JPS6338707B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a non-impact printer that applies electrostatic recording technology such as electrophotography, and particularly to a non-impact printer suitable for two-color printing.

[Background of the Invention] Non-impact printers have been developed that take advantage of the high-speed printing properties of electrostatic recording techniques such as electrophotography. This kind of non-impact printer is the first
A typical device has the configuration shown in the figure.

In FIG. 1, 1 is an electrophotographic photosensitive drum, 2
3 is a charger, 3 is an overlay film, 4 is an overlay light source, and 5 is an imaging lens. Also,
6 is a laser oscillation device, 7 is a laser beam modulation device, 8
9 is a mirror scanning device, and 9 is an imaging lens. 10
1 is a developing device, 11 is a copying medium, 12 is a transfer charger, 13 is a residual charge erasing lamp, and 14 is an afterimage toner removing device.

A charger 2 applies a uniform charge to the surface of the photosensitive drum 1 in a dark place. This photosensitive drum 1
is mainly used for the ruled lines of slips and patterns that are predetermined and printed repeatedly over many pages.
Overlay exposure involves exposing an overlay film 3 containing a so-called format using an overlay light source 4 and an imaging lens 5, and a laser light modulation device 7 that converts laser light from a laser oscillation device 6 into electrical signals (not shown). The laser beam is turned on and off, or the intensity of the laser beam is converted, and the laser beam thus modulated is guided to a mirror scanning device 8 to perform linear scanning. Two types of exposure are performed: laser beam exposure, which forms an image on the surface of the substrate, and performs desired exposure. Additionally, the output information of the computer is converted into a visible image, which will be described later, by the laser beam exposure means.

The photosensitive drum 1 has an electrostatic charge pattern formed on its surface by the above-described exposure, and this electrostatic charge pattern is converted into a toner powder image by the action of the developing device 10. Then, this toner image is transferred to the photosensitive drum 1 by a transfer charger 12.
The image is transferred onto a transfer medium 11 that is driven at the same circumferential speed as the image data.

Charges and toner images still remain on the photosensitive drum 1, but these are cleaned by the residual charge erasing lamp 13 and the residual toner removing device 14, and the surface of the photosensitive drum 1 is cleaned, and the next The recording cycle begins with charging.

In such a non-impact printer, if the ruled lines of a slip, for example, and the calculated values or data values are printed in different colors, the printed matter becomes extremely clear and easy to understand. In addition, it is a common experience that it is easier to understand when calculating numerical values by classifying them into two colors.

Such requirements can be realized by the following electrophotographic method. In other words, the charged photoreceptor is
The image is exposed to light by a light source containing information of , and developed by a first developing device to form a first visible image. Next, the drum on which the first visible image is formed is subsequently exposed to light by a light source containing second information, and developed by a second developing device having a color different from that of the first visible image. In the transfer process of the photosensitive drum on which the first visible image and the second visible image are formed, the first visible image and the second visible image are simultaneously transferred to a transfer medium, A two-color printed image will be obtained.

However, in this method, when performing the second development, a portion of the toner image formed on the drum by the first development is removed, and the first toner image is mixed into the second toner in the second development device. There was a drawback that toner was mixed in. This simply means that the first
This not only reduces the image density of the toner image, but also
A problem arises in that the developing characteristics of the second developing device deteriorate due to the contamination of the first toner.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a non-impact printer capable of obtaining clear images in at least two colors, while eliminating the drawbacks of the prior art described above.

[Summary of the invention]

To achieve this object, the present invention provides at least a device for forming a first charge latent image on a recording medium, a first developing device for developing the first charge latent image, and a first development device for developing the first charge latent image. a device for forming a second charge latent image on the recording medium on which the charge latent image has been developed;
In a non-impact printer that performs multicolor printing of two or more colors, the non-impact printer is equipped with a second developing device that develops the second charge latent image in a color different from that of the first charge latent image. Second development A magnetic toner development method is used to prevent the toner image developed by the first development device from falling off the recording medium during development by the second development device. shall be.

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 2 is a schematic configuration diagram for explaining the operating principle of an exposure/developing section of a two-color printing non-impact printer according to an embodiment of the present invention. In this figure, 15 is a first exposure light source, 16 is a first developing device, 17 is a first developing bias voltage source, 18 is a second exposure light source, and 19 is a second developing device that uses magnetic toner development. is used. 20 is a second developing bias voltage source. Note that parts that have the same operating principle as a normal electrophotographic non-impact printer are not illustrated to avoid duplication.

Further, FIGS. 3a to 3e are process diagrams of the non-impact printer shown in FIG. 2. In the figure, + indicates a positive polarity charge, and indicates toner.

First of all, the electrophotographic photosensitive drum 1 is connected to the charger 2.
As a result, the surface is uniformly charged as shown in FIG. 3a. At this time, the surface potential of drum 1 is approximately
It is 700V.

The drum 1, whose surface is charged, is exposed as shown in FIG. 3b by a first exposure light source 15 carrying first information to be printed in a first color. The residual potential of the exposed portion is about 0-300V.

Next, it is developed into a first color by the first developing device 16 as shown in FIG. 3c. The potential of the exposed portion of the drum 1 increases due to the adhesion of toner having a positive polarity charge. In this case, a bias voltage V _b1 of approximately 0 to 300 V is applied to the first developing device 16 from the first bias voltage source 17 .

These first charging, exposure and development processes are the same as those in conventional electrophotographic non-impact printers. Normally, in such non-impact printers, reversal development is used to prevent background smearing of recordings. That is, the area corresponding to the image area is exposed to light to dissipate the surface charge, and toner is adhered to the area where the charge has dissipated. For example, in the case of a selenium photoreceptor, the surface of the photoreceptor is charged to a positive polarity, and the portion corresponding to the image area is dissipated by exposure to light and becomes close to the ground potential.
It is a well-known technique that the developer is formed of a carrier that has a tendency to triboelectrically charge to a negative polarity and a toner that is charged to a positive polarity, and that a toner image is formed at the location where the charge is dissipated. bias voltage
V _b1 is effective for improving this developing effect.

The photoreceptor 1 is used for printing in the second color.
The second color is developed again after the first color development is completed.
By the second exposure light source 18 carrying information of
It is exposed as shown in Figure 3d (in this case, the residual potential of the exposed part is about 0 to
300V), and must be further developed into a second color by a second developing device 19, as shown in FIG. 3e. At this time, when the second image is developed with a two-component developer consisting of carrier and toner,
As mentioned above, a portion of the toner image previously deposited on the photosensitive drum produced by the first developing device is removed and mixed into the second developing device, resulting in a decrease in the density of the first toner image, This resulted in a significant decrease in the functionality of the second developer.

The reason why the above phenomenon occurs is schematically shown in FIG. 22 is frictionally charged with negative polarity as in the case of the first developer, so the first toner 21 is electrostatically attracted to the second carrier 22 during development, and the first toner 21
This is because some of them fall off the surface of the electrophotographic photosensitive drum and mix into the second developer. Note that in the figure, 23 indicates the second toner.

In the present invention, the magnetic toner 24 is used as the developer in the second developing device, and when transferring to the transfer medium 11, it is preferable to use a high-resistance magnetic toner. The optimum printed image is obtained when the bias voltage source 25 applies a bias voltage to the surface potential of the unexposed area of the photosensitive drum (approximately 700 V), and the image quality remains unchanged even if the bias voltage is lower or higher than this. is getting worse. In this way, magnetic toner is developed by applying a relatively high bias voltage.

When a magnetic brush is formed using magnetic toner in this way, the magnetic brush is softer than a two-component developer, and there is no need to make tight contact with the latent image surface. Furthermore, the above-mentioned electrostatic attractive force between the carrier and the toner does not work, and the electrostatic field acts in the direction of pressing the first toner against the latent image surface due to the relatively high bias voltage during reversal development. , the first toner is less likely to fall off. From the above, it is extremely advantageous to use such magnetic toner 24 as the developer in the second developing device 19.

In addition, when magnetic toner is used as the developer in the second developing device, it is better to perform two-color printing in which the first developing toner is a light color and the magnetic toner is a dark color. It is advantageous. This is because it is difficult to produce light colored toner with magnetic toner. This has the advantage that even if the first toner mixes into the second developer and is developed, it will not be noticeable.

6 to 8 show examples of light sources for two-color printing used in the present invention.

That is, FIG. 6 shows the overlay optical system in the first
The second exposure light source uses a laser beam scanning light, and is suitable for printing ruled lines on a slip and calculation results in two different colors, for example.

In addition, in FIG. 7, laser beam scanning light is used as both the first and second light sources,
The laser beams emitted from the two laser light sources are modulated by respective laser beam modulators 7A and 7B, guided to a mirror scanning device 8, and scanned simultaneously. Thereafter, the two laser beams are guided by the splitter 26 as a first exposure light source and a second exposure light source. Note that if a semiconductor laser is used as the laser light source, the laser light modulation device 7
Those skilled in the art can easily understand that it is sufficient to install two semiconductor lasers at positions A and 7B.

Furthermore, in FIG. 8, one laser beam is divided into two output beams at the laser beam modulator 7. In FIG. Such an optical modulation device 7
Diffraction development, which is an acousto-optic effect, is usually used. In an acousto-optic device, one element is
It is a well-known fact that when excitation is performed at two different excitation frequencies f ₁ and f ₂ by two excitation signal sources 27A and 27B, the output beam is separated into two beams. Of course, it goes without saying that the excitation frequencies f ₁ and f ₂ are modulated by the output signal. These two beams are guided to a scanning mechanism similar to that shown in FIG. 7, and are used as first and second exposure light sources.

In the above explanation, the case using an electrophotographic method has been described, but the present invention is not limited to this, and can be widely applied to other electrostatic recording methods where formation and development of a latent charge image are repeated twice. Moreover, it can be applied not only to a method of transferring a toner image but also to a method of recording and fixing directly onto a recording medium.

Furthermore, if a device for forming a third charge latent image and a third developing device for developing the third charge latent image in a color different from that of the first and second developing devices are added, three
Color printing can be performed, and multicolor printing of four or more colors can also be performed.

〔Effect of the invention〕

Since the second developing device does not use a carrier, the electrostatic attraction between the carrier and the first color toner in the first developing device does not work, causing the first color toner to fall off and enter the second color toner. Even if a small amount of toner is mixed in, the brightness of the second color toner is lower than that of the first color, so even if it is developed in the second developing device, it will not be noticeable, and at least two colors will be clear. You can get the image.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a general electrophotographic non-impact printer, and FIG. 2 is a schematic diagram of an exposure/developing section of an electrophotographic two-color non-impact printer according to an embodiment of the present invention. 3a to 3e are process diagrams of the non-impact printer shown in FIG. 6 to 8, which are explanatory diagrams of the developing operation when magnetic toner is used, are schematic configuration diagrams showing examples of light sources for two-color printing used in the present invention. 1...
Electrophotographic photosensitive drum, 2... Charger, 15... First exposure light source, 16... First developing device, 17...
...First development bias voltage source, 18...Second exposure light source, 19...Second magnetic toner developing device, 20...
...Second development bias voltage source.

Claims (1)

[Claims] 1. At least a charger that uniformly charges the surface of a recording medium, a first exposure device that forms a first charge latent image on the recording medium by first image exposure, and a first developing device that reversely develops a charge latent image using a two-component developer consisting of two components, a carrier and a first color toner; and the recording medium on which the first charge latent image is developed. a second exposure device for forming a second charge latent image thereon by second imagewise exposure; 1 consisting of toner
A non-impact printer characterized by having a second developing device that performs reversal development using component developers, and a transfer device that simultaneously transfers toner images of at least two colors formed on the same recording medium to a transfer medium. .