Image forming apparatus

Abstract

To provide an image forming apparatus that can prevent the generation of a pinhole.SOLUTION: An image forming apparatus comprises: an image carrier that carries toner images; a secondary transfer body that sandwiches a recording material with the image carrier; and an electric potential difference forming unit that forms the electric potential difference between the electric potential of the image carrier and the electric potential of the secondary transfer body. The image carrier and the secondary transfer body have a belt shape including resin having electronic conductivity, and the volume resistivity of the secondary transfer body is 1×109.7 Ω cm or more.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus. [Background technology]

[0002] In recent years, there has been a demand for image forming apparatuses to form images on thinner recording materials. Thin recording materials tend to stick to the transfer section. This makes them susceptible to transport problems. To address transport problems, image forming apparatuses employ intermediate transfer belt systems and secondary transfer belt systems (see, for example, Patent Document 1). The recording material is sandwiched between the intermediate transfer belt and the secondary transfer belt, so that the toner image formed on the intermediate transfer belt is transferred to the recording material. An image forming apparatus configured in this way ensures good separation properties even for thin recording materials.

[0003] The intermediate transfer belt system and the image forming apparatus equipped with the secondary transfer belt system described in Patent Document 1 are equipped with an intermediate transfer belt in which a resin layer, an elastic layer, and a coating layer are laminated. Patent Document 1 also describes polyimide as a material constituting the resin layer of the intermediate transfer belt. The image forming apparatus described in Patent Document 1 includes a low-hardness resin and an elastic body in the secondary transfer body. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-072689 A Summary of the Invention [Problem to be solved by the invention]

[0005] The image forming apparatus described in Patent Document 1 adjusts the transfer bias to the recording material to suppress the occurrence of minute print defects, so-called pinholes (white defects, white spots), in the image formed on the recording material. However, in the image forming apparatus, there are cases where the adjustment or control of the transfer bias alone is insufficient to suppress the occurrence of pinholes. For this reason, there is a demand for an image forming apparatus that can further suppress the occurrence of pinholes.

[0006] In order to solve the above-mentioned problems, the present invention provides an image forming apparatus capable of suppressing the occurrence of pinholes. [Means for solving the problem]

[0007] The image forming apparatus of the present invention includes an image carrier that carries a toner image, a secondary transfer body that sandwiches a recording material together with the image carrier, and a potential difference forming unit that forms a potential difference between the potential of the image carrier and the potential of the secondary transfer body. The image carrier and the secondary transfer body have a belt shape that contains a resin having electronic conductivity, and the volume resistivity of the secondary transfer body is 1×10 9.7 Ω·cm or more. Effect of the Invention

[0008] According to the present invention, it is possible to provide an image forming apparatus capable of suppressing the occurrence of pinholes. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram illustrating a schematic configuration of an image forming apparatus. [Diagram 2] FIG. 2 is a diagram illustrating a configuration of the periphery of a secondary transfer unit of the image forming apparatus. [Diagram 3] 4 is a schematic diagram of a secondary transfer nip formed at a transfer position. FIG. [Figure 4] FIG. 13 is a diagram showing the configuration of a straight roller. [Diagram 5] FIG. 13 is a diagram showing the configuration of a roller having a non-straight shape. [Figure 6]FIG. 13 is a diagram showing the configuration of a roller having a non-straight shape. [Figure 7] FIG. [Figure 8] FIG. [Figure 9] FIG. 4 is a diagram showing a configuration of a separation auxiliary part. [Figure 10] 11A and 11B are diagrams showing the shapes (modifications) of the electrodes of the separation auxiliary part. [Figure 11] FIG. 4 is an enlarged view of a transfer position in a secondary transfer process. [Figure 12] FIG. 4 is an enlarged view of a transfer position in a secondary transfer process. [Figure 13] FIG. 13 is an enlarged view of a transfer position in the secondary transfer process when a pinhole occurs. [Figure 14] FIG. 13 is an enlarged view of a transfer position in the secondary transfer process when a pinhole occurs. [Figure 15] 1 is a graph showing the relationship between volume resistivity and pinholes. [Figure 16] 1 is a graph showing the relationship between volume resistivity and pinhole OK current value range. [Figure 17] 11 is a graph showing the relationship between the current value flowing into the opposing roller and the secondary transfer voltage. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, examples of embodiments of the present invention will be described, but the present invention is not limited to the following examples. 1. Image forming apparatus The configuration of the image forming apparatus of this embodiment will be described below with reference to the drawings. In the following description, the same elements are given the same reference numerals, and duplicated descriptions will be omitted. The dimensional ratios in the drawings are exaggerated for the convenience of explanation, and may differ from the actual ratios. In the following description, the numerical ranges indicated with "~" include the upper and lower limit values ​​unless otherwise specified.

[0011] The configuration of an image forming apparatus according to the present embodiment is shown in Fig. 1. The image forming apparatus 1 shown in Fig. 1 includes a control unit 10, an operation display unit 20, an image forming unit 30, and a conveying unit 40. The control unit 10 is composed of a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), etc. (not shown). The CPU is an example of a calculation unit related to the image forming apparatus 1. The CPU centrally controls the operation of each unit of the image forming apparatus 1. The CPU reads out program code of software related to various processes of the image forming apparatus 1 stored in a ROM (an example of a recording medium) and expands it into the RAM. The CPU then controls the image forming apparatus 1 in accordance with the expanded program. Note that the control unit 10 may include another calculation device, such as an MPU (Micro Processing Unit), as a calculation unit instead of a CPU.

[0012] The operation display unit 20 has a display unit and an operation unit. The display unit is composed of a display such as a liquid crystal display device. The operation unit is composed of a touch panel and a plurality of keys superimposed on the display. The operation display unit 20 is an example of a display unit and an operation unit, and displays an instruction menu for the user, information related to the acquired image data, and the like.

[0013] [Image forming section] The image forming section 30 includes an image creating section 31 , an intermediate transfer belt 32 , a secondary transfer section 34 , and a fixing section 37 . The image forming units 31 each have a configuration corresponding to one of the basic colors, yellow (Y), magenta (M), cyan (C), and black (K). In Fig. 1, the image forming units 31 for each basic color are represented as image forming unit 31Y, image forming unit 31M, image forming unit 31C, and image forming unit 31K, respectively.

[0014] The imaging units 31Y, 31M, 31C, and 31K each include a photoconductor drum, a charging electrode, an exposure unit, a developing unit, a cleaning unit, and a primary transfer unit, etc. The imaging units 31Y, 31M, 31C, and 31K are identical in configuration except for the color of the toner of the developer stored in the developing unit.

[0015] The developing devices of the imaging units 31Y, 31M, 31C, and 31K contain a two-component developer. The two-component developer is composed of small particle size toner of yellow, magenta, cyan, and black, respectively, and a carrier. The carrier has a ferrite core coated with insulating resin. The toner is mainly made of polyester, with added colorants such as pigments or carbon black, charge control agents, silica, and external additives such as titanium oxide.

[0016] The carrier has a particle size of 15 to 100 μm and a saturation magnetization of 10 to 80 emu / g. The toner has a particle size of 3 to 15 μm. The toner has a negative charging characteristic. The toner has an average charge amount of -20 to -60 μC / g. In the two-component developer, the carrier and toner are mixed to a toner concentration of 4 to 10 mass %.

[0017] (Intermediate transfer belt) The intermediate transfer belt 32 is a toner carrier (image carrier). The intermediate transfer belt 32 is rotatably stretched by a plurality of rollers. The intermediate transfer belt 32 drives in a clockwise direction in the drawing. The plurality of rollers stretching the intermediate transfer belt 32 include an opposing roller r21 (FIG. 2). The opposing roller r21 forms a transfer nip between itself and the secondary transfer unit 34. The opposing roller r21 includes, for example, nitrile rubber (NBR: Nitrile Butadiene Rubber) as a material. The rubber hardness of the opposing roller r21 is 40° (Asker-C), and the volume resistivity is 1×10 8 It is Omega.

[0018] The intermediate transfer belt 32 includes a resin base and an electronically conductive material. Examples of the resin base include acrylic, polyester, polycarbonate, polyimide, urethane, nylon, vinyl chloride, polyamide, PPS (polyphenylene sulfide), and PEEK (polyether ether ketone). The volume resistivity of the intermediate transfer belt 32 is adjusted by the amount of electronically conductive material contained in the resin base. The volume resistivity of the intermediate transfer belt 32 is 108 ~10 11 Ω·cm is preferred.

[0019] Examples of the electronically conductive material include carbon black, SAF (Super Abrasion Furnace), ISAF (Intermediate SAF), HAF (High Abrasion Furnace), FEF (Fast Extruding Furnace), GPF (General Purpose Furnace), SRF (Semi-Reinforcing Furnace), FT (Fine Thermal), and MT (Medium Thermal). Examples of the electronically conductive material include conductive carbon-based materials such as color (ink) carbon that has been subjected to oxidation treatment, pyrolytic carbon, natural graphite, and artificial graphite. Examples of the electronically conductive material include conductive metal oxides such as titanium oxide, zinc oxide, antimony-doped tin oxide, and indium oxide-tin oxide composite oxide (ITO). Examples of the electronically conductive material include metals and oxides thereof such as nickel, copper, silver, germanium, aluminum, and copper alloys. Examples of the electronically conductive material include conductive polymers such as polyaniline, polypyrrole, and polyacetylene.

[0020] The thickness of the intermediate transfer belt 32 is preferably 50 to 90 μm. In particular, the thickness of the intermediate transfer belt 32 is preferably 50 μm to less than 70 μm. If the intermediate transfer belt 32 is too thick, the cost increases. If the intermediate transfer belt 32 is too thin, it is prone to breakage and assembly is difficult. If the intermediate transfer belt 32 is too thin, pinholes are likely to occur.

[0021] The intermediate transfer belt 32 may contain a metal oxide that has been surface-treated with a silane coupling agent. The intermediate transfer belt 32 may have a coating layer (surface layer) that contains SiO2. By including the metal oxide or the coating layer, the intermediate transfer belt 32 can form a high release surface and a highly durable surface. Furthermore, in consideration of the impact on the environment, it is preferable that the intermediate transfer belt 32 does not contain fluorine or fluorine compounds, in particular, organic fluorine materials and organic fluorine compounds.

[0022] The toner images formed in the image creating units 31Y, 31M, 31C, and 31K are sequentially transferred to the surface of the intermediate transfer belt 32 by the primary transfer unit, superimposed, and then transferred onto the recording material S transported to the transfer position p1 (Figure 2). The secondary transfer unit 34 comes into contact with the back side of the recording material S at a transfer position p1. The secondary transfer unit 34 transfers the toner to the front side of the recording material S. The recording material S onto which the full-color toner image has been transferred is transported to the fixing unit 37. The fixing unit 37 heats and pressurizes the recording material S and the toner image. As a result, the image forming unit 30 forms a full-color image on the recording material S.

[0023] Toner that is not transferred to the recording material S remains on the intermediate transfer belt 32. Hereinafter, the toner remaining on the intermediate transfer belt 32 will be referred to as "residual toner." The residual toner is collected by a cleaning device 33 installed on the intermediate transfer belt 32. The cleaning device 33 includes a brush roller, a lubricant supplying unit, a cleaning blade, and a housing that houses these components. The residual toner on the intermediate transfer belt 32 is cleaned by the cleaning blade. In addition, a lubricant (lubricant) is applied to the surface of the intermediate transfer belt 32 by the lubricant supplying unit.

[0024] The conveying unit 40 includes a plurality of supply trays 41 and recording material conveying paths 42 and 43. A plurality of sheets of recording material S are stacked on the supply tray 41. The conveying unit 40 conveys the recording material S one by one from the supply tray 41. The conveying unit 40 includes a plurality of conveying roller pairs arranged along the recording material conveying paths 42 and 43, and a drive motor (not shown) that drives the conveying roller pairs. The conveying unit 40 conveys the recording material S supplied from the supply tray 41 to a transfer position of the secondary transfer unit 34 or to the fixing unit 37.

[0025] When an image is formed on both sides of the recording material S, the conveying section 40 conveys the recording material S with an image formed on one side to a recording material conveying path for both sides (not shown). The recording material S conveyed to the recording material conveying path for both sides is turned over in a switchback path, and then rejoins the recording material conveying path 42 for one side. Then, the image forming apparatus 1 forms an image on the other side of the recording material S in the image forming section 30.

[0026] [Secondary transfer section] Next, a description will be given of the secondary transfer unit 34 of the image forming apparatus 1 and the configuration around the secondary transfer unit 34. Fig. 2 shows the configuration of the secondary transfer unit 34 and its periphery. The secondary transfer unit 34 has a secondary transfer body 341 and rollers r41, r42, r44, r45, r46, and r47. The secondary transfer body 341 is a transfer member formed in an endless belt shape. The secondary transfer body 341 is rotatably stretched by a plurality of rollers r41, r42, r44, r45, r46, and r47. The secondary transfer body 341 drives counterclockwise in the drawing (in the direction of the arrow).

[0027] (Secondary transfer material) The secondary transfer body 341 includes a resin base and an electronically conductive material. The resin base is, for example, acrylic, polyester, polycarbonate, polyimide, urethane, nylon, vinyl chloride, polyamide, PPS (polyphenylene sulfide), or PEEK (polyether ether ketone).

[0028] Examples of the electronically conductive material include carbon black, SAF, ISAF, HAF, FEF, GPF, SRF, FT, and MT. Examples of the electronically conductive material include conductive carbon-based materials such as color (ink) carbon that has been subjected to oxidation treatment, pyrolytic carbon, natural graphite, and artificial graphite. Examples of the electronically conductive material include conductive metal oxides such as titanium oxide, zinc oxide, antimony-doped tin oxide, and indium oxide-tin oxide composite oxide (ITO). Examples of the electronically conductive material include metals and oxides thereof such as nickel, copper, silver, germanium, aluminum, and copper alloys. Examples of the electronically conductive material include conductive polymers such as polyaniline, polypyrrole, and polyacetylene.

[0029] The secondary transfer body 341 preferably has a thickness of about 0.07 to 0.1 mm. The secondary transfer body 341 may be sufficiently hard. For example, the Young's modulus of the secondary transfer body 341 measured by a tensile test method (JIS K 6301) is preferably about 700 MPa or more and 10 GPa or less.

[0030] The secondary transfer body 341 may have a coating layer (surface layer) containing silicon dioxide (SiO2) on the surface. The coating layer of the secondary transfer body 341 reduces the mechanical adhesion force C described below. By having the SiO2 coating layer, the secondary transfer body 341 can have a pure water contact angle of 90° to 95°. When the secondary transfer body 341 is a polyimide substrate having electronic conductivity, the pure water contact angle is 75° to 80°. Therefore, the secondary transfer body 341 can increase the pure water contact angle and improve the releasability of the recording material S by using the SiO2 coating layer.

[0031] Increasing the surface roughness of the secondary transfer body 341 reduces the mechanical adhesion force C, which will be described later. Increasing the surface roughness of the secondary transfer body 341 and reducing the contact area with the recording material S reduces the mechanical adhesion force C (FIG. 8), which will be described later. For example, the surface roughness can be increased by spraying particles onto the secondary transfer body 341 by sandblasting or wet blasting, or by bringing a blade into contact with the surface of the rotating secondary transfer body 341 to supply abrasive particles.

[0032] (Secondary transfer roller) The roller r41 is a secondary transfer roller (secondary transfer member). The roller r41 presses the secondary transfer body 341 toward the opposing roller r21. The roller r41 presses the secondary transfer body 341 with, for example, 70 N. The opposing roller r21 is disposed on the inner circumferential surface side of the intermediate transfer belt 32. Roller r41 and opposing roller r21 sandwich the intermediate transfer belt 32 and secondary transfer body 341. A secondary transfer nip is formed between the intermediate transfer belt 32 and secondary transfer body 341 at transfer position p1 by pressing between roller r41 and opposing roller r21. When a toner image is transferred to the recording material S, a predetermined voltage is applied to roller r41 from an external potential difference forming unit (FIG. 11). Alternatively, when a toner image is transferred to the recording material S, a current is supplied to roller r41 from the potential difference forming unit. The potential difference forming unit is composed of a high-voltage power supply or the like.

[0033] The roller r41 includes a conductive core (not shown) and a resin layer formed around the conductive core. The conductive core is, for example, stainless steel (SUS). The resin layer includes rubber or resin material such as polyurethane, EPDM, silicone, or nitrile rubber (NBR: Nitrile Butadiene Rubber), and a filler dispersed in the rubber or resin material. The resin layer may have a semiconductive coating material (about 0.05 to 0.5 mm) on the surface. Furthermore, the coating material may be a semiconductive material obtained by incorporating an ionic conductive material into a rubber or resin material. The resin layer has a thickness of about 0.05 to 0.5 mm. The roller r41 is preferably made of SUS only and does not include the resin layer or the coating material. The roller r41 and the opposing roller r21 have approximately the same outer diameter. For example, the roller r41 and the opposing roller r21 both have an outer diameter of 30 mm.

[0034] Fig. 3 is a schematic diagram of the secondary transfer nip formed at the transfer position p1. Note that Fig. 3 omits the configuration of the intermediate transfer belt 32 and the secondary transfer body 341, and only shows the shapes of the opposing roller r21 and the roller r41. The roller r41 (secondary transfer roller) is preferably made of a material with high hardness such as SUS as described above. That is, the roller r41 is made of a material with a higher hardness than the opposing roller r21. If the roller r41 has a higher hardness than the opposing roller r21, the roller r41 protrudes toward the opposing roller r21 at the transfer position p1 as shown in FIG. 3. Therefore, as shown in FIG. 3, the secondary transfer nip has a convex shape toward the opposing roller r21. This makes it easier for the recording material S discharged from the secondary transfer nip to move in the direction of the arrow D. The direction of the arrow D is a direction away from the intermediate transfer belt 32 from the exit of the secondary transfer nip. Therefore, the recording material S is easier to separate from the intermediate transfer belt 32. And the recording material S is easier to follow the secondary transfer body 341. As a result, it is possible to prevent transport jams caused by the recording material S wrapping around the intermediate transfer belt 32. The roller r41 only needs to have a harder hardness than the opposing roller r21. Theoretically, the roller r41 preferably has an Asker C hardness of 40° or more. The roller r41 more preferably has an Asker C hardness of 70° or more. Furthermore, the roller r41 is preferably a rigid body rather than rubber or foam, and is preferably made of, for example, metal with a Vickers hardness of 50HV or more.

[0035] Moreover, the roller r41 (secondary transfer roller) has a straight shape. As shown in FIG. 4, the straight shape is such that the outer diameter of the area of ​​the roller r41 that comes into contact with the recording material S is the same at any of the one end, the center, and the other end. It is preferable that the outer diameter of the roller r41 is within 30 mm±0.15 mm over the entire area that comes into contact with the recording material S. More preferably, the outer diameter of the roller r41 is 30 mm±0.1 mm or less over the entire area that comes into contact with the recording material S. The roller r41 (secondary transfer roller) may have a non-straight shape. An example of the configuration of a roller having a non-straight shape is shown in Fig. 5 and Fig. 6. As shown in Fig. 5 and Fig. 6, the roller r41 (secondary transfer roller) may have intentionally different outer diameters at the ends and the center. For example, the difference in outer diameter between the center and ends of the roller r41 may be 0.2 to 3 mm.

[0036] (Drive rollers / steering rollers) The roller r45 functions as a driving roller. The roller r45 is driven by a driving unit 60. The driving unit 60 is composed of a stepping motor, gears, etc. The roller r46 functions as a steering roller. The roller r46 is connected to a steering mechanism (not shown). The steering mechanism has a drive source, an actuator, and a detection sensor. The steering mechanism shifts (tilts) at least one end position of the roller r46. The steering mechanism shifts (tilts) the end position according to the end position of the secondary transfer body 341 detected by a detection sensor (not shown). The steering mechanism tilts the rotation axis of the roller r46 with respect to the rotation axes of the rollers r41, r45, etc. As a result, the steering mechanism and the roller r46 control the travel of the secondary transfer body 341 and prevent meandering.

[0037] [Cleaning device] Foreign matter such as fragments of the recording material S and toner remains on the secondary transfer body 341. The foreign matter is collected by a cleaning device 35 (cleaning unit) installed on the secondary transfer body 341. The cleaning device 35 cleans the surface of the secondary transfer body 341. The secondary transfer unit 34 and the cleaning device 35 are replaceable as one unit with the secondary transfer unit.

[0038] The cleaning device 35 includes a first blade 351, a second blade 352, a third blade 353 for pressing, a lubricant applicator 354, a conveying screw 355, and a storage case 356. For example, the first blade 351 (hereinafter also simply referred to as blade 351, and the same is true for blades 352 and 353) is mainly made of a rigid member. The second blade 352 is mainly made of an elastic member. The blades 351, 352, and 353 are thin plate-like members, and the length in the short direction is about 10 and a few mm. Furthermore, the length in the long direction of the blades 351, 352, and 353 is slightly longer than the overall width of the recording material, for example, 300 mm to 400 mm. As shown in Figure 2, each blade 351, 352, 353 is arranged so as to abut against the surface of the secondary transfer body 341 in the following order from the upstream side of the rotation direction of the secondary transfer body 341, based on the transfer position p1: blade 352, blade 351, lubricant application portion 354, and blade 353.

[0039] (Second Blade) The second blade 352 is made of an elastic material such as a rubber material. As the rubber material, urethane rubber is preferably used. The blade 352 may be fluororubber, styrene butadiene rubber, or nitrile rubber. The blade 352 has a thickness of, for example, 2 mm, and is held by a holder so as to abut against the secondary transfer body 341 at a contact angle of 15° and a contact pressure of 30 N / m. The blade 352 is, for example, of a fixed type, and the holder is fixed to a storage case 356. The free length of the blade 352 from the holder is 9 mm. The roller r47 is disposed at a position facing the contact position of the blade 352. The roller r47 functions as an opposing roller inside the secondary transfer body 341. The roller r47 is made of, for example, a metal such as SUS, and has an outer diameter of 12 mm.

[0040] (First Blade) The first blade 351 is made of a material that is harder than the second blade 352 as a whole. The blade 351 includes a substrate 501 and a coating layer 502, as shown in the enlarged view surrounded by a circle in FIG. 2. The coating layer 502 covers the substrate 501. The coating layer 502 covers at least the substrate 501 in the region that contacts the secondary transfer body 341. For example, the coating layer 502 covers the substrate 501 in the region of several mm (for example, within 2 mm from the tip) on the tip side that contacts the toner carrier. The substrate 501 is preferably a rigid body made of metal, and more preferably a rigid body made of SUS (especially SUS304). The blade 351 has a thickness of, for example, 0.1 mm, and is held by a holder fixed to the storage case 356 so as to contact the secondary transfer body 341 at a contact angle of 10° and a contact pressure of 5 N / m. The blade 351 is designed to have a bite amount of 0.3 mm (for example, fixed type). The blade 351 has a free length from the holder of 10 mm.

[0041] Coat layer 502 is made of a material harder than substrate 501. Coat layer 502 is, for example, a boron-carbon-nitrogen (BCN)-based hard film. Coat layer 502 is preferably a diamond-like carbon film (DLC: Diamond Like Carbon). The thickness of coat layer 502 can be set within a range of, for example, 0.01 to 10 μm. By providing such hard coat layer 502 on the tip edge of substrate 501 of blade 351, wear of the tip can be suppressed and durable and stable cleaning performance can be ensured.

[0042] In addition, at the position where the blade 351 contacts, there is no roller that faces the secondary transfer body 341. Therefore, even if the contact pressure of the blade 351 suddenly increases excessively, the secondary transfer body 341 can retreat inward (be pressed down). This makes it possible to suppress damage or breakage of the secondary transfer body 341 caused by the blade 351, which has high hardness. In addition, the secondary transfer body 341 at the position where the roller is inscribed rises outward. If the blade 351 is disposed at a position facing the roller through the secondary transfer body 341, a gap is likely to be generated between the secondary transfer body 341 and the blade 351. This is because the blade 351 cannot absorb the rise of the secondary transfer body 341 due to its high hardness and low flexibility. Therefore, if a roller faces the secondary transfer body 341 through the secondary transfer body 341 at the position where the blade 351 contacts, foreign matter attached to the secondary transfer body 341 is likely to slip through the gap between the secondary transfer body 341 and the blade 351. This reduces the cleaning ability of the blade 351.

[0043] [Third Blade] The third blade 353 is a fixing blade that smoothes the lubricant supplied onto the secondary transfer body 341 from a lubricant application unit 354 described later and presses it against the surface. As shown in FIG. 2, the first blade 351 and the second blade 352 abut against the secondary transfer body 341 in a counter manner. The counter manner is an abutment manner in which the tip of the blade faces the upstream side of the moving direction of the secondary transfer body 341. On the other hand, the third blade 353 is held by a holder so as to abut against the secondary transfer body 341 in a trail manner. The trail manner is a manner in which the tip faces the downstream side of the moving direction of the secondary transfer body 341. The third blade 353 abuts against the secondary transfer body 341 with a thickness of 1.6 mm and an abutment angle of 51°, for example. The designed biting amount is 0.3 mm. The free length from the holder is 6 mm.

[0044] [Lubricant application section] The lubricant application unit 354 includes a brush roller 54a, a solid lubricant 54b, and a support 54c. One end of the support 54c is fixed to the housing. The solid lubricant 54b is formed by solidifying molten lubricant powder into a substantially rectangular parallelepiped shape. The solid lubricant 54b is, for example, 4.5 mm in height and 8 mm in depth and width. The lubricant used for the solid lubricant 54b is selected from materials that can be applied to the surface of the secondary transfer body 341 and can reduce the surface energy to reduce the adhesive force between the toner and other adhering substances and the secondary transfer body 341. For example, the lubricant may be a fatty acid metal salt, a fluorine-based resin, or the like, and may be used alone or in combination of two or more. In particular, the lubricant is preferably a fatty acid metal salt. The fatty acid constituting the fatty acid metal salt is preferably a straight-chain hydrocarbon. For example, the hydrocarbon is preferably myristic acid, palmitic acid, stearic acid, oleic acid, or the like, and stearic acid is particularly preferred. The metal constituting the fatty acid metal salt may be lithium, magnesium, calcium, strontium, zinc, cadmium, aluminum, cerium, titanium, or iron. Among these, zinc stearate, magnesium stearate, aluminum stearate, and iron stearate are preferred. In particular, zinc stearate is the most preferred.

[0045] The support portion 54c is composed of a holder and an elastic body. The holder holds the solid lubricant 54b. The elastic body is composed of a coil spring or the like. The elastic body presses (brings into contact) the solid lubricant 54b against the brush roller 54a via the holder with a predetermined pressing force. The amount of penetration of the brush roller 54a into the secondary transfer body 341 is, for example, 0.5 mm. The pressing force of the brush roller 54a at this time is 1N. The brush roller 54a is made by implanting or winding brush fibers around a core metal having an outer diameter of 6 mm. The brush roller 54a has an overall outer diameter of 12 mm, for example. The brush fibers have a pile diameter of 4d and a pile density of 150 KF / inch. 2 The brush fibers are made of polyester material. The resistance of the brush fibers is 10 12The resistance is on the order of Ω. The brush roller 54a is rotationally driven by a drive unit (not shown) in a counter direction to the moving direction of the secondary transfer body 341. The brush roller 54a scrapes off the lubricant (lubricant powder) from the solid lubricant 54b by the rotational drive, and applies it to the surface of the secondary transfer body 341. The toner, external additives, etc. scraped off from the secondary transfer body 341 by the blades 351 and 352 fall downward along the inner surface of a storage case 356 that covers the blades 351 and 352. A conveying screw 355 is disposed at the bottom of the storage case 356. The fallen toner, etc. are conveyed to the rear side of the main body of the apparatus by the conveying screw 355 and collected in a collection box disposed on the rear side.

[0046] [Separation section] As shown in FIG. 2, the image forming apparatus 1 has a separation portion at the position of roller r45 of the secondary transfer body 341. The separation portion is a position where the recording material S is separated from the secondary transfer body 341. FIG. 7 shows an enlarged view of the vicinity of the separation portion. As shown in FIG. 7, the second surface (rear surface) S2 of the recording material S contacts the secondary transfer body 341. The second surface S2 of the recording material S is charged by a current at the transfer position p1. At the separation portion, the first surface (front surface) S1 of the recording material S is released from contact with the intermediate transfer belt 32.

[0047] The recording material S and the surface of the secondary transfer body 341 retain charge due to the transfer current at the transfer position p1. As a result, residual charge remains on the recording material S and the secondary transfer body 341 even during transport. In FIG. 7, the residual charge on the back surface of the recording material S is indicated by "+" and the residual charge on the secondary transfer body 341 is indicated by "-". The back surface of the recording material S and the surface of the secondary transfer body 341 are transported to the separation section in a state of being electrostatically attracted to each other by the residual charge. Note that FIG. 7 shows the recording material S and the secondary transfer body 341 as being separated for illustrative purposes. In reality, the recording material S and the secondary transfer body 341 are in contact with each other due to electrostatic attraction.

[0048] The recording material S conveyed to the separation section is separated from the secondary transfer body 341 due to the curvature formed by the roller r45. The leading edge of the recording material S separated from the secondary transfer body 341 enters the fixing section 37. If the recording material S cannot be separated from the secondary transfer body 341, the recording material S is wound up in the direction of the arrow E shown in FIG. 7. This results in the recording material S being wound up (poor separation) or clogging.

[0049] FIG. 8 is a schematic diagram showing the force relationship in the separation section. In the separation portion, a mechanical force A is generated on the recording material S. The mechanical force A is a force that resists bending of the recording material S due to its rigidity against the secondary transfer body 341 that bends according to the curvature of the roller r45. On the other hand, between the recording material S and the secondary transfer body 341, the above-mentioned electrostatic attraction force B and a mechanical adhesion force C caused by contact are generated. At this time, if the force relationship is [A>B+C], the recording material S is separated from the secondary transfer body 341 .

[0050] In contrast, the following conditions are likely to cause separation failure of the recording material S. When the force A is small and the forces B and C are large, separation failure is likely to occur. When the recording material S is thin, the rigidity of the recording material S is low. Therefore, the mechanical force A due to the rigidity of the recording material S tends to be small. If the recording material S is smooth, it is easy for the recording material S to come into close contact with the secondary transfer body 341. For this reason, the mechanical adhesive force C is liable to become large. When the secondary transfer current is large, that is, when the potential difference formed between the opposing roller r21 and the roller r41 is large, the residual charge increases and the electrostatic adsorptive force B tends to increase. When the process speed is high, that is, when the moving speed of the secondary transfer body 341 and the recording material S is high, the influence of the mechanical force A of the recording material S becomes relatively small. If the surface resistance of the secondary transfer body 341 is high, the residual charge generated at the transfer position p1 is difficult to dissipate. This causes the electrostatic attraction force B to become large at the separation portion. The secondary transfer body 341, which has a base material of high hardness resin material and has electronic conductivity, controls its resistance by the amount of electronic conductive agent added. The secondary transfer body 341 is also required to have a high volume resistivity in order to suppress pinholes. For this reason, if the amount of high electronic conductive agent added to the secondary transfer body 341 is reduced in order to increase the volume resistivity, the surface resistance also increases. As a result, the residual charge is difficult to dissipate, the electrostatic adsorption force B increases, and separation failure of the thin recording material S is likely to occur.

[0051] (Separation auxiliary part) The image forming apparatus 1 includes a separation auxiliary section 36 in the vicinity of the separation section. A detailed configuration of the separation auxiliary section 36 is shown in Fig. 9 and Fig. 10. As shown in Fig. 9 and Fig. 10, the separation auxiliary section 36 is disposed on the outlet side of the transfer position p1, adjacent to the most downstream side of the area where the secondary transfer body 341 is responsible for transporting the recording material S. That is, the separation auxiliary section 36 is disposed on the rear end side in the driving direction of the secondary transfer body 341 with reference to the transfer position p1. In addition, the separation auxiliary section 36 is disposed at a position where it does not come into contact with the secondary transfer body 341 or the recording material S.

[0052] The separation auxiliary section 36 forms a potential difference between the contact surface between the recording material S and the secondary transfer body 341. The separation auxiliary section 36 cancels out the remaining charge on the second surface S2 of the recording material S with a charge of the opposite polarity, thereby reducing the electrostatic adsorption force B shown in FIG. 8 and assisting separation. The separation auxiliary section 36 includes a casing 362 and an electrode 361. The electrode 361 applies a voltage of the opposite polarity to the charge polarity of the second surface S2 of the recording material S from a power source (not shown).

[0053] The electrode 361 emits electric charge in the direction of the second surface S2 of the recording material S, which is the opening direction of the casing 362. The electrode 361 emits electric charge of the applied polarity by corona discharge. The casing 362 is grounded. The casing 362 protects the electrode 361 from discharging in any direction other than the second surface S2 of the recording material S.

[0054] As shown in Fig. 9, the electrode 361 may be a wire electrode suspended in the depth direction, i.e., in the direction of the rotation axis of the secondary transfer body 341. Alternatively, the electrode 361 may be a needle-shaped electrode, as shown in Fig. 10. In the case of a needle-shaped electrode, the electrode 361 is likely to discharge from the tip 361a of the needle. For this reason, by directing the tip 361a of the needle toward the second surface S2 of the recording material S, the charge can be efficiently discharged onto the recording material S.

[0055] By providing the separation auxiliary section 36 in the separation section, the electrostatic attraction force B between the recording material S and the secondary transfer body 341 is reduced. The electrode 361 of the separation auxiliary section 36 has a conductive member such as metal at least in a portion close to the recording material S. The distance between the electrode 361 and the recording material S is about 1 to 5 mm. The separation auxiliary section 36 generates a discharge in the recording material S due to a potential difference between the electrode 361 and the recording material S. The electrostatic attraction force B can be reduced by removing the residual charge of the recording material S. In addition, the separation auxiliary section 36 may be provided with a static elimination power source (not shown) that applies a voltage of a polarity opposite to the charging polarity of the recording material S, making it easier for discharge to occur from the electrode 361.

[0056] [Pinhole generation mechanism] Next, we will explain minute printing defects, so-called pinholes (white defects, white spots), that occur in an image formed on the recording material S. Note that the following explanation is an example of the mechanism by which pinholes occur that is presumed by the inventors, and the principle by which pinholes occur is not limited to this.

[0057] First, a normal transfer process will be described. Fig. 11 and Fig. 12 show enlarged views of transfer position p1. Fig. 11 and Fig. 12 are schematic diagrams of the secondary transfer process. At transfer position p1, the intermediate transfer belt 32, the recording material S, and the secondary transfer body 341 are sandwiched between an opposing roller r21 and a roller (secondary transfer roller) r41. The intermediate transfer belt 32 carries toner T on its surface. Also, a predetermined voltage is applied to the roller r41 from an external potential difference forming section 70 (high voltage power supply). As a result, as shown in FIG. 11, a potential difference (secondary transfer bias) is formed at the transfer position p1 by the DC power supply supplied from the potential difference forming section. Then, while the recording material S is being nipped, a secondary transfer electric field is generated, and the negatively charged toner T is transferred to the surface of the recording material S by Coulomb force. As a result, as shown in FIG. 12, the toner T moves from the intermediate transfer belt 32 to the recording material S, and an image is formed on the surface of the recording material S.

[0058] Next, the secondary transfer process when a pinhole occurs will be described. Enlarged views of the transfer position p1 are shown in Fig. 13 and Fig. 14. Fig. 13 and Fig. 14 have the same configuration as Fig. 11 and Fig. 12 described above. During the transfer of toner T, a potential difference is formed between the potential of the opposing roller r21 and the potential of the roller r41. If there is a localized low resistance portion in the gap with respect to this potential difference, a conductive path is formed there. In this case, a discharge (discharge current) as shown by the arrow F is generated in the conductive path. 14, the toner in the discharged portion is not transferred to the surface of the recording material S, but remains on the surface of the intermediate transfer belt 32. This causes white pinholes to appear in the image on the surface of the recording material S.

[0059] If the potential difference (secondary transfer bias) is too large for a localized low resistance portion in the gap, discharge is likely to occur. This discharge is likely to occur under the following conditions: -The secondary transfer bias is large. There is a gap (discharge gap) between the surface (front surface) of the intermediate transfer belt 32 that carries the toner image and the surface (first surface; front surface) of the recording material S onto which the toner image is transferred. The intermediate transfer belt 32 is vibrating near the secondary transfer portion. When the intermediate transfer belt 32 is vibrating, a gap is likely to occur between the intermediate transfer belt 32 and the recording material S. The thickness of the recording material S is small and the surface roughness is large. In this case, a gap is likely to occur between the intermediate transfer belt 32 and the recording material S. The process speed is high, that is, the moving speed of the secondary transfer body 341 and the recording material S is high. In this case, the gap between the intermediate transfer belt 32 and the secondary transfer body 341 narrows at high speed, which makes it easy for discharge to occur. The opposing roller r21, the intermediate transfer belt 32, and the secondary transfer body 341 have low resistance portions. This is likely to occur due to non-uniform dispersion of the conductive agent (electronically conductive material) of the intermediate transfer belt 32. The resistances of the opposing roller r21, the intermediate transfer belt 32, and the secondary transfer body 341 vary.

[0060] [Process Speed] The control unit 10 controls the conveying speed of the recording material S in the conveying unit 40. The conveying speed of the recording material S is controlled by controlling the driving speed (rotation speed) of the intermediate transfer belt 32 and the secondary transfer body 341. When the thickness of the recording material S is small and the process speed is high, pinholes are more likely to occur. Also, paper jams due to poor separation are more likely to occur. The higher the end of the image forming apparatus, the greater the challenge of balancing pinholes with separation of thin recording materials S. On-demand printers that are required to handle thin recording materials S are often A4 landscape 80 ppm or more. That is, as calculated from the following formula, the image forming apparatus 1 is required to have a process speed of 310 mm / sec or more (distance between recording materials is about 20 mm). For this reason, the control unit 10 is required to control the transport of the recording material S at a process speed of 310 mm / sec or more. (A4 width 210[mm] + paper gap [20mm]) x 80[sheets / min] =230[mm / sheet] x 80[sheets / min] =18400[mm / min]=306.7[mm / sec]≒310[mm / sec] EXAMPLES

[0061] An image forming apparatus, AccurioPress C14000, manufactured by Konica Minolta, was prepared. The secondary transfer member of the AccurioPress C14000 was changed to the secondary transfer members of Examples 1-6 and Comparative Example 1 described below.

[0062] (Examples 1-3, Example 6, Comparative Example 2) The pellets made by mixing the base resin with an electronic conductive material and desired additives were melted and extruded from a cylindrical mold, or melted and applied to a cylindrical mold to form the pellets. The pellets were then annealed in a controlled environment to adjust the shape and produce a secondary transfer body. At this time, secondary transfer members having different volume resistivities were produced by changing the amount of electronic conductivity added in Example 1, Example 2, Example 3, Example 6, and Comparative Example 2. The volume resistivities of the secondary transfer members are shown in Table 1 below.

[0063] Example 4 In the second embodiment, the driving of the separation auxiliary unit of the image forming apparatus was turned off.

[0064] Example 5 The surface of the secondary transfer member of Example 2 was roughened by wet blasting to prepare a secondary transfer member of Example 4.

[0065] Comparative Example 1 A secondary transfer member of Comparative Example 1 was prepared by changing the substrate of the secondary transfer member of Example 1 to polyvinylidene fluoride (PVDF).

[0066] [Evaluation method] The secondary transfer members of Examples 1-6 and Comparative Examples 1-2 prepared by the above-mentioned methods were subjected to the following measurements and evaluations. (Resistance measurement) The volume resistivity and surface resistivity of the secondary transfer body were measured in an environment of 23°C and 50% humidity. A Mitsubishi Chemical Analytech Hiresta UX MCP-HT450 URS probe was used for the measurements. The volume resistivity was measured under conditions of an applied voltage of 500V and 10 seconds later. The surface resistivity was measured under conditions of an applied voltage of 1kV and 10 seconds later.

[0067] (Pinhole evaluation) A Konica Minolta AccurioPress C14000 was modified so that a given secondary transfer voltage could be applied and the inflow current at the transfer position could be measured. The measurements were performed under the following conditions: Toner: Konica Minolta AccurioPress C14000 toner -Recording material: Konica Minolta J Paper A3 68g / m2 Image: Two 10mm x 10mm squares were placed evenly horizontally in the center of the recording material in the paper feed direction (vertical direction). Each square was filled with monochrome black at 50% density (black 50%) and with 100% magenta and 100% cyan (blue 100%). Preparation: While changing the secondary transfer voltage by 250V each time, a full white image was printed and the inflow current flowing to the transfer position was measured. The secondary transfer voltage that should be applied to obtain the desired inflow current (secondary transfer current) was determined.

[0068] Evaluation method: The target inflow current value was changed in 20μA increments from 10μA to 250μA, and images were printed on both sides at each current value (at each secondary transfer voltage in the work area). The second side was visually observed with 50% black and 100% blue, and ranked according to the following criteria. Rank 5: No pinholes Rank 4: A small number of pinholes are observed in 50% of the black. Rank 3: 100% blue with a few pinholes Rank 2: Pinholes are clearly visible in 50% of the black. Rank 1: Pinholes are clearly visible in 100% blue. Pinhole evaluation: A rank of 3 or above was considered a pass. Pinhole OK current range evaluation: If it is less than 50μA, it is rated as "C", if it is between 50μA and 70μA, it is rated as "B", and if it is 70μA or more, it is rated as "A". The pinhole OK current range is the current range in which pinholes do not occur. The current range in which pinholes do not occur is the range from the reference current value, which is the inflow current value in which pinholes do not occur, to the upper limit current value in which pinholes do not occur when the inflow current is increased (in increments of 10μA) from this reference current value.

[0069] (Surface roughness measurement method) The surface roughness of the secondary transfer body was measured under the following conditions in an environment of 20°C and 50% humidity. Equipment: Tokyo Seimitsu Co., Ltd. surfcom ·JIS94 standard roughness measurement Measurement length: 5mm ·Speed ​​0.15mm / sec Measurement range: ±64μm λc 2.5m Measurement method: Calculate the average value of the measurements taken at four points (two points in the width direction of the image on the secondary transfer body and two points in the rotation direction).

[0070] (Contact angle measurement method) The water contact angle of the surface of the secondary transfer member was measured under the following conditions. Equipment: Contact angle meter manufactured by Kyowa Interface Science Co., Ltd. ·Liquid type: Pure water 2θ method Measurement method: The average value of the measurements at 20 points in the width direction of the secondary transfer body image was calculated, and the approximate range of the measurements at 3 points in the rotation direction and on two belts was calculated.

[0071] (Evaluation of recording material separation) In an environment of 10° C. and 15%, the peelability of the recording material was evaluated under the following conditions using an AccurioPress C14000 manufactured by Konica Minolta. Recording material: Nippon Paper Industries Co., Ltd. Auro Roller L A3 64g / m 2 Y Eyes Image type: Double-sided full white Evaluation method: The target inflow current value was changed from 120μA to 240μA in 20μA increments, and five sheets were printed on both sides at each current value (work area: each secondary transfer voltage). If a paper jam occurred even once, it was considered NG.

[0072] [result] Table 1 shows the main configurations and evaluation results of the above-mentioned examples and comparative examples.

[0073] [Table 1]

[0074] As shown in Table 1, in Example 1, a fluorine-free electronic conductive material (polyimide) is used as the secondary transfer body. The volume resistivity of the secondary transfer body is 1×10 9.7 Ω cm. Volume resistivity is 1×10 9.7 By setting the resistivity at Ω·cm, the occurrence of low resistance areas against the secondary transfer bias was suppressed, which in turn suppressed the formation of conductive paths and the occurrence of discharge currents, thereby suppressing the occurrence of pinholes. In Example 2, the occurrence of pinholes was suppressed by increasing the volume resistivity of the secondary transfer body compared to Example 1. The recording material separation property was OK at 200 μA or less, which is at a practical level. In Example 3, the volume resistivity of the secondary transfer body was made higher than in Example 2, suppressing the occurrence of pinholes. The recording material separation property is acceptable at 120 μA or less. In Example 3, the volume resistivity is higher than in Example 2, and the surface resistance is also higher. This is thought to have strengthened the electrostatic adhesion of the recording material to the secondary transfer body at the separation portion. In Example 4, like Example 2, the occurrence of pinholes was suppressed. However, the recording material separation performance deteriorated. In Example 4, the driving of the separation auxiliary unit was stopped, so the remaining charge on the back surface of the leading edge of the recording material was not removed in the separation unit. For this reason, it is believed that the recording material was attracted to the secondary transfer body by static electricity. In Example 5, the occurrence of pinholes was suppressed, similarly to Example 2. Furthermore, in Example 5, the roughness of the secondary transfer body was Rz=2 μm, and the pure water contact angle was 75 to 80°. That is, in Example 5, it is believed that the mechanical adhesive force with the recording material was reduced due to the roughness of the belt surface. In Example 6, the occurrence of pinholes was suppressed, similarly to Example 2. In Example 6, the roughness of the secondary transfer body was Rz=1.2 μm, and the pure water contact angle was 90-95°. In Example 6, the release property was high due to the coating layer, and the mechanical adhesion of the recording material S to the secondary transfer body at the separation portion was thought to be reduced due to the high surface roughness. Comparative Example 1 is good in terms of both pinhole and recording material separation, but the secondary transfer body is ion-conductive (PVDF). In Comparative Example 2, the secondary transfer body is made of fluorine-free electronic conductivity (polyimide) like Example 1. However, because the volume resistivity is low, the formation of conductive paths and the generation of discharge current are not suppressed, and the occurrence of pinholes is aggravated.

[0075] [Relationship between volume resistivity and pinholes] Next, the relationship between the volume resistivity of the secondary transfer body and the occurrence of pinholes will be described based on the measurement results of the above-mentioned Examples 1-6 and Comparative Examples 1-2. FIG. 15 is a graph of pinhole rank versus secondary transfer voltage. FIG. 15 shows the case where an electronically conductive (polyimide) secondary transfer body (Example 1) and an ionically conductive (PVDF) secondary transfer body (Comparative Example 1) are used. FIG. 15 also shows the variation in pinhole rank due to temperature and humidity environment for each secondary transfer body. When the secondary transfer voltage is increased, the potential difference (secondary transfer bias) increases with respect to the local low resistance portion in the gap at transfer position p1, causing discharge and lowering the pinhole rank. Also, in a low temperature and low humidity environment, resistance increases, and therefore the secondary transfer voltage required to obtain the required inflow current increases.

[0076] In Figure 15, the dotted line indicates the stability of the pinhole rank against environmental changes. In a low temperature and low humidity environment, at the secondary transfer voltage indicated by the dotted line, both electronic conductivity (polyimide) and ionic conductivity (PVDF) are ranked 5. On the other hand, when the same voltage is applied in a general environment (23°C, 50%), ionic conductivity (PVDF) is ranked 1. In contrast, electronic conductivity (polyimide) is ranked 2. As such, in terms of pinhole rank stability against changes in temperature and humidity environments, electronic conductivity (polyimide) has a smaller change in resistance. As a result, by using a high-hardness resin for the secondary transfer body and combining it with a high-load cleaning system, it is possible to achieve both high quality (reduced wiping residue) and high durability. This makes it possible to configure an image forming device with a secondary transfer body that does not use fluorine and does not have a high-release surface.

[0077] FIG. 16 is a graph showing the relationship between the volume resistivity of the secondary transfer body and the pinhole OK current value range in the examples and comparative examples. The graph in FIG. 16 shows the relationship between volume resistivity and pinholes when using an electronically conductive (polyimide) secondary transfer body (Examples 1-6, Comparative Example 2) and an ionically conductive (PVDF) secondary transfer body (Comparative Example 1). The horizontal axis is the volume resistivity of each belt. The volume resistivity is expressed as a multiplier (1×10 X The vertical axis indicates the current width (μA) at which no pinholes occur.

[0078] As shown in FIG. 16, when the volume resistivity of the electronic conductor (polyimide) is increased, the pinhole OK current value range is expanded. This means that pinholes can be suppressed by increasing the volume resistivity of the secondary transfer body. In addition, at the same volume resistivity (approximately 10 9.7 ), electronic conductivity (polyimide) has a narrower pinhole OK current value range than ionic conductivity (PVDF). This result shows that the occurrence of pinholes does not depend only on volume resistivity. Since it is difficult to uniformly disperse electronic conductive agents in resin, the uniformity of resistance is inferior to PVDF. For this reason, it is presumed that conductive paths are formed in low resistance areas, causing discharge and making it easier for pinholes to occur. Volume resistivity of electronic conductor (polyimide) 107.17 The pinhole OK current width for the secondary transfer body is as narrow as 10μA. In an actual device where various errors are added, it is practically impossible to control the current value to such a narrow range and prevent pinholes from occurring. Volume resistivity of electronic conductor (polyimide) 10 9.7 The belt has a pinhole-OK current width of 50 μA, and it is expected that the current value can be controlled in an actual device. Therefore, the volume resistivity of the secondary transfer body is 10 9.7 Ω·cm or more is preferable. Furthermore, since a pinhole OK current value width of 70 μA equivalent to ion conductivity (PVDF) can be secured, the volume resistivity of the secondary transfer body is 1×10 12.8 Ω·cm or more is more preferable.

[0079] [Current-voltage characteristics] Next, based on the evaluation results of the secondary transfer body (polyimide) of Example 1 and the secondary transfer body (PVDF) of Comparative Example 1, the flow-in current value to the opposing roller r21 with respect to the secondary transfer voltage will be described. FIG. 17 shows the relationship between the flow-in current value to the opposing roller of the secondary transfer body of Example 1 and Comparative Example 1 and the secondary transfer voltage. FIG. 17 shows the fluctuation of the flow-in current due to the temperature and humidity environment for each secondary transfer body. As shown in FIG. 17, the higher the resistance of the secondary transfer body, the smaller the flow-in current. In general, it is said that the resistance of the ion conductive type is more likely to fluctuate due to the temperature and humidity environment than that of the electronic conductive type. From FIG. 17, when comparing the change in the current value (i.e., resistance) due to the change in the temperature and humidity environment, it can be seen that the secondary transfer body (polyimide) of Example 1 has a smaller change in the current value and a smaller change in resistance than the secondary transfer body (PVDF) of Comparative Example 1.

[0080] [Transfer efficiency] Next, the relationship between transfer efficiency and pinholes will be described. The relationship between transfer efficiency and pinholes was evaluated using the secondary transfer member of Example 3 described above and the secondary transfer member of Example 7 described below. Example 7 In Example 7, the secondary transfer member of Example 3 was attached to an image forming apparatus AccurioPress C6100 manufactured by Konica Minolta. Then, image formation was performed under conditions of a process speed slower than that of Example 3, that is, 460 mm / sec.

[0081] (Transfer efficiency) The transfer efficiency was measured under the following conditions: Equipment: Konica Minolta FD7 Fluorescence Spectrodensitometer Image: Pinhole evaluation image -Evaluation method: Transfer efficiency was estimated from density measurements of 100% blue areas. If the image density and color tone targeted by the image forming device are achieved, then the transfer efficiency is 100%. Transfer efficiency under each condition was then estimated according to the density drop from 100% transfer efficiency and color difference. Transfer efficiency of 90% or more was evaluated as ○, and less than 90% as ×. Note that in reality, on the side where the inflow current value is high, image density drop and color difference occur along with the occurrence of white spots, but the evaluation of white spots has been omitted as it is determined by the image rank.

[0082] [Evaluation Results] Table 2 shows the evaluation results of pinholes and transfer efficiency in the above-mentioned Examples 3 and 7.

[0083] [Table 2]

[0084] As shown in Table 2, the evaluation was performed starting from images with low inflow current (secondary transfer current), and when the inflow current value was equal to or higher than the inflow current value judged as "○", the transfer efficiency was judged to be "○". In Example 3, pinholes were rated "○" when the inflow current was 90 to 230 μA, and the transfer efficiency was rated "○" when the inflow current was 130 μA or more. A proper image was obtained at 130 to 230 μA. In Example 7, pinholes were rated "○" when the inflow current was 30 to 150 μA, and the transfer efficiency was rated "○" when the inflow current was 70 μA or more. A suitable image was obtained at 70 to 150 μA. Even when the process speed changed, appropriate images were obtained in the range of 70 to 230 μA enclosed by a dotted line in Table 2. Also, even when the process speed changed, appropriate images were obtained in the range of 130 to 150 μA enclosed by a solid line in Table 2. For this reason, the inflow current value is preferably 70 to 230 μA, and particularly preferably 130 to 150 μA.

[0085] The present invention is not limited to the configurations described in the above-mentioned embodiments, and various modifications and variations are possible without departing from the scope of the present invention. [Explanation of symbols]

[0086] 1 image forming apparatus, 10 control section, 20 operation display section, 30 image forming section, 31, 31C, 31K, 31M, 31Y imaging section, 32 intermediate transfer belt, 33, 35 cleaning device, 34 secondary transfer section, 36 separation auxiliary section, 37 fixing section, 40 conveying section, 41 supply tray, 42 recording material conveying path, 54a brush roller, 54b solid lubricant, 54c support section, 60 drive section, 70 potential difference forming section, 341 secondary transfer body, 351 first blade, 352 second blade, 353 third blade, 354 lubricant application section, 355 conveying screw, 356 storage case, 361 electrode, 361a tip, 362 casing, 501 substrate, 502 coating layer, p1 transfer position, r21 Opposing rollers, r41, r44, r45, r46, r47 rollers

Claims

1. an image carrier that carries a toner image; a secondary transfer member that sandwiches a recording material together with the image carrier; a potential difference forming unit that forms a potential difference between the potential of the image carrier and the potential of the secondary transfer body, the image carrier and the secondary transfer body have a belt shape containing a resin having electronic conductivity, The volume resistivity of the secondary transfer body is 1×10 ９．７ Ω cm or more Image forming device.

2. the image carrier, the toner image, the recording material, and the secondary transfer body are sandwiched between an opposing member that contacts the image carrier and a secondary transfer member that contacts the secondary transfer body; The potential difference generating unit generates a potential difference between the opposing member and the secondary transfer member by a direct current. The image forming apparatus according to claim 1 .

3. The potential difference generating unit supplies a current of 70 μA or more and 230 μA or less to at least one of the opposing member and the secondary transfer member. The image forming apparatus according to claim 2 .

4. a separation assistant portion provided at a position where the recording material is separated from the secondary transfer body; The separation auxiliary portion has an electrode that generates a potential difference between the secondary transfer body and the recording material. The image forming apparatus according to claim 1 .

5. The secondary transfer body has a surface that comes into contact with the recording material and has a maximum height Rz of 1.2 μm or more. The image forming apparatus according to claim 1 .

6. The secondary transfer member has a straight shape. The image forming apparatus according to claim 2 .

7. The surface of the secondary transfer member is a rigid body. The image forming apparatus according to claim 6.

8. The surface of the secondary transfer member is metal. The image forming apparatus according to claim 7.

9. a cleaning unit that removes foreign matter adhering to a surface of the secondary transfer body, The cleaning unit has a blade that comes into contact with the surface of the secondary transfer body. The image forming apparatus according to claim 1 .

10. a lubricant application unit for supplying a lubricant to the surface of the secondary transfer body; The image forming apparatus according to claim 1 .

11. The surface of the secondary transfer body includes polyimide. The image forming apparatus according to claim 1 .

12. The secondary transfer body includes a substrate containing polyimide and a surface layer formed on the substrate. The image forming apparatus according to claim 1 .

13. The surface layer of the secondary transfer body is SiO ２ Includes The image forming apparatus according to claim 12.

14. The contact angle of the surface of the secondary transfer body with pure water is 90° or more. The image forming apparatus according to claim 1 .

15. The image carrier has a thickness of 50 μm or more and less than 70 μm. The image forming apparatus according to claim 1 .

16. a control unit for controlling the driving of the secondary transfer body, The control unit drives the surface of the secondary transfer body at a moving speed of 310 mm / sec or more. The image forming apparatus according to claim 1 .

Images