Heat-sensitive recording material

Abstract

The present invention relates to a heat-sensitive recording material, comprising: a carrier substrate, which has a first side and a second side facing away from the first side; and a heat-sensitive colour-forming layer, which is arranged on the first side of the carrier substrate, wherein the heat-sensitive colour-forming layer comprises at least one colour former, at least one colour developer, and at least one stabiliser; wherein the at least one stabiliser is selected as a compound of formula (1), Ar1-SO2-NH-C6H4-SO2-C6H4-NH-CO-NH-Ar2, wherein Ar1 and Ar2 are, independently of one another, an unsubstituted or substituted phenyl group, and / or wherein the at least one stabiliser is selected as a compound of formula (2), Ar1-NH-CO-NH-C6H4-SO2-O-C6H4-NH-CO-NH- Ar2, wherein Ar1 and Ar2 are, independently of one another, an unsubstituted or substituted phenyl, naphthyl and / or heteroaryl group; wherein the weight ratio of stabiliser to colour developer in the heat-sensitive colour-forming layer is selected such that, according to the stability test 1 defined in the description, a remaining optical density of the heat-sensitive colour-forming layer of at least 85% of the original optical density of the heat-sensitive colour-forming layer is present before storage under dry storage conditions after a storage period of 7 days, and / or that, according to the stability test 2 defined in the description, a remaining optical density of the heat-sensitive colour-forming layer of at least 80% of the original optical density of the heat-sensitive colour-forming layer is present before storage under moist storage conditions after a storage period of 7 days; and / or that, according to the stability test 3 defined in the description, a remaining optical density of the heat-sensitive colour-forming layer of at least 70% of the original optical density of the heat-sensitive colour-forming layer before storage is present under storage conditions under light after a storage period of 7 days.

Description

[0001] HEAT-SENSITIVE RECORDING MATERIAL

[0002] TECHNICAL AREA

[0003] 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, at least one color developer, and at least one stabilizer.

[0004] Here, at least one stabilizer is selected as a compound of formula (1), Ar 1 -SO2-NH-C6H4-SO2-CeH4-NH-CO-NH-Ar 2 , where Ar 1 and Ar 2 independently of each other are an unsubstituted or substituted phenyl residue, and / or at least one stabilizer is selected as a compound of formula (2), Ar 1-NH-CO- NH-C6H4-SO2-O-CeH4-NH-CO-NH-Ar 2 , where Ar 1 and Ar 2 are independently of each other an unsubstituted or substituted phenyl, naphthyl and / or heteroaryl residue.

[0005] Here, the weight ratio of stabilizer to color developer in the heat-sensitive color-forming layer is chosen such that, according to stability test 1 defined in the description, after a storage period of 7 days under dry storage conditions, the remaining optical density of the heat-sensitive color-forming layer is at least 85% of the original optical density of the heat-sensitive color-forming layer before storage, and / or that, according to stability test 2 defined in the description, after a storage period of 7 days under humid storage conditions, the remaining optical density of the heat-sensitive color-forming layer is at least 80% of the original optical density of the heat-sensitive color-forming layer before storage;and / or that, according to the stability test 3 defined in the description, after a storage period of 7 days, the remaining optical density of the heat-sensitive color-forming layer is at least 70% of the original optical density of the heat-sensitive color-forming layer before storage.

[0006] According to a second aspect, the present invention relates to a method for producing a heat-sensitive recording material, comprising the following process steps: providing a carrier substrate having a first side and a second side facing away from the first side; applying a coating suspension to the first side of the carrier substrate, wherein the coating suspension comprises at least one color former, at least one color developer, and at least one stabilizer, wherein the at least one stabilizer is selected as a compound of formula (1), AH-SCH-NH-CeH^SCH-CeH^NH-CO-NH-Ar 2 , where Ar 1 and Ar 2 independently of each other are an unsubstituted or substituted phenyl residue, and / or wherein at least one stabilizer is selected as a compound of formula (2), Ar 1 -NH-CO-NH-C6H4-SO2-O-C6H4-NH-CO-NH-Ar 2 , where Ar 1 and Ar 2independently of each other are an unsubstituted or substituted phenyl, naphthyl and / or heteroaryl residue; and drying of the application suspension to obtain a heat-sensitive color-forming layer arranged on the first side of the support substrate.

[0007] The weight ratio of stabilizer to color developer in the heat-sensitive color-forming layer is selected such that, according to stability test 1 defined in the description, after a storage period of 7 days under dry storage conditions, the remaining optical density of the heat-sensitive color-forming layer is at least 85% of the original optical density of the heat-sensitive color-forming layer before storage, and / or that, according to stability test 2 defined in the description, after a storage period of 7 days under humid storage conditions, the remaining optical density of the heat-sensitive color-forming layer is at least 80% of the original optical density of the heat-sensitive color-forming layer before storage;and / or that, according to the stability test 3 defined in the description, after a storage period of 7 days, the remaining optical density of the heat-sensitive color-forming layer is at least 70% of the original optical density of the heat-sensitive color-forming layer before storage.

[0008] According to a third aspect, the present invention relates to a heat-sensitive recording material producible by the method according to the second aspect.

[0009] According to a fourth aspect, the present invention relates to the use of at least one stabilizer and at least one color developer in a heat-sensitive recording material, comprising a support substrate having a first side and a second side facing away from the first side, and 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, at least one color developer, and at least one stabilizer, wherein the at least one stabilizer is selected as a compound of formula (1), Ar 1 - SO2-NH-C6H4-SO2-CeH4-NH-CO-NH-Ar 2 , where Ar 1 and Ar 2 independently of each other are an unsubstituted or substituted phenyl residue, and / or wherein at least one stabilizer is selected as a compound of formula (2), Ar 1-NH-CO-NH-CeH4- SO2-O-C6H4-NH-CO-NH-Ar 2 , where Ar 1 and Ar 2 are independently of each other an unsubstituted or substituted phenyl, naphthyl and / or heteroaryl residue.

[0010] The weight ratio of stabilizer to color developer in the heat-sensitive color-forming layer is selected such that, according to stability test 1 defined in the description, after a storage period of 7 days under dry storage conditions, the remaining optical density of the heat-sensitive color-forming layer is at least 85% of the original optical density of the heat-sensitive color-forming layer before storage, and / or that, according to stability test 2 defined in the description, after a storage period of 7 days under humid storage conditions, the remaining optical density of the heat-sensitive color-forming layer is at least 80% of the original optical density of the heat-sensitive color-forming layer before storage;and / or that, according to the stability test 3 defined in the description, after a storage period of 7 days, the remaining optical density of the heat-sensitive color-forming layer is at least 70% of the original optical density of the heat-sensitive color-forming layer before storage.

[0011] TECHNICAL BACKGROUND

[0012] Heat-sensitive recording materials for direct thermal printing applications, which feature a heat-sensitive color-forming layer, also known as a thermo-reaction layer, applied to a substrate, have been known for a long time. The heat-sensitive color-forming layer typically contains a color former and a color developer, which react with each other under the influence of heat, thus resulting in color development.

[0013] Among the known materials are inexpensive (bis)phenolic color developers, such as bisphenol A and bisphenol S, which can be used to produce heat-sensitive recording materials with acceptable performance for numerous applications. Also known are heat-sensitive recording materials that contain a non-phenolic color developer in the heat-sensitive color-forming layer. These were developed to improve the durability of the printed image, particularly when the printed heat-sensitive recording material is to be stored for extended periods at higher temperatures and / or humidity.

[0014] A variety of non-phenolic color developers are known from the prior art, for example the color developer Pergafast 425, 5-(N-3-methylphenyl-sulfonylamido)-(N',N"-bis-{3-methylphenyl)-isophthalic diamide, which is described, for example, in the publications WO 2022 / 038242, WO 2021 / 041600 and DE 10 2019 126 220.

[0015] Other non-phenolic color developers known from the prior art include the color developer NKK-1304, N-(2-(3-Phenylureido)phenyl)benzenesulfonamide, which is described, among other things, in combination with the further color developer TG-MD, N-[3- ((4-Methylphenyl)sulfonyloxy)phenyl]- / \ / '-phenylurea, in publication WO 2023 / 199975 and JP 2021-100798. The combination of the color developer TG-MD, N-[3-((4-Methylphenyl)sulfonyloxy)phenyl]- / \ / '-phenylurea, with the non-phenolic color developer Pergafast 425, 5-(N-3-Methylphenyl-sulfonylamido)-(N',N"-bis-{3-methylphenyl)-isophthalic diamide, is also described in publications JP2022-160290 and WO 2023 / 199975.

[0016] German patent application DE 10 2018 133 168 further describes a heat-sensitive recording material comprising a support substrate and a heat-sensitive color-forming layer containing at least one color former and at least one phenol-free color developer, as well as the use of the non-phenolic color developer contained in the heat-sensitive recording material, wherein one of the disclosed color developers comprises N-(4-((4-(3-Phenylureido)phenyl)sulfonyl)phenyl)benzenesulfonamide, represented by the following formula:

[0017] German patent application DE 10 2020 112 411 describes a heat-sensitive recording material comprising a support substrate and a heat-sensitive color-forming layer containing at least one color former and at least one non-phenolic color developer, as well as the use of the non-phenolic color developer contained in the heat-sensitive recording material, wherein one of the disclosed color developers is 2'-(3'-phenylureido)phenyl 3-(3-phenylureido)benzenesulfonate, as shown by the following formula:

[0018]

[0019] Although suitable non-phenolic color developers possess good hydrogen bond acceptor and donor properties and are therefore appropriate for stabilizing the color complex with the color former, the optical density of printed images suffers under the influence of various external factors. To counteract this negative change, the color complex that creates the printed image is stabilized by a stabilizer through the formation of hydrogen bonds, Pi-Pi interactions, and / or ionic or van der Waals interactions.

[0020] Furthermore, heat-sensitive recording materials produced with non-phenolic color developers may not always exhibit sufficient resistance to plasticizers, adhesives, and water, which can be disadvantageous, for example, in the case of self-adhesive labels known from the prior art, where an adhesive layer is applied to the back of the carrier substrate, and may negatively affect the specific values ​​of the optical density of the print (e.g., the barcode or the text image).

[0021] The adhesive layer on the back of the film is considered partly responsible for this phenomenon. During storage, substances from this layer migrate through the substrate into the chemically reactive, heat-sensitive recording layer and interact with it in a way that is detrimental to the color complex. Substances with a relatively low molar mass (< 10 kDa) contribute most significantly to this migration problem. Impaired performance after storage can also occur when a heat-activated adhesive, i.e., one that is solid at room temperature, is used.

[0022] Existing solutions known from the state of the art are often economically disadvantageous, as they require additional production steps and / or further additives, which make the heat-sensitive recording material more complex and therefore more expensive overall.

[0023] DESCRIPTION OF THE INVENTION

[0024] The object of the present invention is to optimize the property profile of a thermally printed heat-sensitive recording material, in particular to achieve the greatest possible limitation of the loss of image stability or optical density after storage of the heat-sensitive recording material.

[0025] A further object of the present invention is to optimize the property profile of a thermally printed heat-sensitive recording material, in particular to achieve the greatest possible limitation of the loss of image stability or optical density when the heat-sensitive recording material is stored under unfavorable storage conditions, for example at high humidity, high temperature and / or under light exposure.

[0026] A further object of the present invention is to optimize the property profile of a thermally printed heat-sensitive recording material, in particular to achieve the greatest possible limitation of the loss of image stability or optical density when the heat-sensitive recording material comes into contact with plasticizers, water and / or adhesives.

[0027] A further object of the present invention is to optimize the property profile of a thermally printed heat-sensitive recording material, in particular to achieve the greatest possible limitation of the loss of image stability or optical density, preferably without having to use special additives with limited availability and / or high price, and thus to be able to provide the heat-sensitive recording material cost-effectively.

[0028] Thus, the present invention aims to improve the minimum durability of a heat-sensitive recording material while maintaining the usual high requirements for such a heat-sensitive recording material, such as the optical density of a printed image obtained with such a heat-sensitive recording material, as well as cost-effective manufacturing.

[0029] Surprisingly, it has now been found that the disadvantages of the prior art described above can be overcome by using a combination of at least one color developer with groups capable of forming hydrogen bonds, selected from the group consisting of -NHCO-, -CONH-, -NHCONH-, -CONHNHCO-, -NHCOCONH-, -SO2NH- and -NHSO2, with at least one of the compounds of the following formula (1), Ar 1 -SO2-NH-C6H4-SO2-C6H4-NH-CO-NH-Ar 2 , and / or the following formula (2), Ar 1-NH-CO-NH-C6H4-SO2-O-C6H4-NH-CO-NH-Ar 2 , can be remedied as a stabilizer in the heat-sensitive layer of the heat-sensitive recording material.

[0030] In particular, the use of this combination, consisting of the corresponding at least one color developer and at least one stabilizer in the heat-sensitive layer of the heat-sensitive recording material, leads to a limitation of the loss of image stability or optical density after storage under demanding environmental conditions, and especially in the case of heat-sensitive recording materials with back-side preparations, so that the use of both components in the heat-sensitive layer leads to a synergistic effect.

[0031] The aforementioned problem is 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; and 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, at least one color developer, and at least one stabilizer; wherein the at least one stabilizer is selected as a compound of formula (1), Ar 1 -SO2-NH-C6H4-SO2-C6H4-NH-CO-NH-Ar 2 , where Ar 1 and Ar 2 independently of each other are an unsubstituted or substituted phenyl residue, and / or wherein at least one stabilizer is selected as a compound of formula (2), Ar 1 - NH-CO-NH-C6H4-SO2-O-CeH4-NH-CO-NH-Ar 2 , where Ar 1 and Ar 2independently of one another are an unsubstituted or substituted phenyl, naphthyl and / or heteroaryl residue; wherein the weight ratio of stabilizer to color developer in the heat-sensitive color-forming layer is selected such that, according to stability test 1 defined in the description, after a storage period of 7 days under dry storage conditions, the remaining optical density of the heat-sensitive color-forming layer is at least 85% of the original optical density of the heat-sensitive color-forming layer before storage, and / or that, according to stability test 2 defined in the description, after a storage period of 7 days under humid storage conditions, the remaining optical density of the heat-sensitive color-forming layer is at least 80% of the original optical density of the heat-sensitive color-forming layer before storage;and / or that, according to the stability test 3 defined in the description, after a storage period of 7 days, the remaining optical density of the heat-sensitive color-forming layer is at least 70% of the original optical density of the heat-sensitive color-forming layer before storage.

[0032] The combination of at least one stabilizer and at least one color developer in the heat-sensitive color-forming layer advantageously limits the loss of optical density, whereby the optical density according to stability test 1, 2, or 3 (as defined below) of the stored heat-sensitive recording material is always greater than the value obtained using the same heat-sensitive recording material without the stabilizer. This effect is particularly noticeable in the commercially available current range of 12.79 mJ / mm². 2in appearance.

[0033] Without being bound to the theory, it is assumed that the stabilizer, due to the color complex stabilizing interactions resulting from its functional groups, such as hydrogen bonds, TT-TT interactions and / or ionic interactions, contributes to the preservation of the color complex, in conjunction with color developer and color former, and the character of the typeface under the influence of destabilizing factors such as water, chemicals and critical climatic conditions.

[0034] In particular, at least one stabilizer has a compound of formula (1) and / or formula (2) which does not include a hydroxy-substituted phenyl group and can therefore also be described as a phenol group-free or non-phenolic compound.

[0035] The heat-sensitive recording material is well suited for applications in which the heat-sensitive recording material is equipped on the back with an adhesive layer, which is printed using the thermal direct process and must guarantee high storage stability even under critical environmental conditions, with regard to the specified image stability.

[0036] The present invention is not subject to any significant limitations with regard to the choice of adhesive applied to the reverse side. Both room-temperature adhesives and those that only become tacky after activation, for example by heat, are suitable. Both permanent and removable adhesives can be used. The application technology for the adhesive to the reverse side of the heat-sensitive recording material also does not limit the scope of the invention in any way. Aqueous dispersions of the adhesive, adhesives dissolved or suspended in organic media, as well as adhesives applied in a molten state, so-called hot-melt adhesives, can be used.

[0037] In summary, it can be stated that it has surprisingly been shown that by using at least one color developer and the stabilizer according to the first aspect of the present invention, it is possible to obtain heat-sensitive recording materials, in particular thermal labels, which are characterized by high image stability after long-term storage under critical environmental conditions when thermally printed. The heat-sensitive recording material according to the invention relates in particular to the application-relevant case of a self-adhesive heat-sensitive recording material, i.e., a heat-sensitive recording material that has an adhesive layer on the side of the carrier substrate facing away from the heat-sensitive color-forming layer.

[0038] In the context of the present disclosure, the stability test 1 defined below comprises storing the heat-sensitive recording material for a period of 7 days at 50°C, at a relative humidity of 0% and in the absence of light. Here, the heat-sensitive recording material is stored suspended freely in a drying oven.

[0039] In the context of the present disclosure, the stability test 2 defined below comprises storing the heat-sensitive recording material for a period of 7 days at 40°C, at a relative humidity of 85%, and in the absence of light. The humidity is generated using a saturated KCl solution, the liquid container being placed in a drying oven at 40°C, in which the heat-sensitive recording material is stored suspended freely.

[0040] In the context of the present disclosure, the stability test 3 defined below comprises storing the heat-sensitive recording material for a period of 7 days at 23°C, at a relative humidity of between 40% and 60%, and under artificial light irradiation from fluorescent tubes with an illuminance of 16,000 lux. The heat-sensitive recording materials are placed in a drawer under the aforementioned irradiation.

[0041] In particular, in the context of the present disclosure, a freshly manufactured heat-sensitive recording material was used in the stability tests 1, 2, and / or 3. This material was stored for less than 4 hours after the final production step before being subjected to the respective stability test 1, 2, and / or 3. In the stability test 1, 2, and / or 3 according to the present disclosure, the image stability of the heat-sensitive recording material is determined by measuring its optical density once before storage and once after a storage period of 7 days. The two determined optical density values ​​are then compared, as illustrated by the following formula A, where the variation of the calculated percentage values ​​is <±2 percentage points.

[0042] Image retention in % = (optical density after storage / optical density before storage) x 100

[0043] (Formula A)

[0044] As part of the stability test according to the present disclosure, the optical density was measured using a SpectroEye densitometer from X-Rite, with the measurement uncertainty of the measured value being estimated at <2%.

[0045] The image stability of a heat-sensitive recording material tested according to stability test 1 according to the present invention is, preferably at an energization energy of 12.79 mJ / mm². 2 , after a storage period of 7 days at least 85%, preferably at least 90%, more preferably at least 95%.

[0046] The image stability of a heat-sensitive recording material tested according to stability test 2 according to the present invention is, preferably at an energization energy of 12.79 mJ / mm². 2 , after a storage period of 7 days at least 80%, preferably at least 85%, more preferably at least 90%.

[0047] The image stability of a heat-sensitive recording material tested according to stability test 3 is as follows, according to the present invention, preferably at an energization energy of 12.79 mJ / mm². 2 , after a storage period of 7 days at least 70%, preferably at least 75%, more preferably at least 80%.

[0048] To perform the stability test, a DIN A4 heat-sensitive recording material is cut lengthwise into 6 cm wide strips. Each strip is printed and measured to determine its optical density before storage. The printed strip is then stored for 7 days under the specified storage conditions.

[0049] After storage and acclimatization to room temperature, the optical density is determined, averaged and set in relation to the optical density values ​​determined at the beginning before storage in order to determine the image stability according to the above-mentioned formula A.

[0050] According to one embodiment, for the combination of formula (1) Ar 1 and / or Ar 2 a phenyl residue.

[0051] In particular, for the combination of formula (1) Ar 1a phenyl group. In particular, for the compound of formula (1) Ar 2 a phenyl group. In particular, for the compound of formula (1) Ar 1 and Ar 2 a phenyl residue.

[0052] According to one embodiment, for the combination of formula (1) Ar 1 and / or Ar 2 substituted with at least one Ci-Cs alkyl, alkenyl, alkynyl, benzyl, formyl, CN, halogen, NO2, RO, R-CO, RO2C, R-OCO, R-SO2O, RO-SO2, R-SO2-NH, R-NH-SO2, R-NH-CO or R-CO-NH group, wherein R is a C1-C5 alkyl, alkenyl, alkynyl, phenyl, tolyl or benzyl group.

[0053] According to one embodiment, for the combination of formula (1) Ar 1 and / or Ar 2 a singly substituted phenyl group. In particular, for the compound of formula (1) Ar 1a singly substituted phenyl group. In particular, for the compound of formula (1) Ar 2 a singly substituted phenyl group. In particular, for the compound of formula (1) Ar 1 and Ar 2 a simply substituted phenyl residue.

[0054] According to one embodiment, for the combination of formula (1) Ar 1 and / or Ar 2 in the 4- or 4'-position or in the 3- or 3'-position, preferably in the 4- or 4'-position, arranged to the -CeF - SCh-CeF -group.

[0055] According to one embodiment, the compound of formula (1) is selected as N-(4-((4-(3-Phenylureido)phenyl)sulfonyl)phenyl)benzenesulfonamide, wherein the compound of formula (1) is preferably N-(4-((4-(3-Phenylureido)phenyl)sulfonyl)phenyl)benzenesulfonamide, which in the polymorphic form a 21 2is present, which is characterized by an X-ray powder diffractogram with Bragg angles (20 / CuKa) 8.7, 9.8, 10.8, 13.2, 13.9, 14.9, 15.2, 16.0, 17.4, 17.7, 18.7, 20.4, 21.2, 21.6, 22.3, 23.0, 23.3, 23.9, 24.4, 25.0, 25.8, 26.6, 28.1, 28.9, 29.4, 30.1, 30.6, 31.8, 34.5, 35.3, 35.6, 36.9, and / or which is characterized by a melt range determined by DSC of 219°C to 221°C, and / or those in the polymorphic form co 189 is present, which is characterized by an X-ray powder diffractogram with the Bragg angles (20 / CuKa) 10.9, 11.7, 14.6, 15.0, 15.8, 16.6, 17.6, 18.9, 19.4, 20.9, 21.2, 22.0, 23.3, 24.4, 24.7, 26.1, 27.4, 29.4, 34.2, and / or which is characterized by a melting range of 232°C to 233°C determined by DSC.

[0056] In particular, the polymorphic form a 21 2 preferably of N-(4-((4-(3-Phenylureido)phenyl)sulfonyl)phenyl)benzenesulfonamide.

[0057] 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.

[0058] In particular, the corresponding melting point determined by DSC (DSC = Differential scanning calorimetry) was measured 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.

[0059] According to an advantageous embodiment, the polymorphic form a 21 2 Absorption bands characteristic of N-(4-((4-(3-Phenylureido)phenyl)sulfonyl)phenyl)benzenesulfonamide according to Fourier transform infrared spectroscopy at wavenumbers of 1089 cm' 1 , 1110 cm- 1 , 1149 cm' 1 , 1237 cnr 1 , 1311 cnr 1 , 1321 cnr 1 , 1500 cnr1 , 1556 crrr 1 , 1597 cm' 1 , 1697 cm' 1 , 3365 cm' 1 , 3408 cm' 1 on, and exhibits the polymorphic form co 189 Absorption bands characteristic of N-(4-((4-(3-Phenylureido)phenyl)sulfonyl)phenyl)benzenesulfonamide according to Fourier transform infrared spectroscopy at wavenumbers of 1092 cm' 1 , 1105 cm' 1 , 1145 cm' 1 , 1233 cm' 1 , 1319 cm' 1 , 1495 cm' 1 , 1548 cm' 1 , 1598 cm' 1 , 1655 cm' 1 , 3239 cm' 1 on.

[0060] In particular, the respective Fourier transform infrared spectrum of the polymorphic form a was determined. 21 ' 2 and the polymorphic form co 189of N-(4-((4-(3-Phenylureido)phenyl)sulfonyl)phenyl)benzenesulfonamide using an IR spectrometer called “Bruker Tensor 27” with ATR unit (ATR = attenuated total reflection), provided by the company Bruker.

[0061] In particular, the respective Fourier transform infrared spectrum of the polymorphic form a was determined. 21 ' 2 and the polymorphic form co 189 of N-(4-((4-(3-Phenylureido)phenyl)sulfonyl)phenyl)benzenesulfonamide by using a KBr pellet taking into account the ATR unit.

[0062] In particular, the polymorphic form a 21 2 N-(4-((4-(3-Phenylureido)phenyl)sulfonyl)phenyl)benzenesulfonamide characteristic absorption bands according to Fourier-transform infrared spectroscopy with high intensity at wavenumbers of 1149 cm' 1 , 1311 cm' 1 , 1321 cm' 1 , 1500 cm' 1 , 1556 cm' 1 , 1597 cm' 1, 1697 cm' 1 on.

[0063] In particular, the polymorphic form a 21 2 Absorption bands characteristic of N-(4-((4-(3-Phenylureido)phenyl)sulfonyl)phenyl)benzenesulfonamide according to Fourier-transform infrared spectroscopy with a mean intensity at wavenumbers of 1089 cm' 1 , 1110 cm' 1 , 1237 cm' 1 , 3365 cm' 1 , 3408 cm' 1 in particular the polymorphic form co 189 N-(4-((4-(3-Phenylureido)phenyl)sulfonyl)phenyl)benzenesulfonamide characteristic absorption bands according to Fourier-transform infrared spectroscopy with high intensity at wavenumbers of 1105 cm' 1 , cm' 1 , 1145 cm' 1 , 1233 cm' 1 , 1319 cm' 1 , 1495 cm' 1 , 1548 cm' 1 , 1598 cm' 1 , 1655 cm' 1 on.

[0064] In particular, the polymorphic form co 189Absorption bands characteristic of N-(4-((4-(3-Phenylureido)phenyl)sulfonyl)phenyl)benzenesulfonamide according to Fourier-transform infrared spectroscopy with a mean intensity at wavenumbers of 1092 cm' 1 , 3239 cm' 1 on.

[0065] According to one embodiment, for the connection of formula (2) Ar 1 and / or Ar 2 a phenyl residue.

[0066] In particular, for the connection of formula (2) Ar 1 a phenyl group. In particular, for the compound of formula (2) Ar 2 a phenyl group. In particular, for the compound of formula (2) Ar 1 and Ar 2 a phenyl residue.

[0067] According to one embodiment, for the combination of formula (2) Ar 1 and / or Ar 2substituted with at least one Ci-Cs alkyl, alkenyl, alkynyl, benzyl, formyl, halogen, NO2, CN, R-CO, RO, RO2C, R-OCO, R-SO2-O, RO-SO2, R-SO2-NH, R-NH-SO2, R-NH-CO or R-CO-NH residue, wherein R is a Ci-Cs alkyl, alkenyl, alkynyl, phenyl, tolyl or benzyl residue.

[0068] According to one embodiment, for the combination of formula (2) Ar 1 and / or Ar 2 simply substituted. In particular, for the combination of formula (2) Ar 1 a singly substituted phenyl group. In particular, for the compound of formula (2) Ar 2 a singly substituted phenyl group. In particular, for the compound of formula (2) Ar 1 and Ar 2 a simply substituted phenyl residue.

[0069] According to one embodiment, for the connection of formula (2) the Ar 1 -NH- CO-NH residue and the Ar 2 -NH-CO-NH residue in 2- and 3'-, in 2- and 4'-, in 3- and 2'-, in 3- and 3'-, in 3- 4'-, in 4- 2'-, in 4- 3'- or in 4- 4'-position to the -CeF -SCH-O-CeF group.

[0070] According to one embodiment, the compound of formula (2) is selected as 2'-(3'-phenylureido)phenyl 3-(3-phenylureido)benzenesulfonate, wherein the compound of formula (2) is preferably 2'-(3'-phenylureido)phenyl 3-(3-phenylureido)benzenesulfonate, which is in the polymorphic form β 22 2 is present, which is characterized by an X-ray powder diffractogram with Bragg angles (20 / CuKa) 8.4, 11.0, 12.0, 12.7, 14.7, 16.5, 18.2, 19.4, 20.8, 21.1, 22.2, 25.7, 26.6, 26.9, 33.2 and / or which is characterized by a melting range determined by DSC of 214 °C to 217 °C, and / or which exists in the polymorphic form a 92is present, which is characterized by an X-ray powder diffractogram with Bragg angles (20 / CuKa) 8.3, 9.2, 15.1 , 17.6, 20.0, 22.2, 23.1 , 23.4, and / or which is characterized by a melting range of 190 °C to 192 °C determined by DSC.

[0071] 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.

[0072] In particular, the corresponding melting point determined by DSC was measured by differential scanning calorimetry using a Netzsch DSC 200 F3 Maia® instrument, an aluminum 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 a nitrogen atmosphere. According to an advantageous embodiment, the polymorphic form β 22 2Absorption bands characteristic of 2'-(3'- phenylureido)phenyl 3-(3-phenylureido)benzenesulfonate according to Fourier transform infrared spectroscopy at wavenumbers 1154 cm' 1 , 1165 cm' 1 , 1190 cm' 1 , 1231 cm' 1 , 1298 cm' 1 , 1310 cm' 1 , 1364 cm' 1 , 1449 cm' 1 , 1495 cm' 1 , 1550 cm -1 , 1595 cm -1 , 1634 cm -1 , 3291 cm -1 on, and has the polymorphic form a 9 ' 2 Absorption bands characteristic of 2'-(3'-phenylureido)phenyl 3-(3-phenylureido)benzenesulfonate according to Fourier transform infrared spectroscopy at wavenumbers 1103 cm' 1 , 1158 cm' 1 , 1193 cm' 1 , 1237 cm' 1 , 1314 cm' 1 , 1364 cm' 1 , 1421 cm -1 , 1441 cm -1 , 1499 cm -1 , 1544 cm -1 , 1599 cm -1 , 1682 cm -1 , 1711 cm -1 , 3392 cm-1 on.

[0073] In particular, the respective Fourier transform infrared spectrum of the polymorphic form β was determined. 22 2 and the polymorphic form a 92 of 2'-(3'-Phenylureido)phenyl 3-(3-phenylureido)benzenesulfonate by means of an IR spectrometer called "Bruker Tensor 27" with ATR unit (ATR = attenuated total reflection), provided by the company Bruker.

[0074] In particular, the respective Fourier transform infrared spectrum of the polymorphic form β was determined. 22 2 and the polymorphic form a 92 of 2'-(3'-phenylureido)phenyl 3-(3-phenylureido)benzenesulfonate by using a KBr pellet taking into account the ATR unit.

[0075] In particular, the polymorphic form ß exhibits 22 22'-(3'-phenylureido)phenyl 3-(3-phenylureido)benzenesulfonate exhibits characteristic absorption bands according to Fourier transform infrared spectroscopy with high intensity at wavenumbers of 1190 cm'. 1 , 1231 cm' 1 , 1364 cm' 1 , 1449 cm' 1 , 1550 cm' 1 , 1595 cm' 1 , 1634 cm' 1 on.

[0076] In particular, the polymorphic form ß exhibits 22 2 Absorption bands characteristic of 2'-(3'-phenylureido)phenyl 3-(3-phenylureido)benzenesulfonate according to Fourier transform infrared spectroscopy with a mean intensity at wavenumbers of 1154 cm⁻¹ -1 , 1165 cm -1 , 1298 cm' 1 , 1310 cm' 1 , 1495 cm' 1 , 3291 cm' 1 in particular the polymorphic form a 922'-(3'-phenylureido)phenyl 3-(3-phenylureido)benzenesulfonate exhibits characteristic absorption bands according to Fourier transform infrared spectroscopy with high intensity at wavenumbers 1314 cnr 1 , cm -1 , 1441 cm -1 , 1544 cm -1 , 1599 cm -1 , 1682 cm -1 on.

[0077] In particular, the polymorphic form a 92 Absorption bands characteristic of 2'-(3'-phenylureido)phenyl 3-(3-phenylureido)benzenesulfonate according to Fourier transform infrared spectroscopy with a mean intensity at wavenumbers of 1103 cm' 1 , 1158 cm- 1 , 1193 cm- 1 , 1237 cm' 1 , 1364 cm' 1 , 1421 cnr 1 , 1499 cm' 1 , 1711 cm' 1 , 3392 cm' 1 on.

[0078] According to one embodiment, the at least one color developer comprises a

[0079] Combination of formula (I): where R and Ri are independently selected from the group comprising hydrogen, Ci-Cis-alkyl, Ci-Cs-alkoxy-Ci-Cs-alkyl, and (Rg^N-Ci-Cs-Al-kyl, where Rg is selected from the group comprising Ci-Cs-alkyl, Cs-Ce-cycloalkyl; or a compound of formula (II) wherein R2, R3, R4, Rs, and Re are independently selected from the group comprising hydrogen, Ci-Cs-alkyl, -NH-C(=O)-R?, and -C(=O)-NH-Ry, wherein R? is selected as Ci-Cs-alkyl or -C(=O)ORs, wherein Rs is selected as Ci-Cs-alkyl or halogen, or wherein R2 and R3, or R4 and Rs or both, or wherein R3 and R4, or Rs and Re or both, or wherein R2 and R3 and Rs and Re, together form a hydrocarbon group with three or four carbon atoms, and wherein Q comprises a single bond or Ci-Cs-alkylene, which may be branched or unbranched, and wherein the Ci-Cs-alkylene comprises a main chain having one or more oxygen atoms between two carbon atoms if the Ci-Cs-alkylene has more than two carbon atoms.

[0080] In particular, the hydrocarbon group formed by R2 and R3 and Rs and Rs together comprises trimethylene, tetramethylene, propenylene, 2-butenylene or 1,3-butadienylene.

[0081] Preferably, Rs is selected as a halogen, wherein Rs is further preferably selected as chlorine.

[0082] Preferably, Q is selected as -CH2-, -CH2-CH2-, -CH2-O-, -CH2-CH2-O-, -CH2-CH2- CH2-, -CH2-CH2-CH2-CH2-, -C(Me)H-, -C(Et)H-, -C(n-Pr)H-, -C(i-Pr)H-, -C(n-Bu)H-, -C(i- Bu)H-, -C(sec-Bu)H-, -C(tert-Bu)H-, -C(Me)HCH2-, -CMe2CH2-, where Q is further preferably selected as -CH2-, -CH2-CH2-, -CH2-CH2-O- or -C(Me)H-.

[0083] Bevorzugt umfasst die Auswahl „Ci-Cis-Alkyl“ Methyl, Ethyl, Propyl, Isopropyl, N-butyl, Isobutyl, Sec-butyl, Tert-butyl, Amyl, Tert-amyl (1 ,1 -dimethylpropyl), 1 ,1 ,3,3-tetrame- thylbutyl, N-hexyl, 2-methylpentyl, Neopentyl, N-heptyl, 2-ethyl-hexyl oder N-octyl, N- nonyl, N-decyl, N-undecyl, N-dodecyl, N-tridecyl, N-tetradecyl, N-pentadecyl, N-hexa- decyl, N-heptadecyl, oder N-octadecyl.

[0084] Bevorzugt umfasst die Auswahl „Ci-Cs-Alkyl“ Methyl, Ethyl, Propyl, Isopropyl, N-butyl, Isobutyl, Sec-butyl, Tert-butyl, Amyl, Tert-amyl (1 ,1 -dimethylpropyl), 1 ,1 ,3,3-tetrame- thylbutyl, N-hexyl, 2-methylpentyl, Neopentyl, N-heptyl, 2-Ethyl-hexyl oder N-octyl, oder Tridecyl, weiter bevorzugt Methyl, Ethyl, N-propyl, Isopropyl, N-butyl, Isobutyl, Sec- butyl, Tert- butyl, 2-ethyl-hexyl oder Tridecyl.

[0085] Bevorzugt umfasst die Auswahl „Ci-Cs-Alkoxy“ Methoxy, Ethoxy, N-propoxy, Isopropoxy, N-butyloxy, N-pentyloxy, N-hexyloxy, N-heptyloxy, oder N-octyloxy. Weiter bevorzugt umfasst die Auswahl „Ci-Cs-Alkoxy“ die Auswahl „Ci-Cs-Alkoxy“, noch weiter bevorzugt Methoxy, Ethoxy, N-propoxy, Isopropoxy, N-butyloxy, oder N-hexyloxy.

[0086] Bevorzugt umfasst die Auswahl „Ci-Cs-Alkoxy-Ci-Cs-Alkyl“ Methoxymethyl, Ethoxymethyl, N-propoxymethyl, Isopropoxymethyl, N-butyloxymethyl, N-pentyloxymethyl, N-he- xyloxymethyl, N-heptyloxymethyl, N-octyloxymethyl, Methoxyethyl, Ethoxyethyl, N- propoxyethyl, Isopropoxyethyl, N-butyloxyethyl, N-pentyloxyethyl, N-hexyloxyethyl, N- heptyloxyethyl, N-octyloxyethyl, Methoxymethyl, 1 -methoxyethyl, 2-methoxyethyl, 3- methoxy-n-propyl, 1-methoxy-2-propyl, 4-methoxy-n-butyl, 5-methoxy-n-pentyl, 6-me- thoxy-n-hexyl, 7-methoxy-n-heptyl, 8-methoxy oder N-octyl, weiter bevorzugt 2-me- thoxyethyl.

[0087] Preferably, the selection includes “Cs-Cs-cycloalkyl” cyclopentyl or cyclohexyl, more preferably cyclohexyl.

[0088] Preferably, the selection “(R^N-Ci-Cs-Alkyl”) includes 2-(dimethylamino)-methyl, 2-(dimethylamino)-ethyl, 2-(diethylamino)-ethyl, 2-(diisopropylamino)-ethyl, 2-(n-propylamino)-ethyl, 3-(dimethylamino)-propyl, or 3-(cyclohexylamino)-propyl.

[0089] Preferably, the selection “R2 and R3 together” includes tetramethylene if R2 and R3, or R4 and R5 or both, or if R3 and R4, or R5 and Re or both, or if (R2 and R3) and (R5 and Re) together form a hydrocarbon group with three or four carbon atoms, such as in particular trimethylene, tetramethylene, propenylene, 2-butenylene, or 1,3-butadienylene.

[0090] The compound of formula (II) phenyl, benzyl, 3-methylphenyl, 2,6-diethylphenyl, o-isopropylphenyl, p-acetamidophenyl, 1-phenylethyl, 2-phenylethyl, 2-phenoxyethyl, 1-tetralino, or 2-tetralino is preferred. According to one embodiment, the color developer comprises a compound of the formula or the color developer includes a compound of formula (Ib):

[0091] Preferably, 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 acid diamide, 5-(N-1-tetralino-sulfonylamido)-(N',N”-bis-(1-tetralino)-isophthalic acid diamide, 5-(N- 3-methylphenyl-sulfonylamido)-(N',N"-bis-(3-methylphenyl)-isophthalic acid diamide, 5-(N-1-phenylethyl-sulfonylamido)-(N',N"-bis-(1-phenylethyl)-isophthalic acid diamide, 5-(N-2-phenylethyl-sulfonylamido)-(N',N"-bis-(2-phenylethyl)-isophthalic acid 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.,

[0092] In particular, the heat-sensitive marking material comprises a bisamide of formula (Ic):

[0093] Preferably, the color developer is selected as a compound of formula (1a) and the heat-sensitive recording material comprises a bisamide of formula (Ic), wherein the amount of bisamide (Ic) is more preferably from 0.01 mol% to 10 mol% with respect to the compound of formula (1a).

[0094] According to one embodiment, the color developer comprises 5-(N-3-methylphenylsulfonylamido)-(N',N"-bis-{3-methylphenyl)-isophthalic diamide, which is also marketed under the trade name Pergafast 425. 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.

[0095] According to one embodiment, the at least one color developer comprises a compound of formula (Nl): wherein Ri, R2, and R3 are independently selected from the group comprising hydrogen, halogen, nitro, Ci-Ce alkyl, Ci-Ce alkoxyl, C2-C6-Al-kenyl, Ci-Ce fluoroalkyl, N(R4)2, NHCORs, optionally substituted phenyl, and optionally substituted benzyl, wherein R4 is selected from the group comprising hydrogen, phenyl, benzyl, and Ci-Ce alkyl, wherein R5 is selected as Ci-Ce 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

[0096] Preferably, the compound of formula (Nl) is a compound of formula (IV) or a compound of formula (V), where Ri and R3 are defined as for the compound of formula (Nl):

[0097] (IV) (V)

[0098] Preferably, the compound of formula (Nl) is a benzenesulfonamide compound.

[0099] Preferably Ri, R2 and / or R3 is selected as hydrogen, halogen, more preferably fluorine, chlorine, bromine or iodine, nitro, a straight, branched or cyclic Ci-Ce alkyl group, more preferably methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, T-butyl, pentyl, isopentyl, neopentyl, hexyl, isohexyl, cyclopropyl, cyclobutyl, 2-methylcyclopropyl, cyclopropylmethyl, cyclopentyl, or cyclohexyl, a straight, branched or cyclic Ci-Ce 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-Ce-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 Ci-Ce-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 Ci-Ce-alkyl, an NHCORs group, wherein R5 is more preferably selected as a C1-Ce-alkyl, an optionally substituted phenyl group; and as an optionally substituted benzyl group.;

[0100] Further preferably, Ri, R2 and / or R3 is selected as hydrogen or a straight Ci-Ce alkyl group, wherein Ri is most preferably hydrogen or methyl, and R2 and R3 are each hydrogen.

[0101] Even more preferably, the selections for the Ci-Ce alkyl group selected according to R4 or R5 are the same as for the Ci-Ce alkyl group selected according to Ri. Even more preferably, the optional substituents of the optionally substituted groups are selected as hydroxy, halogen, most preferably fluorine, chlorine, bromine, or iodine; Ci-Ce alkyl, most preferably methyl, ethyl, N-propyl, isopropyl, N-butyl, sec-butyl, T-butyl, N-pentyl, isopentyl, neopentyl, T-pentyl, N-hexyl, isohexyl, 1-methylpentyl, or 2-methylpentyl; and Ci-Ce alkoxy, most preferably methoxy, ethoxy, N-propoxy, isopropoxy, N-butoxy, sec-butoxy, or T-butoxy.

[0102] Preferably the compound of formula (Nl) 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.

[0103] According to one embodiment, the at least one color developer comprises a compound of formula (Nl), wherein Ri, R2, and R3 are selected as hydrogen.

[0104] 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.

[0105] In particular, the α-polymorph of N-(2-(3-Phenylureido)phenyl)benzenesulfonamide is characterized by an X-ray diffraction pattern with Bragg angles (20 / CuKa) of 5.8, 9.3, 13.2,

[0106] 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

[0107] 27.8, 28.1 , 29.3, 29.6, 30.2, 31.6, 32.3, 32.8 and / or a melting point determined by DSC of 158°C to 159°C (onset).

[0108] In particular, the β-polymorph of N-(2-(3-Phenylureido)phenyl)benzenesulfonamide is characterized by an X-ray diffraction pattern with Bragg angles (20 / CuKa) 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 determined by DSC of 173°C to 174°C (onset). 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.

[0109] 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 below ^-atmosphere.

[0110] The corresponding compound, N-(2-(3-Phenylureido)phenyl)benzenesulfonamide, is also marketed under the name NKK-1304.

[0111] According to one embodiment, the at least one color developer comprises a compound of formula (III): where Ri is selected from the group comprising unsubstituted or substituted phenyl, naphthyl and Ci-C2O-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, Ci-Ci2-alkylene, and an unsubstituted or substituted heterocyclic group, where 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 —CO —NH —, —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 Ci-C2o-alkyl, provided that if B is not a group of the formula — O — SO2 —,Then R2 is unsubstituted or substituted phenyl, naphthyl, or Ci-Cs-alkyl, and if B is non-O, then R2 is non-alkyl. Preferably, Ri is selected as phenyl or naphthyl, which may be unsubstituted or substituted by, for example, Ci-Cs-alkyl, Ci-Cs-alkoxy, or halogen.

[0112] The substituents are further preferably selected as Ci-C4-alkyl, most preferably methyl or ethyl, Ci-C4-alkoxy, more preferably methoxy or ethoxy, or halogen, more preferably chlorine.

[0113] Ri is further preferred as unsubstituted naphthyl.

[0114] Ri is further preferably selected as a substituted phenyl, with the most preferred substituents being selected as one of the above-mentioned alkyl substituents.

[0115] Ri is preferably selected as unsubstituted or substituted Ci-C2o-alkyl, further preferably Ci-Cs-alkoxy or halogen, even more preferably Ci-C4-alkoxy, most preferably methoxy or ethoxy, or halogen, most preferably chlorine.

[0116] Ri is further preferably selected as unsubstituted Ci-C2o alkyl.

[0117] Ri is further preferred to be unsubstituted phenyl or phenyl substituted by Ci-Cs alkyl, Ci-Cs alkoxy, or halogen, with substituted phenyl being even more preferred. Most preferred is phenyl substituted by Ci-C4 alkyl, or even more preferably, methyl.

[0118] Preferably, X is a group of the formula -C(=S)- or -C(=O)-, further preferably a group of the formula -C(=O)-.

[0119] Preferably, A is an unsubstituted phenylene or an unsubstituted naphthylene group, or a phenylene or a naphthylene group further preferably substituted by Ci-Cs alkyl, halogen-substituted Ci-Cs alkyl, Ci-Cs alkoxy-substituted Ci-Cs alkyl, Ci-Cs alkoxy, halogen-substituted Ci-Cs alkoxy, Ci-Cs alkylsulfonyl, halogen, phenyl, phenoxy, or phenoxycarbonyl. Even more preferably are alkyl and alkoxy substituents comprising 1 to 4 carbon atoms, with Ci-Cs alkyl, halogen-substituted Ci-Cs alkyl, Ci-Cs alkylsulfonyl, or halogen being most preferred.

[0120] A is further preferred as an unsubstituted naphthylene group.

[0121] Preferably, A is a heterocyclic group which further preferably comprises unsubstituted pyrimidylene or pyrimidylene which is substituted by Ci-Cs-alkyl, or even more preferably by Ci-C4-alkyl.

[0122] Preferably, A is a Ci-Ci2-alkylene group, more preferably a Ci-Cs-alkylene group, and even more preferably a Ci-C4-alkylene group.

[0123] Further preferably is A unsubstituted phenylene or phenylene substituted by Ci-Cs-alkyl, halogen-substituted Ci-Cs-alkyl, Ci-Cs-alkoxy-substituted Ci-Cs-alkyl, Ci-Cs-alkoxy, halogen-substituted Ci-Cs-alkoxy, Ci-Cs-alkylsulfonyl, halogen, phenyl, phenoxy or phenoxycarbonyl, even more preferably Ci-Cs-alkyl, halogen-substituted Ci-Cs-alkyl, Ci-Cs-alkylsulfonyl or halogen.

[0124] Most preferred is A unsubstituted phenylene or phenylene substituted by Ci-C4 alkyl or halogen, even more preferred is unsubstituted phenylene.

[0125] B is preferably selected as — O — SO2 — , — SO2 — O — , — SO2 — NH — , — S — SO2 — , — O — , — O — CO — and — O — CO — NH — , further preferred as — O — SO2 — , — SO2 — O — and — SO2 — NH — , and most preferred as — O — SO2 — and — O — .

[0126] R2 is preferably aryl, more preferably phenyl or naphthyl, which is unsubstituted or substituted, and even more preferably by Ci-Cs-alkyl, halogen-substituted Ci-Cs-alkyl, Ci-Cs-alkoxy-substituted Ci-Cs-alkyl, Ci-Cs-alkoxy, halogen-substituted Ci-Cs-alkoxy or halogen, wherein alkyl and alkoxy substituents comprising 1 to 4 carbon atoms are most preferred, with Ci-C4-alkyl and halogen being the even more preferred substituents.

[0127] R2 naphthyl is preferred, which is further preferably unsubstituted.

[0128] R2 is preferably benzyl, which is substituted by the substituents already mentioned for the selection of R2 as phenyl or naphthyl, with unsubstituted benzyl being further preferred.

[0129] R2 is preferably Ci-C2o-alkyl, more preferably Ci-Cs-alkyl, and even more preferably Ci-Cs-alkyl, which is unsubstituted or substituted by, for example, Ci-Cs-alkoxy, halogen, phenyl or naphthyl, wherein unsubstituted alkyl groups are most preferred, and Ci-C4-alkyl is even more preferred.

[0130] R2 is further preferred as Ci-Cs-alkyl, halogen-substituted Ci-Cs-alkyl, phenyl-substituted Ci-Ce-alkyl, naphthyl-substituted Ci-Ce-alkyl, unsubstituted phenyl, or phenyl substituted by Ci-Cs-alkyl, halogen-substituted Ci-Cs-alkyl, Ci-Cs-alkoxy-substituted Ci-Cs-alkyl, Ci-Cs-alkoxy, halogen-substituted Ci-Cs-alkoxy or halogen, naphthyl and benzyl substituted by Ci-C4-alkyl or halogen.

[0131] R2 is further preferred Ci-C4-alkyl, halogen-substituted Ci-C4-alkyl, phenyl which is unsubstituted or substituted by Ci-C4-alkyl or halogen, naphthyl and benzyl which is unsubstituted or substituted by Ci-C4-alkyl or halogen, most preferred is phenyl which is unsubstituted or substituted by Ci-C4-alkyl or halogen.

[0132] Ri is preferably phenyl substituted by Ci-C4-alkyl, more preferably methyl, X is -C(=O)-, A is phenylene unsubstituted or substituted by Ci-Cs-alkyl or halogen, wherein unsubstituted phenylene is more preferably, 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 Ci-C4-alkyl is more preferably. According to one embodiment, the at least one color developer of formula (1) comprises N-((4-methylphenyl)sulfonyl)-N'-(3-((4-methylphenyl)sulfonyloxy)phenyl)urea, preferably the α-polymorph and / or the β-polymorph of N-((4-methylphenyl)sulfonyl)-N'-(3-((4-methylphenyl)sulfonyloxy)phenyl)urea.

[0133] The β-polymorph of N-((4-methylphenyl)sulfonyl)-N'-(3-((4-methylphenyl)sulfonyloxy)phenyl)urea can be prepared as follows: 10 g of the α-polymorph of N-((4-methylphenyl)sulfonyl)-N'-(3-((4-methylphenyl)sulfonyloxy)phenyl)urea are suspended in 80 mL of toluene and heated at 100 °C for two hours. After cooling to room temperature, the suspension is filtered. The residue is dried at 40 °C and a vacuum of 10 mbar for four hours to obtain 9.5 g of the β-polymorph of N-((4-methylphenyl)sulfonyl)-N'-(3-((4-methylphenyl)sulfonyloxy)phenyl)urea.

[0134] In particular, the α-polymorph of N-((4-methylphenyl)sulfonyl)-N'-(3-((4-methylphenyl)sulfonyloxy)phenyl)urea is characterized by an X-ray diffraction pattern with Bragg angles (26 / CuKa) 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.

[0135] In particular, the β-polymorph of N-((4-methylphenyl)sulfonyl)-N'-(3-((4-methylphenyl)sulfonyloxy)phenyl)urea is characterized by an X-ray diffraction pattern with Bragg angles (26 / CuKa) 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.

[0136] 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.

[0137] The corresponding melting point determined by DSC was measured using differential scanning calorimetry with 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 IXb atmosphere.

[0138] According to one embodiment, the at least one color developer comprises the compound of formula (VI): wherein Ri, R2, R3, R4 and R5 are independently selected from the group comprising hydrogen, Ci-Ce-alkyl, Ci-Ce-alkenyl and Ci-Ce-alkynyl, wherein the compound of formula (VI) preferably comprises N-[3-((4-methylphenyl)sulfonyloxy)phenyl]- / V'-phenylurea.

[0139] According to one embodiment, the at least one color developer comprises 5-(N-3-methylphenylsulfonylamido)-(N',N"-bis-{3-methylphenyl)-isophthalic diamide, which preferably exists in the polymorphic form a, characterized by an X-ray powder diffractogram with Bragg angles (20 / CuKa) 5.5, 6.1, 6.4, 12.1, 16.1, 16.8, 17.1, 18.3, 19.1, 19.9, 20.2, 21.4, 22.1, 22.7, 23.3, 24.3, 24.7, 25.0, 26.4, 27.7, 29.3 and / or which is characterized by a melting range of 211 determined by DSC °C, and / or which preferably exists in the polymorphic form β, which is characterized by an X-ray powder diffractogram with the Bragg angles (20 / CuKa) 6.2, 8.1 , 10.1 , 11.8, 12.2, 13.4, 14.1 , 15.3, 16.1 , 17.2, 18.4, 19.1 , 20.6, 21.4, 22.4, 24.5, 25.0, 25.9, 26.2, 26.9, 28.4 and / or which is characterized by a melting range of 192 °C determined by DSC.

[0140] 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, wherein in particular the α-polymorph is characterized by an X-ray diffraction pattern with Bragg angles (20 / CuKa) 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 range of 158 °C to 159 °C determined by DSC, wherein in particular the β-polymorph is characterized by an X-ray diffraction pattern with Bragg angles (20 / CuKa) 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,

[0141] 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 range of 173 °C to 174 °C determined by DSC.

[0142] According to one embodiment, the at least one color developer comprises N-((4-methylphenyl)sulfonyl)-N'-(3-((4-methylphenyl)sulfonyloxy)phenyl)urea, preferably the α-polymorph and / or the β-polymorph of N-((4-methylphenyl)sulfonyl)-N'-(3-((4-methylphenyl)sulfonyloxy)phenyl)urea, wherein in particular the α-polymorph is characterized by an X-ray diffraction pattern with Bragg angles (20 / CuKa) of 8.5, 9.5, 11.8, 12.1, 12.2,

[0143] 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 range of 161 °C to 162 °C determined by DSC, wherein in particular the β-polymorph is characterized by an X-ray diffraction pattern with Bragg angles (20 / CuKa) 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 range of 166 °C to 167 °C determined by DSC.

[0144] According to one embodiment, the weight ratio of the at least one color developer to the at least one stabilizer in the heat-sensitive color-forming layer is from 25 to 1 to 1 to 1 to 1, preferably from 11 to 1 to 3 to 1.

[0145] With the corresponding weight ratios of stabilizer to color developer in the heat-sensitive color-forming layer, the stability test 1 , 2 or 3 defined in the description shows a particularly high image stability of the heat-sensitive marking material after a period of 7 days.

[0146] In particular, the stabilizer is selected as N-(4-((4-(3-Phenylureido)phenyl)sulfonyl)phenyl)benzenesulfonamide and / or 2'-(3'-Phenylureido)phenyl 3-(3-phenylureido)benzenesulfonate and the at least one color developer is selected as N-(2-(3-Phenylureido)phenyl)benzenesulfonamide (trade name NKK-1304), wherein the weight ratio of color developer to stabilizer in the heat-sensitive color-forming layer is from 11:1 to 1:1, preferably from 8:1 to 1:1.

[0147] According to one embodiment, the at least one stabilizer has a weight fraction of 0.1 wt.% to 25 wt.% based on the total solids content of the heat-sensitive color-forming layer, wherein the weight fraction is preferably from 1 wt.% to 15 wt.%.

[0148] With the corresponding weight fraction of the stabilizer in the heat-sensitive color-forming layer, the stability test 1 , 2 or 3 defined in the description shows a particularly high remaining image stability of the heat-sensitive color-forming layer after a period of 7 days.

[0149] In particular, the stabilizer is selected as 2'-(3'-phenylureido)phenyl 3-(3-phenylureido)benzenesulfonate and the stabilizer has a weight fraction of 1 wt.% to 10 wt.% based on the total solid content of the heat-sensitive color-forming layer, wherein the weight fraction is preferably from 2 wt.% to 8 wt.%, more preferably from 3 wt.% to 6 wt.%, and most preferably 4 wt.%.

[0150] According to one embodiment, the at least one color developer has a weight fraction of 1 wt.% to 35 wt.% based on the total solids content of the heat-sensitive color-forming layer, wherein the weight fraction is preferably from 5 wt.% to 25 wt.%.

[0151] With the corresponding weight fraction of at least one color developer in the heat-sensitive color-forming layer, the stability tests 1, 2, and 3 defined in the description show a particularly high residual image stability of the heat-sensitive color-forming layer after a period of 7 days. Specifically, the at least one color developer is selected as N-((4-methylphenyl)sulfonyl)-N'-(3-((4-methylphenyl)sulfonyloxy)phenyl)urea.

[0152] (trade name Pergafast 201), and / or N-(2-(3-Phenylureido)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 20 wt.% to 30 wt.%, and most preferably 24 wt.%.

[0153] According to one embodiment, the heat-sensitive recording material has an adhesive layer which is arranged on the second side of the support substrate, wherein the adhesive layer comprises at least one adhesive.

[0154] In particular, the adhesive comprises an adhesive and / or a heat-activated adhesive, wherein the adhesive is preferably a permanent hot-melt adhesive based on styrene-isoprene and PVC copolymers, and / or wherein the adhesive is preferably a removable acrylate-based adhesive, and / or wherein the adhesive is preferably a permanent hot-melt adhesive based on synthetic rubber.

[0155] This achieves the technical advantage that a variety of different adhesive types can be used in the adhesive layer of the heat-sensitive recording material according to the invention, and yet the image retention remaining after a period of 7 days according to the stability tests 1, 2, and 3 is at least 35%.

[0156] For example, a permanently adhesive hot melt adhesive based on styrene-isoprene and PVC copolymers is the S2200 adhesive from Avery Dennison.

[0157] For example, a removable, acrylate-based adhesive is Avery Dennison's R5000N. For example, a permanent, hot-melt adhesive based on synthetic rubber is Henkel's Technomelt PS 8746.

[0158] 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.

[0159] 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.

[0160] 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-toludinamino)-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-diethylamino-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.

[0161] According to one embodiment, the at least one color former has a weight fraction of 5 wt.% to 30 wt.% based on the total solids content of the heat-sensitive color-forming layer, wherein the weight fraction is preferably 8 wt.% to 20 wt.%.

[0162] The choice of the substrate is not critical. According to one embodiment, the substrate comprises paper, synthetic paper, or a plastic film. The substrate is not limited in this respect. The substrate material preferably has a basis weight of 30 g / m². 2 up to 100 g / m² 2 , especially of 40 g / m² 2 up to 80 g / m² 2 on.

[0163] In particular, the carrier substrate comprises a paper substrate made from hardwood and / or softwood pulp.

[0164] 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 color-forming layer, wherein the intermediate layer preferably comprises at least one pigment, and more preferably organic hollow sphere pigments and / or calcined kaolins.

[0165] Preferably, the organic hollow sphere pigments comprise a styrene-acrylate copolymer. Preferably, the organic hollow sphere pigments have a glass transition temperature of 40 °C to 80 °C and / or a mean particle size of 0.1 .m to 2.5 .m. In particular, the mean particle size includes the mean particle size (D50).

[0166] 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.

[0167] According to one embodiment, the heat-sensitive recording material has at least one protective layer and / or print support layer arranged on the heat-sensitive color-forming layer, wherein the protective layer and / or print support layer preferably comprises a binder and at least one pigment, and more preferably a binder and an inorganic pigment.

[0168] The protective layer and / or print support 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.According to one embodiment, the binder 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 polymers, 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.

[0169] According to one embodiment, the binder has a weight fraction of 30 wt.% to 90 wt.% based on the total solids content of the protective layer, with the weight fraction preferably being from 40 wt.% to 80 wt.%.

[0170] According to one embodiment, the binder is designed as a cross-linked binder, wherein the cross-linked binder is preferably designed as a self-cross-linking binder, or wherein the protective layer comprises a cross-linker which is designed to react with the binder in order to obtain the cross-linked binder.

[0171] To achieve specific application-related performance characteristics of a heat-sensitive recording material, the binder is preferably present in cross-linked form in the protective layer, with the optimal degree of cross-linking of the binder being achieved during a drying step of the coating process, particularly in the presence of a cross-linker.

[0172] According to one embodiment, the self-crosslinking binder comprises modified polyvinyl alcohols and / or modified acrylates. Self-crosslinking binders, 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 binder.

[0173] According to one embodiment, the crosslinker 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, 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.

[0174] According to one embodiment, the crosslinker has a weight fraction of 0.01 wt.% to 25.0 wt.% based on the total solids content of the protective layer, with the weight fraction preferably being from 0.05 wt.% to 15 wt.%.

[0175] According to one embodiment, the pigment comprises an 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 dioxide, bentonite and mixtures thereof, or wherein the pigment comprises an organic pigment selected from the group consisting of hollow pigments having a styrene / acrylate copolymer wall, urea / formaldehyde condensation polymers, and mixtures thereof.

[0176] According to one embodiment, the pigment has a weight fraction of 5 wt.% to 50 wt.% based on the total solids content of the protective layer, wherein the weight fraction is preferably 10 wt.% to 45 wt.%. According to one embodiment, the protective layer comprises at least one lubricant / release agent, wherein the lubricant / release agent 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, natural waxes, preferably carnauba wax or montan wax, and mixtures thereof.

[0177] According to one embodiment, the lubricant / release agent 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.%.

[0178] According to one embodiment, the protective layer comprises at least one brightener, wherein the brightener is preferably selected as a stilbene.

[0179] The brightener allows the surface whiteness of the heat-sensitive color-forming layer to be adjusted to a favorable level.

[0180] 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 .

[0181] According to one embodiment, the protective layer has a thickness of 0.3 m to 6.0 m, preferably 0.5 m to 2.0 m.

[0182] According to one embodiment, the protective layer has a Bekk smoothness of 100 see to 3000 see, preferably of 500 see to 2000 see, as measured according to the standard ISO 5267:1995-03.

[0183] A correspondingly advantageous Bekk smoothness can be achieved by a smoothing process. According to one embodiment, the protective layer has a surface roughness of 0.5 µm to 2.50 µm, preferably of 1.00 µm and 2.00 µm, as measured according to ISO 8791-4:2008-05.

[0184] To control specific application-related properties, it may be advantageous if one or more additional (bis)phenolic or non-phenolic color developers are present in the heat-sensitive color-forming layer in addition to the previously disclosed application forms of the color developer.

[0185] According to one embodiment, the heat-sensitive color-forming layer comprises at least one sensitizing agent and / or at least one pigment and / or at least one lubricant / release agent and / or at least one binder.

[0186] 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.

[0187] The at least one sensitizing agent is preferably selected from the group comprising a fatty acid amide, in particular stearic acid amide, behenamide or palmitamide, an ethylenebis fatty acid amide, in particular 1 / V,1 / V'-ethylenebis-stearic acid amide or 1 / V,1 / V'-ethylenebis-oleic acid amide, a fatty acid alkanolamide, in particular N-(hydroxymethyl)stearic acid amide, 1 / V-hydroxymethyl palmitamide or hydroxyethylstearic acid amide, a wax, in particular polyethylene wax or montan wax, a carboxylic acid ester, in particular dimethyl terephthalate, dibenzyl terephthalate, benzyl 4-benzyloxybenzoate, di-(4-methylbenzyl)oxalate, di-(4-chlorobenzyl)oxalate or di-(4-benzyl)oxalate, an aromatic ether, in particular 1,2-diphenoxyethane, 1,2-di-(3-methylphenoxy)ethane, 2-Benzyloxynaphthalene or 1,4-diethoxynaphthalene, an aromatic sulfone, in particular diphenyl sulfone, an aromatic sulfonamide, in particular benzenesulfonanilide or ZV-benzyl-4-toluenesulfonamide, aromatic hydrocarbons,in particular 4-benzylbiphenyl and mixtures thereof. According to one embodiment, the sensitizing agent has a weight fraction of 2 wt.% to 40 wt.% based on the total solids content of the heat-sensitive color-forming layer, wherein the weight fraction is preferably 5 wt.% to 25 wt.%.

[0188] According to one embodiment, the heat-sensitive color-forming layer comprises at least one anti-aging agent.

[0189] The anti-aging agent preferably comprises sterically hindered phenols, particularly preferably 1,1,3-Tris-(2-methyl-4-hydroxy-5-cyclohexyl-phenyl)butane, 1,1,3-Tris-(2-methyl-4-hydroxy-5-tert-butylphenyl)butane, 1,1-Bis-(2-methyl-4-hydroxy-5-tert-butylphenyl)butane.

[0190] Urea-urethane compounds (trade product UU) or ethers derived from 4,4'-dihydroxy-diphenylsulfone, such as 4-benzyloxy-4'-(2-methylglycidyloxy)-diphenylsulfone (trade name NTZ-95®, Nippon Soda Co. Ltd.), or oligomeric ethers (trade name D90®, Nippon Soda Co. Ltd.) can also be used as aging protection agents in the recording material according to the invention.

[0191] The use of 5-(N-3-methylphenylsulfonylamido)-(N',N"-bis-{3-methyl-phenyl)isophthalic diamide (trade name PF425®, Solenis) is also possible.

[0192] The anti-aging agent is preferably present in an amount of 0.05 to 0.5 parts by weight, based on the at least one color developer.

[0193] In a further preferred embodiment, the heat-sensitive color-forming layer contains at least one binder, wherein the binder is selected from the group comprising water-soluble starches, starch derivatives, starch-based biolatics of the EcoSphere type, methylcellulose, hydroxyethylcellulose, carboxymethylcellulose, gelatin, casein, partially or fully saponified polyvinyl alcohols, chemically modified polyvinyl alcohols, ethylene-vinyl alcohol copolymers, sodium polyacrylates, styrene-maleic anhydride copolymers, ethylene-maleic anhydride copolymers, styrene-butadiene copolymers, acrylamide-(meth)acrylate copolymers, acrylamide-acrylate-methacrylate terpolymers, polyacrylates, poly(meth)acrylic acid esters, acrylate-butadiene copolymers, polyvinyl acetates, acrylonitrile-butadiene copolymers, and mixtures thereof.

[0194] According to one embodiment, the at least one binder is present in the heat-sensitive layer in an amount of 2 wt.% to 40 wt.%, preferably in an amount of 5 wt.% to 20 wt.%, based on the total dry mass of the heat-sensitive layer.

[0195] According to one embodiment, the heat-sensitive color-forming layer comprises a lubricant / release agent, which is preferably selected from the group consisting of fatty acid metal salts, more preferably zinc stearate or calcium stearate, behenate salts, synthetic waxes, in particular in the form of fatty acid amides, more preferably stearic acid amide and behenic acid amide, fatty acid alkanolamides, more preferably stearic acid methylolamide, paraffin waxes of different melting points, ester waxes of different molecular weights, polyethylene waxes, propylene waxes of different hardnesses, natural waxes, more preferably carnauba wax or montan wax or soy wax and mixtures thereof.

[0196] Preferably, lubricants / release agents are based on waxes or fats, fatty acids or salts, especially metal salts, of fatty acids.

[0197] According to one embodiment, the lubricant / release agent has a weight fraction of 1 wt.% to 10 wt.% based on the total solids content in the heat-sensitive color-forming layer, wherein the weight fraction is preferably 3 wt.% to 6 wt.%.

[0198] According to one embodiment, the heat-sensitive color-forming layer has an additional pigment, which has the advantage that these additional pigments can fix the chemical melt produced in the thermal printing process on their surface, and that the surface whiteness and opacity of the heat-sensitive color-forming layer and its printability with conventional printing inks can be controlled via these additional pigments. Furthermore, the corresponding additional pigments have an "extender function," for example, for the relatively expensive color-forming functional chemicals.

[0199] The further pigment is preferably selected from the group comprising inorganic pigments, both synthetic and natural origin, precipitated or natural calcium carbonates, clays, aluminium oxides, aluminium hydroxides, silicas, precipitated and pyrogenic silicas, diatomaceous earths, magnesium carbonates, talc, but also organic pigments, further preferably hollow pigments with a styrene / acrylate copolymer wall, urea / formaldehyde condensation polymers and mixtures thereof.

[0200] Preferably, the additional pigment has a weight fraction of 5 wt.% to 50 wt.% based on the total solids content in the heat-sensitive color-forming layer, wherein the weight fraction is preferably from 10 wt.% to 40 wt.%.

[0201] 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.

[0202] 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.

[0203] The additional brightener allows the surface whiteness of the heat-sensitive recording material to be controlled.

[0204] According to one embodiment, the heat-sensitive color-forming layer comprises a rheology aid, preferably a thickener and / or a surfactant. This offers the advantage that certain coating properties of the heat-sensitive color-forming layer can be improved during the manufacturing process.

[0205] According to one embodiment, the surface application weight of the heat-sensitive color-forming layer is 1 g / m². 2 up to 10 g / m² 2 , preferably 3 g / m² 2 up to 5 g / m² 2 .

[0206] The aforementioned problem is solved according to the second aspect by a method for producing a heat-sensitive recording material, comprising the following process steps: providing a support substrate having a first side and a second side facing away from the first side; applying a coating suspension to the first side of the support substrate, wherein the coating suspension comprises at least one color former, at least one color developer, and at least one stabilizer, wherein the at least one stabilizer is selected as a compound of formula (1), AH-SCH-NH-CeH^SCH-CeH^NH-CO-NH-Ar 2 , where Ar 1 and Ar 2 independently of each other are an unsubstituted or substituted phenyl residue, and / or wherein at least one stabilizer is selected as a compound of formula (2), Ar 1 -NH-CO-NH-C6H4-SO2-O-C6H4-NH-CO-NH-Ar 2 , where Ar 1 and Ar 2independently of each other are an unsubstituted or substituted phenyl, naphthyl and / or heteroaryl residue; and drying of the application suspension to obtain a heat-sensitive color-forming layer arranged on the first side of the support substrate;wherein the weight ratio of stabilizer to color developer in the heat-sensitive color-forming layer is selected such that, according to stability test 1 defined in the description, after a storage period of 7 days under dry storage conditions, the remaining optical density of the heat-sensitive color-forming layer is at least 85% of the original optical density of the heat-sensitive color-forming layer before storage, and / or that, according to stability test 2 defined in the description, after a storage period of 7 days under humid storage conditions, the remaining optical density of the heat-sensitive color-forming layer is at least 80% of the original optical density of the heat-sensitive color-forming layer before storage;and / or that, according to the stability test 3 defined in the description, after a storage period of 7 days, the remaining optical density of the heat-sensitive color-forming layer is at least 70% of the original optical density of the heat-sensitive color-forming layer before storage.

[0207] It is preferred to obtain the recording material according to the invention by a process in which an aqueous suspension containing the starting materials of the heat-sensitive color-forming layer is applied to a carrier substrate and dried, wherein the aqueous coating suspension has a solids content of about 20 to about 75 wt.%, preferably about 30 to about 50 wt.%, and is applied and dried using the curtain coating process at an operating speed of the coating system of at least about 400 m / min.

[0208] This method is particularly advantageous from an economic point of view.

[0209] If the solids content falls below approximately 20% by weight, efficiency deteriorates because a large quantity of water must be removed from the coating quickly through gentle drying, which negatively impacts the application speed. Conversely, if the value exceeds 75% by weight, this only results in increased technical effort to ensure the stability of the coating curtain during the application process.

[0210] 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 its 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, including heat-sensitive recording materials, whereby multilayer recording layers are created by applying the curtain, consisting of several coating dispersion films, to substrates (maximum speed 200 m / min). Setting the operating speed of the coating system to at least approximately 400 m / min offers both economic and technical advantages.Preferably, the operating speed is at least about 750 m / min, particularly preferably at least about 1000 m / min, and most preferably at least about 1500 m / min. It was particularly surprising that even at the latter speed, the heat-sensitive recording material obtained is in no way affected and that the operation proceeds optimally even at this high speed.

[0211] In particular, the aqueous deaerated coating suspension has a viscosity of approximately 150 to approximately 800 mPas (Brookfield, 100 U / rnin, 20 °C). If the value falls below approximately 150 mPas or exceeds approximately 800 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 200 to approximately 500 mPas.

[0212] In particular, to optimize the process, the surface tension of the aqueous coating suspension can be adjusted to approximately 25 to approximately 60 mN / m, preferably to approximately 35 to approximately 50 mN / m (measured according to the static ring method according to Du Noüy, DIN 53914).

[0213] The formation of the heat-sensitive, color-forming layer can take place online or in a separate offline application process. This also applies to any subsequent layers or intermediate coats.

[0214] It is advantageous if the dried, heat-sensitive, color-forming layer is subjected to a smoothing process.

[0215] It is advantageous to set the Bekk smoothness, measured according to ISO 5627:1995-03, to approximately 100 to approximately 1000 seconds, preferably to approximately 250 to approximately 600 seconds.

[0216] The surface roughness (PPS) according to ISO 8791-4:2008-05 is in the range of approximately 0.50 to approximately 2.50 pm, preferably between 1.00 and 2.00 pm. The method described above is advantageous from an economic point of view and allows for high process control of the coating system even at speeds exceeding 1500 m / min, without any impairment of the product, i.e., the heat-sensitive recording material according to the invention. The process can be carried out online and offline, resulting in desirable flexibility.

[0217] The heat-sensitive recording material according to the invention is phenol-free and well-suited for POS (point-of-sale), label, and / or ticket applications. It is also suitable for the production of parking tickets, travel tickets, admission tickets, lottery and betting slips, etc., which can be printed using the thermal direct process and require high image retention even during long-term storage, including under harsh climatic conditions with regard to temperature and humidity.

[0218] According to one embodiment, the method includes the process step of applying an adhesive layer to the second side of the carrier substrate.

[0219] In particular, applying the adhesive layer to the second side of the substrate may include applying, especially laminating, an adhesive film to the second side of the substrate.

[0220] In particular, the application of the adhesive layer to the second side of the support substrate can include the application of an adhesive dispersion to the second side of the support substrate and the subsequent drying of the adhesive dispersion to obtain the adhesive layer arranged on the second side of the support substrate.

[0221] In particular, the drying of the adhesive layer is carried out at a temperature of 60 °C to 80 °C, preferably at 70 °C.

[0222] In particular, 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.

[0223] In particular, the application of the adhesive layer comprises the application of an adhesive dispersion and the subsequent drying of the adhesive dispersion, wherein the process includes the further process step which is carried out before the application of the adhesive dispersion: applying another release paper to the second side of the carrier substrate, wherein the adhesive dispersion is applied to the further release paper.

[0224] In particular, the application and drying of the coating dispersion to the first side of the carrier substrate is carried out before the application of the adhesive layer to the second side of the carrier substrate, or the application of the adhesive layer to the second side of the carrier substrate is carried out before the application and drying of the coating dispersion to the first side of the carrier substrate, preferably the application and drying of the coating dispersion to the first side of the carrier substrate is carried out before the application of the adhesive layer to the second side of the carrier substrate.

[0225] In particular, 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.

[0226] In particular, the application rate of the coating dispersion is between 3 g / m². 2 and 5 g / m² 2 , preferably between 3.6 g / m³ 2 and 4.8 g / m² 2 , and / or the application rate of the adhesive dispersion is between 10 g / m² 2 and 30 g / m² 2 , preferably 20 g / m² 2 .

[0227] According to one embodiment, the coating suspension is produced in particular by grinding, and preferably has a mean particle size D<4,3) of 0.5 pm to 5.0 pm, particularly preferably of 0.50 pm to 1.50 pm and most preferably of 1.5 pm to 2.50 pm.

[0228] 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.

[0229] The aforementioned task is solved according to a third aspect by a heat-sensitive recording material that can be produced by a method according to the second aspect.

[0230] 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.

[0231] According to a fourth aspect, the present invention relates to the use of at least one stabilizer and at least one color developer in a heat-sensitive recording material, comprising a support substrate having a first side and a second side facing away from the first side, and 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, at least one color developer, and at least one stabilizer, wherein the at least one stabilizer is selected as a compound of formula (1), Ar 1 - SO2-NH-C6H4-SO2-CeH4-NH-CO-NH-Ar 2 , where Ar 1 and Ar 2 independently of each other are an unsubstituted or substituted phenyl residue, and / or wherein at least one stabilizer is selected as a compound of formula (2), Ar 1-NH-CO-NH-CeH4- SO2-O-CeH4-NH-CO-NH-Ar 2 , where Ar 1 and Ar 2The components are, independently of one another, an unsubstituted or substituted phenyl, naphthyl, and / or heteroaryl residue. The weight ratio of stabilizer to color developer in the heat-sensitive color-forming layer is selected such that, according to stability test 1 defined in the description, after a storage period of 7 days under dry storage conditions, the remaining optical density of the heat-sensitive color-forming layer is at least 85% of the original optical density of the heat-sensitive color-forming layer before storage, and / or that, according to stability test 2 defined in the description, after a storage period of 7 days under humid storage conditions, the remaining optical density of the heat-sensitive color-forming layer is at least 80% of the original optical density of the heat-sensitive color-forming layer before storage.and / or that, according to the stability test 3 defined in the description, after a storage period of 7 days, the remaining optical density of the heat-sensitive color-forming layer is at least 70% of the original optical density of the heat-sensitive color-forming layer before storage.

[0232] 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 use of at least one stabilizer and at least one color developer in a heat-sensitive recording material according to the fourth aspect.

[0233] EXAMPLES OF EXECUTION

[0234] In the following detailed examples, a variety of heat-sensitive recording materials or thermal papers were produced by applying aqueous coating suspensions and adhesive dispersions to form a composite structure on a carrier substrate.

[0235] Production of heat-sensitive recording materials: Heat-sensitive recording materials or thermal papers were produced, whereby the following compositions of aqueous coating suspensions were used to form a composite structure on a carrier substrate and subsequently further layers, in particular a protective layer, were formed in the usual manner.

[0236] The application of an aqueous coating suspension to form the heat-sensitive color-forming layer of a heat-sensitive recording paper was carried out on a laboratory scale using a doctor blade, either on the coating side of a paper pre-coated with a pigment coating with a basis weight of 65 g / m². 2 and 72 g / m² 2 (Substrate 1), or on one side of a synthetic base paper (Yupo® FP680) with a basis weight of 63 g / m² 2 (Substrate 2).

[0237] 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 and / or starch. Primers with organic (hollow sphere) pigments, possibly mixed with inorganic pigments, are also suitable. The application rate of this pigmented layer or intermediate coat is approximately 2 to 10 g / m². 2 .

[0238] After drying the aqueous application suspension of the heat-sensitive coating compound, the heat-sensitive color-forming layer is obtained. The application quantity of the heat-sensitive color-forming layer is between 3.8 g / m². 2 and 4.2 g / m² 2 .

[0239] The following describes the production of the dispersions (each for 1 part by weight) for the coating suspensions:

[0240] Color forming dispersion A:

[0241] Colorant dispersion A was prepared by milling 20 parts by weight of 3-n-dibutylamine-6-methyl-7-anilinofluorane (ODB-2) with 33 parts by weight of a 12% aqueous solution of Gohsenx™ L-3266 (sulfonated polyvinyl alcohol, Nippon Gohsei) in a bead mill. Stabilizer dispersions B:

[0242] Stabilizer dispersions B were prepared by milling N-(4-((4-(3-Phenylureido)phenyl)sulfonyl)phenyl)benzenesulfonamide (referred to as compound II in the following table), or the polymorphic form a of 2'-(3'-Phenylureido)phenyl 3-(3-phenylureido)benzenesulfonate (referred to as compound IIa in the following table), or the polymorphic form β of 2'-(3'-Phenylureido)phenyl 3-(3-phenylureido)benzenesulfonate (referred to as compound III-b in the following table) together with 66 parts by weight of a 12% aqueous solution of Gohsenx™ L-3266 (sulfonated polyvinyl alcohol, Nippon Gohsei) in a bead mill.

[0243] Color developer dispersions C:

[0244] The aqueous color developer dispersions C were prepared by milling 40 parts by weight of the respective color developer N-((4-methylphenyl)sulfonyl)-N'-(3-((4-methylphenyl)sulfonyloxy)phenyl)urea (CAS# 232938-43-1, referred to as Compound IV in the table below), or N-(2-(3-phenylureido)phenyl)benzenesulfonamide (CAS# 215917-77-4, referred to as Compound V in the table below), or N-[3-((4-methylphenyl)sulfonyloxy)phenyl]- / \ / '-phenylurea (referred to as Compound VI in the table below) together with 66 parts by weight of a 12% aqueous solution of Gohsenx™ L-3266 (sulfonated polyvinyl alcohol, Nippon Gohsei) in a bead mill.

[0245] Sensitizing dispersion D:

[0246] The sensitizing dispersion D was prepared by milling 40 parts by weight of 1,2-diphenoxyethane (DPE) with 33 parts by weight of a 12% aqueous solution of Gohsenx™ L-3266 (sulfonated polyvinyl alcohol, Nippon Gohsei) in a bead mill.

[0247] All dispersions A, B, C, and D produced by milling exhibit a mean particle size D(4,3) of 0.8 pm to 1.2 pm. The particle size distribution of the dispersions was measured by laser diffraction using a Coulter LS13320 instrument from Beckman Coulter.

[0248] Lubricant / T release agent dispersion E: The lubricant-ZT release agent dispersion E is a 20% zinc stearate dispersion comprising 9 wt. parts zinc stearate, 1 wt. part Gohsenx™ L-3266 (sulfonated polyvinyl alcohol, Nippon Gohsei) and 40 wt. parts water.

[0249] Piqmentsuspension P:

[0250] The pigment suspension P is a 72% spreadable kaolin suspension (Lustra® S, BASF).

[0251] Binder solution:

[0252] The binder solution consists of a 10% aqueous polyvinyl alcohol solution (Poval 28-99, Kuraray Europe).

[0253] The heat-sensitive coating suspension was prepared by mixing and stirring 1 part by weight of the colorant dispersion A, 0.625 parts by weight of the respective stabilizer dispersion B, 1.875 parts by weight of the respective color developer dispersion C, 2.5 parts by weight of the sensitizing dispersion D, 1 part by weight of the lubricant / release agent dispersion E, 2.1 parts by weight of the pigment dispersion P, and 2.5 parts by weight of the binder solution, taking into account the addition sequence C, D, B, E, P, A, and then diluted with water to a solids content of approximately 25%. The coating suspension is presented as an example for a color developer-to-stabilizer ratio of 3:1.

[0254] The heat-sensitive coating suspensions obtained in this way were used to produce composite structures made of paper substrate and heat-sensitive color-forming layer.

[0255] Adhesives

[0256] To assemble self-adhesive thermal labels, the following commercially available adhesives were used on the side of the paper carrier facing away from the heat-sensitive color-forming layer, or on the second side of the carrier substrate:

[0257] - R5000N (Avery Dennison) is a removable, acrylate-based adhesive. - S2200 (Avery Dennison) is a permanent, hot-melt adhesive for deep-freeze applications, based on styrene-isoprene and PVC copolymers.

[0258] - Technomelt PS 8746 (Henkel company) is a permanently adhesive hot melt adhesive based on synthetic rubber.

[0259] The heat-sensitive recording materials thus obtained were stored in the absence of light at room temperature and humidity and promptly examined and evaluated using the following measurement methods, as summarized below in Tables 1, 2, 3, 4 and 5:

[0260] Measurement of optical density:

[0261] Six-centimeter-wide strips were produced from the appropriately manufactured heat-sensitive recording materials. These strips were thermally printed using a GeBE PrinterLab GPT-10000 test printer (GeBE Elektronik und Feinwerktechnik GmbH, Germany) with a Kyocera printhead at 305 dpi, a voltage of 24 V, and a checkerboard pattern with 10 energy levels, at a printing speed of approximately 100 mm / s and a contact pressure of 19 N. The area of ​​one square of the printed pattern corresponds to 80 x 80 dots.

[0262] The optical densities (oD) shown in the following tables were determined using an X-Rite SpectroEye densitometer at an energy level of 7.73 mJ / mm². 2 and 12.79 mJ / mm 2 measured, with the measurement uncertainty of the oD values ​​estimated at <2%. The variance of the correspondingly calculated % values ​​is <±2 percentage points.

[0263] Durability test of the printed image under artificial aging:

[0264] One sample of the heat-sensitive recording material, recorded according to the above procedure for measuring optical density, was stored for seven days under the following conditions: 50°C and 0% relative humidity in the absence of light (dry storage conditions according to stability test 1), 40°C and 85% relative humidity in the absence of light (humid storage conditions according to stability test 2), and 23°C and 40% to 60% relative humidity under artificial light provided by Osram Lumilux Cool Daylight fluorescent tubes (1300 lm and 18 W) with an illuminance of 16,000 lux (storage conditions under light according to stability test 3). The samples of the heat-sensitive recording material were stored suspended freely in a drying oven.

[0265] A freshly produced heat-sensitive recording material was used, which was stored for less than 4 hours after the final production step before being subjected to the respective stability test 1, 2, or 3.

[0266] After the storage period had ended and the sample had been acclimatized to room temperature, the optical density (oD) of each stored sample was determined at an irradiation energy of 12.79 mJ / mm². 2 measured and related to the optical density (oD) of the sample before storage according to the formula A shown below:

[0267] Remaining optical density in % = (optical density after storage / optical density before storage) x 100

[0268] (Formula A)

[0269] The dispersion of the % values ​​calculated according to formula A is <±2 percentage points.

[0270] Resistance test of the printed image to adhesive:

[0271] A strip of transparent Tesa self-adhesive tape (tesafilm® crystal clear, #57315) and, separately, a strip of Tesa packaging tape (#04204) were affixed to the sample of heat-sensitive recording material, which had been recorded according to the above procedure for measuring optical density, taking care to avoid creases and air inclusions. After storage at room temperature (20 to 22 °C), the optical density (oD) was measured after 24 hours and after 7 days at an irradiation energy of 12.79 mJ / mm². 2 Measurements were taken through the respective adhesive tape and related to the analogously determined optical density values ​​of the freshly applied samples according to formula A. Resistance test of the printed image to plasticizers:

[0272] A plasticized cling film (PVC film with 20 to 25% dioctyl adipate) was applied to the sample of heat-sensitive recording material, recorded according to the above procedure for measuring optical density. This film was carefully wrapped around the material, avoiding creases and air inclusions, and stored for 16 hours. One sample was stored at room temperature (20 to 22 °C), and a second sample at 40 °C. After removing the film, the optical density (oD) was determined at an energic energy of 12.79 mJ / mm². 2 measured and related to the corresponding optical density values ​​before the plasticizer effect according to formula A.

[0273] Resistance test of the printed image to water:

[0274] A sample of the heat-sensitive recording material, recorded according to the above procedure for measuring optical density, was stored at room temperature (20 to 22 °C) for 16 hours. After drying the paper at room temperature, the optical density (oD) was determined at an irradiance of 12.79 mJ / mm². 2 measured and related to the corresponding image density values ​​before storage according to formula A.

[0275] Durability test of the printed image under extreme climatic conditions without adhesive:

[0276] A sample of the heat-sensitive recording material, recorded according to the above procedure for measuring optical density, was placed between two glass plates at 60 °C and a pressure of 1350 N / m² for 4 weeks. 2The papers were stored at a relative humidity of 50% and in the absence of light. After acclimatizing the papers to room temperature, the optical density (oD) was determined at an electrical energy of 12.79 mJ / mm². 2 measured and related to the corresponding optical density values ​​before storage according to formula A.

[0277] Durability test of the printed image under extreme climatic conditions with adhesive: A sample of the heat-sensitive recording material, recorded according to the above procedure for measuring optical density, was laminated with commercially available adhesives on the side of the paper carrier facing away from the heat-sensitive ink-forming layer, or on the second side of the carrier substrate, and placed between two glass plates for 4 weeks at 60 °C, under a pressure of 1350 N / m². 2The papers were stored at a relative humidity of 50% and in the absence of light. After acclimatizing the papers to room temperature, the optical density (oD) was determined at an electrical energy of 12.79 mJ / mm². 2 measured and related to the corresponding optical density values ​​before storage according to formula A.

[0278] Evaluation

[0279] Tables 1 and 2 below describe the results of the image stability measurements for a variety of different heat-sensitive recording materials, which have a heat-sensitive color-forming layer on a first side of the substrate.

[0280] The results obtained in the table are based on the analysis of the optical density of the respective heat-sensitive recording material as a function of artificial aging, which, after a storage period of 7 days, leads to a reduced proportion of the optical density in % calculated according to formula A.

[0281] For information on the stabilizers and color developers used in the heat-sensitive color-forming layer, please refer to the preceding explanations.

[0282] The static starting point (°C) shown in the tables was determined as follows:

[0283] The recording sheet was pressed against five metallic dies, heated and thermostatically controlled to different temperatures, with a contact pressure of 4 bar and a contact time of 30 seconds, using the Rycobel GHS-03 device. The optical density of the resulting images was measured with an X-Rite SpectroEye densitometer, where the static starting point is defined as the lowest temperature in °C at which an optical density of 0.2 is achieved. The accuracy of the measurement method is <±0.5 °C. Table 1 below summarizes the remaining optical density, starting point, and artificial aging based on paper pre-coated with a pigment coating, using substrate 1 with a basis weight of 4 g / m². 2 was investigated, whereby in particular the heat-sensitive color-forming layer of substrate 1 had a basis weight of 4 g / m². 2exhibits:

[0284] Remaining percentage image density according to formula A

[0285] Table 1

[0286] An analysis of Table 1 shows that the use of the color developer N-((4-methylphenyl)sulfonyl)-N'-(3-((4-methylphenyl)sulfonyloxy)phenyl)urea (compound IV) or N-(2-(3-phenylureido)phenyl)benzenesulfonamide (compound V) alone, without a stabilizer, results in a heat-sensitive recording material with a reduced optical density compared to a heat-sensitive recording material in which, in addition to the color developers of compounds IV or V, the stabilizer N-(4-((4-(3-phenylureido)phenyl)sulfonyl)phenyl)benzenesulfonamide (compound II), or the polymorphic form a of 2'-(3'-phenylureido)phenyl 3-(3-phenylureido)benzenesulfonate (compound II a), or the polymorphic form β of 2'-(3'-phenylureido)phenyl 3-(3-phenylureido)benzenesulfonate (compound III-B) was added.

[0287] The corresponding optimum optical density of the heat-sensitive recording material is achieved with a ratio of color developer to stabilizer of 11 to 1.

[0288] In the analysis of the artificial aging of the corresponding heat-sensitive recording material, the addition of stabilizer to the color developer also leads to an increase in the remaining optical density under the storage conditions.

[0289] Under appropriate dry storage conditions and storage conditions at high humidity, the addition of the stabilizer to the color developer led to an increase in the remaining optical density in all cases. The same was true under storage conditions exposed to light, as the addition of the stabilizer to the color developer similarly improved the remaining optical density.

[0290] Table 2 below summarizes the optical density, starting temperature and artificial aging based on a synthetic base paper according to substrate 2:

[0291] Remaining percentage image density according to formula A

[0292] Table 2

[0293] According to Table 2, the use of the color developer N-[3-((4-Methylphen- nyl)sulfonyloxy)phenyl]- / \ / '-phenylurea (compound VI) alone and in combination with the stabilizer N-(4-((4-(3-Phenylureido)phenyl)sulfonyl)phenyl)benzenesulfonamide (compound II), or with the polymorphic form a of 2'-(3'-Phenylureido)phenyl 3-(3- phenylureido)benzenesulfonate (compound III-a) was investigated.

[0294] In the analysis of artificial aging according to stability tests 1 to 3, an analogous trend emerges from Table 2, since the addition of the stabilizer of compound II or III-a to the color developer of compound VI leads to an improved remaining optical density of the heat-sensitive recording material than when only the color developer of compound VI is used alone.

[0295] Table 3 below summarizes the results of the resistance test of the printed image to adhesive, plasticizer and water based on a paper pre-coated with a pigment coating according to the remaining optical density of formula A, where substrate 1 with a basis weight of 4 g / m² is used as the support substrate. 2 was investigated, whereby in particular the heat-sensitive color-forming layer of substrate 1 had a basis weight of 4 g / m². 2 exhibits: 11:01 I (V:lll-b) | 36 | 27 | 16 | 31 | 95 | 63 | 81 |

[0296] * Remaining percentage image density according to formula A

[0297] Table 3

[0298] According to Table 3, the use of the color developer N-((4-methylphenyl)sulfonyl)-N'-(3-((4-methylphenyl)sulfonyloxy)phenyl)urea (compound IV), or N-(2-(3-phenylureido)phenyl)benzenesulfonamide (compound V) alone and in combination with the stabilizer N-(4-((4-(3-phenylureido)phenyl)sulfonyl)phenyl)benzenesulfonamide (compound II), or the polymorphic form a of 2'-(3'-phenylureido)phenyl 3-(3-phenylureido)benzenesulfonate (compound III-a), or the polymorphic form β of 2'-(3'-phenylureido)phenyl 3-(3-phenylureido)benzenesulfonate (compound III-b) was investigated.

[0299] The effect of adding stabilizer to the color developer is most clearly seen when assessing the plasticizer resistance and water resistance of the heat-sensitive recording material. Here, the color developer according to compound IV or V alone exhibits a lower residual optical density than the combination of the color developer according to compound IV or V with the stabilizer according to formula II, III-a and III-b.

[0300] When examining the remaining optical density of the corresponding heat-sensitive recording material when using Tesa adhesive tape, it can be seen that an increasing stabilizer content correlates with a higher remaining image density.

[0301] Table 4 below summarizes the results of the resistance test of the printed image to adhesive, plasticizer and water based on a paper pre-coated with a pigment coating according to the remaining optical density of formula A, where substrate 2 was tested as the support substrate:

[0302] Table 4

[0303] According to Table 4, the use of the color developer N-[3-((4-Methylphen- nyl)sulfonyloxy)phenyl]- / \ / '-phenylurea (compound VI) alone and in combination with the stabilizer N-(4-((4-(3-Phenylureido)phenyl)sulfonyl)phenyl)benzenesulfonamide (compound II), or the polymorphic form a of 2'-(3'-Phenylureido)phenyl 3-(3- phenylureido)benzenesulfonate (compound III-a) was investigated.

[0304] Here too, the results according to Table 4 for plasticizer and water resistance are similar to the results according to Table 3, according to which the addition of the stabilizer according to compounds II or III-a to the corresponding color developer leads to higher remaining optical densities.

[0305] Table 4 shows that for the tape designated #04204 under all storage conditions and for the tape designated #57315 for a 7-day storage period, a higher remaining optical density of the respective recording material is achieved when a combination of the color developer of compound VI with the stabilizer of compounds II or III-a is used, as opposed to the use of compound VI alone.

[0306] Tables 5 and 6 below summarize the results of the durability test of the printed image under extreme climatic conditions based on a paper pre-coated with a pigment coating according to the remaining optical density of formula A, where substrate 1 with a basis weight of 4 g / m² is used as the support substrate. 2 was investigated, whereby in particular the heat-sensitive color-forming layer of substrate 1 had a basis weight of 4 g / m². 2 exhibits:

[0307] Remaining percentage image density according to formula A

[0308] Table 5

[0309] Remaining percentage image density according to formula A

[0310] Table 6

[0311] According to Tables 5 and 6, the use of the color developer N-((4-methylphenyl)sulfonyl)-N'-(3-((4-methylphenyl)sulfonyloxy)phenyl)urea (compound IV), or N-(2-(3-phenylureido)phenyl)benzenesulfonamide (compound V) alone and in combination with the stabilizer N-(4-((4-(3-phenylureido)phenyl)sulfonyl)phenyl)benzenesulfonamide (compound II), or the polymorphic form a of 2'-(3'-phenylureido)phenyl 3-(3-phenylureido)benzenesulfonate (compound III-a), or the polymorphic form β of 2'-(3'-phenylureido)phenyl 3-(3-phenylureido)benzenesulfonate (compound III-b) was investigated.

[0312] The results in Tables 5 and 6 clearly show that for all color developer and stabilizer combinations and for all adhesives used, the optical density, or the remaining optical density of the heat-sensitive recording material, is better than when only a color developer without a stabilizer is used.

[0313] In summary, the addition of non-phenolic stabilizers comprising N-(4-((4-(3-Phenylureido)phenyl)sulfonyl)phenyl)benzenesulfonamide (compound II), or the polymorphic form a of 2'-(3'-Phenylureido)phenyl 3-(3-phenylureido)benzenesulfonate (compound III-a), or the polymorphic form β of 2'-(3'-Phenylureido)phenyl 3-(3-phenylureido)benzenesulfonate (compound III-b) to the corresponding color developers according to compounds IV, V and VI leads to an improvement in a variety of application-related properties of the heat-sensitive recording material, such as optical density, storage stability, and resistance to plasticizers, water and adhesives.

Claims

1. REQUIREMENTS 1. Heat-sensitive recording material comprising: a support substrate having a first side and a second side facing away from the first side; and 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, at least one color developer, and at least one stabilizer; wherein the at least one stabilizer is selected as a compound of formula (1), AH-SCH-NH-CeH^SCH-CeH^NH-CO-NH-Ar 2 , where Ar 1 and Ar 2 independently of each other are an unsubstituted or substituted phenyl residue, and / or wherein the at least one stabilizer is selected as a compound of formula (2), AH-NH-CO-NH-CeH^SCH-O-CeH^NH-CO-NH-Ar 2 , where Ar 1 and Ar 2independently of one another are an unsubstituted or substituted phenyl, naphthyl, and / or heteroaryl residue; wherein the weight ratio of stabilizer to color developer in the heat-sensitive color-forming layer is selected such that, according to stability test 1 defined in the description, under dry storage conditions, after a storage period of 7 days, the remaining optical density of the heat-sensitive color-forming layer is at least 85% of the original optical density of the heat-sensitive color-forming layer before storage; and / or that, according to stability test 2 defined in the description, under humid storage conditions, after a storage period of 7 days, the remaining optical density of the heat-sensitive color-forming layer is at least 80% of the original optical density of the heat-sensitive color-forming layer before storage; and / or that, according to the stability test 3 defined in the description, after a storage period of 7 days under storage conditions under light, a remaining optical density of the heat-sensitive color-forming layer of at least 70% of the original optical density of the heat-sensitive color-forming layer before storage is present.

2. Heat-sensitive recording material according to claim 1, wherein for the compound of formula (1) Ar 1 and / or Ar 2 a phenyl residue.

3. Heat-sensitive recording material according to claim 1 or 2, wherein for the compound of formula (1) Ar 1 and / or Ar 2is substituted with at least one C1-C5-Al-kyl, one alkenyl, one alkynyl, one benzyl, one formyl, one CN, one halogen, one NO2, one RO, one R-CO, one RO2C, one R-OCO, one R-SO2O, one RO-SO2, one R-SO2-NH, one R-NH-SO2, one R-NH-CO or one R-CO-NH group, wherein R is a Ci-Cs alkyl, one alkenyl, one alkynyl, one phenyl, one tolyl or one benzyl group.

4. Heat-sensitive recording material according to one of the preceding claims, wherein for the compound of formula (1) Ar 1 and / or Ar 2 a simply substituted phenyl residue.

5. Heat-sensitive recording material according to one of the preceding claims, wherein for the compound of formula (1) Ar 1 and / or Ar 2 in the 4- or 4'-position or in the 3- or 3'-position, preferably in the 4- or 4'-position, to the -C6H4-SO2-C6H4- group.

6. Heat-sensitive recording material according to any one of the preceding claims, wherein the compound of formula (1) is selected as N-(4-((4-(3-phenylureido)phenyl)sulfonyl)phenyl)benzenesulfonamide, wherein the compound of formula (1) is preferably N-(4-((4-(3-phenylureido)phenyl)sulfonyl)phenyl)benzenesulfonamide, which in the polymorphic form a 21 2 is present, which is characterized by an X-ray powder diffractogram with Bragg angles (20 / CuKa) 8.7, 9.8, 10.8, 13.2, 13.9, 14.9, 15.2, 16.0, 17.4, 17.7, 18.7, 20.4, 21.2, 21.6, 22.3, 23.0, 23.3, 23.9, 24.4, 25.0, 25.8, 26.6, 28.1, 28.9, 29.4, 30.1, 30.6, 31.8, 34.5, 35.3, 35.6, 36.9, and / or which is characterized by a melting range of 219°C to 221°C determined by DSC, and / or which exists in the polymorphic form co 189is present, which is characterized by an X-ray powder diffractogram with the Bragg angles (20 / CuKa) 10.9, 11.7, 14.6, 15.0, 15.8, 16.6, 17.6, 18.9, 19.4, 20.9, 21.2, 22.0, 23.3, 24.4, 24.7, 26.1 , 27.4, 29.4, 34.2, and / or which is characterized by a melting range of 232°C to 233°C determined by DSC.

7. Heat-sensitive recording material according to one of the preceding claims, wherein for the compound of formula (2) Ar 1 and / or Ar 2 are a phenyl residue.

8. Heat-sensitive recording material according to one of the preceding claims, wherein for the compound of formula (2) Ar 1 and / or Ar 2with at least one Ci-Cs alkyl, alkenyl, alkynyl, benzyl, formyl, halogen, NO2, CN, R-CO, RO, RO2C, R-OCO, R-SO2-O, RO-SO2, R-SO2-NH, R-NH-SO2, R-NH-CO or R-CO-NH group substituted, wherein R is a Ci-Cs alkyl, alkenyl, alkynyl, phenyl, tolyl or benzyl group.

9. Heat-sensitive recording material according to one of the preceding claims, wherein for the compound of formula (2) Ar 1 and / or Ar 2 simply substituted.

10. Heat-sensitive recording material according to one of the preceding claims, wherein for the compound of formula (2) the Ar 1 -NH-CO-NH residue and the Ar 2 -NH-CO-NH residues are arranged in 2- and 3'-, in 2- and 4'-, in 3- and 2'-, in 3- and 3'-, in 3- 4'-, in 4- 2'-, in 4- 3'- or in 4- 4'-position to the -CsH^SCH-O-CsH^group.

11. Heat-sensitive recording material according to any one of the preceding claims, wherein the compound of formula (2) is selected as 2'-(3'-phenylureido)phenyl 3-(3-phenylureido)benzenesulfonate, wherein the compound of formula (2) is preferably 2'-(3'-phenylureido)phenyl 3-(3-phenylureido)benzenesulfonate, which in the polymorphic form β 22 2 is present, which is characterized by an X-ray powder diffractogram with Bragg angles (20 / CuKa) 8.4, 11.0, 12.0, 12.7, 14.7, 16.5, 18.2, 19.4, 20.8, 21.1, 22.2, 25.7, 26.6, 26.9, 33.2 and / or which is characterized by a melting range determined by DSC of 214 °C to 217 °C, and / or which exists in the polymorphic form a 92 is present, which is characterized by an X-ray powder diffractogram with Bragg angles (20 / CuKa) 8.3, 9.2, 15.1 , 17.6, 20.0, 22.2, 23.1 , 23.4, and / or which is characterized by a melting range of 190 °C to 192 °C determined by DSC.

12. Heat-sensitive recording material according to any of the preceding claims, wherein the at least one color developer comprises a compound of formula (I): where R and Ri are independently selected from the group comprising hydrogen, Ci-Cis-alkyl, Ci-Cs-alkoxy-Ci-Cs-alkyl, and (Rg^N-Ci-Cs-Al-kyl, where Rg is selected from the group comprising Ci-Cs-alkyl, Cs-Ce-cycloalkyl; or a compound of formula (II) wherein R2, R3, R4, Rs, and Re are independently selected from the group comprising hydrogen, Ci-Cs-alkyl, -NH-C(=O)-R?, and -C(=O)-NH-Ry, wherein R? is selected as Ci-Cs-alkyl or -C(=O)ORs, wherein Rs is selected as Ci-Cs-alkyl or halogen, or wherein R2 and R3, or R4 and Rs or both, or wherein R3 and R4, or Rs and Re or both, or wherein R2 and R3 and Rs and Re, together form a hydrocarbon group with three or four carbon atoms, and wherein Q comprises a single bond or Ci-Cs-alkylene, which may be branched or unbranched, and wherein the Ci-Cs-alkylene comprises a main chain having one or more oxygen atoms between two carbon atoms if the Ci-Cs-alkylene has more than two carbon atoms 13. Heat-sensitive recording material according to any of the preceding claims, wherein the at least one color developer comprises a compound of formula (Nl): wherein Ri, R2, and R3 are independently selected from the group comprising hydrogen, halogen, nitro, Ci-Cs-alkyl, Ci-Cs-alkoxyl, C2-C6-Al-kenyl, Ci-Cs-fluoroalkyl, N(R4)2, NHCORs, optionally substituted phenyl, and optionally substituted benzyl, wherein R4 is selected from the group comprising hydrogen, phenyl, benzyl, and Ci-Cs-alkyl, wherein Rs is selected as Ci-Cs-alkyl, wherein n1 and n3 are independently selected as an integer from 1 to 5, and where n2 is an integer from 1 to 4.

14. Heat-sensitive recording material according to any of the preceding claims, wherein the at least one color developer comprises a compound of formula (III): where Ri is selected from the group comprising unsubstituted or substituted phenyl, naphthyl and Ci-C2O-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, Ci-Ci2-alkylene, and an unsubstituted or substituted heterocyclic group, where 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 —CO —NH —, —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 Ci-C2o-alkyl, provided that if B is not a group of the formula — O — SO2 —,Then R2 is unsubstituted or substituted phenyl, naphthyl, or Ci-Cs alkyl, and if B is O, then R2 is not alkyl.

15. Heat-sensitive recording material according to any of the preceding claims, wherein the at least one color developer comprises a compound of formula (VI): wherein Ri, R2, R3, R4 and R5 are independently selected from the group comprising hydrogen, Ci-Ce-alkyl, Ci-Ce-alkenyl and Ci-Ce-alkynyl, wherein the compound of formula (VI) preferably comprises N-[3-((4-methylphenyl)sulfonyloxy)phenyl]- / V'-phenylurea.

16. 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 support substrate, wherein the coating suspension comprises at least one color former, at least one color developer, and at least one stabilizer, wherein the at least one stabilizer is selected as a compound of formula (1), AH-SCH-NH-CeH^SCH-CeH^NH-CO-NH-Ar 2 , where Ar 1 and Ar 2 independently of each other are an unsubstituted or substituted phenyl residue, and / or wherein at least one stabilizer is selected as a compound of formula (2), Ar 1 -NH-CO-NH-C6H4-SO2-O-CeH4-NH-CO-NH-Ar 2 , where Ar 1 and Ar 2 are independently of each other an unsubstituted or substituted phenyl, naphthyl and / or heteroaryl residue; and Drying the coating suspension to obtain a heat-sensitive color-forming layer arranged on the first side of the support substrate; wherein the weight ratio of stabilizer to color developer in the heat-sensitive color-forming layer is selected such that that, according to stability test 1 defined in the description, after a storage period of 7 days under dry storage conditions, the remaining optical density of the heat-sensitive color-forming layer is at least 85% of the original optical density of the heat-sensitive color-forming layer before storage, and / or that, according to stability test 2 defined in the description, after a storage period of 7 days under humid storage conditions, the remaining optical density of the heat-sensitive color-forming layer is at least 80% of the original optical density of the heat-sensitive color-forming layer before storage;and / or that, according to the stability test 3 defined in the description, after a storage period of 7 days, the remaining optical density of the heat-sensitive color-forming layer is at least 70% of the original optical density of the heat-sensitive color-forming layer before storage.

17. Heat-sensitive recording material producible by a method according to claim 16.

18. Use of at least one stabilizer and at least one color developer in a heat-sensitive recording material, comprising a support substrate having a first side and a second side facing away from the first side, and 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, at least one color developer, and at least one stabilizer, wherein the at least one stabilizer is selected as a compound of formula (1), Ar 1 -SO2-NH-C6H4-SO2-CeH4-NH-CO-NH-Ar 2 , where Ar 1 and Ar 2 independently of each other are an unsubstituted or substituted phenyl residue, and / or wherein at least one stabilizer is selected as a compound of formula (2), Ar 1 - NH-CO-NH-C6H4-SO2-O-CeH4-NH-CO-NH-Ar 2 , where Ar 1 and Ar2independently of one another are an unsubstituted or substituted phenyl, naphthyl and / or heteroaryl residue; wherein the weight ratio of stabilizer to color developer in the heat-sensitive color-forming layer is selected such that, according to stability test 1 defined in the description, after a storage period of 7 days under dry storage conditions, the remaining optical density of the heat-sensitive color-forming layer is at least 85% of the original optical density of the heat-sensitive color-forming layer before storage, and / or that, according to stability test 2 defined in the description, after a storage period of 7 days under humid storage conditions, the remaining optical density of the heat-sensitive color-forming layer is at least 80% of the original optical density of the heat-sensitive color-forming layer before storage;and / or that, according to the stability test 3 defined in the description, after a storage period of 7 days, the remaining optical density of the heat-sensitive color-forming layer is at least 70% of the original optical density of the heat-sensitive color-forming layer before storage.

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