EP3352991B1 - Heat sensitive recording material - Google Patents

Description

The present invention relates to a thermosensitive recording material comprising a) a compound of the formula (I) and b) a compound of the formula (II), a use of the thermosensitive recording material and a process for producing a thermosensitive recording material.

Heat-sensitive recording materials have been known for many years and enjoy a high level of popularity. This popularity is due, among other things, to the fact that their use has the advantage that the color-forming components are contained in the recording material itself and therefore toner and color cartridge-free printers can be used. It is therefore no longer necessary to acquire toner cartridges or color cartridges, to stockpile, to change or to refill. Thus, this innovative technology has largely prevailed, especially in public transport and retail.

• □ Bisphenol-A, das ist 2,2 bis (4-hydroxyphenyl)-Propan, und
• □ Bisphenol-S, das ist 4,4'-Dihydroxydiphenylsulfon,

verstärkt im Zentrum öffentlicher Kritik und werden deshalb mitunter ersetzt durch

• ▪ Pergafast® 201, das ist N-(4-Methylphenylsulfonyl)-N-(3-(4-methylphenylsulfonyloxy)phenyl)harnstoff, der Firma BASF SE,
• ▪ D8, das ist 4-Hydroxy-4'-isopropoxydiphenylsulfon, und
• ▪ N-{2-[(Phenylcarbamoyl)amino]phenyl}benzolsulfonamid.

In the recent past, however, increased concerns about the environmental compatibility of particular (color) developers, also known as color acceptors, sometimes even of dye precursors with which react the (color) developers with heat to form a visually recognizable color, come up, not ignored by industry and especially by trade can be. For example, the (color) developers have recently become well-known and scientifically well-studied components, known as

• □ bisphenol-A, which is 2,2 bis (4-hydroxyphenyl) propane, and
• □ bisphenol-S, which is 4,4'-dihydroxydiphenyl sulfone,

reinforced in the center of public criticism and are therefore sometimes replaced by

• ▪ Pergafast® 201, which is N - (4-methylphenylsulphonyl) - N - (3- (4-methylphenylsulfonyloxy) phenyl) urea, from BASF SE,
• ▪ D8, which is 4-hydroxy-4'-isopropoxydiphenylsulfone, and
• ▪ N - {2 - [(phenylcarbamoyl) amino] phenyl} benzenesulfonamide.

With the aim of improving heat-sensitive recording materials, particularly in their use as tickets or lottery tickets, in terms of their resistance to environmental influences such as heat, moisture and chemicals, the underlying chemistry and the production technique for producing such recording materials has been further developed.

To increase the durability of a thermo-print (heat-induced recording) available on a heat-sensitive recording material against water, aqueous alcohol solutions and plasticizers, US Pat DE 10 2004 004 204 A1 a heat-sensitive recording material whose heat-sensitive recording layer has conventional dye precursors and the combination of a phenolic color developer and a urea-urethane-based color developer.

In the DE 10 2015 104 306 A1 a heat-sensitive recording material is described which comprises a carrier substrate and a heat-sensitive color-forming layer containing at least one color former and at least one phenol-free color developer, wherein, as phenol-free color developer, for example N-phenyl-N '[(phenylamino) sulfonyl] urea, N- (4- methylphenyl) -N '[(4-ethylphenylamino) sulfonyl] urea, N- (4-ethoxycarbonylphenyl) -N' [(4-ethoxycarbonylphenylamino) sulfonyl] urea or structurally similar compounds.

In the JP 2014-218062 A there is described a thermosensitive recording material having a thermosensitive recording layer containing at least a leuco dye and a color developer on a support. As the color developer, a mixture of 4,4'-bis (3-tosylureido) diphenylmethane and N- [2- (3-phenylureido) phenyl] benzenesulfonamide is used.

In the international patent application WO 2016/136203 A1 discloses a crystalline form of N- (2- (3-phenylureido) phenyl) phenylsulfonamides and the use of this crystalline form in a recording material. The crystalline form is characterized by specifying diffraction reflections in the X-ray powder diffractogram and diffraction diagram and by the melting point, thereby distinguishing it from other crystalline forms of this compound. It is additionally mentioned that the crystalline forms can likewise be distinguished from one another by the absorption bands in the IR spectrum. It is also shown that different crystalline forms of a compound can lead to different properties of the recording materials prepared using this compound.

Subject of the US 2005/0148467 A1 is a thermosensitive recording material containing at least the components of two color-forming systems to form an irreversible printed image, one being a chelate-type system and the other being a conventional leuco-dye system.

However, there is a continuing need for other heat-sensitive recording materials for a variety of uses, which must be due to high sales volumes in a fiercely competitive market at low production costs and therefore must have a simple structure. Another challenge is to expose a printed thermosensitive recording material to its typical uses as a ticket, ticket, ticket, parking ticket, and the like to a variety of different environmental conditions such as moisture, heat, or chemicals.

Thus, during normal use, thermosensitive recording materials may come into contact with a variety of different substances which may affect the resistance of the thermal term. These include, in addition to water and organic solvents, fats and oils contained in hand care products, for example, and touching the heat-sensitive recording material can be transferred to this. In particular, the resistance to fats and oils is therefore very relevant.

In addition to the resistance to chemicals which may come into contact with the heat-sensitive recording materials, heat-sensitive recording materials must also have a high resistance to thermal influences. On the one hand, the heat-sensitive recording material should be energy-saving and easy to print, for example, to consume low energy in mobile applications. On the other hand, the printed image should remain after printing, and when exposed to heat, the printed image should not fade, nor should the unprinted background be discolored, which would make the print no longer legible. For example, in the case of parking tickets, which are stored behind the windshield after printing and are exposed to high temperatures and direct sunlight in summer, the thermal resistance is extremely relevant.

Also, for tickets such as concert tickets or air tickets, which are often made a long time in advance, or for receipts required as proof of purchase over a long warranty period, the long-term durability of the heat-sensitive recording material is very important.

There is therefore a continuing need to improve the resistance of the thermal term to various environmental conditions. The object of the present invention is thus to provide a heat-sensitive recording material which, when printed, has a high resistance to environmental influences, such as moisture, heat or chemicals.

Preferably, the heat-sensitive recording materials should have a low long-term aging, even at high temperatures (40 to 60 ° C) and possibly high humidity and thereby have a relation to the prior art improved or at least consistent resistance to fat.

1. i) ein Trägersubstrat und
2. ii) eine wärmeempfindliche Aufzeichnungsschicht,

wobei die wärmeempfindliche Aufzeichnungsschicht einen Farbbildner und ein Farbentwicklergemisch umfasst und das Farbentwicklergemisch

1. a) eine Verbindung der Formel (I)
   
   enthält, wobei die Verbindung der Formel (I) in einer kristallinen Form vorliegt, die im IR-Spektrum eine Absorptionsbande bei 3401±20 cm^-1 aufweist,
   und
2. b) eine Verbindung der Formel (II)
   
   enthält.

This problem is solved by a heat-sensitive recording material comprising

1. i) a carrier substrate and
2. ii) a heat-sensitive recording layer,

wherein the heat-sensitive recording layer comprises a color former and a color developer mixture and the color developer mixture

1. a) a compound of the formula (I)
   
   wherein the compound of formula (I) is in a crystalline form having an absorption band at 3401 ± 20 cm ^-1 in the IR spectrum,
   and
2. b) a compound of the formula (II)
   
   contains.

In the compound of formula (II) is already known compound N - (4-methylphenylsulphonyl) - N '- (3- (4-methylphenylsulfonyloxy) phenyl) urea, which is sold under the name Pergafast 201 and, for example, in the EP 1 140 515 B1 is described. Pergafast 201 is the most widely used phenol-free color developer.

The compound of the formula (I) is likewise already known and is described, for example, in US Pat EP 2 923 851 A1 described. It is sold under the name NKK. However, it has been found that the compound of formula (I) can exist in two different crystalline forms. Both crystalline forms have different physical properties that may affect the thermosensitive recording material.

A crystalline form of the compounds of formula (I) has a melting point of about 158 ° C, while the second used in the invention crystalline form of the compounds of formula (I) has a melting point of 175 ° C. In connection with heat-sensitive recording materials, only the compound of the formula (I) which is the crystalline form having a melting point of about 158 ° C. has been described in the literature so far (cf., for example, US Pat EP 2 923 851 A1 Paragraph [0084]). Neither the preparation nor the use of the crystalline form of the compounds of the formula (I) having a melting point of about 175 ° C. used according to the invention are described in the literature. Accordingly, it is to be understood that the crystalline form of the compound of the formula (I) having a melting point of about 158 ° C has always been used, although the melting point is not explicitly mentioned in the corresponding document. The crystalline form of the compound of the formula (I) having a melting point of 175 ° C. used according to the invention has recently become commercially available as well.

According to the invention, preference is therefore given to a heat-sensitive recording material, the crystalline form of the compound of the formula (I) having a (preferably endothermic) transition at a temperature between 170 ° C and 178 ° C, preferably between 173 ° C and 177 ° C, more preferably between 174 ° C and 176 ° C as determined by differential scanning calorimetry (DKK) at a heating rate of 10 K / min.

Both crystalline forms of the compounds of the formula (I) can also be distinguished from one another in the IR absorption spectrum. Particularly characteristic in the crystalline form of the compounds of the formula (I) used according to the invention is an absorption band in the IR spectrum at 3401 ± 20 cm ^-1 . In the crystalline form of the compounds of the formula (I), which has a melting point of about 158 ° C, this band is not present, but in each case a band at 3322 and 3229 cm ^-1 .

According to the invention, preference is given to a thermosensitive recording material, wherein the crystalline form of the compound of the formula (I) in the IR spectrum has absorption bands at 689 ± 10 cm ^-1 , 731 ± 10 cm ^-1 , 1653 ± 10 cm ^-1 3364 ± 20 cm ^-1 and 3401 ± 20 cm ^-1 .

According to the invention, preference is given to a heat-sensitive recording material, wherein the IR absorption spectrum of the crystalline form of the compound of the formula (I) is substantially identical to that in Fig. 1a ), 2a) and / or 3a) matches the IR absorption spectrum.

Both crystalline forms of the compounds of the formula (I) can likewise be distinguished from one another in the X-ray powder diffractogram or diffraction diagram. According to the invention, preference is given to a heat-sensitive recording material, wherein the crystalline form of the compound of the formula (I) has an X-ray powder diffractogram with diffraction reflections at ° 20 values of 10.00 ± 0.20, 11.00 ± 0.20, 12.40 ± 0, 20, 13.80 ± 0.20 and 15.00 ± 0.20.

According to the invention, preference is given to a heat-sensitive recording material, wherein the crystalline form of the compound of the formula (I) has an X-ray powder diffractogram which substantially corresponds to that in FIG Fig. 4b ) corresponds to the X-ray powder diffractogram shown.

For the purposes of this text, a compound of the formula (I) is always described as being the crystalline form which has an absorption band at 3401 ± 20 cm ^-1 in the IR spectrum or has a melting point of 175 ° C. or a transition at one temperature between 170 ° C. and 178 ° C. (determined by means of differential scanning calorimetry (DKK) at a heating rate of 10 K / min) or in the X-ray powder diffractogram at 20 ° of at least 10.00 ± 0.20, 11.00 ± 0.20, 12.40 ± 0.20, 13.80 ± 0.20, and 15.00 ± 0.20, unless the existence of the other crystal structure is explicitly described.

It is understood that the indication a) of the melting point, b) of the diffraction reflexes in the X-ray powder diffractogram or c) of the absorption bands in the IR spectrum only serve to describe the crystalline form of the compound and thus make possible this crystalline form of other crystalline forms of the Distinguish connection. The indication of one of these measured variables is usually already sufficient to carry out a differentiation of the different crystalline forms. Particular preference is given to specifying the absorption bands in the IR spectrum, since an IR spectrum can be measured very easily and with high reproducibility for the expert and include IR spectrometers to the basic equipment in the chemical laboratory.

It has surprisingly been found that heat-sensitive recording materials according to the invention have a significantly improved long-term stability than heat-sensitive recording materials in which the color developer mixture has been replaced in equal parts by weight by a compound of formula (I) or a compound of formula (II). The combination of a compound of the formula (I) used according to the invention with a compound of the formula (II) thus has a synergistic effect which was unpredictable and therefore completely surprising.

According to the invention, a heat-sensitive recording material is preferred, wherein the aging of the heat-sensitive recording material is less than the aging of a heat-sensitive recording material when stored for 24 hours at a temperature of 90 ° C, wherein the color developer mixture in equal parts by weight by a compound of formula (I) or a compound of formula (II) has been replaced.

Also preferred according to the invention is a heat-sensitive recording material, wherein the aging of the heat-sensitive recording material when stored for 38 days at 40 ° C and 90% relative humidity is less than the aging of a thermosensitive recording material, wherein the color developer mixture in equal parts by weight by a compound of formula (I) or a compound of formula (II) has been replaced.

The aging of the thermosensitive recording material is considered to be lower if the printing density of a printed area decreases less than that of the comparative sample.

Surprisingly, it has been found that recording materials according to the invention, in addition to the improved long-term stability, also have improved resistance to fat, in particular lanolin, as heat-sensitive recording materials in which the color developer mixture according to the invention has been replaced in equal parts by weight with a compound of the formula (I). In this case, the resistance to fat, in particular lanolin, may also be better than the fat resistance of a heat-sensitive recording material in which the color developer mixture according to the invention has been replaced in equal parts by weight by a compound of the formula (I) or (II). Accordingly, therefore, there is also a synergistic effect in terms of resistance to fat, which was unpredictable and therefore completely surprising.

According to the invention, a thermosensitive recording material is preferred, wherein the stability of the thermosensitive recording material to lanolin after 14 days is higher than the resistance of a thermosensitive recording material in which the color developer mixture has been replaced in equal parts by weight by a compound of formula (I).

Also preferred in the invention is a thermosensitive recording material, wherein the durability of the thermosensitive recording material to lanolin is higher than or equal to 14 days, than the resistance of a thermosensitive recording material in which the color developing agent in equal parts by weight has been replaced by a compound of formula (II).

The durability of the thermosensitive recording material to lanolin is considered to be higher if the printing density of a printed area decreases less than that of the comparative sample.

It is known to the person skilled in the art that the combination of different developers, such as compounds of the formula (I) or (II), usually leads to a deterioration of the properties of the heat-sensitive recording material. Usually, the combination of two or more developers leads to an undesirable change in the color of the thermosensitive recording material, so that the thermosensitive recording material, for example, gray effect, without thereby improving the other properties. Accordingly, when attempting to solve the above-described problem, the person skilled in the art would not have considered combining different developers with one another and did not carry out corresponding tests. For this reason too, the solution according to the invention shown here is surprising, since the skilled person first had to overcome the technical prejudice that two developers should not be combined with one another in order to achieve the object.

According to the invention, preference is given to a heat-sensitive recording material, the mass ratio between the compound of the formula (I) and the compound of the formula (II) being 0.5: 99.5 to 99.5: 0.5. It has been shown in our own investigations that at a level of less than 0.5% by weight of the compound of the formula (I) or (II), based on the total weight of the compounds of the formula (I) and (II ), the positive influence of the respective compound is not so pronounced.

Particularly preferred according to the invention is a heat-sensitive recording material, the mass ratio between the compound of the formula (I) and the compound of the formula (II) being 35:65 to 65:35, preferably 40:60 to 60:40, particularly preferably 45: 55 to 55: 45.

It has been shown in own investigations that mixtures with a mass ratio between the compound of the formula (I) and the compound of the formula (II) of about 1: 1 or in the above-defined ranges from 35: 65 to 65: 35 , preferably 40:60 to 60:40, more preferably 45:55 to 55:45, have a synergistic effect both in terms of improved long-term stability and improved resistance to lanolin. Heat-sensitive recording materials containing, as color developer mixture, mixtures with these mass ratios, i. Mixtures having the same or approximately equal proportions by weight of the compounds of the formula (I) and (II) show better properties than heat-sensitive recording materials in which the color developer mixture in equal parts by weight has been replaced by only one compound of the formula (II) or (I).

According to the invention, a heat-sensitive recording material is preferred, wherein the carrier substrate is a paper, synthetic paper or a plastic film. As a carrier substrate, a non-surface treated base paper is particularly preferred because it has good recyclability and good environmental compatibility. A non-surface treated base paper is to be understood as meaning a base paper which has not been treated in a size press or in a coater. As plastic films, films of polypropylene or other polyolefins are preferred. Also preferred according to the invention are papers coated with one or more polyolefins (in particular polypropylene).

In a very particularly preferred embodiment, the carrier substrate is a paper with a fraction of recycled fibers of at least 70% by weight, based on the total pulp content in the paper.

According to the invention, preference is given to a heat-sensitive recording material, additionally comprising an intermediate layer located between the carrier substrate and the heat-sensitive recording layer, the intermediate layer preferably containing pigments. The pigments can be organic pigments, inorganic pigments or a mixture of organic pigments and inorganic pigments.

It is inventively preferred if the basis weight of the intermediate layer in the range of 5 to 20 g / m ² , preferably in the range of 7 to 12 g / m ² .

In the case where the intermediate layer contains pigments, it is preferred in one embodiment of the invention if the pigments are organic pigments, preferably organic hollow-body pigments.

Our own investigations have shown that the incorporation of organic pigments into the intermediate layer is advantageous, since organic pigments have a high heat reflectivity. Increased heat reflection of the intermediate layer formed with organic pigments increases the response of the heat-sensitive recording layer to heat because the radiated heat is at least partially reflected in the heat-sensitive recording layer instead of being conducted to the support substrate. This significantly increases the sensitivity and resolving power of the thermosensitive recording material, and further increases the printing speed in the thermal printer. In addition, the energy consumption during the printing process can be reduced, which is particularly advantageous for mobile devices. Hollow body pigments have air in their interior, whereby they usually have even higher heat reflection, and the sensitivity and resolving power of the thermosensitive recording material can be further increased.

In the case of the intermediate layer containing pigments, it is preferred in an alternative embodiment of the invention, when the pigments are inorganic pigments, preferably selected from the list consisting of calcined kaolin, silica, bentonite, calcium carbonate, alumina and boehmite ,

When inorganic pigments are incorporated in the intermediate layer sandwiched between the recording layer and the substrate, these pigments can absorb the components (e.g., waxes) of the thermosensitive recording layer liquefied by heat from the thermal head in the typeface formation, thus promoting even safer and faster operation of the heat-induced recording.

It is particularly advantageous if the inorganic pigments of the intermediate layer has an oil absorption of at least 80 ^cm3 / 100 g, and more preferably 100 ^cm3 / 100 g, determined according to the Japanese standard JIS K 5101, is having. Calcined kaolin has become especially proven due to its large absorption reservoir in the cavities. Also mixtures of several different types of inorganic pigments are conceivable.

The ratio between organic and inorganic pigment is a combination of the two types of pigments caused effects, which is particularly advantageously solved when the pigment mixture to 5 to 30 wt .-% or better to 8 to 20 wt .-% of organic and 95 to 70 wt .-% or better to 92 to 80 wt .-% consists of inorganic pigment. Pigment mixtures of different organic pigments and / or inorganic pigments are conceivable.

According to the invention, preference is given to a heat-sensitive recording material, the intermediate layer optionally containing, in addition to the inorganic and / or organic pigments, at least one binder, preferably based on a synthetic polymer, with styrene-butadiene latex giving particularly good results. The use of a synthetic binder with the admixture of at least one natural polymer, particularly preferably starch, is a particularly suitable embodiment. In the context of experiments with inorganic pigments, it was further found that a binder-to-pigment ratio within the intermediate layer of between 3: 7 and 1: 9, in each case based on wt .-% in the intermediate layer, represents a particularly suitable embodiment.

According to the invention, preference is given to a heat-sensitive recording material, wherein the color former is selected from derivatives of compounds from the group consisting of fluoran, phthalide, lactam, triphenylmethane, phenothiazine and spiropyran.

Our own investigations have shown that these color formers have particularly good properties in combination with the color developer mixture used according to the invention.

A preferred heat-sensitive recording material according to the invention preferably comprises, as color formers, fluoran-type compounds selected from the group consisting of 3-diethylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7- (3'-methylphenylamino) fluoran ( 6 '- (diethylamino) -3'-methyl-2' - (m-tolylamino) -3H-spiro [isobenzofuran-1,9'-xanthene] -3-one; ODB-7), 3-di-n- pentylamino-6-methyl-7-anilinofluoran, 3- (diethylamino) -6-methyl-7- (3-methylphenylamino) fluoran, 3-di-n-butylamino-7- (2-chloroanilino) fluoran, 3 Diethylamino-7- (2-chloroanilino) fluoran, 3-diethylamino-6-methyl-7-xylidinofluoran, 3-diethylamino-7- (2-carbomethoxyphenylamino) fluoran, 3-pyrrolidino-6-methyl-7-anilinofluoran, 3-pyrrolidino-6-methyl-7- (4-n-butylphenylamino) fluoran, 3-piperidino 6-methyl-7-anilinofluoran, 3-Nn-dibutylamine-6-methyl-7-anilinofluoran (ODB-2), 3- (N-methyl-N-cyclohexyl) amino-6-methyl-7-anilinofluoran, 3- (N-methyl-N-propyl) amino-6-methyl-7-anilinofluoran, 3- (N-methyl-N-tetrahydrofurfuryl) amino-6-methyl-7-anilinofluoran), 3- (N-ethyl-N- isoamyl) amino-6-methyl-7-anilinofluoran, 3- (N-ethyl-N-tolyl) amino-6-methyl-7-anilinofluoran, 3- (N-ethyl-N-tetrahydrofuryl) amino-6-methyl- 7-anilinofluoran, 3- (N-ethyl-N-isopentylamino) -6-methyl-7-anilinofluoran, 3- (N-ethyl-4-toluidino) -6-methyl-7- (4-toluidino) -fluoran and 3- (N-cyclopentyl-N-ethyl) amino-6-methyl-7-anilinofluoran.

Likewise preferred are heat-sensitive recording materials according to the invention which, as color formers, are those described in paragraphs [0049] to [0052] of the EP 2 923 851 A1 contained compounds.

Particularly preferred according to the invention is a heat-sensitive recording material, wherein the color former is selected from the group consisting of 3-N-di-n-butylamine-6-methyl-7-anilinofluoran (ODB-2) and 3- (N-ethyl-N- isopentylamino) -6-methyl-7-anilinofluoran.

Preferred in the invention is a heat-sensitive recording material, wherein the heat-sensitive recording layer contains a sensitizer.

When a sensitizer is used, the sensitizer is first melted during the application of heat during printing, and the molten sensitizer dissolves the color formers and color developers coexisting in the thermosensitive recording layer and / or lowers the melting temperature of the color formers and color developers to cause a color development reaction. The sensitizer does not participate in the color-winding reaction itself.

A sensitizer is therefore understood to mean substances which serve to adjust the melting temperature of the heat-sensitive recording layer and with which preferably a melting temperature of about 70 to 80 ° C. can be set without the sensitizers themselves being involved in the color-winding reaction.

For example, fatty acid salts, fatty acid esters and fatty acid amides (eg zinc stearate, stearic acid amide, palmitic acid amide, Oleic acid amide, lauric acid amide, ethylene and methylenebisstearic acid amide, methylolstearic acid amide), naphthalene derivatives, biphenyl derivatives, phthalates and terephthalates.

Particularly preferred according to the invention is a heat-sensitive recording material, wherein the sensitizer is selected from the group consisting of 1,2-bis (3-methylphenoxy) ethane, 1,2-diphenoxyethane, 1,2-di (m-methylphenoxy) ethane, 2 (2H-Benzotriazol-2-yl) -p-cresol, 2,2'-bis (4-methoxyphenoxy) diethyl ether, 4,4'-diallyloxydiphenylsulfone, 4-acetylacetophenone, 4-benzylbiphenyl, acetoacetic anilides, benzyl 2-naphthyl ether, Benzyl naphthyl ether, benzyl 4- (benzyloxy) benzoate, benzyl paraben, bis (4-chlorobenzyl) oxalate ester, bis (4-methoxyphenyl) ether, dibenzyl oxalate, dibenzyl terephthalate, dimethyl terephthalate, dimethyl sulfone, diphenyl adipate, diphenyl sulfone, ethylenebisstearic acid amine, fatty acid anilides, m-terpenyl , N-hydroxymethylstearic acid amine, N-methylolstearamide, N-stearylurea, N-stearylstearic acid amide, p-benzylbiphenyl, phenylbenzenesulfonate ester, salicylic anilide, stearamide and α, α'-diphenoxyxylene, wherein benzylnaphthyl ether, diphenylsulfone, 1,2-di (m-methylphenoxy) e and 1,2-diphenoxyethane are particularly preferred.

Also preferred are heat-sensitive recording materials according to the invention which act as sensitizers in paragraphs [0059] to [0061] of the EP 2 923 851 A1 contained compounds.

According to a first preferred embodiment, these sensitizers are each used alone, that is, not in combination with the other sensitisers mentioned above. According to a second, as it were preferred embodiment, at least two sensitizers selected from the above list are incorporated in the thermosensitive recording layer.

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

Further, in the heat-sensitive recording materials of the present invention, the use of 4,4'-diaminodiphenylsulfone (4,4'-DDS, dapsone) as an additional additive in the heat-sensitive recording layer may prove useful as appropriate. The use of 4,4'-diaminodiphenyl sulfone in thermal papers is eg in the WO 2014/143174 A1 described. The invention may then in this case relate to a heat-sensitive recording material, 4,4'-diaminodiphenylsulfone in the heat-sensitive recording layer, in particular additionally as an additive, is included.

Preferred in the invention are heat-sensitive recording materials, wherein the heat-sensitive recording layer contains a binder, preferably a crosslinked or uncrosslinked binder selected from the group consisting of polyvinyl alcohol, carboxyl group-modified polyvinyl alcohol, ethylene-vinyl alcohol copolymer, a combination of polyvinyl alcohol and ethylene-vinyl alcohol copolymer, silanol group-modified polyvinyl alcohol, diacetone-modified polyvinyl alcohol, acrylate copolymer and film-forming acrylic copolymers.

If desired, the coating composition for forming the thermosensitive recording layer of the thermosensitive recording material of the present invention contains, besides one or more binders, one or more crosslinking agents for the binder or binders. Preferably, the crosslinking agent is selected from the group consisting of zirconium carbonate, polyamidaminepichlorohydrin resins, boric acid, glyoxal, dihydroxy bis (ammonium lactato) titanium (IV) ( CAS-No. 65104-06-5 ; Tyzor® LA) and glyoxal derivatives.

A heat-sensitive recording material of the present invention whose heat-sensitive recording layer is formed from such a coating composition containing one or more binders and one or more crosslinking agents for the binder or binders contains one or more binders crosslinked by reacting with one or more crosslinking agents in the heat-sensitive recording layer. wherein the crosslinking agent or crosslinking agents are selected from the group consisting of zirconium carbonate, polyamidaminepichlorohydrin resins, boric acid, glyoxal, dihydroxy bis (ammonium lactato) titanium (IV) ( CAS-No. 65104-06-5 ; Tyzor® LA) and glyoxal derivatives. By "crosslinked binder" is meant the reaction product formed by reaction of a binder with one or more crosslinking agents.

According to the invention, a heat-sensitive recording material is preferred, wherein the basis weight of the heat-sensitive recording layer is in the range of 1.5 to 6 g / m ² , preferably in the range of 2.0 to 5.5 g / m ² , particularly preferably in the range of 2.0 to 4.8 g / m ² .

Also preferred according to the invention is a heat-sensitive recording material, the proportion of the color developer mixture in the heat-sensitive recording layer being 35 to 15% by weight, preferably 31 to 19% by weight, particularly preferably 28 to 22% by weight, based on the total solids content the heat-sensitive recording layer.

In recording materials according to the invention may additionally image stabilizers, dispersants, antioxidants, release agents, defoamers, light stabilizers, brighteners, as are known in the art, can be used. Each of the components is usually used in an amount of 0.01 to 15 wt .-%, in particular - with the exception of defoamers - 0.1 to 15 wt .-%, preferably 1 to 10 wt .-%, based on the total Solid content of the heat-sensitive recording layer. When defoamers are used in the relevant formulations, the antifoaming agent may be present in amounts of from 0.03 to 0.05% by weight in the recording materials according to the invention, based on the total solids content of the heat-sensitive recording layer.

In one embodiment of the heat-sensitive recording materials according to the invention, the heat-sensitive recording layer is completely or partially covered with a protective layer.

By disposing a protective layer covering the heat-sensitive recording layer, the heat-sensitive recording layer is also shielded to the outside or the supporting substrate of the next layer within a roll, so that it is protected from external influences.

Such a protective layer in such cases, in addition to the protection of the heat-sensitive recording layer arranged under the protective layer against environmental influences, often has the additional positive effect of being able to print the heat-sensitive recording material according to the invention, in particular in the indigo range. Improve offset and flexo printing. For this reason, it may be desirable for certain applications that the heat-sensitive recording material of the present invention has a protective layer although the presence of a color developing agent as defined above in the heat-sensitive recording layer of the heat-sensitive recording material of the present invention selects the resistance of a thermal printable on a heat-sensitive recording material of the present invention to cloths from the group consisting of water, Alcohols, fats, oils and their mixtures even without protective layer is already sufficient.

The protective layer 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 carboxyl-modified polyvinyl alcohols, silanol-modified polyvinyl alcohols, diacetone-modified polyvinyl alcohols, partially and fully hydrolyzed polyvinyl alcohols and film-forming acrylic copolymers.

Preferably, if present, the coating composition for forming the protective layer of the heat-sensitive recording material according to the invention contains, in addition to one or more binders, one or more crosslinking agents for the binder (s). The crosslinking agent is then preferably selected from the group consisting of boric acid, polyamines, epoxy resins, dialdehydes, formaldehyde oligomers, epichlorohydrin resins, adipic dihydrazide, melamine formaldehyde, urea, methylol urea, ammonium zirconium carbonate and polyamide-epichlorohydrin resins.

A heat-sensitive recording material according to the invention, the protective layer of which is formed from such a coating composition comprising one or more binders and one or more crosslinking agents for the binder or binders, contains in the protective layer one or more binders crosslinked by reaction with one or more crosslinking agents, wherein the one or more Crosslinking agents are selected from the group consisting of boric acid, polyamines, epoxy resins, dialdehydes, formaldehyde oligomers, epichlorohydrin resins, adipic 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 ). By "crosslinked binder" is meant the reaction product formed by reaction of a binder with one or more crosslinking agents.

In a first embodiment variant, the protective layer wholly or partly covering the heat-sensitive recording layer is obtainable 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 is modified with carboxyl or in particular silanol groups. Also mixtures of different Carboxyl-group- or silanol-modified polyvinyl alcohols are preferably usable. Such a protective layer has a high affinity with respect to the preferably UV-crosslinking printing ink used in the offset printing process. This critically supports meeting the demand for excellent printability within offset printing.

The one or more crosslinking agents for the protective layer according to this embodiment are preferably selected from the group consisting of boric acid, polyamines, epoxy resins, dialdehydes, formaldehyde oligomers, polyamine epichlorohydrin resin, adipic dihydrazide, melamine formaldehyde and dihydroxybis (ammonium lactato) titanium (IV) Tyzor® LA (cf. CAS-No. 65104-06-5 ). It is also possible to use mixtures of different crosslinking agents.

Preferably, in the coating composition for forming the protective layer according to this embodiment, the weight ratio of the modified polyvinyl alcohol to the crosslinking agent is in a range of 20: 1 to 5: 1, and more preferably in a range of 12: 1 to 7: 1 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 have been achieved when the protective layer according to this embodiment additionally contains an inorganic pigment. In this case, the inorganic pigment is preferably selected from the group consisting of silicon dioxide, bentonite, aluminum hydroxide, calcium carbonate, kaolin and mixtures of said inorganic pigments.

It is preferred to apply the protective layer according to this embodiment with a basis weight in a range from 1.0 g / m ² to 6 g / m ² and more preferably from 1.2 g / m ² to 3.8 g / m ² , In this case, the protective layer is preferably formed in one layer.

In a second embodiment, the coating composition for forming the protective layer comprises a water-insoluble, self-crosslinking acrylic polymer as a binder, a crosslinking agent and a pigment component, wherein the pigment component of the protective layer consists of one or more inorganic pigments and at least 80 wt .-% of a highly purified alkaline treated Bentonite are formed, the binder of the protective layer of one or more water-insoluble, self-crosslinking acrylic polymers and the binder / pigment ratio ranges from 7: 1 to 9: 1.

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

The choice of a water-insoluble, self-crosslinking acrylic polymer as a binder and its weight ratio (i) to pigment in a range of 7: 1 to 9: 1 and (ii) to crosslinking agent greater than 5: 1 is already a protective layer with a relatively low surface 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 itself can be applied by means of conventional brushing, for which inter alia a coating color is usable, preferably with a surface-related mass in a range from 1.0 to 4.5 g / m ² . In an alternative variant, the protective layer is printed. Processing technology and particularly suitable in terms of their technological properties are those protective layers which are curable by means of actinic radiation. The term "actinic radiation" UV or ionizing radiation, such as electron beams to understand.

The appearance of the protective layer is significantly determined by the type of smoothing and the friction in the calender and calender influencing roll surfaces and their materials. In particular, due to existing market requirements, a roughness (Parker Print Surf roughness) of the protective layer of less than 1.5 microns (determined in accordance with ISO standard 8791, Part 4) is considered preferable. In the experimental work preceding this invention, the use of calenders using NipcoFlex ™ or zone controlled Nipco-P ™ rolls has proven particularly useful; however, the invention is not limited thereto.

A further aspect of the present invention relates to the use of a heat-sensitive recording material according to the invention as entrance tickets, air tickets, rail tickets, bus tickets, gambling papers, parking tickets, labels, receipts, bank statements, self-adhesive labels, medical chart paper, fax paper, security paper or barcode labels.

A further aspect of the present invention relates to products, preferably tickets, air, rail, boat or bus ticket, gambling document, parking ticket, label, receipt, bank statements, self-adhesive label, medical chart paper, fax paper, security paper or bar code labels, comprising a heat-sensitive according to the invention recording material.

wobei die Verbindung der Formel (I) in einer kristallinen Form vorliegt, die im IR-Spektrum eine Absorptionsbande bei 3401±20 cm^-1 aufweist,
zur Verbesserung der Wasserbeständigkeit (insbesondere bei 40 °C und 90 % r.F.) eines Druckbildes eines wärmeempfindlichen Aufzeichnungsmaterials, bei dem eine Verbindung der Formel (II)

als Farbentwickler enthalten ist, wobei das Massenverhältnis zwischen der Verbindung der Formel (I) und der Verbindung der Formel (II) 0,5 : 99,5 bis 99,5 : 0,5 beträgt, vorzugsweise 35 : 65 bis 65 : 35 beträgt, weiter bevorzugt 40 : 60 bis 60 : 40 beträgt, weiter bevorzugt 45 : 55 bis 55 : 45 beträgt.A further aspect of the present invention relates to a use of a compound of the formula (I)

wherein the compound of formula (I) is in a crystalline form having an absorption band at 3401 ± 20 cm ^-1 in the IR spectrum,
for improving the water resistance (especially at 40 ° C and 90% RH) of a printed image of a thermosensitive recording material, wherein a compound of formula (II)

as a color developer, wherein the mass ratio between the compound of the formula (I) and the compound of the formula (II) is 0.5: 99.5 to 99.5: 0.5, preferably 35: 65 to 65: 35 , more preferably 40: 60 to 60: 40, more preferably 45: 55 to 55: 45.

1. i. Bereitstellen oder Herstellen eines Trägersubstrates;
2. ii. Bereitstellen oder Herstellen einer Beschichtungszusammensetzung, umfassend eine Verbindung der Formel (I) wie in einem erfindungsgemäßen wärmeempfindlichen Aufzeichnungsmaterial eingesetzt und eine Verbindung der Formel (II) wie in einem erfindungsgemäßen wärmeempfindlichen Aufzeichnungsmaterial eingesetzt;
3. iii. Aufbringen der bereitgestellten oder hergestellten Beschichtungszusammensetzung auf das bereitgestellte oder hergestellte Trägersubstrat;
4. iv. Trocknen der aufgebrachten Beschichtungszusammensetzung unter Ausbildung einer wärmeempfindlichen Aufzeichnungsschicht.

A further aspect of the present invention relates to a process for producing a heat-sensitive recording material, at least comprising the following process steps:

1. i. Providing or producing a carrier substrate;
2. ii. Providing or preparing a coating composition comprising a compound of the formula (I) as used in a heat-sensitive recording material of the invention and a compound of the formula (II) as used in a heat-sensitive recording material of the invention;
3. iii. Applying the provided or prepared coating composition to the provided or prepared carrier substrate;
4. iv. Drying the applied coating composition to form a heat-sensitive recording layer.

1. a) Bereitstellen oder Herstellen einer Beschichtungszusammensetzung umfassend Pigmente;
2. b) Aufbringen der bereitgestellten oder hergestellten Beschichtungszusammensetzung auf dem Trägersubstrat;
3. c) Trocknen der aufgebrachten Beschichtungszusammensetzung unter Ausbildung einer Zwischenschicht;

wobei die Verfahrensschritte a) bis c) vor dem Verfahrensschritt ii. durchgeführt werden und die Zwischenschicht zwischen dem Trägersubstrat und der wärmeempfindlichen Aufzeichnungsschicht angeordnet ist. Sofern eine Zwischenschicht ausgebildet wird, erfolgt das Aufbringen der bereitgestellten oder hergestellten Beschichtungszusammensetzung in Schritt iii. des erfindungsgemäßen Verfahrens auf die ausgebildete Zwischenschicht und nicht direkt auf das bereitgestellte oder hergestellte Trägersubstrat.According to the invention, a method additionally comprising the method steps is preferred

1. a) providing or preparing a coating composition comprising pigments;
2. b) applying the provided or prepared coating composition to the carrier substrate;
3. c) drying the applied coating composition to form an intermediate layer;

wherein the method steps a) to c) before the method step ii. and the intermediate layer is disposed between the support substrate and the heat-sensitive recording layer. If an intermediate layer is formed, the coating composition provided or prepared is applied in step iii. of the inventive method on the formed intermediate layer and not directly on the provided or prepared carrier substrate.

1. A) Bereitstellen oder Herstellen einer Beschichtungszusammensetzung;
2. B) Aufbringen der bereitgestellten oder hergestellten Beschichtungszusammensetzung auf der wärmeempfindlichen Aufzeichnungsschicht;
3. C) Trocknen der aufgebrachten Beschichtungszusammensetzung unter Ausbildung einer Schutzschicht;

wobei die Verfahrensschritte A) bis C) nach dem Verfahrensschritt iv. durchgeführt werden und die Schutzschicht auf der wärmeempfindlichen Aufzeichnungsschicht angeordnet ist.Also preferred according to the invention is a method additionally comprising the method steps

1. A) providing or preparing a coating composition;
2. B) applying the provided or prepared coating composition to the heat-sensitive recording layer;
3. C) drying the applied coating composition to form a protective layer;

wherein the method steps A) to C) after the method step iv. and the protective layer is disposed on the heat-sensitive recording layer.

FIG. 1 shows a comparison of IR spectra in the wavenumber range of about 4000 to 2000 cm ^{-1 of} the two crystalline forms of the compound of formula (I). Shown in the upper part and denoted by a) is the IR spectrum of the crystalline form used according to the invention of the compound of formula (I) with a melting point of 175 ° C. Shown in the lower part and labeled b) is the IR spectrum of the crystalline form of the compound of the formula (I) having a melting point of about 158 ° C.

FIG. 2 shows a comparison of IR spectra in the wavenumber range of about 2400 to 400 cm ^{-1 of} the two crystalline forms of the compound of formula (I). Shown in the upper part and denoted by a) is the IR spectrum of the crystalline form used according to the invention of the compound of formula (I) with a melting point of 175 ° C. Shown in the lower part and labeled b) is the IR spectrum of the crystalline form of the compound of the formula (I) having a melting point of about 158 ° C.

FIG. 3 shows a comparison of IR spectra of the two crystalline forms of the compound of formula (I). Shown in the upper part and denoted by a) is the IR spectrum of the crystalline form used according to the invention of the compound of formula (I) with a melting point of 175 ° C. Shown in the lower part and labeled b) is the IR spectrum of the crystalline form of the compound of the formula (I) having a melting point of about 158 ° C.

FIG. 4 shows a comparison of X-ray powder diffraction patterns of the two crystalline forms of the compound of formula (I). Shown in the upper part and denoted by a) is the X-ray powder diffractogram of the crystalline form of the compound of formula (I) with a melting point of about 158 ° C. Shown in the lower part and denoted by b) is the X-ray powder diffractogram of the crystalline form of the compound of the formula (I) having a melting point of 175 ° C. used according to the invention.

FIG. 5 shows the results of determination of long-term climatic resistance of heat-sensitive recording materials (at 40 ° C and 90% RH). In the diagram shown, the density is plotted as a function of time in days.

FIG. 6 shows the results of determination of long-term climatic resistance of heat-sensitive recording materials (at 60 ° C). In the diagram shown, the density is plotted as a function of time in days.

FIG. 7 shows the results of determination of the resistance of thermosensitive recording materials to lanolin. In the diagram shown, the density is plotted as a function of time in hours ("h").

FIG. 8 shows the measurement results of a measurement using liquid chromatography with mass spectrometry coupling (LC-MS) of the two crystalline forms of the compound of formula (I). Shown in the upper part and denoted by a) is the chromatogram of the crystalline form of the compound of formula (I) having a melting point of about 158 ° C shown. Shown in the lower part and denoted by b) is the chromatogram of the crystalline form of the compound of the formula (I) having a melting point of 175 ° C. used according to the invention. It can be clearly seen that both measured compounds of the formula (I) contain no impurities. The lower range shows the mass spectrum of the crystalline form of the compound of the formula (I) having a melting point of 175.degree. C. which is used according to the invention. The base peak (ion peak with the highest intensity) has a molar mass of 366.09 m / z, which corresponds to the molar mass of the compounds of formula (I) minus H ⁺ . The formation of solvates or the presence of impurities that could cause a change in the melting point can thus be ruled out. In addition, the structures of the compound of the formula (I) and of a possible, ionized fragment of the compound of the formula (I) are shown in the lower area.

FIG. 9 shows the measurement results of thermal analysis (differential thermal analysis (DTA) and thermogravimetry (TG)) of the two crystalline forms of the compound of formula (I). The lines marked with a) correspond to the crystalline form of the compound of the formula (I) having a melting point of 175.degree. C. used according to the invention. The lines marked b) correspond to the crystalline form of the compound of formula (I) with a melting point of about 158 ° C. In both crystalline forms of the compound of the formula (I), up to temperatures of above 150 ° C., no mass change can be observed in the thermogravimetric curve. Thus, the presence of solvates can be excluded, as it would be observed evaporation of the solvent under mass change. The first inflection point in the thermogravimetric curve for both compounds is about 186 ° C. In differential thermal analysis, the different melting points can be observed at 158 ° C and 174 ° C, respectively.

FIG. 10 Figure 3 shows the measurement results of differential scanning calorimetry (DSC) measurement of the two crystalline forms of the compound of formula (I). Shown in the upper part and denoted by a) is the curve of the crystalline form of the compound of formula (I) with a melting point of about 158 ° C. Shown in the lower part and denoted by b) is the curve of the crystalline form used according to the invention of the compound of formula (I) having a melting point of 175 ° C. In both crystalline forms of the compound of the formula (I) no enthalpy changes can be observed up to the respective melting point of the compound. Thus, the presence of solvates can be ruled out, since here an enthalpy change would be observed on evaporation of the solvent.

FIG. 11 Figure ¹ shows ¹ H-NMR spectra of the two crystalline forms of the compound of formula (I). Shown in the upper part and denoted by a) is the ¹ H-NMR spectrum of the crystalline form used according to the invention of the compound of formula (I) having a melting point of 175 ° C. Shown in the lower part and labeled b) is the ¹ H-NMR spectrum of the compound of formula (I) with a melting point of about 158 ° C shown. Further down in FIG. 11 In each case, an enlarged section of the aromatic region of about 10 to 6 ppm is shown. It can be clearly seen that these are the same compounds. The aliphatic signals at about 3.3 ppm and 2.5 ppm are the signals of the solvent deuterated dimethyl sulfoxide DMSO-d5 or dissolved therein monodeuterated water molecules DOH. In ¹ H NMR spectroscopy (nuclear magnetic resonance spectroscopy (NMR spectroscopy from English Nuclear Magnetic Resonance)), the absorption behavior of ¹ H nuclei is detected.

The following examples and comparative examples will further illustrate the invention:

Examples 1 to 3 and Comparative Examples 1 and 2:

On a fourdrinier paper machine, a paper web of bleached and ground hardwood and softwood pulps with a basis weight of 67 g / m ² is prepared as the carrier substrate with the addition of customary additives in conventional amounts. On the front side, an intermediate layer comprising hollow-shell pigments and calcined kaolin as pigment, styrene-butadiene latex as binder and starch as cobinder with a mass per unit area of 9 g / m ^{2 is} applied using a roller-blade coating unit and dried conventionally.

Using a coater, a heat-sensitive recording layer with a basis weight of 6.0 g / m ^{2 is} applied to the intermediate layer by means of a roller blade coating unit and dried conventionally after the application.

For the heat-sensitive recording layer, there is used a formulation comprising as a binder a mixture comprising polyvinyl alcohol and an acrylate copolymer and as a pigment calcium carbonate. Further constituents of the heat-sensitive recording layers of the individual exemplary embodiments are given in Table 1 below: Table 1 Compound of the formula (I) Compound of the formula (II) 3-N-di-n-butylamine-6-methyl-7-anilinofluoran (color former) Example 1 (according to the invention) 50 atro parts by weight 50 atro parts by weight 50 atro parts by weight Example 2 (according to the invention) 90 atro parts by weight 10 atro parts by weight 50 atro parts by weight Example 3 (according to the invention) 10 atro parts by weight 90 atro parts by weight 50 atro parts by weight Comparative Example 1 (not according to the invention) 100 atro parts by weight 0 atro parts by weight 50 atro parts by weight Comparative Example 2 (not according to the invention) 0 atro parts by weight 100 atro parts by weight 50 atro parts by weight

In papermaking, three grades are given for the dry content of paper and pulp: "atro" (absolutely dry), "lutro" (air-dry) and "otro" (oven-dry). The information is given in "% atro", "% lutro" and "% otro". Where "atro" stands for a paper or pulp with 0% water content. For "lutro" a "normal" (basically necessary for the paper) moisture content is used as the basis of the calculation. In the case of pulp and groundwood, the invoice mass generally refers to 90: 100, ie 90 parts of fabric, 10 parts of water. The state of paper or pulp after drying under defined defined conditions is referred to as "otro".

Examples 4 to 6

Examples 4 to 6 were carried out analogously to Examples 1 to 3. However, the intermediate layer is not applied with a roller blade coating unit, but a contour line is drawn with a blade as an intermediate layer.

The heat-sensitive recording layer is applied by means of curtain coating, the basis weight being from 1.5 to 6.0 g / m ² , preferably from 2 to 5.5 g / m ² . The 3-N-di-n-butylamine-6-methyl-7-anilinofluoran (color former) is added in an amount of 40-60 parts by dry weight.

Determination of the long-term climatic resistance of thermosensitive recording materials (at 40 ° C and 90% RH);

For metrological detection of the climatic resistance of a thermal print on the heat-sensitive recording materials of Examples 1, 2 and 3 and Comparative Examples 1 and 2 were respectively on the heat-sensitive recording materials to be tested black / white checkered designed Thermoprobeausdrucke with a device of the type Atlantek 400 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 preparation of the black / white checkered thermoprobing printout, after a rest period of more than 5 minutes, a determination of the print density was carried out on three areas of the black colored areas of the thermoprobing printout using a TECHKON® SpectroDens Advanced spectral densitometer densitometer. From the respective measured values of the black-colored areas, the mean value was formed in each case.

A thermoprobing print was hung in a climatic cabinet at 40 ° C and 90% relative humidity. After 1, 2, 3, 6, 10, 20 and 38 days, the thermal paper printout was taken, cooled to room temperature and again a determination of the print density by means of a densitometer TECHKON® SpectroDens Advanced - Spektral at three points of the black colored surfaces of Thermoprobeausdrucks Densitometer performed. The mean value was formed from the respective measured values of black-colored areas. After each measurement, the thermographic printout was again placed in the climatic chamber at 40 ° C and a relative humidity of 90% until the next measurement.

The measurement results thus obtained are listed in Table 2 and in FIG. 5 displayed: Table 2 print density 1d 2d 3d 6d 10d 20d 38d Example 1 [Formula (II) 90% / Formula (I) 10%] 0.92 0.88 0.87 0.86 0.84 0.82 0.74 Example 2 [Formula (II) 50% / Formula (I) 50%] 1.04 1.02 1.01 1.01 1.00 0.99 0.93 Example 3 [Formula (II) 10% / Formula (I) 90%] 1.12 1.10 1.09 1.08 1.06 0.99 0.89 Comparative Example 1 [Formula (II)] 0.88 0.84 0.83 0.81 0.79 0.76 0.68 Comparative Example 2 [Formula (I)] 1.10 1.07 1.06 1.01 0.96 0.84 0.64

The measurement results shown in Table 2 show that the printing density of Examples 1, 2 and 3 decreases less than the printing density of Comparative Examples 1 and 2. The durability of the printed image at 40 ° C and 90% r. F. is therefore higher in the examples according to the invention than in comparative examples 1 and 2. The combination of a compound of the formula (I) used according to the invention with a compound of the formula (II) thus has a synergistic effect, since the mixture of the compounds of the formula (I) and (II) have better properties than the respective compounds alone.

Inventive Examples 4 to 6 were also measured and also showed that the print density decreases less than the print density from Comparative Examples 1 and 2.

Determination of the climatic resistance of thermosensitive recording materials (at 60 ° C);

The determination was carried out analogously to the determination of the climatic resistance of heat-sensitive recording materials (at 40 ° C and 90% R.F.), but the storage was not carried out in a climatic chamber, but in a drying oven at 60 ° C.

The measurement results thus obtained are listed in Table 3 and in FIG. 6 displayed: Table 3 print density 1d 2d 3d 6d 10d 20d 38d Example 1 [Formula (II) 90% / Formula (I) 10%] 1.10 1.09 1.07 1.04 1.02 0.97 0.92 Example 2 [Formula (II) 50% / Formula (I) 50%] 1.13 1.11 1.10 1.07 1.05 1.01 0.97 Example 3 [Formula (II) 10% / Formula (I) 90%] 1.14 1.12 1.10 1.07 1.03 0.98 0.94 Comparative Example 1 [Formula (II)] 1.09 1.07 1.06 1.03 0.99 0.95 0.90 Comparative Example 2 [Formula (I)] 1.06 1.02 0.98 0.91 0.87 0.80 0.78

The measurement results shown in Table 3 show that the print density of Examples 1, 2 and 3 decreases less than the print density of Comparative Examples 1 and 2. The resistance of the printed image at 60 ° C is therefore higher in the inventive examples than in Comparative Examples 1 and 2. The combination of a compound of formula (I) with a compound of formula (II) used according to the invention thus has a synergistic effect, since the mixture of compounds of formula (I) and (II) has better properties than the respective Connections alone.

Inventive Examples 4 to 6 were also measured and also showed that the print density decreases less than the print density from Comparative Examples 1 and 2.

Determination of the resistance of thermosensitive recording materials to lanolin:

For measuring the resistance of a thermal print on the heat-sensitive recording materials of Examples 1, 2 and 3 and Comparative Examples 1 and 2 to lanolin were on each of the thermosensitive recording materials to be tested black / white checkered designed Thermoprobeausdrucke with a device of the type Atlantek 400 of 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 preparation of the black-and-white plaid thermo-printouts, after a rest period of more than 5 minutes, a determination of the print density was carried out at three points of the black-colored areas of the thermoprobographic prints using a TECHKON® SpectroDens Advanced spectral densitometer densitometer. From the respective measured values, the mean value was formed.

Subsequently, the prepared Thermoprobeausdruck the test thermosensitive recording material was coated with lanolin. After a contact time of 10 minutes, the lanolin is carefully wiped off and then stored at 23 ° C and 50% humidity. After 1, 2, 4, 24 and 96 hours, the thermal paper printout was taken and again a determination of the print density by means of a densitometer TECHKON® SpectroDens Advanced - Spectral Densitometer was carried out on three sites each of the black colored areas of the thermoprobeable prints. After each measurement, the thermographic sample was again placed in the climatic chamber at 23 ° C and a relative humidity of 50% until the next measurement.

From the respective measured values, the mean value was formed.

The measurement results obtained are listed in Table 4 and in FIG. 7 displayed: Table 4 print density 1h 2h 4h 24 hours 96h Example 1 [Formula (II) 90% / Formula (I) 10%] 0.82 0.82 0.79 0.74 0.72 Example 2 [Formula (II) 50% / Formula (I) 50%] 0.85 0.83 0.83 0.78 0.75 Example 3 [Formula (II) 10% / Formula (I) 90%] 0.78 0.76 0.74 0.38 0.18 Comparative Example 1 [Formula (II)] 0.79 0.79 0.77 0.72 0.68 Comparative Example 2 [Formula (I)] 0.72 0.62 0.54 0.19 0.13

The measurement results shown in Table 4 show that the print density of Examples 1 and 3 decreases less than the print density of Comparative Examples 1 and 2. The resistance of the printed image of Examples 1 and 3 to lanolin is therefore higher in the inventive examples than in the Comparative Examples 1 and 2. In Example 2, the printing density decreases less than in Comparative Example 1. The The combination of a compound of the formula (I) with a compound of the formula (II) used according to the invention thus has a synergistic effect, since the mixture of the compounds of the formula (I) and (II) has better properties than the respective compounds alone.

Inventive Examples 4 to 6 were also measured and also showed that the print density decreases less than the print density from Comparative Examples 1 and 2.

Resistance to water and aqueous ethanol solutions (23 ° C., 50% R.F., 24 h):

By means of these tests, the resistance of the image formed on the recording layer to water and aqueous solutions is evaluated. Apply a drop of distilled water or the selected aqueous 25% ethanol solution to the printed areas produced with the ATLANTEK Model 400 Thermal Intensity Media Level 10 Printer. The excess test liquid is dabbed after 20 minutes exposure time with a filter paper or cotton cloth and the test sheet then stored for 24 hours at room temperature (23 ° C, 50% relative humidity). Before applying the respective test liquid and after expiry of the storage period, the TECHKON® SpectroDens Advanced spectral densitometer determines the optical density of the printed areas and their difference.

The resistance to water or aqueous ethanol solutions corresponds to the quotient of the average value of the print density formed before and after the treatment with the respective test liquid multiplied by 100.

The measurement results obtained in this way are listed in Table 5 below: Tables 5: Results of Resistance Testing against Water and Aqueous Ethanol Solutions (Part 1) (Cf. for Comparative Example) Example Nr .: 1 2 3 See 1 See 2 Water resistance (23 ° C, 50% RH, 24h): resistance 80.2 81.7 84.7 80.2 80.2 Resistance to 25% aqueous ethanol solution (23 ° C., 50% rh 24 h): resistance 86.3 87.0 89.9 89.7 87.0

The reproduced measurement results show that the resistance of the printed image to water and aqueous ethanol solution in Inventive Examples 1 to 3 did not deteriorate as compared with Comparative Examples 1 and 2.

Inventive Examples 4 to 6 were also measured and also showed no deterioration in resistance to water and aqueous ethanol solution.

Preparation of the crystalline form of the compound of the formula (I) used according to the invention:

The commercially available or in WO 2014/080615 A1 described compound of formula (I) having a melting point of about 158 ° C is recrystallized from ethanol. The compound of the formula (I) used according to the invention having a melting point of about 175.degree. C. is obtained. The compound of the formula (I) used according to the invention has an absorption band at 3401 ± 20 cm -1 in the IR spectrum.

The compound of the formula (I) obtained by recrystallization from ethanol is characterized as solvent with the aid of ¹ H-NMR spectroscopy in DMSO-D6. The ¹ H-NMR spectrum of the compound of the formula (I) prepared by recrystallization does not differ from the ¹ H-NMR spectrum of the starting compound. This is not to be expected either, since no solids are present after the dissolution of the crystalline forms in DMSO-D6. However, it can be ruled out that during the recrystallization an unexpected chemical reaction took place, for example with ethanol, or that solvates were formed. Solvates with ethanol would be affected by the presence of additional signals in ¹ H NMR (triplet at about 1.06 ppm (CH ₃ ), quartet at about 3.44 ppm (CH ₂ ) and an OH signal at about 3 , 39 ppm), which is not the case here.

In the thermogravimetric analysis (TGA) of the compound of the formula (I) obtained by recrystallization from ethanol shows no change in mass in the temperature range between 25 and 150 ° C when heating the sample. In the case of contaminants with volatile compounds, such as ethanol, a mass change of the sample at the boiling point of the volatile compound would be observable, as the volatile compound boils and thus escapes from the sample and thus leads to a mass decrease. This is not the case here. The results of the thermogravimetric analysis are in FIG. 9 displayed.

Even in measurements with the aid of differential scanning calorimetry (DSC), no exothermic or endothermic processes or phase changes can be observed in the compound of the formula (I) obtained by recrystallization from ethanol up to a temperature of more than 170 ° C. The first phase change on heating corresponds to the melting point of the compound prepared at 175 ° C. In the presence of solvates, corresponding phase changes would be observed in differential scanning calorimetry, for example, when the boiling point of the solvating compound is reached. The presence of solvates can therefore be ruled out in the present case. The results of differential scanning calorimetry are in FIG. 10 displayed.

Both a sample of the starting compound and a sample of the crystalline form of the compound of formula (I) prepared by recrystallization from ethanol were analyzed by liquid chromatography with mass spectrometry coupling (LC-MS). During the investigation, no impurities could be detected in both samples and both compounds had the identical molar mass, with identical isotope distribution. The results of liquid chromatography with mass spectrometry coupling are in FIG. 8 displayed.

The investigations show that it is possible to use the commercially available or in WO 2014/080615 A1 described compound of formula (I) having a melting point of about 158 ° C by recrystallization from ethanol in the compound of formula (I) used according to the invention with a melting point of about 175 ° C. In the compound of formula (I) can be detected by these experiments polymorphism, ie, it is a substance that can occur in various forms (modifications). These have the same chemical composition (stoichiometry), but differ in the spatial arrangement of the molecules and have different physical properties. It can be excluded by these investigations that an undesired chemical reaction of the compound took place or that solvates were present after the recrystallization.

In addition to the recrystallization from ethanol, it is also possible to use other solvents in order to obtain a compound of the formula (I) used according to the invention.

Claims (14)

1. Heat-sensitive recording material comprising

   i) a supporting substrate and

   ii) a heat-sensitive recording layer,

   where the heat-sensitive recording layer comprises a colour former and a colour developer mixture, and the colour developer mixture comprises

   a) a compound of the formula (I)

   

   where the compound of the formula (I) is in a crystalline form having an absorption band at 3401 ± 20 cm^-1 in the IR spectrum,
   and

   b) a compound of the formula (II)

   
2. Heat-sensitive recording material according to Claim 1, where the mass ratio between the compound of the formula (I) and the compound of the formula (II) is 0.5:99.5 to 99.5:0.5, preferably 35:65 to 65:35, further preferably 40:60 to 60:40, more preferably 45:55 to 55:45.
3. Heat-sensitive recording material according to either of the preceding claims, where the supporting substrate is a paper, synthetic paper or a polymeric film.
4. Heat-sensitive recording material according to any of the preceding claims, where the fraction of the colour developer mixture in the heat-sensitive recording layer is 35 to 15 wt%, preferably 31 to 19 wt%, more preferably 28 to 22 wt%, based on the total solids fraction of the heat-sensitive recording layer.
5. Heat-sensitive recording material according to any of the preceding claims, where the mass of the heat-sensitive recording layer per unit area is in the range from 1.5 to 6 g/m², preferably in the range from 2.0 to 5.5 g/m².
6. Heat-sensitive recording material according to any of the preceding claims, further comprising an interlayer located between the supporting substrate and the heat-sensitive recording layer, where the interlayer preferably comprises pigments.
7. Heat-sensitive recording material according to Claim 6, where the pigments are

   a) organic pigments, preferably organic hollow-body pigments,
   and/or

   b) inorganic pigments, preferably selected from the list consisting of calcined kaolin, silicon oxide, bentonite, calcium carbonate, aluminium oxide and boehmite.
8. Heat-sensitive recording material according to any of the preceding claims, where the heat-sensitive recording layer is wholly or partly covered by a protective layer.
9. Heat-sensitive recording material according to any of the preceding claims, where the colour former is selected from derivatives of compounds from the group consisting of fluoran, phthalide, lactam, triphenylmethane, phenothiazine and spiropyran.
10. Heat-sensitive recording material according to any of the preceding claims, where the heat-sensitive recording layer comprises a binder, preferably a crosslinked or uncrosslinked binder selected from the group consisting of polyvinyl alcohol, carboxyl-modified polyvinyl alcohol, ethylene-vinyl alcohol copolymer, a combination of polyvinyl alcohol and ethylene-vinyl alcohol copolymer, polyvinyl alcohol modified with silanol groups, diacetone-modified polyvinyl alcohol, acrylate copolymer and film-forming acrylic copolymers.
11. Heat-sensitive recording material according to any of the preceding claims, where the heat-sensitive recording layer comprises a sensitizer, preferably a sensitizer having a melting point of 60°C to 180°C, more preferably having a melting point of 80°C to 140°C, more preferably a sensitizer selected from the group consisting of benzyl p-benzyloxybenzoate, stearamide, N-methylolstearamide, p-benzylbiphenyl, 1,2-di(phenoxy)ethane, 1,2-di(m-methylphenoxy)ethane, m-terphenyl, dibenzyl oxalate, benzyl naphthyl ether and diphenyl sulfone, more preferably benzyl naphthyl ether, diphenyl sulfone, 1,2-di(m-methylphenoxy)ethane and 1,2-di-(phenoxy)ethane.
12. Use of a heat-sensitive recording material according to any of Claims 1 to 11 as entrance tickets, flight, rail, ship or bus ticket, gambling ticket, pay and display ticket, label, till receipt, bank statements, sticker, medical diagram paper, fax paper, security paper or barcode labels.
13. Use of a compound of the formula (I) as defined in Claim 1 for improving the water resistance of a printed image on a heat-sensitive recording material comprising a compound of the formula (II) as defined in Claim 1 as a colour developer, where the compound of the formula (I) is in a crystalline form having an absorption band at 3401 ± 20 cm^-1 in the IR spectrum and where the mass ratio between the compound of the formula (I) and the compound of the formula (II) is 0.5:99.5 to 35:65, preferably 5:95 to 30:70, more preferably 15:85 to 25:75.
14. Method for producing a heat-sensitive recording material, at least comprising the following steps:

    i. providing or producing a supporting substrate;

    ii. providing or producing a coating composition comprising a compound of the formula (I) as defined in Claim 1, where the compound of the formula (I) is in a crystalline form having an absorption band at 3401 ± 20 cm^-1 in the IR spectrum, and a compound of the formula (II) as defined in Claim 1;

    iii. applying the coating composition provided or produced;

    iv. drying the applied coating composition to form a heat-sensitive recording layer.

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