Field of the Invention
The present invention relates to a liquid discharging head that performs recording by discharging liquid, such as ink, toward various kinds of media, a liquid discharging apparatus, and a liquid suction method.
Description of the Related Art
A liquid discharging head, such as an inkjet head, includes a common liquid chamber that supplies liquid, such as ink, to a plurality of discharge ports. The common liquid chamber is connected to a liquid reservoir tank, and forms a part of a liquid flow passage extending from the liquid reservoir tank to the discharge ports. During liquid discharging, a meniscus of liquid repeats forward movement and backward movement near a discharge port. Rapid forward and backward movements of the meniscus deteriorate print quality. That is, when the meniscus moves forward, unexpected dispersion (splash) of the liquid from the discharge port may occur. When the meniscus moves backward, refilling the discharge port with the liquid is not quickly performed, and this may make it difficult to obtain sufficient discharging speed and discharging amount. Such rapid forward and backward movements of the meniscus are caused by a pressure fluctuation inside the common liquid chamber. In particular, the pressure in the common liquid chamber rises immediately after discharging of the liquid is completed.
Japanese Patent Laid-Open No. 2007-030459 discloses a liquid discharging head in which a buffer chamber is provided in a flow passage between a common liquid chamber and a liquid reservoir tank. Japanese Patent Laid-Open No. 2006-240150 discloses a liquid discharging head including a buffer chamber that has an opening in a wall of a common liquid chamber. The buffer chamber stores gas, and this suppresses a rapid pressure fluctuation inside the common liquid chamber.
In the liquid discharging head disclosed in Japanese Patent Laid-Open No. 2007-030459, since the buffer chamber is located far from discharge ports, the effect of suppressing the pressure fluctuation immediately after completion of liquid discharging is small, and it is difficult to sufficiently prevent defective printing. In the liquid discharging head disclosed in Japanese Patent Laid-Open No. 2006-240150, since the buffer chamber is located at a position near discharge ports, the effect of suppressing pressure fluctuation immediately after completion of liquid discharging is large. On the other hand, a bubble in the buffer chamber catches bubbles contained in liquid or the like, and grows with time. The grown bubble is partly peeled, and is ejected from the discharge port. If this phenomenon occurs during printing, the bubble clogs the discharge port, and discharging failure occurs.
Peeling of the bubble is promoted by flow of the liquid inside the common liquid chamber. For this reason, the bubble is hardly peeled but easily grows in a section where fluidity of the liquid is low. When a bubble having a large volume peels off a grown bubble, discharging failure is more likely to occur. Particularly in an end portion of the common liquid chamber and a region where the height of the common liquid chamber is small, a large bubble is easily produced because fluidity of the liquid is low.
The present invention provides a liquid discharging head in which a bubble hardly grows inside a buffer chamber, a liquid discharging apparatus, and a liquid suction method.
A liquid discharging head according to an aspect of the present invention includes a recording element board in which a plurality of discharge ports configured to discharge liquid are arrayed in a first direction, a support member configured to support the recording element board and including a common liquid chamber extending in the first direction to supply the liquid to the plurality of discharge ports and a buffer chamber configured to have an opening in a ceiling surface of the common liquid chamber opposed to the recording element board and to hold a bubble, and a heater located in a region of the recording element board opposed to a part of the ceiling surface extending from the opening of the buffer chamber to an end portion in the first direction and configured to generate heat when the liquid is not discharged from the plurality of discharge ports.
A liquid discharging head according to another aspect of the present invention includes a recording element board having a plurality of discharge ports configured to discharge liquid, a support member configured to support the recording element board and including a common liquid chamber configured to supply the liquid to the plurality of discharge ports, a buffer chamber configured to have an opening in a ceiling surface of the common liquid chamber opposed to the recording element board and to hold a bubble, and a liquid supply port configured to have an opening in the ceiling surface and to supply the liquid to the common liquid chamber, the ceiling surface including a first part located between the opening of the liquid supply port and the opening of the buffer chamber and a second part located on a side of the opening of the buffer chamber opposite from the first part and located at a shorter distance from the recording element board than the first part, and a heater located in a region of the recording element board opposed to the second part and configured to generate heat when the liquid is not discharged from the plurality of discharge ports.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Configurations of liquid discharging heads according to some embodiments of the present invention will be described with reference to the drawings. While the following embodiments relate to inkjet heads for discharging ink onto a recording medium, the present invention is not limited thereto, and can be widely applied to liquid discharging heads for discharging liquid. In the following description, a direction in which discharge ports are arrayed, that is, a direction in which a discharge port array extends is sometimes referred to as an x-direction or a first direction, a direction parallel to a discharge port formation surface and orthogonal to the x-direction is sometimes referred to as a y-direction, and a direction orthogonal to the x- and y-directions is sometimes referred to as a z-direction. While the x-direction or the first direction coincides with the longitudinal direction of a recording element board or a common liquid chamber in the embodiments, the present invention is not limited thereto. The z-direction is orthogonal to the discharge port formation surface, and coincides with a vertical direction in an installation state of a liquid discharging apparatus in which the liquid discharging head is assembled.
Each recording element board 4 includes a substrate 19 and a discharge port formation substrate 20 bonded to the substrate 19.
The support member 2 has a common liquid chamber that supplies liquid to the discharge port arrays 22. The common liquid chamber 6 extends in the longitudinal direction serving as the x-direction, and is connected to the ink supply channel 16 of the substrate 19. The common liquid chamber 6 is defined by the recording element board 4, a ceiling surface 23 opposed to the recording element board 4, and side walls 24 that connect the ceiling surface to the recording element board 4. The z-direction distance from the ceiling surface 23 to the recording element board 4 is the longest in a longitudinal center portion 25 and is the shortest in both longitudinal end portions 26. Therefore, the common liquid chamber 6 is nearly shaped like an isosceles triangle whose bottom side is formed by the recording element board 4, when viewed from the y-direction. In the longitudinal center portion 25 of the ceiling surface 23 where the z-direction distance to the recording element board 4 is the longest, a liquid supply port 7 is provided to supply liquid to the common liquid chamber 6 therethrough. The liquid supply port 7 penetrates a ceiling plate 27 of the support member 2 that forms the ceiling surface 23, and is connected to the ink tank supported by the housing 10. The support member 2 can be produced using a metallic die. Alternatively, the support member 2 can be produced by compacting powder with a press.
On both longitudinal sides of the liquid supply port 7, that is, between the liquid supply port 7 and the longitudinal end portions 26 of the ceiling surface 23, two buffer chambers 3 are open. The buffer chambers 3 extend in the vertical direction z, and end in a middle portion of the support member 2. That is, the buffer chambers 3 are dead-end spaces having openings only in the ceiling surface 23. The buffer chambers 3 hold bubbles. Pressure vibrations of ink are induced in the common liquid chamber 6 for the purpose of flow of the ink during printing. The bubbles in the buffer chambers 3 reduce these pressure vibrations by expanding when the pressure decreases and shrinking when the pressure increases. The bubble in the buffer chambers 3 also absorb a rapid change in negative pressure inside the common liquid chamber 6 when the ink is discharged from the discharge ports 8 at a high frequency.
The ceiling surface 23 includes first parts 23a located between an opening 7a of the liquid supply port 7 and openings 3a of the buffer chambers 3 and second parts 23b located between the openings 3a of the buffer chambers 3 and the longitudinal end portions 26. The second parts 23b are located on sides of the openings 3a of the buffer chambers 3 opposite from the first parts 23a, and the z-direction distance from the second parts 23b to the recording element board 4 is shorter than that of the first parts 23a. While the first and second parts 23a and 23b are flat surfaces, they may be curved or may have irregularities.
After the ink is not discharged for a fixed time, it may not be normally discharged owing to clogging or thickening thereof. For this reason, the liquid discharging apparatus is provided with a suction mechanism that sucks ink from the discharge port arrays 22. Specifically, the liquid discharging head 1 is retracted to a predetermined region and preliminary discharging is performed to discharge the ink from the discharge ports 8 at regular intervals or before or after a recording operation. At this time, the ink is forcibly discharged from the liquid discharging head 1 by bringing a cap 14 of the suction mechanism 28 into contact with the discharge port formation surface 21 to cover the plurality of discharge ports 8 and operating a suction pump (not illustrated) connected to the cap 14. This recovers discharging performance of the liquid discharging head 1 and allows normal discharging. These series of operations are referred to as a suction recovery operation.
Next, states of bubbles in the buffer chambers 3 will be described with reference to
When printing is further performed in this state, the parts of the bubbles 12 protruding outside from the buffer chambers 3 peel at a certain time, and the peeled parts of the bubbles 12 are brought toward the discharge ports 8 by the ink 11. The bubbles 12 entering the discharge ports 8 hinder refilling of the ink 11, and this causes defective printing. Further, the following problem is caused because of the shape of the common liquid chamber and the positional relationship between the buffer chambers 3 in the common liquid chamber 6.
The height in the z-direction (the cross-sectional area) of the second parts 23b of the ceiling surface 23 is less than that of the first parts 23a. That is, the inertial resistance of the second parts 23b is lower than that of the first parts 23a, and the ink 11 less easily moves than at the first parts 23a. In other words, the common liquid chamber 6 includes first regions 23a having a relatively high inertial resistance and second regions 23b having a relatively low inertial resistance. The openings 3a of the buffer chambers 3 are disposed in the first regions 23a. When a suction recovery operation or preliminary discharging is performed, since the volume is small in the portions near the longitudinal end portions 26 of the common liquid chamber 6, fluidity of the ink 11 becomes lower than in the other portions. Since the portions near the longitudinal end portions 26 of the common liquid chamber 6 also face the side walls 24 of the common liquid chamber 6, the fluidity of the ink 11 further worsens. In contrast, the flow velocity of the ink 11 is high in a portion near the liquid supply port 7. This is because the ink 11 is introduced from the liquid supply port 7 and the height in the z-direction of the common liquid chamber 6 is large in the portion near the liquid supply port 7. The ink 11 mainly flows near the longitudinal center portion 25 of the common liquid chamber 6, and stays near the longitudinal end portions 26 closer to the ends than the buffer chambers 3. Thus, the force of peeling the bubbles 12 in the buffer chambers 3 is not sufficiently applied, and the bubbles 12 continue growth. When the grown bubbles 12 partly peel with a large volume, not only large bubbles 12 invade in the discharge ports 8, but also the ink 11 is not supplied in time in the longitudinal end portions 26 of the common liquid chamber 6. As a result, refilling of the discharge ports 8 in the longitudinal end portions 26 is not sufficiently performed, and this is likely to cause defective printing.
For this reason, in in this embodiment, as illustrated in
While the ink 11 is heated before and during operation of the suction mechanism 28, that is, before the start of suction and during a period in which suction is performed in this embodiment, it can be heated at least before or during the operation of the suction mechanism 28. While the heating resistance elements 18 are used for the original ink discharging purpose and the ink heating purpose peculiar to the present invention in the embodiment, the ink 11 is not discharged during heating. The printing operation is also not performed during the operation of the suction mechanism 28. Since the operation of the heating resistance elements 18 for heating the ink 11 is thus performed out of the printing operation, it is possible to decrease the probability that the bubbles 12 peel during the printing operation and cause defective printing.
When the longitudinal end portions 26 of the common liquid chamber 6 are heated, a voltage lower than the voltage in preliminary discharging and printing is applied to the heating resistance elements 18 so that the ink 11 is not discharged. That is, at this time, the heating amount of the heating resistance elements 18 is smaller than the heating amount for applying discharging energy to the liquid. Here, the heating resistance elements 18 located outside the heating regions 29 are referred to as first heating resistance elements 18a, and the heating resistance elements 18 located inside the heating regions 29 are referred to as second heating resistance elements 18b (see
In this embodiment, intersections 32 of the second parts 23b and the buffer chambers 3 are located closer to the recording element board 4 than extension lines 33 of lines that connect intersections 30 of the first parts 23a and the liquid supply port 7 and intersections 31 of the first parts 23a and the buffer chambers 3. In other words, portions of the buffer chambers 3 on the sides of the longitudinal end portions 26 are located closer to the recording element board 4 than extension surfaces of the first parts 23a of the ceiling surface 23. Thus, bubbles easily peel before they glow large.
Although the present invention can be applied to the liquid discharging head that discharges liquid, it can be suitably applied particularly to a long liquid discharging head in which the length of a recording element board exceeds one inch and there is much variation in the flow of ink inside a common liquid chamber. The present invention is also suitably applicable to a liquid discharging head in which low-viscosity ink is supplied at high velocity because of high-speed driving. This is because pressure vibrations of the low-viscosity ink inside the common liquid chamber are large and the volume of bubbles held in buffer chambers needs to be kept constant. When heat-retention driving is performed to maintain a predetermined temperature of the ink, there is a tendency to decrease the viscosity of the ink and to increase pressure vibrations inside the common liquid chamber. Hence, the present invention can be suitably applied to such a case. The present invention can also be suitably applied to a case in which the support member is formed of a resin having a small thermal capacity, because the temperature of the ink is likely to rise. The present invention can also be suitably applied to a case in which the support member is formed of a metal having a large thermal capacity.
In the present invention, the heating regions 13 are not limited to the ones in the above-described embodiments. In the present invention, when the buffer chambers are provided in the regions of the common liquid chamber 6 where the ink relatively hardly moves, the temperature of ink in the regions where the ink relatively hardly moves is made higher than the temperature of ink in the regions where the ink relatively easily moves by the heating unit. In the above-described embodiments, the regions where the ink relatively hardly moves are the first parts 23a, and the regions where the ink relatively easily moves are the second parts 23b. The present invention is applicable to the range that satisfies this condition. For example, the present invention can be suitably applied not only to the common liquid chamber having a triangular cross section in the above-described embodiments, but also to a common liquid chamber having a rectangular cross section when the height (in the z-direction) of the common liquid chamber is low and the length of the common liquid chamber in the x-direction is long. The region where the ink easily moves means that the inertial resistance is relatively low in the region, and the region where the ink hardly moves means that the internal resistance is relatively high in the region.
According to the above configurations, fluidity of the liquid increases near the buffer chambers of the common liquid chamber, and bubbles held in the buffer chambers partly and easily peel. For this reason, the size (amount) of the bubbles is adjusted, and the bubbles hardly grow inside the buffer chambers. Therefore, according to the present invention, it is possible to provide a liquid discharging head in which bubbles hardly grow large inside buffer chambers, a liquid discharging apparatus, and a liquid suction method.
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. 2015-146462, filed Jul. 24, 2015, which is hereby incorporated by reference herein in its entirety.
Number | Date | Country | Kind |
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2015-146462 | Jul 2015 | JP | national |