JP2684035B2 - Multicolor image forming method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multicolor image forming method for forming a multicolor image on a recording material using electrophotography. BACKGROUND OF THE INVENTION In an image forming apparatus using an electrophotographic method or an electrostatic recording method, an electrostatic latent image is formed on an image forming body, and the electrostatic latent image is developed with a toner which is a charged particle. This device is commercialized as a copying machine, a printer, and the like. Furthermore, multi-colored images and composite images (overlaying multiple originals and image information with original images)
In order to obtain the above, the above principle is used as follows. That is, it is realized by performing charged image exposure / development as one cycle on an image forming body having a photoconductive layer on a conductive substrate, and performing this twice or more (for example, Japanese Patent Application No. 58-184381).
issue). Alternatively, a method in which a transparent insulating layer is provided on the outer side of a photoconductive layer as an image forming body, and primary charging, secondary charging, simultaneous image exposure, uniform exposure and development are performed twice or more in one cycle, or a primary charging secondary A method of exposing and developing the next charged image two or more times in one cycle (eg, Japanese Patent Application No.
58-183152) etc. All of these methods enable multicolor development and image composition on the image forming body.
Since these superposed images can be transferred onto the transfer body by a single transfer process, the device can obtain a multicolor image or a composite image with a simple configuration. As a developing method for this purpose, for example, a developing agent composed of a mixture of a non-magnetic toner and a magnetic carrier is used to develop under the conditions described in Japanese Patent Application No. 58-57446 or 60-192712. It is necessary. This developing method is a kind of magnetic brush developing method,
It is characterized in that only the toner is made to fly to the latent image surface of the image forming body by an AC bias without the magnetic brush coming into contact with the image forming body. An example of the above-mentioned image forming apparatus is one in which the latent image forming means forms a latent image for each color and develops each latent image by a developing device using toner of a corresponding color. In such a multicolor image forming apparatus, an electrostatic latent image is formed by irradiating an image forming body (hereinafter also referred to as a photoconductor) having a photoconductive substance on a conductive substrate with a light beam such as a laser. The thing is typical. In such an apparatus, a multicolor image is formed as shown in the flowchart of FIG. FIG. 4 shows changes in the surface potential of the image forming body, where PH is the exposed area of the image forming body, DA is the unexposed area of the image forming body,
T ₁ is the toner adhered on the image forming body in the first development, T ₂
Is the toner that has adhered to the image forming body during the second development.
P indicates the amount of increase in potential caused by the toner T ₁ adhering to the exposed portion PH in the first development. For explanation, the polarity of the latent image is positive. The image forming body is uniformly charged by the charger to have a constant positive surface potential E. First image exposure is performed using a laser, a cathode ray tube, an LED, etc. as an exposure source, and the potential of the exposed portion PH decreases according to the amount of light. The electrostatic latent image thus formed is reversely developed by a developing device to which a positive bias approximately equal to the surface potential E of the unexposed portion is applied. As a result, the positively charged toner T ₁ adheres to the exposed portion PH having a relatively low potential, and a first toner image is formed. In the area where the toner image is formed, the potential rises by DUP due to the adhesion of the positively charged toner T _1, but normally it does not become the same potential as the unexposed portion DA. Next, the surface of the image forming body on which the first toner image is formed is charged a second time by the charger, and as a result, the toner T ₁
The surface potential E is uniform regardless of the presence or absence of. A second image exposure is performed on the surface of the image forming body to form an electrostatic latent image. Similarly to the above, the positively charged toner T ₂ of a color different from that of the toner T ₁ is developed to obtain a second toner image. Thereafter, the same process is repeated a required number of times to obtain a multicolor toner image on the image forming body. A multicolor recording image is obtained by transferring this onto a transfer material and further fixing it by heating or pressurizing it. In this case, the toner and charges remaining on the surface of the image forming body are cleaned and used for the next multicolor image formation. Problems to be Solved by the Invention A method of expressing various colors by the method described above will be described. The present invention is a system in which toners having different colors are overlapped with each other to obtain a multicolored color. As shown in FIG. 5 (A), the latent image potential and the developing bias are controlled to superimpose the toner image made of toner T _{2 of a} different color on the toner image made of toner T ₁ of a certain color. The color is developed to generate a color (subtractive color mixture). However, in the, be irradiated with light from the top of the toner T ₁ that is previously developed, not reach sufficiently to the photoconductive layer is absorbed by the toner T _1, and the toner T ₁ is has a charge Therefore, since there is a potential of the toner layer and the latent image is not completely formed, the adhesion amount of the toner T ₂ developed later is remarkably reduced as shown in FIG. 5 (B). In order to avoid this problem, a method of developing yellow and magenta first by using a laser beam having a long wavelength as an image exposing means has been proposed (Japanese Patent Application No. 59-181087 and 18).
No. 1550). According to this method, the yellow image is below the other color on the image forming body and above the other color on the transfer material. However, yellow has a larger surface reflection than other colors, and in the multicolor image obtained by the above method, yellow is emphasized more than necessary, especially in colors including yellow such as green and red. Therefore, there is a problem that it is very difficult to control the color. That is, the color developed earlier tends to be emphasized. This problem becomes a serious obstacle especially when trying to express black from yellow, magenta, and cyan toners. Therefore, it is preferable to use a dedicated toner for expressing black. However, when forming a multicolor image from yellow, magenta, cyan, and black toners, conventional black toner absorbs most of the visible light and invisible light, so the black toner must be developed later. I won't. To this end, the light contrast of the yellow, magenta, and cyan toners previously developed and the potential of the black toner finally developed due to the toner layer potential become small, and the development amount of the black toner image becomes small. , The black portion in the recorded image is reduced, the density is low, and the character portion becomes unclear. Further, for color reproduction having a gray component, any one of yellow, magenta, and cyan toners is superposed on black toner. In such a case, since the black toner is difficult to be developed by the color toner, there is a problem that the color balance is easily deviated. SUMMARY OF THE INVENTION It is an object of the present invention to provide a multicolor image forming method using a black toner capable of always recording black clearly and expressing colors in a well-balanced manner. According to the above object, an image forming body having a photoconductive layer is charged and imagewise exposed to form a first electrostatic latent image, which substantially absorbs light in the entire visible region and has a wavelength of 750 nm or more. The black toner for electrophotography obtained by using a plurality of colorants having a spectral transmittance characteristic of transmitting light in the wavelength range of 1 and complementing each other in the visible range is developed by the developer carrier. The first electrostatic latent image is reversely developed with the black toner for electrophotography to form a first black toner image, and subsequently, an image forming body having the first black toner image is formed. Recharged, imagewise exposing the image forming body with light passing through the black toner to form a second electrostatic latent image,
The second electrostatic latent image is reverse-developed with a color toner of a second color selected from cyan, magenta, and yellow color toners, and the second electrostatic latent image is superimposed on the first black toner image to form a second image. On the image forming body after forming a color toner image on the image forming body by further repeating the third color toner image and the fourth color toner image for each color with color toners of different colors. A method for forming a multicolor image, wherein the color toner images formed by superimposing on each other are collectively transferred to a transfer material, and the black toner image is positioned at the uppermost layer on the transfer material. Achieved by In the present invention, the black toner is not made of a single colorant such as carbon black, but is obtained by synthesizing a plurality of colorants such as yellow, magenta and cyan. Each of these colorants is selected to have a transmissive component in the non-visible light region to absorb visible light substantially completely, and as a result, the resulting black synthetic colorant is also invisible light-sensitive. Make it transparent to the area. A toner is produced using the colorant thus obtained. This toner becomes black toner. When this toner is used in the multicolor image forming method described above, the black toner can be developed first. At this time,
As a light source used for image exposure, one having a spectral distribution in the transmission wavelength range in the above-mentioned invisible light range is used. As a result, the black toner image can be reliably formed without being affected by the light shielding of other colors and the toner layer potential. Then, a latent image of yellow, magenta, and cyan can be formed by superposing on the black toner, and yellow, magenta, and cyan toners of other colors can be superposed on the black toner image and developed. Then, by transferring the toner image superimposed on the image forming body to the transfer material, the black toner is formed on the transfer material, so that the black portion is clear and the specific color is not emphasized. In particular, the chromatic portion containing the black component can be reproduced with good color balance. Embodiments FIG. 1 shows a multicolor image forming apparatus which is an embodiment constructed according to the present invention. In the figure, 1 is an image forming member made of a photosensitive member that rotates in the direction of the arrow and has sensitivity in the infrared region, 21 is a corona charger, L is infrared image exposure light emitted from a laser optical system 26, 5A, 5B, 5C and 5D are developing devices having yellow, magenta, cyan and black toners, 32 is a pre-transfer exposure lamp having an infrared light component, 33 is a transfer electrode, 34 is a separation electrode, P is a recording paper, and 36 is a cleaning device. In the apparatus, 36a is a fur brush, 36b is a toner collecting roller, and 36c is a scraper. This forms a multicolor image as follows. The surface of the image forming body 1 is uniformly charged by a corona charger 21 including a scorotron band electrode. Then, the infrared image exposure light L from the laser optical system 26 according to the recording data of the black component
Are irradiated onto the image forming body 1. Thus, an electrostatic latent image is formed. This electrostatic latent image is developed by the developing device 5D containing the toner T ₁ which is the first black toner. The image forming body on which the toner image is formed is again a corona charger.
It is uniformly charged by 21 and receives the image exposure light L according to the recording data of another color component. The formed electrostatic latent image is developed by the developing unit 5C which the second (e.g. cyan) toner T ₂ are accommodated. As a result, the first image is formed on the image forming body 1.
A two-color toner image is formed by the black toner T ₁ and the second toner T ₂ . In the same manner, the toner T ₃ (for example, magenta color) (developing device 5B) and the toner T ₄ (for example, yellow color) are similarly processed.
(Developing device 5A) is overlaid and developed, and a four-color toner image is formed on the image forming body 1. The multicolor toner image thus obtained on the image forming body 1 is transferred onto the recording paper P by the transfer pole 33. The recording paper P is separated from the image forming body 1 by the separation pole 34 and fixed by the fixing device 31. On the other hand, the image forming body 1 is cleaned by the cleaning device 36. The fur brush 36a of the cleaning device 36 is kept in non-contact with the image forming body 1 during image formation, and when a multicolor image is formed on the image forming body 1, the image forming body 1 is transferred after the transfer.
, And scrapes the transfer residual toner while rotating in the direction of the arrow. When the cleaning is completed, the fur brush 36a is separated from the image forming body 1 again. An appropriate bias is applied to the toner collecting roller 36b while rotating in the direction of the arrow to collect the toner T and the like from the fur brush 36a. It is then scraped off by scraper 36c. The laser optical system 26 in the embodiment is shown in FIG. 37 in the figure
Is, for example, a semiconductor laser diode that emits infrared light, 38
Is a rotating polygon mirror, and 39 is an fθ lens. FIG. 3 is a sectional view of the developing device 5A. In the figure, 51 is a housing, 53 is a sleeve, 54 is a developer carrier, that is, a magnetic field generating means provided in the sleeve, a magnetic roll having N and S poles, 55 is a layer forming member, and 56 is a fixing member for the member. , 57
Is a first stirring member, and 58 is a second stirring member. Reference numeral 59 is a sleeve cleaning member, 60 is a developing bias power source, 18 is a developing area, that is, an area where the toner conveyed by the sleeve 53 can be transferred to the image forming body by receiving an electrostatic force, T is toner, and D is developer. Represents In such a developing device, the two stirring members 57, 58 are screw-shaped and rotate in the direction of the arrow in the drawing to stir and convey the developer. The stirring member 57 has a shape such that it is conveyed toward the front side of the paper, and the stirring member 58 has a shape such that it is conveyed toward the back side of the paper. A wall 52 is provided so as to prevent the developer from staying in the intermediate portion between the two, so that the developer is exchanged in the left-right direction of the paper in this area. Replenishment of toner to the developing device 5 is performed from the front side of FIG. 3, and is roughly circulated to the back side of the paper by the stirring member 58 and to the front side of the paper by the stirring member 57 to uniformly mix the toner and the carrier. . However, the position of toner replenishment is not particularly limited to this, and for example, a method of uniformly replenishing the sleeve shaft from the right side of FIG. 3 may be used. In this way, the developer D is sufficiently agitated and mixed, and is conveyed in the same direction as the rotating direction of the sleeve 53 by the conveying force of the sleeve 53 rotating in the arrow direction and the magnetic roll 54. A layer forming member 55, which is held by a fixing member 56 extending from the housing 52, is pressed against the surface of the sleeve 53 to regulate the amount of the developer D to be conveyed and form a developer layer. As another means for forming a developer layer when carrying out the development of this embodiment, for example, a magnetic or non-magnetic regulating plate arranged with a certain gap from the sleeve, or a magnetic or non-magnetic regulating plate arranged in proximity to the sleeve. Any conventionally known one such as a magnetic roll may be used. The carrier and toner constituting the developer preferably have a small particle diameter in terms of the resolution of image quality and the reproducibility of gradation. For example, even when the carrier of the developer layer has a small particle size of 40 μm or less, impurities such as impurities and agglomerates in the developer are automatically removed by using the means such as the layer forming member 55 described above to obtain a uniform length. Can form a magnetic brush. Moreover, even when the carrier has a particle size as small as that of the toner, the mixing of impurities is similarly eliminated, and the magnetic brush having a uniform length can be formed. The sleeve cleaning roller 59 rotates in the direction of the arrow (FIG. 3) and passes through the developing area 18 to scrape the developer which has consumed the toner T from the sleeve 53. Therefore, the amount of the toner T conveyed to the developing area can be kept constant, and the developing condition becomes stable. Next, the constitution of the developer of this embodiment used in the above developing method will be described. (Developer formulation) Toner composition: Polystyrene 45 parts by weight Polymethylmethacrylate 44 〃 Varifast 0.2 〃 (Charge control agent) Colorant 10.5 〃 Mixing, kneading and classifying the above composition to obtain the desired toner ing. Carrier (resin-coated carrier) composition: Core: Ferrite coating Resin: Styrene / acrylic (4: 6) Magnetization 27emu / g Particle size 30μm Specific gravity 5.2g / cm ³ Specific resistance 10 ¹³ Ωcm or more Mix the above composition and mix After the classification, hot air treatment was performed to obtain a sphere, which was used as a carrier. A conventionally known colorant is used as a colorant for chromatic (yellow, magenta, cyan, etc.) toner. As the colorant for the black toner, plural kinds of colorants are mixed and used. The conditions of the plural kinds of colorants to be mixed include the following. (1) Absorptive regions do not complement each other in the entire visible light range (wavelength 360 to 700 nm) (2) There is a common wavelength range that transmits in the wavelength range of 750 nm or more. Black can be expressed by the condition (1). Further, under the condition (2), the light in the common wavelength range passes through the black toner, and therefore, when such light is used for image exposure, a latent image can be formed well as described above. The inventor mixed the following pigments and measured the absorbance. Pigment Yellow 97; 3.5 parts Pigment Red 146; 4 parts Pigment Blue 15.3; 3 parts Main resin (polyester resin) of the above pigments; 100 parts Release agent (wax); 6 parts Pigment; 5 to 10 parts Resin; 100 parts Are mixed, and the melted and kneaded meat is crushed and classified. The measuring method is as follows. Five times the weight of the solvent was added to the resin, and glass beads were added and dispersed with a stirring blade. This is applied on an OHP sheet so as to have a thickness of 5 to 10 μm. This is cut out and the absorbance is measured with a spectrophotometer (HITACHI 330 type). The wavelength was measured in the range of 360 to 850 nm. The absorbance is defined by log (1 / T) (T is the reflectance (= reflected light quantity / incident light quantity). The results are shown in Fig. 6. As is clear from the figure, the absorption is almost uniform in the visible light region. In other words, the transmittance is high in the infrared region of 750 nm or more. Next, using the following: Pigment Red 57: 1; 6 parts: Pigment Blue 15: 3 6 parts, a toner was prepared in the same manner, and the absorbance was measured. The results are shown in Fig. 7. The inventor made various black toners using various colorants, and the following facts were revealed: (1) Absorbance of 0.8 over the entire visible range. (2) When the maximum value of the absorbance of each colorant alone is 0.9 or more at each wavelength in the visible range, (1) is achieved. When used under the conditions shown in Table 1 in the apparatus shown in FIG. When the ratio was 4 or less, preferably 0.2 or less, a latent image with high contrast was obtained regardless of the color of the image.
A black toner obtained by using a plurality of colorants having a spectral transmittance characteristic of transmitting light in a wavelength range of m or more and complementing each other in the visible range is used as a toner image on an image forming body. Is a multicolor image forming method in which the images are formed by superimposing them on one another and are collectively transferred to a transfer material. A developer that first performs reversal development on image formation before reversal development with color toners such as yellow, magenta, and cyan. By using as
It was confirmed that on the transfer material, a black portion was clear, and a gray-colored chromatic portion containing a black component had a particularly well-balanced reproduced multicolor image. EFFECTS OF THE INVENTION The present invention provides a multicolor image forming method capable of always recording a clear black color and expressing a well-balanced color without emphasizing a specific color and without damaging the gray balance. Became.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic configuration diagram of a multicolor image forming apparatus using an image forming method of the present invention, FIG. 2 is a configuration diagram of a laser optical system, FIG. 3 is a sectional view of a developing device, FIG. 4 is a diagram showing a change in surface potential on the image forming body, FIG. 5 is a schematic diagram showing a toner adhesion state on the image forming body, and FIGS. 6 and 7 show an embodiment of the present invention. 6 is a graph showing the absorbance of toner. 1 ... Image forming member 5A, 5B, 5C, 5D ... Developing device, 21 ... Corona charger 26 ... Laser optical system, 33 ... Transfer electrode 34 ... Separation electrode, 36 ... Cleaning device T ₁ , T ₂ …… Toner

   ────────────────────────────────────────────────── ─── Continuation of front page        Panel     Referee Takehiko Takahashi     Judge Ichino Kasuke     Judge Tetsuo Taki                (56) References JP-A-61-172159 (JP, A)                 JP-A-57-119363 (JP, A)                 JP 58-140754 (JP, A)                 JP-A-59-46655 (JP, A)

Claims (1)

(57) [Claims] The first electrostatic latent image is formed by charging and imagewise exposing the image forming body having the photoconductive layer so that light in the entire visible region is substantially absorbed and light in the wavelength range of 750 nm or more is transmitted. It has various spectral transmittance characteristics, and is obtained by using a plurality of colorants that complement each other's absorption in the visible region, the absorbance is 0.8 or more over the entire visible region, and the absorbance is 0.4 or less at the main wavelength of image exposure. Of the electrophotographic black toner is conveyed to a developing area by a developer conveying body, and the first electrostatic latent image is reversely developed with the electrophotographic black toner to form a first black toner image. The image forming body having the first black toner image is recharged, and the image forming body is image-exposed with light passing through the black toner to form a second electrostatic latent image. Electrostatic latent image of any one selected from cyan, magenta, and yellow color toners And reversal development with 2 color color toner to form a second color toner image superimposed on the first black toner image, further, a third for each color
Color toner image and the fourth color toner image are similarly repeated with color toners of different colors to form a color toner image, and then the color toner image formed by superimposing on the image forming body is used as a transfer material. A method for forming a multicolor image, wherein the black toner image is transferred in a batch and the black toner image is located on the uppermost layer on a transfer material.