Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
2002-01-08
2004-05-11
Loney, Donald J. (Department: 1772)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C428S031000, C428S174000, C428S515000, C428S516000, C296S191000
Reexamination Certificate
active
06733870
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to the use of extrusion coating techniques for forming multilayer paint coated films. More particularly, multilayer coatings are made by extrusion coating one or more layers onto a surface-controlled plastic carrier sheet to produce high quality films at high speeds while avoiding solvent emission problems characteristic of the use of solvent-based paints.
BACKGROUND OF THE INVENTION
1. Exterior Automotive Applications
Exterior automotive body panels have been made in the past by spray painting sheet metal parts. Multilayer 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 avoids 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 an approach in which paint films are made by coextruding a base coat and a clear coat as separate extruded layers onto a carrier sheet. The carrier is used as a supporting sheet for the clear coat and color coat in a subsequent injection molding process. The extruded clear coat and color coat are supported in the mold by the carrier and shaped in the mold. The clear coat is a coextruded sheet having different proportions of polyvinylidene fluoride (PVDF) and acrylic resins in each layer of the coextrusion.
U.S. Pat. No. 4,317,860 and U.S. Pat. No. 4,364,886 to Strassel also disclose coextrusion of multilayer films such as a two-layer coextrusion of predominantly PVDF on one side and a predominantly acrylic resin on the other side of the extruded 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 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 approach 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 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 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 needed to solubilize the resin in solution casting or can be 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 quality films at high line speeds and at low cost.
The present invention provides an extrusion coating process that is an alternative to solution or dispersion casting of polymeric films and conventional extrusion. The invention is particularly useful with PVDF/acrylic films while avoiding use of the strong solvents and their related problems described previously. Use of the extrusion coating techniques of this invention provides the advantages of avoiding expensive solvents, producing no VOC emissions, and avoiding cross-contamination associated with solvent casting. In addition, and as emphasized in more detail below, the present invention has the added advantage of greatly increasing line speed, eliminating steps in the manufacturing process, and reducing costs for producing the clear coat/color coat films.
Further, the invention has particular applicability to the manufacture of molded plastic exterior automotive body panels and parts. The invention provides a means for producing high gloss, high DOI clear coat/color coat paint films of exterior automotive quality.
2. Exterior Siding Panel Applications
Although the invention is described above with respect to exterior automotive applications, the invention also has applicability as a protective and decorative coating for other articles such as interior automotive components, exterior siding panels and related outdoor construction products, marine products, signage, and other interior or exterior film products with similar constructions.
The following description relating to vinyl (PVC) siding panels is an example of one use of the invention for producing outdoor weatherable decorative surfaces on extruded plastic sheets. The invention, however, is applicable to plastic substrate panels other than vinyl.
Wood, metal and vinyl are materials commonly used as boards or shingles for siding in the construction and remodeling of commercial and residential structures. Painted wood is perhaps the most aesthetically pleasing of these materials to the consumer, but wood suffers from deterioration by rotting and attack by insects, rodents and birds.
Enlow Howard H.
McCready Russell J.
Roys John E.
Truog Keith L.
Young Frederick
Avery Dennison Corporation
Christie Parker & Hale LLP
Loney Donald J.
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