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 facing away from the first side; optionally an insulating layer arranged on the first or second side of the carrier substrate; a colour layer arranged on the first or second side of the carrier substrate or on the optional insulating layer, the at least one colour layer having at least one colouring substance; and at least one heat-sensitive layer that is arranged on the colour layer and at least partially covers the colour layer, the heat-sensitive layer being designed such that it becomes translucent by local action of heat, with the result that the colour layer lying underneath becomes visible. The colour layer and / or the optional insulating layer comprise at least one polymer binder and at least one thermally expanded hollow pigment. In this case, the heat-sensitive layer comprises at least one polymer binder and in particular at least one hollow pigment that is not thermally expanded.

Description

HEAT-SENSITIVE RECORDING MATERIAL TECHNICAL AREA According to a first aspect, the present invention relates to a heat-sensitive recording material comprising a carrier substrate having a first side and a second side facing away from the first side; optionally an insulating layer arranged on the first or second side of the carrier substrate, a color layer arranged on the first or second side of the carrier substrate or on the optional insulating layer, wherein the at least one color layer comprises at least one coloring agent, and at least one 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 upon local application of heat, allowing the underlying color layer to be seen. The color layer and / or the optional insulating layer comprises at least a polymeric binder and at least one thermally expanded hollow pigment. In this case, the heat-sensitive layer comprises at least a polymeric binder and, in particular, at least one non-thermally expanded hollow pigment. According to a second aspect, the present invention relates to a method 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; optionally applying an insulating layer suspension to the first or second side of the carrier substrate, in particular optionally drying the insulating layer suspension to obtain an insulating layer arranged on the first or second side of the carrier substrate; applying a color layer suspension to the first or second side of the carrier substrate or on the optional insulating layer, wherein the color layer suspension comprises at least one coloring agent, wherein the color layer suspension and / or the optional insulating layer suspension comprises at least one polymeric binder and at least one thermally expanded hollow pigment; in particular, drying the color layer suspension to obtain a color layer arranged on the first or second side of the support substrate or on the optional insulating layer; applying a coating suspension to the color layer, wherein the coating suspension comprises at least one polymeric binder and in particular at least one non-thermally expanded hollow pigment; in particular, drying the coating suspension to obtain a heat-sensitive layer arranged on the color layer. According to a third aspect, the present invention relates to a heat-sensitive recording material producible by a method according to the second 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, linerless paper, or carbonless copy paper. TECHNICAL BACKGROUND Heat-sensitive recording materials, also known as thermal papers, are used in a variety of applications, such as retail sales receipts. From the prior art, heat-sensitive recording materials, so-called thermal labels, are known for thermal direct printing, whereby two types of heat-sensitive recording materials, especially for thermal direct printing, are distinguished. The first type of heat-sensitive recording materials includes heat-sensitive recording materials in which the printed image is affected by local heat induced by A color reaction is a chemical reaction that occurs within a paint layer, for example, between a color former, such as a leuco dye, and a color developer, such as bisphenol A or a phenol-free alternative. The paint layer typically also contains a heat-sensitive solvent that melts upon exposure to heat and may 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 paint layer may contain heat-sensitive sensitizers. The second type of heat-sensitive recording materials comprises materials in which the printed image is generated by making a heat-sensitive top layer, which according to the present invention is referred to as a heat-sensitive recording layer, translucent through local application of heat, for example by means of a direct thermal printer, so that an underlying color layer becomes visible. This technology is described or interpreted differently in the prior art, and such a heat-sensitive recording material is obtained by means of partially different compositions, porosities, and materials of the heat-sensitive top layer, optimized for direct thermal printing, and explained in more detail below. In the second type of heat-sensitive recording material, the heat-sensitive top layer should cover the underlying ink layer as effectively as possible. This is achieved primarily through light scattering, particularly using scattering particles, and light absorption. The heat-sensitive top layer should exhibit the highest possible contrast to the underlying ink layer in order to produce a printed image readable by the human eye and / or a machine, such as a scanner, for example, white / black or blue / yellow. The second type of heat-sensitive recording material has a heat-sensitive top layer that is sufficiently heat-sensitive to become translucent when exposed to local heat, particularly using conventional direct thermal printers. Ideally, a conventional direct thermal printer should be able to print both types of recording materials. usable and comparable printer settings, especially printhead temperature and printer speed. The present invention relates to heat-sensitive recording materials of the second type described above. GB 997289 describes a recording material for thermal direct printing, comprising a substrate, a color layer and a heat-sensitive top layer, wherein the heat-sensitive top layer becomes translucent through local application of heat by means of a thermal direct printer, so that the underlying color layer is visible and a printed image is thus produced. US 6043193 describes a heat-sensitive recording material comprising a substrate and an opaque recording layer applied to that substrate, which includes hollow spherical beads dispersed in a hydrophilic binder, wherein the beads have a mean diameter of 0.2 μm to 1.5 μm and a cavity volume of 40% to 90%. US Patent 6133342 describes a heat-sensitive recording material comprising a colorant and an opaque polymer material whose opacity changes substantially irreversibly, making the colorant more visible when exposed to heat. 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 cavity layer with a collapsible layer structure in which several cavities are dispersed, the multiple cavities being formed by orienting the multilayer, wherein the extruded image reproduction layer and the collapsible layer structure are in a non-collapsed state, which is essentially opaque in order to conceal the pigment layer below. US Patent 2010 / 245524 A describes a heat-sensitive recording material comprising a heat-sensitive substrate with an opaque polymer that is sensitive to the application of heat and pressure and that, when heated to a predetermined temperature and under the influence of a predetermined pressure, causes the opaque polymer to become transparent, and a color material arranged in relation to the substrate in such a way that it is obscured by the opaque polymer before the application of the predetermined heat and pressure and becomes visible thereafter. US Patent 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 containing polymeric particles with a core-shell structure and, when dry, hollow to scatter visible light, wherein the particles have an inner first polymer shell with a Tg of 40 °C to 130 °C and an outer second polymer shell with a Tg of -55 °C to 50 °C, the Tg of the outer polymer shell being lower than that of the inner polymer shell. US Patent 2011 / 251060 A describes a heat-sensitive recording material consisting of a dye and a flexible support substrate, wherein 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 wherein the heat-sensitive layer is arranged on the dye. The heat-sensitive layer may be provided with a barrier layer and a protective layer. WO 2012 / 145456 A1 describes a heat-sensitive recording material optimized for conventional thermal direct printing, which has a substrate in the form of a planar structure, including at least one colored surface, 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 they are dry, contain at least one cavity, and comprise 1 wt.% to 90 wt.%, based on the weight of the polymer particles, an opacity reducer with a melting point of 45 °C to 200 °C. WO 2013 / 152287 A1 describes a heat-sensitive recording material with a two-layer, monoaxially oriented film comprising a first layer comprising an opaque polymer based on beta-nucleated propylene, and a second layer comprising a dark pigment. US Patent 2015 / 049152 A describes a heat-sensitive recording material comprising a heat-sensitive layer arranged 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 that differs 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. EP 2993054 A1 describes a web-shaped heat-sensitive recording material with at least one first layer and a second layer at least partially covering the first layer, wherein the first layer has an intense color at least facing the second layer and the second layer has hollow pigments which can be melted to form a writing image by locally limited heat treatment, characterized in that the second layer also has one or more fatty acids and one or more heat-sensitive sensitizers in addition to the hollow pigments. In the recording material disclosed in EP 1778499 A1, which differs in its structure only in the type of coloring of the second layer from EP 2993055 A1, whereby the writing becomes visible under UV irradiation instead of 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. EP 2993055 A1 describes a web-shaped heat-sensitive recording material with at least one first layer and a second layer at least partially covering the first layer, wherein the first layer has an intense coloration at least facing the second layer and the second layer has hollow pigments which can be melted to form a written image by locally limited heat treatment, characterized in that the recording material has at least one protective layer at least partially covering the second layer. The physical process here, according to the wording, distinguishes between two different methods for generating the printed image: In the first method, the printed image is created by making a heat-sensitive top layer translucent through the local application of heat using a direct thermal printer. This top layer comprises meltable hollow pigments. In the second method, the printed image is created by making a heat-sensitive top layer translucent through the local application of heat using a direct thermal printer. This top layer comprises softenable or soluble hollow pigments. According to this document, an acceptable, grey recording material with the following specifications 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 printhead 300 dpi, 16 mJ / mm²). 2 ) In the related divisional application EP 3517309 A1, in particular the feature of the top layer is specified, which comprises manipulable hollow body pigments and at least one fatty acid, namely stearic acid and / or palmitic acid or stearic acid amide and / or methylolstearic acid amide, to form a writing image. US Patent 2017 / 337851 A discloses a recording material comprising a release liner base layer, an optional adhesive layer, a label base layer, a thermal insulation layer arranged over the label base layer, an ink layer arranged over the thermal insulation layer, the ink layer comprising at least one color, a cover layer arranged over the printed ink layer, and a top coat layer arranged over the cover layer, the cover layer comprising 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 is applied by a printhead that causes the cover layer to transition from the first state to the second state, thereby enablingthat at least one color of the ink layer becomes visible through the top layer. In WO 2019 / 183471 A1, a recording medium is disclosed comprising a substrate, wherein the substrate is involved in the first scattering particles having a melting point, which comprise 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 solid scattering particles, and wherein the first light scattering layer is porous and the second scattering particles are arranged to fill the space between the recording medium during the melting of the solid. WO 2019 / 219391 A1 describes a heat-sensitive recording material comprising a support 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 support substrate, wherein the thermoresponsive layer comprises nanoparticles of at least one cellulose ester. 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 is in in an opaque state comprising a multitude of irregular and / or oddly shaped opaque polymer particles that define cavities between them and have different shapes and / or different sizes, and further wherein the opaque material is configured such that, upon application of sufficient temperature and / or pressure, it changes from the opaque state to a transparent state to expose the color material beneath the opaque material. 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 with a first melting point, and several second scattering particles near 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 when melting, and wherein the first scattering particles comprise perforated particles. EP 3 957 489 A1 discloses a heat-sensitive recording material comprising or consisting of a support substrate and a melt layer arranged on one side of the support substrate or paper substrate. All of these conventionally used heat-sensitive recording materials require improvement, particularly with regard to their functionality, sustainability, and cost-effectiveness. Especially with heat-sensitive recording materials of the first type mentioned, color developers must be used, which often have harmful effects on health or the environment, leading to efforts to eliminate them. Furthermore, conventionally used heat-sensitive recording materials often require a variety of special raw materials, which may be nanoscale, porous, perforated, and so on, or require the use of two different scattering particles. In particular, it is desirable to reduce the occurrence of errors in barcode prints, which are detrimental to electronic reading devices, in order to improve the print image. In particular, it is desirable to at least maintain or further enhance the protection of heat-sensitive recording materials from external influences such as pressure, friction, humidity, liquids, and moisture. Furthermore, the functionality, properties, and economic manufacturability of conventional heat-sensitive recording materials should at least be maintained and ideally even improved, especially with regard to the optical density of corresponding printed images produced using these materials. Furthermore, contact between heat-sensitive recording materials and food should be made possible in a way that is harmless to the user of food, and advantageous recyclability of corresponding conventional heat-sensitive recording materials should be achieved. DESCRIPTION OF THE INVENTION Task One object of the present invention is to provide a heat-sensitive recording material which does not exhibit any print image defects after printing. A further object of the present invention is to provide a heat-sensitive recording material which is able to guarantee the application-related functional properties necessary, such as high optical density and / or good barcode readability of printed images obtained using heat-sensitive recording materials. Another object of the present invention is to provide a heat-sensitive recording material that can be brought into contact with food and is environmentally friendly, i.e., can be advantageously recycled. Another object of the present invention is to provide a heat-sensitive recording material that uses readily available raw materials and is therefore inexpensive to produce. Surprisingly, it has now been found that the disadvantages of the prior art described above can be overcome by using thermally expanded hollow pigments in the color layer and / or in the optional insulating layer of the heat-sensitive recording material. By using thermally expanded hollow pigments in the ink layer and / or in the optional insulating layer, the optical density and barcode readability of corresponding printed images obtained using the heat-sensitive recording material could be improved. Heat-sensitive recording material The aforementioned tasks are solved according to the first aspect by a heat-sensitive recording material comprising: a carrier substrate which has a first side and a second side facing away from the first side;Optionally, an insulating layer arranged on the first or second side of the support substrate, a color layer arranged on the first or second side of the support substrate or on the optional insulating layer, wherein the at least one color layer comprises at least one coloring agent, and at least one heat-sensitive layer arranged on the color layer and at least partially covering the color layer, wherein the heat-sensitive layer is configured to become translucent upon local application of heat, allowing the underlying color layer to become visible, the color layer and / or the optional insulating layer comprising at least one polymeric binder and at least one thermally expanded hollow pigment, and the heat-sensitive layer comprising at least one polymeric binder and, in particular, at least one non-thermally expanded hollow pigment. By using the thermally expanded hollow pigment in the ink layer and / or the optional insulating layer according to the first aspect, it is not only possible to achieve optimal machine reading of a barcode print image obtained by means of the heat-sensitive recording material, but also to achieve a significantly improved optical density of the print image. In the heat-sensitive recording material according to the first aspect, a printed image is produced by locally subjecting the heat-sensitive recording layer arranged on the ink layer to a heat source, whereby the heat-sensitive recording layer becomes translucent at the heated areas, so that the underlying ink layer becomes visible. As already explained in detail in the preceding section, the heat-sensitive recording material of the second type according to the present invention differs from the heat-sensitive recording materials of the first type often described in the prior art, in which a chemical color reaction in the color-forming layer leads to the formation of the printed image through the reaction of a dye precursor with a color developer. The heat-sensitive recording material according to the present invention, in particular the heat-sensitive layer, contains no chemical color developer and no chemical color former, in particular no leuco dye. However, trace amounts of a chemical color developer and / or a chemical color former, in particular a leuco dye, may be present. The insulating layer optionally present between the substrate and the color layer in the heat-sensitive recording material, as described in the first aspect, provides advantageous thermal insulation and thus limits heat transfer within the heat-sensitive recording material when a heat source acts on the heat-sensitive recording layer during thermal exposure of the heat-sensitive recording material. If the optional insulating layer is present in the heat-sensitive recording material according to the first aspect, this means that the insulating layer is located on the first or second side of the support substrate, and that the color layer of the heat-sensitive recording material is located on the insulating layer. According to the first aspect, the insulating layer arranged on the first or second side of the support substrate is optional, which means that the insulating layer may also be absent in the heat-sensitive recording material, in which case the color layer is arranged directly on the first or second side of the support substrate. According to the first aspect, the thermally expanded hollow pigment is present in the color layer and / or the optional insulating layer. This means that the thermally expanded hollow pigment can be present exclusively in the color layer. However, this also means that the thermally expanded hollow pigment can be present exclusively in the insulating layer. However, this also means that the thermally expanded hollow pigment can be present in both the insulating layer and the color layer. According to the first aspect, the color layer and / or the optional insulating layer includes at least one thermally expanded hollow pigment, which means that there may be only a single type of thermally expanded hollow pigment, or alternatively, there may be a plurality of types of thermally expanded hollow pigment. The at least one thermally expanded hollow pigment of the color layer and / or the optional insulating layer is characterized by having a closed cavity bounded by a polymer shell in which a gas is present, wherein the gas present in the cavity is formed during the production of the thermally expanded hollow pigment by the application of heat to expand the polymer shell. The at least one non-thermally expanded hollow pigment present in the heat-sensitive layer is characterized by having a closed cavity bounded by a polymer shell, in which air is predominantly present. The at least one non-thermally expanded hollow pigment in the heat-sensitive layer comprises, in particular, a Ropaque®-type hollow pigment. In particular, the polymer shell of at least one non-thermally expanded hollow pigment and / or the thermally expanded hollow pigment is a thermoplastic polymer shell. In contrast to a non-thermally expanded hollow pigment, the gas present in the closed cavity of the thermally expanded hollow pigment exerts pressure on the polymer shell bounding the cavity due to heat exposure during the manufacturing process, causing the polymer shell to expand and resulting in a variety of different effects. In a non-thermally expanded hollow pigment, the polymer shell limiting the cavity is not gas-tight, and the cavity is particularly filled with air, and there is no temperature-dependent change in the size of the hollow pigment. Among other things, the expansion of the polymer shell of the thermally expanded hollow pigment, as the name suggests, leads to a larger diameter of the pigment compared to a non-thermally expanded hollow pigment, as well as a decreasing thickness of the polymer shell with a corresponding increase in pigment diameter. In contrast to a non-thermally expanded hollow pigment, the expansion of the polymer shell of the thermally expanded hollow pigment results in an increased specific surface area and a reduced density. The production of a thermally expanded hollow pigment is achieved by subjecting the hollow pigment to heat, which causes the corresponding gas to expand within it. The cavity of the hollow pigment is expanded, thereby widening the polymer shell of the hollow pigment, which allows the thermally expanded hollow pigment to be obtained. In particular, the gas present in the cavity of the thermally expanded hollow pigment does not contain air as its main component, and in particular, no air at all. In particular, the gas present in the cavity of the thermally expanded hollow pigment comprises at least one hydrocarbon, in particular a low molecular weight hydrocarbon, in particular an aliphatic low molecular weight hydrocarbon, in particular a low-boiling hydrocarbon, in particular isobutane. In particular, the gas present in the cavity of the thermally expanded hollow pigment comprises a mixture of air and at least one hydrocarbon, in particular a low molecular weight hydrocarbon, in particular an aliphatic low molecular weight hydrocarbon, in particular a low-boiling hydrocarbon, in particular isobutane. In particular, the gas present in the cavity of the thermally expanded hollow pigment comprises hydrocarbon gas, which is present in the cavity of the thermally expanded hollow pigment due to the manufacturing process. For example, corresponding thermally expanded hollow pigments include at least one hollow pigment of the Expancel® type, which is currently distributed by the company Nouryon. Examples include thermally expanded hollow pigments in the paragraph

[0243] described in publication EP 4046813 A1, which refers to the specific Expancel® type 461 WE20d36. The paragraph describes

[0056] EP 4046 813 A1, in particular the use of an easily evaporable liquid in the corresponding hollow pigment, which evaporates when the hollow pigments are heated, expands and thereby expands the hollow pigments, so that the corresponding thermally expanded hollow pigments are obtained. The corresponding thermally expanded hollow pigments according to the first aspect are subsequently further characterized in the context of further embodiments based on their relevant physical parameters. The use of thermally expanded hollow pigments in the ink layer and / or in the optional insulating layer of the heat-sensitive recording material, as described in the present invention, significantly improves the thermal response of the heat-sensitive recording layer in the thermal printer. This is due to the greatly improved thermal insulation properties of the ink layer and / or optional insulating layer containing the thermally expanded hollow pigments. As a result, a maximum of the heat output provided by the thermal printer's thermal printhead is made available to the heat-sensitive recording layer, thus enabling optimal utilization of this heat for the thermal response of the heat-sensitive recording layer. According to the present invention, the thermally expanded hollow pigments present in the color layer and / or optional insulating layer are to be distinguished from the optional, or in particular the, non-thermally expanded hollow pigments present in the heat-sensitive recording layer. Corresponding non-thermally expanded hollow pigments also possess a polymer shell that defines a cavity. However, in contrast to the previously mentioned thermally expanded hollow pigment, the volume of the cavity in a non-thermally expanded hollow pigment is smaller. For example, corresponding non-thermally expanded hollow pigments include at least one Ropaque®-type hollow pigment, which is currently marketed by Dow Chemical. Examples include corresponding non-thermally expanded hollow pigments in the paragraph

[0230] described in EP 4 046 813 A1, in which the substance Ropaque SN-1055, supplied by Dow Chemical, is explicitly described as non-thermally expanded (“non-foaming type”). Reference is also made to paragraph

[0054] the printed publication EP 4046813 A1 referred to, in which a distinction is made between a non-thermally expanded hollow pigment (“non-foaming type”) and a thermally expanded hollow pigment (“foaming type”) based on particle sizes and cavity dimensions. The heat-sensitive recording material also features the color layer containing the coloring agent. The coloring agent imparts to the color layer, in particular, a black, red, green, or blue color, or any color that can be obtained from a mixture of red, green, and blue. In particular, the coloring agent imparts to the color layer a color that is not white. In particular, the color layer on the side facing the heat-sensitive layer is black, red, green, or blue, or any color that can be obtained from a mixture of red, green, and blue. Specifically, the coloring agent imparts a color other than white to the color layer on the side facing the heat-sensitive layer. 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 rather the color of the side of the ink layer facing the heat-sensitive layer, is not visible due to the heat-sensitive layer being opaque under normal conditions. Only when the heat-sensitive layer becomes translucent due to local heat exposure can the underlying ink layer, or rather the side of the ink layer facing the heat-sensitive layer, become visible, thus creating a printed image on the heat-sensitive recording material. According to one embodiment, the at least one thermally expanded hollow pigment of the color layer and / or the optional insulating layer has a mean particle size (d50) between 5 μm and 50 μm, preferably between 5 μm and 40 μm, more preferably between 5 μm and 30 μm, and most preferably between 5 μm and 20 μm. According to one embodiment, the at least one thermally expanded hollow pigment of the color layer and / or the optional insulating layer has a mean particle size (d4,3) between 5 μm and 50 μm, preferably between 5 μm and 40 μm, more preferably between 5 μm and 30 μm, and most preferably between 5 μm and 20 μm. According to one embodiment, the at least one thermally expanded hollow pigment of the color layer and / or the optional insulating layer has a mean particle size (d10) between 1 μm and 50 μm, preferably between 1 μm and 20 μm, more preferably between 2 μm and 10 μm, and most preferably between 3 μm and 5 μm. According to one embodiment, the at least one thermally expanded hollow pigment of the color layer and / or the optional insulating layer has a mean particle size (d100) between 1 μm and 100 μm, preferably between 2 μm and 50 μm, more preferably between 5 μm and 40 μm, and most preferably between 10 μm and 30 μm. According to one embodiment, the at least one thermally expanded hollow pigment of the color layer and / or the optional insulating layer has a mean particle size (d90) between 1 μm and 100 μm, preferably between 2 μm and 50 μm, more preferably between 5 μm and 40 μm, and most preferably between 10 μm and 20 μm. In particular, the mean particle size (d50), (d4.3), (d10), (d100) and / or d(90) of the thermally expanded hollow pigment is determined by laser diffraction, specifically using a Coulter laser diffraction analyzer. Specifically, the mean particle size (d50), (d4.3), (d10), (d100) and / or d(90) of the thermally expanded hollow pigment is determined according to ISO 13320. In particular, the value of the mean particle size (d50) describes the 50% percentile of the particle size distribution, such that the proportion of particles smaller than the claimed value is 50%. In particular, the value of the mean particle size (d4,3) describes the De Brouckere mean or the volume-weighted mean of the particle size distribution. In particular, the value of the mean particle size (d10) describes the 10% percentile of the particle size distribution, such that the proportion of particles smaller than the claimed value is 10%. In particular, the value of the mean particle size (d100) describes the 100% percentile of the particle size distribution, such that the proportion of particles smaller than the claimed value is 100%. In particular, the value of the mean particle size (d90) describes the 90th percentile of the particle size distribution, such that the proportion of particles smaller than the claimed value is 90%. According to one embodiment, the at least one thermally expanded hollow pigment of the paint layer and / or the optional insulating layer has a density between 20 kg / m³. 3 and 100 kg / m² 3 on. According to one embodiment, the at least one thermally expanded hollow pigment of the color layer and / or the optional insulating layer has a polymer shell wall thickness between 0.01 μm and 5 μm, preferably between 0.03 μm and 1.5 μm, more preferably between 0.05 μm and 0.5 μm. According to one embodiment, the at least one thermally expanded hollow pigment of the color layer and / or the optional insulating layer has a specific surface area between 400 m² 2 / kg and 6400 m 2 / kg up. According to one embodiment, the at least one thermally expanded hollow pigment of the color layer and / or the optional insulating layer has a cavity volume of more than 70%, preferably more than 75%, more preferably more than 80%, even more preferably more than 85%, further still more preferably more than 90%, and most preferably more than 95%. According to one embodiment, the at least one thermally expanded hollow pigment of the color layer and / or the optional insulating layer comprises a polymer comprising acrylonitrile and / or methacrylonitrile as a monomer. In particular, the polymer comprises a copolymer which includes acrylonitrile and / or methacrylonitrile as a monomer, and which includes another monomer which is the same as or different from acrylonitrile and / or methacrylonitrile. According to one embodiment, at least one thermally expanded hollow pigment of the color layer and / or the optional insulating layer is a hollow pigment of the Expan-cel® type, in particular from the company Nouryon. By using at least one thermally expanded hollow pigment in the ink layer and / or the optional insulating layer with the corresponding characteristics, it is possible to create heat-sensitive recording materials whose printed images have a high optical density and particularly advantageous barcode readability. According to one embodiment, at least one thermally expanded hollow pigment of the paint layer and / or the optional insulating layer is present in the paint layer and / or the optional insulating layer in an amount of 1 wt.% to 50.0 wt.%, preferably in an amount of 2 wt.% to 35.0 wt.%, and most preferably in an amount of 3 wt.% to 20 wt.% based on the total dry mass of the paint layer and / or the optional insulating layer. This achieves the technical advantage that the weight ranges defined for the thermally expanded hollow pigment in the color layer and / or in the optional insulating layer ensure advantageous properties of the resulting heat-sensitive recording material. According to one embodiment, the color layer and / or the optional insulating layer comprises at least one non-thermally expanded hollow pigment. This achieves the technical advantage that, by combining at least one thermally expanded hollow pigment and at least one non-thermally expanded hollow pigment in the ink layer and / or the optional insulating layer, the advantageous properties of the printed images obtained using the heat-sensitive recording material can be further improved, which is based in particular on an improved packing density of the hollow pigments. According to one embodiment, at least one non-thermally expanded hollow pigment is present in the heat-sensitive layer and / or the color layer and / or the optional insulating layer in an amount of 1 wt.% to 50.0 wt.%, preferably in an amount of 2 wt.% to 45.0 wt.%, and most preferably in an amount of 3 wt.% to 40 wt.% based on the total dry mass of the heat-sensitive layer and / or the color layer and / or the optional insulating layer. This achieves the technical advantage that the weight ranges defined for the non-thermally expanded hollow pigment in the heat-sensitive layer and / or in the color layer and / or in the optional insulating layer ensure advantageous properties of the resulting heat-sensitive recording material. According to one embodiment, the at least one non-thermally expanded hollow pigment of the color layer and / or the optional insulating layer and / or, in particular, the heat-sensitive layer comprises styrene / acrylate copolymers or urea / formal- Dehyde condensation polymers and / or mixtures thereof, wherein preferably the at least one non-thermally expanded hollow pigment of the color layer and / or the optional insulating layer and / or in particular the heat-sensitive layer is a hollow pigment of the Ropaque® type, in particular Ropaque® TH-500EF; Ropaque® HP-1055, Ropaque® OP-96, Ropaque®-NT2900 and / or Ropaque® TH-1000. According to one embodiment, the color layer and / or the heat-sensitive layer and / or the optional insulating layer comprises at least one inorganic pigment, preferably selected from the group consisting of clays, precipitated, ground, filtered or natural calcium carbonates, aluminum oxides, aluminum hydroxides, silicas, precipitated and pyrogenic silicas, for example Aerodisp types, diatomaceous earths, magnesium carbonates, talc, kaolin (natural and / or calcined), titanium dioxide, bentonite, calcium silicate hydrate and mixtures thereof, preferably calcium carbonates, more preferably precipitated calcium carbonate (PCC) and / or ground calcium carbonate (GCC), calcined kaolin, and / or pyrogenic silicas. This offers the technical advantage that these pigments can fix the chemical melt produced during the thermal printing process on their surface. Furthermore, these pigments can be used to control the surface whiteness and opacity of the heat-sensitive layer and its printability with conventional printing inks. According to one embodiment, at least one inorganic pigment of the paint layer is present in the paint layer in an amount of 1 wt.% to 90 wt.%, preferably 10 wt.% to 85 wt.%, more preferably 15 wt.% to 80 wt.%, and most preferably 20 wt.% to 72 wt.% based on the total dry mass of the paint layer. According to one embodiment, the at least one inorganic pigment of the heat-sensitive layer is present in an amount of 0 wt.% to 50 wt.%, preferably from 0.1 wt.% to 30 wt.%, more preferably from 1 wt.% to 20 wt.%, and at Most preferably from 1 wt.% to 15 wt.% based on the total dry mass of the heat-sensitive layer and / or present in the heat-sensitive layer. According to one embodiment, the at least one inorganic pigment of the optional insulating layer is present in the optional insulating layer in an amount of 5 wt.% to 90 wt.%, preferably 10 wt.% to 85 wt.%, more preferably 25 wt.% to 80 wt.%, and most preferably 40 wt.% to 75 wt.% based on the total dry mass of the optional insulating layer. This achieves the technical advantage that the weight ranges defined for the inorganic pigment of the color layer and / or the heat-sensitive layer and / or the optional insulating layer ensure advantageous properties of the resulting heat-sensitive recording material. According to one embodiment, the heat-sensitive recording material has a single color layer and no insulating layer, wherein the single color layer preferably has an basis weight of 1.0 g / m² as determined by standard ISO 536. 2 up to 10.0 g / m² 2 The heat-sensitive recording material has an insulating layer and a color layer arranged thereon, wherein preferably the insulating layer and the color layer have an basis weight of 1.0 g / m² as determined by ISO 536. 2 up to 10.0 g / m² 2 exhibits. This achieves the technical advantage that an advantageous heat-sensitive recording material can be obtained both by using a single color layer arranged between the substrate and the heat-sensitive recording layer, and by using an insulating layer and a color layer, where the insulating layer is on the substrate, the color layer is on the insulating layer, and the heat-sensitive recording layer is on the color layer. The advantages include, in particular, advantageous rheology, less black pigment, advantageous surface properties, and overall lower line thicknesses. In the case of an additional insulating layer, maximum heat yield is achieved. If the heat-sensitive recording material has, in particular, an insulating layer and a color layer arranged thereon, then preferably one of the insulating layers has a basis weight of 1.0 g / m² as determined by the ISO 536 standard. 2 up to 5.0 g / m² 2 and the paint layer has a basis weight of 5.0 g / m² as determined by the ISO 536 standard. 2 up to 10.0 g / m² 2 on. According to one embodiment, the heat-sensitive layer has an areal weight of 1.0 g / m² as determined by the ISO 536 standard. 2 up to 10.0 g / m² 2 on, preferably from 2.0 g / m² 2 up to 8.0 g / m² 2 , further preferably of 2.5 g / m³ 2 up to 6.0 g / m² 2 . According to one embodiment, the heat-sensitive layer does not contain a chemical color developer or a chemical color former, in particular no Leuco dye. Chemical color formers comprise chemically activatable dyes, for example leuco dyes, which are colorless in the unactivated state and are only activated, i.e., become colored, by chemical reaction with a chemical color developer, such as bisphenol A. It is advantageous for the purposes of the present invention that the heat-sensitive layer of the heat-sensitive recording material contains neither a chemical color developer nor a chemical color former. In particular, trace amounts of a chemical color developer and / or a chemical color former, especially a Leuco dye, may be present. According to one embodiment, the color layer and / or the heat-sensitive layer and / or the optional insulating layer comprises at least one crosslinking agent, wherein the at least one crosslinking agent is preferably selected from the group comprising polyhydric aldehydes, such as glyoxal, dialdehyde starch, glutaraldehyde, salts or esters of glyoxylic acid, crosslinkers based on ammonium zirconium carbonate, organic titanates, polyamidoamine epichlorohydrin resins (PAA E resins), polyamide resins, polyamine resins, polyamidoamine resins, polyamide-polyurea resins, polyamine-polyurea resins, adipic acid dihydrazide (ADH), polyamidoamines, epoxy resins, Formaldehyde oligomers, cyclic ureas, methylol urea, melamine formaldehyde oligomers, oxazoline resins, carbodiimide, borate compounds and mixtures thereof, wherein the at least one crosslinking agent is most preferably selected as ammonium zirconium carbonate and / or polyamidoamine epichlorohydrin resins (PAAE resin). According to one embodiment, the at least one crosslinking agent of the paint layer and / or the heat-sensitive layer and / or the optional insulating layer is present in the paint layer and / or the heat-sensitive layer in an amount of 0.01 wt.% to 10.0 wt.%, preferably in an amount of 0.1 wt.% to 5.0 wt.%, and most preferably in an amount of 0.5 wt.% to 2.0 wt.% based on the total dry mass of the paint layer and / or the heat-sensitive layer. To achieve specific application-related performance characteristics of heat-sensitive recording materials, the polymeric binder present in the color layer and / or heat-sensitive layer is preferably in cross-linked form in the color layer and / or in the heat-sensitive layer, wherein the optimal degree of cross-linking of the polymeric binder is achieved in the drying step of the coating process in the presence of a cross-linking agent. Ammonium zirconium carbonate and polyamidoamine epiclorhydrin resins (PAAE resins) are particularly preferred for reasons of food compliance. 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. According to one embodiment, the heat-sensitive layer comprises at least one wax, which is preferably selected from the group comprising at least one fatty acid, at least one fatty acid amide, at least one metal salt of a fatty acid, at least one metal salt of a fatty acid amide and mixtures thereof, wherein the at least one fatty acid amide, fatty acid monoamide, fatty acid diamide is further preferably selected. comprising fatty acid alkanolamide, N-methyl fatty acid amide and mixtures thereof, and / or wherein the at least one fatty acid preferably comprises a saturated fatty acid and / or an unsaturated fatty acid with at least 8 carbon atoms. In particular, the at least one wax includes at least one synthetic wax and / or at least one biogenic wax, wherein the at least one biogenic wax includes in particular at least one wax based on a vegetable oil, as is characterized, for example, in EP 3508545. According to one embodiment, the at least one fatty acid is selected from the group comprising behenic acid, stearic acid, and / or palmitic acid, and / or the at least one fatty acid amide is selected from the group comprising ethylenebisfatty acid amide, ethylenebisstearamide, ethylenebispalmitamide, behenamide, erucamide, stearic acid amide, oleamide, palmitic acid amide, and / or lauramide, preferably stearic acid amide, and / or the at least one metal salt of the fatty acid is selected from the group comprising calcium stearate, magnesium stearate, zinc stearate and mixtures thereof, preferably calcium stearate and / or zinc stearate. According to one embodiment, the at least one fatty acid, the at least one fatty acid amide, the at least one metal salt of a fatty acid, and / or the at least one metal salt of a fatty acid amide is present in the heat-sensitive layer in an amount of 1 wt.% to 80 wt.%, preferably in an amount of 2 wt.% to 75 wt.%, and most preferably in an amount of 3 wt.% to 70 wt.%, based on the total dry mass of the heat-sensitive layer. According to one embodiment, the at least one polymeric binder of the color layer and / or the optional insulating layer and / or the heat-sensitive layer 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, wherein the at least one binder comprises in particular at least one binder of synthetic or biogenic nature, wherein the at least one binder of biogenic nature comprises in particular biogenic polymers based on modified, in particular chemically and / or thermally modified, and unmodified starches, celluloses, proteins, chitin, chitosan, lignin, casein, gelatin, collagen, shellac, vegetable oil, lipids, polylactic acid (PLA), polyhydroxyalkanoates (PHA), and mixtures thereof. In particular, this includes at least one binder of a synthetic or biogenic nature. The at least one biogenic binder includes, in particular, biogenic polymers based on modified, especially chemically and / or thermally modified, and unmodified starches, celluloses, proteins, chitin, chitosan, lignin, casein, gelatin, collagen, shellac, vegetable oil, lipids, polylactic acid (PLA), polyhydroxyalkanoates (PHA), and mixtures thereof. According to one embodiment, the at least one polymeric binder of the paint layer and / or the optional insulating layer and / or the heat-sensitive layer is present in the paint layer and / or the optional insulating layer and / or the heat-sensitive layer in an amount of 0.5 wt.% to 30.0 wt.%, preferably in an amount of 1 wt.% to 20.0 wt.%, based on the total dry mass of the paint layer and / or the optional insulating layer and / or the heat-sensitive layer. 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. According to one embodiment, the heat-sensitive layer comprises, in particular, inorganic oil-absorbing white pigments. In particular, the inorganic oil-absorbing white pigments include natural or calcined kaolin, kaolinite, silicon dioxide, bentonite, calcium carbonate, aluminum hydroxide, especially boehmite, aluminum oxide, talc, calcium silicates, especially circolit, and mixtures thereof. 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. According to one embodiment, the color layer and / or the optional insulating layer and / or the heat-sensitive layer comprises at least one auxiliary component. According to one embodiment, at least one 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; dispersing agents, preferably polyphosphate, sodium tripolyphosphate, sodium pyrophosphate, and / or salts of polycarboxylic acids; defoamers; wet strength-enhancing agents, preferably melamine-formaldehyde resins, urea-formaldehyde resins, formalin and / or glyoxal; preservatives, preferably antibacterial additives and / or antifungal additives; lubricants, preferably polyglycol, zinc stearate and / or calcium stearate; pH-controlling agents, preferably sodium hydroxide and / or ammonia; dyes; optical brighteners; conductivity agents and mixtures thereof. Preferably, this includes at least one additive: zinc stearate and / or calcium stearate. According to one embodiment, at least one auxiliary agent is present in a range of 0.01 wt.% to 8 wt.%, preferably from 0.1 wt.% to 2 wt.%, based on the total dry mass of the paint layer and / or the optional insulating layer and / or the heat-sensitive layer. This results in the technical advantage of achieving a beneficial optimization of the applicability and / or the properties of the paint layer and / or the optional insulating layer and / or the heat-sensitive layer. According to one embodiment, the color layer and / or the optional insulating layer and / or the heat-sensitive layer comprises at least one rheology aid selected from the group comprising: a) Sugar alcohols selected from the group comprising: diglycerol, triglycerol, fructose, ribose, xylose, D-mannitol, triacetin, and mixtures thereof; b) Polyols selected from the group comprising: pentaerythritol, dipen-taerythritol, xylitol, sorbitol and mixtures thereof; c) 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-dime-thyl-1,2-butanediol and mixtures thereof; d) Glycols selected from the group comprising: Polyethylene glycol 300, Polyethylene glycol 400, alkoxylated polyethylene glycol and mixtures thereof; (e) Caprolactam, cyclic trimethylolpropane, resin esters, eurikamide and mixtures thereof, (f) Acrylic acid esters and / or acrylamide copolymer, including mixtures of subgroups a) to f). According to one embodiment, the color layer and / or the optional insulating layer and / or the heat-sensitive layer comprises at least one surfactant. In particular, this includes at least one surfactant, at least one ionic surfactant, wherein the at least one ionic surfactant includes in particular sulfosuccinate. In particular, the surfactant comprises a trimethyl nonyl ether, ethylene oxide / propylene oxide copolymers or oligomers, and / or ethoxylated acetylenediol. According to one embodiment, the natural surfactant is present in a range of 0.05 wt.% to 3 wt.%, preferably 0.1 wt.% to 1.5 wt.%, based on the total dry mass of the paint layer and / or the optional insulating layer and / or the heat-sensitive layer. carrier substrate According to one embodiment, the carrier substrate is selected from the group comprising paper, single-sided coated paper, and double-sided coated paper. According to one embodiment, the carrier substrate has a basis weight of 20 to 100 g / m². 2 , preferably from 35 to 80 g / m² 2 , on. According to one embodiment, a starch layer is present directly on at least one side of the carrier substrate, preferably directly on both sides of the carrier substrate, wherein the starch layer is present in an amount of 0.1 g / m². 2 up to 3 g / m² 2 , particularly preferably of 0.2 g / m³ 2 up to 1.5 g / m² 2 , is applied. Applying a thickened coat to the side of the substrate where the paint layer is located has the advantage of sealing the substrate, thus improving the adhesion of the paint layer and reducing or preventing penetration of the paint layer into the substrate. A thickened layer on the side of the substrate where the ink layer is not present has the advantage of reducing or preventing ink bleed-through and enabling favorable reverse printing. This thickened layer on the side of the substrate where the ink layer is not present is also referred to as the reverse layer of the heat-sensitive recording material. The layer, comprising thickness, preferably has a Bekk smoothness of greater than 10 s, particularly preferably greater than 15 s, as measured according to DIN 53107, in particular DIN 53107 (2016). According to one embodiment, the starch layer comprises at least one pigment and / or at least one crosslinking agent. Insulating layer The optional insulating layer is positioned between the substrate and the paint layer. If the insulating layer is not present and there is only a single layer of paint located between the substrate and the heat-sensitive layer, this single layer of paint simultaneously performs the function of a paint layer and an insulating layer. The insulating layer, if present, or the single ink layer that simultaneously acts as both an ink and an insulating layer, reduces heat conduction through the heat-sensitive recording material. This makes the local application of heat by a direct thermal printer more efficient and allows for higher thermal printing speeds. The heat-sensitive layer becomes translucent more quickly due to the applied heat, thus improving its sensitivity. This reduces the amount of dye required, resulting in improved recyclability of the heat-sensitive recording material in the recycling loop, particularly in the waste paper loop, through easier deinkability and separation of dye and substrate components. The insulating layer, if present, or the single paint layer that acts simultaneously as a paint layer and an insulating layer, preferably has a Bekk smoothness of greater than 50 s, particularly preferably greater than 100 s and most preferably of 100 to 350 s, as measured according to DIN 53107, in particular DIN 53107 (2016). The insulating layer, if present, or the single paint layer that acts simultaneously as a paint layer and an insulating layer, comprises at least one heat-insulating material. Preferably, the heat-sensitive recording material with an insulating layer, if present, or the single color layer that simultaneously acts as a color layer and an insulating layer, has a lower thermal conductivity than a heat-sensitive recording material that does not include an insulating layer or a color layer that simultaneously acts as a color layer and an insulating layer. The heat-insulating material preferably comprises kaolin, particularly preferably calcined kaolin and mixtures thereof, and / or organic hollow pigments, preferably at least one organic hollow pigment, particularly preferably at least one thermally expanded hollow pigment. The heat-insulating material is preferably present in the insulating layer in an amount of 10 wt.% to 80 wt.%, particularly preferably in an amount of 15 wt.% to 60 wt.%, based on the total dry mass of the insulating layer. In a paint layer that simultaneously acts as 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 that simultaneously acts as a paint layer and an insulating layer. The insulating layer preferably has a basis weight of 1 to 5 g / m². 2 , especially from 2 to 4 g / m³ 2 , on. The insulating layer preferably has a maximum thickness of 20 µm. The paint layer, which acts simultaneously as a paint layer and an insulating layer, preferably has a basis weight of 1 to 10 g / m². 2 , especially from 2 to 8 g / m³ 2 , on. The paint layer, which acts simultaneously as a paint layer and an insulating layer, preferably has a thickness of 1 to 15 µm, in particular of 4 to 12 µm. Intermediate shift According to one embodiment, the heat-sensitive recording material has at least one intermediate layer, which is in particular designed as a transparent intermediate layer, which is arranged between the color layer and the heat-sensitive layer, wherein the at least one intermediate layer preferably comprises a polymeric binder and a pigment. Protective layer and / or non-stick coating According to one embodiment, the heat-sensitive recording material has a protective layer and / or a non-stick coating which is arranged on the heat-sensitive layer. The protective layer and / or non-stick coating is therefore located on the side of the heat-sensitive layer facing away from the paint layer. Preferably, the protective layer comprises at least one polymer and at least one wax. According to one embodiment, the protective layer has a Bekk smoothness of at least 300 s, preferably at least 350 s and particularly preferably at least 400 s, as measured according to DIN 53107, in particular DIN 53107 (2016). Preferably, the Bekk smoothness of the protective layer, measured according to DIN 53107, in particular DIN 53107 (2016), is no more than 3000 s, preferably no more than 2000 s. 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. In another embodiment, the protective layer contains no pigment or pigments. 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 15 wt.%, in particular from more than 0 wt.% to less than 15 wt.%, based on the total dry mass of the protective layer. 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. Unavoidable impurities or unavoidable traces of pigments can enter the protective layer, for example, due to the manufacturing process, if pigments were processed in the production plant (pigment-containing paints) or are introduced, for example, during the application of previously applied, pigment-containing layers (pigments of the insulating layer, the paint layer or the heat-sensitive layer). The at least one pigment is preferably selected from organic and / or inorganic pigments. Suitable pigments include inorganic pigments, both synthetic and natural in origin, 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 dioxide, bentonite, and also 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 mixtures. Suitable pigments also include, in particular, composite pigments. 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 of fatty acids, or silicones, a crosslinking agent, and / or a rheology aid. Preferably, the protective layer 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 mixtures. The binder preferably comprises polyvinyl alcohol, and most preferably a polyvinyl alcohol with a degree of saponification of more than 88%. The binder is preferably present in the protective layer in an amount of 30 wt.% to 90 wt.%, particularly preferably in an amount of 40 wt.% to about 80 wt.%, based on the total dry mass of the protective layer. To achieve specific application-related performance characteristics of heat-sensitive recording materials, the binder is preferably in a cross-linked form. The form is located in the protective layer, whereby the optimal degree of cross-linking of the binder is achieved in the drying step of the coating process in the presence of a cross-linking agent (crosslinker). The crosslinking agents can be polyhydric aldehydes such as glyoxal, dialdehyde starch, glutaraldehyde, salts or esters of glyoxylic acid, crosslinking agents based on ammonium zirconium carbonate, polyamidoamine-epichlorohydrin resins (PAAE resins), adipic acid dihydrazide (ADH), polyamidoamines, epoxy resins, formaldehyde oligomers, cyclic ureas, methylolurea, melamine-formaldehyde oligomers, borate compounds, and others. These can be used alone or in any mixtures. Ammonium zirconium carbonate and polyamidoamine epiclorhydrin resins (PAAE resins) are particularly preferred for reasons of food compliance. 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. The crosslinking agent 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. Preferably, the protective layer comprises at least one lubricant. 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 different melting points, ester waxes of different molecular weights, ethylene waxes, propylene waxes of different hardnesses and / or natural waxes, such as carnauba wax, montan wax or soy wax. Preferred lubricants are those based on waxes or fats, fatty acids or 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. Preferably, the protective layer comprises at least one release agent. Preferably, release agents based on silicones are known, for example, from US 2006 / 0063013A1, the disclosure of which is hereby fully incorporated. 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. Preferably, the protective layer comprises at least one rheology aid. Preferred rheological additives are thickeners and surfactants. For further details, please refer to the selections for the heat-sensitive layer, which also apply fully to the protective layer. Preferably, the protective layer comprises at least one lubricant / release agent, at least one binder and at least one crosslinking agent. 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. Preferably, the protective layer has a basis weight in the range of 0.01 g / m². 2 and 3.5 g / m² 2 , preferably in the range of greater than 0.05 g / m³ 2 and 2.5 g / m² 2 and particularly preferably in the range of 0.1 g / m³ 2 and 1.5 g / m² 2 on. Surprisingly, it has been shown that the basis weight of the protective layer can be reduced without compromising its protective effect for certain requirements. At the same time, the relative print contrast can even be increased and / or improved. The protective layer preferably has a thickness of 0.3 µm to 6.0 µm, in particular of 0.5 µm to 2.0 µm. Instead of a protective layer, a non-stick coating may be present, or the protective layer itself may be designed as a non-stick coating, or the non-stick coating may be applied to the protective layer. Thus, the protective layer or non-stick coating may exhibit a "non-stick effect," particularly against an adhesive layer on the back of the heat-sensitive recording material, and / or against pressure-sensitive adhesives, particularly on the back of the heat-sensitive recording material. This has the advantage that the heat-sensitive recording material can be used as carrierless ("linerless" or "carrierless") heat-sensitive recording material. This has the particular advantage that the heat-sensitive recording material can be wound onto itself without the need for a carrier ("linerless"), and after unwinding the self-wound heat-sensitive recording material, the heat-sensitive recording material does not exhibit any deterioration in its paper and application-related properties. This also has the advantage that manufacturing costs can be further reduced, more linear meters per roll are achievable, no disposal costs are necessary for the disposal of the liner, and more labels can be transported per specific cargo space volume. A suitable non-stick coating preferably comprises a siliconized coating based on siloxanes. Separating layer 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 layer. The siliconized separating layer preferably has a Bekk smoothness of greater than 400 s, particularly preferably greater than 800 s and most preferably of 800 to 2000 s, as measured according to DIN 53107, in particular DIN 53107 (2016). If a protective layer, in particular as defined above, is present on the heat-sensitive layer, the siliconized separating layer is preferably located on this protective layer. 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 diffuse application of at least a portion of the siliconized separating layer into the upper region of the underlying layer, wherein preferably 5 wt.% to 50 wt.%, more preferably 6 wt.% to 45 wt.%, and particularly 7 wt.% to 40 wt.% of the siliconized separating layer diffuse into the upper region of the underlying layer. Such a diffusion layer is described, for example, in EP 3221 153 A1. A siliconized release layer is preferably present when an adhesive layer, as described above, is also present. The presence of a siliconized release layer on the heat-sensitive layer and an adhesive layer on the substrate on the side where no The fact that the color layer is located has the advantage that the heat-sensitive recording material can be used as a carrierless ("linerless") heat-sensitive recording material. This has the particular advantage that the heat-sensitive recording material can be wound onto itself without the need for a support ("linerless"), and after unwinding the self-wound heat-sensitive recording material, the heat-sensitive recording material does not exhibit any significant deterioration of its properties. This also has the advantage that manufacturing costs can be further reduced, more linear meters per roll are achievable, no disposal effort is necessary for the disposal of the liner, and more labels can be transported per specific cargo space volume. If a siliconized separating layer is present, it is particularly preferred that the layer directly below the siliconized separating layer contains at least one platelet-shaped pigment. The at least one platelet-shaped pigment is preferably selected from the group consisting of kaolin, in particular kaolinite as the main component of kaolin, Al(OH)3, and / or talc. The use of kaolin is particularly preferred. The use of a spreadable kaolin is especially preferred. Such a product is available, for example, under the trade name Kaolin ASP 109 (BASF, Germany). The use of these platelet-shaped pigments, especially kaolin, has the main advantage that the heat-sensitive layer, or the layer directly below the siliconized separating layer, can be siliconized very effectively. A platelet-shaped pigment is understood to be a pigment in which the ratio of diameter to thickness is approximately 7 to 40 to 1, preferably approximately 15 to 30 to 1. The particle size of the platelet-shaped pigment is preferably adjusted such that at least about 70%, preferably at least about 85%, of the particles have a particle size of about < 2 pm (sedigraph). The pH value of the platelet-shaped pigment in aqueous solution is preferably 6 to 8. The at least one platelet-shaped pigment is present in the heat-sensitive layer or in the layer directly below the siliconized separating layer, preferably in an amount of about 5 to about 60 wt.%, particularly preferably in an amount of about 15 to about 55 wt.%, based on the total dry mass of the respective layer. If the protective layer is located directly below the siliconized separating layer, the platelet-shaped pigment is contained in the quantities described above for the pigments contained in the protective layer. 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 acrylic poly(organo)siloxane. In another embodiment, the siliconized separating layer comprises a mixture of at least two siloxanes. Preferably, a mixture of at least two acrylo-poly(organo)siloxanes is used. Examples of particularly preferred siloxanes are siloxanes available under the trade names TEGO®RC902 and TEGO®RC711 (Evonik, Germany). In another embodiment, the heat-sensitive recording material is preferably characterized in that the siliconized separating layer contains at least one polysilicone acrylate, which is preferably formed by condensation of at least one silicone acrylate. In a preferred embodiment, the siliconized separating layer is a heat-cured separating layer. The formation of this separating layer takes place in the presence of a Pt catalyst. The siliconized separating layer is preferably anhydrous. It is also preferred that the siliconized separating layer does not contain any Pt catalysts. The siliconized release layer preferably contains an initiator, particularly preferably a photoinitiator. This serves to cure the silicone by radical action. The TEGO®Photoinitiator A18 (from Evonik, Germany) is particularly preferred. The siliconized release layer may preferably contain further additives, such as matting agents and / or adhesion additives. The siliconized release layer preferably has a basis weight of 0.3 to 5.0 g / m². 2 , especially from 1.0 to 3.0 g / m³ 2 , on. The siliconized separating layer preferably has a thickness of 0.3 to 6.0 pm, in particular 0.5 to 2.0 pm. adhesive layer According to one embodiment, the heat-sensitive recording material has an adhesive layer and / or a backing 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-activated adhesive, and more preferably a pressure-sensitive adhesive, and / or wherein the backing layer is preferably designed as a starch coating. If, in particular, a starch coating or starch screed is present as a back layer and an adhesive layer is present, this starch coating lies between the substrate and the adhesive layer. For further details regarding the starch coating described as a back layer, please refer to the extensive previous explanations under the sub-item "carrier substrate". The adhesive layer preferably comprises at least one adhesive, preferably a heat-activated adhesive, in particular a pressure-sensitive adhesive. The adhesive, preferably the heat-activated adhesive, and especially the pressure-sensitive adhesive, is particularly preferably a rubber- and / or acrylate-based adhesive. Preferably, the protective layer exhibits a "non-stick effect" against rubber- and / or acrylate-based adhesives. According to one embodiment, the adhesive layer has a basis weight of 1 to 40 g / m². 2 , especially from 12 to 25 g / m² 2 , on. According to one embodiment, the heat-sensitive recording material has a basis weight of 20 g / m² as determined by the ISO 536 standard. 2 up to 100 g / m² 2 on, preferably from 35 g / m² 2 up to 80 g / m² 2 . According to one embodiment, the heat-sensitive recording material has a thickness of 10 pm to 100 pm as determined by the ISO 534 standard, preferably from 20 pm to 80 pm. According to one embodiment, the heat-sensitive layer has a thickness of 1 to 10 pm, in particular 2 to 8 pm, as determined by the ISO 534 standard. The paint layer preferably has a basis weight of 1 to 10 g / m². 2 , especially from 3 to 10 g / m² 2 , on. The paint layer preferably has a thickness of 1 to 25 pm, in particular of 2 to 20 pm. parameter According to one embodiment, the paint layer on the side on which the heat-sensitive layer is applied has a Bekk smoothness of 50 to 800 s, particularly preferably 100 to 600 s and most preferably 150 to 350 s as measured according to DIN 53107 (2016). According to one embodiment, the carrier substrate has a Bekk smoothness of greater than 20 s, preferably greater than 30 s, and more preferably greater than 50 s, as measured according to DIN 53107 (2016). According to one embodiment, the paint layer on the side on which the heat-sensitive layer is applied has a Bekk smoothness of greater than 50 s, preferably greater than 100 s and most preferably greater than 150 s as measured according to DIN 53107 (2016). According to one embodiment, the heat-sensitive layer on the side where the paint layer is not located has a Bekk smoothness of greater than 100 s, particularly preferably greater than 250 s, as measured according to the standard DIN 53107 (2016). According to one embodiment, the carrier substrate has a Bekk smoothness of 20 to 400 s, preferably 30 to 300 s and particularly preferably 50 to 200 s, as measured according to DIN 53107 (2016) on the side on which the color layer is applied. According to one embodiment, the paint layer on the side on which the heat-sensitive layer is applied has a Bekk smoothness of 50 to 400 s, particularly preferably 100 to 250 s and most preferably 150 to 250 s as measured according to DIN 53107 (2016). According to one embodiment, the heat-sensitive layer on the side where the paint layer is not located preferably has a Bekk smoothness of 100 to 1000 s, measured according to DIN 53107 (2016), particularly preferably of 500 to 1000 s. According to one embodiment, the heat-sensitive recording material has an optical density (o. D.) defined according to the description of at least 0.9, preferably at least 1.0, and most preferably at least 1.10, particularly at an energy level of 7.73 mJ / mm². 2 was measured, and / or the heat-sensitive recording material has an optical density (o. D.) defined according to the description of at least 1.2, preferably at least 1.25, and most preferably at least 1.3, particularly at an energy level of 9.00 mJ / mm² 2 was measured. The optical density (n.d.) was determined in particular using an X-Rite SpectroEye densitometer (model SpectroDens) at an energy level of 7.73 mJ / mm². 2 or 9.00 mJ / mm 2 or 6.47 mJ / mm 2 measured. The measurement uncertainty of the O.D. values ​​is, in particular, ≤2%. In particular, 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 bar of 305 dpi at an applied voltage of 24 V and a printhead pressure of 15.7 N with a bar pattern (53 x 12 mm) with 10 energy levels. According to one embodiment, the heat-sensitive recording material has a surface whiteness of more than 35%, preferably more than 40%, as measured according to ISO 2470-2 (2008). The surface whiteness (paper whiteness) can be determined in particular according to ISO 2470-2 (2008) using an Elrepho 3000 spectrophotometer. According to one embodiment, the heat-sensitive recording material is defined as one according to the description at an energy level of 7.73 mJ / mm². 2 or 9.00 mJ / mm 2Heat-sensitive recording material printed with a barcode test pattern (code UPC-A, longitudinal and transverse) using a GeBE PrinterLab GPT-10000 test printer, wherein the printed heat-sensitive recording material has a barcode machine readability grade of 1 or more, preferably 2 or more, and most preferably 3 or more, as defined in the description and evaluated according to the ISO 15416 standard. Method, Product-by-Process, and Use According to a second aspect, the present invention relates to a method 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; optionally applying an insulating layer suspension to the first or second side of the carrier substrate, in particular optionally drying the insulating layer suspension to obtain an insulating layer arranged on the first or second side of the carrier substrate; applying a color layer suspension to the first or second side of the carrier substrate or to the optional insulating layer, wherein the color layer suspension comprises at least one coloring agent, and wherein the color layer suspension and / or the optional insulating layer suspension comprises at least one polymeric binder and at least one thermally expanded hollow pigment;In particular, drying the paint layer suspension to obtain a paint layer arranged on the first or second side of the substrate; applying a coating suspension to the paint layer, wherein the coating suspension comprises at least a polymeric binder and in particular at least one non-thermally expanded hollow pigment; in particular, drying the coating suspension to obtain a heat-sensitive layer arranged on the paint layer. It is preferred to obtain the heat-sensitive recording material according to the invention by a method in which dispersions, in particular aqueous dispersions, comprising the starting materials of the individual layers, are successively applied to the carrier substrate, wherein the, in particular aqueous, application suspensions The coatings must have a dry matter content of 8 to 60 wt.% and be applied using a blade coater coating process at an operating speed of the coating system of at least 200 m / min, in particular at least 900 m / min. Specifically, the optional insulating layer is applied using a film press, the color layer is applied using a blade coater, and / or the heat-sensitive layer is applied using a curtain coating process. This method is particularly advantageous from an economic point of view and due to the uniform application across the substrate. If the dry matter content falls below 8% by weight, efficiency suffers because a large amount of water must be removed quickly through gentle drying, which negatively impacts the coating speed. Conversely, if the dry matter content exceeds 60% by weight, this only results in 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 then operate at a very high speed. In the curtain coating process, a freely falling curtain of coating dispersion is formed. The coating dispersion, in the form of a thin film (curtain), is "poured" onto a substrate by free fall, thus applying the coating dispersion to the substrate. DE 10 196052 T1 discloses the use of the curtain coating process in the production of information recording materials, wherein multilayer recording layers are realized by applying the curtain, consisting of several coating dispersion films, to substrates. It is also conceivable to implement the method according to the invention in which a "double curtain" is used. This means that two successive layers are applied immediately one after the other. The application is carried out so immediately one after the other that the first layer applied has not yet dried. is before the next layer is applied. The application of the two layers is therefore preferably done "wet-on-wet". All definitions relating to the curtain coating process apply analogously to the double curtain coating process. 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, the need for intermediate adhesion promoters can be eliminated. In a preferred embodiment of the inventive method, the aqueous deaerated coating suspension has a viscosity of approximately 50 to approximately 2500 mPas (Brookfield, 100 rpm, 20 °C). If the value falls below approximately 50 mPas or exceeds approximately 2500 mPas, this leads to poor flowability of the coating compound on the coating unit. A viscosity of approximately 200 to approximately 500 mPas is particularly preferred for the aqueous deaerated coating suspension. The viscosities of successive coating compounds in the double curtain should decrease from bottom to top. With incorrectly adjusted coatings, the probability of heel formation at the point of contact of the curtain as well as the occurrence of wetting problems increases. In a preferred embodiment, to optimize the process, the surface tension of the aqueous coating suspension can be adjusted to approximately 25 to approximately 70 mN / m, preferably to approximately 35 to approximately 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 paint and adjusting it precisely by selecting the appropriate surfactant and determining the required amount of surfactant. The dynamic surface tension is measured using a bubble pressure tensiometer. The maximum internal pressure of a gas bubble formed in a liquid via a capillary is measured. The internal pressure p of a spherical gas bubble (Laplace pressure) depends, according to the Young-Laplace equation, on the radius of curvature r and on the surface tension σ: Fl — - rr 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 pressure maximum. The greatest curvature, and therefore the greatest pressure, occurs when the radius of curvature equals the capillary radius. Pressure curve during bladder pressure measurement, location of the pressure maximum: The radius of the capillary is determined using a reference measurement with a liquid of 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 in modern measuring instruments), must be subtracted from the measured pressure. This leads to the following formula for the bubble pressure method: 2 The measured value corresponds to the surface tension at a specific surface age, the time from the start of bubble formation until the occurrence of the pressure maximum. By varying the rate of bubble formation, the dependence of the surface tension on the surface age can be determined, resulting in a curve that plots the surface tension over time. This dependency plays an important role in the use of surfactants, as the equilibrium value of the interfacial tension is not reached in many processes due to the sometimes low diffusion and adsorption rates of surfactants. The formation of the individual layers can be done online or offline in a separate painting process. In particular, to ensure that the layers described above in detail exhibit the Bekk smoothing mentioned above, the following process steps are preferably carried out. The substrate is preferably smoothed in a first cylinder. This high degree of smoothness on one or both sides, achieved through this process, already provides an advantage to the substrate. Additional satin finishing by a downstream calender, preferably before a first coating unit, can further improve the smoothness and / or contribute to good profiling. If a thickness coat, as defined above, is applied, this is preferably done by a film press before the color layer is applied using a blade coater. The thickness on the back is particularly advantageous to prevent the paint from bleeding through with the blade coater. It would also be possible to apply the color layer directly with a film press. However, this would have a disadvantage regarding the smoothness development compared to a blade coater. Using a blade coater gives the material a good base smoothness, which is crucial for the dynamic sensitivity of the final product. There is a correlation between final smoothness and dynamic sensitivity. It would also be conceivable to apply the color layer using a film press or even a curtain coating machine. While this would eliminate the advantage of a smooth surface, it could be compensated for, especially with a film press, using a calender. The insulating layer, if present, is applied in the same way. The same applies to the protective layer. Alternatively, the protective layer can also be printed on or applied using a curtain coater. Protective layers that can be cured using actinic radiation are particularly suitable in terms of processing technology and technological properties. The term "actinic radiation" refers to UV or ionizing radiation, such as electron beams. The heat-sensitive layer is preferably applied using curtain coating, as described above. If substrates, especially papers, are coated on one side, the resulting curl should subsequently be corrected. This is preferably done with a LAS (Liquid Applicator System). A film of water is applied to the less coated side and then dried. This restores the surface to a flat position. Applying the water film slightly degrades the surface finish. A preferred option for protecting the surface would be a steam humidifier. This uses steam instead of water, thus preventing damage to the surface. This method is very well suited for applications requiring the highest surface quality. Another option would be a spray humidifier, which applies a water mist. All of the above-mentioned layers can be single-layered or multi-layered. The embodiments listed for the heat-sensitive recording material according to the first aspect are also embodiments for the method of producing a heat-sensitive recording material according to the second aspect and vice versa. According to a third aspect, the present invention relates to a heat-sensitive recording material producible by a method according to the second aspect. The embodiments listed for the heat-sensitive recording material according to the first aspect and for the method of 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, linerless paper, or carbonless copy paper. The embodiments listed for the heat-sensitive recording material according to the first aspect and the embodiments listed for the method of producing a heat-sensitive recording material according to the second aspect are also embodiments for use according to the fourth aspect. EXAMPLES OF EXECUTION In the following detailed examples, several heat-sensitive recording materials were produced by applying aqueous coating suspensions to form a composite structure on a support substrate and were examined and evaluated using different measurement methods. In all examples, the substrate used as a carrier is a paper substrate made from hardwood and softwood pulp with a basis weight of 38 g / m² determined according to the ISO 536 standard. 2 used. In particular, enzymatically treated cellulose and / or cellulose from bamboo can be used as a carrier substrate, either alternatively or additionally. Measurement methods Measurement of optical density (n.d.): 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 printhead at 305 dpi, a voltage of 24 V, and a print speed of approximately 101 mm / s, using a bar pattern (53 x 12 mm) with 10 energy levels. The optical density (n.d.) was determined using a Techkon SpectroDens densitometer at an energy level of 6.47 mJ / mm². 2 , 7.73 mJ / mm 2, or 9.00 mJ / mm 2 measured. The measurement uncertainty of the O.D. values ​​is estimated at ≤2%. Measurement of barcode machine readability: A barcode pattern printout lengthwise and crosswise according to the UPC-A code was produced at an energy level of 7.73 mJ / mm². 2 or 9.00 mJ / mm 2Barcodes were generated using a GeBE PrinterLab GPT-10000 test printer on specially prepared heat-sensitive recording materials. Barcode machine readability was evaluated using an REA VeriCube barcode verification device from REA Elektronik Deutschland, in accordance with ISO 15416, with the laser scanner operating at a wavelength of 660 nm. The software "TransWin32 V.1.2.0.2 / 16829" was used for evaluation. Barcode machine readability was assessed based on the scan reflection profile class in descending order of quality for each barcode: A (corresponds to a score of at least 4), B (corresponds to a score of 3), C (corresponds to a score of 2), D (corresponds to a score of 1), F (corresponds to a score of 0). Production of heat-sensitive recording materials According to the comparative examples 1 and 1a described below, as well as the embodiments 2, 3, 4, 5, 6 and 7 described below, a layer of starch was first applied to both sides of the paper substrate using a film press at a speed of 1250 m / min to obtain a coated paper substrate. The insulating layer (if present), the ink layer, and the heat-sensitive layer are applied to the paper substrate, which has a starch layer, using a hand squeegee. The layers are applied consecutively. In particular, the insulating layer, the paint layer, and the heat-sensitive layer, if present, can be applied consecutively using a single and / or simultaneously using a double curtain coater at a speed of 950 m / min. After each application, the drying process of the coated paper substrate is carried out in the usual manner, without negatively affecting the properties of the heat-sensitive recording material according to the invention. After each application, drying is performed using a hot air gun (40 cm distance) at a temperature of 90 to 110 °C for 1 to 3 minutes. The quantities [wt. %] refer to the oven-dried state (otro). Comparative example 1 As a comparative example 1, a heat-sensitive recording material was provided, which had a color layer applied to the paper substrate with a basis weight of 7.5 g / m² as determined by the ISO 536 standard. 2 and a heat-sensitive recording layer applied to the ink layer with a basis weight of approximately 3.2 g / m² as determined by the ISO 536 standard. 2 includes. The paint layer used in comparative example 1 has the following composition: 10.6 wt.% styrene-butadiene latex as a polymeric binder, 52.2 wt.% calcined kaolin as an inorganic pigment, 24.6 wt.% precipitated calcium carbonate as an inorganic pigment, 11.2 wt.% carbon black pigment as a black pigment, and 1.4 wt.% other additives, such as rheology aids, dispersing aids, or surfactants. The heat-sensitive layer used in comparative example 1 and also in embodiments 2, 3, 4, 5, 6 and 7 has the following composition: 7.5 wt% polyvinyl alcohol (high viscosity) as a polymeric binder, 0.9 wt% polyamidoamine epichlorohydrin (10%) as a crosslinking agent, 9 wt% calcium carbonate as an inorganic pigment, 37 wt% of a non-thermally expanded hollow pigment (Ropaque® type), 40.4 wt% stearic acid amide dispersion, 3.85 wt% zinc stearate dispersion and 1.35 wt% other additives. Comparative example 1a As a comparative example 1a, a heat-sensitive recording material was provided, which had a first insulating layer applied to the paper substrate with a basis weight of 2.8 g / m². 2 , a second layer of paint applied to the first insulating layer with a basis weight of 7.5 g / m² 2 and a heat-sensitive recording layer applied to the color layer with a basis weight of 3.2 g / m² 2 includes. The first insulating layer used in comparative example 1a has the following composition: 7.1 wt.% styrene-butadiene latex as a polymeric binder, 6.3 wt.% polyvinyl alcohol (18% dry weight fraction) as a further polymeric binder, 30.9 wt.% non-thermally expanded hollow pigment (Ropaque), 54.9 wt.% precipitated calcium carbonate as an inorganic pigment, and 0.8 wt.% other additives, such as rheology aids, dispersing aids, or surfactants. The second color layer used in comparative example 1a has the following composition: 10.6 wt.% styrene-butadiene latex as a polymeric binder, 52.2 wt.% calcined kaolin as an inorganic pigment, 24.6 wt.% precipitated calcium carbonate as an inorganic pigment, 11.2 wt.% carbon black pigment as a black pigment, and 1.4 wt.% other additives, such as rheology aids, dispersing aids, or surfactants. The composition of the heat-sensitive layer of comparison example 1a corresponds to the composition of the heat-sensitive layer of comparison example 1. Example 2 As embodiment 2, a heat-sensitive recording material was provided, which has a first insulating layer applied to the paper substrate with a basis weight of 2.8 g / m² 2 , a second layer of paint applied to the first insulating layer with a basis weight of 7.5 g / m² 2 and a heat-sensitive recording layer applied to the color layer with a basis weight of 3.2 g / m² 2 includes. The first insulating layer used in embodiment 2 has the following composition: 7.1 wt.% styrene-butadiene latex as a polymeric binder, 6.3 wt.% polyvinyl alcohol (18% dry weight fraction) as a further polymeric binder, 30.9 wt.% thermally expanded hollow pigment (Expancel), 54.9 wt.% precipitated calcium carbonate as an inorganic pigment, and 0.8 wt.% other additives, such as rheology aids, dispersing aids, or surfactants. The second color layer used in embodiment 2 has the following composition: 10.6 wt.% styrene-butadiene latex as a polymeric binder, 52.2 wt.% calcined kaolin as an inorganic pigment, 24.6 wt.% precipitated calcium carbonate as an inorganic pigment, 11.2 wt.% carbon black pigment as a black pigment, and 1.4 wt.% other additives, such as rheology aids, dispersing aids, or surfactants. The composition of the heat-sensitive layer of embodiment 2 corresponds to the composition of the heat-sensitive layer of comparative example 1. Example 3 As embodiment 3, a heat-sensitive recording material was provided, which has a first insulating layer applied to the paper substrate with a basis weight of 2.8 g / m². 2 , a second layer of paint applied to the first insulating layer with a basis weight of 7.5 g / m² 2 and a heat-sensitive recording layer applied to the color layer with a basis weight of 3.2 g / m² 2 includes. The first insulating layer used in embodiment 3 has the following composition: 7.1 wt.% styrene-butadiene latex as a polymeric binder, 6.3 wt% polyvinyl alcohol (18% dry weight fraction) as a further polymeric binder, 15.0 wt% thermally expanded hollow pigment (Expancel), 70.8 wt% precipitated calcium carbonate as an inorganic pigment, and 0.8 wt% other additives, such as rheology aids, dispersing aids, or surfactants. The second color layer used in embodiment 3 has the following composition: 10.6 wt.% styrene-butadiene latex as a polymeric binder, 52.2 wt.% calcined kaolin as an inorganic pigment, 24.6 wt.% precipitated calcium carbonate as an inorganic pigment, 11.2 wt.% carbon black pigment as a black pigment, and 1.4 wt.% other additives, such as rheology aids, dispersing aids, or surfactants. The composition of the heat-sensitive layer of embodiment 3 corresponds to the composition of the heat-sensitive layer of comparative example 1. Example 4 As embodiment 4, a heat-sensitive recording material was provided, which has a first insulating layer applied to the paper substrate with a basis weight of 2.8 g / m². 2 , a second coat of paint applied to the first coat with a basis weight of 7.5 g / m² 2 and a heat-sensitive recording layer applied to the color layer with a basis weight of 3.2 g / m² 2 includes. The first insulating layer used in embodiment 4 has the following composition: 7.1 wt.% styrene-butadiene latex as a polymeric binder, 6.3 wt.% polyvinyl alcohol (18% dry weight fraction) as a further polymeric binder, 15.0 wt.% thermally expanded hollow pigment (Expancel), 15.0 wt.% non-thermally expanded hollow pigment (Ropaque), 55.8 wt.% precipitated calcium carbonate as an inorganic pigment, and 0.8 wt.% other additives, such as rheology aids, dispersing aids, or surfactants. The second color layer used in embodiment 4 has the following composition: 10.6 wt.% styrene-butadiene latex as a polymeric binder, 52.2 wt.% calcined kaolin as an inorganic pigment, 24.6 wt.% precipitated calcium carbonate as an inorganic pigment, 11.2 wt.% carbon black pigment as a black pigment, and 1.4 wt.% other additives, such as rheology aids, dispersing aids, or surfactants. The composition of the heat-sensitive layer of embodiment 4 corresponds to the composition of the heat-sensitive layer of comparative example 1. Example 5 As embodiment 5, a heat-sensitive recording material was provided which has a color layer with a basis weight of 7.5 g / m². 2 and a heat-sensitive recording layer applied to the color layer with a basis weight of 3.2 g / m² 2 includes. The paint layer used in embodiment 5 has the following composition: 10.6 wt.% styrene-butadiene latex as a polymeric binder, 43.2 wt.% calcined kaolin as an inorganic pigment, 24.6 wt.% precipitated calcium carbonate as an inorganic pigment, 9.0 wt.% thermally expanded hollow pigment (Expancel), 11.2 wt.% carbon black pigment as a black pigment, and 1.4 wt.% other additives, such as rheology aids, dispersing aids, or surfactants. The composition of the heat-sensitive layer of embodiment 5 corresponds to the composition of the heat-sensitive layer of comparative example 1. Example 6 As embodiment 6, a heat-sensitive recording material was provided which has a color layer with a basis weight of 7.5 g / m². 2 and a heat-sensitive recording layer applied to the color layer with a basis weight of 3.2 g / m²2 includes. The paint layer used in embodiment 6 has the following composition: 10.6 wt.% styrene-butadiene latex as a polymeric binder, 45.7 wt.% calcined kaolin as an inorganic pigment, 24.6 wt.% precipitated calcium carbonate as an inorganic pigment, 6.5 wt.% thermally expanded hollow pigment (Expancel), 11.2 wt.% carbon black pigment as a black pigment, and 1.4 wt.% other additives, such as rheology aids, dispersing aids, or surfactants. The composition of the heat-sensitive layer of embodiment 6 corresponds to the composition of the heat-sensitive layer of comparative example 1. Example 7 As embodiment 7, a heat-sensitive recording material was provided which has a color layer with a basis weight of 7.5 g / m². 2and a heat-sensitive recording layer applied to the color layer with a basis weight of 3.2 g / m² 2 includes. The paint layer used in embodiment 7 has the following composition: 10.6 wt.% styrene-butadiene latex as a polymeric binder, 48.2 wt.% calcined kaolin as an inorganic pigment, 24.6 wt.% precipitated calcium carbonate as an inorganic pigment, 4.0 wt.% thermally expanded hollow pigment (Expancel), 11.2 wt.% carbon black pigment as a black pigment, and 1.4 wt.% other additives, such as rheology aids, dispersing aids, or surfactants. The composition of the heat-sensitive layer of embodiment 7 corresponds to the composition of the heat-sensitive layer of comparative example 1. Results The following table shows the comparison of the respective heat-sensitive recording materials according to embodiments 1, 2, 3, 4, 5, 6 and 7, as well as comparison example 1 or 1a, with regard to the measured optical density (n.d.). at an energy level of 6.47 mJ / mm 2 (designated as O. D-6 in the table), 7.73 mJ / mm 2 (designated as O. D-7 in the table), or 9.00 mJ / mm² 2 (designated as O. D-9 in the table), as well as the barcode machine readability (Code 1 to Code 5) according to the corresponding grade: Beio. D-6 or D-7 or D-9 Code 1 Code 2 Code 3 Code 4 Code 5 play Ver0.86 1.09 1.24 1.2 2.2 0.8 1.7 5.9 example 1 Ver0.91 1.13 1.28 1.3 2.6 1.3 2.1 7.3 example 1a 2 1.21 1.36 1.42 2.6 3.6 2.2 3.2 11.5 3 0.97 1.17 1.35 1.3 3.2 2.2 3.1 9.8 4 1.02 1.30 1.41 1.9 3.8 1.6 2.5 9.8 5 1.24 1.32 1.34 3.5 3.6 3.3 2.9 13.3 6 1.14 1.29 1.33 2.7 3.4 2.7 3.0 11.8 7 1.00 1.18 1.29 1.5 3.1 1.5 2.4 8.5 Table The column “Code 1” describes the barcode machine readability rating for a printed longitudinal grid with an energy dose of 7.73 mJ / mm². 2 The column “Code 2” describes the barcode machine readability rating for a printed longitudinal grid with an energy dose of 9.00 mJ / mm². 2 . The column “Code 3” describes the barcode machine readability rating for a printed cross-hatch pattern with an energy dose of 7.73 mJ / mm². 2 The column “Code 4” describes the barcode machine readability rating for a printed cross-hatch pattern with an energy dose of 9.00 mJ / mm². 2 . The column “Code 5” describes, for the respective example, the sum of the grades in the columns “Code 1”, “Code 2”, “Code 3”, “Code 4” and “Code 5”. A comparison of the optical densities between comparative example 1 or 1a and the respective embodiments 2, 3, 4, 5, 6 or 7 reveals a significant improvement between the respective embodiments 2, 3, 4, 5, 6 or 7 and comparative example 1 or 1a, since for all energy levels of 6.47 mJ / mm² 2 , 7.73 mJ / mm 2 and 9.00 mJ / mm 2 the measured optical density in the respective embodiment 2, 3, 4, 5, 6, or 7 is higher than the measured optical density in the comparison example 1 or 1a. This potential for improvement is also evident when comparing the barcode machine readability according to the table, since comparison example 1, or 1a, shows a significantly reduced barcode machine readability for all columns “Code 1” to “Code 5” compared to the barcode machine readability of embodiments 2, 3, 4, 5, 6 and 7. The comparison of the optical density and barcode machine readability values ​​between comparison example 1 and embodiments 5, 6 and 7 in the table clearly shows a significant improvement when at least part of the inorganic pigment in the color layer (Ansilex) is replaced by a thermally expanded hollow pigment (Expancel). Thus, the results shown in the table demonstrate that the use of a thermally expanded hollow pigment, such as Expancel, in the ink layer and / or the optional insulating layer of a heat-sensitive recording material results in a significant improvement in optical density and barcode machine readability of corresponding printed images compared to the exclusive use of an inorganic pigment, such as calcined kaolin. The use of thermally expanded hollow pigments in the ink layer and / or in the optional insulating layer of the heat-sensitive recording layer, as described in the present invention, significantly improves the thermal response of the heat-sensitive recording layer in the thermal printer. This is due to the greatly improved thermal insulation properties of the respective ink layer and / or optional insulating layer containing the thermally expanded hollow pigments. Thus, a maximum of the heat output provided by the thermal printer's printhead is made available to the heat-sensitive recording layer, enabling optimal utilization of this heat for the thermal response of the heat-sensitive recording layer.

Claims

REQUIREMENTS 1. Heat-sensitive recording material, including: a carrier substrate which has a first side and a second side facing away from the first side; optionally an insulating layer, which is arranged on the first or second side of the support substrate, a color layer arranged on the first or second side of the support substrate or on the optional insulating layer, wherein the at least one color layer comprises at least one coloring agent, and at least one heat-sensitive layer which is arranged on the paint layer and at least partially covers the paint layer, wherein the heat-sensitive layer is designed in such a way that it becomes translucent through local application of heat, so that the underlying paint layer becomes visible, characterized by the fact that the color layer and / or the optional insulating layer comprises at least one polymeric binder and at least one thermally expanded hollow pigment, and that the heat-sensitive layer comprises at least a polymeric binder and, in particular, at least one non-thermally expanded hollow pigment.

2. Heat-sensitive recording material according to claim 1, characterized in that the at least one thermally expanded hollow pigment of the color layer and / or the optional insulating layer has a mean particle size (d50) between 5 μm and 50 μm, preferably between 5 μm and 40 μm, more preferably between 5 μm and 30 μm, and most preferably between 5 μm and 20 μm.

3. Heat-sensitive recording material according to claim 1 or 2, characterized in that the at least one thermally expanded hollow pigment of the color layer and / or the optional insulating layer has a density between 20 kg / m³ 3 and 100 kg / m²3 exhibits.

4. Heat-sensitive recording material according to one of the preceding claims, characterized in that the at least one thermally expanded hollow pigment of the color layer and / or the optional insulating layer has a wall thickness of the polymer shell between 0.01 μm and 5 μm, preferably between 0.03 μm and 1.5 μm, more preferably between 0.05 μm and 0.5 μm.

5. Heat-sensitive recording material according to one of the preceding claims, characterized in that the at least one thermally expanded hollow pigment of the color layer and / or the optional insulating layer has a specific surface area between 400 m² 2 / kg and 6400 m 2 / kg 6. Heat-sensitive recording material according to one of the preceding claims, characterized in that the at least one thermally expanded hollow pigment of the color layer and / or the optional insulating layer has a cavity volume of more than 70%, preferably more than 75%, further preferably more than 80%, even more preferably more than 85%, further still more preferably more than 90%, most preferably more than 95%.

7. Heat-sensitive recording material according to one of the preceding claims, characterized in that the at least one thermally expanded hollow pigment of the color layer and / or the optional insulating layer comprises a polymer comprising acrylonitrile and / or methacrylonitrile as a monomer.

8. Heat-sensitive recording material according to one of the preceding claims, characterized in that the at least one thermally expanded hollow pigment of the color layer and / or the optional insulating layer is present in an amount of 1 wt.% to 50.0 wt.%, preferably in an amount of 2 wt.% to 35.0 wt.%, and most preferably in an amount of 3 wt.% to 20 wt.% based on the total dry mass of the paint layer and / or the optional insulating layer, in which the paint layer and / or the optional insulating layer is present.

9. Heat-sensitive recording material according to one of the preceding claims, characterized in that the at least one non-thermally expanded hollow pigment of the heat-sensitive layer comprises styrene / acrylate copolymers or urea / formaldehyde condensation polymers and / or mixtures thereof, wherein the at least one non-thermally expanded hollow pigment of the heat-sensitive layer is a Ropaque® type hollow pigment, in particular Ropaque®-NT2900.

10. Heat-sensitive recording material according to one of the preceding claims, characterized in that the color layer and / or the optional insulating layer comprises at least one non-thermally expanded hollow pigment.

11. Heat-sensitive recording material according to one of the preceding claims, characterized in that the at least one non-thermally expanded hollow pigment of the heat-sensitive layer and / or the color layer and / or the optional insulating layer is present in the heat-sensitive layer and / or the color layer and / or the optional insulating layer in an amount of 1 wt.% to 50.0 wt.%, preferably in an amount of 2 wt.% to 45.0 wt.%, and most preferably in an amount of 3 wt.% to 40 wt.% based on the total dry mass of the heat-sensitive layer and / or the color layer and / or the optional insulating layer.

12. Heat-sensitive recording material according to one of the preceding claims, characterized in that the at least one non-thermally expanded hollow pigment of the color layer and / or the optional insulating layer and / or, in particular, the heat-sensitive layer comprises styrene / acrylate copolymers or urea / formaldehyde condensation polymers and / or mixtures thereof, wherein preferably the at least one non-thermally expanded hollow pigment of the The color layer and / or the optional insulating layer and / or, in particular, the heat-sensitive layer is a hollow pigment of the Ropaque® type, especially Ropaque® TH-500EF; Ropaque® HP-1055, Ropaque® OP-96, Ropaque®-NT2900 and / or Ropaque® TH-1000.

13. Heat-sensitive recording material according to any of the preceding claims, characterized in that the color layer and / or the heat-sensitive layer and / or the optional insulating layer comprises at least one inorganic pigment, which is preferably selected from the group comprising clays, precipitated, ground, filtered or natural calcium carbonates, aluminum oxides, aluminum hydroxides, silicas, precipitated and pyrogenic silicas, for example aero-disp types, diatomaceous earths, magnesium carbonates, talc, kaolin, titanium oxide, bentonite, calcium silicate hydrate and mixtures thereof, preferably calcium carbonates, further preferably precipitated calcium carbonate (PCC) and / or ground calcium carbonate (GCC), calcined kaolin, and / or pyrogenic silicas.

14. Heat-sensitive recording material according to claim 13, characterized in that the at least one inorganic pigment of the color layer is present in the color layer in an amount of 1 wt.% to 90 wt.%, preferably 10 wt.% to 85 wt.%, more preferably 15 wt.% to 80 wt.%, and most preferably 20 wt.% to 72 wt.% based on the total dry mass of the color layer.

15. Heat-sensitive recording material according to claim 13 or 14, characterized in that the at least one inorganic pigment of the heat-sensitive layer is present in the heat-sensitive layer in an amount of 0 wt.% to 50 wt.%, preferably 0.1 wt.% to 30 wt.%, more preferably 1 wt.% to 20 wt.%, and most preferably 1 wt.% to 15 wt.% based on the total dry mass of the heat-sensitive layer.

16. Heat-sensitive recording material according to one of claims 13 to 15, characterized in that the at least one inorganic pigment of the optional insulating layer is present in an amount of 5 wt.% to 90 wt.%, preferably 10 wt.%. wt.% to 85 wt.%, more preferably from 25 wt.% to 80 wt.%, and most preferably from 40 wt.% to 75 wt.% based on the total dry mass of the optional insulating layer in which it is present.

17. Heat-sensitive recording material according to one of the preceding claims, characterized in that the heat-sensitive recording material has a single color layer and no insulating layer, wherein the single color layer preferably has an basis weight of 1.0 g / m² as determined by ISO 536. 2 up to 10.0 g / m² 2exhibits, or that the heat-sensitive recording material has an insulating layer and a color layer arranged thereon, wherein preferably the insulating layer and the color layer have an basis weight of 1.0 g / m² as determined by the ISO 536 standard. 2 up to 10.0 g / m² 2 exhibits.

18. Heat-sensitive recording material according to one of the preceding claims, characterized in that the ink layer and / or the heat-sensitive layer and / or the optional insulating layer comprises at least one crosslinking agent, wherein the at least one crosslinking agent is preferably selected from the group comprising polyhydric aldehydes, such as glyoxal, dialdehyde starch, glutaraldehyde, salts or esters of glyoxylic acid, crosslinkers based on ammonium zirconium carbonate, polyamidoamine epichlorohydrin resins (PAAE resins), polyamide resins, polyamine resins, polyamidoamine resins, polyamide-polyurea resins, polyamine-polyurea resins, adipic acid dihydrazide (ADH), polyamidoamines, epoxy resins, formaldehyde oligomers, cyclic ureas, methylolurea, melamine formaldehyde oligomers, oxazoline resins, carbodiimide, borate compounds, and Mixtures thereof, with at least one crosslinking agent being the most preferred choice,as ammonium zirconium carbonate and / or polyamidoamine epichlorohydrin resins (PAAE resin).

19. Heat-sensitive recording material according to claim 18, characterized in that the at least one crosslinking agent of the ink layer and / or the heat-sensitive layer and / or the optional insulating layer is present in an amount of 0.01 wt.% to 10.0 wt.%, preferably in an amount of 0.1 wt.% to 5.0 wt.%, and most preferably in an amount of 0.5 wt.% to 2.0 wt.% related to the total dry mass of the paint layer and / or the heat-sensitive layer in which the paint layer and / or the heat-sensitive layer is present.

20. Heat-sensitive recording material according to one of the preceding claims, characterized in that the heat-sensitive layer comprises at least one wax, which is preferably selected from the group comprising at least one fatty acid, at least one fatty acid amide, at least one metal salt of a fatty acid, at least one metal salt of a fatty acid amide and mixtures thereof, wherein the at least one fatty acid amide more preferably comprises fatty acid monoamide, fatty acid diamide, fatty acid alkanolamide, N-methyl fatty acid amide and mixtures thereof, and / or wherein the at least one fatty acid more preferably comprises a saturated fatty acid and / or an unsaturated fatty acid with at least 8 carbon atoms.

21. Heat-sensitive recording material according to claim 20, characterized in that the at least one fatty acid is selected from the group comprising behenic acid, stearic acid, and / or palmitic acid, and / or the at least one fatty acid amide is selected from the group comprising ethylenebisfatty acid ureamide, ethylenebisstearamide, ethylenebispalmitamide, behenamide, erucamide, stearic acid amide, oleamide, palmitic acid amide, and / or lauramide, preferably stearic acid amide, and / or the at least one metal salt of the fatty acid is selected from the group comprising calcium stearate, magnesium stearate, zinc stearate and mixtures thereof, preferably calcium stearate and / or zinc stearate.

22. Heat-sensitive recording material according to claim 20 or 21, characterized in that the at least one fatty acid, the at least one fatty acid amide, the at least one metal salt of a fatty acid, and / or the at least one metal salt of a fatty acid amide is present in the heat-sensitive layer in an amount of 1 wt.% to 80 wt.%, preferably in an amount of 2 wt.% to 75 wt.%, and most preferably in an amount of 3 wt.% to 70 wt.%, based on the total dry mass of the heat-sensitive layer.

23. Heat-sensitive recording material according to one of the preceding claims, characterized in that a starch layer is present directly on at least one side of the support substrate, preferably directly on both sides of the support substrate, wherein the starch layer is present in particular in an amount of 0.1 g / m² 2 up to 3 g / m² 2 , particularly preferably of 0.2 g / m³ 2 up to 1.5 g / m² 2, is applied.

24. Heat-sensitive recording material according to one of the preceding claims, characterized in that the heat-sensitive recording material has a protective layer and / or a non-stick coating which is arranged on the heat-sensitive layer.

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

26. Heat-sensitive recording material according to one of the preceding claims, characterized in that the ink layer on the side on which the heat-sensitive layer is applied has a Bekk smoothness of 50 to 800 s, particularly preferably 100 to 600 s and most preferably 150 to 350 s as measured according to DIN 53107 (2016).

27. 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 0.9, preferably at least 1.0, and most preferably at least 1.10, wherein in particular at an energy level of 7.73 mJ / mm 2 was measured, and / or that the heat-sensitive recording material has an optical density (o. D.) defined according to the description of at least 1.2, preferably at least 1.25, and most preferably at least 1.3, wherein in particular at an energy level of 9.00 mJ / mm 2 was measured.

28. Method for producing a heat-sensitive recording material, comprising the following process steps: Providing a support substrate which has a first side and a second side facing away from the first side; Optionally, an insulating layer suspension can be applied to the first or second side of the support substrate. in particular optionally drying the insulating layer suspension to obtain an insulating layer arranged on the first side or second side of the support substrate; Applying a color layer suspension to the first or second side of the support substrate or to the optional insulating layer, wherein the color layer suspension comprises at least one coloring agent, wherein the paint layer suspension and / or the optional insulating layer suspension comprises at least a polymeric binder and at least one thermally expanded hollow pigment; in particular drying the paint layer suspension to obtain a paint layer arranged on the first or second side of the support substrate or on the optional insulating layer; Application of a coating suspension to the paint layer, wherein the coating suspension comprises at least a polymeric binder and in particular at least one non-thermally expanded hollow pigment; in particular drying the application suspension to obtain a heat-sensitive layer arranged on the paint layer.

29. Heat-sensitive recording material producible by a method according to claim 28.

30. Use of a heat-sensitive recording material according to any one of claims 1 to 27 or 29 as a receipt roll, adhesive label roll, ticket roll, linerless paper, or carbonless copy paper.

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