JP2015152731A - Transfer device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent streaky transfer failure.SOLUTION: A transfer device 50 includes: a circulating transfer body 52; and a transfer member 54 which is supported by a bearing section 102 and rotates following the transfer body 52, to transfer a toner image carried on an image holding body 42 to the transfer body 52. A relation between slide load Y (N) applied by the bearing section 102 to the transfer member 54 and contact pressure X (Pa) of the transfer member 54 with respect to the transfer body 52 satisfies Y≤0.02X-1.07 and X≤95.

Description

  The present invention relates to a transfer device and an image forming apparatus.

  Patent Document 1 discloses an intermediate transfer belt having an arithmetic average roughness of an inner peripheral surface of Rat (μm), and a plurality of suspension rolls suspended on the intermediate transfer belt. And in patent document 1, when the arithmetic mean roughness of the outer peripheral surface of at least one suspension roll is Rar (μm), 1.0 ≦ Rat ≦ 3.5, 1.0 ≦ Rar ≦ 3.5 and A configuration of an image forming apparatus that satisfies the relationship of 2.5 ≦ Rat + Rar ≦ 6.0 is disclosed.

  In Patent Document 2, a roller-shaped charging member 14 that rotates while abutting on the image carrier 12 and charges the image carrier 12, rotates while always in contact with the charging member 14, and an elastic layer is formed on the surface. A roller-shaped cleaning member 100 is disclosed. Patent Document 2 discloses a configuration of an image forming apparatus in which a repulsive load at a compression rate of 50% of the elastic layer 100B of the cleaning member 100 is 30 kPa or less.

Patent Document 3 discloses a transfer roll which is a conductor and a rigid body and transfers a toner image onto an intermediate transfer belt. In Patent Document 3, the surface resistivity of the intermediate transfer belt when 1000 V is applied to the transfer roll is 1 × 10 ¹² (Ω / cm ² ) or less, and the transfer current is in the range of 8 to 20 μA. Configuration of image forming apparatus in which sum of arithmetic average roughness Ra (B) of transfer roller side surface of intermediate transfer belt and arithmetic average roughness Ra (R) of transfer roll surface is 1.2 (μm) or less Is disclosed.

JP 2009-115886 A JP 2010-282236 A Japanese Patent No. 4649986

  An object of the present invention is to suppress streaky transfer failure.

  According to a first aspect of the present invention, there is provided a transfer device that transfers a toner image held on an image holding member to the transfer member while rotating around the transfer member and a bearing member supported by a bearing unit. And the relationship between the sliding load Y (N) of the transfer member by the bearing portion and the contact pressure X (Pa) of the transfer member with respect to the transfer body is Y ≦ 0.02X−1. .07 and X ≦ 95.

  The transfer device according to claim 2 of the present invention is the transfer device according to claim 1, wherein the transfer member is a roll having a metal outer peripheral surface.

  The transfer device according to claim 3 of the present invention is the transfer device according to claim 1 or 2, wherein the transfer member has an outer diameter of 7 mm or less.

  According to a fourth aspect of the present invention, there is provided an image forming apparatus comprising: an image holding member; a developing device that develops a latent image formed on the image holding member as a toner image; The transfer device according to claim 1, wherein the held toner image is transferred to the transfer body by the transfer member.

  According to the transfer apparatus of the first aspect of the present invention, streaky transfer defects are suppressed as compared with a transfer apparatus that satisfies the relationship of Y> 0.02X−1.07 and X ≦ 95.

  According to the transfer device of claim 2 of the present invention, spot-like transfer failure is suppressed as compared with a transfer device in which the outer peripheral surface of the transfer member is a rubber roll.

  According to the transfer device of the third aspect of the present invention, the driving torque of the transfer body can be reduced as compared with the transfer device in which the outer diameter of the transfer member is larger than φ7 mm.

  According to the image forming apparatus of the fourth aspect of the present invention, image formation defects are suppressed as compared with an image forming apparatus having a transfer device that satisfies the relationship of Y> 0.02X-1.07 and X ≦ 95. Is done.

1 is a schematic view (back view) of an image forming apparatus according to an embodiment. 1 is a schematic diagram (rear view) of a primary transfer roll and its surroundings that constitute an image forming apparatus of an embodiment. Experiments (Experiments 1 to 15) for determining the relationship between the sliding load Y (N) of the primary transfer roll by the bearing and the contact pressure X (Pa) of the primary transfer roll to the intermediate transfer belt in the transfer device of the embodiment. It is a table | surface which shows conditions and a result. 16 is a graph showing the results of Experiments 1 to 15 (relationship between the sliding load Y (N) of the primary transfer roll by the bearing portion and the contact pressure X (Pa) of the primary transfer roll with respect to the intermediate transfer belt).

  An example of this embodiment will be described with reference to the drawings. First, the overall configuration and operation of the image forming apparatus will be described, and then the main part (transfer apparatus) of this embodiment will be described. In the following description, the direction indicated by the arrow H in FIGS. 1 and 2 is the apparatus height direction, and the apparatus width direction is the direction indicated by the arrow W. In addition, a direction perpendicular to each of the apparatus height direction and the apparatus width direction (shown by an arrow D as appropriate) is defined as an apparatus depth direction.

<Overall configuration of image forming apparatus>
"The entire"
The image forming apparatus 10 includes an image forming unit 8 and a control unit 24. Hereinafter, a description will be given with reference to FIG.

  The image forming unit 8 includes a medium storage unit 12, a toner image forming unit 14, a transport unit 16, a fixing device 18, a discharge unit 20, and a supply mechanism 22. The image forming unit 8 forms an image on a recording medium P described later. The control unit 24 controls the operation of each unit of the image forming apparatus 10.

<Image forming unit>
[Toner image forming section]
The toner image forming unit 14 includes image forming units 40Y, 40M, 40C, and 40K, and an intermediate transfer unit 50. Here, yellow (Y), magenta (M), cyan (C), and black (K) are examples of toner colors. Here, the intermediate transfer unit 50 is an example of a transfer device.

  The image forming units 40Y, 40M, 40C, and 40K have substantially the same configuration except for the toner used. Therefore, in FIG. 1, the reference numerals of the respective parts constituting the image forming units 40M, 40C, and 40K are omitted.

<Image forming unit>
The image forming unit 40Y includes a photosensitive drum 42Y, a charging device 44Y, an exposure device 30Y, a developing device 46Y, and a removing device 48Y. Similarly, the image forming units 40M, 40C, and 40K correspond to the respective colors, and the photosensitive drums 42M, 42C, and 42K, the charging devices 44M, 44C, and 44K, the exposure devices 30M, 30C, and 30K, and the development are developed. Devices 46M, 46C and 46K and removal devices 48M, 48C and 48K are provided. In the following description, the subscripts Y, M, C, and the image forming units 40Y, 40M, 40C, and 40K and the members constituting them will be described when it is not necessary to distinguish the toner colors (Y, M, C, and K). K is omitted.

  In each of the image forming units 40Y, 40M, 40C, and 40K, yellow (Y), magenta (M), cyan (C), and black (K) colors are provided on the outer peripheral surfaces of the photosensitive drums 42Y, 42M, 42C, and 42K. A toner image is formed. In addition, the image forming units 40Y, 40M, 40C, and 40K are disposed in a state where the image forming units 40 are inclined and arranged with respect to the apparatus width direction as a whole (see FIG. 1).

(Photosensitive drum)
The photosensitive drum 42 has a function of holding a toner image developed by the developing device 46. The photosensitive drum 42 is formed in a cylindrical shape, and is driven to rotate about its own axis (in the direction of arrow R1 (see FIG. 1)) by a driving unit (not shown). The photosensitive drum 42 includes an aluminum base material and a photosensitive layer (not shown) formed on the base material in the order of an undercoat layer, a charge generation layer, and a charge transport layer. Here, the photosensitive drum 42 is an example of an image carrier.

(Charging device)
The charging device 44 is disposed along the own axis direction (device depth direction) of the photosensitive drum 42. The charging device 44 includes a charging roll 440 and a cleaning roll 450. A voltage necessary for charging the outer peripheral surface of the photosensitive drum 42 is applied to the shaft (not shown) of the charging roll 440. The charging roll 440 charges the outer peripheral surface of the photosensitive drum 42 to a negative polarity. The cleaning roll 450 is configured to remove impurities such as toner, external additives, paper dust, and dust attached to the outer peripheral surface of the charging roll 440.

<Exposure equipment>
The exposure device 30 has a function of forming a latent image on the outer peripheral surface of the photosensitive drum 42 charged by the charging device 44. The exposure apparatus 30 emits exposure light from a light emitting diode array (not shown) in accordance with image data received from an image signal processing unit (not shown) that constitutes the control unit 24. Then, the exposure light irradiates the outer peripheral surface of the photosensitive drum 42 charged by the charging device 44 to form a latent image on the outer peripheral surface.

(Developer)
The developing device 46 has a function of developing the latent image formed on the photosensitive drum 42 as a toner image. The developing device 46 is disposed along the own axis direction of the photosensitive drum 42. The developing device 46 includes a toner supply body 46A that supplies toner to the outer peripheral surface of the photosensitive drum 42, a plurality of transport members 46B that transport the developer including toner and carrier to the toner supply body 46A, And a toner density sensor 60 for detecting the toner density.

  The toner concentration sensor 60 detects the magnetic permeability of the developer in the developing device 46 using the fact that the magnetic permeability of the developer including toner and carrier changes according to the toner concentration, and based on the detection result. The toner density is calculated.

(Removal device)
The removing device 48 removes toner and external additives that are not transferred to the outer peripheral surface of the photosensitive drum 42 after the toner image formed on the outer peripheral surface of the photosensitive drum 42 is primarily transferred to the intermediate transfer belt 52. Etc. are removed from the outer peripheral surface of the photosensitive drum 42. The removing device 48 includes a blade 48 </ b> A that is disposed along the own axis direction of the photosensitive drum 42 and that contacts the outer peripheral surface of the photosensitive drum 42.

<Intermediate transfer unit>
The intermediate transfer unit 50 has a function of superimposing the toner images of the respective colors held on the respective photosensitive drums 42 and transferring them onto the recording medium P. The intermediate transfer unit 50 includes an intermediate transfer belt 52, a plurality (four) of primary transfer units 100, a drive roll 56, and a secondary transfer roll 58. Each primary transfer portion 100 includes a primary transfer roll 54, a pair of bearing portions 102, and a compression spring 102 (see FIG. 2). Here, the primary transfer roll 54 is an example of a transfer member. The intermediate transfer belt 52 is an example of a transfer body.

  The intermediate transfer belt 52 is an endless belt. The plurality (four) of primary transfer rolls 54 and drive rolls 56 are arranged so as to contact the inner peripheral surface of the intermediate transfer belt 52. The posture of the intermediate transfer belt 52 is determined by a plurality of (four) primary transfer rolls 54, a drive roll 56, a tension applying roll 59, and the like that are in contact with the inner peripheral surface thereof. Inclined with respect to direction. Further, the outer peripheral surface of the intermediate transfer unit 50 facing the lower side in the apparatus height direction is in contact with the outer peripheral surface of each photoconductive drum 42 constituting each image forming unit 40 arranged in an inclined manner with respect to the apparatus width direction. doing.

  The drive roll 56 is disposed so as to face the secondary transfer roll 58 with the intermediate transfer belt 52 interposed therebetween, and is rotated around its own axis by a drive source (not shown). In addition, each primary transfer roll 54 has the intermediate transfer belt 52 sandwiched therebetween, and the intermediate transfer belt 52 is moved in the circumferential direction with respect to a virtual straight line along the apparatus height direction passing through the center of its own axis of each photosensitive drum 42. (Arrow R2 direction) Arranged in a state offset to the downstream side. For this reason, the intermediate transfer belt 52 is configured to move around while being wound around the outer peripheral surface of the photosensitive drum 42 (see FIG. 2).

  The primary transfer roll 54 applies a voltage necessary for primary transfer to transfer the toner images formed on the outer peripheral surfaces of the photosensitive drums 42Y, 42M, 42C, and 42K to the outer peripheral surface of the intermediate transfer belt 52. Primary transfer.

  The secondary transfer roll 58 applies a voltage necessary for the secondary transfer, and secondarily transfers the toner image primarily transferred onto the outer peripheral surface of the intermediate transfer belt 52 onto the recording medium P. Yes.

  The intermediate transfer unit 50 is configured to be removable from the image forming apparatus main body 10A. Therefore, as an example, the intermediate transfer belt 52 can be removed from the image forming apparatus main body 10A and replaced when it reaches the end of its life (when the function of the intermediate transfer belt 52 cannot be performed).

  As described above, the intermediate transfer unit 50 has been briefly described, but the intermediate transfer unit 50 and the primary transfer unit 100 constituting the intermediate transfer unit 50 are the main parts of the present embodiment, and will be described later.

[Replenishment mechanism]
The replenishing mechanisms 22Y, 22M, 22C, and 22K have a function of replenishing the developer to the developing devices 46Y, 46M, 46C, and 46K. Note that the replenishment operation of the developer to the developing device 46 by each replenishment mechanism 22 is performed based on the detection result of the toner density sensor 60.

[Transport section]
The transport unit 16 has a function of transporting the recording medium P stored in the medium storage unit 12 to the discharge unit 20 described later. The transport unit 16 includes a delivery roll 16A, a plurality of transport roll pairs 16B, a reverse transport unit 16D, and a discharge roll 16E described later. The delivery roll 16A is configured to send the recording medium P stored in the medium storage unit 12 to the downstream side in the transport direction of the recording medium P from the discharge roll 16A. The plurality of transport roll pairs 16B are arranged along a transport path 16C through which the recording medium P sent out by the delivery roll 16A is transported. The plurality of transport roll pairs 16B transport the recording medium P sent out by the feed roll 16A to a facing position (secondary transfer position T2) between the facing roll 56 and the secondary transfer roll 58.

  Further, the transport unit 16 is provided with a reverse transport unit 16D that transports the recording medium P by reversing the front and back so that an image can be formed on both sides of the recording medium P. The reverse conveyance unit 16D is provided on the opposite side of the intermediate transfer unit 50 with the conveyance path 16C interposed therebetween when the image forming apparatus 10 is viewed from the front side. The reverse conveyance unit 16D switches back the recording medium P having the toner image fixed on the surface. Thereafter, the reverse conveying unit 16D conveys the recording medium P to the secondary transfer position T2 so that the back surface of the recording medium P faces the outer peripheral surface of the intermediate transfer belt 52.

[Fixing device]
The fixing device 18 has a function of fixing the toner image secondarily transferred to the recording medium P to the recording medium P. The fixing device 18 includes a fixing roll 18A and a pressure roll 18B. The fixing device 18 is disposed on the downstream side in the transport direction of the recording medium P with respect to the secondary transfer position T2. The fixing roll 18A is arranged on the recording medium P on the side where the toner image is transferred, and a halogen heater (not shown) is arranged on the inner peripheral surface side thereof. The pressure roll 18B pressurizes the recording medium P, which is transported through the transport path 16C and passes the position T3 (see FIG. 1) facing the fixing roll 18A, toward the fixing roll 18A.

[Discharge part]
The discharge unit 20 is formed downstream of the fixing device 18 in the conveyance direction of the recording medium P and on a part of the outer upper surface of the main body of the image forming apparatus 10. The recording medium P on which the toner image is fixed is discharged to the discharge unit 20 by a discharge roll 16E provided at a portion between the fixing device 18 and the discharge unit 20 in the conveyance path 16C.

<Operation of Image Forming Apparatus>
Next, the operation of the image forming apparatus 10 will be described with reference to FIG.

  The control unit 24 operates the image forming apparatus 10 when an image signal is transmitted from an external apparatus (PC as an example). The control unit 24 converts this image signal into image data of each color of yellow (Y), magenta (M), cyan (C), and black (K). The image data of each color is output to the exposure apparatus 30.

  Subsequently, the exposure light emitted according to the image data of each color from the exposure device 30 is incident on the outer peripheral surface of the photosensitive drum 42 charged by the charging device 44. A latent image corresponding to the image data of each color is formed on the outer peripheral surface of each photosensitive drum 42.

  Further, the latent image formed on the outer peripheral surface of each photosensitive drum 42 is developed as a toner image of each color by each developing device 46.

  Then, the toner images of the respective colors on the outer peripheral surface of the respective photosensitive drums 42 are primarily transferred onto the outer peripheral surface of the intermediate transfer belt 52 by the respective primary transfer rolls 54 facing the respective photosensitive drums 42.

  On the other hand, the recording medium P has a medium accommodating portion so as to match the timing at which the outer peripheral surface of the intermediate transfer belt 52 and the toner image is transferred to the secondary transfer position T2 by the circular movement. 12 is transported to the secondary transfer position T2. Then, the toner image primarily transferred onto the outer peripheral surface of the intermediate transfer belt 52 is secondarily transferred onto the recording medium P which is conveyed to the secondary transfer position T2 and passes therethrough.

  Subsequently, the recording medium P onto which the toner image has been transferred is conveyed toward the fixing device 18. Then, the toner image is heated and pressed by a fixing roll 18A and a pressure roll 18B constituting the fixing device 18 and fixed on the recording medium P.

  The recording medium P on which the toner image is fixed is discharged to the discharge unit 20 and the image forming operation is completed.

  When images are formed on both sides of the recording medium P, the recording medium P is transported to the reversal transport unit 16D after the toner image is fixed on the surface by the fixing device 18. Then, the recording medium P having the toner image fixed on the surface is switched back by the reversing conveyance unit 16D. Thereafter, the toner image is secondarily transferred to the back surface of the recording medium P at the secondary transfer position T2, and the toner image secondarily transferred by the fixing device 18 is fixed. Finally, the recording medium P having the toner images fixed on both sides is discharged to the discharge unit 20 and the image forming operation is completed.

<Configuration of main parts (primary transfer unit and intermediate transfer unit 50)>
Next, the primary transfer unit 100 and the intermediate transfer unit 50 which are the main parts of the present embodiment will be described with reference to the drawings.

<Primary transfer section>
As shown in FIG. 2, the primary transfer unit 100 includes a primary transfer roll 54, a bearing unit 102, and a compression spring 104.

[Primary transfer roll]
The primary transfer roll 54 has a long shape, and includes a contact portion 54A that contacts the inner peripheral surface of the intermediate transfer belt 52, and a pair of protrusion portions 54B that protrude from both ends of the contact portion 54A. . The contact portion 54A is a columnar member having an outer peripheral surface with an outer diameter φ6 (mm). The primary transfer roll 54 is a metal roll as an example.

(Bearing part)
The bearing portion 102 is a long member, and a through hole 102A is formed on one end side thereof. The bearing portion 102 supports both ends (a pair of protrusions 54B) of the primary transfer roll 54, and functions as a sliding bearing.

[Compression spring]
The compression spring 104 is disposed on the upper side in the apparatus height direction with respect to the bearing portion 102 and is sandwiched between the other end portion of the bearing portion 102 and a part 106 of the casing of the intermediate transfer unit 50 in a compressed state. ing. The compression spring 104 presses the bearing portion 102 from the upper side in the apparatus height direction to the lower side.

[Relationship between primary transfer roll, bearing and compression spring]
The primary transfer roll 54 supported by the bearing portion 102 presses the inner peripheral surface of the intermediate transfer belt 52 by the compression spring 104 pressing the bearing portion 102. Then, when the intermediate transfer belt 52 moves in the direction of the arrow R2, the primary transfer roll 54 receives the frictional force from the intermediate transfer belt 52 and is driven to rotate about its own axis (in the direction of the arrow R3). ing.

<< Relationship between sliding load Y (N) of primary transfer roll and contact pressure X (Pa) of primary transfer roll >>
Next, the sliding load Y (N) of the primary transfer roll 54 by the bearing portion 102 (hereinafter, referred to as the sliding load Y (N)) and the contact pressure X of the primary transfer roll 54 with respect to the intermediate transfer belt 52 ( Pa) (hereinafter referred to as contact pressure X (Pa)) will be described.

In the intermediate transfer unit 50 of the present embodiment, the above relationship satisfies the following [Formula 1].
[Formula 1] Y ≦ 0.02X−1.07 and X ≦ 95

[Contact pressure X (Pa)]
As shown in FIG. 2, the primary transfer roll 54 is disposed on the upper side in the apparatus height direction with respect to a portion of the inner peripheral surface of the intermediate transfer belt 52 that contacts the primary transfer roll 54. The primary transfer roll 54 presses the inner peripheral surface of the intermediate transfer belt 52 while being supported by the bearing portion 102 pressed by the compression spring 104. Therefore, the contact pressure X (Pa) corresponds to the sum of the pressure caused by the weight of the primary transfer roll 54 and the bearing portion 102 and the pressure caused by the pressing force of the pair of compression springs 104.

[Sliding load Y (N)]
As shown in FIG. 2, the primary transfer roll 54 is driven by the intermediate transfer belt 52 as the intermediate transfer belt 52 rotates during the image forming operation, and rotates by receiving a force in the direction of the arrow R3. On the other hand, during this period, the primary transfer roll 54 receives rolling resistance (friction) from the bearing portion 102. Here, the sliding load Y (N) is a physical quantity corresponding to this rolling resistance. In the present embodiment, the speed at which the intermediate transfer belt 52 rotates during the image forming operation (hereinafter referred to as process speed) is, for example, 126 (mm / s).

  As described above, the intermediate transfer unit 50 of the present embodiment includes the primary transfer unit 100 having the above-described configuration and is configured to satisfy [Equation 1].

[Basis of [Formula 1]]
Next, the basis of [Formula 1] (the test that derived [Formula 1]) will be described with reference to the drawings.

<Test method>
In this test, the primary transfer roll 54 is used in the image forming apparatus 10 to print 5% color on the entire printing area of 10,000 sheets of A4 size paper as the recording medium P, and the sensory evaluation of the image quality. It is done by doing. In this test, as shown in the table shown in FIG. 3, 15 types (tests 1 to 15) of combinations of the contact pressure X (Pa) and the sliding load Y (N) are set.

  Here, the contact pressure X (Pa) is set by using a plurality of compression springs 104 having different spring constants. The sliding load Y (N) is set by using a plurality of through holes 102A having different hole diameters in the bearing portion 102.

(Measuring method of contact pressure X (Pa))
The contact pressure X (Pa) is measured by attaching a compression spring 104 selected from a plurality of compression springs 104 to the primary transfer unit 100 and forming a nip formed by the primary transfer roll 54 and the intermediate transfer belt 52. (Hereinafter referred to as the primary transfer nip portion) is measured. In this measurement, a tactile sensor system I-SCAN (manufactured by Nitta Corporation) is used.

(Measuring method of sliding load Y (N))
The sliding load Y (N) is measured as follows. First, in this measurement, a primary transfer roll 54 is attached to a bearing portion 102 selected from among a plurality of bearing portions 102, and one end of a string is fixed to a contact portion 54A of the primary transfer roll 54. Wind a string around 54. Next, the other end of the string is fixed to a push-pull gauge (manufactured by Imada Co., Ltd.), and the tensile force is measured while pulling the string at a constant speed. The measured tensile force is defined as a sliding load Y (N).

(Method of sensory evaluation)
Sensory evaluation of image quality is performed by visually observing and evaluating whether or not a streak-like image formation defect (hereinafter referred to as a streak-like image formation defect) occurs along the paper conveyance direction. Yes. In the sensory evaluation of the image quality, as a result of visual observation, a case where no streak-like image formation failure has occurred is determined to be acceptable, and a case where it has occurred is regarded as unacceptable. The streak-like image formation failure will be described later.

<Experimental result>
As shown in the table of FIG. 3, in Tests 1 to 9, after 5% color printing was performed on 50,000 sheets of A4 size paper over the entire print area of the paper, the stripes along the paper transport direction No image formation failure occurred. On the other hand, in Tests 10 to 15, after 5% color printing was performed on 10,000 sheets of A4 size paper over the entire print area of the paper, streaky image formation defects along the paper transport direction were observed. It has occurred. That is, according to this test, tests 1 to 9 are accepted and tests 10 to 15 are rejected.

  Also, as shown in FIG. 4, the conditions of tests 1 to 15 (contact pressure X (Pa) and sliding load Y (N)) are plotted with the contact pressure X (Pa) on the horizontal axis and the sliding load on the vertical axis. Plot on a two-dimensional graph with Y (N). At this time, the pass tests 1 to 9 are marked with ◯, and the failing tests 10 to 15 are marked with x. Then, in this graph, a straight line Y = 0.02X−1.07 can be drawn at the boundary between ○ and ×.

  In the graph of FIG. 4, if Y ≦ 0.02X−1.07, it is determined that the test has passed, and if Y> 0.02X−1.07, the test fails. It is considered as an area.

<Operation of this embodiment>
Hereinafter, the operation of the present embodiment will be described with reference to the drawings. First, the generation mechanism of the above-described streak-like image formation failure will be described. Next, the operation of this embodiment will be described in comparison with comparative examples (Comparative Examples 1 and 2). In the following description, when using the components used in this embodiment, the description will be made using the reference numerals of the components as they are.

[Generation mechanism of streak-like image formation failure]
The streak-like image formation failure occurs when the primary transfer roll 54 is not rotated by the intermediate transfer belt 52 for some reason. When the primary transfer roll 54 is not driven and rotated by the intermediate transfer belt 52, a streak-like image formation defect occurs due to the following mechanism. When impurities (hereinafter referred to as impurities) such as toner, external additive, carrier, paper dust, and dust in the image forming apparatus 10 adhere to the inner peripheral surface of the intermediate transfer belt 52, the impurities are transferred to the inner transfer belt 52. Move around with the adhering surface. Then, impurities accumulate on the primary transfer nip portion. For this reason, the electrical resistance increases at a site where impurities in the axial direction of the primary transfer roll 54 are deposited. As a result, even when a voltage necessary for primary transfer is applied to the primary transfer roll 54, the electric field formed on the toner sandwiched between the intermediate transfer belt 52 and the photosensitive drum 42 is used for primary transfer. Since the required electric field strength is not obtained, it is assumed that a streak-like image formation defect occurs. A primary transfer failure that causes a streak-like image formation failure is referred to as a streak-like transfer failure.

  Moreover, in [Formula 1], it is set as X <= 95 about contact pressure X (Pa). That is, in [Formula 1], when X ≦ 95, Y ≦ 0.02X−1.07 is satisfied. Thus, in [Formula 1], the reason why the upper limit is set for the contact pressure X (Pa) is as follows. As described above, the primary transfer roll 54 of the present embodiment has an outer diameter of φ6 (mm), which is compared with a commonly used primary transfer roll (for example, an outer diameter of φ10 (mm) or more). And the width of the primary transfer nip is narrow. In other words, the primary transfer roll that is generally used is heavier than the primary transfer roll 54 and has a wider primary transfer nip portion. For this reason, in the intermediate transfer unit including the primary transfer roll, the primary transfer roll does not follow the intermediate transfer belt 52. As a result, no impurities are deposited in the primary transfer nip portion.

  On the other hand, when the outer diameter of the primary transfer roll is reduced from the generally used primary transfer roll, the pressure due to the weight of the primary transfer roll is reduced. Further, the width of the primary transfer nip portion is narrowed. For this reason, in the intermediate transfer unit including the primary transfer roll having a small outer diameter, the driving torque received from the intermediate transfer belt 52 is small, and the intermediate transfer belt 52 is difficult to be driven to rotate. In the case of the intermediate transfer unit 50 including the primary transfer roll 54 having a smaller outer diameter than that of a generally used primary transfer roll, the inventor has contact pressure X (Pa) and sliding load Y (N). It has been found that there is no follow-up failure of the primary transfer roll 54 by the combination. Therefore, in [Formula 1], when X ≦ 95, Y ≦ 0.02X−1.07 is satisfied.

[Comparison with Comparative Example 1]
First, a comparative example 1 described below is assumed as a comparative example of the present embodiment, and then compared with the present embodiment.

  In the intermediate transfer unit of Comparative Example 1, the relationship between the contact pressure X (Pa) and the sliding load Y (N) satisfies the following [Equation 2]. In the image forming apparatus of Comparative Example 1, the relationship between the contact pressure X (Pa) and the sliding load Y (N) satisfies the following [Equation 2]. Except for this point, the configuration is the same as that of the present embodiment.

  [Formula 2] Y> 0.02X-1.07 and X ≦ 95

  When the test of the present embodiment is performed using the intermediate transfer unit of Comparative Example 1, as shown in the table of FIG. 3 and the graph of 4, the region of x in this graph, in other words, is rejected. In the case of the intermediate transfer unit of Comparative Example 1, it was confirmed that the primary transfer roll was poorly driven with respect to the intermediate transfer belt 52. In the intermediate transfer unit of Comparative Example 1, impurities accumulated in the primary transfer nip portion, resulting in streak-like image formation defects.

  On the other hand, when the test of the present embodiment is performed using the intermediate transfer unit 50 of the present embodiment, as shown in the table of FIG. 3 and the graph of 4, in other words, Passed.

  Therefore, according to the intermediate transfer unit 50 of the present embodiment, the driven rotation failure of the primary transfer roll 54 with respect to the intermediate transfer belt 52 is suppressed as compared with the intermediate transfer unit of Comparative Example 1. For this reason, in the intermediate transfer unit 50, the accumulation of impurities in the primary transfer nip portion that causes the streaky primary transfer failure is suppressed.

The primary transfer roll 54 constituting the intermediate transfer unit 50 of the present embodiment has an outer diameter of the contact portion 54A of φ6 (mm).
Therefore, according to the intermediate transfer unit 50 of the present embodiment, the driving torque of the intermediate transfer belt 52 is reduced as compared with an intermediate transfer unit having a primary transfer roll having an outer diameter larger than φ6 (mm). The driven rotation failure of the primary transfer roll 54 is suppressed.

[Comparison with Comparative Example 2]
Next, a comparative example 2 described below is assumed as a comparative example of the present embodiment, and then compared with the present embodiment.

  In the primary transfer roll of Comparative Example 2, the outer peripheral surface of the contact portion is made of rubber. That is, the outer peripheral surface of the primary transfer roll of Comparative Example 2 is softer (is more likely to be recessed) than the primary transfer roll 54 of the present embodiment in which the contact portion is made of metal. The intermediate transfer unit of Comparative Example 2 has the primary transfer roll of Comparative Example 2. The image forming apparatus of Comparative Example 2 includes the intermediate transfer unit of Comparative Example 2. Except for this point, the configuration is the same as that of the present embodiment. The primary transfer roll, the intermediate transfer unit, and the image forming apparatus of Comparative Example 2 are included in the present invention.

In the case of the intermediate transfer unit of Comparative Example 2, the relationship between the contact pressure X (Pa) and the sliding load Y (N) satisfies [Equation 1], similarly to the intermediate transfer unit 50 of the present embodiment. The driven rotation failure of the primary transfer roll of Comparative Example 2 with respect to the intermediate transfer belt 52 hardly occurs. for that reason,
In the intermediate transfer unit of Comparative Example 2, streaky primary transfer failure hardly occurs.

  However, when impurities such as toner, external additives, carrier, paper dust, and dust in the image forming apparatus 10 adhere to the inner peripheral surface of the intermediate transfer belt 52 and the intermediate transfer belt 52 moves around, the impurities are In the nip portion formed by the inner peripheral surface of the intermediate transfer belt 52 and the primary transfer roll, it bites into the primary transfer roll. Therefore, the primary transfer roll of Comparative Example 2 may continue to be driven and rotated by the intermediate transfer belt 52 with these impurities attached to the outer peripheral surface thereof. As a result, in the primary transfer, these impurities adhere to the outer peripheral surface of the primary transfer roll, which may cause a spotted primary transfer failure.

  On the other hand, the outer peripheral surface of the primary transfer roll 54 of this embodiment is made of metal. For this reason, in the intermediate transfer unit 50 including the primary transfer roll 54 of the present embodiment, it is difficult for impurities to bite into and adhere to the primary transfer roll 54 as compared with the case of Comparative Example 2.

  Therefore, according to the intermediate transfer unit 50 of the present embodiment, as compared with the intermediate transfer unit of Comparative Example 2, the spot-like transfer failure due to the impurities adhering to the outer peripheral surface of the primary transfer roll 54 is suppressed.

  As a result, according to the image forming apparatus 10 of the present embodiment, compared to the image forming apparatus of Comparative Example 2, image formation defects caused by spot-like transfer defects are suppressed.

  As mentioned above, although this invention was demonstrated in detail about specific embodiment, this invention is not limited to embodiment mentioned above, Other embodiment is possible within the scope of the present invention.

  For example, the primary transfer roll 54 of the present embodiment has been described as a cylindrical member having a long shape and an outer peripheral surface having an outer diameter of φ6 (mm). As long as it is a member having a cylindrical shape (pipe shape), for example. The primary transfer roll 54 is a long member, and the relationship between the contact pressure X (Pa) and the sliding load Y (N) only needs to satisfy [Equation 1].

  In the present embodiment, each primary transfer roll 54 is described as being disposed on the upper side in the apparatus height direction with respect to each photosensitive drum 42 with the intermediate transfer belt 52 interposed therebetween. 54 may be disposed on the lower side in the apparatus height direction with respect to each photosensitive drum 42. In this case, the pressure due to the weight of each primary transfer roll 54 does not apply to the inner peripheral surface of the intermediate transfer belt 52, but the contact pressure X (Pa) and the sliding load Y (N) caused by the compression spring 104 As long as the relation of [Formula 1] is satisfied.

10 Image forming apparatus 42 Photosensitive drum (an example of an image carrier)
46 Developing device 50 Intermediate transfer unit (an example of a transfer device)
52 Intermediate transfer belt (an example of a transfer member)
54 Primary transfer roll (an example of a transfer member)
102 Bearing part

Claims (4)

A transfer body moving around,
A transfer member that is supported by a bearing portion and is driven to rotate by the transfer body while transferring the toner image held by the image holding body to the transfer body;
With
The relationship between the sliding load Y (N) of the transfer member by the bearing portion and the contact pressure X (Pa) of the transfer member with respect to the transfer body is Y ≦ 0.02X−1.07 and X ≦ 95,
Transfer device. The transfer member is a roll whose outer peripheral surface is made of metal.
The transfer device according to claim 1. The transfer member has an outer diameter of 7 mm or less.
The transfer device according to claim 1 or 2. An image carrier,
A developing device for developing the latent image formed on the image carrier as a toner image;
The transfer device according to claim 1, wherein the toner image developed by the developing device and held on the image holding member is transferred to the transfer member by the transfer member;
An image forming apparatus.

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