradiated with an electron beam of the irradiated object or a container containing the irradiated object. An irradiation dose adjusting plate that supports the irradiation dose adjusting plate between the electron beam extraction window of the electron beam irradiating device and the irradiated object and conveys the irradiation dose adjusting plate at the same speed as the conveying speed of the irradiated object. The electron beam sterilization method according to any one of claims 1 to 3 , which uses a support transport means. Before irradiating the irradiated object with an electron beam, imaging is performed by irradiating the irradiated object with X-rays, and the arrangement of the shielding material on the irradiation dose adjusting plate is determined based on the obtained information. Item 4. The electron beam sterilization method according to any one of Items 1 to 4 .

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