Container sterilization method and container sterilization equipment

Electron beams are irradiated to substantially identical sterilization surfaces on a container from a first upstream electron-beam irradiating device and a first downstream electron-beam irradiating device that are spaced with a predetermined distance upstream and downstream on a container carrier path. A sterilization controller controls the sum of electron beam outputs irradiated from the upstream electron-beam irradiating device and the downstream electron-beam irradiating device so as to allow sterilization on the sterilization surfaces of the container.

TECHNICAL FIELD

The present invention relates to a container sterilization method and container sterilization equipment in which a plurality of electron-beam irradiating devices are provided in parallel along a container conveyance path.

BACKGROUND ART

The container sterilization equipment includes two heads that irradiate an object to be treated with electron beams and two filament power supplies that supply power to the filaments of the two heads. Each of the filament power supplies for the respective heads has a switch that compares a beam depletion threshold value estimated according to the magnitude of a beam control signal with an actual beam current measured value. When the beam current measured value is not higher than the beam depletion threshold value, it is decided that beams are depleted. This stops power supply to the filament of the beam-depleted head while keeping filament power to other heads.

Thus, in an electron-beam irradiating device with power sharing multiple beam heads, discharge from one head stops only an abnormal head but keeps beams to other heads. This eliminates the need for stopping the operations of all the heads.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

For example, electron beam sterilization equipment that sterilizes a container by irradiation of electron beams can sterilize about 600 containers per minute and is interlocked with a filling device provided downstream of the equipment. If an electron-beam irradiating device requires replacement of an electron beam emitter because of an accident or deterioration, the electron beam sterilization equipment needs to be stopped for a sufficient time period.

Moreover, each container is irradiated with electron beams for 0.1 seconds. If sparking occurs on the electron-beam irradiating device, it takes about 0.1 to 0.2 seconds to recover the original irradiation output. Thus, a container passing through the sparked electron-beam irradiating device may directly contaminate a sterilizing chamber or the filling device that is equipment downstream of the electron-beam irradiating device. In this case, the overall equipment needs to be stopped to be cleaned.

Thus, in electron-beam container sterilization equipment for high-speed sterilization, it is important to operate an electron-beam irradiating device with minimum spark and prevent an unsterilized container from being transported and contaminating downstream equipment in the event of sparking.

An object of the present invention is to provide a container sterilization method and container sterilization equipment which can continuously operate an electron-beam irradiating device by shortening the stop time of the device, prevent an unsterilized container from contaminating a downstream device even if sparking temporarily reduces an electron beam output, and suppress the occurrence of sparking.

Solution to Problem

A container sterilization method according to a first aspect for sterilizing a container with electron beams irradiated from electron-beam irradiating devices while transporting the container along a carrier path,

the method including:

irradiating substantially identical outside surface of the container with electron beams irradiated from one or more upstream electron-beam irradiating device and one or more downstream electron-beam irradiating device spaced to each other with a predetermined distance along the carrier path; and

controlling a sum of electron beam outputs irradiated from the upstream and downstream electron-beam irradiating devices by means of a sterilization controller so as to at least allow sterilization on the surface of the container.

A container sterilization method according to a second aspect, in the method of the first aspect, when the electron beam output irradiated from the upstream electron-beam irradiating device changes from a set range, changing the electron beam output irradiated from the downstream electron-beam irradiating device so as to control the sum of the electron beam outputs from the upstream and downstream electron-beam irradiating devices to be equal to or higher than the set range of an electron beam output that allows external sterilization on the container when the container irradiated with the changed electron-beam output at the upstream electron-beam irradiating device is transported to the downstream electron-beam irradiating device.

A container sterilization method according to a third aspect, in the method of the first or second aspect, wherein each of the electron-beam irradiating device has a vacuum chamber, the method further including: monitoring a vacuum state in the vacuum chamber of each of the electron-beam irradiating devices; and controlling an electron beam output of the electron-beam irradiating device including the vacuum chamber with a low degree of vacuum to be smaller than an electron beam output of the electron-beam irradiating device including the vacuum chamber with a high degree of vacuum in order to prevent sparking in the electron-beam irradiating device including the vacuum chamber with the low degree of vacuum.

Container sterilization equipment according to a fourth aspect for externally sterilizing a container with electron beams irradiated from electron-beam irradiating devices facing a carrier path while transporting the container along the carrier path, including

one or more upstream electron-beam irradiating device and one or more downstream electron-beam irradiating device spaced to each other with a predetermined distance along the carrier path for irradiating substantially identical surface of the container with electron beams, and

a sterilization controller for controlling a sum of electron beam outputs irradiated from the upstream electron-beam irradiating device and the downstream electron-beam irradiating device so as to allow sterilization on the surface of the container,

wherein the sterilization controller controls such that, when the electron beam output from the upstream electron-beam irradiating device changes from a set range, the container irradiated from the upstream electron-beam irradiating device with the electron beam is transported so as to face the downstream electron-beam irradiating device, and an electron beam output from the downstream electron-beam irradiating device is controlled to change the sum of the upstream electron beam output and the downstream electron beam output so as to at least allow external sterilization on the container.

Container sterilization equipment according to a fifth aspect, in the configuration of the fourth aspect, further including a rejecting device provided downstream of the downstream electron beam sterilization equipment on the carrier path so as to eject the container on the carrier path,

the sterilization controller operating the rejecting device so as to eject, from the carrier path, the container with a changed electron beam output irradiated from the upstream electron-beam irradiating device.

Container sterilization equipment according to a sixth aspect externally sterilizes a container with electron beams irradiated from electron-beam irradiating devices having a vacuum chamber and facing a carrier path while transporting the container along the carrier path,

wherein the electron-beam irradiating devices includes one or more upstream electron-beam irradiating device and one or more downstream electron-beam irradiating device spaced to each other with a predetermined distance along the carrier path, the upstream and downstream electron-beam irradiating devices irradiating substantially identical sterilization surface of the container with electron beams,

the electron-beam irradiating device includes a vacuum chamber,

the container sterilization equipment includes a vacuum sensor for detecting a degree of vacuum in the vacuum chamber and a sterilization controller, and

the sterilization controller controls an electron beam output of the electron-beam irradiating device including the vacuum chamber with a low degree of vacuum such that the electron beam output thereof is smaller than an electron beam output of the electron-beam irradiating device including the vacuum chamber with a high degree of vacuum; meanwhile, the sterilization controller controls a sum of electron beam outputs irradiated from the upstream electron-beam irradiating device and the downstream electron-beam irradiating device so as to allow sterilization on the surface of the container.

Advantageous Effects of Invention

According to the invention of the first aspect, the electron-beam irradiating devices sterilize the substantially identical surfaces of the container with electron beams. Thus, if the electron beam irradiation dose of the electron-beam irradiating device is reduced by a failure, maintenance, deterioration caused by an extended operating time, or secular change, the maintained electron beam output of the other not reduced electron-beam irradiating device can be increased by the sterilization controller. This can eliminate a stop time and enables a continuous operation.

According to the configuration of the second aspect, if an electron dose irradiated upstream to the container is reduced below a set amount because of sparking or the like, the downstream electron-beam irradiating device increases an electron dose irradiated to the container, thereby externally sterilizing the container with reliability. This prevents an insufficiently sterilized container from being transported to downstream equipment, eliminating contamination of the downstream equipment. This may less frequently stop the sterilization equipment, leading to a longer operating time.

According to the invention of the third aspect, a vacuum state is monitored in the vacuum chamber of the electron-beam irradiating device, allowing the electron-beam irradiating device having a low degree of vacuum to operate with a reduced electron beam output. This can prevent sparking that is likely to occur in the electron-beam irradiating device having a low degree of vacuum, thereby suppressing the occurrence of insufficiently sterilized containers.

According to the configuration of the fourth aspect, the electron-beam irradiating devices that sterilize the substantially identical surfaces of the container are spaced with the predetermined distance on the conveyance path. The electron beam output of the electron-beam irradiating device with an electron beam irradiation dose reduced by a failure, maintenance, deterioration, or secular change is adjusted to as to enable an extended continuous operation. In the event of an accident that may reduce the electron beam output of the electron-beam irradiating device or stop the electron-beam irradiating device, the electron beam output of the other electron-beam irradiating device is increased so as to continue an extended operation without stopping the sterilization equipment. This can flexibly respond to the accident.

According to the invention of the fifth aspect, the container with a changed electron beam output may be deteriorated in quality by excessive irradiation of electron beams. Such a container is ejected as an insufficiently sterilized container from the conveyance path by the rejecting device, preferably achieving continuous sterilization of containers.

According to the invention of the sixth aspect, a vacuum state of the vacuum chamber is monitored by the vacuum sensor in the electron-beam irradiating devices that are spaced with the predetermined distance on the conveyance path, and the sterilization controller reduces the electron beam output of the electron-beam irradiating device including the vacuum chamber with a low degree of vacuum and increases the electron beam output of the electron-beam irradiating device including the vacuum chamber with a high degree of vacuum. This controls the sum of the electron beam outputs of the upstream electron-beam irradiating device and the downstream electron-beam irradiating device so as to allow sterilization on the sterilization surfaces of the container, thereby preventing the occurrence of sparking in the electron-beam irradiating device with a low degree of vacuum and considerably reducing the occurrence of insufficiently sterilized containers.

DESCRIPTION OF EMBODIMENTS

First Embodiment

Referring toFIGS. 1 to 5, a first embodiment of electron-beam container sterilization equipment according to the present invention will be described below.

As shown inFIG. 1, a plurality of first to seventh shielded chambers11A to11G are connected in series via container entrances/exits11ato11h. The first to seventh shielded chambers11A to11G contain first to seventh container carrier devices12A to12G that transport containers B at regular intervals P.

The first shielded chamber11A on the entrance side has a circular container carrier path L1along which the first container carrier device12A transports the containers B. The first shielded chamber11A prevents leakage of electron beams (X-rays) to the container entrance11a.

The second shielded chamber11B and the third shielded chamber11C are external sterilization chambers that sterilize the outer surfaces of the containers B. In the second shielded chamber11B, a first upstream electron-beam irradiating device21and a first downstream electron-beam irradiating device22are spaced with a certain distance (e.g., twice as large as the interval P) on the outer periphery of a container carrier path L2formed by the second container carrier device12B. In the third shielded chamber11C, a second upstream electron-beam irradiating device23and a second downstream electron-beam irradiating device24are spaced with a certain distance (twice as large as the interval P) on the outer periphery of a container carrier path L3.

The fourth shielded chamber11D is an internal sterilization chamber that sterilizes the inner surfaces of the containers B. Along the upper part of a circular fourth container carrier path L4where the containers B are transported by the fourth container carrier device12D, a plurality of internal electron-beam irradiating devices (not shown) shaped like nozzles insertable into the containers B from the openings of the containers B are paired with internal sterilization power supplies so as to be spaced at regular intervals.

The fifth to seventh shielded chambers11E to11G are exit-side shielded chambers that prevent leakage of electron beams (X-rays) from the container exit11h. Circular carrier paths L5to L7are formed along which the fifth to seventh container carrier devices12E to12G transport the containers B. The intermediate sixth shielded chamber11F contains a rejecting device26that ejects the insufficiently sterilized containers B from the circular carrier path L6.

For example, as shown inFIGS. 3 and 4, the second container carrier device12B includes a turning table14rotatably supported by a main shaft13raised on a pedestal and container holding devices16that are provided at the regular intervals P on the outer periphery of the turning table14so as to hold the necks of the containers B with pairs of holding arms15R and15L. Reference numeral17denotes a pivot shaft that pivotally penetrates the turning table14. An arm open/close cam18is attached to the upper end of the pivot shaft17so as to open the holding arms15R and15L restrained with a spring in a closing direction. An open/close cam follower20is attached to the lower end of the pivot shaft17via an arm member so as to follow a holding open/close cam19fixed below the turning table14.

The second container carrier device12B was described above. The first, third, and fifth to seventh container carrier devices12A,12C, and12E to12G other than the fourth container carrier device12D are substantially identical in configuration to the second container carrier device12B. The fourth container carrier device12D has an elevating mechanism (not shown) that relatively moves up and down the containers B held by the container holding devices16and the internal electron-beam irradiating devices shaped like nozzles, inserting the internal electron-beam irradiating devices from the openings of the containers B.

As shown inFIG. 2, the second shielded chamber11B contains a first upstream electron-beam irradiating device21and a first downstream electron-beam irradiating device22that irradiate sterilization surfaces F on the containers B with electron beams. The electron-beam irradiating devices21and22are spaced with, for example, a distance P′ twice as large as the interval P upstream and downstream on the outer periphery of the carrier path L2. The third shielded chamber11C contains a second upstream electron-beam irradiating device23and a second downstream electron-beam irradiating device24that irradiate external sterilization surfaces R on the containers B with electron beams. The electron-beam irradiating devices23and24are spaced with, for example, the distance P′ twice as large as the interval P upstream and downstream on the outer periphery of the carrier path L3. In this configuration, the sterilization surfaces F and R are irradiated with electrons at angles larger than 90° with respect to the irradiation direction of electron beams because of the irradiation characteristics of electron beams.

The electron-beam irradiating devices21to24include a first upstream power supply21PS, a first downstream power supply22PS, a second upstream power supply23PS, and a second downstream power supply24PS, respectively, that supply predetermined power for generating electron beams. A sterilization controller25controls the power supplies21PS,22PS,23PS, and24PS so as to control the outputs of electron beams irradiated from the electron-beam irradiating devices21to24. Moreover, the sterilization controller25controls the rejecting device26of the sixth shielded chamber11F.

As shown inFIG. 5, each of the electron-beam irradiating devices21to24has a cylindrical housing31in a vertical position. The housing31has an irradiation hole34having a predetermined position formed at a predetermined height on the side of the housing31. A metallic thin film34ais attached to the irradiation hole34so as to seal a vacuum chamber30in a vacuum in the housing31. A filament32is placed in the housing31and an electrode33having transparent windows33aformed is provided around the filament32. Power is supplied from the first upstream power supply21PS (22PS to24PS) to the electrodes33and then is supplied to the filament32through a filament power supply35. This generates electron beams between the filament32and the electrode33. Electron beams are irradiated from the transparent windows33ato the containers B through the vacuum chamber30and the irradiation hole34.

The vacuum chambers30of the electron-beam irradiating devices21to24has a first upstream vacuum sensor21VS, a first downstream vacuum sensor22VS, a second upstream vacuum sensor23VS, and a second downstream vacuum sensor24VS, respectively, that detect a vacuum state. Degrees of vacuum in the vacuum chambers30are inputted to the sterilization controller25by the vacuum sensors21VS to24VS.

In this configuration, the first electron-beam irradiating devices21and22of the second shielded chamber11B and the second electron-beam irradiating devices23and24of the third shielded chamber11C are substantially identical in configuration except for irradiation of electron beams for sterilizing the substantially half sterilization surfaces F and R that are symmetrical to each other on the container B. Thus, only the first electron-beam irradiating devices21and22of the second shielded chamber11B will be described below and the explanation of the second electron-beam irradiating devices23and24of the third shielded chamber11C is omitted.

Based on the degree of vacuum of the vacuum chamber30in each of the first electron-beam irradiating devices21and22, the sterilization controller25is set so as to reduce the electron beam output of the electron-beam irradiating device (e.g.,21) including the vacuum chamber30with a low degree of vacuum and increase the electron beam output of the electron-beam irradiating device22including an electron beam generator with a high degree of vacuum. This is because a decrease in the degree of vacuum of the vacuum chamber30is likely to cause sparking between the electrode33and the housing31grounded in the electron-beam irradiating device21(22to24), temporarily (for 0.1 to 0.2 seconds) stopping outputting electron beams. This may reduce an electron dose irradiated to the sterilization surface F of the container B and cause poor sterilization.

Moreover, the sterilization controller25controls the sum of electron beam outputs irradiated from the first electron-beam irradiating devices21and22so as to allow sterilization on the sterilization surface F of the container B.

The sterilization controller25can detect the output of electron beams irradiated from the first upstream electron-beam irradiating device21to the container B according to a supplied current if the output is changed (reduced) from a set range (threshold) by sparking between the grounded housing31and the electrode33. The occurrence of sparking temporarily (for 0.1 to 0.2 seconds) stops the output of electron beams irradiated from the first upstream electron-beam irradiating device21. Thus, the sum of electron beam outputs irradiated from the first electron-beam irradiating devices21and22may be reduced below the set value (threshold) that allows sterilization on the sterilization surface F of the container B. In addition to sparking, the output of electron beams may be stopped if the metallic thin film34aof the irradiation hole34is broken by deterioration of the electron-beam irradiating device.

At this point, the sterilization controller25controls the electron beam output of the first downstream electron-beam irradiating device22such that after a time period during which the container B is transported to the subsequent irradiation position by two pitches, the electron beam output irradiated to the container B is increased and the sum of the electron beam output of the first downstream electron-beam irradiating device22and the electron beam output irradiated by the first upstream electron-beam irradiating device21(in a state of a reduced output) is not lower than the lower limit of the set value (threshold) that allows sterilization on the sterilization surface F of the container B.

In this way, the electron beam output irradiated to the sterilization surface F of the container B is large enough to at least allow sterilization on the sterilization surface F, preventing the containers B from passing through being unsterilized. This can prevent the containers B transported to the container carrier paths L3to L7from contaminating the interiors of the third to seventh shielded chambers11C to11G.

Since the container B with a varying electron beam output may excessively radiate electron beams, the sterilization controller25operates the rejecting device26of the sixth shielded chamber11F so as to remove the container B from the container carrier path L6.

In this case, at least the first downstream electron-beam irradiating device22can preferably output electron beams so as to allow sterilization on the sterilization surface F of the container B even if the electron beam output of the first upstream electron-beam irradiating device21is stopped.

For example, if the sterilization equipment can treat (sterilize) 600 containers B per minute, each of the electron-beam irradiating devices21to24irradiates the container B with electron beams for 0.1 seconds. The container B is transported in 0.2 seconds from the first and second upstream electron-beam irradiating devices21and23to the first and second downstream electron-beam irradiating devices22and24. The sterilization controller25has to adjust the outputs of the first and second downstream electron-beam irradiating devices22and24in 0.2 seconds.

In the first embodiment, an electron beam output is set based on a vacuum state in each of the vacuum chambers30of the electron-beam irradiating devices21to24. The electron beam outputs of the upstream electron-beam irradiating devices21and23and the downstream electron-beam irradiating devices22and24may be set based on the operating times and conditions of the upstream electron-beam irradiating devices21and23and the downstream electron-beam irradiating devices22and24.

For the sterilization surfaces F and R, the second shielded chamber11B and the third shielded chamber11C each include two of the first and second electron-beam irradiating devices21to24. At least three electron-beam irradiating devices may be provided in each of the shielded chambers.

In the first embodiment, the electron beam output is controlled according to a lapse of time. The electron beam output may be controlled by detecting the angle of rotation of the turning table14with a detector (e.g., a rotary encoder) and monitoring the position of the container B.

Second Embodiment

Referring toFIGS. 6 and 7, a second embodiment of electron-beam container sterilization equipment according to the present invention will be described below. An electron-beam irradiating device according to the second embodiment is configured in consideration of sparking that is more likely to occur with a reduction in the degree of vacuum in a vacuum chamber. Vacuum sensors21VS to24VS are provided to detect degrees of vacuum in vacuum chambers30of electron-beam irradiating devices21to24. The same parts as those of the first embodiment are indicated by the same reference numerals and the explanation thereof is omitted. For example, “Equipment overview” and “container carrier device” are identical in configuration to those of the first embodiment and thus the explanation thereof is omitted. Furthermore, “electron-beam irradiating device” is identical to that of the first embodiment except for the provision of the vacuum sensors.FIGS. 2 to 4are also identical to the configuration of the present embodiment and thus the explanation thereof is omitted.

As shown inFIG. 1, a plurality of first to seventh shielded chambers11A to11G are connected in series via container entrances/exits11ato11h. The first to seventh shielded chambers11A to11G contain first to seventh container carrier devices12A to12G that transport containers B at regular intervals P.

The first shielded chamber11A on the entrance side has a circular container carrier path L1formed along which the first container carrier device12A transports the containers B. The first shielded chamber11A prevents leakage of electron beams (X-rays) to the container entrance11a.

The second shielded chamber11B and the third shielded chamber11C are external sterilization chambers that sterilize the outer surfaces of the containers B. In the second shielded chamber11B, a first upstream electron-beam irradiating device21and a first downstream electron-beam irradiating device22are spaced with a certain distance (twice as large as the interval P) on the outer periphery of a container carrier path L2formed by the second container carrier device12B. In the third shielded chamber11C, a second upstream electron-beam irradiating device23and a second downstream electron-beam irradiating device24are spaced with a certain distance (twice as large as the interval P) on the outer periphery of a container carrier path L3.

The fourth shielded chamber11D is an internal sterilization chamber that sterilizes the inner surfaces of the containers B. Along the upper part of a circular fourth container carrier path L4where the containers B are transported by the fourth container carrier device12D, a plurality of internal electron-beam irradiating devices (not shown) shaped like nozzles insertable into the containers B from the openings of the containers B are paired with internal sterilization power supplies30so as to be spaced at predetermined intervals.

The fifth to seventh shielded chambers11E to11G are exit-side shielded chambers that prevent leakage of electron beams (X-rays) from the container exit11h. Circular carrier paths L5to L7are formed along which the fifth to seventh container carrier devices12E to12G transport the containers B. The intermediate sixth shielded chamber11F contains a rejecting device26that ejects the insufficiently sterilized containers B from the circular carrier path L6.

For example, as shown inFIGS. 3 and 4, the second container carrier device12B includes a turning table14rotatably supported by a main shaft13raised on a pedestal and container holding devices16that are provided at the regular intervals P on the outer periphery of the turning table14so as to hold the necks of the containers B with pairs of holding arms15R and15L. Reference numeral17denotes a pivot shaft that pivotally penetrates the turning table14. An arm open/close earn18is attached to the upper end of the pivot shaft17so as to open the holding arms15R and15L restrained with a spring in a closing direction. An open/close cam follower20is attached to the lower end of the pivot shaft17via an arm member so as to follow a holding open/close cam19fixed below the turning table14.

The second container carrier device12B was described above. The first, third, and fifth to seventh container carrier devices12A,12C, and12E to12G other than the fourth container carrier device12D are substantially identical in configuration to the second container carrier device12B. The fourth container carrier device12D has an elevating mechanism (not shown) that relatively moves up and down the containers B held by the container holding devices16and the internal electron-beam irradiating devices shaped like nozzles, inserting the internal electron-beam irradiating devices from the openings of the containers B.

As shown inFIG. 2, the second shielded chamber11B contains a first upstream electron-beam irradiating device21and a downstream electron-beam irradiating device22that irradiate sterilization surfaces F on the containers B with electron beams. The electron-beam irradiating devices21and22are spaced with, for example, a distance P′ twice as large as the interval P upstream and downstream on the outer periphery of the carrier path L2. The third shielded chamber11C contains a second upstream electron-beam irradiating device23and a second downstream electron-beam irradiating device24that irradiate sterilization surfaces R on the containers B with electron beams. The electron-beam irradiating devices23and24are spaced with, for example, the distance P′ twice as large as the interval P upstream and downstream on the outer periphery of the carrier path L3. In this configuration, the sterilization surfaces F and R are irradiated with electrons at angles larger than 90° with respect to the irradiation direction of electron beams because of the irradiation characteristics of electron beams.

The electron-beam irradiating devices21to24include a first upstream power supply21PS, a first downstream power supply22PS, a second upstream power supply23PS, and a second downstream power supply24PS, respectively, that supply predetermined power for generating electron beams. A sterilization controller25controls the power supplies21PS,22PS,23PS, and24PS so as to control the outputs of electron beams irradiated from the electron-beam irradiating devices21to24. Moreover, the sterilization controller25controls the rejecting device26of the sixth shielded chamber11F.

As shown inFIG. 5, each of the electron-beam irradiating devices21to24has a cylindrical housing31in a vertical position. The housing31has an irradiation hole34having a predetermined position formed at a predetermined height on the side of the housing31. A metallic thin film34ais attached to the irradiation hole34so as to seal the vacuum chamber30in a vacuum in the housing31. A filament32is placed in the housing31and an electrode33having transparent windows33aformed is provided around the filament32. Power is supplied from the first upstream power supply21PS (22PS to24PS) to the electrodes33and then is supplied to the filament32through a filament power supply35. This generates electron beams between the filament32and the electrode33. Electron beams are irradiated from the transparent windows33ato the containers B through the vacuum chamber30and the irradiation hole34.

The vacuum chambers30of the electron-beam irradiating devices21to24has a first upstream vacuum sensor21VS, a first downstream vacuum sensor22VS, a second upstream vacuum sensor23VS, and a second downstream vacuum sensor24VS, respectively, that detect a vacuum state. Degrees of vacuum in the vacuum chambers30are inputted to the sterilization controller25by the vacuum sensors21VS to24VS.

In this configuration, the first electron-beam irradiating devices21and22of the second shielded chamber11B and the second electron-beam irradiating devices23and24of the third shielded chamber11C are substantially identical in configuration except for irradiation of electron beams for sterilizing the substantially half sterilization surfaces F and R that are symmetrical to each other on the container B. Thus, only the first electron-beam irradiating devices21and22of the second shielded chamber11B will be described below and the explanation of the second electron-beam irradiating devices23and24of the third sterilizing chamber11C is omitted.

Based on the degree of vacuum of the vacuum chamber30in each of the first electron-beam irradiating devices21and22, the sterilization controller25is set so as to reduce the electron beam output of the electron-beam irradiating device (e.g.,21) including the vacuum chamber30with a low degree of vacuum and increase the electron beam output of the electron-beam irradiating device22including an electron beam generator with a high degree of vacuum. This is because a decrease in the degree of vacuum of the vacuum chamber30is likely to cause sparking between the electrode33and the housing31grounded in the electron-beam irradiating device21(22to24), temporarily (for 0.1 to 0.2 seconds) stopping outputting electron beams. This may reduce an electron dose irradiated to the sterilization surface F of the container B and cause poor sterilization.

Moreover, the sterilization controller25controls the sum of electron beam outputs irradiated from the first electron-beam irradiating devices21and22so as to allows sterilization on the sterilization surface F of the container B.

In addition to the same effect as the first embodiment, the configuration of the second embodiment can considerably reduce the occurrence of sparking by lowering an electron beam output, though the vacuum chambers30of the electron-beam irradiating devices21to24decrease in degree of vacuum.

For example, if the sterilization equipment can treat (sterilize) 600 containers B per minute, each of the electron-beam irradiating devices21to24irradiates the container B with electron beams for 0.1 seconds. The container B is transported in 0.2 seconds from the first and second upstream electron-beam irradiating devices21and23to the first and second downstream electron-beam irradiating devices22and24. The sterilization controller25has to adjust the outputs of the first and second downstream electron-beam irradiating devices22and24in 0.2 seconds.

In the second embodiment, an electron beam output is set based on a vacuum state in each of the vacuum chambers30of the electron-beam irradiating devices21to24. The electron beam outputs of the upstream electron-beam irradiating devices21and23and the downstream electron-beam irradiating devices22and24may be set based on the operating times and conditions of the upstream electron-beam irradiating devices21and23and the downstream electron-beam irradiating devices22and24.

For the sterilization surfaces F and R, the second shielded chamber11B and the third shielded chamber11C each include two of the first and second electron-beam irradiating devices21to24. At least three electron-beam irradiating devices may be provided in each of the shielded chambers.