Patent Application
20070237933
The invention will now be described with reference to the drawings wherein:
While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and described herein in detail a specific embodiment with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the invention to the embodiment illustrated.
It will be understood that like or analogous elements and/or components, referred to herein, may be identified throughout the drawings by like reference characters. In addition, it will be understood that the drawings are merely schematic representations of the invention, and some of the components may have been distorted from actual scale for purposes of pictorial clarity.
Referring now to the drawings and in particular to
Coating 14 is shown in
Coating 14 includes an IR absorbing member 15 dispersed within the polymer matrix. Among other contemplated embodiments, carbon black IR absorber is included in the coating 14. The carbon black member may be between about 2% and about 10% solids content. Other IR absorbing materials are contemplated for use, such as, nigrosine dye at, preferably, a similar solids content as the carbon black member.
As will be explained below, coating 14 is imprinted with an embossing roller so as to impart an embossed surface configuration to the underlying coating. It will be understood that substrate 12 has a surface roughness which defines a variable thickness ranging between a maximum thickness t1, and a minimum thickness t2. The coating has a uniform depth d1. With reference to
In the presently shown embodiment, and in many typical embodiments, the surface roughness of substrate 12 (i.e., the average peak-to-valley surface height variation), varies from about 1.0 to about 3.0 microns. Of course, rougher or smoother substrates 12 may also be used. For example, substrates having surface peak-to-valley roughness of up to 5.0 microns, or even higher may also be used.
With reference to
To form the coated sheet, it is necessary to first apply coating 14 upon substrate 12. In certain embodiments, coating 14 may be applied through extrusion. In other embodiments, as is shown in
Once the substrate has been coated with coating 14 to the appropriate thickness, it is necessary to heat the coating to a temperature which allows for embossing. With the method of the present embodiment, the use of ovens is minimized, and IR heaters, such as IR heater 25 shown in
Due to the direction of IR heaters upon the coating 14 which includes the IR absorber dispersed therewithin, the temperature of the coating increases while minimizing heat imparted (i.e., conducted) to the underlying substrate. Furthermore, the inclusion of an IR absorber minimizes the exposure time of the substrate and coating to the IR heaters. Still further, while for some applications, an oven, such as a gas oven may be necessary as a supplement, ovens may be eliminated from certain applications. Furthermore, even where such ovens are required, the exposure to same can be minimized.
Once the coating of the coated sheet exits the IR heaters, it is at an elevated temperature and therefore softened state wherein it can be processed by the embossing rollers. Specifically, once coating 14 has been softened, an embossing arrangement is employed for decoration. As is shown in
The temperature of the embossing master (embossing roller 31) is preferably below the effective softening temperature of coating 14. The temperature of embossing roller 31, however, should not be so low as to harden coating 14 before the embossing is completed. It has been found that the preferred temperature for embossing roller 31 (embossing master) can vary depending on its thermal conductivity and specific heat, the embossing nip pressure, operating speed and the temperature to which coating 14 is heated immediately prior to contact with the embossing roller 31. Despite the large number of variables, applicant has determined that the embossing master (roller 31) preferred temperature in the process of the present invention is between about 20° F. to about 60° F. below the self-adhesive temperature of the coating 14. The self-adhesive temperature of the coating 14 is defined as the minimum temperature at which two layers of the coating (excluding any release agents added to the coating) will mutually adhere when pressed together. It has been determined that, in the context of the present process, this generally places the preferred embossing master (embossing roller 31) temperature between about 120° F. and 220° F. Of course, the invention is not limited to such temperature ranges, and can vary with different substrate and coating materials.
Once embossed, the coated sheet may be transmitted through another process which applies a metalized coating 16 to the embossed coated sheet in device 37 (
A number of experiments were conducted comparing the coated sheet of the present invention with the conventional coated sheets. In particular, two different formulations of acrylate-based polymer coatings were provided. Each such coating was provided on Dunn 605/300 base paper. The first formulation included carbon black IR absorber at 3.3% solids. The second formulation did not include any IR absorber within the acrylate-based polymer coating.
Both of the sheets were processed at 400 FPM through an embosser utilizing IR heating. The coated surface temperature of the coated sheet made in accordance with the present invention was approximately 412° F. The coated surface temperature of the conventional coated sheet was approximately 372° F. Not only was the temperature of the web increased with the use of the coated sheet of the present invention, but the quality of the embossing increased. In particular, the embossing transfer efficiency for the coated sheet of the present invention was approximately 2.6, whereas the embossing transfer efficiency of the conventional sheet was approximately 1.1. The embossing transfer efficiency scale is derived from a function that assigns a 1-to-10-scale in accordance with the effective area transferred from the master to the web surfaces. A zero would indicate no transfer and a ten would indicate complete transfer.
By relying on IR heaters, instead of gas ovens, the underlying substrate can remain cooler, while heating the coating to a desired temperature. Thus, a comparatively large temperature gradient can be created across the coated sheet. Furthermore, the time in which the substrate is exposed to heating can be minimized, thereby minimizing degradation to the substrate such as dehydration and fiber deformation. Moreover, cooling time can be reduced. The coated sheet also exhibits less curling and less trimming of waste. Furthermore the embossing cylinder and the pressing rubber nip roller exhibit longer life. Specifically, the embossing cylinder exhibits longer shim life and has less polymer transfer to the shim.
The foregoing description merely explains and illustrates the invention and the invention is not limited thereto except insofar as the appended claims are so limited, as those skilled in the art who have the disclosure before them will be able to make modifications without departing from the scope of the invention.
