DE69927693T2 - Thermal printhead - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION

The The present invention relates to a device for heating a Recording medium with heat energy, the device having a thermal head with individually addressable contains excitable heating elements. In particular, the recording medium is a thermographic one Material and the head is a head for usually called thermography designated thermal imaging.

GENERAL STATE OF THE ART

at thermal imaging or thermography is concerned a recording method in which images are imagewise modulated Thermal energy be generated. Thermography is a material which are not sensitive to radiation but are sensitive to heat and where a pictorial admission with heat is sufficient to chemical or physical processes that a change the optical density, a visible change in a heat-sensitive Create imaging material.

What 1 is concerned, it shows a global principle embodying scheme of a usable according to the present invention (eg EP 0 724 964 Agfa-Gevaert known) thermal printing device 10 , This device can print lines of pixels Pi on a thermographic recording material m which often includes thermal imaging elements indicated by the letters Ie or (short and to success) imaging elements. Since an imaging element Ie is part of a thermographic recording material (discussed below), both elements in the present patent specification will be commonly assigned reference number 3 designated. The thermographic recording material m contains, on a support, an organic silver salt-containing heat-sensitive layer which is generally in the form of a sheet. The imaging element 3 is on a rotary drum 15 which is driven by a drive mechanism (not shown) supporting the drum 15 and the imaging element 3 continuously on a fixed thermal print head 16 passed (indicated by arrow Y, which represents the so-called slow scan direction). This head 16 pushes the imaging element 3 against the drum 15 and receives the output of the driver circuits (this is not shown for clarity). The thermal printhead 16 usually contains a large number of heating elements in the same number as the number of pixels in the image data present in a line memory. The imagewise heating of the heating element is carried out line by line, wherein the "line" depending on the structure of the printer can extend horizontally or vertically and the heating resistors are geometrically arranged side by side and the output darkness is gradually built up. These resistors can each be energized by heating pulses whose energy is controlled according to the required blackening of the corresponding picture element. As the value of the image input data increases, the output energy increases and, as a result, the optical density of the hard copy image increases 17 on the imaging element 3 , On the contrary, image data of lower density cause a reduction in heating energy, which gives a softer picture 17 results.

First, in input data block 22 received a digital signal representation, after which the image signal via a digital interface in a (not shown) storage means of the thermal printer 10 is fed.

In the processing unit 24 the processing of the digital image signal takes place. Subsequently, the recording head becomes 16 so controlled that in each pixel the density value corresponding to the value of the processed digital image signal is obtained. After processing, the relevant heating elements can be electrically energized. In this way, a thermal hard copy 17 recorded the electrical image data. By varying the heat applied to the carrier by each heating element, a variable density image pixel is formed.

3 (known from eg EP 0 627 319 Agfa-Gevaert) is a detailed cross-section of a flat thermal head TH shown as part of the figures of the present invention 16 is shown.

This head comprises at least one insulating substrate 34 (For example, a ceramic substrate such as a filled with Al ₂ O ₃ (alumina) glass substrate with a relatively high thermal conductivity of, for example, 40 · 10 ^-3 Kal./cm·sek.°C and a thickness between 1 and 60 microns), a projection 35 (Eg, a layer of glass or similar material with a circular adjustment bulb or Profileinstellbirne with a low Thermal conductivity of, for example, 2.times.10.sup.- ³ cal./cm.sek.°C), a heating element 36 made of electrically resistant material (eg 1 micron tungsten W, chromium oxide CrO ₂ , tantalum nitride Ta ₂ N, tantalum silicate TaSi or TaSiO, ruthenium oxide RuO ₂ , CrSiO or the like), a protective layer 37 (For example, glass or silicon nitride with a thickness of 5 to 10 microns) and electrodes 48 and 49 (eg with a thickness of 0.7 microns and composed of a metal such as Al or Cu). The protective layer 37 itself can microns from an oxidation-resistant agent SiO ₂ layer having a thickness of about 2 and an abrasion-resistant Ta ₂ O ₅ layer to be composed with a thickness of about 8 microns, or the like.

As a rule, the head also contains a heat sink 31 (with a thickness of at least 1 mm), a temperature sensor 32 and an adhesive layer 33 ,

4 which is not necessarily to scale, is a detailed cross-section of another type of state-of-the-art (eg US 5 635 974 from Kyocera) known thermal head 16 , In this figure represents reference number 34 an electrically insulating, ceramic substrate 34a and a glossy layer 34b composite substrate. Further, the figure shows a heating element 36 , Electrodes 48 and 49 (made of Al, Au, Cu or the like) and a protective layer 37 (eg made of filled glass).

Actually remains the use of thermal heads still fraught with many problems. Certain of these problems will be discussed below.

First, it is in direct thermography, for example EP 0 654 355 (by Agfa-Gevaert), "that it is difficult to obtain a neutral black tone image ... Furthermore, it is difficult to obtain a desired number of gray levels required for a particular application, especially if the image is used in medical diagnostics. " (For the sake of brevity, only the most important passages of the mentioned references and not the whole sections are reproduced here.) According to the same patent EP 0 654 355 discloses a solution comprising "the following steps: preheating each heating element ..., setting a pulse duty ratio ... retrieving, per single pixel, an individual writing time related to the desired density on the image recording element, and the Energizing the heating elements according to the set gradient impulse duty cycle for a time set relative to the retrieved individual writing time. " It is obvious that in some respects it would be advantageous if the means for implementing the EP 0 654 355 proposed solution could be compact.

Secondly, it is also known in photothermography, for example from EP-A 96.200.689.6 (by Agfa-Gevaert NV), that "it is desirable to increase the photosensitivity of radiation-sensitive heat-developable photographic materials ..." in the same invention "A method is provided for enhancing the photosensitivity of a radiation-sensitive heat-developable photographic material, characterized in that the radiation-sensitive heat-developable photographic material is present on one and the same holding or guiding agent during both the informational exposure step and the heating step of the informational exposure step. " Further, as stated in EP-A 96,200,689.6, "it is also desirable to increase the photosensitivity to such an extent that the construction of the photothermographic processing apparatus can be simplified, as described, for example, in DE-A 196 36 253.0 or WO 98/10333 (both in the name of Agfa-Gevaert) ". Again, it would be advantageous in some respects if the means for implementing the EP 0 795 995 proposed solution could be compact.

In the description of the known in the art US 4,763,136 discloses a thermal indicating system having separate translucent resistive elements in combination with a temperature indicating layer.

In the description of the known in the art US 4,763,136 For example, as a display system, a flat thermal head may be used, and other embodiments may be used for thermal printing.

TASKS OF PRESENT INVENTION

task the present invention is to provide a thermal head the one solution for the above mentioned Problem of a compact device offers.

Other objects and advantages of the present invention will become apparent from the following description Bung, the following examples and the figures below.

SHORT PRESENTATION THE PRESENT INVENTION

Be solved the above objects by a thermal head with the in claim 1 defined indicator. Special properties for preferred Embodiments of the invention are in the subclaims described.

SUMMARY THE FIGURES

The The present invention will be described below with reference to FIGS (not necessarily true to scale) associated, the scope of protection according to the invention not restrictive Figures described.

It demonstrate:

1 the basic functions of a direct thermal printer,

2 the basic functions of a thermal printer containing a reducing agent-containing protective tape or donor ribbon or a ribbon containing thermally sublimable consumables;

3 a cross section of a known from the prior art thermal head,

4 a cross section of another known from the current state of the art thermal head,

5 a recording method using a translucent thermal head according to the present invention,

6.1 a cross section of an embodiment of a light-transmitting thermal head according to the invention,

6.2 a cross section of another embodiment of a translucent thermal head according to the invention,

6.3 a top view of an embodiment of a light-transmitting thermal head according to the invention,

7 a top view of a part of a thermal head, which illustrates a plurality of heating elements Hi {H1, H2, H3 ...},

8th a plan view of a portion of a thermal head and some components for reproducing a plurality of pixels Pi {A, B, C ...},

9 a graphic usable according to the invention, in which the light transmission of ITO is plotted against the measuring wavelength,

10 a graphic usable according to the invention, in which the light transmittance of ORGACON-EL is plotted against the measuring wavelength,

11 a graph useful according to the invention, in which the light transmittance, the absorption and the reflectance of ORGACON-EL is plotted against the measurement wavelength.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The The following description mainly comprises six sections, i. (i) terms and definitions in the present patent application, (ii) preferred embodiments a translucent thermal head, (iii) usable according to the invention Heating materials, (iv) use of a thermal head according to the invention, (V) Use of a thermal head according to the invention in combination with a laser and (vi) further fields of use of a thermal head according to the invention.

More about procedures, the a thermal head according to the invention can be found in the pending, filed on the same date and as a reference to this application recorded with Title "IMPROVED METHOD FOR THERMAL RECORDING "(" IMPROVED PROCESS FOR THERMAL Imaging ").

(i) explanation of terms used in the description of the present invention

clarity the meaning of certain specific, in the present description and the claims used terms explained in advance.

Of the (hereinafter referred to by symbol m) term "thermographic Material "(in which it is a thermographic recording material) comprises both a heat-sensitive Image-forming material as a photothermographic imaging material (which is a photosensitive heat developable photographic Material is).

For the purposes of the present invention, a thermographic imaging element Ie is part of a thermographic material m (both elements are denoted by reference numeral 3 designated). Symbolically this results in the following: m ∍ Ie.

In By analogy, a thermographic imaging element comprises Ie is both a (direct or indirect) thermal imaging element as a photothermographic imaging element. In the present Patent application is the term thermographic imaging element Ie mostly abbreviated to the term imaging element.

Under the term "heating material" (hereinafter denoted by the symbol hm) is understood to mean a layer of one Material that is electrically conductive and when exposed to Electricity heat generated.

In In the present patent specification, a heating element is Hi part of the heating material hm. Symbolically this results in the following: hm ∍ Hi.

One Heating element Hi (such as H1, H2, H3 ...), the part of the heating material hm is, is usually a rectangular or square, more suitable by the geometry Electrode shaped part.

In In the present specification, a heating element is also part a heating system, further comprising a power supply unit, a Data acquisition unit, a processor, a switch matrix, lines etc. contains.

A "template" is any hard copy (Printout, hard copy) or test presentation (Softcopy), the information in the form of a picture with varying optical density, translucence or opacity. each Template is composed of several pixels, called pixels. Further, the terms "pixel" and "dot" in the present Patent application regarded as synonyms.

henceforth can the terms "pixel" and "dot" in the present Invention both on an input image (known as a template) as a Output image (softcopy or hardcopy, known for example as an expression) Respectively.

The preparation of both monochrome and color halftone images using a thermal printhead, a heat-sensitive receiver (in so-called single-sheet thermal printing) or a combination of a heat-sensitive donor material and a receiver (acceptor) (in so-called double-sheet thermal printing) and one of the receiver or donor-acceptor combination The conveyor moving along the thermal print head is known and has become a very common technique in many commercially available systems (eg Drystar ^™ from Agfa-Gevaert NV). The thermal head typically consists of a one-dimensional array of heating elements mounted on a ceramic substrate mounted on a heat-dissipating support or cooling body hs. In the next paragraphs, a thermal head according to the present invention and a working method will be described in detail.

(ii) Preferred Embodiments a translucent thermal head according to the invention

• (ii-a) Ein gemeinsames Kennzeichen der verschiedenen Ausführungsformen der vorliegenden Erfindung ist ein lichtdurchlässiger Thermokopf mit einer lichtdurchlässigen leitfähigen Schicht als Heizmaterial hm.

A thermal head TH according to the invention is translucent. The description which follows in the next section is divided into three subsections: (ii-a) a description of general characteristics common to various embodiments of the present invention, (ii-b) a description of some preferred embodiments of the present invention with sectional views, and ( ii-c) a description of the electrodes and the heating elements with top views of a thermal head.

• (ii-a) A common feature of the various embodiments of the present invention is a translucent thermal head having a translucent conductive layer as the heating material hm.

In a first preferred embodiment if the heating material is hm e.g. Indium tin oxide (ITO). In the following follows the description of a method of making a translucent thermal head, although other methods may be useful. An electrically conductive Layer as heating material hm is by atomization, vapor deposition by chemical process, spraying and subsequent pyrolysis, Metallic vaporization and subsequent Oxidation, etc., on a translucent substrate, preferably Glass (e.g., Baltron 255, Balzers). Then you can the full surface coated substrate by spatially structured selective removal of the electrically conductive layer become. For this, e.g. a band attached as a mask and later the ITO layer at non-tape sites using lithographic Techniques are removed.

Of the not taped area of the ITO layer is then e.g. by etching removed from the glass substrate. So for example, a small amount Zinc powder to be etched away Area attached and riddled. Subsequently, a few drops semi-concentrated hydrochloric acid by means of a disposable pipette pipetted onto the zinc powder. The hydrochloric acid is poured from the substrate and any zinc residue by rinsing with removed a few drops of hydrochloric acid. The substrates become dipped in a water-containing cup, rinsed with water and with Wiped dry. Following the etching process The tape is peeled off and the substrate with Acetone, then with ethanol and finally with distilled water cleaned. This cleaning process is repeated until on the surface no traces of glue can be observed anymore.

In a final step, the heating material hm is connected to an electrically conductive layer such as a silver layer (R <1 Ω / □) to form electrodes. The uncovered central area is heating element Hi (see, for example, those discussed below 6.1 - 6.3 ). Now the electrodes are electrically connected to wires and a voltage can be applied. The resistance of this system is, for example, between 5 and 25 Ω / □, for example between about 8 and 10 Ω / □.

• (iib) Die nachstehende Beschreibung einer weiteren bevorzugten Ausführungsform der vorliegenden Erfindung erfolgt unter Verweis auf die Querschnittsfiguren 6.1 und 6.2 und 6.3, die eine Draufsicht von Ausführungsformen eines erfindungsgemäßen lichtdurchlässigen Thermokopfes darstellt.

In one of our experimental examples, the size of the thermal head is 50 mm × 50 mm. Although the number and size (ie, resolution in dpi) of the structure are not limited, in one experiment, a 3 mm x 50 mm ITO structure is used in the center of a substrate.

• (iib) The following description of another preferred embodiment of the present invention will be made with reference to the cross-sectional figures 6.1 and 6.2 and 6.3 showing a plan view of embodiments of a translucent thermal head according to the invention.

From these figures and the following Beschreibug clearly shows that a flat thermal head according to the invention at least one heat sink 31 , Heating elements 39 , Electrodes 48 and 49 and optionally comprises additional layers, wherein at least the heating elements are translucent. In particular, the heating elements 39 Part of a heating material 36 , in particular a translucent heating material.

The 6.1 and 6.2 are two typical embodiments of the present invention. 6.1 illustrates a heat-conducting and translucent heat sink 31 (Eg, glass, flexible glass, polycarbonate or polyacrylonitrile, optionally with a filler), a light-transmitting electrically conductive layer as a heating hm (eg an ITO layer) with translucent heating elements 39 (eg 39a . 39b . 39c ...), electrodes 48 - 49 and preferably a light-transmitting protective layer 37 ,

6.2 shows a heat sink 31 which is thermally conductive, but not necessarily translucent (eg of aluminum), and has a locally open enough area (see reference number 29 ), a translucent electrically conductive layer as heating material hm (eg an ITO layer) with translucent heating elements 39 (eg 39a . 39b . 39c ...), electrodes 48 - 49 , preferably a light-transmitting protective layer 37 and optionally an insulating substrate 34 ,

ever according to the resistance characteristics of the heating material hm is between different cases: (i) Heating material hm with surface conductivity or (ii) mass conductivity fuel hm.

At the Heating medium hm with surface conductivity and non-executive Mass (i) may be the non-conductive side of the heating material hm in direct contact with the heat sink hs be arranged, even if the latter of electrically conductive material (like aluminum) is made.

When heating material hm with conductive mass (ii), the heating material hm may only be in direct contact with the heat sink hs, if the latter is made of a non-electrically conductive material (eg glass, flexible glass, polycarbonate or polyacrylonitrile, optionally with a filler ). It is clear that heating material hm must not be placed in direct contact with heat sink hs, if the latter is made of electrically conductive material (such as aluminum). This is between the heating elements 39 and heat sink 31 to install an additional insulating layer (see eg insulating substrate 34 in 6.2 ). In the case of an aluminum heat sink hs, such an insulating layer may be an oxide layer, usually a thin oxide layer, which is both electrically insulating and sufficiently heat-conducting.

Also regarding the heat sink 31 can be distinguished between different embodiments. In the case of a heat sink hs with electrical insulating properties is thus between the heating elements 39 and heat sink 31 no additional insulating layer needed (this case is eg in 6.1 illustrated). In the case of a heat sink hs without electrical insulating properties (such as aluminum), however, is between the heating elements 39 and heat sink 31 an additional insulating layer is required (this case is eg in 6.2 illustrated).

insulating 34 For example, a ceramic material such as glass or Al ₂ O ₃ (alumina) filled glass having a relatively high thermal conductivity of, for example, 40 × 10 ^-3 cal / cm ³ sec × c (≈ 2 × 10 ^-3 W × m ^-1) · K ^-1 ) and a thickness between 30 and 60 microns included. Other suitable materials for forming such an insulating substrate 34 include (optionally doped) silicon nitride, AlN or a diamond-like thin film layer such as Dylyn ^™ , etc.

Dylyn ^™ is a trademark of Advanced Refractory Technologies Inc., USA, and is available in Europe through Bekaert Dymonics, Belgium. As technical properties, among others, a thickness between 0.01 and 10 μm, a heat resistance up to 400 ° C (or 673 K), a dielectric breakdown strength of more than 10 ⁶ V / cm, a between 10 ¹⁴ and 10 ^-2 Ω · cm controllable electrical resistivity and a thermal conductivity of about 70 W / m · K to call.

From another perspective can be between heating element 39 and heat sink 31 optionally, an additional layer may be applied to reduce potential heat transfer resistance. For example, Fisher Elektronik sells (i) silicone-containing thermal compounds made from silicone oil and inorganic filler (eg metal oxides) and (ii) silicone-free thermal compounds from a synthetic liquid and inorganic filler (eg metal oxides). These materials have interesting properties such as thermal conductivity up to 1 W / mK, dielectric breakdown up to 40 kV / mm, electrical resistivity greater than 10 ¹² Ω · cm, operating temperature range up to + 250 ° C (or 523 K), etc. (see datasheets from Fischer Elektronik & Dau).

It should be noted that in practice, usually the temperature of the insulating substrate 34 rarely exceeding + 100 ° C (or 373 K), usually not exceeding + 70 ° C (or 343 K). The temperature of the heat sink 31 rarely exceeds + 60 ° C (or 333 K).

A more general overview of eight different embodiments (designated I. to VIII.) Of a translucent thermal head according to the invention is summarized schematically in Table 1. In assembling this table, it was assumed that in the case of a surface-conduction heating medium hm, the electrically conductive side in contact with the electrodes (FIG. 48 . 49 ) and thus not in contact with the heat sink hs ( 31 ) was arranged. If a cross' x 'is indicated on a horizontal row' Action ', then no special measures are to be taken for the construction Without cross, x', special attention must be paid to the design of the thermal head (and, for example, an opening 29 or an insulating substrate 34 be provided). Although all embodiments of Table 1 are protected by the present application, for the sake of brevity only two figures (eg 6.1 and 6.2 ) (these figures correspond to Embodiments III and VI).

Table I

(ii-c) Definitions of Electrodes and heating elements

According to a preferred embodiment of the present invention, the above-mentioned optional additional layers contain a protective layer 37 and optionally at least one adhesive layer. In a further preferred embodiment, the protective layer contains 37 Glass or silicon nitride or is composed of an oxidation-resistant SiO ₂ layer and an abrasion-resistant Ta ₂ O ₅ layer.

To a preferred embodiment Further, according to the present invention, a thermal head includes a temperature sensor.

In the thermal head TH according to the invention are the heat sink 31 , the adhesive layer 33 , the insulating substrate 34 and the additional layers (eg 37 ) Translucent at least in the areas of the heating elements.

The illustrated embodiment includes discontinuous areas of heating material hm (see reference numbers 39a . 39b , etc.).

The thermal printhead 16 usually includes an array of individually addressable, electrically resistant heating elements. These individually excitable heating elements arranged side by side 39 for the image-wise heating of the heat-sensitive layer are excited by applying a voltage, wherein the current flowing through the layer generates heat. The heat generated by a heating element is applied to a localized pixel area in contact with the energized element on the imaging element, activating the dye and generating a visible pixel therein.

The 6.1 and 6.2 illustrate a heat sink hs (reference no. 31 ), which by using a translucent material (see 6.1 ) or by leaving a sufficiently open area open (see reference no. 29 in 6.2 ) is made translucent. The 6.1 and 6.2 further show a light-transmitting conductive layer as a heating material 39 (eg an ITO layer) with interrupted heating elements 39a . 39b and 39c , Wires or wires with signal electrodes 48a . 48b . 48c ... and counter electrodes 49a . 49b . 49c ...

Each individual heater H in the linear array can be excited simply by applying a voltage between its respective electrodes. When applying an excitation voltage, which is usually between 12 and 18 V, between the electrodes 48a and 49a becomes a current through the intervening, designated as element H1, rectangular area 39a of the heating material flow. The current flowing through the resistor material hm of heater H1 generates heat energy that heats the pixel region of the imaging member in contact with heater H1, and the image-forming thermographic system undergoes a color change when a threshold temperature is exceeded. The next element H2 in the array may be by applying a voltage between its respective electrodes 48b and 49b be excited. Similarly, the next succeeding element H3 may be by applying a voltage between the electrodes 48c and 49c be excited, ... etc.

Another type of preferred embodiment of a thermal printing head according to the invention 16 comprises a continuous strip of heating material hm and is schematically in the 7 and 8th shown. For the sake of clarity, it should be noted that 7 mainly and in a clear way, the heating elements Hi = {H1, H2, H3 ...} of the fuel hm represents while 8th illustrates the printed pixels Pi = {A, B, C ...} on the print. 8th further illustrates some components of the signal processing system (eg power supply and signal processor 44 and switch matrix 46 ).

In these figures, the thermal head comprises an elongate rectangular substrate 34 of ceramic material, glass or the like, an elongated continuous strip of heating material 36 that extends over the length of the substrate 34 and consists of a film of electrically conductive or non-conductive heating material hm, and a plurality of equidistant toothed electrodes 48 - 49 that make the electrical contact with heating material 36 (the technical term "interlocked" used here means almost the same as interlocked or interpenetrated).

The signal electrodes 48 and the counter electrodes 49 divide the continuous strip of heating material 36 in a serial arrangement of individually addressable heating elements Hi on. When applying an excitation voltage, which is usually between 12 and 18 V, between the electrodes 48a and 49x is a current through the intervening, for example, rectangular, designated as heating element H1 region of the heating material 36 flow. The current flowing through the resistor material of heater H1 generates thermal energy that heats the pixel region of the imaging member in contact with heater H1, which dye reacts in that region and undergoes a color change when the threshold temperature is exceeded. The next element H2 in the array may be by applying a voltage between its respective electrodes 48b and 49x be excited. Similarly, the next succeeding element H3 may be by applying a voltage between the electrodes 48c and 49Y be excited, ... etc.

each single heating element Hi in the linear arrangement can easily through Applying a voltage between its respective electrodes be excited. As a rule, cables or wires are connected to a Matrix switching system connected by the excitation voltage can be easily applied to targeted electrodes. About the Switching system can be any heating element Hi or all heating elements Hi at the same time respond to and be excited by adequate data input signals.

Like it 8th shows is the printhead 16 of the row printing type and includes a laterally extending support member or substrate 34 made of electrically insulating material. substratum 34 has an oblong window extending laterally over the length of one line of the image to be recorded 47 on. The free ends of several signal electrodes 48a . 48b . 48c ... extend in a comb structure in the window into a plurality of counterelectrodes arranged at the same distance from each other as the signal electrodes 49x . 49Y . 49z ... the electrodes 48 and 49 are on substrate 34 attached and each containing a separate electrical contact whose end opposite the free end to one by a printhead signal processor and a power supply unit 44 controlled matrix switching device 46 connected.

The free ends of the electrodes 48 and 49 fit in a comb structure in a corresponding Seg ment of heating element hm. When printing a pixel in area A (also abbreviated as "point A" or "pixel A") between the first two electrodes, the first one becomes the first counter electrode 49x paired signal electrode 48a applied with recording signal Vs. The printhead signal processor 44 controls the matrix switching device 46 so on that on electrode 48a Voltage Vs applied and the counter electrode 39x to ground potential, based on the Vs value. In this case, a current flow path I is created between the two electrodes, which generates heat in the corresponding pixel area zone of the imaging element. For selective printing of a pixel in the next region B, the second, to the first counter electrode 49x paired signal electrode 48b supplied with signal voltage Vs. The printing of one pixel in the next adjacent area C is done by means of the pair of second signal electrodes 48b and the next counter electrode 39y ..., etc. Over the entire length of windows 47 additional electrode pairs are arranged. By using appropriate software and matrix switching techniques, electrode pairs, each associated with a given pixel area zone in the row, can be individually addressed.

In a preferred embodiment of the present invention, the electrodes are 38 to purely individual electrodes 48 . 49 , each a single heating element 39 excite (as in the 6.3 . 7 and 8th illustrated).

In a further preferred embodiment of the present invention, the electrodes are 38 around a common electrode (not shown) and a single electrode (not shown) each exciting a heating element.

It It should be noted that the width of the heating elements according to a preferred embodiment of the present invention less than 80 or even less than 70 microns. One Resolution of 320 dpi or even 360 dpi is achievable.

(iii) Suitable heating materials for use in the present invention

As mentioned in the beginning, is the translucent Heating material hm in a first preferred embodiment e.g. Indium tin oxide (ITO).

It However, there are other suitable metal oxides for use in electrically conductive layers, for example non-stoichiometric and doped oxides of tin, indium, cadmium, zinc and their alloys. Well-known examples of the latter category are u.a. Tin oxide (TO) containing antimony (ATO) or Fluorine (FTO) doped, indium oxide (IO), which is doped with tin (ITO), and indium-doped zinc oxide (IZO). These metal oxides have a high permeability in the visible spectral range and almost metallic conductivity on. Both the electrical and the optical properties These materials can be through Control of deposition conditions and other process steps precise be set.

Some useful translucent heating materials are summarized below:
In ₂ O ₃ , optionally doped with O ₂ , Sn, Ti, Pb or F,
SnO / O ₂ , optionally doped with O ₂ , Sb, F, Cl, Br, I, P, As, In, Th, Te or W,
ZnO, optionally doped with O ₂ , In or Al,
Cd ₂ SnO ₄ or CdSnO ₃ or mixtures thereof (such as cadmium stannate),
Bi ₂ O ₃ , MoO ₃ , TiO ₂ , WO ₂ , RhO ₂ , ReO ₂ , Na _x WO ₃ and Zn ₂ SnO ₄ .

9 is a graph in which the light transmission of an ITO layer is plotted against the usable wavelength according to the invention. reference number 81 is the light transmittance curve of an ITO fuel hm.

The The heating medium hm used in the thermal head according to the invention is translucent due to a translucency of more than 70% in the wavelength range between 350 and 1,200 nm.

Especially Preferably, the heating material hm in the wavelength range between 700 and 1,100 nm a light transmission of more than 80%.

A preferred thermal head TH according to the invention contains heating material hm from the group consisting of In ₂ O ₃ , optionally doped with oxygen, Sn, Ti, Pb or F, SnO / O ₂ optionally substituted with oxygen, Sb, F, Cl, Br , I, P, As, In, Th, Te or W, ZnO optionally doped with oxygen, In or Al, Cd ₂ SnO ₄ , CdSnO ₃ or mixtures thereof (such as cadmium stannate), Bi ₂ O ₃ , MoO ₃ , TiO ₂ , WO ₂ , RhO ₂ , ReO ₂ , Na _x WO ₃ , Zn ₂ SnO ₄ and V2O5.

In a further preferred embodiment According to the present invention, the light-transmissive layer (e.g., ITO layer, i.e. a layer of indium tin oxide) by translucent electrical conductive organic Polymers such as e.g. Polyacetylene, polypyrrole, polyaniline (PANI), polythiophene, e.g. Polydioxylthiophene (PEDT), etc. replaced. The advantage of this Material change is in the higher Flexibility and lower brittleness such layers compared to ITO and thus a prolonged Lifetime of the device.

• (a) ein Polythiophen der Formel:
  
  in der R¹ und R² unabhängig voneinander jeweils ein Wasserstoffatom oder eine C_1-4-Alkylgruppe oder zusammen eine gegebenenfalls substituierte C_1-4-Alkylengruppe oder eine Cycloalkylengruppe, vorzugsweise eine Ethylengruppe, eine gegebenenfalls durch Alkylgruppen substituierte Methylengruppe, eine gegebenenfalls durch C_1-12-Alkylgruppen oder Phenylgruppen substituierte 1,2-Ethylengruppe, eine 1,3-Propylengruppe oder eine 1,2-Cyclohexylengruppe bedeuten,
• (b) eine Polyanionverbindung und
• (c) eine organische Verbindung mit 2 oder mehr OH- und/oder COOH-Gruppen oder Amid- oder Lactamgruppen.

In a further particularly preferred embodiment of the present invention, the light-transmitting electrically conductive layer is produced by applying a mixture comprising the following substances:

• (a) a polythiophene of the formula:
  
  in the R ¹ and R ² independently of one another each represent a hydrogen atom or a C _1-4 alkyl group or together an optionally substituted C _1-4 alkylene group or a cycloalkylene group, preferably an ethylene group, an optionally substituted by alkyl groups methylene group, optionally substituted by C _1-12- alkyl groups or phenyl groups substituted 1,2-ethylene group, a 1,3-propylene group or a 1,2-cyclohexylene group,
• (b) a polyanion compound and
• (c) an organic compound having 2 or more OH and / or COOH groups or amide or lactam groups.

Such electrically conductive Polymers are described in EP-A 686 662 (in the name of Bayer) and in the unpublished European Patent Application No. 99,201,645.1 (in the name of Agfa-Gevaert).

A commercial electrically conductive and translucent Film with a heat-resistant polyester film, the one with an aqueous translucent is coated electrically conductive polymer is known under the name ORGACON (registered trademark of Agfa-Gevaert), e.g. Type ORGACON-EL.

10 is a graph in which the light transmittance of ORGACON-EL is plotted against the usable wavelength according to the invention. reference number 82a is the light transmittance curve of the heating material.

11 is a graph in which the optical transmittance, the absorption and the reflectance of ORGACON-EL are plotted against the usable wavelength according to the invention. reference number 82b is the translucency curve, reference number 83 the absorption curve and reference number 84 the reflection curve of a heating material ORGACON-EL. It should be noted that especially in the range above 350 nm both the absorption and the reflection of the heating material hm are very low.

• (i) Der Widerstand R des Heizmaterials hm ist das Verhältnis der angelegten Spannung zum durch die elektrisch leitende Schicht fließenden Strom.
• (ii) Auf der Basis einer mittleren Stärke der elektrisch leitenden Schicht (z.B. t μm) ist der spezifische elektrische Widerstand ρ (ausgedruckt in Ω·cm) gleich R multipliziert mit einem ersten geometrischen Faktor g1 (der die Geometrie des geprüften Musters berücksichtigt).
• (iii) Die spezifische elektrische Leitfähigkeit σ (ausgedrückt in S/cm) kann durch mathematisches Umkehren des spezifischen elektrischen Widerstands erhalten werden.
• (iv) Der Oberflächenwiderstand SR kann aus dem spezifischen elektrischen Widerstand multipliziert mit einem zweiten geometrischen Faktor g2 (der ebenfalls die Geometrie des geprüften Musters berücksichtigt) berechnet werden: SR = R × g2 (ausgedrückt in Ω/☐).
• (v) Gegebenenfalls kann eine Oberflächenleitfähigkeit σ durch mathematisches Umkehren des Oberflächenwiderstands erhalten werden.

All resistance values in this document are measured according to the following procedure. A pattern of the heating material hm is cut into a strip having, for example, a length of 275 mm and a width of 35 mm. About the width of the strip electrodes are attached at a distance of 100 mm from each other. For example, the electrodes are made of an electrically conductive polymer, ECCOCOAT CC-2, available from Emerson & Cumming Specialty Polymers, or other material that ensures good electrical contacts (eg, Ag). A constant voltage is then applied to the electrodes and the current flowing through the circuit is measured by means of, for example, a pico-ammeter KEITHLEY 485.

• (i) The resistance R of the heating material hm is the ratio of the applied voltage to the current flowing through the electroconductive layer.
• (ii) Based on a mean thickness of the electrically conductive layer (eg, t μm), the specific elec trical resistance ρ (expressed in Ω · cm) equals R multiplied by a first geometric factor g1 (taking into account the geometry of the tested sample).
• (iii) The specific electrical conductivity σ (expressed in S / cm) can be obtained by mathematically reversing the resistivity.
• (iv) The surface resistance SR can be calculated from the resistivity multiplied by a second geometric factor g2 (which also takes into account the geometry of the tested sample): SR = R × g2 (expressed in Ω / □).
• (v) Optionally, a surface conductivity σ can be obtained by mathematically reversing the surface resistance.

In a preferred embodiment In the present invention, the heating material hm has a surface resistance (SR) between 5 and 3,000 Ω / □.

In a further preferred embodiment of the present invention, the heating material hm has a specific electrical resistance ρ between 10 ^-5 Ω · cm and 1 Ω · cm or a specific electrical conductivity σ between 1 and 10 ⁵ S / cm, between 1 and 10 ⁴ S. / cm or even between 1 and 10 ³ S / cm.

A such specific electrical conductivity σ thus varies from semimetallic to almost metallic conductivity.

(iv) Applicability of a thermal head according to the invention

It It will be apparent to those skilled in the art that several thermal heads of the invention are longitudinal (in a so-called adjacent or staggered arrangement) with each other can be coupled to form a wider thermal head.

In a further preferred embodiment In the present invention, a thermal head TH scans in the X direction (the so-called fast scan direction) the heating m of one Side of a print line to the other side (so-called commuting) and thus will get a page wide warming.

Although in the above description line printing heads with one-dimensional matrix discussed also come two-dimensionally arranged Druckkopfmatrizes for use in the present invention.

ever According to production requirements and possibilities, a thermal head according to the invention TH according to one so-called thick film technology (such as lithography and screen printing, where Heating elements with a thickness from e.g. 20 μm obtained) or a so-called thin-film technique (such as vapor deposition or atomization, being heating elements with a strength from e.g. 0.1 μm to be obtained). More details can be found in the collective review "Transparent conductors - a status review "of the authors Chopra, Major and Pandya, in "Electronics and optics - Thin Solid Films ", 102 (1983), pp. 1-46, Publisher Elsevier Sequoia.

Out The description of the present invention is clear, that a thermal head according to the invention TH advantageously, e.g. in thermography and photothermography can be used. Furthermore, the head is also suitable for Use in a variety of machines such as printers, plotters, facsimiles, Copiers, output terminals such as CAD systems, etc.

One type of thermographic material m useful in the present invention comprises on a support a heat-sensitive layer containing an organic silver salt and a reductant optionally also contained in one or more other layers. A cross-sectional view of such a thermographic material m can be found in the co-pending patent application entitled "IMPROVED METHOD FOR THERMAL RECORDING" filed the same day EP 0 692 733 (in the name of Agfa-Gevaert).

It should be noted that such a thermal printhead can be used for uniform heating, eg in thermography. This application provides a method of uniformly heating an imaging member (m), comprising the steps of providing an imaging member (m) and a thermal head (TH) with energizable heating elements (H _i ) and driving each heating element, wherein the imaging member is at a uniform temperature (TO) is received. For a uniform heating is also a non-translucent thermal head, eg in so-called Vor heating or so-called reheating.

A uniform heating by means of a translucent or non-translucent Thermal head TH can also advantageously in an imaging or recording device be applied. Sheets conveyed by a recording device for example then dried before their artwork to the moisture content to reduce, e.g. below 60%. A low moisture content yes, a bow promotion without paper jam and / or promote image quality. Such paper conditioning or dehumidifiers can a thermal head according to the invention include.

Except in imaging devices and imaging method is a uniform heating by means of a translucent or non-translucent Thermal head also for other applications such as electrophotography (e.g. Fixing a powder image), for drying wet-developed photographic materials (such as microfilm, medical prints, printing plates ...), during the warming of inkjet images, etc.

(v) Applicability of a translucent Thermal head in combination with a laser

As mentioned above, can be more detailed information Method comprising a translucent thermal head according to the invention TH, in particular a translucent thermal head in combination using a laser, the still pending, filed on the same date Registration with title "IMPROVED METHOD FOR THERMAL RECORDING "(" IMPROVED PROCESS FOR THERMAL IMAGING ") remove.

A graphic representation of an example of such use can be found in FIG 5 in which a recording method using a translucent thermal head according to the present invention in combination with a laser is illustrated.

Such a method for recording an image on a heat-sensitive imaging element Ie comprises the following steps: providing (for example by means of a rotary drum 15 ) of a thermographic material m (reference number 3 ) with a heat-sensitive imaging element Ie, a light-transmitting thermal head TH (reference number 16 ) with excitable heating elements (Hi) and a beam L (reference number 41 ), Acquisition of input data (see input data block 22 ), Processing (in processing unit 24 ) of the digital image signals, driving heating elements of the thermal head and imagewise scanning exposure of the imaging member by means of the beam, the beam radiating through translucent areas of the thermal head during the imagewise scanning exposure.

The present invention includes several advantages. For the sake of brevity, however, no detailed description will be repeated in this specification. However, it should be noted that an important advantage of a translucent thermal head is that, for example, the density can be controlled via the thermal head; for example, the density can be controlled during imaging on the thermographic material. Because the pixel formation is not through the head 16 is masked, it can easily monitor with a photocell sensor.

(vi) other uses a thermal head according to the invention

The method of the invention can be applied to a variety of printing techniques. This is going on 2 which schematically shows the basic functions of a thermal printer operating with a reducing agent (donor) belt. Because many elements in 2 a similar structure and way of working as that for 1 described structural elements with corresponding reference number, can here on a complete description of 2 be waived.

Reductant belt pressure works with a thermal printhead 16 , which may be a thick film or thin film thermal print head, with the targeted areas of the donor element 2 in contact with a receiving element 1 to be heated. supply roll 13 and take-up roll 14 are powered by a variable speed motor 18 with predetermined tension in the web or band of the donor element 2 driven.

A thermal head TH according to the present invention may also be used in a method characterized by the following steps for recording an image on a thermosensitive imaging member (m): providing a thermographic material with a thermosensitive material An imaging element and providing at least two thermal heads (TH ₁ and TH ₂ ) each with energizable heating elements (Hi), energizing heating elements of the first thermal head to heat the imaging element to a preheating temperature (T ₀ ) lower than the transformation temperature (Tc) of the imaging element and imagewise heating the imaging member by means of the second thermal head with energy corresponding to a gradation (which may also correspond eg to density, color, etc.) of the image to be recorded on the imaging member, at least one of the thermal heads being translucent.

In such an embodiment The application of energy involves two steps: first, a uniform condition and secondly, the warming will be according to the precise final state fine adjusted, with the second step so short and thus so exactly as possible is.

is ie e.g. reach a final temperature of 125 ° C (or 398 K), so would a warm up from ambient temperature to 80 ° C (or 353 K) less favorable be as a warm-up from ambient to 110 ° C (or 383K).

More specifically, embodiments using at least two thermal heads according to the present invention can be found in the pending application filed on the same date and incorporated herein by reference, entitled "IMPROVED METHOD FOR THERMAL RECORDING". In particular, it will open 6 this pending patent application and in particular to the specified and explained in this pending patent application reference numbers 71 . 74 . 91 . 94 and 96 , For the sake of brevity, however, no detailed description will be repeated in this specification.

The While the present invention has been described in terms of preferred embodiments of the invention, however, it should be noted that the present invention is not to these embodiments limited becomes. After the detailed description according to the invention more preferred embodiments might Moreover, it will be clear to the experts in this field that here within the scope as defined in the following claims Numerous modifications are possible with the present invention.

• (i) Der Druckkopf 16 kann eine sich 'waagerecht' erstreckende, die Papierbreite überspannende, jeweils eine Zeile druckende Matrix von Elementen umfassen oder kann eine schmalere Matrix von Elementen umfassen, die sich horizontal nach hinten und nach vorne über das Papier bewegt und dabei Buchstaben seriell druckt.
• (ii) Obgleich in vorstehender Beschreibung Zeilendruckköpfe mit eindimensionaler Matrix erörtert worden sind, kommen auch zweidimensional angeordnete Druckkopfmatrizes zur Verwendung in der vorliegenden Erfindung in Frage.

Some typical modifications include:

• (i) The printhead 16 may comprise a horizontally extending, paper-width-spanning, one-line matrix of elements, or may comprise a narrower array of elements that move horizontally back and forth across the paper, printing letters serially.
• (ii) Although in the foregoing description, one-dimensional array line printheads have been discussed, two-dimensionally arranged printhead matrices are also contemplated for use in the present invention.

thermal imaging can for used the generation of both transparencies and overheads become. Hard copies use recording materials a white one opaque carrier, while in medical diagnostics when working with a viewing device Examination techniques Black-image transparency find widespread application.

A another obvious application of the present invention Color images. For color images, different color separations are appropriate electrical image signals successively over typical corresponding Lookup tables converted to optimal diagnostic to get visual observation of the colored hard copy.

To the detailed description of preferred embodiments according to the invention might It should be clear to the experts in this field that here within of the scope as defined in the following claims numerous modifications possible are.

1

receiving element

2

donor

3

thermographic Material / Thermographic Imaging Element Ie

10

thermal printer

13

supply roll

14

up roll

15

drum

16

Thermal printhead TH

17

hard copy image

18

engine

22

input data

24

processing unit

29

opening

31

Heatsink hs

32

temperature sensor

33

adhesive layer

34

insulating

35

head Start

36

fuel Hm

37

protective layer

39

heating element Hi

41

laser beam

44

Power supply & processor

47

window

46

switching matrix

48

signal electrodes

49

counter electrodes

81

Transmittance curve of heating material ITO

82

Transmittance curve of heating material ORGACON-EL

83

absorption curve of heating material ORGACON-EL

84

reflection curve of heating material ORGACON-EL

Claims (9)

A translucent thermal printhead TH ( 16 ) with a heat sink ( 31 ), Heating elements ( 39 ), which are part of a heating material hm ( 36 ), and electrodes ( 48 . 49 ), characterized in that the heating material hm is translucent due to a light transmittance of more than 70% in the wavelength range between 350 and 1200 nm. Translucent A thermal printing head according to claim 1, characterized in that the Heating material hm due to a light transmission of more than 80% in Wavelength range between 700 and 1,100 nm is translucent. Translucent thermal printing head according to claim 1 and 2, characterized in that the heating material hm from the group consisting of In ₂ O ₃ , optionally doped with oxygen, Sn, Ti, Pb or F st, SnO / O ₂ , optionally with oxygen, Zb, optionally doped with oxygen, In or Al, Cd ₂ SnO ₄ , CdSnO ₃ or mixtures thereof (such as cadmium stannate ₎ ), Bi ₂ O ₃ , MoO ₃ , TiO ₂ , WO ₂ , RhO ₂ , ReO ₂ , Na _x WO ₃ , Zn ₂ SnO ₄ and V2O5. Translucent Thermal printing head according to claim 1 and 2, characterized in that the heating material hm is an electrically conductive polymer. Translucent A thermal printing head according to claim 4, characterized in that the electrically conductive polymer polypyrrole, polyaniline or polythiophene is. A transparent thermal print head according to claim 5, characterized in that the polythiophene has the following formula:

in the R ¹ and R ² independently of one another each represent a hydrogen atom or a C _1-4 alkyl group or together an optionally substituted C _1-4 alkylene group or a cycloalkylene group, preferably an ethylene group, an optionally substituted by alkyl groups methylene group, optionally substituted by C _1-12 alkyl groups or phenyl groups substituted 1,2-ethylene group, a 1,3-propylene group or a 1,2-cyclohexylene group. Translucent Thermal printing head according to one of the preceding claims, characterized in that the heating material hm has a surface resistance (SR) has between 5 and 3,000 Ω / □. A transparent thermal print head according to any one of the preceding claims, characterized in that the heating material hm has a specific electrical resistance ρ between 10 ^-5 Ω · cm and 1 Ω · cm or a specific electrical conductivity σ between 1 S / cm and 10 ⁴ S / cm , Translucent Thermal printing head according to one of the preceding claims, characterized characterized in that the width of the heating elements is less than 70 microns.