EP0380920B1 - Thermal ink ribbon,method of its manufacture and its use - Google Patents

Abstract

A thermal ink ribbon, in particular a thermal carbon ribbon, having a conventional substrate and having a layer formed on one side of the substrate and consisting of wax- and/or plastics-bound fusion ink for producing scratch-resistant markings by subsequent heat treatment, which is characterised in that small non-melting, colorant-containing polymer spheres which melt in a heat treatment following the thermal printing process are present in the fusion ink during the thermal printing process. Such a thermal carbon ribbon can be produced in particular by a method in which an aqueous dispersion which contains the small polymer spheres and fine particles of the binder is applied to the substrate of the thermal carbon ribbon, and the aqueous part of the dispersion is removed in a customary manner. If, by means of the thermal carbon ribbon according to the invention, a symbol is applied to any substrate and this symbol is subjected to subsequent heat treatment which leads to melting of the small polymer spheres, the printed symbol has a different structure, with the result that the symbol is now scratch-resistant. The scratch resistance plays a role in various industrial areas, such as in labels and other recording media. <IMAGE>

Description

The invention relates to a thermal ribbon, with a carrier and a layer of a wax and / or plastic-bound melting ink formed on one side of the carrier for producing scratch-resistant, heat-stable markings by subsequent heat treatment, a particularly suitable method for producing this thermal ribbon and its special use for the production scratch-resistant, heat-stable markings.

Thermal ribbons have been known for a long time. On a film-like support, which can consist of paper, a plastic or the like, they have a melting color which contains a dye or a pigment. These are bound in a plastic or in a wax.

In this transfer material, the melting ink is melted by means of a thermal print head and transferred to a recording paper or printing paper. Thermal printers or thermal print heads that are used for this process are generally known. In particular, e.g. as follows: on the thermal print head of the printer, a letter consisting of heated dots and to be printed on a paper sheet is formed. The thermal print head presses the thermal ribbon onto the paper to be written on. The melting ink is melted in the heated areas and transferred to the paper sheet. The used part of the thermal ribbon is fed to a spool.

The thermal ink ribbon can have different melting colors next to each other. With the combination of the colors blue, yellow, red and black, color printed images can thus be produced. Thermal printers can be operated at high speed (a DIN-A-₄ sheet can be printed in about 10 seconds) and without disturbing background noises.

In addition to the thermal ribbons described above, there are also those in which the heat symbol is not generated by a thermal print head, but by resistance heating of a specially designed film-like carrier. The melting color, which is the actual "functional layer" during the printing process, also contains the materials already described above. Here one speaks of an "ETR" thermal ribbon ("Electro Thermal Ribbon"). Such thermal transfer printing systems are also generally known.

The imprints obtained with the thermal ribbons described above, for example on paper, have the disadvantage that they are not scratch-resistant. However, the scratch resistance is important in various technical areas, for example in the case of labeled tool parts that are subject to strong mechanical influences.

EP-A-0 106 663 describes a thermal printer which includes an image melting station following a thermal transfer station. At the thermal transfer station, a thermal ribbon, which contains a melting ink, is brought into contact with the sheet to be printed. A downstream heat treatment is also provided. This is intended to result in the printed image penetrating into the recording sheet in order to obtain a matt image or an image with reduced gloss.

The invention was therefore based on the object of developing the thermal ribbon mentioned at the outset in such a way that it enables the desirable scratch resistance of the symbols printed out in various technical fields.

According to the invention, this object is achieved in that the melting ink in the thermal printing process contains non-melting, colorant-containing polymer beads which can be melted in a heat treatment downstream of the thermal printing process.

The minimum constituents which are contained in the melting color of the thermal ribbon according to the invention are consequently any binder which can be melted during the printing process. This can be a wax or a wax-like material, as well as a plastic that melts at the printing temperature. For example, the following are suitable: paraffins, natural waxes, such as carnauba wax, beeswax, ozokerite and paraffin wax, synthetic waxes, such as. Synthetic waxes, ester waxes, partially saponified ester waxes, polyethylene waxes as well as polyglycols. This list is not exhaustive. In particular, ethylene / vinyl acetate copolymer, polyvinyl ether, polyethylene and hydrocarbon resin are to be stated as plastic binders which can be used instead of or in admixture with the waxes. In the practical implementation of the invention, it has proven to be advantageous if the waxes are mixed with these plastics. About 1 part by weight of plastic preferably accounts for about 2 parts by weight of wax.

Particularly advantageous results are achieved when 20 to 70% by weight of binder of the type described above is accounted for by 30 to 80 parts by weight of polymer beads.

In order to obtain particularly good results in the implementation of the present invention, it is preferred that the polymer beads have a diameter of 0.3 to 30 μm, in particular 1 to 10 μm. The type of colorant included is not essential, so it can be pigments and / or dyes according to the usual definitions. The content of colorants in the polymer beads is preferably between 10 and 30% by weight, in particular 15 to 20% by weight, a pigment, in particular carbon black, being preferred as the colorant.

The polymeric plastic of the colorant-containing polymer beads can consist of polystyrene and styrene copolymers, polyvinyl acetate, polyamide, maleic acid resins, styrene hydrocarbon resins, (meth) acrylates, polyvinyl chloride, phenolic resins, polyvinyl ethers and / or epoxy resins. An important requirement of the invention is that these materials differ in terms of melting point or softening point from the binders, which are a further component of the melting ink. This means that in the thermal printing process the polymer beads or toner particles should not melt, or should only melt insignificantly, while the part of the melting ink which creates the wax and / or plastic bond melts in the thermal printing process. This requirement is met for the plastic in the polymer beads when the melting point or the softening point is between 80 and 200 ° C., in particular 100 to 150 ° C.

It is thus shown that the polymer beads contained in the melting ink in the thermal ink ribbon according to the invention can be compared with the fusible toner particles which are used in conventional copying machines.

The thickness of the layer of the melting ink of the thermal ink ribbon according to the invention is not essential for the objective according to the invention. In practical applications, the thickness of the melting ink layer will be 3 to 20, in particular 4 to 10 μm.

The type of carrier is also not critical for the effects sought with the invention. For example, polyesters, in particular polyethylene terephthalate, polycarbonates, polyamide, polyvinyl compounds, in particular polyvinyl chloride, polyvinyl acetate, polyvinyl alcohol and polyvinyl propionate, polyethylene, polypropylene and polystyrene, are suitable for this purpose. Condenser paper is also suitable, for example. The carrier film will usually have a thickness of about 3 to 12 µm. Of course, this range can also be more or less far below or exceeded.

The type of colorant contained in the polymer beads mentioned is also not critical to achieving the object described above. It can be both inorganic and organic colorants, each in natural or synthetic form. The inorganic colorants are pigments such as carbon black, iron oxide and magnetic pigments. The organic pigments or dyes are those which are known in the toner technology mentioned, for example Nigrosine, phthalocyanine blue.

The polymer beads contained in the thermal ink ribbon according to the invention are produced in accordance with the technology which is also used in toner technology. This can be done, for example, by fusing and extruding the colorants and the plastic materials with subsequent granulation and grinding.

The production of the thermal ink ribbon according to the invention is advantageously carried out as follows: dispersion in a commercially available aqueous dispersion of the binder, in particular in the form of a mixture of a wax and one during the thermal printing process melting plastic, the colorant-containing polymer particles. The commercial dispersions used are approximately 30 to 50% by weight, in particular approximately 40% by weight. The aqueous dispersion obtained is applied to the support by customary application techniques. The application quantity (based on dry matter) is about 3 to 20 g / m² of carrier area. For example, a doctor blade can be used for the application. The job can be done at room temperature. The coated carrier is then passed through a drying tunnel in which the aqueous phase of the applied aqueous dispersion is evaporated. In addition to this application method, there is also the possibility of applying a system of meltable wax or meltable plastic / colorant-containing polymer particles in the form of a melt using customary technologies, such as, for example, using a screen printing method. However, it is important here that the melting points of the polymer beads and the binder chosen in each case are sufficiently far apart that the polymer beads themselves do not already melt in this application process.

• Fig. 1 einen Querschnitt durch das erfindungsgemäße Thermofarbband ,
• Fig. 2 einen Querschnitt durch ein Drucksystem aus Thermofarbband und Substrat nach dem Druckvorgang,
• Fig. 3 das Substrat mit aufgedrucktem Symbol nach Fig. 2 unter Bestrahlung und
• Fig. 4 das Substrat mit verschmolzenem Symbol.

If a symbol is now printed on any substrate using the thermal ink ribbon described above, then this does not initially have the desirable scratch resistance. The scratch resistance can, however, be achieved by adding further heat to this symbol, with the result that it melts in itself and forms a closed phase, the waxes or the plastics which can be melted during the thermal printing process being now partially or completely absorbed by the polymer beads. This creates a new structure for the printed symbol. These structural differences can be illustrated using the figures described below. In these figures:

• 1 shows a cross section through the thermal ribbon according to the invention,
• 2 shows a cross section through a printing system made of thermal ink ribbon and substrate after the printing process,
• Fig. 3 shows the substrate with the printed symbol of FIG. 2 under irradiation and
• Fig. 4 shows the substrate with the fused symbol.

1, a thermal ribbon 1 is shown. The 8 mm thick melting ink 3 is located on the carrier 2 made of polyethylene terephthalate and has a thickness of about 6 µm. Copolymer is located. This means that the polymer beads 4 are embedded in the binder 5 mentioned.

The thermal printing process using a conventional thermal printer produces on the substrate 7, e.g. in the form of a paper, a printed symbol 6, which further contains the binder 5 and the polymer beads 4 in the structure shown in FIG. 1. Thus, the polymer beads 4 are still embedded in the binder 5.

Is the symbol 6 printed on the paper, as shown in Fig. 2, according to Fig. 3 with e.g. an infrared heater 8 heated with sufficient heat, so to about 200 ° C, then this leads to the fact that the polymer beads melt and absorb the binder 5 more or less due to this melting process. A closed phase 9 is formed, as shown in FIG. 4.

The advantage which can be achieved with the invention is therefore to be seen in the fact that where scratch-resistant imprints such as labels and other recording media are required, these can be obtained by subjecting the imprinted symbol to a subsequent heat treatment, as a result of which a suitable structure of the imprint is obtained results. Thus, the advantage of thermal printing was used in technical areas not previously considered.

The invention will be explained in more detail below with the aid of a few examples.

example 1 (Production of the toner)

An epoxy resin (trade name: EUMPOX ^R (Schering)) with a melting point of about 120 ° C and carbon black were placed in a heat ratio of 90: 1 in a heatable extruder. The mixture was homogenized at temperatures above the melting point of the epoxy resin. The emerging strand was cut into pieces and ground in a pin mill to a grain size of about 2 to 8 microns.

Example 2 (Production of the polymer beads)

Example 1 was modified in such a way that instead of the epoxy resin with a melting point of about 120 ° C., a commercially available styrene copolymer (trade name: Radiant fusing copolymer / company: Diamond Shamrock) with a melting point of 90 ° C. was used. The weight ratio of styrene copolymer to carbon black was approximately 80:20.

Example 3 (Production of the melting ink)

30 parts by weight of the toner prepared according to Example 1 were melted together with 20 parts by weight of ethylene vinyl acetate (trade name: EVA (JCJ)) and 50 parts by weight of paraffin at 90 ° C. and mixed. The melting ink thus obtained is applied at 90 ° C. using a flexographic printing unit to a 6 μm thick polyester film in a thickness of approximately 8 μm.

Example 4 (Production of the melting ink)

30 parts by weight of the toner prepared according to Example 2 were mixed with 35 parts by weight of a 35% by weight aqueous polyvinyl acetate dispersion (trade name: Mowilith ^R DC / Hoechst) and 50 parts by weight of a 40% by weight aqueous paraffin dispersion (trade name: Vikonyl ^R GL / company: Süddeutsche Emulsions-Chemie) mixed together. The ink thus obtained was applied to an approximately 8 μm thick polyester film using a doctor knife. The water was evaporated by passing over air at about 80 ° C. The dried color layer had a thickness of about 10 microns.

The thermal ribbons produced according to Examples 3 and 4 were used in a conventional thermal printer. Label paper has been written. Then this label paper with a Infrared heater heated to around 200 ° C. The polymer beads melted together with the other particles contained in the melting ink to form a closed, uniform and scratch-resistant layer.

Claims (14)

1. A thermal ink ribbon with a carrier (2) and a layer of wax-bonded and/or plastic-bonded layer of hot-melt dye (3) on one side of the carrier (2) for the creation of scratch-proof, heat-stabile markings through subsequent heat treatment, characterised in that the hot-melt dye (3) contains small dye-containing polymer spheres (4) which do not melt during the thermal printing process but which are fusible through heat treatment following the thermal printing process.
2. A thermal ink ribbon according to Claim 1, characterised in that the polymer spheres (4) are fusible toner particles.
3. A thermal ink ribbon according to Claim 2, characterised in that the polymeric synthetic component of toner materials is polystyrene, styrene copolymers, polyvinyl acetate, polyamides, maleic acid resin, styrene hydrocarbon resin, (meth-)acrylate, polyvinylchloride, phenol resins, polyvinyl ether and/or epoxy resins.
4. A thermal ink ribbon according to at least one of Claims 1 to 3, characterised in that the binding agent (5) of the hot-melt dye (3) comprises a mixture of a hydrocarbon wax and/or ester wax with an ethylene/vinyl acetate copolymer and/or hydrocarbon resin.
5. A thermal ink ribbon according to at least one of Claims 1 to 4, characterised in that there is a ratio of 20 to 70 parts by weight of binding agent to approximately 30 to 80 parts by weight of polymer spheres (4).
6. A thermal ink ribbon according to at least one of Claims 1 to 5, characterised in that the polymer spheres (4) have a diameter of 0.3 to 30 µm.
7. A thermal ink ribbon according to Claim 6, characterised in that the polymer spheres (4) have a diameter of 1 to 10 µm.
8. A thermal ink ribbon according to at least one of Claims 1 to 7, characterised in that the polymer spheres (4) contain 10 to 30 per cent by weight of dye.
9. A thermal ink ribbon according to at least one of Claims 1 to S, characterised in that the polymer spheres (4) contain 15 to 20 per cent by weight of dye.
10. A thermal ink ribbon according to at least one of Claims 1 to 9, characterised in that the polymer spheres (4) contain a pigment as dye.
11. A thermal ink ribbon according to Claim 10, characterized in that the pigment is carbon black.
12. A thermal ink ribbon according to at least one of Claims 1 to 11, characterised in that the synthetic material in the polymer spheres (4) has a melting point of 80 to 200, especially approximately 100 to 150°C.
13. A method for the manufacture of the thermal ink ribbon according to the foregoing claims, characterised in that an aqueous dispersion is applied to the carrier (2) of the thermal ink ribbon, said aqueous dispersion containing the polymer spheres (4) and fine particles of the binding agent, and that the aqueous component of the dispersion is removed.
14. The use of the thermal ink ribbon according to at least one of Claims 1 to 12 whereby the symbols created therewith through thermal printing are subsequently melted by the application of increased heat to melt the polymer spheres (4) and to form a uniform scratch-proof phase (9).

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