HEAT-SENSITIVE RECORDING MATERIAL

Description

[0001] The present invention relates to a heat-sensitive recording material comprising a substrate, a heat-sensitive recording layer comprising N-(4-methylphenylsulfonyl)-N'-(3-(4-methylphenylsulfonyloxy)phenyl)urea and / or N-[2-(3-phenylureido)phenyl]benzenesulfonamide, and an intermediate layer comprising calcined aluminum silicate arranged between the substrate and the heat-sensitive recording layer. The present invention further relates to a method for producing a heat-sensitive recording material and to the use of calcined aluminum silicate in an intermediate layer of a heat-sensitive recording material.

[0002] Heat-sensitive recording materials have been known for many years and enjoy widespread popularity. This popularity stems, in part, from the advantage that the color-forming components are contained within the recording material itself, thus enabling the use of toner- and ink-cartridge-free printers. Consequently, there is no longer any need to purchase, store, replace, or refill toner or ink cartridges. This innovative technology has therefore become widely adopted, particularly in public transportation and retail.

[0003] In the recent past, however, increasing concerns have arisen regarding the environmental compatibility of certain (bis)phenolic color developers, also known as color acceptors, and sometimes also of dye precursors with which the color developers react when heat is applied to form a visually recognizable color. These concerns cannot be ignored by industry and especially by retailers. For example, the well-known and scientifically extensively researched components of color developers, known as... □ Bisphenol-A, which is 2,2 bis (4-hydroxyphenyl)-propane, and □ Bisphenol-S, which is 4,4'-dihydroxydiphenylsulfone, increasingly the focus of public criticism and are therefore sometimes replaced by ▪ N-(4-Methylphenylsulfonyl)-N'-(3-(4-methylphenylsulfonyloxy)phenyl)urea, also known as Pergafast 201, marketed by BASF SE, ▪ 4-Hydroxy-4'-isopropoxydiphenylsulfone, also known as "D8", and ▪ N-[2-(3-Phenylureido)phenyl]benzenesulfonamide, also known as "NKK".

[0004] With the aim of improving the resistance of heat-sensitive recording materials, especially in their use as tickets or lottery slips, to environmental influences such as heat, humidity and chemicals, the underlying chemistry and manufacturing technology for producing such recording materials has been continuously developed.

[0005] To increase the resistance of a thermal print (heat-induced recording) obtainable on a heat-sensitive recording material to water, aqueous alcohol solutions and plasticizers, DE 10 2004 004 204 A1 proposes a heat-sensitive recording material whose heat-sensitive recording layer contains conventional dye precursors as well as the combination of a phenolic color developer and a urea-urethane-based color developer.

[0006] In DE 10 2015 104 306 A1, a heat-sensitive recording material is described, 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, wherein, for example, N-phenyl-N'[(phenylamino)sulfonyl]urea, N-(4-methylphenyl)-N'[(4-ethylphenylamino)sulfonyl]urea, N-(4-ethoxycarbonylphenyl)-N'[(4-ethoxycarbonylphenylamino)sulfonyl]urea or structurally similar compounds are used as phenol-free color developers.

[0007] JP 2014-218062 A describes a heat-sensitive recording material with a heat-sensitive recording layer containing at least a leuco dye and a color developer on a support. The color developer used is a mixture of 4,4'-bis(3-tosylureido)diphenylmethane and N-[2-(3-phenylureido)phenyl]benzenesulfonamide.

[0008] International patent application WO 2016 / 136203 A1 describes a crystalline form of N-[2-(3-phenylureido)phenyl]benzenesulfonamide and the use of this crystalline form in a recording material. The crystalline form is characterized by diffraction patterns in the X-ray powder diffractogram and diffraction diagram, and by its melting point, thereby distinguishing it from other crystalline forms of this compound. It is further noted that the crystalline forms can also be distinguished by their absorption bands in the IR spectrum. The application also demonstrates that different crystalline forms of a compound can lead to different properties in the recording materials produced using this compound.

[0009] The subject of US 2005 / 0148467 A1 is a heat-sensitive recording material which, to form an irreversible printed image, contains at least the components of two color-forming systems, one of which is a chelate system and the other a conventional leuco-dye system.

[0010] However, there is a constant need for additional heat-sensitive recording materials for a wide variety of applications. Due to high sales volumes in a highly competitive market, these materials must be producible at low production costs and therefore require a simple design. A further challenge lies in the fact that printed heat-sensitive recording materials, when used as tickets, admission tickets, travel passes, parking tickets, and similar items, are exposed to a multitude of different environmental influences, such as humidity, heat, or chemicals.

[0011] During normal use, heat-sensitive recording materials can come into contact with a variety of substances that can affect the durability of the thermal print. These include water and organic solvents, as well as fats and oils found, for example, in hand care products, which can be transferred to the heat-sensitive recording material when touched. Therefore, resistance to fats and oils is particularly important.

[0012] In addition to resistance to chemicals that may come into contact with the heat-sensitive recording materials, these materials must also exhibit high resistance to thermal influences and light exposure. On the one hand, the heat-sensitive recording material should be energy-efficient and easy to print on, for example, to minimize energy consumption in mobile applications. On the other hand, the printed image should remain intact after printing, and exposure to heat or light should neither cause the printed image to fade nor discolor the unprinted background, which would render the print illegible.For example, in the case of parking tickets, which are stored behind the windshield after printing and are therefore exposed to high temperatures and direct sunlight in the summer, thermal resistance and resistance to light are extremely relevant.

[0013] The long-term durability of heat-sensitive recording materials is also crucial for tickets such as concert tickets or airline tickets, which are often issued well in advance, or for receipts or proof of purchase required as proof of purchase over a long warranty period. This is especially important when it must be assumed that the heat-sensitive recording materials may come into contact with moisture, for example, if the materials used as concert tickets, airline tickets, or proof of purchase are kept close to the body (e.g., in a trouser pocket) and thus come into contact with perspiration. In such cases, it must be ensured that the recording materials remain easily legible even after exposure to moisture.

[0014] There is therefore a constant need to improve the resistance of thermal prints to various environmental influences. The primary object of the present invention is thus to provide a heat-sensitive recording material that, in its printed state, exhibits improved resistance to environmental influences such as daylight and heat input, and ideally also possesses very good printability.

[0015] Further tasks arise from the following description and the patent claims.

[0016] The subject matter of the invention is defined in the attached patent claims and in the following description.

[0017] The aforementioned task is solved by a heat-sensitive recording material comprising or consisting of a substrate having a front side and a back side opposite the front side, a heat-sensitive recording layer arranged on the front side of the web-shaped substrate, wherein this heat-sensitive recording layer contains at least one dye precursor and at least one color developer reactive with this dye precursor, wherein the color developer is a) a compound of formula (I) shown below or b) a combination of the formula (II) shown below is or c) a mixture comprising the compound of formula (I) and the compound of formula (II) and an intermediate layer arranged between the substrate and the heat-sensitive recording layer, comprising calcined aluminium silicate, wherein the mass fraction of the calcined aluminium silicate in the intermediate layer is 50 to 90%, based on the total mass of the solid fractions in the intermediate layer, wherein the compound of formula (I) exists in a crystalline form which exhibits an absorption band at 3401±20 cm in the IR spectrum -1 exhibits.

[0018] Surprisingly, it has been found that heat-sensitive recording materials according to the invention exhibit increased daylight resistance. Furthermore, our own investigations have shown that the optical density and stability of the printed heat-sensitive recording material are improved. Another positive and unexpected effect is that the contrast between printed and unprinted areas (background) of the heat-sensitive recording material has also been improved and exhibits high stability.

[0019] In addition, it has surprisingly been shown that the dynamic pressure density of heat-sensitive recording materials according to the invention could be improved, so that a higher pressure density (blackness) can be obtained for a certain amount of energy acting on the heat-sensitive recording material.

[0020] Surprisingly, it has also been shown that the maximum print density (Dmax) is higher for recording materials according to the invention, so that a deeper black can be obtained in the printed area.

[0021] Our own investigations have also shown that by using calcined aluminum silicate in heat-sensitive recording materials according to the invention, smearing of the printed image into the unprinted area (e.g., "tailing" or "bleeding") can be significantly reduced or even completely avoided, particularly in comparison with heat-sensitive recording materials that have organic hollow-body pigments as pigments in the intermediate layer. "Tailing" describes smearing of the printed image in the processing direction, and "bleeding" describes undirected smearing of the printed image radiating from a central point or center.

[0022] These results are surprising because it was previously assumed that improving the properties of the heat-sensitive recording material required varying or optimizing the components of the heat-sensitive recording layer. For example, in the prior art cited above, only the components of the heat-sensitive recording layer were varied to obtain improved properties. It was previously assumed that the composition of the intermediate layer had no influence on the properties of the heat-sensitive recording layer and that inorganic pigments could be freely interchanged without significantly altering the properties of the heat-sensitive recording layer or the resulting heat-sensitive recording material.An improvement in the response behavior of the heat-sensitive recording material was previously known only when hollow-body pigments were used in the intermediate layer. This was explained by the fact that hollow-body pigments, which contain air within them, exhibit high thermal reflectivity, and therefore the resulting intermediate layer acts as a good thermal insulator. The intermediate layer optimized with hollow-body pigments as a heat-reflective layer thus specifically enhances the response of the recording layer to heat. It is therefore all the more surprising that heat-sensitive recording materials according to the invention exhibit a higher dynamic pressure density, a higher maximum pressure density (Dmax), and higher light resistance than materials in which hollow-body pigments are used in the intermediate layer instead of calcined aluminum silicate.

[0023] In some embodiments of the present invention, it is advantageous that the compound of formula (I) is used as a color developer and that the compound of formula (II) is not included in the heat-sensitive recording layer. Alternatively, in other embodiments of the present invention, it is advantageous that the compound of formula (II) is used as a color developer and that the compound of formula (I) is not included in the heat-sensitive recording layer.

[0024] If a mixture comprising the compound of formula (I) and the compound of formula (II) is used as a color developer, it has proven particularly advantageous if the compound of formula (I) is in a crystalline form which has an absorption band at 3401±20 cm -1< in the IR spectrum.

[0025] The combination of (A) the developers of formula (I), formula (II) or mixtures thereof used according to the invention and (B) calcined aluminum silicate in the intermediate layer exhibits a synergistic effect, resulting in improved properties of the heat-sensitive recording materials.

[0026] The compound with formula (I) is the already known compound N-[2-(3-Phenylureido)phenyl]benzenesulfonamide, which is described, for example, in EP 2 923 851 A1. It is marketed under the name NKK.

[0027] The compound with formula (II) is the already known compound. N -(4-Methylphenylsulfonyl)- N'-(3-(4-methylphenylsulfonyloxy)phenyl)urea, which is marketed under the name Pergafast 201 and is described, for example, in EP 1 140 515 B1. Pergafast 201 is currently the most widely used phenol-free color developer.

[0028] Our own investigations have shown that the compound of formula (I) can exist in two different crystalline forms. Both crystalline forms exhibit different physical properties that can influence the heat-sensitive recording material.

[0029] One crystalline form of the compound with formula (I) has a melting point of approximately 158 °C, while the second crystalline form of the compound with formula (I) has a melting point of 175 °C. In connection with heat-sensitive recording materials, only the compound with formula (I), which is the crystalline form with a melting point of approximately 158 °C, has been described in the literature to date (see, for example, EP 2 923 851 A1 paragraph

[0084] ). Neither the preparation nor the use of the crystalline form of the compound with formula (I) with a melting point of approximately 175 °C has been described in the literature to date. Accordingly, it must be assumed that the crystalline form of the compound with formula (I) with a melting point of approximately 158 °C has always been used, even if the melting point is not explicitly mentioned in the relevant document.The crystalline form of the compound of formula (I) with a melting point of 175 °C has recently become commercially available.

[0030] A heat-sensitive recording material is preferred according to the invention, wherein the crystalline form of the compound of formula (I) has a (preferably endothermic) transition at a temperature between 170 °C and 178 °C, preferably between 173 °C and 177 °C, particularly preferably between 174 °C and 176 °C, determined by differential dynamic calorimetry (DKK) at a heating rate of 10 K / min.

[0031] Both crystalline forms of the compounds with formula (I) can also be distinguished from each other in the IR absorption spectrum. A particularly characteristic feature of the crystalline form of the compounds with formula (I) used according to the invention is an absorption band in the IR spectrum at 3401 ± 20 cm⁻¹. This band is not present in the crystalline form of the compounds with formula (I) that has a melting point of approximately 158 °C; instead, bands are found at 3322 and 3229 cm⁻¹.

[0032] Our own investigations have shown that both crystalline forms of the compound with formula (I) can be used. However, the resulting heat-sensitive recording materials exhibit slightly different properties. Although improvements in dynamic pressure density, maximum pressure density (Dmax), and light resistance can be achieved with both crystalline forms in heat-sensitive recording materials, it has been shown that heat-sensitive recording materials in which the compound of formula (I) is in a crystalline form exhibiting an absorption band at 3401 ± 20 cm⁻¹ in the IR spectrum and a melting point of approximately 175 °C show slightly improved properties compared to heat-sensitive recording materials in which the compound of formula (I) is in the other crystalline form.

[0033] However, our own investigations have shown that recording materials in which the compound of formula (I) is in a crystalline form, exhibiting two absorption bands at 3322±5 and 3229±5 cm⁻¹ in the IR spectrum and having a melting point of approximately 158 °C, show slightly increased stability against fats (lanolin), ethanol, and when stored at high humidity at 40 °C. If high stability against fats, such as lanolin, and / or solvents, such as ethanol, is desired, or if resistance at high humidity is required, it is preferable to use the crystalline form of the compound of formula (I), which exhibits two absorption bands at 3322±5 and 3229±5 cm⁻¹ in the IR spectrum and has a melting point of approximately 158 °C.

[0034] In one embodiment of the heat-sensitive recording material according to the invention, the developer is a mixture of the compound of formula (I) and the compound of formula (II).

[0035] It is known to those skilled in the art that combining different developers, such as compounds of formula (I) or (II), usually leads to a deterioration of the properties of the heat-sensitive recording material. Typically, combining two or more developers results in an undesirable change in the color of the heat-sensitive recording material, so that the heat-sensitive recording material appears, for example, gray, without improving its other properties. Accordingly, when attempting to provide a heat-sensitive recording material that, in the printed state, exhibits high resistance to environmental influences such as humidity, heat, or chemicals, a person skilled in the art would not have considered combining different developers and would not have conducted such tests.For this reason, the embodiment of the solution according to the invention shown here is surprising, since the person skilled in the art first had to overcome the technical prejudice that two developers should not be combined in order to solve the problem.

[0036] In one embodiment of the invention, a heat-sensitive recording material is preferred according to the invention, wherein the mass ratio between the compound of formula (I) and the compound of formula (II) is 0.5 : 99.5 to 99.5 : 0.5. Our own investigations have shown that when the mass fraction of the compound with formula (I) or (II) is less than 0.5%, based on the total mass of the compounds with formulas (I) and (II), the positive influence of the respective compound is not as pronounced.

[0037] According to one embodiment of the invention, a heat-sensitive recording material is particularly preferred, wherein the mass ratio between the compound of formula (I) and the compound of formula (II) is 35 : 65 to 65 : 35, preferably 40 : 60 to 60 : 40, and particularly preferably 45 : 55 to 55 : 45.

[0038] Our own investigations have shown that mixtures with a mass ratio between the compound of formula (I) and the compound of formula (II) of approximately 1:1, or in the ranges defined above of 35:65 to 65:35, preferably 40:60 to 60:40, and particularly preferably 45:55 to 55:45, exhibit a synergistic effect with regard to both improved long-term stability and improved resistance to lanolin. Heat-sensitive recording materials that use color developer mixtures with these mass ratios, i.e., mixtures with equal or nearly equal mass fractions of the compounds of formula (I) and (II), show better properties than heat-sensitive recording materials in which the color developer mixture has been replaced in equal mass parts by only one compound of formula (II) or (I).

[0039] Particularly with regard to resistance at high temperatures (60 °C), it has been shown that the printed image of heat-sensitive recording materials according to the invention, in which the mass ratio between the compound of formula (I) and the compound of formula (II) is 0.5 : 99.5 to 35 : 65, deteriorates less even after storage for 24 hours at 60 °C than in heat-sensitive recording materials in which the color developer mixture has been replaced by an equal mass fraction of a compound of formula (I). In some cases, the printed image of heat-sensitive recording materials according to the invention exhibits a higher print density after storage for 24 hours at 60 °C than in heat-sensitive recording materials in which the color developer mixture has been replaced by an equal mass fraction of a compound of formula (I) or (II).The combination of a compound of formula (I) with a compound of formula (II) used according to the invention thus exhibits a synergistic effect that was not foreseeable and is therefore completely surprising.

[0040] In a further embodiment of the present invention, a heat-sensitive recording material is preferred according to the invention, wherein the mass ratio between the compound of formula (I) and the compound of formula (II) is 5 : 95 to 30 : 70, preferably 15 : 85 to 25 : 75.

[0041] Our own investigations have shown that mixtures with a mass ratio between the compound of formula (I) and the compound of formula (II) of approximately 20:80, or in the ranges defined above of 5:95 to 30:70, preferably 15:85 to 25:75, exhibit a synergistic effect with regard to improved stability for at least 24 hours at 60 °C. Heat-sensitive recording materials containing developer mixtures with these mass ratios show better stability at 60 °C than heat-sensitive recording materials in which the color developer mixture has been replaced in equal parts by only one compound of formula (II) or (I).

[0042] In a further embodiment of the present invention, a heat-sensitive recording material is preferred according to the invention, wherein the mass ratio between the compound of formula (I) and the compound of formula (II) is 97 : 3 to 85 : 15, preferably 95 : 5 to 90 : 10.

[0043] Our own investigations have shown that mixtures with a mass ratio between the compound of formula (I) and the compound of formula (II) of approximately 93:7, or in the ranges defined above of 97:3 to 85:15, preferably 95:5 to 90:10, exhibit particularly good properties with regard to resistance for at least 24 hours at 40 °C and high humidity, and improved resistance to grease (especially lanolin). Heat-sensitive recording materials containing mixtures with these mass ratios as the developer mixture show better properties (moisture resistance or grease resistance) than heat-sensitive recording materials in which the developer mixture has been replaced in equal parts by only one compound of formula (II) or (I).

[0044] Commercially available lanolin is a mixture obtained, for example, according to the German Pharmacopoeia 10 (DAB 10), by melting together 65 parts by mass of wool wax, 20 parts by mass of water, and 15 parts by mass of liquid paraffin. An additional 100 parts by mass of water can be incorporated by kneading without altering the external consistency. Wool wax (wool grease, Adeps Lanae, INCI name: Lanolin, E 913) is the secretion of the sebaceous glands of sheep. It is obtained by extracting sheep fleece with isopropanol. The name lanolin is derived from the Latin words lana = wool and oleum = oil.

[0045] Surprisingly, it has been found that in heat-sensitive recording materials according to the invention, where the mass ratio between the compound of formula (I) and the compound of formula (II) is 99.5 : 0.5 to 65 : 35, no graying of the unprinted recording material is observed. In particular, at a mass ratio between the compound of formula (I) and the compound of formula (II) of 99 : 1 to 75 : 25, no relevant graying of the unprinted recording material occurs. This mixing ratio is therefore preferred.

[0046] Depending on the expected influences acting on the thermal paper, the properties of the resulting heat-sensitive recording material can be optimized for the intended application by adjusting the mixing ratio between the compound of formula (I) and the compound of formula (II). For example, heat-sensitive recording materials intended for use as parking tickets have different requirements than those intended for use as concert tickets. These optimized properties can be further improved by combining the mixture of the compounds of formula (I) and formula (II) with calcined aluminum silicate in the intermediate layer.

[0047] In one embodiment of the heat-sensitive recording material according to the invention, the developer is the compound of formula (I), without the compound of formula (II) being present.

[0048] According to the invention, it is preferred if the heat-sensitive recording layer has a Bekk smoothness of 100 to 1200 seconds, preferably 150 to 1100 seconds, as determined according to DIN 53107:2016-05 (title: Testing of paper and cardboard - determination of smoothness according to Bekk).

[0049] Our own investigations have shown that when the heat-sensitive recording layer is the outer layer and has a Bekk smoothness of 100 to 1200 seconds, or preferably 150 to 1100 seconds, the heat-sensitive recording materials exhibit particularly good properties. The high smoothness of the heat-sensitive recording material, among other advantages, protects the thermal printhead of the thermal printer. Furthermore, smooth heat-sensitive recording materials have a particularly good feel and appearance and are especially easy to print on.

[0050] As already explained above, heat-sensitive recording materials according to the invention exhibit improved resistance to light and improved contrast compared to the prior art. It has been shown that heat-sensitive recording materials according to the invention in which the compound of formula (I) is used as the developer exhibit higher resistance to light, better contrast, and a higher maximum printing density (Dmax) than heat-sensitive recording materials according to the invention in which the compound of formula (II) is used as the developer.

[0051] It has also been shown that heat-sensitive recording materials according to the invention, in which the compound of formula (I) is present as the developer, do not exhibit any background graying after storage for at least 24 hours at 90 °C.

[0052] In a preferred embodiment according to the invention, the calcined aluminum silicate in the intermediate layer is platelet-shaped. Our own investigations, comparing non-platelet-shaped aluminum silicate with platelet-shaped aluminum silicate, have surprisingly shown that the use of platelet-shaped, calcined aluminum silicate results in particularly good properties of the heat-sensitive recording material. When platelet-shaped calcined aluminum silicate is used in the intermediate layer, the individual platelets of the aluminum silicate are staggered and arranged one above the other, resulting in a very dense layer structure. Calcined aluminum silicate that is not platelet-shaped does not form these layer structures.Non-platelet-shaped calcined aluminum silicate can be obtained, for example, by milling platelet-shaped calcined aluminum silicate or by appropriately adjusting the manufacturing parameters. Platelet-shaped (also referred to as flake-like or flake-like) particles are understood to have a diameter significantly larger than their thickness.

[0053] According to the invention, it is particularly preferred if the platelet-shaped, calcined aluminum silicate has an (preferably average) aspect ratio of 3 to 100, preferably 5 to 95, and most preferably 10 to 90. In a preferred embodiment, the (preferably average) aspect ratio of the inorganic pigment is greater than 15. The aspect ratio (also called "shape factor") is the quotient between the diameter and the thickness of the platelet of the inorganic pigment before mixing with the other components. An aspect ratio of 15 means that the diameter of the platelet is 15 times larger than the thickness of the platelet.

[0054] In a preferred embodiment of the recording material according to the invention, 85 to 93% of the calcined aluminium silicate particles used to produce the intermediate layer have a particle size of less than or equal to 2 µm as determined by X-ray granulometry.

[0055] Our own investigations have shown that these calcined aluminium silicate particles are particularly well suited for the production of intermediate layers used according to the invention.

[0056] In a preferred embodiment of the recording material according to the invention, the calcined aluminium silicate used has a brightness (also called whiteness or brightness) of greater than or equal to 85%, preferably greater than or equal to 90%, and particularly preferably greater than or equal to 92%.

[0057] It is particularly advantageous if the calcined aluminum silicate in the intermediate layer has an oil number of at least 80 cm³ / 100 g and even better of 100 cm³ / 100 g, determined according to DIN EN ISO 787-5:1995-10 (Title: General test methods for pigments and fillers - Part 5: Determination of the oil number (ISO 787-5:1980); German version EN ISO 787-5:1995).

[0058] Surprisingly, our own investigations have shown that the high mass fraction of calcined aluminum silicate of over 50% in the recording materials according to the invention leads to particularly good properties.

[0059] According to the invention, it is preferred if the mass fraction of the calcined aluminium silicate in the intermediate layer is 60 to 89%, preferably 70 to 88%, based on the total mass of the solid components in the intermediate layer.

[0060] According to the invention, it is further preferred if the mass fraction of the calcined aluminium silicate in the intermediate layer is 80 to 87%, preferably 83 to 87%, based on the total mass of the solid components in the intermediate layer.

[0061] Our own investigations have shown that the heat-sensitive recording materials exhibit particularly good properties—especially little or no smearing of the printed image into the unprinted area, high daylight and heat resistance, high sensitivity, and high maximum ink density (Dmax)—when the mass fraction of the calcined aluminum silicate is within the limits specified above. An optimal value of approximately 86% calcined aluminum silicate was found to be optimal. At a mass fraction above 90%, the smearing of the printed image no longer decreases significantly, but the other properties of the heat-sensitive recording material deteriorate sharply. This deterioration can be explained by the fact that, firstly, the bonding strength of the intermediate layer is significantly reduced.It has been shown that when calcined aluminum silicate is used in the interlayer with a mass fraction exceeding 90%, the aluminum silicate particles are no longer sufficiently held together, and the interlayer can detach or tear. This detachment can lead to a deterioration of the print image and deposits on the printhead. Deposits on the printhead can lead to printhead failure or further deterioration of the print image. Furthermore, a mass fraction of over 90% calcined aluminum silicate in the interlayer means that, due to the interlayer's high porosity, the binder of the heat-sensitive recording layer is partially absorbed by the interlayer during the production of the heat-sensitive recording material and is therefore no longer available to bind the heat-sensitive recording layer.To compensate for this binder absorption, the binder content of the coating composition used to produce the heat-sensitive recording layer must be increased. However, this increase in binder content leads to a deterioration in pressure sensitivity and maximum pressure density.

[0062] In an alternative embodiment, it is particularly preferred according to the invention if the mass fraction of the calcined aluminium silicate in the intermediate layer is 60 to 79%, preferably 65 to 75%, based on the total mass of the solid components in the intermediate layer.

[0063] In a preferred embodiment of the heat-sensitive recording material according to the invention, no further organic or inorganic pigments are present besides the calcined aluminum silicate.

[0064] In some embodiments, however, it may also be preferred if, in addition to the calcined aluminum silicate, other inorganic or organic pigments are present in the intermediate layer. Besides organic pigments, which are preferably present as organic hollow-body pigments, the intermediate layer may also contain other inorganic pigments, wherein the inorganic pigments are selected individually or in combination from the list, including natural kaolin, silicon dioxide, and in particular bentonite, calcium carbonate, and aluminum oxide hydroxides, and in particular boehmite.

[0065] A heat-sensitive recording material is preferred according to the invention, wherein the intermediate layer also contains one or more components selected from the group consisting of biocides, binders, dispersants, release agents, defoamers, thickeners and optical brighteners.

[0066] A heat-sensitive recording material is preferred according to the invention, wherein the intermediate layer contains, in addition to the calcined aluminum silicate and optionally in addition to the other inorganic and / or organic pigments, at least one binder, preferably based on a synthetic polymer, with styrene-butadiene latex yielding particularly good results. The use of a synthetic binder with the addition of at least one natural polymer, such as starch, is a particularly suitable embodiment. Furthermore, tests have shown that a binder-pigment ratio within the intermediate layer of between 3:7 and 1:9, based on the mass fraction in the intermediate layer, is a particularly suitable embodiment.

[0067] In a particularly preferred embodiment, a mixture of styrene-butadiene latex and starch is used as a binder in the intermediate layer.

[0068] Our own investigations have shown that the combination of styrene-butadiene latex and starch has a positive influence on the properties of the heat-sensitive recording material. Using pure styrene-butadiene latex results in heat-sensitive recording materials with very strong bonding. However, the styrene-butadiene latex closes the pores of the calcined aluminum silicate. Surprisingly, the addition of starch allows the intermediate layer to retain a high degree of open porosity. Thus, the combination of styrene-butadiene latex and starch produces an intermediate layer that exhibits excellent bonding while simultaneously maintaining the high open porosity of the calcined aluminum silicate. The combination of styrene-butadiene latex and starch therefore leads to intermediate layers that cannot be achieved using either binder alone.

[0069] Surprisingly, it has also been shown that the properties of the intermediate layer, which contains styrene-butadiene latex and starch, can be further improved if the intermediate layer contains methylcellulose and / or a dispersing agent.

[0070] Compared to polyvinyl alcohol, styrene-butadiene latex exhibits a significantly higher binding strength and is therefore preferred. Additionally, styrene-butadiene latex is preferred because it is not water-soluble and, after the intermediate layer has dried, is not dissolved when the heat-sensitive recording layer is applied.

[0071] A heat-sensitive recording material is preferred according to the invention, wherein the area-related mass of the intermediate layer is in the range of 4.0 to 15.0 g / m 2<, preferably in the range of 6.0 to 12.0 g / m 2<, and particularly preferably in the range of 7.0 to 10 g / m 2<.

[0072] Our own investigations have shown that particularly good results can be achieved when the intermediate layer is comparatively thick.

[0073] A heat-sensitive recording material is preferred according to the invention, wherein the dye precursor is selected from derivatives of compounds from the group consisting of fluorane, phthalide, lactam, triphenylmethane, phenothiazine and spiropyran.

[0074] Our own investigations have shown that these dye precursors exhibit particularly good properties in combination with the color developers or color developer mixture used according to the invention.

[0075] A preferred heat-sensitive recording material according to the invention preferably comprises fluorane-type compounds as dye precursors, selected from the group consisting of 3-diethylamino-6-methyl-7-anilinofluorane, 3-diethylamino-6-methyl-7-(3'-methylphenylamino)fluorane (6'-(diethylamino)-3'-methyl-2'-(m-tolylamino)-3H-spiro[isobenzofuran-1,9'-xanthene]-3-one; ODB-7), 3-di-n-pentyl-amino-6-methyl-7-anilinofluorane, 3-(diethylamino)-6-methyl-7-(3-methylphenylamino)fluorane, 3-di-n-butylamino-7-(2-chloranilino)fluorane, 3-diethylamino-7-(2-chloranilino)fluorane, 3-diethylamino-6-methyl-7-xylidinofluorane, 3-Diethylamino-7-(2-carbomethoxyphenylamino)fluoran, 3-pyrrolidino-6-methyl-7-anilinofluoran, 3-pyrrolidino-6-methyl-7-(4-n-butyl-phenylamino)fluoran, 3-piperidino-6-methyl-7-anilinofluoran, 3-Nn-dibutylamine-6-methyl-7-anilinofluoran (ODB-2), 3-(N-methyl-N-cyclohexyl)amino-6-methyl-7-anilinofluoran, 3-(N-methyl-N-propyl)amino-6-methyl-7-anilinofluoran,3-(N-methyl-N-tetrahydrofurfuryl)amino-6-methyl-7-anilinofluoran), 3-(N-ethyl-N-isoamyl)amino-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-tolyl)amino-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-tetrahydrofuryl)amino-6-methyl-7-ani-linofluoran, 3-(N-ethyl-N-isopentylamino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-4-toluidino)6-methyl-7-(4-toluidino)fluorane and 3-(N-Cyclopentyl-N-ethyl)amino-6-methyl-7-ani-linofluoran.,

[0076] Heat-sensitive recording materials according to the invention are also preferred, which contain as dye precursors the compounds mentioned in paragraphs

[0049] to

[0052] of EP 2 923 851 A1.

[0077] According to the invention, a heat-sensitive recording material is particularly preferred, wherein the dye precursor is selected from the group consisting of 3-N-Di-n-butylamine-6-methyl-7-anilinofluorane (ODB-2) and 3-(N-Ethyl-N-isopentylamino)-6-methyl-7-anilinofluorane.

[0078] A heat-sensitive recording material is preferred according to the invention, wherein the heat-sensitive recording layer also contains one or more components selected from the group consisting of binders, sensitizers, pigments, dispersants, antioxidants, release agents, defoamers, light stabilizers and optical brighteners.

[0079] A heat-sensitive recording material is preferred according to the invention, wherein the heat-sensitive recording layer contains a sensitizer.

[0080] When a sensitizer is used, it is first melted during the application of heat in the printing process. The molten sensitizer then dissolves the color formers and developers present side-by-side in the heat-sensitive recording layer and / or lowers the melting temperature of the color formers and developers to initiate a color development reaction. The sensitizer itself does not participate in the color development reaction.

[0081] A sensitizer is therefore understood to be a substance that serves to adjust the melting temperature of the heat-sensitive recording layer and with which a melting temperature of approximately 70 to 80 °C can preferably be set without the sensitizers themselves being involved in the color development reaction.

[0082] According to the invention, sensitizers can include, for example, fatty acid salts, fatty acid esters and fatty acid amides (e.g., zinc stearate, stearic acid amide, palmitic acid amide, oleic acid amide, lauric acid amide, ethylene and methylene bisstearic acid amide, methylolstearic acid amide) (preferably fatty acid amides with a number of carbon atoms in the range of 16 to 24), fatty acid amide derivatives (e.g., N-(2-hydroxyethyl)octadecanamide, N-(hydroxymethyl)octadecanamide), ethylene glycol m-tolyl ether, naphthalene derivatives, biphenyl derivatives, phthalates and terephthalates.

[0083] A heat-sensitive recording material is particularly preferred according to the invention, wherein the sensitizer is selected from the group consisting of 1,2-bis(3-methylphenoxy)ethane, 1,2-diphenoxyethane, 1,2-di(m-methylphenoxy)ethane, 2-(2H-benzotriazol-2-yl)-p-cresol, 2,2'-bis(4-methoxyphenoxy)diethyl ether, 4,4'-diallyloxydiphenyl sulfone, 4-acetylacetophenone, 4-benzybiphenyl, acetoacetic acid anilides, benzyl-2-naphthyl ether, benzyl-naphthyl ether, benzyl-4-(benzyloxy)benzoate, benzylparaben, bis(4-chlorobenzyl)o-xalate ester, bis(4-methoxyphenyl) ether, dibenzyl oxalate, dibenzyl terephthalate, dimethyl terephthalate, Dimethyl sulfone, diphenyl adipate, diphenyl sulfone, ethylenebisstearamine, fatty acid anilides, m-terpenyl, N-hydroxymethylstearamine, N-methylolstearamide, N-stearyl urea, N-stearylstearamide, N-(2-hydroxyethyl)octadecanamide, N-(hydroxymethyl)octadecanamide, p-benzylbiphenyl, phenylbenzenesulfonate ester, salicylic anilide, stearamideEthylene glycol m-tolyl ether and α,α'-diphenoxyxylene, wherein ethylene glycol m-tolyl ether, benzyl naphthyl ether, diphenyl sulfone, 1,2-di(m-methylphenoxy)ethane and 1,2-diphenoxyethane are particularly preferred.

[0084] In a particularly preferred embodiment of the heat-sensitive recording material according to the invention, the heat-sensitive recording layer contains 1,2-diphenoxyethane, ethylene glycol m-tolyl ether or a mixture of 1,2-diphenoxyethane and ethylene glycol m-tolyl ether as a sensitizer.

[0085] Our own investigations have shown that when using 1,2-diphenoxyethane as a sensitizer, the resistance to lanolin and the heat resistance at 90 °C can be improved compared to other sensitizers.

[0086] Heat-sensitive recording materials according to the invention are also preferred, which contain as a sensitizer the compounds mentioned in paragraphs

[0059] to

[0061] of EP2923851A1.

[0087] According to a first preferred embodiment, these sensitizers are used individually, that is, not in combination with the other sensitizers from the preceding list. According to a second, equally preferred embodiment, at least two sensitizers selected from the preceding list are incorporated into the heat-sensitive recording layer.

[0088] A heat-sensitive recording material is preferred according to the invention, wherein the sensitizer has a melting point of 60 °C to 180 °C, preferably a melting point of 80 °C to 140 °C.

[0089] Furthermore, in the heat-sensitive recording materials according to the invention, the use of 4,4'-diaminodiphenylsulfone (4,4'-DDS, dapsone) as an additional additive in the heat-sensitive recording layer may prove advantageous. The use of 4,4'-diaminodiphenylsulfone in thermal papers is described, for example, in WO 2014 / 143174 A1. In this case, the invention may then relate to a heat-sensitive recording material wherein 4,4'-diaminodiphenylsulfone is included in the heat-sensitive recording layer, in particular additionally as an additive.

[0090] Heat-sensitive recording materials are also preferred, wherein the heat-sensitive recording layer contains a binder, preferably a cross-linked or uncross-linked binder selected from the group consisting of polyvinyl alcohol, carboxyl group-modified polyvinyl alcohol, ethylene vinyl alcohol copolymer, a combination of polyvinyl alcohol and ethylene vinyl alcohol copolymer, silanol group-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, acrylate copolymer and film-forming acrylic copolymers.

[0091] Preferably, the coating compound for forming the heat-sensitive recording layer of the heat-sensitive recording material according to the invention contains, in addition to one or more binders, one or more crosslinking agents for the binder(s). Preferably, the crosslinking agent is selected from the group consisting of zirconium carbonate, polyamide amines, epichlorohydrin resins, boric acid, glyoxal, dihydroxy bis(ammonium lactato)titanium(IV) (CAS No. 65104-06-5; Tyzor LA), and glyoxal derivatives.

[0092] A heat-sensitive recording material according to the invention, the heat-sensitive recording layer of which is formed from such a coating mass containing one or more binders and one or more crosslinking agents for the binder(s), contains in the heat-sensitive recording layer one or more binders crosslinked by reaction with one or more crosslinking agents, wherein the crosslinking agent(s) are selected from the group consisting of zirconium carbonate, polyamide amines, epichlorohydrin resins, boric acid, glyoxal, dihydroxy bis(ammonium lactato)titanium(IV) (CAS No. 65104-06-5; Tyzor LA) and glyoxal derivatives. The term "crosslinked binder" is understood to mean the reaction product formed by reacting a binder with one or more crosslinking agents.

[0093] A heat-sensitive recording material is preferred according to the invention, wherein the area-related mass of the heat-sensitive recording layer is in the range of 1.5 to 6 g / m², preferably in the range of 2.0 to 5.5 g / m², particularly preferably in the range of 2.0 to 4.8 g / m², and more preferably in the range of 2.5 to 3.5 g / m².

[0094] A heat-sensitive recording material is also preferred according to the invention, wherein the mass fraction of the color developer mixture in the heat-sensitive recording layer is 35 to 15%, preferably 31 to 19%, particularly preferably 28 to 22%, based on the total solid fraction of the heat-sensitive recording layer.

[0095] In addition, image stabilizers, dispersants, antioxidants, release agents, defoamers, light stabilizers, and brighteners, as known in the prior art, can be used in the recording materials according to the invention. Each of the components is typically used in an amount with a mass fraction of 0.01 to 15%, in particular – with the exception of defoamers – 0.1 to 15%, preferably 1 to 10%, based on the total solid content of the heat-sensitive recording layer. When defoamers are used in the relevant formulations, the defoamer in the recording materials according to the invention can be present in amounts with a mass fraction of 0.03 to 0.05%, based on the total solid content of the heat-sensitive recording layer.

[0096] According to the invention, heat-sensitive recording materials designed as self-adhesive labels are preferred. The use of self-adhesive labels is extremely popular in numerous applications. For example, postage stamps, parcel labels, advertising labels, vignettes, and price tags are offered and used as self-adhesive labels. Printable labels are also widely used in retail for labeling self-weighing products or in public transportation – for example, as luggage tags.

[0097] A heat-sensitive recording material is therefore preferred according to the invention, wherein an adhesive layer is arranged on the back of the substrate facing away from the front of the substrate.

[0098] Self-adhesive labels are equipped with an adhesive layer that allows them to be applied to the desired location. Until the label is used, the adhesive layer is typically covered by a separate release paper to prevent contamination and ensure the label doesn't stick prematurely. Using a separate release paper is particularly advantageous for pre-cut labels. For continuous labels on a roll, it is much more common and practical to use front-side coatings that are non-stick to the adhesive layers on the back. In this case, the adhesive layers on the back are covered by the non-stick front-side coatings until needed.Since the self-adhesive labels thus serve as their own release paper, a separate release paper is unnecessary, eliminating the need to dispose of it at the point of use. This technique has proven particularly effective for labels that are printed and used on-site. Without a release paper or release layer, storing labels would be virtually impossible.

[0099] A heat-sensitive recording material is preferred according to the invention, wherein a separating layer is arranged on the heat-sensitive recording layer, which is designed to be non-adhesive towards adhesive layers, wherein this separating layer contains at least one organosiloxane group-containing compound or a wax.

[0100] In the context of this invention, a wax is understood to be a wax obtained by chemical modification of a vegetable oil. This chemical modification can, for example, involve partial or complete hydrogenation with a metallic catalyst, such as nickel, and hydrogen, whereby all or some of the oil's double bonds are hydrogenated to single bonds. Unlike vegetable oils, the waxes are not liquid but solid at 20 °C. The chemical modification of the vegetable oil thus raises its melting point.

[0101] A vegetable oil is understood to be a fatty acid triglyceride obtained from plants or plant parts. The oil is typically extracted by pressing, extraction, or refining. This process is well-known to experts. When plant seeds are used for oil production, they are called oilseeds. The oil is present in the seeds in the form of lipids, which constitute the cell membrane and energy reserves. Depending on the proportion of unsaturated fatty acids in the oil, a distinction is made between non-drying (e.g., olive oil), semi-drying (e.g., soybean or rapeseed oil), and drying oils (e.g., linseed or poppy seed oil). The term "drying" here refers not to evaporation, but to the solidification of the oil caused by the oxidation and polymerization of the unsaturated fatty acids.The use of semi-drying and drying oils as starting materials for the production of the waxes used according to the invention is preferred.

[0102] Possible sources of vegetable oils include açaí oil, algae oil, argan oil (from the fruit of the argan tree), avocado oil (from the pulp of the avocado tree), babaçu oil, cottonseed oil (from the seeds of the cotton plant), borage oil or borage seed oil (from the seeds of the borage plant), cupuaçu butter, cashew shell oil, safflower oil (from the seeds of the safflower or carthamus), peanut oil (from the fruit of the peanut plant), hazelnut oil (from the hazelnuts of the hazelnut bush), hemp oil (from the seeds of the hemp plant), jatropha oil (from the seeds of Jatropha curcas), jojoba oil (actually a liquid wax; from the seeds of the jojoba shrub), camellia oil (from the seeds of Camellia oleifera, Camellia sinensis, or Camellia japonica), cocoa butter, and coconut oil. (from the seed flesh of the coconut, the fruit of the coconut palm), pumpkin seed oil (also known as kernel oil;from the seed kernels of the Styrian oil pumpkin), linseed oil (from the ripe flax seeds of the flax plant), camelina oil (from the seeds of the camelina, a member of the Brassicaceae family), macadamia oil (from the nuts of the macadamia tree), corn germ oil (from the germ of corn), almond oil (from the almonds of the almond tree), mango butter (from Mangifera indica), apricot kernel oil (from the apricot kernel - i.e., the almond of the apricot stone - of the apricot), poppy seed oil (from the seeds of the poppy), evening primrose oil, olive oil (from the pulp and the pit of the olive, the fruit of the olive tree;

[0103] Palm oil (from the pulp of the palm fruit, the fruit of the oil palm), palm kernel oil (from the kernels of the palm fruit, the fruit of the oil palm), papaya oil, pistachio oil, pecan oil, perilla oil from the seeds of the perilla plant (shiso, sesame leaf), rapeseed oil (from the seeds of rapeseed, family Brassicaceae), rice oil, castor oil (from the seeds of the castor bean plant), sea buckthorn oil (from the pulp of the sea buckthorn berry, the fruit of the sea buckthorn shrub), sea buckthorn kernel oil (from the kernels of the sea buckthorn berry, the fruit of the sea buckthorn shrub), mustard oil (from the seeds of black mustard), black cumin oil (from the seeds of the fruit capsule of the black cumin plant), sesame oil (from the seeds of the sesame plant), shea butter (from the seeds of the shea tree), soybean oil (from the beans of the soybean), sunflower oil (from the seeds of the sunflower), tung oil, Walnut oil (from the kernels of the nuts of the walnut tree), watermelon seed oil, grapeseed oil (from the kernels of the fruit (grape) of the grapevine or grapes).Grapevine), wheat germ oil (from wheat germ) and / or cedar oil (from the wood of the Lebanese cedar). This list is not exhaustive; it shows possibilities for obtaining vegetable oils that can be converted into a wax used according to the invention.

[0104] According to the invention, it is preferred if the wax is an oil-based wax selected from the list comprising palm oil, coconut oil, poppy seed oil, olive oil, linseed oil, soybean oil, sunflower oil, safflower oil and rapeseed oil; preferably, the vegetable oil-based wax is a soybean oil-based wax, i.e., soybean oil wax or soybean wax.

[0105] According to the invention, waxes having a melting point above 40 °C, preferably above 50 °C, and particularly preferably above 60 °C are preferred.

[0106] Our own investigations have shown that very good results can already be achieved using waxes with a melting point above 20 °C. Surprisingly, however, it has been shown that the resistance of the release layer to mechanical stress can be increased when using waxes with a melting point above 40 °C. This resistance is further enhanced with even higher melting points of the waxes. Our own investigations have also shown that the optimal melting point of the waxes lies in the range of 60 to 80 °C if the release layer is to be used at temperatures between 6 °C and 30 °C. If the release layer is to be used at higher temperatures, it may be advantageous to use a wax with a higher melting point.

[0107] According to the invention, separating layers are preferred in which the mass fraction of the wax in the separating layer is 6 to 98%, preferably 20 to 90%, and particularly preferably 50 to 89%, based on the total mass of the separating layer.

[0108] According to the invention, it is preferred if, in addition to the wax, the separating layer also contains a polymeric binder, preferably a cross-linked or uncross-linked binder, selected from the group consisting of starch, polyvinyl alcohol, carboxyl group-modified polyvinyl alcohol, ethylene-vinyl alcohol copolymer, a combination of polyvinyl alcohol and ethylene-vinyl alcohol copolymer, ethylene-vinyl acetate copolymer, silanol group-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, modified polyethylene glycol, unmodified polyethylene glycol, α-isodecyl-ω-hydroxy-poly(oxy-1,2-ethanediyl), styrene-butadiene latex, styrene-acrylate polymers, acrylic copolymers and mixtures thereof.

[0109] If the separating layer contains an organosiloxane group-containing compound, various investigations carried out in connection with the present invention have shown that an area-related mass in the separating layer is set in a range of 0.5 g / m² to 3 g / m², preferably 0.8 g / m² to 1.85 g / m², particularly preferably 0.85 g / m² to 1.35 g / m².

[0110] The heat-sensitive recording material is preferably manufactured such that, after application of a coating composition containing the organosiloxane group, parts of the compound containing the organosiloxane group initially remain on the heat-sensitive recording layer and partially diffuse or penetrate it before the coating composition cross-links. This forms a diffusion zone that improves the adhesion between the two layers. This ensures that the adhesively formed release layer adheres to the heat-sensitive recording layer and does not detach.

[0111] According to the invention, it is preferred if the diffusion zone is formed by diffuse-through of parts of at least the organosiloxane group-containing compound from the coating composition containing the organosiloxane group-containing compound into the upper region of the heat-sensitive recording layer applied before the coating composition, which is oriented towards the coating composition, and wherein a mass fraction of 1.5 to 50% of the total amount of the organosiloxane group-containing compound has diffused into the upper region of the heat-sensitive recording layer formed.

[0112] The binders and pigments that are preferentially incorporated into the heat-sensitive recording layer play an important role in influencing the amount of the diffused portion. Firstly, it has been found to be very helpful and therefore preferred if the heat-sensitive recording layer contains at least one preferably inorganic pigment selected from the list comprising natural kaolinite, calcined kaolinite, magnesium silicate hydrate (talc), calcium carbonate, and silicon dioxide (silica).

[0113] It is particularly preferred if the inorganic pigment in the heat-sensitive recording layer is platelet-shaped, as can be the case, for example, with kaolinite and talc. Kaolinite and talc are therefore particularly preferred in the heat-sensitive recording layer. In particular, it is preferred if the inorganic, platelet-shaped pigment in the heat-sensitive recording layer (especially kaolinite and talc) has an aspect ratio of 5 to 100, preferably 15 to 100, and most preferably 20 to 100. In a preferred embodiment, the aspect ratio of the inorganic pigment in the heat-sensitive recording layer is greater than 20.

[0114] Regarding the amount of pigment in the heat-sensitive recording layer, a range with a mass fraction of 8 to 18% (atro) relative to the total mass of the heat-sensitive recording layer is considered particularly suitable, which is narrowed downwards by the increasing risk of possible thermal printhead deposits and upwards by an increasing reduction in sensitivity to the heat of the thermal printheads that causes the printed image.

[0115] Due to the hydrophobic properties of organosiloxane-containing compounds in the separating layer, which diffuse into the heat-sensitive recording layer, it is preferred if the heat-sensitive recording layer contains at least one hydrophilic binder. Binders selected from the list, including ethylene-vinyl acetate copolymer, polyvinyl alcohol, styrene-butadiene latex, styrene-acrylate latex, and starch, are particularly preferred.

[0116] It is preferred that the polyvinyl alcohol used as a binder for the heat-sensitive recording layer has a degree of saponification of more than 99 mol% and a viscosity of more than 7 mPas, preferably more than 12 mPas, and particularly preferably more than 15 mPas, as measured according to DIN 53015 in an aqueous solution with 4 wt% at 20 °C. Particularly preferred is a polyvinyl alcohol (PVA) 15-99 or a corresponding PVA with a higher degree of saponification and / or higher viscosity than PVA 15-99.

[0117] In a preferred embodiment of the present invention, the binder of the heat-sensitive recording layer is crosslinking (self- or crosslinking) and / or modified polyvinyl alcohol, wherein the modified polyvinyl alcohol is preferably diacetone-modified polyvinyl alcohol, silanol group-modified polyvinyl alcohol or carboxyl group-modified polyvinyl alcohol, preferably diacetone-modified polyvinyl alcohol or silanol group-modified polyvinyl alcohol.

[0118] In particular, when a non-self-crosslinking polyvinyl alcohol is used as a binder, it is preferred in a preferred embodiment of the present invention if the heat-sensitive recording layer contains at least one crosslinking aid selected from the list comprising: boric acid, polyamine, epoxy resin, dialdehyde, formaldehyde oligomers, epiochlorohydrin resin, adipic acid dihydrazide, dimethyl urea, melamine formaldehyde, alone or in mixtures with each other.

[0119] For the purposes of the present invention, ethylene-vinyl acetate copolymer is considered as the sole binder or in combination with polyvinyl alcohol as a particularly preferred binder, which, based on the total mass of the heat-sensitive recording layer, is incorporated into the heat-sensitive recording layer in a range with a mass fraction of 10 to 20%.

[0120] In one embodiment of the heat-sensitive recording materials according to the invention, the heat-sensitive recording layer is completely or partially covered with a protective layer. By arranging a protective layer covering the heat-sensitive recording layer, the heat-sensitive recording layer is also shielded from the outside or from the substrate of the next layer within a roll, thus providing protection from external influences.

[0121] In such cases, such a protective layer, in addition to protecting the heat-sensitive recording layer located beneath it from environmental influences, often has the additional positive effect of improving the printability of the heat-sensitive recording material according to the invention, particularly in indigo, offset, and flexographic printing. For this reason, it may be desirable for certain applications for the heat-sensitive recording material according to the invention to have a protective layer, even though the presence of a color developer mixture as defined above in the heat-sensitive recording layer of the heat-sensitive recording material according to the invention already provides sufficient resistance to substances selected from the group consisting of water, alcohols, fats, oils, and mixtures thereof, even without a protective layer.

[0122] According to the invention, it is preferred if the protective layer has a Bekk smoothness of 350 to 1500 seconds, preferably 400 to 1400 seconds, as determined according to DIN 53107:2016-05 (title: Testing of paper and cardboard - determination of smoothness according to Bekk).

[0123] Our own investigations have shown that when the protective layer is the top layer and has a Bekk smoothness of 350 to 1500 seconds, or preferably 400 to 1400 seconds, the heat-sensitive recording materials exhibit particularly good properties. The high smoothness of the heat-sensitive recording material, among other advantages, protects the thermal printhead of the thermal printer. Furthermore, smooth heat-sensitive recording materials have a particularly good feel and appearance and are especially easy to print on.

[0124] Preferably, the protective layer of the heat-sensitive recording material according to the invention contains one or more cross-linked or uncross-linked binders selected from the group consisting of polyvinyl alcohols modified with carboxyl groups, polyvinyl alcohols modified with silanol groups, diacetone-modified polyvinyl alcohols, partially and fully saponified polyvinyl alcohols and film-forming acrylic copolymers.

[0125] Preferably, if present, the coating compound for forming the protective layer of the heat-sensitive recording material according to the invention contains, in addition to one or more binders, one or more crosslinking agents for the binder(s). Preferably, the crosslinking agent is selected from the group consisting of boric acid, polyamines, epoxy resins, dialdehydes, formaldehyde oligomers, epichlorohydrin resins, adipic acid dihydrazide, melamine formaldehyde, urea, methylol urea, ammonium zirconium carbonate, polyamide epichlorohydrin resins, and dihydroxybis(ammonium lactato)titanium(IV) Tyzor LA (CAS No. 65104-06-5).

[0126] A heat-sensitive recording material according to the invention, the protective layer of which is formed from such a coating mass containing one or more binders and one or more crosslinking agents for the binder(s), contains in the protective layer one or more binders crosslinked by reaction with one or more crosslinking agents, wherein the crosslinking agent(s) are selected from the group consisting of boric acid, polyamines, epoxy resins, dialdehydes, formaldehyde oligomers, epichlorohydrin resins, adipic acid dihydrazide, melamine-formaldehyde, urea, methylol urea, ammonium zirconium carbonate, polyamides, epichlorohydrin resins, and dihydroxybis(ammonium lactato)titanium(IV) Tyzor LA (CAS No. 65104-06-5). The term "crosslinked binder" is understood to mean the reaction product formed by reacting a binder with one or more crosslinking agents.

[0127] In a first embodiment, the protective layer, which completely or partially covers the heat-sensitive recording layer, is made from a coating compound comprising one or more polyvinyl alcohols and one or more crosslinking agents. It is preferred that the polyvinyl alcohol of the protective layer is modified with carboxyl or, in particular, silanol groups. Mixtures of different carboxyl- or silanol-modified polyvinyl alcohols are also preferred. Such a protective layer has a high affinity for the printing ink used in the offset printing process, preferably UV-curing ink. This significantly contributes to meeting the requirement for excellent printability in offset printing.

[0128] The crosslinking agent(s) for the protective layer according to this embodiment are preferably selected from the group consisting of boric acid, polyamines, epoxy resins, dialdehydes, formaldehyde oligomers, polyamine epichlorohydrin resin, adipic acid dihydrazide, melamine formaldehyde, and dihydroxybis(ammonium lactato)titanium(IV) Tyzor LA (CAS No. 65104-06-5). Mixtures of different crosslinking agents are also possible.

[0129] Preferably, in the coating compound for forming the protective layer according to this embodiment, the mass ratio of the modified polyvinyl alcohol to the crosslinking agent is in the range of 20:1 to 5:1 and particularly preferably in the range of 12:1 to 7:1. A ratio of the modified polyvinyl alcohol to the crosslinking agent in the range of 100 parts by mass to 8 to 11 parts by mass is particularly preferred.

[0130] Particularly good results were achieved when the protective layer, according to this design variant, additionally contained an inorganic pigment. The inorganic pigment is preferably selected from the group consisting of silicon dioxide, bentonite, boehmite, calcium carbonate, natural kaolin, calcined kaolin, and mixtures of the aforementioned inorganic pigments.

[0131] It is preferred that the protective layer according to this embodiment be applied with a mass per unit area in the range of 1.0 g / m² to 6 g / m² and particularly preferably from 1.2 g / m² to 3.8 g / m². The protective layer is preferably formed in a single layer.

[0132] In a second embodiment, the coating mass for forming the protective layer comprises a water-insoluble, self-crosslinking acrylic polymer as a binder, a crosslinking agent and a pigment component, wherein the pigment component of the protective layer consists of one or more inorganic pigments and is formed with at least 80% by mass from a highly purified alkali-treated bentonite, the binder of the protective layer consists of one or more water-insoluble, self-crosslinking acrylic polymers and the binder / pigment ratio is in the range of 7:1 to 9:1.

[0133] A self-crosslinking acrylic polymer within the protective layer according to the second embodiment described herein is preferably selected from the group consisting of styrene-acrylic acid ester copolymers, copolymers of styrene and acrylic acid ester containing acrylamide groups, and copolymers based on acrylonitrile, methacrylamide, and acrylic ester. The latter are preferred. Alkaline-treated bentonite, natural or precipitated calcium carbonate, kaolin, silica, or aluminum hydroxide can be incorporated into the protective layer as a pigment. Preferred crosslinking agents are selected from the group consisting of cyclic urea, methylol urea, ammonium zirconium carbonate, and polyamide-pichlorohydrin resins.

[0134] By selecting a water-insoluble, self-crosslinking acrylic polymer as a binder and its mass ratio (i) to the pigment in the range of 7:1 to 9:1 and (ii) to the crosslinking agent greater than 5:1, a high level of environmental resistance of the heat-sensitive recording material according to the invention is achieved even with a protective layer having a relatively low mass per unit area. Such mass ratios are therefore preferred.

[0135] The protective layer itself can be applied using conventional brushes, for which, among other things, a coating paint can be used, preferably with a mass per unit area in the range of 1.0 to 4.5 g / m². Alternatively, the protective layer can be printed on. Protective layers that can be cured using actinic radiation are particularly suitable in terms of processing technology and technological properties. The term "actinic radiation" refers to UV or ionizing radiation, such as electron beams.

[0136] The appearance of the protective layer is largely determined by the type of smoothing and the roller surfaces and materials that influence friction in the smoothing unit and calender. Particularly due to existing market requirements, a roughness (print surf roughness) of the protective layer of less than 1.5 µm (determined according to ISO standard 8791, Part 4) is considered preferable. The use of smoothing units employing NipcoFlex or zone-controlled Nipco-P rollers has proven particularly successful in the preliminary tests conducted for this invention; however, the invention is not limited to this.

[0137] A heat-sensitive recording material is preferred according to the invention, wherein the substrate is or comprises paper, synthetic paper, cardboard, paperboard or plastic film.

[0138] Although not limited to paper as a substrate, paper, and specifically untreated coated paper, is the preferred substrate in the context of the invention, having established itself on the market also due to its good environmental compatibility and recyclability. Untreated coated paper is understood to mean coated paper that has not been treated in a size press or coating device. For the invention, films made of, for example, polypropylene or polyolefin, and papers coated with polyolefin, are equally suitable as web-like substrates, without this being an exclusionary characteristic.

[0139] In one embodiment of the present invention, the heat-sensitive recording material comprises or consists of, a substrate having a front side and a back side opposite the front side, wherein the substrate is or comprises paper, a heat-sensitive recording layer arranged on the front side of the web-shaped substrate, wherein this heat-sensitive recording layer contains at least one dye precursor and at least one color developer reactive with this dye precursor, wherein the color developer is a compound of formula (II) shown below and does not include a color developer of the illustrated formula (I) and an intermediate layer arranged between the substrate and the heat-sensitive recording layer, comprising calcined aluminum silicate, wherein the mass fraction of the calcined aluminum silicate in the intermediate layer is 60 to 75%, based on the total mass of the solid components in the intermediate layer, wherein the calcined aluminum silicate is platelet-shaped and has an aspect ratio of 5 to 95, wherein the intermediate layer contains a styrene-butadiene latex, starch and methylcellulose, wherein the heat-sensitive recording layer comprises 1,2-diphenoxyethane and / or benzyl naphthyl ether and wherein the areal mass of the interlayer is in the range of 4.0 to 15.0 g / m² 2 is preferably in the range of 6.0 to 12.0 g / m³ 2 is, particularly preferably in the range of 7.0 to 10 g / m³ 2 lies and the area-related mass of the heat-sensitive recording layer is in the range of 1.5 to 6 g / m² 2 is preferably in the range of 2.0 to 5.5 g / m³ 2 lies, particularly preferably in the range of 2.0 to 4.8 g / m³ 2 lies.

[0140] In one embodiment of the present invention, the heat-sensitive recording material comprises or consists of, a substrate having a front side and a back side opposite the front side, wherein the substrate is or comprises paper, a heat-sensitive recording layer arranged on the front side of the web-shaped substrate, wherein this heat-sensitive recording layer contains at least one dye precursor and at least one color developer reactive with this dye precursor, wherein the color developer is a compound of formula (I) shown below wherein the compound of formula (I) is in a crystalline form which exhibits an absorption band at 3401±20 cm -1< in the IR spectrum, and does not comprise a color developer of the illustrated formula (I). and an intermediate layer arranged between the substrate and the heat-sensitive recording layer, comprising calcined aluminum silicate, wherein the mass fraction of the calcined aluminum silicate in the intermediate layer is 60 to 75%, based on the total mass of the solid components in the intermediate layer, wherein the calcined aluminum silicate is platelet-shaped and has an aspect ratio of 5 to 95, wherein the intermediate layer contains a styrene-butadiene latex, starch and methylcellulose,

[0141] wherein the heat-sensitive recording layer comprises 1,2-diphenoxyethane and / or benzyl naphthyl ether and wherein the areal mass of the intermediate layer is in the range of 4.0 to 15.0 g / m², preferably in the range of 6.0 to 12.0 g / m², particularly preferably in the range of 7.0 to 10 g / m² and wherein the areal mass of the heat-sensitive recording layer is in the range of 1.5 to 6 g / m², preferably in the range of 2.0 to 5.5 g / m², particularly preferably in the range of 2.0 to 4.8 g / m².

[0142] In one embodiment of the present invention, the heat-sensitive recording material comprises or consists of, a substrate having a front side and a back side opposite the front side, wherein the substrate is or comprises paper, a heat-sensitive recording layer arranged on the front side of the web-shaped substrate, wherein this heat-sensitive recording layer contains at least one dye precursor and at least one color developer reactive with this dye precursor, wherein the color developer is a compound of formula (II) shown below and includes a color developer of the illustrated formula (I) wherein the compound of formula (I) is in a crystalline form exhibiting an absorption band at 3401±20 cm⁻¹ in the IR spectrum, and an intermediate layer arranged between the substrate and the heat-sensitive recording layer, comprising calcined aluminum silicate, wherein the mass fraction of the calcined aluminum silicate in the intermediate layer is 60 to 75%, based on the total mass of the solid components in the intermediate layer, wherein the calcined aluminum silicate is platelet-shaped and has an aspect ratio of 5 to 95, and wherein the intermediate layer contains a styrene-butadiene latex, starch, and methylcellulose. wherein the heat-sensitive recording layer comprises 1,2-diphenoxyethane and / or benzyl naphthyl ether and wherein the areal mass of the interlayer is in the range of 4.0 to 15.0 g / m² 2 is preferably in the range of 6.0 to 12.0 g / m³ 2 is, particularly preferably in the range of 7.0 to 10 g / m³ 2 lies and the area-related mass of the heat-sensitive recording layer is in the range of 1.5 to 6 g / m² 2 is preferably in the range of 2.0 to 5.5 g / m³ 2 lies, particularly preferably in the range of 2.0 to 4.8 g / m³ 2 lies.

[0143] A further aspect of the present invention relates to products, preferably admission tickets, TITO tickets (ticket-in, ticket-out), flight, train, ship or bus tickets, gambling receipts, parking tickets, labels, cash register receipts, bank statements, self-adhesive labels, medical and / or technical diagram paper, fax paper, security paper or barcode labels, comprising a heat-sensitive recording material according to the invention.

[0144] Another aspect of the present invention is the use of a heat-sensitive recording material according to the invention as a barcode label, self-adhesive ticket, self-adhesive admission ticket, self-adhesive receipt, self-adhesive label, self-adhesive admission ticket, admission ticket, TITO tickets (ticket-in, ticket-out), flight, train, ship or bus ticket, gambling receipt, parking ticket, label, cash register receipt, bank statement, medical and / or technical diagram paper, fax paper or security paper.

[0145] Another aspect of the present invention relates to a method for producing a heat-sensitive recording material, preferably a heat-sensitive recording material according to the invention, comprising the following steps Providing or manufacturing a substrate comprising a front side and a back side opposite the front side; providing or manufacturing a first coating composition comprising calcined aluminum silicate; applying the first coating composition to the front side of the substrate; drying and / or crosslinking the applied first coating composition to form at least one intermediate layer; providing or manufacturing a second coating composition comprising at least one dye precursor and at least one color developer reactive with that dye precursor, wherein the color developer is a) a compound of formula (I) shown below or b) a combination of the formula (II) shown below is or c) a mixture comprising the compound of formula (I) and the compound of formula (II) is applied to the at least one intermediate layer, drying and / or crosslinking of the applied second coating composition so that a heat-sensitive recording layer is formed.

[0146] One method is preferred according to the invention, wherein the method additionally includes the following steps Providing or manufacturing an adhesive coating composition containing at least one adhesive or adhesive precursor, applying the adhesive coating composition to the reverse side of the substrate opposite the front side, and optionally drying and / or crosslinking the applied adhesive coating composition to form an adhesive layer.

[0147] One method is preferred according to the invention, wherein the method additionally includes the following steps Providing or manufacturing an interlayer coating composition, applying the interlayer coating composition to the heat-sensitive recording layer, and drying and / or crosslinking the applied interlayer coating composition to form a second interlayer.

[0148] One method is preferred according to the invention, wherein the method additionally includes the following steps Providing or manufacturing a protective layer coating composition, applying the protective layer coating composition to the heat-sensitive recording layer, and drying and / or crosslinking the applied protective layer coating composition to form a protective layer.

[0149] One method is preferred according to the invention, wherein the method additionally includes the following steps Providing or manufacturing a separating layer coating composition, wherein this separating layer coating composition comprises at least an organosiloxane group-containing compound or a wax, applying the separating layer coating composition to the heat-sensitive recording layer or to the second intermediate layer, drying and / or crosslinking the applied separating layer coating composition to form a separating layer which is non-adhesive to adhesives.

[0150] With regard to preferred embodiments and combinations for a coating composition used in a method according to the invention, the explanations given above for the heat-sensitive recording materials according to the invention apply accordingly (where applicable, analogously), and vice versa.

[0151] Within the scope of the present invention and in accordance with the general understanding in the field of paper technology, the term "coating composition" refers to coating materials containing or consisting of pigments or matrix pigments, binders, and additives, which are applied ("coated") to the paper surface or to layers already applied to paper surfaces using special coating devices for surface finishing or modification of the paper. Papers produced in this way are referred to as "coated papers" and are characterized, for example, by improved feel. The term "coating composition" is thus the generic term for all brushable coating masses, preparations, and / or solutions used in the paper industry for the treatment, modification, or finishing of a paper surface.

[0152] For applying the coating composition to a substrate or intermediate layer, those skilled in the art are familiar with various brushing techniques, for example: blade brushing, film press brushing, casting, curtain coating, doctor blade brushing, airbrushing, or spray brushing. All of these known brushing techniques are suitable for applying the coating compositions according to the invention to a substrate, preferably paper which includes one or more primers or intermediate coats, or which does not include any primer or intermediate coat.

[0153] Another aspect of the present invention relates to the use of calcined aluminum silicate in an intermediate layer of a heat-sensitive recording material, wherein the heat-sensitive recording material comprises or consists of the following components in addition to the intermediate layer. a substrate, wherein the substrate has a front side and a back side opposite the front side and a heat-sensitive recording layer arranged on the front side of the web-shaped substrate, wherein this heat-sensitive recording layer contains at least one dye precursor and at least one color developer reactive with this dye precursor, wherein the color developer is a) a compound of formula (I) shown below or b) a combination of the formula (II) shown below is or c) a mixture comprising the compound of formula (I) and the compound of formula (II), and wherein the intermediate layer is arranged between the substrate and the heat-sensitive recording layer and wherein the mass fraction of the calcined aluminium silicate in the intermediate layer is 50 to 90%, based on the total mass of the solid fractions in the intermediate layer.

[0154] Within the scope of the present invention, several of the aspects designated as preferred above are preferably implemented simultaneously; in particular, the combinations of such aspects and the corresponding features resulting from the attached claims are preferred.

[0155] The attached Figure 1 , 2 and 3 These are graphic representations (clean drawings) of machine-generated original spectra.

[0156] Figure 1Figure 1 shows a comparison of IR spectra in the wavenumber range of approximately 4000 to 2000 cm⁻¹ of the two crystalline forms of the compound of formula (I). The IR spectrum of the crystalline form of the compound of formula (I) used according to the invention, with a melting point of 175 °C, is shown in the upper part and labeled a). The IR spectrum of the crystalline form of the compound of formula (I) used according to the invention, with a melting point of approximately 158 °C, is shown in the lower part and labeled b).

[0157] Figure 2Figure 1 shows a comparison of IR spectra in the wavenumber range of approximately 2400 to 400 cm⁻¹ of the two crystalline forms of the compound of formula (I). The IR spectrum of the crystalline form of the compound of formula (I) used according to the invention, with a melting point of 175 °C, is shown in the upper part and labeled a). The IR spectrum of the crystalline form of the compound of formula (I) used according to the invention, with a melting point of approximately 158 °C, is shown in the lower part and labeled b).

[0158] Figure 3Figure 1 shows a comparison of IR spectra of the two crystalline forms of the compound of formula (I). The IR spectrum of the crystalline form of the compound of formula (I) used according to the invention, with a melting point of 175 °C, is shown in the upper part and labeled a). The IR spectrum of the crystalline form of the compound of formula (I) used according to the invention, with a melting point of approximately 158 °C, is shown in the lower part and labeled b).

[0159] The following examples and comparative examples will further illustrate the invention: Example 1:

[0160] A paper with a basis weight of 64 g / m² is produced on a Fourdrinier paper machine from bleached and ground hardwood and softwood pulps, with the addition of AKD sizing (based on the total solids content (atro) of the pulp supplied to the paper machine) at a mass fraction of 0.8%, as well as other usual additives.

[0161] In papermaking, three grades are distinguished for the dryness of paper and pulp: "atro" (absolutely dry), "lutro" (air-dried), and "otro" (oven-dried). These are expressed as "% atro," "% lutro," and "% otro," respectively. "atro" refers to paper or pulp with 0% water content. For "lutro," a "normal" moisture content (essential for papermaking) is used as the basis for calculation. For pulp and groundwood, the calculation is generally based on a 90:100 ratio, meaning 90 parts pulp to 10 parts water. The state of paper or pulp after drying under specific, defined conditions is designated as "otro."

[0162] On the front side, an intermediate layer with an area-related mass of 9 g / m² is applied using a coating knife, comprising the following composition in percentage mass fractions: 83% calcined aluminum silicate as pigment, 12% styrene-butadiene latex as binder, 2.5% starch as co-binder and 2.5% other additives (biocide 0.05%, dispersant 0.35%, methylcellulose 0.2%, thickener 0.2%).

[0163] A heat-sensitive recording layer with a mass per unit area of ​​3.2 g / m² is applied to this intermediate layer containing calcined aluminum silicate using a roller-squeegee applicator. The aqueous coating compound used contains the following components according to the formula shown in Table 1: Table 1: Data in mass fractions [%] (atro), based on the total mass of the heat-sensitive recording layer Dye precursor 3-dibutylamino-6-methyl-7-anilinofluorane (ODB-2) 9 Color developer N-(p-toluenesulphonyl)-N'-3-(p-toluenesulphonyl-oxyphenyl)-urea (Pergafast 201 (BASF)) 20 sensitizer Benzyl 2-naphthyl ether (BNE) 16 binder Polyvinyl alcohol-co-ethylene copolymer (EVOH) 15 Cobinder Acrylate copolymers 10 Methylcellulose 2 pigment Talc (platelet-shaped with an aspect ratio of 25) 16 88

[0164] Other components of the heat-sensitive recording layer, which are not specified as percentages and in mass fractions [%] (atro) of the total mass, include dispersants, defoamers, optical brighteners, thickeners, waxes and crosslinking agents.

[0165] After the application of the heat-sensitive recording layer, it is dried and smoothed, whereby a value of 500 Bekk / sec according to DIN 53107:2016-05 (title: Testing of paper and cardboard - determination of smoothness according to Bekk) is measured for the front surface smoothness.

[0166] The manufactured web-shaped substrate with an intermediate layer and a heat-sensitive recording layer is coated on the front side (onto the heat-sensitive recording layer) using an anilox roller applicator with a standard UV-curing, radical-curing silicone system. The solvent-free Evonik standard silicone system used for this purpose contains a formulation shown in Table 2. The silicone application rate is approximately 1.2 g / m². Table 2: RC-711 silicone acrylate 25 mass fractions RC-902 silicone acrylate 50 mass fractions RC-1772 Silicone acrylate (mixture with matting agent) 25 mass fractions TEGO Photoinitiator A-18 2 mass fractions

[0167] The resulting coating containing the release agent is cured with a UV lamp (80 W / cm) under a protective atmosphere of nitrogen.

[0168] A heat-sensitive recording material according to the invention is obtained in which the separating layer containing organosiloxane group compounds does not detach from the heat-sensitive recording layer. Even after storage of 30 days, the separating layer containing the release agent cannot be separated from the heat-sensitive recording layer. The recording material produced exhibits good sensitivity. Example 2:

[0169] Example 1 was repeated, except that instead of N-(p-toluenesulfonyl)-N'-3-(p-toluenesulfonyl-oxyphenyl)-urea (Pergafast 201 (BASF)), the compound N-[2-(3-Phenylureido)phenyl]benzenesulfonamide (NKK) with a melting point of 178 °C was used as the color developer. Example 3:

[0170] An adhesive layer was produced on the back side of the substrate of the heat-sensitive recording layer produced in Example 1 by applying a polyacrylic resin adhesive.

[0171] The substrate was then rolled up so that the adhesive layer lay on the release layer containing an organosiloxane group. Even after storage of 30 days, individual layers of the heat-sensitive recording material can be unrolled without the release agent-containing release layer separating from the heat-sensitive recording layer or leaving any adhesive residue on the release agent-containing release layer. Example 4:

[0172] An adhesive layer was produced on the back side of the substrate of the heat-sensitive recording layer produced in Example 2 by applying a polyacrylic resin adhesive.

[0173] The web-shaped substrate was then rolled up so that the adhesive layer lay on the release layer containing organosiloxane compounds. Even after storage of 30 days, individual layers of the heat-sensitive recording material can be unrolled without the release layer separating from the heat-sensitive recording layer or leaving any adhesive residue on the release layer. Comparative example 1:

[0174] Example 1 was repeated, except that hollow body pigments (particle size: 1.5 µm) were used as the pigment in the intermediate layer instead of the calcined aluminum silicate. Comparative example 2:

[0175] Example 3 was repeated, except that hollow body pigments (particle size: 1.5 µm) were used as the pigment in the intermediate layer instead of the calcined aluminum silicate.

[0176] The daylight stability of the heat-sensitive recording materials from Examples 1 and 2, as well as from Comparison Example 2, was determined. The heat-sensitive recording material from Example 1 shows an improvement in stability of approximately 3% (image and contrast stability) compared to the heat-sensitive recording material from Comparison Example 1, and the heat-sensitive recording material from Example 2 shows an improvement in stability of approximately 7% (image and contrast stability) compared to the heat-sensitive recording material from Comparison Example 1. The results are presented in the Figures 4 and 5 reproduced. Determination of the durability of heat-sensitive recording materials in daylight:

[0177] The daylight resistance of the heat-sensitive recording materials from examples 1 and 2, as well as from comparison example 2, was determined.

[0178] To measure the daylight resistance of a thermal print on the heat-sensitive recording materials of Examples 1 and 2 and Comparative Example 1 according to the invention, black / white checkered thermal test prints were produced on the heat-sensitive recording materials to be tested using a device of the type Atlantek Model 400 "Thermal Response Test System" from Global Media Instruments, LLC (USA), wherein a thermal printhead with a resolution of 300 dpi and an energy per unit area of ​​16 mJ / mm² was used.

[0179] After creating the black and white checkered thermal sample printout, and after a resting period of more than 5 minutes, the density was determined at three points each on the black and uncolored areas of the thermal sample printout using a TECHKON SpectroDens Advanced spectral densitometer. The mean value was calculated from the respective measurements of the black and uncolored areas.

[0180] A thermal printout was irradiated for 24 hours with a daylight lamp providing an energy of 21,600 kJ / m². After 24 hours, the thermal printout was removed, and the print density was measured again at three locations each in the black and uncolored areas of the thermal printout using a TECHKON SpectroDens Advanced spectral densitometer. The mean value was calculated from the respective measurements in the black and uncolored areas.

[0181] The durability of the printed image in % corresponds to the quotient of the calculated average of the print density of the colored areas before and after storage under the daylight lamp multiplied by 100.

[0182] The heat-sensitive recording material from Example 1 shows an improvement in stability of approximately 3% (image and contrast stability) compared to the heat-sensitive recording material from Comparison Example 1, and the heat-sensitive recording material from Example 2 shows an improvement in stability of approximately 7% (image and contrast stability) compared to the heat-sensitive recording material from Comparison Example 1. The results are presented in the Figures 4 and 5 reproduced. Determination of the durability of heat-sensitive recording materials (at 90 °C for one hour):

[0183] To measure the durability of a thermal print on the heat-sensitive recording materials of Examples 1 and 2 and Comparative Example 1 according to the invention, black / white checkered thermal test prints were produced on the heat-sensitive recording materials to be tested using a device of the type Atlantek Model 400 "Thermal Response Test System" from Global Media Instruments, LLC (USA), wherein a thermal printhead with a resolution of 300 dpi and an energy per unit area of ​​16 mJ / mm² was used.

[0184] After creating the black and white checkered thermal sample printout, and after a resting period of more than 5 minutes, the density was determined at three points each on the black and uncolored areas of the thermal sample printout using a TECHKON SpectroDens Advanced spectral densitometer. The mean value was calculated from the respective measurements of the black and uncolored areas.

[0185] A thermal printout was placed in a climate chamber at 90 °C. After one hour, the printout was removed, cooled to room temperature, and the density was measured again at three points each on the black and uncolored areas of the thermal printout using a TECHKON SpectroDens Advanced spectral densitometer. The average value was calculated from the respective measurements taken on the black and uncolored areas.

[0186] The durability of the printed image in % corresponds to the quotient of the calculated average of the print density of the colored areas before and after storage in the climate chamber multiplied by 100.

[0187] The heat-sensitive recording material from Example 1 shows an improvement in image stability of approximately 1% compared to the heat-sensitive recording material from Comparison Example 1, and the heat-sensitive recording material from Example 2 shows an improvement in background stability (contrast stability) of approximately 7% compared to the heat-sensitive recording material from Comparison Example 1. The results are presented in the Figures 6 and 7 reproduced.

[0188] In comparison to the heat-sensitive recording materials from Example 1 and Comparison Example 1, the recording material from Example 2 shows no background graying whatsoever. The background image remains completely white. Determination of the dynamic pressure density:

[0189] To measure the dynamic pressure density of a thermal print on the heat-sensitive recording materials of Examples 1 and 2 and Comparative Example 1 according to the invention, ten rectangles with different energy inputs were printed on each of the heat-sensitive recording materials to be tested. The thermal test prints were produced using an Atlantek Model 400 "Thermal Response Test System" from Global Media Instruments, LLC (USA). A thermal printhead with a resolution of 300 dpi and an energy per unit area of ​​3.22, 4.62, 6.07, 7.49, 8.88, 10.32, 11.74, 13.17, 14.57, and 16.00 mJ / mm² was used.

[0190] After creating the thermal printout, and after a resting period of more than 5 minutes, the density of the printout was determined at three points on each of the black-colored areas using a TECHKON SpectroDens Advanced spectral densitometer. The average value was then calculated from the respective measurements of the black-colored areas.

[0191] The dynamic pressure density was determined for the heat-sensitive recording materials from Examples 1 and 2, as well as from Comparison Example 2. The heat-sensitive recording materials from Examples 1 and 2 exhibit a higher pressure density (sensitivity) at higher energies (from approximately 7 mJ / mm²) than the material from Comparison Example 2. Furthermore, these materials show a higher maximum pressure density (Dmax) and a higher pressure density at higher energies (16 mJ / mm²). The results are presented in Table 3 below. Figure 8reproduced. Table 3: 3,22 4,62 6,07 7,49 8,88 10,32 11,74 13,17 14,57 16,00 (mJ / mm²<) (mJ / mm²<) (mJ / mm²<) (mJ / mm²<) (mJ / mm²<) (mJ / mm²<) (mJ / mm²<) (mJ / mm²<) (mJ / mm²<) (mJ / mm²<) Example 1 0,06 0,19 0,70 1,14 1,39 1,47 1,50 1,44 1,38 1,31 Example 2 0,06 0,16 0,64 1,09 1,38 1,46 1,45 1,44 1,41 1,38 Comparative example 1 0,07 0,19 0,66 1,06 1,32 1,42 1,44 1,40 1,35 1,28

Claims

1. Heat-sensitive recording material comprising or consisting of - a web-form substrate, having a front side and a reverse side opposite the front side, - a heat-sensitive recording layer disposed to the front side of the web-form substrate, said heat-sensitive recording layer comprising at least one dye precursor and at least one colour developer which is reactive with said dye precursor and which a) is a compound of the formula (I) depicted below or b) is a compound of the formula (II) depicted below or c) is a mixture comprising the compound of the formula (I) and the compound of the formula (II) and - an interlayer disposed between the substrate and the heat-sensitive recording layer and comprising calcined aluminium silicate, the mass fraction of the calcined aluminium silicate in the interlayer being 50% to 90%, based on the total mass of the solids fractions in the interlayer, wherein the compound of the formula (I) is in a crystalline form which in the IR spectrum has an absorption band at 3401±20 cm-1.

2. Heat-sensitive recording material according to Claim 1, wherein the calcined aluminium silicate in the interlayer is platelet-shaped, wherein the platelet-shaped, calcined aluminium silicate preferably has an aspect ratio of 3 to 100, preferably of 5 to 95, especially preferably of 10 to 90.

3. Heat-sensitive recording material according to any of the preceding claims, wherein a compound of the formula (II) is present as colour developer and the heat-sensitive recording layer or the heat-sensitive recording material comprises no compound of the formula (I) or wherein a compound of the formula (I) is present as colour developer and the heat-sensitive recording layer or the heat-sensitive recording material comprises no compound of the formula (II).

4. Heat-sensitive recording material according to any of the preceding claims, wherein the heat-sensitive recording layer comprises a sensitizer and the sensitizer is preferably selected from the group consisting of 1,2-bis(3-methylphenoxy)ethane, 1,2-diphenoxyethane, 1,2-di(m-methylphenoxy)ethane, 2-(2H-benzotriazol-2-yl)-p-cresol, 2,2'-bis(4-methoxyphenoxy)diethyl ether, 4,4'-diallyloxydiphenyl sulfone, 4-acetylacetophenone, 4-benzylbiphenyl, acetoacetanilides, benzyl 2-naphthyl ether, benzyl naphthyl ether, benzyl 4-(benzyloxy)benzoate, benzyl paraben, bis(4-chlorobenzyl) oxalate ester, bis(4-methoxyphenyl) ether, dibenzyl oxalate, dibenzyl terephthalate, dimethyl terephthalate, dimethyl sulfone, diphenyl adipate, diphenyl sulfone, ethylenebisstearamide, fatty acid anilides, m-terpenyl, N-hydroxymethylstearamide, N-methylolstearamide, N-stearylurea, N-stearylstearamide, N-(2-hydroxyethyl)octadecanamide, N-(hydroxymethyl)octadecanamide, p-benzylbiphenyl, phenyl benzenesulfonate ester, salicylanilide, stearamide, ethylene glycol m-tolyl ether, and α,α'-diphenoxyxylene, wherein the sensitizer is more preferably 1,2-diphenoxyethane or benzyl naphthyl ether.

5. Heat-sensitive recording material according to any of the preceding claims, wherein the heat-sensitive recording layer has a Bekk smoothness as determined according to DIN 53107:2016-05 of 100 to 1200 seconds, preferably of 150 to 1100 seconds.

6. Heat-sensitive recording material according to any of the preceding claims, wherein the mass per unit area of the interlayer is in the range from 4.0 to 15.0 g / m2, preferably in the range from 6.0 to 12.0 g / m2, more preferably in the range from 7.0 to 10 g / m2 and the mass per unit area of the heat-sensitive recording layer is in the range from 1.5 to 6 g / m2, preferably in the range from 2.0 to 5.5 g / m2, more preferably in the range from 2.0 to 4.8 g / m2.

7. Heat-sensitive recording material according to any of the preceding claims, wherein the mass fraction of the calcined aluminium silicate in the interlayer is 60% to 90%, preferably 70% to 88%, based on the total mass of the solids fractions in the interlayer, wherein the mass fraction of the calcined aluminium silicate in the intermediate layer is more preferably 65% to 75%, based on the total mass of the solids fractions in the interlayer and / or wherein the interlayer further comprises one or more constituents selected from the group consisting of biocides, binders, dispersants, release agents, defoamers, thickeners, and optical brighteners, wherein the interlayer preferably comprises one or more dispersants, wherein the dispersant is preferably a sodium polyacrylate homopolymer and / or wherein the interlayer comprises a styrene-butadiene latex, starch, and methyl cellulose.

8. Heat-sensitive recording material according to any of the preceding claims, wherein the substrate is or comprises paper, synthetic paper, cardboard, paperboard or polymeric film.

9. Heat-sensitive recording material according to any of the preceding claims, wherein the heat-sensitive recording layer further comprises one or more constituents selected from the group consisting of binders, sensitizers, pigments, dispersants, antioxidants, release agents, defoamers, light stabilizers, and optical brighteners.

10. Heat-sensitive recording material according to any of the preceding claims, wherein the heat-sensitive recording layer is wholly or partly covered with a protective layer.

11. Heat-sensitive recording material according to any of the preceding claims, wherein a layer of adhesive is disposed on the reverse side of the substrate, facing away from the front side of the substrate and / or wherein a release layer is disposed on the heat-sensitive recording layer and is dehesive towards layers of adhesive, wherein the release layer preferably comprises at least one compound containing organosiloxane groups, or a wax.

12. Products, preferably entry tickets, flight, rail, ship or bus ticket, gaming coupon, parking display ticket, label, till receipt, bank statements, self-adhesive label, medical diagram paper, fax paper, security paper or barcode labels, comprising heat-sensitive recording material according to any of Claims 1 to 11.

13. Use of heat-sensitive recording material according to any of Claims 1 to 11 as barcode label, self-adhesive ticket, self-adhesive entry ticket, self-adhesive proof of purchase, self-adhesive label, self-adhesive entry ticket, entry ticket, flight, rail, ship or bus ticket, gaming coupon, parking display ticket, label, till receipt, bank statement, medical diagram paper, fax paper or security paper.

14. Method for producing a heat-sensitive recording material according to any of Claims 1 to 11, comprising the following steps: - providing or producing a web-form substrate comprising a front side and a reverse side disposed opposite to the front side, - providing or producing a first coating composition, said first coating composition comprising calcined aluminium silicate, wherein the mass fraction of the calcined aluminium silicate in the first coating composition is 50% to 90%, based on the total mass of the solids fractions in the first coating composition, - applying the first coating composition to the front side of the web-form substrate, - drying and / or crosslinking the applied first coating composition, to form at least one interlayer, - providing or producing a second coating composition, the second coating composition comprising at least one dye precursor and at least one colour developer which is reactive with this dye precursor and which a) is a compound of the formula (I) depicted below wherein the compound of the formula (I) is in a crystalline form which in the IR spectrum has an absorption band at 3401±20 cm-1, or b) is a compound of the formula (II) depicted below or c) is a mixture comprising the compound of the formula (I) and the compound of the formula (II) - applying the second coating composition to the at least one interlayer, - drying and / or crosslinking the applied second coating composition, to form a heat-sensitive recording layer.

15. Method for producing a heat-sensitive recording material, preferably according to Claim 11, comprising the following steps: - providing or producing a heat-sensitive recording material according to any of Claims 1 to 10, said producing taking place preferably by the method according to Claim 14, - providing or producing a release layer coating composition, this release layer coating composition comprising at least one compound containing organosiloxane groups, or a wax, - applying the release layer coating composition to the heat-sensitive recording layer or to a second interlayer formed on the heat-sensitive recording layer, - drying and / or crosslinking the applied release layer coating composition to form a release layer which is dehesive with respect to adhesives.

16. Use of calcined aluminium silicate in an interlayer of a heat-sensitive recording material, the heat-sensitive recording material, besides the interlayer, comprising or consisting of the following components: - a web-form substrate, said substrate having a front side and a reverse side disposed opposite the front side, and - a heat-sensitive recording layer disposed to the front side of the web-form substrate, said heat-sensitive recording layer comprising at least one dye precursor and at least one colour developer which is reactive with said dye precursor and which a) is a compound of the formula (I) depicted below or b) is a compound of the formula (II) depicted below or c) is a mixture comprising the compound of the formula (I) and the compound of the formula (II), wherein the compound of the formula (I) is in a crystalline form which in the IR spectrum has an absorption band at 3401±20 cm-1 and wherein the interlayer is disposed between the substrate and the heat-sensitive recording layer and wherein the mass fraction of the calcined aluminium silicate in the interlayer is 50% to 90%, based on the total mass of the solids fractions in the interlayer.