EP2765007B1 - Heat-sensitive recording material - Google Patents

Description

The present invention relates to a thermosensitive recording material comprising a substrate, and to a thermosensitive recording layer comprising one or more dye precursors and one or more color developers.

Heat-sensitive recording materials of the type described above with, for example, a sheet of paper, a synthetic paper sheet or a plastic film as substrate are known since the early years of chemically reactive recording materials and enjoy a constantly growing distribution, which is due, inter alia, that their use in particular as a ticket for the Ticket issuing is associated with great benefits. Because the color-forming components are located in the thermosensitive recording material itself, the production of a thermally-induced recording (heat-induced printing image, hereinafter also referred to as thermal expression) on such thermosensitive recording material is carried out by toner and ink cartridge-free and hence low-maintenance and inexpensive printer. This is particularly advantageous for applications where large amounts of thermal prints are required to be generated quickly. Thus, this technology has prevailed in particular in public transport, buses and trains as well as air traffic, stadium and museum funds, ticket sales for major events and parking ticket issuers.

With the aim of improving heat-sensitive recording materials, in particular in their use as tickets or lottery tickets, with regard to their resistance to environmental influences such as heat, moisture and chemicals, innovations in the underlying chemistry and the production technology for producing such recording materials have always been incorporated.

To increase the durability of a thermo-print (heat-induced recording) available on a heat-sensitive recording material against water, aqueous alcohol solutions and plasticizers, US Pat DE 10 2004 044 204 A1 a heat-sensitive recording material whose heat-sensitive recording layer has conventional dye precursors and the combination of a phenolic color developer and a urea-urethane-based color developer.

Subject of the US 2005/0148467 A1 is a thermosensitive recording material containing at least the components of two color-forming systems to form an irreversible printed image, one being a chelate-type system and the other being a conventional leuco-dye system.

A disadvantage of the recording materials corresponding to the publications discussed above is, in particular in the first case, too low plasticizer resistance, associated with very low whiteness of the recording material, and the much too expensive production processes.

• die Farbbildner ausgewählt sind aus der Gruppe bestehend aus 3-Diethylamino-6-methyl-7-anilinofluoran, 3-Dibutylamino-6-methyl-7-anilinofluoran, 3-(N-methyl-N-propyl)amino-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-isoamyl)amino-6-methyl-7-anilinofluoran, 3-(N-methyl-N-cyclohexyl)amino-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-tolyl)amino-6-methyl-7-anilinofluoran und 3-(N-ethyl-N-tetrahydrofuryl)amino-6-methyl-7-anilinofluoran,
• die wärmeempfindliche Aufzeichnungsschicht zwei Farbakzeptoren aufweist, nämlich N-(p-toluensulphonyl)-N'-3-(p-toluensulphonyl-Oxy-phenyl)-harnstoff sowie eine Harnstoff-Urethan-Verbindung
• das auf Gew.-% in der wärmeempfindlichen Aufzeichnungsschicht bezogene Verhältnis von N-(p-toluensulphonyl)-N'-3-(p-toluensulphonyl-Oxy-phenyl)-harnstoff zu der Harnstoff-Urethan-Verbindung in einem Bereich von (1 : größer 1) bis (1 : 3) liegt.

From the EP 2 033 799 A1 For example, a thermosensitive recording material is known which is characterized by a high resistance of thermal printing to water, to a 25% ethanol solution and to plasticizers. This heat-sensitive recording material comprises a substrate and a color former (dye precursor) and color acceptor (color developer) containing heat-sensitive recording layer, wherein

• the color formers are selected from the group consisting of 3-diethylamino-6-methyl-7-anilinofluoran, 3-dibutylamino-6-methyl-7-anilinofluoran, 3- (N-methyl-N-propyl) amino-6-methyl- 7-anilinofluoran, 3- (N-ethyl-N-isoamyl) amino-6-methyl-7-anilinofluoran, 3- (N -methyl-N-cyclohexyl) amino-6-methyl-7-anilinofluoran, 3- (N ethyl-N-tolyl) amino-6-methyl-7-anilinofluoran and 3- (N-ethyl-N-tetrahydrofuryl) amino-6-methyl-7-anilinofluoran,
• the heat-sensitive recording layer has two color acceptors, namely N- (p-toluenesulphonyl) -N'-3- (p-toluenesulphonyl-oxy-phenyl) urea and a urea-urethane compound
• the ratio of N- (p-toluenesulphonyl) -N'-3- (p-toluenesulphonyl-oxy-phenyl) -urea, based on wt% in the heat-sensitive recording layer, to the urea-urethane compound in a range of (1 : greater than 1) to (1: 3).

However, there is a continuing need for other heat-sensitive recording materials for a variety of uses, which can be produced due to high sales volumes in a fiercely competitive market at low production costs and therefore must have a simple structure. Another challenge is that a printed thermosensitive recording material may be used in its typical uses as a ticket, ticket, ticket, parking ticket, and the like. can come in contact with a variety of different substances that can affect the durability of the thermal expression. In addition to water and substances acting as solvents, these also include fats and oils. The latter often act much like plasticizers. Therefore, there is a continuing need to improve the resistance of the thermal term to various environmental conditions. The object of the present invention is thus to provide a heat-sensitive recording material which, when printed, has a high resistance of the thermal expression to one or more substances selected from the group consisting of water, solvents, fats, oils and mixtures thereof, preferably both to water and solvents as well as fats and oils.

• einen oder mehrere Farbstoffvorläufer;
• N-(p-toluensulphonyl)-N'-3-(p-toluensulphonyl-Oxyphenyl)-harnstoff
• und ein oder mehrere Kondensationsprodukte der Formel (I)
  
  wobei in Formel (I)
  jedes Strukturelement R¹ ausgewählt ist aus der Gruppe bestehend aus Halogenatom, Hydroxygruppe, Alkylgruppen mit 1 bis 5 Kohlenstoffatomen, Alkoxygruppen mit 1 bis 5 Kohlenstoffatomen, Cyanogruppe, Nitrogruppe, Arylgruppen und Alkarylgruppen, und die einzelnen Strukturelemente R¹ identisch oder verschieden sind,
  jedes Strukturelement R² ausgewählt ist aus der Gruppe bestehend aus Wasserstoffatom, Alkylgruppen mit 1 bis 5 Kohlenstoffatomen und Arylgruppen, und die einzelnen Strukturelemente R² identisch oder verschieden sind,
  m eine ganze Zahl von 0 bis 3 ist,
  n eine ganze Zahl von 0 bis 3 ist.

This object is achieved according to the invention by a heat-sensitive recording material comprising
a substrate
and
comprising a heat-sensitive recording layer

• one or more dye precursors;
• N- (p-toluensulphonyl) -N'-3- (p-toluensulphonyl-oxyphenyl) -urea
• and one or more condensation products of the formula (I)
  
  in formula (I)
  each structural element R ^{1 is} selected from the group consisting of halogen atom, hydroxy group, alkyl groups having 1 to 5 carbon atoms, alkoxy groups having 1 to 5 carbon atoms, cyano group, nitro group, aryl groups and alkaryl groups, and the individual structural elements R ^{1 are} identical or different,
  each structural element R ^{2 is} selected from the group consisting of hydrogen atom, alkyl groups having 1 to 5 carbon atoms and aryl groups, and the individual structural elements R ^{2 are} identical or different,
  m is an integer from 0 to 3,
  n is an integer from 0 to 3.

Surprisingly, it has been found that the presence of one or more condensation products of the formula (I) as defined above in the heat-sensitive recording layer of a heat-sensitive recording material whose heat-sensitive recording layer contains the color developer N- (p-toluenesulphonyl) -N'-3- (p-toluenesulphonyl) Oxyphenyl) urea, improves the durability of a thermal term available on such a thermosensitive recording material to substances selected from the group consisting of water, alcohols, fats, oils and mixtures thereof.

Color developers are substances which color-form with the dye precursor or dye precursors under the action of heat. In the heat-sensitive recording paper of the present invention, additional color developers can be used; Frequently, however, no further color developers are provided in addition to the substances mentioned.

Thus, the present invention also relates to the use of a condensation product of the formula (I) as defined above for improving the durability of the heat-sensitive recording material whose heat-sensitive recording layer contains the color developer N- (p-toluenesulphonyl) -N'-3- (p-toluenesulphonyl -Oxyphenyl) urea, available thermal terms to substances selected from the group consisting of water, alcohols, fats, oils and mixtures thereof.

Condensation products of the formula (I) as defined above and their preparation are known, for example from EP 1 393 923 A1 . EP 1 437 231 A1 . EP 1 724 119 A1 . EP 2 072 274 A1 . EP 2 181 853 A1 and EP 2 261 045 A1 ,

• Ist R¹ eine Alkylgruppe mit 1 bis 5 Kohlenstoffatomen, so ist diese ausgewählt aus der Gruppe bestehend aus Methyl-, Ethyl-, n-Propyl-, i-Propyl-, n-Butyl-, t-Butyl- und t-Amylgruppe, wobei für bestimmte Anwendungsfälle Methyl-, Isopropyl- und t-Butylgruppe bevorzugt sind.

With regard to preferred condensation products of the formula (I):

• R ^{1 is} an alkyl group having 1 to 5 carbon atoms, this is selected from the group consisting of methyl, ethyl, n-propyl, i-propyl, n-butyl, t-butyl and t-amyl, although methyl, isopropyl and t-butyl are preferred for certain applications.

When R ^{1 is} an alkoxy group having 1 to 5 carbon atoms, it is preferably selected from the group consisting of methoxy, ethoxy, n-propoxy, i-propoxy, n-butoxy, i-butoxy and t-butoxy ,

If R ^{1 is} an aryl group, this is preferably selected from the group consisting of phenyl, toluyl and naphthyl group, and is preferably a phenyl group. When R ^{1 is} an aralkyl group, it is preferably selected from the group consisting of cumyl and o-methylbenzyl groups.

The structural elements R ¹ are preferably attached to one or both meta positions and / or to the para position to the hydroxyl group of the phenol ring, more preferably the or at least one of the structural elements R ^{1 is} attached to the para position to the hydroxyl group of the phenol group.

When R ^{2 is} an alkyl group having 1 to 5 carbon atoms, it is preferably selected from the group consisting of methyl, ethyl, n-propyl, i-propyl, n-butyl and t-butyl.

When R ^{2 is} an aryl group, it is preferably selected from the group consisting of phenyl, tolyl and naphthyl, and is preferably a phenyl group.

Preferably, n = 0, ie, preference is given to condensation products of the formula (I) with two phenol rings, where phenol rings which may be present in the structural elements R ¹ and R ² are not to be included. Preference is likewise given to mixtures of a plurality of condensation products of the formula (I) in which condensation products of the formula (I) where n = 0 (ie condensation products of the formula (I) with two phenol rings, where phenol rings which may be present in the structural elements R ¹ and R ² are not are to be counted) as the main constituent in addition to one or more condensation products with n = 1, 2 or 3 (condensation products of the formula (I) with three, four or five phenol rings, where phenol rings optionally contained in the structural elements R ¹ and R ² are not included) , "Condensation products of the formula (I) where n = 0 as the main constituent" means that within the mixture condensation products of the formula (I) with n = 0 represent the highest mass fraction based on all condensation products of the formula (I) forming the mixture.

If a mixture of several condensation products of the formula (I) is used as described above, the proportion of the condensation products of the formula (I) with two phenol rings is preferably 40 to 99%, more preferably 45 to 98%, particularly preferably 50 to 80%. , based on area in the analysis by high performance liquid chromatography.

A condensation product of formula (I) is obtainable by reacting one or more optionally substituted phenols with a ketone compound or an aldehyde compound in the presence of an acid catalyst (eg, hydrochloric acid, p-toluenesulfonic acid and the like). The reaction is usually carried out in a suitable inert solvent in which the starting materials and the condensation product are soluble, such as water, methanol, ethanol, n-propyl alcohol, isopropyl alcohol, acetonitrile, toluene, chloroform, diethyl ether, N, N-dimethylacetamide, benzene, chlorobenzene , Dichlorobenzene, diethyl ketone, ethyl methyl ketone, acetone, tetrahydrofuran and the like, at a reaction temperature of 0 to 150 ° C for several hours to several dozen hours performed. After the reaction, unreacted (optionally substituted) phenol can be separated by distillation, so that the condensation product is obtained in high yield. In addition, by recrystallization in a suitable solvent, a condensation product of high purity can be obtained.

The phenols for preparing a condensation product of the formula (I) are preferably selected from the group consisting of phenol, p-chlorophenol, m-chlorophenol, o-chlorophenol, catechol, resorcinol, hydroquinone, p-cresol, m-cresol, o-cresol , p-ethylphenol, m-ethylphenol, o-ethylphenol, p-propylphenol, o-propylphenol, p-isopropylphenol, m-isopropylphenol, o-isopropylphenol, pt-butylphenol, mt-butylphenol, ot-butylphenol, pt-amylphenol, p Methoxyphenol, m-methoxyphenol, o-methoxyphenol, p-phenylphenol, m-phenylphenol, o-phenylphenol, p-cumylphenol, p- (α-methylbenzyl) phenol and o- (α-methylbenzyl) phenol. Para-substituted phenols having at least one unsubstituted ortho position are preferred, and of these, p-cresol, p-ethylphenol and p-t-butylphenol are particularly preferred, and p-cresol and p-t-butylphenol are most preferred.

The ketone and aldehyde compounds for preparing a condensation product of the formula (I) are preferably selected from the group consisting of dimethyl ketone, diethyl ketone, ethyl methyl ketone, methyl isobutyl ketone, formaldehyde and benzaldehyde.

Condensation products of the formula (I) are structurally novolaks.

The use of specific novolak-type phenol condensation products as color developers for thermosensitive recording materials is basically known, but their use has the disadvantage of low stability to plasticizers.

1. (a) in Formel (I) gilt:
   • m ist eine ganze Zahl von 1 bis 3,
   • jedes Strukturelement R¹ ist ausgewählt aus der Gruppe bestehend aus Alkylgruppen mit 1 bis 5 Kohlenstoffatomen und die einzelnen Strukturelemente R¹ sind identisch oder verschieden,
   • alle Strukturelemente R² sind Wasserstoffatome,
   • n hat die Bedeutung wie oben angegeben
     und/oder
2. (b) das oder die Kondensationsprodukte der Formel (I) sind erhältlich durch Kondensation eines alkylsubstituierten Phenols mit Formaldehyd in Gegenwart eines sauren Katalysators.

Preferably, the condensation product of formula (I) is an alkylphenol-formalin condensation product as in EP 2 181 853 A1 and EP 2 261 045 A1 disclosed. That is, with respect to the condensation product of the formula (I), it is preferable in the invention that

1. (a) in formula (I):
   • m is an integer from 1 to 3,
   • each structural element R ¹ is selected from the group consisting of alkyl groups having 1 to 5 carbon atoms and the individual structural elements R ¹ are identical or different,
   • all structural elements R ² are hydrogen atoms,
   • n has the meaning as stated above
     and or
2. (b) the condensation product or products of formula (I) are obtainable by condensation of an alkyl-substituted phenol with formaldehyde in the presence of an acidic catalyst.

Particularly preferred for certain applications is an alkylphenol-formalin condensation product, wherein R ¹ is a tert-butyl group.

The dye precursor (s) contained in the thermosensitive recording layer of the thermosensitive recording material of the present invention are preferably selected from the group consisting of 3-dibutylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6-methyl-7-anilinofluoran, 3- (N -methyl-N-propyl) amino-6-methyl-7-anilinofluoran, 3- (N-ethyl-N-isoamyl) amino-6-methyl-7-anilinofluoran, 3- (N-methyl-N-cyclohexyl) amino 6-methyl-7-anilinofluoran and 3- (N-ethyl-N-tolyl) amino-6-methyl-7-anilinofluoran.

In embodiments which are particularly preferred for certain applications, the recording material according to the invention contains, in addition to one or more dye precursors, one or more near infrared absorbing compounds selected from the group consisting of 3,6-bis (dimethylamino) fluorene-9-spiro-3 '- ( 6'-dimethylaminophthalide), 3-diethylamino-6-dimethylaminofluorene-9-spiro-3 '- (6'-dimethylaminophthalide), 3,6-bis (diethylamino) -fluorene-9-spiro-3' - (6'- dimethylaminophthalide), 3-dibutylamino-6-dimethylaminofluorene-9-spiro-3 '- (6'-dimethylaminophthalide), 3-dibutylamino-6-diethylaminofluorene-9-spiro-3' - (6'-dimethylaminophthalide), 3.6 Bis (dimethylamino) fluorene-9-spiro-3 '- (6'-diethylaminophthalide), 3-diethylamino-6-dimethylaminofluorene-9-spiro-3' - (6'-diethylaminophthalide), 3-dibutylamino-6-dimethylaminofluorene 9-spiro-3 '- (6'-diethylaminophthalide), 3,6-bis (diethylamino) fluorene-9-spiro-3' - (6'-diethylaminophthalide), 3,6-bis (dimethylamino) - fluorene-9-spiro-3 '- (6'-dibutyla minophthalide), 3-dibutylamino-6-di-ethylaminofluorene-9-spiro-3 '- (6'-diethylaminophthalide), 3-diethylamino-6-dimethylaminofluorene-9-spiro-3' - (6'-dibutylaminophthalide) and 3 , 3-bis [2- (4-dimethylamino-phenyl) -2- (4-methoxyphenyl) ethenyl] -4,5,6,7-tetrachlorophthalid.

In particularly preferred embodiments for certain applications, the heat-sensitive recording layer of the heat-sensitive recording material according to the invention contains one or more sensitizers having a melting point of 60 ° C to 180 ° C, more preferably having a melting point of 80 ° C to 140 ° C. Such sensitizers are preferably selected from A group consisting of benzyl p-benzyloxybenzoate, stearamide, N-methylol stearamide, p-benzylbiphenyl, 1,2-di (phenoxy) ethane, 1,2-di (m-methylphenoxy) ethane, m-terphenyl, dibenzyl oxalate, Benzyl naphthyl ether and diphenyl sulfone, with benzyl naphthyl ether, diphenyl sulfone, 1,2-di (m-methylphenoxy) ethane and 1,2-di (phenoxy) ethane being particularly preferred. The addition of one or more sensitizers increases the thermal responsiveness of the thermosensitive recording material.

In the heat-sensitive recording material of the present invention, the atro weight ratio of the total amount of the condensation product (s) of formula (I) to N- (p-toluenesulphonyl) -N'-3- (p-toluenesulphonyl-oxyphenyl) urea is preferably in the range of 1: 2.5 to 1:14, more preferably from 1: 3.2 to 1: 12.8, more preferably in the range of 1: 5 to 1: 8.

At a lower atro-weight ratio of the condensation product (s) of the formula (I) to N- (p-toluenesulphonyl) -N'-3- (p-toluenesulphonyl-oxyphenyl) -urea than 1:14, for many applications sufficient resistance of the catalyst is not obtained Thermal expression achieved against the above substances.

At a higher atro-weight ratio of the condensation product (s) of the formula (I) to N- (p-toluenesulphonyl) -N'-3- (p-toluenesulphonyl-oxyphenyl) -urea than 1: 2.5, no further improvement in the resistance of the thermal expression against the above-mentioned substances, but the cost of producing the heat-sensitive recording material increases.

All area basis weight or weight% (weight%) information given in the specification and claims, respectively, refers to the "atro" weight, i. on absolutely dry parts by weight. If the heat-sensitive recording material according to the invention contains a plurality of condensation products of the formula (I), the calculation of the weight ratio of the condensation products of the formula (I) gives N- (p-toluenesulphonyl) -N'-3- (p-toluenesulphonyl-oxyphenyl) -urea to take into account the total weight of all condensation products of formula (I).

Suitable binders for the heat-sensitive recording layer are, for example, water-soluble binders such as starch, hydroxyethyl cellulose, methyl cellulose, carboxymethyl cellulose, gelatin, casein, polyvinyl alcohols, modified polyvinyl alcohols, sodium polyacrylates, acrylamide-acrylate copolymers, Acrylamide-acrylate-methacrylate terpolymers, alkali metal salts of styrene-maleic anhydride copolymers or ethylene-maleic anhydride copolymers, which binders may 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 binders for the heat-sensitive recording layer.

In a preferred embodiment, the thermosensitive recording layer of the thermosensitive recording material of the present invention contains a crosslinked or uncrosslinked binder, which preferably contains a polyvinyl alcohol and an acrylate copolymer. In this invention preferred embodiment, the total weight content of polyvinyl alcohol and acrylate copolymer is in a range of 12 to 21 wt .-%, based on the total weight of the heat-sensitive recording layer.

Preferably, the coating composition for forming the heat-sensitive recording layer of the heat-sensitive recording material of the present invention contains, in addition to the binder, one or more crosslinking agents for the binder. Preferably, the crosslinking agent (s) is selected from the group consisting of zirconium carbonate, polyamine epichlorohydrin resins, boric acid, glyoxal and glyoxal derivatives.

A heat-sensitive recording material of the present invention whose heat-sensitive recording layer is formed from such a coating composition containing a binder and one or more crosslinking agents for the binder contains, in the heat-sensitive recording layer, a binder crosslinked by reaction with one or more crosslinking agents, wherein the crosslinking agent (s) are selected the group consisting of zirconium carbonate, polyamine-epichlorohydrin resins, boric acid, glyoxal and glyoxal derivatives. By "crosslinked binder" is meant the reaction product formed by reaction of a binder with one or more crosslinking agents.

Suitable glyoxal derivatives are, for example, adducts of glyoxal with S, O and / or N nucleophiles. Suitable S-nucleophiles are sodium bisulfite and potassium bisulfite, suitable O-nucleophiles are adducts with aliphatic (C1 to C20) Monoalcohols or polyhydric alcohols, suitable N-nucleophiles are aliphatic monoamines, amides, urea and / or cyclic ureas.

In order to prevent sticking of the heat-sensitive recording material to the thermal head and excessive wear of the thermal head, the heat-sensitive recording layer may contain lubricants and release agents such as metal salts of higher fatty acids, for example, zinc stearate and / or calcium stearate, and waxes such as paraffin, oxidized paraffin, polyethylene, polyethylene oxide , Stearamide and castor wax. Further constituents of the heat-sensitive recording layer are, for example, pigments, preferably inorganic pigments such as, for example, aluminum (hydr) oxide, silica and calcium carbonate. Preferably, as the inorganic pigment, calcium carbonate is used, which is preferably contained in an amount of from 10 to 18% by weight, based on the total weight of the heat-sensitive recording layer, in the heat-sensitive recording layer.

In order to ensure a good contrast between printed and unprinted areas, the heat-sensitive recording layer preferably has a whiteness in a range of 79 to 85% when using light having no UV portion and whitening in a range of 87 to 93% when using light with UV Each measured according to ISO 2469 / ISO 2470, but D65 light is used at a viewing angle of 8 °.

As a coating device for applying the heat-sensitive recording layer to the substrate, in particular, a roll doctor coater, a knife coater, a curtain coater or an air brush are suitable. According to a preferred embodiment, the coating composition used to form the heat-sensitive recording layer is aqueous. The subsequent drying of the coating composition is usually done by a method in which heat is supplied, as is done by hot-air floating dryer or contact dryer. Proven is also a combination of the listed dry processes. The basis weight of the heat-sensitive recording layer in the final heat-sensitive recording material of the present invention is preferably in the range of 2 to 6 g / m ^2, and more preferably 2.3 to 5.8 g / m ² .

Although the present invention is not limited to paper as the substrate, paper, and especially a non-surface treated base paper, is preferred a basis weight in the range of 45 to 130 g / m ^2, a substrate which has prevailed in the market and is preferred for use in a heat-sensitive recording material according to the invention. This is especially true because of the good recyclability of such papers. A non-surface treated base paper is to be understood as meaning a base paper which has not been treated in a size press or in a coater. A non-surface-treated, sized in the coating base paper with an inorganic pigment, in particular calcium carbonate, in the mass is particularly suitable for use in a heat-sensitive recording material according to the invention. To the same extent, films (for example of polyolefin) and coated with polyolefin papers are suitable as a substrate.

Between the thermosensitive recording layer and the substrate of the thermosensitive recording material of the present invention (as defined above, preferably as mentioned above as preferred), in some embodiments of the present invention, one or more intermediate layers differ in structure from both the substrate and the thermosensitive recording layer preferably one or more pigments. The term "structure" here includes the microscopic and macroscopic structure, the chemical composition and other aspects of the nature of the layers concerned.

In a preferred embodiment, the intermediate layer is applied with leveling coating devices, such as roller coater, doctor blade or doctor blade coaters. Thus, the intermediate layer contributes to the leveling of the substrate surface, whereby the amount of coating material to be applied necessarily for forming the heat-sensitive recording layer is regularly reduced. The basis weight of the intermediate layer is preferably in the range of 5 to 20 g / m ² and more preferably 7 to 11 g / m ² .

If inorganic oil-absorbing pigments are incorporated into the intermediate layer disposed between the heat-sensitive recording layer and the substrate, these pigments can absorb the wax constituents of the heat-sensitive recording layer liquefied by heat of the thermal head during the printing image formation and thus promote an even safer and faster functioning of the heat-induced recording, which is why such an embodiment is considered preferable.

It is particularly advantageous if the pigments of the intermediate layer has an oil absorption of at least 80 ^cm3 / 100 g, and more preferably 100 ^cm3 / 100 g, determined according to the Japanese standard JIS K 5101, is having. Calcined kaolin has proven particularly useful due to its large absorption reservoir in the cavities. However, the following inorganic pigments are also very well suited as constituents of the intermediate layer: silicon dioxide, bentonite, calcium carbonate and aluminum (hydr) oxide and here in particular boehmite. Also mixtures of several different types of inorganic pigments are conceivable.

Experiments have shown that the incorporation of organic pigments in the intermediate layer can also be very advantageous, which may be due to the fact that such organic pigments are to a particular extent conducive to a high heat reflectivity of the intermediate layer. Organic, so-called hollow body pigments arranged in an intermediate layer of a heat-sensitive recording material according to the invention are preferred; they have in their interior air, which is a good heat insulator. An interlayer thus formed as a heat reflection layer increases the response of the heat-sensitive recording layer to heat. This significantly increases the resolving power of the thermosensitive recording material and further increases the printing speed in the thermal printer.

By adjusting the amount ratio between organic and inorganic pigment, a compromise of the effects caused by the two types of pigments is achieved; it is preferred if the pigment mixture to 5 to 30 wt .-% or better to 8 to 20 wt .-% of organic and 95 to 70 wt .-% or better to 92 to 80 wt .-% of inorganic Pigment exists. With regard to preferred inorganic pigments, the above applies. Pigment mixtures comprising different organic pigments are also suitable.

In addition to the inorganic and optionally also organic pigments, the intermediate layer contains at least one binder, preferably a binder comprising a synthetic polymer, wherein, for example, styrene-butadiene latex as binder agent gives particularly good results. The use of a synthetic binder with admixture of at least one natural polymer, as particularly preferred Starch, represents a particularly preferred embodiment. In the context of experiments with inorganic pigments was also found that with a binder-pigment weight ratio within the intermediate layer in the range of 3: 7 to 1: 9 particularly good results are achieved. The synthetic polymer blended with the natural polymer is referred to in this context as a cobinder.

In embodiments of the heat-sensitive recording material according to the invention which are particularly preferred for certain applications, the heat-sensitive recording layer is completely or partially covered with a protective layer.

In such cases, such a protective layer, in addition to the protection of the heat-sensitive recording layer from environmental influences, often has the additional positive effect of improving the printability of the heat-sensitive recording material according to the invention, in particular in offset and flexographic printing. For this reason in particular, it is preferred for certain applications that the heat-sensitive recording material according to the invention has a protective layer, although the presence of one or more condensation products of the formula (I) as defined above in the heat-sensitive recording layer of the heat-sensitive recording material according to the invention, the stability of a on a inventive heat-sensitive recording material available thermal expression compared to substances selected from the group consisting of water, alcohols, fats, oils and mixtures thereof, even without a protective layer for certain applications is already sufficient.

The protective layer of the heat-sensitive recording material according to the invention preferably comprises one or more crosslinked or uncrosslinked binders selected from the group consisting of carboxyl-modified polyvinyl alcohols, silanol-modified polyvinyl alcohols, diacetone-modified polyvinyl alcohols, partially and fully hydrolyzed polyvinyl alcohols and film-forming acrylic copolymers.

Preferably, the coating composition for forming the protective layer of the heat-sensitive recording material according to the invention contains, in addition to one or more binders, one or more crosslinking agents for the one or more binders Binder. The crosslinking agent is preferably selected from the group consisting of boric acid, polyamines, epoxy resins, dialdehydes, formaldehyde oligomers, epichlorohydrin resins, adipic dihydrazide melamine formaldehyde, urea, methylol urea, ammonium zirconium carbonate and polyamide-epichlorohydrin resins.

A heat-sensitive recording material according to the invention, the protective layer of which is formed from such a coating composition comprising one or more binders and one or more crosslinking agents for the binder or binders, contains in the protective layer one or more binders crosslinked by reaction with one or more crosslinking agents, wherein the one or more Crosslinking agents are selected from the group consisting of boric acid, polyamines, epoxy resins, dialdehydes, formaldehyde oligomers, epichlorohydrin resins, adipic dihydrazide melamine formaldehyde, urea, methylol urea, ammonium zirconium carbonate and polyamide epichlorohydrin resins. By "crosslinked binder" is meant the reaction product formed by reaction of a binder with one or more crosslinking agents.

In a first embodiment, the protective layer completely or partially covering the heat-sensitive recording layer is obtainable from a coating composition comprising one or more polyvinyl alcohols and one or more crosslinking agents. It is preferred that the polyvinyl alcohol of the protective layer is modified with carboxyl or in particular silanol groups. It is also possible to use mixtures of different carboxyl-group- or silanol-modified polyvinyl alcohols. Such a protective layer has a high affinity with respect to the preferably UV-crosslinking printing ink used in the offset printing process. This helps significantly to meet the demand for excellent printability within the offset printing.

The one or more crosslinking agents for the protective layer according to this embodiment are 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 this embodiment, the weight ratio of the modified polyvinyl alcohol to the crosslinking agent in a range of 20: 1 to 5: 1, and more preferably in a range of 12: 1 to 7: 1. Particularly preferred is a 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 to apply the protective layer according to this embodiment with a basis weight in a range from 1.0 g / m ² to 6 g / m ² and more preferably from 1.2 g / m ² to 3.8 g / m ² , In this case, the protective layer is preferably formed in one layer.

• der Pigmentbestandteil der Schutzschicht aus einem oder mehreren anorganischen Pigmenten besteht und mindestens 80 Gew.-% aus einem hoch gereinigten alkalisch aufbereiteten Bentonit gebildet sind,
• das Bindemittel der Schutzschicht aus einem oder aus mehreren wasserunlöslichen, selbstvernetzenden Acrylpolymeren besteht,
• und das Bindemittel-/Pigmentverhältnis in einem Bereich von 7 : 1 bis 9 : 1 liegt.

In a second embodiment, the coating composition for forming the protective layer comprises a water-insoluble, self-crosslinking acrylic polymer as a binder, a crosslinking agent and a pigment constituent, wherein

• the pigment constituent of the protective layer is composed of one or more inorganic pigments and at least 80% by weight are formed from a highly purified, alkaline-treated bentonite,
• the binder of the protective layer consists of one or more water-insoluble, self-crosslinking acrylic polymers,
• and the binder / pigment ratio ranges from 7: 1 to 9: 1.

A self-crosslinking acrylic polymer within the protective layer according to the second embodiment described herein is preferably selected from the group consisting of styrene-acrylic acid ester copolymers, acrylamide-containing copolymers of styrene and acrylic acid esters and copolymers based on acrylonitrile, methacrylamide and acrylic esters. The latter are preferred. As a pigment alkaline bentonite, natural or precipitated calcium carbonate, kaolin, silica or aluminum hydroxide may be incorporated into the protective layer. Preferred crosslinking agents are selected from the group consisting of cyclic urea, methylol urea, ammonium zirconium carbonate and polyamide-epichlorohydrin resins.

The choice of a water-insoluble, self-crosslinking acrylic polymer as a binder and its weight ratio (i) to pigment in a range of 7: 1 to 9: 1 and (ii) to crosslinking agent greater than 5: 1 is already a protective layer with a relatively low surface mass given a high environmental resistance of the heat-sensitive recording material according to the invention. Such weight ratios are thus preferred.

The protective layer itself may be applied by means of conventional brushing, for which, inter alia, a coating color is usable, preferably with a surface-related mass in a range of 1.0 to 4.5 g / m ² . In an alternative variant, the protective layer is 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.

The appearance of the protective layer is significantly determined by the type of smoothing and the friction in the calender and calender influencing roll surfaces and their materials. In particular, due to existing market requirements, a roughness (Parker Print Surf roughness) of the protective layer is less than 1.5 microns (determined in accordance with ISO standard 8791, Part 4) considered preferred. In the experimental work preceding this invention, the use of calenders using NipcoFlex ™ or zone controlled Nipco-P ™ rolls has proven particularly useful; however, the invention is not limited thereto.

In some cases, a protective layer can be dispensed with, because the presence of one or more condensation products of the formula (I) as defined above in the heat-sensitive recording layer of the heat-sensitive recording material of the present invention, the durability of a thermal printable on a heat-sensitive recording material according to the invention is selected from materials Group consisting of water, alcohols, fats, oils and their mixtures sufficient for certain applications. This is advantageous in that a protective layer is cost-intensive both in terms of the necessary raw materials as well as in terms of the necessary for their production machines and process energies.

Another aspect of the present invention relates to a thermal term, i. thermally-induced recording, thermosensitive recording material of the present invention, i. a printed thermosensitive recording material. In the regions of the thermosensitive recording material which are printed, the thermosensitive recording layer contains dyes formed on printing by a heat-induced reaction of the dye precursor (s) with the color developer (s).

• einen oder mehrere Farbstoffvorläufer,
• N-(p-toluensulphonyl)-N'-3-(p-toluensulphonyl-Oxyphenyl)-harnstoff
• ein oder mehrere Kondensationsprodukte der Formel (I) wie oben sowie
• einen oder mehrere durch Reaktion des oder der Farbstoffvorläufer mit N-(p-toluensulphonyl)-N'-3-(p-toluensulphonyl-Oxyphenyl)-harnstoff gebildete Farbstoffe.

A printed thermosensitive recording material of the invention comprises a substrate
and
comprising a heat-sensitive recording layer

• one or more dye precursors,
• N- (p-toluensulphonyl) -N'-3- (p-toluensulphonyl-oxyphenyl) -urea
• one or more condensation products of the formula (I) as above and
• one or more dyes formed by reaction of the dye precursor (s) with N- (p-toluenesulphonyl) -N'-3- (p-toluenesulphonyl-oxyphenyl) urea.

• Auf einer Langsieb-Papiermaschine wird als Substrat eine Papierbahn aus gebleichten und gemahlenen Laub- und Nadelholzzellstoffen mit einer flächenbezogenen Masse von 67 g/m² unter Zusatz üblicher Zuschlagstoffe in üblichen Mengen hergestellt. Frontseitig wird online innerhalb der Streichmaschine mit einem Rollrakel-Streichwerk eine Zwischenschicht umfassend Hohlraumpigmente und kalziniertes Kaolin als Pigment, Styrolbutadienlatex als Bindemittel und Stärke als Cobinder mit einer flächenbezogenen Masse von 9 g/m² aufgebracht und konventionell getrocknet.

The following examples and comparative 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 a substrate with the addition of conventional additives in conventional amounts. On the front side, an intermediate layer comprising hollow-shell pigments and calcined kaolin as pigment, styrene-butadiene latex as binder and starch as cobinder with a basis weight of 9 g / m ^{2 is} applied online and conventionally dried inside the coating machine with a roller-blade coating unit.

By using a coater, a heat-sensitive recording layer having a face-related one is applied to the intermediate layer in this order and within a coater passage by means of a doctor blade coater Mass of 5.4 g / m ² and applied by means of air brush, a protective layer with a basis weight of 2.0 g / m ² and dried conventionally after each order.

For the heat-sensitive recording layer, a formulation is used which comprises as binder a mixture comprising polyvinyl alcohol and an acrylate copolymer and as the pigment calcium carbonate. Further constituents of the heat-sensitive recording layers of the individual exemplary embodiments are given in Table 1 below: Table 1 component Comparative example Example 1 (according to the invention) Example 1 (according to the invention) Data in atro-parts by weight N- (p-toluensulphonyl) -N'-3- (p-toluensulphonyl-oxyphenyl) -urea 100.00 100.00 100.00 dye precursor 47.92 47.92 47.97 Condensation product as defined above - 31.25 15.63

For the preparation of the protective layer, a coating composition comprising a diacetone-modified polyvinyl alcohol (100 parts by weight), kaolin (40 parts by weight), zinc stearate (26.5 parts by weight) and adipic dihydrazide as a crosslinking agent (10 parts by weight) is used.

• Wasser
• eine Ethanol-Wasser-Mischung umfassend 20 Vol.% Ethanol als Beispiel für eine ein Lösungsmittel enthaltende Substanz
• Milch als Beispiel für eine flüssige fetthaltige Substanz
• Margarine als Beispiel für eine pastenförmige fetthaltige Substanz
• Lanolin als Beispiel für eine ölhaltige, als Weichmacher wirkende Substanz.

For measuring the resistance of a thermographic expression on the heat-sensitive recording materials of Examples 1 and 2 and of the Comparative Example to various substances, black-and-white checkered thermoprinting prints were respectively made with an Atlantek 400 device from Printrex (USA), a thermal head with a resolution of 300 dpi and an energy per unit area of 16 mJ / mm ² was used. Subsequently, the samples were treated with the substance whose influence on the stability of the thermal expression should be investigated. The following substances were used:

• water
• an ethanol-water mixture comprising 20% by volume of ethanol as an example of a substance containing a solvent
• Milk as an example of a liquid fatty substance
• Margarine as an example of a pasty fatty substance
• Lanolin as an example of an oily substance acting as a plasticizer.

• Für die messtechnische Erfassung der Beständigkeit gegenüber Ethanol (Ethanol-Wasser-Mischung umfassend 20 Vol.% Ethanol), Milch (Fettgehalt 3,5%) und Wasser wurde eine mit dem oben beschriebenen Thermoprobeausdruck versehene Probe des zu testenden wärmeempfindlichen Aufzeichnungsmaterials in ein Bad der jeweiligen Substanz eingelegt, anschließend über den in Tabelle 2 angegebenen Zeitraum bei 23 °C unter Luftabschluss ruhen gelassen und danach über 60 Minuten bei 23 °C und 50 % Luftfeuchte getrocknet.

Tabelle 2: Substanz Zeitraum [h] Ethanol 20 Vol.% 2 Milch 3,5% Fett 8 Wasser 24 The tests are as follows:

• For the measurement of resistance to ethanol (ethanol-water mixture comprising 20% by volume of ethanol), milk (fat content 3.5%) and water, a sample of the thermosensitive recording material to be tested was bathed in a bath of the above-described thermal printing each substance is inserted, then allowed to rest for the period shown in Table 2 at 23 ° C with exclusion of air and then dried for 60 minutes at 23 ° C and 50% humidity.

Table 2: substance Period [h] Ethanol 20 vol.% 2 Milk 3.5% fat 8th water 24

For metrological detection of margarine and lanolin resistance, a sample of the thermosensitive recording material to be tested was satisfactorily coated with the above-described thermoprob expression and then allowed to stand for 24 hours at 23 ° C and 50% humidity. Thereafter, the margarine or lanolin was wiped off by the thermoprobe print.

On the samples pretreated as described above, a determination of the dynamic print density was carried out at three points of the black-colored areas by means of a densitometer Gretag MacBeth TYPE D19C NB / U. From the respective measured values, the mean value was formed. The measurement results obtained are listed in Table 3: Table 3 substance Comparative example example 1 Example 2 dynamic printing density [optical density units ODU] Ethanol 20 vol.% 0.36 0.97 1.21 Milk 3.5% fat 0.78 1.05 1.24 water 0.37 0.99 1.19 margarine 0.81 1.02 1.16 lanolin 1.36 1.48 1.54

The measurement results shown in Table 3 show that the thermal proof prints on the heat-sensitive recording material of Comparative Example whose heat-sensitive recording layer contains no condensation product of the formula (I) as defined above have significantly lower resistance to all substances tested (water, ethanol-water mixture, Milk, margarine and lanolin) compared to the Thermoprobeausdrucken on the heat-sensitive recording materials according to the invention of Examples 1 and 2. The thermosensitive recording material of Example 2 represents a particularly preferred embodiment of the present invention, because compared to all substances tested, the dynamic print density remains at a value of more than 1 ODU. It is an example of a heat-sensitive recording material of the invention having an atro-weight ratio of the condensation product of the formula (I) in the range of 1: 5 to 1: 8.

Claims (12)

1. Heat-sensitive recording material comprising a substrate
   and
   a heat-sensitive recording layer comprising

   - one or more dye precursors;

   - N-(p-toluenesulphonyl)-N'-3-(p-toluenesulphonyl-oxyphenyl)-urea

   - and one or more condensation products of formula (I)

   

   wherein in formula (I)

   - each structural element R¹ is selected from the group consisting of halogen atom, hydroxy group, alkyl groups having from 1 to 5 carbon atoms, alkoxy groups having from 1 to 5 carbon atoms, cyano group, nitro group, aryl groups and alkaryl groups, and the individual structural elements R¹ are identical or different,

   - each structural element R² is selected from the group consisting of hydrogen atom, alkyl groups having from 1 to 5 carbon atoms and aryl groups, and the individual structural elements R² are identical or different,

   - m is a whole number from 0 to 3,

   - n is a whole number from 0 to 3.
2. Heat-sensitive recording material according to claim 1, wherein

   (a) in formula (I):

   - m is a whole number from 1 to 3,

   - each structural element R¹ is selected from the group consisting of alkyl groups having from 1 to 5 carbon atoms and the individual structural elements R¹ are identical or different,

   - all structural elements R² are hydrogen atoms,

   - n is as defined in claim 1,
   and/or

   (b) the condensation product(s) of formula (I) are obtainable by condensation of an alkyl-substituted phenol with formaldehyde in the presence of an acid catalyst.
3. Heat-sensitive recording material according to claim 1 or 2, wherein the dye precursor(s) of the heat-sensitive recording layer are selected from the group consisting of 3-diethylamino-6-methyl-7-anilinofluoran, 3-dibutylamino-6-methyl-7-anilinofluoran, 3-(N-methyl-N-propyl)amino-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-isoamyl)amino-6-methyl-7-anilinofluoran, 3-(N-methyl-N-cyclohexyl)amino-6-methyl-7-anilinofluoran and 3-(N-ethyl-N-tolyl)amino-6-methyl-7-anilinofluoran.
4. Heat-sensitive recording material according to any one of claims 1 to 3, wherein the ratio by absolutely dry weight
   of the total amount of the condensation product(s) of formula (I) to
   N-(p-toluenesulphonyl)-N'-3-(p-toluenesulphonyl-oxyphenyl)-urea is in the range from 1 : 2.5 to 1 : 14, preferably from 1 : 3.2 to 1 : 12.8,
   especially preferably in the range from 1 : 5 to 1 : 8.
5. Heat-sensitive recording material according to any one of claims 1 to 4, wherein the heat-sensitive recording layer contains a crosslinked or uncrosslinked binder which preferably contains a polyvinyl alcohol and an acrylate copolymer.
6. Heat-sensitive recording material according to any one of claims 1 to 5, containing in the heat-sensitive recording layer a binder crosslinked by reaction with one or more crosslinking agent(s), the crosslinking agent(s) being selected from the group consisting of zirconium carbonate, polyamine epichlorohydrin resins, boric acid and glyoxal.
7. Heat-sensitive recording material according to any one of claims 1 to 6, wherein the heat-sensitive recording material has one or more intermediate layers arranged between the substrate and the heat-sensitive recording layer, the intermediate layers differing in structure from the substrate and from the heat-sensitive recording layer.
8. Heat-sensitive recording material according to any one of claims 1 to 7, wherein the heat-sensitive recording layer is fully or partially covered by a protective layer.
9. Heat-sensitive recording material according to claim 8, wherein the protective layer contains one or more crosslinked or uncrosslinked binders selected from the group consisting of polyvinyl alcohols modified with carboxy groups, polyvinyl alcohols modified with silanol groups, diacetone-modified polyvinyl alcohols, partially and fully hydrolysed polyvinyl alcohols and film-forming acrylic copolymers.
10. Heat-sensitive recording material according to either one of claims 8 and 9, containing in the protective layer one or more binders crosslinked by reaction with one or more crosslinking agent(s), the crosslinking agent(s) being selected from the group consisting of boric acid, polyamines, epoxy resins, dialdehydes, formaldehyde oligomers, epichlorohydrin resins, dimethylurea, melamine formaldehyde, adipic acid dihydrazide urea, methylolurea, ammonium zirconium carbonate and polyamide epichlorohydrin resins.
11. Use of a condensation product of formula (I) as defined in either one of claims 1 and 2 for improving the stability - towards substances selected from the group consisting of water, alcohols, fats, oils and mixtures thereof - of the thermal printout obtainable on a heat-sensitive recording material the heat-sensitive recording layer of which contains the colour developer N-(p-toluenesulphonyl)-N'-3-(p-toluenesulphonyl-oxyphenyl)-urea.
12. Printed heat-sensitive recording material, comprising
    a substrate
    and
    a heat-sensitive recording layer comprising

    - one or more dye precursors,

    - N-(p-tofuenesulphonyl)-N'-3-(p-toluenesulphonyl-oxyphenyl)-urea

    - and one or more condensation products of formula (I) as defined in either one of claims 1 and 2,

    and also

    - one or more dyes formed by reaction of the dye precursor(s) with N-(p-toluenesulphonyl)-N'-3-(p-toluenesulphonyl-oxyphenyl)-urea.