CA1252629A - Heat-transferable inked ribbon - Google Patents

Abstract

Abstract of the Disclosure For the purpose of preventing a heat-transferable inked ribbon comprising a thermoplastic film foundation from being stuck to a thermal head of a printer during its operation, the back surface of the film foundation is roughened. The roughening is preferably embodied by forming a number of minute projections on the entire area of the back surface of the film foundation. The roughening produces an effect of requiring no provision of a specific sticking-preventive layer on the back surface of the foundation which is a conventional technique.

Description

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FIELD OF THE INVENTION
_ The present invention relates to a heat-transferable inked ribbon for use in formation of an image on a receiving medium such as a recording paper by melt-transferring the ink comprised in a heat-transferable ink layer of the inked ribbon by applying heat discharged from a thermal head of a printing device to the ink layer. It relates more particularly to a means of preventing the sticking of a thermoplastic film foundation of the inked ribbon to the thermal head which is brought in slidable contact with the ribbon during its operation.

BACkGROUND OF THE INVENTION
15 It is well known in the province of the printing art that a coated layer of a material which is not stuck ~o a thermal head when heated thereby (referred to as "sticking-preventive layer" hereinafter) is formed on the back surface of a thermoplastic film foundation to prevent the sticking of the film foundation to the thermal head which is brought in slidable contact with the foundation during its operation.
The above-mentioned measures, however, has the following drawbacks.
(1) The sticking-preventive layer provided on the back surface of the film foundation tends to migrate to the heat-transferable ink layer provided on the front surface of the foundation while being left wound on a core or spool, which fact results in the deterioration of the transfer capability of the heat-transferable ink layer onto a receiving medium, and consequently in an incomplete or ruined print.

(2) The sticking-preventive layer tends to stick to a guide post and so forth, which hinders the operation or run of the ribbon.
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SUMMARY OF THF INVENTION
Accordingly, it is an object of the present invention to prevent the sticking of a thermoplastic film foundation of an inked ribbon to a thermal head which is brought in slidable contact with the ribbon without providing the sticking-preventive layer on the foundation.
This and other objects of the invention will become apparent from the description hereinafter.
In accordance with the present invention, the above object is attained by roughening the back surface of the film foundation which is brought in slidable contact with a thermal head.
It is conventionally considered that the back surface of a thermoplastic film foundation which is brought in slidable contact with a thermal head should be as smooth as possible for the purpose of ensuring the conductivity of heat discharged from a thermal head. As against this accepted opinion, the present invention has discovered the fact that a roughened back surface of a thermoplastic film foundation accompanies almost no difficulty in conducting heat, and consequently providing a print of undegraded quality, and also discovered that the film foundation whose back surface is roughened becomes free of the habit of sticking to the thermal head without carrying a sticking-preventive layer.
DETAILED DE_CRIPTION
The film foundation used in the present invention is a thermoplastic film. Examples of the thermoplastic film include polyester film, polyamide film, polypropylene film and polystyrene film. The thickness of the film foundation is preferably within a range from 1 to 15 ~m~ A ribbon comprising a film foundation whose thickness is less than 1 ~m is short of mechanical strength, which results in the breakage or crinkling of the ribbon during its operation. A ribbon comprising a film foundation whose thickness is more than 15 ~m requires more heat energy for a thermal head to melt the ink to be transferred onto the receiving medium, t;~

for which reason the printing velocity must be irresistibly reduced.
It is further preferable that the roughening of the back surface of the film foundation is embodied by forming a number of uniform minute projections on the entire back surface thereof. In this embodiment, the average height, diameter and density of the projections are preferably within the ranges of 0.05 to 1 um, 0.1 to 10 ~m, and 107 to 1012 projections/m2, respectively.
It should be noted that the projections whose average height is more than 1 ~m lead to the deterioration of the heat-conductivity between the thermal head and the ribbon, while the projections whose height is less than 0.05 ~ lead to the reduction of the sticking-preventive effect of the projections.
It should be further noted that the projections whose average diameter is more than 10 ~m lead to the uneven heat-conductivity o the projections, which causes a ruined or degraded print formation, while the projections whose average diameter is less than O.l ~m lead to an unstable presence of the projections on the back surface of the film foundation.
It should be furthermore noted that the projections whose average density is out of the above-mentioned range lose the sticking-preventive effect thereof.
The formation of the minute projections can be put into practice by means of a conventional surface-roughening technique such as sand-matting method or a method of incorporating a powdered material in a film foundation.
A preferred embodiment of the heat-transferable ink layer is an ordinary heat-sensitive ink layer which can be fluidized or softened by being exposed to heat from a thermal head, the ink layer comprising a binder material mainly consisting of a heat-meltable resin and/or a wax, and a pigment and/or a dye. Another preferred embodiment of the heat-transferable ink layer is an oxdinary heat-sensitive ink layer comprising a binder material layer mainly consisting of a heat-resisting resin and a heat-sublimating ink layer containing a heat-sublimating dye being applied onto the binder material layer by way of hot-melt coating or solvent coating so as to form a coated layer of a ordinary thickness.
The above-mentioned single-use ink layer can be also replaced by an ordinary reusable heat-sensitive ink layer~
The present invention is more specifically described and explained by means of the following Examples. It is to be understood that the present invention is not limited to the Examples, and various change and modifications may be made in the invention without departing from the spirit and scope thereof.

Examples l to 7 and Comparative Examples l_to 2 Table 1 shows inked ribbons of Examples 1 to 7 according to the present invention, each of which comprised a thermoplastic film foundation whose back surface was roughened, and inked ribbons of Comparative Examples l and 2 (the foundation of the former had a silicone resin layer of l ~m thick on the smooth back surface thereof, while the foundation of the latter had an untreated smooth back surface), each of all the foundations being combined with corresponding heat-sensitive ink layer comprising heat-sensitive ink exhibiting a specific melting temperature and thickness as shown in Table,l to form an inked ribbon.

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The thus-obtained inked ribbons were subjected to a thermal transfer printing on~o a recording paper by means of a thermal transfer printer EP-20 (made by Brother Industries, Limited) wherein the thermal head was conditioned for each of the inked ribbons as shown in Table 1.
The experiment result showed that the inked ribbons of Examples 1 to 7 provided undegraded print images substantially equivalent to the counterpart provided especially by the early stage of the printing employing the inked ribbon of Compar.ative Example 1 having a heat-resisting sticking-preventive layer, and were free of sticking to the thermal head, which ensured the stable operation and run of the ribbons.
In comparison with the above, the experiment result of Comparative Example 2 wherein the inked ribbon had the untreated smooth back surface showed the sticking thereof to the thermal head which was brought in slidable contact therewith, which resulted in an unstable operation and run of the ribbon. On the other hand, the experiment result of Comparative Example 1 showed the cloging of the silicone resin on the thermal head after 50 meters run. of the ribbon, and a print image carrying a void. Throughout the experiment, the inked ribbons of Comparative Examples 1 and 2 could not continuously provide complete printed images.
In addition to the ingredients and elements used in the Examples, other ingredients can be used in the Examples as set forth in the specification to obtain substantially the~same results~

Claims (16)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A heat-transfer inked ribbon comprising:
a thermoplastic film foundation having a front surface and a back surface; and a heat-sensitive ink layer provided on the front surface;
said back surface which is brought in contact with a thermal head of a printing device during the oper-ation thereof being a uniformly rough surface of said foundation, devoid of any sticking-preventive layer and providing a good sliding contact between itself and the thermal head;
said rough surface comprising a number of min-ute projections distributed substantially uniformly on the entire area of the back surface thereof, the average height of the projections being from 0.05 to 1 µm, the average diameter of the projections being from 0.1 to 10 µm, and the average density of the projections being from 107 to 1012 projections/m2.

2. An inked ribbon as recited in claim 1, in which the thermoplastic film foundation is a film of a thermoplastic resin selected from the group consisting of polyester, polyamide, polypropylene and polyethylene, and has a thickness of 1 to 15 µm.

3. An inked ribbon as recited in claim 2, in which the back surface of the film foundation is made rough by means of a sandmatting method.

4. An inked ribbon as recited in claim 2, in which the back surface of the film foundation is made rough by incorporating a powdered material in the film foundation.

5. An inked ribbon as recited in claim 1, in which the heat-sensitive ink layer comprises a binder material comprising at least one of a heat-meltable resin and a wax, and a coloring agent comprising at least one of a pigment and a dye.

6. An inked ribbon as recited in claim 5, in which the heat-sensitive ink layer is capable of releas-ing ink thereof once.

7. An inked ribbon as recited in claim 5, in which the heat-sensitive ink layer is capable of releas-ing ink thereof a plurality of times.

8. An inked ribbon as recited in claim 1, in which the heat-sensitive ink layer comprises a binder material layer comprising a heat-resisting resin, and a heat-sublimatable ink layer coated thereon.

9. An inked ribbon as recited in claim 8, in which the heat-sensitive ink layer is capable of releas-ing ink thereof once.

10. An inked ribbon as recited in claim 8, in which the heat-sensitive ink layer is capable of releas-ing ink thereof a plurality of times.

11. An inked ribbon as recited in claim 2, in which the heat-sensitive ink layer comprises a binder material comprising at least one of a heat-meltable resin and a wax, and a coloring agent comprising at least one of a pigment and a dye.

12. An inked ribbon as recited in claim 11, in which the heat-sensitive ink layer is capable of releas-ing ink thereof once.

13. An inked ribbon as recited in claim 11, in which the heat-sensitive ink layer is capable of releas-ing ink thereof a plurality of times.

14. An inked ribbon as recited in claim 2, in which the heat-sensitive ink layer comprises a binder material layer comprising a heat-resisting resin, and a heat-sublimatable ink layer coated thereon.

15. An inked ribbon as recited in claim 14, in which the heat-sensitive ink layer is capable of releas-ing ink thereof once.

16. An inked ribbon as recited in claim 14, in which the heat-sensitive ink layer is capable of releas-ing ink thereof a plurality of times.