Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03C—PHOTOSENSITIVE MATERIALS FOR PHOTOGRAPHIC PURPOSES; PHOTOGRAPHIC PROCESSES, e.g. CINE, X-RAY, COLOUR, STEREO-PHOTOGRAPHIC PROCESSES; AUXILIARY PROCESSES IN PHOTOGRAPHY
  • G03C1/00—Photosensitive materials
  • G03C1/494—Silver salt compositions other than silver halide emulsions; Photothermographic systems ; Thermographic systems using noble metal compounds
  • G03C1/498—Photothermographic systems, e.g. dry silver
  • G03C1/49881—Photothermographic systems, e.g. dry silver characterised by the process or the apparatus
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41J—TYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
  • B41J2/00—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
  • B41J2/315—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective application of heat to a heat sensitive printing or impression-transfer material
  • B41J2/32—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective application of heat to a heat sensitive printing or impression-transfer material using thermal heads
  • B41J2/35—Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed characterised by selective application of heat to a heat sensitive printing or impression-transfer material using thermal heads providing current or voltage to the thermal head
  • B41J2/355—Control circuits for heating-element selection
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03C—PHOTOSENSITIVE MATERIALS FOR PHOTOGRAPHIC PURPOSES; PHOTOGRAPHIC PROCESSES, e.g. CINE, X-RAY, COLOUR, STEREO-PHOTOGRAPHIC PROCESSES; AUXILIARY PROCESSES IN PHOTOGRAPHY
  • G03C1/00—Photosensitive materials
  • G03C1/494—Silver salt compositions other than silver halide emulsions; Photothermographic systems ; Thermographic systems using noble metal compounds
  • G03C1/498—Photothermographic systems, e.g. dry silver
  • G03C1/4989—Photothermographic systems, e.g. dry silver characterised by a thermal imaging step, with or without exposure to light, e.g. with a thermal head, using a laser

Definitions

• the present invention concerns a non-label-printing process for the printing of substantially light-insensitive thermographic monosheet materials.
• Thermal imaging or thermography is a recording process wherein images are generated by the use of thermal energy.
• a visible image pattern is produced by image-wise heating of a recording material e.g. image signals can be converted into electric pulses and then via a driver circuit selectively transferred to a thermal printhead, which consists of microscopic heat resistor elements, thereby converting the electrical energy into heat via the Joule effect. This heat brings about image formation in the thermographic material.
• EP-A 754 564 discloses a heat sensitive recording material comprising a support and, provided thereon, a heat sensitive recording layer containing a colorless or light colored dye precursor and an electron accepting color developer which reacts with the dye precursor upon heating to cause color formation of the dye precursor, where the heat sensitive recording material contains at least one water-insoluble resin selected from the group consisting of an aromatic resin, a resin having a low or no acid value and a resin having a carbonyl group and an alicyclic unit.
• EP-A 754 564 disclose applied energy per unit area in the ranges of 20-140 mJ/mm 2 , 80-140 mJ/mm 2 , 30-50 mJ/mm 2 , 80-100 mJ/mm 2 , 30-35 mJ/mm 2 and 20-200 mJ/mm 2 ; as well as specific energies of 30 mJ/mm 2 , 40 mJ/mm 2 , 80 mJ/mm 2 and 90 mJ/mm 2 .
• EP 736 799A discloses a recording material comprising a support having provided thereon at least a recording layer comprising (a) a heat-responsive microcapsule having encapsulated therein an organic silver salt; (b) a developer for the organic silver salt and (c) a water-soluble binder.
• a heat recording energy per unit area of 60 mJ/mm 2 is disclosed in the invention examples.
• thermographic monosheet materials A major problem with black and white substantially light-insensitive thermographic monosheet materials is the production of high densities with a sufficiently neutral image tone.
• thermographic monosheet materials It has been surprisingly found that the image density of black and white substantially light-insensitive thermographic monosheet materials is primarily dependent upon the heating energy used to produce a image dot, regardless of how the heating power is supplied.
• thermographic monosheet material having two edges parallel to one another and > 12 cm apart (non-label) for obtaining a desired optical density and a desired colour tone
• a non-label for the purposes of the present invention is a sheet material having two edges parallel to one another and > 12 cm apart.
• a preferred shape of non-label according to the present invention has two parallel edges separated by a distance of > 12 cm measured perpendicular to the parallel edges.
• Dot energy is the heating energy used to produce a dot.
• Perceptible printed characters are composed of printed dots each dot representing a print pixel.
• a line LL may be parallel or non-parallel to the direction of transportation of the substantially light-insensitive thermographic monosheet material.
• the line LL On a landscape non-label, for example, the line LL is substantially parallel to and on a portrait non-label the line LL is substantially perpendicular to the direction of transportation.
• Each line may be composed of a plurality of printing-lines PL. Examples of a printing-line PL are "-----------" and "--- ---- -".
• a printing-line PL is printed by a column C of heating elements Hi.
• the printing-line PL is substantially parallel to the column C; but the printing-line PL may be parallel or non-parallel to a line LL.
• Each printing-line is generated by a printing cycle of activation pulses in which all heating elements of a column can be activated at least once.
• the time taken to print a printing-line PL is a line-time LT.
• Each activation pulse may either have an "off-state” (corresponding to a logical zero “0”) or an "on-state” (corresponding to a logical one "1").
• a line-duty-cycle ⁇ is the ratio of activation time to total line time for the heating elements which can be activated in producing a printing-line.
• a printing-line may comprise several printing-sublines.
• Each printing-subline SL takes a time-slice or a time-step or a column-time (being the time wherein all heating elements of at least one section of a column can be activated once).
• a column-duty-cycle ⁇ is the ratio of the sum of all activation-times during a column-time of all heating elements of a printing-subline divided by the column-time.
• a transport system can consist of a moving belt, motor-driven drums, capstans etc.
• Substantially light-insensitive means not intentionally light sensitive.
• aqueous in the term aqueous medium includes mixtures of water-miscible organic solvents such as alcohols e.g. methanol, ethanol, 2-propanol, butanol, iso-amyl alcohol etc.; glycols e.g. ethylene glycol; glycerine; N-methyl pyrrolidone; methoxypropanol; and ketones e.g. 2-propanone and 2-butanone etc. with water in which water constitutes more than 50% by weight of the aqueous medium with 65% by weight of the aqueous medium being preferred and 80% by weight of the aqueous being particularly preferred.
• alcohols e.g. methanol, ethanol, 2-propanol, butanol, iso-amyl alcohol etc.
• glycols e.g. ethylene glycol
• glycerine N-methyl pyrrolidone
• methoxypropanol methoxypropanol
• ketones e
• the encapsulated organic silver salt in a heat-responsive microcapsule disclosed in EP 736 799A whose use in the thermosensitive element of the present invention is preferably excluded has a wall which isolates the substances incorporated therein from the exterior at room temperature, but becomes permeable without being destroyed when pressure is applied or when heated.
• the microcapsule can be prepared by any of interfacial polymerization, internal polymerization and external polymerization. Interfacial polymerization comprises emulsifying a core substance comprising an organic silver salt that has been dissolved or dispersed in an organic solvent in an aqueous solution having a water-soluble polymer therein and then forming a polymer wall around the emulsified oil droplets of the core substance.
• a leuco-dye is a colourless or weakly coloured compound derived from a dye.
• Colourless or light coloured dye precursor leuco-dye systems whose use in the thermosensitive element of the present invention is preferably excluded include leuco triarylmethane, indolyl phthalide, diphenylmethane, 2-anilinofluoran, 7-anilinofluoran, xanthene and spiro compounds such as disclosed in EP-A 754 564.
• heat solvent in this invention is meant a non-hydrolyzable organic material which is in a solid state in the recording layer at temperatures below 50°C, but becomes a plasticizer for the recording layer when thermally heated and/or a liquid solvent for the organic silver salt or the reducing agent.
• thermographic monosheet materials based on organic silver salts are critically dependent upon the conditions applying during image formation as can be seen from INVENTION EXAMPLES 12 to 33.
• the image density of a dot achieved with a black and white substantially light-insensitive thermographic monosheet material based on an organic silver salt appears surprisingly mainly to depend upon the heating energy applied to the adjacent heating element during the thermographic development process, the so-called dot energy. Since dot energy is the product of heating power and heating pulse-length, this implies that the image density is surprisingly almost independent of the heating power.
• the heating power will largely determine the temperature attained by the heating element and hence that attained by the substantially light-insensitive thermographic monosheet materials based on an organic silver salt in proximity to the heating element during the thermal development process.
• this dot energy can be supplied to one or more heating elements activated to produce the dot with a particular image density i.e. the heating power (i.e. drive voltage squared divided by the heating element resistance) applied to the one or more heating elements, in one or more heat pulses and the duration of the one or more pulses.
• the heating power be as low as possible and the column-duty-cycle ⁇ be as high as possible.
• INVENTION EXAMPLES 1 to 11 show that the image density increases with increasing dot energy up to a maximum image density.
• the dot energy corresponding to this maximum image density has been found to be dependent upon the choice of reducing agent for a particular organic silver salt, the choice of toning agent and the ratio of binder to organic silver salt in the thermosensitive element. At still higher energies the image density decreases with further increase in dot energy.
• the image density potential of the material has been found mainly to depend upon the weight per unit area of substantially light-insensitive organic silver salt therein.
• the range of heat energy for the formation of an image dot is 50 to 200 mJ/mm 2 , with 66 to 150 mJ/mm 2 of heating element surface area being preferred and 66 to 120 mJ/m 2 of heating element surface area being particularly preferred.
• the non-label-printing process preferably comprises the further step of selecting the supply-voltage which determines the heating power, the column-time and/or the column-duty-cycle ⁇ for obtaining the optical density and the colour tone with the selected black and white thermographic monosheet material.
• the operating temperature of common thermal printheads is in the range of 300 to 400°C and the heating time per picture element (pixel) may be less than 1.0ms, the pressure contact of the thermal printhead with the recording material being e.g. 200-1000g/cm 2 to ensure a good transfer of heat.
• Activation of the heating elements can be power-modulated or pulse-length modulated at constant power.
• Image-wise heating of the direct thermal material can also be carried out using an electrically resistive ribbon incorporated into the material.
• Image- or pattern-wise heating of the thermographic monosheet material may also proceed by means of pixel-wise modulated ultra-sound.
• the energisable heating elements are grouped in at least two sections S.
• the printhead consists of more than one column of energisable heating elements.
• the energising of the heating elements printing-line by printing-line is carried out section by section.
• the heating power is as low as possible and the column-duty-cycle ⁇ is as high as possible in achieving a particular heat energy for the formation of the image dot.
• Possible embodiments of the invention having the same effect of lowering the power and increasing the duty cycle comprise e.g.: reducing the voltage and increasing the duty cycle while keeping the column-time constant; reducing the voltage and increasing the column-time while keeping the duty cycle constant; and reducing the voltage, increasing the duty cycle and increasing the column-time.
• a configuration memory contains characteristics of at least one thermographic monosheet material relating to a range of available column-times, to a range of available transportation speeds, to a range of available voltages.
• the column is at an angle to the transport direction of between 0 and 100°, with an angle between 90 and 99° being particularly preferred.
• selection of the supply-voltage, the column-time and/or the column-duty-cycle ⁇ for obtaining the optical density and the colour tone with the selected black and white thermographic monosheet material includes the steps of:
• the black and white substantially light-insensitive thermographic monosheet material used in the present invention comprises a thermosensitive element containing a substantially light-insensitive organic silver salt, a reducing agent therefor in thermal working relationship therewith and a binder.
• This thermosensitive element excludes encapsulated organic silver salt in a heat-responsive microcapsule and preferably excludes colourless or light coloured dye precursor leuco-dye systems.
• the thermosensitive element may comprise a layer system in which the ingredients may be dispersed in different layers, with the proviso that the substantially light-insensitive organic silver salt and the reducing agent are in thermal working relationship with one another i.e. during the thermal development process the reducing agent must be present in such a way that it is able to diffuse to the substantially light-insensitive organic silver salt particles so that reduction of the substantially light-insensitive organic silver salt can take place.
• Preferred substantially light-insensitive organic silver salts for use in the thermosensitive element of the black and white substantially light-insensitive thermographic monosheet material used in the present invention are silver salts of aliphatic carboxylic acids known as fatty acids, wherein the aliphatic carbon chain has preferably at least 12 C-atoms, which silver salts are also called "silver soaps". Combinations of different organic silver salts may also be used in the imaging materials of the present invention.
• Suitable organic reducing agents for the reduction of the substantially light-insensitive organic silver salts are organic compounds containing at least one active hydrogen atom linked to O, N or C.
• the choice of reducing agent influences the thermal sensitivity of the imaging material and the gradation of the image. Imaging materials using gallates, for example, have a high gradation.
• thermosensitive element contains a 3,4-dihydroxyphenyl compound in which a benzene ring substituted with any group in the 1-position is further substituted with hydroxy-groups in the 3- and 4-positions, the 3,4-dihydroxyphenyl compound being preferably selected from the group consisting of gallic acid derivatives, gallates, ethyl 3,4-dihydroxybenzoate, butyl 3,4-dihydroxybenzoate and 3,4-dihydroxybenzonitrile.
• thermosensitive element of the black and white substantially light-insensitive thermographic monosheet material used in the present invention may be coated onto a support in monosheet- or web-form from an organic solvent containing the binder dissolved therein or may be applied from an aqueous medium using water-soluble or water-dispersible binders.
• Suitable binders for coating from an organic solvent are all kinds of natural, modified natural or synthetic resins or mixtures of such resins, wherein the organic heavy metal salt can be dispersed homogeneously or mixtures thereof.
• Suitable water-soluble film-forming binders are; polyvinyl alcohol, polyacrylamide, polymethacrylamide, polyacrylic acid, polymethacrylic acid, polyethyleneglycol, polyvinylpyrrolidone, proteinaceous binders such as gelatin and modified gelatins, such as phthaloyl gelatin, polysaccharides, such as starch, gum arabic and dextrin, and water-soluble cellulose derivatives.
• Suitable water-dispersible binders are any water-insoluble polymer.
• Binder to organic silver salt weight ratios decreases the gradation of the image increasing. Binder to organic silver salt weight ratios of 0.2 to 6 are preferred with weight ratios between 0.5 and 3 being particularly preferred.
• binders or mixtures thereof may be used in conjunction with waxes or "heat solvents" to improve the reaction speed of the organic silver salt reduction at elevated temperatures.
• the black and white substantially light-insensitive thermographic monosheet material used in the present invention may contain one or more toning agents.
• the toning agents should be in thermal working relationship with the substantially light-insensitive organic silver salt and reducing agents during thermal processing. Any known toning agent from thermography or photothermography may be used.
• stabilizers and antifoggants may be incorporated into the black and white substantially light-insensitive thermographic monosheet material used in the present invention.
• Suitable stabilizers compounds for use in the thermographic monosheet material used in the present invention are represented by general formula I : where Q are the necessary atoms to form a 5- or 6-membered aromatic heterocyclic ring, A is selected from hydrogen, a counterion to compensate the negative charge of the thiolate group or a group forming a symmetrical or an asymmetrical disulfide.
• the black and white substantially light-insensitive thermographic monosheet material used in the present invention may contain one or more surfactants, which may be anionic, non-ionic or cationic surfactants and/or one or more dispersants.
• Suitable dispersants are natural polymeric substances, synthetic polymeric substances and finely divided powders, e.g. finely divided non-metallic inorganic powders such as silica.
• the black and white substantially light-insensitive thermographic recording material used in the present invention may contain other additives such as free fatty acids, antistatic agents, e.g. non-ionic antistatic agents including a fluorocarbon group as e.g. 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 radiation reflecting pigments, silica, and/or optical brightening agents.
• antistatic agents e.g. non-ionic antistatic agents including a fluorocarbon group as e.g. in F 3 C(CF 2 ) 6 CONH(CH 2 CH 2 O)-H
• silicone oil e.g. in F 3 C(CF 2 ) 6 CONH(CH 2 CH 2 O)-H
• ultraviolet light absorbing compounds e.g. in F 3 C(CF 2 ) 6 CONH(CH 2 CH 2 O)-H
• silicone oil e.g. in F 3 C(CF 2 ) 6 CONH(CH
• the support of the black and white substantially light-insensitive thermographic monosheet material used in the present invention may be transparent or translucent and is preferably a thin flexible carrier made transparent resin film, e.g. made of a cellulose ester, e.g. cellulose triacetate, polypropylene, polycarbonate or polyester, e.g. polyethylene terephthalate.
• the support may be in monosheet, ribbon or web form and subbed if needs be to improve the adherence to the thereon coated thermosensitive element.
• the support may be dyed or pigmented to provide a transparent coloured background for the image.
• thermosensitive element In a preferred embodiment of the present invention a protective layer is provided for the thermosensitive element. In general this protects the thermosensitive element from atmospheric humidity and from surface damage by scratching etc. and prevents direct contact of printheads or heat sources with the recording layers.
• Protective layers for thermosensitive elements which come into contact with and have to be transported past a heat source under pressure, have to exhibit resistance to local deformation and good slipping characteristics during transport past the heat source during heating.
• a slipping layer being the outermost layer, may comprise a dissolved lubricating material and/or particulate material, e.g. talc particles, optionally protruding from the outermost layer. Examples of suitable lubricating materials are a surface active agent, a liquid lubricant, a solid lubricant or mixtures thereof, with or without a polymeric binder.
• any layer of the black and white substantially light-insensitive thermographic monosheet material used in the present invention may proceed by any coating technique e.g. 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, USA. Coating may proceed from aqueous or solvent media with overcoating of dried, partially dried or undried layers.
• thermosensitive element Preparation of the thermosensitive element
• thermosensitive element with the composition:
• thermosensitive element Overcoating of thermosensitive element with a protective layer
• thermosensitive element was overcoated with a protective layer with the composition: PIOLOFORMTM LL4160, a polyvinyl butyral from WACKER CHEMIE 1.539 g/m 2 BAYSILONTM MA, a silicone oil from BAYER 0.006 g/m 2 MICRODOLTM SUPER, a talc from Norwegian Talc AS 0.092 g/m 2 TINUVINTM 320 from CIBA-GEIGY 0.229 g/m 2 TEGOGLIDETM 410 from Goldschmidt 0.02 g/m 2 DESMODURTM N100, a hexamethylene diisocyanate from BAYER 0.154 g/m 2
• thermographic printer used for printing the black and white substantially light-insensitive thermographic materials of INVENTION EXAMPLES 1 to 11 was a thermal head printer having a nominal resistance of 1850 ohms, 85 ⁇ m by 85 ⁇ m heating elements, with a line time of 11.5ms and a process speed of 7.36 mm/s. The number of heating pulses, printhead voltages and pulse times were completely variable.
• the printing was carried out with a single pulse per line time and at the voltages and pulse times given in table 1 below.
• the image density D vis and the CIELAB L*, a* and b* values determined in refection according to ASTM Norm E308 of the resulting prints are given in table 1 below.
• Colour neutrality on the basis of CIELAB-values corresponds to a* and b* values of zero, with a negative a*-value indicating a greenish image-tone becoming greener as a* becomes more negative, a positive a*-value indicating a reddish image-tone becoming redder as a* becomes more positive, a negative b*-value indicating a bluish image-tone becoming bluer as b* becomes more negative and a positive b*-value indicating a yellowish image-tone becoming more yellow as b* becomes more positive.
• the NGV-value of thermographic the recording material used in INVENTION EXAMPLES 1 to 11 was found to be 4.09, from the sensitometric curve formed by these INVENTION EXAMPLES.
• the direct thermal black and white substantially light-insensitive thermographic recording material used in the experiments of INVENTION EXAMPLES 12 to 33 was produced by coating the thermosensitive element overcoated with a protective layer used in INVENTION EXAMPLES 1 to 11 and coating the opposite side of the support to that coated with the thermosensitive element and its protective layer sequentially with a 5.5g/m 2 coating of a white acrylic water-based ink pigmented with titanium dioxide having an optical density of 0.38 and overcoating with a white pressure sensitive water-based dispersion to a coating weight of 26g/m 2 , the two layers together having an optical density of 0.65.
• the second layer was then pressure laminated with the silicone-coated side of 65g/m 2 glassine-based paper coated with a silicone layer, which acts as a release foil.
• thermographic materials of INVENTION EXAMPLES 12 to 33 were printed with a thermal head printer, the thermal head having a nominal resistance of 102.6 ohms and 115 ⁇ m by 142 ⁇ m heating elements. It printed with a line time of 11.5ms, was powered by six 1.5 volt batteries and had a DC-motor driven drum transport at a process speed of 7.3mm/s with three heating pulses evenly distributed over the line time at the voltages and pulse times given in table 2.
• the image density D vis and the CIELAB L*, a* and b* values determined in refection according to ASTM Norm E308 of the resulting prints are given in table 2 below.
• L*, a* and b* were also found to be dependent upon the dot energy, L* increasing with increasing dot energy, indicating decreasing optical density, and a* and b* increasing with increasing dot energy from values in the region of zero indicating colour neutrality at lower dot energies to increasingly less neutral colour tone with increasing dot energy.
• the dot energies for INVENTION EXAMPLES 14 & 15 were approximately 80mJ/mm 2
• those for INVENTION EXAMPLES 20 & 21 were approximately 110mJ/mm 2
• those for 23 & 24 were approximately 126mJ/mm 2
• those for INVENTION EXAMPLES 28 & 29 were approximately 154mJ/mm 2 .
• These INVENTION EXAMPLES show that the dot energy is the principal determinant of the image density, D vis .
• INVENTION EXAMPLES 34 to 51 were carried out on the same material as that used for INVENTION EXAMPLES 1 to 11 at a dot energy per pixel of approximately 74mJ/mm 2 with the thermographic printer also used for INVENTION EXAMPLES 1 to 11.

Landscapes

• Physics & Mathematics (AREA)
• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Heat Sensitive Colour Forming Recording (AREA)

Priority Applications (1)

Applications Claiming Priority (3)

Publications (2)

Family

ID=26150926

Family Applications (1)

Country Status (1)

Cited By (3)

Citations (2)

• 1999
  • 1999-11-24 EP EP19990204002 patent/EP1006404B1/de not_active Expired - Lifetime

Patent Citations (2)

Also Published As

Similar Documents

Legal Events