Inkjet recording apparatus

Abstract

This invention relates to inkjet recording apparatus. It improves the collection efficiency of ink mist using a cyclone separator. The mist collector includes: a nozzle that draws air in from an intake port and discharges air from an outlet port; and a cyclone separator having an outer cylinder and an inner cylinder. The inner cylinder has an intake port, and the air drawn in through this intake port forms an airflow inside the inner cylinder, thereby separating ink mist from the air.

Description

Technical Field

[0001] This invention relates to inkjet recording apparatus. Background Technology

[0002] An inkjet recording device is a device that forms an image on a recording medium by having ink ejected from an inkjet head adhere to it. Not all the ink ejected from the inkjet head contributes to image formation; some becomes ink mist and floats on the surface.

[0003] Because ink mist consists of tiny ink droplets, it is easily swept away by the surrounding airflow. If the ink mist swept away by the airflow deviates from its designated path and adheres to the recording medium, it will lead to a decrease in image quality. In addition, if ink mist adheres to parts other than the recording medium, it will cause ink contamination in the inkjet recording device. Therefore, inkjet recording devices are equipped with mist collectors to collect ink mist.

[0004] Patent Document 1 describes a technique for separating and collecting ink mist that moves with an airflow from the air using centrifugal force. In the technique described in Patent Document 1, a spiral airflow is generated inside the shell of a cyclone separator, and the centrifugal force generated when the airflow swirls causes the ink mist to adhere to the inner wall of the shell of the cyclone separator, thereby separating the ink mist from the air.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2014-151642 Summary of the Invention

[0008] The problem that the invention aims to solve

[0009] Ink mist is generated when ink is ejected from the inkjet head, but the particle size of the generated ink mist varies. In the technology described in Patent Document 1, a filter is used to capture ink mist that has not been completely removed by a cyclone separator using centrifugal separation. In this case, in order to reduce the frequency of filter replacement, it is required to separate the smaller ink mist particles from the air before the ink mist reaches the filter.

[0010] The present invention was made to solve the above-mentioned problems, and its purpose is to provide an inkjet recording device that can improve the collection efficiency of ink mist using a cyclone separator.

[0011] Solution for solving the problem

[0012] The inkjet recording apparatus of the present invention includes a mist collector for collecting ink mist, wherein the mist collector comprises: a nozzle that draws in air containing ink mist from an intake port and discharges it from an outlet port; and a cyclone separator having an outer cylinder connected to the outlet port of the nozzle and an inner cylinder disposed inside the outer cylinder, the cyclone separator forming a first airflow between the outer cylinder and the inner cylinder using air drawn into the interior of the outer cylinder through the outlet port, thereby separating ink mist from the air. The inner cylinder has an intake port for drawing air into the interior of the inner cylinder, and forming a second airflow inside the inner cylinder using air drawn in through the intake port, thereby separating ink mist from the air.

[0013] Invention Effects

[0014] According to the present invention, the collection efficiency of ink mist collected by cyclone separator can be improved. Attached Figure Description

[0015] Figure 1 This is a schematic perspective view of an inkjet recording apparatus according to an embodiment of the present invention.

[0016] Figure 2 It means Figure 1 A schematic diagram of the internal structure of the inkjet recording device is shown.

[0017] Figure 3 This is a perspective view of the mist collector of this embodiment, viewed from the upstream side in the paper conveying direction.

[0018] Figure 4 This is a perspective view of the mist collector of this embodiment as viewed from the downstream side in the paper conveying direction.

[0019] Figure 5 This is a longitudinal sectional view (one) of the fog collector of this embodiment.

[0020] Figure 6 This is a perspective view showing the structure of the cyclone separator and filter unit included in the fog collector of this embodiment.

[0021] Figure 7 This is a cross-sectional view of the cyclone separator of this embodiment.

[0022] Figure 8 This is a longitudinal sectional view (second one) of the fog collector of this embodiment.

[0023] Figure 9 This is a side view showing the state of the cyclone separator after the outer cylinder has been removed, so that the inner cylinder of the cyclone separator can be seen.

[0024] Figure 10 This is a perspective view of the second section of the inner cylinder, cut parallel to the horizontal plane.

[0025] Figure 11 This is a side view showing the structure of a cyclone separator before the inner and outer plates are installed in the second section of the inner cylinder.

[0026] Figure 12 This is a side view showing the structure of a cyclone separator with the inner plates installed after the second section of the inner cylinder.

[0027] Figure 13 This is a graph showing the results of a simulation of the airflow in a cyclone separator.

[0028] Figure 14 This is a cross-sectional view showing an example of the movement trajectory of ink mist with different particle sizes.

[0029] Figure 15 This is a graph showing the simulation results of particle tracking in the fog collector of this embodiment.

[0030] Explanation of reference numerals in the attached figures

[0031] 10 Inkjet Recording Device

[0032] 22 Fog Collectors

[0033] 31 Nozzles

[0034] 32 Cyclone Separator

[0035] 33 Suction port

[0036] 34 Discharge outlets

[0037] 41 outer cylinder

[0038] 42 Inner cylinder

[0039] 57 Suction port

[0040] 59. Protrusion

[0041] 59a Above

[0042] 59b below

[0043] 61 First airflow

[0044] 62 Second airflow Detailed Implementation

[0045] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In this specification and the accompanying drawings, elements having substantially the same function or structure are labeled with the same reference numerals, and repeated descriptions are omitted.

[0046] <Structure of an inkjet recording device>

[0047] Figure 1This is a schematic perspective view of an inkjet recording apparatus according to an embodiment of the present invention.

[0048] like Figure 1 As shown, the inkjet recording apparatus 10 includes a paper supply unit 11, an image forming unit 12, a paper discharge unit 13, and an ink supply tank 14. The paper supply unit 11 supplies paper as a recording medium. The recording medium is not limited to paper; any sheet-like medium capable of forming an image using ink is acceptable. Furthermore, when using paper as the recording medium, the paper can be cut paper or continuous paper. Continuous paper includes roll paper. In this embodiment, cut paper is used as an example of the recording medium.

[0049] The image forming unit 12 is the part that uses ink to form an image on paper. The paper discharge unit 13 is the part that discharges the paper after the image formation is completed. The ink supply tank 14 is a tank used to store a predetermined amount of ink and supply the ink to the image forming unit 12.

[0050] Figure 2 It means Figure 1 A schematic diagram of the internal structure of the inkjet recording device is shown.

[0051] like Figure 2 As shown, a paper supply tray 11a is provided in the paper supply section 11. Paper 15, which is to be used to form an image, is loaded on the paper supply tray 11a. The paper supply section 11 separates and supplies the paper 15 loaded on the paper supply tray 11a one sheet at a time, starting from the top.

[0052] The image forming unit 12 is provided with a transport drum 20, multiple inkjet heads 21Y, 21M, 21C, 21K, a fog collector 22, an ultraviolet irradiation unit 23, an in-line sensor 24, a flipping unit 25, and two transport rollers 26a and 26b of different sizes.

[0053] The transport drum 20 is configured to rotate in the A direction. The transport drum 20 rotates while winding the paper 15 supplied from the paper supply section 11 around its outer peripheral surface, thereby transporting the paper 15. For example, the transport drum 20 can attract the paper 15 to its outer peripheral surface by air suction, and rotate in this state to transport the paper 15 in the A direction. Figure 2 The direction A indicated by the middle arrow is the rotation direction of the conveyor drum 20, which is also the conveying direction of the paper 15. In the following description, it is sometimes referred to as the rotation direction A of the conveyor drum 20, and sometimes as the conveying direction A of the paper 15.

[0054] Multiple inkjet heads 21Y, 21M, 21C, and 21K form images on paper 15 using ink of their respective corresponding colors. Specifically, inkjet head 21Y uses yellow (Y) ink to form an image, and inkjet head 21M uses magenta (M) ink. Additionally, inkjet head 21C uses cyan (C) ink to form an image, and inkjet head 21K uses black (K) ink. In this embodiment, ultraviolet-curable ink is used.

[0055] Each inkjet head 21Y, 21M, 21C, and 21K is arranged facing the upper outer peripheral surface of the transport drum 20. Furthermore, each inkjet head 21Y, 21M, 21C, and 21K is arranged at offset positions in the circumferential direction of the transport drum 20. It should be noted that in this embodiment, four inkjet heads 21Y, 21M, 21C, and 21K are provided in the image forming unit 12 to enable the formation of a color image using four colors of ink; however, the number of inkjet heads can also be more than four.

[0056] The mist collector 22 is a device for collecting ink mist generated when ink is ejected from each of the inkjet heads 21Y, 21M, 21C, and 21K. Most of the ink mist is swept away in the direction A by the airflow generated when the delivery drum 20 rotates. Therefore, the mist collector 22 is disposed downstream of the inkjet head 21K in the rotation direction A of the delivery drum 20.

[0057] The ultraviolet irradiation unit 23 is disposed downstream of the mist collector 22 in the rotation direction A of the conveyor drum 20. The ultraviolet irradiation unit 23 cures the ink on the paper 15 that is conveyed by the rotation of the conveyor drum 20 by irradiating it with ultraviolet light.

[0058] The inline sensor 24 is disposed downstream of the ultraviolet irradiation section 23 in the rotation direction A of the conveyor drum 20. The inline sensor 24 is used to check the color density, tilt, etc. of the image formed on the paper 15 during the conveying process by the conveyor drum 20. The flipping section 25 is the part that flips the front and back of the paper 15 so that images can be formed on both sides of the paper 15. The conveyor rollers 26a and 26b are rollers that convey the paper 15, after the image formation is completed, toward the paper discharge section 13.

[0059] A paper discharge tray 13a is provided in the paper discharge section 13. Paper sheets 15, on which the image has been formed, are loaded sequentially on the paper discharge tray 13a.

[0060] <Operation of the inkjet recording device>

[0061] Next, the operation of the inkjet recording apparatus 10 of this embodiment will be explained.

[0062] First, the sheets 15 loaded on the paper feed tray 11a of the paper feed unit 11 are sequentially separated and fed to the image forming unit 12, starting from the top. The paper 15 supplied to the image forming unit 12 is held at its front end by a transport claw (not shown). The transport claw feeds the paper 15 into the transport drum 20 at predetermined intervals. As a result, the paper 15 is attracted to the outer peripheral surface of the transport drum 20 and is transported by the rotation of the transport drum 20.

[0063] On the other hand, each inkjet head 21Y, 21M, 21C, and 21K ejects ink onto the paper 15, which is being transported by the rotation of the transport drum 20, at a predetermined time, thereby adhering the ink to the paper 15. Thus, an image is formed on the paper 15. Afterward, the paper 15 is irradiated with ultraviolet light by the ultraviolet irradiation unit 23. This cures the ink that formed the image on the paper 15.

[0064] Next, the paper 15, whose image has been formed, is conveyed by conveyor rollers 26a and 26b and fed into the paper discharge section 13. The paper 15 fed into the paper discharge section 13 is discharged onto the paper discharge tray 13a in an overlapping manner. Through the above actions, paper 15 with a completed image is obtained.

[0065] <Structure of a Fog Collector>

[0066] Next, the structure of the mist collector included in the inkjet recording apparatus according to the embodiments of the present invention will be described in detail.

[0067] Figure 3 This is a perspective view of the mist collector of this embodiment, viewed from the upstream side in the paper conveying direction. Figure 4 This is a perspective view of the mist collector of this embodiment as viewed from the downstream side in the paper conveying direction.

[0068] like Figure 3 as well as Figure 4 As shown, the mist collector 22 is equipped with a structure that is aligned with the paper conveying direction A (refer to...). Figure 2 A plurality of nozzles 31 and a plurality of cyclone separators 32 are arranged in an orthogonal direction (hereinafter also referred to as the "paper width direction") X. In this embodiment, as an example, four nozzles 31 and four cyclone separators 32 are provided.

[0069] Four nozzles 31 are arranged in the paper width direction X. Each nozzle 31 is a hollow component. The nozzles 31 are arranged at an angle relative to the horizontal plane. Each nozzle 31 has a suction port 33. The suction port 33 is an opening for drawing in air containing ink mist. The suction port 33 is a rectangle that is longer in the paper width direction X, i.e., it is horizontally elongated. The suction ports 33 of the four nozzles 31 are adjacent to each other in the paper width direction X.

[0070] Here, along the length of the nozzle 31, the nozzle end on the side where the suction port 33 is located is designated as the front end of the nozzle 31, and the nozzle end on the side opposite to the suction port 33 is designated as the rear end of the nozzle 31. In this case, the front end of the nozzle 31 is positioned lower than the rear end of the nozzle 31, and the suction port 33 opens obliquely downwards. Furthermore, the shape of the nozzle 31 is transversely elongated at the front end and longitudinally elongated at the rear end. That is, the longitudinal cross-sectional shape of the nozzle 31 gradually changes from a transversely elongated shape towards the rear end. An outlet 34 is provided at the rear end of the nozzle 31. The outlet 34 is an opening for discharging the air drawn in from the suction port 33. The outlet 34 is longitudinally elongated.

[0071] Four cyclone separators 32 are arranged in the same direction (X) as the nozzles 31 along the paper width. The cyclone separators 32 are configured in a vertical position. The outlet 34 of the nozzles 31 is connected to the upper part of the cyclone separators 32. The cyclone separators 32 centrifugally separate ink mist from the air drawn in through the nozzles 31.

[0072] Furthermore, the mist collector 22 includes a fan cover 36 and four filter housings 35. The filter housings 35 are positioned above the cyclone separators 32. Filters (not shown) are detachably mounted on the filter housings 35. The fan cover 36 is a cover that covers four exhaust fans (not shown). The four filter housings 35 and the four exhaust fans are respectively provided corresponding to the four cyclone separators 32. In addition, the exhaust fans are provided as an example of an airflow generating unit. The airflow generating unit generates airflow along the path from the nozzle 31 through the cyclone separators 32 to the filter. In addition, four exhaust ports 37 are provided on the fan cover 36 corresponding to the four exhaust fans. The exhaust ports 37 are openings for discharging air outside the machine by the rotation drive of the exhaust fans.

[0073] The structure of the nozzle 31, cyclone separator 32, filter housing 35 and exhaust fan will be described in more detail below.

[0074] Figure 5 This is a longitudinal sectional view of the fog collector of this embodiment. Figure 6 This is a perspective view showing the structure of the cyclone separator and filter unit included in the fog collector of this embodiment.

[0075] like Figure 5 As shown, the outlet 34 of nozzle 31 is connected to the air inlet 38 of cyclone separator 32. The air inlet 38 is an opening for guiding air drawn from the suction port 33 of nozzle 31 and discharged from outlet 34 into the interior of cyclone separator 32. Like the outlet 34 of nozzle 31, the air inlet 38 is also shaped as a long rectangle. Figure 6 ).

[0076] The cyclone separator 32 includes an outer cylinder 41 and an inner cylinder 42. The outer cylinder 41 is preferably made of resin. The outer cylinder 41 is cylindrical. The upper end 41a of the outer cylinder 41 is open, and the lower end 41b of the outer cylinder 41 is closed. That is, the outer cylinder 41 is a bottomed cylindrical shape. The upper end 41a of the outer cylinder 41 is connected to the lower end of the filter housing 35. The lower end of the filter housing 35 is open in such a way that air is drawn into the interior of the filter housing 35 from the upper end of the cyclone separator 32. A filter 40 is housed in the filter housing 35. When the air drawn into the filter housing 35 from the cyclone separator 32 contains ink mist, the filter 40 captures the ink mist.

[0077] like Figure 5 As shown, an exhaust fan 47 is disposed above the filter housing 35. The exhaust fan 47 functions as an airflow generating unit, as described above. Specifically, when the exhaust fan 47 is driven to rotate, a negative pressure is created on the primary side of the exhaust fan 47, and air is drawn in from the suction port 33 of the nozzle 31 by this negative pressure. At this time, the exhaust fan 47 draws in the air drawn from the suction port 33 of the nozzle 31 in sequence through the interior of the nozzle 31, the interior of the cyclone separator 32, and the interior of the filter housing 35, and then discharges it to the outside of the machine from the exhaust port 37. Thus, a first airflow is formed in the first space 45, and a second airflow is formed inside the inner cylinder 42. The first and second airflows will be described in detail later.

[0078] An outlet 34 of a nozzle 31 is connected to the outer cylinder 41. More specifically, an air inlet 43 is formed in the upper part of the outer cylinder 41. The air inlet 43 is integrally formed with the outer cylinder 41. The air inlet 43 is the portion that guides the air discharged from the outlet 34 of the nozzle 31 into the space 45 between the outer cylinder 41 and the inner cylinder 42 (hereinafter also referred to as the "first space"). Figure 7 As shown in the cross-sectional view, the air inlet 43 has an air inlet 38 and an air outlet 39. The air outlet 39 is an opening for discharging air introduced from the air inlet 38 toward the first space 45. Figure 7 In the cross-sectional view shown, the air inlet 43 supplies air in the direction (tangential direction) along the peripheral wall 44 of the outer cylinder 41. The outlet 34 of the nozzle 31 is connected to the air inlet 38 of the air inlet 43. Thus, the outlet 34 of the nozzle 31 is connected to the upper part of the outer cylinder 41.

[0079] The inner cylinder 42 is preferably formed of resin. The inner cylinder 42 is cylindrical. The inner cylinder 42 and the outer cylinder 41 are arranged concentrically. That is, the central axis of the inner cylinder 42 and the central axis of the outer cylinder 41 are on the same axis. The interior of the inner cylinder 42 forms a space (hereinafter also referred to as the "second space") 46. The second space 46 is surrounded by the peripheral wall portion 48 of the inner cylinder 42. The upper end portion 42a of the inner cylinder 42 is open, and the lower end portion 42b of the inner cylinder 42 is closed. The inner cylinder 42 is integrally formed with the filter housing 35, for example, by integral molding of resin. However, the inner cylinder 42 may also be separately formed from the filter housing 35. The upper end portion 42a of the inner cylinder 42 opens upwards, and the interior of the inner cylinder 42 and the interior of the filter housing 35 communicate through this opening. Communication refers to a state of spatial connection.

[0080] like Figure 8 As shown, the upper end portion 42a of the inner cylinder 42 is positioned at approximately the same height as the upper end portion 41a of the outer cylinder 41. On the other hand, the lower end portion 42b of the inner cylinder 42 is positioned higher than the lower end portion 41b of the outer cylinder 41. In other words, the length of the inner cylinder 42 along its central axis is shorter than the length of the outer cylinder 41 along its central axis. Furthermore, the lower end portion 42b of the inner cylinder 42 is formed into a downward-facing hemispherical shape. This allows for smooth airflow in the formation of the first airflow 61 (described later) while suppressing a decrease in wind speed.

[0081] Figure 9 This is a side view showing the state of the cyclone separator after the outer cylinder has been removed, so that the inner cylinder of the cyclone separator can be seen.

[0082] like Figure 9 As shown, the inner cylinder 42 of the cyclone separator 32 is divided into a first cylinder portion 51 and a second cylinder portion 52 along its central axis. The first cylinder portion 51 includes the upper end portion 42a of the inner cylinder 42. The second cylinder portion 52 is the portion located between the first cylinder portion 51 and the lower end portion 42b of the inner cylinder 42. Both the first cylinder portion 51 and the second cylinder portion 52 are formed by the peripheral wall portion 44 of the inner cylinder 42.

[0083] Figure 10 This is a perspective view of the second section of the inner cylinder, cut parallel to the horizontal plane.

[0084] exist Figure 10 In the inner cylinder 42, an inner sheet 56 and an outer sheet 58 are stacked sequentially on the outer peripheral surface of the peripheral wall portion 44 that forms the second cylindrical portion 52. Both the inner sheet 56 and the outer sheet 58 are elements constituting the inner cylinder 42.

[0085] The inner sheet 56 is located radially between the outer circumferential surface of the peripheral wall portion 44 and the outer sheet 58 of the inner cylinder 42. It should be noted that... Figure 10In order to make it easier to understand the structure of the second cylindrical part 52 of the inner cylinder 42, the outer piece 58 is omitted on the left side of the figure. Both the inner piece 56 and the outer piece 58 are arranged around the entire circumference of the peripheral wall part 44.

[0086] Figure 11 This is a side view showing the structure of a cyclone separator before the inner and outer plates are installed in the second section of the inner cylinder.

[0087] like Figure 11 As shown, a plurality of through holes 55 are formed on the second cylindrical portion 52. The plurality of through holes 55 are arranged at predetermined intervals in the circumferential direction of the inner cylinder 42. Furthermore, the plurality of through holes 55 are arranged in upper and lower sections, staggered in the central axis direction of the inner cylinder 42. Each through hole 55 is formed as a rectangle with a longer section in the central axis direction of the inner cylinder 42. In addition, each through hole 55 is arranged to penetrate the peripheral wall portion 48 forming the second cylindrical portion 52. In contrast, no through holes 55 are provided on the peripheral wall portion 48 forming the first cylindrical portion 51. That is, the first cylindrical portion 51 is a non-perforated structure, while the second cylindrical portion 52 is a perforated structure.

[0088] Figure 12 This is a side view of the structure of a cyclone separator, showing the state in which the inner sheet is installed in the second cylinder of the inner cylinder.

[0089] exist Figure 12 In the inner cylinder 42, an inner sheet 56 is attached to the outer peripheral surface. The inner sheet 56 is thin enough compared to the thickness of the peripheral wall 48 of the inner cylinder 42. The thickness of the inner sheet 56 is preferably less than 1 / 3 of the thickness of the peripheral wall 48 (however, not including zero). A plurality of suction holes 57 are formed on the inner sheet 56. The plurality of suction holes 57 are provided on the inner sheet 56 corresponding to the plurality of through holes 55. The plurality of suction holes 57 are also arranged offset from the plurality of through holes 55 in the circumferential direction of the inner cylinder 42. In addition, the plurality of suction holes 57 are also arranged offset from the plurality of through holes 55 in the central axis direction of the inner cylinder 42.

[0090] Each intake port 57 is an elongated, slit-like opening that extends along the central axis of the inner cylinder 42. The intake port 57 is used to draw air into the interior of the inner cylinder 42. Additionally, the intake port 57 is also used to draw air from the first space 45 into the second space 46. Figure 13 As shown, the suction hole 57 is formed in a slit shape, intersecting the direction of the rotating (swirling) first airflow 61 and the direction of the second airflow 62. The long side dimension of the suction hole 57 is shorter than the long side dimension of the through hole 55, and the short side dimension of the suction hole 57 is shorter than the short side dimension of the through hole 55. That is, the opening size of the suction hole 57 is smaller than the opening size of the through hole 55. The suction hole 57 is disposed on the outer surface side of the peripheral wall portion 48. Furthermore, by... Figure 10It can be seen that the suction hole 57 is located inside the opening edge of the through hole 55. Therefore, when the inner sheet 56 is installed in the inner cylinder 42, the internal space of the inner cylinder 42 and the external space of the inner cylinder 42 are connected through the suction hole 57, whose opening size is smaller than that of the through hole 55. Figure 8 As shown, in the direction of the central axis of the outer cylinder 41, the positions of the suction hole 57 and the discharge port 34 are staggered in a manner that does not overlap with each other.

[0091] The above Figure 9 The structure of a cyclone separator is shown with both the inner and outer plates mounted on the second section of the inner cylinder.

[0092] exist Figure 9 In this design, an outer sheet 58 is attached to the outer peripheral surface of the second cylindrical portion 52. The outer sheet 58 is attached in a manner that covers the inner sheet 56. That is, the inner sheet 56 and the outer sheet 58 are sequentially overlapped and attached to the outer peripheral surface of the second cylindrical portion 52. A plurality of protrusions 59 are formed on the outer sheet 58. The plurality of protrusions 59 are provided on the outer sheet 58 corresponding to the plurality of through holes 55 and the plurality of suction holes 57.

[0093] Also Figure 7 As shown, the protrusion 59 is arranged to extend radially outward from the outer periphery of the inner cylinder 42. Additionally, as... Figure 9 As shown, the protrusion 59 is formed into a blade shape having an upper side 59a, a lower side 59b, a longitudinal side 59c, and an oblique side 59d. The protrusion dimension of the blade-shaped protrusion 59 gradually increases from the upstream side of the first airflow 61 to the downstream side, as described later.

[0094] The upper side 59a is positioned near the outlet 34 of the nozzle 31, compared to the lower side 59b. The upper side 59a is shorter than the lower side 59b. The upper side 59a is positioned parallel to the direction of the first airflow formed in the first space 45. The lower side 59b is positioned perpendicular to the direction of the first airflow. The longitudinal side 59c is positioned along the central axis of the inner cylinder 42. The inclined side 59d is inclined relative to the central axis of the inner cylinder 42. The protrusion 59 is connected to the other part of the outer piece 58 at the portion of the inclined side 59d. The protrusion 59 bends outward at the portion of the inclined side 59d, and through this bend, the protrusion 59 extends radially outward.

[0095] A gap 60 is formed around the protrusion 59. The gap 60 is formed along the three sides (59a, 59b, 59c) of the protrusion 59. Furthermore, the gap 60 is connected to the suction hole 57 of the inner sheet 56. The size of the gap 60 formed along the upper side 59a gradually increases from the inclined side 59d towards the longitudinal side 59c according to the bending angle of the protrusion 59. The size of the gap 60 formed along the lower side 59b also gradually increases from the inclined side 59d towards the longitudinal side 59c according to the bending angle of the protrusion 59. The size of the gap 60 formed along the longitudinal side 59c gradually increases from the upper side 59a towards the lower side 59b.

[0096] <The Actions of the Fog Collector>

[0097] Next, the operation of the fog collector constructed with the above structure will be explained.

[0098] When ink is ejected from inkjet heads 21Y, 21M, 21C, 21K onto paper 15 conveyed by transport drum 20 to form an image, the fog collector 22 operates by the rotation of exhaust fan 47.

[0099] When the exhaust fan 47 rotates, air containing ink mist is drawn into the nozzle 31 from the suction port 33. After flowing from the lower end to the upper end of the nozzle 31, the air drawn into the nozzle 31 is discharged from the discharge port 34. The air discharged from the discharge port 34 is drawn into the interior of the outer cylinder 41 through the air inlet 43 of the cyclone separator 32.

[0100] Figure 13 This is a graph showing the results of a simulation of the airflow in a cyclone separator.

[0101] like Figure 13 As shown, air drawn into the interior of the outer cylinder 41 through the air inlet 43 forms a first airflow 61 in the first space 45. Figure 13 In this process, the first airflow 61 becomes a flow of air rotating (swirling) in a clockwise direction. A portion of the air forming the first airflow 61 passes through the intake hole 57 of the inner plate 56. Figure 12 The air is drawn into the inner cylinder 42. Additionally, the air drawn in through the suction port 57 creates a second airflow 62 inside the inner cylinder 42. Figure 13 In this process, the second airflow 62 becomes a flow of air that rotates (swirls) in a counterclockwise direction. In other words, the first airflow 61 and the second airflow 62 rotate in opposite directions. Furthermore, both the first airflow 61 and the second airflow 62 become airflows that rotate in a spiral shape.

[0102] In this embodiment, to cause the first airflow 61 and the second airflow 62 to rotate in opposite directions, a protrusion 59 is provided upstream of the first airflow 61 at the intake port 57. The air on the inner circumference side (near the inner cylinder 42) forming the first airflow 61 is obstructed by the presence of the protrusion 59. Furthermore, the air obstructed by the protrusion 59 is guided to the intake port 57 by making a U-shaped turn around the protrusion 59, and is then drawn into the interior of the inner cylinder 42 through this intake port 57. Thus, the direction of the air drawn into the interior of the inner cylinder 42 is reversed by the aforementioned U-shaped turn. Therefore, a second airflow 62 rotating in the opposite direction to the first airflow 61 is formed inside the inner cylinder 42.

[0103] Thus, by forming a first airflow 61 and a second airflow 62 inside the cyclone separator 32, ink mist is separated from the air drawn into the cyclone separator 32 from the nozzle 31. Specifically, a portion of the ink mist contained in the air flowing through the first space 45 is subjected to centrifugal force generated by the first airflow 61 and collides with the peripheral wall 44 of the outer cylinder 41, thereby separating from the air (centrifugal separation). The ink mist thus separated then moves downward and accumulates at the lower end 41b of the outer cylinder 41.

[0104] On the other hand, a portion of the ink mist contained in the air flowing from the first space 45 toward the second space 46 collides with the peripheral wall 48 of the inner cylinder 42 and the edge of the suction hole 57 when it makes a U-shaped turn in a manner that bypasses the protrusion 59, thereby separating from the air. The ink mist separated in this way then moves downward and accumulates at the lower end 42b of the inner cylinder 42.

[0105] Additionally, some of the ink mist contained in the air drawn into the inner cylinder 42 moves upward with the second airflow 62 and is captured by the filter 40. Other ink mist is subjected to centrifugal force generated by the second airflow 62 and collides with the peripheral wall 48 of the inner cylinder 42, thereby separating from the air (centrifugal separation).

[0106] Here, based on particle size, the ink mist contained in the air drawn into the outer cylinder 41 through the air inlet 43 is roughly divided into large-particle ink mist, medium-particle ink mist, and small-particle ink mist. Assuming the airflow velocity is constant, the centrifugal force acting on the ink mist is directly proportional to the mass of the ink mist and inversely proportional to the rotation radius of the airflow. Therefore, a stronger centrifugal force acts on ink mist with a larger particle size.

[0107] Figure 14 This is a cross-sectional view showing an example of the movement trajectory of ink mist with different particle sizes.

[0108] like Figure 14As shown, large ink mist particles M1 are pushed outward by centrifugal force corresponding to their own mass, colliding with the peripheral wall 44 of the outer cylinder 41. Therefore, large ink mist particles M1 can be separated from the air forming the first airflow 61. However, medium-sized ink mist particles M2 and small ink mist particles M3 cannot be separated.

[0109] In this embodiment, the medium-sized ink mist M2 and the small-sized ink mist M3 move along with the flow of air that is about to flow from the first space 45 around the protrusion 59 into the second space 46. At this time, the rotation radius of the airflow around the protrusion 59 becomes extremely small compared to the rotation radius of the first airflow 61. For example, if the rotation radius of the first airflow 61 is about 30 mm, the rotation radius of the airflow around the protrusion 59 is about 1 / 10 of it, that is, about 3 mm.

[0110] Therefore, when passing around the protrusion 59, a very strong centrifugal force acts on the medium-sized ink mist M2 and the small ink mist M3. Furthermore, a stronger centrifugal force than that acting on the small ink mist M3 acts on the medium-sized ink mist M2. As a result, the medium-sized ink mist M2 collides with the inner cylinder 42 (or the edge of the suction port 57) when passing around the protrusion 59. Therefore, the medium-sized ink mist M2 can be separated from the air sucked into the second space 46 from the first space 45. Meanwhile, the small ink mist M3 enters the filter 40 along with the second airflow 62 and is captured by the filter 40. Therefore, the air discharged from the exhaust port 37 becomes clean air after ink mist has been removed by the cyclone separator 32 and the filter 40. Furthermore, the air entering the filter 40 becomes air from which not only the large ink mist M1 but also the medium-sized ink mist M2 has been removed.

[0111] Figure 15 This is a graph showing the simulation results of particle tracking in the fog collector of this embodiment.

[0112] like Figure 15 As shown, after moving along the inclined nozzle 31, the particles spiral (swirl) around the inner cylinder 42 while moving downwards. Additionally, some particles bypass the protrusion 59 and collide with the inner cylinder 42, or are drawn into the inner cylinder 42 through the suction port 57. Afterwards, the particles drawn into the inner cylinder 42 move upwards with the second airflow 62.

[0113] As explained above, the inkjet recording apparatus 10 of this embodiment separates ink mist from the air through a first airflow 61 formed in the first space 45, and further separates ink mist from the air through a second airflow 62 formed in the second space 46 by air drawn into the inner cylinder 42 from the suction port 57. Thus, even small-sized ink mist particles that cannot be separated by the first airflow 61 alone can be separated from the air inside the cyclone separator 32. Therefore, compared to centrifugal separation of ink mist using only the first airflow 61, the collection efficiency of collecting ink mist using the cyclone separator 32 can be improved. As a result, the amount of mist captured by the filter 40 per unit time can be reduced, and the replacement frequency of the filter 40 can be reduced.

[0114] Furthermore, in this embodiment, the suction hole 57 is formed in a slit shape, intersecting the direction of the first airflow 61. This maintains a small radius of rotation for the airflow entering the second space 46 from the first space 45, and ensures a large opening area for the suction hole 57. Therefore, a stronger centrifugal force can act on the small-particle-size ink mist, separating it from the air. Additionally, the flow resistance of air passing through the suction hole 57 is minimized.

[0115] Furthermore, in this embodiment, the protrusion 59 is formed in a blade shape. This prevents air from flowing in from the sides (upper 59a and lower 59b) of the protrusion 59 when air is drawn from the first space 45 into the second space 46. Therefore, more ink mist can collide with the peripheral wall 48 of the inner cylinder 42 and the edge of the suction hole 57, thereby improving the centrifugal separation effect.

[0116] Furthermore, in this embodiment, the length of the upper side 59a, which is closer to the outlet 34, is shorter than the length of the lower side 59b, which is farther from the outlet 34. This prevents air from flowing into the inner cylinder 42 through the gap 60 in the upper side 59a.

[0117] Furthermore, in this embodiment, the angle of inclination of the upper side 59a near the outlet 34 and the lower side 59b away from the outlet 34 of the protrusion 59 is smaller relative to the first airflow 61. This prevents air from flowing into the inner cylinder 42 through the gap 60 in the upper side 59a.

[0118] Furthermore, in this embodiment, the upper edge 59a near the outlet 34 is configured to be parallel to the direction of the first airflow 61 (see reference). Figure 15 This allows for more effective suppression of air flowing into the inner cylinder 42 from the gap 60 at the top 59a.

[0119] Furthermore, in this embodiment, the lower edge 59b, which is away from the outlet 34, is configured to be perpendicular to the direction of the first airflow 61 (see reference). Figure 15 This allows for more effective suppression of air flowing into the inner cylinder 42 from the gap 60 at the bottom 59b.

[0120] Furthermore, in this embodiment, the positions of the suction port 57 and the discharge port 34 are staggered in a non-overlapping manner along the central axis direction of the outer cylinder 41. This ensures that the area where ink mist is centrifugally separated by the first airflow 61 formed in the first space 45 is secured.

[0121] Furthermore, in this embodiment, multiple suction holes 57 are provided on the inner cylinder 42. As a result, compared with the case where only one suction hole 57 is provided on the inner cylinder 42, the flow resistance can be reduced.

[0122] Furthermore, in this embodiment, a structure is adopted in which multiple nozzles 31 and multiple cyclone separators 32 are arranged in the paper width direction X. As a result, the air attraction force can be made uniform in the paper width direction X.

[0123] It should be noted that in this embodiment, an inner sheet 56 and an outer sheet 58 are provided in the second cylindrical portion 52 of the inner cylinder 42, but a structure in which at least one of the inner sheet 56 and the outer sheet 58 is not provided may also be adopted.

[0124] For example, in a structure where neither the inner sheet 56 nor the outer sheet 58 is provided in the second cylindrical portion 52, a structure in which the suction hole 57 is directly formed on the peripheral wall portion 48 forming the second cylindrical portion 52 can be considered. With this structure, the first airflow 61 formed in the first space 45 and the second airflow 62 formed in the second space 46 become airflows rotating in the same direction. Furthermore, a portion of the ink mist contained in the air flowing from the first space 45 into the second space 46 collides with the edge of the suction hole 57 in the peripheral wall portion 48, thereby separating from the air. This is also true when only the inner sheet 56 is provided in the second cylindrical portion 52 of the inner cylinder 42.

[0125] Furthermore, when the inner sheet 56 is provided in the second cylinder 52, the inner sheet 56 is very thin compared to the peripheral wall 48. Therefore, when the ink mist collides with the edge of the suction hole 57, the ink mist is difficult to accumulate at the edge of the suction hole 57. Even if it does accumulate, the force (wind pressure, etc.) of the air passing through the suction hole 57 can be used to peel off the ink mist.

[0126] Furthermore, when the structure of inner sheet 56 and outer sheet 58 is adopted in the second cylinder 52, the U-shaped turn of the airflow by the protrusion 59 can reduce the rotation radius of the airflow and make the centrifugal force act on the ink mist more powerfully. Therefore, it is possible to more reliably separate small ink mist particles that cannot be separated by the first airflow 61 alone.

[0127] Furthermore, in the above embodiment, an inkjet recording apparatus 10 for forming an image by ejecting ink from each inkjet head 21Y, 21M, 21C, 21K onto paper 15 wound and conveyed around a transport drum 20 has been described as an example, but the present invention is not limited thereto. For example, the present invention can also be applied to an inkjet recording apparatus for forming an image by ejecting ink from each inkjet head onto paper conveyed horizontally along a pressure plate (not shown).

Claims

1. An inkjet recording apparatus, the inkjet recording apparatus comprising a mist collector for collecting ink mist, wherein, The fog collector has the following features: A nozzle that draws in air containing the ink mist from an intake port and discharges it from an outlet port; as well as A cyclone separator has an outer cylinder connected to the outlet of the nozzle and an inner cylinder disposed inside the outer cylinder. The cyclone separator utilizes air drawn into the interior of the outer cylinder through the outlet to form a first airflow between the outer cylinder and the inner cylinder, thereby separating the ink mist from the air. The inner cylinder has an intake hole on its circumferential surface for drawing air into the interior of the inner cylinder. The air drawn in through the intake hole forms a second airflow inside the inner cylinder, thereby separating the ink mist from the air. The inner cylinder has a protrusion on the upstream side of the first airflow at the suction port. The protrusion causes a portion of the air forming the first airflow to be U-shaped and guided to the intake port.

2. The inkjet recording apparatus as claimed in claim 1, wherein, The intake hole is formed as a slit in a manner that intersects the direction of the first airflow.

3. The inkjet recording apparatus as claimed in claim 1, wherein, The protrusion is formed in the shape of a blade extending radially outward from the outer periphery of the inner cylinder.

4. The inkjet recording apparatus as claimed in claim 3, wherein, The protrusion size of the protrusion gradually increases from the upstream side of the first airflow toward the downstream side.

5. The inkjet recording apparatus as claimed in claim 3, wherein, The protrusion in the blade shape has an upper side and a lower side, wherein the length of the side of the upper side and the lower side closer to the outlet is shorter than the length of the side farther from the outlet.

6. The inkjet recording apparatus as claimed in claim 3, wherein, The protrusion in the blade shape has an upper side and a lower side, and the side of the upper side and the lower side closer to the outlet has a smaller angle of inclination relative to the first airflow compared to the side farther from the outlet.

7. The inkjet recording apparatus as claimed in claim 6, wherein, The side closest to the outlet is configured to be parallel to the direction of the first airflow.

8. The inkjet recording apparatus as claimed in claim 6, wherein, The side away from the outlet is configured to be perpendicular to the direction of the first airflow.

9. The inkjet recording apparatus as claimed in claim 1, wherein, Along the central axis of the outer cylinder, the positions of the suction hole and the discharge port are staggered in a manner that does not overlap with each other.

10. The inkjet recording apparatus as claimed in claim 1, wherein, The inner cylinder has a plurality of suction holes.

11. The inkjet recording apparatus of claim 10, wherein, The plurality of suction holes are arranged at staggered positions in the circumferential direction of the inner cylinder.

12. The inkjet recording apparatus of claim 10, wherein, The plurality of suction holes are arranged at staggered positions along the central axis of the inner cylinder.

13. The inkjet recording apparatus as claimed in claim 1, wherein, The mist collector has a plurality of the nozzles and a plurality of the cyclone separators arranged in a direction orthogonal to a conveying direction of the recording medium.

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