Thin film optical and electronic devices including, but not limited to, photovoltaic devices, electrical circuits, displays, optical filters and the like, are often disposed upon thin, flexible substrates in order to decrease the device weight and/or provide a flexible device. These substrates may comprise metallic sheets or polymeric bodies, and in particular instances, such polymers may comprise polyimides.
Use of a thin substrate body can complicate fabrication of the device, particularly if high speed, high volume processes, such as roll-to-roll deposition processes, are utilized. In such instances, the thin, flexible substrate is frequently supported upon a body of carrier material, such as a sheet of metal or polymer. Following the device fabrication, the carrier is removed by physical and/or chemical methods. In one particular example, a thin, polymeric substrate comprised of a polyimide is supported upon a carrier comprising a sheet of ferrous alloy such as stainless steel. Following device fabrication, the stainless steel is removed by etching. One such process is disclosed in U.S. Pat. No. 7,176,543, the disclosure of which is incorporated herein by reference.
In a process of the type described above, it is necessary to affix the thin, flexible substrate to the carrier member so as to provide a smooth, uniform surface for deposition of the thin film layers. Such affixation is typically accomplished by lamination using a combination of heat and pressure, and optionally a hot or other thermally activated melt adhesive to bond the substrate to the carrier. The lamination process may be readily implemented for relatively small area substrates; however, when large area substrates, such as relatively long webs of materials are being prepared, problems of uniformity can arise. Typically, the lamination process is carried out under low pressure so as to avoid the formation of any bubbles or inclusions which could compromise the laminated surface. One approach to laminating long webs of material involves rolling the webs, in an interleaved configuration, onto a cylindrical support, under tension, and then disposing the rolled material in a low-pressure environment and heating the material to cause the lamination.
Lamination of the substrate materials is typically carried out at fairly high temperatures and these temperatures can cause problems in the lamination process, since the high temperatures can cause deformation or other adverse effects on the roller upon which the webs are wound. Such deformation can result in unevenness, buckling, wrinkling or other defects in the laminated product. In some instances, rollers are provided with an elastomeric surface which can operate to maintain tension in the wound webs and thus accommodate thermal stresses; however, because of problems such as outgassing, thermal degradation or the like, such elastomeric materials cannot be utilized in high temperature ranges typically employed for laminating substrates of this type. Ceramic rollers or various metal alloy rollers can tolerate high temperatures; however, thermal expansion of such rollers is nonuniform, and in general they tend to expand to a greater degree in their center (“barrel”) when heated, thereby compressing the webs in a nonuniform manner. The present invention, as will be explained in detail hereinbelow, has been developed to overcome these shortcomings of the prior art and to provide a lamination process and system which is operative to uniformly laminate long webs of materials under relatively high temperature conditions so as to produce laminated materials having sufficiently high quality to allow their use as substrates for the preparation of thin film electronic and optical devices.