1. Field of the Invention
The present invention relates to an element substrate that discharges liquid by applying discharge energy to the liquid, and to a liquid discharging head including the element substrate.
2. Description of the Related Art
A liquid discharging head that discharges liquid is required to discharge small droplets having a volume of 2 pl or less. By applying such small droplets onto a printing medium at high density, a high-definition image can be obtained. With downsizing of the droplets, the number of discharges dramatically increases. When increasing the number of discharges, it has a limitation to simply increase the discharge frequency. Further, as the discharge frequency increases, the discharging speed sometimes decreases. To prevent the decrease in discharging speed and to discharge a predetermined amount of liquid in a shorter time, there has been adopted an element substrate in which multiple discharge ports are arranged at high density.
The element substrate that discharges liquid has a problem of the increase in viscosity of liquid due to the decrease in temperature of the liquid. To suppress such a problem, a method is adopted which heats liquid before supplying the liquid to action chambers that apply discharge energy to the liquid. However, in the element substrate that discharges small droplets, there is found a problem in that the discharge characteristics are deteriorated by the increase in viscosity with the increase in temperature of the liquid. That is, heated liquid evaporates via the discharge ports even when it stays in the action chambers. In the element substrate that discharges small droplets, the amount of liquid to be discharged from each discharge port is small. Hence, even when a small amount of solvent evaporates, the viscosity of the liquid easily increases. Further, since the discharge ports and the action chambers are relatively small, the liquid is likely to be affected by the increase in flow resistance due to the increase in viscosity. Such a problem is pronounced particularly in pigment ink that is likely to aggregate and high-function ink having a high content of additive resin.
The increase in flow resistance deteriorates the discharge characteristics of the element substrate. When the discharge characteristics are deteriorated, the element substrate is sometimes brought into a state in which it cannot discharge the liquid unless a recovery process is performed for liquid supply channels that reach the discharge ports and the action chambers.
U.S. Patent Application Publication No. 2009/160896 A1 discloses an element substrate that is controlled so that liquid in action chambers is not heated more than necessary.
In the element substrate described in the above publication, heating resistance elements serving as energy generating elements preheat the liquid in the action chambers to a predetermined temperature, and then discharge the liquid by boiling the liquid. However, it is difficult for the heat amount of preheating to rapidly heat the liquid. For this reason, in a low-temperature environment, a long standby time is required to heat the liquid to the predetermined temperature by preheating. This decreases the throughput of the element substrate.
In this way, the element substrate disclosed in the above publication cannot evenly cope with the increase in viscosity of the liquid within the usual use range. Further, to cope with the increase in viscosity of the liquid, it has been proposed to add heating elements different from the heat generating elements in the action chambers and to heat the liquid in the action chambers by the heating elements only by the necessary amount when needed. In such a case in which the heating elements are mounted in the substrate, most heat generated from the heating elements is transferred to the substrate, and this lowers the efficiency. Further, since the heat transferred to the substrate is stored in a liquid discharging head, it may continue heating the liquid even after the heating elements stop heating. For this reason, the heating state continues for a long time, and more liquid than necessary sometimes evaporates.
The present invention provides an element substrate and a liquid discharging head that efficiently heat liquid and achieve good discharge characteristics.
An element substrate according to an aspect of the present invention includes a discharge port from which liquid is discharged, an energy generating element configured to generate energy for discharging the liquid from the discharge port, a heating element having a shape with a longitudinal axis, including at least two heating surfaces exposed to the liquid, and configured to heat the liquid to an extent such as not to discharge the ink, a first support portion configured to support one end portion of the heating element, a second support portion configured to support the other end portion of the heating element, and a third support portion configured to support a portion between the first end portion and the other end portion.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
An embodiment of the present invention will be described below with reference to the drawings.
Ink is supplied from ink reservoirs (not illustrated) to the discharge ports 5 via common liquid chambers 6 common to discharge port rows each two of which correspond to each color. The discharge ports 5 adjacent in a row direction are arranged at an array density of 800 dpi (dots per inch). Further, the discharge ports 5 in different rows for the same color are shifted from each other by a half pitch. Therefore, the element substrate 2 can apply ink onto a printing medium at a printing density of 1600 dpi.
The action chambers 8 communicate with the common liquid chambers 6 (see
The heating resistance element 7 preferably has a shape with a longitudinal axis (for example, a platelike shape, a columnar shape, and a prismatic shape). In the embodiment, the heating resistance element 7 is shaped like a plate like a strip. Both ends of the heating resistance element 7 are fixed to a wall of the action chamber 8, and both surfaces of the heating resistance element 7 along the longitudinal axis are exposed to ink to be able to heat the ink. Therefore, heat can be applied to the ink from both surfaces of the heating resistance element 7. This allows the ink to cause film boiling in a shorter time.
The element substrate 2 further includes partitions 9 provided on both sides of each heating resistance element 7. The partitions 9 are formed of the same material as that of the heating resistance element 7 and by the same process as that for forming the heating resistance element 7. Hence, as illustrated in
The upper and lower spaces formed in the action chamber 8 communicate through gaps between the heating resistance element 7 and the partitions 9, an aperture 10 formed in one of the partitions 9, and a through hole 11 serving as an opening formed in the other partition 9. The plural spaces formed in the lower space of the action chamber 8 communicate through an aperture 12 provided in the one partition 9.
The other partition 9 includes a narrow portion, and the narrow portion is electrically connected to an electrode (not illustrated). The narrow portion generates heat by the application of voltage thereto via the electrode. That is, the narrow portion functions as a heating element (also referred to as a sub-heater) 15. The sub-heater 15 can be driven independently of the heating resistance element 7. Further, the sub-heater 15 is specified so that a bubble generating phenomenon does not occur even when the sub-heater 15 is driven alone. That is, the sub-heater 15 can heat the ink to an extent such as not to discharge the ink.
The sub-heater 15 of the embodiment is shaped like a plate having a longitudinal axis, and includes at least two heat generating surfaces. That is, both principal surfaces of the sub-heater 15 serve as heat generating surfaces. The heat generating surfaces are disposed at a predetermined distance from the substrate 19, and are both exposed to ink in the action chamber 8. In the embodiment, both ends of the sub-heater 15 are fixed to the wall of the action chamber 8, and both surfaces of the sub-heater 15 in the longitudinal direction are exposed to ink to be able to heat the ink. Therefore, heat can be applied from the surfaces of the sub-heater 15 to the ink, and this suppresses heat dissipation to the substrate 19. Hence, the ink can be heated to a predetermined temperature in a shorter time. The shape of the sub-heater 15 of the present invention is not limited to such a platelike shape, and may be, for example, a columnar shape or a prismatic shape.
The ink is supplied from the support member 3 (see
According to the embodiment, the ink in the action chamber 8 is heated by the sub-heater 15 when needed. For this reason, a state in which the temperature of the ink is high can be limited to the needed time in contrast to the related art in which the substrate is entirely heated. Hence, evaporation of the ink from the discharge port and evaporation of solvent in the ink can be suppressed more than before. Therefore, the increase in viscosity of the liquid can be suppressed. Further, since the sub-heater 15 is provided separately from the heating resistance element 7, the ink in the action chamber 8 can be heated to the predetermined temperature at an arbitrary timing.
Next, with reference to
When the ink is heated by the heating resistance element 7, it boils on the surfaces of the heating resistance element 7. Energy of ink boiling applies kinetic energy to the surrounding ink, and a bubble grows. Since the rectifying element 14 defines a closed space except for the apertures 10 and 12, it functions as a channel resistance that efficiently directs discharge energy to the ink near the discharge port 5.
After the ink in the action chamber 8 is discharged from the discharge port 5, the pressure in the grown bubble becomes a negative pressure. When the inertial force of ink transmitted during boil forming falls below the negative pressure, the bubble rapidly disappears. As a result, a force acts to take the ink into a region where the bubble was present. By virtue of this force, the ink flows into the action chamber 8 from the supply port 13.
At this time, the ink introduced from the supply port 13 first reaches the rectifying element 14, and flows into the upper and lower spaces of the action chamber 8 from the apertures 10 and 12 of the rectifying element 14, as shown by arrows in
The liquid passing through the back side of the heating resistance element 7 further flows to a position near the sub-heater 15, and flows into the space on the side of the discharge port 5 through the through hole 11. In this specification, a channel through which the ink reaches the region on the side of the discharge port 5 through the through hole 11 is referred to a “bypass channel”. In other words, the through hole 11 forms a part of the bypass channel, and the sub-heater 15 serves as a channel wall of the bypass channel. The ink flows through the bypass channel and the aperture 10, and is then supplied to a front side of the heating resistance element 7 (a side of the discharge port 5).
Next, the structure of the sub-heater 15 will be described in detail.
The liquid discharging head of the related art mainly includes the sub-heater for the purpose of suppressing the increase in viscosity of ink in a low-temperature environment. In this case, the sub-heater is often provided on a member having high thermal conductivity (for example, a liquid discharging head board or a support member also having a heat dissipating function) in terms of the design such as to heat the entire liquid discharging head and advantageous arrangement layout. In such a structure, heat is dissipated from the liquid discharging head. Therefore, the sub-heater requires not only the heat quantity that heats the entire liquid discharging head, but also the heat quantity that covers the heat to be dissipated. As a result, a considerably large-sized sub-heater is needed. In such a large-sized sub-heater (provided on the member having high thermal conductivity), since it is difficult to finely control the temperature, a heating resistance element preheats ink to adjust the temperature of the ink in environments other than a normal temperature environment. This is because the discharge amount subtly changes with the decrease in viscosity in the high-temperature environment and the optical density (OD) of a printed image increases. This phenomenon is likely to be conspicuous in a high-duty image.
The phenomenon in which the optical density of the printed image is increased by the increase in temperature is more conspicuous in the above-described environment in which small droplets are discharged. This is because the ratio of the increase in discharge amount with respect to discharge droplets increases.
Further, as described above, the high-temperature environment in discharging of small droplets also causes thickening due to evaporation. That is, the high-temperature environment in discharging of small droplets causes the decrease in viscosity resulting from the increase in kinetic energy of the liquid in the short term, and then causes the increase in viscosity resulting from evaporation of moisture in the ink in the long term. In this way, in the element substrate for discharging small droplets, it is seriously difficult to control the viscosity.
Accordingly, in the embodiment, the sub-heater that performs heating with front and back surfaces is provided within the action chamber 8. To efficiently heat only a required amount of ink when needed, it is preferable that the ink between the discharge port and the heating resistance element should be heated and the ink upstream of the heating resistance element should be hardly heated. In this case, heating in a short time is possible, the ink does not evaporate more than necessary, and the backward resistance is ensured on the upstream side of the heating resistance element. This enhances the discharge efficiency. When the heating element 15 serving as the sub-heater is disposed on the downstream side of the heating resistance element 7 in the flow direction of liquid in the action chamber 8, heating of the ink upstream of the heating resistance element 7 is minimized. From a different viewpoint, as illustrated in
When the heating resistance element and the sub-heater are provided in the member having high thermal conductivity, heat generated from the heating resistance element and the sub-heater is transferred not only to the ink, but also to the member having high thermal conductivity. Therefore, the member having high thermal conductivity is sometimes unsuitable for the element substrate that discharges small droplets, for example, because a sub-heater having a certain size is needed and a large area is required between the heating resistance element and the discharge port.
In addition, heat transferred to the member having high-thermal conductivity is stored in other members within the liquid discharging head. For this reason, even after the sub-heater stops heating the ink, the heat stored in the other members is likely to heat the ink. As a result, the heating state continues for a long time, and more ink than necessary easily evaporates.
In the embodiment, the sub-heater 15 is shaped like a long plate, and is provided within the action chamber 8 with its front and back surfaces being exposed to the ink. More specifically, shorter-side portions of the long plate are fixed to the wall of the action chamber 8. Therefore, heat generated by the sub-heater 15 is unlikely to be transferred to the wall of the action chamber 8. Further, since the front and back surfaces of the sub-heater 15 are exposed to the ink, the ink can be heated efficiently.
Moreover, according to this structure, the amount of ink to be heated is far smaller than in the liquid discharging head of the related art. Therefore, it is unnecessary to change the dimension between the heating resistance element 7 and the discharge port 5 to add the sub-heater 15. Further, most heat generated by the sub-heater 15 is transferred only to the ink to be discharged. Therefore, the ink is unlikely to evaporate, and the increase in viscosity can be minimized. In addition, since the ink within the action chamber is heated, the temperature can be adjusted speedily. Therefore, the standby time during a warm-up can be made shorter than in the element substrate of the related art in which only preheating is performed by the heating resistance element. Since the element substrate 2 of the embodiment can expand the range of temperature adjustment of the ink and can speedily adjust the temperature, it is easier to correct discharging variation during printing.
To more effectively enjoy the effect of temperature adjustment with the sub-heater 15, the heating resistance element 7 preferably adopts a structure for performing heating with front and back surfaces, similarly to the sub-heater 15. When a protective layer is provided on the surface of the heating resistance element 7, extra energy is needed, and accumulated heat in the protective layer sometimes affects the temperature adjustment. From the viewpoint of temperature management in the action chamber 8, the heating resistance element 7 and the sub-heater 15 are preferably formed of a material having sufficient durability without using the protective layer. Such a material of the heating resistance element 7 and the sub-heater 15 is, for example, an amorphous-based high-resistance material mainly composed of a high-melting-point metal such as TiAlN. Alternatively, the material may be a laminate of TiAlN and TiAl.
From the viewpoint of enhancement of discharging efficiency, the sub-heater 15 is preferably disposed at a position such as to speedily heat the ink near the heating resistance element 7 and such as to be out of the area between the discharge port 5 and the heating resistance element 7 that may affect discharging. Such a position is, for example, a position on the partition 9, which forms the bypass channel, on the side of the heating resistance element 7.
Further, from the viewpoint of heating efficiency of the sub-heater 15, it is preferable that the electric resistance of the sub-heater 15 should be higher. Although the electric resistance can be increased by selecting a material having high specific resistance, when the same material is used, the electric resistance can also be increased by decreasing the cross-sectional area of the sub-heater 15, that is, by decreasing the thickness of the sub-heater 15.
When the thickness of the sub-heater 15 is decreased, the mechanical strength of the sub-heater 15 decreases. Since the sub-heater 15 repeats heating, it suffers structural fatigue due to thermal stress. Further, the sub-heater 15 itself vibrates owing to, for example, a Karman vortex caused by movement of the ink through the through hole 11 of the sub-heater 15 and its surroundings, and accumulation of vibration may cause structural fatigue. If the sub-heater 15 is used in the state of structural fatigue, it is broken, and this causes trouble with the element substrate 2 and the liquid discharging head 1.
In the embodiment, as illustrated in
According to this structure, even when both surfaces of the heat generating part of the sub-heater 15 are separate from the substrate 19 and are exposed to the ink, rigidity of the entire sub-heater 15 can be increased, breakage resulting from thermal stress and structural fatigue due to vibration can be prevented, and the operating life can be lengthened. Further, the sub-heater 15 can be prevented from being broken by vibration or unexpected fall during transportation of the liquid discharging head 1 or a liquid discharging apparatus (not illustrated) incorporating the liquid discharging head 1.
The third support portion 18 is preferably connected to the wall of the action chamber 8 with an insulator being disposed therebetween. By electrically insulating the third support portion 18 from the wall of the action chamber 8, thermal diffusion to the wall of the action chamber 8 (substrate main body and discharge-port forming member) due to free electrons can be prevented, and the decrease in efficiency of the sub-heater 15 can be avoided. Further, when the third support portion 18 is electrically insulated from the wall of the action chamber 8, it becomes an electrically suspended component, and does not greatly change the total resistance of the sub-heater 15. Therefore, the sub-heater 15 can ensure an amount of heat generation similar to that when the third support portion 18 is not provided. As illustrated in
In the embodiment, the supply port 13 is provided in each action chamber 8, and the channel length of the supply port 13 is longer than the channel length from an exit end of the supply port 13 to the discharge port 5. This structure can make the backward resistance of the ink high and can make the forward resistance low. Thus, the discharge efficiency can be further enhanced in combination with the liquid resistance at the supply port 13 having a length more than or equal to the predetermined length.
While the heating resistance element 7 is used as the energy generating element in the embodiment, a piezoelectric element having a vibrating plate may be used as the energy generating element. When the energy generating element is the piezoelectric element, the sub-heater 15 is preferably disposed at a position such as to be opposed to the piezoelectric element within the action chamber 8 and such as to be shifted to a fixed portion of the vibrating plate on a side of the discharge port 5.
While the present invention is applicable to any kind of ink, it is advantageous particularly for pigment ink that is likely to aggregate and high-function ink having a high content of additive resin. The present invention is, of course, not limited to the element substrate that discharges ink, and is also applicable to an element substrate that discharges liquid.
While the heating element 15 serving as the sub-heater is provided within the action chamber 8 in the above-described embodiment, the present invention is not limited thereto. The heating element may be provided at any position as long as it is exposed to liquid in the liquid discharging head. For example, the heating element may be provided within the supply port 13, the channel communicating between the supply port 13 and the action chamber 8, or the common liquid chamber.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2014-126412, filed Jun. 19, 2014, which is hereby incorporated by reference herein in its entirety.
Number | Date | Country | Kind |
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2014-126412 | Jun 2014 | JP | national |
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Number | Date | Country | |
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20150367642 A1 | Dec 2015 | US |