DE69814546T2 - Thermographic recording materials - Google Patents

Description

Technical field of present invention.

The present invention relates to substantially light-insensitive thermographic black and white recording materials with a heat sensitive Element that is an essentially light-insensitive organic silver salt and contains a new reducing agent.

State of the art.

In thermal imaging or thermography is a recording process where pictures with the help of thermal energy be generated.

There are three approaches to thermography possible

• 1. Direct thermal generation of a visible Image pattern through pictorial heating a recording material that contains substances, their color or optical Density changes due to chemical or physical processes.
• 2. Pictorial transmission of an ingredient that is necessary for the chemical or physical Process by which changes the color or optical density are caused on a receiving element.
• 3. thermal dye transfer printing, whereby a visible image pattern is formed by transfer a colored substance from an imagewise heated donor element on a receiving element.

Most of the "direct" thermographic Recording materials are those of the chemical Type. When heated to a certain transition temperature an irreversible chemical reaction and it turns into a colored picture generated. US-P 3,080,254 discloses a typical heat sensitive copy paper described that in the heat sensitive Layer a thermoplastic binder, e.g. B. ethyl cellulose, a water insoluble Silver salt, e.g. B. silver stearate, and a suitable organic Reducing agent, for the 4-methoxy-1-hydroxydihydronaphthalene is a typical example.

EP-A 248 405 describes a heat-sensitive Recording material with a color-developing layer disclosed the except the usual Contains ingredients an electron acceptor and an electron donor, where the electron acceptor has a metal double salt of a long chain fatty acid Is 16 to 35 carbon atoms.

entsprechend den Formeln (I) und (II) ist in der R Propyl, Isopropyl oder Butyl bedeutet,

der Elektronenakzeptor ein Doppelsalz eines Metalls einer langkettigen Fettsäure mit 16 bis 35 Kohlenstoffatomen ist und der Elektronendonor eine mehrwertige aromatische Verbindung der Formel (III) ist

in der R eine C₁₈- bis C₃₅-Alkylgruppe,

bedeutet,
wobei R₁ eine C₁₈- bis C35-Alkylgruppe, n die ganze Zahl 2 oder 3 und -X- -CH₂-, -CO₂-, -CO-, -O-, -CONH-, -CO(R')N- (wobei R' eine C₁₈- bis C₃₅-Gruppe ist), -SO₂-, -SO₃- oder -SO₂NH- bedeutet.EP-A 599 580 discloses a heat-sensitive recording sheet which contains in order: (a) a substrate, (b) an intermediate layer which contains a pigment having an oil absorption according to Japanese Industrial Standard (JIS) K501 of 100 ml / Contains 100 g or less, and (c) a heat sensitive color developing layer comprising a leuco dye type color component consisting of a leuco dye and an organic color developer and a metal chelate type color component consisting of an electron acceptor and an electron donor, the organic color developer at least one of the connections

corresponding to formulas (I) and (II) in which R is propyl, isopropyl or butyl,

the electron acceptor is a double salt of a metal of a long chain fatty acid having 16 to 35 carbon atoms and the electron donor is a polyvalent aromatic compound of formula (III)

in which R is a C ₁₈ to C ₃₅ alkyl group,

means
where R _{1 is} a C ₁₈ to C35 alkyl group, n is the integer 2 or 3 and -X- -CH ₂ -, -CO ₂ -, -CO-, -O-, -CONH-, -CO (R ' ) N- (where R 'is a C ₁₈ to C ₃₅ group), -SO ₂ -, -SO ₃ - or -SO ₂ NH-.

In US-P 5 582 953 a method is described for direct Record disclosed in which a direct thermal recording material heated at points and the direct thermal recording material on a Substrate contains an image-forming layer that is uniform in one film-forming polymeric binder distributes (i) one or more organic light salts, insensitive to light - however no double salts - in thermally effective relationship to (ii) an organic reducing agent for the Contains silver salt, wherein the reducing agent is a benzene compound whose benzene nucleus through an over a carbonyl group substituted on the benzene nucleus substituted with the carbonyl group in the 1-position on the benzene nucleus is bound to the benzene nucleus, the benzene nucleus still in a 3-position, based on the 1-position, by a single one Hydroxyl group and in a 4-position, based on the 1-position, is substituted by a single hydroxyl group, the reducing agent from the group consisting of an alkyl or aryl ester of 3,4-dihydroxybenzoic acid, 3,4-dihydroxybenzaldehyde, 3,4-dihydroxybenzamide and an alkyl or aryl (3,4-dihydroxyphenyl) ketone chosen becomes.

Deductions made with direct thermal Recording materials using reducing agents obtained according to the teaching of US Pat. No. 5,582,953, but have a unsatisfactory archivability, inadequate light resistance over the whole sensitometric range and an unsatisfactory color neutrality. It there is therefore still a need for direct thermal recording materials, by coating from a solvent or an aqueous medium are produced and their deductions an improved archivability, an improved light resistance over the entire sensitometric range and have improved color neutrality.

Tasks of the present Invention.

It is accordingly an object of the present invention to provide thermographic recording materials, the prints of which have a high D _max value and low D _min value and improved archivability and / or improved light resistance and / or improved color neutrality over the entire range of printing densities.

Other tasks and advantages of present invention will become apparent from the description below seen.

Short presentation of the present invention.

It turned out unexpectedly that deductions from thermographic Recording materials made from both new 3,4-dihydroxyphenyl compounds containing aqueous media as well as new 3,4-dihydroxyphenyl compounds containing solvent media can be coated a noticeably improved one Can be archived via the entire density range, a noticeably improved light resistance and have improved color neutrality compared to deductions thermographic recording materials containing a reducing agent according to the teaching of US-P 5 582 953 included.

in der bedeuten
R -P(=O)R¹R², -SO_xR³, -CN , -NO₂ oder -CR⁴=NR⁵, wenn n 0 ist,
R -P(=O)R¹R², -SO_xR³, -CN, -NO2, -CR⁴=NR⁵ oder -COR⁶, wenn n eine ganze Zahl ist,
R¹ und R² unabhängig voneinander eine Alkylgruppe, eine substituierte Alkylgruppe, eine Arylgruppe, eine substituierte Arylgruppe, eine Alkoxygruppe, eine substituierte Alkoxygruppe, eine Aryloxygruppe, eine substituierte Aryloxygruppe, eine Hydroxylgruppe, eine Aminogruppe oder eine substituierte Aminogruppe,
R³ eine Alkylgruppe, eine substituierte Alkylgruppe, eine Arylgruppe, eine substituierte Arylgruppe, eine Aminogruppe oder eine substituierte Aminogruppe,
R⁴ eine Alkylgruppe, eine substituierte Alkylgruppe, eine Arylgruppe, eine substituierte Arylgruppe oder ein Wasserstoffatom,
R⁵ eine Alkylgruppe, eine substituierte Alkylgruppe, eine Arylgruppe, eine substituierte Arylgruppe, eine Hydroxylgruppe, eine Alkoxygruppe, eine Aryloxygruppe, eine Acylgruppe, eine Aminogruppe oder eine substituierte Aminogruppe,
R⁶ eine Alkylgruppe, eine substituierte Alkylgruppe, eine Arylgruppe, eine substituierte Arylgruppe, eine Alkoxygruppe, eine substituierte Alkoxygruppe, ein Aryloxygruppe, eine substituierte Aryloxygruppe, eine Hydroxylgruppe, eine Aminogruppe oder eine substituierte Aminogruppe oder ein Wasserstoffatom, × 1, 2 oder 3,
und wobei der Benzolring der 1,2-Dihydroxyphenylverbindung der Formel (I) noch weitere Substitutionen aufweisen kann. Substituierte Aminogruppen können ebenfalls ein heterocyclisches Ringsystem bilden, das selbst substituiert sein kann.The object of the invention is achieved by a substantially light-insensitive thermographic black and white single-sheet recording material which contains a support and a heat-sensitive element with a substantially light-insensitive organic silver salt, a 1,2-dihydroxyphenyl compound in a thermally effective relationship thereto and a binder, the 1,2 -Dihydroxyphenylverbindung corresponds to the following formula (I)

in the mean
R -P (= O) R ¹ R ² , -SO _x R ³ , -CN, -NO ₂ or -CR ⁴ = NR ⁵ if n is 0,
R -P (= O) R ¹ R ² , -SO _x R ³ , -CN, -NO2, -CR ⁴ = NR ⁵ or -COR ⁶ , if n is an integer,
R ¹ and R ² independently of one another are an alkyl group, a substituted alkyl group, an aryl group, a substituted aryl group, an alkoxy group, a substituted alkoxy group, an aryloxy group, a substituted aryloxy group, a hydroxyl group, an amino group or a substituted amino group,
R ^{3 is} an alkyl group, a substituted alkyl group, an aryl group, a substituted aryl group, an amino group or a substituted amino group,
R ^{4 is} an alkyl group, a substituted alkyl group, an aryl group, a substituted aryl group or a hydrogen atom,
R ^{5 is} an alkyl group, a substituted alkyl group, an aryl group, a substituted aryl group, a hydroxyl group, an alkoxy group, an aryloxy group, an acyl group, an amino group or a substituted amino group,
R ^{6 is} an alkyl group, a substituted alkyl group, an aryl group, a substituted aryl group, an alkoxy group, a substituted alkoxy group, an aryloxy group, a substituted aryloxy group, a hydroxyl group, an amino group or a substituted amino group or a hydrogen atom, × 1, 2 or 3,
and wherein the benzene ring of the 1,2-dihydroxyphenyl compound of the formula (I) can have further substitutions. Substituted amino groups can also form a heterocyclic ring system, which can itself be substituted.

The object of the invention is achieved also by one identified by the steps below Process for producing a substantially light-insensitive described above thermographic black and white Single sheet recording material Make one or more aqueous casting compositions, which together form the essentially light-insensitive organic silver salt, contain the reducing agent and the binder, and application the one or more aqueous casting compositions, as an adhesive layer, on the same side of the support, after drying the heat sensitive element is obtained.

Preferred embodiments of the present Invention are detailed in the Description of the present invention.

Detailed description of the present Invention.

Aqueous

For the purposes of the invention, the term "aqueous" includes mixtures of water and water-miscible organic solvents such as alcohols, e.g. B. methanol, ethanol, 2-propanol, butanol, isoamyl alcohol etc., Glycols, e.g. B. ethylene glycol, glycerin, N-methylpyrrolidone, methoxypropanol and ketones, e.g. B. 2-propanone and 2-butanone etc.

Essential

"Substantially insensitive to light" is not to be understood deliberately sensitive to light. “Substantially solvent-free aqueous medium” means that, if appropriate solvent used in an amount below 10% by volume, based on the aqueous medium, is included.

1,2-dihydroxyphenyl compounds

The organic reducing agent used in the present invention is a 1,2-dihydroxyphenyl compound of the formula (I). If formula (I) is an acid, formula (I) also includes salts of the acid. Preferred substituents of the benzene ring of the 1,2-dihydroxyphenyl compound of the formula (I) are halogen atoms, aryl groups, alkyl groups, the atoms required to form a fused, carbocyclic or heterocyclic, optionally self-substituted ring and the atoms required to react with the optionally self-substituted R - (CH = CH) _x substituents to form a fused ring system.

Preferred R (CH = CH) x substituents for the 1,2-dihydroxyphenyl compounds of the formula (I) are tetraalkylphosphonium, Arylalkylphosphonium, tetraarylphosphonium, dialkylphosphonate, Arylalkyl phosphonate, alkyl sulfinate, aralkyl sulfinate, aryl sulfinate, Alkarylsulfinate, alkylsulfonamide, aralkylsulfonamide, arylsulonamide, Alkarylsulfonamide, alkylsulfonate, aralkylsulfonate, arylsulfonate, Alkarylsulfonate, alkylsulfinate vinyl, aralkylsulfinate vinyl, arylsulfinate vinyl, Alkarylsulfinate vinyl, alkylsulfonamide vinyl, aralkylsulfonamide vinyl, arylsulonamide vinyl, Alkarylsulfonamide vinyl, alkylsulfonate vinyl, aralkylsulfonate vinyl, Arylsulfonate vinyl, alkarylsulfonate vinyl, cyan, cyanvinyl, nitro and nitrovinyl groups, which can also be substituted.

Preferred reducing agents for use in the present invention are selected from the group consisting of Aryl (3,4-dihydroxyphenyl) sulfinates, Alkyl (3,4-dihydroxyphenyl) sulfinates, 3,4-dihydroxyphenylalkyl sulfones, 3,4-dihydroxyphenylaryl sulfones, aryl (3,4-dihydroxyphenyl) sulfonates, Alkyl (3,4-dihydroxyphenyl) sulfonates and 3,4-dihydroxybenzonitrile compounds.

Particularly preferred reducing agents for use in the present invention correspond to the formulas

Suitable 1,2-dihydroxyphenyl compounds for use in the present invention

Heat sensitive element

The present invention provides a thermographic recording material which is a heat sensitive Element contains which is an essentially light-insensitive organic silver salt, an organic reducing agent for the silver salt in thermal effective relationship and contains a binder. The element can contain a layered dressing in which the ingredients in different layers can be dispersed, provided that this is essential light-insensitive organic silver salt and the 1,2-dihydroxyphenyl compound have a thermally effective relationship to one another, d. H. during heat generation must the 1,2-dihydroxyphenyl so contained that it to diffuse over to the substantially light-insensitive organic silver salt particles capable of reducing the substantially light-insensitive organic silver salt.

Organic silver salts

Preferred much less sensitive to light organic silver salts for use in the thermographic invention Recording materials are silver salts of known as fatty acids aliphatic carboxylic acids, where the aliphatic carbon chain is preferably at least Contains 12 carbon atoms, z. B. silver laurate, silver palmitate, silver stearate, silver hydroxystearate, Silver oleate and silver behenate, these silver salts also be called "silver soaps". Silver salts of aliphatic modified with a thioether group Carboxylic acids, such as B. in GB-P 1 111 492, and other organic silver salts, as described in GB-P 1 439 478, e.g. B. silver benzoate also come for the production of a thermally developable silver picture in question. Combinations of different organic silver salts are suitable also for use in the thermographic invention Recording materials. A preferred method of manufacture a suspension, the particles of a substantially light-insensitive contains organic silver salt, is disclosed in EP-A 754 969.

Auxiliary reducing agents

The reducing agents used according to the invention, the as the primary or main reducing agents can be considered in conjunction with so-called Auxiliary reducing agents are used. Such auxiliary reducing agents are z. B. hydroquinone or pyrocatechin, substituted by strong electron-withdrawing groups such as sulfonic acid groups, sterically hindered Phenols as described in U.S. Patent 4,001,026, bisphenols, e.g. B. of in U.S. Patent 3,547,648, sulfonamide phenols as described in Research Disclosure, article 17842, published in February 1979, in U.S. Patent 4,360,581, U.S. Patent 4,782,004 and EP-A 423,891, hydrazides, such as described in EP-A 762 196, sulfonyl hydrazide reducing agent, as described in US Pat. No. 5,464,738, trityl hydrazides and formylphenyl hydrazides, as described in U.S. Patent No. 5,496,695, trityl hydrazides and formylphenyl hydrazides with various auxiliary reducing agents, as described in US-P 5 545 505, US-P 5 545 507 and US-P 5 558 983, acrylonitrile compounds, as described in US-P 5,545,515 and US-P 5,635,339, 2-substituted Malondialdehyde compounds as described in US Pat. No. 5,654,130 and organic reducing metal salts, e.g. B. tin distearate, as in U.S. Patent Nos. 3,460,946 and 3,547,648. The auxiliary reducing agents can in the imaging layer or in a more thermally effective Relationship to the imaging layer of polymeric binder layer be included.

In a preferred embodiment of the present invention the thermographic recording material is a carrier and a heat sensitive Element that continues to be a strong electron-attracting Contains group substituted pyrocatechol compound.

binder

The heat sensitive element of the thermographic according to the invention Recording materials can be made from an organic solvent, that the binder in dissolved Contains form, or from an aqueous medium, the water-soluble or contains water-dispersible binders, in an arch or web form present carrier be applied.

As a binder for an organic solvent coated materials come all kinds of natural, modified natural or synthetic resins or mixtures of such resins, in which the organic heavy metal salt is homogeneously dispersed can, e.g. B. cellulose derivatives, cellulose esters, Carboxymethyl cellulose, starch ether, Gallactomannan, polyurethanes, polycarbonates, polyesters, polymers derived from α, β-ethylenic unsaturated Compounds such as post-chlorinated polyvinyl chloride, partially hydrolyzed Polyvinyl acetate, polyvinyl alcohol, polyvinyl acetals, preferably Polyvinyl butyral, and homopolymers and copolymers made from monomers from the group consisting of vinyl chloride, vinylidene chloride, vinyl esters, Acrylonitrile, acrylamides, methacrylamides, methacrylates, acrylates, Methacrylic acid, acrylic acid, vinyl esters, Styrenes, dienes and alkenes are formed, or mixtures thereof.

Suitable water-soluble film-forming binders are polyvinyl alcohol, polyacrylamide, polymethacrylamide, polyacrylic acid, polymethacrylic acid, polyethylene glycol, Polyvinyl pyrrolidone, proteinaceous binders such as gelatin, modified Gelatins such as phthaloyl gelatin, polysaccharides such as starch, gum arabic and Dextran, and water soluble Cellulose derivatives.

Suitable water-dispersible binders are all insoluble in water Polymers. It should be noted that there are tiny polymer particles no clear transition between a polymer dispersion and a polymer solution, causing the smallest particles of the polymer in dissolved form and the slightly larger particles will be in dispersed form.

Preferred water-dispersible binders for use in the present invention are water dispersible film-forming polymers with covalently bound ionic groups from the group consisting of sulfonate, sulfinate, carboxylate, phosphate, quaternary Ammonium groups, tertiary Sulfonium groups and quaternary Phosphonium. Other preferred water-dispersible binders for use in the present invention are water dispersible film-forming polymers with covalently bound portions with a or more acid groups.

Water-dispersible binders with networkable groups, e.g. B. epoxy groups, acetoacetoxy groups and crosslinkable double bonds are also preferred. Further preferred water-dispersible binders for use in the present invention are polymeric latices. Compositions of usable according to the invention polymeric latices are listed in the table below

The weight ratio of the binder to the organic Silver salt is preferably between 0.2 and 6, the strength of the Recording layer preferably between 1 and 50 microns.

Thermal solvents

The above binders or mixtures of binders can in combination with grow or "thermal Solvents ", also called" thermal solvents ", the the reaction rate of the redox reaction at elevated temperature increase, be used. The term "thermal solvent" means in the present invention on a non-hydrolyzable organic material that can be used at temperatures below 50 ° C in solid state in the recording layer, but at Heating to a plasticizer for the recording layer is and / or as a liquid solvent for at least operated one of the redox reagents.

tint

To get a neutral black Image tones in the upper density zones and from neutral gray in the lower ones Density zones can the thermographic according to the invention Recording materials contain one or more toning agents. The tint are supposed to during heat processing in a thermally effective relationship to the essentially light-insensitive organic silver salt and reducing agents. As a tint any come from thermography or photothermography known tinting agents in question. Suitable tinting agents are those corresponding to the general formulas in U.S. Patent 4,082,901 Phthalimides and phthalazinones and those described in US-P 3,074,809, US-P 3 446,648 and U.S. Patent 3,844,797. Particularly usable tint are the heterocyclic toner compounds of benzoxazinedione or naphthoxazinedione type as described in GB-P 1 439 478, US-P 3,951,660 and U.S. Patent 5,599,647.

Polycarboxylic acids and polycarboxylic

According to a preferred according to the invention embodiment contains the heat sensitive Element of the substantially light-insensitive thermographic black and white single sheet recording material continues at least one polycarboxylic acid and / or a polycarboxylic anhydride in a molar ratio of at least 15, based on the substantially light-insensitive organic silver salt and in a thermally effective relationship to it.

The polycarboxylic acid can be an aliphatic (saturated or unsaturated aliphatic and also cycloaliphatic) polycarboxylic acid, such as described in U.S. Patent No. 5,527,758, or an aromatic polycarboxylic acid. The polycarboxylic can be substituted and in anhydride form or partially esterified Form, provided that contain at least two free carboxylic acids or in the heat recording stage available.

stabilizers and antifoggants

To improve shelf life and for limitation the formation of fog in the thermographic according to the invention Recording materials stabilizers and antifoggants be embedded.

Surfactants and dispersant

Surfactants and dispersing agents make it easier to disperse ingredients that are not soluble in the dispersion medium used. The thermographic recording materials according to the invention can contain one or more anionic, non-ionic or cationic surfactants and / or one or more dispersing agents. Examples of suitable surfactants are Surfactant No.1 = HOSTAPAL ^™ B, a sodium trisalkylphenyl polyethylene glycol (EO 7-8) sulfate from Hoechst, Surfactant no.2 = MERSOLAT ^TM H80, a sodium hexadecyl sulfonate from Bayer, Surfactant no.3 = ULTRAVON ^TM W, a sodium aryl sulfonate from Ciba-Geigy, Surfactant No.4 = TERGITOL ^™ 4, a sodium 1- (2'-ethylbutyl) -4-ethylhexyl sulfate, Surfactant no. 5 = MARLON ^TM A-396, a sodium dodecylphenyl sulfonate from Hüls, Surfactant no.6 = HOSTAPAL ^TM W, a nonylphenyl polyethylene glycol from Hoechst.

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

Other ingredients

In addition to the ingredients mentioned above, the thermographic recording material may contain other ingredients such as free fatty acids, antistatic agents, e.g. B. non-ionic antistatic agents with a fluorocarbon group such as. B. in F ₃ C (CF ₂ ) ₆ CONH (CH ₂ CH ₂ O) -H, silicone oil, ultraviolet light absorbing compounds, white light reflecting and / or ultraviolet reflecting pigments and / or optical brighteners.

carrier

The support for the thermographic according to the invention Recording material can be translucent, translucent, or opaque and is preferably a thin one flexible support from z. B. paper or polyethylene-coated paper or a Transparent resin sheet, e.g. B. from a cellulose ester, e.g. B. cellulose triacetate, polypropylene, polycarbonate or polyester, z. B. polyethylene terephthalate. The carrier can be in the form of an arch, of a band or a web and is subbed if necessary to the Adhesion to the heat-sensitive recording layer applied thereon to improve. The carrier can be made from an opacified resin composition.

protective layer

In a preferred embodiment of the present invention, the heat sensitive element is covered with a protective layer. This protective layer usually protects the heat-sensitive element from humidity and surface damage due to scratching, etc. and prevents direct contact of printheads or heating sources with the recording layers. Protective layers for heat-sensitive elements which come into contact with a heat source and have to be conveyed past them under pressure are required to be resistant to local deformation and to have good sliding properties if they are conveyed past the heat source during heating ,

An outer protective layer can be a dissolved sliding material and / or particulate material, e.g. B. Talc particles protruding from the outer layer if necessary. Examples of suitable sliding materials are surfactants, liquid lubricants, solid lubricants or mixtures thereof, with or without a polymeric binder. Examples of liquid lubricants include silicone oils, synthetic oils, saturated hydrocarbons and glycols. Examples of solid lubricants include several higher alcohols such as stearyl alcohol, fatty acids and fatty acid esters. Suitable compositions for sliding layers are described in, for example, EP-A 138 483, EP-A 227 090, US-P 4 567 113, US-P 4 572 860, US-P 4 717 711, EP-A 311 841, US 5,587,350 , US 5,536,696, US 5,547,914, WO 95/12495, EP-A 775 592 and EP-A 775 595.

coating techniques

The order of any layer of the thermographic according to the invention Recording materials can be made using any casting technique take place such. B. 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, USA. The application can be from aqueous media or solvent media with covering of dried, partially dried or undried Layers take place.

Thermographic printing

Thermographic imaging takes place through pictorial exposure with warmth, either in an analogous manner by direct exposure through an image or by reflection from an image or by digital means pixel-wise exposure with an infrared heating source, for example a Nd-YAG laser or another infrared laser, or by direct thermal imaging with a thermal head.

In thermal printing with thermal heads, image signals are converted into electrical pulses, 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 impulses thus converted into thermal signals are expressed as heat, which is transferred to the surface of the thermal paper in which the chemical reaction leading to color development 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 print heads is between 300 and 400 ° C and the heating time per picture element (pixel) is 1.0 ms or less, the pressure contact of the thermal print head with the recording material, for. B. is between 200 and 500 g / cm ² to ensure good heat transfer.

To make direct contact with the thermal print heads a recording layer not covered with an outer protective layer to prevent the pictorial heating takes place the recording layer with the thermal print heads by means of a (n) Contactable, but removable, resin sheet or resin sheet, from the (the) during no recording material can be transferred to the heating.

The image signals for modulating the Laser beam or current in the micro resistors of a thermal printhead are either received directly or from a buffer, optionally connected to a digital image work station in which the image information can be processed to meet special needs meet.

The control of the heating elements can be power modulated or pulse length modulated for constant power become. EP-A 654 355 describes a method for production of an image through pictorial heating by means of a thermal head with excitable heating elements, the Activation of the heating elements after a duty cycle operation he follows. When used in thermographic, thermal print heads The thermographic recording materials are suitable for recording not for the reproduction of images with a fairly high number of Grayscale, as is required for halftone reproduction. In EP-A 622 217 discloses a method for generating an image under Use one for direct thermal imaging suitable element disclosed, whereby an improved halftone reproduction is achieved.

An electrical resistance band built into the material is also suitable for imagewise heating of the thermographic recording material. The imagewise or pattern-based heating of the thermographic recording material can also be carried out by a pixel-wise modulated ultrasound treatment. B. an ultrasonic pixel printer is used, such as. B. described in U.S. Patent 4,908,631.

industrial application

Thermographic recording materials according to the invention can for the Generation of both transparent images, for example in the area medical diagnostics, where black and white banners are widely used at with a viewing device working testing techniques are used as well as supervisory copies are used to Example in the hard copy area. For such applications, the carrier becomes translucent or opaque, d. H. a white light having a reflective aspect. When using a translucent support the carrier colorless or colored be, e.g. B. colored blue for medical Diagnostic applications.

The following examples according to the invention and comparative examples illustrate the present invention. The percentages and ratios in these examples are by weight unless otherwise noted. In addition to the above ingredients, the following ingredients are also used in the heat sensitive element AgBeh = Silver behenate, K7598 = KOEPF ^TM Type 7598, a calcium-free gelatin, B79 = BUTVAR ^TM B79, a polyvinyl butyral from MONSANTO, CR01 Ethyl 3,4-dihydroxybenzoate, a reducing agent according to the teaching of US Pat. No. 5,582,953, S01 = Adipic acid, S02 = Tetrachlorophthalic anhydride, S03 = Benzotriazole, T01 = Benzo [e] - [1,3] -oxazin-2,4-dione, T02 = 7- (ethyl carbonate) benzo [e] - [1,3] oxazin-2,4-dione, oil = Baysilon ^TM MA, a silicone oil from BAYER AG.

COMPARATIVE EXAMPLE 1 and EXAMPLES OF THE INVENTION 1 & 2

Preparation of an aqueous dispersion of silver behenate

9,000 g of silver behenate are added with stirring to 9,000 g of a 10% aqueous solution of surfactant No. 5 diluted with 20,146 g of demineralized water, after which the mixture is stirred for 30 minutes with a KOTTHOFF ^™ stirrer. The dispersion obtained is then passed four times at a pressure of 400 bar through a MICROFLUIDICS ^™ high-pressure homogenizer in order to obtain a finely divided aqueous silver behenate dispersion.

production a sound modifier dispersion

To prepare the clay modifier dispersion, 8.8 g of K7598 are first dissolved in 71.4 g of demineralized water. For this purpose, the gelatin is first added, the gelatin is then allowed to swell for 30 minutes and the solution is finally heated to 50 ° C. 20 g of T01 are stirred into this gelatin solution at 50 ° C. in a ULTRA-TURRAX ^™ stirrer, after which stirring is continued for 5 minutes. Finally, the resulting dispersion is pumped in a DYNOMILL ^™ (a horizontal bead mill from BACHOFEN) for 2 hours to obtain the final clay modifier dispersion containing 20% T01 and 8.8% gelatin.

manufacturing of the silver behenate emulsion layers

For the preparation of the casting dispersions of the comparative thermographic recording materials EXAMPLE 1 and EXAMPLES 1 & 2 OF THE INVENTION are first dissolved 1.927 g K7598 at 38 ° C in demineralized water (amount of water: see Table 1), after which first 19.0 g of the silver behenate dispersion, then 5.9 g of a 30% dispersion polymeric latex # 1 and 5.68 g of the clay modifier dispersion in flake form, after which a 5 minute stir follows, then the (s) dissolved in 1.71 g ethanol Reducing agent (amount and type: see Table 1) and finally 1.310 g of a 3.7% by weight solution of formaldehyde are stirred into the warm K7598 solution to make the various pouring dispersions to obtain.

Table 1

The emulsions obtained are then in a wet film thickness of 60 μm at a doctor blade setting of 100 μm to a 175 μm doctored strong subbed polyethylene terephthalate and 10 minutes at 50 ° C dried. Thereby receives one the heat sensitive Elements of the COMPARATIVE thermographic recording materials EXAMPLE 1 and EXAMPLES 1 & 2 OF THE INVENTION with the in Compositions listed in Table 2.

Table 2

Thermographic printing

While the print cycle with the COMPARATIVE recording materials EXAMPLE 1 and EXAMPLES 1 & 2 becomes the printhead through a thin intermediate material in contact with a sliding layer separable, 5 μm strong polyethylene terephthalate tape from the imaging layer kept separate, the tape in turn with an adhesive layer, a heat-resistant Layer and the sliding layer (anti-friction layer) coated is and a total strength of 6 μm.

The printer is with a thin film thermal print head with a resolution of 300 dpi and is equipped with a line time of 19 ms (the line time is the time required to print a single line). While the printhead is constantly energized during this line time. The middle Print power, the total amount of electrical required to print a line Energy divided by the line time and the surface of the heat-generating resistors, corresponds to 1.6 mJ / point and is sufficient to cover all of the thermographic recording materials of COMPARATIVE EXAMPLE 1 and OF THE INVENTION EXAMPLES 1 & 2 a maximum to obtain optical density.

image analysis

To evaluate the color neutrality of the optical density (D) of the images obtained, the optical densities are measured behind a blue, green and red filter using a MacBeth ^™ TR924 densitometer. The lowest, the second highest and the highest optical density are referred to as optical densities D ₁ , D ₂ and D ₃ , respectively. Substituting these values in the following equation gives a numerical color value (NCV).

The higher the NCV value, the better the color neutrality of the image obtained. The maximum color neutrality corresponds an NCV value of 1. The NCV values are at optical densities (D) of 1, 2 and 3 for the fresh prints the materials of COMPARATIVE EXAMPLE 1 and the INVENTION EXAMPLES 1 & 2, the same deductions after a 3 day Storage at 35 ° C and a relative humidity of 80% and the same deductions a 3 day Exposure at 30 ° C and a relative humidity of 85% in the light box described above determined. The NCV values obtained are in the table below 3 listed.

Table 3

Allow the NCV values in Table 3 a comparison of materials with different reducing agents based on their color neutrality and dependency their color neutrality on the optical image density. The NCV values for fresh prints and thermographic prints Recording materials of the invention EXAMPLES 1 & 2 after one 3-day Exposure at 30 ° C and a relative humidity of 85% in the light box are clear better than the NCV values for the COMPARATIVE EXAMPLE thermographic recording material 1, which contains a reducing agent according to the teaching of US Pat. No. 5,582,953, while at deductions, that of a 3 day Store in the dark at 35 ° C and have been subjected to a relative humidity of 80%, comparable NCV values can be obtained. It speaks for itself that deductions that with the thermographic recording materials with the new ones reducing agents according to the invention are preserved, with a color neutrality that the from superior materials known to the current state of the art is.

The maximum density and minimum density of the prints listed in Table 4 are corresponding in a MACBETH ^TM TR924 densitometer behind an optical filter or a blue filter in the gray scale steps measured at data levels 64 and 0, respectively.

archivability

The archivability of prints obtained using the thermographic recording materials of COMPARATIVE EXAMPLE 1 and the EXAMPLES 1 & 2 according to the invention is evaluated on the basis of the changes in the NCV values and the minimum density (ΔD _min ), which were obtained after heating the prints at 35 for 3 days ° C and a relative humidity (RF) of 80% can be measured in the dark. The test results are listed in Table 4.

Light Box Test

The evaluation of the stability of the image background of the prints made with the thermographic recording materials of COMPARATIVE EXAMPLE 1 and the INVENTION EXAMPLES 1 & 2 is carried out on the basis of the change in the NCV values and the minimum density (background) and maximum density using a MACBETH ^™ TR924 densitometer is measured behind a blue filter, whereby the exposure is a 3-day exposure on the white PVC window of a specially built light box in a VOTSCH climate test cabinet set to a temperature of 30 ° C and a relative humidity (RF) of 85%. The test materials are only placed on a central, 550 mm long and 500 mm wide area of the window to ensure even exposure.

The stainless steel light box is 650 mm long, 600 mm wide and 120 mm high and has a 610 mm long and 560 mm wide opening and a 10 mm wide and 5 mm deep rim around the opening, creating a platform for a 5 mm thick, 630 mm long and 580 mm wide plate made of white PVC, with the white PVC plate lying in the same plane as the light box and preventing light loss from the light box, apart from the light loss through the white PVC plate. On this light box, 9 PLANILUX ^TM TLD 36W / 54 fluorescent lamps with a diameter of 27 mm are arranged in the length and at the same distance from the two sides, the lamps being arranged at the same distance from one another and to the sides over the entire width of the light box and the top of the fluorescent tubes is 30 mm below the bottom of the white PVC plate and 35 mm below the materials to be tested. The results are listed in Table 4.

Table 4

The results of the thermographic evaluation of the prints of the thermographic recording materials of INVENTION EXAMPLES 1 & 2, the new reducing agent according to the invention contain, clearly show improved archivability and light resistance measured in the light box (= reduced ΔD _min values) compared to the prints made with the thermographic recording material of COMPARATIVE EXAMPLE 1, which contains a reducing agent according to the teaching of US Pat. No. 5,582,953 , are preserved.

COMPARATIVE EXAMPLE 2 & EXAMPLES ACCORDING TO THE INVENTION 3 to 6

Preparation of a silver behenate dispersion

2.5 g of a 30% solution of B79 in 2-butanone, 10 g silver behenate and 37.5 g 2-butanone become 72 h in a ball mill mixed, after which 30.83 g of a 30% solution of B79 and 7.67 g of 2-butanone were added to make a 2-butanone dispersion containing 11.3% silver behenate and contains 11.3% by weight of B79.

manufacturing of the heat sensitive Elements

On the subbed polyethylene terephthalate support with a strength of 175 μm becomes a 2-butanone as a solvent / dispersion medium containing casting composition doctored, after after 1 hour Drying at 50 ° C a heat sensitive Is obtained element that the in Tables 5 and 6 listed compositions for COMPARATIVE EXAMPLE 2 or the INVENTION EXAMPLES Contains 3 to 6

Table 5

Table 6

Thermographic evaluation

The thermographic evaluation of the COMPARATIVE EXAMPLE thermographic recording materials 2 and EXAMPLES OF THE INVENTION 3 to 6 is carried out analogously to the thermographic evaluation of the COMPARATIVE EXAMPLE 1 and EXAMPLES 1 & 2, with the difference however, that at the archivability tests a 3-day storage at 57 ° C and a relative Humidity of 34% instead of a 3-day storage at 35 ° C and one relative humidity of 80% is made. The NCV values for the thermographic COMPARATIVE EXAMPLE 2 and EXAMPLES OF THE INVENTION 3 to 6 for fresh prints and deductions, that of a 3 day Storage at 30 ° C and subjected to a relative humidity of 85% in the light box have been listed in Table 7 below.

Table 7

Allow the NCV values in Table 7 a comparison of materials with different reducing agents based on their color neutrality and dependency their color neutrality on the optical image density. The higher the value, the better the color neutrality. The NCV values for fresh prints the thermographic recording materials of the EXAMPLES OF THE INVENTION 3 to 6 are comparable to the NCV values of the thermographic COMPARATIVE EXAMPLE Recording Material 2. Will the obtained with these thermographic recording materials deductions but a 3 day Exposure at 30 ° C and subjected to a relative humidity of 85% COMPARATIVE EXAMPLE thermographic recording material 2, which contains a reducing agent according to the teaching of US Pat. No. 5,582,953, one major deterioration of color neutrality than the thermographic recording material of the invention 4 and a much bigger deterioration than the thermographic recording materials of the EXAMPLES OF THE INVENTION 3, 5 and 6, where a change is difficult to see of color neutrality can be observed. The most critical NCV value in relation to the visual recognition of an observer is that at a density of 1.0 measured NCV value. The change of the NCV value ΔNCV at a density (D) of 1 for deductions those with the thermographic recording materials of the EXAMPLES OF THE INVENTION 3 to 6 is significantly lower (-0.08 to +0.02) as the change in the COMPARATIVE EXAMPLE thermographic recording material 2 (-0.10).

The D _max , ΔD _max , D _min and ΔDmin values obtained in the archivability tests and light box tests for COMPARATIVE EXAMPLE 2 and the EXAMPLES 3 to 6 according to the invention are listed in Table 8 below.

Table 8

The results of the thermographic evaluation of the prints of the thermographic recording materials of EXAMPLES 3 to 6, which contain new reducing agents according to the invention, clearly show improved archivability and light resistance measured in the light box (= reduced ΔD _max values and ΔD _min values) compared to the Prints obtained with the comparative EXAMPLE 2 thermographic recording material containing a reducing agent as taught by U.S. Patent No. 5,582,953.

However, these values are no explanation for the noticeable Improve lightfastness all over sensitometric area with the deductions of thermographic recording materials OF THE INVENTION EXAMPLES 3 to 6 is obtained compared to the improvement in those with the COMPARATIVE EXAMPLE thermographic recording material 2 prints made. Therefore, the density values and density changes can be found in Table 9 with different pulse energy values over the whole sensitometric Area for deductions that with the thermographic recording materials of the COMPARATIVE EXAMPLE 2 and OF THE INVENTION EXAMPLES 3 to 6 are preserved.

Table 9

Table 9 clearly shows that the Lightfastness above the whole sensitometric range of prints with the thermographic Recording materials of EXAMPLES 3 to 6 according to the invention were prepared are, to a noticeable degree has become better than the lightfastness of prints that with the comparative thermographic recording material EXAMPLE 2, which is a reducing agent according to the teaching of US-P 5 582 953 contains are made.

After reading the preferred embodiments of the present described in detail Various modifications of the description according to the invention will be open to those skilled in the art without departing from the scope of protection according to the invention as defined in the claims below.

Claims (9)

A substantially light-insensitive black and white single sheet thermographic recording material which contains a support and a heat-sensitive element with a substantially light-insensitive organic silver salt, a 1,2-dihydroxyphenyl compound in a thermally effective relationship thereto and a binder, characterized in that the 1,2-dihydroxyphenyl compound corresponds to the following formula (I)

in which R denotes -P (= O) R ¹ R ² , -SO _x R ³ , -CN, -NO ₂ or -CR ⁴ = NR ⁵ , if n is 0, R -P (= O) R ¹ R ² , -SO _x R ³ , -CN, -NO ₂ , -CR ⁴ = NR ⁵ or -COR ⁶ , if n is an integer, R ¹ and R ² independently of one another are an alkyl group, a substituted alkyl group, an aryl group, a substituted aryl group, an alkoxy group, a substituted alkoxy group, an aryloxy group, a substituted aryloxy group, a hydroxyl group, an amino group or a substituted amino group, R ^{3 is} an alkyl group, a substituted alkyl group, an aryl group, a substituted aryl group, an amino group or a substituted amino group , R ^{4 is} an alkyl group, a substituted alkyl group, an aryl group, a substituted aryl group or a hydrogen atom, R ^{5 is} an alkyl group, a substituted alkyl group, an aryl group, a substituted aryl group, a hydroxyl group, an alkoxy group, an aryloxy group, an acyl group, an amino group or a substit ized amino group, R ^{6 is} an alkyl group, a substituted alkyl group, an aryl group, a substituted aryl group, an alkoxy group, a substituted alkoxy group, an aryloxy group, a substituted aryloxy group, a hydroxyl group, an amino group or a substituted amino group or a hydrogen atom, x 1, 2 or 3, and wherein the benzene ring of the 1,2-dihydroxyphenyl compound of the formula (I) may have further substitutions. A substantially light-insensitive thermographic black and white Single sheet recording material according to claim 1, characterized in that this Reducing agents from the group of compounds consisting of aryl (3,4-dihydroxyphenyl) sulfinates, Alkyl (3,4-dihydroxyphenyl) sulfinates, 3,4-dihydroxyphenylalkyl sulfones, 3,4-dihydroxyphenylaryl sulfones, aryl (3,4-dihydroxyphenyl) sulfonates, Alkyl (3,4-dihydroxyphenyl) sulfonates and 3,4-dihydroxybenzonitrile compounds chosen becomes. A substantially light-insensitive thermographic black and white single sheet recording material according to claim 1 or 2, characterized in that the reducing agent corresponds to the following formula

A substantially light-insensitive thermographic black and white single sheet recording material according to claim 1 or 2, characterized in that the reducing agent corresponds to the following formula

A substantially light-insensitive thermographic black and white single sheet recording material according to claim 1 or 2, characterized in that the reducing agent corresponds to the following formula

A substantially light-insensitive thermographic black and white Single sheet recording material according to one of the preceding claims, characterized characterized that the thermosensitive Element furthermore at least one polycarboxylic acid and / or a polycarboxylic anhydride in a molar ratio of at least 15, based on the substantially light-insensitive organic silver salt and in a thermally effective relationship to it contains. A substantially light-insensitive thermographic black and white Single sheet recording material according to one of the preceding claims, characterized characterized that the thermosensitive Element covered with a protective layer is. A substantially light-insensitive thermographic black and white Single sheet recording material according to one of the preceding claims, characterized characterized that the essential photosensitive organic silver salt a silver salt of an organic carboxylic acid is. One identified by the steps below Process for producing a substantially light-insensitive thermographic black and white Single sheet recording material according to one of the preceding claims: Manufacture one or more aqueous casting compositions, which together form the essentially light-insensitive organic silver salt, contain the reducing agent and the binder, and application the one or more aqueous casting compositions, as an adhesive layer, on the same side of the support, after drying the heat sensitive Element is obtained.