Low energy e-beam sterilization – process monitoring.

Tetra Pak® produces lines for filling liquid (water, milk, fruit juices) into containers. The containers are folded in the filling machine from rolls of specially prepared packaging material.

To ensure an adequate degree of sterility of the packaging material, it is irradiated using low-energy electrons in an in-line process. The selected energy at 80 keV is great enough to ensure a needed dose on the surface, and small enough to avoid deterioration of the packaging material.

Characterization of the in-line e-beam facility and measurement of dose to the product are done using the Dµ-method with thin-film Risø B3 dosimeters and with traceability ensured through Risø HDRL.

A tool – the DCT - was developed to verify that initial process characterization is maintained by measurement of electron current delivered from the lamps (e-beam accelerator). The DCT signal is calibrated in terms of surface dose Dµ and represents therefore virtual dose with traceability to national standards.

The claim for traceable dose measurements is valid for controlled machine parameters (mainly energy and speed) within specified limits. Deviations from the limits shuts down the facility.

Effect of influence parameters on the DCT signal was measured and correction factors were determined to allow the DCT to be used under varying conditions.

The calibration of a DCT is confirmed by irradiation at a dedicated test facility where its response is compared with actual Dµ measurements.

Figure 1                                                                              

Tetra Pak® filling machine

Figure 2

DCT response = = f(dose)