A 2 or 3 points to eliminate, (1) Contaminates in the form of Paper dust from prior jobs, (2) Anti set off powder from prior jobs, (Intergram/French chalk etc.) (3) Airborne, Aerosol propellant, always suspect and often unseen.
As Thomas hints at (above) can You try the same Ink on different stock, OR
Oil based Ink on the same stock, are You printing on the rear of the Envelopes (return address etc.) with the Stock already contaminated with - lick and stick - or similar.
Silly possibilities, maybe, but Good Luck. Mick U.K.
Can you explain better what’s happening with your rubber base ink? And, maybe a photo would help here…
A 2 or 3 points to eliminate, (1) Contaminates in the form of Paper dust from prior jobs, (2) Anti set off powder from prior jobs, (Intergram/French chalk etc.) (3) Airborne, Aerosol propellant, always suspect and often unseen.
As Thomas hints at (above) can You try the same Ink on different stock,
OR
Oil based Ink on the same stock, are You printing on the rear of the Envelopes (return address etc.) with the Stock already contaminated with - lick and stick - or similar.
Silly possibilities, maybe, but Good Luck. Mick U.K.