Ink jet recording method

Abstract: An ink jet head includes a plurality of liquid flow paths (31) for ejecting the ink; and a plurality of heat generating resistors (2a,2b) for the respective liquid flow paths. The heat generating resistors being independently drivable; wherein a preliminary heat generating resistor (44) is disposed between the ejection outlet (40) and the ink generating resistors.

Description: The present invention relates to a gradation recording method. In this specification, recording includes applicatin of ink onto any ink supporting material for receiving the ink, such as textile, thread, paper, sheet material (print), and what is recorded includes meaningful image such as letter or the like and meaningless image such as pattern images. A recording device includes various information processing device or a printer as an output device therefor, and the present invention is applicable to all of them. An ink jet recording device which ejects ink onto a recording material to effect the recording has been put into practice, and may of them are produced, since it is advantageous in the easiness of downsizing, low noise or the like. Recently, further downsizing or further improvement of the image quality particularly in color image recording, is demanded. In order to meet the demand, Japanese Laid Open Patent Application No. SHO-55-132259 has proposed a construction wherein a plurality of electrical heat exchange elements are provided in one nozzle. These electrothermal transducer elements are independently controlled and driven, so that size of the ink droplet ejected is controlled to accomplish high image quality recording (tone gradient recording method). The investigations of the inventors in this respect have revealed the following. An area of electrothermal transducer element is normally one of an important factors of determination of ejection amount of the ink. However, the maximum ejection amount of the ink when the plurality of the electrothermal transducer elements are used, is not determined by the total of the areas of the plurality of electrothermal transducer elements. Since the heat produced by an electrothermal transducer element is influential to another electrothermal transducer. Therefore, the desired ink ejection amount is not accomplished easily. The circuit construction on an element substrate (heater board) for driving the electrothermal transducer element in an example, is as shown in Figure 6 or Figure 7. In Figure 6, the electric signal is directly supplied to the electrothermal transducer element 012 through wiring and outside end portion 015 (direct wiring construction). With such a circuit construction, the construction in the element substrate is simple, but as to the number of of the contacts, when the number of of the electrothermal transducer elements is n, at least n+ one contacts are necessary. When a plurality of electrothermal transducer elements are provided in a single nozzle with such a circuit construction used, a very many electrical connections are necessary between the element substrate and the outside devices, with the result of complication of the manufacturing step and bulkiness of the element substrate. The element substrate of Figure 23 has electrothermal transducer element 012, wiring 013, diode 014 and contact for external connection. When electric energy supply is effected by the matrix construction constituted by wiring and diode. By the use of the diode matrix construction, the number of of the contacts 015 for the external connection is reduced to 2n when the number of of the electrothermal transducer elements is n. Even if, however, such a wiring construction is used, the number of of the connection contacts is quite large in the case of tone gradient recording head. As described above, the head having a plurality of of heat generating resistors in 1 nozzle, involves the problem of lowering of the ejection efficiency or deviation from a desired ejection amount. According to document US-A-4 251 824 there is disclosed a recording method using ink jet recording by means of an ink jet recording head. The ink jet recording head comprises a plurality of independently driven resistors which are supplied with different amounts of energy. According to the further document US-4 646 110 there is disclosed a recording method using ink jet recording by means of an ink jet head having a number of bubble generating portions driven in a different way so as to create bubbles and thus to control the pressure generated in the liquid flow path. By means of this control the size of the discharged drops of liquid can be varied of a wide range and therefore highly efficient density control can be effected on a recording medium. It is the object of the present invention to provide a gradation recording method capable of effecting high image quality recording with high tone gradient and improved ejection efficiency. The object of the invention is achieved by the combination of the features set forth in claim 1. A preferable embodiment of the method according to the invention is defined in claim 2. In the following, the invention is further explained by an embodiment with reference to the enclosed drawings. In the drawings: Figure 1 illustrates a bubble generation region of an electrothermal transducer element. Figure 2 illustrates a bubble generation region of an electrothermal transducer element. Figure 3 illustrates a structure wherein a plurality of of electrothermal transducer are provided in 1 flow path. Figure 4 illustrates a bubble generation region of the electrothermal transducer element in Figure 3. Figure 5 shows example of a construction for analog tone gradient in an ink jet recording head for carying out a gradation recording method according to an embodiment of the present invention. Figure 6 shows example of control for construction of Figure 5. Figure 7 shows example of reflection temperature in the construction of Figure 19. Figure 8 shows an equivalent circuit for a construction of a substrate of a conventional ink jet head. Figure 9 shows an equivalent circuit of a substrate construction of an ink jet head. Referring to the accompanying drawings, an embodiment of the present invention will be described. In this embodiment, ink is used as the liquid to be ejected, but the present invention is not limited to the ink and is usable with the liquid which can be ejected using the device of the present invention. Before describing the embodiment, the description will be made as to the finding obtained by the inventors. Figure 1 is a top plan view (a) of an electrothermal transducer element on an element substrate, and a A-A sectional view (b) thereof. The electrothermal transducer element on the element substrate comprises a heat generating resistor (ejection heater) 2 for producing the heat and electrodes 3A and 3B connected to the ejection heater 2 through a thin film forming process. By application of an electric signal between the two electrodes, current flows through the ejection heater 2 to generate the heat. The heat produced by the ejection heater 2 heat radiates in a direction of arrow 107 in (a) namely along the surface, and in a direction thereacross as shown in same figure (b). The ejection heater 2 has a sandwich structure comprising a heat accumulation layer 105 of low thermal conductivity, a protection layer 103 for protection of the heater and an anti-cavitation layer 104 against shock wave upon collapse of bubble in ink. The base 106 is of silicon crystal or the like. The thickness of the respective layers is determined so as to transfer the heat from the ejection heater 2 to the ink 108. In the case of of the present invention, anti-cavitation layer 104 is 0.1-1.0 micron, protection layer 103 is 0.3-2.0 microns, and heat accumulation layer 105 is 0.5- 5.0 microns approx., and the base 106 is 0.5-1.0mm, in thickness, usually. When the of the contact surface between the anti-cavitation layer 104 and the ink 108 is approx. 300°C, the bubble generation starts, and is set as a temperature at which the bubble generation occurs stably at the temperature of not less than 300°C. The ejection heater 2 exhibit low durability abruptly when the surface exceeds the temperature of approx. 700-800°C due to the stress resulting from inserting in thermal-expansion coefficients between the protection layer 103 or between the heat accumulation layer 105 or due to the durable temperature. It is desirable that the surface temperature is controlled so as not to exceed the temperature. Referring to Figure 2, this will be described further using the surface temperature distribution shown therein. The ordinate represents a temperature, and the abscissa represents a distance of the ejection heater in the direction of the flow path cross-section. Here, a-a' corresponds to the width of the heater in Figure 1, (a), and the temperature distribution at the surface of the anti-cavitation layer 104 is indicated by Temp A. The δT 1 is a bubble generation start temperature and is approx. 300°C, and δT 2 is a temperature at which the durability changes abruptly. It is different if the thin film material is different but is usually approx. 700-800°C. With Temp a, the range of δT 1 - δT 2 temperature region is the region where the bubble generation occurs in the ink, as indicated by b-b' Here, it will be noted that the temperature distribution at the central portion is flat, and the bubble generation/collapse are stably repeated, and therefore, the more stable printing property can be provided if this region is larger. Adjacent the end portion of the heater, the heat radiation occurs in the direction of the surface, as shown in Figure 1 with the result that the temperature gradually decreases, and W A is a non-bubble-generation region incapable of bubble generation of the ink although it is on the ejection heater. A further outside portion of the ejection heater exhibit some degree of temperature rise due to the heat radiation in the direction of the surface. Thus, the temperature distribution has an exponentially expanding nature (curve), and therefore, around the ejection heater, a width (approx. 8 microns)of non-bubble-generation exists (non-bubble-generation region). In order to improve the ejection efficiency of the ink by reducing this region, it would be considered to rise the overall temperature. However, if this is done, the temperature of the maximum temperature region at the center portion of the ejection heater would exceed the durability deterioration temperature, that is δT 2 with the result of reduced lifetime of the ejection heater. For this reason, it is difficult to increase the overall temperature. According to the ink ejection structure shown in Figure 3, one liquid flow path (nozzle) 31 has a plurality of of ejection heater s(heat generating resistor s) which are independently drivable. In this structure, as shown in Figure 3, there are provided ejection heaters of rectangular forms which are substantially the same having long sides along the liquid flow path. The two ejection heaters are disposed substantially in parallel with each other. They are remote from the ejection outlet substantially at the same distances. By doing so, a temperature distribution as shown in Figure 4 can be provided by optimizing the positions of the plurality of heat generating resistors, so that the non-bubble-generation region can be reduced while maintaining the temperature of the heater in the stabilization region at δT 1 -δT 2 . Figure 4 shows a temperature distribution on B-B line between the two heaters in Figure 3. When the ejection heaters 2A and 2B are independently driven, the temperatures are as indicated by Temp a, Temp a', and therefore, the respective temperatures are the same as conventional ones. When they are simultaneously driven, the portions of the temperature distribution exponentially expanding at the heater edges are overlapped so that the total temperature distribution is as indicated by Temp B, and the effective bubble generation region of the heater is larger as indicated by B than the conventional one as indicated by A. Thus, the non-bubble-generation region is reduced, and the bubble generation efficiency can be enhanced. The non-bubble-generation region is normally a-b which is approx. 8 microns wide, but by using 12 microns as the clearance between 2 heaters (the distance between adjacent edges), it can be reduced to approx. 5 microns. The smaller the distance between heaters, the more effective. If the point at which δT=0 in the distribution Temp a of one of the heaters is over the other ejection heater, the effect of enlargement of the area of effective bubble generation is provided. Particularly, the effect is high if the distance between the heaters is such that the δT=0 point of the Temp a reaches the effective bubble generation region of the other heater. The condition satisfying this is d≤8 microns. The non-bubble-generation region is decreased by decreasing the clearance between heater s(heat generating resistor s) to not more than 8 microns so that effective bubble generation area can be enlargement. If d≤6 microns is satisfied, the temperature rise due to the heat radiation from the 8 microns width of the non-bubble-generation regions become not less than twice, and the minimum temperature point in the temperature distribution Temp b exceeds the level δT 1 with the result that the non-bubble-generation region is reduced. Further preferably, if d≤4 microns is satisfied, the bubble generation region can be assured stably with flatter temperature distribution. As will be understood from Temp a of Figure 2, if the heater width is not more than 16 microns (2 W A ), the bubble generation region does not have a flat surface, and therefore, the effective region hardly exists between the unstable region and the durability deterioration region. However, in the case of the multi- heater as in the present invention, the stabilized effective bubble generation region can be provided even if the heater has a width not more than 16 microns. The clearance between the heat generating resistors is a clearance between adjacent edges of the heat generating resistors. By the reduction of the non-bubble-generation region, the following effects are provided. 1. corresponding to the reduction of the heater size required for the predetermined ejection amount, energy saving is accomplished, so that the voltage source cost and the driver cost can be saved. 2. since the heat generation in the non-bubble-generation region results in the wasteful energy and in addition functions to rise the temperature of the head, the viscosity of the ink having the temperature dependence property decreases with the result of variation of the ejection amount and therefore deterioration of the printing quality. However, the above-described reduction of the non-bubble-generation region can suppress the reduction of the viscosity and the deterioration of the printing quality. These effects are particularly remarkable in a narrow heater having a smaller width. Figure 5 shows a construction for carying out a gradation recording method according to the invention for achieving an analog tone gradient. This embodiment of the method according to the invention uses the fact that the temperature of the ink in the ink jet recording head is influential to the ejection amount, and the ink temperature is controlled to provide a predetermined ejection amount. As shown in Figure 5, in this embodiment, there are provided large and small ejection heaters 2a and 2b juxtaposed and an ink pre-heating heater 44 in front thereof in the ink ejecting direction. This embodiment utilizes the fact that an amount of larger with the same bubble generation power amount of the ink can be ejected if the temperature is higher, since then the ink viscosity is lower, the ink pre-heating heater 44 is effective for pre-heating of the ink to provide fine change of the ejection amount. For example, as shown in Figure 6, the ink temperature is raided by the signal A applied to the ink pre-heating heater 44, and then the signal B is applied to the ejection heater 2a or 2b to eject the ink. At this time, point C designates the temperature at which the bubble generation of the ink occurs, and the temperature of the ink provided by the ink pre-heating heater 44 does not exceed this temperature. With the method according to the invention the digital tone gradient of the ink ejection structure explained with reference to Figures 3 and 4 can be operated as analog-like tone gradient in effect, as shown in Figure 8. The change of the ejection amount due to the change of the head temperature can be suppressed by controlling the ink temperature in the ejection nozzle 104 by the ink pre-heating heater 44 to provide a predetermined ejection amount. In a conventionally method of ejection amount control for a single heater, a pre-pulse is applied prior to the main pulse to effect the pre-heating. If the pre-pulse is large, the bubble generation may occur, and therefore, the ink heating is limited to a degree lower than predetermined. However, according to this this embodiment, the ink pre-heating heater 44 is independent from the ejection heater, and therefore, a large heater having low power per unit area of the heater for heating up to a degree of not producing bubble generation, is usable for pre-heating so that the ejection amount control can be enhanced. As described above, a plurality of heaters are provided in a single nozzle, and the function element is provided in the substrate, by which the following advantageous effects can be provided. 1. the heater size for providing a predetermined ejection amount can be reduced, and therefore, the energy saving can be accomplished correspondingly, so that the voltage source cost and the driver cost can be reduced. 2. since the heat generation in the non-bubble-generation region results in the wasteful energy and in addition functions to rise the temperature of the head, the viscosity of the ink having the temperature dependence property decreases with the result of variation of the ejection amount and therefore deterioration of the printing quality. However, the above-described reduction of the non-bubble-generation region can suppress the reduction of the viscosity and the deterioration of the printing quality. 3. the tone gradient control is possible with downsized head and device without cost increase. 4. the tone gradient control is possible without shortening the lifetime of the electrothermal transducer element. 5. the tone gradient control is possible with a smaller number of data (2x tone gradient levels with x bit) so that the data transfer time can be reduced, and the memory cost reduction is accomplished. 6. the tone gradient controllable is possible without increasing the driving oscillation of the nozzle. 7. since the position of the pixel is not deviated, the image quality is not deteriorated. 8. by sharing the ejection jobs by same size heaters, the lifetime expansion is accomplished. 9. by using a heater not producing a bubble, the effect of ejection amount control can be enhanced. Particularly, it should be noted that the cost increase is hardly required despite the foregoing advantages, and the downsizing is accomplished, in the embodiment wherein the function element is provided in the substrate. While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the scope of the following claims.

Claims: A gradation recording method using ink jet recording, comprising the steps of: preparing an ink jet recording head comprising: an ink ejection outlet (40) for ejecting an ink; an ink passage (104) being in fluid communication with said ink ejection outlet and comprising a preliminary heat generating resistor (44) and a plurality of ink ejection heat generating resistors (2a, 2b), said preliminary heat generating resistor being suitable for being supplied with energy in an amount insufficient to generate a bubble and to eject the ink so as to adjust the temperature of the ink in the ink passage and hence the amount of ink ejected by said plurality of ink ejection heat generating resistors (2a, 2b) for ejecting an amount of ink which is controlled; ejecting different amounts of ink by driving said ink ejection heat generating resistors (2a, 2b); and supplying energy in an amount insufficient to generate a bubble and to eject the ink to said preliminary heat generating resistor (44) to heat the ink so as to adjust its temperature and hence the amount of ink ejected by said ink ejection heat generating resistors (2a, 2b) thereby to control the amount of ink ejected. A method according to claim 1, wherein analog gradation recording is effected by said energy supplying step.

Inventors: ARASHIMA TERUO, FURUKAWA TATSUO, ISHINAGA HIROYUKI, IZUMIDA MASAAKI, KAMIYAMA YUJI, KASAMOTO MASAMI, KAWAI JUN, MARU HIROYUKI, MASUDA KAZUAKI, MISUMI YOSHINORI, MUROOKA FUMIO, SHIMODA JUNJI, ARASHIMA, TERUO, FURUKAWA, TATSUO, ISHINAGA, HIROYUKI, IZUMIDA, MASAAKI, KAMIYAMA, YUJI, KASAMOTO, MASAMI, KAWAI, JUN, MARU, HIROYUKI, MASUDA, KAZUAKI, MISUMI, YOSHINORI, MUROOKA, FUMIO, SHIMODA, JUNJI
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1995
Main classification: B41J2
IPC codes: B41J2