Image forming apparatus and heating control method.

Abstract

To provide an image formation device and a heating control method capable of shortening a time of warm-up operation.SOLUTION: An image formation device includes an ink channel part for supplying ink stored in an ink storage part into an ink jet head, a heating part for heating the ink channel part, and a control part for controlling the heating part so as to heat the ink channel part at a second heating temperature higher than a first heating temperature at the image formation operation time, when warm-up operation is performed in order that a temperature of ink in the ink jet head reaches a proper temperature range.SELECTED DRAWING: Figure 9

Description

Technical Field

[0001] The present invention relates to an image forming apparatus and a heating control method.

Background Art

[0002] Conventionally, an inkjet image forming apparatus is known which includes an inkjet head that discharges ink from nozzles, and forms an image on a recording medium by discharging and landing the ink from the inkjet head toward the recording medium.

[0003] Some of the inks used in inkjet image forming apparatuses undergo a phase change between a gel state and a liquid (sol) state depending on the temperature. This ink has a phase change temperature of a predetermined temperature, for example, about 40 to 100°C, and uniformly liquefies (solates) when heated above this phase change temperature, while solidifying (gelating) at or below the predetermined temperature including normal room temperature (0 to 30°C). In order to smoothly feed such ink from an ink tank to an inkjet head and stably discharge it from the inkjet head, a warm-up operation is required to reach an appropriate temperature range for the ink in the inkjet head before the image forming operation, that is, to preheat the ink before discharge and keep the ink within an appropriate temperature range.

[0004] Therefore, a technique has been provided in which a heating unit is provided on the outer surface of an ink tank that supplies ink to an inkjet head, and the ink tank is heated by the heating unit to set the ink in the ink tank to an appropriate temperature (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, when the warm-up operation is performed, the ink supplied from the ink tank to the inkjet head is heated to a liquefied (solated) state at a heating target temperature set using the specific heat of the ink. Therefore, even when the temperature of the actual heating unit reaches the heating target temperature, depending on the heating target temperature, it may take time for the ink to be solated, and as a result, the time for the warm-up operation may become long, which is a problem.

[0007] An object of the present invention is to provide an image forming apparatus and a heating control method capable of shortening the time for the warm-up operation.

Means for Solving the Problems

[0008] The image forming apparatus according to the present invention includes an ink flow path unit that supplies the ink stored in the ink storage unit to the inkjet head, a heating unit that heats the ink flow path unit, A temperature detection unit that detects the temperature of the ink in the ink flow path portion as the ink temperature; a control unit that controls the heating unit to heat the ink flow path unit at a second heating temperature higher than a first heating temperature during the image forming operation when a warm-up operation for bringing the temperature of the ink in the inkjet head to an appropriate temperature range is performed. is provided with; The control unit controls the heating unit so as to change the heating temperature of the ink flow path portion according to the detected ink temperature, and when the printing coverage is greater than a predetermined coverage during the image forming operation and the detected ink temperature is lower than the first heating temperature, the control unit controls the heating unit to heat the ink flow path portion at the second heating temperature .

[0009] The heating control method according to the present invention is a heating control method in an image forming apparatus including an ink flow path unit that supplies the ink stored in the ink storage unit to the inkjet head and a heating unit that heats the ink flow path unit, wherein when a warm-up operation for bringing the temperature of the ink in the inkjet head to an appropriate temperature range is performed, the heating unit is controlled to heat the ink flow path unit at a second heating temperature higher than a first heating temperature during the image forming operation and; controls the heating unit so as to change the heating temperature of the ink flow path portion according to the ink temperature in the ink flow path portion detected by the temperature detection unit, and when the printing coverage is greater than a predetermined coverage during the image forming operation and the detected ink temperature is lower than the first heating temperature, the control unit controls the heating unit to heat the ink flow path portion at the second heating temperature ​。

Advantages of the Invention

[0010] According to the present invention, the time of the warm-up operation can be shortened.

Brief Description of the Drawings

[0011]

Figure 1

Figure 2A

Figure 2B

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Modes for Carrying Out the Invention

[0012] FIG. 1 is a diagram showing the main configuration of an inkjet image forming apparatus 1 (functioning as the "image forming apparatus" of the present invention) according to an embodiment of the present invention.

[0013] The inkjet image forming apparatus 1 includes a paper feeding unit 10, an image forming unit 20, a paper discharging unit 30, and a control unit 40. In the inkjet image forming apparatus 1, based on the control of the control unit 40, after an image is formed on a recording medium P conveyed from the paper feeding unit 10 to the image forming unit 20, the recording medium P is discharged to the paper discharging unit 30.

[0014] The paper feeding unit 10 holds the recording medium P on which an image is to be formed and supplies it to the image forming unit 20 before image formation. The paper feeding unit 10 includes a paper feeding tray 11 and a conveying unit 12.

[0015] The paper feeding tray 11 is a plate-like member provided so that one or a plurality of recording media P can be placed thereon. The paper feeding tray 11 is provided so as to move up and down according to the amount of the placed recording media P, and is held at a position where the uppermost recording medium P is conveyed by the conveying unit 12.

[0016] The conveying unit 12 includes a conveying mechanism that rotationally drives an annular belt 123 by a plurality of (for example, two) rollers 121 and 122 to convey the recording medium P on the belt 123, and a supply unit that delivers the uppermost one of the recording media P placed on the paper feeding tray 11 to the belt 123. The conveying unit 12 conveys the recording medium P delivered to the belt 123 by the supply unit along with the rotational movement of the belt 123.

[0017] The image forming unit 20 forms an image by ejecting ink onto the recording medium P. The image forming unit 20 includes an image forming drum 21, a delivery unit 22, a paper heating unit 23, a head unit 24, an irradiation unit 25, and a delivery unit 26.

[0018] The image forming drum 21 carries the recording medium P along the cylindrical outer peripheral surface, and conveys the recording medium P as it rotates. The conveyance surface of the image forming drum 21 faces the paper heating unit 23, the head unit 24, and the irradiation unit 25, and performs processing related to image formation on the conveyed recording medium P.

[0019] The delivery unit 22 is provided at a position between the conveyance unit 12 of the paper feeding unit 10 and the image forming drum 21, and delivers the recording medium P conveyed by the conveyance unit 12 to the image forming drum 21. The delivery unit 22 has a swing arm unit 221 that supports one end of the recording medium P conveyed by the conveyance unit 12, a cylindrical delivery drum 222 that delivers the recording medium P supported by the swing arm unit 221 to the image forming drum 21, etc. The recording medium P on the conveyance unit 12 is picked up by the swing arm unit 221 and delivered to the delivery drum 222, thereby guiding the recording medium P in the direction along the outer peripheral surface of the image forming drum 21 and delivering it to the image forming drum 21.

[0020] The paper heating unit 23 heats the recording medium P carried by the image forming drum 21. The paper heating unit 23 has, for example, an infrared heater or the like, and generates heat in response to energization. The paper heating unit 23 is provided in the vicinity of the outer peripheral surface of the image forming drum 21, upstream of the head unit 24 in the conveyance direction of the recording medium P due to the rotation of the image forming drum 21. The heat generation of the paper heating unit 23 is controlled by the control unit 40 so that the recording medium P carried by the image forming drum 21 and passing near the paper heating unit 23 reaches a predetermined temperature.

[0021] The head unit 24 discharges ink onto the recording medium P carried by the image forming drum 21 to form an image. The head unit 24 is provided individually for each color of C (cyan), M (magenta), Y (yellow), and K (black). In FIG. 1, head units 24 corresponding to the colors of Y, M, C, and K are provided in order from upstream with respect to the conveyance direction of the recording medium P conveyed as the image forming drum 21 rotates.

[0022] The head unit 24 of the present embodiment is provided with a length (width) that covers the entire recording medium P in the direction perpendicular to the conveyance direction of the recording medium P (width direction). That is, the inkjet image forming apparatus 1 is a one-pass type line head type inkjet recording apparatus. The head unit 24 can configure a line head by arranging a plurality of inkjet heads 241 (see FIGS. 2A and 2B).

[0023] FIGS. 2A and 2B are diagrams showing the internal configuration of the head unit 24. FIG. 2A is a schematic diagram of the internal configuration when the head unit 24 is viewed from the side. FIG. 2B is a schematic diagram of the internal configuration when the head unit 24 is viewed from the side of the recording medium P. Note that viewing the head unit 24 from the side means viewing the head unit 24 from a plane along the vertical direction of the head unit 24 and the direction (X direction) perpendicular to the plane of FIG. 1.

[0024] Also, as shown in FIGS. 2A and 2B, the head unit 24 has a plurality of inkjet heads 241. In the illustrated example, 16 inkjet heads 241 are provided in one head unit 24. The 16 inkjet heads 241 are each grouped into two inkjet heads 241 to form 8 inkjet modules 242.

[0025] Each inkjet head 241 has a plurality of nozzles 2411. The inkjet head 241 discharges ink from the plurality of nozzles 2411 to form an image on the recording medium P carried on the image forming drum 21. That is, the inkjet head 241 is provided such that the plurality of nozzles 2411 are exposed on the lower surface side of the head unit 24. The inkjet head 241 shown in FIG. 2B has a plurality of nozzles 2411 arranged in a configuration where two rows of nozzles along the X direction are provided.

[0026] The eight inkjet modules 242 form two columns along the X direction, as shown in, for example, FIG. 2B. The two columns are arranged such that the inkjet modules 242 are staggered with respect to each other in a direction orthogonal to the X direction. Further, the head unit 24 is provided with an ink heating device 80 that heats the ink supplied to the inkjet head 241. Details of the ink heating device 80 will be described later.

[0027] The irradiation unit 25 irradiates energy rays for curing the ink after the ink used in the inkjet image forming apparatus 1 of the present embodiment is ejected onto the recording medium P. The irradiation unit 25 has, for example, a fluorescent tube such as a low-pressure mercury lamp, and emits light from the fluorescent tube to irradiate energy rays such as ultraviolet rays. The irradiation unit 25 is provided on the downstream side of the head unit 24 with respect to the conveyance direction of the recording medium P by the rotation of the image forming drum 21 in the vicinity of the outer peripheral surface of the image forming drum 21. The irradiation unit 25 irradiates energy rays onto the recording medium P carried on the image forming drum 21 and on which ink has been ejected, and cures the ink ejected onto the recording medium P by the action of the energy rays.

[0028] Examples of the fluorescent tube that emits ultraviolet rays include, in addition to the low-pressure mercury lamp, a mercury lamp having an operating pressure of about several hundred Pa to 1 MPa, a light source that can be used as a germicidal lamp, a cold cathode tube, an ultraviolet laser light source, a metal halide lamp, a light-emitting diode, and the like. Among these, a light source (for example, a light-emitting diode, etc.) that can irradiate ultraviolet rays with higher illuminance and consumes less power is more desirable. Further, the energy rays are not limited to ultraviolet rays, and any energy rays having the property of curing the ink according to the properties of the ink may be used, and the light source is also replaced according to the wavelength of the energy rays and the like.

[0029] The delivery unit 26 conveys the recording medium P irradiated with energy rays by the irradiation unit 25 from the image forming drum 21 to the paper discharge unit 30. The delivery unit 26 includes a conveyance mechanism that rotationally drives an annular belt 263 by a plurality (for example, two) of rollers 261 and 262 to convey the recording medium P on the belt 263, and a cylindrical delivery drum 264 that delivers the recording medium P from the image forming drum 21 to the conveyance mechanism. The delivery unit 26 conveys the recording medium P delivered to the belt 263 by the delivery drum 264 by the belt 263 and sends it out to the paper discharge unit 30.

[0030] The paper discharge unit 30 stores the recording medium P sent out from the image forming unit 20 by the delivery unit 26. The paper discharge unit 30 includes a plate-shaped paper discharge tray 31 and the like, and the recording medium P after image formation is placed on this paper discharge tray 31.

[0031] The control unit 40 controls the operations of each part of the inkjet image forming apparatus 1 and overall operation. The control unit 40 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like. In the control unit 40, various processing programs such as system programs stored in the ROM are read out and expanded in the RAM, and the programs expanded in the RAM are executed by the CPU, whereby various control processes such as image formation processing are executed.

[0032] The ink used in the inkjet image forming apparatus 1 of the present embodiment is not particularly limited, but is, for example, an ultraviolet (UV) curable ink. This UV curable ink undergoes a phase change between a gel state and a liquid (sol) state according to temperature when not irradiated with UV. For example, this ink has a phase change temperature of a predetermined temperature, for example, about 40 to 100 °C, and uniformly liquefies (solates) when heated above this phase change temperature. On the other hand, this ink gels at a temperature below the predetermined temperature including normal room temperature (0 to 30 °C).

[0033] Here, with reference to FIGS. 3 to 8, the ink heating device 80 provided in the head unit 24 will be described. The ink heating device 80 includes an ink tank 50 in which a plurality of sub-tanks for storing ink are arranged in the longitudinal direction and integrally formed, and an ink tank heating device 60 provided on the outer surface of the ink tank 50 for heating the ink tank 50.

[0034] FIGS. 3 and 4 are schematic perspective views of the ink heating device 80. FIG. 5 is a schematic plan view of the ink tank 50. FIG. 6 is a schematic view showing the state after attachment of the attachment portion of the ink tank heating device 60 to the ink tank 50, and is a cross-sectional view taken along the line IV-IV of FIG. 3.

[0035] FIG. 7 is an enlarged view of a part of FIG. 3, and is a schematic perspective view showing the attachment portion of the thermistor 65. FIG. 8 is a schematic view showing the main configuration of the ink ejection mechanism 300 including the ink tank 50 and the connection between the respective parts of the ink ejection mechanism 300. In FIG. 8, a part of the plurality of ink jet heads 241 and the plurality of second sub-tanks 52 is shown in an omitted manner.

[0036] Here, the direction along the ink ejection direction of the head unit 24 where the ink heating device 80 is provided is defined as the Z direction, and the direction orthogonal to the X direction and the Z direction is defined as the Y direction.

[0037] The ink tank 50 (functioning as the "ink flow path portion" of the present invention) stores the ink supplied from the ink supply unit 70 (see FIG. 8) and supplies the stored ink to the ink jet head 241. Further, the ink tank 50 collects and stores the ink that has not been ejected from the ink jet head 241.

[0038] The ink tank 50 is formed to be long in the X direction, and is configured by integrally molding the first sub-tank 51 and the four second sub-tanks 52. The first sub-tank 51 and the four second sub-tanks 52 are arranged in the longitudinal direction of the ink tank 50.

[0039] The first sub-tank 51 (functioning as the "ink storage unit" of the present invention) is recessed in the central portion in the longitudinal direction of the ink tank 50 as shown in FIGS. 3 to 5, stores the ink supplied from the ink supply unit 70, and stores the ink recovered from the ink jet head 241.

[0040] The first sub-tank 51 has a flow path 511 that allows the supplied ink to flow in a meandering manner as shown by the solid line arrows in FIG. 5. At one end of the flow path 511, an inflow portion 512 is formed through which the ink supplied or recovered from the ink supply unit 70 or the ink jet head 241 flows in as shown by the broken line arrows in FIG. 5. Also, at the other end of the flow path 511, a storage portion 513 is formed that stores the ink that has passed through the flow path 511 and supplies it to the second sub-tank 52. Thus, the ink supplied from the inflow portion 512 passes through the flow path 511 while meandering in the direction of the arrow in FIG. 5 and is stored in the storage portion 513. The ink that has reached the storage portion 513 is sent out to a plurality of second sub-tanks 52 by a plurality of pumps P1 (see FIG. 8).

[0041] The storage portion 513 is provided with a liquid-contact thermistor 90 (functioning as the "temperature detection unit" of the present invention) that detects the temperature of the ink stored in the storage portion 513. Each time the liquid-contact thermistor 90 detects the temperature of the ink stored in the storage portion 513, it outputs the detected ink temperature to the control unit 40.

[0042] The second sub-tanks 52 are recessed in two at each of the longitudinal direction both ends as shown in FIGS. 3 to 5, and store the ink supplied from the first sub-tank 51 respectively. The ink stored in each second sub-tank 52 is supplied to two of the eight ink jet modules 242 provided in the head unit 24 respectively. Thus, maintenance can be performed in units of two for the eight ink jet modules 242 provided in the head unit 24.

[0043] Note that the number of the second sub-tank 52 is not limited to four, and may be appropriately changed according to the number of the ink jet modules 242 provided in the head unit 24.

[0044] As shown in FIGS. 3 and 4, the ink tank heating device 60 is attached so as to cover the entire one side surface of the ink tank 50 configured as described above. As shown in FIG. 6, the ink tank heating device 60 includes a planar heating member 61 (functioning as the “heating unit” of the present invention) provided on the outer surface of the ink tank 50, an elastic member 62 laminated on the side opposite to the ink tank 50 of the planar heating member 61, a metal plate 63 laminated on the side opposite to the planar heating member 61 of the elastic member 62, a fixing screw 64 for pressing and fixing the metal plate 63 toward the ink tank 50 side, a thermistor 65 provided in contact with the ink tank 50, the control unit 40 for individually controlling the heating temperature of the planar heating member 61, and the like.

[0045] As shown in FIGS. 3 and 4, the planar heating member 61, the elastic member 62, the metal plate 63, the fixing screw 64, and the thermistor 65 are provided separately at three locations, i.e., the central portion and both end portions in the longitudinal direction of the ink tank 50. The planar heating member 61 and the like provided separately at the three locations are arranged at positions corresponding to the first sub-tank 51 provided at the central portion in the longitudinal direction of the ink tank 50 and the second sub-tanks 52 provided at both end portions in the longitudinal direction of the ink tank 50, respectively.

[0046] As shown in FIG. 6, the planar heating member 61 is provided in direct contact with the outer surface of the ink tank 50, and heats the ink in the ink tank 50 by heating the outer surface of the ink tank 50. A lubricant such as grease may be applied between the planar heating member 61 and the ink tank 50, but the lubricant may not be applied because the man-hours increase during the manufacture of the ink jet image forming apparatus 1 or during the repair and replacement of the ink tank heating device 60. Further, the temperature of the planar heating member 61 is controlled by the control unit 40 based on the temperature detected by the thermistor 65.

[0047] As such a planar heating member 61, for example, a heater in which a strip-shaped heating element is arranged in a waveform on a thin plate-shaped heat insulating material, specifically, a rubber heater or the like is used. When a rubber heater is used, the adhesion to the ink tank 50 can be improved and the manufacturing cost can be reduced.

[0048] As shown in FIG. 6, the elastic member 62 is provided between the planar heating member 61 and the metal plate 63. The elastic member 62 is arranged in a state of being elastically deformed in the thickness direction (Y direction) by being pressed by the fixing screw 64 via the metal plate 63, and presses the planar heating member 61 with a substantially uniform force in the plane direction (XZ plane) by its restoring force, pressing the planar heating member 61 against the ink tank 50. Any material can be used as the elastic member 62 as long as it can be elastically deformed by the pressing of the fixing screw 64 or the like and can press the planar heating member 61 by its restoring force. For example, rubber, sponge, other sponge-like materials or porous materials may be used.

[0049] As shown in FIG. 6, the metal plate 63 is provided in contact with the elastic member 62 and constitutes the outer surface of the ink tank heating device 60.

[0050] As shown in FIGS. 3, 4, and 6, the fixing screws 64 are provided so as to penetrate each of the metal plates 63 provided at three positions in the longitudinal direction of the ink tank 50, and these are respectively fixed to the ink tank 50. In the examples shown in FIGS. 3 and 4, three fixing screws 64 are provided for the metal plate 63 provided at the central portion in the longitudinal direction of the ink tank 50, and two fixing screws 64 are provided for each of the metal plates 63 provided at both ends in the longitudinal direction of the ink tank 50. The number and attachment positions of the fixing screws 64 provided on each of the metal plates 63 are not limited to the illustrated examples, and any number and attachment positions may be used as long as the metal plate 63 can be pressed and fixed to the ink tank 50 side.

[0051] As shown in Fig. 6, the fixing screw 64 is configured to include a spacer portion 643 between the head portion 641 and the shaft portion 642 in the axial direction, with a diameter smaller than that of the head portion 641 and larger than that of the shaft portion 642. The fixing screw 64 is fixed to the ink tank 50 by screwing the shaft portion 642 into a female screw portion 53 formed on the outer wall surface of the ink tank 50 through the planar heating member 61, the elastic member 62, and the metal plate 63. When the shaft portion 642 of the fixing screw 64 is screwed into the female screw portion 53 of the ink tank 50 by a predetermined length, the tip surface 644 of the spacer portion 643 abuts against the outer wall surface of the ink tank 50, and the shaft portion 642 is configured not to be inserted further into the female screw portion 53.

[0052] Also, as shown in Fig. 6, holes 611, 621, and 631 corresponding to the fixing screw 64 are respectively formed in the portions of the planar heating member 61, the elastic member 62, and the metal plate 63 through which the fixing screw 64 passes. The diameters of the holes 611 in the planar heating member 61 and the holes 621 in the elastic member 62 are formed to be sufficiently larger than the diameter of the spacer portion 643, and the diameter of the holes 631 in the metal plate 63 is formed to be approximately the same as the diameter of the spacer portion 643. Thereby, when the fixing screw 64 is attached, the fixing screw 64 can be easily inserted through the planar heating member 61 and the elastic member 62. Also, after the fixing screw 64 is attached, the head portion 641 of the fixing screw 64 can abut against the metal plate 63 and firmly press the metal plate 63 toward the ink tank 50, and further, displacement of the metal plate 63 in the plane direction (XZ plane direction) can be suppressed.

[0053] Also, as shown in Fig. 6, the spacer portion 643 of the fixing screw 64 is formed such that the axial length L thereof is shorter than the sum of the thickness of the planar heating member 61, the thickness of the elastic member 62 before elastic deformation, and the thickness of the metal plate 63. Therefore, when the shaft portion 642 of the fixing screw 64 is screwed into the female screw portion 53 through the holes 611, 621, and 631, the head portion 641 sandwiches the planar heating member 61, the elastic member 62, and the metal plate 63 between the head portion 641 and the ink tank 50, and the metal plate 63 abutting against the head portion 641 is pressed toward the elastic member 62 side. Thereby, the elastic member 62 is elastically deformed, and the planar heating member 61 is pressed toward the ink tank 50 by the restoring force thereof.

[0054] Note that by adjusting the axial length L of the spacer portion 643, the elastic deformation amount of the elastic member 62 in the thickness direction can be adjusted, and the pressing force applied to the planar heating member 61 by the restoring force of the elastic member 62 can be appropriately set.

[0055] As shown in FIG. 7, the thermistor 65 is attached in contact with the ink tank 50. Specifically, notches are formed at the edges of the planar heating member 61, the elastic member 62, and the metal plate 63 to expose the ink tank 50, and the thermistor 65 is attached to the exposed portion 54 with a screw 651. Note that the thermistor 65 does not necessarily have to be fixed with the screw 651. For example, it may be formed in a thin film shape and fixed so as to be sandwiched between the ink tank 50 and the planar heating member 61. Further, two thermistors 65 are provided side by side at one exposed portion 54, and one of them is provided as a spare.

[0056] Further, the ink tank heating device 60 further includes a thermostat 66 (see FIG. 4). The thermostat 66 operates when the planar heating member 61 becomes excessively hot and stops the energization to the planar heating member 61. By providing the thermostat 66, damage to the planar heating member 61 due to excessive temperature rise can be more effectively suppressed.

[0057] As described above, the planar heating member 61, the elastic member 62, the metal plate 63, the fixing screw 64, and the thermistor 65 are respectively provided at three locations, i.e., the longitudinal center portion and both end portions of one side surface of the ink tank 50, and the heating temperature of each planar heating member 61 is individually controlled by the control unit 40.

[0058] Next, with reference to FIG. 8, the ink ejection mechanism 300 in the inkjet image forming apparatus 1 will be described.

[0059] The ink ejection mechanism 300 includes an ink supply unit 70 that supplies ink, an ink tank 50 that stores the ink supplied from the ink supply unit 70, an inkjet head 241 that ejects the ink supplied from the ink tank 50, a pressure control unit 305 that applies negative pressure to the nozzles 2411 of the inkjet head 241, a path 304 that connects the ink supply unit 70 and the ink tank 50, a path 303 that connects the first sub-tank 51 and the second sub-tank 52 in the ink tank 50, a supply path 301 that connects the second sub-tank 52 and the inkjet head 241, a recovery path 302 that connects the inkjet head 241 and the first sub-tank 51, a ventilation path 306 that connects the second sub-tank 52 and the pressure control unit 305, and the like.

[0060] In FIG. 8, each path that serves as an ink passage is indicated by a dashed line or the like, but the specific configuration of each of these paths is a closed path through which the ink is conducted.

[0061] The ink supply unit 70 stores the ink that circulates through each part of the ink ejection mechanism 300, and the ink is supplied to the first sub-tank 51 of the ink tank 50.

[0062] The first sub-tank 51 stores the ink supplied from the ink supply unit 70, and the stored ink is supplied to the second sub-tank 52. The ink supplied to the first sub-tank 51 flows in from the inflow portion 512, is stored in the storage portion 513 through the flow path 511, and is supplied from the storage portion 513 to the second sub-tank 52.

[0063] The first sub-tank 51 is supplied with room-temperature ink that has not been heated from the ink supply unit 70. However, since the supplied ink is supplied to the second sub-tank 52 through the flow path 511, it takes a certain amount of time to reach the second sub-tank 52. During this time, the room-temperature ink supplied to the first sub-tank 51 is sufficiently heated by the ink tank heating device 60 provided outside the first sub-tank 51. As a result, even when the ink ejection amount is large, the supply of low-temperature ink from the first sub-tank 51 to the second sub-tank 52 is suppressed.

[0064] The second sub-tank 52 stores the ink supplied from the first sub-tank 51, and the stored ink is supplied to the inkjet head 241.

[0065] The pressure control unit 305 is connected to the second sub-tank 52 and adjusts the pressure inside the second sub-tank 52 under the control of the control unit 40. Thereby, the pressure control unit 305 makes the pressure of the nozzles 2411 of the inkjet head 241 in a negative pressure state via the second sub-tank 52 and the supply path 301. This prevents the ink from leaking out of the nozzles when image formation and various maintenance operations are not performed.

[0066] The supply path 301, the recovery path 302, and the paths 303 and 304 are each tube-shaped members through which the ink passes inside, and are made of, for example, a resin or the like, or are composed of members with good heat conductivity.

[0067] The path 304 connects the first sub-tank 51 and the ink supply unit 70, and a pump P2 is provided in the path 304. The pump P2 operates under the control of the control unit 40 and supplies ink from the ink supply unit 70 to the first sub-tank 51. As the pump P2, for example, a positive displacement pump such as a diaphragm pump or a tube pump is used.

[0068] The path 303 connects the second sub-tank 52 and the first sub-tank 51, and a pump P1 is provided in the path 303. The pump P1 operates under the control of the control unit 40 and supplies ink from the first sub-tank 51 to the second sub-tank 52. As the pump P1, for example, a positive displacement pump such as a diaphragm pump or a tube pump is used.

[0069] The supply path 301 connects the inlet 2412 of the inkjet head 241 and the second sub-tank 52.

[0070] The recovery path 302 connects the outlet 2413 of the inkjet head 241 and the first sub-tank 51.

[0071] The ventilation path 306 connects the second sub-tank 52 and the pressure control unit 305. The ventilation path 306 is a tube-shaped member through which air passes inside, and is made of, for example, resin or the like.

[0072] The ventilation path 306 has a structure in which it branches from a single common ventilation path 3061 connected to the pressure control unit 305 into a plurality of branch ventilation paths 3062 each connected to each of the plurality of second sub-tanks 52.

[0073] Also, electromagnetic valves 307, 308, and 309 are provided in the recovery path 302, the path 303, and the branch ventilation path 3062, respectively. The electromagnetic valves 307 to 309 open and close the ink flow path and the ventilation path in which they are respectively provided under the control of the control unit 40. That is, the electromagnetic valve 307 provided in the recovery path 302 switches the opening and closing of the recovery path 302. The electromagnetic valve 308 provided between the first sub-tank 51 and the pump P1 in the path 303 switches the opening and closing of the connection between the first sub-tank 51 and the pump P1. The electromagnetic valve 309 provided in the branch ventilation path 3062 switches the opening and closing of the connection between the second sub-tank 52 and the pressure control unit 305.

[0074] Note that the second sub-tank 52 is a tank-shaped container sealed except for the above-mentioned various connection points. That is, the pressure inside the second sub-tank 52 changes depending on the degree of negative pressure applied by the pressure control unit 305, the presence or absence of ink supply from the first sub-tank 51, and the like. For example, when the electromagnetic valve 309 is in a closed state and the negative pressure applied by the pressure control unit 305 is lost, and the second sub-tank 52 receives ink supply from the first sub-tank 51, the pressure inside the second sub-tank 52 increases as the amount of ink inside the second sub-tank 52 increases.

[0075] On the other hand, the first sub-tank 51 is a container open to the outside and is maintained at approximately atmospheric pressure regardless of the increase or decrease in the amount of ink.

[0076] As described above, the ink used in the inkjet image forming apparatus 1 is a UV curable ink that undergoes a phase change between a gel state and a liquid (sol) state according to temperature without being irradiated with UV. This ink has a phase change temperature of a predetermined temperature, for example, about 40 to 100°C, and liquefies (gelsolizes) uniformly when heated above this phase change temperature. On the other hand, this ink gels at a temperature below the predetermined temperature including normal room temperature (0 to 30°C). In order to smoothly feed the ink from the ink tank 50 to the inkjet head 241 and stably eject it from the inkjet head 241, a warm-up operation is required to reach the appropriate temperature range for the ink temperature in the inkjet head 241 before the image forming operation, that is, to preheat the ink before ejection to keep the ink in an appropriate temperature range.

[0077] However, when the warm-up operation is performed, the ink fed from the ink tank 50 to the inkjet head 241 is heated and liquefied (gelsolized) at the heating target temperature set using the specific heat of the ink. Therefore, even when the temperature of the actual heating part (planar heating member 61) reaches the heating target temperature, depending on the heating target temperature, it may take time for the ink to gelsolize, and as a result, the time for the warm-up operation may become long.

[0078] Therefore, in the present embodiment, from the viewpoint of shortening the time of the warm-up operation, when the warm-up operation for reaching the appropriate temperature range for the ink temperature in the inkjet head 241 is performed, the control unit 40 controls the planar heating member 61 to heat the ink tank 50 at a second heating temperature (a heating temperature capable of preventing ink deterioration) higher than the first heating temperature (a heating temperature capable of ensuring ink fluidity) during the image forming operation. Here, the control unit 40 controls the heating temperature of the ink tank 50 by controlling the heating target temperature of the planar heating member 61. In the present embodiment, in order to improve the temperature rising efficiency of the ink as much as possible, the second heating temperature is set to the highest heating temperature capable of preventing ink deterioration.

[0079] Next, with reference to the flowchart of FIG. 9, an example of the heating control operation (corresponding to the "heating control method" of the present invention) in the inkjet image forming apparatus 1 will be described. Note that the process shown in FIG. 9 is executed when the power of the inkjet image forming apparatus 1 is turned on. Also, the temperature of the ink stored in the storage unit 513 (ink tank 50) is room temperature.

[0080] First, the control unit 40 starts executing a warm-up operation to bring the temperature of the ink in the inkjet head 241 to an appropriate temperature range before the image forming operation (step S100).

[0081] Next, the control unit 40 acquires the temperature of the ink detected by the liquid-contact thermistor 90 provided in the storage unit 513 (ink tank 50) as the ink temperature (step S120).

[0082] Next, the control unit 40 determines whether the ink temperature acquired in step S120 is lower than a second heating temperature (a heating temperature capable of preventing ink deterioration, for example, 95°C) that is higher than a first heating temperature (a heating temperature capable of ensuring ink fluidity, for example, 85°C) during the image forming operation (step S140).

[0083] As a result of the determination, if the ink temperature acquired in step S120 is not lower than the second heating temperature, that is, if the ink temperature is equal to or higher than the second heating temperature (step S140, NO), the control unit 40 determines that the ink temperature detected by the liquid-contact thermistor 90 is abnormal and the liquid-contact thermistor 90 is malfunctioning, and the inkjet image forming apparatus 1 ends the process in FIG. 9.

[0084] On the other hand, when the ink temperature acquired in step S120 is lower than the second heating temperature (step S140, YES), the control unit 40 sets the second heating temperature as the heating target temperature of the planar heating member 61 and performs control to heat the ink tank 50 with the planar heating member 61 (step S160). Specifically, the control unit 40 uses the detection result of a control thermistor (not shown) that detects the temperature of the planar heating member 61 to control the heating amount of the planar heating member 61 so that the actual temperature of the planar heating member 61 becomes the second heating temperature.

[0085] Next, the control unit 40 acquires the ink temperature detected by the liquid-contact thermistor 90 provided in the storage unit 513 (ink tank 50) (step S180).

[0086] Next, the control unit 40 determines whether or not the ink temperature acquired in step S120 is equal to or higher than the first heating temperature (step S200). As a result of the determination, when the ink temperature acquired in step S180 is lower than the first heating temperature (step S200, NO), the process returns to before step S160.

[0087] On the other hand, when the ink temperature acquired in step S180 is equal to or higher than the first heating temperature (step S200, YES), the control unit 40 sets the first heating temperature (< second heating temperature) as the heating target temperature of the planar heating member 61 and performs control to heat the ink tank 50 with the planar heating member 61 (step S220). Specifically, the control unit 40 uses the detection result of a control thermistor that detects the temperature of the planar heating member 61 to control the heating amount of the planar heating member 61 so that the actual temperature of the planar heating member 61 becomes the first heating temperature. When the process of step S220 is completed, the inkjet image forming apparatus 1 ends the process in FIG. 9.

[0088] FIG. 10 corresponds to the flowchart of FIG. 9 and shows an example of the temporal change in the temperature of the ink stored in the storage unit 513 (ink tank 50). In FIG. 10, the solid line LA indicates the control of heating the ink tank 50 at a second heating temperature (e.g., 95° C.) higher than the first heating temperature T1 until the temperature of the ink stored in the storage unit 513 rises from the room temperature T0 and reaches the first heating temperature T1 (e.g., 85° C.) during the image forming operation. The dotted line LB indicates the temporal change in the temperature of the ink when the control of heating the ink tank 50 at the first heating temperature is performed until the temperature of the ink stored in the storage unit 513 rises from the room temperature T0 and reaches the first heating temperature T1 during the image forming operation. Between the solid line LA and the dotted line LB, the temporal change in the temperature of the ink is the same except for the time t2 to t4.

[0089] In FIG. 10, the power of the inkjet image forming apparatus 1 is turned on at time t0. Then, as shown by the solid line LA, at time t1, the control of setting the second heating temperature as the heating target temperature of the planar heating member 61 and heating the ink tank 50 with the planar heating member 61 is started. When performing the control of heating the ink tank 50 at a second heating temperature higher than the first heating temperature T1 during the image forming operation, after the temperature of the ink reaches the first heating temperature T1 at time t3, the control is switched to the control of setting the first heating temperature T1 as the heating target temperature of the planar heating member 61 and heating the ink tank 50 with the planar heating member 61 (holding control). As a result, after the temperature of the ink reaches the first heating temperature T1 at time t3, the first heating temperature T1 is maintained and the warm-up operation is completed.

[0090] On one hand, as shown by the dotted line LB, at time t1, control is started to set the first heating temperature to the target heating temperature of the planar heating member 61 and heat the ink tank 50 with the planar heating member 61. When performing control to heat the ink tank 50 at the first heating temperature T1 during the image forming operation, at time t4 after time t3, the temperature of the ink reaches the first heating temperature T1, and thereafter, control (holding control) is performed to set the first heating temperature T1 to the target heating temperature of the planar heating member 61 and heat the ink tank 50 with the planar heating member 61. As a result, after the temperature of the ink reaches the first heating temperature T1 at time t4, the first heating temperature T1 is maintained and the warm-up operation is completed.

[0091] The reason why the time to reach the first heating temperature T1 is delayed by the dotted line LB compared to the solid line LA is that due to the difference in the target heating temperature of the planar heating member 61, the melting speed of the ink, specifically, the time change rate (slope) of the temperature of the ink after time t2 becomes smaller than that of the solid line LA. Thus, when performing control to heat the ink tank 50 at a second heating temperature higher than the first heating temperature T1 during the image forming operation, compared to the case of performing control to heat the ink tank 50 at the first heating temperature, the temperature rise of the ink is made more efficient, and the time until the temperature of the ink reaches the first heating temperature T1, specifically, the time until the ink is heated and undergoes a phase change from the gel state to the liquid (sol) state, can be shortened by the time indicated by t3 to t4 (shortening time). Consequently, the time of the warm-up operation can be shortened.

[0092] As described above, according to the above-described embodiment, the inkjet image forming apparatus 1 includes an ink tank 50 (ink flow path portion) that supplies the ink stored in the first sub-tank (ink storage portion) to the inkjet head 241, a planar heating member 61 (heating portion) that heats the ink tank 50 (ink flow path portion), and a control unit 40 that controls the planar heating member 61 (heating portion) to heat the ink tank 50 (ink flow path portion) at a second heating temperature higher than the first heating temperature T1 during the image forming operation when a warm-up operation is performed to bring the temperature of the ink in the inkjet head 241 to an appropriate temperature range.

[0093] By performing control to heat the ink tank 50 at a second heating temperature higher than the first heating temperature T1 during the image forming operation, compared with the case of performing control to heat the ink tank 50 at the first heating temperature, the temperature increase of the ink can be made more efficient, and the time until the temperature of the ink reaches the first heating temperature T1, specifically, the time until the ink is heated and phase-changed from the gel state to the liquid (sol) state can be shortened. As a result, the time of the warm-up operation can be shortened.

[0094] In the above embodiment, the control unit 40 may control the planar heating member 61 so as to change the heating temperature of the ink tank 50 according to the temperature of the ink detected by the liquid-contact thermistor 90. Specifically, for example, when the power of the inkjet image forming apparatus 1 is re-supplied and the warm-up operation is performed after the image formation is completed, if the difference between the temperature of the ink detected by the liquid-contact thermistor 90 and the first heating temperature T1 is less than a predetermined temperature (that is, when the fluidity of the ink can be ensured), the control unit 40 may control the planar heating member 61 to heat the ink tank 50 at the first heating temperature T1. In this case, it is not necessary to heat the ink tank 50 at a second heating temperature higher than the first heating temperature T1, and the power consumption of the planar heating member 61 can be suppressed compared with the case of heating the ink tank 50 at the second heating temperature.

[0095] Further, when the printing coverage is larger than a predetermined coverage (solid printing) during the image forming operation and the temperature of the ink detected by the liquid-contact thermistor 90 is lower than the first heating temperature T1, the control unit 40 may control the planar heating member 61 to heat the ink tank 50 at the second heating temperature. Thereby, during the image forming operation, the temperature increase of the ink can be made more efficient, and the time until the temperature of the ink reaches the first heating temperature T1, specifically, the time until the ink is heated and phase-changed from the gel state to the liquid (sol) state can be shortened. As a result, the productivity of the image forming process can be improved.

[0096] Further, the control unit 40 may control the planar heating member 61 so as to change the heating temperature of the ink tank 50 according to the temperature of the ink detected by a plurality of liquid-contact thermistors 90 provided at a plurality of positions of the ink tank 50. For example, the liquid-contact thermistors 90 are provided in the storage section 513 and the second sub-tank 52, and the control unit 40 controls the heating temperature of the planar heating member 61 disposed at the position corresponding to the storage section 513 based on the detection result of the liquid-contact thermistor 90 provided in the storage section 513, and controls the heating temperature of the planar heating member 61 disposed at the position corresponding to the second sub-tank 52 based on the detection result of the liquid-contact thermistor 90 provided in the second sub-tank 52.

[0097] Also, in the above embodiment, the planar heating members 61 are provided at three locations, i.e., the central portion and both end portions in the longitudinal direction of the outer surface of the ink tank 50, but the present invention is not limited thereto. That is, for example, one planar heating member 61 may be provided so as to cover the entire longitudinal direction of the ink tank 50, or two planar heating members 61 may be provided so as to cover the entire longitudinal direction.

[0098] Also, for example, the planar heating members 61 may be provided at four or more locations in the longitudinal direction on the outer surface of the ink tank 50. In this case, as described above, it is preferable that the control unit 40 sets the planar heating members 61 disposed on both end portions side in the longitudinal direction to be at a higher temperature than the planar heating members 61 disposed on the central portion side in the longitudinal direction of the ink tank 50.

[0099] Also, in the above embodiment, the heating temperatures of the three planar heating members 61 are individually controlled by the control unit 40, but the present invention is not limited thereto. For example, the three planar heating members 61 may be integrally configured such that the wiring density of the strip-shaped heating element constituting the planar heating member 61 is sparse on the central portion side in the longitudinal direction of the ink tank 50 and dense on both end portions side in the longitudinal direction of the ink tank 50. Thereby, the heating temperature on both end portions side can be made higher than that on the central portion in the longitudinal direction of the ink tank 50.

[0100] In the above embodiment, the ink tank heating device 60 is configured to include three planar heating members 61, three elastic members 62, and three metal plates 63 in the longitudinal direction of the ink tank 50, respectively. However, the present invention is not limited thereto. For example, it may be configured such that one elastic member 62 and one metal plate 63 cover all three planar heating members 61, or it may be configured such that two or more elastic members 62 and metal plates 63 cover all three planar heating members 61.

[0101] In the above embodiment, a metal plate 63 is used as the plate-like member. However, it does not have to be made of metal as long as it has a rigidity sufficient to transmit the pressing force of the fixing screw 64 to the elastic member 62. For example, it may be made of resin.

[0102] In the above embodiment, the fixing screw 64 is used as the pressing and fixing member. However, any means may be used as long as the metal plate 63 can be fixed in a state where the metal plate 63 is pressed against the ink tank 50 side. For example, a so-called snap lock may be used.

[0103] In the above embodiment, the ink tank heating device 60 is provided with the thermistor 65. However, any detection means may be used as long as it can be attached to the ink tank 50 or the planar heating member 61 and can detect the temperature. For example, a thermocouple may be used. In that case, it is provided so as to be sandwiched between the outer wall surface of the ink tank 50 and the planar heating member 61.

[0104] In the above embodiment, the planar heating member 61 is provided on the outer surface of the ink. However, the present invention is not limited thereto. It may be provided inside the ink tank 50, or may be provided in a non-contact manner with respect to the ink tank 50. When the planar heating member 61 is provided in a non-contact manner with respect to the ink tank 50, the heating portion does not have to be formed in a planar shape, or may be a heat source configured to radiate infrared rays.

[0105] Also, in the above embodiments, each only shows an example of the implementation of the present invention, and the technical scope of the present invention should not be construed in a limited manner by these. That is, the present invention can be implemented in various forms without departing from its gist or its main features.

Explanation of Reference Numerals

[0106] 1 Inkjet Image Forming Apparatus 40 Control Unit 50 Ink Tank 51 First Sub - tank 52 Second Sub - tank 60 Ink Tank Heating Device 61 Planar Heating Member 62 Elastic Member 63 Metal Plate 64 Fixing Screw 65 Thermistor 90 Liquid - Contact Thermistor 80 Ink Heating Device 241 Inkjet Head 511 Flow Path 513 Storage Portion

Claims

1. An ink flow path section that supplies ink stored in an ink storage section to an inkjet head, a heating section that heats the ink flow path section, a temperature detection section that detects the temperature of the ink in the ink flow path section as an ink temperature, a control section that controls the heating section to heat the ink flow path section at a second heating temperature higher than a first heating temperature during an image forming operation when a warm-up operation for bringing the temperature of the ink in the inkjet head to an appropriate temperature range is performed, the control section controls the heating section to change the heating temperature of the ink flow path section according to the detected ink temperature, and when the printing coverage is greater than a predetermined coverage and the detected ink temperature is lower than the first heating temperature during the image forming operation, controls the heating section to heat the ink flow path section at the second heating temperature, An image forming apparatus.

2. The temperature detection section detects the temperature of the ink at a plurality of positions in the ink flow path section. The image forming apparatus according to claim 1.

3. The second heating temperature is a heating temperature capable of preventing deterioration of the ink. The image forming apparatus according to claim 1 or 2.

4. The first heating temperature is a heating temperature capable of ensuring the fluidity of the ink. The image forming apparatus according to any one of claims 1 to 3.

5. The heating section heats an ink tank constituting the ink flow path section. The image forming apparatus according to any one of claims 1 to 4.

6. The ink changes to a gel state or a sol state depending on the temperature of the ink. The image forming apparatus according to any one of claims 1 to 5.

7. The control section controls the heating temperature of the ink flow path section by controlling the heating target temperature of the heating section. The image forming apparatus according to any one of claims 1 to 6.

8. A heating control method in an image forming apparatus including an ink flow path section that supplies ink stored in an ink storage section to an inkjet head and a heating section that heats the ink flow path section, when a warm-up operation for bringing the temperature of the ink in the inkjet head to an appropriate temperature range is performed, controls the heating section to heat the ink flow path section at a second heating temperature higher than a first heating temperature during an image forming operation, ​ Control the heating unit so as to change the heating temperature of the ink flow path portion according to the ink temperature in the ink flow path portion detected by the temperature detection unit, and when the printing coverage is greater than a predetermined coverage during the image forming operation and the detected ink temperature is lower than the first heating temperature, control the heating unit to heat the ink flow path portion at the second heating temperature. Heating control method.

Images