EP0955182B1 - Thermal transfer ribbon - Google Patents

Description

The invention relates to a thermal transfer ribbon with a support, with one on one Side of the carrier trained thermal transfer ink and optionally with other Layers, the thermal transfer color in addition to a colorant an amorphous Contains polymer and a wax.

A thermal transfer ribbon of the type described above goes from DE 36 13 846 out. The thermal transfer ink of this known thermal transfer ribbon contains a amorphous polymer which has a weight average molecular weight Mw of no more than 10,000, a number average molecular weight Mn of less than 5,000 and one Glass transition temperature of 50 to 80 ° C has. The amorphous polymer does at least 50% by weight of the thermal transfer ink, based on its solids content, out. This thermal transfer ribbon is intended to provide clear color reproduction when printing enable and in terms of resolution, sensitivity, Transfer and fixation properties should be satisfactory. These goals will be thereby achieved by the binder for the thermal transfer ink in which it is conventionally deals with crystalline wax-based binders by an im essential amorphous, transparent polymer is replaced. To favor the effects are aimed at a small amount of a "release agent" in the Thermal transfer color incorporated, which improves the image quality and especially the Resolution is increased. An excellent fixation should be achieved the flexibility and abrasion resistance inherent in polymers is exploited. Achieving scratch-resistant prints on which, among other things, the following above described invention is not expressly addressed here.

In particular, the issue of achieving scratch-resistant prints is dealt with EP-B-0 380 920 and DE 196 12 393 A1: EP-B-0 380 920 recommends for Achieving scratch-resistant prints that in the thermal transfer ink during printing non-melting, colorant-containing polymer spheres are included, which in a the heat treatment downstream of the printing process are fusible. The after symbols immediately obtained during the printing process do not initially show the desirable scratch resistance. This is achieved by adding further symbols Heat is supplied. This creates a new structure of the printed Symbol. This proposal is disadvantageous in that it follows the actual one Printing process requires a second heat treatment step.

DE 196 12 393 A1 provides a certain remedy here. It strikes Thermal transfer ribbon with a conventional carrier, with one on one side of the carrier trained layer of a thermal transfer ink and a separating layer between Carrier and layer of thermal transfer ink before. The interface is wax-bound and contains waxes with a melting point of about 70 to 110 ° C and one polymeric wax plasticizer with a glass transition temperature Tg of -30 to + 70 ° C. The Thermal transfer ink layer further contains at least about 20% by weight Natural resin, modified natural resin and / or synthetic resin. With this A thermal transfer ribbon is proposed, the transferred one Thermal transfer ink when printing on paper labels in particular has good adhesion as well as good abrasion and scratch resistance, and when printing quickly and is delivered precisely with the underlying separation or release layer. The disadvantage, however, is the fact that with a certain effort described separation layer is to be formed, which is at least one three-tier system.

Starting from the prior art described above, the present invention the object of the above Develop thermal transfer ribbon so that no separation layer is required, and nevertheless that in connection with the description of the subject of DE 196 12 393 A1 achieved advantages can be achieved. A good abrasion and scratch resistance of the Printing on labels, especially plastic labels, especially here Barcode labels are important, should be increased. Beyond that too sufficient solvent resistance is provided.

According to the invention this object is achieved in that the thermal transfer ink as Binder is a polar polyethylene wax and an amorphous polymer that is a Weight average molecular weight Mw greater than about 10,000 and a number average of Has molecular weight Mn of less than about 6,000.

This proposed solution means that the thermal transfer color of the thermal transfer ribbon contains an amorphous polymer as an essential binder component, in particular of at least about 50% by weight, based on the dry matter content of the Thermal transfer ink. If one speaks of an "amorphous" polymer, then so this is supposed to mean that its structural characteristics appearing below radiographic aspects can be described as amorphous. As a result, Under the term "amorphous polymer", such oligomers and / or Polymers fall that contain certain partially crystalline components, for example up to about 30% by weight, especially up to about 10% by weight. Contrary to the trend-setting According to DE 36 13 846 C2, the invention uses an amorphous polymer which has a weight average molecular weight Mw greater than about 10,000. This is surprising. The explanation that the weight average molecular weight Mw is more than is about 10,000, probably explained by the fact that an additional and mandatory polar polyethylene wax must be present. If the Mw value of Below 10,000, which would be in accordance with DE 36 13 846 C2, then there is the disadvantageous effect that the adhesion of the thermal transfer ink to Carrier film is too high and there is no homogeneous color transfer during printing is guaranteed.

It is particularly advantageous if the amorphous polymer is a weight average Molar mass Mw from 10,000 to about 15,000 and a number average molar mass Mn less than about 5,000, especially about 2,000 to 3,000. As preferred quantitative framework for the ratio of polar Polyethylene wax and amorphous polymer can be specified to 1 part by weight polar polyethylene wax about 3 to 5 parts by weight, in particular about 4 parts by weight, no amorphous polymer.

If the amorphous polymer content is less than about 50% by weight, then this can lead to the desirable transparency of the thermal transfer ink and thus the color reproducibility is impaired. So in general it is preferred if the amorphous polymer content is more than about 50% by weight, in particular more than about 70 wt .-%, but the maximum is about 80 wt .-% could be specified to still have a sufficient amount of polar polyethylene wax. As part of the above quantitative framework, it is not excluded that additional Binding agents are present in small amounts in the thermal transfer ink, so in Thermal transfer ribbons usually used waxes, for example Paraffin wax, caranauba wax, montan wax, beeswax, japan wax, Candelilla wax as well as materials used as plastic binders, such as polyolefins with an average molecular weight of about 1,000 to 10,000, for example low molecular weight polyethylene, polypropylene or polybutylene and the same. In individual cases it can also be advantageous to use other common ones Include additives that improve the properties of the tape. Here will the specialist within the framework of craft considerations, the one with which he wants to set a desired effect.

Examples of usable amorphous polymers include homo- and copolymers, styrene or their derivatives or substituted compounds thereof (e.g. styrene; Vinyl, toluene), acrylic acid esters, for example methyl acrylate, ethylene acrylate and butyl acrylate copolymers, especially polyester resins, by polycondensation saturated dibasic acid are available (for example phthalic acid, Phthalic anhydride), polycarbonates, polyamides, epoxy resins, polyurethanes, silicone resins, Phenolic resins, terpene resins, petroleum resins, hydrogenated petroleum resins, alkyd resins and Cellulose derivatives.

An amorphous polyester resin with an MFI value (105 ° C / 2.16 kg) is preferred from about 1.3 to 2.3, especially from about 1.5 to 2.0 g / min and a glass transition temperature Tg of about 45 to 65 ° C, especially about 52 to 56 ° C, used.

An amorphous polyester resin that meets these framework conditions and in particular is advantageously used is a polyester resin based on bisphenol A, such as the commercial product Setafix P 120 (distributed by Akzo Noble Resins B.V., Netherlands), which is characterized by the following characteristics: MFI value (105 ° C / 2.16 kg) of about 1.5 to 2.0 g / min, glass transition temperature Tg of 52 up to 56 ° C and acid number from 14 to 24 mg KOH / g, Mn value about 2,500 and Mw value about 12,000. A polyester resin of the trade name is also suitable Atlac T 500 (sold by ICI Specialty Chemicals, Great Britain). in this connection is a linear, unsaturated polyester resin that was originally used for Manufacture of dry toners is used. The following information applies to this: MFI value 105 ° C / 2.16 kg, 8 to 20 g / 10 min (according to ASTM D.12348-70), Softening point from 94 to 106 ° C (according to ASTM E 28-67), acid number from 10 to 15 mg KOH / g (ISO 2114), glass transition temperature from 47 to 53 ° C (D.S.C.), Mn value of 3,500 and Mw value of 14,000 (measured by the GPC method).

Another important binder component is the polar polyethylene wax mentioned. Such waxes are obtained either by oxidation of polyethylene wax or by oxidative degradation of plastic-like polyethylene. This creates a range of polar, emulsifiable polyethylene waxes. The so-called Hoechst waxes PED and the type designations 521 and 522 are particularly suitable. These belong to the series of more flexible emulsifiable polyethylene waxes, the melting point of which allows emulsification in an open vessel. A preferred dropping point of about 100 to 110 ° C, in particular about 102 to 108 ° C and very particularly preferably of about 102 to 106 ° C, measured according to DIN 51 801, is the preferred framework for the polar polyethylene waxes polar polyethylene wax, the following sizes are given: ball indentation hardness according to the test method DGF-M III-90 (57) of approx. 1 to 3 · 10 ⁷ Pa (100 to 300 bar), a flow hardness of approx. 1 to 3 · 10 ^-7 Pa (100 up to 300 bar) and a viscosity, measured according to DIN 51 550 at a temperature of about 120 ° C, of about 50 to 700 mPas, in particular from about 100 to 500 mPas.

According to the invention, the coloring of the thermal transfer color can be done by any Colorants are made. It can be pigments, especially soot, but also to solvent and / or binder-soluble colorants, such as the commercial product Basoprint, organic color pigments and various acco colorants (Cerces and Sudan dyes) act. Soot is considered in the context of the present invention particularly suitable. The thermal transfer ink preferably contains the colorant, in particular color pigment, in an amount of about 20 to 40 wt .-%.

The viscosity of the thermal transfer ink must be sufficiently low for the ink can be delivered quickly and precisely. Therefore, the thermal transfer color shows preferably a viscosity of about 500 to 3,000 mPas, measured with a Brookfield rotational viscometer at 140 ° C. In particular, the range of 600 to 1,500 mPas aimed for.

The thickness of the thermal transfer ink or the ink layer is not critical. A thickness of approximately 1 to 5 g / m ² application, in particular approximately 1 to 3 g / m ² application, is preferred on the carrier. The type of carrier is also not critical here. It is preferably a film made of polyethylene terephthalate (PET) or a capacitor paper. The selection parameters are the highest possible tensile elongation values and thermal stability with small film thicknesses, for example in the range of approximately 1 to 6 μm. The PET films are available up to about 2.5 µm, capacitor paper up to about 6 µm.

An advantageous further development of the idea according to the invention, in particular to achieve an advantageous pressure, is based on the inclusion of the teaching of EP-B-0 133 638. Thereafter, a thin layer of a wax or wax-like material, preferably an application thickness, is formed on the back of the carrier from about 0.01 to 1 g / m ² , in particular from about 0.05 to 0.10 g / m ² . This back coating material preferably consists of paraffin, silicone, natural waxes, in particular carnauba wax, beeswax, ozocerite and paraffin wax or synthetic waxes, in particular acid waxes, ester waxes, partially saponified ester waxes and polyethylene waxes, glycols or polyglycols and / or surfactants.

For the practical implementation of the present invention, the following general conditions can be specified with regard to the application amounts of the individual layers: On a carrier film, in particular a carrier made of polyethylene terephthalate, the thickness of approximately 2 to 8 μm, in particular a thickness of approximately 4 to 5 μm, entirely the following are particularly preferably applied with a thickness of about 3.5 to 4.5 μm: the thermal transfer color layer in an amount of about 1 to 5 g / m ² , preferably about 1 to 3 g / m ² . The range of 1.4 to 2.0 g / m ² , in particular approximately 1.6 to 1.8 g / m ² , is very particularly preferred for the strength of the thermal transfer ink. Furthermore, the above-mentioned backside coating is optionally applied on the back in a thickness of about 0.01 to 1 g / m ² , in particular about 0.05 to 0.10 g / m ² . These layers can be formed in a variety of ways using customary application methods. This can be done, for example, by spraying or printing on a solution or dispersion, be it with water or an organic solvent, by application from the melt, which is particularly true for the thermal transfer layer, or by application by means of a doctor blade in the form of an aqueous suspension with finely divided therein material to be applied. Coating methods such as reverse roll and / or gravure coating have proven to be particularly advantageous for applying the thermal transfer layer.

The particular advantages associated with the invention can be as follows represent: The invention surprisingly requires compared to DE 196 12 393 A1 no additional separating layer and comes with a total of two layers from, advantageously a back coating for the reasons mentioned is provided. It will not only be scratch-resistant but also achieved solvent-resistant prints on plastic labels, especially in Connection with so-called barcode labels. Against the trend-setting Information from DE 36 13 846 C2 uses the present invention amorphous Polymers with an Mw of more than 10,000. This feature in conjunction with The polar polyethylene wax used according to the invention has a functional effect Working together in such a way that the essential properties of a such a tape must not be impaired, but that in printing transferred thermal transfer ink a good one, especially on plastic labels Adhesion and good abrasion and scratch resistance shows and quickly and precisely is transmitted. These advantages are particularly evident with plastic labels, such as. made of polyethylene, polypropylene, vinyl chloride, for coated PET films and glossy papers. In doing so, these favorable results are in the upper energy level of the thermal transfer printer. The polyethylene waxes are used apparently to convey a good release function and thus make the Adhesion to the printed film. They mediate because of their good gliding behavior the particularly favorable scratch resistance of the printouts.

The invention will be explained in more detail below using an example:

example 1

A material of the following recipe is applied to a conventional carrier made of polyethylene terephthalate with a thickness of about 4.5 µm to form a thermal transfer color layer: Parts by weight Polyester resin based on a bisphenol A (trade name: Setafix P 120, sold by Akzo Nobel Resins BV) 60 Polar polyethylene wax (trade name: PED 521, sold by Hoechst AG) 7.5 Polar polyethylene (trade name: P 522, sold by Hoechst AG) 7.5 Hoechst AG) soot 25 total 100

The properties of the above binder components are as follows: PED 521 Dropping point: 105 ° C (DIN 51 801), acid number: 17 mg KOH / g (DIN 53 402), saponification number: 35 mg KOH / g (DIN 53 401), density: 0.95 g / cm ³ at 20 ° C (DIN 53 479), ball pressure hardness: 1 to 3 · 10 ⁷ Pa (100-300 bar) (DGF-M III-90 (57)), flow hardness: 1 to 3 · 10 ⁷ Pa (100-300 bar) and viscosity 100-500 mPas at 120 ° C (DIN 51 550). PED 522 Dropping point: 103 ° C (DIN 51 801), acid number: 25 mg KOH / g (DIN 53 402), saponification number: 55 mg KOH / g (DIN 53 401), density: 0.96 g / cm ³ at 20 ° C (DIN 53 479), ball pressure hardness: 1 to 3 · 10 ⁷ Pa (100-300 bar) (DGF-M III-90 (57)), flow hardness: 1 to 3 · 10 ⁷ Pa (100-300 bar) and viscosity 100-500 mPas at 120 ° C (DIN 51 550).

The above material is reversed in a solvent dispersion about 20% (toluene / isopropanol: 80:20) in a dry strength of about 1.5 µm applied. The solvent is evaporated off by passing it over hot air at a temperature of around 100 ° C. The material obtained proved when printing in the high energy level of a thermal transfer printer as scratch and solvent resistant.

Claims (11)

1. Thermal transfer ribbon including a carrier, a thermal transfer ink formed on one side of the carrier and optionally further layers, the thermal transfer ink including, in addition to a colorant, an amorphous polymer and a wax, characterised in that the thermal transfer ink contains, as a bonding agent, a polar polyethylene wax and an amorphous polymer, which has a weight average molecular weight Mw of more than 10,000 and a number average molecular weight Mn of less than 6,000.
2. Thermal transfer ribbon as claimed in Claim 1, characterised in that the amorphous polymer has a weight average molecular weight Mw of 10,000 to about 15,000 and a number average molecular weight Mn of less than about 5,000, particularly about 2,000 to 3,000.
3. Thermal transfer ribbon as claimed in one of the preceding claims, characterised in that associated with one part by wt. polar polyethylene wax there are about 3 to 5 parts by wt., particularly about 4 parts by wt., amorphous polymer.
4. Thermal transfer ribbon as claimed in one of the preceding claims, characterised in that the amorphous polymer constitutes an amorphous polyester resin, particularly based on a bisphenol A.
5. Thermal transfer ribbon as claimed in Claim 3, characterised in that the polar polyethylene wax has a dropping point of about 100 to 110°C, particularly about 102 to 108°C.
6. Thermal transfer ribbon as claimed in Claim 5, characterised in that the dropping point is about 102 to 106°C.
7. Thermal transfer ribbon as claimed in at least one of the preceding claims, characterised in that the polar polyethylene wax has a ball indentation hardness in accordance with the test method DGF-M III-90 (57) of 1 to 3·10⁷ Pa (100 to 300 bar), a flow hardness of about 1 to 3·10⁷ Pa (100 to 300 bar) and a viscosity, measured in accordance with DIN 51 550 at a temperature of about 120°C of about 50 to 700 mPas, particularly about 100 to 500 mPas.
8. Thermal transfer ribbon as claimed in one of Claims 4 to 7, characterised in that the amorphous polyester resin has an MFI value (105°C/2.16 kg) of about 1.3 to 2.3, particularly of about 1.5 to 2.0 g/10 min. and a glass conversion temperature Tg of about 45 to 65°C, particularly about 52 to 56°C.
9. Thermal transfer ribbon as claimed in one of the preceding claims, characterised in that the thermal transfer ribbon has a thickness of about 1 to 5 g/m², particularly about 1 to 3 g/m².
10. Thermal transfer ribbon as claimed in one of the preceding claims, characterised in that the carrier comprises polyethylene terephthalate.
11. Thermal transfer ribbon as claimed in one of the preceding claims, characterised in that formed on the rear side of the carrier there is a layer of a wax or a wax-like material of a thickness of about 0.01 to 1 g/m², particularly of about 0.05 to 0.10 g/m².