JP2010048848A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve transfer efficiency in transferring an image on a photoreceptor drum to an intermediate transfer belt. <P>SOLUTION: An image forming apparatus includes: a first photoreceptor drum (10Y); a second photoreceptor drum (10M); a transfer belt (80) coming into contact with the first photoreceptor drum and second photoreceptor drum in this order; a transfer roller 51Y; and a transfer roller 51M. The apparatus further includes: a pressure roller (62), which is disposed on the opposite surface side of an image support surface 85 from a virtual reference plane L1 including the abutting position of the first photoreceptor drum and the transfer roller 51Y and the abutting position of the second photoreceptor drum and the transfer roller 51M, to press the transfer belt to the image support surface 85 side apart from the virtual reference surface L1; and a bias application roller 63, which is disposed at the side of the image support surface 85 and rather closer to the second photoreceptor drum than the pressure roller to come into contact with the transfer belt pressed by the pressure roller at the side of the image support surface 85. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and in particular, can be suitably applied to an image forming apparatus that uses a liquid developer in which toner is dispersed in a carrier liquid.

There is known an image forming apparatus including a photosensitive drum, a transfer member such as an intermediate transfer belt or a paper conveyance belt, and a transfer member (transfer roller or the like) that contacts the photosensitive drum via the transfer member. . As such an image forming apparatus, as shown in FIG. 5, with the intermediate transfer belt 80 sandwiched, the transfer roller 51Y is brought into contact with the upper end of the photosensitive drum 10Y, and the intermediate transfer belt 80 is brought into contact with the photosensitive drum 10Y. Is disclosed (see FIG. 1 of Patent Document 1).
JP 2001-166611 A.

  However, in this conventional example, it is desired to improve the transfer efficiency when transferring the image on the photosensitive drum 10Y to the intermediate transfer belt 80.

  The present invention has been made in view of such circumstances, and an image forming apparatus capable of improving transfer efficiency when transferring an image on a photosensitive drum to a recording medium held on an intermediate transfer belt or a paper transport belt. The purpose is to provide.

  As a result of repeated studies to achieve the above-mentioned object, the present inventors have obtained the following points. That is, as shown in FIG. 5, when the intermediate transfer belt 80 is wound around the photosensitive drum 10Y to form an arc-shaped nip N, the following two can be divided into sections for convenience. That is, a section (hereinafter referred to as “upstream winding nip section A”) located upstream of the contact position between the primary transfer roller 51Y and the photosensitive drum 10Y along the moving direction of the intermediate transfer belt 80. ) And a section located on the downstream side in the moving direction of the intermediate transfer belt 80 (hereinafter referred to as “downstream winding nip section B”).

  On the other hand, the present inventors have found that it is effective to improve the transfer efficiency if the nip N is provided in an arc shape and the contact amount between the intermediate transfer belt 80 and the photosensitive drum 10Y is increased. On the other hand, in this arc-shaped nip N, the width of the upstream winding nip section A (hereinafter referred to as “upstream winding nip width”) is the width of the downstream winding nip section B (hereinafter referred to as “downstream”). It has also been found that the transfer efficiency decreases as the length becomes relatively longer than the “wrapping nip width”). Details of this point will be described later.

As a result of further research, the inventors have found that the transfer efficiency can be improved by adjusting the upstream winding nip width and the downstream winding nip width by a method using a pressing roller, a bias application roller, or the like. The present invention was completed.
An image forming apparatus according to a first aspect of the present invention develops a first photosensitive drum on which a liquid developer containing toner particles and a carrier liquid is developed, and a liquid developer containing toner particles and a carrier liquid. The second photosensitive drum, the transfer belt conveyed while bringing the image bearing surface into contact with the first photosensitive drum and the second photosensitive drum in this order, and the first photosensitive drum to the first photosensitive drum. A first transfer member that is in contact with the transfer belt, a second transfer member that is in contact with the second photosensitive drum with the transfer belt in between, the first photosensitive drum, and the first transfer member The transfer position is disposed on the opposite side of the image bearing surface from a virtual reference surface including a contact position of the member and a contact position of the second photosensitive drum and the second transfer member. Pushing the belt toward the image bearing surface side with respect to the virtual reference surface And the roller contacts with the image bearing surface of the transfer belt and the transfer belt which is pressed by the pressing roller, and having a bias applying roller to which a bias is applied, the.

  In the image forming apparatus according to the first aspect, a cleaning member may be brought into contact with the bias application roller to remove the liquid developer from the bias application roller. The contact position between the bias applying roller and the transfer belt may be on the virtual reference plane or above the virtual reference plane in the vertical direction.

  An image forming apparatus according to a second aspect of the present invention includes a first photosensitive drum, a second photosensitive drum, an image carrying surface of the first photosensitive drum, and the second photosensitive drum. A transfer belt that is conveyed while being in contact with each other, a first transfer member that is in contact with the first photosensitive drum with the transfer belt in between, and a transfer belt that is in contact with the second photosensitive drum with the transfer belt in between A second transfer member, a transfer unit for transferring an image transferred to the image carrying surface of the transfer belt after contacting the second photoconductor drum to a recording medium, the first photoconductor drum, Arranged on the opposite surface side of the image bearing surface from a virtual reference surface including a contact position of the first transfer member and a contact position of the second photosensitive drum and the second transfer member. And press the transfer belt closer to the image bearing surface than the virtual reference surface. A pressing roller, and having a bias applying roller that contacts with the pressed the transfer belt and the image bearing surface in the pressing roller.

An image forming apparatus according to a third aspect of the present invention includes a first photosensitive drum, a second photosensitive drum, a recording medium holding surface serving as the first photosensitive drum, and the second photosensitive drum. A recording medium conveyance belt that is conveyed while being in contact with each other, a first transfer member that is in contact with the first photosensitive drum with the paper conveyance belt interposed therebetween, and a conveyance of the recording medium to the second photosensitive drum. A second transfer member that is in contact with the belt, a peeling unit that peels the recording medium from the recording medium conveyance belt after contacting the second photosensitive drum, the first photosensitive drum, and the first photosensitive drum. 1 on the opposite side of the recording medium holding surface from a virtual reference surface including a contact position of one transfer member and a contact position of the second photosensitive drum and the second transfer member. The recording medium transport belt in front of the virtual reference plane. A pressing roller that presses toward the recording medium holding surface; and a bias application roller that is closer to the recording medium holding surface than the virtual reference surface and contacts the opposite side of the recording medium holding surface from the virtual reference surface of the transfer belt It is characterized by having.
Examples of the “recording medium” include paper, film, cloth, and the like.

  In the present invention, it has a collecting member for collecting the developer squeezed by the bias applying roller, and the collecting member is disposed on the vertically lower side of the pressing roller and has an opening on the vertically upper side. May be a feature. In addition, the photosensitive drum cleaning member includes a photosensitive drum cleaning member and a recovery member that recovers the developer removed by the photosensitive drum cleaning member. An opening may be provided on the upper side. Furthermore, a first support member that supports the first photosensitive drum and the second photosensitive drum, a second support member that supports the pressing roller and the bias application roller, a first support member, and And a positioning member that positions the second support member.

  In the image forming apparatus of the present invention, the transfer belt and the paper transport belt are pressed between the first photosensitive drum and the second photosensitive drum by the pressing roller, and thus formed on the first photosensitive drum. In the nip, the width of the downstream winding nip section can be increased. Further, by pressing the transfer belt and the paper transport belt pressed by the pressing roller in the reverse direction by the bias application roller, the upstream winding nip section can be eliminated in the nip formed on the second photosensitive drum. The width of the upstream winding nip section can be reduced. For this reason, the transfer efficiency from the first photosensitive drum and the second photosensitive drum to the transfer belt and the paper transport belt is improved.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the embodiment of the present invention, a liquid developing type image forming apparatus will be described as an example. However, the present invention is also applicable to an image forming apparatus of a dry electrophotographic process.

A. Example 1
a. Basic Configuration First, the basic configuration of the image forming apparatus A according to the first embodiment will be briefly described with reference to FIGS. The image forming apparatus A includes a total of four image forming units 5Y, 5M, 5C, and 5K of yellow (Y), magenta (M), cyan (C), and black (K), an intermediate transfer belt 80, and a first transfer belt 80. 1st roller 81, second roller 82, support rollers 61Y, 61M, 61C, 61K, bias application rollers 62Y, 62M, 62C, 62K, backup rollers 63Y, 63M, 63C, 63K, and secondary transfer And a unit 90.

  The image forming units 5Y, 5M, 5C, and 5K are horizontally arranged between the first roller 81 and the second roller 82, and the photosensitive drums 10Y, 10M, 10C, and 10K, and the latent image eraser 6Y. , 6M, 6C, 6K, cleaning devices 8Y, 8M, 8C, 8K, charging members 11Y, 11M, 11C, 11K, exposure units 12Y, 12M, 12C, 12K, and developing units 30Y, 30M, 30C, 30K And photosensitive drum squeeze devices 70Y, 70M, 70C, and 70K, and primary transfer rollers 51Y, 51M, 51C, and 51K. In FIG. 3, which will be described later, the relationship among the photosensitive drum, the primary transfer roller, the intermediate transfer belt, and the like is three-dimensionally displayed. A schematic view of a “cross-sectional portion perpendicular to the substantially central portion in the axial direction of the rotation shaft” is displayed.

  Each of the photosensitive drums 10Y, 10M, 10C, and 10K is configured in a substantially cylindrical shape having a photosensitive layer formed on the outer peripheral surface, and all have the same outer diameter (80 mm). Further, the outer peripheral surface thereof rotates in the direction of following the “corresponding latent image eraser, cleaning device, charging member, exposure unit, developing unit, and photosensitive drum squeeze device” in this order. Further, the photosensitive layers of the photosensitive drums 10Y, 10M, 10C, and 10K are formed of an amorphous silicon image carrier.

  Each of the charging members 11Y, 11M, 11C, and 11K is configured using a corona charger, and a bias having the same polarity as the charging polarity of the liquid developer is applied from a power supply device (not shown). The charging members 11Y, 11M, 11C, and 11K charge the corresponding photosensitive drums 10Y, 10M, 10C, and 10K, respectively. Each of the charging members 11Y, 11M, 11C, and 11K can be constituted by a charging roller. Further, the exposure units 12Y, 12M, 12C, and 12K form latent images by irradiating the corresponding photosensitive drums 10Y, 10M, 10C, and 10K with a light image from an LED head, a laser scanning optical system, or the like.

  Each of the developing units 30Y, 30M, 30C, and 30K includes developing rollers 20Y, 20M, 20C, and 20K, and developer containers 31Y, 31M, 31C, and 31K that store liquid developers of respective colors (Y, M, C, and K). And developer supply rollers 32Y, 32M, 32C, 32K for supplying the liquid developer from the developer containers 31Y, 31M, 31C, 31K to the developing rollers 20Y, 20M, 20C, 20K. Then, the latent images formed on the photosensitive drums 10Y, 10M, 10C, and 10K are developed by the developing units 30Y, 30M, 30C, and 30K. In the present embodiment, a liquid developer composed of toner particles and a carrier liquid (for example, a non-volatile liquid carrier) is used as the developer contained in each developer container 31Y, 31M, 31C, 31K. Used.

  The photosensitive drum squeeze device 70 is disposed on the downstream side of the developing unit 30 in the rotation direction of the photosensitive drum 10, and collects an excess of the developer on the photosensitive drum 10. Each of the photosensitive drum squeeze devices 70Y, 70M, 70C, and 70K includes two photosensitive member squeeze rollers 71, a cleaning blade 72 disposed for each squeeze roller 71, and a collection container 73.

A photoreceptor squeeze roller (diameter: 20 mm) 71 has a metal base portion and a substantially cylindrical surface layer portion (thickness 2) mounted on the outer peripheral portion (for example, urethane rubber) of the base portion while being substantially cylindrical. 0.5 mm, hardness; JIS-30 ° electric resistance; volume resistance value when applying 250V is 10 ⁴ Ωcm). Further, the squeeze roller 71 is rotated in the opposite direction while being in sliding contact with the photosensitive drums 10Y, 10M, 10C, and 10K to remove the carrier liquid from the photosensitive drums 10Y, 10M, 10C, and 10K. Each cleaning blade 72 is configured by using an elastic body such as rubber, and is brought into contact with the corresponding squeeze roller 71 in a pressed state to scrape off and remove the carrier liquid remaining on the squeeze roller 71. Further, the collection container 73 as a collection member collects the developer scraped off by each cleaning blade 72.

  The first roller 81 and the second roller 82 are disposed at a predetermined interval in the horizontal direction. Further, the intermediate transfer belt 80 is configured to be endless, is stretched between the first roller 81 and the second roller 82, and is rotated and driven by the second roller 82 that constitutes a driving roller. It circulates between the roller 81 and the second roller 82. The first roller 81 is a tension roller for applying tension to the intermediate transfer belt 80.

The intermediate transfer belt 80 is a belt made of conductive polyimide (belt width: 324 mm, thickness: 0.08 mm, electric resistance; volume resistance value when applied with 250 V is 10 ¹⁰ Ωcm, and surface resistance is 10 ¹¹ Ω / □), and the image bearing surface 85 is constituted by the outer circumferential surface thereof. However, instead of the intermediate transfer belt 80, a base material layer (thickness; 80 μm) constituted by using conductive polyimide and an elastic layer (thickness; 200 μm, JIS-A30) constituted by urethane rubber. Degree) and a coating layer (thickness; 200 μm) made of fluorine resin (PFA or the like) or fluorine rubber or the like, laminated in this order (belt width: 324 mm, thickness: 290 μm, It is also possible to use electric resistance of all layers; volume resistance of 10 ¹⁰ Ωcm).

The primary transfer rollers (outer diameter: 30 mm) 51Y, 51M, 51C, and 51K constitute transfer members and are so-called “bias rollers”. The photosensitive drum 10 is in contact with the drums 10Y, 10M, 10C, and 10K with the intermediate transfer belt 80 interposed therebetween. The primary transfer rollers 51Y, 51M, 51C, and 51K include a metal base portion and a substantially cylindrical surface layer portion (thickness 5.0 mm, material) that is substantially cylindrical and is attached to the outer periphery of the base portion. Urethane rubber, hardness; JIS-30 °, electrical resistance; 10 ⁴ Ωcm in volume resistance value when 250 V is applied). The primary transfer rollers 51Y, 51M, 51C, and 51K are pressed in the direction of the rotation shafts 14Y, 14M, 14C, and 14K of the corresponding photosensitive drums 10Y, 10M, 10C, and 10K by using biasing means (springs or the like). A constant load (primary transfer load; 5 kgf) is applied toward the intermediate transfer belt 80.

  When a bias is applied to each of the primary transfer rollers 51Y, 51M, 51C, and 51K, the toner images of the respective colors attached to the developed photosensitive drums 10Y, 10M, 10C, and 10K are applied to the image carrying surface 85 of the intermediate transfer belt 80. The image is transferred, and a full-color toner image (a full-color toner image or a single-color toner image) is formed on the image carrying surface 85 of the intermediate transfer belt 80. As the “transfer member”, not only a transfer roller but also a transfer member including an electrode plate formed in a substantially arc shape can be exemplified.

  The latent image erasers 6Y, 6M, 6C, and 6K and the cleaning devices 8Y, 8M, 8C, and 8K are upstream of the primary transfer rollers 51Y, 51M, 51C, and 51K in the rotational direction of the photosensitive drums 10Y, 10M, 10C, and 10K. On the side, they are arranged in this order. Further, the cleaning devices 8Y, 8M, 8C, and 8K provide “developer remaining on the photosensitive drums 10Y, 10M, 10C, and 10K without moving to the intermediate transfer belt 80 during the primary transfer process”. For removal from 10M, 10C, 10K.

  The support rollers 61Y, 61M, 61C, and 61K constitute “pressing rollers”, and are conveyed from the first roller 81 to the second roller 82 rather than the photosensitive drums 10Y, 10M, 10C, and 10K. Downstream of the intermediate transfer belt 80 in the conveyance direction (hereinafter, this downstream side is expressed as “downstream in the conveyance direction” and the opposite direction is expressed as “upstream in the conveyance direction”) ”. The bias application rollers 62Y, 62M, 62C, and 62K are disposed further “on the downstream side in the transport direction” than the support rollers 61Y, 61M, 61C, and 61K.

  The support rollers 61 </ b> Y, 61 </ b> M, 61 </ b> C, 61 </ b> K are metal rollers (outer diameter: 12 mm) and are “conveyed from the first roller 81 toward the second roller 82 in the intermediate transfer belt 80. "Part" is pressed from above. For this reason, the conveyance path of the intermediate transfer belt 80 meanders and the tension is increased. However, the primary transfer rollers 51Y, 51M, 51C, and 51K may float unintentionally due to the tension of the intermediate transfer belt 80. Is prevented.

  The bias application rollers 62Y, 62M, 62C, and 62K have the same configuration as the above-described photosensitive member squeeze roller 71, and are in sliding contact with the image carrying surface 85 of the intermediate transfer belt 80 in the direction opposite to the moving direction of the image carrying surface 85. Rotate. The bias application rollers 62Y, 62M, 62C, and 62K are applied with a bias having the same polarity as the toner in the liquid developer carried on the image carrying surface 85, and this toner is applied to the image carrying surface 85. Move in the direction of.

  The backup rollers 63Y, 63M, 63C, and 63K are disposed vertically above the corresponding bias application rollers 62Y, 62M, 62C, and 62K. The backup rollers 63Y, 63M, 63C, and 63K press the intermediate transfer belt 80 against the bias application rollers 62Y, 62M, 62C, and 62K. A bias having a polarity different from that of the toner in the liquid developer carried on the image carrying surface 85 can be applied to the backup rollers 63Y, 63M, 63C, and 63K.

  The secondary transfer unit 90 constitutes a “transfer portion”, and includes a secondary transfer roller 91 disposed so as to face the second roller 82 with the intermediate transfer belt 80 interposed therebetween, and a cleaning device 92. I have. Then, at the transfer position where the secondary transfer roller 91 is disposed, the image formed on the intermediate transfer belt 80 is secondary to the recording medium (paper, film, cloth, etc.) conveyed through the recording medium conveyance path L. Transcribed. Further, the image transferred to the recording medium is fixed on the recording medium by a fixing unit (not shown).

b. Characteristic Configuration Next, a characteristic configuration of the image forming apparatus A according to the first embodiment will be described. In each of the photosensitive drums 10Y, 10M, 10C, and 10K constituting the image forming apparatus A, as shown in FIGS. 1 and 2, between the adjacent ones along the conveyance direction of the intermediate transfer belt 80, The relationship between the first photosensitive drum and the second photosensitive drum is established. That is, among the adjacent photoconductor drums (10Y and 10M, 10M and 10C, 10C and 10K), the one located on the “upstream side in the transport direction” is the “first photoconductor drum” and on the downstream side in the transport direction. The one positioned is the “second photosensitive drum”. For this reason, the photosensitive drum 10Y on the “upstream” upstream side in the transport direction constitutes the first photosensitive drum, and the photosensitive drum 10K on the downstream side in the transport direction only constitutes the second photosensitive drum. However, the photosensitive drum 10M and the photosensitive drum 10C positioned at the intermediate portion in the transport direction become the second photosensitive drum in relation to the photosensitive drums (10Y, 10M) on the upstream side in the transport direction, and the transport direction thereof. In relation to the downstream photosensitive drum (10C, 10K), this is the first photosensitive drum.

  In this image forming apparatus A, as shown in FIG. 1, four photosensitive drums 10Y, 10M, 10C, and 10K each having the same outer diameter have the same rotating shafts 14Y, 14M, 14C, and 14K. They are arranged at equal intervals while being aligned in height and parallel (the axis is oriented in a direction perpendicular to the plane of FIG. 1). The contact modes of the primary transfer rollers 51Y, 51M, 51C, and 51K that contact the photosensitive drums 10Y, 10M, 10C, and 10K via the intermediate transfer belt 80 are as follows. That is, as shown in FIG. 2, the primary transfer roller (51Y, 51M, etc.) has its rotating shaft 54J vertically above the rotating shaft (14Y, 14M, etc.) of the corresponding photosensitive drum (10Y, 10M, etc.). In addition, they are arranged in parallel (the axis is oriented in a direction perpendicular to the paper surface of FIG. 2).

  For this reason, the contact positions Y1, M1, C1, and K1 of the primary transfer rollers 51Y, 51M, 51C, and 51K with the corresponding photosensitive drums 10Y, 10M, 10C, and 10K are continuously rotated. In the part located in the upper end of 10M, 10C, 10K, it will exist in the state parallel to rotating shaft 14Y, 14M, 14C, 14K. As shown in FIG. 3, the contact positions (for example, Y1, M1) in the pair of adjacent image forming units (for example, 5Y and 5M) are at the same height position. The virtual reference plane L1 including the contact positions (for example, Y1, M1) of the image portions (for example, 5Y and 5M) is a substantially horizontal surface. In the following description, the “region between the contact position Y1 and the contact position M1” is the first region R1, and the “region between the contact position M1 and the contact position C1” is the second region R2. The “region between the contact position C1 and the contact position K1” is referred to as a third region R3.

  As shown in FIG. 1, the virtual reference planes L1 formed respectively in the first region R1, the second region R2, and the third region R3 are aligned at the same height to form a virtual surface that is flush with the entire surface. To do. A virtual surface set by extending the virtual reference plane L1 formed in the third region R3 toward the secondary transfer unit 90 is referred to as a virtual extension plane L2. Furthermore, a virtual surface that is set by extending the virtual reference surface L1 formed in the first region R1 to the first roller 81 side is referred to as an upstream extended surface L3.

  In each of the regions R1 to R3, one support roller 61Y, 61M, 61C and one bias application roller 62Y, 62M, 62C are disposed, and each support roller 61Y, 61M, 61C is located upstream in the transport direction (first). The bias application rollers 62Y, 62M, and 62C are positioned on the downstream side in the transport direction (second photosensitive drum side).

  As shown in FIG. 2, the intermediate transfer belt 80 passing through the first region R1 is pressed below the virtual reference plane L1 by the support roller 61Y, and then pressed upward by the bias applying roller 62Y. For this reason, in the first region R1, the “downstream winding nip width” is enlarged by the action of the support roller 61Y in the photosensitive drum 10Y (constituting the first photosensitive drum) located upstream in the transport direction, In the photosensitive drum 10M (constituting the second photosensitive drum) located on the downstream side in the conveying direction, the “upstream winding nip width” can be prevented from being enlarged by the action of the bias application roller 62Y. Similarly, also in the second region R2, the “downstream winding nip width” of the photosensitive drum 10M on the upstream side in the transport direction is increased, and the “upstream winding nip width” of the photosensitive drum 10C on the downstream side in the transport direction is increased. Prevention is achieved. Similarly, also in the third region R3, the “downstream winding nip width” of the photosensitive drum 10C on the upstream side in the transport direction is enlarged, and the “upstream winding nip width” of the photosensitive drum 10K on the downstream side in the transport direction is increased. Expansion prevention is achieved.

  Further, since the lower end position of the first roller 81 is above the contact position Y1, the intermediate transfer belt 80 reaches the photosensitive drum 10Y from above the contact position Y1. Therefore, since the intermediate transfer belt 80 contacts the primary transfer roller 51Y and then contacts the photosensitive drum 10Y, the “upstream winding nip width” of the photosensitive drum 10Y is set to “zero”. Further, between the most downstream photosensitive drum 10K and the second roller 82, the support roller 61K causes the intermediate transfer belt 80 to be below the virtual extension plane L2 (that is, below the virtual reference plane L1). In order to press, the “downstream winding nip width” formed on the photosensitive drum 10K is enlarged. As described above, in this embodiment, in all the image forming units 5Y, 5M, 5C, and 5K, a measure for reducing the “upstream winding nip width” and the prevention of the expansion of the “downstream winding nip width”. Measures are taken for.

c. Performance Test Next, a performance test performed to evaluate the performance of the image forming apparatus of each example will be described. This performance test was conducted for the following test examples. This performance test was performed by creating test examples (test examples 1 to 4) in which the formation mode of the nip N was changed in the yellow (Y) image forming portion 5Y of the present embodiment.

b-1. Test Example 1 and Test Example 2
In Test Example 1 and Test Example 2, as shown in FIG. 4A, an upstream winding nip section A is formed in an arc-shaped nip N in which the intermediate transfer belt 80 is wound around the photosensitive drum 10Y. The central angle V2 of the portion constituting the downstream winding nip section B is made larger than the central angle V1 of the portion. For this reason, in Test Example 1 and Test Example 2, the downstream winding nip width is larger than the upstream winding nip width. However, in Test Example 1, the upstream winding nip width is “3 mm” and the downstream winding nip width is “7 mm”, whereas in Test Example 2, the upstream winding nip width is “1 mm”. ”And the downstream winding nip width is“ 7 mm ”.

b-2. Test example 3
In Test Example 3, as shown in FIG. 4B, the arc-shaped nip N is configured only by the downstream winding nip section B. Specifically, in Test Example 3, the upstream winding nip width is “zero mm” and the downstream winding nip width is “7 mm”.

b-3. Test example 4
In Test Example 4, as shown in FIG. 5, the central angle V1 of the portion constituting the upstream winding nip section A in the arcuate nip N and the central angle of the portion constituting the downstream winding nip section B are included. V2 is made equal. Specifically, the upstream winding nip width and the downstream winding nip width are both “7 mm”.

b-4. Method of Performance Test This performance test was performed by calculating the transfer efficiency in the image forming unit 5Y. This “transfer efficiency” is calculated by measuring “change in toner optical density” on the photosensitive drum 10 using “optical measurement of X-Lite”. Specifically, (i) the photosensitive drum is received at a stage before receiving the developer (yellow developer) from the developing unit 30Y, passing through the photosensitive drum squeeze device 70Y, and transferring the image onto the intermediate transfer belt 80. Toner optical density adhering to the outer peripheral surface of 10Y (hereinafter referred to as “toner optical density before transfer”), and (ii) a stage before the image is transferred to the intermediate transfer belt 80 and reaches the cleaning device 8Y. The toner optical density (hereinafter referred to as “post-transfer toner optical density”) adhering to the outer peripheral surface of the photosensitive drum 10 is calculated.

More specifically, the transfer efficiency from the photosensitive drum 10Y to the intermediate transfer belt 80 was calculated using the following equation.
Transfer efficiency [%] =
{("Toner optical density before transfer"-"toner optical density after transfer") / (toner optical density before transfer)} × 100
The performance test was performed with the bias (V) applied to the primary transfer roller 51Y being “−400 V” while the test environment was “room temperature 23 ° C.” and “humidity 65%”. The results of this performance test are shown in FIG.

  FIG. 6 is a chart showing the relationship between “how to wind” and “primary transfer efficiency”. According to this chart, in Test Example 4 in which the upstream winding nip width is equal to the downstream winding nip width, the transfer efficiency remains at “80%” even when the bias (V) reaches “−400 V”. Yes. On the other hand, in Test Example 1 and Test Example 2 in which the downstream winding nip width is larger than the upstream winding nip width, and in Test Example 3 in which the upstream winding nip width is “zero”, the bias (V) Can reach “−400 V”, a high transfer efficiency of “90%” or more can be obtained. According to the above performance test, it can be seen that the transfer efficiency is further improved as the upstream winding nip width is reduced or the downstream winding nip width is increased.

  The present inventors assume the reason why the above results are obtained as follows. That is, as a means for improving the transfer efficiency, it is considered effective to form an arc-shaped nip N and increase the contact amount of the intermediate transfer belt 80 to the photosensitive drum 10Y. However, in the case where the upstream winding nip section A is provided, the toner layer on the intermediate transfer belt 80 and the photosensitive drum 10Y in the portion A1 (see FIG. 5) where the electric field is not applied in the upstream winding nip section A. When contacted, the toner layer is mechanically pressed against the photosensitive drum 10, and the toner layer becomes difficult to be separated from the photosensitive drum 10Y, or the electric charge of the toner is caused by discharge in the minute gap portion of the upstream winding nip section A. It is considered that the transfer efficiency is lowered due to instability.

  For this reason, as the upstream winding nip width becomes relatively larger than the downstream winding nip width, the transfer efficiency of the intermediate transfer belt 80 with respect to the photosensitive drum 10 is increased. Decreases. In other words, when the upstream winding nip width is relatively small or the downstream winding nip width is relatively large, “the amount of contact of the intermediate transfer belt 80 with respect to the photosensitive drum 10Y by forming an arc-shaped nip N”. High transfer efficiency can be obtained in combination with "enlarging".

c. Effects of Embodiment 1 In Embodiment 1, the upstream winding nip width is relatively small while the arc-shaped nip portion N is formed in each of the image forming portions 5Y, 5M, 5C, and 5K, and the downstream winding nip width is reduced. By adopting a measure for relatively increasing the image quality, it is possible to improve transfer efficiency in the entire image forming apparatus A as a color machine. In addition, the form of the nip portion N is improved by a simple method of improving the arrangement of the components (support rollers 61Y, 61M, 61C, bias applying rollers 62Y, 62M, 62C) constituting the image forming apparatus A. In order to improve transfer efficiency.

  Next, a modification of the first embodiment will be described. In the image forming apparatuses B to D of the first to third modifications shown below, as shown in FIGS. 7 to 9, the cleaning blade V is applied to the bias applying rollers 62Y, 62M, 62C, and 62K. Touching. The cleaning blade V is configured by using an elastic body such as rubber and is in contact with the corresponding bias application rollers 62Y, 62M, 62C, and 62K in a pressed state, and the carrier liquid on the bias application rollers 62Y, 62M, 62C, and 62K. Scrape and remove. In the image forming apparatus B according to the first modification shown in FIG. 7, collection containers 64M, 64M, 64C, and 64K are disposed vertically below the cleaning blade V. The collection containers 64M, 64M, 64C, and 64K have an opening that opens vertically upward, and collect the developer scraped off by the cleaning blade V.

  Further, in the image forming apparatus C according to the second modification shown in FIG. 8, a collection container 73 constituting the photosensitive drum squeeze devices 70Y, 70M, 70C, and 70K is disposed vertically below the cleaning blade V. The collection container 73 also has an opening that opens vertically upward, and collects the developer scraped off by the cleaning blade V. Furthermore, in the image forming apparatus D according to the third modification shown in FIG. 9, large collection containers 65Y, 65M, and 65C are disposed in the first to third regions R1 to R3, and the photosensitive member. A large collection container 65K is also disposed in an area (hereinafter referred to as “fourth area”) R4 between the drum 10K and the secondary transfer unit 90. The opening that opens above the collection containers 65Y, 65M, 65C, 65K covers from the vertical lower side of the support rollers 61Y, 61M, 61C, 61K to the vertical lower side of the cleaning blade V, and the cleaning blade V scrapes. In addition to the dropped developer, it is also possible to collect the developer that drops from “the portion of the intermediate transfer belt 80 pressed downward by the support rollers 61Y, 61M, 61C, and 61K”.

  Furthermore, as a modification of the first embodiment, a fourth modification shown in FIG. 10A and a fifth modification shown in FIG. 10B can be exemplified. In FIGS. 10A and 10B, only the first region R1 is illustrated, and the second region R2, the third region R3, and the fourth region R4 are not illustrated. Here, in the image forming apparatus according to the fourth modification example, the “photosensitive drum squeeze device” is vertically below the “portion of the intermediate transfer belt 80 pressed downward by the support rollers 61Y, 61M, 61C, 61K”. 70 Y, 70 M, 70 C, and 70 K constituting recovery containers 73 ”are arranged, and the opening of the recovery container 73 is opened vertically upward. With this image forming apparatus, the developer falling below the support rollers 61Y, 61M, 61C, 61K can also be collected.

  In the image forming apparatus according to the fifth modification, the cleaning blade V is brought into contact with the bias applying rollers 62Y, 62M, 62C, and 62K, and the collection containers 64Y, 64M, 64C, and 64K are vertically below the cleaning blade V. The relay container 66T is disposed vertically below the support rollers 61Y, 61M, 61C, and 61K and above the collection containers 64Y, 64M, 64C, and 64K. The relay container 66T temporarily collects the developer falling from “the portion of the intermediate transfer belt 80 pressed downward by the support rollers 61Y, 61M, 61C, 61K”. Then, the developer is discharged from the first discharge port 66H toward the “collection container 73 constituting the photosensitive drum squeeze devices 70Y, 70M, 70C, and 70K”, or the recovery containers 64Y and 64M are discharged from the second discharge port 66I. , 64C, 64K.

  According to each of the above modifications, in addition to the effect of the first embodiment, the effect that the contamination with the carrier liquid can be prevented is obtained. It should be noted that the above modification can be configured not as a modification of the first embodiment but as modifications of the second to fifth embodiments described later. In Example 1 and each modification, the lower end position of the first roller 81 is set above the contact position Y1, and the “upstream winding nip width” of the photosensitive drum 10Y is set to “zero”. The lower end position of the first roller 81 and the contact position Y1 may be the same height, or the lower end position of the first roller 81 is disposed below the contact position Y1 so that the upstream winding nip section is defined. It may be generated. However, even if the upstream winding nip width is increased in the image forming unit 5Y, the transfer efficiency is improved in the other image forming units 5Y, 5C, and 5M, so that “the entire image forming apparatus A as a color machine” Can obtain high transfer efficiency.

B. Example 2
In the image forming apparatus G of Embodiment 2, as shown in FIGS. 11 and 12, the arrangement positions of the bias application rollers 62Y, 62M, and 62C and the backup rollers 63Y, 63M, and 63C are shifted vertically upward. This is different from the first embodiment. That is, in the second embodiment, the intermediate transfer belt 80 pressed below the virtual reference surface L1 by the support rollers 61Y, 61M, and 61C in each of the regions R1 to R3 is virtualized by the bias application rollers 62Y, 62M, and 62C. It is pushed up above the reference plane L1.

  In this image forming apparatus G, the intermediate transfer belt 80 reaches the photosensitive drum 10Y from above the upstream extended surface L3, and the other photosensitive drums 10M, 10C, and 10K from above the virtual reference surface L1. To reach. Accordingly, since the “upstream winding nip width” can be eliminated from each of the photosensitive drums 10Y, 10M, 10C, and 10K, the transfer efficiency from the photosensitive drums 10M, 10C, and 10K to the intermediate transfer belt 80 can be further improved. . In the second embodiment, the intermediate transfer belt 80 is pushed up above the virtual reference plane L1 by the bias application rollers 62Y, 62M, and 62C. However, even if the intermediate transfer belt 80 is pushed up on the virtual reference plane L1, the same effect as in the second embodiment is obtained. can get.

C. Example 3
The image forming apparatus H according to the third embodiment corresponds to a modification of the image forming apparatus G according to the second embodiment. As illustrated in FIG. 13, an area between the photosensitive drum 10 </ b> K and the secondary transfer unit 90. (In other words, the fourth region R4) has the same configuration as each of the regions R1 to R3. That is, in the fourth region R4, the support roller 61K and the bias application roller 62K are disposed along the conveyance direction of the intermediate transfer belt 80. Among these, the support roller 61K is disposed on the upstream side in the transport direction of the intermediate transfer belt 80 (photosensitive drum 10K side), and the bias application roller 62K is downstream in the transport direction of the intermediate transfer belt 80 (second side). On the roller 82 side).

  In the image forming apparatus H, bias is applied to the intermediate transfer belt 80 that is pressed below the virtual reference plane L1 (that is, below the virtual extension plane L2) by the support roller 61K in the fourth region R4. The roller 62K is pushed up above the virtual extension plane L2. In the third embodiment, the same effect as that of the second embodiment can be obtained. Further, as a modification of the third embodiment, an image forming apparatus I shown in FIG. 14 can be exemplified. In this image forming apparatus H, the intermediate transfer belt 80 pressed below the virtual reference surface L1 by the support roller 61K is pushed up to the virtual reference surface L1 by the bias application roller 62K. In the third embodiment, when any one of the first to fifth modifications is applied, the support roller 61K and the bias application roller 62K (cleaning blade V) are also provided in the fourth region 4. The first to fifth modifications can be applied.

D. Example 4
In the image forming apparatus J of the fourth embodiment, as shown in FIG. 15, when a paper transport belt 180 is used instead of the intermediate transfer belt 80, the paper charger 181 is disposed in the vicinity of the first roller 81. And the point where the sheet static eliminator 182 is disposed close to the second roller 82 and the support roller 61K is pressed below the virtual reference plane L1 (that is, below the virtual extension plane L2). The second embodiment is the same as the third embodiment except that the paper conveying belt 180 is pushed up to the height position of the virtual reference plane L1 (that is, to the height position of the virtual extension plane L2) by the bias application roller 62K. .

  In this image forming apparatus J, the paper transport belt 180 transported from the first roller 81 toward the second roller 82 has a paper holding surface 180B directed downwardly on the photosensitive drum 10Y and the photosensitive drum. 10M, the photosensitive drum 10C, and the photosensitive drum 10K are contacted in this order. In the image forming apparatus J, the paper 180G supplied toward the lower end of the first roller 81 is charged by the paper charger 181 and held on the paper holding surface 180B. Further, after the images of the photosensitive drums 10Y, 10M, 10C, and 10K are transferred, the image reaches the lower end position of the second roller 82, and is neutralized by the sheet neutralizer 182 at this position, and peeled off from the sheet holding surface 180B. Is done. According to the fourth embodiment, the same effect as that of the third embodiment can be obtained.

E. Example 5
The image forming apparatus K according to the fifth embodiment corresponds to a modification of the image forming apparatus H according to the third embodiment. As illustrated in FIGS. 16 to 18, a main body frame 100 as a first support member, The transfer frame 110 as a second support member is positioned by a second roller (transfer belt drive roller) 82 as a positioning member.
As shown in FIG. 17, the main body frame 100 has a pair of side plates 100 </ b> A and 100 </ b> B that are erected substantially parallel to each other at intervals. The pair of side plates 100 </ b> A and 100 </ b> B includes a horizontally long and substantially rectangular main body 101 and an extending portion 102 extending upward from an upper end on one end side of the main body 101. One body 101 supports one end of the rotation shafts 14Y, 14M, 14C, and 14K in a rotatable manner, and the other body 101 can rotate the other ends of the rotation shafts 14Y, 14M, 14C, and 14K. I support it.

The transfer frame 110 has a pair of side plates 110 </ b> A and 110 </ b> B that are disposed above both the main body portions 101 and are erected substantially in parallel with a space therebetween. The pair of side plates 110 </ b> A and 110 </ b> B are configured in a horizontally long and substantially rectangular shape, and one end side portion 111 is inserted inside the pair of extending portions 102. The second roller 82 is disposed inside the one end side portion 111, and each end portion of the rotation shaft 82A is rotatably supported by the one end side portion 111 and the extending portion 102.
That is, the bearing members J1 to J4 are mounted on both the “extending portion 102” and the two “one end side portions 111”, and the bearing members J1 and J3 disposed on the one “extending portion 102 and one end side portion 111”. The one end of the rotating shaft 82A is supported by the other end, and the other end of the rotating shaft 82A is supported by the bearing members J2 and J4 disposed on the other “extending portion 102 and one end side portion 111”. Thus, since the rotation shaft 82A of the second roller 82 is supported by both the transfer frame 110 and the main body frame 100, the transfer frame 110 and the main body frame 100 are positioned by the rotation shaft 82A. Yes.

  As shown in FIGS. 16 and 18, the first roller 81 is rotatably supported on the other end side of the both side plates 110A and 110B, and the first roller 81 and the second roller are supported on the both side plates 110A and 110B. Support rollers 61Y, 61M, 61C, and 61K, bias application rollers 62Y, 62M, 62C, and 62K, and backup rollers 63Y, 63M, 63C, and 63K are rotatably supported at a portion between the rollers 82. At the same time, the primary transfer rollers 51Y, 51M, 51C, and 51K are supported in a slidable state. In addition, four slide holes 151 are formed in each of the side plates 110A and 110B, and a slider 152 that supports the primary transfer rollers 51Y, 51M, 51C, and 51K in a rotatable state is vertically provided in the slide holes 151. It is mounted so that it can move up and down in the direction. The slider 152 is urged vertically downward by urging means (spring) 155 attached to the side plates 110A and 110B.

  In the present embodiment, the main body frame 100 and the transfer frame 110 are positioned using the second roller (rotating shaft 82A) 82, so that the photosensitive drums 10Y, 10M, 10C, and 10K, the support roller 61Y, 61M, 61C, 61K, bias application rollers 62Y, 62M, 62C, 62K, and backup rollers 63Y, 63M, 63C, 63K are positioned.

  Although the embodiments have been described as described above, the following modifications can be further exemplified in the inventions of the claims. For example, between the first roller 81 and the second roller 82, from the first roller 81 side, the black (K) image forming unit 5K, the yellow (Y) image forming unit 5Y, and magenta (M ) Image forming unit 5M and cyan (C) image forming unit 5C. In this case, the number of times the black developer passes through the electric field is increased, and the transfer efficiency of transferring the black developer to the intermediate transfer belt 80 or the paper 180G can be improved.

  The present invention can be used, for example, in the field of sales, construction, processing, and the like of printers, copiers, and facsimile machines.

FIG. 3 is an explanatory diagram illustrating main components constituting the image forming apparatus according to the first exemplary embodiment. FIG. 2 is a partially enlarged view of FIG. 1. It is a perspective view for demonstrating a virtual reference plane etc. FIG. (A) is explanatory drawing for demonstrating the test example 1 and the test example 2, (b) is explanatory drawing for demonstrating the test example 3. FIG. It is explanatory drawing for demonstrating the test example 4 (conventional example). It is a graph which shows the result of a performance test. It is explanatory drawing which shows the main components which comprise the image forming apparatus of a 1st modification. It is explanatory drawing which shows the main components which comprise the image forming apparatus of a 2nd modification. It is explanatory drawing which shows the main components which comprise the image forming apparatus of a 3rd modification. (A) is explanatory drawing which shows the main component which comprises the image forming apparatus of a 4th modification, (b) is explanatory drawing which shows the principal component which comprises the image forming apparatus of a 5th modification. FIG. 6 is an explanatory diagram illustrating main components constituting an image forming apparatus according to a second exemplary embodiment. FIG. 14 is a partially enlarged view of FIG. 13. FIG. 10 is an explanatory diagram illustrating main components constituting an image forming apparatus according to a third exemplary embodiment. FIG. 10 is an explanatory diagram illustrating main components constituting an image forming apparatus according to a modification example of Example 3. FIG. 10 is an explanatory diagram illustrating main components constituting an image forming apparatus according to a fourth embodiment. FIG. 10 is an explanatory diagram illustrating main components constituting an image forming apparatus according to Embodiment 5. It is explanatory drawing which shows a transfer frame, a main body frame, and a belt drive roller. (A) is a partial side view of the transfer frame, (b) is a partial cross-sectional view of the transfer frame.

Explanation of symbols

  A to D, G to K; image forming apparatus, 10, 10Y, 10M, 10C, 10K; photosensitive drum, 51, 51Y, 51M, 51C, 51K; primary transfer roller (primary transfer member), 61Y, 61M, 61C, 61K; support roller (pressing roller), 62Y, 62M, 62C, 62K; bias application roller, 80; intermediate transfer belt, 82; second roller (positioning member), 85; image carrying surface, 180; Belt, 180B; paper holding surface (recording medium holding surface), L1: virtual reference surface.

Claims (8)

A first photosensitive drum on which a liquid developer containing toner particles and a carrier liquid is developed;
A second photosensitive drum on which a liquid developer containing toner particles and a carrier liquid is developed;
A transfer belt that is conveyed while contacting an image carrying surface in the order of the first photosensitive drum and the second photosensitive drum;
A first transfer member in contact with the first photosensitive drum with the transfer belt interposed therebetween;
A second transfer member in contact with the second photosensitive drum with the transfer belt interposed therebetween;
The image carrier more than a virtual reference plane including a contact position of the first photosensitive drum and the first transfer member and a contact position of the second photosensitive drum and the second transfer member. A pressing roller that is disposed on the opposite side of the surface and presses the transfer belt to the image bearing surface side with respect to the virtual reference surface;
A bias applying roller to which a bias is applied while being in contact with the transfer belt pressed by the pressing roller on the image bearing surface side of the transfer belt;
An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein a cleaning member is brought into contact with the bias application roller to remove the liquid developer from the bias application roller.   3. The image forming apparatus according to claim 1, wherein a contact position between the bias applying roller and the transfer belt is on the virtual reference plane or vertically above the virtual reference plane. A first photosensitive drum;
A second photosensitive drum;
A transfer belt that is conveyed while contacting an image carrying surface in the order of the first photosensitive drum and the second photosensitive drum;
A first transfer member in contact with the first photosensitive drum with the transfer belt interposed therebetween;
A second transfer member in contact with the second photosensitive drum with the transfer belt interposed therebetween;
A transfer unit for transferring an image transferred to the image carrying surface of the transfer belt after contacting the second photosensitive drum to a recording medium;
The image carrier more than a virtual reference plane including a contact position of the first photosensitive drum and the first transfer member and a contact position of the second photosensitive drum and the second transfer member. A pressing roller that is disposed on the opposite side of the surface and presses the transfer belt to the image bearing surface side with respect to the virtual reference surface;
A bias applying roller in contact with the transfer belt pressed by the pressing roller on the image carrying surface side;
An image forming apparatus comprising: A first photosensitive drum;
A second photosensitive drum;
A recording medium conveyance belt conveyed while bringing a recording medium holding surface into contact with the first photosensitive drum and the second photosensitive drum in this order;
A first transfer member that is in contact with the first photosensitive drum with the recording medium conveyance belt interposed therebetween;
A second transfer member that is in contact with the second photosensitive drum with the recording medium conveyance belt interposed therebetween;
A peeling portion for peeling the recording medium from the recording medium conveyance belt after contacting the second photosensitive drum;
The recording medium more than a virtual reference surface including a contact position between the first photosensitive drum and the first transfer member and a contact position between the second photosensitive drum and the second transfer member. A pressing roller that is disposed on the opposite side of the holding surface and presses the recording medium transport belt to the recording medium holding surface side from the virtual reference surface;
A bias application roller that is closer to the recording medium holding surface than the virtual reference surface and is in contact with the opposite side of the recording medium holding surface from the virtual reference surface of the recording medium transport belt;
An image forming apparatus comprising: While having a recovery member for recovering the developer squeezed by the bias application roller,
The image forming apparatus according to claim 1, wherein the collecting member is disposed on a vertically lower side of the pressing roller and has an opening on a vertically upper side. A photosensitive drum cleaning member; and a recovery member for recovering the developer removed by the photosensitive drum cleaning member;
The image forming apparatus according to claim 1, wherein the collecting member is disposed vertically below the pressing roller and has an opening vertically upward.   A first support member for supporting the first photosensitive drum and the second photosensitive drum; a second support member for supporting the pressing roller and the bias applying roller; a first support member and a second support member; An image forming apparatus according to claim 1, further comprising a positioning member that positions the support member.

Images