How to inspect a thermal-transfer overprint on a preprinted label
On a preprinted label, the thermal-transfer overprint is judged on its own: the black type and the barcode that were added later. Do not mix that judgment with the base-print template.
On a preprinted label, the thermal-transfer overprint is judged on its own: the black type and the barcode that were added later. Do not mix that judgment with the base-print template. If the base stock was already inspected, the thermal-transfer station answers only for the batch number, the date, and the code. Light type, a missing stroke, and type in the wrong place all stop.
Why it is judged this way
The usual thermal-transfer fault is a half-length of light type after the ribbon runs out. That is not the same class as a base-print defect. If the camera compares the whole label to one template, light type can still look like the template. There must be a region that looks only at the black type, and a sample of the lightest black that is still acceptable.
What to compare
| What you see | What to call it | What not to do |
|---|---|---|
| The second half of the batch number goes light | Stop | Release it because the base stock passed |
| The date is missing a stroke | Stop | Ignore the type because a gun still scans the barcode |
| The type lands on the artwork | Stop it for position | Accept it as long as it reads |
At job change or when a roll is opened
- Build a template for the thermal-transfer region alone.
- Use a sample with a half-length of light type and confirm the alarm.
- File the base-stock conclusion and the thermal-transfer conclusion apart.
