Heat-sensitive recording material

Abstract

The invention relates to a heat-sensitive recording material, comprising a carrier substrate and at least one heat-sensitive thermal reaction layer, which is applied to at least one side of the carrier substrate and contains at least one fluoran color former, at least one color developer, at least one melting aid, and optionally typical additives, such as lubricants, stabilizers (anti-aging agents), and/or pigments, characterized in that the color developer is dodecyl gallate and the melting aid is an ethylene bis fatty acid amide of formula (I), wherein R.sub.1 and R.sub.2 are CH.sub.3(CH.sub.2).sub.mCH.sub.2 with m=13 and/or 15. The invention further relates to a method for producing said recording material. ##STR00001##

Claims

1. A heat-sensitive recording material, comprising a carrier substrate and at least one heat-sensitive thermal reaction layer applied to at least one side of the carrier substrate, which layer contains at least one fluoran colour former, at least one colour developer, at least one melting aid and optionally a slip additive, a stabiliser, an anti-ageing agent, and/or a pigment, wherein the colour developer is dodecyl gallate and the melting aid is an ethylene-bis-fatty acid amide of Formula I, ##STR00005## wherein R.sup.1 and R.sup.2 are CH.sub.3(CH.sub.2).sub.mCH.sub.2 with m=13 and/or 15, and wherein 1.5 to 4 parts by weight dodecyl gallate are used per 1 part by weight fluoran colour former; and wherein the melting aid has from 83.7 to 93.6 percent surface area of C.sub.15/C.sub.18, C.sub.16/C.sub.16, or C.sub.18/C.sub.18 ethylene-bis-fatty acid amides and combinations thereof relative to the total of all ethylene-bis-fatty acid amides present and wherein the C.sub.16/C.sub.18, C.sub.16/C.sub.16, or C.sub.18/C.sub.18 ethylene-bis-fatty acid amides are: a) R.sup.1=CH.sub.2(CH.sub.2).sub.13CH.sub.3, (m=13) and R.sup.2=CH.sub.2 (CH.sub.2).sub.15CH.sub.3, (m=15), (C.sub.16/C.sub.18-ethylene-bis-amide, ethylene-N-palmitamide-N1-steramide), b) R.sup.1=R.sup.2=CH.sub.2(CH.sub.2).sub.13CH.sub.3, (m=13), (C.sub.16/C.sub.16-ethylene-Ns-amide, N,N1-ethylene-bis-palmitamide), and c) R.sub.1=R.sub.2=CH.sub.2(CH.sub.2).sub.15CH.sub.3, (m=15), (C.sub.18/C.sub.18-ethylene-Ns-amide, N,N1-ethylene-bis-steramide), respectively.

2. A heat-sensitive recording material according to claim 1, wherein the at least one fluoran colour former is selected from the group 3-diethylamino-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-p-toluidinamino)-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-diethylamino-7-(m-trifluoromethylanilino)fluoran, 3-N-n-dibutylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-(m-methylanilino)fluoran, 3-N-n-dibutylamino-7-(o-chloroanilino)fluoran, 3-(N-ethyl-N-tetrahydrofurfurylamino)-6-methyl-7-anilinofluoran, 3-(N-methyl-N-propylamino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-ethoxypropylamino)-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-isobutylamino)-6-methyl-7-anilinofluoran, and/or 3-dipentylamino-6-methyl-7-anilinofluoran.

3. A heat-sensitive recording material according to claim 1, wherein 0.5 to 5 parts by weight ethylene-bis-fatty acid amide of Formula I are used per 1 part by weight dodecyl gallate.

4. A heat-sensitive recording material according to claim 1, wherein the colour developer is present in an amount of from 3 to 35% by weight, relative to the total solids content of the heat-sensitive thermal reaction layer.

5. A heat-sensitive recording material according to claim 1, wherein the stabiliser is used in the form of sterically hindered phenols, 1,1,3-tris-(2-methyl-4-hydroxy-5-cyclohexylphenyl)-butane, 1,1,3-tris-(2-methyl-4-hydroxy-5-tert butylphenyl)-butane, 1,1-bis-(2-methyl-4-hydroxy-5-tert butyl-phenyl)-butane, urea-urethane compounds of the general formula III, ##STR00006## or oligomeric ethers of the general formula IV, ##STR00007## where n=1-3.

6. A heat-sensitive recording material according to claim 1, wherein precipitated calcium carbonate, aluminium hydroxide, kaolins, precipitated silicas or mixtures thereof are used as the pigment.

7. A heat-sensitive recording material according to claim 1, wherein paper, synthetic paper or plastics-material film, optionally with intermediate layers formed thereon, is used as the carrier substrate.

8. A heat-sensitive recording material according to claim 1, wherein the fluoran colour former comprises ODB-2.

9. A method for producing the heat-sensitive recording material of claim 1 comprising applying an aqueous application suspension containing at least one fluoran color former, at least one color developer, and at least one melting aid to a carrier substrate using a curtain coating method, optionally with intermediate layers formed thereon, and drying, the aqueous application suspension having a solids content of approximately 20 to 75% by weight, containing as the colour developer dodecyl gallate and as the melting aid an ethylene-bis-fatty acid amide of Formula I, ##STR00008## wherein R.sup.1 and R.sup.2 are CH.sub.3(CH.sub.2).sub.mCH.sub.2 with m=13 and/or 15, the aqueous application suspension being applied using the curtain coating method at an operating speed of at least approximately 400 m/min.

10. A method according to claim 9, wherein the curtain coating method is operated at a speed of at least approximately 1000 m/min.

11. A method according to claim 9, further comprising forming a layer on the thermal reaction layer online or offline as a protective layer and/or a layer which promotes printability.

12. A method according to claim 9, further comprising forming a layer on a side of the carrier substrate opposite the thermal reaction layer online or offline as a barrier layer and/or a layer which promotes printability.

13. A method according to claim 10, wherein the curtain coating method is operated at a speed of at least approximately 1500 m/min.

14. A heat-sensitive recording material, comprising a carrier substrate and at least one heat-sensitive thermal reaction layer applied to at least one side of the carrier substrate, which layer contains at least one fluoran colour former, at least one colour developer, at least one melting aid and optionally a slip additive, a stabiliser, an anti-ageing agent, and/or a pigment, wherein the colour developer is dodecyl gallate and the melting aid is an ethylene-bis-fatty acid amide of Formula I, ##STR00009## wherein R.sup.1 and R.sup.2 are CH.sub.3(CH.sub.2).sub.mCH.sub.2 with m=13 and/or 15 and wherein the colour developer is present in an amount of from 3 to 35% by weight relative to the total solids content of the heat-sensitive thermal reaction layer, wherein 1.5 to 4 parts by weight dodecyl gallate are used per 1 part by weight fluoran colour former; and wherein the melting aid has from 83.7 to 93.6 percent surface area of C.sub.16/C.sub.18, C.sub.16/C.sub.16, or C.sub.18/C.sub.18 ethylene-bis-fatty acid amides and combinations thereof relative to the total of all ethylene-bis-fatty acid amides present and wherein the C.sub.16/C.sub.18, C.sub.16/C.sub.16, or C.sub.18/C.sub.18 ethylene-bis-fatty acid amides are: a) R.sup.1=CH.sub.2(CH.sub.2).sub.13CH.sub.3, (m=13) and R.sup.2=CH.sub.2 (CH.sub.2).sub.15CH.sub.3, (m=15), (C.sub.16/C.sub.18-ethylene-bis-amide, ethylene-N-palmitamide-N1-steramide), b) R.sup.1=R.sup.2=CH.sub.2(CH.sub.2).sub.13CH.sub.3, (m=13), (C.sub.16/C.sub.16-ethylene-bis-amide, N,N1-ethylene-bis-palmitamide), and c) R.sub.1=R.sub.2=CH.sub.2(CH.sub.2).sub.15CH.sub.3, (m=15), (C.sub.18/C.sub.18-ethylene-bis-amide, N,N1-ethylene-bis-steramide), respectively.

15. A heat-sensitive recording material according to claim 14, wherein 0.5 to 5 parts by weight ethylene-bis-fatty acid amide of Formula I are used per 1 part by weight dodecyl gallate.

16. A heat-sensitive recording material according to claim 14, wherein the stabiliser is used in the form of sterically hindered phenols, 1,1,3-tris-(2-methyl-4-hydroxy-5-cyclohexylphenyl)-butane, 1,1,3-tris-(2-methyl-4-hydroxy-5-tert butylphenyl)-butane, 1,1-bis-(2-methyl-4-hydroxy-5-tert butyl-phenyl)-butane, urea-urethane compounds of the general formula III, ##STR00010## or oligomeric ethers of the general formula IV, ##STR00011## where n=1-3.

17. A heat-sensitive recording material according to claim 14, wherein the fluoran colour former comprises ODB-2.

18. A heat-sensitive recording material according to claim 14 comprising at least two ethylene-bis-stearic acid amides.

19. A heat-sensitive recording material according to claim 14, wherein a total EBS fraction is 88.5, 84.1, 85.5, 92.5, 91.2, 93.6, 83.7 or 89.1.

Description

EXAMPLES

(1) An aqueous application suspension was applied on a laboratory scale by means of a rod blade on the coated side of a thin pre-coated paper of 50 g/m.sup.2 to form the thermal reaction layer of a heat-sensitive recording paper. It was dried with hot air (hairdryer), and a thermal recording sheet was obtained. The application amount of the heat-sensitive layer was between 4.0 and 4.5 g/m.sup.2. The pre-coated paper is a wood-free paper with a weight of 43 g/m.sup.2, to which was applied an aqueous coating compound, consisting of 100 parts calcined kaolin (Ansilex from BASF), 20 parts of a 50% styrene/butadiene copolymer emulsion and 125 parts water, with a dry application of 7 g/m.sup.2 by means of a doctor bar in order to form an intermediate layer.

(2) On a production scale, the aqueous heat-sensitive application suspension was applied to a paper provided with an intermediate layer (see above), of a base weight of 50 g/m.sup.2 by means of the curtain coating method.

(3) The viscosity of the aqueous application suspension was 450 mPas (according to Brookfield, 100 rpm, 20° C.) (in the deaerated state). The surface tension thereof was 46 mN/m (static ring method). The coating apparatus was arranged inline. The curtain coating method was operated at a speed of 1250 m/min.

(4) Using the particulars given above, a heat-sensitive recording material or thermal paper was produced, with the following formulations of aqueous application suspensions being used to form a composite structure on a carrier substrate and then the further layers, especially a protective layer, being formed in conventional manner: this will not be discussed separately here, since the core of the invention is not affected thereby.

(5) Formulation 1

(6) An aqueous application suspension was produced by thoroughly mixing an aqueous dispersion of the colour former which was produced by grinding 19 parts of a colour former (FBB) with 34 parts 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 17.5 parts gallic acid ester together with 16 parts of the melting aid and with 54 parts of a 15%-strength aqueous solution of Ghosenex™ L-3266 in a bead mill, 140 parts of a 56%-strength PCC dispersion (precipitated calcium carbonate, Precarb®, Schaefer Kalk), 40 parts of an aqueous 20%-strength zinc stearate dispersion, 50 parts of a 10%-strength aqueous polyvinyl alcohol solution (Mowiol 28-99, Kuraray Europe) and 1 part of a 31% aqueous solution of the optical brightener Blankophor® PT.

(7) The heat-sensitive coating suspensions thus obtained, which can be seen from Table 2, were set to a solids content of 30% in each case with 153 parts water, and used to produce a composite structure of paper carrier and thermal reaction layer.

(8) Formulation 2

(9) An aqueous application suspension was produced by thoroughly mixing an aqueous dispersion of the colour former which was produced by grinding 14.2 parts FBB I with 25.4 parts of a 15% aqueous solution of Ghosenex™ L-3266 (sulphonated polyvinyl alcohol, Nippon Ghosei) in a bead mill, an aqueous dispersion which was produced by grinding 4.8 parts FBB II with 8.6 parts 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 17.5 parts of gallic acid ester together with 16 parts of the melting aid and with 55 parts of a 15%-strength aqueous solution of Ghosenex™ L-3266 in a bead mill, 140 parts of a 56%-strength PCC dispersion (precipitated calcium carbonate, Precarb®, Schaefer Kalk), 40 parts of an aqueous 20%-strength zinc stearate dispersion, 50 parts of a 10%-strength aqueous polyvinyl alcohol solution (Mowiol 28-99, Kuraray Europe) and 1 part of an aqueous solution of the optical brightener Blankophor® PT.

(10) The heat-sensitive coating suspension thus obtained, which can be seen from Table 2, was set to a solids content of 30% in each case with 153 parts water, and used to produce a composite structure of paper support and thermal reaction layer.

(11) Formulation 3

(12) An aqueous dispersion of the anti-ageing agent, which was produced by grinding 6 parts anti-ageing agent with 11.7 parts of a 15%-strength aqueous solution of Ghosenex™ L-3266 (sulphonated polyvinyl alcohol, Nippon Ghosei) in a bead mill, was admixed to 524.5 parts of the application suspension produced according to Formulation 1, and the mixture was homogenised well by stirring.

(13) The heat-sensitive coating suspensions thus obtained, which can be seen from Table 2, were set to a solids content of 30% in each case with 8 parts water, and used to produce a composite structure of paper support and thermal reaction layer.

(14) Formulation 4

(15) An aqueous dispersion of the anti-ageing agent, which was produced by grinding 6 parts anti-ageing agent with 11.7 parts of a 15% aqueous solution of Ghosenex™ L-3266 (sulphonated polyvinyl alcohol, Nippon Ghosei) in a bead mill, was admixed to 525.5 parts of the application suspension produced according to Formulation 2, and the mixture was homogenised well by stirring.

(16) The heat-sensitive coating suspension thus obtained, which can be seen from Table 2, was set to a solids content of 30% in each case with 7 parts water, and used to produce a composite structure of paper support and thermal reaction layer.

(17) Formulation 5a

(18) In Formulation 2, 109 parts of a 72%-strength coating kaolin dispersion (Lustra® S from BASF) were used instead of the PCC dispersion.

(19) The heat-sensitive coating suspension thus obtained, which can be seen from Table 2, was set to a solids content of 30% with 185 parts water, and used to produce a composite structure of paper support and thermal reaction layer.

(20) Formulation 5b

(21) In Formulation 2, 140 parts of a 56%-strength aluminium hydroxide dispersion (Martifin® OL from Albermarle) were used instead of the PCC dispersion.

(22) The heat-sensitive coating suspension thus obtained, which can be seen from Table 2, was set to a solids content of 30% with 153 parts water, and used to produce a composite structure of paper support and thermal reaction layer.

(23) Formulation 5c

(24) In Formulation 2, 109 parts of a pigment dispersion, which had been obtained by stirring 15.5 parts of an amorphous precipitated silica (Sipernat® from Evonik) into 110 parts of a 56%-strength PCC dispersion (precipitated calcium carbonate, Precarb®, Schaefer Kalk), was used instead of the PCC dispersion.

(25) The heat-sensitive coating suspension thus obtained, which can be seen from Table 2, was set to a solids content of 30% with 163 parts water, and used to produce a composite structure of paper support and thermal reaction layer.

(26) Formulation 5d

(27) In Formulation 2, 109 parts of a pigment dispersion, which had been obtained by stirring 15.5 parts of an amorphous precipitated silica (Sipernat® from Evonik) into 110 parts of a 56%-strength aluminium hydroxide dispersion (Martifin® OL from Albermarle), was used instead of the PCC dispersion.

(28) The heat-sensitive coating suspension thus obtained, which can be seen from Table 2, was set to a solids content of 30% with 163 parts water, and used to produce a composite structure of paper support and thermal reaction layer.

(29) Formulation 5e

(30) In Formulation 2, 109 parts of a pigment dispersion, which had been obtained by stirring 15.5 parts of an amorphous precipitated silica (Sipernat® from Evonik) into 86 parts of a 72%-strength coating kaolin dispersion (Lustra® S from BASF), was used instead of the PCC dispersion.

(31) The heat-sensitive coating suspension thus obtained, which can be seen from Table 2, was set to a solids content of 30% with 188 parts water, and used to produce a composite structure of paper support and thermal reaction layer.

(32) The grain size (D4.3 value in μm) of the ground functional chemicals was set to 1.0±0.1 μm. The grain-size distribution was measured by laser diffraction with a Coulter LS230 apparatus from Beckman Coulter.

(33) The thermal recording materials according to Table 2 were evaluated as described below.

(34) (1) Dynamic Colour Density

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

(36) (2) Static Colour Density (Starting Temperature):

(37) The recording sheet was pressed against a row of thermostatically controlled metal punches heated to different temperatures with a pressure of 0.2 kg/cm.sup.2 and a contact time of 5 sec (thermal tester TP 3000QM, Maschinenfabrik Hans Rychiger AG, Steffisburg, Switzerland). The image density (opt. density) of the images thus produced was measured with a Macbeth densitometer RD-914 from Gretag. The static starting point by definition is the lowest temperature at which an optical density of 0.2 is achieved.

(38) (3) Fastness of the Printed Image Under Conditions of Artificial Ageing:

(39) One specimen of the thermal recording paper in each case, dynamically recorded in accordance with the method of (1), was stored for 7 days under the following conditions:

(40) 50° C. (dry ageing),

(41) 40° C., 85% relative humidity (wet ageing) and

(42) artificial light from fluorescent tubes, illumination intensity 16000 lux (light fastness).

(43) Once the test period had elapsed, the image density (o. d.) was measured and related to the corresponding image density values before the artificial ageing in accordance with Formula (V).

(44) $\begin{array}{cc}\%\mathrm{change}\mathrm{in}o.d.=\left(\frac{\mathrm{image}\mathrm{density}\mathrm{after}\mathrm{ageing}}{\mathrm{image}\mathrm{density}\mathrm{before}\mathrm{ageing}}-1\right)\times 100& \left(V\right)\end{array}$

(45) The constituents of the EBS samples were quantified after GC separation and FID detection.

(46) Percentages of surface area were calculated using the integration region underlying the solvent peak (from a retention time of 5 min. onwards).

(47) 0.2 μl of a 0.05% by weight o-xylene solutions of the EBS specimens were injected splitless.

(48) GC conditions:

(49) Injector temperature: 360° C.

(50) Separating column Varian CP 7491, 15 max 0.32 mm ID, column flow 1.5 ml/min

(51) Carrier gas: He

(52) Temperature program: 100° C. for 2 min., 20° C. per min. up to 250° C., 10° C. per min. up to 360° C.

(53) Detector temperature 370° C.

(54) Chemical assignment took place by means of GC-MS coupling.

(55) TABLE-US-00002 TABLE 2 Assignment of the paper samples to the formulations of the heat-sensitive coating Colour former* Sample Formulation I II Colour developer Melting aid ** Anti-ageing Pigment *** 1 1 ODB-2 — Dodecyl gallate EBS I — PCC 2 1 ODB-2 — Dodecyl gallate EBS II — PCC 3 1 ODB-2 — Dodecyl gallate EBS III — PCC 4 1 ODB-2 — Dodecyl gallate EBS IV — PCC 5 1 ODB-2 — Dodecyl gallate EBS V — PCC 6 1 ODB-2 — Dodecyl gallate EBS VI — PCC 7 1 ODB-2 — Dodecyl gallate EBS VII — PCC 8 1 ODB-2 — Dodecyl gallate EBS VIII — PCC 9 2 ODB-2 S205 Dodecyl gallate EBS I — PCC 10 3 ODB-2 — Dodecyl gallate EBS I DH-43 PCC 11 4 ODB-2 S205 Dodecyl gallate EBS I DH-43 PCC 12 3 ODB-2 — Dodecyl gallate EBS I UU PCC 13 4 ODB-2 S205 Dodecyl gallate EBS I UU PCC 14 3 ODB-2 S205 Dodecyl gallate EBS I DH-37 PCC 15 4 ODB-2 S205 Dodecyl gallate EBS I DH-43 PCC 16  5c ODB-2 S205 Dodecyl gallate EBS I — PCC: silica 17  5a ODB-2 S205 Dodecyl gallate EBS I — Clay 18  5e ODB-2 S205 Dodecyl gallate EBS I — Clay: silica 19  5b ODB-2 S205 Dodecyl gallate EBS I — Al(OH).sub.3 20  5d ODB-2 S205 Dodecyl gallate EBS I — Al(OH).sub.3: silica V1 1 ODB-2 — Methyl gallate EBS I — PCC V2 1 ODB-2 — Ethyl gallate EBS I — PCC V3 1 ODB-2 — Propyl gallate EBS I — PCC V4 1 ODB-2 — Octyl gallate EBS I — PCC V5 1 ODB-2 — Stearyl gallate EBS I — PCC V6 1 ODB-2 — Dodecyl gallate Stearamide — PCC V7 1 ODB-2 — Dodecyl gallate N-methylolstearamide — PCC V8 1 ODB-2 — Dodecyl gallate Behenamide — PCC V9 1 ODB-2 — Dodecyl gallate Erucamide — PCC  V10 1 ODB-2 — Dodecyl gallate Ethylene-bis-oleamide — PCC *S205 = 3-(N-ethyl-N-isoamylamino)-6-methyl-7-anilinofluoran, ODB-2 = 3-N-n-dibutylamino-6-methyl-7-anilinofluoran ** see Table 1 *** PCC = precipitated CaCO.sub.3

(56) Table 3 summarises the results of the application-specific paper tests.

(57) TABLE-US-00003 TABLE 3 Results of the application−specific paper tests Static starting Artificial ageing Sample Max. o.d. point (° C.) dry moist light 1 1.15 77 −28 −37 −43 2 1.16 77 −15 −19 −43 3 1.15 75 −7 −31 34 4 1.17 77 −12 −20 −34 5 1.16 77 −10 −20 −38 6 1.16 77 −18 −19 −37 7 1.16 76 −16 −19 −38 8 1.15 77 −13 −22 −40 9 1.14 72 −5 −19 −37 10 1.15 75 −3 −18 −33 11 1.16 73 −3 −15 −32 12 1.16 77 −1 −12 −31 13 1.18 76 0 −11 −34 14 1.18 75 −2 −13 −33 15 1.16 75 −2 −10 −31 16 1.21 74 −19 −31 −44 17 1.16 72 −15 −34 −36 18 1.20 74 −18 −36 −43 19 1.13 74 −20 −33 −41 20 1.21 75 −26 −36 −42 V1 0.98 79 −15 −47 −45 V2 0.83 112 −14 −38 −42 V3 1.20 <60 −6 −40 −42 V4 1.23 <60 −15 −29 −42 V5 0.92 79 −43 −51 −38 V6 1.05 70 −32 −46 −51 V7 1.05 74 −44 −51 −48 V8 1.13 69 −31 −48 −35 V9 1.14 <60 −75 −81 −58  V10 1.04 <60 −46 −58 −51

(58) The heat-sensitive recording material according to the invention has the following advantageous properties: (1) The heat-sensitive recording materials according to the invention (samples 1 to 8) simultaneously exhibit a significantly higher responsiveness in thermal printers (o. d. 1.15 to 1.17) and a higher starting temperature (75 to 77° C.) compared with the comparison samples with alternative gallic add esters (samples V1-V5) or with other melting aids of natural origin, such as primary fatty acid amides or alternative ethylene-bis-amides (samples V6 to V10). (2) Using colour former mixtures in the heat-sensitive recording materials according to the invention does not have any adverse effects on the high starting temperature and the high thermal printing sensitivity, regardless of whether formulations without (sample 9) or with anti-ageing agent (samples 11, 13, 14 and 15) are used, and contribute substantially to improving the image fastness, as proved by the artificial ageing values. (3) It is likewise advantageously possible to use anti-ageing agent in combination with only one colour former (samples 10, 12). (4) The combination of fluoran colour former, dodecyl gallate and melting aid of Formula I is compatible with a very wide variety of pigments without the properties suffering (samples 16 to 20). This possibility is advantageous especially for controlling further application-specific properties of the heat-sensitive recording material according to the invention, such as whiteness, gloss, receptivity and fixing capacity for inks, prevention of deposits on the print head during thermal printing, abrasiveness, etc. (5) Owing to the high starting point, the coating-specific window is sufficiently large to be able to produce a recording material with good surface whiteness and low moisture content even at high coating speeds.