Browse Prior Art Database

Improved Coating Apparatus and Method

IP.com Disclosure Number: IPCOM000122559D
Original Publication Date: 1991-Dec-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 7 page(s) / 271K

Publishing Venue

IBM

Related People

Bradley, JW: AUTHOR [+3]

Abstract

This article discusses major improvements to the preferred embodiment of an apparatus for forming a coating on a substrate, which is commonly called a "hydropneumatic" coating head. A hydropneumatic coating head employs a pressurized membrane and a smoothing film to form an extrusion opening through which the coating liquid is carried by the substrate. The substrate is supported by a back-up roller which also serves to carry the substrate along its path. A reservoir for the coating fluid is formed by the substrate, the smoothing film and its support, and a pair of end seals, one at each end of the membrane/ smoothing film assembly. At the bottom of the reservoir the pressurized membrane forces the smoothing film against the substrate. The arrangement of these parts is shown in Figure 1.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 31% of the total text.

Improved Coating Apparatus and Method

      This article discusses major improvements to the
preferred embodiment of an apparatus for forming a coating on a
substrate, which is commonly called a "hydropneumatic" coating head.
A hydropneumatic coating head employs a pressurized membrane and a
smoothing film to form an extrusion opening through which the coating
liquid is carried by the substrate.  The substrate is supported by a
back-up roller which also serves to carry the substrate along its
path.  A reservoir for the coating fluid is formed by the substrate,
the smoothing film and its support, and a pair of end seals, one at
each end of the membrane/ smoothing film assembly.  At the bottom of
the reservoir the pressurized membrane forces the smoothing film
against the substrate.  The arrangement of these parts is shown in
Figure 1.  The pressurized membrane 14 is held in place by a membrane
support mandrel 11.  The back-up roller 13 is shown supporting the
substrate 16.  The end seals 17 and the smoothing film support 18 are
designed to be an integrated assembly.  The smoothing film 12 is
attached to the support 18 near the upper part of the support.  The
reservoir 15 of coating fluid is formed between the end seals 17, the
substrate 16, and the smoothing film 12.

      The complete coating apparatus and its operations are well
defined in many patents.  The improvements described here were made
to overcome problems that were not anticipated in the original
inventions.  The first of these improvements concerns the pneumatic
membrane and its supporting mandrel.  As the line speed of the
substrate is increased the pressure in the membrane must also be
increased to maintain a desired coating thickness.  As the pressure
is increased the membrane stretches in the circumferential direction
but is constrained from moving in the axial direction by the
fastening clamps at the ends.  It can be shown that a critical
pressure exists for a membrane constrained at the ends to prevent
axial motion.  The formula for this critical pressure is:
       P = E t / r v  3(1-v)
 where   E = Young's Modulus
         t = membrane thickness
         r = membrane radius
         v = Poisson's ratio of the
             membrane material

      This critical pressure will cause the membrane to buckle in a
manner similar to a thin-walled column under excessive load.  In the
case of the membrane the buckling is due to Poisson's ratio and the
constraints preventing transverse strain from occurring.

      In a high production manufacturing operation, line speeds of
five hundred to nine hundred feet per minute are common.  In order to
keep the coating thickness to a desired value the critical buckling
pressure of the membrane must be exceeded.  When the membrane buckles
a series of half waves form along the surface of the membrane.  These
half waves are radial dimension changes and tend to be...