EP1457345B1 - Imprimante à tête thermique et et procédé d'impression sur materiaux d'impression thermographiques - Google Patents

Imprimante à tête thermique et et procédé d'impression sur materiaux d'impression thermographiques Download PDF

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Publication number
EP1457345B1
EP1457345B1 EP20040100796 EP04100796A EP1457345B1 EP 1457345 B1 EP1457345 B1 EP 1457345B1 EP 20040100796 EP20040100796 EP 20040100796 EP 04100796 A EP04100796 A EP 04100796A EP 1457345 B1 EP1457345 B1 EP 1457345B1
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EP
European Patent Office
Prior art keywords
dpln
thermographic material
print density
thermal head
print
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EP20040100796
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German (de)
English (en)
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EP1457345A1 (fr
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Stefaan c/o AGFA-GEVAERT De Meutter
Eric c/o AGFA-GEVAERT Kaerts
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Agfa HealthCare NV
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Agfa HealthCare NV
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    • 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
    • B41J2/375—Protection arrangements against overheating
    • 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
    • B41J2/36—Print density control

Definitions

  • the present invention concerns a process for calibrating a thermal head printer for use with a substantially light-insensitive recording material.
  • Thermography is an image-forming process including a heating step and hence includes photothermography in which the image-forming process includes image-wise exposure and direct thermal processes in which the image-forming process includes an image-wise heating step.
  • 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 head, 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 substantially light-insensitive thermographic material.
  • thermal heads only those regions which produce heat higher than a certain value are effective for printing, and the regions capable of generating sufficient heat for the printing spread in proportion to voltage applied to the heating resistors. If, therefore, higher voltage is applied to the heating resistors, the size of the printing dots increases in proportion.
  • US 6,462,766 discloses a method and an apparatus for limiting the peak power consumed by a thermal recorder connected to portable battery-powered equipment.
  • the battery-powered equipment is designed with a filter and an electronic circuit breaker.
  • a circuit breaker current sense resistor and an output capacitor form an RC filter and provide a large current reservoir for the thermal recorder which averages the peak current demands seen at the circuit input.
  • the electronic circuit breaker provides a current limit function and will not allow a current greater than a predetermined amperage level to be drawn.
  • the thermal recorder has a CPU which provides pulses to a thermal print head in dependence on data incorporated in a pulse-width limit table.
  • the values in the pulse-width limit table can be substituted for calculated pulse widths that would produce peak currents large enough to trip the circuit breaker.
  • said gradation test print and for applying a detection output from said density detecting sensor means to said gradation density detection means; and a first memory element for storing said data of different amounts of energy with respect to address values corresponding to said gradation levels, in response to said coincidence signal from said gradation density detecting means.
  • EP-A 0 922 585 discloses a method for correcting density irregularity in image recording using a line head, comprising the steps of: printing a belt-like pattern at a predetermined-gradation value in a first main scanning direction which is corresponding to a scanning direction of said line head; moving a line sensor relatively along said first main scanning direction while aligning a second main scanning direction, which is corresponding to a scanning direction of said line sensor, with a subsidiary scanning direction, being substantially perpendicular to said first main direction, to detect printing density of said belt-like pattern; obtaining a correction condition for each pixel position based on detected said printing-density values and said predetermined-gradation values; and correcting image data for image recording on the basis of said correction condition.
  • EP-A 1 247 654 discloses that the traditional technique for calibrating a thermal printer is as follows: first, a first calibration page is printed with a limit setting to produce the desired maximum density and a full range of print settings. The next step is to determine whether this is the desired limit setting by visually inspecting the printed page. The normal objective is to find the minimum exposure required to print the full range of desired densities. The lower the limit setting, the more nearly continuous the grey scale in the printed film. The process of printing and adjusting the maximum limit setting is repeated until a desired limit setting is determined. Next, a second calibration page is printed with the limit system setting selected and with a subset of print system settings which cover the full range of print settings.
  • the resulting densities of the printed page are then measured and a print setting to density table created for the full range of print settings.
  • An output lookup table that can be used to set exposure to produce the desired density for any digital image value is created using the print setting to density table. Thereafter the thermal printer prints pages with this output lookup table to produce the desired densities while the same maximum exposure is appropriate.
  • EP-A 1 247 654 discloses that the traditional technique for calibrating a thermal printer is as follows: first, a first calibration page is printed with a limit setting to produce the desired maximum density and a full range of print settings. The next step is to determine whether this is the desired limit setting by visually inspecting the printed page. The normal objective is to find the minimum exposure required to print the full range of desired densities. The lower the limit setting, the more nearly continuous the grey scale in the printed film. The process of printing and adjusting the maximum limit setting is repeated until a desired limit setting is determined. Next, a second calibration page is printed with the limit system setting selected and with a subset of print system settings which cover the full range of print settings.
  • the resulting densities of the printed page are then measured and a print setting to density table created for the full range of print settings.
  • An output lookup table that can be used to set exposure to produce the desired density for any digital image value is created using the print setting to density table. Thereafter the thermal printer prints pages with this output lookup table to produce the desired densities while the same maximum exposure is appropriate.
  • US 5,711,621 discloses in a printer having a print region defined by a thermal print head and a rotatable platen adapted to draw a print media therebetween, a method for calibrating the printer comprises the steps of: identifying a type of print media which is selected for use on said printer, wherein said selected type of print media has unknown printer parameter values; printing a series of test labels onto said selected type of print media using a parameter of said printer having a unique value for each individual one of said test labels of said series with identifying information of said unique parameter value being printed thereon; after printing said series of test labels, inspecting said series of test labels to select one of said test labels of said series having a desired level of image quality; and specifying said unique parameter value of said selected one of said test labels for further operation of said printer with said selected type of print media.
  • US 2001/004284 discloses a calibration pattern printing method for a printer that prints an image in an image recording area on a recording paper, comprising the steps of: printing a calibration pattern in a marginal area on the recording paper outside said image recording area; and cutting said marginal area with said calibration pattern off the recording paper after the image is printed in said image recording area.
  • thermographic materials are increasingly being used for graphic arts, medical and other applications which require high maximum print densities. Attaining such high print densities in thermographic materials requires that the heating elements be driven at higher powers and hence to higher temperatures, which increases the probability of premature heating element failure due to overheating and of image faults in the thermographic materials due to overheating. A means is therefore required to avoid such failure of the heating elements due to overheating and to avoid such image faults in the thermographic materials without significant loss in maximum print density and significant loss in image information.
  • thermographic materials due to overheating without significant loss in image information.
  • thermo head printer capable of printing a substantially light-insensitive thermographic material without unacceptable heating element failure and image faults in the thermographic materials due to overheating without significant loss in image information.
  • thermographic material It is also an aspect of the present invention to provide a calibration process for printing a substantially light-insensitive thermographic material to avoid failure of the heating elements due to overheating and to avoid such image faults in the thermographic materials due to overheating without significant loss in image information during the printing of the thermographic material.
  • thermographic material It is also an aspect of the present invention to provide a printing process for a substantially light-insensitive thermographic material which avoids heating element failure and image faults in the thermographic materials due to overheating without significant loss in image information.
  • thermo head printer (1) with image-invariant printing speeds (2) for printing a substantially light-insensitive thermographic material (3) having a print density-driving power level characteristic (4)
  • the thermal head printer (1) comprising a transport means (5), one or more thermal heads (6) each having an array of heating elements (7), a thermal print head drive system (8) capable of supplying power to each of the printing elements, and a calibration means (9) based on the print density-driving power level characteristic (4) of the thermographic material (3).
  • thermo head printer (1) comprising one or more thermal heads (6) each having an array of heating elements (7) connected to a power supply capable of supplying a given number of heating element driving power levels from 0 to a maximum driving power level number, corresponding to P max , to each heating element for printing a substantially light-insensitive thermographic material (3) by image-wise heating the thermographic material (3) with the heating elements
  • the process comprising the steps of: (i) putting the printer into a calibration mode; (ii) printing one or more step-wedges of print densities by heating the thermographic material (3) with the heating elements at different DPLN's; (iii) determining the optical density of each step of the step-wedge(s) of print densities with a densitometer thereby obtaining the dependence of the print density upon DPLN; (iv) deriving from the dependence, or all the dependences of the print density upon DPLN
  • aspects of the present invention are also realized by a process for printing a substantially light-insensitive thermographic material (3) with a thermal head printer (1) comprising one or more thermal heads (6) each having an array of heating elements (7) connected to a power supply capable of supplying a given number of heating element driving power levels from 0 to a maximum driving power level number, corresponding to P max , the process comprising the steps of: calibrating the thermal head printer (1) according to the above-described calibration process, transporting the substantially light-insensitive thermographic material (3) past the thermal head, and image-wise heating of the substantially light-insensitive thermographic material (3) by means of the heating elements.
  • a heating element as used in disclosing the present invention is a resistor, which becomes hot upon being energized.
  • Transport speed i.e. the speed of the substantially light-insensitive thermographic material (3), as used in disclosing the present invention, is the distance between adjacent lines of image dots in the transport direction divided by the line time.
  • Printing speed is the speed at which the printing medium is transported through a printer.
  • image-invariant printing speed means that the image density has no influence upon the printing speed.
  • dimensionless by normalization means dividing a quantity by a reference value of that quantity e.g. the maximum value of that quantity which can be realized.
  • single smoothed dependence of the rate of change of print density means that all the measured values are represented by a dependence in the form of a smooth curve.
  • a transport means (5) can, for example, consist of a moving belt, a motor-driven drums, capstans or a combination thereof.
  • the print density-driving power level characteristic (4) of a substantially light-insensitive thermographic recording material is the dependence of print density upon the driving power level of heating elements upon printing the thermographic material (3) in the thermal head printer (1), according to the present invention.
  • the available driving power range from 0 to a maximum driving power, P max is divided into a sufficient number of dimensionless i.e. normalized sub-units (the power increment between successive DPLN's being preferably constant) to enable the printing of sufficient grey tones to obtain prints without significant loss of imaging information, while providing the number of sub-units necessary to be able to achieve these grey tones with every heating element in the one or more thermal heads (6) used in the printing process.
  • These dimensionless sub-units are referred to as heating element driving power level numbers (DPLN's) in disclosing the present invention.
  • DPLN will refer to the actual DPLN, if there is no variation in heating effect between the heating elements of the one or more thermal heads (6), or to the reference DPLN, if there is variation in heating effect between the heating elements of the one or more thermal heads (6).
  • ⁇ D/ ⁇ DPLN is the rate of change of print density per heating element driving power level number.
  • the foot of the dependence of the print density upon DPLN is that part of the S-shaped print density upon DPLN dependence forming the bottom of the "S" and observed from the lowest DPLN at which an optical density above the background density D min is observed.
  • the shoulder of the dependence of the print density upon DPLN is that part of the S-shaped print density upon DPLN dependence forming the top of the "S" and ends with the maximum density D max .
  • the threshold rate of change of print density per DPLN for the specific thermographic material (3) being printed i.e. threshold ⁇ D/ ⁇ DPLN, as used in disclosing the present invention, is that rate of change of print density per DPLN at an optical density level above the foot of the dependence of the print density upon DPLN, which corresponds to an acceptably high optical density, an acceptable level of information loss, an acceptable level of heating element failure and an acceptable level of damage to the thermographic material (3).
  • Substantially rectangular means having angles which deviate from 90° by no more than 20°.
  • Substantially light-insensitive means not intentionally light sensitive.
  • a leuco-dye is a colourless or weakly coloured compound derived from a dye.
  • Colourless or light coloured dye precursor leuco-dye systems include leuco triarylmethane, indolyl phthalide, diphenylmethane, 2-anilinofluoran, 7-anilinofluoran, xanthene and spiro compounds such as disclosed in EP-A 754 564 .
  • thermo head printer (1) with image-invariant printing speeds (2) for printing a substantially light-insensitive thermographic material (3) having a print density-driving power level characteristic (4)
  • the thermal head printer (1) comprising a transport means (5), one or more thermal heads (6) each having an array of heating elements (7), a thermal print head drive system (8) capable of supplying power to each of the printing elements, and a calibration means (9) based on the print density-driving power level characteristic (4) of the thermographic material (3).
  • the maximum driving power applied to the thermographic material (3) during the printing process is adjusted as a function of the print density-driving power level characteristic (4) of the thermographic material (3).
  • the driving power level in the print density-driving power level characteristic (4) of the thermographic material (3) is rendered dimensionless by normalization.
  • the thermal head printer (1) further comprises at least one densitometer capable of measuring the print density of a print produced with the thermal head printer (1).
  • the thermal print head drive system (8) is capable of being calibrated by using the dependence of print density upon power supply level for the substantially light-insensitive thermographic material (3).
  • the thermal head printer (1) is battery powered.
  • the thermal head printer (1) is mains powered.
  • the thermal head printer (1) has a single printing speed.
  • the calibration process according to the present invention excludes setting a maximum allowable temperature of a heating element.
  • thermo head printer (1) comprising one or more thermal heads (6) each having an array of heating elements (7) connected to a power supply capable of supplying a given number of heating element driving power levels from 0 to a maximum driving power level number, corresponding to P max , to each heating element for printing a substantially light-insensitive thermographic material (3) by image-wise heating the thermographic material (3) with the heating elements
  • the process comprising the steps of: (i) putting the printer into a calibration mode; (ii) printing one or more step-wedges of print densities by heating the thermographic material (3) with the heating elements at different DPLN's; (iii) determining the optical density of each step of the step-wedge(s) of print densities with a densitometer thereby obtaining the dependence of the print density upon DPLN; (iv) deriving from the dependence, or all the dependences of the print density upon DPLN,
  • the DPLN's for the printing of the step wedges can be default settings or these DPLN's can be determined from a reference print density-DPLN dependence obtained by determining the print density as a function of DPLN over the whole range of DPLN's.
  • each heating element exhibiting a different heating effect will exhibit a different dependence of print density upon DPLN which will be manifested as a variation in print density at each DPLN used.
  • the data obtained by measuring this print density variation at each DPLN can be used to derive a reference print density-DPLN dependence, i.e. the reference DPLN required to obtain a particular print density, e.g. by plotting the average print density obtained at each DPLN versus DPLN. This can be used to determine the reference print density-DPLN dependence i.e. the reference DPLN's necessary to realize a particular density.
  • step (ii) is preceded by a determination of the dependence of print density upon DPLN i.e. the reference print density-DPLN dependence for the particular thermographic material (3).
  • a compensation procedure is necessary to determine the print-density-DPLN characteristic for each heating element.
  • the DPLN's required for each heating element can be represented as percentage changes in DPLN with respect to the reference DPLN obtained from the reference print density-DPLN dependence.
  • Calibration of the drive characteristics of the heating elements for the specific thermographic material (3) being printed independent of the thermal printing head conditions i.e. thermal printing head, installation variations and environmental conditions is achieved, according to the present invention, by normalizing the print density-driving power characteristic by dividing the available driving power range from 0 to a maximum driving power level number, corresponding to P max , into a given number of power levels (DPLN's), printing a step-wedge at predetermined DPLN's, measuring the print density at each of the predetermined DPLN's, differentiating the resulting print density-DPLN characteristic, establishing a threshold rate of change of print density per driving power, Th, for the specific thermographic material (3) being printed i.e.
  • the thermal head printer (1) setting the thermal head printer (1) so that the thermal printing head is driven in such a way that the rate of change of print density per driving power level does not undercut the threshold rate of print density per DPLN i.e. the threshold value of ⁇ D/ ⁇ DPLN.
  • the threshold rate of print density change per DPLN is in the shoulder of the S-shaped print density upon DPLN dependence.
  • the one or more step wedges of print densities are printed simultaneously i.e. substantially at an angle of 90° to the transport direction and substantially parallel to the thermal head or thermal heads.
  • steps (i) to (iii) are repeated at different places on the thermographic material (3) to obtain further dependencies of the print density upon the heat produced by the heating elements for the thermographic material (3).
  • the step-wedges of print densities are printed in the transport direction.
  • the threshold rate of change of print density per DPLN for the specific thermographic material (3) being printed can, for example, be established by first determining the print density at which the highest rate of print density per DPLN is observed, then determining the dependence of print density upon the rate of change of print density per DPLN for print densities higher than that corresponding to the maximum rate of change of print density per DPLN and selecting a DPLN, the critical DPLN, at which an acceptable rate of heating element failure and an acceptable rate of damage of the thermographic material (3) is observed and at which there is an insignificant loss of imaging information.
  • This last criterion means that the critical DPLN will be in the shoulder of the "S"-shaped dependence of print density upon DPLN.
  • thermographic material (3) damage can be the incidence of pinholes as shown in INVENTION EXAMPLE 1.
  • a possible measure of the failure rate of heating elements could be the drift in heating element heating characteristics, which could be obtained from the above-mentioned compensation procedure data.
  • the rate of change of print density per DPLN corresponding to this critical DPLN i.e. the threshold rate of change of print density per DPLN, Th, is the threshold ⁇ D/ ⁇ DPLN value below which unacceptable printing conditions obtain.
  • the print density-DPLN characteristics are determined by printing an array of areas of the thermographic material (3), each area being printed with heating elements each supplied with the power to give the same grey level response, these areas being sufficiently large to enable the print density to be determined by a densitometer, preferably being wide enough to enable sufficient densitometric measurements to be carried out that a reliable and consistent print density value can be established by taking the average of values left after rejecting measurements which vary by more than a predetermined percentage from the average print density value. These areas may form an array substantially parallel to the printing head or printing heads or form an array in the transport direction of the printer. If more than one print density-DPLN characteristic is combined to produce a master characteristic, the print density-DPLN characteristic used can be generated at the same or different power level numbers. If the heating effect of the heating elements varies from heating element to heating element, the DPLN value in the above-mentioned print density-DPLN characteristics will be the reference DPLN value.
  • the delay between printing and optical density measurement should be as constant as possible to allow for print density variation subsequent to printing.
  • the densitometric measurements are performed on the array or arrays of areas with different print densities corresponding to different DPLN's with one or more static densitometers while the thermographic material (3) is transported under the densitometer head(s). This can be on-line with or without stopping the transport of the thermographic material (3) between the printing and the densitometric measurements or off-line. If performed on-line without stopping the transport of thermographic material (3), the delay after printing is the transport time between the thermal head and the densitometer head i.e. the quotient of the distance between the thermal head and the densitometer head and the transport speed.
  • the densitometric measurements are performed with the thermographic material (3) stationary and with one or more dynamic densitometers scanning over the array or arrays of areas with different print densities corresponding to different DPLN's or different reference DPLN's.
  • Such measurements can be carried out on-line i.e. in the printer itself by stopping the transport of the thermographic material (3) and scanning the array or arrays of areas with different print densities corresponding to different DPLN's or reference DPLN's, or off-line.
  • the array or arrays of areas with different print densities corresponding to different DPLN's or reference DPLN's be printed substantially parallel to the thermal head or thermal heads and that the one or more dynamic densitometers scan in a direction substantially parallel to the thermal head or thermal heads.
  • thermographic material (3) may vary in its thermal response over the area thereof, it is advantageous to combine data obtained from different areas of the thermographic material (3) e.g. by combining print density-DPLN or reference DPLN characteristics from different areas of the thermographic material (3). These arrays of printed areas can be substantially at 90° to or substantially parallel to the transport direction of the thermographic material (3). If print density-DPLN or reference DPLN data from different areas of the thermographic material (3) with slightly different thermal response characteristics are combined into a master curve before differentiating to obtain the rate of print density per DPLN as a function of DPLN, prior smoothing of the raw print density-DPLN or reference DPLN data is preferred. Any of the standard smoothing procedures may be used, but the floating point method is preferred.
  • the width of the area traversed by the densitometer should be sufficient to enable multiple densitometric measurements to be carried out and will depend upon the scanning speed of the densitometer, if it is dynamic, the transport speed of the thermographic material (3), if it is moving, the available light intensity, the spot size, the degree of overlap from measurement to measurement and the measurement rate of the densitometer. These factors will also determine the number of areas that can be printed. If several print density-DPLN or reference DPLN characteristics are used to yield a master curve, as few as eight points per characteristic has been found to be sufficient to yield a reliable master curve after smoothing.
  • the densitometer can be a transmission or reflection densitometer depending if the thermographic material (3) is transparent, but only a reflection densitometer if the thermographic material (3) is opaque.
  • a process for printing a substantially light-insensitive thermographic material (3) with a thermal head printer (1) comprising one or more thermal heads (6) each having an array of heating elements (7) connected to a power supply capable of supplying a given number of heating element driving power levels from 0 to a maximum driving power level number, corresponding to P max , the process comprising the steps of: calibrating the thermal head printer (1) according to the above-described calibration process, transporting the substantially light-insensitive thermographic material (3) past the thermal head, and image-wise heating of the substantially light-insensitive thermographic material (3) by the driving power levels to the heating elements.
  • the operating temperature of common thermal heads is in the range of 300 to 400°C and the pressure contact of the thermal printhead with the recording material is exerted to ensure a good transfer of heat.
  • Activation of the heating elements can be power-modulated or pulse-length modulated at constant power.
  • thermographic material substantially light-insensitive thermographic material
  • substantially light-insensitive thermographic material includes all materials which produce a change in optical density upon the application of heat.
  • the substantially light-insensitive thermographic material (3) is a black and white material.
  • the substantially light-insensitive thermographic material (3) is a two sheet material in which an ingredient necessary for the image-forming process is transferred upon image-wise application of heat from one sheet to the other where it reacts with one or more further ingredients to produce an image.
  • the substantially light-insensitive thermographic material (3) is a monosheet material.
  • the substantially light-insensitive thermographic material (3) contains a thermosensitive element comprising one or more layer, the one or more layers containing an image-forming system.
  • Suitable image-forming systems include monosheet substantially light-insensitive thermographic material (3)s such as colourless or light coloured dye precursor leuco-dye systems, as disclosed in US-P 4,370,370 , EP-A 479 578 and EP-A 754 564 , diazo systems, as disclosed in JP 60-01077A , or two-sheet thermal dye transfer systems, such as disclosed in EP-A 656 264 and US-P 4,943,555 .
  • monosheet substantially light-insensitive thermographic material (3)s such as colourless or light coloured dye precursor leuco-dye systems, as disclosed in US-P 4,370,370 , EP-A 479 578 and EP-A 754 564 , diazo systems, as disclosed in JP 60-01077A , or two-sheet thermal dye transfer systems, such as disclosed in EP-A 656 264 and US-P 4,943,555 .
  • the image-forming systems may comprise at least one substantially light-insensitive organic silver salt and at least one organic reducing agent therefor either in a two-sheet material in which upon image-wise application of heat at least one organic reducing agent is image-wise transferred to a sheet containing the at least one substantially light-insensitive organic silver salt whereupon the image-forming reaction takes place or in a monosheet material in which the at least one substantially light-insensitive organic silver salt is in thermal working relationship with the at least one organic reducing agent therefor.
  • the substantially light-insensitive thermographic material (3) is a monosheet material comprising a thermosensitive element and a support, the thermosensitive element comprising at least one substantially light-insensitive organic silver salt, at least one organic reducing agent therefor in thermal working relationship therewith, i.e. during the thermal development process the organic 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, and a binder.
  • Such materials include the possibility of one or more substantially light-insensitive organic silver salts and/or one of more organic reducing agents therefor being encapsulated in heat-responsive microcapsules, such as disclosed in EP-A 0 736 799 .
  • thermographic materials exhibit a print density-driving power characteristic, which has a weak print density-driving power response at very low driving powers, a strong print density-driving power response to low to high driving powers and a weak print density-driving power response at very high driving powers, which may even become negative at extremely high driving powers due to image defects such as pin-holes.
  • a balance has to be struck in thermographic materials between shelf-life stability and thermosensitivity, which means that, if very high print densities are required, the maximum density required is often to be found in the weak print density-driving power response at very high driving powers.
  • Preferred substantially light-insensitive organic silver salts for use in the thermosensitive element of the substantially light-insensitive elongated imaging 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.
  • 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.
  • the thermosensitive element contains a 3,4-dihydroxyphenyl compound with ethyl 3,4-dihydroxybenzoate, n-butyl 3,4-dihydroxybenzoate, 3,4-dihydroxy-benzophenone and 3,4-dihydroxy-benzonitrile being particularly preferred.
  • thermosensitive element of the substantially light-insensitive elongated imaging material used in the present invention may be coated onto a support in sheet- 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 include: 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 polymers. Poly(vinylbutyral) is the preferred binder.
  • the binder to organic silver salt weight ratio 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 image-forming reaction at elevated temperatures.
  • the substantially light-insensitive thermographic 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.
  • Suitable toning agents are described in US 3,074,809 , US 3,446,648 and US 3,844,797 and US 4,082,901 .
  • Other particularly useful toning agents are the heterocyclic toning compounds of the benzoxazine dione or naphthoxazine dione type as disclosed in GB 1,439,478 , US 3,951,660 and US 5,599,647 .
  • the substantially light-insensitive thermographic material contains a thermosensitive element, the thermosensitive element containing one or more toning agents selected from the group consisting of phthalazinone, benzo[e][1,3]oxazine-2,4-dione, 7-methyl-benzo[e] [1,3]oxazine-2,4-dione, 7-methoxy-benzo[e][1,3]oxazine-2,4-dione and 7-(ethylcarbonato)-benzo[e][1,3]oxazine-2,4-dione.
  • phthalazinone benzo[e][1,3]oxazine-2,4-dione
  • 7-methyl-benzo[e] [1,3]oxazine-2,4-dione 7-methoxy-benzo[e][1,3]oxazine-2,4-dione
  • stabilizers and antifoggants may be incorporated into the substantially light-insensitive thermographic material used in the present invention.
  • Suitable stabilizers compounds for use in the substantially light-insensitive thermographic material used in the present invention include benzotriazole, tetrachlorophthalic acid anhydride and those compounds 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 substantially light-insensitive thermographic 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 substantially light-insensitive thermographic material has a transparent or translucent support 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 sheet, 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 other 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 substantially light-insensitive thermographic 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.
  • Type 1 and type 2 substantially light-insensitive thermographic materials were prepared by coating a 175 ⁇ m thick blue-pigmented poly(ethylene terephthalate) support with a subbing layer with the following composition: copolymer of 88% vinylidene chloride, 10% methyl acrylate and 2% itaconic acid 79.1 mg/m 2 Kieselsol® 100F, a colloidal silica from BAYER 18.6 mg/m 2 Mersolat® H, a surfactant from BAYER 0.4 mg/m 2 Ultravon® W, a surfactant from CIBA-GEIGY 1.9 mg/m 2
  • thermosensitive element types 1 and 2 respectively as given below from coating dispersions in 2-butanone to a coating thickness of 100 ⁇ m:
  • thermosensitive elements were then further coated with an aqueous composition with the following ingredients, which was adjusted to a pH of 3.8 with IN nitric acid, to a wet layer thickness of 85 ⁇ m and then dried at 50°C for 15 minutes to produce a protective layer with the composition: [g/m 2 ] ERCOLTM 48 20, a polyvinylalcohol from ACETEX EUROPE 2.1 LEVASILTM VP AC 4055, a 15% aqueous dispersion of colloidal silica with acid groups predominantly neutralized with sodium ions and a specific surface area of 500 m 2 /g from BAYER AG, which has been converted into the ammonium salt 1.05 ULTRAVONTM W, a 75-85% concentrate of a sodium arylsulfonate from Ciba Geigy converted into acid form by passing through an ion exchange column 0.075 SYLOIDTM 72, a silica from Grace 0.09 SERVOXYLTM VPDZ 3/100, a mono[isotri
  • the protective layer was hardened by heating the substantially light-insensitive thermographic material at 45°C for 7 days at a relative humidity of 70%.
  • step-wedges were simultaneously printed with the type 1 substantially light-insensitive thermographic material in an environment with a temperature of 25°C and a relative humidity of 50% relative humidity with a DRYSTARTM 4500M printer with a line time of 7ms from AGFA-GEVAERT N.V. consisting each of 13 areas 4 mm in width and ca. 200 mm in length along the transport direction of the printer with a maximum power level of 38.2 mW.
  • Each of the 52 areas was printed at a different DPLN from a total number of 13bit (8192) with each of the 13 areas covering the whole DPLN range.
  • the optical densities were measured with a built in dynamic transmission densitometer with a spot size of 0.6 mm by taking the average of 10 measurements. The densitometer scanned over the areas at substantially 90° to the transport direction with the substantially light-insensitive thermographic material stationary.
  • Curve 5 of Figure 3 in which [D max x 100] is plotted against [Th x 100], shows the influence of increasing the threshold value of print density change with DPLN, Th, i.e. the threshold ⁇ D/ ⁇ DPLN value, from 0.0003 to 0.0010 upon the maximum print density D max upon printing in an environment with a temperature of 30°C and 80% relative humidity i.e. more critical conditions for print quality.
  • Table 1 provides the maximum print density values D max obtained with different threshold slopes and the incidence of pin-holes.
  • a threshold slope setting of 0.00045 represented an acceptable compromise between acceptable D max reduction of 0.15 together with an acceptable level of pin-holes.
  • Table 1 Dmax without threshold slope setting Threshold slope, Th D max with threshold slope setting Assessment of pinholes 2.99 0.0003 2.90 4 3.00 0.00035 2.89 4 3.01 0.0004 2.87 3 3.01 0.00045 2.85 2 2.98 0.0005 2.77 1 2.99 0.001 2.15 0
  • step-wedges were simultaneously printed with the type 2 substantially light-insensitive thermographic material in an environment with a temperature of 25°C and a relative humidity of 50% relative humidity with a DRYSTARTM 4500 printer with a line time of 7ms from AGFA-GEVAERT N.V. consisting each of 13 areas 4 mm in width and ca. 200 mm in length along the transport direction of the printer with a maximum power level of 47.6 mW.
  • Each of the 52 areas was printed at a different DPLN from a total number of 13bit (8192) with each of the 13 areas covering the whole DPLN range.
  • the optical densities were measured with a built in dynamic transmission densitometer with a spot size of 0.6 mm by taking the average of 10 measurements.
  • the densitometer scanned over the areas at an angle of substantially 90° to the transport direction with the substantially light-insensitive thermographic material stationary.
  • the four sets of print density-DPLN data were combined into a single smoothed master curve, see curve 7 of Figure 4 , in which [D x 100] is plotted against DPLN, and the slope calculated as a function of DPLN, see curve 10 of Figure 5 , in which [ ⁇ D x 100]/ ⁇ DPLN is plotted against DPLN.
  • This experiment was then repeated with maximum power levels of 44.6 mW (see curve 8 of Figure 4 and curve 11 of Figure 5 respectively) and 41.7 mW (see curve 9 of Figure 4 and curve 12 of Figure 5 respectively).
  • Figure 5 shows the dependencies of the slope of the dependence of print density (D) upon DPLN, ⁇ D/ ⁇ DPLN, represented by [ ⁇ D x 100]/ ⁇ DPLN, upon DPLN for the results of curves 7, 8 and 9 of Figure 4 in curves 10, 11 and 12 respectively.
  • Two step-wedges consisting each of 16 areas, 337mm in width and ca. 9.5mm in length along the transport direction of the printer were simultaneously printed on the type 1 substantially light-insensitive thermographic material at a temperature of 25°C and a relative humidity of 50% with a DRYSTARTM 5300 printer from AGFA-GEVAERT N.V. with a maximum power level of 62.4mW and a line time of 8,35ms.
  • Each of the 32 areas was printed at a different DPLN from a total number of 13bit (8192) with the 16 areas covering the whole DPLN range.
  • the optical densities were measured with a built-in static transmission densitometer with a spot size of 30x70mm by taking the average of 13 measurements.
  • the densitometer scanned over the areas in the transport direction while the substantially light-insensitive thermographic material moved to the output tray.
  • the two sets of print density-DPLN data were combined into a single smoothed master curve and the dependence of slope, ⁇ D/ ⁇ DPLN, represented by [ ⁇ D x 100]/ ⁇ DPLN, upon DPLN in shown in Figure 6.
  • Figure 7 shows the dependence of the slope, ⁇ D/ ⁇ DPLN, represented by [ ⁇ D x 100]/ ⁇ DPLN, upon optical density D, represented by [D x 100].
  • the initial threshold slope setting of 0.04 gives a maximum density of 302.
  • the threshold slope of this system was decreased to 0.03 in order to achieve a better compromise between Dmax and an acceptable level of thermal print head contamination.

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Claims (10)

  1. Une imprimante à tête thermique opérant (1) à des vitesses d'impression indépendantes de l'image, servant à imprimer sur un matériau thermographique essentiellement insensible à la lumière (3) ayant une caractéristique densité d'impression/puissance d'excitation (4), l'imprimante à tête thermique comprenant un moyen de transport (5), une ou plusieurs têtes thermiques (6) comprenant chacune une matrice d'éléments chauffants (7), un système d'excitation des têtes d'impression thermiques (8), capable d'exciter chacun des éléments d'impression d'une puissance comprise entre 0 et une valeur de puissance d'excitation maximale (DPLN) correspondant à Pmax, et un moyen d'étalonnage (9) basé sur la caractéristique densité d'impression/puissance d'excitation du matériau thermographique, ledit moyen d'étalonnage étant adapté à exécuter les étapes ci-après :
    (i) la mise en mode d'étalonnage de l'imprimante,
    (ii) l'impression d'un ou de plusieurs coins à échelons de densités d'impression en chauffant le matériau thermographique à l'aide des éléments chauffants à différentes valeurs DPLN,
    (iii) la détermination de la densité optique de chaque échelon du (des) coin(s) à échelons de densités d'impression à l'aide d'un densitomètre, permettant d'obtenir la dépendance de la densité d'impression de la valeur DPLN,
    (iv) la dérivation, à partir de la (de toutes les) dépendance(s) de la densité d'impression de la valeur DPLN, d'une seule dépendance lissée du taux de changement de la densité d'impression D de la valeur DPLN (ΔD/ΔDPLN) en fonction de la valeur DPLN pour le matériau thermographique,
    (v) la détermination d'une valeur seuil du changement de la densité d'impression par valeur DPLN pour le matériau thermographique imprimé, et
    (vi) le réglage de l'imprimante à tête thermique de façon à assurer que l'augmentation de la densité d'impression par valeur DPLN ne descend pas sous la valeur seuil.
  2. Imprimante à tête thermique selon la revendication 1, caractérisée en ce que la puissance d'excitation maximale appliquée au matériau thermographique pendant le processus d'impression est réglée en fonction de la caractéristique densité d'impression/puissance d'excitation du matériau thermographique.
  3. Imprimante à tête thermique selon la revendication 1 ou 2, caractérisée en ce que la valeur de puissance d'excitation reprise dans la caractéristique densité d'impression/puissance d'excitation du matériau thermographique est rendue adimensionnelle par normalisation.
  4. Imprimante à tête thermique selon l'une quelconque des revendications précédentes, caractérisée en ce que l'imprimante à tête thermique est en outre équipée d'au moins un densitomètre capable de mesurer la densité d'impression d'une copie imprimée à l'aide de l'imprimante à tête thermique.
  5. Imprimante à tête thermique selon l'une quelconque des revendications précédentes, caractérisée en ce que le(s) coin(s) à échelons de densités d'impression sont imprimés simultanément.
  6. Imprimante à tête thermique selon l'une quelconque des revendications précédentes, caractérisée en ce que les étapes (i) à (iv) sont répétées à différents endroits sur le matériau thermographique afin d'obtenir des dépendances supplémentaires de la densité d'impression de la chaleur produite par les éléments chauffants pour le matériau thermographique.
  7. Un procédé pour l'étalonnage d'une imprimante à tête thermique (1) opérant à des vitesses d'impression indépendantes de l'image (2), ladite imprimante à tête thermique comprenant une ou plusieurs têtes thermiques (6) comprenant chacune une matrice d'éléments chauffants (7) couplés à une source d'alimentation électrique capable d'exciter chaque élément chauffant d'un nombre spécifique de valeurs de puissance d'excitation pour les éléments chauffants, lesdites valeurs étant comprises entre 0 et une valeur de puissance d'excitation maximale correspondant à Pmax, afin d'imprimer sur un matériau thermographique essentiellement insensible à la lumière (3) et ce en chauffant sous forme d'image ledit matériau thermographique à l'aide des éléments chauffants, ledit procédé comprenant les étapes ci-après :
    (i) la mise en mode d'étalonnage de l'imprimante,
    (ii) l'impression d'un ou de plusieurs coins à échelons de densités d'impression en chauffant le matériau thermographique à l'aide des éléments chauffants à différentes valeurs DPLN,
    (iii)la détermination de la densité optique de chaque échelon du (des) coin(s) à échelons de densités d'impression à l'aide d'un densitomètre, permettant d'obtenir la dépendance de la densité d'impression de la valeur DPLN,
    (iv) la dérivation, à partir de la (de toutes les) dépendance(s) de la densité d'impression de la valeur DPLN, d'une seule dépendance lissée du taux de changement de la densité d'impression D de la valeur DPLN (ΔD/ΔDPLN) en fonction de la valeur DPLN pour le matériau thermographique,
    (v) la détermination d'une valeur seuil du changement de la densité d'impression par valeur DPLN pour le matériau thermographique imprimé, et
    (vi) le réglage de l'imprimante à tête thermique de façon à assurer que l'augmentation de la densité d'impression par valeur DPLN ne descend pas sous la valeur seuil.
  8. Procédé selon la revendication 7, caractérisé en ce que le(s) coin(s) à échelons de densités d'impression sont imprimés simultanément.
  9. Procédé selon la revendication 7 ou 8, caractérisé en ce que les étapes (i) à (iv) sont répétées à différents endroits sur le matériau thermographique afin d'obtenir des dépendances supplémentaires de la densité d'impression de la chaleur produite par les éléments chauffants pour le matériau thermographique.
  10. Un procédé d'impression sur un matériau thermographique essentiellement insensible à la lumière (3) à l'aide d'une imprimante à tête thermique (1), ladite imprimante à tête thermique comprenant une ou plusieurs têtes thermiques (6) comprenant chacune une matrice d'éléments chauffants (7) couplés à une source d'alimentation électrique capable d'appliquer un nombre spécifique de valeurs de puissance d'excitation pour les éléments chauffants, lesdites valeurs étant comprises entre 0 et une valeur de puissance d'excitation maximale (DPLN) correspondant à Pmax, ledit procédé comprenant les étapes ci-après : l'étalonnage de l'imprimante à tête thermique selon l'une quelconque des revendications 7 à 9, le transport du matériau thermographique essentiellement insensible à la lumière le long de la tête thermique et le chauffage sous forme d'image du matériau thermographique essentiellement insensible à la lumière à l'aide des éléments chauffants.
EP20040100796 2003-03-12 2004-03-01 Imprimante à tête thermique et et procédé d'impression sur materiaux d'impression thermographiques Expired - Fee Related EP1457345B1 (fr)

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US4939581A (en) * 1988-11-23 1990-07-03 Hanoch Shalit Method and system in video image hard copy reproduction
JPH0832462B2 (ja) * 1990-02-27 1996-03-29 三菱電機株式会社 階調記録プリンタ
JPH1155534A (ja) * 1997-07-29 1999-02-26 Fuji Photo Film Co Ltd 色変換・濃度階調補正方法およびそのカラープリンター
JP3703061B2 (ja) * 1997-12-08 2005-10-05 富士写真フイルム株式会社 濃度ムラ補正方法及び該方法を用いた画像記録装置
EP1006404B1 (fr) * 1998-11-30 2004-04-14 Agfa-Gevaert Procédé d'impression de format supérieur à l'étiquette pour des matériaux d'enregistrement direct thermique d'images comprenant un sel d'argent organique
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