Heat-sensitive recording material

Abstract

The present invention relates to a heat-sensitive recording material, comprising: a carrier substrate which has a first side and a second side which faces away from the first side; a colour layer which is arranged on the first or second side of the carrier substrate, wherein the colour layer has at least one colouring substance, and a heat-sensitive layer which is arranged on the colour layer and at least partially covers the colour layer, wherein the heat-sensitive layer is configured in such a way that it becomes translucent by local action of heat, with the result that the colour layer lying underneath becomes visible. The heat-sensitive layer comprises a first material which comprises at least one fatty acid and / or at least one fatty acid amide, and the heat-sensitive layer comprises a second material which comprises at least one metal salt of a fatty acid, wherein the first material has a first melting temperature Ts1, wherein the second material has a second melting temperature Ts2, wherein the first melting temperature Ts1 is lower than the second melting temperature Ts2.

Description

[0001] HEAT-SENSITIVE RECORDING MATERIAL

[0002] TECHNICAL FIELD

[0003] According to a first aspect, the present invention relates to a heat-sensitive recording material comprising a carrier substrate which has a first side and a second side facing away from the first side, an ink layer which is arranged on the first or second side of the carrier substrate, wherein the ink layer has at least one colorant, and a heat-sensitive layer which is arranged on the ink layer and at least partially covers the ink layer, wherein the heat-sensitive layer is designed such that it becomes translucent due to the local action of heat, so that the underlying ink layer becomes visible.

[0004] Here, the heat-sensitive layer comprises a first material which comprises at least one fatty acid and / or at least one fatty acid amide, and the heat-sensitive layer comprises a second material which comprises at least one metal salt of a fatty acid, wherein the first material has a first melting temperature Tsi, wherein the second material has a second melting temperature Ts2, wherein the first melting temperature Tsi is lower than the second melting temperature Ts2.

[0005] According to a second aspect, the present invention relates to a method for producing a heat-sensitive recording material, comprising the following method steps: providing a carrier substrate having a first side and a second side facing away from the first side; applying a color layer suspension to the first side or second side of the carrier substrate, wherein the color layer suspension comprises at least one colorant; drying the color layer suspension to obtain a color layer arranged on the first side or second side of the carrier substrate;Applying an application suspension to the ink layer, wherein the application suspension comprises a first material comprising at least one fatty acid and / or at least one fatty acid amide, and wherein the application suspension comprises a second material comprising at least one metal salt of a fatty acid, wherein the first material has a first melting temperature Tsi, wherein the second material has a second melting temperature Ts2, wherein the first melting temperature Tsi is lower than the second melting temperature Ts2; and drying the application suspension to obtain a heat-sensitive layer arranged on the ink layer;

[0006] According to a third aspect, the present invention relates to a heat-sensitive recording material producible by a method according to the second aspect.

[0007] According to a fourth aspect, the present invention relates to a use of a heat-sensitive recording material according to the first or third aspect as a receipt roll, adhesive label roll, ticket roll or as printer paper for mechanical printers or pens.

[0008] TECHNICAL BACKGROUND

[0009] Heat-sensitive recording materials, also known as thermal paper, are used in a variety of applications, such as sales receipts in retail stores.

[0010] Heat-sensitive recording materials, so-called thermal labels, for direct thermal printing are known from the state of the art, whereby two types of heat-sensitive recording materials, in particular for direct thermal printing, are distinguished here.

[0011] The first type of heat-sensitive recording materials includes heat-sensitive recording materials in which the printed image is created by a local heat-induced chemical reaction in an ink layer, for example, between a color former, such as a leuco dye, and a color developer, such as bisphenol A or a non-phenolic alternative. Typically, the ink layer also contains a heat-sensitive solvent that melts under the influence of heat and can include, for example, long-chain aliphatic alcohols, amides, esters, or carboxylic acids, thus enabling the color reaction between the color former and the color developer. Furthermore, the ink layer can contain heat-sensitive sensitizers.

[0012] The second type of heat-sensitive recording materials includes heat-sensitive recording materials in which the printed image is created by a heat-sensitive cover layer becoming translucent due to the local application of heat, for example, using a direct thermal printer, so that an underlying ink layer becomes visible. This technology is described and interpreted differently in the prior art, and such a heat-sensitive recording material is obtained by using various compositions, porosities, and materials for the heat-sensitive cover layer, optimized for direct thermal printing, and explained in more detail below.

[0013] In the second type of heat-sensitive recording materials, the heat-sensitive top layer should cover the underlying ink layer as well as possible. This is achieved primarily through light scattering, particularly by means of scattering particles, and light absorption. The heat-sensitive top layer should exhibit the highest possible contrast with the underlying ink layer in order to produce a print image readable by the human eye and / or a machine such as a scanner, for example, white / black or blue / yellow.

[0014] With the second type of heat-sensitive recording materials, the heat-sensitive cover layer should exhibit sufficient heat sensitivity to allow it to become translucent upon local exposure to heat, particularly with conventional direct thermal printers. With a conventional direct thermal printer, recording materials of the first and second types should be usable, and the printer settings should be comparable, particularly with regard to print head temperature and printer speed.

[0015] The present invention relates to heat-sensitive recording materials of the second type described above. GB 997289 describes a recording material for direct thermal printing, comprising a support material, an ink layer, and a heat-sensitive cover layer. The heat-sensitive cover layer becomes translucent through the local application of heat by means of a direct thermal printer, so that the underlying ink layer becomes visible, thus creating a printed image.

[0016] US 6043193 describes a heat-sensitive recording material comprising a support and an opaque recording layer applied to this support, which layer comprises hollow spherical beads dispersed in a hydrophilic binder, the beads having an average diameter of 0.2 pm to 1.5 pm and a void volume of 40% to 90%.

[0017] US 6133342 describes a heat-sensitive recording material comprising a colorant and an opaque polymer material whose opacity changes substantially irreversibly and makes the colorant more visible when exposed to heat.

[0018] WO 2015 / 119964 A1 discloses an oriented multilayer film for printing, comprising an extruded outer layer, an extruded inner pigment layer, and an extruded image reproduction layer located between the outer layer and the inner pigment layer, wherein the image reproduction layer comprises a void layer having a collapsible layer structure in which a plurality of voids are dispersed, wherein a plurality of voids are formed by orienting the multilayer, wherein the extruded image reproduction layer and the collapsible layer structure are in a non-collapsed state which is substantially opaque to conceal the pigment layer underneath.

[0019] US 2010 / 245524 A describes a heat-sensitive recording material comprising a heat-sensitive substrate with an opaque polymer which is sensitive to the application of heat and pressure and which, when heated to a predetermined temperature and under the action of a predetermined pressure, causes the opaque polymer to become transparent, and a color material which is arranged with respect to the substrate in such a way that it is concealed by the opaque polymer before the application of the predetermined heat and the predetermined pressure and becomes visible thereafter.

[0020] US 2011 / 172094 A discloses a recording material comprising a support having a surface impregnated with a colorant or coated with a coating containing a pigment or dye, and comprising a layer comprising polymeric particles having a core-shell structure and, when dry, hollow to scatter visible light, wherein the particles have an inner first polymer shell having a Tg of 40°C to 130°C and an outer second polymer shell having a Tg of -55°C to 50°C, wherein the Tg of the outer polymer shell is lower than that of the inner polymer shell.

[0021] US 2011 / 251060 A describes a heat-sensitive recording material consisting of a colorant and a flexible carrier substrate. The heat-sensitive recording material further comprises a heat-sensitive layer, the heat-sensitive layer consisting of a binder, a plurality of organic hollow sphere pigments, and a thermal solvent, and the heat-sensitive layer is disposed on the colorant. The heat-sensitive layer can be provided with a barrier layer and a protective layer.

[0022] WO 2012 / 145456 A1 describes a heat-sensitive recording material optimized for conventional direct thermal printing, which has a support in the form of a sheet-like structure, comprising at least one colored surface, and arranged thereon, and which has a layer comprising polymer particles with a core-shell structure, wherein the particles have an outer first polymer shell with a calculated Tg of 40 °C to 130 °C, wherein the particles, when dry, contain at least one cavity, and comprising 1 wt.% to 90 wt.%, based on the weight of the polymer particles, of an opacity reducer with a melting point of 45 °C to 200 °C.WO 2013 / 152287 A1 describes a heat-sensitive recording material having a two-layer, monoaxially oriented film comprising a first layer comprising an opaque beta-nucleated propylene-based polymer and a second layer comprising a dark pigment.

[0023] US 2015 / 049152 A describes a heat-sensitive recording material comprising a heat-sensitive layer disposed on a colored solid support substrate, wherein the heat-sensitive layer includes single-phase scattering polymer particles, each of which has a center, a surface, a refractive index at the center thereof which is different from a refractive index at the surface thereof, and a continuous refractive index gradient, wherein the heat-sensitive layer further includes heat-deformable particles and a binder.

[0024] EP 2993054 A1 describes a web-shaped heat-sensitive recording material having at least a first layer and a second layer at least partially covering the first layer, wherein the first layer has an intensive color at least facing the second layer and the second layer has hollow pigments which can be melted by locally limited heat treatment to form a typeface, which is characterized in that the second layer, in addition to the hollow pigments, also has one or more fatty acids and one or more heat-sensitive sensitizers.

[0025] In the recording material disclosed in EP 1778499 A1, which differs from the structure of EP 2993055 A1 fundamentally only in the type of coloring of the second layer, wherein the typeface becomes visible upon UV irradiation instead of being visible in the visible range of light, the protective layer can contribute to better printability and to improving environmental resistance, in particular resistance to plasticizers, oils, greases and moisture, such as splashed water.

[0026] EP 2993055 A1 describes a web-shaped heat-sensitive recording material having at least a first layer and a second layer at least partially covering the first layer, wherein the first layer has an intensive color at least facing the second layer and the second layer has hollow pigments which can be melted by locally limited heat treatment to form a typeface, which is characterized in that the recording material has at least one protective layer at least partially covering the second layer.

[0027] In the physical process, a distinction is made between two different methods for producing the print image:

[0028] In the first process, the printed image is created by a heat-sensitive cover layer becoming translucent through the local application of heat using a direct thermal printer, with the cover layer comprising meltable hollow pigments. In the second process, the printed image is created by a heat-sensitive cover layer becoming translucent through the local application of heat using a direct thermal printer, with the cover layer comprising softenable or dissolvable hollow pigments.

[0029] According to this document, an acceptable gray recording material with the following characteristics can be obtained: whiteness of 56% or 52% with or without UV content, optical density (unprinted) of 0.33 ODU, optical density (printed) of 1.22 ODU and contrast of 0.89 ODU (thermal head 300 dpi, 16 mJ / mm 2 ).

[0030] The associated divisional application EP 3517309 A1 specifies in particular the feature of the cover layer, which comprises manipulable hollow pigments and at least one fatty acid, namely stearic acid and / or palmitic acid or stearic acid amide and / or methylstearic acid amide, to form a typeface.

[0031] US 2017 / 337851 A discloses a recording material comprising a release liner base material layer, an optional adhesive layer, a label base layer, a thermal insulation layer disposed over the label base layer, an ink layer disposed over the thermal insulation layer, wherein the ink layer comprises at least one color, a cover layer disposed over the printed ink layer, and a top coat layer disposed over the cover layer, wherein the cover layer comprises an acrylic-based composition containing light-scattering particles that cause the cover layer to be opaque in a first state and transparent in a second state, wherein at least heat or pressure from a print head is applied, causing the cover layer to transition from the first state to the second state, thereby enablingthat at least one color of the ink layer is visible through the cover layer.,

[0032] WO 2019 / 183471 A1 discloses a recording medium comprising a substrate, wherein the substrate is comprised of first scattering particles having a melting point comprising a first solid light scattering layer, and the first light scattering layer is arranged as close as possible to a plurality of second solid scattering particles, wherein the second solid scattering particles have a lower melting point than the first melting point of the second solid scattering particles, and wherein the first light scattering layer is porous and the second scattering particles are arranged between the first solid scattering particles during melting of the solid to fill the space between the recording medium.

[0033] WO 2019 / 219391 A1 describes a heat-sensitive recording material comprising a carrier substrate that is black or colored on at least one side and a thermoresponsive layer on the at least one black or colored side of the carrier substrate, wherein the thermoresponsive layer comprises nanoparticles of at least one cellulose ester.

[0034] WO 2021 / 055719 A1 describes a heat- or pressure-sensitive recording material comprising a layer of an opaque material, color material arranged on a first side of the layer of opaque material, wherein the layer of opaque material covers the color material, wherein the opaque material, in an opaque state, comprises a plurality of irregular and / or odd-shaped opaque polymer particles defining voids therebetween and having different shapes and / or different sizes, and further wherein the opaque material is configured to change from the opaque state to a transparent state upon application of a sufficient temperature and / or pressure to expose the color material beneath the opaque material.

[0035] WO 2021 / 062230 A1 discloses a recording medium comprising a substrate, a first light scattering layer supported by the substrate and containing first scattering particles having a first melting point, and a plurality of second scattering particles in the vicinity of the first light scattering layer, wherein the second scattering particles have a second melting point lower than the first melting point, wherein the first light scattering layer is porous and the second scattering particles are arranged to fill spaces between the first scattering particles upon melting, and wherein the first scattering particles comprise perforated particles.

[0036] EP 3 957 489 A1 discloses a heat-sensitive recording material comprising or consisting of a carrier substrate and a melt layer arranged on one side of the carrier substrate or paper substrate.

[0037] All of these conventionally used heat-sensitive recording materials require improvement, particularly in terms of their functionality, sustainability, and cost-effective production. Heat-sensitive recording materials of the first type mentioned above, in particular, require the use of color developers, which often have harmful effects on health, and there are therefore efforts to eliminate them.

[0038] In particular, it is desirable to at least maintain or further increase the protection of heat-sensitive recording materials against external influences such as pressure, friction, humidity, liquids, and wetness. Furthermore, the functionality, properties, and economic manufacturability of conventional heat-sensitive recording materials should at least be maintained and ideally even improved, particularly with regard to sensitivity or optical density, water abrasion resistance, and the deposition behavior of heat-sensitive recording materials on the thermal print head of thermal printers, with as little or no deposits as possible that could negatively impact long-term operation of the thermal printer (more than 10 km of throughput).In addition, corresponding conventionally known heat-sensitive recording materials of the second type often contain organic pigments, in particular hollow sphere pigments, which, as micro- or nanoplastics, often contribute to a high environmental burden and therefore there is also a reason to dispense with corresponding organic pigments, in particular hollow sphere pigments, in the heat-sensitive recording materials.

[0039] DESCRIPTION OF THE INVENTION

[0040] Task

[0041] An object of the present invention is to provide a heat-sensitive recording material which has a balanced application-technical property profile and achieves a practical print density (optical density) which is comparable to or better than conventional heat-sensitive recording materials from the prior art, but at the same time has a high resistance of the printed image, in particular when the surface of the heat-sensitive recording material is brought into contact with hydrophobic substances, such as plasticizers from film materials, oils, fats and the like.

[0042] A further object of the present invention is to provide a heat-sensitive recording material which is capable of ensuring the functional properties required for application technology (in particular a high relative print contrast) even when stored for extended periods and / or under extreme climatic conditions (high humidity and / or temperature) of the printed (image stability) or unprinted (rewriting / writing performance) heat-sensitive recording material.

[0043] In addition, the present invention sets itself the further objective of improving the deposition behavior of heat-sensitive recording materials on the thermal print head of thermal printers. Surprisingly, it has now been found that the above-described disadvantages of the prior art can be overcome by using at least one fatty acid and / or at least one fatty acid amide as the first material with a lower melting point Tsi and by using at least one metal salt of a fatty acid as the second material with a higher melting point Ts2 in the heat-sensitive layer of the heat-sensitive recording material.

[0044] Corresponding fatty acids, fatty acid amides and metal salts of fatty acids are not harmful to health and are also biodegradable, thus preventing microplastics from being generated as waste during the degradation of the heat-sensitive recording materials, so that the environmental compatibility of the corresponding heat-sensitive recording materials can be increased.

[0045] Corresponding fatty acids, fatty acid amides and metal salts of fatty acids used in the heat-sensitive recording materials act as lubricants, which is significantly more advantageous since corresponding lubricants act simultaneously as sensitizers and release agents, so that according to the present invention, no different classes of substances have to be used to achieve the effects.

[0046] In addition, the fatty acids, fatty acid amides and metal salts of fatty acids used in the heat-sensitive recording materials ensure advantageous deposition behavior of the heat-sensitive recording materials on the thermal print head of thermal printers, and no or only minimal deposits occur that could negatively affect the long-term operation of the thermal printer (more than 10 km of throughput).

[0047] In addition, the present invention sets itself the further object of optimizing the property profile of a thermally printed heat-sensitive recording material, in particular ensuring greater environmental compatibility of the heat-sensitive recording material by using no organic pigments, in particular no hollow sphere pigments, so that no microplastics are produced as environmentally harmful waste during the degradation of the heat-sensitive recording material.

[0048] Heat-sensitive recording material

[0049] The above-mentioned objects are achieved according to the first aspect by a heat-sensitive recording material comprising: a carrier substrate having a first side and a second side facing away from the first side;a color layer arranged on the first or second side of the carrier substrate, wherein the color layer comprises at least one colorant, and a heat-sensitive layer arranged on the color layer and at least partially covering the color layer, wherein the heat-sensitive layer is designed such that it becomes translucent through the local action of heat, so that the underlying color layer becomes visible, wherein the heat-sensitive layer comprises a first material which comprises at least one fatty acid and / or at least one fatty acid amide, and that the heat-sensitive layer comprises a second material which comprises at least one metal salt of a fatty acid, wherein the first material has a first melting temperature Tsi, wherein the second material has a second melting temperature Ts2, wherein the first melting temperature Tsi is lower than the second melting temperature Ts2;

[0050] The combination of fatty acids or fatty acid amides as the first material with a metal salt of a fatty acid as the second material makes it possible to dispense with organic pigments, in particular hollow sphere pigments, within the heat-sensitive layer and thus provides a heat-sensitive recording material which ensures high environmental compatibility, since the release of microplastics during the degradation of the heat-sensitive recording material is prevented or reduced.

[0051] In particular, the heat-sensitive recording material, in particular the heat-sensitive layer, contains no organic pigments, in particular no hollow sphere pigments. A corresponding heat-sensitive recording material according to the present invention also exhibits a comparable, in particular improved, image quality of the printed image compared to conventional recording materials, which is characterized by the degree of whiteness according to ISO 2470-1:1:2016-09, the contrast between the printed and non-printed areas, the optical density, and / or the image stability after storage of the heat-sensitive recording material.

[0052] The heat-sensitive recording material has a color layer with a coloring substance.

[0053] The coloring substance imparts, in particular, a black, red, green, or blue color to the paint layer, or any color that can be obtained from a mixture of red, green, and blue. In particular, the coloring substance imparts a color to the paint layer that is not white.

[0054] In particular, the ink layer on the side facing the heat-sensitive layer has a black, red, green, or blue color, or any color that can be obtained from a mixture of the colors red, green, and blue. In particular, the coloring substance imparts a color other than white to the ink layer on the side facing the heat-sensitive layer.

[0055] The heat-sensitive layer of the heat-sensitive recording material at least partially covers the ink layer, so that the color of the ink layer, or the color of the side of the ink layer facing the heat-sensitive layer, is not visible due to the normally non-transparent heat-sensitive layer arranged above it. Only when the heat-sensitive layer becomes translucent due to the local exposure to heat can the underlying ink layer, or the side of the ink layer facing the heat-sensitive layer, become visible, thereby creating a printed image on the heat-sensitive recording material.In particular, the use of a metal salt of a fatty acid as a second material with the second melting temperature Ts2 in the heat-sensitive layer ensures improved layer adhesion and improved wettability of the polar components, so that in the event of unwanted heat exposure, such as environmental influences or solar radiation, no loss of opacity occurs and, in addition, advantageous deposition behavior is achieved.

[0056] In particular, the heat-sensitive layer does not contain any chemical color developer or chemical color former.

[0057] In particular, the heat-sensitive layer does not contain any dye, in particular no colored and / or black dye.

[0058] According to one embodiment, the first melting temperature Tsi is at least 1°C, preferably at least 2°C, more preferably at least 5°C and most preferably at least 10°C lower than the second melting temperature Ts2.

[0059] In particular, the first material comprises stearic acid amide having a first melting temperature Tsi of 108 °C and the second material comprises calcium stearate having a second melting temperature Ts2 of 125 °C and / or zinc stearate having a second melting temperature TS2 of 124 °C.

[0060] According to one embodiment, the at least one fatty acid of the first material is selected from the group comprising behenic acid, stearic acid, and / or palmitic acid, and / or the at least one fatty acid amide of the first material is selected from the group comprising behenamide, erucamide, stearic acid amide, oleamide, palmitic acid amide, and / or lauramide, preferably stearic acid amide.

[0061] In particular, behenic acid has a melting point of 80°C, with behenic acid from Croda (behenic acid 86 / 89.9%-BE-(HU), CAS No. 112-85-6) being used. In particular, stearic acid has a melting point of 72°C, with stearic acid from Sigma Aldrich (CAS No. 57-11-4) being used. In particular, palmitic acid has a melting point of 65°C, with palmitic acid from Carl Roth (palmitic acid >98% pure, CAS No. 57-10-3) being used. In particular, behenamide has a melting point of 112°C, with behenamide from TCI Europe NV (behenamide, CAS No. 3061-75-4) being used. In particular, erucamide has a melting point of 83°C, with erucamide from TCI Europe NV (Erucamide, CAS No. 112-84-5) being used. In particular, stearamide has a melting point of 108°C, with stearamide from TCI Europe NV (Stearamide, CAS No. 112-84-5) being used.124-26-5) was used. In particular, oleamide has a melting point of 74°C, with oleamide from TCI Europe NV (oleamide, CAS No. 301-02-0) being used. In particular, palmitic acid amide has a melting point of 108°C, with palmitic acid amide from Cayman Chemical Company (hexadecanamide, CAS No. 629-54-9) being used. In particular, lauramide has a melting point of 104°C, with lauramide from TCI Europe NV (lauramide, CAS No. 1120-16-7) being used.

[0062] The respective melting point was determined in particular by differential scanning calorimetry (DSC) measurements using a DSC 200 F3 Maia® device from Netzsch-Gerätebau GmbH, Selb, using an Al crucible with a cold-welded perforated lid, at a heating rate of 10 K / min, and at a temperature of 25°C to 200°C under an ^ atmosphere, whereby the respective melting point was determined via the peak minima or the endothermic peak of the melting process.

[0063] According to one embodiment, the first material is present in the heat-sensitive layer in an amount of 1 wt.% to 90 wt.%, preferably in an amount of 30 wt.% to 80 wt.%, based on the total dry mass of the heat-sensitive layer.

[0064] According to one embodiment, the at least one metal salt of the fatty acid of the second material is selected from the group comprising calcium stearate, magnesium stearate, zinc stearate, and mixtures thereof, preferably calcium stearate and / or zinc stearate. In particular, calcium stearate has a melting point of approximately 125°C, in particular a melting point in a range from 125°C to 127°C. In particular, calcium stearate from Sigma Aldrich with 6.6 to 7.4% calcium base (CAS No. 1592-23-0) can be used, which has a melting point of 127°C. In particular, calcium stearate from Carl Roth with greater than or equal to 95% calcium stearate (CAS No. 1592-23-0) can be used, which has a melting point of 126°C.

[0065] In particular, magnesium stearate has a melting point of approximately 71°C, especially a melting point in a range from 100°C to 125°C. In particular, magnesium stearate from Sigma Aldrich (CAS No. 557-04-0), which has a melting point of 125°C, can be used. In particular, magnesium stearate from Carl Roth with greater than or equal to 95% magnesium stearate (CAS No. 557-04-0), which has a melting point of 100°C, can be used.

[0066] In particular, zinc stearate has a melting point of approximately 124°C, especially a melting point in a range of 124°C to 126°C. In particular, zinc stearate from Thermo Fisher Scientific (CAS No. 557-05-1) can be used, which has a melting point of 126°C.

[0067] The respective melting point was determined in particular by differential scanning calorimetry (DSC) measurements using a DSC 200 F3 Maia® device from Netzsch-Gerätebau GmbH, Selb, using an Al crucible with a cold-welded perforated lid, at a heating rate of 10 K / min, and at a temperature of 25°C to 200°C under an ^ atmosphere, whereby the respective melting point was determined via the peak minima or the endothermic peak of the melting process.

[0068] According to one embodiment, the at least one metal salt of the fatty acid of the second material is present in the heat-sensitive layer in an amount of more than 10 wt.%, based on the total dry mass of the heat-sensitive layer.

[0069] According to one embodiment, the second material is present in the heat-sensitive layer in an amount of 10.1 wt.% to 90 wt.%, preferably 25 wt.% to 40 wt.%, based on the total dry mass of the heat-sensitive layer.

[0070] In particular, the second material is present in the heat-sensitive layer in an amount of 10.5 wt.% to 60 wt.%, based on the total dry mass of the heat-sensitive layer, preferably from 11.0 wt.% to 60 wt.%, more preferably from 11.5 wt.% to 60 wt.%, even more preferably from 12.0 wt.% to 60 wt.%, even more preferably from 12.5 wt.% to 60 wt.%, even more preferably from 13.0 wt.% to 60 wt.%, even more preferably from 12.5 wt.% to 60 wt.%, even more preferably from 13.5 wt.% to 60 wt.%, even more preferably from 14.0 wt.% to 60 wt.%, even more preferably from 14.5 wt.% to 60 wt.%, even more preferably from 15.0 wt.% to 60 wt.%, even more preferably from 15.5 wt.% to 60 wt.%, even more preferably from 16.0 wt% to 60 wt%, even more preferably from 16.5 wt% to 60 wt%, even more preferably from 17.0 wt% to 60 wt%, even more preferably from 17.5 wt% to 60 wt%.-%, even more preferably from 18.0 wt.% to 60 wt.%, even more preferably from 18.5 wt.% to 60 wt.%, even more preferably from 19.0 wt.% to 60 wt.%, even more preferably from 19.5 wt.% to 60 wt.%, even more preferably from 20.0 wt.% to 60 wt.%, even more preferably from 20.5 wt.% to 60 wt.%, even more preferably from 21.0 wt.% to 60 wt.%, even more preferably from 21.5 wt.% to 60 wt.%, even more preferably from 22.0 wt.% to 60 wt.%, even more preferably from 22.5 wt.% to 60 wt.%, even more preferably from 23.0 wt.% to 60 wt.%, even more preferably from 23.5 wt.% to 60 wt.%, even more preferably from 24.0 wt.% to 60 wt.%, even more preferably from 24.5 wt% to 60 wt%, and most preferably 25 wt% to 60 wt%. In particular, the second material is present in an amount of 10.5 wt% to 59 wt%.-% based on the total dry mass of the heat-sensitive layer, in the heat-sensitive layer, preferably from 11.0 wt.% to 58 wt.%, more preferably from 11.5 wt.% to 57 wt.%, even more preferably from 12.0 wt.% to 56 wt.%, even more preferably from 12.5 wt.% to 55 wt.%, even more preferably from 13.0 wt.% to 54 wt.%, even more preferably from 12.5 wt.% to 53 wt.%, even more preferably from 13.5 wt.% to 52 wt.%, even more preferably from 14.0 wt.% to 51 wt.%, even more preferably from 14.5 wt.% to 50 wt.%, even more preferably from 15.0 wt.% to 49 wt.%, even more preferably from 15.5 wt.% to 48 wt.%, even more preferably from 16.0 wt.% to 47 wt.%, even more preferably from 16.5 wt% to 46 wt%, even more preferably from 17.0 wt% to 45 wt%, even more preferably from 17.5 wt% to 44 wt%, even more preferably from 18.0 wt% to 43 wt%, even more preferably from 18.5 wt% to 42 wt%.-%, even more preferably from 19.0 wt% to 41 wt%, even more preferably from 19.5 wt% to 40 wt%, even more preferably from 20.0 wt% to 39 wt%, even more preferably from 20.5 wt% to 38 wt%, even more preferably from 21.0 wt% to 37 wt%, even more preferably from 21.5 wt% to 36 wt%, even more preferably from 22.0 wt% to 35 wt%, even more preferably from 22.5 wt% to 34 wt%, even more preferably from 23.0 wt% to 33 wt%, even more preferably from 23.5 wt% to 32 wt%, even more preferably from 24.0 wt% to 31 wt%, even more preferably from 24.5 wt% to 30 wt%, and most preferably 25 wt% to 29 wt%.

[0071] According to one embodiment, the first material and the second material are present in the heat-sensitive layer in an amount of 30 wt% to 95 wt%, preferably in an amount of 40 wt% to 90 wt%, and most preferably in an amount of 50 wt% to 85 wt% based on the total dry mass of the heat-sensitive layer.

[0072] In particular, the specified weight ranges for the first material and the second material include the presence of at least 25% by weight of the first material. In particular, the first material and the second material are each present as a mixture.

[0073] According to one embodiment, there is no organic pigment, in particular no hollow sphere pigment, in the heat-sensitive layer.

[0074] In particular, there is no styrene-acrylate copolymer hollow sphere pigment and / or no styrene-butadiene solid sphere pigment in the heat-sensitive layer.

[0075] By avoiding organic pigments, especially hollow sphere pigments, we ensure that no microplastics are produced as waste when the heat-sensitive recording material degrades.

[0076] According to one embodiment, the heat-sensitive layer comprises at least one binder, wherein the binder is selected from the group comprising water-soluble starches, starch derivatives, starch-based biolatices of the EcoSphere type, methylcellulose, hydroxyethylcellulose, carboxymethylcellulose, gelatin, casein, partially or fully saponified polyvinyl alcohols, chemically modified polyvinyl alcohols, ethylene-vinyl alcohol copolymers, sodium polyacrylates, styrene-maleic anhydride copolymers, ethylene-maleic anhydride copolymers, styrene-butadiene copolymers, acrylamide-(meth)acrylate copolymers, acrylamide-acrylate-methacrylate terpolymers, polyacrylates, poly(meth)acrylic acid esters, acrylate-butadiene copolymers, polyvinyl acetates, acrylonitrile-butadiene copolymers, and mixtures thereof.

[0077] According to one embodiment, the at least one binder is present in the heat-sensitive layer in an amount of 2 wt.% to 40 wt.%, preferably in an amount of 5 wt.% to 20 wt.%, based on the total dry mass of the heat-sensitive layer.

[0078] According to one embodiment, the heat-sensitive layer comprises at least one pigment, wherein the pigment is selected from the group comprising inorganic pigments, both of synthetic and natural origin, preferably clays, precipitated or natural calcium carbonates, aluminum oxides, aluminum hydroxides, silicas, precipitated and pyrogenic silicas, for example Aerodisp types, diatomaceous earths, magnesium carbonates, talc, kaolin, titanium oxide, bentonite but also organic pigments, such as hollow pigments with a styrene / acrylate copolymer wall or urea / formaldehyde condensation polymers and mixtures thereof, preferably calcium carbonates, aluminum hydroxides, and / or pyrogenic silicas.

[0079] According to one embodiment, the at least one pigment is present in the heat-sensitive layer in an amount of 2 wt.% to 50 wt.%, preferably in an amount of 5 wt.% to 20 wt.%, based on the total dry mass of the heat-sensitive layer.

[0080] The pigments of the heat-sensitive layer can be the same or different from the pigments of the ink layer. The use of these pigments has the advantage, among other things, that they can fix the chemical melt created during the thermal printing process to their surface. Pigments can also be used to control the surface whiteness and opacity of the heat-sensitive layer and its printability with conventional printing inks.

[0081] Particularly suitable pigments are inorganic pigments, both synthetic and natural, preferably clays, precipitated or natural calcium carbonates, aluminum oxides, aluminum hydroxides, silicas, precipitated and pyrogenic silicas (e.g., Aerodisp types), diatomaceous earths, magnesium carbonates, talc, kaolin, titanium oxide, bentonite, and also organic pigments. These can be used alone or in any mixture.

[0082] Calcium carbonates, aluminum hydroxides, and fumed silicas are preferred, as they provide particularly advantageous performance properties for the heat-sensitive recording materials with regard to their subsequent printability with commercially available printing inks. The heat-sensitive layer may also contain carbon black components and / or dyes / color pigments.

[0083] According to one embodiment, the heat-sensitive layer comprises optical brighteners, in particular stilbenes, which are used to control the surface whiteness of the heat-sensitive recording material according to the invention.

[0084] According to one embodiment, the heat-sensitive layer comprises in particular inorganic oil-absorbing white pigments.

[0085] In particular, the inorganic oil-absorbing white pigments include natural or calcined kaolin, silicon oxide, bentonite, calcium carbonate, aluminum hydroxide, in particular boehmite, and mixtures thereof.

[0086] The inorganic oil-absorbing white pigments are preferably present in the heat-sensitive layer in an amount of 2 wt.% to 50 wt.%, particularly preferably in an amount of 5 wt.% to 20 wt.%, based on the total dry mass of the heat-sensitive layer.

[0087] According to one embodiment, the heat-sensitive layer comprises at least one crosslinking agent, wherein the crosslinking agent is selected from the group comprising polyvalent aldehydes, such as glyoxal, dialdehyde starch, glutaraldehyde, optionally in admixture with boron salts, for example borax, salts or esters of glyoxylic acid, crosslinkers based on ammonium zirconium carbonate, polyamidoamine epichlorohydrin resins (PAE resins), adipic acid dihydrazide (AHD), boric acid or salts thereof, polyamines, epoxy resins, formaldehyde oligomers, cyclic ureas, methylol urea, melamine formaldehyde oligomers and mixtures thereof.

[0088] In order to achieve specific performance characteristics of heat-sensitive recording materials, a binder present in the heat-sensitive layer is preferably present in cross-linked form in the heat-sensitive layer, with the optimal degree of cross-linking of the binder being established in the drying step of the coating process in the presence of a cross-linking agent. The corresponding crosslinking agents can be polyvalent aldehydes, such as glyoxal, dialdehyde starch, glutaraldehyde, optionally in admixture with boron salts (borax), salts or esters of glyoxylic acid, crosslinking agents based on ammonium zirconium carbonate, polyamidoamine epichlorohydrin resins (PAE resins), adipic acid dihydrazide (AHD), boric acid or its salts, polyamines, epoxy resins, formaldehyde oligomers, cyclic ureas, methylol urea, melamine formaldehyde oligomers, etc. These can be used alone or in any mixture.

[0089] Ammonium zirconium carbonate and polyamidoamine epichlorohydrin resins (PAE resins) are particularly preferred for reasons of food contact conformity.

[0090] Self-crosslinking binders, such as specially modified polyvinyl alcohols or acrylates, enable crosslinking without any crosslinking agents, thanks to the reactive, crosslinkable groups that are already incorporated into the binder polymer.

[0091] According to one embodiment, the at least one crosslinking agent is present in the heat-sensitive layer in an amount of 0.01 wt.% to 25.0 wt.%, preferably in an amount of 0.05 wt.% to 10.0 wt.%, based on the total dry mass of the heat-sensitive layer.

[0092] According to one embodiment, the heat-sensitive layer comprises at least one auxiliary agent, wherein the auxiliary agent is selected from the group comprising rheology auxiliary agents, such as thickeners and / or surfactants.

[0093] According to one embodiment, the auxiliary agent is selected from the group comprising viscosity-controlling agents, preferably dicyandiamides, polyethylene glycol and / or urea as viscosity-reducing agents, or preferably alginate, carboxymethylcellulose and / or acrylic acid esters as viscosity-increasing agents, dispersants, preferably polyphosphate, sodium tripolyphosphate, sodium pyrophosphate, and / or salts of polycarboxylic acids, defoamers, agents for increasing wet strength, preferably melamine-formaldehyde resins, urea-formaldehyde resins, formalin and / or glyoxal, preservatives, preferably antibacterial additives and / or antifungal additives, lubricants, preferably polyglycol, pH-controlling agents, preferably sodium hydroxide and / or ammonia, dyes, optical brighteners, conductivity agents and mixtures thereof, and polyacrylamide, in particular anionically modified.

[0094] According to one embodiment, the auxiliary agent is present in a range from 0.01 wt.% to 5 wt.%, preferably from 0.1 wt.% to 2 wt.%, based on the total dry mass of the heat-sensitive layer.

[0095] This provides the technical advantage that an advantageous optimization of the applicability and / or the properties of the heat-sensitive layer can be achieved.

[0096] According to one embodiment, the at least one rheology aid is selected from the group comprising: a) polyols, in particular sugar alcohols and their derivatives, selected from the group comprising: diglycerol, triglycerol, glucose, fructose, maltose, lactose, mannose, ribose, xylose, D-mannitol, triacetin, pentaerythritol, dipentaerythritol, erythritol, xylitol, sorbitol, glycerol, mannitol, maltitol and mixtures thereof; b) diols selected from the group comprising: methylpentanediol, 1,2-propanediol, 1,4-butanediol, 2-hydroxy-1,3-propanediol, 3-methyl-1,3-butanediol, 3,3-dimethyl-1,2-butanediol and mixtures thereof; c) glycols selected from the group comprising: polyethylene glycol 300, polyethylene glycol 400, polyethylene glycol 2000, alkoxylated polyethylene glycol and mixtures thereof;

[0097] (d) caprolactam, cyclic trimethylolpropane, rosin esters, euricamide and mixtures thereof,

[0098] (e) fatty acids, in particular stearic acid, and / or fatty acid amides, in particular erucamide, stearic acid amide, and / or palmitic acid amide, and mixtures thereof; including mixtures of subgroups a) to e). According to one embodiment, the surfactant is a natural surfactant, most preferably saponin and / or phospholipid.

[0099] In particular, the surfactant comprises a water-soluble nonionic ethoxylated alcohol, in particular having a solids content between 4 and 15%, wherein the surfactant preferably has the formula RO(CH2CH2O)xH, wherein the substituent R is selected as iso-Ci3H27 and the substituent x is 8 or more; or wherein the substituent R is selected as iso-Cw and the substituent x is selected from the group comprising 5, 6, 7, 8, or 11.

[0100] According to one embodiment, the natural surfactant is present in a range from 0.05 wt% to 3 wt%, preferably from 0.1 wt% to 1.0 wt%, based on the total dry mass of the heat-sensitive layer.

[0101] According to one embodiment, the heat-sensitive layer has a basis weight of 1 to 8 g / m 2 , especially from 2 to 6 g / m 2 on.

[0102] According to one embodiment, the heat-sensitive layer has a thickness of 1 to 10 .m, in particular of 2 to 8 .m.

[0103] Bekk smoothness

[0104] According to one embodiment, the carrier substrate on the side on which the ink layer is applied has a Bekk smoothness measured according to the standard ISO 5267:1995-03 of greater than 30 s, preferably greater than 50 s.

[0105] According to one embodiment, the ink layer on the side on which the heat-sensitive layer is applied has a Bekk smoothness measured according to ISO 5267:1995-03 of greater than 50 s, preferably greater than 100 s and most preferably greater than 150 s.

[0106] According to one embodiment, the heat-sensitive layer, on the side not bearing the ink layer, has a Bekk smoothness measured according to ISO 5267:1995-03 of greater than 100 s, particularly preferably greater than 250 s. According to one embodiment, the carrier substrate, on the side bearing the ink layer, has a Bekk smoothness measured according to ISO 5267:1995-03 of 20 to 400 s, preferably 30 to 300 s, and particularly preferably 50 to 200 s.

[0107] According to one embodiment, the ink layer on the side on which the heat-sensitive layer is applied has a Bekk smoothness measured according to ISO 5267:1995-03 of 50 to 400 s, more preferably of 100 to 250 s and most preferably of 150 to 250 s.

[0108] According to one embodiment, the heat-sensitive layer on the side on which the ink layer is not located preferably has a Bekk smoothness measured according to ISO 5267:1995-03 of 100 to 1000 s, particularly preferably of 250 to 800 s.

[0109] In particular, each layer applied to the carrier substrate has on its upper side, ie on the side on which the carrier substrate is not located, a Bekk smoothness measured according to ISO 5267:1995-03 which is at least as great as or greater than that of the layer below it.

[0110] In particular, each layer applied to the carrier substrate has on its upper side, ie on the side on which the carrier substrate is not located, a Bekk smoothness measured according to ISO 5267:1995-03 of at least 5% (percentage increase) compared to the layer below it.

[0111] In particular, each layer applied to the carrier substrate has on its upper side, ie on the side on which the carrier substrate is not located, a Bekk smoothness measured according to ISO 5267:1995-03 of at least 5 s (absolute increase) compared to the layer below it.

[0112] It is advantageous to provide a smooth carrier substrate and maintain this smoothness throughout the individual layers, since the smoother the substrate is built up from below, the better the final smoothness and thus the sensitivity of the final product.

[0113] According to one embodiment, the carrier substrate is selected from the group comprising paper, single-side coated paper, and double-side coated paper.

[0114] According to one embodiment, the carrier substrate has a basis weight of 30 to 100 g / m 2 , preferably from 40 to 80 g / m 2 , on.

[0115] According to one embodiment, the heat-sensitive recording material is characterized in that a layer comprising starch, which is also referred to as starch coating, and / or modifications thereof is present directly on at least one side of the carrier substrate, preferably directly on both sides of the carrier substrate.

[0116] The starch coating is preferably applied in an amount of 0.1 g / m 2 up to 3 g / m 2 , particularly preferably 0.2 g / m 2 up to 1.5 g / m 2 , applied.

[0117] A starch coating on the side of the carrier substrate where the ink layer is present has the advantage of sealing the carrier substrate, thus improving the adhesion of the ink layer and reducing or preventing penetration of the ink layer into the carrier substrate.

[0118] A starch coating on the side of the carrier substrate where the ink layer is not present has the advantage that bleed-through of the ink layer through the carrier substrate can be reduced or prevented.

[0119] The layer comprising starch preferably has a Bekk smoothness measured according to ISO 5267:1995-03 of greater than 20 s, more preferably greater than 50 s and most preferably from 50 to 200 s.

[0120] Paint layer

[0121] According to one embodiment, the coloring substance of the color layer comprises at least one pigment and / or dye. In particular, the pigments and / or dyes comprise various organic and inorganic pigments, dyes, and / or carbon black. These can be used alone or in any desired mixtures.

[0122] In a preferred embodiment, the heat-sensitive recording material according to the invention is further characterized in that the at least one dye is selected from the group comprising bleachable dyes, hydrophobic dyes, hydrophobizable dyes and / or magnetic dyes.

[0123] The pigment, the dye and / or the carbon black are preferably each contained in the ink layer in an amount of 2 to 50 wt.%, particularly preferably 10 to 35 wt.%, based on the total dry mass of the ink layer.

[0124] According to one embodiment, the color layer comprises a binder.

[0125] Preferred binders are water-soluble starches, starch derivatives, starch-based EcoSphere-type biolatices, methylcellulose, hydroxyethylcellulose, carboxymethylcellulose, gelatin, casein, partially or fully saponified polyvinyl alcohols, chemically modified polyvinyl alcohols, ethylene-vinyl alcohol copolymers, sodium polyacrylates, styrene-maleic anhydride copolymers, ethylene-maleic anhydride copolymers, styrene-butadiene copolymers, acrylamide-(meth)acrylate copolymers, acrylamide-acrylate-methacrylate terpolymers, polyacrylates, poly(meth)acrylic acid esters, acrylate-butadiene copolymers, polyvinyl acetates, and / or acrylonitrile-butadiene copolymers. These can be used alone or in any desired mixtures.

[0126] The binder is preferably contained in the paint layer in an amount of 2 wt.% to 40 wt.%, particularly preferably 10 wt.% to 30 wt.%, based on the total dry mass of the paint layer.

[0127] The ink layer preferably has a basis weight of 1 to 10 g / m 2 , especially from 3 to 8 g / m 2 The color layer preferably has a thickness of 1 to 10 pm, in particular 2 to 8 pm.

[0128] protective layer

[0129] According to one embodiment, the heat-sensitive recording material has a protective layer arranged on the heat-sensitive layer.

[0130] This protective layer is therefore located on the side of the heat-sensitive layer facing away from the ink layer.

[0131] According to one embodiment, the protective layer has a Bekk smoothness measured according to ISO 5267:1995-03 of at least 500 s, preferably of at least 750 s and particularly preferably of at least 1000 s.

[0132] Preferably, the Bekk smoothness of the protective layer measured according to ISO 5267:1995-03 is not more than 2000 s, preferably not more than 1600 s.

[0133] According to one embodiment, the protective layer comprises at least one pigment, at least one binder, at least one lubricant, at least one crosslinking agent, and / or at least one rheology aid.

[0134] In another embodiment, the protective layer contains no pigment(s).

[0135] If at least one pigment is present in the protective layer, this at least one pigment is present in the protective layer in an amount of less than 5 wt.%, in particular from more than 0 wt.% to less than 5 wt.%, based on the total dry mass of the protective layer.

[0136] In a preferred embodiment, the protective layer contains the at least one pigment in an amount of less than 4 wt.%, in particular from more than 0 wt.% to less than 4 wt.%, or less than 3 wt.%, in particular from more than 0 wt.% to less than 3 wt.%, or less than 2 wt.%, in particular from more than 0 wt.% to less than 2 wt.%, or less than 1 wt.%, in particular from more than 0 wt.% to less than 1 wt.%, or less than 0.5 wt.%, in particular from more than 0 wt.% to less than 0.5 wt.%, or less than 0.2 wt.%, in particular from more than 0 wt.% to less than 0.2 wt.%, or less than 0.1 wt.%, in particular from more than 0 wt.% to less than 0.1 wt.%, or less than 0.01 wt.%, in particular from more than 0 wt.% to less than 0.01 wt.%, or except for unavoidable Impurities or unavoidable traces no pigments or no pigments at all.These quantities refer to the dry mass of the protective layer.

[0137] Unavoidable impurities or unavoidable traces of pigments can, for example, enter the protective layer due to manufacturing reasons, if pigments were or are processed in the production plant (pigment-containing coating colours), e.g. when applying previously applied pigment-containing layers (pigments of the insulating layer, the colour layer or the heat-sensitive layer).

[0138] Without being bound by this theory, the inventors have observed that the less pigment contained in the protective layer, the higher the Bekk smoothness can be adjusted, which in turn is beneficial for the sensitivity, or optical density, of the heat-sensitive recording material. Surprisingly, it has been shown that the proportion of pigment in the protective layer can be reduced without compromising the protective effect for certain requirements. Furthermore, it has been shown that the relative print contrast can even be increased and / or improved.

[0139] The at least one pigment is preferably selected from organic and / or inorganic pigments.

[0140] Suitable inorganic pigments include inorganic pigments, both synthetic and natural, preferably clays, precipitated or natural calcium carbonates, aluminum oxides, aluminum hydroxides, silicas, precipitated and fumed silicas (e.g., Aerodisp grades), diatomaceous earths, magnesium carbonates, talc, kaolin, titanium oxide, bentonite, as well as organic pigments, such as hollow pigments with a styrene / acrylate copolymer wall or urea / formaldehyde condensation polymers. These can be used alone or in any mixture.

[0141] The protective layer is further preferably characterized in that the protective layer comprises at least one of the following components, selected from a binder, a lubricant / release agent, in particular based on waxes or fats, fatty acids or salts, in particular metal salts, of fatty acids, or of silicones, a crosslinking agent, in particular a boron-free crosslinking agent, and / or a rheology aid.

[0142] The protective layer preferably comprises at least one binder, more preferably water-soluble starches, starch derivatives, starch-based biolatices of the EcoSphere type, methylcellulose, hydroxyethylcellulose, carboxymethylcellulose, partially or fully saponified polyvinyl alcohols, chemically modified polyvinyl alcohols, such as acetoacetyl-, diacetone-, carboxy-, or silanol-modified polyvinyl alcohols, or styrene-maleic anhydride copolymers, styrene-butadiene copolymers, acrylamide-(meth)acrylate copolymers, acrylamide-acrylate-methacrylate terpolymers, polyacrylates, poly(meth)acrylic acid esters, acrylate-butadiene copolymers, polyvinyl acetates, and / or acrylonitrile-butadiene copolymers. These can be used alone or in any desired mixtures.

[0143] More preferably, the binder comprises polyvinyl alcohol, most preferably a polyvinyl alcohol having a degree of saponification equal to or greater than 88%.

[0144] The binder is preferably present in the protective layer in an amount of 40 wt.% to 90 wt.%, particularly preferably in an amount of 50 wt.% to about 80 wt.%, based on the total dry mass of the protective layer.

[0145] To achieve specific performance characteristics for heat-sensitive recording materials, the binder is preferably present in crosslinked form in the protective layer, with the optimal degree of crosslinking of the binder occurring during the drying step of the coating process in the presence of a crosslinking agent (crosslinker). Crosslinkers can be polyhydric aldehydes such as glyoxal, dialdehyde starch, glutaraldehyde, optionally mixed with boron salts (borax), salts or esters of glyoxylic acid, crosslinkers based on ammonium zirconium carbonate, polyamidoamine epichlorohydrin resins (PAE resins), adipic acid dihydrazide (AHD), boric acid or its salts, polyamines, epoxy resins, formaldehyde oligomers, cyclic ureas, methylol urea, melamine-formaldehyde oligomers, and others. These can be used alone or in any mixture.

[0146] Boron-free crosslinking agents are preferred.

[0147] Ammonium zirconium carbonate and polyamidoamine epichlorohydrin resins (PAE resins) are particularly preferred for reasons of food contact conformity.

[0148] Self-crosslinking binders, such as specially modified polyvinyl alcohols or acrylates, enable crosslinking without any crosslinking agents, thanks to the reactive, crosslinkable groups that are already incorporated into the binder polymer.

[0149] The crosslinker is preferably present in an amount of 0.01 wt.% to 25.0 wt.%, particularly preferably in an amount of 0.05 wt.% to 15.0 wt.%, based on the total dry mass of the protective layer.

[0150] Preferably, the protective layer comprises at least one lubricant.

[0151] These agents are preferably a metal salt of a fatty acid, such as zinc stearate or calcium stearate, or also behenate salts, synthetic waxes, e.g. in the form of fatty acid amides, such as stearic acid amide and behenic acid amide, fatty acid alkanolamides, such as stearic acid methylolamide, paraffin waxes of various melting points, ester waxes of various molecular weights, ethylene waxes, propylene waxes of various hardnesses and / or natural waxes, such as carnauba wax, montan wax or soy wax.

[0152] Preferred lubricants are those based on waxes or fats, fatty acids, or salts, especially metal salts, of fatty acids. The lubricant is preferably present in an amount of 1 to about 30 wt.%, particularly preferably in an amount of about 2 to about 20 wt.%, based on the total dry mass of the protective layer.

[0153] Preferably, the protective layer comprises at least one release agent.

[0154] Preference is given to release agents based on silicones, such as those known from US 2006 / 0063013A1, the disclosure of which is hereby incorporated in its entirety.

[0155] The release agent is preferably present in an amount of about 1 to about 30 wt.%, particularly preferably in an amount of about 2 to about 20 wt.%, based on the total dry mass of the protective layer.

[0156] Preferably, the protective layer comprises at least one rheology aid.

[0157] Preferred rheology aids are thickeners and surfactants. For further details, please refer to the selections for the heat-sensitive layer, which also fully apply to the protective layer.

[0158] The protective layer preferably comprises at least one lubricant / release agent, at least one binder and at least one crosslinker.

[0159] To control the surface whiteness of the heat-sensitive recording material according to the invention, optical brighteners, preferably stilbenes, can be incorporated into the protective layer.

[0160] The protective layer preferably has a basis weight in the range of 0.01 g / m 2 and 3.5 g / m 2 , preferably in the range of greater than 0.05 g / m2 and 2.5 g / m 2 and particularly preferably in the range of 0.1 g / m 2 and 1.5 g / m 2 on.

[0161] Surprisingly, it has been shown that the basis weight of the protective layer can be reduced without compromising the protective effect for certain requirements. At the same time, the relative print contrast can even be increased and / or improved.

[0162] The protective layer preferably has a thickness of 0.3 pm to 6.0 pm, in particular of 0.5 pm to 2.0 pm.

[0163] The protective layer preferably has an “anti-stick effect”, in particular with respect to an adhesive layer on the back of the heat-sensitive recording material, and / or with respect to pressure-sensitive adhesives, in particular on the back of the heat-sensitive recording material.

[0164] This has the advantage that the heat-sensitive recording material can be used as a linerless heat-sensitive recording material.

[0165] This has the particular advantage that the heat-sensitive recording material can be wound onto itself without the need for a carrier (“linerless”), whereby after the heat-sensitive recording material wound onto itself has been re-rolled, the heat-sensitive recording material does not show any deterioration in its paper and application properties.

[0166] This also has the advantage that production costs can be further reduced, more running meters can be achieved per roll, no disposal effort is required for the disposal of the liner and more labels can be transported per specific cargo space volume.

[0167] Adhesive layer

[0168] According to one embodiment, the heat-sensitive recording material has an adhesive layer arranged on the first or second side of the carrier substrate facing away from the ink layer. The adhesive layer comprises at least one adhesive, preferably a heat-activatable adhesive, and more preferably a pressure-sensitive adhesive. If a starch coating is present, this is located between the carrier substrate and the adhesive layer.

[0169] The adhesive layer preferably comprises at least one adhesive, preferably a heat-activatable adhesive, in particular a pressure-sensitive adhesive. The adhesive, preferably the heat-activatable adhesive, and in particular the pressure-sensitive adhesive, is particularly preferably a rubber- and / or acrylate-based adhesive.

[0170] The protective layer preferably has a “non-stick effect” against the rubber and / or acrylate-based adhesives.

[0171] According to one embodiment, the adhesive layer has a basis weight of 1 to 40 g / m 2 , especially from 12 to 25 g / m 2 , on.

[0172] Separating layer

[0173] According to one embodiment, the heat-sensitive recording material has a separating layer, in particular a siliconized separating layer, which is arranged on the heat-sensitive recording layer.

[0174] The siliconized release layer preferably has a Bekk smoothness measured according to ISO 5267:1995-03 of greater than 400 s, particularly preferably greater than 800 s and most preferably from 800 to 2000 s.

[0175] If a protective layer, in particular as defined above, is present on the heat-sensitive layer, the siliconized release layer is preferably located on this protective layer.

[0176] In a further preferred embodiment, the heat-sensitive recording material is preferably characterized in that a diffusion layer is formed between the siliconized separating layer and the underlying layer, preferably the heat-sensitive layer. This diffusion layer is preferably formed by the surface diffusion of at least parts of the siliconized separating layer into the upper region of the underlying layer, with preferably 5% to 50% by weight, particularly preferably 6% to 45% by weight, and in particular 7% to 40% by weight of the siliconized separating layer diffusing into the upper region of the underlying layer. Such a diffusion layer is described, for example, in EP 3 221 153 A1.

[0177] A siliconized release layer is preferably present when an adhesive layer, as described above, is also present.

[0178] The presence of a siliconized release layer on the heat-sensitive layer and an adhesive layer on the carrier substrate on the side where the ink layer is not located has the advantage that the heat-sensitive recording material can be used as a linerless heat-sensitive recording material.

[0179] This has the particular advantage that the heat-sensitive recording material can be wound onto itself without the need for a carrier (“linerless”), whereby after re-rolling the heat-sensitive recording material wound onto itself, the heat-sensitive recording material does not exhibit any significant deterioration in its properties.

[0180] This also has the advantage that production costs can be further reduced, more running meters can be achieved per roll, no disposal effort is required for the disposal of the liner and more labels can be transported per specific cargo space volume.

[0181] If a siliconized release layer is present, it is preferred that the layer directly beneath the siliconized release layer contains at least one platelet-shaped pigment. The at least one platelet-shaped pigment is preferably selected from the group consisting of kaolin, Al(OH)3, and / or talc. Kaolin is particularly preferred. Spreadable kaolin is even more preferred. Such a kaolin is available, for example, under the trade name Kaolin ASP 109 (BASF, Germany).

[0182] The use of these platelet-shaped pigments, especially kaolin, has the advantage that the heat-sensitive layer or the layer directly beneath the siliconized release layer can be siliconized very well.

[0183] A platelet-shaped pigment is understood to mean a pigment in which the ratio of diameter to thickness is about 7 to 40 to 1, preferably about 15 to 30 to 1.

[0184] The particle size of the platelet-shaped pigment is preferably adjusted so that at least about 70%, preferably at least about 85%, of the particles have a particle size of about <2 μm (Sedigraph). The pH of the platelet-shaped pigment in aqueous solution is preferably 6 to 8.

[0185] The at least one platelet-shaped pigment is present in the heat-sensitive layer or in the layer located directly beneath the siliconized release layer, preferably in an amount of about 5 to about 60% by weight, particularly preferably in an amount of about 15 to about 55% by weight, based on the total dry mass of the respective layer.

[0186] If the protective layer is located directly beneath the siliconized release layer, the platelet-shaped pigment is contained in the amounts described above for the pigments contained in the protective layer.

[0187] In a further preferred embodiment, the heat-sensitive recording material is preferably characterized in that the siliconized separating layer comprises at least one siloxane, preferably a poly(organo)siloxane, in particular an acrylopoly(organo)siloxane. In a further embodiment, the siliconized separating layer comprises a mixture of at least two siloxanes. A mixture of at least two acrylopoly(organo)siloxanes is preferred.

[0188] Examples of particularly preferred siloxanes are siloxanes available under the trade names TEGO®RC902 and TEGO®RC711 (Evonik, Germany).

[0189] In another embodiment, the heat-sensitive recording material is preferably characterized in that the siliconized separating layer contains at least one polysilicone acrylate, which was preferably formed by condensation of at least one silicone acrylate.

[0190] In a preferred embodiment, the siliconized release layer is a heat-cured release layer. This release layer is formed in the presence of a Pt catalyst.

[0191] The siliconized release layer is preferably water-free. It is also preferred that the siliconized release layer does not contain any Pt catalysts.

[0192] The siliconized release layer preferably contains an initiator, particularly preferably a photoinitiator. This serves to radically cure the silicone.

[0193] The most preferred photoinitiator is TEGO®Photoinitiator A18 (from Evonik, Germany).

[0194] The siliconized release layer may preferably contain further additives, such as matting agents and / or adhesion additives.

[0195] The siliconized release layer preferably has a basis weight of 0.3 to 5.0 g / m 2, in particular from 1.0 to 3.0 g / m 2 , on.

[0196] The siliconized separating layer preferably has a thickness of 0.3 to 6.0 pm, in particular 0.5 to 2.0 pm. Insulating layer

[0197] According to one embodiment, an insulating layer is present between the carrier substrate and the color layer.

[0198] According to an alternative embodiment, the color layer is formed simultaneously as a color layer and an insulating layer.

[0199] Such an insulating layer, or an ink layer that simultaneously serves as an ink layer and an insulating layer, reduces heat conduction through the heat-sensitive recording material. This makes the local application of heat using a direct thermal printer more efficient, enabling higher thermal printing speeds. The applied heat causes the cover layer to translucent more quickly, thus improving sensitivity.

[0200] This means that less dye is required, which results in improved recyclability in the material cycle, particularly in the waste paper cycle, due to easier deinkability and separation of dye and carrier substrate components.

[0201] The insulating layer or the paint layer, which is simultaneously a paint layer and an insulating layer, preferably has a Bekk smoothness measured according to standard 5267:1995-03 of greater than 50 s, more preferably greater than 100 s and most preferably of 100 to 250 s.

[0202] The insulating layer or the paint layer, which is simultaneously a paint layer and an insulating layer, preferably comprises a heat-insulating material.

[0203] Preferably, the heat-sensitive recording material with an insulating layer or a color layer that simultaneously serves as an insulating layer has a lower thermal conductivity than a heat-sensitive recording material that does not comprise an insulating layer or a color layer that simultaneously serves as an insulating layer. The heat-insulating material preferably comprises kaolin, particularly preferably calcined kaolin, and mixtures thereof.

[0204] The heat-insulating material is preferably present in the insulating layer in an amount of 20 wt.% to 80 wt.%, particularly preferably in an amount of 40 wt.% to 60 wt.%, based on the total dry mass of the insulating layer.

[0205] In a paint layer which is simultaneously a paint layer and an insulating layer, the heat-insulating material is preferably present in an amount of 30 wt.% to 70 wt.%, particularly preferably in an amount of 40 wt.% to 60 wt.%, based on the total dry mass of the paint layer which is simultaneously a paint layer and an insulating layer.

[0206] The insulating layer preferably has a basis weight of 1 to 5 g / m 2 , especially from 2 to 4 g / m 2 , on.

[0207] The insulating layer preferably has a thickness of 1 to 10 pm, in particular of 2 to 8 pm.

[0208] The ink layer, which is both a color layer and an insulating layer, preferably has a basis weight of 1 to 10 g / m 2 , especially from 3 to 8 g / m 2 , on.

[0209] The color layer, which is simultaneously a color layer and an insulating layer, preferably has a thickness of 1 to 12 pm, in particular of 4 to 8 pm.

[0210] parameter

[0211] According to one embodiment, the relative print contrast of the heat-sensitive layer defined according to the description is at least 50%, preferably at least 55%, and more preferably at least 60%.

[0212] The relative print contrast (DK in %) is calculated based on the optical density (o. D.) of a thermally printed area, i.e. an optical density of a print pattern (oDs) and the optical density of a non-printed area (oDO) according to the following equation 1, where s corresponds to the printed area, and where 0 corresponds to the non-printed area, and where the scatter of the calculated % values ​​is <±2 percentage points:

[0213] Relative print contrast in % = ((oDs - oDO) / oDs) x 100

[0214] (Equation 1)

[0215] According to a first variant, the optical density (n.d.) was measured using a SpectroEye densitometer from X-Rite, in particular at an energy level of 12.79 mJ / mm 2 measured. The measurement uncertainty of the o. D. values ​​is in particular <2%.

[0216] In particular, according to the first variant, 6 cm wide strips of the heat-sensitive recording materials were thermally printed using a GeBE Printer-Lab GPT-10000 test printer (GeBE Elektronik und Feinwerktechnik GmbH, Germany) with a Kyocera print bar of 305 dpi and 1146 ohms at an applied voltage of 24 V with a checkerboard pattern with 10 energy gradations, a printing speed of approximately 100 mm / s and a contact pressure of 19 N, whereby the area of ​​one checker of the printing pattern corresponds to 80 x 80 dots.

[0217] According to a second variant for determining the optical density (n.d.), 6 cm wide strips of the heat-sensitive recording materials were thermally printed using a GeBE PrinterLab GPT-10000 test printer (GeBE Elektronik und Feinwerktechnik GmbH, Germany) with a Kyocera print head of 305 dpi and 1146 ohms at an applied voltage of 24 V with a checkerboard pattern without energy gradations, a print speed of approximately 100 mm / s, and a contact pressure of 19 N. The energy gradation was selected to achieve an optical density of 1.20 ± 0.05. The area of ​​one checkerboard of the print pattern corresponds to 80 x 80 dots. The optical density (OD) of the printed and non-printed areas was measured using an X-Rite SpectroEye densitometer. The measurement uncertainty of the OD values ​​is estimated at < 2%. The scatter of the calculated % values ​​is ±2 percentage points.

[0218] According to one embodiment, according to the image stability storage test defined in the description, after a period of four weeks, a remaining image stability of the heat-sensitive layer of at least 95%, preferably at least 96%, more preferably at least 97%, even more preferably at least 98%, furthermore even more preferably at least 99%, and most preferably 100% of the original image stability of the heat-sensitive layer is obtained.

[0219] In the context of the present disclosure, the image durability storage test defined below comprises storing the printed heat-sensitive recording material for a period of four weeks between two glass plates at 60°C, at a pressure of 1350 N / m 2 , at a relative humidity of 50% and under exclusion of light.

[0220] In the storage test according to the present disclosure, the image stability of the heat-sensitive recording material is determined based on the relative print contrast determined according to Equation 1, once before storage of the heat-sensitive recording material and once after the heat-sensitive recording material has been stored for four weeks. The two determined values ​​of the relative print contrast are related to each other, as illustrated by the following Equation 2, with the scatter of the calculated % values ​​being <±2 percentage points:

[0221] Image stability or writing performance in % = (relative print contrast after storage / relative print contrast before storage) x 100

[0222] (Equation 2)

[0223] In particular, the printed and unprinted areas of the printed strip were analyzed to determine image stability. According to one embodiment, according to the writing performance storage test defined in the description, after a period of four weeks, a writing performance of the heat-sensitive layer of at least 95%, preferably at least 96%, more preferably at least 97%, even more preferably at least 98%, furthermore even more preferably at least 99%, and most preferably 100% of the original writing performance of the heat-sensitive recording material is obtained.

[0224] In the context of the present disclosure, the writing performance storage test defined below comprises the storage of an unprinted heat-sensitive recording material for a period of four weeks between two glass plates at 60°C, at a pressure of 1350 N / m 2, at a relative humidity of 50% and in the absence of light. After storage and adjustment to room temperature, the unprinted heat-sensitive recording material was printed according to the second method mentioned above to determine the optical density. The printed and unprinted areas were measured to determine the optical density (n.d.) and, to determine the relative print contrast, were related to the corresponding optical density values ​​of the printed strip before storage according to the above-mentioned equation 2.

[0225] According to one embodiment, the heat-sensitive recording material has a surface whiteness of 35 to 60%, in particular 45 to 50%, measured according to ISO 5267:1995-03.

[0226] After printing, there is a high relative print contrast with advantageous application properties, such as better readability.

[0227] The surface whiteness (paper whiteness) can be determined according to ISO 2470-2 (2008) using an Elrepho 3000 spectrophotometer. According to one embodiment, the heat-sensitive recording material is characterized in that the contrast between areas where the heat-sensitive layer has become translucent due to local exposure to heat and areas where the heat-sensitive layer has not become translucent due to local exposure to heat is 40 to 80%, in particular 50 to 70%.

[0228] This contrast can be calculated by calculating the difference between the optical density of the background and the typeface. Optical density (OD) can be measured using a densitometer, for example.

[0229] According to one embodiment, the heat-sensitive recording material is preferably characterized by exhibiting a settling behavior of at least "Grade 2" in a thermal printer endurance test (10 km) under printing a checkerboard pattern with 10 energy levels. After a test run of 10 km on a commercially available thermal printer (model: Zebra ZD420), a visual inspection for deposits on the thermal print head was performed. The assessment was based on the following grading system: Grade 0 = no settling, Grade 1 = slight settling, Grade 2 = moderate settling, Grade 3 = severe settling. Commercially viable heat-sensitive recording materials exhibit no settling (Grade 0).

[0230] According to one embodiment, the heat-sensitive recording material is preferably characterized in that the heat-sensitive recording material has an optical density (o. D.) of at least 1.35, measured at an energy level of 12.79 mJ / mm2 , has.

[0231] Process, product-by-process, and use

[0232] The above-mentioned objects are achieved according to the second aspect by a method for producing a heat-sensitive recording material, comprising the following method steps:

[0233] Providing a carrier substrate having a first side and a second side facing away from the first side; applying a color layer suspension to the first side or second side of the carrier substrate, wherein the color layer suspension comprises at least one colorant;

[0234] Drying the ink layer suspension to obtain an ink layer arranged on the first side or second side of the carrier substrate;

[0235] Applying an application suspension to the paint layer, wherein the application suspension comprises a first material which comprises at least one fatty acid and / or at least one fatty acid amide, and wherein the application suspension comprises a second material which comprises at least one metal salt of a fatty acid, wherein the first material has a first melting temperature Tsi, wherein the second material has a second melting temperature Ts2, wherein the first melting temperature Tsi is lower than the second melting temperature Ts2; and

[0236] Drying the application suspension to obtain a heat-sensitive layer arranged on the ink layer.

[0237] It is preferred to obtain the heat-sensitive recording material according to the invention by a process in which suspensions, in particular aqueous ones, comprising the starting materials of the individual layers are applied successively to the carrier substrate, the application suspensions, in particular aqueous ones, having a dry mass of 8 to 50% by weight, preferably of 10 to 40% by weight, and are applied by the curtain coating process at an operating speed of the coating system of at least 200 m / min, in particular at least 900 m / min.

[0238] This process is particularly advantageous from an economic point of view and due to the uniform application over the carrier substrate.

[0239] If the dry matter content falls below 8 wt.%, the cost-effectiveness deteriorates, as a large amount of water must be removed quickly through gentle drying, which adversely affects the coating speed. On the other hand, if the value exceeds 60 wt.%, this simply leads to increased technical effort to ensure the stability of the coating curtain during the coating process and the drying of the applied film, as the machine must again run at very high speeds.

[0240] In the curtain coating process, a freely falling curtain of a coating dispersion is formed. The coating dispersion, in the form of a thin film (curtain), is "poured" onto a substrate by free fall to apply the coating dispersion to the substrate. DE 10 196 052 T1 discloses the use of the curtain coating process in the production of information recording materials, whereby multilayer recording layers are realized by applying the curtain, consisting of several coating dispersion films, to substrates.

[0241] Embodiments of the method according to the invention are also conceivable in which a "double curtain" is used. This means that two consecutive layers are applied directly one after the other. The application takes place so closely one after the other that the first layer applied has not yet dried before the next layer is applied. The two layers are therefore preferably applied "wet-on-wet."

[0242] All definitions regarding the curtain coating process apply analogously to the double curtain coating process.

[0243] The advantage of a "wet-on-wet" application using a double curtain coating process is that the two layers have a stronger bond and, in particular, there is no need for an intermediate adhesion promoter.

[0244] In a preferred embodiment of the process according to the invention, the aqueous deaerated application suspension has a viscosity of approximately 100 to approximately 1000 mPas (Brookfield, 100 rpm, 20°C). If the value falls below approximately 100 mPas or exceeds approximately 1000 mPas, this leads to poor runnability of the coating composition on the coating unit. The viscosity of the aqueous deaerated application suspension is particularly preferably approximately 200 to approximately 500 mPas. The viscosities of successive coating compositions in the double curtain should decrease from bottom to top. Incorrectly adjusted coatings increase the likelihood of heel formation at the point of impact of the curtain, as well as the occurrence of "wetting disturbances."

[0245] In a preferred embodiment, to optimize the process, the surface tension of the aqueous coating suspension can be adjusted to about 25 to about 70 mN / m, preferably about 35 to about 60 mN / m, measured in accordance with the standard for bubble pressure tensiometry (ASTM D 3825-90), as described below. Better control over the coating process is achieved by determining the dynamic surface tension of the coating color and adjusting it specifically by selecting the appropriate surfactant and determining the required amount of surfactant.

[0246] Dynamic surface tension is measured using a bubble pressure tensiometer. It measures the maximum internal pressure of a gas bubble formed in a liquid via a capillary. The internal pressure p of a spherical gas bubble (Laplace pressure) depends on the radius of curvature r and the surface tension o according to the Young-Laplace equation:

[0247] When a gas bubble is created at the tip of a capillary in a liquid, the curvature initially increases and then decreases again, resulting in a maximum pressure. The greatest curvature and thus the greatest pressure occur when the radius of curvature equals the capillary radius.

[0248] Pressure curve during bladder pressure measurement, position of the pressure maximum:

[0249] The capillary radius is determined using a reference measurement performed with a liquid with a known surface tension, usually water. Once the radius is known, the surface tension can be calculated from the maximum pressure pmax. Since the capillary is immersed in the liquid, the hydrostatic pressure pO, which results from the immersion depth and the density of the liquid (this is done automatically with modern measuring instruments), must be subtracted from the measured pressure. This yields the following formula for the bubble pressure method:

[0250] The measured value corresponds to the surface tension at a specific surface age, the time from the onset of bubble formation to the occurrence of the pressure maximum. By varying the bubble generation rate, the dependence of surface tension on surface age can be determined, resulting in a curve plotting surface tension over time.

[0251] This dependence plays an important role in the use of surfactants, since the equilibrium value of the interfacial tension is not reached in many processes due to the sometimes low diffusion and adsorption rates of surfactants.

[0252] The formation of the individual layers can take place online or in a separate coating process offline.

[0253] In particular, to ensure that the layers described in detail above have the Bekk smoothness mentioned above, the following process steps are preferably carried out.

[0254] The carrier substrate is preferably smoothed in a first cylinder. This one- or two-sided high smoothness, which is created by this process technique, already confers an advantage on the carrier substrate. Additional calendering by a downstream calender, preferably before a first coating device, can further improve smoothness and / or serves to achieve good profiling. If a starch coating, as defined above, is applied, this is preferably done using a film press before the color layer is applied using a blade coater.

[0255] The thickness on the back is particularly advantageous in order to prevent the coating colour from bleeding through with the blade coater.

[0256] It would also be possible to apply the ink layer directly with a film press. However, this would have a disadvantage regarding the smoothness compared to a blade coater. Using a blade coater gives the material a good base smoothness for the important dynamic sensitivity of the final product. There is a correlation between final smoothness and dynamic sensitivity.

[0257] It would also be conceivable to apply the ink layer using a film press or even a curtain coater. While this would eliminate the smoothness advantage, it could also be compensated for with a calender, especially with a film press. However, this only makes sense if hollow spheres are not used, as these would be destroyed by the film press.

[0258] The insulating layer, if present, is applied analogously.

[0259] The siliconized layer, if present, is also applied in the same way.

[0260] The same applies to the protective layer. Alternatively, the protective layer can also be printed. In terms of processing and technological properties, protective layers that are curable using actinic radiation are particularly suitable. The term "actinic radiation" refers to UV or ionizing radiation, such as electron beams.

[0261] The heat-sensitive layer is preferably applied by curtain coating, as described above. If carrier substrates, especially paper, are coated on one side, the resulting curl should be smoothed out afterward.

[0262] This is preferably done with a LAS (Liquid Applicator System) dampening system. A water film is applied to the less coated side and then dried. This restores the flatness. Applying the water film slightly deteriorates the surface.

[0263] A preferred option for surface protection would be a steam humidifier. This uses steam instead of water. This method does not damage the surface. This is ideal for applications where the highest surface quality is required.

[0264] Another option would be a spray humidifier, which applies a mist of water.

[0265] All of the above-mentioned layers can be single-layered or multi-layered.

[0266] The embodiments given for the heat-sensitive recording material according to the first aspect are also embodiments for the method for producing a heat-sensitive recording material according to the second aspect and vice versa.

[0267] The above-mentioned objects are achieved according to the third aspect by a heat-sensitive recording material producible by a method according to the second aspect.

[0268] The embodiments cited for the heat-sensitive recording material according to the first aspect and the method for producing a heat-sensitive recording material according to the second aspect are also embodiments for the heat-sensitive recording material producible by a method according to the third aspect. According to a fourth aspect, the present invention relates to the use of a heat-sensitive recording material according to the first or third aspect as a receipt roll, adhesive label roll, ticket roll, or as printing paper for mechanical printers or pens.

[0269] The embodiments given for the heat-sensitive recording material according to the first aspect and the method for producing a heat-sensitive recording material according to the second aspect are also embodiments for use according to the fourth aspect.

[0270] EXAMPLES OF IMPLEMENTATION

[0271] In the following detailed embodiments, a large number of heat-sensitive recording materials or thermal papers were produced by applying aqueous coating suspensions to form a composite structure on a carrier substrate and were examined using a large number of measuring methods.

[0272] In all examples, a paper substrate made of hardwood and softwood pulp with a basis weight of 41 g / m 2 or 58 g / m 2 used.

[0273] Measurement methods

[0274] Measurement of optical density (n.d.) according to method 1 :

[0275] The heat-sensitive recording materials (6 cm wide strips) were thermally printed using a GeBE PrinterLab GPT-10000 test printer (GeBE Elektronik und Feinwerktechnik GmbH, Germany) with a Kyocera print head of 305 dpi and 1146 ohms at an applied voltage of 24 V with a checkerboard pattern with 10 energy levels, a print speed of approximately 100 mm / s, and a contact pressure of 19 N. The area of ​​one checkerboard pattern corresponds to 80 x 80 dots. The optical density (o.d.) was measured with an X-Rite SpectroEye densitometer at an energy level of 12.79 mJ / mm 2 measured. The measurement uncertainty of the o. D. values ​​is estimated at <2%. Measurement of optical density (o. D.) according to method 2:

[0276] The heat-sensitive recording materials (6 cm wide strips) were thermally printed using a GeBE PrinterLab GPT-10000 test printer (GeBE Elektronik und Feinwerktechnik GmbH, Germany) with a Kyocera print head of 305 dpi and 1146 ohms at an applied voltage of 24 V with a checkerboard pattern without energy gradations, a print speed of approximately 100 mm / s, and a contact pressure of 19 N. The energy gradation was selected (determined from preliminary tests (see method 1)) to achieve an optical density of 1.20 ± 0.05. The area of ​​one checkerboard of the print pattern corresponds to 80 x 80 dots. The optical density (OD) of the printed and non-printed areas was measured using an X-Rite SpectroEye densitometer. The measurement uncertainty of the OD values ​​is estimated at < 2%. The scatter of the calculated % values ​​given below is ±2 percentage points.

[0277] Measuring the relative print contrast:

[0278] The relative print contrast was calculated from the value of the optical density of a thermally printed area (oDs) and the optical density of a non-printed area (oDO) according to the following equation 1, where s corresponds to the printed area and 0 to the non-printed area:

[0279] Relative print contrast in % = ((oDs - oDO) / oDs) x 100

[0280] (Equation 1)

[0281] Measurement of surface whiteness:

[0282] The surface whiteness was determined according to ISO 2470-2 (2008) using an Elrepho 3000 spectrophotometer.

[0283] Measuring Bekk smoothness:

[0284] The Bekk smoothness was determined according to the standard DIN 53107 (2016).

[0285] Measurement of settling behavior: The settling behavior of a thermal printer head was evaluated using a commercially available thermal printer (model: Zebra ZD420) in a thermal printer endurance test (10 km) under a checkerboard pattern with 10 energy levels. After the 10 km test run, a visual inspection of the thermal print head was performed for deposits. The assessment was based on the following grading system: Grade 0 = no settling, Grade 1 = slight settling, Grade 2 = moderate settling, Grade 3 = severe settling. Commercially available heat-sensitive recording materials exhibit no settling (Grade 0).

[0286] Measurement of resistance to plasticizers (Omni-Film):

[0287] A plasticized cling film (PVC film with 20 to 25% dioctyl adipate) was placed in contact with two strips of heat-sensitive recording material printed according to the optical density method (n.d.) according to Method 2, avoiding wrinkles and air pockets. The film was wound into a roll and stored for 16 hours. One strip was stored at room temperature (20 to 22°C), the second at 40°C. After peeling off the film, the optical density of the printed and non-printed areas was measured and related to the corresponding optical density values ​​before exposure to the plasticizer to determine image stability or writing performance, according to Equation 2.

[0288] Image stability or writing performance in % = (relative print contrast after storage / relative print contrast before storage) x 100

[0289] (Equation 2)

[0290] Measuring resistance to pressure sensitive adhesives:

[0291] Two strips of the heat-sensitive recording material were printed using method 2, and the optical density (n.d.) was determined as described. Transparent Tesa self-adhesive tape (tesafilm® crystal clear, #57315) was applied to each strip, and a separate strip of Tesa packaging tape (#04204) was applied, avoiding wrinkles and air pockets. After storage at room temperature (20-22 °C), the optical density (n.d.) of the printed and non-printed areas was measured through the respective adhesive tape after seven days. To determine the relative print contrast, the values ​​were related to the corresponding optical density values ​​of the freshly applied samples (Equation 2) according to the formula (Equation 1).

[0292] Measurement of resistance to hydrophobic and hydrophilic agents:

[0293] On each strip of heat-sensitive recording material printed according to process 2, one drop / fingertip of sunflower oil (Nestle - Thomy 100% pure sunflower oil), lard (LARII GmbH pork lard), hand cream (lanolin hand cream), sweat (manufactured according to DIN EN ISO 105-E04), milk (3.5% fat), ethanol (40% in water), and water (tap water) was applied to a printed and a non-printed area. After a contact time of 30 minutes, the agents were removed by brief contact with a standard kitchen towel, and the papers were stored at room temperature (20-22 °C). After a specific storage period (see Table 1), the optical density (o. D.) of the printed and non-printed areas was measured and related to the corresponding optical density values ​​before exposure to the agent (Equation 2) to determine the relative print contrast according to the formula (Equation 1).

[0294] Measuring the storage life of heat-sensitive recording materials:

[0295] A strip of the heat-sensitive recording material was printed according to method 2 and the optical density (n.d.) was measured as described (n.d. before storage) and, together with an unprinted strip of the heat-sensitive recording material, was stored for four weeks between two glass plates at 60 °C, a pressure of 1350 N / m 2 , a relative humidity of 50% and exclusion of light.

[0296] After storage and adjustment to room temperature, the unprinted strip was printed according to method 2 (= remaining print performance). The printed and non-printed areas were measured to determine the optical density (n.d.). The printed and non-printed areas of the printed strip were also measured (= remaining image stability) and the relative print contrast was determined using equation 2, which was then related to the corresponding optical density values ​​before storage.

[0297] Applying heat-sensitive recording materials as self-adhesive labels. The following procedure describes the reverse application of an adhesive layer to an A4 sheet. The adhesive dispersion is applied with a squeegee to the back of an A4 sheet of paper (heat-sensitive recording material) bearing the heat-sensitive layer on the front and dried with a hot air dryer at a maximum of 70°C. To protect the adhesive layer during further processing, a siliconized release paper is laminated to the adhesive layer, avoiding air pockets and wrinkles.

[0298] In the case of an "adhesive-liner sandwich" consisting of a thin adhesive layer between two release papers, after removing one of the two liner papers, the adhesive layer (sticky side) is laminated to the back of the A4 thermal paper, avoiding air pockets and wrinkles.

[0299] It is irrelevant whether, during label production, the adhesive layer is applied first and then the heat-sensitive recording layer is applied to the opposite side bearing the adhesive layer. In particular, the insulating or ink layer is applied first, followed by the heat-sensitive layer.

[0300] To produce self-adhesive labels, a removable acrylate-based adhesive (R5000N, Avery Fasson) was used as a commercially available adhesive.

[0301] Adhesive migration test of heat-sensitive labels

[0302] A strip of the heat-sensitive recording material was printed and measured (n.d. before storage) according to method 2 (measurement of optical density (n.d.)) and, together with an unprinted strip of the heat-sensitive recording material, was stored for four weeks between two glass plates at 60 °C, a pressure of 1350 N / m 2, a relative humidity of 50% and exclusion of light.

[0303] After storage and conditioning to room temperature, the unprinted strip was printed according to method 2 (measurement of the optical density (n.d.) (= remaining writing power)), the printed and non-printed areas were measured and related to the corresponding optical density values ​​of the printed strip before storage to determine the relative print contrast according to equation 2.

[0304] The printed and non-printed areas of the printed strip are also measured (= remaining image permanence) and related to the corresponding optical density values ​​before storage (Equation 2) to determine the relative print contrast according to Equation 1.

[0305] Production of heat-sensitive recording materials

[0306] The dry solids content (DW) of the respective layer formulations of the following layers is adjusted by adding water as follows: insulating layer (30%), color layer (26%), heat-sensitive layer (20%) and protective layer (10%).

[0307] The raw materials used are used as a dispersion or as a solution with the following dry contents: styrene-acrylate copolymer (21%), styrene-butadiene latex (48%), carbon black (45%), sodium metaborate tetrahydrate (2%), stearic acid amide wax (22%), silicon oxide (28%), zinc stearate (35%), calcium stearate (35%), polyvinyl alcohol (high viscosity) (10%), calcined kaolin (45%), precipitated calcium carbonate (58%), ammonium zirconium carbonate (9%), polyamidoamine epichlorohydrin (10%), polyvinyl alcohol (low viscosity) (7%) and kaolin (75%).

[0308] The quantities [wt.%] refer to the oven-dry state (otro).

[0309] On a laboratory scale, the aqueous application suspensions for forming the ink layer, the heat-sensitive layer, and the protective layer of a heat-sensitive recording material were applied consecutively to the paper substrate using a bar doctor blade. After each application, the coating was dried within 1 to 3 minutes using a hot air dryer (40 cm distance) at a temperature range of 90 to 110 °C.

[0310] Examples 1a, 2a, 3a and 4, as well as comparative example V1

[0311] In working examples 1a, 2a, 3a and 4, as well as in comparative example C1, the insulating layer is applied to the paper substrate on a paper machine using a film press at a speed of 800 m / min. The ink layer and the heat-sensitive layer are applied consecutively to the paper substrate provided with an insulating layer on a paper coating machine using a single and / or simultaneously using a double curtain coater at a speed of 900 m / min. The protective layer is applied to the heat-sensitive layer on a paper coating machine using a curtain coater at a speed of 900 m / min. After each application, the coated paper support is dried in the usual way without adversely affecting the properties of the heat-sensitive recording material according to the invention, such as the surface whiteness or paper whiteness of the heat-sensitive layer.

[0312] The compositions of the working examples 1a, 2a, 3a and 4, as well as of the comparative example V1, are given below.

[0313] Example 1a:

[0314]

[0315] Example 2a:

[0316]

[0317] Example 3a:

[0318]

[0319] Example 4:

[0320]

[0321] Comparison example 1:

[0322] Examples 1b, 1c, 2b, 2c, 3b and 3c

[0323] In working examples 1b, 1c, 2b, 2c, 3b, and 3c, the color layer and the heat-sensitive layer are applied consecutively to the paper substrate using a single and / or simultaneously using a double curtain coater on a paper coating machine at a speed of 900 m / min. The protective layer is applied to the heat-sensitive layer using a curtain coater on a paper coating machine at a speed of 900 m / min. After each application, the coated paper support is dried in the usual manner without adversely affecting the properties of the heat-sensitive recording material according to the invention, such as the surface whiteness or paper whiteness of the heat-sensitive layer.

[0324] The compositions of the embodiments 1b, 1c, 2b, 2c, 3b and 3c are given below.

[0325] Example 1 b:

[0326]

[0327] Example 1c:

[0328] Example 2b:

[0329] Example 2c:

[0330]

[0331] Example 3b:

[0332]

[0333] Example 3c:

[0334] Examples 1 d, 1f, 1q, and 1h

[0335] In the working examples 1d, 1f, 1g and 1h, a starch precoat (0.5 g / m 2) is applied to the front and back of the paper substrate using a film press at a speed of 800 m / min. The ink layer is applied to the starch-coated paper substrate on a paper coating machine using a blade coater at a speed of 600 m / min. The heat-sensitive layer and the protective layer are applied consecutively to the starch-coated paper substrate provided with an ink layer on a paper coating machine using a single and / or simultaneously using a double curtain coater at a speed of 900 m / min. After each application, the coated paper base is dried in the usual way without negatively affecting the properties of the heat-sensitive recording material according to the invention, such as the surface whiteness or paper whiteness of the heat-sensitive layer.

[0336] The compositions of the working examples 1d, 1f, 1g and 1h are given below.

[0337] Example 1d:

[0338]

[0339] Example 1f:

[0340] Example 1g:

[0341] Example 1h:

[0342] Implementation example 1e

[0343] In Example 1e, the ink layer and the heat-sensitive layer are applied consecutively to the paper substrate using a single and / or simultaneously using a double curtain coater on a paper coating machine at a speed of 900 m / min. The protective layer is applied to the heat-sensitive layer using a curtain coater on a paper coating machine at a speed of 900 m / min. After each application, the coated paper substrate is dried in the usual way without adversely affecting the properties of the heat-sensitive recording material according to the invention, such as the surface whiteness or paper whiteness of the heat-sensitive layer.

[0344] The composition of the embodiment 1e is given below. Embodiment 1e:

[0345] Furthermore, it is emphasized that for all embodiments, a protective layer can optionally be applied to the outside of the heat-sensitive layer, according to the optional protective layers 1, 2, 3 and 4 shown below.

[0346] Protective layer 1 Protective layer 2

[0347] Protective layer 3 Protective layer 4

[0348] Results

[0349] The results of the measurements of the above-mentioned parameters are summarized in the following tables 1, 2a, 2b and 3 for the embodiments 1a to 1h, 2a to 2c, 3a to 3c, and 4, as well as for the comparative example V1. * only the Bekk smoothness of a printed area was taken into account here

[0350] Table 1

[0351] In all embodiments 1 to 3c and 4 according to the invention, stearic acid amide is present as the first material in the heat-sensitive layer and a metal salt of a fatty acid, in particular zinc stearate, is present as the second material.

[0352] In the non-inventive comparative example V1, the heat-sensitive layer contains stearic acid amide as the first material, but no metal salt of a fatty acid, in particular no zinc stearate, as the second material, or as a lubricant or

[0353] Release agent. In embodiments 1a, 2a, 3a, and 4, the heat-sensitive recording material has an insulating layer arranged on the carrier substrate, an ink layer arranged on the insulating layer, and a heat-sensitive layer arranged on the ink layer. In embodiments 1b to 1h, 2b to 2c, the heat-sensitive recording material has an ink layer arranged directly on the carrier substrate, with a heat-sensitive layer arranged on the ink layer. In embodiments 1a to 1h, 2b to 2c, 3b to 3c, and 4, the basis weight, as well as the materials and the weight proportions of the individual layers, were varied.

[0354] As can be seen from Table 1, by replacing conventionally used hollow sphere pigments in the heat-sensitive marking layer with fatty acids or fatty acid amides as the first material and metal salts of a fatty acid as the second material, acceptable or good printing parameters could be achieved in all cases, since in all examples according to method 1 values ​​of the optical density of at least 1.35 could be achieved, since in all examples values ​​of a relative print contrast of at least 60% could be achieved, since in all examples values ​​of a surface whiteness of at least 30% could be achieved, and since in all cases Bekk smoothing before and after printing of more than 250 s and more than 100 s could be achieved.

[0355] However, there is a difference in the evaluation of the shedding behavior.

[0356] In Comparative Example V1, the heat-sensitive layer contains stearic acid amide as the first material, but no metal salt of a fatty acid, in particular no zinc stearate, as the second material, or as a lubricant or release agent. Accordingly, according to Table 1, Comparative Example V1 also exhibits severe and thus disadvantageous settling behavior (settling rating = 3) compared to the advantageous, non-existent settling behavior of Working Examples 1a to 3c (settling rating = 0).

[0357] In Example 4, the heat-sensitive layer contains stearic acid amide as the first material, but only an extremely small weight fraction of 3.9 wt.% of a metal salt of a fatty acid, in particular zinc stearate, as the second material, or as a lubricant or release agent. Accordingly, according to Table 1, Example 4 (lay-off rating = 1) achieves a better result compared to Comparative Example C1. However, a disadvantageous lay-off behavior is still observed compared to the advantageous non-existent lay-off behavior of Working Examples 1a to 3c (lay-off rating = 0).

[0358] It should be emphasized here that in all exemplary embodiments 1a to 3c, a weight fraction of more than 10 wt.% of a metal salt of a fatty acid was used as the second material. However, in exemplary embodiments 3a to 3c, only a weight fraction of just over 10 wt.% was used, and in exemplary embodiments 1a to 2c, the metal salt of a fatty acid was used as the second material with a weight fraction of significantly more than 10 wt.%. Accordingly, the best deposition behavior is obtained in exemplary embodiments 1a to 2c (deposition rating = 0) compared to exemplary embodiments 3a to 3c (deposition rating = 1).

[0359] Tables 2a and 2b below demonstrate the tested resistance of Examples 1a to 3c and 4, or Comparative Example V1, to hydrophilic and hydrophobic reagents. * Percentage remaining image stability / write performance in % according to equation 2

[0360] Table 2a

[0361] Percentage remaining image stability / write performance in % according to equation 2

[0362] Table 2b

[0363] As can be seen from Tables 2a and 2b, all examples show an effective resistance of more than 90% to different hydrophobic and hydrophilic agents.

[0364] Table 3

[0365] As can be seen from Table 3, all examples demonstrate effective storage stability and also effective resistance in an adhesive migration test, characterized by a storage stability of the printed heat-sensitive recording materials (image stability) of more than 95% and a storage stability of the unprinted heat-sensitive recording materials (writing performance) of 100%. Thus, it can be summarized that the use of a fatty acid, ora fatty acid amide having a lower melting point as the first material of the heat-sensitive recording layer, and that the use of a metal salt of a fatty acid having a higher melting point as the second material of the heat-sensitive recording layer ensures at least consistent image properties of the printed image and also at least consistent resistance to hydrophilic and hydrophobic reagents compared to conventionally used heat-sensitive coating materials.

[0366] What is crucial, however, is that, compared to conventional recording materials, the use of a fatty acid or a fatty acid amide with a lower melting point as the first material of the heat-sensitive recording layer and the use of a metal salt of a fatty acid with a higher melting point as the second material of the heat-sensitive recording layer enables improved deposition behavior in direct thermal printing and also ensures that environmentally harmful organic pigments, in particular hollow sphere pigments, can be dispensed with.

Claims

A N S P R Ü C H E 1. A heat-sensitive recording material comprising: a carrier substrate having a first side and a second side facing away from the first side;a color layer arranged on the first or second side of the carrier substrate, wherein the color layer comprises at least one colorant, and a heat-sensitive layer arranged on the color layer and at least partially covering the color layer, wherein the heat-sensitive layer is designed such that it becomes translucent through the local action of heat, so that the underlying color layer becomes visible, characterized in that the heat-sensitive layer comprises a first material which comprises at least one fatty acid and / or at least one fatty acid amide, and in that the heat-sensitive layer comprises a second material which comprises at least one metal salt of a fatty acid, wherein the first material has a first melting temperature Tsi, wherein the second material has a second melting temperature Ts2, wherein the first melting temperature Tsi is lower than the second melting temperature Ts2; 2. Heat-sensitive recording material according to claim 1, characterized in that the first melting temperature Tsi is at least 1°C, preferably at least 2°C, more preferably at least 5°C and most preferably at least 10°C lower than the second melting temperature Ts2.

3. Heat-sensitive recording material according to claim 1 or 2, characterized in that the at least one fatty acid of the first material is selected from the group comprising behenic acid, stearic acid, and / or palmitic acid, and / or that the at least one fatty acid amide of the first material is selected from the group comprising behenamide, erucamide, stearic acid amide, oleamide, palmitic acid amide, and / or lauramide, preferably stearic acid amide.

4. Heat-sensitive recording material according to one of the preceding claims, characterized in that the first material is present in the heat-sensitive layer in an amount of 1 wt.% to 90 wt.%, preferably in an amount of 30 wt.% to 80 wt.%, based on the total dry mass of the heat-sensitive layer.

5. Heat-sensitive recording material according to one of the preceding claims, characterized in that the at least one metal salt of the fatty acid of the second material is selected from the group comprising calcium stearate, magnesium stearate, zinc stearate and mixtures thereof, preferably calcium stearate and / or zinc stearate.

6. Heat-sensitive recording material according to one of the preceding claims, characterized in that the at least one metal salt of the fatty acid of the second material is present in the heat-sensitive layer in an amount of more than 10% by weight, based on the total dry mass of the heat-sensitive layer.

7. Heat-sensitive recording material according to claim 6, characterized in that the second material is present in the heat-sensitive layer in an amount of 10.1 wt.% to 90 wt.%, preferably 25 wt.% to 40 wt.%, based on the total dry mass of the heat-sensitive layer.

8. Heat-sensitive recording material according to one of the preceding claims, characterized in that the heat-sensitive layer comprises at least one binder, wherein the binder is selected from the group comprising water-soluble starches, starch derivatives, starch-based biolatices of the EcoSphere type, methylcellulose, hydroxyethylcellulose, carboxymethylcellulose, gelatin, Casein, partially or fully saponified polyvinyl alcohols, chemically modified polyvinyl alcohols, ethylene-vinyl alcohol copolymers, sodium polyacrylates, styrene-maleic anhydride copolymers, ethylene-maleic anhydride copolymers, styrene-butadiene copolymers, acrylamide-(meth)acrylate copolymers, acrylamide-acrylate-methacrylate terpolymers, polyacrylates, poly(meth)acrylic acid esters, acrylate-butadiene copolymers, polyvinyl acetates, acrylonitrile-butadiene copolymers, and mixtures thereof.

9. Heat-sensitive recording material according to one of the preceding claims, characterized in that the heat-sensitive layer comprises at least one pigment, wherein the pigment is selected from the group comprising inorganic pigments, both of synthetic and natural origin, preferably clays, precipitated or natural calcium carbonates, aluminum oxides, aluminum hydroxides, silicas, precipitated and pyrogenic silicas, for example Aerodisp types, diatomaceous earths, magnesium carbonates, talc, kaolin, titanium oxide, bentonite but also organic pigments, such as hollow pigments with a styrene / acrylate copolymer wall or urea / formaldehyde condensation polymers and mixtures thereof, preferably calcium carbonates, aluminum hydroxides, and / or pyrogenic silicas.

10. Heat-sensitive recording material according to one of the preceding claims, characterized in that the heat-sensitive layer comprises at least one crosslinking agent, wherein the crosslinking agent is selected from the group comprising polyvalent aldehydes, such as glyoxal, dialdehyde starch, glutaraldehyde, optionally in admixture with boron salts, for example borax, salts or esters of glyoxylic acid, crosslinkers based on ammonium zirconium carbonate, polyamidoamine epichlorohydrin resins (PAE resins), adipic acid dihydrazide (AHD), boric acid or salts thereof, polyamines, epoxy resins, formaldehyde oligomers, cyclic ureas, methylol urea, melamine formaldehyde oligomers and mixtures thereof.

11. Heat-sensitive recording material according to one of the preceding claims, characterized in that the heat-sensitive recording material has a protective layer which is arranged on the heat-sensitive layer.

12. Heat-sensitive recording material according to one of the preceding claims, characterized in that the heat-sensitive recording material has an adhesive layer which is arranged on the first or second side of the carrier substrate facing away from the ink layer, wherein the adhesive layer comprises at least one adhesive, preferably a heat-activatable adhesive, and more preferably a pressure-sensitive adhesive.

13. Heat-sensitive recording material according to one of the preceding claims, characterized in that the heat-sensitive recording material has an optical density (o. D.) defined according to the description of at least 1.35, wherein in particular at an energy level of 12.79 mJ / mm 2 was measured.

14. Heat-sensitive recording material according to one of the preceding claims, characterized in that the recording material has a surface whiteness measured according to the standard ISO 5267:1995-03 of 35 to 60%, in particular of 45 to 50%.

15. A process for producing a heat-sensitive recording material, comprising the following process steps: Providing a carrier substrate having a first side and a second side facing away from the first side; Applying a color layer suspension to the first side or second side of the carrier substrate, wherein the color layer suspension comprises at least one colorant; Drying the ink layer suspension to obtain an ink layer arranged on the first side or second side of the carrier substrate; Applying an application suspension to the paint layer, wherein the application suspension comprises a first material which comprises at least one fatty acid and / or at least one fatty acid amide, and wherein the application suspension comprises a second material which comprises at least one metal salt of a fatty acid, wherein the first material has a first melting temperature Tsi, wherein the second material has a second melting temperature Ts2, wherein the first melting temperature Tsi is lower than the second melting temperature Ts2; and Drying the application suspension to obtain a heat-sensitive layer arranged on the ink layer.

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