JP5200760B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an electrophotographic tandem type color image forming apparatus such as a copying machine, a facsimile machine, a printer, or a combination of these, and more particularly, a primary transfer bias on an intermediate transfer unit side in a removable intermediate transfer unit. The present invention relates to the improvement of the connection terminal.

  In recent years, electrophotographic color image forming apparatuses such as copiers, facsimiles, and printers are provided with a plurality of image forming units corresponding to the three primary colors and black (yellow, magenta, cyan, black) toner, Tandem type intermediate transfer that transfers a single color toner image formed by an image forming unit to an intermediate transfer belt consisting of an endless belt, and then superimposes a plurality of single color toner images on the intermediate transfer belt, and then transfers them to a recording medium such as copy paper. A color image forming apparatus of the type has become mainstream.

  Conventionally, in such a tandem type intermediate transfer type image forming apparatus, a configuration in which the attachment / detachment direction of the intermediate transfer unit is the same as the attachment / detachment direction of the photosensitive drum has been common. The reason is that the workability is improved when the photosensitive drum and the intermediate transfer unit are replaced in the same direction when they are replaced. However, in recent years, it has become possible to extend the life of the intermediate transfer unit (intermediate transfer belt), and the necessity of frequently replacing the intermediate transfer unit by the user has become scarce. For this reason, when a problem or the like occurs in the intermediate transfer unit, it is only necessary to repair or replace it by a service staff.

  If the intermediate transfer unit is replaced by the service staff, there is little need to make the attachment / detachment direction of the intermediate transfer unit and the attachment / detachment direction of the image forming unit the same as described above. An image forming apparatus has been developed which is configured to be detachable from the front door and the intermediate transfer unit is configured to be detachable from the side surface of the apparatus. This is because the intermediate transfer unit can be attached and detached from the side surface (side plate) of the apparatus, so that the strength of the front plate (front door support plate) of the apparatus main body (housing) can be prevented. In other words, when the intermediate transfer unit and the image forming unit are configured to be attached and detached from the same front door side, naturally, not only the hole for allowing the intermediate transfer unit to pass through the front plate of the apparatus main body but also the proximity of the intermediate transfer unit. Holes to pass through the image forming unit (necessary holes for replacing new toner bottles are also required), and a large hole must be provided in the front plate of the main body of the apparatus. This is because the strength is reduced, but by adopting a system in which the intermediate transfer unit is attached and detached from the hole provided in the side plate, the hole in the front plate can be reduced to prevent the strength from being lowered.

  On the other hand, in the tandem type image forming apparatus, the intermediate transfer unit is formed on a plurality of image forming units in which an additional module such as a charging unit, a developing unit, and a cleaning unit and a photosensitive drum are set and an outer peripheral surface of the intermediate transfer belt. Due to the configuration that must be in contact, the image forming apparatus inevitably occupies a large space. Therefore, it is effective to reduce the size of the intermediate transfer unit in order to reduce the size of the entire apparatus. As one contrivance, the pressing member such as a pressure roller is pressed from the surface side of the intermediate transfer belt to bend, thereby forming an image forming unit. There has already been proposed an image forming apparatus that realizes space saving while securing the arrangement space.

  In addition, the intermediate transfer unit has a bias power supply on the apparatus main body side in view of attachment / detachment from the apparatus main body and application of a primary transfer bias for electrostatically adsorbing the toner image from the photosensitive drum as described above. It is necessary to provide a bias terminal, which is a conductive contact for conducting between the toner and the primary transfer roller (primary transfer member) of the intermediate transfer unit, on both the apparatus main body side and the intermediate transfer unit side. This bias terminal is provided with a coupling connector composed of a receptacle part and a drawer part as described in Patent Document 1, for example, in the conventional system in which the intermediate transfer unit is attached and detached from the front door side. In general, the system can be attached and detached at the same time by simply attaching and detaching the unit by making the direction coincide with the attachment direction of the intermediate transfer unit. Such a system has an advantage that the arrangement space can be reduced because both the apparatus main body side and the unit side can be concentrated in one place using a plurality of bias terminals as connectors.

  However, in the system in which the intermediate transfer unit is attached / detached from the side of the apparatus, an intermediate transfer belt is stretched in the attaching / detaching direction of the intermediate transfer unit, and the connector fitting direction and the attaching direction of the intermediate transfer unit are matched. It was difficult to provide. In other words, since such a connector (receptacle portion of Patent Document 1) cannot be provided on the belt surface of the intermediate transfer belt, if the intermediate transfer unit is provided on the frame (front plate or rear plate), the intermediate transfer unit Therefore, there is a problem that the front-and-rear direction of the apparatus main body, that is, the depth increases, and the downsizing is hindered. This problem is that the color image device of the tandem type intermediate transfer system has four image forming units of YMCK (yellow, magenta, cyan, black), so that not only four conductive contacts are required, but also In addition, a large number of bias conduction contacts such as a secondary transfer bias applied when transferring from the intermediate transfer belt to the recording medium and a cleaning bias applied to the cleaning roller of the intermediate transfer belt are necessary. It became a big problem especially because of the increase in the number of connectors and the connector.

JP 2004-109466 A

  Therefore, in order to solve the problems of the prior art, the present invention can secure the strength of the apparatus main body by changing the attaching / detaching direction of the intermediate transfer unit and the image forming unit in different directions, and can realize space saving. An object is to provide an image forming apparatus.

  In order to solve the above-mentioned problems, the invention according to claim 1 is characterized in that a frame serving as a base, a plurality of stretching rollers pivoted on the frame, and an endless belt-shaped stretched on the stretching roller. In a tandem type color image forming apparatus having an intermediate transfer belt and a plurality of primary transfer members for applying a primary transfer bias to the intermediate transfer belt, and including an intermediate transfer unit that is detachable from the apparatus main body, The intermediate transfer unit is configured to be detachable in a direction perpendicular to the axial direction of the stretching roller, and the intermediate transfer belt is pressed in the vertical direction by a pressing member from the outside and curved inwardly, and its upper surface is curved. A plurality of unit-side bias terminals that supply a primary transfer bias to each of the plurality of primary transfer members are accommodated in a space formed by the intermediate transfer belt being recessed inward. Sea urchin, characterized in that it is arranged side by side in a row along the detachment direction of the intermediate transfer unit to the frame.

  According to a second aspect of the present invention, in the first aspect, the unit side bias terminal has an outwardly convex curved surface that is inclined along the mounting or detaching direction of the intermediate transfer unit.

  According to a third aspect of the present invention, in the second aspect, the unit side bias terminal has a vertical cross section formed in an arcuate shape, one end of which is a fixed end fastened to the upper surface or the lower surface of the frame, and the other end Is a free end.

  According to a fourth aspect of the present invention, in the third aspect, an engagement claw is formed at the free end of the unit side bias terminal, and an upper surface or a lower surface of the frame is spaced apart from the engagement claw by a predetermined distance. The folding prevention member having the engaging portion arranged in a standing manner is erected, and the free end of the unit side bias terminal is configured not to spread beyond a predetermined interval by engaging the engaging claw and the engaging portion. It is characterized by that.

  According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the unit-side bias terminal is formed of an elastic member biased toward the apparatus main body.

  According to a sixth aspect of the present invention, in the fifth aspect, the unit side bias terminal is made of a stainless material.

  According to the first aspect of the present invention, in the tandem type color image forming apparatus including the intermediate transfer unit that is detachable from the apparatus main body, the intermediate transfer unit is attached to the stretching roller. It is possible to secure the strength of the main body of the apparatus by reducing the opening for attachment and detachment provided in the main body of the apparatus, and the intermediate transfer belt is curved inward. Since the bias terminal is accommodated in the space, the space can be saved. In addition, since the plurality of unit side bias terminals are arranged in a line in the frame along the attaching / detaching direction of the intermediate transfer unit, the plurality of unit side bias terminals can be easily attached by simply attaching / detaching the intermediate transfer unit. At the same time, it can be connected to and separated from the bias terminal on the apparatus body side.

  According to the second aspect of the present invention, the unit-side bias terminal has an outwardly convex curved surface that is inclined along the mounting or detaching direction of the intermediate transfer unit. The friction force acting between the main body and the unit can be reduced, and the durability of the unit side bias terminal can be improved.

  According to the invention of claim 3, the unit side bias terminal has a vertical cross section formed in an arcuate shape, one end of which is a fixed end fastened to the upper surface or the lower surface of the frame, and the other end is a free end. In other words, since one end is a free end, the unit side bias terminal itself has the function of an elastic spring. In addition to the above effect, when attaching or detaching, the unit side bias is further increased. The frictional force acting between the terminal and the apparatus main body can be reduced, and when attached, the bias voltage can be reliably conducted to the intermediate transfer unit via the unit side bias terminal.

  According to the fourth aspect of the present invention, the engaging claw is formed at the free end of the unit side bias terminal, and the upper surface or the lower surface of the frame is disposed at a predetermined distance from the engaging claw. Since the folding prevention member having the engagement portion is erected and the engagement claw and the engagement portion are engaged, the free end of the unit side bias terminal is configured not to spread beyond a predetermined interval. When the intermediate transfer unit is slid in the direction in which the frictional force acts on the unit side bias terminal from the free end side to the fixed end side, either during mounting or removal, the engaging claw and the engaging portion are engaged. By combining the unit, the free end of the unit-side bias terminal is configured not to spread beyond a predetermined interval, so even if a compressive force is applied to the unit-side bias terminal due to frictional force, the free end that becomes the weak axis is outside Bending direction Can bias terminal to prevent deformation of preventing buckling, in addition to the effect, it is possible to further improve the durability of the unit-side bias terminal.

  According to the fifth aspect of the present invention, since the unit side bias terminal is made of an elastic member biased toward the apparatus main body, in addition to the above effect, when performing the attachment / detachment operation, the attachment / detachment operation is repeated to repeat the attachment / detachment operation. It is possible to reduce the accumulation of permanent distortion at the bias terminal, and when attached, the bias is biased toward the main body of the apparatus, so that the bias voltage is reliably supplied to the intermediate transfer unit via the unit side bias terminal. It can be made conductive.

  According to the sixth aspect of the invention, since the unit side bias terminal is made of stainless steel, in addition to the above effects, the wear resistance and corrosion resistance of the unit side bias terminal are improved, and the intermediate transfer unit is repeatedly attached and detached. This reduces wear on the unit-side bias terminal and prevents oxidation of the friction powder and rusting due to moisture in the atmosphere to prevent the formation of an oxide film on the terminal surface, ensuring reliable bias voltage conduction. Can take.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[Image forming apparatus]
FIG. 1 is a configuration explanatory diagram showing a schematic configuration of an image forming apparatus according to an embodiment of the present invention as viewed from the front. Reference numeral 1 in the drawing denotes a four-tandem type intermediate transfer type color printer that forms a color image from toners of four colors of yellow, magenta, cyan, and black exemplified as an embodiment of the image forming apparatus of the present invention. The color printer 1 includes an apparatus main body 10 that is a casing, a new toner storage unit 2 that is disposed above the apparatus main body 10 and that individually stores the four colors of new toner, and an abbreviation of the apparatus main body 10. An image forming unit 3 that is disposed in the center and forms respective single color toner images from the four color toners, and is disposed below the image forming unit 3, and electrostatic latent image carriers in the image forming unit 3 are electrostatically An optical unit 4 serving as an exposure unit for writing a latent image, a transfer unit 5 disposed above the image forming unit 3 and transferring a toner image formed by the image forming unit 3 to a recording medium, and an upper portion of the transfer unit 5 A fixing unit 6 that is disposed near one end of the apparatus and fixes the toner image transferred by the transfer unit 5 to the recording medium, and a recording medium such as a copy sheet that is disposed at the lowermost part of the apparatus main body 10. A sheet feeding unit 7 that feeds paper and a sheet discharge unit 8 that stacks recording media that are formed on the upper surface of the apparatus main body 10 and on which an image is fixed by the fixing unit 6 are configured.

  The new toner storage unit 2 is a space for storing new toner, which is a new toner that is not used for development, and a new toner that individually stores each toner of yellow, magenta, cyan, and black in a bottle-shaped container. The bottles 2Y, 2M, 2C, and 2K are provided, and these new toner bottles 2Y, 2M, 2C, and 2K are configured to be detachable from the front (front door) side of the apparatus main body 10.

  The image forming unit 3 includes four image forming units 3Y and 3M, which will be described later, centering on four photosensitive drums Y, M, C, and K as latent image carriers corresponding to yellow, magenta, cyan, and black toners. , 3C, 3K, and each single color of the image forming units 3Y, 3M, 3C, 3K from the new toners of yellow, magenta, cyan, and black supplied from the new toner bottles 2Y, 2M, 2C, 2K. A toner image is formed.

  The optical unit 4 has a laser light source (not shown) such as a semiconductor laser (LD) or a light emitting diode (LED), and irradiates the photosensitive drums Y, M, C, and K with the laser light from the laser light source. The surfaces of the photosensitive drums Y, M, C, and K that are uniformly charged to a predetermined polarity by the charging means are exposed, and the polarity of the exposed portions is reduced to form an electrostatic latent image.

  The transfer unit 5 is mainly composed of an intermediate transfer unit 5a that is detachable from the apparatus main body 10, and will be described in detail later. The intermediate transfer unit 5a includes a unit (not shown) that serves as a base of the intermediate transfer unit 5a. A frame 50; five tension rollers 51 to 55 pivoted on the unit frame 50; an endless belt-like intermediate transfer belt 56 stretched between the tension rollers 51 to 55; Four primary transfer rollers 57 (Y, M, and Y) that are primary transfer members that apply a primary transfer bias to the belt 56 and transfer a toner image from the photosensitive drums Y, M, C, and K to the intermediate transfer belt 56. C, K) and the like.

  In addition to the intermediate transfer unit 5a, the transfer unit 5 includes a secondary transfer unit 5b for transferring a toner image from the intermediate transfer belt 56 to a recording medium, and a transfer remaining on the intermediate transfer belt 56 after the secondary transfer. A belt cleaning unit 5c for cleaning the remaining toner is also provided. The secondary transfer unit 5b is a bias power supply PS and a contact-type bias applying member that is electrically connected to the bias power supply PS and applies a transfer bias having a polarity opposite to that of the toner image in contact with the recording medium. It consists of a next transfer roller 58 and the like.

  The secondary transfer roller 58 is pressed against the intermediate transfer belt 56 by an urging means (not shown) on the outer periphery of the stretching roller (drive roller) 51 of the intermediate transfer unit 5 a, and between the secondary transfer roller 58 and the stretching roller 51. A secondary transfer nip is formed. In addition, the tension roller 51 may be a bias applying member. In this case, a transfer bias having the same polarity as that of the toner image to be transferred is applied. The details of the belt cleaning unit 5c will be described later.

In the present embodiment, the secondary transfer roller 58 is coated on a metal core such as stainless steel with an elastic body such as urethane adjusted to a resistance value of 10 ⁶ to 10 ¹⁰ Ω with a conductive material. . If the resistance value of the secondary transfer roller 58 exceeds the above range, it becomes difficult for the current to flow. Therefore, a higher voltage must be applied in order to obtain a required transfer property, which causes an increase in power supply cost. In addition, when a high voltage is applied, void discharge occurs in the voids before and after the secondary transfer nip, and white spots are lost due to the discharge on the halftone image. On the other hand, if the resistance value of the secondary transfer roller 58 is below the above range, the transferability between the superimposed toner image (for example, three color superimposed color toner image) portion and the single color toner image portion existing on the same image cannot be achieved. . This is because the resistance value of the secondary transfer roller 58 is low, so that a sufficient transfer current flows to transfer a single color toner image at a relatively low voltage. This is because a voltage value higher than the voltage is required, and if the optimum voltage is set for the superimposed toner image, the transfer current becomes excessive in the monochromatic toner image portion, resulting in a decrease in transfer efficiency.

  The resistance value of the secondary transfer roller 58 is determined by installing the secondary transfer roller 58 on a conductive metal plate and applying a load of 4.9 N on one side (total of 9.8 N on both sides) to both ends of the core metal. In this state, it was calculated from the value of the current flowing when a voltage of 1000 V was applied between the metal core and the metal plate. In this embodiment, the secondary transfer is controlled by constant current control, and the set value is +30 μA.

  The fixing unit 6 includes a fixing roller 60 having a heater as a heat generating means, a pressure roller 61, and the like, and the pressure roller 61 is urged and pressed against the fixing roller 60 by an urging means (not shown). A fixing nip is formed. In this fixing nip, recording is performed by the transfer unit 5 by applying heat from the fixing roller 60 and pressure from the pressure roller 61 (and urging means) to a recording medium conveyed from a paper feeding unit 7 described later. The unfixed toner image transferred to the medium is fixed to the recording medium.

  The paper feed unit 7 is in pressure contact with a paper feed cassette 70 that accommodates and stocks a recording medium of a predetermined size such as copy paper, resin sheet (OHP sheet, etc.), and the stocked recording medium at a predetermined pressure. A pickup roller 71 that feeds the recording medium one by one to the conveyance path based on a control signal of a control unit (not shown), and a conveyance roller pair 72 that conveys the storage medium sent from the pickup roller 71 to the next registration roller pair. And a registration roller pair 73 for adjusting and conveying the conveyance timing of the recording medium sent from the conveyance roller pair 72 to the secondary transfer nip.

  The paper discharge unit 8 is a paper discharge tray 80 formed on the upper surface of the apparatus main body 10, and a discharge medium that discharges from the apparatus main body 10 a recording medium on which the toner image has been fixed after passing through the fixing unit 6. A paper roller pair 81 and the like are provided, and recording media discharged from the paper discharge roller pair 81 are stacked on the paper discharge tray 80.

(Image forming unit)
Next, the image forming unit of the printer 1 will be described with reference to FIG.
FIG. 2 is a configuration explanatory diagram showing an enlargement of the vicinity of the yellow image forming unit in the configuration explanatory diagram viewed from the front of FIG. 1. As described above, the color printer 1 includes the four image forming units 3Y, 3M, 3C, and 3K in the order of yellow, magenta, cyan, and black from the upstream side in the movement direction along the lower surface of the intermediate transfer belt 56. (See FIG. 1). Since these image forming units 3Y, 3M, 3C, and 3K have substantially the same configuration, the image forming unit 3Y for yellow disposed in the most upstream will be described as an example, and image formation of other colors is performed. A description of the units 3M, 3C, 3K is omitted.

  With reference to the primary transfer nip, the image forming unit 3Y remains on the photosensitive drum Y after the primary transfer from the upstream side in the rotation direction centering on the photosensitive drum Y as a latent image carrier. Cleaning means Y1 for cleaning the transfer residual toner, charging means Y2 for uniformly charging the outer peripheral surface of the photosensitive drum Y to a predetermined polarity, and the electrostatic latent image carried on the photosensitive drum Y with yellow toner The developing means Y3 and the like for visualizing the image are housed integrally in a process cartridge (not shown) and are detachable from the front side of the apparatus main body 10 (see also FIGS. 1 and 5).

  The cleaning means Y1 is a cleaning blade Y10 that scrapes and cleans the toner on the photosensitive drum Y, a storage case Y11 that stores the transfer residual toner scraped off by the cleaning blade Y10, and a transfer collected in the storage case Y11. The primary toner is composed of a toner conveying screw Y12 that conveys residual toner to a waste toner tank (not shown) and the like, and a cleaning blade Y10 is brought into contact with the photosensitive drum Y and adheres to the outer peripheral surface of the photosensitive drum Y even after primary transfer. The transfer residual toner is scraped off and cleaned by the cleaning blade Y10.

  The charging unit Y2 is connected to a power source (not shown), a charging roller Y20 as a charging member that is connected to the power source and disposed in proximity to the photosensitive drum Y, and is disposed in proximity to the outer peripheral surface of the charging roller Y20. It comprises a cleaning roller Y21 that removes the adhering toner, and has a function of uniformly charging the outer peripheral surface of the photosensitive drum Y to a predetermined polarity by the charging roller Y20.

  The developing means Y3 accommodates a two-component developer composed of a carrier and toner, and a developing case Y30 that can be replenished with new toner from a new toner bottle 2Y (see FIG. 1) by a replenishing means (not shown), and a shaft on the developing case Y30. A developing roller Y31 as a developer carrying member that supports and supplies the developer to the photosensitive drum Y, and the like. The developing roller Y31 supplies toner to the electrostatic latent image carried by the photosensitive drum Y. And has a function of developing a toner image.

  As described above, the image forming units 3Y, 3M, 3C, and 3K according to the present embodiment are configured to be detachable from the front (front) side of the apparatus main body 10 as process cartridges. Since 2M, 2C, and 2K have the same configuration (see also FIG. 5), the user can access replacement parts such as a photosensitive drum and a toner bottle by simply opening a front cover (not shown), and replacement by the user. Work is easy. The photosensitive drums and developing means that need to be replaced and replaced regularly are housed in the process cartridge, and the cleaning means, the charging means, etc. are integrated in the process cartridge. It does not have to be stored and removable.

(Intermediate transfer unit)
Next, the intermediate transfer unit will be described with reference to FIGS. 3 is a front view showing a schematic configuration of the intermediate transfer unit according to the embodiment of the present invention, FIG. 4 is a plan view of the intermediate transfer unit, and FIG. 5 is a frame of the apparatus main body. It is a perspective view which shows the state to mount | wear. The intermediate transfer unit 5a shown in the figure includes a unit frame 50 composed of two plates, a front plate 50a and a rear plate 50b serving as a base, and five stretching rollers 51 pivoted on the front plate 50a and the rear plate 50b. To 55, an endless belt-like intermediate transfer belt 56 stretched around these stretch rollers 51 to 55, and a primary transfer bias is applied to the intermediate transfer belt 56 to provide photosensitive drums Y, M, C, The four primary transfer rollers 57Y, 57M, 57C, and 57K, which are primary transfer members for transferring a toner image from K to the intermediate transfer belt 56, are formed.

  The tension roller 51 is configured so that the driving force of a driving means (not shown) can be transmitted via a clutch or the like, and is a driving roller that drives the intermediate transfer belt 56 in the direction of the arrow. The other tension rollers are driven rollers. It has become. In the present embodiment, the driving roller 51 is set so that the peripheral speed, that is, the process speed which is the surface moving speed of the intermediate transfer belt 56, is 150 mm / sec. The tension roller 52 has a pressure spring 52a that is an urging means that urges the vicinity of both shaft ends to the outside (left side in the figure), and an appropriate tension (tensile) is applied to the endless belt-shaped intermediate transfer belt 56. (Tension roller). The tension roller 55 presses the endless belt-like intermediate transfer belt 56 from above to bend (indent) the inner side, and the upper surface thereof becomes substantially horizontal so that the intermediate transfer unit 5a is bent. This is a push-down roller as a pressing member that saves space. The pressing member (pressing roller) 55 may not have a roller shape as long as the endless belt can be curved inward. However, the surface of the intermediate transfer belt 56 may be damaged or deteriorated. Thus, it is desirable to reduce the frictional resistance as a roller shape.

The intermediate transfer belt 56 is formed into a single layer or a plurality of layers from a tubular film such as PVDF (vinylidene fluoride), ETFE (ethylene-tetrafluoroethylene copolymer), PI (polyimide), PC (polycarbonate), etc. A conductive material such as carbon black is dispersed, and the volume resistivity is adjusted to be in the range of 10 ⁸ to 10 ¹² Ωcm and the surface resistivity is in the range of 10 ⁹ to 10 ¹³ Ωcm. In addition, you may coat a mold release layer on the surface (outer peripheral surface) as needed. Materials used for the release layer include ETFE (ethylene-tetrafluoroethylene copolymer), PTFE (polytetrafluoroethylene), PVDF (vinylidene fluoride), PEA (perfluoroalkoxy fluororesin), FEP ( Fluorine resins such as tetrafluoroethylene-hexafluoropropylene copolymer) and PVF (vinyl fluoride) are preferred. Further, as a method for manufacturing the intermediate transfer belt 56, there are a casting method, a centrifugal molding method, and the like, and the surface thereof may be polished if necessary.

  If the volume resistivity of the intermediate transfer belt 56 exceeds the above-described range, a bias (primary transfer bias or secondary transfer bias) necessary for transfer becomes high, which causes a problem of increasing power supply cost. In addition, the charging potential of the intermediate transfer belt 56 becomes too high at the time of transfer or when the recording medium after the transfer is peeled off, and the charging potential of the intermediate transfer belt 56 is too late to decrease only by self-discharge. Therefore, it is necessary to provide a static eliminating means because the recording medium is disturbed by static electricity. Also, if the volume resistivity and surface resistivity are below the above ranges, the charge potential decays faster due to self-discharge, and there is no need to provide a charge eliminating means, but the toner scatters because the current during transfer flows in the surface direction. The problem that it occurs occurs. Therefore, it is desirable that the volume resistivity and the surface resistivity of the intermediate transfer belt 56 in the present embodiment are within the above ranges. The volume resistivity and surface resistivity were measured by connecting an HRS probe (inner electrode diameter 5.9 mm, ring electrode inner diameter 11 mm) to a high resistivity meter (manufactured by Mitsubishi Chemical Corporation: Hiresta IP), and the intermediate transfer belt 56. A value measured 100 seconds after applying a voltage of 100 V (surface resistivity is 500 V) to the front and back of the film was used.

The primary transfer rollers 57Y, 57M, 57C, and 57K consider the image deterioration due to the gap discharge, and the intermediate transfer belt from the directly facing position where the photosensitive drums Y, M, C, and K are in contact with the intermediate transfer belt 56 therebetween. 50 is a contact-type transfer bias (transfer voltage) application member arranged at a position slightly shifted downstream in the conveyance direction (arrow direction in the figure), and is connected to a bias power source (not shown) arranged in the apparatus body 10; A contact / separation mechanism (not shown) is configured to be contactable / separable, and contacts the inside of the intermediate transfer belt 56 corresponding to each photosensitive drum to form a primary transfer nip, and primary transfer with a predetermined voltage having a polarity opposite to that of the toner image. The bias is applied from the back surface (inner peripheral surface) of the intermediate transfer belt 56. In this embodiment, the transfer voltage applied at the time of primary transfer from the primary transfer roller is set to + 1800V.
The transfer bias applying means may be a non-contact type using a transfer charger. However, in the present embodiment, the primary transfer roller which is a roller-type contact bias applying member with less generation of transfer dust is provided. It has been adopted. Further, the primary transfer roller 57K that is frequently used may not be configured to be separated from the intermediate transfer belt 56 by the contact / separation mechanism.

(Intermediate transfer unit attachment / detachment direction)
As shown in FIG. 5, the intermediate transfer unit 5 a is configured to be attached and detached (attached and detached) from the right side when viewed from the front of the apparatus main body 10. In this embodiment, the intermediate transfer unit 5a is attached and detached by sliding in the horizontal direction perpendicular to the axial direction of the stretching rollers 51 to 55. FIG. 5 shows the apparatus main body 10 so that the opening (hole) for replacing the new toner bottle, the opening (hole) for replacing the process cartridge of the image forming unit, the opening for attaching / detaching the intermediate transfer unit, etc. can be easily understood. Shows only the apparatus main body frame 100. The apparatus main body frame 100 includes a front plate 101 on which a front door (not shown) is mounted, left and right side plates 102 and 103, and a rear plate 104. As described above, the opening provided with the intermediate transfer unit 5a on the right side plate. Since it is configured to be detachable from the (hole), it is not necessary to further provide an opening for the intermediate transfer unit between the opening for the adjacent new toner bottle and the opening for the image forming unit. It can be clearly seen from FIG. 5 that the strength (rigidity) of the 100 front plates 101 can be prevented from lowering. In the color printer 1 which is the image forming apparatus according to the present embodiment, as shown in the figure, the intermediate transfer unit 5a is configured to be attached / detached from the right side surface. Good. That is, the attachment / detachment direction of the intermediate transfer unit 5a may be perpendicular to the axial direction of the stretching rollers 51 to 55, which is the attachment / detachment direction of the image forming units 3Y, 3M, 3C, 3K, and the horizontal direction.

  As described in the background art, when the intermediate transfer unit 5a is detachable, the contact terminals that connect the primary transfer rollers 57Y, 57M, 57C, and 57K to the bias power source on the apparatus main body side are connected to the intermediate transfer unit 5a side. Necessary for both of the apparatus main body 10 side. Therefore, the intermediate transfer unit 5a according to the present embodiment includes unit side bias terminals TY, TM, TC, and TK connected to the primary transfer rollers through conductive wires, as shown in the drawing, on the rear plate of the unit frame 50. On the upper surface of 50b, yellow, magenta, cyan, and black toner colors are arranged in a line along the attaching / detaching direction of the intermediate transfer unit, and biases are applied to the primary transfer rollers 57Y, 57M, 57C, and 57K. It has a function to supply. These unit side bias terminals TY, TM, TC, and TK will be described in detail later.

  As described above, the push-down roller 55 can achieve the space saving of the intermediate transfer unit 5a, and can increase the winding angle of the belt with respect to the drive roller 51, thereby stabilizing the intermediate transfer belt 56. Can be rotated. In addition, the peelability between the intermediate transfer belt 56 and the recording medium is improved. Further, a bias may be applied to the push-down roller 55 to prevent the toner on the intermediate transfer belt 56 from adhering to the push-down roller 55.

(Cleaning unit)
Next, the belt cleaning unit 5c will be described with reference to FIG. FIG. 6 is a configuration explanatory diagram showing the vicinity of the belt cleaning unit in the configuration explanatory diagram of FIG. 1 in an enlarged manner. As shown in FIG. 6, the cleaning unit 5c is mainly composed of a unit case 50c and a lubricant applying means 59. The unit case 50 c is provided with a cleaning blade 51 c made of urethane rubber. The cleaning blade 51 c is brought into contact with and separated from the surface of the intermediate transfer belt 56 on the outer peripheral surface of a tension roller 52. The blade tip can be contacted and separated by the mechanism. The cleaning unit 5c uses the tension roller 52 as a backup roller, causes the cleaning blade 51c to contact the intermediate transfer belt 56, and removes residual toner adhering to the surface of the intermediate transfer belt 56 after the secondary transfer at the tip of the cleaning blade 51c. The remaining toner thus scraped off is temporarily stored in the unit case 50c, and the stored residual toner is transported to a waste toner storage bottle (not shown) by transport means such as a transport screw 52c.

(Lubricant application means)
The lubricant application means 59 is a solid lubricant 59a shaped in a rectangular column (cuboid) shape that is long in the width direction of the intermediate transfer belt 56, and a lubricant application that scrapes and applies the solid lubricant 59a to the intermediate transfer belt 56. A brush roller 59b, which is a member, and a plurality of pressing springs 59c as a lubricant pressurizing unit that presses the solid lubricant 59a against the brush roller 59b are pressed against the brush roller 59b with a predetermined pressure by the pressing spring 59c. The solid lubricant 59a is scraped off little by little and is applied and supplied as powder to the surface of the intermediate transfer belt 56. In this embodiment, the predetermined pressure is set such that the resultant force of the plurality of pressing springs 59c is 1N to 4N, and the width of the solid lubricant 59a is set wider than the maximum image width that can be output by the color printer 1. Therefore, it is shaped to 304 mm or more. Further, the width of the brush roller 59b is larger than the width of the solid lubricant 59a in order to evenly scrape the solid lubricant 59a. As described above, if the lubricant 59a is applied onto the intermediate transfer belt, the lubricant is interposed between the toner and the surface of the intermediate transfer belt. This improves the cleaning with the belt cleaning unit 5c, and also improves the transfer efficiency during secondary transfer.

  In the present embodiment, a fatty acid metal salt having a linear hydrocarbon structure is employed as the solid lubricant 59a, and the fatty acid metal salt is selected from stearic acid, palmitic acid, myristic acid, and oleic acid. It is sufficient if it contains at least one kind of fatty acid and contains at least one kind of metal selected from zinc, aluminum, calcium, magnesium and lithium. Among these, zinc stearate is produced on an industrial scale and has been used in many fields, so that it can be said to be the most preferable material in consideration of production cost, quality stability, reliability, and the like. The higher fatty acid metal salts generally used industrially are not the compound composition of the name, but include other fatty acid metal salts, metal oxides, free fatty acids and the like that are more or less similar.

  As described above, as the lubricant application means 59, the solid lubricant 59a is scraped little by little and supplied in the form of powder. However, the lubricant may be externally added to the toner. There is also a method of supplying. However, the method of supplying the lubricant externally to the toner has a problem that it cannot always be supplied to the entire surface of the intermediate transfer belt because the supply amount of the lubricant depends on the output image area. For this reason, when the lubricant is to be stably supplied to the entire surface of the intermediate transfer belt with a simple apparatus configuration, the solid lubricant is scraped off and applied by a rotating brush roller as in the present embodiment. The method is preferred.

(Image forming operation)
Next, the image forming operation of the color printer 1 will be described with reference to FIGS.
In the case of forming a color image, first, when an image forming operation is started in the color printer 1, the photosensitive drums Y, M, C, and K of the image forming units 3Y, 3M, 3C, and 3K are rotated. While being driven, the outer peripheral surfaces of the photosensitive drums Y, M, C, and K are uniformly charged with a predetermined polarity (for example, minus) by the charging units Y2, M2, C2, and K2. Next, a laser beam that is light-modulated from the optical unit 4 is irradiated for each toner color based on the color-separated image information on the charged surface, whereby the outer peripheral surface of each photosensitive drum Y, M, C, K An electrostatic latent image is formed thereon. The electrostatic latent image is visualized as a single color toner image by the developing units Y3, M3, C3, and K3, and the toner images of the respective colors are respectively converted by the corresponding primary transfer rollers 57Y, 57M, 57C, and 57K. A primary transfer bias supplied from a bias power source on the apparatus main body 10 side is applied via the unit side bias terminal, and a color toner image is formed by superimposing sequentially on the intermediate transfer belt 56. In the case of forming a monochromatic image, the above operation is performed only by the black image forming unit 3K.

  On the other hand, the recording medium conveyed from the sheet feeding unit 7 through the conveyance path by the conveyance roller pair 72 is sent to the secondary transfer nip after the transfer timing is adjusted by the registration roller pair 73. Therefore, a secondary transfer bias is applied from the bias power source PS through the secondary transfer roller 58 by the secondary transfer unit 5b, and the full-color toner image on the intermediate transfer belt 56 is transferred to the recording medium. Next, the recording medium carrying the full-color toner image is sent to the fixing nip between the fixing roller 60 of the fixing unit 6 and the pressure roller 61, and heat and pressure are applied to the recording medium. The toner image is fixed on the recording medium. As described above, after the toner image is fixed on the recording medium, the sheet is discharged onto the discharge tray 80 by the discharge roller pair 81 of the discharge unit 8 and stacked. Residual toner adhering to the surface of the intermediate transfer belt 56 after the secondary transfer is removed by the belt cleaning unit 5c together with the process pattern patch pattern removal toner, and is transferred to each of the photosensitive drums Y, M, C, and K. Residual toner that adheres even after the primary transfer is removed by the cleaning units Y1, M1, C1, and K1, and is prepared for another image forming operation. The transfer residual toner removed by the belt cleaning unit 5c and the cleaning means Y1, C1, M1, and K1 is transported to a waste toner storage bottle (not shown), and is exchanged or discarded by the user or service staff when the toner is full. Is done.

Next, a toner suitably used in the image forming apparatus according to the present embodiment will be described with reference to FIGS. FIG. 7 is an explanatory view schematically showing the shape of the toner for explaining the shape factor SF-1, and FIG. 8 is an explanation showing schematically the shape of the toner for explaining the shape factor SF-2. FIG.
The toner according to the present embodiment used in the above-described color printer 1 employs a polymerized toner generated by a polymerization method, and the toner according to the present embodiment has a shape factor SF-1 of 100 to 180. The shape factor SF-2 is preferably in the range of 100 to 180.

Here, the shape factor SF-1 indicates the ratio of the roundness of the toner shape, and is represented by the following formula (1).
SF-1 = {(MXLNG) ² AREA} × (100π / 4) (1)
As shown in FIG. 7, the shape factor SF-1 of the toner is a value obtained by dividing the square of the maximum length MXLNG of the shape formed by projecting the toner on a two-dimensional plane by the figure area AREA and multiplying by 100π / 4. is there. When the value of SF-1 is 100, the shape of the toner is a true sphere, and becomes irregular as the value of SF-1 increases.

The shape factor SF-2 indicates the ratio of the unevenness of the toner shape and is represented by the following formula (2).
SF-2 = {(PERI) ² / AREA} × (100 / 4π) (2)
As shown in FIG. 8, the shape factor SF-2 of the toner is a value obtained by dividing the square of the perimeter PERI of the figure formed by projecting the toner on the two-dimensional plane by the figure area AREA and multiplying by 100 / 4π. is there. When the value of SF-2 is 100, there is no unevenness on the toner surface, and as the value of SF-2 increases, the unevenness of the toner surface becomes more prominent.

  These shape factors were measured by taking a photograph of the toner with a scanning electron microscope (S-800: manufactured by Hitachi, Ltd.), introducing it into an image analyzer (LUSEX3: manufactured by Nireco), and analyzing and calculating it. When the shape of the toner is close to a sphere, the contact state between the toner and the toner or between the toner and the photosensitive drum becomes a point contact, so that the attractive force between the toners becomes weak. Therefore, it is preferable because the fluidity is increased, the force that the toner is adsorbed to the photosensitive member is weakened, and the transfer efficiency is increased. On the other hand, when either of the shape factors SF-1 and SF-2 exceeds 180, the transfer efficiency is lowered and the cleaning property of the toner attached to the image carrier such as the photosensitive drum or the intermediate transfer belt is also lowered. Therefore, it is not preferable.

  The toner used in the color printer 1 preferably has a volume average particle diameter in the range of 4 to 10 μm. If the particle size is smaller than this, it may cause stains at the time of development, the fluidity may deteriorate, and further, it tends to agglomerate. On the other hand, when the particle diameter is larger than this, high-definition images cannot be obtained due to toner scattering and resolution deterioration. In this embodiment, a toner having a volume average particle diameter of 6.5 μm is used.

[Bias terminal]
Next, the bias terminal, which is a characteristic part of the present invention, will be described with reference to FIGS.
9 is a partially enlarged plan view mainly showing the unit-side transfer bias terminal according to the present embodiment, FIG. 10 is a vertical sectional view mainly showing the unit-side transfer bias terminal, and FIG. 11 is the unit-side transfer bias. It is a vertical sectional view showing a state where a bias terminal is attached to the apparatus main body. As described above, the unit side bias terminals TY, TM, TC, and TK are arranged on the upper surface of the rear plate 50b of the unit frame 50 along the attaching / detaching direction of the intermediate transfer unit 5a for each of the yellow, magenta, cyan, and black toner colors. The unit-side bias terminals TY, TM, TC, TK and the later-described breakage prevention member B (BY, BM, BC, BK) have the same configuration. The description will be made collectively, and the suffixes (Y, M, C, K) of the reference numerals will be omitted.

  The unit-side bias terminal T is formed by processing a strip-shaped flat plate made of a stainless material that is an elastic member. As shown in the drawing, the unit-side bias terminal T includes a fixed portion T1, a curved surface portion T2, and an engaging claw T3. Yes. The fixing portion T1 has two through holes T1a and T1b that are substantially flat in the form of a flat plate, and the curved surface portion T2 has an arcuate vertical cross section and protrudes outward, that is, upward on the apparatus main body 10 side. The engaging claw T3 is formed in a curved surface shape, and has a flat plate shape in which the curved surface portion T2 is folded at a substantially right angle. The unit-side bias terminal T is fixed to the upper surface of the rear plate 50b of the unit frame 50 at the fixing portion T1, and the engaging claw T3 which is the other end is a free end.

  The fixing portion T1 is fixed to the rear plate 50b by inserting a boss Bo, which is a columnar protrusion provided on the upper surface of the rear plate 50b, into the through hole T1a and mounting the boss Bo on the upper surface of the rear plate 50b. This is done by screwing (screwing) the rear plate 50b through the hole T1b. By fixing in this way, the unit-side bias terminal T can be fixed at two points, the unit-side bias terminal T can be prevented from rotating easily, and only one place can be screwed. This is because work efficiency is good.

  Further, on the upper surface of the rear plate 50b of the unit frame 50, a folding preventing member B (BY, BM, BC, BK) that engages with the engaging claws T3 is erected. The folding preventing member B includes a vertical surface B1 that rises perpendicularly from the upper surface of the rear plate 50b, and an engaging portion B2 that is orthogonal to the vertical surface B1 and is spaced apart from the engaging claw T3 by a predetermined distance. Thus, the engaging portion B2 is configured to engage with the engaging claw T3 so that the free end of the unit side bias terminal T does not spread beyond a predetermined interval.

  In this way, the unit side bias terminal T is mounted because the curved surface portion T2 is formed into an upward convex curved surface shape having an inclined surface having a gentle slope gradually inclined along the mounting direction. Sometimes, a large frictional force does not work between the apparatus main body 10 and it can be set smoothly. In addition, at the time of attachment / detachment, that is, pulling out, the frictional force can be reduced by the upper convex curved surface near the top of the curved surface portion T2, and the compressive force acts on the unit side bias terminal T due to the frictional force with the apparatus body 10. However, as described above, since the free end is configured not to extend beyond a predetermined interval, the free end that becomes a weak axis (the one with a small second moment of section and a small buckling load) is bent upward. Can be prevented. Further, since there is the vertical plane B1, it is possible to prevent the unit side bias terminal T from being bent to the back side (the rear plate 104 side of the apparatus main body 10).

  As shown in FIG. 11, the top of the curved surface portion T2 is set slightly higher than the height of the bias terminal 10T on the apparatus main body 10 side when the intermediate transfer unit 5a is attached to the apparatus main body 10. At the time of mounting, the unit side bias terminal T is urged toward the apparatus main body by the elastic force. For this reason, the bias terminal 10T and the unit-side bias terminal T are in reliable contact, and the bias voltage can be stably supplied to the intermediate transfer unit 5a.

  As described above, the unit side bias terminal T according to the present embodiment is provided on the upper surface of the rear plate 50b of the unit frame 50 and is in contact with the bias terminal 10T on the apparatus body 10 side in the vertical direction. Although touched, the dimension of the intermediate transfer unit 5a in the width direction (that is, the depth direction of the entire apparatus) can be reduced as compared with the case where the unit frame 50 is provided on the side surface side. Further, the unit side bias terminal T (TY, TM, TC, TK) according to the present embodiment has a bottom surface formed by pushing down the intermediate transfer belt 56 by the push-down roller 55 and is accommodated in a triangular prism-like space. Therefore, the height of the intermediate transfer unit 5a can be reduced. As a result, the entire apparatus can be made compact. In addition, since the intermediate transfer unit 5a is arranged in a line in a direction perpendicular to the axial direction of the stretching roller, which is the attaching / detaching direction of the intermediate transfer unit 5a, and in the horizontal direction, only the attaching / detaching operation of the intermediate transfer unit 5a is performed. Thus, the plurality of unit side bias terminals T (TY, TM, TC, TK) can be simultaneously connected to and separated from the bias terminal 10T on the apparatus body 10 side.

  Further, when the intermediate transfer unit 5a is attached / detached, the unit side bias terminal T rubs against the main body of the apparatus, so if it is a material with low wear resistance, the terminal is worn, and the wear powder forms an oxide film, resulting in poor conduction. There is a possibility of waking up. However, since the unit-side bias terminal T according to the present embodiment is made of a stainless steel material, it has high wear resistance, hardly generates wear powder, and is not easily oxidized (rusted). The oxide film which worsens is not formed. Therefore, reliable conduction can be obtained even when the attachment / detachment operation is repeated.

Next, another embodiment which is a modification of the bias terminal will be described with reference to FIG.
FIG. 12 is a vertical cross-sectional view showing the unit-side transfer bias terminal according to the modification in a mounting operation state.
The unit-side transfer bias terminal T ′ according to the illustrated modification has the same configuration as the unit-side transfer bias terminal T, but the fixed end and the free end are interchanged, and the outer side of the apparatus main body is out of the inclined surface of the curved surface portion T2 ′. It is different in that it is installed so that the inclined surface with a gentle slope faces (to the right in the figure). Therefore, contrary to the unit-side transfer bias terminal according to the above-described embodiment, the intermediate transfer unit can be slid and moved more smoothly during attachment / detachment (when pulled out) than during attachment. Further, since the folding preventing member B ′ is provided at the time of mounting, even if a compressive force acts on the unit side bias terminal T ′ due to a frictional force with the apparatus main body 10, as described above, at the free end. It is possible to prevent buckling such that a certain engagement claw T3 ′ bends upward.

  As described above, the four-tandem type indirect transfer system has been described as an example of the image forming apparatus according to the embodiment of the present invention. However, the present invention is not necessarily applied to such an image forming apparatus. For example, a five-tandem tandem type intermediate transfer system including black and toner for halftone may be used. That is, any tandem type color image forming apparatus provided with an intermediate transfer unit that is detachable from the apparatus main body may be used. Further, the new toner storage unit, image forming unit, optical unit, belt cleaning unit, fixing unit, paper feed unit, paper discharge unit are merely examples, and other known devices and means are configured. Can be adopted. Even in such a case, it is clear that the same effect can be obtained with respect to the above-mentioned problem. Note that the shape, structure, and the like of each component shown in the drawings are merely preferable examples, and can be appropriately changed within the scope of the claims.

1 is a configuration explanatory diagram showing a schematic configuration of an image forming apparatus according to an embodiment of the present invention as viewed from the front; FIG. 2 is a configuration explanatory diagram showing an enlargement of the vicinity of a yellow image forming unit in the configuration explanatory diagram of the same. FIG. 2 is a front view showing a schematic configuration of an intermediate transfer unit according to the present embodiment. It is a top view of an intermediate transfer unit same as the above. FIG. 3 is a perspective view showing a state where the intermediate transfer unit is mounted on the frame of the apparatus main body. FIG. 2 is a configuration explanatory diagram showing an enlarged vicinity of a belt cleaning unit in the configuration explanatory diagram of FIG. 1. FIG. 6 is an explanatory diagram schematically illustrating the shape of a toner for explaining a shape factor SF-1. FIG. 6 is an explanatory diagram schematically showing the shape of a toner for explaining a shape factor SF-2. It is a partial enlarged plan view mainly showing a unit side transfer bias terminal according to the present embodiment. It is a vertical sectional view mainly showing the unit side transfer bias terminal of the same. FIG. 3 is a vertical cross-sectional view showing the unit-side transfer bias terminal same as that shown in FIG. FIG. 10 is a vertical cross-sectional view showing a unit-side transfer bias terminal according to a modification in a mounting operation state.

Explanation of symbols

1 Color printer (image forming device)
10 apparatus body 100 apparatus body frame 101 front plate 102, 103 side plate 104 rear plate 3Y, 3M, 3C, 3K image forming unit 5a intermediate transfer unit 50 unit frame (frame)
50a Front plate 50b Rear plates 51 to 55 Stretching roller 51 Driving roller 55 Pressing roller (pressing member)
56 Intermediate transfer belt 57 Primary transfer roller (primary transfer member)
5b Secondary transfer means 58 Secondary transfer roller TY, TM, TC, TK Unit side bias terminal T1 fixed part (fixed end)
T2 curved surface part T3 engagement claw (free end)
B Folding prevention member B1 Vertical surface B2 Engagement part

Claims (6)

A frame serving as a base, a plurality of stretching rollers pivoted on the frame, an endless belt-shaped intermediate transfer belt stretched around the stretching roller, and a primary transfer bias applied to the intermediate transfer belt A tandem type color image forming apparatus having an intermediate transfer unit that is detachable from the apparatus main body, and a plurality of primary transfer members;
The intermediate transfer unit is configured to be detachable in a direction perpendicular to the axial direction of the stretching roller, and the intermediate transfer belt is pressed in the vertical direction by a pressing member from the outside and curved inwardly, and its upper surface is curved. Almost horizontal,
Attaching / detaching the intermediate transfer unit to / from the frame so that a plurality of unit-side bias terminals that respectively supply primary transfer biases to the plurality of primary transfer members are accommodated in a space formed by indenting the intermediate transfer belt. An image forming apparatus arranged in a line along a direction.   The image forming apparatus according to claim 1, wherein the unit-side bias terminal has an outwardly convex curved surface that is inclined along a mounting or detaching direction of the intermediate transfer unit.   The unit side bias terminal has a vertical cross section formed in an arcuate shape, one end of which is a fixed end fastened to the upper surface or the lower surface of the frame, and the other end is a free end. The image forming apparatus according to claim 2.   An engagement claw is formed at the free end of the unit-side bias terminal, and the frame has an engagement portion disposed on the upper surface or the lower surface of the frame at a predetermined distance from the engagement claw. 4. A member is erected so that the free end of the unit-side bias terminal does not expand beyond a predetermined interval by engaging the engaging claw and the engaging portion. The image forming apparatus described in 1.   5. The image forming apparatus according to claim 1, wherein the unit side bias terminal is made of an elastic member biased toward the apparatus main body.   The image forming apparatus according to claim 5, wherein the unit-side bias terminal is made of a stainless material.

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