Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2001-07-02
2003-04-15
Yao, Sam Chuan (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S212000, C156S247000, C264S176100
Reexamination Certificate
active
06547912
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to the use of solventless extrusion coating techniques for forming high transparency protective films and multi-layer paint coated films and laminates. More particularly, coatings are made by extrusion coating one or more layers onto a carrier sheet to produce films of high optical quality at high speeds while avoiding solvent emission problems characteristic of the use of solvent-based coatings. Techniques are also disclosed for removing multiple sources of defects from the resin manufacturing, handling and extrusion process, with the result that extruded clear films can be produced with an essentially defect-free glass-like clarity.
BACKGROUND OF THE INVENTION
The present invention is described below with respect to its application to the manufacture of exterior automotive body panels, although other end-uses of the films made by this invention also are considered to be within the scope of this invention.
Exterior automotive body panels have been made in the past by spray painting sheet metal parts. Multi-layer paint coats, such as those referred to as a clear coat/color coat paint finish, have been used to produce desirable optical effects. In addition to high gloss and high distinctness-of-image (DOI), these paint coats also are highly durable by providing chemical resistance, abrasion resistance and weatherability that significantly reduces degradation by ultraviolet light.
In more recent years molded plastic car body panels have been made with decorative clear coat/color coat paint films bonded to the molded plastic panel. Use of such films avoids certain environmental problems associated with evaporation of paint solvents while also reducing or eliminating the need for paint facilities and emission controls at the automotive production plant.
Because of the growing need to reduce the amount of atmospheric pollution caused by solvents emitted during the painting process, many different approaches have been taken in recent years for producing these decorative films. These processes are generally categorized by solution casting techniques or extrusion techniques. For instance, U.S. Pat. No. 4,810,540 to Ellison et al. and U.S. Pat. No. 4,902,557 to Rohrbacher use solution casting techniques in which liquid-cast, solvent-based clear coats and pigmented base coats are applied to a flexible casting sheet by a coating process such as reverse roll coating or gravure printing. The liquid cast layers are separately applied and then dried at high temperatures to evaporate the solvents.
As an alternative, extruded films have been used for making exterior automotive clear coat/color coat films. International Application PCT US93 07097 to Duhme describes a process in which an injection molded laminate is made from an extruded clear coat layer, a color coat layer, a reinforcing layer laminated to the color coat layer, a bonding layer on a side of the reinforcing layer opposite from the color coat, and an injection molded substrate bonded to the bonding layer. The outer clear coat layer is a coextruded sheet having different proportions of polyvinylidene fluoride (PVDF) and acrylic resins in each layer of the coextrusion. An extruded thermoplastic liner layer is laminated to the outer surface of the clear coat layer to assist in injection molding the paint film laminate to the substrate. The coextruded outer clear coat layer is laminated to a polyester carrier which supports the clear coat layer during subsequent lamination steps. The outer clear coat layer can optionally be extruded onto the thermoplastic liner layer to provide gloss control. The color coat is made by solvent casting it on a carrier and laminating the dried paint coat to the clear coat. The reinforcing layer is laminated to the exposed side of the color coat, and the bonding layer may be coated on or laminated to the reinforcing layer. This process involves time-consuming multiple coating and lamination steps and slow processing speeds disclosed in the various examples.
U.S. Pat. Nos. 4,317,860 and 4,364,886 to Strassel also disclose coextrusion of multi-layer films such as a two-layer coextrusion of predominantly PVDF on one side and a predominantly acrylic resin on the other side of the coextruded sheet. These unitary structures are used to make molded articles, or to adhere the sheets to a molded polymer.
Film extrusion techniques also have been used in the past for making free films in which the extruded polymeric material is coated on a polished drum. These films are then undercoated with various color coats. The exterior surface of the extruded free film that contacts the drum (and is separated from the drum as a free film) does not have a high gloss and high distinctness-of-image. Also films manufactured in this manner do not have a carrier sheet attached, which makes them hard to handle and easily damaged in subsequent processing.
Another process disclosed in U.S. Pat. No. 5,114,789 to Reafler comprises a pigmented base coat which is solvent-die extrusion coated onto a flexible, stretchable carrier sheet and dried at elevated temperatures to evaporate the solvents, followed by extrusion coating a reactive clear coat on the base coat. The carrier film and extrusion coated paint layers are then heat softened as a unitary sheet and applied to a molded shaped substrate by a shrink wrap process.
In a currently used process for making exterior automotive paint films, a clear coat and color coat comprising blends of PVDF and acrylic resins are cast by reverse roll coater, either by solution or dispersion casting. The film thickness of the paint coats used in the process generally is dictated by end user requirements. In some instances the need to produce relatively thick films can impose certain production constraints. To adequately dry the material and to prevent air entrapment, line speeds are typically at 25 feet per minute. This slow throughput limits the coating capacity of the reverse roll coater and also releases a large amount of organic solvents. This solvent release is particularly evident when a solution-cast PVDF/acrylic clear coat is coated from a solvent-based solution having a relatively high amount of solvent. VOC emissions are high. PVDF has limited solubility and requires strong solvents to dissolve. One such solvent known as N-methyl pyrrolidone (trade name M-Pyrol) is either needed to solubilize the resin in solution casting or used as a coalescing aid in dispersion casting. In addition, cross contamination can occur from solubilizing residual material in previously used drums, hoses, pans, pumps, etc. Also, during coating, the strong solvent can dissolve caked-on resins in a drying oven, causing them to cascade down on the web being coated. As a further concern, these strong solvents are expensive.
Thus, there is a need for producing decorative and protective surfacing films while avoiding the adverse effects of low production line speed, high VOC, cross-contamination, and the use of expensive solvents.
Extrusion techniques can be an alternative that avoids the use of strong solvents and their related solvent emission problems. Extrusion techniques such as those described above, however, have not been successfully adapted to producing high optical quality films at high line speeds and at low cost.
Application Ser. No. 08/793,836 to Enlow et al. describes a solventless extrusion coating process that provides an alternative to both solvent casting and conventional extrusion of polymeric films. Use of the extrusion coating techniques of that invention provide the advantages of avoiding expensive solvents, producing no VOC emissions, and avoiding cross-contamination associated with solvent casting. In addition, the invention has the added advantages of greatly increasing line speed, eliminating steps in the manufacturing process, and reducing the cost of producing clear coat/color coat films. The invention has particular applicability to the manufacture of molded plastic exterior automotive body panels and parts, in that it provides a means for
Enlow Howard H.
Markey John J.
Roys John E.
Truog Keith L.
Young Frederick
Avery Dennison Corporation
Christie Parker & Hale LLP
Yao Sam Chuan
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