EP0828615A1

EP0828615A1 - Heat transfer tape

Info

Publication number: EP0828615A1
Application number: EP97915423A
Authority: EP
Inventors: Heinrich Krauter
Original assignee: Pelikan Produktions AG
Current assignee: Pelikan Produktions AG
Priority date: 1996-03-28
Filing date: 1997-03-24
Publication date: 1998-03-18
Anticipated expiration: 2017-03-24
Also published as: WO1997036753A1; DE59700820D1; CA2221814A1; US6074760A; DE19612393A1; EP0828615B1

Abstract

A heat transfer tape has a usual substrate, a layer of heat transfer ink on one side of the substrate and a separation layer between the substrate and the layer of heat transfer ink. The separation layer is waxed and contains waxes having a melting point from about 70 to 110 °C, as well as a wax softening polymer with a glass transition temperature Tg from -30 to +70 °C. The layer of heat transfer ink contains at least 20 wt % natural resin, modified natural resin and/or synthetic resin. This heat transfer tape gives particularly scratch- and solvent-resistant prints.

Description

Thermal transfer ribbon

The invention relates to a thermal transfer ribbon with a conventional carrier and a layer of a thermal transfer ink formed on one side of the carrier and a separating layer between the carrier and the layer of the thermal transfer ink.

Thermal transfer ribbons have been known for a long time. On a film-like carrier, for example made of paper, a plastic or the like, they have a thermal transfer color, in particular in the form of a plastic and / or wax-bound colorant or carbon black layer. In thermal printing technology, the thermal transfer ink is softened by means of a thermal print head and transferred to a recording paper or a printing paper. Thermal printers or thermal print heads that can be used for this process are known for example from DE-ASen 20 62 495 and 24 06 613 and DE-OS 32 24 445. 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 prints the thermal transfer ribbon on a paper to be written on. The heated letter of the thermal print head with a temperature of about 400 ° C leads to the fact that the thermal transfer ink softens at the heated point and is transferred to the paper sheet in contact with it. The used part of the thermal transfer ribbon is then fed to a spool.

So-called serial printers or line printers can be used for printing. The serial printers work with a relatively small, movable printhead up to approx. 1 cm ² . There are 1 or 2 dot rows perpendicular to the writing direction (dot = controllable heating point). The dot diameter is between about 0.05 to 0.25 mm. The number of dots per row of dots is between 6 and 64, which corresponds to a resolution of 2 to 16 dots / mm. Higher resolutions, eg 24 to 32 dots / mm, are expected in the near future. It is characteristic of the serial thermal head that it is moved horizontally to the transport direction of the paper during the printing process. In contrast to the serial print head, a line print head is a stationary head or a bar. Since the print bar is not movable, it must span the width of the substrate to be printed. Print bars are available in lengths of up to 297 mm. The resolution and dot size correspond to those of serial heads. The Serial printers are used in typewriters, video printouts, in the PC area and in word processors, while the line printers are used in particular in the case of barcode graphic printers, in the case of a computer output unit in the event of high data loads, in the facsimile, ticket printer, address printer, color copier and CAD / CAM systems are used.

In the systems of thermal transfer ribbons described above, the font sharpness and the optical density of the font generated are, inter alia, depending on the adhesion of the thermal transfer ink to the paper. This is proportional to the adhesive surface and the adhesive force. Rough paper has a small adhesive area, since only the raised parts of the paper surface are wetted by the melted thermal transfer ink. In EP-A-0 137 532 and DE-A-35 07 097, a so-called "filling layer" is therefore formed on the layer of thermal transfer ink, which consists of a material which is low-viscosity in the molten state and which is produced during the printing process flows into the valleys of the rough paper surface, thus increasing the adhesive surface. It is disadvantageous here that the melted filling layer cannot penetrate the paper in the case of very smooth paper with a roughness of more than 200 Bekk during the printing process, so that a layer remains between the paper surface and the color layer. This layer therefore has the effect of a hold-off layer, as described in EP-A-0 042 954. However, this hold-off layer leads to poor document authenticity, since it prevents the thermal transfer ink from penetrating into the paper. A hold-off layer effect is undesirable for a document-correct layer.

In order to avoid the above-mentioned disadvantages of the prior art, in particular to advantageously enable writing on rough as well as smooth paper, EP-B-0 348 661 proposes that the hold-off layer or adhesive layer, also as topcoat referred to incorporate an embedded in a paraffin in a finely divided form, hydrocarbon tackifying resin, said wax having a melting point of 60 to 95 ^C C. The teaching according to EP 0 206 036 tries to avoid the need for such an adhesive layer or a top coat by forming a wax layer on the layer of a plastic-bound thermal transfer ink and the plastic-bound thermal transfer ink containing a thermoplastic plastic with a softening point of 60 to 140 ° C.

^' The thermal ribbons described above are finding more and more use in the industrial sector, whereby a print head of the so-called "near-edge" type is often used here. In these printheads, the row of dots is arranged on a ceramic substrate near the edge. The edge-type heads have the advantage of being shorter Cooling down times and accordingly a higher write frequency. This enables printing speeds of 2 to 4 "per second to be achieved. Particular demands are placed on the prints achieved in terms of print quality, ie good edge sharpness, resolution and optical density. A particular area of application is the printing of paper labels, in particular for the bar code a high scratch resistance and solvent resistance of the prints is desirable, the printed labels should withstand a temperature load of up to 100 ° C. without becoming unsightly.

To achieve scratch-resistant prints, EP-B-0 380 920 recommends 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 symbols obtained immediately after the printing process initially do not show the desirable scratch resistance. The scratch resistance is achieved by adding further heat to the symbol, which results in a new structure of the printed symbol. This proposal is disadvantageous in that it requires a second heat treatment step after the actual printing process.

The thermal ribbons previously provided in the prior art for the field of industrial printers do not meet the requirements mentioned to the desired extent.

The invention was therefore based on the object of providing a thermal transfer ribbon, the thermal transfer ink transferred during printing on paper labels in particular shows good adhesion and good abrasion and scratch resistance, but is released quickly and precisely together with the release or release layer underneath during the printing process.

According to the invention, this object is achieved in that the separating layer is wax-bound and contains waxes with a melting point of about 70 to 110 ° C and a polymeric wax plasticizer with a glass transition temperature Tg of about -30 to + 70 ° C, and the layer of thermal transfer ink at least about 20 wt .-% contains natural resin, modified natural resin and / or synthetic resin.

In a preferred embodiment of the thermal transfer ribbon according to the invention, the layer of thermal transfer ink also contains a wax-compatible polymer. The waxes used in the separating layer in the context of the invention follow the customary wax definition with the above limitation of the melting point to approximately 70 to 110 ° C. 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 divided into hydrocarbon waxes (alkanes without functional groups) and waxes from long-chain organic compounds with functional groups (especially ester and acid waxes). In addition to earth wax, hydrocarbon waxes include solid hydrocarbons extracted from oil and tar, as well as synthetic paraffins. The waxes with functional groups include all vegetable waxes and chemically modified waxes. Ester waxes essentially consist of esters which are formed from linear carboxylic acids with about 18 to 34 carbon atoms and linear alcohols of about the same length. Acid waxes contain large amounts of free carboxylic acids. Waxes with functional groups are preferred. Ester waxes, for example based on montan wax, partially saponified ester waxes, acid waxes and oxidized and esterified synthesis waxes are particularly worth mentioning here. Plant waxes such as carnauba wax and candelilla wax are among the particularly preferred ester waxes. Waxes with a melting point of 80 to 105 ^° C. are particularly preferred within the scope of the invention. Carnauba wax, LG wax BASF and Hoechst wax E.

The separating layer also contains a polymeric wax plasticizer with a glass transition temperature Tg of approximately -30 to + 70 ° C, preferably approximately -30 to + 15 ° C. This has the effect that the hard waxes used particularly preferably in the context of the invention, in particular in the form of ester waxes, are plasticized and thus lose their brittleness and "splinter". They ensure good anchoring or adhesion of the separating layer to the carrier material. Ester waxes are very hard or brittle waxes, i.e. they can be pulverized when cold. If these are mixed with the designated polymeric wax plasticizers, elastic products are created that can hardly be pulverized.

Polymers, copolyesters, polyvinyl acetate and polystyrenes come into consideration as polymer wax plastifiers. Of these, polyesters and copolyesters are preferred. ^" These are preferably linear saturated polyesters or copolyesters with an average molecular weight of 1500 to 18000. The polymeric wax plasticizer is preferably used in the release layer in an amount of about 1 to 25% by weight, in particular about 4 to 15% by weight. Higher amounts of polymeric wax plasticizers should be avoided because otherwise the release effect to the carrier, for example a polyester film, is not sufficient. Too little polymer wax plasticizer may result in the brittle wax being insufficiently plasticized and poor adhesion to the carrier.

The layer of thermal transfer ink contains a natural resin, modified natural resin or synthetic resin as a binder. The suitable resins can be hydrocarbon resins, hydrogenated hydrocarbon resins, rosins, modified rosins, rosin esters, natural and synthetic polyterpenes and the like. In particular, the suitable resins include any compatible resin or mixtures thereof, such as (1) glycerol and pentaerythritol esters of natural and modified rosins, such as the glycerol esters of tall oil and wood resin, the glycerol esters of polymerized rosin, the pentaerythritol esters of hydrogenated rosin and the phenol modified pentaerythritol ester of rosin (2) copolymers and terpolymers of natural terpenes, e.g. styrene / terpene and alpha-methylstyrene / terpene (3) polyterpene resins with a ring and ball softening point of 60 to 150 ° C and hydrogenated polyterpene resins, (4) phenol-modified terpene resins and their hydrogenated Derivatives such as the resin product, which is formed by condensation in an acidic medium of a bicyclic terpene and a phenol, (5) aliphatic hydrocarbon resins with a ring and ball softening point of 60 to 135 ° C., the latter resins obtained by polymerizing monomers that are primarily from oil There exist efines and diolefins, as well as hydrogenated aliphatic hydrocarbon resins, (6) aromatic hydrocarbon resins, such as the coumarone indene resins, and their hydrogenated derivatives, (7) alicyclic hydrocarbon resins and their hydrogenated derivatives and (8) acrylic styrene copolymers, (9) adducts from dienophiles to resins such as maleinate resins. Of these, hydrocarbon resins, rosin resins, modified rosin resins, rosin esters, maleate resins, coumarone-indene resins, polyterpene resins and / or terpene-phenol resins are preferred. Mixtures of two or more of the resins described above may be required for certain applications. Preferably, the resin used or the resin mixture used on a ring, Ball softening point of 80 to 120 ^C C. Lower softening points lead to an ^' insufficient temperature resistance of the printouts, higher softening points require an inadmissibly high energy consumption during printing. The color layer generally contains about 20 to 80, preferably about 40 to 60 wt .-%, natural resin, modified natural resin and / or synthetic resin.

In a preferred embodiment, the color layer also contains a wax-compatible polymer. "Wax compatible" is understood to mean that this polymer is compatible with a liquid wax and that no phase separation occurs when a solution or a dispersion of the polymer is cooled in wax. These primarily include ethylene-vinyl acetate copolymer and other vinyl acetate copolymers. Suitable polymers are, for example Elvax 40W ^® by Dupont and Evatane ^® 28-800 of Atochem. Other suitable wax-compatible polymers are ethylene-acrylic acid copolymers, polyamides, ionomer resins, polyisobutenes (Oppanol ^®, BASF) and Polyvinylethyl-, methyl and isobutyl ether (Lutonal ^®, BASF). About 1 to 20% by weight, in particular about 2 to 8% by weight, of the wax-compatible polymer is present in the layer of the thermal transfer ink.

The coloring can be done by any colorant. It can be pigments, such as 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 color pigment, in an amount of about 20 to 40% by weight.

The viscosity of the thermal transfer ink must be sufficiently low so that the ink can be released quickly and precisely. The thermal transfer ink of the thermal transfer ribbon of the invention preferably has a viscosity of about 500 to 3000 mPa.s, measured with a Brookfield rotational viscometer at 140 ^C C. In particular, the range from 600 to 1500 mPa.s is aimed for.

It is of crucial importance for the present invention that the colored layer contains a natural resin, modified natural resin or synthetic resin as a binder. The resin envelops the colorant particles and thus guarantees good scratch resistance of the printouts. This increase in the abrasion and scratch resistance is based on the property of the resins to anchor themselves very well on the paper during the printing process and ^, in contrast to waxing in thin layers, to be more resilient. Resins to be used according to the invention harden in air in a thin layer after the printing process. This also means an improved temperature stability of the printouts. However, the use of resins as binders for the layer of thermal transfer ink leads to the ink layer becoming very brittle. Adequate adhesion of this "brittle" color layer to the partition layer is achieved by including relatively large amounts of polymeric wax plasticizer in the wax-bound separating layer. On the other hand, this means that the separating layer is also transferred during the printing process. This can be seen from the glossy appearance of the printouts, which originates from a thin layer of wax over the actual transferred print symbol of the resin-bound color layer. The transfer of the separating layer brings about an additional improvement in the scratch resistance, since it is composed of hard ester waxes and polyester resins. The natural resins, modified natural resins and / or synthetic resins used in the color layer are therefore preferably wax-compatible.

After the printing process, the ribbon is separated from the acceptor when the transferred thermal transfer ink has already solidified. This is particularly important when used with near-edge type print heads.

The thickness of the paint layer and the separation layer is not critical. The separating layer preferably has a thickness of approximately 0.5 to 4 μm, in particular approximately 1 to 2 μm. The layer of thermal transfer ink is preferably about 1 to 5 μm, in particular about 1 to 3 μm, thick.

The type of carrier of the ribbon according to the invention is also not critical. It is preferably polyethylene terephthalate film (PETP) or capacitor papers. The selection parameters are the highest possible tensile elongation values and thermal stability with low film thicknesses. The PETP films are available down to about 2.5 μm, capacitor paper down 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. A layer of a wax or wax-like material is then formed on the back of the carrier, in particular in a layer Thickness of not more than 1 μm and very particularly preferably in the form of a molecularly formed, up to 0.01 ^“ μm, the coating material in this case preferably consists of paraffin, silicone, natural waxes, in particular carnauba wax, beeswax, ozokerite and paraffin wax or synthetic waxes, in particular Acid waxes, ester waxes, O 97/36753 PC17EP97 / 01488

-8th-

partially saponified ester waxes and polyethylene waxes, glycols or polyglycols and / or surfactants.

In individual cases, it can be advantageous to incorporate additives that improve the properties of the tape. In this context, the skilled person will select the one with which he would like to set a desired effect within the framework of craft considerations.

The thermal transfer ribbon according to the invention can be produced in a variety of ways using customary application methods. This can be done, for example, by spraying on or printing on a solution or dispersion, be it with water or an organic solvent as the dispersion or solvent, by applying from the melt, which applies in particular to the wax-bound separating layer, or by applying a doctor blade in the form of a aqueous suspension with finely divided material to be applied. Coating methods such as reverse roll and / or gravure coating have proven to be particularly advantageous for the application of both the release and the color layers.

For the practical implementation of the present invention, the following general conditions can be specified with regard to the application quantities of the individual layers: on a carrier film, in particular polyester film with a thickness of approximately 2 to 8 μm, in particular with a thickness of approximately 4 to 5 μm, are applied in succession: separating layer 0.5 to 4 g / m ² , preferably about 1 to 2 g / m ² , and thermal transfer color layer 1 to 5 g / m ² , preferably about 1 to 3 g / m ² . Optionally, 1 g / m ² is formed on the backside of the support mentioned above, a back coating having a thickness of about 0.01 to 0.2 g / m ^2, in particular from about 0.05 to 0 formed.

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 form a separating layer on a conventional carrier made of a polyester with a layer thickness of approximately 6 μm: separating layer:

Carnauba wax 85 parts by weight

Dynapol ^® S 1420 (saturated linear copolyester) 15 parts by weight

100 parts by weight The above material is applied with a doctor blade in a solvent dispersion (about 10%, toluene / isopropanol 80:20) in a dry thickness of about 1.5 μm. The solvent is evaporated by passing hot air at a temperature of around 100 ° C. The thermal transfer ink is then applied using the following recipe in the form of a solvent dispersion (about 15%, toluene / isopropanol 80:20) using the reverse roll method.

Color layer: Dercolyte M 90 (polyterpene resin) 67 parts by weight

Evatane ^® 28-800 (ethylene-vinyl acetate copolymer, vinyl acetate content approx. 28%) 3 parts by weight of carbon black 30 parts by weight

100 parts by weight of example 2

Example 1 was repeated with the modification that the following recipes were used for the separating layer or the colored layer: separating layer:

Candel purple wax 90 parts by weight

Dynapol L205 (saturated high molecular weight linear copolyester) 10 parts by weight

100 parts by weight of transfer ink layer:

Foralyn 90 (glycerol ester of hydrogenated rosin) 65 parts by weight

Elvax ^® 40W (ethylene vinyl acetate copolymer, vinyl acetate content 40% by weight) 5 parts by weight

Soot 30 parts by weight

100 parts by weight ***

Claims

claims

1. thermal transfer ribbon with a conventional carrier, with a layer of a thermal transfer ink formed on one side of the carrier and a separating layer between the carrier and the layer of thermal transfer ink, characterized in that the separating layer is wax-bound and waxes of a melting point of about 70 to 110 ° C and a polymeric wax plasticizer has a glass transition temperature Tg of about -30 to +70 ^C C and the layer of thermal transfer ink contains at least about 20 wt .-% natural resin, modified natural resin and / or synthetic resin.

2. Thermal transfer ribbon according to claim 1, characterized in that the wax of the separation layer has a melting point of about 80 to 105 ° C.

3. Thermal transfer ribbon according to claim 1 or 2, characterized in that the polymeric wax plasticizer has a glass transition temperature Tg of about -30 to + 15 ° C.

4. Thermal transfer ribbon according to one of claims 1 to 3, characterized in that the wax of the separating layer is an ester wax.

5. Thermal transfer ribbon according to one of claims 1 to 4, characterized in that the separating layer contains about 1 to 25 wt .-% polymeric wax plasticizer.

6. Thermal transfer ribbon according to at least one of claims 1 to 5, characterized in that the wax plasticizer is in the form of a polyester and / or copolyester resin.

7. Thermal transfer ribbon according to at least one of claims 1 to 6, characterized in that the natural resin, modified natural resin or synthetic resin

Layer of thermal transfer ink a hydrocarbon resin, a rosin, a modified rosin, a rosin ester, a maleate resin, a coumarone

- Inden resin, a polyterpene resin and / or a terpene phenol resin.

8. Thermal transfer ribbon according to at least one of claims 1 to 7, characterized in that the layer of thermal transfer ink contains about 40 to 60% by weight of natural resin, modified natural resin and / or synthetic resin.

9. Thermal transfer ribbon according to at least one of claims 1 to 8, characterized in that the layer of thermal transfer ink additionally contains about 1 to 20 wt .-% wax compatible polymer.

10. Thermal transfer ribbon according to claim 9, characterized in that the wax-compatible polymer is an ethylene-vinyl acetate copolymer, ethylene acrylic acid.

Is copolymer, polyamide and / or ionomer resin.

11. Thermal transfer ribbon according to at least one of claims 1 to 10, characterized in that the thickness of the separation layer is about 0.5 to 4 microns, in particular about 1 to 2 microns.

12. Thermal transfer ribbon according to at least one of claims 1 to 11, characterized in that the thickness of the layer of thermal transfer ink is about 1 to 5 microns, in particular about 1 to 3 microns.

13. Thermal transfer ribbon according to at least one of the preceding claims, characterized in that the carrier is a polyethylene terephthalate film.

14. Thermal transfer ribbon according to at least one of the preceding claims, characterized in that a layer of a on the back of the carrier

Wax or a wax-like material is formed in a thickness of not more than about 1 micron.

15. Use of the thermal transfer ribbon according to at least one of claims 1 to 14, in industrial high-speed printers, in particular with a

Near-edge type printhead.

***