JP7292940B2 - Liquid ejection head, liquid ejection module, and liquid ejection device - Google Patents

Description

The present invention relates to a liquid ejection head, a liquid ejection module, and a liquid ejection apparatus.

Japanese Patent Application Laid-Open No. 2002-200002 discloses a liquid ejection unit that brings a liquid that serves as an ejection medium and a liquid that serves as a bubbling medium into contact with each other at an interface, and ejects the ejection medium as bubbles generated in the bubbling medium grow by applying thermal energy. disclosed. According to Patent Document 1, it is described that one or both of the ejection medium and the bubbling medium are pressurized to form a flow.

JP-A-6-305143

However, Patent Document 1 does not specifically describe the correspondence relationship between the physical properties of the ejection medium and the foaming medium and the flow rate for stabilizing the interface, and the method for controlling the flow of the ejection medium and the foaming medium is unknown. is. Therefore, depending on the combination of the ejection medium and the bubbling medium, the interface cannot be formed satisfactorily, and as a result, it becomes difficult to improve the ejection performance such as the ejection amount and the ejection speed, and to perform the ejection operation stably.

The present invention has been made to solve the above problems. Accordingly, it is an object of the present invention to provide a liquid ejection head capable of appropriately controlling the interface between the ejection medium and the bubbling medium and performing a stable ejection operation.

To this end, the present invention provides a liquid liquid comprising a pressure chamber in which a first liquid and a second liquid flow, a pressure generating element that pressurizes the first liquid, and an ejection port that ejects the second liquid. In the ejection head, in the pressure chamber, the first liquid and the second liquid flowing on the side closer to the ejection port than the first liquid are in contact with each other in a direction intersecting the ejection direction. The first liquid and the second liquid flowing in the pressure chamber have a viscosity of the first liquid η ₁ , a viscosity of the second liquid η ₂ , and a viscosity of the first liquid When the flow rate is Q ₁ and the flow rate of the second liquid is Q ₂ ,

is characterized by satisfying

According to the present invention, it is possible to appropriately control the position of the interface between the ejection medium and the bubbling medium and perform a stable ejection operation.

3 is a perspective view of an ejection head; FIG. 3 is a block diagram for explaining the control configuration of the liquid ejection device; FIG. 3 is a cross-sectional perspective view of an element substrate in the liquid ejection module; FIG. 3 is an enlarged detailed view of liquid flow paths and pressure chambers formed in the element substrate; FIG. It is a figure which shows the relationship between a viscosity ratio and an aqueous-phase thickness ratio, and the relationship between the height of a pressure chamber, and a flow velocity. FIG. 4 is a diagram showing the relative relationship between exact solutions and approximate solutions for forming parallel flows; FIG. 4 is a diagram schematically showing a transient state of ejection operation; FIG. 4 is a diagram schematically showing a transient state of ejection operation; FIG. 4 is a diagram schematically showing a transient state of ejection operation; FIG. 10 is a diagram showing ejected liquid droplets when the water phase thickness ratio is changed; FIG. 10 is a diagram showing ejected liquid droplets when the water phase thickness ratio is changed; FIG. 10 is a diagram showing ejected liquid droplets when the water phase thickness ratio is changed; It is a figure which shows the relationship between the height of a flow path (pressure chamber), and water phase thickness ratio. It is a figure which shows the content rate of water, and the relationship of a foaming pressure.

(Structure of Liquid Ejection Head)
FIG. 1 is a perspective view of a liquid ejection head 1 that can be used in the present invention. The liquid ejection head 1 of this embodiment is configured by arranging a plurality of liquid ejection modules 100 (a plurality of modules are arranged) in the x direction. Each liquid ejection module 100 has an element substrate 10 on which a plurality of ejection elements are arranged, and a flexible wiring board 40 for supplying electric power and an ejection signal to each ejection element. Each of the flexible wiring boards 40 is commonly connected to an electric wiring board 90 on which power supply terminals and ejection signal input terminals are arranged. The liquid ejection module 100 can be easily attached to and detached from the liquid ejection head 1 . Therefore, any liquid ejection module 100 can be easily attached to or removed from the outside of the liquid ejection head 1 without disassembling it.

As described above, with the liquid ejection head 1 configured by arranging a plurality of liquid ejection modules 100 in the longitudinal direction (a plurality of modules are arranged), even if an ejection failure occurs in any of the ejection elements, It is sufficient to replace only the liquid ejection module in which the ejection failure has occurred. Therefore, it is possible to improve the yield in the manufacturing process of the liquid ejection head 1 and reduce the cost at the time of replacing the head.

(Structure of liquid ejection device)
FIG. 2 is a block diagram showing the control configuration of the liquid ejection device 2 that can be used in the present invention. The CPU 500 controls the entire liquid ejecting apparatus 2 according to programs stored in the ROM 501 while using the RAM 502 as a work area. The CPU 500 performs predetermined data processing on ejection data received from, for example, an externally connected host device 600 according to a program and parameters stored in the ROM 501 to generate an ejection signal that enables the liquid ejection head 1 to eject. . Then, while driving the liquid ejection head 1 according to the ejection signal, the transport motor 503 is driven to transport the target medium to which the liquid is to be applied in a predetermined direction. attach to

The liquid circulation unit 504 is a unit for supplying the liquid to the liquid ejection head 1 while circulating it, and for adjusting the flow rate of the liquid in the ejection head 1 . The liquid circulation unit 504 includes a sub-tank that stores liquid, a flow path that circulates the liquid between the sub-tank and the liquid ejection head 1, a plurality of pumps, valve mechanisms, and the like. Under the instructions of the CPU 500, the plurality of pumps and valve mechanisms are controlled so that the liquid flows through the liquid ejection head 1 at a predetermined flow rate.

(Structure of element substrate)
FIG. 3 is a cross-sectional perspective view of the element substrate 10 provided in each liquid ejection module 100. FIG. The element substrate 10 is configured by stacking an orifice plate 14 (ejection port forming member) on a silicon (Si) substrate 15 . The orifice plate 14 has a plurality of ejection openings 11 for ejecting liquid arranged in the x direction. In FIG. 3, the ejection ports 11 arranged in the x direction eject the same kind of liquid (for example, liquid supplied from a common sub-tank or supply port). Although an example in which the orifice plate 14 also forms the liquid flow path 13 is shown here, the liquid flow path 13 is formed by a separate member (flow path wall member), and the orifice plate on which the discharge port 11 is formed. 14 may be provided.

Pressure generating elements 12 (not shown in FIG. 3) are arranged on the silicon substrate 15 at positions corresponding to the individual ejection ports 11 . The ejection port 11 and the pressure generating element 12 are provided at opposing positions. When a voltage is applied in response to the ejection signal, the pressure generating element 12 pressurizes at least the first liquid in the z-direction intersecting the flow direction (y-direction) so that the liquid is discharged from the ejection port 11 facing the pressure generating element 12 . , at least the second liquid is ejected as droplets. Electric power and drive signals to the pressure generating element 12 are supplied from the flexible wiring board 40 via terminals 17 arranged on the silicon substrate 15 .

The orifice plate 14 is formed with a plurality of liquid flow paths 13 extending in the y-direction and individually connected to the discharge ports 11 . In addition, the plurality of liquid flow paths 13 arranged in the x direction are composed of a first common supply flow path 23, a first common recovery flow path 24, a second common supply flow path 28, and a second common recovery flow path 29. and are connected in common. The liquid flows in the first common supply channel 23, the first common recovery channel 24, the second common supply channel 28, and the second common recovery channel 29 are controlled by the liquid circulation unit 504 described with reference to FIG. controlled by Specifically, the first liquid that has flowed into the liquid flow path 13 from the first common supply flow path 23 flows toward the first common recovery flow path 24, and flows from the second common supply flow path 28 into the liquid flow path 13. The pump is driven and controlled so that the second liquid that has flowed into is directed to the second common recovery channel 29 .

In FIG. 3, the ejection ports 11 and the liquid flow paths 13 arranged in the x-direction, and the first and second common supply flow paths 23, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 28, 29, 28, 28, 28, 28, 29, 28, 28, 28, 28, 28, and 28 of which which are commonly used to supply and recover ink. 2 shows an example in which pairs of first and second common recovery channels 24 and 29 are arranged in two rows in the y direction.

(Structure of liquid flow path and pressure chamber)
4A to 4D are diagrams for explaining in detail the configuration of one liquid flow path 13 and pressure chamber 18 formed in the element substrate 10. FIG. 4(a) is a perspective view seen from the ejection port 11 side (+z direction side), and FIG. 4(b) is a cross-sectional view taken along line IVb-IVb of FIG. 4(a). 4(c) is an enlarged view of the vicinity of one liquid flow path 13 in the element substrate shown in FIG. Further, FIG. 4(d) is an enlarged view of the vicinity of the ejection port in FIG. 4(b).

In the silicon substrate 15 corresponding to the bottom of the liquid channel 13, a second inlet 21, a first inlet 20, a first outlet 25, and a second outlet 26 are formed in this order in the y direction. It is A pressure chamber 18 including the discharge port 11 and the pressure generating element 12 is arranged substantially in the center between the first inlet 20 and the first outlet 25 in the liquid flow path 13 . The second inlet 21 connects to the second common supply channel 28, the first inlet 20 connects to the first common supply channel 23, and the first outlet 25 connects to the first common recovery channel 24. , the second outlet 26 is connected to the second common recovery channel 29 (see FIG. 3).

With the above configuration, the first liquid 31 supplied from the first common supply channel 23 to the liquid channel 13 through the first inlet 20 flows in the y direction (the direction indicated by the arrow). After that, it passes through the pressure chamber 18 and is recovered in the first common recovery channel 24 via the first outlet 25 . Further, the second liquid 32 supplied from the second common supply channel 28 to the liquid channel 13 through the second inlet 21 flows in the y direction (the direction indicated by the arrow), and then flows into the pressure chamber. 18 and is recovered in a second common recovery channel 29 via a second outlet 26 . That is, both the first liquid and the second liquid flow in the y-direction between the first inlet 20 and the first outlet 25 in the liquid flow path 13 .

In the pressure chamber 18, the pressure generating element 12 is in contact with the first liquid 31, and near the ejection port 11, the second liquid 32 exposed to the atmosphere forms a meniscus. In the pressure chamber 18, the first liquid 31 and the second liquid are arranged such that the pressure generating element 12, the first liquid 31, the second liquid 32, and the ejection port 11 are arranged in this order. 32 is flowing. That is, the second liquid 32 is flowing on the first liquid 31 when the pressure generating element 12 side is the lower side and the discharge port 11 side is the upper side. Then, the first liquid 31 is pressurized by the lower pressure generating element 12, and the second liquid is discharged upward from below. The vertical direction is the height direction of the pressure chamber 18 and the liquid flow path 13 .

In this embodiment, as shown in FIG. 4D, the first liquid 31 and the second liquid 32 are in contact with each other in the pressure chamber and flow along each other. The flow rate and the flow rate of the second liquid are adjusted according to the physical properties of the first liquid 31 and the physical properties of the second liquid 32 . Such two liquid flows include not only parallel flows in which two liquids flow in the same direction as shown in FIG. There is a liquid flow that In the following, the parallel flow will be described as an example.

In the case of parallel flow, the interface between the first liquid 31 and the second liquid 32 is not disturbed, that is, the flow in the pressure chamber 18 where the first liquid 31 and the second liquid 32 flow is in a laminar flow state. is preferred. In particular, when trying to control ejection performance such as maintaining a predetermined ejection amount, it is preferable to drive the pressure generating element while the interface is stable. However, the present invention is not limited to this. Even if the flow in the pressure chamber 18 becomes turbulent and the interface between the two liquids is disturbed to some extent, the first liquid mainly flows at least on the pressure generating element 12 side, and the first liquid mainly flows on the discharge port 11 side. The pressure generating element 12 may be driven as long as the second liquid is flowing. An example in which the flow in the pressure chamber is a parallel flow and is in a laminar flow state will be mainly described below.

(Conditions for formation of laminar parallel flow)
First, the conditions under which the liquid becomes a laminar flow in the pipe will be described. Generally, the Reynolds number Re representing the ratio of viscous force and interfacial tension is known as an index for evaluating flow.

Here, if the density of the liquid is ρ, the flow velocity is u, the representative length is d, and the viscosity is η, the Reynolds number Re can be expressed by (Equation 1).
Re=ρud/η (Formula 1)

Here, it is known that the smaller the Reynolds number Re, the easier it is to form a laminar flow. Specifically, it is known that when the Reynolds number Re is less than about 2200, the flow in the circular pipe becomes laminar, and when the Reynolds number Re is greater than about 2200, the flow in the circular pipe becomes turbulent.

A laminar flow means that the streamlines are parallel to each other and do not intersect with each other. Therefore, if the two liquids in contact are laminar flows, parallel flows with a stable interface between the two liquids can be formed. Here, considering a general inkjet recording head, the flow path height (pressure chamber height) H [μm] in the vicinity of the discharge port in the liquid flow path (pressure chamber) is about 10 to 100 μm. Therefore, when water (density ρ=1.0×103 kg/m ³ , viscosity η=1.0 cP) is caused to flow through the liquid flow path of the inkjet recording head at a flow rate of 100 mm/s, the Reynolds number is Re=ρud/η≈ From 0.1 to 1.0<<2200, it can be considered that a laminar flow is formed.

As shown in FIG. 4, even if the cross sections of the liquid flow paths 13 and the pressure chambers 18 are rectangular, the height and width of the liquid flow paths 13 and the pressure chambers 18 are sufficiently small in the liquid ejection head. Therefore, the liquid flow path 13 and the pressure chamber 18 can be treated in the same way as a circular pipe, that is, the height of the liquid flow path and the pressure chamber 18 can be treated as the diameter of the circular pipe.

(Theoretical conditions for forming parallel laminar flow)
Next, with reference to FIG. 4(d), the conditions for forming parallel flows in which the interface between the two liquids is stable in the liquid flow path 13 and the pressure chamber 18 will be described. First, the distance from the silicon substrate 15 to the ejection port surface of the orifice plate 14 is H [μm], and the distance from the ejection port surface to the liquid-liquid interface between the first liquid 31 and the second liquid 32 (the second liquid is phase thickness) is h ₂ [μm]. The distance from the liquid-liquid interface to the silicon substrate 15 (phase thickness of the first liquid) is h ₁ [μm]. That is, H=h ₁ +h ₂ .

Here, as a boundary condition within the liquid flow path 13 and the pressure chamber 18, the velocity of the liquid on the wall surfaces of the liquid flow path 13 and the pressure chamber 18 is assumed to be zero. It is also assumed that the velocity and shear stress at the liquid-liquid interface between the first liquid 31 and the second liquid 32 have continuity. In this assumption, if the first liquid 31 and the second liquid 32 form two layers of parallel steady flow, the quartic equation shown in (Equation 2) is established in the parallel flow section.

In (Formula 2), η ₁ [cP] is the viscosity of the first liquid, η ₂ [cP] is the viscosity of the second liquid, and Q ₁ [mm ³ /s] is the flow rate of the first liquid. Q ₂ [mm ³ /s] indicates the flow rate of the second liquid. That is, within the range of the above quartic equation (Equation 2), the first liquid and the second liquid flow so as to have a positional relationship according to their respective flow rates and viscosities, and a parallel flow with a stable interface is formed. It is formed. In the present invention, it is preferable to form the parallel flows of the first liquid and the second liquid within the liquid flow path 13 , at least within the pressure chamber 18 . When such parallel flows are formed, the first liquid and the second liquid are only mixed by molecular diffusion at the liquid-liquid interface, and flow parallel to the y direction without substantially mixing. In the present invention, the flow of liquid in a part of the pressure chamber 18 does not have to be laminar. It is preferable that the liquid flowing through at least the area above the pressure generating element is in a laminar flow state.

For example, even when immiscible solvents such as water and oil are used as the first liquid and the second liquid, if (Equation 2) is satisfied, A stable parallel flow is formed. Even in the case of water and oil, as described above, even if the flow in the pressure chamber is somewhat turbulent and the interface is disturbed, at least the pressure generating element side is mainly the first liquid. It is preferable that the second liquid flows mainly on the ejection port side.

FIG. 5A shows the relationship between the viscosity ratio η _r =η ₂ /η ₁ and the phase thickness ratio h _r =h ₁ /(h ₁ +h ₂ ) of the first liquid based on (Equation 2). It is the figure which showed the case where the flow rate ratio _Qr = _Q2 / _Q1 is varied in multiple steps. Although the first liquid is not limited to water, the "phase thickness ratio of the first liquid" is hereinafter referred to as "aqueous phase thickness ratio". The horizontal axis indicates the viscosity ratio η _r =η ₂ /η ₁ , and the vertical axis indicates the aqueous phase thickness ratio h _r =h ₁ /(h ₁ +h ₂ ). As the flow rate ratio Q _r increases, the water phase thickness ratio h _r decreases. Also, for any flow rate ratio Q _r , the water phase thickness ratio h _r decreases as the viscosity ratio η _r increases. That is, the water phase thickness ratio h _r (interface position between the first liquid and the second liquid) in the liquid flow path 13 (pressure chamber) is determined by the viscosity ratio η _r and the flow rate ratio of the first liquid and the second liquid It can be adjusted to a predetermined value by controlling _Qr . In addition, according to the figure, when the viscosity ratio η _r and the flow rate ratio Q _r are compared, it can be seen that the flow rate ratio Q _r has a greater effect on the aqueous phase thickness ratio _{h r than} the viscosity ratio η r. .

Regarding the water phase thickness ratio h _r =h ₁ /(h ₁ +h ₂ ), if 0<h _r <1 (condition 1) is satisfied, the first A parallel flow of the first liquid and the second liquid is formed. However, as will be described later, in this embodiment, the first liquid mainly functions as a bubbling medium, and the second liquid mainly functions as an ejection medium. A desired proportion of the second liquid is stabilized. Considering such circumstances, the water phase thickness ratio h _r is preferably 0.8 or less (condition 2), more preferably 0.5 or less (condition 3).

Here, state A, state B, and state C shown in FIG. 5(a) respectively indicate the following states.
State A) When the viscosity ratio η _r =1 and the flow rate ratio Q _r =1, the water phase thickness ratio h _r =0.50
State B) When the viscosity ratio η _r =10 and the flow rate ratio Q _r =1, the water phase thickness ratio h _r =0.39
State C) When the viscosity ratio η _r =10 and the flow ratio Q _r =10, the water phase thickness ratio h _r =0.12

FIG. 5B is a diagram showing the flow velocity distribution in the height direction (z direction) of the liquid flow path 13 (pressure chamber) for each of the states A, B, and C described above. The horizontal axis indicates a normalized value Ux normalized with the maximum value of flow velocity in state A as 1 (reference). The vertical axis indicates the height from the bottom when the height H of the liquid flow path 13 (pressure chamber) is 1 (reference). In the curves showing the respective states, markers indicate the position of the interface between the first liquid and the second liquid. It can be seen that the interface position changes depending on the state, such as the interface position in state A being higher than the interface position in state B and state C. This is because when two liquids with different viscosities each flow in parallel in a tube (laminar flow as a whole), the interface between the two liquids will have a pressure of This is because the gap is formed at a position where the Laplace pressure caused by the difference and the interfacial tension are balanced.

(Experimental formation conditions for laminar parallel flow)
The present inventors have determined the practical ranges of the flow rate ratio Q _r (=Q ₂ /Q ₁ ) and the viscosity ratio η _r (=η ₂ /η ₁ ) based on the types and flow rates of inks that can be used in the inkjet recording apparatus. , the water phase thickness ratio h _r was actually measured for a plurality of cases in which the flow ratio Q _r and the viscosity ratio η _r were varied. Then, from these multiple cases, an approximation formula (Formula 3) for obtaining the water phase thickness ratio h _r from the flow rate ratio Q _r and the viscosity ratio η _r was obtained.

In addition, the effectiveness of (Formula 3) is
It was confirmed in the range of 0.1≦Q _r ≦100 and 1≦η _r ≦20. As described above, (Formula 3) is obtained within the range of the realistic flow rate ratio and viscosity ratio in the inkjet recording apparatus, so the two liquid flows in the pressure chamber are laminar parallel flows. It is based on the premise that However, (Equation 3) holds true even when the flow in the pressure chamber is somewhat turbulent, or when two liquids cross each other.

(Correlation between theoretical and experimental conditions)
FIG. 6 is a diagram showing the correspondence relationship between the exact solution based on (Formula 2) and the approximate solution based on (Formula 3). The horizontal axis shows the exact solution of the water phase thickness ratio _hr , and _{the vertical axis shows the approximate solution of the water phase thickness ratio hr .} Plotting the values of the approximate solution against the exact solution. As a result of calculating the correlation coefficient y based on these plotted values, a correlation value of y=0.987, which is very close to 1, was obtained.

That is, even if the quartic equation shown in (Equation 2) is not used, if the flow rate ratio Q _r and the viscosity ratio η _r can be controlled based on (Equation 3), the water phase thickness ratio h _r can be adjusted to a preferable range. Adjustment is possible. Furthermore, when the viscosity _ratio η _r and _the flow rate ratio Q _r are compared, as _already explained using FIG. We know it has a big impact. In addition, while the viscosity ratio η _r is fixed according to the type of liquid, the flow rate ratio Q _r can be adjusted by controlling a pump or the like that circulates the liquid. From the above, the inventors of the present invention have found that in order to form a stable flow of two liquids in the liquid flow path 13 (pressure chamber) using two different liquids, the flow rate ratio _Qr of the two liquids must be ( The inventors have found that it is effective to adjust the water phase thickness ratio _hr by controlling based on the equation (3).

The first liquid and the second liquid may form a liquid-liquid interface anywhere in the liquid flow path and the pressure chamber as long as the conditions for forming parallel flows are satisfied. That is, as described above, when the pressure generating element 12 is located at the bottom and the ejection port 11 is located at the top, the first liquid is on the lower side (pressure generating element) and the second liquid is on the upper side (ejection port). (see FIG. 4(d)). Alternatively, the first liquid and the second liquid may flow at the same height in the vertical direction, and the liquid-liquid interface may be formed along the height direction. That is, the first liquid and the second liquid may flow side by side in the x direction (see FIG. 4). At this time, h _r in (Equation 3) is the thickness of the first liquid in the x direction.

Here, the three conditions 1 to 3 of the water phase thickness ratio _hr for causing the first liquid to mainly function as a foaming medium and the second liquid to mainly function as an ejection medium will be considered again. In this case, considering together with the above (Equation 3), (Equation 4) is required to satisfy Condition 1, (Equation 5) is required to satisfy Condition 2, and (Equation 5) is required to satisfy Condition 3. (Equation 6) is required to be satisfied.

(Transient state of discharge operation)
Next, the transient state of the ejection operation in the liquid flow path 13 and the pressure chamber 18 in which parallel flows are formed will be described. FIGS. 7A to 7E are diagrams schematically showing the transient state of the ejection operation in the liquid channel 13 with the channel (pressure chamber) height H [μm]=20 μm. 8A to 8E are diagrams schematically showing the transient state of the discharge operation in the liquid channel 13 (pressure chamber) having a channel (pressure chamber) height H [μm]=33 μm. be. Further, FIGS. 9A to 9E are diagrams schematically showing the transient state of the discharge operation in the liquid channel 13 (pressure chamber) having a channel (pressure chamber) height H [μm]=10 μm. be. Note that the ejected droplets in these figures are the results obtained when a simulation is performed with the viscosity of the first liquid set to 1 cP, the viscosity of the second liquid set to 8 cP, and the ejection speed of the droplets set to 11 m/s. It is shown based on

7(a), 8(a) and 9(a) show the state before a voltage is applied to the pressure generating element 12. FIG. The first liquid 31 and the second liquid 32 are parallel flows and flow parallel to the y direction.

7(b), 8(b) and 9(b) show a state in which a voltage has started to be applied to the pressure generating element 12. FIG. The pressure generating element 12 of this embodiment is an electrothermal transducer (heater). That is, the pressure generating element 12 abruptly generates heat when a voltage pulse is applied in response to the ejection signal, and causes film boiling in the contacting first liquid. The drawing shows a state in which bubbles 16 are generated by film boiling. As the bubbles 16 are generated, the interface between the first liquid 31 and the second liquid 32 moves in the z direction, and the second liquid 32 is pushed out from the ejection port 11 in the z direction (the height direction of the pressure chamber). is

FIGS. 7(c), 8(c), and 9(c) show the state in which the voltage application to the pressure generating element 12 is continued. The volume of the bubble 16 increases due to film boiling, and the second liquid 32 is further pushed out from the ejection port 11 in the z direction.

After that, when the voltage application to the pressure generating element 12 is continued, the liquid flow path 13 (pressure chamber) shown in FIGS. This is because the flow path (pressure chamber) height H of the liquid flow path 13 shown in FIGS. 5(d) and 7(d) is not so large. On the other hand, in the liquid channel 13 (pressure chamber) shown in FIG. 6(d) where the channel (pressure chamber) height H is relatively large, the bubbles contract without communicating with the atmosphere.

FIGS. 7(e), 8(e), and 9(e) show a state in which droplets (ejected droplets) 30 are ejected. 7(d) and 9(d) when the bubble 16 communicates with the atmosphere, or when the bubble contracts as shown in FIG. 8(d). Due to the inertial force, the droplets are separated from the liquid flow path 13 (pressure chamber) and become ejected droplets 30, which fly in the z-direction. On the other hand, in the liquid flow path 13 (pressure chamber), the liquid consumed by the ejection is supplied from both sides of the ejection port 11 by the capillary force of the liquid flow path 13 (pressure chamber), and is supplied to the ejection port 11 again. A meniscus is formed.

The ejection operation as described above can be performed while the liquid is flowing, or can be performed while the liquid is temporarily stopped. This is because, if the interface between the first liquid 31 and the second liquid 32 is held at a stable position, the discharging operation can be performed in a stable state regardless of the presence or absence of flow.

For example, when the ejection operation is performed while the liquid is flowing, there is concern that the liquid flow may affect the ejection performance. However, in a general inkjet recording head, the droplet ejection speed is on the order of several m/s to ten and several m/s, and the liquid flow path (pressure chamber) is on the order of several mm/s to several m/s. ) is much larger than the flow velocity in Therefore, even if the ejection operation is performed while the first liquid and the second liquid flow at several mm/s to several m/s, the ejection performance is unlikely to be affected.

On the other hand, when the ejection operation is performed while the liquid is stopped, there is a concern that the position of the interface between the first liquid and the second liquid may fluctuate along with the ejection operation. For this reason, it is preferable to discharge while flowing the first liquid and the second liquid. It should be noted that the interface between the first liquid and the second liquid is not immediately mixed due to diffusion by stopping the flow of the liquids. Even if the flow is stopped, if the stop period is short enough to perform the ejection operation, the interface between the first liquid and the second liquid is maintained, and the ejection operation may be performed in that state. be. After the ejection operation is completed, the parallel flow in the liquid flow path 13 (pressure chamber) is maintained in a stable state by causing the liquid to flow again at a flow rate that satisfies (Equation 3).

However, since the influence of diffusion is suppressed as much as possible and there is no need for ON/OFF switching control of the flow, in the present embodiment, the former, that is, the ejection operation is performed while the liquid is flowing.

(Proportion of liquid contained in ejected droplets)
10(a) to (g) show that the water phase thickness ratio _hr was changed stepwise in the liquid channel 13 (pressure chamber) with a channel (pressure chamber) height H [μm]=20 μm. FIG. 10 is a diagram for comparing ejected liquid droplets in each case; In FIGS. 10(a) to (f), the water phase thickness ratio h _r is increased by 0.1, and in FIGS. 10(f) to (g), the water phase thickness ratio h _r is increased by 0.5.

The closer the water phase thickness ratio h _r (=h ₁ /(h ₁ +h ₂ )) to 0, the smaller the water phase thickness _{h 1} of the first liquid 31 . The water phase thickness h ₁ of the liquid 31 of is large. Therefore, the ejected droplet 30 mainly contains the second liquid 32 near the ejection port 11, but the closer the water phase thickness ratio h _r approaches 1, the more the first liquid 32 included in the ejected droplet 30 becomes. The proportion of liquid 31 also increases.

In the case of FIGS. 10(a) to 10(g) where the channel (pressure chamber) height is H [μm]=20 μm, when the water phase thickness ratio is h _r =0.00, 0.10, and 0.20, the Only the second liquid 32 is included in the ejected droplet 30 and the first liquid 31 is not included in the ejected droplet 30 . However, after the water phase thickness ratio h _r =0.30, the first liquid 31 is included in the ejected droplet 30 together with the second liquid 32, and the water phase thickness ratio h _r =1.00 (that is, the second in the absence of liquid), only the first liquid 31 is included in the ejected droplet 30 . Thus, the ratio of the first liquid 31 and the second liquid 32 contained in the ejected droplet 30 changes depending on the water phase thickness ratio h _r in the liquid flow path 13 (pressure chamber).

On the other hand, in FIGS. 11(a) to (e), the water phase thickness ratio h _r is changed stepwise in the liquid channel 13 (pressure chamber) with a channel (pressure chamber) height H [μm]=33 μm. 3A and 3B are diagrams for comparing ejected liquid droplets 30 in the cases where the liquid droplets are ejected. In this case, only the second liquid 32 is included in the ejected droplet 30 until the water phase thickness ratio h _r =0.36, and the second liquid 32 and the second liquid 32 are included together with the water phase thickness ratio after h _r =0.48. The first liquid 31 is also included in the ejected droplets 30 .

12(a) to (c) show that the water phase thickness ratio h _r is changed stepwise in the liquid channel 13 (pressure chamber) having a channel (pressure chamber) height H [μm]=10 μm. 3A and 3B are diagrams for comparing ejected liquid droplets 30 in the cases where the liquid droplets are ejected. In this case, even if the water phase thickness ratio is h _r =0.10, the first liquid 31 is included in the ejected droplet 30 .

FIG. 13 shows the relationship between the flow channel (pressure chamber) height H and the water phase thickness ratio h _r when the proportion R of the first liquid 31 contained in the ejected droplet 30 is fixed. FIG. 10 is a diagram showing cases of %, 20%, and 40%. At any rate R, the larger the channel (pressure chamber) height H, the larger the permissible water phase thickness ratio _hr . Note that the ratio R of the first liquid 31 included indicates the ratio of the liquid flowing as the first liquid 31 in the liquid flow path 13 (pressure chamber) to the ejected droplets. Therefore, even if the first liquid and the second liquid each contain the same component such as water, the water contained in the second liquid is of course not included in the above ratio.

When the ejected droplet 30 contains only the second liquid 32 and does not contain the first liquid (R=0%), the flow channel (pressure chamber) height H [μm] and the water phase thickness ratio The relationship of h _r is the trajectory indicated by the solid line in the figure. According to studies by the present inventors, the water phase thickness ratio h _r can be approximated by a linear function of the channel (pressure chamber) height H [μm] shown in (Equation 7).

Further, when the ejection droplet 30 is to contain 20% of the first liquid (R=20%), the water phase thickness ratio h _r is the height H It can be approximated by a linear function of [μm].

Further, when the ejected droplets 30 are to contain 40% of the first liquid (R=40%), according to the studies of the present inventors, the water phase thickness ratio h _r is given by (Equation 9) It can be approximated by a linear function of the indicated channel (pressure chamber) height H [μm].

For example, when the first liquid is not included in the ejected droplet 30, if the channel (pressure chamber) height H [μm] is 20 μm, the water phase thickness ratio h _r is adjusted to 0.20 or less. are required to do so. Further, if the channel (pressure chamber) height H [μm] is 33 μm, the water phase thickness ratio h _r is required to be adjusted to 0.36 or less. Furthermore, if the channel (pressure chamber) height H [μm] is 10 μm, the water phase thickness ratio h _r is required to be adjusted to almost zero (0.00).

However, if the water phase thickness ratio h _r is too small, it becomes necessary to increase the viscosity η2 and the flow rate Q ₂ of the second liquid relative to the first liquid, and there is concern about adverse effects due to an increase in pressure loss. For example, referring to FIG. 5(a) again, when realizing the water phase thickness ratio h _r =0.20, the flow rate ratio is Q _r =5 at the viscosity ratio η _r =10. Also, while using the same ink (that is, the same viscosity ratio η _r ), in order to obtain certainty that the first liquid is not ejected, if the water phase thickness ratio is set to h _r =0.10, the flow rate ratio gives Q _r =15. That is, when adjusting the water phase thickness ratio h _r to 0.10, it is necessary to triple the flow rate ratio Q _r compared to the case of adjusting the water phase thickness ratio h _r to 0.20. There are concerns about increased losses and the associated adverse effects.

From the above, when only the second liquid 32 is to be ejected while minimizing the pressure loss, it is preferable to adjust the water phase thickness ratio h _r to a value as large as possible under the above conditions. Again referring to FIG. 13, for example, when the height of the flow path (pressure chamber) is H=20 μm, the water phase thickness ratio h _r is smaller than 0.20 and as close to 0.20 as possible. values are preferred. Further, when the channel (pressure chamber) height is H [μm]=33 μm, the water phase thickness ratio h _r is preferably adjusted to a value smaller than 0.36 and as close to 0.36 as possible.

The above (Equation 7), (Equation 8), and (Equation 9) are numerical values for a general liquid ejection head, that is, a liquid ejection head in which the ejection speed of ejection droplets is in the range of 10 m/s to 18 m/s. is. Also, the pressure generating element and the ejection port are positioned to face each other, and the pressure generating element, the first liquid, the second liquid, and the ejection port are arranged in this order in the pressure chamber. These numerical values are based on the assumption that the liquid and the second liquid are flowing.

As described above, according to the present embodiment, by setting the aqueous phase thickness ratio h _r in the liquid flow path (pressure chamber) to a predetermined value and stabilizing the interface, the first liquid and the second liquid are kept constant. It is possible to stably perform the ejection operation of droplets contained in the ratio of .

(Specific examples of first liquid and second liquid)
In the configuration of this embodiment described above, the first liquid is a bubbling medium for causing film boiling, and the second liquid is an ejection medium for ejecting into the atmosphere. Be clear. According to the configuration of the present embodiment, it is possible to increase the degree of freedom of components to be contained in the first liquid and the second liquid as compared with the conventional one. Hereinafter, the foaming medium (first liquid) and the ejection medium (second liquid) in such a configuration will be described in detail with specific examples.

As the foaming medium (first liquid) of the present embodiment, film boiling occurs in the foaming medium when the electrothermal converter generates heat, and the generated bubbles rapidly increase. is required to have a high critical pressure that can be converted into foaming energy. Water is particularly suitable as such a medium. Water has a high boiling point (100° C.), a high surface tension (58.85 dyne/cm at 100° C.) and a large critical pressure of about 22 MPa in spite of its low molecular weight of 18. That is, the foaming pressure during film boiling is also very high. In general, even in an ink jet recording apparatus that uses film boiling to eject ink, an ink containing a colorant such as a dye or a pigment in water is preferably used.

However, the foaming medium is not limited to water. If the critical pressure is 2 MPa or more (preferably 5 MPa or more), it can function as a foaming medium. Examples of foaming media other than water include methyl alcohol and ethyl alcohol, and a mixture of these liquids in water can also be used as the foaming medium. Further, as described above, it is also possible to use water containing coloring materials such as dyes and pigments, and other additives.

On the other hand, the ejection medium (second liquid) of the present embodiment is not required to have physical properties for causing film boiling unlike the bubbling medium. In addition, when kogation adheres to the electrothermal converter (heater), the smoothness of the heater surface is impaired and the thermal conductivity is lowered, leading to a decrease in bubbling efficiency. Since it does not come into contact with the , there is no risk of burning the contained ingredients. That is, in the ejection medium of the present embodiment, the physical property conditions for causing film boiling and avoiding kogation are relaxed compared to the ink of the conventional thermal head, and the degree of freedom of the components is increased, resulting in ejection. It becomes possible to more positively contain components suitable for later use.

For example, pigments that have not been used in the past because they tend to burn on a heater can be positively included in the ejection medium in the present embodiment. Liquids other than water-based inks with very low critical pressures can also be used as ejection media in this embodiment. In addition, various inks with special functions that were difficult to handle with conventional thermal heads, such as UV curable ink, conductive ink, EB (electron beam) curable ink, magnetic ink, and solid type ink, can be used as the ejection medium. It becomes possible to use it as Also, if blood or cells in a culture solution are used as the ejection medium, the liquid ejection head of the present embodiment can be used for various purposes other than image formation. It is also effective for applications such as biochip production and electronic circuit printing. The second liquid is not limited, and the same liquid as the first liquid can be used. For example, even if both of the two liquids are inks containing a large amount of water, one ink can be used as the first liquid and the other ink can be used as the second liquid, depending on the situation such as the mode of use. .

(Ejection medium requiring parallel flow of two liquids)
When the liquid to be ejected has already been determined, whether or not it is necessary to cause the two liquids to flow parallel to each other in the liquid flow path (pressure chamber) is determined according to the critical pressure of the liquid to be ejected. You may For example, when the critical pressure of the liquid to be ejected is insufficient, the liquid to be ejected may be the second liquid and the bubbling medium may be prepared as the first liquid.

FIGS. 14(a) and 14(b) are diagrams showing the relationship between the content of water and the foaming pressure during film boiling when water is mixed with diethylene glycol (DEG). In FIG. 14(a), the horizontal axis indicates the mass ratio (mass %) of water to the liquid, and in FIG. 14(b), the horizontal axis indicates the molar ratio of water to the liquid.

As can be seen from both figures, the lower the water content (content ratio), the lower the foaming pressure during film boiling. That is, the smaller the water content, the lower the bubbling pressure and the lower the ejection efficiency. However, since the molecular weight of water (18) is sufficiently smaller than the molecular weight of diethylene glycol (106), even if the mass ratio of water is about 40 wt%, the molar ratio is about 0.9, and the foaming pressure ratio is 0. .9. On the other hand, when the mass ratio of water is less than 40 wt%, as can be seen from FIGS. 14(a) and 14(b), the foaming pressure ratio sharply decreases with the molar concentration.

From the above, when the mass ratio of water is less than 40 wt %, it is preferable to separately prepare the first liquid as the bubbling medium and form parallel flows of these two liquids in the liquid flow path (pressure chamber). In this way, when the liquid to be discharged is already determined, whether or not it is necessary to form a parallel flow in the liquid flow path (pressure chamber) depends on the critical pressure of the liquid to be discharged (or the bubbling during film boiling). pressure).

(Ultraviolet curable ink as an example of ejection medium)
As an example, a preferred component configuration of an ultraviolet curable ink that can be used as the ejection medium of this embodiment will be described. UV curable inks can be classified into 100% solid type inks that do not contain a solvent and are composed of a polymerizable reactive component, and solvent type inks that contain water or a solvent as a diluent. UV curable inks that have been widely used in recent years are 100% solid type UV curable inks that do not contain solvents and are composed of non-aqueous photopolymerizable reaction components (monomers or oligomers). The composition contains a monomer as a main component, and contains a small amount of other additives such as a photopolymerization initiator, a colorant, a dispersant, and a surfactant. The ratio is generally 80 to 90 wt % monomer, 5 to 10 wt % photopolymerization initiator, 2 to 5 wt % coloring material, and the remainder other additives. As described above, even ultraviolet curable ink, which is difficult to handle with a conventional thermal head, can be ejected from the liquid ejection head by a stable ejection operation when used as the ejection medium of the present embodiment. As a result, it is possible to print an image with superior image fastness and abrasion resistance compared to conventional printing methods.

(Example of using mixed liquid as ejected droplets)
Next, a case will be described in which the first liquid 31 and the second liquid 32 are mixed in the ejected liquid droplets 30 at a predetermined ratio. For example, when the first liquid 31 and the second liquid 32 are inks of different colors, if the viscosities and flow rates of both liquids satisfy the relationship of (Equation 2) or (Equation 3), these inks are It can stably flow in the liquid channel 13 and the pressure chamber 18 without color mixing. That is, by controlling the flow rate ratio Q _r of the first liquid 31 and the second liquid 32 in the liquid flow path and the pressure chamber, the water phase thickness ratio _h , the mixing ratio of the liquid 32 can be adjusted to a desired ratio.

For example, if the first liquid is clear ink and the second liquid is cyan ink (or magenta ink), light cyan ink (or light magenta ink) with various color material densities can be obtained by controlling the flow rate ratio _Qr . ) can be discharged. If yellow ink is used as the first liquid and magenta ink is used as the second liquid, a plurality of types of red ink with different hues can be ejected by controlling the flow rate ratio Q _r . That is, if droplets in which the first liquid and the second liquid are mixed at a desired ratio can be ejected, the color reproduction range expressed on the print medium can be expanded by adjusting the mixing ratio. can be expanded.

The configuration of the present embodiment is also effective when using two types of liquids that are preferably mixed immediately after ejection without being mixed until just before ejection. For example, in image printing, it may be preferable to simultaneously apply a high-concentration pigment ink with excellent color development and a resin EM (resin emulsion) with excellent fastness such as abrasion resistance to a printing medium. However, when the distance between the particles of the pigment component contained in the pigment ink and the solid content contained in the resin EM is close, they tend to aggregate and impair the dispersibility. Therefore, by using the high-concentration resin EM as the first liquid and the high-concentration pigment ink as the second liquid in this embodiment, the flow velocities of these liquids are controlled based on (Equation 2) or (Equation 3). By forming parallel flows, the two liquids are mixed and aggregated on the print medium after ejection. That is, it is possible to obtain an image having high color developability and high fastness after landing while maintaining a suitable ejection state under high dispersibility.

In addition, when aiming at such mixing after ejection, the effectiveness of flowing two liquids in the pressure chamber is exhibited regardless of the form of the pressure generating element. That is, the present invention functions effectively even in a configuration in which the problem of critical pressure limitation and kogation does not occur in the first place, such as a configuration using a piezo element as a pressure generating element.

As described above, according to the present embodiment, in order to set the first liquid having the viscosity η ₁ and the second liquid having the viscosity η ₂ to the predetermined water phase pressure ratio _hr , (Equation 4 ) to (Equation 6), the flow rate ratio Q _r is adjusted. As a result, the aqueous phase thickness ratio h _r in the liquid flow path (pressure chamber) is set to a predetermined value, the interface is stabilized at a predetermined position, and the liquid containing the first liquid and the second liquid at a constant ratio is obtained. It is possible to stably perform a droplet ejection operation.

The first liquid and the second liquid flowing inside the pressure chamber may circulate with the outside of the pressure chamber. If circulation is not performed, a large portion of the first liquid and the second liquid that form parallel flows in the liquid flow path and the pressure chamber will not be ejected. Therefore, when the first liquid and the second liquid are circulated with the outside, the liquid that has not been discharged can be used to form the parallel flow again.

(Other embodiments)
The liquid ejection head and liquid ejection apparatus of the present invention are not limited to inkjet recording heads and inkjet recording apparatuses that eject ink. The liquid ejection head, the liquid ejection apparatus, and the liquid ejection method of the present invention can be applied to industries in which printers, copiers, facsimiles having communication systems, word processors having printer units, etc., and various processing devices are combined in a composite manner. Applicable to recording devices. In particular, since various liquids are used as the second liquid, it can also be used for applications such as biochip production and electronic circuit printing.

1 liquid ejection head 11 ejection port 12 pressure generating element 13 liquid flow path 30 droplet 31 first liquid 32 second liquid

Claims (18)

a pressure chamber in which the first liquid and the second liquid flow;
a pressure generating element that pressurizes the first liquid;
an ejection port for ejecting the second liquid;
In a liquid ejection head comprising
In the pressure chamber, a first liquid and a second liquid flowing closer to the ejection port than the first liquid are in contact with each other and flow in a direction crossing the ejection direction ,
The first liquid and the second liquid flowing in the pressure chamber have a viscosity of the first liquid η ₁ , a viscosity of the second liquid η ₂ , and a flow rate of the first liquid Q _{1 .} , when the flow rate of the second liquid is _Q2 ,

A liquid ejection head characterized by satisfying The first liquid and the second liquid flowing in the pressure chamber are

2. The liquid ejection head according to claim 1, wherein: The first liquid and the second liquid flowing in the pressure chamber are

2. The liquid ejection head according to claim 1, wherein: 4. The liquid ejection head according to claim 1, wherein the first liquid and the second liquid flow in the pressure chambers in a laminar flow. 5. The liquid ejection head according to claim 1, wherein the first liquid and the second liquid flow parallel to each other in the pressure chamber. 6. The liquid ejection head according to any one of claims 1 to 5, wherein the ejection liquid droplets ejected from the ejection ports contain less than 20% of the first liquid. 6. The liquid ejection head according to any one of claims 1 to 5, wherein the ejection liquid droplets ejected from the ejection ports contain less than 1% of the first liquid. The pressure generating element and the ejection port are provided at positions facing each other, and the pressure generating element, the first liquid, the second liquid, and the ejection port are arranged in the pressure chamber. 8. The liquid ejection head according to any one of claims 1 to 7, wherein the first liquid and the second liquid flow such that they are arranged in this order. In the pressure chamber, when the height of the pressure chamber is H [μm], the phase thickness of the first liquid is h ₁ , and the phase thickness of the second liquid is h ₂ ,

9. The liquid ejection head according to claim 8, wherein: In the pressure chamber, when the height of the pressure chamber is H [μm], the phase thickness of the first liquid is h ₁ , and the phase thickness of the second liquid is h ₂ ,

9. The liquid ejection head according to claim 8, wherein: In the pressure chamber, when the height of the pressure chamber is H [μm], the phase thickness of the first liquid is h ₁ , and the phase thickness of the second liquid is h ₂ ,

9. The liquid ejection head according to claim 8, wherein: When a voltage is applied to the pressure generating element, the pressure generating element generates heat to cause film boiling in the first liquid, and the second liquid is ejected from the ejection port by growth of generated bubbles. 12. The liquid ejection head according to any one of Items 1 to 11. 13. The liquid ejection head according to claim 1, wherein the first liquid has a critical pressure of 5 MPa or higher. 14. The liquid ejection head according to any one of claims 1 to 13, wherein the second liquid is water-based ink or emulsion containing pigment. 14. The liquid ejection head according to any one of claims 1 to 13, wherein the second liquid is solid type ultraviolet curing ink. 16. The liquid ejection head according to any one of Claims 1 to 15, wherein the first liquid flowing through the pressure chambers is circulated to and from the outside of the pressure chambers. A liquid ejection apparatus comprising the liquid ejection head according to any one of claims 1 to 14. A liquid ejection module for configuring the liquid ejection head according to any one of claims 1 to 16,
A liquid ejection module, wherein the liquid ejection head is configured by arranging a plurality of liquid ejection modules.

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