EP0955181B1 - Thermal transfer ribbon with a release layer - Google Patents

Description

The invention relates to a thermal transfer ribbon with a conventional carrier, with a wax-bonded layer of a thermal transfer ink formed on one side of the carrier and with a wax- bonded release layer located between the carrier and the wax-bonded layer, the wax-bonded layer B) of the thermal transfer ink containing a wax-soluble polymer.

Similar thermal transfer ribbons are known from the prior art. So describes DE 195 48 401 A1 a thermal transfer ribbon with a conventional carrier, a plastic-bonded layer formed on one side of the carrier Thermal transfer ink and a separating layer between the support and the layer of thermal transfer ink, the interface is wax-bound and the waxes are one Melting point of about 70 to 110 ° C and a polymeric wax plasticizer with contains a glass transition temperature Tg of -30 to + 70 ° C and the plastic-bound Thermal transfer ink contains a wax-compatible polymer. It is similar Thermal transfer ribbon of DE 196 12 393 A1 constructed, the separation layer is wax-bonded, but the layer of thermal transfer ink is at least about 20 % By weight natural resin, modified natural resin and / or synthetic resin.

The teaching of EP-A-0 826 512 relates to a thermal transfer ribbon comprising a support and a thermofusible ink layer, between which a Intermediate adhesive layer is provided, the 20 to 80 wt .-% of a polyester resin with a glass transition temperature of not more than 20 ° C and 20 to 80% by weight has at least one pigment and carbon black.

JP-A-07089253 describes a thermal transfer sheet composed of a carrier, a removable layer and a thermofusible ink layer. The removable Layer is a mixture of wax and styrene-butadiene rubber as main components, wherein the waxes used have a melting point of 60 to 90 ° C and the rubber has a glass transition temperature of -30 to + 20 ° C. The Thermal transfer ink layer contains a wax component as a binder, a dye and optionally resins such as acrylic resin, styrene-acrylic resin or other additives.

A thermal transfer ribbon of the type described above goes from DE 195 48 033 A1 forth. The wax-bound separating layer described therein serves the better Separation of the wax-bound layer of the thermal transfer ink from the respective one Carrier. A particular goal of this well-known teaching is the need for training a so-called "top coat" (adhesive layer) or a two-layer thermal transfer ink exclude and satisfactory mat during thermal printing Get printouts. This is ensured by the fact that both the wax-bound Separating layer as well as the wax-bound layer of the thermal transfer ink contain a wax-soluble polymer in a sufficiently large amount. Prefers contains the wax-bound layer of thermal transfer ink about 2 to 20 wt .-% wax-soluble polymer and the separating layer 10 to 60 wt .-%.

The thermal transfer ribbon described above is highly suitable, the one addressed Satisfying objectives. However, it is too with other objectives improve.

The so-called "inline packaging" printing process plays an increasing role, with printing speeds of 300 to 600 mms ^{-1 being} used. The thermal transfer ribbons used must meet various requirements: They should be usable on normal and high-speed printers with conventional print heads. At the same time, the thermal transfer ribbon should also show good print quality at printing speeds of up to 600 mms ^-1 . In the case of products known in the prior art which meet the aforementioned requirements, however, it is still problematic to achieve good scratch resistance on films and paper. The desired solvent resistance of these tapes is also insufficient. So far there is no product on the market that meets these requirements.

The invention was therefore based on the object of a thermal transfer ribbon at the outset to propose the type described, with which the above-mentioned objectives for improvement the print quality as well as the scratch and solvent resistance. The thermal transfer ribbon should be used in many ways and for normal and high-speed printers be equally suitable with conventional printheads.

According to the invention, this object is achieved in that the wax-bound separating layer A) contains less than 20% by weight but more than 0% by weight , in particular 3 to 8% by weight, of wax-insoluble polymer, the wax-insoluble polymer having wax-plasticizing properties and a Glass temperature Tg from -30 ° to + 70 ° C.

A separation layer or release layer is understood here to mean a layer that during the printing process, the transfer of the thermal transfer ink onto the receiving substrate controls and is itself partially transferred to the substrate.

Both in the separation layer A) and the layer B) of the thermal transfer ink are wax-bound layers.

A central feature of the thermal transfer ribbon of the invention is that is contained in the layer B) of the thermal transfer ink, a wax-soluble polymer which is an ethylene-vinyl acetate copolymer is present in a particularly preferred embodiment in shape. “Wax-soluble” is understood here to mean that this polymer shows solubility in a liquid wax. These are not necessarily "real solutions", but mostly stable dispersions. As a result, when such a solution of the polymer in wax is cooled, no phase separation occurs or this polymer is compatible with the wax.

The wax-soluble ethylene-vinyl acetate copolymer has a softening point in the range from 50 ° to 65 ° C., in particular from 60 ° C. In order to increase the adhesion between the separating layer A) and the layer B), the ethylene-vinyl acetate copolymer preferably has a vinyl acetate content of 30 to 40% by weight.

Layer B) preferably contains the ethylene-vinyl acetate copolymer in an amount of 10 to 40% by weight, in particular 12 to 20% by weight. If the value falls below 10% by weight, the scratch resistance on the packaging material is no longer guaranteed. A value of more than 40% by weight leads to insufficient resolution of the printed characters.

By using ethylene-vinyl acetate copolymers, especially with a low one Softening point in the range around 60 ° C and a vinyl acetate portion above 30 wt .-%, good mechanical anchoring and thus excellent Print quality on the used film and paper receiving materials.

The waxes used in the separating layer A) and layer B) in accordance with the invention correspond to the customary wax definition, "narrowly cut" waxes being preferred, ie the melting and solidification point of the waxes must lie closely together. In particular, waxes with a melting point of 75 to 90 ° C. are used. In the broadest sense, it is a material that is solid to brittle, hard, coarse to fine crystalline, translucent to opaque, but not glassy, melts above approx. 70 ° C, but is relatively low-viscosity and not stringy just above the melting point. Waxes of this type can be assigned to natural waxes, chemically modified waxes and synthetic waxes. Among the natural waxes, vegetable waxes in the form of carnauba wax, candelilla wax, mineral waxes in the form of higher-melting ceresin and higher-melting ozokerite (earth wax), petrochemical waxes, such as, for example, petrolatum, paraffin waxes and microwaxes, are particularly preferred. Among the chemically modified waxes, montan ester waxes, hydrogenated castor oil and hydrogenated jojoba oil are particularly preferred. Among the synthetic waxes, polyalkylene waxes and polyethylene glycol waxes and products made therefrom by oxidation and / or esterification are preferred. Amide waxes can also be used. Specifically, the following are particularly preferred: modified microcrystalline waxes.

A variety of additives can be incorporated into the wax materials of the wax-bonded thermal transfer ink, such as, in particular, tackifiers in the form of terpene phenol resins (such as the commercial products Zonatac lite 85 from Arizona Chemical) and hydrocarbon resins (such as the commercial products KW-Harz 61 B1 / 105 from VFT , Frankfurt). An adhesive layer with tackifier can be applied to layer B). In one embodiment, there is an adhesive layer on layer B), in particular a paraffin layer with a content of finely divided tackifying hydrocarbon resin, the paraffin having a melting point of in particular 60 to 95 ° C.

The coloring can be done by any colorant. It can be pigments, in particular carbon black, but also solvent and / or binder-soluble colorants, such as the commercial product Basoprint, organic color pigments and various azo dyes (Cerces and Sudan dyes). Carbon black is particularly suitable in the context of the present invention. The thermal transfer ink preferably contains the colorant, in particular pigment, in an amount of 15 to 40% by weight. The melting point of the wax-bound thermal transfer ink is preferably between 60 and 70 ° C.

The use of ethylene-vinyl acetate copolymer of about 30 wt .-% and one Soot content of about 20% by weight in layer B) can impair processing lead to high viscosity. The separation layer A) and / is preferred or layer B) is then coated with a solvent. Comes as a solvent a mixture of isopropanol and toluene, preferably in the ratio 2: 1 is used.

The application thickness of the separating layer A) and the layer B) is not critical. The separating layer A) preferably has an application thickness of 0.5 to 5 g / m ² , in particular 1.5 to 3 g / m ² , and the layer B) an application thickness of 1.0 to 5 g / m ² , in particular of 1.5 to 2.5 g / m ² .

The carrier of the ribbon according to the invention is not critical. Polyethylene terephthalate (PET) or capacitor papers are preferably used as the base film for thermal transfer ribbons. The selection parameters are the highest possible tensile elongation values and thermal stability with low film thicknesses. The PET films are available down to about 2.5 µm , capacitor paper down to about 6 µm . During the printing process, the thermal print head reaches temperatures of up to 400 ° C, ie temperatures that are above the softening point of PET. When using PET film on the back of the film that comes into contact with the thermal head, it is advisable to provide a layer that is particularly resistant to heat.

An advantageous further development of the idea according to the invention, in particular to achieve an advantageously sharp pressure, is based on the incorporation of the teaching of EP-B-0 133 638. Thereafter, a layer of a wax or a wax-like material is formed on the back of the carrier, in particular in a thickness of not more than about 1 μm and very particularly preferably in the form of a molecular layer of 0.05 to 0.10 μm thick. In this case, the coating material preferably consists of paraffin, silicone, natural waxes, in particular carnauba wax, beeswax, ozokerite and paraffin wax, synthetic waxes, in particular acid waxes, ester waxes, partially saponified ester waxes and polyethylene waxes, glycols or polyglycol, antistatic agents and / or surfactants. If such a rear coating is provided, then there is an undisturbed heat transfer from the thermal print head to the thermal transfer ribbon, with the result that particularly sharp prints are achieved. This thin layer is preferably coated with one of the solvents listed above.

The thermal transfer ribbon according to the invention described above can be varied Make way using standard application methods. For example by spraying or printing on a solution or dispersion, either with Water or an organic solvent as a dispersion or solvent, by application from the melt, which is particularly important for the wax-bound thermal transfer ink applies, or by normal application using a doctor blade in the form an aqueous suspension with finely divided material to be applied.

The following procedure has proven to be particularly advantageous from an environmental point of view: First, an aqueous suspension of the starting materials of the separating layer is applied to the support in a thin layer, which gives rise to the separating layer A) when the water is evaporated. After the formation of the separating layer A), the application of an aqueous suspension of the starting material of the wax-bound thermal transfer dye follows, the water being evaporated off in the usual manner after the application of this material. The double-layer covering formed fulfills all the requirements that lie within the scope of the task. However, the thermal transfer ink can also be applied to the separating layer in the form of a melt using customary application technologies, for example using a doctor blade. The temperature of the respective melt should generally be 100 to 130 ° C. After application, the applied materials are only allowed to cool.

Thermotransferfarbschicht B): 1 bis 10 g/m², vorzugsweise 1,5 bis 5 g/m², ganz besonders bevorzugt 1,8 bis 2,0 g/m²;

Trennschicht A) 0,5 bis 5 g/m², vorzugsweise 1,5 bis 3,0 g/m², ganz besonders bevorzugt 1,6 bis 2,8 g/m²;

Trägerfilm, insbesondere Polyethylenterephthalatfilm, einer Stärke von 2 bis 8 µm, insbesondere einer Stärke von 3,5 bis 4,5 µm, sowie

eine Rückseitenbeschichtung in einer Auftragsstärke von 0,01 bis 0,30 µm, insbesondere von 0,05 bis 0,10 µm.

Bevorzugt sind die Schicht B), die Trennschicht A) und die Rückseitenbeschichtung in einem Lösemittel aufgetragen.

For the practical or particularly advantageous implementation of the present invention, the following general conditions for the application quantities of the individual layers or their application thickness can be specified:

Thermal transfer color layer B): 1 to 10 g / m ² , preferably 1.5 to 5 g / m ² , very particularly preferably 1.8 to 2.0 g / m ² ;

Separating layer A) 0.5 to 5 g / m ² , preferably 1.5 to 3.0 g / m ² , very particularly preferably 1.6 to 2.8 g / m ² ;

Carrier film, in particular polyethylene terephthalate film, a thickness of 2 to 8 microns , in particular a thickness of 3.5 to 4.5 microns , and

a back coating in an application thickness of 0.01 to 0.30 µm , in particular from 0.05 to 0.10 µm .

Layer B), the separating layer A) and the back coating are preferably applied in a solvent.

The advantages associated with the invention can be seen in particular in the fact that the wax-soluble polymer present exclusively in layer B) , which, according to a particularly preferred embodiment, is an ethylene-vinyl acetate copolymer with a softening point in the range from 50 to 65 ° C. and in particular with a vinyl acetate content of about 30 wt .-% is, causes a high mechanical anchoring of the thermal transfer ink on the receiving material, thereby resulting in excellent print quality. At the same time, the wax-bound separating layer A), which is also transferred up to 80% during the printing process, leads to an unexpectedly high scratch resistance and additional resistance to solvents.

These advantages are achieved in particular in that the layer B has a high has mechanical anchoring on the receiving paper and at the same time up to 80% of the separation layer A is also transferred. Only in this way can the combination of the properties described above can be achieved.

The invention will be explained in more detail below with the aid of examples:

example 1

A material of the following recipe is applied to a customary carrier made of a polyester with a layer thickness of 6 μm using a doctor blade to form the wax-bound separating layer A): Carnauba wax 95 parts by weight (Melting point 83-85 ° C) Polyester resin (Tg = -4 ° C) 5 parts by weight 100 parts by weight

The above material is applied in a solvent dispersion (10%, in toluene / isopropanol 80:20) in a dry thickness of 1.0 to 2.0 µm . The solvent is evaporated by passing hot air at a temperature of 100 ° C.

The thermal transfer ink B) is then shaped using the following recipe a solvent dispersion (15% in toluene / isopropanol 30:70) with a reverse roll pressure upset.

Recipe of thermal transfer ink B): Paraffin wax 50 parts by weight Petrolite WB17® 5 parts by weight EVA 33-400 15 parts by weight filler 15 parts by weight Soot 15 parts by weight 100 parts by weight

Example 2:

Example 1 was repeated with the modification that the following recipes were used for the separation layer A) and the color layer B): Interface A): Ester wax (melting point 80-85 ° C) 72 parts by weight Paraffin HNP 20 parts by weight Polyester resin ( Dynapol® Hüls AG, D-Tg: 28 ° C) 8 parts by weight 100 parts by weight Transfer color layer B): Paraffin wax 40 parts by weight Petrolite WB 17® 12 parts by weight Zonatac lite 85 7 parts by weight EVA 33-400 14 parts by weight filler 7 parts by weight Soot 20 parts by weight 100 parts by weight

The two thermal transfer ribbons produced in Examples 1 and 2 were tested on high-speed printers and so-called "inline packaging" printers with printing speeds of 300 and 600 mms ^-1 and the printing results were evaluated. In both cases, the print quality was very good with excellent scratch and solvent resistance.

Claims (12)

1. Thermal transfer ribbon having a conventional substrate, having a wax-bonded layer of a thermal transfer ink formed on one side of the substrate, and having a wax-bonded release layer located between substrate and wax-bonded layer, the wax-bonded layer B) of the thermal transfer ink containing a wax-soluble polymer, characterized in that the wax-bonded release layer A) contains less than 20% by weight but more than 0% by weight, in particular 3 to 8% by weight, of wax-insoluble polymer, the wax-insoluble polymer having wax-plasticizing properties and. having a glass temperature Tg of -30 to +70°C.
2. Thermal transfer ribbon according to Claim 1, characterized in that the wax-soluble polymer is an ethylene-vinyl acetate copolymer with a vinyl acetate content of 30 to 40% by weight.
3. Thermal transfer ribbon according to Claim 2, characterized in that the ethylene-vinyl acetate copolymer has a softening point in the range from 50 to 65°C, in particular of 60°C.
4. Thermal transfer ribbon according to at least one of the preceding claims, characterized in that the wax-bonded layer B) of the thermal transfer ink contains 10 to 40% by weight, in particular 12 to 20% by weight, of ethylene-vinyl acetate copolymer.
5. Thermal transfer ribbon according to at least one of the preceding claims, characterized in that the wax-bonded layer B) of the thermal transfer ink, and/or the release layer A), are coated with a solvent.
6. Thermal transfer ribbon according to Claim 5, characterized in that the solvent is isopropanol and/or toluene.
7. Thermal transfer ribbon according to at least one of the preceding claims, characterized in that the release layer A) has an application thickness of 0.5 to 5 g/m², in particular 1.5 to 3 g/m².
8. Thermal transfer ribbon according to at least one of the preceding claims, characterized in that the layer B) of the thermal transfer ink has an application thickness of 1 to 5 g/m², in particular of 1.5 to 2.5 g/m².
9. Thermal transfer ribbon according to at least one of the preceding claims, characterized in that the thermal transfer ink contains a colorant, in particular a pigment, in a quantity of 15 to 40% by weight.
10. Thermal transfer ribbon according to Claim 9, characterized in that the coloured pigment is carbon black.
11. Thermal transfer ribbon according to at least one of the preceding claims, characterized in that on the rear of the substrate there is a thin layer of a wax or a wax-like material which has an application thickness of 0.01 to 0.30 µm, in particular of 0.05 to 0.10 µm.
12. Thermal transfer ribbon according to at least one of the preceding claims, characterized in that the substrate consists of polyethylene terephthalate.