EP3636438B1

EP3636438B1 - Inkjet head and inkjet recording device

Info

Publication number: EP3636438B1
Application number: EP18812806.0A
Authority: EP
Inventors: Hikaru Hamano
Original assignee: Konica Minolta Inc
Current assignee: Konica Minolta Inc
Priority date: 2017-06-09
Filing date: 2018-05-28
Publication date: 2021-08-11
Anticipated expiration: 2038-05-28
Also published as: WO2018225553A1; CN110709251B; EP3636438A4; EP3636438A1; JPWO2018225553A1; JP7078044B2; CN110709251A

Description

Technological Field

The present invention relates to an inkjet head and an inkjet recording device.

Background Art

Conventionally, there have been inkjet recording devices in which ink stored in a pressure chamber is jetted from multiple nozzles disposed on an inkjet head to form an image on a recording medium.
In such inkjet recording devices, problems such as a jetting error may be caused as the nozzles are clogged by air bubbles, foreign objects, etc. getting in the inkjet head. The viscosity of some kinds of ink may get higher around the nozzles due to precipitation of ink particles after suspension of use for a long time, which makes it harder to obtain a stable ink jetting performance.
In view of the above, there have been known inkjet heads with a flow path to circulate ink in the pressure chamber, in which air bubbles, foreign objects, etc. in the head can be ejected along with ink to the outside of the head (for example, see JP 5385975 B2 ).
For example, disclosed in JP 5385975 B2 is an inkjet head with individual ink ejection paths through which ink can be ejected respectively from the pressure chambers, and a common ink ejection path which the multiple individual ink ejection paths join.
US 2016/0288499 A discloses an inkjet head with a flow path unit that has plural nozzle groups disposed alongside each other in rows which extend parallel to the conveyance direction and are spaced apart in a scanning direction perpendicular to the conveyance direction. The inkjet head has plural orifice paths which each extend to a respective nozzle via a pressure chamber and a communication path from plural manifolds that extend in the conveyance direction respectively between and along a pair of adjacent rows. The ink is circulated in that it is supplied from a sub-tank, flows serially through the manifolds, and returns back to the sub-tank.
JP 2015-071289 A discloses an inkjet which includes common supply passages which supply recording liquid to pressure chambers, respectively, common return passages to which a part of the recording liquid in the pressure chambers returned, respectively, piezoelectric elements which generate pressure in the pressure chambers, respectively, and a nozzle plate. The droplet discharge head circulates the recording liquid supplied to the pressure chambers to the common return passages, and discharges droplets of the recording liquid from nozzle holes when pressure is generated in the pressure chambers. The common supply passages and the common return passages are respectively arranged on the same side with respect to the pressure chambers in a longitudinal direction of the pressure chambers.
DE 102005031646 A1 discloses an inkjet head with a pair of individual ink ejection paths leading from common ink ejection paths to each of a plurality of pressure chambers. The common ink ejection paths are arranged in the outermost zones adjacent to the outer surfaces/edges without any nozzle row in between.

SUMMARY

Technical Problem

As shown in FIG. 16, a head chip 1 includes therein nozzles 111, pressure chambers 131 disposed on the upper side of the nozzles 111, individual ink ejection paths 121 extended from the pressure chambers 131, common ink ejection paths 133 (first common ink ejection paths 134) which the individual ink ejection paths 121 join.
An outer surface DS of the head chip 1 as shown is an outer surface along the longitudinal direction of the head chip 1, and the nozzles 111 and the pressure chambers 131 connected thereto are disposed in rows (R1, R2). Two rows each including the nozzles 111 and the pressure chambers 131 connected thereto are disposed between the outer surface DS and the central plane DC that is central in the direction perpendicular to the outer surface DS, for example, as shown.
The common ink ejection paths 133 each extend in the direction along the outer surface DS so that the individual ink ejection paths 121 from the multiple pressure chambers 131 in a row in the direction along the outer surface DS join the common ink ejection path 133.
The area from the outer surface DS to the central plane DC of the head chip 1 described above is divided, for explanation, into zones D11 to D15 in the depth direction perpendicular to the outer surface DS toward the inside, as shown.
The thermal condition is not uniform between the zones D11 to D15, for the common ink ejection paths 133 have a cooling effect or an insulation effect due to a comparatively large amount of ink circulating therein. The temperature distribution TD in a case where a high heat source is present at an outer side of the outer surface is shown in the figure, for example. A higher temperature is shown by a darker color in the temperature distribution TD. The external heat is transferred more and the temperature gets higher in the zone D11 because the common ink ejection path 133 is not present in the area to the outer surface DS. In contrast, in the zone D13, the heat is transferred less than in the zone D11 and the temperature is relatively low because the common ink ejection path 133 is present there.
Thus, the ink temperature in the pressure chambers 131 in the zone D11 is relatively high, and the ink temperature in the pressure chambers 131 in the zone D13 is relatively low, vice versa in a case where heat is dissipated to the outside. In either case, the temperature of ink to be jetted is not equal, which may affect the image quality.
One of the two areas from the outer surface DS to the central plane DC is shown in FIG. 16, and the other area from the opposite outer surface to the central plane DC is typically symmetrically configured.
The present invention has been achieved in view of the above-described problems, and an object thereof is to provide an inkjet head and inkjet recording device that can alleviate the temperature difference between the pressure chambers in the head chip.

Solution to Problem

In order to achieve at least one of the abovementioned objects, the invention provides an inkjet head as defined in claim 1, including:

a plurality of nozzles from which ink is jetted;
a plurality of pressure chambers that stores ink and that respectively communicates with the plurality of nozzles;
a plurality of pressure generating means that is disposed corresponding to the respective plurality of pressure chambers and that applies pressure to the ink in the plurality of pressure chambers;
a plurality of individual ink ejection paths that is respectively branched from the plurality of pressure chambers and that is capable of ejecting the ink in the plurality of pressure chambers; and
a common ink ejection path to which the plurality of individual ink ejection paths is connected;
wherein the plurality of nozzles and the plurality of pressure chambers are arrayed in a plurality of rows in a direction along two opposite outer surfaces of a head chip,
wherein the plurality of rows is disposed in parallel in a direction perpendicular to the outer surfaces,
wherein the common ink ejection path extends in the direction along the two outer surfaces,
wherein the common ink ejection path is disposed only in outermost zones adjacent to the respective two outer surfaces without the plurality of rows in between and/or a central zone between the two outer surfaces.

Preferably, the plurality of rows is three or more rows.
Preferably, the plurality of rows is even-numbered rows.
Preferably, each of the plurality of individual ink ejection paths is disposed between adjacent two of the plurality of pressure chambers in one of the plurality of rows, and connects the common ink ejection path to one of the plurality of pressure chambers in another of the plurality of rows that is on an opposite side of the one row from the common ink ejection path.
Preferably, the head chip includes a nozzle plate in which the plurality of nozzles is disposed, a flow path spacer plate in which the plurality of individual ink ejection paths is disposed, and a pressure chamber plate in which the plurality of pressure chambers is disposed, in which the nozzle plate, the flow path spacer plate and the pressure chamber plate are layered in a written order.
Preferably, the plurality of pressure chambers and air chambers isolated from an ink flow path are disposed alternately in each of the plurality of rows, wherein the plurality of individual ink ejection paths overlaps the air chambers viewed from an axial direction of the plurality of nozzles.
Preferably, the plurality of individual ink ejection paths are disposed such that at least two individual ink ejection paths are provided for each of the plurality of pressure chambers.
According to the invention, the common ink ejection path is disposed in both of the outermost zones.
According to the invention, the common ink ejection path is disposed in the central zone.
Preferably, the common ink ejection path includes two common ink ejection paths that are disposed in the central zone without the plurality of rows in between.
In order to achieve at least one of the abovementioned objects, the invention also provides an inkjet recording device recited in claim 11, including:

the inkjet head according to the invention; and
an ink supplying means for generating a circulation flow from the plurality of pressure chambers to the plurality of individual ink ejection paths.

Advantageous Effects of Invention

According to the present invention, provided is an inkjet head and inkjet recording device that can alleviate the temperature difference between the pressure chambers in the head chip.

Brief Description of Drawings

FIG. 1 is a schematic drawing of an inkjet recording device.
FIG. 2 is a bottom view of a head unit.
FIG. 3A is a perspective view of an inkjet head.
FIG. 3B is a cross-sectional view of the inkjet head.
FIG. 4 is an exploded perspective view of the inkjet head.
FIG. 5 is an exploded perspective view of the head chip.
FIG. 6A is a plan view of the pressure chamber plate.
FIG. 6B is a bottom view of the pressure chamber plate.
FIG. 7A is a plan view of the flow path spacer plate.
FIG. 7B is a bottom view of the flow path spacer plate.
FIG. 8 is a plan view of the nozzle plate.
FIG. 9A is a cross-sectional view of the head chip taken along IXA-IXA.
FIG. 9B is a cross-sectional view of the head chip taken along IXB-IXB.
FIG. 10A is a cross-sectional view of the head chip taken along XA-XB.
FIG. 10B is a cross-sectional view of the head chip taken along XA-XB.
FIG. 11 schematically shows an ink circulation system.
FIG. 12 is a schematic planar view of an exemplary disposition of components in the head chip.
FIG. 13 is a schematic planar view of another exemplary disposition of components in the head chip.
FIG. 14 is a schematic planar view of another exemplary disposition of components in the head chip.
FIG. 15 is a schematic planar view of another exemplary disposition of components in the head chip (not according to the invention as claimed).
FIG. 16 is a schematic planar view of the disposition of components in a head chip in a comparative example.

Description of Embodiments

Hereinafter described is an embodiment of the present invention with reference to the drawings. The scope of the invention is not limited to the illustrated examples, the invention is defined in the appended claims. In this description, the direction of the printing width, which is the direction of the disposition of nozzles 111 of an inkjet head 100, is referred to as the left-right direction, the direction of conveyance of a recording medium under the nozzles 111 is referred to as the front-back direction, and the direction perpendicular to the left-right direction and the front-back direction is referred to as the up-down direction, for convenience of explanation. The arrows in the flow path in the drawings indicate the direction of ink flow.

[Inkjet Recording Device]

The inkjet recording device 200 includes a sheet feeder 210, an image recorder 220, a sheet ejection unit 230, and an ink circulation system 8 as an ink supplying means (see FIG. 11), as shown in FIG. 1. In the inkjet recording device 200, the recording medium M stored in the sheet feeder 210 is conveyed to the image recorder 220, and an image is formed on the recording medium M with the image recorder 220. Then, the recording medium M on which the image is formed is conveyed to the sheet ejection unit 230.
The sheet feeder 210 includes a sheet feeding tray 211 that stores recording media M, and a medium feeder 212 that conveys recording media M from the sheet feeding tray 211 to the image recorder 220 to feed them. The medium feeder 212, which includes a circle belt supported inside by two rollers, rotates the rollers with the recording medium M being placed on the belt so as to convey the recording medium M from the sheet feeding tray 211 to the image recorder 220.
The image recorder 220 includes a conveyance drum 221, a bridging unit 222, a heater 223, a head unit 224, a fixing unit 225, and a delivery unit 226.
The conveyance drum 221 is in a cylindrical shape, and its peripheral surface serves as a conveyance surface to place the recording medium M thereon. The conveyance drum 221 rotates in the arrow direction in FIG. 1 with the recording medium M being held on the conveyance surface so as to convey the recording medium M along the conveyance surface. The conveyance drum 221, which further includes a nail part and an air suction part (not shown in the drawings), presses the edge of the recording medium M with the nail part and draws the recording medium M with the air suction part to hold the recording medium M on the conveyance surface.
The bridging unit 222, which is disposed between the medium feeder 212 of the sheet feeder 210 and the conveyance drum 221, picks up one edge of the recording medium M conveyed from the medium feeder 212 by holding it with a swing arm 222a, and delivers it to the conveyance drum 221 through the bridging drum 222b.
The heater 223, which is disposed between the position of the bridging drum 222b and the position of the head unit 224, heats the recording medium M conveyed by the conveyance drum 221 so that the said recording medium M is at a temperature in a predetermined zone. The heater 223 includes an infrared heater, for example, and applies electric power to the infrared heater according to a control signal provided by the controller (not shown in the drawings) to cause the heater to generate heat.
The head unit 224 forms an image by jetting ink onto the recording medium M on the basis of image data at appropriate timings according to the rotation of the conveyance drum 221 holding the recording medium M. The head unit 224 is disposed such that the ink jetting surface faces the conveyance drum 221 at a predetermined interval. The inkjet recording device 200 in the present embodiment includes four head units 224 respectively corresponding to four colors of ink, yellow (Y), magenta (M), cyan (C), and black (K), which are disposed at predetermined intervals in the order of Y, M, C, and K from the upstream side in the conveyance direction of the recording medium M.
In the head unit 224, two sets of inkjet heads 100 next to each other yet positioned alternately in the front-back direction are disposed in a staggered pattern, for example, as shown in FIG. 2. The head unit 224 is used at a fixed position relative to the rotation axis of the conveyance drum 221 in image recording. Specifically, the inkjet recording device 200 records an image in a single-pass imaging method by using line heads.
The fixing unit 225, which includes a light emitter disposed over the width in the direction X of the conveyance drum 221, irradiates the recording medium M placed on the conveyance drum 221 with energy beam such as ultraviolet rays from the light emitter to solidify and fix ink jetted on the recording medium M. The light emitter of the fixing unit 225 is disposed to face the conveyance surface on the downstream side of the position of the head units 224 and on the upstream side of the position of the bridging drum 226a of the delivery unit 226 in the conveyance direction.
The delivery unit 226, which includes a belt loop 226b of a circle belt supported inside by two rollers and a bridging drum 226a in a cylindrical shape to transfer the recording medium M from the conveyance drum 221 to the belt loop 226b, conveys, with the belt loop 226b, the recording medium M transferred from the conveyance drum 221 to the belt loop 226b by the bridging drum 226a to send the said recording medium M to the sheet ejection unit 230.
The sheet ejection unit 230 includes a sheet ejection tray 231 in a plate shape on which recording media P sent out from the image former 220 by the delivery unit 226 are placed.

[Inkjet Head]

The inkjet head 100 in the present embodiment includes, as shown in FIGs. 3A, 3B, 4, etc., a head chip 1, a wiring plate 2 on which the head chip 1 is set, a driving circuit plate 4 connected with the wiring plate 2 via a flexible plate 3, a manifold 5 for storing ink to be supplied to the pressure chamber 131 in the head chip 1, a casing 6 in which the manifold 5 is housed, a cap receiving board 7 attached to cover the bottom opening of the casing 6, and a cover 9 attached to the casing 6.
The manifold 5 is not shown in FIG. 3A, and the cover 9 is not shown in FIGs. 3B and 4.
The present embodiment is based on an example in which the number of the rows of the nozzles 111 of the head chip 1 is four.
The head chip 1 is substantially in a square pillar shape that is long in the left-right direction. The head chip 1 includes a pressure chamber plate 13, a flow path spacer plate 12, and a nozzle plate 11, which are layered in the written order (FIGs. 5 to 11).
The pressure chamber plate 13 includes the pressure chambers 131, the air chambers 132, and the common ink ejection paths 133 (see FIGs. 5, 6A, 6B, etc.).
The pressure chambers 131 and the air chambers 132 are disposed in a large number alternately in the left-right direction in four rows in the front-back direction.
Each pressure chamber 131, which has a substantially rectangular cross section, is formed along the up-down direction with an inlet on the upper surface of the pressure chamber plate 13 and an outlet on the lower surface. The pressure chamber 131 communicates with an ink storage 51 at the upper end, and ink is supplied from the ink storage 51 to the pressure chamber 131, and the pressure chamber 131 stores the ink to be jetted from the nozzle 111 therein. The pressure chamber 131 is formed along the up-down direction across the pressure chamber plate 13 and the flow path spacer plate 12 such that it has substantially rectangular cross-sections equal in area, and communicates with the nozzle 111 at the lower end (see FIGs. 9A, 9B, etc.).
Each air chamber 132, which has a substantially rectangular cross section slightly larger than that of the pressure chamber 131, is formed in parallel to the pressure chamber 131 in the up-down direction. The air chamber 132 does not communicate with the ink storage 51, unlike the pressure chamber 131, so that ink does not flow into the air chamber 132. The air chamber 132 does not communicate with the nozzle 111, either (see FIGs. 9A, 9B, etc.).
The pressure chamber 131 and the air chamber 132 are separated by a partition 136 which is a pressure generating means made of a piezoelectric material (see FIG. 10A). Driving electrodes not shown in the drawings are disposed on the partition 136, and pressure is applied to ink in the pressure chamber 131 by repetitive displacement in the shear mode at the partition 136 between the adjacent pressure chambers 131 when voltage is applied to the driving electrodes. Among the pressure chambers 131 shown in FIGs. 5 to 10, etc., the pressure chamber 131 with the partition 136 on one side only, which is positioned at the end in the left-right direction, is not used, and the other pressure chambers 131 with the partitions 136 on both sides are used.
It is possible not to provide the air chambers 132 and to provide only the pressure chambers 131. However, the pressure chambers 131 and the air chambers 132 are preferably disposed alternately, as described above. This allows the pressure chambers 131 not to be adjacent to each other, and, as a result, deformation of the partition 136 adjacent to a certain pressure chamber 131 may be prevented from affecting the other pressure chambers 131.
Each common ink ejection path 133 is constituted by the first common ink ejection path 134 and a second ink ejection path 135 communicating with each other (see FIGs. 5, 6B, etc.).
The first common ink ejection paths 134 are disposed in three rows on the front and back sides and in the middle thereof of the head chip 1 along the left-right direction on the lower surface of the pressure chamber plate 13, away from where the pressure chambers 131 and the air chambers 132 are disposed. The multiple individual ink ejection paths 121 disposed on the flow path spacer plate 12 are connected to the lower surface of each first common ink ejection path 134 such that ink flowing from the individual ink ejection paths 121 (the second individual ink ejection paths 123) canjoin together in the first ink ejection path 134 (FIGs. 6B, 7A, and 9A). The first common ink ejection path 134 is connected, near the right end, to the second ink ejection path 135 through which ink can be ejected out of the head chip 1. Accordingly, the first common ink ejection path 134 is a flow path through which ink flowing from the individual ink ejection paths 121 (the second individual ink ejection paths 123) flows to the second common ink ejection path 135.
Each second common ink ejection path 135 is formed in the up-down direction similarly to the pressure chambers 131. The second common ink ejection path 135, which communicates with the first common ink ejection path 134 at the lower surface part of the pressure chamber plate 13 and communicates with a waste liquid chamber 57 at the top surface part, serves as a flow path through which ink flowing from the first common ink ejection path 134 is to be ejected to the upper side (the opposite side from the nozzle plate 11) to the outside of the head chip 1. As the second common ink ejection path 135 has a volume greater than each of the pressure chambers 131, the ink ejection efficiency may be improved.
The pressure chambers 131 and the individual ink ejection paths 121 branched from the pressure chambers 131 are formed on the flow path spacer plate 12 (see FIGs. 5, 7A, 7B, 9A, 9B, etc.).
Each pressure chamber 131 is formed in the up-down direction with a substantially rectangular cross section of a constant area across the flow path spacer plate 12 and the pressure chamber plate 13.
Each individual ink ejection path 121, which communicates with the pressure chamber 131 at one end and communicates with the first common ink ejection path 134 at the other end, serves as a flow path through which ink in the pressure chamber 131 is ejected to the first common ink ejection path 134.
The individual ink ejection paths 121 are preferably at least two in number for each of the pressure chambers 131 in view of making it easier to eject air bubbles and foreign objects along with ink. It is preferred to provide a single individual ink ejection path 121 each in the front direction and in the back direction of the pressure chamber 131, two in total, as shown in FIGs. 9A and 9B, for example, because it is possible to obtain the effect of making it easier to eject air bubbles and foreign objects along with ink as well as a high manufacturing efficiency.
Each individual ink ejection path 121 is constituted by the first individual ink ejection path 122 and the second individual ink ejection path 123 that are connected together. The first individual ink ejection path 122 is connected to the pressure chamber 131 at one end and extends in the front-back direction on the lower surface part of the flow path spacer plate 12. The second individual ink ejection path 123 is connected to the other end of the first individual ink ejection path 122, and extends upward to be connected to the first common ink ejection path 134.
The disposition of the nozzles 111, the pressure chambers 131, the air chambers 132, the individual ink ejection path 121, and the common ink ejection paths 133 (first common ink ejection paths 134) described above viewed in the axial direction of the nozzles 111 is described with reference to the schematic drawings of FIGs. 12 to 15. The disposition is intended for alleviation of the temperature difference in the pressure chambers in the head chip 1.
In the head chip 1 shown in FIG. 12, the multiple nozzles 111 and the multiple pressure chambers 131 are arrayed in rows (hereinafter referred to as "channel row") in the direction (the left-right direction) along the two outer surfaces DS, DS of the head chip 1 opposite to each other to form four channel rows (R1 to R4) lined in the direction perpendicular to the outer surfaces DS (the front-back direction).
The first common ink flow paths 134 extend in the direction along the two outer surface DS, DS (the left-right direction).
The area from one outer surface DS to the other outer surface DS of the head chip 1 is divided, for explanation, into zones D1 to D7 in the depth direction from the outer surface DS perpendicularly to the inside as shown in the drawings.
The first common ink ejection path 134 is disposed both in the outermost zones (D1 + D2, D6 + D7) next to either of the outer surfaces DS without any channel rows R1 to R4 in between and in the central zone D4 between the two outer surfaces DS, DS, exclusively.
That is, the first common ink ejection paths 134 are disposed in the zones D2, D4, and D6. The zones D1 and D7 are the outer walls to the outer surfaces DS. The channel rows R1 and R2 are disposed in the zone D3 between the zone D2 and the central zone D4. The two channel rows R3 and R4 are disposed in the zone D5 between the zone D6 and the central zone D4. The number of channel rows R1 to R4 is an even number of three or more. The even-numbered channel rows make it possible to provide the first common ink ejection path 134 extending in the central plane DC and to provide the equal number of channel rows on the both sides of the central plane DC. In that way, the thermal condition can be balanced.
Some of the individual ink ejection paths 121 are each disposed between adjacent pressure chambers 131, 131 in one row, and connect a first common ink ejection path 134 to a pressure chamber 131 in another row on the opposite side of the one row from the first common ink ejection path 134.
For example, an explanation is given as follows assuming that the one row described above is the channel row R1. The individual ink ejection path 121 disposed between the adjacent pressure chambers 131, 131 in the channel row R1 connects the first common ink ejection path 134 in the zone D2 to the pressure chamber 131 in the channel row R2.
An explanation is given as follows assuming that the one row described above is the channel row R2. The individual ink ejection path 121 disposed between the adjacent pressure chamber 131, 131 in the channel row R2 connects the first common ink ejection path 134 in the zone D4 to the pressure chamber 131 in the channel row R1.
The same applies to the zone D5.
The structure described above allows the pressure chambers 131 in each of the channel rows R1 to R4 to be connected to the first common ink ejection paths 134, 134 on the both sides by the individual ink ejection paths 121 extended both in the front and back directions. This can improve circulation of ink, and alleviate the temperature difference in the head chip 1.
The channel row is configured such that the pressure chambers 131 and the air chambers 132 separate from the ink flow path are disposed alternately as described above. As shown in FIG. 12, the individual ink ejection paths 121 overlap the air chambers 132 in a view in the axial direction of the nozzles 111 (the up-down direction). This improves the thermal conductivity.
The head chip 1 configured as described above alleviates the temperature difference in the zone D3 and in the zone D5, and also the temperature difference between the zones D3 and D5.
For example, the temperature distribution TD in a case where a heat source is placed at the outer side of the outer surface DS is shown in the drawings. A higher temperature is shown by a darker color in the temperature distribution TD. The external heat is transferred and the temperature gets higher in the zones D1 and D7 because the first common ink ejection paths 134 are not present in the areas to the outer surface DS. In contrast, in the ranges D3 and D5, the heat is transferred less than in the zone D1, and the temperature is relatively low because the common ink ejection path 133 is present there. However, the temperature in the zones D3 and D5 is equalized because the thermal condition, i.e. the number of the common ink ejection paths 133 in the area to the outer surfaces DS, is equal. In a case where the heat is dissipated to the outside, the reversal effect is obtained, and the temperature is lower in the zones D1 and D7 than in the zones D3 and D5, but the temperature in the zones D3 and D5 is equalized.
Thus, the temperature difference in the pressure chambers 131 in the channel rows R1 to R4 is alleviated, and the temperature of ink to be jetted is equalized, which can solve one of the thermal issues affecting the image quality.
FIGs. 13 to 15 are modifications of the structure shown in FIG. 12.
FIG. 13 shows a structure in which one individual ink ejection path 121 extends from each pressure chamber 131 and is connected to the first common ink ejection path 134 nearby. As the thermal condition, i.e. the number of common ink ejection paths 133 in the area to the outer surface DS, is equal also in the head chip 1 of such a structure, the temperature in the zones D3 and D5 including the channel rows R1 to R4 is equalized.
FIG. 14 shows a structure in which two of the first common ink ejection paths 134 are disposed in the central zone D4 without a channel row in between, and FIG. 15 shows a structure in which the common ink ejection path 133 is not disposed in the central zone D4 (not according to the invention as claimed). Whether the common ink ejection path is provided in the central zone D4, and if it is, the number of common ink ejection paths do not affect the thermal condition, i.e. the number of the common ink ejection paths 133 in the area to the outer surface DS. Thus, the temperature in the zones D3 and D5 including the channel rows R1 to R4 is equalized.
In the head chip 1 shown in FIG. 14, no channel row is disposed between the two first common ink ejection paths 134, 134 in the central zone D4. That is because, if a channel row is disposed there, the thermal condition, i.e. the number of common ink ejection paths 133 in the area to the outer surface DS, differs between the channel row and the other channel rows.
As described above with reference to FIGs. 12 to 15, it is possible to alleviate the temperature difference in the pressure chambers 131 in the head chip 1.
The first ink ejection paths 122 in the present embodiment are disposed on the lower surface part of the flow path spacer plate 12 next to the nozzle plate 11, though not limited thereto. For example, the first individual ink ejection paths 122 may be disposed across the nozzle plate 11 and the flow path spacer plate 12 or only in the nozzle plate 11. Alternatively, the first individual ink ejection paths 122 may be disposed slightly above the bottom surface of the flow path spacer plate 12 such that they are not adjacent to the nozzle plate 11.
The circuit plate 2 is disposed on the upper surface of the head chip 1, and two flexible plates 3 connected to the driving circuit plate 4 are disposed at the both edges in the front-back direction of the wiring plate 2, as shown in FIG. 4.
The wiring plate 2 is formed in a shape of a substantially rectangular plate that is long in the left-right direction, and has an opening 22 at the substantially central part. The widths of the wiring plate 2 in the left-right and front-back directions are each longer than those of the head chip 1.
The opening 22 is formed in a substantially rectangular shape that is long in the left-right direction, and exposes to the upper side the inlets of the pressure chambers 131 and the outlets of the second common ink ejection paths 135 in the head chip 1, in a state where the head chip 1 is attached to the wiring plate 2.
The flexible plate 3 electrically connects the driving circuit plate 4 and the electrodes of the wiring plate 2, and signals from the driving circuit plate 4 can be applied to the driving electrodes disposed on the partitions 136 in the head chip 1 via the flexible plate 3.
The lower end of the manifold 5 is fixed on the periphery of the wiring plate 2 by adhesion. That is, the manifold 5 is disposed on the inlet side (the upper side) of the pressure chambers 131 in the head chip 1 and is connected to the head chip 1 via the wiring plate 2.
The manifold 5 is a member made of resin disposed on the upper side of the pressure chambers 131 of the head chip 1, and stores ink to be introduced into the pressure chambers 131. Specifically, the manifold 5 is long in the left-right direction, and includes a main body 52 that is hollow as the ink storage 51, and the first to fourth ink ports 53 to 56. The ink storage 51 is divided into a first liquid chamber 51a on the upper side and a second liquid chamber 51b on the lower side by a filter F to remove dust in ink.
A first ink port 53 communicates with the first liquid chamber 51a at the upper right end, and is used to introduce ink into the ink storage 51. A first joint 81a is attached to the tip of the first ink port 53.
A second ink port 54 communicates with the first liquid chamber 51a at the upper left end, and is used to remove air bubbles in the first liquid chamber 51a. The second joint 81b is attached to the tip of the second ink port 54.
The third ink port 55 communicates with the second liquid chamber 51a at the upper left end, and is used to remove air bubbles in the second liquid chamber 51b. The third joint 82a is attached to the tip of the third ink port 55.
The fourth ink port 56 communicates with the liquid chamber for ejection 57 communicating with the second common ink ejection path 135 in the head chip 1, and ink ejected from the head chip 1 is ejected to the outside of the inkjet head 100 through the fourth ink port 56.
The casing 6 is a member made of aluminum by the die casting method, for example, and is long in the left-right direction. The casing 6 is formed to house the manifold 5 to which the head chip 1, the wiring plate 2, and the flexible plate 3 are attached, and the casing 6 is open on the bottom surface. An attachment hole 68 for attachment of the casing 6 to the printer main body is each formed at the both ends of the casing 6 in the left-right direction.
The cap receiving board 7 has an opening for nozzles 71 which are long in the left-right direction and formed at the substantially central part, and is attached to cover the bottom opening of the casing 6 such that the nozzle plate 11 is exposed through the opening for nozzles 71.

[Ink Circulation System]

The ink circulation system 8 is an ink supplying means for generating a circulating flow of ink from the pressure chambers 131 to the individual ink ejection paths 121 in the inkjet head 100. The ink circulation system 8 includes a sub tank for ink supply 81, a sub tank for circulation 82, and a main tank 83 (FIG. 11).
The sub tank for ink supply 81 is loaded with ink to be supplied to the ink storage 51 of the manifold 5, and is connected to the first ink port 53 by the ink flow path 84.
The sub tank for circulation 82 is loaded with ink ejected from the liquid chamber for ejection 57 of the manifold 5, and is connected to the fourth ink port 56 by the ink flow path 85.
The sub tank for supply 81 and the sub tank for circulation 82 are disposed at positions different in the up-down direction (the gravitational direction) from the nozzle surface of the head chip 1 (hereinafter also referred to as "the positional reference surface"). This generates a pressure P1 caused by difference in hydraulic head between the positional reference surface and the sub tank for supply 81 and a pressure P2 caused by difference in hydraulic head between the positional reference surface and the sub tank for circulation 82.
The sub tank for supply 81 and the sub tank 82 for circulation 82 are connected to each other by the ink flow path 86. The pressure applied by the pump 88 can return ink from the sub tank for circulation 82 to the sub tank for supply 81.
The main tank 83 is loaded with ink to be supplied to the sub tank for supply 81, and is connected to the sub tank for supply 81 by the ink flow path 87. The pressure applied by the pump 89 can supply ink from the main tank 83 to the sub tank for supply 81.
The amount of ink loaded in each sub tank and the position in the up-down direction (the gravitational direction) of each sub tank may be suitably modified so as to adjust the pressure P1 and the pressure P2. The gap between the pressure P1 and the pressure P2 can cause ink in the inkjet head 100 to circulate at a suitable circulation flow speed. In that way, air bubbles and foreign objects in the head chip 1 can be removed and clogging of the nozzle 111 and a jetting error can be suppressed.
While a method of controlling ink circulation by difference in hydraulic head is described as an example of the ink circulation system 8, the configuration may be suitably modified as long as it can generate a circulation flow of ink.

[Other]

The embodiment of the present invention described above is merely an example in every respect and not limitative in any way. Thus, the scope of the present invention should not be defined by the descriptions given above but by terms of the appended claims.
For example, one of the flow path walls of the first ink ejection paths 122 is formed by the nozzle plate 11, though not limited thereto.
The nozzle plate 11, the flow path spacer plate 12, and the pressure chamber plate 13 layered in the written order are shown as an example of the head chip 1 in the present embodiment, though not limited thereto. The head chip 1 may have a two-layer structure of the nozzle plate 11 and the pressure chamber plate 13. In that case, the individual ink ejection paths 121 may be provided to at least one of the nozzle plate 11 and the pressure chamber plate 13.
The inkjet head 100 in the present embodiment is, for example, of the shear mode type, though not limited thereto, as long as it has a means to apply pressure to ink in the pressure chambers 131.
A single-pass imaging system using line heads is shown as an example of the imaging system of the inkjet recording device 200 in the present embodiment, though not limited thereto, and a scanning-system may be employed.
Ink inside the head chip 1 is circulated as an example of the ink circulation system 8 in the present embodiment. Alternatively, ink in the second common ink ejection paths 135 may be ejected without being circulated, or may be ejected or circulated by choice.
The head chip 1 in the present embodiment is, for example, of a straight type in which the pressure chamber 131 and the second common ink ejection path 135 open on the upper and lower surfaces, though not limited thereto. For example, they may open on any of the lateral surfaces in the up-down and left-right directions of the head chip 1, or may have a bending part that changes the direction of ink flow halfway on the flow path.
In the head chip 1 shown in FIGs. 12 to 15, two rows are disposed on each side of the central plane DC, making four rows in total, though not limited thereto. Alternatively, three or more rows may be disposed on one side of the central plane DC.
In the head chip 1 shown in FIGs. 12 to 15, the channel rows in even number are disposed, though not limited thereto. The channel rows in odd number of three or more may be disposed. For example, in the head chip 1 shown in FIG. 15, a channel row may be disposed in the central zone D4, and the same number of channel rows may be disposed on each side thereof. The number of common ink ejection paths 133 in the area to the outer surfaces DS, i.e. the thermal condition, is equal also in that case.

Industrial Applicability

The present invention is applicable to an inkjet head and an inkjet recording device.

Reference Signs List

1: Head Chip
8: Ink Circulation System (Ink Feeder)
11: Nozzle Plate
111: Nozzle
12: Flow Path Spacer Plate
121: Individual Ink Ejection Path
122: First Individual Ink Ejection Path
123: Second Individual Ink Ejection Path
13: Pressure Chamber Plate
131: Pressure Chamber
132: Air Chamber
133: Common Ink Ejection Path
134: First Common Ink Ejection Path
135: Second Common Ink Ejection Path
136: Partition (Pressure Generating Means)
100: Inkjet Head
200: Inkjet Recording Device

Claims

An inkjet head (100), comprising:
a plurality of nozzles (111) from which ink can be jetted;

a plurality of pressure chambers (131) that are configured to store ink and that respectively communicate with the plurality of nozzles (111);

a plurality of pressure generating means (136) that is disposed corresponding to the respective plurality of pressure chambers (131) and that is configured to apply pressure to the ink in the plurality of pressure chambers (131) ;

a plurality of individual ink ejection paths (121) that is respectively branched from the plurality of pressure chambers (131) and that is capable of ejecting the ink in the plurality of pressure chambers (131); and

a plurality of common ink ejection paths (133) to which the individual ink ejection paths (121) are connected,

wherein the plurality of nozzles (111) and the plurality of pressure chambers (131) are arrayed in a plurality of rows (R1,R2,R3,R4) in a direction along two opposite outer surfaces (DS) of a head chip (1),

wherein the plurality of rows (R1,R2,R3,R4) is disposed in parallel in a direction perpendicular to the outer surfaces (DS),

wherein the plurality of common ink ejection paths (133) extends in the direction along the two outer surfaces (DS),

characterised in that

the common ink ejection paths (133) are disposed only in both outermost zones (D1,D2,D6,D7) adjacent to the respective two outer surfaces (DS) without the plurality of rows (R1,R2,R3,R4) in between the respective common ink ejection path (133) and the respective outer surface (DS) and in a central zone (D4) between the two outer surfaces (DS).
The inkjet head (100) according to claim 1, wherein the plurality of rows (R1,R2,R3,R4) is three or more rows.
The inkjet head (100) according to claim 1 or 2, wherein the plurality of rows (R1,R2,R3,R4) is even-numbered rows.
The inkjet head (100) according to any one of claims 1 to 3, wherein each of the plurality of individual ink ejection paths (121) is disposed between adjacent two of the plurality of pressure chambers (131) in one of the plurality of rows (R1,R2,R3,R4), and connects the common ink ejection path (133) to one of the plurality of pressure chambers (131) in another of the plurality of rows (R1,R2,R3,R4) that is on an opposite side of the one row from the common ink ejection path (133).
The inkjet head (100) according to any one of claims 1 to 4, wherein the head chip (1) comprises a nozzle plate (11) in which the plurality of nozzles (111) is disposed, a flow path spacer plate (12) in which the plurality of individual ink ejection paths (121) is disposed, and a pressure chamber plate (13) in which the plurality of pressure chambers (131) is disposed, in which the nozzle plate (11), the flow path spacer plate (12) and the pressure chamber plate (13) are layered in a written order.
The inkjet head (100) according to any one of claims 1 to 5,
wherein the plurality of pressure chambers (131) and a plurality of air chambers (132) isolated from an ink flow path are disposed alternately in each of the plurality of rows (R1,R2,R3,R4),
wherein the plurality of individual ink ejection paths (121) overlaps the air chambers (132) viewed from an axial direction of the plurality of nozzles (111).
The inkjet head (100) according to any one of claims 1 to 6, wherein the plurality of individual ink ejection paths (121) are disposed such that at least two individual ink ejection paths (121) are provided for each of the plurality of pressure chambers (131).
The inkjet head (100) according to any one of claims 1 to 7, wherein the common ink ejection paths (133) comprise two common ink ejection paths (133) that are disposed in the central zone (D4) without the plurality of rows (R1,R2,R3,R4) in between.
An inkjet recording device (200), comprising:
the inkjet head (100) according to any one of claims 1 to 8; and

an ink supplying means (8) for generating a circulation flow from the plurality of pressure chambers (131) to the plurality of individual ink ejection paths (121).