A LIQUID INJECTION RECORDING SYSTEM, A LIQUID INJECTION RECORDING HEAD, A BASE PLATE FOR THE RECORDING HEAD, AND A RECORDING APPARATUS HAVING THE LIQUID INJECTION RECORDING HEAD

Abstract: In a liquid injection recording system wherein an electrical signal is input to an electro-thermal conversion element to cause it to generate heat and produce bubbles in liquid and the liquid is injected by the action of the bubbles, a substance whose electrical resistance is varied by phase transition is used for a portion of the electro-thermal conversion element and harmonious recording is effected by the utilization of the phase transition characteristic of the substance.

Description: BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a liquid ejection recording system in which the bubbling of liquid caused by the power supply for heating of an electro-thermal conversion element is utilized to form flying liquid droplets and the liquid droplets are discharged to a recording medium to thereby accomplish recording of information such as characters, and also relates to a liquid ejection recording head, a base plate for the recording head, and a recording apparatus having the liquid ejection recording head. Related Background Art In the liquid ejection recording system of this type utilizing heat energy, as the technique for accomplishing smooth gradation recording over a wider range, there are generally known a technique whereby a heat generation gradient is caused in an electro-thermal conversion element (Japanese Laid-Open Patent Application No. 132258/1980 (U.S. Patent No. 4,339,762)) and a technique which uses a plurality of electro-thermal conversion elements to which signals can be independently input (Japanese Laid-Open Patent Application No. 132259/1980). The former gradation recording system in which a heat generation gradient is caused in an electro-thermal conversion element can provide analog gradation in which the amount of liquid ejected can be continuously freely changed by continuously changing the driving voltage or the drive pulse width. Accordingly, this system has the advantage that it can provide abundant gradation while, on the other hand, it has sometimes suffered from the problem peculiar to the analog system that the amount of liquid ejected is varied under the influence of even a slight change in temperature and other external conditions. In contrast, the latter gradation recording system using a plurality of electro-thermal conversion elements to which signals can be independently input is a digital gradation system and therefore, it is difficult for such system to be affected by external factors such as temperature,etc., but to make the gradation abundant, a number of independent electro-thermal conversion elements must be provided, and this has led to the problem that electrical wiring becomes very complex. SUMMARY OF THE INVENTION In view of the above-noted problems, it is an object of the present invention to provide a liquid ejection recording system which eliminates the complexity of the wiring which poses a problem when digital gradation recording is to be realized. It is another object of the present invention to provide a liquid ejection recording system for ejecting liquid by utilizing thermal energy generated upon application of an electrical signal to an electro-thermal conversion element, characterized in that a substance whose electrical resistance is varied by phase transition is used for at least a portion of said electro-thermal conversion element and gradation recording is effected by the utilization of the phase transition characteristic of said substance. It is still another object of the present invention to provide a liquid ejection recording head provided with a base plate having an electro-thermal conversion element provided with a resistance material provided on a support member and a set of electrodes electrically connected to said resistance material and disposed at an interval, a heat-acting zone including a portion in which heat energy generated by said electro-thermal conversion element acts on liquid, and a discharge port which is a portion which is communicated with said heat-acting zone and through which the liquid is discharged by the action of said heat energy, characterized in that at least a part of said resistance material consists of a substance whose electrical resistance is varied by phase transition. It is yet still another object of the present invention to provide a base plate for a liquid ejection recording head having an electro-thermal conversion element provided with a resistance material provided on a support member and a set of electrodes electrically connected to said resistance material and disposed at an interval, characterized in that at least a part of said resistance material consists of a substance whose electrical resistance is varied by phase transition. It is a further object of the present invention to provide a recording apparatus having a liquid ejection recording head provided with a base plate having an electro-thermal conversion element provided with a resistance material provided on a support member and a set of electrodes electrically connected to said resistance material and disposed at an interval, a heat-acting zone including a portion in which heat energy generated by said electro-thermal conversion element acts on liquid, and a discharge port which is a portion which is communicated with said heat-acting zone and through which the liquid is discharged by the action of said heat energy, and drive means for driving said recording head, characterized in that at least a part of said resistance material consists of a substance whose electrical resistance is varied by phase transition. In the present invention, a substance whose electrical resistance is varied by phase transition is used for at least a part of the electro-thermal conversion element and therefore, the amount of heat generated in the portion which has caused phase transition is varied by the variation in the electrical resistance based on the phase transition and the volume of bubbles generated is varied and thus, the amount of liquid ejected becomes variable, whereby gradation recording by digital gradation abundant in gradation can be accomplisehd without complicating the wiring. BRIEF DESCRIPTION OF THE DRAWINGS Figures 1A and 1B are a plan view and a cross-sectional view, respectively, showing the construction of an embodiment of the present invention. Figure 2 is a graph showing the relation between the variations in time and current in the embodiment of Figures 1A and 1B. Figure 3 is a schematic perspective view for illustrating a preferred embodiment of the liquid ejection recording head of the present invention. Figure 4 is a schematic perspective view for illustrating a recording apparatus having the liquid ejection recording head of the present invention. Figure 5 illustrates a preferred embodiment of a block diagram for driving the liquid ejection recording head of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will hereinafter be described in detail with reference to the drawings. Figures 1A and 1B show a schematic plane view and a schematic cross-sectional view, respectively, of a base plate provided with an electro-thermal conversion element used in a liquid ejection recording head to which the system of the present invention is applied. As shown in Figures 1A and 1B, the electro-thermal conversion element of the present embodiment is one provided by forming a layer 3 of resistance material HfB₂ having a thickness of 0.13 µm on a substrate 2 (a support member) of Si provided with a surface layer 1 of oxide SiO₂ (which is not always necessary) having a thickness of about 5 µm as a heat accumulating layer, by sputtering, thereafter removing a part of the HfB₂ layer 3 by etching, forming a layer 4 of resistance material V₈C₇ having a thickness of 0.13 µm by sputtering and forming A1 layers (electrodes) 5 having a thickness of 0.5 µm by the EB (electron beam) evaporation method, thereafter effecting the patterning by etching, and thereafter forming an insulating layer 6 of SiO₂ having a thickness of 1.9 µm and a protective layer 7 of Ta having a thickness of 0.55 µm by sputtering. Liquid such as ink is directed to a portion designated by 8 on the protective layer 7. The size of the above-mentioned layer of resistance material which generates heat when an electric power is supplied thereto is such that the width is 30 µm and the length (the direction in which an electric current flows) is 140 µm, and the left half layer 3 of resistance material as viewed in Figure 1 is constructed of HfB₂ and the right half layer 4 of resistance material is constructed of V₈C₇ which is one of substances whose electrical resistance is varied by phase transition as will be described later. When a rectangular pulse of heating pulse width 12 µsec., voltage 20V and frequency 1KHz was applied between the electrodes 5 of Figures 1A and 1B and the electric current flowing therethrough was measured, there was obtained a result as shown in Figure 2. It is generally known that V₈C₇ causes phase transition at a temperature of 1123°C and its specific electrical resistance varies from 115 µΩcm (below 1123°C) to 135 µΩcm (above 1123°C). It is because the temperature of the layer 4 of resistance material V₈C₇ exceeded 1123°C due to the temperature rise resulting from heating and the layer 4 of V₈C₇ caused phase transition that in Figure 2, the current value is low in the vicinity of the lapse of 8 µsec. after heating. Also, it is because a finite time is taken for the phase transition that the then variation in the current value is gentle. If the resistance of the Al electrodes 5 is Rc and the resistance of the layer 3 of resistance material HfB₂ is R₁ and the resistance of the layer 4 of resistance material V₈C₇ is R₂, the current I flowing to the resistance materials 3 and 4 when the driving voltage is Vop is given by the following equation (1): Accordingly, if the amounts of heat per unit time generated in the layer 3 of resistance material HfB₂ and the layer 4 of resistance material V₈C₇ are Q₁ and Q₂, respectivley, Q₁ and Q₂ are given by the following equations (2) and (3), respectively: The specific electrical resistance of the layer 3 of resistance material HfB₂ in the present embodiment was 250 µΩcm, and the resistances R₁ and R₂ were R₁ > R₂. Accordingly, from equations (2) and (3) above, Q₁ > Q₂, but the amount of generated heat Q₁ per unit time of the layer 3 of resistance material HfB₂ decreases and the amount of generated heat Q₂ per unit time of the layer 4 of resistance material V₈C₇ increases when the resistance R₂ of the layer 4 of resistance material V₈C₇ rises. That is, with the lapse of 8 µsec. after heating as the boundary, the former amount of generated heat Q₁ decreased and the latter amount of generated heat Q₂ increased. By thus changing the heating pulse width applied between the electrodes 5 by the use of the electro-thermal conversion element as shown in Figure 1, gradation recording which varies smoothly has become possible. That is, it has been confirmed that when the heating pulse width is 6 µsec., only that portion of liquid 8 which is above the layer 3 of resistance material HfB₂ is foamed and when the heating pulse width is 12 µsec., that portion of the liquid which is above both of the layer 3 of resistance material HfB₂ and the layer 4 of resistance material V₈C₇ is foamed. The then amount of discharged liquid is shown in Table 1 below. Pulse width Amount of discharged liquid (10⁻⁶ mm³) 6 µsec. 86 12 µsec. 118 In the above-described embodiment, only one kind of substance has made phase transition, but gradation recording of multi-value could be accomplished by using a plurality of substances which make phase transition (such as, for example, V₆C₅ and Ta). It is not always necessary to arrange a plurality of resistance materials in series, but the resistance materials may be arranged in parallel or in any combination of series and parallel. Also, to cause phase transition, besides the method of increasing temperature, a method of varying any strength-indicative state parameter (such as pressure, magnetic field or chemical potential) can be used. Of course, the present invention is not restricted to the above-described embodiment, but is usable for various modifications as far as they do not depart from the scope of the claims. A preferred example of the liquid ejection recording head used in the present embodiment will now be described with reference to Figure 3. In Figure 3 the reference numeral 2 designates a support member, the reference numerals 3 and 4 denote layers of resistance material, the reference numeral 5 designates electrodes, the reference numeral 6 denotes an insulating layer, the reference numeral 7 designates a protective layer, the reference numeral 9 denotes a top plate, the reference numeral 10 designates discharge ports, and the reference numeral 11 denote a heat-acting zone. As shown, the layers 3 and 4 of resistance material have been provided on the support member 2 and the electrodes have been provided on the layers 3 and 4 of resistance material. The insulating layer 6 as a protective layer for preventing entry of liquid has been provided between the electrodes 5 of the layers 3 and 4 of resistance material and on at least a portion of each electrode 5, and the protective layer 7 has been further provided on the insulating layer 6. The electro-thermal conversion element has at least the layers of resistance material and the electrodes, and the protective layer 7 need not always be provided if the layers of resistance material and/or the electrodes have sufficient corrosion resistance to liquid and have resistance to mechanical damages caused by the cavitation during the extinction of bubbles. Likewise, the insulating layer 6 need not always be provided if the liquid has a necessary resistance value. In Figure 3, walls 12 have been formed on the base plate so as to partition the electro-thermal conversion element provided on the support member 2, and the top plate 11 has been further provided on the walls 12 to form the heat acting zone 11 and the discharge ports 10 communicating with the heat-acting zone 11. (In Figure 3, the surface layer of oxide is not shown.) The heat-acting zone 11 is an area including a portion in which the heat energy generated by the electro-thermal conversion element acts on the liquid (ink) introduced into the recording head, and approximately, it is a liquid path (an area into which the liquid is introdued) corresponding to the upper area between the electrodes connected to the layers of resistance material. The liquid ejection recording head thus constructed is driven in a block diagram as shown, for example, in Figure 5. That is, an image siganl 501 is input to a discharge signal generator 502 and a signal corresponding to the image signal 501 is input to a discharge controller 504. The discharge controller 504 is connected to a power supply 503 and inputs a signal corresponding to the image signal to a recording head 505, thereby effecting recording. In the present invention, the functions of the discharge signal generator 502, the discharge controller 504 and the power supply 503 are generically named drive means. Figure 4 shows a schematic perspective view of an apparatus having the liquid ejection recording head of the present invention (not shown). In Figure 4, the reference numeral 401 designates an apparatus body cover, and the reference numeral 402 denotes an operating panel on which is provided a switch and/or a diplay device connected to various control mechanisms for controlling the apparatus. The liquid ejection recording head of the present invention is covered with the apparatus body cover 401. This recording apparatus is the same as the generally known recording apparatus in that a recording member is disposed in opposed relationship with the orifice of the recording head. The recording head of the present invention disposed in such a recording apparatus could always accomplish recording of high accuracy and high quality even when the recording operation was performed for a long time. As described above, according to the present invention, the electro-thermal conversion element is constructed with a substance which causes phase transition being used for at least a portion thereof, and this leads to the obtainment of the effect that gradation recording can be accomplished by simple wiring. In a liquid ejection recording system for ejecting liquid by utilizing thermal energy generated upon application of an electrical signal to an electro-thermal conversion element, a substance whose electrical resistance is varied by phase transition is used for at least a portion of the electro-thermal conversion element and gradation recording is effected by the utilization of the phase transition characteristic of the substance.

Claims: A liquid ejection recording system for ejecting liquid by utilizing thermal energy generated upon application of an electrical signal to an electro-thermal conversion element, characterized in that a substance whose electrical resistance is varied by phase transition is used for at least a portion of said electro -thermal conversion element and gradation recording is effected by the utilization of the phase transition characteristic of said substance. A liquid ejection recording system according to Claim 1, wherein said phase transition is caused by the heat generated by said electro-thermal conversion element. A liquid ejection recording system according to Claim 1, wherein said substance is at least a part of the resistance material of said electro-thermal conversion element. A liquid ejection recording head provided with a base plate having an electro-thermal conversion element provided with a resistance material provided on a support member and a set of electrodes electrically connected to said resistance material and disposed at an interval, a heat-acting zone including a portion in which heat engergy generated by said electro-thermal conversion element acts on liquid, and a discharge port which is a portion which is communicated with said heat-acting zone and through which the liquid is discharged by the action of said heat energy, characterized in that at least a part of said resistance material consists of a substance whose electrical resistance is varied by phase transition. A liquid ejection recording head according to Claim 4, wherein said substance is a substance in which phase transition occurs due to heat energy. A liquid ejection recording head according to Claim 5, wherein said substance is a substance chosen from among V₈C₇, V₆C₅ and Ta. A liquid ejection recording head according to Claim 4, wherein said support member has a heat accumulating layer. A liquid ejection recording head according to Claim 4, wherein said electro-thermal conversion element has a protective layer on said heat-acting zone side. A liquid ejection recording head according to Claim 4, wherein said substance is connected to one of said electrodes and is connected to the other of said electrodes through a resistance material. A liquid ejection recording head according to Claim 4, wherein said substance and said resistance material are connected to said set of electrodes and said substance is disposed adjacent to said resistance material. A liquid ejection recording head according to Claim 10, wherein said substance and said resistance material are in contact with each other. A base plate for a liquid ejection recording head having an electro-thermal conversion element provided with a resistance material provided on a support member and a set of electrodes electrically connected to said resistance material and disposed at an interval, characterized in that at least a part of said resistance material consists of a substance whose eletrical resistance is varied by phase transition. A base plate according to Claim 12, wherein said substance is a substance in which phase transition occurs due to heat energy. A base plate according to Claim 13, wherein said substance is chosen from among V₈C₇, V₆C₅ and Ta. A recording apparatus having a liquid ejection recording head provided with a base plate having an electro-thermal conversion element provided with a resistance material provided on a support member and a set of electrodes electrically connected to said resistance material and disposed at an interval, a heat-acting zone including a portion in which heat energy generated by said electro-thermal conversion element acts on liquid, and a discharge port which is a portion which is communicated with said heat-acting zone and through which the liquid is discharged by the action of said heat energy, and drive means for driving said recording head, characterized in that at least a part of said resistance material consists of a substance whose electrical resistance is varied by phase transition. A recording apparatus according to Claim 15, wherein said substance is a substance in which phase transition occurs due to heat energy. A recording apparatus according to Claim 16, wherein said substance is a substance chosen from among V₈C₇, V₆C₅ and Ta.

Inventors: ASAI, AKIRA
Applicants: CANON KABUSHIKI KAISHA
Application year: 1987
Main classification: B41J2
IPC codes: B41J2