Incremental printing of symbolic information – Thermal marking apparatus or processes
Reexamination Certificate
1999-10-15
2001-05-08
Tran, Huan (Department: 2861)
Incremental printing of symbolic information
Thermal marking apparatus or processes
C347S218000
Reexamination Certificate
active
06229556
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a printer and a method for using the printer for printing an image on a thermoplastic medium. More particularly, the present invention relates to a printer having a thermal head or thermal imaging means and method of using the printer to form an image on a thermoplastic foam, the image being comprised of a relief image of open cells and a background image of closed cells.
BACKGROUND OF THE INVENTION
A number of traditional ways exist for forming images on a printing plate. These include, but are not limited to, molding, photoflash imaging, and thermal imaging. The present invention is directed broadly to the area of thermal imaging or thermography. Thermal imaging or thermography is a process wherein an image is generated by the use of image-wise modulated thermal energy. Traditionally, “direct thermography” refers to a method whereby a visible image pattern is formed by the image-wise heating of a recording material containing matter that by chemical or physical process changes color or optical density. Most of the direct thermographic recording materials are of a chemical type. Upon heating the recording material to a certain conversion temperature, an irreversible chemical reaction takes place and a colored image is produced.
In recent years, the field of manufacturing or producing printing plates (e.g., rubber stamps) has experienced rapid advancement. Resinous relief printing plates, planographic printing plates, and intaglio printing plates all formed using photosensitive resins now enjoy widespread use. In addition, a number of methods are known for forming printing plates using stencil images. These methods generally involve the use of a thermal printer or a wire dot printer to form a stencil image on a sheet, which is then utilized as a printing plate.
As the use of relatively simple printing systems has expanded, the need for a simple, yet reliable, method of printing a printing plate has come into existence. In an attempt to address this need, U.S. Pat. No. 5,665,524 (which is hereby incorporated herein in its entirety by reference) describes a printing plate which is formed from an open celled thermoplastic medium wherein the open cells are sealed upon exposure to energy rays. The methods described in this reference generally require the presence of a negative to block photorays which results in a portion of the photosensitive thermoplastic medium remaining unhardened by the blocking of the energy rays, and a separate portion which is hardened by exposure to the energy rays. The exposed portion forms a background of the image to be formed on the stamp. The background portion prevents the transfer of ink from the thermoplastic foam to the receiving medium (i.e., paper) in these regions. It is speculated in U.S. Pat. No. 5,665,524 that an expensive laser system may be driven to seal predetermined portions of the foam to form the background image. This reference also places a great deal of emphasis on forming the open-cell image in the same plane as the background image by sealing only a surface layer of open cells, thereby forming a plate having little or no relief.
SUMMARY OF THE INVENTION
One embodiment of the present invention is directed to a printer for printing on a thermoplastic medium, wherein the printer is generally comprised of a housing or frame which functions as a support structure for the mechanical pieces of the printer. The printer includes a thermal head or thermal printing means which is generally attached to the frame and which functions as a source of thermal energy to be placed in contact with selected portions of the thermoplastic medium. The term “contact” or “direct thermal contact” as defined herein with regard to the formation of an image on a thermoplastic medium is very similar to “direct thermography” as known in the related art, except that the recording material is an open-celled thermoplastic material and the chemical or physical change is the closing or sealing of the open-cells to form a background image. When the thermal head is placed in “direct” contact with the thermoplastic medium, the thermal head heats and melts selected portions of the thermoplastic medium. “Direct thermal contact” does not mean that the thermal head or the thermal imaging means must be in physical contact with the thermoplastic medium but rather the thermal energy generated must be in sufficient contact with the thermoplastic material so as to cause a physical change (e.g., melting) of the thermoplastic medium.
The heated or melted portions of the thermoplastic medium are sealed (that is the open cells of the thermoplastic medium are closed), which results in the formation of a background image or non-image on the thermoplastic medium. The sealed or closed portions are substantially impermeable to the printing fluid (ink). Although the printer is described in specific detail and with reference to specific embodiments herein, it is to be understood that the present invention should not be so limited and can be incorporated into a large number of different embodiments with each of them sharing the contact of a thermal energy on thermoplastic foam, whereby a relief is formed on the thermoplastic foam.
In the present invention, it is preferable, although certainly not requisite, to utilize a thermoplastic material which contains an ink constituent at a predetermined concentration. The thermoplastic resin sheet is preferably open-celled. “Open-celled” refers to a continuous cell structure where the cells communicate directly or indirectly with other cells in the thermoplastic resin sheet, whereby liquid can pass from cell to cell. “Open-cell” may be used herein to interchangeably refer to the characteristic of the thermoplastic medium and to the fact that the cells of the thermoplastic medium have interstitial spaces which may be filled with an ink constituent. “Open-celled” refers to microporous and porous structures within the thermoplastic medium which are sufficiently sized to store and/or transfer ink and which communicate either directly or indirectly with each other and therefore which may function to transfer ink to the material to be printed on. “Closing”, “solidification”, “melting”, “sealing”, “thermalizing” or “hardening” of the surface of the thermoplastic medium are all terms that may be used herein to refer to the substantial elimination of open cells in a specific area which renders that portion of the thermoplastic medium impermeable to an ink constituent. Generally, the thermoplastic medium is a flat sheet having a predetermined length, width, thickness and density.
When mounted in a hand stamper, the thermoplastic medium effuses ink when pressure is applied. Eliminating the necessity of inking the printing plate after the image is formed is one advantage of the present invention. Another advantage is the fact that a large number of oddly shaped stamps can be formed, which based on the layout/template formed reduces the mess normally present when using such ink pads. Additionally, by inking at the desirable saturation levels of the thermoplastic material, the pre-inked thermoplastic material can be used in standard thermal head printers without concern for unwanted effusion of the ink out of the foam during the processing of the thermoplastic material. To further prevent undesirable effusion of ink onto the printer a thermal transfer ribbon, for example, available from Markem TTR, Part No. 81716002135 MJ, 716 Black 00, Lot No. 5980A6, 135MMX300M, may be used between the thermoplastic foam and the printer head or thermal head. Even minimally pre-inking the thermoplastic material allows for better “wicking” of the ink. This condition improves the capillary action of the thermoplastic material. As a result, if the printing plate or thermoplastic material is more fully inked after the image is formed, the capillary action is much faster and thus the absorption of the ink occurs in a much more timely manner.
Disclosed herein is a printer capable of and specifically designed for print
Identity Group, Inc.
Reed Smith LLP
Tran Huan
LandOfFree
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