Response to Query on Curl

                                    Response to Query on Curl
                                        Edward D Cohen

In response to your question about curl when ink is applied to film, the curl is the usually towards the coated side of the film.  It is caused by   residual stresses in the coating applying a force to the substrate, which causes the substrate to bend. The stresses can arise form several causes. Stresses generated, as the coating shrinks during the drying process will cause curl if not relieved. The magnitude of these stresses will depend on the amount of shrinkage, the properties of the binder system, the substrate physical properties transition temperatures and stress relieving in the dryer.  Often a high relative humidity et eh end of the dryer and in ambient air.  A stronger substrate may also be needed.following diagram shows  curl and stresses.

The following diagram shows  curl and stresses.

Comments

[Gilberto Martinez]

Based on the book "Coating and drying defects", in order to control the curl level we need control the Humidity at the process.

We have Ceramic coating on PET carrier, we are experienced curling with thicker coating for the same ceramic, that it's driving Us to reduce process speed to control curling.

In order to keep same speed so i need to control the humidity at the chamber or at the exit of the dry chamber?

What are other key variables that We need to consider in our controls?