Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
  • B41M5/26—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used
  • B41M5/40—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used characterised by the base backcoat, intermediate, or covering layers, e.g. for thermal transfer dye-donor or dye-receiver sheets; Heat, radiation filtering or absorbing means or layers; combined with other image registration layers or compositions; Special originals for reproduction by thermography
  • B41M5/42—Intermediate, backcoat, or covering layers
  • B41M5/44—Intermediate, backcoat, or covering layers characterised by the macromolecular compounds
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41M—PRINTING, DUPLICATING, MARKING, OR COPYING PROCESSES; COLOUR PRINTING
  • B41M5/00—Duplicating or marking methods; Sheet materials for use therein
  • B41M5/26—Thermography ; Marking by high energetic means, e.g. laser otherwise than by burning, and characterised by the material used
  • B41M5/382—Contact thermal transfer or sublimation processes
  • B41M5/392—Additives, other than colour forming substances, dyes or pigments, e.g. sensitisers, transfer promoting agents

Definitions

• the invention relates to a thermal transfer ribbon with a conventional carrier, with a wax-bound layer of a thermal transfer ink formed on one side of the carrier and with a resin-bound release layer located between the carrier and the wax-bound layer.
• a thermal transfer ribbon of the type described above emerges from DE 195 48 033 A1.
• the resin-bound separating layer described therein serves to better separate the wax-bound layer of the thermal transfer ink from the respective carrier.
• the particular aim of this known teaching is to exclude the need for the formation of a so-called “top coat” (adhesive layer) or a two-layer thermal transfer ink and to obtain satisfactory matt prints during the thermal printing process. This is ensured by the fact that both the resin-bound separating layer and the wax-bound layer of the thermal transfer ink contain a wax-soluble polymer in a sufficiently large amount. It is particularly preferred that the wax-bonded layer of the thermal transfer ink contains about 5 to 10% by weight of wax-soluble polymer.
• the thermal transfer ribbon described above is highly suitable to meet the stated objective. However, it has to be improved with other objectives. This applies in particular to thermal transfer printing on uncoated paper ("plain paper”), which has a comparatively high roughness.
• the following physical properties are essential for good print quality and quality products:
• the force of the mechanical anchoring of the thermal transfer ink on the printed paper must be greater than the cohesion of the thermal transfer ink during the separation process in the thermal printer - separation of ribbon from paper itself and the adhesion of the thermal transfer ink to the substrate, ie low ink application, low ink viscosity and low adhesion of the ink to the release layer during the printing process lead to optimal print quality.
• Prior art products also show that print quality undesirably varies with "cold” and "hot” printheads.
• the invention was therefore based on the object of proposing a thermal transfer ribbon of the type mentioned at the outset, with which the objectives mentioned above for improving the print quality, in particular in the case of "cold” or “hot” printing, in particular also on uncoated paper of high roughness, are achieved.
• this object is achieved in that at least the resin-bound separating layer A) contains a wax-soluble polymer and the wax-bound layer B) of the thermal transfer ink contains less than about 8% by weight, in particular about 0 to 5% by weight, of wax-soluble polymer, the Waxes of the wax-bound layer B) tightly cut waxes are closely spaced melting and solidification points. Accordingly, the wax-bound layer B preferably does not contain any substantial amounts of wax-soluble polymer, very particularly about 0 to 1.5% by weight or even less than about 0.5% by weight.
• a separating layer or release layer is understood in the present technical field to mean a layer which controls the delivery of the thermal transfer ink to the receiving substrate during the printing process, but is not itself transferred to the substrate.
• a separating layer does not melt during the printing process, but softens at most and also has high adhesion to the carrier.
• An essential aspect in solving the described problem is the use of "tightly cut" waxes in the wax-bound layer, ie the melting and solidification point of the waxes must lie close together.
• the temperature difference between the melting and solidification point is preferably less here than about 10 ° C, especially less than about 7 ° C, and most preferably less than about 5 ° C.
• waxes used in the wax-bound layer B) of the thermal transfer ink in the context of the invention follow the customary wax definition with the above restriction to narrow-cut waxes.
• waxes with a melting point of approximately 75 to 90 ° C. are used in particular.
• 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.
• 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.
• petrochemical waxes such as, for example, petrolatum, paraffin waxes and microwaxes
• montan ester waxes montan ester waxes, hydrogenated castor oil and hydrogenated jojoba oil
• 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.
• modified microcrystalline waxes are to be specified here as particularly preferred.
• the framework of the melting point to be observed according to the invention for the waxes used is critical. If the temperature falls below 70 ° C, this means that the mechanical anchoring is insufficient and thus color transfer and color resolution are unsatisfactory. Melting points higher than about 95 ° C disadvantageously lead to increased energy expenditure during the printing process.
• a good example of a wax which can be used according to the invention is carnauba wax, the melting point of which is approximately 85 ° C. and the solidification point of which is approximately 78 ° C.
• the indicated waxes lead to a desirable low cohesion of the thermal transfer ink during the printing process.
• 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 Zonataclite 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).
• 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 color pigment, in an amount of about 5 to 20% by weight.
• the melting point of the wax-bound thermal transfer ink is generally between about 60 and 80 ° C.
• the thermal transfer color of the above-mentioned layer B) of the thermal transfer ribbon according to the invention preferably has a viscosity, determined with the Rheomat 30 rotary viscometer with rheograph (principle: rotary viscometer, see Bulletin T 304d-7605 from Contraves AG Zurich / CH) at a temperature of 100 ° C of about 50 to 150 mPa ⁇ s, in particular from 70 to 120 mPa ⁇ s. Falling below the value of about 50 mPa ⁇ s leads to blurring ("spreading"). If the value of 250 mPa ⁇ s is exceeded, the desired resolution can deteriorate.
• a viscosity determined with the Rheomat 30 rotary viscometer with rheograph (principle: rotary viscometer, see Bulletin T 304d-7605 from Contraves AG Zurich / CH) at a temperature of 100 ° C of about 50 to 150 mPa ⁇ s, in
• a central feature of the thermal transfer ribbon according to the invention is that a wax-soluble polymer is mainly contained in layer A).
• “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 melt index MFI is 25 to 1000 g / 10 min (220 ° C / 2.16 kg), preferably 400 to 800 g / 10 min (DIN 53735 / ISO 1133, see also Römpp-Chemie Lexikon, Volume 5, 9th ed., P. 4036, r. Sp.).
• Wax-soluble polymers in the sense of the invention are distinguished by the fact that they melt below approximately 100 ° C. and show stickiness in the molten state.
• Suitable polymers are e.g. Ethylene-vinyl acetate copolymers, polyamides, ethylene-alkyl acrylate copolymer, ethylene-acrylic acid copolymers, polyvinyl ether, and polyisobutene and ionomer resins. Of these, ethylene-acrylic acid copolymers and ethylene-vinyl acetate copolymers (EVA) are particularly preferred.
• a vinyl acetate content of approximately 16 to 42, in particular approximately 18 to 40% by weight is preferred to increase the adhesion between the separating layer A) and the layer B).
• the melt index MFI (in accordance with DIN 53735) of the ethylene-vinyl acetate copolymer should be about 20 g / 10 min, in particular about 30 g / 10 min (220 ° C / 2.16 kg).
• the ethylene-vinyl acetate copolymer preferably has a vinyl acetate content of about 3 to 17, in particular about 6 to 12,% by weight in order to establish a low adhesion between the separating layer A) and the layer B).
• wax-soluble polymers also includes those which show a certain stickiness even at room temperature, such as, for example, certain polyisobutenes with an oily, viscous to rubbery consistency. Products of this type are sold under the trade name Oppanol (BASF, Germany, cf. Römpp Chemie Lexikon 9th edition, vol. 4, p. 3121/3122). These wax-soluble polymers which are sticky at room temperature also include raw materials based on polyvinylethyl, methyl and isobutyl ether, which are sold under the trade name Lutonal are sold (BASF, Germany, see Römpp-Chemie Lexikon, 9th edition, Vol. 3, p. 2566).
• a special feature of the present invention is the displacement of the majority of the wax-soluble polymer under discussion from layer B) into the separation layer A).
• the wax-soluble polymers can be used individually or as a mixture with one another. The same or different wax-soluble polymers can be used in the separating layer A) and, if present, in the layer B).
• the wax-soluble polymer is preferably contained in the separating layer A) in an amount of approximately 10 to 60% by weight, in particular approximately 20 to 40% by weight. If the value falls below 10% by weight, then the adhesion to the ink layer is too high and no homogeneous ink transfer is guaranteed. A value of more than 60% by weight leads to inadequate adhesion to the ink layer and thus to poor resolution of the printed characters.
• the transfer of the main amount of the wax-soluble polymer, in particular in the form of ethylene-vinyl acetate copolymer, from the thermal transfer ink into the separating layer results in a relatively low color viscosity even when using a large amount of ester wax (melting point ⁇ 80 ° C).
• the thus lower viscosity and good soot dispersibility in ester waxes allows a higher concentration of pigment, in particular soot, and thus a lower color application (g / m 2 ) with the same OD.
• the separating layer A) containing the main part of wax-soluble polymers also fulfills the function of a " matt layer".
• the matt layer means that really matt prints are produced during the thermal printing process. This is due to the fact that during the printing process not only the thermal transfer ink becomes liquid and thus sticks to the substrate, in particular in the form of a paper acceptor, but also softens the separating layer and retains a noticeable adhesion to the ink layer, so that there is a completely flat transfer of, for example, printing symbols the paper acceptor is not possible. Rather, the surface of the printed symbols slightly roughened so that the surface of the symbol transferred appears matt as a result of light refraction / light diffusion.
• layer B) contains a black pigment and the separating layer additionally contains carbon black, in particular in an amount of about 20 to 50% by weight, which leads to the fact that the thermal transfer tape written off offers adequate data protection.
• the separating layer is preferably also incorporated with silica and dispersing agents. During the production of the layer, this means that the soot remains finely distributed in the layer and does not sediment out.
• the separation layer A contains release agents in an amount of about 5 to 30% by weight, these being in the form of nonionic surfactants, emulsifiers, polyethylene glycols, etc.
• 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 approximately 0.2 to 5 g / m 2 , in particular approximately 1 to 3 g / m 2
• the layer B) an application thickness of approximately 1.0 to 10 g / m 2 , in particular from about 3 to 6 g / m 2 .
• the separating layer A) is a resin-bound layer, the resin binder preferably being a solid resin with a softening range in the range from about 70 to 200 ° C.
• the resin preferably comprises an alkyd, epoxy, melamine, phenol, urethane and / or polyester or copolyester resin and / or a polyamide, hydrocarbon resin, natural resin, polyvinyl ether and / or polyisobutene.
• the carrier of the ribbon according to the invention is not critical.
• Polyethylene terephthalate (PETP) 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 PETP films are available down to about 2.5 ⁇ m, capacitor paper down to about 6 ⁇ m.
• the thermal print head reaches temperatures of up to 400 ° C, ie temperatures that are above the softening point of PETP.
• 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.
• top coat adheresive layer approximately 0.5 to 0.7 g / m 2
• wax-bonded layer of thermal transfer ink B. about 4.0 to 4.5 g / m 2
• separating layer A about 0.5 to 1.0 g / m 2
• thickness of the support for example polyethylene terephthalate
• Non-stick layer about 0.05 to 0.1 g / m 2 .
• the thermal transfer ribbon according to the invention described above 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 a dispersion or solvent, by applying from the melt, which applies in particular to the wax-bound thermal transfer ink, or by normal application using a doctor blade Form an aqueous suspension with finely divided material to be applied.
• the following procedure has proven to be particularly advantageous: 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 evaporates.
• the application of an aqueous suspension of the starting material of the wax-bound thermal transfer dye follows, the water being evaporated off in a conventional manner after the application of this material.
• the double-layer covering formed fulfills all the requirements that lie within the scope of the task.
• the thermal transfer ink can also be applied in the form of a melt to the separating layer using customary application technologies, for example using a doctor blade.
• the temperature of the respective melt should generally be about 100 to 130 ° C. After application, the applied materials are only allowed to cool.
• thermal transfer color layer B about 1 to 10 g / m 2 , preferably about 3 to 6 g / m 2 , separating layer A) 0.2 to 5 g / m 2 , preferably about 0.5 to 1.5 g / m 2 , carrier film, in particular polyester film, of a thickness of about 2 to 8 ⁇ m, in particular of a thickness of about 4 up to 5 ⁇ m and the mentioned back coating in an application thickness of about 0.01 to 0.2 g / m 2 , in particular of about 0.05 to 0.1 g / m 2 .
• a material of the following recipe is applied to a customary carrier made of a polyester with a layer thickness of approximately 6 ⁇ m using a doctor blade to form the separating layer A): Polyester resin 40 parts by weight wax soluble polymer (EVA) 30 parts by weight soot 29 parts by weight Silica 1 part by weight 100 parts by weight ⁇
• the above material is applied in a solvent dispersion (about 15%, in toluene / isopropanol 80:20) at a dry thickness of about 1.0 ⁇ m.
• the solvent is evaporated by passing hot air at a temperature of around 100 ° C.
• the thermal transfer ink B) is then applied using the following recipe in the form of a melt at a temperature of approximately 105 ° C. using flexographic printing.
• Example 1 was repeated with the modification that the following recipes were used for the separation layer A) and the color layer B):
• Polyester resin 25 parts by weight wax-soluble polymer EVA 40 parts by weight Polyether alcohol 10 parts by weight Color pigments 25 parts by weight 100 parts by weight ⁇
• Transfer color layer B (4-layer version):

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• Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Thermal Transfer Or Thermal Recording In General (AREA)

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• 1998
  • 1998-05-08 DE DE19820769A patent/DE19820769B4/de not_active Expired - Fee Related
• 1999
  • 1999-05-05 DE DE59907677T patent/DE59907677D1/de not_active Expired - Fee Related
  • 1999-05-05 EP EP99108565A patent/EP0955183B1/fr not_active Expired - Lifetime
  • 1999-05-07 CA CA002271430A patent/CA2271430A1/fr not_active Abandoned

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