Method and apparatus for coating on baggy web

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

• contacting a Mayer rod with a back-up roll, wherein the back-up roll includes a deformable inner layer with a surface thereof covered by a deformable outer layer, the inner layer being softer than the outer layer, wherein the deformable inner layer of the back-up roll has a hardness less than 20 Shore A, and the deformable outer layer of the back-up roll has a hardness greater than about 40 Shore A;
• disposing a flexible web between the back-up roll and the Mayer rod;
• wrapping the flexible web around at least one of the back-up roll and the Mayer rod;
• pressing the Mayer rod and the back-up roll against each other to form a nip therebetween, wherein the Mayer rod and the flexible web at a contacting area are impressed into the back-up roll with a machine-direction nip width W and a nip engagement depth D;
• and
• providing a coating material upstream of the nip to form a coating on a surface of the web downstream of the nip,
• wherein the back-up roll has a S-Factor, averaged over a range of the nip engagement D from about 0.05 mm to about 1 mm, being less than about 10 (106·N/m5/2), where the S-Factor is defined by an equation
• S
• =
• F
• D
• ·
• R
• E
• ,
• where S represents the S-Factor, D represents the nip engagement depth, F represents an applied force, and RE represents an effective radius of the Mayer rod and the back-up roll, and
• wherein the Mayer rod comprises one or more predefined openings that remain open when the Mayer rod and the back-up roll are pressed against each other to allow the coating material to pass through.