EP2993054B1 - Sheet-form heat-sensitive recording material with at least two layers - Google Patents

Description

The invention relates to a web-shaped heat-sensitive recording material having at least a first layer and a first layer at least partially covering the second layer, the web-shaped heat-sensitive recording material proposed on this side taking into account environmental-friendly aspects to a particular extent.

The object of the invention is defined in the appended claims.

Heat-sensitive recording materials have been known for many years and enjoy a generally unbroken popularity, which, among other things, is due to the fact that their use for the ticket and / or purchase document issuing businessman is associated with great advantages. Since the color-forming components are contained in the recording material itself in the known color-reactive recording materials attributable to the heat-sensitive recording method, the toner and color-cartridge-free thermal printers, which in their function no longer need to be regularly monitored by anyone, can be used in large numbers be set up. Thus, this innovative technology has largely prevailed, especially in public transport and retail.

• insbesondere von bestimmten (Farb-)Entwicklern, auch als Farbakzeptoren bezeichnet,
• teilweise auch von Farbstoffvorläufern, mit denen die (Farb-)Entwickler bei Wärmezufuhr unter Ausbildung einer visuell erkennbaren Farbe reagieren,

aufgekommen, die zwar einerseits keineswegs naturwissenschaftlich begründet sind, andererseits jedoch von der Industrie und insbesondere vom Handel nicht außer Acht gelassen werden können. So stehen in letzter Zeit, zwar ungerechtfertigt aber dennoch, bei den (Farb-)Ent-wick-lern beispielsweise die gut bekannten und naturwissenschaftlich hervorragend untersuchten Komponenten, bekannt als

• □ Bisphenol-A, das ist 2,2 bis (4-hydroxyphenyl)-Propan, und
• □ Bisphenol-S, das ist 4,4'-Dihydroxydiphenylsulfon,

verstärkt im Zentrum öffentlicher Kritik und werden deshalb mitunter ersetzt durch

• ▪ Pergafast® 201, das ist N-(p-toluensulphonyl)-N'-3-(p-toluensulphonyl-Oxy-phenyl)-harnstoff, der Firma BASF Corporation, und
• ▪ D8, das ist 4-[(4-(1-methylethoxy)phenyl)sulfonyl]phenol,

In the recent near past, however, there are increasing concerns about environmental compatibility

• in particular of certain (color) developers, also referred to as color acceptors,
• partially also of dye precursors with which the (color) developers react when supplied with heat to form a visually recognizable color,

On the one hand, they are by no means scientifically founded, but on the other hand can not be ignored by industry and especially by trade. For example, while the (color) developers are well-known and scientifically excellently studied components known as

• □ bisphenol-A, which is 2,2 bis (4-hydroxyphenyl) propane, and
• □ bisphenol-S, which is 4,4'-dihydroxydiphenyl sulfone,

reinforced in the center of public criticism and are therefore sometimes replaced by

• ▪ Pergafast® 201, which is N- (p-toluenesulphonyl) -N'-3- (p-toluenesulphonyl-oxy-phenyl) -urea, the BASF Corporation, and
• ▪ D8, that is 4 - [(4- (1-methylethoxy) phenyl) sulfonyl] phenol,

• die erste Lage zumindest zugewandt zur zweiten Lage eine intensive Färbung aufweist und
• die zweite Lage Hohlkörperpigmente aufweist, die zur Ausbildung eines Schriftbildes manipulierbar sind.

Taking into account this completely changed market situation in a very short time, the inventors recognized the need for a completely new heat-sensitive recording material, which takes special account of environmentally friendly aspects. As a solution, a web-shaped heat-sensitive recording material with at least one first layer and a second layer at least partially covering the first layer is hereby proposed, wherein

• the first layer at least facing the second layer has an intense coloration and
• the second layer has hollow body pigments that can be manipulated to form a typeface.

As the closest prior art, the inventors considered the EP 0 512 114 A1 That as a recording material for a tachograph at least 2-layer sheet proposed with a colored substrate to which an opaque layer from an aqueous suspension containing polymer particles is plotted. By way of example, a sheet of a paper with a black topcoat is disclosed, wherein paper including topcoat together serve as a colored support and onto which an opaque layer of hollow body pigments is spread. When such a sheet is treated by way of example with a needle, the layer containing the hollow body pigment is scratched open and the underlying black topcoat becomes visible as a typeface. In this case, therefore, the manipulation of the hollow body pigments to form a typeface their removal, which is very easy in their involvement in the top coat due to the low degree of interconnectedness within the top coat having them.

Subject of the international patent application WO 2012/145 456 A1 is an identically constructed recording material, but here the manipulation of the hollow body pigments is their fusion, which takes place by the external supply of pressure or heat. Utilized is the well-known effect that a layer containing hollow body pigments in large quantities, loses its opacity where the hollow body pigments by the externally constructed pressure or by the externally applied heat, the latter, for example, generated by a thermal print head, are fused.

• der Maskierungsschicht in diesem hervorragend bewährten Aufzeichnungsmaterial gemäß der EP 1 778 499 B1 ,
• der Hohlkörperpigment enthaltende Schicht gemäß der WO 2012 /145 456 A1 ,
• und der zweiten Lage in dem wärmeempfindlichen Aufzeichnungsmaterial gemäß vorliegendem Vorschlag

können identisch sein. Somit wird klar, dass der Offenbarungsgehalt der zuvor diskutierten WO 2012 /145 456 A1 vollständig vorweggenommen wird durch die älteren und zuvor diskutierten Schriften EP 0 512 114 A1 und EP 1 778 499 B1 . Exactly this property of the hollow body pigments containing layer is in the EP 1 778 499 B1 discloses and exploited, this document proposes a configured in different embodiments recording material having as a security feature a radiation layer with luminescent constituents, which is covered by a masking layer with fusible hollow body pigments. Function and structure

• the masking layer in this well-established recording material according to the EP 1 778 499 B1 .
• the hollow body pigment-containing layer according to the WO 2012/145 456 A1 .
• and the second layer in the heat-sensitive recording material according to the present proposal

can be identical. Thus it is clear that the disclosure content of the previously discussed WO 2012/145 456 A1 is anticipated in full by the older and previously discussed writings EP 0 512 114 A1 and EP 1 778 499 B1 ,

• die erste Lage zumindest zugewandt zur zweiten Lage eine intensive Färbung aufweist und
• die zweite Lage Hohlkörperpigmente aufweist, die zur Ausbildung eines Schriftbildes manipulierbar sind,

erkannte die Erfinderschaft, dass ein derartiges wärmeempfindliches Aufzeichnungsmaterial letztendlich zwei Nachteile aufweist. Zum einen ist nach Zufuhr von ein Schriftbild erzeugender Hitze, letztere beispielsweise abgegeben durch einen Thermodruckkopf, der optische Unterschied zwischen Schriftbild und Hintergrundweiße, zu bemessen in der optischen Druckdichte vor und nach der Schriftbildausbildung, zu gering, was als primärer Nachteil im Sinne der vorliegenden Erfindung erkannt wurde. Zum anderen reagiert ein derart aufgebautes Aufzeichnungsmaterial zu empfindlich auf normale Alltaghandhabung, was bedeutet, dass das Aufzeichnungsmaterial bei mechanischen Eingriffen, wie beispielsweise leichte abrasive Beanspruchung, durch Reibung, gegebenenfalls Falten, Kratzen oder dergleichen, sofort Verfärbungen zeigt und dass die Lage mit den Hohlkörperpigmenten sehr rasch beschädigt wird, was erneut zu Verfärbungen des Aufzeichnungsmaterials führt. Diesen Nachteil gilt es sekundär zu lösen. Zur Lösung dieser aufgezeigten Problematiken wird diesseits nun ein bahnförmiges wärmeempfindliches Aufzeichnungsmaterial vorgeschlagen, wie es in den Ansprüchen definiert ist.After intensive investigations on generic heat-sensitive recording materials, as described in the upper paragraph [0004] , with at least a first layer and a first layer at least partially covering the second layer, wherein

• the first layer at least facing the second layer has an intense coloration and
• the second layer has hollow body pigments which can be manipulated to form a typeface,

The inventors recognized that such a heat-sensitive recording material ultimately has two disadvantages. On the one hand, after supplying a print generating heat, the latter for example given by a thermal printhead, the optical difference between typeface and background white, to be measured in the optical print density before and after the typeface formation, is too small, which is a primary disadvantage in the sense of the present invention was detected. On the other hand, such a recorded material reacts too sensitive to normal everyday handling, which means that the recording material in mechanical interventions, such as light abrasive stress, by friction, possibly wrinkles, scratching or the like, immediately discoloration shows and that the situation with the hollow body pigments very is rapidly damaged, which again leads to discoloration of the recording material. This disadvantage has to be solved secondarily. To solve this problem, this is now a web-shaped heat-sensitive Recording material proposed as defined in the claims.

The initially required environmentally friendly aspects of the sheet-like heat-sensitive recording material proposed here result from the complete abandonment of dye precursors and with those reactive (color) developers.

In order to form the heat-sensitive recording material according to the invention, its first layer with the intensive coloring facing the second layer is first covered with high opacity, that is to say almost opaque, by the second layer with the hollow-body pigments. Because of the opacity of the second layer caused by the hollow-body pigments, no or only little of the coloring of the first layer can be determined. By locally, preferably sharply delimited, heat in the form of any pattern, that is in the form of whatever typeface the hollow body pigments of the second layer are melted, for example by means of the printhead of a thermal printer, as well as the remarks in paragraph [0006] can be found. As a result, the fusion or collapse of the hollow body pigments results in an increased light transmission of the second layer. However, as an essential and underlying discovery of this invention, in the second layer there are still irregular empty spaces between the molten hollow body pigments and unmelted components which maintain an albeit reduced opacity of that second layer. The additional inclusion of at least one fatty acid amide and / or hydroxymethylated fatty acid amide and at least one heat-sensitive sensitizer in the second layer significantly improves the effect of reducing confused light scattering because the at least one fatty acid amide and / or hydroxymethylated fatty acid amide and the at least one heat-sensitive sensitizer envelop the unmelted components of the second layer and fill the empty spaces within the second layer. In the result There is a significant increase in the visual difference between externally applied heat, such as a thermal head, typeface caused, and background whiteness.

Fatty acid amides and hydroxymethylated fatty acid amides can also be used in combination within a preferred embodiment of the present invention, in particular in a mixing ratio of 1: 2 to 2: 1 based on% by weight (atro) in the second layer, within the second layer. As an example of the fatty acid amides is preferably stearic acid amide, as an example of hydroxymethylated fatty acid amides is preferably Methylolstearinsäureamid. Again, the combination of stearinamide and methylol stearinamide within the second layer is a preferred embodiment of the present invention.

• Benzyl-p-benzyloxy-benzoat,
• 2-(2H-benzotriazol-2-yl)-p-cresol,
• p-Benzylbiphenyl,
• 1,2-Di(phenoxy)-ethan, auch EGPE genannt,
• 1,2-Di(m-methylphenoxy)ethan,
• 2-(2H-benzotriazol-2-yl)-p-cresol, auch bekannt als Tinuvin® der Firma CIBA Speciality Chemicals Inc.,
• Dibenzyloxalat,
• Benzylnaphthylether, auch BNE genannt,
• Dimethylterephthalat,
• Diphenylsulfon,

wobei Benzylnaphthylether und 1,2-Di(phenoxy)-ethan als ganz besonders bevorzugt gelten. Im Sinne der Erfindung kann ein wärmeempfindlicher Sensibilisator, aber auch die Kombination aus mindestens zwei verschiedenen wärmeempfindlichen Sensibilisatoren, ausgesucht aus der obigen Liste, in die zweite Lage eingebunden sein.With regard to the heat-sensitive sensitizers, those selected from the list are considered to be preferred:

• Benzyl-p-benzyloxy benzoate,
• 2- (2H-benzotriazol-2-yl) -p-cresol,
• p-benzylbiphenyl,
• 1,2-di (phenoxy) ethane, also called EGPE,
• 1,2-di (m-methylphenoxy) ethane,
• 2- (2H-benzotriazol-2-yl) -p-cresol, also known as Tinuvin® from CIBA Specialty Chemicals Inc.,
• dibenzyl,
• Benzylnaphthyl ether, also called BNE,
• dimethyl terephthalate,
• diphenyl sulfone,

Benzylnaphthylether and 1,2-di (phenoxy) ethane are considered to be very particularly preferred. For the purposes of the invention, a heat-sensitive sensitizer, but also the combination of at least two different heat-sensitive sensitizers selected from the above list, may be incorporated into the second layer.

• Fettsäureamiden und/oder hydroxymethylierten Fettsäureamiden zu wärmeempfindlichen Sensibilisatoren,
  genauer von
• Fettsäureamiden und/oder hydroxymethylierten Fettsäureamiden zu wärmeempfindlichen Sensibilisatoren, bevorzugt ausgesucht aus der Liste umfassend Benzylnaphthylether und insbesondere 1,2-Di(phenoxy)-ethan
  in einem Bereich von
  • 1 : 2 bis 2 : 1
    und noch besser von
  • 1,0 : 1,5 bis 1,5 : 1,0
    besonders bevorzugt einzustellen ist.

Finally, in numerous series of investigations based on this document, the inventors recognized that a ratio of

• Fatty acid amides and / or hydroxymethylated fatty acid amides to heat-sensitive sensitizers,
  more exactly from
• Fatty acid amides and / or hydroxymethylated fatty acid amides to heat-sensitive sensitizers, preferably selected from the list comprising benzyl naphthyl ether and in particular 1,2-di (phenoxy) ethane
  in a range of
  • 1: 2 to 2: 1
    and even better of
  • 1.0: 1.5 to 1.5: 1.0
    is particularly preferred to adjust.

• • 1,0 : 2,5 bis 1 : 4,5
  und noch besser von
• • 1,0 : 2,5 bis 1,0 : 3,5
  besonders zufriedenstellende Ergebnisse hinsichtlich des optischen Unterschieds zwischen Schriftbild und Hintergrundweiße, auch Kontrast genannt, gewährleistet, gegeben durch die duale Fähigkeit der zweiten Lage zwischen Opazität und Transparenz.

Further, the inventors recognized that a ratio of the total amount of hollow body pigments to the total amount of fatty acid amides and / or hydroxymethylated fatty acid amides and thermosensitive sensitizers based on wt.% (Atro) in the second layer, both selected in particular from all of the preferred embodiments disclosed herein,
in a range of

• • 1.0: 2.5 to 1: 4.5
  and even better of
• • 1.0: 2.5 to 1.0: 3.5
  gives particularly satisfactory results in terms of the optical difference between typeface and background white, also called contrast, given by the dual ability of the second layer between opacity and transparency.

The hollow body pigments within the second layer have a wall of plastic, ideally of thermoplastic resin, which melts under high heat input. This thermoplastic resin or the hollow body pigment outer wall itself preferably comprises (meth) acrylonitrile copolymer, polyvinyl chloride, polyvinylidene chloride, polystyrene, styrene acrylate, Styrene (meth) acrylate copolymer, polyacrylonitrile, polyacrylic acid ester or else the mixture of at least two of the components mentioned on. Similarly, pigment mixtures of different hollow body pigments for the second layer are conceivable. For the purposes of the present invention, so-called "cup-shaped" pigments in particular also apply as hollow-body pigments. Unlike the classic hollow body pigments in which an inner core of gas, usually air, is completely enclosed by a shell of organic, usually thermoplastic, components, the "cup-shaped" pigments do not have a closed shell and surround the inner core only in the form of a - as far as possible closed - cup or cup (= "cup").

A glass transition temperature for the thermoplastic resin of the hollow body pigment outer wall in a range from 35 ° C to less than or equal to 200 ° C and preferably in a range from 75 ° C to less than or equal to 120 ° C has been found advantageous because below temperatures of 35 ° C, the wall of the hollow body pigments is no longer sufficiently stable at room temperature. Above temperatures of 200 ° C, there are handling problems of over heating the surface of the recording material. The preferred temperature range between 75 ° C to less than or equal to 120 ° C provides the simplest conditions in terms of processing quality and speed in the formation of the second layer and its use to create a typeface by merging the hollow body pigments in the form of this typeface, which in the sense of The present invention is to be understood not limited to the mere reproduction of alphanumeric characters, but just as markings of any kind, such as characters, symbols or monochrome or gray-tone images.

Suitable binders for incorporation in the second layer of the heat-sensitive recording material proposed herein 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 copolymer or ethylene-maleic anhydride copolymer, which binders can be used alone or in combination with one another; Also water-insoluble latex binders such as styrene-butadiene copolymers, acrylonitrile-butadiene copolymers and methyl acrylate-butadiene copolymers are suitable as binders for incorporation into the second layer. For the purposes of the present invention is polyvinyl alcohol as a particularly preferred binder, based on the total weight of the second layer, in a range of 12 to 18 wt .-% in the second layer of this proposed heat-sensitive recording material is involved.

In addition to hollow-body pigments, fatty acid amides and / or hydroxymethylated fatty acid amides and heat-sensitive sensitizers, the second layer generally comprises lubricants, which are preferably waxes such as, and most preferably, zinc stearates and paraffin waxes, as well as other additives, including but not limited to wetting agents and defoamers.

As a base color for the second layer of the proposed heat-sensitive recording material is particularly white, since heat-sensitive recording materials, especially in their intended and preferred use as a receipt and / or label and / or ticket in white appearance usually are desired in the market. Also, the non-fused hollow body pigments, as long as no further coloring components of the second layer are admixed, appear white. However, the proposed heat-sensitive recording material can be used without limitation also with a particularly light coloration of the second layer and is consequently regarded as a possible form of the proposed heat-sensitive recording material.

In a first possible embodiment, which is particularly simple and inexpensive to implement, the first layer is a mass-dyed web-shaped substrate, to which the substrate in a preferred embodiment carbon black components and / or dyes are added in such an amount that the substrate has an intensive color. Although not limited to paper as a sheet-like substrate of the present invention, paper is particularly preferred in a range of basis weight between 35 and 180 g / m ² as the preferred substrate.

• □ ein bahnförmiges Substrat, hier besonders bevorzugt Papier,
• □ mindestens eine gefärbte Zwischenschicht als erste Lage sowie
• □ eine die gefärbte Zwischenschicht als erste Lage zumindest teilweise abdeckende zweite Lage

umfasst, wobei die zweite Lage aufweist:

• ▪ Hohlkörperpigmente, die zur Ausbildung eines Schriftbildes durch lokal begrenzte Wärmebehandlung schmelzbar sind,
• ▪ eine oder mehrere Fettsäuren und
• ▪ einen oder mehrere wärmeempfindliche Sensibilisatoren.

In a second possible embodiment, a web-shaped heat-sensitive recording material having at least one first layer and a second layer at least partially covering the first layer is proposed

• □ a web-shaped substrate, here particularly preferably paper,
• □ at least one colored intermediate layer as first layer as well as
• □ a second layer at least partially covering the colored intermediate layer as a first layer

comprising, wherein the second layer comprises:

• Hollow body pigments, which can be melted to form a typeface by localized heat treatment,
• ▪ one or more fatty acids and
• ▪ one or more heat-sensitive sensitizers.

If the heat-sensitive recording material proposed here has a colored intermediate layer, it is possible, but no longer necessary, for the substrate carrying the intermediate layer as a first layer to have a coloration. The dyed intermediate layer as the first layer can be applied by printing technology to a substrate acting as the base support, for example in the form of paper or film. However, this colored intermediate layer is preferably applied to a substrate, wherein it is particularly preferred if the colored intermediate layer is applied with leveling coating devices, such as, for example, roller coater, doctor blade or doctor blade coater. Then, the colored intermediate layer can make a positive contribution to the leveling of the substrate surface, which on the one hand reduces the amount of coating material necessarily applied to form the second layer and on the other hand, the function of the second layer is supported. For the basis weight of the colored intermediate layer as the first layer within the heat-sensitive recording material according to the invention, a fairly wide range between 2 and 10 g / m ² and preferably between 2 and 7 g / m ^{2 has} proven to be particularly suitable, especially when applied with a doctor blade between 2 and 4 g / m ² , while in printing technical order of the colored intermediate layer as a first layer values well below 2 g / m ² then with layer thicknesses preferably between 0.5 .mu.m and 1.5 .mu.m are possible. For the smoothness (according to Bekk) of the first layer, a range of 200 sec to 500 sec has proven to be suitable, which is why such a range is considered to be preferred in the context of the present invention. In particular, the particularly preferred higher values between 300 sec and 500 sec are achieved by smoothing the substrate with applied first layer, for example by means of a two-, three- or Mehrwalzenglättwerks or even by means of a calender.

Regardless of whether the dyed intermediate layer is printed or preferably painted on as the first layer, in both cases it is preferred if inorganic oil-absorbing white pigments, preferably in a range from 20 to 45% by weight, based on the total weight of the intermediate layer, are added to the dyed intermediate layer , which are of great relevance for the external appearance and for the improvement of the later printability. Preferred inorganic white pigments of the intermediate layer are those Proven, selected from the group comprising natural and calcined kaolin, silica, bentonite, calcium carbonate and aluminum hydroxide and especially boehmite here. Also mixtures of several different types of inorganic white pigments are conceivable.

The particle size of the inorganic white pigments present in the colored interlayer, determined as the D50 value, is preferably in a range of less than 2 μm. Pigments having 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, in each case based on the total amount of white pigments in the intermediate layer, have proved to be advantageous.

To achieve intensive coloring of the intermediate layer as the first layer, it preferably has carbon black constituents and / or dyes in an appropriate amount, in the case of carbon black pigments preferably in a range from 30 to 40% by weight, based on the total weight of the intermediate layer. Carbon black pigments having an average particle size of 50 nm have proved to be advantageous.

In addition to the inorganic white pigments and the carbon black pigments, the intermediate layer dyed as the first layer and additionally pigmented contains at least one binder based on a synthetic polymer, with styrene-butadiene latex giving particularly good results, for example. The use of a synthetic binder with the admixture of at least one natural polymer is a particularly suitable embodiment. Also very particularly preferred as a binder is highly saponified polyvinyl alcohol. In the context of experiments it was further found that with a ratio
Binder: total amount of white pigments and carbon black pigments within the pigmented intermediate layer between 1: 3 and 1: 4 is a particularly suitable embodiment.

• □ ein bahnförmiges Substrat, hier besonders bevorzugt Papier,
• □ eine erste Zwischenschicht mit zur zweiten Zwischenschicht eingeebneter Oberfläche,
• □ eine zweite Zwischenschicht mit intensiver Färbung als erste Lage sowie
• □ eine die zweite Zwischenschicht zumindest teilweise abdeckende zweite Lage

umfasst, wobei die zweite Lage aufweist:

• ▪ Hohlkörperpigmente, die zur Ausbildung eines Schriftbildes durch lokal begrenzte Wärmebehandlung schmelzbar sind,
• ▪ eine oder mehrere Fettsäuren und
• ▪ einen oder mehrere wärmeempfindliche Sensibilisatoren.

In a third possible embodiment, a web-shaped heat-sensitive recording material having at least one first layer and a second layer at least partially covering the first layer is proposed

• □ a web-shaped substrate, here particularly preferably paper,
• □ a first intermediate layer with a surface leveled to the second intermediate layer,
• □ a second intermediate layer with intense coloration as the first layer as well
• □ a second layer at least partially covering the second intermediate layer

comprising, wherein the second layer comprises:

• Hollow body pigments, which can be melted to form a typeface by localized heat treatment,
• ▪ one or more fatty acids and
• ▪ one or more heat-sensitive sensitizers.

In this last disclosed third embodiment, it is the task of the first intermediate layer, for the subsequently applied second intermediate layer to ensure a particularly flat surface, so that the basis weight of the second intermediate layer is particularly low, preferably in a range between 1 and 8 g / m ² and even better between 2 and 5 g / m ² , can be selected. In this way, the amount of carbon black pigments, which can lead to difficulties within the recycling, can be reduced. While the constitution and ingredients of the second intermediate layer according to the third embodiment of the recording material proposed herein can be selected identically to the structure and ingredients of the intermediate layer according to the second embodiment, the first intermediate layer according to the third embodiment mainly comprises white pigments as disclosed in paragraph [0023], binders and others also usual additives. Decisive is their job with a leveling coating device, such as with a doctor blade or (roller) doctor blade coating with subsequent treatment by means of calender and / or calender.

In order to protect the heat-sensitive recording material proposed here in all of the embodiments and variants disclosed herein against damage and limitations of normal everyday handling, in particular mechanical interventions, such as light abrasive stress, friction, possibly wrinkles, scratching or the like, the heat-sensitive recording material is quite particularly preferably a second layer at least partially covering the protective layer.

• mindestens ein anorganisches Pigment,
• mindestens ein Bindemittel,
• mindestens ein Wachs, wobei hier besonders bevorzugt Paraffinwachse und insbesondere Zinkstearate sind,

weshalb die oben genannten Bestandteile als bevorzugt gelten zum strukturellen Aufbau einer Schutzschicht, wie sie im Rahmen der vorliegenden Erfindung ganz besonders bevorzugt zum Einsatz kommt. Optional weist eine derartige Schutzschicht neben weiteren gegebenenfalls notwendigen Hilfsmitteln in geringen Mengen auch optische Aufheller und ganz besonders bevorzugt Vernetzer, auch Vernetzungsmittel genannt, auf.In order to meet the special requirements of such a protective layer within the meaning of the present invention to a particularly high degree, the inventors consider it particularly advantageous if such a protective layer has at least the following constituents:

• at least one inorganic pigment,
• at least one binder,
• at least one wax, with particular preference being given here to paraffin waxes and in particular zinc stearates,

Therefore, the above-mentioned components are considered to be preferred for the structural structure of a protective layer, as it is very particularly preferably used in the context of the present invention. Optionally, such a protective layer comprises, in addition to further, if necessary, necessary auxiliaries in small amounts also optical brighteners and very particularly preferably crosslinkers, also called crosslinking agents.

• mindestens ein Bindemittel und hier bevorzugt ein oder mehrere wasserunlösliche, selbstvernetzende Acrylpolymere,
• mindestens ein Vernetzer und
• mindestens ein Pigment auf,

wobei das Pigment der Schutzschicht aus einem oder mehreren anorganischen Pigmenten besteht und mindestens 80 Gew.-% aus einem hoch gereinigten alkalisch aufbereiteten Bentonit gebildet sind. Das bevorzugte Bindemittel-/Pigmentverhältnis innerhalb der Schutzschicht liegt in einem Bereich zwischen 7 : 1 und 9 : 1.In a first variant, a protective layer, as introduced above,

• at least one binder and here preferably one or more water-insoluble, self-crosslinking acrylic polymers,
• at least one crosslinker and
• at least one pigment,

wherein the pigment of the protective layer consists of one or more inorganic pigments and at least 80 wt .-% of a highly purified alkaline treated bentonite are formed. The preferred binder / pigment ratio within the protective layer is in a range between 7: 1 and 9: 1.

• zyklischen Harnstoff,
• Methylolharnstoff,
• Amoniumzirkoniumkarbonat und
• besonders bevorzugt Polyamidepichlorhydrinharz.

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

• cyclic urea,
• methylol,
• Amonium zirconium carbonate and
• more preferably polyamide-epichlorohydrin resin.

By choosing a water-insoluble, self-crosslinking acrylic polymer as a binder and its ratio on the one hand to the pigment in a range between 7: 1 and 9: 1, on the other hand, and particularly preferably to the crosslinker greater than 5: 1 is already in a Protective layer with a relatively small surface-related mass given a high scratch resistance of the recording material proposed here.

The protective layer itself can be applied by means of conventional brushing, for which, inter alia, a coating color is usable, as described above and for which a surface-related mass in a range of 1.5 to 4.5 g / m ^{2 is} preferred, or the protective layer may alternatively be printed. Processing technology and in terms of their technological properties are particularly suitable such protective layers which are curable by means of actinic radiation. The term "actinic radiation" UV or ionizing radiation, such as electron beams to understand.

An alternative to the above-described embodiment very particularly preferred variant for a second layer completely or partially covering the protective layer provides as a binder a polyvinyl alcohol, zinc stearate, as a pigment aluminum hydroxide or alternatively also silica and one or more crosslinkers, with particularly preferred amounts for such a protective layer in Table 1 below: <u> Table 1: </ u> product % By weight [atro] aluminum hydroxide 10 - 25 polyvinyl alcohol 55 - 70 zinc stearate 7 - 9 crosslinkers 6 - 7

In a third embodiment variant for a protective layer which completely or partially covers the second layer, it is obtainable from a coating composition comprising at least one polyvinyl alcohol and at least one crosslinking agent. It is preferred if the polyvinyl alcohol of the protective layer according to the third embodiment variant is modified with carboxyl, diacetone or in particular silanol groups. It is also possible to use mixtures of various carboxyl, diacetone or silanol-modified polyvinyl alcohols.

The at least one crosslinking agent for the protective layer according to the third embodiment is preferably selected from the group consisting of boric acid, polyamines, epoxy resins, dialdehydes, formaldehyde oligomers, polyamine epichlorohydrin resin, adipic dihydrazide and melamine-formaldehyde. It is also possible to use mixtures of different crosslinking agents.

Preferably, in the coating composition for forming the protective layer according to the third embodiment, the weight ratio of the modified polyvinyl alcohol to the crosslinking agent is in a range of 20: 1 to 5: 1, and more preferably in a range of 12: 1 to 7: 1 Ratio of the modified polyvinyl alcohol to the crosslinking agent in the range of 100 parts by weight to 8 to 11 parts by weight.

Particularly good results have been achieved when the protective layer according to this embodiment additionally contains an inorganic pigment. In this case, the inorganic pigment is preferably selected from the group consisting of silicon dioxide bentonite, aluminum hydroxide, calcium carbonate, kaolin and mixtures of said inorganic pigments.

It is preferred that the protective layer according to this third embodiment with a basis weight in a range of 1.0 g / m ² to 6 g / m ² and particularly preferably from 1.2 g / m ² to 3.8 g / m ² apply. In this case, the protective layer is preferably formed in one layer, without being limited in this regard.

In a particular embodiment, the heat-sensitive recording material according to the invention and having a protective layer is provided as a label with a backside (self) adhesive layer. The usual construction then provides a web-shaped substrate, preferably a paper web, which has a front side and a rear side opposite it. On the reverse side, the sheet-shaped heat-sensitive recording material then has the (self) adhesive layer. On the front side, a first layer, a second layer at least partially covering the first layer and a protective layer at least partially covering the second layer are applied to the substrate in this order.

Depending on requirements, the adhesive layer may be covered with a release material such as a silicone-containing release paper or the outer layer formed on the second layer protective layer of the recording material according to the invention is provided with an additional release layer, which is preferably applied by means of a so-called five-roller applicator. The release layer in this case has release agents, preferably based on silicone oil. By the execution of the release layer with silicone oil, the proposed recording material with self-adhesive backing without release paper in a Roll are wound so that come in the role of the self-adhesive layer and the release layer in contact, without causing a permanent bonding.

In a particularly preferred embodiment, the release layer is curable or crosslinkable under the influence of high-energy radiation, such as UV or electron radiation. If the release layer is to be cured by means of UV rays, the monomers or prepolymers used for the preparation of this layer must contain additives of photoinitiators in a known manner. By electron beam curing, a particularly uniform over its cross-section, that is cured release layer could be achieved.

FIG. 1 shows the basic structure of the web-like heat-sensitive recording material according to the invention with an intense coloration - here uniformly black, for example, soot colors shown - having first layer (1) and a first layer (1) covering the second layer (2). In the figure, the regions (2-1) of the second layer (2) in which the hollow body pigments are fused by heat treatment and why the second layer (2) is translucent at these regions (2-1) are hatched, while the second layer (2) Regions (2-2) of the second layer (2) with non-fused hollow body pigments uniform white - an opaque covering characterizing - are shown. In the following figures, a different representation of translucent and opaque regions of the second layer (2) is dispensed with.

In a first, very simple embodiment of the invention, the first layer is a mass-dyed web-shaped substrate (11). On the substrate (11), the second layer (2) is then applied, for which in principle a range with respect to the basis weight between 2 and 10 g / m ^{2 is} considered to be preferred, as very particularly preferred is a range between 4 and 8 g / to look at m ² . In various series of tests, it was recognized that with a basis weight of the second layer of less than 2 g / m ^2, the coverage of the first layer is often no longer adequately ensured, whereas a second layer with a basis weight of well over 10 g / m ² for economic reasons does not make sense.

Optionally, on the second layer (2), a protective layer (40) or the printability - if necessary, also in the inkjet process - even further improving pigment coating may be applied. Although such a layer weakens the recognition of the formed by heat treatment typeface, but remains at a white or not too dark colored pigment coating and even more so in a preferably colorless designed protective layer, the color from the first layer (1, 11) appearing at the fused points through the second layer to a sufficient extent visible.

FIG. 2 shows in this respect, a sheet-like heat-sensitive recording material according to the invention, wherein the recording material is designed in one of its simplest embodiments. The second layer (2), whose hollow body pigments are fused by means of the print head of a thermal printer in the form of a typeface, is applied to a substrate (11) formed as a first layer here, for example with carbon black constituents for coloring the substrate. The second layer (2) completely covers the subjacent substrate (11). The second layer (2) is in turn covered by a protective layer (40).

If no coloring constituents are usually incorporated into the substrate for reasons of production technology, it is preferable, as explained in detail in the description above, to form a pigmented intermediate layer as the first layer on the then undyed, executable web-shaped substrate. FIG. 3 shows such an embodiment of the proposed heat-sensitive recording material, wherein the recording material in this case, a polyolefin-coated paper as a substrate (10) on which a pigmented intermediate layer (21) is applied as a first layer. This first layer is covered over the entire area by the second layer (2), whose hollow-chamber pigments are partially fused in the form of a typeface. The second layer (2) is in turn covered by a protective layer (40).

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 hollow body pigments of the second layer, the relevant figures are calculated from the "lutro" weight, i. air-dry parts by weight, less the proportion by weight of water in the interior of the pigments as supplied.

The invention will be further clarified by the following example.

Example:

• zu 36,4 Gew.-% Aluminiumhydroxid als Weißpigment,
• zu 36,4 Gew.-% Rußpigment,
• und zu 20,3 Gew.-% hochverseifter Polyvinylalkohol als Bindemittel

aufweisende Zwischenschicht von 3 g/m² als erste Lage aufgebracht und getrocknet.On a fourdrinier paper machine, the substrate used is a paper web made of bleached and ground hardwood and softwood pulps with a mass per unit area of 67 g / m ² prepared with the addition of conventional additives in conventional amounts. On one side of the substrate with a doctor blade a

• to 36.4% by weight of aluminum hydroxide as white pigment,
• to 36.4% by weight carbon black pigment,
• and to 20.3 wt .-% highly saponified polyvinyl alcohol as a binder

applied intermediate layer of 3 g / m ² as a first layer and dried.

• 15,3 Gew.-% (atro) hochverseifter Polyvinylalkohol als Bindemittel,
• 19,8 Gew.-% Hohlkörperpigmente,
• 29,8 Gew.% Stearinsäureamid,
• 29,8 Gew.-% 1,2-Di(phenoxy)-ethan als wärmeempfindlichen Sensibilisator und
• zusammen 4,4 Gew.-% Zinkstearate und Paraffinwachse als Gleitmittel.

On the intermediate layer, a second layer is applied using a Rollrakelstreicherwerks and dried with

• 15.3% by weight (atro) highly saponified polyvinyl alcohol as binder,
• 19.8% by weight of hollow body pigments,
• 29.8% by weight stearic acid amide,
• 29.8 wt .-% 1,2-di (phenoxy) ethane as a heat-sensitive sensitizer and
• together 4.4% by weight of zinc stearates and paraffin waxes as lubricants.

In this case, the percentages are based on the total weight (atro) of the finished second layer whose basis weight is 5.5 g / m ² . The thus-finished heat-sensitive recording material is fed to a thermal printer. The second layer hollow body pigments, along with the stearic acid amide and thermosensitive sensitizer, are melted by the print head of the thermal printer according to a predetermined check pattern to form areas in the second layer with fused components and filled intermediate areas and areas with unfused components and unfilled intermediate areas. The thus prepared recording material thus has a very well recognizable, sharp-edged typeface on with blackened areas where the hollow body pigments are fused together in the second layer by the heat input of the printhead of the thermal printer. The blackened areas originate from the uniform color of the intermediate layer, the color of which can be recognized by the transparent areas of the second layer with the hollow body pigments fused there.

Samples of the heat-sensitive recording material according to the invention thus produced are now subjected to a further metrological examination. For this purpose, the whiteness of the heat-sensitive recording material according to the invention is determined once with light, once with no UV content, the measurements being carried out in accordance with the specifications of ISO 2469 / ISO 2470 with the Assuming that the measurements made here use D65 light with a viewing angle of 8 °. The white measurements are carried out using a device of the type Elrepho 3000 (illuminant D 65/10). The values determined are 65% (with UV content) and 66% (without UV), which to a large extent corresponds to a gray paper, but in view of this coating and functional technology this is considered to be acceptable and salable.

To measure the optical difference between the typeface and the background white, the respective optical print density is determined before and after the formation of a black-and-white checkered thermo-printout with an Atlantek 400 device from Printrex (USA) using a thermal head with a resolution of 300 dpi and an energy per unit area of 16 mJ / mm ² is used. For each individual determination, the respectively non-printed area or the respective thermo-printed area is measured at three locations with the Gretag MacBeth Densitometer TYPE D19C NB / U densitometer (Gretag MacBeth, 8105 Regensdorf, Switzerland). The unprinted areas have a mean optical density of 0.24 ODU (Optical Density Units), and for the thermo-printed areas a mean optical density of 1.28 ODU. With a difference of 1.04 ODU as the contrast between printed and unprinted areas, the present invention proves that a skilled typeface is easy to see, underscoring the value of the present invention.

Term list :

(1)

first layer, having an intense coloration

(2)

second location

(2-1)

translucent areas of the second layer

(2-2)

opaque areas of the second layer

(10)

substratum

(11)

Substrate as a first layer

(21)

Interlayer as the first layer

(40)

protective layer

Claims (10)

1. Heat-sensitive recording material in web form, having at least one first ply and a second ply at least partly concealing the first ply, where

   ∘ the first ply, at least facing the second ply, has an intensive coloration and

   ∘ the second ply comprises hollow-body pigments which can be melted to form a script by locally confined heat treatment,

   characterized in that the first ply is concealed virtually opaquely by the second ply and in that second ply, besides the hollow-body pigments, also the comprises

   ▪ one or more fatty acid amides and/or hydroxymethylated fatty acid amides and

   ▪ one or more heat-sensitive sensitizers where the heat-sensitive sensitizers are selected from the list encompassing: benzyl p-benzyloxybenzoate, 2-(2H-benzotriazol-2-yl)-p-cresol, p-benzylbiphenyl, 1,2-di(phenoxy)ethane, 1,2-di(m-methylphenoxy)ethane, 2-(2H-benzotriazol-2-yl)-p-cresol, dibenzyl oxalate, benzyl naphthyl ether, dimethyl terephthalate and diphenyl sulfone.
2. Heat-sensitive recording material in web form according to Claim 1, characterized in that the hollow-body pigments of the second ply are fused in the form of a script by means of locally confined heat treatment.
3. Heat-sensitive recording material in web form according to either of Claims 1 and 2, characterized in that a ratio, based on wt% in the second ply, of fatty acid amides and/or hydroxymethylated fatty acid amides to heat-sensitive sensitizers, preferably selected from the list encompassing benzyl naphthyl ether and 1,2-di(phenoxy)ethane, is in a range from 1:2 to 2:1, where the figure for wt% is based on absolutely dry parts by weight.
4. Heat-sensitive recording material in web form according to any of Claims 1 to 3, characterized in that a ratio, based on wt% in the second ply, of the total amount of hollow-body pigments to the total amount of fatty acid amides and hydroxymethylated fatty acid amides and heat-sensitive sensitizers is in a range from 1.0:2.5 to 1:4.5, where the figure for wt% is based on absolutely dry parts by weight.
5. Heat-sensitive recording material in web form according to any of Claims 1 to 4, characterized in that the hollow-body pigments of the second ply are formed as cup-shaped pigments.
6. Heat-sensitive recording material in web form according to any of Claims 1 to 3, characterized in that the first ply is a substrate in web form that is coloured in the mass.
7. Heat-sensitive recording material in web form according to any of Claims 1 to 6, characterized in that the recording material has at least one protective layer at least partly concealing the second ply.
8. Heat-sensitive recording material in web form according to Claim 7, characterized in that the at least one protective layer at least partly concealing the second ply comprises as constituents at least:

   - at least one inorganic pigment,

   - at least one binder,

   - at least one wax.
9. Heat-sensitive recording material in web form according to Claim 7, characterized in that the at least one protective layer at least partly concealing the second ply additionally comprises at least:

   - optical brighteners,

   - crosslinkers.
10. Heat-sensitive recording material in web form according to any of Claims 7 to 9, characterized in that the recording material, as a label, has an adhesive layer or self-adhesive layer on the reverse side.

Images