JPH0373864B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an image forming apparatus, and more particularly, to an image forming apparatus that sequentially forms different color developments on an image carrier. Conventionally, latent images corresponding to different color component images are formed on an image carrier such as an electrophotographic photoreceptor as latent images with mutually different charge polarities, or even if the charge polarities are the same, they are formed on different surfaces. A color image is formed by forming potential latent images and sequentially developing these latent images with corresponding color developers. A method has been proposed in which a latent image is formed and, prior to development of each color, the potential of the corresponding latent image is increased to perform corresponding development to form a color image. All of these methods have in common that different colors are developed sequentially on the same image carrier. In such an image forming apparatus, magnetic brush development is generally used to develop the latent image. However, in such an apparatus, there is a risk that the previously formed images may be disturbed during subsequent development, and color mixing is also difficult to avoid. The present invention has been made in view of the above-mentioned points, and relates to an image forming apparatus that enables good image formation without image quality disturbance and color mixture. Furthermore, the present invention relates to an apparatus that prevents the occurrence of mixed color development even after long-term use. The present invention provides a first latent image forming means for forming a first electrostatic latent image on an image bearing member, a first developing means for developing the first electrostatic latent image, and a first electrostatic latent image developed by the first developing means. a second latent image forming means for forming a second electrostatic latent image on the image carrier carrying the developed image;
In an image forming apparatus equipped with a second developing means that performs development with a developer of a different color from that of the developing means, the first developing means carries and conveys a developer layer and supplies the developer to the image carrier. The second developing means has a member,
A developer carrying member that carries and conveys a developer layer and supplies it to an image carrier, the developer carrying member having a developer carrying member that faces the image carrier with a gap wider than the thickness of the developer layer. However, an AC bias voltage of the same value is applied to the developer carrying member of the first developing means and the developer carrying member of the second developing means, and the voltage between the developer carrying member of the second developing means and the image carrier is applied. The image forming apparatus is characterized in that the gap is wider than the gap between the developer carrying member and the image carrier of the first developing means. Hereinafter, details of the present invention will be explained using specific examples with reference to the drawings. FIG. 1 is a schematic diagram of a specific example image forming apparatus based on the present invention. 1 is a photosensitive drum, which rotates in the direction of the arrow. 2 is a corona discharger that uniformly charges the surface of the photoreceptor drum to a predetermined polarity. L ₁ is the first information illumination light, which is, for example, a full-color original green component light image. This light image is
It may be a light beam modulated by a signal such as a laser, light emitted from an LED element, or a normal optical image. Reference numeral 3 denotes a first developing device, which applies, for example, a magenta color developer to the photosensitive drum 1, and the developing method for developing a latent image corresponding to the optical image may be a well-known magnetic brush developing method. However, the illustrated example is based on a jumping development method which will be described in detail later. 4 is a second corona discharger that applies corona discharge of the same polarity as the corona discharger 2 to the surface of the photoreceptor drum 1. L ₂ is the second information illumination light, for example, the original red component light image. Reference numeral 5 denotes a second developing device, which supplies, for example, a cyan developer to develop a latent image corresponding to the two-light image. The developing method is a so-called jumping developing method in which the developer layer is faced to the surface of the photoreceptor drum at a predetermined distance, and the developer is caused to fly onto the drum surface in accordance with the latent image on the drum surface. The specific structure of the developing means will be described in detail later. Reference numeral 6 denotes a third corona discharger which applies corona discharge of the same polarity as the aforementioned corona discharger to the surface of the photoreceptor drum. _L3 is the third information illumination light, for example, the original blue component light image. Reference numeral 7 denotes a third developing device, which supplies a yellow developer, for example, and develops a latent image corresponding to the third optical image. The developing method is a jumping developing method like the second developing means. However, as will be detailed later, the distance between the developer layer and the surface of the photoreceptor drum is
It is wider than that of the developing means. The full-color images thus formed on the photosensitive drum are transferred onto the transfer material P by the action of the transfer corona discharger 8. After the transfer is completed, the transfer material P is separated by a separation roller 9 and fixed by a fixing means (not shown). On the other hand, after the transfer is completed, the surface of the photosensitive drum 1 is cleaned of residual developer by the cleaning means 10 and is ready for reuse. With the above configuration device, it is possible to obtain a good multicolor image without color mixture. Hereinafter, the color mixing prevention mechanism in the above-described device will be sequentially explained. FIG. 2 is a side view illustrating a jumping developing device used as a developing device of a specific example of the present invention. The non-magnetic sleeve 31 is rotatably supported and rotated in the direction of the arrow by a drive source (not shown). A six-pole magnetized magnet roller 32 is fixed inside the non-magnetic sleeve 31 . _N1 of the magnetized poles of the magnet roller contributes to regulating the formation of a developer layer on the sleeve surface. Further, S ₁ contributes to the development action on the surface of the photoreceptor drum. The other magnetic poles contribute to developer transport and leakage prevention. 33 is a developer layer thickness regulating blade made of a magnetic material. It cooperates with the magnetic pole _N1 to form a magnetic field that crosses the direction of movement of the sleeve 31, thereby regulating the thickness of the developer layer adhering to the surface of the sleeve 31. The thickness of the developer layer is usually 30μ or more and about 100μ. Between the non-magnetic sleeve surface and the photoreceptor drum,
The thickness should be maintained at 250 to 300μ so that the developer layer on the sleeve surface does not come into direct contact with it. Then, the developer particles selectively fly to the latent image portion due to an electric field formed between the latent image portion on the photoreceptor drum and the non-magnetic sleeve. The magnetic pole S ₁ placed at this development position prevents unnecessary developer movement. On the other hand, the magnetic field strength gradually decreases from the sleeve surface toward the photoreceptor drum to assist in directing the flying developer particles toward the photoreceptor drum. 34 is a bias power supply that applies an alternating voltage of a predetermined frequency to the sleeve surface. Further, the structure is such that a DC bias voltage is applied as necessary. By applying this alternating voltage, selective flying of the developer can be easily and reliably carried out. 35 is a stirring blade, which prevents the developer in the housing from solidifying into particles. With the above configuration, the latent image on the photoreceptor is developed. By the way, magnetic developers require the inclusion of a magnetic material such as magnetite, which is black or reddish brown, so it is actually difficult to obtain colored developers other than black, red, or magenta. Therefore, for good color reproduction, it is necessary to use a non-magnetic developer for colors such as yellow and cyan. The above-mentioned image forming apparatus of the present invention uses a developing device that enables jumping development using a non-magnetic developer for developing these colors. FIG. 3 is a side view of a specific example developing device that performs jumping development using a non-magnetic developer. A developing roller 51 is a conductive member made of aluminum, stainless steel, or the like. 52 is a developing layer thickness regulating blade, and the layer thickness is approximately 30μ or more as mentioned above.
It should be around 100μ. 53 is a bias power supply. A developer feeding screw 54 feeds the developer to the developing roller and promotes triboelectric charging of the developer during the feeding operation. Each feed screw 51
₁ , 54 ₂ , 54 ₃ may be rotated at a constant speed, but high speed -
It is also possible to increase the frictional effect by varying the rotational speed, such as between low speed and high speed. The feed screw material is selected in consideration of the triboelectric charging series relationship with respect to the developer. In the illustrated example, it is made of stainless steel. Jumping development of non-magnetic developer is possible with the above-described developing device. The third developing device of the device shown in the first diagram also utilizes the above-mentioned configuration device.Of course, even if each of the first to third developing devices uses the magnetic developer system shown in the second diagram, the non-magnetic developer system shown in the third diagram applies. It may be unified to Moreover, each may be set independently as desired. A non-magnetic method is better when color sensitivity is required. On the other hand, in terms of simplicity, a magnetic developer method is preferable. By using a non-contact type developing device such as the above-mentioned jumping type in which the developer is selectively splashed onto the latent image portion, disturbance and color mixing of the multicolor image formed on the photoreceptor can be effectively prevented. Although the illustrated apparatus uses a photoreceptor as the latent image carrier, a simple insulating latent image carrier may be used for a latent image transfer method or an electrostatic recording method using an electrode pin array. By the way, the inventors have discovered that when non-contact type developing devices are arranged in sequence under the same conditions as in the above configuration and used for a long period of time, color mixing may occur in the developing device placed at the rear. Ta. When this phenomenon occurs, the developer in the current device must be replaced, resulting in the inconvenience of requiring frequent maintenance and inspection. In the apparatus of the present invention, as a countermeasure against the above, when the non-contact type developing devices are sequentially arranged, the developing devices (developing sleeve rollers 31, 51, 71, respectively) as shown in FIG.
(only shown) and the image carrier surface = d(1, 2, 3)
and the others are set wider than in the case of the first developing device. That is, when the distance between the first developing device and the image carrier 〓 d ₁ is taken as a reference, the distance between the subsequent second developing device and the image carrier 〓
Let d ₂ be in the relationship d ₁ <d ₂ , and let _{d 3} be in the relationship d ₁ <d ₃ between the third image carrier and the image carrier. Further, if necessary, the second developing device and the third developing device may have d ₂ =d ₃ , but preferably d ₂ <d ₃ . The above relationship will be further explained using examples. Example 1 A two-color image was formed by operating the first developing device and the second developing device under the conditions shown in the table below using the first illustrated configuration device. Moreover, each latent potential was set to +450V.

[Table] When two-color images were formed under the above conditions, good images were obtained on up to about 3,000 sheets of A4 size transfer material. When the number of sheets exceeded 3,000, black developer was found to be mixed in the second developing device. Image quality was also affected. Next, between the drum and sleeve of the second developing device
When similar two-color image formation was performed with d ₂ set to 200μ and other conditions as shown in Table 1, good image quality could be formed even after more than 3000 sheets were printed. Although the same AC bias is applied to each sleeve of the first and second developing devices as described above, the difference between the drum and sleeve of the second developing device is
is wider than the distance between the drum and the sleeve of the first developing device, so this stripping electric field during the phase of stripping the developer from the drum of the AC bias voltage is larger in the second developing device than in the first developing device. This also makes it possible to prevent damage to the first developed image and color mixing in the second developing device. As described above in detail in the specific examples, the apparatus of the present invention can successfully develop latent images sequentially formed on the same carrier without disturbing them, and can also perform successive developments without disturbing the previous ones. It is excellent for forming multicolor images.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a specific example image forming apparatus based on the present invention, FIG. 2 is a side sectional view of a specific example developing device used in the device of the present invention, and FIG. FIG. 4, a side sectional view of a specific example developing device, is a schematic diagram illustrating the arrangement of each developing device in the apparatus of the present invention. In the figure, 1: photoreceptor (image carrier), 2, 4, 6:
Corona discharger, 3, 5, 7: developing device, 8: transfer corona discharger.

Claims (1)

[Claims] 1. A first latent image forming means for forming a first electrostatic latent image on an image carrier, a first developing means for developing the first electrostatic latent image, and a developed image developed by the first developing means. a second latent image forming means for forming a second electrostatic latent image on the carried image carrier; and a second developing means for developing the second electrostatic latent image with a developer of a different color from that of the first developing means. In the image forming apparatus, the first developing means has a developer carrying member that carries and conveys the developer layer and supplies it to the image carrier, and the second developing means has a developer carrying member that carries and conveys the developer layer. The first developing means has a developer carrying member that supplies the developer to the image carrier through a gap wider than the thickness of the developer layer. An AC bias voltage of the same value is applied to the developer carrying member of the second developing means and the developer carrying member of the second developing means. An image forming apparatus characterized in that the space between a developer carrying member and an image carrying member is wider than the distance between the developer carrying member and the image carrying member.