EP0044756B1 - Heating resistor and thermal printing head using such a heating resistor - Google Patents

Heating resistor and thermal printing head using such a heating resistor Download PDF

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Publication number
EP0044756B1
EP0044756B1 EP81400923A EP81400923A EP0044756B1 EP 0044756 B1 EP0044756 B1 EP 0044756B1 EP 81400923 A EP81400923 A EP 81400923A EP 81400923 A EP81400923 A EP 81400923A EP 0044756 B1 EP0044756 B1 EP 0044756B1
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EP
European Patent Office
Prior art keywords
layer
resistivity
temperature
deposited
resistance
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Expired
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EP81400923A
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German (de)
French (fr)
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EP0044756A2 (en
EP0044756A3 (en
Inventor
Christian Val
Didier Pribat
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Thales SA
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Thomson CSF SA
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    • BPERFORMING OPERATIONS; TRANSPORTING
    • B41PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41JTYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/315Typewriters 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
    • B41J2/32Typewriters 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
    • B41J2/335Structure of thermal heads
    • B41J2/33505Constructional details
    • B41J2/33515Heater layers
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B41PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41JTYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/315Typewriters 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
    • B41J2/32Typewriters 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
    • B41J2/335Structure of thermal heads
    • B41J2/33505Constructional details
    • B41J2/33535Substrates
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B41PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41JTYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/315Typewriters 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
    • B41J2/32Typewriters 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
    • B41J2/335Structure of thermal heads
    • B41J2/3355Structure of thermal heads characterised by materials
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B41PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
    • B41JTYPEWRITERS; SELECTIVE PRINTING MECHANISMS, i.e. MECHANISMS PRINTING OTHERWISE THAN FROM A FORME; CORRECTION OF TYPOGRAPHICAL ERRORS
    • B41J2/00Typewriters or selective printing mechanisms characterised by the printing or marking process for which they are designed
    • B41J2/315Typewriters 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
    • B41J2/32Typewriters 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
    • B41J2/335Structure of thermal heads
    • B41J2/33555Structure of thermal heads characterised by type
    • B41J2/3357Surface type resistors

Definitions

  • the invention relates to a structure of heating elements, of the type of resistors mounted in series in the form of rectilinear plates, more particularly intended for the production of thermal printer heads. It also relates to the circuit for controlling thermal printer heads, which is simplified by the adoption of resistors according to the invention.
  • Such a printer head is described in patent FR-A-2 220 139.
  • Thermal printers are peripheral devices of computer or telecommunications systems, in which the printing of a line of text is obtained by means of a strip of heating resistors: the heat given off by an elementary resistance chemically modifies the paper on which registration is done.
  • Printing a line of characters using a thermal printer head is obtained by repeating several lines of dots at the rate of 8 points per millimeter.
  • a thermal printer head for a standard paper size 21 cm wide, has 1728 resistors, deposited on a glass or ceramic plate. Each resistor has dimensions of the order of 250 microns in width and the resistors are spaced from each other by 250 microns.
  • Thermal printer heads pose two problems: that of controlling a specific resistance and that of heat dissipation.
  • Each programmed unit resistor is controlled by a circuit comprising, among other things, two transistors and a diode.
  • the diodes connected in series with the non-programmed resistors limit the potential across its terminals and prevent them from heating.
  • a thermal printer head therefore requires a circuit comprising as many diodes as there are heating resistors or at best, according to the scheme adopted, a number of diodes equal to half the number of heating resistors, the number of diodes remaining significant since 'so it is at least 863 diodes, for 1728 points.
  • the characteristics of the resistors according to the invention which comprise at least one layer operating as a non-linear resistance with a negative temperature coefficient, with a tilting point, make it possible to eliminate the diodes in the supply circuit of the heating resistors.
  • the heating resistors which are small, have a low calorific capacity, and the heat released is partly absorbed by the substrate whose calorific capacity is much greater.
  • an in-line heating resistance strip is produced on a substrate which is a glass or ceramic plate, the length of which is equal to the width of the printing paper, and the thickness of which is of the order of a few millimeters so as to ensure the rigidity and non-brittleness of the thermal printer module. It is therefore an improvement to the thermal heads provided by the invention according to which the heating resistors comprise a warmer outer layer which dissipates the heat preferentially towards the paper rather than towards the substrate wafer.
  • the invention consists of an electrical heating resistor, deposited on an insulating substrate of glass or ceramic, whose heat capacity is much higher than that of the heating resistor, characterized in that it comprises at least a first layer of a material of relatively constant resistivity as a function of temperature, deposited on the substrate and at least a second surface layer of a material of resistivity varying non-linearly with temperature, with a negative temperature coefficient, this second layer being deposited on the first layer.
  • Fig. 1 shows the electrical diagram of the current supply to the heating resistors in a thermal head. The explanation of its operation will better show the advantages of the invention.
  • the heating resistors numbered from 1 to 5 are connected in series and are supplied by group, from several power transistors, two of which have been represented in 6 and 7.
  • the power transistor 6 supplies the resistors 1, 4 and 5, while the power transistor 7 supplies the resistors 2 and 3.
  • the groups are interdigitated and the choice or the programming of a resistor which must heat is determined by a transistor such as 8, 9 or 10, the base of which is controlled by a shift register.
  • Resistor 1 is controlled by transistor 6 and transistor 8
  • resistor 2 is controlled by transistor 7 and transistor 8
  • the resistor 3 is controlled by the transistor 7 and the transistor 9 ... and so on.
  • diodes 12, 13 and 14 in fig . 1 are diodes 12, 13 and 14 in fig . 1.
  • the heating resistors according to the known art have relatively low values and the simple leakage current through an unprogrammed transistor is sufficient to heat an unprogrammed resistor: the presence of the diodes limits the potential at the terminals of the resistors not programmed.
  • the replacement of conventional heating resistors by heating resistors according to the invention has the advantage of eliminating the diodes, because of the high value that the heating resistors have when cold, a value which decreases very quickly as soon as the surface layer which is consisting of a resistance with a negative temperature coefficient has reached and exceeded its tipping point.
  • Fig. 2 shows the sectional view of a heating resistor according to the known art. This figure provides a better understanding of the problems of heat dissipation.
  • each heating resistor 16 deposited by screen printing, by vacuum evaporation or by any other similar process has a thickness which is best counted in tenths of a millimeter.
  • the resistors according to the known art are deposited by means of one or more passages by accumulation of layers which are all made from the same base material, and therefore all the layers have the same characteristics of resistivity and temperature coefficient.
  • Fig. 3 shows a sectional view of a resistor according to the invention.
  • a first resistance layer 18 which will be conventionally called fixed as opposed to a second layer 19 of non-linearly variable resistance with a negative temperature coefficient.
  • a first resistance layer 18 which will be conventionally called fixed as opposed to a second layer 19 of non-linearly variable resistance with a negative temperature coefficient.
  • the first layer 18 being a fixed resistor
  • the second layer 19 being a variable NTC resistor mounted in parallel with the fixed resistor R.
  • all of the two resistors 18 and 19 which constitute the resistance according to the invention has a high value.
  • the resistor R heats the variable resistor CTN until it reaches its tipping point: from this temperature the CTN considerably decreases in resistance, it becomes conductive and the heat released is largely released by the external surface of the heating resistance, that is to say in contact with the sheet of paper.
  • the first resistance layer 18 can be of the linear type, that is to say that its value practically does not vary with temperature, in comparison with the variation of the CTN. But it is an improvement to the invention to use as a first layer a resistance with positive temperature coefficient PTC: this behaves like a linear resistance up to its tilting temperature, temperature at which its resistance increases considerably and abruptly. This solution, however, requires a fairly good choice of materials from the CTP and the CTN, so that the two changeover temperatures substantially overlap, that is to say that the CTN becomes "conductive" when the CTP ceases to 'be.
  • the invention provides that the layer 19 is deposited on the layer 18 without exceed it in such a way that the layer 19 does not have contact with the substrate 15.
  • Fig. 4 represents the resistance characteristics as a function of the temperature of the resistors with a non-linear negative temperature coefficient.
  • the heating resistors according to the invention therefore have the advantage of having a high value at ordinary temperature and then, when they have been programmed and the underlying resistance layer has heated the variable resistance layer, they do not have more than a low resistance value, which allows on the one hand to remove diodes in the supply circuit since the other resistors, not programmed, have high values, and on the other hand to dissipate the heat mainly towards paper.
  • An improvement to the invention consists in permanently programming a low current through all of the heating resistors so as to maintain them at a constant temperature apart from any programming which is slightly lower than the switching temperature.
  • Fig. 5 shows an improvement made to the structure of the heating resistors according to the invention.
  • the description of the invention, in fig. 3, was based on the simplest case where a variable resistivity layer 19 is deposited on a single layer with constant resistivity 18. However, it is an improvement to produce a variable resistivity layer 19 on a plurality of layers with constant resistivity, two of which have been represented at 18 and at 20 in FIG. 5.
  • variable resistivity layer 19 on a support composed of a plurality of layers from 1 to n, the resistivity of each layer decreasing from layer 1 to layer n.
  • each layer is deposited so that only the first layer touches the substrate 15 of the thermal printer head, so as to focus the heat given off in each layer, heat which is greater in one layer than in the previous one, towards the external surface of the thermal resistance, which means that the external surface is the warmest and which modifies the paper used in the thermal printer.

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Description

L'invention concerne une structure d'éléments chauffants, du type des résistances montées en série sous forme de plaquettes rectilignes, plus particulièrement destinées à la réalisation de têtes d'imprimantes thermiques. Elle concerne également le circuit de commande des têtes d'imprimantes thermiques, lequel est simplifié par l'adoption des résistances selon l'invention.The invention relates to a structure of heating elements, of the type of resistors mounted in series in the form of rectilinear plates, more particularly intended for the production of thermal printer heads. It also relates to the circuit for controlling thermal printer heads, which is simplified by the adoption of resistors according to the invention.

Une telle tête imprimante est décrité dans le brevet FR-A-2 220 139.Such a printer head is described in patent FR-A-2 220 139.

Les imprimantes thermiques sont des dispositifs pérphériques de systèmes informatiques ou de télécommunications, dans lesquels l'impression d'une ligne de texte est obtenue au moyen d'une barrette de résistances chauffantes: la chaleur dégagée par une résistance élémentaire modifie chimiquement le papier sur lequel se fait l'inscription. L'impression d'une ligne de caractères au moyen d'une tête d'imprimante thermique est obtenue par la répétition de plusieurs lignes de points à raison de 8 points par millimètre. Une tête d'imprimante thermique, pour un format de papier normalisé 21 cm de large, comporte 1728 résistances, déposées sur une plaquette de verre ou de céramique. Chaque résistance a des dimensions de l'ordre de 250 microns de largeur et les résistances sont éloignées entre elles de 250 microns.Thermal printers are peripheral devices of computer or telecommunications systems, in which the printing of a line of text is obtained by means of a strip of heating resistors: the heat given off by an elementary resistance chemically modifies the paper on which registration is done. Printing a line of characters using a thermal printer head is obtained by repeating several lines of dots at the rate of 8 points per millimeter. A thermal printer head, for a standard paper size 21 cm wide, has 1728 resistors, deposited on a glass or ceramic plate. Each resistor has dimensions of the order of 250 microns in width and the resistors are spaced from each other by 250 microns.

Les têtes d'imprimantes thermiques posent deux problèmes: celui de la commande d'une résistance déterminée et celui de la dissipation de chaleur.Thermal printer heads pose two problems: that of controlling a specific resistance and that of heat dissipation.

Chaque résistance unitaire programmée est commandée par un circuit comprenant, entre autres, deux transistors et une diode. Les diodes montées en série avec les résistances non programmées limitent le potentiel aux bornes de celle-ci et les empêchent de chauffeur. Une tête imprimante thermique nécessite donc un circuit comportant autant de diodes qu'il y a de résistances chauffantes ou au mieux, selon le schéma adopté, un nombre de diodes égal à la moitié du nombre de résistances chauffantes, le nombre de diodes restant important puisqu'il est donc d'au moins 863 diodes, pour 1728 points.Each programmed unit resistor is controlled by a circuit comprising, among other things, two transistors and a diode. The diodes connected in series with the non-programmed resistors limit the potential across its terminals and prevent them from heating. A thermal printer head therefore requires a circuit comprising as many diodes as there are heating resistors or at best, according to the scheme adopted, a number of diodes equal to half the number of heating resistors, the number of diodes remaining significant since 'so it is at least 863 diodes, for 1728 points.

Les caractéristiques des résistances selon l'invention qui comportent au moins une couche fonctionnant en résistance non linéaire à coefficient de température négatif, avec un point de basculement, permettent de supprimer les diodes dans le circuit d'alimentation des résistances chauffantes.The characteristics of the resistors according to the invention which comprise at least one layer operating as a non-linear resistance with a negative temperature coefficient, with a tilting point, make it possible to eliminate the diodes in the supply circuit of the heating resistors.

Par ailleurs, les résistances chauffantes, qui sont de petites dimensions, ont une faible capacité calorifique, et la chaleur dégagée est en partie absorbée par le substrat dont la capacité calorifique est beaucoup plus grande.Furthermore, the heating resistors, which are small, have a low calorific capacity, and the heat released is partly absorbed by the substrate whose calorific capacity is much greater.

En effet, une barrette de résistance chauffantes en ligne est réalisée sur un substrat qui est une plaquette de verre ou de céramique, dont la longueur est égale à la largeur de papier d'impression, et dont l'épaisseur est de l'ordre de quelques millimètres de façon à assurer la rigidité et la non-fragilité de la barrette d'imprimante thermique. C'est donc un perfectionnement aux têtes thermiques qu'apporte l'invention selon laquelle les résistances chauffantes comportent une couche externe plus chaude qui dissipe la chaleur préférentiellement vers le papier plutôt que vers la plaquette de substrat.Indeed, an in-line heating resistance strip is produced on a substrate which is a glass or ceramic plate, the length of which is equal to the width of the printing paper, and the thickness of which is of the order of a few millimeters so as to ensure the rigidity and non-brittleness of the thermal printer module. It is therefore an improvement to the thermal heads provided by the invention according to which the heating resistors comprise a warmer outer layer which dissipates the heat preferentially towards the paper rather than towards the substrate wafer.

De façon plus précise, l'invention consiste en une résistance électrique chauffante, déposée sur un substrat isolant en verre ou céramique, dont la capacité calorifique est très supérieure à celle de la résistance chauffante, caractérisé en ce qu'elle comporte au moins une première couche d'un matériau de résistivité relativement constante en fonction de la température, déposée sur le substrat et au moins une seconde couche superficielle d'un matériau de résistivité variable de façon non-linéaire avec le température, à coefficient de température négatif, cette seconde couche étant déposée sur la première couche.More specifically, the invention consists of an electrical heating resistor, deposited on an insulating substrate of glass or ceramic, whose heat capacity is much higher than that of the heating resistor, characterized in that it comprises at least a first layer of a material of relatively constant resistivity as a function of temperature, deposited on the substrate and at least a second surface layer of a material of resistivity varying non-linearly with temperature, with a negative temperature coefficient, this second layer being deposited on the first layer.

L'invention sera mieux comprise par les explications qui suivent, lesquelles décrivent un exemple d'application d'une tête imprimante thermique, et s'appuient sur les figures suivantes, qui représentent:

  • - fig. 1 schéma électrique de l'alimentation des résistances d'une tête d'imprimante thermique.
  • - fig. 2 vue en coupe d'une résistance chauffante, montrant la dissipation thermique.
  • - fig. 3 vue en coupe d'une résistance chauffante selon l'invention.
  • - fig. 4 courbe des caractéristiques de résistance en fonction de la température d'une résistance à coefficient de température négatif.
  • - fig. 5 vue en coupe d'une résistance selon l'invention, selon un perfectionnement.
The invention will be better understood by the explanations which follow, which describe an example of application of a thermal printer head, and are based on the following figures, which represent:
  • - fig. 1 electrical diagram of the power supply to the resistors of a thermal printer head.
  • - fig. 2 sectional view of a heating resistor, showing the heat dissipation.
  • - fig. 3 sectional view of a heating resistor according to the invention.
  • - fig. 4 curve of the resistance characteristics as a function of the temperature of a resistance with a negative temperature coefficient.
  • - fig. 5 sectional view of a resistor according to the invention, according to an improvement.

La fig. 1 représente le schéma électrique de l'alimentation en courant des résistances chauffantes dans une tête thermique. De l'explication de son fonctionnement ressortiront mieux les avantages de l'invention.Fig. 1 shows the electrical diagram of the current supply to the heating resistors in a thermal head. The explanation of its operation will better show the advantages of the invention.

Etant donné le grand nombre de résistances chauffantes dans une tête d'imprimante thermique, 863 ou 1728 résistances selon le schéma adopté pour un format de papier standard, seule une partie de la tête thermique est schématisée fig. 1.Given the large number of heating resistors in a thermal printer head, 863 or 1728 resistors according to the scheme adopted for a standard paper size, only part of the thermal head is shown diagrammatically. 1.

Les résistances chauffantes, numérotées de 1 à 5 sont montées en série et sont alimentées par groupe, à partir de plusieurs transistors de puissance dont deux ont été représentés en 6 et 7. Le transistor de puissance 6 alimente les résistances 1, 4 et 5, tandis que le transistor de puissance 7 alimente les résistances 2 et 3. Les groupes sont interdigités et le choix ou la programmation d'une résistance qui doit chauffer est déterminé oar un transistor tel que 8, 9 ou 10, dont la base est commandée par un registre à décalage. La résistance 1 est commandée par le transistor 6 et le transistor 8, la résistance 2 est commandée par le transistor 7 et le transistor 8, la résistance 3 est commandée par le transistor 7 et le transistor 9... et ainsi de suite.The heating resistors, numbered from 1 to 5 are connected in series and are supplied by group, from several power transistors, two of which have been represented in 6 and 7. The power transistor 6 supplies the resistors 1, 4 and 5, while the power transistor 7 supplies the resistors 2 and 3. The groups are interdigitated and the choice or the programming of a resistor which must heat is determined by a transistor such as 8, 9 or 10, the base of which is controlled by a shift register. Resistor 1 is controlled by transistor 6 and transistor 8, resistor 2 is controlled by transistor 7 and transistor 8, the resistor 3 is controlled by the transistor 7 and the transistor 9 ... and so on.

De façon à éviter que le courant envoyé dans une résistance ne passe à travers d'autres résistances, il est nécessaire de monter des diodes en série avec les transistors de puissance 6 et 7: ce sont les diodes 12, 13 et 14 sur la fig. 1. En effet, les résistances chauffantes selon l'art connu ont des valeurs relativement faibles et le simple sou- rant de fuite à travers un transistor non programmé suffit à chauffer une résistance non programmée: la présence des diodes limite le potentiel aux bornes des résistances non programmées.In order to prevent the current sent into a resistor from passing through other resistors, it is necessary to mount diodes in series with power transistors 6 and 7: these are diodes 12, 13 and 14 in fig . 1. In fact, the heating resistors according to the known art have relatively low values and the simple leakage current through an unprogrammed transistor is sufficient to heat an unprogrammed resistor: the presence of the diodes limits the potential at the terminals of the resistors not programmed.

Bien que le schéma de la fig. 1 ne soit que très partiel par rapport au schéma complet d'une tête d'imprimante thermique, il ressort que le montage électrique nécessite le montage, entre autres, d'un grand nombre de diodes qui sont implantées sur des circuits relativement complexes par le grand nombre de conducteurs qu'ils nécessitent ainsi que le grand nombre de soudures, ce qui représent un inconvénient pour le montage industriel d'une tête d'imprimante thermique.Although the diagram in fig. 1 is only very partial compared to the complete diagram of a thermal printer head, it appears that the electrical mounting requires the mounting, inter alia, of a large number of diodes which are implanted on relatively complex circuits by the large number of conductors they require as well as the large number of welds, which represents a disadvantage for the industrial assembly of a thermal printer head.

Le remplacement des résistances chauffantes conventionnelles par des résistances chauffantes selon l'invention présente l'avantage de supprimer les diodes, en raison de la valeur élevée qu'ont à froid les résistances chauffantes, valeur qui diminue très rapidement dès que la couche superficielle qui est constituée par une résistance à coefficient de température négatif a atteint et dépassé son point de basculement.The replacement of conventional heating resistors by heating resistors according to the invention has the advantage of eliminating the diodes, because of the high value that the heating resistors have when cold, a value which decreases very quickly as soon as the surface layer which is consisting of a resistance with a negative temperature coefficient has reached and exceeded its tipping point.

La fig. 2 représente la vue en coupe d'une résistance chauffante selon l'art connu. Cette figure permet de mieux appréhender les problèmes de dissipation de la chaleur.Fig. 2 shows the sectional view of a heating resistor according to the known art. This figure provides a better understanding of the problems of heat dissipation.

Sur un substrat 15, en verre ou en céramique, est déposée une résistance chauffante et la feuille de papier 17 défile au contact de la résistance chauffante. Les échelles relatives de la fig. 2 ont été adoptées de façon à permettre de mieux voir la figure, et, en fait, pour une épaisseur du substrat 15 de l'ordre de 1 à 5 mm environ, chaque résistance chauffante 16 désposée par sérigraphie, par évaporation sous vide ou par tout autre procédé analogue, a une épaisseur qui se compte au mieux en dizièmes de millimètre. En outre, les résistances selon l'art connu sont déposée au moyen d'un ou plusieurs passages par accumulation de couches qui sont toutes réalisées à partir du même matériau de base, et par conséquent toutes les couches ont les mêmes caractéristiques de résistivité et de coefficient de température.On a substrate 15, glass or ceramic, is deposited a heating resistor and the sheet of paper 17 scrolls in contact with the heating resistor. The relative scales of fig. 2 have been adopted so as to allow a better view of the figure, and, in fact, for a thickness of the substrate 15 of the order of approximately 1 to 5 mm, each heating resistor 16 deposited by screen printing, by vacuum evaporation or by any other similar process has a thickness which is best counted in tenths of a millimeter. In addition, the resistors according to the known art are deposited by means of one or more passages by accumulation of layers which are all made from the same base material, and therefore all the layers have the same characteristics of resistivity and temperature coefficient.

Lorsque une résistance chauffante telle que 16 est programmée, la chaleur qu'elle dégage est symbolisée sur la fig. 2 au moyen de flèches qui représentent une quantité »Q« de chaleur qui se dissipe vers le substrat et d'autres flèches qui représentent une quantité de chaleur »q« qui se dissipe vers la feuille de papier. Les capacités calorifiques en présence du substrat 15 épais, de la résistance 16 relativement fine, et de la feuille de papier 17 qui en outre défile devant la résistance font qu'une bonne partie de l'énergie mise en jeu est en fait dissipée vers le substrat, ce qui n'est pas le but recherché.When a heating resistor such as 16 is programmed, the heat it gives off is symbolized in FIG. 2 by means of arrows which represent an amount »Q« of heat which dissipates towards the substrate and other arrows which represent an amount of heat »q« which dissipates towards the sheet of paper. The heat capacities in the presence of the thick substrate 15, of the relatively thin resistor 16, and of the sheet of paper 17 which, moreover, passes past the resistor, mean that a good part of the energy involved is in fact dissipated towards the substrate, which is not the goal.

Le remplacement d'une telle résistance conventionnelle par une résistance selon l'invention, outre le précédent avantage décrit à l'occasion de la fig. 1 permet de dissiper préférentiellement la chaleur vers la feuille de papier, c'est à dire que d'adoption de résistances selon l'invention permet en fait de simplifier toute la partie électronique de commande puisque l'énergie requise est moindre et que les composants tels que les transistors doivent dissiper moins d'énergie.The replacement of such a conventional resistance with a resistance according to the invention, in addition to the previous advantage described on the occasion of FIG. 1 makes it possible to dissipate the heat preferentially towards the sheet of paper, that is to say that by adopting resistors according to the invention in fact makes it possible to simplify the whole electronic control part since the required energy is less and that the components such as transistors must dissipate less energy.

La fig. 3 représente une vue en coupe d'une résistance selon l'invention.Fig. 3 shows a sectional view of a resistor according to the invention.

Sur une plaquette de substrat 15 sont déposées, par tout procédé conforme à ce que sait faire l'homme de l'art, au moins une première couche de résistance 18 que l'in appellera conventionnellement fixe par opposition à une seconde couche 19 d'une résistance variable de façon non linéaire à coefficient de température négatif. Sur le côté de la fig. 3 est symbolisé le schéma électrique des deux résistances 18 et 19, la première couche 18 étant une résistance fixe et la seconde couche 19 étant une résistance CTN variable montée en parallèle avec la résistance fixe R. A la température ordinaire, l'ensemble des deux résistances 18 et 19 qui constituent la résistance selon l'invention a une valeur élevée. Lorsqu'un courant est adressé par l'intermédiaire des transistors de commande à travers cette résistance chauffante composée, la résistance R échauffe la résistance variable CTN jusqu'à ce que celle-ci atteigne son point de basculement: à partir de cette température la CTN diminue considérablement en résistance, c'est elle qui devient conductrice et la chaleur dégagée est en grande partie dégagée par la surface externe de la résistance chauffante, c'est à dire au contact de la feuille de papier.On a wafer of substrate 15 are deposited, by any process in accordance with what a person skilled in the art can do, at least a first resistance layer 18 which will be conventionally called fixed as opposed to a second layer 19 of non-linearly variable resistance with a negative temperature coefficient. On the side of fig. 3 is symbolized by the electrical diagram of the two resistors 18 and 19, the first layer 18 being a fixed resistor and the second layer 19 being a variable NTC resistor mounted in parallel with the fixed resistor R. At ordinary temperature, all of the two resistors 18 and 19 which constitute the resistance according to the invention has a high value. When a current is addressed via the control transistors through this compound heating resistor, the resistor R heats the variable resistor CTN until it reaches its tipping point: from this temperature the CTN considerably decreases in resistance, it becomes conductive and the heat released is largely released by the external surface of the heating resistance, that is to say in contact with the sheet of paper.

La première couche de résistance 18 peut être du type linéaire, c'est à dire que sa valeur ne varie pratiquement pas avec la température, en comparaison avec la variation de la CTN. Mais c'est un perfectionnement à l'invention que d'utiliser comme première couche une résistance à coefficient de température positif CTP: celle-ci se comporte comme une résistance linéaire jusqu'à sa température de basculement, température à laquelle sa résistance augmente considérablement et de façon abrupte. Cette solution nécessite toutefois un assez bon choix des matériaux de la CTP et de la CTN, de façon à ce que les deux températures de basculement se recouvrent sensiblement, c'est à dire que la CTN devienne »conductrice« lorsque la CTP cesse de l'être.The first resistance layer 18 can be of the linear type, that is to say that its value practically does not vary with temperature, in comparison with the variation of the CTN. But it is an improvement to the invention to use as a first layer a resistance with positive temperature coefficient PTC: this behaves like a linear resistance up to its tilting temperature, temperature at which its resistance increases considerably and abruptly. This solution, however, requires a fairly good choice of materials from the CTP and the CTN, so that the two changeover temperatures substantially overlap, that is to say that the CTN becomes "conductive" when the CTP ceases to 'be.

Pour simplifier la figure et l'exposé, on n'a représenté que le cas limite de l'invention lorsque une seule couche de résistance fixe 18 est déposée sur le substrat. Un cas plus général qui sera exposé ultérieurement prévoit de déposer successivement plusieurs couches de résistances fixes.To simplify the figure and the description, only the limiting case of the invention has been shown when a single layer of fixed resistance 18 is deposited on the substrate. A more general case which will be explained later plans to file suc several layers of fixed resistances.

De façon à éviter qu'une partie de la chaleur dégagée par la CTN 19, lorsque celle-ci a dépassé son point de basculement, ne soit communiquée au substrat 16, l'invention prévoit que la couche 19 est déposée sur la couche 18 sans la dépasser de telle façon que la couche 19 n'ait pas de contact avec le substrat 15.In order to prevent part of the heat given off by the CTN 19, when the latter has passed its tipping point, from being communicated to the substrate 16, the invention provides that the layer 19 is deposited on the layer 18 without exceed it in such a way that the layer 19 does not have contact with the substrate 15.

La fig. 4 représente les caractéristiques de résistance en fonction de la température des résistances à coefficient de température négatif non linéaire.Fig. 4 represents the resistance characteristics as a function of the temperature of the resistors with a non-linear negative temperature coefficient.

Les températures étant données en abscisse, les résistances sont représentées en ordonnée. Lorsqu'une résistance CTN s'échauffe, sa résistance diminue peu à peu jusqu'au moment où une température dite de basculement Tb est atteinte. Dans une faible zone de température entourant la température de basculement Tb, c'est à dire pour plus ou moins 3 à 5° en moyenne, la résistance de la CTN diminue considérablement et l'on sait actuellement réaliser des CTN dont la résistance est affectée de part et d'autre de la température de basculement d'une coefficient dépassant 103 et atteignant 104 à 105. C'est ainsi que l'on sait réaliser des thermistances qui pour une valeur initiale de 2.104 à 105 ohms à la température ordinaire ne font plus que de 2 à 5 ohms à 80° C.The temperatures being given on the abscissa, the resistances are represented on the ordinate. When a CTN resistor heats up, its resistance gradually decreases until a so-called tilting temperature T b is reached. In a low temperature zone surrounding the tilting temperature T b , that is to say more or less 3 to 5 ° on average, the resistance of the CTN decreases considerably and it is currently known to produce CTNs whose resistance is affected on either side of the changeover temperature by a coefficient exceeding 10 3 and reaching 10 4 to 10 5 . This is how we know how to make thermistors which for an initial value of 2.10 4 to 10 5 ohms at ordinary temperature do no more than 2 to 5 ohms at 80 ° C.

Les résistances chauffantes selon l'invention présentent donc l'avantage d'avoir une valeur élevée à la température ordinaire puis, lorsqu'elles ont été programmées et que la couche de résistance sous-jacente a échauffé la couche de résistance variable, elles n'ont plus qu'une faible valeur de résistance, ce qui permet d'une part de supprimer des diodes dans le circuit d'alimentation puisque les autres résistances, non programmées, ont des valeurs élevées, et d'autre part de ne dissiper la chaleur qu'en direction du papier principalement.The heating resistors according to the invention therefore have the advantage of having a high value at ordinary temperature and then, when they have been programmed and the underlying resistance layer has heated the variable resistance layer, they do not have more than a low resistance value, which allows on the one hand to remove diodes in the supply circuit since the other resistors, not programmed, have high values, and on the other hand to dissipate the heat mainly towards paper.

Un perfectionnement à l'invention consiste à programmer en permanence un faible courant à travers l'ensemble des résistances chauffantes de façon à les maintenir à une température constante en dehors de toute programmation qui soit légèrement inférieure à la température des basculement. Ainsi, lorsqu'une résistance doit être programmée pour inscrire un point sur la feuille de papier il suffit d'un faible courant à travers le circuit des transistors de commande pour faire basculer la couche superficielle à coefficient de température négatif, ce qui augmente la vitesse de réponse de la tête d'imprimante thermique et permet de diminuer la puissance nécessaire dissipée à travers les transistors de commande.An improvement to the invention consists in permanently programming a low current through all of the heating resistors so as to maintain them at a constant temperature apart from any programming which is slightly lower than the switching temperature. Thus, when a resistor must be programmed to write a point on the sheet of paper, it only takes a small current through the circuit of the control transistors to switch the surface layer with negative temperature coefficient, which increases the speed. response of the thermal printer head and reduces the necessary power dissipated through the control transistors.

La fig. 5 représente un perfectionnement apporté à la structure des résistances chauffantes selon l'invention. L'exposé de l'invention, en fig. 3, s'appuyait sur le cas le plus simple où une couche à résistivité variable 19 est déposée sur une seule couche à résistivité constante 18. Cependant, c'est un progrès que de réaliser une couche à résistivité variable 19 sur une pluralité de couches à résistivité constante dont deux ont été représentées en 18 et en 20 sur la fig. 5.Fig. 5 shows an improvement made to the structure of the heating resistors according to the invention. The description of the invention, in fig. 3, was based on the simplest case where a variable resistivity layer 19 is deposited on a single layer with constant resistivity 18. However, it is an improvement to produce a variable resistivity layer 19 on a plurality of layers with constant resistivity, two of which have been represented at 18 and at 20 in FIG. 5.

Ainsi selon ce perfectionnement à l'invention, il est avantageux de déposer la couche à résistivité variable 19 sur un support composé par une pluralité de couches de 1 à n, la résistivité de chaque couche diminuant de la couche 1 vers la couche n. En outre, chaque couche est déposée de telle façon que seule la première couche touche le substrat 15 de tête d'imprimante thermique, de façon à focaliser la chaleur dégagée dans chaque couche, chaleur qui est plus importante dans une couche que dans la précédente, vers la surface externe de la résistance thermique, ce qui fait que c'est la surface externe qui est la plus chau et qui modifie le papier utilisé dans l'imprimante thermique.Thus according to this improvement to the invention, it is advantageous to deposit the variable resistivity layer 19 on a support composed of a plurality of layers from 1 to n, the resistivity of each layer decreasing from layer 1 to layer n. In addition, each layer is deposited so that only the first layer touches the substrate 15 of the thermal printer head, so as to focus the heat given off in each layer, heat which is greater in one layer than in the previous one, towards the external surface of the thermal resistance, which means that the external surface is the warmest and which modifies the paper used in the thermal printer.

Claims (7)

1. Electrical heating resistance, deposited on an insulating substrate (15) made of glass or ceramic, the thermal capacity of which is much higher than that of the heating resistance, characterized in that it comprises at least a fist layer (15) of material with a resistivity relatively constant in function of the temperature, deposited on the substrate (15) and at least a second superficial layer (19) of a material with a resistivity variable in a non-linear manner with temperature, and showing a negative temperature coefficient (NTC), this second layer (19) being deposited on the first layer.
2. Electrical heating resistance according to claim 1, characterized in that its resistance, raised to ordinary temperature (20°C), becomes weak once the constant resistivity layer (18), passed through by a current, bring the variable resistivity layer (19) to the temperature of sudden variation of its resistivity, called tipping temperature of the NTC.
3. Electrical heating resistance according to claim 2, characterized in that, once the variable resistivity layer (19) has reached its tipping temperature, the calorific emission is localized in the superficial layer (19).
4. Electrical heating resistance according to claim 1, characterized in that the superficial layer (19), of variable resistivity, is maintained at a temperature close to and slightly below its tipping temperature, by application of a permanent current passing through the subjacent resistive layer.
5. Electrical heating resistance according to claim 1, characterized in that the superificial layer (19), with a variable resistivity, is deposited on a plurality of layers (18, 20) with a constant resistivity, the resistivity of these layers ranging in decreasing order from, that (15) which is deposited on the substrate (15) to that (20) which is underlying the superificial layer (19).
6. Thermal printing head, comprising at least one strip of heating resistances in line, characterized in that it comprises resistances according to any one of claims 1 to 5.
7. Thermal printing head according to claim 6, comprising heating resistances mounted in series (.1 to 5) supplied by power transistors (6, 7) and controlled by transistors (8, 9, 10) each of which authorizes the passage of the current through a determined resistance, characterized in that the heating resistances are connected by direct connections to the power transistors and to the control transistors.
EP81400923A 1980-06-24 1981-06-11 Heating resistor and thermal printing head using such a heating resistor Expired EP0044756B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR8013967A FR2485796A1 (en) 1980-06-24 1980-06-24 HEATING ELECTRIC RESISTANCE AND THERMAL PRINTER HEAD COMPRISING SUCH HEATING RESISTORS
FR8013967 1980-06-24

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EP0044756A2 EP0044756A2 (en) 1982-01-27
EP0044756A3 EP0044756A3 (en) 1982-02-10
EP0044756B1 true EP0044756B1 (en) 1984-08-29

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DE3165766D1 (en) 1984-10-04
US4413170A (en) 1983-11-01
FR2485796B1 (en) 1983-07-22
EP0044756A2 (en) 1982-01-27
FR2485796A1 (en) 1981-12-31
EP0044756A3 (en) 1982-02-10

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