WO2009033589A1 - Thermosensitive recording material - Google Patents

Abstract

The invention relates to a thermosensitive recording material comprising a substrate. Said substrate comprises a thermosensitive recording layer with a dye precursor and a dye acceptor on at least one side, the dye precursor and the dye acceptor reacting with each other under the effect of heat to form a dye. The thermosensitive recording material is characterized in that the thermosensitive recording layer comprises an N-(ptoluenesulphonyl)-N'-3-(p-toluenesulphonyl-oxy-phenyl) urea of formula (1) as the dye acceptor and a 2-(2H-benzotriazol-2-yl)-p-cresol of formula (2) as the sensitizer.

Description

 page 1

Heat sensitive recording material

The invention relates to a heat-sensitive recording material having a substrate which carries on at least one of its two sides a heat-sensitive recording layer. The at least one heat-sensitive recording layer has a dye precursor and a color acceptor which react color-forming with each other under the action of heat. The invention also relates to the use of the proposed heat-sensitive recording material as a ticket to the same extent.

Heat-sensitive recording materials of the type described above with, for example, a sheet of paper, a synthetic paper sheet or a plastic film as a substrate are known since the early years chemically reactive recording materials and enjoy a steadily growing popularity, which is due, inter alia, that their use in particular as Ticket for the ticket issuer is associated with great benefits. Because the color-forming components are stuck in the recording material itself in the heat-sensitive recording method, the toner and color-cartridge-free printers, which in their function no longer need to be controlled by anyone, can be set up in large numbers. Thus, this innovative technology has prevailed especially in public passenger transport, buses and trains as well as in air traffic, stadium and museum funds and parking ticket issuers.

With the aim to improve the heat-sensitive recording materials, especially in their use as tickets in terms of their resistance to environmental influences such as heat and moisture, flowed again and again innovations in the underlying chemistry and manufacturing technology for the production of such recording materials.

[0004] The subject matter of US 2005/0148467 A1 is a heat-sensitive recording material which contains at least the components of two color-forming systems for forming an irreversible printed image, one of the latex-type system and the other a conventional leuco-dyeing system. System is. As possible Page 2

Developers are a variety of sulfonylureas, including N- (p-to! Uensu! Phony!) - N ^' -3- (p-toluenesulfony! Oxy-phenyl) urea, called to fulfill there inevitably have to be combined with a second developer.

A disadvantage of the known recording material of the type described above is the complicated use of two color-forming systems, which makes the recording material so known costly. Also, the document mentioned no hint that the known recording material is particularly good to print. However, it is precisely for this purpose that a task aspect for the new heat-sensitive recording material is aimed.

Namely, the inventors recognized that with the intended use of the new recording material as a ticket, increased market demands exist for good printing in flexographic and offset printing on the at least one side of the recording material comprising the heat-sensitive recording layer. Further, and of paramount importance to the new recording material, it is said to have excellent resistance to environmental influences such as ethanol, water and plasticizer, as well as excellent lightfastness with sufficient sensitivity to supplied heat in the form of a thermal print image.

Preferred is a heat-sensitive recording material having only one side of a heat-sensitive recording layer. Should, as given here, in the task in a preferred manner, a heat-sensitive recording material to be considered, which in addition to the good printability and excellent resistance to environmental influences (especially ethanol) and light on the side with the heat-sensitive recording layer also has a very good back-printability It should be borne in mind that the front and back coatings of a centrally positioned substrate influence each other. To solve such a problem, the focus of the invention is not only to be directed to the side of the new recording material having the heat-sensitive recording layer but also to its opposite rear side. Page 3

For economic considerations, although the new recording material as possible without any further. Protective layer cover manage, but alternatively, a recording material is conceivable that manages with a simply constructed protective layer on the recording layer.

To solve these objects, a heat-sensitive recording material having a substrate is proposed,

having on at least one side a heat-sensitive recording layer with a dye precursor and a color acceptor, wherein the dye precursor and color acceptor react in a color-forming manner under the action of heat,

- and wherein the heat-sensitive recording material is characterized in that the heat-sensitive recording layer as a color acceptor N- (p-toluenesulphonyl) -N ^' -3- (p-toluenesulphonyl-oxy-phenyl) -urea according to the following formula (1):

und ferner 2-(2H-benzotriazol-2-yl)-p-cresol gemäß der folgenden Formel (2)

and further 2- (2H-benzotriazol-2-yl) -p-cresol according to the following formula (2)

as a sensitizer.

Particularly preferred is when 2- (2H-benzotriazol-2-yl) -p-cresol according to the formula (2) is the sole sensitizer in the heat-sensitive recording layer.

State of the art

In principle, heat-sensitive recording materials which comprise benzotriazole-based UV-absorbing components are known from EP 0 992 363 page 4

A 1 is known without there a sensitizer according to the formula (2) is disclosed. Lt. According to the known proposal, by ensuring a concentration gradient for UV-absorbing agents in a plurality of coatings applied to a substrate, the problem of photostability of formed thermal printing images is to be solved. Possible acceptors are known from the prior art and proven components disclosed for the present invention, partly as combination partners for the invention substantially color acceptor N- (p-toluensulphonyl) -N ^'-3- (p-toluensulphonyl-oxy-phenyl) However, a disclosure in terms of N- (p-toluenesulphonyl) -N ^' -3- (p-toluenesulphonyl-oxy-phenyl) -urea can not be found in the known font on the other hand. Consequently, this document is also no reference to the inventive combination of N- (p-toluenesulphonyl) -N ^' -3- (p-toluenesulphonyl-oxy-phenyl) -urea according to formula (1) with 2- (2H-benzotriazole-2 -yl) -p-cresol according to formula (2) It. here in the present invention.

In order to solve the problem of a fading typeface as a result of strong light irradiation, high temperatures or on contact with water and / or plasticizers, EP 1 842 688 A1, corresponding to WO 2006/080 293 A1, proposes Combination of a special developer with a member of a group of novel reagents. Neither the developer corresponds to the color acceptor according to formula (1) proposed here, nor does any of the group of these novel reagents correspond to the sensitizer according to formula (2) proposed on this side. Also, the use of such a sensitizer according to formula (2) is not mentioned as possible elsewhere in the literature. As an example of more than 20 additional color acceptors, N- (p-toluenesulphonyl) -N ^' -3- (p-toluenesulphonyl-oxy-phenyl) -urea according to formula (1) is mentioned, without any mention of a preference in this Font would come soon.

Similar to the previously acknowledged document, EP 1 738 920 A1, WO 2003/031 194 A1, EP 1 637 337 A1 and EP 1 707 399 A1 each lead to N- (p-toluenesulphonyl) -N ^' -3- (p-toluenesulphonyl-oxy-phenyl) urea as one of very many possible color acceptors, which can be used in combination with sensitizers, without causing a sensitizer, as claimed here by means of formula (2) is called. page 5

From the already older EP 0 159 874 A 2, the exemplary use of a sensitizer according to the formula (2) is known, a thermosensitive recording material with color acceptors, as they are similar to those according to formula (1), but the font can not be removed.

All the writings appreciated in the preceding paragraphs have in common that they neither mention nor suggest the combination of a color acceptor according to formula (1) with a sensitizer according to formula (2), either because they are only for use a color acceptor according to formula (1) or only the use of a sensitizer according to formula (2) considered to be worth mentioning.

Embodiments of the present invention

[0016] The color acceptor N- (p-toluensulphonyl) -N ^'-3- (p-toluensulphonyl-oxy-phenyl) - urea according to formula (1) of the present invention, either in combination with other color acceptors, in particular selected from the list comprising: 2,2 bis (4-hydroxyphenyl) propane, 4 - [(4- (1-methylethoxy) phenyl) sulfonyl] -phenol, 4-hydroxy-4 ^{'-isopropoxydiphylsulfon, 4,4'} - dihydroxy-diphenyl , ^{2,4'-dihydroxy-diphenyl} sulfone, (2-hydroxyphenyl) -2- [(4-hydroxyphenyl) thio] acetamide, or very particularly preferably be incorporated as the sole color acceptor in the heat-sensitive recording layer N-. The very special preference for the embodiment with N- (p-toluensulphonyl) -N ^'-3- (p-toluensulphonyl-oxy-phenyl) -urea according to formula (1) as the sole color acceptor results from the fact that in this way a heat-sensitive recording material may be provided which preferably has a whiteness in the range from 82 to 87% on the side having the heat-sensitive recording layer when using non-UV light as measured by ISO 2469 / ISO 2470, but D65 Light is used at a viewing angle of 8 °. page 6

If the color acceptor N- (p-toluenesulphonyl) -N ^' -3- (p-toluenesulphonyl-oxy-phenyl) -urea according to formula (1) in combination with other color acceptors, in particular selected from the list, comprising: 2 , 2-bis (4-hydroxyphenyl) propane, 4 - [(4- (1-methylethoxy) phenyl) sulfonyl] -phenol, 4-hydroxy-4 ^{'-isopropoxydiphylsulfon, 4,4'} -dihydroxy-diphenylsulfone, 2,4 ^' Dihydroxy-diphenylsulfone and N- (2-hydroxyphenyl) -2 - [(4-hydroxyphenyl) thio] acetamide incorporated in the heat-sensitive recording layer, it represents a particularly suitable embodiment, when the wt .-% (atro) -based ratio of the other color acceptors -hamstoff to N- (p-toluensulphonyl) -N ^'-3- (p-toluensulphonyl-oxy-phenyl) according to formula (1) in a range of 1: 2 to 1: 25, more preferably in a range of from 1:10 to 1:25, and most preferably from 1: 17.5 to 1:25.

As the ratio of the sensitizer according to formula (2) to the color acceptor according to formula (1), a range from 5:10 to 9:10 is particularly preferred, this ratio being independent of the fact whether the color acceptor according to formula (1) is used alone or in combination.

With regard to the heat-sensitive recording layer, the inventors recognized with reference to the stated object that the recording layer can include virtually all known dye precursors, and combinations of a plurality of dye precursors are also possible. As dye precursors, particular preference is given to:

- θ'-CdipentylaminoJ-S'-methyl ^ '- CphenylaminoJ-spirolisobenzofuran- ^ SH), ^ - [9H] xanthene] -3-ones and

- spiro [isobenzofuran-1 (3H), 9 '- [9H] xanthene] -3-one-6' - (diethylamino) -3'-methyl-2 '- (3-tolylamino) and those selected from the group the fluoran compounds, in particular

3-diethylamino-6-methyl-7-anilinofluoran,

3-dibutylamino-6-methyl-7-anilinofluoran,

3- (N-methyl-N-propyl) amino-6-methyl-7-anilinofluoran,

3- (N-ethyl-N-isoamyl) amino-6-methyl-7-anilinofluoran,

3- (N-methyl-N-cyclohexyl) amino-6-methyl-7-anilinofluoran,

3- (N-ethyl-N-tolyl) amino-6-methyl-7-anilinofluoran and

- 3- (N-ethyl-N-tetrahydrofuryl) -amino-6-methyl-7-anilinofluoran. Page 7

For commercial reasons, 3-dιbuty! Amino-6-methyl-7-Anιlιnofluoran as the most suitable dye precursor, the one or more in combination with other Fa rbstoffvorla, preferably selected from the above-mentioned dye precursors, is used

Suitable binders for incorporation into the heat-sensitive recording layer are, for example, water-soluble binders such as starch, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, polyvinyl alcohols, modified polyvinyl alcohols, sodium polyacrylates, acrylamide-acrylate copolymers, acrylamide-acrylate methacrylate Terpolymers, alkali salts of styrene-maleic anhydride copolymers or ethylene-maleic anhydride copolymers which can be used alone or in combination with each other, also water-insoluble latex binders such as styrene-butadiene copolymers, acrylonitrile-butadiene copolymers and methyl acrylate Butadiene copolymers are suitable as binders for incorporation into the heat-sensitive recording layer. For the purposes of the present invention, polyvinyl alcohol in combination with acrylate copolymer are particularly preferred binders whose combination as the sole binder accounts for 12 to 27.5 G % by weight, based on the total weight of the recording layer, of the heat-sensitive recording layer

To avoid sticking to a thermal head and avoiding excessive wear of the thermal head, the coating composition for forming the heat-sensitive recording layer may further contain lubricants and release agents, such as metal salts of higher fatty acids, for example, zinc stearate, calcium stearate, and waxes, such as paraffin. oxidized paraffin, polyethylene, polyethylene oxide, stearamides and castor wax Further constituents of the recording layer are, for example, pigments, preferably inorganic pigments such as, for example, aluminum hydroxides, silicic acid and calcium carbonate, in which case in particular calcium carbonate, which is preferably present in an amount of from 10 to 18% by weight %, based on the total weight of the recording layer, should be included in the recording layer is considered to be preferred

It is considered preferable if a permanent color or typeface can be formed in the recording layer under the action of heat page 8

The basis weight of the heat-sensitive recording layer is preferably between 2.5 and 12 g / m ² and more preferably between 3 and 6.5 g / m ² . As a brush for applying the heat-sensitive recording layer, in particular doctor blade and (RoII) blade coating, curtain coater and air brush offer.

It is preferred if the coating color used to form the recording layer is aqueous. The subsequent drying of the coating color can be done by means of microwave irradiation. Usually and proven it is just as much to supply heat, as happens by hot-air floatation dryer or contact dryer. Also conceivable is a combination of the listed dry processes.

Further preferred is the formation of a pigment-containing intermediate layer between the substrate layer and the recording layer. As pigments of the intermediate layer, both organic void pigments and inorganic pigments have proven useful, the latter preferably selected from the group comprising natural and calcined kaolin, silica and in particular bentonite, calcium carbonate and aluminum hydroxide, in particular boehmite here. On the one hand, such an intermediate layer can make a positive contribution to the leveling of the base layer surface, which reduces the amount of coating color necessarily required for the heat-sensitive recording layer. For this reason, offer to coat the intermediate layer leveling brush strokes, such as roller coater, doctor blade and (RoII-) Rakelstreichwerke. On the other hand, the pigments of this intermediate layer can absorb the heat-liquefied wax constituents of the thermosensitive recording layer in the typeface formation and thus promote a safe and rapid operation of the heat-induced recording. The basis weight of the pigmented intermediate layer is preferably between 5 and 20 g / m ² and more preferably between 7 and 1 1 g / m ² .

The recording material according to the invention may have a protective layer which is applied to the heat-sensitive recording layer and covers it in whole or in part. The protective layer takes on a task, as it also partially fulfilled by a preferred provided backside coating Page 9

namely, on the one hand the protection of the recording layer arranged under it against environmental influences such as oils, fats, water and plasticizers and on the other hand a further improvement in the printability, especially in offset and flexographic printing.

In a first embodiment, such a protective layer as a binder, a water-insoluble, self-crosslinking acrylic polymer, a crosslinking agent and as a pigment predominantly an alkaline-treated bentonite, wherein

The pigment of the protective layer consists of one or more inorganic pigments and at least 80% by weight is formed from a highly purified bentonite treated with an alkaline solution,

The binder of the protective layer consists of one or more water-insoluble, self-crosslinking acrylic polymers,

And the binder / pigment ratio ranges between 7: 1 and 9: 1.

A self-crosslinking acrylic polymer within the protective layer according to the first embodiment described herein is a self-crosslinking binder selected from the group consisting of styrene-acrylate copolymer, a copolymer of styrene / acrylic ester containing acrylamide groups, and most preferably a copolymer based on Acrylonitrile, methacrylamide and acrylic ester. In addition to the alkaline bentonite can be incorporated as a pigment and natural or precipitated calcium carbonate, kaolin, silica, aluminum hydroxide or titanium oxide in the protective layer. With regard to the crosslinking agents, particular preference is given to those which are selected from the group comprising

- cyclic urea,

- methylolurea,

Amonium zirconium carbonate and

- Particularly preferably polyamide epichlorohydrin resin.

By the choice of a water-insoluble, self-crosslinking acrylic polymer as a binder and its ratio on the one hand to the pigment in a range between 7: 1 and 9: 1, on the other hand and particularly preferably to the crosslinking agent greater than 5: 1 is already relatively low with a protective layer area-based Page 10

Mass given a high environmental resistance of the proposed recording material.

The protective layer itself may be applied by means of conventional brushing, for which, inter alia, a coating color is usable, as described above and for which a surface-related mass in a range of 1, 5 to 4.5 g / m ^{2 is} preferred or the protective layer may alternatively be printed. Processing technology and in terms of their technological properties are particularly suitable such protective layers which are curable by means of actinic radiation. The term "actinic radiation" is understood to mean UV or ionizing radiation, such as electron beams.

A second alternative embodiment which is possible as an alternative to the first embodiment described above for a protective layer wholly or partly covering the heat-sensitive recording layer contains at least one polyvinyl alcohol and a crosslinking aid. It is preferred that the polyvinyl alcohol of the protective layer is modified with carboxyl or silanol groups. Such a protective layer has a high affinity to the preferably UV-crosslinking ink used in the offset printing process, which decisively helps to meet the requirement for improved printability within the offset printing. It is also conceivable to use mixtures of different carboxyl-group- or silanol-modified polyvinyl alcohols.

Suitable crosslinking aids in the protective layer according to the second embodiment are in particular those selected from the group comprising: boric acid, polyamine, epoxy resin, dialdehyde, formaldehyde oligomers, polyamine nepichlorohydrin resin, dimethylurea, melamine formaldehyde. It is also possible to use mixtures of different crosslinking aids.

It is preferable if, within the protective layer according to the second embodiment, the ratio of the weight% of the modified polyvinyl alcohol to the crosslinking aid is in a range of 20: 1 to 5: 1, and more preferably in a range of 12: 1 to 7: 1 lies. It can be said that a ratio of the modified polyvinyl alcohol to the crosslinking aid of 100 parts by volume to 15 to 30 parts by volume has been proven. Page 11

Particularly good results were obtained when the protective layer according to the second embodiment additionally contains an inorganic pigment. It is particularly recommended that the inorganic pigment is selected from the group comprising silica, aluminum hydroxide, calcium carbonate, kaolin or a mixture of said inorganic pigments.

It is preferred that as economical as possible single layer trainee protective layer according to the second embodiment with a basis weight in a range of 1, 5 g / m ² to 6 g / m ² and especially between 1, 7 g / m ² and 3 g / m ² , without being limited to the Einschichtigkeit the protective layer. It has been found to be advantageous to have a smoothness of the protective layer in the range of 500 and preferably from 800 or better still 1,000 Bekk seconds (sec) to less than 3,000 Bekk-sec. In particular, values of 1,000 Bekk-sec to less than 2,500 Bekk-sec and most preferably from 1,200 Bekk-sec to 2,000 Bekk-sec are suitable.

The appearance of the protective layer is largely determined by the type of smoothing and the friction in the calender and calender influencing roll surfaces and their materials. In particular, because of existing market requirements, a preferred range is between 30% and 50%, and most preferably between 40% and 48%, measured according to Tappi 450 or ISO 2813 at a reflection angle of 75 °. Another preferred range is between 10% and 15%, determined according to the same rules and parameters.

Particularly useful in the context of the experimental work preceding this invention has been the use of calenders which employ NipcoFlex ™ or zone controlled Nipco-P ™ rolls without limitation in any way.

A particularly good printability for the offset printing process is present when the protective layer of the novel heat-sensitive recording material has the lowest possible polar fraction of the surface tension to be determined as the sum of disperse and polar fraction. The surface tension is determined according to Owens Wendt as in the Journal of Applied Polymer Science, page 12

Vol. 13, 1969, pages 1741-1747: Estimation of the Surface Free Energy of Polymers; D. K. Owens, R. C. Wendt. A suitable range for the measurements of the polar component of the surface tension is above zero and below 15 mN / m (milli-Newton per meter). A polar fraction of the surface tension is particularly preferably less than 10 mN / m.

In a preferred embodiment, the novel recording material has a non-heat-sensitive, backside pigment coating. Particularly suitable pigments in the backcoat have been calcium carbonate - preferably having a particle size in a colloidal range of 60% <2 μm to 90% <2 μm - and / or magnesium carbonate. The following pigments were also able to convince with positive results:

natural and calcined kaolin, preferably in the colloidal particle size range from 60% to 90% <2 μm,

Clay, silicic acid, silica, the latter having a preferred mean particle size in a range from 1 to 6 μm,

Aluminum hydroxide and boehmite, the latter having possible average particle sizes of up to 0.5 to 3 μm, but very particular preference is given to those boehmite products which have an average particle size in the range from 10 to 100 nm,

- And to a special extent talc with a preferred average particle size in a range of 1 to 10 microns.

In numerous experiments on which this invention is based, it has also been possible to successfully use mixtures, in particular of the pigments mentioned here.

Preferably, the backcoat comprises at least one component acting as a crosslinking agent based on polyurethane, preferably an anionic polyurethane in aqueous solution, for example Eka SP AP 29, Eka Chemicals AB, 32301 Düren.

In addition to the pigments and the crosslinking component based on polyurethane, the backcoat preferably comprises binders and in particular starch, styrene-butadiene latex and optionally carboxymethyl cellulose. The mixture of different binders in sometimes highly divergent mixing ratios is possible and preferred. Furthermore, optical brighteners, Page 13

foamer and components for controlling the viscosity according to the respective requirements of conventional additives.

It is preferred that the backside coating

^From 75% to 90% by weight and most preferably from 77% to 85% by weight of pigments,

^■ from 5 to 25% by weight of binder,

^■ and to 0.5 to 8 wt .-% and most preferably to 1, 5 to 3.5 wt .-% crosslinking agent based on polyurethane.

If the binder according to the preceding embodiments is present as a mixture, the backcoating preferably has 1 to 5% by weight of starch and, with particular preference, corn starch and 4 to 20% by weight, very particularly preferably 12 to 19% by weight. %, Styrene butadiene latex.

In the experimental realities underlying this invention, it has been found that a backsize coat with

^■ a pigment to binder ratio of 10: 1 to 2: 1 and better between 7.5: 1 to 3: 1 and

■ a binder to crosslinker ratio of 20: 1 to 1: 1 and better between 10.5: 1 to 5: 1, the requirements met him particularly well.

Particularly positive results can be achieved with a coating weight for the back coating in a range of 2 to 15 g / m ² . Depending on the available brushing and intended use of the recording material according to the invention, on the one hand a range for the coating weight of the back coating of 2.5 to 4.5 g / m ² , on the other hand also a range of 8.5 to 12 g / m ^{2 is} very particularly preferred. Particularly suitable coating units for application of the backside coating are, in particular, equalizing application devices, such as doctor blade and doctor blade coaters, as well as roller coating units, without being restricted to this in any way.

The inventors recognized that a particularly high-quality printed image on the back of the heat-sensitive recording material according to the invention Page 14

can win, if the backside coating is formed in two layers, of which the first layer oriented toward the substrate layer can be formed as a pure binder pigment coating, while the second outer layer containing the crosslinking agent acting component based on polyurethane. In this case, it is possible that only one layer is applied with a leveling applicator, while for the second layer as an applicator also air brush and curette coater offers.

Since the heat-sensitive recording layer essential to the invention is very easy to dry, as well as the proposed backcoat of the heat-sensitive recording material of the invention, both the backside coating and the heat-sensitive recording layer may be coated and dried in a single operation, for example, including the protective layer completely covering it become.

For this purpose, such a coating machine (a) a rolling device, (b) a first coating, for example, a curtain coater, an air brush o- a roller blade coating unit for applying the heat-sensitive recording layer, (c) a first contactless Schwebetrocknerkanal (d) a curtain coater or an airbrush for applying the protective layer, (e) optional and depending on the type a contactless web guiding system, (f) a film applicator for application of the backside coating, (g) a second non-contact floating dryer channel, (h) an after-dryer section with several drying cylinders, (i) a remoistening system or a coating installation such as a film applicator for optimizing the flatness or for reducing the roll tendency, (j) an IR drying system, (k) one or more calenders with one or more press nips each in particular using zonenregelbaren- and / or shoe press rolls or belt calender and ( I) provide a retractor.

Further, it is conceivable if between the unwinding device and the first coating unit (a, b) a further coating unit (b ^' ), carried out for example as a doctor blade applicator with associated drying apparatus (b ^" ), which can Schwebetrocknerkanal and / or drying cylinder be provided. Page 15

Although not limited to paper as a substrate, paper is the substrate that has prevailed on the market with regard to the good environmental compatibility because of good recyclability and is preferred in the context of the invention.

The details given in the description and claims on basis weight,% by weight (% by weight), parts by weight (parts by weight) and component ratios relate, unless expressly stated otherwise, each to the "Dry" weight, ie absolutely dry parts by weight The abbreviation "lutro" stands for air-dry, and means, if used, that the components marked in this way are described in their commercial delivery form.

The following example and the following comparative examples will further illustrate the invention:

A paper web of bleached and ground deciduous and softwood pulps with a basis weight of 67 g / m ² with the addition of customary additives in conventional amounts is produced on a fourdrinier paper machine as the substrate layer. On the front, a mainly calcined kaolin pigment, Styrolbutadienlatex as a binder and starch as Cobinder having intermediate layer of 9 g / m ^{2 is} applied online within the coater with a roller blade coating.

Using a coater as described in paragraph [0048] in its construction, a thermosensitive recording layer having a basis weight of 5.4 g / m ² , by means of air brush, is applied to the intermediate layer in this order by means of a doctor blade coater a protective layer of 2.0 g / m ² and applied by means of roller coater with downstream roller blade a back coat of 3 g / m ² .

[0055] In one series of experiments different coating colors are applied to the formation of heat-sensitive recording layers, in which sibilisator exchanged each of the transmitter and all other components are left the same (only Example 1 of the invention comprises Tinuvin ^® P, only the Comparative Example 2 includes Tinuvin ^® 144, Comparative example 3 contains only the Tinuvin ^® 234, only the Comparative example 4 containing Tinuvin ^® 312, only the Comparative example 5 contains Tinuvin ^® Page 16

477 DW, only Comparative Example 6 contains GNI). In the following Table 1, the formulations of the finished recording layer are reproduced, while Example 1 according to the invention and gray for identification, Examples 2 to 6 are Vergleichsbeispieie.

To form the protective layer, a recipe is used which

as pigment a highly purified, alkaline treated bentonite with platelet structure,

- Has as binder the aqueous dispersion of a self-crosslinking copolymer of acrylonitrile, methacrylamide and acrylic ester and as a crosslinking agent polyamide epichlorohydrin resin. A binder: pigment ratio of 8: 1 and a binder to crosslinker ratio of 5.5: 1 are set. By calender treatment, a smoothness of the finished recording material on the side with the recording layer covering protective layer of 1,800 Bekk-sec is also achieved.

Page 17

For metrological detection of the resistance, more precisely the percentage resistance of a Thermoprobeausdruckes against Ethanoi or to light respectively black / white checkered-designed Thermoprobeausdrucke with a device of the type Atlantek 400 made by Printrex (USA) created using a thermal head with resolution of 300 dpi and an energy per unit area of 16 mJ / mm ² is used. For each individual determination of the percentage stability of a Thermoprobeausdruckes first, the print density of the black-colored surfaces with the densitometer Gretag MacBeth TYPE D19C NB / U measured at a Thermoprobeausdruck (Fa Gretag MacBeth, 8105 Regensdorf, Switzerland). Subsequently, the respective treatment of the Thermoprobeausdrucks.

This treatment, in the case of percent resistance to ethanoi, provides for dipping the Thermoprobertedruckes in a 25% ethanol solution (25 vol .-% solution, 23 ° C) over 20 minutes. The printout is then carefully blotted with blotting paper and allowed to rest for 24 hours at 23 ° and 50% humidity.

In the case of examining the light resistance of a Thermoprobeausdrucks the treatment of Thermoprobeausdrucks his irradiation with xenon light before, for which the device Suntest CPS + Atlas (63589 Linsengericht, Germany) using a filter with UV transmission (290 nm), what the irradiation with sunlight simulated, is used. The irradiation of the thermoprob expression is carried out until an energy of 64,800 kJ / m ² has been reached. The print will then rest for 24 hours at 23 ° and 50% humidity.

After resting, the determination of the dynamic printing density at three points of the black-colored areas is carried out again with the densitometer Gretag MacBeth TYPE D19C NB / U. The respective mean values of the measurements before / after the bath in the ethanol solution and before / after the light irradiation are formed and the mean value after the bath (after the irradiation) as a percentage of the mean value before the bath (before the irradiation).

For measuring the dynamic printing density in ODU (= Optical Density Units, according to DIN 16536-1, May 1997 issue), a black / white Page 19

checkered thermoprobe print-out using an Atlantek 400 device from Printrex (USA) using a thermal head with a resolution of 300 dpi and an energy per unit area of 11.7 mJ / mm ² . The print density even of the black-colored areas are measured with the densitometer Gretag MacBeth TYPE D19C NB / U (Gretag MacBeth, 8105 Regensdorf, Switzerland), where the dynamic printing densities are measured at three points for each measured value and the arithmetic mean is formed from the three individual values becomes.

[0062] According to the above-described specifications, the resistance to ethanol as an example of the environmental resistance, the resistance to light and the sensitivity to supplied heat were in the form of the samples It. Example 1 and It. Comparative Examples 2 to 6 a thermal print image measured. The measured values can be found in the last three columns of Table 1.

From the measured values of Table 1 it can be seen that the samples of Inventive Example 1 have a very good resistance to ethanol, a very good dynamic sensitivity and a superior light resistance. Thus, only Example 1 according to the invention fulfills the requirements of excellent resistance to environmental influences as well as excellent light resistance combined with sufficient sensitivity to supplied heat in the form of a thermal printing image. At the same time, a very good printability was determined on the samples of Example 1 according to the invention, and, in view of the offset printability, also excellent pick resistance.

Although Comparative Example 3 has a higher resistance to ethanol than the inventive Example 1, but the measured values of Comparative Example 3 are far too poor in light resistance and dynamic printing density: in the context of the invention, the light resistance should preferably one Value should exceed 55%, the dynamic printing density should preferably exceed a value of 1.0 ODU and the resistance to ethanol should preferably exceed a value of 80% - particularly preferably have a value of at least 81%, wherein the values mentioned with reference to the above definition for metrological detection of the corresponding measured variables apply. Page 20

Although Comparative Example 6 has higher dynamic print density values than Inventive Example 1, the Comparative Example 6 readings are far too poor in light fastness and resistance to ethanol - even worst, in terms of resistance to ethanol Value in the test series.

The experiments described above thus clearly illustrate the superior properties of the novel recording material.

Claims

Page 21Patent claims 1. A heat-sensitive recording material having a substrate having on at least one side a heat-sensitive recording layer with a dye precursor and a color acceptor, dye precursor and color acceptor under the action of heat color forming react with each other, characterized in that the heat-sensitive recording layer as a color acceptor N- (p-toluenesulphonyl ) -N ^' -3- (p-toluenesulphonyl-oxy-phenyl) urea according to the following formula (1):

and further 2- (2H-benzotriazol-2-yl) -p-cresol according to the following formula (2)

as a sensitizer. The heat-sensitive recording material according to claim 1, characterized in that 2- (2H-benzotriazol-2-yl) -p-cresol according to the formula (2) is the sole sensitizer in the thermosensitive recording layer. 3. Heat-sensitive recording material according to any one of claims 1 or 2, characterized in that N- (p-toluenesulphonyl) -N ^' -3- (p-toluenesulphonyl-oxy-phenyl) -urea according to formula (1) sole dye acceptor in the heat-sensitive Recording layer is. Page 22 Heat-sensitive recording material according to any one of claims 1 to 3, characterized in that the ratio of the sensitizer according to formula (2) to the color acceptor according to formula (1) in a range of 5 10 to 9 10 Heat-sensitive recording material according to one of claims 1 to 4, characterized in that the heat-sensitive recording layer comprises 3 -dιbutylamιno-6-methyl-7-Anιlιnofluoran as dye precursor Heat-sensitive recording material according to one of claims 1 to 5, characterized in that the heat-sensitive recording layer contains as binder exclusively polyvinyl alcohol in combination with an acrylate copolymer Heat-sensitive recording material according to one of claims 1 to 6, characterized in that the recording material between the substrate and the heat-sensitive recording layer contains a pigmented intermediate layer Heat-sensitive recording material according to one of claims 1 to 7, characterized in that the heat-sensitive recording layer is wholly or partially covered with a protective layer, wherein the protective layer contains as binders carboxyl group- or silanol-modified polyvinyl alcohols Heat-sensitive recording material according to claim 8, characterized in that the protective layer contains crosslinking aids which are selected from the group comprising boric acid, polyamine, epoxy resin, dialdehyde, formaldehyde isomers, epiochlorohydrin resin, dimethylurea, melamine formaldehyde Heat-sensitive recording material according to one of claims 1 to 9, characterized in that the recording material has a non-heat-sensitive, backside pigment coating Page 23 11. The heat-sensitive recording material according to claim 10, wherein the backcoat layer contains at least one polyurethane-based component acting as a crosslinker. 12. Heat-sensitive recording material according to one of claims 10 or 11, characterized in that the backside coating a pigment selected from the list comprising calcium carbonate, natural and calcined kaolin, clay, silicic acid, silica, aluminum hydroxide, boehmite and talc. - And contains a binder selected from the list, comprising starch, styrene butadiene latex and optionally carboxy-methyl cellulose. 13. A heat-sensitive recording material according to claim 12, characterized in that the backside coating ^From 75% to 90% by weight and most preferably from 77% to 85% by weight of pigments, ■ from 5 to 25% by weight of binder, ■ and to 0.5 to 8 wt .-% and most preferably to 1, 5 to 3.5 wt .-% crosslinking agent based on polyurethane. 14. A heat-sensitive recording material according to any one of claims 12 or 13, characterized in that the backside coating a pigment to binder ratio of from 10: 1 to 2: 1, and more preferably from 7.5: 1 to 3: 1 as well a binder to crosslinker ratio of 20: 1 to 1: 1, and more preferably between 10.5: 1 to 5: 1.