JP3755348B2 - Color image forming apparatus and color image forming method - Google Patents

Description

表１の結果から明らかなように、本願発明に係る実施例によれば、粒状性、画像濃度、および画像の官能評価ともに、高い評価が得られることがわかった。
【０１３５】
【発明の効果】
以上説明したように、本願発明に係るカラー画像形成装置及びカラー画像形成方法では、視感度の最も低い色のトナー像から転写体上に順次転写するので、転写時に上方に転写されるトナー像のトナー粒子が画素の周囲に散らばっても目立ちにくい。このため、画質劣化のない高品質な画像を得ることができる。
さらに、転写体上に定着された面積率50%の単色画像の平均厚みと、転写体上に定着された面積率100%の単色画像の平均厚みとの比、及び面積率100%の単色画像の平均厚み等を適切に設定することにより、画素ごとの面積の変動を低減し、ノイズの少ない滑らかな画像を作製することができる。さらに、各色画像のスクリーン線数、スクリーン角度を適切に設定することで、より高画質な画像を作製することができる。
さらに、光散乱の最も大きなカラートナー層を、転写材上の最下層に転写することで、深みのあるより好ましい画像が得られる。
【図面の簡単な説明】
【図１】 本願発明の一実施形態であるカラー画像形成装置を示す概略構成図である。
【図２】 本願発明の他の実施形態であるカラー画像形成装置を示す概略構成図である。
【図３】 上記実施形態のカラー画像形成装置で用いられるサイアン画像の画像ドット形成パターンを示す図および画素を示す部分拡大図である。
【図４】 上記実施形態のカラー画像形成装置で用いられるマゼンタ画像の画像ドット形成パターンを示す図である。
【図５】 上記実施形態のカラー画像形成装置で用いられるイエロー画像の画像ドット形成パターンを示す図である。
【図６】 上記実施形態のカラー画像形成装置で用いられるブラック画像の画像ドット形成パターンを示す図である。
【符号の説明】
１ 像担持体
２ 帯電装置
３ 像書き込み装置
４ 回転式現像装置
５ 転写ドラム
６ 転写コロトロン
７ 定着装置
１１ 用紙トレイ
１３ 吸着用帯電器
１４ 転写体
２１ 原稿読み取り部
２２ 画像処理装置
３７ カラーＣＣＤ
５０ 中間転写体
５１ 転写ロール（一次転写装置）
５２ 転写ロール（二次転写装置）
５３ 支持ロール[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a color image forming apparatus and a color image forming method which are used in a copying machine, a printer, and the like using an electrophotographic method and an electrostatic recording method, and form a color image using powder toner.
[0002]
[Prior art]
  Conventionally, in an image forming apparatus that forms a color image using electrophotography, for example, the following processing is performed.
  First, the reflected light from the original is color-separated by a color CCD, and image processing and color correction are performed by an image processing apparatus to obtain a plurality of color image signals. A plurality of electrostatic latent images are formed by irradiating the photosensitive member a plurality of times, one by one for each color, as a laser beam modulated by a color, for example, using a semiconductor laser. These toner images are developed in order with four colors, for example, chromatic toners of Y (yellow), M (magenta), and C (cyan), and achromatic toner K (black, black toner). Is transferred by electrostatic force from a photoreceptor onto a transfer material such as paper using a corotron. Thereafter, the transfer image formed on the transfer material is heated and fixed with a heat fixing roll or the like to form a color image.
[0003]
  As the photoconductor, for example, an inorganic photoconductor made of Se, amorphous silicon, or the like, or an organic photoconductor using a phthalocyanine pigment, a bisazo pigment or the like as a charge generation layer is used.
  In addition, the color toner includes 1 to 15 μm particles in which a pigment as a colorant is dispersed in a thermoplastic binder resin such as a polyester resin or a styrene-acrylic copolymer, for example, silicon oxide, titanium oxide, It is obtained by adhering 5 to 100 nm inorganic particles such as aluminum oxide, or resin fine particles such as PMMA and PVDF.
[0004]
  In the development step, the toner is inserted into a developing device having a magnetic roll as a two-component developer mixed with magnetic carrier particles, a magnetic brush is formed on the magnetic roll, and the magnetic brush is brought into contact with the photoreceptor, By applying a bias electric field, a toner image is formed on the photoreceptor by electrostatic force. Here, the magnetic carrier is formed by coating the surface of magnetic particles such as ferrite having an average particle diameter of 20 to 100 nm with a coating agent such as an acrylic resin, a fluorine resin, or a styrene resin.
[0005]
  In the transfer, for example, a transfer roll or transfer belt formed in advance with a dielectric or the like is used to adsorb a transfer material using electrostatic force, and a transfer corotron, a transfer roll to which bias is applied, or a transfer brush to which bias is applied. For example, there is known a method or apparatus for electrostatically transferring a toner image to a transfer material one color at a time by applying an electric field having a polarity opposite to that of toner charging from the back of a transfer roll or transfer belt.
[0006]
  In the transfer, for example, a toner image developed on a photoreceptor is transferred onto an intermediate belt formed of a dielectric material, for example, a transfer corotron, a transfer roll to which a bias is applied, or a transfer brush to which a bias is applied. By applying an electric field having the opposite polarity to the charging of the toner from the back of the intermediate belt, the toner images are transferred onto the intermediate belt one by one, and a color toner image is once formed on the intermediate belt. After that, for example, using a transfer corotron, a biased transfer roll, or a biased transfer brush, an electric field having a polarity opposite to that of the toner is applied from the back side of the transfer material to transfer the color toner image. Methods and apparatuses for electrostatically transferring to a material are known.
[0007]
  In the fixing, for example, using a fixing roll made of a metal roll whose surface is covered with fluororesin, fluororubber, silicon rubber, etc., and a pressure roll made of a metal roll whose surface is covered with fluorine rubber, silicon rubber, etc., The two rolls are pressed to obtain a desired pressure, and a heat source such as a lamp or a heater is inserted in the center of the two rolls so as to obtain a desired temperature. There are known methods and apparatuses in which after two rolls are heated with these heat sources, a sheet on which the toner image is transferred is inserted into a pressure contact portion between the two rolls, and the toner image is fixed by heating and pressing. There is also known a method and apparatus for irradiating a sheet of heat-transferred toner on a surface using an oven, an infrared lamp, or the like to heat and fix the toner in a non-contact manner.
[0008]
  As a method for gradation reproduction, area modulation is generally used. For this purpose, the laser beam is scanned on a photoconductor using a polygon mirror or the like, and the lighting time per pixel is determined according to the image signal of each pixel. A method for obtaining an area-modulated electrostatic latent image by changing the exposure area ratio by changing the exposure area ratio is known.
[0009]
  As a method for converting an image signal into a laser lighting time, Oda et al., In Japan Hardcopy 95, 143-146 (1995), show a method using an analog screen generator (ASG) that facilitates high-speed processing. Among them, it is reported that it is good to use a screen with a low line number in the low density part and a screen with a high line number in the high density part because an image faithful to the image signal cannot be obtained with a high screen line number. ing. Here, the ASG compares the triangular wave output from the triangular wave generator with the analog image signal output from the DA converter, and performs pulse width modulation.
[0010]
  As a method for converting an image signal into a laser lighting time, a method for producing a halftone image signal such as a dither pattern using a digital screen generator (DSG) is known. In this case, the image signal calculated by the image processing device is converted into halftone image data obtained by halftone processing using a printer driver or the like, stored in a buffer memory, etc., synchronized for each scanning line, and pulse width The modulated image data is output to the exposure apparatus.
[0011]
[Problems to be solved by the invention]
  However, when a color image is formed by the conventional image forming apparatus as described above, there are the following problems.
  When the image formed on the photoconductor is transferred onto the transfer material using static electricity, the electric field becomes non-uniform due to the unevenness of the surface of the transfer material and the uneven distribution of the voids inside the transfer material, and the toner image on the photoconductor In comparison, the toner image formed on the transfer material is irregularly scattered, or a part of the toner is not transferred from the photoreceptor and the nest is vacant. Further, even after fixing, the toner image remains turbulent, and such a fixed image has poor granularity, and when viewed by humans, it is noisy and rough without any smoothness. Furthermore, depending on the fixing temperature and pressure, there is a problem in that the toner image spreads sideways or permeates into the paper and the disturbance of the toner image is enlarged.
[0012]
  Also, the higher the number of screen lines forming an image, the smaller the area of the pixels to be formed, and the screen structure is not recognized, resulting in a smoother image. In addition to being able to obtain a faithful image, image noise also increases. In addition, even when two types of analog screen generators are used and different screen line numbers are used for the low density area and the high density area as described above, the gap between pixels is collapsed in the high density area, or the joint between the two screens is broken. Since it is not smooth, good gradation reproduction cannot be obtained. Furthermore, a smooth image cannot be obtained in a low line number portion where the screen structure can be seen. Further, as a current problem when outputting using DSG, there is a problem that sufficient resolution, number of gradations and high printing speed cannot be achieved at the same time. For this reason, the obtained image cannot be obtained because the screen structure is visible or the gradation is not smooth.
[0013]
  In order to obtain an image faithful to the image signal even at a high number of lines, it is known to use a small particle size toner, but in this case, the charge amount of each toner is lowered and the fogging of the background portion occurs, Adhesive force with the photoreceptor is increased, transferability is deteriorated, and a smooth image cannot be obtained.
[0014]
  In order to produce a color image, it is necessary to reproduce a color such as blue, green, or red by superimposing a plurality of colors of toner, but if the colors are superimposed, the disturbance of the toner expands and the smoothness is lost. In addition, when the image of each color is shifted, the color changes, so that a faithful color cannot be obtained or color unevenness occurs. Further, depending on the type of toner, transfer, fixing conditions, etc., there is a problem that a high image density cannot be obtained and a deep image such as a silver salt photograph cannot be reproduced.
[0015]
  The present invention is for solving the above-mentioned problems, and by using a powder toner to perform pixel reproduction faithfully to an image signal, a smooth image with less noise and color unevenness, and silver It is an object of the present invention to provide a color image forming apparatus and a color image forming method capable of producing a deep color image such as a salt photograph.
[0016]
[Means for Solving the Problems]
  The above problem can be solved by the following apparatus or method.
  The invention described in claim 1 includes an image carrier, a charging device that charges the image carrier almost uniformly, and an image writing device that forms an electrostatic latent image on the image carrier based on image information. A developing device that forms a toner image by transferring a chromatic toner of at least cyan, magenta, and yellow to an electrostatic latent image on the image carrier using a two-component developer obtained by mixing toner and a magnetic carrier; A color image forming apparatus comprising: a transfer device that transfers the toner image onto a transfer material; and a fixing device that heat-fixes the toner image of the transfer material. The thickness of a monochrome image having an area ratio of 100% fixed on the transfer material is t1, and the area ratio fixed on the transfer material is 50%. When the thickness of the monochrome image is t2. t1 and t2 and is,
    0.7 ≤ t2 / t1 ≤ 1.3
ofVolume resistance value as a powdery body of the magnetic carrier so as to satisfy the relationship ( Ω cm) Is setThis is a color image forming apparatus.
[0017]
  According to a second aspect of the present invention, there is provided an image carrier, a charging device that charges the image carrier almost uniformly, and an image writing device that forms an electrostatic latent image on the image carrier based on image information. A developing device that forms a toner image by transferring a chromatic toner of at least cyan, magenta, and yellow to an electrostatic latent image on the image carrier using a two-component developer obtained by mixing toner and a magnetic carrier; A color image forming apparatus comprising: a transfer device that transfers the toner image onto a transfer material; and a fixing device that heat-fixes the toner image of the transfer material. The thickness of a monochrome image having an area ratio of 100% fixed on the transfer material is t1, and the area ratio fixed on the transfer material is 50%. When the thickness of the monochrome image is t2. t1 and t2 and is,
    0.7 ≤ t2 / t1 ≤ 1.3
ofThe heating temperature or pressing force at the time of fixing in the fixing device is set so as to satisfy the relationship.This is a color image forming apparatus.
[0018]
  According to a third aspect of the present invention, there is provided an image carrier, a charging device that charges the image carrier almost uniformly, and an image writing device that forms an electrostatic latent image on the image carrier based on image information; A developing device that forms a toner image by transferring a chromatic toner of at least cyan, magenta, and yellow to an electrostatic latent image on the image carrier using a two-component developer obtained by mixing toner and a magnetic carrier; An intermediate transfer device that sequentially transfers the toner images onto the intermediate transfer member, and a secondary transfer device that collectively transfers the toner images onto the transfer material after all color toner images are transferred onto the intermediate transfer member. And a fixing device that heat-fixes the toner image on the transfer material, and sequentially transfers the toner image having the lowest visibility to the intermediate transfer member to form a transfer image. Is set to When the thickness of a monochrome image with an area ratio of 100% fixed on the transfer material is t1, and the thickness of a monochrome image with an area ratio of 50% fixed on the transfer material is t2, t1 and t2 are:
    0.7 ≤ t2 / t1 ≤ 1.3
ofVolume resistance value as a powdery body of the magnetic carrier so as to satisfy the relationship ( Ω cm) Is setThis is a color image forming apparatus.
[0019]
  According to a fourth aspect of the present invention, there is provided an image carrier, a charging device that charges the image carrier almost uniformly, and an image writing device that forms an electrostatic latent image on the image carrier based on image information. A developing device that forms a toner image by transferring a chromatic toner of at least cyan, magenta, and yellow to an electrostatic latent image on the image carrier using a two-component developer obtained by mixing toner and a magnetic carrier; An intermediate transfer device that sequentially transfers the toner images onto the intermediate transfer member, and a secondary transfer device that collectively transfers the toner images onto the transfer material after all color toner images are transferred onto the intermediate transfer member. And a fixing device that heat-fixes the toner image on the transfer material, and sequentially transfers the toner image having the lowest visibility to the intermediate transfer member to form a transfer image. Is set to When the thickness of a monochrome image with an area ratio of 100% fixed on the transfer material is t1, and the thickness of a monochrome image with an area ratio of 50% fixed on the transfer material is t2, t1 and t2 are:
    0.7 ≤ t2 / t1 ≤ 1.3
ofThe heating temperature or pressing force at the time of fixing in the fixing device is set so as to satisfy the relationship.This is a color image forming apparatus.
[0020]
  The invention described in claim 5Any one of claims 1 to 4In the color image forming apparatus described in 1), development is performed in which a two-component developer in which transparent toner and a magnetic carrier are mixed is used, and the transparent toner is transferred to an electrostatic latent image on the image carrier to form a toner image. A color image forming apparatus having an apparatus and configured to transfer the transparent toner to the entire surface of the transfer material or a portion where the chromatic toner is not developed.
[0021]
  In the invention according to claim 6, the average thickness t1 (μm) of the monochrome image having the area ratio of 100% is:
    2.0 ≤ t1 ≤ 4.0
The color image forming apparatus according to any one of claims 1 to 5, wherein the color image forming apparatus is in a range of the above.
[0022]
  In the invention according to claim 7, the number of screen lines of the formed image is 4 lpm or more and 12
The color image forming apparatus according to any one of claims 1 to 6, wherein the color image forming apparatus is set to lpm or less.
[0023]
  The invention according to claim 8 uses a black toner in addition to the chromatic toner,
  When the screen angles of the four colors are A, B, C, and D, A, B, and C have different angles, and the difference between the angles is set in the range of 26 degrees or more and 34 degrees or less. When C> B> A, D is
    A-12 degrees or more, A-18 degrees or less
    (A + B) x 0.5-3 degrees or more, (A + B) x 0.5 + 3 degrees or less
    (B + C) × 0.5-3 degrees or more, (B + C) × 0.5 + 3 degrees or less
    C + 12 degrees or more, C + 18 degrees or less
The color image forming apparatus according to any one of claims 1 to 7, wherein the color image forming apparatus is set to any one of the ranges and the color having the highest visibility is assigned to D 1. .
[0024]
  The invention according to claim 9 is characterized in that the average particle size of the toner accommodated in the developing device is set to 4 μm or more and 7 μm or less. The image forming apparatus described.
[0025]
  The invention according to claim 10 is set so that the chromatic color toner image is transferred onto the transfer material with the toner image having the largest light scattering in the chromatic color toner layer having an area ratio of 100% as the lowest layer. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.
[0026]
  According to an eleventh aspect of the present invention, there is provided a charging step for charging the image carrier substantially uniformly, an exposure step for forming an electrostatic latent image on the image carrier based on image information, and an image on the image carrier. A developing step of forming at least a cyan, magenta, and yellow chromatic toner image on the electrostatic latent image; a transfer step of forming the transfer image by transferring the toner image onto the transfer material; and the toner of the transfer material A color image forming method having a fixing step of heat-fixing an image, wherein the transfer material is set so as to form a transfer image by sequentially transferring toner images having the lowest visibility on the transfer material. When the thickness of a monochrome image having an area ratio of 100% fixed on the surface is t1, and the thickness of a monochrome image having an area ratio of 50% fixed on the transfer material is t2, t1 and t2 are:
    0.7 ≤ t2 / t1 ≤ 1.3
The color image forming method is characterized by satisfying the above relationship.
[0027]
  According to a twelfth aspect of the present invention, there is provided a charging step for charging the image carrier substantially uniformly, an exposure step for forming an electrostatic latent image on the image carrier based on image information, and an image on the image carrier. A development process for forming at least cyan, magenta, and yellow chromatic toner images on the electrostatic latent image, an intermediate transfer process for sequentially transferring the toner images onto the intermediate transfer body, and all colors on the intermediate transfer body In a color image forming method comprising: a secondary transfer step in which the toner images are collectively transferred onto a transfer material after the toner image is transferred; and a fixing step in which the toner images on the transfer material are heated and fixed. The toner image of the lowest color is set to sequentially transfer onto the intermediate transfer member to form a transfer image, and the thickness of a monochrome image with an area ratio of 100% fixed on the transfer material is t1, 50% area ratio fixed on the transfer material When the thickness of the monochrome image of t2 is t2, t1 and t2 are
    0.7 ≤ t2 / t1 ≤ 1.3
The color image forming method is characterized by satisfying the above relationship.
[0028]
  Here, the area ratio in the present invention is an area ratio calculated from image data input to the exposure apparatus.
  Here, in the present invention, the visual sensitivity represents the property that the brightness perceived by the human eye is different for each wavelength of light, and the higher the visible wavelength is, the higher the visibility is (Toshi Ota, Color Engineering Tokyo Denki University Press). In the present invention, the visibility S of each color toner image is obtained by integrating a value obtained by multiplying the spectral reflectance R (λ) and the spectral visibility V (λ) of each color in the visibility wavelength region. That is,
        S = ∫V (λ) R (λ) dλ
It is.
[0029]
  As described above, in the color image forming apparatus using the powder toner, the toner image is more likely to be disturbed due to the scattering of the toner as the transfer order is later. For this reason, by sequentially transferring toners with low visibility, that is, toners that easily distinguish the difference from the transfer material, noise and color unevenness are less noticeable, and a smooth and preferable image can be obtained.
[0030]
  In the present invention, the thickness t1, t2 of the monochrome image is measured as follows. That is, a monochrome image having an area ratio of 100% and 50% formed on a transfer material is cut into a strip shape and embedded in an epoxy resin embedding agent. After the embedding agent has hardened, the two images are sliced together with the transfer material with a diamond knife attached to a microtome to produce a thin film slice. The prepared slice is observed with a transmission electron microscope, and the thickness of the color material layer having a cross section corresponding to t1 and t2 is obtained. The average thickness of each image can be calculated with high accuracy by taking a cross-sectional observation image with a scanner or the like, converting it to a digital image, performing image processing, or repeating the measurement a plurality of times.
[0031]
  When the image thickness ratio t2 / t1 is less than 0.7, irregular toner scattering and pixel enlargement are conspicuous and there is a lot of noise, and a smooth image cannot be obtained. If the image thickness ratio t2 / t1 exceeds 1.3, the density difference between the image edges also increases, resulting in a non-smooth image with too strong edge enhancement.
A more preferable range of the image thickness ratio is
        0.85 ≦ t2 / t1 ≦ 1.0
It is.
[0032]
  Claim 3 or claim 4In the described image forming apparatus, an intermediate transfer device (primary transfer device) such as a transfer corotron or transfer roll for copying an image on the image carrier onto the intermediate transfer member, and an image on the intermediate transfer member on the transfer material Secondary transfer devices such as transfer corotrons and transfer rolls.
  In these devices, the toner on the image carrier is first transferred and held on the intermediate transfer member one color at a time, and after all color images are transferred onto the intermediate transfer member, the image is transferred to the transfer material in a batch. Have.
  By using the intermediate transfer member, the transfer of the toner image onto the thick paper becomes good, and the image thickness ratio can be kept within a desired range regardless of the transfer material. Further, the color order of the toner image transferred to the intermediate transfer body by the primary transfer and the color order of the toner image transferred onto the transfer material by the secondary transfer can be reversed.
[0033]
  The transparent toner is made of a thermoplastic resin that does not contain a color material or the like and has little light absorption in the visible region. By providing the transparent toner layer on the transfer material, enlargement of the toner image during thermal fixing can be suppressed, the image thickness ratio t2 / t1 can be set in a desired range, and a smooth and preferable image can be obtained.
[0034]
  In addition, by mixing organic or inorganic fine particles in the toner at a ratio of 5 to 25 parts by weight with respect to 100 parts by weight of the binder resin, expansion of the toner image during heat fixing can be suppressed, and the image thickness ratio t2 / t1 can be reduced. A desired range can be set, and a smooth and preferable image can be obtained.
[0035]
  The volume resistivity R as a powder of the carrier is determined by enclosing the carrier powder in a cell having a desired thickness and diameter having metal electrodes at both ends, and applying a voltage V to the electrodes at both ends. The current I flowing between them,
    R = V / I
Can be obtained.
  When R is changed, it is considered that the edge effect changes, but the image thickness ratio t2 / t1 changes. Therefore, the image thickness ratio t2 / t1 can be adjusted to a desired range by adjusting R. Since the desired R value varies depending on the configuration of the apparatus and the toner composition, it is necessary to set a preferable R value according to the image thickness ratio t2 / t1.
[0036]
  In fixing, the transferred toner image is enlarged. However, as the area ratio is higher, the ratio of image enlargement is lower. Therefore, the image thickness ratio t2 / t1 of the fixed toner image is smaller than that of the transferred toner image. For this reason, the spread of the toner image changes in the halftone portion depending on the heating temperature and pressure during fixing. Since the degree of deformation changes depending on the viscosity of the toner, it is possible to keep the image thickness ratio within a desired range by preferably setting the heating temperature and pressure at the time of fixing, so that a preferable image thickness ratio can be obtained and a smooth image can be obtained. Obtainable.
[0037]
  The t1 is preferably not less than 2.0 μm and not more than 4.0 μm. When the transfer material is less than 2.0 μm, the toner image is greatly deformed during fixing when the transfer material is plain paper, and a desired image thickness ratio cannot be obtained, increasing noise. A smooth image cannot be obtained. If it exceeds 4.0 μm, the toner image will be greatly deformed during fixing and transfer in the halftone part, and the desired image thickness ratio cannot be obtained because t2 is reduced. Furthermore, the human eye can identify the height of the toner image. The gloss changes depending on the area ratio, and a smooth image cannot be obtained.
[0038]
  The number of screen lines is the reciprocal of the distance between a pixel and its nearest neighbor pixel, and means the number of pixels in a 1 mm interval on a straight line connecting the nearest neighbor pixels. When the number of lines exceeds 12 lpm (lines per mm), the toner image of each pixel becomes small at an area ratio of 50%, and the smaller the toner image, the greater the rate of disturbance in fixing and transfer, so t2 becomes smaller and desired. The image thickness ratio cannot be obtained and the smoothness is impaired. The lower the number of lines, the closer the thickness ratio is to 1, which is preferable in this respect. However, when the number of lines is 4 lpm (lines per mm) or less, the coarse structure of the screen is noticeably impaired.
[0039]
  Inking with an achromatic black toner in addition to the chromatic toner, the height of the toner image can be reduced, and the image thickness ratio t2 / t1 can be set within a preferable range. The height of the toner image cannot be identified, and the gloss change due to the area ratio is reduced. As a result, a smooth image is obtained.
[0040]
  The screen angle is an angle formed between a straight line connecting a certain pixel and the nearest pixel and a main scanning direction of the laser. When the screen angles of the four colors are in the desired range, the overlapping of the toner images of each color does not appear at a low frequency, the moiré becomes inconspicuous, and the color that produces the moiré at the lowest frequency has the highest visibility. Color and difficult to identify with human eyes. Further, as described above, the toner image of the color to be overlaid last is easy to scatter, and if the splatter becomes large, the moire intensity is increased. Therefore, amplification does not occur. For these reasons, a smooth image can be obtained.
[0041]
  The average particle diameter of the toner is a volume average particle diameter. For example, D50 in a Coulter counter corresponds to this. When the toner particle diameter is less than 4 μm, the charge of each toner is lowered, so that fogging occurs, adhesion to the photosensitive member increases, and transfer omission occurs, so that a smooth image cannot be obtained. When the toner particle diameter exceeds 7 μm, noise increases and a smooth image cannot be obtained.
[0042]
  The light scattering can be measured as follows.
  That is, a solid image having an area ratio of 100% is transferred and fixed onto a transfer material using a transparent and smooth film on the front and back surfaces as a transfer material. The surface of the image is covered with a transparent cover glass, and the gap between the image and the glass is soaked with a transparent solvent that has a refractive index difference of 0.2 or less from the resin constituting the toner and does not dissolve the toner layer. This image is measured for reflectance Y (CIE XYZ color system) using a colorimeter such as X-rite 968 on a black box whose inner wall is painted black and has virtually no light scattering. If there is no light scattering of the toner layer, the illumination light of the colorimeter is absorbed by the black box, and the observed reflectance becomes 0, but the reflectance that is observed according to the scattering by the color material or external additive Will increase. Therefore, Y corresponds to the value of light scattering.
[0043]
  It is preferable to superimpose the toner images so that the toner image with the largest light scattering is in the lowermost layer on the transfer material. When the toner layer having a large light scattering is in the uppermost layer, the scattered light directly increases the reflectance, so that a high image density cannot be obtained and a deep image such as a silver salt photograph cannot be obtained. However, when a toner layer with large light scattering is in the lowermost layer, the light reaching this layer is absorbed by the toner layer above it, and in addition to reducing the absolute value of light scattering, the scattered light is Again, since it is absorbed by the upper toner layer, it hardly affects the image density. Therefore, a high image density can be obtained and a deep image can be reproduced.
[0044]
DETAILED DESCRIPTION OF THE INVENTION
  Hereinafter, embodiments of the present invention will be described with reference to the drawings.
  FIG. 1 is a schematic configuration diagram illustrating a color image forming apparatus according to an embodiment of the present invention.
  The color image forming apparatus includes an image carrier 1 on which an electrostatic latent image is formed by irradiating a laser beam after uniform charging. A document reading unit 21 is provided above the image carrier 1. And an image writing device 3 that irradiates the surface of the image carrier 1 with image light, and an image processing device 22 that performs image processing by color-separating an image signal from a document reading unit.
[0045]
  Further, around the image carrier 1, four developing devices 4a, 4b, 4c, and 4d that visualize the latent images formed on the image carrier 1 with M, C, Y, and K toners, respectively. A mounted rotary developing device 4; a transfer drum 5 that rotates while electrostatically adsorbing a transfer material 14 to the surface; a transfer corotron 6 that transfers a toner image formed on the image carrier 1 to the transfer material 14; It has.
  Further, around the transfer drum 5, a suction charger 13 that takes out the transfer material 14 one by one from the paper tray 11 and attracts it to the transfer drum 5, and a fixing device that fixes the toner image transferred onto the transfer material 5. 7.
[0046]
  As the image carrier 1, a known organic photoreceptor or inorganic photoreceptor is used. In addition, when forming an image by the electrostatic recording method, a known electrostatic recording material can also be used.
  The document reading unit 21 travels and moves to expose a document 33 on the platen glass 31, a full-rate mirror 34 that travels with the lamp 33, and a half-rate mirror 35 that travels at a speed half of these. And a lens 36 that forms an image of the reflected light applied to the document, and a CCD 37 that reads the reflected light.
[0047]
  The image processing device 22 color-separates the image signal from the document reading unit into four color signals Y, M, C, and K, and adds image processing such as color correction and sharpness correction. The image writing device 3 includes a semiconductor laser that outputs the signals from the image processing device 22 as optical signals one by one in order, and scans the optical carrier 1 through the optical system and a polygon mirror. It is supposed to be exposed.
[0048]
  Here, depending on the settings of the image processing device 22 and the image writing device 3, the number of screen lines of each color image is in a range of 4 lpm to 12 lpm, and the screen angle of each color image is within the following range. Shall be adjusted to
  The screen angles are A, B, C, and D when the screen angles of the four colors are A, B, C, and D, and the difference between the angles is 26 degrees or more and 34 degrees or less. When C> B> A, D is
    A-12 degrees or more, A-18 degrees or less
    (A + B) × 0.5-3 degrees or more, (A + B) × 0.5 + 3 degrees or less
    (B + C) × 0.5-3 degrees or more, (B + C) × 0.5 + 3 degrees or less
    C + 12 degrees or more, C + 18 degrees or less
In this range, the color toner having the highest visual sensitivity is assigned to D 1.
[0049]
  The rotary developing device 4 performs reversal development with a magnetic brush of a two-component developer composed of toner and a magnetic carrier. The rotary developing device 4 rotates each time an electrostatic latent image corresponding to each color is developed, and visualizes the latent image with toner of a color corresponding to each formed latent image. At this time, a bias voltage is applied to the developing roll that rotates while carrying the magnetic brush, and the amount of toner developed on the latent image is controlled. For example, the image carrier 1 is previously negatively charged (-300V), the bias voltage is set between the charged potential and the decay potential (-150V) of the image carrier 1, and the negative polarity toner is a latent image. It adheres to the exposed part.
[0050]
  Next, the toner accommodated in the rotary developing device 4 will be described.
  Yellow, magenta, cyan, and black toners are obtained by dispersing and containing color materials such as pigments and dyes in a binder resin.
  Any known colorant and binder resin can be used and are not particularly limited. Examples of the color material include the following.
  Yellow color material; benzidine yellow, quinoline yellow, Hansa yellow
  Magenta color material; Rhodamine B, Rose Bengal, Pigment Red
  Sian color material; phthalocyanine blue, aniline blue, pigment blue
  Black color material; carbon black, aniline black, color pigment blend
Etc. are used.
[0051]
  As the binder resin, for example, styrene resin, acrylic resin, styrene-acrylic resin, styrene-butadiene resin, vinyl chloride resin, vinyl acetate resin, polyester resin, polyurethane resin, polyamide resin, epoxy resin, and the like can be used. However, considering the fixability of the powder toner image on the transfer material, the viscosity of the powder toner at the time of fixing is 10²Pa ・ s or more, 10^FiveThose of Pa · s or less can be suitably used. The viscosity of the powder toner at the time of fixing is 10²When it is less than Pa · s, offset to the fixing roll occurs when fixing with the fixing roll. Also 10^FiveWhen Pa · s is exceeded, the powder toner is not melted and softened, and adhesion to the transfer material and adhesion between the toner particles become insufficient, so that sufficient fixing strength cannot be obtained. Further, when the viscosity at the time of fixing is lowered, the image thickness ratio is lowered and a preferable image cannot be obtained.
[0052]
  In order to obtain a more preferable color tone reproducibility, the colorant preferably has a primary particle diameter in the range of 0.01 to 1 μm, particularly in the range of 0.1 to 1 μm. It is preferable to use a colorant that is flushed and dispersed, that is, melted and dispersed in a resin in the same size as the primary particle diameter. Here, the color material melt-dispersed in the resin means that the color material is obtained by kneading a resin melted in a solvent or dissolved in a solvent and a color material wet cake obtained in the color material forming step. It is dispersed in a primary particle state in a resin, solidified by cooling or solvent removal, and then pulverized. When the primary particle size is small and the dispersion is good, light scattering by the color material is suppressed, the image density is increased, and a deep image can be obtained.
[0053]
  In addition to the binder resin and coloring material, organic fine particles such as styrene resin particles and PMMA particles having a particle size of 5 to 100 nm and inorganic fine particles such as silica having a particle size of 5 to 100 nm are added to 100 parts by weight of the binder resin. Thus, it is preferable to use toner mixed in a proportion of 5 to 25 parts by weight. By adding the resin particles, the penetration of the toner into the transfer material can be suppressed, the disturbance of the toner image can be reduced, and a desired image thickness ratio can be obtained.
[0054]
  When developing a latent image using toner, for example, inorganic powder may be adhered to the surface of the toner particles as fine particles imparting fluidity. As the inorganic powder, any known external additive can be used, and examples thereof include silica, titanium oxide, tin oxide, and aluminum oxide. Those having a particle size in the range of 0.001 to 0.1 μm can be used. Further, the inorganic powder adhered to the toner particles may be treated with various treatment agents in order to impart charging environment stability and the like.
[0055]
  Further, the particle diameter of the powder toner accommodated in the developing device is preferably 4 μm to 7 μm. When the toner particle size is larger than 7 μm, the toner particles are recognized and the granularity is remarkably disturbed, and it has been found that the effect of the present invention cannot be obtained sufficiently. Further, it was found that when the toner particle diameter is less than 4 μm, the toner charged with the opposite polarity increases and fogging occurs on the background, and a satisfactory image cannot be obtained.
  The average particle size of the toner as described above was measured using a Coulter counter manufactured by Coulter, and a volume average d50 was applied.
[0056]
  The magnetic carrier will be described. The magnetic carrier is formed by coating the surface of magnetic particles such as ferrite having an average particle diameter of 20 to 100 nm with a coating agent such as an acrylic resin, a fluorine resin, or a styrene resin. By changing the type and amount of the coating agent and the type of the magnetic particles, the volume resistance value of the carrier powder can be changed to a desired range. It is preferable to have a function of adjusting the image thicknesses t1 and t2 within a desired range by adjusting the volume resistance value.
  The fixing device in the present embodiment preferably has a mechanism for adjusting the fixing temperature and pressure and has a function of adjusting the image thicknesses t1 and t2 to be in a desired range.
[0057]
  In this embodiment, chromatic toners of Y, M, and C and achromatic K toner are used. However, in addition to these, a configuration may be provided that includes a device for developing transparent toner. In this case, in place of the rotary developing device 4 having four developing devices shown in FIG. 1, a rotary developing device having five developing devices is provided, and one of the five developing devices is provided. Contains transparent toner. Such an image forming apparatus has a function of adjusting the image thickness ratio t2 / t1 to a desired range by transferring the transparent toner to the entire surface of the image or a portion where the chromatic toner is not developed.
[0058]
  The transparent toner is made of at least a binder resin, and both the resin having the same type and molecular weight as the chromatic toner and a resin different from the chromatic toner can be used. Similarly to the chromatic toner, it is possible to use an internal or external addition of organic or inorganic fine particles.
  The transparent toner can be developed as a two-component developer mixed with carrier particles in the same manner as the chromatic toner, using the same device as the chromatic toner.
[0059]
  The transfer corotron 6 transfers a toner image on the image carrier 1 onto a transfer material using electrostatic force by applying a substantially constant transfer electric field to the wire. Further, a transfer device using a bias transfer roll using both electrostatic force and pressure can be used.
[0060]
  Any material can be used as the transfer material 14 as long as it can receive image transfer, such as a paper sheet of wood pulp fiber, processed paper, synthetic paper, plastic sheet, and metal sheet. . However, in a normal wood pulp fiber paper sheet, since there are many gaps in the transfer material, CaO, BaO, SrO, ZnO₂TiO₂, BaSO_FourA resin in which a white pigment such as the above is dispersed on a paper sheet surface and the gap is filled is preferably used.
[0061]
  The order in which the toner image on the image carrier 1 is transferred onto the transfer material 14 to form a transfer image is set so as to transfer from a color with low visibility. In the present embodiment, the chromatic color toner is set to form a transfer image in the order of magenta, cyan, and yellow, for example. In addition to these chromatic toners, achromatic black toner is used. However, black toner is unlikely to mix with other colors and affect tone reproduction. The transfer order is not particularly limited.
[0062]
  The fixing device 7 conveys the toner image on the transfer material 14 while sandwiching it between two fixing rolls, and melts and fixes the toner image on the transfer material by heating and pressing. Fixing temperature is about 150 ° C, for example, and fixing pressure is about 6 kgf / cm²Is initially set. Furthermore, it is preferable to have a function of receiving the measurement result of the image thickness ratio and adjusting the pressure and temperature to adjust the image thickness ratio to a more preferable range.
  In addition, fixing methods such as oven fixing and radiant fixing can also be used for the fixing device.
[0063]
  Also,Claim 3 or claim 4As an image forming apparatus according to an embodiment of the described invention, a transfer drum shown in FIG. 1 is used.Instead toAs shown in FIG. 2, a primary transfer device using the intermediate transfer member 50 and a secondary transfer device for transferring from the intermediate transfer member 50 to the transfer material 14 may be provided. In this case, the primary transfer device is a transfer roll 51 for copying an image on the image carrier onto the intermediate transfer member, and the secondary transfer device is a transfer roll 52 for copying the image on the intermediate transfer member onto the transfer material. . A transfer corotron may be provided in place of the transfer rolls 51 and 52. The intermediate transfer member 50 is composed of an endless belt-like member, and is configured to move around in the direction of the arrow by being stretched around the four support rolls 53 and the transfer rolls 51 and 52.
  In the case of this apparatus, first, the toner on the image carrier 1 is transferred to the intermediate transfer member 50 one by one, and the images of all colors are transferred onto the intermediate transfer member 50 while holding this image. It has a function of transferring to the transfer material 14.
[0064]
  In the present embodiment, the intermediate transfer member 50 has a function of sequentially transferring the toner image on the image carrier 1 to the surface of the intermediate transfer member 50 and holding it until all color toners are transferred. A known intermediate transfer member can be used. For example, the intermediate transfer member may be an intermediate transfer belt or an intermediate transfer roll made of a dielectric film such as PVDF or PET. In addition, a charger or a charging roll for applying an electric field between the photosensitive member and the intermediate transfer roll or intermediate transfer belt is provided. By using the intermediate transfer member, the transfer of the toner image onto the thick paper becomes good, and the image thickness ratio can be kept within a desired range regardless of the transfer material. Further, the color order of the toner image transferred to the intermediate transfer body by the primary transfer and the color order of the toner image transferred onto the transfer material by the secondary transfer can be reversed, and a more preferable image can be obtained. .
[0065]
  In the present invention, the thickness t1, t2 of the monochromatic image was measured by the following method.
Single-color images with an area ratio of 100% and 50% formed on the transfer material are cut into strips and embedded in epoxy resin embedding agents, respectively. After the embedding agent had hardened, the two images were sliced together with the transfer material with a diamond knife attached to a microtome to produce an ultrathin film slice having a thickness of 0.15 μm. The prepared section is loaded into a transmission electron microscope, and the structure of the image cross section on the transfer material is observed. After observing the cross-sectional observation image on a negative film, it was captured by a scanner and converted into a digital image consisting of digital signals. Note that LEICA ULTRACUT UCT manufactured by Nissan Sangyo Co., Ltd. was used as the microtome, and H-9000 manufactured by Hitachi, Ltd. was used as the transmission electron microscope.
[0066]
  This digital image was processed using a known image processing apparatus, and the image thickness was determined from the thickness of the fixing toner layer in the image cross section on the transfer material. By repeating this measurement 10 times, the average thickness of each image was accurately calculated.
[0067]
  Here, the image processing method is as follows.
  First, the digital image was displayed on the display, and the boundary was determined by detecting the embedding material portion, the color material layer portion, and the transfer material portion. Next, the average thickness of the monochrome image was calculated by calculating the area of the color material layer portion and dividing by the measured width of the image. The results of repeating this measurement 10 times were averaged to obtain the average thicknesses t1 and t2 of each monochromatic image.
[0068]
  The image forming apparatus according to the present exemplary embodiment is set so that the toner having the lowest visibility is sequentially transferred onto the transfer material.
  Here, the visibility S of the toner image of each color was obtained by integrating the value obtained by multiplying the spectral reflectance R (λ) of each color by the spectral visibility V (λ) in the visibility wavelength region. That is,
        S = ∫V (λ) R (λ) dλ
It is.
[0069]
  In this apparatus, the toner image of the color with the largest light scattering can be transferred to the lowermost layer of the transfer material, and thereby a more preferable image can be produced.
  A method for determining the magnitude of light scattering of the toner layer in the present invention will be described below.
  First, an image with an area ratio of 100% was produced on an OHP film manufactured by Fuji Xerox Co., Ltd. using a color image forming apparatus. One drop of tetradecane was dropped on the surface of this image, and a cover glass was placed in a state containing no bubbles. This image is measured on a black box with a height of 50 cm or more with the inner wall blackened to a density of 1.3 or more, using X-rite 968, and the Y value in the CIE XYZ space under the condition of a D50 2-degree field of view. It was.
[0070]
  In the first aspect of the invention, the chromatic toner images are superimposed on the transfer material in the order of low visibility, but in the case of a general toner image, the visibility increases in the order of M, C, Y. Therefore, the chromatic toner images are superimposed on the transfer material in the order of M, C, and Y. On the other hand, in the case of a toner using a pigment used for general printing, the light scattering of the uppermost Y toner layer is larger than that of the M and C toners. Therefore, although a smooth image with little noise can be obtained, the image density is not increased and the image is not the best in terms of color depth.
[0071]
  There are roughly two ways to reduce the scattering of the uppermost toner layer. There are a method of changing the color order and a method of reducing the light scattering of the uppermost toner layer.
  As the former method, for example, there is a method using an intermediate transfer member as described in claim 2. As shown in FIG. 2, if chromatic color toner is transferred onto the intermediate transfer member in the order of M, C, Y, the transfer material will be superposed on the transfer material in the order of Y, C, M. In addition to suppressing the scattering of low toner, only the light absorbed by the C and M toner layers located at the upper layer reaches the lowermost Y toner layer, and the scattered light can be reduced. Is absorbed by the C and M layers again when emitted from the image, so that the scattered light of the Y toner layer can be significantly reduced. As a result, a smooth and deep image can be obtained.
[0072]
  Furthermore, as the former method, for example, using a transparent film as a transfer material,Claim 1 or claim 2A primary image is produced by transferring and fixing a chromatic color toner image on a transfer material in the order of M, C, and Y toner images having low visibility, for example, on the transfer material. There is a method of pasting a white diffusing surface as a transfer material. In this case, since the image is observed from the transparent film side, the color order superimposed on the paper as the transfer material is in the order of Y, C, M from the paper side. Since only the light absorbed by the C and M toner layers located in the area reaches the light, the scattered light can be reduced, and the scattered light is again absorbed by the C and M layers when emitted from the image. Y Scattered light from the toner layer can be significantly reduced. As a result, a smooth and deep image can be obtained.
[0073]
  Examples of the method for reducing scattering in the uppermost toner layer include a method in which the uppermost toner colorant is melt-dispersed to reduce the dispersion unit, and the uppermost toner colorant is dye-based rather than pigment-based. There is a way to use. Thereby, a deep image can be reproduced.
[0074]
  Next, an operation of the color image forming apparatus shown in FIG. 1 and a color image forming method according to an embodiment of the invention described in claim 12 will be described.
  The image carrier 1 is driven to rotate and is charged almost uniformly by the charging device 2 on the upstream side of the position where exposure is performed.
  The reflected light emitted from the illumination 33 to the document 32 is read by the color CCD 37, and is subjected to color separation by the image processing device 22 into four-color signals of magenta, yellow, cyan and black, and subjected to image processing. And output as an optical signal from the semiconductor laser. First, the magenta light signal of the first color is exposed to the image carrier 1 charged in advance through the optical system, and an electrostatic latent image in which the image portion has a low potential is formed on the image carrier.
[0075]
  The rotary developing device 4 moves so that the magenta developing device faces the image carrier 1, and the electrostatic latent image formed on the image carrier 1 is conveyed to this development position. The magenta toner is selectively attached to the latent image of the image carrier 1 and developed by the action of the bias voltage.
  The toner image obtained by the development moves to a position facing the transfer drum 5 by the rotation of the image carrier 1. On the other hand, the transfer material 14 is attracted to the transfer drum 5 by electrostatic force, and the toner image on the image carrier is transferred onto the transfer material by the action of the transfer corotron 6.
[0076]
  Thereafter, the image carrier 1 is again charged by the charging device 2 to form a latent image of the second color. Then, image exposure, development, and transfer are performed in the same manner as described above, and magenta, cyan, yellow, and black toner images are sequentially formed and sequentially transferred onto the transfer material 14 on the transfer drum 5.
  When the transfer of the magenta, cyan, yellow, and black toner images onto the transfer material 14 adsorbed on the transfer drum 5 is completed, the transfer material 14 adsorbed on the transfer drum 5 is transferred by a peeling charging device (not shown). The electrostatic attracting force with the drum 5 is removed, and the drum 5 is peeled off. Then, it is fused and fixed by the fixing device 7 to form a color image.
[0077]
  The color image formed in this way has an average thickness t1 of a 100% area monochrome image fixed on the transfer material 14 and an average thickness t2 of an area ratio 50% monochrome image fixed on the transfer material. And
    0.7 ≤ t2 / t1 ≤ 1.3
Meet the relationship.
  Furthermore, the average thickness t1 of a monochrome image having an area ratio of 100% is preferably set to be 2 μm or more and 4 μm or less.
[0078]
  In the color image forming apparatus as described above, a toner image of a color with low visibility is sequentially transferred to form a transfer image. For example, toner particles of a yellow toner image transferred upward are scattered around the pixels. However, yellow toner particles are not noticeable on the transfer material because of high visibility. Therefore, it is possible to form a good image by preventing image quality deterioration such as interference fringes.
[0079]
  Further, the ratio (t2 / t1) between the average thickness t2 of the monochrome image with an area ratio of 50% fixed on the transfer material and the average thickness t1 of the monochrome image with the area ratio of 100% fixed on the transfer material is Since it is within the range, it is possible to prevent the area of the fixed image from spreading irregularly compared to the toner image, resulting in a large area fluctuation for each pixel and poor reproducibility of the low-medium density region. it can. For this reason, it becomes possible to produce a smooth image with little noise.
  In addition, since the average thickness t1 of the monochrome image having the area ratio of 100% is 2 μm or more and 4 μm or less, the image thickness ratio is set to a more preferable range, and the thickness of the image portion is not conspicuous. High-quality images can be produced.
[0080]
【Example】
  Specific examples of the present invention are shown below.
  In this example, two images were produced: a portrait for comprehensive image quality evaluation, an image thickness, and a gradation patch for image quality evaluation. The latter includes a magenta monochrome image with an area ratio of 100% and 50% for measuring the image thickness t1, t2.
[0081]
Example 1
  The method for preparing the toner used in the following examples is shown below.
  Binder resin, color material, and resin fine particles are mixed in a ratio of 100 parts by weight of binder resin, 6 parts by weight of color material, and 15 parts by weight of resin particles, melt kneaded with a Banbury mixer, and pulverized with a jet mill. After that, the toner was classified by a wind classifier to prepare a toner with d50 = 5 μm. As the binder resin, a linear polyester obtained from terephthalic acid / bisphenol A ethylene oxide adduct / cyclohexanedimethanol (molar ratio = 5: 4: 1, Tg = 62 degrees, Mn = 4500, Mw = 10000) was used. . Also, C.I.Pigment Blue 15: 1, C.I.Pigment Red 57: 1, C.I.Pigment Yellow 97, and carbon black # 25 were used for the color materials of C, M, Y, and K, respectively. Each color material is flushed and mixed with the binder resin. As the resin particles, styrene resin particles having a particle diameter of 50 nm were used.
[0082]
  Further, the following two kinds of inorganic fine particles A and B were adhered to 100 parts by weight of the toner by a high speed mixer. Inorganic fine particle A is SiO₂(The surface is hydrophobized with a silane coupling agent, the average particle diameter is 0.05 μm, and the addition amount is 1.1 parts by weight). Inorganic fine particle B is TiO₂(The surface is hydrophobized with a silane coupling agent, the average particle size is 0.02 μm, the refractive index is 2.5, and the addition amount is 1.4 parts by weight).
  When the light scattering of the chromatic toner layer was measured, Y toner was the largest. Further, as a result of measuring the visibility of each chromatic toner image of C, M, and Y, the visibility was M, C, and Y in ascending order.
[0083]
  As a carrier used in combination with the above toner, spherical ferrite particles having a particle diameter of about 50 μm coated with a styrene methyl methacrylate copolymer were used. The coating was carried out at a ratio of 0.6 part by weight of styrene methyl methacrylate copolymer to 100 parts by weight of ferrite particles so that the image thickness ratio t2 / t1 was within the desired range. The toner was added at a ratio of 8 parts by weight to 100 parts by weight of the carrier and mixed with a tumbler shaker mixer to obtain a two-component developer.
[0084]
  The color image forming apparatus used in this example has the same configuration as that shown in FIG. 2 and has an intermediate transfer member. The resolution of the exposure apparatus is 4800 dpi in the main scanning direction and 600 dpi in the sub-scanning direction. The two-component developer was put in a developing device and developed by applying a developing bias. The development weight (DMA) per unit area of the solid image is 0.30 mg / cm for each color toner²The charging on the photoreceptor, the exposure potential, and the developing bias voltage were set so that
[0085]
  Rotation halftone screen was adopted as the screen. The screen line number and screen angle of C, M, Y, K images are 5.7lpm (lines / mm) 14 degrees, 5.6lpm (lines / mm) 45 degrees, 6.0lpm (lines / mm) 0 degrees, respectively. 5.7lpm (lines / mm) was set to 76 degrees. The screen pattern of each color image is shown in FIGS. 3 (a), 4, 5 and 6. FIG. FIG. 3B is an enlarged view of one pixel.
  The reference line representing the screen angle is the horizontal axis of the grid in FIGS. 3 to 5 and 6, but in the present invention, the difference in the screen angle of each color is important, so the position of the reference line is limited to the horizontal axis. is not.
[0086]
  As a result of measuring the visibility of each chromatic color toner image of C, M, Y, the order of transfer to the intermediate transfer member was K, M, C, Y because the visibility was M, C, Y in the order of low visibility. did. Since the color order is reversed by the secondary transfer to the transfer material, the color order of the toner layer on the transfer material is Y, C, M, K from the transfer material side.
[0087]
  As a transfer material, OK super art paper (manufactured by Shin-Oji Paper Co., Ltd.) was used.
  Both the fixing roll and the pressure roll were made by coating a 7 mm thick aluminum pipe with 3 mm thick fluororubber. The nip pressure between the fixing roll and the pressure roll is 5 kgf / cm.²The surface temperature of the fixing roll and the pressure roll was fixed at 150 ° C.
[0088]
  By observing a cross section of a monochromatic magenta image having an area ratio of 100% and 50% obtained by such an apparatus and obtaining t1 and t2, the thickness ratio t2 / t1 = 0.8, the image thickness t1 = 2.3 μm, It was found to be in the desired range.
[0089]
Example 2
  In Example 2, the same developer as in Example 1 was used except for the Y toner developer. The production method of Y toner developer is shown below.
  Like other toners, the binder resin is a linear polyester obtained from terephthalic acid / bisphenol A ethylene oxide adduct / cyclohexanedimethanol (molar ratio = 5: 4: 1, Tg = 62 degrees, Mn = 4500, Mw = 10000) was used. The dye material Solvent Yellow 162 was used as the Y color material. As other toners, styrene resin particles having a particle diameter of 50 nm were used as the resin particles. Binder resin, color material, and resin fine particles are mixed in a ratio of 100 parts by weight of binder resin, 15 parts by weight of color material, and 15 parts by weight of resin particles, melt kneaded with a Banbury mixer, and pulverized with a jet mill. After that, Y toner with d50 = 5 μm was prepared by classifying with a wind classifier.
[0090]
  The following two types of inorganic fine particles A and B were adhered to 100 parts by weight of the above Y toner with a high speed mixer. Inorganic fine particle A is SiO₂(The surface is hydrophobized with a silane coupling agent, the average particle diameter is 0.05 μm, and the addition amount is 1.1 parts by weight). Inorganic fine particle B is TiO₂(The surface is hydrophobized with a silane coupling agent, the average particle size is 0.02 μm, the refractive index is 2.5, and the addition amount is 1.4 parts by weight).
[0091]
  As a carrier used in combination with the above Y toner, spherical ferrite particles having a particle diameter of about 50 μm coated with a styrene methyl methacrylate copolymer were used. The coating was carried out at a ratio of 0.6 part by weight of styrene methyl methacrylate copolymer to 100 parts by weight of ferrite particles so that the image thickness ratio t2 / t1 was within the desired range. The toner was added at a ratio of 8 parts by weight to 100 parts by weight of the carrier and mixed with a tumbler shaker mixer to obtain a two-component developer.
  When the light scattering of the chromatic toner layer was measured, M toner was the largest. Further, as a result of measuring the visibility of each chromatic toner image of C, M, and Y, the visibility was M, C, and Y in ascending order.
[0092]
  The color image forming apparatus used in this embodiment is the same as the configuration shown in FIG. 1, and is an apparatus that electrostatically transfers a toner image on a photosensitive member directly onto a transfer material electrostatically attracted onto a transfer drum. The resolution of the exposure apparatus is 4800 dpi in the main scanning direction and 600 dpi in the sub-scanning direction. The two-component developer was put in a developing device and developed by applying a developing bias. The development weight (DMA) per unit area of the solid image is 0.30 mg / cm for each color toner²The charging on the photoreceptor, the exposure potential, and the developing bias voltage were set so that
[0093]
  The screen angle and the number of lines were set in the same manner as in Example 1.
  Based on the results of measuring the visibility of each chromatic toner image of C, M, and Y, the images were transferred onto the transfer material in the order of K, M, C, and Y with the lowest visibility. Therefore, the color order of the toner layer on the transfer material is K, M, C, Y from the transfer material side.
  As the transfer material, OK super art paper (manufactured by Shin-Oji Paper Co., Ltd.) was used as in Example 1.
  The fixing device and conditions were the same as in Example 1.
[0094]
  By observing a cross section of a monochromatic magenta image having an area ratio of 100% and 50% obtained with such an apparatus and obtaining t1 and t2, a thickness ratio t2 / t1 = 0.9, an image thickness t1 = 2.4 μm, It was found to be in the desired range.
[0095]
Example 3
  The developer used in Example 3 is the same as in Example 2. However, a transparent toner developer was used instead of the achromatic K toner developer. A method for producing a transparent toner developer will be described below.
  Like other toners, the binder resin is a linear polyester obtained from terephthalic acid / bisphenol A ethylene oxide adduct / cyclohexanedimethanol (molar ratio = 5: 4: 1, Tg = 62 degrees, Mn = 4500, Mw = 10000) was used. Color materials and resin particles were not used. The binder resin was pulverized with a jet mill and then classified with a wind classifier to prepare a transparent toner with d50 = 7 μm.
[0096]
  The following two types of inorganic fine particles A and B were adhered to 100 parts by weight of the transparent toner with a high speed mixer. Inorganic fine particle A is SiO₂(The surface is hydrophobized with a silane coupling agent, the average particle diameter is 0.05 μm, and the addition amount is 1.1 parts by weight). Inorganic fine particle B is TiO₂(The surface is hydrophobized with a silane coupling agent, the average particle size is 0.02 μm, the refractive index is 2.5, and the addition amount is 1.4 parts by weight).
  The above-mentioned transparent toner was added at a ratio of 8 parts by weight to 100 parts by weight of the same carrier as in Example 2, and mixed with a tumbler shaker mixer to obtain a two-component developer.
[0097]
  The color image forming apparatus used in this example has the configuration shown in FIG. However, the K toner developing device was replaced with a transparent toner developing device containing the transparent toner developer. The development weight (DMA) per unit area of solid image of C, M, Y toner is 0.30mg / cm for each color toner²The charging on the photoreceptor, the exposure potential, and the developing bias voltage were set so that The transparent toner is 1.0 mg / cm²The charging, exposure potential, and development bias voltage on the photoconductor were set so that the entire image was developed with the DMA.
[0098]
  Rotation halftone screen was adopted as the screen. The number of screen lines and screen angles for C, M, and Y images were 5.7lpm (lines / mm) 14 degrees, 5.6 lpm (lines / mm) 45 degrees, and 5.7 lpm (lines / mm) 76 degrees, respectively. . The screen patterns of the images of the respective colors are the same as those in FIGS. 3 (a), 4 and 6.
[0099]
  Based on the results of measuring the visibility of C, M, and Y chromatic color toner images, M, C, Y, and transparent toners with low visibility were transferred to the transfer material in this order. Therefore, the color order of the toner layer on the transfer material was M, C, Y, and transparent toner from the transfer material side.
  As the transfer material, OK super art paper (manufactured by Shin-Oji Paper Co., Ltd.) was used as in Example 1.
  The fixing device and conditions were the same as in Example 1.
[0100]
  By observing a cross section of a monochromatic magenta image having an area ratio of 100% and 50% obtained by such an apparatus and obtaining t1 and t2, a thickness ratio t2 / t1 = 0.95, an image thickness t1 = 2.6 μm, It was found to be in the desired range.
[0101]
Example 4
  A production method as a developer of K, Y, M, and C used in Example 4 is shown below.
  Mix the binder resin and coloring material in a ratio of 100 parts by weight of binder resin and 5 parts by weight of coloring material, melt and knead them with a Banbury mixer, pulverize them with a jet mill, and classify them with a wind classifier. Thus, a toner having d50 = 7.5 μm was prepared. As the binder resin, a linear polyester obtained from terephthalic acid / bisphenol A ethylene oxide adduct / cyclohexanedimethanol (molar ratio = 5: 4: 1, Tg = 62 degrees, Mn = 4500, Mw = 10000) was used. . Also, C.I.Pigment Blue 15: 1, C.I.Pigment Red 57: 1, C.I.Pigment Yellow 97, and carbon black # 25 were used for the color materials of C, M, Y, and K, respectively. Each color material is flushed and mixed with the binder resin.
[0102]
  Further, the following two kinds of inorganic fine particles A and B were adhered to 100 parts by weight of the toner by a high speed mixer. Inorganic fine particle A is SiO₂(The surface is hydrophobized with a silane coupling agent, the average particle size is 0.05 μm, and the addition amount is 0.6 parts by weight). Inorganic fine particle B is TiO₂(The surface is hydrophobized with a silane coupling agent, the average particle size is 0.02 μm, the refractive index is 2.5, and the addition amount is 0.8 parts by weight).
[0103]
  As a carrier used in combination with the above toner, spherical ferrite particles having a particle diameter of about 50 μm coated with a styrene methyl methacrylate copolymer were used. The coating was carried out at a ratio of 0.6 part by weight of styrene methyl methacrylate copolymer to 100 parts by weight of ferrite particles so that the image thickness ratio t2 / t1 was within the desired range. The toner was added at a ratio of 8 parts by weight to 100 parts by weight of the carrier and mixed with a tumbler shaker mixer to obtain a two-component developer.
[0104]
  The color image forming apparatus used in this example is the same as that in Example 2. The two-component developer was put in a developing device and developed by applying a developing bias. The development weight (DMA) per unit area of the solid image is 0.65 mg / cm for each color toner²The charging on the photoreceptor, the exposure potential, and the developing bias voltage were set so that
[0105]
  The number of screen lines and the screen angle of images of C, M, Y, and K were the same as those in Example 1.
  When the light scattering of the chromatic toner layer was measured, Y toner was the largest. Further, as a result of measuring the visibility of each chromatic toner image of C, M, and Y, the visibility was M, C, and Y in ascending order.
  As a result, the order of transfer onto the transfer material was K, M, C, Y, so the color order of the toner layer on the transfer material was K, M, C, Y from the transfer material side.
[0106]
  As a transfer material, OK super art paper (manufactured by Shin-Oji Paper Co., Ltd.) was used.
  Both the fixing roll and the pressure roll were made by coating a 7 mm thick aluminum pipe with 3 mm thick fluororubber. The nip pressure between the fixing roll and pressure roll is 5 kgf / cm.²The surface temperature of the fixing roll and the pressure roll was fixed at 150 ° C.
[0107]
  By observing a cross section of a monochromatic magenta image having an area ratio of 100% and 50% obtained with such an apparatus, t1 and t2 were obtained, and the thickness ratio t2 / t1 = 0.75 and the image thickness t1 = 4.5 μm. I understood it.
[0108]
Example 5
  A method for producing the toner used in this example will be described below.
  The binder resin and color material having the same composition as in Example 1 were mixed at a ratio of 100 parts by weight of the binder resin and 5 parts by weight of the color material, melt-kneaded with a Banbury mixer, and pulverized with a jet mill. By classifying with a wind classifier, a toner with d50 = 3.5 μm was produced.
[0109]
  Further, the following two kinds of inorganic fine particles A and B were adhered to 100 parts by weight of the toner by a high speed mixer. Inorganic fine particle A is SiO₂(The surface is hydrophobized with a silane coupling agent, the average particle size is 0.05 μm, and the addition amount is 2.0 parts by weight). Inorganic fine particle B is TiO₂(The surface is hydrophobized with a silane coupling agent, the average particle size is 0.02 μm, the refractive index is 2.5, and the addition amount is 3.0 parts by weight).
[0110]
  As a carrier used in combination with the above toner, spherical ferrite particles having a particle diameter of about 50 μm coated with a styrene methyl methacrylate copolymer were used. The coating was carried out at a ratio of 1.0 part by weight of styrene methyl methacrylate copolymer to 100 parts by weight of ferrite particles so that the image thickness ratio t2 / t1 was within the desired range. A toner was added at a ratio of 12 parts by weight to 100 parts by weight of the carrier, and mixed with a tumbler shaker mixer to obtain a two-component developer.
[0111]
  The color image forming apparatus used in this example is the same as that shown in Example 2. The two-component developer was put in a developing device and developed by applying a developing bias. The development weight (DMA) per unit area of the solid image is 0.20mg / cm for each color toner²The charging on the photoreceptor, the exposure potential, and the developing bias voltage were set so that
[0112]
  The number of screen lines and the screen angle of images of C, M, Y, and K were the same as those in Example 1.
  When the light scattering of the chromatic toner layer was measured, Y toner was the largest. Further, as a result of measuring the visibility of each chromatic toner image of C, M, and Y, the visibility was M, C, and Y in ascending order.
  As a result, the order of transfer onto the transfer material was K, M, C, Y, so the color order of the toner layer on the transfer material was K, M, C, Y from the transfer material side.
[0113]
  As a transfer material, OK super art paper (manufactured by Shin-Oji Paper Co., Ltd.) was used.
  Both the fixing roll and the pressure roll were made by coating a 7 mm thick aluminum pipe with 3 mm thick fluororubber. The nip pressure between the fixing roll and the pressure roll is 5 kgf / cm.²The surface temperature of the fixing roll and the pressure roll was fixed at 160 ° C.
[0114]
  By observing a cross section of a monochromatic magenta image having an area ratio of 100% and 50% obtained with such an apparatus and obtaining t1 and t2, the thickness ratio t2 / t1 = 1.05 and the image thickness t1 = 1.8 μm. I understood it.
[0115]
Example 6
  The developer used in this example is the same as in Example 4.
  The color image forming apparatus used in the present embodiment is the same as that shown in the first embodiment. The two-component developer was put in a developing device and developed by applying a developing bias. The development weight (DMA) per unit area of the solid image is 0.8 mg / cm for each color toner.²The charging on the photoreceptor, the exposure potential, and the developing bias voltage were set so that
[0116]
  The screen line number and screen angle of C, M, Y, K images are 2.9lpm (lines / mm) 14 degrees, 2.8lpm (lines / mm) 45 degrees, 3lpm (lines / mm) 0 degrees, 2.9lpm (lines / mm) was set to 76 degrees.
  When the light scattering of the chromatic toner layer was measured, Y toner was the largest. Further, as a result of measuring the visibility of each chromatic toner image of C, M, and Y, the visibility was M, C, and Y in ascending order.
  As a result, since the order of transfer to the intermediate transfer member was K, M, C, Y, the color order of the toner layer on the transfer material was Y, M, C, K from the transfer material side.
[0117]
  As a transfer material, OK super art paper (manufactured by Shin-Oji Paper Co., Ltd.) was used.
  Both the fixing roll and the pressure roll were made by coating a 7 mm thick aluminum pipe with 3 mm thick fluororubber. The nip pressure between the fixing roll and pressure roll is 4 kgf / cm.²The surface temperature of the fixing roll and the pressure roll was fixed at 145 ° C.
[0118]
  By observing the cross section of a monochromatic magenta image with an area ratio of 100% and 50% obtained with such an apparatus, t1 and t2 were obtained. I understood it.
[0119]
Example 7
  In Example 7, K developer was not used and only Y, M, and C developers were used. The same developer as in Example 4 was used for Y, M and C.
  The color image forming apparatus used in this example is the same as that in Example 2. The two-component developer was put in a developing device and developed by applying a developing bias. The development weight (DMA) per unit area of the solid image is 0.65 mg / cm for each color toner²The charging on the photoreceptor, the exposure potential, and the developing bias voltage were set so that
[0120]
  All screens of C, M, Y, K images were all line screens, and the number of lines and screen angle were all set equal to 8lpm and 45 degrees.
  When the light scattering of the chromatic toner layer was measured, Y toner was the largest. Further, as a result of measuring the visibility of each chromatic toner image of C, M, and Y, the visibility was M, C, and Y in ascending order.
  As a result, the transfer order to the transfer material was M, C, Y, so the color order of the toner layer on the transfer material was M, C, Y from the transfer material side.
  As a transfer material, OK super art paper (manufactured by Shin-Oji Paper Co., Ltd.) was used.
  The fixing device and conditions were the same as in Example 1.
[0121]
  By observing the cross section of a monochromatic magenta image having an area ratio of 100% and 50% obtained with such an apparatus, the thickness ratio t2 / t1 = 0.8 and the image thickness t1 = 4.5 μm were obtained. I understood it.
[0122]
<Comparative Example 1>
  The toner used in this comparative example is the same as in Example 4.
  As a carrier used in combination with the above toner, spherical ferrite particles having a particle diameter of about 50 μm without a coating layer were used. The toner was added at a ratio of 8 parts by weight to 100 parts by weight of the carrier and mixed with a tumbler shaker mixer to obtain a two-component developer.
[0123]
  The color image forming apparatus used in this example has the same configuration as that shown in Example 2. The two-component developer was put in a developing device and developed by applying a developing bias. The development weight (DMA) per unit area of the solid image is 0.65 mg / cm for each color toner²The charging on the photoreceptor, the exposure potential, and the developing bias voltage were set so that
[0124]
  When the light scattering of the chromatic toner layer was measured, Y toner was the largest. Further, as a result of measuring the visibility of each chromatic toner image of C, M, and Y, the visibility was M, C, and Y in ascending order.
  The same rotation halftone screen as in Example 1 was adopted as the screen.
  As described above, the order of transfer to the transfer material was K, M, C, Y because the visual sensitivity was M, C, Y in ascending order. The color order of the toner layer on the transfer material was K, M, C, Y from the transfer material side.
  As a transfer material, OK super art paper (manufactured by Shin-Oji Paper Co., Ltd.) was used.
  The fixing device and conditions were the same as in Example 1.
[0125]
  By observing a cross section of a monochromatic magenta image having an area ratio of 100% and 50% obtained with such an apparatus and obtaining t1 and t2, the thickness ratio t2 / t1 = 0.5 and the image thickness t1 = 3.9 μm. I understood it.
[0126]
<Comparative Example 2>
  The developer used in this comparative example is the same as in Example 4.
  The color image forming apparatus used in this example has the same configuration as that shown in Example 2. The two-component developer was put in a developing device and developed by applying a developing bias. The development weight (DMA) per unit area of the solid image is 0.65 mg / cm for each color toner²The charging on the photoreceptor, the exposure potential, and the developing bias voltage were set so that
[0127]
  When the light scattering of the chromatic toner layer was measured, Y toner was the largest. Further, as a result of measuring the visibility of each chromatic toner image of C, M, and Y, the visibility was M, C, and Y in ascending order.
  The same rotation halftone screen as in Example 1 was adopted as the screen.
  The order of transfer onto the transfer material was K, Y, M, C. The color order of the toner layer on the transfer material was K, Y, M, C from the transfer material side.
  As a transfer material, OK super art paper (manufactured by Shin-Oji Paper Co., Ltd.) was used.
  The fixing device and conditions were the same as in Example 1.
[0128]
  By observing a cross section of a monochromatic magenta image having an area ratio of 100% and 50% obtained with such an apparatus, t1 and t2 were obtained, and the thickness ratio t2 / t1 = 0.75 and the image thickness t1 = 4.5 μm. I understood it.
[0129]
  The evaluation methods and results of images obtained in Examples 1 to 7 and Comparative Examples 1 and 2 are shown below.
((Evaluation of graininess))
  Graininess was evaluated by visual evaluation using a uniform magenta image having a size of 3 × 3 cm and 50% and 100% image signals. The following five-level evaluation was conducted for 20 evaluators.
    1. very rough,
    2. coarse texture,
    3. Normal,
    4. Fine texture,
    5. Very fine
[0130]
  Next, the average value was calculated and evaluated according to the following criteria.
    × ... If the average value is less than 3,
    △ ... 3 to less than 3.5,
    ○ ... If it is 3.5 or more and less than 4.5,
    ◎ ... For 4.5 and above
[0131]
((Evaluation of image density))
  The image density was measured as follows. Using X-rite 404 (manufactured by X-rite), the visual density of a process black image with a size of 3 × 3 cm and 100% C, M, and Y image signals was measured. The following ranking was performed based on this concentration.
    × ... Less than 1.0,
    △ ... 1.0 or more and less than 1.4,
    ○ ... 1.4 or more and less than 1.8,
    ◎ ... 1.8 or higher
[0132]
((Image sensory evaluation))
  Sensory evaluation of the entire image was performed by visual evaluation of a person photograph. The following five levels were evaluated for 20 evaluators.
    1. very bad without smoothness and depth,
    2. Poor smoothness and depth
    3. Normal,
    4. Smooth, deep and good,
    5. Very smooth and deep, very good
[0133]
  Next, the average value was calculated and evaluated according to the following criteria.
    × ... If the average value is less than 3,
    △ ... 3 or more and less than 3.5,
    ○ ... If it is 3.5 or more and less than 4.5,
    ◎ ... For 4.5 and above
[0134]
  Table 1 shows the image quality evaluation results of the example and the comparative example obtained by the above method.
[Table 1]

  As is apparent from the results in Table 1, according to the examples of the present invention, it has been found that high evaluations can be obtained for graininess, image density, and sensory evaluation of images.
[0135]
【The invention's effect】
As described above, in the color image forming apparatus and the color image forming method according to the present invention, since the toner image having the lowest visibility is sequentially transferred onto the transfer body, the toner image transferred upward at the time of transfer is transferred. Even if toner particles are scattered around the pixel, it is difficult to stand out. For this reason, a high-quality image without image quality deterioration can be obtained.
  Furthermore, the ratio of the average thickness of a monochrome image with an area ratio of 50% fixed on the transfer body to the average thickness of the monochrome image with an area ratio of 100% fixed on the transfer body, and a monochrome image with an area ratio of 100% By appropriately setting the average thickness and the like, it is possible to reduce the variation of the area for each pixel and to produce a smooth image with little noise. Furthermore, by appropriately setting the number of screen lines and the screen angle of each color image, it is possible to produce a higher quality image.
  Furthermore, a deeper and more preferable image can be obtained by transferring the color toner layer having the largest light scattering to the lowermost layer on the transfer material.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram illustrating a color image forming apparatus according to an embodiment of the present invention.
FIG. 2 is a schematic configuration diagram illustrating a color image forming apparatus according to another embodiment of the present invention.
FIG. 3 is a diagram showing an image dot formation pattern of a cyan image used in the color image forming apparatus of the embodiment and a partially enlarged view showing pixels.
FIG. 4 is a diagram showing an image dot formation pattern of a magenta image used in the color image forming apparatus of the embodiment.
FIG. 5 is a diagram showing an image dot formation pattern of a yellow image used in the color image forming apparatus of the embodiment.
FIG. 6 is a diagram illustrating an image dot formation pattern of a black image used in the color image forming apparatus of the embodiment.
[Explanation of symbols]
    1 Image carrier
    2 Charging device
    3 Image writing device
    4 Rotating developing device
    5 Transfer drum
    6 Transcription corotron
    7 Fixing device
  11 Paper tray
  13 Charger for adsorption
  14 Transcript
  21 Document reader
  22 Image processing device
  37 color CCD
  50 Intermediate transfer member
  51 Transfer roll (primary transfer device)
  52 Transfer roll (secondary transfer device)
  53 Support roll

Claims (12)

An image carrier, a charging device that charges the image carrier almost uniformly, an image writing device that forms an electrostatic latent image on the image carrier based on image information, and a toner and a magnetic carrier are mixed A developing device that uses a two-component developer to transfer at least cyan, magenta, and yellow chromatic toner to the electrostatic latent image on the image carrier, and forms the toner image, and transfers the toner image onto a transfer material A color image forming apparatus comprising: a transfer device that performs heat transfer; and a fixing device that heat-fixes the toner image of the transfer material.
It is set so that a transfer image is formed by sequentially transferring the toner image of the color with the lowest visibility onto the transfer material,
When the thickness of a monochrome image having an area ratio of 100% fixed on the transfer material is t1, and the thickness of a monochrome image having an area ratio of 50% fixed on the transfer material is t2, t1 and t2 are:
0.7 ≤ t2 / t1 ≤ 1.3
So as to satisfy the relation, the volume resistivity of a powdery material of magnetic carrier (Omega cm) color image forming apparatus characterized by is set. An image carrier, a charging device that charges the image carrier almost uniformly, an image writing device that forms an electrostatic latent image on the image carrier based on image information, and a toner and a magnetic carrier are mixed A developing device that uses a two-component developer to transfer at least cyan, magenta, and yellow chromatic toner to the electrostatic latent image on the image carrier, and forms the toner image, and transfers the toner image onto a transfer material A color image forming apparatus comprising: a transfer device that performs heat transfer; and a fixing device that heat-fixes the toner image of the transfer material.
It is set so that a transfer image is formed by sequentially transferring the toner image of the color with the lowest visibility onto the transfer material,
When the thickness of a monochrome image having an area ratio of 100% fixed on the transfer material is t1, and the thickness of a monochrome image having an area ratio of 50% fixed on the transfer material is t2, t1 and t2 are:
0.7 ≤ t2 / t1 ≤ 1.3
A color image forming apparatus , wherein a heating temperature or a pressing force at the time of fixing in the fixing device is set so as to satisfy the relationship . An image carrier, a charging device that charges the image carrier almost uniformly, an image writing device that forms an electrostatic latent image on the image carrier based on image information, and a toner and a magnetic carrier are mixed A developing device that uses a two-component developer to transfer a chromatic toner of at least cyan, magenta, and yellow to the electrostatic latent image on the image bearing member to form a toner image; and the toner image on the intermediate transfer member An intermediate transfer device that sequentially transfers, a secondary transfer device that collectively transfers the toner images onto a transfer material after all color toner images have been transferred onto the intermediate transfer member, and a toner image on the transfer material; A color image forming apparatus having a fixing device that heat-fixes
It is set so as to form a transfer image by sequentially transferring the toner image having the lowest visibility to the intermediate transfer member,
When the thickness of a monochrome image with an area ratio of 100% fixed on the transfer material is t1, and the thickness of a monochrome image with an area ratio of 50% fixed on the transfer material is t2, t1 and t2 are:
0.7 ≤ t2 / t1 ≤ 1.3
So as to satisfy the relation, the volume resistivity of a powdery material of magnetic carrier (Omega cm) color image forming apparatus characterized by is set. An image carrier, a charging device that charges the image carrier almost uniformly, an image writing device that forms an electrostatic latent image on the image carrier based on image information, and a toner and a magnetic carrier are mixed A developing device that uses a two-component developer to transfer a chromatic toner of at least cyan, magenta, and yellow to the electrostatic latent image on the image bearing member to form a toner image; and the toner image on the intermediate transfer member An intermediate transfer device that sequentially transfers, a secondary transfer device that collectively transfers the toner images onto a transfer material after all color toner images have been transferred onto the intermediate transfer member, and a toner image on the transfer material; A color image forming apparatus having a fixing device that heat-fixes
It is set so as to form a transfer image by sequentially transferring the toner image having the lowest visibility to the intermediate transfer member,
When the thickness of a monochrome image with an area ratio of 100% fixed on the transfer material is t1, and the thickness of a monochrome image with an area ratio of 50% fixed on the transfer material is t2, t1 and t2 are:
0.7 ≤ t2 / t1 ≤ 1.3
A color image forming apparatus , wherein a heating temperature or a pressing force at the time of fixing in the fixing device is set so as to satisfy the relationship . In the color image forming apparatus according to any one of claims 1 to 4 ,
Using a two-component developer in which a transparent toner and a magnetic carrier are mixed, and having a developing device that forms a toner image by transferring the transparent toner to an electrostatic latent image on the image carrier, A color image forming apparatus, wherein the transparent toner is set to be transferred to the entire surface or a portion of the chromatic color toner not developed. The average thickness t1 (μm) of the monochrome image with the area ratio of 100% is
2.0 ≤ t1 ≤ 4.0
The color image forming apparatus according to any one of claims 1 to 5, wherein the color image forming apparatus is in a range of the following.     The color image forming apparatus according to any one of claims 1 to 6, wherein the number of screen lines of an image to be formed is set to 4 lpm or more and 12 lpm or less. In addition to the chromatic toner, a black toner is used,
When the screen angles of the four colors are A, B, C, and D, A, B, and C have different angles, and the difference between the angles is set in the range of 26 degrees or more and 34 degrees or less. When C>B> A, D is
A-12 degrees or more, A-18 degrees or less
(A + B) × 0.5-3 degrees or more, (A + B) × 0.5 + 3 degrees or less
(B + C) × 0.5-3 degrees or more, (B + C) × 0.5 + 3 degrees or less
The color is set to any one of C + 12 degrees or more and C + 18 degrees or less, and the color having the highest visibility is assigned to D 1. The color image forming apparatus according to any one of the above.     9. The image forming apparatus according to claim 1, wherein an average particle diameter of toner contained in the developing device is set to 4 μm or more and 7 μm or less.     The chromatic color toner image having an area ratio of 100% is set to transfer the chromatic color toner image on the transfer material with the toner image having the largest light scattering in the lowermost layer as a lowermost layer. The image forming apparatus according to claim 1. A charging step for charging the image carrier substantially uniformly; an exposure step for forming an electrostatic latent image on the image carrier based on image information; and at least cyan and magenta on the electrostatic latent image on the image carrier. A development process for forming a yellow chromatic toner image, a transfer process for forming a transfer image by transferring the toner image onto a transfer material, and a fixing process for heating and fixing the toner image on the transfer material. In a color image forming method having
It is set so that a transfer image is formed by sequentially transferring toner images having the lowest visibility onto the transfer material,
The thickness of a monochrome image fixed on the transfer material with an area ratio of 100% is t1,
When the thickness of a monochrome image with an area ratio of 50% fixed on the transfer material is t2, t1 and t2 are:
0.7 ≤ t2 / t1 ≤ 1.3
A color image forming method characterized by satisfying the relationship: A charging step for charging the image carrier substantially uniformly; an exposure step for forming an electrostatic latent image on the image carrier based on image information; and at least cyan and magenta on the electrostatic latent image on the image carrier. A developing step for forming a yellow chromatic toner image, an intermediate transfer step for sequentially transferring the toner image onto the intermediate transfer member, and after the toner images of all colors are transferred onto the intermediate transfer member, In a color image forming method comprising a secondary transfer step of transferring toner images onto a transfer material in a batch, and a fixing step of heating and fixing the toner images on the transfer material,
It is set so as to form a transfer image by sequentially transferring the toner image having the lowest visibility to the intermediate transfer member,
The thickness of a monochrome image fixed on the transfer material with an area ratio of 100% is t1,
When the thickness of a monochrome image with an area ratio of 50% fixed on the transfer material is t2, t1 and t2 are:
0.7 ≤ t2 / t1 ≤ 1.3
A color image forming method characterized by satisfying the relationship:

Images