Heat-sensitive recording material

Abstract

A heat-sensitive recording material having 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) N-[2-(3-phenylureido)phenyl]benzenesulfonamide (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) N-(4-methylphenylsulfonyl)-N-(3-(4-methylphenylsulfonyloxy)phenyl) urea (compound of the formula (II)), 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 or 99.5:0.5 to 65:35.

Claims

1. A heat-sensitive recording material, comprising: i) a supporting substrate; and ii) a heat-sensitive recording layer, comprising: a colour former; and a colour developer mixture, that comprises: a) a compound of a formula (I) ##STR00013## where the compound of the formula (I) is in a crystalline form having an absorption band at 340120 cm.sup.1 in an IR spectrum, and b) a compound of a formula (II) ##STR00014## wherein i) a mass ratio between the compound of the formula (I) and the compound of the formula (II) is at least one of: 0.5:99.5 to 35:65, 5:95 to 30:70, and 15:85 to 25:75 or ii) the mass ratio between the compound of the formula (I) and the compound of the formula (II) is at least one of: 99.5:0.5 to 65:35, 97:3 to 85:15, and 95:5 to 90:10.

2. The heat-sensitive recording material according to claim 1, wherein a fraction of the colour developer mixture in the heat-sensitive recording layer is at least one of: 35 to 15 wt %, 31 to 19 wt %, and 28 to 22 wt %, based on a total solids fraction of the heat-sensitive recording layer.

3. The heat-sensitive recording material according to claim 1, wherein a mass of the heat-sensitive recording layer per unit area is in a range from at least one of: 1.5 to 6 g/m.sup.2, and 2.0 to 5.5 g/m.sup.2.

4. The heat-sensitive recording material according to claim 1, further comprising: an interlayer located between the supporting substrate and the heat-sensitive recording layer.

5. The heat-sensitive recording material according to claim 4, wherein the interlayer comprises pigments and wherein the pigments are: a) organic pigments, and/or b) inorganic pigments.

6. The heat-sensitive recording material according to claim 1, wherein the heat-sensitive recording layer is at least in part covered by a protective layer.

7. The heat-sensitive recording material according to claim 1, wherein the heat-sensitive recording material is configured as one of a flight ticket, a rail ticket, a ship ticket, a bus ticket, a gambling ticket, a pay and display ticket, a label, a till receipt, a sticker, a medical diagram paper, fax paper, and a barcode label.

8. The heat-sensitive recording material according to claim 4, wherein the interlayer comprises pigments.

9. Heat-sensitive recording material according to claim 5, wherein the interlayer comprises pigments and wherein: the organic pigments are organic hollow-body pigments, and/or the inorganic pigments, are selected from the list consisting of calcined kaolin, silicon oxide, bentonite, calcium carbonate, aluminium oxide, and boehmite.

10. A heat-sensitive recording material comprising: i) a supporting substrate; and ii) a heat-sensitive recording layer, comprising: a colour former; and a colour developer mixture, that comprises: a) a compound of a formula (I) ##STR00015## where the compound of the formula (I) is in a crystalline form having an absorption band at 340120 cm.sup.1 in an IR spectrum, and b) a compound of a formula (II) ##STR00016## wherein the compounds of formula (I) and formula (II) improve the moisture resistance or lanolin resistance of a printed image of the heat-sensitive recording material, wherein: i) the mass ratio between the compound of the formula (I) and the compound of the formula (II) is at least one of: 0.5:99.5 to 35:65, 5:95 to 30:70, and 15:85 to 25:75 or ii) the mass ratio between the compound of the formula (I) and the compound of the formula (II) is at least one of: 99.5:0.5 to 65:35, 97:3 to 85:15, and 95:5 to 90:10.

11. A method for producing a heat-sensitive recording material, comprising: i) providing or producing a supporting substrate; ii) providing or producing a coating composition comprising a compound of a compound of the formula (I) ##STR00017## where the compound of the formula (I) is in a crystalline form having an absorption band at 340120 cm.sup.1 in an IR spectrum, and b) a compound of the formula (II) ##STR00018## iii) applying the coating composition provided or produced to the supporting substrate; and iv) drying the applied coating composition to form a heat-sensitive recording layer, wherein i) a mass ratio between the compound of the formula (I) and the compound of the formula (II) is at least one of: 0.5:99.5 to 35:65, 5:95 to 30:70, and 15:85 to 25:75 or ii) the mass ratio between the compound of the formula (I) and the compound of the formula (II) is at least one of: 99.5:0.5 to 65:35, 97:3 to 85:15, and 95:5 to 90:10.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a comparison of IR spectra in the wave number range from about 4000 to 2000 cm.sup.1 of the two crystalline forms of the compound of the formula (I);

(2) FIG. 2 shows a comparison of IR spectra in the wave number range from about 2400 to 400 cm.sup.1 of the two crystalline forms of the compound of the formula (I);

(3) FIG. 3 shows a comparison of IR spectra of the two crystalline forms of the compound of the formula (I);

(4) FIG. 4 shows a comparison of X-ray powder diffractograms of the two crystalline forms of the compound of the formula (I);

(5) FIG. 5 shows the results of the determination of the long-term climatic resistance of heat-sensitive recording materials (at 40 C. and 90% relative humidity);

(6) FIG. 6 shows the results of the determination of the resistance of heat-sensitive recording materials with respect to lanolin;

(7) FIG. 7 shows the measured results of a measurement with the assistance of liquid chromatography with mass spectrometry coupling (LC-MS) of the two crystalline forms of the compound of the formula (I);

(8) FIG. 8 shows the measured results of a thermal analysis (differential thermoanalysis (DTA) and thermogravimetry (TG)) of the two crystalline forms of the compound of the formula (I);

(9) FIG. 9 shows the measured results of a dynamic differential calorimetry measurement (DSC) of the two crystalline forms of the compound of the formula (I); and

(10) FIG. 10 shows .sup.1H-NMR spectra of the two crystalline forms of the compound of the formula (I).

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

(11) FIG. 1 shows a comparison of IR spectra in the wave number range from about 4000 to 2000 cm.sup.1 of the two crystalline forms of the compound of the formula (I). Shown in the upper part and designated by a) is the IR spectrum of the crystalline form of the compound of the formula (I) used according to the invention having a melting point of 175 C. Shown in the lower part and designated by b) is shown the IR spectrum of the crystalline form of the compound of the formula (I) having a melting point of about 158 C.

(12) FIG. 2 shows a comparison of IR spectra in the wave number range from about 2400 to 400 cm.sup.1 of the two crystalline forms of the compound of the formula (I). Shown in the upper part and designated by a) is the IR spectrum of the crystalline form of the compound of the formula (I) used according to the invention having a melting point of 175 C. Shown in the lower part and designated by b) is shown the IR spectrum of the crystalline form of the compound of the formula (I) having a melting point of about 158 C.

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

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

(15) FIG. 5 shows the results of the determination of the long-term climatic resistance of heat-sensitive recording materials (at 40 C. and 90% relative humidity). In the diagram shown, resistance of the printed image in % in dependence on the ratio of the compounds of the formulae (I) and (II) is shown.

(16) FIG. 6 shows the results of the determination of the resistance of heat-sensitive recording materials with respect to lanolin. In the diagram shown, resistance of the printed image in % in dependence on the ratio of the compounds of the formulae (I) and (II) is shown.

(17) FIG. 7 shows the measured results of a measurement with the assistance of liquid chromatography with mass spectrometry coupling (LC-MS) of the two crystalline forms of the compound of the formula (I). Shown in the upper part and designated by a) is shown the chromatogram of the crystalline form of the compound of the formula (I) having a melting point of about 158 C. Shown in the lower part and designated by b) is the chromatogram of the crystalline form of the compound of the formula (I) used according to the invention having a melting point of 175 C. It can be seen clearly that both measured compounds of the formula (I) do not contain impurities. In the lower region is shown the mass spectrum of the crystalline form of the compound of the formula (I) used according to the invention having a melting point of 175 C. 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 the formula (I) minus H.sup.+. The formation of solvates or the presence of impurity, which could effect a change in the melting point, may thus be ruled out. In addition, the structures of the compound of the formula (I) and one possible, ionized fragment of the compound of the formula (I) are shown in the lower region.

(18) FIG. 8 shows the measured results of a thermal analysis (differential thermoanalysis (DTA) and thermogravimetry (TG)) of the two crystalline forms of the compound of the formula (I). The lines characterized by a) correspond to the crystalline form of the compound of the formula (I) used according to the invention having a melting point of 175 C. The lines characterized by b) correspond to the crystalline form of the compound of the formula (I) having a melting point of about 158 C. In both crystalline forms of the compound of the formula (I), no mass change in the thermogravimetry trace can be observed up to temperatures of over 150 C. Hence, the presence of solvates may be ruled out, since here evaporation of the solvent with mass change would be observed. The first inflection point in the thermogravimetry trace is at about 186 C. for both compounds. The different melting points at 158 C. or 174 C. may be observed in the differential thermoanalysis.

(19) FIG. 9 shows the measured results of a dynamic differential calorimetry measurement (DSC) of the two crystalline forms of the compound of the formula (I). Shown in the upper part and designated by a) is the trace of the crystalline form of the compound of the formula (I) having a melting point of about 158 C. Shown in the lower part and designated by b) is the trace of the crystalline form of the compound of the formula (I) used according to the invention 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. Hence, the presence of solvates may be ruled out, since here an enthalpy change during evaporation of the solvent would be observed.

(20) FIG. 10 shows .sup.1H-NMR spectra of the two crystalline forms of the compound of the formula (I). Shown in the upper part and designated by a) is the .sup.1H-NMR spectrum of the crystalline form of the compound of the formula (I) used according to the invention having a melting point of 175 C. Shown in the lower part and designated by b) is shown the .sup.1H-NMR spectrum of the compound of the formula (I) having a melting point of about 158 C. Further below in FIG. 10, in each case an enlarged cut-out of the aromatic range from about 10 to 6 ppm is shown. It can be seen clearly that they 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 mono-deuterated water molecules DOH dissolved therein. In .sup.1H-NMR spectroscopy (nuclear magnetic resonance spectroscopy (NMR spectroscopy from the English Nuclear Magnetic Resonance)), the absorption behaviour of .sup.1H nuclei is detected.

(21) The examples and comparative examples below will further explain the invention:

Examples 1 to 15 and Comparative Examples 1 and 2

(22) A paper web of bleached and ground deciduous and coniferous pulps with a mass per unit area of 67 g/m.sup.2 with addition of conventional additives in conventional quantities is produced as supporting substrate on a fourdrinier paper machine. On the front side an interlayer comprising hollow-space pigments and calcined kaolin as pigment, styrene-butadiene latex as binder and starch as co-binder with a mass per unit area of 9 g/m.sup.2 is applied using a roller doctor-knife coating mechanism and dried conventionally.

(23) A heat-sensitive recording layer with a mass per unit area of 6.0 g/m.sup.2 is applied to the interlayer by means of roller doctor-knife coating mechanism using a coating machine and dried conventionally after the application.

(24) A formulation, which comprises as binder a mixture comprising polyvinyl alcohol, 3-N-di-n-butylamine-6-methyl-7-anilinofluoran (50 absolutely dry parts by weight) as colour former and an acrylate copolymer and as pigment calcium carbonate, is used for the heat-sensitive recording layer. Further constituents of the heat-sensitive recording layers of the individual exemplary embodiments are indicated in Table 1 below (Examples 1-15 according to the invention):

(25) TABLE-US-00001 TABLE 1 Compound of the Compound of the Formula (I) Formula (II) Comparative example 1 (not 100 absolutely dry 0 absolutely dry according to the invention) parts by weight parts by weight Comparative example 2 (not 0 absolutely dry 100 absolutely according to the invention) parts by weight dry parts by weight Example 1 99 absolutely dry 1 absolutely dry parts by weight parts by weight Example 2 97 absolutely dry 3 absolutely dry parts by weight parts by weight Example 3 95 absolutely dry 5 absolutely dry parts by weight parts by weight Example 4 93 absolutely dry 7 absolutely dry parts by weight parts by weight Example 5 90 absolutely dry 10 absolutely dry parts by weight parts by weight Example 6 80 absolutely dry 20 absolutely dry parts by weight parts by weight Example 7 70 absolutely dry 30 absolutely dry parts by weight parts by weight Example 8 60 absolutely dry 40 absolutely dry parts by weight parts by weight Example 9 50 absolutely dry 50 absolutely dry parts by weight parts by weight Example 10 40 absolutely dry 60 absolutely dry parts by weight parts by weight Example 11 30 absolutely dry 70 absolutely dry parts by weight parts by weight Example 12 20 absolutely dry 80 absolutely dry parts by weight parts by weight Example 13 10 absolutely dry 90 absolutely dry parts by weight parts by weight Example 14 5 absolutely dry 95 absolutely dry parts by weight parts by weight Example 15 3 absolutely dry 97 absolutely dry parts by weight parts by weight

(26) In paper production, three grades of dry content of paper and pulp are differentiated absolutely dry, air dry and oven dry. The detail is effected in each case in % absolutely dry, % air dry and % oven dry. Where absolutely dry represents a paper or pulp with 0% water content. A normal moisture content (basically necessary for the paper) is thus used as the basis of the calculation for air dry. For pulp and wood pulp, the calculation mass usually relates to 90:100, that is, 90 parts of the material, 10 parts of water. The state of paper or pulp after drying under fixed, defined conditions is designated as oven dry.

Examples 16 to 30

(27) Examples 16 to 30 were carried out analogously to Examples 1 to 15. However, the interlayer is not applied using a roller doctor-knife coating mechanism, but an outline coating is pulled as an interlayer using a blade.

(28) The heat-sensitive recording layer is applied by means of curtain coating mechanism, where the mass per unit area is 1.5 up to 6.0 g/m.sup.2, preferably 2 to 5.5 g/m.sup.2. The 3-N-di-n-butylamine-6-methyl-7-anilinofluoran (colour former) is added in a quantity of 40-60 absolutely dry parts by weight.

(29) Determination of the Climatic Resistance of Heat-Sensitive Recording Materials (at 40 C. and 90% Relative Humidity for 24 Hours):

(30) To record the climatic resistance of a thermal print-out in terms of measuring technology on the heat-sensitive recording materials of Examples 1 to 15 of the invention and of Comparative example 1, in each case black/white-chequered thermal sample print-outs were generated on the heat-sensitive recording materials to be tested using a device of the type Atlantek 400 from Printrex (USA), where a thermal head with a resolution of 300 dpi and an energy per surface unit of 16 mJ/mm.sup.2 was used.

(31) After generating the black/white-chequered thermal sample print-out, after a rest time of more than 5 minutes, a determination of the print density by means of a densitometer TECHKON SpectroDens Advancedspectral densitometer was carried out on in each case three points of the black-coloured surfaces and of the uncoloured surfaces of the thermal sample print-out. In each case the average value was formed from the respective measured values of the black-coloured surfaces and of the uncoloured surfaces.

(32) A thermal sample print-out was suspended in a climatic test cabinet at 40 C. and a relative humidity of 90%. After 24 hours, the thermal paper print-out was removed, cooled to room temperature and a determination of the print density by means of a densitometer TECHKON SpectroDens Advancedspectral densitometer was carried out again on in each case three points of the black-coloured surfaces and of the uncoloured surfaces of the thermal sample print-out. In each case the average value was formed from the respective measured values of black-coloured surfaces and of the uncoloured surfaces.

(33) The resistance of the printed image in % corresponds to the quotient from the average value of the print density of the coloured surfaces formed before and after the storage in the climatic test cabinet multiplied by 100.

(34) The measured results thus obtained are listed in Table 2 and shown in FIG. 5 (Examples 1-15 according to the invention):

(35) TABLE-US-00002 TABLE 2 Resistance of the Example printed image in % Example 1 97.3 Example 2 95.5 Example 3 96.4 Example 4 95.5 Example 5 95.4 Example 6 95.5 Example 7 93.6 Example 8 92.5 Example 9 89.4 Example 10 87.6 Example 11 85.3 Example 12 80.8 Example 13 75.5 Example 14 74.0 Example 15 71.9 Comparative 96.4 example 1 Comparative 70.8 example 2 (not according to the invention)

(36) The measured results reproduced in Table 2 show that the climatic resistance of heat-sensitive recording materials (at 40 C. and 90% relative humidity for 24 hours) of Examples 1 to 7 of the invention remains approximately unchanged and the climatic resistance of Examples 11 to 15 of the invention is better than the climatic resistance of Comparative example 2. Through the addition of even small amounts of the compound of the formula (I) to the compound of the formula (II) it is possible to improve significantly the climatic resistance. This improvement in climatic resistance is accomplished, surprisingly, exponentially on addition of the compound of the formula (I).

(37) Determination of the Resistance of Heat-Sensitive Recording Materials with Respect to Lanolin (10 Minutes):

(38) To record the resistance of a thermal print-out in terms of measuring technology on the heat-sensitive recording materials of the examples of the invention and of the comparative examples with respect to lanolin, in each case black/white-chequered thermal sample print-outs were generated on the heat-sensitive recording materials to be tested using a device of the type Atlantek 400 from Printrex (USA), where a thermal head with a resolution of 300 dpi and an energy per surface unit of 16 mJ/mm.sup.2 was used.

(39) After generating the black/white-chequered thermal sample print-outs, after a rest time of more than 5 minutes, a determination of the print density by means of a densitometer TECHKON SpectroDens Advancedspectral densitometer was carried out on three points of the black-coloured surfaces and of the uncoloured surfaces of the thermal sample print-outs. The average value was formed in each case from the respective measured values of the black-coloured surfaces and of the uncoloured surfaces.

(40) Subsequently, the generated thermal sample print-out of the heat-sensitive recording material to be tested was coated fully with lanolin. After an action time of 10 minutes, the lanolin is carefully wiped away and there was a determination of the print density by means of a densitometer TECHKON SpectroDens Advancedspectral densitometer again on in each case three points of the black-coloured surfaces and of the uncoloured surfaces of the thermal sample print-outs. In each case the average value was formed from the respective measured values of the black-coloured surfaces and of the uncoloured surfaces.

(41) The resistance with respect to lanolin in % corresponds to the quotient from the average value of the print density formed before the lanolin treatment and after the lanolin treatment multiplied by 100.

(42) The measured results thus obtained are listed in Table 3 and shown in FIG. 6 (Examples 1-15 according to the invention):

(43) TABLE-US-00003 TABLE 3 Resistance with respect Example to lanolin in % Example 1 14.3 Example 2 16.2 Example 3 23.3 Example 4 33.3 Example 5 45.1 Example 6 61.7 Example 7 65.8 Example 8 63.4 Example 9 64.2 Example 10 64.9 Example 11 63.0 Example 12 62.9 Example 13 61.0 Example 14 63.4 Example 15 62.7 Comparative 13.0 example 1 (not according to the invention) Comparative 62.7 example 2 (not according to the invention)

(44) The measured results reproduced in Table 3 show that the resistance of the printed image to lanoline in the case of Examples 11 to 15 of the invention does not change significantly and exhibits very good values between 61 and 63.4%. This is surprising because the expert would assume that the addition of the compound of the formula (I) would bring about an impairment in the lanoline resistance. The resistance of the printed image to lanoline in the case of Examples 1 to 7 of the invention is better than the resistance of a printed image in which the colour developer mixture has been replaced in equal parts by weight by a compound of the formula (I) (Comparative example 1). Through the addition even of small amounts of the compound of the formula (II) to the compound of the formula (I) it is possible to improve significantly the resistance to lanoline. Surprisingly, the improvement in the resistance of the printed image to lanoline is exponential in the case of recording materials of the invention.

(45) Resistance to Water and Aqueous Ethanol Solutions (23 C., 50% Relative Humidity, 24 hours):

(46) The resistance of the image generated on the recording layer to water and aqueous solutions is assessed with the aid of these tests. One drop of distilled water or the selected aqueous 25% strength ethanol solution is applied to the printed surfaces generated using the printer ATLANTEK Model 400Thermal Response Test System with the energy level Medium Stage 10. The excess test liquid is blotted after 20 minutes action time using a filter paper or cotton cloth and the test sheet is then stored for 24 hours at room climate (23 C., 50% relative moisture). Before applying the respective test liquid and after lapsing of the storage time, the optical density of the printed surfaces and the difference thereof is determined using the densitometer TECHKON SpectroDens Advancedspectral densitometer.

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

(48) The measured results thus obtained are listed in Tables 4 and 5 below:

(49) TABLE-US-00004 TABLE 4 Results of the resistance test to water and aqueous ethanol solutions (Part 1) (Comparison represents Comparative example) Example No.: 11 12 13 14 15 Comparison 1 Comparison 2 1 2 Water resistance (23 C., 50% relative humidity, 24 h): Resistance 83.5 83.5 82.8 82.7 83.3 86.8 82.4 85.7 87.2 Resistance to 25% strength aqueous ethanol solution (23 C., 50% relative humidity, 24 h): Resistance 81.7 81.1 78.8 79.6 78.4 81.7 79.2 79.7 80.3

(50) TABLE-US-00005 TABLE 5 Results of the resistance test to water and aqueous ethanol solutions (Part 2) (Comparison represents Comparative example) Example No.: 3 4 5 6 7 8 9 10 Water resistance (23 C., 50% relative humidity, 24 h): Resistance 87.2 87.7 88.6 84.3 87 90.3 83.6 83.8 Resistance to 25% strength aqueous ethanol solution (23 C., 50% relative humidity, 24 h): Resistance 82.1 82.6 84.2 85.2 84.3 85 83.6 81.1

(51) The reproduced measured results show that the resistance of the printed image with respect to water and aqueous ethanol solution in Examples 1 to 15 of the invention has not diminished compared to Comparative examples 1 and 2.

(52) Production of the Crystalline Form Used According to the Invention of the Compound with the Formula (I):

(53) The commercially available compound of the 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 C. is obtained. The compound of the formula (I) used according to the invention has an absorption band at 340120 cm1 in the IR spectrum.

(54) The compound of the formula (I) obtained by recrystallization from ethanol is characterized by means of .sup.1H-HMR spectroscopy in DMSO-D6 as solvent. The .sup.1H-HMR spectrum of the compound of the formula (I) produced by recrystallization does not differ from the .sup.1H-HMR spectrum of the starting compound. This is also not to be expected, since after resolving the crystalline forms in DMSO-D6, solids are no longer present. However, it may be ruled out by the investigation that during recrystallization an unexpected chemical reactionfor example with ethanolhas taken place or that solvates were formed. Solvates with ethanol would be able to be detected by the presence of additional signals in the .sup.1H-NMR (triplet at about 1.06 ppm (CH.sub.3), quartet at about 3.44 ppm (CH.sub.2) and an OH signal at about 3.39 ppm), which is not the case here.

(55) In the thermogravimetric analysis (TGA) of the compound of the formula (I) obtained by recrystallization from ethanol, no mass change is shown when heating the sample in the temperature range between 25 and 150 C. For impurities with volatile compounds, such as for example ethanol, a mass change of the sample would have been observable at the boiling point of the volatile compound, since the volatile compound boils and thus escapes from the sample and thus leads to a drop in mass. This is not the case here. The results of the thermogravimetric analysis are shown in FIG. 8.

(56) Even for measurements by dynamic differential calorimetry (DSC), in the compound of the formula (I) obtained by recrystallization from ethanol no exothermic or endothermic processes or phase changes may be observed up to a temperature of over 170 C. The first phase change during heating corresponds to the melting point of the compound produced at 175 C. In the presence of solvates, in dynamic differential calorimetry a corresponding phase change would have been observable, for example if the boiling point of the solvating compound is achieved. Presence of solvates may therefore be ruled out in the present case. The results of dynamic differential calorimetry are shown in FIG. 9.

(57) Both a sample of the starting compound and a sample of the crystalline form of the compound of the formula (I) produced by recrystallization from ethanol was investigated with assistance of liquid chromatography with mass spectrometry coupling (LC-MS). In the investigation, no impurities could be detected in either sample and both compounds had the identical molar mass, with identical isotope distribution. The results of liquid chromatography with mass spectrometry coupling are shown in FIG. 7.

(58) The investigations show that it is possible to convert the commercially available compound of the formula (I) or that described in WO 2014/080615 A1 having a melting point of about 158 C. into the compound of the formula (I) used according to the invention having a melting point of about 175 C. by recrystallization from ethanol. In the compound of the formula (I), polymorphy may be detected by these tests, that is, it is a substance which may occur in different modes (modifications). They have the same chemical composition (stoichiometry), but differ in the spatial arrangement of the molecules and have different physical properties. These investigations may rule out the fact that an undesirable chemical reaction of the compound has taken place or that solvates were present after recrystallization.

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

(60) Thus, while there have shown and described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.