DE69909720T2 - Thermographic black and white recording material with improved image tone - Google Patents

Description

technical Field of the invention

The present invention relates improved substantially light-insensitive black-and-white monochrome thermographic recording materials.

general State of the art

In thermal imaging or thermography is a recording method, at the pictures with the help of heat energy be generated. In direct thermal generation becomes a visible Image created by imagewise heating a recording material containing substances whose color or optical Density changes due to chemical or physical processes. at most of the "direct" thermographic Recording materials are those of the chemical Type. When heated to a certain transformation temperature takes place an irreversible chemical reaction, and it becomes a colored picture generated.

In US-P 3,846,136 it is disclosed that the thermosensitive or other curable Layers in thermographic materials with organic or inorganic hardeners such as aldehydes and blocked aldehydes, ketones, carboxylic acid and Carbonic acid derivatives, Sulfonate esters, sulfonyl halides and Vinylsulfonylethern, active Halogen compounds, epoxy compounds, aziridines, active olefins, Isocyanates, carbodiimides, hardeners with mixed function and polymeric hardeners such as oxidized polysaccharides such as dialdehyde starch and oxyguar gum and the like can be cured. This Description is just an invitation to experiments and though because the list is almost all for wet-processed photographic photosensitive silver halide gelatin emulsion materials Harder comprises and no example in which they are used is given.

In WO 95/12495 (= US 5,710,095 ) discloses a method of recording an image by image-wise heating a recording material, wherein the recording material on the same side of a support, called a heat-sensitive side, comprises (1) one or more layers having an image-forming composition consisting essentially of (i) a substantially light-insensitive organic silver salt in effective thermal relationship to a (ii) reducing agent; and (2) on the same side a protective layer covering the image-forming composition, characterized in that the imagewise heating with a thermal head is in contact with the heat-sensitive side and through the protective ingredient layer containing as main ingredients a cured polymer or a cured polymer composition is carried out. In a preferred embodiment, the protective layer contains hydrophilic polymers having active hydrogen atoms, at least a portion of which has reacted with curing agents selected from the group consisting of polyisocyanates, polyepoxides, aldehydes, and hydrolyzed tetraalkylorthosilicates.

In US 5,468,603 discloses a thermographic emulsion layer comprising an organic silver salt, a polyisocyanate, a binder, e.g. BUTVAR ^™ B-79, and a wide variety of reducing agents, with sterically hindered bisphenols being preferred, coated with a protective layer containing a polymeric fluorinated surfactant. DESMODUR ^TM 3300 will be available in US 5,468,603 for use in combination with photothermographic emulsion layers.

In US 5,468,228 discloses a thermographic emulsion layer comprising an organic silver salt, a binder, e.g. BUTVAR ^™ B-79, a substituted propene compound, and a wide variety of reducing agents, with sterically hindered bisphenols being preferred, coated with a protective layer containing a polymeric fluorinated surfactant. DESMODUR ^TM 3300 will be available in US 5,468,228 for use in combination with photothermographic emulsion layers.

When made from solvents Coating of thermographic materials with a protective layer it is desirable for economic and logistical reasons, the order of the organic silver salt-containing layer and the protective layer to perform at once. Therefore, the two layers are to harden because otherwise in essential Dimensions of mixing can occur. However, it has turned out that the use such hardener the image gradation of the resulting materials is significantly impaired.

Tasks of present invention

Object of the present invention it is accordingly, a material light-insensitive black-and-white thermographic recording material with tempered thermosensitive Provide element

Accordingly, it is another object of the present invention to provide a substantially light-insensitive black-and-white thermographic recording material which has an image gradation in printing which is not greatly affected by the hardening of the thermosensitive element.

Other tasks and benefits of The present invention will become apparent from the following description seen.

Short illustration of the present invention

It turned out unexpectedly that this adverse influence on the image gradation during curing the heat-sensitive Elements by using 1,2-dihydroxybenzene derivatives as Reducing agents in combination with specific polyisocyanates as hardeners can be corrected, the influence of the hardening process on the gradation substantially light-insensitive monochrome monochrome thermographic recording materials based on essentially light-insensitive organic silver salts and reducing agents therefor negligible limited is.

Are solved the above Tasks by a substantially light-insensitive thermographic Black and white monosheet recording material with a carrier and a heat-sensitive, with a protective layer coated Element, being the heat-sensitive Element a substantially light-insensitive organic silver salt, a 1,2-dihydroxybenzene derivative in a thermally effective relationship thereto and a first polymer having active hydrogen atoms, wherein at least part of these atoms with a first polyisocyanate the group consisting of hexamethylene diisocyanate, toluene diisocyanate, Diphenylmethanediisocyanate, naphthylene diisocyanate and triphenylmethane p, p ', p' '- trityltriisocyanat has reacted and the protective layer contains no fluorine-containing compounds.

Are solved the above Tasks also by a marked by the following steps Recording method: (i) arranging an outer layer of the above-described thermographic recording material in the vicinity of a heating source, (ii) imagewise of the recording material with heat supplied from the heat source Preparation of an image, wherein the recording material in the Near the Heat source is maintained, and (iii) removing the recording material of the heat source.

Embodiments preferred according to the invention are in the subclaims described.

Detailed description of the present Invention.

In a preferred embodiment the recording method according to the invention it is the heat source is a thermal head and is a thin-film thermal head particularly preferred.

definitions

By "substantially insensitive to light" is meant "not on purpose sensitive to light. "

By "substantially solvent-free aqueous medium" is meant that optionally used solvent in an amount of less than 10% by volume, based on the aqueous medium, is included.

1,2-dihydroxybenzene derivatives Compounds with one by two hydroxyl groups in the ortho position mutually substituted benzene ring.

By "polymer having active hydrogen atoms" is meant a Polymer with substituents with very reactive hydrogen atoms such as Hydroxyl groups, thiol groups, carboxyl groups, -N-H groups, amino groups, Amido groups etc.

By "polyisocyanate" is meant a Compound having at least two isocyanate groups, optionally with while a hardening quickly displaceable Groups are blocked, wherein the polyisocyanate with the active Hydrogen atoms of a polymer reacts with active hydrogen atoms.

The term "fluorine-containing compounds" includes all fluorine-containing compounds and all compounds which contain fluorine-containing compounds as impurities, as well as polymeric fluorinated surfactants as described in US Pat US 5,468,603 , In US 5,468,603 discloses a polymeric fluorinated surfactant having at least three different groups derived from reactive monomers in the polymer chain, wherein as monomers (a) a fluorinated ethylenically unsaturated monomer, (b) a hydroxyl-containing ethylenically unsaturated monomer and (c) a polar, by addition copolymerization produced , ethylenically unsaturated monomer are mentioned.

reducing agent

Organic reducing agents suitable according to the invention are 1,2-dihydroxybenzene derivatives, such as catechol, 3- (3,4-dihydroxyphenyl) propionic acid, 3,4-dihydroxybenzoic acid and its esters formed therefrom, gallic acid and gallic acid esters, eg. Methyl gallate, ethyl gallate, propyl gallate, tannic acid, 1,2-dihydroxy naphthalene and 2,3-dihydroxynaphthalene.

in der bedeuten:
n 0 oder 1,
R -(C=O)R¹, -(C=O)NR¹R², -CN, -SO₃R¹, -SO₂R¹, -SOR¹, -SO₂NR¹R² oder -PO₃R¹R²,
R¹ ein Wasserstoffatom, eine Alkylgruppe oder eine Arylgruppe,
R² ein Wasserstoffatom, eine Alkylgruppe oder eine Arylgruppe, und wobei R¹ und R² zusammen die zum Schließen eines Ringes benötigten Atome bedeuten dürfen, wobei es sich um einen carbocyclischen Ring handeln kann, dessen Atome ausschließlich Kohlenstoffatome sind, oder um einen heterocyclischen Ring, dessen Atome Kohlenstoffatome und zumindest ein Atom wie z. B. Stickstoff, Schwefel, Sauerstoff, Phosphor usw. sind. Die Alkylgruppen und Arylgruppen dürfen ebenfalls mit einer oder mehreren Gruppen aus der Reihe bestehend aus einer Hydroxylgruppe, einer Cyangruppe, einer Thiolgruppe und einem Halogenatom substituiert sein. Besonders bevorzugte -(CH=CH)_nR-Gruppen sind eine Formylgruppe, eine Oxoalkylgruppe, eine Oxoarylgruppe, eine Cyangruppe, eine Carbamidogruppe, eine Diphenoxyphosphorylgruppe, eine Alkylsulfinylgruppe, eine Alkylsulfonylgruppe und eine Sulfonylaminogruppe.In a preferred embodiment of the substantially light-insensitive monochrome monochrome thermosensitive recording material of the present invention, the 1,2-dihydroxybenzene derivative is a 3,4-dihydroxybenzoic acid derivative. In a further preferred embodiment of the substantially light-insensitive black and white single-sheet thermographic recording material according to the invention, the 1,2-dihydroxybenzene derivative is a compound of the formula (I):

in which mean
n 0 or 1,
R - (C =O) R ¹ , - (C =O) NR ¹ R ² , -CN, -SO ₃ R ¹ , -SO ₂ R ¹ , -SOR ¹ , -SO ₂ NR ¹ R ² or -PO ₃ R ¹ R ² ,
R ^{1 represents} a hydrogen atom, an alkyl group or an aryl group,
R ^{2 represents} a hydrogen atom, an alkyl group or an aryl group, and wherein R ¹ and R ² together may represent the atoms needed to close a ring, which may be a carbocyclic ring whose atoms are exclusively carbon atoms, or a heterocyclic ring whose atoms have carbon atoms and at least one atom such as. As nitrogen, sulfur, oxygen, phosphorus, etc. are. The alkyl groups and aryl groups may also be substituted with one or more of the group consisting of a hydroxyl group, a cyano group, a thiol group and a halogen atom. Particularly preferred - (CH = CH) _n R groups are a formyl group, an oxoalkyl group, an oxoaryl group, a cyano group, a carbamido group, a diphenoxyphosphoryl group, an alkylsulfinyl group, an alkylsulfonyl group and a sulfonylamino group.

Preferred reducing agents for use in the present invention are selected from the group consisting of Ethyl 3,4-dihydroxybenzoate, butyl 3,4-dihydroxybenzoate, 3,4-dihydroxybenzonitrile, 2,3,4-trihydroxyacetophenone, 2,3,4-trihydroxypropionophenone, 2,3,4-trihydroxybenzaldehyde, 2,3,4-trihydroxybutyrophenone and 2,3,4-trihydroxybenzonitrile selected.

There can also be combinations be used by reducing agents that when heated to participants on the reduction reaction of the substantially light-insensitive organic Become silver salt.

polyisocyanates

The first in the heat-sensitive Elements of the invention essential light-insensitive black-and-white thermographic monochrome recording material Polyisocyanate is selected from the group consisting of hexamethylene diisocyanate, Toluene diisocyanate, diphenylmethane diisocyanate, naphthylene diisocyanate and triphenylmethane-p, p ', p "-trityltriisocyanate.

• – Hexamethylendiisocyanat-Derivate (HDI), z. B. die Biuret-HDIs DESMODUR^TM N100 und DESMODUR^TM N75 und die Isocyanurate (HDI-Trimere) von BAYER,
• – Toluol-(2,4/2,6)-diisocyanat-Derivate (TDI), z. B. DESMODUR^TM L75, ein Produkt von Diisocyantoluol und Trimethylolpropan von BAYER,
• – 4,4'-Diisocyanatodiphenylmethan (MDI), z. B. DESMODUR^TM VL von BAYER,
• – Naphthylen-1,5-diisocyanat (NDI),
• – p-Phenylendiisocyanat (PPDI),
• – m-Xylylendiisocyanat (XDI),
• – Cyclohexandiisocyanat (CHDI), z. B. DESMODUR^TM W von BAYER,
• – Triphenylmethantriisocyanat, z. B. DESMODUR^TM R von BAYER,
• – Triphenylmethan-p,p',p''-trityltriisocyanat, und
• – polymere Isocyanate (PMDI).

As a second polyisocyanate is any polyisocyanate in question, which is capable of reacting with polymers having active hydrogen atoms, for. A polyisocyanate having free isocyanate groups or a polyisocyanate having a blocking group that prevents reaction at room temperature. Suitable polyisocyanates include

• Hexamethylene diisocyanate derivatives (HDI), e.g. B. the biuret HDIs DESMODUR ^™ N100 and DESMODUR ^™ N75 and the isocyanurates (HDI-trimers) from BAYER,
• - Toluene (2,4 / 2,6) diisocyanate derivatives (TDI), z. B. DESMODUR ^™ L75, a product of diisocyanate toluene and trimethylolpropane from BAYER,
• 4,4'-diisocyanatodiphenylmethane (MDI), e.g. B. DESMODUR ^™ VL from BAYER,
• - Naphthylene-1,5-diisocyanate (NDI),
• P-phenylene diisocyanate (PPDI),
• - m-xylylene diisocyanate (XDI),
• - Cyclohexane diisocyanate (CHDI), z. B. DESMODUR ^™ W from BAYER,
• - Triphenylmethane triisocyanate, z. B. DESMODUR ^™ R from BAYER,
• - triphenylmethane-p, p ', p "-trityltriisocyanate, and
• - polymeric isocyanates (PMDI).

The choice of polyisocyanate directed depending on the required curing rate.

The first and the second polyisocyanate allowed be the same or different.

thermosensitive element

The heat-sensitive element of the present invention contains a substantially light-insensitive organic silver salt, a 1,2-dihydroxybenzene derivative in thermally effective relationship thereto, and a polymer having active hydrogen atoms, at least a portion of which has reacted with a first polyisocyanate. The element may contain a layered structure in which the ingredients may be dispersed in different layers, provided that the substantially light-insensitive organic silver salt and the 1,2-dihydroxybenzene derivative are in reactive relation to each other, ie during the heat development the 1 , 2-dihydroxybenzene derivative so as to be able to diffuse to the particles of the substantially light-insensitive organic silver salt to effect the reduction to silver. The thermosensitive element preferably contains no substituted propenenitrile compound of the formula (X) NC = R ¹ R ² in which R ^{1 represents} a hydroxyl group or a metal salt of a hydroxyl group, R ^{2 represents} an alkyl group or an aryl group, and X represents an electron attracting group or in which R ² and X together may form an electron-attracting group-containing ring as described in EP-A-0 022 831 US 5 686 228 ,

Organic silver salts

Preferred substantially light-insensitive organic silver salts for use in the thermosensitive element of used according to the invention substantially light-insensitive black-and-white thermographic recording material are silver salts of as fatty acids known aliphatic carboxylic acids, in which the aliphatic carbon chain is preferably at least Contains 12 carbon atoms, these silver salts are also referred to as "silver soaps". Combinations of various organic silver salts are also suitable for Use in the recording materials according to the invention.

tint

To obtain a neutral black Picture tones in the upper density zones and from neutral gray in the lower ones Contains density zones the heat sensitive Element preferably a so-called, from the thermography or Photothermography known Tönungsmittel.

Suitable toning agents are the general ones Formulas in US-P 4 082 901 corresponding phthalimides and phthalazinones and the in US Pat. No. 3,074,809, US Pat. No. 3,446,648 and US Pat. No. 3,844,797. Other particularly useful toning agents are the heterocyclic toner compounds of the benzoxazinedione or naphthoxazinedione type as described in GB-P 1,439,478, US-P 3,951,660 and U.S. Patent 5,599,647.

Polymer with active hydrogen atoms

For the first polymer with active hydrogen atoms the heat-sensitive Elements and the second polymer with active hydrogen atoms the protective layer can be any kind of natural, modified natural or synthetic resins or mixtures of such resins, in which the organic silver salt is either in an aqueous medium or a solvent medium is homogeneously dispersible, for. B. cellulose derivatives such as ethyl cellulose, Cellulose esters, e.g. Cellulose nitrate, carboxymethyl cellulose, starch ethers, partially hydrolyzed polyvinyl acetate, polyvinyl alcohol, polyvinyl acetals, the polyvinyl alcohol as starting material, in which only a part the repeating vinyl alcohol units optionally with reacted with an aldehyde, preferably polyvinyl butyral, Polyacrylamide, polymethacrylamide, polyacrylic acid, polymethacrylic acid, proteinaceous Binders such as gelatin, modified gelatins such as phthaloyl gelatin, Polysaccharides, such as starch, Gum arabic and dextran, and water-soluble cellulose derivatives or Mixtures thereof.

In a preferred embodiment of the invention essential light-insensitive black-and-white monochrome thermographic recording material the first polymer with active hydrogen atoms from the group from polyvinyl alcohol, polyvinyl acetals and proteinaceous binders selected.

The weight ratio of the binder to organic silver salt in the heat-sensitive Element is preferably between 0.2 and 6 and the thickness of thermosensitive Elements preferably between 5 and 50 microns.

stabilizers and antifreeze

in der Q die zur Bildung eines 5- oder 6-gliedrigen, aromatischen, heterocyclischen Ringes benötigten Atome bedeutet und A ein Wasserstoffatom, ein Gegenion, das die negative Ladung der Thiolatgruppe ausgleicht, oder eine ein symmetrisches oder asymmetrisches Disulfid bildende Gruppe bedeutet.In order to improve the storage stability and to limit fogging, stabilizers and antifoggants may be embedded in the substantially light-insensitive black-and-white thermographic recording material of the present invention. Stabilizer compounds useful in the present invention are unsaturated, carbocyclic or heterocyclic -SA group substituted compounds wherein A is a hydrogen atom, a counterion to balance the negative charge of the thiolate group, or a symmetrical or asymmetric disulfide forming group. Such stabilizers may be further substituted, wherein the substitution also includes the atoms needed to form a fused unsaturated carbocyclic or heterocyclic ring system. Preferred stabilizer compounds used according to the invention have an unsaturated 5- or 6-membered ring. Particularly suitable compounds correspond to the formula (II):

wherein Q represents the atoms needed to form a 5- or 6-membered aromatic heterocyclic ring and A represents a hydrogen atom, a counterion which balances the negative charge of the thiolate group, or a symmetrical or asymmetric disulfide-forming group.

Surfactants and dispersant

Facilitate surfactants and dispersants dispersing ingredients that are not in the dispersion medium used soluble are. The invention used substantially light-insensitive black-and-white thermographic recording material may be one or more anionic, nonionic or cationic surfactants and / or one or more dispersants.

Suitable dispersants are natural polymeric substances, synthetic polymeric substances and finely divided Powder, for example, finely divided non-metallic inorganic Powder like silica.

Other ingredients

Except for the above ingredients may be the substantially light-insensitive black-and-white thermographic recording material contain other ingredients, such as free fatty acids, antistatic agents, eg. Non-ionic Antistatic agents, silicone oil, Ultraviolet light absorbing compounds, white light reflective and / or ultraviolet radiation reflective pigments, silicic acid and / or optical brightening agents.

carrier

The carrier for the substantially light-insensitive black and white thermographic recording material can be translucent, translucent or opaque and is preferred a thinner one flexible carrier or a carrier made of translucent Resin, z. B. from a cellulose ester, for. B. cellulose triacetate, Polypropylene, polycarbonate or polyester, e.g. For example, polyethylene terephthalate. The carrier may be in the form of a bow, ribbon or web and if necessary subbed to bond to the heat-sensitive material applied to it Element to improve. The carrier can be colored or pigmented to give the picture a translucent colored background to rent.

protective layer

In a preferred embodiment of the invention essential light-insensitive black-and-white monochrome thermographic recording material contains the protective layer a second polymer with active hydrogen atoms and a second one Polyisocyanate. This protective layer protects the heat-sensitive element in usually against humidity and surface damage due to scratching etc. and prevents direct contact of printheads or heat sources with the Recording layers. Preferably, the protective layer therefore contains no fluorine-containing compounds, because such compounds in the while the heat development occurring high temperatures in the protective layer with others Ingredients react and / or become volatile fluorine-containing compounds decompose, which attack the thermal head and its service life to a considerable extent to reduce.

On protective layers for heat-sensitive elements, which come in contact with a heat source and under pressure must be conveyed past it, the requirement is made that they must be resistant to local deformation and have good sliding properties, if they are conveyed during the heating of the heat source over.

Solid or liquid lubricants or combinations the same are suitable for improving the sliding properties the thermographic invention Recording materials. Solid lubricants usable in accordance with the invention are polyolefin waxes, ester waxes, polyolefin-polyether block copolymers, amide waxes, Polyglycols, fatty acids, Fatty alcohols, natural Waxes and solid phosphoric acid derivatives. preferred Solid lubricants are thermally melting particles such as those in WO 94/11199 described. Usable according to the invention liquid lubricant are fatty acid esters such as glycerol trioleate, sorbitan monooleate and sorbitan trioleate, silicone oil derivatives and phosphoric acid derivatives.

The outer layer of the recording material according to the invention may contain a matting agent. Suitable matting agents are described in WO 94/11198, u. a. Talc particles, and optionally protrude from the outer layer out.

antihalation

Exterior of the above ingredients can the invention used thermographic recording materials also infrared light contain anti-halation dyes or shade dyes, the infrared light, which is the heat-sensitive one Element has penetrated, absorb and convert into heat and thus reflection to prevent this light. Such dyes can in the heat-sensitive Element or incorporated into any other layer of the novel recording material become.

coating techniques

The order of any layer of the used according to the invention substantially light-insensitive black-and-white thermographic recording material can be done by any coating technique, such. As described in "Modern Coating and Drying Technology ", Edited by Edward D. Cohen and Edgar B. Gutoff, (1992) VCH Publishers Inc. 220 East 23rd Street, Suite 909 New York, NY 10010, UNITED STATES. The coating may be from an aqueous medium or a solvent medium by coating dried, partially dried or non-dried layers take place.

thermographic pressure

The direct thermal imaging takes place by imagewise admission with heat, either analogously by direct exposure through an image or by reflection from an image or in a digital manner pixel-by-pixel exposure with an infrared heater source, for example an Nd-YAG laser or other infrared laser, or through direct thermal imaging with a thermal head.

Under thermal pressure, image signals are converted into electrical impulses which are then selectively applied to a thermal print head via a driver circuit. The thermal print head consists of microscopic thermal resistance elements that convert the electrical energy into heat via the Joule effect. The electrical pulses thus converted into thermal signals express themselves as heat transmitted to the surface of the thermal paper in which the color-developing chemical reaction takes place. Such thermal printheads may be placed in contact with or in close proximity to the recording layer. The operating temperature of conventional thermal printheads is between 300 and 400 ° C and the heating time per pixel is 1.0 ms or less, wherein the pressure contact of the thermal print head with the recording material z. B. between 200 and 500 g / cm ² , to ensure good heat transfer.

For direct contact of the thermal print heads with a recording layer not covered with an outer protective layer to prevent allowed the imagewise heating the recording layer with the thermal printheads by a (n) so im Contact (s), but removable, resin sheet or resin sheet, from the (the) during the heating no recording material can be transmitted, are performed.

The image signals for modulating the Laser beam or current in the micro-resistances of a thermal printhead are either received directly or from a cache, optionally connected to a digital imaging workstation in which The image information can be processed to special needs meet.

The control of the heating elements can be power modulated or pulse length modulated at constant power. EP-A 654 355 describes a method for forming an image by imagewise heating by means of a thermal head with excitable heating elements, the heating elements being driven after a duty-cycle pulse operation. When used in thermographic, with thermal printing head The recording materials are not suitable for reproducing images with a fairly high number of gray levels, as is required for halftone reproduction. EP-A-622 217 discloses a method of forming an image using a direct thermal imaging element wherein improved halftone reproduction is achieved. For the imagewise heating of the thermographic material is also an embedded in the material electrical resistance band. The imagewise or patternwise heating of the thermographic material may also be done by a pixel-wise modulated ultrasonic treatment.

industrial application

The thermographic imaging can for the generation of both transparencies and supervisory copies be used. Purpose as an application of the present invention are the areas of graphic images where high-contrast Pictures with very steep dependence the print density of the energy applied to a point is required, as well as the halftones, in which a weaker dependence the print density of the energy applied to a point is required, as in medical diagnostics is required. Hard copies use thermographic recording materials on a white opaque carrier, while in medical diagnostics when working with a viewing device exam techniques Find black-image transparent widespread application.

The following examples of the invention and comparative examples the present invention. The percentages and ratios in these examples are in weight, unless otherwise stated is. Except The above-mentioned ingredients are used in the examples according to the invention and Comparative Examples also the following ingredients

• – organisches Silbersalz: AgBeh = Silberbehenat,
• – das Bindemittel: BR 18 = PIOLOFORM BR 18, ein Polyvinylbutyral von WACKER CHEMIE,
• – Polyisocyanate: N100 = DESMODUR^TM N100 von BAYER, N75 = DESMODUR^TM N75 von BAYER, N3300 = DESMODUR^TM N3300 von BAYER, W = DESMODUR^TM W von BAYER, L75 = DESMODUR^TM L75, ein Toluoldiisocyanat (TDI) von BAYER, VL = DESMODUR^TM VL, ein 4,4'-Diisocyanatdiphenylmethan von BAYER,
• – Katalysator für die Härtung des Polyisocyanats: DBTDL = Dibutylzinndilaurat,
• – andere Härter: CYMEL^TM 303 = ein hochmethyliertes Melaminharz von DYNO-CYTEC Industries, CYCAT^TM 600 = Dodecylbenzolsulfonsäure von DYNO-CYTEC Industries,
• – Reduktionsmittel: R01 = Ethyl-3,4-dihydroxybenzoat, R02 = Propyl-2,3,4-trihydroxybenzoat (Propylgallat), R03 = Methyl-3,4-dihydroxy-5-methoxybenzoat, R04 = 2,3,4-Trihydroxypropionophenon, R05 = Propyl-3,4-dihydroxy-5-methoxybenzoat, R06 =
  
  R07 = 2,3,4-Trihydroxybutyrophenon, R08 = 1,1-Bis-(2-hydroxy-3,5-dimethylphenyl)-3,5,5-trimethylhexan (NONOX^TM),
• – Tönungsmittel: T01 = 7-(Ethylcarbonat)-benzo[e]-[1,3]-oxazin-2,4-dion,
• – Silikonöl: Öl = BAYSILON^TM MA, ein Polydimethylsiloxan von BAYER,
• – Stabilisatoren S01 = Tetrachlorphthalsäureanhydrid, S02 = 3'-Decanoylamino-1-phenyl-1H-tetrazol-5-thiol
  
  und in der Schutzschicht werden die nachstehenden zusätzlichen Ingredienzien verwendet
• – MICRODOL^TM SUPER, ein Talk von Norwegian Talc AS,
• – TINUVIN^TM 320 von CIBA-GEIGY,
• – SERVOXYL^TM VPAZ 100, ein Gemisch aus Monolaurylphosphat und Dilaurylphosphat von SERVO DELDEN B.V.

In heat-sensitive element:

• - organic silver salt: AgBeh = silver behenate,
• - the binder: BR 18 = PIOLOFORM BR 18, a polyvinyl butyral from WACKER CHEMIE,
• - polyisocyanates: N100 = DESMODUR ^™ N100 from BAYER, N75 = DESMODUR ^™ N75 of BAYER, N3300 = DESMODUR ^™ N3300 from Bayer, W = DESMODUR ^™ W from Bayer, L75 = DESMODUR ^™ L75, a toluene diisocyanate (TDI) from BAYER, VL = DESMODUR ^™ VL, a 4,4'-diisocyanatodiphenylmethane from BAYER,
• Catalyst for the curing of the polyisocyanate: DBTDL = dibutyltin dilaurate,
• Other hardeners: CYMEL ^™ 303 = a highly methylated melamine resin from DYNO-CYTEC Industries, CYCAT ^™ 600 = dodecylbenzenesulfonic acid from DYNO-CYTEC Industries,
• Reducing agent: R01 = ethyl-3,4-dihydroxybenzoate, R02 = propyl-2,3,4-trihydroxybenzoate (propyl gallate), R03 = methyl-3,4-dihydroxy-5-methoxybenzoate, R04 = 2,3,4- Trihydroxypropionophenone, R05 = propyl-3,4-dihydroxy-5-methoxybenzoate, R06 =
  
  R07 = 2,3,4-trihydroxybutyrophenone, R08 = 1,1-bis- (2-hydroxy-3,5-dimethylphenyl) -3,5,5-trimethylhexane (NONOX ^™ ),
• Tinting agent: T01 = 7- (ethyl carbonate) benzo [e] - [1,3] oxazine-2,4-dione,
• Silicone oil: oil = BAYSILON ^™ MA, a BAYER polydimethylsiloxane,
• Stabilizers S01 = tetrachlorophthalic anhydride, SO 2 = 3'-decanoylamino-1-phenyl-1H-tetrazole-5-thiol
  
  and in the protective layer, the following additional ingredients are used
• - MICRODOL ^™ SUPER, a talc from Norwegian Talc AS,
• TINUVIN ^TM 320 from CIBA-GEIGY,
• - SERVOXYL ^TM VPAZ 100, a mixture of monolauryl phosphate and dilauryl phosphate from SERVO DELDEN BV

INVENTIVE EXAMPLES 1 to 5 and COMPARATIVE EXAMPLE 1

Preparation of a silver behenate dispersion

72 kg of a 25% solution of BR 18 in 2-butanone, 180 kg of silver behenate and 455 kg of 2-butanone in a ball mill mixed. After 4 days, 72 kg of a 25% solution of BR 18 in 2-butanone and 22 kg of 2-butanone were added, after which the mixture several days in the ball mill is mixed further. Subsequently be 576 kg of a 25% solution of BR 18 in 2-butanone, 0.684 kg of oil, 326.2 kg of 2-butanone and 10.08 g T01 was added, after which the resulting mixture on the ball mill for 10 h on is mixed. The final Contains 2-butanone dispersion 10.5% silver behenate, 10.5% BR 18, 0.59% T01 and 0.04% oil.

manufacturing the heat-sensitive Elements

A 2-butanone solvent / dispersion medium containing composition is then on a 120 microns thick subbed polyethylene terephthalate supported and dried. It receives one is heat sensitive Element having the compositions listed in Table 1 below:

Table 1

Evaluation of the degree of hardening

To determine the degree of cure, a drop of 2-butanone is allowed to absorb from the heat-sensitive element, wiping the film to remove softening areas, and finally heating the thermographic recording material over the entire surface. Insufficient curing is observed in those areas of the thermographic recording material where development does not occur due to softening and removal of the silver-containing binder. The results are visually evaluated: no non-developed areas excellent hardening slight staining acceptable hardening large non-developed areas weak hardening

The results are in Table 2 composed.

Table 2

These results show that using the CYMEL ^™ 303 / CYCAT ^™ 600 combination achieves acceptable cure for all the polyisocyanates evaluated.

Thermographic pressure

While of the printing cycle with the recording materials of the COMPARATIVE EXAMPLE 1 and INVENTION EXAMPLES 1 to 5 the printhead by a thin one intermediate material in contact with a sliding layer of a separable, 5 microns strong polyethylene terephthalate tape from the image-forming layer held separated, the tape in turn with an adhesive layer, a heat resistant Layer and the sliding layer (friction protection layer) coated is and a total strength of Has 6 microns.

The printer comes with a thin-film thermal print head with a resolution equipped with 300 dpi and is at a line time of 6.5 ms (the line time is the time required to print a single line). While This line time, the print head is constantly energized. The middle Printing power, which is the total amount needed to print a line Energy, divided by the line time and the surface of the heat-generating resistors, corresponds to 1.6 mJ / dot and extends to all the thermographic recording materials COMPARATIVE EXAMPLE 1 and the INVENTION EXAMPLES 1 to 5 to obtain a maximum optical density.

The maximum and minimum densities of the prints listed in Table 3 are measured in a MACBETH ^™ TR924 densitometer behind an optical filter in the gray scale step corresponding to data planes 64 and 0, respectively. The measured values are listed in Table 3.

For evaluating the steepness of the gradation curve of the thermographic recording materials of COMPARATIVE EXAMPLE 1 and INVENTION EXAMPLES 1 to 5, the numerical gradation (NGV) is determined according to the quotient of the fraction [2, 5 - (1, 0 + D _min ) / [E _{2 , 5} - E _{(1, 0 +} D _min) ], where E _{2.5 is} the Joule energy with which a dot area of 87 μm × 87 μm of the recording layer is printed to obtain an optical density of 2.5 , and E _{(1.0 +} D _{min) is} the energy in joules with which a dot surface of the recording layer material is printed to have an optical density of (1.0 + D _min ) hold. The applied energy in joules is actually the electrical power measured at each thermal head resistance. The NGV values of the thermographic recording materials of COMPARATIVE EXAMPLE 1 and INVENTION EXAMPLES 1 to 5 are listed in Table 3.

Storage stability test

For the evaluation of the light fastness of the thermographic recording materials of COMPARATIVE EXAMPLE 1 and INVENTION EXAMPLES 1 to 5, the change of the maximum density (ΔD _max ) and the change of the CIELAB values a * and b * at the minimum density are determined. The CIELAB values are determined according to spectrophotometric measurements according to ASTM standard E179-90 in an R (45/0) geometry and the evaluation is carried out according to ASTM standard E308-90. The results are listed in Table 3.

Table 3

The results in Table 3 show that after 3 minutes of cure at 85 ° C, which is adequate cure for all curing systems evaluated, acceptable D _max and D _min values are obtained for all cured systems evaluated and the image tone values, their rating CIELAB measurements carried out after 3 days storage at 57 ° C and 34% relative humidity are comparable, but the NGV found in the polyisocyanate-free curing system of COMPARATIVE EXAMPLE 1 is markedly lower, ie 12.8 , than the NGV values obtained with the polyisocyanate hardeners, ie, 17.0 to 18.4, indicating a significantly smaller interfering interaction between the curing system and the image-forming components. The highest NGV values, which indicate the lowest interfering interaction, are found in the polyisocyanates DES MODUR ^™ N3300, DESMODUR ^™ L75 and DESMODUR ^™ W.

From the comparison between the NGV values of the INVENTION EXAMPLES 1 to 5 and the NGV value of COMPARATIVE EXAMPLE 1, it can be seen that that despite the appropriate hardening effect of the melamine curing system CYMEL 303 / CYCAT 600 the NGV value is noticeably lower than that at the polyisocyanate hardeners achieved NGV value. This indicates a much greater degree of reaction between the CYMEL 303 / CYCOAT 600 curing system and the combination the 1,2-dihydroxybenzene reducing agent R01 and R02 as in the Polyisocyanate curing agents.

INVENTIVE EXAMPLES 6 to 11

The thermosensitive elements of the substantially light-insensitive monochrome monochrome thermographic recording materials of the INVENTION EXAMPLES 6 to 11 will be like for the INVENTION EXAMPLES 1 to 5 and COMPARATIVE EXAMPLE 1 are prepared, except what the changes listed in Table 4 below concerns.

Table 4

On the thermosensitive elements of the thermographic recording materials of INVENTION EXAMPLES 6 to 11, the following protective layer composition is then applied PIOLOFORM BR 18 1.5 g / m ² MICRODOL ^TM SUPER 0.18 g / m ² BAYSILON ^TM MA 0.012 g / m ² DESMODUR ^TM VL 0.15 g / m ²

The thermographic evaluation of the substantially light-insensitive black and white monosheet thermographic recording materials of INVENTION EXAMPLES 6 to 11 is made as described for INVENTION EXAMPLES 1 to 5 and COMPARATIVE EXAMPLE 1 with the difference that the printhead on the same side of the support as the side carrying the thermosensitive element is not separated from the outer layer by the thin intermediate material. The results are listed in Table 5.

The use of R04, which is a reducing agent of the formula (I), or a combination of R04 with ethyl 3,4-dihydroxybenzoate (R01) in thermographic recording materials whose heat-sensitive Element and protective layer are cured with a polyisocyanate, gives thermographic recording materials (INVENTION EXAMPLES 7 to 11), their deductions have a noticeably steeper sensitometry than an analogous one thermographic recording material (INVENTION EXAMPLE 6) using the combination of reducing agents R01 and R02 becomes.

Table 5

INVENTIVE EXAMPLES 12 to 17

The thermosensitive elements of the substantially light-insensitive monochrome monochrome thermographic recording materials of the INVENTION EXAMPLES 12 to 17 will be like for the INVENTION EXAMPLES 1 to 5 and COMPARATIVE EXAMPLE 1 are prepared, except what the changes listed in Table 6 below concerns.

Table 6

On the thermosensitive elements of the thermographic recording materials of the INVENTION EXAMPLES 12 to 17 then becomes the same protective layer composition as the for the thermographic recording materials of the INVENTION EXAMPLES Applied 6 to 11 used protective layer composition.

The thermographic evaluation of substantially light-insensitive monochrome monochrome thermographic recording materials of the INVENTION EXAMPLES 6 to 11 will be like for the INVENTIVE EXAMPLES 1 to 5 and COMPARATIVE EXAMPLE 1 are described, however with the difference that the Printhead on the same side of the support as the heat-sensitive Element bearing side not through the thin intermediate material from the outer layer is disconnected. The results are listed in Table 7.

Table 7

The use of R06, which is a spiroindane reducing agent, or a combination of R06 with ethyl 3,4-dihydroxybenzoate (R01) in thermographic recording materials whose thermosensitive element and protective layer are cured with a polyisocyanate gives thermographic recording materials (INVENTIVE EXAMPLES 13) to 17), the prints of which have a slightly less steepensitometry than an analogous thermographic recording material (INVENTIVE EXAMPLES 12) using the combination of the reducing agents R01 and R02. In the R01 / R06 combinations, however, the D _min is noticeably less yellow, as is clear from the CIELAB a * values, the relative after a 3-day storage at 57 ° C and 34% humidity are much closer to zero.

INVENTIVE EXAMPLES 18 to 21

The thermosensitive elements of the substantially light-insensitive monochrome monochrome thermographic recording materials of the INVENTION EXAMPLES 18 to 21 will be like for the INVENTION EXAMPLES 1 to 5 and COMPARATIVE EXAMPLE 1 are prepared, except what the changes listed in Table 8 below concerns.

Table 8

The thermographic evaluation of substantially light-insensitive monochrome monochrome thermographic recording materials of the INVENTION EXAMPLES 18 to 21 will be like for the INVENTIVE EXAMPLES 1-5 and COMPARATIVE EXAMPLE 1 are described. The Results are listed in Table 9.

Table 9

These results show a markedly higher NGV for thermographic recording materials made with DESMODUR ^™ N3300 than thermographic recording materials made with DESMODUR ^™ VL, N75 or N100.

INVENTIVE EXAMPLES 21 to 27

The heat-sensitive elements of the substantially light-insensitive black and white monosheet thermographic recording materials of INVENTION EXAMPLES 21 to 27 are prepared as described for INVENTION EXAMPLES 1 to 5 and COMPARATIVE EXAMPLE 1, except that the following composition is used for the thermosensitive element: AgBeh 3.89 [g / m ² ] R01, reducing agent 0.855 [g / m ² ] PIOLOFORM ^TM BR 18 3.89 [g / m ² ] DESMODUR ^TM N100 0.401 [g / m ² ] oil 0.144 [g / m ² ] TINUVIN ^TM 320 0.15 [g / m ² ] T01 0.219 [g / m ² ] S01 0.235 [g / m ² ] S02 0.085 [g / m ² ]

On the thermosensitive element of thermographic recording materials of the INVENTION EXAMPLES 21 to 27 then become different, in Table 10 below listed protective coating compositions applied

Table 10

The thermographic evaluation of the substantially light-insensitive monochrome black-and-white single-sheet recording materials of INVENTION EXAMPLES 21 to 27 is made as described for INVENTION EXAMPLES 1 to 5 and COMPARATIVE EXAMPLE 1, except that the printhead is attached to the same side of the support as that shown in Figs the thermosensitive element-bearing side is not separated from the outer layer by the thin intermediate material and the NGV values for the optical density range (0.3 + D _min ) to (1.0 + D _min ) instead of the optical density range (1.0 + D _min ) to (2.5 + D _min ). This change in the density range is due to the heat-sensitive element having a lower silver behenate ratio than the heat-sensitive elements of the thermographic recording materials of COMPARATIVE EXAMPLE 1 and INVENTION EXAMPLES 1 to 20. The results are listed in Table II.

The image tone of the thermographic recording material of INVENTION EXAMPLE 21 containing DESMODUR ^™ N100 in the protective layer is remarkably better than the image tone obtained with the DESMODUR ^™ VL-containing thermographic recording materials of INVENTION EXAMPLES 22 to 27. Furthermore, it has been found that the amount of DESMODUR ^™ VL in the protective layers of the thermographic recording materials of INVENTION EXAMPLES 22 to 27 has a limited influence on the NGV values and an increase in the amount of DESMODUR ^™ VL after 24 hours of heating at 80 ° C in significantly lower CIELAB b * value.

Table 11

After taking note of the detailed described preferred embodiments The present invention will be apparent to those skilled in the art Modifications of the description according to the invention open, without from the invention, in the following claims deviate from the defined scope of protection.

Claims (8)

A substantially light-insensitive thermographic Black and white monosheet recording material with a carrier and a heat-sensitive, coated with a protective layer Element, being the heat-sensitive Element a substantially light-insensitive organic silver salt, a 1,2-dihydroxybenzene derivative in a thermally effective relationship thereto and a first polymer having contains active hydrogen atoms, wherein at least a part of these atoms with a first polyisocyanate from the group consisting of hexamethylene diisocyanate, toluene diisocyanate, Diphenylmethanediisocyanate, naphthylene diisocyanate and triphenylmethane p, p ', p' '- trityltriisocyanat has reacted and the protective layer contains no fluorine-containing compounds. Thermographic recording material according to claim 1, characterized in that the 1,2-dihydroxybenzene derivative is a compound of the formula (I)

in which n is 0 or 1, R - (C =O) R ¹ , - (C =O) NR ¹ R ² , -CN, -SO ₃ R ¹ , -SO ₂ R ¹ , -SOR ¹ , -SO ₂ NR ¹ R ² or -PO ₃ R ¹ R ² , R ^{1 is} a hydrogen atom, an optionally substituted alkyl group or an optionally substituted aryl group, R ^{2 is} a hydrogen atom, an optionally substituted alkyl group or an optionally substituted aryl group, and wherein R ¹ and R ² together may mean the atoms needed to close a ring. Thermographic recording material according to claim 1, characterized in that the 1,2-dihydroxybenzene derivative selected from the group consisting of ethyl 3,4-dihydroxybenzoate, Butyl 3,4-dihydroxybenzoate, 3,4-dihydroxybenzonitrile, 2,3,4-trihydroxyacetophenone, 2,3,4-trihydroxypropionophenone, 2,3,4-trihydroxybenzaldehyde, 2,3,4-trihydroxybutyrophenone and 2,3,4-trihydroxybenzonitrile is selected. Thermographic recording material according to a the preceding claims, characterized in that the first polymer with active hydrogen atoms from the group from polyvinyl alcohol, polyvinyl acetals and proteinaceous binders chosen becomes. Thermographic recording material according to a the preceding claims, characterized in that the essentially light-insensitive organic silver salt, a silver salt an aliphatic carboxylic acid with at least 12 carbon atoms. Thermographic recording material according to a the preceding claims, characterized in that the Protective layer a second polymer with active hydrogen atoms and a second polyisocyanate. A marked by the following steps Recording method: (i) arranging an outer layer of a thermographic A recording material according to any one of the preceding claims in Near one Heat source, (ii) imagewise of the thermographic recording material from the heat source supplied heat for producing an image, wherein the recording material in nearby the heat source is maintained, and (iii) removing the thermographic Recording material from the heat source. Recording method according to claim 7, characterized in that that the Heat source a thin-film thermal head is.