Heat-sensitive recording material

Abstract

The invention relates to a heat-sensitive recording material. A heat-sensitive recording material, comprising a carrier substrate and a heat-sensitive, color-forming layer that contains at least one color former and at least one phenol-free color developer, is characterized in that said at least one color developer is a compound of formula (I) where Ar.sub.1 and Ar.sub.2 are a phenyl group and/or a C.sub.1-C.sub.4-alkyl substituted phenyl group. The invention also relates to a method for producing this heat-sensitive recording material and to the use, in a heat-sensitive recording material, of the color developer of formula (I) that is present in said heat-sensitive, color-forming layer. ##STR00001##

Claims

1. Heat-sensitive recording material, comprising a carrier substrate and also a heat-sensitive colour-forming layer containing at least one colour former, at least one phenol-free colour developer and at least one sensitising agent, characterised in that the at least one colour developer is a compound of the formula (I) ##STR00006## wherein Ar.sub.1 and Ar.sub.2 are a phenyl radical and/or a C.sub.1-C.sub.4alkyl-substituted phenyl radical wherein the at least one sensitising agent is 1,2-Diphenoxyethane and wherein the dried heat-sensitive colour-forming layer is subjected to a smoothing step such that the Bekk smoothness is adjusted to from 300 to 700 sec (measured according to DIN 53107).

2. Heat-sensitive recording material according to claim 1, characterised in that Ar.sub.1 and Ar.sub.2 are each a phenyl radical.

3. Heat-sensitive recording material according to claim 1, characterised in that the carrier substrate is paper, synthetic paper and/or a plastics film.

4. Heat-sensitive recording material according to claim 1, characterised in that the at least one colour former is a dye of the triphenylmethane type, of the fluoran type, of the azaphthalide type and/or of the fluorene type.

5. Heat-sensitive recording material according to claim 4, characterised in that the dye of the fluoran type is selected from the group consisting of 3-diethylamino-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-p-toludinamino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-isoamylamino)-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-(o,p-dimethylanilino)fluoran, 3-pyrrolidino-6-methyl-7-anilinofluoran, 3-(cyclohexyl-N-methylamino)-6-methyl-7-anilinofluoran, 3-diethylamine-7-(m-trifluoromethylanilino)fluoran, 3-N-n-dibutylamine-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-(m-methylanilino)fluoran, 3-N-n-dibutylamine-7-(o-chloroanilino)fluoran, 3-(N-ethyl-N-tetrahydrofurfurylamine)-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-propylamine)-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-ethoxypropylamine)-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-isobutylamine)-6-methyl-7-anilinofluoran and/or 3-dipentylamine-6-methyl-7-anilinofluoran.

6. Heat-sensitive recording material according to claim 1, further comprising, in addition to the compound of the formula (I), one or more further non-phenolic colour developers, selected from the group of sulphonylureas, consisting of N-(p-toluenesulphonyl)-N-phenylurea,N-(p-toluenesulphonyl)-N-3-(p-toluenesulphonyloxyphenyl)-urea and/or 4,4-bis-(p-tolylsulphonylureido)-diphenylmethane.

7. Heat-sensitive recording material according to claim 1, characterised in that from approximately 0.5 to approximately 10 parts by weight, of the compound of the formula (I), based on the colour former, are present.

8. Heat-sensitive recording material according to claim 1, characterised in that the compound of the formula (I) is present in an amount of from approximately 3 to approximately 35% by weight, based on the total solids content of the heat-sensitive layer.

9. Heat-sensitive recording material according to claim 1, characterised in that the heat-sensitive colour-forming layer contains additives comprising one or more of stabilisers, binders, release agents, pigments and brighteners.

10. Heat-sensitive recording material according to claim 1, characterised in that the application weight of the (dry) heat-sensitive layer is from approximately 1 to approximately 10 g/m.sup.2.

11. Heat-sensitive recording material according to claim 1, characterised in that the heat-sensitive colour-forming layer contains a urea-urethane compound of the general formula (II) ##STR00007##

12. Method of producing a heat-sensitive recording material according to claim 1, characterised in that an aqueous suspension containing the starting materials of the heat-sensitive colour-forming layer is applied to a carrier substrate and dried, wherein the aqueous application suspension has a solids content of from approximately 20% to approximately 75% by weight, and is applied using a curtain coating method and apparatus at an operating speed of the coating apparatus of at least approximately 400 m/min and dried.

13. Heat-sensitive recording material according to claim 1, characterised in that the at least one colour former is a dye of the fluoran type.

14. Heat-sensitive recording material according to claim 1 characterised in that from approximately 1.5 to approximately 4 parts by weight of the compound of the formula (I), based on the colour former, are present.

15. Heat-sensitive recording material according to claim 1 characterised in that the compound of the formula (I) is present in an amount of from approximately 10 to approximately 25% by weight based on the total solids content of the heat-sensitive layer.

16. Heat-sensitive recording material according to claim 1 characterised in that the application weight of the (dry) heat-sensitive layer is from approximately 3 to approximately 6 g/m.sup.2.

17. Method of producing a heat-sensitive recording material according to claim 1 characterised in that an aqueous suspension containing the starting materials of the heat-sensitive colour-forming layer is applied to a carrier substrate and dried, wherein the aqueous application suspension has a solids content of from approximately 30% to approximately 50% by weight, and is applied using a curtain coating method and apparatus at an operating speed of the coating apparatus of at least approximately 400 m/min and dried.

18. Method of producing a heat-sensitive recording material according to claim 1 characterised in that an aqueous suspension containing the starting materials of the heat-sensitive colour-forming layer is applied to a carrier substrate and dried, wherein the aqueous application suspension has a solids content of from approximately 20% to approximately 75% by weight, and is applied using a curtain coating method and apparatus at an operating speed of the coating apparatus of at least approximately 1000 m/min and dried.

19. Method of producing a heat-sensitive recording material according to claim 1 characterised in that an aqueous suspension containing the starting materials of the heat-sensitive colour-forming layer is applied to a carrier substrate and dried, wherein the aqueous application suspension has a solids content of from approximately 20% to approximately 75% by weight, and is applied using a curtain coating method and apparatus at an operating speed of the coating apparatus of at least approximately 1500 m/min and dried.

20. Method of producing a heat-sensitive recording material according to claim 1 characterised in that an aqueous suspension containing the starting materials of the heat-sensitive colour-forming layer is applied to a carrier substrate and dried, wherein the aqueous application suspension has a solids content of from approximately 30% to approximately 50% by weight, and is applied using a curtain coating method and apparatus at an operating speed of the coating apparatus of at least approximately 1000 m/min and dried.

Description

EXAMPLES

(1) The application of an aqueous application suspension to one side of a synthetic base paper (Yupo FP680) of 63 g/m.sup.2 to form the heat-sensitive colour-forming layer of a heat-sensitive recording paper was carried out on a laboratory scale by means of a doctor bar. After drying, a thermal recording sheet was obtained. The application rate of the heat-sensitive colour-forming layer was between 4.0-4.5 g/m.sup.2.

(2) On a production scale, the application of the aqueous application suspension to a paper web having a weight per unit area of 43 g/m.sup.2 was carried out by means of the curtain coating method. The viscosity of the aqueous application suspension was 450 mPas (according to Brookfield, 100 rev/min, 20 C.) (in the deaerated state). The surface tension thereof was 46 mN/m (statistical ring method). The coating apparatus was arranged inline. The curtain coating method was operated at a speed of 1550 m/min.

(3) After the application of the aqueous application suspension, the operation of drying the coated paper carrier was carried out in the customary way. The application weight of the dry heat-sensitive layer was 4.0-4.5 g/m.sup.2.

(4) A heat-sensitive recording material or thermal paper was produced with reference to the details given above, the following formulations of aqueous application suspensions being used to form a composite structure on the carrier substrate and then the further layers, especially a protective layer, being formed in the customary way, which will not be discussed separately here.

(5) Formulation 1

(6) An aqueous application suspension was prepared by thoroughly mixing together an aqueous dispersion of the colour former, which was produced by grinding 20 parts by weight of 3-N-n-dibutylamine-6-methyl-7-anilinofluoran (ODB-2) with 33 parts by weight of a 15% aqueous solution of Ghosenex L-3266 (sulphonated polyvinyl alcohol, Nippon Ghosei) in a bead mill, an aqueous colour developer dispersion, which was produced by grinding 40 parts by weight of the colour developer together with 66 parts by weight of a 15% aqueous solution of Ghosenex L-3266 in the bead mill, a dispersion which was produced by grinding 40 parts by weight of sensitising agent with 33 parts by weight of a 15% aqueous solution of Ghosenex L-3266 in a mill, 189 parts by weight of a 56% PCC dispersion (precipitated calcium carbonate), 50 parts by weight of an aqueous 20% zinc stearate dispersion, 138 parts by weight of a 10% aqueous polyvinyl alcohol solution (Mowiol 28-99, Kuraray Europe).

(7) The heat-sensitive coating suspensions so obtained, which can be seen in Table 1 below, were used to produce composite structures composed of paper carrier and thermal reaction layer.

(8) TABLE-US-00001 TABLE 1 Serial. No. Specimen Colour developer Sensitising agent 1 AI B-TUM diphenyl sulphone 2 AII B-TUM stearamide 3 AIII B-TUM 1,2-diphenoxyethane 4 BI TUPH diphenyl sulphone 5 BII TUPH stearamide 6 BIII TUPH 1,2-diphenoxyethane 7 CI phenylureido-phenyl- diphenyl sulphone benzenesulphonamide 8 CII phenylureido-phenyl- stearamide benzenesulphonamide 9 CIII phenylureido-phenyl- 1,2-diphenoxyethane benzenesulphonamide 10 DI PF201 diphenyl sulphone 11 DII PF201 stearamide 12 DII PF201 1,2-diphenoxyethane

(9) Formulation 2a

(10) An aqueous application suspension was prepared by thoroughly mixing together an aqueous dispersion of the colour former, which was produced by grinding 20 parts by weight of 3-N-n-dibutylamine-6-methyl-7-anilinofluoran (ODB-2) with 33 parts by weight of a 15% aqueous solution of Ghosenex L-3266 in a bead mill, an aqueous colour developer dispersion, which was produced by grinding 40 parts by weight of the colour developer together with 33 parts by weight of a 15% aqueous solution of Ghosenex L-3266 in the bead mill, a dispersion which was produced by grinding 40 parts by weight of sensitising agent with 33 parts by weight of a 15% aqueous solution of Ghosenex L-3266 in a mill, 200 parts by weight of a 56% PCC dispersion (precipitated calcium carbonate), 50 parts by weight of an aqueous 20% zinc stearate dispersion, 138 parts by weight of a 10% aqueous polyvinyl alcohol solution (Mowiol 28-99).

(11) Formulation 2b

(12) An aqueous application suspension was prepared by thoroughly mixing together an aqueous dispersion of the colour former, which was produced by grinding 20 parts by weight of 3-N-n-dibutylamine-6-methyl-7-anilinofluoran (ODB-2) with 33 parts by weight of a 15% aqueous solution of Ghosenex L-3266 L-3266 in a bead mill, an aqueous colour developer dispersion, which was produced by grinding 40 parts by weight of the colour developer together with 33 parts by weight of a 15% aqueous solution of Ghosenex L-3266 in the bead mill, a dispersion which was produced by grinding 40 parts by weight of sensitising agent with 33 parts by weight of a 15% aqueous solution of Ghosenex L-3266 in a mill, a dispersion which was produced by grinding 12.5 parts by weight of ageing protector with 10 parts by weight of a 15% aqueous solution of Ghosenex L-3266 in a mill, 174 parts by weight of a 56% PCC dispersion (precipitated calcium carbonate), 50 parts by weight of an aqueous 20% zinc stearate dispersion, 138 parts by weight of a 10% aqueous polyvinyl alcohol solution (Mowiol 28-99). The heat-sensitive coating suspensions so obtained, which can be seen in Table 2 below, were used to produce composite structures composed of paper carrier and thermal reaction layer.

(13) TABLE-US-00002 TABLE 2 Serial Ageing No. Specimen Colour developer Sensitising agent protector** 13 EI-a PF201 2-benzyloxynaphthalene 14 EI-b DH-43 15 EII-a 1,2-di-(3-methyl- 16 EII-b phenoxy)ethane DH-43 17 EIII-a 2-benzyloxynaphthalene: 18 EIII-b steramide* DH-43 19 FI-a phenyureido-phenyl- 2-benzyloxynaphthalene 20 FI-b benzenesulphonamide DH-43 21 FII-a 1,2-di-(3-methyl- 22 FII-b phenoxy)ethane DH-43 23 FIII-a 2-benzyloxynaphthalene: 24 FIII-b steramide* DH-43 *ratio by weight 1:1 **DH-43: 1,1,3-tris-(2-methyl-4-hydroxy-5-cyclohexyl-phenyl)-butane

(14) The particle size (D.sub.4.3 value in m) of the ground functional chemicals was adjusted in accordance with Table 3 (0.1 m).

(15) TABLE-US-00003 TABLE 3 Colour former Colour developer Sensitising agent (m) (m) (m) Grinding 1.0 0.5 1.0 series 1 Grinding 1.0 1.0 1.0 series 2

(16) The measurement of the particle size distribution was effected by laser diffraction using a Coulter LS230 apparatus from Beckman Coulter.

(17) The thermal recording materials according to Tables 1, 2 and 3 were analysed as follows.

(18) Paper whiteness on the coating side was determined in accordance with DIN/ISO 2470 using an Elrepho 3000 spectral photometer.

(19) Dynamic colour density:

(20) The papers (6 cm wide strips) were printed thermally using the Atlantek 200 test printer (Atlantek, USA) with a Kyocera printhead of 200 dpi and 560 Ohm at an applied voltage of 20.6 V and a maximum pulse width of 0.8 ms with a chequered pattern with 10 energy stages. The image density (optical density, o.d.) was measured using a Macbeth densitometer RD-914 from Gretag.

(21) (3) Storage stability of the unprinted material:

(22) A sheet of recording paper is cut into three identical strips. One strip is dynamically recorded in accordance with the method of (2) and the image density is determined. The two other strips, in the unprinted (white) state, are exposed to a climate of 40 C. and 85% relative humidity (climate 1) and a climate of 60 C. and 50% relative humidity (climate 2), respectively, for 4 weeks. After climate conditioning of the papers they are dynamically printed in accordance with the method of (2) and the image density is determined using the densitometer. The % change in the writing performance on printing of the stored specimens was calculated in accordance with the following equation (I).

(23) $\begin{array}{cc}\%\mathrm{change}\mathrm{in}\mathrm{writing}\mathrm{performance}=\left(\frac{\mathrm{image}\mathrm{density}\mathrm{after}\mathrm{storage}}{\mathrm{image}\mathrm{density}\mathrm{before}\mathrm{storage}}-1\right)*100& \left(I\right)\end{array}$

(24) (4) Plasticiser stability of the printed image:

(25) A plasticiser-containing clingfilm (PVC film with 20-25% dioctyl adipate) was brought into contact with the sample of the thermal recording paper, which had been dynamically recorded in accordance with the method of (2), avoiding folds and inclusions of air, then rolled up into a roll and stored for 16 hours at room temperature (20-22 C.). After removal of the film, the image density (o.d.) was measured and, in accordance with equation (II), set in relation to the corresponding image density values before the action of the plasticiser.

(26) $\begin{array}{cc}\%\mathrm{change}\mathrm{in}\mathrm{optical}\mathrm{density}=\left(\frac{\mathrm{image}\mathrm{density}\mathrm{after}\mathrm{plasticiser}}{\mathrm{image}\mathrm{density}\mathrm{before}\mathrm{plasticiser}}-1\right)*100& \left(\mathrm{II}\right)\end{array}$

(27) (5) Quantification of the coating components (colour former and colour developer) is effected after HPLC separation using a series 1200 HPLC apparatus from Agilent having a DAD detector.

(28) Sample preparation: 2 circular areas are cut out from the paper specimen using a punch and weighed. The paper samples are extracted with 3 ml of acetonitrile (HPLC quality) in an ultrasonic bath for 30 minutes and the extract is filtered through a PTFE syringe filter (0.45 m).

(29) HPLC separation of the ingredients: using an autosampler the above extract was applied to a separating column (Zorbax Eclipse XDB-C18) and eluted using the eluant acetonitrile:THF:H.sub.2O (450:89:200 parts by weight) with an acetonitrile gradient. Quantitative analysis of the chromatograms is carried out by comparing the areas of the sample peaks assigned by means of tR times with a calibration curve determined by means of the reference specimens. The measurement error in the HPLC quantification is 2%.

(30) Table 4 summarises the analysis of the papers corresponding to formulation 1 (Table 1), grinding series 1; Table 5 summarises the analysis of the papers corresponding to formulation 1 (Table 1), grinding series 2; and Table 6 summarises the analysis of the papers corresponding to formulation 2a and 2b (Table 3), grinding series 2.

(31) The maximum achieved image densities (o.d. max) of the fresh papers are compared with the corresponding values after printing of the stored papers under two climate conditions: Climate 1: storage of the unprinted papers for 4 weeks at 40 C. and 85% relative humidity Climate 2: storage of the unprinted papers for 4 weeks at 60 C. and 50% relative humidity

(32) For selected papers, quantitative determination of the colour developer in the fresh and stored papers was also carried out and, as control, corresponding determination of the colour former as coating component, which, according to experience, undergoes virtually no change over the storage period.

(33) The values of the plasticiser test (P-test) quantify the durability of the printed image under the influence of dioctyl adipate (representing hydrophobic agents) with reference to the % change in the maximum writing performance (o.d. max) during the test.

(34) Changes in the o.d. of 10% are tolerable and do not impair the usability of the papers.

(35) TABLE-US-00004 TABLE 4 Test parameter AI-1* AII-1 AIII-1 BI-1 BII-1 BIII-1 CI-1 CII-1 CIII-1 DI-1 DII-1 DIII-1 Paper whiteness fresh 82.2 85.2 83.5 86.2 85.7 87.4 86.4 86.1 87.4 86.2 85.5 81.6 (%) 4 wks (climate 1) 83.4 84.8 85.0 86.6 86.6 86.5 86.1 86.2 85.1 66.0 63.6 66.4 % change 1 0 2 0 1 1 0 0 3 23 26 19 o.d. max. fresh 1.20 1.13 1.18 1.28 1.18 1.31 1.27 1.24 1.30 1.27 1.24 1.28 4 wks (climate 1) 0.68 0.74 0.51 0.48 0.57 0.40 1.29 1.25 1.30 0.89 0.87 0.91 % change 43 35 57 63 52 69 +2 +1 0 30 30 29 4 wks (climate 2) 0.63 0.90 0.65 0.30 0.52 0.28 1.16 1.23 1.20 0.74 0.80 0.90 % change 48 20 45 77 56 79 9 1 8 42 35 30 CD (mg/m.sup.2) fresh 548 507 568 647 4 wks (climate 1) 303 382 563 590 % change 45 25 1 9 4 wks (climate 2) 475 242 550 436 % change 13 52 3 33 CF (mg/m.sup.2) fresh 294 296 284 292 4 wks (climate 1) 288 293 287 294 % change 2 1 1 1 4 wks (climate 2) 292 294 281 277 % change 1 1 1 5 P-test fresh 1.18 1.05 1.17 1.26 1.12 1.33 1.25 1.25 1.30 1.27 1.24 1.26 16 h test 1.15 1.09 1.13 1.11 1.02 1.20 1.17 1.17 1.24 1.24 1.21 1.19 % change 3 4 3 12 9 10 6 6 5 2 2 6 CD: colour developer, CF: colour former *AI-1 = formulation AI (Table 1), grinding series 1 (Table 3)

(36) TABLE-US-00005 TABLE 5 Test parameter Mod. AI-2 AII-2 AIII-2 BI-2 BII-2 BIII-2 CI-2 CII-2 CIII-2 DI-2 DII-2 DIII-2 Paper fresh 85.7 85.7 83.8 85.7 85.4 87.0 86.7 86.4 87.3 86.1 85.4 87.0 whiteness 4 wks (climate 1) 85.2 85.5 85.0 86.3 86.1 85.9 86.5 86.4 85.1 64.9 67.4 70.9 (%) % change 1 0 1 1 1 1 0 0 3 25 21 19 o.d. max. fresh 1.17 1.09 1.18 1.29 1.22 1.29 1.30 1.26 1.29 1.25 1.21 1.28 4 wks (climate 1) 0.86 0.81 0.51 0.47 0.65 0.50 1.32 1.26 1.28 0.93 0.82 0.91 % change 26 26 57 64 47 61 +2 0 1 26 32 29 4 wks (climate 2) 0.67 0.96 0.65 0.31 0.65 0.31 1.17 1.24 1.20 0.88 0.76 0.55 % change 43 12 45 76 47 76 10 2 7 30 37 57 CD (mg/m.sup.2) fresh 478 455 607 653 4 wks (climate 1) 357 300 577 687 % change 25 34 5 10 4 wks (climate 2) 442 222 562 438 % change 8 51 7 33 CF (mg/m.sup.2) fresh 277 291 288 293 4 wks (climate 1) 300 280 284 291 % change +8 4 1 1 4 wks (climate 2) 280 283 266 278 % change +1 3 8 5 P-test fresh 1.16 1.08 1.11 1.27 1.17 1.27 1.30 1.25 1.30 1.26 1.23 1.29 16 h test 1.13 1.10 1.10 1.09 1.09 1.13 1.23 1.19 1.25 1.26 1.22 1.24 % change 3 2 1 14 7 11 5 5 4 0 1 4 CD: colour developer, CF: colour former

(37) TABLE-US-00006 TABLE 6 Test parameter Specimen EI-a EI-b EII-a EII-b EIII-a EIII-b FI-a FI-b FII-a FII-b FIII-a FIII-b o.d. max. fresh 1.24 1.24 1.25 1.30 1.32 1.25 1.33 1.26 1.26 1.30 1.29 1.29 4 wks (climate 2) 0.81 0.86 0.78 1.03 0.77 0.92 1.16 1.14 1.15 1.21 1.23 1.22 % change 35 31 38 21 42 26 8 5 9 7 5 5 CD (mg/m.sup.2) fresh 536 546 556 685 596 584 672 680 621 613 599 615 4 wks (climate 2) 398 430 403 546 380 376 685 666 608 605 583 605 % change 26 21 28 20 36 36 2 2 2 1 3 2 CF (mg/m.sup.2) fresh 300 299 328 318 328 313 324 326 296 309 303 302 4 wks (climate 2) 295 298 310 319 313 296 328 316 290 307 297 296 % change 2 0 5 0 5 5 1 3 2 1 2 2 CD: colour developer, CF: colour former

(38) The heat-sensitive recording material of the present invention exhibits especially the following advantageous properties:

(39) (1) The heat-sensitive recording material according to the invention exhibits virtually the same writing performance before and after four weeks' storage in the unprinted state under two different storage conditions. The fall in the maximum print density in all papers having the colour developer according to the invention is 10% of the print density of the fresh papers (CI-1, CII-1, CIII-1, CI-2, CII-2, CIII-2, FI-1, FI-2, FII-1, FII-2, FIII-1, FIII-2).

(40) In comparison, the comparison materials AI-1, AII-1, AIII-1, BI-1, BII-1, BIII-1, DI-1, DII-1, DIII-1, EI-1, EI-2, EII-1, EII-2, EIII-1, EIII-2, exhibit marked losses in writing performance.

(41) (2) The decrease in colour developer concentration in the heat-sensitive colour-forming layer is minimal for the colour former according to the invention (7%) and hardly impairs the writing performance. In contrast, the use of known non-phenolic developers leads to significant losses in the amount of colour developer in the paper and in an unacceptable low writing performance after storage.

(42) (3) The recorded image of the heat-sensitive papers according to the invention having the colour developer according to the invention has a maximum print density that is in no way inferior to the developers of the comparison specimens (fresh max. o.d. values from Tables 4, 5, 6), is stable and, after the action of plasticisers, barely fades, comparable to the performance of the known non-phenolic comparison developers (P-test line, Tables 4 and 5).

(43) (4) Using typical ageing-protection agents, the storage stability of the papers cannot be improved or exhibits only an inadequate improvement (E-a series versus E-b, Table 6).

(44) (5) The surface-whiteness of the recording papers according to the invention is stable and, after the storage tests, exhibits good values comparable to those of the best comparison papers and considerably better values than those based on the Pergafast 201 developer that is widely used in practice (D-series, Tables 4 and 5).

(45) (6) Using the production method according to the invention, a heat-sensitive recording material exhibiting high quality in all important use-related aspects can be produced under economically advantageous conditions.