JPH0466970A - Color printer - Google Patents

Abstract

PURPOSE:To obtain a printed image quality required for respective sheets by detecting the classifications of printing sheets and setting a developing bias voltage for reducing an image density when the sheet is an OHP one. CONSTITUTION:An OHP sensor 11 detects whether the sheet for forming a color image is an ordinary sheet or the OHP sheet. When it is the OHP sheet, a developing bias driver 13 is controlled via a developing bias control circuit 12, a developing bias voltage setting value is changed, and the toner density of a color image is reduced to obtain the image quality having high light transmissivity. On the other hand, when the sheet is the ordinary one, a normal developing bias voltage is set not to degrade the image quality. Thus, color printed image quality required for respective sheets is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a color printer in which a developing bias voltage is controlled depending on paper type.

(Prior Art) Regarding the print image quality of color printed matter, when printing on plain paper, it is desirable that the colors be glossy or non-glossy for ease of viewing. Furthermore, when printing on OHP paper, it is required to have high light transmittance so that the colors of the image will be well-developed when it is applied to a projector.

However, if the printed image is glossy or not, the light transmittance will be low due to scattering, and conversely, if the printed image is high in light transmittance, the image quality will be sparkling and glossy. In other words, it can be said that glossiness and light transmittance have a two-way relationship when it comes to image quality needs.

(Problem to be solved by the invention) The image quality of color printed matter produced by electrophotography, especially the gloss, is mostly determined by the physical properties of the toner and the image formation of the fixing conditions, and the frequency of use is overwhelmingly determined by the paper type. This is often the case with plain paper. For this reason, the image forming conditions for devices that record images on cut paper, such as color laser printers, have traditionally been such that the image quality meets the needs of plain paper, and the image quality of OHP paper has poor light transmittance, making it difficult to record images on a projector. The video quality was very poor.

In conventional printers that only print in black and white, the light transmittance of printed images on OHP has not been a problem, but the use of color printed matter has caused a new problem unique to color machines.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a color printer that can achieve print image quality that meets the requirements of plain paper and OHP paper.

(Means for Solving the Problems) In order to solve the above problems and achieve the objects, the present invention forms an electrostatic latent image on a photoreceptor using an image signal, and a visible image is formed using a developing device for three primary colors and black. An electrophotographic color printer that transfers an image to paper and then transfers it all at once to paper, comprising means for detecting the type of paper on which an image is printed, and a developing bias controller & for setting different developing bias voltages in at least two modes depending on the type of paper. If the paper is OHP paper, the image formation is performed by setting a developing bias voltage that lowers the image forming density.

(Function) The present invention depends on whether the paper on which the color image is formed is plain paper or not.
It detects whether the paper is HP paper, and if it is OHP paper, changes the setting value of the developing bias voltage to lower the toner density of the color image and obtain an image quality with high light transmittance. Furthermore, in the case of plain paper, conventional development bias voltage (image forming conditions) is used to avoid deterioration of image quality.

(Embodiment) FIG. 1 shows a configuration diagram of an embodiment of the present invention. In each existing unit, reference numeral 1 denotes a photoreceptor, which is a latent image carrier rotating in the six directions of arrows. A charging charger 2 uniformly charges the surface of the photoreceptor 1 by corona discharge or the like. Reference numeral 3 denotes a laser beam scanner which irradiates the photoreceptor 1 with a laser beam L modulated by an image signal S to form an electrostatic latent image on the photoreceptor. Here, the direction of rotation of the photoconductor (arrow A) is the sub-scanning direction, and the direction perpendicular to the paper surface (long axis direction of the photoconductor)
is the main scanning direction. 4 is a developing device in which toners of three primary colors (yellow Y4-1, magenta M 4-2, cyan C43) and black BK4-4 are prepared separately. Reference numeral 5 denotes a pair of conveyance rollers that conveys the paper on the paper conveyance path 6 toward the photoreceptor l side. A transfer charger 7 transfers the toner image on the photoreceptor 1 to a sheet of paper by electrostatic transfer or the like to form a visible image. 8
A heating fixing device fixes the transferred visible image on the paper using heat and pressure, and discharges the paper toward the notch DB. A cleaning mechanism 69 removes toner remaining on the photoreceptor. 1
Reference numeral 0 denotes a static elimination lamp, which performs a static elimination action on the photoreceptor after cleaning.

In addition to the above-mentioned existing unit, the present invention also includes an OHP sensor 1),
Development bias control circuit 12 and development bias driver 1
It has 3. The second OHP sensor 11 uses a transmissive photo sensor and is disposed on the paper conveyance path 6, and detects the type of paper, plain paper or OHP paper, based on the transparency of the paper passing through the detection surface. The developing bias control circuit judges the detection signal from the OHP sensor 11 and selects plain paper or OHP paper.
Set the development bias voltage for P paper. The developing bias driver 13 applies the developing bias voltage to the developing roller 4-I.
R to 4-4 Apply to R (rotating contact with photoreceptor 1).

To briefly explain the case of color printing in this configuration, the charging of the charging charger 2, the exposure of the laser beam scanner 3, and the toner of each color (yellow Y, magenta M, cyan, and black BK) of the developing device 4 are repeated multiple times. A toner image in which toner of each color is superimposed is formed on the photoreceptor l.

Then, the toner image on the paper is transferred all at once by a transfer charger 7, fixed onto the paper by a heat fixing device 8 to obtain a color print, and the paper is discharged in the direction of arrow B.

On the other hand, in order to prepare the photoreceptor after the transfer for the next image formation, residual toner on the photoreceptor E is removed by a cleaning mechanism 9, and static electricity is removed by a charge removal lamp 10.

Next, the setting of the developing bias voltage applied to the developing rollers 4-IR to 4-4R according to the paper type will be explained. First, the OHP sensor 11 detects the type of paper conveyed to the paper conveyance path 6 and outputs it to the developing bias control circuit 12 .

The developing bias control circuit 12 sets the developing bias voltage for plain paper or OHP paper based on the detection signal.

Next, the laser beam scanner 3 is operated by an image signal S sent from an external source such as a host computer (not shown), and forms an image on the photoreceptor l. In this case, the developing bias control circuit 12 sets the developing bias voltage to VB for plain paper as shown in FIG. 2, and sets the developing bias voltage to VB for OHP paper as shown in FIG.
B, and perform image formation for each color.

FIG. 2 is a characteristic diagram showing the relationship between the development bias voltage (VB) and the amount of development (C2/+c++t) in positive charging and negative/positive development. As can be seen from the figure, the amount of development is approximately proportional to the development bias voltage. Therefore, if the developing bias voltage of the present invention is set under the conditions of VB and )VB, the amount of development on OHP paper will be smaller than on plain paper, and the final image density will also be lower.

Figure 3 shows the results after transfer (1) on plain paper (A) and OHP paper (B).
2) is a simulation showing the amount of toner in (2) and the state of the toner layer after fixing (2). In the figure, Y is yellow toner, M
○ indicates magenta toner, ○ indicates cyan toner R indicates red color, and C indicates cyan (blue) color. Plain paper (A) as shown in the diagram
Since the toner layer of OHP paper (a) is thinner than that of OHP paper (a), when the OHP paper is applied to a projector, light passes through the image area more easily, resulting in a printed matter with improved light transmittance.

(Effects of the Invention) As explained above, according to the present invention, it is determined whether the paper is plain paper or OHP paper, and control is performed to change the setting of developing bias conditions for color image formation. Therefore, O
It is possible to provide a color printer that can produce printed matter with high light transmittance and high print quality for color images on HP paper.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a characteristic example diagram showing the relationship between the development bias voltage and the amount of development.
FIG. 3 is a diagram schematically showing the amount of toner after transfer and the state of the toner layer after fixing on plain paper and OHP paper. 1... Photoreceptor, 2... Charger 3゛°
°Laser beam scanner, 4...Developer,
4-IR ~ 4-4 shaku...Developing rollers for each color, 61
Paper conveyor, 7... Transfer charger, 8.
...heating fixing device, 9. . Cleaning mechanism, 1o... Static elimination lamp, II...
0HPf=sensor-12...Development bias control circuit,
13...Development bias driver

Claims (1)

[Scope of Claim] An electrophotographic color printer that forms an electrostatic latent image on a photoreceptor using an image signal, visualizes it using a developing device for three primary colors and black, and then transfers the image all at once to paper. It is equipped with a means for detecting the type of paper to be printed, and a developing bias control means for setting different developing bias voltages in at least two modes depending on the paper type, and when the paper is OHP.
A color printer is characterized in that image formation is performed by setting a developing bias voltage that lowers the image formation density in the case of paper.