JP7352132B2 - liquid discharge unit - Google Patents

Description

The present invention relates to a liquid ejection unit.

2. Description of the Related Art Image recording apparatuses are used that eject liquid such as ink onto a medium such as paper through a liquid ejecting device, thereby recording an image on the medium. A liquid ejection device generally includes a number of pressure chambers each containing a liquid, a nozzle fluidly connected to each of the pressure chambers, an actuator for applying pressure to the liquid in the desired pressure chamber, and an actuator for applying pressure to the liquid in the desired pressure chamber. and a control section that controls the drive.

The liquid is discharged by the liquid discharge device by a control unit driving an actuator to apply pressure to the liquid within a desired pressure chamber. As a result, the liquid in the pressure chamber to which the pressure is applied is ejected from the corresponding nozzle to form an image on a medium such as paper.

2. Description of the Related Art As one form of an image recording apparatus including a liquid ejection device, an apparatus is known that includes a liquid ejection unit having a plurality of liquid ejection devices and simultaneously ejects droplets from the plurality of liquid ejection devices. Regarding such an image recording apparatus, in order to suppress heat generation of the liquid ejection apparatus due to continuous use for a long time, it has been proposed to cool a plurality of liquid ejection apparatuses with a cooling liquid (Patent Document 1).

JP2007-237486

Heat generated in the control unit of the liquid ejecting device is transmitted to the liquid flowing in the pressure chamber or the like, and can cause a change in the characteristics of the liquid. For example, when the liquid is ink, changes occur in the concentration and viscosity of the ink. Therefore, in an image forming apparatus that uses a plurality of liquid ejection devices at the same time, if the plurality of liquid ejection devices cannot be cooled uniformly, the concentration and viscosity of the internal ink will differ for each liquid ejection device, for example. If image formation is performed in such a state, the quality of the formed image may deteriorate. With the structure of Patent Document 1, it is difficult to say that a plurality of liquid ejection devices can be cooled uniformly.

An object of the present invention is to provide a liquid ejection unit including a cooling structure that can cool a plurality of liquid ejection devices more evenly.

According to the first aspect of the invention,
a plurality of liquid ejection devices each ejecting liquid;
A liquid ejection unit comprising a cooling structure that cools the plurality of liquid ejection devices with a cooling liquid,
The cooling structure includes:
a plurality of cooling channels through which the cooling liquid flows, each of which is thermally connected to each of the plurality of liquid discharge devices;
a plurality of supply channels each connected to one end of the plurality of cooling channels;
a supply manifold flow path connected to the plurality of supply flow paths above the plurality of liquid discharge devices and distributing the cooling liquid to the plurality of supply flow paths;
a plurality of recovery channels each connected to the other end of the plurality of cooling channels;
defining a recovery manifold flow path that is connected to the plurality of recovery flow paths above the plurality of liquid discharge devices and that joins the cooling liquid from the plurality of recovery flow paths;
A liquid ejection unit is provided in which the cross-sectional area of the supply manifold flow path is smaller than the cross-sectional area of the recovery manifold flow path.

In the liquid ejection unit of the first aspect, the cross-sectional area of each of the plurality of supply channels may be smaller than the cross-sectional area of the supply manifold channel. According to this aspect, the flow rate of the liquid in the supply channel becomes higher, so that the bubbles sent from the supply manifold channel to the supply channel can be efficiently pushed downstream.

In the liquid ejection unit of the first aspect, the cross-sectional area of each of the plurality of supply channels may be equal to the cross-sectional area of each of the plurality of recovery channels. According to this aspect, the members forming the supply flow path and the members forming the recovery flow path can be made into a common member, thereby simplifying the manufacturing process and reducing manufacturing costs.

In the liquid ejection unit of the first aspect, the cross-sectional area of the recovery manifold flow path may be twice or more of the cross-sectional area of the supply manifold flow path. According to this aspect, the coolant in the supply manifold flow path can be more evenly distributed to the plurality of cooling flow paths, and the coolant in the plurality of cooling flow paths can be more evenly caused to flow into the recovery manifold flow path. I can do it. Therefore, the plurality of liquid ejection devices can be cooled more evenly.

In the liquid discharge unit of the first aspect, the recovery manifold flow path includes a first recovery manifold flow path connected to some of the plurality of recovery flow paths, and a first recovery manifold flow path connected to some of the plurality of recovery flow paths. may include a second recovery manifold flow path connected to some other flow paths, and the supply manifold flow path, the first recovery manifold flow path, and the second recovery manifold flow path are arranged in a first direction in a horizontal plane. The supply manifold flow path may be provided between a first recovery manifold flow path and a second recovery manifold flow path in a second direction orthogonal to the first direction in a horizontal plane. It's okay. Further, the cooling structure includes a supply port for distributing the coolant toward an upstream end of the supply manifold, and a recovery port that is vertically aligned with the supply port and for distributing the coolant from the recovery manifold. The supply port and the recovery port may be provided on the upstream end side of the supply manifold flow path in a first direction, and may be provided on the same side as the supply manifold flow path in a second direction. It may be provided at a certain position. In this aspect, the lengths (flow path resistances) of the branch paths leading from the supply port and the recovery port to each manifold flow path (supply manifold flow path, recovery manifold flow path) can be set equally, so the flow rate of the cooling liquid can be set equal to the length (flow path resistance). The first recovery manifold flow path and the second recovery manifold flow path can be made equal, and it is possible to prevent the cooling response power from becoming uneven.

In the liquid ejection unit of the first aspect, the plurality of liquid ejection devices are arranged along the predetermined direction so as to form a first row arranged in a predetermined direction in a horizontal plane, and a second row parallel to the first row. The supply manifold channels may be arranged in a staggered manner, and the supply manifold channels may extend parallel to the first and second rows between the first and second rows. In this aspect, a space can be secured above the liquid ejection device, and the space can be effectively utilized. Note that in this specification and the present invention, "parallel" includes a substantially parallel state in which one side is inclined relative to the other by a predetermined angle of greater than 0 degrees and less than or equal to 5 degrees.

In the liquid ejection unit according to the first aspect, the recovery manifold flow path is arranged such that at least one of the plurality of liquid ejection devices is sandwiched between the recovery manifold flow path and the supply manifold flow path. They may extend in parallel. In this aspect, a space can be secured above the liquid ejection device, and the space can be effectively utilized.

The liquid ejection unit of the first aspect may further include a plurality of liquid channel members connected to each of the plurality of liquid ejection devices and supplying the liquid to each of the liquid ejection devices. Further, in the liquid discharge unit of the first aspect, the supply flow path and the recovery flow path connected to each of the plurality of cooling flow paths are inclined with respect to the vertical direction and extend upward to flow into the supply manifold. and the recovery manifold flow path, the supply flow path and the recovery flow path may be inclined such that the distance between them increases as they go upward, and the plurality of liquid flows A channel member may be arranged to extend upwardly from the liquid ejection device and pass between the supply manifold channel and the recovery manifold channel. In this aspect, the liquid ejection unit can be downsized by effectively utilizing the space above the liquid ejection device and arranging the liquid flow path member.

The liquid ejection unit of the first aspect may further include a holding member that holds the plurality of liquid ejection devices together. According to this aspect, a configuration including a plurality of liquid ejecting devices can be maintained and managed as one unit, so that alignment, replacement, etc. within the printer can be easily handled.

In the liquid discharge unit of the first aspect, the cooling structure may include a pump connected to the supply manifold flow path and the recovery manifold flow path. According to this aspect, the cooling liquid can be efficiently caused to flow by the pump, and the plurality of liquid discharge devices can be cooled more uniformly.

According to the liquid ejection unit of the present invention, the cooling structure allows a plurality of liquid ejection devices to be cooled more evenly.

FIG. 1 is a diagram showing a schematic configuration of a printer according to an embodiment. FIG. 2 is a perspective view of an inkjet head unit according to an embodiment of the invention. FIG. 3 is a perspective view showing an inkjet head, a spacer, and a cooling member that is part of the cooling structure. FIG. 4 is a plan view of the flow path unit. FIG. 5 is a sectional view taken along line VV in FIG. 4. FIG. 6(a) is a plan view of an inkjet head unit according to an embodiment of the present invention. FIG. 6(b) is a side view of the inkjet head unit according to the embodiment of the present invention. FIG. 7 is a diagram showing the shape of a flow path that is an analysis target in a simulation analysis for examining the relationship between the cross-sectional area of the supply manifold flow path and the cross-sectional area of the recovery manifold flow path. FIGS. 8A and 8B are tables showing the results of simulation analysis for examining the relationship between the cross-sectional area of the supply manifold flow path and the cross-sectional area of the recovery manifold flow path. FIGS. 9A and 9B are graphs showing the results of simulation analysis for examining the relationship between the cross-sectional area of the supply manifold flow path and the cross-sectional area of the recovery manifold flow path. FIG. 10(a) is a plan view of an inkjet head unit according to a modification of the present invention. FIG. 10(b) is a side view of an inkjet head unit according to a modification of the present invention.

[Embodiment]
An inkjet head unit (liquid ejection unit) 100 and a printer 1000 equipped with the same according to an embodiment of the present invention will be described with reference to FIGS. 1 to 10.

<Printer 1000>
As shown in FIG. 1, the printer 1000 mainly includes four inkjet head units 100, a platen 500, a pair of transport rollers 601 and 602, and a housing 900 that houses these. Further provided inside the housing 900 are an ink tank 700 and a control device CONT.

In the following description, the direction in which the pair of transport rollers 601 and 602 are lined up, that is, the direction in which the paper P is transported during image formation, will be referred to as the "paper transport direction" of the printer 1000 and the inkjet head unit 100. Regarding the "paper feeding direction," the upstream side in the direction in which the paper P is transported is called the "sheet feeding side," and the downstream side is called the "sheet discharging side." Further, the direction in the horizontal plane perpendicular to the paper feeding direction, that is, the direction in which the rotating shafts of the transport rollers 601 and 602 extend, is called the "paper width direction", and the direction orthogonal to the "paper feeding direction" and the "paper width direction" is called the "paper width direction". This is called the "vertical direction." In the description of the flow path in this specification, "upstream side" and "downstream side" mean the upstream side and the downstream side in the direction in which the liquid flows inside.

Each of the four inkjet head units 100 is a mechanism for ejecting ink for image formation, and is supported by a support 100a at both ends in the paper width direction. In this embodiment, the four inkjet head units 100 are configured to eject ink of four different colors. These four colors are, for example, cyan, magenta, yellow, and black. The specific structure and function of each inkjet head unit 100 will be described later.

The platen 500 is a plate-like member that supports the paper P from the side opposite to the inkjet head unit 100 (from below) when ink is ejected from the inkjet head unit 100 toward the paper P. The width of the platen 500 in the paper width direction is larger than the width of the largest paper on which the printer 1000 can record an image.

A pair of transport rollers 601 and 602 are arranged to sandwich the platen 500 in the paper feeding direction. A pair of transport rollers 601 and 602 transport the paper P in a predetermined manner toward the paper discharge side in the paper feeding direction when the inkjet head unit 100 forms an image on the paper P.

The ink tank 700 is a storage section that stores ink ejected by the inkjet head unit 100, and is divided into four parts so that it can store ink of four colors. The ink tank 700 is connected to a sub-tank 810 (FIG. 6(b)) above the inkjet head unit 100 via an ink channel member 800, and the sub-tank 810 is connected to the inkjet head unit via an ink channel member 820. 100. An ink supply path 821 for sending ink from the sub-tank 810 to the inkjet head unit 100 and an ink recovery path 822 for returning ink from the inkjet head unit 100 to the sub-tank 810 are defined inside the ink flow path member 820. has been done.

The control device CONT generally controls each unit included in the printer 1000 and causes image formation on paper P to be performed.

<Inkjet head unit 100>
Next, the inkjet head unit 100 will be explained.

As shown in FIG. 2, the inkjet head unit 100 includes a holding member 10, ten inkjet heads 20 that are integrally supported by the holding member 10, and a cooling structure 30 that cools the ten inkjet heads 20.

The holding member 10 is a plate-like member having a rectangular shape in a plan view, with the paper width direction as the longitudinal direction and the paper feeding direction as the transversal direction. Both ends of the holding member 10 in the longitudinal direction are supported parts supported by the support body 100a.

The ten inkjet heads 20 are integrally held by the holding member 10 by being arranged inside a plurality of openings (not shown) of the holding member 10 .

The ten inkjet heads 20 are arranged in a staggered manner along the paper width direction in plan view (FIG. 6(a)). Specifically, among the ten inkjet heads, five inkjet heads 20 are lined up in a straight line at equal intervals in the paper width direction, forming the first row L1. The remaining five inkjet heads 20 are lined up in a straight line at equal intervals in the paper width direction on the paper discharge side in the paper feed direction of the first row L1, forming a second row L2. The inkjet heads 20 constituting the second row L2 are arranged offset in the paper feeding direction with respect to the inkjet heads 20 constituting the first row L1. Thereby, the inkjet head 20 is positioned without any gap in the paper width direction of the holding member 10.

<Inkjet head 20>
Each of the plurality of inkjet heads 20 includes a flow path unit 21, a piezoelectric actuator 22, and an ejection control section 23, as shown in FIG.

The flow path unit 21 is formed with a flow path CH (FIG. 4) for distributing and ejecting ink from the sub-tank 810 to appropriate positions. As shown in FIG. 5, the channel unit 21 has a laminated structure in which a diaphragm 21A, plates 21B to 21I, and a nozzle plate 21J are stacked in this order from above, and each of the plates 21B to 21I and the nozzle plate 21J A channel CH is formed by removing a part of the channel CH.

As shown in FIGS. 4 and 5, the flow path CH includes a plurality of individual flow paths ICH arranged in the paper feed direction and the paper width direction, and a plurality of ink supplied from the sub tank 810 via the ink supply path 821. It mainly includes a distribution channel DCH that distributes to the individual channels ICH. The channel CH further includes an ink supply port PI ₂₁ that connects the ink supply channel 821 and the distribution channel DCH, and an ink recovery port PO ₂₁ that connects the ink recovery channel 822 and the distribution channel DCH.

A plurality of individual channels ICH lined up in the paper width direction constitute an individual channel array _LICH . One distribution channel DCH is provided for each of the four individual channel arrays L _ICH , and one ink supply port PI ₂₁ and one ink recovery port PO ₂₁ are provided for each distribution channel DCH. It is provided. In this embodiment, eight individual flow path rows _LICH are formed in the paper feeding direction, and two distribution flow paths DCH, two ink supply ports PI ₂₁ , and two ink recovery ports PO ₂₁ are formed.

As shown in FIG. 5, each of the plurality of individual channels ICH includes a throttle channel 1, a pressure chamber 2, a descender channel 3, and a nozzle 4 along the ink flow from the upstream side to the downstream side.

The throttle channel 1 is formed by removing a portion of the plates 21C and 21D, and is connected to the distribution channel DCH at the upstream end and to the pressure chamber 2 at the downstream end.

The pressure chamber 2 is a space for applying pressure to ink by the piezoelectric actuator 22, and is formed by removing a part of the plate 21B. The upper surface of the pressure chamber 2 is formed by a diaphragm 21A. The shape of the pressure chamber 2 in plan view is an ellipse that is elongated in the paper feeding direction (Fig. 4), and the throttle flow path 1 is connected near one arcuate portion, and the descender flow path 3 is connected near the other arcuate portion. There is.

The descender flow path 3 is a flow path through which ink in the pressure chamber 2 flows to the nozzle 4, and is formed by coaxially providing circular through holes in each of the plates 21C to 21I. The descender flow path 3 extends in the vertical direction from the pressure chamber 2 toward the nozzle 4.

The nozzle 14 is a minute opening that discharges ink toward the paper P, and is formed in the nozzle plate 21J.

The two ink supply ports PI ₂₁ and the two ink recovery ports PO ₂₁ are alternately arranged near one end of the flow path unit 21 in the paper width direction along the paper feeding direction.

As shown in FIG. 5, each of the two ink supply ports PI ₂₁ is formed by coaxially providing a through hole in each of the diaphragm 21A and the plates 21B to 21D. The ink supply port PI ₂₁ is connected to the ink supply path 821 via the ink supply ports PI ₄₀ and PI ₃₃ on the upper side, and is connected to the distribution channel DCH on the lower side.

Each of the two ink recovery ports PO ₂₁ , similarly to the ink supply port PI ₂₁ , is formed by coaxially providing through holes in each of the diaphragm 21A and the plates 21B to 21D. The ink recovery port PO ₂₁ is connected to the ink recovery path 822 via the ink recovery ports PO ₄₀ and PO ₃₃ on the upper side, and is connected to the distribution channel DCH on the lower side.

Each of the two distribution channels DCH is formed by removing a portion of the plates 21E to 21H.

Each of the two distribution channels DCH is a substantially U-shaped channel in plan view, and is connected to the ink supply port PI ₂₁ at the upstream end and to the ink recovery port PO ₂₁ at the downstream end. Specifically, each of the two distribution channels DCH includes a first linear portion DCH1 extending linearly from the ink supply port PI ₂₁ toward one side in the paper width direction, and a first linear portion DCH1 extending linearly from the ink recovery port PO ₂₁ toward one side in the paper width direction. , and a connecting portion DCH3 that extends in the paper feeding direction and connects the first linear portion DCH1 and the second linear portion DCH2.

On the upper surface of the first linear portion DCH1 and the upper surface of the second linear portion DCH2 of the distribution channel DCH, the throttle channels 1 of the plurality of individual channels ICH of the two corresponding individual channel arrays L _ICH are arranged in the paper width direction. are connected in a staggered manner along the

As shown in FIG. 5, the piezoelectric actuator 22 includes a first piezoelectric layer 221 provided on the upper surface of the channel unit 21, a second piezoelectric layer 222 above the first piezoelectric layer 221, a first piezoelectric layer 221, a first piezoelectric layer 222, and a second piezoelectric layer 222 above the first piezoelectric layer 221. It is composed of a common electrode 223 sandwiched between two piezoelectric layers 222 and a plurality of individual electrodes 224 provided on the upper surface of the second piezoelectric layer 222.

The first piezoelectric layer 221 is provided on the upper surface of the diaphragm 21A so as to cover all of the plurality of individual channels ICH formed in the channel unit 21. A common electrode 223 is provided on the upper surface of the first piezoelectric layer 221 to cover almost the entire upper surface of the first piezoelectric layer 221. A second piezoelectric layer 222 is provided covering the entire area.

The common electrode 223 is grounded via wiring (not shown) and is always held at ground potential.

Each of the plurality of individual electrodes 224 has a substantially rectangular planar shape whose longitudinal direction is the paper feeding direction. The plurality of individual electrodes 224 are provided on the upper surface of the second piezoelectric layer 222 so as to be located above the pressure chambers 2 of the plurality of individual channels ICH (FIG. 5). Each of the plurality of individual electrodes 224 is aligned so as to be located above the center of the corresponding pressure chamber 2.

In the structure in which the first piezoelectric layer 221, the second piezoelectric layer 222, the common electrode 223, and the plurality of individual electrodes 224 are arranged as described above, the common electrode 223 and the plurality of individual electrodes 224 of the second piezoelectric layer 222 are arranged as described above. The portion sandwiched between each becomes an active portion 222a polarized in the thickness direction.

The discharge control unit 23 mainly includes a holding plate 231, an FPC (Flexible Printed Circuits) 232 wrapped around the holding plate 231, and two driver ICs 233 mounted on the FPC 232.

A plurality of contacts (not shown) are formed in a portion of the FPC 232 located on the lower surface 231d side of the holding plate 231. Two driver ICs 233 are mounted on a portion of the FPC 232 located on the upper surface 231u side of the holding plate 231.

The discharge control unit 23 is arranged on the upper surface of the piezoelectric actuator 22 such that each of the plurality of contacts of the FPC 232 is electrically connected to each of the plurality of individual electrodes 224 of the piezoelectric actuator 22. Thereby, each of the plurality of individual electrodes 224 of the piezoelectric actuator 22 is connected to the driver IC 233 via the FPC 232. Further, the driver IC 233 is connected to the control unit CONT via wiring (not shown).

<Cooling structure 30>
The cooling structure 30 is a structure for cooling the inkjet head 100 using a cooling liquid (coolant), and includes first and second supply manifolds 311 and 312, first and second recovery manifolds 321 and 322, A cooling member 33 thermally connected to each of the ten inkjet heads 20, ten supply pipes 34 connecting the first and second supply manifolds 311, 312 and the cooling member 33, and the first and second It mainly includes ten recovery pipes 35 that connect recovery manifolds 321 and 322 and a cooling member 33.

Note that in this specification and the present invention, the expression that a member is "thermally connected" to another member does not necessarily mean that the two are in direct contact with each other, but rather that the two are in contact or in a manner that allows heat exchange. means close to each other.

The cooling structure 30 further includes a cooling liquid tank 36 , a connecting pipe 371 and a branch pipe 372 that connect the first and second supply manifolds 311 and 312 and the cooling liquid tank 36 , first and second recovery manifolds 321 , A connecting pipe 381 and a merging pipe 382 connecting the refrigerant tank 322 and the refrigerant tank 36, and a coolant pump 39 provided in the middle of the connecting pipe 371 are provided.

The first and second supply manifolds 311 and 312 are arranged above the holding member 10 and the plurality of inkjet heads 20. The first and second supply manifolds 311 and 312 are each linear circular tubes extending in the paper width direction, and are made of, for example, a nylon tube.

Upstream ends 311a and 312a of the first and second supply manifolds 311 and 312 are connected to a branch pipe 372. The downstream ends 311b and 312b of the first and second supply manifolds 311 and 312 are closed. Inside the first and second supply manifolds 311 and 312, first and second supply manifold channels 311C and 312C are defined that extend linearly from upstream ends 311a and 312a to downstream ends 311b and 312b.

As shown in FIG. 6(a), the first and second supply manifolds 311 and 312 are arranged between the first row L1 and the second row L2 of the inkjet head 20. arranged in parallel. The first and second supply manifolds 311 and 312 are provided at a different position from the inkjet head 20, that is, at a position that does not overlap with the inkjet head 20, in plan view. Thereby, the space above the inkjet head 20 can be used effectively. In this embodiment, an ink flow path member 820 extending between the sub-tank 810 and the inkjet head 20 is arranged in this space (FIG. 6(b)).

The first and second supply manifold channels 311C and 312C defined inside the first and second supply manifolds 311 and 312 each have a circular cross-sectional shape and a cross-sectional area of A [mm ² ]. The lengths of the first and second supply manifold channels 311C and 312C are, for example, about 300 [mm] to 330 [mm].

The first and second collection manifolds 321 and 322 are arranged above the holding member 10 and the plurality of inkjet heads 20. The first and second collection manifolds 321 and 322 are each linear circular tubes extending in the paper width direction, and are made of, for example, a nylon tube.

Upstream ends 321a and 322a of the first and second recovery manifolds 321 and 322 are closed, and downstream ends 321b and 322b of the first and second recovery manifolds 321 and 322 are connected to the confluence pipe 382. Inside the first and second recovery manifolds 321 and 322, first and second recovery manifold channels 321C and 322C are defined that extend linearly from upstream ends 321a and 322a to downstream ends 321b and 322b.

As shown in FIG. 6A, the first collection manifold 321 is arranged on the paper feeding side of the first row L1 of the inkjet head 20 in the paper feeding direction and parallel to the first row L1. is arranged on the paper ejection side of the second row L2 of the inkjet head 20 in the paper feeding direction, in parallel with the second row L2. That is, the first collection manifold 321 and the first supply manifold 311 sandwich the first row L1 of the inkjet heads 20 in the paper feeding direction, and the second collection manifold 322 and the second supply manifold 312 sandwich the first row L1 of the inkjet heads 20 . The row L2 is sandwiched in the paper feeding direction.

The first and second collection manifolds 321 and 322 are provided at a different position from the inkjet head 20, that is, at a position that does not overlap with the inkjet head 20, in plan view. Thereby, the space above the inkjet head 20 can be used effectively.

The cross-sectional shapes of the first and second recovery manifold channels 321C and 322C defined inside the first and second recovery manifolds 321 and 322 are circular, respectively. The cross-sectional area of the recovery manifold channels 321C and 322C is twice the cross-sectional area A [mm ² ] of the first and second supply manifold channels 311C and 312C, that is, 2A [mm ² ]. The lengths of the first and second recovery manifold channels 321C and 322C are, for example, about 300 [mm] to 330 [mm].

As shown in FIG. 3, each of the cooling members 33 is a thick plate-like member that is approximately square in plan view. Each of the cooling members 33 may be made of a material with high thermal conductivity, such as aluminum, for example.

Inside each of the cooling members 33, a cooling flow path 33C having a substantially U-shape in plan view is formed. The cooling channel 33C includes an inflow portion 33C1 extending downward from the upper surface 33u of the cooling member 33, a first cooling portion 33C2 extending from the downstream end of the inflow portion 33C1 to one side in the sheet width direction, and a downstream side of the first cooling portion 33C2. A connecting portion 33C3 extending from the end in the paper feeding direction, a second cooling portion 33C4 extending from the downstream end of the connecting portion 33C3 to the other side in the paper width direction, and a second cooling portion 33C4 extending upward from the downstream end of the second cooling portion 33C4 of the cooling member 33. It includes an outflow portion 33C5 that reaches the upper surface 33u. The upstream end of the inflow section 33C1 is the upstream end 33Ca of the cooling channel 33C, and the downstream end of the outflow section 33C5 is the downstream end 33Cb of the cooling channel 33C.

Note that FIG. 3 shows the cooling member 33 attached to the inkjet head 20 included in the first row L1. The shape of the cooling member 33 attached to the inkjet head 20 included in the second row L2 is also the same, but in the cooling channel 33C, the downstream end 33Cb in FIG. 3 is the upstream end, and the upstream end 33Ca is the downstream end. Become.

The cross-sectional shape of the cooling flow path 33C is circular, and the cross-sectional area is smaller than the cross-sectional area A [mm ² ] of the first and second supply manifold flow paths 311C and 312C. The length from the upstream end 33Ca to the downstream end 33Cb of the cooling channel 33C is, for example, about 70 [mm] to 80 [mm].

Each of the cooling members 33 is provided with two ink supply ports PI ₃₃ and two ink recovery ports PO ₃₃ adjacent to the cooling channel 33C in the sheet width direction. The two ink supply ports PI ₃₃ and the two ink recovery ports PO ₃₃ are arranged alternately along the paper feeding direction.

Each of the cooling members 33 is fixedly connected to each of the channel units 21 of the inkjet head 20 via a spacer 40. The spacer 40 is a plate-like member that is approximately square in plan view, and has a through hole 40A that is rectangular in plan view passing through most of the plate member, and two ink supply ports PI ₄₀ and 2 that are adjacent to the through hole 40A in the paper width direction. It has two ink collection ports PO ₄₀ . The two ink supply ports PI ₄₀ and the two ink recovery ports PO ₄₀ are arranged alternately along the paper feeding direction.

When the cooling member 33 is connected to the flow path unit 21 via the spacer 40, the piezoelectric actuator 22 and the discharge control section 23 are housed inside the through hole 40A of the spacer 40, and the driver IC 233 is connected to the cooling member 33. It comes into contact with the lower surface 33d. Thereby, the driver IC 233 is thermally connected to the cooling member 33 and the cooling channel 33C. More specifically, one of the driver ICs 233 is located at a position overlapping the first cooling unit 33C2 in a plan view, and the other driver IC 233 is located at a position overlapping the second cooling unit 33C4 in a plan view. It comes into contact with the lower surface 33d.

Further, in a state where the cooling member 33 is connected to the flow path unit 21 via the spacer 40, the two ink supply ports PI ₂₁ of the flow path unit 21, the two ink supply ports PI ₄₀ of the spacer 40, the cooling member 33 The two ink supply ports PI ₃₃ overlap coaxially to define an ink supply port PI (FIG. 2) that extends vertically. Similarly, the two ink recovery ports PO ₂₁ of the flow path unit 21, the two ink recovery ports PO ₄₀ of the spacer 40, and the two ink recovery ports PO ₃₃ of the cooling member 33 are coaxially overlapped and extend vertically. Define the PO (Figure 2).

Five supply pipes 34 are provided for the first supply manifold 311 and five supply pipes are provided for the second supply manifold 312, respectively. Each of the supply pipes 34 is a straight circular pipe, and is made of, for example, a nylon tube. A supply flow path 34C is defined inside each of the supply pipes 34.

The upstream ends 34a of each of the supply pipes 34 provided for the first and second supply manifolds 311 and 312 are arranged at equal intervals along the extending direction of the first and second supply manifolds 311 and 312. , are connected to second supply manifolds 311, 312. Each upstream end 34a is connected to the circumferential surface of the first and second supply manifolds 311 and 312 below the vertical centers of the first and second supply manifolds 311 and 312. The supply pipe 34 located at the most downstream side of the first and second supply manifolds 311 and 312 is connected to the first and second supply manifolds 311 and 312 at the downstream ends 311b and 312b of the first and second supply manifolds 311 and 312, respectively. It is connected to the.

The five supply pipes 34 provided for the first supply manifold 311 extend from the connection part with the first supply manifold 311 to the paper feeding side and downward in the paper feeding direction, perpendicular to the first supply manifold 311. , are connected to a cooling member 33 fixed to the inkjet heads 20 constituting the first row L1. Specifically, the downstream ends 34b of the five supply pipes 34 are connected to the upstream ends 33Ca of the five cooling channels 33C. The five supply pipes 34 provided for the second supply manifold 312 extend from the connection part with the second supply manifold 312 to the paper discharge side and downward in the paper feeding direction, perpendicular to the second supply manifold 312. , are connected to a cooling member 33 fixed to the inkjet heads 20 constituting the second row L2. Specifically, the downstream ends 34b of the five supply pipes 34 are connected to the upstream ends 33Ca of the five cooling channels 33C.

The cross-sectional shape of the supply flow path 34C is circular, and the cross-sectional area is smaller than the cross-sectional area A [mm ² ] of the first and second supply manifold flow paths 311C and 312C, and the same as the cross-sectional area of the cooling flow path 33C. be. The length from the upstream end 34a to the downstream end 34b of the supply channel 34C is, for example, about 75 [mm] to 85 [mm].

Five collection pipes 35 are provided for the first collection manifold 321 and five collection pipes 35 are provided for the second collection manifold pipe 322. Each of the recovery tubes 35 is a straight circular tube, and is made of, for example, a nylon tube. A recovery channel 35C is defined inside each recovery tube 35.

The downstream ends 35b of each of the recovery pipes 35 provided for the first and second recovery manifolds 321 and 322 are arranged at equal intervals along the extending direction of the first and second recovery manifolds 321 and 322. , are connected to the peripheral surfaces of the second recovery manifolds 321 and 322. Each downstream end 35b is connected to the circumferential surface of the first and second recovery manifolds 321 and 322 below the vertical centers of the first and second recovery manifolds 321 and 322. Among the recovery pipes 35, the recovery pipe 35 located most upstream of the first and second recovery manifolds 321 and 322 is located at the upstream ends 321a and 322a of the first and second recovery manifolds 321 and 322. It is connected to two recovery manifolds 321 and 322.

The five collection pipes 35 provided for the first collection manifold 321 extend from the connection part with the first collection manifold 321 to the paper discharge side and downward in the paper feeding direction, perpendicular to the first collection manifold 321. , are connected to a cooling member 33 fixed to the inkjet heads 20 constituting the first row L1. Specifically, the upstream ends 35a of the five recovery pipes 35 are connected to the downstream ends 33Cb of the five cooling channels 33C. The five collection pipes 35 provided for the second collection manifold 322 extend from the connection part with the second collection manifold 322 to the paper feeding side and downward in the paper feeding direction, perpendicular to the second collection manifold 322. , are connected to a cooling member 33 fixed to the inkjet heads 20 constituting the second row L2. Specifically, the upstream ends 35a of the five supply pipes 35 are connected to the downstream ends 33Cb of the five cooling channels 33C.

The cross-sectional shape of the recovery channel 35C is circular, and the cross-sectional area is smaller than the cross-sectional area A [mm ² ] of the first and second supply manifold channels 311C and 312C, and the same as the cross-sectional area of the cooling channel 33C. be. The length from the upstream end 35a to the downstream end 35b of the recovery channel 35C is, for example, about 75 [mm] to 85 [mm].

An upstream end 311a of the first supply manifold 311 and an upstream end 312a of the second supply manifold 312 are each connected to a branch pipe 372. Furthermore, the downstream end 321b of the second recovery manifold 321 and the downstream end 322b of the second recovery manifold pipe 322 are each connected to the confluence pipe 382. The upstream end (supply port) 372a of the branch pipe 372 and the downstream end (recovery port) 382b of the merging pipe 382 are arranged vertically at the same position in the paper feeding direction.

The branch pipe 372 is connected to the coolant tank 36 via a connecting pipe 371, and the merging pipe 382 is connected to the coolant tank 36 via a connecting pipe 381. Although the coolant pump 39 is provided in the middle of the connecting pipe 371 in this embodiment, the coolant pump 39 is not limited to this, and can send the coolant to an arbitrary position from the coolant tank 36 to the cooling channel 33C. It can be arranged as follows.

A supply path for sending the coolant from the coolant tank 36 to the plurality of cooling members 33 is configured by a connecting pipe 371, a branch pipe 372, first and second supply manifolds 311, 312, and a plurality of supply pipes 34. . Further, a recovery path for returning the coolant from the plurality of cooling members 33 to the coolant tank 36 is constituted by a plurality of recovery pipes 35, first and second recovery manifolds 321, 322, a confluence pipe 382, and a connecting pipe 381. Ru.

<Image forming method>
Image formation on paper P using printer 1000 and inkjet head unit 100 is performed as follows.

First, paper P in a paper feed tray (not shown) is sent to the paper feeding side of the transport roller 601, and is sent onto the platen 500 by the transport roller 601. The plurality of inkjet heads 20 of the inkjet head unit 100 form an image on the paper P by continuously ejecting ink droplets onto the paper P that is fed in the paper feed direction by the transport rollers 601 and 602. The paper P on which the image has been formed is sent to the paper ejection side of the transport roller 602, and is ejected to a paper ejection tray (not shown).

Ejection of ink droplets using the inkjet head 20 is performed by applying pressure to the ink in a predetermined pressure chamber 2 (referred to as "target pressure chamber") using a piezoelectric actuator 22. Specifically, first, the driver IC 233 applies a drive potential to the individual electrode 224 corresponding to the target pressure chamber via the FPC 232 under instructions from the control device CONT. As a result, an electric field parallel to the polarization direction is generated in the active part 222a sandwiched between the individual electrode 224 and the common electrode 223 to which the driving potential is applied, and the active part 222a contracts in the horizontal direction perpendicular to the polarization direction. . As a result, the diaphragm 21A above the target pressure chamber vibrates, applying pressure to the ink in the target pressure chamber, and ink droplets are ejected from the nozzle 4 communicating with the pressure chamber 2 via the descender flow path 3. Ru.

Furthermore, the inkjet head unit 100 and printer 1000 of this embodiment use the cooling structure 30 to cool the driver IC 233 and, by extension, the inkjet head 20 during the above-described image formation.

Specifically, the coolant pump 39 is driven to transfer the low-temperature coolant held in the coolant tank 36 to the connecting pipe 371, the branch pipe 372, the first and second supply manifolds 311 and 312, and the supply pipe 34. , to the cooling channels 33C of the plurality of cooling members 33. As a result, heat exchange occurs between the coolant flowing through the cooling channel 33C and the driver IC 233 thermally connected to the cooling channel 33C, the temperature of the driver IC 233 decreases, and the temperature of the coolant increases. do. The coolant whose temperature has increased is returned to the coolant tank 36 via the recovery pipe 35, first and second recovery manifolds 321, 322, merging pipe 382, and connection pipe 381, and is cooled by a cooling device (not shown). Ru.

The inkjet head unit 100 and printer 1000 of this embodiment thus cool the driver IC 233 using the cooling mechanism 30. This prevents the heat of the driver IC 233 from being transmitted to the ink in the flow path unit 21, causing changes in the characteristics of the ink (for example, changes in density and viscosity), and further suppressing the quality deterioration of the formed image. .

<Cross-sectional area of supply manifold flow path and recovery manifold flow path>
In the inkjet head unit 100 of this embodiment, the cross-sectional area of the first and second supply manifold channels 311C and 312C is A [mm ² ], and the cross-sectional area of the first and second recovery manifold channels 321C and 322C is A [mm 2 ]. , it is 2A [mm ² ], which is twice that. In other words, the cross-sectional area of the first and second supply manifold channels 311C and 312C is 1/2 of the cross-sectional area of the first and second recovery manifold channels 321C and 322C. This feature has the following significance.

The first and second supply manifold channels 311C and 312C are arranged above the inkjet head 20. Therefore, in order to discharge air bubbles mixed into the coolant in the first and second supply manifold channels 311C and 312C, the supply channel 34C extending downward from the first and second supply manifold channels 311C and 312C is It is necessary to send the air bubbles to the first and second recovery manifold channels 321C and 322C via the cooling channel 33C.

However, since the bubbles move upward due to buoyancy, if the flow rate of the coolant flowing through the first and second supply manifold channels 311C and 312C is low, the bubbles that are about to move upward are forced to extend downward. It is difficult to force it into the supply channel 34C. In this case, air bubbles inside the first and second supply manifold channels 311C and 312C may remain in the first and second supply manifold channels 311C and 312C. When the amount of the remaining air bubbles increases, the air bubbles impede uniform distribution of the coolant from the first and second supply manifold channels 311C and 312C to the five supply channels 34C. Specifically, for example, air bubbles gather near the downstream ends 311b and 312b of the first and second supply manifolds 311 and 312 and obstruct the flow of the coolant, thereby causing the first and second supply manifold channels 311C, More cooling fluid flows into the supply flow path 34C connected to the more upstream side of 312C, and more cooling fluid flows to the supply flow path 34C connected to the more downstream side of the first and second supply manifold flow paths 311C and 312C. A phenomenon may occur in which the amount decreases. As a result, the cooling liquid is not evenly sent to the plurality of cooling channels 33C, and it becomes difficult to uniformly cool the plurality of inkjet heads 20.

Therefore, it is preferable to reduce the cross-sectional area of the first and second supply manifold channels 311C and 312C to increase the channel resistance and increase the flow rate of the coolant flowing therein. Thereby, bubbles can be efficiently sent to the supply channel 34C using the cooling liquid having a high flow rate.

On the other hand, the cooling liquid flows into each of the first and second recovery manifold channels 321C and 322C from the plurality of recovery channels 35C. Turbulent flow occurs at the confluence point where the cooling liquid flows from the recovery channel 35C to the first and second recovery manifold channels 321C and 322C, and the cooling fluid flows through the first and second recovery manifold channels 321C and 322C. A pressure loss occurs in the liquid. When the pressure loss is large, the speed of the flow from the upstream side to the downstream side in the first and second recovery manifold channels 321C and 322C decreases, or the flow stagnates.

Specifically, for example, due to turbulent flow at a confluence point between a certain recovery channel 35C and the first and second recovery manifold channels 321C and 322C, the flow from the upstream side of the confluence point to the downstream side of the confluence point Flow may be obstructed. As a result, in the recovery channel 35C that joins the first and second recovery manifold channels 321C and 322C on the upstream side of the confluence point, the coolant whose temperature has increased due to heat exchange with the driver IC 233 is transferred to the first and second recovery manifold channels 321C and 322C. 2 It cannot flow into the recovery manifold channels 321C and 322C and stagnates in the recovery channel 35C. In this way, when the discharge of the coolant whose temperature has increased is obstructed in some of the cooling channels 33C, it becomes difficult to uniformly cool the plurality of inkjet heads 20.

Therefore, it is preferable to increase the cross-sectional area of the first and second recovery manifold channels 321C and 322C to suppress the generation of turbulence and pressure loss. Thereby, the flow of the coolant from the upstream side to the downstream side can be maintained.

In this embodiment, in view of the above two points, the cross-sectional area of the first and second supply manifold channels 311C and 312C is set to 1/2 of the cross-sectional area of the first and second recovery manifold channels 321C and 322C. . As a result, in the first and second supply manifold channels 311C and 312C, the flow rate of the cooling liquid becomes relatively high, and air bubbles are effectively swept away. Furthermore, in the first and second recovery manifold flow paths 321C and 322C, pressure loss due to turbulence is relatively small, and the coolant efficiently flows downstream.

As a result, the coolant in the first and second supply manifold channels 311C and 312C evenly flows into the five supply channels 34C and the five cooling channels 33C without being obstructed by air bubbles. The five inkjet heads 20 in the L1 and second rows L2 are uniformly cooled. In addition, the coolant whose temperature has increased due to heat exchange with the driver IC 233 in the five cooling channels 33C is transferred from the five recovery channels 35C to the first and second recovery manifold channels 321C without being obstructed by turbulence. , 322C and returned to the coolant tank 36. That is, the supply and recovery of the cooling liquid to the ten cooling channels 33C is performed almost evenly, and the ten inkjet heads 20 are cooled almost evenly.

Note that the cross-sectional area of the first and second supply manifold channels 311C and 312C is not limited to 1/2 of the cross-sectional area of the first and second recovery manifold channels 321C and 322C; It only needs to be smaller than the cross-sectional area of the channels 321C and 322C. Further, the cross-sectional area of the first and second recovery manifold channels 321C and 322C may be twice or more the cross-sectional area of the first and second supply manifold channels 311C and 312C. The reason for this is as follows.

The inventor of the present invention has determined how large the cross-sectional area of the first and second recovery manifold channels 321C and 322C is relative to the size of the cross-sectional area of the first and second supply manifold channels 311C and 312C. The following simulation was performed to examine whether it is preferable to have the following.

In the simulation, as shown in FIG. 7, a channel C having a straight main channel M and five branch channels B1 to B5 connected to the main channel M at equal intervals was analyzed. The cross-sectional shape of the main flow path M is circular, and the cross-sectional areas are 0.25S [mm ² ], 1.00S [mm ² ], 2.00S [mm ² ], 2.25S [mm ^{2 ], and 4.00S [mm 2} ]. mm ² ]. Here, S [mm ² ] is a desired cross-sectional area of the first and second supply manifold channels 311 and 312, which was set by the inventor based on various conditions such as channel length.

The interval between the branch channels B1 to B5 was set to 70 mm, and the branch channel B5 was connected to one end of the main channel M. The length of each of the branch channels B1 to B5 was 80 [mm]. The cross-sectional shape of the branch channels B1 to B5 was circular, and the diameter thereof was set to 1/2 of the diameter of the cross-sectional shape of the main channel M. The ends of the branch channels B1 to B5 opposite to the end connected to the main channel M were exposed to the atmosphere.

Figures 8(a) and 9(a) are the results of simulation analysis, in which a liquid having a viscosity equivalent to that of the cooling liquid flows from the end M1 of the main channel M at a rate of 1000 [cc/min]. The flow rate of the liquid flowing into each of the branch channels B1 to B5 when the flow rate of the liquid flows into each of the branch channels B1 to B5 is shown for each cross-sectional area of the main channel M.

As shown in FIG. 8(a), when the cross-sectional area of the main channel M is 1.00S [mm ² ], the inflow amount (=217.9 [cc/min]) and the amount of liquid flowing into the branch channel B5 where the amount of liquid flowing in is the smallest (=188.9 [cc/min]) is 29.0 [cc/min]. In this case, it can be said that the liquid flows almost evenly into the branch channels B1 to B5.

On the other hand, when the cross-sectional area of the main channel M is 0.25S [mm ² ], the amount of liquid flowing into the branch channel B1, which has the largest amount of inflow (=324.7 [cc/min]) The difference between the amount of liquid flowing into the branch channel B5 where the amount of liquid flowing in is the smallest (=133.4 [cc/min]) is as large as 191.3 [cc/min]. In this case, the amount of liquid flowing into the branch channel B1 located at the most upstream side of the main channel M is 2.4 times or more of the amount of liquid flowing into the branch channel B5 located at the most downstream side of the main channel M. Therefore, it is difficult to say that the liquid flows into the branch channels B1 to B5 almost evenly.

On the other hand, when the cross-sectional area of the main flow path M is 2.25S [mm ² ] and 4.00S [mm ² ], the amount of liquid flowing into the branch flow path is the largest. The difference from the amount of liquid flowing into the branch channel where the amount of liquid flowing in is the smallest is 20.8 [cc/min] and 45.0 [cc/min], respectively. In these cases as well, it can be said that the liquid flows almost evenly into the branch channels B1 to B5.

From the above simulation results, the cross-sectional area S [mm ² ] of the first and second supply manifold channels 311 and 312 set by the inventor of the present invention sends the cooling liquid almost equally to the plurality of cooling channels 33C. It was confirmed that this is the optimal value for That is, if the cross-sectional area of the first and second supply manifold channels 311 and 312 is made smaller than S [mm ² ], the pressure loss due to channel resistance increases, and the cooling liquid is not uniformly supplied to the plurality of cooling channels 33C. They tend to be difficult to send. On the other hand, if the cross-sectional area of the first and second supply manifold channels 311 and 312 is made larger than S [mm ² ], the above-mentioned accumulation of air bubbles becomes a problem. Generally, a person skilled in the art can appropriately set such an optimal cross-sectional area S [mm ² ] based on the shape of the channel, the viscosity and flow rate of the liquid flowing through the channel, and the like.

Figures 8(b) and 9(b) are the results of simulation analysis, in which a liquid having the same viscosity as the cooling liquid is collected from the end M1 of the main channel M at a rate of 1000 [cc/min]. In this case, the flow rate of liquid flowing into the main channel M from each of the branch channels B1 to B5 is shown for each cross-sectional area of the main channel M.

As shown in FIG. 8(b), when the cross-sectional area of the main channel M is 2.00S [mm ² ], the inflow amount ( = 230.9 [cc/min]) and the inflow amount from the branch channel B5, where the amount of liquid outflow is the smallest, to the main channel M (= 177.7 cc/min) is 53.2 [cc/min]. min]. In this case, it can be said that the liquid flows almost uniformly from the branch channels B1 to B5.

When the cross-sectional area of the main channel M is 1.00S [mm ² ], the inflow amount from the branch channel B1, which has the largest outflow amount of liquid (=297.0 [cc/min]), and the The difference between the inflow amount (=135.5 cc/min) from the branch channel B5 where the outflow amount is the smallest is 161.5 [cc/min]. This degree of variation is the lower limit at which it can be considered that the liquid is almost uniformly flowing in from the branch channels B1 to B5.

On the other hand, when the cross-sectional area of the main channel M is 0.25S [mm ² ], the inflow amount from the branch channel with the largest amount of liquid flowing out and the branch channel with the smallest amount of liquid flowing out. The difference between the amount of inflow from and the inflow amount is as large as 580.5 [cc/min]. In this case, the amount of inflow from the branch channels located upstream of the main channel M is small, and it cannot be said that the liquid flows almost evenly from the branch channels B1 to B5.

On the other hand, when the cross-sectional area of the main channel M is 2.25×S [mm ² ] and 4.00 S [mm ² ], the inflow from the branch channel where the largest amount of liquid flows out The difference between this amount and the inflow amount from the branch flow path where the outflow amount of liquid is the smallest is as small as 39.2 [cc/min] and 48.7 [cc/min], respectively. In these cases, it can be said that the liquid flows almost equally from the branch channels B1 to B5.

From the above simulation results, the optimal cross-sectional area of the first and second recovery manifold channels 321 and 322 in order to recover the cooling liquid almost evenly from the plurality of cooling channels 33C is determined by the first and second supply manifolds. Assuming that the cross-sectional area of the channels 311C and 312C is S [mm ² ], it is at least S [mm ² ] or more, and it can be said that it is preferable that it is at least twice S [mm ² ], that is, 2S [mm ² ] or more. .

The main effects of the inkjet head unit 100 of this embodiment are summarized below.

The inkjet head unit 100 of this embodiment includes a plurality of cooling channels 33C thermally connected to a plurality of inkjet heads 20, a first supply manifold channel 311C, a second supply manifold channel 312C, and a plurality of supply channels 34C. Coolant is supplied in parallel through the That is, the cooling liquid that has not undergone heat exchange with the inkjet head 20 is sent in parallel to all of the plurality of cooling channels 33C. Therefore, the plurality of inkjet heads 20 can be cooled more evenly.

In the inkjet head unit 100 of this embodiment, the cross-sectional areas of the first and second supply manifold channels 311C and 312C are smaller than the cross-sectional areas of the first and second recovery manifold channels 321C and 322C. Therefore, in the first and second supply manifold channels 311C and 312C, bubbles can be efficiently discharged by the flow of the cooling liquid with a relatively high flow rate, and in the first and second recovery manifold channels 321C and 322C, bubbles can be efficiently discharged. , it is possible to suppress the occurrence of turbulence and to suppress stagnation of the coolant flow due to pressure loss. Thereby, the cooling liquid can be more evenly supplied to the plurality of cooling channels 33C and the cooling liquid can be recovered from the plurality of cooling channels 33C, and the plurality of inkjet heads 20 can be cooled more evenly. I can do it.

In the inkjet head unit 100 of this embodiment, the cross-sectional area of the supply flow path 34C is smaller than the cross-sectional area of the first and second supply manifold flow paths 311C and 312C, so the cooling liquid is supplied to the first and second supply manifolds. It is accelerated when flowing into the supply channel 34C from the manifold channels 311C and 312C. Further, the coolant flows through the supply flow path 34C at a flow rate higher than that within the first and second supply manifold flow paths 311C and 312C. Thereby, air bubbles can be efficiently swept away.

In the inkjet head unit 100 of this embodiment, the cross-sectional area of the recovery channel 35C is equal to the cross-sectional area of the supply channel 34C. Therefore, it is possible to maintain the flow rate of the liquid in the supply channel 34C and efficiently push the bubbles to the first and second recovery manifold channels 321C and 322C. Further, by making the supply pipe 34 and the recovery pipe 35 the same member, the manufacturing process can be simplified and manufacturing costs can be reduced.

[Modified example]
In the embodiments described above, the following variations can also be used.

Although the inkjet head unit 100 of the above embodiment includes a first supply manifold 311 and a second supply manifold 312, the inkjet head unit 100 may include only one supply manifold 313 (see FIG. 10(a) ).

In this aspect, the supply manifold 313 is arranged parallel to the first row L1 and the second row L2 of the inkjet heads 20 and between the first row L1 and the second row L2. The supply manifold 313 includes five supply pipes 34 connected to cooling members 33 fixed to the inkjet heads 20 constituting the first row L1, and cooling members 33 fixed to the inkjet heads 20 constituting the second row L2. Five supply pipes 34 connected to the member 33 are connected.

Further, the inkjet head unit 100 may have one supply manifold and one collection manifold, or may have three or more supply manifolds and/or three or more collection manifolds. The number and arrangement of supply manifolds and collection manifolds can be changed as appropriate depending on the number and arrangement of inkjet heads 20 that inkjet head unit 100 has. Furthermore, at least one of the supply manifold and the collection manifold may be arranged directly above the inkjet head 20 so that they overlap in plan view.

Although the inkjet head unit 100 of the above embodiment has ten inkjet heads 20, the invention is not limited to this. The inkjet head unit 100 may include at least two inkjet heads 20.

In the embodiment described above, the cross-sectional area of the cooling flow path 33C, the cross-sectional area of the supply flow path 34C, and the cross-sectional area of the recovery flow path 35C are the same, and the cross-sectional area of the first and second supply manifold flow paths 311C and 312C is the same. Although it is smaller than the area, it is not limited to this. The cross-sectional area of the cooling flow path 33C, the cross-sectional area of the supply flow path 34C, and the cross-sectional area of the recovery flow path 35C may be made different from each other. Any one or more of the cross-sectional area of the cooling flow path 33C, the cross-sectional area of the supply flow path 34C, and the cross-sectional area of the recovery flow path 35C is made larger than the cross-sectional area of the first and second supply manifold flow paths 311C and 312C. Good too.

In the above embodiment, the cross-sectional shape of the first and second supply manifold channels 311C and 312C, the cross-sectional shape of the first and second recovery manifold channels 321C and 322C, the cross-sectional shape of the cooling channel 33C, and the cross-sectional shape of the supply channel 34C. The cross-sectional shape of the recovery channel 35C and the cross-sectional shape of the recovery flow path 35C are both circular. However, the cross-sectional shape of each flow path is not limited to this, and may be any shape such as a rectangle, square, or polygon. Further, the cross-sectional shapes of the respective channels may be different from each other.

In the embodiment described above, the driver IC of the inkjet head 20 is brought into contact with the cooling member 33 of the cooling structure 30, but the present invention is not limited to this. The driver IC may be arranged in any manner that allows heat exchange with the cooling fluid flowing through the cooling channel 33C of the cooling member 33.

As long as the characteristics of the present invention are maintained, the present invention is not limited to the above-described embodiments, and other forms that can be considered within the scope of the technical idea of the present invention are also included within the scope of the present invention. It will be done.

According to the liquid ejection unit of the present invention, it is possible to uniformly cool a plurality of liquid ejection devices and perform good image formation.

10 Holding member 20 Inkjet head 30 Cooling structure 311 First supply manifold 312 Second supply manifold 321 First recovery manifold 322 Second recovery manifold 33 Cooling member 34 Supply pipe 35 Recovery pipe 36 Coolant tank 39 Coolant pump 100 Inkjet head unit 500 Platen 601, 602 Conveyance roller 700 Ink tank 800 Ink channel member 900 Housing 1000 Printer

Claims (9)

a plurality of liquid ejection devices each ejecting liquid to form an image on a medium;
a liquid channel member that supplies the liquid to the plurality of liquid ejection devices;
A liquid ejection unit comprising a cooling structure that cools the plurality of liquid ejection devices with a cooling liquid different from the liquid,
The cooling structure includes:
a plurality of cooling channels through which the cooling liquid flows, each of which is thermally connected to each of the plurality of liquid discharge devices;
a plurality of supply channels each connected to one end of the plurality of cooling channels;
a supply manifold flow path connected to the plurality of supply flow paths above the plurality of liquid discharge devices and distributing the cooling liquid to the plurality of supply flow paths;
a plurality of recovery channels each connected to the other end of the plurality of cooling channels;
defining a recovery manifold flow path that is connected to the plurality of recovery flow paths above the plurality of liquid discharge devices and that joins the cooling liquid from the plurality of recovery flow paths;
The cross-sectional area of the supply manifold flow path is smaller than the cross-sectional area of the recovery manifold flow path,
The recovery manifold channel is connected to a first recovery manifold channel connected to some of the plurality of recovery channels, and connected to some other channels of the plurality of recovery channels. a second recovery manifold flow path;
The supply manifold flow path, the first recovery manifold flow path, and the second recovery manifold flow path extend along a first direction in a horizontal plane,
The supply manifold flow path is provided between a first recovery manifold flow path and a second recovery manifold flow path in a second direction perpendicular to the first direction in a horizontal plane,
The cooling structure includes:
a supply port through which the cooling liquid flows toward an upstream end of the supply manifold;
further defining a recovery port that is vertically aligned with the supply port and allows the cooling liquid from the recovery manifold to flow therethrough;
The supply port and the recovery port are provided at the upstream end side of the supply manifold flow path in a first direction, and the liquid discharge unit is provided at the same position as the supply manifold flow path in a second direction. . a plurality of liquid ejection devices each ejecting liquid to form an image on a medium;
a liquid channel member that supplies the liquid to the plurality of liquid ejection devices;
A liquid ejection unit comprising a cooling structure that cools the plurality of liquid ejection devices with a cooling liquid different from the liquid,
The cooling structure includes:
a plurality of cooling channels through which the cooling liquid flows, each of which is thermally connected to each of the plurality of liquid discharge devices;
a plurality of supply channels each connected to one end of the plurality of cooling channels;
a supply manifold flow path connected to the plurality of supply flow paths above the plurality of liquid discharge devices and distributing the cooling liquid to the plurality of supply flow paths;
a plurality of recovery channels each connected to the other end of the plurality of cooling channels;
defining a recovery manifold flow path that is connected to the plurality of recovery flow paths above the plurality of liquid discharge devices and that joins the cooling liquid from the plurality of recovery flow paths;
The cross-sectional area of the supply manifold flow path is smaller than the cross-sectional area of the recovery manifold flow path,
The plurality of liquid ejection devices are arranged in a staggered manner along the predetermined direction so as to form a first row arranged in a predetermined direction in a horizontal plane and a second row parallel to the first row,
The supply manifold channel is a liquid discharge unit that extends between the first row and the second row in parallel to the first row and the second row. The liquid according to claim 2, wherein the recovery manifold flow path extends parallel to the supply manifold flow path, with at least one of the plurality of liquid ejection devices sandwiched between the recovery manifold flow path and the supply manifold flow path. discharge unit. a plurality of liquid ejection devices each ejecting liquid to form an image on a medium;
a liquid channel member that supplies the liquid to the plurality of liquid ejection devices;
A liquid ejection unit comprising a cooling structure that cools the plurality of liquid ejection devices with a cooling liquid different from the liquid,
The cooling structure includes:
a plurality of cooling channels through which the cooling liquid flows, each of which is thermally connected to each of the plurality of liquid discharge devices;
a plurality of supply channels each connected to one end of the plurality of cooling channels;
a supply manifold flow path connected to the plurality of supply flow paths above the plurality of liquid discharge devices and distributing the cooling liquid to the plurality of supply flow paths;
a plurality of recovery channels each connected to the other end of the plurality of cooling channels;
defining a recovery manifold flow path that is connected to the plurality of recovery flow paths above the plurality of liquid discharge devices and that joins the cooling liquid from the plurality of recovery flow paths;
The cross-sectional area of the supply manifold flow path is smaller than the cross-sectional area of the recovery manifold flow path,
The liquid flow path member includes a plurality of flow path members that are connected to each of the plurality of liquid ejection devices and supply the liquid to each of the liquid ejection devices,
The supply flow path and the recovery flow path connected to each of the plurality of cooling flow paths extend upward at an angle with respect to the vertical direction and are connected to the supply manifold flow path and the recovery manifold flow path. Ori,
The supply flow path and the recovery flow path are inclined so that the distance between them increases as they move upward;
A liquid ejection unit, wherein the plurality of flow path members are arranged to extend upward from the liquid ejection device and pass between the supply manifold flow path and the recovery manifold flow path. The liquid ejection unit according to claim 1, wherein the cross-sectional area of each of the plurality of supply channels is smaller than the cross -sectional area of the supply manifold channel. The liquid ejection unit according to claim 1, wherein the cross-sectional area of each of the plurality of supply channels is equal to the cross-sectional area of each of the plurality of recovery channels. The liquid ejection unit according to any one of claims 1 to 6 , wherein the cross-sectional area of the recovery manifold flow path is at least twice the cross-sectional area of the supply manifold flow path. The liquid ejection unit according to any one of claims 1 to 7 , further comprising a holding member that holds the plurality of liquid ejection devices together. A liquid dispensing unit according to any one of claims 1 to 8 , wherein the cooling structure comprises a pump connected to the supply manifold flow path and the recovery manifold flow path.

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