HEAT-SENSITIVE RECORDING MATERIAL

Abstract

Described are colour developers of formula (I)

Ar.sup.1—NH—CO—NH—C.sub.6H.sub.4—SO.sub.2—O—C.sub.6H.sub.4—NH—CO—NH—Ar.sup.2   (I),

a heat-sensitive recording material comprising a carrier substrate and also a heat-sensitive, colour-forming layer containing at least one colour former and at least one phenol-free colour developer, wherein the at least one colour developer is the compound of formula (I), and a method for producing this heat-sensitive recording material.

Claims

1. A compound of formula (I),
Ar.sup.1—NH—CO—NH—C.sub.6H.sub.4—SO.sub.2—O—C.sub.6H.sub.4—NH—CO—NH—Ar.sup.2   (I), wherein Ar.sup.1 and Ar.sup.2 independently of one another are an unsubstituted or substituted phenyl group, naphthyl group and/or heteroaryl group.

2. The compound according to claim 1, wherein Ar.sup.1 is a phenyl group.

3. The compound according to claim 1, wherein Ar.sup.2 is a phenyl group.

4. The compound according to claim 1, wherein Ar.sup.1 is substituted with at least one C.sub.1-C.sub.5 alkyl group, an alkenyl group, an alkynyl group, a benzyl group, a formyl group, a halogen group, an NO.sub.2 group, a CN group, an R—CO group, an RO group, an RO.sub.2C group, an R—OCO group, an R—SO.sub.2O group, an R—O—SO.sub.2 group, an R—SO.sub.2—NH group, an R—NH—SO.sub.2 group, an R—NH—CO group or an R—CO—NH group, wherein R is a C.sub.1-C.sub.5 alkyl group, an alkenyl group, an alkynyl group, a phenyl group, a tolyl group, or a benzyl group.

5. The compound according to claim 1, wherein Ar.sup.1 is substituted once.

6. The compound according to claim 1, wherein Ar.sup.2 is substituted with at least one C.sub.1-C.sub.5 alkyl group, an alkenyl group, an alkynyl group, a benzyl group, a formyl group, a halogen group, an NO.sub.2 group, a CN group, an R—CO group, an RO group, an RO.sub.2C group, an R—OCO group, an R—SO.sub.2O group, an R—O—SO.sub.2 group, an R—SO.sub.2—NH group, an R—NH—SO.sub.2 group, an R—NH—CO group or an R—CO—NH group, wherein R is a C.sub.1-C.sub.5 alkyl group, an alkenyl group, an alkynyl group, a phenyl group, a tolyl group, or a benzyl group.

7. The compound according to claim 1, wherein Ar.sup.2 is substituted once.

8. The compound according to claim 1, wherein Ar.sup.1 is a phenyl group, and wherein Ar.sup.2 is a phenyl group.

9. The compound according to claim 1, wherein the Ar.sup.1—NH—CO—NH group and the Ar.sup.2—NH—CO—NH group are arranged respectively in the 2 and 3′, in the 2 and 4′, in the 3 and 2′, in the 3 and 3′, in the 3 and 4′, in the 4 and 2′, in the 4 and 3′ or in the 4 and 4′ position relative to the —C.sub.6H.sub.4—SO.sub.2—O—C.sub.6H.sub.4 group.

10. A heat-sensitive recording material comprising a carrier substrate and a heat-sensitive colour-forming layer, which contains at least one colour former and at least one phenol-free colour developer, wherein the at least one colour developer is the compound of formula (I) according to claim 1.

11. The heat-sensitive recording material according to claim 10, wherein the colour developer is present in an amount of from about 3 to about 35% by weight in relation to the total solids content of the heat-sensitive layer.

12. The heat-sensitive recording material according to claim 10, wherein the at least one colour former is a triphenylmethane, a fluoran, a azaphthalide and/or a fluorene type.

13. The heat-sensitive recording material according to claim 10, wherein one or more non-phenolic colour developers are present in addition to the phenol-free colour developer.

14. A method for producing a heat-sensitive recording material according to claim 10, wherein 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 about 20 to about 75% by weight and is applied and dried by the curtain coating process at an operating speed of the coating plant of at least about 400 m/min.

15. A heat-sensitive recording material obtainable by the method according to claim 14.

16. A method for producing a heat-sensitive recording material according to claim 10, wherein 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 about 30 to about 50% by weight and is applied and dried by the curtain coating process at an operating speed of the coating plant of at least about 1000 m/min.

17. The compound according to claim 1, wherein Ar.sup.1 is a phenyl group substituted once.

18. The compound according to claim 1, wherein Ar.sup.2 is a phenyl group substituted once.

19. The compound according to claim 9, wherein the Ar.sup.1—NH—CO—NH group and the Ar.sup.2—NH—CO—NH group are arranged respectively in the 3 and 2′ or 4 and 3′ position relative to the —C.sub.6H.sub.4—SO.sub.2—O—C.sub.6H.sub.4 group.

20. The heat-sensitive recording material according to claim 10, wherein the colour developer is present in an amount of from about 10 to about 25% by weight in relation to the total solids content of the heat-sensitive layer.

Description

EXAMPLES

[0107] Production of the compounds of formula (I) according to the invention.

[0108] Step A—Production of the Dinitro Sulfonates (According to JP 2014 094 888 A)

[0109] A solution of 60 mmol of the corresponding nitrobenzenesulfonyl chloride in 15 mL THF is added dropwise at room temperature with stirring to a solution of 60 mmol of the corresponding nitrophenol and 84 mmol triethylamine in 20 mL THF. The reaction solution is stirred for two hours at room temperature and then mixed with 65 mL water. The suspension is stirred for three hours at room temperature and then filtered. The residue is then washed with 10 mL water (3 to 6 times). The dinitro sulfonates were used in step B without further purification.

[0110] Step B—Reduction of the Nitro Groups to Primary Amines

[0111] 0.420 mol SnCl.sub.2.Math.2H.sub.2O is added (in portions) at room temperature with stirring to a solution of 0.060 mol of the product from step A in 200 mL ethyl acetate. The reaction solution is refluxed. The course of the reaction is monitored by means of thin-film chromatography (eluents: cyclohexane/ethyl acetate 1:1). Once the reaction is complete (about 2 to 3 h), 200 mL of a 50% aqueous potassium carbonate solution are added and the mixture is stirred for 30 min at room temperature. The phases are separated from one another. The aqueous phase is extracted with 100 mL ethyl acetate. The purified organic phases are dried over magnesium sulfate. The solvent is removed in a vacuum. The diamino sulfonates are used in step C without further purification.

[0112] Step C—Production of the Bis-Urea Compounds.

[0113] A solution of 15.2 mmol of the corresponding isocyanate in 25 mL ethyl acetate is added dropwise at room temperature with stirring to a solution of 7.6 mmol of the product from step B in 40 mL ethyl acetate. The reaction mixture is refluxed. The reaction mixture is refluxed and the progress of the reaction is monitored by means of HPLC. Once the reaction is complete, the precipitated bis-urea is filtered off, washed with 10 mL ethyl acetate (3 times), and dried in a vacuum. A further purification is possibly performed by recrystallisation from ethyl acetate or dichloromethane. In some cases the reaction solution is concentrated in a vacuum and the crystallisation is triggered by addition of a few drops of n-hexane.

[0114] The starting compounds are commercially obtainable.

[0115] Table 2 summarises the compounds of formula (I) produced here for the first time.

TABLE-US-00002 TABLE 2 Composition of compounds of formula (1) produced for the first time Arrangement of Ar.sup.1—NH— CO—NH— and Ar.sup.2—NH— CO—NH— on the —C.sub.6H4— SO.sub.2—O— C.sub.6H.sub.4 group Ar.sup.1 Ar.sup.2 I 2,3′ C.sub.6H.sub.5 C.sub.6H.sub.5 II 2,4′ C.sub.6H.sub.5 C.sub.6H.sub.5 III 3,2′ C.sub.6H.sub.S C.sub.6H.sub.5 IV 3,3′ C.sub.6H.sub.5 C.sub.6H.sub.5 V 3,4′ C.sub.6H.sub.5 C.sub.6H.sub.5 VI 4,2′ C.sub.6H.sub.5 C.sub.6H.sub.5 VII 4,3′ C.sub.6H.sub.5 C.sub.6H.sub.5 VIII 4,4′ C.sub.6H.sub.5 C.sub.6H.sub.5 IX 4,3′ 2-CH.sub.3—C.sub.6H.sub.4 2-CH.sub.3—C.sub.SH.sub.4 X 4,3′ 3-CH.sub.3—C.sub.6H.sub.4 3-CH.sub.3—C.sub.6H.sub.4 XI 4,3′ 4-CH.sub.3—C.sub.6H.sub.4 4-CH.sub.3—C.sub.6H.sub.4 XII 4,3′ 2,4,6-triCH.sub.3—C.sub.6H.sub.2 2,4,6-triCH.sub.3—C.sub.6H.sub.2 XIII 4,3′ 1-Naph 1-Naph XIV 4,3′ 4-CH.sub.3O—C.sub.6H.sub.4 4-CH.sub.3O—C.sub.6H.sub.4 XV 4,3′ 4-Cl—C.sub.6H.sub.4 4-Cl—C.sub.6H.sub.4 XVI 4,3′ 4-F—C.sub.6H.sub.4 4-F—C.sub.6H.sub.4 XVII 4,3′ 4-CH.sub.3CO—C.sub.6H.sub.4 4-CH.sub.3CO—C.sub.6H.sub.4 XVIII 4,3′ 4-(CO.sub.2C.sub.2H.sub.5)—C.sub.6H.sub.4 4-(CO.sub.2C.sub.2H.sub.5)—C.sub.6H.sub.4 XIX 4,3′ 4-CN—C.sub.6H.sub.4 4-CN—C.sub.6H.sub.4 XX 4,3′ 4-NO.sub.2—C.sub.6H.sub.4 4-NO.sub.2—C.sub.6H.sub.4 XXI 4,3′ 4-CH.sub.3O—C.sub.6H.sub.4 4-NO.sub.2—C.sub.6H.sub.4 XXII 4,3′ 4-NO.sub.2—C.sub.6H.sub.4 4-CH.sub.3O—C.sub.6H.sub.4

[0116] Analytical Data:

[0117] I, C.sub.26H.sub.22N.sub.4O.sub.5S, M=502.5, 3′-(3′-phenylureido)phenyl 2-(3-phenylureido)benzenesulfonate

[0118] MS (ESI): m/z (%)=503.1 (100) [M+H].sub.+.

[0119] .sup.1H-NMR (500 MHz, DMSO-d.sub.6): δ (ppm)=9.88 (1H, s), 8.82 (1H, s), 8.63 (1H, s), 8.43 (1H, s), 8.17-8.16 (1H, m), 7.75-7.70 (2H, m), 7.53-7.51 (2H, m), 7.46-7.43 (3H, m), 7.32-7.26 (5H, m), 7.23-7.20 (2H, m), 7.03-6.97 (2H, m), 6.55 (1H, ddd, J=8.0, 2.4, 1.0 Hz).

[0120] .sup.13C-NMR (126 MHz, DMSO-d.sub.6): δ (ppm)=152.13 (NHCONH), 151.80 (NHCONH), 149.06, 141.21, 139.25, 139.25, 137.88, 135.43, 129.94, 129.87, 128.71, 128.66, 124.57, 122.82, 122.69, 122.31, 122.00, 118.60, 118.34, 116.89, 114.27, 111.37.

[0121] II, C.sub.26H.sub.22N.sub.4O.sub.5S, M=502.5, 4′-(3′-phenylureido)phenyl 2-(3-phenylureido)benzenesulfonate

[0122] MS (ESI): m/z (%)=503.1 (100) [M+H].sub.+.

[0123] .sup.1H-NMR (500 MHz, DMSO-d.sub.6): δ (ppm)=9.88 (1H, s), 8.73 (1H, s), 8.63 (1H, s), 8.42 (1H, s), 8.13 (1H, dd, J=8.4, 1.0 Hz), 7.76-7.72 (1H, m), 7.66 (1H, dd, J=8.1, 1.5 Hz), 7.52-7.50 (2H, m), 7.43-7.40 (4H, m), 7.32-7.29 (2H, m), 7.28-7.25 (2H, m), 7.22-7.19 (1H, m), 7.02-6.99 (1H, m), 6.98-6.93 (3H, m).

[0124] .sup.13C-NMR (126 MHz, DMSO-d.sub.6): δ (ppm)=152.25 (NHCONH), 151.88 (NHCONH), 142.82, 139.37, 139.23, 138.99, 137.83, 135.39, 130.04, 128.73, 128.64, 124.83, 122.92, 122.80, 122.32, 122.14, 121.89, 118.96, 118.58, 118.25.

[0125] III, C.sub.26H.sub.22N.sub.4O.sub.5S, M=502.5, 2′-(3′-phenylureido)phenyl 3-(3-phenylureido)benzenesulfonate

[0126] MS (ESI): m/z (%)=503.2 (100) [M+H].sub.+.

[0127] .sup.1H-NMR (500 MHz, DMSO-d.sub.6): δ (ppm)=9.05 (1H, s), 8.98 (1H, s), 8.60 (1H, s), 8.27-8.27 (1H, m), 8.19 (1H, s), 8.03 (1H, dd, J=8.3, 1.3 Hz), 7.54-7.52 (1H, m), 7.43-7.37 (6H, m), 7.30-7.27 (2H, m), 7.24-7.19 (3H, m), 7.13 (1H, dd, J=8.2, 1.2 Hz), 7.01-6.97 (2H, m), 6.96-6.93 (1H, m).

[0128] .sup.13C-NMR (126 MHz, DMSO-d.sub.6): δ (ppm)=152.08 (NHCONH), 151.53 (NHCONH), 140.66, 139.32, 139.10, 138.10, 134.47, 132.13, 129.67, 128.63, 128.58, 127.45, 123.73, 122.11, 122.07, 122.03, 121.81, 121.13, 121.03, 118.43, 118.05, 116.91.

[0129] IV, C.sub.26H.sub.22N.sub.4O.sub.5S, M=502.5, 3′-(3′-phenylureido)phenyl 3-(3-phenylureido)benzenesulfonate

[0130] MS (ESI): m/z (%)=503.1 (100) [M+H].sub.+.

[0131] .sup.1H-NMR (500 MHz, DMSO-d.sub.6): δ (ppm)=9.13 (1H, s), 8.86 (1H, s), 8.73 (1H, s), 8.62 (1H, s), 8.23-8.22 (1H, m), 7.72 (1H, ddd, J=8.2, 2.2, 1.0 Hz), 7.58-7.55 (1H, m), 7.48-7.42 (6H, m), 7.31-7.25 (6H, m), 7.00 (1H, tt, J=7.4, 1.1 Hz), 6.98 (1H, tt, J=7.4, 1.1 Hz), 6.62 (1H, ddd, J=7.6, 2.3, 1.6 Hz).

[0132] .sup.13C-NMR (126 MHz, DMSO-d.sub.6): δ (ppm)=152.30 (NHCONH), 152.18 (NHCONH), 149.34, 141.17, 140.91, 139.27, 139.11, 135.07, 130.09, 129.86, 128.68, 128.67, 123.76, 122.22, 122.01, 120.87, 118.59, 118.37, 116.67, 116.61, 114.58, 111.38.

[0133] V, C.sub.26H.sub.22N.sub.4O.sub.5S, M=502.5, 4′-(3′-phenylureido)phenyl 3-(3-phenylureido)benzenesulfonate

[0134] MS (ESI): m/z (%)=503.1 (100) [M+H].sub.+.

[0135] .sup.1H-NMR (500 MHz, DMSO-d.sub.6): δ (ppm)=9.13 (1H, s), 8.76 (1H, s), 8.74 (1H, s), 8.63 (1H, s), 8.19-8.19 (1H, m), 7.72 (1H, ddd, J=8.2, 2.2, 1.0 Hz), 7.58-7.55 (1H, m), 7.48-7.42 (6H, m), 7.41 (1H, ddd, J=7.8, 1.8, 1.0 Hz), 7.31-7.25 (4H, m), 7.01-6.95 (4H, m).

[0136] .sup.13C-NMR (126 MHz, DMSO-d.sub.6): δ (ppm)=152.34 (NHCONH), 152.33 (NHCONH), 143.22, 140.88, 139.40, 139.12, 138.78, 134.97, 130.06, 128.69, 128.67, 123.76, 122.31, 122.24, 121.92, 120.99, 119.04, 118.62, 118.30, 116.74.

[0137] VI, C.sub.26H.sub.22N.sub.4O.sub.5S, M=502.5, 2′-(3′-phenylureido)phenyl 4-(3-phenylureido)benzenesulfonate

[0138] MS (ESI): m/z (%)=503.1 (100) [M+H].sub.+.

[0139] .sup.1H-NMR (500 MHz, DMSO-d.sub.6): δ (ppm)=9.15 (1H, s), 9.10 (1H, s), 8.71 (1H, s), 8.13 (1H, s), 8.05 (1H, dd, J=8.3, 1.5 Hz), 7.75-7.74 (2H, m), 7.60-7.58 (2H, m), 7.44-7.42 (2H, m), 7.42-7.40 (2H, m), 7.31-7.21 (5H, m), 7.14 (1H, dd, J=8.2, 1.4 Hz), 7.02-6.97 (2H, m), 6.95-6.92 (1H, m).

[0140] .sup.13C-NMR (126 MHz, DMSO-d.sub.6): δ (ppm)=151.71 (NHCONH), 151.62 (NHCONH), 145.83, 139.25, 138.91, 138.07, 132.15, 129.83, 128.68, 128.63, 127.30, 125.32, 122.32, 122.18, 122.01, 121.90, 120.94, 118.54, 118.29, 117.19.

[0141] VII, C.sub.26H.sub.22N.sub.4O.sub.5S, M=502.5, 3′-(3′-phenylureido)phenyl 4-(3-phenylureido)benzenesulfonate

[0142] MS (ESI): m/z (%)=503.1 (100) [M+H].sub.+.

[0143] .sup.1H-NMR (500 MHz, DMSO-d.sub.6): δ (ppm)=9.28 (1H, s), 8.84 (1H, s), 8.81 (1H, s), 8.62 (1H, s), 7.79-7.77 (2H, m), 7.72-7.71 (2H, m), 7.48-7.46 (2H, m), 7.45-7.43 (2H, m), 7.38-7.38 (1H, m), 7.32-7.24 (6H, m), 7.03-7.00 (1H, m), 6.98-6.95 (1H, m), 6.60-6.59 (1H, m).

[0144] .sup.13C-NMR (126 MHz, DMSO-d.sub.6): δ (ppm)=152.16 (NHCONH), 151.93 (NHCONH), 149.43, 145.61, 141.08, 139.27, 138.94, 129.76, 129.56, 128.71, 128.64, 125.98, 122.36, 121.96, 118.56, 118.35, 117.60, 116.51, 114.74, 111.47.

[0145] VIII, C.sub.26H.sub.22N.sub.4O.sub.5S, M=502.5, 4′-(3′-phenylureido)phenyl 4-(3-phenylureido)benzenesulfonate

[0146] MS (ESI): m/z (%)=503.2 (100) [M+H].sub.+.

[0147] .sup.1H-NMR (500 MHz, DMSO-d.sub.6): δ (ppm)=9.28 (1H, s), 8.82 (1H, s), 8.74 (1H, s), 8.63 (1H, s), 7.75-7.73 (2H, m), 7.71-7.70 (2H, m), 7.48-7.47 (2H, m), 7.44-7.43 (4H, m), 7.32-7.29 (2H, m), 7.29-7.25 (2H, m), 7.03-7.00 (1H, m), 6.98-6.96 (1H, m), 6.96-6.92 (2H, m).

[0148] .sup.13C-NMR (126 MHz, DMSO-d.sub.6): δ (ppm)=152.32 (NHCONH), 151.94 (NHCONH), 145.56, 143.28, 139.40, 138.95, 138.63, 129.62, 128.72, 128.64, 125.89, 122.39, 122.37, 121.87, 118.96, 118.57, 118.26, 117.58.

[0149] IX, C.sub.28H.sub.26N.sub.4O.sub.5S, M=530.6, 3′-(3′-(2′-tolyl)ureido)phenyl 4-(3-(2-tolyl)ureido)benzenesulfonate

[0150] MS (ESI): m/z (%)=531.1 (100) [M+H].sub.+.

[0151] .sup.1H-NMR (500 MHz, DMSO-d.sub.6): δ (ppm)=9.58 (1H, s), 9.17 (1H, s), 8.09 (1H, s), 7.90 (1H, s), 7.79-7.76 (4H, m), 7.73-7.70 (2H, m), 7.40-7.39 (1H, m), 7.31-7.28 (1H, m), 7.27-7.24 (1H, m), 7.20-7.12 (4H, m), 7.01-6.98 (1H, m), 6.97-6.93 (1H, m), 6.59 (1H, ddd, J=7.7, 2.4, 1.4 Hz), 2.25 (3H, s), 2.23 (3H, s).

[0152] .sup.13C-NMR (126 MHz, DMSO-d.sub.6): δ (ppm)=152.31 (NHCONH), 152.11 (NHCONH), 149.46, 145.75, 141.25, 136.96, 136.61, 130.15, 130.06, 129.81, 129.61, 128.35, 127.88, 126.07, 126.03, 125.84, 123.37, 122.91, 121.70, 121.36, 117.44, 116.29, 114.63, 111.29, 17.68 (CH.sub.3), 17.68 (CH.sub.3).

[0153] X, C.sub.28H.sub.26N.sub.4O.sub.5S, M=530.6, 3′-(3′-(3′-tolyl)ureido)phenyl 4-(3-(3-tolyl)ureido)benzenesulfonate

[0154] MS (ESI): m/z (%)=531.1 (100) [M+H].sub.+.

[0155] .sup.1H-NMR (500 MHz, DMSO-d.sub.6): δ (ppm)=9.26 (1H, s), 8.83 (1H, s), 8.73 (1H, s), 8.54 (1H, s), 7.78-7.76 (2H, m), 7.72-7.70 (2H, m), 7.40-7.39 (1H, m), 7.31-7.31 (1H, m), 7.29-7.21 (5H, m), 7.19-7.13 (2H, m), 6.84-6.82 (1H, m), 6.80-6.78 (1H, m), 6.59 (1H, ddd, J=7.6, 2.4, 1.5 Hz), 2.29 (3H, s), 2.27 (3H, s).

[0156] .sup.13C-NMR (126 MHz, DMSO-d.sub.6): δ (ppm)=152.14 (NHCONH), 151.90 (NHCONH), 149.43, 145.63, 141.12, 139.19, 138.86, 137.94, 137.86, 129.75, 129.55, 128.55, 128.49, 125.95, 123.11, 122.72, 119.08, 118.85, 117.58, 116.47, 115.74, 115.53, 114.69, 111.44, 21.07 (CH.sub.3), 21.07 (CH.sub.3).

[0157] XI, C.sub.28H.sub.26N.sub.4O.sub.5S, M=530.6, 3′-(3′-(4′-tolyl)ureido)phenyl 4-(3-(4-tolyl)ureido)benzenesulfonate

[0158] MS (ESI): m/z (%)=531.1 (100) [M+H].sub.+.

[0159] .sup.1H-NMR (500 MHz, DMSO-d.sub.6): δ (ppm)=9.23 (1H, s), 8.79 (1H, s), 8.71 (1H, s), 8.50 (1H, s), 7.77-7.75 (2H, m), 7.71-7.70 (2H, m), 7.37-7.35 (3H, m), 7.33-7.31 (2H, m), 7.26-7.23 (2H, m), 7.11-7.10 (2H, m), 7.07-7.05 (2H, m), 6.60-6.57 (1H, m), 2.25 (3H, s), 2.21 (3H, s).

[0160] .sup.13C-NMR (126 MHz, DMSO-d.sub.6): δ (ppm)=152.18 (NHCONH), 151.94 (NHCONH), 149.44, 145.72, 141.18, 136.69, 136.38, 131.29, 130.82, 129.73, 129.56, 129.11, 129.05, 125.85, 118.65, 118.44, 117.53, 116.43, 114.66, 111.41, 20.24 (CH.sub.3), 20.19 (CH.sub.3).

[0161] XII, C.sub.32H.sub.34N.sub.4O.sub.5S, M=586.7, 3′-(3′-(2′,4′,6′-trimethylphenyOureido)phenyl 4-(3-(2,4,6-trimethylphenyl)ureido)benzenesulfonate

[0162] MS (ESI): m/z (%)=587.2 (100) [M+H].sub.+.

[0163] .sup.1H-NMR (500 MHz, DMSO-d.sub.6): δ (ppm)=9.34 (1H, s), 8.86 (1H, s), 7.82 (1H, s), 7.73-7.71 (2H, m), 7.69-7.67 (2H, m), 7.61 (1H, s), 7.35-7.35 (1H, m), 7.29-7.28 (1H, m), 7.23-7.20 (1H, m), 6.90-6.87 (4H, m), 6.54-6.53 (1H, m), 2.23 (3H, s), 2.23 (3H, s), 2.17 (6H, s), 2.14 (6H, s).

[0164] .sup.13C-NMR (126 MHz, DMSO-d.sub.6): δ (ppm)=152.90 (NHCONH), 152.59 (NHCONH), 149.42, 146.17, 141.73, 135.24, 135.22, 135.20, 134.94, 132.29, 131.99, 129.62, 129.49, 128.26, 128.19, 125.50, 117.25, 116.19, 114.21, 111.23, 20.37 (CH.sub.3), 17.98 (CH.sub.3).

[0165] XIII, C.sub.34H.sub.26N.sub.4O.sub.5S, M=602.7, 3′-(3′-(1′-naphthyl)ureido)phenyl 4-(3-(1-naphthyl)ureido)benzenesulfonate

[0166] MS (ESI): m/z (%)=603.2 (100) [M+H].sub.+.

[0167] .sup.1H-NMR (500 MHz, DMSO-d.sub.6): δ (ppm)=9.64 (1H, s), 9.23 (1H, s), 8.91 (1H, s), 8.75 (1H, s), 8.12-8.09 (2H, m), 7.99-7.96 (2H, m), 7.95-7.94 (1H, m), 7.92-7.91 (1H, m), 7.83-7.81 (2H, m), 7.79-7.77 (2H, m), 7.70-7.68 (1H, m), 7.64-7.62 (1H, m), 7.61-7.45 (7H, m), 7.35 (1H, ddd, J=8.2, 2.0, 1.1 Hz), 7.31-7.28 (1H, m), 6.63 (1H, ddd, J=8.0, 2.4, 1.0 Hz).

[0168] .sup.13C-NMR (126 MHz, DMSO-d.sub.6): δ (ppm)=152.63 (NHCONH), 152.48 (NHCONH), 149.51, 145.70, 141.18, 133.90, 133.64, 133.62, 133.58, 129.90, 129.69, 128.32, 128.30, 126.32, 126.08, 126.00, 125.90, 125.80, 125.78, 125.73, 125.70, 125.65, 123.70, 123.19, 121.33, 121.25, 118.34, 117.81, 117.62, 116.47, 114.82, 111.44.

[0169] XIV, C.sub.28H.sub.26N.sub.4O.sub.7S, M=562.6, 3′-(3′-(4′-methoxyphenyl)ureido)phenyl 4-(3-(4-methoxyphenyl)ureido)benzenesulfonate

[0170] MS (ESI): m/z (%)=563.2 (100) [M+H].sub.+.

[0171] .sup.1H-NMR (500 MHz, DMSO-d.sub.6): δ (ppm)=9.21 (1H, s), 8.76 (1H, s), 8.63 (1H, s), 8.42 (1H, s), 7.77-7.74 (2H, m), 7.71-7.69 (2H, m), 7.39-7.32 (5H, m), 7.28-7.22 (2H, m), 6.90-6.87 (2H, m), 6.87-6.84 (2H, m), 6.58 (1H, ddd, J=7.4, 2.3, 1.7 Hz), 3.73 (3H, s), 3.69 (3H, s).

[0172] .sup.13C-NMR (126 MHz, DMSO-d.sub.6): δ (ppm)=154.89, 154.61, 152.34 (NHCONH), 152.09 (NHCONH), 149.44, 145.81, 141.28, 132.28, 131.92, 129.71, 129.55, 125.74, 120.45, 120.23, 117.48, 116.39, 114.55, 113.99, 113.92, 111.37, 55.14 (OCH.sub.3), 55.07 (OCH.sub.3).

[0173] XV, C.sub.26H.sub.20Cl.sub.2N.sub.4O.sub.5S, M=571.4, 3′-(3′-(4′-chlorophenyl)ureido)phenyl 4-(3-(4-chlorophenyl)ureido)benzenesulfonate

[0174] MS (ESI): m/z (%)=571.0 (100) [M+H].sub.+.

[0175] .sup.1H-NMR (500 MHz, DMSO-d.sub.6): δ (ppm)=9.31 (1H, s), 8.95 (1H, s), 8.87 (1H, s), 8.76 (1H, s), 7.78-7.76 (2H, m), 7.72-7.69 (2H, m), 7.51-7.48 (2H, m), 7.48-7.45 (2H, m), 7.37-7.36 (1H, m), 7.36-7.33 (2H, m), 7.31-7.28 (2H, m), 7.28-7.25 (2H, m), 6.61 (1H, ddd, J=6.0, 3.1, 2.4 Hz).

[0176] .sup.13C-NMR (126 MHz, DMSO-d.sub.6): δ (ppm)=152.05 (NHCONH), 151.86 (NHCONH), 149.41, 145.45, 140.88, 138.29, 137.96, 129.77, 129.56, 128.57, 128.47, 126.13, 126.00, 125.55, 120.09, 119.84, 117.74, 116.62, 114.94, 111.58.

[0177] XVI, C.sub.26H.sub.20F.sub.2N.sub.4O.sub.5S, M=538.5, 3′-(3′-(4′-fluorophenyl)ureido)phenyl 4-(3-(4-fluorophenyl)ureido)benzenesulfonate

[0178] MS (ESI): m/z (%)=539.2 (100) [M+H].sub.+.

[0179] .sup.1H-NMR (500 MHz, DMSO-d.sub.6): δ (ppm)=9.28 (1H, s), 8.85 (1H, s), 8.84 (1H, s), 8.65 (1H, s), 7.78-7.75 (2H, m), 7.72-7.69 (2H, m), 7.50-7.42 (4H, m), 7.37-7.36 (1H, m), 7.29-7.23 (2H, m), 7.16-7.06 (4H, m), 6.60 (1H, ddd, J=7.5, 2.3, 1.6 Hz).

[0180] .sup.13C-NMR (126 MHz, DMSO-d.sub.6): δ (ppm)=158.49 (d, J=29.7 Hz), 156.59 (d, J=29.3 Hz), 152.26 (NHCONH), 152.05 (NHCONH), 149.43, 145.60, 141.06, 135.60 (d, J=2.3 Hz), 135.26 (d, J=2.3 Hz), 129.75, 129.56, 126.01, 120.45 (d, J=7.8 Hz), 120.17 (d, J=7.7 Hz), 117.65, 116.56, 115.27 (d, J=13.4 Hz), 115.10 (d, J=13.4 Hz), 114.78, 111.52.

[0181] XVII, C.sub.30H.sub.26N.sub.4O.sub.7S, M=586.6, 3′-(3′-(4′-acetylphenyl)ureido)phenyl 4-(3-(4-acetylphenyl)ureido)benzenesulfonate

[0182] MS (ESI): m/z (%)=587.1 (100) [M+H].sub.+.

[0183] .sup.1H-NMR (500 MHz, DMSO-d.sub.6): δ (ppm)=9.41 (1H, s), 9.24 (1H, s), 9.06 (1H, s), 8.98 (1H, s), 7.92-7.91 (2H, m), 7.89-7.87 (2H, m), 7.80-7.78 (2H, m), 7.74-7.73 (2H, m), 7.60-7.59 (2H, m), 7.57-7.56 (2H, m), 7.38-7.38 (1H, m), 7.28-7.27 (2H, m), 6.65-6.63 (1H, m), 2.52 (3H, s), 2.46 (3H, s).

[0184] .sup.13C-NMR (126 MHz, DMSO-d.sub.6): δ (ppm)=196.23 (COCH.sub.3), 196.14 (COCH.sub.3), 151.83 (NHCONH), 151.69 (NHCONH), 149.43, 145.29, 143.94, 143.58, 140.69, 130.95, 130.61, 129.89, 129.66, 129.54, 129.51, 126.34, 117.94, 117.51, 117.27, 116.81, 115.27, 111.75, 26.26 (CH.sub.3), 26.17 (CH.sub.3).

[0185] XVIII, C.sub.32H.sub.30N.sub.4O.sub.9S, M=646.7, ethyl 4-(3-(4-((3-(3-(4-(ethoxycarbonyl)phenyOureido)phenoxy)sulfonyl)phenyl)ureido)benzoate

[0186] MS (ESI): m/z (%)=647.2 (100) [M+H].sub.+.

[0187] .sup.1H-NMR (500 MHz, DMSO-d.sub.6): δ (ppm)=9.38 (1H, s), 9.21 (1H, s), 9.03 (1H, s), 8.95 (1H, s), 7.91-7.89 (2H, m), 7.88-7.86 (2H, m), 7.80-7.77 (2H, m), 7.74-7.72 (2H, m), 7.60-7.58 (2H, m), 7.58-7.55 (2H, m), 7.38-7.37 (1H, m), 7.28-7.27 (2H, m), 6.66-6.63 (1H, m), 4.29 (2H, q, J=7.1 Hz), 4.26 (2H, q, J=7.1 Hz), 1.31 (3H, q, J=7.1 Hz), 1.29 (3H, q, J=7.1 Hz).

[0188] .sup.13C-NMR (126 MHz, DMSO-d.sub.6): δ (ppm)=165.27 (COO), 165.26 (COO), 151.79 (NHCONH), 151.65 (NHCONH), 149.40, 145.26, 143.87, 143.52, 140.65, 130.21, 130.20, 129.82, 129.59, 126.35, 123.34, 122.96, 117.90, 117.61, 117.36, 116.75, 115.22, 111.71, 60.21, 60.13 (CH.sub.2), 14.11 (CH.sub.3).

[0189] XIX, C.sub.28H.sub.20N.sub.6O.sub.5S, M=552.6, 3′-(3′-(4′-cyanophenyl)ureido)phenyl 4-(3-(4-cyanophenyl)ureido)benzenesulfonate

[0190] MS (ESI): m/z (%)=553.1 (100) [M+H].sub.+.

[0191] .sup.1H-NMR (500 MHz, DMSO-d): δ (ppm)=9.45 (1H, s), 9.32 (1H, s), 9.14 (1H, s), 9.02 (1H, s), 7.80-7.77 (2H, m), 7.76-7.71 (4H, m), 7.70-7.67 (2H, m), 7.65-7.63 (2H, m), 7.62-7.60 (2H, m), 7.36-7.36 (1H, m), 7.28-7.27 (2H, m), 6.66-6.63 (1H, m).

[0192] .sup.13C-NMR (126 MHz, DMSO-d.sub.6): δ (ppm)=151.74 (NHCONH), 151.62 (NHCONH), 149.37, 145.10, 143.79, 143.45, 140.50, 133.20, 133.10, 129.88, 129.61, 126.50, 119.05, 119.03, 118.36, 118.13, 118.01, 116.88, 115.37, 111.80, 103.95, 103.46.

[0193] XX, C.sub.26H.sub.20N.sub.6O.sub.9S, M=592.5, 3′-(3′-(4′-nitrophenyl)ureido)phenyl 4-(3-(4-nitrophenyl)ureido)benzenesulfonate

[0194] MS (ESI): m/z (%)=593.1 (100) [M+H].sub.+.

[0195] .sup.1H-NMR (500 MHz, DMSO-d.sub.6): δ (ppm)=9.52 (1H, s), 9.48 (1H, s), 9.36 (1H, s), 9.06 (1H, s), 8.20-8.17 (2H, m), 8.15-8.12 (2H, m), 7.81-7.78 (2H, m), 7.75-7.73 (2H, m), 7.70-7.64 (4H, m), 7.37-7.36 (1H, m), 7.31-7.27 (2H, m), 6.69-6.66 (1H, m).

[0196] .sup.13C-NMR (126 MHz, DMSO-d.sub.6): δ (ppm)=151.60 (NHCONH), 151.51 (NHCONH), 149.38, 145.93, 145.54, 145.00, 141.46, 141.12, 140.36, 129.88, 129.62, 126.64, 124.93, 124.90, 118.13, 117.79, 117.53, 116.97, 115.57, 111.91.

[0197] XXI, C.sub.27H.sub.23N.sub.5O.sub.8S, M=577.6, 3′-(3′-(4′-nitrophenyl)ureido)phenyl 4-(3-(4-methoxyphenyl)ureido)benzenesulfonate

[0198] MS (ESI): m/z (%)=578.1 (100) [M+H].sub.+.

[0199] .sup.1H-NMR (500 MHz, DMSO-d.sub.6): δ (ppm)=9.37 (1H, s), 9.20 (1H, s), 9.07 (1H, s), 8.62 (1H, s), 8.18-8.15 (2H, m), 7.76-7.74 (2H, m), 7.71-7.66 (4H, m), 7.37-7.34 (3H, m), 7.31-7.27 (2H, m), 6.89-6.86 (2H, m), 6.67-6.65 (1H, m), 3.72 (3H, s).

[0200] .sup.13C-NMR (126 MHz, DMSO-d.sub.6): δ (ppm)=154.89, 152.08 (NHCONH), 151.64 (NHCONH), 149.42, 145.94, 145.87, 141.17, 140.36, 131.88, 129.87, 129.57, 125.63, 124.94, 120.44, 117.59, 117.51, 116.95, 115.56, 113.97, 111.94, 55.13 (OCH.sub.3).

[0201] XXII, C.sub.27H.sub.23N.sub.5O.sub.8S, M=577.6, 3′-(3′-(4′-methoxyphenyl)ureido)phenyl 4-(3-(4-nitrophenyl)ureido)benzenesulfonate

[0202] MS (ESI): m/z (%)=578.1 (100) [M+H].sub.+.

[0203] .sup.1H-NMR (500 MHz, DMSO-d.sub.6): δ (ppm)=9.52 (2H, s), 8.75 (1H, s), 8.42 (1H, s), 8.22-8.19 (2H, m), 7.81-7.79 (2H, m), 7.75-7.73 (2H, m), 7.73-7.70 (2H, m), 7.37-7.36 (1H, m), 7.35-7.31 (2H, m), 7.26-7.22 (2H, m), 6.86-6.82 (2H, m), 6.60-6.56 (1H, m), 3.68 (3H, s).

[0204] .sup.13C-NMR (126 MHz, DMSO-d.sub.6): δ (ppm)=154.60, 152.33 (NHCONH), 151.55 (NHCONH), 149.41, 145.61, 144.94, 141.47, 141.30, 132.28, 129.73, 129.60, 126.77, 124.98, 120.20, 118.11, 117.86, 116.43, 114.53, 113.91, 111.34, 55.07 (OCH.sub.3).

[0205] Non-phenolic colour developers from the prior art were used as comparative developers, specifically N-(2-(3-phenylureido)phenyl)benzene-sulfonamide (NKK 1304, Nippon Soda) and a sulfonylurea, Pergafast 201®, (PF 201, BASF).

[0206] An aqueous coating suspension was applied to one side of a 63 g/m.sup.2 synthetic base paper (Yupo® FP680) using a doctor bar on a laboratory scale to form the heat-sensitive colour-forming layer of a heat-sensitive recording paper. After drying, a thermal recording sheet was obtained. The application rate of the heat-sensitive colour-forming layer was between 3.8 and 4.2 g/m.sup.2.

[0207] On the basis of the above information, 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 other layers, especially a protective layer, being formed in the usual manner, which will not be discussed separately here.

[0208] Production of the dispersions (in each case for 1 part by weight) for the application suspensions

[0209] The aqueous dispersion A (colour former dispersion) is produced by grinding 20 parts by weight of 3-N-n-dibutylamino-6-methyl-7-anilinofluoran (ODB-2) with 33 parts by weight of a 15% aqueous solution of Ghosenex™ L-3266 (sulfonated polyvinyl alcohol, Nippon Ghosei) in a bead mill.

[0210] The aqueous dispersion B (colour developer dispersion) is 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 a bead mill.

[0211] The aqueous dispersion C (sensitising agent dispersion) is produced by grinding 40 parts by weight of 1,2-diphenoxyethane with 33 parts by weight of a 15% aqueous solution of Ghosenex™ L-3266 in a bead mill.

[0212] All dispersions produced by grinding have an average particle size D.sub.(4.3) of 0.80-1.20 μm. The particle size distribution of the dispersions was measured by laser diffraction using a Coulter LS230 instrument from Beckman Coulter.

[0213] Dispersion D (lubricant dispersion) is a 20% zinc stearate dispersion consisting of 9 parts by weight of Zn-stearate, 1 part by weight of Ghosenex™ L-3266, and 40 parts by weight of water.

[0214] Pigment P is a 72% coating kaolin suspension (Lustra® S, BASF).

[0215] The binder consists of a 10% aqueous polyvinyl alcohol solution (Poval 28-99, Kuraray Europe).

[0216] The heat-sensitive application suspension is produced by mixing, with stirring, 1 part of A, 1 part of B, 1 part of C, 56 parts of D, 146 parts of pigment P and 138 parts of binder solution (all parts by weight), taking into account the order of introduction B, D, C, P, A, binder, and bringing the mixture to a solids content of about 25% with water.

[0217] The heat-sensitive coating suspensions thus obtained were used to produce composite structures of paper carrier and thermal reaction layer.

[0218] The thermal recording materials were evaluated as below (see Tables 3, 4 and 5).

[0219] (1) Dynamic Colour Density:

[0220] The papers (6 cm wide strips) were thermally printed with a chessboard pattern with 10 energy levels using an Atlantek 200 test printer (Atlantek, USA) with a Kyocera print bar of 200 dpi and 560 ohms 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 SpectroEye densitometer from X-Rite at an energy level of 0.45 mJ/dot. The measurement uncertainty of the o.d. values is estimated at 2%.

[0221] (2) Static Colour Density (Starting Temperature):

[0222] The recording sheet was pressed against a series of thermostatically controlled metallic stamps heated to different temperatures with a contact pressure of 0.2 kg/cm.sup.2 and a contact time of 5 seconds (thermal tester TP 3000QM, Maschinenfabrik Hans Rychiger AG, Steffisburg, Switzerland). The image density (opt. density) of the images thus produced was measured with a SpectroEye densitometer from X-Rite.

[0223] The static starting point is, by definition, the lowest temperature at which an optical density of 0.2 is achieved. The accuracy of the measuring method was ≤±0.5° C.

[0224] (3) Resistance Test of the Printed Image

[0225] a) Resistance Test of the Printed Image Under Artificial Ageing Conditions:

[0226] A sample of the thermal recording paper recorded dynamically in accordance with the method from (1) was stored for 7 days under each of the following conditions: i) 50° C. (dry ageing), ii) 40° C., 85% relative humidity (damp ageing) and iii) under artificial light from fluorescent tubes, illumination level 16000 Lux (light ageing).

[0227] Once the test time had passed, the image density was measured at an applied energy of 0.45 mJ/dot and was set in relation to the corresponding image density values prior to the artificial ageing in accordance with the formula (Eq. 1).

[00001]$\begin{array}{cc}\%\mathrm{remaining}\mathrm{image}\mathrm{density}=\left(\frac{\mathrm{image}\mathrm{density}\mathrm{after}\mathrm{test}}{\mathrm{image}\mathrm{density}\mathrm{before}\mathrm{test}}\right)*100& \left(\mathrm{Eq}.1\right)\end{array}$

[0228] The spread of the % values calculated according to (Eq. 1) is ≤±2 percentage points.

[0229] b) Resistance to Plasticiser:

[0230] A plasticiser-containing plastic wrap (PVC film with 20 to 25% dioctyladipate) was brought into contact with the sample of thermal recording paper recorded dynamically in accordance with the method from (1), avoiding folds and inclusions of air, wound into a roll, and stored for 16 hours. A second sample was stored at 40° C. at room temperature (20 to 22° C.). Once the film had been removed, the image density (o.d.) was measured and set in relation with the corresponding image density values prior to the plasticiser influence in accordance with the formula (Eq. 1).

[0231] c) Resistance to Adhesive:

[0232] A strip of transparent tesa self-adhesive tape (Tesafilm® crystal-clear, #57315) and, separately, a strip of tesa packaging adhesive tape (#04204) were glued to the sample of thermal recording paper dynamically recorded in accordance with the method from (1), avoiding folds and inclusions of air. Following storage at room temperature (20 to 22° C.), the image density (o.d.) was measured after 24 hours and after 7 days—through the adhesive tape in question—and was set in relation to the image density values, determined in a similar way, of the freshly glued sample in accordance with the formula (Eq. 1).

[0233] 4) Shelf Life of the Unprinted Thermal Paper:

[0234] A sheet of recording paper was cut into three identical strips. One strip was dynamically recorded according to the process of (1) and the image density was determined. The other two strips were stored in the unprinted (white) state for 4 weeks in a climate of a) 40° C. and 85% relative humidity (r. h.) and b) 60° C. and 50% relative humidity (r. h.).

[0235] After conditioning the papers at room temperature, they were dynamically printed in accordance with the method from (1) and the image density was determined using a densitometer at an applied energy of 0.45 mJ/dot. The remaining writing performance (%) of the stored samples in relation to the fresh (not aged) samples was calculated according to equation (Eq. 1).

[0236] Tables 3 to 5 summarise the evaluation of the recording materials produced.

TABLE-US-00003 TABLE 3 Image density, starting temperature and artificial ageing o.d. Starting (0.45 point Artificial ageing* Colour developer mJ/dot) (° C.) dry damp light III 1.21 75 97 98 87 IV 1.28 81 100 98 87 V 1.25 87 99 100 91 VII 1.32 76 100 100 86 VIII 1.30 83 100 100 88 X 1.21 79 100 100 80 XIV 1.29 104 99 99 91 XV 1.32 85 97 100 87 XVI 1.30 86 98 99 88 XVII 1.32 83 97 99 77 XVIII 1.28 76 99 100 81 XIX 1.35 87 98 98 85 XX 1.28 78 99 100 84 XXI 1.27 77 97 98 88 XXII 1.30 76 97 98 86 Comparative example 1.25 86 100 99 72 NKK 1304 Comparative example 1.21 77 99 97 70 PF 201 *Percentage of remaining image density in accordance with Eq. 1

TABLE-US-00004 TABLE 4 Resistance of the printed image Plasticiser Tesa adhesive tape* film* Colour 24 h 7 days 16 h developer #57315 #04204 #57315 #04204 R.T. 40° C. III 67 42 29 22 94 73 IV 73 53 49 32 99 92 V 78 61 57 43 100 94 VII 82 62 56 34 99 90 VIII 83 69 67 49 98 91 X 74 61 49 40 98 86 XIV 81 72 56 33 89 26 XV 83 73 57 42 97 90 XVI 73 57 43 36 98 86 XVII 89 92 78 77 94 94 XVIII 75 65 45 38 99 89 XIX 85 84 68 64 98 90 XX 81 76 58 54 97 92 XXI 80 73 56 53 98 91 XXII 84 80 63 64 98 91 Comparative 40 18 10 10 76 15 example NKK 1304 Comparative 66 33 25 12 92 63 example PF 201 *Percentage of remaining image density in accordance with Eq. 1.

TABLE-US-00005 TABLE 5 Writing performance after storage 4 weeks 40° C./ 4 weeks 60° C./ o.d. 85% r.h. 50% r.h. prior o.d. re- o.d. re- Colour to after maining after maining developer storage storage o.d.* (%) storage o.d.* (%) III 1.21 1.21 100 1.19 98 IV 1.28 1.28 100 1.25 98 V 1.25 1.25 100 1.24 99 VII 1.32 1.31 99 1.28 97 VIII 1.30 1.29 99 1.29 99 X 1.21 1.21 100 1.12 93 XIV 1.29 1.29 100 1.29 100 XV 1.32 1.32 100 1.32 100 XVI 1.30 1.30 100 1.30 100 XVII 1.32 1.29 98 1.19 90 XVIII 1.28 1.28 100 1.23 96 XIX 1.35 1.33 99 1.31 97 XX 1.28 1.28 100 1.24 97 XXI 1.27 1.27 100 1.27 100 XXII 1.30 1.30 100 1.30 100 Comparative 1.25 1.27 100 1.20 96 example NKK 1304 Comparative 1.21 1.18 98 0.79 65 example PF 201 *Percentage of remaining image density in accordance with Eq. 1

[0237] It can be deduced from the above examples that the heat-sensitive recording material of the present invention shows the following advantageous properties especially:

[0238] (1) The recorded image of the heat-sensitive recording materials based on the colour developers according to the invention has print densities (optical densities) which are better than/comparable to those of the comparative examples with known colour developers (Table 3).

[0239] (2) The temperature from which a visually perceptible greying of the recording materials according to the invention occurs (static starting point) is comparable to or higher than that of the comparative examples with known colour developers (Table 3).

[0240] (3) The heat-sensitive recording materials subjected to the ageing test reveal a high image stability, better than or comparable to that of the comparative examples with known colour developers (Table 3).

[0241] (4) The printed image is hardly faded or only slightly faded following the effect of hydrophobic agents (adhesives, plasticisers). The image resistance is better in comparison to heat-sensitive recording materials with known non-phenolic colour developers and largely satisfies the requirements of marketable heat-sensitive recording materials (Table 4).

[0242] (5) Printing of the heat-sensitive recording materials stored for several weeks under extreme conditions results in image densities that are practically identical to those of unstored (fresh) heat-sensitive recording materials (Table 5).

[0243] (6) A heat-sensitive recording material that is considered to be high-quality in all key respects of its application can be obtained with the colour developers according to the invention. No recording material based on known colour developers has a comparably good/balanced performance profile over all tested properties.