HEAT-SENSITIVE RECORDING MATERIAL

Abstract

The invention relates to a heat-sensitive recording material comprising: a support substrate having a first side and a second side facing away from the first side; a heat-sensitive color-forming layer arranged on the first side of the support substrate, wherein the heat-sensitive color-forming layer comprises at least one color former and at least one color developer; wherein the heat-sensitive layer comprises at least one polymeric binder 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, and wherein the precipitated calcium carbonate (PCC) comprises sieved precipitated calcium carbonate (PCC) and / or ground precipitated calcium carbonate (PCC) and / or filtered precipitated calcium carbonate (PCC).

Description

TECHNICAL AREA

[0001] 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 heat-sensitive color-forming layer arranged on the first side of the carrier substrate and comprising at least one color former and at least one color developer, wherein the heat-sensitive layer comprises at least one polymeric binder and at least one inorganic pigment.

[0002] In this context, 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, and wherein the precipitated calcium carbonate (PCC) comprises sieved precipitated calcium carbonate (PCC) and / or ground precipitated calcium carbonate (PCC) and / or filtered precipitated calcium carbonate (PCC).

[0003] According to a second aspect, the present invention relates to a method for producing a heat-sensitive recording material, comprising the following method steps: providing a carrier substrate having a first side and a second side facing away from the first side;Applying a coating suspension to the first side of the support substrate, wherein the coating suspension comprises at least one color former and at least one color developer, wherein the coating suspension comprises at least one polymeric binder 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, and wherein the precipitated calcium carbonate (PCC) comprises sieved precipitated calcium carbonate (PCC) and / or milled precipitated calcium carbonate (PCC) and / or filtered precipitated calcium carbonate (PCC); and drying the coating suspension to obtain a heat-sensitive color-forming layer arranged on the first side of the support substrate.

[0004] According to a third aspect, the present invention relates to a heat-sensitive recording material producible by a method according to the second aspect.

[0005] 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 for thermal direct printing, for example as a receipt, label or ticket. TECHNICAL BACKGROUND

[0006] Heat-sensitive recording materials, also known as thermal papers, are used in a variety of applications, such as retail sales receipts.

[0007] From the prior art, heat-sensitive recording materials, so-called thermal labels, are known for thermal direct printing, whereby two types of heat-sensitive recording materials, especially for thermal direct printing, are distinguished.

[0008] The first type of heat-sensitive recording materials comprises those in which the printed image is created by a local, heat-induced chemical reaction within an ink 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 ink layer also contains a heat-sensitive solvent that melts upon exposure to heat and may include, for example, long-chain aliphatic alcohols, amides, esters, or carboxylic acids, thus enabling the color reaction between the color former and the color developer. Furthermore, the ink layer may contain heat-sensitive sensitizers.

[0009] The second type of heat-sensitive recording materials comprises those 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 direct thermal printer, thus revealing an underlying ink layer. This technology is described and interpreted differently in the prior art, and such a heat-sensitive recording material is obtained through varying compositions, porosities, and materials of the heat-sensitive top layer. It is optimized for direct thermal printing and will be explained in more detail below.

[0010] In the second type of heat-sensitive recording material, the heat-sensitive top layer should cover the underlying ink layer as effectively as possible. This is achieved primarily through light scattering, particularly using scattering particles, and light absorption. The heat-sensitive top layer should exhibit the highest possible contrast to the underlying ink layer in order to produce a printed image readable by the human eye and / or a machine, such as a scanner, for example, white / black or blue / yellow.

[0011] The present invention relates to heat-sensitive recording materials of the first type described above.

[0012] Heat-sensitive recording materials, so-called thermal labels, are known from the state of the art for use in direct thermal printing.

[0013] In JPS 59 162 087 A, US 4 370 370 A and US 4 388 362 A, thermal labels are written on using release paper.

[0014] DE 19 757 589 B4 describes a release paper-free ("linerless") thermal label with a protective layer over the heat-sensitive layer.

[0015] DE 19 806 433 B4 discloses a linerless thermal label with a protective layer free of silicone compounds, which was hardened by means of actinic radiation.

[0016] EP 0 600 622 A1 and DE 19 724 647 C1 describe a linerless thermal label with a protective layer, which is coated on the back with hot melts.

[0017] EP 1 085 069 B1 and EP 2 474 963 B1 disclose thermal label materials in linerless design with a heat-activated adhesive, describing thermal labels both with and without a protective layer.

[0018] EP 3 219 507 A1 claims a linerless thermal label without an actual protective layer, in which the surface of the heat-sensitive layer is designed to be non-adhesive to adhesives.

[0019] Heat-sensitive recording materials equipped with so-called "back-coat" coatings to improve reverse printing with conventional printing methods or to minimize the tendency of a substrate to curl under unfavorable humidity conditions are also known from the prior art.

[0020] The differing shrinkage behavior of the two sides of the substrate in heat-sensitive recording materials under different ambient humidity, i.e., under different water vapor absorption of the two sides / lines, can be effectively improved by backside coatings. US 6,667,275 B2, for example, discloses a multilayer backside coating for heat-sensitive recording materials for advantageously influencing the curl tendency of the substrate web.

[0021] JP 2018 167 483 discloses methods for improving the durability of thermally produced print on heat-sensitive recording materials that have been printed on the reverse side with oil-based inks or inks, by, among other things, applying coatings to the reverse side. The formulations of these reverse-side coatings often contain aqueous emulsion polymers, such as styrene-butadiene or acrylate latices, as a key component.

[0022] For example, JP 2003 175 671 claims back-coat formulations for heat-sensitive recording materials produced with aqueous latices, which form soft polymer films (glass transition temperature ≥ -30°C). JPH 0 720 735 B2 and JP 2000 204 123 disclose back-coat formulations with acrylate emulsion polymers for heat-sensitive recording materials.

[0023] The publications EP 3 957 488 A1 and WO 2022 / 038242 A1 describe a heat-sensitive recording layer comprising phenol-group-free organic color developers, a coating composition for producing the heat-sensitive recording layer, and a heat-sensitive recording material, in particular thermal paper, comprising the heat-sensitive recording layer. The publications further describe the use of the heat-sensitive recording layer for producing the heat-sensitive recording material, a process for producing the heat-sensitive recording material, and the use of the heat-sensitive recording material in thermal paper applications. Due to its composition, the heat-sensitive recording material exhibits particularly good recyclability and high environmental compatibility.

[0024] Heat-sensitive recording materials are also described in the publications US 2021 / 0060994, CA 3 149 562 A1 and WO 2021 / 041600 A2.

[0025] Reference is also made to the publications DE 10 2019 126 220 A1, WO 2021 / 058661 A1, KR 2022 070 021 A, and DE 20 2020 005 616 U1.

[0026] For all these conventionally used heat-sensitive recording materials, it is desirable to reduce the occurrence of white or light defects in correspondingly dark printed areas, which are perceived as disturbing to the viewer's eye or are detrimental to electronic reading devices, in order to improve the print image.

[0027] In particular, it is desirable to at least maintain or further enhance the protection of heat-sensitive recording materials from external influences such as pressure, friction, humidity, liquids, and moisture. Furthermore, the functionality, properties, and cost-effectiveness of conventional heat-sensitive recording materials should at least be maintained and ideally even improved, especially with regard to optical density and the optical appearance of the printed image on the heat-sensitive recording materials.

[0028] Furthermore, conventional heat-sensitive recording materials often suffer from the problem of a less than optimal surface smoothness or high surface roughness, which significantly limits the operating life of corresponding printers due to the resulting abrasion behavior and is therefore disadvantageous. DESCRIPTION OF THE INVENTION Task

[0029] One object of the present invention is to provide a heat-sensitive recording material which, after printing, has an advantageous printed image and which, in particular, has a reduced number of white or light defects in correspondingly dark printed areas.

[0030] Another object of the present invention is to provide a heat-sensitive recording material which is able to guarantee the functional properties required for the application (in particular a high optical density).

[0031] Another object of the present invention is to provide a heat-sensitive recording material which ensures an advantageous smoothness of the surface or a low roughness of the surface of the heat-sensitive recording material.

[0032] Surprisingly, it has now been found that the disadvantages of the prior art described above can be overcome by using sieved, and / or ground, and / or filtered 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.

[0033] By using sieved, and / or ground, and / or filtered 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.

[0034] Furthermore, the sieved, and / or ground, and / or filtered precipitated calcium carbonate (PCC) with a mean particle size (d90) of less than 50 µm can be used as an inorganic pigment in the heat-sensitive layer to achieve an advantageous smoothness of the surface or a low roughness of the surface of the heat-sensitive recording material.

[0035] The use of sieved, and / or ground, and / or filtered 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 improved barcode readability and also allows for a favorable print image.

[0036] Sieved, and / or ground, and / or filtered precipitated calcium carbonate (PCC) is available at a very low price, which reduces the manufacturing costs of corresponding heat-sensitive recording materials. Heat-sensitive recording material

[0037] 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 heat-sensitive color-forming layer arranged on the first side of the support substrate, wherein the heat-sensitive color-forming layer comprises at least one color former and at least one color developer;wherein the heat-sensitive layer comprises at least a polymeric binder 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, and wherein the precipitated calcium carbonate (PCC) comprises sieved precipitated calcium carbonate (PCC) and / or ground precipitated calcium carbonate (PCC) and / or filtered precipitated calcium carbonate (PCC).

[0038] By using sieved, and / or ground and / or filtered 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, it is possible to significantly reduce the number of white or light defects in dark printed areas.

[0039] Within the scope of the present invention, the sieved, and / or ground and / or filtered precipitated calcium carbonate (PCC) can be mixed as desired in the heat-sensitive color-forming layer. In particular, the at least one inorganic pigment comprises exclusively sieved precipitated calcium carbonate (PCC), or exclusively ground precipitated calcium carbonate (PCC), or exclusively filtered precipitated calcium carbonate (PCC).Alternatively, and in particular, this includes at least one inorganic pigment, a mixture of sieved precipitated calcium carbonate (PCC) and ground precipitated calcium carbonate (PCC), or a mixture of sieved precipitated calcium carbonate (PCC) and filtered precipitated calcium carbonate (PCC), or a mixture of ground precipitated calcium carbonate (PCC) and filtered precipitated calcium carbonate (PCC), or a mixture of sieved precipitated calcium carbonate (PCC) and ground precipitated calcium carbonate (PCC) and filtered precipitated calcium carbonate (PCC).

[0040] In particular, the mean particle size (d90) of the sieved, and / or ground and / or filtered precipitated calcium carbonate (PCC) is determined by laser diffraction, specifically using a Coulter laser diffraction analyzer. Specifically, the mean particle size (d90) of the sieved, and / or ground and / or filtered precipitated calcium carbonate (PCC) is determined according to ISO 13320.

[0041] Furthermore, the use of sieved, and / or ground and / or filtered precipitated calcium carbonate (PCC) with a mean particle size (d90) of less than 50 µm as an inorganic pigment of the heat-sensitive layer ensures, according to the first aspect, that no further disturbances occur in the printed image.

[0042] Furthermore, a corresponding heat-sensitive recording material according to the present invention has an image quality of the printed image that is comparable to, and in particular improved to, conventional recording materials, and which is characterized by the optical density of the heat-sensitive recording material.

[0043] In particular, the sieved precipitated calcium carbonate (PCC) has a mean particle size (D4,3) of 2.3 to 2.5 µm, the mean particle size (D4,3) of the sieved precipitated calcium carbonate (PCC) being determined according to ISO 13320.

[0044] In particular, the sieved precipitated calcium carbonate (PCC) has a mean particle size (d10) of 1.1 to 1.3 µm, the mean particle size (d10) of the sieved precipitated calcium carbonate (PCC) being determined according to ISO 13320.

[0045] 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.

[0046] 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.

[0047] In particular, the sieved precipitated calcium carbonate (PCC) is characterized by a sieve residue obtained after treatment in accordance with the standard DIN EN ISO 787-7 in a range of 0.01 to 0.03%, especially of approximately 0.02% or 0.03%.

[0048] In particular, the sieved precipitated calcium carbonate (PCC) can be produced by sieving precipitated calcium carbonate (PCC) using a sieve which in particular has a pore size between 20 and 50 µm, in particular of 25 µm.

[0049] In particular, filtered precipitated calcium carbonate (PCC) can be produced by filtering a dispersion of precipitated calcium carbonate (PCC) using a filter which in particular has a pore size between 20 and 50 µm, especially 25 µm.

[0050] In particular, the filtered precipitated calcium carbonate (PCC) has a mean particle size (D4,3) of 2.2 to 2.3 µm, the mean particle size (D4,3) of the filtered precipitated calcium carbonate (PCC) being determined according to ISO 13320.

[0051] In particular, the filtered precipitated calcium carbonate (PCC) has a mean particle size (d10) of 1.0 to 1.1 µm, the mean particle size (d10) of the filtered precipitated calcium carbonate (PCC) being determined according to the ISO 13320 standard.

[0052] In particular, the filtered precipitated calcium carbonate (PCC) has a mean particle size (d50) of 2.0 to 2.2 µm, the mean particle size (d50) of the filtered precipitated calcium carbonate (PCC) being determined according to the ISO 13320 standard.

[0053] In particular, the filtered precipitated calcium carbonate (PCC) has a mean particle size (d90) of 3.6 to 3.8 µm, the mean particle size (d90) of the filtered precipitated calcium carbonate (PCC) being determined according to the ISO 13320 standard.

[0054] In particular, the filtered precipitated calcium carbonate (PCC) is characterized by a sieve residue obtained after treatment in a range of 0.01 to 0.03%, in accordance with the standard DIN EN ISO 787-7.

[0055] In particular, the ground precipitated calcium carbonate (PCC) can be produced by grinding precipitated calcium carbonate (PCC) using a mill, in particular a bead mill, in particular a cooled bead mill, in particular a bead mill cooled to a temperature of less than or equal to 40°C, which in particular has a throughput of between 20 and 50 L / min. In particular, the bead mill has a peripheral speed of 8.0 to 11.0 m / s. In particular, the bead mill has mill beads with a diameter between 0.8 and 1.0 mm, and / or the bead mill has a fill level of greater than or equal to 50%. In particular, up to 1%, in particular 0.1%, of an aqueous solution of a sodium salt of polyacrylic acid is added as a dispersing agent during the grinding process, and / or the precipitated calcium carbonate (PCC) is diluted with water to a solids content of 45% to 55%.

[0056] In particular, the ground precipitated calcium carbonate (PCC) has a mean particle size (D4,3) of 1.2 to 2.1 µm, the mean particle size (D4,3) of the ground precipitated calcium carbonate (PCC) being determined according to ISO 13320.

[0057] 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.

[0058] 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.

[0059] 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 (d90) of the ground precipitated calcium carbonate (PCC) being determined according to ISO 13320.

[0060] In particular, the ground precipitated calcium carbonate (PCC) is characterized by a sieve residue obtained after treatment in the range of 0.01 to 0.03%, according to the standard DIN EN ISO 787-7.

[0061] According to one embodiment, the sieved and / or ground and / or filtered 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, even more preferably less than 20 µm, most preferably less than 10 µm, more preferably less than 7 µm, more preferably less than 5 µm, and more preferably less than 4.5 µm.

[0062] In particular, the mean particle size (d90) of the sieved and / or ground and / or filtered precipitated calcium carbonate (PCC) is determined by laser diffraction, specifically using a Coulter laser diffraction analyzer. Specifically, the mean particle size (d90) of the precipitated calcium carbonate (PCC) is determined according to ISO 13320.

[0063] According to one embodiment, the sieved and / or ground and / or filtered 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, 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, furthermore more preferably less than 3 µm and additionally more preferably less than 2.5 µm.

[0064] In particular, the mean particle size (d50) of the sieved and / or milled and / or filtered precipitated calcium carbonate (PCC) is determined by laser diffraction, specifically using a Coulter laser diffraction analyzer. Specifically, the mean particle size (d50) of the sieved and / or milled and / or filtered precipitated calcium carbonate (PCC) is determined according to ISO 13320.

[0065] According to one embodiment, the sieved and / or ground and / or filtered 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, 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, furthermore more preferably less than 2 µm and additionally more preferably less than 1.5 µm.

[0066] In particular, the mean particle size (d10) of the sieved and / or ground and / or filtered precipitated calcium carbonate (PCC) is determined by laser diffraction, specifically using a Coulter laser diffraction analyzer. Specifically, the mean particle size (d10) of the precipitated calcium carbonate (PCC) is determined according to ISO 13320.

[0067] According to one embodiment, the sieved and / or ground and / or filtered 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, 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, and further still most preferably less than 3 µm.

[0068] In particular, the mean particle size (D4,3) of the sieved and / or ground and / or filtered precipitated calcium carbonate (PCC) is determined by laser diffraction, specifically using a Coulter laser diffraction analyzer. Specifically, the mean particle size (D4,3) of the sieved and / or ground and / or filtered precipitated calcium carbonate (PCC) is determined according to ISO 13320.

[0069] This achieves the technical advantage that the very small mean particle sizes (d90), (d50), (d10), and (D4,3) of the sieved and / or ground and / or filtered precipitated calcium carbonate (PCC) ensure the advantageous properties of the heat-sensitive recording material.

[0070] According to one embodiment, the sieved and / or ground and / or filtered 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 sieved and / or ground and / or filtered 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%.

[0071] According to one embodiment, the sieved and / or ground and / or filtered 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 sieved and / or ground and / or filtered 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%.

[0072] According to one embodiment, the sieved and / or ground and / or filtered 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 sieved and / or ground and / or filtered 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%.

[0073] According to one embodiment, the sieved and / or ground and / or filtered 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 sieved and / or ground and / or filtered 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%.

[0074] This achieves the technical advantage that the specific structures of the sieved and / or ground and / or filtered precipitated calcium carbonate (PCC) ensure the advantageous properties of the heat-sensitive recording material.

[0075] According to one embodiment, the sieved and / or ground and / or filtered precipitated calcium carbonate (PCC) is characterized by a sieve residue obtained after treatment according to the standard DIN EN ISO 787-7 of less than 1%, preferably less than 0.5%, more preferably less than 0.1%, and most preferably less than 0.05%.

[0076] This achieves the technical advantage that the sieve residue of the sieved and / or ground and / or filtered precipitated calcium carbonate (PCC) ensures the advantageous properties of the heat-sensitive recording material.

[0077] According to one embodiment, the sieved and / or ground and / or filtered precipitated calcium carbonate (PCC) is present in the heat-sensitive layer in an amount of 5 wt.% to 60 wt.%, preferably in an amount of 10 wt.% to 50 wt.%, more preferably in an amount of 15 wt.% to 50 wt.% based on the total dry mass of the heat-sensitive layer.

[0078] 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.

[0079] According to one embodiment, the at least one inorganic pigment comprises at least one further inorganic pigment selected from the group consisting of calcium silicate hydrate, barium sulfate, kaolinite, calcium silicate, calcium sulfate, sodium aluminum silicate, aluminum oxides, aluminum hydroxides, silicas, precipitated and pyrogenic silicas, diatomaceous earths, magnesium carbonates, silicon dioxide, talc, kaolin, titanium dioxide, bentonite and mixtures thereof, preferably silicon dioxide, kaolin and / or aluminum hydroxide.

[0080] According to one embodiment, the at least one further inorganic pigment has a weight fraction of 0.1 wt.% to 20 wt.% based on the total solids content of the heat-sensitive layer, wherein the weight fraction is preferably from 1 wt.% to 10 wt.%.

[0081] This achieves the technical advantage that the use of the additional inorganic pigment makes it possible to achieve particularly advantageous properties of the heat-sensitive recording material.

[0082] According to one embodiment, the heat-sensitive layer comprises at least one crosslinking agent, which is preferably selected from the group consisting of polyhydric aldehydes such as glyoxal, dialdehyde starch, glutaraldehyde, salts or esters of glyoxylic acid, crosslinkers based on ammonium zirconium carbonate, organic titanates, polyamidoamine epichlorohydrin resins (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 particularly preferably selected as ammonium zirconium carbonate and / or Polyamidoamine-epichlorohydrin resins (PAAE resin).

[0083] According to one embodiment, the at least one crosslinking agent is present in the heat-sensitive layer in an amount of 0.01 wt.% to 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 2.5 wt.% based on the total dry mass of the heat-sensitive layer.

[0084] To achieve specific application-related performance characteristics of heat-sensitive recording materials, the polymeric binder present in the heat-sensitive layer is preferably in cross-linked form in the heat-sensitive layer, wherein the optimal degree of cross-linking of the polymeric binder is achieved in the drying step of the coating process in the presence of a cross-linking agent.

[0085] Ammonium zirconium carbonate and polyamidoamine epichlorohydrin resins (PAAE resins) are particularly preferred.

[0086] Self-crosslinking binders, such as specially modified polyvinyl alcohols or acrylates, enable crosslinking without any crosslinking agents, thanks to the reactive, crosslinkable groups that are already incorporated into the binder polymer.

[0087] According to one embodiment, the heat-sensitive layer comprises at least one sensitizing agent, which is preferably selected from the group consisting of a fatty acid amide, particularly preferably stearamide, behenamide or palmitamide, an ethylenebis fatty acid amide, particularly preferably N,N'-ethylenebis-stearic acid amide or N,N'-ethylenebis-oleic acid amide, a wax, particularly preferably polyethylene wax or montan wax, a carboxylic acid ester, particularly preferably dimethyl terephthalate, dibenzyl terephthalate, benzyl p-benzyloxybenzoate, di-(p-methylbenzyl)oxalate, di-(p-chlorobenzyl)oxalate or di-(p-benzyl)oxalate, an aromatic ether, particularly preferably 1,2-diphenoxyethane, 1,2-di-(3-methylphenoxy)ethane, 2-benzyloxynaphthalene or 1,4-diethoxynaphthalene, an aromatic sulfone, particularly preferably diphenylsulfone, and / or an aromatic sulfonamide, particularly preferably benzenesulfonanilide or N-benzyl-p-toluenesulfonamide, o-toluenesulfonamide, o-toluenesulfonamide,p-Benzylbiphenyl (PBBP), 1,2-bis-(phenoxymethyl)benzene, 4-(4-tolyloxy)biphenyl, 1,2-bis-(3,4-dimethylphenyl)ethane and / or mixtures thereof.

[0088] Generally, crystalline substances with a melting point between approximately 90°C and 150°C are advantageously suited as sensitizing agents. In their molten state, these substances dissolve the color-forming components, including at least one color former and at least one color developer, without disrupting the formation of the color complex. Sensitizing agents can be present alone or as mixtures.

[0089] According to one embodiment, the sensitizing agent has a weight fraction of 1 wt.% to 40 wt.% based on the total solids content of the heat-sensitive color-forming layer, wherein the weight fraction is preferably from 2 wt.% to 25 wt.%.

[0090] According to one embodiment, the heat-sensitive layer comprises at least one optical brightener in the form of white toners, which is selected from the group comprising diaminostilbene disulfonic acid, distyryl biphenyls, benzoxazole derivatives, fluorescent substances in the form of daylight fluorescent pigments of different shades or fluorescent fibers and mixtures thereof, and / or the heat-sensitive layer comprises at least one anti-aging agent in the form of sterically hindered phenols, preferably 1,1,3-tris-(2-methyl-4-hydroxy-5-cyclohexylphenyl)butane, 1,1,3-tris-(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, 1,1'-bis-(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, 1,1'-bis-(4-hydroxyphenyl)cyclohexane and mixtures thereof.

[0091] In particular, the at least one optical brightener has a weight fraction of 0.1 wt.% to 3.0 wt.% based on the total fraction of the color developer in the heat-sensitive color-forming layer and / or the at least one anti-aging agent has a weight fraction of 0.2 wt.% to 30.0 wt.%, preferably 5 wt.% to 25.0 wt.% based on the total fraction of the color developer in the heat-sensitive color-forming layer.

[0092] According to one embodiment, the at least one polymeric binder of the heat-sensitive layer is selected from the group comprising water-soluble starches, starch-based biolatices of the Ecosphere type, starch derivatives, methylcellulose, hydroxyethylcellulose, carboxymethylcelluloses, partially or fully saponified polyvinyl alcohols, ethylene-vinyl alcohol copolymers, chemically 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 and mixtures thereof, and wherein the at least one binder is preferably selected as polyvinyl alcohol.

[0093] In particular, this includes at least one binder of a synthetic or biogenic nature. The at least one biogenic binder includes, in particular, biogenic polymers based on modified, especially chemically and / or thermally modified, and unmodified starches, celluloses, proteins, chitin, chitosan, lignin, casein, gelatin, collagen, shellac, vegetable oil, lipids, polylactic acid (PLA), polyhydroxyalkanoates (PHA), and mixtures thereof.

[0094] 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 30.0 wt.%, preferably in an amount of 2.5 wt.% to 20.0 wt.%, based on the total dry mass of the heat-sensitive layer.

[0095] To achieve specific application-related performance characteristics of heat-sensitive recording materials, preferably self-adhesive heat-sensitive recording materials, in particular self-adhesive labels, the binder is preferably present in cross-linked form in the heat-sensitive layer, wherein the optimal degree of cross-linking of the binder is achieved in the drying step of the coating process in the presence of a cross-linker.

[0096] Preferably, the binder is configured as a cross-linked further binder, wherein the cross-linked further binder is preferably configured as a self-cross-linking further binder, or wherein the heat-sensitive color-forming layer comprises a further cross-linker configured to react with the further binder to obtain the cross-linked further binder.

[0097] The self-crosslinking binder preferably comprises modified polyvinyl alcohols and / or modified acrylates.

[0098] According to one embodiment, the heat-sensitive layer comprises at least one release agent, which is preferably selected as fatty acid metal salts, particularly preferably zinc stearate or calcium stearate, or also behenate salts, synthetic waxes, particularly preferably in the form of fatty acid amides, further particularly preferably stearic acid amide and behenic acid amide, fatty acid alkanolamides, particularly preferably stearic acid methylolamide, paraffin waxes of different melting points, ester waxes of different molecular weights, ethylene waxes, propylene waxes of different hardnesses and / or natural waxes, particularly preferably carnauba wax or montan wax.

[0099] The release agent is preferably present in an amount of about 1 to about 30 wt.%, particularly preferably in an amount of about 2 to about 30 wt.%, and even more preferably in an amount of about 3 to about 25 wt.%, based on the total dry mass of the heat-sensitive layer.

[0100] According to one embodiment, the heat-sensitive layer has an areal weight of 1 g / m² as determined by the ISO 536 standard. 2 up to 10 g / m² 2 on, preferably from 2 g / m² 2 up to 6 g / m² 2 .

[0101] According to one embodiment, the heat-sensitive recording material, in particular the heat-sensitive layer, does not contain any organic pigments, in particular no unexpanded and / or expanded hollow pigments.

[0102] In particular, the heat-sensitive layer does not contain a styrene-acrylate copolymer hollow pigment and / or a styrene-butadiene solid spherical pigment.

[0103] According to one embodiment, the heat-sensitive recording material has at least one intermediate layer which is arranged between the support substrate and the heat-sensitive layer, wherein the intermediate layer preferably has at least one binder, and / or preferably at least one pigment.

[0104] In particular, the at least one binder of the intermediate layer is selected from the group comprising water-soluble starches, oxidized starch, Ecosphere-type biolatex, starch derivatives, methylcellulose, hydroxyethylcellulose, carboxymethylcelluloses, partially or fully saponified polyvinyl alcohols, ethylene-vinyl alcohol copolymers, chemically 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, acrylonitrile-butadiene copolymers and / or styrene-butadiene latex and mixtures thereof, wherein the at least one binder is preferably selected as polyvinyl alcohol and / or styrene-butadiene latex, more preferably a mixture of polyvinyl alcohol and styrene-butadiene latex or Styrene-butadiene latex.

[0105] In particular, at least one pigment of the intermediate layer is selected from the group comprising calcium silicate hydrate, barium sulfate, kaolinite, calcium silicate, calcium sulfate, sodium aluminum silicate, calcium carbonates, preferably synthetic, natural or precipitated calcium carbonates, aluminum oxides, aluminum hydroxides, silicas, precipitated and pyrogenic silicas, diatomaceous earths, magnesium carbonates, silicon dioxide, talc, kaolin, titanium dioxide, bentonite, organic hollow pigments, in particular expanded or non-expanded organic hollow pigments and mixtures thereof, preferably silicon dioxide, kaolin, in particular calcined kaolin, calcium carbonate, and / or organic hollow pigments, in particular expanded or non-expanded organic hollow pigments.

[0106] The composition of the pigmented primer or intermediate coat is not critical. This coating consists primarily of calcined kaolin and a binder based on styrene-butadiene, polyvinyl alcohol, and / or starch. Primers with non-expanded and / or expanded organic (hollow) pigments, possibly mixed with inorganic pigments, are also possible. The application rate of this pigmented layer or intermediate coat is typically between 2 and 12 g / m². 2 .

[0107] In particular, the at least one pigment of the intermediate layer comprises unexpanded and / or expanded organic hollow pigments, preferably a styrene-acrylate copolymer. Preferably, the unexpanded and / or expanded organic hollow pigments have a glass transition temperature of 40 °C to 100 °C and / or an average particle size of up to 20 µm.

[0108] The intermediate layer serves firstly as a heat barrier between the carrier substrate and the heat-sensitive color-forming layer, and secondly enables the surface smoothness of the carrier substrate to be improved for the heat-sensitive color-forming layer.

[0109] According to one embodiment, the heat-sensitive recording material has at least one protective layer arranged on the heat-sensitive layer, wherein the protective layer preferably comprises at least one polymer, particularly preferably comprising polyvinyl alcohols, modified polyvinyl alcohols, polyacrylates and polyurethanes, and / or at least one pigment and / or at least one crosslinking agent.

[0110] The protective layer arranged on the outside of the heat-sensitive color-forming layer ensures effective protection or advantageous printability of the heat-sensitive color-forming layer.

[0111] According to one embodiment, the at least one polymer of the protective layer is selected from the group comprising 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-, silanol-modified polyvinyl alcohols, ethylene-vinyl alcohol copolymer (EVOH) 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, acrylonitrile-butadiene copolymers and mixtures thereof, wherein in particular (meth)acrylamide-acrylic acid ester-based copolymers of the Bariastar® type are used.which preferably exist in the form of core-shell structures and / or wherein, in particular, chemically modified polyvinyl alcohols are present, which especially comprise ethylene-modified polyvinyl alcohol and / or ethylene vinyl acetate.

[0112] According to one embodiment, the at least one polymer of the protective layer has a weight fraction of 30 wt.% to 90 wt.% based on the total solids content of the protective layer, wherein the weight fraction is preferably from 40 wt.% to 80 wt.%.

[0113] According to one embodiment, at least one polymer of the protective layer is configured as a cross-linked polymer, wherein the cross-linked polymer is preferably configured as a self-cross-linking polymer, or wherein the protective layer comprises a cross-linker configured to react with the polymer to obtain the cross-linked polymer.

[0114] To achieve specific application-related performance characteristics of a heat-sensitive recording material, at least one polymer is preferably present in cross-linked form in the protective layer, wherein the optimal degree of cross-linking of the polymer is achieved during a drying step of the coating process, particularly in the presence of a cross-linker.

[0115] According to one embodiment, the self-crosslinking polymer comprises modified polyvinyl alcohols and / or modified acrylates.

[0116] Self-crosslinking polymers, such as specially modified polyvinyl alcohols and / or modified acrylates, enable crosslinking without the addition of a crosslinking agent due to the reactive groups that are already part of the polymer of the self-crosslinking polymer.

[0117] According to one embodiment, the at least one crosslinking agent of the protective layer is selected from the group comprising polyhydric aldehydes, preferably glyoxal, dialdehyde starch, and / or glutaraldehyde, in particular alone or in mixture with borate salts, salts or esters of glyoxylic acid, ammonium zirconium carbonate, organic titanates, polyamidoamine epichlorohydrin resins, adipic acid dihydrazide, boric acid or their salts, polyamines, epoxy resins, formaldehyde oligomers, cyclic ureas, methylol urea, and melamine formaldehyde oligomers and mixtures thereof, wherein the crosslinker is further preferably selected from the group comprising ammonium zirconium carbonate and polyamidoamine epichlorohydrin resins.

[0118] According to one embodiment, the at least one crosslinking agent of the protective layer has a weight fraction of 0.01 wt.% to 25.0 wt.% based on the total solids content of the protective layer, wherein the weight fraction is preferably from 0.05 wt.% to 15 wt.%.

[0119] According to one embodiment, the at least one pigment of the protective layer comprises at least one inorganic pigment selected from the group consisting of calcium carbonates, preferably synthetic, natural or precipitated calcium carbonates, aluminum oxides, aluminum hydroxides, silicas, precipitated and pyrogenic silicas, diatomaceous earths, magnesium carbonates, talc, kaolin, titanium oxide, bentonite and mixtures thereof.

[0120] According to one embodiment, the at least one pigment of the protective layer has a weight fraction of 2.5 wt.% to 50 wt.% based on the total solids content of the protective layer, wherein the weight fraction is preferably from 10 wt.% to 45 wt.%.

[0121] According to one embodiment, the protective layer comprises at least one lubricant, wherein the lubricant is preferably selected from the group consisting of fatty acid metal salts, preferably zinc stearate or calcium stearate, behenate salts or synthetic waxes, preferably in the form of fatty acid amides, more preferably stearic acid amide and behenic acid amide, fatty acid alkanolamides, preferably stearic acid methylolamide, paraffin waxes of different melting points, ester waxes of different molecular weights, polyethylene waxes, polypropylene waxes of different hardnesses, Chemipearl®-type polyolefin particles, natural waxes, preferably carnauba wax or montan wax, and mixtures thereof.

[0122] According to one embodiment, the at least one lubricant of the protective layer has a weight fraction of 1 wt.% to 30 wt.% based on the total solids content of the protective layer, wherein the weight fraction is preferably from 2 wt.% to 20 wt.%.

[0123] According to one embodiment, the protective layer comprises at least one brightener and / or at least one tinting dye, wherein the brightener is preferably selected as a stilbene.

[0124] The brightener and / or nuanced dye can be used to advantageously adjust the surface whiteness and / or the color of the protective layer.

[0125] According to one embodiment, the protective layer has a basis weight of 0.3 g / m². 2 up to 5.0 g / m² 2 on, preferably from 1.0 g / m² 2 up to 3.0 g / m² 2 .

[0126] According to one embodiment, the protective layer has a thickness of 0.3 µm to 6.0 µm, preferably from 0.5 µm to 3.0 µm.

[0127] According to one embodiment, the protective layer has a Bekk smoothness measured according to DIN 53107 of 100 sec to 3000 sec, preferably of 500 sec to 2500 sec.

[0128] A correspondingly advantageous Bekk smoothness can be achieved through a smoothing process.

[0129] According to one embodiment, the protective layer has a surface roughness of 0.5 µm to 2.50 µm, preferably of 0.80 µm and 2.00 µm, as measured according to the ISO 8791-4 standard.

[0130] According to one embodiment, the heat-sensitive recording material, in particular the heat-sensitive layer and / or the intermediate layer, comprises a biopolymeric material, preferably starch or other polysaccharides, cellulose, plant gums, proteins, and more preferably gelatin or whey protein.

[0131] According to one embodiment, the heat-sensitive color-forming layer has at least one further brightener, wherein the further brightener is preferably selected as a stilbene.

[0132] The additional brightener allows the surface whiteness of the heat-sensitive recording material to be controlled.

[0133] According to one embodiment, the heat-sensitive color-forming layer comprises a rheology aid, preferably a thickener and / or a surfactant.

[0134] This offers the advantage that certain coating properties of the heat-sensitive color-forming layer can be improved during the manufacturing process.

[0135] According to one embodiment, the heat-sensitive color-forming layer comprises at least one defoamer.

[0136] According to one embodiment, the heat-sensitive recording material has a basis weight of 20 g / m² as determined by the ISO 536 standard. 2 up to 100 g / m² 2 on, preferably from 35 g / m² 2 up to 90 g / m² 2 .

[0137] According to one embodiment, the heat-sensitive color-forming layer has a Bekk smoothness of 150 sec to 1500 sec, preferably 250 sec to 1000 sec, as measured according to DIN 53107.

[0138] According to one embodiment, the heat-sensitive recording material has an optical density (o. D.) defined according to the description of at least 0.75, preferably at least 0.9, and most preferably at least 1.0, particularly at an energy level of 8.88 mJ / mm². 2 was measured.

[0139] The optical density (o. D.) was determined in particular using a SpectroDens densitometer from Techkon, especially at an energy level of 8.88 mJ / mm².2 measured. The measurement uncertainty of the O.D. values ​​is in particular approximately ≤2%.

[0140] In particular, 6 cm wide strips of the heat-sensitive recording materials were thermally treated using a GeBE PrinterLab GPT-10000 test printer (GeBE Elektronik und Feinwerktechnik GmbH, Germany), specifically with a Kyocera print bar of 305 dpi, particularly at an applied voltage of 24 V, and particularly with a bar pattern at an energy level of 8.88 mJ / mm. 2 and in particular printed at a printing speed of approximately 100 mm / s. The area of ​​one bar of the printed pattern corresponds in particular to 53 × 12 mm.

[0141] According to one embodiment, the heat-sensitive recording material has a roughness of less than 5 µm, preferably less than 4.5 µm, more preferably less than 4 µm, more preferably less than 3 µm, and more preferably less than 2.5 µm, as measured according to DIN ISO 8791-4 using a Parker Print Surf tester.

[0142] According to one embodiment, the heat-sensitive recording material is defined as one according to the description at an energy level of 8.88 mJ / mm². 2 or 10.32 mJ / mm 2Heat-sensitive recording material printed with a barcode test pattern using a GeBE PrinterLab GPT-10000 test printer, wherein the printed heat-sensitive recording material has a barcode machine readability grade of 1 or more, preferably 2 or more, and most preferably 3 or more, as defined in the description and evaluated according to the ISO 15416 standard.

[0143] In particular, a barcode pattern printout according to the UPC-A code is printed lengthwise and crosswise on the printed heat-sensitive recording material.

[0144] In particular, the evaluation of barcode machine readability is carried out with a barcode verification device REA VeriCube from REA Elektronik Deutschland in accordance with the ISO 15416 standard, whereby the laser scanner operates at a wavelength of 660 nm.

[0145] In particular, the evaluation is carried out using the software “TransWin32 V.1.2.0.2 / 16829”.

[0146] In particular, the evaluation of barcode machine readability is based on the scan reflection profile class in descending order of quality of the respective barcode: A (corresponds to a grade of at least 4), B (corresponds to a grade of 3), C (corresponds to a grade of 2), D (corresponds to a grade of 1), F (corresponds to a grade of 0).

[0147] According to one embodiment, the at least one color developer comprises a compound of formula (I): wherein R and R1 are independently selected from the group comprising hydrogen, C1-C 18-Alkyl, C1-C8-alkoxy-C1-C8-alkyl, and (R9)2N-C1-C8-alkyl, wherein R9 is selected from the group comprising C1-C8-alkyl, C5-C6-cycloalkyl; or a compound of formula (II) wherein R2, R3, R4, R5, and R6 are independently selected from the group comprising hydrogen, C1-C8-alkyl, -NH-C(=O)-R7, and -C(=O)-NH-R7, wherein R7 is selected as C1-C8-alkyl or -C(=O)OR8, wherein R8 is selected as C1-C8-alkyl or halogen, or wherein R2 and R3, or R4 and R5 or both, or wherein R3 and R4, or R5 and R6 or both, or wherein R2 and R3 and R5 and R6, together form a hydrocarbon group with three or four carbon atoms, and wherein Q comprises a single bond or C1-C8 alkylene, which may be branched or unbranched, and wherein the C1-C8 alkylene comprises a main chain having one or more oxygen atoms between two carbon atoms, if the C1-C8 alkylene has more than two carbon atoms, wherein the compound of formula (I) preferably comprises a compound of formula (1a):or wherein the compound of formula (I) preferably comprises a compound of formula (Ib):and wherein the compound of formula (I) particularly preferably comprises 5-(N-3-methylphenylsulfonylamido)-(N',N''-bis-{3-methylphenyl)-isophthalic diamide.

[0148] In particular, the compound of formula (1a) comprises at least one of the following compounds: 5-(N-benzylsulfonylamido)-(N',N''-dibenzyl)-isophthalic diamide, 5-(N-3-methylphenylsulfonylamido)-(N',N''-bis-(3-methylphenyl)-isophthalic diamide, 5-(N-2,6-diethylphenylsulfonylamido)-(N',N''-bis-(2,6-diethylphenyl)-isophthalic diamide, 5-(N-phenylsulfonylamido)-(N',N''-bisphenyl)-isophthalic diamide, 5-(O-isopropylphenylsulfonylamido)-(N',N''-bis-(o-isopropylphenyl)-isophthalic diamide, 5-(Np-acetamido-phenyl-sulfonylamido)-(N',N''-bis-(p-acetamido-phenyl)-isophthalic diamide, 5-(N-1-tetralino-sulfonylamido)-(N',N''-bis-(1-tetralino)-isophthalic diamide, 5-(N-3-methylphenyl-sulfonylamido)-(N',N''-bis-(3-methylphenyl)-isophthalic diamide, 5-(N-1-phenylethyl-sulfonylamido)-(N',N''-bis-(1-phenylethyl)-isophthalic diamide, 5-(N-2-phenylethyl-sulfonylamido)-(N',N''-bis-(2-phenylethyl)-isophthalic diamide, 5-(N-2,6-diethylphenyl-sulfonylamido)-(N',N''-bis-(2,6-diethylphenyl)-isophthalsäurediamid, 5-(N-n-butyl-sulfonylamido)-(N',N''-di-n-butyl-isophthalsäurediamid, 5-(N-2-ethylhexyl- sul-fonylamido)-(N',N''-di-2-ethylhexyl-isophthalsäurediamid, 5-(N-benzyl-sulfonylamido)-(N',N''-diphenyl)-isophthalsäurediamid, 5-(N-phenyl-sulfonylamido)-(N',N''-dibenzyl)-isophthalsäurediamid, 5-(N-benzylsulfonylamido)-(N',N''-bis-(3-methyl-phenyl)-isoph-thalsäurediamid, 5-(N-butyl-sulfonylamido)-(N',N''-bis-(3-methyl-phenyl)-isophthalsäu-rediamid, 5-(N-1-phenyl-ethyl-sulfonylamido)-(N',N''-bis-(3-methyl-phenyl)-isophthal-säurediamid, 5-(N-2-phenyl-ethyl-sulfonylamido)-(N',N''-bis-(3-methyl-phenyl)-isoph-thalsäurediamid, 5-(N-2-methoxy-ethyl-sulfonylamido)-(N',N''-bis-(3-methyl-phenyl)-isophthalsäurediamid, 5-(N-n-octyl-sulfonylamido)-(N',N''-bis-(3-methyl-phenyl)-isoph-thalsäurediamid, 5-(N-benzyl-sulfonylamido)-(N',N''-bis-(2,6-diethyl-phenyl)-isophthal-säurediamid, 5-(N-n- octyl-sulfonylamido)-(N',N''-bis-(2,6-diethyl-phenyl)-isophthalsäu-rediamid,and 5-(N-2-phenoxy-ethylsulfonylamido)-(N',N''-bis-(2,6-diethyl-phenyl)-isophthalic diamide.,

[0149] The compound 5-(N-3-methylphenylsulfonylamido)-(N',N''-bis-{3-methylphenyl)-isoph-thaladiamide is also marketed under the name Pergafast 425.

[0150] The compound 5-(N-3-methylphenylsulfonylamido)-(N',N''-bis-{3-methylphenyl)-isophthalic diamide comprises in particular three different polymorphic forms, including an α-polymorphic form with a melting point of 211.2 °C determined by DSC, a β-polymorphic form with a melting point of 192.2 °C determined by DSC and a γ-polymorphic form with a melting point of 215.6 °C determined by DSC.

[0151] According to one embodiment, the at least one color developer comprises a compound of the formula (NI): wherein R1, R2, and R3 are independently selected from the group comprising hydrogen, halogen, nitro, C1-C6 alkyl, C1-C6 alkoxyl, C2-C6 alkenyl, C1-C6 fluoroalkyl, N(R4)2, NHCOR5, optionally substituted phenyl, and optionally substituted benzyl, wherein R4 is selected from the group comprising hydrogen, phenyl, benzyl, and C1-C6 alkyl, wherein R5 is selected as C1-C6 alkyl, wherein n1 and n3 are independently selected as an integer from 1 to 5, and wherein n2 is an integer from 1 to 4; where R1, R2, and R3 are preferably selected as hydrogen, further preferably comprising the compound of formula (NI) N-(2-(3-Phenylureido)phenyl)benzenesulfonamide, and even more preferably comprising the α-polymorph and / or the β-polymorph of N-(2-(3-Phenylureido)phenyl)benzenesulfonamide, wherein the α-polymorph is characterized in particular by an X-ray diffraction pattern with Bragg angles (2θ / CuKα) of 5.8, 9.3, 13.2, 15.7, 17.3, 18.3, 18.7, 19.5, 20.3, 21.1, 21.9, 22.8, 23.3, 23.6, 24.4, 24.9, 25.6, 26.7, 27.8, 28.1, 29.3, 29.6, 30.2, 31.6, 32.3, 32.8 and / or a melting point of 158°C to 159°C determined by DSC, wherein the β-polymorph is characterized in particular by an X-ray diffraction pattern with Bragg angles (2θ / CuKα) of 10.0, 11.0, 12.3, 12.7, 13.8, 14.9, 15.6, 16.8, 17.7, 18.5, 20.1, 20.9, 21.6, 22.0, 22.8, 23.0, 23.6, 24.3, 25.5, 26.7, 27.8, 28.4, 29.0, 29.8, 30.5, 31.1, 31.3 and / or a melting point of 173°C to 174°C determined by DSC.

[0152] In particular, the compound of formula (NI) is a compound of formula (IV) or a compound of formula (V), where R1 and R3 are defined as for the compound of formula (NI):

[0153] In particular, the compound of formula (NI) is a benzenesulfonamide compound.

[0154] In particular, R1, R2 and / or R3 is selected as hydrogen, halogen, more preferably fluorine, chlorine, bromine or iodine, nitro, a straight, branched or cyclic C1-C6 alkyl group, more preferably methyl, ethyl, propyl, isopropyl, butyl, isobutyl, secbutyl, T-butyl, pentyl, isopentyl, neopentyl, hexyl, isohexyl, cyclopropyl, cyclobutyl, 2-methylcyclopropyl, cyclopropylmethyl, cyclopentyl, or cyclohexyl, a straight, branched or cyclic C1-C6 alkoxy group, more preferably methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, sec-butoxy, T-butoxy, pentyloxy, isopentyloxy, hexyloxy, cyclopropoxy, cyclobutoxy, 2-methylcyclopropoxy, cyclopropylmethoxy, cyclopentyloxy, or cyclohexyloxy;a C2-C6 alkenyl group, more preferably a vinyl group, an allyl group, an isopropenyl group, a 1-propenyl group, a 2-propenyl group, a 1-butenyl group, a 2-butenyl group, a 3-butenyl group, a 1,3-butanedienyl group, or a 2-methyl-2-propenyl group, a C1-C6 fluoroalkyl group, more preferably a trifluoromethyl group, a perfluoroethyl group, a perfluoropropyl group, a perfluorobutyl group, a perfluorohexyl group, or a perfluorocyclohexyl group, an N(R4)2 group, wherein R4 is more preferably selected as hydrogen, phenyl, benzyl or C1-C6 alkyl, an NHCOR5 group, wherein R5 is more preferably selected as C1-C6 alkyl, an optional substituted phenyl group; and as an optionally substituted benzyl group.;

[0155] In particular, R1, R2 and / or R3 is selected as hydrogen or an even C1-C6 alkyl group, wherein R1 is more preferably hydrogen or methyl, and R2 and R3 are each hydrogen.

[0156] In particular, the choices for the C1-C6 alkyl group selected according to R4 or R5 are the same as for the C1-C6 alkyl group selected according to R1.

[0157] In particular, the optional substituents of the optionally substituted groups are selected as hydroxy, halogen, most preferably fluorine, chlorine, bromine or iodine, C1-C6 alkyl, most preferably methyl, ethyl, N-propyl, isopropyl, N-butyl, secbutyl, T-butyl, N-pentyl, isopentyl, neopentyl, T-pentyl, N-hexyl, isohexyl, 1-methylpentyl, or 2-methylpentyl, and C1-C6 alkoxy, most preferably methoxy, ethoxy, N-propoxy, isopropoxy, N-butoxy, sec-butoxy, or T-butoxy.

[0158] Preferably the compound of formula (NI) is selected as 4-methyl-N-(2-(3-phenylureido)phenyl)benzenesulfonamide and N-(2-(3-phenylureido)phenyl)benzenesulfonamide, further preferably N-(2-(3-phenylureido)phenyl)benzenesulfonamide.

[0159] According to one embodiment, the at least one color developer comprises N-(2-(3-Phenylureido)phenyl)benzenesulfonamide, preferably the α-polymorph and / or the β-polymorph of N-(2-(3-Phenylureido)phenyl)benzenesulfonamide.

[0160] In particular, the corresponding X-ray diffraction pattern was obtained by X-ray diffraction (XRD) measurement using a Bruker D2 phaser, a Cu electrode, a voltage of 30 kV and a Lynxeye detector.

[0161] In particular, the corresponding melting point determined by DSC was measured by differential scanning calorimetry using a Netzsch DSC 200 F3 Maia® device, an Al crucible with a cold-welded, perforated lid, a heating rate of 10 K / min and a temperature range of 25°C to 200°C under N2 atmosphere.

[0162] The corresponding compound, N-(2-(3-Phenylureido)phenyl)benzenesulfonamide, is also marketed under the name NKK-1304.

[0163] According to one embodiment, the at least one color developer comprises a compound of formula (1): wherein R1 is selected from the group comprising unsubstituted or substituted phenyl, naphthyl and C1-C 20 -Alkyl, where X is selected from the group comprising -C(=NH) -, -C(=S) - and -C(=O) -, where A is selected from the group comprising unsubstituted or substituted phenylene, naphthylene, C1-C 12-Alkylene, and an unsubstituted or substituted heterocyclic group, wherein B is selected from the group comprising -O-SO2-, -SO2-O-, -NH-SO2-, -SO2-NH-, -S-SO2-, -O-CO-, -O-CO-NH-, -NH-CO-, -NH-CO-O-, -S-CO-NH-, -S-CS-NH-, -CO-NH-SO2-, -O-CO-NH-SO2-, -NH=CH-, -CO-NH-CO-, -S-, -CO-, -O-, -SO2-NH-CO-, -O-CO-O- and -O-PO-(OR2)2, and wherein R2 is selected from the group comprising unsubstituted or substituted aryl, benzyl and C1-C 20 -Alkyl, provided that if B is not a group of the formula -O-SO2-, then R2 is unsubstituted or substituted phenyl, naphthyl or C1-C8 alkyl, and that if B is -O-, then R2 is not alkyl; wherein X is preferably selected as -C(=O)-, wherein R1 is selected as substituted or substituted phenyl, preferably as C1-C3-alkyl substituted phenyl, wherein R2 is selected as unsubstituted or substituted aryl, preferably unsubstituted phenyl, wherein B is selected as -O-SO2-, and wherein R2 is selected as substituted or substituted aryl, preferably as C1-C3-alkyl substituted phenyl, and wherein the at least one color developer of formula (1) preferably comprises 4-methyl-N-(((3-(((4-methylphenyl)sulfonyl)oxy)phenyl)amino)carbonyl)benzenesulfonamide, more preferably the α-polymorph and / or the β-polymorph of 4-methyl-N-(((3-(((4-methylphenyl)sulfonyl)oxy)phenyl)amino)carbonyl)benzenesulfonamide, wherein the α-polymorph is characterized in particular by an X-ray diffraction pattern with Bragg angles (2θ / CuKα) of 8.5, 9.5, 11.8, 12.1, 12.2, 13.7, 14.1, 16.6, 17.1, 18.3, 18.6, 19.1, 19.3, 20.1, 20.4, 20.9, 21.3, 23.1, 24.2, 24.6, 25.0, 27.9, 28.6 and / or a melting point of 161°C to 162°C determined by DSC, where in particular the β-polymorph is characterized by an X-ray diffraction pattern with Bragg angles (2θ / CuKα) of 10.3, 11.0, 12.9, 13.2, 15.4, 17.1, 18.0, 18.2, 19.4, 20.0, 20.7, 21.2, 23.0, 24.9, 25.3, 26.5, 26.8, 27.5, 30.7, 32.7 and / or a melting point of 166°C to 167°C determined by DSC.

[0164] The compound 4-methyl-N-(((3-(((4-methylphenyl)sulfonyl)oxy)phenyl)amino)carbonyl)benzenesulfonamide is also marketed under the name Pergafast 201.

[0165] In particular, R1 is selected as phenyl or naphthyl, which may be unsubstituted or substituted by, for example, C1-C8 alkyl, C1-C8 alkoxy or halogen.

[0166] In particular, the substituents are selected as C1-C4 alkyl, more preferably methyl or ethyl, C1-C4 alkoxy, more preferably methoxy or ethoxy, or halogen, and more preferably chlorine.

[0167] In particular, R1 is selected as unsubstituted naphthyl.

[0168] In particular, R1 is selected as a substituted phenyl, with the substituents being further preferably selected as one of the alkyl substituents mentioned above.

[0169] In particular, R1 is selected as unsubstituted or substituted C1-C 20 -Alkyl, preferably C1-C8 alkoxy or halogen, further preferably C1-C4 alkoxy, even more preferably methoxy or ethoxy, or halogen, most preferably chlorine.

[0170] In particular, R1 is selected as an unsubstituted C1-C 20 -Alkyl.

[0171] In particular, R1 is unsubstituted phenyl or phenyl substituted by C1-C8 alkyl, C1-C8 alkoxy, or halogen, with substituted phenyl being further preferred. Most preferred is phenyl substituted by C1-C4 alkyl, and even more preferably by methyl.

[0172] In particular, X is a group of the formula -C(=S)- or -C(=O)-, preferably a group of the formula -C(=O)-.

[0173] In particular, A is an unsubstituted phenylene or an unsubstituted naphthylene group, or a phenylene or a naphthylene group which is preferably substituted by C1-C8 alkyl, halogen-substituted C1-C8 alkyl, C1-C8 alkoxy-substituted C1-C8 alkyl, C1-C8 alkoxy, halogen-substituted C1-C8 alkoxy, C1-C8 alkylsulfonyl, halogen, phenyl, phenoxy or phenoxycarbonyl.

[0174] In particular, alkyl and alkoxy substituents comprising 1 to 4 carbon atoms are preferred, with C1-C8 alkyl, halogen-substituted C1-C8 alkyl, C1-C8 alkyl sulfonyl or halogen being preferred.

[0175] In particular, A is an unsubstituted naphthylene group.

[0176] In particular, A is a heterocyclic group which preferably comprises unsubstituted pyrimidylene or pyrimidylene which is substituted by C1-C8 alkyl, or even more preferably by C1-C4 alkyl.

[0177] In particular, A is a C1-C 12 -Alkylene group, preferably C1-C8 alkylene, further preferably C1-C4 alkylene.

[0178] In particular, A is unsubstituted phenylene or phenylene substituted by C1-C8 alkyl, halogen-substituted C1-C8 alkyl, C1-C8 alkoxy-substituted C1-C8 alkyl, C1-C8 alkoxy, halogen-substituted C1-C8 alkoxy, C1-C8 alkylsulfonyl, halogen, phenyl, phenoxy or phenoxycarbonyl, more preferably C1-C8 alkyl, halogen-substituted C1-C8 alkyl, C1-C8 alkylsulfonyl or halogen.

[0179] In particular, A is unsubstituted phenylene or phenylene substituted by C1-C4 alkyl or halogen, preferably unsubstituted phenylene.

[0180] In particular, B is selected as -O-SO2-, -SO2-O-, -SO2-NH-, -S-SO2-, -O-, -O-CO- and -O-CO-NH-, preferably as -O-SO2-, -SO2-O- and -SO2-NH-, and most preferably as -O-SO2- and -O-.

[0181] In particular, R2 is aryl, more preferably phenyl or naphthyl, which is unsubstituted or substituted, and even more preferably by C1-C8 alkyl, halogen-substitutes C1-C8 alkyl, C1-C8 alkoxy-substitutes C1-C8 alkyl, C1-C8 alkoxy, halogen-substitutes C1-C8 alkoxy or halogen, wherein the most preferred are alkyl and alkoxy substituents comprising 1 to 4 carbon atoms, with C1-C4 alkyl and halogen being the even more preferred substituents.

[0182] In particular, R2 is naphthyl, which is further preferentially unsubstituted.

[0183] In particular, R2 is benzyl, which is substituted by the substituents already mentioned for the selection of R2 as phenyl or naphthyl, with unsubstituted benzyl being further preferred.

[0184] In particular, R2 C1-C 20-Alkyl, more preferably C1-C8 alkyl, even more preferably C1-C6 alkyl, which is unsubstituted or substituted by, for example, C1-C8 alkoxy, halogen, phenyl or naphthyl, wherein most preferably are unsubstituted alkyl groups, even more preferably C1-C4 alkyl.

[0185] In particular, R2 is C1-C6 alkyl, halogen-substituted C1-C6 alkyl, phenyl-substituted C1-C6 alkyl, naphthyl-substituted C1-C6 alkyl, unsubstituted phenyl, or phenyl substituted by C1-C8 alkyl, halogen-substituted C1-C8 alkyl, C1-C8 alkoxy-substituted C1-C8 alkyl, C1-C8 alkoxy, halogen-substituted C1-C8 alkoxy or halogen, naphthyl and benzyl substituted by C1-C4 alkyl or halogen.

[0186] In particular, R2 is C1-C4 alkyl, halogen-substituted C1-C4 alkyl, phenyl which is unsubstituted or substituted by C1-C4 alkyl or halogen, naphthyl and benzyl which is unsubstituted or substituted by C1-C4 alkyl or halogen, most preferably phenyl which is unsubstituted or substituted by C1-C4 alkyl or halogen.

[0187] In particular, R1 is phenyl substituted by C1-C4 alkyl, more preferably methyl, X is -C(=O)-, A is phenylene unsubstituted or substituted by C1-C8 alkyl or halogen, wherein unsubstituted phenylene is more preferred, such as 1,3-phenylene, B is a group of the formula -O-SO2- or -O-, and R2 is phenyl, naphthyl or benzyl unsubstituted or substituted by C1-C4 alkyl or halogen, wherein phenyl substituted by C1-C4 alkyl is more preferred.

[0188] In particular, the corresponding X-ray diffraction pattern was obtained by X-ray diffraction (XRD) measurement using a Bruker D2 phaser, a Cu electrode, a voltage of 30 kV and a Lynxeye detector.

[0189] In particular, the corresponding melting point determined by DSC was measured by differential scanning calorimetry using a Netzsch DSC 200 F3 Maia® device, an Al crucible with a cold-welded, perforated lid, a heating rate of 10 K / min and a temperature range of 25°C to 200°C under N2 atmosphere.

[0190] According to one embodiment, the at least one color developer comprises a compound of formula (2), J1-K1-L1-N(H)-C(=O)-N(H)-L2-K2-J2 where J1 and J2 are independently selected as unsubstituted or substituted aryl, where K1 and K2 are selected as -O-SO2-, where L1 and L2 are independently selected as unsubstituted or substituted aryl, wherein J1 and J2 are preferably selected as unsubstituted or substituted phenyl, preferably as C1-C3 alkyl substituted phenyl, and wherein L1 and L2 are preferably selected as unsubstituted phenyl, and the most preferred is the one comprising at least one color developer according to the formula 2 N,N'-Bis[3-[[(4-methylphenyl)sulfonyl]oxy]phenyl]urea.

[0191] In particular, L1 and L2 are independently selected as unsubstituted or substituted phenyl, further preferably substituted phenyl, even more preferably C1-C8 alkyl-substituted phenyl, most preferably methyl-substituted phenyl.

[0192] In particular, J1 and J2 are independently selected as unsubstituted or substituted phenyl, with unsubstituted phenyl being preferred.

[0193] According to one embodiment, the at least one color developer comprises [3-(3-phenylureido)phenyl]-4-methylbenzenesulfonate, 4,4'-bis(N,N'-p-toluenesulfonyl-aminocarbonylaminophenyl)methane, N,N'-p-toluenesulfonyl-aminocarbonylamino-phenyl, n-butyl-4(3-(p-toluenesulfonyl)ureido)benzoate, N,N'-diphenylurea, bisphenol A, 4,4'-dihydroxy-diphenylsulfone, 2,4'-dihydroxy-diphenyl-sulfone, 4-hydroxy-4'-iso-propoxy-diphenylsulfone, bis-(3-allyl-4-hydroxy-phenyl)sulfone, 4-Hydroxy-4'-benzyloxy-diphenyl sulfone, 4-hydroxy-4'-n-propoxy-diphenyl sulfone, N-phenyl-p-hydroxyphenylsulfonamide, 4-hydroxy-4'-allyloxydiphenyl sulfone, 2,4-Bis(phenylsulfonyl)phenol, N-(4-((4-(3-Phenylureido)phenyl)sulfonyl)phenyl)benzenesulfonamide, 2'-(3'-Phenylureido)phenyl 3-(3-phe-nylureido)benzenesulfonate, N-phenyl-N'[(phenylamino)sulfonyl]urea, and / or a urea compound according to the following formula, in particular comprising 4,4'-bis[(4-methyl-3-phenoxycarbonylaminophenyl)ureido]diphenylsulfone, 4,4'-bis[(2-methyl-5-phenoxycarbonylaminophenyl)ureido]diphenylsulfone, 4-(2-methyl-3-phenoxycarbonylaminophenyl)ureido-4'-(4-methyl-5-phenoxycarbonylaminophenyl)ureidodiphenylsulfone: and mixtures thereof.

[0194] According to one embodiment, the at least one color developer comprises at least one stabilizer, which is in particular selected from the group comprising sterically hindered phenolic compounds or sterically hindered amine compounds, wherein the sterically hindered amine compounds, as electron-absorbing compounds, have relatively low coloring activity and can only optionally be added to the heat-sensitive recording layer.

[0195] In particular, the at least one stabilizer comprises 2,2'-methylenebis(4-ethyl-6-tert-butylphenol), 4,4'-butylidene bis(6-tert-butyl-2-methylphenol), 1,1,3-tris(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, 1,1,3-tris(2-methyl-4-hy[1]droxy-5-cyclohexylphenyl)butane, 4,4'-thiobis(6-tert-butyl-2-methylphenol), tetrabromobisphenol A, tetrabromobisphenol S, 4,4-thiobis(2-methylphenol), 4,4'-thiobis(2-chlorophenol), tetrakis(1,2,2,6,6-pentamethyl-4-piperidyl)-1,2,3,4-butane tetracarboxylate, tetrakis(1,2,2,6,6-tetramethyl-4-piperidyl)-1,2,3,4-butanetetracarboxylate, Bis(2-chloroethyl)ether-4,4'-dihydroxydiphenylsulfone copolymer and mixtures thereof.

[0196] According to one embodiment, the at least one color developer has a weight fraction of 6 wt.% to 35 wt.% based on the total solids content of the heat-sensitive color-forming layer, wherein the weight fraction is preferably from 10 wt.% to 30 wt.%, and more preferably from 10 wt.% to 20 wt.%.

[0197] In particular, the at least one color developer is selected as N-(2-(3-phenyllureido)phenyl)benzenesulfonamide (trade name NKK-1304), wherein the at least one color developer has a weight fraction of 6 wt.% to 35 wt.% based on the total solids content of the heat-sensitive color-forming layer, wherein the weight fraction is preferably from 10 wt.% to 30 wt.%, more preferably from 10 wt.% to 20 wt.%, and most preferably from 12 wt.% to 18 wt.%

[0198] In particular, the at least one color developer is selected as 4-methyl-N-(((3-(((4-methylphenyl)sulfonyl)oxy)phenyl)amino)carbonyl)benzenesulfonamide (trade name Pergafast 201), wherein the at least one color developer has a weight fraction of 6 wt.% to 35 wt.% based on the total solids content of the heat-sensitive color-forming layer, wherein the weight fraction is preferably from 10 wt.% to 30 wt.%, more preferably from 10 wt.% to 20 wt.%, and most preferably from 12 to 18 wt.%.

[0199] In particular, the at least one color developer is selected as N,N'-Bis[3-[[(4-methylphenyl)sulfonyl]oxy]phenyl]urea, wherein the at least one color developer has a weight fraction of 6 wt.% to 35 wt.% based on the total solids content of the heat-sensitive color-forming layer, wherein the weight fraction is preferably from 10 wt.% to 30 wt.%, more preferably from 10 wt.% to 20 wt.%, and most preferably from 12 to 18 wt.%.

[0200] In particular, the at least one color developer is selected as 3-(3-phenylu-reido)phenyl]-4-methylbenzenesulfonate, wherein the at least one color developer has a weight fraction of 6 wt.% to 35 wt.% based on the total solids content of the heat-sensitive color-forming layer, wherein the weight fraction is preferably from 10 wt.% to 30 wt.%, more preferably from 10 wt.% to 20 wt.%, and most preferably from 12 wt.% to 18 wt.%.

[0201] In particular, the at least one color developer is selected as 4-hydroxy-4'-isopropoxy-diphenylsulfone, wherein the at least one color developer has a weight fraction of 6 wt.% to 35 wt.% based on the total solids content of the heat-sensitive color-forming layer, wherein the weight fraction is preferably from 10 wt.% to 30 wt.%, more preferably from 10 wt.% to 20 wt.%, and most preferably from 12 wt.% to 18 wt.%.

[0202] In particular, the at least one color developer is selected as bis-(3-allyl-4-hydroxyphenyl)sulfone, wherein the at least one color developer has a weight fraction of 6 wt.% to 35 wt.% based on the total solids content of the heat-sensitive color-forming layer, wherein the weight fraction is preferably from 10 wt.% to 30 wt.%, more preferably from 10 wt.% to 20 wt.%, and most preferably from 12 wt.% to 18 wt.%.

[0203] In particular, the at least one color developer is selected as 4,4'-sulfonyldiphenol (trade name BPS), wherein the at least one color developer has a weight fraction of 6 wt.% to 35 wt.% based on the total solids content of the heat-sensitive color-forming layer, wherein the weight fraction is preferably from 10 wt.% to 30 wt.%, more preferably from 10 wt.% to 20 wt.%, and most preferably from 12 wt.% to 18 wt.%.

[0204] According to one embodiment, the at least one color former is a dye of the triphenylmethane type, the fluorane type, the azaphthalide type and / or the fluorene type, preferably a dye of the fluorane type.

[0205] The use of the particularly preferred fluorane-type dye as at least one color former enables, due to its availability and balanced application-related properties, the provision of a heat-sensitive recording material with an advantageous price-performance ratio.

[0206] According to one embodiment, a fluorane-type dye is selected from the group comprising 3-diethylamino-6-methyl-7-anilinofluorane, 3-(N-ethyl-N-4-toludina-mino)-6-methyl-7-anilinofluorane, 3-(N-ethyl-N-isoamylamino)-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-(2,4-dimethylanilino)fluorane, 3-pyrrolidino-6-methyl-7-anilinofluorane, 3-(cyclohexyl-N-methylamino)-6-methyl-7-anilinofluorane, 3-diethylamino-7-(3-trifluoromethylanilino)fluorane, 3-n-dibutylamino-6-methyl-7-anilinofluorane, 3-diethyla-mino-6-methyl-7-(3-methylanilino)fluorane, 3-n-Dibutylamino-7-(2-chloroanilino)fluoran, 3-(N-ethyl-N-tetrahydrofurfurylamino)-6-methyl-7-anilinofluoran, 3-(N-methyl-N-propylamino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-ethoxypropylamino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-isobutylamino)-6-methyl-7-anilinofluoran, 3-dipentylamino-6-methyl-7-anilinofluoran and mixtures thereof.

[0207] According to one embodiment, the at least one color former has a weight fraction of 2 wt.% to 20 wt.% based on the total solids content of the heat-sensitive color-forming layer, wherein the weight fraction is preferably 4 wt.% to 15 wt.%, most preferably 4 wt.% to 12 wt.%.

[0208] According to one embodiment, the support substrate comprises paper, synthetic paper, and / or a plastic film, preferably paper.

[0209] The substrate used is not limited. The substrate material preferably has a basis weight of 30 g / m². 2 up to 100 g / m² 2 , preferably 30 g / m² 2 up to 80 g / m² 2 , even more preferably 32 to 76 g / m² 2 on.

[0210] In particular, the carrier substrate comprises a paper substrate made from hardwood and / or softwood pulp.

[0211] According to one embodiment, the heat-sensitive recording material comprises an adhesive layer arranged on the second side of the support substrate, wherein the adhesive layer comprises at least one adhesive, the adhesive preferably comprising a pressure-sensitive adhesive and / or a heat-activated adhesive and / or a permanently adhesive hot melt adhesive based on styrene-isoprene and PVC copolymers and / or a permanently adhesive hot melt adhesive based on synthetic rubber and / or a removable acrylate-based adhesive.

[0212] For example, a permanently adhesive hot melt adhesive based on styrene-isoprene and PVC copolymers is the S2200 adhesive from Avery Dennison.

[0213] For example, a removable acrylate-based adhesive is the R5000N adhesive from Avery Dennison.

[0214] For example, a permanently adhesive hot melt adhesive based on synthetic rubber is the Technomelt PS 8746 adhesive from Henkel. Method, Product-by-Process, and Use

[0215] The aforementioned tasks 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;Applying a coating suspension to the first side of the support substrate, wherein the coating suspension comprises at least one color former and at least one color developer, wherein the coating suspension comprises at least one polymeric binder 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, and wherein the precipitated calcium carbonate (PCC) comprises sieved precipitated calcium carbonate (PCC) and / or milled precipitated calcium carbonate (PCC) and / or filtered precipitated calcium carbonate (PCC); drying the coating suspension to obtain a heat-sensitive color-forming layer arranged on the first side of the support substrate.

[0216] It is preferred to obtain the heat-sensitive recording material according to the invention using 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 application suspensions, particularly aqueous dispersions, have a dry mass of 8 to 60 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 850 m / min. Alternatively, the application can also be carried out using a film press or curtain coating method.

[0217] This method is particularly advantageous from an economic point of view and due to the uniform application across the substrate.

[0218] If the dry matter content falls below 8% by weight, efficiency suffers because a large amount of water must be removed quickly through gentle drying, which negatively impacts the application speed. Conversely, if the dry matter content exceeds 60% by weight, this only results in increased technical effort to ensure the stability of the coating curtain during the application process and the drying of the applied film, as the machine must then operate at a very high speed.

[0219] In the curtain coating process, a freely falling curtain of coating dispersion is formed. The coating dispersion, in the form of a thin film (curtain), is "poured" onto a substrate by free fall, thus applying the coating dispersion to the substrate. DE 10 196 052 T1 discloses the use of the curtain coating process in the production of information recording materials, wherein multilayer recording layers are realized by applying the curtain, consisting of several coating dispersion films, to substrates.

[0220] It is also conceivable to implement the method according to the invention in which a "double curtain" is used. This means that two successive layers are applied immediately one after the other. The application is carried out so immediately one after the other that the first layer applied has not yet dried before the next layer is applied. The application of the two layers is thus preferably carried out "wet-on-wet".

[0221] All definitions relating to the curtain coating process apply analogously to the double curtain coating process.

[0222] The advantage of a "wet-on-wet" application using a double curtain coating process is that the two layers have a stronger bond and, in particular, the need for intermediate adhesion promoters can be eliminated.

[0223] In a preferred embodiment of the inventive method, the aqueous, deaerated coating suspension has a viscosity of approximately 50 to approximately 2500 mPas (Brookfield, 100 rpm, 20 °C). If the value falls below approximately 50 mPas or exceeds approximately 2500 mPas, this leads to poor flowability of the coating compound on the coating unit. The viscosity of the aqueous, deaerated coating suspension is particularly preferably approximately 100 to approximately 700 mPas. The viscosities of successive coating compounds in the double curtain should decrease from bottom to top. With incorrectly adjusted coatings, the probability of heel formation at the point of contact of the curtain as well as the occurrence of wetting problems increases.

[0224] In a preferred embodiment, to optimize the process, the surface tension of the aqueous coating suspension can be adjusted to approximately 25 to approximately 70 mN / m, preferably to approximately 35 to approximately 60 mN / m, measured in accordance with the standard for bubble pressure tensiometry (ASTM D 3825-90), as described below. Better control over the coating process is achieved by determining the dynamic surface tension of the coating paint and adjusting it precisely by selecting the appropriate surfactant and determining the required amount of surfactant.

[0225] Dynamic surface tension is measured using a bubble pressure tensiometer. The maximum internal pressure of a gas bubble formed in a liquid via a capillary is measured. 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: p=2σr

[0226] When a gas bubble is created at the tip of a capillary in a liquid, the curvature initially increases and then decreases again, resulting in a pressure maximum. The greatest curvature, and therefore the greatest pressure, occurs when the radius of curvature equals the capillary radius. Pressure curve during bladder pressure measurement, location of the pressure maximum:

[0227] The radius of the capillary is determined using a reference measurement performed with a liquid of known surface tension, usually water. Once the radius is known, the pressure maximum p can be calculated. max The surface tension must be calculated. Since the capillary is immersed in the liquid, the hydrostatic pressure p0, which results from the immersion depth and the density of the liquid (this is done automatically in modern measuring instruments), must be subtracted from the measured pressure. This results in the following formula for the bubble pressure method: σ=(pmax−p0)⋅r2

[0228] The measured value corresponds to the surface tension at a specific surface age, the time from the start of bubble formation until the occurrence of the pressure maximum. By varying the rate of bubble formation, the dependence of the surface tension on the surface age can be determined, resulting in a curve that plots the surface tension over time.

[0229] This dependency plays an important role in the use of surfactants, as the equilibrium value of the interfacial tension is not reached in many processes due to the sometimes low diffusion and adsorption rates of surfactants.

[0230] The formation of the individual layers can be done online or offline in a separate painting process.

[0231] In particular, to ensure that the layers described above in detail exhibit the Bekk smoothing mentioned above, the following process steps are preferably carried out.

[0232] The substrate is preferably smoothed in a first cylinder. This high degree of smoothness on one or both sides, achieved through this process, already provides an advantage to the substrate. Additional satin finishing by a downstream calender, preferably before a first coating unit, can further improve the smoothness and / or contribute to good profiling.

[0233] If a thickness coating, as defined above, is applied, this is preferably done by a film press before the intermediate layer is applied.

[0234] The thickness on the back is particularly advantageous to prevent the paint from bleeding through with the blade coater.

[0235] The use of a blade coater gives the material a good base smoothness, which is important for the dynamic sensitivity of the final product. There is a correlation between final smoothness and dynamic sensitivity.

[0236] The same applies to the protective layer. Alternatively, the protective layer can also be printed on or applied using a curtain coater. Protective layers that can be cured using actinic radiation are particularly suitable in terms of processing technology and technological properties. The term "actinic radiation" refers to UV or ionizing radiation, such as electron beams.

[0237] The heat-sensitive layer is preferably applied using curtain coating, as described above.

[0238] If substrates, especially papers, are coated on one side, the resulting curl should subsequently be corrected.

[0239] This is preferably done with a LAS (Liquid Applicator System). A film of water is applied to the less coated side and then dried. This restores the surface to a flat position. Applying the water film slightly degrades the surface finish.

[0240] A preferred option for protecting the surface would be a steam humidifier. This uses steam instead of water, thus avoiding damage to the surface. This method is very well suited for applications requiring the highest surface quality.

[0241] Another option would be a spray humidifier, which applies a water mist.

[0242] All of the above-mentioned layers can be single-layered or multi-layered.

[0243] According to one embodiment, the method comprises applying an adhesive dispersion to the second side of the carrier substrate and drying the applied adhesive suspension to obtain an adhesive layer, wherein the application quantity of the adhesive dispersion is preferably between 10 g / m² 2 and 30 g / m² 2 , especially preferably 20 g / m² 2 amounts.

[0244] According to one embodiment, the drying of the adhesive layer is carried out at a temperature of 60 °C to 80 °C, preferably at 70 °C.

[0245] According to one embodiment, the method includes the further process step, which is carried out after the application of the adhesive layer: applying a release paper to the adhesive layer, wherein the release paper is preferably designed as a siliconized release paper.

[0246] According to one embodiment, the application of the coating dispersion to the first side of the substrate is carried out by means of a curtain brush or by means of a squeegee on the coating side of a substrate pre-coated with a pigment coating, wherein the pigmented primer preferably comprises calcined kaolin and a binder based on styrene-butadiene, and / or polyvinyl alcohol (PVA), and / or starch, or organic pigments in a mixture with inorganic pigments, wherein the application rate of the pigmented primer is further preferably 2 g / m² 2 up to 12 g / m² 2 amounts.

[0247] According to one embodiment, the application rate of the coating dispersion is between 2 g / m². 2 and 5 g / m² 2 , preferably between 3.6 g / m³ 2 and 4.8 g / m² 2 .

[0248] The embodiments listed for the heat-sensitive recording material according to the first aspect are also embodiments for the method of producing a heat-sensitive recording material according to the second aspect and vice versa.

[0249] 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.

[0250] The embodiments listed for the heat-sensitive recording material according to the first aspect and for the method of producing a heat-sensitive recording material according to the second aspect are also embodiments for the heat-sensitive recording material producible by a method according to the third aspect.

[0251] 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 for thermal direct printing, for example as a receipt, label or ticket.

[0252] The embodiments listed for the heat-sensitive recording material according to the first aspect and the embodiments listed for the method of producing a heat-sensitive recording material according to the second aspect are also embodiments for use according to the fourth aspect. FIGURE 1

[0253] In the Fig.For the following comparative examples V1, V2, V3 and V4 (see Figures A, C, E and G) and for the following embodiments 1, 2, 3 and 4 (see Figures B, D, F and H), a dark printed area is shown in which light defects or white dots occur, which are disadvantageous and which are to be avoided or their number reduced within the scope of the present invention. EXAMPLES OF EXECUTION

[0254] In the following detailed examples, several heat-sensitive recording materials or thermal papers were produced by applying aqueous coating suspensions to form a composite structure on a carrier substrate and were examined and evaluated using different measurement methods.

[0255] In all examples, a paper substrate made from hardwood and softwood pulp with a basis weight of 34 or 38 g / m² is used as the carrier substrate.2 used. Measurement methods: Measurement of optical density:

[0256] Six-centimeter-wide strips were obtained from the appropriately produced heat-sensitive recording materials and 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 with a bar pattern at an energy level of 8.88 mJ / mm. 2 and were printed at a printing speed of approximately 100 mm / s. The area of ​​one bar of the printed pattern corresponds to 53 x 12 mm. The optical density (oD) shown in the following table was measured with a Techkon SpectroDens densitometer, with a measurement uncertainty of ≤2% for the oD values. Measurements of the occurrence of white dots or light defects in a dark printed area:

[0257] To assess the occurrence of white dots or light defects in a dark printed area, an area of ​​approximately 7 x 2.5 cm of specially manufactured heat-sensitive recording materials was thermally printed across the entire surface using a standard Epson TM T-88VI thermal printer. The perception of white dots and their frequency were then qualitatively assessed based on the following criteria (as described, for example, in the...). Fig. (shown): “--” (very bad), “-” (bad), “0” (average), “+” (good), “++” (very good). Measurement of barcode machine readability:

[0258] A barcode pattern printout, both lengthwise and crosswise, according to the UPC-A code, was produced at an energy level of 8.88 mJ / mm². 2 or 10.32 mJ / mm 2Barcodes were generated using a GeBE PrinterLab GPT-10000 test printer on specially prepared heat-sensitive recording materials. Barcode machine readability was evaluated using an REA VeriCube barcode verification device from REA Elektronik Deutschland, in accordance with ISO 15416, with the laser scanner operating at a wavelength of 660 nm. The software "TransWin32 V.1.2.0.2 / 16829" was used for evaluation. Barcode machine readability was assessed based on the scan reflection profile class in descending order of quality for each barcode: A (corresponds to a score of at least 4), B (corresponds to a score of 3), C (corresponds to a score of 2), D (corresponds to a score of 1), F (corresponds to a score of 0). Measurement of Bekk smoothness:

[0259] The Bekk smoothness was determined according to the DIN 53107 standard. Roughness measurement:

[0260] The roughness is determined using the airflow method according to the standard DIN ISO 8791-4 using a Parker Print Surf test device. Production of heat-sensitive recording materials

[0261] The heat-sensitive recording materials described below according to embodiments 1, 2, 3 and 4, as well as comparative examples V1, V2, V3 and V4, each have an intermediate layer applied to the substrate and a heat-sensitive recording layer applied to the intermediate layer.

[0262] The aqueous coating suspensions for the formation of the intermediate layer of the heat-sensitive recording material were applied one-sided online in the paper machine using a film press and a coating weight of 2.5 g / m². 2 up to 3.0 g / m² 2 at an operating speed of 1600 m / min on a paper web with a basis weight of at least 34 g / m² 2(Exemplary 4 and comparative example V4) or 38 g / m² 2 (Examples 1, 2 and 3, as well as comparative examples V1, V2 and V3).

[0263] The heat-sensitive layer is applied offline to the intermediate layer afterwards.

[0264] The following describes the production of the dispersions for the coating suspensions of embodiments 1, 2, 3 and 4, as well as the comparative examples V1, V2, V3 and V4. Color forming dispersion A1:

[0265] The color-forming dispersion A1 was prepared by milling 1.0 wt. parts of 3-(N-ethyl-N-isopentylamino)-6-methyl-7-anilinofluorane (S-205) with 1.2 wt. parts of a 20% aqueous solution of Poval 4-85 (polyvinyl alcohol solution, Kuraray company) in a bead mill. Color forming dispersion A2:

[0266] The colorant dispersion A2 was prepared by milling 9 parts by weight of 3-n-dibutylamine-6-methyl-7-anilinofluorane (ODB-2) with 11 parts by weight of a 20% aqueous solution of Poval 4-85 (polyvinyl alcohol solution, Kuraray) (Exemplary Example 2 and Comparative Example V2), or 16.5 parts by weight of 3-n-dibutylamine-6-methyl-7-ani-linofluorane (ODB-2) with 22 parts by weight of a 20% aqueous solution of Poval 4-85 (polyvinyl alcohol solution, Kuraray) (Exemplary Examples 3 and 4 and Comparative Examples V3 and V4), or 19 parts by weight of 3-n-dibutylamine-6-methyl-7-ani-linofluorane (ODB-2) with 25 parts by weight of a 20% aqueous solution of Poval 4-85 (polyvinyl alcohol solution, Kuraray) (Exemplary Examples 3 and 4 and Comparative Examples V3 and V4). aqueous solution of Poval 4-85 (polyvinyl alcohol solution, Kuraray company) (example 1 and comparative example V1) produced in a bead mill. Color developer dispersions B:

[0267] The aqueous color developer dispersions B were prepared by milling 35 parts by weight of the respective color developer 4,4'-sulfonyldiphenol (BPS) with 25 parts by weight of a 20% aqueous solution of Poval 4-85 (polyvinyl alcohol solution, Kuraray) (Exemplary 2 and Comparative Example V2), or 33 parts by weight of the respective color developer 4-methyl-N-(((3-(((4-methylphenyl)sulfonyl)oxy)phenyl)amino)carbonyl)benzenesulfonamide (Pergafast 201, CAS# 232938-43-1, α-polymorph) with 16 parts by weight of a 20% aqueous solution of Poval 4-85 (polyvinyl alcohol solution, Kuraray) (Exemplary 3 and 4 and Comparative Examples V3 and V4), or 41 parts by weight of the respective Color developer N-(2-(3-Phenylureido)phenyl)benzenesulfonamide (NKK-1304, CAS# 215917-77-4, β-polymorph) is prepared with 20 parts by weight of a 20% aqueous solution of Poval 4-85 (polyvinyl alcohol solution, Kuraray) (Exemplary 1 and Comparative Example V1) in a bead mill. Sensitizing dispersions C:

[0268] The sensitizing dispersions C were prepared by milling 7.5 parts by weight of 1,2-diphenylsulfone (DPS) with 5 parts by weight of a 20% aqueous solution of Poval 4-85 (polyvinyl alcohol solution, Kuraray) (Exemplary 2 and Comparative Example V2), or by milling 7 parts by weight of diphenoxyethane (DPE) with 7 parts by weight of a 20% aqueous solution of Poval 4-85 (polyvinyl alcohol solution, Kuraray) (Exemplary 3 and 4 as well as Comparative Examples V3 and V4), or by milling 8 parts by weight of 1,2-diphenoxyethane (DPE) with 9 parts by weight of a 20% aqueous solution of Poval 4-85 (polyvinyl alcohol solution, Kuraray) (Exemplary 1 as well as Comparative Example V1) in a bead mill. manufactured. Sensitizing dispersions D:

[0269] The sensitizing dispersions D each comprise 50 parts by weight (Exemplary 2 and Comparative Example V2), 58 parts by weight (Exemplary 3 and 4 as well as Comparative Examples V3 and V4), or 70 parts by weight (Exemplary 1 as well as Comparative Example V1) of a 25% stearic acid amide dispersion.

[0270] All dispersions A1, A2, B, C, and D produced by milling have a mean particle size D (4,3) from 0.7 µm to 1.3 µm. The particle size distribution of the dispersions was measured by laser diffraction using a Coulter LS13320 instrument from Beckman Coulter. Release agent dispersions E:

[0271] The release agent dispersions E each comprise 21 parts by weight (Exemplary 2 and Comparative Example V2), or 17.5 parts by weight (Exemplary 3 and 4 and Comparative Examples V3 and V4), or 21 parts by weight (Exemplary 1 and Comparative Example V1) of a 35% zinc stearate dispersion. Pigment dispersions P:

[0272] The pigment dispersions P each comprise 187 parts by weight (Exemplary 2 and Comparative Example V2), 179 parts by weight (Exemplary 3 and 4 as well as Comparative Example V3 and V4), or 205 parts by weight (Exemplary 1 and Comparative Example V1) of a 45% dispersion of precipitated calcium carbonate (PCC). Binder solutions:

[0273] The binder solutions each comprise 126 parts by weight (Exemplary 2 and Comparative Example V2), 128 parts by weight (Exemplary 3 and 4 as well as Comparative Examples V3 and V4), or 144 parts by weight (Exemplary 1 as well as Comparative Example V1) of a 9% aqueous polyvinyl alcohol solution (Poval 28-99, Kuraray Europe). Additives:

[0274] Furthermore, the coating suspensions according to embodiments 1, 2, 3 and 4, or comparative examples V1, V2, V3 and V4, include further additives which are present in small quantities. Intermediate shift

[0275] The intermediate layer used in embodiments 1 to 4, as well as in comparative examples V1 to V4, is based on a styrene-acrylate copolymer, contains calcium carbonate as a pigment, and has a basis weight of between 2.5 g / m². 2 up to 3.0 g / m² 2 applied to the carrier substrate. Examples 1, 2, 3 and 4, as well as comparative examples V1, V2, V3 and V4

[0276] As already described, the heat-sensitive recording materials according to embodiments 1, 2, 3 and 4, as well as comparative examples V1, V2, V3 and V4 are produced by applying an intermediate layer to the base paper, and subsequently by applying the respective heat-sensitive recording layer to the intermediate layer.

[0277] The coating suspension used for embodiment 2 and for comparison example V2 to produce the heat-sensitive recording layer comprises the color forming dispersion A1, the respective color forming dispersion A2, the respective color developer dispersion B, the respective sensitizing dispersion C, the respective sensitizing dispersion D, the respective release agent dispersion E, the respective pigment dispersion P, and the respective binder solution, as well as additives in small quantities.

[0278] The basis weight of the heat-sensitive recording material according to comparative example V2 and according to embodiment 2 is 48 g / m² in each case. 2 .

[0279] The coating suspension used for embodiment 1 and for comparison example V1 to produce the heat-sensitive recording layer comprises the respective color forming dispersion A2, the respective color developer dispersion B, the respective sensitizing dispersion C, the respective sensitizing dispersion D, the respective release agent dispersion E, the respective pigment dispersion P, the respective binder solution and additives in small quantities.

[0280] The basis weight of the heat-sensitive recording material according to comparison example V1 and according to embodiment 1 is 48 g / m² in each case. 2 .

[0281] The coating suspension used for embodiments 3 and 4 as well as for comparative examples V3 and V4 to produce the heat-sensitive recording layer comprises the respective color forming dispersion A2, the respective color developer dispersion B, the respective sensitizing dispersion C, the respective sensitizing dispersion D, the respective release agent dispersion E, the respective pigment dispersion P, the respective binder solution and additives in small quantities.

[0282] The compositions of the coating suspensions for comparative examples V3 and V4 for embodiments 3 and 4 do not differ. The only difference between comparative examples V3 and V4 and embodiments 3 and 4 lies in the basis weight of the heat-sensitive recording material.

[0283] The basis weight of the heat-sensitive recording material according to comparison example V3 and according to embodiment 3 is 48 g / m² in each case. 2 .

[0284] The basis weight of the heat-sensitive recording material according to comparative example V4 and according to embodiment 4 is 44 g / m² in each case. 2 .

[0285] Exemplary embodiments 1, 2, 3 and 4 differ from the corresponding comparative examples V1, V2, V3 and V4 only in the use of the respective pigment, which is chosen as precipitated calcium carbonate (PCC).

[0286] While untreated precipitated calcium carbonate (PCC) is used in comparative examples V1, V2, V3 and V4, ground precipitated calcium carbonate (PCC) is used in embodiments 1, 2, 3 and 4, whereby the grinding carried out according to embodiments 1, 2, 3 and 4 is performed as follows: Before milling, the pigment dispersion P is diluted to a solids content of 40% or greater, and up to 1.0% sodium polyacrylate is added as a dispersant. This pigment dispersion is then pumped through a stirred ball mill. The mill is filled with grinding beads with a diameter of 0.8 to 1.0 mm to a fill level of 50% or greater. The residence time of the pigment dispersion in the mill is a maximum of 10 minutes, preferably 5 minutes. The rotor speed of the mill is 10 m / s or greater to keep the beads sufficiently in motion. The mill is cooled to ensure that the product temperature remains below 40°C. At the mill outlet, the product is cooled to 30°C or less via a plate heat exchanger. Mills from Bühler, model Centex T3, are used.

[0287] The appropriately treated pigment dispersion P is used directly in the coating compounds according to embodiments 1, 2, 3 and 4.

[0288] The treatment according to the exemplary embodiments is monitored by measuring the particle size and determining the sieve residue of ground precipitated calcium carbonate (PCC). The ground precipitated calcium carbonate (PCC) according to exemplary embodiments 1, 2, 3 and 4 has a particle size distribution (d90) determined according to ISO 13320 from 1.9 µm to 3.4 µm, a particle size distribution (d50) determined according to ISO 13320 from 1.1 µm to 1.9 µm, a particle size distribution (d10) determined according to ISO 13320 from 0.1 µm to 1.0 µm, and a particle size distribution (d4,3) determined according to ISO 13320 from 1.2 µm to 2.1 µm. The ground precipitated calcium carbonate (PCC) according to embodiments 1, 2, 3 and 4 has a sieve residue obtained after treatment according to DIN EN ISO 787-7 of between 0.01% and 0.03% when filtered with a sieve with a pore size of 25 µm.

[0289] In comparison, the inorganic pigment of the heat-sensitive layer according to comparison examples 1, 2, 3 and 4 consists of untreated precipitated calcium carbonate (PCC), which has a particle size distribution (d90) determined according to ISO 13320 from 3.3 µm to 4.3 µm, which has a particle size distribution (d50) determined according to ISO 13320 from 2.00 µm to 2.40 µm, which has a particle size distribution (d10) determined according to ISO 13320 from 0.80 µm to 1.40 µm, and which has a particle size distribution (D4,3) determined according to ISO 13320 from 2.20 µm to 2.60 µm. The untreated precipitated calcium carbonate (PCC) according to embodiment 1 has a sieve residue of between 0.35% and 1.0% as obtained according to the standard DIN EN ISO 787-7 when filtered with a sieve with a pore size of 25 µm.

[0290] Although this was not done in the examples presented, it is also optionally possible to carry out the described milling of the precipitated calcium carbonate (PCC) of the respective pigment dispersion P in combination with another partial mass, for example the respective color developer dispersion B, the respective sensitizing dispersion C and / or the respective sensitizing dispersion D.

[0291] The following table shows the comparison of the respective heat-sensitive recording materials according to embodiments 1, 2, 3 and 4, as well as comparison examples V1, V2, V3 and V4 with regard to the measured optical density (oD), the smoothness in Bekk seconds, the roughness in pps, and the barcode machine readability (code 1 to code 4) according to the corresponding grade: Table Example oD smoothness roughness Code 1 Code 2 Code 3 Code 4 V1 1,00 457 2,04 2,3 3,1 1,7 2,4 1 1,05 466 1,97 2,9 3,6 2,0 2,9 V2 0,86 591 1,75 2,1 3,0 1,5 2,1 2 0,91 618 1,67 2,6 3,2 1,7 2,7 V3 1,00 446 2,28 2,5 3,1 1,8 2,7 3 1,06 526 2,05 2,7 3,3 2,4 3,1 V4 1,01 494 2,26 2,1 2,9 1,1 2,0 4 1,08 587 2,07 2,2 3,2 1,1 2,6

[0292] The column “Code 1” describes the barcode machine readability rating for a printed longitudinal grid with an energy dose of 8.88 mJ / mm². 2 The column “Code 2” describes the barcode machine readability rating for a printed longitudinal grid with an energy dose of 10.32 mJ / mm². 2 .

[0293] The column “Code 3” describes the barcode machine readability rating for a printed cross-hatch pattern with an energy dose of 8.88 mJ / mm². 2 The column “Code 4” describes the barcode machine readability rating for a printed cross-scratch with an energy dose of 10.32 mJ / mm². 2 .

[0294] A comparison of the optical densities between the respective reference examples V1, V2, V3, and V4 and the respective embodiments 1, 2, 3, and 4 reveals a significant improvement, achievable with minimal effort, between the respective embodiments 1, 2, 3, and 4 and the respective reference examples V1, V2, V3, and V4 (for example, for the pair V3 / 3, 1.06 / 1.00 = 6%). The same applies to the determined other parameters such as smoothness, roughness, and barcode machine readability according to codes 1 to 4, with the corresponding improvement being attributable to the use of ground precipitated calcium carbonate (PCC).

[0295] The use of ground precipitated calcium carbonate (PCC) has the additional benefit compared to conventional, untreated precipitated calcium carbonate (PCC) that the occurrence of white defects or white spots can be significantly reduced, as is the case, for example, in the Fig. is shown.

[0296] Thus, figure A shows the Fig. a test print on the heat-sensitive recording material according to the comparison example V1 and shows figure B of the Fig. a test print on the heat-sensitive recording material according to embodiment 1.

[0297] Furthermore, the Fig. C of the Fig. a test print on the heat-sensitive recording material according to the comparison example V2 and shows the Fig. D the Fig. a test print on the heat-sensitive recording material according to embodiment 2.

[0298] Furthermore, figure E shows the Fig. a test print on the heat-sensitive recording material according to the comparison example V3 and shows figure F of the Fig. a test print on the heat-sensitive recording material according to embodiment 3.

[0299] Furthermore, figure G shows the Fig. a test print on the heat-sensitive recording material according to the comparison example V4 and shows figure H of the Fig. a test print on the heat-sensitive recording material according to embodiment 4.

[0300] From the respective comparison of figures B, D, F and H of the Fig. can be compared to the respective figures A, C, E and G of the Fig. A significant reduction in the occurrence of white defects or white spots was observed in the respective embodiments 1, 2, 3 and 4 in contrast to the comparison examples V1, V2, V3 and V4.

[0301] Although not shown in the table and figures, filtered precipitated calcium carbonate (PCC) can be used instead of the ground precipitated calcium carbonate (PCC) of embodiments 1, 2, 3, and 4 to achieve comparably positive results.

[0302] A corresponding filtered precipitated calcium carbonate (PCC) is obtained by diluting the pigment dispersion P to a solids content of 40% or less to reduce its viscosity. The diluted pigment dispersion is then filtered through a 25 µm filter. Filtration can be carried out under pressure or without pressure. Filter bags, shaker sieves, or scraped pressure filters can be used, particularly nylon filter bags from Wolftechnik. The coarse particles are retained in the filter and discarded; the diluted pigment dispersion can be reused.

[0303] The filtered precipitated calcium carbonate (PCC) has a particle size distribution (d90) determined according to ISO 13320 of 3.6 µm to 3.8 µm, a particle size distribution (d50) determined according to ISO 13320 of 2.0 µm to 2.2 µm, a particle size distribution (d10) determined according to ISO 13320 of 1.0 µm to 1.10 µm, and a particle size distribution (D4,3) determined according to ISO 13320 of 2.2 µm to 2.3 µm. The filtered precipitated calcium carbonate (PCC) according to embodiment 2 has a sieve residue of 0.01 to 0.03% obtained after treatment according to the standard DIN EN ISO 787-7, in particular of approximately 0.02% or 0.03% when filtered with a sieve with a pore size of 25 µm.

[0304] Although not shown in the table and figures, sieved precipitated calcium carbonate (PCC) can be used instead of the ground precipitated calcium carbonate (PCC) of embodiments 1, 2, 3, and 4 to achieve comparably positive results.

[0305] In particular, the sieved precipitated calcium carbonate (PCC) has a mean particle size (D4,3) of 2.3 to 2.5 µm, the mean particle size (D4,3) of the sieved precipitated calcium carbonate (PCC) being determined according to ISO 13320.

[0306] In particular, the sieved precipitated calcium carbonate (PCC) has a mean particle size (d10) of 1.1 to 1.3 µm, the mean particle size (d10) of the sieved precipitated calcium carbonate (PCC) being determined according to ISO 13320.

[0307] 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.

[0308] 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.

[0309] In particular, the sieved precipitated calcium carbonate (PCC) is characterized by a sieve residue obtained after treatment in a range of approximately 0.01% to approximately 0.03%, in accordance with the standard DIN EN ISO 787-7. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] JPS 59 162 087 A

[0013] US 4 370 370 A

[0013] US 4 388 362 A

[0013] DE 19 757 589 B4

[0014] DE 19 806 433 B4

[0015] EP 0 600 622 A1

[0016] DE 19 724 647 C1

[0016] EP 1 085 069 B1

[0017] EP 2 474 963 B1

[0017] EP 3 219 507 A1

[0018] US 6 667 275 B2

[0020] JP 2018 167 483

[0021] JP 2003 175 671

[0022] JPH 0 720 735 B2

[0022] JP 2000 204 123

[0022] EP 3 957 488 A1

[0023] WO 2022 / 038242 A1

[0023] US 2021 / 0060994

[0024] CA 3 149 562 A1

[0024] WO 2021 / 041600 A2

[0024] DE 10 2019 126 220 A1

[0025] WO 2021 / 058661 A1

[0025] KR 2022 070 021 A

[0025] DE 20 2020 005 616 U1

[0025] DE 10 196 052 T1

[0219] Cited non-patent literature

[0000] DIN ISO 8791-4

[0141] Standard ISO 15416

[0142]

Claims

[1] Heat-sensitive recording material, comprising: a carrier substrate which has a first side and a second side facing away from the first side; a heat-sensitive color-forming layer arranged on the first side of the support substrate, wherein the heat-sensitive color-forming layer comprises at least one color former and at least one color developer; characterized by that the heat-sensitive layer comprises at least one polymeric binder and at least one inorganic pigment, where 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, and wherein the precipitated calcium carbonate (PCC) comprises a sieved precipitated calcium carbonate (PCC) and / or a ground precipitated calcium carbonate (PCC) and / or a filtered precipitated calcium carbonate (PCC). [2] Heat-sensitive recording material according to claim 1, characterized by , that the sieved and / or ground and / or filtered 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, even more preferably less than 20 µm, most preferably less than 10 µm, further most preferably less than 7 µm, even more preferably less than 5 µm, and furthermore preferably less than 4.5 µm. [3] Heat-sensitive recording material according to claim 1 or 2, characterized by, that the sieved and / or ground and / or filtered precipitated calcium carbonate (PCC) has a mean particle size (d50) 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 3 µm and furthermore more preferably less than 2.5 µm. [4] Heat-sensitive recording material according to any of the preceding claims, characterized by, that the sieved and / or ground and / or filtered 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 furthermore more preferably less than 1.5 µm. [5] Heat-sensitive recording material according to any one of the preceding claims, characterized by, that the sieved and / or ground and / or filtered 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 sieved and / or ground and / or filtered 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 of the preceding claims, characterized by, that the sieved and / or ground and / or filtered precipitated calcium carbonate (PCC) comprises precipitated calcium carbonate (PCC) having a prismatic, rhombohedral or aragonite structure, wherein in particular the proportion of the precipitated calcium carbonate (PCC) with the prismatic, rhombohedral or aragonite structure in the sieved and / or ground and / or filtered 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%. [7] Heat-sensitive recording material according to any of the preceding claims, characterized by, that the sieved and / or ground and / or filtered precipitated calcium carbonate (PCC) is characterized by a sieve residue obtained after treatment according to the standard DIN EN ISO 787-7 of less than 1%, preferably less than 0.5%, more preferably less than 0.1%, and most preferably less than 0.05%. [8] Heat-sensitive recording material according to any of the preceding claims, characterized by , that the sieved and / or ground and / or filtered precipitated calcium carbonate (PCC) is present in the heat-sensitive layer in an amount of 5 wt.% to 60 wt.%, preferably in an amount of 10 wt.% to 50 wt.%, more preferably in an amount of 15 wt.% to 50 wt.% based on the total dry mass of the heat-sensitive layer. [9] Heat-sensitive recording material according to any of the preceding claims, characterized by, that the at least one inorganic pigment is at least one further inorganic pigment selected from the group comprising calcium silicate hydrate, barium sulfate, kaolinite, calcium silicate, calcium sulfate, sodium aluminum silicate, aluminum oxides, aluminum hydroxides, silicas, precipitated and pyrogenic silicas, diatomaceous earths, magnesium carbonates, silicon dioxide, talc, kaolin, titanium dioxide, bentonite and mixtures thereof, preferably silicon dioxide, kaolin and / or aluminum hydroxide. [10] Heat-sensitive recording material according to any one of the preceding claims, characterized bythat the heat-sensitive layer comprises at least one sensitizing agent, which is preferably selected from the group comprising a fatty acid amide, particularly preferably stearamide, behenamide or palmitamide, an ethylenebis fatty acid amide, particularly preferably N,N'-ethylenebis-stearic acid amide or N,N'-ethylenebis-oleic acid amide, a wax, particularly preferably polyethylene wax or montan wax, a carboxylic acid ester, particularly preferably dimethyl terephthalate, dibenzyl terephthalate, benzyl p-benzyloxybenzoate, di-(p-methylbenzyl)oxalate, di-(p-chlorobenzyl)oxalate or di-(p-benzyl)oxalate, an aromatic ether, particularly preferably 1,2-diphenoxyethane, 1,2-di-(3-methylphenoxy)ethane, 2-benzyloxynaphthalene or 1,4-diethoxynaphthalene, an aromatic sulfone, particularly preferably diphenylsulfone, and / or a aromatic sulfonamide, particularly preferably benzenesulfonanilide or N-benzyl-p-toluenesulfonamide, o-toluenesulfonamide, p-toluenesulfonamide, p-benzylbiphenyl (PBBP), 1,2-Bis-(phenoxymethyl)benzene, 4-(4-tolyloxy)biphenyl, 1,2-Bis-(3,4-dimethylphenyl)ethane and / or mixtures thereof. [11] Heat-sensitive recording material according to any of the preceding claims, characterized by, that the at least one polymeric binder of the heat-sensitive layer is selected from the group comprising water-soluble starches, starch-based biolatices of the Ecosphere type, starch derivatives, methylcellulose, hydroxyethylcellulose, carboxymethylcelluloses, partially or fully saponified polyvinyl alcohols, ethylene vinyl alcohol copolymers, chemically modified polyvinyl alcohols or styrene maleic anhydride copolymers, styrene butadiene copolymers, acrylamide (meth) acrylate copolymers, acrylamide acrylate methacrylate terpolymers, polyacrylates, poly(meth) acrylic esters, acrylate butadiene copolymers, polyvinyl acetates and / or acrylonitrile butadiene copolymers and mixtures thereof, wherein the at least one binder is preferably selected as polyvinyl alcohol. [12] Heat-sensitive recording material according to any one of the preceding claims, characterized bythat the heat-sensitive recording material has at least one intermediate layer which is arranged between the support substrate and the heat-sensitive layer, wherein the intermediate layer preferably has at least one binder, and / or preferably at least one pigment. [13] Heat-sensitive recording material according to any of the preceding claims, characterized by that the heat-sensitive color-forming layer has a Bekk smoothness of 150 sec to 1500 sec, preferably 250 sec to 1000 sec, as measured according to the DIN 53107 standard. [14] Heat-sensitive recording material according to any of the preceding claims, characterized by that the heat-sensitive recording material has an optical density (o. D.) defined according to the description of at least 0.75, preferably at least 0.9, and most preferably at least 1.0, wherein in particular at an energy level of 8.88 mJ / mm 2 was measured. [15] Heat-sensitive recording material according to any of the preceding claims, characterized by , that the heat-sensitive recording material has a roughness measured according to DIN ISO 8791-4 using a Parker Print Surf tester of less than 5 µm, preferably less than 4.5 µm, more preferably less than 4 µm, even more preferably less than 3 µm, and furthermore preferably less than 2.5 µm. [16] Heat-sensitive recording material according to any of the preceding claims, characterized by , that the heat-sensitive recording material is defined as one according to the description at an energy level of 8.88 mJ / mm 2 or 10.32 mJ / mm 2a heat-sensitive recording material printed with a barcode test pattern using a GeBE PrinterLab GPT-10000 test printer, wherein the printed heat-sensitive recording material has a barcode machine readability grade of 1 or more, preferably 2 or more, and most preferably 3 or more, as defined in the description and evaluated according to the ISO 15416 standard. [17] Heat-sensitive recording material according to any of the preceding claims, characterized by , that at least one color developer comprises a compound of formula (I): where R and R1 are independently selected from the group comprising hydrogen, C1-C 18-Alkyl, C1-C8-alkoxy-C1-C8-alkyl, and (R9)2N-C1-C8-alkyl, wherein R9 is selected from the group comprising C1-C8-alkyl, C5-C6-cycloalkyl; or a compound of formula (II) wherein R2, R3, R4, R5, and R6 are independently selected from the group comprising hydrogen, C1-C8-alkyl, -NH-C(=O)-R7, and -C(=O)-NH-R7, wherein R7 is selected as C1-C8-alkyl or -C(=O)OR8, wherein R8 is selected as C1-C8-alkyl or halogen, or wherein R2 and R3, or R4 and R5 or both, or wherein R3 and R4, or R5 and R6 or both, or wherein R2 and R3 and R5 and R6, together form a hydrocarbon group with three or four carbon atoms, and wherein Q comprises a single bond or C1-C8 alkylene, which may be branched or unbranched, and wherein the C1-C8 alkylene comprises a main chain having one or more oxygen atoms between two carbon atoms, if the C1-C8 alkylene has more than two carbon atoms, wherein the compound of formula (I) preferably comprises a compound of formula (1a): or wherein the compound of formula (I) preferably comprises a compound of formula (Ib): and wherein the compound of formula (I) particularly preferably comprises 5-(N-3-methylphenylsulfonylamido)-(N',N''-bis-{3-methylphenyl)-isophthalic diamide. [18] Heat-sensitive recording material according to any of the preceding claims, characterized by, that the at least one color developer comprises a compound of the formula (NI): wherein R1, R2, and R3 are independently selected from the group comprising hydrogen, halogen, nitro, C1-C6 alkyl, C1-C6 alkoxyl, C2-C6 alkenyl, C1-C6 fluoroalkyl, N(R4)2, NHCOR5, optionally substituted phenyl, and optionally substituted benzyl, wherein R4 is selected from the group comprising hydrogen, phenyl, benzyl, and C1-C6 alkyl, wherein R5 is selected as C1-C6 alkyl, wherein n1 and n3 are independently selected as an integer from 1 to 5, and wherein n2 is an integer from 1 to 4; where R1, R2, and R3 are preferably selected as hydrogen, further preferably comprising the compound of formula (NI) N-(2-(3-Phenylureido)phenyl)benzenesulfonamide, and even more preferably comprising the α-polymorph and / or the β-polymorph of N-(2-(3-Phenylureido)phenyl)benzenesulfonamide, wherein the α-polymorph is characterized in particular by an X-ray diffraction pattern with Bragg angles (2θ / CuKα) of 5.8, 9.3, 13.2, 15.7, 17.3, 18.3, 18.7, 19.5, 20.3, 21.1, 21.9, 22.8, 23.3, 23.6, 24.4, 24.9, 25.6, 26.7, 27.8, 28.1, 29.3, 29.6, 30.2, 31.6, 32.3, 32.8 and / or a melting point of 158°C to 159°C determined by DSC, wherein the β-polymorph is characterized in particular by an X-ray diffraction pattern with Bragg angles (2θ / CuKα) of 10.0, 11.0, 12.3, 12.7, 13.8, 14.9, 15.6, 16.8, 17.7, 18.5, 20.1, 20.9, 21.6, 22.0, 22.8, 23.0, 23.6, 24.3, 25.5, 26.7, 27.8, 28.4, 29.0, 29.8, 30.5, 31.1, 31.3 and / or a melting point of 173°C to 174°C determined by DSC. [19] Heat-sensitive recording material according to any one of the preceding claims, characterized by, that at least one color developer comprises a compound of formula (1): where R1 is selected from the group comprising unsubstituted or substituted phenyl, naphthyl and C1-C 20 -Alkyl, where X is selected from the group comprising -C(=NH) -, -C(=S) - and -C(=O) -, where A is selected from the group comprising unsubstituted or substituted phenylene, naphthylene, C1-C 12 -Alkylene, and an unsubstituted or substituted heterocyclic group, wherein B is selected from the group comprising -O-SO2-, -SO2-O-, -NH-SO2-, -SO2-NH-, -S-SO2-, -O-CO-, -O-CO-NH-, -NH-CO-, -NH-CO-O-, -S-CO-NH-, -S-CS-NH-, -CO-NH-SO2-, -O-CO-NH-SO2-, -NH=CH-, -CO-NH-CO-, -S-, -CO-, -O-, -SO2-NH-CO-, -O-CO-O- and -O-PO-(OR2)2, and wherein R2 is selected from the group comprising unsubstituted or substituted aryl, benzyl and C1-C 20-Alkyl, provided that if B is not a group of the formula -O-SO2-, then R2 is unsubstituted or substituted phenyl, naphthyl or C1-C8 alkyl, and that if B is -O-, then R2 is not alkyl; wherein X is preferably selected as -C(=O)-, wherein R1 is selected as substituted or substituted phenyl, preferably as C1-C3-alkyl substituted phenyl, wherein R2 is selected as unsubstituted or substituted aryl, preferably unsubstituted phenyl, wherein B is selected as -O-SO2-, and wherein R2 is selected as substituted or substituted aryl, preferably as C1-C3-alkyl substituted phenyl, and wherein the at least one color developer of formula (1) preferably comprises 4-methyl-N-(((3-((4-methylphenyl)sulfonyl)oxy)phenyl)amino)carbonyl)benzenesulfonamide, more preferably the α-polymorph and / or the β-polymorph of 4-methyl-N-(((3-(((4-methylphenyl)sulfonyl)oxy)phenyl)amino)carbonyl)benzenesulfonamide, wherein the α-polymorph is characterized in particular by an X-ray diffraction pattern with Bragg angles (2θ / CuKα) of 8.5, 9.5, 11.8, 12.1, 12.2, 13.7, 14.1, 16.6, 17.1, 18.3, 18.6, 19.1, 19.3, 20.1, 20.4, 20.9, 21.3, 23.1, 24.2, 24.6, 25.0, 27.9, 28.6 and / or a melting point of 161°C to 162°C determined by DSC, where in particular the β-polymorph is characterized by an X-ray diffraction pattern with Bragg angles (2θ / CuKα) of 10.3, 11.0, 12.9, 13.2, 15.4, 17.1, 18.0, 18.2, 19.4, 20.0, 20.7, 21.2, 23.0, 24.9, 25.3, 26.5, 26.8, 27.5, 30.7, 32.7 and / or a melting point of 166°C to 167°C determined by DSC. [20] Heat-sensitive recording material according to any one of the preceding claims, characterized by , that at least one color developer comprises a compound of formula (2), J1-K1-L1-N(H)-C(=O)-N(H)-L2-K2-J2 where J1 and J2 are independently selected as unsubstituted or substituted aryl, where K1 and K2 are selected as -O-SO2-, where L1 and L2 are independently selected as unsubstituted or substituted aryl, wherein J1 and J2 are preferably selected as unsubstituted or substituted phenyl, preferably as C1-C3 alkyl substituted phenyl, and wherein L1 and L2 are preferably selected as unsubstituted phenyl, and the most preferred one is at least one color developer according to the formula 2 N,N'-Bis[3-[[(4-methylphenyl)sulfonyl]oxy]phenyl]urea [21] Heat-sensitive recording material according to any of the preceding claims, characterized bythat the at least one color developer is [3-(3-phenylureido)phenyl]-4-methylbenzenesulfonate, 4,4'-bis(N,N'-p-toluenesulfonyl-aminocarbonylaminophenyl)methane, N,N'-p-toluenesulfonyl-aminocarbonylaminophenyl, n-butyl-4(3-(p-toluenesulfonyl)ureido)benzoate, N,N'-diphenyl urea, bisphenol A, 4'-dihydroxy-diphenyl sulfone, 2,4'-dihydroxy-diphenyl sulfone, 4-hydroxy-4'-iso-propoxy-diphenyl sulfone, bis-(3-allyl-4-hydroxy-phenyl) sulfone, 4-Hydroxy-4'-benzyloxy-diphenyl sulfone, 4-hydroxy-4'-n-propoxy-diphenyl sulfone, N-phenyl-p-hydroxyphenylsulfonamide, 4-hydroxy-4'-allyloxydiphenyl sulfone, 2,4-Bis(phenylsulfonyl)phenol, N-(4-((4-(3-Phenylureido)phenyl)sulfonyl)phenyl)benzenesulfonamide, 2'-(3'-Phenylureido)phenyl 3-(3-phe-nylureido)benzenesulfonate, N-phenyl-N'[(phenylamino)sulfonyl]urea, and / or a urea compound according to the following formula, in particular comprising 4,4'-bis[(4-methyl-3-phenoxycarbonylaminophenyl)ureido]diphenylsulfone, 4,4'-bis[(2-methyl-5-phenoxycarbonylaminophenyl)ureido]diphenylsulfone, 4-(2-methyl-3-phenoxycarbonylaminophenyl)ureido-4'-(4-methyl-5-phenoxycarbonylaminophenyl)ureidodiphenylsulfone: and mixtures thereof. [22] Heat-sensitive recording material according to one of the preceding claims, wherein the at least one color developer has a weight fraction of 6 wt.% to 35 wt.% based on the total solids content of the heat-sensitive color-forming layer, wherein the weight fraction is preferably from 10 wt.% to 30 wt.%, more preferably from 10 wt.% to 20 wt.%. [23] Method for producing a heat-sensitive recording material, comprising the following process steps: Providing a support substrate which has a first side and a second side facing away from the first side; Applying a coating suspension to the first side of the substrate, wherein the coating suspension comprises at least one color former and at least one color developer, wherein the application suspension comprises at least one polymeric binder and at least one inorganic pigment, where 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, and wherein the precipitated calcium carbonate (PCC) comprises a sieved precipitated calcium carbonate (PCC) and / or a ground precipitated calcium carbonate (PCC) and / or a filtered precipitated calcium carbonate (PCC); [24] Heat-sensitive recording material producible by a method according to claim 23. [25] Use of a heat-sensitive recording material according to one of claims 1 to 22 or 24 for thermal direct printing, for example as a receipt, label or ticket.

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