JPH0812502B2 - Image forming method - Google Patents

Description

The present invention relates to an image forming method for obtaining a two-color image.

[Prior Art] At present, an electrophotographic electrostatic recording method is often applied to a printer as a terminal device of information equipment such as a computer, a facsimile, and a CAD.

In these printers, an information signal is written as an electrostatic latent image on a photoconductor (electrostatic latent image holder) by a laser beam, an LED, an LCD, etc., and after the electrostatic latent image is visualized by a developing device, This visible image is transferred to a transfer paper, and the transferred image is fixed to the transfer paper to obtain a recorded image. The recorded image is generally a single color such as black. there were.

However, for example, if the calculated value or data value is formed in a color different from the format color, or if a part of the drawing output by CAD is formed in another color and the image is distinguished by two colors,
The image becomes clear and the contents are easy to understand. As described above, distinguishing an image by two colors is an effective means for better understanding of information.

Therefore, conventionally, an image forming method for forming an image of two colors by an electrostatic recording method has been proposed.

In this image forming method, first, a laser beam or the like forms a first electrostatic latent image on a photosensitive member based on a first information signal, and magnetic particles and negatively charged non-magnetic chromatic color toner are mixed. A magnetic brush developing device or the like containing the developed developer reversely develops the first electrostatic latent image, and a first toner image is formed by this development. Next, another laser beam or the like forms a second electrostatic latent image on the photoconductor based on the second information signal,
A japping developing device containing a positively charged black magnetic toner normally develops the second electrostatic latent image, and a second toner image is formed by this development.

Further, in another image forming method, an electrostatic latent image having a three-valued potential level, that is, a potential lower than the reference potential is set on the basis of a certain potential on the photosensitive body uniformly charged in the negative polarity. First
An electrostatic latent image, a second electrostatic latent image having a potential higher than the reference potential are formed, and the first electrostatic latent image is reversely developed with a negatively charged non-magnetic chromatic toner, respectively sequentially or simultaneously. The second electrostatic latent image is normally developed with positively charged black magnetic toner to form two color toner images. Then, the post charger charges the first and second toner images to make the charging polarities uniform, and then the transfer charger transfers the first and second toner images to the transfer paper. As a result, a two-color image is formed on the transfer paper. In this image forming method, since the toners having different polarities are used, the chromatic color toner and the black toner are formed on the image during the second development. It is known that it is effective in preventing the mixed color phenomenon and the mixed phenomenon in which the chromatic color toner is mixed in the second developing device.

[Problems to be Solved by the Invention] However, in the above-described image forming method, the toner images are uniformized in the charging polarity by the post-charger, but at this time, the toner whose charging polarity changes is the magnetic toner. In this case, the following inconvenience occurs.

That is, when the magnetic toner receives an electric charge by the post-charger, the magnetic substance such as magnetite dispersed in the magnetic toner particle body discharges the charged electric charge by the high electric field, so that as shown in FIG. The charge density differs between the edge portions 21a and 21a of the toner image 21 which are relatively susceptible to electric charge and the central portion 21b of the toner image 21 in which the toner charge is not sufficiently inverted by discharge. For this reason, the transfer electric field E by the transfer charger concentrates on the edge portions 21a, 21a of the toner image 21 (in particular, this tendency is strong when the toner image 21 is line-shaped), and the line center portion 21b is defective in transfer. Therefore, there is a problem that the line-shaped image becomes a transfer image with a void.

[Object] An object of the present invention is to provide an image forming method capable of preventing the occurrence of defective transfer at the central portion of a toner image.

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention is directed to a chromatic color toner image of a chromatic color toner on an electrostatic latent image carrier and a black toner image of a black toner charged to the opposite polarity to the chromatic color toner. In the image forming method, the chromatic toner image and the black toner image are made to have the same charging polarity by a charging device, and these toner images are collectively transferred to a transfer paper, wherein a non-magnetic toner is used as the chromatic toner. A magnetic toner is used as the black toner, and the charging polarity of the non-magnetic toner is converted to the opposite polarity by the charger to match the charging polarity of the magnetic toner.

Therefore, according to the present invention, the charge density is substantially constant between the edge portion and the central portion of the toner image, so that the transfer failure does not occur at the central portion of the toner image.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic configuration diagram of an image forming apparatus for carrying out the method of the present invention. In the figure, 1 is a photoconductor (electrostatic latent image carrier), 2 is the photoconductor 1 of about -800 volts. A primary charger 3 that uniformly charges the negative polarity is a laser beam that exposes the photoconductor 1 to form a first electrostatic latent image corresponding to the first information on the photoconductor 1. The potential of the portion exposed by the first laser beam is attenuated to about -100 volts.

Further, 4 is a magnetic brush developing device (first developing device), which comprises magnetic particles such as iron powder and ferrite, and chromatic non-magnetic toner such as red composed of a negatively charged resin component. The first electrostatic latent image is reversely developed with the mixed developer. By this development, a first toner image of red color or the like is formed.

Reference numeral 5 denotes a laser beam which exposes the photoconductor 1 to the background to form a second electrostatic latent image corresponding to the second information on the photoconductor 1. Reference numeral 6 denotes a jumping developing device (second developing device), which has a developer carrying member (developing sleeve) 6a installed at a position slightly separated from the photoconductor 1 and has a developer carrying member 6a. The second electrostatic latent image is developed with a black positively-charged one-component magnetic toner applied on the top of the thin film with a distance less than the distance. By this development, a black second toner image is formed.

By the way, when the jumping developing device is used as the second developing device, the electrostatic latent image is generated without the developing sleeve 6a coming into direct contact with the photoconductor 1, so that the first toner image is not scraped, and therefore, the mixed color is obtained. Phenomenon and the phenomenon of mixing of the first toner into the second developing device 6 can be prevented, and the peeling phenomenon of the first toner image due to flying of the magnetic particles can be prevented because magnetic particles are not used unlike the two-component developing device. This is because there are many advantages such as being possible.

Further, in the figure, 7 is a post charger for charging the first and second toner images to the same polarity (positive polarity) as the charging of the one-component magnetic toner, which is a negatively charged first toner. By reversing the polarity of the toner image, the charging polarities of the first and second toner images are made positive.

In FIG. 1, 8 is a transfer charger (secondary charger) that transfers the first and second toner images onto the transfer paper 9, and 10 is the transfer image transferred onto the transfer paper 9. A fixing device 11 for fixing is a cleaning device for removing toner remaining on the photoconductor 1.

Next, an image forming method by the image forming apparatus will be described.

First, the photosensitive member 1 is negatively and uniformly charged by the primary charger 2, and then the photosensitive member 1 is irradiated with the laser beam 3.
To form a first electrostatic latent image on the basis of the first information. Then, the magnetic brush developing device 4 develops the first electrostatic latent image with a developer in which magnetic particles such as iron powder and ferrite are mixed with non-magnetic toner such as red which is negatively charged and has a red color. To form the first toner image.

Then, the laser beam 5 is used to form a second electrostatic latent image on the photoconductor 1 based on the second information. Then, the jumping developing device 6 develops the second electrostatic latent image to form a second toner image. After this, the post charger 7 is
A positive charge is applied to the toner image, whereby the polarity of the negatively charged first toner image is inverted and the charge polarities of the first and second toner images are made positive.

By the way, chromatic non-magnetic toner such as red has a high resistance because it is composed of a resin component. Therefore, the positive charge of the first toner image 15 is not discharged even when receiving a high electric field, and as shown in FIG. 2, even if the first toner image 15 is linear, its charge density is almost constant. In addition, the first toner image 15 holds a sufficient amount of charge necessary for transfer.
Further, since the black toner having the magnetic material inside the particles is charged to the same polarity, the second toner image also holds a sufficient amount of charge necessary for transfer.

Then, the first and second toner images are transferred onto the transfer paper 9 by the transfer charger 7, but at this time, the transfer electric field E by the transfer charger 7 becomes uniform as shown in FIG. The transferred image does not have a hollow image at the center of the line, and a good transferred image can be obtained. Then, this transfer image is fixed on the transfer paper 9 by the fixing device 10 as in the conventional case.

As described above, according to the present invention, the non-magnetic toner is used as the chromatic toner, the magnetic toner is used as the black toner, and the charging polarity of the non-magnetic toner is converted to the opposite polarity by the charger. Since the charge polarity is made to coincide with the charging polarity of the magnetic toner, the charge density becomes substantially constant at the edge portion and the central portion of the toner image, and it is possible to prevent the occurrence of transfer failure at the central portion of the toner image.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus for carrying out the method of the present invention, FIG. 2 is an explanatory diagram showing a relationship between lines and charge density in the present invention, and FIG. 3 is a diagram of a conventional image forming method. It is explanatory drawing which showed the relationship between a line and charge density. 1 ... Photoconductor (electrostatic latent image holder), 4 ... Magnetic brush developing device, 6 ... Jumping developing device, 7 ... Post charger (charger), 9 ... Transfer paper.

Claims (1)

[Claims] 1. A chromatic color toner image formed by a chromatic color toner and a black toner image formed by a black toner charged to the opposite polarity to the chromatic color toner are formed on an electrostatic latent image holding member, and the chromatic color toner image and a black color are formed by a charger. An image forming method in which toner particles have the same charging polarity and are collectively transferred onto a transfer sheet, wherein a non-magnetic toner is used as the chromatic toner, a magnetic toner is used as the black toner, and the charger is used. The image forming method is characterized in that the charging polarity of the non-magnetic toner is converted into a reverse polarity to match the charging polarity of the magnetic toner.