Liquid ejection device

Abstract

To suppress waviness of a sheet caused by moisture absorption of the sheet after drying processing.SOLUTION: A liquid ejection device includes: a sheet supply section configured to unwind a rolled sheet S and supply the unwound sheet S; a liquid ejection section configured to eject liquid onto the supplied sheet S; a drying section 13 configured to dry the sheet S onto which the liquid has been ejected; a sheet recovery section 5 configured to roll up and recover the dried sheet S; and a humidifying section 20 arranged between the drying section 13 and the sheet recovery section 5 and configured to spray fine droplets onto and thereby humidify both surfaces of the sheet S.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a liquid ejection device. [Background technology]

[0002] 2. Description of the Related Art As an example of a liquid ejection device, an inkjet image forming device that ejects ink onto a sheet to form an image is known.

[0003] Furthermore, some inkjet image forming apparatuses are provided with a drying unit that dries the ink ejected onto the sheet.

[0004] For example, Patent Document 1 (JP 2012-111081 A) proposes an invention relating to an image recording device equipped with a drying unit that dries ink that has landed on roll paper. This invention humidifies the roll paper before it is fed to the printing area to prevent the roll paper from shrinking if the moisture content of the roll paper is reduced too much by the drying unit.

[0005] However, although Patent Document 1 proposes a technique for preventing shrinkage of paper due to drying, it does not propose any measures to suppress waviness of the sheet due to moisture absorption by the sheet after drying processing. Summary of the Invention [Problem to be solved by the invention]

[0006] Therefore, an object of the present invention is to suppress waviness of the sheet due to moisture absorption by the sheet after drying treatment. [Means for solving the problem]

[0007] In order to solve the above problems, the liquid ejection device of the present invention is characterized by comprising a sheet supply unit that unwinds and supplies a rolled sheet, a liquid ejection unit that ejects liquid onto the supplied sheet, a drying unit that dries the sheet onto which the liquid has been ejected, a sheet recovery unit that rolls up and recovers the dried sheet, and a humidifying unit that is arranged between the drying unit and the sheet recovery unit and sprays fine droplets onto both sides of the sheet to humidify it. [Effects of the Invention]

[0008] According to the present invention, it is possible to suppress waviness of the sheet caused by moisture absorption of the sheet after drying treatment. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagram illustrating the overall configuration of an image forming apparatus according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a block diagram showing the configuration of a control unit according to the first embodiment of the present invention. [Figure 3] 1 is a schematic diagram showing the configuration of a characteristic part of an image forming apparatus according to a first embodiment of the present invention. [Figure 4] FIG. 2 is a perspective view showing an example of a humidifying unit according to the first embodiment of the present invention. [Figure 5] FIG. 3 is a diagram illustrating the operation of a humidifier according to the first embodiment of the present invention. [Figure 6] FIG. 10 is a schematic plan view of an image forming apparatus according to a second embodiment of the present invention. [Figure 7] FIG. 10 is a schematic view of a humidifier according to a second embodiment of the present invention, as viewed from the upstream side in the sheet conveying direction. [Figure 8] FIG. 10 is a schematic view of an image forming apparatus according to a third embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be described below with reference to the accompanying drawings. In each drawing for explaining the present invention, components such as members and components having the same function or shape are designated by the same reference numerals as far as they can be distinguished, and once they have been described, their description will be omitted.

[0011] <Overall configuration of liquid ejection device> First, the overall configuration of a liquid ejection apparatus according to a first embodiment of the present invention will be described using an inkjet image forming apparatus as an example.

[0012] FIG. 1 is a diagram showing the overall configuration of an image forming apparatus 100 according to a first embodiment of the present invention.

[0013] As shown in FIG. 1, the image forming apparatus 100 according to the first embodiment of the present invention includes a sheet supply unit 1, a first image forming unit 2, an inversion mechanism unit 3, a second image forming unit 4, a sheet recovery unit 5, a first sheet detection unit 6, a second sheet detection unit 7, a third sheet detection unit 8, and a control unit 9.

[0014] The sheet supply unit 1 has a supply roller around which a long sheet S is wound in a roll. When the supply roller rotates, the sheet S is fed out and supplied to the first image forming unit 2.

[0015] The first image forming unit 2 forms an image on a first surface (front surface) of the sheet S supplied from the sheet supply unit 1. In this case, the first image forming unit 2 has a first liquid ejection unit 10 that ejects ink, which is a liquid, onto the first surface of the sheet S, and a first drying unit 11 that dries the sheet S onto which the ink has been ejected.

[0016] The first liquid ejection section 10 has a plurality of liquid ejection units 10Y, 10M, 10C, and 10K that eject ink (liquid) of different colors, such as yellow, magenta, cyan, and black. An image is formed on the first side of the sheet S by ejecting ink from the plurality of liquid ejection units 10Y, 10M, 10C, and 10K onto the first side of the sheet S. The number of liquid ejection units is not limited to four, and may be one, two, three, or five or more. Furthermore, the ink ejected from the liquid ejection units is not limited to yellow, magenta, cyan, and black, and may be ink of another color.

[0017] The first drying unit 11 has a cylindrical heating drum 11a in which a heat source such as a halogen heater is disposed. After ink is ejected onto the first surface of the sheet S, the sheet S is transported to the first drying unit 11, where the sheet S is transported while being wrapped around the heating drum 11a, and the sheet S is heated. This evaporates moisture or solvent contained in the ink on the sheet S, drying the sheet S. Note that, as a heating means for heating the sheet S, instead of a contact-type heating means such as the heating drum 11a, a non-contact heating means such as a hot air generator that blows hot air onto the sheet S may be used. Alternatively, a contact-type heating means and a non-contact heating means may be used in combination.

[0018] The reversing mechanism 3 has a function of reversing a first side (front side) of the sheet S to a second side (back side) opposite to the first side. When the sheet S that has passed through the first drying unit 11 is conveyed to the reversing mechanism 3, the first side and the second side of the sheet S are reversed, and the sheet S is conveyed to the second image forming unit 4. That is, when the sheet S is conveyed to the reversing mechanism 3 with the first side facing up, the sheet S is reversed so that the first side faces down, and the sheet S is conveyed to the second image forming unit 4 in the reversed state.

[0019] The second image forming unit 4 forms an image on the second surface (back surface) of the inverted sheet S. In this case, the second image forming unit 4 has a second liquid ejection unit 12 that ejects ink onto the second surface of the sheet S, and a second drying unit 13 that dries the sheet S onto which the ink has been ejected.

[0020] The second liquid ejection section 12 has the same configuration as the first liquid ejection section 10, and has a plurality of liquid ejection units 12Y, 12M, 12C, and 12K. When the sheet S is conveyed to the second liquid ejection section 12, ink is ejected onto the second side of the sheet S from the plurality of liquid ejection units 12Y, 12M, 12C, and 12K, thereby forming an image on the second side of the sheet S. The number of liquid ejection units included in the second liquid ejection section 12 and the ink ejected from the liquid ejection units can be changed as appropriate.

[0021] The second drying section 13 has the same configuration as the first drying section 11, and includes a heating drum 13a as a heating means. Therefore, when the sheet S with ink ejected onto its second surface is transported to the second drying section 13, the sheet S is dried by being wrapped around the heating drum 13a while being transported. The heating means of the second drying section 13 is not limited to a contact type, and may be a non-contact type. Furthermore, a contact type heating means and a non-contact type heating means may be used in combination.

[0022] The sheet recovery section 5 has a recovery roller that winds up and recovers the sheet S. As the recovery roller rotates, the sheet S is wound up into a roll and recovered. In this case, the sheet S is transported continuously without interruption from the sheet supply section 1 to the sheet recovery section 5, so as the transport of the sheet S progresses, the amount of the sheet S in the sheet supply section 1 decreases, and conversely, the amount of the sheet S recovered in the sheet recovery section 5 increases.

[0023] The first sheet detection unit 6, the second sheet detection unit 7, and the third sheet detection unit 8 are configured with transmission-type optical sensors. In the first embodiment of the present invention, the first sheet detection unit 6 is arranged between the sheet supply unit 1 and the first image forming unit 2. The second sheet detection unit 7 is arranged between the first liquid discharge unit 10 and the first drying unit 11. The third sheet detection unit 8 is arranged between the second liquid discharge unit 12 and the second drying unit 13. When the sheet S passes through these sheet detection units 6, 7, and 8, they output detection signals according to the state of the sheet S.

[0024] The control unit 9 generates image data to be formed on the sheet S, and also controls various operations of the sheet supply unit 1, the first image forming unit 2, the reversing mechanism unit 3, the second image forming unit 4, and the sheet collection unit 5. The control unit 9 also determines whether the condition of the sheet S is abnormal or not based on the detection signals output by the sheet detection units 6, 7, and 8.

[0025] <Controller configuration> Next, the configuration of the control unit 9 according to the first embodiment of the present invention will be described.

[0026] FIG. 2 is a block diagram showing the configuration of the control unit 9 according to the first embodiment of the present invention.

[0027] As shown in FIG. 2, the control unit 9 according to the first embodiment of the present invention includes a discharge amount calculation unit 202, a conveying speed setting unit 204, a sheet thickness setting unit 205, a main control unit 201, a discharge control unit 207, a conveying control unit 208, and a drying temperature control unit 209.

[0028] The discharge amount calculation unit 202 is a part that calculates the amount of ink (liquid) to be discharged onto a sheet based on image information input by the input unit 300. The input unit 300 is, for example, an external device such as a PC (Personal Computer), or a touch panel input device. The ink discharge amount is obtained by calculating the ink discharge amount per unit area or unit time. Information on the ink discharge amount calculated by the discharge amount calculation unit 202 is sent to the main control unit 201.

[0029] The conveying speed setting unit 204 is a part that sets the sheet conveying speed based on speed information input by the input unit 300. Information on the conveying speed set by the conveying speed setting unit 204 is sent to the main control unit 201.

[0030] The sheet thickness setting unit 205 is a part that sets the thickness of a sheet based on thickness information input by the input unit 300. The input thickness information may be a thickness that is preset for each type of sheet, or, instead of thickness, basis weight, which is correlated with the thickness of the sheet, may be used. Basis weight is a value that represents the mass per unit area of ​​a sheet, and generally, the greater the basis weight, the greater the thickness of the sheet. The sheet thickness information set by the sheet thickness setting unit 205 is sent to the main control unit 201.

[0031] The main control unit 201 is a part that controls the overall operation of the image forming apparatus 100 .

[0032] Specifically, the main control unit 201 generates an image formation control signal based on image information input by the input unit 300. Then, when the image formation control signal is sent from the main control unit 201 to the discharge control unit 207, the discharge control unit 207 controls the liquid discharge operations of the first liquid discharge unit 10 and the second liquid discharge unit 12. In this way, images are formed on the first and second surfaces of the sheet.

[0033] Furthermore, the main control unit 201 generates a conveying speed control signal based on information about the conveying speed set by the conveying speed setting unit 204. Then, when the conveying speed control signal is sent from the main control unit 201 to the conveying control unit 208, the conveying control unit 208 controls the conveying operation of the conveying unit 500. The conveying unit 500 includes a supply roller of the sheet supply unit 1 and a collection roller for sheet collection, as well as other conveying rollers for conveying the sheet. By controlling the conveying unit 500, the sheet is conveyed at a set speed.

[0034] The main control unit 201 also generates a drying temperature control signal based on information about the ink ejection amount calculated by the ejection amount calculation unit 202, thickness information set by the sheet thickness setting unit 205, and temperature information detected by the drying temperature detection unit 400. The drying temperature detection unit 400 is a contact or non-contact temperature sensor that detects the temperatures of the heating drums 11a, 13a of the first drying unit 11 and the second drying unit 13. When the drying temperature control signal is sent from the main control unit 201 to the drying temperature control unit 209, the drying temperature control unit 209 controls the temperatures of the heating drums 11a, 13a of the first drying unit 11 and the second drying unit 13. As a result, the temperature of each heating drum 11a, 13a is controlled based on the amount of liquid ejected onto the sheet, the thickness of the sheet, and the temperature of the nearest heating drum 11a, 13a, and the sheet is heated and dried at an appropriate temperature.

[0035] Furthermore, the main control unit 201 determines whether the state of the sheet is abnormal based on the detection signals output by the first sheet detection unit 6, the second sheet detection unit 7, and the third sheet detection unit 8. As a result, if at least one of the detection signals from these sheet detection units 6, 7, and 8 indicates an abnormality in the sheet, the main control unit 201 issues an instruction to the conveyance control unit 208, and the conveyance control unit 208 controls the conveyance unit 500 to stop the rotation of the supply roller, collection roller, and other conveyance rollers or to slow down the rotation speed. When the rotation speed is slowed down, the deceleration amount may be the same for the supply roller, collection roller, and conveyance roller, or may be different.

[0036] <Issues of sheet waviness> Here, the problem of waviness of the sheet will be described.

[0037] When a sheet onto which ink has been ejected is heated and dried, not only does the water or solvent contained in the ink evaporate, but the water contained in the sheet also evaporates, resulting in a decrease in the moisture content of the sheet. For example, the moisture content of the sheet after drying decreases from approximately 5% to approximately 1%. If the sheet is left in a state with a reduced moisture content, it will absorb moisture from the air, causing it to partially expand and deform into a wavy shape, resulting in sheet rippling. In particular, if the sheet is left cut to a specified size, the surface of the sheet exposed to the air is larger than when the sheet is left rolled up, which increases the amount of moisture absorbed by the sheet and tends to result in more pronounced rippling.

[0038] Therefore, in the image forming apparatus according to the first embodiment of the present invention, the following configuration is adopted to suppress waviness of the sheet due to moisture absorption by the sheet after drying processing. The configuration of the characteristic parts according to the first embodiment of the present invention will be described below.

[0039] <Configuration of Characteristic Part According to the First Embodiment of the Present Invention> FIG. 3 is a schematic diagram showing the configuration of a characteristic part of the image forming apparatus 100 according to the first embodiment of the present invention.

[0040] 3, in the image forming apparatus 100 according to the first embodiment of the present invention, a humidifying unit 20 that humidifies the sheet S is disposed between the second drying unit 13 and the sheet recovery unit 5. The humidifying unit 20 has a spraying unit 21 that sprays fine droplets in a mist, a liquid supply source 22 that supplies liquid to the spraying unit 21, and an air supply source 23 that supplies atomized air to the spraying unit 21.

[0041] The spray units 21 are disposed both above and below the sheet conveying path between the second drying unit 13 and the sheet recovery unit 5. Each spray unit 21 is connected to a liquid supply pipe 24 for transporting the humidifying liquid supplied from the liquid supply source 22 and an air supply pipe 25 for transporting the atomized air supplied from the air supply source 23. In the first embodiment of the present invention, an example is described in which the humidifying liquid is water, but the humidifying liquid supplied from the liquid supply source 22 may be a liquid other than water. The atomized air supplied from the air supply source 23 may be air or a gas other than air.

[0042] The liquid supply source 22 and the air supply source 23 are controlled by the control unit 9. This controls the spray start timing and spray stop timing of each spray unit 21, the spray amount, and the like.

[0043] FIG. 4 is a perspective view showing an example of the humidifying section 20 according to the first embodiment of the present invention.

[0044] As shown in Figure 4, the humidifying unit 20 is provided with a frame 26 that supports the spray unit 21. The frame 26 is made up of a rectangular parallelepiped frame member that is open in each of the three directions: up / down, left / right, and front / rear (three mutually perpendicular directions).

[0045] Each spray unit 21 is attached to and supported by the frame 26 via an L-shaped mounting member 27. In this case, two spray units 21 are attached to the upper part of the frame 26 via the mounting members 27, and another two spray units 21 are attached to the lower part of the frame 26 via the mounting members 27. The sheet S passes between the spray units 21 attached to the upper part of the frame 26 and the spray units 21 attached to the lower part of the frame 26 in the direction of arrow A in FIG. 4 and is transported to the sheet recovery unit 5. That is, in the first embodiment of the present invention, of the four spray units 21, the two spray units 21 attached to the upper part of the frame 26 are arranged to face the upper surface (second surface) of the sheet S, and the two spray units 21 attached to the lower part of the frame 26 are arranged to face the lower surface (first surface) of the sheet S.

[0046] In the first embodiment of the present invention, the spray unit 21 includes a storage unit 28 that stores humidification liquid (water) supplied from a liquid supply source 22, and a plurality of nozzles 29 that spray the humidification liquid stored in the storage unit 28 as fine droplets. The fine droplets sprayed from the plurality of nozzles 29 are mist-like fine droplets known as dry fog, with an average particle diameter of 10 μm or less and a maximum particle diameter of 50 μm or less. Because these fine droplets have a smaller particle diameter than droplets sprayed by a typical sprayer, which have a particle diameter of approximately 100 μm, they tend to float in the air and are less likely to be absorbed by objects even if they adhere to them, making them less likely to wet the object. The "average particle diameter" here refers to the Sauter mean particle diameter measured using a laser diffraction particle size distribution analyzer for the fine droplets sprayed from the nozzles, measured at a point 30 cm from the tip of the nozzle.

[0047] <Humidification unit operation> Next, the operation of the humidifying unit 20 according to the first embodiment of the present invention will be described with reference to FIG.

[0048] When sheet conveyance begins with the start of the image forming operation, as shown in FIG. 5, in the humidifying unit 20, fine droplets F are sprayed from the spray unit 21 facing the upper surface (second surface) of the sheet S and the spray unit 21 facing the lower surface (first surface) of the sheet. At this time, the fine droplets F are sprayed from directions intersecting each of the two surfaces (first surface and second surface) of the sheet S, float in the air, and adhere to both surfaces of the sheet S. Some of the floating fine droplets F enter the sheet recovery unit 5 together with the sheet S. Then, while the sheet S is conveyed in a serpentine manner along a conveyance path 30 provided in the sheet recovery unit 5, more fine droplets F adhere to the sheet S. Thereafter, the sheet S is wound into a roll by a recovery roller 31 and recovered.

[0049] In the first embodiment of the present invention, the sprayed fine droplets F are dry fog that is not easily absorbed even if it adheres to an object. Therefore, even if the fine droplets F adhere to the sheet S, the fine droplets F are not immediately absorbed by the sheet S but remain attached to the surface of the sheet S. However, when the sheet S is subsequently wound up by the recovery roller 31, the fine droplets F are pressurized between the wound sheets S and are absorbed into the sheet S. This replenishes moisture within the sheet S, increasing the moisture content of the sheet S. Furthermore, in the first embodiment of the present invention, the fine droplets F floating within the sheet recovery unit 5 adhere to the sheet S while the sheet S is transported along the meandering transport path 30 within the sheet recovery unit 5, thereby effectively increasing the amount of fine droplets F adhering to both sides of the sheet S. In other words, the meandering transport path 30 ensures a long transport distance for the sheet S within the sheet recovery unit 5, making it easier for the fine droplets F to adhere to the sheet S.

[0050] In this way, in the first embodiment of the present invention, the fine droplets F are effectively attached to both sides of the sheet S, and then the fine droplets F on both sides can be effectively absorbed into the sheet S by winding up the sheet S, thereby appropriately increasing the moisture content of the sheet S. As a result, even if the wound-up sheet S is cut to a predetermined size and left as it is, the subsequent moisture absorption of the sheet S can be reduced, and waviness of the sheet S due to moisture absorption can be suppressed.

[0051] Furthermore, in the first embodiment of the present invention, dry fog is used as the fine droplets F that adhere to the sheet S, which does not easily wet the object even when it adheres to the sheet S. Therefore, even if the fine droplets F adhere to peripheral components other than the sheet S, the peripheral components can be prevented from wetting. In particular, in the humidifying unit 20, since the spray unit 21 is not covered by an exterior of the device, excess fine droplets F are absorbed into the air. Therefore, according to the first embodiment of the present invention, excess fine droplets F do not adhere to the internal components of the humidifying unit 20 and the sheet recovery unit 5 and cause waterlogging, making maintenance and management of the device easier. Furthermore, since there is no need to install a mechanism to exhaust or recover excess fine droplets F, costs can be reduced. Furthermore, a spraying method using dry fog is easier to maintain than a method of humidifying a sheet using a wetting roller, etc., and therefore has the advantage of reducing maintenance costs.

[0052] Furthermore, in order to prevent components inside the device from getting wet with the fine droplets F, it is preferable that the frame 26 (see FIG. 4) provided in the humidifying unit 20 is a frame that is open in at least four directions, among the up-down direction, the left-right direction, and the front-rear direction. By opening the frame 26 in four or more directions, breathability is ensured within the frame 26, and excess fine droplets F are easily absorbed into the air. This prevents the humidifying unit 20 from becoming flooded with excess fine droplets F, making it easier to maintain and manage the device.

[0053] Furthermore, in the first embodiment of the present invention, the conveyance path 30 provided in advance in the sheet recovery unit 5 is used to cause the sheet S to meander, thereby ensuring a long conveyance path for the sheet S. However, the meandering conveyance path is not limited to being provided in the sheet recovery unit 5, and may be provided in, for example, the humidifier unit 20. Even in such a case, a long conveyance path for the sheet S passing through the floating fine droplets F can be ensured, which makes it easier for the fine droplets F to adhere to the sheet S. On the other hand, when the meandering conveyance path is substituted with the conveyance path 30 provided in advance in the sheet recovery unit 5, as in the first embodiment of the present invention, it is not necessary to provide a new meandering conveyance path, thereby reducing manufacturing costs.

[0054] Furthermore, as in the first embodiment of the present invention, it is preferable that a plurality of spray units 21 are arranged across the width direction of both sides of sheet S (see FIG. 4). Note that the "width direction" here refers to the direction along the first or second surface of sheet S, and is perpendicular to the sheet conveying direction A (see FIG. 4). The "width direction" in the following description also has the same meaning. By arranging a plurality of spray units 21 across the width direction of sheet S, it becomes easier to uniformly humidify sheet S across the width direction, and therefore waviness of sheet S can be more reliably suppressed.

[0055] Furthermore, if there is a difference in the amount of humidification between the first surface and the second surface of the sheet S, there is a risk that the sheet S will curl. For this reason, it is preferable that the nozzle 29 of the spray unit 21 facing the first surface of the sheet S and the nozzle 29 of the spray unit 21 facing the second surface of the sheet S are disposed at the same distance from the first surface or the second surface of the sheet S that they face. By disposing each nozzle 29 at the same distance from both surfaces of the sheet S, the amount of humidification on both surfaces can be made approximately the same, and curling due to differences in the amount of humidification can be suppressed.

[0056] Furthermore, it is preferable that the spraying of the fine droplets F by the spraying unit 21 be started simultaneously with or after the start of the supply operation of the sheet S by the sheet supply unit 1 and the collection operation of the sheet S by the sheet collection unit 5. If the spraying of the fine droplets F were started in a stopped state before the sheet S was conveyed, there is a risk that too many fine droplets F would adhere to the stopped sheet S. For this reason, it is preferable that the spraying of the fine droplets F be started while the sheet S is being conveyed.

[0057] Furthermore, since the spraying of the fine droplets F only needs to be performed after the sheet S has been finally dried and before it is wound up, as in the first embodiment of the present invention, the humidifying unit 20 may be disposed between the second drying unit 13, which performs the final drying process, and the sheet recovery unit 5. An inspection device for inspecting the sheet S may be disposed between the humidifying unit 20 and the sheet recovery unit 5. However, to effectively absorb the fine droplets F by winding up the sheet S, it is preferable to dispose the humidifying unit 20 immediately before the sheet recovery unit 5. By disposing the humidifying unit 20 immediately before the sheet recovery unit 5, the sheet S is wound up immediately after the fine droplets F adhere to it, allowing the fine droplets F to be absorbed into the sheet S before they evaporate. Note that "immediately before" here means that no device that performs any other process other than the humidifying process and the recovery process is interposed between the humidifying unit 20 and the sheet recovery unit 5.

[0058] Furthermore, in the first embodiment of the present invention, the amount of fine droplets F sprayed can be controlled by the control unit 9, and the amount of fine droplets F sprayed can be controlled based on at least one piece of information: the type of sheet, the sheet conveying speed by the sheet supply unit 1 and the sheet recovery unit 5, and the drying temperatures of the first drying unit 11 and the second drying unit 13. The type of sheet, the sheet conveying speed, and the drying temperature can be acquired by the main control unit 201 from, for example, information input by the input unit 300 shown in FIG. 2, speed information set by the conveying speed setting unit 204, and temperature information detected by the drying temperature detection unit 400. The main control unit 201 controls the liquid supply source 22 and the air supply source 23, so that the amount of fine droplets F sprayed from the spray unit 21 can be controlled to an appropriate amount depending on the type of sheet, the sheet conveying speed, or the drying temperature.

[0059] Next, another embodiment of the present invention will be described. In the following description, differences from the first embodiment of the present invention will be mainly described, and descriptions of the same parts will be omitted as appropriate.

[0060] <Second embodiment of the present invention> Fig. 6 is a schematic plan view of an image forming apparatus 100 according to a second embodiment of the present invention, and Fig. 7 is a schematic view of a humidifier 20 according to the second embodiment of the present invention, viewed from the upstream side in the sheet conveying direction.

[0061] 6 and 7, in the humidifier unit 20 according to the second embodiment of the present invention, the spray units 21 are disposed at positions on both outer sides in the width direction of the sheet S. In other words, the spray units 21 are disposed at positions facing both ends in the width direction of the sheet S. Other than that, the configuration is the same as that of the first embodiment of the present invention.

[0062] In this case, when spraying of fine droplets F starts from the spray unit 21, the fine droplets F are sprayed onto the sheet S from the lateral direction, that is, from the outside in the width direction of the sheet S. The sprayed fine droplets F move along and adhere to both surfaces of the sheet S. Then, as in the first embodiment of the present invention, the sheet S is taken up in the sheet recovery unit 5, and the fine droplets F on the sheet S are absorbed into the sheet S.

[0063] In this way, also in the second embodiment of the present invention, the fine droplets F are attached to both sides of the sheet S, and then the fine droplets F on both sides can be effectively absorbed into the sheet S by winding up the sheet S, thereby appropriately increasing the moisture content of the sheet S. As a result, even if the wound-up sheet S is cut to a predetermined size and left as it is, the subsequent moisture absorption of the sheet S can be reduced, and therefore, waviness of the sheet S due to moisture absorption can be suppressed.

[0064] Third Embodiment of the Present Invention FIG. 8 is a schematic diagram of an image forming apparatus 100 according to a third embodiment of the present invention.

[0065] 8, in the third embodiment of the present invention, an image forming apparatus 100 includes a moisture content detection unit 40 that detects the moisture content of a sheet S after it has passed through a humidifying unit 20. As the moisture content detection unit 40, a known moisture content detection device such as a near-infrared type or a microwave type can be applied.

[0066] The moisture content of the sheet S is detected by the moisture content detection unit 40, and the control unit 9 controls the liquid supply source 22 and the air supply source 23 based on the detected moisture content, thereby controlling the amount of fine droplets F sprayed from the spray unit 21 to an appropriate amount according to the moisture content of the sheet S. Furthermore, if possible, the detected moisture content may be fed back in real time to control the amount of fine droplets F sprayed.

[0067] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and appropriate design modifications are possible within the scope of the gist of the present invention.

[0068] In the above embodiment, the case where the fine droplets F sprayed by the spray unit 21 are dry fog has been described as an example, but the fine droplets F may also be droplets sprayed by a general spray, etc. In this case, there is a risk that the inside of the device will become wet with water droplets compared to dry fog, but by taking measures such as exhausting excess fine droplets F to the outside of the device or recovering excess moisture, it is possible to prevent the inside of the device from becoming flooded with water.

[0069] Furthermore, in the above-described embodiment, an image forming apparatus that forms images on both sides of a sheet has been described as an example, but the image forming apparatus according to the present invention may also form an image on only one side of a sheet. Therefore, the image forming apparatus may include an image forming unit that forms an image on only one side of a sheet, and a drying unit that dries the sheet with an image formed on one side. Furthermore, the image forming apparatus according to the present invention may include a so-called line-type liquid ejection unit that ejects liquid while remaining stationary onto a sheet being transported, or may include a so-called serial-type liquid ejection unit that ejects ink while moving in the width direction of the sheet.

[0070] Furthermore, in the above-described embodiment, the liquid ejection device according to the present invention has been described as an inkjet image forming device, but the liquid ejection device according to the present invention may be an image forming device, or may be a liquid ejection device that ejects a treatment liquid or the like to modify the surface of a sheet before image formation.

[0071] Furthermore, the sheet used in the liquid ejection device according to the present invention may be paper or a sheet made of a material other than paper. Even if the sheet is made of a material other than paper, if the sheet may become wavy due to moisture absorption after drying, the present invention can be applied to humidify the sheet to suppress the wavy state.

[0072] To summarize the above-described aspects of the present invention, the present invention includes at least the following aspects.

[0073] [First aspect] The first aspect is a liquid ejection device comprising a sheet supply unit that unwinds and supplies a rolled sheet, a liquid ejection unit that ejects liquid onto the supplied sheet, a drying unit that dries the sheet onto which the liquid has been ejected, a sheet recovery unit that rolls up and recovers the dried sheet, and a humidifying unit that is positioned between the drying unit and the sheet recovery unit and sprays fine droplets onto both sides of the sheet to humidify it.

[0074] [Second aspect] In a second aspect, in the first aspect, the humidifying unit sprays the fine droplets onto each of the two surfaces of the sheet in directions that intersect with each other.

[0075] [Third aspect] A third aspect is the second aspect, wherein the humidifying unit has a spray unit that sprays the fine droplets, and a plurality of the spray units are arranged across the width direction of both surfaces of the sheet.

[0076] [Fourth aspect] In a fourth aspect, in the second or third aspect, the humidifying unit has a spray unit that sprays the fine droplets, and the nozzles of the spray unit are arranged so as to face both sides of the sheet at the same distance.

[0077] [Fifth aspect] In a fifth aspect, in the first aspect, the humidifying unit sprays the fine droplets from a lateral direction that is outside the width direction of the sheet.

[0078] [Sixth aspect] A sixth aspect is any one of the first to fifth aspects, wherein the humidifying unit is disposed immediately before the sheet recovery unit.

[0079] [Seventh aspect] A seventh aspect is any one of the first to sixth aspects, wherein the spraying of the fine droplets is started simultaneously with or after the start of the sheet supply operation and the sheet recovery operation.

[0080] [Eighth aspect] An eighth aspect is any one of the first to seventh aspects, wherein the fine droplets are mist-like droplets having an average particle size of 10 μm or less and a maximum particle size of 50 μm or less.

[0081] [Ninth aspect] A ninth aspect is any one of the first to eighth aspects, wherein the amount of fine droplets sprayed is controlled based on at least one piece of information: the type of sheet, the sheet conveying speed by the sheet supply section and the sheet recovery section, and the drying temperature of the drying section.

[0082] [Tenth aspect] A tenth aspect is any one of the first to ninth aspects, further comprising a moisture content detection unit that detects the moisture content of the sheet after it has passed through the humidification unit, and the amount of fine droplets sprayed is controlled based on the moisture content of the sheet detected by the moisture content detection unit.

[0083] [Eleventh aspect] An eleventh aspect is any one of the first to tenth aspects, wherein the humidifier unit has a spray unit that sprays the fine droplets, and the spray unit is arranged within a frame body that is open in at least four directions, including the up-down direction, the left-right direction, and the front-back direction. [Explanation of symbols]

[0084] 1 Sheet supply unit 5 Sheet collection section 10 First liquid ejection unit 11 First drying section 12 Second liquid discharge unit 13 Second drying section 20 Humidification unit 21 Spray section 26 Frame 29 nozzles 40 Moisture content detector 100 Image forming device (liquid ejection device) F Fine droplet S seat [Prior art documents] [Patent documents]

[0085] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-111081

Claims

1. a sheet supply unit that unwinds and supplies a rolled sheet; a liquid ejection unit that ejects liquid onto the supplied sheet; a drying unit that dries the sheet onto which the liquid has been ejected; a sheet recovery unit that winds up and recovers the dried sheet; a humidifying unit disposed between the drying unit and the sheet recovery unit, which sprays fine droplets onto both sides of the sheet to humidify the sheet; A liquid ejection device comprising:

2. The liquid ejection device according to claim 1 , wherein the humidifying unit sprays the fine droplets onto both surfaces of the sheet in directions that intersect with each other.

3. The humidifying unit has a spray unit that sprays the fine droplets, The liquid ejection device according to claim 2 , wherein a plurality of the spray units are arranged across the width of both sides of the sheet.

4. The humidifying unit has a spray unit that sprays the fine droplets, The liquid ejection device according to claim 2 , wherein the nozzles of the spray unit are arranged to face both sides of the sheet at equal distances.

5. The liquid ejection device according to claim 1 , wherein the humidifying unit sprays the fine droplets from a lateral direction that is an outer side in the width direction of the sheet.

6. The liquid ejection apparatus according to claim 1 , wherein the humidifying unit is disposed immediately before the sheet recovery unit.

7. The liquid ejection device according to claim 1 , wherein the spraying of the fine droplets is started simultaneously with or after the start of the sheet supply operation and the sheet recovery operation.

8. 2. The liquid ejection device according to claim 1, wherein the fine droplets are mist-like droplets having an average particle size of 10 [mu]m or less and a maximum particle size of 50 [mu]m or less.

9. The liquid ejection device according to claim 1 , wherein the amount of the fine droplets sprayed is controlled based on at least one of information on the type of the sheet, the sheet transport speed by the sheet supply unit and the sheet recovery unit, and the drying temperature of the drying unit.

10. a moisture content detection unit that detects the moisture content of the sheet after passing through the humidifying unit, The liquid ejection device according to claim 1 , wherein the amount of the fine droplets sprayed is controlled based on the moisture content of the sheet detected by the moisture content detection unit.

11. The humidifying unit has a spray unit that sprays the fine droplets, The liquid ejection device according to claim 1 , wherein the spray unit is disposed within a frame that is open in at least four directions among the up-down direction, the left-right direction, and the front-rear direction.

Images