JPH01267569A - Formation of image - Google Patents

Abstract

PURPOSE:To obtain an image with good color reproducibility while preventing colors from being mixed by making toner used for a precedent developing process larger in particle size then toner used for a following developing process. CONSTITUTION:Toner particles which differ in color are stuck in a mutually superposed state on a high-potential latent image part V01 between different- potential latent images formed on a photosensitive body 1 in developing devices 4 and 5, and they are transferred to copying paper 10 and then fixed. Namely, toner TB1 of large particle size which is stuck in the precedent developing process is on the upper side on the copying paper 10 after the transfer and shield toner TR2 on the lower side which is stuck in the following developing process. The toner on the upper side is large in particle size, so its shielding force is large and the color of the toner is reproduced visually. Consequently, while toner particles of different colors are prevented from being mixed, the image with excellent color reproduction is obtained.

Description

[Detailed description of the invention] [Use field of +U industry-F] The present invention relates to a multicolor image forming method.

[Prior Art] Conventionally, as disclosed in Japanese Patent Publication No. 53-115238, for example, different potential latent images formed on a photoreceptor are developed into different colors by utilizing differences in spectral sensitivity of the photoreceptor. An image forming method is known in which image forming agents are used for sequential development. For example, when printing a two-color copy image of red and black, a black groove @FIIVO3 and a red latent image area V Oa are formed with different potentials depending on the color by exposing the photoreceptor to light (the second color). (see Figure 7), and then the first development is done with black 1-S-Ta2 on the black latent image area VO.
By performing the development with a bias VB3 intermediate between 3 and the red latent image area VO4, black toner TB3 is deposited only on the black latent image area VO3 (see FIG. 8).

Next, the second 11. using red toner TR4. ! By performing the development bias VB4 lower than that of the red latent image portion V○4, the red latent image portion VO4 and the black latent image portion VO3 are
A red toner TR4 is applied to (see FIG. 9). After that, transfer the toner image to the composite Ti 100 (No. 10
(see figure), two-color copy images can be printed 1!1 by heating, melting, and fixing.

[Problems to be Solved by the Invention] However, in the case of the above-mentioned conventional image forming method, the portion of the copy image that is desired to be black is colored with C. Therefore, if the hiding power of the black tonneau TB3 is small, the red 1-toner TRa underneath it will be exposed and color mixing will easily occur (
(See Figure 11). As a result, the parts of the copied image that you want to make black appear reddish, making it impossible to reproduce faithful black.

The present invention was devised in view of the above-mentioned problems, and its purpose is to prevent color mixing by improving the hiding horn of the toner on the upper side where toners of different colors overlap. An object of the present invention is to provide an image forming method capable of obtaining an image with good color reproducibility.

[Means for Solving the Problems] The image forming method of the present invention is an image forming method in which different potential latent images formed on a photoreceptor are sequentially developed with toners of different colors, in which each developing step is performed in a subsequent developing step. The method is characterized in that the particle size of the toner used in the previous development process is made larger than that of the toner used.

[Function] In the image forming method of the present invention, toners of different colors are adhered in a wide manner to the high potential latent image portions of the different potential latent images formed on the photoreceptor in each development process, and is transferred to copy paper and fixed. That is, on the copy paper after transfer, the toner with a large particle size that was deposited in the previous developing step is on the upper side, and hides the toner that was deposited on the lower side that was deposited in the subsequent developing step. Since the 1-toner on the upper side has a large particle size, it has a large hiding power, and the color of the toner is visually reproduced.

[Example] Hereinafter, specific examples of the present invention will be described with reference to the accompanying drawings.

FIG. 1 schematically shows an electronic copying machine for implementing the present invention. The photosensitive drum 1 is a well-known type having a photoconductive layer on its outer peripheral surface, and is provided so as to be rotatable in the direction of arrow a. Around the photosensitive drum 1, members and devices described below are arranged.

The charger 2 is for first charging the surface of the photoreceptor drum 1 with a constant potential, and a power supply 21 is connected to the charge wire, and a voltage of -5.5 KV is applied thereto. be done.

The exposure device if3 is for forming an electrostatic latent image corresponding to the original image on the surface of the photoreceptor drum 1 using a well-known slit exposure method, and is composed of an exposure lamp, a mirror, a lens, etc. .

The first developing device 4 and the second developing device 5 include NK,
This is a well-known magnetic brush system comprising a magnet roller 42.52 having an S pole magnetized and a developing sleeve 41.51 held rotatably around the outer periphery of the magnet roller 42.52. The developing sleeve 41.51, which also functions as the developing 'Fi pole, is equipped with a power source 4 for developing bias.
3.53 are connected to each other. And the first current @ device 4
A developing bias of -250 V is applied to the developing sleeve 41 of the second developing device, and a developing bias of -150 V is applied to the developing sleeve 51 of the second developing device. The first developing device 4 and the second developing device 5 are charged with a developer consisting of a mixture of a magnetic carrier and an insulating non-magnetic positively charged toner, and the first developing device 4 is charged with a developer consisting of a mixture of a magnetic carrier and an insulating non-magnetic positively charged toner. The black toner TB1 with an average particle size of 14.2 μm is used as the developer in the second developing device 5, and the red toner 1 to TR with an average particle size of 8.3 μm mainly composed of resin is used as the developer in the second developing device 5.
2 are mixed in each. That is, the black toner TB+ of the first developing device 4 that performs the first development has a larger particle size than the red toner TR2 of the second developing device 5 that performs the second development.

The magnetic carrier has an average particle size of 57 μm and a resistance of 1Q+3.
It is a binder-type insulating magnetic carrier of Ω·cm, and the same carrier is mixed into each developer.

The transfer charger 6 applies an electric field to the copy paper 10 being conveyed in the direction of the arrow from the back side thereof, and transfers the toner image formed on the surface of the photoreceptor drum 1 by the pre-distribution device 4.5. A voltage of -5°8 KV, which has the opposite polarity to that of the insulating toner, is applied from a power source 61 to the transfer voltage source for transferring the toner onto the copy paper 10.

The separation charger 7 applies an alternating current electric field to the copy paper 10 immediately after transfer to remove electricity from the copy paper 10 and peel the copy paper 10 from the surface of the photoreceptor drum 1. Power supply 71 to 4.3KV
AC voltage is applied.

The cleaning device 8 uses a blade method to remove debris remaining on the surface of the photoreceptor drum 1.

The eraser lamp 9 is used to remove charges remaining on the surface of the photoreceptor drum 1 by irradiating light in order to prepare for the next copying process.

Note that on the right side of the photosensitive drum 1 in the figure, there is a constant 'I'I' device (not shown) that heats and melts the toner image transferred to the copy paper 10 that is separated by the separation charger 7 and is fed to fix it. is provided.

To form an image in the electronic copying machine configured as described above, first, the surface of the photoreceptor drum 1 is uniformly charged by the charging charge t2, and then a two-color image original consisting of black and red is formed by the exposure device 3. Image exposure is performed.

As a result, a static latent image having a different potential depending on the color of the information is formed on the surface of the photoreceptor drum 1. That is, as shown in FIG. 2, a black layer @ portion VO+ with a high potential and a red latent image portion o1 with a lower potential are formed. This electrostatic latent image is processed into a black latent image portion o1 by the first developing device W14.
By performing the first color development with a developing bias VB+ intermediate between the latent image area and the red latent image area VO2, black toner T8+ is attached only to the black developing area VO+ (see FIG. 3). Next, the second developing device 5 performs a second color development with a bias VB2 lower than the red latent image 81IVO2.

As a result, the black latent image area VO+ and the red latent image area VOz
Red toner TR2 is attached to the black latent image area VO+.
, red toner TR2 is superimposed on black toner T[31 (see FIG. 4), and the two-color developed toner image is transferred to copy paper 1 by transfer charger 6.
0 (see FIG. 5), and fixed by heating and melting using a constant volume device. As a result, as shown in FIG. 6, in the area where the black toner TB+ and the red toner TR2 overlap, the black toner TB+, which is on the tenth side on the copy vAio, has larger grains (¥ is larger and has a greater hiding power. Therefore, red toner TR2
The image is reproduced as a black image with less influence of color. Therefore, the contrast between the black part and the red part is strong in the two-color copy image number that has been tl'd.

As described above, according to the image forming method of this embodiment, it is possible to prevent color mixing in areas where two color toners overlap, and it is possible to obtain an image with good color reproducibility.

As a comparative example, the first development was conducted with an average particle size of 9.2μ.
The second development was done with black toner of m, with an average particle size of 13.9.
A two-color copy image was formed by using a red toner with a diameter of .mu.m and using smaller black toner grains than the red toner.

However, the part where the black toner and red toner overlapped had a reddish color due to color mixing with the red toner because the black toner on the upper side had a small hiding power. Therefore, the resulting two-color copy image had weak contrast between the black and red parts.

[Effects of the Invention] The image forming method of the present invention is an image forming method in which different potential latent images formed on a photoconductor are sequentially developed with toners of different colors, and each developing step uses a toner that is used in a later developing step. This is done by increasing the particle size of the toner used in the previous development step. As a result, in the portion of copy paper L where toners of different colors overlap, the toner on the upper side has a larger particle size, so that its hiding power can be improved. Therefore, according to the present invention, it is possible to prevent the occurrence of color mixing between toners of different colors and the same IJ, and to obtain an image with good color reproducibility.

[Brief explanation of the drawing]

Figures 1 to 6 are the fruits of the present invention! For example, Figure 1 is a schematic diagram showing the outline of an electronic copy, Figure 2 is an explanatory diagram of an electrostatic tpJ image formed on a photoreceptor, and Figure 3 is the state after the first color phenomenon process is completed. FIG. 4 is an explanatory diagram showing the state after the second color phenomenon process is completed, FIG. 5 is an explanatory diagram showing the state after transfer, and FIG. 6 is an explanatory diagram showing the state after heat fixing. It is a diagram. 7 to 11 relate to the conventional image forming method,
Fig. 7 is an explanatory diagram corresponding to Fig. 2, Fig. 8 is an explanatory diagram corresponding to Fig. 3, Fig. 9 is an explanatory diagram corresponding to Fig. 4,
0 is an explanatory diagram corresponding to FIG. 5, and FIG. 11 is an explanatory diagram corresponding to FIG. 6. 1...Photoconductor drum 11th edition applicant, 1st generation member of Minolta Camera Co., Ltd.
For patent attorney Hiroshi Okawa Figure 1 Figure 2 Figure 3 Illustrations 〒〒1 Figure 7 Figure 8 Figure 9 Figure 11

Claims (1)

[Claims] (1) In an image forming method in which different potential latent images formed on a photoconductor are sequentially developed with toners of different colors, each development step uses more toner used in a previous development step than the toner used in a later development step. An image forming method characterized in that the image forming method is carried out by increasing the particle size.