Image forming apparatus and image forming method

Abstract

This image forming apparatus forms an image by forming an ink film on a recording surface of a recording medium. The image forming apparatus includes: a drying unit that dries the ink film formed on the recording surface; and a conveyance mechanism including a contact type conveyance unit that is disposed downstream of the drying unit and that conveys the recording medium by bringing a contact member into contact with the recording surface of the recording medium conveyed downstream from the drying unit. The friction coefficient of a surface of the ink film when the recording surface of the recording medium first contacts with the contact member is 0.6 or less.

Description

Image forming apparatus and image forming method

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

[0002] Image forming devices such as inkjet printing devices that use aqueous ink generally include a drying unit for fixing and drying an ink film formed by applying ink to the recording surface of a recording medium, i.e., paper, and a transport mechanism for transporting paper within the device (e.g., JP 2016-150444 A, JP 2016-113235 A, etc.).

[0003] The transport mechanisms described in JP 2016-150444 A and JP 2016-113235 A perform non-contact transport within the drying unit, transporting the paper without contacting a contact member with the recording surface, and after the paper is discharged from the drying unit, perform contact transport, transporting the paper by contacting a contact member such as a roller with the recording surface.

[0004] The ink on the recording surface of the paper is heated by a drying unit, and the water and solvent in the ink are evaporated. However, if the drying is insufficient, or if the paper is transported by contact transport without its temperature having dropped sufficiently, the ink film may rub against the contacting members such as rollers, resulting in image defects and reduced print quality.

[0005] In view of the above circumstances, an object of the present disclosure is to provide an image forming apparatus and an image forming method that can suppress the occurrence of image defects.

[0006] The image forming apparatus of the present disclosure is an image forming apparatus that forms an image by forming an ink film on the recording surface of a recording medium, and is equipped with: a drying unit that dries the ink film formed on the recording surface; and a transport mechanism that is arranged downstream of the drying unit and includes a contact-type transport unit that transports the recording medium by bringing a contact member into contact with the recording surface of the recording medium transported downstream from the drying unit, and the friction coefficient of the surface of the ink film when the recording surface of the recording medium first comes into contact with the contact member is 0.6 or less.

[0007] In the image forming apparatus of the present disclosure, it is preferable that the coefficient of friction of the ink film surface when the recording surface of the recording medium first comes into contact with the contact member is 0.4 or more.

[0008] The contact type transport unit preferably includes a pair of rollers, a drive roller and a pinch roller disposed opposite the drive roller, the pinch roller being the contact member, and transporting the recording medium by pinching it between the pair of rollers.

[0009] The transport mechanism preferably includes a non-contact transport unit that transports the recording medium without contacting the recording surface from the time when the ink film is formed on the recording surface until the time when the recording medium passes through the drying unit.

[0010] The non-contact type transport unit preferably transports the recording medium while suctioning it using an adsorption belt system.

[0011] The image forming apparatus of the present disclosure preferably further includes a cooling unit that cools the dried ink film.

[0012] The non-contact transport unit is preferably arranged from the drying unit to the cooling unit and transports the recording medium even within the cooling unit, and the contact transport unit is preferably arranged downstream of the cooling unit.

[0013] It is preferable that the printer further comprises a processor for controlling the drying unit, and the processor controls the drying unit under conditions in which the coefficient of friction is 0.6 or less depending on the type of recording medium.

[0014] The ink that forms the ink film is preferably a water-based ink.

[0015] The water-based ink preferably contains wax, and the drying unit preferably heats the surface temperature of the ink film to a temperature equal to or higher than the melting point of the wax.

[0016] It is preferable that the ink constituting the ink film is an aqueous ink containing wax, the drying unit heats the surface temperature of the ink film to a first temperature that is equal to or higher than the melting point of the wax minus 13°C, and the cooling unit cools the surface temperature of the ink film to a second temperature that is 17°C or more lower than the first temperature.

[0017] The image forming apparatus of the present disclosure preferably further includes a switchback mechanism that reverses the recording medium, and forms images on both sides of the recording medium.

[0018] It is preferable that the switchback mechanism is disposed downstream of the drying unit, and that the contact-type transport unit transports the recording medium in the switchback mechanism.

[0019] The image forming method disclosed herein is an image forming method in an image forming apparatus that forms an image by forming an ink film on the recording surface of a recording medium, and includes a drying process for drying the ink film formed on the recording surface, and a contact-type transport process for transporting the recording medium by bringing a contact member into contact with the recording surface of the recording medium after the drying process has been carried out, wherein the friction coefficient of the surface of the ink film when the recording surface of the recording medium first comes into contact with the contact member in the contact-type transport process is set to 0.6 or less.

[0020] According to the image forming apparatus and image forming method of the present disclosure, the occurrence of image defects can be suppressed.

[0021] 1 is an overall configuration diagram of an inkjet printing apparatus according to an embodiment; FIG. 2 is an enlarged view of a portion of the inkjet printing apparatus shown in FIG. 1; FIG. 3 is a functional block diagram showing a schematic configuration of a control system of the inkjet printing apparatus; FIG. 4 is a diagram showing a lookup table of combinations of paper types, drying conditions, and cooling conditions; FIG. 5 is a diagram showing a measurement system for friction coefficient testing; FIG. 6 is a diagram showing the relationship between friction coefficient and rating in the case of OK top coat; and FIG. 7 is a diagram showing the relationship between friction coefficient and rating in the case of Bon Ivory.

[0022] Hereinafter, an embodiment of an image forming apparatus and an image forming method 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.

[0023] "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 showing a part of the paper discharge side of the inkjet printing apparatus 1 shown in Fig. 1.

[0024] 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 sides of the paper P. The paper P is an example of a recording medium of the technology disclosed herein.

[0025] 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.

[0026] 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. The paper P is transported along the transport path 12 to various units, where it is subjected to various processes.

[0027] The transport path 12 includes a main transport path 13, a supply path 14 that supplies paper P to the main transport path 13, 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 constitutes a path that returns paper P that has passed through the main transport path 13 back to the main transport path 13 for double-sided printing.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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. That is, 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 recording side by the image forming unit 40 to the image forming unit 40, allowing an image to be formed on its second recording side. Here, the first recording side and the second recording side refer to the two sides of the paper P. The side that is printed first is the first recording side, and will be referred to as the first side hereinafter. The side of the paper P opposite to the first side is the second recording side, and will be referred to as the second side hereinafter.

[0032] 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.

[0033] The second connection section 22 is provided with a first switching mechanism 18 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 first switching mechanism 18 provided in the second connection section 22 includes a support member 18a, a branch guide 18b (see FIG. 2), and an actuator (not shown). One end of the branch guide 18b is fixed to the support member 18a and is rotatable around the support member 18a. The actuator is, for example, a solenoid that rotates the branch guide 18b.

[0034] The first switching mechanism 18 rotates the branch guide 18b 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. That is, the first switching mechanism 18 switches between a first state in which the paper transported from the main transport path 13 is discharged to the discharge path 15 and a second 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. In Fig. 2, the branch guide 18b indicated by the solid line is in the first state, and the branch guide 18b indicated by the dashed line is in the second state.

[0035] The return transport path 16 is provided with a switchback section 17 that reverses the traveling direction of the paper P. The switchback section 17 temporarily pulls out the paper P from the return transport path 16 to reverse the traveling direction of the paper P. That is, the leading edge of the paper P in the traveling direction when it was transported on the return transport path 16 before being pulled into the switchback section 17 becomes the trailing edge in the traveling direction after it is returned from the switchback section 17 to the return transport path 16. By passing through this switchback section 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.

[0036] A second switching mechanism 19 is provided at the connection between the switchback unit 17 and the return transport path 16. The second switching mechanism 19 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 second switching mechanism 19 provided at the second connection unit 22 includes a support member 19a, a branch guide 19b (see FIG. 2), and an actuator (not shown). One end of the branch guide 19b is fixed to the support member 19a and is rotatable around the support member 19a. The actuator is, for example, a solenoid that rotates the branch guide 19b.

[0037] 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, a transport roller pair, a chain gripper, and a transport guide. A transport roller pair 25, a paper feed drum 24, a pretreatment liquid application drum 32, a pretreatment liquid drying drum 36, an imaging drum 42, and belt conveyors 54 and 64, 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 also includes a transport guide (not shown) arranged along the transport path 12. The transport mechanism 10 also includes a motor (not shown) and a drive unit (not shown), such as a motor drive circuit (not shown), as a power source. The paper P is transported along the transport path 12 by these elements that constitute the transport mechanism 10. The transport mechanism 10 will be described in further detail below.

[0038] The paper feed device 20 includes a paper feed tray on which a stack of multiple sheets of paper P is 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).

[0039] 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 .

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] In the image forming unit 40, an image forming process is performed on the recording surface of the paper P. The image forming unit 40 forms an image by forming an ink film on the recording surface of the paper P. 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. The print drum 42 includes a gripper (not shown) on its circumferential surface, and by gripping the leading edge of the paper P with the gripper and rotating, the paper P is wound around the drum circumferential surface and transported. The print drum 42 also includes a suction mechanism (not shown), which adsorbs the paper P wound around the drum circumferential surface and transports it. Negative pressure is used for adsorption. The print drum 42 includes multiple suction holes on its circumferential surface, and by applying suction from the inside of the print drum 42 through these suction holes, the paper P is adsorbed to the circumferential surface of the print drum 42.

[0046] 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 that contains water and a coloring material such as a pigment or a dye.

[0047] 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.

[0048] At least one of the inkjet heads 46C, 46M, 46Y, and 46K ejects ink droplets toward the paper P being transported by the image forming drum 42, and the ejected droplets adhere to the paper P, thereby forming an image on the paper P. That is, in the image forming unit 40, an image is formed by applying ink to the recording surface of the paper P to form an ink film on the recording surface.

[0049] 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.

[0050] The drying unit 50 performs a drying process to dry the ink film formed on the recording surface of the paper P. The drying unit 50 conveys the paper P while applying heat to the paper P on which an image has been formed by the image forming unit 40, i.e., on which an ink film has been formed on the recording surface, to dry the ink. The drying unit 50, for example, includes a belt conveyor 54 equipped with a heating belt 51 and a 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 an endless conveying belt having a conveying surface made of a material with high thermal conductivity, such as metal, and is heated from the back side of the conveying surface by a heat source, such as a heater, via a suction box 55 (described later). The paper P is heated by the heating belt 51 and the heater 57 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, in the range of 80° C. to 150° C., and can be changed as needed. Similarly, the heater 57 can change its heating temperature and adjust the amount of heat applied to the paper P by changing its output. The heater 57 can be a convection heating means such as a hot air blower, a radiant heating means such as an infrared (IR) lamp, an ultraviolet (UV) lamp, or a microwave generator, or a superheated steam generator.

[0051] 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.

[0052] The paper P is handed over from the imaging drum 42 to the chain gripper 27, and with the leading edge of the paper P gripped by the gripper 27a, it is placed on the heating belt 51 and 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 by the heating belt 51 while being adsorbed by the heating belt 51. In this way, the paper P is heated and dried by the heating belt 51 and heater 57 while being transported by the belt conveyor 54.

[0053] The belt conveyor 54 provided in the drying unit 50 conveys the paper P without bringing the recording surface of the paper P into contact with a conveying member.

[0054] The cooling unit 60 performs a cooling process to cool the ink film formed on the recording surface of the paper P and dried. The cooling unit 60 is located immediately after the drying unit 50 on the main transport path 13. The cooling unit 60 cools the ink film heated and dried by the drying unit 50. The cooling unit 60 includes, as an example, a blower 67 that blows air at room temperature or air that is cooler than room temperature. The blower 67 is located opposite the recording surface (i.e., the ink film surface) of the paper P. The blower 67 is capable of changing the blowing air temperature and output. The cooling means included in the cooling unit 60 may be a contact cooling mechanism that cools the paper P by contacting the side opposite the recording surface instead of the blower 67 that cools the paper P without contacting the paper P, or both the blower 67 and the cooling unit 60.

[0055] In the inkjet printing apparatus 1, the cooling unit 60 cools the ink film on the paper P while transporting the paper P. The cooling unit 60 includes a belt conveyor 64 similar to the belt conveyor 54 of the drying unit 50. The belt conveyor 64 includes a transport belt 61, a drive roller 62, and a driven roller 63. The transport belt 61 has multiple suction holes for adsorbing and transporting the paper P, and a suction box 65 is disposed in the space between the drive roller 62 and the driven roller 63 on the back side of the transport surface of the transport belt 61. The suction box 65 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 65 generates suction pressure in the suction holes of the transport belt 61, thereby adsorbing the paper P to the transport surface. The belt conveyor 64 that transports the paper P constitutes part of the transport mechanism 10.

[0056] The stacking device 70 stacks the sheets P on which images have been formed. 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).

[0057] The transport mechanism 10 will now be described in further detail. As described above, the transport mechanism 10 includes multiple transport members that transport the paper P along the transport path 12. As shown in FIG. 1 , the transport mechanism 10 includes multiple transport roller pairs 25 arranged in the supply path 14, the main transport path 13 upstream of the pretreatment liquid application unit 30, the main transport path 13 downstream of the image forming unit 40, the discharge path 15, and the return transport path 16. The transport roller pairs 25 include a drive roller 25 a and a pinch roller 25 b that are arranged facing each other. The drive roller 25 a is made of, for example, ethylene propylene diene rubber (EPDM), and the pinch roller 25 b is made of, for example, polyacetal resin (POM). The transport roller pair 25 sandwiches the paper P between the drive roller 25 a and the pinch roller 25 b, and transports the paper P by rotation of the transport roller pair 25. As described above, the transport mechanism 10 includes, as transport members, the paper feed drum 24, the pretreatment liquid application drum 32, the pretreatment liquid drying drum 36, the image forming drum 42, and the chain gripper 27. The belt conveyor 54 of the drying unit 50 and the belt conveyor 64 of the cooling unit 60 are also part of the transport mechanism 10.

[0058] The belt conveyors 54 and 64 are suction belt type transport units that transport the paper P by adsorbing it to the heating belt 51 and the transport belt 61. The belt conveyors 54 and 64 transport the paper P without bringing any transport members into contact with the recording surface on which an ink film has been formed by the image forming unit 40. In this specification, a means for transporting the paper P without bringing a transport member into contact with the recording surface of the paper P, such as the belt conveyors 54 and 64, is referred to as a non-contact type transport unit. In contrast to the non-contact type transport unit, a unit that transports the paper P with a transport member in contact with the recording surface is referred to as a contact type transport unit. The transport roller pair 25, the paper feed drum 24, the pretreatment liquid application drum 32, the pretreatment liquid drying drum 36, the imaging drum 42, and the like are contact type transport units.

[0059] As described above, in the inkjet printing apparatus 1, the transport mechanism 10 includes non-contact transport units in the drying unit 50 and the cooling unit 60, and includes contact transport units in other portions.

[0060] The non-contact transport unit provided in the inkjet printing device 1 is not limited to a suction belt type that adsorbs onto the belt conveyor 54, but may also be an adhesive belt type that uses a transport belt with adhesive on the transport surface, or a type that transports the paper P placed on a table together with the table. Furthermore, the method of adsorbing onto the belt conveyor 54 may be a method that uses vacuum suction or an electrostatic adsorption method.

[0061] The pinch roller 25b of the conveying roller pair 25 arranged immediately after the cooling unit 60 is the first to come into contact with the recording surface on which the ink film is formed in the image forming unit 40. In Fig. 1, the conveying roller pair arranged immediately after the cooling unit 60 is denoted by the symbol 25A in order to distinguish it from the other conveying roller pairs 25.

[0062] The plurality of conveying roller pairs 25, including the conveying roller pair 25A, arranged downstream of the cooling unit 60 constitute a "contact-type conveying unit" in the technology of the present disclosure, and a "contact-type conveying process" is carried out. The pinch roller 25b of the conveying roller pair 25A is the contact member that first comes into contact with the ink film formed on the recording surface of the paper P conveyed downstream from the drying unit 50.

[0063] The inkjet printing device 1 is configured so that the coefficient of friction of the ink film surface when the pinch roller 25b of the transport roller pair 25A first comes into contact with the recording surface is 0.6 or less. It is preferable that the coefficient of friction of the ink film surface when the pinch roller 25b of the transport roller pair 25A first comes into contact with the recording surface is 0.4 or more.

[0064] If the ink is a water-based ink containing wax particles, the drying unit 50 may be configured to heat the surface of the ink film to a temperature equal to or higher than the melting point Tm (°C) of the wax. For example, if the wax particles are made of carnauba wax, the drying unit 50 preferably heats the surface of the ink film to a temperature equal to or higher than the melting point of carnauba wax, 83°C.

[0065] Alternatively, when the ink is a water-based ink containing wax particles, the drying unit 50 may be configured to heat the surface temperature of the ink film to a first temperature T1 that is equal to or higher than the melting point Tm of the wax minus 13° C., and the cooling unit 60 may be configured to cool the surface temperature of the ink film to a second temperature T2 that is equal to or lower than T1 minus 17° C. For example, when the wax particles are made of carnauba wax, it is preferable that the drying unit 50 heats the surface temperature of the ink film to 70° C. or higher, and the cooling unit 60 cools the surface temperature by 17° C. or more from the heated surface temperature.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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 paper type of the paper P, and the like.

[0075] 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.

[0076] 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.

[0077] 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. In detail, 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 following processes are sequentially performed on the first side of the paper P: a pretreatment liquid application process by the pretreatment liquid application unit 30, a pretreatment liquid drying process by the pretreatment liquid drying unit 35, an image formation process by the image forming unit 40, a drying process by the drying unit 50, and a cooling process by the cooling unit 60. Thereafter, the paper P with an image printed on its first side is transported to the discharge path 15 and discharged to the stacking device 70.

[0078] 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 sequentially performed. 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. The paper P is returned to the main transport path 13 from the first connection unit 21 via the return transport path 16. When the paper P is returned to the main transport path 13, it is inverted so that the second side of the paper P becomes the image formation side. The application of the 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 on the main transport path 13. 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.

[0079] The processor 100 controls the drying unit 50 and the cooling unit 60 under the condition that the friction coefficient of the ink film when the pinch roller 25b of the conveying roller pair 25A contacts the recording surface of the paper P discharged from the cooling unit 60 is 0.6 or less. The control of the drying unit 50 and the cooling unit 60 by the processor 100 will be described later.

[0080] "Processing by Processor 100" The processor 100 causes each unit to execute various processes in accordance with information input from the input device 106.

[0081] For example, the processor 100 receives a designation of single-sided printing or double-sided printing from the input device 106 and sets the single-sided printing or double-sided printing mode. That is, the processor 100 controls the conveying mechanism 10 to switch the conveying path to the single-sided printing path or the double-sided printing path. The path switching is achieved by the path switching using the branch guide 18b of the first switching mechanism 18 of the second connection part 22.

[0082] 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.

[0083] The processor 100 performs various types of image processing, such as conversion processing, correction processing, and halftone processing, on image data to be printed.

[0084] 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.

[0085] 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.

[0086] The processor 100 also controls and operates the drying unit 50. The processor 100 changes the drying conditions of the drying unit 50. The drying conditions are, for example, the heating output of the heating unit and the conveying speed of the conveying unit. The heating output of the heating unit is, for example, the IR heater output if the heat source is an IR heater, and the temperature and flow rate of the hot air blown out from the hot air blower if the heat source is a hot air blower.

[0087] The processor 100 operates the cooling unit 60. The processor 100 controls the cooling output and / or cooling time of the cooling unit 60. When the cooling source is the blower 67 as in this embodiment, the cooling output refers to the temperature and volume of air blown out from the blower 67.

[0088] An example of a configuration for setting the coefficient of friction of the ink film surface to 0.6 or less when the contact member first comes into contact with the recording surface after the ink film is formed in the inkjet printing device 1 will be described. For example, the coefficient of friction of the ink film can be changed by changing the drying conditions in the drying unit 50 and the cooling conditions in the cooling unit 60. In this inkjet printing device 1, an ink film surface with a coefficient of friction of 0.6 or less is achieved by adjusting the drying conditions and cooling conditions.

[0089] 4 is created and stored in advance in the storage device 102. The lookup table T records the paper type of the paper P and a combination of drying and cooling conditions that can make the coefficient of friction of the ink film surface 0.6 or less before the ink film contacts the pinch roller 25b of the conveying roller pair 25A when the ink film is formed on the paper P. The paper type is information that identifies the type of recording medium, including, for example, the brand, paper type, and paper thickness of the paper P.

[0090] The processor 100 may be configured to refer to the lookup table T and set the drying conditions of the drying unit 50 and the cooling conditions of the cooling unit 60 in accordance with input information about the paper P (here, the paper type). The lookup table T shown in Fig. 4 indicates that, for paper type A, for example, the drying condition α1 and the cooling condition β1 should be selected.

[0091] The drying conditions may include a drying output and a transport time (drying time), but since changing the transport time makes control complicated, it is preferable that the drying condition be the drying output.Similarly, the cooling conditions may include a cooling output and a transport time (cooling time), but since changing the transport time makes control complicated, it is preferable that the cooling condition be the cooling output.

[0092] The coefficient of friction of the ink film formed on the recording surface of the paper P can be measured using a commercially available friction measuring device. Specific measuring devices and measuring methods will be described later.

[0093] The lookup table T is created, for example, by conducting tests in advance for each paper type to determine the combination of drying and cooling conditions that can make the coefficient of friction 0.6 or less.

[0094] If the ink is an aqueous ink containing wax particles, it is preferable to satisfy the drying and cooling conditions that satisfy either the first or second condition below. The first condition is that the ink film is heated to a temperature at which the surface temperature is equal to or higher than the melting point Tm (°C) of the wax. For example, if the wax particles are made of carnauba wax, the drying unit 50 may be configured to heat the ink film to a temperature at which the surface temperature is equal to or higher than the melting point of carnauba wax, 83°C. The second condition is that the ink film is heated to a first temperature T1 at which the surface temperature is equal to or higher than the melting point Tm of the wax minus 13°C, and then cooled to a second temperature T2 at which the surface temperature is equal to or lower than T1 minus 17°C. For example, if the wax particles are made of carnauba wax, the drying unit 50 may be configured to heat the ink film to a surface temperature of 70°C or higher, and the cooling unit 60 may be configured to cool the ink film to a surface temperature at which the surface temperature is lowered by 17°C or more from the heated surface temperature.

[0095] Therefore, when the ink is a water-based ink containing wax particles, the processor 100 may be configured to control the drying unit 50 under drying conditions in which the drying unit 50 heats the surface temperature of the ink film to a temperature equal to or higher than the melting point Tm (°C) of the wax. For example, when the wax particles are made of carnauba wax, the processor 100 may be configured to control the drying unit 50 under drying conditions in which the surface temperature of the ink film is equal to or higher than the melting point of carnauba wax, 83°C.

[0096] Alternatively, when the ink is an aqueous ink containing wax particles, the processor 100 may be configured such that the drying unit 50 heats the surface temperature of the ink film to a first temperature T1 that is equal to or higher than the melting point Tm of the wax minus 13° C., and the cooling unit 60 cools the surface temperature of the ink film to a second temperature T2 that is at least 17° C. lower than the first temperature T1. For example, when the wax particles are made of carnauba wax, the processor 100 may be configured such that the drying unit 50 heats the surface temperature of the ink film to 70° C. or higher, and the processor 100 controls the cooling unit 60 under cooling conditions that cool the surface temperature by at least 17° C. from the heated surface temperature.

[0097] The hardware structure of the processor 100 can 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.

[0098] 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.

[0099] Furthermore, more specifically, the hardware structure of these processors can be an electric circuit that combines circuit elements such as semiconductor elements.

[0100] As described above, the inkjet printing apparatus 1 according to this embodiment is an image forming apparatus that forms an image by applying ink to the recording surface of a recording medium (paper P in this case) to form an ink film. The inkjet printing apparatus 1 includes a drying unit 50 that dries the ink film formed on the recording surface, and a transport mechanism including a transport unit (here, multiple transport roller pairs 25) disposed downstream of the drying unit 50. The transport unit is a contact-type transport unit that transports the recording medium by bringing a contact member into contact with the recording surface of the recording medium transported downstream from the drying unit 50. In the inkjet printing apparatus 1, after the ink film is formed and dried, the coefficient of friction of the ink film surface when the recording surface of the recording medium first comes into contact with the contact member is 0.6 or less. By setting the coefficient of friction of the ink film to 0.6 or less, the occurrence of image defects can be suppressed.

[0101] Conventionally, a non-contact unit transports the ink within the drying unit, and a contact transport unit transports the ink after it leaves the drying unit. In this case, if the ink is sent to the contact transport unit in an insufficiently dried state, image defects can occur due to friction between the ink film and the contact member. However, by satisfying the above-mentioned friction coefficient condition, the occurrence of image defects can be reliably suppressed.

[0102] Furthermore, the above configuration may provide cost benefits. Specifically, one possible measure to prevent image defects is to lengthen the transport path of the non-contact transport so that the sheet does not come into contact with the recording surface for a long period of time even after being discharged from the drying unit 50. However, non-contact transport units are more expensive than contact transport units, and the longer the transport path of the non-contact transport unit, the higher the device costs. To prevent image defects, it is necessary to provide a sufficient transport path for the non-contact transport unit, making it difficult to reduce device costs. In contrast, as described above, by setting the coefficient of friction when the contact member first comes into contact with the recording surface after image formation to 0.6 or less, the transport path of the non-contact transport unit does not need to be unnecessarily long, thereby reducing device costs.

[0103] It is preferable that the coefficient of friction of the ink film surface when the recording surface of the recording medium first comes into contact with the contact member is 0.4 or more. If the coefficient of friction is 0.4 or more, the contact member does not slip on the ink film surface, and the recording medium can be transported reliably.

[0104] Although the inkjet printing apparatus 1 of the above embodiment is configured to be capable of double-sided printing, the image forming apparatus of the present disclosure may be an apparatus capable of single-sided printing only. Also, the image forming apparatus of the present disclosure may be configured without the pretreatment liquid application unit 30 and the pretreatment liquid drying unit 35.

[0105] 1 includes the cooling unit 60, it may be configured without the cooling unit 60. In this case, it is sufficient that the drying conditions are set so that the coefficient of friction becomes 0.6 or less by drying using the drying unit 50.

[0106] 1 is equipped with non-contact transport units in the drying unit 50 and the cooling unit 60. However, downstream of the drying unit 50, as long as the coefficient of friction of the ink film surface is 0.6 or less when the contact member first comes into contact with the recording surface, a contact transport unit may be disposed immediately after the drying unit 50. Also, as long as the coefficient of friction of the ink film surface is 0.6 or less, a configuration in which transport by a contact transport unit is performed from the beginning of the cooling unit 60 or midway through the cooling unit 60 is acceptable.

[0107] In the above embodiment, the user inputs the paper type, and the drying and cooling conditions are set based on that information, achieving the above-mentioned coefficient of friction of 0.6 or less. Alternatively, a sensor for detecting the paper type may be provided in the paper feeder 20 or the supply path 14, and the processor 100 may be configured to set the drying and cooling conditions by referencing the lookup table T in accordance with the detection results from the sensor.

[0108] 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.

[0109] 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.

[0110] The above-described embodiments of the present invention may be modified, added, or deleted as appropriate within the scope of the spirit of the present invention. The present invention is not limited to the above-described embodiments, and many modifications are possible within the technical concept of the present invention by those having ordinary skill in the relevant field.

[0111] "Friction Coefficient Evaluation Test" The friction coefficient that can suppress the deterioration of image quality that occurs when paper P on which an ink film has been formed by the image forming unit is conveyed in contact with the paper P was determined by the following test.

[0112] The measurement experiment system 200 is shown in Figure 5. An ink application unit 202, a drying unit 204, a cooling unit 206, and a roller pressing unit 208 were installed on a transport path 201 for paper P. Paper P was placed on a holding table 210, and the configuration was such that the paper P could be transported together with the holding table 210 from the ink application unit 202 to the drying unit 204, the cooling unit 206, and the roller pressing unit 208. The roller pressing unit 208 was equipped with a roller 209 that came into contact with the ink-coated surface of the paper P (i.e., the recording surface on which the ink film 220 was formed). The material of the roller 209 was POM (polyacetal resin). The roller 209 corresponds to the contact member that first comes into contact with the recording surface on which the ink film has been formed of the paper P discharged from the drying unit 204. Also, on the conveying path 201, there were arranged a surface temperature measuring device 212 for measuring the temperature of the surface of the ink film 220 immediately after it was discharged from the drying unit 204, and a surface temperature measuring device 214 for measuring the temperature of the surface of the ink film 220 immediately before it came into contact with the roller 209. The drying unit 204 was a hot air blower, and the cooling unit was a room temperature air blower.

[0113] The following experiment was conducted using the measurement experiment system 200. First, ink was applied to one side of the paper P, which was the recording surface, using the ink application unit 202. A water-based ink containing carnauba wax was used as the ink. The amount of ink applied was 5.4 pl / pixel. Next, the drying unit 204 blew hot air onto the recording surface to dry the ink film 220. Then, the cooling unit 206 blew room-temperature air onto the recording surface to cool the ink film 220. After that, the roller 209 was pressed against the recording surface. The printing pressure when pressing the roller 209 against the paper P was 8 N. To evaluate under the worst conditions, the roller 209 was pressed in a fixed, non-rotating state.

[0114] The relationship between the coefficient of friction of the ink film 220 formed by changing the drying temperature and time, the cooling time, etc., and image failure was investigated. In addition, the heating temperature during drying was measured as the temperature immediately after being discharged from the drying unit 204 (post-drying temperature), and the temperature immediately before contact with the roller 209 after cooling (post-cooling temperature). Keyence FTH-30 models were used as the surface temperature measuring devices 212 and 214.

[0115] Two sheets of the same paper type were subjected to ink film formation, drying, and cooling under the same conditions, with one sheet being pressed with the roller 209 described above and the other sheet being used for friction coefficient measurement. The friction coefficient measurement was carried out at the same timing as the roller pressing after cooling. A portable friction meter, 3D Muse Type: 37i manufactured by Shinto Scientific Co., Ltd., was used to measure the friction number. With this friction meter, the coefficient of friction can be measured from the thrust force at which the slider inside the meter starts to move when the meter is placed against the surface of the ink film.

[0116] After pressing the roller 209 against the paper P, the recording surface was observed and image defects on the recording surface were evaluated according to the criteria shown in Table 1. The evaluation of image defects was a sensory evaluation. A rating of 4 or higher was considered to be sufficient suppression of image defects.

[0117] As the paper P, measurements were carried out on two types of paper, "OK Top Coat+" 157 gsm, manufactured by Oji Paper Co., Ltd., and "Bon Ivory" 310 gsm, manufactured by Oji Paper Co., Ltd.

[0118] For the OK top coat + 157 gsm, Samples No. 1 to 7 were dried and cooled under different conditions, and the post-drying temperature, post-cooling temperature, friction coefficient, and image defects on the recording surface were evaluated. The results are shown in Table 2.

[0119] For Bon Ivory 310 gsm, Samples No. 11 to 22 were dried and cooled under different conditions, and the results of evaluation of the temperature after drying, the temperature after cooling, the coefficient of friction, and image defects on the recording surface are shown in Table 3.

[0120] Figure 6 shows the relationship between the coefficient of friction and the rating (image failure rating) for the OK top coat, and Figure 7 shows the relationship between the coefficient of friction and the rating for Bon Ivory.

[0121] 6 and 7, when the coefficient of friction was 0.6 or less, image defects were sufficiently suppressed and the rating was 4 or more. In other words, it was revealed that when the coefficient of friction of the ink film 220 was 0.6 or less, image quality with almost no rubbing could be obtained even under the forced condition of contact with the non-rotating roller 209.

[0122] From Tables 2 and 3, it can be seen that if the post-drying temperature, i.e., the temperature of the surface of the ink film 220 when dried, is heated to or above the melting point Tm of the wax (here, the melting point of carnauba wax, 83°C), the coefficient of friction can be reduced to or below 0.6, and a rating of 4 or higher can be obtained. Furthermore, even if the post-drying temperature, i.e., the temperature of the surface of the ink film 220 when dried, is not equal to or above the melting point Tm of the wax, it can be reduced to or below 0.6 and a rating of 4 or higher if it is heated to or above the melting point Tm - 13°C (here, 70°C or higher) and then cooled by 17°C or more from that heating temperature.

[0123] The following supplementary notes are further disclosed regarding the above embodiments. <Supplementary Note 1> An image forming apparatus that forms an image by forming an ink film on the recording surface of a recording medium, comprising: a drying unit that dries the ink film formed on the recording surface; and a transport mechanism that is arranged downstream of the drying unit and includes a contact-type transport unit that transports the recording medium by bringing a contact member into contact with the recording surface of the recording medium transported downstream from the drying unit, wherein the coefficient of friction of the surface of the ink film when the recording surface of the recording medium first comes into contact with the contact member is 0.6 or less. <Supplementary Note 2> The image forming apparatus according to Supplementary Note 1, wherein the coefficient of friction of the surface of the ink film when the recording surface of the recording medium first comes into contact with the contact member is 0.4 or more. <Supplementary Note 3> The image forming apparatus according to Supplementary Note 1 or Supplementary Note 2, wherein the contact-type transport unit comprises a pair of rollers, a drive roller and a pinch roller arranged opposite the drive roller, the pinch roller being the contact member, and transporting the recording medium by sandwiching it between the pair of rollers. <Appendix 4> The image forming apparatus according to any one of Appendices 1 to 3, wherein the transport mechanism includes a non-contact transport unit that transports the recording medium without contacting the recording surface after an ink film has been formed on the recording surface until the recording medium passes through the drying unit. <Appendix 5> The image forming apparatus according to Appendices 4, wherein the non-contact transport unit transports the recording medium while adsorbing it using a suction belt system. <Appendix 6> The image forming apparatus according to any one of Appendices 1 to 5, further comprising a cooling unit that cools the dried ink film. <Appendix 7> The image forming apparatus according to Appendices 6, wherein the non-contact transport unit is arranged from the drying unit to the cooling unit and transports the recording medium even within the cooling unit, and the contact transport unit is arranged downstream of the cooling unit. <Appendix 8> The image forming apparatus according to any one of Appendices 1 to 7, further comprising a processor that controls the drying unit, and the processor controls the drying unit under conditions where the coefficient of friction is 0.6 or less depending on the type of recording medium. <Supplementary Note 9> The image forming apparatus according to any one of Supplementary Note 1 to Supplementary Note 8, wherein the ink constituting the ink film is a water-based ink.<Supplementary Note 10> The image forming apparatus according to Supplementary Note 9, wherein the aqueous ink contains wax, and the drying unit heats the surface temperature of the ink film to a temperature equal to or higher than the melting point of the wax. <Supplementary Note 11> The image forming apparatus according to Supplementary Note 6 or Supplementary Note 7, wherein the ink constituting the ink film is aqueous ink containing wax, and the drying unit heats the surface temperature of the ink film to a first temperature that is equal to or higher than the melting point of the wax minus 13°C, and the cooling unit cools the surface temperature of the ink film to a second temperature that is 17°C or higher lower than the first temperature. <Supplementary Note 12> The image forming apparatus according to any one of Supplementary Notes 1 to 11, further comprising a switchback mechanism that reverses the recording medium, and forms images on both sides of the recording medium. <Supplementary Note 13> The image forming apparatus according to Supplementary Note 12, wherein the switchback mechanism is arranged downstream of the drying unit, and a contact-type transport unit transports the recording medium in the switchback mechanism. <Supplementary Note 14> An image forming method in an image forming apparatus that forms an image by forming an ink film on a recording surface of a recording medium, comprising: a drying step of drying the ink film formed on the recording surface; and a contact-type transport step of bringing a contact member into contact with the recording surface of the recording medium and transporting the recording medium after the drying step has been carried out, wherein the friction coefficient of the surface of the ink film when the recording surface of the recording medium first comes into contact with the contact member in the contact-type transport step is 0.6 or less.

[0124] The disclosure of Japanese Patent Application No. 2024-106462, filed on July 1, 2024, is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards mentioned herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. An image forming apparatus that forms an image by forming an ink film on the recording surface of a recording medium, comprising: a drying unit that dries the ink film formed on the recording surface; and a transport mechanism that is arranged downstream of the drying unit and includes a contact-type transport unit that transports the recording medium by bringing a contact member into contact with the recording surface of the recording medium transported downstream from the drying unit, wherein the coefficient of friction of the surface of the ink film when the recording surface of the recording medium first comes into contact with the contact member is 0.6 or less.

2. The image forming apparatus according to claim 1, wherein the friction coefficient of the surface of the ink film when the recording surface of the recording medium first comes into contact with the contact member is 0.4 or more.

3. The image forming apparatus according to claim 1, wherein the contact-type transport unit comprises a pair of rollers, a drive roller and a pinch roller disposed opposite the drive roller, the pinch roller being the contact member, and transporting the recording medium by sandwiching it between the pair of rollers.

4. The image forming apparatus according to claim 2, wherein the contact-type transport unit comprises a pair of rollers, a drive roller and a pinch roller disposed opposite the drive roller, the pinch roller being a contact member, and transporting the recording medium by sandwiching it between the pair of rollers.

5. The image forming apparatus according to claim 1, wherein the transport mechanism includes a non-contact transport unit that transports the recording medium without contacting the recording surface from the time the ink film is formed on the recording surface until the time the recording medium passes through the drying unit.

6. The image forming apparatus according to claim 2, wherein the transport mechanism includes a non-contact transport unit that transports the recording medium without contacting the recording surface from the time the ink film is formed on the recording surface until the recording medium passes through the drying unit.

7. The image forming apparatus according to claim 5, wherein the non-contact transport unit transports the recording medium while adsorbing it using an adsorption belt system.

8. The image forming apparatus according to claim 6, wherein the non-contact transport unit transports the recording medium while adsorbing it using an adsorption belt system.

9. The image forming apparatus according to claim 1, further comprising a cooling unit that cools the dried ink film.

10. The image forming apparatus according to claim 2, further comprising a cooling unit that cools the dried ink film.

11. An image forming apparatus according to claim 5, further comprising a cooling unit that cools the dried ink film, wherein the non-contact transport unit is arranged from the drying unit to the cooling unit and transports the recording medium even within the cooling unit, and the contact transport unit is arranged downstream of the cooling unit.

12. An image forming apparatus according to claim 6, further comprising a cooling unit that cools the dried ink film, wherein the non-contact transport unit is arranged from the drying unit to the cooling unit and transports the recording medium even within the cooling unit, and the contact transport unit is arranged downstream of the cooling unit.

13. An image forming apparatus according to any one of claims 1 to 12, further comprising a processor that controls the drying unit, wherein the processor controls the drying unit under conditions such that the coefficient of friction is 0.6 or less depending on the type of recording medium.

14. The image forming apparatus according to any one of claims 1 to 12, wherein the ink constituting the ink film is a water-based ink.

15. The image forming apparatus according to claim 14, wherein the water-based ink contains wax, and the drying unit heats the surface temperature of the ink film to a temperature equal to or higher than the melting point of the wax.

16. An image forming apparatus according to any one of claims 9 to 12, wherein the ink constituting the ink film is an aqueous ink containing wax, the drying unit heats the surface temperature of the ink film to a first temperature that is equal to or higher than the melting point of the wax minus 13°C, and the cooling unit cools the surface temperature of the ink film to a second temperature that is 17°C or more lower than the first temperature.

17. The image forming apparatus according to any one of claims 1 to 12, further comprising a switchback mechanism that reverses the recording medium, and forms images on both sides of the recording medium.

18. The image forming apparatus according to claim 17, wherein the switchback mechanism is disposed downstream of the drying unit, and the contact-type transport unit transports the recording medium in the switchback mechanism.

19. An image forming method for an image forming device that forms an image by forming an ink film on the recording surface of a recording medium, comprising: a drying process for drying the ink film formed on the recording surface; and a contact-type transport process for transporting the recording medium by bringing a contact member into contact with the recording surface of the recording medium after the drying process has been carried out, wherein the friction coefficient of the surface of the ink film when the recording surface of the recording medium first comes into contact with the contact member in the contact-type transport process is 0.6 or less.

Images