EP3957489A1 - Developer-free thermosensitive recording material - Google Patents

Abstract

The present invention relates to a heat-sensitive recording material comprising or consisting of a) a carrier substrate (preferably paper substrate) and b) a melt layer arranged on one side of the carrier substrate or paper substrate, the melt layer i) an amide wax having a melting point in the range of 60 ° C to 180 ° C, ii) an inorganic pigment and ii) comprises or consists of a polymeric binder. The present invention also relates to a coating composition for producing a corresponding fused layer, a method for producing a heat-sensitive recording material and the use of a heat-sensitive recording material.

Description

The present invention relates to a heat-sensitive recording material comprising or consisting of a) a carrier substrate (preferably paper substrate) and b) a melt layer arranged on one side of the carrier substrate or paper substrate, the melt layer i) an amide wax having a melting point in the range of 60 ° C to 180 ° C, ii) an inorganic pigment and iii) comprises or consists of a polymeric binder. The present invention also relates to a coating composition for producing a corresponding fused layer, a method for producing a heat-sensitive recording material and the use of a heat-sensitive recording material.

Heat-sensitive recording materials have been known for many years and are very popular. This popularity is due, among other things, to the fact that their use is associated with the advantage that the typeface is formed solely by the irradiation of heat, and printers without toner and ink cartridges can therefore be used. It is therefore no longer necessary to purchase, store, change or refill toner or color cartridges. As a result, this innovative technology has established itself across the board, especially in public transport and retail.

In the recent past, however, concerns about the environmental compatibility of heat-sensitive recording materials have increased. In systems where the formation of the image is induced by a chemical reaction between two or more components, there are concerns about the ingredients used in the heat-sensitive recording layers. In particular, certain (color) developers, also referred to as color acceptors, and in some cases also dye precursors, with which the (color) developers react with the application of heat to form a visually recognizable color, have come under criticism. For example, bisphenol-A (2,2-bis(4-hydroxyphenyl)propane) has been the focus of public criticism among (color) developers and has not been allowed to be used as a (color) developer within the EU since 2020 be used. The industry has switched or has switched to alternative (color) developers such as N- (4-methylphenylsulfonyl) -N '-(3-(4-methylphenylsulfonyloxy)phenyl)urea or 4-hydroxy-4'-isopropoxydiphenylsulfone developed systems that do not require a (color) developer.

In the international patent application with the publication number WO 2019/183471 A1 describes a heat-sensitive recording material that does not require (color) developer. Two layers, each containing particles, are arranged on a substrate, a first type of particle being arranged in one layer and a second type of particle being arranged in the second layer. When exposed to heat, one type of particle melts and the melted particles are absorbed by the other particles in the other layer. As a result, the layers become transparent or semi-transparent and the colored substrate underneath becomes visible, as a result of which a printed image is formed. As particles, the use of polymer particles, e.g. B. polyethylene or polystyrene described.

Also in the international patent application with the publication number WO 2012/145456 A1 describes a heat-sensitive recording material that does not require (color) developers or color acceptors. Polymer particles having a core-shell structure are arranged in a layer arranged on a substrate, whereby this layer is opaque. Upon exposure to heat, the polymer particles melt and the core-shell structure collapses, revealing the previously opaque layer and revealing the underlying colored substrate.

Our own investigations have shown that the recording materials described in the prior art or that are commercially available do not have sufficient whiteness or that they are bluish or greyish in color. However, in many applications it is desirable if the paper has a high degree of whiteness according to ISO 2470-1:2016-09 (also known as brightness).

The primary object of the present invention was therefore to provide a heat-sensitive recording material that can be produced without (color) developer and at the same time has a high degree of whiteness according to ISO 2470-1:2016-09 (also referred to as brightness) having.

Our own investigations have shown that the recording materials described in the prior art or commercially available have a low contrast between the printed and non-printed image. This is because the background, i.e. the non-printed area of the paper, has a low degree of whiteness. In addition, the contrast of the image is significantly deteriorated during storage at high temperatures, resulting in a deterioration in readability. For example, when storing heat-sensitive recording materials in a car parked in the sun during the summer months, the interior of the car can heat up to temperatures of up to approx. 65°C. This can lead to heat-sensitive recording materials (e.g. a parking ticket) no longer being readable or only difficult to read.

A further object of the present invention was therefore to provide a heat-sensitive recording material that has an improved contrast between the non-printed and printed areas, in particular after storage of the recording material at high temperatures (such as can occur in a car in summer, for example). ). The aim is therefore to provide a recording material which has better readability of the printed image.

The recording materials described in the prior art also have the disadvantage that microplastics or nanoplastics are used in the layers. Pollution of the environment by micro- or nanoparticles poses a problem for ecosystems and the latest research results suggest that such particles can pose risks for smaller organisms as well as for humans.

A further object of the present invention was therefore to provide a heat-sensitive recording material which can be produced without microplastics or nanoplastics and as a result has excellent environmental compatibility combined with excellent printability.

1. a) einem Trägersubstrat (2)
   und
2. b) einer auf einer Seite des Trägersubstrats angeordneten Schmelzschicht (3),
   wobei die Schmelzschicht (3)
   1. i) ein oder mehrere Amidwachse, welche einen Schmelzpunkt im Bereich von 60 °C bis 180 °C aufweisen,
   2. ii) ein oder mehrere anorganische Pigmente
      und
   3. iii) ein oder mehrere polymere Bindemittel
   umfasst oder daraus besteht.

Surprisingly, it has now been found that the primary object and other objects and/or sub-objects of the present invention are achieved by a heat-sensitive recording material (1) comprising or consisting of

1. a) a carrier substrate (2)
   and
2. b) a melting layer (3) arranged on one side of the carrier substrate,
   wherein the enamel layer (3)
   1. i) one or more amide waxes which have a melting point in the range from 60 °C to 180 °C,
   2. ii) one or more inorganic pigments
      and
   3. iii) one or more polymeric binders
   includes or consists of.

The invention as well as combinations of preferred parameters, properties and/or components of the present invention which are preferred according to the invention are defined in the appended claims. Preferred aspects of the present invention are also specified or defined in the following description and in the examples.

Surprisingly, it has been found that heat-sensitive recording materials according to the invention have a high degree of whiteness (determined according to ISO 2470-1:2016-09).

Surprisingly, it was found that a high contrast between printed and non-printed areas can be obtained with heat-sensitive recording materials according to the invention. A high contrast leads to a high legibility of the typeface. This is particularly advantageous, for example, in the case of barcodes that are read by machines or in the case of writing that is read by the user. In doing so Surprisingly, it has also been shown that the high contrast is retained even after prolonged storage (e.g. 24 hours) at high temperatures (e.g. 90° C.). Our own investigations have shown that the high contrast can be obtained by using an amide wax in combination with an inorganic pigment. Without wishing to be bound by any particular theory, it is believed that the amide wax is particularly compatible with inorganic pigments due to the hydrophobic hydrocarbon residues and the hydrophilic amide group. Our own investigations have shown that, surprisingly, the amide waxes are not (or not significantly) absorbed by the inorganic pigments during the printing process, but remain in the melt layer or are partially absorbed by the adjacent layers. After printing, the amide waxes together with the inorganic pigments form a nearly transparent layer through which the underlying support substrate or other layers can be seen. However, before the printing process, the amide waxes form a very opaque layer with the inorganic pigments, which covers the colored substrate to a high degree. A high contrast is obtained as a result.

It goes without saying, of course, that high contrast can only be obtained if a layer underlying the enamel layer is colored. Preferably, the substrate or the colored intermediate layer (4) is black or has a dark shade such as blue or red. Possibilities of coloring the carrier substrate or of (conventionally) printing it, for example, with a colored intermediate layer, for example a printing ink, are known to the person skilled in the art. According to the invention, preference is given to using a colored intermediate layer (4) which comprises carbon black and an inorganic pigment, preferably natural kaolin or calcium carbonate. Alternatively, the carrier substrate can be colored with carbon black (or other dyes). The use of carbon black has the advantage that it has very good temperature resistance and light stability. The use of inorganic pigments in the intermediate layer serves only to be able to adjust the color of the intermediate layer as best as possible. Depending on the dye used in the interlayer, it is also possible that the interlayer does not contain any inorganic pigments. This does not affect the technical effect of the enamel layer.

However, the presence of a colored carrier substrate or a colored intermediate layer is not absolutely necessary, although this is preferred. For example, a heat-sensitive recording material can already be obtained if a corresponding melting layer is printed on commercially available white paper (ie not colored) or a transparent film is applied as a carrier substrate. After printing by the selective action of heat, a printed image can also be recognized without a colored carrier substrate or a colored intermediate layer. A possible area of use for this embodiment is security paper, in which the printed image is initially barely visible and only becomes visible when the paper is irradiated with light of a specific wavelength (eg UV light). For example, a material that absorbs (invisible) ultraviolet and blue light and emits visible light with longer wavelengths can be used as the carrier substrate or intermediate layer (4), while the melting layer has no fluorescence. After the paper has been printed, the printed image is initially not or hardly visible to the human eye and becomes visible after exposure to light of a specific wavelength, which excites the substrate to fluoresce. If the carrier substrate is transparent, a colored layer can also be applied to the back of the carrier substrate, or a contrast can be obtained if the printed recording material is placed on a colored surface.

According to the invention, however, preference is given to a heat-sensitive recording material in which the carrier substrate has a coloring or in which a colored layer is arranged between the carrier substrate and the melting layer. It is particularly preferred here if the paper substrate or the color layer arranged between the paper substrate and melt layer has an optical density (blackening) of at least 0.50, preferably at least 1.0, more preferably at least 1.20.

1. a) die Schmelzschicht umfasst vorzugsweise im Wesentlichen kein Mikro- oder Nanoplastik
2. b) die Schmelzschicht umfasst vorzugsweise im Wesentlichen keine (organischen) (Farb-)Entwickler oder Leukoverbindungen.

Surprisingly, it has been found that heat-sensitive recording materials according to the invention are very well suited for forming a printed image without having to use microplastics or nanoplastics, (color) developers or leuco compounds. Because it is preferred according to the invention that the molten layer meets at least one, preferably both, of the following conditions:

1. a) the enamel layer preferably comprises substantially no micro- or nanoplastic
2. b) the melt layer preferably comprises essentially no (organic) (color) developers or leuco compounds.

It is particularly preferred if the conditions a) and b) listed above are met by the entire heat-sensitive recording material.

In the context of the present invention, the term “essentially no microplastics or nanoplastics” means that the melting layer or the heat-sensitive recording material contains less than 0.5% by weight, preferably less than 0.1% by weight, microplastics or nanoplastics has, based on the total weight of the melting layer or the heat-sensitive recording material. No microplastic or nanoplastic is particularly preferably added, so that no microplastic or nanoplastic is present. However, small amounts of microplastics or nanoplastics cannot be ruled out, since they may be contained in some starting materials as impurities, for example in one embodiment in which paper is used as the carrier substrate that has a proportion of recycled fibers.

In the context of the present invention, small plastic particles, for example made of PET (polyethylene terephthalate), PP (polypropylene), PE (polyethylene) or other plastics, which are smaller than 5 mm, are referred to as microplastics or nanoplastics. Nanoplastic refers to a subgroup of microplastic and differs only in particle size, with nanoplastic having a particle size of less than 1 µm, while microplastic has a particle size of greater than or equal to 1 µm and less than 5 mm.

In the context of the present invention, the term "essentially no (organic) (color) developers or leuco compounds" means that the melting layer or the heat-sensitive recording material contains less than 0.5% by weight, preferably less than 0.1% by weight. -%, more preferably less than 0.02% by weight of (color) developer and leuco compounds, based on the total weight of the melting layer or the heat-sensitive recording material. Particularly preferably, no (color) developers and leuco compounds are added to the melting layer, so that no (color) developers and leuco compounds are present. However, small amounts of (color) developer and leuco compounds cannot be ruled out, since they may be present as impurities in some starting materials.

Surprisingly, it has been shown that heat-sensitive recording materials according to the invention also have the advantage that they have a high resistance to some chemicals. Our own investigations have shown that the melted layer retains a high level of whiteness in the tape test and the melted layer does not gray, while recording materials from the prior art show graying of the respective recording layer. In the tape test, part of a sample is covered with commercially available adhesive tape and left for 24 let absorb. The sample is then examined. It has been shown that printed parts of the recording materials remain the same black while in comparison samples the unprinted part shows a greyish discoloration of the melting layer after storage at ambient temperature. A recognizable discoloration occurs after 96 hours and is clearly pronounced after 21 days. In contrast to the sample of the present invention, this effect is even more pronounced in the unprinted part of the comparison samples when the sample is stored or stored for a longer period of time, for example after a period of several days to a few weeks, which is therefore advantageous for longer storage or storage, eg of receipts, proves to be very disadvantageous. Here the present invention thus provides a significant improvement over the prior art.

It is preferred according to the invention that the melt layer (in the unprinted state) has an opacity according to ISO 2471 of at least 50%, preferably at least 60%, particularly preferably at least 70%. The melt layers in recording materials according to the invention usually have an opacity of more than 75%, more than 80% or even more than 85%.

The opacity of the enamel layer is determined according to ISO 2471, with the isolated layer being measured. For example, a melt layer with the same composition and thickness can be applied to a completely transparent substrate (e.g. quartz glass) and measured.

Numerous pigments commonly used in papermaking can be used as the inorganic pigment, for example pigment selected from the group consisting of calcined kaolin, natural kaolin, kaolinite, magnesium silicate hydrate, silicon dioxide, bentonite, calcium carbonate, calcium silicate hydrate, calcium aluminate sulfate, aluminum hydroxide, aluminum oxide and boehmite.

However, our own investigations have shown that not all of these pigments deliver equally good results. For example, of the pigments listed above, natural kaolin has been shown to give the worst results. When using natural kaolin as a pigment, it has been shown that the dynamic print density is significantly worse at energy levels greater than 9 mJ/mm ² . The use of silicon dioxide, aluminum hydroxide and aluminum oxide also leads to heat-sensitive recording materials with good but not optimal dynamic print densities.

In one embodiment, it is therefore preferred according to the invention if the enamel layer does not contain any natural kaolin.

In one embodiment, it is preferred according to the invention if the melting layer and preferably the entire heat-sensitive recording material does not contain any organic pigments. It is particularly preferred here if the melting layer and preferably the entire heat-sensitive recording material does not contain any hollow sphere pigments (eg core-shell pigments).

In one embodiment, it is preferred according to the invention if the melt layer does not comprise aluminum trihydrate (ATH), calcium carbonate, polyethylene, polystyrene and/or silicon dioxide.

In one embodiment, it is preferred according to the invention if the entire heat-sensitive recording material does not comprise aluminum trihydrate (ATH), polyethylene, polystyrene and/or silicon dioxide.

In one embodiment, it is preferred according to the invention if the melting layer, preferably the entire recording material, contains no aluminum hydroxide and/or aluminum oxide. The use of aluminum hydroxide and/or aluminum oxide is less preferred, particularly in the case of recording materials that can come into direct contact with the consumer or with food, since the market demands materials that do not contain aluminum compounds due to the controversial effect of aluminum compounds on the human body.

According to the invention, it is particularly preferred if the inorganic pigment has a (preferably average) aspect ratio of from 3 to 100, preferably from 5 to 95, particularly preferably from 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 "aspect ratio" or "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 greater than the thickness of the platelet.

The form of the inorganic pigments is preferably plate-like or rod-like, with rod-like pigments being particularly preferred.

Our own investigations have shown that the use of platelet-shaped or rod-shaped pigments leads to particularly advantageous enamel layers. Without wishing to be bound to a specific theory here, it is assumed that corresponding pigments form particularly ordered layers which have a high degree of opacity. Platelet-shaped pigments can overlap in such a way that they form a kind of "scale structure" that is particularly dense. Rod-shaped pigments can also arrange themselves accordingly and form very dense layers. It is therefore surprising and was not foreseeable for the person skilled in the art that in a system according to the invention a transparency of the melt layer can be obtained when this is treated with heat. The person skilled in the art would not have expected that layers with flake or rod-shaped pigments, which form a very opaque layer, would become transparent through the action of heat.

According to the invention, preference is given to heat-sensitive recording materials in which the inorganic pigment has a particle diameter d ₅₀ in the range from 0.8 to 2.0 μm, preferably in the range from 1.0 to 1.8 μm, more preferably in the range from 1.2 to 1.6 μm having.

According to the invention, preference is given to heat-sensitive recording materials in which the inorganic pigment has a particle diameter d ₉₇ in the range from 2.0 to 15.0 μm, preferably from 6.0 to 10.0 μm, more preferably in the range from 7.0 to 9.0 μm having.

The measurement of the particle diameter can be determined by means of laser granulometry (for example with a Cilas 1064).

Surprisingly, it has been found that recording materials according to the invention with the abovementioned inorganic pigments have particularly good properties in terms of high opacity before printing and high transparency after printing. This would not be expected since the particles have a larger particle diameter compared to the wavelength of visible light (400 to 800 nm).

Surprisingly, it has been shown that of the inorganic pigments listed above, the calcium silicate has particularly good properties and leads to heat-sensitive recording materials with particularly good properties (higher White value of unprinted enamel layer with high opacity and very low opacity after printing). The use of calcium silicate, preferably as calcium silicate hydrate, is therefore particularly preferred according to the invention.

Our own investigations have shown that of the calcium silicates, xonotlite is particularly preferred.

In a preferred embodiment, the inorganic pigment has a pH value determined according to DIN EN ISO 787-9:2019-06 of greater than 7, preferably in the range from greater than or equal to 9 to less than or equal to 14, particularly preferably in the range from greater than or equal to 10, 5 to less than or equal to 12.5. Our own investigations have shown that the use of alkaline pigments makes it possible to dispense with the use of biocides. This is particularly advantageous for recording materials that can come into direct contact with food or the user. According to the invention, therefore, preference is given to a heat-sensitive recording material in which the melting layer and preferably the entire heat-sensitive recording material does not contain any biocides. The use of alkaline pigments has hitherto been avoided in heat-sensitive recording materials, since a high pH has a negative effect on the (color) developer or dye precursor.

In the context of the present invention, biocides are any substance or mixtures as defined in Article 2 of Regulation (EU) No. 528/2012 (Biocide Regulation) of the European Union.

A heat-sensitive recording material is particularly preferred according to the invention, in which the melt layer and preferably the entire recording material comprises essentially none of the following compound selected from the group consisting of diphenyl sulfone (DPS), diphenoxyethane (DPE), ethylene glycol m-tolyl ether (EGTE) and beta -Naphthyl benzyl ether (BON). Our own investigations have shown that these compounds, which are usually used as sensitizers in heat-sensitive recording materials, have no advantages in recording materials according to the invention and that these compounds can therefore be dispensed with. This makes it possible to use systems that have as few components as possible. This improves the environmental performance of the recording materials, such as recyclability, and reduces costs during manufacture.

In the context of the present invention, the term "essentially none" means in connection with the above-mentioned compounds that the melting layer or the heat-sensitive recording material contains less than 0.5% by weight, preferably less than 0.1% by weight. -% of the above sensitizers, based on the total weight of the melting layer or the heat-sensitive recording material. More preferably none of the above sensitizers are added such that none of the above sensitizers are present.

The amide wax used in recording materials according to the invention can be selected, for example, from the group consisting of lauramide ( CAS No. 1120-16-7 ), palmitamide ( CAS No. 629-54-9 ), stearamide ( CAS No. 124-26-5 ), 12-hydroxystearamide ( CAS No. 7059-49-6 ), oleamide ( CAS No. 301-02-0 ), erucamide ( CAS No. 112-84-5 ), N-stearyl stearamide ( CAS No. 13276-08-9 ), N-stearyloleamide ( CAS No. 6592-63-2 ), N-oleyl stearamide ( CAS No. 41562-24-7 ), N-stearyl erucamide (10094-45-8), N-methylolstearamide ( CAS No. 3370-35-2 ), ethylene bis oleamide ( CAS No. 110-31-6 ), hexamethylenebis oleamide ( CAS No. 6283-37-0 ), N,N'-dioleyl adipamide ( CAS No. 85888-37-5 ), methylenebis stearamide ( CAS No. 109-23-9 ), ethylene bis capramide ( CAS No. 51139-08-3 ), ethylenebis lauramide ( CAS No. 7003-56-7 ), ethylene bis stearamide ( CAS No. 110-30-5 ), ethylenebis 12-hydroxystearamide ( CAS No. 123-26-2 ), ethylene-bis-behenamide ( CAS No. 7445-68-3 ), hexamethylene-bis-stearamide ( CAS No. 4112-25-8 ), hexamethylene bis behenamide ( CAS No. 96548-58-2 ), hexamehylenebis 12-hydroxystearamide ( CAS No. 55349-01-4 ) and N,N'-distearyl adipamide ( CAS No. 25151-31-9 ), preferably selected from the group comprising Lauramid ( CAS No. 1120-16-7 ), palmitamide ( CAS No. 629-54-9 ), stearamide ( CAS No. 124-26-5 ), 12-hydroxystearamide ( CAS No. 7059-49-6 ), erucamide ( CAS No. 112-84-5 ), N-stearyl stearamide ( CAS No. 13276-08-9 ), N-methylolstearamide ( CAS No. 3370-35-2 ), ethylene bis oleamide ( CAS No. 110-31-6 ), hexamethylene-bis-oleamide ( CAS No. 6283-37-0 ) and N,N'-dioleyl adipamide ( CAS No. 85888-37-5 ).

Our own investigations have shown that it is particularly preferred if the amide wax is stearamide (octadecanamide, CAS No. 124-26-5 ) or N-methylolstearamide (N-(hydroxymethyl)octadecanamide, CAS No. 3370-35-2 ) is. In our own investigations, stearamide leads to the best results and is particularly preferred according to the invention.

Depending on the area of use of the heat-sensitive recording material, it can be advantageous if the amide wax has a melting point that is tailored to the area of use having. Our own investigations have surprisingly shown that heat-sensitive recording materials are particularly preferred when the amide wax has a melting point in the range from 80 to 120.degree. These heat-sensitive recording materials show the best properties in classic printing in a thermal printer.

Heat-sensitive recording materials in which the amide wax is a fatty acid monoamide are preferred according to the invention. It is particularly preferred here if the amide wax is a monoamide of a saturated fatty acid whose fatty acid residue has a total number of carbon atoms in the range from ≧14 to ≦20, preferably in the range from ≧16 to ≦18.

The amide wax is preferably a synthetically produced wax, which is preferably produced by reacting technical fatty acids, fatty acid esters and/or triacylglycerols with ammonia, monovalent amines, polyvalent amines and/or amino alcohols.

A heat-sensitive recording material is preferred according to the invention, the quantitative ratio between i) the one or more amide waxes (total) and ii) the one or more inorganic pigments (total) having a value in the range from 2:8 to 9:1 , preferably from 2.5:7.5 to 7.5:2.5, more preferably from 0.3:0.7 to 0.7:0.3, and most preferably 6.5 ± 0.3:3 .5 ± 0.3.

A heat-sensitive recording material is preferred according to the invention, the amide wax being present in a total amount in the range from ≥ 40 to ≤ 78 percent by mass, preferably from ≥ 44 to ≤ 73 percent by mass, more preferably in the range from 50 to 67 percent by mass, based on the dry mass of the melt layer . If the proportion of amide wax is too high, there is a possibility that parts of the wax will be deposited on the print head, rendering the heat-sensitive recording material unusable. If the amount of the amide wax is too small, there is a possibility that sufficient transparency of the melt layer cannot be obtained during printing.

A heat-sensitive recording material is preferred according to the invention, the binder being present in a total amount in the range from ≧1 to ≦30 percent by mass, preferably from ≧2 to ≦20 percent by mass, more preferably from ≧4 to ≦16 Percentage by mass, based on the dry mass of the enamel layer. Excessive amounts of binder can lead to insufficient opacity of the recording material before printing. With no or too small amounts (often less than 1% by mass) there is a possibility that the adhesion of the melt layer to the substrate will be impaired.

A heat-sensitive recording material is preferred according to the invention, the inorganic pigment being present in a total amount in the range from ≧18 to ≦50 percent by mass, preferably from ≧22 to ≦45 percent by mass, particularly preferably in the range from ≧25 to ≦39 percent by mass, based on the Dry mass of the enamel layer.

“Dry mass” in the context of the present invention is preferably understood to mean the water- and moisture-free mass of a sample (here: the melt layer) measured (under laboratory conditions at 23° C. and 50% RH). For the purposes of the present invention, the dry mass is preferably determined—as is customary in the field—on the sample to be examined (here: the heat-sensitive recording layer according to the invention), which had been dried at 105° C. to constant weight before the determination. Methods for determining the dry matter of a sample are known to those skilled in the art:
For example, the dry mass of a sample (in particular a sample of the enamel layer) can be determined for the purposes of the present invention by holding a sample of defined mass before drying (eg 1.5 g of the sample before drying) for five hours at 105° C. in a drying oven dries and then, after cooling to room temperature (in case of doubt, to 23 °C), check the constancy of weight in a manner known per se (sample, e.g. by heating it up again and determining the mass again), whereby, of course, reabsorption of water during the cooling process must be avoided (desiccator).

Likewise, for the purposes of the present invention, the dry mass of a sample (in particular a sample of the enamel layer) can be determined in a manner known per se using a moisture determination device, for example a halogen moisture determination device known per se, under the conditions specified above (105 °C, heating up to to constant weight) are determined.

A heat-sensitive recording material is preferred according to the invention, the area-related dry mass of the melt layer being in the range from ≧2 g/m ² to ≦15 g/m ² , preferably in the range from ≧3.0 g/m ² to ≦12 g/m ² , more preferably in the range from ≧4.0 g/m ² to ≦10 g/m ² .

A heat-sensitive recording material is preferred according to the invention, the carrier substrate being a paper, synthetic paper or a plastic film. Coating base paper is particularly preferred as the carrier substrate, since it has good recyclability and good environmental compatibility. Coating base paper is understood to be paper that has been treated in a size press or in a coating device. Films made of polypropylene or other polyolefins are preferred as plastic films.

In a particularly preferred embodiment, the carrier substrate is a paper substrate. It is preferred here if the paper substrate contains a proportion of ≧80 percent by mass of recycled fibers, based on the total mass of the air-dried paper substrate.

A heat-sensitive recording material is preferred according to the invention, the paper substrate containing ≦25 percent by mass of fresh fibers, based on the total mass of the air-dried paper substrate.

For the purposes of the present invention, the mass of an "air-dry" paper substrate given above is determined under standard ambient conditions (23°C, 50% RH, 1013 hPa). A water content of the paper substrate of 10 percent by mass is assumed for an air-dried paper substrate--as is customary in the technical field.

In an alternative embodiment of the heat-sensitive recording material according to the invention, a high proportion of more than 80 percent by mass of fresh fibers can also be used, or only fresh fibers are used. This has the advantage that the resulting material has fewer impurities and substrates with low grammages (eg less than or equal to 42 or 30 g/m ² ) can also be used.

A heat-sensitive recording material is preferred according to the invention, wherein the one or more polymeric binders are selected from the group consisting of starch and polyvinyl alcohol (PVA).

It is preferred if the polyvinyl alcohol used as a binder has a degree of saponification of more than 99 mol % and a viscosity of more than 7 mPas, preferably more than 12, measured according to DIN 53015 on an aqueous solution with 4% by mass at 20 °C mPas, particularly preferably more than 15 mPas.

1. a) ein oder mehrere Amidwachse, welche jeweils einen Schmelzpunkt im Bereich von 60 °C bis 180 °C, vorzugsweise 80 bis 120 °C aufweisen
   und
2. b) ein oder mehrere polymere Bindemittel

aber im Wesentlichen kein organisches oder anorganisches Pigment umfasst. Eigene Untersuchungen haben gezeigt, dass die Schicht (6) als Releaseschicht dienen kann, insbesondere zeigt die Schicht (6) eine gute dehäsive Wirkung, wenn der Amidwachsanteil bei über 70 Gew.-% liegt, bezogen auf das Gesamtgewicht der Schicht (6).In one embodiment of the present invention, a heat-sensitive recording material is preferred, wherein an additional layer (6) is arranged on the melting layer, the

1. a) one or more amide waxes, each of which has a melting point in the range from 60.degree. C. to 180.degree. C., preferably from 80 to 120.degree
   and
2. b) one or more polymeric binders

but essentially no organic or inorganic pigment. Our own investigations have shown that the layer (6) can serve as a release layer; in particular, the layer (6) has a good dehesive effect when the proportion of amide wax is more than 70% by weight, based on the total weight of the layer (6).

In the context of the present invention, the wording “substantially no organic or inorganic pigment” means that the further layer (6) has less than 0.5% by weight, preferably less than 0.1% by weight, of organic and inorganic pigments , based on the total weight of the further layer (6). No pigments are particularly preferably added to the further layer (6), so that no pigments are present.

A heat-sensitive recording material is preferred according to the invention, with an additional protective layer (5) being arranged on the melting layer.

In one embodiment of the heat-sensitive recording materials according to the invention, the melting layer is completely or partially covered with a protective layer (5). The arrangement of a protective layer (5) covering the melted layer also shields the melted layer from the outside or from the carrier substrate of the next layer within a roll, so that protection from external influences takes place.

Such a protective layer (5) often has the additional positive effect of improving the printability of the heat-sensitive recording material according to the invention, in particular in the indigo to improve offset and flexographic printing.

The protective layer (5) of the heat-sensitive recording material according to the invention preferably contains one or more crosslinked or uncrosslinked 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 hydrolyzed polyvinyl alcohols, ethylene-acrylic acid copolymer waxes and film-forming acrylic copolymers.

If present, the coating composition for forming the protective layer (5) of the heat-sensitive recording material according to the invention preferably contains one or more crosslinking agents for the binder or binders in addition to one or more binders. The crosslinking agent is then preferably 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 ).

A heat-sensitive recording material according to the invention, whose protective layer (5) is formed from such a coating composition containing one or more binders and one or more crosslinking agents for the binder or binders, contains in the protective layer (5) one or more crosslinked by reaction with one or more crosslinking agents Binders, wherein the crosslinking agent or agents are selected from the group consisting of boric acid, polyamines, epoxy resins, dialdehydes, formaldehyde oligomers, epichlorohydrin resins, adipic acid dihydrazide, melamine formaldehyde, urea, methylolurea, ammonium zirconium carbonate, polyamideepichlorohydrin resins and dihydroxybis(ammonium lactato)titanium(IV) Tyzor ^® LA ( CAS no. 65104-06-5 ).

“Crosslinked binder” is understood to mean the reaction product formed by reacting a binder with one or more crosslinking agents.

In a first embodiment variant, the protective layer (5) that completely or partially covers the molten layer can be obtained from a coating composition comprising one or more polyvinyl alcohols and one or more crosslinking agents. It is preferred that the polyvinyl alcohol of the protective layer (5) is modified with carboxyl or especially silanol groups. Mixtures of different carboxyl- or silanol-modified polyvinyl alcohols can also be used with preference. Such a protective layer (5) has a high affinity for the preferably UV-crosslinking printing ink used in the offset printing process. This provides crucial support in meeting the requirement for excellent printability within offset printing.

The crosslinking agent or agents for the protective layer (5) according to this embodiment variant 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.

In the coating composition for forming the protective layer (5) according to this embodiment variant, the weight ratio of the modified polyvinyl alcohol to the crosslinking agent is preferably in a range from 20:1 to 5:1 and particularly preferably in a range from 12:1 to 7:1 preferred is a ratio of the modified polyvinyl alcohol to the crosslinking agent in the range of 100 parts by weight to 8 to 11 parts by weight.

Particularly good results were achieved when the protective layer (5) according to this embodiment variant additionally contains an inorganic pigment. The inorganic pigment is preferably selected from the group consisting of silicon dioxide, bentonite, aluminum hydroxide, calcium carbonate, kaolin and mixtures of the inorganic pigments mentioned. However, the use of silicon dioxide and aluminum hydroxide is less preferred in some embodiments.

It is preferred that the protective layer (5) according to this embodiment variant has a mass per unit area in a range from 0.5 g/m ² to 6 g/m ² and is particularly preferred from 0.75 g/m ² to 3.8 g/m ² , more preferably in the range from 0.95 to 2.0 g/m ² . The protective layer (5) is preferably formed in one layer.

In a second embodiment variant, the coating composition for forming the protective layer (5) comprises a water-insoluble, self-crosslinking acrylic polymer as a binder, a crosslinking agent and a pigment component, the pigment component of the protective layer (5) consisting of one or more inorganic pigments and at least 80% by weight are formed from a highly purified alkaline processed bentonite, the binder of the protective layer (5) consists of one or more water-insoluble, self-crosslinking acrylic polymers and the binder/pigment ratio is in a range from 7:1 to 9:1.

A self-crosslinking acrylic polymer within the protective layer (5) according to the second variant described here is preferably selected from the group consisting of styrene-acrylic acid ester copolymers, acrylamide-containing copolymers of styrene and acrylic acid ester and copolymers based on acrylonitrile, methacrylamide and acrylic ester. The latter are preferred. Alkaline bentonite, natural or precipitated calcium carbonate, kaolin, silicic acid or aluminum hydroxide (the last two pigments are less preferred) can be incorporated into the protective layer (5) as a pigment. Preferred crosslinking agents are selected from the group consisting of cyclic urea, methylol urea, ammonium zirconium carbonate and polyamide epichlorohydrin resins.

By choosing a water-insoluble, self-crosslinking acrylic polymer as a binder and its weight ratio (i) to the pigment in a range from 7: 1 to 9: 1 and (ii) to the crosslinking agent greater than 5: 1 is already in a protective layer (5) with relatively low surface-related mass given a high environmental resistance of the heat-sensitive recording material according to the invention. Such weight ratios are thus preferred.

The protective layer (5) itself can be applied using conventional coating units, for which a coating color can be used, among other things, preferably with a mass per unit area in the range from 0.5 to 4.5 g/m ² , more preferably in the range from 0.75 up to 3 g/m ² . In an alternative variant, the protective layer (5) is printed on. Such are particularly suitable for processing and with regard to their technological properties Protective layer (5)s which can be cured by means of actinic radiation. The term "actinic radiation" means UV or ionizing radiation such as electron beams.

The appearance of the protective layer (5) is decisively determined by the type of smoothing and the roll surfaces influencing the friction in the calender and calender and their materials. In particular because of existing market requirements, a roughness (Parker Print Surf roughness) of the protective layer (5) of less than 1.5 μm (determined in accordance with ISO standard 8791, part 4) is considered preferable. The use of calenders in which NipcoFlex ^™ or zone-controlled Nipco-P ^™ rolls are used has particularly proven itself in the context of the experimental work preceding this invention; however, the invention is not limited to this.

In one embodiment of the recording material according to the invention, the melting layer can be arranged on both sides of the paper substrate. This makes it possible to produce recording materials that can be printed on both sides. If the paper substrate is colored, both melt layers can be applied directly to the paper substrate. Otherwise, a colored intermediate layer can be arranged between the paper substrate and each melting layer.

In a particular embodiment, the heat-sensitive recording material according to the invention is equipped as a label with a (self-)adhesive layer on the back. The usual structure then provides a carrier substrate, preferably a paper substrate, which has a front side and a back side opposite it. The heat-sensitive recording material then has the (self-)adhesive layer on the back. The enamel layer and optionally a protective layer (5) partially or completely covering the enamel layer can then be applied on the front side. A colored layer can also be applied between the carrier substrate and the melting layer, for example if the carrier substrate itself is not colored.

Depending on requirements, the adhesive layer can be covered with a release material such as a release paper containing silicone, or the protective layer (5) formed on the outer melt layer of the recording material according to the invention is provided with an additional release layer (7), which is preferably applied using a so-called five-roller applicator . The release layer has release agents, preferably based on silicone oil or silicones. By executing the release layer With silicone oil or silicones, the proposed recording material with a self-adhesive layer on the back can be wound up in a roll without release paper, so that the self-adhesive layer and the release layer come into contact in the roll without permanent adhesion occurring. In some embodiments, the release layer can also be applied directly to the melt layer.

Our own investigations have also shown that, because of the amide wax contained in the melting layer (3), in some embodiments it is even possible to dispense with the use of a release layer. In the case of higher proportions of amide wax of more than 70 percent by weight in the enamel layer in particular, our own investigations have shown that these are often sufficiently dehesive and that a further release layer can be dispensed with. Of course, it goes without saying that this also depends on the adhesive used. Adhesives that can be used for self-adhesive labels are known to those skilled in the art. Our own investigations have also shown that a layer (6) arranged on the melt layer can also serve as a release layer.

In a particularly preferred embodiment, the release layer can be cured or crosslinked under the influence of high-energy radiation, for example UV or electron beams. If the release layer is to be cured by means of UV rays, the monomers or prepolymers used to produce this layer must contain additions of photoinitiators in a known manner. Electron beam curing made it possible to achieve a release layer that was particularly uniform over its cross section, that is to say a cured release layer.

Preference is given to a recording material according to the invention, additionally comprising one or more processing aids in the melt layer, preferably selected from the group consisting of defoamers, dispersants and wetting agents, preferably in a total amount of ≦5 percent by mass, particularly preferably in a total amount in the range of ≥ 0.1 to ≤ 3% by mass, and more preferably in the range of ≥ 0.1 to ≤ 2% by mass, based on the dry mass of the heat-sensitive recording layer. In some cases it can also be useful if biocides are contained in the enamel layer, which is less preferred according to the invention. In particular, the use of biocides can be dispensed with or the amount of biocide used can be significantly reduced if alkaline pigments are used.

The one or more processing aids preferably serve to facilitate or enable the processing of a coating composition according to the invention for the production of a melted layer in the industrial manufacturing process, in particular in the industrial process of paper manufacture.

In some cases, an above-mentioned heat-sensitive recording material according to the invention which additionally comprises one or more optical brighteners may be preferred. The optical brighteners can be contained in the melting layer, in the carrier substrate or in the protective layer (5). If a heat-sensitive recording material according to the invention additionally comprises one or more optical brighteners, it is preferred if the heat-sensitive recording material according to the invention contains this one or more optical brighteners in a total amount of ≤ 1 percent by mass, more preferably in a total amount of ≤ 0.75 percent by mass , related to the dry mass of the respective layer. The above-mentioned heat-sensitive recording material according to the invention particularly preferably contains no optical brighteners.

1. a) einem Papiersubstrat (2)
   und
2. b) einer auf einer Seite des Papiersubstrats angeordneten Schmelzschicht (3),
   wobei die Schmelzschicht (3)
   1. i) ein oder mehrere Amidwachse, welche einen Schmelzpunkt im Bereich von 80 °C bis 120 °C aufweisen, vorzugsweise in einer Gesamtmenge im Bereich von ≥ 40 bis ≤ 78 Massenprozent, besonders bevorzugt von ≥ 44 bis ≤ 73 Massenprozent vorliegen, weiter bevorzugt im Bereich von 50 bis 67 Massenprozent vorliegen, bezogen auf die Trockenmasse der Schmelzschicht,
   2. ii) ein oder mehrere anorganische Pigmente, vorzugsweise in einer Gesamtmenge im Bereich von ≥ 18 bis ≤ 50 Massenprozent, besonders bevorzugt von ≥ 22 bis ≤ 45 Massenprozent vorliegen, weiter bevorzugt im Bereich von ≥ 25 bis ≤ 39 Massenprozent vorliegt, bezogen auf die Trockenmasse der Schmelzschicht
      und
   3. iii) ein oder mehrere polymere Bindemittel, vorzugsweise in einer Gesamtmenge im Bereich von ≥ 1 bis ≤ 30 Massenprozent, vorzugsweise von ≥ 2 bis ≤ 20 Massenprozent vorliegen, weiter bevorzugt von ≥ 4 bis ≤ 16,5 Massenprozent vorliegen, bezogen auf die Trockenmasse der Schmelzschicht
   umfasst oder daraus besteht.

A heat-sensitive recording material (1) comprising or consisting of is particularly preferred according to the invention

1. a) a paper substrate (2)
   and
2. b) a melting layer (3) arranged on one side of the paper substrate,
   wherein the enamel layer (3)
   1. i) one or more amide waxes, which have a melting point in the range from 80 ° C to 120 ° C, preferably in a total amount in the range from ≥ 40 to ≤ 78 percent by mass, particularly preferably from ≥ 44 to ≤ 73 percent by mass, more preferably in range from 50 to 67 percent by mass, based on the dry mass of the enamel layer,
   2. ii) one or more inorganic pigments, preferably present in a total amount in the range from ≧18 to ≦50 percent by mass, more preferably from ≧22 to ≦45 percent by mass, more preferably in the range of ≥ 25 to ≤ 39 percent by mass, based on the dry mass of the enamel layer
      and
   3. iii) one or more polymeric binders, preferably present in a total amount in the range from ≧1 to ≦30 percent by mass, preferably from ≧2 to ≦20 percent by mass, more preferably from ≧4 to ≦16.5 percent by mass, based on the dry mass of the enamel layer
   includes or consists of.

The explanations given below for the coating composition according to the invention for producing a melt layer and/or the method according to the invention and/or the use according to the invention apply with regard to preferred embodiments of the recording material according to the invention given above and possible combinations of one or more aspects of the invention given here above accordingly, and vice versa.

• a) einem Trägersubstrat (2),
• b) einem auf einer Seite des Trägersubstrats angeordneten Druck (8),
  und
• b) einer auf dem Druck angeordneten Schmelzschicht (3),
  wobei die Schmelzschicht (3)
  1. i) ein oder mehrere Amidwachse, welche einen Schmelzpunkt im Bereich von 60 °C bis 180 °C aufweisen,
  2. ii) ein oder mehrere anorganische Pigmente
     und
  3. iii) ein oder mehrere polymere Bindemittel
  umfasst oder daraus besteht.

A further aspect of the present invention relates to a temperature indicator comprising or consisting of

• a) a carrier substrate (2),
• b) a print (8) arranged on one side of the carrier substrate,
  and
• b) a melt layer (3) arranged on the print,
  wherein the enamel layer (3)
  1. i) one or more amide waxes which have a melting point in the range from 60 °C to 180 °C,
  2. ii) one or more inorganic pigments
     and
  3. iii) one or more polymeric binders
  includes or consists of.

Our own investigations have shown that corresponding temperature indicators are suitable for monitoring and documenting the temperature of a product. This can provide evidence of whether products or devices have been heated above a certain temperature. The temperature indicators are distinguished by the fact that they are irreversible and—in contrast to temperature indicators known in the prior art—a printed image can be displayed. For example, the printed image can be a warning (as text, code or pictogram) that indicates that the temperature has been exceeded. The temperature indicators known in the prior art are characterized by discoloration, so that an area printed with the thermochromic is discolored.

By choosing an appropriate amide wax with an appropriate melting point or a mixture of two or more amide waxes, the temperature indicator can be adjusted to a desired transition or triggering temperature. According to the invention, temperature indicators with a transition temperature in the range from 60 to 180° C. can be produced.

The embodiments and combinations of embodiments specified above for the recording material according to the invention apply correspondingly to preferred embodiments of the temperature indicator according to the invention specified above and possible combinations of one or more aspects of the invention in this regard. This applies in particular to the configurations specified as preferred or particularly preferred.

A further aspect of the present invention relates to the use of the heat-sensitive recording material as a temperature indicator.

A further aspect of the present invention relates to a coating composition for producing a melt layer of a heat-sensitive recording material (preferably a recording material according to the invention) comprising the components i) to iii) as defined above.

A further aspect of the present invention relates to the use of a coating composition according to the invention as a printing ink. It has surprisingly turned out that coating compositions according to the invention can also be used as a printing ink. It is thus possible to print a print image (e.g. text or images). This printed image is preferably printed on a colored substrate and initially appears white after printing. If heat acts on the printed image, it becomes transparent and the printed image disappears or is no longer visible.

With regard to preferred configurations of the coating composition according to the invention specified above and possible combinations of one or more aspects of the invention with one another in this regard, the configurations and combination of configurations specified above for the recording material according to the invention apply correspondingly. This applies in particular to the configurations specified as preferred or particularly preferred.

1. a. Bereitstellen oder Herstellen eines Trägersubstrats, vorzugsweise eines Papiersubstrats;
2. b. Bereitstellen oder Herstellen einer Beschichtungszusammensetzung zur Herstellung einer Schmelzschicht, wobei die Beschichtungszusammensetzung folgende Bestandteile umfasst
   • i) ein oder mehrere Amidwache, welche einen Schmelzpunkt im Bereich von 80 °C bis 120 °C aufweisen,
   • ii) ein oder mehrere anorganische Pigmente
     und
   • ii) ein oder mehrere polymere Bindemittel
3. c. Aufbringen der bereitgestellten oder hergestellten Beschichtungszusammensetzung auf eine Seite des Trägersubstrats;
4. d. Trocknen der in Schritt c aufgebrachten Beschichtungszusammensetzung unter Ausbildung einer Schmelzschicht.

A further 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

1. a. Providing or producing a carrier substrate, preferably a paper substrate;
2. b. Providing or preparing a coating composition for producing a melt layer, the coating composition comprising the following components
   • i) one or more amide waxes which have a melting point in the range from 80°C to 120°C,
   • ii) one or more inorganic pigments
     and
   • ii) one or more polymeric binders
3. c. applying the provided or prepared coating composition to one side of the carrier substrate;
4. i.e. Drying the coating composition applied in step c to form a fused layer.

• e. Bereitstellen oder Herstellen einer Beschichtungszusammensetzung zur Herstellung einer Schutzschicht (5),
• f. Aufbringen der in Schritt e. bereitgestellten oder hergestellten Beschichtungszusammensetzung auf die Schmelzschicht;
• g. Trocknen oder Härten der in Schritt f aufgebrachten Beschichtungszusammensetzung unter Ausbildung einer Schutzschicht (5).

In one embodiment of the method according to the invention, the method additionally includes the following steps:

• e. Providing or producing a coating composition for producing a protective layer (5),
• f. Applying the in step e. provided or prepared coating composition onto the melt layer;
• G. drying or curing the coating composition applied in step f to form a protective layer (5).

The coating composition for producing a protective layer (5) can have the same configuration as described above for the heat-sensitive recording material.

1. i. Bereitstellen oder Herstellen einer Beschichtungszusammensetzung zur Herstellung einer gefärbten Zwischenschicht, vorzugsweise umfassend einen Farbstoff, vorzugsweise Ruß, und ein anorganisches Pigment, vorzugsweise Kaolin oder Calciumcarbonat,
2. ii. Aufbringen der in Schritt i. bereitgestellten oder hergestellten Beschichtungszusammensetzung auf das Trägersubstrat;
3. iii. Trocknen der in Schritt ii aufgebrachten Beschichtungszusammensetzung unter Ausbildung einer gefärbten Zwischenschicht.

A colored carrier substrate, for example a colored paper substrate or a colored film, can be used as the carrier substrate in a method according to the invention. Alternatively, there is the possibility that a colored intermediate layer (4), which is arranged between the carrier substrate and the melting layer, is first applied to the carrier substrate. In this case, the method according to the invention additionally comprises the following steps:

1. i. providing or preparing a coating composition for producing a colored intermediate layer, preferably comprising a dye, preferably carbon black, and an inorganic pigment, preferably kaolin or calcium carbonate,
2. ii. Applying in step i. provided or prepared coating composition onto the carrier substrate;
3. iii. Drying the coating composition applied in step ii to form a colored intermediate layer.

Steps i are performed after step a and before step b. In this case, the coating composition for producing a melt layer in step c is not applied to the carrier substrate but to the colored intermediate layer.

The colored intermediate layer can be applied completely or only partially to the carrier substrate.

With regard to preferred embodiments of the above-mentioned method according to the invention for the production of a heat-sensitive recording material and in this respect possible combinations of one or more aspects of the invention given here above with one another, the above for the coating composition according to the invention and / or for the heat-sensitive recording material according to the invention and / or for the invention Use of a heat-sensitive recording layer according to the invention in accordance with the explanations given in each case, and vice versa.

A further aspect of the present invention relates to the use of a heat-sensitive recording material according to the invention as an admission ticket, receipt, self-adhesive label, ticket, TITO ticket (ticket-in, ticket-out), flight, train, ship or bus ticket, parking ticket, label , gambling receipt, sales receipt, bank statement, medical and/or technical chart paper, fax paper or security paper.

With regard to preferred embodiments of the above-mentioned use according to the invention of a heat-sensitive recording material according to the invention and possible combinations of one or more aspects of the invention given here above, the explanations given above for the heat-sensitive recording material according to the invention and/or for the coating composition according to the invention apply accordingly, and vice versa .

Fig. 1 bis 8

schematisch mögliche Schichtaufbauten von erfindungsgemäßen wärmeempfindlichen Aufzeichnungsmaterialien.

Fig. 9

Abbildungen von Mustern von drei verschiedenen Proben beim Tape-Test (Weichmacherbeständigkeit) (24 Stunden, 50 % r.F. 23°C und 20 Tage bei Umgebungsbedingungen). Hierbei ist die Probe 9a erfindungsgemäß.

Fig. 10

Abbildungen von Mustern von drei verschiedenen Proben beim Lagerungstest bei 60°C (24 Stunden). Hierbei ist die Probe 10a erfindungsgemäß.

Fig. 11

Abbildungen von Mustern von drei verschiedenen Proben beim Lagerungstest bei 90°C (1 Stunde). Hierbei ist die Probe 11a erfindungsgemäß.

Fig. 12

Wiedergabe der dynamischen Druckdichte der Aufzeichnungsmaterialien aus Beispiel 17 und den Vergleichsbeispielen 7 und 8 als Diagramm.

Fig. 13

Wiedergabe der dynamischen Sensitivität der Aufzeichnungsmaterialien aus Beispiel 17 und den Vergleichsbeispielen 7 und 8 als Diagramm.

Fig. 14

zeigt eine Fotographie eines erfindungsgemäßen Aufzeichnungsmaterials, das mit Schwarzlicht (UV-Licht) bestrahlt wird.

Further embodiments result from the exemplary embodiments explained in more detail in the figures and the example. In the figures show:

Figures 1 to 8

schematically possible layer structures of heat-sensitive recording materials according to the invention.

9

Images of patterns from three different samples in the tape test (plasticiser resistance) (24 hours, 50% RH 23°C and 20 days at ambient conditions). Here, the sample 9a is according to the invention.

10

Images of samples from three different samples in the storage test at 60°C (24 hours). Here, the sample 10a is according to the invention.

11

Images of samples from three different samples in the storage test at 90°C (1 hour). Here, the sample 11a is according to the invention.

12

Representation of the dynamic print density of the recording materials from Example 17 and Comparative Examples 7 and 8 as a diagram.

13

Representation of the dynamic sensitivity of the recording materials from Example 17 and Comparative Examples 7 and 8 as a diagram.

14

shows a photograph of a recording material according to the invention, which is irradiated with black light (UV light).

figure 1 shows a heat-sensitive recording material (1) that comprises a carrier substrate 2) and a melting layer (3) arranged on one side of the carrier substrate. The supporting substrate consists of a carbon black colored paper while the melt layer comprises i) stearamide as an amide wax, ii) calcium silicate hydrate as an inorganic pigment and iii) a PVA as a polymeric binder. Alternatively, the carrier substrate can also be a foil, a transparent foil or white paper.

figure 2 Fig. 1 shows a heat-sensitive recording material (1) comprising a supporting substrate 2), a colored intermediate layer (4) arranged on one side of the supporting substrate, and a melting layer (3) arranged on the colored intermediate layer (4). The carrier substrate consists of paper. A colored intermediate layer is arranged on the carrier substrate, the PVA as a binder, carbon black as a colorant and kaolin as an inorganic pigment. The melt layer disposed on the colored intermediate layer comprises i) stearamide as an amide wax, ii) calcium silicate hydrate as an inorganic pigment, and iii) a PVA as a polymeric binder. Alternatively, the carrier substrate can also be a film or a transparent film.

figure 3 shows a heat-sensitive recording material (1) according to figure 1 in which a protective layer (5) is arranged on the melting layer (3).

figure 4 shows a heat-sensitive recording material (1) according to figure 2 in which a protective layer (5) is arranged on the melting layer (3).

figure 5 shows a heat-sensitive recording material (1) according to figure 3 in which the colored intermediate layer (4) is not completely applied to the carrier substrate 2 and as a result a typeface (here text) is formed. This is a print (8). By heating the melting layer 3 to a specific temperature, it becomes transparent and the typeface becomes visible from the outside. In the areas in which the colored intermediate layer (4) is not arranged on the carrier substrate (2), the melting layer can lie directly on the carrier substrate 2 (not shown here). An adhesive layer (9, not shown here) can optionally be arranged on the rear side of the carrier substrate 2 . In one embodiment, the in figure 6 Imaged recording material to a temperature indicator, which - if an adhesive layer 9 is present - can be lived on surfaces.

figure 6 shows a heat-sensitive recording material (1) that comprises a carrier substrate 2) and a melting layer (3) arranged on one side of the carrier substrate. The carrier substrate consists of a transparent film while the melt layer comprises i) stearamide as an amide wax, ii) calcium silicate hydrate as an inorganic pigment, and ii) a PVA as a polymeric binder. A print 8 is arranged on the rear side of the carrier substrate. The printout 8 (here text) is preferably printed mirror-inverted. After the melting layer 3 has been heated, it becomes transparent and the printed image can be seen from above because of the transparent film. An adhesive layer (9, not shown here) can optionally be arranged on the print 8 . In one embodiment, the in figure 6 Imaged recording material to a temperature indicator, which - if an adhesive layer 9 is present - can be lived on surfaces.

figure 7 shows a heat-sensitive recording material (1) according to figure 2 in which an adhesive layer 9 is arranged on the back of the carrier material.

figure 8 shows a heat-sensitive recording material (1) according to figure 4 in which an adhesive layer 9 is arranged on the back of the carrier material and a release layer 7 is arranged on the protective layer 5 .

figure 9 shows images of the in during the determination of the plasticizer resistance (tape test) of Example 17 ( Figure 9a ) and Comparative Example 7 ( Figure 9b ) and Comparative Example 8 ( Figure 9c ). In the test, samples are printed, covered with a strip of transparent adhesive tape and left to stand for 24 hours at 50% RH and 23°C and for an additional 20 days at ambient conditions. It can be seen from the figures that the recording material according to the invention ( Figure 9a ) there is no discoloration of the unprinted part (light areas). The glued-on strip of tape is barely visible. In the case of the recording materials from Comparative Examples 7 and 8, it can be seen that the components of the adhesive tape (plasticizers) lead to discoloration of the unprinted areas. It is currently not known which components in the recording materials lead to the discoloration, but it is assumed that the sensitizers used in these samples react with the plasticizers in the adhesive tape and cause darkening.

figure 10 shows images of in during the determination of the temperature resistance of Example 17 ( Figure 10a ) and Comparative Example 7 ( Figure 10b ) and Comparative Example 8 ( Figure 10c ). In the test, samples are printed and stored at 60°C for 24 hours. It can be seen that the samples from Comparative Examples 7 ( Figure 10b ) and Comparative Example 8 ( Figure 10c ) are significantly darker than the sample according to the invention from Example 17 ( Figure 10a ).

figure 11 shows images of in during the determination of the temperature resistance of Example 17 ( Figure 11a ) and Comparative Example 7 ( Figure 11b ) and Comparative Example 8 ( Figure 11c ). In the test, samples are printed and stored at 90 °C for 21 hours. It can be seen that the samples from Comparative Examples 7 ( Figure 11b ) and Comparative Example 8 ( Figure 11c ) are significantly darker than the sample according to the invention from Example 17 ( Figure 11a ).

figure 12 shows the reproduction of the dynamic print density of the recording materials from Example 17 and Comparative Examples 7 and 8 as a diagram.

figure 13 shows the reproduction of the dynamic sensitivity of the recording materials from Example 17 and Comparative Examples 7 and 8 as a diagram.

figure 14 shows a photograph of a recording material according to the invention that is irradiated with black light (UV light). The recording material was produced by coating a conventionally available white writing paper with a melt layer described in Example 17. This was followed by a test print in a conventional thermal printer. The printed recording material obtained was then exposed to black light. The writing paper used as the carrier substrate shows a high level of fluorescence, which is only visible in the printed areas. Without the effect of black light, the printed area is difficult or impossible to see.

Examples:

The examples given below are intended to describe and explain the invention in more detail without restricting its scope.

In papermaking and in the following examples, a distinction is made between three grades for the dryness of paper and pulp: “atro” (absolutely dry), “air dry” (air dry) and “otro” (oven dry). The information is given in "% atro", "% atro" and "% otro". "atro" stands for paper or pulp with 0% water content. For "lutro" a "normal" (essentially necessary for the paper) moisture content is used as the basis for the calculation. In the case of cellulose and groundwood, the calculation mass usually refers to 90:100, i.e. 90 parts of pulp and 10 parts of water. The state of paper or pulp after drying under specified, defined conditions is referred to as "otro".

Examples 1 to 3 and Comparative Examples 1 and 2: Production of a recording material and variation of the ratio between amide wax and inorganic pigment:

A paper web made from bleached and ground hardwood and softwood pulps with a mass per unit area of 42 g/m ² is produced as the carrier substrate on a fourdrinier paper machine with the addition of customary additives in customary amounts and carbon black. The paper substrate produced was jet black.

To produce a coating composition required for the production of the melt layer, first two suspensions, a wax suspension and a pigment suspension, are prepared and then mixed in the ratios given in Table 3. The components of the suspensions are given in Tables 1 and 2 below: <u>Table</u> 1: Composition of the pigment dispersion pigment dispersion: component Otro amount [%] Air [g] water - 53.55 calcium silicate hydrate 85 117:10 PVA 15 79.35 total 100 250 wax dispersion: component Otro amount [%] Air [g] water - 0.33 stearamide 85 170,32,10 PVA 15 79.35 total 100 250.00 Preparation of the coating composition from both prepared suspensions examples Proportion of pigment suspensions Proportion of wax suspensions See example 1 (3.5) 100% - Example 1 (4.7) 70% 30% Example 2 (5.8) 50% 50% Example 3 (6.9) 30% 70% Compare example 2 (4,6) - 100%

Using a coating machine, a coating composition for producing a molten layer with a mass per unit area of 5.0 g/m ² is applied to the felt side of the paper web produced (paper substrate) by means of a doctor blade and dried conventionally after application.

To determine the maximum dynamic print density of the heat-sensitive recording materials listed in Table 4 below, black and white checkered thermal printouts were created using a GeBE printer, with the heat-sensitive recording materials (see Table 4) being printed with an energy in the range from 3 to 16 mJ /mm ² were printed. Each thermal printout was then examined with a TECHKON ^® SpectroDens Advanced spectral densitometer. The measurement results obtained using a densitometer (as print density data in ODU) are given in Table 4 below against the corresponding energy inputs. <u>Table 4</u>: Dynamic sensitivity (print density) of heat-sensitive recording materials Heat-sensitive recording material Energy input [mJ/mm ² ] 3.22 4.62 6.07 7.49 8.88 10:32 11.74 13:17 14.57 16.00 See Ex. 1 - - - - - - - - - - Ex 1 0.44 0.46 0.50 0.50 0.48 0.49 0.48 0.47 0.45 0.44 Ex 2 0.52 0.67 0.79 0.89 0.90 0.88 0.84 0.81 0.78 0.75 Ex 3 0.72 0.87 1:11 1.35 1.51 1.55 1.62 1.58 1.55 1.53 See Ex. 2 0.76 0.91 1.10 1.35 1.54 1.68 1.75 1.76 1.75 1.73

The heat-sensitive recording materials according to Comparative Example 1 were not printable. From the data given in Table 4 above, it can be seen that the heat-sensitive recording materials of the present invention (Examples 1 to 3) have good dynamic sensitivity. Recording materials according to Comparative Example 2 also showed good dynamic sensitivity, but there were heavy deposits on the thermal print head, so that this recording material cannot be used.

Examples 4 to 9 and Comparative Examples 3 to 6 Production of a recording material:

The previous example was repeated but the basis weight of the melt layer was changed to 3.0 or 7.0 g/m ² . The ratios between a wax suspension and a pigment suspension were retained and are in each case in Examples 1, 4 and 7 or 2, 5 and 8 or 3, 6 and 9 and cf.Ex.1, cf.Ex.3 and cf. Ex 5 and Ex 2, cf Ex 4 and cf Ex 6 are identical.

The results of determining the dynamic sensitivity are shown in Tables 5 and 6 below: <u>Table</u> 5: Dynamic sensitivity (print density) of heat-sensitive recording materials with a mass per unit area of 3.0 g/m² Heat-sensitive recording material Energy input [mJ/mm ² ] 3.22 4.62 6.07 7.49 8.88 10:32 11.74 13:17 14.57 16.00 See example 3 - - - - - - - - - - Ex 4 0.87 0.91 0.92 0.90 0.92 0.90 0.88 0.86 0.88 0.88 Ex 5 0.94 1.01 1.06 1.09 1.08 1.04 1.05 1.00 1.01 0.99 Ex 6 0.71 0.85 1.05 1.26 1.44 1.53 1.56 1.55 1.54 1.50 See example 4 1.04 1:21 1.34 1.47 1.58 1.65 1.65 1.65 1.63 1.65 Heat-sensitive recording material Energy input [mJ/mm ² ] 3.22 4.62 6.07 7.49 8.88 10:32 11.74 13:17 14.57 16.00 See Ex 5 - - - - - - - - - - Ex 7 0.26 0.29 0.31 0.31 0.33 0.34 0.33 0.33 0.31 0.32 Ex 8 0.35 0.42 0.55 0.69 0.76 0.82 0.86 0.81 0.74 0.74 Ex 9 0.60 0.65 0.75 0.96 1.25 1.52 1.69 1.72 1.73 1.73 See Ex 6 0.61 0.66 0.72 0.74 0.84 1.20 1.43 1.55 1.67 1.64

The heat-sensitive recording materials according to Comparative Examples 3 and 5 were not printable. From the data presented in Tables 5 and 6 above, it can be seen that the heat-sensitive recording materials of the present invention (Examples 4 to 9) have good dynamic sensitivity. Best printing results could be obtained with a ratio between wax amide and inorganic pigment of 7:3 with a melt layer mass per unit area of 7 g/m ² . Also in Comparative Examples 4 and 6, the deposits on the thermal print head were excessive, so that this recording material cannot be used. For example, in Example 9, an excellent contrast of 1.13 could be obtained.

All of the examples according to the invention showed a high degree of whiteness, this improving as the proportion of pigment increased.

Examples 10 to 16 Production of a Recording Material and Variation of the Binder Content:

Example 9 was repeated, but the proportion of binder was varied. The pigment to amide wax ratio was kept constant at 3:7. <u>Table 7</u>: Percentage of binder in the coating composition examples Percentage of binder (PVA) Example 10 4% Example 11 8th% Example 12 12% Example 13 16% Example 14 20% Example 15 24% Example 16 28%

The maximum dynamic print density of the recording materials obtained was determined as in the previous examples. <u>Table 8</u>: Dynamic print density of examples 10 to 16 sample 3.22 (mJ/mm ² ) 4.62 (mJ/mm ² ) 6.07 (mJ/mm ² ) 7.49 (mJ/mm ² ) 8.88 (mJ/mm ² ) 10.32 (mJ/mm ² ) 11.74 (mJ/mm ² ) 13.17 (mJ/mm ² ) 14.57 (mJ/mm ² ) 16.00 (mJ/mm ² ) 4% binder 0.36 0.42 0.50 0.67 0.87 1:11 1.39 1.49 1.55 1.56 8% binder 0.39 0.44 0.54 0.71 0.92 1:19 1.41 1.50 1.59 1.61 12% binder 0.56 0.60 0.67 0.78 1.00 1.25 1.48 1.59 1.68 1.73 16% binder 0.85 0.88 0.89 0.94 1.10 1.33 1.51 1.64 1.78 1.78 20% binder 1.09 1.09 1.09 1:13 1.24 1.41 1.54 1.65 1.78 1.81 24% binder 1:16 1:19 1:18 1:21 1.31 1.48 1.58 1.73 1.76 1.79 28% binder 1:21 1.26 1.26 1.27 1.41 1.53 1.63 1.75 1.80 1.82

Particularly good properties can be achieved with a binder content of between 4 and 16%. Below 4%, the whiteness of the fusible layer can be improved, but the adhesion of the fusible layer to the paper substrate deteriorates. With a binder content of more than 20%, the opacity of the enamel layer is reduced.

Example 17

A paper web made from bleached and ground hardwood and softwood pulps with a mass per unit area of 42 g/m ² is produced as the carrier substrate on a fourdrinier paper machine with the addition of customary additives in customary amounts and carbon black. The paper substrate produced was jet black.

A coating composition with the composition given in Table 9 was prepared to produce a coating composition required for the production of the hot-melt layer. <u>Table 9:</u> Composition of the dispersion Coating composition: component Otro amount [%] water - calcium silicate hydrate 28.0 stearamide 60.0 PVA 12.0 total 100.0

Using a coating machine, a coating composition for producing a molten layer with a mass per unit area of 7.0 g/m ² is applied to the felt side of the paper web produced (paper substrate) by means of a doctor blade and dried conventionally after application.

Example 18

Example 17 was repeated in several runs using amounts of ingredients within the range given in Table 9a. <u>Table 9a</u>: Composition of the dispersion Coating composition: component Otro amount [%] water - calcium silicate hydrate 28.0 to 39.0 stearamide 50.0 to 67 PVA 4.0 to 16.0 Total 100.0

The recording materials produced showed good properties with regard to sensitivity, dynamic print density, contrast, plasticizer stability (tape test) and optical appearance (whiteness).

Comparative example 7

A commercially available product with hollow body pigments in the enamel layer was used.

Comparative example 8

Another commercially available product with hollow body pigments in the enamel layer was used.

Comparison of Example 17 with Comparative Examples 7 and 8:

The recording material from Comparative Example 7 has a green-grey appearance on the printable side. The material of Comparative Example 8 has a blue-grey appearance on the printable side. The recording material according to the invention from Example 17 has a white-grey appearance.

To determine the maximum dynamic print density of the heat-sensitive recording materials listed in Table 10 below, black and white checkered thermal test prints were created with a GeBE printer, with the heat-sensitive recording materials (see Table 4) being printed with an energy in the range from 3 to 16 mJ /mm ² were printed. Each thermal printout was then examined with a TECHKON ^® SpectroDens Advanced spectral densitometer. The measurement results obtained using a densitometer (as print density data in ODU) are given in Table 10 below against the corresponding energy inputs. <u>Table 10</u>: Dynamic print density from Example 17 and Comparative Examples 7 and 8 example 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 ) See Ex. 7 0.49 0.57 0.75 0.95 1.07 1.22 1.29 1.32 1.35 1.35 Example 17 0.42 0.49 0.63 0.88 1:13 1.32 1.37 1.38 1.41 1.32 See Ex. 8 0.47 0.60 0.91 1.20 1.34 1.35 1.33 1.30 1.25 1.23

For a better overview, the results are shown in figure 13 graphically depicted.

Determining the temperature stability of heat-sensitive recording materials (at 60°C for 24 hours):

For the metrological determination of the temperature resistance of a thermal printout on the heat-sensitive recording materials of Example 17 according to the invention and Comparative Examples 7 and 8, black and white checkered thermal test printouts were created on the heat-sensitive recording materials to be tested using an Atlantek 400 device from Printrex (USA). , using a thermal head with a resolution of 300 dpi and an energy per unit area of 16 mJ/mm ² .

After the black/white checkered thermal printout had been created, after a rest period of more than 5 minutes, the print density was determined in three places each on the black colored areas and the uncolored areas of the thermal printout using a Techkon SpectroDens Advanced densitometer. The mean value was formed from the respective measured values of the black-colored areas and the uncolored areas.

A thermal printout was hung in a heating cabinet at 60°C. After 24 hours, the thermal paper printout was removed, cooled to room temperature and the print density was again determined at three points each on the black colored areas and the uncolored areas of the thermal test printout using a Techkon SpectroDens Advanced densitometer. The mean value was formed from the respective measured values for the black-colored areas and the uncolored areas.

The permanence of the printed image in % corresponds to the quotient of the mean value of the print density of the colored areas before and after storage in the climatic cabinet multiplied by 100.

The results are summarized in Table 11. Images of the thermal test prints produced are in the figure 10 pictured.

Determining the temperature stability of heat-sensitive recording materials (at 90°C for 1 hour):

For the metrological determination of the temperature resistance of a thermal printout on the heat-sensitive recording materials of Example 17 according to the invention and Comparative Examples 7 and 8, black and white checkered thermal test printouts were created on the heat-sensitive recording materials to be tested using an Atlantek 400 device from Printrex (USA). , using a thermal head with a resolution of 300 dpi and an energy per unit area of 16 mJ/mm ² .

After the black/white checkered thermal printout had been created, after a rest period of more than 5 minutes, the print density was determined in three places each on the black colored areas and the uncolored areas of the thermal printout using a Techkon SpectroDens Advanced densitometer. The mean value was formed from the respective measured values of the black-colored areas and the uncolored areas.

A thermal printout was hung in a heating cabinet at 90°C. After one hour, the thermal paper printout was removed, cooled to room temperature and the print density was again determined at three points each on the black colored areas and the uncolored areas of the thermal test printout using a Techkon SpectroDens Advanced densitometer. The mean value was formed from the respective measured values for the black-colored areas and the uncolored areas.

The permanence of the printed image in % corresponds to the quotient of the mean value of the print density of the colored areas before and after storage in the climatic cabinet multiplied by 100.

The results are summarized in Table 11. Images of the thermal test prints produced are in the figure 11 pictured.

Determination of the climate resistance of heat-sensitive recording materials (at 40°C and 90% RH for 24 hours):

In order to measure the climate resistance of a thermal printout on the heat-sensitive recording materials of Example 17 according to the invention and Comparative Examples 7 and 8, black and white checkered thermal test printouts were created on the heat-sensitive recording materials to be tested using an Atlantek 400 device from Printrex (USA). , using a thermal head with a resolution of 300 dpi and an energy per unit area of 16 mJ/mm ² .

After the black/white checkered thermal printout had been created, after a rest period of more than 5 minutes, the print density was determined in three places each on the black colored areas and the uncolored areas of the thermal printout using a Techkon SpectroDens Advanced densitometer. The mean value was formed from the respective measured values of the black-colored areas and the uncolored areas.

A thermal printout was hung in a climatic cabinet at 40° C. and a relative humidity of 90%. After 24 hours, the thermal paper printout was removed, cooled to room temperature and the print density was again determined at three points each on the black colored areas and the uncolored areas of the thermal test printout using a Techkon SpectroDens Advanced densitometer. The mean value was formed from the respective measured values for the black-colored areas and the uncolored areas.

The permanence of the printed image in % corresponds to the quotient of the mean value of the print density of the colored areas before and after storage in the climatic cabinet multiplied by 100.

The measurement results thus obtained are in Table 11: <u>Table 11</u> parameter See Ex. 7 Ex 17 See Ex.8 Heat resistance (60°C, 24h) before image dd 1.34 1.37 1.23 background dd 0.47 0.40 0.45 contrast dd 0.87 0.97 0.78 later image dd 1.34 1.36 1.23 background dd 0.46 0.39 0.44 contrast dd 0.88 0.98 0.79 stability image % 100.2 99.5 100.0 contrast % 101.5 100.3 101.3 Heat resistance (90°C, 1h) before image dd 1.36 1.37 1.24 background dd 0.47 0.40 0.45 contrast dd 0.89 0.97 0.78 later image dd 1.39 1.34 1.27 background dd 0.89 0.35 0.63 contrast dd 0.51 0.99 0.64 stability image % 102.7 97.8 103.0 contrast % 56.9 102.1 81.7 Climatic resistance (40°C, 90% rh, 24h) before image dd 1.34 1.38 1.22 background dd 0.47 0.40 0.45 contrast dd 0.87 0.98 0.77 later image dd 1.34 1.37 1:21 background dd 0.46 0.40 0.44 contrast dd 0.89 0.97 0.77 stability image % 100.5 99.5 99.7 contrast % 101.9 99.3 100.4

Determination of plasticizer resistance (tape test)

For the metrological determination of the plasticizer resistance (tape test) of a thermal printout on the heat-sensitive recording materials of Example 17 according to the invention and Comparative Examples 7 and 8, black and white checkered thermal printouts were made on the heat-sensitive recording materials to be tested using an Atlantek 400 device from the company Printrex (USA) using a thermal head with a resolution of 300 dpi and an energy per unit area of 16 mJ/mm ² .

After the black/white checkered thermal printout had been created, after a rest period of more than 5 minutes, the print density was determined in three places each on the black colored areas and the uncolored areas of the thermal printout using a Techkon SpectroDens Advanced densitometer. The mean value was formed from the respective measured values of the black-colored areas and the uncolored areas.

A strip of commercially available adhesive tape was stuck to part of the print area. The thermal test print with adhesive tape was hung in a climatic cabinet at 23° C. and a relative humidity of 50%. After 24 hours, the thermal paper printout was removed and the print density was again determined at three points each on the black colored areas and the uncolored areas of the thermal test printout, using a Techkon SpectroDens Advanced densitometer. The mean value was formed from the respective measured values for the black-colored areas and the uncolored areas.

The permanence of the printed image in % corresponds to the quotient of the mean value of the print density of the colored areas before and after storage in the climatic cabinet multiplied by 100.

After 20 more days, the samples were reassessed (21 days after printing and pasting). It can be seen that the sample from Comparative Example 7 has a very strong graying of the background (unprinted area) (cf. Figure 9b ), the sample from Comparative Example 8 has a moderate graying of the background (cf. Figure 9c ) and the sample according to the invention from Example 17 does not show any graying (cf. Figure 9a ). Images of the thermal test prints produced are in the figure 9 pictured, shows Figure 9a the recording material according to the invention, Figure 9b the recording material of Comparative Example 7 and Figure 9c the recording material from Comparative Example 8.

The results are summarized in Table 12. <u>Table 12:</u> Tape test results after 24 hours See Ex. 7 Ex 17 See Ex.8 tape test (23°C, 50% rh, 24 hours) before dd 1:19 1:17 1.09 later dd 1:21 1.20 1:12 stability % 101.7 102.8 102.1

Claims (15)

Heat-sensitive recording material (1) comprising a) a carrier substrate (2)
and b) a melting layer (3) arranged on one side of the carrier substrate,
wherein the enamel layer (3) i) an amide wax which has a melting point in the range from 60 °C to 180 °C, ii) an inorganic pigment
and iii) a polymeric binder
includes. Heat-sensitive recording material according to claim 1, wherein the quantitative ratio between i) the amide wax and ii) the inorganic pigment has a value in the range from 2: 8 to 9: 1, preferably from 2.5: 7.5 to 7.5: 2, 5, more preferably from 0.3:0.7 to 0.7:0.3, and most preferably 6.5±0.3:3.5±0.3. Heat-sensitive recording material according to any one of the preceding claims, wherein the amide wax is present in a total amount in the range from ≥ 40 to ≤ 78 percent by mass, preferably from ≥ 44 to ≤ 73 percent by mass, more preferably in the range from 50 to 67 percent by mass, based on the dry mass of the enamel layer. Heat-sensitive recording material according to any one of the preceding claims, wherein the binder is present in a total amount in the range from ≥ 1 to ≤ 30 percent by mass, preferably from ≥ 2 to ≤ 20 percent by mass, more preferably from ≥ 4 to ≤ 16.5 percent by mass, based on the Dry mass of the enamel layer. Heat-sensitive recording material according to any one of the preceding claims, wherein the inorganic pigment is present in a total amount in the range from ≥ 18 to ≤ 50 percent by mass, preferably from ≥ 22 to ≤ 45 percent by mass, particularly preferably in the range from ≥ 25 to ≤ 39 percent by mass, based on the dry mass of the enamel layer. Heat-sensitive recording material according to any one of the preceding claims, wherein the amide wax is a monoamide of a saturated fatty acid, the fatty acid residue of which has a total number of carbon atoms in the range ≥ 14 to ≤ 20, preferably in the range ≥ 16 to ≤ 18. Heat-sensitive recording material according to any one of the preceding claims, wherein the amide wax is stearamide (octadecanamide, CAS No. 124-26-5). Heat-sensitive recording material according to one of the preceding claims, wherein the dry mass per unit area of the melt layer is in the range from ≥ 2 g/m ² to ≤ 15 g/m ² , preferably in the range from ≥ 3.0 g/m ² to ≤ 12 g/m ² , particularly preferably in the range from ≧4.0 g/m ² to ≦10 g/m ² . Heat-sensitive recording material according to any one of the preceding claims, wherein the pigment is selected from the group consisting of calcined kaolin, natural kaolin, kaolinite, magnesium silicate hydrate, silica, bentonite, calcium carbonate, calcium silicate hydrate, calcium aluminate sulfate, aluminum hydroxide, aluminum oxide and boehmite. Heat-sensitive recording material according to one of the preceding claims, in which the inorganic pigment is calcium silicate, preferably calcium silicate hydrate. Heat-sensitive recording material according to any one of the preceding claims, wherein the inorganic pigment has a particle diameter d ₅₀ in the range of 0.8 to 2.0 µm, preferably 1.0 to 1.8 µm, more preferably in the range of 1.2 to 1.6 µm. Heat-sensitive recording material according to any one of the preceding claims, wherein the one or more polymeric binders are selected from the group consisting of starch and polyvinyl alcohol. A coating composition for producing a melt layer of a heat-sensitive recording material, comprising components i) to iii) as defined in any one of the preceding claims. A method for producing a heat-sensitive recording material, comprising the following steps a. Providing or producing a carrier substrate; b. Providing or preparing a coating composition for producing a melt layer, the coating composition comprising the following components i) an amide wax which has a melting point in the range from 60 °C to 180 °C, ii) an inorganic pigment
and iii) a polymeric binder c. applying the provided or prepared coating composition to one side of the carrier substrate; i.e. Drying the coating composition applied in step c to form a fused layer. Use of a heat-sensitive recording material according to one of Claims 1 to 12 as a temperature indicator, security paper, entrance ticket, receipt, self-adhesive label, ticket, TITO ticket (ticket-in, ticket-out), plane, train, ship or bus ticket, parking ticket, label, gambling receipt, cash register receipt, bank statement, medical and/or technical chart paper, fax paper or security paper.

Images