JP2014224864A - Transfer device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress, when an AC component voltage is applied to a transfer member to transfer a developer image to a recording medium, the developer image from being transferred with a developer being deviated in the conveyance direction of the recording medium.SOLUTION: A transfer device 100 includes a secondary transfer roll 106 that forms a secondary transfer part N2 with an intermediate transfer belt 102, a power source 120 that applies an AC voltage, and an auxiliary roll 108. The secondary transfer roll 106 and auxiliary roll 108 applies pressure to the secondary transfer part N2 so that a pressure acting on the boundary K between an upstream side transfer area Sa and a downstream side transfer area Sb becomes 0.03 MPa or more. When a toner image TA is transferred onto recording paper P at the secondary transfer part N2, even if the AC voltage vibrates a toner, the secondary transfer roll 106 and auxiliary roll 108 applies pressure to the toner to regulate the movement of the toner, and thereby suppressing the toner from being transferred while being deviated in the conveyance direction of the recording paper P.

Description

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

  In the transfer device of Patent Document 1, a transfer charging member that contacts the back side of the transfer material is provided within the nip width between the photosensitive drum and the transfer material in the moving direction of the transfer material.

  In the image forming apparatus of Patent Document 2, a transfer nip portion having a nip width L1 is formed by bringing a recording material holding sheet of a transfer drum into contact with a photosensitive drum. In the image forming apparatus disclosed in Patent Document 2, the width of the transfer nip portion is widened to L1 + L2 by a pre-transfer push-up member including a base and a blade.

JP-A-9-230709 JP 7-210004 A

  The present invention relates to a transfer device capable of suppressing a developer from being shifted and transferred in the conveyance direction of a recording medium when an AC component voltage is applied to a transfer member to transfer the developer image to the recording medium. An object is to obtain an image forming apparatus.

  A transfer device according to a first aspect of the present invention is a transfer member that is rotatably provided and forms a transfer portion of a developer onto a recording medium between an image holding member that holds a developer image, and the image holding A voltage applying means for applying at least an alternating current component voltage between the member and the transfer member; and in the transfer portion, upstream of the maximum position where the amount of developer transferred becomes maximum, in the rotation direction of the transfer member. The pressure acting on the set position at which the amount of developer transferred by application of the voltage is 40% of the amount of developer transferred at the maximum position is 0.03 [MPa] or more. And setting means for setting a pressure distribution in the transfer section.

  In the transfer device according to a second aspect of the present invention, the setting unit includes a pressure member that pressurizes the image holding member or the recording medium toward the transfer member.

  In the transfer device according to a third aspect of the present invention, the image holding member is an endless belt that is provided so as to be capable of circular movement, and the setting means spreads the transfer section upstream in the rotation direction. And a pressing member that presses the belt against the transfer member.

  In the transfer device according to a fourth aspect of the present invention, the transfer member constitutes at least a part of the setting means.

  The image forming apparatus according to claim 5 of the present invention is a developer image forming unit that forms a developer image on the image holding member, and a developer image held on the image holding member is transferred to a recording medium. And a transfer device according to any one of claims 1 to 4.

  According to the first aspect of the present invention, in the transfer portion, an AC component is applied to the transfer member in comparison with a configuration in which the pressure acting on the position where the maximum amount of developer to be transferred is 40% is lower than 0.03 [MPa]. When a developer image is transferred to a recording medium by applying a voltage, it is possible to prevent the developer from being shifted and transferred in the conveyance direction of the recording medium.

  The invention of claim 2 makes it easier to adjust the pressure applied in the upstream transfer region and the downstream transfer region than in a configuration that does not have a pressure member that presses the image holding member or the recording medium toward the transfer member. Can be done.

  According to the invention of claim 3, the pressure distribution can be set regardless of the position of the transfer member, as compared with the configuration having no pressing member.

  According to the fourth aspect of the present invention, the transfer device can be made simpler than that in which the transfer member does not constitute the setting means.

  The invention according to claim 5 is a recording medium having a transfer unit having a transfer device in which the pressure acting on the position corresponding to 40% of the maximum amount of developer to be transferred is lower than 0.03 [MPa]. It is possible to suppress image defects caused by the transfer of the developer in the transport direction.

1 is an overall configuration diagram of an image forming apparatus according to a first embodiment. FIG. 2 is a configuration diagram of an image forming unit according to the first embodiment. (A) It is a schematic diagram of the transfer part of the transfer apparatus which concerns on 1st Embodiment. (B) It is a graph which shows the relationship between the position in the transfer part which concerns on 1st Embodiment, and nip pressure. FIG. 6 is a schematic diagram illustrating a transfer state of a toner image in a transfer unit according to the first embodiment. (A) It is a schematic diagram which shows the confirmation method of the prenip area | region and downstream transfer area | region in the transfer part which concerns on 1st Embodiment. FIG. 5B is a schematic diagram of the toner image transferred to the recording paper by the transfer unit according to the first embodiment. 6 is a graph showing a relationship between a position and a toner amount in a transfer unit according to the first embodiment, with and without a transfer bias. (A) It is a schematic diagram of the transfer part of the transfer apparatus which concerns on 2nd Embodiment. (B) It is a graph which shows the relationship between the position in the transfer part which concerns on 2nd Embodiment, and nip pressure. (A) It is a schematic diagram of the transfer part of the transfer apparatus which concerns on the modification of 2nd Embodiment. (B) It is a graph which shows the relationship between the position in the transfer part and nip pressure which concern on the modification of 2nd Embodiment. (A) It is a schematic diagram of the transfer part of the transfer apparatus which concerns on 3rd Embodiment. (B) It is a graph which shows the relationship between the position in the transfer part which concerns on 3rd Embodiment, and nip pressure. (A) It is a schematic diagram of the transfer part of the transfer apparatus which concerns on the other modification of 2nd Embodiment. (B) It is a schematic diagram of the transfer part of the transfer apparatus which concerns on the modification of 3rd Embodiment. It is a schematic diagram showing a transfer state of a toner image in a transfer portion according to a comparative example. (A), (C) It is a schematic diagram which shows the state which changed arrangement | positioning of the secondary transfer roll in the transfer part of the transfer apparatus of a comparative example. (B), (D) It is a graph which shows the relationship between the position in the transfer part of the transfer apparatus of a comparative example, and nip pressure. (A) It is a schematic diagram which shows the state of the lattice image after transfer at the time of using the transfer apparatus which concerns on this embodiment. (B) It is a schematic diagram which shows the state of the lattice image after transfer at the time of using the transfer apparatus which concerns on a comparative example.

[First embodiment]
An example of the transfer device and the image forming apparatus according to the first embodiment will be described.

(overall structure)
FIG. 1 shows an image forming apparatus 10 according to the first embodiment. The image forming apparatus 10 includes an apparatus main body 15 formed of a member including a plurality of frames and plate materials. Further, the image forming apparatus 10 is provided on a sheet storage unit 12 that stores a recording sheet P as an example of a recording medium and a sheet storage unit 12 from the lower side to the upper side in the vertical direction (Y direction). And a main operation unit 14 that forms an image on the recording paper P supplied from the paper storage unit 12. Further, the image forming apparatus 10 includes a document reading unit 16 provided on the main operation unit 14 for reading a document (not shown), and a control provided in the main operation unit 14 for controlling the operation of each unit of the image forming apparatus 10. Part 20.

  In the figure, “x” in “○” means an arrow heading from the front to the back, and “•” in “○” in the figure is It means an arrow from the back to the front. Further, when the image forming apparatus 10 is viewed from the side where a user (not shown) stands, the X direction is the right direction, the -X direction is the left direction, the Y direction is the upward direction, the -Y direction is the downward direction, and the Z direction is the The depth direction and the −Z direction correspond to the front direction.

(Paper compartment)
The sheet storage unit 12 includes a first storage unit 22, a second storage unit 24, a third storage unit 26, and a fourth storage unit 28 that can store recording sheets P of different sizes. In the first storage unit 22, the second storage unit 24, the third storage unit 26, and the fourth storage unit 28, a feed roll 32 that feeds the stored recording paper P one by one, and the fed recording paper P A transport roll 34 that transports the transport path 30 provided in the image forming apparatus 10 is provided.

  Further, on the downstream side of the conveyance roll 34 in the conveyance path 30, a plurality of conveyance rolls 36 that convey the recording paper P one by one are provided. Further, the recording paper P is stopped at one end downstream of the transport roll 36 in the transport direction of the recording paper P in the transport path 30 and sent to a secondary transfer position described later at a predetermined timing. An alignment roll 38 for performing alignment is provided.

  The upstream portion of the conveyance path 30 is provided in a straight line from the −X direction side of the sheet storage unit 12 to the −X direction lower side of the main operation unit 14 in the arrow Y direction in the front view of the image forming apparatus 10. ing. Further, the downstream portion of the transport path 30 is provided from the lower portion of the main operating unit 14 on the −X direction side to the paper discharge unit 13 provided on the side surface of the main operating unit 14 in the X direction. Further, a double-sided conveyance path 31 through which the recording paper P is conveyed and reversed in order to form an image on both sides of the recording paper P is connected to the conveyance path 30. Note that the conveyance direction of the recording paper P when the double-sided conveyance is not performed is indicated by an arrow A (hereinafter referred to as A direction).

  The double-sided conveyance path 31 has a reversing unit 33 that is linearly provided in the arrow Y direction from the lower part of the main operation unit 14 in the X direction to the X direction side of the paper storage unit 12 in a front view of the image forming apparatus 10. ing. Furthermore, the double-sided conveyance path 31 includes a conveyance unit 35 that conveys the recording sheet P to the −X direction side (shown by an arrow B) illustrated in the figure while the trailing end of the recording sheet P conveyed to the reversing unit 33 enters. ing. The downstream end of the transport unit 35 is connected to the upstream side of the alignment roll 38 of the transport path 30 by a guide member (not shown). In FIG. 1, a plurality of transport rolls are provided at intervals in the reversing unit 33 and the transport unit 35, but the illustration is omitted. Further, a switching member that switches between the conveyance path 30 and the double-sided conveyance path 31 and a switching member that switches between the reversing unit 33 and the conveyance unit 35 are also omitted in the drawing.

(Original reading section)
The document reading unit 16 has a document table 41 on which a plurality of documents (not shown) can be placed, a glass 42 on which one document is placed, and a document reading device 44 that reads a document placed on the glass 42. A document discharge unit 43 for discharging the read document is provided.

  The document reader 44 irradiates the document placed on the glass 42 with light, and reflects the reflected light reflected from the document irradiated by the light irradiator 46 in a direction parallel to the glass 42 and folded back. A full rate mirror 48 and a half rate mirror 52 are provided. Further, the document reading device 44 includes an imaging lens 54 on which reflected light reflected by the full-rate mirror 48 and the half-rate mirror 52 enters, and photoelectric conversion that converts the reflected light imaged by the imaging lens 54 into an electrical signal. And an element 56.

  The electrical signal converted by the photoelectric conversion element 56 is subjected to image processing by an image processing apparatus (not shown) and used for image formation. The full rate mirror 48 moves at a full rate along the glass 42, and the half rate mirror 52 moves at a half rate along the glass 42.

(Main operation part)
The main operation unit 14 is formed in the apparatus main body 15 by an image forming unit 60 as an example of a developer image forming unit that forms a toner image (an example of a developer image) on the recording paper P, and the image forming unit 60. And a fixing device 90 for fixing the developer image on the recording paper P.

  The image forming unit 60 includes photosensitive members 62K, 62C, 62M provided corresponding to toners of yellow (Y), magenta (M), cyan (C), and black (K) as an example of a developer. The image forming units 64K, 64C, 64M, and 64Y having 62Y are provided. In the following description, if it is necessary to distinguish Y, M, C, and K, an alphabetic letter Y, M, C, or K will be added after the numeral, and the same configuration will be used. , M, C, and K need not be distinguished from each other, description of Y, M, C, and K is omitted.

  In addition, the image forming unit 60 includes exposure units 66K, 66C, 66M, and 66Y that emit light beams L and expose the outer peripheral surfaces of the photoreceptors 62K, 62C, 62M, and 62Y. Further, the image forming unit 60 includes a transfer device 100 that transfers the toner images formed by the image forming units 64K, 64C, 64M, and 64Y onto the recording paper P.

  The exposure unit 66 scans a light beam emitted from a light source (not shown) with a rotary polygon mirror (polygon mirror: no symbol) and reflects it with a plurality of optical components including a reflection mirror, so that light corresponding to each toner. The beam L is emitted toward the photoconductor 62. The photoconductor 62 is provided on the lower side (−Y direction side) of the exposure unit 66.

  As shown in FIG. 2, the image forming unit 64 includes a photoconductor 62 that is rotatably provided in the arrow + R direction (the clockwise direction in the drawing). Further, the image forming unit 64 includes a charger 72, a developing device 74, and a cleaning unit 76 that are arranged in order from the upstream side to the downstream side in the rotation direction so as to face the outer peripheral surface of the photoconductor 62. Note that the charger 72 and the developing device 74 are arranged so that the light beam L is irradiated to a position between the charger 72 and the developing device 74 on the outer peripheral surface of the photosensitive member 62. In addition, an intermediate transfer belt 102 (to be described later) to which a toner image developed by the developing device 74 is primarily transferred is in contact with a position between the developing device 74 and the cleaning unit 76 on the outer peripheral surface of the photosensitive member 62.

  The photoreceptor 62 includes a cylindrical base material (not shown) that is electrically conductive and grounded, and a charge generation layer, a charge transport layer, and a protective layer that are sequentially laminated in the radial direction on the outer peripheral surface of the base material. And a surface layer (not shown). The photosensitive member 62 can be rotated in the arrow + R direction by driving a motor (not shown).

  As an example, the charger 72 includes a corotron charging unit that applies a voltage to the wire and charges the outer peripheral surface of the photosensitive member 62 to the same polarity as the toner by corona discharge. In the image forming unit 64, a latent image (electrostatic latent image) is formed by irradiating the outer peripheral surface of the charged photoreceptor 62 with the light beam L based on the image data.

  For example, the developing device 74 contains a developer G in which carrier particles made of a magnetic material and toner are mixed. The developing device 74 includes a magnet roll (not shown) having a plurality of magnetic poles in the circumferential direction. A cylindrical developing sleeve 75 provided inside is provided. The developing device 74 forms a magnetic brush at a portion facing the photosensitive member 62 and applies a developing bias to the developing sleeve 75 to make the latent image on the outer peripheral surface of the photosensitive member 62 visible with toner. Thus, a toner image is formed. Each developing device 74 is supplied with toner from each toner cartridge 79 (see FIG. 1) provided above the image forming unit 60.

  The cleaning unit 76 has a cleaning blade 77 that is disposed with the front end facing in the rotational direction of the photoconductor 62 and that contacts the outer peripheral surface of the photoconductor 62. The cleaning unit 76 is configured to scrape and collect the residual toner remaining on the outer peripheral surface of the photosensitive member 62 with a cleaning blade 77.

  As shown in FIG. 1, a cleaning blade 116 that removes residual toner and paper dust on the intermediate transfer belt 102 after the secondary transfer is located near the drive roll 112 and facing the outer peripheral surface of the intermediate transfer belt 102. Is provided. As an example, a seal member (not shown) that reflects light is fixed at the reference position of the non-downstream transfer area where the toner image is not transferred on the outer peripheral surface of the intermediate transfer belt 102. Further, the reference position of the intermediate transfer belt 102 is obtained by irradiating the non-downstream transfer area of the intermediate transfer belt 102 with light and receiving the light reflected by the seal member at a position where the seal member can be opposed. There is provided a position sensor (not shown) for detecting. Thereby, in the image forming unit 60, the image forming operation of each unit is performed based on the signal of the reference position obtained by the position sensor.

  A transport belt 96 is provided on the downstream side of the secondary transfer roll 106 in the moving direction of the recording paper P to transport the recording paper P, on which the secondary transfer of the toner image has been completed, to the fixing device 90. The conveyance belt 96 is wound around a support roll 97 and a drive roll 98, and a recording sheet P is conveyed to the fixing device 90 by a motor (not shown) rotating the drive roll 98. .

<Main part configuration>
Next, an example of the transfer device 100 will be described.

  As shown in FIG. 1, the transfer apparatus 100 includes an intermediate transfer belt 102 as an example of an image holding member and a belt, a primary transfer roll 104, a transfer member, a setting unit, and a secondary transfer as an example of a pressure member. It has a roll 106 and an auxiliary roll 108. Further, the transfer apparatus 100 includes a power source 120 (see FIG. 4) as an example of a voltage applying unit that applies a transfer voltage to the secondary transfer roll 106.

(Intermediate transfer belt)
As an example, the intermediate transfer belt 102 is formed of an endless belt in which carbon black (antistatic agent) is contained in a resin made of polyimide or polyamide. Inside the intermediate transfer belt 102, there are a drive roll 112 disposed on the image forming unit 64Y and the primary transfer roll 104Y side and driven to rotate by a motor (not shown), and a plurality of transport rolls 114 provided rotatably. Has been placed.

  The intermediate transfer belt 102 is wound around a drive roll 112, a transport roll 114, and an auxiliary roll 108. As a result, the intermediate transfer belt 102 moves in the C direction (in the direction of arrow C, which is the counterclockwise direction shown in the figure) when the drive roll 112 rotates counterclockwise as shown in the figure. In this embodiment, as an example, the intermediate transfer belt 102 has a reverse obtuse triangular posture that is long in the X direction when viewed in the Z direction, and the auxiliary roll 108 is positioned at the top on the −Y side. .

(Primary transfer roll)
For example, the primary transfer roll 104 has a structure in which a sponge layer (not shown) is formed around a cylindrical shaft made of stainless steel, and both ends of the shaft are supported by bearings. , Rotation is possible with the Z direction as the axial direction. The primary transfer roll 104 is in contact with the inner peripheral surface of the intermediate transfer belt 102 so as to sandwich the intermediate transfer belt 102 with the photosensitive member 62, thereby forming a primary transfer portion N1. Further, the primary transfer roll 104 applies a transfer voltage having a polarity opposite to the polarity of the toner from a power source (not shown) to the shaft so that the toner image is primarily transferred from the photoreceptor 62 onto the intermediate transfer belt 102. It has become.

(Secondary transfer roll)
As an example, the secondary transfer roll 106 has the same configuration as the primary transfer roll 104, and is disposed on the downstream side of the alignment roll 38 in the conveyance path 30, and is rotatably provided with the Z direction as an axial direction. Yes. Further, the secondary transfer roll 106 is in contact with the outer peripheral surface of the intermediate transfer belt 102 so as to sandwich the intermediate transfer belt 102 with the auxiliary roll 108, so that the secondary transfer roll 106 is a second transfer unit as an example of a transfer section between the secondary transfer roll 106. A next transfer portion N2 is formed. The secondary transfer roll 106 is configured to set a pressure distribution (described later) of the secondary transfer portion N2 together with the auxiliary roll 108.

(Auxiliary roll)
As an example, the auxiliary roll 108 has a grounded stainless steel shaft (not shown), and forms a counter electrode of the secondary transfer roll 106. Here, when a transfer voltage is applied to the secondary transfer roll 106 from the power source 120, a potential difference is generated between the auxiliary roll 108 and the secondary transfer roll 106, and the toner image on the intermediate transfer belt 102 is transferred to the secondary transfer roll 106. Secondary transfer is performed on the recording paper P conveyed to the portion N2.

(Power supply)
As shown in FIG. 4, the power source 120 is electrically connected to the secondary transfer roll 106. The power source 120 applies a transfer voltage obtained by superimposing a voltage of an AC component on a DC voltage having a polarity opposite to the polarity of the toner image TA to the secondary transfer roll 106. Note that the DC voltage is applied to form an electric field for transferring the toner image TA from the intermediate transfer belt 102 to the recording paper P in the secondary transfer portion N2. The AC component voltage is applied so that the toner particles constituting the toner image TA on the intermediate transfer belt 102 are vibrated in the thickness direction of the intermediate transfer belt 102 so that the toner image TA can be easily separated from the intermediate transfer belt 102. Is done.

<Comparative example>
11 and 12C show the secondary transfer portion N2 of the transfer device 200 of the comparative example. The transfer device 200 includes an intermediate transfer belt 102, a secondary transfer roll 106, an auxiliary roll 108, and a power source 120. In the transfer device 200, the rotation center position OA of the secondary transfer roll 106 is arranged on the −X side with respect to the rotation center position OB of the auxiliary roll 108 in the X direction. Here, an angle (offset angle) between a straight line V passing through the rotation center position OA and extending along the Y direction and a line segment AB connecting the rotation center positions OA and OB is θa.

  In addition, the intermediate transfer belt 102 of the transfer device 200 has a portion on the downstream side of the transport roll 114 in the movement direction (C direction) and a portion on the upstream side of the secondary transfer portion N2 in a straight line H along the X direction. In contrast, the angle θb extends to the Y side. As an example, in the transfer apparatus 200, θa = 30 [°] and θb = 15 [°].

  A change in nip pressure at each position in a contact portion (hereinafter referred to as a nip portion) between the intermediate transfer belt 102 and the secondary transfer roll 106 is as shown by a graph Gb in FIG. Here, the nip portion in the C direction is distinguished into an upstream transfer region Sa and a downstream transfer region Sb based on a boundary K defining method described later. The downstream transfer region Sb is a region where the amount of toner transferred to the recording paper P is larger than that of the upstream transfer region Sa when a transfer voltage is applied.

  In the graph Gb, the nip pressure gradually increases from the upstream side of the upstream transfer area Sa, the nip pressure reaches the maximum value Pc at the maximum position NPb in the downstream transfer area Sb, and the outlet side (downstream) of the downstream transfer area Sb. The nip pressure is decreasing toward the Further, at the boundary position NPa between the upstream transfer area Sa and the downstream transfer area Sb, the nip pressure of the transfer device 200 is lower than the nip pressure Pa as an example of a set pressure described later. In the following description, the boundary between the upstream transfer area Sa and the downstream transfer area Sb is referred to as a boundary K.

  As a modification of the transfer device 200, when the offset angle θa = 0 [°] is set in FIG. 12C, the respective members are in the arrangement state shown in FIG. In this setting, as shown in FIG. 12B, in the graph Ga of the nip pressure, the nip pressure gradually increases from the upstream side, and the nip pressure reaches the maximum value Pb in the downstream transfer region Sb. The nip pressure decreases toward the downstream side of the transfer area Sb. Further, the nip pressure at the boundary K is lower than the nip pressure Pa described later.

  Here, in the image forming unit 60 (see FIG. 1), a lattice image (see FIG. 13A) composed of a plurality of orthogonal vertical lines and horizontal lines is formed, and as shown in FIG. 200, the toner image TA was secondarily transferred to the recording paper P. As a result, as shown in FIG. 13B, a phenomenon (hereinafter referred to as toner scattering Ts) in which the toner image is shifted and transferred in the A direction (the conveyance direction of the recording paper P) on the recording paper P is seen. It was.

  The toner scattering Ts in the A direction is estimated to be generated on the recording paper P because the pressure acting on the toner is insufficient when the transfer electric field acts on the toner and the toner can move freely. . In other words, in order to suppress the toner scattering Ts in the A direction, a nip pressure that can regulate the movement of the toner is provided in the vicinity of the boundary K between the upstream transfer region Sa and the downstream transfer region Sb shown in FIG. It is thought that it only has to act. For this reason, a confirmation experiment was performed with respect to the definition of the boundary K and the pressure required near the boundary K in order to suppress the toner scattering Ts.

<Boundary definition method>
An image density that represents a state in which a predetermined amount of toner is attached to a unit area of the recording paper P as 100% is called Cin. As an example, Cin 20% means an image density that attaches 20% of a preset mass to the unit area of the recording paper P. Here, in the image forming unit 60 shown in FIG. 1, a toner image Tw (see FIG. 5A) having a single color Cin of 20% is formed and primarily transferred onto the intermediate transfer belt 102.

Subsequently, the intermediate transfer belt 102 is moved in a state where the secondary transfer roll 106 is separated from the intermediate transfer belt 102, and the toner image Tw is disposed in the secondary transfer portion N2. Then, the recording paper P is disposed between the intermediate transfer belt 102 and the secondary transfer roll 106, and the secondary transfer roll 106 is moved toward the intermediate transfer belt 102 (returned to the original position). As an example of the recording paper P, OS coated paper W (127 [g / m ² ]) is used.

  As a result, as shown in FIG. 5A, the toner image Tw on the intermediate transfer belt 102 and the recording paper P come into contact with each other. After maintaining this contact state for 10 seconds, the secondary transfer roll 106 is separated from the intermediate transfer belt 102 and the recording paper P is taken out. Then, a Scotch mending tape (manufactured by Sumitomo 3M Co., Ltd.) is applied so as to cover the toner image Tw transferred onto the recording paper P, and the image density of the transfer area (nip portion) of the toner image Tw is measured by a density measuring device. taking measurement. The image density is measured at a plurality of locations so that the boundary K can be seen from the inlet side to the outlet side of the nip portion.

  In order to convert the measured image density into the toner amount, a calibration curve between the image density and the toner amount is created in advance. In addition, the above-described tape is attached to the recording paper P in the absence of the toner image Tw, and the image density is measured, so that the deviation of the image density due to the tape alone is excluded from the measured value. As an example of the concentration measuring device, X-rite 938 (manufactured by X-Rite Co., Ltd.) is used, but a fluorescence spectral densitometer FD-7 (manufactured by Konica Minolta Co., Ltd.) may be used. The measurement environment is, for example, a temperature of 22 [° C.] and a humidity of 55 [%]. Here, the toner amount at each position of the toner image Tw transferred to the recording paper P in the secondary transfer portion N2 is obtained from the calibration curve of the image density and the toner amount and the measured image density.

  Subsequently, the toner image Tw (the same image as the first time) on the intermediate transfer belt 102 and the recording paper P are brought into contact with each other in the same procedure. Here, at the same time when the secondary transfer roll 106 is brought into contact with the recording paper P, a transfer voltage (for example, a current value of 0.2 [μA] at 50 [V]) is applied to the secondary transfer roll 106. After maintaining this state for 10 seconds, the secondary transfer roll 106 is separated from the intermediate transfer belt 102 and the recording paper P is taken out. Then, the above-described tape is attached so as to cover the toner image Tw transferred onto the recording paper P, and the image density of the transfer area of the toner image Tw is measured by the above-described density measuring device and converted into the toner amount. .

  FIG. 6 shows graphs G1 and G2 of the toner amount from the entrance to the exit of the nip portion (secondary transfer portion N2). A graph G1 (dashed line) represents the toner amount when no transfer voltage is applied (only pressure), and a graph G2 (solid line) represents the toner amount when a transfer voltage is applied. From the graphs G1 and G2, the nip portion in the C direction (see FIG. 3A) has an upstream region where the toner adhesion amount due to the transfer voltage application is small, and a toner adhesion amount due to the transfer voltage application (maximum value). It was found that it has a downstream region. Note that the amount of toner adhesion in the graph G2 is larger than that in the graph G1.

  Here, the value of ΔW / Wp in the nip portion was confirmed as the maximum toner amount Wp in the graph G2 and the toner adhesion amount difference ΔW between the toner adhesion amount in the graph G1 and the toner adhesion amount in the graph G2. As a result, the upstream region where the toner adhesion amount is small has ΔW / Wp smaller than 0.4, and the downstream region where the toner adhesion amount is large has ΔW / Wp of 0.4 or more. I understood. Specifically, under the condition of level (2), which will be described later, numerical values of ΔW / Wp = 0.39 on the upstream side of the nip portion and ΔW / Wp = 0.69 on the downstream side are confirmed. Further, under the condition of level (5) described later, the numerical values of ΔW / Wp = 0.31 on the upstream side and ΔW / Wp = 0.72 on the downstream side are confirmed. From these, a boundary of ΔW / Wp = 0.4 is defined. Therefore, in the present embodiment, an area where ΔW / Wp <0.4 is an upstream transfer area Sa, and an area where ΔW / Wp ≧ 0.4 is a downstream transfer area Sb.

  In other words, in this embodiment, the toner image Tw adhesion area on the recording paper P shown in FIG. 5B is divided into an upstream transfer area Sa and a downstream transfer area Sb with a boundary K therebetween.

<Evaluation of toner scattering>
In the image forming apparatus 10 shown in FIG. 1, the toner scatter Ts after transferring the toner image Tw onto the recording paper P by changing the nip pressure at the boundary K between the upstream transfer region Sa and the downstream transfer region Sb (FIG. 1). 13 (B)). Note that the nip pressure at the boundary K is changed by the offset angle of the secondary transfer roll 106 with respect to the auxiliary roll 108 (the aforementioned offset angle θa (see FIG. 11)) and the secondary transfer roll 106 to the intermediate transfer belt 102. I changed the amount of bite. Further, it was confirmed that the toner image Tw did not cause toner scattering Ts at the primary transfer stage to the intermediate transfer belt 102.

  As an evaluation condition, the secondary transfer roll 106 was made of SUS and coated with a CO and ECO conductive rubber layer on a shaft having an outer diameter of 15 [mm] to an outer diameter of 28 [mm]. The electrical resistance of the secondary transfer roll 106 is 8.0 [logΩ] when 100 [V] is applied. The secondary transfer roll 106 was applied with a superimposed voltage obtained by superimposing an AC voltage having an amplitude of 8 [kV] and a frequency of 150 [Hz] on a DC voltage of 0.5 [kV].

  The auxiliary roll 108 was made of SUS and coated with a CO, ECO-based conductive rubber layer on a shaft having an outer diameter of 14 [mm] to an outer diameter of 20 [mm]. The electric resistance of the auxiliary roll 108 is 6.4 [logΩ] when 1500 [V] is applied. The auxiliary roll 108 was grounded.

  The intermediate transfer belt 102 is made of polyimide and has a thickness of 80 [μm]. The volume resistance of the intermediate transfer belt 102 was 10.0 [log Ω · cm] as measured by applying 500 [V] for 5 seconds under a load of 19.6 [N]. . As a volume resistance measuring device, R8340A digital ultrahigh resistance / microammeter (manufactured by Advantest) and UR probe MCP-HTP12 (manufactured by Dia Instruments Co., Ltd.) were used. The measurement environment was 22 [° C.] and 55 [%]. Further, the moving speed of the intermediate transfer belt 102 was 110 [mm / s], and the recording paper P used was a lazac 250 gsm.

  The evaluation of toner scattering Ts is ○ when the scattering is almost invisible visually, a slight scattering is visually observed partially, but the acceptable level is Δ, and the scattering is unacceptable visually. As x, a three-stage evaluation was performed. The toner scattering Ts was evaluated by changing the offset angle of the secondary transfer roll 106 with respect to the auxiliary roll 108 and the amount of biting of the secondary transfer roll 106 into the intermediate transfer belt 102 as described above.

  Specifically, the offset angle is 22.8, 30.8, 33.6, 36.5, 39.6, 42.7 [°], and the biting amount is constant at 0.9 [mm]. Evaluations were made from (1) to level (6) and the level (7) set for comparison. Level (7) has an offset angle of 30.8 [°] and a biting amount of 2.0 [mm].

  For the levels (2), (4), and (5), the nip pressure at the boundary K (see FIG. 5B) was measured and compared. The nip pressure was measured by sandwiching a tactile sensor (manufactured by Nitta Corporation) between the intermediate transfer belt 102 and the secondary transfer roll 106 and reading the numerical value after 30 seconds had elapsed. As a result, the level (2) was 0.01 [MPa], the level (4) was 0.02 [MPa], and the level (3) was 0.03 [MPa]. Here, the evaluation result of the toner scattering Ts is shown in Table 1.

  As shown in Table 1, the toner scattering state is x at levels (1), (2), (3), and (7), Δ at level (4), and ◯ at levels (5) and (6). It was. That is, it was found that if the nip pressure at the boundary K is 0.03 [MPa] or more, toner scattering is suppressed. Based on these evaluation results, in the transfer apparatus 100 according to the first embodiment (see FIG. 3A), the offset angle θa is 39.6 [°], the biting amount is 0.9 [mm], and the angles described above. θb = 15 [°].

  FIG. 3B shows a graph Gc of nip pressure (pressure distribution) in the secondary transfer portion N2 (see FIG. 3A) of the transfer apparatus 100. The graph Gc shows that the nip pressure at the boundary K (boundary position NP1 as an example of the set position) between the upstream transfer area Sa and the downstream transfer area Sb is Pa, and the nip pressure (maximum) at the maximum position NP2 in the downstream transfer area Sb. Pressure) is Pd. Here, in the transfer apparatus 100, the nip pressure Pa at the boundary K is set to 0.03 [MPa]. In the configuration in which the nip pressure is smaller than 0.03 [MPa] at the boundary K even if the nip pressure is 0.03 [MPa] or more on the inlet side with respect to the central portion of the upstream transfer region Sa, The effect of this embodiment cannot be obtained. This is because the binding force of the toner due to the nip pressure is reduced. That is, it is a necessary condition that the nip pressure near the boundary K is 0.03 [MPa] or more.

(Function)
Next, the operation of the first embodiment will be described.

  As shown in FIG. 4, the toner image TA on the intermediate transfer belt 102 is transferred onto the recording paper P in the secondary transfer portion N <b> 2 of the transfer device 100. At this time, in the upstream transfer area Sa, the toner image TA is pressed against the recording paper P by the secondary transfer roll 106 and the auxiliary roll 108. Then, the toner image TA enters the downstream transfer region Sb in a pressurized state, and is transferred to the recording paper P by the action of the transfer electric field E.

  Here, even if the toner forming the toner image TA is vibrated by the application of the superimposed voltage from the power source 120, a nip pressure of 0.03 [MPa] acts on the boundary K (see FIG. 3B). . For this reason, in the transfer apparatus 100, the vibration (movement) of the toner in the peripheral portion of the boundary K including the boundary K is restricted as compared with the configuration in which the nip pressure at the boundary K is lower than 0.03 [MPa]. In this state, the transfer electric field E acts. As a result, in the transfer device 100, the toner is prevented from being transferred and scattered (scattered) in the conveyance direction (A direction) of the recording paper P.

  In the image forming apparatus 10, as shown in FIG. 13A, toner scattering at the secondary transfer portion N2 is suppressed, so that the nip pressure acting on the boundary K is lower than 0.03 [MPa]. As compared with the configuration having the above, image defects due to toner scattering are suppressed.

  The transfer device 100 is configured such that the secondary transfer roll 106 presses the intermediate transfer belt 102 and the recording paper P toward the auxiliary roll 108. For this reason, in the transfer device 100, compared with the case where the intermediate transfer belt 102 and the recording paper P are not configured to pressurize the recording paper P toward the auxiliary roll 108, the applied pressure in the upstream transfer area Sa and the downstream transfer area Sb is increased. The adjustment becomes easier.

  Furthermore, since the secondary transfer roll 106 also serves as a setting unit for the secondary transfer portion N2 in the transfer device 100, the configuration of the transfer device 100 is compared to a configuration in which the secondary transfer roll 106 does not also serve as a setting unit. Simple configuration.

[Second Embodiment]
Next, an example of a transfer device and an image forming apparatus according to the second embodiment of the present invention will be described. Note that the same reference numerals as those in the first embodiment are given to the same members and parts as those in the first embodiment described above, and the description thereof is omitted.

  FIG. 7A shows the secondary transfer portion N2 and its peripheral portion of the transfer device 130 according to the second embodiment. The transfer device 130 is provided in place of the transfer device 100 (see FIG. 1) in the image forming apparatus 10 (see FIG. 1) of the first embodiment. The transfer device 130 has the same configuration as that of the transfer device 100 except for the secondary transfer portion N2.

  The transfer device 130 includes an intermediate transfer belt 102, a secondary transfer roll 106, an auxiliary roll 108, and a winding roll 132 as an example of a setting unit and a pressing member. The auxiliary roll 108 is grounded, and a superimposed voltage is applied to the secondary transfer roll 106 from a power source 120 (see FIG. 4).

  As an example, the winding roll 132 is a roll having a smaller diameter than the auxiliary roll 108, and is disposed on the −X side of the auxiliary roll 108 inside the intermediate transfer belt 102, and the outer peripheral surface thereof is the same as the inner peripheral surface of the intermediate transfer belt 102. In contact. Further, the winding roll 132 is rotatable around the shaft portion along the Z direction, like the secondary transfer roll 106. Further, the winding roll 132 is electrically floated (not grounded).

  Here, the intermediate transfer belt 102 is pressed (projected) to the −Y side by being wound around the winding roll 132. Thus, a part of the outer peripheral surface of the intermediate transfer belt 102 is wound around a part of the outer peripheral surface of the secondary transfer roll 106 (in the range of the central angle θc). Note that the offset angle θa <the center angle θc. Thus, the winding roll 132 presses the intermediate transfer belt 102 against the secondary transfer roll 106 so as to widen the secondary transfer portion N2.

  FIG. 7B shows a graph Gd of the nip pressure (pressure distribution) in the secondary transfer portion N2 (see FIG. 7A) of the transfer device 130. The graph Gd shows that the nip pressure at the boundary K (boundary position NP3 as an example of the set position) between the upstream transfer area Sa and the downstream transfer area Sb is Pe (> 0.03 [MPa]), and the downstream transfer area Sb. The nip pressure (maximum pressure) at the maximum position NP4 is Pf (> Pe). In the present embodiment, as an example, the nip pressure Pe is set to 0.04 [MPa]. FIG. 7B does not show actual values (absolute values). Further, the width of the upstream transfer area Sa in the moving direction (A direction) of the recording paper P is wider than that in the first embodiment.

(Function)
Next, the operation of the second embodiment will be described.

  As shown in FIGS. 7A and 7B, the toner image TA on the intermediate transfer belt 102 is transferred onto the recording paper P in the secondary transfer portion N <b> 2 of the transfer device 130. At this time, even if the toner forming the toner image TA tries to vibrate, a nip pressure of 0.04 [MPa] acts on the boundary K. For this reason, in the transfer device 130, the vibration (movement) of the toner around the boundary K including the boundary K is restricted as compared with the configuration in which the nip pressure at the boundary K is lower than 0.03 [MPa]. The transfer electric field acts in the state. Thereby, in the transfer device 130, the toner is suppressed from being scattered in the conveyance direction (A direction) of the recording paper P.

  Further, the transfer device 130 has a configuration in which the winding roll 132 presses (presses) the intermediate transfer belt 102 toward the secondary transfer roll 106, so that the nip pressure can be changed by changing the position of the winding roll 132. Is changed. Thereby, in the transfer device 130, the nip pressure (pressing force) in the upstream transfer region Sa and the downstream transfer region Sb can be easily adjusted as compared with the configuration in which the winding roll 132 is not provided.

  Furthermore, since the nip pressure at the boundary K is changed by changing the position of the winding roll 132 to the Y side or the −Y side, the transfer device 130 has a boundary K compared to a configuration in which the winding roll 132 is not provided. This makes it easy to change the nip pressure.

(Modification)
FIG. 8A shows a secondary transfer portion N2 of the transfer device 140 and its peripheral portion as a modification of the transfer device 130 (see FIG. 7A). The transfer device 140 has the same configuration as the transfer device 130 except for the secondary transfer portion N2.

  The transfer device 140 is configured such that the winding roll 132 of the transfer device 130 is brought close to the auxiliary roll 108 side, and the intermediate transfer belt 102 is sandwiched between the winding roll 132 and the secondary transfer roll 106. A part of the outer peripheral surface of the intermediate transfer belt 102 is wound around a part of the outer peripheral surface of the secondary transfer roll 106 (in the range of the central angle θd). The center angle θd is an angle formed by the line segment AB and the line segment AC connecting the rotation center positions OA and OC, where the rotation center position of the winding roll 132 is OC. Note that the offset angle θa <the center angle θd. As described above, even when the winding roll 132 directly presses the intermediate transfer belt 102 against the secondary transfer roll 106, the same operation as that of the transfer device 130 can be obtained.

  FIG. 8B shows a graph Ge of the nip pressure (pressure distribution) in the secondary transfer portion N2 (see FIG. 8A) of the transfer device 140. In the graph Ge, the nip pressure at the boundary K (boundary position NP6 as an example of the set position) between the upstream transfer area Sa and the downstream transfer area Sb is Pe (> 0.03 [MPa]). Further, in the graph Ge, the peak pressure at the position NP5 of the upstream transfer region Sa is Pg, and the maximum pressure at the maximum position NP7 of the downstream transfer region Sb is Pf (> Pg). As an example, the nip pressure Pe = 0.04 [MPa]. Note that FIG. 8B does not show actual values (absolute values). Further, the width of the upstream transfer area Sa in the moving direction (A direction) of the recording paper P is wider than that in the first embodiment.

[Third embodiment]
Next, an example of a transfer device and an image forming apparatus according to the third embodiment of the present invention will be described. The same reference numerals as those in the first and second embodiments are given to the same members and parts as those in the first and second embodiments described above, and the description thereof is omitted.

  FIG. 9A shows the secondary transfer portion N2 and its peripheral portion of the transfer device 150 according to the third embodiment. The transfer device 150 is provided in place of the transfer device 100 (see FIG. 1) in the image forming apparatus 10 (see FIG. 1) of the first embodiment. The transfer device 150 has the same configuration as the transfer device 100 except for the secondary transfer portion N2.

  The transfer device 150 includes an intermediate transfer belt 102, a transfer member, a setting unit, a secondary transfer roll 152 as an example of a pressure member, and an auxiliary roll 108. The auxiliary roll 108 is grounded, and a superimposed voltage is applied to the secondary transfer roll 152 from the power source 120 (see FIG. 4).

  As an example, the secondary transfer roll 152 is a foam rubber roll whose base layer is made of foamed epichlorohydrin rubber, and has an outer diameter larger than the outer diameter of the secondary transfer roll 106 (shown by a broken line) of the first embodiment. It is said that. In addition, the outer peripheral surface of the secondary transfer roll 152 is in contact with the outer peripheral surface of the intermediate transfer belt 102 and can rotate around the shaft portion along the Z direction. Further, in the secondary transfer roll 152, an angle formed by a straight line V passing through the rotation center position OD and along the Y direction and a line segment BD connecting the rotation center positions OD and OB is θe.

  FIG. 9B shows a graph Gf of nip pressure (pressure distribution) in the secondary transfer portion N2 (see FIG. 9A) of the transfer device 150. The graph Gf shows that the nip pressure at the boundary K (boundary position NP8 as an example of the set position) between the upstream transfer area Sa and the downstream transfer area Sb is Ph (> 0.03 [MPa]), and the downstream transfer area Sb. The nip pressure (maximum pressure) at the maximum position NP9 is Pi (> Ph). In the present embodiment, as an example, the nip pressure Ph is set to 0.04 [MPa]. FIG. 9B does not show actual values (absolute values).

(Function)
Next, the operation of the third embodiment will be described.

  As shown in FIGS. 9A and 9B, the toner image TA on the intermediate transfer belt 102 is transferred onto the recording paper P in the secondary transfer portion N2 of the transfer device 150. At this time, even if the toner forming the toner image TA tries to vibrate, a nip pressure of 0.04 [MPa] acts on the boundary K. For this reason, in the transfer device 150, the vibration (movement) of the toner around the boundary K including the boundary K is restricted as compared with the configuration in which the nip pressure at the boundary K is lower than 0.03 [MPa]. The transfer electric field acts in the state. Thereby, in the transfer device 150, the toner is suppressed from being scattered in the conveyance direction (A direction) of the recording paper P.

  Further, since the nip pressure of the transfer device 150 is changed by changing the outer diameter of the secondary transfer roll 152, it is not necessary to use another pressure member, and the number of parts is reduced.

  In addition, this invention is not limited to said embodiment.

  FIG. 10A shows a secondary transfer portion N2 of the transfer device 160 and its peripheral portion as another modification of the transfer device 130 (see FIG. 7A) of the second embodiment. The transfer device 160 includes a cylindrical transfer drum 162 as an example of an image holding member, a secondary transfer roll 106, and a pressure block 164 as an example of a setting unit and a pressure member. The transfer drum 162 is rotatably supported at both ends in the axial direction, and the toner image TA is primarily transferred at a portion (not shown) of the outer peripheral surface.

  The pressure block 164 is arranged in a non-contact state with the transfer drum 162 and the secondary transfer roll 106 on the inlet side of the secondary transfer portion N2. Specifically, the pressure block 164 has a facing surface 164 </ b> A that is disposed to face the outer peripheral surface of the transfer drum 162, and a facing surface 164 </ b> B that is disposed to face the outer peripheral surface of the secondary transfer roll 106.

  The distance between the facing surface 164A and the outer peripheral surface of the transfer drum 162 is such that the toner image TA does not come into contact with the facing surface 164A. The distance between the facing surface 164B and the outer peripheral surface of the secondary transfer roll 106 is such that the recording paper P (not shown) can enter in the A direction. The opposing surface 164B is arranged such that the recording paper P that has entered between the opposing surface 164B and the secondary transfer roll 106 contacts the opposing surface 164B and is pressed against the outer peripheral surface of the transfer drum 162 (transfer drum 162). Incline (so that the winding area is widened).

  As described above, even if the member for performing the intermediate transfer is a drum instead of a belt, the recording paper P is pressed toward the secondary transfer roll 106 by the pressure block 164. The same operation as that of the transfer devices 130 and 140 is obtained.

  FIG. 10B shows a secondary transfer portion N2 and its peripheral portion of the transfer device 170 as a modification of the transfer device 150 (see FIG. 9A) of the third embodiment. The transfer device 170 has a transfer drum 162 and a secondary transfer roll 152, and does not have an intermediate transfer belt. As described above, even if the member that performs the intermediate transfer is not a belt but a drum, the recording paper P is pressed by the secondary transfer roll 152, and thus the same operation as that of the transfer device 150 is obtained.

  The transfer member and the pressure member are not limited to rotating rolls, and may be members that are fixed and on which the intermediate transfer belt 102 slides. Further, the transfer member and the pressure member are not limited to one and may be composed of a plurality.

10 Image forming apparatus 60 Image forming section (an example of developer image forming means)
100 transfer device 102 intermediate transfer belt (an example of an image holding member and a belt)
106 Secondary transfer roll (an example of a transfer member, setting means, and pressure member)
108 Auxiliary roll (an example of a transfer member, setting means, and pressure member)
120 power supply (an example of voltage application means)
130 Transfer Device 132 Winding Roll (Example of Setting Unit and Pressing Member)
140 Transfer device 150 Transfer device 152 Secondary transfer roll (an example of transfer member, setting means, and pressure member)
160 Transfer Device 162 Transfer Drum (Example of Image Holding Member)
164 Pressure block (an example of setting means and pressure member)
170 Transfer device N2 Secondary transfer unit (an example of transfer unit)
NP1 boundary position (example of setting position)
NP2 Maximum position NP3 Boundary position (Example of setting position)
NP4 Maximum position NP6 Boundary position (Example of setting position)
NP7 Maximum position NP8 Boundary position (Example of setting position)
NP9 Maximum position Sa Upstream transfer area Sb Downstream transfer area

Claims (5)

A transfer member that is rotatably provided and forms a transfer portion of the developer to the recording medium between the image holding member that holds the developer image; and
Voltage applying means for applying a voltage of at least an alternating current component between the image holding member and the transfer member;
In the transfer section, the amount of developer transferred by application of the voltage at a position upstream of the maximum position where the amount of developer transferred becomes the maximum in the rotation direction of the transfer member is the maximum position. Setting means for setting the pressure distribution in the transfer section so that the pressure acting on the setting position that is 40% of the amount of the developer transferred in is 0.03 [MPa] or more;
A transfer device.   The transfer device according to claim 1, wherein the setting unit includes a pressure member that pressurizes the image holding member or the recording medium toward the transfer member. The image holding member is an endless belt provided so as to be able to move around,
3. The transfer device according to claim 1, wherein the setting unit includes a pressing member that presses the belt against the transfer member so as to spread the transfer unit upstream in the rotation direction.   The transfer device according to claim 1, wherein the transfer member constitutes at least a part of the setting means. Developer image forming means for forming a developer image on the image holding member;
The transfer device according to claim 1, wherein the developer image held on the image holding member is transferred to a recording medium.
An image forming apparatus.