Image forming device

Abstract

This image forming device comprises: a transport mechanism having a transport path for transporting a recording medium; an image forming unit that forms an image onto the recording medium; a drying unit that dries the recording medium onto which an image has been formed; and a cooling unit that cools the dried recording medium, wherein the transport path has a main transport path where the image forming unit and the drying unit are located, a delivery path that transports the recording medium from the main transport path to an accumulation device, and a return transport path, which is a path provided branching off with the delivery path from the main transport path and which returns the recording medium from the main transport path to the image forming unit, and the cooling unit includes a cooling unit for duplex printing located on the return transport path.

Description

Image forming device

[0001] The present disclosure relates to an image forming apparatus.

[0002] Some image forming apparatuses, such as inkjet printers using aqueous inks, are equipped with a drying unit for drying an image formed on the recording surface of a recording medium (see, for example, Japanese Patent Application Laid-Open No. 2023-008699). If the recording surface on which an image is formed (hereinafter referred to as the image surface) comes into contact with a conveying member or the like while the image is not yet sufficiently dried, fine white spots may appear in the image due to bleeding of the ink in an insufficiently dried state. The drying unit is used to prevent image defects such as fine white spots by drying the formed image after the image is formed and before the image surface comes into contact with a conveying member or the like.

[0003] The printing device described in JP 2023-008699 A is a double-sided printing device equipped with a return transport path that returns the recording medium to the image forming unit after an image has been recorded on a first recording side of the recording medium by an image forming unit, for image recording on a second recording side, which is the reverse side of the first recording side. In a printing device equipped with such a return transport path, when the recording medium is returned to the image forming unit, the image side of the recording medium is transported in the return transport path while in contact with a transport member, which makes it more likely that force will be applied to the image side, and this makes it more likely that image defects will occur compared to when the recording medium is discharged without being transported on the return transport path.

[0004] The present disclosure has been made in consideration of the above circumstances, and has an object to provide an image forming apparatus that can suppress poor quality of image formation during double-sided printing.

[0005] The image forming apparatus of the present disclosure comprises a transport mechanism having a transport path for transporting a recording medium, an image forming unit that applies ink to the recording medium to form an image, a drying unit that dries the recording medium on which the image has been formed, and a cooling unit that cools the dried recording medium, wherein the transport path comprises a main transport path in which the image forming unit and the drying unit are arranged, a discharge path that transports the recording medium from the main transport path to an accumulation device, and a return transport path that is a path branched from the main transport path to the discharge path and returns the recording medium from the main transport path to the image forming unit, and the cooling unit includes a cooling unit for double-sided printing that is arranged on the return transport path.

[0006] It is preferable that the main transport path further includes a first cooling unit arranged after the drying unit, and the cooling unit for double-sided printing is a second cooling unit that further cools the recording medium cooled by the first cooling unit.

[0007] It is preferable that the transport mechanism includes a plurality of transport members, and transports the recording medium from the image forming unit to a position where it passes through the cooling unit for double-sided printing without bringing the image surface of the recording medium, on which the image is recorded, into contact with the transport members.

[0008] The conveying mechanism includes a plurality of conveying members, and among the plurality of conveying members, it is preferable that the adhesive work between the conveying member that first comes into contact with the image surface on which the image of the recording medium has been recorded after passing through the image forming unit and the image surface is 110 mNm or less, and more preferably 80 mNm or less.

[0009] The ink is an aqueous ink, and the aqueous ink contains resin particles, and the glass transition temperature Tg°C of the resin particles, the temperature T1°C of the image surface on which the image is recorded immediately after drying by the drying unit, and the temperature T2°C of the image surface at the time of initial contact between the conveying member and the image surface on which the image is recorded preferably satisfy the relationship T1>Tg-40>T2. It is more preferable that T1>Tg-35 Tg-57>T2, and it is even more preferable that T1>Tg-17 Tg-59>T2.

[0010] The conveying mechanism includes a plurality of conveying members, and it is preferable that among the plurality of conveying members, the conveying member with which the image surface of the recording medium on which the image is recorded after passing through the image forming unit comes into contact, and that the conveying member that conveys the recording medium by curving it, has a radius of curvature of 50 mm or more.

[0011] The apparatus may further include a processor that controls the conveying mechanism, the image forming unit, the drying unit, and the cooling unit, and the processor may be configured to control the conveying mechanism, the drying unit, and the cooling unit under conditions such that the moisture content of the recording medium after being cooled by the cooling unit for double-sided printing is 1.0 to 14.5%.

[0012] The apparatus further includes a processor for controlling the conveying mechanism, the image forming unit, the drying unit, and the cooling unit, and the processor is configured to determine whether the amount of residual solvent in the recording medium after being cooled by the cooling unit for double-sided printing is 160 μg / cm ２ The conveying mechanism, the drying unit, and the cooling unit may be controlled under the following conditions:

[0013] According to the image forming apparatus of the present disclosure, it is possible to suppress poor quality of image formation during double-sided printing.

[0014] It is an overall configuration diagram of an inkjet printing apparatus according to an embodiment. It is an enlarged view of a part of the inkjet printing apparatus shown in FIG. It is a functional block diagram showing a schematic configuration of a control system of the inkjet printing apparatus. It is an overall configuration diagram of an inkjet printing apparatus according to a modified example.

[0015] Hereinafter, an embodiment of an image forming apparatus according to the present disclosure will be described with reference to the drawings. In each drawing, the same elements are denoted by the same reference numerals.

[0016] "Configuration of Inkjet Printing Apparatus" Fig. 1 is a diagram showing the overall configuration of an inkjet printing apparatus 1 according to an embodiment of the image forming apparatus of the present disclosure. Fig. 2 is an enlarged view of the left half of the inkjet printing apparatus 1 shown in Fig. 1.

[0017] The inkjet printing device 1 is an inkjet color digital printing device that forms a desired image on a sheet of paper P. The inkjet printing device 1 is capable of single-sided printing, in which an image is formed on only one side of the paper P, and double-sided printing, in which an image is formed on both the first and second sides, i.e., the front and back sides, of the paper P. The paper P is an example of a recording medium of the technology disclosed herein.

[0018] 1, the inkjet printing apparatus 1 includes a transport mechanism 10, a paper feeding device 20, a pretreatment liquid application unit 30, a pretreatment liquid drying unit 35, an image forming unit 40, a drying unit 50, a cooling unit 60, and an accumulation device 70. Although not shown in FIG. 1, the inkjet printing apparatus 1 also includes a processor 100 (see FIG. 3) as a control device. The cooling unit 60 includes a first cooling unit 61 and a second cooling unit 62.

[0019] The transport mechanism 10 has a transport path 12 along which the paper P is transported. In Fig. 1, the transport path 12 along which the paper P is transported is indicated by a two-dot chain line. The pretreatment liquid application unit 30, the image forming unit 40, the drying unit 50, and the cooling unit 60 are arranged on the transport path 12, and the paper P is transported along the transport path 12 to various units, where it is subjected to various processes.

[0020] The transport path 12 includes a main transport path 13, a supply path 14 that supplies paper to the main transport path, a discharge path 15 that discharges paper from the main transport path 13, and a return transport path 16 that branches off from the main transport path 13 and the discharge path 15. The return transport path 16 forms a path that returns paper P that has passed through the main transport path 13 back to the main transport path 13.

[0021] The supply path 14 is connected to the main conveying path 13 at a first connection portion 21. The discharge path 15 is connected to the main conveying path 13 at a second connection portion 22. The starting end of the return conveying path 16 is connected to the main conveying path 13 at the second connection portion 22. The terminal end of the return conveying path 16 is connected to the main conveying path 13 at the first connection portion 21. In this way, the starting end of the return conveying path 16 is connected to the terminal end of the main conveying path 13, and the terminal end is connected to the starting end of the main conveying path 13, forming a circular path together with the main conveying path 13.

[0022] The supply path 14 supplies paper P from the paper feed device 20 to the main transport path 13. One end of the supply path 14 is disposed on the paper feed device 20 side, and the other end is connected to the main transport path 13 by a first connection portion 21. The paper P is supplied from the paper feed device 20 to one end of the supply path 14, transported along the supply path 14, and supplied from the other end of the supply path 14 to the main transport path 13.

[0023] The discharge path 15 transports the paper P from the main transport path 13 to the stacking device 70. One end of the discharge path 15 is connected to the main transport path 13 at the second connection portion 22, and the other end is connected to the stacking device 70. The paper P is discharged from the main transport path 13 to one end of the discharge path 15, transported along the discharge path 15, and discharged from the other end of the discharge path 15 to the stacking device 70.

[0024] The return transport path 16 forms a circular path together with the main transport path 13, and is a path for returning the paper P that has passed through the main transport path 13 back to the main transport path 13. In other words, the return transport path 16 returns the paper P that has passed through the main transport path 13 and has an image formed on its first side by the image forming unit 40 to the image forming unit 40, allowing an image to be formed on its second side.

[0025] The first connection portion 21 is configured to be able to receive the paper P transported from the supply path 14 and the paper P transported from the return transport path 16 into the main transport path 13. The paper P transported from the return transport path 16 is transported to the main transport path 13 in a state where the front and back of the paper P transported from the supply path 14 are reversed.

[0026] The second connection part 22 is provided with a switching mechanism that switches between a state in which the main transport path 13 and the discharge path 15 are connected and a state in which the main transport path 13 and the return transport path 16 are connected. In this example, the switching mechanism provided in the second connection part 22 includes a rotatable branch guide 18 (see FIG. 2 ) and an actuator (not shown) such as a solenoid that rotates the branch guide 18.

[0027] The switching mechanism rotates the branch guide 18 to switch the path of the paper P at the second connection portion 22 between a path from the main transport path 13 toward the discharge path 15 and a path toward the return transport path 16. In other words, the switching mechanism switches between a state in which the paper transported from the main transport path 13 is discharged to the discharge path 15 and a state in which the paper is transported to the return transport path 16 and circulated from the return transport path 16 to the main transport path 13.

[0028] The return transport path 16 is provided with a switchback unit 17 that reverses the traveling direction of the paper P (see FIG. 2). The switchback unit 17 temporarily pulls out the paper P from the return transport path 16 and reverses the traveling direction of the paper P. That is, the leading edge of the paper P in the traveling direction when the paper P was transported on the return transport path 16 before being pulled into the switchback unit 17 becomes the trailing edge in the traveling direction after the paper P is returned from the switchback unit 17 to the return transport path 16. By passing through this switchback unit 17, the front and back of the paper P that is supplied again from the return transport path 16 to the main transport path 13 is reversed.

[0029] A switching mechanism is provided at the connection between the switchback unit 17 and the return transport path 16, which switches between a path for pulling the paper P from the return transport path 16 into the switchback unit 17 and a path for returning the paper from the switchback unit 17 to the return transport path 16. In this example, the switching mechanism provided in the switchback unit 17 includes a rotatable branch guide 19 (see FIG. 2) and an actuator (not shown), such as a solenoid, that rotates the branch guide 19.

[0030] The pretreatment liquid application unit 30, the pretreatment liquid drying unit 35, the image forming unit 40, the drying unit 50, and the first cooling unit 61 are arranged on the main transport path 13, and the second cooling unit 62 is arranged on the return transport path 16.

[0031] The transport mechanism 10 includes a plurality of transport members arranged along the transport path 12. Examples of the plurality of transport members include a transport drum, a belt conveyor, transport roller pairs, chain grippers, and transport guides. The paper feed drum 24, pretreatment liquid application drum 32, pretreatment liquid drying drum 36, imaging drum 42, and belt conveyor 54, which will be described later, are also transport members and constitute part of the transport mechanism 10. The plurality of transport members of the transport mechanism 10 include a roller transport unit 90 including a plurality of belt conveyors 81 to 85 and a plurality of transport roller pairs 91, which are arranged along the transport path 12. The transport mechanism 10 also includes a motor (not shown) as a power source and a drive unit such as a motor drive circuit (not shown). The paper P is transported along the transport path 12 by these elements that constitute the transport mechanism 10. Details of the transport mechanism 10 will be described later.

[0032] The paper feeder 20 includes a paper feed tray on which a stack of multiple sheets of paper can be placed. The type of paper P is not particularly limited, but printing paper primarily made of cellulose, such as high-quality paper, coated paper, and art paper, can be used. The maximum paper size that can be used in the inkjet printing device 1 is, for example, A0 size (841 mm x 1189 mm).

[0033] The paper feeder 20 takes out the sheets P from the stack set therein one by one in order from the top, and supplies them to the supply path 14 of the transport path 12 .

[0034] The pretreatment liquid application unit 30 applies a pretreatment liquid to the paper P. The pretreatment liquid may be called a "precoat," "preconditioner," "undercoat liquid," or "treatment agent." The pretreatment liquid is a liquid that has the function of aggregating, insolubilizing, or thickening colorant components in ink. The pretreatment liquid application unit 30 includes a pretreatment liquid application drum 32 and a pretreatment liquid application device 33. The pretreatment liquid application drum 32 receives the paper P from the paper feed drum 24 and transports the received paper P to the pretreatment liquid drying unit 35. The pretreatment liquid application drum 32 includes a gripper (not shown) on its circumferential surface. The gripper grips the leading edge of the paper P and rotates, thereby wrapping the paper P around the drum circumferential surface and transporting it.

[0035] The pretreatment liquid application device 33 includes an application roller 34, and applies pretreatment liquid to the paper P transported by the pretreatment liquid application drum 32. The application roller 34 is supported by a movement mechanism (not shown) that is movable between an application position where the application roller 34 comes into contact with the paper P to apply pretreatment liquid to the paper P and a retracted position where the application roller 34 is separated from the paper P and does not apply pretreatment liquid.

[0036] The area where the pretreatment liquid is applied to the paper P may be a full application where the pretreatment liquid is applied to the entire paper P, or a partial application where the pretreatment liquid is applied to a portion of the area where ink is applied in the image forming unit 40. From the viewpoints of uniformly adjusting the amount of pretreatment liquid applied, uniformly recording thin lines and fine image portions, and suppressing density unevenness such as image irregularities, a full application where the pretreatment liquid is applied to the entire image forming surface of the paper P by application using an application roller or the like is preferred.

[0037] The method for applying the pretreatment liquid is not limited to the roller application method, and other methods may be applied to the pretreatment liquid application device 33. Examples of other methods for the pretreatment liquid application device 33 include application using a blade, ejection using an inkjet method, and spraying using a spray method.

[0038] The pretreatment liquid drying unit 35 dries the paper P on which the pretreatment liquid has been applied. The pretreatment liquid drying unit 35 includes a pretreatment liquid drying drum 36. The pretreatment liquid drying drum 36 receives the paper P from the pretreatment liquid application drum 32 and transports the received paper P to the image forming unit 40. The pretreatment liquid drying drum 36 includes a gripper (not shown) on its circumferential surface. The pretreatment liquid drying drum 36 transports the paper P by rotating while gripping the leading edge of the paper P with the gripper. The circumferential surface of the pretreatment liquid drying drum 36 is made of a material with high thermal conductivity, such as metal. The circumferential surface is heated by a heat source, such as a heater, provided inside the circumferential surface, thereby drying the pretreatment liquid while the paper P is transported by the pretreatment liquid drying drum 36.

[0039] The image forming unit forms an image by applying ink to a recording medium. The image forming unit 40 includes a print drum 42 and a head unit 44. The print drum 42 receives the paper P from the pretreatment liquid drying drum 36 and transports the received paper P to the drying unit 50 via a chain gripper 27 (see FIG. 2 ). The print drum 42 includes a gripper (not shown) on its circumferential surface. The gripper grips the leading edge of the paper P and rotates, thereby wrapping the paper P around the drum circumferential surface and transporting it. The print drum 42 also includes a suction mechanism (not shown) that suctions the paper P wrapped around the drum circumferential surface and transports it. Negative pressure is used for suction. The print drum 42 includes multiple suction holes on its circumferential surface, and suction is applied from the inside of the print drum 42 through these suction holes, thereby suctioning the paper P to the circumferential surface of the print drum 42.

[0040] The head unit 44 includes inkjet heads 46C, 46M, 46Y, and 46K. The inkjet head 46C is a recording head that ejects droplets of cyan ink. The inkjet head 46M is a recording head that ejects droplets of magenta ink. The inkjet head 46Y is a recording head that ejects droplets of yellow ink. The inkjet head 46K is a recording head that ejects droplets of black ink. Each of the inkjet heads 46C, 46M, 46Y, and 46K is supplied with ink from an ink tank (not shown), which is an ink supply source of the corresponding color, via a piping path (not shown). For example, a water-based ink is used as the ink for drawing. Water-based ink refers to ink in which a coloring material such as a pigment or dye is dissolved or dispersed in water and / or a water-soluble solvent.

[0041] The inkjet ink described in WO 2023 / 047767 is particularly suitable as an aqueous ink. The inkjet ink described in WO 2023 / 047767 contains water, a pigment, and at least one of resin particles and wax particles, has a pH of 7.2 to 11, and satisfies the following inequality (X): ORPi - [285 - 59 x (pHi - 6.2)] ≧ 0 Inequality (X) In inequality (X), ORPi represents the oxidation-reduction potential of the inkjet ink in units of V, measured under apparatus conditions such that the oxidation-reduction potential of water at a pH of 6.2 is 310 mV, and pHi represents the pH of the inkjet ink.

[0042] Ink droplets are ejected from at least one of the inkjet heads 46C, 46M, 46Y, and 46K toward the paper P being transported by the drawing drum 42, and the ejected droplets adhere to the paper P, thereby forming an image on the paper P.

[0043] In this example, a configuration using four ink colors, CMYK, is illustrated, but the combination of ink colors and the number of colors is not limited to this embodiment, and light ink, dark ink, special color ink, etc. may be added as needed. For example, a configuration is also possible in which inkjet heads that eject light-colored inks such as light cyan and light magenta are added, and / or inkjet heads that eject special color inks such as green, orange, or white are added. Furthermore, the arrangement order of the inkjet heads of each color is not particularly limited.

[0044] The drying unit 50 applies heat to the paper P on which an image has been formed by the image forming unit 40, thereby drying the paper P. The drying unit 50, for example, includes a belt conveyor 54 with a heating belt 51 and an infrared (IR) heater 57 positioned opposite the conveying surface of the heating belt 51. In addition to the heating belt 51, the belt conveyor 54 includes a drive roller 52 and a driven roller 53. The belt conveyor 54, which conveys the paper P, constitutes part of the conveying mechanism 10. The heating belt 51 is a belt with a conveying surface made of a highly thermally conductive material such as metal, and is heated from the back side of the conveying surface by a heat source such as a heater (not shown). The paper P is heated by the heating belt 51 while being conveyed along the heating belt 51. The temperature of the conveying surface of the heating belt 51 is set to a desired temperature, for example, between 80°C and 150°C, and can be changed as needed. Similarly, the heating temperature of the IR heater 57 can be changed by changing the output.

[0045] The heating belt 51 has a plurality of suction holes for suctioning and conveying the paper P. A suction box 55 is disposed in the space between the drive roller 52 and the driven roller 53 on the back side of the conveying surface of the heating belt 51. The suction box 55 is connected to an exhaust pump (not shown). A vacuum blower such as a ring blower can be used as the exhaust pump. The suction box 55 generates suction pressure in the suction holes of the heating belt 51. This allows the paper P to be adsorbed to the conveying surface.

[0046] The paper P is transferred from the imaging drum 42 to the chain gripper 27 (see FIG. 2), not shown in FIG. 1, and placed on the heating belt 51 with the leading edge of the paper P gripped by the gripper 27a, and is adsorbed to the heating belt 51. The leading edge of the paper P gripped by the gripper 27a is a non-image forming portion where no image is formed. When the paper P is adsorbed to the heating belt 51, the gripper 27a releases the paper P, and the paper P is transported only by the heating belt 51. As a result, the paper P is heated and dried by the heating belt 51 and the IR heater 57 while being transported by the heating belt 51.

[0047] As described above, the cooling unit 60 includes a first cooling unit 61 and a second cooling unit 62. The first cooling unit 61 is disposed on the main transport path 13 after the drying unit 50. The first cooling unit 61 includes, for example, a blower. The second cooling unit 62 is disposed on the return transport path 16. In this example, the second cooling unit 62 is disposed after the switchback section 17. The second cooling unit 62 includes, for example, a blower. The first cooling unit 61 and the second cooling unit 62 blow, for example, room temperature air onto the paper P.

[0048] The second cooling unit 62 is a cooling unit for double-sided printing of the present disclosure, and is provided to cool the paper P during double-sided printing. In this example, since the first cooling unit 61 is provided on the main transport path 13, the second cooling unit 62 further cools the paper P cooled by the first cooling unit 61.

[0049] The first cooling unit 61 and the second cooling unit 62, for example, blow room temperature air (about 25°C) onto the paper P. By cooling the paper P after it has been dried in the drying unit 50, the ink film is solidified and the evaporation of moisture is promoted. Either or both of the first cooling unit 61 and the second cooling unit 62 may blow cooling air (about 0 to 24°C) that is lower in temperature than room temperature air onto the paper P.

[0050] The stacking device 70 stacks the image-formed sheets P. The stacking device 70 receives the sheets P discharged from the discharge path 15 of the conveyance path 12, and stacks the sheets P in a bundle on a stacking tray (not shown).

[0051] Here, the transport mechanism 10 will be further described. As described above, the transport mechanism 10 includes a plurality of transport members, which transport the paper P along the transport path 12. As shown in FIG. 1 , a plurality of transport roller pairs 25 and a transport guide 26 are arranged on the most upstream side of the supply path 14 and the main transport path 13, and the paper P is transported by the transport roller pairs 25. The configuration of the transport roller pairs 25 is substantially the same as the configuration of a transport roller pair 91, which will be described later. Furthermore, the paper P is transported along the main transport path 13 by the paper feed drum 24, the pretreatment liquid application drum 32, the pretreatment liquid drying drum 36, and the imaging drum 42.

[0052] As described above, the paper P on which the image has been formed by the image forming drum 42 is transported along the transport guide 28 gripped by the chain gripper 27 and delivered to the heating belt 51 of the drying unit 50 .

[0053] The transport mechanism 10 includes a roller transport section 90 including a plurality of belt conveyors 81 to 85 and a plurality of transport roller pairs 91 along the transport path 12 as transport members for transporting the paper P discharged from the drying unit 50 .

[0054] As shown in FIG. 2, the belt conveyors 81 to 85 each include endless conveyor belts 81a to 85a, drive rollers 81b to 85b, and driven rollers 81c to 85c.

[0055] Each of the conveyor belts 81a to 85a has a plurality of suction holes for suctioning and conveying the paper P. The belt conveyors 81 to 85 are equipped with suction boxes (not shown) in the spaces between the drive rollers 81b to 85b and the driven rollers 81c to 85c on the backside of the conveyor belts 81a to 85a. The suction boxes are connected to exhaust pumps (not shown). A vacuum blower such as a ring blower can be used as the exhaust pump. The suction boxes generate suction pressure in the suction holes of the conveyor belts 81a to 85a, thereby adsorbing the paper P to the conveyor surface. The belt conveyors 81 to 85 transport the paper P by adsorbing it to the conveyor surface. While the paper P is being transported by the belt conveyors 81 to 85, the conveyor members do not come into contact with the image forming surface on which the image is formed.

[0056] The belt conveyor 81 is disposed from the main conveying path 13 to the return conveying path 16, and is provided with a guide roller 81d for changing the direction of travel at a second connecting portion 22 connecting the main conveying path 13 and the return conveying path 16, and an auxiliary roller 81e for assisting the conveyance of the conveyor belt 81a. The belt conveyor 81 has a conveying surface that is disposed horizontally along the main conveying path 13, and a conveying surface that is disposed inclined relative to the horizontal along the return conveying path 16.

[0057] The belt conveyor 82 is disposed on the discharge path 15. The conveying surface of the belt conveyor 82 is disposed horizontally. The conveying surface of the belt conveyor 82 is substantially flush with the horizontal conveying surface of the belt conveyor 81 along the main conveying path 13. The belt conveyor 82 receives the paper P traveling in a straight line from the horizontal conveying surface of the belt conveyor 81, and conveys it to the stacking device 70.

[0058] The belt conveyor 83 constitutes the switchback section 17. The conveying surface of the belt conveyor 83 is arranged horizontally. The belt conveyor 83 draws the paper P from the return conveying path 16 into the switchback section 17, and discharges the paper P into the return conveying path 16 by rotating the drive roller 83b in the reverse direction.

[0059] The belt conveyor 84 is disposed at a position where it receives the paper P discharged from the belt conveyor 83 of the switchback section 17, with its conveying surface inclined relative to the horizontal.

[0060] The belt conveyor 85 is disposed at a position where it receives the paper P transported by the belt conveyor 84, with its transport surface being horizontal.

[0061] In this way, multiple belt conveyors 81 to 85 are provided following the belt conveyor 54 in the drying unit 50, and the conveying mechanism 10 is configured to convey the paper P without contacting the conveying member while passing through the image forming unit 40 and transporting the paper P with an image formed on one side to a position where it passes through the second cooling unit 62.

[0062] Here, the belt conveyors 54, 81 to 85 all use suction to attract the paper P to the transport surface and transport it, but the method of attracting the paper P to the transport surface may also be electrostatic attraction or the like.

[0063] In addition, while the conveying mechanism 10 conveys the paper P that has passed through the image forming unit 40 and has an image formed on one side to a position where it passes through the second cooling unit 62, the conveying means for conveying the paper P without it coming into contact with the conveying member is not limited to a belt conveyor.

[0064] Returning to FIG. 1 , a roller conveyance unit 90 is provided downstream of the belt conveyor 85 on the return conveyance path 16. The roller conveyance unit 90 includes multiple conveyance roller pairs 91 and a conveyance guide 92 arranged along the return conveyance path 16. The conveyance roller pair 91 is composed of two rollers that press against each other, an upper roller 91a with a relatively small diameter and a lower roller 91b with a relatively large diameter. The conveyance roller pair 91 sandwiches the sheet P between the upper roller 91a and the lower roller 91b and sends it downstream in the conveyance direction. The upper roller 91a is a conveyance member that contacts the image surface of the sheet P. In FIG. 1 , the conveyance roller pair 91 arranged most upstream of the roller conveyance unit 90, immediately after the belt conveyor 85, is denoted by the reference symbol 91A. In other words, the "conveyance roller pair 91A" refers to the conveyance roller pair arranged most upstream of the roller conveyance unit 90, immediately after the belt conveyor 85. In this example, the upper roller 91a of the conveying roller pair 91A, which is located at the most upstream side of the roller conveying section 90, immediately after the belt conveyor 85, is the conveying member that first comes into contact with the image surface (the first surface on which the image is formed) of the paper P after it has passed through the image forming unit 40 for the first time in double-sided printing mode.

[0065] Thus, in the double-sided printing mode, after the paper P passes through the image forming unit 40 and an image is formed on the first side, it is preferable that the transport member having the surface that first comes into contact with the image side of the paper P is positioned downstream of the double-sided printing cooling unit 62 on the return transport path 16.

[0066] Furthermore, it is preferable that the adhesive force between the image surface and the conveying member (here, the upper roller 91a of the conveying roller pair 91A) that the image surface of the paper P first comes into contact with after passing through the image forming unit 40 is 110 mNm or less, and it is more preferable that it is 80 mNm or less.

[0067] Adhesion work W ｓｌ [mN / m] is the polar surface energy γ of the conveying member that comes into contact with the image surface of the recording medium (here, paper P). ｓ ｐ [mN / m] and the dispersive surface free energy γ ｓ ｄ [mN / m], polar surface energy γ of the image surface of the recording medium ｌ ｐ [mN / m] and the dispersive surface free energy γ ｌ ｄ The adhesive force is calculated from the adhesive strength [mN / m]. The smaller the adhesive work value, the less likely the ink peeling from the image surface when adhered. According to the studies of the present inventors, if the adhesive work is 110 mNm or less, ink peeling can be effectively suppressed, and if the adhesive work is 80 mNm or less, ink peeling can be more effectively suppressed.

[0068] Surface free energy γ of the conveying member ｓｖ、 Surface free energy γ of the image surface of the recording medium ｌｖ , and the interfacial free energy γ between the conveying member and the recording medium ｓｌ are respectively, γ ｓｖ = γ ｓ ｄ +γ ｓ ｐ gamma ｌｖ = γ ｌ ｄ +γ ｌ ｐ gamma ｓｌ = {(γ ｓ ｄ ) ０．５ - (γ ｌ ｄ ) ０．５} ２ + {(γ ｓ ｐ ) ０．５ - (γ ｌ ｐ ) ０．５}２ The adhesive work is expressed as W ｓｌ is expressed by the following formula 1: ｓｌ = γ ｓｖ +γ ｌｖ -γ ｓｌ = 2 × (γ ｓ ｄ gamma ｌ ｄ ) ０．５ +2 × (γ ｓ ｐ gamma ｌ ｐ ) ０．５ (Equation 1) (Owens and Wendt equation)

[0069] The work of adhesion can be derived, for example, by using a Kruss "Double Titration Handy Contact Angle / Surface Free Energy Analyzer MSA" to measure 2 μL of diiodomethane and pure water, and calculating the surface free energy components from the contact angles. The work of adhesion in this specification is a value derived by using a Kruss "Double Titration Handy Contact Angle / Surface Free Energy Analyzer MSA" to measure 2 μL of diiodomethane and pure water, and calculating the surface free energy components from the contact angles measured for each. The contact angles are values ​​measured 2 seconds after 2 μL of diiodomethane and pure water are dropped.

[0070] For example, when the transport surface of the transport member that comes into contact with the image surface of the recording medium is made of stainless steel (SUS), the adhesive work can be changed by changing the coating material on this transport surface.

[0071] As an example, Bonarivory 210 gsm (manufactured by Oji Paper Co., Ltd.) was used as the recording medium, and the adhesion work between the image surface and the conveying surface was calculated when the coating material of the conveying member was changed. The results are shown in Table 1.

[0072] As shown in Table 1, by using, for example, hard chrome plating, nickel plating, or Teflon (registered trademark) nickel plating as the coating material, it is possible to satisfy the work of adhesion of 110 mN / m or less. Note that a work of adhesion of 35 mN / m or more is realistic. The coating material is not limited to those listed in the above table. For example, a fluororesin such as hexafluoropropylene, which has high hydrophobicity, may also be used as the coating material.

[0073] As described above, in this example, the transport member that the image surface of the paper P first comes into contact with after passing through the image forming unit 40 is the upper roller 91a of the transport roller pair 91A that is located at the most upstream side of the roller transport section 90. Therefore, in the inkjet printing device 1, the adhesive work between the transport surface of this upper roller 91a and the image surface of the paper P is preferably 110 mN / m or less, and more preferably 80 mN / m or less.

[0074] The transport mechanism 10 further includes, as transport members, a transport drum 94 and guide rollers 95 and 96 at the end of the roller transport section 90. The transport drum 94 has a gripper (not shown) on its circumferential surface, and by gripping the leading end of the paper P with the gripper and rotating, the paper P is wrapped around the drum circumferential surface and transported. The transport drum 94 re-supplies the paper P to the main transport path 13 at the first connection section 21.

[0075] The transport drum 94 is a transport member that has a surface that comes into contact with the image surface of the paper P after it has passed through the image forming unit 40, and transports the paper P while curving it.

[0076] Thus, in the double-sided printing mode, after the paper P passes through the image forming unit 40 and an image is formed on the first side, it is preferable that the transport member having the surface that first comes into contact with the image side of the paper P is positioned downstream of the double-sided printing cooling unit 62 on the return transport path 16.

[0077] The radius of curvature of the transport drum 94 is preferably 50 mm or more, and more preferably 150 mm or more. The radius of curvature of the transport drum 94 is preferably equal to or smaller than the maximum paper size in the feed direction (here, 841 mm).

[0078] The transport mechanism in the image forming apparatus of the present disclosure is not limited to the transport mechanism 10 of the above embodiment. Depending on the configuration of the transport mechanism, in double-sided printing mode, the transport member having a surface that first contacts the image side of the paper P after the paper P passes through the image forming unit 40 and an image is formed on the first side may not be the upper roller 91a of the transport roller pair 91A, but may be another transport member such as a transport drum. Even in such a case, the adhesive work between the transport member that first contacts the image side of the paper P after the paper P passes through the double-sided printing cooling unit and the image side is preferably 110 mNm or less, and more preferably 80 mNm or less. Furthermore, depending on the configuration of the transport mechanism, the transport member that has a surface that contacts the image side of the paper P after the paper P passes through the image forming unit 40 and conveys the paper P while curving it may not be limited to the transport drum 94, but may be another transport member such as a transport guide. Even in such a case, the radius of curvature of the transport member that has a surface that contacts the image side of the paper P after the paper P passes through the image forming unit 40 and conveys the paper P while curving it is preferably 50 mm or more, and more preferably 150 mm or more.

[0079] In the inkjet printing device 1, when an aqueous ink containing resin particles is used as the ink, it is preferable that the glass transition temperature Tg [°C] of the resin particles, the temperature T1 [°C] of the image surface on which the image is recorded immediately after drying by the drying unit 50, and the temperature T2 [°C] of the image surface at the time of first contact between the conveying member and the image surface on which the image is recorded satisfy the following relationship: T1>Tg-40>T2 (A).

[0080] In the inkjet printing apparatus 1, the temperature T1 is the temperature measured by a non-contact first surface temperature measuring device on the image surface of the paper immediately after it has been discharged from the drying unit 50. The first surface temperature measuring device may be located downstream of the drying unit 50 and above the image surface of the paper discharged from the drying unit 50. More specifically, the first surface temperature measuring device may be located above the discharge port of the drying unit 50 through which the paper is discharged. The temperature T2 is the temperature measured by a non-contact second surface temperature measuring device on the image surface of the paper immediately before it is sandwiched between the transport roller pair 91A. The first surface temperature measuring device may be located upstream of the transport roller pair 91A and above the image surface of the paper immediately before it is sandwiched between the transport roller pair 91A after it has been discharged from the second cooling unit 62.

[0081] It is more preferable that the glass transition temperature Tg [°C], the temperature T1 [°C], and the temperature T2 [°C] satisfy the following relationship: T1>Tg-35 and Tg-57>T2 (B).

[0082] Furthermore, it is more preferable that the following relationships are satisfied: T1>Tg-17 and Tg-59>T2 (C).

[0083] The glass transition temperature Tg is measured by actual measurement. The glass transition temperature Tg is measured under normal measurement conditions using a differential scanning calorimeter, such as a differential scanning calorimeter manufactured by SII Nanotechnology Inc. (product name: EXSTAR6220). However, if measurement is difficult due to material decomposition or the like, the calculated value Tgk (absolute temperature [K]) calculated using the following formula is converted to Celsius temperature [°C] and used as the glass transition temperature Tg: 1 / Tgk = Σ(Xi / Tgi) Here, the polymer to be calculated is assumed to be a copolymer of n main monomer components, i = 1 to n. Xi is the mass fraction of the i-th monomer (ΣXi = 1), and Tgi is the glass transition temperature (absolute temperature) of a homopolymer of the i-th monomer. Σ is the sum from i = 1 to n. The glass transition temperature (Tgi) of the homopolymer of each monomer is taken from the Polmer Handbook (3rd Edition) (by J. Brandrup and EH Immergut (Wiley-Interscience, 1989)).

[0084] 3 is a functional block diagram showing a schematic configuration of a control system of the inkjet printing apparatus 1. In addition to a processor 100, the inkjet printing apparatus 1 includes a storage device 102, a communication unit 104, an input device 106, and a display device 108.

[0085] The processor 100 includes a CPU (Central Processing Unit). The processor 100 functions as a processing unit and / or a control unit that performs various processes by executing instructions of a program stored in the storage device 102. The processor 100 comprehensively controls the conveyance mechanism 10, the paper feed device 20, the pretreatment liquid application unit 30, the pretreatment liquid drying unit 35, the image forming unit 40, the drying unit 50, the cooling unit 60, and the stacking device 70.

[0086] The storage device 102 is a non-transitory storage medium and a tangible computer-readable medium. The storage device 102 includes a memory serving as a main storage device and a storage serving as an auxiliary storage device. The storage device 102 may be, for example, a semiconductor memory, a hard disk drive (HDD), a solid state drive (SSD), or a combination of these. A part or all of the storage area of ​​the storage device 102 may be included in the processor 100.

[0087] The storage device 102 stores various parameters used in the inkjet printing apparatus 1 and programs used in each section of the inkjet printing apparatus 1. The storage device 102 also functions as a temporary storage section for various data including image data.

[0088] Various parameters stored in the storage device 102 are read out via the processor 100 and set in each part of the device. Various programs stored in the storage device 102 are read out via the processor 100 and executed in each part of the device.

[0089] The communication unit 104 has a required communication interface. The inkjet printing apparatus 1 is connected to the host computer 110 via the communication unit 104, and can send and receive data to and from the host computer 110. Here, "connection" includes a wired connection, a wireless connection, or a combination of these. The communication unit 104 may be equipped with a buffer memory for speeding up communication processing. The communication unit 104 serves as an image input interface unit for acquiring image data representing an image to be printed. The image data acquired from the host computer 110 via the communication unit 104 is stored in the storage device 102.

[0090] The input device 106 is configured by, for example, operation buttons, a keyboard, a mouse, a touch panel, a multi-touch screen, other pointing devices, a voice input device, or an appropriate combination of these. The input device 106 accepts various inputs from an operator.

[0091] The display device 108 is configured by, for example, a liquid crystal display, an organic electro-luminescence (OEL) display, a projector, or an appropriate combination of these.

[0092] Information input via the input device 106 is sent to the processor 100. The processor 100 causes each unit to execute various processes in accordance with the information input from the input device 106. Information input from the input device 106 includes the print mode (single-sided printing or double-sided printing), the type of paper P, and the like.

[0093] The display device 108 can display various information such as various setting information of the device or abnormality information in response to commands from the processor 100. A user (operator) can set various parameters and input and edit various information using the input device 106 while viewing the content displayed on the display device 108.

[0094] The inkjet printing device 1 is capable of single-sided printing and double-sided printing, and is configured to be able to selectively switch between a single-sided printing mode and a double-sided printing mode. Depending on which mode is selected, the transport path is switched, and the paper P is transported along the transport path appropriate for each mode.

[0095] In the single-sided printing mode, the paper P is transported along a path that passes through the supply path 14, the main transport path 13, and the discharge path 15. More specifically, the paper P fed from the paper feed device 20 to the supply path 14 is transported to the main transport path 13, and along the main transport path 13, the pretreatment liquid is applied to the first side by the pretreatment liquid application unit 30, the pretreatment liquid is dried by the pretreatment liquid drying unit 35, an image is formed on the paper by the image forming unit 40, the drying unit 50 drys the paper, and the first cooling unit 61 cools the paper, in this order. Thereafter, the paper P with the image printed on its first side is transported to the discharge path 15 and discharged to the stacking device 70.

[0096] In the double-sided printing mode, the paper P is transported along a path that passes through the supply path 14, the main transport path 13, the return transport path 16, the main transport path 13, and the discharge path 15 in this order. Specifically, the paper P fed from the paper feed device 20 to the supply path 14 is transported to the main transport path 13, where the application of pretreatment liquid to a first side of the paper P, drying of the pretreatment liquid, image formation on the first side, drying, and cooling are performed in this order. The paper P is then transported from the main transport path 13 to the return transport path 16, where it is inverted to its front and rear ends by passing through the switchback unit 17, and the paper P with its front and rear ends inverted is transported along the return transport path 16. In the return transport path 16, the paper P is cooled by the second cooling unit 62. The paper P cooled by the second cooling unit 62 is returned from the return transport path 16 to the main transport path 13. When the paper P is returned to the main transport path 13, it is turned over so that the second side, which is the reverse side of the first side of the paper P, becomes the image forming side. In the main transport path 13, the application of pretreatment liquid to the second side, drying of the pretreatment liquid, image formation on the second side, drying, and cooling are carried out in this order. Then, the paper P with images printed on both sides is transported from the main transport path 13 to the discharge path 15 and discharged to the stacking device 70.

[0097] "Processing by Processor 100" The processor 100 causes each unit to execute various processes in accordance with information input from the input device 106.

[0098] For example, the processor 100 receives a designation of single-sided printing or double-sided printing from the input device 106 and sets the mode to single-sided printing or double-sided printing. That is, the processor 100 controls the conveying mechanism 10 to switch the conveying path to a path for single-sided printing or a path for double-sided printing. The path switching is achieved by a path switching using the branch guide 18 of the switching mechanism of the second connection unit 22.

[0099] The transport mechanism 10 includes elements such as transport members and a power source involved in transporting the paper P from the paper feed device 20 to the stacking device 70 described in Fig. 1. The processor 100 controls each element of the transport mechanism 10 so as to transport the paper P from the paper feed device 20 to the stacking device 70 according to the set transport path. The processor 100 also controls the paper feed device 20 to start feeding the paper P and stop feeding the paper P.

[0100] The processor 100 performs various types of image processing, such as conversion processing, correction processing, and halftone processing, on image data to be printed.

[0101] The processor 100 operates the pretreatment liquid application unit 30 and the pretreatment liquid drying unit 35. The processor 100 controls the application operation of the pretreatment liquid application device 33, such as the amount and timing of application of the pretreatment liquid. The processor 100 controls the pretreatment liquid drying unit 35 to control the drying output and / or drying time. The drying output is the output of the heat source, and, for example, if the heat source is a heater, it is the heater output, and if the heat source is a hot air blower, it is the temperature and flow rate of the hot air blown out from the hot air blower.

[0102] The processor 100 operates the image forming unit 40 to form an image on the paper P based on the image data stored in the storage device 102. The processor 100 controls the ejection operations of the inkjet heads 46C, 46M, 46Y, and 46K based on the dot data of each ink color generated through image processing, so as to record an image on the paper P being transported by the image recording drum 42.

[0103] The processor 100 also operates the drying unit 50. The processor 100 controls the drying output and / or drying time of the drying unit 50. The drying output is the output of the heat source, for example, if the heat source is a heater, it is the heater output, and if the heat source is a hot air blower, it is the temperature and flow rate of the hot air blown out from the hot air blower.

[0104] The processor 100 operates the cooling unit 60. The processor 100 controls the cooling output and / or cooling time of the first cooling unit 61 and the second cooling unit 62. If the cooling source is a fan, the processor 100 controls the temperature and volume of the air blown out from the fan.

[0105] When an aqueous ink containing resin particles is used as the ink in the inkjet printing apparatus 1, the processor 100 is preferably configured to control the conveying mechanism 10, the drying unit 50, and the cooling unit 60 so as to satisfy formula (A): T1>Tg-40>T2 (A) where Tg is the glass transition temperature [°C] of the resin particles, T1 is the temperature [°C] of the image surface on which the image is recorded immediately after drying by the drying unit 50, and T2 is the temperature [°C] at the time of initial contact between the conveying member and the image surface on which the image is recorded (here, the time of contact between the upper roller 91a of the conveying roller pair 91A and the image surface).

[0106] It is also preferable that the processor 100 is configured to control the drying unit 50 and the cooling unit 60 so as to more preferably satisfy the formula (B), and further preferably satisfy the formula (C): T1>Tg-35 and Tg-57>T2 (B) T1>Tg-17 and Tg-59>T2 (C)

[0107] For example, a lookup table is created that associates the type of paper P used with the conveying speed, drying output, drying time, cooling output, and cooling time that satisfy the above formula (A), (B), or (C), and is stored in advance in the storage device 102. The processor 100 may then refer to the lookup table in accordance with input information about the paper P (here, the type of paper P), and control the conveying mechanism 10, the drying unit 50, the first cooling unit 61, and the second cooling unit 62 so as to achieve the associated conveying speed, drying output, and cooling output.

[0108] The processor 100 preferably controls the conveying mechanism 10, the drying unit 50, and the cooling unit 60 under conditions such that the moisture content of the recording medium, i.e., the paper P, after being cooled by the second cooling unit 62, which is a cooling unit for double-sided printing, is 1.0 to 14.5%. More preferably, the moisture content of the paper P after being cooled by the cooling unit for double-sided printing is 1.2 to 14.3%. The moisture content is a value measured by the Karl Fischer method. Note that, in this specification, "after being cooled by the cooling unit for double-sided printing" refers to the period from the time the paper passes through the cooling unit for double-sided printing to the first pair of conveying rollers 91 (the period indicated by the double-headed arrow A in FIG. 2).

[0109] For example, a lookup table is created that associates the type of paper P used with the conveying speed, drying output, drying time, cooling output, and cooling time that will result in the moisture content of the paper P being 1.0 to 14.5% after being cooled by the second cooling unit 62, and the lookup table is stored in advance in the storage device 102. The processor 100 may then refer to the lookup table in accordance with input information about the paper P (here, the type of paper P), and control the associated conveying speed by the conveying mechanism 10, the drying output of the drying unit 50, the cooling output of the first cooling unit 61, and the cooling output of the second cooling unit 62.

[0110] The processor 100 also determines whether the amount of organic solvent on the paper P after being cooled by the second cooling unit 62, i.e., the amount of remaining solvent, is 160 μg / cm ２ In this case, for example, the type of paper and the amount of residual solution may be set to 160 μg / cm . ２ A lookup table that correlates the conveying speed, drying power, drying time, cooling power, and cooling time to the following may be created and stored in the storage device 102. Note that the residual solvent amount is 135 μg / cm ２ More preferably, it is 123 μg / cm or less. ２ It is more preferable that the residual solvent amount is 40 μg / cm or less. ２ The above is preferable.

[0111] Furthermore, the processor 100 determines whether the moisture content of the paper P after being cooled by the cooling unit for double-sided printing is 1.0 to 14.5% and the amount of residual solvent is 160 μg / cm ２ In this case, for example, the type of paper, the moisture content described above is 1.0 to 14.5%, and the amount of residual solution described above is 160 μg / cm 3 . ２ A lookup table that associates the transport speed, drying output, drying time, cooling output, and cooling time to satisfy the following may be created and stored in the storage device 102.

[0112] When an aqueous ink containing resin particles is used as the ink, the processor 100 satisfies the above formula (A), (B), or (C), and the moisture content of the paper P after being cooled by the cooling unit for double-sided printing is 1.0 to 14.5%, and the amount of residual solvent is 160 μg / cm ２ In this case, for example, the conveying mechanism 10, the drying unit 50, and the cooling unit 60 may be controlled under the condition that the type of paper satisfies any one of the above formulas (A) to (C), the moisture content is 1.0 to 14.5%, and the amount of residual solution is 160 μg / cm ２ A lookup table that associates the transport speed, drying output, drying time, cooling output, and cooling time to satisfy the following may be created and stored in the storage device 102.

[0113] In the present disclosure, the residual solvent amount Y of the organic solvent remaining on the recording surface is a value measured by forming an image under the following conditions: In the image forming method and image forming apparatus under consideration, an ink application amount of 12.3 g / m2 of 100% blue ink is applied to the recording surface of a recording medium having a size of 585 mm x 750 mm, which corresponds to a paper size of B2. ２A full-area blue image (solid image) is formed using this method. Immediately after the solid image is formed and the recording medium is transported to the accumulation position, it is removed and four 1.5 cm x 0.8 cm samples are cut from the center of the recording medium (i.e., the center of the image). This sample is placed in a vial, and 0.5 mL each of methanol and THF (tetrahydrofuran) is weighed and added to the vial, which is then capped and subjected to extraction over one day. The amount of residual solvent in the resulting extract is quantified using gas chromatography.

[0114] The hardware structure of the processor 100 may be any of the various processors listed below. The various processors include a CPU, which is a general-purpose processor that executes software (programs) and functions as various processing units, as well as dedicated electrical circuits such as a PLD (Programmable Logic Device) that can change its circuit configuration after manufacture, such as an FPGA (Field-Programmable Gate Array), and an ASIC (Application Specific Integrated Circuit), which is a processor with a circuit configuration designed specifically for executing specific processing.

[0115] The above-described processing may be performed by one of these various processors, or by a combination of two or more processors of the same or different types (e.g., a plurality of FPGAs, or a combination of a CPU and an FPGA). Furthermore, a plurality of processing units may be configured by a single processor. An example of configuring a plurality of processing units by a single processor is a system-on-chip (SOC), in which a processor is used to realize the functions of an entire system including a plurality of processing units on a single IC (Integrated Circuit) chip.

[0116] Furthermore, more specifically, the hardware structure of these processors can be an electric circuit that combines circuit elements such as semiconductor elements.

[0117] As described above, the inkjet printing apparatus 1 according to this embodiment includes a transport mechanism 10 having a transport path 12 for transporting a recording medium (paper P in this example), an image forming unit 40 for forming an image on the recording medium, a drying unit 50 for drying the recording medium on which the image has been formed, and a cooling unit 60 for cooling the dried recording medium. The transport path 12 includes a main transport path 13 in which the image forming unit 40 and the drying unit 50 are disposed, a discharge path 15 for transporting the recording medium from the main transport path 13 to the stacking device 70, and a return transport path 16 that branches off from the main transport path 13 and the discharge path 15 and returns the recording medium to the image forming unit 40. The cooling unit 60 includes a cooling unit for double-sided printing (a second cooling unit 62 in this example) disposed on the return transport path 16. By providing the cooling unit for double-sided printing on the return transport path 16, the image surface of a recording medium with an image formed on one side can be sufficiently cooled when the recording medium is transported back to the image forming unit 40, accelerating evaporation of moisture on the image surface, sufficiently solidifying the ink, and reducing stickiness of the image surface. As a result, it is possible to prevent quality defects such as image defects that occur when the image surface comes into contact with the conveying member, etc. The return conveying path 16 forms a circular path together with the main conveying path 13, and by arranging the cooling unit for double-sided printing inside the circular path, it is possible to reduce the installation space and prevent the device from becoming larger.

[0118] The inkjet printing device 1 of this embodiment further includes a first cooling unit 61 arranged on the main transport path 13 after the drying unit 50, so that the image surface of the recording medium that is not transported to the return transport path 16 but is transported to the discharge path 15 can also be cooled.

[0119] In the inkjet printing apparatus 1, the cooling unit 60 includes a first cooling unit 61 and a second cooling unit 62 as a cooling unit for double-sided printing (hereinafter, sometimes referred to as the double-sided printing cooling unit 62). However, the inkjet printing apparatus 1 may also include only the cooling unit for double-sided printing 62 arranged on the return transport path 16 without including the first cooling unit 61. However, including the first cooling unit 61 arranged on the main transport path 13 in addition to the cooling unit for double-sided printing 62 is more preferable because it can further reduce stickiness of the image surface of the recording medium to be double-sided printed and improve the effectiveness of suppressing image defects. Furthermore, by including two cooling units 61 and 62, the cooling capacity of each cooling unit can be smaller than when only one cooling unit is provided and cooling is performed by only one cooling unit.

[0120] In the inkjet printing apparatus 1 of this embodiment, the transport mechanism 10 is configured to transport the recording medium without the image side, on which an image is recorded, coming into contact with the transport members while transporting the recording medium from the image forming unit 40 to a position where it passes through the cooling unit 62 for double-sided printing. In this example, after passing through the image forming unit 40, the recording medium is transported by the belt conveyors 54, 81 to 85 until it passes through the cooling unit 62 for double-sided printing. The belt conveyors 54, 81 to 85 all transport the recording medium by suction from the back side, and can transport the recording medium without the transport members coming into contact with the image side immediately after the image is formed by the image forming unit 40. In this way, by preventing the image side from coming into contact with the transport members until the image side is sufficiently dried and solidified, quality defects due to the occurrence of image defects and the like can be more effectively suppressed.

[0121] If the work of adhesion between the transport member (here, upper roller 91a) that the image surface of the recording medium first comes into contact with after passing through image forming unit 40 and the image surface is 80 mNm or less, it is possible to suppress ink peeling that occurs upon contact with the image surface, and to suppress the occurrence of stains and image defects. In the double-sided printing mode, it is preferable that the transport member having the surface that first comes into contact with the image surface of the recording medium after passing through image forming unit 40 is located downstream of double-sided printing cooling unit 62 on return transport path 16.

[0122] Furthermore, if the conveying member has a surface that first comes into contact with the image surface of the recording medium after it has passed through the image forming unit 40 and conveys the recording medium while curving it, and the curvature radius of the conveying member is 50 mm or greater, the contact pressure generated when the conveying member comes into contact with the image surface can be suppressed. When conveying a recording medium while curving it, contact pressure is applied to the image surface, making it prone to problems such as ink peeling, but if the curvature radius is 50 mm or greater, ink peeling can be suppressed, and the occurrence of stains and image defects can be suppressed.

[0123] As described above, when an aqueous ink containing resin particles is used as the ink, it is preferable that the glass transition temperature Tg [°C] of the resin particles, the temperature T1 [°C] of the image surface on which the image is recorded immediately after drying by the drying unit 50, and the temperature T2 [°C] of the image surface at the time of first contact between the conveying member and the image surface on which the image is recorded satisfy the following relationship: T1>Tg-40>T2 (A) By satisfying the above formula (A), it is possible to reduce the adhesion of the image surface and to improve the effect of suppressing the occurrence of image defects.

[0124] In this embodiment, the processor 100 controls the conveying mechanism 10, the drying unit 50, and the cooling unit 60 under conditions such that the moisture content of the recording medium after being cooled by the cooling unit for double-sided printing is 1.0 to 14.5%. Therefore, the moisture content of the recording medium after being cooled by the cooling unit for double-sided printing 62 can be suppressed to 1.0 to 14.5%, which suppresses stickiness of the image surface and more effectively suppresses quality defects such as image defects that occur when the image surface comes into contact with a conveying member or the like.

[0125] In addition, the processor 100 determines that the amount of residual solvent in the recording medium after being cooled by the cooling unit for double-sided printing is 160 μg / cm ２ When the conveying mechanism 10, the drying unit 50, and the cooling unit 60 are controlled under the following conditions, the amount of residual solvent in the recording medium after being cooled by the cooling unit 62 for double-sided printing is 160 μg / cm ２ This can suppress stickiness of the image surface and more effectively suppress quality defects such as image defects that occur when the image surface comes into contact with a conveying member or the like.

[0126] In the inkjet printing apparatus 1 of the above embodiment, by continuously supplying a plurality of sheets of paper P to the transport path 12, image formation can be performed on the plurality of sheets of paper P in sequence, thereby improving throughput.

[0127] In the above embodiment, the drying unit 50 includes the heating belt 51 and the IR heater 57, and the heating belt 51 and the IR heater 57 heat and dry the paper P, but the configuration of the drying unit 50 is not limited to this. The drying unit 50 may include any of a heating belt, an IR heater, a hot air blower, a microwave generator, a superheated steam generator, a UV lamp, an IR lamp, or any combination thereof, as long as it has the effect of reducing the moisture content of the paper P.

[0128] The image forming apparatus according to the present disclosure may be configured without the pretreatment liquid application unit 30 and the pretreatment liquid drying unit 35, as in the modified inkjet printing apparatus 2 shown in Fig. 4. In Fig. 4, the same components as those in the inkjet printing apparatus 1 shown in Fig. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted. The inkjet printing apparatus 2 does not include the pretreatment liquid application unit 30 and the pretreatment liquid drying unit 35, but the other components are similar to those of the inkjet printing apparatus 1 described above.

[0129] The term "recording medium" is a general term for various terms such as paper, recording paper, printing paper, printing medium, print medium, print-receiving medium, image-forming medium, image-receiving medium, image-receiving medium, and ejection-receiving medium. The material and shape of the medium are not particularly limited, and various sheet bodies can be used, regardless of material or shape, such as sticker paper, resin sheet, film, cloth, nonwoven fabric, etc. Furthermore, the recording medium is not limited to a sheet body, and may be an inflexible medium such as building material. However, if the image forming apparatus is equipped with a transport member that curves and transports the recording medium, the recording medium is a flexible sheet body.

[0130] The configurations described in the above embodiments and the features described in the modified examples can be used in appropriate combinations, and some features can also be replaced.

[0131] The embodiments of the present disclosure described above may have their constituent elements modified, added, or deleted as appropriate without departing from the spirit of the present disclosure. The present disclosure is not limited to the embodiments described above, and many modifications may be made by those having ordinary skill in the relevant art within the technical concept of the present disclosure.

[0132] Here, the results of a study on water-based inks suitable for the inkjet printing device 1 and cooling and drying conditions when using water-based inks will be described.

[0133] "Ink" A water-based ink containing resin particles was prepared as follows.

[0134] (Preparation of Resin Particles) The resin particles contain structural units c1 to c3 shown in Table 2 below. n in the chemical formula represents the number of repetitions, and the mass % in Table 2 means the content of each structural unit.

[0135] A three-neck flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube was charged with water (250 g), 12-methacrylamidodecanoic acid (6.7 g), potassium hydrogen carbonate (0.17 g), and isopropanol (20 g), and the temperature was raised to 85° C. under a nitrogen stream. To this was added a mixed solution consisting of 4,4′-azobis(4-cyanovaleric acid) (radical polymerization initiator, product name "V-501", Fujifilm Wako Pure Chemical Industries, Ltd.) (0.11 g), potassium hydrogen carbonate (0.08 g), and water (9 g), and the mixture was stirred for 10 minutes. Next, a monomer solution consisting of styrene (14 g), benzyl methacrylate (14 g), methyl methacrylate (48 g), butyl methacrylate (3.3 g), and hydroxylethyl methacrylate (14 g) was added dropwise to the three-neck flask at a constant rate so that the addition would proceed over a period of 3 hours. Furthermore, a mixed solution consisting of V-501 (0.06 g), potassium bicarbonate (0.04 g), and water (6 g) was added in two portions: immediately after the start of the addition of the monomer solution and 1.5 hours after the start of the addition of the monomer solution. After the addition of the monomer solution was completed, the mixture was stirred for 1 hour. Subsequently, a mixed solution consisting of V-501 (0.06 g), potassium bicarbonate (0.04 g), and water (6 g) was added to the resulting reaction mixture, and the mixture was stirred for an additional 3 hours. The resulting reaction mixture was filtered through a 50 μm mesh to obtain an aqueous dispersion of resin particles.

[0136] (Preparation of pigment dispersion in which dispersant is crosslinked) As a pigment dispersion in which the dispersant is crosslinked (specifically, a crosslinked polymer), Projet Cyan APD1000 (manufactured by FUJIFILM Imaging Colorants, cyan pigment dispersion, pigment concentration in the pigment dispersion: 12% by mass) was prepared.

[0137] The active ingredients of the ink shown in Table 3 were mixed with water, and coarse particles were removed from the resulting mixture to obtain an ink. The total amount of the active ingredients of the ink shown in Table 3 and the amount of water was 100 parts by mass.

[0138] The glass transition temperature Tg of the resin particles was measured using a differential scanning calorimeter (product name "EXSTAR6220") manufactured by SII NanoTechnology Inc. The glass transition temperature Tg of the resin particles was 100°C.

[0139] Printing was performed on paper using the aqueous ink prepared as described above in the inkjet printing apparatus 1 shown in FIG. 1. By adjusting the drying conditions in the drying unit and the cooling conditions in the cooling unit, prints were performed in Tests No. 1 to 5, in which the film surface temperature immediately after drying and the film surface temperature at the time of contact between the upper roller 91a of the transport roller pair 91A and the image surface were varied, as shown in Table 4. The film surface temperature T1 immediately after drying was measured immediately after the print was discharged from the drying unit 50. The film surface temperature T1 immediately after drying was measured using a non-contact surface temperature measuring device positioned above the discharge outlet of the drying unit 50. The film surface temperature T2 at the time of contact between the upper roller 91a and the image surface (when in contact with the transport member) ... the temperature immediately before contact with the transport member that first contacts the recording surface after the image is formed by the image forming unit 40. Here, the film surface temperature T2 was measured using a non-contact surface temperature measuring device positioned between the rear end of the belt conveyor 85 and the transport roller pair 91A. A radiation thermometer (FT-H20 manufactured by Keyence Corporation) was used as the surface temperature measuring device.

[0140] For each of Test Nos. 1 to 5, the recording surface on which the image was formed, i.e., the printed surface, was visually evaluated based on the following evaluation criteria. The results are shown in Table 4. The higher the evaluation number (score), the better. 5: Fairly good (no visible image defects) 4: Good (almost no visible image defects) 3: Acceptable (slightly visible image defects, but to a small extent and not at a problematic level) 2: Poor (visible image defects) 1: Fairly bad (visible image defects)

[0141]

[0142] As shown in Table 4, Test No. 1, which satisfied T1 > Tg-40 > T2, suppressed image defects more effectively than Test Nos. 4 and 5, which did not. Furthermore, Test No. 2, which satisfied T1 > Tg-35 and Tg-57 > T2, exhibited a greater effect in suppressing image defects than Test No. 1, and Test No. 3, which satisfied T1 > Tg-17 and Tg-59 > T2, exhibited an even greater effect than Tests Nos. 1 and 2.

[0143] The following supplementary notes are further disclosed regarding the above-described embodiments. <Supplementary Note 1> An image forming apparatus comprising: a transport mechanism having a transport path for transporting a recording medium; an image forming unit that applies ink to the recording medium to form an image; a drying unit that dries the recording medium on which the image has been formed; and a cooling unit that cools the dried recording medium, wherein the transport path includes a main transport path in which the image forming unit and the drying unit are arranged, a discharge path that transports the recording medium from the main transport path to a stacking device, and a return transport path that is a path branched from the main transport path from the discharge path and returns the recording medium from the main transport path to the image forming unit, and the cooling unit includes a cooling unit for double-sided printing that is arranged on the return transport path. <Supplementary Note 2> The image forming apparatus according to Supplementary Note 1 further comprises a first cooling unit arranged on the main transport path subsequent to the drying unit, wherein the cooling unit for double-sided printing is a second cooling unit that further cools the recording medium cooled by the first cooling unit. <Supplementary Note 3> The image forming apparatus according to Supplementary Note 1 or Supplementary Note 2, wherein the transport mechanism includes a plurality of transport members, and transports the recording medium without bringing the image side on which an image is recorded into contact with the transport members while transporting the recording medium from the image forming unit to a position where it passes through a cooling unit for double-sided printing. <Supplementary Note 4> The image forming apparatus according to any one of Supplementary Note 1 to Supplementary Note 3, wherein the transport mechanism includes a plurality of transport members, and wherein the work of adhesion between the image side and a transport member, among the plurality of transport members, which comes into contact first with the image side on which an image is recorded after the recording medium has passed through the image forming unit, is 110 mNm or less. <Supplementary Note 5> The image forming apparatus according to Supplementary Note 4, wherein the work of adhesion is 80 mNm or less. <Supplementary Note 6> The image forming apparatus according to Supplementary Note 4, wherein the ink is a water-based ink, the water-based ink contains resin particles, and the glass transition temperature Tg°C of the resin particles, the temperature T1°C of the image surface on which the image is recorded immediately after drying by the drying unit, and the temperature T2°C of the image surface at the time of initial contact between the conveying member and the image surface on which the image is recorded satisfy the relationship T1>Tg-40>T2.<Appendix 7> The image forming apparatus according to Appendix 4, wherein the ink is a water-based ink and contains resin particles, and wherein the glass transition temperature Tg°C of the resin particles, the temperature T1°C of the image surface on which the image has been recorded immediately after drying by the drying unit, and the temperature T2°C of the image surface at the time of first contact between the conveying member and the image surface on which the image has been recorded satisfy the following: T1>Tg-35 Tg-57>T2. <Appendix 8> The image forming apparatus according to Appendix 4, wherein the ink is a water-based ink and contains resin particles, and wherein the glass transition temperature Tg°C of the resin particles, the temperature T1°C of the image surface on which the image has been recorded immediately after drying by the drying unit, and the temperature T2°C of the image surface at the time of first contact between the conveying member and the image surface on which the image has been recorded satisfy the following: T1>Tg-17 Tg-59>T2. <Appendix 9> The image forming apparatus according to any one of Appendices 1 to 8, wherein the transport mechanism includes a plurality of transport members, and among the plurality of transport members, a transport member with which an image surface of the recording medium having an image recorded thereon comes into contact after the recording medium has passed through the image forming unit, the transport member curving the recording medium while transporting it has a radius of curvature of 50 mm or more. <Appendix 10> The image forming apparatus according to any one of Appendices 1 to 9, further comprising a processor that controls the transport mechanism, the image forming unit, the drying unit, and the cooling unit, and the processor controls the transport mechanism, the drying unit, and the cooling unit under conditions such that the moisture content of the recording medium after being cooled by the cooling unit for double-sided printing is 1.0 to 14.5%. <Appendix 11> The image forming apparatus according to any one of Appendices 1 to 9, further comprising a processor that controls the transport mechanism, the image forming unit, the drying unit, and the cooling unit, and the processor controls the amount of residual solvent in the recording medium after being cooled by the cooling unit for double-sided printing to be 160 μg / cm. ２ 10. The image forming apparatus according to claim 1, wherein the conveying mechanism, the drying unit, and the cooling unit are controlled under the following conditions:

[0144] The disclosures of Japanese Patent Application No. 2024-018864, filed on February 9, 2024, and Japanese Patent Application No. 2024-104442, filed on June 27, 2024, are incorporated herein by reference in their entirety. All documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually indicated to be incorporated by reference.

Claims

1. An image forming apparatus comprising: a transport mechanism having a transport path for transporting a recording medium; an image forming unit that applies ink to the recording medium to form an image; a drying unit that dries the recording medium on which the image has been formed; and a cooling unit that cools the dried recording medium, wherein the transport path has a main transport path in which the image forming unit and the drying unit are arranged, a discharge path that transports the recording medium from the main transport path to a stacking device, and a return transport path that is a path branched from the main transport path to the discharge path and returns the recording medium from the main transport path to the image forming unit, and the cooling unit includes a cooling unit for double-sided printing arranged on the return transport path.

2. The image forming apparatus according to claim 1, further comprising a first cooling unit disposed on the main transport path after the drying unit, and the cooling unit for double-sided printing is a second cooling unit that further cools the recording medium cooled by the first cooling unit.

3. The image forming apparatus according to claim 1 or 2, wherein the transport mechanism includes a plurality of transport members, and transports the recording medium from the image forming unit to a position where the recording medium passes through the cooling unit for double-sided printing without the image surface of the recording medium on which the image is recorded coming into contact with the transport members.

4. An image forming apparatus according to claim 1 or 2, wherein the transport mechanism includes a plurality of transport members, and among the plurality of transport members, the transport member with which the image surface of the recording medium on which the image has been recorded after passing through the image forming unit first comes into contact has an adhesive work between the image surface and the transport member of the plurality of transport members of the recording medium which first comes into contact with the image surface after passing through the image forming unit, and the image surface.

5. An image forming apparatus according to claim 3, wherein the adhesive work between the image surface of the recording medium and the conveying member that first comes into contact with the image surface of the recording medium after passing through the image forming unit is 110 mNm or less.

6. The image forming apparatus according to claim 4, wherein the work of adhesion is 80 mNm or less.

7. The image forming apparatus according to claim 4, wherein the ink is a water-based ink, the water-based ink contains resin particles, and the glass transition temperature Tg°C of the resin particles, the temperature T1°C of the image surface on which the image is recorded immediately after drying by the drying unit, and the temperature T2°C of the image surface at the time of first contact between the conveying member and the image surface on which the image is recorded satisfy the relationship T1>Tg-40>T2.

8. The image forming apparatus according to claim 4, wherein the ink is a water-based ink, the water-based ink contains resin particles, and the glass transition temperature Tg°C of the resin particles, the temperature T1°C of the image surface on which the image is recorded immediately after drying by the drying unit, and the temperature T2°C of the image surface at the time of initial contact between the conveying member and the image surface on which the image is recorded satisfy the following relationships: T1>Tg-35 Tg-57>T2 9. The image forming apparatus according to claim 4, wherein the ink is a water-based ink, the water-based ink contains resin particles, and wherein the glass transition temperature Tg°C of the resin particles, the temperature T1°C of the image surface on which the image is recorded immediately after drying by the drying unit, and the temperature T2°C of the image surface at the time of initial contact between the conveying member and the image surface on which the image is recorded satisfy the following relationships: T1>Tg-17 Tg-59>T2 10. The image forming apparatus according to claim 1 or 2, wherein the transport mechanism includes a plurality of transport members, and among the plurality of transport members, a transport member that comes into contact with the image surface of the recording medium on which the image has been recorded after passing through the image forming unit, and which transports the recording medium while curving, has a radius of curvature of 50 mm or more.

11. The image forming apparatus according to claim 3, wherein among the plurality of conveying members, a conveying member that comes into contact with the image surface of the recording medium after passing through the image forming unit and conveys the recording medium while curving it has a radius of curvature of 50 mm or more.

12. An image forming apparatus according to claim 4, wherein among the plurality of conveying members, a conveying member that comes into contact with the image surface of the recording medium after passing through the image forming unit, and that conveys the recording medium while curving it, has a radius of curvature of 50 mm or more.

13. The image forming apparatus according to claim 1 or 2, further comprising a processor that controls the transport mechanism, the image forming unit, the drying unit, and the cooling unit, wherein the processor controls the transport mechanism, the drying unit, and the cooling unit under the condition that the moisture content of the recording medium after being cooled by the cooling unit for double-sided printing is 1.0 to 14.5%.

14. The image forming apparatus according to claim 4, further comprising a processor that controls the transport mechanism, the image forming unit, the drying unit, and the cooling unit, wherein the processor controls the transport mechanism, the drying unit, and the cooling unit under the condition that the moisture content of the recording medium after being cooled by the cooling unit for double-sided printing is 1.0 to 14.5%.

15. The image forming apparatus according to claim 10, further comprising a processor that controls the transport mechanism, the image forming unit, the drying unit, and the cooling unit, wherein the processor controls the transport mechanism, the drying unit, and the cooling unit under the condition that the moisture content of the recording medium after being cooled by the cooling unit for double-sided printing is 1.0 to 14.5%.

16. The image forming apparatus according to claim 12, further comprising a processor that controls the transport mechanism, the image forming unit, the drying unit and the cooling unit, wherein the processor controls the transport mechanism, the drying unit and the cooling unit under the condition that the moisture content of the recording medium after being cooled by the cooling unit for double-sided printing is 1.0 to 14.5%.

17. The apparatus further includes a processor for controlling the conveying mechanism, the image forming unit, the drying unit, and the cooling unit, and the processor is configured to determine whether the amount of residual solvent in the recording medium after being cooled by the cooling unit for double-sided printing is 160 μg / cm ２ The image forming apparatus according to claim 1 , wherein the conveying mechanism, the drying unit, and the cooling unit are controlled under the following conditions:

18. The apparatus further includes a processor for controlling the conveying mechanism, the image forming unit, the drying unit, and the cooling unit, and the processor is configured to determine whether the amount of residual solvent in the recording medium after being cooled by the cooling unit for double-sided printing is 160 μg / cm ２ The image forming apparatus according to claim 4 , wherein the conveying mechanism, the drying unit, and the cooling unit are controlled under the following conditions:

19. The apparatus further includes a processor for controlling the conveying mechanism, the image forming unit, the drying unit, and the cooling unit, and the processor is configured to determine whether the amount of residual solvent in the recording medium after being cooled by the cooling unit for double-sided printing is 160 μg / cm ２ The image forming apparatus according to claim 10 , wherein the conveying mechanism, the drying unit, and the cooling unit are controlled under the following conditions:

20. The apparatus further includes a processor for controlling the conveying mechanism, the image forming unit, the drying unit, and the cooling unit, and the processor is configured to determine whether the amount of residual solvent in the recording medium after being cooled by the cooling unit for double-sided printing is 160 μg / cm ２ The image forming apparatus according to claim 12 , wherein the conveying mechanism, the drying unit, and the cooling unit are controlled under the following conditions:

21. The apparatus further includes a processor for controlling the conveying mechanism, the image forming unit, the drying unit, and the cooling unit, and the processor is configured to determine whether the amount of residual solvent in the recording medium after being cooled by the cooling unit for double-sided printing is 160 μg / cm ２ The image forming apparatus according to claim 13 , wherein the conveying mechanism, the drying unit, and the cooling unit are controlled under the following conditions:

22. The apparatus further includes a processor for controlling the conveying mechanism, the image forming unit, the drying unit, and the cooling unit, and the processor is configured to determine whether the amount of residual solvent in the recording medium after being cooled by the cooling unit for double-sided printing is 160 μg / cm ２ The image forming apparatus according to claim 14 , wherein the conveying mechanism, the drying unit, and the cooling unit are controlled under the following conditions:

23. The apparatus further includes a processor for controlling the conveying mechanism, the image forming unit, the drying unit, and the cooling unit, and the processor is configured to determine whether the amount of residual solvent in the recording medium after being cooled by the cooling unit for double-sided printing is 160 μg / cm ２ The image forming apparatus according to claim 15 , wherein the conveying mechanism, the drying unit, and the cooling unit are controlled under the following conditions:

24. The apparatus further includes a processor for controlling the conveying mechanism, the image forming unit, the drying unit, and the cooling unit, and the processor is configured to determine whether the amount of residual solvent in the recording medium after being cooled by the cooling unit for double-sided printing is 160 μg / cm ２ The image forming apparatus according to claim 16 , wherein the conveying mechanism, the drying unit, and the cooling unit are controlled under the following conditions:

Images