EP1778499A1

EP1778499A1 - Security feature for recording materials

Info

Publication number: EP1778499A1
Application number: EP05759525A
Authority: EP
Inventors: Takao Masuda
Original assignee: Mitsubishi HiTech Paper Flensburg GmbH; Stora Spezialpapiere GmbH
Current assignee: Mitsubishi HiTech Paper Flensburg GmbH; Stora Spezialpapiere GmbH
Priority date: 2005-06-22
Filing date: 2005-06-22
Publication date: 2007-05-02
Anticipated expiration: 2025-06-22
Also published as: JP4751447B2; US20080157517A1; JP2008546566A; ATE398534T1; EP1778499B1; ES2308516T3; US8524633B2; WO2006136188A1; DE502005004468D1

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

Security feature for recording materials

The invention relates to a security feature in the form of a luminescent marking for inclusion in a recording material and 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.

Authenticity proofs for documents in the form of passive examinations are made possible, for example, 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.

[0004] From the prior art to be discussed here, for example, DE 690 01 677 T 2 discloses the proposal for a synthetic print carrier with pseudo-water mark, which is a plastic substrate, at least one, preferably gravure printed, the opacity of the Print carrier changing authentication and at least one printable pigment coating covering the indicia. 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 counterfeited relatively easily, which can not be prevented even by simple pigment coatings to be applied thereto.

[0005] In principle, heat-sensitive recording materials with authenticity-proofing security features in the form of fake and fluorescent watermarks are also known. Thus, EP 0 844 097 A1 for a thermosensitive recording material discloses, as a first security feature, a latent image printed on the back side of the recording material, which is produced by means of a security 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.

Another disadvantage of the basic nature of the commonly known from the prior art spurious watermarks, as it also applies to the above discussed font, is in their subsequent application to the finished paper by embossing or single-layer imprint, which is why their fake relatively easily to realize.

Based on the above-reproduced prior art, the object is to provide a universal security feature for inclusion in a recording material that is difficult to fake as possible. 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.

The inventor first recognized in general that basically the above-mentioned prior art can be summarized such that the closer the creation of a security feature in the manufacturing and processing chain is moved to the original production point, the more difficult is the imitation of the security feature in fraudulent intent. Against this background, a security feature coated with one, ideally still aftertreated, or further coatings, satisfies to a very particular extent the requirement profile of the security feature of a counterfeiting or imitation intended for counterfeiting which is as far as possible unrealizable.

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 having a radiation layer with luminescent constituents and a masking layer with hollow-shell pigments at least partially covering the radiation layer, and wherein the cavity pigments of the masking layer are fused by localized heat treatment in the form of a marking.

As luminescent constituents in the context of the invention in all proposed embodiments and variants apply, for example, the radiation layer added pigments, colors - such as optical brighteners - and treated with such pigments or dyes particles, such as fibers excited by energy absorption for light emission can be. 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 hollow-body pigments of the masking layer have a wall of plastic which melts under high heat input, ideally of thermoplastic material. Shiny resin. This thermoplastic resin or the Hohlraumpigment- outer wall itself preferably comprises (meth) acrylonitrile copolymer, polyvinyl chloride, polyvinylidene chloride, polystyrene, styrene acrylate, styrene (meth) acrylate copolymer, polyacrylonitrile, polyacrylate or the mixture of at least two of the above Components on. 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 are also considered as hollow-shell pigments, in contrast to conventional hollow-shell pigments in which an inner core of gas, usually of air, is completely enclosed by a shell of organic, usually thermoplastic constituents , The "cup-shaped" - pigments have no 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 Hohlraumpigment in a range of 35 ⁰ C to less than or equal to 200 ⁰ C and preferably in a range of 75 ⁰ C to less than or equal to 120 ⁰ C was found to be advantageous because below of temperatures of 35 ⁰ C, the wall of the cavity pigments at room temperature is no longer sufficiently stable. Above temperatures of 200 ⁰ C, there are handling problems in terms of excessive heating of the surface of the recording material. The preferred temperature range between 75 ⁰ C to less than or equal to 120 ⁰ C provides the simplest conditions in terms of processing quality and speed at the completion of the proposed security feature by merging the Hohlraumpigmente in the form of a pattern.

To form the security feature according to the invention whose radiation layer with the luminescent or preferably under UV light fluorescent constituents initially opaque covered by the masking layer with the Hohlraumpigmenten. 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, the Hohf raumpigmente 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 completion of production of the two layers of the proposed security feature having recording material. 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.

Figure 1 shows the basic structure of the security feature according to the invention with a radiation layer (1) and a radiation layer (1) covering masking layer (2). 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. On the substrate, the masking layer is applied, for which in principle a range with respect to the area-related mass between 1 and 6 g / m ^{2 is} considered preferred, is considered to be very particularly preferably a range between 2 and 3 g / m ² . 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. In the preferred case where the luminescent constituents 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.

To improve the external appearance of a recording material with the proposed security feature may be applied to the masking layer, a protective layer or the printability - if necessary, also in the inkjet process - improving pigment coating. 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.

Figure 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. On a formed as a radiation layer substrate (11) here, for example, with fluorescent under UV light fibers, the masking layer (2) is applied, the Hohlraumpigmente are fused by means of a print head of a Thermod jerkers in the form of a pattern. 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 under UV light fluorescent constituents usually incorporated in the substrate usually for technical production considerations, it makes sense to form below the masking layer, a separate first coating as a radiation layer with the luminescent / fluorescent constituents. 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, may 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 constituents which fluoresce under UV light in a preferred embodiment and a masking layer comprising hollow-body pigments at least partially covering the radiation layer, wherein the cavity pigments of the masking layer are produced by locally limited heat treatment in the form of a marking are fused or can be merged. 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.

[0022] In a first, simple embodiment, luminescent components or preferably components which fluoresce under UV light 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 a few centimeters in size in the form of small, for example, rectangular or circular surface areas - so-called "spots" - this means preferably imprinted Here, areas covered by the masking layer are adjacent While the areas with the spot-like heat-sensitive recording layer are particularly suitable for the formation of individual fields, for example with seat numbers on entrance tickets, the remaining areas can be covered by areas which are covered by the heat-sensitive recording layer with underlying masking layer. areas covered not with the heat-sensitive recording layer but only with the masking layer, in particular frame information, for example event marking and advertising on tickets, by being printed accordingly, for example by 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 hollow-shell 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 Fluoreszenzstrahiung the substrate shine through as unhindered, or the heat temp 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 two ü- arranged one above the other Layers are formed as radiation layers. In this case, it is also possible for the two radiation layers then to have different luminescent or preferably UV-fluorescent components which emit, for example, light of different colors, as well as different luminescent or preferably UV-fluorescent components in only one radiation layer according to all embodiments and variants of the proposed invention are possible.

From technical production considerations, sometimes the introduction of luminescent constituents in both the substrate as well as in the heat-sensitive recording layer prohibits. 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. If the intermediate layer is in a preferential zugten embodiment applied with egalisierenden coating devices, such as roller coater, doctor blade or (RoII-) Rakelstreichwerke, the intermediate layer can also make a positive contribution to equalization of the substrate surface, which reduces the amount of necessarily applied coating material for the heat-sensitive recording layer. 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 interlayer underneath the heat-sensitive recording layer, these pigments can absorb the wax constituents of the heat-sensitive recording layer liquefied by heat from the thermal head in the case of typeface formation and thus promote a still safer and faster functioning of the heat-induced recording which is of particular importance because of a possible energy-absorbing masking layer It. of a claimed embodiment applied to the recording layer. Similarly, a layer structure is possible in which above the pigmented and formed as a radiation layer intermediate layer, first the masking layer and then the heat-sensitive recording layer is applied.

Preferred inorganic pigments of the intermediate layer are those selected from the group comprising natural and calcined kaolin, silica, bentonite, calcium carbonate and alumina, and 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 as D ₅₀ white 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.

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

[0030] In a first embodiment, the protective layer embodied in one or more layers can be a coating applied conventionally in a coating machine by means of a curtain or spray coater, airbrush, doctor blade or doctor blade coating, wherein here one has surface mass in a range of 1.5 to 6 g / m ² and especially between 1, 8 and 4 g / m ^{2 has} proven.

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 also If appropriate, and depending on the selected binders and crosslinking agents. As crosslinking agents, cyclic urea, methylolurea, polyamide-epichlorohydrin resin, ammonium zirconium carbonate and glyoxal are particularly suitable here.

As an alternative to the more conservative protective layer described above, the proposed recording material may also preferably have a crosslinkable under the influence of UV radiation protective layer, which optionally applied classically by means of curtain or spray coater, air brush, doctor blade or (RoII) doctor blade coating or printed in a very particularly preferred embodiment. 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 in turn a heat-sensitive component Recording layer is 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 contour-sharp 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 acting as the radiation layer and then the masking layer heat-sensitive recording layer is coated 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 areas - so-called "spots", which are preferably printed on top Areas before that are covered by the heat-sensitive recording layer with underlying masking layer.

3 shows an embodiment of the proposed heat-sensitive recording material with security feature, wherein the recording material in this case has a polyolefin coated paper as a substrate (10) on which an interlayer (21) formed as a radiation haze with here, for example, fluorescent under UV light colors formed ) is applied. 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, in addition to the cavity pigments, since the masking layer (2) has a heat-sensitive recording layer (30), the masking layer (2) may additionally comprise inorganic oil-absorbing pigments which suppress the wax components of the heat-sensitive recording layer (30) liquefied by heat of the thermal head ) can take in the typeface education. 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 only in the form of small areas ("spots"). The recording material is covered on the side with the heat-sensitive recording layer (30) by means of a protective layer (40) because of the "spot" type formation of the thermosensitive recording layer (30) is partially applied on the masking layer (2) and partly on the thermosensitive recording layer (30).

In Figure 4 is another embodiment of the proposed heat-sensitive recording material with security feature! 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 UV-fluorescent pigments, inorganic oil-absorbing pigments which reduce the heat constituent of the heat-sensitive element liquefied by the thermal action of the thermal head Recording layer (30) in the writing to take up image training. In the case illustrated in FIG. 4, the heat-sensitive recording layer (30) is applied over the entire surface to the second intermediate layer (21). On the heat-sensitive recording layer (30) are first applied a masking layer (2) with partially fused in the form of a pattern Hohlraumpigmenten and then a protective layer (40).

For partial fusion of the Hohlraumpigmente in the form of a pattern of the proposed heat-sensitive recording material, for example by means of the printhead of a thermal printer locally supplied heat such that, although the pattern-like security feature is formed in the masking layer, if possible not the typeface within the heat-sensitive recording layer. For this purpose, it is necessary, in particular, to raise the color forming temperature of the thermosensitive recording layer to a temperature T ₂ which is above the fusing temperature Ti of the cavity pigments in the masking layer. Because of T ₂ > Ti, 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, whose hollow-shell pigments are fused in the form of a pattern belonging to the security feature, causes the print head to form the typeface in the recording layer, for example when the recording material is fed to the thermal printer On the other hand, in addition to the formed security pattern, the cavity pigments of the masking layer are fused at the places where the typeface is caused in the recording layer, thus revealing the typeface formed in the recording layer.

In order to increase the color forming temperature or to reduce the color forming sensitivity, there is a well-known and industrially used and preferred way 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. Especially in the production of multicolored heat-sensitive recording materials, the encapsulation of dye precursor and / or dye acceptor is common. Various types of methods for preparing the dye precursors or color acceptor-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 the encapsulation of dye precursor and / or dye acceptor is proposed in DE 198 54 866 A 1 on page 4 from line 5 to page 13, line 18, which is why this encapsulation method also very particularly preferred in the sense of the present Invention applies.

The formation of a thermosensitive recording layer covering, optionally multilayer protective layer and according to a variant, the arrangement of the masking layer between thermosensitive 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-Aniiinofluoran,

3- (N-methyl-N-cyclohexyl) amino-6-methyl-7-anilinofluoran, 3- (N-ethyl-N-tolyl) amino-6-methyl-7-anilinofluoran 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-toluenesulphonyl) -N ^' - (3-p-toluenesulphonyl-oxy-phenyl) -ureas,

^{2,4'-dihydroxy-diphenylsulfone} 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.

Roll coating 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 material 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 substrate, paper and especially a non-surface treated base paper is preferably in a range for the basis weight between 50 and 180 g / m ² substrate, which is also in the market with regard to the good Environmental compatibility due to 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 not 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 equipped as a label with back (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 under the influence of high-energy radiation, such as UV or electron radiation, hard or crosslinkable. 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 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 "Iutro" weight, ie air-dry weight solids. Ie, minus the proportion by weight of water around and inside the pigments in their form of delivery.

The invention will be further illustrated by the following examples.

Example - !:

On a fourdrinier paper machine, a paper web of bleached and ground deciduous and softwood pulps with a basis weight of 67 g / m ² is prepared as a substrate with the addition of customary admixtures 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 in accordance with a predetermined check pattern by the printhead of the thermal printer, so that areas in the masking layer with fused hollow-shell pigments and areas with unfused hollow-space pigments are formed. Under daylight, the paper coated with radiation and masking layer appears uniformly white. Under UV light, strong fluorescence is visible at the areas of the masking layer in which the cavities 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 already used in Example 1 paper with substrate, formed as a radiation layer intermediate layer and the masking layer applied thereto is provided with a heat-sensitive recording layer, which is applied over the entire surface with a basis weight of 4 g / m ² on the masking layer. 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. In this case, the method described in DE 198 54866 A1 has been used as the encapsulation method. 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 in accordance with a predetermined fringe pattern by the printhead of the thermal printer at a temperature Ti of 101 ° C., so that areas in the masking layer with fused hollow-shell pigments and areas with unmelted hollow-space pigments are formed. Using a temperature T ₂ of 145 ⁰ C is generated in the heat-sensitive recording layer by the print head of the thermal printer a predetermined typeface. Under daylight, the heat-sensitive recording paper appears uniformly white with a thermoformed 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. 050] list of terms:

(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

claims

1. security feature in the form of a luminescent marking for incorporation into a recording material, characterized in that the security feature has a radiation layer with luminescent constituents and a masking layer at least partially covering the radiation layer with Hohü- spacepigmenten, wherein the cavity pigments of the masking layer by locally limited heat treatment in the form a mark can be merged.

2. Security feature according to claim 1, characterized in that the Hohlraumpigmente the masking layer are fused by locally limited heat treatment in the form of a marker.

3. Security feature according to one of claims 1 and 2, characterized marked, that the constituents of the radiation layer are fluorescent under UV light.

4. Security feature according to one of claims 1 to 3, characterized in that the Hohlraumpigmente the masking layer are formed as a "cup-shaped" - pigments.

5. Security feature according to one of claims 1 to 4, characterized in that the radiation layer and the masking layer are formed in the same color.

6. Security feature according to one of claims 1 to 5, characterized in that the recording material has a substrate which has the luminescent constituents as the radiation layer of the security feature.

7. Security feature according to one of claims 1 to 6, characterized in that the masking layer is coated with a protective layer.

8. A heat-sensitive recording material having a security feature in the form of a luminescent marking, characterized in that the security feature is a radiation layer with luminescent constituents and a masking layer comprising hollow-body pigments which at least partially covers the radiation layer, wherein the cavity pigments of the coating layer can be fused by localized heat treatment in the form of a marking.

9. Heat-sensitive recording material according to claim 8, characterized in that the cavity pigments of the masking layer by loka! limited heat treatment are fused in the form of a marker.

10. Recording material according to one of claims 8 and 9, characterized in that the constituents of the radiation layer are fluorescent under UV light.

11. A recording material according to any one of claims 8 to 10, characterized in that the recording material comprises a substrate having as the radiation layer, the luminescent constituents.

12. A recording material according to any one of claims 8 to 11, characterized in that the recording material has a heat-sensitive recording layer which is applied in the form of a localized "spot" on the masking layer.

13. A recording material according to any one of claims 8 to 10, characterized in that the recording material at least

a substrate,

a heat-sensitive recording layer,

an intermediate layer formed between the substrate and the thermosensitive recording layer formed as a luminescent constituent radiation layer

- Has as well as a masking layer with Hohlraumpigmenten.

14. Recording material according to claim 13, characterized in that the intermediate layer contains inorganic pigments selected from the group consisting of comprising natural and calcined kaolin, silica, bentonite, calcium carbonate, alumina and boehmite.

15. A recording material according to any one of claims 13 and 14, characterized in that the masking layer at least partially covers the heat-sensitive Aufzeichnuπgs-.

16. A recording material according to any one of claims 13 and 14, characterized in that the masking layer is located between the heat-sensitive recording layer and the intermediate layer formed as a radiation layer.

17. A recording material according to claim 16, characterized in that the heat-sensitive recording layer is applied in the form of a localized "spot" on the masking layer.

18. A recording material according to any one of claims 8 to 17, characterized in that the recording material has at least one protective layer which is applied to the side of the substrate with the heat-sensitive recording layer as the substrate removed farthest layer.

19. A recording material according to any one of claims 8 to 18, characterized in that the recording material comprises a heat-sensitive recording layer containing at least one dye precursor and at least one color acceptor, wherein dye precursor and color acceptor react with each other under the action of heat color-forming and wherein at least one component of dye precursor and color acceptor in microcapsules.