Drying process

Claim 1

A process for drying a coating of wet latex paint on a heat-deformable plastic film, the paint containing water, one or more higher boiling organic solvents and a colloidally dispersed, coalescable, hardenable, elastomeric film-forming polymer to obtain a smooth, stretchable dried paint layer substantially free of bubble defects, which comprises passing continuously through a series of drying stages a heat-deformable plastic carrier film having an upper and an under surface and having on its upper surface a coating of the wet latex paint, introducing a flow of heated, moderately humid air to each stage to supply heat and cause evaporation of water and organic solvent, the air flow in at least the first three stages being so directed that more than half of the heat required for evaporation is supplied to the film through its under surface, in a first stage of at least 30 seconds duration, controlling the evaporation conditions, including the flow rate, humidity and temperature of the air to maintain the temperature of the paint layer within about 10 degrees C below and 5 degrees C above its initial temperature, in a second stage of at least 30 seconds duration maintaining conditions which heat the paint layer to a temperature higher than in said first stage but no higher than 10 degrees C above its initial temperature, in a third stage of at least 30 seconds duration maintaining conditions which heat the paint layer to a temperature higher than in said second stage but no higher than 25 degrees C above its initial temperature; thereafter in a final stage maintaining conditions which heat the paint layer to a maximum temperature at least 30 degrees C higher than the highest temperature in the third stage and at least 50 degrees C higher than its initial temperature for sufficient time to evaporate remaining water and organic solvent and harden the paint layer, the temperature being below the heat deformation temperature of the carrier film.