JP2005250329A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of preventing "scattering" occurring in a transfer process and always realizing a stable image quality without deteriorating image quality caused by the reduction of transferrability . <P>SOLUTION: In the image forming apparatus wherein a process of transferring a toner image on a first image carrier to a second image carrier is provided and a transfer member for performing the transfer step has a conductive elastic roller which is brought into contact with the second image carrier and to which a prescribed bias is applied, an auxiliary member is arranged in a position opposed to the image carrier with the conductive elastic roller between them while the auxiliary member extends in a lengthwise direction of the conductive elastic roller and in parallel with the conductive elastic roller. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus using an electrophotographic system such as a copying machine or a laser beam printer.

  In an image forming apparatus using a conventional electrophotographic system, a toner image formed on an image carrier such as a photosensitive drum is electrostatically transferred to a second image carrier by a roller-shaped transfer member to which a bias is applied. Some have been given a device for transferring to the body. The roller-shaped transfer member is formed of an elastic body around a circular metal rod.

  Hereinafter, a conventional image forming apparatus will be described with reference to FIG.

  The photoreceptor unit including the first image carrier 1 is a unit in which the charging member 2 and the cleaning member 9 are integrated with the periphery of the on-drum photoreceptor 1 as the first image carrier. The exposure device 3 is a device that forms an electrostatic latent image on the surface of the photosensitive member 1 on the photosensitive member 1 that has been charged to a predetermined potential by the charging member 2.

  The developing device 40 is a device that develops the electrostatic latent image formed on the surface of the photoreceptor 1 with a developer (toner). In order to form a multicolor image, the developing device 40 includes four colors (yellow 4Y, magenta 4M, cyan 4C, and black 4K).

  The intermediate transfer unit including the second image carrier has a plurality of rollers 51 and 52 that stretch the first transfer member 54 (roller) and the belt 5 on the inner periphery of the belt as the second image carrier. , 53 and the toner image formed on the photosensitive member 1 is sequentially transferred onto the belt 5 to carry a multicolor image as a basis of the final image.

  The belt 5 as the second image carrier is an intermediate transfer belt that forms a multicolor image by forming toner images of four colors on the belt 5 and transferring them onto a transfer material at once. This intermediate transfer belt 5 satisfies the transferability from the photoreceptor 1 and the transferability to the transfer material, and from the viewpoint of durability that can withstand long-term use, from the engineering plastic and super engineering plastic. Resin belts (polyimide, polyvinylidene fluoride, etc.) are used.

  As the roller-shaped transfer member 54, an elastic roller is used from the viewpoint of ensuring a uniform contact width (nip width) and maintaining high transferability.

  The transfer device 6 includes a power source (not shown) for applying a bias and an elastic roller 61. The transfer material P is a toner image on the intermediate transfer belt 5 fed from a paper feeding unit at a predetermined timing. It is a device to transfer on. For the transfer device 6 as well, an elastic roller is suitable for the same reason as the transfer member 54.

  The fixing device 8 includes pressure members 83 and 84 that include heat sources 81 and 82, and is a device that fixes a toner image on the transfer material P to the transfer material P by heating and pressurizing to form a multicolor image. .

  After the transfer process of the toner image on the photosensitive drum 1 to the intermediate transfer belt 5 is completed, the toner remaining on the photosensitive drum 1 is collected by the cleaning member 9 to prepare for the next image formation.

Japanese Patent Laid-Open No. 10-20625 (page 6, FIG. 1)

However, in the case of a conventional multicolor image forming apparatus,
The toner image is not transferred faithfully in the transfer area, and the toner image is disturbed.
There is a drawback of forming a defective image.

  This phenomenon occurs when the toner image is transferred from the first image carrier to the second image carrier or from the second image carrier to the transfer material.

  It is possible to eliminate the influence of electrostatic force on the toner image T on the first image carrier by downsizing the transfer member. However, when the roller-shaped transfer member is downsized, that is, when the outer diameter of the roller is reduced, the transfer member bends due to the urging force applied to both ends of the transfer member. The transfer member that has been bent cannot contact the second image carrier with a uniform contact width and contact pressure over the entire length. As a result, the transferability of the toner image is affected and the image quality is degraded. In particular, transfer defects due to the bending of the transfer member at the longitudinal center portion become significant.

  By making the roller-shaped transfer member a rigid body, it is possible to reduce the deflection of the roller. However, pressing the rigid body against the second image carrier induces damage to the second image carrier and further affects the first image carrier, so that it is suitable for use. Not.

  The above problem is not limited to the multicolor image forming apparatus having the intermediate transfer belt illustrated in FIG. This is a problem that occurs in all image forming apparatuses that employ a method of transferring a toner image on an image carrier with electrostatic force.

  The present invention has been made in view of the above problems, and the intended process is to avoid “scattering” that has occurred in the transfer process, and to reduce image quality due to a decrease in transferability. An object of the present invention is to provide an image forming apparatus capable of always realizing stable high image quality without incurring.

  In order to achieve the above object, the invention described in claim 1 includes a step of transferring the toner image on the first image carrier to the second image carrier, and the transfer member that performs the transfer step is the second member. In an image forming apparatus having a conductive elastic roller that is in contact with an image carrier and to which a predetermined bias is applied, the conductive elastic roller extends in the longitudinal direction of the conductive elastic roller and is in parallel with the conductive elastic roller. An auxiliary member is disposed at a position facing the image carrier at the center.

The invention according to claim 2 is the invention according to claim 1,
The image forming apparatus according to claim 1, wherein the auxiliary member is a roller-shaped member configured by covering the periphery of the metal shaft with an elastic body, and has higher bending rigidity than the conductive elastic roller.

  According to a third aspect of the present invention, in the first aspect of the present invention, the outer diameter of the conductive elastic roller is such that the toner image on the first image carrier that is not in contact with the second image carrier is conductive. It is characterized by being below the region where the electric field due to the transfer bias applied to the elastic roller does not act.

  According to a fourth aspect of the invention, in the second aspect of the invention, the conductive elastic roller is pressed against the image carrier by the conductive elastic roller.

  According to a fifth aspect of the present invention, in the second aspect of the present invention, the conductive elastic roller is pressed against the image carrier through an auxiliary member.

  According to the present invention, by using a roller-shaped transfer member having a small diameter smaller than the contact width between the first image carrier and the second image carrier, “scattering” that has occurred in the transfer process is avoided. It became possible. At the same time, by arranging the transfer auxiliary member so that the small-diameter roller-shaped transfer member can be brought into contact with the image carrier without being bent, it is possible to avoid transfer defects caused by the transfer member being bent. As a result, it has become possible to always achieve a stable high image quality without degrading the image quality due to a decrease in transferability.

  Embodiments of the present invention will be described below with reference to the accompanying drawings.

<Embodiment 1>
1 to 3 are a schematic sectional view and an explanatory view of a multicolor image forming apparatus for explaining the present embodiment. The feature is that
A small-diameter transfer roller is employed, and the deflection due to the pressure of the small-diameter transfer roller is corrected by the auxiliary roller.

  The basic configuration and operation are the same as those in FIG. 6, and the same reference numerals are given to common members as functions.

  Details of each member will be described below.

  The photosensitive drum 1 is an organic photosensitive drum having an outer diameter of 45 (mm), and the surface of the photosensitive member is charged to −600 (V) by the charging member 2 during normal image formation.

The intermediate transfer belt 5 has a circumferential length of 440 (mm), a thickness of 100 (μm), and is made of a polyimide resin having a volume resistance adjusted to 10 ¹⁰ (Ω / cm).

The transfer roller 6 as the transfer device 6 is a foaming elastic roller having an outer diameter of 18 (mm), and is adjusted to a volume resistivity of 10 ⁷ (Ω / cm). In order to reliably transfer the toner image formed on the intermediate transfer belt 5 to the transfer material and to stably convey the transfer material, pressure of 2 kgf is applied to both ends thereof. Since the transfer roller 6 realizes transfer properties with respect to various types of transfer materials, the transfer roller 6 is larger than the transfer roller 54 that transfers the toner image formed on the photosensitive drum 1 to the intermediate transfer belt 5. Pressure is required.

  The transfer roller 54 as the first transfer member is a small-diameter roller that is characteristic in the present invention. The small diameter roller in the present invention satisfies the following.

When the line connecting the transfer roller 54 and the axis of the photosensitive drum 1 as the first image carrier is on the contact point between the photosensitive drum 1 and the intermediate transfer belt 5 as the second image carrier, the radius of the transfer roller 54 However, the toner image carried on the photosensitive drum 1 immediately before coming into contact with the intermediate transfer belt 5 falls within a region that is not affected by the electric field due to the transfer bias applied to the transfer roller 54. These are the outer diameter (curvature) of the first image carrier,
This depends on the electric resistance value of the second image carrier, the outer diameter (curvature) of the transfer roller 54, and the electric resistance value.

  Therefore, the transfer roller 54 in the image forming apparatus shown in FIG.

It is a foaming elastic roller (core metal diameter φ2 (mm)) having an outer diameter of 4 (mm) and adjusted to a volume resistivity of 10 ⁸ (Ω / cm). At both ends of the transfer roller, 500 gf of pressure is applied to each end of the transfer roller by a biasing means S1 (FIG. 3) via a roller holder 56 to secure a nip width to the intermediate transfer belt 5.

The auxiliary transfer roller 55 is an elastic roller having an outer diameter of 14 (mm) (core metal diameter of 6 (mm)). The axial center of the auxiliary transfer roller 55 is arranged so as to be positioned on a line in the urging direction of the transfer roller 54 to the photosensitive drum 1. Further, both ends of the shaft are fixed to the image forming apparatus main body via a roller holder 56 (FIG. 3).
The auxiliary transfer roller 55 itself is kept in a rotatable state so as not to affect the rotation operation of the transfer roller 54. As the elastic layer, an elastic member having a hardness higher than that of the elastic layer of the transfer roller 54 is used. The material is not particularly limited,
Either foamable or solid rubber or elastomer may be used. By making the hardness of the auxiliary transfer roller 55 larger than that of the transfer roller 54, the auxiliary effect of the transfer roller 54 is further enhanced.

  As illustrated in FIG. 3, the distance between the axes of the transfer roller 54 and the transfer auxiliary roller 55 is fixed by the holder 56 so that the transfer auxiliary roller 55 does not enter the transfer roller 54. The relationship of outer diameter + transfer auxiliary roller 55 outer diameter) / 2 is maintained. By maintaining this positional relationship, it is possible to avoid permanent deformation or the like of the transfer roller 54. Further, the longitudinal width of the elastic layer of the auxiliary transfer roller 55 is at least the longitudinal width of the elastic layer of the transfer roller 54.

  During image formation, a DC voltage of about +1 kV is applied to the core of the transfer roller 54 by a power source (not shown) in the image forming apparatus. Further, the transfer auxiliary roller is electrically floated.

  Since the dielectric breakdown voltage of gas is around +500 V, transfer scattering due to pre-transfer occurs in the case of a multicolor image forming apparatus employing a conventional transfer roller having an outer diameter. However, when the small-diameter transfer roller 54 having an outer diameter of 4 mm is employed as in the present embodiment, the area where pre-transfer occurs is within the area where the photosensitive drum 1 and the intermediate transfer belt 5 are in contact (within the nip area). Therefore, the phenomenon that the toner scatters to the intermediate transfer belt 5 to cause transfer scattering does not occur.

  In this embodiment, a transfer roller having an outer diameter of 4 (mm) is used, but with the assistance of the transfer auxiliary roller, the transfer roller does not bend and the transferability is stably maintained. The above effect will be described with reference to Table 1.

表１は長さ２５０（ｍｍ）の丸棒の鋼材（縦弾性係数２．１×１０⁴ｋｇｆ／ｍｍ²、基準強さ応力７０．０ｋｇｆ／ｍｍ²）から成る芯金について、図２に示すように、その両端を点支持し、芯金の長手中央部に１ｋｇｆの荷重を加えた場合の芯金の撓み量δを芯金の外径（ｍｍ）についてまとめたものである。

Table 1 shows a cored bar made of a round bar steel material having a length of 250 (mm) (longitudinal elastic modulus 2.1 × 10 ⁴ kgf / mm ² and standard strength stress 70.0 kgf / mm ² ). In this manner, the deflection amount δ of the cored bar when the both ends thereof are point-supported and a load of 1 kgf is applied to the longitudinal center part of the cored bar is summarized for the outer diameter (mm) of the cored bar.

  The deflection amount δ (mm) in Table 1 is not a numerical value that directly represents the deflection amount of the transfer roller 54, but is used as a substitute characteristic. In the case of the transfer roller having a cored bar diameter of 2 (mm) shown in the present embodiment, the cored bar exhibits a deflection amount δ of 19.7 (mm). When there is no transfer auxiliary roller, the nip formation at the center is incomplete due to the deflection of the transfer roller, and a good image cannot be obtained.

However, since the transfer auxiliary roller suppresses the bending of the transfer roller, a small-diameter transfer roller can be used. In particular,
In this embodiment, since an auxiliary roller having a cored bar of 6 mm is used, the amount of bending is 0.25 mm, and the amount of bending can be greatly reduced.

When the electrical resistance of the transfer auxiliary roller 55 is, for example, a conductive elastic roller having a volume resistance value of 10 ⁵ (Ω / cm) or less, a transfer bias applied to the transfer roller 54 is applied via the transfer auxiliary roller 55. It may be more effective. For example, the following cases.

  When a transfer bias is applied to the transfer roller 54 having a core metal diameter of 2 (mm), the transfer bias contact is brought into contact with the end of the core metal. However, since the diameter is small, there may be a case where the contact is not stable due to vibration or the like during the image forming operation. On the other hand, since the core diameter of the auxiliary transfer roller is sufficiently large, a stable transfer bias can be applied without causing the contact failure as described above.

  As described above, by reducing the diameter of the transfer roller, it is possible to suppress the occurrence of pre-transfer between the transfer roller and the intermediate transfer belt and to suppress the occurrence of transfer scattering caused by the pre-transfer. Furthermore, the transfer roller is restrained from being bent by the transfer auxiliary roller due to the reduction in the diameter of the transfer roller, and a transfer nip can be formed over the entire length of the transfer roller. Transfer defects and image quality degradation are eliminated, and high-quality images can be reproduced.

<Embodiment 2>
FIG. 4 is a schematic sectional view of a multicolor image forming apparatus for explaining the present embodiment. The feature of this embodiment is that
The pressurizing process of the transfer roller is performed by the bias of the transfer auxiliary roller.

The transfer roller 54 as the first transfer member is a foaming elastic roller (core metal diameter φ2 (mm)) having an outer diameter of 4 (mm),
The volume resistivity is adjusted to 10 ⁸ (Ω / cm). The transfer auxiliary roller 55 is an elastic roller having an outer diameter of 14 (mm).

  The end portion of the transfer roller 54 is held and held by a holder 57 and is configured to be movable in the urging direction by the transfer auxiliary roller 55. The end of the transfer auxiliary roller 55 is fixed by a holder 57.

  Since the axial direction of the transfer roller 54 and the auxiliary transfer roller 55 is fixed by the holder 57, the urging direction by the urging means S2 is coaxial with the axial direction. By applying 500 gf of pressure to the holder 57 by the urging means S2, the transfer auxiliary roller 55 brings the transfer roller 54 into contact with the intermediate transfer belt 5 while ensuring a predetermined nip width.

  Further, since the transfer roller 54 can be moved, the pressing by the transfer auxiliary roller 55 having a larger diameter than the transfer roller 54 stabilizes the contact of the transfer roller 54 with the second image carrier 5.

  By pressing the transfer roller 54 with a predetermined pressure by the transfer auxiliary roller 55, the transfer roller 54 is not bent while using the transfer roller 54 with a small diameter. As a result, it is possible to suppress the occurrence of pre-transfer and realize narrow-area transfer. Further, since there is no bending of the transfer roller, the transfer roller 54 can be brought into contact with the intermediate transfer belt 5 uniformly, and a multicolor image forming apparatus that does not cause image deterioration due to a decrease in transferability is provided. It becomes possible to provide.

<Embodiment 3>
Next, Embodiment 3 of the present invention will be described with reference to FIG. FIG. 5 is a schematic sectional view of the image forming apparatus for explaining the present embodiment.

  The peripheral constituent members and their functions will be described focusing on the transfer roller 6 as a transfer device and its transfer auxiliary roller.

  The intermediate transfer belt 5 is the same as that in the first embodiment.

  The tension roller 53 of the intermediate transfer belt 5 is a roller facing the transfer roller 6 and is an elastic roller having an outer diameter of 30 (mm) having a rubber layer (conductive EPDM) having a thickness of 1 (mm) as an outermost layer. By having the elastic layer, the transportability of the intermediate transfer belt 5 is improved, and the transferability is improved due to the increased adhesion between the intermediate transfer belt 5 and the transfer material due to the pressure of the transfer roller 61.

The transfer roller 61 is an elastic roller having an outer diameter of 4 (mm) having a volume resistivity adjusted to 10 ⁷ (Ω / cm) and having an outermost layer of 1 (mm) as an elastic layer. This roller is supported in a state where both ends are fixed by bearings. At the time of image formation, power is supplied to the cored bar portion of the transfer roller 61.

  The auxiliary transfer roller 62 is an elastic roller having an outer diameter of 20 (mm). Both ends of the roller are designed so that a load of 2 kgf on one side is applied and a desired pressure is applied to the transfer material via the transfer roller 61.

表２は実施の形態１中の表１と同様の撓み量を示したものである。表２においては、図２で例示した芯金の長手中央部に４ｋｇｆの荷重を加えた場合の芯金の撓み量δである。

Table 2 shows the same amount of deflection as Table 1 in the first embodiment. In Table 2, the deflection amount δ of the metal core when a load of 4 kgf is applied to the longitudinal central portion of the metal core illustrated in FIG.

  As described above, as in this embodiment, the transfer to the transfer material is also controlled by the (small-diameter roller + transfer auxiliary roller) structure, thereby suppressing the transfer scattering caused by the pre-transfer of the transfer portion. It becomes possible to do. Further, since the small-diameter transfer roller is prevented from being bent by the auxiliary roller, a uniform transfer nip can be obtained and satisfactory transferability can be maintained.

  In the present embodiment, the configuration using the intermediate transfer belt is described. However, the effect of the present embodiment is not limited to the multicolor image forming apparatus from the viewpoint of maintaining good transferability with respect to the transfer material. This also shows that the same effect can be obtained in a monochrome image forming apparatus.

  The present invention is useful for image forming apparatuses such as copying machines and laser beam printers that employ an electrophotographic system.

It is a figure explaining the image forming apparatus which concerns on Embodiment 1 of this invention. It is a figure explaining the measuring method of the deflection amount of the transfer member which concerns on this invention. It is a figure explaining the biasing means which concerns on Embodiment 1 of this invention. It is a figure explaining the biasing means which concerns on Embodiment 2 of this invention. It is a figure explaining the image forming apparatus which concerns on Embodiment 3 of this invention. It is a figure explaining a prior art example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging member 3 Exposure apparatus 4 Developing apparatus 5 Intermediate transfer belt 8 Fixing apparatus 54 Transfer roller 55 Transfer auxiliary roller 61 Transfer roller 62 Transfer auxiliary roller

Claims (5)

A step of transferring a toner image on the first image carrier to the second image carrier, and a transfer member that performs the transfer step is in contact with the second image carrier, and a conductive material to which a predetermined bias is applied In an image forming apparatus having an elastic roller,
An image forming apparatus characterized in that an auxiliary member is disposed at a position facing the image carrier centering on the conductive elastic roller in a state of extending in parallel with the longitudinal direction of the conductive elastic roller. apparatus.   The image forming apparatus according to claim 1, wherein the auxiliary member is a roller-shaped member configured by covering the periphery of the metal shaft with an elastic body, and has higher bending rigidity than the conductive elastic roller.   The outer diameter of the conductive elastic roller is less than the region where the toner image on the first image carrier that is not in contact with the second image carrier is not affected by the electric field due to the transfer bias applied to the conductive elastic roller. The image forming apparatus according to claim 1, wherein the image forming apparatus is provided.   3. The image forming apparatus according to claim 2, wherein the conductive elastic roller is pressed against the image carrier by the conductive elastic roller.   The image forming apparatus according to claim 2, wherein the conductive elastic roller is pressed against the image carrier through an auxiliary member.

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