JPH02281273A - Method and device for forming two-color image - Google Patents

Abstract

PURPOSE:To obtain a satisfactory two-color image without disturbing a visible image already forming on a latent image carrier by employing specific carriers. CONSTITUTION:After a first latent image forming means 14 forms an electrostatic latent image on the latent image carrier 10, the electrostatic latent image is further formed with toner electrified to one polarity. Then, a second electrostatic latent image forming means 18 forms a second electrostatic latent image composed of an image part potential and a background potential staying between the image part and the surface potential of the toner image on the latent image carrier 10, after which a second developing means 20 employs a two- component developer made of toner and carriers that are electrified to another polarity, applies a developing bias of potential higher than the intermediate one to the latent image carrier 10 and develops the second electrostatic latent image. The carriers of the developer used in the second developing and forming stage have a volume resistivity of 10<7> - 10<13>OMEGAcm in a 1kV/cm electric field. Consequently, a satisfactory two-color image can be obtained without disturbing a visible image on the latent image carrier.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a two-color image forming method and an apparatus thereof, and more specifically, it relates to a two-color image forming method and an apparatus thereof, and more specifically, to a two-color image forming method and an apparatus for the same. The present invention relates to a two-color image forming method and apparatus capable of obtaining a good two-color image without any problems.

[Prior Art] As a conventional image forming method of this type, for example, the method shown in FIG.
) to (e), the latent image carrier is uniformly charged (see FIG. 3(a)), and then a negative image is projected onto the light-projected charge-eliminating portion of the latent image carrier. Reversal development is performed using toner of the same polarity as that of the latent image carrier (see Figure 3 (C)), and then a positive image is projected to cover the residual charge area on the surface of the latent image carrier except for the area where the positive image is projected. (see Figure 3(d)), and regular development is performed on the residual charge portion of the positive projection section using toner of a different polarity than that of the latent image carrier (see Figure 3(e)). A known method is to form different types of toner images on the same surface of a latent image carrier, align the polarities of the two types of toner images (negative and positive), and then transfer them to a transfer medium at the same time. In this case, when performing the second development, in order to suppress the disturbance of the toner image of the first color that has already been developed, the image area potential Vi2 of the second color and the surface area potential ■t of the first toner image
1 (see FIG. 3(e)).

[Problems to be Solved by the Invention] However, in the image forming method as described above, when the second development is performed using an insulating carrier as the chitria of the second developer, the problem shown by the broken line in FIG. As shown in FIG.
Since the colored toner is developed, the difference between the second developing bias Vb2 and the foreground potential vh2 (V b2 - V
h2) needs to be increased, resulting in a decrease in the second development contrast (Vi2-Vb2), resulting in a problem in that the density of the second color toner image decreases.

Furthermore, the difference (Vb2-Vt1) between the second developing bias Vb2 and the surface potential Vt1 of the first color toner image increases, causing the carrier of the second developer to enter the first color toner image. There is a problem that crowds (carryover) occur.

In order to solve the above problem, it is possible to suppress the generation of fringe electric fields by using a conductive carrier, but this is not preferable because the conductive carrier has a problem of poor fine line reproducibility in terms of image quality.

Therefore, it is an important issue to be able to obtain a two-color image with good fine line reproducibility without disturbing the visible image already formed on the latent image carrier.

This invention was made in view of the above-mentioned circumstances, and in order to solve the above-mentioned problems, it is possible to obtain a two-color image with good fine line reproducibility without disturbing the visible image already formed on the latent image carrier. An object of the present invention is to provide a two-color image forming method and an apparatus thereof, which are characterized by the following.

[Means for Solving the Problems] That is, in order to achieve the above-mentioned object, the two-color image forming method of the present invention applies an image area potential and the above-mentioned first toner image to a latent image carrier carrying a first toner image. A second electrostatic latent image is formed with a foreground potential at an intermediate potential between the surface potential of the first toner image and the image potential; When developing with a two-component developer consisting of a second toner having a polarity different from that of the first toner image and a carrier while applying a developing bias of an intermediate potential with the partial potential, the carrier is used in an electric field of 1 KV/cm. 10～
It is characterized by using a material having a volume resistance value of 10 13 Ωcrn. Further, the two-color image forming apparatus of the present invention includes a latent image carrier, a first latent image forming means for forming a first electrostatic latent image on the latent image carrier, and a first latent image forming device charged to one polarity. a first developing means for developing the first electrostatic latent image with a first toner to form a first toner image; and a first developing means for developing the first electrostatic latent image with a first toner; a second latent image forming means for forming a second electrostatic latent image consisting of a background potential at an intermediate potential between and a second developing means to which a developing bias of an intermediate potential between the image area potential and the background area potential is applied, and the volume resistance value of the carrier of the two-component developer is 1 K V /
It is characterized in that it is set in the range of 10 to 1013 Ωcm in an electric field of 10 cm to 10 13 Ωcm.

In this invention, it is possible to use a conductive carrier as the carrier in the second developing means, but in order to improve fine line reproducibility, it is preferable to use an insulating carrier as the carrier in the second developing means. is preferable.

Any method can be used as a method for developing the second developed toner in the second developing means, but preferably a magnetic anti-developed image or a two-component magnetic brush development method is more preferable, and more preferably a magnetic anti-developed image. It is better to have a method.

As the developing step performed in each toner image forming step, any one may be applied as long as one is normal development and the other is reversal development.

In addition, the latent image carrier may be appropriately selected from a photoreceptor, a dielectric material, etc. as long as it can form a latent image by the latent image forming means, and its specific structure may include a drum shape, a belt shape, etc. Regardless of the situation.

[Production use] The above technical means works as follows.

First, a first electrostatic latent image is formed on the latent image carrier by the first latent image forming means, and then the first electrostatic latent image is formed with a first toner charged to one polarity. Ru. Next, a second electrostatic latent image is formed on the latent image carrier by the second electrostatic latent image means, which has a background potential that is at an intermediate potential between the image potential and the surface potential of the first toner image. After that, a developing bias higher than the potential of the intermediate potential portion is applied to the second developing means using a second two-component developer consisting of a second toner charged to the other polarity and a second carrier. The voltage is applied to the latent image carrier to develop the second electrostatic latent image portion.

At this time, as a carrier for the developer in the second development step, 107 to 1013 Ωc is used in an electric field of 1 KV/cm.
By using a toner having a volume resistivity of m, problems with the image quality of the first and second colors due to fringe electric fields can be avoided, and a good two-color toner image can be obtained.

[Examples] Examples of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows a schematic side view of a two-color image forming apparatus according to the present invention.

In the two-color image forming apparatus of the present invention, a charger 12, a first latent image forming means 14, a first developing means 16, a first developing means 16, a second developing means A second latent image forming means 18, a second developing means 20, a pre-transfer corotron 22, and a transfer means 24 (transfer corotron) are arranged, and on the post-processing side of the transfer means 24, a static eliminating corotron 26, A cleaner 28 and an optical static eliminator 30 are provided. In this case, the first latent image forming means 14 and the second latent image forming means 18 are formed by laser diodes.

In the two-color image forming apparatus configured as described above, two
When forming a color image, a process as shown in FIGS. 2(a) to 2(e) is employed.

That is, first, the photoconductive layer of the photoreceptor drum 10 is negatively charged to +850 (V) by the charger 12 (see FIG.
a)).

Next, the photosensitive drum 1 is formed by the first latent image forming means 14.
The low potential Vi1 (6
After the first electrostatic latent image of 0 (V) is formed (Fig. 2 (
(see b)), using a first two-component developer consisting of a first toner and a first carrier charged to a positive polarity by the first developing means 16, and a developing bias lower than the charging potential (780 m). A first toner image (black toner image) is formed by applying b1 and developing the low potential portion 11 (see FIG. 2(C)).

Next, after a second electrostatic latent image with a high potential Vi2 forming a red latent image portion is formed on the photoreceptor drum 10 carrying the first toner image by the second latent image forming means 18 (a second electrostatic latent image is formed). 2(d)), the second developing means 20 uses a second two-component developer consisting of a second toner charged to a negative polarity and a second carrier to develop a potential lower than the foreground potential Vh2. A second toner image (red toner image) is formed by applying a high developing bias Vb2 and developing the high potential portion Vi2 (see FIG. 2(e)).

The photosensitive drum 10 is then transferred by the pre-transfer corotron 22.
After the polarities of both upper toner images are aligned, both toner images are transferred to the recording sheet 32 at once by the transfer means 24, and a two-color image of red and black is formed on the recording sheet 32.

In such an image forming process, the volume resistance value of the carrier of the second developer is appropriately changed, and the image density of the second color and the latent image of the first color are adjusted under conditions that do not cause a fringe phenomenon around the first color toner image. A test was conducted to investigate the carryover phenomenon and the reproducibility of fine lines of the second color.

When conducting the test, the following points were observed: ◎Conformity and distribution Positive charging system (selenium system) photoreceptor Process speed: 200 rrm/sec ◎First developing means 16 ☆Developing roll configuration: Aluminum sleeve with a diameter of 40 m The magnetic flux density of the main pole (developing magnetic pole) of the 8-type magnetized magnet roll is 1,200 Gauss ☆ Parameters ・Trimming gap: 0.5all+ ・Gap between photoconductor drum 10 and developing roll: 0.6#・Magnet setting angle: +5° ・Rotational speed of developing roll 3 times that of photoreceptor drum 10 ☆ Developer (black) ・Toner (positive) Styrene/acrylic copolymer 85% by weight Carbon black 10% by weight Positive charge control agent
Black toner carrier (negative) with an average particle size of 10 μm made by melt-kneading/pulverizing/classifying 5% by weight of Prosyn dye) Ferritic carrier with an average particle size of 90 μm ◎Second developing means 20 ☆Configuration of the developing roll・Magnetic roll main pole (developing magnetic pole) with a repulsive magnetic pole having a stainless steel sleeve with a diameter of 40 m Magnetic flux density 1, 200 Gauss ☆ Parameters - Trimming gap: 0.4 m - Gap between photoreceptor drum 10 and developing roll: 0 .5
#III+ ・Magnet setting angle: +6° ・Rotational speed of developing roll 1.5 times that of photoreceptor drum 10 ☆Developer (red) ・Toner (negative) Styrene/acrylic copolymer 90% red dye by weight
Red toner carrier (positive) with an average particle size of 12 μm made by melting and kneading 10% by weight (Lysol Scarlet) Styrene/acrylic copolymer 30% by weight and 70% by weight of magnetite having an average particle size of 80 μm By obtaining a polymeric carrier core of about 100% and then changing the carbon black content of a coding layer of polymethyl methacrylate with carbon black dispersed on the surface of the obtained carrier core, a material with a volume resistivity of 1KV/cm was obtained. Five types of carriers A2 to E2 were obtained which touched approximately ≦10 to ≧10 14 ΩCm in an electric field.

When a test was conducted in the process shown in FIG. 2 under the above conditions, the results shown in Table 1 were obtained in the second development step.

As is clear from the results shown in Cloth-1 above, 1KV/ca is used as a carrier for the developer in the second development process.
In the case of a volume resistance value of approximately 1014 Ωcm or more in a + electric field, a decrease in the second color image density, occurrence of carrier carryover into the first color latent image, and poor fine line reproducibility of the second color occurred. . Also, as a carrier for the second developer in the second development step, about 10
In the case of a volume resistivity value of 5 Ωcm or less, poor second color fine line reproducibility occurred. Therefore, by using a developer carrier having a volume resistance of approximately 10 to 1013 Ωcm in an electric field of 1 KV/cm as a carrier for the developer in the second development step, the image density of the second color can be improved, and the Carrier carryover into the image can be prevented, and fine line reproducibility of the second color can be improved.

In the above embodiment, a repulsive magnetic pole is used as the developing roll of the second developing means 20 and the developing method is a magnetic repulsion image method.
A similar test was conducted when the development method of 0 was changed to a magnetic repulsion method and a two-component magnetic brush development method was used, and a slight decrease in accuracy was observed compared to the example. Similar results were obtained. Further, in the above embodiment, the case where the carrier core of the second developer is made of a polymer is described, but when a test similar to the above was conducted using a ferrite carrier core, substantially the same results were obtained.

In the above embodiment, the first and second latent image forming means are formed by laser diodes, but these latent image forming means do not necessarily have to be laser diodes. Of course, it is possible to use any light source, such as a liquid crystal light valve consisting of a liquid crystal microshutter, an LED array, or a light beam, depending on the purpose.

[Effects of the Invention] As explained above, since the present invention is configured as described above, the following effects can be obtained.

1) It is possible to improve the image density of the second color, and to prevent carrier carryover into the first color latent image.

2) According to claims 2 and 5, in addition to the above 1), it is possible to further improve the fine line reproducibility of the first color.

[Brief explanation of drawings]

FIG. 1 is a schematic side view of a two-color image forming apparatus according to the present invention, FIGS. 2(a) to (e) are explanatory views showing image forming steps according to an embodiment, and FIGS. ) is an explanatory diagram showing a conventional image forming process, and FIG. 4 is an explanatory diagram showing an electric field action state in the conventional image forming process. Code explanation (10)... Photosensitive drum (latent image carrier) (12)
...Charger (14)...Latent image forming means (16)...First developing means (18)...Second latent image forming means (20)...Second developing means

Claims (6)

[Claims] (1) A latent image carrier (10) carrying a first toner image
A second electrostatic latent image is formed of an image area potential (Vi2) and a background area potential (Vh2) at an intermediate potential between the surface potential (Vt1) of the first toner image and the image area potential (Vi2). forming the second electrostatic latent image at the image portion potential (V
i2) and the background potential (Vh2) (Vb2)
When developing with a two-component developer consisting of a second toner having a polarity different from that of the first toner image and a carrier while applying a developing bias of 1 KV/cm as the carrier.
A two-color image forming method characterized by using a volume resistivity of 10^7 to 10^1^3 Ωcm in an electric field of . (2) The two-color image forming method according to claim 1, wherein the carrier of the two-component developer is an insulating carrier. (3) The two-color image forming method according to claim 1 or 2, wherein the developing method using the two-component developer is a magnetic anti-image development method or a two-component magnetic brush developing method. (4) Latent image carrier (10) and the latent image carrier (10)
a first latent image forming means (14) for forming a first electrostatic latent image on
), a first developing means (16) for developing the first electrostatic latent image with a first toner charged to one polarity to form a first toner image, and the latent image carrier ( 10) The image area potential (Vi2) and the surface potential of the first toner image (V
a second latent image forming means (18) for forming a second electrostatic latent image consisting of a background potential (Vh2) at an intermediate potential between the image potential (Vi2) and the image potential (Vi2); It has a two-component developer consisting of a charged second toner and a carrier, and has the above image area potential (Vi2) and background area potential (V
h2) and a second developing means (20) to which a developing bias of an intermediate potential (Vb2) is applied, and the volume resistivity of the carrier of the two-component developer is increased to 10^ in an electric field of 1 KV/cm. A two-color image forming apparatus characterized in that the setting range is from 7 to 10^1^3 Ωcm. (5) The two-color image forming apparatus according to claim 4, wherein the carrier of the two-component developer is an insulating carrier. (6) The two-color image forming apparatus according to claim 4 or 5, wherein the developing method of the second developing means is a magnetic anti-image developing method or a two-component magnetic brush developing method.