Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
1998-08-28
2001-01-09
Schwartz, Pamela R. (Department: 1774)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S206000, C428S207000, C428S484100, C428S488110, C428S488410, C428S913000, C428S914000
Reexamination Certificate
active
06171690
ABSTRACT:
FIELD OF THE INVENTION
This invention pertains to thermal transfer ribbons derived from wax dispersions and emulsions. Such ribbons find use in thermal transfer printing wherein images are formed on a receiving substrate by selectively transferring portions of a thermal transfer layer of a print ribbon to a receiving substrate by heating extremely precise areas thereof with thin film resistors within the print head of a thermal transfer printer. More particularly, the present invention relates to thermal transfer ribbons with thermal transfer layers with a high density of non-melting (hard) particles which transfer rapidly to a receiving substrate and preferably are suitable for use in high speed thermal transfer printers.
BACKGROUND OF THE INVENTION
Thermal transfer printing is widely used in special applications such as in the printing of machine-readable bar codes on labels or directly on articles to be coded. The thermal transfer process employed by these printing methods provides great flexibility in generating images and allows for broad variations in style, size and color of the printed images, typically from a single machine with a single thermal print head. Representative documentation in the area of thermal transfer printing includes the following patents:
U.S. Pat. No. 3,663,278, issued to J. H. Blose et al. on May 16, 1972, discloses a thermal transfer medium having a coating composition of cellulosic polymer, thermoplastic resin, plasticizer and a “sensible” material such as a dye or pigment.
U.S. Pat. No. 4,315,643, issued to Y. Tokunaga et al. on Feb. 16, 1982, discloses a thermal transfer element comprising a foundation, a color developing layer and a hot melt ink layer. The ink layer includes heat conductive material and a solid wax as a binder material.
U.S. Pat. No. 4,403,224, issued to R. C. Winowski on Sep. 6, 1983, discloses a surface recording layer comprising a resin binder, a pigment dispersed in the binder, and a smudge inhibitor incorporated into and dispersed throughout the surface recording layer, or applied to the surface recording layer as a separate coating.
U.S. Pat. No. 4,463,034, issued to Y. Tokunaga et al. on Jul. 31, 1984, discloses a heat-sensitive magnetic transfer element having a hot melt or a solvent coating.
U.S. Pat. No. 4,523,207, issued to M. W. Lewis et al. on Jun. 11, 1985, discloses a multiple copy thermal record sheet which uses crystal violet lactone and a phenolic resin.
U.S. Pat. No. 4,628,000, issued to S. G. Talvalkar et al. on Dec. 9, 1986, discloses a thermal transfer formulation that includes an adhesive-plasticizer or sucrose benzoate transfer agent and a coloring material or pigment.
U.S. Pat. No. 4,687,701, issued to K. Knirsch et al. on Aug. 18, 1987, discloses a heat sensitive inked element using a blend of thermoplastic resins and waxes.
U.S. Pat. No. 4,698,268, issued to S. Ueyama on Oct. 6, 1987, discloses a heat resistant substrate and a heat-sensitive transferring ink layer. An overcoat layer may be formed on the ink layer.
U.S. Pat. No. 4,707,395, issued to S. Ueyama, et al., on Nov. 17, 1987, discloses a substrate, a heat-sensitive releasing layer, a coloring agent layer, and a heat-sensitive cohesive layer.
U.S. Pat. No. 4,777,079, issued to M. Nagamoto et al. on Oct. 11, 1988, discloses an image transfer type thermosensitive recording medium using thermosoftening resins and a coloring agent.
U.S. Pat. No. 4,778,729, issued to A. Mitsubishi on Oct. 18, 1988, discloses a heat transfer sheet comprising a hot melt ink layer on one surface of a film and a filling layer laminated on the ink layer.
U.S. Pat. No. 4,869,941, issued to Ohki on Sep. 26, 1989, discloses an imaged substrate with a protective layer laminated on the imaged surface.
U.S. Pat. No. 4,923,749, issued to Talvalkar on May 8, 1990, discloses a thermal transfer ribbon which comprises two layers, a thermal sensitive layer and a protective layer, both of which are water based.
U.S. Pat. No. 4,975,332, issued to Shini et al. on Dec. 4, 1990, discloses a recording medium for transfer printing comprising a base film, an adhesiveness improving layer, an electrically resistant layer and a heat sensitive transfer ink layer.
U.S. Pat. No. 4,983,446, issued to Taniguchi et al. on Jan. 8, 1991, describes a thermal image transfer recording medium which comprises as a main component, a saturated linear polyester resin.
U.S. Pat. No. 4,988,563, issued to Wehr on Jan. 29, 1991, discloses a thermal transfer ribbon having a thermal sensitive coating and a protective coating. The protective coating is a wax-copolymer mixture which reduces ribbon offset.
U.S. Pat. Nos. 5,128,308 and 5,248,652, issued to Talvalkar, each disclose a thermal transfer ribbon having a reactive dye which generates color when exposed to heat from a thermal transfer printer.
And, U.S. Pat. No. 5,240,781, issued to Obatta et al., discloses an ink ribbon for thermal transfer printers having a thermal transfer layer comprising a wax-like substance as a main component and a thermoplastic adhesive layer having a film forming property.
High speed thermal transfer printers such as “near edge,” “true edge,” “corner edge” and “Fethr®” printers have been developed, wherein the thin film resistors are positioned right at the edge of the thermal print head, allowing rapid separation of the donor film from the receiving substrate after the thin film resistors are fired.
Conventional general purpose ribbons often cannot meet the requirements of high speed printers since the ribbon and receiving substrate are separated almost instantaneously after the thin film resistors are fired. There is little time for waxes and/or resins to melt/soften and flow onto the surface of the receiving substrate before the ribbon is separated from the receiving substrate. In conventional ribbons, the adhesion of the melted/softened material to the receiving substrate is typically lower than its adhesion to the supporting substrate of the ribbon at the time of separation with a high speed printer. As a result, the functioning thermal transfer layer is usually split and the transfer incomplete, resulting in light printed images where the functional layer is an ink layer.
One approach to this problem has been to increase the speed of transfer of a functional layer to match the capability of high speed printers by using binder components (waxes and resins) having a low melt temperature A problem with this approach is that the environmental stability of such ribbons decreases and the integrity of the print decreases. For example, as the melting point of the wax used to produce the ribbon decreases, the ribbon has a tendency to “block” wherein the coating transfers to the backside of the ribbon when wound onto itself. This blocking phenomenon tends to occur when the ribbon is subjected to temperatures in the range of 45° to 55° C. and above and when the ribbon is wound onto itself coating side in.
Another approach is to increase the concentration of carbon black to enhance the print density of the image formed. This approach has limitations in that the melt viscosity of the thermal transfer layer increases with the increase in concentration of the non-melting carbon black particles, making transfer more difficult. Reducing the concentration of carbon black within the thermal transfer layer to enhance transfer is counter productive in that light images will still be produced due to the reduction in the print density of the image formed.
It is generally desirable to use carbon black pigments and other non-melting solid components of the thermal transfer media ground to a fine size to simplify dispersion and enhance resolution. One exception is the ribbon of Micke et al., U.S. Pat. No. 5,132,139, which is a thermal printing ribbon with multistrike capacity wherein large size solid particles are employed in a thick thermal transfer layer between 10 and 20 microns (see columns 7, line 21).
SUMMARY OF THE INVENTION
It is an objective of the present invention to provide thermal transfer media such as thermal transfer ribbons which pro
Millen White Zelano & Branigan PC
NCR Corporation
Schwartz Pamela R.
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