JP2010175952A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of reducing excessive electrification of a transfer material, soiling on a transfer guide by toner, and leakage of a transfer current to the transfer guide, also, capable of achieving good conveyance and good image quality with simple configuration. <P>SOLUTION: The image forming apparatus includes: a photoreceptor drum 1, an intermediate transfer belt 6 to which a toner image is primarily transferred; a second transfer roller 7 that forms a secondary transfer nip portion T2 in press contact with the intermediate transfer belt 6; and the transfer guide for guiding the transfer material S to the secondary transfer nip portion T2. The transfer guide includes an upper transfer guide 15 and a lower transfer guide 16, a minimum distance D(mm) between the upper transfer guide 15 and the lower transfer guide 16 is 1 mm≤D≤3 mm. Regarding the upper transfer guide 15 and the lower transfer guide 16, the surface roughness Ra(μm) of the surface facing the passing transfer material S is 0.1 μm≤Ra≤3.0 μm. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a printer, a copying machine, and a facsimile.

  Transfer material guide means (hereinafter referred to as “transfer material guide means”) that guides a transfer material (paper, resin film) onto which the toner image carried on the image carrier is transferred to a transfer nip formed between the image carrier and the transfer member. An image forming apparatus provided with a transfer guide) is known.

  Before the transfer material enters the transfer electric field region, the transfer material does not form a gap between the transfer material and the image carrier in the transfer electric field region formed by applying a transfer bias to the transfer member. It is desirable to be conveyed along the surface. If there is a gap between the image carrier and the transfer material in the transfer electric field region, the toner image may scatter when moving from the image carrier to the transfer material, or abnormal discharge may occur in the gap. May occur. Therefore, in order to prevent the occurrence of image defects, it is necessary to transport the transfer material along the surface of the image carrier before the transfer material enters the transfer electric field region.

  Therefore, the above-described transfer guide is provided at a position close to the image carrier and the transfer electric field region in order to increase the positional accuracy of the transfer material entering the image carrier.

  In particular, in the case of an intermediate transfer type image forming apparatus, it is necessary to keep the position accuracy of the rush of the transfer material guided to the transfer nip portion high. In other words, when multiple colors of toner are superimposed on the intermediate transfer member to form a multicolor image and the image is transferred to the transfer material at the secondary transfer portion, the amount of toner on the intermediate transfer member is large. Is susceptible to the gap between the intermediate transfer member and the transfer material. As a result, the toner image is likely to scatter and image defects due to abnormal discharge are likely to occur. Therefore, in the case of the intermediate transfer method, it is necessary to keep the positional accuracy of the rushing of the transfer material with respect to the intermediate transfer member, and for this purpose, the transfer guide needs to be as close as possible to the intermediate transfer member and the transfer electric field region. is there.

  However, if the transfer guide is too close to the intermediate transfer body and the transfer electric field region, the toner is likely to adhere to the transfer guide and the transfer guide may be contaminated by the toner (hereinafter, this phenomenon is referred to as “transfer guide toner”). Called "dirt"). When toner adheres to the transfer guide, there arises a problem that the transfer material guided by the transfer guide becomes dirty.

  Further, the transfer guide rubs against the transfer material in the process of transporting the transfer material to the transfer electric field region due to its property. For this reason, depending on the configuration of the transfer guide, the transfer material may be triboelectrically charged by sliding friction between the transfer material and the transfer guide (overcharge of the transfer material). When the transfer material is frictionally charged in this way, the transfer of toner to the transfer material when a transfer bias is applied is inhibited by the charge on the transfer material caused by frictional charging, and the toner image is transferred from the image carrier. Instead, it may remain on the image carrier and appear as an abnormal image (transfer defect).

  Therefore, various techniques relating to the transfer guide have been disclosed in order to prevent the above-described problems, that is, toner contamination of the transfer guide and overcharging of the transfer material due to sliding between the transfer material and the transfer guide. .

For example, as a technique for preventing toner contamination of the transfer guide, a technique is disclosed in which the transfer guide is made of a conductive member and a bias having the same polarity as the toner is applied. In addition, a technique is disclosed in which a transfer guide of a conductive member is grounded via a varistor having a certain resistance so that the potential of the transfer guide charged by rubbing against the transfer material is kept in the same polarity as the toner. Further, a technique is disclosed in which an insulating material is selected as the material of the transfer guide and the toner is repelled by making the charging series with the transfer material the same polarity as the toner (Patent Documents 1 and 2). . As a technique for preventing the transfer material from being overcharged due to the friction between the transfer material and the transfer guide, a technique is disclosed in which the transfer guide is grounded to remove excessive charges on the transfer material (patent). References 3, 4).

Japanese Patent Application Laid-Open No. 07-056451 JP 11-338276 A Japanese Patent Laid-Open No. 10-048969 Japanese Patent Laid-Open No. 10-250891

  Recent image forming apparatuses such as printers, facsimiles, and copiers are required to support various media. For example, it is required to deal with media such as thin paper with small basis weight and low rigidity to thick paper with high basis weight and high rigidity, or gloss paper, gloss film, and OHT with a smooth surface that requires high image quality. Yes. In order to form a good image on these various media, the transfer guide is brought close to the intermediate transfer body and the transfer electric field region to increase the positional accuracy of the transfer material into the intermediate transfer body, It is necessary to regulate the entry position and posture of the.

  In particular, in order to stably transfer a low-stiffness transfer material such as thin paper and improve the positional accuracy of the entry into the intermediate transfer member, it is necessary to bring the transfer guide closer to that of other transfer materials.

  On the other hand, when the transfer guide is brought close to the media and the transfer position and posture of the transfer material are restricted in order to cope with various media, there are the following problems.

  First, when the entry position and orientation of the transfer material are excessively restricted, for example, when a high-resistance medium is passed, the transfer material may be frictionally charged due to excessive rubbing and transfer defects may occur. This problem is particularly noticeable when the transfer material is in a dry state or when the transfer guide of the image forming apparatus is configured to have a stronger friction with the transfer material.

  Second, as a new issue, when a low-resistance medium or moisture-absorbing paper is passed, the transfer current leaks to the transfer guide via the transfer material due to strong rubbing with the transfer guide placed close to the transfer guide. There is a problem (transfer current leakage) that transfer failure occurs due to insufficient current. This problem is remarkable in a high humidity environment where the transfer material is in a hygroscopic state.

  Third, as described above, when the transfer current flows excessively to the transfer guide, a force that electrostatically attracts the transfer material to the transfer guide works, which affects the transfer speed of the transfer material, resulting in image blurring. There is a problem that occurs. This image blurring phenomenon is particularly noticeable in the case of media having a smooth surface such as gloss paper and a relatively low surface resistance. Since the surface is smooth and the contact area with the transfer guide increases, the leakage of transfer current to the transfer guide increases, and the force that electrostatically attracts to the transfer guide works, resulting in friction with the transfer guide. This is because force is generated and affects the conveyance speed.

As a solution to these problems, a structure is known in which a transfer guide is formed of a conductive member and grounded via a varistor or resistor to prevent frictional charging. Up will occur. On the other hand, when the ground resistance is lowered, leakage current is likely to occur. That is, with the conventional configuration, it is difficult to prevent the frictional charging of the transfer material and the leakage of the transfer current to the transfer guide.

  Accordingly, the present invention provides an image forming apparatus capable of reducing overcharge of a transfer material, toner contamination of a transfer guide, and leakage of transfer current to the transfer guide, and obtaining good transportability and good image quality. The purpose is to provide.

In order to achieve the above object, the present invention provides:
An image carrier that carries a toner image, an image forming unit that forms a toner image on the image carrier, a rotatable intermediate transfer member on which a toner image is primarily transferred from the image carrier, and the intermediate transfer A secondary transfer member that forms a transfer nip portion in which a toner image is secondarily transferred from the intermediate transfer body to the transfer material, and a transfer guide that guides the transfer material to the transfer nip portion. In the image forming apparatus comprising
The transfer guide has an upper transfer guide and a lower transfer guide that are arranged to face each other in the vertical direction, and a transfer material is passed between the upper transfer guide and the lower transfer guide, and the transfer material Is guided by the transfer nip portion, and the minimum distance D (mm) between the transfer upper guide and the transfer lower guide is 1 mm ≦ D ≦ 3 mm, and the transfer upper guide and the transfer lower guide In the guide, the surface roughness Ra (μm) of the surface through which the transfer material is passed is 0.1 μm ≦ Ra ≦ 3.0 μm.

An image bearing member for carrying a toner image; image forming means for forming a toner image on the image bearing member; a rotatable intermediate transfer member on which a toner image is primarily transferred from the image bearing member; A secondary transfer member that presses against the intermediate transfer member to form a transfer nip portion where a secondary transfer of a toner image is performed from the intermediate transfer member to the transfer material; and a transfer guide that guides the transfer material to the transfer nip portion; ,
In an image forming apparatus comprising:
The transfer guide has an upper transfer guide and a lower transfer guide that are arranged to face each other in the vertical direction, and a transfer material is passed between the upper transfer guide and the lower transfer guide, and the transfer material Is guided by the transfer nip portion, and the minimum distance D (mm) between the transfer upper guide and the transfer lower guide is 1 mm ≦ D ≦ 3 mm, and the transfer upper guide and the transfer lower guide It is characterized in that the dynamic frictional force between the transfer material and the surface of the guide through which the transfer material passes is 1.96 N or less.

  According to the present invention, it is possible to reduce overcharge of the transfer material, toner contamination of the transfer guide, and leakage of transfer current to the transfer guide, and to obtain good transportability and good image quality with a simple configuration. It is possible to provide a simple image forming apparatus.

1 is a schematic sectional view of an image forming apparatus according to a first embodiment. FIG. 3 is an enlarged view of a secondary transfer nip portion in the first embodiment. FIG. 3 is an enlarged view of a secondary transfer nip portion in the first embodiment. FIG. 3 is an enlarged view of a secondary transfer nip portion in the first embodiment. FIG. 3 is an enlarged view of a secondary transfer nip portion in the first embodiment. FIG. 3 is an enlarged view of a secondary transfer nip portion in the first embodiment. A table showing the relationship between the minimum distance between guides and the occurrence of image defects. The graph which showed the relationship between surface roughness Ra of a transfer guide, and leakage current. The table | surface which shows the relationship between a setting angle | corner and an image evil, and the relationship between a material and an image blur. The simplification figure which shows the measuring method of dynamic friction force.

  The best mode for carrying out the present invention will be exemplarily described in detail below based on the embodiments with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified. Absent.

<First Embodiment>
An image forming apparatus according to a first embodiment to which the present invention is applicable will be described with reference to FIGS.

(Schematic configuration of image forming apparatus)
With reference to FIG. 1, a schematic configuration of the image forming apparatus according to the present embodiment will be described. FIG. 1 shows a schematic cross section of a tandem type color image forming apparatus according to the present embodiment.

  The image forming apparatus A includes a photosensitive drum 1 (image carrier) corresponding to toner of each color of yellow, magenta, cyan, and black. Hereinafter, each member and each device will be described using symbols corresponding to the colors of yellow (a), magenta (b), cyan (c), and black (d).

  A roller-shaped charging device 2 (2a, 2b, 2c, 2d) is in contact with the photosensitive drum 1 (1a, 1b, 1c, 1d) rotating at a predetermined speed, and a bias is applied to the charging device 2. When applied, the surface of the photosensitive drum 1 is uniformly charged to a predetermined potential. Thereafter, the photosensitive drum 1 charged to a predetermined potential is irradiated with irradiation light L from the exposure device 3 (3a, 3b, 3c, 3d) according to the image pattern, and the surface of each photosensitive drum 1 is statically exposed. An electrostatic latent image is formed (exposure processing).

The electrostatic latent image formed on the surface of each photosensitive drum 1 is applied to the developing device 4 (4a, 4b, 4c).
4d), toner is supplied, and the electrostatic latent image is developed as a toner image of each color. The members and apparatuses that form a toner image on the photosensitive drum 1 (on the image carrier) mentioned above are referred to herein as image forming means.

  The toner image formed on the surface of the photosensitive drum 1 is a toner image of each color on the intermediate transfer belt 6 (intermediate transfer member) by a primary transfer roller 5 (5a, 5b, 5c, 5d) as a primary transfer member. The images are transferred with the timing controlled so as to overlap each other. A predetermined bias is applied to the primary transfer roller 5.

  The full-color toner image formed on the intermediate transfer belt 6 is transferred onto the transfer material S fed at a predetermined timing by a secondary transfer roller 7 as a secondary transfer member. A predetermined bias is applied to the secondary transfer roller 7, whereby secondary transfer to the transfer material S is performed. Here, the predetermined bias is a bias for electrostatically transferring the toner image from the intermediate transfer belt 6 onto the transfer material S, and indicates a bias having a polarity opposite to the polarity of the toner image. In this embodiment, since negative polarity toner is used, the polarity of the predetermined bias is positive polarity.

  The full-color toner image formed on the transfer material S is fixed on the transfer material S in the fixing device 8 that performs the heating and pressurizing steps, and is discharged out of the image forming apparatus A as a fixed color image. .

The toner remaining on the photosensitive drum 1 at the time of primary transfer is collected by the cleaning device 9 (9a, 9b, 9c, 9d) of the photosensitive drum 1 and used for the next image formation. Similarly, the toner remaining on the intermediate transfer belt 6 at the time of secondary transfer is collected by the cleaning device 10 for the intermediate transfer belt 6 and used for the next image formation.

  Next, the configuration of each unit will be described in detail.

The photosensitive drum 1 is configured by applying an organic photoconductor layer (OPC photosensitive member) to the outer peripheral surface of an aluminum cylinder having a diameter of 30 mm. Both ends of the photosensitive drum 1 are rotatably supported by a support member (not shown), and a driving force from a drive motor (not shown) is transmitted to one end, thereby rotating counterclockwise in the figure. Is driven to rotate.

  The charging device 2 is a conductive roller formed in a roller shape. The roller is brought into contact with the surface of the photosensitive drum 1 and a negative charging bias is applied from a power source (not shown), whereby the photosensitive drum. The surface of 1 is uniformly charged.

  The exposure device 3 is a laser optical unit, the laser light L corresponding to the image signal is controlled to be turned on by a drive circuit (not shown), and selectively exposes the surface of the charged photosensitive drum 1 to form an electrostatic latent image. Form.

  The developing device 4 is provided with a developing device that stores toners charged in negative colors of yellow, magenta, cyan, and black in order from the upstream side in the rotation direction of the intermediate transfer belt 6 (left side in FIG. 1). When developing the electrostatic latent image on the photosensitive drum 1, a developing bias is applied between the developing roller and the photosensitive drum 1 on which the electrostatic latent image is formed, so that the toner adheres to the electrostatic latent image. It develops as a toner image.

The primary transfer roller 5 is a conductive roller. In the present embodiment, a foamed elastic roller having an outer diameter of 12 mm is provided around an outer diameter 6 mm shaft made of metal such as SUS. The foamable elastic roller has an actual resistance of 10 ⁶ to 10 ⁹ Ω, and the primary transfer roller 5 is pressed toward the photosensitive drum 1 with the intermediate transfer belt 6 (intermediate transfer member) interposed therebetween. A toner image on the photosensitive drum 1 is transferred onto the intermediate transfer belt 6 by applying a positive primary transfer bias from a power source (not shown).

The intermediate transfer belt 6 ^is composed of a film-like member endless thickness of about 50~150μm having a volume resistivity of ¹⁰ 7 ~10 ¹⁴ Ω · cm. The volume resistivity is obtained by applying 50 to 100 V under the conditions of a high resistance meter R8340 manufactured by ADVANTEST, using a measurement probe in accordance with JIS method K6911, at a temperature of 25 ° C. and a relative humidity of 50%. Value. Inside the intermediate transfer belt 6, there are provided a driving roller 61 for rotating the intermediate transfer belt, and driven rollers 62 and 63 for applying appropriate tension to the intermediate transfer belt. These rollers are driven to perform intermediate transfer. A belt 6 is rotatably stretched.

  The driven roller 62 functions as a member facing the secondary transfer roller 7 and is pressed toward the secondary transfer roller 7 with the intermediate transfer belt 6 interposed therebetween. The driven roller 63 functions as a counter roller of the cleaning device 10. The secondary transfer roller 7 has the same configuration and physical properties as the primary transfer roller 5. The secondary transfer roller 7 is in pressure contact with the intermediate transfer belt 6, thereby forming a secondary transfer nip portion T2. A positive secondary transfer bias is applied to the secondary transfer roller 7 from a power source (not shown), whereby a toner image is transferred onto the transfer material S guided by the secondary transfer nip T2. Can be transferred.

In the present embodiment, the transfer upper guide 15 and the transfer lower guide 16 (both of them are guided by the transfer material S to the secondary transfer nip portion T2 formed by the secondary transfer roller 7 and the opposing member 62 described above. A transfer guide). These transfer guides are formed of a conductive member. The upper transfer guide 15 and the lower transfer guide 16 are arranged to face each other in the vertical direction, and the transfer material S is guided to the secondary transfer nip portion T2 by passing the transfer material S between the two guides. Has been. In the case of single-sided printing, the guide on the side of the transfer material S that contacts the surface on which the image is formed is the upper transfer guide 15, and the opposite guide is the lower transfer guide 16.

  The cleaning device 9 is a device in which a rubber plate-like member is brought into contact with the surface of the photosensitive drum 1. The toner developed on the photosensitive drum 1 by the developing device 4 is primarily transferred to the intermediate transfer belt 6 and then removed so-called primary transfer residual toner remaining on the surface of the photosensitive drum 1 without being transferred. It is a thing. Similarly to the cleaning device 9, the cleaning device 10 also has a rubber plate-like member brought into contact with the intermediate transfer belt 6 so as to face the driven roller 63. After the toner image on the intermediate transfer belt 6 is secondarily transferred to the transfer material S by the secondary transfer roller 7, it is provided to remove so-called secondary transfer residual toner that remains on the intermediate transfer belt 6 without being transferred. It is what was done.

  When the image forming process is started by the image forming apparatus, the transfer materials S stored in the feeding cassette 11 mounted at the lower part of the apparatus main body are separated and fed one by one by the feeding roller 12, and the transfer materials S are sequentially fed. It is conveyed to the secondary transfer nip T2 by the conveyance roller pair 13. At this time, the transfer direction of the transfer material S is guided by the upper transfer guide 15 and the lower transfer guide 16 arranged on the upstream side of the secondary transfer nip T 2, and the secondary transfer is performed along the intermediate transfer belt 6. It is conveyed to the nip portion T2. Then, the full color toner image on the intermediate transfer belt 6 is secondarily transferred to the transfer material S at the secondary transfer nip portion T2. Then, the transfer material S is passed through a fixing device 8 including a roller pair of a heating roller 81 and a pressure roller 82 to fix the toner image, and is discharged to the upper portion of the apparatus by a discharge roller pair 14. By performing the above steps, a series of image forming steps is completed.

(Schematic configuration of transfer guide)
As described above, in the present embodiment, the transfer guide including the transfer upper guide 15 and the transfer lower guide 16 is provided in order to accurately convey the transfer material S to the secondary transfer nip portion T2. The schematic configuration of this transfer guide will be described below.

  FIG. 2 shows an enlarged view of the vicinity of the secondary transfer nip portion T2 shown in FIG. In FIG. 2, the secondary transfer roller 7 is pressed against the intermediate transfer belt 6 as a member facing the driven roller 62 over which the intermediate transfer belt 6 is stretched, and a secondary transfer nip portion T <b> 2 is formed between the secondary transfer roller 7 and the intermediate transfer belt 6. is doing. The transfer material S transported from the feeding cassette 11 is guided in its transport position and direction by an upper transfer guide 15 and a lower transfer guide 16 provided opposite to each other across the transport path, and is subjected to secondary transfer. It is conveyed to the nip T. The toner image primarily transferred onto the intermediate transfer belt 6 is secondarily transferred to the transfer material S at the secondary transfer nip T2.

  In the present embodiment, the upper transfer guide 15 and the lower transfer guide 16 are arranged substantially parallel to each other, and by narrowing the distance between the two, the variation of the transfer material S during conveyance is suppressed, and the transfer material S is accurate. The first feature is that the ink is introduced into the secondary transfer nip T2.

Here, it supplements about the space | interval (minimum distance) between the members of the transfer upper guide 15 and the transfer lower guide 16. FIG. This interval (minimum distance) is the minimum distance between the upper transfer guide 15 and the lower transfer guide 16 that substantially determines the posture of the transfer material S before entering the secondary transfer nip T2. In this form, D1 in FIG. 2 corresponds to the minimum distance defined here. As shown in FIG. 2, in this embodiment, the distance D1 between the upper and lower guides arranged to face each other substantially in parallel is set as the minimum distance between the upper and lower guides. However, as shown in FIG. 3, when the upper and lower guides are not parallel to each other, the minimum distance D3 between the upper and lower guides in the region where the transfer material S is contacted and conveyed when the posture of the transfer material S is actually regulated. Is the “minimum distance” defined here.

  The guide distance D2 between the entrances of the transfer upper guide 15 and the transfer lower guide 16 is not particularly limited as long as the transfer material S can be easily introduced into the transfer guide. It is set as wide as 7 mm.

  Next, the posture during conveyance of the transfer material S in the present embodiment will be described.

  The transfer material S conveyed by the conveyance roller 13 or the like is first conveyed to the entrance portions of the upper transfer guide 15 and the lower transfer guide 16. The transfer material S that has passed through the entrance is further transported along the upper transfer guide 15 and the lower transfer guide 16, and first the leading edge of the transfer material S is in the middle of the transfer material transport direction (direction A in FIG. 4). It is conveyed at an angle that contacts the transfer belt 6. At this time, by narrowing the interval between the upper transfer guide 15 and the lower transfer guide 16, the transfer material S can be transferred even when transporting thin paper whose transfer material S is not stable, or the transfer material S with a curled tip. The posture of the tip of the material S can be stabilized. As a result, it is possible to stabilize the posture during transfer of the transfer material S so that the leading edge of the transfer material S first contacts the intermediate transfer belt 6.

  FIG. 5 and FIG. 6 are schematic diagrams showing differences in the conveyance state of the transfer material S due to differences in the minimum distance D between the transfer guides.

  FIG. 5 shows a case where the minimum distance D between the transfer guides is large. If the leading edge state of the transfer material S is greatly different under the conditions of FIG. 5 (for example, when the curl direction is upward (solid line S1 in the figure) and downward (broken line S2 in the figure)), the intermediate transfer at the leading edge is performed. The position of contact with the belt 6 varies greatly (the difference in L1 occurs). Therefore, the leading edge posture of the transfer material S varies when the transfer material S enters the secondary transfer nip portion T2. As described above, when the minimum distance D between the transfer guides is large, the effect of regulating the leading edge is small, and the transfer material S is conveyed to the secondary transfer nip portion T2 with the leading edge of the transfer material S being unstable. As a result, image registration problems such as a large variation in tip registration, skewing of the tip, toner scattering, and image blurring occur.

  On the other hand, when the minimum distance D between the transfer guides is narrow as shown in FIG. 6, the transfer material S can be conveyed while correcting the curl state of the tip even if the leading edge state of the transfer material S is greatly different. .

  As a result, the variation in the contact position of the transfer material S on the intermediate transfer belt 6 can be suppressed to a small level (L2 <L1), and the leading edge posture of the transfer material S at the time of entering the secondary transfer nip portion T2. Is stable. That is, even when the leading edge of the transfer material S is in a curled state or the like, there is little variation in registration of the leading edge, and it is possible to form a good image without image defects such as skewing of the transfer material S, scattering of toner, and image blurring. It becomes.

  FIG. 7A shows the minimum distance D (mm) between the guides and the occurrence of image defects (tip registration variation (tip variation), tip rush blur, scattering). Here, the occurrence level of image defects is defined as no occurrence: ◯, a slight occurrence but no problem in actual use: Δ, a level that can be clearly confirmed: x. This definition can also be applied to FIGS. 7B, 7C, and 7D described later.

  From the results shown in FIG. 7, it can be confirmed that the above-mentioned image adverse effect is suppressed when the minimum distance D between guides is set to about 3 mm or less, and sufficient effect is confirmed when the minimum distance D between guides is set to 2 mm or less. I was able to.

  However, if the minimum distance D between the guides is too narrow, there is a problem that an image is disturbed due to overcharging of the transfer material S due to friction during conveyance, and transfer defects occur. Further, as described above, when passing glossy paper or the like in a high humidity environment, there is a possibility that transfer failure due to transfer current leakage and rear end image blurring may occur. The mechanism of occurrence of rear end image blurring and solutions to these problems will be described later.

  FIG. 7B is a table showing the relationship between the transfer failure of the left paper with respect to the minimum distance D between the guides, the transfer failure due to the transfer current leakage of the gloss paper or the like in a high humidity environment, and the trailing edge image blur. From the result shown in FIG. 7 (b), when the minimum distance D between the guides is 3 mm or less, the transfer failure of the left paper, the transfer failure due to the leakage of the transfer current of the gloss paper in a high humidity environment, and the trailing edge image blurring occur slightly. You can see that Further, when the minimum distance D between the guides was set to 2 mm or less, an image defect that could be sufficiently visually confirmed occurred.

  Therefore, from the results of FIGS. 7 (a) and 7 (b), leading edge variation, leading edge blurring, scattering, transfer failure of left paper, transfer failure due to leakage of transfer current of gloss paper in a high humidity environment, It can be said that it is difficult to set the minimum distance D between guides that simultaneously avoids edge image blurring.

  That is, it is difficult to obtain good transportability and good image quality only by the first feature of the present embodiment (narrowing the minimum distance D between guides). Therefore, in addition to the first feature described above, the present embodiment has a second feature described below.

  As a second feature, in the present embodiment, the surface roughness Ra of the material of the upper transfer guide 15 and the lower transfer guide 16 is set to 0.1 μm ≦ Ra ≦ 3.0 μm. According to this, it was confirmed that the image detrimental effect that is remarkable when the minimum distance D between guides shown in FIG. 7B is 2 mm or less can be suppressed.

The Ra described here is a so-called “centerline average roughness”, which is a value obtained by folding the roughness curve from the centerline and dividing the area obtained by the roughness curve and the centerline by the length L. It is expressed in micrometers (μm). In the present embodiment, using a surface roughness measuring instrument “SE-3400” manufactured by Kosaka Laboratory, the transfer material contact surface side of the transfer guide is in the transfer material transport direction, the measurement length is 4 mm, the speed is 0.1 mm / sec, The value measured at the cutoff of 0.8 is used as Ra.

  7 (c) and 7 (d) show the distance D between guides and the occurrence of image defects when the surface roughness Ra of the transfer guide used in FIG. 7 (b) is set to Ra ≧ 0.1 μm. It is shown. Specifically, in FIG. 7B, a transfer guide having a surface roughness Ra = 0.05 μm was used. In contrast, in FIGS. 7C and 7D, transfer guides having surface roughness Ra = 0.1 μm and 0.2 μm were used, respectively.

  As can be seen from the results shown in FIG. 7 (c) and FIG. 7 (d), when Ra ≧ 0.1 μm, the minimum distance D between guides is not more than 3 mm, but not more than 2 mm. Also, it was found that transfer defects and rear end image blurring can be avoided.

  On the other hand, when the minimum distance D between the guides was 1 mm, slight rear end image blurring started to occur. Therefore, it can be said that the minimum distance between guides is desirably set to 1 mm or more.

As described above, the surface roughness Ra of the material of the transfer guide is set to Ra ≧ 0.1 μm while the minimum distance D between the guides is maintained at 1 mm ≦ D ≦ 3 mm. The contact area can be reduced, and the contact resistance between the two can be reduced. Therefore, the transfer material can be conveyed stably.

  Further, since the contact area between the transfer material S and the transfer guide is reduced, it is possible to suppress transfer failure and image blur due to charge-up due to rubbing and leakage of transfer current.

  In particular, it is possible to reduce a leakage current generated by contact with the transfer guide during conveyance in a high humidity environment, and thereby image adverse effects such as image blur caused by the transfer material S adsorbed to the transfer guide. It became possible to avoid.

  Further, here, the case of Ra = 0.1 μm and Ra = 0.2 μm has been described in detail. However, as a result of performing similar verification in the range of Ra of 0.1 μm to 3.0 μm, transfer defects and trailing edge blurring are caused. There was no occurrence, and it was confirmed that there was an effect as well.

  However, when Ra is larger than 3.0 μm, scratches on the surface of the transfer material due to friction between the transfer material S and the transfer guide begin to occur in the glossy media having a smooth surface, and therefore Ra = 3.0 μm as the upper limit. The degree is preferred.

  In the present embodiment, the transfer upper guide 15 and the transfer lower guide 16 that guide the transfer material S are formed of metal (here, stainless steel (SUS)), and the transfer guides have a resistance of 1 GΩ (not shown). Is grounded.

This effect will be described with reference to FIG. FIG. 8 is a graph showing the relationship between the surface roughness Ra of the transfer guide and the leakage current in the configuration of the present embodiment. In the graph, the solid line indicates the transfer guide with the surface roughness Ra = 0.05 μm of the comparison target (REF), and the broken line indicates the transfer guide with the surface roughness Ra = 0.1 μm of the present embodiment. The horizontal axis represents time, and the vertical axis represents leakage current [μA] from the transfer guide.

  Here, when the minimum distance D between the guides is set to 2 mm and a sheet of glossy paper (gloss media) having a thickness of 200 g is passed in an environment of a temperature of 23 to 25 ° C. and a humidity of 50 to 60%, the secondary transfer is performed. The current flowing through the transfer material S from the roller to the transfer guide was plotted. The glossy paper (gloss media) used here is characterized by a smooth surface and low surface resistance in order to give gloss to the output image. The image forming conditions are a process speed of 60 mm / sec and a transfer bias of 5 μA.

  From this graph, it can be seen that the leakage current varies greatly depending on the difference in Ra. For example, when converted and compared with the integrated current when one sheet is passed, it was about 160 μA in the case of REF (Ra = 0.05 μm), whereas in the case of this embodiment (Ra = 0.1 μm), it is about It was found to be 115 μA, and in this embodiment, the leakage current was reduced by about 30%.

  Here, a mechanism that causes image blur will be described. When the leakage current is large, the transfer material may be attracted to the transfer guide by the electrostatic attraction force, which may cause blurring as a transport brake. As the timing at which the blur occurs, in this embodiment, the timing at which the rear end portion of the transfer material S comes out of the transfer guide can be mentioned. At this timing, since there is no brake applied to the transfer material S with a constant force during rubbing with the transfer guide, the speed changes rapidly, which leads to blurring in the secondary transfer nip T2. This image blur phenomenon is noticeable in the case of a halftone or horizontal line image.

When the conveyance state when image blurring occurred was observed, a behavior in which the transfer material S was electrostatically attracted was observed when Ra = 0.05 μm of REF. However, when Ra = 0.1 μm as in the present embodiment, it was confirmed that the behavior of electrostatically attracting the transfer material S was improved and that the transfer material S could be stably conveyed.

  As described above, in the present embodiment, it is possible to obtain a good image quality in which image blurring at the time of rear end omission, which is slight in the REF configuration, is hardly seen.

  As described above, it can be seen that as the surface roughness Ra of the transfer guide and the minimum distance D between the guides become smaller, the occurrence of blurring becomes remarkable. However, when the minimum distance D between guides is set to 1 mm ≦ D ≦ 3 mm and the surface roughness Ra is set to Ra ≧ 0.1 μm as in the present embodiment, occurrence of blurring can be suppressed, and good transportability and good It becomes possible to obtain a good image quality.

  As described above, the minimum distance D between the upper transfer guide 15 and the lower transfer guide 16 is 1 mm ≦ D ≦ 3 mm, and the surface roughness Ra on the sheet passing surface side of the upper transfer guide 15 and the lower transfer guide 16 is 0.1 μm ≦ By setting Ra ≦ 3.0 μm, the conventional problem can be solved.

  In other words, while preventing the occurrence of abnormal images during transfer due to the friction between the transfer guide and the transfer material, the transfer material due to toner contamination of the transfer guide can be eliminated, and further, leakage of the transfer bias to the transfer guide can be prevented. A forming apparatus can be provided.

  In this embodiment, the second feature is that the surface roughness Ra on the sheet passing surface side of the upper transfer guide 15 and the lower transfer guide 16 is 0.1 μm ≦ Ra ≦ 3.0 μm. The portion for setting in this way may be a part of the transfer guide.

  That is, if the surface roughness Ra of the portion of the transfer guide that rubs strongly against the transfer material S is 0.1 μm ≦ Ra ≦ 3.0 μm, the above-described effects can be obtained. In the case of the configuration shown in FIG. 3, the “portion that is strongly rubbed with the transfer material P in the transfer guide” includes the bent portion B of the transfer upper guide 15 and the like.

<Second Embodiment>
With reference to FIG. 9A, an image forming apparatus according to a second embodiment to which the present invention is applicable will be described. The present embodiment is characterized in that the angle θ formed by the transfer material conveyance direction A and the intermediate transfer belt 6 is defined as a predetermined angle.

  As described above, in order to obtain good image quality, the transfer material S is transported along the intermediate transfer belt 6 before entering the transfer electric field region, and the photosensitive drum 1 and the transfer are transferred in the transfer electric field region. It is necessary not to form a gap with the material S. From this point of view, particularly when the leading edge of the transfer material S is curled or when a thin paper having low rigidity is transported, an angle θ (set angle θ) between the transport direction A of the transfer material S and the intermediate transfer belt 6 is set. It is desirable to transport the transfer material S so that) is within a predetermined range.

  Here, the definition of the setting angle θ will be described. The setting angle θ refers to an intersection angle between the transfer direction extension line A at the front end of the transfer material S immediately after passing through the transfer guide and the intermediate transfer belt 6.

  For example, in the case shown in FIG. 4, since the upper transfer guide 15 and the lower transfer guide 16 are arranged substantially in parallel, the sheet passing surface of the upper transfer guide 15 and the lower transfer guide 16 and the conveyance direction A of the transfer material S are substantially parallel. it is conceivable that. In this case, an angle that intersects the intermediate transfer belt 6 on the extension line of the conveyance surface of the upper transfer guide 15 and the lower transfer guide 16 is defined as a set angle θ. In the case shown in FIG. 3, the crossing angle between the intermediate transfer belt and the extension line in the front end direction of the transfer material S immediately after passing through the upper transfer guide 15 and the lower transfer guide 16 is defined as a set angle θ.

When the set angle θ is close to 0 °, for example, when the tip of the transfer material S is curled toward the transfer roller 6, the transfer material S may directly contact the transfer roller 6. A gap is formed in front of the area, and there is a risk that image defects such as toner scattering may occur. On the other hand, if θ is too large, the transfer material S is transferred when the leading edge of the transfer material S enters the intermediate transfer belt 6, and the leading edge is shaken or bent greatly during the conveyance. Is rubbed against the transfer guide with a strong force.

  FIG. 9A is a table showing the state of occurrence of image defects when the set angle θ defined here is set in the range of 0 ° to 60 °.

  From the results shown in FIG. 9 (a), it was confirmed that when the set angle θ is set in the range of 5 ° ≦ θ ≦ 45 °, various image defects can be suppressed simultaneously.

  For example, it has been found that when the set angle θ is smaller than 5 °, the scattering is worsened. Further, if the set angle θ is larger than 45 °, the effect of correcting the posture of the transfer material S is effective, but the rubbing force with the transfer guide increases, so the effect described in the first embodiment (the tip) It was found that the effect on image blur and rear end blur was reduced.

  Accordingly, the set angle θ is preferably in the range of 5 ° ≦ θ ≦ 45 °. In this embodiment, the angle (set angle θ) formed between the transport direction A and the intermediate transfer belt 6 is the most transportable. Was set at a stable 15 °. Thus, the rigidity of the transfer material S is utilized by arranging the transfer guide so that the transfer material S can be conveyed in the direction of the intermediate transfer belt 6 with an angle in the range of 5 ° ≦ θ ≦ 45 °°. Thus, the posture of the transfer material S can be suitably regulated by the transfer guide. As a result, the transfer material S can be stably conveyed to the secondary transfer nip T2 in a state along the intermediate transfer belt 6, so that a gap is formed between the transfer material S and the photosensitive drum 1. It is possible to suppress image adverse effects.

  As described above, in this embodiment, overcharge of the transfer material, toner contamination of the transfer guide, and leakage of transfer current to the transfer guide are reduced, and good transportability and good image quality are obtained with a simple configuration. It is possible to provide an image forming apparatus capable of performing the above.

<Third Embodiment>
With reference to FIG. 9B and FIG. 10, an image forming apparatus according to a third embodiment to which the present invention is applicable will be described.

  In the first embodiment, the minimum distance D between guides and the surface roughness Ra of the transfer guide are defined to prevent the occurrence of abnormal images during transfer due to friction between the transfer guide and the transfer material S. Leakage of bias to the transfer guide was prevented and occurrence of rear end blurring was suppressed.

  By the way, the trailing edge blur causes a transfer current to leak when the transfer material S is rubbed strongly with the transfer guide, and affects the transport speed by being transported with the transfer guide in an adsorbing manner. It has been explained that this occurs due to the change in the speed of the transfer material when it passes through the guide.

  Therefore, in the present embodiment, instead of defining Ra, the dynamic friction force at the time of sliding between the transfer guide and the transfer material S is more directly regulated, thereby suppressing the speed change of the transfer speed of the transfer material S, It is characterized by suppressing image blur. The details will be described below.

First, when the same amount of leakage current occurs, the effect on the transfer speed of the transfer material S is dominated by the slipping property between the transfer material and the transfer guide, in other words, the dynamic friction force. For example, when the dynamic frictional force during sliding between the transfer material S and the transfer guide is small, the influence on the transfer speed of the transfer material S is small, so that a large speed difference does not occur before and after the rear end of the transfer material S passes through the guide. . Therefore, the occurrence of rear end image blur can be suppressed. However, when the dynamic friction force is large, a significant speed difference occurs in the transfer material before and after the rear end of the transfer material S passes through the guide, and this causes rear end image blurring.

  FIG. 9B shows the measurement results of the dynamic friction force when the material A: SUS, material B: KN plating, material C: gin-coated steel plate 1, material D: gin-coated are used for the transfer guide, It shows the occurrence of image blur at that time. As can be seen from the result shown in FIG. 9B, it can be seen that the image blurring is suppressed when the material has a small dynamic friction force, and the image blurring becomes remarkable when the material has a large dynamic friction force. Therefore, in this embodiment, a transfer guide having a dynamic friction force of 1.96 N or less is used. As a result, the occurrence of image blur can be reduced. Even when the same material is used, the dynamic friction force differs because the surface state of the material changes depending on the manufacturing conditions and the shape, such as finishing of the bent portion. The term “dynamic frictional force of 1.96 N or less” in the present embodiment refers to the dynamic frictional force of the transfer guide, particularly the portion that rubs against the transfer material.

  Next, a method for measuring the dynamic friction force described above will be described with reference to FIG. FIG. 10 is a simplified diagram showing a method for measuring the dynamic friction force, and shows a diagram viewed from an oblique direction and a diagram viewed from the side.

  When measuring the dynamic frictional force, one of the samples of the transfer material S cut into a strip having a width of W = 20 mm is connected to a force gauge set parallel to the ground, and is parallel to the force gauge and the transfer material. Place and fix the transfer guide as shown. Then, a sample is set so as to be placed on the transfer guide, and a weight (100 g) is connected to one side to lower it vertically. From this state, the value when the force gauge is pulled at a constant speed (180 mm / min) in the direction of the arrow is defined as the dynamic friction force between the transfer material S and the transfer guide. Here, the transfer guide material was changed under the above method, and the dynamic friction force was measured each time.

  As described above, in this embodiment, instead of defining Ra, the dynamic friction force between the transfer guide and the transfer material S is regulated more directly, thereby suppressing the speed change of the conveying speed and suppressing the image blur. As a result, overcharge of the transfer material, toner contamination of the transfer guide, and leakage of transfer current to the transfer guide are reduced, and image formation capable of obtaining good transportability and good image quality with a simple configuration. An apparatus can be provided.

Reference Signs List 1 photosensitive drum 6 intermediate transfer belt 5 primary transfer roller 7 secondary transfer roller 15 transfer upper guide 16 transfer lower guide 62 driven roller T2 secondary transfer nip S transfer material D minimum distance between transfer guides

Claims (4)

An image carrier for carrying a toner image;
Image forming means for forming a toner image on the image carrier;
A rotatable intermediate transfer member on which a toner image is primarily transferred from the image carrier;
A secondary transfer member that presses against the intermediate transfer member to form a transfer nip portion where a secondary transfer of a toner image is performed from the intermediate transfer member to a transfer material;
A transfer guide for guiding a transfer material to the transfer nip,
In an image forming apparatus comprising:
The transfer guide is
It has a transfer upper guide and a transfer lower guide that are arranged opposite to each other in the vertical direction,
A transfer material is passed between the upper transfer guide and the lower transfer guide, and the transfer material is guided to the transfer nip portion,
The minimum distance D (mm) between the transfer upper guide and the transfer lower guide is 1 mm ≦ D ≦ 3 mm,
An image forming apparatus, wherein a surface roughness Ra (μm) of a surface through which a transfer material is passed in the upper transfer guide and the lower transfer guide is 0.1 μm ≦ Ra ≦ 3.0 μm. An image carrier for carrying a toner image;
Image forming means for forming a toner image on the image carrier;
A rotatable intermediate transfer member on which a toner image is primarily transferred from the image carrier;
A secondary transfer member that presses against the intermediate transfer member to form a transfer nip portion where a secondary transfer of a toner image is performed from the intermediate transfer member to a transfer material;
A transfer guide for guiding a transfer material to the transfer nip,
In an image forming apparatus comprising:
The transfer guide is
It has a transfer upper guide and a transfer lower guide that are arranged opposite to each other in the vertical direction,
A transfer material is passed between the upper transfer guide and the lower transfer guide, and the transfer material is guided to the transfer nip portion,
The minimum distance D (mm) between the transfer upper guide and the transfer lower guide is 1 mm ≦ D ≦ 3 mm,
An image forming apparatus characterized in that a dynamic frictional force between the transfer material and a surface of the transfer upper guide and the transfer lower guide through which the transfer material passes is 1.96 N or less. . The transfer upper guide and the transfer lower guide,
The image forming apparatus according to claim 1, wherein the image forming apparatus is made of a conductive material. In a state where the tip of the transfer material has slipped out between the upper transfer guide and the lower transfer guide,
An angle θ formed by the extension line in the transport direction of the tip and the intermediate transfer member is
5 ° ≦ θ ≦ 45 °,
The transfer guide is
4. The apparatus according to claim 1, wherein the tip is disposed so as to contact the intermediate transfer member upstream of the transfer nip portion in the rotation direction of the intermediate transfer member. Image forming apparatus.

Images