Thermo-transfer ribbon

Details Thermo-transfer ribbon Thermo-transfer ribbon

1999-05-06

2001-09-18

Hess, Bruce H. (Department: 1774)

Stock material or miscellaneous articles

Structurally defined web or sheet

Discontinuous or differential coating, impregnation or bond

C428S488410, C428S913000, C428S914000

Reexamination Certificate

active

06291055

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 wax-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 serves for improved 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 achieved by both the wax-bonded separation layer as well as the wax-bonded layer of the thermo-transfer color containing a wax-soluble polymer in sufficiently large quantity. The wax-bonded layer of the thermo-transfer color preferably contains approximately 2 to 20% by weight of wax-soluble polymer and the separation layer 10 to 60% by weight.
The above described thermo-transfer ribbon is highly suited to meet the stated goal. However, if the goals are different, it requires improvement. An increasingly greater role is played by the so-called “inline packaging” print process, in which printing speeds from 300 to 600 mm/sec are employed. The utilized thermo-transfer ribbons must satisfy different requirements in such process: they must be deployable on standard and high-speed printers with conventionally employed print heads. Concurrently, the thermo-transfer ribbon shall present excellent print quality even with printing speeds of up to 600 mm/sec.
With respect to the known state of the art products which satisfy these mentioned prerequisites, there still remains the problem of obtaining good scratch resistance. The desired solvent resistance of these ribbons is also inadequate. There is no product on the market as yet which satisfies these requirements.
Therefore, it is an object of the invention to propose a thermo-transfer ribbon of the initially identified type whereby the above addressed goals can be achieved relative to improvement of print quality and also with respect to scratch and solvent resistance. The thermo-transfer ribbon shall have multiple applications and be equally suitable for standard and high speed printers having conventional print heads.
According to the invention, the object is achieved in that the wax-bonded layer B) of the thermo-transfer ribbon contains a wax-soluble polymer and that the wax-bonded separation layer A) contains less that approximately 20% by weight, specifically 3 to approximately 8% by weight, of wax-insoluble polymer, whereby the wax-insoluble polymer possesses wax-plastifiable properties and has a glass temperature Tg of −30° to +70° C.
A separation layer or release layer in this context means a layer which regulates the transfer of the thermo-transfer color to the receiving substrate during the printing process and which is itself partially transferred to the substrate.
The separation layer A) and also layer B) of the thermo-transfer ribbon are wax-bonded layers.
A central characteristic of the thermo-transfer ribbon according to the invention consists in that layer B) of the thermo-transfer color contains a wax-soluble polymer in the form of an ethylene-vinylacetate-copolymer. The term “wax-soluble” in this context means that this polymer is soluble in liquid wax. This does not necessarily involve “genuine solutions” but mostly stable dispersions. The result is that during the cooling of such polymer solution in wax there will be no phase separation or that said polymer is compatible with the wax.
The wax-soluble ethylene-vinyl-acetate-copolymer has a softening point in the range of approximately 50° to 65° C., specifically 60° C. In order to increase the adhesion between the separation layer A) and the layer B), the ethylene-vinylacetate-copolymer preferably has a vinyl-acetate content of approximately 30 to 40% by weight.
Layer B) contains ethylene-vinylacetate-copolymer, preferably in volume of approximately 10 to 40% by weight, specifically of approximately 12 to 20% by weight. If the value falls below 10% by weight, the scratch resistance on the packing material is no longer assured. A value in excess of 40% by weight leads to inadequate dissolution of printed symbols.
By using an ethylene-vinylacetate-copolymer, specifically with a low softening point in the range of approximately 60° C. and a vinylacetate percentage of more than 30% by weight, good mechanical anchoring is obtained and thus excellent print quality on the employed foil- and paper acceptance materials.
The waxes employed in the separation layer A) and layer B) within the scope of the invention agree with the customary definition for wax, whereby “narrowly cut” waxes are preferred, in other words melting- and coagulation point of the waxes must lie close together. In particular, waxes are employed having a melting point of approximately 75 to 90° C. In the broadest sense this involves material which is solid to brittle hard, coarse to finely crystalline, transparent to opaque, but which is not glass-like, which melts above approximately 70° C., but which is, however, only slightly above the melting point of relatively low viscosity without being stringy. 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), petrochemical 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.
Multiple additives can be incorporated in 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-r 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, 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 receives the coloring substance, specifically pigment, in a volume of approximately 15 to 40% by weight. The melting point of the wax-bonded thermo-transfer color lies preferably between approximately 60 and 70° C.
The use of ethylene-vinyl-co-polymer in volume of approximately 30% by weight and a carbon black percentage of approximately 20% by weight in layer B) may result in high viscosity which detrimentally affects the processing. The separation layer A) and/or the layer B) is then coated with a solvent. A mixture of isopropanol and toluol, which is preferably employed at a ratio of 2:1, is suitable for this step. The application thickness of the separation layer A) and of layer B) is not critical. The separation layer A) preferably has an application thickness of approximately 0.5 to 5 g/m
2
, specifically approximately 1.5 to 3 g/m
2
, and l

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