EP0823332B1 - Thermal transfer dye ribbon for luminescent writing - Google Patents

Description

The invention relates to a thermal transfer ribbon for luminescent characters or codings.

Modern sorting machines, such as those used for sorting a large number of objects e.g. Letters that are used do not speak to the human eye necessary visible luminescent coding. For this purpose, the Prior to the sorting process, mark the pieces to be sorted with a symbol Luminescent material included. For this purpose, thermal transfer ribbons are increasingly being used used a layer of thermal transfer ink with one contained therein Have luminescent pigment. The luminescent transfer color, which on the The surface of the substrate being transferred is very thin and for visual inspection transparent.

Luminescent colors have the property of ultraviolet light and visible light to absorb in the blue part of the spectrum and this absorbed part at the bottom Broadcast again at the end of the spectrum. From the large number of organic Compounds exposed to light under the action of short-wave rays emit are only suitable as luminescent dyes or lumogens Substances in the solid, undissolved state due to intense fluorescence are excellent. Of the greatest technical interest are the luminescent dyes, which fluoresce in color in daylight and as daylight fluorescent pigments be used. Soluble such dyes are e.g. Rhodamine, eosin, Brillantsulfoflaven FF and the strong yellow-green fluorescent pyranine, furthermore Color pigments, e.g. the 2,2-dihydroxy-alpha-naphthaldiazine and the anthrapyrimidine. Since the dyes are organic in nature, it is necessary to use them in an organic Loosen medium or carrier. Dyed carriers are mainly used, e.g. pulverized polymers with soluble dyes or finely divided pigments are stained. The type of material that meets the needs of a carrier or matrix for which dyes are equivalent are transparent organic resins. By implementing acidic polyester resins with basic dyes or solidified by pulverizing Dye solutions are also obtained with colored carriers. Also urea-formaldehyde resins, Acrylic resins and melamine resins are used as carriers where the dyes are possibly lacquered. Daylight fluorescent pigments So are organic plastic particles that are colored with fluorescent dyes are. The physical structure of the pigment particles is predominantly amorphous. The Daylight fluorescent pigment come under the names Lumogene (BASF), Day-Glo® Colors, Goldfire-Colors, Fluorzink or Brillink-Leuchtfarben in stores.

Thermal transfer ribbons have been known for a long time. They point to a foil-like Carrier, for example made of paper, a plastic or the like, a Thermal transfer ink in particular in the form of a plastic and / or wax-bound colorant or soot layer. The thermal transfer color is used for the Thermal printing technology by means of a thermal print head softens and onto a substrate transfer. Thermal printers or thermal print heads that are used for this process can be used, for example, from DE-ASen 20 62 495 and 24 06 613 and DE-OS 32 24 445 known. In particular, e.g. as follows be followed: On the thermal print head of the printer is a heated from Dots existing letter and to be printed on a sheet of paper. The thermal print head presses the thermal transfer ribbon onto a paper to be written on. The heated letter of the thermal print head with a temperature of up to about 400 ° C leads to the fact that the thermal transfer ink softens at the heated point and transferred to the paper sheet in contact with it. The part used 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. 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 bar. Since the print bar is not movable, it must span the width of the substrate to be printed. The resolution and dot size correspond to those of serial heads.

When luminescent material is deposited on the surface of white paper , the whiteness of the paper serves as a light reflector. Most of the incident Light is returned from the paper through the printed luminescent material reflected. The reflected light perceived by the observer contains both incident light as well as luminescent light.

If the luminescent material on the surface of a dark colored paper is transmitted so part of the incident light that the luminescent layer has been absorbed by the paper. The amount of through back reflection available light is reduced. In addition, the proportion of the Luminescence color layer absorbs light emitted in the direction of Paper surface is emitted.

To compensate for differences in luminescence intensity, depending on the type of carrier are to be attributed, DE-OS 30 42 526 proposes a fluorescent printing tape that characterized by the addition of a barrier material to the fluorescent pigment material to block the absorption of the incident light in the medium which the pigment and barrier coatings are transferred during printing. The barrier material is preferred as a second layer over the pigment material layer upset. The two layers are printed in reverse order transferred to the substrate. The barrier material contains reflective metal particles or pearlescent pigments.

DE-AS 12 22 725 discloses a transmission material for luminescent Characters with a layer of paper or foil and one on it arranged luminescent color layer, being over the luminescent Color layer, a light-reflecting pigmented top layer is placed, the participates in the writing process. The cover layer preferably contains titanium white and / or aluminum pressure cut powder.

The known proposals aim to absorb the incident light the luminescent layer happens to suppress in the substrate, so that this portion is reflected and the luminescent color layer passes again so that the Increase overall excitation yield. The disadvantage here is that the observer perceived luminescent light always with the reflected part of incident light is mixed. The luminescent expressions therefore appear always pale, i.e. they have a low optical density.

Trying to increase the optical density of the printouts by adding a non-luminescent To increase pigment to the layer of luminescent pigment, it is found that the addition of foreign pigments of more than 1% Fluorescence quality is very badly affected. With increasing additional amount the brilliance of the fluorescent pigments, the fluorescence quality and color purity Interferences occurring increasingly impaired. Lead even higher additional quantities almost complete extinction of the fluorescence. One from the standpoint of Fluorescence power allowable additional amount of 1% or less would be the optical Increase density only insignificantly.

The state of the art evident from the following publications represents in essentially represent the technological background against which the claimed invention can be seen: GB-A-2 270 392 relates to a thermal transfer process. Here, a thermal transfer ribbon from a carrier film, the at least a first and has a second transfer layer. The first transfer layer is the second transfer layer and is connected to this. With thermal transfer printing both the first and the second transfer layer are opened in selected areas transfer a print receiving surface to form a printout. The two Transfer layers are made from different materials to them to give different properties. In one embodiment of this known In the process there is a visible pigment in one layer and in another Layer a luminescent pigment to print barcodes. JP-A-63 283986 discloses a thermal transfer ribbon in which the heat-fusible ink layer is a contains fluorescent substance to a transferred image with high color density and to form a fluorescent color with high intensity. In particular, if a fluorescent substance is used in combination with a colorant High intensity fluorescent light can be emitted because a larger amount of fluorescent substance is contained in the first layer, which is close to the heat-fusible layer is present. This technical proposal aims at the possibility of Eliminate falsification, improve the color density of the transferred image and it make it possible to obtain a fluorescent color of high intensity. JP-A-63 281890 relates to a thermal transfer material in which on a heat-resistant carrier are provided: a heat-fusible layer of paint, which is a fluorescent substance contains, and a heat-meltable color layer containing a colorant and an extender pigment contains. On the other hand, the colorant in the heat-fusible color layer and the Stretch pigment in a further heat-meltable color layer. With this known proposal to prevent bleaching or discoloration of the printed image become.

The invention was therefore based on the object of providing a thermal transfer ribbon To provide luminescent encodings with high optical printouts Density without affecting the luminescent performance of the luminescent Pigment and regardless of the substrate to be printed can be achieved.

According to the invention, this object is achieved by a thermal transfer ribbon, which (a) a support, (b) a layer of one formed on one side of the support a first thermal transfer color containing luminescent pigment and (c) one the layer of the first thermal transfer ink is a non-luminescent layer Has pigment-containing second thermal transfer ink, wherein in the reflectance spectrum of the non-luminescent pigment in the wavelength range a maximum reflectance of the light emitted by the luminescent pigment or there is a rising edge of remission. Between the carrier and the layer of the first thermal transfer ink and / or the layer of the first and second Thermal transfer ink may have other layers.

The non-luminescent pigment to be used according to the invention thus reflects only the light emitted by the luminescent pigment and the wavelength portion of the unabsorbed incident light at or near the (long wave) Emission band of the luminescent pigment is. The printouts obtained work so much higher contrast and show improved optical density. The choice of non-luminescent pigment also allows the hue of the expression to vary within certain limits without loss of brilliance by the emitted Light and the light remitted by the non-luminescent pigment interfere.

The non-luminescent pigment is a pigment whose remission is strong is wavelength-dependent. The color impression of a non-luminescent pigment arises as a result of selective reflection of some segments of the visible white Spectrum of light. The non-reflected part is absorbed and in heat converted. An orange-red color e.g. reflects the orange-red part of the light and absorbs all other colors of the spectrum. Good non-luminescent Pigments are able to add about 90% of the corresponding portion of the spectrum reflect. White pigments, on the other hand, show an unselective high reflection on the entire visible spectrum.

For the purposes of the invention it is preferred that the luminescent pigment is a Daylight fluorescent pigment and the non-luminescent pigment a colored pigment is. Issued with a view to its intended use in franking printers the daylight fluorescent pigment preferably in the wavelength range of orange to red, i.e. at about 580 to 620 nm (with an excitation energy of 254 nm). The the preferred colored pigment is a red pigment, this term being largely used is to be understood.

Although the type of binder for the first thermal transfer paint for the invention is not critical, it is preferred that the binder be the first thermal transfer ink from a mixture of a hydrocarbon wax and / or ester wax with a Ethylene / vinyl acetate copolymer and / or hydrocarbon resin. Likewise it is preferred that the binder of the second thermal transfer ink from a Mixture of a hydrocarbon wax and / or ester wax with one Ethylene / vinyl acetate copolymer and / or hydrocarbon resin.

Hydrocarbon waxes and / or ester waxes preferably used a melting point of about 70 to 110 ° C, especially about 75 to 90 ° C. Waxes of this type are natural waxes, chemically modified waxes and assigned to the synthetic waxes. Are particularly preferred 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, petrochemical waxes, such as petrolatum, Paraffin waxes and micro waxes. Among the chemically modified waxes are especially montan ester waxes, hydrogenated castor oil and hydrogenated jojoba oil prefers. Among the synthetic waxes are polyalkylene waxes and Polyethylene glycol waxes and from them by oxidation and / or esterification manufactured products preferred. Modified microcrystalline waxes are special prefers. If the melting point falls below 70 ° C, this means that the mechanical anchoring is not sufficient. Melting points higher than 110 ° C disadvantageously lead to increased energy expenditure during the printing process.

The waxes used according to the invention are preferably narrow cut waxes are used, their melting and solidification points close together lie. The temperature difference is preferably between melting and Freezing point less than about 10 ° C, especially less than about 7 ° C and whole more preferably less than about 5 ° C. A good example of this is Camauba wax, whose melting point is around 85 ° C and its solidification point at is about 78 ° C. The waxes indicated lead to a during the printing process desirable low cohesion of thermal transfer ink.

The wax materials of the wax-bound thermal transfer ink (s) are preferred Embodiments of an ethyl / vinyl acetate copolymer and / or Hydrocarbon resin incorporated. These additives regulate the stickiness of the preferably used hard waxes and cause their plasticization, take the Thermal transfer paint is brittleness or "splinter".

The thermal transfer color (s) of the thermal transfer ribbon according to the invention has (have) preferably a viscosity, determined with the rotary viscometer Rheomat 30 with rheograph (see Bulletin T 304d-7605 from Contraves AG Zurich / CH) at a temperature of 100 ° C, from about 50 to 200 mPa.s, in particular from about 70 to 120 mPa.s.

The layer preferably has the first one containing the luminescent pigment Thermal transfer ink a thickness of about 2 to 5 microns, in particular about 3 to 3.5 microns, on. The layer of the second containing the non-luminescent pigment Thermal transfer ink is preferably about 1 to 3.5 microns, especially about 2 to 2.5 µm, thick.

The carrier of the ribbon according to the invention is not critical. As a base film for Thermal transfer ribbons are preferably polyethylene terephthalate foils (PETP) or capacitor papers used. The selection parameters are as high as 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. A preferred film thickness is about 3.5 to 5 microns, especially about 4.5 microns.

Between the carrier and the layer of the first thermal transfer paint and / or the Layer of the first and second thermal transfer ink can have additional layers such as Release or release layers or adhesion-promoting layers.

During the printing process, the thermal print head reaches temperatures of up to 400 ° C, i.e. Temperatures that are above the softening point of PETP. It recommends itself, when using PETP films on the back of the film, which with the Thermal head comes into contact, a particularly resistant to heat Layer.

In a preferred embodiment there is a layer on the back of the carrier formed from a wax or a wax-like material, especially in one Thickness of no more than about 1 µm and most preferably in the form of a molecularly formed, about 0.01 to 0.1 micron thick layer. The In this case, coating material preferably consists of silicone, natural waxes, in particular carnauba wax, beeswax, ozokerite and paraffin wax, Synthetic waxes, especially 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, 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.

The thermal transfer ribbon according to the invention is advantageously in a printer from near-edge type, especially used in franking machines. It is surprising making any paper, i.e. smooth as well as rough papers with excellent Print quality can be used. The layer of the second thermal transfer ink seems to act as a "top coat", the surface unevenness of the paper equalized.

The invention is now illustrated in more detail by the following example.

example

A thermal transfer ink of the following recipe is applied in the form of a melt to a conventional carrier made of a polyester with a layer thickness of 4.5 µm: Paraffin wax 42 parts by weight EVA 28/800 (ethylene-vinyl acetate copolymer, vinyl acetate content 28%, melt index 800 g / 10 min) 8 parts by weight EVA 1 wax (polyethylene wax based on an ethylene-vinyl acetate copolymer) 8 parts by weight Carnauba wax 15 parts by weight Petrolite® WB 17 (microcrystalline wax) 2 parts by weight Dayglo Rocket Red (luminescent pigment) 25 parts by weight 100 parts by weight

After solidification, a thermal transfer ink of the following recipe is applied in the form of a melt in a second step: Paraffin wax 41 parts by weight EVA 28/800 (ethylene-vinyl acetate copolymer, vinyl acetate content 28%, melt index 800 g / 10 min) 10 parts by weight Hoechst® Wachs-S 35 parts by weight Permanent lacquer red (pigment) 14 parts by weight 100 parts by weight

The ribbon obtained compared to an ink ribbon, which only the Layer of the luminescent transfer color, prints with clear increased optical density without loss of luminescence power.

For clarification, the fluorescence spectrum (E) of the used luminescent pigment as well as the reflectance spectrum (R) of the used non-luminescent pigment reproduced. Has permanent lacquer red its absorption maximum in the range up to about 550 nm. At 580 nm only absorbs about 50% of the light. At higher wavelengths up to 700 nm the Remission 90%. The Dayglo Rocket Red has an emission maximum at 600 nm.

In the production of the ribbon according to the invention, the layers of Thermal transfer inks successively in the form of a melt according to the usual Application technologies on the carrier or the solidified layer of the first Thermal transfer ink applied, for example with a squeegee. The temperature of the respective melt should generally be about 100 to 130 ° C. The Luminescent pigment must be in a hot wax / EVA mixture up to at least 120 ° C be tolerable. A luminescent pigment with a highly heat-resistant thermoset matrix that does not melt under these conditions or glued. After the application, the materials applied are simply left cooling down.

Claims (7)

1. Thermal transfer ink ribbon including (a) a carrier, (b) a layer formed on one side of the carrier of a first thermal transfer ink containing luminescent pigment and (c) a layer formed on the layer of the first thermal transfer ink of a second thermal transfer ink containing a non-luminescent pigment, characterised in that located in the reflectance spectrum of the non-luminescent pigment in the wavelength range of the light emitted from the luminescent pigment there is a reflectance maximum or an ascending flank of the reflectance, whereby further layers can be situated between the carrier and the layer of the first thermal transfer ink and/or the layer of the first and second thermal transfer inks.
2. Thermal transfer ink ribbon as claimed in Claim 1, characterised in that the luminescent pigment is a daylight-fluorescent pigment and the non-luminescent pigment is a coloured pigment.
3. Thermal transfer ink ribbon as claimed in Claim 2, characterised in that the daylight-fluorescent pigment emits in the wavelength range of orange to red and the coloured pigment is a red pigment.
4. Thermal transfer ink ribbon as claimed in one of the preceding claims, characterised in that the bonding agent of the first thermal transfer ink comprises a mixture of a hydrocarbon wax and/or ester wax with an ethylene/ vinyl acetate copolymerisate and/or hydrocarbon resin.
5. Thermal transfer ink ribbon as claimed in one of the preceding claims, characterised in that the bonding agent of the second thermal transfer ink comprises a mixture of a hydrocarbon wax and/or ester wax with an ethylene/ vinyl acetate copolymerisate and/or hydrocarbon resin.
6. Thermal transfer ink ribbon as claimed in one of the preceding claims, characterised in that the layer of the first thermal transfer ink has a thickness of about 2 to 5 µm.
7. Thermal transfer ink ribbon as claimed in one of the preceding claims, characterised in that the layer of the second thermal transfer ink has a thickness of about 1 to 3.5 µm.

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