JP7358153B2 - liquid dispensing module - Google Patents

Description

The present invention relates to a liquid ejection module.

In a liquid ejection module such as an inkjet recording head, volatile components may evaporate at ejection ports where no ejection operation is performed for a while, resulting in deterioration of the quality of the ink (liquid). This is because when volatile components evaporate, the concentration of contained components such as colorants increases, and if the colorant is a pigment, aggregation or sedimentation of the pigment occurs, which affects the discharge state. Specifically, the ejection amount and ejection direction may vary, and density unevenness or streaks may be observed within the image.

In order to suppress such deterioration of ink quality, in recent years, a method has been proposed in which ink is circulated within a liquid ejection module to constantly supply fresh ink to ejection ports. Patent Document 1 discloses a configuration in which an actuator is disposed adjacent to an energy generating element for ejection to promote ink circulation at a position very close to an ejection port.

International Publication No. 2013/032471

However, in the configuration of Patent Document 1, the actuator placed adjacent to the energy generating element moves up and down so as to squeeze the flow path (pressure chamber), so a pressure chamber with a height that takes into account the amplitude of the actuator is required. Become. For this reason, the energy efficiency for the ejection operation in the energy generating element decreases. Further, since the actuator is disposed within the plane in which the ejection port is formed, the thickness of the plate on which the ejection port is formed is subject to constraints on the formation of the actuator, making it difficult to make the ejection port thinner, that is, downsized. Therefore, there is a problem in that the pressure loss within the discharge port is large and more energy is consumed during discharge.

The present invention has been made to solve the above problems. Therefore, the objective is to provide a liquid ejection module that can perform a stable ejection operation with high energy efficiency while circulating and supplying fresh ink near the ejection ports.

To this end, the present invention provides a pressure chamber communicating with a discharge port and accommodating a liquid to be discharged from the discharge port, and an energy generator provided in the pressure chamber and generating energy for discharging the liquid from the discharge port. an element, a supply channel for supplying liquid to the pressure chamber, a recovery channel for recovering liquid from the pressure chamber, a liquid feeding chamber connected to the recovery channel, and the liquid feeding chamber and the supply channel. By expanding and contracting the volumes of the connection flow path connecting the liquid supply flow path, the pressure chamber, the recovery flow path, the liquid flow chamber, and the connection flow path, a liquid discharging module comprising a circulating liquid sending means, wherein the ratio of the sum of the flow path resistances of the supply flow path, the pressure chamber, and the recovery flow path to the flow path resistance of the connection flow path is 0. It is characterized by being .5 or more.

According to the present invention, it is possible to perform a stable ejection operation with high energy efficiency while circulating and supplying fresh ink near the ejection opening.

FIG. 2 is a perspective view of an inkjet recording head. FIG. 3 is a diagram showing a flow path configuration of a flow path block. FIG. 3 is a diagram for explaining the structure and operation of a liquid feeding mechanism. FIG. 7 is a diagram showing the voltage applied to the actuator and the amount of change in volume of the liquid feeding chamber. FIG. 3 is a diagram showing the relationship between flow path resistance, fluid inertance, Reynolds number, and liquid feeding efficiency. It is a figure which shows the relationship between the maximum Reynolds number at the time of expansion, the Reynolds number at the time of contraction, and liquid feeding efficiency.

FIG. 1 is a perspective view of an inkjet recording head 100 (hereinafter also simply referred to as a recording head) that can be used as a liquid ejection module of the present invention. The recording head 100 includes an element substrate 4 in which a plurality of ejection elements are arranged in the Y direction, and a plurality of ejection elements are further arranged in the Y direction. Here, a full-line recording head 100 is shown in which the element substrates 4 are arranged in the Y direction by a distance corresponding to the width of an A4 size sheet.

Each of the element substrates 4 is connected to the same electrical wiring board 102 via a flexible wiring board 101. The electric wiring board 102 is provided with a power supply terminal 103 for receiving electric power and a signal input terminal 104 for receiving an ejection signal. On the other hand, the ink supply unit 105 is formed with a circulation flow path for supplying ink supplied from an ink tank (not shown) to each element substrate 4 and for recovering ink not consumed during printing. .

Based on the above configuration, each of the ejection elements arranged on the element substrate 4 uses the power supplied from the power supply terminal 103 based on the recording data input from the signal input terminal 104, and the ink supply unit 105. The supplied ink is ejected in the Z direction in the figure.

FIGS. 2A and 2B are diagrams showing the flow path configuration of one flow path block on the element substrate 4. FIG. A plurality of channel blocks are formed on one element substrate 4, and FIG. 2(a) shows one of the plurality of channel blocks viewed from the side facing the discharge port surface (+Z direction side). FIG. Further, FIG. 2(b) is a sectional view taken along line IIb-IIb in FIG. 2(a).

As shown in FIG. 2(a), one flow path block includes eight discharge ports 2 arranged in the Y direction, eight pressure chambers 3 prepared in correspondence with each of these discharge ports, and two pressure chambers 3. One supply channel 5 and two recovery channels 6 are included. Each of the two supply channels 5 commonly supplies ink to each of the four pressure chambers 3, and each of the two recovery channels 6 commonly supplies ink from each of the four pressure chambers 3. Collect. One liquid feeding mechanism 8, which will be described later, is provided for one channel block.

As shown in FIG. 2(b), the element substrate 4 of this embodiment includes a second substrate 13, an intermediate layer 14, a first substrate 12, a functional layer 9, a channel forming member 10, and an ejection port forming member 11. are stacked in this order in the Z direction. An energy generating element 1, which is an electrothermal conversion element, is disposed on the surface of the functional layer 9, and an ejection port 2 is formed at a position corresponding to the energy generating element 1 of the ejection port forming member 11. Between the plurality of energy generating elements 1 arranged in the Y direction, a flow path forming member 10 interposed between the functional layer 9 and the discharge port forming member 11 is arranged as a partition, and the individual energy generating elements 1 and A pressure chamber 3 corresponding to the discharge port 2 is formed.

The ink contained in the pressure chamber 3 forms a meniscus at the ejection port 2 in a stable state. When a voltage pulse is applied to the energy generating element 1 according to the ejection signal, film boiling occurs in the ink that contacts the energy generating element 1, and the ink is ejected as droplets from the ejection port 2 in the Z direction due to the growth energy of the generated bubbles. Ru. If the direction in which liquid is ejected from the ejection port 2 (the Z direction in this case) is from below to above, ink is ejected from below to above. In actual ink ejection, ink may be ejected from above in the direction of gravity to below, and in this case, the upward direction in the direction of gravity is the downward direction, and the downward direction in the direction of gravity is the upward direction. The ink in the pressure chamber 3 consumed by the ejection operation is newly supplied by the capillary force of the pressure chamber 3 and the ejection port 2, and a meniscus is re-formed at the ejection port 2. In this embodiment, a combination of the discharge port 2, the energy generating element 1, and the pressure chamber 3 is referred to as a discharge element.

As shown in FIG. 2(b), the element substrate 4 of this embodiment includes a second substrate 13, an intermediate layer 14, a first substrate 12, a functional layer 9, a channel forming member 10, and an ejection port forming member. Each of 11 serves as a wall to form a circulation flow path. This circulation flow path can be divided into a supply flow path 5, a pressure chamber 3, a recovery flow path 6, a liquid feeding chamber 22, and a connection flow path 7.

A pressure chamber 3 is prepared for each ejection element. The supply channel 5 and the recovery channel 6 are prepared for each of the four ejection elements in the block, the supply channel 5 commonly supplies ink to the four pressure chambers 3, and the recovery channel 6 supplies ink to the four pressure chambers 3. Ink is commonly collected from chamber 3.

One liquid feeding chamber 22 and one connecting channel 7 are prepared for each of the eight ejection elements, that is, one channel block. The liquid feeding chamber 22 is arranged at a position overlapping with the eight energy generating elements 1 in the XY plane. A liquid feeding mechanism 8 that can change the volume of the liquid feeding chamber 22 is provided in the liquid feeding chamber 22, and the liquid feeding mechanism 8 circulates ink in common to the eight pressure chambers 3. The connection flow path 7 is arranged approximately at the center of the flow path block in the Y direction, and connects the liquid feeding chamber 22 and the supply flow path. Here, the position of the supply flow path to which the connection flow path 7 connects is a position on the upstream side of the point where it is branched into the two supply flow paths 5.

With the above configuration, by appropriately driving the liquid feeding mechanism 8, the ink supplied through the supply port 15 is transferred to the supply channel 5, the pressure chamber 3, the recovery channel 6, the liquid feeding chamber 22, It can be circulated in the order of connection channel 7. Such circulation is performed stably regardless of the presence or absence of ejection operation or the frequency, and it becomes possible to always supply fresh ink to the vicinity of the ejection port 2. Although not shown in the figure, it is preferable to provide a filter midway through the supply channel 5 before the pressure chamber 3 to prevent foreign matter, air bubbles, etc. from flowing into the supply channel 5. A columnar structure or the like can be used as the filter.

In the element substrate 4, a structure is formed in advance on each of the first substrate 12 and the second substrate 13, and then the first substrate 12 and the second substrate 13 are connected to each other, which will later become the connecting channel 7. It can be manufactured by attaching the intermediate layer 14 having grooves formed therebetween as shown in the figure. At this time, in the figure, the connection channel 7 is arranged between the intermediate layer 14 and the first substrate 12, but the connection channel 7 is arranged between the intermediate layer 14 and the second substrate. Good too. Specifically, by bonding the surfaces with the grooves facing toward the first substrate 12, a connecting channel 7 is formed between the intermediate layer 14 and the first substrate 12 as shown in FIG. 2(b). The configuration will be as follows. On the other hand, if they are bonded together with the surface on which the grooves are formed facing the second substrate 13, a configuration is created in which the connection channel 7 is formed between the intermediate layer 14 and the second substrate 13.

Note that the liquid feeding chamber 22 and the connecting flow path 7 do not necessarily need to be formed using the intermediate layer 14, and may be formed on at least one of the −Z direction side of the first substrate 12 and the +Z direction side of the second substrate 13. It may be formed by etching.

Hereinafter, specific example dimensions of the above structure will be explained. In this embodiment, the individual ejection elements, that is, the energy generating element 1, the ejection port 2, and the pressure chamber 3 are arranged in the Y direction at a density of 1200 npi (nozzles per inch). The size of the energy generating element 1 is 32 μm×12 μm, the diameter of the discharge port 2 is 15 μm, and the thickness of the discharge port 2, that is, the thickness of the discharge port forming member 11 is 8 μm. The size of the pressure chamber 3 is 37 μm (length) in the X direction x 17 μm (width) in the Y direction x 13 μm (height) in the Z direction. Note that the viscosity of the ink used is 3 cP, and the amount of ink ejected from each ejection port is 4 pL.

In this embodiment, the driving frequency of each energy generating element 1 is 15 KHz. Such a driving frequency is required for each ejection element from when voltage is applied to the energy generating element 1 to when ink is actually ejected and from when new ink is refilled to enable the next ejection operation. is set based on the time that the

In order to suppress thickening of the ink at the ejection port 2 to the extent that stable ejection operation can be maintained, it is preferable that the ink is circulated up to at least 1/2 of the height of the ejection port 2 or higher. To do this, if the height of the pressure chamber 3 is H, the thickness of the discharge port 2 is P, and the opening length (usually diameter) of the discharge port 2 along the circulation flow is W, then the following (formula) is required. 1) is required. The example dimensions of this embodiment described above are designed to satisfy (Formula 1).
H ^-0.34 ×P ^-0.66 ×W>1.5 (Formula 1)

On the other hand, in the element substrate 4 of this embodiment, the size of the supply channel 5 is 50 μm in the X direction x 30 μm in the Y direction x 200 μm in the Z direction. Further, the size of the recovery channel 6 is 25 μm in the X direction x 25 μm in the Y direction x 200 μm in the Z direction. The size of the connection channel 7 is 25 μm in the X direction x 13 μm in the Y direction x 25 μm in the Z direction.

In this embodiment, by setting the above-mentioned dimensional relationship, the flow path resistance and inertance of the connection flow path 7 can be changed from the flow path resistance and inertance of the flow path including the supply flow path 5, the recovery flow path 6, and the pressure chamber 3. It is lower than the inertance. Here, "the flow path resistance and inertance of the combined flow path of the supply flow path 5, the recovery flow path 6, and the pressure chamber 3" means the two supply flow paths 5, the eight pressure chambers 3, and the two recovery flow paths. 6 shows the sum of the parallel flow path resistances and the sum of these series flow path resistances. Note that the dimensions of each part shown above are merely examples, and may be changed as appropriate depending on the required specifications.

FIGS. 3(a) to 3(c) are diagrams for explaining the structure and operation of the liquid feeding mechanism 8. FIG. In this embodiment, a piezoelectric actuator having a thin film piezoelectric body 24, two electrodes 23 and a diaphragm 21 that sandwich this thin film piezoelectric body from the front and back surfaces is employed as the liquid feeding mechanism 8. The liquid feeding mechanism 8 (hereinafter also referred to as actuator 8) is arranged on the second substrate 13 so that the diaphragm 21 is exposed to the liquid feeding chamber 22.

The diaphragm 21 is made of Si or the like and has a size of approximately 250 μm in the X direction, 120 μm in the Y direction, and 2 μm in the Z direction. The thin film piezoelectric body 24 is a PZT piezoelectric thin film, and its thickness is about 2 μm. The thin film piezoelectric material 24 can be formed by a sol-gel method, sputtering, or the like, and can be patterned on the second substrate 13 together with the electrode 23 and the like by photolithography.

When a voltage is applied to the thin film piezoelectric body 24 via the two electrodes 23, the diaphragm 21 bends with respect to the thin film piezoelectric body 24, and the volume of the liquid feeding chamber 22 changes. That is, by varying the voltage applied to the two electrodes 23, the diaphragm 21 can be displaced in the ±Z direction, and the volume of the liquid feeding chamber 22 can be changed.

FIG. 3(b) shows a default state in which no voltage is applied to the thin film piezoelectric body 24. In the default state, a bias voltage is applied between the electrodes of the thin film piezoelectric body 24, and the diaphragm 21 is in a state of protruding into the liquid feeding chamber 22. On the other hand, FIG. 3(c) shows an expanded state in which a maximum voltage of 30 V is applied to the thin film piezoelectric body 24. At this time, the driving voltage and the bias voltage cancel each other out, the diaphragm 21 sticks to the thin film piezoelectric body 24 side, and the volume of the liquid feeding chamber 22 becomes larger than the volume in the default state shown in FIG. 3(b). The diaphragm 21 is displaced between the default state shown in FIG. 3(a) and the expanded state shown in FIG. 3(b) depending on the degree of voltage applied to the thin film piezoelectric body 24.

As explained above, in the element substrate 4 of this embodiment, the actuator 8 and the plurality of energy generating elements 1 are arranged on different surfaces. Therefore, unlike Patent Document 1, the displacement of the actuator does not affect the volume of the pressure chamber 3, and the energy efficiency during discharge can be improved compared to Patent Document 1. Furthermore, since the surface on which the actuator 8 is arranged and the surface on which the energy generating elements 1 are arranged are shifted in the Z direction so that they overlap when viewed from the normal direction of these surfaces, it is better than Patent Document 1. Ejection elements can be arranged with high density. As a result, it becomes possible to achieve both high resolution and miniaturization.

By the way, a system using an actuator has a unique Helmholtz resonance frequency. The Helmholtz resonance frequency in the above-mentioned system is 150 kHz, that is, the Helmholtz period is about 6.7 μsec, and in this embodiment, the actuator 8 is driven using this resonance frequency.

FIGS. 4A and 4B are diagrams showing the voltage applied to drive the actuator 8 and the amount of change in volume of the liquid feeding chamber 22 that increases or decreases depending on the voltage. In both figures, the applied voltage is shown by a solid line, and the amount of change in volume is shown by a broken line. Furthermore, in both figures, the direction in which the volume of the liquid feeding chamber 22 expands is the positive direction of the voltage, the maximum voltage is 30V, and the drive cycle is 50.0 μsec. That is, the drive frequency of the actuator 8 is 20 KHz, which is sufficiently higher than the drive frequency of the energy generating element, 15 KHz. In this way, by making the drive frequency of the actuator 8 sufficiently higher than the drive frequency of the ejection elements, it is possible to suppress variations in the ejection operations of the individual ejection elements due to the influence of the drive of the actuators.

Hereinafter, the voltage and volume change amount with respect to the elapsed time t will be explained for each case of FIGS. 4(a) and 4(b).

In the case of FIG. 4(a), the voltage is increased at a constant slope from 0V to 30V from drive start t=0.0μsec to t=2.5μsec, and then from t=2.5μsec to t=50.0μsec. The voltage is lowered at a constant slope from 30V to 0V. Then, such rise and fall of the voltage is repeated at a cycle of 50.0 μsec. Here, the rise time Δt=2.5 μsec when increasing the voltage is a value adjusted to be around 1/2 of the Helmholtz period (6.7 μsec).

Here, when paying attention to the broken line indicating the amount of change in volume, it can be seen that the volume of the liquid feeding chamber 22 suddenly increases at the start-up time Δt=2.5 μsec. Such efficient expansion of the liquid feeding chamber 22 can be obtained by setting the start-up time Δt to around 1/2 of the Helmholtz period (6.7 μsec), that is, Δt=2.5 μsec. On the other hand, the volume after the start-up time Δt repeats increases and decreases due to the residual vibration of the Helmholtz period (6.7 μsec) as the voltage decreases, and the amplitude gradually decreases, returning to the original value (volume change amount 0). It's back.

Here, when the liquid feeding chamber 22 rapidly expands, a high flow velocity is obtained, so the Reynolds number is large and a vortex is generated near the connecting channel 7, and this vortex flows from the connecting channel 7 to the liquid feeding chamber 22. obstruct the flow of On the other hand, when the liquid feeding chamber 22 slowly contracts, a slow flow velocity is obtained, so the Reynolds number is small and parallel flow tends to occur, and the flow from the liquid feeding chamber 22 to the connection channel 7 and the recovery channel 6 has a slow velocity. The liquid will flow out. This embodiment utilizes the fact that there is a difference between the speed of inflow into the liquid feeding chamber 22 due to such rapid expansion and the speed of outflow from the liquid feeding chamber 22 due to gradual contraction. Then, the flow rate that eventually moves from the liquid feeding chamber 22 to the connection channel 7 is quantified, and the pump function of the actuator 8 is realized.

Here, if the ratio of the flow rate sent to the connecting channel to the volume change of the liquid sending chamber 22 is defined as the liquid sending efficiency, then in the case of the drive shown in FIG. 4(a), the liquid sending efficiency is 0.50%. .

On the other hand, FIG. 4(b) shows the pulse shape and volume change when voltage control is performed so as to cancel out the volume increase/decrease due to the residual vibration of the Helmholtz period. In the drive pulse of this example as well, the voltage is increased from 0 V to 30 V at a rise time of Δt=2.5 μsec, thereby effectively expanding the liquid feeding chamber 22. However, after that, the voltage is lowered stepwise to 0V while repeating lowering, increasing, or maintaining the voltage.

Specifically, the voltage is maintained at 30V from t=2.5μsec to t=8.0μsec, and the voltage is lowered from 30V to 23V from t=8.0μsec to t=8.7μsec. Then, the voltage is maintained at 23V from t=8.7μsec to t=11.4μsec, and the voltage is increased from 23V to 26V from t=11.4μsec to t=11.9μsec. The voltage is maintained at 26V from t=11.9μsec to t=14.7μsec, and the voltage is lowered from 26V to 18V from t=14.7μsec to t=16.0μsec. The voltage is maintained at 18V from t=16.0 μsec to t=18.3 μsec, and the voltage is lowered from 18V to 16V from t=18.3 μsec to t=18.9 μsec. Further, the voltage is maintained at 16V from t=18.9μsec to t=24.5μsec, and the voltage is lowered at a constant slope from 16V to 0V from t=24.5μsec to t=50.0μsec. Thereafter, such rise and fall of the voltage is repeated at a cycle of 50.0 μsec.

Here, paying attention to the broken line showing the amount of change in volume, the volume of the liquid feeding chamber 22 increases at once at the start-up time Δt=2.5 μsec, and then increases and decreases once or twice before returning to the original volume (volume change amount). Return to 0). Comparing this example with the broken line in FIG. 4(a), it can be seen that the degree and number of changes in volume are more suppressed in this example than in FIG. 4(a). This is because, in this example, the voltage value is controlled so as to go against the volume increase/decrease due to the residual vibration of the Helmholtz period. In the case of the drive shown in FIG. 4(b), the liquid feeding efficiency is 3.20%, which is higher than that in FIG. 4(a). That is, after the expansion for the start-up time Δt, the volume of the liquid feeding chamber 22 is increased or decreased by increasing, decreasing, or maintaining the voltage in synchronization with the period of Helmholtz resonance so as to counter the increase or decrease in volume caused by residual vibration. As a result, it is possible to gradually change the liquid transfer efficiency.

In the case of the recording head 100 of this embodiment, in order to maintain stable ejection operation at each ejection port, the circulating flow velocity near the ejection port must be at least 27 times the evaporation rate from the ejection port, and approximately 3 mm/sec or more. It is preferable that In order to obtain a circulating flow rate of 3 mm/sec or more, it is required to obtain a liquid feeding efficiency of 1.00% or more for an ink with a viscosity of 3 cP, and 1.75% or more for an ink with a viscosity of 10 cP. In other words, if the driving method shown in Fig. 4(b), which achieves a liquid delivery efficiency of 3.20%, is adopted, the meniscus will be It becomes possible to circulate ink to the vicinity and maintain stable ejection operation.

According to the studies conducted by the present inventors, when the driving method shown in FIG. It was confirmed that the average flow velocity could be obtained. Further, when a similar study was conducted on a system using a high viscosity ink with a viscosity of about 10 cP, an average flow velocity of about 5.5 mm/sec was confirmed near the ejection port 2.

In this embodiment, the circulation flow is improved by disposing the connecting flow path 7 whose flow path resistance or fluid inertance is appropriately adjusted in a position fluidly adjacent to the liquid feeding chamber 22 provided with the liquid feeding mechanism 8. This improves the efficiency of liquid transfer throughout the channel. Hereinafter, the relationship between the flow path resistance and fluid inertance in the connection flow path 7 and the liquid feeding efficiency will be explained.

FIGS. 5(a) to 5(c) are diagrams for explaining the relationship between the flow path resistance, fluid inertance, and maximum Reynolds number Re of the connecting flow path 7, respectively, and liquid feeding efficiency. These figures show the results obtained by simulation for the case where the liquid ejection head shown in FIGS. 1 to 3 is used. However, in this simulation, the condition is that the actuator 8 is linearly displaced without being affected by residual vibration. In this case, under the above-mentioned dimensions, it is assumed that a liquid feeding efficiency of 5.6% can be obtained when the maximum voltage is set to 30V. Therefore, if the driving method shown in FIG. 4(b), which achieves a liquid transfer efficiency of 3.20% under the above-mentioned dimensions, is adopted, the actually obtained liquid transfer efficiency will be as shown in FIGS. 5(a) to ( It is approximately 4/7 (≈3.20/5.60) of the value shown in the graph of c).

In FIG. 5(a), the horizontal axis represents the ratio of the sum of the flow path resistances of the supply flow path 5, pressure chamber 3, and recovery flow path 6 to the flow path resistance of the connection flow path 7 (hereinafter referred to as flow path resistance ratio). It shows. This simulation uses the liquid ejection head shown in FIGS. 1 to 3 as a model. Therefore, the "sum of channel resistances" here refers to the sum of the parallel channel resistances of the two supply channels 5, the eight pressure chambers 3, and the two recovery channels 6, and the sum of the channel resistances of these channels in series. The result obtained by combining the sum of flow path resistances is shown.

In this simulation, the flow path resistance of the connection flow path 7 is changed by adjusting the cross-sectional dimension of the connection flow path 7. That is, it means that the further to the right on the horizontal axis, the larger the cross section of the connecting channel 7 becomes and the smaller the channel resistance becomes. In the figure, the liquid feeding efficiency of the actuator 8 and the maximum Reynolds number (Re) at the time of expansion of the liquid feeding chamber 22, that is, at the start-up time Δt, are plotted against such a flow path resistance ratio. In calculating the Reynolds number, the hydraulic equivalent diameter of the connecting channel 7 is used as a representative dimension.

It can be seen that when the flow path resistance ratio is 0.3, the Reynolds number Re and the liquid feeding efficiency are significantly reduced compared to other plot positions. This is because when the flow resistance of the connection flow path 7 increases, the flow velocity decreases and vortices are less likely to occur, making it difficult for a difference between the inflow speed and the outflow speed into the liquid feeding chamber 22 to occur. On the other hand, if the flow path resistance ratio is set to 0.5 or more, the Reynolds number Re and the liquid feeding efficiency will greatly increase, and the value will be such that the effect of suppressing viscosity increase at the discharge port can be sufficiently expected in actual use. According to the figure, it can be seen that a more preferable liquid feeding efficiency can be obtained by setting the flow path resistance ratio to 0.7 or more and 6.0 or less.

In FIG. 5(b), the horizontal axis indicates the ratio of the sum of the fluid inertances of the supply channel 5, pressure chamber 3, and recovery channel 6 to the fluid inertance of the connection channel 7 (hereinafter referred to as fluid inertance ratio). . The fluid inertance of the connecting channel 7 is changed by adjusting the cross-sectional dimension of the connecting channel 7. That is, it means that the further to the right on the horizontal axis, the larger the cross section of the connecting channel 7 becomes and the smaller the fluid inertance becomes. In the figure, the liquid feeding efficiency of the actuator 8 and the maximum Reynolds number (Re) when the liquid feeding chamber 22 is expanded are plotted against such a fluid inertance ratio. In calculating the Reynolds number, the hydraulic equivalent diameter of the connecting channel 7 is used as a representative dimension, as in FIG. 5(a).

It can be seen that when the fluid inertance ratio is 2.1, the Reynolds number Re and the liquid feeding efficiency are significantly lower than at other plot positions. When the fluid inertance of the connection channel 7 is small, the amount of fluid flowing in and out between the connection channel 7 and the liquid feeding chamber 22 and the amount of fluid flowing in and out between the recovery channel 6 and the liquid feeding chamber 22 are This is because the difference between the On the other hand, if the fluid inertance ratio is set to 2.5 or more, the Reynolds number Re and the liquid feeding efficiency will greatly increase, and the value will be such that the effect of suppressing viscosity increase at the discharge port can be sufficiently expected in actual use. According to the figure, it can be seen that a more preferable liquid feeding efficiency can be obtained by setting the fluid inertance ratio to 3.0 or more and 8.0 or less.

FIG. 5(c) is a diagram showing the relationship between the maximum Reynolds number (Re) when the liquid feeding chamber is expanded and the liquid feeding efficiency. The maximum Reynolds number (Re) is changed by adjusting the cross-sectional dimension of the connecting channel 7. A maximum Reynolds number of 40 or more during expansion has been obtained.

FIGS. 6A and 6B show the relationship between the maximum Reynolds number during expansion, the average absolute value of the Reynolds number during contraction (Ave|Re|), and liquid feeding efficiency. Here, the average |Reynolds number|(Ave|Re|) represents the average of the absolute values of Re(t) at each time. The flow during contraction includes an oscillating flow, and it is appropriate to use absolute values to express the magnitude of the flow. FIG. 6(a) is a graph showing the difference between the maximum Reynolds number Re during expansion and the average |Reynolds number|(Ave|Re|) (maximum Reynolds number during expansion−average |Reynolds number| during contraction). From FIG. 6(a), it can be seen that if the difference is approximately 10 or more, liquid feeding efficiency is obtained and the pump functions as a pump.

FIG. 6(b) is a graph in which the maximum Reynolds number Re during expansion and the average |Reynolds number|(Ave|Re|) during contraction are plotted separately. The average |Reynolds number| when the liquid feeding chamber 22 contracts (liquid chamber displacement corresponding to the drive waveform t=2.5 to 50 μs) is 10 or less (approximately 10 or less). As a result, a vortex is generated near the connecting channel 7 on the side where a high flow velocity is obtained between expansion and contraction (during expansion in this example), and no vortex is generated at a slow flow velocity, so that during expansion and contraction. A difference in flow rate occurs depending on the presence or absence of a vortex. This provides high liquid feeding efficiency.

Such a difference in Reynolds number during expansion and contraction causes a difference between the amount flowing into the liquid feeding chamber 22 from the connecting channel 7 and the amount flowing from the liquid feeding chamber 22 into the connecting channel 7. As a result, a certain amount of ink is moved from the liquid feeding chamber 22 to the connecting channel 7. The larger the maximum Reynolds number (Re) when the liquid feeding chamber is expanded, the more the above-mentioned constant amount increases, and the liquid feeding efficiency can be improved.

As explained above, in the element substrate 4 of this embodiment, the actuator 8 and the plurality of energy generating elements 1 are arranged on different surfaces. Therefore, unlike Patent Document 1, the displacement of the actuator does not affect the volume of the pressure chamber 3 and thus the ejection operation of the ejection element, and the energy efficiency during ejection can be improved compared to Patent Document 1. Furthermore, since the surface on which the actuator 8 is arranged and the surface on which the energy generating elements 1 are arranged are shifted in the Z direction so that they overlap when viewed from the normal direction of these surfaces, it is better than Patent Document 1. It is possible to achieve miniaturization while arranging the ejection elements at high density.

In addition, according to the present invention, the connection flow path 7 whose flow path resistance and fluid inertance are appropriately adjusted is provided at the position connecting to the liquid feeding chamber 22 in which the liquid feeding mechanism 8 is provided, thereby improving circulation. Improves liquid transfer efficiency throughout the channel. As a result, it is possible to circulate the ink located near the ejection port 2, suppress the thickening of the ink at the ejection port 2, and maintain stable ejection operation.

In the above, a constant amount of liquid flow was generated by repeating rapid expansion and gradual contraction of the liquid feeding chamber, but the relationship between the length of time for expansion and the time for contraction can be reversed. good. That is, even by repeating gradual expansion and rapid contraction of the liquid feeding chamber, the liquid can be circulated due to the difference in flow velocity between expansion and contraction. For example, if the voltage drop time is shortened to about 2.5 μsec, the maximum Reynolds number when the liquid feeding chamber 22 contracts becomes 40 or more, and when the liquid feeding chamber 22 contracts, the A vortex is generated. If the remaining time is allocated to the time for increasing the voltage, the average |Reynolds number| when the liquid feeding chamber 22 expands is suppressed to 10 or less, and vortices are less likely to occur. Therefore, by repeating such rapid contraction and gradual expansion, it is possible to move a certain amount of ink from the connection channel 7 to the liquid feeding chamber 22 every 50.0 μsec, which is the opposite of the above embodiment. Circulating flow in the direction of can be generated. In other words, when the volume of the liquid feeding chamber expands and contracts, if the maximum Reynolds number on one side is 10 or more (preferably 40 or more) and the average |Reynolds number| on the other side is 10 or less, then the flow is performed at a preferable speed. Ink can be circulated.

However, in the case of an inkjet recording head like this embodiment, the ink consumed by ejection is required to be replenished into the ejection ports 2 as quickly as possible. Therefore, it can be said that of the two flow paths connected to the pressure chamber 3, the circulation direction of this embodiment in which the flow path directly communicating with the supply port 15 is used as the supply flow path is more preferable.

Moreover, although the effects of this embodiment have been described above on the premise that the driving method shown in FIG. 4(b) is employed, the present invention is not limited to the driving method shown in FIG. 4(b). The voltage waveform that can be employed to counter the volume increase/decrease due to Helmholtz periodic resonance may also have other shapes. That is, the width of the voltage rise or fall may be other than the values shown in FIG. 4(b), and the time required for rising, falling, and maintaining the voltage is also limited to the values shown in FIG. 4(b). Never.

In addition, the present invention does not necessarily need to employ a drive waveform that opposes the residual vibration of the Helmholtz period; for example, the drive control shown in FIG. 4(a) may be employed. Even with the driving waveform as shown in FIG. 4(a), if the connecting flow path 7 with appropriately adjusted flow path resistance and fluid inertance is placed in a position fluidly adjacent to the liquid feeding chamber 22, It is possible to create a difference in outflow velocity during expansion and contraction. In other words, it is possible to improve the ink delivery efficiency compared to the conventional method.

Moreover, the fluid block of this embodiment is not limited to the form shown in FIG. 2(a). The number of ejection elements (pressure chambers 3) that circulate ink in one liquid feeding mechanism 8 may be greater than or less than eight. Furthermore, the number of supply channels 5 and recovery channels 6 provided in one fluid block may be greater than or less than two. In general, there are N×M pressure chambers, M supply channels that commonly supply liquid to each of the N pressure chambers, and M supply channels that commonly collect liquid from each of the N pressure chambers. A unit in which the entire flow path including the recovery flow path is circulated by one liquid sending mechanism 8 can be one block. Here, N and M are integers of 1 or more.

Furthermore, in FIGS. 2(a) and 2(b), the explanation was given using the element substrate 4 in which the ejection elements are arranged in one row in the Y direction, but the element substrate 4 has such ejection element rows in the X direction. They may be arranged in two or more rows.

Further, in the above description, an electrothermal conversion element is used as the energy generating element 1, and ink is ejected using the growth energy of bubbles generated by causing film boiling, but the present invention is limited to such an ejection method. It is not something that will be done. For example, various types of elements can be employed as the energy generating element, such as a piezoelectric actuator, an electrostatic actuator, a mechanical/impact drive type actuator, a voice coil actuator, a magnetostrictive drive type actuator, etc.

Further, in the above description, referring to FIG. 1, a full-line type recording head is described as an example in which the element substrates 4 are arranged in the Y direction by a distance corresponding to the width of an A4 size sheet. The ejection module can also be used in a serial type recording head. However, with a long recording head such as a full-line type, the problems of the present invention, such as ink evaporation and deterioration, are more likely to appear, so the effects of the present invention can be more significantly enjoyed.

Furthermore, although the description has been made above using an example of a recording head that discharges ink containing a coloring material, the liquid discharge module of the present invention is not limited to this. For example, it may be a module that discharges a transparent liquid prepared to improve image quality, or a module that is used for purposes other than recording images, such as uniformly applying some kind of liquid to an object. Good too. In any case, the present invention can effectively function as long as it is a liquid ejection module that ejects fine liquid droplets from a plurality of ejection ports.

1 Energy generating element 2 Discharge port 3 Pressure chamber 4 Element substrate 5 Supply channel 6 Recovery channel 7 Connection channel 8 Liquid feeding mechanism 22 Liquid feeding chamber

Claims (16)

a pressure chamber communicating with the discharge port and accommodating a liquid to be discharged from the discharge port;
an energy generating element that is provided in the pressure chamber and generates energy for discharging liquid from the discharge port;
a supply channel that supplies liquid to the pressure chamber;
a recovery channel for recovering liquid from the pressure chamber;
a liquid feeding chamber connected to the recovery channel;
a connection flow path connecting the liquid feeding chamber and the supply flow path;
A liquid feeding means that circulates the liquid in the supply channel, the pressure chamber, the recovery channel, the liquid feeding chamber, and the connection channel by expanding and contracting the volume of the liquid feeding chamber;
A liquid ejection module comprising:
A liquid ejection module characterized in that a ratio of the sum of the flow resistances of the supply flow path, the pressure chamber, and the recovery flow path to the flow resistance of the connection flow path is 0.5 or more. The ratio of the sum of the flow path resistances of the supply flow path, the pressure chamber, and the recovery flow path to the flow path resistance of the connection flow path is 0.7 or more and 6.0 or less. Liquid dispensing module. a pressure chamber communicating with the discharge port and accommodating a liquid to be discharged from the discharge port;
an energy generating element that is provided in the pressure chamber and generates energy for discharging liquid from the discharge port;
a supply channel that supplies liquid to the pressure chamber;
a recovery channel for recovering liquid from the pressure chamber;
a liquid feeding chamber connected to the recovery channel;
a connection flow path connecting the liquid feeding chamber and the supply flow path;
A liquid feeding means that circulates the liquid in the supply channel, the pressure chamber, the recovery channel, the liquid feeding chamber, and the connection channel by expanding and contracting the volume of the liquid feeding chamber;
A liquid ejection module comprising:
A liquid ejection module characterized in that a ratio of the sum of fluid inertances of the supply flow path, the pressure chamber, and the recovery flow path to the fluid inertance of the connection flow path is 2.5 or more. Liquid discharge according to claim 3, wherein the ratio of the sum of fluid inertances of the supply channel, the pressure chamber, and the recovery channel to the fluid inertance of the connection channel is 3.0 or more and 8.0 or less. module. 5. The liquid ejection module according to claim 1, wherein the liquid feeding means is driven such that the rate at which the volume of the liquid feeding chamber expands is greater than the rate at which it contracts. Among the Reynolds number when the volume of the liquid feeding chamber expands and the Reynolds number when the volume of the liquid feeding chamber contracts, the maximum Reynolds number when the volume of the liquid feeding chamber expands, and the Reynolds number when the volume of the liquid feeding chamber expands. Liquid discharge according to any one of claims 1 to 5, wherein the difference between the absolute value of the Reynolds number and the average value when the volume of the liquid chamber contracts is 10 or more, and the average value is 10 or less. module. The liquid feeding means includes a thin film piezoelectric body, an electrode for applying a voltage to the thin film piezoelectric body, and a diaphragm that is displaced when a voltage is applied to the thin film piezoelectric body and changes the volume of the liquid feeding chamber. 7. The liquid ejection module according to claim 1, wherein the liquid ejection module is an actuator having: . 8. The liquid ejection module according to claim 7, wherein the voltage waveform for driving the actuator includes a waveform for suppressing residual vibration of the diaphragm. 9. The liquid ejection module according to claim 1, wherein the driving frequency of the liquid feeding means is higher than the driving frequency of the energy generating element. The plane on which the energy generating elements are arranged and the plane on which the liquid feeding means is arranged are arranged so as to overlap when viewed from the normal direction of the plane, and the direction in which the liquid is discharged from the discharge port is downward. 10. The liquid ejection module according to claim 1, wherein the liquid feeding means is located below a surface on which the energy generating elements are arranged, when viewed in an upward direction. 11. The supply flow path commonly supplies liquid to a plurality of pressure chambers, and the recovery flow path commonly collects liquid from a plurality of pressure chambers. Liquid dispensing module. 12. The liquid ejection module according to claim 1, wherein the liquid feeding means commonly circulates the liquid in the plurality of pressure chambers. one said liquid feeding means, M said supply channels that commonly supply liquid to each of said N pressure chambers, and M said supply channels that commonly collect liquid from said pressure chambers each of N; having a plurality of blocks including the recovery channel and N×M of the pressure chambers,
13. The N×M pressure chambers, the M supply channels, the M recovery channels, and the plurality of blocks are arranged in parallel. The liquid dispensing module described. 14. The liquid ejection module according to claim 1, wherein the connecting channel is provided between a surface where the energy generating elements are arranged and a surface where the liquid feeding means is arranged. 15. The liquid ejection module according to claim 1, wherein the liquid feeding means is driven so that the liquid moves at a speed of 3 mm/sec or more in the pressure chamber. 16. The liquid ejection module according to claim 1, wherein the liquid is ink containing a coloring material, and the energy generating element is driven according to print data.

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