Slot die coating using concave die lip over deformable back-up roll

A method of applying a coating onto a web, the method comprising:

• disposing a flexible web between a back-up roll having a deformable inner layer with a surface thereof covered by a deformable outer layer and one or more die lips of a slot die having the one or more die lips extending along a cross direction, wherein at least one of the die lips includes a coating surface positioned proximate to the back-up roll, at least a portion of the coating surface of the die lip being substantially concave and facing to the back-up roll;
• and
• dispensing a liquid coating material from the slot die onto the flexible web,
• wherein the flexible web at a contacting area is impressed into the back-up roll with an engagement depth D that is from 0.01 mm to 10 mm due to the pressure that builds between the slot die and the flexible web;
• wherein the deformable inner layer is softer than the deformable outer layer;
• and
• wherein the coating surface of the die lip has a concave radius curvature of at least 1.1 times a radius of curvature of the back-up roll under an undeformed state.