EP1778499B1 - Security feature for recording materials - Google Patents

Abstract

The invention relates to a novel security feature in the form of a luminescent marking for integration in a recording material. The security feature comprises a radiation layer (21) with luminescent components and a masking layer (2) with cavity pigments at least partly masking the radiation layer. The pigments in the masking layer (2) are fused by locally defined heal treatment into the form of a marking. The invention particularly relates to a heat-sensitive recording material comprising, in a preferred embodiment, at least one substrate (10), a heat-sensitive recording layer (30), an intermediate layer (21), between the substrate and the heat-sensitive recording layer in the form of a radiation layer with luminescent components and a masking layer with cavity pigments (2), the pigments of the masking layer (2) being fused in the form of a marking by locally defined fusion.

Description

The invention relates to a security feature in the form of a luminescent marking for incorporation into a recording material and to a heat-sensitive recording material in which a security feature of the proposed type is incorporated.

Recording materials determine daily life in society and in professional life. For the use of recording materials, the authorized use of which is generally to be demonstrated by a specific marking of the material approved for this purpose, various solutions of authenticity-proofing security features have already been proposed in the past.

Proof of authenticity for documents in the form of passive examinations, for example, is made possible by watermarks. A watermark in the original sense is understood to mean a drawing in the paper that is caused by different paper thicknesses. A distinction is made between genuine watermarks which are produced by displacement (so-called light watermarks) or by enrichment (so-called shadow watermarks) of the fiber mass, for example using a dandy cutter in the wire section of a paper machine, so-called molten watermarks. which are produced by the embossing of the still wet paper in the press section of a paper machine, and finally spurious watermarks, the latter usually outside the paper machine either by embossing or by printing the finished paper with a colorless, even under UV light fluorescent Paint to be created. Of course, in the example of a fake watermark described last, no different paper thickness is caused by the drawing in the paper.

From the state of the art to be discussed here is, for example, the DE 690 01 677 T2 the proposal for a synthetic print carrier with pseudo watermark, which is a substrate made of plastic, at least one, preferably by means of gravure applied, the opacity of the print carrier changing authentication or safety mark and at least one printable pigment coating covering the mark. The monochrome or polychrome character should hardly be visible in reflected light, but should be clearly visible in transmitted light. A disadvantage of the known print carrier is that the printed pseudo watermark can be forged relatively easily, which can not be prevented even by simple pigment coatings to be applied thereto.

In principle, heat-sensitive recording materials having authenticity-proofing security features in the form of spurious and fluorescent watermarks are also known. So revealed the EP 0 844 097 A1 for a thermosensitive recording material as a first security feature, a latent image printed on the back surface of the recording material, which is prepared by means of a fluorescent ink containing a fluorescent reagent. To form a second security feature in the form of a watertight image on the backside of the thermosensitive recording material, the security ink contains a water-repellent agent. The thus constructed security ink with the fluorescent reagent in the form of pigment or dye and with the water-repellent agent is contained or dispersed in an aqueous vehicle, which may contain a binder other than these components. The disadvantage of this proposal is first that the water-repellent character of the security ink complicates the often common arrangement of pictorial Vorbedruckungen or labels by means of the usual printing process.
EP-A-854 451 is another example of the prior art.

A further disadvantage of the basic type of spurious watermarks conventionally known from the prior art, as it also applies to the above-discussed document, lies in their subsequent application to the finished paper by embossing or single-layer printing, which is why their counterfeiting can be realized relatively easily ,

Based on the above-described prior art, the object is to provide a security feature that is as universally applicable as possible for incorporation into a recording material that is as difficult as possible to falsify. Another object is, in particular, a heat-sensitive To provide recording material with a new security feature that is as universally applicable and difficult to fake as possible.

In general, the inventor first recognized that basically the above-described prior art can be summarized such that the closer the creation of a security feature in the manufacturing and processing chain is to the original creation point, the more difficult it becomes to imitate the security feature in counterfeiting intent. Against this background, a security feature coated with a, ideally still aftertreated or further coatings, fulfills to a very special degree the requirement profile of the security feature of a counterfeiting or imitation intended for counterfeiting which is unlikely to be realized.

In particular, the inventor recognized that the object can be achieved with a security feature in the form of a luminescent label for incorporation into a recording material, the security feature comprising a radiation layer with luminescent constituents and a masking layer with cavity pigments at least partially covering the radiation layer, and wherein the cavity pigments the masking layer may be fused by localized heat treatment in the form of a marking and at the heat treated sites the masking layer may become transparent.

As luminescent constituents in the sense of the invention in all proposed embodiments and variants apply, for example, the radiation layer added pigments, colors - such as optical brightener - and treated with such pigments or dyes particles, such as fibers that can be excited by energy absorption to emit light. To a particular extent, the luminescent constituents are to be understood as those which can be excited by excitation with UV light for the emission of visible light over a period of fractions of a second to more than half an hour. Such ingredients are referred to as fluorescent within the meaning of this invention and are considered to be particularly preferred.

The cavity pigments of the masking layer have a wall of plastic which melts under a high heat input, ideally of thermoplastic Resin on. This thermoplastic resin or the hollow shell pigment outer wall itself preferably comprises (meth) acrylonitrile copolymer, polyvinyl chloride, polyvinylidene chloride, polystyrene, styrene acrylate, styrene (meth) acrylate copolymer, polyacrylonitrile, polyacrylic acid ester or else the mixture of at least two of the components mentioned , In the same way pigment mixtures of different hollow-shell pigments are conceivable for the masking layer. For the purposes of the present invention, so-called "cup-shaped" pigments also apply as hollow-shell pigments. Unlike the classic cavity pigments, where an inner core of gas, usually air, is completely enclosed by a shell of organic, usually thermoplastic, components, the cup-shaped pigments do not have a closed shell and surround the inner core only in the form of a - as far as possible closed - cup or cup (= "cup").

A glass transition temperature for the thermoplastic resin of the outer shell of the hollow-shell pigment in a range from 35 ° C to less than or equal to 200 ° C and preferably in a range from 75 ° C to less than or equal to 120 ° C has been found advantageous because below temperatures of 35 ° C, the wall of the Hohlraumpigmente at room temperature is no longer sufficiently stable. Above temperatures of 200 ° C, there are handling problems of over heating the surface of the recording material. The preferred temperature range of between 75 ° C to less than or equal to 120 ° C provides the simplest conditions in terms of processing quality and speed in completing the proposed security feature by fusing the cavity pigments into a pattern.

In order to form the security feature according to the invention, its radiation layer with the luminescent or preferably UV-fluorescent constituents is first opaque covered by the masking layer with the cavity pigments. Because of the opacity of the masking layer caused by the hollow-shell pigments, no luminescence or fluorescence of the radiation layer can thus be detected. By locally, preferably sharply delimited, heat supply in the form of any pattern, the cavity pigments of the masking layer are fused, for example by means of the printhead of a thermal printer. In the masking layer are then at the heat treated sites, the Hohlraumpigmente no longer in the form of individual particles, each consisting of a thermoplastic shell and in its interior of an enclosed by the shell core with air, but in the form of a uniform, milky translucent enamel layer, which has thus lost its opacity. The loss of opacity is explained by the different refractive indexes of the plastic wall of the cavity pigments and the air in the interior of the non-fused cavity pigments. If the masking layer is not covered by at least one further, white or other colored layer, the radiation layer and the masking layer of the proposed security feature should have the same color, since at the heat treated areas the masking layer becomes transparent and releases the view of the radiation layer arranged below it. The color for the radiation layer and for the masking layer of the proposed security feature is particularly suitable for whitening, since the masking layer is already white because of the non-fused state of white cavity pigments without the addition of further pigments or colors. However, the proposed security feature can also be used without restriction with a bright coloring of the radiation layer and the masking layer and is consequently regarded as a possible form of the proposed security feature.

An important advantage of the security feature according to the invention is its completion in the form of an individual pattern using, for example, a thermal printer only after completed production of a recording material having the two layers of the proposed security feature. Thus, on the one hand a recording material with authentizitätsnachweisendem security feature of the public can be proposed, which can be produced economically without the need for individual tools, on the other hand, the security feature virtually no longer be falsified, because now even on a single copy related security features, for example, created with consecutive number can be.

FIG. 1 shows the basic structure of the security feature according to the invention with a radiation layer (1) and a masking layer (2) covering the radiation layer (1). In the figure, the areas (2-1) of the masking layer (2) are those in which the cavity pigments are fused by heat treatment and why the masking layer (2) is milky translucent at these areas (2-1), hatched, while the areas (2-2) of the masking layer (2) are uniformly blackened with unfused cavity pigments - indicative of opaque coverage , In the following figures is dispensed with a different representation of milky translucent and opaque areas of the masking layer (2).

In a first, very simple embodiment of the invention, a recording material having the new security feature comprises a luminescent constituent white substrate as the radiation layer. The masking layer is applied to the substrate, for which a region is generally considered to be preferred in terms of basis weight between 1 and 6 g / m ² , and a range between 2 and 3 g / m ² is considered to be particularly preferred. In various series of tests it was recognized that with a basis weight of the masking layer of less than 1 g / m ^2, the coverage of the radiation layer is often no longer sufficiently to ensure, while forming the masking layer with a basis weight of well over 6 g / m ² for economic reasons does not make sense. The masking layer generally has, in addition to the hollow-shell pigments with a percentage weight fraction based on the total weight (atro) of the masking layer in a preferred range of from 50 to 95% by weight, only binders in the required amount. The Hohlraumpigmente are partially fused in the form of a pattern. For the preferred case that the luminescent components are fluorescent under UV light, the recording material appears white under daylight, there is no indication of any incorporated security feature. On the other hand, when the recording material is observed under UV light, the fluorescent components of the substrate become visible at the positions through the masking layer where the cavity pigments of the masking layer are fused by heat treatment.

In order to improve the external appearance of a recording material with the proposed security feature, a protective layer or a pigment coating which improves the printability-if necessary also by the inkjet process-can be applied to the masking layer. Although such a layer weakens the recognition of the incorporated security feature, but remains at a white or not darkened pigment coating and even more so in a preferably colorless designed protective layer visible at the fused sites through the masking layer fluorescence from the radiation layer sufficiently visible.

FIG. 2 shows a recording material with the security feature according to the invention, wherein the recording material is designed in one of its simplest embodiments. The masking layer (2), whose hollow-chamber pigments are fused by means of a print head of a thermal printer in the form of a pattern, is applied to a substrate (11) in the form of a radiation layer, for example with fibers which fluoresce under UV light. The masking layer (2) completely covers the underlying substrate (11). The masking layer (2) is in turn covered by a protective layer (40).

If no luminescent or preferably UV-fluorescent constituents are usually incorporated into the substrate for reasons of production technology, it is advisable to form a separate first coating as the radiation layer with the luminescent / fluorescent constituents below the masking layer. In this case, a surface-related mass for the radiation layer in a range of 5 g / m ² to 20 g / m ² is preferred. At the same time, the percentage by weight of luminescent / fluorescent constituents in the radiation layer related to the total weight (atro) of the radiation layer is preferably in a range from 0.2 to 5% by weight (atro). Other particularly leveling coatings, which may be applied between the substrate and the radiation layer, have the necessary need for luminescent / fluorescent constituents to be incorporated because of the radiation layer to be applied with only a very small area-related mass, optionally in a range between 1 g / m ² and 5 g / m ² , in which case the proportion of luminescent / fluorescent constituents in the radiation layer may well be in a range from 1 to 10% by weight (atro). Irrespective of this, a protective layer or the printability - if necessary also in the inkjet process - which improves the pigment coating can additionally be applied above the masking layer.

Because of the completion of the pattern-containing security feature, preferably using the printhead of a thermal printer, the proposed security feature is particularly suitable for incorporation into a heat-sensitive recording material.

According to the invention, such a heat-sensitive recording material comprises a radiation layer with luminescent, in a preferred embodiment under UV light fluorescent constituents and a masking layer at least partially covering the radiation layer with Hohlraumpigmenten, wherein the Hohlraumpigmente the masking layer are fused or fused by localized heat treatment in the form of a marker can be. The radiation layer comprising the luminescent constituents, which are preferably fluorescent under UV light, and the masking layer containing the hollow-content pigments of the proposed heat-sensitive recording material should preferably have the same color.

In a first, simple embodiment, luminescent or preferably UV-fluorescent components are incorporated into the substrate as the radiation layer of the proposed heat-sensitive recording material. On the substrate, a masking layer is applied with Hohlraumpigmenten, which are fused by localized heat treatment in the form of a marker. Applied to the masking layer is a heat-sensitive recording layer having at least one dye precursor and at least one color acceptor, the dye precursor and color acceptor reacting with each other in a color-forming manner under the action of heat. The heat-sensitive recording layer can completely and completely cover the masking layer arranged below it in a first variant. In a further variant, the heat-sensitive recording layer is applied to the masking layer only in the form of small, for example, rectangular or circular surface areas - so-called "spots" - of a few centimeters in size, that is to say preferably imprinted here. Then, areas covered by the masking layer are adjacent to areas covered by the heat-sensitive recording layer having an underlying masking layer. While the regions with the spot-like heat-sensitive recording layer are particularly suitable for the formation of individual fields, for example with seating on admission tickets, the remaining ones can be used Areas that are not covered with the heat-sensitive recording layer, but only with the masking layer, in particular frame information, such as event marking and advertising on tickets, play, for example, by printing them, for example, in flexographic printing.

As an alternative to the structure described above, the heat-sensitive recording layer can also be applied to the substrate first, which in turn is at least partially covered by the subsequently applied masking layer with the cavity pigments. In this variant, either the substrate can act as a radiation layer with the luminescent or preferably under UV light fluorescent constituents, wherein the heat-sensitive recording layer is formed as transparent as possible to let the luminescence or fluorescence radiation of the substrate shine through as unhindered as possible, or the heat-sensitive Recording layer contains the luminescent or preferably under UV light fluorescent constituents and acts as a radiation layer. Of course, it is also possible that both substrate and heat-sensitive recording layer have the luminescent or preferably under UV light fluorescent constituents, just as it is generally possible for all proposed embodiments and variants of the present invention, that also two superimposed layers as Radiation layers are formed. In this case, it is also possible for the two radiation layers then to have different luminescent constituents or components preferably fluorescent under UV light which emit light of different colors, for example, as well as different luminescent or preferably UV fluorescent constituents also in only one radiation layer According to all embodiments and variants of the proposed invention are possible.

For reasons of production engineering, it is sometimes impossible to introduce luminescent constituents into the substrate as well as into the heat-sensitive recording layer. Therefore, in a preferred embodiment, the proposed thermosensitive recording material comprising a substrate, a heat-sensitive recording layer and a masking layer comprises at least one intermediate layer interposed between the substrate and the thermosensitive recording layer and functioning as a radiation layer. Is the intermediate layer in a preferred Furthermore, when applied to leveling coaters, such as roll coaters, doctor blade or doctor roll coaters, the intermediate layer can further positively contribute to leveling of the substrate surface, thus reducing the amount of coating material necessary for the heat-sensitive recording layer to be applied. For the basis weight of the intermediate layer, a preferred range between 5 and 20 g / m ² and even better between 6 and 10 g / m ^{2 has} proven. The percentage by weight of luminescent / fluorescent components based on the total weight (atro) of the intermediate layer is preferably in a range of 0.2 to 5% (atro).

If inorganic oil-absorbing pigments are incorporated into the intermediate layer located below the thermosensitive recording layer, these pigments can absorb the thermally-curable wax components of the thermosensitive recording layer in the typeface formation and thus promote a still safer and faster functioning of the heat-induced recording, which is possible because of a possible energy-absorbing, On the recording layer applied masking layer lt. A claimed embodiment is of particular importance. Likewise, a layer construction is possible in which the masking layer and then the heat-sensitive recording layer are applied first above the pigmented intermediate layer formed as a radiation layer.

Preferred inorganic pigments of the intermediate layer are those selected from the group comprising natural and calcined kaolin, silica, bentonite, calcium carbonate and aluminum oxide, in particular boehmite here. Also mixtures of several different types of inorganic pigments are conceivable.

The particle size of the inorganic pigments present in the intermediate layer, determined as the D ₅₀ value, is preferably in a range of less than 2 μm. Pigments which have a particle size distribution of from 34 to 40% by weight of less than 1 μm and from 57 to 63% by weight of less than 2 μm have proved to be advantageous.

In addition to the inorganic pigments, the pigmented intermediate layer contains at least one binder, preferably based on a synthetic polymer, wherein, for example, styrene-butadiene latex gives particularly good results. The use of a synthetic binder with admixture of at least one natural polymer is a particularly suitable embodiment. It has also been found in experiments that with a binder to pigment ratio within the pigmented interlayer between 1:10 and 1:20 a particularly suitable embodiment is present.

In order to improve environmental resistance, which is to be understood here in particular as resistance to plasticizers, oils, fats and moisture in general and sprayed-on water in particular, the proposed heat-sensitive recording material according to all proposed embodiments and variants preferably has a protective layer comprising the recording material completely covers the side with the recording layer. Depending on the embodiment, with a recording layer applied to the masking layer, optionally only as a "spot" application, or alternatively with a masking layer applied to the recording layer, the protective layer can be applied both to the recording layer and to the masking layer.

The single-layer or multi-layered protective layer may in a first embodiment be a coating applied conventionally in a coating machine by means of a curtain or spray coater, airbrush, doctor blade or (roll) doctor blade coating, with a surface-related mass in a range of 1.5 to 6 g / m ² and especially between 1.8 and 4 g / m ^{2 has} proven.

In order to increase the printing, the protective layer initially contains one or more inorganic pigments, wherein in particular the incorporation of a highly purified, alkaline-treated bentonite is advantageous. Other pigments are in particular natural or precipitated calcium carbonate, kaolin, titanium oxide and especially aluminum hydroxide and silicas. In addition to the pigments, the protective layer contains one or more binders, for example selected from the list comprising water-insoluble, self-crosslinking acrylic polymers, polyvinyl alcohol and polyvinyl alcohol derivatives, in particular silanized polyvinyl alcohol, and optionally and depending on the chosen binders also crosslinking agents. In particular, cyclic urea, methylol urea, polyamide-epichlorohydrin resin, ammonium zirconium carbonate and glyoxal are suitable as crosslinking agents.

As an alternative to the more conservative protective layer described above, the proposed recording material may also preferably have a protective layer crosslinkable under the influence of UV radiation, which may optionally be applied conventionally by means of a curtain or spray coater, airbrush, doctor blade or doctor blade coater or alternatively in a very particularly preferred embodiment is printed. After the application / imprinting of the protective layer, the curing takes place by means of UV irradiation.

In combination with the above-described embodiments and variants, it is suitable, inter alia, and to a particular extent, to apply to a substrate at least one pigmented intermediate layer formed as a radiation layer with constituents that are preferably fluorescent under UV light, to which a heat-sensitive recording layer is in turn applied , Between the recording layer and the final protective layer, the masking layer is located in the form of a pattern of fused cavity pigments. With a view to a particularly contoured thermal print image formed by the irradiation of the heat-sensitive recording layer with the printhead of a thermal printer, it may also be advantageous if the masking layer acts on the at least one intermediate layer functioning as the radiation layer, and on the heat-sensitive recording layer is applied with the final protective layer. Both embodiments are suitable to a very special extent to provide a heat-sensitive recording material with high environmental resistance and individually producible, difficult to falsifying security feature of the public, which is why they are considered to be preferred in a very special degree. As a variant of the last-described embodiment with a marking layer applied to the radiation layer, the heat-sensitive recording layer is applied to this masking layer only in the form of small surface areas, so-called "spots", which means here preferably printed. Then, areas covered by the masking layer are adjacent to areas that are covered by the heat-sensitive recording layer with underlying masking layer.

FIG. 3 shows an embodiment of the proposed thermosensitive recording material with security feature, wherein the recording material in this case, a polyolefin coated paper as a substrate (10), on which an applied as a radiation layer with here, for example, under UV light fluorescent colors formed intermediate layer (21). The intermediate layer (21) is covered over its entire surface with a masking layer (2), the hollow-shell pigments of which are partially fused in the form of a pattern. In this case, besides the masking layer (2), since a heat-sensitive recording layer (30) is to be applied to the masking layer (2), in addition to the cavity pigments, inorganic oil-absorbing pigments may additionally contain the wax components of the thermosensitive recording layer (30) liquefied by heat of the thermal head can take the Schnugbildbildbildung. In this case, a ratio of hollow pigments to inorganic pigments in the masking layer (2) between 5: 1 and 2: 1 is recognized as advantageous. The heat-sensitive recording layer (30) is applied to the masking layer (2) here only in the form of small areas - so-called "spots". The recording material is covered on the heat-sensitive recording layer (30) side by means of a protective layer (40) formed partly on the masking layer (2) and partly on the heat-sensitive recording layer ('spotwise') forming the heat-sensitive recording layer (30). 30) is applied.

In FIG. 4 Another embodiment of the proposed heat sensitive recording material with security feature is shown. A substrate (10) in this case made of a non-surface-treated coated base paper has a first leveling intermediate layer (20) and a second intermediate layer (21) formed as a radiation layer with pigments that fluoresce under UV light. Since a heat-sensitive recording layer (30) is to be applied to the second intermediate layer (21), the second intermediate layer (21) additionally contains, in addition to the pigments which fluoresce under UV light, inorganic oil-absorbing pigments which reduce the heat constituents of the heat-sensitive recording layer liquefied by the thermal action of the thermal head (30) in typeface education be able to record. The heat-sensitive recording layer (30) is in the in FIG. 4 shown case the entire surface of the second intermediate layer (21) applied. On the heat-sensitive recording layer (30) are first a masking layer (2) pigmented in the form of a pattern partially fused cavity and then a protective layer (40) applied.

For partially fusing the cavity pigments in the form of a pattern, heat is locally supplied to the proposed thermosensitive recording material by, for example, the printhead of a thermal printer so that the pattern-like security feature is formed in the masking layer, if possible not the typeface within the thermosensitive recording layer. For this purpose, it is necessary, in particular, that the color forming temperature of the heat-sensitive recording layer be raised to a temperature T ₂ which is above the fusing temperature T _{1 of} the hollowing pigments in the masking layer. Because of T ₂ > T _{1, it} is also possible to form the masking layer above the heat-sensitive recording layer in one embodiment. If such a heat-sensitive recording material according to the invention, the cavity pigments of which are fused in the security feature masking layer in the form of a pattern to be printed by thermal printer causes when the recording material in the thermal printer, the print head on the one hand, the formation of the typeface in the recording layer, on the other the cavity pigments of the masking layer at the locations where the typeface is caused in the recording layer are fused in addition to the formed security pattern, thus exposing the typeface formed in the recording layer.

To increase the color formation temperature or to reduce the color formation sensitivity, there is a well-known, industrially used and preferred option for all embodiments and variants of the proposed thermosensitive recording material in the incorporation of at least one compound from under the action of heat color forming mutually reactive Dye precursor and color acceptor in microcapsules, which are incorporated into the heat-sensitive recording layer.

In particular, in the production of multicolor heat-sensitive recording materials, the encapsulation of dye precursor and / or dye acceptor is common. Various types of methods for preparing the dye precursor-containing microcapsules have been found to be particularly suitable, including, inter alia, the interfacial polymerization method, a coacervation method, a spray-drying method, and the emulsion evaporation-solidification method. A particularly suitable method for encapsulating dye precursor and / or dye acceptor is disclosed in U.S. Pat DE 198 54 866 A1 on page 4 from line 5 to page 13, line 18, proposed, which is why this encapsulation method also applies as very particularly preferred in the context of the present invention.

The formation of a heat-sensitive recording layer covering, optionally multi-layer protective layer and according to a variant, the arrangement of the masking layer between heat-sensitive recording layer and protective layer increases the distance between the recording layer and the print image causing printhead of a thermal printer. As the distance between the recording layer and the printhead of the thermal printer becomes larger, the resolution inevitably deteriorates, and the resolution is approximately inversely proportional to the square of the distance between the recording layer and the thermal head. A heat-sensitive recording layer, which effectively counteracts this physical effect by guaranteeing optimized resolution, is of particular importance against this background. In principle, the heat-sensitive recording layer may contain all known dye precursors and, in particular, color acceptors suitable for this purpose, in particular organic dye acceptors. Without being limited thereto, however, particularly preferred dye precursors are selected from the group comprising
3-diethylamino-6-methyl-7-anilinofluoran,
3-dibutylamino-6-methyl-7-anilinofluoran,
3- (N-methyl-N-propyl) amino-6-methyl-7 anilinofluoran,
3- (N-ethyl-N-isoamyl) amino-6-methyl-7-anilinofluoran,
3- (N-methyl-N-cyclohexyl) amino-6-methyl-7-anilinofluoran,
3- (N-ethyl-N-tolyl) amino-6-methyl-7-anilinofluorane
and 3- (N-ethyl-N-tetrahydrofuryl) amino-6-methyl-7-anilinofluoran,
as well as in detail suitable organic color acceptors selected from the group comprising
2,2 bis (4-hydroxyphenyl) propane,
4 - [(4- (1-methylethoxy) phenyl) sulfonyl] -phenol,
4,4'-dihydroxy-diphenyl sulfone,
N- (p-toluensulphonyl) -N '- (3-p-toluensulphonyl-oxy-phenyl) -ureas,
2,4'-dihydroxy-diphenyl sulfone
and N- (2-hydroxyphenyl) -2 - [(4-hydroxyphenyl) thio] acetamide,
Of course, without being limited to the color acceptors mentioned. For the dye precursors, an average particle size in a range from greater than 0.3 μm to a maximum of 1.5 μm, in particular from 0.45 μm to 0.9 μm, is recommended. The limits are given upwards by a too low sensitivity and down by an otherwise too strong inclination of the heat-sensitive recording material for graying.

Roller coater, knife coater, curtain coater or air brush are particularly suitable as coating apparatus for applying the heat-sensitive recording layer. According to a preferred embodiment, the coating composition used to form the recording layer is aqueous. The subsequent drying of the coating composition is usually done by a method in which heat is supplied, as is done by hot-air floating dryer or contact dryer. Proven is also a combination of the listed dry processes. The basis weight of the heat-sensitive recording layer is preferably from 2 to 6 g / m ^2, and more preferably from 2.3 to 5.8 g / m ² .

Although not limited to paper as a substrate, paper is especially non-surface treated here. In a range for the basis weight between 50 and 180 g / m ^2, a coating of raw paper prefers the substrate, which is also marketable with regard to good environmental compatibility because of its good recyclability has enforced and which is preferred for the purposes of the invention. A non-surface treated base paper is to be understood as meaning a base paper which has not been treated in a size press or in a coating device. For the invention, films of, for example, polyolefin and polyolefin-coated papers as a substrate are possible to the same extent, without such an embodiment having an exclusive character.

In a particular embodiment, the heat-sensitive recording material according to the invention is provided as a label with a backside (self) adhesive layer. Depending on requirements, the adhesive layer can be covered with a release material such as a silicone-containing release paper or the outer protective layer of the novel recording material is provided with an additional release layer which is preferably printed - ideally by means of flexographic printing. The release layer in this case has release agents based on silicone oil and / or silicone grease. By carrying out the release layer with silicone oil and / or silicone grease, the proposed recording material with self-adhesive backing without release paper can be wound up in a roll, so that the self-adhesive layer and the release layer come into contact in the roll without permanent bonding.

In a particularly preferred embodiment, the release layer is curable or crosslinkable under the influence of high-energy radiation, such as UV or electron radiation. If the release layer is to be cured by means of UV rays, the monomers or prepolymers used for the preparation of this layer must contain additives of photoinitiators in a known manner. By electron beam curing, a particularly uniform over its cross-section, that is cured release layer could be achieved.

The details given in the description and patent claims relating to basis weight,% by weight (% by weight) and parts by weight (parts by weight) relate in each case to the "atro" weight, ie absolutely dry parts by weight. In the comments on the cavity pigments of the masking layer, the relevant figures are calculated from the "lutro" weight, ie air-dry parts by weight, minus the proportion by weight of water around and inside the pigments as supplied.

The invention will be further illustrated by the following examples.

Example 1:

On a Langsieb paper machine, a paper web of bleached and ground hardwood and softwood pulps with a basis weight of 67 g / m ² is prepared as a substrate with the addition of conventional blending substances in conventional amounts. On one side of the substrate, a mainly calcined kaolin pigment, Styrolbutadienlatex as a binder and starch as Cobinder having intermediate layer of 8 g / m ^{2 is} applied and dried with a doctor blade. For the formation of the intermediate layer as a radiation layer in the context of the present invention, the intermediate layer under UV light contains fluorescent colors in the form of optical brighteners in an amount of 2% by weight (atro), based on the total weight of the intermediate layer (atro). A masking layer is applied to the intermediate layer using a roller blade coater and dried with 16.67% by weight of (atro) binder and 83.33% by weight of voided pigments. In this case, the percentages are based on the total weight (atro) of the finished masking layer whose basis weight is 2.5 g / m ² . The finished paper is fed to a thermal printer. The cavity pigments of the masking layer are partially fused by the printhead of the thermal printer according to a predetermined check pattern to form areas in the masking layer with fused cavity pigments and areas of unfused cavity pigments. Under daylight, the paper coated with radiation and masking layer appears uniformly white. Under UV light, strong fluorescence is seen at the areas of the masking layer in which the high-rise pigments are fused together by the heat input of the printhead of the thermal printer. The fluorescence originates from the fluorescent constituents of the intermediate layer, whose emitted light beams can be recognized by the transparent regions of the masking layer with the cavity pigments fused there.

Example 2:

The paper with substrate already used in Example 1, the intermediate layer formed as a radiation layer and the masking layer applied thereon are provided with a heat-sensitive recording layer which is applied to the masking layer over its entire area with a basis weight of 4 g / m ² . The heat-sensitive recording layer comprises 13.89% by weight of binder, 27.78% by weight of color acceptor, and 58.33 of encapsulated dye precursors. Here is as encapsulation in the DE 198 54 866 A1 described method has been used. On the heat-sensitive recording layer, a UV-curable protective layer of 2 g / m ^{2 has been} applied by flexographic printing. The thus-finished heat-sensitive recording paper is fed to a thermal printer. The cavity pigments of the masking layer are partially fused according to a predetermined stripe pattern by the printhead of the thermal printer at a temperature T ₁ of 101 ° C, so that areas in the masking layer with fused Hohlraumpigmenten and areas with unfused Hohlraumpigmenten arise. Using a temperature T ₂ of 145 ° C, a predetermined typeface is formed in the heat-sensitive recording layer by the printhead of the thermal printer. Under daylight, the heat sensitive recording paper appears uniformly white with thermo typed image. Under UV light, strong fluorescence can be seen at the areas of the masking layer in which the cavity pigments are fused together by the heat input of the printhead of the thermal printer. The fluorescence originates from the fluorescent constituents of the intermediate layer, whose emitted light rays can be recognized by the transparent regions of the masking layer with the cavity pigments fused there.

Term list :

• (1) radiation layer
• (2) masking layer
  • (2-1) milky translucent areas of the masking layer
  • (2-2) opaque areas of the masking layer
• (10) Substrate
  • (11) Substrate as a radiation layer
• (20) Interlayer
  • (21) Intermediate layer as a radiation layer
• (30) heat-sensitive recording layer
• (40) protective layer

Claims (19)

1. Safety feature in the form of a luminescent marker for incorporation into a recording material by bonding, wherein the safety feature has a radiation layer having luminescent components and has a masking layer having hollow pigments, which masking layer covers the radiation layer at least partially, it being possible for the hollow pigments of the masking layer to be fused together in the form of a marker by locally delimited heat treatment and for the masking layer to be transparent at the heat-treated sites.
2. Safety feature according to claim 1, characterised in that the hollow pigments of the masking layer are fused together in the form of a marker by locally delimited heat treatment.
3. Safety feature according to claim 1 or 2, characterised in that the components of the radiation layer are fluorescent under UV light.
4. Safety feature according to any one of claims 1 to 3, characterised in that the hollow pigments of the masking layer are formed as "cup-shaped" pigments.
5. Safety feature according to any one of claims 1 to 4, characterised in that the radiation layer and the masking layer are the same colour.
6. Safety feature according to any one of claims 1 to 5, characterised in that the recording material has a substrate which, as radiation layer of the safety feature, contains the luminescent components.
7. Safety feature according to any one of claims 1 to 6, characterised in that the masking layer is coated with a protective layer.
8. Heat-sensitive recording material having a safety feature in the form of a luminescent marker, characterised in that the safety feature has a radiation layer having luminescent components and has a masking layer having hollow pigments, which masking layer covers the radiation layer at least partially, it being possible for the hollow pigments of the masking layer to be fused together in the form of a marker by locally delimited heat treatment.
9. Heat-sensitive recording material according to claim 8, characterised in that the hollow pigments of the masking layer are fused together in the form of a marker by locally delimited heat treatment.
10. Heat-sensitive recording material according to claim 8 or 9, characterised in that the components of the radiation layer are fluorescent under UV light.
11. Heat-sensitive recording material according to any one of claims 8 to 10, characterised in that the recording material has a substrate which, as radiation layer, contains the luminescent components.
12. Heat-sensitive recording material according to any one of claims 8 to 11, characterised in that the recording material has a heat-sensitive recording layer which is applied in the form of a locally delimited "spot" to the masking layer.
13. Heat-sensitive recording material according to any one of claims 8 to 10, characterised in that the recording material has at least

    - a substrate,

    - a heat-sensitive recording layer,

    - an intermediate layer, formed as a radiation layer having luminescent components, which is located between the substrate and the heat-sensitive recording layer

    - and a masking layer having hollow pigments.
14. Heat-sensitive recording material according to claim 13, characterised in that the intermediate layer contains inorganic pigments selected from the group comprising natural, such as calcined, kaolin, silicon dioxide, bentonite, calcium carbonate, aluminium oxide and boehmite.
15. Heat-sensitive recording material according to claim 13 or 14, characterised in that the masking layer covers the heat-sensitive recording layer at least partially.
16. Heat-sensitive recording material according to claim 13 or 14, characterised in that the masking layer is located between the heat-sensitive recording layer and the intermediate layer formed as radiation layer.
17. Heat-sensitive recording material according to claim 16, characterised in that the heat-sensitive recording layer is applied in the form of a locally delimited "spot" to the masking layer.
18. Heat-sensitive recording material according to any one of claims 8 to 17, characterised in that the recording material has at least one protective layer, which is applied as the layer the most remote from the substrate to the side of the substrate having the heat-sensitive recording layer.
19. Heat-sensitive recording material according to any one of claims 8 to 18, characterised in that the recording material has a heat-sensitive recording layer, which contains at least one colour precursor and at least one colour acceptor, wherein colour precursor and colour acceptor react with one another under the action of heat to form colour, and wherein at least one component from colour precursor and colour acceptor is present in microcapsules.

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