JP4074229B2 - Color image forming apparatus - Google Patents

Description

（シート感光体の幅を０．３５ｍとするとシート感光体の厚さｔは１．８×１０^−４ｍ （0.18ｍｍ）となる。）
【００３８】
実際の実施例ではシート感光体１−２の厚さは、容易に入手可能なベースシート厚さから、０．２ｍｍとしている。
【００３９】
これによってシート感光体１−２の中間転写媒体６による伸びは０．０４ｍｍ以下に抑えることが可能となり、ひいては画像重ね合わせ誤差が許容値を超えることがない構成が実現できた。また、ヤング率Ｅが３．５×１０^９ Ｐａ〜４．５×１０^９ Ｐａの範囲内で変更しても、画像重ね合せ誤差が許容値を超えることがない構成が実現できた。
【００４０】
上記（１）式に基づいた場合、上記の伸びを０．０４ｍｍ以下にするには、シート断面積をいくらにすればいいか、又は、シート厚みをいくらにすればいいかを、図５（ａ）または（ｂ）に示す。すなわち、図５（ａ）、（ｂ）においては、ともに、Ｆ ＝ ３０ Ｎ、Ｌexp＝３３５ ｍｍとし、縦弾性係数をパラメータとしている。パラメータは、ポリエチレンテレフタレート（ＰＥＴ）、ポリイミド（Ｐｌ）、アルミニュウムの３種類を用いている。そして、図５（ａ）は、シート断面積とシート伸びの関係を示している。この図５（ａ）から、それぞれの材質のとき、つまり、それぞれのパラメータのときに、０．０４ｍｍ以下とするには、シート断面積をいくらにすればいいかが分かる。また、図５（ｂ）は、シート断面積に代えて、シート厚みを、横軸にとっている。つまり、シート幅を、０．３５ｍに決め、そのときのシート厚みを横軸にとっている。この図５（ｂ）によっても、伸びを、０．０４ｍｍ以下にするに当たり、シート厚みをいくらにすればいいかが分かる。
【００４１】
本発明の実施形態では液体トナーを用いた画像形成プロセスについて説明してきたが、乾式トナーを用いる画像形成プロセスを採用するカラー画像形成装置に本発明を適用できることは明白である。また、シート感光体にかかる接線力が上記本実施形態のような中間転写媒体によるもの以外にも、例えばブレードクリーニングによる感光体クリーナを採用した画像形成装置に代表されるよう他の構成による接続力で伸ばされるものにも適用可能である。
【００４２】
【発明の効果】
以上説明したように、本発明によれば、感光体に中間転写媒体を圧接させ、感光体上の画像を中間転写媒体に転写させるようにしたこの感光体として、シート感光体を採用するカラー画像形成装置において、中間転写媒体の接線力によってシート感光体が伸張しようとても、この伸びを許容範囲内に納めることができ、よって、複数の色の画像を重ね合わせる際に発生する画像間のずれを極力抑制し、実際上問題がない範囲とすることが可能となる。ひいては、画像重ね合わせ精度を高く維持できるために、極めて良好な画質のカラー画像形成装置を提供することができる。
【図面の簡単な説明】
【図１】本発明のある実施態様によるカラー画像形成装置の要部の概要構成を示す側面図。
【図２】図１に示す本発明にかかる実施形態のシート感光体保持機構部を説明する部分構成図。
【図３】図１の本発明にかかる実施形態で感光体がLexpだけ回転した場合を説明する説明図。
【図４】本発明にかかるシート感光体の剛性モデルを表す概略説明図。
【図５】ある決められた条件のもとで、伸びを０．０４ｍｍ以下にするためには、シート感光体の断面積または厚みをいくらにすればいいかを示すグラフ。
【符号の説明】
１ 画像記録媒体（感光ドラム）
１−２ シート感光体
２−１〜２−４ 帯電器
３−１〜３−４ LED（プリント）ヘッド（露光器）
４−１〜４−４ 現像器
６ 中間転写媒体
７ 加圧ローラ
９ 用紙
３０ 転写ニップ部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a color image forming apparatus for transferring an image from a sheet-like image recording medium as a photoreceptor to a sheet via an intermediate transfer medium for forming a color image.
[0002]
[Prior art]
There are various image forming methods for forming a color image on an image forming medium (transfer material) such as paper. For example, an electrophotographic method in which an electrostatic image (electrostatic latent image) is formed on a photosensitive drum, visualized with toner, and transferred onto paper, an ink jet method in which ink droplets are directly sprayed on paper, and a photosensitive color developing material. A silver salt photographic system in which an image is exposed and recorded is known. Printing apparatuses using an electrophotographic system include the following. That is, one has a drum-shaped photoreceptor, and a toner image of one color of yellow, magenta, and cyan (and black if necessary) as the three primary colors for color image formation is exposed to the photosensitive material. This is a one-photoreceptor sequential transfer system in which the toner is formed on a body and transferred onto paper, and this process is repeated three times (or four times) for each color. Also, four units (black and three primary colors) of a single-color image forming unit that forms a single-color toner image are arranged in the paper transport direction, and each unit sequentially superimposes a single-color image on one sheet of paper to form a composite color on this sheet. There is a tandem method for forming an image. Further, image forming means for three primary colors are arranged around the photoconductor, and a plurality of single-color images are sequentially superimposed on the surface of the photoconductor by these image forming means, thereby forming a color image on the photoconductor. There is also a batch transfer method in which images are transferred onto paper at once.
[0003]
The image formation speed of the batch transfer method can achieve a color image formation speed that is 3 to 4 times faster than the one-photoreceptor sequential transfer method when the rotational surface speed of the photoreceptor is the same. . Further, when this batch transfer method is compared with the tandem method, it can be said as follows. That is, both the batch transfer method and the tandem method are suitable for high-speed color image formation. In general, each of the plurality of sheets has various mechanical characteristics, and due to this, a slight variation in the transfer position tends to occur. For this reason, in the tandem system, it is difficult to maintain the accuracy of superimposing each single color image. On the other hand, since the batch transfer method first superimposes monochromatic images on the surface of a single photoconductor, it has the advantage that the overlay accuracy is relatively good compared to the tandem method. . However, in this batch transfer method, in order to form an image for the second color and thereafter, irradiation light for forming an image for the second color and later is applied to a photoconductor on which a toner image of a certain color is already formed on the surface. Irradiate (multiple exposure). At present, dry toners, which dominate the electrophotographic system, have a large particle size (7 to 13 μm) and have poor translucency because they are toners before heat fixing. As a result, the first color image becomes a shadow for the irradiation light for forming the second and subsequent images, and there is a drawback that a high-quality color image cannot be obtained because the electrostatic latent image is not sufficiently formed. A wet electrophotographic method using a liquid developer is being researched and developed as a method capable of overcoming this drawback and achieving both high-speed image formation and high-quality image formation. One of the merits is that a toner having a very small particle size of submicron size is used. That is, since such a liquid developer of toner having a small particle diameter is used, the problem at the time of multiple exposure as in the case of using a dry toner having a large particle diameter as described above is solved.
[0004]
Further, the advantages of a wet electrophotographic color image forming apparatus using a liquid developer include the following. That is, a sufficient image density can be obtained with a small amount of toner, which is economical and can achieve a texture similar to printing. In addition, energy can be saved because it can be fixed on paper at a relatively low temperature.
[0005]
In the batch transfer method described above, a composite color image of a plurality of colors is created on the surface of one photoconductor. This color image is transferred to an intermediate transfer medium in pressure contact with the photoreceptor and having a rubber layer formed on the surface. Thereafter, a transfer process is performed in which the color image on the surface of the intermediate transfer medium is transferred to the conveyed paper. The purpose of this transfer process is as follows. That is, to obtain a good color image regardless of the type of paper on which the color image is transferred. Furthermore, the liquid image in which the solvent component and the toner as the image material are mixed together causes the solvent component contained in the color image formed on the surface of the photoreceptor to evaporate as much as possible, and is transferred to the paper. This is because there is as little solvent component as possible and only toner component.
[0006]
In such a batch transfer system (color image forming system using multiple exposure), an image forming means (unit) comprising a charger, an exposure unit, and a developing unit is provided around the photosensitive drum (image recording medium). Since the arrangement is made for four colors, magenta, cyan, and black, it is inevitable that the diameter of the photosensitive drum becomes large.
[0007]
In the case of a large-diameter photosensitive drum, there are cases where the replacement work of the photosensitive drum is complicated and there is a problem such as high cost. For this reason, it is common to employ a photosensitive drum (image recording medium) having a structure in which a sheet-shaped photosensitive member is wound around an element tube for a photosensitive drum. When such a sheet photoreceptor is used, it is only necessary to replace the sheet photoreceptor when the life of the photosensitive layer is reached, or the sheet photoreceptor is sent to the inside of the tube for the photosensitive drum and provided with a winding mechanism. It is also possible to automatically perform an exchange operation for shifting the used portion of the sheet photoreceptor to the unused portion. Moreover, it is very economical without replacing the above-mentioned element pipe, which is expensive because of its large diameter.
[0008]
On the other hand, in a color image forming apparatus using liquid toner, the photosensitive drum and the intermediate transfer medium are pressed against each other with a linear load of about 1 to 4 kg / cm in order to transfer the color image therebetween. It has been. Further, the surface speed of the photosensitive drum is set to be about 2 to 3% faster than that of the intermediate transfer medium. For this reason, the sheet photosensitive member wound around the surface of the bare tube of the photosensitive drum always receives a tangential force from the intermediate transfer medium in the transfer process to the intermediate transfer medium.
[0009]
As described above, the life of the photoconductor is shorter than the life of the entire image forming apparatus, and is a component that must be replaced as a consumable. The method of adhering the entire back surface of the sheet photoreceptor to the surface of the raw tube with an adhesive or the like can be practically employed when the area of the sheet photoreceptor is small. However, when the area of the sheet photosensitive member is increased or the length thereof is increased, it is very difficult to uniformly attach or remove the entire surface of the sheet photosensitive member to the surface of the raw tube. For example, a wrinkle is generated in the new sheet photosensitive member during the replacement operation to the new sheet photosensitive member. Further, when the sheet photosensitive member is increased in size, the operation of removing the sheet photosensitive member that has reached the end of its life becomes very complicated.
[0010]
In order to solve such a problem, the end of the sheet photosensitive member on the winding side is fixed to a state where a sheet elongation absorbing mechanism such as a tensioner is provided at the end of the winding reel. As a result, even if elongation occurs in the sheet photosensitive member, the elongation is absorbed by the elongation absorbing mechanism, so that the occurrence of the above-described problems such as pressure rupture due to the intermediate transfer medium is suppressed.
[0011]
However, there are also problems with the above configuration, which are as follows. That is, since the sheet photoreceptor is allowed to stretch due to the tangential force of the intermediate transfer medium, the position of the image recorded by the exposure means for the first color when forming a color image, and the next That is, the position of the image recorded by the color exposure means is shifted by the elongation of the sheet photoreceptor.
[0012]
That is, an image is recorded by the first exposure means, then an image is recorded by the second exposure means, and this is repeated in sequence, and the photosensitive drum is rotated to the position recorded by the nth exposure means. To do. In this case, naturally, the sheet photosensitive member is stretched by receiving a tangential force from the intermediate transfer medium. The elongation is absorbed by the elongation absorbing mechanism at the rear end of the sheet photoreceptor. For this reason, the position of the nth image position is changed by an amount equivalent to the elongation of the sheet photoreceptor relative to the first image position. For this reason, an overlay error occurs in images of a plurality of colors.
[0013]
As described above, the color image forming apparatus forms a full-color image by superposing a plurality of basic colors of yellow, magenta, cyan, and black. For this reason, it is natural that the overlay accuracy of each color is an important factor for improving the image quality. However, a conventional color image forming apparatus using a sheet photoreceptor has a problem in that an overlay error due to the elongation of the sheet photoreceptor occurs and the quality of the color image is lowered due to the above-described reason.
[0014]
[Patent Document 1]
JP 2000-347520 A
[0015]
[Problems to be solved by the invention]
As described above, in a color image forming apparatus including a sheet photoreceptor and an intermediate transfer medium, it is inevitable that the sheet photoreceptor is stretched by a tangential force from the intermediate transfer medium. That is, in an image forming apparatus in which a plurality of color image forming units (image forming units) are arranged around a photoconductor and images of each color are sequentially superimposed on the surface of the sheet photoconductor to form a color image. It is inevitable that an image overlay error occurs due to the elongation of the sheet photosensitive member. And when each color deviation exceeds an error amount allowed for a color image, there is a problem that the image quality is remarkably deteriorated.
[0016]
The present invention uses a photosensitive drum in which a sheet photosensitive member is wound around an element tube, temporarily transfers a color image formed on the surface of the sheet photosensitive member to an intermediate transfer medium, and transfers the color image from the intermediate transfer medium to paper. An object of the present invention is to provide a color image forming apparatus in which the sheet photoconductor is little stretched and the image overlay error of each color is less than an allowable value and the image quality is good.
[0017]
[Means for Solving the Problems]
In order to achieve the above object, the present invention takes the following configurations and means. That is, the color image forming apparatus of the present invention is a drum-shaped image recording medium, in which a sheet photoreceptor is wound around an outer periphery of a raw tube so as to be freely slidable with respect to each other. A plurality of different color forming units arranged around the image recording medium, each unit including a charger, an exposure unit, and a developing unit. A plurality of image forming units that form images with different color toners as superimposed images on the outer peripheral surface thereof as they rotate, and the image recording medium in a state of being in pressure contact with the image recording medium The intermediate transfer medium on which the superimposed image on the image recording medium is transferred, and the opposite direction while being in pressure contact with the intermediate transfer medium. A pressure roller that passes the material to be transferred between the sheet and fixes the superimposed image on the object to be processed, and the sheet photoreceptor is in contact with the intermediate transfer medium at a lower speed. The elongation Δx per distance Lexp on the outer peripheral surface of the image recording medium between the first and last exposure units of the plurality of units, which is extended by the force F received from the intermediate transfer medium, The longitudinal elastic modulus E of the sheet photoconductor and the cross-sectional area A of the sheet photoconductor in the cross section along the axis of the image recording medium are set so as to be 0.04 mm or less as an allowable value. It is characterized by.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to FIGS.
In this embodiment, a color image forming apparatus using liquid toner as a developer will be described as an example.
[0019]
An image recording medium (photosensitive drum) 1 is obtained by winding a sheet photoconductor 1-2 around a base 1-1. The sheet photoreceptor 1-2 is formed as a multilayer structure in which a conductive substrate is formed on the surface of a resin sheet and an organic photosensitive layer is provided on the surface. A method for attaching the sheet photosensitive member 1-2 to the base will be described later.
[0020]
Around the image recording medium 1, developing means (units) of yellow, magenta, cyan, and black are sequentially provided along the rotation direction of the medium 1. This will be described below.
[0021]
First, the yellow developing means will be described. The image recording medium 1 is uniformly charged by a first charger 2-1 as a well-known corona charger (or scorotron charger). Thereafter, the first LED head (LED print head) (exposure unit) 3-1 is exposed to form an electrostatic latent image on the surface. After that, the electrostatic latent image is visualized by the first developing device (developing device) 4-1 that stores the liquid developer. (In the case of a monochromatic color image forming apparatus, the liquid developer (or toner) adhering to the electrostatic latent image reaches the transfer process as it is and is transferred onto the paper by the transfer apparatus 5.) Development is performed. That is, a second developing device that forms a second electrostatic latent image by laser exposure of the second charger 2-2 and the second LED head 3-2 and stores a second developer (magenta). Develop this with 4-2. Thereby, after the second development, two color toner images of yellow and magenta are formed in an overlapped state on the image recording medium 1.
[0022]
Similarly, third and fourth development (cyan and black development) are performed. That is, on the image recording medium 1, four color images are superposed to form a full color toner image. This toner image is transferred onto the paper 9 by the transfer device 5. That is, as can be seen from FIG. 1, the image is transferred to the paper 9 via the intermediate transfer medium 6.
[0023]
In order to transfer from the image recording medium 1 to the intermediate transfer medium 6 and further from the intermediate transfer medium 6 to the paper 9, a transfer system using pressure and heat is used. A drying unit 25 is provided to improve the transfer efficiency from the image recording medium 1 to the intermediate transfer medium 6 and prevent the solvent component contained in the liquid toner from adhering to the paper 9. That is, the solvent component is dried and removed from the toner image on the surface of the image recording medium 1 by the drying unit 25. Since the drying unit 25 is a well-known unit, although not described in detail here, the solvent is removed by blowing a large amount of air and high-speed air onto the image recording medium 6 and drying it. In this way, the color image having only the toner solid component on the image recording medium 1 by the drying unit 25 is first transferred to the intermediate transfer medium 6. As described above, the method using pressure and heat is adopted as the transfer method. More specifically, in the intermediate transfer medium 6, the surface of the roller as a substrate is covered with a transfer layer made of silicon rubber, and a heater is installed inside the roller, so that the silicon rubber as the surface layer is about 80%. It can be heated to about ~ 100 ° C. The intermediate transfer medium 6 is energized and pressed against the image forming medium 1 with a linear load of about 1 to 4 kg / cm. The toner image formed on the surface of the image forming medium 1 is transferred to the intermediate transfer medium 6 so as to be peeled off by a shearing force. In order to improve the transfer efficiency, the surface speed due to the rotation of the intermediate transfer medium 6 is set to be about 2 to 3% slower than the surface speed due to the rotation of the image forming medium 1.
[0024]
Next, the full color image transferred from the image recording medium 1 to the intermediate transfer medium 6 in this way is further transferred to the paper 9 by the transfer device 5. That is, the pressure roller is heated to about 100 ° C. by an internal heater. The pressure roller 7 and the intermediate transfer medium 6 are in pressure contact with each other. The full-color toner image on the intermediate transfer medium 6 is pressed and transferred onto the sheet 9 conveyed by the nip between these two members (6, 7). Thus, a series of color image forming steps is completed.
[0025]
Next, the substrate 1-1 and the sheet photosensitive member 1-2 in the photosensitive drum 1 will be described in more detail with reference to FIG. In the present embodiment, a feeding mechanism and a winding mechanism are provided at both ends of the long sheet photosensitive member 1-2. That is, both ends of the sheet photosensitive member 1-2 are wound in a roll shape to form the feeding portion 1-3 and the winding portion 1-4. Further, the feeding portion 1-3 and the winding portion 1-4 of the sheet photosensitive member 1-2 are rotatably supported by shafts 6 and 1-7 so as to be fed into the substrate 1-1 and rotated. Yes. Then, the sheet photosensitive member 1-2 is sent out in a rewind state from the sending-out unit 1-3, and the slit 1-5 is provided from the inside to the outside, and covers the outer periphery of the base body 1-1 in the counterclockwise direction in FIG. This time, conversely, the slit 1-5 is passed through from the outside to the winding section 1-4.
[0026]
The delivery mechanism is provided with a lock mechanism (not shown) that restrains rotation of the shafts 1-6 and 1-7 that rotatably support the delivery unit 1-3 on the image recording medium 1. When the sheet photosensitive member 1-2 is fed out, the lock mechanism is set free, and is locked during image formation to restrict the feeding of the sheet photosensitive member 1-2.
[0027]
On the other hand, in the winding mechanism 1-4, the shaft 1-7 is wound around the shaft 1-7 in a fixed state, and the shaft 1-7 is driven by a driving device (not shown). The sheet photoreceptor 1-2 is wound up by rotating counterclockwise. A one-way clutch (not shown) is attached to this shaft 1-7 so that it can rotate only in the winding direction. Further, a downward preload (biasing force) in the drawing is applied to the shaft 1-7 by a tension spring 1-8 via a bearing that rotatably holds both ends of the shaft. As a result, the sheet photosensitive member 1-2 is always tensioned in the winding direction, so that it is pulled along the left rotation direction of the outer peripheral surface of the substrate 1-1 in the drawing and is tightly stretched without wrinkles. Maintained.
[0028]
As described above, the surface rotation speed of the intermediate transfer medium 6 was set to be 2-3% slower than the surface rotation speed of the image recording medium 1. For this reason, the sheet photosensitive member 1-2 receives a tangential force F at the contact portion with the intermediate transfer medium 6. The tangential force F causes the sheet photoreceptor 1-2 to stretch. This elongation is absorbed within the elastic range of the tension spring 1-8 provided at the winding portion of the sheet photoreceptor 1-2. For this reason, even if the sheet photosensitive member 1-2 rotates while receiving the tangential force F from the intermediate transfer medium 6, the sheet photosensitive member 1-2 is bent by the elongation, or the bent portion is bent by the intermediate transfer medium 6. Therefore, it is possible to prevent the occurrence of problems such as breakage as much as possible.
[0029]
As described above, even if the elongation of the sheet photosensitive member 1-2 is absorbed by the winding mechanism, the sheet photosensitive member 1-2 itself does not extend. For this reason, the image position on the sheet photoreceptor 1-2 formed by the first LED head 3-1 and the image position formed by the nth LED head are the extension of the sheet photoreceptor 1-2. It is inevitable that they will shift by minutes. This will be described more specifically with reference to FIGS.
[0030]
In the present embodiment, the image position is most shifted between the image position by the first LED head 3-1 and the image position by the fourth LED head 3-4. The following description will be made by paying attention to the shift of the second image position.
[0031]
The distance between the installations of the first and fourth LED heads 3-1 and 3-4 is Lexp as shown in FIG. The sheet photosensitive member 1-2 has a sheet photosensitive member length from the fixed end FP of the feeding portion 1-3 of the sheet photosensitive member 1-2 to the contact point 30 of the intermediate transfer medium 6 due to the tangential force F of the intermediate transfer medium 6. Elongation occurs in response to. As shown in FIG. 1, when the intermediate transfer medium 6 is in contact with the slit portion 1-5 of the substrate (element tube) 1-1 of the photosensitive drum, the tangential force F applied to the sheet photosensitive member 1-2 is zero. . At this time, it is assumed that image formation of the first color is started by the first LED head 3-1. On the sheet photoconductor 1-2, images are sequentially formed in the first to fourth colors with rotation. As can be seen from FIG. 3, when the leading edge of the image formed with the first color (yellow) reaches the fourth LED head 3-4, the first color (black) already has the first 1-th color. Further image formation is started on the image formed with the third color. The amount of movement of the photosensitive drum at this time is Lexp, and the sheet length from the fixed end FP on the delivery side of the sheet photosensitive member 1-2 to the contact point 30 of the intermediate transfer medium 6 is Lexp. As described above, since the tangential force F is applied to the sheet photosensitive member 1-2 by the intermediate transfer medium 6, the elongation Δx occurs. The elongation Δx of the sheet photosensitive member 1-2 is absorbed by the tension spring 1-8 of the winding mechanism. For this reason, at the timing when the fourth LED head 3-4 starts image formation, the leading edge of the first color image is shifted backward by the elongation Δx of the sheet photosensitive member 1-2. That is, the fourth color image is superimposed on the first color image with a shift of Δx. This Δx is an image overlay error.
[0032]
In the present embodiment, this image overlay error is suppressed as follows.
[0033]
In FIG. 3, it is assumed that the sheet photosensitive member 1-2 receives a tangential force F from the intermediate transfer medium 6 at a point 30 of a length Lexp from the fixed end FP, and an elongation Δx occurs. At this time, the sheet photoreceptor 1-2 is provided with rigidity so that the elongation Δx is smaller than the allowable image overlay error XL.
[0034]
As shown in FIG. 4, the sheet photosensitive member 1-2 is assumed to have a model in which one end is a fixed end FP and a tensile force corresponding to a tangential force F from the intermediate transfer medium 6 is added to the other end. The elongation of the sheet photoreceptor 1-2 at this time is expressed by the following formula.
Δx = F · Lexp / E · A (1)
Here, E: longitudinal elastic modulus, A: cross-sectional area.
[0035]
Based on the equation (1), the specifications of the sheet photosensitive member 1-2 are determined so that the image overlay error due to the elongation Δx is smaller than the allowable value. In the present embodiment, the material and shape are such that the elongation Δx of the sheet photoreceptor 1-2 is 0.04 mm.
[0036]
The basis for setting the amount of elongation is as follows. In general, it is said that the tolerance value XL for overlay deviation is 0.06 to 0.07 mm as a level at which image deviation in a color image is not a concern. Therefore, the overlay error other than that caused by the elongation of the sheet photosensitive member is set to be about 0.02 mm.
[0037]
One example of the sheet photoreceptor 1-2 is shown below.

(If the width of the sheet photosensitive member is 0.35 m, the thickness t of the sheet photosensitive member is 1.8 × 10 ^-4 m (0.18 mm). )
[0038]
In the actual embodiment, the thickness of the sheet photoreceptor 1-2 is set to 0.2 mm from the readily available base sheet thickness.
[0039]
As a result, the elongation of the sheet photosensitive member 1-2 due to the intermediate transfer medium 6 can be suppressed to 0.04 mm or less, and as a result, a configuration in which the image overlay error does not exceed the allowable value can be realized. Young's modulus E is 3.5 × 10 ⁹ Pa ~ 4.5 × 10 ⁹ Even if it is changed within the range of Pa, a configuration in which the image overlay error does not exceed the allowable value can be realized.
[0040]
Based on the above equation (1), in order to reduce the elongation to 0.04 mm or less, how much the sheet cross-sectional area should be increased or how much the sheet thickness should be increased is shown in FIG. Shown in a) or (b). That is, in FIGS. 5A and 5B, both F = 30 N and Lexp = 335 mm, and the longitudinal elastic modulus is used as a parameter. Three types of parameters are used: polyethylene terephthalate (PET), polyimide (Pl), and aluminum. FIG. 5A shows the relationship between the sheet cross-sectional area and the sheet elongation. From FIG. 5 (a), it can be seen how much the sheet cross-sectional area should be set to 0.04 mm or less for each material, that is, for each parameter. FIG. 5B shows the sheet thickness on the horizontal axis instead of the sheet cross-sectional area. That is, the sheet width is determined to be 0.35 m, and the sheet thickness at that time is on the horizontal axis. Also from FIG. 5 (b), it can be seen how much the sheet thickness should be set when the elongation is 0.04 mm or less.
[0041]
In the embodiments of the present invention, the image forming process using liquid toner has been described. However, it is obvious that the present invention can be applied to a color image forming apparatus employing an image forming process using dry toner. Further, in addition to the tangential force applied to the sheet photosensitive member by the intermediate transfer medium as in the present embodiment, for example, the connecting force by another configuration such as an image forming apparatus employing a photosensitive cleaner by blade cleaning is used. It can also be applied to those stretched by.
[0042]
【The invention's effect】
As described above, according to the present invention, a color image employing a sheet photoreceptor as this photoreceptor in which an intermediate transfer medium is pressed against the photoreceptor and an image on the photoreceptor is transferred to the intermediate transfer medium. In the forming apparatus, the sheet photosensitive member is stretched by the tangential force of the intermediate transfer medium, and this elongation can be kept within an allowable range. Therefore, the shift between images generated when superimposing a plurality of color images is eliminated. It is possible to suppress it as much as possible and to make it practically no problem. As a result, since the image overlay accuracy can be maintained high, a color image forming apparatus with extremely good image quality can be provided.
[Brief description of the drawings]
FIG. 1 is a side view showing a schematic configuration of a main part of a color image forming apparatus according to an embodiment of the present invention.
FIG. 2 is a partial configuration diagram illustrating a sheet photoconductor holding mechanism unit according to the embodiment shown in FIG. 1;
FIG. 3 is an explanatory diagram for explaining a case where the photoconductor rotates by Lexp in the embodiment according to the present invention of FIG. 1;
FIG. 4 is a schematic explanatory diagram showing a stiffness model of a sheet photosensitive member according to the present invention.
FIG. 5 is a graph showing how much the cross-sectional area or thickness of a sheet photosensitive member should be reduced in order to make elongation equal to or less than 0.04 mm under a predetermined condition.
[Explanation of symbols]
1 Image recording medium (photosensitive drum)
1-2 Sheet photoconductor
2-1 to 2-4 Charger
3-1 to 3-4 LED (print) head (exposure device)
4-1 to 4-4 Developer
6 Intermediate transfer media
7 Pressure roller
9 paper
30 Transfer nip

Claims (5)

A drum-shaped image recording medium, wherein the sheet photosensitive member is disposed on the outer periphery of the raw tube in a wound state so as to be freely slidable with each other;
A plurality of units for forming images of different colors arranged around the image recording medium, each unit having a charger, an exposure unit and a developing unit for rotating the image recording medium Along with this, on the outer peripheral surface, a plurality of image forming units for forming images with different color toners as superimposed images,
An intermediate transfer medium on which the superimposed image on the image recording medium is transferred in a state of being pressed against the image recording medium, rotating in a direction opposite to each other at a lower speed than the image recording medium, and
A pressure roller that rotates in a direction facing each other in a state of being pressed against the intermediate transfer medium, passes a transfer material between the two, and fixes the superimposed image on the object to be processed,
The sheet photosensitive member is stretched by a force F received from the intermediate transfer medium at a contact portion with the intermediate transfer medium at a lower speed than that between the first and last exposure units of the plurality of units. The longitudinal elastic modulus E of the sheet photosensitive member and the image of the sheet photosensitive member so that the elongation Δx per distance Lexp on the outer peripheral surface of the image recording medium is 0.04 mm or less as an allowable value. A color image forming apparatus, wherein a cross-sectional area A in a cross section along an axis of a recording medium is set. The longitudinal elastic modulus E and the cross-sectional area A are
Δx = F ・ Lexp / E ・ A
The color image forming apparatus according to claim 1, wherein the color image forming apparatus is determined based on the following formula. 3. The color image forming apparatus according to claim 1, wherein the longitudinal elastic modulus is 3.5 × 10 ⁹ Pa to 4.5 × 10 ⁹ Pa. 4. Both ends of the sheet photoreceptor are wound around a feeding-side shaft and a winding-side shaft, respectively, and the feeding-side shaft is also fed and rotated by the winding-up rotation of the winding-side shaft. 4. The color image forming apparatus according to claim 1, wherein the sheet photosensitive member wound around the outer periphery of the tube can be renewed. 5. Rotation restraining means for restraining the rotation of the feeding side shaft in the sheet photosensitive member is provided, and in this state, on the winding side shaft side of the sheet photosensitive member on the raw tube of the sheet photosensitive member. 5. A color image forming apparatus according to claim 4, further comprising an urging force applying means for applying an urging force in a direction in which sagging is taken.

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