JP3869948B2 - Liquid ejection method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a liquid discharge head that discharges a desired liquid by generation of bubbles caused by applying thermal energy to a liquid, a head cartridge using the liquid discharge head, and a liquid discharge apparatus, and in particular, uses generation of bubbles. The present invention relates to a liquid discharge head having a movable member that displaces, a head cartridge using the liquid discharge head, and a liquid discharge apparatus.
[0002]
The present invention also includes a printer, a copier, a facsimile having a communication system, and a printer unit that perform recording on a recording medium such as paper, thread, fiber, fabric, leather, metal, plastic, glass, wood, and ceramics. The present invention can be applied to an apparatus such as a word processor and an industrial recording apparatus combined with various processing apparatuses.
[0003]
In the present invention, “recording” means not only giving an image having a meaning such as a character or a figure to a recording medium but also giving an image having no meaning such as a pattern. To do.
[0004]
[Prior art]
By applying energy such as heat to the ink, the ink undergoes a change in state accompanied by a steep volume change (bubble generation), and the ink is discharged from the discharge port by the action force based on this change in state, and this is recorded 2. Description of the Related Art An ink jet recording method for forming an image by adhering to a medium, a so-called bubble jet recording method is conventionally known. In a recording apparatus using this bubble jet recording method, as disclosed in US Pat. No. 4,723,129, an ejection port for ejecting ink, and an ink flow communicating with the ejection port are disclosed. Generally, an electrothermal converter as an energy generating means for ejecting ink disposed in the path and the ink flow path is disposed.
[0005]
According to such a recording method, a high-quality image can be recorded at high speed and with low noise, and the ejection ports for ejecting ink can be arranged with high density in the head that performs this recording method. Therefore, it has many excellent points that a high-resolution recorded image and a color image can be easily obtained with a small apparatus. For this reason, in recent years, this bubble jet recording method has been used in many office devices such as printers, copiers, and facsimiles, and further has been used in industrial systems such as textile printing apparatuses.
[0006]
As the bubble jet technology is used in various products in this way, the following various demands have been increasing in recent years.
[0007]
In order to obtain a high-quality image, a drive condition for providing a liquid discharge method capable of performing a good ink discharge based on a stable generation of bubbles with a high ink discharge speed is proposed. In order to obtain a liquid discharge head having a high filling (refill) speed of the discharged liquid into the liquid flow path, an improved flow path shape has been proposed.
[0008]
In addition to such a head, paying attention to back waves (pressures going in the direction opposite to the direction toward the discharge port) generated with the generation of bubbles, a structure that prevents back waves that become lost energy in ejection Is disclosed in Japanese Patent Laid-Open No. 6-31918 (particularly FIG. 3). In the invention described in this publication, a triangular portion of a triangular plate-shaped member is opposed to a heater that generates bubbles. In the present invention, the back wave is temporarily and slightly suppressed by the plate-like member. However, since the correlation between the bubble growth and the triangular portion is not mentioned at all and there is no idea, the above-described invention includes the following problems.
[0009]
That is, in the invention described in the above publication, since the heater is positioned at the bottom of the recess and cannot take a linear communication state with the discharge port, the droplet shape cannot be stabilized, and the bubble growth is at the apex of the triangle. Since it is allowed from the periphery of the part, bubbles grow from one side of the triangular plate member to the entire other side, and as a result, normal bubble growth in the liquid as if no plate member was present Will be completed. Therefore, the presence of the plate-like member has nothing to do with the grown bubbles. Conversely, since the entire plate-like member is surrounded by bubbles, refilling the heater located in the recesses causes turbulent flow during the bubble contraction stage, causing microbubbles to accumulate in the recesses and growing. The principle of discharging based on bubbles will be disturbed.
[0010]
On the other hand, EP Publication No. 436047A1 discloses a first valve that shuts off these between the vicinity of the discharge port and the bubble generating unit, and a second valve that completely shuts off these between the bubble generating unit and the ink supply unit. Has been proposed (FIGS. 4 to 9 of EP436047A1). However, since the present invention divides these three chambers into two, the ink that follows the droplet becomes a large tail at the time of ejection, and compared with a normal ejection system that performs bubble growth, contraction, and defoaming. The number of satellite dots increases considerably (it is estimated that the meniscus receding effect due to defoaming cannot be used). Also, during refilling, liquid is supplied to the bubble generating part along with defoaming, but since the liquid cannot be supplied until the next foaming occurs in the vicinity of the discharge port, not only the dispersion of discharged droplets is large, The discharge response frequency is extremely small and not at a practical level.
[0011]
[Problems to be solved by the invention]
The present applicant has proposed many inventions using a movable member (such as a plate-like member having a free end on the discharge port side with respect to the fulcrum) that can contribute effectively to droplet discharge, which is completely different from the above-described conventional technology. Yes. Among the inventions, Japanese Patent Application Laid-Open No. 9-48127 discloses an invention that regulates the upper limit of the displacement of the movable member in order to prevent the behavior of the movable member described above from being slightly disturbed. Japanese Patent Laid-Open No. 9-323420 discloses that the position of the common liquid chamber upstream of the movable member is shifted to the free end side of the movable member; that is, the downstream side using the advantage of the movable member. An invention for enhancing the refill capability is disclosed. These are based on the premise that the invention is created, and since the growth of bubbles was temporarily opened to the discharge port side from the state of being temporarily wrapped by a movable member, the entire bubbles are individual elements involved in droplet formation. And the correlation between them has not been noticed.
[0012]
As the next step, the applicant of the present invention disclosed in Japanese Patent Laid-Open No. 10-24588 as an invention (acoustic wave) focusing on bubble growth due to pressure wave propagation as an element related to liquid ejection. An invention for releasing from a movable member is disclosed. However, in the present invention, attention is paid only to the growth of bubbles at the time of discharging the liquid, so that the entire bubbles are not paid attention to individual elements related to the formation of the droplets themselves and their correlation.
[0013]
Although it is known that the front part of bubbles (edge shooter type) due to film boiling, which has been known so far, has a great influence on ejection, it has been known that this part can contribute to the formation of ejected droplets more efficiently. There is nothing to focus on, and the present inventors have conducted intensive research to clarify these technical aspects.
[0014]
The present invention is one of many inventions by analyzing in detail the process from the generation of bubbles to the defoaming from the viewpoint of the formation of ejected droplets, and is caused by the displacement of the movable member. Regarding the improvement of the refill characteristics after forming a substantially sealed space on the upstream side, it was made by examining preferable characteristics required for the movable member from the growth of the front part of the bubble to the start of defoaming. is there.
[0015]
The present invention pays attention to the substantial liquid retention state on the upstream side with respect to the change on the discharge port side of the substantially sealed space at the time of droplet ejection, and can contribute to refilling the inertial force of the fluid in the stationary state. By changing the state in advance, the purpose is to improve the refill characteristics of the inkjet head and to ensure stability.
[0016]
[Means for Solving the Problems]
  In order to achieve the above object, the present invention relates to a heating element that generates thermal energy for generating bubbles in a liquid, a discharge port that is a portion for discharging the liquid, and a liquid that communicates with the discharge port. A liquid flow path having a bubble generation region for generating bubbles, a movable member that is provided in the bubble generation region and is displaced as the bubble grows, and a regulating unit that restricts the displacement of the movable member to a desired range. A liquid discharge head that discharges the liquid from the discharge port by energy when the bubbles are generatedA liquid ejection method using
The movable member is deformed so as to be elastically convex toward the upstream side while being substantially in contact with the restricting portion before the bubble is maximally foamed, and the liquid flow path having the bubble generation region is the discharge port. A process that becomes a substantially closed space except for,
A step of shrinking the bubbles for a certain period in a state where the movable member is substantially in contact with the restricting portion;
A step of moving the movable member away from the restricting portion and displacing to the downstream side by contraction of the bubbles;
HaveIt is characterized by that.
[0019]
Furthermore, the movable member has contacted the restricting portion.In a state for a certain periodIn the step of shrinking the bubbles, most of the movement of the liquid accompanying the shrinkage of the bubbles is directed upstream from the discharge port, and the meniscus is rapidly drawn into the discharge port.
[0020]
Moreover,By moving the movable member away from the restricting portion due to the shrinkage of the bubbles,In the bubble generation areaAboveA liquid flow in a downstream direction toward the discharge port is generated, and the meniscus pull-in is suddenly braked.
[0021]
According to the above configuration, the movable member is elastically displaced so as to be convex upstream before the maximum bubble volume, and the convex portion is displaced downstream by the elastic force in the bubble contraction stage. Before refilling is started, the inertial force in the stationary state can be relaxed to enable initial movement in the refill direction. As a result, refilling is performed stably and promptly, so that sufficient contribution can be made to droplet formation.
Other effects of the present invention can be understood from the description of each embodiment.
[0022]
The terms “upstream” and “downstream” used in the description of the present invention are related to the flow direction of the liquid from the liquid supply source to the discharge port through the bubble generation region (or movable member), or the direction of this configuration. It is expressed as an expression.
[0023]
In addition, the “downstream side” with respect to the bubble itself means a bubble generated in a region downstream of the flow direction and the structural direction with respect to the center of the bubble or downstream of the area center of the heating element. To do. Similarly, the “upstream side” with respect to the bubble itself means the bubble generated in the upstream side with respect to the center of the bubble, the upstream side with respect to the flow direction or the structural direction, or the region upstream of the heating element area center. To do.
[0024]
Further, the “substantial contact” between the movable member and the restricting portion used in the present invention may be a proximity state in which a liquid of about several μm is interposed between them or a direct contact state.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0026]
FIG. 1 is a cross-sectional view of one embodiment of the liquid discharge head of the present invention cut along the direction of the liquid flow path, and the characteristic phenomenon in the liquid flow path is divided into steps (a) to (f). It is shown.
[0027]
In the liquid ejection head of this embodiment, a heating element 2 that applies thermal energy to the liquid is provided on the smooth element substrate 1 as an ejection energy generating element for ejecting the liquid, and the heating element 2 is provided on the element substrate 1. The liquid flow path 10 is arranged corresponding to the above. The liquid flow path 10 communicates with the discharge ports 18 and also communicates with a common liquid chamber 13 for supplying liquid to the plurality of liquid flow paths 10, and has an amount corresponding to the liquid discharged from the discharge ports 18. The liquid is received from the common liquid chamber 13. The symbol M represents a meniscus formed by the discharge liquid, and the meniscus M corresponds to the internal pressure of the common liquid chamber 13 which is normally a negative pressure due to the capillary force generated by the discharge port 18 and the inner wall of the liquid flow path 10 communicating therewith. It is balanced near the discharge port 18.
[0028]
The liquid flow path 10 is configured by joining the element substrate 1 including the heating element 2 and the top plate 50, and the heating element 2 is disposed in a region near the surface where the heating element 2 and the discharge liquid are in contact with each other. There is a bubble generation region 11 that is heated rapidly to cause foaming in the discharged liquid. At least a part of the movable member 31 is arranged in the liquid flow path 10 having the bubble generation region 11 so as to face the heating element 2. The movable member 31 has a free end 32 on the downstream side toward the discharge port 18 and is supported by a support member 34 disposed on the upstream side. In particular, in this embodiment, the free end 32 is arranged near the center of the bubble generation region 11 in order to suppress the growth of the upstream half of the bubble, which affects the upstream back wave and the inertial force of the liquid. The movable member 31 can be displaced with respect to the support member 34 as the bubbles generated in the bubble generation region 11 grow. The fulcrum 33 at the time of displacement is a support portion of the movable member 31 in the support member 34.
[0029]
A stopper (regulator) 64 is located above the center of the bubble generation region 11 and restricts the displacement of the movable member 31 within a certain range in order to suppress the growth of the upstream half of the bubble. In the flow from the common liquid chamber 13 to the discharge port 18, a low flow path resistance region 65 having a relatively low flow resistance compared to the liquid flow path 10 is provided upstream from the stopper 64. The flow path structure in this region 65 has no upper wall or has a large cross-sectional area of the flow path, thereby reducing the resistance received from the flow path for liquid movement.
[0030]
With the above configuration, the liquid flow path 10 having the bubble generation region 11 becomes a substantially closed space except for the discharge port 18 due to the contact between the displaced movable member 31 and the stopper 64. A simple head structure is proposed.
[0031]
Next, the discharge operation of the liquid discharge head of this embodiment will be described in detail.
[0032]
FIG. 1A shows a state before energy such as electric energy is applied to the heating element 2 and before the heating element generates heat. What is important here is that the movable member 31 is provided at a position facing the upstream half of the bubble with respect to the bubble generated by the heat generation of the heating element 2, and restricts the displacement of the movable member 31. That is, the stopper 64 is provided above the center of the bubble generation region 11. That is, the upstream half of the bubbles is pressed into the movable member 31 depending on the liquid flow path structure and the position of the movable member.
[0033]
FIG. 1B shows a state in which a part of the liquid filling the bubble generation region 11 is heated by the heating element 2 and the bubbles 40 accompanying the film boiling grow almost to the maximum. At this time, a pressure wave based on the generation of the bubble 40 propagates in the liquid flow path 10, and accordingly, the liquid moves downstream and upstream from the central region of the bubble generation region. The movable member 31 is displaced by the flow of the liquid accompanying the growth, and the discharge droplet 66 is being discharged from the discharge port 18 on the downstream side. Here, the movement of the liquid toward the upstream side, that is, the direction of the common liquid chamber 13, is a low flow path in which the resistance from the flow path is lower than the downstream side with respect to the movement of the liquid and the liquid flow is easy. Although a large flow is caused by the resistance region 65, if the movable member 31 is displaced until it approaches or contacts the stopper 64, further displacement is restricted, so that the liquid movement in the upstream direction is also greatly limited there. Accordingly, the upstream growth of the bubbles 40 is also restricted by the movable member 31. However, since the moving force of the liquid in the upstream direction is large, the movable member 31 receives a large amount of stress pulled in the upstream direction. Further, a part of the bubble 40 whose growth is restricted by the movable member 31 passes through a slight gap between both side walls forming the liquid flow path 10 and the side portion of the movable member 31, and rises on the upper surface side of the movable member 31. is doing. This raised bubble is referred to as “raised bubble (41)” in this specification.
[0034]
In this state, the entire shape of the liquid flow path toward the discharge port with respect to the movable member 31 has a structure that spreads from the upstream side toward the downstream side.
[0035]
In the present invention, as shown in FIG. 11, the portion on the discharge port side of the bubble 40 and the discharge port are in a “linear communication state” in which a straight channel structure is maintained with respect to the liquid flow. More preferably, the discharge direction of the discharge droplet 66 such as the discharge direction and the discharge speed of the discharge droplet 66 is linearly matched with the propagation direction of the pressure wave generated when bubbles are generated and the flow direction of the liquid and the discharge direction. It is desirable to create an ideal state that stabilizes at a very high level. In the present invention, as one definition for achieving or approximating this ideal state, the discharge port 18 and the heating element 2, particularly the discharge port side (downstream side) of the heating element having an influence on the bubble discharge port side, Can be directly connected in a straight line. This is a state in which the heating element, particularly the downstream side of the heating element, can be observed from the outside of the discharge port when there is no fluid in the flow path. It is.
[0036]
On the other hand, as described above, since the displacement of the movable member 31 is restricted by the stopper 64 in the upstream portion of the bubble 40, the movable member 31 is curved in a convex shape upstream by the inertial force of the liquid flow upstream. It is a small size that stays until the stress is charged. As a whole of this portion, the stopper portion and the liquid flow path partition wall 101, the movable member 31, and the fulcrum 33 almost eliminate the amount of entering the upstream region. (However, partially raised bubbles are allowed for a space of 10 μm or less in the gap between the movable member 31 and the liquid flow path partition wall 101.)
The convex deflection amount is about 20 microns at the maximum and is in a minute range.
[0037]
This greatly restricts the liquid flow to the upstream side, and prevents fluid crosstalk to adjacent nozzles and backflow of liquid and pressure oscillation in the supply path system that impedes high-speed refill described later.
[0038]
FIG. 1C shows a state in which the bubble 40 starts contracting after the film boiling described above, and the negative pressure inside the bubble overcomes the movement of the liquid downstream in the liquid flow path. At this time, since the force in the upstream direction of the liquid due to the bubble growth remains large, the movable member 31 is still in contact with the stopper 64 for a certain period after the bubble 40 starts to contract, and much of the bubble 40 contracts. Generates a liquid moving force in the upstream direction from the discharge port 18. In the state shown in FIG. 1B, the movable member 31 is in a stress-charged state that is curved in a convex shape toward the upstream side. Therefore, in FIG. A force is generated that pulls the flow back and becomes concave in the upstream direction. For this reason, the moving force of the movable member from the upstream direction overcomes the moving force of the liquid in the upstream direction from a certain point in time, and a slight flow starts from the upstream side to the discharge port side. However, the deflection is reduced and the displacement toward the concave shape starts in the upstream direction. That is, an unbalanced state between the upstream side and the downstream side of the bubble 40 is generated in which a total of the liquid in the liquid channel temporarily flows unidirectionally toward the discharge port.
[0039]
At the timing immediately after that, as a whole in the liquid flow path, the liquid flow path 10 having the bubble generation region 11 is substantially closed except for the discharge port 18 due to the contact between the movable member 31 still displaced and the stopper 64. Therefore, the contraction energy of the bubbles 40 acts strongly as a force that moves the liquid in the vicinity of the discharge port 18 in the upstream direction as a whole balance. Therefore, the meniscus M is largely drawn into the liquid flow path 10 from the discharge port 18 at this time, and the liquid column connected to the discharge droplet 66 is quickly separated with a strong force. As a result, as shown in FIG. 1D, the number of liquid droplets, that is, satellites (sub-droplets) 67 left outside the discharge port 18 is reduced.
[0040]
FIG. 1D shows a state in which the defoaming process is almost finished and the discharge droplet 66 and the meniscus M are separated. In the low flow path resistance region 65, the reversing force of the movable member 31 and the contraction force due to the defoaming of the bubbles 40 against the moving force in the upstream direction of the liquid cause the downward displacement of the movable member 31 and the accompanying low flow path resistance region 65. The flow in the downstream direction is started, and the proximity or contact state between the movable member 31 and the stopper 64 starts to be released. Along with this, the flow in the downstream direction in the low flow path resistance region 65 has a small flow path resistance, so it rapidly becomes a large flow and flows into the liquid flow path 10 through the stopper 64 portion. As a result, the flow of rapidly pulling the meniscus M into the liquid flow path 10 is suddenly reduced, so that the meniscus M remains outside from the discharge port 18 or protrudes toward the discharge port 18. It begins to return to the position before foaming at a relatively low speed while taking up as much as possible without separating. In particular, the meniscus convergence is good by forming a region where the flow velocity is almost zero between the discharge port 18 and the heater 2 by the flow of the return of the meniscus M and the refill from the upstream. Although this depends on the viscosity and surface tension of the ink, according to the present invention, this liquid column separates and becomes satellites and adheres to the printed matter, degrading the image quality, or adheres to the vicinity of the orifice and adversely affects the ejection direction. Can be drastically reduced.
[0041]
Further, since the meniscus M itself starts to be restored before it is largely drawn into the liquid flow path, the liquid movement speed itself is not so high, so that the meniscus M can be restored in a short time. It is possible to reduce the amount of the convex shape toward the outside of the discharge port 18 without stopping, and to end the damped oscillation phenomenon with the discharge port 18 generated following the overshoot as a convergence point in a very short time. Since this damped vibration phenomenon also adversely affects printing quality, the present invention enables stable high-speed printing.
[0042]
Further, the flow into the liquid flow path 10 through the portion between the movable member 31 and the stopper 64 described above increases the flow velocity on the wall surface on the top plate 50 side as shown in FIG. Residues such as microbubbles are extremely small, contributing to the stability of ejection. On the other hand, some of the satellites 67 that exist immediately after the ejection droplet 66 are very close to the ejection droplet due to rapid meniscus drawing in FIG. 1C, and air generated behind the flight of the ejection droplet 66. The phenomenon of receiving the force attracted to the ejected droplets by the vortex of the so-called slip stream phenomenon occurs.
[0043]
This phenomenon will be described in detail. In a conventional liquid discharge head, a droplet does not form a sphere at the moment when the liquid is discharged from the discharge port, but is discharged in a state close to a liquid column having a spherical portion at the tip. It is known that when the tail portion is pulled by both the main droplet and the meniscus and is separated from the meniscus, satellite dots are formed from the tail portion and fly to the recording medium together with the main droplet. . Since the satellite dots fly after the main droplet, the discharge speed is low by the amount pulled by the meniscus, and the landing position is shifted from the main droplet, so that the print quality is deteriorated. In the liquid discharge head according to the present invention, the force for retracting the meniscus is larger than that of the conventional liquid discharge head as described above. Therefore, the force for pulling the tail portion after the main droplet is discharged is strong. The separation force becomes stronger, and the timing of this separation is also accelerated. Accordingly, the satellite dots formed from the tailing portion are reduced, and the distance between the main droplet and the satellite dots is reduced. Furthermore, since the tail portion is not continuously pulled by the meniscus, the discharge speed does not decrease, and the satellite 67 is attracted by the so-called slip stream phenomenon behind the discharge droplet 66.
[0044]
FIG. 1E shows a state in which the state of FIG. Further, the satellite 67 approaches the ejected droplet 66 and is attracted at the same time, and the pulling force due to the slip stream phenomenon is also increased. On the other hand, the movement of the liquid from the upstream side toward the discharge port 18 is caused to be displaced downward from the initial position by the completion of the defoaming process of the bubble 40 and the displacement overshoot of the movable member 31, thereby drawing in the liquid from the upstream side and the discharge port. The liquid is pushed out in 18 directions. In addition, the liquid flow in the direction of the discharge port 18 increases due to the enlarged cross-sectional area of the liquid flow path in which the stopper 64 exists, and the return of the meniscus M to the discharge port 18 is accelerated. As a result, the refill characteristics in this embodiment are dramatically improved.
[0045]
Further, when cavitation occurs when the bubbles disappear, the defoaming point and the discharge port 18 are separated by the downward displacement of the movable member 31, so that the shock wave due to cavitation is not directly transmitted to the discharge port 18 but is absorbed by the movable member 31. Therefore, the shock wave due to cavitation reaches the meniscus, and micro droplets called microdots are hardly generated from the meniscus, but the microdots adhere to the printed matter and deteriorate the image quality, or near the discharge port 18. The phenomenon of adhering and destabilizing the discharge is drastically reduced.
[0046]
Furthermore, since the cavitation generation point due to defoaming is also shifted to the fulcrum 33 side by the movable member 31, damage to the heater 2 is reduced. In addition, forced ejection of the thickened ink between the movable member 31 and the heater 2 is caused and excluded from this closed region, thereby improving the discharge durability. At the same time, the same phenomenon reduces the adhesion of burns to the heater in this region, thus improving the discharge stability.
[0047]
FIG. 1 (f) shows a state in which the state of FIG. 1 (e) has further advanced and the satellite 67 has been taken into the ejection droplet 66. The combination of the ejection droplet 66 and the satellite 67 is not necessarily a phenomenon that occurs every ejection in other embodiments, and may or may not occur depending on conditions. However, by reducing or eliminating the amount of satellites at least, the landing positions of the main droplets and the satellite dots are hardly displaced on the recording medium, and the influence on the print quality is extremely reduced. That is, it is possible to improve image sharpness and improve printing quality, and to reduce adverse effects such as contamination of the printing medium and the recording apparatus as mist.
[0048]
On the other hand, the movable member 31 is displaced again in the direction of the stopper 64 due to the reaction of the overshoot. This converges by the damping vibration determined by the shape and Young's modulus of the movable member 31, the viscosity of the liquid in the liquid flow path, and the specific gravity, and finally stops at the initial position.
[0049]
The liquid flow from the common liquid chamber 13 toward the discharge port 18 is controlled by the upward displacement of the movable member 31, and the movement of the meniscus M converges immediately in the vicinity of the discharge port. Therefore, it is possible to greatly reduce factors such as meniscus overshoot and the like that make the discharge state unstable and lower the print quality.
[0050]
Next, further characteristic effects of this embodiment will be described.
[0051]
FIG. 2 is a see-through perspective view of a part of the head shown in FIG. 1B, and basically shows the same state as FIG. In the present embodiment, there is a slight clearance between both side walls of the wall constituting the liquid flow path 10 and both side portions of the movable member 31, and the movable member 31 can be smoothly displaced. Further, in the foaming growth process by the heating element 2, the bubble 40 displaces the movable member 31, rises to the upper surface side of the movable member 31 through the clearance, and slightly enters the low flow path resistance region 65. The invading raised bubbles 41 wrap around the back surface of the movable member 31 (the surface opposite to the bubble generation region 11), thereby suppressing blurring of the movable member 31 and stabilizing the discharge characteristics.
[0052]
Further, in the defoaming step of the bubbles 40, the raised bubbles 41 promote the liquid flow from the low flow path resistance region 65 to the bubble generation region 11, and coupled with the high-speed meniscus pull-in from the discharge port 18 side described above, Complete the foam as soon as possible. In particular, the liquid flow caused by the raised bubbles 41 hardly accumulates bubbles in the corners of the movable member 31 or the liquid flow path 10.
[0053]
As described above, in the liquid discharge head having the above-described configuration, at the moment when the liquid is discharged from the discharge port due to the generation of bubbles, the discharged droplet is discharged in a state close to a liquid column having a spherical portion at the tip. This is the same in the conventional head structure, but in the present invention, when the movable member is displaced by the bubble growth process and the displaced movable member comes into contact with the restricting portion, the liquid flow path having the bubble generation region is formed. Except for the discharge port, a substantially closed space is formed. Therefore, if the bubbles are defoamed in this state, the above-mentioned closed space is maintained until the movable member moves away from the restricting portion due to defoaming. Therefore, most of the defoaming energy of the bubbles is directed to the liquid in the vicinity of the discharge port in the upstream direction. It will work as a force to move to. As a result, immediately after the bubble defoaming starts, the meniscus is rapidly drawn into the liquid flow path from the discharge port, and the tail portion that forms the liquid column by connecting to the discharge droplet outside the discharge port is the meniscus. It is quickly separated with a stronger force. As a result, the satellite dots formed from the tail portion are reduced, and the print quality can be improved.
[0054]
Furthermore, since the tailing portion does not continue to be pulled by the meniscus, the discharge speed does not decrease, and the distance between the discharge droplet and the satellite dot is also shortened. Gravitate. As a result, coalescence of the ejection droplets and satellite dots can occur, and a liquid ejection head having almost no satellite dots can be provided.
[0055]
Furthermore, the present invention is characterized in that, in the head described above, the movable member is provided to suppress only bubbles that grow in the upstream direction with respect to the flow of liquid toward the ejection port. More preferably, the free end of the movable member is located at a substantially central portion of the bubble generation region. According to this configuration, the upstream wave due to bubble growth and the inertial force of the liquid, which are not directly related to the discharge of the liquid, can be suppressed, and the growth component toward the downstream side of the bubble can be directly directed toward the discharge port. Is possible.
[0056]
Furthermore, the present invention is characterized in that in the head described above, the flow path resistance of the liquid flow path on the side opposite to the discharge port is low with the restricting portion as a boundary. According to this configuration, since the movement of the liquid in the upstream direction due to the growth of the bubbles becomes a large flow due to the liquid flow path having the low flow resistance, when the displaced movable member comes into contact with the restricting portion, the movable member moves upstream. It will receive the stress of the shape pulled in the direction. As a result, even if the defoaming is started in this state, the liquid moving force in the upstream direction due to the growth of the bubbles remains largely, so that the above-described period of time until the repulsive force of the movable member wins against the liquid moving force is described above. Can keep the closed space. In other words, this configuration ensures more reliable high-speed meniscus pull-in. In addition, when the bubble defoaming process proceeds and the repulsive force of the movable member wins against the liquid moving force in the upstream direction due to bubble growth, the movable member is displaced downward to return to the initial state. Even in the region, a downstream flow occurs. The flow in the downstream direction in the low flow path resistance region has a small flow path resistance, so it rapidly becomes a large flow and flows into the liquid flow path through the restricting portion. As a result, the liquid movement toward the discharge port in the downstream direction makes it possible to suddenly brake the meniscus pull-in and converge the meniscus vibration at high speed.
[0057]
(Other embodiments)
Hereinafter, various embodiments applicable to a head using the above-described liquid ejection method will be described.
[0058]
<Moveable member>
FIG. 3 shows another shape of the movable member 31. (A) is a rectangular shape, (b) is a shape in which the fulcrum side is narrow and the movable member is easy to operate, and (c) in FIG. The shape is improved in rigidity.
[0059]
In the previous embodiment, the movable member 31 is made of nickel having a thickness of 3 μm. However, the movable member 31 is not limited to this, and the material constituting the movable member has a solvent resistance to the discharged liquid and is good as the movable member. As long as it has elasticity to operate smoothly.
[0060]
The material of the movable member 31 is a highly durable metal such as silver, nickel, gold, iron, titanium, aluminum, platinum, tantalum, stainless steel, phosphor bronze, and alloys thereof, or acrylonitrile, butadiene, styrene, etc. Resins having a nitrile group, resins having an amide group such as polyamide, resins having a carboxyl group such as polycarbonate, resins having an aldehyde group such as polyacetal, resins having a sulfone group such as polysulfone, other resins such as liquid crystal polymers and the like Compounds, metals with high ink resistance, metals such as gold, tungsten, tantalum, nickel, stainless steel, titanium, alloys thereof and ink resistance, those coated on the surface, or resins having an amide group such as polyamide, Aldehydes such as polyacetal Resin having a ketone group such as polyetheretherketone, resin having an imide group such as polyimide, resin having a hydroxyl group such as phenol resin, resin having an ethyl group such as polyethylene, alkyl group such as polypropylene Resins, resins having epoxy groups such as epoxy resins, resins having amino groups such as melamine resins, resins having methylol groups such as xylene resins and compounds thereof, and ceramics such as silicon dioxide and silicon nitride, and compounds thereof are desirable. . The movable member 31 in the present invention is intended for a thickness of the order of μm.
[0061]
Next, the arrangement relationship between the heating element and the movable member will be described. By optimal arrangement of the heating element and the movable member, the flow of liquid during foaming by the heating element can be appropriately controlled and effectively used.
[0062]
By applying energy such as heat to the ink, the ink undergoes a change in state accompanied by a steep volume change (bubble generation), and the ink is discharged from the discharge port by the action force based on this change in state, and this is recorded In the conventional technique of the ink jet recording method in which an image is formed by adhering to a medium, that is, a so-called bubble jet recording method, as shown in FIG. 4, the heating element area and the ink discharge amount are in a proportional relationship, but contribute to ink discharge. It can be seen that there is a non-foaming effective region S that does not. Further, it can be seen from the state of the kogation on the heating element that this non-foaming effective region S exists around the heating element. From these results, the width of about 4 μm around the heating element is not involved in foaming.
[0063]
Therefore, in order to effectively use the foaming pressure, the area immediately above the foaming effective area approximately 4 μm or more from the periphery of the heating element is the area that effectively acts on the movable member. A stage that allows the upstream and downstream bubbles to act independently on the liquid flow in the liquid channel in the almost central region (actually in the range of ± 10 μm from the center to the liquid flow direction) It can be said that it is extremely important to dispose the movable member so that only the portion upstream from the central region faces the movable member, focusing on the fact that it is divided from the caulking stage. In this embodiment, the effective foaming area is set to about 4 μm or more inside from the periphery of the heating element, but it is not limited to this depending on the type of heating element and the forming method.
[0064]
Furthermore, in order to satisfactorily form the substantially enclosed space described above, the distance between the movable member and the heating element in the standby state is preferably 10 μm or less.
[0065]
<Element substrate>
Next, the configuration of the element substrate will be described.
[0066]
FIG. 5 shows a longitudinal sectional view of the liquid discharge head of the present invention. FIG. 5 (a) shows a head having a protective film, which will be described later, and FIG. 5 (b) shows no protective film.
[0067]
On the element substrate 1, a liquid plate 10, a discharge port 18 that communicates with the liquid flow channel 10, a low flow path resistance region 65, and a top plate 50 provided with grooves constituting the common liquid chamber 13 are disposed.
[0068]
On the element substrate 1, a silicon oxide film or silicon nitride film 106 for insulating and heat storage is formed on a base 107 such as silicon, and a hafnium boride (HfB 2) constituting the heating element 2 is formed thereon. An electric resistance layer 105 (0.01-0.2 μm thickness) such as tantalum nitride (TaN) and tantalum aluminum (TaAl) and a wiring electrode 104 (0.2-1.0 μm thickness) such as aluminum are shown in FIG. ). A voltage is applied from the wiring electrode 104 to the resistance layer 105, and a current is passed through the resistance layer to generate heat. On the resistance layer between the wiring electrodes, a protective layer 103 made of silicon oxide, silicon nitride or the like is formed with a thickness of 0.1 to 2.0 μm. Further, a cavitation resistant layer 102 made of tantalum or the like (0.1 to 0. 6 μm thick) to protect the resistance layer 105 from various liquids such as ink.
[0069]
In particular, the pressure and shock wave generated when bubbles are generated and defoamed are very strong, and the durability of the hard and fragile oxide film is remarkably lowered. Therefore, a metal material such as tantalum (Ta) is used as the anti-cavitation layer 102. It is done.
[0070]
Moreover, the structure which does not require the protective layer 103 to the above-mentioned resistance layer 105 by the combination of a liquid, a liquid flow path structure, and resistance material may be sufficient, and the example is shown in FIG.5 (b). Examples of the material of the resistance layer 105 that does not require the protective layer 103 include iridium-tantalum-aluminum alloy.
[0071]
As described above, the structure of the heating element described above may be only the resistance layer (heating part) between the electrodes described above, or may include a protective layer for protecting the resistance layer.
[0072]
Here, a heating element having a heating part composed of a resistance layer that generates heat in response to an electrical signal is used. However, the present invention is not limited to this, and bubbles sufficient to discharge the discharge liquid are used in the foaming liquid. Anything can be used. For example, a light-to-heat conversion body that generates heat when receiving light from a laser or the like as a heat generating section, or a heating element that includes a heat generating section that generates heat by receiving high frequency may be used.
[0073]
The element substrate 1 includes the electric heat converter in addition to the electrothermal transducer formed of the resistance layer 105 constituting the heat generating portion and the wiring electrode 104 for supplying an electric signal to the resistance layer. Functional elements such as transistors, diodes, latches, and shift registers for selectively driving the conversion elements may be integrally formed by a semiconductor manufacturing process.
[0074]
Further, in order to drive the heat generating portion of the electrothermal transducer provided on the element substrate 1 as described above and discharge the liquid, the resistance layer 105 is shown in FIG. Such a rectangular pulse is applied, and the resistance layer 105 between the wiring electrodes is rapidly heated. In the heads of the above-described embodiments, the heating element is driven by applying a voltage of 24 V, a pulse width of about 4 μsec, a current of about 100 mA, and an electric signal of 6 kHz or more. Some ink was ejected. However, the condition of the drive signal is not limited to this, and any drive signal that can appropriately foam the foaming liquid may be used.
[0075]
<Discharged liquid>
Among such liquids, as a liquid (recording liquid) used for recording, ink having a composition used in a conventional bubble jet apparatus can be used.
[0076]
Further, it can be used even for liquids that have been difficult to discharge, such as liquids with low foamability, liquids that are easily altered or deteriorated by heat, and high-viscosity liquids.
[0077]
However, it is desirable that the discharged liquid itself is not a liquid that hinders discharge, foaming, operation of the movable member, and the like as a property of the discharged liquid.
[0078]
High viscosity ink or the like can also be used as the recording discharge liquid.
[0079]
In the present invention, recording was performed using an ink having the following composition as a recording liquid that can be used as a discharge liquid. The accuracy is improved and a very good recorded image can be obtained.
[0080]
Composition of dye ink (viscosity 2cP)
(C-1. Food Black 2) Dye 3% by weight
Diethylene glycol 10% by weight
Thiodiglycol 5% by weight
Ethanol 5% by weight
77% by weight of water
[0081]
<Liquid discharge head structure>
FIG. 7 is an exploded perspective view showing the overall configuration of the liquid discharge head of the present invention.
[0082]
An element substrate 1 provided with a plurality of heating elements 2 is arranged on a support 70 such as aluminum. A support member 34 that supports the movable member 31 is provided thereon so as to face the half of each heating element 2 on the common liquid chamber 13 side. Furthermore, a top plate 50 provided with a plurality of grooves constituting the liquid flow path 10 and concave grooves of the common liquid chamber 13 is provided thereon.
[0083]
<Side shooter type>
Here, a description will be given of a case where the liquid discharge principle described with reference to FIGS. 1 and 2 is applied to a side shooter type head in which a heating element and a discharge port face each other on a parallel plane. FIG. 8 is a view for explaining this side shooter type head.
[0084]
In FIG. 8, the heating element 2 on the element substrate 1 and the discharge port 18 formed in the top plate 50 are disposed so as to face each other. The discharge port 18 communicates with the liquid flow path 10 passing over the heating element 2. A bubble generation region exists in a region near the surface where the heating element 2 and the liquid are in contact. Two movable members 31 are supported on the element substrate 1, and each movable member is formed so as to be plane-symmetric with respect to a plane passing through the center of the heating element, and the free end of each movable member 31 is It is located on the heating element 2 so as to face each other. In addition, each movable member 31 has the same projected area on the heating element 2, and the free ends of each movable member 31 are separated by a desired size. Here, when it is assumed that each movable member is divided by a dividing wall of a plane passing through the center of the heating element, the movable member is provided so that the free end of the movable member is positioned near the center of each divided heating element. .
[0085]
The top plate 50 is provided with a stopper 64 that restricts the displacement of each movable member 31 within a certain range. In the flow from the common liquid chamber 13 to the discharge port 18, a low flow path resistance region 65 having a relatively low flow resistance compared to the liquid flow path 10 is provided upstream from the stopper 64. The channel structure in the region 65 has a larger channel cross-sectional area than the liquid channel 10, thereby reducing the resistance received from the channel against the movement of the liquid.
[0086]
Next, characteristic actions and effects of the structure of this embodiment will be described.
[0087]
FIG. 8A shows a state in which a part of the liquid filling the bubble generation region 11 is heated by the heating element 2 and the bubble 40 accompanying film boiling grows to the maximum. At this time, the liquid in the liquid flow path 10 moves in the direction of the discharge port 18 due to the pressure based on the generation of the bubbles 40, the movable members 31 are displaced by the growth of the bubbles 40, and the discharge droplets 66 are likely to jump out of the discharge ports 18. It is said. Here, the movement of the liquid in the direction of the common liquid chamber 13 becomes a large flow by each low flow path resistance region 65, but if the two movable members 31 are displaced until approaching or contacting each stopper 64, the movement of the liquid is further increased. Since the displacement is restricted, the movement of the liquid in the direction of the common liquid chamber 13 is also greatly limited there. At the same time, the growth of the bubbles 40 to the upstream side is also restricted by the movable member 31. However, since the liquid moving force in the upstream direction is large, a part of the bubbles 40 whose growth is restricted by each movable member 31 has a gap between the side wall forming the liquid flow path 10 and the side portion of the movable member 31. As described above, the upper surface of the movable member 31 is raised. That is, the raised bubbles 41 are formed.
[0088]
When the contraction of the bubble 40 is started after such film boiling, since the force in the upstream direction of the liquid remains large at this time, each movable member 31 is still in contact with the stopper 64, and the contraction of the bubble 40 is performed. Most of them cause liquid movement from the discharge port 18 in the upstream direction. Therefore, the meniscus is drawn largely into the liquid flow path 10 from the discharge port 18 at this time, and the liquid column connected to the discharge droplet 66 is quickly separated with a strong force. As a result, the number of droplets, that is, satellites left outside the discharge port 18 is reduced.
[0089]
When the defoaming step is almost finished, the repulsive force (restoring force) of the movable member 31 is superior to the moving force in the upstream direction of the liquid in each low flow path resistance region 65, and the downward displacement of the movable member 31 and the accompanying low flow path The downstream flow in the resistance region 65 is started. At the same time, the flow in the downstream direction in the low flow path resistance region 65 has a low flow resistance, and thus rapidly becomes a large flow and flows into the liquid flow path 10 through the stopper 64 portion. FIG. 8B shows a liquid flow AB in the defoaming process of the bubbles 40. The liquid flow A indicates a component in which the liquid from the common liquid chamber 13 flows in the direction of the discharge port 18 through the upper surface (opposite surface of the heating element) of the movable member 31, and the liquid flow B indicates both sides of the movable member 31 and the heating element. 2 shows the component flowing over.
[0090]
As described above, in this embodiment, the refill property is increased at a higher speed by supplying the discharge liquid from the low flow path resistance region 65. In addition, since the common liquid chamber 13 adjacent to the low flow path resistance region 65 further reduces the flow path resistance, a higher speed refill is possible.
[0091]
Furthermore, in the defoaming process of the bubbles 40, the raised bubbles 41 promote the liquid flow from each low flow path resistance region 65 to the bubble generation region 11, and coupled with the above-described high-speed meniscus drawing from the discharge port 18 side, Complete defoaming promptly. In particular, the liquid flow caused by the raised bubbles 41 hardly accumulates bubbles in the corners of the movable member 31 or the liquid flow path 10.
[0092]
<Liquid ejection device>
FIG. 9 shows a schematic configuration of a liquid ejection apparatus equipped with the liquid ejection head having the structure described in FIG. 1 and FIG. In the present embodiment, description will be made using an ink discharge recording apparatus that uses ink as the discharge liquid. The carriage HC of the liquid ejection device is equipped with a head cartridge in which a liquid tank section 90 for containing ink and a liquid ejection head section 200 can be attached and detached, and a recording medium such as a recording sheet conveyed by a recording medium conveying means. The recording medium 150 reciprocates in the width direction.
[0093]
When a drive signal is supplied from a drive signal supply means (not shown) to the liquid discharge means on the carriage, the recording liquid is discharged from the liquid discharge head to the recording medium in response to this signal.
[0094]
In the liquid ejection apparatus according to the present embodiment, the motor 111 as a drive source for driving the recording medium transport unit and the carriage, the gears 112 and 113 for transmitting the power from the drive source to the carriage, and the carriage shaft 115. Etc. With this recording apparatus and the liquid ejection method performed by this recording apparatus, it was possible to obtain recorded images with good images by ejecting liquid onto various recording media.
[0095]
FIG. 10 is a block diagram of the entire apparatus for operating ink discharge recording in the liquid discharge method and liquid discharge head of the present invention.
[0096]
The recording apparatus receives print information from the host computer 300 as a control signal. The print information is temporarily stored in the input interface 301 inside the printing apparatus, and at the same time, converted into data that can be processed in the recording apparatus and input to the CPU 302 that also serves as a head drive signal supply unit. Based on a control program stored in the ROM 303, the CPU 302 processes the data input to the CPU 302 using a peripheral unit such as the RAM 304 and converts it into data (image data) to be printed.
[0097]
The CPU 302 generates drive data for driving a drive motor that moves the recording paper and the recording head in synchronization with the image data in order to record the image data at an appropriate position on the recording paper. The image data and the motor drive data are transmitted to the head 200 and the drive motor 306 via the head driver 307 and the motor driver 305, respectively, and are driven at controlled timings to form an image.
[0098]
The recording medium that can be applied to the recording apparatus as described above and to which liquid such as ink is applied includes various papers, OHP sheets, plastic materials used for compact discs, decorative plates, etc., fabrics, aluminum, copper, etc. Metal materials, leather materials such as cowhide, pig skin, and artificial leather, wood such as wood and plywood, ceramic materials such as bamboo and tiles, and three-dimensional structures such as sponges can be targeted.
[0099]
Further, as the above-mentioned recording apparatus, a printer apparatus that records on various papers and OHP sheets, a plastic recording apparatus that records on a plastic material such as a compact disc, a metal recording apparatus that records on a metal plate, Leather recording device for recording on leather, wood recording device for recording on wood, ceramic recording device for recording on ceramic material, recording device for recording on three-dimensional network structure such as sponge, and fabric It also includes a textile printing apparatus that performs recording.
[0100]
In addition, as a discharge liquid used in these liquid discharge apparatuses, a liquid suitable for each recording medium and recording conditions may be used.
[0101]
【The invention's effect】
According to the present invention, before the main refill is started, the inertial force in the stationary state can be relaxed, and the initial movement in the refill direction can be made possible. As a result, refilling is performed stably and promptly, so that sufficient contribution can be made to droplet formation. In addition, the movement of the liquid in the upstream direction due to the back wave, that is, the upstream pressure wave is suppressed, and at the same time, the meniscus is rapidly drawn into the discharge port, thereby preventing satellite dots, stabilizing the discharge amount, and improving the print quality. Can be improved.
[0102]
Particularly, according to the present invention, according to the configuration in which the trailing portion that forms the liquid column connected to the ejected droplet and the meniscus are separated quickly, the stabilization of the droplet is achieved and high-quality recording is enabled. be able to.
[Brief description of the drawings]
FIG. 1 shows a cross-sectional view of one embodiment of a liquid discharge head of the present invention cut in the direction of a liquid flow path, and the characteristic phenomenon in the liquid flow path is represented by steps (a) to (f). They are shown separately.
FIG. 2 is a perspective view of a part of the head shown in FIG.
3 shows another shape of the movable member shown in FIG.
FIG. 4 is a graph showing a relative relationship between a heating element area and an ink discharge amount.
5A and 5B are longitudinal sectional views of a liquid discharge head according to the present invention, in which FIG. 5A shows a protective film and FIG. 5B shows a liquid discharge head without a protective film.
FIG. 6 is a waveform diagram for driving a heating element used in the present invention.
FIG. 7 is an exploded perspective view showing the overall configuration of the liquid ejection head of the present invention.
FIG. 8 is a diagram for explaining a side shooter type head to which the liquid ejection method of the present invention is applied.
FIG. 9 is a diagram showing a schematic configuration of a liquid discharge apparatus equipped with the liquid discharge head having the structure described in FIG. 1 and FIG.
FIG. 10 is a block diagram of an entire apparatus for operating ink discharge recording in a liquid discharge method and a liquid discharge head according to the present invention.
FIG. 11 is a cross-sectional view of the flow path for explaining the “linear communication state”.
[Explanation of symbols]
1 Element substrate
2 Heating element
10 Liquid flow path
11 Bubble generation area
13 Common liquid chamber
18 Discharge port
31 Movable member
32 Free end
33 fulcrum
34 Support members
40 bubbles
41 Raised bubbles
50 Top plate
64 stopper
65 Low flow resistance region
66 Droplets
67 Satellite
70 Support
90 Ink tank
102 Anti-cavitation layer
103 protective layer
104 Wiring electrode
105 resistance layer
106 Silicon nitride film
107 substrate
111 motor
112,113 Gear
115 Carriage shaft
150 recording media
200 heads
300 Host computer
301 I / O interface
302 CPU
303 ROM
304 RAM
305 Motor driver
306 Drive motor
307 head driver

Claims (3)

A heating element that generates thermal energy for generating bubbles in the liquid, a discharge port that is a part that discharges the liquid, and a bubble generation region that is in communication with the discharge port and generates bubbles in the liquid A flow path, a movable member that is provided in the bubble generation region and is displaced as the bubble grows, and a restriction unit that restricts the displacement of the movable member to a desired range, and the discharge is performed by energy generated when the bubble is generated. A liquid discharge method using a liquid discharge head for discharging the liquid from an outlet,
The movable member is deformed so as to be elastically convex toward the upstream side while being substantially in contact with the restricting portion before the bubble is maximally foamed, and the liquid flow path having the bubble generation region is the discharge port. A process that becomes a substantially closed space except for,
A step of shrinking the bubbles for a certain period in a state in which the movable member is substantially in contact with the restricting portion;
A step of moving the movable member away from the restricting portion and displacing to the downstream side by contraction of the bubbles;
A liquid discharge method comprising: In the step in which the bubble contracts for a certain period while the movable member is in contact with the regulating portion, most of the movement of the liquid accompanying the contraction of the bubble is directed upstream from the discharge port, The liquid ejection method according to claim 1 , wherein the meniscus is drawn rapidly. The movable member is separated from the restricting portion due to the contraction of the bubbles, thereby generating a liquid flow in the downstream direction toward the discharge port in the bubble generation region, and suddenly braking the meniscus drawing. The liquid discharge method according to claim 2 .

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