JP3787507B2 - Liquid ejection method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a liquid discharge method, a liquid discharge head, and a liquid discharge apparatus that discharge a desired liquid by generation of bubbles caused by applying thermal energy to a liquid, and in particular, displacement is performed by using generation of bubbles. The present invention relates to a liquid ejection method using a movable member.
[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 (liquid), the liquid undergoes a state change accompanied by a steep volume change (bubble generation), and the liquid is discharged from the discharge port by the action force based on this state change. A liquid jet recording method in which an image is formed by adhering to a recording medium, that is, 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, a discharge port for discharging a liquid and a liquid flow communicating with the discharge port are disclosed. Generally, an electrothermal converter as an energy generating means for discharging a path and a liquid disposed in the liquid 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 in the head for performing this recording method, the discharge ports for discharging liquid can be arranged at high density. 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 has also been used in industrial systems such as textile printing apparatuses.
[0006]
FIG. 10 is a schematic cross-sectional view around the electrothermal transducer of the conventional liquid discharge head that performs recording by such a recording method. In the example shown in the figure, the electrothermal transducer is composed of a resistance layer 100 and electrodes 101a and 101b which are stacked on the resistance layer 100 and formed as a pair with a gap therebetween. That is, a heat generating portion 105 that generates heat when a voltage is applied is formed between the electrode 101a and the electrode 101b, and this portion becomes a bubble generation region where bubbles are formed by film boiling. Further, two protective layers 102 and 103 are formed on the resistance layer 100 and the electrodes 101a and 101b to protect them.
[0007]
When the discharge port for discharging the liquid by generating the bubble 104 by the heat generation in the heat generation unit 105 is provided at a position facing the heat generation unit 105 like the discharge port S (so-called side shooter type), the discharge port E As in the case of a so-called edge shooter type. In any case, in the liquid discharge head having such a configuration, the bubble 104 grows relatively large toward the liquid chamber side X where the flow path resistance is relatively small. In many cases, it is in the middle or slightly liquid chamber side.
[0008]
As described above, in the liquid ejection head as shown in FIG. 10, the liquid is pushed back relatively large toward the liquid chamber side X as the bubble 104 grows. Accordingly, the meniscus, which is the interface between the liquid and the outside air formed on the discharge port side, retreats relatively greatly with defoaming after the liquid is discharged, and vibrates relatively greatly. Further, in the defoaming process, the liquid flow from the liquid chamber side toward the heat generating portion 105 and the liquid flow from the discharge port toward the heat generating portion 105 are generated in substantially the same degree. Since the timing at which refilling is substantially started is relatively late after the liquid flow from the discharge port side has substantially converged, it takes a relatively long time for the meniscus to return to the steady position and stabilize. For this reason, when liquid is continuously ejected, the ejection time interval needs to be relatively long, and there is a limit to the drive frequency at which liquid can be ejected satisfactorily.
[0009]
The liquid discharge head includes 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. A configuration in which the liquid flow path having the bubble generation region becomes a substantially closed space except for the discharge port by the substantial contact between the displaced movable member and the restricting portion. It has been known. In this liquid discharge head, since the movable member is displaced so as to substantially close the upstream flow path of the bubble generation region during bubble growth, relatively little liquid is pushed back to the upstream side during bubble growth. Further, at the time of defoaming, the movable member is displaced so as to reduce the upstream flow path resistance, and defoaming at the upstream side of the bubble generation region is promoted and preceded from the downstream side. For this reason, the retraction amount of the meniscus is small, and the liquid refill is performed efficiently.
[0010]
Further, in the liquid discharge head, there is a case where micro bubbles are formed and remain in the liquid flow path because the gas dissolved in the liquid is released when the bubbles are formed. Therefore, a recovery operation such as sucking out the liquid in the vicinity of the discharge port and removing the microbubbles is periodically performed so that a large amount of the microbubbles remain and the discharge operation is not hindered. On the other hand, in the liquid discharge head provided with the movable member, the liquid is rarely pushed back to the upstream side, so that the microbubbles are discharged from the discharge port and remain before increasing so as to hinder the discharge operation. There are few things. For this reason, continuous recording can be performed over a relatively long period, and recording of 100 sheets or more can be performed continuously at the maximum.
[0011]
[Problems to be solved by the invention]
As described above, the liquid discharge head including the movable member can quickly refill the liquid without causing a large meniscus retraction, so that the liquid can be discharged at a relatively short time interval. It has the advantage that it can be driven at a relatively high frequency.
[0012]
Conventionally, in order to be able to drive at a higher frequency, it is practically effective to perform the next discharge by quickly eliminating bubbles formed for the previous discharge. It is considered to be. This is because it is considered necessary to perform the next discharge after the meniscus returns to the steady position through the vibration process and the refill is stably completed in order to perform the next discharge satisfactorily. This is because completion and meniscus return stability are brought about by the completion of defoaming.
[0013]
However, theoretically, a certain amount of time is required to complete the defoaming, and this time limits the drive interval. That is, a voltage pulse having a width of several μs is applied in order to discharge the liquid, and the bubble generation / growth / defoaming period is set to about 30 to 50 μs from the start of pulse application in consideration of response delay. it can. Therefore, even if the next pulse is applied immediately after defoaming and the next ejection is performed, the drive frequency is limited to 20 to 30 kHz. Therefore, the inventors of the present invention thought that there would be no technological development without breaking through such reality, and conducted extensive research.
[0014]
That is, an object of the present invention is to break the conventional limit related to performing liquid discharge at a higher frequency, and the present invention is a novel liquid discharge capable of performing liquid discharge continuously at a higher frequency. We are going to propose a method.
[0015]
[Means for Solving the Problems]
The ideas and knowledge gained in the research to achieve the above-mentioned objectives were again the idea of reversal. That is, the liquid discharge method according to the present invention communicates with a heating element that generates thermal energy for generating bubbles in the liquid, a discharge port that is a portion for discharging the liquid, and the discharge port. Shi Bubbles But Occurrence You A liquid channel having a bubble generating region, a liquid chamber for supplying a liquid to the liquid channel, a movable member provided in the bubble generating region and displaced as the bubble grows, Provided facing the bubble generation area of the liquid flow path, It has a regulating part that regulates the displacement of the movable member to a desired range, and the heating element and the discharge port are in a linear communication state , Strange By using a liquid discharge head in which the liquid flow path having the bubble generation region becomes a substantially closed space except for the discharge port due to substantial contact between the moved movable member and the regulating portion Vomit Continuously from the exit First Droplet And the second droplet A liquid discharge method for discharging
First Liquid Drops vomit Make Bubbles formed for Will shrink start After The state where the bubbles remain biased toward the discharge port side of the bubble generation region, and there is a portion where no bubbles exist on the liquid chamber side of the bubble generation region At the time of , Heating element The drive Then liquid Bubble inside The growth Let To eject the second droplet It is characterized by that.
[0016]
The present invention First liquid Drop of After completion of defoaming of bubbles formed during discharge Second liquid Drop of Instead of driving for discharge, First liquid Drop of While using bubbles formed by discharge, Second liquid Drop of This is an epoch-making invention in which continuous ejection is performed at a timing that takes into account the balance between ejection bubble formation and ejection.
[0017]
The present invention pays attention to the movable member that gives the above-described efficient refill characteristics, and in the liquid discharge head including the movable member, the change of the bubble is taken as a hint that the defoaming position is located on the discharge port side of the bubble generation region. And the position of the meniscus, First liquid Drop of Before defoaming is complete Second liquid Drop of This is achieved by finding that there is a timing at which ejection can be performed.
[0018]
That is, in a liquid discharge head provided with a movable member, First liquid Drop of During the defoaming process of discharge, First liquid Drops vomit Make For this reason, there is a timing at which the bubbles that are formed to disappear are present on the discharge port side of the bubble generation region, and there are no bubbles on the liquid chamber side. And at this timing, the meniscus retreat has begun but not at its maximum. Further, since the movable member side of the heating element is defoamed, the replenishment of the liquid is substantially completed and the refilling state is sufficient. Therefore, at this timing, the liquid discharge head Of the second droplet It is in an extremely advantageous state for discharging, and at this time The second droplet vomit Make By supplying the drive energy for the heating element to foam the liquid, Drop of The discharge can be performed satisfactorily. Continuous liquid at this timing Drop of Discharging is performed after defoaming is completed as before. Second liquid Drop of Compared to the case of discharging, the liquid is continuously applied at very short intervals. Drop of This means that ejection is performed.
[0019]
In the liquid ejection method of the present invention, First liquid Drop of In the state where some of the bubbles formed during discharge remain on the downstream side Second liquid Drops vomit Make Driving energy for the heating element, First 2 of liquid Drop of At the time of discharge, a liquid flow from the upstream side is accompanied by the defoaming of the bubbles partially remaining on the downstream side. by this, First 2 of liquid Drop of The energy efficiency of liquid discharge for discharge can be improved. Also, by the action of the liquid flow from the upstream side, First 2 of liquid Drop of The volume of ejected droplets ejected during ejection can be made larger than the volume of ejected droplets when liquid is ejected from a steady state. In addition, the liquid flow from the upstream side Second liquid Drop of The flow of liquid during discharge can be accelerated, First 2 of liquid Drop of When discharging Liquid When the liquid is discharged from the steady state Liquid It can be faster than the speed of the drops.
[0020]
like this First liquid Drop of The liquid flow accompanying the defoaming of the bubbles formed at the time of discharge is decelerated just before the end of the defoaming as the defoaming progresses. For this reason, First liquid Drop of Before the defoaming of bubbles formed during discharge ends Second liquid For ejecting drops By initiating foaming, the action of the liquid flow as described above can be effectively obtained.
[0021]
Like this, than usual Second The ability to increase the volume of the droplet or increase the speed provides advantages such as being convenient for performing multi-tone recording.
[0022]
As described above, according to the liquid ejection method of the present invention, the liquid is continuously applied at very short time intervals. Drop of Discharging can be performed. Therefore, First liquid Drop of During dispensing ,liquid A satellite formed by separating the tail-drawing part behind the drop, On the first droplet Continued The second discharged liquid drop Can also be captured. in this way, Second liquid drop Making it possible to capture satellites provides advantages such as being convenient for performing multi-tone recording.
[0024]
In the liquid ejection method according to the present invention, The first liquid Drop of Part of the energy supplied during discharge Second liquid Drop of Because it can contribute to the discharge effectively, First 2 of liquid Drop of During dispensing First 1 of liquid Drop of Energy supplied to the heating element during discharge - Less energy to the heating element, First liquid Drop of The second liquid discharge can be performed with a droplet amount and a droplet velocity equal to or higher than those during discharge.
[0025]
in this way, Second liquid Drop of The energy supplied to the heating element during discharge First 1 When discharging liquid droplets To make smaller than Second liquid Drop of The pulse width of the voltage pulse applied to the heating element during discharge First 1 When discharging liquid droplets Can be made smaller.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a schematic side sectional view of a main part of a liquid discharge head used for liquid discharge according to an embodiment of the present invention. FIGS. 2A to 2E are diagrams illustrating a single discharge process of liquid from the liquid discharge head shown in FIG.
[0027]
First, the configuration of the liquid discharge head will be described with reference to FIG.
[0028]
This liquid discharge head includes an element substrate 1 having a heating element 10 which is a bubble generating means and a movable member 11, a top plate 2 on which a stopper (regulator) 12 is formed, and an orifice plate 5 on which a discharge port 4 is formed. Have.
[0029]
The flow path (liquid flow path) 3 through which the liquid flows is formed by fixing the element substrate 1 and the top plate 2 in a laminated state. In addition, a plurality of flow paths 3 are formed in parallel in one liquid discharge head, and communicate with a discharge port 4 that discharges liquid formed on the downstream side (left side in FIG. 1). There is a bubble generation region in the vicinity of the surface where the heating element 10 and the liquid come into contact. A large-capacity common liquid chamber 6 is provided so as to communicate with the upstream side (right side in FIG. 1) of each flow path 3 at the same time. That is, each flow path 3 has a shape branched from a single common liquid chamber 6. The liquid chamber height of the common liquid chamber 6 is formed higher than the channel height of the channel 3.
[0030]
The movable member 11 has a cantilever shape that is supported at one end, and is fixed to the element substrate 1 on the upstream side of the flow of ink (liquid), and the downstream side of the fulcrum 11a is movable in the vertical direction with respect to the element substrate 1. . The movable member 11 is positioned substantially parallel to the element substrate 1 while maintaining a gap with the element substrate 1 in the initial state.
[0031]
The movable member 11 disposed on the element substrate 1 is disposed such that the free end 11 b is located in the substantially central region of the heating element 10. The stopper 12 provided on the top plate 2 regulates the amount of displacement of the free end 11b upward when the free end 11b of the movable member 11 contacts the stopper 12. When the displacement amount of the movable member 11 is restricted by the movable member 11 coming into contact with the stopper 12 (when the movable member is in contact), the flow path 3 is upstream of the movable member 11 and the stopper 12 due to the movable member 11 and the stopper 12. The side and the downstream side of the movable member 11 and the stopper 12 are substantially cut off.
[0032]
The position Y of the free end 11 b and the end X of the stopper 12 are preferably located on a plane perpendicular to the element substrate 1. More preferably, these X and Y are located on a plane perpendicular to the substrate together with Z which is the center of the heating element 10.
[0033]
Further, the height of the flow path 3 on the downstream side from the stopper 12 is abruptly increased. With this configuration, the bubbles on the downstream side of the bubble generation region have a sufficient flow path height even when the movable member 11 is restricted by the stopper 12 and thus do not hinder the bubble growth. Since the liquid can be smoothly directed toward the outlet 4 and the non-uniformity of the pressure balance in the height direction from the lower end to the upper end of the discharge port 4 is reduced, good liquid discharge can be performed. In addition, in the conventional liquid discharge head that does not have the movable member 11, when such a flow path configuration is adopted, a stagnation occurs in a portion where the flow path height is high on the downstream side of the stopper 12. Bubbles tend to stay in the stagnation part, which is not preferable, but in the present embodiment, as described above, the liquid flow reaches the stagnation part, so the influence of the bubble retention is extremely small.
[0034]
Furthermore, the ceiling shape on the common liquid chamber 6 side is rapidly increased with the stopper 12 as a boundary. In the case where there is no movable member 11 in this configuration, the fluid resistance on the downstream side of the bubble generation region is smaller than the fluid resistance on the upstream side, so that the pressure used for ejection is difficult to go to the ejection port 4 side. However, in this embodiment, since the movement of the bubble to the upstream side of the bubble generation region is substantially blocked by the movable member 11 when the bubble is formed, the pressure used for discharge is positively toward the discharge port 4. At the same time, since the fluid resistance on the upstream side of the bubble generation region is small at the time of liquid supply, the liquid is quickly supplied to the bubble generation region.
[0035]
According to the above configuration, the growth component toward the downstream side of the bubbles and the growth component toward the upstream side are not uniform, the growth component toward the upstream side is reduced, and the liquid movement to the upstream side is suppressed. Since the flow of liquid to the upstream side is suppressed, the retreat amount of the meniscus after discharge is reduced, and the amount of protrusion of the meniscus from the orifice surface (liquid discharge surface) 5a during refilling (the amount of overshoot) is also reduced. To do. Therefore, meniscus vibration is suppressed, and stable ejection is performed at any driving frequency from low frequency to high frequency.
[0036]
In the present embodiment, the portion on the downstream side of the bubbles and the discharge port 4 are in a “linear communication state” in which a straight channel structure is maintained with respect to the liquid flow. More preferably, the direction of propagation of the pressure wave generated when bubbles are generated, and the flow direction of the liquid and the discharge direction associated therewith are linearly matched, so that the discharge direction, discharge speed, etc. It is desirable to form an ideal state that stabilizes the discharge state at a very high level. In the present embodiment, as one definition for achieving or approximating this ideal state, the discharge port 4 and the heating element 10, particularly the discharge port 4 side of the heating element 10 having an influence on the bubble discharge port 4 side ( The downstream side) may be directly connected by a straight line, and as shown in FIG. 4, if there is no liquid in the flow path 3, the heating element 10 is viewed from the outside of the discharge port 4. In particular, the downstream side of the heating element 10 can be observed.
[0037]
Next, the dimension of each component will be described.
[0038]
In this embodiment, when the bubble wrapping around the upper surface of the movable member (the bubble wrapping upstream of the bubble generation region) is studied, the moving speed of the movable member and the bubble growth rate (in other words, the liquid It has been found that it is possible to obtain good discharge characteristics by eliminating bubbles from entering the upper surface of the movable member depending on the relationship with the movement speed of the movable member.
[0039]
That is, in the present embodiment, when the bubble volume change rate and the displacement volume change rate of the movable member are both increasing, the displacement of the movable member is restricted by the restricting portion at the time when the bubble change rate is increased. It eliminates the wrapping of bubbles and obtains good discharge characteristics.
[0040]
This will be described in detail below with reference to FIG.
[0041]
First, when bubbles are generated on the heating element 10 from the state of FIG. 2A, a pressure wave is instantaneously generated, and the bubbles 40 grow as the liquid around the heating element 10 moves due to the pressure waves. To go. Initially, the movable member 11 is displaced upward so as to substantially follow the movement of the liquid (FIG. 2B). As the time further advances, the displacement speed of the movable member 11 rapidly decreases due to the reduced inertial force of the liquid and the elasticity of the movable member 11. At this time, since the moving speed of the liquid is not so small, the difference between the moving speed of the liquid and the moving speed of the movable member 11 is increased. At this time, if the gap between the movable member 11 (free end 11b) and the stopper 12 still exists, the liquid flows into the upstream side of the bubble generation region from the gap, and the movable member 11 is stopped by the stopper. In addition to creating a state in which it is difficult to contact 12, a part of the ejection force is lost. Therefore, in such a case, the effect of restricting (blocking) the movable member 11 by the restricting portion (stopper 12) cannot be fully utilized.
[0042]
Therefore, in the present embodiment, the restriction of the movable member by the restriction portion is performed at a stage where the displacement of the movable member substantially follows the movement of the liquid. In the present invention, for the sake of convenience, the displacement speed of the movable member and the bubble growth speed (liquid movement speed) are expressed as “movable member displacement volume change rate” and “bubble volume change rate”. The “movable member displacement volume change rate” and “bubble volume change rate” are obtained by differentiating the movable member displacement volume or bubble volume.
[0043]
With such a configuration, it is possible to substantially eliminate the flow of liquid that causes bubbles to wrap around the upper surface of the movable member 11, and to further ensure the sealed state of the bubble generation region. Obtainable.
[0044]
Further, according to this configuration, the bubble 40 continues to grow after the movable member 11 is regulated by the stopper 12. At this time, the stopper is used to promote free growth of the downstream component of the bubble 40. It is desirable that a sufficient distance (protrusion height of the stopper 12) between the 12 portion and the surface (upper wall surface) of the flow path 3 facing the substrate 1 is sufficiently provided.
[0045]
In the present invention, the restriction of the displacement of the movable member by the restricting portion refers to a state where the displacement volume change rate of the movable member is 0 or negative.
[0046]
The height of the flow path 3 is 55 μm, the thickness of the movable member 11 is 5 μm, and the lower surface and the element of the movable member 11 in a state where no bubbles are generated (the movable member 11 is not displaced). The clearance between the upper surface of the substrate 1 is 5 μm.
[0047]
In addition, the height from the channel wall surface of the top plate 2 to the tip of the stopper 12 is t ₁ And the clearance between the upper surface of the movable member 11 and the tip of the stopper 12 is t ₂ T ₁ T is 30 μm or more, t ₂ Is 15 μm or less, stable liquid discharge characteristics can be exhibited, and t ₁ T is 20 μm or more, t ₂ Is preferably 25 μm or less.
[0048]
Next, regarding the single ejection operation of the liquid ejection head used in the present embodiment, FIGS. 2A to 2E, the time variation of the bubble displacement speed and volume, and the displacement speed and displacement volume of the movable member. This will be described in detail with reference to FIG.
[0049]
In FIG. 3, the bubble volume change rate v _b Is the solid line, bubble volume V _b Is a two-dot chain line, and the movable member displacement volume change rate v _m Is a broken line and the displacement volume V of a movable member _m Are indicated by alternate long and short dash lines. Also, bubble volume change rate v _b Is the bubble volume V _b Is positive, and bubble volume V _b Is a positive increase in volume, and the displacement rate v of the movable member displacement v _m Is the movable member displacement volume V _m The increase in the displacement is positive, and the movable member displacement volume V _m Indicates positive increases in volume, respectively. The movable member displacement volume V _m 2 has a positive volume when the movable member 11 is displaced from the initial state of FIG. 2A to the top plate 2 side. Therefore, when the movable member 11 is displaced from the initial state to the element substrate 1 side, the movable member 11 Displacement volume V _m Indicates a negative value.
[0050]
FIG. 2A shows a state before energy such as electric energy is applied to the heating element 10 and shows a state before the heating element 10 generates heat. As will be described later, the movable member 11 is located in a region facing the upstream half of the bubble generated by the heat generated by the heating element 10.
[0051]
In FIG. 3, this state corresponds to point A at time t = 0.
[0052]
FIG. 2B shows a state in which a part of the liquid filling the bubble generation region is heated by the heating element 10 and the bubbles 40 accompanying the film boiling start to foam. In FIG. 3, this state is represented by B to C. ₁ Corresponds to immediately before the point, bubble volume V _b Shows a situation that grows with time. At this time, the displacement of the movable member 11 starts later than the volume change of the bubble 40. That is, a pressure wave based on the generation of bubbles 40 due to film boiling propagates in the flow path 3, and accordingly, the liquid moves downstream and upstream from the central region of the bubble generation region. The movable member 11 starts to be displaced by the flow of liquid accompanying the growth of the liquid. In addition, the movement of the liquid toward the upstream side passes between the wall surface of the flow path 3 and the movable member 11 and moves toward the common liquid chamber 6 side. The clearance between the stopper 12 and the movable member 11 at this time becomes narrower as the movable member 11 is displaced. In this state, the discharge droplet 66 starts to be discharged from the discharge port 4.
[0053]
FIG. 2C shows a state in which the free end 11 b of the movable member 11 that has been displaced by the further growth of the bubble 40 is in contact with the stopper 12. In FIG. 3, this state is C ₁ ~ C _Three It corresponds to a point.
[0054]
Movable member displacement volume change rate v _m Is the state shown in FIG. 2B before the movable member 11 in the state shown in FIG. 2C comes into contact with the stopper 12, that is, in FIG. ₁ At the point B ′ when moving to the point, it rapidly decreases. This is because the flow resistance of the liquid between the movable member 11 and the stopper 12 rapidly increases immediately before the movable member 11 contacts the stopper 12. Also, bubble volume change rate v _b Also decreases rapidly.
[0055]
Thereafter, the movable member 11 further approaches and comes into contact with the stopper 12, but the contact between the movable member 11 and the stopper 12 depends on the height t of the stopper 12. ₁ The clearance between the upper surface of the movable member 11 and the tip of the stopper 12 is assured by dimensioning as described above. When the movable member 11 comes into contact with the stopper 12, further upward displacement is restricted (C in FIG. 3). ₁ ~ C _Three Therefore, the movement of the liquid in the upstream direction is also greatly restricted there. Along with this, the growth of the bubbles 40 to the upstream side is also restricted by the movable member 11. However, since the moving force of the liquid in the upstream direction is large, the movable member 11 receives a large amount of stress that is pulled in the upstream direction and slightly deforms upwardly. At this time, the bubble 40 continues to grow, but the downstream side of the bubble 40 further grows by restricting the growth to the upstream side by the stopper 12 and the movable member 11, and the movable member 11 is not provided. Compared to the case, the growth height of the bubbles 40 on the downstream side of the heating element 10 is higher. That is, as shown in FIG. 3, the movable member displacement volume change rate v _m C is due to the fact that the movable member 11 is in contact with the stopper 12. ₁ ~ C _Three Although it is zero between points, the bubble 40 grows downstream, so C ₁ C slightly delayed in time from point ₂ This C continues to grow ₂ Bubble volume at point V _b Is the maximum value.
[0056]
On the other hand, as described above, since the displacement of the movable member 11 is restricted by the stopper 12 in the upstream portion of the bubble 40, the movable member 11 has a convex shape upstream due to the inertial force of the liquid flow upstream. It is a small size that stays until it is bent and stress is charged. The upstream portion of the bubble 40 is regulated to almost zero by the stopper 12, the channel side wall, the movable member 11, and the fulcrum 11a.
[0057]
As a result, the liquid flow to the upstream side is largely restricted, and fluid crosstalk to the adjacent flow path and back flow of liquid and pressure vibration in the supply path system that impedes high-speed refilling are prevented.
[0058]
FIG. 2D shows a state in which the bubble 40 starts to contract by the negative pressure inside the bubble 40 overcoming the movement of the liquid downstream in the flow path 3 after the film boiling described above.
[0059]
Shrinkage of the bubble 40 (C in FIG. ₂ To point E), the movable member 11 is displaced downward (C in FIG. 3). _Three However, the movable member 11 itself has the stress of the cantilever spring and the stress of the upward convex deformation described above, thereby increasing the speed of downward displacement. In addition, the flow in the downstream direction of the liquid on the upstream side of the movable member 11 which is a low flow path resistance region formed between the common liquid chamber 6 and the flow path 3 has a small flow path resistance. Therefore, it rapidly becomes a large flow and flows into the flow path 3 through the stopper 12. By these operations, the liquid on the common liquid chamber 6 side is guided into the flow path 3. The liquid introduced into the flow path 3 passes between the stopper 12 and the movable member 11 displaced downward, flows into the downstream side of the heating element 10, and at the same time defoams the bubbles 40 that have not been defoamed. Acts to accelerate. After the liquid flow assists defoaming, it further creates a flow in the direction of the discharge port 4 to help the meniscus return and improve the refill speed.
[0060]
At this stage, the liquid column composed of the ejection droplets 66 exiting from the ejection port 4 becomes droplets and flies to the outside. FIG. 2D shows a state where the meniscus is drawn into the discharge port 4 by defoaming and the liquid column of the discharge droplet 66 is about to be separated.
[0061]
Moreover, since the flow into the flow path 3 through the portion between the movable member 11 and the stopper 12 described above increases the flow velocity on the wall surface on the top plate 2 side, there is very little residue such as microbubbles in this portion. This contributes to the stability of discharge.
[0062]
Furthermore, since the cavitation generation point due to defoaming is also shifted to the downstream side of the bubble generation region, damage to the heating element 10 is reduced. At the same time, due to the same phenomenon, the adhesion of the burner to the heating element 10 in this region is reduced, so that the discharge stability is improved.
[0063]
FIG. 2E shows a state in which the movable member 11 is displaced by overshooting downward from the initial state (after the point E in FIG. 3) after the bubbles 40 are completely defoamed.
[0064]
Although this overshoot of the movable member 11 depends on the rigidity of the movable member 11 and the viscosity of the liquid to be used, it attenuates and converges in a short time and returns to the initial state.
[0065]
FIG. 2 (e) shows a state in which the meniscus is drawn to the upstream side by defoaming, but it returns to the steady position in a relatively short time, similar to the attenuation convergence of the displacement of the movable member 11. ,Stabilize. In addition, as shown in FIG. 2E, a satellite 67 formed by separating a portion that is tailed by surface tension may be formed behind the ejection droplet 66. .
[0066]
Next, with reference to FIG. 5 which is a perspective view of a part of the head shown in FIG. 1, in particular, details regarding the raised bubbles 41 rising from both sides of the movable member 11 and the liquid meniscus at the discharge port 4 will be given. Explained. Although the shape of the stopper 12 and the shape of the low flow path resistance region 3a upstream of the stopper 12 shown in FIG. 5 are different from those shown in FIG. 1, the basic characteristics are the same.
[0067]
In the present embodiment, there is a slight clearance between both side wall surfaces of the wall constituting the flow path 3 and both side portions of the movable member 11, so that the movable member 11 can be smoothly displaced. Further, in the foaming growth process by the heating element 10, the bubble 40 displaces the movable member 11, rises to the upper surface side of the movable member 11 through the clearance, and slightly enters the low flow path resistance region 3 a. The invading raised bubbles 41 wrap around the back surface of the movable member 11 (the surface opposite to the bubble generation region), thereby suppressing blurring of the movable member 11 and stabilizing the ejection characteristics.
[0068]
Further, in the defoaming process of the bubbles 40, the raised bubbles 41 promote the liquid flow from the low flow path resistance region 3a to the bubble generation region, and coupled with the above-described high-speed meniscus drawing from the discharge port 4 side, To complete promptly. In particular, the liquid flow caused by the raised bubbles 41 hardly causes the bubbles to accumulate at the corners of the movable member 11 or the flow path 3.
[0069]
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 4 due to the generation of the bubble 40, the discharge droplet 66 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 embodiment, when the movable member 11 is displaced by the bubble growth process and the displaced movable member 11 comes into contact with the stopper 12, the flow having a bubble generation region is obtained. A substantially closed space is formed in the passage 3 except for the discharge port. Therefore, if the bubbles are defoamed in this state, the above-mentioned closed space is maintained until the movable member 11 is separated from the stopper 12 by the defoaming. Therefore, most of the defoaming energy of the bubbles 40 is the liquid in the vicinity of the discharge port 4. Will act as a force to move the As a result, immediately after the start of defoaming of the bubbles 40, the meniscus is rapidly drawn into the flow path 3 from the discharge port 4, and is connected to the discharge droplet 66 outside the discharge port 4 to form a liquid column. The part is quickly separated with a strong force by the meniscus. As a result, the satellite dots formed from the tail portion are reduced, and the print quality can be improved.
[0070]
Furthermore, since the trailing portion is not continuously pulled by the meniscus, the discharge speed does not decrease, and the distance between the discharge droplet 66 and the satellite dot is shortened. Dots are drawn. As a result, the ejection droplets 66 and satellite dots can be combined, and a liquid ejection head having almost no satellite dots can be provided.
[0071]
Furthermore, in the present embodiment, in the liquid discharge head described above, the movable member 11 is provided to suppress only the bubbles 40 that grow in the upstream direction with respect to the liquid flow toward the discharge port 4. More preferably, the free end 11b of the movable member 11 is located at the substantial center of the bubble generation region. According to this configuration, the upstream wave due to the bubble growth and the inertial force of the liquid, which are not directly related to the discharge of the liquid, are suppressed, and the component of the growth of the bubbles 40 downstream in the direction of the discharge port 4 is straightforward. Can be directed.
[0072]
Further, since the flow path resistance of the low flow path resistance region 3a opposite to the discharge port 4 with the stopper 12 as a boundary is low, the movement of the liquid in the upstream direction due to the growth of the bubbles 40 is large due to the low flow path resistance region 3a. Therefore, when the displaced movable member 11 comes into contact with the stopper 12, the movable member 11 is subjected to stress in the form of being pulled in the upstream direction. As a result, even if defoaming is started in this state, a large amount of liquid moving force in the upstream direction due to the growth of the bubbles 40 remains, so a certain period until the repulsive force of the movable member 11 wins against this liquid moving force. The above-described closed space can be maintained. In other words, this configuration ensures more reliable high-speed meniscus pull-in. Further, when the defoaming process of the bubbles 40 proceeds and the repulsive force of the movable member 11 wins against the liquid moving force in the upstream direction due to bubble growth, the movable member 11 is displaced downward to return to the initial state. A flow in the downstream direction also occurs in the flow path resistance region 3a. The flow in the downstream direction in the low flow path resistance region 3a has a small flow path resistance, so it rapidly becomes a large flow and flows into the flow path 3 through the stopper 12. As a result, the liquid movement in the downstream direction toward the discharge port 4 makes it possible to suddenly brake the above-described meniscus pull-in and converge the meniscus vibration at high speed.
[0073]
The liquid discharge method of the present invention is characterized in that liquid is continuously discharged at a high frequency using the liquid discharge head as described above. Then, next, with reference to FIG. 6, 7, operation | movement at the time of performing liquid discharge continuously with a short space | interval is demonstrated. FIG. 7 schematically shows the waveform of a voltage pulse applied to the heating element 10.
[0074]
First, as shown in FIG. 6A, the first voltage pulse is applied to the heating element 10 to form the bubble 40 and the first ejection droplet 66a. At this time, in this embodiment, as shown in FIG. 7, a double pulse composed of a pre-pulse P1 and a main pulse P2 is applied as a voltage pulse at a predetermined time t1. In this double pulse drive, by applying the pre-pulse P1, the heating element 10 and the liquid in the vicinity thereof are preheated, and when the main pulse P2 is subsequently applied, the liquid can be foamed satisfactorily. As described above, in this foaming process, the movable member 11 is displaced until it comes into contact with the stopper 12 to substantially close the upstream side, and the movement of the liquid in the upstream direction is greatly limited. And the bubble 40 grows greatly downstream.
[0075]
From this state, as shown in FIG. 6 (b), when the defoaming of the bubble 40 starts to decrease in volume, particularly on the upstream side of the bubble 40, the movable member 11 starts to be displaced downward, and the liquid refilling starts. Is done. As described above, the defoaming of the bubbles is accelerated by the movement of the movable member 11, and is greatly accelerated particularly on the upstream side of the bubble generation region where the movable member 11 is located.
[0076]
As shown in FIG. 6 (c), the defoaming is accelerated on the upstream side of the bubble generation region and the bubbles 40 grow greatly downstream in the foaming process. The defoaming is almost completed on the upstream side of the bubble generation region, and the bubble 40 remains in the vicinity of the downstream end portion only. In this state, the liquid is refilled from the upstream side of the bubble generation region and refilled from the center of the heating element 10 to the downstream side. Further, the meniscus is drawn into the discharge port 4, whereby the first discharge droplet 66 a and the satellite 67 are separated from the liquid in the liquid discharge head. However, the bubble 40 shown in FIG. In the state where the defoaming has not yet been completed on the downstream side, the meniscus is not drawn into the liquid discharge port 4 as shown in FIG. It is still relatively close.
[0077]
In the liquid ejection method of the present embodiment, the second voltage pulse is applied to the heating element 10 in this state, and the second foaming is started. That is, in this state, the meniscus is in the vicinity of the liquid discharge surface, and the refilling of the liquid to the upstream side of the heating element 10 has been completed. From this state, the voltage pulse is applied to start foaming. By doing so, it is possible to discharge the liquid satisfactorily. At the time of the second foaming, as shown in FIG. 7, the double pulse driving is performed by applying the pre-pulse P3 and the main pulse P4 at time t2 after a predetermined time has elapsed from time t1. At this time, the second foaming is started substantially simultaneously with the application of the main pulse P4. Therefore, in the present embodiment, as described above, the start of foaming at the timing when the bubble 40 remains only in the vicinity of the downstream end of the bubble generation region starts the application of the main pulse P4 at this timing. It means that.
[0078]
When the voltage pulse is applied, as shown in FIG. 6D, the bubble 40 starts to grow and the movable member 11 starts to move upward. At this time, since a part of the bubbles 40 remains on the downstream side at the start of foaming, the foaming is performed in a state where a liquid flow is generated from the upstream side due to the defoaming of the remaining bubbles. As a result, the liquid flow accompanying the defoaming after the previous liquid discharge can be applied to the liquid flow generated as the bubble 40 grows, and the liquid flow in the discharge direction can be generated immediately. Then, the meniscus is not drawn as much as the single liquid discharge, and starts moving from the position shown in FIG. 6C to the downstream side as shown in FIG. 6D.
[0079]
Here, the liquid flow accompanying the defoaming of the bubbles formed during the previous liquid discharge is decelerated just before the defoaming is completed as the defoaming progresses. For this reason, it is possible to effectively obtain the action of the liquid flow as described above by starting the second and subsequent foaming before the defoaming of the bubbles formed during the previous liquid discharge is completed.
[0080]
Then, as shown in FIG. 6E, the bubble 40 further grows and the second ejection droplet 66b is ejected. At this time, since the liquid flow accompanying the defoaming after the previous liquid discharge acts as described above, the volume of the second discharge droplet 66b becomes larger than the first time. In particular, the volume V of the second ejection droplet 66b _d2 Is the volume V of the first ejection droplet 66a. _dm1 And its satellite 67 volume V _ds1 Larger than the sum of V, that is, V _d2 > (V _dm1 + V _ds1 ).
[0081]
In addition, since the second foaming is started in a state where a relatively fast liquid flow to the upstream side is generated due to refilling, the liquid flow from the discharge port 4 toward the heating element 10 is canceled by the second foaming. In addition, when a liquid flow toward the upstream side is further formed, momentum of the liquid flow from the upstream side of the heating element 10 is added to the liquid flow toward the discharge port 4 to accelerate the flow. Therefore, the speed v of the first ejection droplet 66a ₁ Compared to the speed v of the second ejection droplet 66b ₂ It is possible to make it faster.
[0082]
V ₁ > V ₂ As described above, the second ejection droplet 66b has a larger volume than the first ejection droplet 66a, that is, V _d2 > (V _dm1 + V _ds1 ) Is also possible. This indicates that a part of the thermal energy generated during the first liquid discharge contributes to the second liquid discharge.
[0083]
Furthermore, it is possible to cause the second discharge droplet 66b to catch up with the liquid column-shaped satellite 67 immediately after being separated, that is, to cause the second discharge droplet 66b to capture the satellite 67. . In this case, the volume of the second ejection droplet 66b after capturing the satellite 67 is V _d2 + V _ds1 Of course, (V _d2 + V _ds1 )> V _dm1 Is possible.
[0084]
In this way, by changing the liquid discharge amount of the first discharge droplet 66a and the second discharge droplet 66b, for example, recording is performed by changing the size of the formed pixel and changing the gradation. can do. In addition, the gradation difference can be increased by causing the second ejection droplet 66b to absorb the satellite 67 during the first liquid ejection. Furthermore, it is possible to perform multi-tone recording by ejecting a plurality of ejected droplets continuously and combining the ejected droplets in the course of flight to a recording medium.
[0085]
As described above, according to the liquid discharge method of the present embodiment, in the first liquid discharge defoaming step, the second liquid discharge is performed while the bubbles 40 still remain on the upstream side of the bubble generation region. By applying a voltage pulse for causing the liquid to foam, it is possible to perform good liquid discharge continuously in a short time interval exceeding the conventional limit, that is, the liquid discharge head is driven at a very high frequency. be able to. At this time, compared to the first liquid discharge in which the liquid discharge is started from the steady state, the discharge amount of the second liquid discharge can be increased and the discharge speed can be further increased. In addition, since a part of the thermal energy generated during the first liquid discharge contributes to foaming during the second liquid discharge, the energy efficiency of the discharge can be improved.
[0086]
Next, a liquid discharge method according to another embodiment of the present invention will be described with reference to FIGS. 8 and 9, the same parts as those of the previous embodiment are denoted by the same reference numerals, and the description thereof is omitted.
[0087]
As described above, according to the liquid discharge method of the present invention, the liquid flow from the upstream side caused by the high-speed refilling of the liquid accompanying the defoaming of the bubbles 40 formed during the previous liquid discharge is effective for the next liquid discharge. Can contribute. That is, part of the energy applied during the previous liquid discharge can be used as the energy for the next liquid discharge. Therefore, even if the energy applied during the second and subsequent liquid discharges of the continuous discharge is smaller than the energy applied during the first liquid discharge, the energy that effectively contributes to the discharge is equal to or equal to the first energy. This can be done. This embodiment pays attention to this, and shows a method of discharging a liquid by making the energy applied at the second and subsequent liquid discharges of continuous discharge smaller than the energy applied at the first liquid discharge. In the present embodiment, specifically, an example in which the applied energy is changed by changing the pulse width of the voltage pulse applied to the heating element 40 is shown.
[0088]
Also in this embodiment, first, a voltage pulse is applied to the heating element 10 to discharge the first discharge droplet 66a as shown in FIG. At this time, as a voltage pulse, as shown in FIG. 9, a double pulse composed of a pre-pulse P1 and a main pulse P2 is applied at a predetermined time t1.
[0089]
After the bubble 40 reaches maximum foaming, as shown in FIG. 8B, it begins to defoam, and the volume is greatly reduced especially on the upstream side. Then, as shown in FIG. 8C, in the state where the bubble 40 remains only near the downstream end of the bubble generation region, the second voltage pulse is applied to start the second bubble.
[0090]
As for the second voltage pulse, as shown in FIG. 9, a double pulse composed of a pre-pulse P3 and a main pulse P4 is applied. Here, in the present embodiment, the pulse widths of the pre-pulse P3 and the main pulse P4 are made shorter than the pulse width at the first foaming. Specifically, the pulse width of the first pre-pulse P1 is 0.7 μs, the pulse width of the main pulse P2 is 1.3 μs, the pulse width of the second pre-pulse P3 is 0.4 μs, and the pulse width of the main pulse P4 is It was set to 0.9 μs.
[0091]
At this time, the timing of the second foaming start is substantially the same as the timing of applying the main pulse P4 as described above. Therefore, in order to start foaming at the timing when the bubble 40 generated by the first foaming remains only near the downstream end of the bubble generation region, the voltage pulse is applied so that the application of the main pulse P4 is started at this timing. Apply. Specifically, in the present embodiment, the application of the second voltage pulse P3 is started at time t2 17 μs after the time t1 when the application of the pre-pulse P1 of the first voltage pulse is started, and the foaming timing is adjusted.
[0092]
In this way, the second voltage pulse is applied to cause the liquid to foam as shown in FIG. 8D, thereby discharging the second ejection droplet 66b as shown in FIG. 8E. Although the size of the bubble 40 and the second ejection droplet 66b generated by the second voltage pulse application is smaller than that in the previous embodiment, the amount of the second ejection droplet 66b is the effect of the liquid flow caused by refilling. Therefore, if necessary, it can be equal to or more than the first ejection droplet 66a. Further, the speed of the ejection droplet 66a can be made equal to or faster than that of the first ejection droplet 66a. As shown in FIG. The ejected droplets 66b can be captured. In particular, the satellite 67 can be captured by the second ejection droplet 66b while it is in the form of a liquid column, and if necessary, the first ejection droplet 66a can be captured by the second ejection droplet 66b during the flight. It is also possible to make it.
[0093]
As described above, according to the present embodiment, part of the energy supplied to the heating element 10 during the previous liquid discharge can be effectively contributed to the next liquid discharge in the form of a liquid flow of high-speed refill. In addition, it is possible to supply the heating element 10 with less energy than in the previous liquid discharge, and to discharge droplets having an amount equal to or higher than that in the previous liquid discharge.
[0094]
Thus, according to this embodiment, the energy supplied in order to obtain required discharge performance can be restrained small. For this reason, the energy consumption of the liquid discharge head can be saved, and an unnecessary temperature rise of the liquid discharge head can be suppressed. Therefore, according to the present embodiment, particularly when the liquid discharge head is driven at a high speed as in the liquid discharge method of the present invention, the power supply and the drive circuit are made to have a large capacity by suppressing the supply energy. This eliminates the need for cost increase. Further, it is possible to suppress a change in ejection characteristics and a decrease in reliability due to heating of the liquid ejection head.
[0095]
【The invention's effect】
As described above, according to the liquid ejection method of the present invention, the voltage pulse for the subsequent liquid ejection in the state where the bubbles still remain downstream of the bubble generation region in the previous liquid ejection defoaming step. By applying the, liquid discharge can be continuously and satisfactorily performed at short time intervals exceeding the conventional limit, that is, the liquid discharge head can be driven at a very high frequency. At this time, compared to the case where liquid discharge is started from a steady state, the discharge amount of discharged droplets when discharging continuously can be increased, and the discharge speed can be further increased. In addition, part of the energy generated during the previous liquid discharge can be contributed to the subsequent liquid discharge, and the energy efficiency of the liquid discharge can be improved.
[0096]
Further, the discharge amount of the first discharge droplet and the discharge amount of the second and subsequent discharge droplets are changed, the satellite of the previous discharge droplet is changed to the discharge droplet of the second and subsequent discharges, and further the previous discharge droplet By capturing itself, the amount of adhering liquid on each image point can be changed, and gradation recording can be suitably performed.
[0097]
In the liquid discharge method of the present invention, even if the energy supplied to the heating element during the second and subsequent liquid discharges of the continuous discharge is smaller than the energy supplied during the first liquid discharge, the droplets generated by the second and subsequent foaming The amount and speed can be made equal to or more than the first time. For this reason, energy saving can be achieved and heating of the liquid discharge head can be suppressed.
[Brief description of the drawings]
FIG. 1 is a schematic side sectional view of a liquid discharge head used in a liquid discharge method according to an embodiment of the present invention.
FIG. 2 is a diagram illustrating a single liquid discharge process from the liquid discharge head illustrated in FIG. 1;
3 is a diagram showing temporal changes in bubble displacement speed and volume, and displacement speed and displacement volume of a movable member in the ejection process shown in FIG. 2; FIG.
4 is a cross-sectional view of a flow path for explaining a linear communication state of the liquid discharge head of FIG. 1. FIG.
FIG. 5 is a perspective view of a part of the head shown in FIG. 1;
6 is a schematic cross-sectional view showing a state in each process when continuous discharge is performed using the liquid discharge head of FIG. 1. FIG.
7 is a schematic diagram showing a waveform of a voltage pulse supplied to a heating element when continuous ejection is performed as shown in FIG.
FIG. 8 is a schematic cross-sectional view showing a state in each process when continuous discharge is performed in another embodiment of the present invention.
FIG. 9 is a schematic diagram showing a waveform of a voltage pulse supplied to a heating element when continuous discharge is performed as shown in FIG.
FIG. 10 is a schematic cross-sectional view showing a configuration in the vicinity of a heating element of a conventional liquid discharge head.
[Explanation of symbols]
1 Element substrate
2 Top plate
3 Flow path
4 Discharge port
5 Orifice plate
5a Orifice surface
6 Common liquid chamber
10 Heating element
11 Movable members
11a fulcrum
11b Free end
40 bubbles
41 Raised bubbles
66 Droplets
100 resistance layer
101a, 101b electrode
102,103 protective layer
104 Bubble 104
106 Defoaming position
v _b Bubble volume change rate
v _m Movable member displacement volume change rate
V _m Movable member displacement volume
V _b Bubble volume

Claims (4)

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 liquid flow path that has a bubble generation region that communicates with the discharge port and generates the bubbles. A liquid chamber that supplies the liquid to the liquid flow path, a movable member that is provided in the bubble generation area and is displaced as the bubbles grow, and is provided to face the bubble generation area of the liquid flow path. A restricting portion for restricting the displacement of the movable member to a desired range, the heating element and the discharge port are in a linear communication state, and the displaced movable member and the restricting portion substantially By using a liquid discharge head in which the liquid flow path having the bubble generation region becomes a substantially closed space by contact, except for the discharge port, the first liquid droplet and the second liquid droplet are continuously formed from the discharge port. A liquid discharge method for discharging droplets,
After the bubble formed to discharge the first droplet starts to shrink, the bubble remains biased toward the discharge port side of the bubble generation region, and the liquid chamber of the bubble generation region A liquid ejection method comprising: driving the heating element to grow bubbles in the liquid and ejecting the second droplet when a portion where the bubbles do not exist is generated on the side .   The liquid ejection method according to claim 1, wherein the first droplet and the second droplet are continuously ejected, and the plurality of droplets are combined in the course of flight to the recording medium. 3. The energy supplied to the heating element when discharging the second droplet is smaller than the energy supplied to the heating element when discharging the first droplet. 4 . The liquid discharge method as described. The width of the voltage pulse applied to the heating element when discharging the second droplet is shorter than the width of the voltage pulse applied to the heating element when discharging the first droplet. The liquid ejection method according to claim 3 .

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