Holding sheet and image formation device

Abstract

To provide a holding sheet that is less likely to cause irregularities due to temperature differences, and to provide an image formation device to which the holding sheet is fitted.SOLUTION: A holding sheet is fitted to a surface of an image formation drum 17 of an image formation device 1 to hold an image formation medium 4 to be an image formation object of the image formation device 1 and includes: a first sheet made of a metal; and a second sheet formed on the first sheet and made of a non-metal material, where the second sheet has a linear expansion coefficient that is lower than that of the first sheet.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a holding sheet and an image forming apparatus. [Background technology]

[0002] Patent Document 1 discloses a printing press comprising: a printing cylinder that includes a metal sheet forming an outer peripheral surface and transports the sheet; an inkjet head that prints by ejecting ink droplets onto the sheet being transported by the printing cylinder; a drying device that is positioned downstream of the inkjet head in the sheet transport direction, faces the printing cylinder, and dries the ink after printing; and a heat dissipation member that is attached to and overlaps the metal sheet of the printing cylinder, absorbs heat from the sheet when facing the drying device, and releases the heat when separated from the drying device, wherein the heat dissipation member includes a sheet-shaped main body made of a non-metallic material and a number of ventilation parts that allow air to pass through in the thickness direction of the main body, and the printing cylinder includes first and second holding parts that detachably hold one end and the other end of the heat dissipation member, respectively, and third and fourth holding parts that hold one end and the other end of the metal sheet, respectively (see claims). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6529347 Summary of the Invention [Problem to be solved by the invention]

[0004] In an image forming apparatus such as that described in Patent Document 1, a holding sheet is attached to an image forming cylinder (called a printing cylinder in Patent Document 1). The holding sheet is called a "masking sheet" or the like. Through holes are formed in this holding sheet. An image forming medium is held on the holding sheet by suction from the inside of the image forming cylinder through the through holes. An image is then formed on the image forming medium using an inkjet method or the like. The holding sheet includes a metal sheet.

[0005] However, metal has a high thermal conductivity. Therefore, metal sheets are prone to temperature changes. The holding sheet must maintain a uniform temperature over a relatively large area. However, with a metal sheet, uneven heating can easily cause uneven temperature differences between different parts of the metal sheet. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a holding sheet that is less susceptible to uneven temperature differences, and an image forming apparatus equipped with such a holding sheet. [Means for solving the problem]

[0006] (1) The present invention is a holding sheet that is attached to the surface of an image forming cylinder of an image forming device and holds an image forming medium on which an image is formed by the image forming device, and that comprises a first sheet made of metal and a second sheet made of non-metal and adhered onto the first sheet.

[0007] (2) The holding sheet according to (1) may be such that the second sheet has a linear expansion coefficient lower than that of the first sheet.

[0008] (3) The second sheet may be a holding sheet according to (2), in which the base material is a fiber.

[0009] (4) The holding sheet may be as described in (3), wherein the base material of the second sheet is glass fiber or aramid fiber.

[0010] (5) The holding sheet according to (3) may be such that the fibers of the second sheet are impregnated with a fluororesin.

[0011] (6) A holding sheet according to (3), wherein the fibers of the second sheet have a plurality of first through holes formed therein, and adjacent first through holes are separated from each other by adhesive.

[0012] (7) The holding sheet may be as described in (6), wherein the first through-holes are breathable.

[0013] (8) The holding sheet according to (6) may be such that the fibers of the second sheet have second through holes for ventilation formed by punching, separate from the first through holes.

[0014] (9) The holding sheet may be as described in (3), wherein the first sheet and the second sheet are bonded together with a silicone adhesive.

[0015] (10) The image forming device may include a rotating image forming cylinder, one or more holding sheets described in any one of (1) to (9) formed on the surface of the image forming cylinder, and an image forming unit arranged around the image forming cylinder and forming an image on an image forming medium held on the holding sheet.

[0016] (11) The image forming apparatus may be as described in (10), in which one end of the holding sheet is fixed to the surface of the image forming drum, and the other end is biased by an elastic member and stretched over the surface.

[0017] (12) The image forming apparatus according to (10) may further include a heating section for heating the holding sheet. [Effects of the Invention]

[0018] According to the present invention, there is provided a holding sheet that is less likely to cause unevenness due to temperature differences, and an image forming apparatus equipped with the holding sheet. [Brief explanation of the drawings]

[0019] [Figure 1]1 is a side view showing the overall configuration of an image forming apparatus according to an embodiment of the present invention; [Figure 2] FIG. 2 is an enlarged cross-sectional view showing the outer peripheral cutout portion of the barrel. [Figure 3] FIG. 2 is an enlarged cross-sectional view showing a main part. [Figure 4] FIG. 2 is a cross-sectional view showing a part of an image forming cylinder. [Figure 5] FIG. 5 is a cross-sectional view taken along line VV in FIG. [Figure 6] FIG. 6 is a cross-sectional view taken along line VI-VI in FIG. 4. [Figure 7] FIG. 2 is a plan view of a perforated resin sheet. [Figure 8] FIG. 2 is an enlarged plan view showing a portion of the perforated resin sheet. [Figure 9] FIG. 2 is a side view showing a portion of the axial end of the image forming cylinder. [Figure 10] FIG. 2 is a partial plan view of the second sheet. DETAILED DESCRIPTION OF THE INVENTION

[0020] An embodiment of an image forming apparatus of the present invention will be described below with reference to the drawings. [Configuration of image forming device] Fig. 1 is a side view showing the overall configuration of an image forming apparatus according to this embodiment. Image forming apparatus 1 supplies paper or other image forming media from a supply section 2 located at the far right in Fig. 1 to an image forming unit 3. This image forming unit 3 is a device that forms an image on one or both sides of image forming media 4. After image formation in image forming unit 3, image forming media 4 is sent to a discharge section 5 and discharged in a stack onto a delivery pile.

[0021] The supply section 2 is structured to transfer the image forming medium 4 from the feeder pile 11 to the feeder board 13 by the sucker 12. The sucker 12 is connected to an intermittent supply valve 14, which allows the image forming medium 4 to be continuously fed to the image forming unit 3. When an image is formed only on the front side of the image forming medium 4, the sucker 12 continuously feeds the image forming medium 4 to the feeder board 13. On the other hand, when an image is formed on both the front and back sides of the image forming medium 4, the sucker 12 feeds the image forming medium 4 intermittently to the feeder board 13.

[0022] The image forming unit 3 includes a supply-side transfer cylinder 16 to which the image forming medium 4 supplied from the supply section 2 is transported by a sheet supply-side swing device 15. The image forming unit 3 includes an image forming cylinder 17 to which the image forming medium 4 is fed from the supply-side transfer cylinder 16. The image forming unit 3 includes a plurality of first discharge-side transfer cylinders 1, a second discharge-side transfer cylinder 19, a third discharge-side transfer cylinder 20, and a pre-reversal double cylinder 21 that feed the image forming medium 4 after image formation. The image forming cylinder 17 is provided with a heating section 101 that heats the image forming medium 4 to a predetermined temperature.

[0023] The image forming cylinder 17 rotates and transports the image forming medium 4 while adsorbing it, and is equipped with an adsorption device 22 (see FIG. 2), which will be described later. The image forming unit 3 also includes first to fourth ink jet heads 23 to 26, which are positioned downstream of the supply-side transfer cylinder 16 in the transport direction of the image forming medium 4. In other words, the first to fourth ink jet heads 23 to 26 form an image forming section. While the image forming method in this example is an ink jet method, the present invention is not limited to this. Other image forming methods that can be used in the present invention include dye sublimation thermal transfer, silver halide photography, direct thermal recording, and melting thermal transfer. An ink drying lamp 27 is provided downstream of the fourth ink jet head 26 in the transport direction of the image forming medium 4 (counterclockwise in FIG. 1).

[0024] The first to fourth ink jet heads 23 to 26 form images by ejecting ink droplets onto the image forming medium 4 using predetermined actuators. The ink drying lamp 27 hardens the ink ejected onto the image forming medium 4 by the first to fourth ink jet heads 23 to 26. One of the multiple conveying drums is a first discharge-side transfer drum 18 that receives the image-forming medium 4 from the image-forming drum 17. Another of the multiple conveying drums is a second discharge-side transfer drum 19 that receives the image-forming medium 4 from the first discharge-side transfer drum 18. The other two of the multiple conveying drums are a third discharge-side transfer drum 20 and a pre-reversal double cylinder 21 that receive the image-forming medium 4 from the second discharge-side transfer drum 19. The image-forming medium 4 that will have an image formed on its back side is conveyed from the second discharge-side transfer drum 19 to the pre-reversal double cylinder 21. The image-forming medium 4 that has an image formed on only its front side or that has an image formed on both its front and back sides is sent from the second discharge-side transfer drum 19 to the third discharge-side transfer drum 20. These image-forming media 4 are then sent to the delivery pile 6 via a delivery belt 28.

[0025] The supply-side transfer cylinder 16, the image forming cylinder 17, the first discharge-side transfer cylinder 18, the second discharge-side transfer cylinder 19, the third discharge-side transfer cylinder 20, and the pre-reversal double cylinder 21 are each equipped with gripper devices 31 to 36. These are devices for transferring the image forming medium 4. These gripper devices 31 to 36 have a conventionally well-known structure for gripping and holding the downstream end of the image forming medium 4 in the transport direction. A reversing operation unit (reversing swing device) 37 is disposed between the pre-reversing doubler cylinder 21 and the supply-side transfer cylinder 16. This reversing operation unit 37 is a device for sending the image forming medium 4 from the pre-reversing doubler cylinder 21 to the image forming cylinder 17. The reversing operation unit 37 grips the upstream end in the transport direction of the image forming medium 4 sent by the pre-reversing doubler cylinder 21. The reversing operation unit 37 then sends the image forming medium 4 to the image forming cylinder 17 with its front side facing the image forming cylinder 17. In other words, after an image is formed on the front side, the reversing operation unit 37 turns the image forming medium 4 over and returns it to the image forming cylinder 17.

[0026] The outer periphery of the image forming cylinder 17 is provided with outer periphery cutouts 41 that accommodate the gripper device 32, and sheet support portions 42 that adsorb and hold the image forming medium 4. The image forming cylinder 17 is provided with a plurality of outer periphery cutouts 41 at positions that divide the outer periphery into four equal parts, for example. The sheet support portions 42, which will be described in detail later, are provided between these outer periphery cutouts 41, 41. In other words, the image forming cylinder 17 is a quadruple cylinder that is provided with, for example, four pairs (not limited to four, as long as there is more than one) of outer periphery cutouts 41 and sheet support portions 42.

[0027] 2 is an enlarged cross-sectional view of the outer peripheral cutout portion of the cylinder. Gripper device 32 of image forming cylinder 17 has a claw shaft 43 provided in outer peripheral cutout portion 41. Gripper device 32 has a claw member 44 provided on claw shaft 43. Gripper device 32 has a claw base 45 that cooperates with claw member 44 to hold holding sheet 102 (FIG. 11), which will be described later. The claw shaft 43 extends parallel to the axis of the image forming cylinder 17 from one end to the other end in the axial direction of the image forming cylinder 17. The claw shaft 43 is rotatably supported by support plates 46a of support plates 46 (FIG. 9) attached to both ends of the image forming cylinder 17.

[0028] The support plate 46a is formed so that a portion of the outer periphery of the support plate 46 partially protrudes radially outward. In this example, the support plate 46a is provided at four locations in the circumferential direction corresponding to the outer peripheral cutouts 41. The support plate 46a is formed so as to cover the outer peripheral cutouts 41 from the outside in the axial direction of the image forming cylinder 17. The claw shaft 43 is driven by a conventionally known cam mechanism (not shown) and rotates at predetermined intervals. The claw members 44 are provided at multiple positions in the axial direction of the claw shaft 43. As the claw shaft 43 rotates, the claw members 44 move between a gripping position shown by a solid line in FIG. 2 and an open position shown by a two-dot chain line in FIG. 2.

[0029] The claw base 45 is placed on the tip of a claw base shaft 47 attached to the outer peripheral cutout portion 41 and fixed by a fixing bolt 48. The claw base shaft 47 is provided with a support member 51 that protrudes from the bottom of the outer peripheral cutout 41 toward the outside in the radial direction of the image forming cylinder 17. The claw base shaft 47 is provided with a retaining member 53 that is secured by a fixing bolt 52 while overlapping a protruding end 51a of the support member 51. The support member 51 and retaining member 53 extend parallel to the axis of the image forming cylinder 17 from one end to the other in the axial direction of the image forming cylinder 17. The support member 51 is secured to the bottom of the outer peripheral cutout 41 by a fixing bolt 54. A mating surface 55 between the protruding end 51a of the support member 51 and the retaining member 53 extends in the axial and radial directions of the image forming cylinder 17.

[0030] As shown in Fig. 2, suction chambers 56 that form part of the suction device 22 are formed in, for example, three sheet support portions 42 (Fig. 1) of the image forming cylinder 17. The suction device 22 includes the suction chambers 56. The suction device 22 includes a suction section 58 that is connected to the suction chambers 56 via an on-off valve 57. The suction chamber 56 is formed in a box-shaped member 59 provided on the outer periphery of the image forming cylinder 17. The box-shaped member 59 opens radially outward from the image forming cylinder 17. The opening of the box-shaped member 59 is covered by a first sheet 61 and a second sheet 62. These two sheets are collectively referred to as a holding sheet 102.

[0031] The first sheet 61 is made of stainless steel or the like and has a large number of ventilation holes 63 formed therethrough. The first sheet 61 is formed in a shape that covers the entire area of ​​the sheet support section 42. Both ends of the first sheet 61 are fixed to the image forming cylinder 17. The both ends here refer to the upstream end and downstream end in the transport direction of the image forming medium 4. As shown in FIG. 2, the downstream end of the first sheet 61 in the sheet conveyance direction is bent radially inward of the image forming cylinder 17 along the end 59a of the box-shaped member 59. The bent portion is held between the protruding end 51a of the support member 51 and the holding member 53. The other end of the first sheet 61 is fixed to a sheet holding shaft 64 provided in the outer peripheral cutout 41 (FIG. 1). Note that the sheet holding shaft 64 shown in FIG. 2 does not support the first sheet 61 covering the sheet support portion 42 located on the right side in FIG. 2. The sheet holding shaft 64 shown in FIG. 2 supports the end of the first sheet 61 covering the other sheet support portion 42 adjacent to it across the outer peripheral cutout 41.

[0032] As shown in FIGS. 7 and 8, the second sheet 62 has a main body 65 formed in a sheet shape from synthetic resin. The second sheet 62 has a number of ventilation holes 66 that allow air to pass through in the thickness direction of the main body 65. The main body 65 has excellent heat resistance, UV resistance, and solvent resistance. The main body 65 is formed from a material that is strong enough not to stretch due to heat and has appropriate tensile strength. The material forming the main body 65 is, for example, PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer). The thickness of the main body 65 is preferably 0.07 mm or more and 0.5 mm or less. The thickness is more preferably 0.1 mm to 0.3 mm.

[0033] A first nozzle 67 and a second nozzle 68 are provided at both ends of the main body 65. The ends here refer to the upstream end and downstream end in the transport direction of the image forming medium 4 (both left and right ends in FIG. 7). The first nozzle 67 is located at one of the downstream ends of the main body 65 in the transport direction of the image forming medium 4. The second nozzle 68 is located at the other downstream end of the main body 65 in the transport direction of the image forming medium 4. 3, the first nozzle 67 and the second nozzle 68 are formed to be thicker than the main body 65 of the second sheet 62. As shown in FIG. 7, the first nozzle 67 is provided with a handle 69 that protrudes to one side in the axial direction of the image forming cylinder 17.

[0034] The ventilation sections 66 are formed by through-holes that penetrate the main body 65 in the thickness direction. The opening shape of the ventilation sections 66 is circular, as shown in FIG. 8 . Adjacent ventilation sections 66 are not connected to each other. The ventilation sections 66 are arranged in the main body 65 at predetermined intervals in the axial direction of the image forming cylinder 17 and the conveyance direction of the image forming medium 4. As shown by the two-dot chain line in FIG. 7 , the ventilation sections 66 are provided over substantially the entire area of ​​the main body 65. The hole diameter of the ventilation sections 66 is preferably 0.2 mm or more and 1 mm or less. This is more preferably 0.3 mm to 0.9 mm. The formation pitch of the ventilation sections 66 is preferably 1.3 mm or less. This is more preferably 0.5 mm to 1.1 mm. Furthermore, the opening ratio is preferably 50% or more and 70% or less. This opening ratio is the ratio of the opening area of ​​all ventilation sections 66 to the total area of ​​the main body 65.

[0035] The second sheet 62 thus formed is attached to the image forming cylinder 17 by using first and second nozzles 67, 68 in a state where it is superimposed on the first sheet 61. The first nozzle 67 is held by a first holding portion 71 provided between the end portion 59a of the box-shaped member 59 and the holding member 53 (FIG. 3). The end portion 59a of the box-shaped member 59 forms a side wall extending in the radial direction of the image forming cylinder 17 downstream of the outer peripheral cutout portion 41 in the conveying direction of the image forming medium 4 (FIG. 2).

[0036] The first holding portion 71 has a space S that accommodates one end of the second sheet 62 extending radially inward from the outer peripheral surface of the image forming cylinder 17 (FIG. 3). The first holding portion 71 has a protruding wall 72 that faces the first mouthpiece 67 inserted into the space S from the radially outer side of the image forming cylinder 17 (from the upper side in FIG. 3). The protruding wall 72 is formed on the holding member 53 of the claw base shaft 47. The first mouthpiece 67 located within the first holding portion 71 faces the protruding wall 72. Therefore, the first mouthpiece 67 cannot move radially outward from the image forming cylinder 17. In other words, the protruding wall 72 restricts movement of the first mouthpiece 67 radially outward from the image forming cylinder 17.

[0037] Figure 9 is a side view showing a portion of the axial end of the image forming cylinder 17. As shown in Figure 9, the space S is in communication with an open portion 73 formed at the axial end of the image forming cylinder 17. The open portion 73 is formed upstream of the support plate 46a of the support plate 46 in the conveyance direction of the image forming medium 4 (to the right in Figure 9). The open portion 73 is open in the axial direction of the image forming cylinder 17. Therefore, the space S can be seen by viewing the image forming cylinder 17 from the axial direction.

[0038] 2, the other end of the second sheet 62 is held by a second holding portion 81 provided in the outer peripheral cutout 41. The second holding portion 81 has a guide member 82 that extends in the axial direction of the image forming cylinder 17 within the outer peripheral cutout 41. The second holding portion 81 has a slider 83 that is movably supported by the guide member 82. The second holding portion 81 has a cover plate 84 that cooperates with the slider 83 to hold the second nozzle 68. Guide member 82 extends from one end to the other end in the axial direction of image forming cylinder 17. Guide member 82 is formed in a groove-like cross section having a pair of ribs 82a, 82b. Guide member 82 is fixed to support plates 46 provided on both axial ends of image forming cylinder 17 by support brackets 85 and fixing bolts 86 (FIG. 4).

[0039] The slider 83 is formed in a plate shape extending in the axial direction of the image forming cylinder 17 along the guide member 82. The slider 83 is attached to the guide member 82 with two types of bolts: an adjustment bolt 87 extending in the transport direction of the image forming medium 4, and a fixing bolt 88 extending in the radial direction of the image forming cylinder 17. The adjustment bolt 87 rotatably passes through a rib 82a of the guide member 82 and is screwed into the slider 83. A stopper 89 (see FIG. 2) is provided opposite the head 87a of the adjustment bolt 87. The stopper 89 extends in the axial direction of the image forming cylinder 17 along the guide member 82 and is fixed to the support bracket 85 with a fixing bolt 90. Therefore, the adjustment bolt 87 can be loosened until the head 87a hits the stopper 89. After the head 87a hits the stopper 89, the adjustment bolt 87 cannot be loosened any further.

[0040] Figure 5 is a cross-sectional view taken along line VV in Figure 4. As shown in Figure 5, the fixing bolt 88 passes through the elongated hole 83a of the slider 83 and is attached to the guide member 82 by a screw action. The fixing bolts 88 are disposed at both ends and the center of the slider 83. In addition, a retaining pin 91 that extends across the fixing bolt 88 is provided at the tip of the fixing bolt 88.

[0041] Fig. 6 is a cross-sectional view taken along line VI-VI in Fig. 4. A recessed groove 92 for accommodating the first nozzle 67 is formed at the downstream end of the slider 83 in the conveying direction of the image recording medium 4 (Fig. 6). 4, the cover plate 84 is formed in the shape of a strip extending in the axial direction of the image forming cylinder 17. The cover plate 84 is provided with a plurality of pressing portions 84a for pressing the second mouthpiece 68. In this embodiment, the image forming cylinder 17 is provided with a plurality of cover plates 84 aligned in the axial direction.

[0042] The cover plate 84 is placed on the slider 83 and fixed to the slider 83 at both longitudinal ends by fixing bolts 93. As shown in Fig. 6, the fixing bolts 93 pass through elongated holes 84b in the cover plate 84 and are screwed into the slider 83. The tip of the fixing bolt 93 is inserted into the elongated hole 82c in the guide member 82. The tip of this fixing bolt 93 is also provided with a retaining pin 91 that extends across the fixing bolt 93.

[0043] Here, the procedure for attaching the second sheet 62 to the image forming cylinder 17 will be described. The following procedure is followed to attach the second sheet 62 to the image forming cylinder 17. First, one longitudinal end of the first mouthpiece 67 is inserted from the outside in the axial direction of the image forming cylinder 17 into an opening 73 formed at one axial end of the image forming cylinder 17. This attachment operation and the operation of removing the second sheet 62 from the image forming cylinder 17 can be easily performed by gripping the handle portion 69. Then, the first mouthpiece 67 is further advanced in the axial direction and inserted into the space S of the first holding portion 71.

[0044] When the second sheet 62 is pulled toward the other end with one end inserted into the space S, the first mouthpiece 67 hits the protruding wall 72. This prevents the first mouthpiece 67 from moving any further. Therefore, by inserting one end of the second sheet 62 into the space S, the one end of the second sheet 62 is held by the first holding portion 71 (image forming cylinder 17) in a state where it is prevented from coming out. Thereafter, the main body 65 of the second sheet 62 is placed on the sheet support portion 42 of the image forming cylinder 17. Then, the second mouthpiece 68 is sandwiched between the slider 83 and the cover plate 84 of the second holding portion 81. Then, the cover plate 84 is fixed to the slider 83 with the fixing bolts 93.

[0045] Next, the adjustment bolt 87 is tightened, and the second sheet 62 is pulled together with the slider 83. By pulling the second sheet 62 in this manner, the second sheet 62 comes into close contact with the first sheet 61 (the outer peripheral surface of the image forming cylinder 17). Thereafter, the slider 83 is fixed to the guide member 82 with the fixing bolt 88 while a predetermined tension is applied to the second sheet 62. By fixing the slider 83 to the guide member 82, the work of attaching the second sheet 62 to the image forming cylinder 17 is completed.

[0046] When the suction device 22 operates with the second sheet 62 attached to the image forming cylinder 17, air passes through the ventilation portion 66 of the second sheet 62 and the ventilation hole 63 of the first sheet 61 and is sucked into the suction chamber 56. This allows the image forming medium 4 to be sucked onto the second sheet 62. The image forming apparatus 1 performs the image forming operation with the suction device 22 operating in this manner. Therefore, the image forming medium 4 is transported while being sucked onto the image forming cylinder 17. Then, ink is ejected from the first to fourth ink jet heads 23 to 26 to form an image.

[0047] The ink adhering to the image-forming medium 4 is sent to a position where the image-forming medium 4 faces the ink drying lamp 27. Then, the ink on the image-forming medium 4 is dried (cured) by being irradiated with ultraviolet or infrared rays by the ink drying lamp 27. At this time, the surface of the image-forming medium 4 is heated, and the heat is transferred from the image-forming medium 4 to the second sheet 62.

[0048] As shown in FIG. 1, a heating section (heater or the like) 103 for heating the surface side (of the image forming medium 4) of the image forming cylinder 17 is provided inside the image forming cylinder 17 (or outside the image forming cylinder 17).

[0049] [Structure and effects of the holding sheet] The holding sheet 102 is attached to the surface of the image forming cylinder 17 of the image forming apparatus 1 and holds the image forming medium 4 on which the image is formed by the image forming apparatus 1. The holding sheet 102 includes a first sheet 61 made of metal. The first sheet 61 is made of a metal such as stainless steel and generally has a thickness of about 0.1 mm. The holding sheet 102 is formed on the first sheet 61 and also includes a second sheet 62 made of a non-metallic material. The second sheet 62 is made of a material such as fluororubber and generally has a thickness of about 0.5 mm.

[0050] Here, the holding sheet 102 is formed by attaching a first sheet 61 to the image forming cylinder 17, and then stretching a removable second sheet 62 over the first sheet 61. However, conventionally, the second sheet 62 and the first sheet 61 have different linear expansion coefficients. Conventionally, second sheet 62 is easily stretched because it is made of a material such as fluororubber. Therefore, to prevent wrinkles from forming in second sheet 62, tension is applied to the second sheet 62 in the circumferential direction of image forming cylinder 17 using an elastic member (not shown).

[0051] However, when the length and width of the holding sheet 102 exceeds approximately 500 mm x 700 mm, the thickness and density of the holding sheet 102 are no longer constant and tend to vary (in-plane variation). As a result, the holding sheet 102 tends to wrinkle. Therefore, the holding sheet 102 stretches in parts, and applying tension to the holding sheet 102 as described above does not resolve this. Therefore, the second sheet 62 is formed using a material with a lower linear expansion coefficient than the first sheet 61. Therefore, even if the temperature of the holding sheet 102 rises, the first sheet 61 can be prevented from stretching excessively. Therefore, even if the size of the holding sheet 102 increases, the occurrence of wrinkles in the holding sheet 102 can be prevented.

[0052] Furthermore, it is preferable that the base material of the second sheet 62 is a fiber. The fiber has the first through holes 121 formed therein without any special hole-punching process. Therefore, ventilation is possible through the first through holes 121. Therefore, since there is no need to carry out a special hole-punching process, the manufacturing cost of the holding sheet 102 can be reduced. The fibers are preferably glass fibers or aramid fibers. These materials are heat-resistant and can withstand temperatures as high as 200° C. Therefore, they are suitable for suppressing thermal expansion of the second sheet 62.

[0053] It is preferable that this fiber be impregnated with a fluororesin. If the second sheet 62 is made of fiber, the ink used in image formation will easily soak into it. If the fiber is impregnated with a fluororesin, the ink will be easy to wipe off (high releasability). Therefore, this is an appropriate material for the holding sheet 102 used in the image forming apparatus 1.

[0054] 10 is a partial plan view of the second sheet 62. As described above, the second sheet 62 is made of fiber. The second sheet 62, which is made of fiber, has a plurality of first through holes 121 formed due to the fiber, and adjacent first through holes 121, 121 are preferably separated from each other by adhesive. Therefore, the first through holes 121 originally formed in the second sheet 62 due to the fiber can prevent air from passing between adjacent holes. This makes it easier to maintain a substantially constant suction force per unit area of ​​the second sheet 62.

[0055] 10, the fibers preferably have second through holes 122 for ventilation formed by punching, separate from the first through holes 121. Therefore, even if the first through holes 121 alone are not enough ventilation holes, the breathability of the holding sheet 102 can be improved. The first sheet 61 and the second sheet 62 are preferably bonded together with a silicone adhesive. Silicon adhesive has high heat resistance and is also a viscous, flexible material. Therefore, by using a silicone adhesive, it is possible to compensate for the difference in expansibility between the stainless steel first sheet 61 and the fiber second sheet 62.

[0056] It is preferable that one end of holding sheet 102 is fixed to the surface of image forming cylinder 17 by a device such as gripper device 32, gripper member 44, gripper base 45, etc., and the other end is biased by an elastic member (not shown) and stretched over the surface of image forming cylinder 17. This is possible despite the configuration of image forming apparatus 1 described above. Therefore, coupled with the characteristics of holding sheet 102 described above, it is possible to sufficiently suppress the occurrence of wrinkles in holding sheet 102.

[0057] The image forming apparatus 1 includes a heating unit that heats the holding sheet 102. However, because the holding sheet 102 has the above-described configuration, the holding sheet 102 can be prevented from wrinkling even when heated. The above-described embodiment is merely one embodiment of the present invention, and the present invention can be implemented in various ways with configurations other than those described above, as long as they do not deviate from the spirit of the present invention. [Explanation of symbols]

[0058] 1. Image forming device 4 Imaging media 17 Image forming cylinder 23-26 1st to 4th ink jet heads (image forming units) 61 Sheet 1 62 2nd Sheet 101 Heating section 102 Retaining Sheet 121 First through hole 122 Second through hole

Claims

1. A holding sheet that is attached to the surface of an image forming drum of an image forming apparatus and holds an image forming medium that is an image forming target of the image forming apparatus, a first sheet made of metal; a second sheet adhered onto the first sheet and made of a non-metallic material;

2. The holding sheet according to claim 1 , wherein the second sheet has a linear expansion coefficient lower than that of the first sheet.

3. The holding sheet according to claim 2 , wherein the second sheet has a base material made of fiber.

4. The holding sheet according to claim 3 , wherein the base material of the second sheet is glass fiber or aramid fiber.

5. The holding sheet according to claim 3 , wherein the fibers of the second fibrous sheet are impregnated with a fluororesin.

6. The holding sheet according to claim 3 , wherein the fibers of the second sheet have a plurality of first through holes formed therein, and the adjacent first through holes are separated from each other by an adhesive.

7. The holding sheet according to claim 6 , wherein the first through-holes are breathable.

8. The holding sheet according to claim 6 , wherein the fibers of the second sheet have second through holes for ventilation formed by punching, separate from the first through holes.

9. The holding sheet according to claim 3 , wherein the first sheet and the second sheet are bonded together with a silicone adhesive.

10. a rotating imaging cylinder; one or more holding sheets according to any one of claims 1 to 9 formed on the surface of the image forming cylinder; an image forming unit disposed around the image forming cylinder and configured to form an image on the image forming medium held on the holding sheet;

11. 11. The image forming apparatus according to claim 10, wherein one end of the holding sheet is fixed to the surface of the image forming drum, and the other end is biased by an elastic member and stretched over the surface.

12. The image forming apparatus according to claim 10 , further comprising a heating section that heats the holding sheet.

Images