Liquid jet recording head

Abstract: A liquid jet recording head includes a plurality of ejection outlets through which a droplet of liquid is ejected by thermal energy; a plurality of liquid passages communicating with the ejection outlets to supply the liquid; a plurality of supply inlet for supplying the liquid to the passages; a plurality of electro-thermal transducers provided for the respective ejection outlets to produce the thermal energy; wherein each of said electro-thermal transducers has a heating surface for heating the liquid on the bottom of said passage, characterized in that a width of the passage measured in the direction in which the passages are arranged is maximum at a position between an end of said electro-thermal transducer element near the ejection outlet and an end thereof near the supply inlet, and that the width reduces toward the ejection outlet and toward the supply inlet.

Description: FIELD OF THE INVENTION AND RELATED ART The present invention relates to a liquid jet recording apparatus wherein recording is effected by ejecting droplets of liquid through an ejection outlet, using thermal energy. Prior Art In a liquid jet recording apparatus using thermal energy, an electro-thermal transducer is used to eject droplets of liquid. The thermal energy produced thereby is effective to vaporize the liquid and form a bubble, producing a pressure to eject the liquid in the form of a droplet. Such a system has advantages, amongst others, in that the ejection outlets can be disposed at a high density so that the high resolution images can be recorded. The high density arrangement, however, requires narrow liquid passages communicating with the ejection outlets. The narrow passages have higher inertia and impedance, resulting in a longer time period for the liquid to refill the passage from the liquid supply side. This prevents increase of the recording speed. By reducing the length of the passage, the refilling time period can be reduced. If, however, this is done, the speed and the volume of the ejected liquid reduces, so that stable recording is not possible. Japanese Laid-open Patent Application No. 204352/1985 proposes, in an attempt to solve this problem of stabilizing liquid ejection using a short passage, that an ink jet recording head has a resistance to reduce the flow of liquid in the passage to the supply side from the electro-thermal transducer. Japanese Laid-open Patent Application No. 87356/1988 proposes, in an attempt to increase the percentage of the energy of the bubble contributing to the ejection of liquid, that the cross-sectional area of the passage adjacent the electro-thermal transducer increases toward the ejection outlet. Japanese Laid-open Patent Application No. 195050/1988 proposes that the top wall of the passage is made higher in the neighborhood of the electro-thermal transducer than the other portion so that the liquid passage is not blocked by the bubble (Japanese Laid-open Patent Application No. 139970/1981). In the system disclosed in Japanese Laid-open Patent Application No. 204352/1985, the following problems arise: (1) the difficulty in providing the resistances in the passages increases with the increase of the density of the nozzles and with the increase of the number of the ejection outlets of the recording apparatus; and (2) if the resistance is too far from the electro-thermal transducer, the effect of the resistance reduces; and if it is too near, the bubble produced develops to the clearance between the wall of the passage and the resistance, reducing the effect of the resistance. Therefore, optimum design of the configuration, dimension and position or the like is difficult, and even if the optimum design is made, the results are not sufficient. The method disclosed in Japanese Laid-open Patent Application No. 87356/1988 involves a problem in that the multi-nozzle structure is difficult, although the energy use efficiency is improved. In this method, the cross-sectional area of the passages is increased toward the ejection side resulting in thin walls between adjacent passages. If the wall is too thin, the strength may become insufficient, or the pressure of the bubble may be transmitted to the adjacent passages, and therefore, proper ejection is not expected. For these reasons, this method is not suitable for increasing of the high density arrangement or increasing in the number of the nozzles. In the arrangement disclosed in the Japanese Laid-open Patent Application No. 95050/1988, the liquid passage is not blocked by the bubble, and therefore, the liquid can be sufficiently supplied, so that the ejection is stabilized. However, the publication simply states that the top wall of the passage is made higher at the energy applying portion than the other portion. JP-A-59-194865 discloses a liquid jet-recording head according to the pre-characterising part of claim 1. According to the present invention there is provided a liquid jet recording head, comprising: a plurality of ejection outlets through which a droplet of liquid is ejected by thermal energy; a plurality of liquid passages communicating with the ejection outlets to supply the liquid; a plurality of supply inlets for supplying the liquid to the passages; and a plurality of electro-thermal transducers provided for the respective ejection outlets to produce the thermal energy, each of said electro-thermal transducers having a heating surface for heating the liquid on the bottom of said passage, wherein the width of the passage, measured transversely of the direction of flow, is a maximum at a position between an end of said electro-thermal transducer element near the ejection outlet and an end thereof near the supply inlet, and wherein the width reduces toward the ejection outlet; characterised in that the width of the passage reduces from the region of the transducer toward the supply inlet. An embodiment of the present invention provides a liquid jet recording head having plural ejection outlets disposed at high density. An embodiment of the present invention provides a liquid jet recording head capable of ejecting a liquid droplet at high speed. An embodiment of the present invention provides a liquid jet recording head capable of ejecting a liquid droplet having a sufficient volume. An embodiment of the present invention provides a liquid jet recording head capable of replacing the ejected liquid at a high speed. In the accompanying drawings:- Figure 1 is a partial perspective view of a liquid jet recording head according to an embodiment of the present invention. Figure 2 is a top plan view of the liquid passage of the liquid jet recording head of Figure 1. Figure 3 is a top plan view of the passage according to a second embodiment of the present invention. Figure 4 is a partial perspective view of the liquid jet recording head according to a third embodiment of the present invention. Figure 5A is top plan view of the passage. Figures 5B and 5C are sectional views of the passage. Figure 6 is a top plan view of a conventional liquid jet recording head. DESCRIPTION OF THE PREFERRED EMBODIMENT Preferred embodiments of the invention will be described in conjunction with the accompanying drawings. As shown in Figure 1, partition walls 7 are formed on a base 4 at regular intervals, and electro-thermal transducer elements 5 are disposed between adjacent walls. A top plate 6 is attached to provide a liquid jet recording head. The space defined by the walls base and the top plate is a liquid passage 1, the liquid to be ejected out is supplied from an inlet and is ejected through the ejection outlet 2. Adjacent the electro-thermal transducer element, the width of the wall is substantially zero to provide the maximum width of the passage, although the wall has a small width for explanation in the Figure. The dimensions are as follows: Cross-sectional area of the ejection outlet: 40x30 microns Length of the passage : 500 microns Height of the liquid passage : 400 microns Size of the electro-thermal transducer element : 32x150 microns Pitch of passages : 105.8 microns The maximum width of the passage is 95 microns (electro-thermal transducer element portion), and the minimum width is 30 microns (inlet portion). Figure 2 is a top plan view of the liquid passage in this embodiment. Figure 6 is a top plan view of a conventional passage. In the conventional passage, the liquid passage is not converging toward the supply inlet 3. The dimensions of the conventional passage are the same as those of the embodiment except that the maximum width is 70 microns (the major portion of the passage, and that the minimum is 35 microns (ejection outlet portion). Operation of the first embodiment will be described in comparison with the conventional structure. When the electric pulse is applied to the electro-thermal transducer element, a bubble 8 is produced, as shown in Figure 2, and it develops. In this embodiment, the width of the passage is maximum at the portion of the electro-thermal transducer element, and therefore, the bubble can develop with less influence of the partition walls, and freely develops into an oval from. In the comparison example, the maximum passage width is smaller than that of this embodiment due to the structure thereof, and therefore, the development of the bubble is influenced by the walls so that the bubble becomes much longer than the length of the electro-thermal transducer element and forms into the shape as shown in Figure 6. therefore, the energy of the bubble can be used more efficiently in this embodiment than in the comparison example. During the subsequent liquid supply period, the liquid flows slowly from the inlet, and therefore, the impedance of the passage during the liquid supply is smaller than in the ejection period, but this does not apply to the conventional passage. The structure of the conventional passage has the same impedance upon the ejection and during the supply, and therefore, the properties different depending on whether it is the ejection period or supply period, cannot be provided. The impedance has been determined as a compromise. According to the present invention. the desirable different properties can be provided. The description will be made in further detail. The structure of the liquid passage, more particularly, the size, position, thermal energy to be produced, passage resistance, dimension of the ejection outlet and the like, is determined in consideration of the size of the droplet and the speed of the droplet. They are not all determined freely because of the limitations due to the manufacturing process and the geometrical limitation. It there were no limitation, the liquid passage would be as short and wide as possible since then the passage resistance (impedance and inertance) the efficiency is high, and size and the speed of the droplet would be determined by the adjustment of the size and position of the electro-thermal transducer element and the side of the ejection outlet. Actually, however, there is a partition wall between adjacent passages in the case of multi-nozzle arrangement, and therefore, the nozzle width is limited, and the consideration should be paid to the mechanical strength of the wall. The embodiment uses the directivity (direction dependence) and the flow-dependence of the liquid impedance. The impedance of the passage is desired to be as small as possible, as described above. If the impedance is different between upon the liquid ejection and upon the liquid supply. Now, the consideration will be made separately for the inlet side (back side) and outlet side (front side) of the electro-thermal transducer. Upon the ejection, the liquid is desirably easily mobile at the front side, and is less mobile at the back aide, that is the impedance is desirably smaller at the front aide and larger at the back side. Upon the liquid supply period, the liquid retracted into the passage tends to return, and therefore, the liquid is desirably easily mobile both at the inlet and outlet sides, that is, the impedance is desirably smaller both at the inlet and outlet side. Therefore, the front impedance is desirably always small, and the back impedance is desirably large upon the ejection and small upon the supply. Thus, the back side impedance is desired to be different. The present invention concerns the width of the liquid passage. The relation between the width and the impedance is that the impedance decreases with increase of the width. Upon the ejection of the recording liquid, the width of the front side is desired to be large, and the width of the back side is desired to be small, but during the liquid supply period, the width at the back side is desired to be large. So, different and contradicting properties are desired. This is difficult to solve, but the inventors have found a solution in consideration of the difference of the liquid movement upon the ejection and during the supply period, More particularly, the inventors have particularly noted the difference between the length of the time period required for the ejection and the length of the tine period required for the liquid supply. The ejection is effected in a short period of time, and therefore, the liquid movement speed is high, but the supply is effected in a long period, and therefore, the speed of the liquid flow is low. It has been found that by considering the flow rate difference and the passage structure, the impedance can acquire the directivity and the speed-dependency. The description will first be made as to the back side of the passage. According to the present invention, the liquid, upon the ejection, tends to flow at a high speed through a passage converging from the electro-thermal transducer to the supply inlet, and therefore, it does not easily flow. In other words, the impedance is larger than when the width is constant, and therefore, the ejection is efficient. During the supply, the liquid flows in the opposite direction at a low speed through the passage diverging from the inlet aide to the electro-thermal transducer, and therefore, the impedance is smaller, so that the liquid supply is effected smoothly. The front side will be described. In the front side the flow of the liquid is toward the outlet, that is, from the electro-thermal transducer to the ejection outlet upon the ejection and the supply. therefore, the passage is desirably diverging toward the ejection outlet, in order to increase the efficiency. From the above, it result that the passage is diverging from the inlet to the outlet. However, the front side of the passage has to take the role for controlling the size of the droplet and the control of the droplet speed. Therefore, the structure cannot be determined only from the standpoint of the efficiency. In addition, the simple diverging structure does not meet the demand for the increased nozzle density. Then, the passage structure of the present invention is achieved. Because of the structure of the present invention, the desired size and speed of the droplet can be provided, and the multi-nozzle structure at high density is achieved. According to the present invention, the back side structure diverging toward the electro-thermal transducer permits the maximum passage width as close as possible to the pitch of the nozzle arrangement at the position where the electro-thermal transducer element is disposed, so that the passage impedance of the entire passage can be reduced. The length of that portion of the passage where the width is maximum is made extremely small, and the passage width linearly reduces both toward the inlet and the outlet, whereby the insufficient mechanical strength resulting from the insufficient thickness of the wall between adjacent passages, can be avoided. In addition, the possible influence from the pressure produced in the adjacent nozzle can be avoided. The length in which the width is maximum is determined on the basis of the property of the material constituting the passage, the degree of converging to the inlet and the outlet and the like. The largest maximum width can be provided when the length is zero, that is, when the maximum width appear only at a point. The nozzle structure is particularly effective when plural nozzles are used, particularly at a high density. In addition, the distances from the electro-thermal transducer and the side walls are large, so that the bubble is not limited by the side walls, and therefore, it can develop freely, by which the energy conversion efficiency to the ejection energy can be increased. As will be understood from Figures 1 and 2, the degree of converging from the electro-thermal transducer toward the ejection outlet is higher than that toward the supply inlet. In other words, the taper of the wall constituting the width of the passage is steeper at the front side than at the rear side. By so doing, the maximum width position can be closer to the ejection outlet, and the width of the electro-thermal transducer element is increased, and in addition, the passage is shortened. The reason why the electro-thermal transducer element can be made closer to the ejection outlet, is that the bubble can develop freely so that the bubble does not expand in the direction of the liquid flow. In the conventional structure, if the electro-thermal transducer element is too close to the ejection outlet, the bubble communicates with the external air with the result of improper ejection. According to the present invention the liability is removed. In addition, since the electro-thermal transducer element is close to the ejection outlet, the ejection can be effected with a small electro-thermal transducer element, and therefore, the efficiency is improved, and the energy consumption can be reduced. Since the length is reduced, the impedance of the entire passage can be reduced. Embodiment 2 The liquid jet recording head of the second embodiment is the same as the first embodiment except that the length of the passage is 200 microns and that the size of the electro-thermal transducer element is 45x35 microns. This embodiment uses most the advantages of the large width of the passages. The maximum width position is further closer to the ejection outlet, and the width of thy electro-thermal transducer element is increased, and in addition, the passage is shortened. As described in the foregoing, the reason why the electro-thermal transducer element is made closer to the ejection outlet, is that the bubble can develop freely so that the bubble does not expand in the direction of the liquid flow. In the conventional structure, if the electro-thermal transducer element is too close to the ejection outlet, the bubble communicates with the external air with the result of improper ejection. according to the present invention the liability is removed. In addition, since the electro-thermal transducer element is close to the ejection outlet, the ejection can be effected with a small electro-thermal transducer element, and therefore, the efficiency is improved, and the energy consumption can be reduced. Since the lenght is reduced, the impedance of the entire passage can be reduced. Embodiment 3 As shown in Figure 4, the electro-thermal transducer elements 5 are disposed at regular intervals on the base 4 (some parts are omitted for the sake of simplicity in this Figure). The top plate 6 has grooves at the positions corresponding to the electro-thermal transducer elements 5 to establish the liquid passages. The top plate 6 is attached to the base to form a liquid jet recording head. The adjacent passages are separated from each other by the partition wall 7. The liquid to be ejected is supplied from the supply inlet 3 and is ejected out through the outlet 2. Adjacent the electro-thermal transducer element, the width of the partition wall is substantially zero (in the Figure, the it has a small width for explanation) to provide the maximum width of the passage. In addition, the height of the passage is made maximum to provide the maximum cross-sectional area of the passage. The dimensions of the passage are the same as those of the first embodiment with the exception that the cross-sectional area of the ejection outlet is 35x35 microns and that the maximum height of the passage is 60 microns. Figure 5(a) is a top plan view of the passage according to this embodiment, and Figures 5(b) and 5(c) are a-a' and b-b' sectional views, respectively. As will be understood from Figure 5 (c), the top wall of the passage is tapered in the similar manner as the side walls described in the foregoing. The same advantageous effects are provided. Ejection volume (10⁻⁹cc) Ejection speed (m/s) Refilling time (micro-sec) Embodiment 1 126 11 282 Embodiment 2 130 14 222 Embodiment 3 136 13 250 Comparison 81 8.5 316 Table 1 shows the properties of the recording head according to Embodiments 1, 2, 3 and comparison example. As will be understood, the recording head according to the embodiments is advantageous. According to the present invention, the efficiency of use of the bubble energy for the ejection is improved, and the high density arrangement of the nozzles is possible. The width of the passage can be used to the maximum extent, so that the efficiency is further improved. the energy consumption can be reduced. The ejection speed is the same or higher than that of the conventional structure.

Claims: A liquid jet recording head, comprising: a plurality of ejection outlets (2) through which a droplet of liquid is ejected by thermal energy; a plurality of liquid passages (1) communicating with the ejection outlets (2) to supply the liquid; a plurality of supply inlets (3) for supplying the liquid to the passages; and a plurality of electro-thermal transducers (5) provided for the respective ejection outlets to produce the thermal energy, each of said electro-thermal transducers having a heating surface for heating the liquid on the bottom of said passage; wherein the width of the passage, measured transversely of the direction of flow, is a maximum at a position between an end of said electro-thermal transducer element near the ejection outlet and an end thereof near the supply inlet, and wherein the width reduces toward the ejection outlet, characterised in that the width of the passage reduces from the region of the transducer toward the supply inlet. A liquid jet recording head as claimed in claim 1, characterised in that the width or height linearly reduces toward the ejection outlet and toward the supply inlet considered from the region of the transducer. A liquid jet recording head as claimed in claim 1, characterized in that the degree of the reduction is steeper toward the ejection outlet than toward the supply inlet considered from the region of the transducer. A liquid jet recording head as claimed in claim 1, characterized in that a height and a width of the passage measured in the direction in which the passages are arranged are maximum at positions between an end of said electrothermal transducer element near the ejection outlet and an end thereof near the supply inlet, and that the height and the width reduce toward the ejection outlet and toward the supply inlet. A liquid jet recording head as claimed in any one of claims 1-4, characterised in that the width of each passage is maximum in the region of the transducer so as to aid bubble development. A liquid jet recording head as claimed in any one of claims 1-5, characterised in that the transducers are positioned asymmetrically at the sides of the passages. A method of producing a liquid jet recording head having a plurality of ejection outlets (2) through which a droplet of liquid is ejected by thermal energy; a plurality of liquid passages (1) communicating with the ejection outlets (2) to supply the liquid; a plurality of supply inlets (3) for supplying the liquid to the passages; and a plurality of electro-thermal transducers (5) provided for the respective ejection outlets to produce the thermal energy, as claimed in any one of the preceding claims, including forming each said liquid passage with a width which increases from the inlet towards the region of the transducer and thereafter decreases towards the outlet.

Inventors: HIRASAWA SHINICHI, TACHIHARA MASAYOSHI, HIRASAWA, SHINICHI, TACHIHARA, MASAYOSHI
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1991
Main classification: B41J2
IPC codes: B41J2