JP2004029514A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device which is hardly affected by variation in volume resistance value of a transfer roller, an intermediate transfer body, etc., has a stable rate of transfer in one print, and also has small density variation values of a document and a print. <P>SOLUTION: The image forming device is equipped with image carriers by colors of yellow, magenta, cyan, and black, a developing means of developing latent images formed on the respective image carriers with respective corresponding color toners, a primary transfer means of transferring respective toner images formed on the image carriers to the same intermediate transfer body one over another, a secondary transfer means of transferring the toner images formed on the intermediate transfer body one over another together to transfer paper, and a fixing means of fixing the toner images. The device is equipped with a control means of estimating the amounts of sticking toners per unit length in the circumferential direction on the image carriers and controlling a primary transfer current and/or a secondary transfer current according to the estimated toner sticking amounts. <P>COPYRIGHT: (C)2004,JPO

Description

【００５５】
表１に示すように、本発明によれば、１ページ内の転写率は一定であり、テスト原稿との濃度変化量は、原稿濃度値±１０％内となった。なお、比較例の場合は原稿との濃度変化量は、原稿濃度値±２０％であった。
【００５６】
（実施例２）
実施例２は実施の形態２に係わる画像形成装置の実施例である。実施例１と異なる部分を中心に説明する。
【００５７】
図４に示すカラー複写機の画像形成装置を用いてテストを行う。この画像形成装置は、実施例１において、バックアップローラ７Ａ、中間転写ローラ７Ｂがない点、中間転写体６が搬送ベルト９にまた、転写ローラ７Ｙ、７Ｍ、７Ｃ、７Ｋがそれぞれ転写ローラ７２Ｙ、７２Ｍ、７２Ｃ、７２Ｋに置き換わった点以外は機構的に同一である。
【００５８】
テストチャート（原稿）は、０％〜１０％ずつ、１００％まで濃度を増加させた幅方向に帯状のチャートである。なお、主走査方向の各濃度の幅は１５ｍｍとしている。比較例の場合は、像担持体上の周方向の単位長さ当たりのトナー付着量を推定し、推定したトナー付着量に基づき転写電流をフィードバック制御しない。テストデータを表２に示す。なお、表中のデータは１ページ内の濃度差を示している。
【００５９】
【表２】

【００６０】
表２に示すように、本発明によれば、１ページ内の転写率は一定であり、テスト原稿との濃度変化量は、原稿濃度値±１０％内となった。なお、比較例の場合は原稿との濃度変化量は、原稿濃度値±２０％であった。
【００６１】
【発明の効果】
以上のように構成したので、下記のような効果を奏する。
【００６２】
請求項１に記載の発明によれば、イエロー、マゼンタ、シアン、およびブラックの４色のトナーを像担持体にそれぞれ現像させ、像担持体から４色共通の１つの中間転写体上に各トナー像を順次１次転写後、中間転写体から転写紙に２次転写し定着する画像形成装置において、像担持体上の周方向の単位長さ当たりのトナー付着量を推定し、推定したトナー付着量に基づき１次転写電流および／または２次転写電流を制御するようにしたので、１プリント内の転写率が安定して、原稿画像とプリント画像との濃度変化量が小さくできるようになり、さらに、転写する電源側の制御は定電流制御であるので中間転写ローラ、中間転写体の体積抵抗値の変動を受けにくい画像形成装置となる。
【００６３】
請求項５に記載の画像形成装置によれば、イエロー、マゼンタ、シアン、およびブラックの４色のトナーを像担持体にそれぞれ現像させ、像担持体から各トナー像を順次転写紙に転写し定着する画像形成装置において、像担持体上の周方向の単位長さ当たりのトナー付着量を推定し、推定したトナー付着量に基づき転写電流を制御するので、１プリント内の転写率が安定して、原稿画像とプリント画像との濃度変化量が小さくできるようになり、さらに、転写する電源側の制御は定電流制御であるので転写ローラの体積抵抗値の変動を受けにくい画像形成装置となる。
【図面の簡単な説明】
【図１】本発明の実施の形態１に係る画像形成装置の構成を示す断面図である。
【図２】図１の要部構成を示す断面図である。
【図３】中間転写体上のＹトナー像の分布状態を示す説明図である。
【図４】本発明の実施の形態２に係る画像形成装置の要部構成を示す断面図である。
【符号の説明】
１Ｙ、１Ｍ、１Ｃ、１Ｋ　感光体ドラム（像担持体）
４Ｙ、４Ｍ、４Ｃ、４Ｋ　現像手段
６　中間転写体
７Ｙ、７Ｍ、７Ｃ、７Ｋ、７２Ｙ、７２Ｍ、７２Ｃ、７２Ｋ　転写ローラ
７Ａ　バックアップローラ
７Ｂ　中間転写ローラ
３０Ａ、３０Ｙ、３０Ｍ、３０Ｃ、３０Ｋ　制御手段[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus used for a copying machine, a printer, and the like.
[0002]
[Prior art]
At present, in most image forming apparatuses that require high speed and high image quality, an image forming method based on an electrostatic latent image method, mainly an electrophotographic method, is adopted. The reason is that high-quality images can be obtained stably at high speed and can be applied to color images and digital image formation. However, the level of performance required for image forming technology from the market is high, and therefore, further improvement in performance is also required in the electrostatic latent image system.
[0003]
2. Description of the Related Art Conventionally, as an image forming apparatus, four color toners of yellow, magenta, cyan, and black have been developed on an image carrier, and each toner image has been formed on the intermediate transfer member common to the four colors from the image carrier. There is known an apparatus in which after the primary transfer, a secondary transfer from the intermediate transfer body to a transfer sheet is performed and fixed.
[0004]
Further, as another image forming apparatus, there is also an apparatus that develops four color toners of yellow, magenta, cyan, and black on an image carrier, and sequentially transfers and fixes each toner image from the image carrier to transfer paper. Are known.
[0005]
As a method of transferring a toner image in the above-described image forming apparatus, a contact transfer method in which a voltage is applied to a transfer member such as a transfer roller and the transfer member is transferred to a transfer material is widely used. I have. The control on the power supply side for the transfer includes constant voltage control and constant current control. In the constant voltage control, even if the resistance value in the transfer nip changes in the width direction, the current value contributing to the actual transfer does not change, but the constant voltage control changes the resistance of the transfer roller or belt due to the environment and durability. This will directly affect the transfer rate. On the other hand, in the constant current control, the current value is generally constant even if the resistance of the transfer roller and the resistance of the intermediate transfer belt fluctuate in the environment.
[0006]
As the developer used in the image forming apparatus, a one-component developer and a two-component developer are used, and the toner of the two-component developer has a small particle size and a uniform particle size distribution and particle shape. It has been known.
[0007]
[Problems to be solved by the invention]
However, as a problem of the prior art, in the constant current control, if the amount of toner adhering per unit length in the circumferential direction of the image carrier (also referred to as a photosensitive drum) is different, the current value flowing to the toner adhering portion varies. Therefore, there is a problem that the transfer rate changes.
[0008]
In addition, as a problem of the related art, a color copier or a color printer usually uses a plurality of photosensitive drums, and sequentially transfers a single-color image formed by each of the photosensitive drums onto a transfer paper to superimpose a color image. However, when the transfer rate is changed and lowered in the case of manufacturing the color image, there is a problem that not only the image density is lowered but also the color balance is lost. In addition, an intermediate transfer member is used for color image formation, and the influence of the transfer rate is further increased by performing primary transfer to the intermediate transfer member and secondary transfer from the intermediate transfer member to transfer paper twice. There's a problem.
[0009]
SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of a first invention is to develop four color toners of yellow, magenta, cyan, and black on an image carrier, respectively, and to apply four colors from the image carrier. In an apparatus for sequentially transferring each toner image on one intermediate transfer member sequentially and then secondary transferring from the intermediate transfer member to transfer paper and fixing the same, the transfer rate in one print is stabilized, and An object of the present invention is to provide an image forming apparatus which has a small density change amount, is less susceptible to fluctuations in volume resistance values of a transfer roller and an intermediate transfer body, and can obtain high image quality.
[0010]
It is another object of the present invention to form an image by developing toners of four colors of yellow, magenta, cyan, and black on an image carrier, and sequentially transferring and fixing each toner image from the image carrier to a transfer paper. Provided is an image forming apparatus in which the transfer rate in one print is stable, the amount of change in density between a document and a print is small, the volume resistance of a transfer roller is less likely to fluctuate, and high image quality is obtained. It is in.
[0011]
[Means for Solving the Problems]
The first invention can be achieved by the following means.
[0012]
(1) Developing an image carrier for each color of yellow (Y), magenta (M), cyan (C), and black (K) and a latent image formed on each image carrier with a corresponding color toner. Developing means, primary transfer means for each color for sequentially superimposing and transferring each color toner image formed on the image carrier onto the same intermediate transfer body, and superimposed toner image formed on the intermediate transfer body In the image forming apparatus having a secondary transfer unit for collectively transferring the toner image onto the transfer paper and a fixing unit for fixing the toner image, the amount of toner adhering per unit length in the circumferential direction on the image carrier is estimated and estimated. An image forming apparatus comprising: a control unit that controls a primary transfer current and / or a secondary transfer current based on the toner adhesion amount.
[0013]
The second invention can be achieved by the following means.
(2) Developing an image carrier for each color of yellow (Y), magenta (M), cyan (C), and black (K) and a latent image formed on each image carrier with a corresponding color toner. Developing means, a transfer means for sequentially transferring the respective color toner images formed on the image carrier on the same transfer paper and transferring the same, and a fixing means for fixing the superposed toner images formed on the transfer paper. The image forming apparatus further includes a control unit configured to estimate a toner adhesion amount per unit length in a circumferential direction on the image carrier, and to control a transfer current based on the estimated toner adhesion amount. apparatus.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
(Embodiment 1)
An image forming apparatus according to a first embodiment of the present invention will be described. FIG. 1 is a cross-sectional view illustrating a configuration of an image forming apparatus according to Embodiment 1 of the present invention, FIG. 2 is a cross-sectional view illustrating a main configuration of FIG. 1, and FIG. 3 is a distribution of a Y toner image on an intermediate transfer member. It is explanatory drawing which shows a state.
[0015]
First, the configuration of the image forming apparatus of the present invention will be described. As shown in FIG. 1, an image reading device YS including an automatic document feeder 201 and a document image scanning exposure device 202 is provided above the image forming apparatus main body GH. The original d placed on the original platen of the automatic original feeder 201 is transported by a transport unit, and one or both side images of the original are scanned and exposed by the optical system of the original image scanning and exposing device 202, and are scanned by the line image sensor CCD. Is read. The analog signal photoelectrically converted by the line image sensor CCD is subjected to analog processing, A / D conversion, shading correction, image compression processing, and the like in an image processing unit, and then to an image writing unit (image exposure unit) 3Y, 3M, Send signals to 3C and 3K.
[0016]
The automatic document feeder 201 has an automatic double-sided document conveying means. Since the automatic document feeder 201 can continuously read the contents of a large number of documents d fed from the document mounting table at once and accumulate it in the storage means (electronic RDH function), the copying operation can be performed. It is conveniently used when copying the contents of a large number of documents by the function, or when transmitting a large number of documents d by the facsimile function.
[0017]
The image forming apparatus main body GH is called a tandem type color image forming apparatus, and includes a plurality of sets of image forming units 10Y, 10M, 10C, and 10K, a belt-shaped intermediate transfer body 6, a sheet feeding and conveying unit, and a fixing unit 24. And
[0018]
The image forming unit 10Y for forming a yellow image has a charging unit 2Y, an image exposing unit 3Y, a developing unit 4Y using toner, and a cleaning unit 8Y arranged around a photosensitive drum 1Y as an image carrier. The image forming unit 10M for forming a magenta image has a photosensitive drum 1M as an image carrier, a charging unit 2M, an image exposing unit 3M, a toner developing unit 4M, and a cleaning unit 8M. The image forming unit 10C for forming a cyan image and the image forming unit 10K for forming a black image have the same configuration.
[0019]
The charging unit 2Y and the image exposing unit 3Y, the charging unit 2M and the image exposing unit 3M, the charging unit 2C and the image exposing unit 3C, and the charging unit 2K and the image exposing unit 3K constitute a latent image forming unit. The intermediate transfer member 6 is an endless belt, stretched by a plurality of rollers, and supported rotatably. The color images of the respective colors formed by the image forming units 10Y, 10M, 10C and 10K are sequentially transferred onto the rotating intermediate transfer member 6 by transfer rollers 7Y, 7M, 7C and 7K as transfer means, and are primarily transferred. Is completed, and a superimposed color image is formed.
[0020]
The transfer paper P accommodated in the paper feed cassette 20 is fed by the paper feeding means 21 and passes through the paper feed rollers 22A, 22B, 22C, and 22D, the registration roller 23, and the like, and the backup roller 7A and the intermediate transfer roller 7B, and the superimposed color image is transferred onto the transfer paper P (secondary transfer). The transfer paper P on which the color image has been transferred is subjected to a fixing process by a fixing unit 24, and is held by a discharge roller 25 and placed on a discharge tray 26 outside the apparatus.
[0021]
After the color image is transferred onto the transfer paper P by the intermediate transfer roller 7B, the residual toner is removed from the intermediate transfer body 6 from which the transfer paper P is separated by the cleaning unit 8A. Reference numerals 5Y, 5M, 5C, and 5K denote toner supply units that supply toner to the developing units 4Y, 4M, 4C, and 4K, respectively.
[0022]
Next, the main configuration of the above-described image forming apparatus will be further described. 2 and 3, the intermediate transfer member 6 is an endless belt, and has a volume resistance of 1 × 10 ⁷ Ωcm to 1 × 10 ¹¹ Ωcm. The secondary transfer means has a backup roller 7A disposed at a position facing the intermediate transfer roller 7B as a secondary transfer member via the intermediate transfer member 6, and the volume resistance value of the intermediate transfer roller 7B is 1 × 10 ^6.バ ッ ク ア ッ プ 1 × 10 ¹⁰ Ωcm, and the volume resistance of the backup roller 7A is 1 × 10 ⁶ -1 × 10 ¹⁰ Ωcm. Within these ranges, transferability and the like are improved.
[0023]
The control units 30Y, 30M, 30C, 30K, and 30A estimate the toner adhesion amount from the printing rate per unit length in the circumferential direction on the photosensitive drums 1Y, 1M, 1C, and 1K, and based on the estimated toner adhesion amount. The primary transfer current of the primary transfer unit and the secondary transfer current of the secondary transfer unit are controlled so that the transfer rate is constant. More specifically, the printing rate per unit length in the circumferential direction of each photoconductor drum is obtained from the image data, the primary current value is obtained from this printing rate according to a conversion table prepared in advance, and the transfer rate of each photoconductor drum is determined. Voltage is applied to the rollers 7Y, 7M, 7C, and 7K to control the transfer rate to be constant. Similarly, a secondary current value is obtained from the printing rate in accordance with a conversion table prepared in advance, and a voltage is applied to the backup roller 7A to control the transfer rate to be constant.
[0024]
Next, estimation of the toner consumption will be described. In this embodiment, the toner consumption is estimated based on the printing rate. The printing rate is defined as 0% for a blank sheet with no printing in the printing area per unit length in the circumferential direction of each photosensitive drum, and 100% for a state in which printing is completely completed. It is defined as the ratio of the print area to the non-print area in the print area. For example, an image of a single color of white has a printing rate of 0%, a solid image of a single color other than white in the entire area has a printing rate of 100%, and an area where half of the printing area has no white portion and the rest is white. In the case of an image, the printing rate is 50%. Next, the printing rate will be further described by taking a binary image as an example. For example, image data having 256 pixel values is processed by a density conversion circuit for performing brightness / density conversion, a spatial filter processing and a gradation correction circuit, and then binarized by an error diffusion circuit. The binarized image data is stored in a local memory or a hard disk and then transmitted to a second image processing circuit, where it is converted into a PWM signal in a PWM circuit. Independently of this, the counting circuit is provided so that bidirectional data can be exchanged with the bus bridge, and the number of black pixels (or the number of white pixels) and the total number of pixels (the number of white pixels) are determined based on image data. The number of black pixels / the total number of pixels (the number of white pixels + the number of black pixels) × 100.
[0025]
Next, the developer, toner, and the like used in the present invention will be described.
1) Developer The developer used in the present invention may be a one-component developer or a two-component developer, but is preferably a two-component developer. When used as a one-component developer, there is a method of using the toner as it is as a non-magnetic one-component developer, but usually, magnetic particles of about 0.1 to 5 μm are contained in toner particles and used as a magnetic one-component developer. . When used as a two-component developer by mixing with a carrier, known materials such as metals such as iron, ferrite and magnetite, and alloys of these metals with aluminum and metals such as lead are used as magnetic particles of the carrier. Used. The carrier is preferably a carrier in which magnetic particles are further coated with a resin, or a so-called resin-dispersed carrier in which magnetic particles are dispersed in a resin. Although there is no particular limitation on the resin composition for coating, for example, olefin-based resins, styrene-based resins, styrene-acrylic-based resins, and the like are used. The resin for constituting the resin dispersion type carrier is not particularly limited, and a known resin can be used. For example, a styrene acrylic resin, a polyester resin, or the like can be used.
[0026]
2) Toner Number Particle Size Distribution, Toner Number Particle Size Distribution Coefficient of Variation, and Toner Volume Average Particle Size First, the toner number particle size distribution (also referred to as particle size distribution) and the toner particle size distribution variation coefficient will be described. . The particle size distribution represents the relative frequency of the toner particles with respect to the particle size. When the particle size of the toner particles is D (μm), the natural logarithm lnD is plotted on the horizontal axis, and the horizontal axis is divided into a plurality at intervals of 0.23. In the histogram showing the number-based particle size distribution divided into classes, the relative frequency (m1) of the toner particles included in the mode and the relative frequency of the toner particles included in the class having the second highest frequency after the mode. The toner (M) with (m2) is preferably 65% or more. When the sum (M) is 65% or more, the dispersion of the particle size distribution of the toner particles is narrowed. Therefore, the transfer rate is improved by using the toner in the image forming step.
[0027]
In the histogram showing the particle size distribution, the natural logarithm lnD is divided into a plurality of classes (0 to 0.23: 0.23 to 0.46: 0.46 to 0.69: 0.69 to 0.92: 0.92 to 1.15: 1.15 to 1.38: 1.38 to 1.61...) Is a histogram showing the number-based particle size distribution, which is divided according to the following conditions. The particle size data of the sample measured by the Coulter Multisizer is transferred to a computer via an I / O unit, and the computer creates the data using a particle size distribution analysis program. The aperture is 100 μm, and the sample preparation method is to add an appropriate amount of a surfactant to 50 to 100 ml of the electrolytic solution, stir, add 10 to 20 mg of the measurement sample, and disperse the system for 1 minute with an ultrasonic disperser. Prepared by The number variation coefficient in the particle size distribution of the toner is calculated by the number variation coefficient = (S / Dn) × 100 (%), where S represents the standard deviation in the particle size distribution, and Dn represents the volume average particle size (μm). Show.
[0028]
The volume average particle diameter of the toner is 2 μm to 7 μm. When the toner has a volume average particle diameter in this range, toner particles having a large adhesive force that flies and adheres to a heating member to generate an offset in a fixing process are reduced, and transfer efficiency is reduced. As the height increases, the image quality of halftone is improved, and the image quality of fine lines and dots is improved. If it is less than 2 μm, charging is not sufficiently performed, and toner scattering may cause deterioration of image quality or a bad influence on a human body, which is disadvantageous in terms of production efficiency. If it exceeds 7 μm, the problem in the transfer step may not be solved. Preferably, it is 3 μm to 6 μm.
[0029]
The volume variation coefficient of the volume which is 100 times the standard deviation divided by the volume average particle size is 15 to 22%. When the volume variation coefficient of the volume average particle diameter is within this range, the voids in the transferred toner layer are reduced, the charge amount distribution is sharpened, and the transfer efficiency is increased.
[0030]
3) Shape Factor of Toner The shape factor of the toner is represented by ((maximum diameter / 2) ² × π) / projected area, and indicates the degree of roundness of the toner particles. Here, the maximum diameter refers to a width of a particle having a maximum interval between the parallel lines when a projected image of a toner particle on a plane is sandwiched between two parallel lines. The projection area refers to the area of the projected image of the toner particles on the plane. The shape factor of the toner can be determined by taking a photograph in which the toner particles are magnified 2000 times with a scanning electron microscope, and analyzing the photograph image based on the photograph using “SCANNING IMAGE ANALYZER” (manufactured by JEOL Ltd.). Can be measured. At this time, the shape factor of the present invention was measured using the above formula using 100 toner particles.
[0031]
The proportion of toner particles having a shape factor of the toner in the range of 1.2 to 1.6 is 60% by volume or more, and the variation coefficient of the shape factor is 18% or less. Within this range, the state of the external additive present on the toner surface becomes uniform, the charge amount distribution becomes sharp, and high fluidity is obtained. As a result, transfer is performed with good transfer efficiency, and Sometimes, it is possible to prevent the electric charge from being concentrated on the projection portion of the toner and causing dielectric breakdown or the like in a minute space between the photosensitive drum and the intermediate transfer member. Here, image formation of a test document by the image forming apparatus according to the first embodiment will be described with reference to FIGS.
[0032]
Test originals having different densities are read by the original image scanning exposure unit 202. From this image data, the printing rate per unit length in the circumferential direction of each photosensitive drum is determined. If the output is a printer, the printing rate is obtained from the file. The current value of the primary transfer means is selected and applied to each transfer roller of each color by a conversion table from a printing rate to a primary current value, and a voltage is applied to each transfer roller. The toner images are sequentially transferred. Here, an example will be described with reference to FIG. In FIG. 3, the printing rate of the toner image per unit length in the circumferential direction on the photosensitive drum 1Y is determined, a voltage is applied to the transfer roller 7Y, and the toner image 6b is placed on the intermediate transfer body 6 in one page area 6a. Is transferred at a good transfer rate. In addition, W in FIG. 3 is a length on the intermediate transfer member 6 corresponding to a unit length in the circumferential direction of the photosensitive drum 1Y.
[0033]
Next, a predetermined current value is selected from a conversion table from the printing rate to a current value, and a voltage is applied. Here, the image is transferred from the intermediate transfer member 6 to the transfer paper P again and fixed to obtain a print image in which the transfer rate in the entirety of one print is stable and the density change between the test document and the print is small.
[0034]
In the embodiment, a description will be given of a control unit that estimates a toner adhesion amount per unit length in a circumferential direction on an image carrier and controls a primary transfer current and a secondary transfer current based on the estimated toner adhesion amount. However, it is also possible to control only the primary transfer current or the secondary transfer current.
[0035]
As described above, according to the image forming apparatus of the first embodiment of the present invention, the transfer rate in one print can be stabilized, and the amount of density change between the original image and the print image can be reduced. Since the control on the power supply side is a constant current control, fluctuations in the volume resistance values of the primary and secondary transfer rollers and the intermediate transfer member can be suppressed.
[0036]
(Embodiment 2)
Next, an image forming apparatus according to Embodiment 2 of the present invention will be described. FIG. 4 is a cross-sectional view illustrating a main configuration of an image forming apparatus according to Embodiment 2 of the present invention. The same parts as those in the first embodiment are denoted by the same reference numerals, and the description thereof is partially omitted.
[0037]
In FIG. 4, an image forming unit 10Y for forming a yellow image includes a charging unit 2Y, an image exposing unit 3Y, a developing unit 4Y using toner, and a cleaning unit disposed around a photosensitive drum 1Y as an image carrier. 8Y. The image forming unit 10M for forming a magenta image has a photosensitive drum 1M as an image carrier, a charging unit 2M, an image exposing unit 3M, a toner developing unit 4M, and a cleaning unit 8M. The image forming unit 10C for forming a cyan image and the image forming unit 10K for forming a black image have the same configuration.
[0038]
The charging unit 2Y and the image exposing unit 3Y, the charging unit 2M and the image exposing unit 3M, the charging unit 2C and the image exposing unit 3C, and the charging unit 2K and the image exposing unit 3K constitute a latent image forming unit. The color images of each color formed by the image forming units 10Y, 10M, 10C and 10K are sequentially superimposed on the transfer paper P on the transport belt 9 by transfer rollers 72Y, 72M, 72C and 72K as transfer means. Is transcribed.
[0039]
On the other hand, the transfer paper P accommodated in the paper feed cassette 20 is fed by the paper feeding means 21 and passes through the paper feed rollers 22A, 22B, 22C, and 22D, the registration rollers 23, and the like, onto the transfer paper P. The superimposed color image is transferred. The transfer paper P on which the color image has been transferred is subjected to a fixing process by the fixing unit 24, and is sandwiched by paper discharge rollers and placed on a paper discharge tray outside the apparatus.
[0040]
The control units 30Y, 30M, 30C, and 30K estimate the toner adhesion amount from the printing rate per unit length in the circumferential direction on the photosensitive drums 1Y, 1M, 1C, and 1K, and transfer unit based on the estimated toner adhesion amount. Is controlled so that the transfer rate becomes constant. More specifically, the printing rate per unit length in the circumferential direction of each photoconductor drum is obtained from the image data, and the current value is obtained from the printing rate according to a conversion table prepared in advance, and each transfer roller of the photoconductor drum is obtained. Voltage is applied to 72Y, 72M, 72C, and 72K to control the transfer rate to be constant.
[0041]
The developer used in the image forming apparatus of the second embodiment is the same as the developer described in the first embodiment.
[0042]
Next, printing of a test document by the image forming apparatus according to the second embodiment will be described with reference to FIGS. First, test originals having different densities are read by the original image scanning exposure unit 202 (FIG. 1). From this image data, the printing rate per unit length in the circumferential direction of each photosensitive drum is determined. If the output is a printer, the printing rate is obtained from the file. Digital exposure is performed on each photosensitive drum.
[0043]
At this time, a current value of the transfer unit is selected and a voltage is applied to each transfer roller of each color by a conversion table from a printing rate to a current value. The toner images are sequentially transferred from the photosensitive drum to the transfer paper P and fixed to obtain a print image in which the transfer rate in the entirety of one print is stable and the density change between the test document and the print is small.
[0044]
As described above, according to the image forming apparatus according to the second embodiment of the present invention, the transfer rate in one print can be stabilized, and the density change between the original image and the print image can be reduced. Since the control on the side is a constant current control, the transfer roller is less susceptible to fluctuations in the volume resistance value.
[0045]
The image forming apparatus of the present invention can be applied to general electrophotographic devices such as copiers, laser printers, LED printers, and liquid crystal shutter printers. It can be widely applied to devices such as printing, plate making, and facsimile.
[0046]
【Example】
Examples of the present invention will be further described, but the configuration of the present invention is not limited thereto.
[0047]
(Example 1)
A test is performed using the image forming apparatus of the tandem full-color copying machine shown in FIG.
[0048]
Each photosensitive drum has an outer diameter of 60 mm, and a phthalocyanine pigment dispersed and applied to polycarbonate as an organic semiconductor layer is used. The film thickness including the charge transport layer is 25 μm. The potential of the non-image portion of each photosensitive drum is detected by a potential sensor, and feedback control (controllable range is -500 V to -900 V), the total exposure potential is -50 V to 0 V, and the linear velocity of each photosensitive drum is 220 mm. / Sec.
[0049]
The exposure uses a laser scanning method, and the power of the semiconductor laser is 300 μW. Development is a two-component development method of carrier and toner. The printing rate per unit length in the circumferential direction of the photosensitive drum is measured by a printing rate counter.
[0050]
The primary transfer means is provided with conductive and foamed transfer rollers 7Y, 7M, 7C and 7K on the back surface of the intermediate transfer member 6, the transfer roller is pressed at 5.88N, the outer diameter of the transfer roller is 20mm, and the volume is The resistance value is 1 × 10 ⁷ Ωcm. A predetermined current value is selected and applied from the printing rate counter value and the current value table. The intermediate transfer member 6 is sandwiched between the backup roller 7A and the intermediate transfer roller 7B, and has a volume resistance of 1 × 10 ⁸ Ωcm. The tension of the intermediate transfer belt, which is the intermediate transfer member 6, is 49N. A predetermined secondary current value is selected and applied from the printing rate counter value and the current value table.
[0051]
The durability test was performed up to 100,000 copies. The test chart (original) uses a test chart having a band in the width direction in which the density is increased from 0% to 10% to 100%. The width of each density in the main scanning direction is 15 mm.
[0052]
The density measured the reflection density. The transfer rate is a rate at which the toner per unit area on the image carrier is transferred to the intermediate transfer body.
[0053]
In the case of the comparative example, the toner adhesion amount per unit length in the circumferential direction on the image carrier is estimated, and the primary transfer current and / or the secondary transfer current are not feedback-controlled based on the estimated toner adhesion amount. Table 1 shows the test data. The data in the table is obtained by calculating the density difference between each density (0 to 100%) of the output sample and each density (0 to 100%) of the document, and calculating the average value of the density differences.
[0054]
[Table 1]

[0055]
As shown in Table 1, according to the present invention, the transfer rate within one page was constant, and the amount of density change with the test document was within the document density value ± 10%. In the case of the comparative example, the amount of density change from the original was ± 20% of the original density value.
[0056]
(Example 2)
Example 2 is an example of the image forming apparatus according to Embodiment 2. The following description focuses on the differences from the first embodiment.
[0057]
A test is performed using the image forming apparatus of the color copying machine shown in FIG. This image forming apparatus is different from the first embodiment in that the backup roller 7A and the intermediate transfer roller 7B are not provided, the intermediate transfer body 6 is provided on the transport belt 9, and the transfer rollers 7Y, 7M, 7C and 7K are provided on the transfer rollers 72Y and 72M, respectively. , 72C, and 72K are mechanically the same.
[0058]
The test chart (document) is a band-shaped chart in the width direction in which the density is increased from 0% to 10% in increments of 100%. The width of each density in the main scanning direction is 15 mm. In the case of the comparative example, the toner adhesion amount per unit length in the circumferential direction on the image carrier is estimated, and the transfer current is not feedback-controlled based on the estimated toner adhesion amount. Table 2 shows the test data. The data in the table shows the density difference within one page.
[0059]
[Table 2]

[0060]
As shown in Table 2, according to the present invention, the transfer rate within one page was constant, and the amount of density change with the test document was within the document density value ± 10%. In the case of the comparative example, the amount of density change from the original was ± 20% of the original density value.
[0061]
【The invention's effect】
The configuration described above has the following effects.
[0062]
According to the first aspect of the present invention, four color toners of yellow, magenta, cyan, and black are respectively developed on the image carrier, and each of the toners is transferred from the image carrier onto one common intermediate transfer member of four colors. In an image forming apparatus in which images are sequentially primary-transferred and then secondary-transferred from an intermediate transfer member to transfer paper and fixed, an amount of toner adhering per unit length in a circumferential direction on an image carrier is estimated, and the estimated toner adhering amount is determined. Since the primary transfer current and / or the secondary transfer current is controlled based on the amount, the transfer rate in one print is stabilized, and the amount of change in density between the original image and the print image can be reduced. Further, since the control on the power supply side for transferring is a constant current control, the image forming apparatus is less susceptible to fluctuations in the volume resistance of the intermediate transfer roller and the intermediate transfer body.
[0063]
According to the image forming apparatus of the present invention, the four color toners of yellow, magenta, cyan and black are respectively developed on the image carrier, and the respective toner images are sequentially transferred from the image carrier to the transfer paper and fixed. In the image forming apparatus, the amount of adhered toner per unit length in the circumferential direction on the image carrier is estimated, and the transfer current is controlled based on the estimated amount of adhered toner. This makes it possible to reduce the amount of change in density between the original image and the print image, and furthermore, since the control on the power supply side for transferring is a constant current control, the image forming apparatus is less susceptible to fluctuations in the volume resistance value of the transfer roller.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating a configuration of an image forming apparatus according to Embodiment 1 of the present invention.
FIG. 2 is a sectional view showing a configuration of a main part of FIG.
FIG. 3 is an explanatory diagram illustrating a distribution state of a Y toner image on an intermediate transfer member.
FIG. 4 is a cross-sectional view illustrating a main configuration of an image forming apparatus according to Embodiment 2 of the present invention;
[Explanation of symbols]
1Y, 1M, 1C, 1K Photoconductor drum (image carrier)
4Y, 4M, 4C, 4K Developing unit 6 Intermediate transfer member 7Y, 7M, 7C, 7K, 72Y, 72M, 72C, 72K Transfer roller 7A Backup roller 7B Intermediate transfer roller 30A, 30Y, 30M, 30C, 30K Control unit

Claims (9)

An image carrier for each color of yellow (Y), magenta (M), cyan (C), and black (K); and developing means for developing a latent image formed on each image carrier with a corresponding color toner. A primary transfer unit for each color for sequentially superimposing and transferring each color toner image formed on the image carrier onto the same intermediate transfer body; and a transfer paper for transferring the superimposed toner image formed on the intermediate transfer body. An image forming apparatus having a secondary transfer means for collectively transferring the toner image and a fixing means for fixing the toner image,
A control unit configured to estimate a toner adhesion amount per unit length in a circumferential direction on the image carrier, and to control a primary transfer current and / or a secondary transfer current based on the estimated toner adhesion amount. Image forming apparatus. The image forming apparatus according to claim 1, wherein the estimation of the amount of adhered toner is estimated based on a printing rate per unit length in a circumferential direction on the image carrier. The image forming apparatus according to claim 1, wherein the intermediate transfer member is an endless belt, and has a volume resistance value of 1 × 10 ⁷ Ωcm to 1 × 10 ¹¹ Ωcm. The secondary transfer unit has a backup roller disposed at a position facing the secondary transfer member via the intermediate transfer member,
A volume resistance value of the secondary transfer member is 1 × 10 ⁶ to 1 × 10 ¹⁰ Ωcm;
4. The image according to claim 1, wherein the backup roller has a volume resistance of 1 × 10 ⁶ to 1 × 10 ¹⁰ Ωcm, and the control on the power supply side for transferring is constant current control. 5. Forming equipment. An image carrier for each color of yellow (Y), magenta (M), cyan (C), and black (K); and developing means for developing a latent image formed on each image carrier with a corresponding color toner. And an image forming apparatus comprising: a transfer unit that sequentially superimposes and transfers each color toner image formed on the image carrier onto the same transfer paper; and a fixing unit that fixes the superposed toner image formed on the transfer paper. At
An image forming apparatus comprising: a control unit that estimates a toner adhesion amount per unit length in a circumferential direction on the image carrier and controls a transfer current based on the estimated toner adhesion amount. 6. The image forming apparatus according to claim 5, wherein the estimation of the toner adhesion amount is performed based on a printing rate per unit length in a circumferential direction on the image carrier. The toner has a volume average particle diameter of 2 μm to 7 μm,
The image forming apparatus according to claim 1, wherein a volume variation coefficient, which is a value obtained by multiplying a standard deviation by the volume average particle size and multiplying by 100, is 15 to 22. When the particle diameter of the toner is D (μm),
The relative frequency (m1) of the toner particles included in the most frequent class in the histogram showing the number-based number particle size distribution in which the natural logarithm InD is plotted on the horizontal axis and the horizontal axis is divided into a plurality of classes at intervals of 0.23, 8. The method according to claim 1, wherein the sum (M) of the relative frequency (m2) of the toner particles included in the class having the second highest frequency after the mode is 65% or more. 9. The image forming apparatus as described in the above. 2. The toner according to claim 1, wherein a ratio of the toner particles whose shape factor is in a range of 1.2 to 1.6 is 60% by volume or more, and a variation coefficient of the shape factor is 18% or less. 3. 9. The image forming apparatus according to any one of 8.

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