EP2487044B1 - Method for producing a heat-sensitive recording material - Google Patents

Description

• □ mit einem bahnförmigen Substrat, aufweisend eine Vorderseite und eine der Vorderseite gegenüberliegende Rückseite,
• □ mit einer auf der Vorderseite des Substrats angeordneten, Farbbildner und Farbakzeptoren enthaltenden wärmeempfindlichen Aufzeichnungsschicht,
• □ mit einer diese wärmeempfindliche Aufzeichnungsschicht abdeckenden Schutzschicht,
• □ und mit mindestens einer auf der Rückseite des Substrats angeordneten Beschichtung

The present document relates to a method for producing a heat-sensitive recording material

• □ with a web-shaped substrate, comprising a front side and a rear side opposite the front side,
• □ with a heat-sensitive recording layer containing on the front side of the substrate, color former and color acceptors,
• □ with a protective layer covering this heat-sensitive recording layer,
• □ and with at least one arranged on the back of the substrate coating

Such a method is for example from the EP 1 684 989 B1 which is characterized in particular by the heat-sensitive recording layer being applied during a machine pass and the at least one protective layer covering this heat-sensitive recording layer being printed. In this respect, the combination of printing and coating processes for producing a heat-sensitive recording material, as it is to be practiced on a coating machine or even on a paper machine, is decisive for the named document. Unfortunately, no further suggestions for the formation of the heat-sensitive recording layer and for the formation of the protective layer covering this heat-sensitive recording layer can be taken from the cited document.

Heat-sensitive recording materials have been known in their general form for many years and are enjoying ever-increasing popularity, which, among other things, is due to the fact that their use, in particular as ticket for the ticket issuer, has great advantages. Because the color-forming components are stuck in the recording material itself in the heat-sensitive recording method, the toner and color-cartridge-free thermal printers, which are no longer required to be regularly controlled by anyone, can be set in large numbers. Thus, this innovative technology has prevailed in particular in public passenger transport, buses and trains as well as in air traffic, stadium and museum funds and parking ticket machines nationwide. But even with the so important application of parking tickets, there are still many problems that, to this day, in their entirety and with regard to various individual problems could not be solved convincingly, which concerns in particular the interplay of economically convincing production and satisfactory product features.

Because parking tickets, if often laid out behind the windshield, can be exposed to direct sunlight at very high temperatures, there is a constant graying of the heat-sensitive tickets, leading to full-scale blackening. The induced by the thermal printer typeface is then no longer recognizable and the tickets are still unusable during the useful life. Also, poor durability of the heat-sensitive recording material used for the parking ticket to fats and plasticizers impairs the readability of the printed information, and parking tickets are very likely to come in contact with these substances because grease often adheres to users' fingers and hands and contains plasticizers in casings are in which the parking tickets are sometimes inserted during the service life.

Another serious and serious problem is the risk of blockage of ticket rolls after water contact: If, for example, in rainy weather or heavy fog rolls or even zigzag stacks with the still issued Parktickets heat-sensitive recording material in the ticket machine filled, it may happen that these roles or Zig-zag stacks get wet through mist or raindrops and then this moisture enters the ticket rolls or zigzag stacks. Due to a possible dissolution of the constituents, in particular in the outer layers of the parking tickets, gluing of the individual layers within a roll or within the zigzag stacks can then occur with the parking tickets still to be issued, which leads to complete failure of the affected parking ticket machine. Dust generation is another problem in the processing of thermosensitive recording material into zig-zag stacks. In particular, heat-sensitive recording materials with protective layers which have a high water resistance are often very brittle and thus it may happen that the protective layers chip off at the cut and folded edges. Dust and production disruption are the result.

The document EP-A1-2 112 000 describes a heat-sensitive recording material. This recording material contains (a) a UV-crosslinked acrylate protective layer, (b) a heat-sensitive recording layer containing an isocyanate component, an imino component, and a dye precursor-color acceptor leuco dye system, (c) a support, and (d) a backing layer.

The described problems of a strong background graying due to direct sunlight or blocking and sticking due to exposure to moisture is even more pronounced in the case of criminal tickets, which are clamped behind the windscreen wiper blades in cars parked incorrectly, because they are exposed to the environmental influences even more.

It raises so far the task, knowledge from the by the EP 1 684 989 B1 take known methods and optimize in a way or even modify that a provided for trouble-free use as a parking and criminal ticket heat-sensitive recording material within a high-quality, but economically still reasonable production costs guaranteeing process is to produce.

• □ mit einem bahnförmigen Substrat, aufweisend eine Vorderseite und eine der Vorderseite gegenüberliegende Rückseite,
• □ mit einer auf der Vorderseite des Substrats angeordneten, Farbbildner und Farbakzeptoren enthaltenden wärmeempfindlichen Aufzeichnungsschicht,
• □ mit einer diese wärmeempfindliche Aufzeichnungsschicht abdeckenden Schutzschicht,
• □ mit mindestens einer auf der Rückseite des Substrats angeordneten Beschichtung,

wobei das Verfahren mindestens die folgenden Verfahrensschritte umfasst:

• ■ Vorbereiten einer ersten Beschichtungszusammensetzung, wobei diese erste Beschichtungszusammensetzung mindestens umfasst:
  • als Farbakzeptor zu mindestens 80 Gew.-% - bezogen auf den Gesamtanteil an Farbakzeptoren in der ersten Beschichtungszusammensetzung - 4,4'-Dihydroxydiphenylsulfon,
  • mindestens einen Sensibilisator, ausgesucht aus der Liste umfassend Stearinsäureamid, Dimethylsulfon, 2-(2H-benzotriazol-2-yl)-p-cresol und Dimethylterephtalat,
• ■ Vorbereiten einer zweiten Beschichtungszusammensetzung, wobei diese zweite Beschichtungszusammensetzung mindestens umfasst:
  • zu 65 bis 95 Gew.-% ein oder mehrere (Meth)acrylate,
  • zu 0 bis 20 Gew.-% Photoinitiatoren und
  • zu 0,5 bis 20 Gew.-% Wachs,
  wobei sich die Gew.-%-Angaben zu 65,5 bis 100 Gew.-% der zweiten Beschichtungszusammensetzung addieren,
• ■ Vorbereiten einer dritten Beschichtungszusammensetzung, wobei diese dritte Beschichtungszusammensetzung mindestens umfasst:
  • zu 65 bis 95 Gew.-% ein oder mehrere (Meth)acrylate,
  • zu 0 bis 20 Gew.-% Photoinitiatoren und
  wobei sich die Gew.-%-Angaben zu 65 bis 100 Gew.-% der zweiten Beschichtungszusammensetzung addieren,
• ■ Ausbilden eines bahnförmigen Substrat, aufweisend eine Vorderseite und eine der Vorderseite gegenüberliegende Rückseite,
• ■ Aufbringen der vorbereiteten ersten Beschichtungszusammensetzung zur Ausbildung der auf der Vorderseite des Substrats angeordneten wärmeempfindlichen Aufzeichnungsschicht,
• ■ Trocknen der ersten Beschichtungszusammensetzung,
• ■ Aufbringen der vorbereiteten zweiten Beschichtungszusammensetzung zur Ausbildung der die wärmeempfindliche Aufzeichnungsschicht abdeckenden Schutzschicht,
• ■ Vernetzen der die wärmeempfindliche Aufzeichnungsschicht abdeckenden Schutzschicht mittels energiereicher Strahlung,
• ■ Aufbringen der vorbereiteten dritten Beschichtungszusammensetzung zur Ausbildung der mindestens einen auf der Rückseite des Substrats angeordneten Beschichtung,
• ■ Vernetzen der mindestens einen auf der Rückseite des Substrats angeordneten Beschichtung mittels energiereicher Strahlung,
• ■ Konfektionieren des wärmeempfindlichen Aufzeichnungsmaterials, dabei mindestens aufweisend:
  • das bahnförmige Substrat,
  • die auf der Vorderseite des Substrats angeordnete wärmeempfindliche Aufzeichnungsschicht, ausgebildet aus der ersten Beschichtungszusammensetzung,
  • die die wärmeempfindliche Aufzeichnungsschicht abdeckenden Schutzschicht, ausgebildet aus der zweiten Beschichtungszusammensetzung,
  • die mindestens eine auf der Rückseite des Substrats angeordnete rückseitige Beschichtung, ausgebildet aus der dritten Beschichtungszusammensetzung.

The solution to this demanding object is achieved by means of a method for producing a heat-sensitive recording material

• □ with a web-shaped substrate, comprising a front side and a rear side opposite the front side,
• □ with a heat-sensitive recording layer containing on the front side of the substrate, color former and color acceptors,
• □ with a protective layer covering this heat-sensitive recording layer,
• □ with at least one coating arranged on the back side of the substrate,

the method comprising at least the following method steps:

• Preparing a first coating composition, said first coating composition comprising at least
  • as color acceptor to at least 80% by weight, based on the total amount of color acceptors in the first coating composition, of 4,4'-dihydroxydiphenylsulfone,
  • at least one sensitiser selected from the list comprising stearic acid amide, dimethylsulfone, 2- (2H-benzotriazol-2-yl) -p-cresol and dimethyl terephthalate,
• Preparing a second coating composition, said second coating composition comprising at least
  • from 65 to 95% by weight of one or more (meth) acrylates,
  • to 0 to 20 wt .-% of photoinitiators and
  • from 0.5 to 20% by weight of wax,
  wherein the weight percentages added to 65.5 to 100 wt .-% of the second coating composition,
• Prepare a third coating composition, said third coating composition comprising at least
  • from 65 to 95% by weight of one or more (meth) acrylates,
  • to 0 to 20 wt .-% of photoinitiators and
  wherein the wt .-% - add to 65 to 100 wt .-% of the second coating composition,
• Forming a web-shaped substrate, comprising a front side and a rear side opposite the front side,
• Applying the prepared first coating composition to form the heat-sensitive recording layer disposed on the front surface of the substrate;
• Drying the first coating composition,
• Application of the prepared second coating composition to form the protective layer covering the heat-sensitive recording layer,
• Crosslinking of the protective layer covering the heat-sensitive recording layer by means of high-energy radiation,
• Applying the prepared third coating composition to form the at least one coating arranged on the back side of the substrate,
• Crosslinking the at least one coating arranged on the back side of the substrate by means of high-energy radiation,
• ■ Preparing the heat-sensitive recording material, at least comprising:
  • the web-shaped substrate,
  • the heat-sensitive recording layer disposed on the front surface of the substrate, formed of the first coating composition;
  • the protective layer covering the heat-sensitive recording layer formed of the second coating composition,
  • the at least one backside coating disposed on the back side of the substrate, formed from the third coating composition.

In the proposed method according to the previous paragraph, the order of the method steps according to local sequence or in a modified sequence is possible. In addition, further method steps may be inserted at different positions.

The proposed method initially provides for the preparation of a first coating composition, with the use of container scales for the precise feeding and metering of bulk components and liquid components to a particular extent.

The first coating composition provided for forming the heat-sensitive recording layer comprises at least 80% by weight, based on the total content of color acceptors in the first coating composition, of 4,4'-dihydroxydiphenylsulfone as a color acceptor. 4,4'-Dihydroxydiphenylsulfone is also commonly referred to as 4,4'-sulfonyldiphenol and is also known under the tradename 4,4 Bisphenol S. 4,4'-Dihydroxydiphenylsulfone has the chemical formula C12H10O4S and can be represented as the following formula (1):

The use of 4,4'-Dihydroxydiphenylsulfon as a color acceptor is for example from the EP 2 279 877 A1 which also discloses the combination of 4,4'-dihydroxydiphenyl sulfone with a sensitizer such as methylol stearamide, stearic acid amide and dimethyl terephthalate. The document, however, are unfortunately no suggestions to refer to a process in which a protective layer or even a back coating each applied to (meth) acrylate-based and then crosslinked.

• 2,2 bis (4-hydroxyphenyl)-Propan - auch bekannt als Bisphenol A,
• 4-[(4-(1-methylethoxy)phenyl)sulfonyl]-Phenol - auch bekannt als D8,
• N-(p-toluensulphonyl)-N'-3-(p-toluensulphonyl-Oxy-phenyl)-harnstoff - auch bekannt als Pergafast® 201.

Within the present invention, the first coating composition may include, in addition to 4,4'-dihydroxydiphenylsulfone, other color acceptors selected from the list

• 2,2 bis (4-hydroxyphenyl) propane - also known as bisphenol A,
• 4 - [(4- (1-methylethoxy) phenyl) sulfonyl] phenol - also known as D8,
• N- (p-toluenesulphonyl) -N'-3- (p-toluenesulphonyl-oxy-phenyl) urea - also known as Pergafast® 201.

In a preferred embodiment, the above color acceptors, individually or also combined with each other, to a maximum of 5.5 wt .-%, most preferably to a maximum of 4.25 wt .-% - based on the total amount of Farbakzeptoren in the first coating composition - in involved in this first coating composition, the remainder forms 4,4'-Dihydroxydiphenylsulfon. Finally, an embodiment in which 4,4'-dihydroxydiphenylsulfone is the sole color acceptor in the first coating composition is preferred as to a very particular extent.

• 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 und 3-(N-ethyl-N-tetrahydrofuryl)amino-6-methyl-7-Anilinofluoran. Ganz besonders bevorzugt ist dabei 3-dibutylamino-6-methyl-7-Anilinofluoran - auch bekannt als ODB-2.

The thermosensitive recording material preferably has, as a color former in the first coating composition, those selected from the list comprising:

• 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. Very particular preference is given to 3-dibutylamino-6-methyl-7-anilinofluoran - also known as ODB-2.

It is possible that the first coating composition has more than one color former, each selected from the color formers listed in the above paragraph.

The method according to the invention for the preparation of a heat-sensitive recording material may contain one or more of the following compounds which absorb in the near infrared range within the first coating composition, in addition to or as an alternative to the substances mentioned in the previous paragraph as color formers:

3,6-Bis (dimethylamino) fluorene-9-spiro-3 '- (6'-dimethylaminophthalide), 3-diethylamino-6-dimethylaminofluorene-9-spiro-3' - (6'-dimethylaminophthalide), 3.6- Bis (diethylamino) -fluorene-9-spiro-3 '- (6'-dimethylaminophthalide), 3-dibutylamino-6-dimethylaminofluorene-9-spiro-3' - (6'-dimethylaminophthalide), 3-dibutylamino-6-diethylaminofluorene -9-spiro-3 '- (6'-dimethylaminophthalide), 3,6-bis (dimethylamino) fluorene-9-spiro-3' - (6'-diethylamino-phthalide), 3-diethylamino-6-dimethylaminofluorene-9 -spiro-3 '- (6'-diethylaminophthalide), 3-dibutylamino-6-dimethylaminofluorene-9-spiro-3' - (6'-diethylaminophthalide), 3,6-bis (di-ethylamino) fluorene-9- spiro-3 '- (6'-diethylaminophthalide), 3,6-bis (dimethylamino) -fluorene-9-spiro-3' - (6'-dibutylaminophthalide), 3-dibutylamino-6-diethylaminofluorene-9-spiro 3 '- (6'-diethylaminophthalide), 3-diethylamino-6-dimethylaminofluorene-9-spiro-3' - (6'-dibutylaminophthalide), 3,3-bis [2- (4-dimethylaminophenyl) -2- (4 methoxyphenyl) ethenyl] -4,5,6,7-tetrachlorophthalid.

The first coating composition contains at least one sensitiser selected from the list comprising stearic acid amide, dimethylsulfone, 2- (2H-benzotriazol-2-yl) -p-cresol and dimethyl terephthalate, which means according to a first preferred embodiment alone, for increasing the thermal responsiveness , not in combination with the other three sensitisers listed above. According to a second, as it were preferred embodiment, at least two sensitisers, selected from the list comprising stearic acid amide, dimethylsulfone, 2- (2H-benzotriazol-2-yl) -p-cresol and dimethyl terephthalate, are incorporated in the first coating composition. Of the four mentioned sensitizers, dimethylsulfone on the one hand and dimethyl terephthalate on the other hand are considered to be very particularly preferred.

The above-mentioned sensitizers may be used in the first coating composition each optionally in combination with the following products: methylol stearamide, benzyl p-benzyloxy benzoate, p-benzyl biphenyl, 1,2-di (phenoxy) ethane, 1,2-di (m-methylphenoxy) ethane, m-terphenyl, dibenzyl oxalate, benzyl naphthyl ether and diphenyl sulfone.

2- (2H-benzotriazol-2-yl) -p-cresol is available as Tinuvin ^® from Ciba Specialty Chemicals Inc. and can be represented by the following formula (2):

Numerous experiments have shown that a ratio based on the weight% within the first coating composition
_Total color _acceptor : _total sensitizer and in particular
4,4'-Dihydroxydiphenylsulfone: _total sensitizer and especially 4,4'-dihydroxydiphenylsulfone: Sensitizer selected from the list comprising: stearic acid amide, dimethylsulfone, 2- (2H-benzotriazol-2-yl) -p-cresol and dimethyl terephthalate preferably in one Range from 1: 0.5 to 1: 2, and
most preferably in a range of 1: 0.8 to 1: 1.4.

Suitable binders for incorporation into the first coating composition are, for example, water-soluble binders such as starch, hydroxyethylcellulose, methylcellulose, carboxymethylcellulose, gelatin, casein, polyvinyl alcohols, modified polyvinyl alcohols, ethylene-vinyl alcohol copolymers, sodium polyacrylates, acrylamide-acrylate copolymers, acrylamide-acrylate-methacrylate Terpolymers and alkali metal salts of styrene-maleic anhydride copolymers or ethylene-maleic anhydride copolymers, which binders may be used alone or in combination with one another; Water-insoluble latex binders such as styrene-butadiene copolymers, acrylonitrile-butadiene copolymers and methyl acrylate-butadiene copolymers are also suitable as binders for incorporation into the first coating composition. For the purposes of the present invention, polyvinyl alcohol, ethylene-vinyl alcohol copolymers or polyvinyl alcohol in combination with ethylene-vinyl alcohol copolymers are particularly preferred binders which together in a range from 10 to 20% by weight, based on the total weight of the first coating composition. incorporated into the first coating composition.

To avoid sticking to a thermal head and avoiding excessive wear of the thermal head, the first coating composition for forming the thermosensitive recording layer may further contain slip 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 first coating composition are, if appropriate, for example pigments, preferably inorganic pigments such as, for example, aluminum (hydr) oxide, silica and calcium carbonate, in which case in particular calcium carbonate, which should preferably be incorporated in an amount of 0 to 28% by weight in the first coating composition , as preferred.

The proposed method according to the invention further provides for the preparation of a second coating composition.

• □ zu 65 bis 95 Gew.-% ein oder mehrere (Meth)acrylate.
  Bevorzugt ist das eine oder sind die mehreren Meth)acrylate ausgewählt aus der Gruppe umfassend Polyether(meth)acrylat, Epoxy(meth)acrylat sowie Urethan (meth)acrylat. Beispiele für die (Meth)acrylate gemäß der zweiten Beschichtungszusammensetzung sind Dipentaerythritolpenta(meth)acrylate und finden sich darüber hinaus beispielsweise in den Literaturstellen US 4,485,123 und EP 0 209 684 A1 .
  Ganz besonders bevorzugt ist mindestens ein (Meth)acrylat der genannten Gruppe ein aminmodifiziertes (Meth)acrylat. Als aminmodifiziertes (Meth)acrylat wird bevorzugt aminmodifiziertes Polyether-acrylat eingesetzt.
  Bevorzugt ist die zweite Beschichtungszusammensetzung nahezu frei von Monomeren bzw. Reaktivverdünnern und weist einen niedrigen Restgehalt an (Meth)acrylsäure auf.
• □ zu 0 bis 20 Gew.-% Photoinitiatoren.
  Als Photoinitiatoren können solche eingesetzt werden, welche die Härtung bzw. radikalische Polymerisation unter Anwendung von energiereicher Strahlung und bevorzugt von UV-Strahlung initiieren und beispielsweise im Wellenbereich von 190 bis 400 nm absorbieren. Derartige Photoinitiatoren sind beispielsweise chlorhaltige Photoinitiatoren, aromatische Ketone, Hydro-Xyalkylphenone, Phosphinoxide. Bevorzugte Photoinitiatoren sind Benzophenonderivate, Phenylketone und Phenyolphosphenate.
• □ zu 0,5 bis 20 Gew.-% Wachs.
  Als Wachse sind bspw. Polyethylenwachse, wie beispielsweise PTFE-modifiziertes Polyethylenwachs verwendbar.

The second, non-aqueous coating composition comprises at least

• To 65 to 95% by weight of one or more (meth) acrylates.
  The one or more methacrylates are preferably selected from the group comprising polyether (meth) acrylate, epoxy (meth) acrylate and urethane (meth) acrylate. Examples of the (meth) acrylates according to the second coating composition are dipentaerythritol penta (meth) acrylates and moreover are found, for example, in the literature US 4,485,123 and EP 0 209 684 A1 ,
  Most preferably, at least one (meth) acrylate of said group is an amine-modified (meth) acrylate. The amine-modified (meth) acrylate used is preferably amine-modified polyether acrylate.
  The second coating composition is preferably virtually free of monomers or reactive diluents and has a low residual content of (meth) acrylic acid.
• □ to 0 to 20 wt .-% of photoinitiators.
  As photoinitiators it is possible to use those which initiate the curing or radical polymerization by using high-energy radiation and preferably by UV radiation and absorb it, for example, in the wavelength range from 190 to 400 nm. Such photoinitiators are, for example, chlorine-containing photoinitiators, aromatic ketones, hydroxyphenylphenones, phosphine oxides. Preferred photoinitiators are benzophenone derivatives, phenyl ketones and phenol phosphenates.
• □ to 0.5 to 20 wt .-% wax.
  As waxes, for example, polyethylene waxes, such as PTFE-modified polyethylene wax used.

Such a coating composition is for example from EP 1 663 662 B1 known. Unfortunately, this document, however, no suggestions to remove a method, as it is the subject of the present document.

• □ zu 65 bis 95 Gew.-% ein oder mehrere (Meth)acrylate.
  Bevorzugt ist das eine oder sind die mehreren Meth)acrylate ausgewählt aus der Gruppe umfassend Polyether(meth)acrylat, Epoxy(meth)acrylat sowie Urethan(meth)acrylat. Ganz besonders bevorzugt ist mindestens ein (Meth)acrylat der genannten Gruppe ein aminmodifiziertes (Meth)acrylat. Als aminmodifiziertes (Meth)acrylat wird bevorzugt aminmodifiziertes Polyether-acrylat eingesetzt.
  Bevorzugt ist auch die dritte Beschichtungszusammensetzung nahezu frei von Monomeren bzw. Reaktivverdünnern und weist einen niedrigen Restgehalt an (Meth)acrylsäure auf.
• □ zu 0 bis 20 Gew.-% Photoinitiatoren.
  Als Photoinitiatoren können solche eingesetzt werden, welche die Härtung bzw. radikalische Polymerisation unter Anwendung von energiereicher Strahlung und bevorzugt von UV-Strahlung initiieren und beispielsweise im Wellenbereich von 190 bis 400 nm absorbieren. Derartige Photoinitiatoren sind beispielsweise chlorhaltige Photoinitiatoren, aromatische Ketone, Hydro-Xyalkylphenone, Phosphinoxide. Bevorzugte Photoinitiatoren sind Benzophenonderivate, Phenylketone und Phenyolphosphenate.

The third, also nonaqueous coating composition comprises at least

• To 65 to 95% by weight of one or more (meth) acrylates.
  The one or more methacrylates are preferably selected from the group comprising polyether (meth) acrylate, epoxy (meth) acrylate and urethane (meth) acrylate. Most preferably, at least one (meth) acrylate of said group is an amine-modified (meth) acrylate. The amine-modified (meth) acrylate used is preferably amine-modified polyether acrylate.
  The third coating composition is preferably also virtually free of monomers or reactive diluents and has a low residual content of (meth) acrylic acid.
• □ to 0 to 20 wt .-% of photoinitiators.
  As photoinitiators it is possible to use those which initiate the curing or radical polymerization by using high-energy radiation and preferably by UV radiation and absorb it, for example, in the wavelength range from 190 to 400 nm. Such photoinitiators are, for example, chlorine-containing photoinitiators, aromatic ketones, hydroxyphenylphenones, phosphine oxides. Preferred photoinitiators are benzophenone derivatives, phenyl ketones and phenol phosphenates.

It represents a possible, simplifying and preferred method according to the proposed method, if as a third coating composition the formulation of the second coating composition is adopted, so that the method manages the preparation and application of the first, second, optionally fourth and optionally fifth coating composition. In this case, the second coating composition is then used both for forming the protective layer covering the heat-sensitive recording layer and for forming the at least one coating arranged on the back of the substrate. Also, and in particular, it is possible that the second and third coating compositions differ only in the presence of the wax in the second coating composition as opposed to its absence in the third coating composition.

In a preferred embodiment, the proposed method provides for the preparation of a fourth coating composition, wherein the fourth coating composition for the preferably desired formation of a pigmented intermediate layer arranged between the front side of the substrate and the heat-sensitive recording layer particularly preferably comprises organic pigments and inorganic pigments which comprise the inorganic pigments individually or in solution Combined among themselves selected from the list comprising: calcined kaolin, silica, bentonite, calcium carbonate and alumina, and here especially boehmite.

The ratio between organic and inorganic pigment is a compromise of the effects caused by the two types of pigments, which is particularly advantageously solved when the pigment mixture to 5 to 30 wt .-% or better to 8 to 20 wt .-% of organic and 95 to 70 wt .-% or better to 92 to 80 wt .-% consists of inorganic pigment. Pigment mixtures of different organic pigments are conceivable.

In addition to the inorganic and possibly also organic pigments, the fourth coating composition contains at least one binder, preferably based on a synthetic polymer, wherein, for example, styrene-butadiene latex gives particularly good results. The use of a synthetic binder with the addition of at least one natural polymer, particularly preferably starch, is a particularly suitable embodiment. In the context of experiments with inorganic pigments it was further found that with a binder-pigment ratio within the fourth coating composition between 3: 7 and 1: 9, in each case based on wt .-%, a particularly suitable embodiment is present.

In a further embodiment, the proposed method provides for the preparation of a fifth coating composition, wherein the fifth coating composition primarily for forming a rear-side intermediate coating positioned between the rear side of the substrate and the at least one coating disposed on the rear side of the substrate comprises a plurality of binders and most preferably is prepared on an aqueous basis. Against this background, polyvinyl alcohol and modified polyvinyl alcohols are particularly suitable as binders. Shares of 0 to 10 wt .-% pigment, based on the entire fifth coating composition, can bring about positive effects, in which case, in particular, calcium carbonate is preferred.

1. (i) das Ausbilden eines bahnförmigen Substrat, aufweisend eine Vorderseite und eine der Vorderseite gegenüberliegende Rückseite,
2. (ii) ein optionales Aufbringen der vorbereiteten vierten Beschichtungszusammensetzung zur Ausbildung der pigmentierten Zwischenschicht auf der Vorderseite des bahnförmigen Substrats,
3. (iii) ein optionales Trocknen der vierten Beschichtungszusammensetzung,
4. (iv) ein optionales Glätten des Substrates mit der aufgebrachten und getrockneten vierten Beschichtungszusammensetzung,
5. (v) das Aufbringen der vorbereiteten ersten Beschichtungszusammensetzung zur Ausbildung der auf der Vorderseite des Substrats angeordneten wärmeempfindlichen Aufzeichnungsschicht,
6. (vi) das Trocknen der ersten Beschichtungszusammensetzung,
7. (vii) ein optionales Aufbringen der vorbereiteten fünften Beschichtungszusammensetzung zur Ausbildung einer rückseitigen Zwischenbeschichtung,
8. (viii)ein optionales Trocknen der fünften Beschichtungszusammensetzung,
9. (ix) ein optionales Glätten des Substrates mit den optional aufgebrachten und getrockneten vierten und fünften Beschichtungszusammensetzungen und der aufgebrachten und getrockneten ersten Beschichtungszusammensetzung,
10. (x) das Aufbringen der vorbereiteten zweiten Beschichtungszusammensetzung zur Ausbildung der die wärmeempfindliche Aufzeichnungsschicht abdeckenden Schutzschicht
11. (xi) das Vernetzen der die wärmeempfindliche Aufzeichnungsschicht abdeckenden Schutzschicht mittels energiereicher Strahlung,
12. (xii) das Aufbringen der vorbereiteten dritten Beschichtungszusammensetzung zur Ausbildung der mindestens einen auf der Rückseite des Substrats angeordneten Beschichtung,
13. (xiii) das Vernetzen der mindestens einen auf der Rückseite des Substrats angeordneten Beschichtung mittels energiereicher Strahlung,
14. (xiv)das Konfektionieren des wärmeempfindlichen Aufzeichnungsmaterials,

in der obigen Abfolge oder in abgeänderter Abfolge kann im Rahmen einer Ausführungsform mittels genau eines Durchlaufs durch genau eine Maschine erfolgen. Eine solche Maschine ist dann, sofern das Substrat wie bevorzugt eine Papierbahn ist, eine Papiermaschine mit integrierten Streichwerken, Druck- und Vernetzungsaggregaten und Konfektionierungseinrichtungen.Carrying out the method steps

1. (i) forming a web-shaped substrate having a front side and a rear side opposite the front side,
2. (ii) optionally applying the prepared fourth coating composition to form the pigmented intermediate layer on the front side of the web-shaped substrate,
3. (iii) optional drying of the fourth coating composition,
4. (iv) optionally smoothing the substrate with the applied and dried fourth coating composition,
5. (v) applying the prepared first coating composition to form the heat-sensitive recording layer disposed on the front surface of the substrate;
6. (vi) drying the first coating composition,
7. (vii) optionally applying the prepared fifth coating composition to form a backside intermediate coating,
8. (viii) optional drying of the fifth coating composition,
9. (ix) optionally smoothing the substrate with the optionally applied and dried fourth and fifth coating compositions and the applied and dried first coating composition,
10. (x) applying the prepared second coating composition to form the protective layer covering the heat-sensitive recording layer
11. (xi) crosslinking the protective layer covering the thermosensitive recording layer by means of high-energy radiation,
12. (xii) applying the prepared third coating composition to form the at least one coating disposed on the back side of the substrate,
13. (xiii) the crosslinking of the at least one coating arranged on the back side of the substrate by means of high-energy radiation,
14. (xiv) preparing the heat-sensitive recording material,

in the above sequence or in a modified sequence, in the context of one embodiment, it is possible for exactly one pass to be performed by exactly one machine. Such a machine, if the substrate is preferably a paper web, is a paper machine with integrated coating units, printing and cross-linking units and packaging devices.

As an alternative to the embodiment of the previous sentence, within the scope of a preferred embodiment, at least two machines can be used to process the above process steps (i) to (xiv), wherein process steps (i) to (iv) and optionally additionally process steps (vii) to ( viii) plus a downstream reeling of the substrate by a machine designed as a paper machine, while the process steps (v) to (xiv), optionally without the process steps (vii) to (viii), plus an upstream unrolling of the substrate with optionally applied fourth and / or fifth coating composition by a second machine designed as a coating machine with integrated printing and cross-linking units and packaging devices. In both machines, of course, the implementation of further process steps is conceivable.

Another particularly preferred embodiment provides for carrying out the method steps (x) to (xiv) plus an upstream unwinding of the substrate with applied coating compositions by a packaging machine with integrated printing and cross-linking units, wherein the packaging machine in the sense of the present invention is to be understood as a machine selected from the list comprising: rewinder, slitter, cross cutter, guillotine, without any of these typical representatives of paper processing and finishing machines Way to be limited. The remaining process steps (i) to (xiv) at least in addition to a subsequent rolling up of the substrate with applied coating compositions are then carried out either by a paper machine or by two machines designed as paper and / or coating machines.

In the same way, it is conceivable and is considered to be preferred if the method steps (i) to (iv) plus a downstream reeling of the substrate are carried out by the first machine designed as a paper machine, while the method steps (v) to (xiv) plus an upstream unwinding the substrate by a second machine or alternatively by a second machine for the process steps (v) to (ix) and by a third machine for the process steps (x) to (xiv), in each case plus the necessary additional roll-up and unrolling process steps, be executed. In all machines, of course, the implementation of further process steps is conceivable.

The formation of the web-like substrate is done for example and in a preferred embodiment on a paper machine, in which at least one upstream Mischbütte a paper pulp of different pulps, optionally groundwood, fillers and water is applied and where preferred to this paper pulp before being fed to the paper machine more Components such as resin size for engine sizing and other conventional additives, such as pigments, Nuancierfarbstoffe and / or optical brightener are added.

• □ das Auftragen der zweiten Beschichtungszusammensetzung auf die zuvor aufgebrachte und getrocknete wärmeempfindliche Aufzeichnungsschicht als eine diese wärmeempfindliche Aufzeichnungsschicht abdeckende Schutzschicht
• □ wie das Auftragen der dritten Beschichtungszusammensetzung auf die Rückseite des Substrates bzw. auf die optionale rückseitige Zwischenbeschichtung.

Der jeweilige Auftrag der zweiten und der dritten Beschichtungszusammensetzung geschieht

• □ hinsichtlich der Ausbildung der Schutzschicht
• □ und hinsichtlich der Ausbildung der mindestens einen rückseitigen Beschichtung jeweils oder nur für eine der beiden Aufträge aus Schutzschicht und rückseitiger Bedruckung
  bevorzugt mittels Analogdruck. Dabei werden als Analogdruck im Sinne dieser Erfindung alle Druckverfahren bezeichnet, die mit Druckplatte bzw. -zylinder arbeiten, wozu Tiefdruck, Siebdruck, Offsetdruck und in einer ganz besonders bevorzugten Ausführung Flexodruck gehört. Bevorzugt werden sowohl die Schutzschicht innerhalb des Verfahrensschritts (x) wie auch die mindestens eine rückseitige Beschichtung innerhalb des Verfahrensschritts (xii) im Rahmen genau eines Maschinendurchlaufs aufgebracht respektive aufgedruckt.

An inventive process aspect is

• □ applying the second coating composition to the previously applied and dried heat-sensitive recording layer as a protective layer covering this heat-sensitive recording layer
• □ such as the application of the third coating composition on the back of the substrate or on the optional backside intermediate coating.

The respective order of the second and the third coating composition happens

• □ regarding the formation of the protective layer
• □ and with regard to the formation of the at least one back coating respectively or only for one of the two jobs of protective layer and back printing
  preferably by analog pressure. Here are referred to as analog printing in the context of this invention, all printing processes that work with printing plate or cylinder, including gravure, screen printing, offset printing and in a very particularly preferred embodiment flexographic belongs. Both the protective layer within the process step (x) and the at least one backside coating within the process step (xii) are preferably applied or printed in the context of exactly one machine pass.

1. (a.) die zweite Beschichtungszusammensetzung zur Ausbildung der die wärmeempfindliche Aufzeichnungsschicht abdeckenden Schutzschicht und/oder
2. (b.) die dritte Beschichtungszusammensetzung zur Ausbildung der mindestens einen auf der Rückseite des Substrats angeordneten Beschichtung
   jeweils in mindestens zwei übereinander angeordneten Lagen aufzubringen respektive aufzudrucken, weil so ein besonders dichter und gleichzeitig optimal dünner Auftrag gewährleistet werden kann.

It represents a preferred embodiment,

1. (a.) the second coating composition for forming the protective layer covering the heat-sensitive recording layer and / or
2. (b.) the third coating composition for forming the at least one coating disposed on the back side of the substrate
   in each case in at least two superimposed layers apply respectively imprint, because so a particularly dense and optimally thin order can be guaranteed.

The second and / or the third coating composition for forming the protective layer covering the heat-sensitive recording layer or for forming the at least one coating arranged on the back side of the substrate are each preferably provided with an application layer and with a mass per unit area in a range from 0.5 to 4.5 g / m ² applied. In two superimposed layers, the basis weight of the total protective layer and / or the back coating is preferably in a range of 1.2 to 6 g / m ² and especially between 1.5 and 4 g / m ² .

For crosslinking the second and / or the third coating composition for forming the protective layer covering the heat-sensitive recording layer or for forming the coating arranged on the back side of the substrate, UV and electron radiation are particularly suitable as high-energy radiation, UV radiation being very particularly preferred applies. In this case, the second contains and / or the third coating composition photoinitiators in a range of 2 to 20 wt .-%.

• zu 65 bis 95 Gew.-% ein oder mehrere (Meth)acrylate. Bevorzugt ist das eine oder sind die mehreren Meth)acrylate. ausgewählt aus der Gruppe umfassend Polyether(meth)acrylat, Epoxy(meth)acrylat sowie Urethan(meth)acrylat. Ganz besonders bevorzugt ist mindestens ein (Meth)acrylat der genannten Gruppe ein aminmodifiziertes (Meth)acrylat. Als aminmodifiziertes (Meth)acrylat wird bevorzugt aminmodifiziertes Polyether-acrylat eingesetzt,
• zu 2 bis 20 Gew.-% Photoinitiatoren und
• zu 0,5 bis 20 Gew.-% Wachs,

wobei sich die Gew.-%-Angaben zu 67,5 bis 100 Gew.-% der zweiten Beschichtungszusammensetzung addieren.In such a case, within this most preferred embodiment, the second coating composition comprises at least:

• from 65 to 95% by weight of one or more (meth) acrylates. Preferably, the one or more meth) acrylates. selected from the group comprising polyether (meth) acrylate, epoxy (meth) acrylate and urethane (meth) acrylate. Most preferably, at least one (meth) acrylate of said group is an amine-modified (meth) acrylate. As amine-modified (meth) acrylate, preference is given to using amine-modified polyether acrylate,
• to 2 to 20 wt .-% of photoinitiators and
• from 0.5 to 20% by weight of wax,

wherein the wt .-% data add to 67.5 to 100 wt .-% of the second coating composition.

• zu 65 bis 95 Gew.-% ein oder mehrere (Meth)acrylate. Bevorzugt ist das eine oder sind die mehreren Meth)acrylate. ausgewählt aus der Gruppe umfassend Polyether(meth)acrylat, Epoxy(meth)acrylat sowie Urethan(meth)acrylat. Ganz besonders bevorzugt ist mindestens ein (Meth)acrylat der genannten Gruppe ein aminmodifiziertes (Meth)acrylat. Als aminmodifiziertes (Meth)acrylat wird bevorzugt aminmodifiziertes Polyether-acrylat eingesetzt,
• zu 2 bis 20 Gew.-% Photoinitiatoren,

wobei sich die Gew.-%-Angaben zu 67 bis 100 Gew.-% der dritten Beschichtungszusammensetzung addieren.The third coating composition, within this most preferred embodiment, comprises at least:

• from 65 to 95% by weight of one or more (meth) acrylates. Preferably, the one or more meth) acrylates. selected from the group comprising polyether (meth) acrylate, epoxy (meth) acrylate and urethane (meth) acrylate. Most preferably, at least one (meth) acrylate of said group is an amine-modified (meth) acrylate. As amine-modified (meth) acrylate, preference is given to using amine-modified polyether acrylate,
• from 2 to 20% by weight of photoinitiators,

wherein the wt .-% data add to 67 to 100 wt .-% of the third coating composition.

Preferably, the first coating composition for forming the thermosensitive recording layer within the process step (v) is applied by means of a coating process selected from the list comprising: a roller blade coater, knife coater, curtain coater or air brush. In this case, the first coating composition used to form the recording layer is preferably aqueous. The subsequent drying of the coating material within the process step (vi) is usually done by a method in which heat is supplied, as is done by hot-air floating dryer or contact dryer. Proven is also a combination of the listed dry processes. The basis weight of the heat-sensitive recording layer is preferably from 2 to 6 g / m ^2, and more preferably from 2.2 to 4.8 g / m ² .

Preferably, the fourth coating composition for forming the pigmented intermediate layer is applied to the front side of the substrate within the optional process step (ii) by a leveling spread process selected from the list comprising: roller coater, doctor blade or doctor blade coater. Especially in a method using any of these coating methods, the intermediate layer can positively contribute to leveling of the substrate surface, thus reducing the amount of the applied mass of the first coating composition for forming the heat-sensitive recording layer. The subsequent drying of the coating material within the optional process step (iii) is usually carried out by a method in which heat is supplied, as is done by hot-air floatation dryer or contact dryer. Proven is also a combination of the listed dry processes. For the basis weight of the intermediate layer, a preferred range between 5 and 20 g / m ² and even better between 7 and 12 g / m ^{2 has} proven.

Preferably, the fifth coating composition for forming a backside intermediate coating positioned between the back of the substrate and the at least one coating disposed on the backside of the substrate is applied within the optional process step (vii) by means of a coating process selected from the list comprising: roller blade coater, knife coater , Curtain coater or airbrush. In this case, the fifth coating composition used to form the backside intermediate coating is preferably aqueous. The subsequent drying of the coating composition within the process step (viii) is usually done by a method in which heat is supplied, as done by hot-air floatation dryer or contact dryer. Proven is also a combination of the listed dry processes. The basis weight of the backside intermediate coating is preferably between 2.0 and 5.5 g / m ² and more preferably between 2.2 and 4.0 g / m ² .

The proposed method for producing a heat-sensitive recording material, in preferred variants within the optional method step (iv), comprises smoothing the substrate with the applied and dried fourth coating composition and within the optional method step (ix) Smoothing the substrate with the optionally applied and dried fourth and / or fifth coating composition and the applied and dried first coating composition. The aim of such smoothing steps, which can be done in both cases by a calender or a calender, is to create a flattened, possibly glossy surface, which appear on the printed protective layer and / or on the printed back coating applied color images vivid and vibrant. Further, a smoother surface of the thermosensitive recording layer by improved contact with the thermal head promotes heat transfer and thus the sensitivity of this thermosensitive recording layer.

Although not limited to the production of a recording material on paper as a substrate, the production of paper and especially of a recording material on a non-surface-treated base paper is the substrate, which prevails on the market also in view of the good environmental performance because of good recyclability and which is preferred for the purposes of the invention. A non-surface treated base paper is to be understood as meaning a base paper which has not been treated in a size press or in a coating device. For the invention, films of, for example, polyolefin and polyolefin-coated papers as a substrate are possible to the same extent, without such an embodiment having an exclusive character.

The present invention, in addition to the disclosed methods - in all its various and mutually complementary embodiments and variants - for producing a heat-sensitive recording material, also claims the use of a heat-sensitive recording material produced by one of these methods as a parking ticket and / or a punitive ticket. Numerous tests and series of heat-sensitive recording materials made by one of the methods disclosed herein have been able to demonstrate their superior effect in their use as a parking and / or toll ticket. In particular, the above-described problems of a strong background graying due to direct sunlight as well as blocking and sticking due to the action of moisture could be regarded as convincingly solved by the recording materials, which were prepared by one of the methods disclosed herein. At the same time, the method, in all its various and mutually complementary embodiments and variants, ensures economically justifiable production costs, including, in particular, the flexibly applicable combination of coating ink applications and two-sided printing jobs together contribute with the perfectly matched components within the first, second, third, and optionally fourth and fifth coating compositions.

The surface mass,% by weight (% by weight) and parts by weight (parts by weight) given in the specification and claims refer to the "atro" weight, respectively. absolutely dry parts by weight. In the comments on the organic pigments of the pigment-containing interlayer, the relevant figures are calculated from the "lutro" weight, i. air-dry parts by weight, minus the proportion by weight of water around and inside the pigments in their form of delivery.

The invention will be further clarified by means of the following example according to the invention:

To form a paper web as a substrate for a heat-sensitive recording material, a paper pulp of eucalyptus pulp and other pulp fibers with fillers and water is applied in a mixing chest. Other constituents of the pulp to be added are resin size for engine sizing with an amount of 0.6% by weight (atro), based on the total weight of the pulp, and other customary additives, such as, for example, pigments and / or optical brighteners. After completion of the pulp this is then fed to a fourdrinier paper machine, where it is processed into a paper web with a basis weight of 69 g / m ² - process step (i).

• □ eine Pigmentmischung aus Hohlkörperpigment und kalziniertem Kaolin mit einem auf Gew.-% bezogenen Verhältnis Hohlkörperpigment : kalziniertem Kaolin von 1:4,
• □ Styrol-Butadien-Latex als Bindemittel,
• □ Stärke als Cobinder
• □ und weitere Hilfsmittel auf.

After a slight calendering, the paper web is fed to a roller blade coater integrated into the paper machine, where it is applied on the front side as process step (ii) a pigmented intermediate layer having a basis weight of 9 g / m ² . In this case, the fourth coating composition used for this purpose has the formation of the intermediate layer

• □ a pigment mixture of hollow body pigment and calcined kaolin with a ratio by weight of hollow body pigment: calcined kaolin of 1: 4
• □ styrene-butadiene latex as a binder,
• □ starch as cobinder
• □ and other resources.

The paper web is still dried within the paper machine by means of radiant heaters and in contact with hot rollers - process step (iii), in a Mehrwalzenglättwerk smoothed - process step (iv) - and then rolled up as a semi-finished paper drum.

• □ Farbbildner: 3-dibutylamino-6-methyl-7-Anilinofluoran, das ist: ODB-2;
• □ Farbakzeptor : 4,4'-Dihydroxydiphenylsulfon, das ist: 4,4 BPS;
• □ Sensibilisator: Dimethylterephtalat, das ist: DMT;
• □ Bindemittel: Ethylen-Vinylalkohol-Coplymer, das ist: EVOH;
• □ Hilfsmittel: Gleitmittel (Zinkstearat), Wachse, Vernetzer

The thus prepared semi-finished paper drum is fed to a coater where the continuously rewound web is first fed to a doctor blade coater where as process step (v) applying the prepared first coating composition to form the heat sensitive recording layer disposed on the front side of the substrate with a basis weight of 4.2 g / m ² happens. As components for the first coating composition are used:

• □ color former: 3-dibutylamino-6-methyl-7-anilinofluoran, which is: ODB-2;
• □ Color acceptor: 4,4'-dihydroxydiphenylsulfone, which is: 4.4 BPS;
• □ sensitizer: dimethyl terephthalate, which is: DMT;
• □ binder: ethylene-vinyl alcohol copolymer, which is: EVOH;
• □ Auxiliaries: Lubricant (zinc stearate), waxes, crosslinkers

The heat-sensitive recording layer is dried as process step (vi) by means of a hot-air floating dryer and in contact with hot rolls. This is followed by the order of the prepared fifth coating composition comprising mainly unmodified polyvinyl alcohol and aqueous-based calcium carbonate to form a backside intermediate coating - process step (vii), drying this application process step (viii) - and, in a multi-roll calender, smoothing the paper web with the respective applied and dried pigmented intermediate layer, the heat-sensitive recording layer and the backside intermediate coating - process step (ix). It follows the re-roll on a spool.

The spool thus produced is fed to a slitter with integrated printing units and UV lamps, where on the continuously rewound paper web by means of a multi-color flexographic printing unit within the used slitter first as process step (x) the prepared second coating composition for forming the heat-sensitive recording layer the covering protective layer and, immediately following process step (xii), the prepared third coating composition for forming the at least one coating arranged on the back side of the substrate, each with a surface-related coating Mass of 2.0 g / m ^{2 is} printed. The second coating composition used was prepared as follows:

40% by weight of dipentaerythritol pentaacrylate are mixed with 40% by weight of low-viscosity amine-modified polyether acrylate and of a combination of 10% by weight of benzophenone derivative and 8.5% by weight of hydroxycyclohexyl phenyl ketone. 1.5% by weight of PTFE-modified polyethylene wax are added to this mixture and homogeneously mixed with one another. The result is a reactive diluent-free composition with low residual acrylic acid content.

The third coating composition is identical to the second coating composition except for the absence of the PTFE-modified polyethylene wax.

Subsequently, within the jointly performed process steps (xi) and (xiii), the two previously printed coatings are crosslinked on the one hand to form the heat-sensitive recording layer covering protective layer and on the other to form the at least one arranged on the back of the substrate coating by means of UV radiation. Finally, the thus finished heat-sensitive recording material is cut into smaller rolls and further assembled according to customer requirements - process step (xiv) - and is then ready for its use as a parking and / or penalty ticket.

Claims (16)

1. Process for producing a heat-sensitive recording material

   □ with a web-form substrate, having a front side and a rear side opposite the front side,

   □ with a heat-sensitive recording layer that is arranged on the front side of the substrate and contains colour formers and colour acceptors,

   □ with a protective layer covering that heat-sensitive recording layer,

   □ with at least one coating arranged on the rear side of the substrate,

   the process comprising at least the following process steps:

   ■ preparation of a first coating composition, such a first coating composition comprising at least:

   - as colour acceptor at least 80 % by weight - based on the total content of colour acceptors in the first coating composition - of 4,4'-dihydroxy-diphenylsulphone,

   - at least one sensitiser, selected from the list comprising stearic acid amide, dimethyl sulphone, 2-(2H-benzotriazol-2-yl)-p-cresol and dimethyl terephthalate,

   ■ preparation of a second coating composition, such a second coating composition comprising at least:

   - from 65 to 95 % by weight of one or more (meth)acrylates,

   - from 0 to 20 % by weight photoinitiators and

   - from 0.5 to 20 % by weight wax,

   the % by weight adding up to from 65.5 to 100 % by weight of the second coating composition,

   ■ preparation of a third coating composition, such a third coating composition comprising at least:

   - from 65 to 95 % by weight of one or more (meth)acrylates,

   - from 0 to 20 % by weight photoinitiators and

   the % by weight adding up to from 65 to 100 % by weight of the second coating composition,

   ■ formation of a web-form substrate having a front side and a rear side opposite the front side,

   ■ application of the prepared first coating composition to form the heat-sensitive recording layer arranged on the front side of the substrate,

   ■ drying of the first coating composition,

   ■ application of the prepared second coating composition to form the protective layer covering the heat-sensitive recording layer,

   ■ crosslinking of the protective layer covering the heat-sensitive recording layer by means of high-energy radiation,

   ■ application of the prepared third coating composition to form the at least one coating arranged on the rear side of the substrate,

   ■ crosslinking of the at least one coating arranged on the rear side of the substrate by means of high-energy radiation,

   ■ finishing of the heat-sensitive recording material, having at least:

   - the web-form substrate,

   - the heat-sensitive recording layer arranged on the front side of the substrate, formed from the first coating composition,

   - the protective layer covering the heat-sensitive recording layer, formed from the second coating composition,

   - the at least one rear-side coating arranged on the rear side of the substrate, formed from the third coating composition.
2. Process for producing a heat-sensitive recording material according to patent claim 1, characterised in that 4,4'-dihydroxy-diphenylsulphone is the sole colour acceptor in the first coating composition.
3. Process for producing a heat-sensitive recording material according to either one of patent claims 1 and 2, characterised in that the colour formers in the first coating composition are selected from the list comprising:

   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.
4. Process for producing a heat-sensitive recording material according to any one of patent claims 1 to 3, characterised in that, based on the % by weight in the first coating composition, the ratio 4,4'-dihydroxy-diphenylsulphone : sensitiser lies in a range of from 1 : 0.5 to 1 : 2.
5. Process for producing a heat-sensitive recording material according to any one of patent claims 1 to 4, characterised in that the process comprises the at least three additional process steps:

   ■ preparation of a fourth coating composition, the fourth coating composition comprising organic pigments and inorganic pigments, the inorganic pigments selected from the list comprising: calcined kaolin, silicon oxide, bentonite, calcium carbonate and also aluminium oxide and here especially boehmite,

   ■ application of the prepared fourth coating composition to form a pigmented intermediate layer arranged between the front side of the substrate and the heat-sensitive recording layer,

   ■ drying of the fourth coating composition,

   these at least three additional process steps being inserted before the process step "application of the prepared first coating composition to form the heat-sensitive recording layer arranged on the front side of the substrate".
6. Process for producing a heat-sensitive recording material according to any one of patent claims 1 to 5, characterised in that the second coating composition for forming the protective layer covering the heat-sensitive recording layer is applied by means of analogue printing.
7. Process for producing a heat-sensitive recording material according to any one of patent claims 1 to 6, characterised in that the third coating composition for forming the at least one coating arranged on the rear side of the substrate is applied by means of analogue printing.
8. Process for producing a heat-sensitive recording material according to any one of patent claims 1 to 7, characterised in that

   (a.) the application of the second coating composition to form the protective layer covering the heat-sensitive recording layer
   and

   (b.) the application of the third coating composition to form the at least one coating arranged on the rear side of the substrate
   is effected in just one pass through the machine.
9. Process for producing a heat-sensitive recording material according to any one of patent claims 1 to 8, characterised in that the high-energy radiation for crosslinking

   (a.) the second coating composition to form the protective layer covering the heat-sensitive recording layer
   and/or

   (b.) the third coating composition to form the at least one coating arranged on the rear side of the substrate
   is UV radiation.
10. Process for producing a heat-sensitive recording material according to any one of patent claims 1 to 9, characterised in that

    (a.) the second coating composition for forming the protective layer covering the heat-sensitive recording layer
    and/or

    (b.) the third coating composition for forming the at least one coating arranged on the rear side of the substrate
    is or are in each case applied in at least two layers arranged one on top of the other.
11. Process for producing a heat-sensitive recording material according to any one of patent claims 1 to 10, characterised in that the first coating composition for forming the heat-sensitive recording layer is applied by means of a coating method, selected from the list comprising: doctor roller coating device, blade coating device, curtain coater and air brush.
12. Process for producing a heat-sensitive recording material according to any one of patent claims 5 to 11, characterised in that the fourth coating composition for forming the pigmented intermediate layer on the front side of the substrate is applied by means of a coating method, selected from the list comprising: roller coating device, blade coating device and doctor (roller) coating device.
13. Process for producing a heat-sensitive recording material according to any one of patent claims 1 to 12, characterised in that the drying

    (a.) of the first coating composition to form the heat-sensitive recording layer and/or

    (b.) of the fourth coating composition to form the pigmented intermediate layer is effected by supplying heat.
14. Process for producing a heat-sensitive recording material according to any one of patent claims 1 to 13, characterised in that the process comprises at least the three additional process steps:

    ■ preparation of a fifth coating composition, the fifth coating composition comprising primarily binders,

    ■ application of the prepared fifth coating composition to form a rear-side intermediate coating - positioned between the rear side of the substrate and the at least one coating arranged on the rear side of the substrate,

    ■ drying or crosslinking of the fifth coating composition.
15. Process for producing a heat-sensitive recording material according to any one of patent claims 1 to 14, characterised in that the substrate is paper.
16. Use of a heat-sensitive recording material produced by a process as claimed in any one of patent claims 1 to 15 as a parking ticket and/or penalty ticket.