Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Physical dimension specified
Reexamination Certificate
1995-08-11
2001-04-17
Nakarani, D. S. (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Physical dimension specified
C428S195100, C428S463000, C428S464000, C428S510000, C428S520000
Reexamination Certificate
active
06218004
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to sheet materials having acrylate polymer coatings thereon and to methods of producing such sheet materials. Certain embodiments of the present invention relate more particularly to sheet materials, such as a metallized paper or film, having a metal layer or substrate and one or more acrylate polymer coatings and to methods of making the same.
BACKGROUND OF THE INVENTION
Metallized paper is used for decorative paper such as for gift wrappings, and for product identification purposes such as for beer labels, canned food labels and the like. Metallized paper is found to be desirable for such uses because of its glossy aluminized appearance and its related ability to attract the attention of a consumer. Metallized paper is usually printed with some sort of product identifier or some type of decorative figure and is made in varying degrees of gloss level and with various different performance characteristics. For example, gift wrap paper must be easily printable, it must be able to be folded without losing the metal coating, and it must usually have a high reflective finish. Beer labels, on the other hand, must be caustic removable to facilitate their removal during glass reclamation, it must hold up well in a wet environment, and it must also be quite abrasion resistant.
Most metallized paper is made by applying prepolymer and aluminum layers on clay-coated Kraft paper which is approximately 30 to 150 microns thick. The process usually involves applying one or two layers of solvent based prepolymer material and drying them in an oven to remove the solvent after each layer. This method provides a relatively smooth base coating on which an aluminum layer is deposited. The method of first coating the Kraft paper with prepolymer before depositing the aluminum layer is needed because the clay-coated paper is typically not smooth enough to achieve a shiny metallized finish without the smoothing prepolymer layers. After the prepolymer layers are cured, the aluminum is then applied in a vacuum metallizer. A solvent-based prepolymer top coating is applied to the aluminum layer and the solvent is evaporated in an oven. This solvent-based coating process involves at least three or four different steps, increasing the process cost and opportunity for manufacturing losses. Additionally, a very high gloss level cannot be obtained via the solvent-based coating process because of the handling and the solvent evaporation that creates a high density of pinholes in the coating surface, thereby providing a metallized paper having only a medium gloss level. Finally, the use of a solvent-based process is neither environmentally desirable, due to the release of volatile solvent vapors into the atmosphere, nor energy efficient, due to the use of an oven to evaporate the solvent after each layer.
An alternative process to metallize paper on a much more limited basis involves applying an initial smoothing prepolymer layer by using a gravure coating method and curing the layers with a high voltage (150-300 KV) electron beam. The substrate paper is then metallized with a layer of aluminum. A top coat of prepolymer material is applied to the aluminum layer using the gravure method and is cured again using a high voltage electron beam. High voltage electron beams are used because the electron beams are generated inside of a sealed system and they must have enough accelerating voltage to enable them to penetrate through a foil window, through an air layer, and through the coating process. The prepolymer materials that are used in such alternative process are acrylate blends of monomers and oligomers.
The gravure coated acrylate/high voltage electron beam process is more environmentally desirable and energy efficient than the solvent-based coating. Additionally, the gravure process results in a metallized paper coating having improved surface gloss over the solvent-based coating level. The coating is quite sensitive to the wetting of the substrate and the inclusion of bubbles in the coating, ultimately resulting in the formation of pinholes in the surface of the coating. Although the pinhole density associated with the gravure coated process is less than that of the solvent-based process, the ability to obtain a high gloss surface finish is still adversely affected.
The gravure coating process also requires three different process steps and the use of a high voltage electron beam to cure the polymer layer. The use of such high-voltage electron beam not only penetrates the coating layer but penetrates the paper and embrittles it, increasing the probability that the substrate will tear when folded. This curing system is also inefficient because it deposits most of the electron beam energy in the substrate and not in the coating.
It is, therefore, desirable that a metallized paper product and, method for producing the same, be developed that displays a high gloss level without pinholes by using a process having a minimum number of steps. It is desirable that the metallized paper experience no embrittling during the curing process. It is desirable that the coating have excellent adhesion to the paper, have excellent inter-layer adhesion between the prepolymer layers and excellent adhesion between the polymer layer and the metal layer. It is desirable that the method of making the metallized paper be capable of being tailored to particular application requirements for the metallized paper, e.g., to accommodate the creation of a multilayer coating tailored to achieve certain objectives. It is also desirable that the metallized paper be manufactured in a manner that is economically efficient and from materials that are readily available.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides, according to one of the presently preferred embodiments disclosed herein, a metallized paper sheet and method for making the same. Metallized paper sheet materials can be produced with superior appearance and performance characteristics which can be tailored to specific end use applications. For example, the metallized paper can be produced with a very shiny, high gloss surface appearance, and/or a high quality metallized layer free of defects or pinholes, and/or an outer surface which is highly receptive to printing.
The present invention, however, provides features and advantages which are applicable not only to paper substrates, but to other sheet material substrates as well, such as polymer film sheet materials or other kinds of metal or metallic sheet materials.
According to one general aspect of the present invention, there is provided a sheet material which is comprised of a sheet material substrate, such as for example a film or paper sheet, with a polymer base coating overlying and adhered to a surface of the sheet material substrate. The base coating comprises a radiation cured crosslinked polymer derived from at least one vapor deposited acrylate prepolymer composition having a molecular weight in the range of from about 150 to 600. A metal layer is deposited on and overlies a surface of the base coating, and a polymer top coating overlies and is adhered to a surface of the metal layer. The top coating comprises a radiation cured crosslinked polymer derived from a vapor deposited acrylate prepolymer composition having a molecular weight in the range of from about 150 to 600 and a ratio of its molecular weight to its number of acrylate groups (MW/Ac) in the range of from about 150 to 600. Desirably, the top coating is derived from at least 20% by weight of a polyfunctional acrylate monomer or blend thereof. Where good printability or good adherence to other surfaces is desired, the prepolymer composition for the top coating preferably also comprises a polar acrylate monomer selected from the group consisting of amine acrylates, acid acrylates, ether acrylates and polyol acrylates. It is also desirable that the acrylate monomer or blend thereof have a ratio of its molecular weight to its number of acrylate groups (MW/Ac) of at least 150 and below 600
Cline Daniel
Dawson Eric
Langlois Marc
Shaw David G.
Christie Parker & Hale LLP
Nakarani D. S.
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