Developer-Free Heat-Sensitive Recording Material

Abstract

A heat-sensitive recording material having a carrier substrate and a fusible layer disposed on one side of the carrier substrate. The fusible layer comprises an amide wax having a melting point in the range from 60° C. to 180° C., an inorganic pigment, and a polymeric binder.

Claims

1. A heat-sensitive recording material comprising: a) a carrier substrate; and b) a fusible layer disposed on one side of the carrier substrate, wherein the fusible layer comprises: i) an amide wax having a melting point in a range from 60° C. to 180° C., wherein the amide wax is present in a total amount in a range from ≥40 to ≤78 percent by mass, based on a dry mass of the fusible layer; ii) an inorganic pigment; and iii) one or more polymeric binder, wherein the fusible layer comprises substantially no developers or leuco compounds.

2. The heat-sensitive recording material according to claim 1, wherein a quantitative ratio between the amide wax and the inorganic pigment has a value in the range of at least one of: from 2:8 to 9:1, from 2.5:7.5 to 7.5:2.5, from 0.3:0.7 to 0.7:0.3, and from 6.5±0.3:3.5±0.3.

3. The heat-sensitive recording material according to claim 1, wherein the amide wax is present in a total amount in a range of at least one of: from ≥44 to ≤73 percent by mass, based on the dry mass of the fusible layer and in a range from 50 to 67 percent by mass, based on the dry mass of the fusible layer.

4. The heat-sensitive recording material according to claim 1, wherein the one or more polymeric binder is present in a total amount in a range from at least one of: ≥1 to ≤30 percent by mass, based on the dry mass of the fusible layer, ≥2 to ≤20 percent by mass, based on the dry mass of the fusible layer, and ≥4 to ≤16.5 percent by mass, based on the dry mass of the fusible layer.

5. The heat-sensitive recording material according to claim 1, wherein the inorganic pigment is present in a total amount in a range of at least one of: from ≥18 to ≤50 percent by mass, based on the dry mass of the fusible layer, from ≥22 to ≤45 percent by mass, based on the dry mass of the fusible layer, and from ≥25 to ≤39 percent by mass, based on the dry mass of the fusible layer.

6. The heat-sensitive recording material according to claim 1, wherein the amide wax is a monoamide of a saturated fatty acid, a fatty acid residue of which has a total number of carbon atoms in a range of at least one of: from ≥14 to ≤20, and from ≥16 to ≤18.

7. The heat-sensitive recording material according to claim 1, wherein the amide wax is stearamide (octadecanamide, CAS No. 124-26-5).

8. The heat-sensitive recording material according to claim 1, wherein an area-based dry mass of the fusible layer is in the range of at least one of: from ≥2 g/m.sup.2 to ≤15 g/m.sup.2, from ≥3.0 g/m.sup.2 to ≤12 g/m.sup.2, and from ≥4.0 g/m.sup.2 to ≤10 g/m.sup.2.

9. The heat-sensitive recording material according to claim 1, wherein the inorganic pigment is selected from the group consisting of calcined kaolin, natural kaolin, kaolinite, magnesium silicate hydrate, silicon dioxide, bentonite, calcium carbonate, calcium silicate hydrate, calcium aluminate sulfate, aluminum hydroxide, aluminum oxide, and boehmite.

10. The heat-sensitive recording material according to claim 1, wherein the inorganic pigment is at least one of calcium silicate and calcium silicate hydrate.

11. The heat-sensitive recording material according to any claim 1, wherein the inorganic pigment has a particle diameter in a range of at least one of: from 0.8 to 2.0 μm, from 1.0 to 1.8 μm, and from 1.2 to 1.6 μm.

12. The heat-sensitive recording material according to claim 1, wherein the one or more polymeric binder is selected from the group consisting of starch and polyvinyl alcohol.

13. A coating composition for production of a fusible layer of a heat-sensitive recording material, comprising: i) an amide wax having a melting point in a range from 60° C. to 180° C., wherein the amide wax is present in a total amount in a range from ≥40 to ≤78 percent by mass, based on a dry mass of the fusible layer; ii) an inorganic pigment; and iii) one or more polymeric binder, wherein the fusible layer comprises substantially no developers or leuco compounds, and wherein the amide wax is present in a total amount in a range from ≥40 to ≤78 percent by mass, based on a dry mass of the coating composition.

14. A process for producing a heat-sensitive recording material, comprising: a. providing or producing a carrier substrate; b. providing or producing a coating composition for production of a fusible layer, wherein the coating composition comprises: i) an amide wax having a melting point in the range from 60° C. to 180° C., wherein the amide wax is present in a total amount in a range from ≥40 to ≤78 percent by mass, based on a dry mass of the coating composition; ii) an inorganic pigment; and iii) a polymeric binder, wherein the coating composition comprises substantially no (color) developers or leuco compounds; c. applying the coating composition provided or produced to one side of the carrier substrate; and d. drying the coating composition applied in step c to form the fusible layer.

15. The heat-sensitive recording material according to claim 1, wherein the heat-sensitive recording material is configured as one of a temperature indicator, an entrance ticket, a documentary evidence, a self-adhesive label, a ticket, a TITO (ticket-in, ticket-out) ticket, an air ticket, a rail ticket, a ship ticket, a bus ticket, a parking ticket, a label, a gambling slip, a till receipt, a bank statement, a medical diagram, a technical diagram, fax paper, or security paper.

16. The heat-sensitive recording material according to claim 1, wherein the developers are color developers.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0160] Further embodiments will be apparent with reference to the working examples elucidated in detail referring to the figures, and the example. The figures show:

[0161] FIGS. 1 to 8 schematically are layer structures of heat-sensitive recording materials of aspects of the invention;

[0162] FIG. 9a-9c are of specimens of three different samples in the tape test (plasticizer resistance) (24 hours, 50% r.h. 23° C. and 20 days under ambient conditions).

[0163] FIG. 10a-10c are specimens of three different samples in the storage test at 60° C. (24 hours);

[0164] FIG. 11a-11c are specimens of three different samples in the storage test at 90° C. (1 hour);

[0165] FIG. 12 is a rendering of the dynamic print density of the recording materials from example 17 and comparative examples 7 and 8 as a diagram;

[0166] FIG. 13 is a rendering of the dynamic sensitivity of the recording materials from example 17 and comparative examples 7 and 8 as a diagram; and

[0167] FIG. 14 is a photograph of a recording material of the invention irradiated with black light (UV light).

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

[0168] FIG. 1 shows a heat-sensitive recording material (1) that comprises a carrier substrate (2) and a fusible layer (3) disposed on one side of the carrier substrate. The carrier substrate consists of a carbon black-colored paper, while the fusible layer comprises i) stearamide as amide wax, ii) calcium silicate hydrate as inorganic pigment, and iii) a PVA as polymeric binder. Alternatively, the carrier substrate may also be a film, a transparent film, or a white paper.

[0169] FIG. 2 shows a heat-sensitive recording material (1) that comprises a carrier substrate (2), a colored interlayer (4) disposed on one side of the carrier substrate, and a fusible layer (3) disposed atop the colored interlayer (4). The carrier substrate (2) consists of paper. Atop the carrier substrate (2) is disposed a colored interlayer which PVA as binder, carbon black as dye, and kaolin as inorganic pigment. The fusible layer (3) disposed atop the colored interlayer comprises i) stearamide as amide wax, ii) calcium silicate hydrate as inorganic pigment, and iii) a PVA as polymeric binder. Alternatively, the carrier substrate may also be a film be a transparent film.

[0170] FIG. 3 shows a heat-sensitive recording material (1) according to FIG. 1 in which a protective layer (5) is disposed atop the fusible layer (3).

[0171] FIG. 4 shows a heat-sensitive recording material (1) according to FIG. 2 in which a protective layer (5) is disposed atop the fusible layer (3).

[0172] FIG. 5 shows a heat-sensitive recording material (1) according to FIG. 3 in which the colored interlayer (4) has not been applied completely atop the carrier substrate (2), and a printed image (text here) is formed thereby. This is a print (8). Heating the fusible layer (3) to a particular temperature makes it transparent, and the printed image becomes visible from the outside. In the regions in which the colored interlayer (4) is not disclosed atop the carrier substrate (2), the fusible layer may lie directly atop the carrier substrate (2) (not depicted here). An adhesive layer (9), not depicted here, may optionally be disposed on the reverse side of the carrier substrate (2). In one embodiment, the recording material depicted in FIG. 6 is a temperature indicator which—if an adhesive layer (9) is present—can be stuck to surfaces.

[0173] FIG. 6 shows a heat-sensitive recording material (1) that comprises a carrier substrate (2) and a fusible layer (3) disposed on one side of the carrier substrate. The carrier substrate consists of a transparent film, while the fusible layer comprises i) stearamide as amide wax, ii) calcium silicate hydrate as inorganic pigment, and ii) a PVA as polymeric binder. A print (8) is disposed on the reverse side of the carrier substrate. The print (8) (text here) is preferably printed here as a mirror image. After the fusible layer 3 has been heated, it becomes transparent, and the printed image becomes visible from above on account of the transparent film. It is optionally possible to dispose an adhesive layer (9), not depicted here, atop the print (8). In one embodiment, the recording material depicted in FIG. 6 is a temperature indicator which—if an adhesive layer (9) is present—can be stuck to surfaces.

[0174] FIG. 7 shows a heat-sensitive recording material (1) according to FIG. 2 in which an adhesive layer (9) is disposed on the reverse side of the carrier material.

[0175] FIG. 8 shows a heat-sensitive recording material (1) according to FIG. 4 in which an adhesive layer (9) is disposed on the reverse side of the carrier material, and a release layer (7) atop the protective layer (5).

[0176] FIG. 9 shows reproductions of the in during the determination of plasticizer resistance (tape test) of example 17 (FIG. 9a) and comparative example 7 (FIG. 9b) and comparative example 8 (FIG. 9c). In the test, samples are printed, a strip of transparent adhesive tape is applied, and the samples are left to stand at 50% r.h. and 23° C. for 24 hours and under ambient conditions for a further 20 days. It can be inferred from the figures that, in the recording material of the invention (FIG. 9a), there is no discoloration of the unprinted portion (light-colored regions). The strip of adhesive tape that has been stuck on is barely apparent. In the recording materials from comparative examples 7 and 8, it is apparent that the constituents of the adhesive tape (plasticizer) lead to discoloration of the unprinted regions. It is currently unknown which components in the recording materials lead to discoloration, but it is assumed that the sensitizers used in these samples react with the plasticizers in the adhesive tape and cause darkening.

[0177] FIG. 10 shows reproductions of the in during the determination of the thermal stability of example 17 (figure l0a) and comparative example 7 (FIG. 10b) and comparative example 8 (FIG. 10c). In the test, samples are printed, and stored at 60° C. for 24 hours. It is apparent that the samples from comparative examples 7 (FIG. 10b) and comparative example 8 (FIG. 10c) are much darker than the inventive sample from example 17 (figure l0a).

[0178] FIG. 11 shows reproductions of the in during the determination of the thermal stability of example 17 (FIG. 11a) and comparative example 7 (FIG. 11b) and comparative example 8 (FIG. 11c). In the test, samples are printed, and stored at 90° C. for 21 hours. It is apparent that the samples from comparative examples 7 (FIG. 11b) and comparative example 8 (FIG. 11c) are much darker than the inventive sample from example 17 (FIG. 11a).

[0179] FIG. 12 shows the rendering of the dynamic print density of the recording materials from example 17 and comparative examples 7 and 8 as a diagram.

[0180] FIG. 13 shows the rendering of the dynamic sensitivity of the recording materials from example 17 and comparative examples 7 and 8 as a diagram.

[0181] FIG. 14 shows a photograph of a recording material of the invention that is irradiated with black light (UV light). The recording material was produced in that a conventionally obtainable white writing paper was coated with a fusible layer described in example 17. This was followed by a test print in a conventional thermal printer. The printed recording material obtained was then exposed to black light. The writing paper used as carrier substrate shows high fluorescence visible only in the printed areas. In the absence of black light, the printed area is invisible or can be seen only with great difficulty.

EXAMPLES

[0182] The examples that follow are intended to describe and elucidate aspects of the invention in detail without restricting its scope.

[0183] In papermaking and in the examples that follow, three grades are used to distinguish the dry content of paper and chemical pulp: “atro” (absolutely dry), “lutro” (air-dry) and “otro” (oven-dry). The respective figure is given in “% atro”, “% lutro” and “% otro”. “atro” here means a paper or chemical pulp with a water content of 0%. For “lutro”, a “normal” moisture content (fundamentally necessary for the paper) is used as basis for the calculation. In the case of chemical pulp and groundwood, the mass used for calculation generally relates to 90:100, i.e. 90 parts pulp, 10 parts water. The condition of paper or chemical pulp after drying under fixed defined conditions is referred to as “otro”.

[0184] Examples 1 to 3 and comparative examples 1 and 2: Production of a recording material and variation of the ratio between amide wax and inorganic pigment:

[0185] A Fourdrinier paper machine is used to produce, as carrier substrate, a paper web from bleached and ground hardwood and conifer pulps with a mass per unit area of 42 g/m.sup.2, with addition of customary admixtures in customary amounts and carbon black. The paper substrate produced was deep black.

[0186] For production of a coating composition required for the production of the fusible layer, two suspensions, a wax suspension, and a pigment suspension, are first prepared and then mixed with the ratios specified in table 3. The constituents of the suspensions are specified in the following tables 1 and 2:

TABLE-US-00001 TABLE 1 Composition of the pigment dispersion Pigment dispersion: Constituent Otro amount [%] Lutro [g] water —  53.55 calcium silicate  85 117.10 hydrate PVA  15  79.35 Total 100 250  

TABLE-US-00002 TABLE 2 Composition of the wax dispersion Wax dispersion: Constituent Otro amount [%] Lutro [g] water —  0.33 stearamide  85 170.32.10 PVA  15  79.35 Total 100 250.00

TABLE-US-00003 TABLE 3 Composition of the coating composition Production of the coating composition from the two suspensions prepared Proportion Proportion of pigment of wax Examples suspensions suspensions Comp. 100% — example 1 (3.5) Example 1 (4.7)  70%  30% Example 2 (5.8)  50%  50% Example 3 (6.9)  30%  70% Comp. — 100% example 2 (4.6)

[0187] Using a coating machine, a coating composition for production of a fusible layer having a mass per unit area of 5.0 g/m.sup.2 is applied to the felt side of the paper web (paper substrate) produced by a roll coater system, and dried conventionally after application.

[0188] The maximum dynamic print density of each of the heat-sensitive recording materials specified in table 4 below was ascertained by creating black/white-checkered thermal sample printouts with a GeBE printer, by printing the heat-sensitive recording materials (cf. table 4) with an energy in the range from 3 to 16 mJ/mm.sup.2. Each thermal sample printout was then examined with a TECHKON® SpectroDens Advanced spectral densitometer. The measurement results obtained with the aid of a densitometer (as print density figures in ODU) are given in table 4 below versus the corresponding energy inputs.

TABLE-US-00004 TABLE 4 Dynamic sensitivity (print density) of heat-sensitive recording materials Heat-sensitive Energy input [mJ/mm.sup.2] recording material 3.22 4.62 6.07 7.49 8.88 10.32 11.74 13.17 14.57 16.00 Comp. ex. 1 — — — — — — — — — — Ex. 1 0.44 0.46 0.50 0.50 0.48 0.49 0.48 0.47 0.45 0.44 Ex. 2 0.52 0.67 0.79 0.89 0.90 0.88 0.84 0.81 0.78 0.75 Ex. 3 0.72 0.87 1.11 1.35 1.51 1.55 1.62 1.58 1.55 1.53 Comp. ex. 2 0.76 0.91 1.10 1.35 1.54 1.68 1.75 1.76 1.75 1.73

[0189] The heat-sensitive recording materials according to comparative example 1 were not printable. It is apparent from the data reported in table 4 above that the heat-sensitive recording materials of the invention (examples 1 to 3) have good dynamic sensitivity. Recording materials according to comparative example 2 likewise showed good dynamic sensitivity, but there were significant deposits on the thermal print head, and so this recording material cannot be used.

Examples 4 to 9 and Comparative Examples 3 to 6: Production of a Recording Material

[0190] The previous example was repeated, except that the mass per unit area of the fusible layer was altered to 3.0 or 7.0 g/m.sup.2. The ratios between wax suspension and a pigment suspension were retained and are respectively identical in examples 1, 4 and 7, and 2, 5 and 8, and 3, 6 and 9, and in comp. ex. 1, comp. ex. 3 and comp. ex. 5, and ex. 2, comp. ex. 4 and comp. ex. 6.

[0191] The results of the determination of dynamic sensitivity are reproduced in the following tables, tables 5 and 6:

TABLE-US-00005 TABLE 5 Dynamic sensitivity (print density) of heat-sensitive recording materials having a mass per unit area of 3.0 g/m.sup.2 Heat-sensitive Energy input [mJ/mm.sup.2] recording material 3.22 4.62 6.07 7.49 8.88 10.32 11.74 13.17 14.57 16.00 Comp. ex. 3 — — — — — — — — — — Ex. 4 0.87 0.91 0.92 0.90 0.92 0.90 0.88 0.86 0.88 0.88 Ex. 5 0.94 1.01 1.06 1.09 1.08 1.04 1.05 1.00 1.01 0.99 Ex. 6 0.71 0.85 1.05 1.26 1.44 1.53 1.56 1.55 1.54 1.50 Comp. ex. 4 1.04 1.21 1.34 1.47 1.58 1.65 1.65 1.65 1.63 1.65

TABLE-US-00006 TABLE 6 Dynamic sensitivity (print density) of heat-sensitive recording materials having a mass per unit area of 7.0 g/m.sup.2. Heat-sensitive Energy input [mJ/mm.sup.2] recording material 3.22 4.62 6.07 7.49 8.88 10.32 11.74 13.17 14.57 16.00 Comp. ex. 5 — — — — — — — — — — Ex. 7 0.26 0.29 0.31 0.31 0.33 0.34 0.33 0.33 0.31 0.32 Ex. 8 0.35 0.42 0.55 0.69 0.76 0.82 0.86 0.81 0.74 0.74 Ex. 9 0.60 0.65 0.75 0.96 1.25 1.52 1.69 1.72 1.73 1.73 Comp. ex. 6 0.61 0.66 0.72 0.74 0.84 1.20 1.43 1.55 1.67 1.64

[0192] The heat-sensitive recording materials according to comparative examples 3 and 5 were not printable. It is apparent from the data given above in tables 5 and 6 that the heat-sensitive recording materials of the invention (examples 4 to 9) have good dynamic sensitivity. The best results were obtained at a ratio between wax amide and inorganic pigment of 7:3 with a mass based on unit area of the fusible layer of 7 g/m.sup.2. In comparative examples 4 and 6 too, there were significant deposits on the thermal print head, and so this recording material cannot be used.

[0193] In example 9, for example, it was possible to obtain an excellent contrast of 1.13.

[0194] All inventive examples showed high brightness, and this improved with rising pigment content.

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

[0195] Example 9 was repeated, except that the binder content was varied. The ratio between pigment and amide wax was kept constant at 3:7.

TABLE-US-00007 TABLE 7 Proportion of binder of the coating composition Proportion of binder Examples (PVA) Example 10  4% Example 11  8% Example 12 12% Example 13 16% Example 14 20% Example 15 24% Example 16 28%

[0196] The maximum dynamic print density of the resulting recording materials was determined as in the previous examples.

TABLE-US-00008 TABLE 8 Dynamic print density of examples 10 to 16 4.62 6.07 7.49 8.88 10.32 11.74 13.17 3.22 (mJ/ (mJ/ (mJ/ (mJ/ (mJ/ (mJ/ (mJ/ 14.57 16.00 sample (mJ/mm.sup.2) mm.sup.2) mm.sup.2) mm.sup.2) mm.sup.2) mm.sup.2) mm.sup.2) mm.sup.2) (mJ/mm.sup.2) (mJ/mm.sup.2)  4% Binder 0.42 0.50 0.67 0.87 1.11 1.38 1.49 1.56  8% Binder 0.44 0.54 0.71 0.92 1.19 1.41 1.50 1.58 1.61 12% Binder 0.60 0.67 0.78 1.00 1.25 1.48 1.59 1.66 1.73 16% Binder 0.85 0.88 0.89 0.94 1.10 1.33 1.51 1.54 1.78 1.78 20% Binder 1.09 1.13 1.24 1.41 1.54 1.78 1.81 24% Binder 1.19 1.18 1.21 1.31 1.48 1.73 1.76 28% Binder 1.21 1.27 1.41 1.53 1.82 indicates data missing or illegible when filed

[0197] Particularly good properties can be achieved with a binder content between 4% and 16%. Below 4%, it is possible to improve the brightness of the fusible layer, but there is a deterioration in the adhesion of the fusible layer on the paper substrate. In the case of a binder content exceeding 20%, the opacity of the fusible layer is lowered.

Example 17

[0198] A Fourdrinier paper machine was used to produce, as carrier substrate, a paper web from bleached and ground hardwood and conifer pulps with a mass per unit area of 42 g/m.sup.2, with addition of customary admixtures in customary amounts and carbon black. The paper substrate produced was deep black.

[0199] For production of a coating composition required for the production of the fusible layer, a composition specified with the in table 9 was produced.

TABLE-US-00009 TABLE 9 Composition of the dispersion Coating composition: Constituent Otro amount [%] water — calcium silicate  28.0 hydrate stearamide  60.0 PVA  12.0 Total 100.0

[0200] Using a coating machine, a coating composition for production of a fusible layer having a mass per unit area of 7.0 g/m.sup.2 is applied to the felt side of the paper web (paper substrate) produced by means of a roll coater system, and dried conventionally after application.

Example 18

[0201] Example 17 was reworked in multiple experiments, using amounts of the constituents within the range specified in table 9a.

TABLE-US-00010 TABLE 9a Composition of the dispersion Coating composition: Constituent Otro amount [%] water — calcium silicate 28.0 to 39.0 hydrate stearamide 50.0 to 67   PVA  4.0 to 16.0 Total 100.0

[0202] The recording materials produced showed good properties with regard to sensitivity, dynamic print density, contrast, plasticizer stability (tape test), and visual appearance (brightness).

Comparative Example 7

[0203] A product available on the market with hollow body pigments was used in the fusible layer.

Comparative Example 8

[0204] A further product available on the market with hollow body pigments was used in the fusible layer.

Comparison of Example 17 with Comparative Examples 7 and 8

[0205] The recording material from comparative example 7 has a green-grayish appearance on the printable side. The material from comparative example 8 has a blue-green appearance on the printable side. The inventive recording material from example 17 has a white-grayish appearance.

[0206] The maximum dynamic print density of each of the heat-sensitive recording materials specified in table 10 below was ascertained by creating black/white-checkered thermal sample printouts with a GeBE printer, by printing the heat-sensitive recording materials (cf. table 4) with an energy in the range from 3 to 16 mJ/mm.sup.2. Each thermal sample printout was then examined with a TECHKON® SpectroDens Advanced spectral densitometer. The measurement results obtained with the aid of a densitometer (as print density figures in ODU) are given in table 10 below versus the corresponding energy inputs.

TABLE-US-00011 TABLE 10 Dynamic print density from example 17 and comparative examples 7 and 8 4.62 6.07 7.49 8.88 10.32 11.74 13.17 3.22 (mJ/ (mJ/ (mJ/ (mJ/ (mJ/ (mJ/ (mJ/ 14.57 16.00 Example (mJ/mm.sup.2) mm.sup.2) mm.sup.2) mm.sup.2) mm.sup.2) mm.sup.2) mm.sup.2) mm.sup.2) (mJ/mm.sup.2) (mJ/mm.sup.2) Comp. ex. 0.49 0.57 0.75 0.95 1.07 1.22 1.29 1.32 1.35 1.35  7 Example 0.42 0.49 0.63 0.88 1.13 1.32 1.37 1.38 1.41 1.32 17 Comp. ex. 0.47 0.60 0.91 1.20 1.34 1.35 1.33 1.30 1.25 1.23  8

[0207] For a better overview, the results are depicted in the form of a graph in FIG. 13.

[0208] Determination of Thermal Stability of Heat-Sensitive Recording Materials (at 60° C. for 24 Hours):

[0209] The thermal stability of a thermal printout on each of the heat-sensitive recording materials of inventive example 17 and comparative examples 7 to 8 was measured by creating black/white-checkered thermal sample printouts on the heat-sensitive recording materials to be tested with an Atlantek 400 instrument from Printrex (USA), using a thermal head having a resolution of 300 dpi and an energy per unit area of 16 mJ/mm.sup.2.

[0210] After the creation of the black/white-checkered thermal sample printout, after a wait time of more than 5 minutes, determination of the print density by means of a Techkon SpectroDens Advanced densitometer was conducted at each of three sites in the black-colored areas and the uncolored areas of the thermal sample printout. The respective measurements of the black-colored areas and the uncolored areas were each used to form the average.

[0211] A thermal sample printout was suspended in a heated cabinet at 60° C. After 24 hours, the thermal paper printout was removed and cooled down to room temperature, and another determination of print density by a Techkon SpectroDens Advanced Densitometer was conducted at each of three sites in the black-colored areas and the uncolored areas of the thermal sample printout. The respective measurements of the black-colored areas and the uncolored areas were each used to form the average.

[0212] The stability of the printed image in % corresponds to the quotient of the average formed from the print density of the colored areas before and after storage in the climate-controlled cabinet, multiplied by 100.

[0213] The results are summarized in table 11. Reproductions of the thermal sample printouts produced are depicted in FIG. 10.

[0214] Determination of the thermal stability of heat-sensitive recording materials (at 90° C. for 1 hour):

[0215] The thermal stability of a thermal printout on each of the heat-sensitive recording materials of inventive example 17 and comparative examples 7 to 8 was measured by creating black/white-checkered thermal sample printouts on the heat-sensitive recording materials to be tested with an Atlantek 400 instrument from Printrex (USA), using a thermal head having a resolution of 300 dpi and an energy per unit area of 16 mJ/mm.sup.2.

[0216] After the creation of the black/white-checkered thermal sample printout, after a wait time of more than 5 minutes, determination of the print density by a Techkon SpectroDens Advanced Densitometer was conducted at each of three sites in the black-colored areas and the uncolored areas of the thermal sample printout. The respective measurements of the black-colored areas and the uncolored areas were each used to form the average.

[0217] A thermal sample printout was suspended in a heated cabinet at 90° C. After one hour, the thermal paper printout was removed and cooled down to room temperature, and another determination of print density by means of a Techkon SpectroDens Advanced densitometer was conducted at each of three sites in the black-colored areas and the uncolored areas of the thermal sample printout. The respective measurements of the black-colored areas and the uncolored areas were each used to form the average.

[0218] The stability of the printed image in % corresponds to the quotient of the average formed from the print density of the colored areas before and after storage in the climate-controlled cabinet, multiplied by 100.

[0219] The results are summarized in table 11. Reproductions of the thermal sample printouts produced are depicted in FIG. 11.

[0220] Determination of the Climate Stability of Heat-Sensitive Recording Materials (at 40° C. and 90% r.h. For 24 Hours):

[0221] The climatic stability of a thermal printout on each of the heat-sensitive recording materials of inventive example 17 and comparative examples 7 to 8 was measured by creating black/white-checkered thermal sample printouts on the heat-sensitive recording materials to be tested with an Atlantek 400 instrument from Printrex (USA), using a thermal head having a resolution of 300 dpi and an energy per unit area of 16 mJ/mm.sup.2.

[0222] After the creation of the black/white-checkered thermal sample printout, after a wait time of more than 5 minutes, determination of the print density by means of a Techkon SpectroDens Advanced Densitometer was conducted at each of three sites in the black-colored areas and the uncolored areas of the thermal sample printout. The respective measurements of the black-colored areas and the uncolored areas were each used to form the average.

[0223] A thermal sample printout was suspended in a climate-controlled cabinet at 40° C. and a relative humidity of 90%. After 24 hours, the thermal paper printout was removed and cooled down to room temperature, and another determination of print density by a Techkon SpectroDens Advanced Densitometer was conducted at each of three sites in the black-colored areas and the uncolored areas of the thermal sample printout. The respective measurements of the black-colored areas and the uncolored areas were each used to form the average.

[0224] The stability of the printed image in % corresponds to the quotient of the average formed from the print density of the colored areas before and after storage in the climate-controlled cabinet, multiplied by 100.

[0225] The measurement results thus obtained are in table 11:

TABLE-US-00012 TABLE 11 Parameter Comp. ex. 7 Ex. 17 Comp. ex. 8    ity (60° C., 24 h) before image Dd 1.34 1.37 1.23 background Dd 0.47 0.40 0.45 contrast Dd 0.87 0.97 0.78 after image Dd 1.34 1.36 1.23 background Dd 0.46 0.39 0.44 contrast Dd 0.88 0.98 0.79 Stability image % 100.2 99.5 100.0 contrast % 101.5 100.3 101.3 Heat stability (90° C., 1 h) before image Dd 1.36 1.37 1.24 background Dd 0.47 0.40 0.45 contrast Dd 0.89 0.97 0.78 after image Dd 1.39 1.34 1.27 background Dd 0.89 0.35 0.63 contrast Dd 0.51 0.99 0.64 Stability image % 102.7 97.8 103.0 contrast % 56.9 102.1 81.7 Climatic stability (40° C., 90% r.h., 24 h) before image Dd 1.34 1.38 1.22 background Dd 0.47 0.40 0.45 contrast Dd 0.87 0.98 0.77 after image Dd 1.34 1.37 1.21 background Dd 0.46 0.40 0.44 contrast Dd 0.89 0.97 0.77 Stability image % 100.5 99.5 99.7 contrast % 101.9 99.3 100.4 indicates data missing or illegible when filed

[0226] Determination of Plasticizer Stability (Tape Test)

[0227] The plasticizer stability (tape test) of a thermal printout on each of the heat-sensitive recording materials of inventive example 17 and comparative examples 7 to 8 was measured by creating black/white-checkered thermal sample printouts on the heat-sensitive recording materials to be tested with an Atlantek 400 instrument from Printrex (USA), using a thermal head having a resolution of 300 dpi and an energy per unit area of 16 mJ/mm.sup.2.

[0228] After the creation of the black/white-checkered thermal sample printout, after a wait time of more than 5 minutes, determination of the print density by means of a Techkon SpectroDens Advanced Densitometer was conducted at each of three sites in the black-colored areas and the uncolored areas of the thermal sample printout. The respective measurements of the black-colored areas and the uncolored areas were each used to form the average.

[0229] A strip of standard commercial adhesive tape was stuck to part of the printed area. The thermal sample printout with the adhesive tape applied was suspended in a climate-controlled cabinet at 23° C. and a relative humidity of 50%. After 24 hours, the thermal paper printout was removed and another determination of print density by means of a Techkon SpectroDens Advanced densitometer was conducted at each of three sites in the black-colored areas and the uncolored areas of the thermal sample printout. The respective measurements of the black-colored areas and the uncolored areas were each used to form the average.

[0230] The stability of the printed image in % corresponds to the quotient of the average formed from the print density of the colored areas before and after storage in the climate-controlled cabinet, multiplied by 100.

[0231] After a further 20 days, the samples were inspected again (21 days after the printing and application of adhesive tape). It is apparent here that the specimen from comparative example 7 has very significant graying of the background (unprinted area) (cf. FIG. 9b), the specimen from comparative example 8 has moderate graying of the background (cf. FIG. 9c), and the inventive specimen from example 17 has no graying (cf. FIG. 9a). Reproductions of the thermal sample printouts produced are depicted in FIG. 9, with FIG. 9a showing the inventive recording material, FIG. 9b the recording material from comparative example 7, and FIG. 9c the recording material from comparative example 8.

[0232] The results are summarized in table 12.

TABLE-US-00013 TABLE 12 Results of the tape test after 24 hours Comp. Comp. ex. 7 Ex. 17 ex. 8 tape test (23° C., 50% r.h., 24 hours) before Dd  1.19  1.17  1.09 after Dd  1.21  1.20  1.12 Stability % 101.7  102.8  102.1 

[0233] 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.