GB2217204A

GB2217204A - Sterilizing packaging materials

Info

Publication number: GB2217204A
Application number: GB8907761A
Authority: GB
Inventors: Karl Nideborn; Magnus Bergstrom
Original assignee: Akerlund and Rausing AB
Current assignee: Akerlund and Rausing AB
Priority date: 1988-04-14
Filing date: 1989-04-06
Publication date: 1989-10-25
Anticipated expiration: 2009-04-06
Also published as: SE8801373D0; GB2217204B; GB8907761D0; FR2630009A1; DE3911749A1

Description

r)f-) 17 204 1 1- 4 9 STERILIZING PACKAGING MATERIALS The present

invention relates to a method O.'L' sterilizing a packaging material, packaging container or elements of such and more precisely to a two-step method, where a microwave treatment is used as a final step.

The present applicant has filed Swedish Patent Applicatin No. 8801200-0 describing a two-step method where, as a final step, microwave energy is used and as a first step water vapor, preferably saturated vapor is supplied. Said two-step method has been developed to comprise also continuous, highly efficient processes and plants.

Surprisingly, it has now been found that hydrogen peroxide combined with microwaves provides a first class sterilization result, especially when the microwave effect is dimensioned to heat the hydrogen peroxide to a temperature well in excess of 1000C. This gives an excellent killiing effect on micro-organisms and results in very low residue amounts of hydrogen peroxide. - Thus, the present invention provides a method for sterilizing packaging material, for instance containers. The method is characterized in that, as a first step, hydrogen peroxide is supplied to the material, and that, as a second step, a microwave field is supplied to the material.

In its broadest aspect, the invention provides a method of sterilizing packaging material wherein a film of hydrogen peroxide is applied to said material and subsequently said film is heated by exposure to a microwave field in a pressurized zone.

In a preferred embodiment there is provided a method of continuously sterilizing packaging material, wherein the packaging material is passed through a - 2 pressurized zone in which a fog of hydrogen peroxide is sprayed onto the packaging material in a first region of said zone, and the packaging material is exposed to a microwave field in a second region following the first recion.

Preferably, the hydrogen peroxide is heated to a temperature of approximately 50 to 80C and as an option the hydrogen peroxide is fastheated further before it 14 is app ed to the packaging material. It also is preferred to spray the hydrogen peroxide in pulses via a check valve.

In order to use the absorption of microwave energy to an optimum in the thin layer of hydroge-n peroxide formed on the packaging material, a microwave reflecting sleeve preferably is arranged for encompassing the packaging naterial in the second region. The heating of the hydrogen peroxide and the strength of the microwave fleld r-referably is selected such that in said second region there is obtained hydrogen peroxide in vapor and/or liquid phase cf: a temperature in excess of 1000C.

Preferablv there is provided means for condensation of the hydrogen peroxide at the output from said second region, and the flow of condensate is controlled such that it corresponds to the flow of hydrogen peroxide to the first region.

The present invention also provides a device for sterilizing packaging material. The device comprises an elongate housing defining a first recion for treating oil packaging material with a fog of hydrogen percxide and a second region for microwave treating of the packaging material; means for forming the hydrogen peroxide fog in said first region; means for irradiating said second region with microwave radiation; and means for transporting packaging material through said regions.

b.

k 3 - Preferably, there is provided a check valve for supplying pressurized hydrocen peroxide tc said first region. It is particularly preferred that means is provided for controlling said valve wit1h, a high operation frequency.

In a specific embodiment the input to the first region is designed as a rotatable turret having storage pockets adapted to the size of packaging containers to be sterilized, and a pump device is arranced for successively lowering the pressure in each turret pocket when the pocket rotates towards the first region.

In order to optimize the microwave atsorption a sleeve of a microwave reflecting material preferably is arranged in the second region and encompasses one or several containers.

Preferably there is arranged a cooling sleeve in the housing, after said second region in ti-ie transport direction, and a vapor trap is dimensioned for condensing an amount of hydrogen peroxide corresponding to that delivered to said first region.

It also is preferred that the output from the housing has a turret of the same type as the input; and a pump device is arranged for reducing the overpressure in each turret pocket when this pocket approaches a container output position. Suitably, the pump device I- z-7.- ned over-ress, re wher t,-- output pocket is in the output position thereof, and said overressure is maintained by a generally closed housing up to a filler.

The means for transporting the containers may comprise a housing inclined relative from the horizontal and having a cross section allowing passage of containers by gravitational force.

The supply of hydrogen peroxide suitably is arranged such that there is created an overp.ressure of the magnitude of 0.5 to 6 atmospheres (50-600 kPa).

One embodiment of the invention will now be described by reference to the accompanying drawings, where Fig. 1 schematically shows a 1;lant for continuously sterilizing packaging containers or parts thereof, and 2 is a diagram showing the killing effect (D-value) of the hydrogen peroxide relative the temperature.

The reference numeral 10 defines an elongate, pressure resistant housing acting as the processing zone where the packag4 ng containers or r-arts thereof undergo the sterilizing process. Such a container has been shown schematically by the reference numeral 11. It may for instance be a can type package, closed at one end thereof, a can closure, tray or similar.

In order to be able to maintain a high pressure inside the housing 10 and an internal environment -ed by the environment, there is an input sluice unaffect 12 arranged at the upper end in said figure. This sluice is arranged as a storage device of turret type rotatable around a shaft 13. The Phantom lines 14 denote incividual st; race i-cckets, and the opening 15 defines the input position for individual containers 11.

The walls 16, 17, which at both sides thereof terminate the turret storage, are manufactured from a low friction material, for instance polytetrafluoroethylene available under the Registered Trade Mark TEFLON. In order to be able to successively lower the pressure in each turret pocket 14, there is a pump arrangement comprising an ejector pump 18 and a rotary c 1 I- - pump 19. The first one is arranged for operating 4 continuously against atmospherLC pressure, and the final pressure reduction is obtained by the rotary pump 19. In practice this means that each turret pocket 14 is in a vacuum state when the pocket arrives at a position opposite to an input opening 20 to a first region 21 of the pressurized zone in the housing 10.

Because the volume of each.individual turret -pocket is small compared with the internal volume of the housing 10, the pockets do not contribute noticeably to pressure variations in the housing.

A conduit 22 from a hydrogen peroxide source (not shown) emerges in the first region 21 of the housing 10. The conduit is terminated by a magneticostrictive high pressure valve 23 controlled by an oscillator 24 and a control unit 25.

The hydrogen peroxide from the conduit 22 preferably is heated to a temperature around 80C. The reason for pulsing the hydrogen peroxide is that this improves the heat transfer to the peroxide layer on the container, and it may be noted that when the container 11 approaches the next processing region i.e. the second region 42, in the zone defined by the housing 10, there is a thin hydrogen peroxide layer on the surface of the container, internally as well as externally, and said 4 laver is at a temperature def_ned by the cooling mass of the container and the heat transfer fog condensate.

In order to give this container the final "push" for obtaining a high external temperature (around 140C), a microwave generator, a magnetrone 26, is used and via a wave guide 27 supplies energy to the container 11 in the second region 42.

In order to make this energy transfer an optimum, a reflector 28 is arranged around the region 42 and thus around the containers 11 having said thin hydrogen - 6 peroxide layer thereon. The microwave radiation will then have the possibility of repeatedly travelling through the thin hydrogen peroxide layers and transfer the major part of the energy thereof. In order to take up non-transferred energy, there is an absorber 29 at the end of the wave guide 27. End walls 30, 31, for instance of ceramics or polytetrafluoroethvlene (TEFLON) delimit the microwave region from the rest of the portions of the processing zone. Preferably there are passages in the walls of the containers. The microwave energy combined with the hydrogen peroxide heating that takes place in the region 21 results in heating to a high surface temperature. In order to maintain a well defined hydrogen peroxide environment in the region 2.1 as well as in region 42, there is provided, at the output opening from the region 42, a trap 32 comprising return conduit 33 to the hydrogen peroxide source and cooling water loop 34 around the housing 10.

Condensation is regulated such that the flow of hydrogen peroxide through the valve 23 corresponds to the amount of hydrogen peroxide recycled through the return conduit 33.

At the output opening 37 from the housing 10, there is a rotating storage device 35 of the turret type and corresponding to the input sluice 12. The overpressure in the individual turret pockets 14' is relieved by a pressure reduction valve 36. The pressure from the housing output opening 37 to the output opening 38 from the turret 35 preferably is reduced such that there exists an overpressure inside the output housing 39 leading from the turret 35. This pressure, for instance of the magnitude of 0.2 0.4 atmospheres (20-40 kPa), prevents the ambient air from emerging into the packaging containers before they reach a filler 40.

This filler 40 may be of turret type and rotatable 1 - 7 around an axis 41 such that individual pockets for receiving a container 11, successively arrive at the output from the housing 39.

As appears from Fig. 2 the killing characteristic (D) of the hydrogen peroxide is extremely good at temperatures in excess of 1000C. The interval 1OVC to 120C represents a level clearly superior to traditional, allowed levels. Such levels may be regarded as represented by the horizontal axis in the figure. It should be observed that the vertical axis has a logarithmic scale. A temperat ure of 120'C represents for instance a killing effect being 101.5 better than the killing effect at 90'C.

1 8 -

Claims

1. A method of sterilizing packaging material wherein a film of hydrogen peroxide is applied to said material and subsequently said film is heated by exposure to a mici:owave field in a pressurized zone.

2. A method of continuously sterilizing packaging material, wherein the packaging material is passed through a pressurized zone in which a fog of hydrogen peroxide is sprayed onto the packaging material in a first region of said zone and the packaging material is exposed to a microwave field in a second r-egion following the first region.

3. A method as claimed in C laim 2, wherein a microwave reflecting sleeve covers at least one side of the packaging material in said second region.

4. A method as claimed in any one of the preceding claims, wherein the hydrogen peroxide is applied at 50 to WC.

5. A method as claimed in any one of the preceding claims, wherein the hydrogen peroxide is sprayed in pulses.

6. A method as claimed in any one of -the preceding claims, wherein the temperature of the hydrogen peroxide and the strength of the microwave field are selected such that the hydrogen peroxide, in vapor and/or liquid phase, has a temperature in excess of 100'C in said second region.

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7 9 - 7. A method as claimed in any one of the preceding claims, wherein the hydrogen peroxide is condensed at the outlet from the second region and recycled to the hydrogen peroxide source for supply to the first region.

8. A method as claimed in any one of the preceding claims, wherein an overpressure of 60-600 kPa (0.5-6 atmospheres) is maintained in the said first and second regions.

9. A method as claimed in Claim 1 and substantially as hereinbefore described with reference to Fig. 1 of the drawings.

10. A device fcr sterilizing packaging material by a L L. I.

method as claimed in Claim 2, comprising an elongate housing defining a first region for treating the packaging material with a fog of hydrogen peroxide and a second region for microwave treating of the packaging material; means for forming the hydrogen peroxide foe in said first region means for irradiatina said second region with microwave radiation; and means for transporting packaging material through said regions.

11. A device as claimed in Claim 10, wherein a microwave re-,:1e--t-2n-s"ee-ve is ar-ranged in the seccnd region to cover at least one side of the packaging material.

12. A device as claimed in Claim 10 or Claim 11, wherein a check valve is arranged for supplying pulses of heated, pressurized hydrogen peroxide to the first region.

13. A device as claimed in any one of Claims 10 to 12, wherein the inlet to the housing comprises a rotatable turret having pockets movable between packaging loading and unloading stations to deliver packaging material to the housing, and pump means for lowering the pressure in each turret pocket when the pocket rotates towards the unloading station.

14. A device as claimed in any one of Claims 10 to 13, wherein a cooling sleeve is arranged in the housing following said second region in the transport direction, for condensing hydrogen peroxide.

15. A device as clainted in any one of Claims 10 to 14, wherein the outlet to the housing comprises a turret having pockets movable between packaging loading and unloading stations to remove packaging material from the housing, and pump means for reducing the overpressure in each turret packet when the pocket approaches the unloading station.

16. A device as claimed in Claim 15, wherein the pump device is arranged to provide an overpressure at the unloading station of the outlet pocket, and a generally closed housing extends to a packaging filler station whereby said overpressure is maintained until said f iller station.

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