EP1543984A2 - Heat-sensitive recording material for double-sided printing - Google Patents

Abstract

Heat sensitive recording material for duplex printing has a web type substrate in which the fraction of heat reacting components in the heat-sensitive recording layer of the substrate lies in the range 35 to 38 percent by weight and the ratio of pigment by weight to binding agent by weight in the heat sensitive recording layer is in the range 0.5 to 1 up to 1.5 to 1. An independent claim is included for the use of the inventive recording material for offset, screen, gravure and flexoprinting.

Description

The present invention relates to heat-sensitive recording materials having a sheet-like substrate, on the first side of which a heat-sensitive recording layer and a protective layer covering the heat-sensitive recording layer are applied. In addition to the pigment and binder, the recording layer contains at least one dye precursor and at least one color acceptor as components which react color-forming with one another under the action of heat. On the side of the substrate opposite to the side of the substrate having the recording layer, the sheet-shaped substrate carries a backside coating.
To the same extent, the invention relates to the use of the proposed thermosensitive recording material for printing with an analog printing method.

From DE-C-38 36 660 a heat-sensitive recording material with substrate and on the front side applied to the substrate recording layer, which is optionally covered by a protective layer, known. On the reverse side, the substrate carries a coating of water-soluble high polymers, such as starch, gelatin, styrene-maleic anhydride copolymer hydrolysates or polyvinyl alcohol, and of water-insoluble polymers, such as latices. The polymers are used alone or as a mixture. With the known backside coating is to prevent that when using the known recording material as a label, in particular plasticizers which are present on a provided with the label sheet can penetrate from the back of the recording layer and thus a weakening or deletion of a possible Effect typeface. By way of example, the recording layer of the known heat-sensitive recording material contains a very high proportion of calcium carbonate as pigment and a content of binders of polyvinyl alcohol and methyl cellulose which precipitates very small in relation to the pigment content.

A similar protective effect is expected from DE-A-37 20 171 for the back-coated barrier layer of a proposed thermosensitive recording material having a colored fluorescent dye composition in its recording layer. The barrier layer comprises substantially water-soluble polymer materials such as polyvinyl alcohol, various cellulose ethers, starch, gelatin, casein, and polyvinylpyrrolidone, as well as water-dispersed resins such as polystyrene emulsions. The function of the barrier layer is to protect against materials such as oils and plasticizers which are known to cause discoloration or discoloration of the images developed in the recording layer.

The subject of US 2003/0073576 A 1 is a medically transparent light-sensitive recording material whose recording layer is coated with a protective layer. This protective layer is intended to improve the resistance of the known recording material to chemicals, water and light, and preferably consists entirely of a resin for which there are scarcely any limits in the list of names; inter alia, diisocyanate is enumerated as a possible material. To improve the hardness, pigments are included in the resin of the protective layer, for which all known inorganic pigments appear suitable. If the known recording material to be provided with a backside coating, the components of the protective layer are also considered to be suitable for the backside coating, without which there are exemplary embodiments thereof.
As a component essential to the invention, this document discloses a color developer based on salicylic acid. The binder content in the recording layer is not limited; up to 65% by weight are considered suitable. No information is given on the proportion of pigments in the recording layer. Surface properties or other uses of the thus proposed recording material are not disclosed.

The desired back printing of a heat-sensitive recording material in the offset and flexographic printing process is the reason for the stated object in WO 99/14056 A 1 for a backside coating , compared to the substances used in offset and flexographic printing, especially organic solvents, as well as plasticizers, oils and fats has a good barrier effect. For solution, the backside coating of the known recording material comprises a mixture containing starch, a non-styrene or vinyl acetate acrylate copolymer having a film-forming temperature of less than 5 ° C and preferably less than 2 ° C and an alkaline catalyst such as calcium carbonate.

Especially from the last acknowledged writing, it is known, the back of heat-sensitive recording materials as a carrier for offset printing to use. The recording materials known from the prior art have what the blocking effect compared to this used related chemicals, well proven. Are however high quality, pigmented Backside coatings, for example, for full-surface presentation desired by multi-color prints, occasionally had difficulties with the actual Printing process with its requirements on the surface to be printed be observed because deposits on the blanket trouble-free and thus make effective printing difficult.

Thus, in principle, from the prior art heat-sensitive recording materials are known which by means of various Printing techniques are to be printed. A disadvantage of the known However, recording materials is often not the necessary Have the cleavage strength, in particular at fast-running, modern Printing machines occurring in the offset process high adhesion forces abrupt removal of the blanket from the surface to be printed too resist. There is an increasing demand for new applications thermosensitive recording materials, both front side and on the reverse, for example, in the offset process without problems and with high Printing press speeds are to be printed. So for example more economical to produce because faster to print tickets allows the front side next to the heat-induced printed images with individual Entry parameters also contain printed general entry information, while printed on the back general information such as advertising is.

The present invention thus provides a first task aspect therein Recording material with front-applied heat-sensitive recording layer to provide the front side over a high durability compared to substances used in offset and flexographic printing and in particular opposite organic solvents, plasticizers, optionally photoinitiators when printing with UV-curing printing inks, oils and greases and simultaneously in offset and flexo printing without problems and at high speeds good to print on.

A second aspect of the task is to provide a front-side recording material to provide an applied heat-sensitive recording layer, the in addition to the above-described frontal properties at the same time on his Rear side has a high blocking effect compared to offset and flexo printing Substances and in particular to organic solvents, plasticizers, Oils and fats and the reverse as well as the front side in the offset and flexo printing without problems and with high speeds is printing.

• wobei das bahnförmige Substrat auf seiner ersten Seite eine wärmeempfindliche Aufzeichnungsschicht mit
• (i) mindestens einem Farbstoffvorläufer und mindestens einem Farbakzeptor als unter Einwirkung von Wärme farbbildend miteinander reagierende Komponenten,
• (ii) mindestens einem Pigment und
• (iii) mindestens einem Bindemittel
• sowie eine die wärmeempfindliche Aufzeichnungsschicht abdeckende Schutzschicht trägt
• und wobei das bahnförmige Substrat auf seiner der ersten Seite gegenüberliegenden zweiten Seite eine pigmenthaltige Rückseitenbeschichtung trägt,

dadurch gekennzeichnet, dass

• der Anteil an unter Einwirkung von Wärme farbbildend miteinander reagierenden Komponenten in der wärmeempfindlichen Aufzeichnungsschicht in einem Bereich von 35 bis 58 Gew.-% (atro) liegt, und
• das Verhältnis von Pigment in Gew.-% (atro) zu Bindemittel in Gew.-% (atro) in der wärmeempfindlichen Aufzeichnungsschicht in einem Bereich von 0,5:1 bis 1,5:1 liegt.

After intensive consideration, the inventors recognized that the object can be achieved by a heat-sensitive recording material having a web-shaped substrate,

• wherein the web-shaped substrate has a heat-sensitive recording layer on its first side
• (i) at least one dye precursor and at least one color acceptor as components which react color-forming with one another under the action of heat,
• (ii) at least one pigment and
• (iii) at least one binder
• and a protective layer covering the heat-sensitive recording layer
• and wherein the web-shaped substrate carries a pigment-containing backcoat on its second side opposite the first side,

characterized in that

• the proportion of heat-color-sensitive components in the thermosensitive recording layer is in a range of from 35 to 58% by weight (atro) under the influence of heat
• the ratio of pigment in wt.% (atro) to binder in wt.% (atro) in the heat-sensitive recording layer is in a range of 0.5: 1 to 1.5: 1.

The statements made above relate to the% by weight of the color-forming mutually reactive components in the heat-sensitive recording layer on the total solids content (atro) of the heat-sensitive recording layer. Likewise, the statements made relate to the ratio of pigment in% by weight (atro) to binder in% by weight (atro) in each case on the total solids content (atro) the heat-sensitive recording layer.

The recording material according to the invention has, in addition to the others Characteristics of claim 1 in particular a particularly high proportion of the color-forming Components dye precursors and color acceptor in the heat-sensitive Recording layer on. In contrast, the pigment content is in the recording layer deliberately kept low. Through these measures could be a with regard to the problem to be solved particularly suitable and essential to the invention pigment / binder ratio be realized in the recording layer. The gripped Measures is based on the finding that heat-sensitive recording materials when printing in high-speed offset printing machines under the influence of strongly acting adhesive forces, especially in the recording layers columns. On the other hand, those applied to the recording layers Protective coatings less problematic, both as their own gap strength as well as their adhesion to the recording layers.

A preferred embodiment of the proposed recording material sees a proportion of color-forming reacting under the action of heat Components in the heat-sensitive recording layer in a range from 36.5 to 48% by weight (atro) and in particular from 37.5 to 42% by weight (atro) in front. The statements made above relate to the% by weight of the color-forming mutually reactive components in the heat-sensitive recording layer again to the total solids content (atro) of the heat-sensitive recording layer.

Furthermore, it is preferred if the ratio of pigment in% by weight (atro) to binder in% by weight (atro) in the heat-sensitive recording layer in a range of 0.65: 1 to 1.45: 1. Again, the information given to the ratio of pigment in wt .-% (atro) to binder in wt .-% (atro) each on the total solids content (atro) of the heat-sensitive recording layer. In addition, a ratio of the color-forming components in% by weight (atro) applies to binder in% by weight (atro) in the heat-sensitive recording layer in a range of 1.5: 1 to 12: 1 and especially between 1.85: 1 and 4: 1 as preferred. Here, too, the statements made relate to the ratio of the color-forming Components in wt .-% (atro) to binder in wt .-% (atro) in each case on the Total solids content (atro) of the heat-sensitive recording layer.

As suitable pigments in the heat-sensitive recording layer apply those that make a good compromise between whiteness, oil absorption behavior and cost-effectiveness represent. As in this sense preferred examples of particular inorganic oil-absorbing pigments are listed: natural and calcined Kaolin, silicon (di) oxide, bentonite, calcium carbonate, alumina and aluminum hydroxide and here especially boehmite, wherein the pigments individually as well as in combination can be used with each other. As a particularly preferred pigment with the most balanced properties in the context of this invention applies Calcium carbonate.

According to the present invention, as a binder in the heat-sensitive Recording layer starch, cellulose derivatives such as CMC and plastic dispersions based on acrylate, butadiene styrene, polyvinyl acetate and particularly preferred Polyvinyl alcohol alone or in admixture with each other in the recording layer be used. Among the polyvinyl alcohols are partially or better yet fully saponified polyvinyl alcohols and ethylene-vinyl alcohol copolymers considered suitable.

Because of the high proportion of reacting under the influence of heat color-forming components in the heat-sensitive recording layer, this can be applied with a relatively low application level, namely with a basis weight preferably in a range of 1.9 to 3.5 g / m ² , in particular with a basis weight ≤ 3.3 g / m ² , wherein the information given here in the description as well as in the claims relating to the basis weight of the recording layer in each case on the "atro" weight, which means to absolutely dry parts by weight , To order preferably curtain coaters or leveling commissioned works of knife and roller doctor type are used. Thus, a flat recording layer is effected which can not cause any interference with the passage of the thermal head during the thermal printing process. According to a preferred embodiment, the coating color used to form the thermosensitive recording layer is aqueous. The subsequent drying of the coating color can be done by means of infrared radiation. Just as well-proven are hot-air floating dryers and contact dryers, such as drying cylinders. At the same time cylinder. The different drying options can be combined in any kind and order.

• 3-N-propyl-N-methylamino-6-methyl-7-anilinofluoran
• 6'-(dibutylamino)-3'-methyl-2'-(phenylamino)-spiro[isobenzofuran-1 (3H),9'-[9H]xanthen]-3-one sowie
• 3,3-Bis-(p-dimethyl-aminophenyl)-6-dimethylaminophthalid
  sowie weitere Fluoranverbindungen, wie
• 2-Anilino-6-(dibutylamino)-3-methylfluoran
• 3-(Ethylisoamylamino)-6-methyl-7-anilinofluoran.

The formation of a protective layer covering the thermosensitive recording layer, and optionally multilayer, allows the distance between the thermosensitive recording layer and the thermal image-forming thermal head of a thermal printer to be forcibly increased. As the distance between the recording layer and the thermal head becomes larger, the resolution inevitably deteriorates, and the resolution is approximately inversely proportional to the square of the distance between the recording layer and the thermal head. A heat-sensitive recording layer, which counteracts this physical effect effectively, in which it guarantees an optimized resolution and a particularly good pressure dynamics, that means, a rapid response to even low heat exposure, is particularly important in this context. In principle, the heat-sensitive recording layer may contain all known dye precursors and, in particular, color acceptors suitable for this purpose, in particular organic dye acceptors. Without being limited to the dye precursors mentioned below, the following dye precursors have proven to be particularly effective and, for this reason, are used singly as in combination with other dye precursors which may also be mentioned here as being particularly preferred:

• 3-N-propyl-N-methylamino-6-methyl-7-anilinofluoran
• 6 '- (dibutylamino) -3'-methyl-2' - (phenylamino) -spiro [isobenzofuran-1 (3H), 9 '- [9H] xanthene] -3-one and also
• 3,3-bis (p-dimethyl-aminophenyl) -6-dimethylaminophthalide
  as well as other fluoran compounds, such as
• 2-anilino-6- (dibutylamino) -3-methylfluoran
• 3- (Ethylisoamylamino) -6-methyl-7-anilinofluoran.

For the dye precursors, an average particle size in one is recommended Range of greater than 0.3 microns to a maximum of 1 .mu.m, in particular from 0.45 .mu.m to 0.9 microns. The limits will be up due to too low sensitivity and down by an otherwise excessive tendency of the heat-sensitive recording material specified for graying.

• 2,2 bis (4-hydroxyphenyl)-propane,
• 4-[(4-(1-methylethoxy)phenyl)sulfonyl]phenole,
• 4,4'-Dihydroxy-Diphenylsulfone,
• N-(p-toluensulphonyl)-N'-(3-p-toluensulphonyl-Oxy-phenyl)-harnstoffe,
• 2,4'-Dihydroxy-Diphenylsulfone,
• N-(2-hydroxyphenyl)-2-[(4-hydroxyphenyl)thio]Acetamide.

The following color acceptors, used individually as in combination with other color acceptors also mentioned here, are considered to be particularly preferred:

• 2,2 bis (4-hydroxyphenyl) -propane,
• 4 - [(4- (1-methylethoxy) phenyl) sulfonyl] phenol,
• 4,4'-dihydroxy-diphenyl sulfones,
• N- (p-toluensulphonyl) -N '- (3-p-toluensulphonyl-oxy-phenyl) -ureas,
• 2,4'-dihydroxy-diphenyl sulfones,
• N- (2-hydroxyphenyl) -2 - [(4-hydroxyphenyl) thio] acetamides.

• Reaktionsbeschleuniger (Sensitizer), die den Schmelzpunkt der Farbakzeptoren herunterzusetzen vermögen,
• Gleitmittel, die sowohl während der Satinage mittels Glättwerk oder Kalander während des Herstellungsprozesses des erfindungsgemäßen Aufzeichnungsmaterials wie auch bei dessen Verwendung beim Passieren der Thermoköpfe von Thermodruckern von Vorteil sind,
• und Vernetzer für die Bindemittel.

Die oben aufgeführten Bestandteile können bis zu 35 Gew.-% (atro) bezogen auf den Gesamtfeststoffgehalt der wärmeempfindlichen Aufzeichnungsschicht ausmachen. Davon entfallen allein auf den oder die Reaktionsbeschleuniger 25 Gew.-% bis zu 30 Gew.-% (atro), ohne jedoch darauf in irgendeiner Art und Weise beschränkt zu sein.In addition to the already discussed pigments, binders and the dye precursors and color acceptors as color-forming components, the heat-sensitive recording layer comprises as further constituents in particular

• Reaction accelerators (sensitizers) that are able to lower the melting point of the color acceptors,
• Lubricants which are advantageous both during calendering by means of a calender or calender during the production process of the recording material according to the invention and also when it is used in passing the thermal heads of thermal printers,
• and crosslinkers for the binders.

The ingredients listed above may be up to 35% by weight (dry) based on the total solids content of the heat-sensitive recording layer. Of these, 25% by weight alone up to 30% by weight (atro) is attributable to the reaction accelerator (s) alone, but without being limited thereto in any way.

In a particularly preferred embodiment, the invention relates to an irreversible thermosensitive recording material contained in the recording layer form a permanent color or typeface under the influence of heat can.

The novel recording material has a protective layer covering the heat-sensitive recording layer, which preferably completely covers it. The protective layer performs a task, as it must also be partially fulfilled by the backside coating, namely on the one hand, the protection of the arranged under her recording layer from environmental influences such as oils, fats, water and plasticizers and on the other the improvement of printability, especially in the offset and flexographic printing. For this purpose, it preferably contains the ink-receptive pigments and is designed particularly gap-resistant. The protective layer itself can be applied by means of conventional brushing or, alternatively, printed, with a surface-related mass in a range from 0.5 to 4.5 g / m ^{2 being} preferred. Processing technology and in terms of their technological properties are particularly suitable such protective layers that are crosslinkable and crosslinked by high-energy radiation. The term high-energy radiation means heat, IR, UV or ionizing radiation, such as electron beams.

Between the recording layer and the substrate of the recording material according to the invention an intermediate layer is expediently arranged, which contains in addition to binder inorganic oil-absorbing and optionally also organic (hollow body) pigments. Preferred examples of the inorganic oil-absorbing pigments include natural and calcined kaolin, silicon (di) oxide, bentonite, calcium carbonate, aluminum oxide and aluminum hydroxide, in particular boehmite, where the pigments can be used individually as well as in combination with one another. If, in addition to the inorganic pigments, organic, so-called hollow body pigments which have air inside them and consequently constitute a good heat insulator are incorporated into the intermediate layer, such an intermediate layer acts as a heat reflector which reflects the heat emitted by the thermal head, the recording layer and previously which penetrates covering protective and printing layers, focused on the heat-sensitive recording layer. In addition to its heat-reflecting properties, the intermediate layer can furthermore make a positive contribution to the leveling of the substrate surface, with the result that the amount of coating color necessarily to be applied for the heat-sensitive recording layer can be further reduced if necessary. For this reason, offer to coat the intermediate layer leveling strokes, such as Walzenstreichwerke, doctor blade or (roll) doctor blade coating. Also, the pigments of this intermediate layer can absorb the heat-liquefied wax components of the thermosensitive recording layer in the typeface formation, thus promoting a safe and rapid operation of the heat-induced recording. For this reason, the preferred intermediate layer also comprises at least one oil or wax-absorbing pigment. The basis weight of the pigmented intermediate layer is preferably between 5 and 20 g / m ² and more preferably between 7 and 10 g / m ² (atro).

Are in the intermediate layer both inorganic oil-absorbing as organic (Hollow body) pigments used, the ratio between Both types of pigment made a compromise of the two types of pigments Effects that is particularly advantageous when the pigment mixture to 15 to 50% by weight, more preferably 18 to 25% by weight, of organic and 85 to 50% Wt .-% and more preferably to 82 to 75 wt .-% of inorganic pigment.

The particle size of the organic pigments present in the intermediate layer, determined as the D ₅₀ value, is in a range from 0.75 μm to less than 1.5 μm, preferably in a range from 0.8 μm to 1.1 μm. Particle sizes below 0.75 microns prohibit due to rheological processing difficulties. Particle sizes above 1.5 microns show too coarse-grained behavior and prevent a preferred leveling effect of the intermediate layer. For the inorganic pigments, the particle size is ideally less than 2 μm, determined as the D ₅₀ value. Pigments which have a particle size distribution of from 34 to 40% by weight of less than 1 μm and from 57 to 63% by weight of less than 2 μm have proved to be advantageous.

In a preferred embodiment, the recording material according to the invention a backside coating with at least one as crosslinker acting substance containing diisocyanate as an effective component. Especially it is preferred if such a crosslinker based on hexamethylene diisocyanate is provided as an effective component.

• wirkungsvolles Vernetzen der zur Ausbildung der Rückseitenbeschichtung zu benutzenden Streichfarbe,
• geringe Viskositätserhöhung bei Einbringen in die Streichfarbe und
• langsame Entfaltung der vernetzenden Wirkung,

von den zunächst getesteten und bekannten Substanzen erfüllt werden konnten. Gerade die beiden letzten Punkte sind dabei von elementarer Wichtigkeit, was die Handhabbarkeit in der produktionstechnischen Umsetzung einer Streichfarbe angeht: die Streichfarbe muss problemlos zusammengemischt und zum Streichwerk gefördert werden können, muss einheitlich ohne Aufbau von Verkrustungs- und Schmutznestern mit dem Streichwerk verarbeitbar sein und darf nicht schon während der Misch- und Verarbeitungsphase anfangen, auszuhärten. Einzig die im Rahmen einer bevorzugten Ausführungsvariante der Erfindung gefundenen Substanzen mit Diisocyanat und insbesondere mit Hexamethylendiisocyanat als wirksame Komponenten konnten überzeugen und helfen, eine Rückseitenbeschichtung für wärmeempfindliche Aufzeichnungsmaterialien zur Verfügung zu stellen, die den vollen Anforderungskatalog erfüllt.The inventors recognized that the observed printing problems on the backs of the known recording materials are accompanied by insufficient water resistance of the surface to be printed. If, during the printing process in the offset process, first a contacting of the surface to be printed with the moist blanket and then a fast, abrupt removal of the blanket from the printing surface, especially in fast-running, modern printing presses, the highest adhesion forces act on this printing surface , Loose or loosened particles of the backside coating can thus be deposited on the blankets of the offset printing units. After recognizing these - in simplified terms - different substances acting as crosslinkers were tested, without the minimum requirements for such a substance, namely

• effectively crosslinking the coating to be used to form the backsize coating,
• low increase in viscosity when introduced into the coating color and
• slow unfolding of the cross-linking effect,

could be met by the initially tested and known substances. Just the last two points are of elementary importance, as far as the handling in the technical production of a coating color is concerned: the coating color must be mixed together and promoted to the coating, must be uniform and without the buildup of Encrustation and dirt nests with the coating process can be processed and allowed do not start to harden during the mixing and processing phase. Only the substances with diisocyanate and, in particular, with hexamethylene diisocyanate as active components found in the context of a preferred embodiment of the invention were able to convince and help to provide a backside coating for heat-sensitive recording materials which fulfills the full catalog of requirements.

In addition to the three minimum requirements listed above for one as a crosslinker Acting substance was the inventors, also with a view to the need for a the greatest possible flexibility in the production process of heat-sensitive recording materials to ensure that this substance helps, a coating color for the backside coating, which over a comparatively long Period is stable, which means that it will not become overly bacterial and / or thickening. The recording material of the invention has in a preferred Embodiment, a backside coating of a coating color, the is stable to storage over 3 days with moderate stirring before its application and thereby also does not start to harden.

• natürliches wie kalziniertes Kaolin, bevorzugt im kolloidalen TeilchengrößenBereich von 60% bis 90% < 2 µm,
• Clay, Kieselsäure, Siliziumoxid, letzteres mit einer bevorzugten mittleren Teilchengröße in einem Bereich von 6 bis 10 µm,
• Aluminiumoxid und hier besonders Böhmit, letzteres bevorzugt mit einer mittleren Teilchengröße in einem Bereich von 10 bis 100 nm,
• sowie in einem besonderen Maße Talkum mit einer bevorzugten mittleren Teilchengröße in einem Bereich von 1 bis 10 µm.

In zahlreichen, den dieser Erfindung zugrunde liegenden Versuchen wurden auch Mischungen insbesondere der hier genannten Pigmente erfolgreich eingesetzt.In particular, calcium carbonate - preferably having a particle size in a colloidal range of 60% <2 μm to 90% <2 μm - and magnesium carbonate have proven suitable as pigments in the backcoat. The following pigments were also able to convince with positive test results:

• natural and calcined kaolin, preferably in the colloidal particle size range of 60% to 90% <2 μm,
• Clay, silicic acid, silica, the latter having a preferred average particle size in a range of 6 to 10 μm,
• Alumina and here especially boehmite, the latter preferably having an average particle size in a range of 10 to 100 nm,
• and, to a particular extent, talc having 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.

In addition to the pigments and the diisocyanate and in a preferred embodiment Hexamethylene diisocyanate includes the backcoat binder and in particular starch, styrene butadiene latex and carboxy-methyl cellulose. Also the mixture of different binders in sometimes highly divergent mixing ratios is possible and preferred. Furthermore, optical brighteners and defoamers customary additives according to the respective requirements.

• zu 75 bis 90 Gew.-% (atro) Pigmente,
• zu 5 bis 22 Gew.-% (atro) Bindemittel,
• sowie zu 0,5 bis 8 Gew.-% (atro) und ganz besonders bevorzugt
• zu 1 bis 4 Gew.-% (atro) Vernetzer mit Diisocyanat bzw. in einer bevorzugten Ausführungsform mit Hexamethylendiisocyanat als wirksame Komponente enthält.

It is preferred that the backside coating, based on its total solids content (atro),

• to 75 to 90% by weight (atro) pigments,
• to 5 to 22% by weight (atro) binder,
• and at 0.5 to 8 wt .-% (atro) and most preferably
• to 1 to 4 wt .-% (atro) crosslinker with diisocyanate or in a preferred embodiment with hexamethylene diisocyanate as an effective component.

If the binder in the backside coating is as above Versions as a mixture, the backside coating is preferred from 1 to 7% by weight of (atro) starch and, with particular preference, cationic cornstarch and from 4 to 15% by weight of (styrene) styrene-butadiene latex while carboxy-methylcellulose only in areas below 0.5 wt .-% (atro) input into the binder mixture place.

• einem Verhältnis von Pigment in Gew.-% (atro) zu Bindemittel in Gew.-% (atro) in der Rückseitenbeschichtung in einem Bereich von 18:1 bis 3,4:1 und besser zwischen 11:1 bis 4,5:1 sowie
• einem Verhältnis von Bindemittel in Gew.-% (atro) zu Vernetzer in Gew.-% (atro) in der Rückseitenbeschichtung in einem Bereich von 20:1 bis 1:1 1 und besser zwischen 8,5:1 bis 2,5:1

die an sie gestellten Anforderungen besonders gut erfüllt. Dabei beziehen sich die oben gemachten Angaben zu den Gew.-% der Pigmente, Bindemittel und Vernetzer in der Rückseitenbeschichtung auf den Gesamtfeststoffgehalt (atro) der Rückseitenbeschichtung.In the experimental realms underlying this invention, it has been found that a backside coating with

• a ratio of pigment in weight percent (atro) to binder in weight percent (atro) in the backside coating in a range of 18: 1 to 3.4: 1, and more preferably between 11: 1 to 4.5: 1 such as
• a ratio of binder in weight percent (atro) to crosslinker in weight percent (atro) in the backside coating in a range of 20: 1 to 1: 1 and more preferably between 8.5: 1 to 2.5: 1

meets the requirements placed on them particularly well. In this case, the information given above on the% by weight of the pigments, binders and crosslinkers in the backside coating refers to the total solids content (atro) of the backcoat.

Particularly positive results can be achieved with a coating weight for the backcoat in a range of 2 to 15 g / m ² , preferably in a range of 8 to 12 g / m ² . As the order of the backside coating particularly suitable brushing particularly equalizing application devices such as doctor blade and (roll) doctor blade coater and Walzenstreichwerke into consideration, without being limited in any way.

The inventors recognized that a particularly high quality print image the back of the heat-sensitive recording material of the invention win, if the backside coating is formed in two layers of the first, oriented towards the substrate layer as a pure binder pigment coating may be formed, while the second outer layer acting as a crosslinker Substance with diisocyanate or even better with hexamethylene diisocyanate as contains effective component. In this case it is possible that only one layer with a leveling applicator is applied, while for the second Location as an application device also air brush and curtain coater offers.

As a web-shaped substrate for the production of the novel recording material In particular, a paper web is suitable, even if the invention not limited to paper as a substrate. This is paper sized in the mass to a particular extent preferred. Alternatively or additionally, the paper can the side, which is optional with the pigmented interlayer as well as with the recording layer is to be provided with a polyolefin coating for sealing be provided.

The present invention also encompasses the use of the invention heat-sensitive recording material in all its proposed Embodiments and variants in the form of its printing with an analog printing method, selected from the group comprising offset printing, gravure printing, screen printing and flexographic printing. The printing can be done on the front and / or back for example for the production of advertising information tickets, Receipts or purchase receipts, guarantee certificates, public transport tickets Transportation such as buses, trains, ships, planes, as well as for ski lifts.

The information given in the description and claims for basis weight,% by weight (% by weight) and parts by weight (parts by weight) each refer to the "atro" weight, i. absolutely dry Weight. In the comments on the organic (hollow body) pigments of Pigment-containing interlayer, the relevant figures are calculated from the "lutro" weight, i. air-dry parts by weight, less weight of water inside the pigments as supplied.

The following examples will further illustrate the invention:

On a fourdrinier paper machine, a paper web of bleached and ground hardwood and softwood pulps with a mass per unit area of 67 g / m ² is prepared as substrate with the addition of customary admixture substances in conventional amounts. For mass sizing, a mixture of different tree resins is used in an amount of 0.5% by weight (atro) based on the total solids content (atro) of the paper web. An intermediate layer of 9 g / m ^{2 is} applied to the substrate on the front side by means of a doctor blade applicator within the paper machine. The intermediate layer comprises a pigment mixture of 20% by weight (atro) organic pigment having a particle size (D50) of 1 μm and 80% by weight (atro) calcined kaolin having a particle size (D50) of 0.9 μm and an oil absorption of 110 cm ³ / 100g. The intermediate layer further comprises a binder mixture of 75% by weight of styrene-butadiene latex and 25% by weight of starch, respectively (atro).

In the context of a first series of experiments comprising the first three individual tests, a thermosensitive recording layer containing a colorant and color acceptors having a basis weight of 3.0 g / m ² and a protective layer of 1.9 g / m ^{2 are} applied to the intermediate layer in this order , The formulation for the protective layer in all three cases provides as pigment a highly purified, alkaline-treated bentonite with platelet structure, whose intrinsic adhesion enables its fixation with low binder requirement and whose specific surface area in the non-dispersed state is given as 85 m ² / g in one area Edge ratio, which in the powdered bentonite ranges from 20 to 50. A binder / pigment ratio of 6: 1 and a crosslinker / binder ratio of 1: 5 are set. The crosslinking agent used is polyamide-epichlorohydrin resin, and the binder used is the aqueous dispersion of a self-crosslinking copolymer of acrylonitrile, methacrylamide and acrylic ester. The coating composition for the preparation of the protective layer contains as further components a defoamer, as a lubricant stearic acid and various dispersants on the one hand for the pigment and on the other hand for the lubricant.

For the recording layer, the following water-based formulations are used: example 1 2 3 dye precursor 2-anilino-6- (dibutylamino) -3-methylfluoran % By weight (atro) 12.83 12,91 9.69 color acceptor N- (p-toluensulphonyl) -N '- (3-p-toluensulphonyl-oxy-phenyl) -urea % By weight (atro) 27.56 25.73 20.81 reaction accelerators Benzyl 2-naphthyl ether % By weight (atro) 27.56 28,10 24.38 pigment calcium carbonate % By weight (atro) 15.75 11.88 26.02 lubricant Mixture of wax and a zinc stearate emulsion % By weight (atro) 3.94 3.96 5.74 binder fully saponified polyvinyl alcohol Ethylene-vinyl alcohol copolymer fully saponified polyvinyl alcohol Wt .-% (absolutely dry) 11.81 16,63 12,80 Crosslinker for binders dimethylolurea % By weight (atro) 0.55 0.79 0.56

In the inventive examples 1 and 2 is in the heat-sensitive Recording layer, a proportion of under the action of heat color forming with each other Reactive components of 40.39 wt .-% and 38.64 wt .-% (atro) found in Comparative Example 3, this proportion is only 30.50 wt .-% (atro). The ratio formed in the heat-sensitive recording layer Pigment in wt .-% (atro) to binder in wt .-% (atro) is in the inventive Examples 1 and 2 at 1.33: 1 and 0.71: 1, in Comparative Example 3 this is Value 2.03: 1. To determine the gap strength, the offset printing process occurring high adhesion forces are simulated.

For this purpose, each of the patterns of the recording material to be examined is placed on a glass plate with the back side. Each approximately 25 cm long adhesive film strip (Scotch 810 Magic Tape, Item No. 11257) is adhered to the protective layer of the recording material by means of a Finat standard pressure roller with a mass of 2 ± 0.05 kg, after gluing the adhesive film strip is still 3 times the pressure roller over the adhesive film strip. The orientation of the adhesive film strip must be in the machine direction of the recording material. When machine direction is considered in the production of a recording paper, the direction of the paper web in the paper or coating machine. Furthermore, the adhesive film strip must not protrude beyond the edges of the pattern.
Finally, the adhesive film strip should be evenly drawn from the pattern at an angle of 45 ° beginning with the last end glued on. The detached adhesive film strip is glued onto a black cardboard sheet. The break-off point on the respective sample is coated with a solvent tincture. If residues of the sample torn out of the black cardboard sheet (individual particles, smaller or larger protective layer and / or recording layer fragments) or discoloration reactions in the area of the tear-off point appear in reaction to the applied solvent tincture, the nip strength of the respective recording material pattern is low and the test results are considered bad. Without a splitting of the recording material pattern only a few or even no particles or layer fragments are torn out and the layer structure of the recording material is retained. There are little or no discoloration reactions in the area of the breakpoint in response to the applied solvent tincture and the test results are considered to be good.

The experiments made here show very good results in the inventive Examples 1 and 2. The recording material It. Comparative Example 3 is cleaved upon peeling off the adhesive film strip within the recording layer, the test result is poor: such a recording material could Increased problems with printing with high-speed offset printing presses prepare.

Starting from a heat-sensitive recording material according to Inventive Example 2, the following coating compositions are prepared for the respective formation of a backcoat according to the second Table of Recipes to be taken from the following Table 2 and using a doctor blade with a basis weight of 10, 1 g / m ² applied to the back of the substrate.

The experimental findings are shown in Table 3. In addition to the pH values, the viscosity of the mixed coating compositions according to Brookfield (spindle 3/100 rpm _{(that is} to say _{: revolutions per minute)} / 23 ° C.) is determined, the latter measured after one minute stirring time with specified stirring frequency, in this way statements about the shelf life to get the different coating color samples. In each case two cases, in particular the crosslinkers based on epichlorohydrin resin and ammonium zirconium carbonate, the danger of a greatly increased viscosity can be observed in their use. The use of oxalaldehyde-based crosslinkers may entail the risk of agglomerate and fractionation. Only the crosslinker tried with hexamethylene diisocyanate can convince in terms of low viscosity increase and delayed unfolding of the crosslinking effect in all examples. The effectiveness of the crosslinking agents used in the examples is investigated by wetting them with a few drops of water on a measuring surface 3 days after preparation of the recording material samples and rubbed with a finger under moderate pressure in a circular motion on the thus moistened measuring surface. It should be considered good if the measuring surface remains smooth on the surface and no particles are released, bad are those samples in which particles are released from the surface or even the entire surface dissolves. Again, only the tried crosslinker with hexamethylene diisocyanate convince. The other crosslinkers have hardly any result-increasing effect in some examples.

Versuch PH-Wert Viskosität [Brookfield (Spindel 3 / 100 rpm / 23°C)] Fingerwischtest (nach 3 Tagen) Kommentare 4 7,7 440_{nach einem Tag} Gut 5 6,9 880 _{nach einem Tag} Schlecht 6 8,4 180 _{nach einem Tag} Nicht ausreichend 7 7,1 2000 _{nach einem Tag} Nicht ausreichend Wg. Zu hoher Viskosität nicht einsetzbar 8 7,5 250 _{nach einem Tag} Schlecht 9 7,5 640_{nach 3 Stunden} Gut 10 6,9 1800 _{nach 3 stunden} Nicht ausreichend 11 8,3 430 _{nach 3 stunden} Nicht ausreichend 12 7,1 590 _{nach 3 stunden} Nicht ausreichend 13 7,4 470 _{nach 3 Stunden} Schlecht 14 7,3 40 _{nach 2 Tagen} Gut 15 6,8 150 _{nach 2 Tagen} Schlecht Geringe Fraktionsbildung in Streichfarbe 16 7,5 Fest Schlecht Fester Bodensatz 17 7,2 25 _{nach 2 Tagen} Mäßig Maßig Starke Fraktionsbildung mit festem Bodensatz 18 7,4 80 _{nach 2 Tagen} Schlecht Starke Fraktionsbildung in Streichfarbe 19 7,1 20 _{nach einem Tag} Gut 20 5,6 210 _{nach einem Tag} Schlecht 21 8,8 20 _{nach einem Tag} Schlecht 22 6,4 20 _{nach einem Tag} Mäßig 23 6,7 20 _{nach einem Tag} Schlecht 24 5,7 290 _{nach 3 stunden} Noch gut 25 5,5 10000 _{nach 3 Stunden} Schlecht Wg. Zu hoher Viskosität nicht einsetzbar 26 --- Fest --- Kein Blatt 27 5,5 75 _{nach 3 Stunden} Mäßig Keine homogene Streichfarbe möglich, leichte Agglomeratbildung 28 5,6 80 _{nach 3 Stunden} Schlecht 29 7,3 650 _{nach 3 Stunden} Gut 30 6,5 170 _{nach 3 Stunden} Schlecht 31 8,9 20 _{nach 3 stunden} Schlecht Fraktionsbildung in Streichfarbe, kein homogener Auftrag möglich 32 7,2 20 _{nach 3 stunden} Mäßig Fraktionsbildung in Streichfarbe, kein homogener Auftrag möglich 33 7,1 20 _{nach 3 Stunden} Schlecht Fraktionsbildung in Streichfarbe, kein homogener Auftrag möglich The experiments described above thus clearly illustrate the superior properties of the recording material according to the invention in all its claimed embodiments and variants.

attempt PH value Viscosity [Brookfield (spindle 3/100 rpm / 23 ° C)] Finger wipe test (after 3 days) Comments 4 7.7 440 _{after a day} Well 5 6.9 880 _{after one day} Bad 6 8.4 180 _{after a day} Unsatisfactory 7 7.1 2000 _{after one day} Unsatisfactory Wg. Too high viscosity can not be used 8th 7.5 250 _{after a day} Bad 9 7.5 640 _{after 3 hours} Well 10 6.9 1800 _{after 3 hours} Unsatisfactory 11 8.3 430 _{after 3 hours} Unsatisfactory 12 7.1 590 _{after 3 hours} Unsatisfactory 13 7.4 470 _{after 3 hours} Bad 14 7.3 40 _{after 2 days} Well 15 6.8 150 _{after 2 days} Bad Low fraction formation in coating color 16 7.5 Firmly Bad Solid sediment 17 7.2 25 _{after 2 days} Moderately moderate Strong fractionation with solid sediment 18 7.4 80 _{after 2 days} Bad Strong faction formation in coating color 19 7.1 20 _{after a day} Well 20 5.6 210 _{after a day} Bad 21 8.8 20 _{after a day} Bad 22 6.4 20 _{after a day} Moderate 23 6.7 20 _{after a day} Bad 24 5.7 290 _{after 3 hours} Still good 25 5.5 10000 _{after 3 hours} Bad Wg. Too high viscosity can not be used 26 --- Firmly --- No leaf 27 5.5 75 _{after 3 hours} Moderate No homogeneous coating color possible, slight agglomeration 28 5.6 80 _{after 3 hours} Bad 29 7.3 650 _{after 3 hours} Well 30 6.5 170 _{after 3 hours} Bad 31 8.9 20 _{after 3 hours} Bad Fraction formation in coating color, no homogeneous application possible 32 7.2 20 _{after 3 hours} Moderate Fraction formation in coating color, no homogeneous application possible 33 7.1 20 _{after 3 hours} Bad Fraction formation in coating color, no homogeneous application possible

Claims (17)

Heat-sensitive recording material with a web-shaped substrate, wherein the web-shaped substrate has a heat-sensitive recording layer on its first side (i) at least one dye precursor and at least one color acceptor as components which react color-forming with one another under the action of heat, (ii) at least one pigment and (iii) at least one binder and a protective layer covering the heat-sensitive recording layer and wherein the web-shaped substrate carries on its first side opposite the second side a pigmented back coating, characterized in that the proportion of components in the heat-sensitive recording layer which undergo color-forming reaction under the influence of heat is in a range from 35 to 58% by weight (atro), the ratio of pigment in wt.% (atro) to binder in wt.% (atro) in the heat-sensitive recording layer is in a range of 0.5: 1 to 1.5: 1. Heat-sensitive recording material according to claim 1, characterized in that the proportion of color-reactive with one another under the action of heat components in the heat-sensitive recording layer in a range of 37.5 to 42 wt .-% (atro). A heat-sensitive recording material according to any one of claims 1 and 2, characterized in that the ratio of pigment in wt .-% (atro) to binder in wt .-% (atro) in the heat-sensitive recording layer in a range of 0.65: 1 to 1.45: 1 is. Heat-sensitive recording material according to one of claims 1 to 3, characterized in that the heat-sensitive recording layer contains calcium carbonate as a pigment. A heat-sensitive recording material according to any one of claims 1 to 4, characterized in that the binder in the recording layer is fully saponified polyvinyl alcohol. A heat-sensitive recording material according to any one of claims 1 to 5, characterized in that the binder in the recording layer is an ethylene-vinyl alcohol copolymer. Heat-sensitive recording material according to one of claims 1 to 6, characterized in that the recording layer is covered by a printed, crosslinkable and crosslinked under the influence of high-energy radiation protective layer. Heat-sensitive recording material according to one of claims 1 to 7, characterized in that the recording layer is completely covered by the protective layer. Heat-sensitive recording material according to one of claims 1 to 8, characterized in that a pigmented intermediate layer is arranged between the substrate and the heat-sensitive recording layer. Heat-sensitive recording material according to one of claims 1 to 9, characterized in that the backside coating contains at least one acting as a crosslinking substance with diisocyanate as an effective component. Heat-sensitive recording material according to one of claims 1 to 10, characterized in that the backside coating contains at least one substance acting as a crosslinking agent with hexamethylene diisocyanate as an effective component. Heat-sensitive recording material according to one of claims 1 to 11, characterized in that the backside coating contains as pigment calcium carbonate. Heat-sensitive recording material according to one of claims 1 to 12, characterized in that the backcoat comprises one or more of the following enumerated binders: starch, styrene-butadiene latex, carboxymethylcellulose. Heat-sensitive recording material according to one of claims 1 to 13, characterized in that the backside coating in a range of 0.5 to 8 wt .-% (atro) containing a crosslinking substance with diisocyanate and / or hexamethylene diisocyanate as an effective component. Heat-sensitive recording material according to one of claims 1 to 14, characterized in that the pigment content in the backside coating is in a range of 75 to 90 wt .-% (atro). Heat-sensitive recording material according to one of claims 1 to 15, characterized in that the ratio of pigment in wt% (atro) to binder in wt% (atro) in the backside coating in a range of 18: 1 to 3.4: 1 and the ratio of binder in weight percent (atro) to crosslinker in weight percent (atro) in the backside coating is in a range of 20: 1 to 1: 1. Use of a heat-sensitive recording material according to one of Claims 1 to 16 selected for printing with an analog printing method from the group comprising offset printing, gravure printing, screen printing and flexographic printing.