U.S. patent application number 12/318936 was filed with the patent office on 2009-05-14 for method of sterilizing a package.
This patent application is currently assigned to TETRA LAVAL HOLDINGS & FINANCE S.A.. Invention is credited to Lars Martensson, Hakan Moller, Laurence Mott.
Application Number | 20090123330 12/318936 |
Document ID | / |
Family ID | 20289853 |
Filed Date | 2009-05-14 |
United States Patent
Application |
20090123330 |
Kind Code |
A1 |
Moller; Hakan ; et
al. |
May 14, 2009 |
Method of sterilizing a package
Abstract
A method of sterilizing packages in production of the packages,
wherein the packages have an open end and a closed end. A gaseous
sterilizing agent is used and kept in the gaseous phase throughout
the sterilization process and an ambient temperature and a
concentration of sterilizing agent in a sterilization zone where
sterilization is performed are measured and used for controlling
the amount of sterilizing agent introduced in the sterilization
zone.
Inventors: |
Moller; Hakan; (Lund,
SE) ; Mott; Laurence; (Trelleborg, SE) ;
Martensson; Lars; (Veberod, SE) |
Correspondence
Address: |
BUCHANAN, INGERSOLL & ROONEY PC
POST OFFICE BOX 1404
ALEXANDRIA
VA
22313-1404
US
|
Assignee: |
TETRA LAVAL HOLDINGS & FINANCE
S.A.
Pully
CH
|
Family ID: |
20289853 |
Appl. No.: |
12/318936 |
Filed: |
January 13, 2009 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10531297 |
Apr 14, 2005 |
7491371 |
|
|
PCT/SE2003/001791 |
Nov 19, 2003 |
|
|
|
12318936 |
|
|
|
|
Current U.S.
Class: |
422/3 |
Current CPC
Class: |
B65B 55/10 20130101;
A61L 2202/18 20130101; A61L 2/208 20130101; B65B 31/041 20130101;
B65B 55/025 20130101; B65B 31/025 20130101; A61L 2/24 20130101 |
Class at
Publication: |
422/3 |
International
Class: |
A61L 2/24 20060101
A61L002/24 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 13, 2002 |
SE |
0203693-7 |
Claims
1. A method of sterilizing a package during production of the
package, the package comprising an open end and a closed end, the
method comprising: sterilizing the package in a sterilization zone
using a gaseous sterilizing agent which is maintained in the
gaseous phase throughout the sterilizing; measuring a relative
humidity outside the sterilization zone where the sterilizing agent
does not flow; measuring ambient temperature outside the
sterilization zone; measuring a concentration of the sterilizing
agent in the sterilization zone where sterilization is performed;
and controlling an amount of sterilizing agent introduced into the
sterilization zone based on the measured ambient temperature, the
measured relative humidity, and the measured concentration of the
sterilizing agent.
2. A method as claimed in claim 1, further comprising introducing
the gaseous sterilizing agent in a top portion of the sterilization
zone, and withdrawing the gaseous sterilizing agent from a bottom
portion of the sterilization zone.
3. A method as claimed in claim 1, further comprising introducing
sterile air in a top portion of a venting zone, and withdrawing the
sterile air from a bottom of the venting zone.
4. A method of sterilizing a package during production of the
package, the package comprising an open end and a closed end, the
method comprising: sterilizing the package in a sterilization zone
using a gaseous sterilizing agent which is maintained in the
gaseous phase throughout the sterilizings; measuring ambient
temperature and a concentration of the sterilizing agent in the
sterilization zone where sterilization is performed; and
controlling an amount of sterilizing agent introduced in the
sterilization zone based on the measured ambient temperature and
the concentration of the sterilizing agent in the sterilization
zone.
5. A method as claimed in claim 4, further comprising using the
measured ambient temperature to control the heating in a heating
zone where heating of the package is performed.
6. A method as claimed in claim 4, further comprising measuring a
temperature of the package entering the heating zone is measured
and used for controlling the heating in the heating zone.
7. A method as claimed in claim 4, further comprising measuring a
temperature of the package just before the package is passed into
the sterilization zone, and controlling the heating in the heating
zone by taking into account the measured temperature of the
package.
8. A method as claimed in claim 4, further comprising maintaining a
positive pressure in the sterilization zone in which the
sterilization is performed.
9. A method as claimed in claim 4, further comprising passing the
package into the heating zone where the package is heated to a
temperature above the dew point of the sterilizing agent.
10. A method as claimed in claim 9, further comprising passing the
heated package through an opening in a partition and into the
sterilization zone where they are subjected to the gaseous
sterilizing agent, the partition separating the heating zone and
the sterilization zone.
11. A method as claimed in claim 10, further comprising passing the
sterilized packages through an opening in a partition and into a
venting zone where the package is subjected to hot sterile air for
venting away the sterilizing agent, the partition separating the
sterilization zone and the venting zone.
12. A method as claimed in claim 10, wherein the gaseous
sterilizing agent in the sterilization zone flows essentially in a
direction from the open end of the packages towards the closed end
of the packages.
13. A method as claimed in claim 12, further comprising introducing
the gaseous sterilizing agent in a top portion of the sterilization
zone and evacuating the sterilizing agent in a bottom portion of
the sterilization zone to maintain an essentially top to bottom
flow of the sterilizing agent.
14. A method as claimed in claim 11, wherein the venting air in the
venting zone flows essentially in a direction from the open end of
the packages towards the closed end of the packages.
15. A method as claimed in claim 14, further comprising introducing
the venting air in a top portion of the venting zone and evacuating
the venting air in a bottom portion of the venting zone to maintain
an essentially top to bottom air flow.
16. A method as claimed in claim 4, further comprising producing
the gaseous sterilizing agent by adding liquid sterilizing agent to
hot air.
17. A method as claimed in claim 16, further comprising controlling
the temperature and flow of air for production of the gaseous
sterilizing agent based on detection of condensation in the
sterilization zone.
18. A method as claimed in claim 4, wherein gaseous hydrogen
peroxide is used as sterilizing agent.
19. A method as claimed in claim 11, wherein a higher pressure is
maintained in a filling zone for filling vented packages than in
the venting zone.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] The present application is a division of application Ser.
No. 10/531,297 filed Apr. 14, 2005, which is a national stage
filing of International Application No. PCT/SE2003/001791 filed
Nov. 19, 2003, which claims the priority of Swedish Application No.
0203693-7 filed Dec. 13, 2002.
TECHNICAL FIELD
[0002] The disclosure here relates to a method of sterilizing
packages in production of the packages, said packages having an
open end and a closed end, wherein a gaseous sterilizing agent is
used and kept in the gaseous phase throughout the sterilization
process. The disclosure also pertains to a device for sterilization
in production of packages, which is adapted for sterilization with
a gaseous sterilizing agent kept in the gaseous phase throughout
the sterilization process, said device comprising a heating zone, a
sterilization zone and a venting zone.
BACKGROUND DISCUSSION
[0003] Devices and methods of the above-mentioned kind are known in
the art, e.g. from U.S. Pat. No. 5,258,162. Here, packages are
passed through a housing divided into zones. In the first zone, hot
air is introduced for heating the packages. In the second zone,
gaseous hydrogen-peroxide is introduced for sterilizing the heated
packages. In the third and final zone, the packages are filled with
sterile contents. The three zones are all contained in one housing
and are not physically separated from each other. Therefore, it may
be difficult to control the flow between the different zones.
[0004] EP-A-394 734 discloses another device and method for
sterilizing objects. In the device and method described, a
vertically displaceable hood is placed over the object to be
sterilized. A negative pressure is produced in the hood and a
sterilization gas is introduced. The fact that a displaceable hood
is needed makes this device somewhat complex.
SUMMARY
[0005] An object of the present invention is to provide a device
for sterilizing packages essentially of the type described above,
but which enables an even safer sterilization process.
[0006] A specific object of the invention is to provide a device
which allows improved control of the gas flow in and between the
different zones.
[0007] Another object is to provide a device which allows improved
control of the heating of packages.
[0008] It is also an object of the present invention to provide a
method of sterilizing packages, which is improved as compared to
prior art methods.
[0009] Yet another object is to provide a method which allows
better control of the flow of air and gas in and between the
different zones where the sterilization takes place.
[0010] According to the invention, these objects are achieved by a
device of the kind mentioned by way of introduction, which has been
given the characteristics disclosed herein. Preferred embodiments
of the inventive device are also disclosed.
[0011] The above-mentioned objects are also achieved by a method
disclosed herein.
[0012] The inventive device for sterilization in production of
packages comprises an ambient temperature sensor for sensing the
ambient temperature outside the device, a concentration meter for
measuring the concentration of sterilizing agent in the
sterilization zone and a first control unit for controlling the
amount of sterilizing agent introduced in the sterilization zone
based on the temperature measured by the ambient temperature sensor
and the concentration measured by the concentration meter. This
makes it possible to achieve improved control of the sterilization
process.
[0013] In a preferred embodiment, the device comprises means for
maintaining a higher pressure in the sterilization zone than in the
heating zone and venting zone. Thus, it is possible to ensure that
any leakage of air and gas is from the sterilization zone towards
the surrounding zones and not the other way round.
[0014] In one embodiment, the heating, sterilization and venting
zones are separated from each other by means of partitionings
having openings for the passage of packages. This makes it easier
to control the conditions in each zone.
[0015] The device is preferably adapted for sterilization with a
gaseous sterilizing agent in the form of gaseous hydrogen peroxide.
Hydrogen peroxide is a useful and reliable sterilizing agent.
[0016] The device is preferably adapted to sterilize packages
before filling of the packages, said packages having an open end
and a closed end. It is convenient to sterilize packages before
filling them, since this makes it possible to maintain the
sterility of sterile contents.
[0017] The heating zone may comprise means for heating the packages
to a temperature above a dew point of the sterilizing agent used in
the sterilization zone. In this way, it may be ensured that the
sterilizing agent does not condensate on the packages.
[0018] In one embodiment, the venting zone comprises means for
venting away the sterilizing agent used in the sterilization zone
from the packages after sterilization. This makes it possible to
ensure that the packages are free from sterilizing agent before
filling.
[0019] The device may further comprise means for controlling a flow
of gaseous sterilizing agent in the sterilization zone, such that
the gaseous sterilizing agent flows essentially in a direction from
the open end of the packages towards the closed end of the
packages. This reduces the risk of recontamination of the
packages.
[0020] The means for controlling the flow of gaseous sterilizing
agent are preferably arranged to introduce the gaseous sterilizing
agent in a top portion of the sterilization zone and to evacuate
the gaseous sterilizing agent in a bottom portion of the
sterilization zone, maintaining a flow of gaseous sterilizing agent
essentially from top to bottom. This provides a secure way of
maintaining a flow from the open end of the packages towards the
closed end of packages standing on their closed end.
[0021] The device may further comprise means for controlling a
venting air flow in the venting zone, such that the venting air
flows essentially in a direction from the open end of the packages
towards the closed end of the packages. Thus, the risk of
recontamination of the sterilized packages may be reduced.
[0022] The means for controlling the flow of venting air are
arranged to introduce the venting air in a top portion of the
venting zone and to evacuate the venting air in a bottom portion of
the venting zone, maintaining a flow of venting air essentially
from top to bottom.
[0023] In one embodiment of the invention, the device comprises an
ambient temperature sensor for sensing the ambient temperature
outside the device. In this way, the heating in the heating zone
may be controlled based on the ambient temperature.
[0024] Alternatively or additionally, the device may comprise a
package heating temperature sensor for sensing the temperature of
the packages entering the heating zone. This may also be used for
controlling the heating.
[0025] In another embodiment, the device comprises an entry
temperature sensor for sensing the temperature of the packages
before entry into the sterilization zone. This is another way of
enabling control of the heating in the heating zone.
[0026] In a preferred embodiment of the invention, the device
comprises a feedback circuit for controlling the heating in the
heating zone based on the temperature of the packages. In this way,
heating to a correct temperature may be ensured and over-heating of
the packages may be avoided.
[0027] In another embodiment, the device further comprises a
condensation detector for detecting condensation in the
sterilization zone. Thus, it is possible to mark or discard
packages that have been subjected to condensate.
[0028] The device of the invention is preferably adapted to
sterilize itself internally. Thus, sterile conditions in the device
may be ensured in a simple manner.
[0029] For sterilizing itself, the device preferably comprises
means for heating its interior. This allows efficient
sterilization.
[0030] The inventive device may comprise a unit for production of
the gaseous sterilizing agent, thus making the device
self-supporting.
[0031] The device may further comprise a filling zone for filling
vented packages, and means for maintaining a higher pressure in the
filling zone than in the venting zone. This makes it possible to
further control the flow of air and gas in the device.
[0032] In the method according to the invention for sterilizing
packages in production of the packages, said packages having an
open end and a closed end, a gaseous sterilizing agent is used and
kept in the gaseous phase throughout the sterilization process. An
ambient temperature and a concentration of sterilizing agent in a
sterilization zone where sterilization is performed are measured
and used for controlling the amount of sterilizing agent introduced
in the sterilization zone. This makes it possible to achieve
improved control of the sterilization process.
[0033] In a preferred variant of the method, a positive pressure is
maintained in the sterilization zone in which the sterilization is
performed.
[0034] Gaseous hydrogen peroxide is preferably used as sterilizing
agent. This is a well-known and reliable sterilizing agent.
[0035] In a variant of the method, the packages are passed into a
heating zone where they are heated to a temperature above the dew
point of the sterilizing agent. This makes it possible to ensure
that the sterilizing agent does not condensate on the packages.
[0036] The heated packages may be passed through an opening in a
partitioning separating the heating zone and the sterilization zone
into the sterilization zone, where they are subjected to the
gaseous sterilizing agent. Since the package has to be passed
through a partitioning for entering the sterilization zone, it is
easier to control the conditions for sterilization.
[0037] Analogously, the sterilized packages may be passed through
an opening in a partitioning separating the sterilization zone and
a venting zone into the venting zone, where they are subjected to
hot sterile air for venting away the sterilizing agent. Thus, the
packages may be subjected to distinctly different conditions during
sterilization and venting.
[0038] The gaseous sterilizing agent in the sterilization zone
preferably flows essentially in a direction from the open end of
the packages towards the closed end of the packages. Thus, the risk
of recontamination of packages may be reduced.
[0039] The gaseous sterilizing agent may be introduced in a top
portion of the sterilization zone and evacuated in a bottom portion
of the sterilization zone, so that a flow of sterilizing agent
essentially from top to bottom is maintained. This is a simple way
of maintaining a suitable flow for packages standing on their
closed end.
[0040] In one variant of the method, the venting air in the venting
zone flows essentially in a direction from the open end of the
packages towards the closed end of the packages. As in the case in
the sterilization zone, this reduces the risk of recontamination of
packages.
[0041] The venting air is preferably introduced in a top portion of
the venting zone and evacuated in a bottom portion of the venting
zone, so that an air flow essentially from top to bottom is
maintained. This is a simple manner of ensuring a suitable flow for
packages standing on their closed end.
[0042] In a preferred variant of the method, the gaseous
sterilizing agent is produced by addition of liquid sterilizing
agent to hot air. Thus, the sterilization process may simply and
reliably be provided with gaseous sterilizing agent.
[0043] An ambient temperature and a concentration of sterilizing
agent in the sterilization zone may be measured for controlling the
amount of sterilizing agent introduced the sterilization zone.
[0044] An ambient temperature may be measured and used for
controlling the heating in the heating zone, thus improving control
of the sterilization process.
[0045] In a variant of the method, a temperature of the packages
entering the heating zone is measured and used for controlling the
heating in the heating zone. This is an alternative or additional
manner of controlling the conditions for the sterilization
process.
[0046] Further, a temperature of the packages just before they are
passed into the sterilization zone may be measured and used for
controlling the heating in the heating zone. This is another
convenient way of controlling the conditions for the sterilization
process.
[0047] In one variant of the method of the invention, the
temperature and flow of air for production of the gaseous
sterilizing agent is controlled based on detection of condensation
in the sterilization zone. This makes it easier to avoid
condensation.
[0048] A higher pressure is preferably maintained in a filling zone
for filling vented packages than in the venting zone. Thus, control
of flow between the different zones may be improved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0049] The invention will be described in more detail with
reference to the appended schematic drawings, which show an example
of a currently preferred embodiment of the invention.
[0050] FIG. 1 is a diagram showing the principles of the
sterilizing device of the invention.
[0051] FIG. 2 is a perspective view of the sterilizing device.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0052] With reference to FIG. 1, the sterilization device 1 has a
heating zone 2, a sterilization zone 3, a venting zone 4 and
connected thereto a filling zone 5. As may be seen from FIG. 2, the
zones 2-5 are separated from each other by partitionings 6-7. In
each partitioning 6, 7 there is an opening 6a, 7a. Packages 8 are
arranged in holders 9 on a conveyor belt 10 which passes through
the zones 2-5. The packages 8 stand on their closed top end 11 with
their open bottom end 12 directed upwards.
[0053] In the heating zone 2 there are nozzles 13 in a top portion
14 for introduction of hot sterile air. In a bottom portion 15 of
the heating zone 2 there are outlets 16 for withdrawing the hot
air.
[0054] Similarly, there are nozzles 17 for introduction of gaseous
hydrogen peroxide in a top portion 18 of the sterilization zone 3.
In a bottom portion 19 of the sterilization zone there are outlets
20 for withdrawing hydrogen peroxide.
[0055] The venting zone 4 also has nozzles 21 for introducing hot
sterile air in a top portion 22. In a bottom portion 23 of the
venting zone 4 there are outlets 24 for withdrawing hot air.
[0056] The sterilizing device has a gas production unit 25 for
producing the gaseous hydrogen peroxide used for sterilization.
[0057] In a manner similar to the heating, sterilization and
venting zones 2-4, the filling zone 5 has nozzles 26 for
introducing sterile air in a top portion 27 of the filling
zone.
[0058] Included in the device 1 is further a catalyst unit 36 for
degrading hydrogen peroxide gas withdrawn from the sterilization
zone 3.
[0059] The method by which packages are treated in this device 1
will now be described. A package 8 standing on its closed top end
11 in one of the holders 9 is transported by the conveyor belt 10
into the heating zone 2. Here, sterile air with a temperature of
approximately 140.degree. C. is introduced in the top portion 14 by
means of the nozzles 13. In this manner the package 8 is heated to
a temperature above the dew point of the gaseous sterilizing agent
to be used in the sterilization zone 3. Thus, it may be ensured
that hydrogen peroxide does not condensate on the package 8. The
temperature to which the package 8 should be heated depends on the
content of hydrogen peroxide in the sterilizing gas, but is
normally approximately 70.degree. C.
[0060] Since the heating air is introduced in the top portion 14 of
the heating zone 2 and withdrawn through the outlets 16 in the
bottom portion 15, an air flow essentially from top to bottom of
the heating zone 2 is ensured. Thus, it is also ensured that air
flows past the package 8 from the open end 11 towards the closed
end 12. This one-way air flow reduces the risk of particles and
micro organisms whirling about in the heating zone 2.
[0061] Heating in the heating zone 2 is controlled based on a
temperature measured on the inside of the package 8 by means of a
package heating temperature sensor 31, e.g. an IR temperature
sensor. This package heating temperature sensor 31 may also be used
in a feed-back circuit providing a safety device for the heating.
If, for instance, the conveyor belt 10 transporting the packages is
stopped, continued heating in the heating zone 2 might lead to
melting of e.g. plastic lids on the packages 8. Therefore, if a
predetermined high temperature is measured by the inside
temperature sensor, hot air will be by-passed via a shunt, thus not
raising the temperature in the heating zone further. When a
predetermined low temperature is measured, heating in the heating
zone 2 recommences. The predetermined high and low temperature
levels are determined based on the properties of the material in
the packages 8 and on the hydrogen peroxide content of the
sterilizing gas.
[0062] The heated package 8 is passed by the conveyor belt 10
through the opening 6a in the partitioning or semi-open wall 6 into
the sterilization zone 3. Here, the package 8 is subjected to
gaseous hydrogen peroxide introduced at a temperature of
approximately 95.degree. C. in the top portion 18 via the nozzles
17. The hydrogen gas is withdrawn through the outlets 20 in the
bottom portion 19 and therefore a one-way gas flow is maintained
from the top of the sterilization zone 3 towards the bottom. This
also means that the flow past the packages 8 is directed from the
open end 12 towards the closed end 11. This reduces the risk of
recontamination of the packages 8.
[0063] Further, an accurate sterilization may be achieved both of
the inside and the outside of the package 8. Sterilization of the
inside of the package 8 is essential in order to maintain sterility
of sterile contents subsequently filled in the package 8. Sterility
of the outside of the package improves manageability of the package
8, since the package 8 may be displaced vertically for moving
towards and away from an injection nozzle during filling of the
package 8 without the risk of particles or micro organisms on the
outside of the package 8 contaminating the inside.
[0064] Gaseous hydrogen peroxide is introduced and withdrawn at
such rate that a positive pressure is maintained in the
sterilization zone 3. Thus, it may be ensured that any leakage of
gas and air between the sterilization zone 3 and the surrounding
heating and venting zones 2, 4 is from the sterilization zone 3
towards the surrounding zones 2, 4. This improves the conditions
for an accurate sterilization. Approximately 20% of the gas leaving
the sterilization zone 3 will seep into the heating and venting
zones 2, 4, the remaining 80% being withdrawn through the outlets
20.
[0065] The sterilizing gas used in the sterilization zone 3 is
produced in the gas production unit 25 by addition of liquid
hydrogen peroxide to hot sterile air. The desired hydrogen peroxide
concentration in the sterilizing agent may be adjusted by
adjustment of the proportion of liquid hydrogen peroxide added to
the air. In the example shown, a sterilizing gas containing
approximately 35% hydrogen peroxide is used for sterilization of
packages.
[0066] Gas withdrawn through the outlets 20 in the bottom portion
19 of the sterilization zone 3 is passed through the catalyst unit
36 for removing hydrogen peroxide from the gas before being
evacuated through the evacuation system of the device 1.
[0067] The fact that the package 8 is heated above the dew point of
the hydrogen peroxide gas before entry into the sterilization zone
3 ensures that hydrogen peroxide does not condensate on the package
8. Therefore, removal of hydrogen peroxide from the package through
venting in the venting zone 4 is facilitated. This allows a
reliable sterilization even of packages with difficult geometries,
e.g. with crevices and pores, without the risk of high residuals of
hydrogen peroxide on the package 8 to be filled with an edible
content.
[0068] The sterilized package 8 is passed through the opening 7a in
the partitioning or semi-open wall 7 into the venting zone 4. In
the venting zone 4, sterile air is introduced via the nozzles 21 in
the top portion 22 at a temperature of approximately 70.degree. C.
The venting air vents away hydrogen peroxide remaining in and on
the package 8. Venting is facilitated by the fact that the heating
of the package 8 has eliminated condensation of hydrogen peroxide
on the package.
[0069] The package 8, now sterilized and essentially free from
residual hydrogen peroxide, is passed into the filling zone 5 where
it is filled with a sterile content, e.g. milk, juice or tomato
paste. In order to ensure an air flow essentially from top to
bottom, thus minimizing the risk of recontamination of the package
8, sterile air is introduced via the nozzles 26 in the top portion
27 of the filling zone 5. A positive pressure is maintained in the
filling zone 5, such that air flow is from the filling zone 5
outwards and not the other way round.
[0070] The filled package 8 is then transported on for sealing and
folding of the bottom.
[0071] The partitionings between the different zones 2-5 make it
possible to control the conditions in each separate zone 2-5 and to
control the flow between zones 2-5.
[0072] When a production run is finished or when a new run is to
begin, the device itself needs to be sterilized. Hot sterile air is
then introduced via the nozzles 13 in the heating zone 2 and the
inside of the device 1 is heated to approximately 35.degree. C.
When the interior has reached the appropriate temperature, gaseous
hydrogen peroxide is introduced in the entire device via the
nozzles 17 in the sterilization zone 3. The flow pattern will be
different during machine sterilization, i.e. sterilization of the
interior of the device 1, as compared to during package
sterilization, since the entire interior is to be heated and
sterilized. As with package sterilization, sterilizing gas is
withdrawn via the catalyst unit 36 for destruction of the hydrogen
peroxide.
[0073] The sterilization process in the device of the invention is
controlled by means of three control loops. In the first control
loop, an ambient temperature sensor 37 measures the temperature
outside the device 1 and a relative humidity sensor 28 measures the
relative humidity outside the device. A concentration meter 29
measures the hydrogen peroxide concentration in the sterilization
zone 3. A first control unit 30 receives signals from the ambient
temperature sensor 37, the relative humidity sensor 28 and the
concentration meter 29 and regulates the amount of hydrogen
peroxide added in production of the sterilizing gas. During machine
sterilization, the data from the temperature sensor 37, relative
humidity sensor 28 and the concentration meter 29 are used for
regulating the amount of hydrogen peroxide added to the air stream
in the gas production unit 25. In this manner, optimal conditions
may be achieved for machine sterilization. During package
sterilization, when the hydrogen peroxide concentration of the
sterilizing gas is normally significantly higher than during
machine sterilization, the relative humidity outside the device 1
is not as important, and therefore only the ambient temperature
sensor 37 and the concentration meter 29 are used for regulating
the hydrogen peroxide amount added in the gas production unit 25.
In this manner, the killing efficiency of the gas may be controlled
for purposes of package sterilization.
[0074] In the second control loop, the package heating temperature
sensor 31 is used for measuring the temperature of the packages 8
before entering the device (i.e., start) and a package heating
temperature sensor 32 is used for measuring the temperature of the
packages 8 just before they leave the heating zone 2. Signals from
these two temperature sensors 31, 32 are sent to a second control
unit 33 which regulates the temperature of the hot air introduced
in the heating zone 2 for heating the packages 8 to the required
temperature above the dew point of the sterilizing gas. Thus, a
correct temperature of the packages 8 may be ensured before they
enter the sterilization zone 3.
[0075] In the third control loop, a condensation detector 34
detects possible occurrence of condensation in the sterilization
zone 3. A signal from the condensation detector 34 is sent to a
third control unit 35. If condensation is detected, a signal is
sent from the third control unit 35 and used for controlling the
temperature and/or flow of hot air in the gas production unit 25.
Thus, the temperature of the sterilizing gas and/or the hydrogen
peroxide content may be adjusted, such that condensation is
avoided. Further, if condensation has been detected, it is possible
to mark or discard the packages concerned.
[0076] The skilled person will realise that a number of
modifications of the invention described above are possible without
departing from the scope of the invention as defined in the
appended claims.
[0077] For instance, only the first of the three control loops
described above could be used, or the first control loop could be
used in combination with one of the two other control loops.
[0078] This first control loop may also be supplemented with a flow
meter (not shown) measuring the air flow to the gas production unit
connected to the first control unit 30. If the flow of air into the
gas production unit 25, and thereby into the sterilization chamber
3, is reduced, e.g. if a filter in the air duct is clogged, the
hydrogen peroxide concentration in the sterilizing gas and thus in
the sterilization chamber 3 will rise. The first control loop would
in such case regulate the amount of hydrogen peroxide added in gas
production downwards. However, this may lead to too small a gas
flow, so that not all parts of the packages are reached by the
sterilizing gas. Therefore, the first control unit 30 may be
arranged to sound an alarm at a predetermined low-level flow, so
that the low flow may be corrected instead of just lowering the
amount of hydrogen peroxide added in the sterilizing gas.
Similarly, an alarm signal may be sent at a predetermined
high-level flow.
[0079] Other means of controlling the heating in the heating zone 2
may also be used. The ambient temperature sensor 37 may be used for
determining the temperature outside the device 1. With knowledge of
the properties of the materials in the package 8, the required
temperature and flow of hot air introduced through the nozzles 13
may be calculated. This may also be combined with the package
heating temperature sensor 32 described above for better control
and for providing a safety feature.
[0080] The package heating temperature sensor 32 may be arranged in
the holders 9 holding the packages for measuring the temperature of
the packages 8 just before they enter the sterilization zone 3.
This temperature sensor 32 may be used for controlling the
temperature and flow of the heating air as well as for controlling
the safety shunt. It may also be combined with one or both of the
previously described temperature sensors for allowing even better
control of the heating.
[0081] Other sterilizing agents than hydrogen peroxide may also be
used, as long as they are suitable for sterilization in the gaseous
phase.
* * * * *