LIQUID EJECTION HEAD, LIQUID EJECTION UNIT, AND DEVICE FOR EJECTION OF LIQUID

Abstract

To provide a liquid discharge head capable of reducing load on a pump, and a liquid discharge unit and a liquid discharge device.SOLUTION: A liquid discharge head 504 includes a liquid channel 10. Ink as a thixotropic liquid in the liquid channel is discharged from a nozzle. The liquid discharge head 504 further includes a supply-side shear force applying member 31a for applying shear force to the thixotropic ink in the liquid channel 10, and a discharge-side shear force applying member 31b.SELECTED DRAWING: Figure 11

Description

[Technical Field]

[0001] The present invention relates to a liquid ejection head, a liquid ejection unit, and an apparatus for ejecting liquid. [Background technology]

[0002] There have been known liquid ejection devices equipped with liquid ejection heads that eject thixotropic (also called thixotropic) liquids from nozzles. Thixotropy is the property of a liquid to become less viscous when subjected to shearing force, and to return to a high viscosity state when the shearing force is removed.

[0003] Patent document 1 describes a device for ejecting the above-mentioned liquid, which applies shear force to the thixotropic ink by circulating the ink between an ink tank containing the liquid ink and a liquid ejection head, thereby reducing the viscosity of the thixotropic ink. Summary of the Invention [Problem to be solved by the invention]

[0004] However, there was a problem in that the load on the pump was large. [Means for solving the problem]

[0005] In order to solve the above problems, the present invention provides a liquid ejection head that ejects a thixotropic liquid in a liquid flow path from a nozzle, the liquid ejection head including a shear force applying member that applies a shear force to the liquid in the liquid flow path. The shearing force applying member is provided so as to be movable within the liquid flow path, and the shearing force applying member moves within the liquid flow path at a timing other than during a liquid ejection operation in which liquid is ejected from the nozzle. It is characterized by the following. [Effects of the Invention]

[0006] According to the present invention, the load on the pump can be reduced. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 2 is a plan view illustrating a main part of the device for discharging liquid according to the embodiment. [Figure 2] FIG. 2 is a side view illustrating a main part of the device for discharging liquid according to the embodiment. [Figure 3] FIG. 10 is an explanatory plan view of a main part of another example of a liquid ejection unit. [Figure 4] FIG. [Figure 5] FIG. 2 is a perspective view showing a liquid ejection head and a liquid flow path within the liquid ejection head. [Figure 6] FIG. [Figure 7] 3A and 3B are diagrams for explaining ink ejection from a nozzle. [Figure 8] 10 is a graph showing the relationship between the viscosity of ink in a liquid flow path of a liquid ejection head and pressure loss. [Figure 9] FIG. 2 is a perspective view showing a liquid ejection head and a shear force applying mechanism that applies shear force to ink in a liquid flow path of the liquid ejection head. [Figure 10] The application of shear force to the ink in the liquid flow path will now be described. [Figure 11] 11(a) is a diagram showing the position of the shear force applying member in the liquid flow path when the pressure plate is separated from the side plate, and FIG. 11(b) is an enlarged view of a portion A in FIG. 11(a). [Figure 12] 10 shows how the pressure plate is pressed by the side plate and the shear force applying member moves within the liquid flow path. [Figure 13] FIG. [Figure 14] FIG. 10 is an enlarged view of a main part of the second modified example. [Figure 15] FIG. 11 is an enlarged view of a main part of the third modified example. [Figure 16] 13A and 13B are diagrams illustrating an example of a mechanism for moving a flat plate in the third modified example. [Figure 17] FIG. 10 is a diagram showing an example of a configuration in which ink circulation by a liquid feed pump is not performed. DETAILED DESCRIPTION OF THE INVENTION

[0008] First, the configuration of a liquid ejection device equipped with a liquid ejection head according to the present invention will be described with reference to the drawings.

[0009] FIG. 1 is an explanatory plan view of the main parts of the device for discharging liquid according to this embodiment, and FIG. 2 is an explanatory side view of the main parts of the device for discharging liquid according to this embodiment. This liquid ejection device is a serial type device, and a carriage 503 is moved back and forth in the main scanning direction by a main scanning movement mechanism 593 serving as a head movement means. The main scanning movement mechanism 593 is composed of a guide member 501, a main scanning motor 505, a timing belt 508, etc. The guide member 501 is hung between side plates 591A and 591B provided on both sides in the longitudinal direction of the device, and movably holds the carriage 503. The carriage 503 is moved back and forth in the main scanning direction, which is the longitudinal direction of the device, by the main scanning motor 505 via a timing belt 508 hung between a drive pulley 506 and a driven pulley 507.

[0010] The carriage 503 is provided with a liquid ejection unit 540 equipped with a liquid ejection head 504. The liquid ejection head 504 of the liquid ejection unit 540 ejects liquid of each color, for example, yellow (Y), cyan (C), magenta (M), and black (K). The liquid ejection head 504 is mounted with a nozzle row consisting of a plurality of nozzles arranged in a sub-scanning direction perpendicular to the main scanning direction, and the ejection direction facing downward. A supply and circulation mechanism 594 supplies liquid stored outside the liquid ejection head 504 to the liquid ejection head 504, and supplies and circulates the liquid within the liquid ejection head 504.

[0011] The liquid ejection device is equipped with a transport mechanism 595 for transporting paper 510. The transport mechanism 595 is composed of a transport belt 512, which is a transport means, and a sub-scanning motor 516 for driving the transport belt 512. The transport belt 512 attracts the paper 510 and transports it to a position facing the liquid ejection head 504. The transport belt 512 is an endless belt that is stretched between a transport roller 513 and a tension roller 514. The paper 510 can be attracted to the transport belt 512 by electrostatic attraction or air suction. The transport belt 512 moves in a circular motion in the sub-scanning direction as the transport roller 513 is rotated and driven by the sub-scanning motor 516 via a timing belt 517 and a timing pulley 518.

[0012] A maintenance and recovery mechanism 520 that maintains and recovers the liquid ejection head 504 is disposed on one side of the carriage 503 in the main scanning direction, beside the conveyor belt 512. The maintenance and recovery mechanism 520 is composed of, for example, a cap member 521 that caps the nozzle surface (the surface on which the nozzles are formed) of the liquid ejection head 504, a wiper member 522 that wipes the nozzle surface, and the like.

[0013] The main scanning movement mechanism 593, supply circulation mechanism 594, maintenance recovery mechanism 520, and transport mechanism 595 are attached to a housing formed by side plates 591A and 591B, a back plate 591C, etc. In a liquid ejecting device configured in this manner, a sheet of paper 510 is fed onto and adsorbed to a conveyor belt 512, and the sheet of paper 510 is transported in the sub-scanning direction by the circular movement of the conveyor belt 512. Then, by driving the liquid ejection head 504 in accordance with an image signal while moving the carriage 503 in the main scanning direction, liquid is ejected onto the stationary sheet of paper 510, thereby forming an image. In this way, the liquid ejection device, equipped with the liquid ejection head 504, can stably form high-quality images.

[0014] Next, another example of the liquid ejection unit 540 will be described with reference to FIG. 3 is a plan view illustrating the main parts of the unit. Of the components that make up the device for discharging the liquid, this liquid discharge unit 540 is made up of a housing portion made up of side plates 591A and 591B and a back plate 591C, a main scanning movement mechanism 593, a carriage 503, and a liquid discharge head 504. It is also possible to configure this liquid discharge unit 540 by further attaching at least one of the maintenance and recovery mechanism 520 and the supply and circulation mechanism 594 described above to, for example, side plate 591B of this liquid discharge unit 540.

[0015] In this embodiment, a "liquid ejection head" refers to a functional component that ejects and sprays liquid from nozzles. The ejected liquid may have a viscosity and surface tension that allows it to be ejected from the head. Specifically, the liquid may be a solution, suspension, emulsion, or the like containing a solvent such as water or an organic solvent, a colorant such as a dye or pigment, a functionalizing material such as a polymerizable compound, a resin, or a surfactant, a biocompatible material such as DNA, amino acids, proteins, or calcium, or an edible material such as a natural dye. These may be used, for example, as inkjet ink, a surface treatment liquid, a liquid for forming components of electronic elements or light-emitting elements, a liquid for forming electronic circuit resist patterns, a material liquid for 3D modeling, and the like.

[0016] A "liquid ejection unit" is a collection of components related to liquid ejection, in which functional components and mechanisms are integrated with a liquid ejection head. For example, a "liquid ejection unit" includes a combination of a liquid ejection head and at least one of a supply / circulation mechanism, a carriage, a maintenance / recovery mechanism, and a main scanning movement mechanism. Here, "integration" includes, for example, a combination in which the liquid ejection head and functional components or mechanisms are fixed to each other by fastening, bonding, engaging, or the like, or a combination in which one is held movably relative to the other. The liquid ejection head, functional components, and mechanisms may also be configured to be detachable from each other.

[0017] For example, some liquid ejection units integrate a liquid ejection head and a supply / circulation mechanism. Others integrate the liquid ejection head and the supply / circulation mechanism by connecting them with a tube or the like. A filter unit can be added between the supply / circulation mechanism and the liquid ejection head of these liquid ejection units. Other liquid ejection units integrate a liquid ejection head and a carriage. Other liquid ejection units integrate a liquid ejection head and a scanning movement mechanism by movably holding the liquid ejection head on a guide member that constitutes part of a scanning movement mechanism. Other liquid ejection units integrate a liquid ejection head, carriage, and maintenance / recovery mechanism by fixing a cap member, which is part of a maintenance / recovery mechanism, to a carriage to which the liquid ejection head is attached. Other liquid ejection units integrate a liquid ejection head and a supply mechanism by connecting a tube to a liquid ejection head to which a supply / circulation mechanism or a flow path component is attached. Liquid from a liquid storage source is supplied to the liquid ejection head via this tube. The main scanning movement mechanism also includes the guide member alone. The supply circulation mechanism also includes the tube alone and the loading unit alone. The supply circulation mechanism also includes a sub-tank that is mounted on the carriage and temporarily stores liquid from the liquid storage source and supplies it to the liquid ejection head.

[0018] A "liquid ejecting device" is a device that has a liquid ejection head or a liquid ejection unit and ejects liquid by driving the liquid ejection head. Liquid ejecting devices include not only devices that can eject liquid onto objects onto which the liquid can adhere, but also devices that eject liquid into air or liquid. This "liquid ejecting device" can also include means for feeding, transporting, and discharging objects onto which the liquid can adhere, as well as pre-processing devices and post-processing devices.

[0019] For example, "liquid ejecting devices" include image forming devices that eject ink to form an image on paper, and three-dimensional modeling devices (three-dimensional modeling devices) that eject modeling liquid onto a powder layer formed by forming a powder in a layered form in order to form a three-dimensional object (a three-dimensional model). Furthermore, "liquid ejecting devices" are not limited to devices that visualize meaningful images such as letters and figures using the ejected liquid. For example, they also include devices that form patterns that have no meaning in themselves, and devices that form three-dimensional images.

[0020] The above-mentioned "substances to which a liquid can adhere" refers to substances to which a liquid can adhere at least temporarily, such as substances to which the liquid can adhere and stick, or substances to which the liquid can adhere and penetrate. Specific examples include media such as paper, recording paper, film, and cloth, electronic substrates, electronic components such as piezoelectric elements, powder layers, organ models, and test cells, and unless otherwise specified, includes all substances to which a liquid can adhere. The above-mentioned "substances to which a liquid can adhere" may be any material to which a liquid can adhere, such as paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, or ceramics, as long as the liquid can adhere even temporarily.

[0021] Furthermore, the term "liquid ejecting device" includes, but is not limited to, a device in which a liquid ejection head and an object onto which the liquid can be attached move relatively. Specific examples include a serial-type device in which the liquid ejection head moves, and a line-type device in which the liquid ejection head does not move. Other examples of "liquid ejecting device" include a treatment liquid application device that ejects a treatment liquid onto paper to apply the treatment liquid to the surface of the paper for purposes such as modifying the surface of the paper. Another example is an injection granulation device that sprays a composition liquid in which raw materials are dispersed through a nozzle to granulate fine particles of the raw materials. In addition, the terms "image formation," "recording," "printing," "imaging," "printing," "shaping," and the like in this application are all synonymous.

[0022] FIG. 4 is a diagram illustrating the supply circulation mechanism 594. The supply and circulation mechanism 594 serving as a liquid supply unit includes an ink tank 410, a liquid feed pump 438, and a paired tube 556 formed by integrating two tubes, a supply tube 556a (see FIG. 9) and a circulation tube 556b (see FIG. 9). The ink in the ink tank 410 is supplied to the liquid ejection head 504 by the liquid feed pump 438 via the supply tube of the paired tube 556. Furthermore, the ink in the liquid flow path of the liquid ejection head 504 is returned to the supply tube via the circulation tube of the paired tube 556. Note that the ink may be returned to the ink tank 410 via the circulation tube.

[0023] Also, a sub-tank may be provided in the carriage 503 to temporarily store ink supplied from the ink tank 410 through a supply tube, and the ink may be supplied from the sub-tank to the liquid ejection head 504. Also, ink may be circulated between the sub-tank and the liquid ejection head 504.

[0024] Next, the liquid flow path 10 inside the liquid ejection head 504 will be described. FIG. 5 is a perspective view showing a liquid ejection head 504 and a liquid flow path 10 inside the liquid ejection head, and FIG. 6 is a perspective view of the liquid flow path 10. As shown in FIG. A supply port 10d and a discharge port 10e of a liquid flow path 10 are provided on one side surface of the liquid ejection head in the main scanning direction. The liquid flow path 10 has a liquid supply path 10a having the supply port 10d, and a liquid discharge path 10b. The liquid flow path 10 also has a relay path 10f that connects the downstream end of the liquid supply path 10a in the ink flow direction to the upstream end of the liquid discharge path 10b in the ink flow direction.

[0025] The liquid supply path 10a is provided with a plurality of individual liquid chambers 10c spaced at predetermined intervals. A nozzle 12 is provided on the bottom surface of each individual liquid chamber. Each individual liquid chamber 10c is also provided with an opening / closing pin 13 as a nozzle opening / closing member for opening and closing the nozzle 12.

[0026] FIG. 7 is a diagram illustrating ink ejection from the nozzles 12. As shown in FIG. In this embodiment, ink is ejected from the nozzles using a valve jet method. Pressure is applied to the ink in the liquid flow path, and the pressure applied to this liquid causes the ink to be ejected from the nozzles 12 to form an image. As shown in Figure 7(a), when ink is not being ejected, the opening / closing pin 13 is lowered to block the nozzles 12, preventing ink from flowing into the nozzles 12.

[0027] 7(b), when ink is ejected, the opening / closing pin 13 is raised to open the nozzle 12, and ink is ejected from the nozzle 12 by the ink pressure in the liquid flow path. An image is formed on the paper 510 by controlling the opening and closing of the nozzle by the opening / closing pin 13 at high speed.

[0028] In this embodiment, thixotropic ink is used. Thixotropy is a property in which the viscosity of a material decreases when shearing force is applied, and returns to a high viscosity state when the shearing force is removed. By using such thixotropic ink, the ink can be ejected from the nozzles 12 with low viscosity, and after ejection onto the paper, the ink becomes highly viscous, preventing bleeding and dripping.

[0029] In this embodiment, the ink is circulated by the liquid feed pump 438, and the ink flow applies shear force to the thixotropic ink, reducing the ink viscosity to 100 mPa·s or less, before performing the image formation operation. This is because if the ink viscosity exceeds 100 mPa·s, there is a risk that the ink will not be ejected from the nozzles 12.

[0030] When the ink circulation by the liquid feed pump 438 is stopped, for example, when the power of the device is turned off, no shear force is applied to the ink, and the thixotropic ink becomes highly viscous. As a result, the energy required to move the ink when the ink circulation starts, such as immediately after starting the device, increases, and a large load is placed on the liquid feed pump 438.

[0031] FIG. 8 is a graph showing the relationship between the viscosity of ink in the liquid flow path 10 of the liquid ejection head and the pressure loss. As shown in Figure 8, when sufficient shear force is applied to the ink and the ink viscosity is 50 mPa·s, the pressure loss (energy required to make the ink flow) is 208 KPa. On the other hand, the viscosity of ink to which no shear force is applied is 1000 mPa·s. In this case, the pressure loss is 3498 KPa, which means that the energy required to make the ink flow is 16.8 times greater than when sufficient shear force is applied to the ink (viscosity 50 mPa·s).

[0032] By increasing the cross-sectional area of ​​the flow path or by increasing the number of paths, it is possible to reduce pressure loss and reduce the large load on the liquid feed pump 438 when the ink starts to circulate. Regarding the supply path that supplies ink from the ink tank 410 to the liquid ejection head 504 and the circulation path that circulates the ink discharged from the liquid ejection head 504, pressure loss can be reduced by using the following configuration. That is, it is possible to reduce pressure loss by using supply tubes and circulation tubes with large pipe diameters or by using multiple supply tubes and circulation tubes.

[0033] However, the liquid flow path 10 in the liquid ejection head cannot be divided into separate paths. Increasing the cross-sectional area of ​​the liquid flow path 10 would result in an increase in the size of the liquid ejection head 504. Furthermore, increasing the cross-sectional area of ​​the liquid flow path 10 would result in a difference in flow between the center and the outside of the liquid flow path 10. That is, ink in the center flows easily, but ink on the outside flows poorly due to flow resistance with the inner wall of the liquid flow path 10. This creates a difference in flow between the center and the outside of the liquid flow path 10, which in turn creates a difference in shear force applied between the center and the outside, potentially resulting in a difference in viscosity between the center and the outside of the liquid flow path 10. If a difference in ink viscosity occurs within the liquid flow path 10, highly viscous ink may be ejected, potentially resulting in poor image formation.

[0034] As described above, it is difficult to reduce pressure loss by varying the shape of the liquid flow path 10 of the liquid ejection head 504. Therefore, in this embodiment, a shear force applying member is provided to apply shear force to the ink in the liquid flow path 10 of the liquid ejection head 504, and this shear force applying member applies shear force to the ink in the liquid flow path 10 before the ink starts circulating, thereby reducing the ink viscosity. This reduces pressure loss in the liquid flow path 10 when the ink starts circulating, and allows the ink circulation to start with less energy. This makes it possible to prevent a large load from being placed on the liquid feed pump 438. Below, the characteristic features of this embodiment will be specifically described using the drawings.

[0035] FIG. 9 is a perspective view showing the liquid ejection head 504 and the shear force applying mechanism 30 that applies shear force to ink in the liquid flow paths of the liquid ejection head 504. As shown in FIG. The shear force applying mechanism 30 has a supply-side shear force applying member 31a and a discharge-side shear force applying member 31b. The supply-side shear force applying member 31a moves back and forth within the liquid supply path 10a of the liquid flow path 10, applying a shear force to the ink in the liquid supply path 10a. The discharge-side shear force applying member 31b moves back and forth within the liquid discharge path 10b of the liquid flow path 10, applying a shear force to the ink in the liquid discharge path 10b.

[0036] One end of each of the supply-side shear force application member 31a and the discharge-side shear force application member 31b is attached to a pressing plate 33 serving as a pressing member. A through-hole is provided in the center of the pressing plate 33, through which a spring support shaft 35 passes, supporting a spring 32 serving as a biasing means. A through-hole 41 through which the spring support shaft 35 passes is also provided in the side plate 591A opposite the pressing plate 33. The spring support shaft 35 is disposed between the supply-side shear force application member 31a and the discharge-side shear force application member 31b in the sub-scanning direction, and is attached to a connecting member 34. The spring 32 is supported by being inserted into the spring support shaft 35. One end of the spring 32 contacts the pressing plate 33, and the other end of the spring 32 contacts the connecting member 34.

[0037] FIG. 10 explains the application of shear force to the ink in the liquid flow path 10. For example, when starting up the device, before the liquid feed pump 438 starts to be driven, shear force is applied to the ink in the liquid flow path 10 . When a shear force is to be applied to the ink in the liquid flow path 10, the main scanning motor 505 (see FIG. 1) is driven to move the carriage 503 toward the side plate 591A. When the carriage 503 moves outside the range of movement in the main scanning direction when forming an image on paper, the pressure plate 33 comes into contact with the side plate 591A. When the carriage 503 is further moved toward the side plate 591A, the spring support shaft 35 passes through the through hole 41 and the pressure plate 33 is pressed by the side plate 591A, moving relatively toward the connecting member 34 against the biasing force of the spring 32. Then, the supply-side shear force applying member 31a and the discharge-side shear force applying member 31b move within the liquid flow path 10 of the liquid ejection head 504.

[0038] As the supply-side shear force applying member 31a moves within the liquid supply path 10a of the liquid flow path 10, a shear force is applied to the ink within the liquid supply path 10a, reducing the viscosity of the ink within the liquid supply path 10a. As the discharge-side shear force applying member 31b moves within the liquid discharge path 10b of the liquid flow path 10, a shear force is applied to the ink within the liquid supply path 10a, reducing the viscosity of the ink.

[0039] Furthermore, as the supply-side shear force application member 31a and the discharge-side shear force application member 31b move within the liquid flow path 10, the ink within the liquid supply path 10a and the liquid discharge path 10b is pushed toward the relay path 10f. As a result, some of the ink within the liquid supply path 10a and the liquid discharge path 10b flows into the relay path 10f, causing an ink flow in the relay path 10f. As a result, a shear force is also applied to the ink in the relay path 10f, which can also reduce the viscosity of the ink in the relay path 10f.

[0040] When the carriage 503 reaches one end of its range of movement in the main scanning direction, the rotation direction of the main scanning motor 505 is switched to move the carriage 503 toward the center in the main scanning direction. Then, the pressing plate 33 moves relatively away from the connecting member 34 due to the biasing force of the spring. As a result, the shear force applying members 31a and 31b in the liquid flow path move toward the connecting member 34, and a shear force is applied to the ink in the liquid supply path 10a and the liquid discharge path 10b. This makes it possible to further reduce the viscosity of the ink.

[0041] When the carriage 503 moves within its range of movement in the main scanning direction when forming an image on paper, the pressure plate 33 moves away from the side plate 591A, and the movement of the shear force applying members 31a and 31b stops. After the above shear force applying operation is performed, the liquid feed pump 438 starts to operate to circulate the ink. The above shear force applying operation may also be performed multiple times.

[0042] Fig. 11(a) shows the positions of the shear force application members 31a and 31b in the liquid flow path when the pressure plate 33 is separated from the side plate 591A, and Fig. 11(b) is an enlarged view of part A in Fig. 11(a). Also, Fig. 12 shows how the pressure plate 33 is pressed by the side plate 591A, causing the shear force application members 31a and 31b to move in the liquid flow path.

[0043] Each shear force applying member 31a, 31b has a bifurcated shape with the center portion of the round rod cut out. In the supply-side shear force applying member 31a, this cutout portion 311 functions as a clearance portion for the open-close pin 13. A plurality of shear flow path plates 312 (three in this embodiment) are provided at predetermined intervals in the cutout portion 311 as a mesh-like shear flow path portion having a plurality of openings formed therein to allow ink to pass through.

[0044] When the shear force applying members 31a and 31b move back and forth within the liquid flow path 10, the ink passes through the openings in the mesh-shaped shear flow path plate 312. When the ink passes through these openings, a shear force is applied to the ink, which can reduce the viscosity of the ink within the liquid flow path 10.

[0045] In this embodiment, the discharge-side shear force applying member 31b is the same as the supply-side shear force applying member 31a. However, the discharge-side shear force applying member 31b may have a different configuration from the supply-side shear force applying member 31a, for example, by increasing the number of shear flow path plates 312 compared to the supply-side shear force applying member 31a.

[0046] The movement amount of each shear force applying member 31a, 31b is equal to the distance between the individual liquid chambers of the liquid supply channel. The shear force applying member 312 is provided on the supply-side shear force applying member 31a so that it moves between the upstream end and downstream end of the individual liquid chambers 10c of the liquid supply channel 10a in the ink flow direction. This configuration allows the shear force applying member 312 to apply shear force evenly to the ink in the liquid supply channel 10a and the liquid discharge channel 10b without the need for each shear force applying member 31a, 31b to move from one end to the other of the liquid supply channel 10a and the liquid discharge channel 10b. When the supply-side shear force applying member 31a moves within the liquid supply channel, an ink flow occurs within the liquid supply channel, and this ink flow applies a shear force to the ink in the individual liquid chambers 10c.

[0047] 9, the distance between the pressure plate 33 and the liquid ejection head can be made shorter than when each shear force application member 31a, 31b is moved from one end of the liquid supply path 10a and the liquid ejection path 10b to the other. This makes it possible to reduce the distance between the side plate 591A and one end of the range of movement of the carriage in the main scanning direction when forming an image on paper, and it is possible to shorten the length of the device that ejects liquid in the main scanning direction, thereby enabling the device to be made more compact.

[0048] Furthermore, the shear flow channel plates 312 of each shear force applying member 31a, 31b are always positioned within the liquid flow channel. As a result, even when ink is circulated by the liquid feed pump 438, the ink passes through the openings of the shear flow channel plates 312 and is subjected to shear force, thereby maintaining the viscosity of the ink in the liquid flow channel at an appropriately low level.

[0049] In this manner, in this embodiment, the shear force application members 31a, 31b are moved back and forth within the liquid flow path 10 to reduce the viscosity of the ink within the liquid flow path 10, thereby reducing the pressure loss during ink flow. This reduces the load on the liquid feed pump 438 when it starts to operate. This eliminates the need to use a large, expensive pump capable of handling high loads as the liquid feed pump 438, thereby reducing the cost and size of the device.

[0050] Furthermore, in this embodiment, when the carriage 503 is within its range of movement in the main scanning direction when forming an image on paper, the pressure plate 33 is separated from the side plate 591A. This prevents the shear force application members 31a and 31b from moving during image formation, suppressing fluctuations in pressure within the liquid flow path during image formation and enabling good liquid ejection.

[0051] Next, a modified example will be described.

[0052] [Variation 1] FIG. 13 is an enlarged view of the main part of the first modified example. The supply side shear force applying member 31a of this modified example 1 is made up of two elastic shafts 313 having elasticity, and a semicircular shear flow path plate 312 is provided at the tip of each elastic shaft 313.

[0053] In this first modification, the supply-side shear force applying member 31a is moved, and the shear flow path plate 312 provided at the tip of each elastic shaft 313 abuts against the arc-shaped side surface of the opening / closing pin 13. This causes the elastic shaft 313 to elastically deform, and the shear flow path plate 312 moves along the arc-shaped side surface of the opening / closing pin 13. This allows the shear flow path plate 312 to move along the liquid supply path 10a while avoiding the opening / closing pin 13. Therefore, the shear flow path plate 312 can apply shear force to the ink in the individual liquid chambers 10c, and the viscosity of the ink in the individual liquid chambers can also be effectively reduced. The discharge-side shear force applying member 31b may have the same configuration as the supply-side shear force applying member 31a.

[0054] [Variation 2] FIG. 14 is an enlarged view of a main part of the second modification. In this second modification, a plurality of elastic protrusions 313a are provided on an elastic shaft 313. The diameter of the supply-side shear force application member including the elastic protrusions 313a is larger than the diameter of the liquid supply path 10a. Therefore, between the individual liquid chambers 10c, the elastic protrusions 313a are elastically deformed and lie flat.

[0055] When the supply-side shear force applying member 31a is moved and the elastic protrusion 313a reaches the individual liquid chamber 10c, the elastic protrusion 313a rises and moves through the space on the nozzle side of the individual liquid chamber 10c and the space on the opposite side from the nozzle side, thereby applying shear force to the ink stored in these spaces and effectively reducing the viscosity of the ink in the individual liquid chamber 10c.

[0056] Furthermore, in the second modification, by moving the elastic shaft 313 while rotating it, the elastic protrusions 313a can apply a stronger shear force to the ink, which is preferable.

[0057] [Variation 3] FIG. 15 is an enlarged view of a main part of the third modification. 15, in Modification 3, flat plates 314 are disposed in the individual liquid chamber 10c as movable wall portions that reciprocate in the same direction as the movement of the opening / closing pin. The flat plates 314 are provided on the nozzle side and the opposite side to the nozzle side so as to face each other across the supply-side shear force application member 31a. A through hole is formed in the center of each of these flat plates 314, through which the opening / closing pin 13 passes.

[0058] Each flat plate 314 normally abuts against the upper and lower surfaces of the individual liquid chamber 10c in the figure, and moves in the direction of the arrow in the figure when the supply-side shear force applying member 31a is moved back and forth. This makes it possible to narrow the individual liquid chamber 10c when the supply-side shear force applying member 31a is moved back and forth, and to effectively apply shear force to the ink in the liquid flow path.

[0059] The flat plate 314 may also be made of a mesh having multiple openings through which ink passes. By making the flat plate 314 mesh-shaped, when the flat plate 314 is moved in the direction of the arrow in the figure, a shear force is applied to the ink in the individual liquid chambers as it passes through the openings in the flat plate. This effectively reduces the viscosity of the ink in the individual liquid chambers 10c.

[0060] The movement of the flat plate 314 within the individual liquid chamber can be controlled by controlling the pressure within the liquid flow path. That is, when the supply-side shear force applying member 31a is moved back and forth, the pressure within the liquid flow path is made negative, thereby moving the flat plate 314 in the direction of the arrow in the figure.

[0061] As described above, when the opening / closing pin is opened by the pressure inside the liquid flow path, ink is ejected from the nozzle 12, so that normally the liquid flow path 10 is pressurized. This pressure causes the flat plate 314 to move in the direction opposite to the direction of the arrow in the figure, and normally the flat plate 314 can be kept in contact with the upper and lower surfaces of the individual liquid chambers 10c in the figure.

[0062] Alternatively, the flat plate 314 may be moved using magnetic force. For example, the flat plate 314 may be made of a magnetic material such as metal, and the flat plate 314 may be brought into contact with the upper and lower surfaces of the individual liquid chambers 10c in the figure by the biasing force of a spring. A magnet serving as a magnetic force generating means may be provided at a predetermined location on the supply-side shear force applying member 31a. When the supply-side shear force applying member 31a is moved, the magnet of the supply-side shear force applying member 31a approaches the flat plate 314, and the magnetic force of the magnet acts on the flat plate 314. This allows the flat plate 314 to be moved in the direction of the arrow in the figure against the biasing force of the spring by the magnetic force of the magnet. Alternatively, a magnet may be provided on the flat plate 314, and a magnetic material such as metal may be provided at a predetermined location on the supply-side shear force applying member 31a.

[0063] Furthermore, when the supply-side shear force application member 31a is a non-elastic member, the supply-side shear force application member 31a may be provided with an inclined portion 313c to move the flat plate 314. Specifically, as shown in Fig. 16, the supply-side shear force application member 31a is provided with a large-diameter portion 313b, a small-diameter portion 313d, and an inclined portion 313c. The flat plate 314 is provided with legs 314a such as contact portions that come into contact with the supply-side shear force application member 31a, and the flat plate 314 is biased toward the supply-side shear force application member 31a by a spring 315.

[0064] As shown in FIG. 16(a), normally, the large diameter portion 313b of the supply-side shear force applying member 31a is positioned in the individual liquid chamber 10c, and at this time, each flat plate 314 abuts against the upper and lower surfaces of the individual liquid chamber 10c in the figure.

[0065] When the supply-side shearing force applying member 31a is pushed in and moves to the left in the figure, the flat plate 314 is guided by the inclined portion 313c of the supply-side shearing force applying member 31a and can move in the direction of the arrow in FIG. 16(b).

[0066] Before the image formation operation, the shear force application members 31a and 31b may be reciprocated to reduce the viscosity of the ink in the liquid flow path, thereby eliminating the need for ink circulation by a liquid feed pump. In this case, as shown in FIG. 17, ink is supplied from the ink tank 410 to the liquid ejection head through the supply tube 556a by increasing the head difference with the ink tank 410 or by increasing the pressure inside the ink tank. The liquid flow path of the liquid ejection head is also pressurized by this head difference with the ink tank 410 or by increasing the pressure inside the ink tank. In addition, when ink circulation is not performed, the liquid flow path of the liquid ejection head is limited to the liquid supply path alone.

[0067] Furthermore, in a configuration in which the supply / circulation mechanism serving as the liquid supply unit has a subtank that temporarily stores ink supplied from the ink tank 410, a shear force application member may be provided in the subtank. By moving the shear force application member within the subtank, shear force is applied to the ink in the subtank, thereby reducing the viscosity of the ink in the subtank. This reduces the load on the liquid feed pump 438 when it starts to operate, in a device that circulates ink using the liquid feed pump. Furthermore, in a device that does not circulate ink using a liquid feed pump, ink with a viscosity suitable for image formation (100 mPa·s or less) can be supplied from the subtank to the liquid flow path 10 of the liquid ejection head 504 during image formation, enabling satisfactory image formation. The movement of the shear force application member within the subtank includes reciprocating and rotating movements.

[0068] Furthermore, a shear force applying member made of an elastic member may be moved inside supply tube 556a or circulation tube 556b of supply / circulation mechanism 594 to apply shear force to the ink inside these tubes, thereby reducing the viscosity of the ink inside these tubes. Furthermore, a shear force applying member may be provided in ink tank 410.

[0069] Although the above description has been given of an example in which the valve jet method is used as the method for ejecting ink, the method for ejecting ink is not limited to this. For example, a piezoelectric method using a piezoelectric actuator (a laminated piezoelectric element or a thin-film piezoelectric element), a thermal method using an electrothermal conversion element such as a heating resistor, or a continuous method using an electrostatic actuator consisting of a vibration plate and an opposing electrode can be used.

[0070] The above description is merely an example, and each of the following aspects provides unique effects. (Aspect 1) The liquid ejection head that ejects the thixotropic liquid in the liquid flow path from the nozzle is provided with shear force applying members 31a and 31b that apply shear force to the liquid in the liquid flow path. In Patent Document 1, when a liquid such as ink starts to circulate, the thixotropic liquid is highly viscous, and circulating this highly viscous liquid places a heavy load on the pump. In particular, because the liquid flow path of the liquid ejection head is narrow, it has the highest flow path resistance among all the liquid circulation paths, and therefore, a heavy load is placed on the pump to flow the highly viscous liquid in the liquid flow path of this liquid ejection head. In contrast to this, in the first aspect, a shear force applying member provided in the liquid flow path of the liquid ejection head applies shear force to the thixotropic liquid in the liquid flow path of the liquid ejection head, thereby lowering the viscosity. Therefore, it becomes possible to start driving the pump after the viscosity of the liquid in the liquid flow path of the liquid ejection head is lowered by the shear force applying member, thereby reducing the load on the pump.

[0071] (Aspect 2) In the first embodiment, the shear force applying members 31a and 31b are provided so as to be movable within the liquid flow path . According to this, as explained in the embodiment, the shear force applying member moves within the liquid flow channel 10, thereby applying a shear force to the liquid within the liquid flow channel.

[0072] (Aspect 3) In the second aspect, the shearing force applying member moves within the liquid flow path at a timing other than during the liquid ejection operation in which the liquid is ejected from the nozzle. According to this, as explained in the embodiment, it is possible to suppress pressure fluctuations in the liquid flow path during liquid ejection operations, and to suppress influences on liquid ejection.

[0073] (Aspect 4) In the second or third embodiment, the shear force applying members 31a and 31b are moved within the liquid flow path 10 by being pushed by a pushing member such as the pressure plate 33. According to this, by pressing a pressing member such as the pressing plate 33, the shear force applying members 31a and 31b can be moved within the liquid flow path .

[0074] (Aspect 5) In the fourth aspect, a pushing member such as the pressure plate 33 pushes the shear force applying members 31a and 31b by hitting a member of the device on which the liquid ejection head is movably mounted, such as the side plate 591A, as the liquid ejection head moves. According to this, it is possible to move the shear force applying members 31a, 31b by pressing a pressing member such as the pressure plate 33 using a moving means such as the main scanning movement mechanism 593 that moves the liquid ejection head. This makes it possible to reduce the number of parts and suppress increases in costs compared to using a drive source dedicated to pressing the pressing member.

[0075] (Aspect 6) In the fourth or fifth embodiment, the pressing member such as the pressure plate 33 is biased by a biasing means such as the spring 32 in a direction opposite to the direction in which the pressing member presses the shear force applying members 31a and 31b. According to this, when a pushing member such as the pressure plate 33 is not pushed in, the shear force applying members 31a, 31b can be held in a predetermined position by the biasing force of the spring 32, etc. This makes it possible to prevent the shear force applying members 31a, 31b from moving during liquid ejection and causing pressure fluctuations in the liquid flow path, thereby preventing the ejection of liquid from being affected. Furthermore, when the pressing force of a pressing member such as the pressing plate 33 is released, the biasing force of the biasing means can move the shearing force applying members 31a, 31b in the direction opposite to the pressing direction. This allows the shearing force applying members 31a, 31b to move back and forth with a simple configuration.

[0076] (Aspect 7) In any of aspects 2 to 6, a nozzle opening / closing member such as an opening / closing pin 13 that opens and closes the nozzle is provided within the liquid flow path, and a shear force applying member such as the supply side shear force applying member 31a is provided with a relief portion such as a notch portion 311 that allows the nozzle opening / closing member to escape. This allows the shear force applying members such as the supply side shear force applying member 31a to move without being hindered by the nozzle opening and closing members such as the opening and closing pin 13, as described in the embodiment.

[0077] (Aspect 8) In any of the second to seventh embodiments, a nozzle opening / closing member such as an opening / closing pin 13 that opens and closes the nozzle is provided within the liquid flow path, and the shear force applying member such as the supply side shear force applying member 31a is made of an elastic body. According to this, as explained in Modification 1, the shear force applying members such as the supply-side shear force applying member 31a can elastically deform and escape from the nozzle opening and closing members such as the opening and closing pins 13. This allows the shear force applying members to move within the liquid flow path without being obstructed by the nozzle opening and closing members such as the opening and closing pins 13.

[0078] (Aspect 9) In the liquid ejection head according to any one of Aspects 2 to 8, the shearing force applying member has a plurality of protrusions that protrude in a direction perpendicular to the direction of movement of the shearing force applying member. According to this, as explained in the second modification, it is possible to apply a shear force to the liquid in the liquid flow path by these protrusions.

[0079] (Aspect 10) In any of the second to ninth embodiments, a movable wall portion such as a flat plate 314 that reciprocates within the liquid flow path in a direction perpendicular to the direction of movement of the shear force applying member is provided. According to this, as explained in Modification 3, the liquid flow path can be narrowed by moving the movable wall portion such as the flat plate 314. Therefore, when the shear force applying member moves, the movable wall portion is moved to narrow the liquid flow path, thereby reducing the liquid to which shear force is not applied by the shear force applying member and whose viscosity is not reduced. This makes it possible to effectively reduce the viscosity of the liquid in the liquid flow path.

[0080] (Aspect 11) In embodiment 10, a movable wall portion such as the flat plate 314 moves back and forth within the liquid flow path due to fluctuations in pressure within the liquid flow path. As explained in variant example 3, by making the pressure inside the liquid flow path negative, the movable wall portion such as the flat plate 314 can be moved toward the inside of the liquid flow path, and by making the pressure inside the liquid flow path positive, the movable wall portion can be moved toward the outside of the liquid flow path.

[0081] (Aspect 12) In the tenth embodiment, the movable wall portion such as the flat plate 314 is moved in conjunction with the movement of the shear force applying member such as the supply-side shear force applying member 31a by the magnetic force between the movable wall portion and the shear force applying member. According to this, as explained in variant example 3, by providing a magnet at a predetermined location on a shear force applying member such as the supply side shear force applying member 31a, and by moving the shear force applying member to reduce the distance between the magnet and the movable wall portion, the movable wall portion can be moved toward the inside of the liquid flow path by magnetic force.

[0082] (Aspect 13) In aspect 10, a movable wall portion such as flat plate 314 has a contact portion such as leg portion 314a that contacts a shear force applying member such as supply side shear force applying member 31a, and the position of the contact point of the contact portion of the shear force applying member changes in the movement direction of the movable wall portion in the movement direction of the shear force applying member. According to this, as explained with reference to FIG. 16, it is possible to move the movable wall portion such as the flat plate 314 in conjunction with the movement of the shear force applying member.

[0083] (Aspect 14) In any of embodiments 10-13, the movable wall, such as plate 314, has a plurality of openings through which liquid can pass. According to this, as explained in Modification 3, the movable wall portion such as the flat plate 314 moves, causing the liquid in the liquid flow path to pass through the opening in the movable wall portion. As the liquid passes through this opening, a shear force is applied to the liquid. This allows the shear force application member and the movable wall portion to apply a shear force to the liquid in the liquid flow path, and effectively reduces the viscosity of the thixotropic liquid in the liquid flow path.

[0084] (Aspect 15) In any of the first to fourteenth embodiments, the shear force applying members 31a and 31b have a shear channel portion such as a shear channel plate 312 having a plurality of openings through which the liquid passes. As a result, as described in the embodiment, a shear force can be applied to the liquid when the liquid passes through the opening of the shear flow path section such as the shear flow path plate 312. This makes it possible to effectively reduce the viscosity of the thixotropic liquid in the liquid flow path.

[0085] (Aspect 16) In the fifteenth aspect, a plurality of shear channel sections such as shear channel plates 312 are provided within the liquid channel. This allows the viscosity of the ink in the entire liquid flow path to be quickly reduced. Also, in a configuration in which the shear force application members 31a, 31b move within the liquid flow path, the viscosity of the ink in the entire liquid flow path can be reduced with a small amount of movement of the shear force application members 31a, 31b.

[0086] (Aspect 17) The liquid ejection unit includes the liquid ejection head according to any one of the first to sixteenth aspects. This allows the viscosity of the thixotropic liquid to be reduced, and the load on the liquid transfer pump to be reduced.

[0087] (Aspect 18) A liquid ejection unit including a liquid ejection head that ejects a thixotropic liquid from a nozzle and a liquid supply section such as a supply circulation mechanism 594 that supplies liquid to the liquid ejection head, is provided with a shear force applying member that moves within the liquid supply section and applies shear force to the liquid in the liquid supply section. This allows the shear force application member to apply shear force to the thixotropic liquid in the liquid supply unit, thereby reducing the viscosity. Therefore, it becomes possible to start driving a pump such as liquid feed pump 438 after the viscosity of the liquid in the liquid supply unit has been reduced by the shear force application member, thereby reducing the load on the pump.

[0088] (Aspect 19) In the seventeenth or eighteenth aspect, the liquid supply unit that supplies the liquid to the liquid ejection head has a pump that causes the liquid to flow, and a shear force is applied to the liquid by a shear force applying member before the pump starts to be driven. This allows the viscosity of the thixotropic liquid to be reduced as described in the embodiment, thereby reducing the pressure loss and then driving the pump, thereby reducing the load on the pump when it starts to be driven.

[0089] (Aspect 20) A liquid ejection device includes the liquid ejection head according to any one of Aspects 1 to 16, or the liquid ejection unit according to any one of Aspects 17 to 19. This allows the viscosity of the thixotropic liquid to be reduced, and the load on the liquid transfer pump to be reduced. [Explanation of symbols]

[0090] 10: Liquid flow path 10a:Liquid supply path 10b:Liquid discharge path 10c: Individual liquid chamber 10d: Supply port 10e: Outlet 10f: Relay flow path 12: Nozzle 13: Opening and closing pin 30: Shear force application mechanism 31a: Supply side shear force applying member 31b: Discharge side shear force applying member 32: Spring 33: Pressure plate 34: Connection member 35: Spring support shaft 41: Through hole 311: Notch 312: Shear channel plate 313: Elastic shaft 313a: Elastic protrusion 313b: Large diameter section 313c: Inclined part 313d: Small diameter part 314: Flat plate 314a: Legs 315: Spring 410: Ink tank 438: Liquid transfer pump 503: Carriage 504: Liquid ejection head 505: Main scanning motor 510: Paper 540: Liquid discharge unit 556: Pair tube 556a: Supply tube 556b: Circulation tube 591A: Side plate 593: Main scanning movement mechanism 594: Supply circulation mechanism [Prior art documents] [Patent documents]

[0091] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-149594

Claims

1. In a liquid ejection head that ejects a thixotropic liquid in a liquid flow path from a nozzle, a shear force applying member that applies a shear force to the liquid in the liquid flow path, the shear force applying member is provided movably within the liquid flow path, The liquid ejection head is characterized in that the shear force applying member moves within the liquid flow path at a timing other than during a liquid ejection operation in which liquid is ejected from the nozzle.

2. A liquid ejection head that ejects a thixotropic liquid in a liquid flow path from a nozzle, a shear force applying member that applies a shear force to the liquid in the liquid flow path, the shear force applying member is provided movably within the liquid flow path, The liquid ejection head is characterized in that the shear force applying member moves within the liquid flow path by being pushed by a pushing member.

3. 3. The liquid ejection head according to claim 2, The liquid ejection head is characterized in that the pushing member pushes the shear force applying member by hitting against a member of a device on which the liquid ejection head is movably mounted as the liquid ejection head moves.

4. 4. The liquid ejection head according to claim 2, The liquid ejection head is characterized in that the pushing member is biased by a biasing means in a direction opposite to a direction in which the pushing member pushes the shearing force applying member.

5. A liquid ejection head that ejects a thixotropic liquid in a liquid flow path from a nozzle, a shear force applying member that applies a shear force to the liquid in the liquid flow path, the shear force applying member is provided movably within the liquid flow path, a nozzle opening / closing member for opening and closing the nozzle is provided within the liquid flow path; The liquid ejection head is characterized in that the shear force applying member is provided with a relief portion for allowing the nozzle opening / closing member to escape.

6. A liquid ejection head that ejects a thixotropic liquid in a liquid flow path from a nozzle, a shear force applying member that applies a shear force to the liquid in the liquid flow path, the shear force applying member is provided movably within the liquid flow path, a nozzle opening / closing member for opening and closing the nozzle is provided within the liquid flow path; The liquid ejection head is characterized in that the shear force applying member is made of an elastic material.

7. A liquid ejection head that ejects a thixotropic liquid in a liquid flow path from a nozzle, a shear force applying member that applies a shear force to the liquid in the liquid flow path, the shear force applying member is provided movably within the liquid flow path, The liquid ejection head is characterized in that the shearing force applying member has a plurality of protrusions that protrude in a direction perpendicular to the direction of movement of the shearing force applying member.

8. A liquid ejection head that ejects a thixotropic liquid in a liquid flow path from a nozzle, a shear force applying member that applies a shear force to the liquid in the liquid flow path, the shear force applying member is provided movably within the liquid flow path, A liquid ejection head comprising a movable wall portion that reciprocates within the liquid flow path in a direction perpendicular to the direction of movement of the shearing force applying member.

9. 9. The liquid ejection head according to claim 8, The liquid ejection head is characterized in that the movable wall portion moves back and forth within the liquid flow path in response to fluctuations in pressure within the liquid flow path.

10. 9. The liquid ejection head according to claim 8, The liquid ejection head is characterized in that the movable wall portion is moved in conjunction with the movement of the shearing force applying member by a magnetic force between the movable wall portion and the shearing force applying member.

11. 9. The liquid ejection head according to claim 8, the movable wall portion has a contact portion that comes into contact with the shear force applying member, The liquid ejection head according to claim 1, wherein the position of the contact portion of the shearing force applying member in the moving direction of the movable wall portion changes in the moving direction of the shearing force applying member.

12. 12. The liquid ejection head according to claim 8, The liquid ejection head is characterized in that the movable wall portion has a plurality of openings through which the liquid passes.

13. A liquid ejection head that ejects a thixotropic liquid in a liquid flow path from a nozzle, a shear force applying member that applies a shear force to the liquid in the liquid flow path, The liquid ejection head is characterized in that the shear force applying member has a shear flow path portion having a plurality of openings through which the liquid passes.

14. 14. The liquid ejection head according to claim 13, A liquid ejection head characterized in that a plurality of the shear flow path sections are provided in the liquid flow path.

15. A liquid ejection unit comprising the liquid ejection head according to claim 1 .

16. A liquid ejection unit comprising a liquid ejection head that ejects a thixotropic liquid in a liquid flow path from a nozzle, and a liquid supply unit that supplies liquid to the liquid ejection head, a shear force applying member that applies a shear force to the liquid in the liquid flow path, the liquid supply unit has a pump for causing the liquid to flow; A liquid discharge unit characterized in that a shear force is applied to the liquid by the shear force applying member before the pump starts to be driven.

17. A liquid ejection unit including a liquid ejection head that ejects a thixotropic liquid from a nozzle, and a liquid supply unit that supplies liquid to the liquid ejection head, a shear force applying member that moves within the liquid supply unit to apply a shear force to the liquid within the liquid supply unit; the liquid supply unit has a pump for causing the liquid to flow; A liquid discharge unit characterized in that a shear force is applied to the liquid by the shear force applying member before the pump starts to be driven.

18. A device for discharging a liquid, 18. A liquid ejection device comprising: a liquid ejection head according to claim 1; or a liquid ejection unit according to claim 15.

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