Heat-sensitive recording material

Abstract

The present invention relates to a heat-sensitive recording material comprising: a carrier substrate which has a first side and a second side which faces away from the first side; a color layer which is disposed on the first or second side of the carrier substrate, the color layer having at least one coloring substance; and a heat-sensitive layer which is disposed on the color layer and at least partially covers the color layer, the heat-sensitive layer being designed such that it becomes translucent by local action of heat, with the result that the color layer lying underneath becomes visible. The heat-sensitive layer comprises at least one polymeric binder, at least one crosslinking agent, and at least one inorganic pigment, the at least one inorganic pigment comprising a precipitated calcium carbonate (PCC), and the precipitated calcium carbonate (PCC) having an average particle size (d90) of less than 50 μm.

Description

[0001]HEAT-SENSITIVE RECORDING MATERIAL TECHNICAL FIELD 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, a color layer arranged on the first or second side of the carrier substrate, wherein the color layer comprises at least one coloring agent, and a heat-sensitive layer arranged on the color layer and at least partially covering the color layer, wherein the heat-sensitive layer is designed such that it becomes translucent upon local application of heat, allowing the underlying color layer to become visible. The heat-sensitive layer comprises at least one polymeric binder, at least one crosslinking agent, and at least one inorganic pigment.wherein the at least one inorganic pigment comprises precipitated calcium carbonate (PCC), wherein the precipitated calcium carbonate (PCC) has a mean particle size (d90) of less than 50 µm. 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 support substrate having a first side and a second side facing away from the first side; applying a color layer suspension to the first side or second side of the support substrate, wherein the color layer suspension comprises at least one coloring agent; in particular, drying the color layer suspension to obtain a color layer arranged on the first side or second side of the support substrate; applying a coating suspension to the color layer, wherein the coating suspension comprises at least one polymeric binder, at least one crosslinking agent,and comprises at least one inorganic pigment, wherein the inorganic pigment comprises precipitated calcium carbonate (PCC), wherein the precipitated calcium carbonate (PCC) has a mean particle diameter (d90) of less than 50 µm; and in particular, drying the coating suspension to obtain a heat-sensitive layer arranged on the ink 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, as printer paper for mechanical printers or writing pens, or as carbonless copy paper. TECHNICAL BACKGROUND Heat-sensitive recording materials, which are also referred to as thermal papers,Thermal labels are used in a variety of applications, such as sales receipts in retail. Thermal labels, also known as heat-sensitive recording materials, are known from the prior art for direct thermal printing. Two types of thermal labels are distinguished, particularly for direct thermal printing. The first type comprises materials in which the printed image is created by a local heat-induced chemical reaction in a color 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. Typically, the color layer also contains a heat-sensitive solvent that melts under the influence of heat and consists, for example, of long-chain aliphatic alcohols, amides,The first type of heat-sensitive recording material may contain esters or carboxylic acids, enabling the color reaction of the color former and developer. Furthermore, the color layer may contain heat-sensitive sensitizers. The second type of heat-sensitive recording material comprises materials in which the printed image is created by making a heat-sensitive top layer translucent through local application of heat, for example, by means of a thermal direct 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 through partially different compositions, porosities, and materials of the heat-sensitive top layer.optimized for thermal direct 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 color 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 color 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. In the second type of heat-sensitive recording material, the heat-sensitive top layer should possess sufficient heat sensitivity so that it can be activated by localized heat application, particularly using conventional thermal direct printers.becomes translucent. Ideally, recording materials of the first and second types should be usable with a conventional thermal direct printer, and the printer settings should be comparable, particularly 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 6,043,193 describes a heat-sensitive recording material comprising a substrate and an opaque recording layer applied to this substrate.which comprises 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 void volume of 40% to 90%. US 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, wherein several cavities are formed by orienting the multilayer.wherein the extruded image reproduction layer and the collapsible layer structure are in a non-collapsed state, which is essentially opaque in order to conceal the pigment layer underneath. US 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 with respect to the substrate such that it is concealed by the opaque polymer before the application of the predetermined heat and pressure and becomes visible thereafter. US 2011 / 172094 A discloses a recording material comprising a support having a surfacewhich is impregnated with a colorant or coated with a coating containing a pigment or dye, and which comprises a layer containing polymeric particles with a core-shell structure and which, when dry, is 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 2011 / 251060 A describes a heat-sensitive recording material consisting of a colorant 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 variety 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, comprising a substrate in the form of a planar structure, including at least one colored surface, and arranged thereon, and comprising a layer comprising polymer particles with a core-shell structure, wherein the particles have an outer first polymer shell with a calculated Tg of 40 °C to 130 °C, wherein the particles, when dry, contain at least one cavity, and comprising, to 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. In WO 2013 / 152287 A1, a heat-sensitive recording material with a two-layer,A monoaxially oriented film comprising a first layer, comprising an opaque polymer based on beta-nucleated propylene, and a second layer comprising a dark pigment is described. US 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 scatter polymer particles, each of which has a center, a surface, a refractive index at the center that differs from a refractive index at the surface therefrom, 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 that at least partially covers the first layer.wherein the first layer has an intense color at least facing the second layer and the second layer comprises hollow-body pigments which can be melted by localized heat treatment to form a character image, described, characterized in that the second layer, in addition to the hollow-body pigments, also comprises one or more fatty acids and one or more heat-sensitive sensitizers. In the recording material disclosed in EP 1778499 A1, which differs in structure from EP 2993055 A1 only in the type of color of the second layer, wherein the character image becomes visible under UV irradiation instead of being visible in the visible range of light, the protective layer can be modified to improve printability and environmental resistance, in particular resistance to plasticizers, oils, fats and moisture.such as sprayed 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 color at least on the side facing the second layer and the second layer has hollow pigments that can be melted to form a printed image by localized heat treatment, characterized in that the recording material has at least one protective layer at least partially covering the second layer. The physical process is described as distinguishing between two different methods for generating the printed image: In the first method, the printed image is generated by making a heat-sensitive top layer translucent through local application of heat using a thermal direct printer.the top layer comprises fusible hollow pigments. In the second method, the printed image is created by making a heat-sensitive top layer translucent through local application of heat using a thermal direct printer, the top layer comprising softenable or soluble hollow pigments. According to this document, an acceptable gray recording material with the following characteristics can be obtained: whiteness of 56% or 52% with or without UV content, optical density (unprinted) of 0.33 ODU, optical density (printed) of 1.22 ODU, and contrast of 0.89 ODU (thermal printhead 300 dpi, 16 mJ / mm). 2In the related divisional application EP 3517309 A1, the feature of the top layer is specified in particular, which comprises manipulable hollow body pigments for the formation of a printed image and at least one fatty acid, namely stearic acid and / or palmitic acid or stearamide and / or methylstearamide. US 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, wherein the ink layer comprises at least one color, a top layer arranged over the printed ink layer, and a top coat layer arranged over the top layer, wherein the top coat comprises an acrylic-based composition containing light-scattering particles that causethat the top layer is opaque in a first state and transparent in a second state, wherein at least heat or pressure is applied by a printhead, causing the top layer to transition from the first state to the second state, thereby enabling the at least one color of the ink layer to become visible through the top layer. WO 2019 / 183471 A1 discloses a recording medium comprising a substrate, wherein the substrate is involved in the first scattering particles having a melting point that 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, during the melting of the solid,wherein the first solid scattering particles are arranged to fill the space between the recording medium. 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, and wherein the opaque material in an opaque state comprises a plurality of irregularly and / or oddly shaped opaque polymer particles.the cavities between them define and have different shapes and / or sizes, and furthermore wherein the opaque material is configured such that, upon application of sufficient temperature and / or pressure, it changes from an opaque state to a transparent state to expose the color material beneath the opaque material. WO 2021 / 062230 A1 defines 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 upon melting.and wherein the first scattering particles comprise perforated particles, is disclosed. In EP 3957489 A1, a heat-sensitive recording material is disclosed, comprising or consisting of a carrier substrate and a melt layer arranged on one side of the carrier substrate or paper substrate. All these conventionally used heat-sensitive recording materials require improvement, particularly with regard to their functionality, sustainability, and economic production. In particular, heat-sensitive recording materials of the aforementioned first type require the use of color developers, which often have harmful effects on health or the environment, and there are therefore efforts to eliminate them. In addition, conventionally used heat-sensitive recording materials often require the use of a large number of special raw materials, which are, for example, nanoscale, porous,If the material is perforated or similar, two different scattering particles must be used. In particular, it is desirable to reduce the occurrence of white or light defects in correspondingly dark printed areas, which are perceived as disturbing by the viewer's eye or are detrimental to electronic reading devices, in order to improve the print image. It is especially desirable to at least maintain or further increase 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, particularly with regard to sensitivity or optical density, and water abrasion resistance.The deposit and abrasion behavior of heat-sensitive recording materials on the thermal printhead of thermal printers, whereby as few or no deposits and dot failures of the thermal printhead (mechanical and / or electrochemical destruction of individual dots) that could negatively affect the long-term operation of the thermal printer (more than 10 km of throughput) should occur. In addition, contact of the heat-sensitive recording materials with food should be possible without hazard to the user of food, and advantageous recyclability of corresponding conventional heat-sensitive recording materials should be achieved. DESCRIPTION OF THE INVENTION Objective One object of the present invention is to provide a heat-sensitive recording material which does not exhibit any print image defects after printing,in which an advantageous deposit behavior on the printhead is achieved during the printing process, and which also exhibits a reduced number of white or light defects in correspondingly dark printed areas. 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 (in particular a high relative print contrast) even during storage over longer periods and / or under extreme climatic conditions (high humidity and / or temperature) of the printed (image retention) or unprinted (rewriting / writing performance) heat-sensitive recording material. A further object of the present invention is to provide a heat-sensitive recording material which ensures high durability of the printed image,especially when the surface of the heat-sensitive recording material comes into contact with hydrophobic substances, such as plasticizers from film materials, oils, fats, and the like. Another object of the present invention is to provide a heat-sensitive recording material that can come 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 requires only readily available raw materials and is therefore inexpensive to produce. Surprisingly, it has now been found thatthat the aforementioned disadvantages of the prior art can be overcome by using precipitated calcium carbonate (PCC) with a mean particle size (d90) of less than 50 µm as an inorganic pigment in the heat-sensitive layer of the heat-sensitive recording material. By using precipitated calcium carbonate (PCC) with a mean particle size (d90) of less than 50 µm as an inorganic pigment in the heat-sensitive layer, the number of white or light defects in correspondingly dark printed areas can be significantly reduced. Furthermore, the precipitated calcium carbonate (PCC) with a mean particle size (d90) of less than 50 µm as an inorganic pigment in the heat-sensitive layer ensures advantageous deposit behavior on the thermal printhead of thermal printers during thermal printing in the application of heat-sensitive recording materials.This results in no or only minimal deposits and dot loss on the thermal printhead that could negatively affect the long-term operation of the thermal printer (more than 10 km of travel). Furthermore, the use of precipitated calcium carbonate (PCC) with a mean particle size (d90) of less than 50 µm as an inorganic pigment in the heat-sensitive layer allows for an advantageous print image free from other printing defects. Since precipitated calcium carbonate (PCC) is harmless, there are no disadvantages when the heat-sensitive recording material comes into contact with food or regarding recyclability. Precipitated calcium carbonate (PCC) is available at a very favorable price.which reduces the manufacturing costs of corresponding heat-sensitive recording materials. Heat-sensitive recording material The aforementioned tasks are solved according to the first aspect by a heat-sensitive recording material comprising: a support substrate having a first side and a second side facing away from the first side; a color layer arranged on the first or second side of the support substrate, wherein the color layer comprises at least one coloring agent; and a heat-sensitive layer arranged on the color layer and at least partially covering the color layer, wherein the heat-sensitive layer is designed such that it becomes translucent upon local application of heat, allowing the underlying color layer to become visible, and wherein the heat-sensitive layer comprises at least one polymeric binder and at least one crosslinking agent.and comprises at least one inorganic pigment, wherein the at least one inorganic pigment comprises precipitated calcium carbonate (PCC), the precipitated calcium carbonate (PCC) having a mean particle size (d90) of less than 50 µm. By using the precipitated calcium carbonate (PCC) with a mean particle size (d90) of less than 50 µm as the inorganic pigment of the heat-sensitive layer according to the first aspect, it is possible to significantly reduce the number of white or light defects in dark printed areas. In particular, the mean particle size (d90) of the precipitated calcium carbonate (PCC) is determined by laser diffraction, in particular by a Coulter laser diffraction analyzer. In particular, the mean particle size (d90) of the precipitated calcium carbonate (PCC) is determined according to ISO 13320, in particular ISO 13320:2020.determined. Furthermore, the use of precipitated calcium carbonate (PCC) with a mean particle size (d90) of less than 50 µm as an inorganic pigment of the heat-sensitive layer according to the first aspect ensures that no further disturbances occur in the printed image. A corresponding heat-sensitive recording material according to the present invention also exhibits an image quality of the printed image comparable to, and in particular improved, that of conventional recording materials, which is characterized by the surface whiteness according to ISO 2470-2 (2008), the contrast between printed and unprinted areas, the optical density, and / or the image stability after storage of the heat-sensitive recording material. The heat-sensitive recording material here comprises a color layer with a 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 mixing red, green, and blue. In particular, the coloring agent imparts a color to the color layer 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 mixing red, green, and blue. In particular, the coloring agent imparts a color to the color layer on the side facing the heat-sensitive layer that is not white. The heat-sensitive layer of the heat-sensitive recording material covers the color layer at least partially, so that the color of the color layer, or the color of the side of the color layer facing the heat-sensitive layer,The heat-sensitive layer is not visible due to the heat-sensitive layer positioned above it, which is normally opaque. 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 enabling a printed image to be created on the heat-sensitive recording material. Furthermore, the use of precipitated calcium carbonate (PCC) with a mean particle size (d90) of less than 50 µm as the inorganic pigment of the heat-sensitive layer, as described in the first aspect, ensures advantageous ink deposition at the thermal printhead during thermal printing when using heat-sensitive recording material.so that no deposits are formed on the thermal printhead. According to one embodiment, the precipitated calcium carbonate (PCC) has a mean particle size (d90) of less than 40 µm, preferably less than 30 µm, more preferably less than 25 µm, more preferably less than 20 µm, most preferably less than 10 µm, and most preferably less than 5 µm. In particular, the mean particle size (d90) of the precipitated calcium carbonate (PCC) is determined by laser diffraction, in particular by a Coulter laser diffraction analyzer. In particular, the mean particle size (d90) of the precipitated calcium carbonate (PCC) is determined according to standard ISO 13320, in particular standard ISO, 13320:2020 bestimmt.According to one embodiment, the precipitated calcium carbonate (PCC) has a mean particle size (d50) of less than 50 µm, preferably less than 40 µm, more preferably less than 30 µm, more preferably less than 25 µm, more preferably less than 20 µm, most preferably less than 10 µm, more preferably less than 5 µm, more preferably less than 3 µm, and more preferably less than 2.5 µm. In particular, the mean particle size (d50) of the precipitated calcium carbonate (PCC) is determined by laser diffraction, especially by a Coulter laser diffraction analyzer. In particular, the mean particle size (d50) of the precipitated calcium carbonate (PCC) is determined according to ISO 13320, in particular ISO 13320. 13320:2020 bestimmt.According to one embodiment, the precipitated calcium carbonate (PCC) has a mean particle size (d10) of less than 50 µm, preferably less than 40 µm, more preferably less than 30 µm, more preferably less than 25 µm, more preferably less than 20 µm, most preferably less than 10 µm, more preferably less than 5 µm, more preferably less than 2 µm, and more preferably less than 1.5 µm. In particular, the mean particle size (d10) of the precipitated calcium carbonate (PCC) is determined by laser diffraction, especially by a Coulter laser diffraction analyzer. In particular, the mean particle size (d10) of the precipitated calcium carbonate (PCC) is determined according to ISO 13320, in particular ISO 13320. 13320:2020 bestimmt.According to one embodiment, the precipitated calcium carbonate (PCC) has a mean particle size (D4,3) of less than 50 µm, preferably less than 40 µm, more preferably less than 30 µm, more preferably less than 25 µm, more preferably less than 20 µm, most preferably less than 10 µm, more preferably less than 5 µm, and more preferably less than 3 µm. In particular, the mean particle size (D4,3) of the precipitated calcium carbonate (PCC) is determined by laser diffraction, especially by a Coulter laser diffraction analyzer. In particular, the mean particle size (D4,3) of the precipitated calcium carbonate (PCC) is determined according to ISO 13320, in particular ISO 13320. 13320:2020 bestimmt.This achieves the technical advantage that the very small mean particle sizes (d90), (d50), (d10), and (d4.3) of the precipitated calcium carbonate (PCC) ensure the advantageous properties of the heat-sensitive recording material. According to one embodiment, the precipitated calcium carbonate (PCC) comprises scalenohedral precipitated calcium carbonate (s-PCC), wherein, in particular, the proportion of the scalenohedral precipitated calcium carbonate (s-PCC) in the precipitated calcium carbonate (PCC) is more than 50%, preferably more than 60%, further preferably more than 70%, even more preferably more than 80%, most preferably more than 90%, and even more preferably more than 98%.In particular, the scalenohedral precipitated calcium carbonate (s-PCC) has a mean particle size (D4,3) of 2.2 to 2.6 µm, the mean particle size (D4,3) of the scalenohedral precipitated calcium carbonate (s-PCC) being determined according to ISO 13320, in particular ISO 13320:2020. In particular, the scalenohedral precipitated calcium carbonate (s-PCC) has a mean particle size (d10) of 0.8 to 1.4 µm, the mean particle size (d10) of the scalenohedral precipitated calcium carbonate (s-PCC) being determined according to ISO 13320, in particular ISO 13320:2020. In particular, the scalenohedral precipitated calcium carbonate (s-PCC) has a mean particle size (d50) from 2.0 to 2.4 ^m, wherein the mean particle size (d50) of the scalenohedral precipitated calcium carbonate (s-PCC) was determined according to standard ISO13320, in particular standard ISO 13320:2020.In particular, the scalenohedral precipitated calcium carbonate (s-PCC) has a mean particle size (d90) of 3.3 to 4.3 µm, the mean particle size (d90) of the scalenohedral precipitated calcium carbonate (s-PCC) being determined according to ISO 13320, in particular ISO 13320:2020. The scalenohedral precipitated calcium carbonate (s-PCC) is specifically characterized by a sieve residue obtained after treatment in the range of 0.37% to 0.83%, according to DIN EN ISO 787-7:2010 DE. According to one embodiment, the precipitated calcium carbonate (PCC) comprises precipitated calcium carbonate (PCC) having an aragonite structure, wherein in particular the proportion of the precipitated calcium carbonate (PCC) with the aragonite structure in the precipitated calcium carbonate (PCC) is more than 50%, preferably more than 60%, further preferably more than 70%, even more preferably more than 80%, most preferably more than 90%, and even more preferably more than 98%.In particular, the precipitated calcium carbonate (PCC) exhibiting an aragonite structure has a mean particle size (D4,3) of 1.5 to 1.7 µm, the mean particle size (D4,3) of the precipitated calcium carbonate (PCC) exhibiting an aragonite structure being determined according to ISO 13320, in particular ISO 13320:2020. In particular, the precipitated calcium carbonate (PCC) exhibiting an aragonite structure has a mean particle size (d10) of 0.4 to 0.6 µm, the mean particle size (d10) of the precipitated calcium carbonate (PCC) exhibiting an aragonite structure being determined according to ISO 13320, in particular ISO 13320:2020.In particular, the precipitated calcium carbonate (PCC) which has an aragonite structure has a mean particle size (d50) of 1.1 to 1.4 ^m, the mean particle size (d50) of the precipitated calcium carbonate (PCC) which has an aragonite structure being determined in accordance with standard ISO 13320, in particular standard ISO 13320:2020. In particular, the precipitated calcium carbonate (PCC), which has an aragonite structure, has a mean particle size (d90) of 3.0 to 3.4 µm, the mean particle size (d90) of the precipitated calcium carbonate (PCC) having an aragonite structure being determined according to ISO 13320, in particular ISO 13320:2020. Specifically, the precipitated calcium carbonate (PCC) having an aragonite structure is characterized by a sieve residue obtained after treatment in the range of approximately 0.02%, according to DIN EN ISO 787-7:2010 DE.According to one embodiment, the precipitated calcium carbonate (PCC) comprises precipitated calcium carbonate (PCC) having a prismatic structure, wherein in particular the proportion of the precipitated calcium carbonate (PCC) with the prismatic structure in the precipitated calcium carbonate (PCC) is more than 50%, preferably more than 60%, further preferably more than 70%, even more preferably more than 80%, most preferably more than 90%, and even more preferably more than 98%. According to one embodiment, the precipitated calcium carbonate (PCC) comprises precipitated calcium carbonate (PCC) having a rhombohedral structure, wherein in particular the proportion of the precipitated calcium carbonate (PCC) with the rhombohedral structure in the precipitated calcium carbonate (PCC) is more than 50%, preferably more than 60%, more preferably more than 70%, even more preferably more than 80%, most preferably more than 90%, and even more preferably more than 98%.This achieves the technical advantage that the specific structures of the precipitated calcium carbonate (PCC) ensure the advantageous properties of the heat-sensitive recording material. According to one embodiment, the precipitated calcium carbonate (PCC) comprises filtered precipitated calcium carbonate (PCC) and / or ground precipitated calcium carbonate (PCC) and / or sieved precipitated calcium carbonate (PCC). This achieves the technical advantage that the use of filtered precipitated calcium carbonate (PCC) and / or ground precipitated calcium carbonate (PCC) and / or sieved precipitated calcium carbonate (PCC) results in a heat-sensitive recording material that exhibits a particularly low number of white dots in a printed area.In particular, the ground precipitated calcium carbonate (PCC) can be produced by grinding precipitated calcium carbonate (PCC) using a mill, especially a bead mill, which has a throughput of between 20 and 60 L / min, preferably between 40 and 55 L / min. In particular, at least 0.1%, preferably 0.10% to 0.50%, and especially preferably 0.30% to 0.40% dispersing agent is added during the grinding process, and / or the precipitated calcium carbonate (PCC) is diluted with water from 55% to 45%. In particular, the sieved precipitated calcium carbonate (PCC) has a mean particle size (D4,3) of 2.3 to 2.5 ^m, the mean particle size (D4,3) of the sieved precipitated calcium carbonate (PCC) being determined in accordance with standard ISO 13320, in particular standard ISO 13320:2020.In particular, the sieved precipitated calcium carbonate (PCC) has a mean particle size (d10) of 1.1 to 1.3 ^m, the mean particle size (d10) of the sieved precipitated calcium carbonate (PCC) being determined in accordance with ISO 13320, in particular ISO 13320:2020. In particular, the sieved precipitated calcium carbonate (PCC) has a mean particle size (d50) of 2.2 to 2.3 µm, the mean particle size (d50) of the sieved precipitated calcium carbonate (PCC) being determined according to ISO 13320, in particular ISO 13320:2020. In particular, the sieved precipitated calcium carbonate (PCC) has a mean particle size (d90) of 3.8 to 4.1 µm, the mean particle size (d90) of the sieved precipitated calcium carbonate (PCC) being determined according to ISO 13320, in particular ISO 13320:2020.In particular, the sieved precipitated calcium carbonate (PCC) is characterized by a sieve residue of approximately 0.01% obtained after treatment, in accordance with the standard DIN EN ISO 787-7:2010 DE. Filtered precipitated calcium carbonate (PCC) can be produced by filtering precipitated calcium carbonate (PCC) through a filter, which in particular has a pore size of 25 µm. Ground precipitated calcium carbonate (PCC) can be produced by grinding precipitated calcium carbonate (PCC) using a mill, in particular a bead mill, which in particular has a throughput of between 20 and 60 L / min, preferably between 40 and 55 L / min. In particular, during the milling process at least 0.1%, preferably 0.10% to 0.50%, especially preferably 0.30% to 0.40% dispersing aid is added, and / or the precipitated calcium carbonate (PCC) is diluted from 55% to 45% with water.In particular, the ground precipitated calcium carbonate (PCC) has a mean particle size (D4,3) of 1.2 to 2.1 ^m, the mean particle size (D4,3) of the ground precipitated calcium carbonate (PCC) being determined in accordance with ISO 13320, in particular ISO 13320:2020. In particular, the ground precipitated calcium carbonate (PCC) has a mean particle size (d10) of 0.1 to 1.0 µm, the mean particle size (d10) of the ground precipitated calcium carbonate (PCC) being determined according to ISO 13320, in particular ISO 13320:2020. In particular, the ground precipitated calcium carbonate (PCC) has a mean particle size (d50) of 1.1 to 1.9 µm, the mean particle size (d50) of the ground precipitated calcium carbonate (PCC) being determined according to ISO 13320, in particular ISO 13320:2020.In particular, the ground precipitated calcium carbonate (PCC) has a mean particle size (d90) of 1.9 to 3.4 µm, the mean particle size (d910) of the ground precipitated calcium carbonate (PCC) being determined according to ISO 13320, in particular ISO 13320:2020. The ground precipitated calcium carbonate (PCC) is also characterized by a sieve residue obtained after treatment in the range of 0.01 to 0.03%, as determined according to DIN EN ISO 787-7:2010 DE. According to one embodiment, the precipitated calcium carbonate (PCC) is characterized by a sieve residue obtained after treatment of less than 1%, preferably less than 0.5%, further preferably less than 0.1%, and most preferably less than 0.05%, in accordance with the standard DIN EN ISO 787-7:2010 DE.This achieves the technical advantage that the sieve residue of the precipitated calcium carbonate (PCC) ensures the advantageous properties of the heat-sensitive recording material. According to one embodiment, the precipitated calcium carbonate (PCC) is present in the heat-sensitive layer in an amount of 3 wt.% to 20 wt.%, preferably in an amount of 5 wt.% to 15 wt.%, more preferably in an amount of 5 wt.% to 13 wt.%, and even more preferably in an amount of 6 wt.% to 12 wt.%, based on the total dry mass of the heat-sensitive layer. This achieves the technical advantage that the weight ranges defined for the precipitated calcium carbonate (PCC) ensure advantageous properties of the resulting heat-sensitive recording material. According to one embodiment, the precipitated calcium carbonate (PCC) has a calcium carbonate content of at least 98%, preferably at least 99%.According to one embodiment, the precipitated calcium carbonate (PCC) has a specific surface area between 1 m. 2 / g and 100 m 2 / g, preferably between 1 m 2 / g and 30 m² / g, more preferably between 7 m² / g and 11 m² / g. According to one embodiment, the heat-sensitive layer contains no chemical color developer and no chemical color former, in particular no leuco dye. Chemical color formers include 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 in the context of the present invention that the heat-sensitive layer of the heat-sensitive recording material contains no chemical color developer and no chemical color former.According to one embodiment, the at least one crosslinking agent is 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, methylol urea, melamine formal dehydrogenated oligomers, oxazoline resins, carbodiimide, borate compounds and mixtures thereof, and wherein the at least one crosslinking agent is preferably selected as ammonium zirconium carbonate and / or Polyamidoamine-epichlorohydrin resins (PAAE resin). According to one embodiment, the at least one crosslinking agent 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.% based on the total dry mass of the heat-sensitive layer, in the heat-sensitive layer. To achieve specific application-related performance characteristics of heat-sensitive recording materials, the polymeric binder present in the heat-sensitive layer is preferably in crosslinked form, with the optimal degree of crosslinking of the polymeric binder being established during the drying step of the coating process in the presence of a crosslinking agent. Ammonium zirconium carbonate and polyamidoamine epiclorohydrin 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 agent, thanks to the reactive, crosslinkable groups already incorporated in the binder polymer.According to one embodiment, the heat-sensitive layer comprises at least one wax selected from the group consisting of 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 preferably the at least one fatty acid amide comprises fatty acid monoamide, fatty acid diamide, fatty acid alkaloid, N-methyl fatty acid amide, and mixtures thereof, and / or wherein preferably the at least one fatty acid comprises a saturated fatty acid and / or an unsaturated fatty acid with at least 8 carbon atoms. In particular, the at least one wax comprises at least one synthetic wax and / or at least one biogenic wax, wherein the at least one biogenic wax particularly comprises at least one wax based on a vegetable oil, as characterized, for example, in EP 3508545.The term "biogenic" is understood in accordance with the standard ISO EN 13833:2013: substances that have been formed by living organisms in natural processes and are neither fossilized nor derived from fossil resources. 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 20 wt.% to 70 wt.%, more preferably in an amount of 25 wt.% to 60 wt.%, even more preferably in an amount of 30 wt.% to 50 wt.%, and most preferably in an amount of 35 wt.% to 45 wt.%.According to one embodiment, the at least one polymeric binder is selected from the group comprising water-soluble starches, starch derivatives, starch-based biolatices of the EcoSphere type, methylcellulose, hydroxyethylcellulose, carboxymethylcellulose, gelatin, casein, partially or fully saponified polyvinyl alcohols, chemically modified polyvinyl alcohols, ethylene-vinyl alcohol copolymers, sodium polyacrylates, styrene-maleic anhydride copolymers, ethylene-maleic anhydride copolymers, styrene-butadiene copolymers, acrylamide-(meth)acrylate copolymers, acrylamide-acrylate-methacrylate terpolymers, polyacrylates, poly(meth)acrylic acid esters, acrylate-butadiene copolymers, polyvinyl acetates, acrylonitrile-butadiene copolymers, and mixtures thereof, wherein the at least one binder is preferably selected as polyvinyl alcohol. In particular, this includes at least one binder of a synthetic or biogenic nature.The at least one binder of biogenic nature comprises, 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. The term "biogenic" is understood in accordance with the standard ISO EN 13833:2013: substances that have been produced by living organisms in natural processes and are neither fossilized nor derived from fossil resources. According to one embodiment, the at least one polymeric binder is present in the heat-sensitive layer in an amount of 0.5 wt.% to 25.0 wt.%, preferably in an amount of 1 wt.% to 10.0 wt.%, based on the total dry mass of the heat-sensitive layer.According to one embodiment, the heat-sensitive recording material, in particular the heat-sensitive layer, contains no organic pigments, especially no hollow sphere pigments. In particular, the heat-sensitive layer contains no styrene-acrylate copolymer hollow sphere pigment and / or no styrene-butadiene solid sphere pigment. According to another embodiment, the heat-sensitive layer contains organic pigments, in particular hollow sphere pigments, wherein the organic pigments, in particular hollow sphere pigments, are present in the heat-sensitive layer in an amount of 10 wt.% to 70.0 wt.%, preferably in an amount of 20 wt.% to 60.0 wt.%, more preferably in an amount of 30 wt.% to 50.0 wt.%, and most preferably in an amount of 35 wt.% to 45 wt.%.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 another embodiment, the heat-sensitive layer comprises, in particular, inorganic oil-absorbing white pigments. Specifically, the inorganic oil-absorbing white pigments comprise natural or calcined kaolin, kaolinite, silicon dioxide, bentonite, calcium carbonate, aluminum hydroxide, in particular boehmite, aluminum oxide, talc, calcium silicates, in particular circolite, 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.%, and 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 heat-sensitive layer comprises at least one auxiliary component.According to one embodiment, the 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.More preferably, the at least one additive comprises zinc stearate and / or calcium stearate. According to one embodiment, the at least one additive is present in a range of 0.01 wt.% to 5 wt.%, preferably 0.1 wt.% to 2 wt.%, based on the total dry mass of the heat-sensitive layer. This achieves the technical advantage of allowing for advantageous optimization of the applicability and / or the properties of the heat-sensitive layer.According to one embodiment, 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, dipentaerythritol, 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-dimethyl-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, euriamide and mixtures thereof, (f) Acrylic acid esters and / or acrylamide copolymer, including mixtures of subgroups a) to f).According to one embodiment, the heat-sensitive layer comprises at least one surfactant. In particular, the at least one surfactant comprises at least one ionic surfactant, wherein the at least one ionic surfactant comprises, in particular, sulfosuccinate. In particular, the surfactant comprises a trimethyl nonyl ether. 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 heat-sensitive layer. According to one embodiment, the heat-sensitive layer has an areal weight determined according to ISO 536 of 1 to 10 g / m², in particular 2 to 8 g / m². 2According to one embodiment, the heat-sensitive recording material has a basis weight of 20 g / m² to 100 g / m² as defined by ISO 536, preferably 35 to 80 g / m². According to one embodiment, the heat-sensitive layer has a thickness of 1 to 10 µm as defined by ISO 534, in particular 2 to 8 µm. According to one embodiment, the heat-sensitive recording material has a thickness of 10 µm to 100 µm as defined by ISO 534, preferably 20 µm to 80 µm. Bekk smoothness According to one embodiment, the carrier substrate on the side on which the color layer is applied has a Bekk smoothness measured according to the standard ISO 5267:1995-03 / DIN 53107 (2016) of greater than 20 s, preferably greater than 30 s, and even more preferably greater than 50 s.According to one embodiment, the paint layer on the side where the heat-sensitive layer is applied has a Bekk smoothness, measured according to ISO 5267:1995-03 / DIN 53107 (2016), of greater than 50 s, preferably greater than 100 s, and most preferably greater than 150 s. According to another embodiment, the heat-sensitive layer on the side where the paint layer is not located has a Bekk smoothness, measured according to ISO 5267:1995-03 / DIN 53107 (2016), of greater than 100 s, and most preferably greater than 250 s. 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, measured according to the standard ISO 5267:1995-03 / DIN 53107 (2016) on the side on which the color layer is applied.According to one embodiment, the paint layer on the side where the heat-sensitive layer is applied has a Bekk smoothness of 50 to 400 s, measured according to ISO 5267:1995-03 / DIN 53107(2016), particularly preferably 100 to 250 s, and most preferably 150 to 350 s. According to another 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 ISO 5267:1995-03 / DIN 53107(2016), and particularly preferably 500 to 1000 s. In particular, each layer applied to the substrate has a Bekk smoothness, measured according to ISO 5267:1995-03 / DIN 53107 (2016), on its top surface, i.e., the side not in contact with the substrate, that is at least as high as or greater than that of the layer below it. Specifically, each layer applied to the substrate has a Bekk smoothness on its top surface, i.e.,On the side not covered by the substrate, each layer must have a Bekk smoothness of at least 5% (percentage increase) as measured according to ISO 5267:1995-03 / DIN 53107 (2016) compared to the layer below it. Specifically, each layer applied to the substrate must have a Bekk smoothness of at least 5s (absolute increase) on its top surface, i.e., on the side not covered by the substrate, as measured according to ISO 5267:1995-03 / DIN 53107 (2016) compared to the layer below it. It is advantageous to begin with a smooth substrate and maintain this smoothness across the individual layers, since the smoother the substrate is built up from the bottom up, the better the final smoothness and thus the sensitivity of the final product.According to one embodiment, the heat-sensitive recording material has a Bekk smoothness of 100 to 1000 s, measured according to ISO 5267:1995-03 / DIN 53107 (2016), particularly preferably 200 to 800 s. Support substrate: According to one embodiment, the support substrate is selected from the group consisting of paper, single-sided coated paper, and double-sided coated paper. According to one embodiment, the support substrate has a basis weight of 20 to 100 g / m², preferably 35 to 80 g / m². According to one embodiment, the heat-sensitive recording material is characterized in that a layer comprising starch, also referred to as a starch coating, and / or its modifications is present directly on at least one side of the support substrate, preferably directly on both sides of the support substrate. The starch coating is preferably applied in an amount of 0.1 g / m². 2 up to 3 g / m² 2 , particularly preferably of 0.2 g / m³2 bis 1.5 g / m 2, applied. A starch coating on the side of the substrate where the ink layer is present has the advantage of sealing the substrate, thus improving the adhesion of the ink layer and reducing or preventing penetration of the ink layer into the substrate. A starch coating on the side of the substrate where the ink layer is not present has the advantage of reducing or preventing bleed-through of the ink layer through the substrate. The starch coating on the side of the substrate where the ink layer is not present is also referred to as the back layer of the heat-sensitive recording material. The layer, comprising starch, preferably has a Bekk smoothness of greater than 10 s, measured according to ISO 5267:1995-03, and particularly preferably greater than 15 s.According to one embodiment, the heat-sensitive recording material is characterized in that, as described in US Patent 8,445,104, a basecoat layer and adhesive layer are present directly on the first, lower side of the support substrate, and a heat-sensitive (color) layer, preferably with a topcoat, is present directly on the second, upper side of the support substrate. According to one embodiment, the coloring agent of the color layer comprises at least a pigment and / or a dye, which is particularly of a synthetic or biogenic nature. The term "biogenic" is understood in accordance with the standard ISO EN 13833:2013 to mean substances that have been produced by living organisms in natural processes and are neither fossilized nor derived from fossil resources.In particular, the raw material source for the general biomass of a corresponding biogenic material is (waste) wood, wood waste, residual wood, lignin, plants, algae, and / or paper fiber sponges. The pigments and / or dyes specifically comprise various organic and inorganic pigments, dyes, and / or carbon black. These can be used alone or in any mixture. The pigment, dye, and / or carbon black are preferably each present in the paint layer in an amount of 2 to 60% by weight, particularly preferably 20 to 55% by weight, based on the total dry mass of the paint layer. According to one embodiment, the paint layer comprises a binder.Preferably, 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, and / or acrylonitrile-butadiene copolymers are used as binders. These can be used alone or in any mixtures. The binder is preferably contained in the paint layer in an amount of 2 wt.% to 40 wt.%, particularly preferably 10 wt.% to 30 wt.%, based on the total dry mass of the paint layer.The paint layer preferably has a basis weight of 1 to 10 g / m². 2, in particular from 3 to 10 g / m². The ink layer preferably has a thickness of 1 to 10 µm, in particular from 2 to 8 µm. Protective layer and / or non-stick coating. According to one embodiment, the heat-sensitive recording material has a protective layer and / or non-stick coating which is arranged on the heat-sensitive layer. The protective layer and / or non-stick coating is thus located on the side of the heat-sensitive layer facing away from the ink 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 500 s, preferably at least 750 s and particularly preferably at least 1000 s, as measured according to ISO 5267:1995-03. Preferably, the Bekk smoothness of the protective layer, measured according to standard ISO 5267:1995-03, is not more than 2000 s, preferably not more than 1600 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(s). If at least one pigment is present in the protective layer, this at least one pigment is present in an amount of less than 5% by weight, in particular from more than 0% by weight to less than 5% by weight, 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% by weight, in particular from more than 0% by weight to less than 4% by weight, or less than 3% by weight, in particular from more than 0% by weight to less than 3% by weight, or less than 2% by weight, in particular from more than 0% by weight to less than 2% by weight, or less than 1% by weight.-%, in particular from more than 0 wt.% to less than 1 wt.%, or from less than 0.5 wt.%, in particular from more than 0 wt.% to less than 0.5 wt.%, or from less than 0.2 wt.%, in particular from more than 0 wt.% to less than 0.2 wt.%, or from less than 0.1 wt.%, in particular from more than 0 wt.% to less than 0.1 wt.%, or from less than 0.01 wt.%, in particular from more than 0 wt.% to less than 0.01 wt.%, or, apart from unavoidable impurities or unavoidable traces, no pigments or no pigments at all. These quantities refer in each case to the dry mass of the protective layer. Unavoidable impurities or unavoidable traces of pigments can, for example, enter the protective layer due to the manufacturing process if pigments were or are processed in the production plant (pigment-containing coatings), e.g.The pigment is introduced during the application of previously applied, pigment-containing layers (pigments of the insulating layer, the color layer, or the heat-sensitive layer). Without being bound by this theory, the inventors observed that the less pigment is contained in the protective layer, the higher the Bekk smoothness can be set, which in turn is advantageous for the sensitivity or optical density of the heat-sensitive recording material. Surprisingly, it has been shown that the proportion of pigments in the protective layer can be reduced without compromising the protective effect for certain requirements. Furthermore, it has been shown that the relative print contrast can even be increased and / or improved as a result. The at least one pigment is preferably selected from organic and / or inorganic pigments.Suitable pigments include inorganic pigments of both synthetic and natural 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, but 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 it 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 an amount of 40% to 90% by weight.-%, particularly preferably in an amount of 50 wt.% to approximately 80 wt.%, based on the total dry mass of the protective layer, in the protective layer. To achieve specific application-related performance characteristics of heat-sensitive recording materials, the binder is preferably present in cross-linked form in the protective layer, the optimal degree of cross-linking of the binder being achieved during the drying step of the coating process in the presence of a cross-linking agent. 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, methylol urea, melamine formal dehydoligomers, etc.These can be used alone or in any mixture. Ammonium zirconium carbonate and polyamidoamine epiclorhydrin resins (PAAE resins) are particularly preferred for food safety reasons. Self-crosslinking binders, such as specially modified polyvinyl alcohols or acrylates, enable crosslinking without any crosslinking agent, thanks to the reactive, crosslinkable groups already incorporated into the binder polymer. The crosslinking agent is preferably present in an amount of 0.01 wt.% to 25.0 wt.%, and 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 lubricants 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...Stearamide and behenamide, fatty acid alkanolamides, such as stearic acid methylolamide, paraffin waxes of various 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. Preferably, the lubricants are based on waxes or fats, fatty acids, or salts of fatty acids. The lubricant is preferably present in an amount of 1 to approximately 30 wt.%, particularly preferably in an amount of approximately 2 to approximately 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 are based on silicones, such as those known from US 2006 / 0063013A1, the disclosure of which is hereby fully incorporated. The release agent is preferably present in an amount of approximately 1 to approximately 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 rheology aids are thickeners and surfactants. For further details, reference is made to the selections for the heat-sensitive layer, which also apply in full to the protective layer. Preferably, the protective layer comprises at least one lubricant / release agent, at least one binder, and at least one crosslinker. 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 / m³2 and 1.5 g / m² 2Surprisingly, 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, particularly 0.5 µm to 2.0 µm. Instead of the protective layer, a non-stick coating can be present, or the protective layer itself can be designed as a non-stick coating, or the non-stick coating can be applied to the protective layer. Thus, the protective layer, or non-stick coating, can 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 a carrier-less ("linerless") heat-sensitive recording material. In particular, this also has the advantage that the heat-sensitive recording material can be wound onto itself without requiring a carrier ("linerless"), and after unwinding the self-wound heat-sensitive recording material, it exhibits no deterioration in its paper-related 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 liner, and more labels can be transported per specific cargo space volume. A corresponding non-stick coating preferably comprises a siliconized coating based on siloxanes. 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. In particular, a starch coating, orIf a starch coating is present as a backing layer and an adhesive layer is also present, this starch coating is located between the substrate and the adhesive layer. For further details regarding the starch coating described as a backing layer, reference is made to the extensive previous descriptions under the sub-section "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 the 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. Separation layer. According to one embodiment, the heat-sensitive recording material has a separation layer, in particular a siliconized separation layer, which is arranged on the heat-sensitive layer. The siliconized separation layer preferably has a Bekk smoothness of greater than 400 s, measured according to ISO 5267:1995-03, particularly preferably greater than 800 s, and most preferably between 800 and 2000 s. If a protective layer, in particular as defined above, is present on the heat-sensitive layer, the siliconized separation 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 separation 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 release 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 release layer diffuse into the upper region of the underlying layer. Such a diffusion layer is described, for example, in EP 3221153 A1. A siliconized release layer is preferably present when an adhesive coating, 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 without the ink layer offers the advantage that the heat-sensitive recording material can be used as a linerless heat-sensitive recording material. This is particularly advantageous because the heat-sensitive recording material can be wound onto itself without requiring a support ("linerless"), and after unwinding, the heat-sensitive recording material exhibits no significant deterioration in its properties.This also has the advantage that manufacturing costs can be further reduced, more linear meters per roll can be achieved, no disposal costs are necessary for the liner, and more labels can be transported per specific cargo space volume. If a siliconized release layer is present, it is particularly preferred that the layer directly beneath the siliconized release layer contains at least one platelet-shaped pigment. The at least one platelet-shaped pigment is preferably selected from the group consisting of kaolin, Al(OH)3, and / or talc. 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, particularly kaolin, has the advantage that the heat-sensitive layer, or the layer directly beneath the siliconized release layer, can be siliconized very effectively. A platelet-shaped pigment is defined as a pigment in which the diameter-to-thickness ratio is approximately 7 to 40:1, preferably approximately 15 to 30:1. The particle size of the platelet-shaped pigment is preferably adjusted such that at least approximately 70%, preferably at least approximately 85%, of the particles have a particle size of approximately < 2 µm (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 beneath the siliconized release layer, preferably in an amount of approximately 5 to approximately 60 wt.-%, particularly preferably in the 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 beneath the siliconized release layer, the platelet-shaped pigment is present in the amounts 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 release layer comprises at least one siloxane, preferably a poly(organo)siloxane, in particular an acrylic poly(organo)siloxane. In a further embodiment, the siliconized release layer comprises a mixture of at least two siloxanes. A mixture of at least two acrylic poly(organo)siloxanes is preferred. Examples of particularly preferred siloxanes are those 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 separation layer contains at least one polysilicone acrylate, preferably formed by the condensation of at least one silicone acrylate. In a preferred embodiment, the siliconized separation layer is a heat-cured separation layer. This separation layer is formed in the presence of a Pt catalyst. The siliconized separation layer is preferably anhydrous. It is also preferred that the siliconized separation layer does not contain any Pt catalysts. The siliconized separation layer preferably contains an initiator, particularly preferably a photoinitiator. This serves for the radical curing of the silicone. 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 promoters. 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 2The siliconized separating layer preferably has a thickness of 0.3 to 6.0 µm, in particular 0.5 to 2.0 µm. Intermediate layer: According to one embodiment, the heat-sensitive recording material has at least one intermediate layer arranged between the support substrate and the heat-sensitive layer, wherein the at least one intermediate layer particularly comprises calcined kaolin and / or a hollow sphere pigment. In particular, the at least one intermediate layer comprises an insulating layer arranged between the support substrate and the color layer. According to an alternative embodiment, the color layer is simultaneously configured as a color layer and an insulating layer. Such an insulating layer, or a color layer that is simultaneously a color layer and an insulating layer, reduces the heat conduction through the heat-sensitive recording material.This makes the local application of heat by means of a direct thermal printer more efficient and allows for higher thermal printing speeds. The top layer becomes translucent more quickly due to the applied heat, thus improving sensitivity. This reduces the amount of ink required, resulting in improved recyclability in the recycling loop, particularly in the waste paper cycle, due to easier deinkability and separation of ink and substrate components. The insulating layer, or the ink layer, which is simultaneously an ink layer and an insulating layer, preferably has a Bekk smoothness, measured according to standard 5267:1995-03, of greater than 50 s, particularly preferably greater than 100 s, and most preferably from 100 to 350 s. The insulating layer, or the ink layer, which is simultaneously an ink layer and an insulating layer, preferably comprises a heat-insulating material.Preferably, the heat-sensitive recording material with an insulating layer or a color layer that is simultaneously 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 is simultaneously an insulating layer. The heat-insulating material preferably comprises kaolin, particularly preferably calcined kaolin, and mixtures thereof. In particular, the heat-insulating material also comprises mixtures of kaolin, particularly preferably calcined kaolin, and calcium carbonate. The heat-insulating material is preferably present in the insulating layer in an amount of 20 wt.% to 80 wt.%, particularly preferably in an amount of 40 wt.% to 60 wt.%, based on the total dry mass of the insulating layer.In a paint layer that simultaneously serves as a paint layer and an insulating layer, the heat-insulating material is preferably present in an amount of 30 wt.% to 70 wt.%, and particularly preferably in an amount of 40 wt.% to 60 wt.%, based on the total dry mass of the paint layer. The insulating layer preferably has a basis weight of 1 to 5 g / m². 2 , especially from 2 to 4 g / m³ 2The insulating layer preferably has a thickness of 1 to 10 µm, in particular 2 to 8 µm. The ink layer, which is simultaneously a color layer and an insulating layer, preferably has an areal weight of 1 to 10 g / m², in particular 2 to 8 g / m². The ink layer, which is simultaneously a color layer and an insulating layer, preferably has a thickness of 1 to 12 µm, in particular 4 to 8 µm. Parameters: According to one embodiment, the heat-sensitive recording material has an optical density (OD) defined according to the description of at least 0.9, preferably at least 1.1, and most preferably at least 1.15, where in particular measurements were taken at an energy level of 8.88 mJ / mm², and / or the heat-sensitive recording material has an optical density (OD) defined according to the description.According to one embodiment, the heat-sensitive recording material has an optical density (o.D.) of at least 1.0, preferably at least 1.2, and most preferably at least 1.3, measured particularly at an energy level of 14.57 mJ / mm². The optical density (o.D.) was measured particularly at a temperature of 100°C using a densitometer from Techkon (model SpectroDens), particularly at an energy level of 8.88 mJ / mm² or 14.57 mJ / mm². 2The measurement uncertainty of the O.D. values ​​is, in particular, ≤2%. Specifically, 6 cm wide strips of the heat-sensitive recording material were thermally printed using a GeBE PrinterLab GPT-10000 test printer (GeBE Elektronik und Feinwerktechnik GmbH, Germany) with a Kyocera printhead of 305 dpi at an applied voltage of 24 V and a printhead pressure of 15.7 N with a checkerboard pattern with 10 energy levels, using, in particular, a printing speed of 101 mm / s. According to one embodiment, the heat-sensitive recording material has a print contrast of the heat-sensitive layer, as defined in the description, of at least 35%, preferably at least 40%, more preferably at least 45%, even more preferably at least 50%, and further still preferably at least 55%.The relative print contrast (DK in %) is calculated from the optical density (o.D.) of a thermally printed area, i.e., the optical density of a print pattern at an energy level of 8.88 mJ / mm² (oDs), and the optical density of an unprinted area (oD0) according to the following Equation 1, where s is the printed area, and where 0 is the unprinted area, and where the dispersion of the calculated % values ​​is ≤^2 percentage points: Relative print contrast in % = (oDs – oD0 / oDs) x 100 (Equation 1). According to one embodiment, after a period of four weeks, according to the image retention storage test defined in the description, a remaining image retention of the heat-sensitive layer of at least 95%, preferably at least 96%, more preferably at least 97%, and still more preferably at least 98%, is obtained. Furthermore, at least 99% are preferred.and most preferably retain 100% of the original image fastness of the heat-sensitive layer. In the context of the present disclosure, the image fastness storage test defined below comprises storing the printed heat-sensitive recording material for a period of four weeks between two glass plates at 60°C, at a pressure of 1350 N / m², at a relative humidity of 50%, and in the absence of light. Within the scope of the storage test according to the present invention, the image fastness of the heat-sensitive recording material is determined based on the relative print contrast determined according to Equation 1, once before storage of the heat-sensitive recording material and once after the four-week storage period. The two determined values ​​of the relative print contrast are compared.as illustrated by the following Equation 2, where the dispersion of the calculated % values ​​is ≤^2 percentage points: Image retention / Writing performance in % = (relative print contrast after storage / relative print contrast before storage) x 100 (Equation 2). In particular, the printed and unprinted areas of the printed strip were analyzed to determine the image retention. According to one embodiment, after a period of four weeks, the writing performance of the heat-sensitive layer is at least 95%, preferably at least 96%, more preferably at least 97%, even more preferably at least 98%, and further still more preferably at least 99%, according to the writing performance storage test defined in the description.and most preferably retain 100% of the original writing performance of the heat-sensitive layer. In the context of the present invention, the writing performance storage test defined below comprises storing an unprinted heat-sensitive recording material for a period of four weeks between two glass plates at 60°C, at a pressure of 1350 N / m², at a relative humidity of 50% and in the absence of light.After storage and acclimatization to room temperature, the unprinted heat-sensitive recording material was printed according to the above-mentioned method for determining the optical density. The printed and unprinted areas were measured to determine the optical density (o. D.) and, to determine the relative print contrast, were related to the corresponding optical density values ​​of the printed strip before storage according to Equation 2 above. According to one embodiment, the heat-sensitive recording material has a surface whiteness, measured according to ISO 2470-2 (2008), of more than 35%, preferably more than 40%. In particular, the surface whiteness is between 40% and 45%. After printing, a high relative print contrast is achieved with advantageous application-related properties, such as improved readability.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 characterized in that the contrast between areas where the heat-sensitive layer has become translucent due to local heat exposure and areas where the heat-sensitive layer has not become translucent due to local heat exposure is 40 to 80%, in particular 50 to 70%. This contrast can be calculated by subtracting the optical density of the background from that of the text. The optical density (o. D.) is measured, for example, using a densitometer. According to one embodiment, the heat-sensitive recording material is characterized in thatthat it exhibits a deposit behavior of at least "average grade ("0")" in a long-term thermal printer test (10 km) under the pressure of a print pattern with 10 energy levels, whereby after a test run of 10 km on a commercially available thermal printer, in particular model Diebold Nixdorf P1200, a visual inspection for deposits on the thermal printhead was carried out, and the assessment was based on the following grading system: grade very good ("++") = no deposit, grade good ("+") = slight deposit, grade average ("0") = medium deposit,A poor rating (“-”) indicates severe delamination. Marketable heat-sensitive recording materials exhibit at least average delamination (average rating “0”). According to one embodiment, the heat-sensitive recording material has a recyclability rating according to INGEDE Method 11 in a range of 0 to 100 points. The recyclability of the heat-sensitive recording material is characterized according to INGEDE Method 11 by the following scores according to the Assessment of Printed Product Recyclability, Deinkability Score (according to Issue 2, January 2017): a) Brightness Y maximum 35 points, b) Colour coefficient a* in the CIELAB system maximum 20 points, c) Dirt points A in the two different size classes A50 maximum 15 points and A250 maximum 10 points, d) Degree of dye removal (printing ink removal) IE maximum 10 points, and e) Filtrate darkening ΔY maximum 10 points, where the sum of all points in the range of 0 to 100,preferably in the range of 51 to 70, particularly preferably in the range of 71 to 100, and / or preferably no single point value is negative. Preferably, the sum of all points is in the range of 0 to 50, preferably in the range of 51 to 70, particularly preferably in the range of 71 to 100. Particularly preferably, no single point value is negative. Most preferably, the sum of all points is in the range of 0 to 50, preferably in the range of 51 to 70, particularly preferably in the range of 71 to 100, and no single point value is negative. Method, Product-by-Process, and Use The aforementioned problems are solved according to the second aspect by a method for producing a heat-sensitive recording material, comprising the following process steps: providing a carrier substrate,which has a first side and a second side facing away from the first side; application of a color layer suspension to the first side or second side of the support substrate, wherein the color layer suspension comprises at least one coloring agent; in particular, drying the color layer suspension to obtain a color layer arranged on the first side or second side of the support substrate; application of a coating suspension to the color layer, wherein the coating suspension comprises at least one polymeric binder, at least one crosslinking agent, and at least one inorganic pigment, wherein the inorganic pigment comprises precipitated calcium carbonate (PCC), wherein the precipitated calcium carbonate (PCC) has a mean particle diameter (d90) of less than 50 µm; and in particular, drying the coating suspension to obtain a heat-sensitive layer arranged on the color layer. It is preferred thatThe heat-sensitive recording material according to the invention is obtained by a method in which dispersions, particularly aqueous dispersions, comprising the starting materials of the individual layers, are successively applied to the carrier substrate, wherein the coating suspensions, particularly aqueous dispersions, have a dry mass of 8 to 50 wt., and are applied using the blade coater coating method at an operating speed of the coating system of at least 200 m / min, particularly at least 900 m / min. This method is particularly advantageous from an economic point of view and due to the uniform application over the carrier substrate. If the dry mass falls below 8 wt.%, the economic efficiency deteriorates, since a large quantity of water must be removed by gentle drying in a short time.which has a negative impact on the coating speed. On the other hand, if the value of 60 wt.% is exceeded, this only leads to increased technical effort to ensure the stability of the coating curtain during the coating process and the drying of the applied film, since the machine must then run very fast again. In the curtain coating process, a freely falling curtain of coating dispersion is formed. By free fall, the coating dispersion, which is present in the form of a thin film (curtain), is "poured" onto a substrate in order to apply the coating dispersion to the substrate. DE 10196052 T1 discloses the use of the curtain coating process in the production of information recording materials, wherein multi-layered recording layers are created by applying the,The coating process can be realized as a curtain consisting of several coating dispersion films on substrates. It is also conceivable to use embodiments of the process according to the invention in which a "double curtain" is employed. 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 before the next layer is applied. The application of the two layers is thus preferably carried out "wet-on-wet". All definitions regarding 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 thatthat the two layers exhibit a stronger bond and, in particular, that intermediate adhesion promoters can be dispensed with. In a preferred embodiment of the method according to the invention, 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. The viscosity of the aqueous, deaerated coating suspension is preferably approximately 200 to approximately 500 mPas. The viscosities of successive coatings in the double curtain should decrease from bottom to top. With incorrectly adjusted coatings, the probability of heel formation at the curtain's point of contact increases, as does the occurrence of "wetting defects." 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...The dynamic surface tension of the coating paint can be determined and adjusted by selecting the appropriate surfactant and calculating the required amount. Dynamic surface tension is measured using a bubble pressure tensiometer. This measures the maximum internal pressure of a gas bubble formed by a capillary in a liquid. According to the Young-Laplace equation, the internal pressure p of a spherical gas bubble (Laplace pressure) depends on the radius of curvature r and the surface tension σ. When a gas bubble is created at the tip of a capillary in a liquid, the curvature initially increases and then decreases, resulting in a pressure maximum. The greatest curvature, and therefore the highest pressure, occurs when the radius of curvature equals the capillary radius. Pressure profile during bubble 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 p0, which results from the immersion depth and the density of the liquid, must be subtracted from the measured pressure (this is done automatically in modern measuring instruments).This results in the following formula for the bubble pressure method: The measured value corresponds to the surface tension at a specific surface age, and the time from the beginning of bubble formation until the pressure maximum occurs. By varying the bubble generation rate, the dependence of the surface tension on the surface age can be determined, resulting in a curve where the surface tension is plotted against time. This dependence plays an important role in the application of surfactants, as the equilibrium value of the interfacial tension is often not reached in many processes due to the sometimes low diffusion and adsorption rates of surfactants. The formation of the individual layers can take place online or offline in a separate coating process.To ensure that the layers described in detail above exhibit the aforementioned Bekk smoothness, the following process steps are preferably carried out. The substrate is preferably smoothed in a first cylinder. This high level of smoothness on one or both sides, produced by this process technique, 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 serves to create good profiling. If a thickness coating, 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 reverse side is particularly advantageous to prevent the coating color 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 with a film press or even a curtain coater. While this eliminates the advantage of smoothness, it could be compensated for, especially with a film press, using a calender. The insulating layer, if present, is applied analogously. The same applies to the protective layer. Alternatively, the protective layer can also be printed on or applied with a curtain coater.Protective coatings 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 coating 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) moistening system. For this purpose, a film of water is applied to the less coated side and then dried. This restores the flatness. Applying the water film slightly degrades the surface. A steam humidifier would be a preferred alternative for protecting the surface.In this process, steam is blown in instead of water being applied. This does not damage the surface. This is very well suited for applications where the highest surface quality is required. Another possibility would be a spray humidifier that applies a water mist. All of the aforementioned layers can be single- or multi-layered. The embodiments described 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. The aforementioned tasks are solved according to the third aspect by a heat-sensitive recording material that can be produced by a method according to the second aspect.The embodiments of the heat-sensitive recording material described in the first aspect and the embodiments of the method for producing a heat-sensitive recording material described in the second aspect are also embodiments of the heat-sensitive recording material producible by a method described in the third aspect. According to a fourth aspect, the present invention relates to the use of a heat-sensitive recording material according to the first or third aspect as a receipt roll, adhesive label roll, ticket roll, or as printer paper for mechanical printers or pens, or as carbonless copy paper. The embodiments of the heat-sensitive recording material described in the first aspect and the embodiments of the method for producing a heat-sensitive recording material described in the second aspect are also embodiments for use according to the fourth aspect.FIGURES 1, 2 and 3 Reference is made to the accompanying Figure 1, which shows electron micrographs of precipitated calcium carbonate (PCC) used in a heat-sensitive layer of a heat-sensitive recording material according to the present invention. Figures 1A, 1B, 1C and 1D show different structures of precipitated calcium carbonate (PCC) obtained using a scanning electron microscope (Hitachi FlexSEM 1000 model) at 10,000x magnification (Figures 1A, 1C and 1D) and at 5,000x magnification, respectively. Figure 1A shows rhombohedral precipitated calcium carbonate (PCC). Figure 1B shows precipitated calcium carbonate (PCC) with a prismatic structure. Figures 1C and 1D show scalenohedral precipitated calcium carbonate (s-PCC).Figure 2 shows a schematic print in which light defects or white dots appear in a dark print area. These defects are disadvantageous and are to be avoided or their number reduced within the scope of the present invention. Figures 3A and 3B show schematic prints. While the print according to Figure 3A shows no print image defects, the print according to Figure 3B shows a multitude of print image defects, which manifest as unprinted and / or weakly printed areas over a large part of the length. Within the scope of the present invention, the corresponding print image defects shown in Figure 3B are to be avoided or their number reduced. EXAMPLES OF EMBODIMENT In the following embodiments described in detail, several heat-sensitive recording materials or...Thermal papers are produced by applying aqueous coating suspensions to form a composite structure on a substrate and are examined and evaluated using various measurement methods. In all examples, a paper substrate made from hardwood and softwood pulp with a basis weight of 38 g / m² is used as the substrate. Measurement methods: Measurements of the occurrence of white dots or light defects in a dark print area: To assess the occurrence of white dots or light defects in a dark print area, an area of ​​approximately 7 x 2.5 cm was thermally printed across the entire surface using a standard Epson TM T-88VI thermal printer. Here, the perception of white dots and their frequency is qualitatively assessed using the following ratings (as shown, for example, in Figure 2): “--” (very bad), “-” (bad), “0” (average), “+” (good), “++” (very good).Measurement of Print Image Defects: Print image defects are determined during the thermal printer long-term test (10 km) to measure the ink drop behavior. After each 1 km run, a visual inspection is performed to check for print image defects within the print motif in the direction of travel. Corresponding print image defects are indicated by unprinted and / or weakly printed areas over a large portion of the run (as shown, for example, in Figure 3B). The evaluation is performed in the categories: "--" (very poor), "-" (poor), "0" (average), "+" (good), "++" (very good). Measurement of Ink Drop Behavior: The ink drop behavior of a thermal printhead was evaluated using a commercially available thermal printer (model: DN P1200) in a thermal printer long-term test (10 km) under the printing of a repeating print motif. After the 10 km test run, a visual inspection for deposits on the thermal printhead was carried out.The assessment was based on the following rating system: Rating “++” = no deposition, “+” = slight deposition, “0” = medium deposition, “-” = severe deposition. Commercially available heat-sensitive recording materials, in particular, exhibit medium deposition (rating: “0”) or better. 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 print bar of 305 dpi at an applied voltage of 24 V and a maximum pulse width of 0.8 ms with a checkerboard pattern with 10 energy levels. The optical density (o. D.) was measured using a Techkon densitometer (model SpectroDens) at energy levels of 8.88 mJ / mm² and 14.57 mJ / mm². The measurement uncertainty of the o. D. values ​​is estimated at ≤2%.Measurement of relative print contrast: The relative print contrast was calculated from the optical density of a thermally printed area (oDs) and the optical density of an unprinted area (oD0) according to Equation 1 below, where s represents the printed area and 0 represents the unprinted area: Relative print contrast in % = (oDs – oD0 / oDs) x 100 (Equation 1) Measurement of surface whiteness: The surface whiteness was determined according to ISO 2470-2 (2008) using an Elrepho 3000 spectrophotometer. Measurement of Bekk smoothness: The Bekk smoothness was determined according to DIN 53107 (2016).Measurement of resistance to plasticizers (omni-film): A plasticizer-containing cling film (PVC film with 20 to 25% dioctyl adipate) was applied to two printed strips of the heat-sensitive recording material, taking care to avoid creases and air inclusions. The film was then rolled into a roll and stored for 16 hours. One strip was stored at room temperature (20 to 22 °C), the second at 40 °C. After removing the film, the optical density of the printed and unprinted areas was measured and, to determine image stability and recording performance, related to the corresponding optical density values ​​before plasticizer exposure, according to the formula in Equation 2.Image retention / writing performance in % = (relative print contrast after storage / relative print contrast before storage) x 100 (Equation 2) Measurement of resistance to adhesive: Two strips of the heat-sensitive recording material were printed and the optical density (n.d.) was determined according to the description. Transparent Tesa self-adhesive tape (tesafilm® crystal clear, #57315) was applied to one strip, and a strip of Tesa packaging tape (#04204) was applied separately, avoiding creases and air inclusions. After storage at room temperature (20-22 °C), the optical density (n.d.) of the printed and unprinted areas was measured through the respective adhesive tape after seven days and related to the corresponding optical density values ​​of the freshly taped samples to determine the relative print contrast according to the formula (Equation 2).Measurement of resistance to hydrophobic and hydrophilic agents: On printed strips of the heat-sensitive recording material, one drop / fingertip each of sunflower oil (Nestle - Thomy 100% pure sunflower oil), lard (LARU GmbH pork lard), hand cream (lanolin hand cream), sweat (manufactured according to DIN EN ISO 105-E04), milk (3.5% fat), ethanol (40% in water), and water (tap water) were applied to a printed and an unprinted area. After an exposure time of 30 minutes, the agents were removed by brief contact with a standard kitchen towel, and the papers were stored at room temperature (20–22 °C). After a specific storage time (see Table 1), the optical density (n.d.) was measured.The optical density of the printed and unprinted areas was measured and related to the corresponding optical density values ​​before the application of the agents, according to formula (Equation 2). Measurement of the storage life of the heat-sensitive recording materials: A strip of the heat-sensitive recording material was printed and its optical density (n.d.) was measured according to the description (n.d. before storage). This strip, along with an unprinted strip of the same heat-sensitive recording material, was then stored for four weeks between two glass plates at 60 °C and a pressure of 1350 N / m. 2The strip was subjected to a relative humidity of 50% and in the absence of light. After storage and acclimatization to room temperature, the unprinted strip was printed (remaining writing performance). The printed and unprinted areas were measured to determine the optical density (n.d.) and the relative print contrast was determined according to Equation 2 in relation to the corresponding optical density values ​​of the printed strip before storage. The printed and unprinted areas of the printed strip were also measured (remaining image fastness) and the relative print contrast was determined according to Equation 2 in relation to the corresponding optical density values ​​before storage. Equipping the heat-sensitive recording materials as self-adhesive labels: The following describes the application of an adhesive layer to the reverse side of an A4 sheet.The adhesive dispersion is applied with a squeegee to the reverse side of an A4 sheet of paper (heat-sensitive recording material) that carries the heat-sensitive layer on the front side, and dried at a maximum temperature of 70 °C using a hot air gun. To protect the adhesive layer during further processing, a siliconized release paper is laminated onto the adhesive layer, taking care to avoid air bubbles and creases. If an "adhesive-liner sandwich" is used, consisting of a thin adhesive layer sandwiched between two release papers, the adhesive layer (sticky side) is laminated to the reverse side of the A4 thermal paper after one of the liner papers has been removed, again avoiding air bubbles and creases. It is irrelevant whether the adhesive layer is applied first during label production and the heat-sensitive recording layer is then applied to the opposite side, which carries the adhesive layer.To assemble self-adhesive labels, a removable acrylate-based adhesive (R5000N, Avery Fasson) was used as a commercially available adhesive. Adhesive migration test of heat-sensitive labels: A strip of the heat-sensitive recording material was printed and measured (no date before storage) and, together with an unprinted strip of the same heat-sensitive recording material, stored for four weeks between two glass plates at 60 °C and a pressure of 1350 N / m. 2, subjected to a relative humidity of 50% and in the absence of light. After storage and acclimatization to room temperature, the unprinted strip was printed (= remaining writing performance), the printed and unprinted areas were measured, and the relative print contrast was determined according to Equation 2 in relation to the corresponding optical density values ​​of the printed strip before storage. The printed and unprinted areas of the printed strip are also measured (= remaining image retention) and the relative print contrast is determined according to Equation 2 in relation to the corresponding optical density values ​​before storage. Production of the heat-sensitive recording materials: The dry content (D) of the respective layer formulations of the layers listed below is adjusted by adding water as follows: Insulating, orColor layer (46%), heat-sensitive layer (20%), and protective layer (10%). The raw materials used are in dispersion or solution form with the following dry solids: styrene-acrylate copolymer (32%), styrene-butadiene latex (48%), carbon black (45%), sodium metaborate tetrahydrate (0.5%), stearamide wax (22%), silicon dioxide (28%), zinc stearate (35%), calcium stearate (35%), high-viscosity polyvinyl alcohol (10%), calcined kaolin (45%), precipitated calcium carbonate (58%), ammonium zirconium carbonate (9%), polyamidoamine epichlorohydrin (10%), and low-viscosity polyvinyl alcohol (7%). The quantities [wt.%] refer to the oven-dry state. On a laboratory scale, the aqueous coating suspensions for the formation of the insulating and ink layer, the heat-sensitive layer and the protective layer of a heat-sensitive recording material were applied consecutively to the paper substrate using a squeegee.After each application, drying is carried out with a hot air gun (40 cm distance) at a temperature of 90 to 110 °C within 1 to 3 minutes. Exemplary embodiments 1, 2, 3, 4 and comparative examples V1, V2, V3 and V4: In exemplary embodiments 1, 2, 3 and 4, as well as in comparative examples V1, V2, V3 and V4, the starch layer is applied to the paper substrate on a paper machine using a film press at a speed of 1250 m / min. On a paper coating machine, the color layer and the heat-sensitive layer are applied consecutively to the paper substrate coated with a starch layer using a single and / or simultaneously using a double curtain coater at a speed of 950 m / min. Optionally, the protective layer is applied to the heat-sensitive layer on a paper coating machine using a curtain coater at a speed of 900 m / min.After each application, the drying process of the coated paper carrier is carried out in the usual manner, without negatively affecting the properties of the heat-sensitive recording material according to the invention, such as the surface whiteness or paper whiteness of the heat-sensitive layer. The ink layer used in embodiments 1 to 4, as well as for comparative examples V1 to V4, has the following composition: styrene-butadiene latex (48%), carbon black (45%), calcined kaolin (45%), precipitated calcium carbonate (58%), acrylate thickener (30%). chicht (Flä- Recipe component function (amount by weight) part (wt%) Color layer Calcined Kaolin Inorganic-52.2 (7.5 g / m²) 2 ) sches Pig- ment Precipitated Calcium Inorgani- 24.6 calcium carbonate, Calcium Pig- ment Styrene-Butadiene Binder 10.6 Latex R uß Farb-11.2 substance / color pigment na rheology residue auxiliary color layer – variant 1. Alternatively, variants 2 and 3 of the color layer, which are shown in detail below, can also be used. S chicht (Flä- Recipe component function (amount by weight) part (wt%) Color layer Calcined Kaolin Inorgani-53 (7.5 g / m²) 2 ) sches Pig- ment Precipitated Calcium Inorgani- 26.6 calcium carbonate, Calcium Pig- ment Styrene-Butadiene Binder 10.6 Latex R uß Farb- 8.5 substance / color pigments n.a. Rheology residue auxiliary color layer – variant 2 layer (surface-formulation component-function quantity weight) part (wt.%) color layer 2 htCalcined kaolin inorganic-53 ( 7,0 g / m ) Precipitated calcium carbonate, inorganic 26.6, calcium carbonate type, styrene-butadiene binder 10.6, Latex R uß Farb-8.5 substance / color pigment na rheology residue auxiliary color layer – variant 3 The heat-sensitive layer used in embodiments 1 to 4, as well as for comparative examples V1 to V4, has the following composition: polyvinyl alcohol (high viscosity), 7.5 wt%, as a polymeric binder, polyamidoamine epichlorohydrin (10%), 0.9 wt% as a crosslinking agent, 9 wt% of an inorganic pigment, which was varied for embodiments 1 to 4 and comparative examples V1 to V4 as follows. Layer formulation component-function quantity (area part (wt.) %) heat-sensitive Styrene-acrylate copolymer particles 34.4 layer polymer (3.5 g / m²) 2Sodium Metaborate Crosslinker 0.05 Tetrahydrate Stearic Acid Heat-sensitive 33.4 Reamide wax material Silicon oxide Inorganic 12.0 Pigment Zinc stearate Lubricant / Release agent 3.2 Polyvinyl alcohol, Binder 10.3 Highly saponified, high viscosityRheology aid residue, additives. In embodiment 1, the inorganic pigment of the heat-sensitive layer comprises untreated precipitated calcium carbonate (PCC) having a particle size distribution (d90) determined according to ISO 13320, in particular ISO 13320:2020, of 3.29 µm to 3.86 µm, having a particle size distribution (d50) determined according to ISO 13320, in particular ISO 13320:2020, of 2.00 µm to 2.35 µm, having a particle size distribution (d10) determined according to ISO 13320, in particular ISO 13320:2020, of 0.82 µm to 1.34 µm, and having a particle size distribution (d4.3) determined according to ISO 13320, in particular ISO 13320:2020. 2.18^^m ​​to 2.46 ^m.The untreated precipitated calcium carbonate (PCC) according to embodiment 1 exhibits a sieve residue of between 0.1% and 2.3% after treatment, according to standard DIN EN ISO 787-7:2010 DE, when filtered with a sieve with a pore size of 20 µm. The formulation for the further embodiments is given below: Layer Formulation Composition Function Quantity (Area Part (Wt.) %) Heat Sensitive Styrene-Acrylates Copolymer Particles 37.0 Layer polymer (3.5 g / m²). 2Polyamidoamine crosslinker 0.9 pichlorohydrin (PAAE) Stearic acid Heat-sensitive 35.0 reamid wax cal precipitated calcium carbonate Inorganic 9.0 pigment Zinc stearate Lubricant / release agent 3.2 Polyvinyl alcohol, binder 7.5 partially saponified, modified (carboxylated) rheology aid residue, additives Heat-sensitive layer – variant 1 Alternatively, variants 2 and 3 of the heat-sensitive layer, which are shown in detail below, can also be used. Layer Formulation component-function Quantity (area part (wt.) %) Heat-sensitive Styrene-acrylate copolymer particles 35.5 polymer (3.5 g / m²) 2) Polyamidoamine crosslinker 0.9 pichlorohydrin (PAAE) Stearic acid Heat-sensitive 33.5 reamid wax ches Material Precipitated calcium carbonate Inorganic 12.0 Calcium carbonate Pigment Zinc stearate Lubricant / release agent 3.2 Polyvinyl alcohol, binder 7.5 Partially saponified, modified (carboxylated) Rheology aid Residue, Additives Heat-sensitive layer – Variant 2-layer Formulation component-function Amount (Area per unit (Wt.) %) Heat-sensitive Styrene-acrylate copolymer particles 37.0 layer polymer (3.5 g / m²) 2) Polyamidoamine crosslinker 0.9 pichlorohydrin (PAAE) Stearic acid Heat-sensitive 33.7 reamid wax material Precipitated calcium carbonate Inorganic 9.0 pigment Zinc stearate Lubricant / release agent 4.5 Polyvinyl alcohol, binder 7.5 partially saponified, modified (carboxylated) Rheology aid residue, additives Heat-sensitive layer – variant 3 In embodiment 2, the inorganic pigment of the heat-sensitive layer comprises filtered precipitated calcium carbonate (PCC), wherein the filtered precipitated calcium carbonate (PCC) was obtained by filtration of a solution using a 20 µm filter.The filtered precipitated calcium carbonate (PCC) according to embodiment 2 has a particle size distribution (d90) determined according to ISO 13320, in particular ISO 13320:2020, of 3.23 µm to 3.78 µm, a particle size distribution (d50) determined according to ISO 13320, in particular ISO 13320:2020, of 1.94 µm to 1.98 µm, a particle size distribution (d10) determined according to ISO 13320, in particular ISO 13320:2020, of 0.43 µm to 1.30 µm, and a particle size distribution (d4,3) determined according to ISO 13320, in particular ISO 13320:2020, of 2.09 µm to 2.11 µm. Filtered precipitated calcium carbonate (PCC) according to embodiment 2 exhibits a sieve residue of approximately 0.48% after treatment according to the standard DIN EN ISO 787-7:2010 DE when filtered with a sieve with a pore size of 20 µm.In embodiment 3, the inorganic pigment of the heat-sensitive layer comprises ground precipitated calcium carbonate (PCC), wherein the ground precipitated calcium carbonate (PCC) was obtained by adding 0.1 wt.% dispersing agent and diluting with a 55% substance to a 45% wt. fraction, and subsequently grinding via a bead mill with a throughput of 24 L / min.The ground precipitated calcium carbonate (PCC) according to embodiment 3 has a particle size distribution (d90) determined according to ISO 13320, in particular ISO 13320:2020, from 1.94 µm to 2.72 µm, a particle size distribution (d50) determined according to ISO 13320, in particular ISO 13320:2020, from 1.08 µm to 1.43 µm, a particle size distribution (d10) determined according to ISO 13320, in particular ISO 13320:2020, from 0.13 µm to 0.67 µm, and a particle size distribution (d4,3) determined according to ISO 13320, in particular ISO 13320:2020, from 1.22 µm to 1.40 µm. Ground precipitated calcium carbonate (PCC) according to embodiment 3 exhibits a sieve residue obtained after treatment between 0.01% and 0.02% according to standard DIN EN ISO 787-7:2010 DE when filtered with a sieve with a pore size of 45 µm.In embodiment 4, the inorganic pigment of the heat-sensitive layer comprises precipitated calcium carbonate (PCC) with an aragonite structure (manufacturer's designation Omyaprima HO 40), wherein the precipitated calcium carbonate (PCC) with an aragonite structure was obtained. The precipitated calcium carbonate (PCC) with the aragonite structure according to embodiment 4 has a particle size distribution (d90) determined according to ISO 13320, in particular ISO 13320:2020, of 3.33 ^m, has a particle size distribution (d50) determined according to ISO 13320, in particular ISO 13320:2020, of 1.38 ^m, has a particle size distribution (d10) determined according to ISO 13320, in particular ISO 13320:2020, of 0.54 ^m, and has a particle size distribution (D4,3) determined according to ISO 13320, in particular ISO 13320:2020, of 1.67 ^m.The precipitated calcium carbonate (PCC) with an aragonite structure according to embodiment 4 exhibits a sieve residue of 0.02% after treatment, as determined by filtration with a sieve with a pore size of 20 µm, according to standard DIN EN ISO 787-7:2010 DE. In comparative example 1, the inorganic pigment of the heat-sensitive layer comprises ground calcium carbonate (GCC) (manufacturer's designation Hydrocarb 95GU), whereby the ground calcium carbonate (GCC) was obtained. The particle size distributions and the sieve residue were not determined. Layer Formulation Composition-Function Quantity (Area Part (Wt. Weight) %) Heat-sensitive Styrene-acrylate copolymer particles 37.0 layer polymer (3.5 g / m²). 2) Polyamidoamine crosslinker 0.9 pich-chlorohydrin (PAAE) Stearic acid heat-sensitive 35.0 reamid wax material Calcium carbonate Inorganic 9.0 (GCC) pigment Zinc stearate Lubricant / release agent 3.2 Polyvinyl alcohol, binder 7.5 partially saponified, modified (carboxylated) na Rheology aid residue, additives In comparative example 2, the inorganic pigment of the heat-sensitive layer comprises silica (manufacturer's designation Aerodisp).The silica according to comparison example 2 has a particle size distribution (d90) determined according to ISO 13320, in particular ISO 13320:2020, of 0.18 µm, a particle size distribution (d50) determined according to ISO 13320, in particular ISO 13320:2020, of 0.12 µm, a particle size distribution (d10) determined according to ISO 13320, in particular ISO 13320:2020, of 0.10 µm, and a particle size distribution (d4,3) determined according to ISO 13320, in particular ISO 13320:2020, of 0.13 µm. The sieve residue was not determined. Layer formulation component function Quantity (area part [(weight) %) Heat-sensitive Styrene-acrylate copolymer particles 37.0 layer polymer (3.5 g / m²) 2) Polyamidoamine crosslinker 0.9 pich-chlorohydrin (PAAE) Stearic acid heat-sensitive 35.0 reamid wax material silicon dioxide inorganic 9.0 pigment zinc stearate lubricant / release agent 3.2 polyvinyl alcohol, binder 7.5 partially saponified, modified (carboxylated) rheology aid residue, additives. In comparative example 3, the inorganic pigment of the heat-sensitive layer comprises Xonotlit (manufacturer's name Circolit).The Xonotlit according to comparison example 3 has a particle size distribution (d90) determined according to ISO 13320, in particular ISO 13320:2020, of 2.22 to 2.54 µm, a particle size distribution (d50) determined according to ISO 13320, in particular ISO 13320:2020, of 0.54 µm, a particle size distribution (d10) determined according to ISO 13320, in particular ISO 13320:2020, of 0.14 to 0.26 µm, and a particle size distribution (d4.3) determined according to ISO 13320, in particular ISO 13320:2020, of 0.89 to 0.99 µm. The sieve residue was not determined. Layer formulation component function Quantity (area per unit (weight) %) Heat-sensitive Styrene-acrylate copolymer particles 37.0 layer polymer (3.5 g / m²). 2Polyamidoamine crosslinker 0.9 pich-chlorohydrin (PAAE) Stearic acid heat-sensitive 35.0 reamid wax material Circolit Inorganic 9.0 Pigment Zinc stearate Lubricant / release agent 3.2 Polyvinyl alcohol, binder 7.5 partially saponified, modified (carboxylated) Rheology aid residue, additives In comparative example 4, the inorganic pigment of the heat-sensitive layer (manufacturer's designation Capim NP) is included. The particle size distributions and the sieve residue were not determined. Layer Formulation component-function Quantity (area part (wt.) Chemical name %) Heat-sensitive Styrene-acrylate copolymer particles 37.0 layer polymer (3.5 g / m²) 2 ) Polyamidoamine crosslinker 0.9 pich-chlorohydrin (PAAE) Stearic acid heat-sensitive 35.0 reamido wax material K aolin Anorganisches9.0 Pigment Zinc stearate Lubricant / Release agent 3.2 Polyvinyl alcohol, Binder 7.5 Partially saponified, modified (carboxylated) na Rheology aid Residue, Additives Results The results of the measurements of the aforementioned parameters are summarized in the following Table 1 for embodiments 1 to 6, as well as for comparison examples V1 to V4. For embodiments 1 to 4, variant 1 of the color layer and variant 1 of the heat-sensitive layer were used. The results of example 5 comprise the combination of the second variant of the color layer and the second variant of the heat-sensitive layer of embodiment example 3. The results of example 6 comprise the combination of the third variant of the color layer and the third variant of the heat-sensitive layer of embodiment example 3.For the corresponding particle size distributions of PCC in Examples 5 and 6, reference is made to the explanations in Implementation Example 3. Here, the occurrence of white spots, the occurrence of print image defects, and the rejection grade are qualitatively assessed using the following ratings: "--" (very poor), (poor), "0" (average), "+" (good), "++" (very good). B. eispiel Auftre- Print- Ab- ten of image disturbances- white rungen note points B eispiel 1 - + ++Example 2 ++ ++ +Example 3 ++ ++ +Example 4 ++ + +Example 5 ++ ++ ++Example 6 ++ ++ ++Example V1 0 - 0Example V2 + - -Example V3 + - 0Example V4 + -- -Table 1 The values ​​summarized in Table 1 show that the use of ground precipitated calcium carbonate (PCC) according to embodiment 3 and of precipitated calcium carbonate (PCC) with an aragonite structure according to embodiment 4 leads to the best results, since in both cases good lay-down behavior (rating: good), no disturbances in the print image (rating: very good) and also very few white dots in a dark printed area (rating: very good) occur. When using untreated precipitated calcium carbonate (PCC) according to embodiment 1, good results were also achieved in the relevant categories including lay-down behavior, disturbances in the print image, but white dots in a dark printed area. receive.When using filtered precipitated calcium carbonate (PCC) according to Example 2, a comparably good result was obtained. When considering other inorganic pigments according to comparison examples V1 to V4, a few white dots were obtained in a dark printed area in all cases (rating: good or average). However, when using ground calcium carbonate (GCC) according to comparison example V1, xonotlite according to comparison example V3, and clay according to comparison example 4, a significant occurrence of print image defects occurred, which excludes the corresponding inorganic pigments for the production of heat-sensitive recording materials. Regardless, poor, at best average, laydown behavior was also observed in comparison examples V1, V3, and V4.Even if only average print image defects could be obtained when using silica according to comparison example V2, it is emphasized that according to comparison example V2, poor deposit behavior was observed, which excludes the corresponding pigment for the production of heat-sensitive recording materials.

Claims

1. Claim 1. Heat-sensitive recording material comprising: a support substrate having a first side and a second side facing away from the first side; a color layer arranged on the first or second side of the support substrate, wherein the color layer comprises at least one coloring agent, and a heat-sensitive layer arranged on the color layer and at least partially covering the color layer, wherein the heat-sensitive layer is designed such that it becomes translucent upon local application of heat, allowing the underlying color layer to become visible, characterized in that the heat-sensitive layer comprises at least one polymeric binder, at least one crosslinking agent, and at least one inorganic pigment, wherein the at least one inorganic pigment comprises a precipitated calcium carbonate (PCC).wherein the precipitated calcium carbonate (PCC) has a mean particle size (d90) of less than 50 µm.

2. Heat-sensitive recording material according to claim 1, characterized in that the precipitated calcium carbonate (PCC) has a mean particle size (d90) of less than 40 µm, preferably less than 30 µm, further preferably less than 25 µm, still more preferably less than 20 µm, most preferably less than 10 µm, still most preferably less than 5 µm.

3. Heat-sensitive recording material according to claim 1 or 2, characterized in that the precipitated calcium carbonate (PCC) has a mean particle size (d90) of less than 40 µm, preferably less than 30 µm, further preferably less than 25 µm, more preferably less than 20 µm, most preferably less than 10 µm, and most preferably less than 5 µm. having a particle size (d50) of less than 50 ^m, preferably less than 40 ^m, further preferably less than 30 ^m, still more preferably less than 25 ^m, furthermore still more preferably less than 20 ^m, most preferably less than 10 ^m, still more preferably less than 5 ^m, furthermore still more preferably less than 3 ^m and additionally furthermore still more preferably less than 2.5 ^m.4.Heat-sensitive recording material according to one of the preceding claims, characterized in that the precipitated calcium carbonate (PCC) has a mean particle size (d10) of less than 50 µm, preferably less than 40 µm, further preferably less than 30 µm, even more preferably less than 25 µm, further still more preferably less than 20 µm, most preferably less than 10 µm, even more preferably less than 5 µm, further still more preferably less than 2 µm and additionally further still more preferably less than 1.5 µm.5.Heat-sensitive recording material according to any one of the preceding claims, characterized in that the precipitated calcium carbonate (PCC) comprises scalenohedral precipitated calcium carbonate (s-PCC), wherein in particular the proportion of the scalenohedral precipitated calcium carbonate (s-PCC) in the precipitated calcium carbonate (PCC) is more than 50%, preferably more than 60%, further preferably more than 70%, even more preferably more than 80%, most preferably more than 90%, and even more preferably more than 98%.

6. Heat-sensitive recording material according to any one of the preceding claims, characterized in that the precipitated calcium carbonate (PCC) comprises precipitated calcium carbonate (PCC) having an aragonite structure, wherein in particular the proportion of the precipitated calcium carbonate (PCC) with the aragonite structure in the precipitated calcium carbonate (PCC) is more than 50%, preferably more than 90%. 60%, more preferably more than 70%, more preferably more than 80%, most preferably more than 90%, and more preferably more than 98%.

7. Heat-sensitive recording material according to one of the preceding claims, characterized in that the precipitated calcium carbonate (PCC) comprises precipitated calcium carbonate (PCC) having a prismatic structure, wherein in particular the proportion of the precipitated calcium carbonate (PCC) with the prismatic structure in the precipitated calcium carbonate (PCC) is more than 50%, preferably more than 60%, more preferably more than 70%, more preferably more than 80%, most preferably more than 90%, and more preferably more than 98%. 8.Heat-sensitive recording material according to one of the preceding claims, characterized in that the precipitated calcium carbonate (PCC) comprises filtered precipitated calcium carbonate (PCC) and / or ground precipitated calcium carbonate (PCC) and / or sieved precipitated calcium carbonate (PCC).

9. Heat-sensitive recording material according to one of the preceding claims, characterized in that the precipitated calcium carbonate (PCC) is characterized by a sieve residue obtained after treatment according to DIN EN ISO 787-7:2010 DE of less than 1%, preferably less than 0.5%, more preferably less than 0.1%, and most preferably less than 0.05%.

10. Heat-sensitive recording material according to one of the preceding claims, characterized in that the precipitated calcium carbonate (PCC) is present in an amount of 3 wt.% to 20 wt.%, preferably in an amount of 5 wt.% to 15 wt.%, further preferably in an amount of 5 wt.%.-% to 13 wt.%, more preferably in an amount of 6 wt.% to 12 wt.% based on the total dry mass of the heat-sensitive layer in which the heat-sensitive layer is present.

11. Heat-sensitive recording material according to one of the preceding claims, characterized in that the heat-sensitive layer does not contain a chemical color developer and no chemical color former, in particular no leuco dye. 12.Heat-sensitive recording material according to one of the preceding claims, characterized in that the at least one crosslinking agent is 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, methylol urea, melamine formaldehyde oligomers, oxazoline resins, carbodiimide, borate compounds and mixtures thereof, and wherein the at least one crosslinking agent is preferably selected as Ammonium zirconium carbonate and / or polyamidoamine epicichlorhydrin resins (PAAE resin).13.Heat-sensitive recording material according to claim 12, characterized in that the at least one crosslinking agent is present in 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 heat-sensitive layer.

14. Heat-sensitive recording material according to any one of the preceding claims, characterized in that the heat-sensitive layer comprises at least one wax 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 preferably the at least one fatty acid amide comprises fatty acid monoamide, fatty acid diamond, fatty acid alkanolamide, N-methyl fatty acid amide, and mixtures thereof. and / or wherein preferably the at least one fatty acid comprises a saturated fatty acid and / or an unsaturated fatty acid with at least 8 carbon atoms.

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

16. Heat-sensitive recording material according to claim 15, characterized in that the at least one polymeric binder is present in the heat-sensitive layer in an amount of 0.5 wt.% to 25.0 wt.%, preferably in an amount of 1 wt.% to 10.0 wt.%, based on the total dry mass of the heat-sensitive layer.

17. Heat-sensitive recording material according to any one of the preceding claims, characterized in thatthat the heat-sensitive recording material, in particular the heat-sensitive layer, contains no organic pigments, in particular no hollow sphere pigments.

18. Heat-sensitive recording material according to any one of the preceding claims 1 to 16, characterized in that the heat-sensitive layer comprises organic pigments, in particular hollow sphere pigments, wherein the organic pigments, in particular hollow sphere pigments, are present in the heat-sensitive layer in an amount of 10 wt.% to 70.0 wt.%, preferably in an amount of 20 wt.% to 60.0 wt.%, further preferably in an amount of 30 wt.% to 50.0 wt.%, and most preferably in an amount of 35 wt.% to 45 wt.% based on the total dry mass of the heat-sensitive layer.

19. Heat-sensitive recording material according to one of the preceding claims, characterized in that the heat-sensitive recording material has an basis weight of 20 g / m2 to 100 g / m2 as determined by the standard ISO 536, preferably of 35 g / m2 to 80 g / m2.20.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.) of at least 0.9, preferably at least 1.1, and most preferably at least 1.15, as defined in the description, in particular measured at an energy level of 8.88 mJ / mm², and / or that the heat-sensitive recording material has an optical density (o.D.) of at least 1.0, preferably at least 1.2, and most preferably at least 1.3, as defined in the description, in particular measured at an energy level of 14.57 mJ / mm².

21. Heat-sensitive recording material according to one of the preceding claims, characterized in that 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). 22.Heat-sensitive recording material according to one of the preceding claims, characterized in that the heat-sensitive recording material exhibits a deposit behavior of at least "average grade ("0")" in a thermal printer long-term test (10 km) under the pressure of a print pattern, wherein according to. During a 10 km test run on a standard thermal printer, specifically a Diebold Nixdorf P1200, a visual inspection for deposits on the thermal printhead was performed, and the assessment was based on the following grading system: very good ("++") = no deposits, good ("+") = slight deposits, average ("0") = moderate deposits, poor = strong deposition.

23. Method for producing a heat-sensitive recording material, comprising the following process steps: providing a support substrate having a first side and a second side facing away from the first side; applying a color layer suspension to the first side or second side of the support substrate, wherein the color layer suspension comprises at least one coloring agent; in particular, drying the color layer suspension to obtain a color layer arranged on the first side or second side of the support substrate; applying a coating suspension to the color layer, wherein the coating suspension comprises at least one polymeric binder, at least one crosslinking agent, and at least one inorganic pigment, wherein the inorganic pigment comprises precipitated calcium carbonate (PCC), wherein the precipitated calcium carbonate (PCC) has a mean particle diameter (d90) of less than 50 µm;and in particular drying the application suspension to obtain a heat-sensitive layer arranged on the ink layer.

24. Heat-sensitive recording material producible by a method according to claim 23.

25. Use of a heat-sensitive recording material according to any one of claims 1 to 22 or 24 as a receipt roll, adhesive label roll, ticket roll or; 5 as printer paper for mechanical printers or writing pens, or as self-copying paper.

Images