Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
1999-05-06
2002-03-19
Hess, Bruce H. (Department: 1774)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C428S484100, C428S488110, C428S488410, C428S914000
Reexamination Certificate
active
06358597
ABSTRACT:
The invention relates to a thermo-transfer ribbon having a customary carrier with a wax-bonded layer of a thermo-transfer color formed on one side of the carrier and a resin-bonded separation layer arranged between the carrier and wax-bonded layer.
A thermo-transfer ribbon of the above described type is known from DE 195 48 033 A1. The wax-bonded separation layer described in same improves separation of the wax-bonded layer from the respective carrier. It is the particular goal of said teaching to exclude the necessity of forming a so-called “top coat” (adhesive layer) or a dual-layered thermo-transfer color, and to achieve satisfactory matt print-outs during the thermo-print process. This is assured in that both the wax-bonded separation layer as well as the wax-bonded layer of the thermo-transfer color contain a wax-soluble polymer in sufficiently large quantity. It is specifically preferred that the wax-bonded layer of the thermo-transfer color contains approximately 5 to 10% by weight of wax-soluble polymer.
The above described thermo-transfer ribbon is to a high degree suitable for satisfying the addressed goal. However, if the targeted goals are different, it requires improvement. This applies specifically with respect to thermo-transfer print on uncoated paper (“plain paper”), which has a comparatively high degree of roughness. The following physical properties are absolutely indispensable for good print quality and for quality products: The force of mechanical anchoring of the thermo-transfer color on the printed paper during separation in the thermo-printer—separation of ribbon from paper—must be greater than the cohesion of the thermo-transfer color itself and the adhesion of the thermo-transfer color to the substrate, i.e. less application of color, low color viscosity and low adhesion of the color vis-a-vis the separation layer (release layer) during the printing process lead to optimal print quality. Furthermore, state of the art products demonstrate that unwelcome variations in print quality occur with a “cold” and “hot” print head.
The invention is therefore based on the object of suggesting a thermo-transfer ribbon of the above-identified type, with which the earlier addressed goals are achieved with respect to improvement of the print quality, specifically with “cold” or “hot” print, specifically also on uncoated paper having a high degree of roughness.
According to the invention, said object is solved in that at least the resin-bonded separation layer A) contains a wax-soluble polymer and that the wax-bonded layer B) of the thermo-transfer color contains less than approximately 8% by weight, specifically approximately 0 to 5% by weight of wax-soluble polymer, whereby the waxes of the wax-bonded layer B) constitute narrowly cut waxes with melting- and coagulation points separated by only a narrow gap. Consequently, the wax-bonded layer B) contains no significant amounts of wax-soluble polymer, specifically approximately 0 to 1.5% by weight or even less than approximately 0.5% by weight.
In the present specialized field, the term “separation layer” or “release layer” means a layer which regulates the transfer of thermo-transfer color to the receiving substrate during the printing process, but which itself is not being transferred to the substrate. A separation layer does not melt during the printing process, but which, at most, softens and has, in addition, high adhesive property vis-a-vis the carrier.
One essential aspect with respect to solving the identified object is the use of “narrowly cut” waxes in the wax-bonded layer, in other words, melting point and coagulation point must lie close together. The temperature difference between melting point and coagulation point is in this case less than approximately 10° C., specifically less than approximately 7° C. and, most particularly preferred, less than approximately 5° C.
The waxes employed within the scope of the invention in the wax-bound layer B) of the thermo-transfer color are in line with the customary definition for wax, subject to the above limitation of restriction to narrowly cut waxes. Waxes with a melting point of approximately 75 to 90° C. are specifically employed within the scope of the invention. In the broadest sense, this involves material which is solid to brittle hard, coarse to finely crystalline, transparent to opaque, of relatively low viscosity without being stringy just slightly above the melting point. Waxes of this type are classified as natural waxes, chemically modified waxes and synthetic waxes.
Specifically preferred among the natural waxes are vegetable waxes in form of carnauba wax, candelilla wax, mineral waxes in form of higher-melting ceresin and higher-melting ozocerite (earth wax), petro-chemical waxes, such as for example petrolatum, paraffin waxes and micro-waxes. Preferred among the chemically-modified waxes are in particular montan-ester waxes, hydrated castor oil and hydrated jojoba oil. Preferred among the synthetic waxes are polyalkylene-waxes and polyethylene-glycol waxes, including products made from same via oxidation and/or esterification. Amide-waxes can likewise be utilized. To be mentioned here as particularly preferred are modified micro-crystalline waxes.
The melting point parameters to be observed for the utilized waxes according to the invention is critical. If the value falls below 70° C. that means that the mechanical anchoring is inadequate and color transfer and color resolution fail to satisfy. Higher melting points than approximately 95° C. adversely result in higher energy expenditure during the printing process.
The carnauba wax constitutes a good example for an employable wax according to the invention, with melting point at approximately 85° C. and coagulation point at approximately 78° C.
The specified waxes result in desirable low cohesion during the printing process of the thermo-transfer color. Multiple additives can be incorporated into the wax materials of the wax-bonded thermo-transfer color, such as specifically tackifiers in form of terpene phenol resins (such as, for example, the commercial products Zonatac lite 85 made by Arizona Chemical) and hydrocarbon resins (such as, for example, the commercial products KW-resin 61 B1/105 made by VFT, Frankfurt).
An adhesive layer with tackifier can be applied on layer B). In one specific embodiment, an adhesive layer is positioned on layer B), specifically a paraffin layer with a contents of finely distributed tackifying hydrocarbon resin, with the paraffin having a melting point of specifically 60 to 95° C.
Tinting can be done by any coloring substances. These may involve pigments, at a temperature of 100° C., such as specifically carbon black, but also solvent-soluble and/or binder-soluble coloring substances, like the commercial product Basoprint, organic color pigments as well as various azo dies (Cerces- and Sudan dies). Carbon black is considered as particularly suitable within the scope of the present invention. The thermo-transfer color preferably contains the coloring substance, specifically pigment, in a volume of approximately 5 to 20% by weight. The melting point of the wax-bonded thermo-transfer color lies generally between approximately 60 and 80° C.
The thermo-transfer color of the above specified layer B) of the thermo-transfer ribbon according to the invention—if applicable with the aforementioned additives—preferably has a viscosity of approximately 50 to 150 mPaos, specifically of 70 to 120 mPaos—determined at a temperature of 100° C. with a rheograph by means of rotation viscometer Rheomat 30 (Principle: rotation viscometer, see Bulletin T-304d-7605 of Messrs. Contraves AG Zuerich/Switzerland). Falling below the value of approximately 50 mPaos results in loss of sharpness (“spreading”). If the value of 250 mPaos is surpassed, deterioration with respect the desired resolution may occur.
A central characteristic of the thermo-transfer ribbon according to the invention consists in that layer A) mainly contains a wax-soluble polymer. The term “wax-soluble” in this context means
Grendzynski Michael E.
Hess Bruce H.
Pelikan Produktions AG
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