JPS6356543B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming a two-color toner image, and in particular, develops two charge latent images formed on the same photoreceptor with toners of different colors to form a two-color toner image. The present invention relates to a two-color toner image forming method for transferring this toner image onto recording paper.

2. Description of the Related Art It is desired that printers for use in computer terminals and the like be capable of recording multicolor toner images of two or more colors. Practical printers of this type use an electrophotographic method, and a laser beam printer has been proposed. A two-color laser beam printer uniformly charges a rotating photoconductive photosensitive drum and negatively exposes the photosensitive drum with a first laser beam modulated with first image information to form a first electrostatic latent image. This first electrostatic latent image is reversely developed by a first developing device to cause a first toner to adhere to the charge emitting area, thereby forming a first toner image. Thereafter, the photosensitive drum is negatively exposed again with a second laser beam modulated with second image information to form a second electrostatic latent image, and this second electrostatic latent image is reversed by a second developing device. Development is performed to deposit a second toner in the charge emitting areas to form a second toner image. The two-color toner image thus formed on the surface of the photosensitive drum is transferred to recording paper and then fixed.

In such a two-color toner image forming method for a laser beam printer, in the process of developing the second charged latent image, the first toner image already attached to the photosensitive drum is removed.
of toner mixed into the second developing device, and as the amount of mixed toner increases, the second toner image becomes cloudy.

In the regular two-color development method, when the toner from the first developing device gets mixed into the second developing device, the mixed first toner is triboelectrically charged with the carrier of the second developer. A method has been proposed in which the latent image charge is reversely charged to have the same polarity as the latent image charge No. 2 to prevent adhesion to the photosensitive drum, thereby preventing color mixing. However, in this two-color regular development method, since the second toner is attached around the carrier of the second developer, there is less chance of friction with the first toner, and therefore the charging polarity is reversed. There is a risk that the second charge latent image will be attached by then.
Furthermore, since the first toner with reversed charging polarity remains in the second developing device, in a device that controls the toner mixing ratio in the developer or the amount of developer at a constant level, the first toner remains in the second developing device. There was a problem in that the amount of the second toner decreased by the amount of toner mixed in, and the developing ability of the second developing device decreased.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a two-color toner image forming method that does not cause color mixing and can stably obtain high-quality toner images of at least two colors.

In order to achieve this object, the present invention uses a material whose charging polarity is reversed by frictional charging with the toner of the second color as the first color toner, and the second color toner.
By frictionally charging the toner of the first color that has entered the developing device of the color with the toner of the second color, the toner of the first color is charged to have a different polarity from the latent image charge of the second color.
In reversal development for the second color, the toner of the second color is attached to the area where the electric charge has disappeared (hereinafter referred to as the electric charge disappearing area) on the surface of the photosensitive drum to form a toner image of the second color. The toner of the first color mixed into the developing device is made to adhere to the area on the surface of the photosensitive drum where the charge remains (hereinafter referred to as the charge remaining area), and the first toner is accumulated in the developing device of the second color. In addition to preventing
Thereafter, by electrostatically transferring the first and second toner images to the recording paper using a bias electric field of a different polarity, the first color toner (bias electric field It is characterized in that it prevents color mixing by not transferring the color (which has the same polarity as the color) to the recording paper.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is an overall side view of a two-color electrophotographic apparatus for carrying out the present invention, and FIG. 2 is an enlarged view of its developing section. The surface of the photoconductive photosensitive drum 1, which is rotated clockwise, is uniformly charged by a charger 2, for example, to a positive polarity. The uniformly charged surface of the photosensitive drum is negatively exposed to a light beam 3 containing first image information to form a first electrostatic latent image.
The electrostatic latent image is reversely developed by a first developing device 5 having a first toner 4 (exaggeratedly shown as a white circle) charged to the same positive polarity as the latent image charge. As a result, the first toner 4 adheres to the charge disappearing area of the photosensitive drum 1, and a first toner image 4A is obtained.

Photosensitive drum 1 on which first toner image 4A is formed
is then negatively exposed again with a light beam 6 containing second image information to form a second electrostatic latent image, which has a positive polarity of the same polarity as the latent image charge. Reversal development is performed by a second developing device 8 having a second toner 7 (exaggeratedly shown as a black circle) charged to . As a result, the second toner 7 adheres to the charge disappearing area due to the second exposure, and a second toner image 7 is formed.
Therefore, if the first toner 4 and the second toner 7 are selected to have different colors, a two-color toner image can be formed on the surface of the photosensitive drum 1. The recording paper 9 is brought into contact with the surface of the photosensitive drum 1 on which the two-color toner images 4A and 7A are formed in this manner, and a bias electric field having a polarity different from that of the toner image is applied from the back side of the recording paper 9 by the charger 10. By applying the voltage, a two-color toner image is electrostatically transferred onto the surface of the recording paper 9. After the toner images 4A and 7A have been transferred, the surface of the photosensitive drum 1 is cleaned by a cleaner 11 and uniformly charged by a charger 2 again.

In this electrophotographic apparatus, the first developing device 5
When the toner 4 is used together with a magnetic carrier to form a two-component developer magnetic brush on the surface of the developing roll 5A, the toner 4 is positively charged by frictional charging with the carrier. Further, the toner 7 of the second developing device 8 is also used together with the magnetic carrier, and the toner 7 is positively charged by frictional charging with the carrier to form a two-component developer magnetic brush on the surface of the developing roll 8A. . When the second electrostatic latent image is developed by the second developing device 8, the first toner image 4A of the first toner 4 is formed on the surface of the photosensitive drum 1. A part of the toner 4 is peeled off from the surface of the photosensitive drum 1 and transferred to the second
mixed into the developing device 8. When the amount of the first toner 4B mixed into the second developing device 8 increases, if the first toner 4 continues to have a positive charge, it forms a second electrostatic latent image together with the second toner 7. This causes the second toner image to become cloudy.

However, in this embodiment, the material is selected so that the triboelectric charging order of the first toner 4 is at a position intermediate between that of the magnetic carrier used in the second developing device 8 and the second toner 7. Therefore, the second developing device 8
The charge polarity of the first toner 4B mixed in the toner 4B quickly reverses to negative polarity due to frictional charging with the second toner 7, and becomes a toner 4C of a different polarity. The residual latent image charge re-adheres to the remaining non-image area) and is removed from the second developing device 8, so that it is not accumulated in the second developing device 8. As a result, a first toner image 4A having a positive polarity charge is formed on the surface of the photosensitive drum 1.
The second toner image 7A having a positive charge and the excess first toner 4C having a negative charge adhere. However, since the electrostatic transfer of the toner image is performed by applying a negative bias charge to the recording paper 9, the positively charged first and second toner images 4A and 7A are attracted to this bias charge. However, the excess negatively charged first toner 4C is repelled and is not transferred, so that the recording paper 9 is not stained.

As the toner used in the present invention, for example,
When toner 4 is black, a resin made of styrene-butyl methacrylate copolymer, carbon black, and nigrosine dye are each added in weight ratios.
Kneaded, solidified, and crushed in a ratio of 85:10:5,
When the second toner 7 is red, a resin made of styrene-butyl methacrylate copolymer and a watching red dye are mixed in a ratio of 96:4 to 96:4, respectively.
The product obtained by kneading, solidifying, and pulverizing at a ratio of . Further, the magnetic carrier used with the toners 4 and 7 in both the developing devices 5 and 8 is preferably DSP-1580 manufactured by Nippon Tetsuko Co., Ltd., and the first and second toners 4 and 7 are blow-off charged to this carrier. The amounts were 25 μc/g and 37 μc/g, respectively.

In FIG. 3, the first developing device 5 in the electrophotographic apparatus shown in FIGS. 1 and 2 is changed to a developing device using one-component magnetic toner. In the figure, the first developing device 5 includes a cylindrical conductive sleeve 5B, a magnet roll 5C, a toner regulating plate 5D,
A toner container 5E is provided. The one-component magnetic toner 12 contained in the toner container 5E is attracted to the magnet roll 5C to form a magnetic brush around the sleeve 5B, and when the magnet roll 5C is moved clockwise,
The thickness of the magnetic brush is regulated by the toner regulating plate 5D, and the magnetic brush moves counterclockwise on the sleeve surface to lightly rub the surface of the photosensitive drum 1. By applying a bias voltage having the same polarity as the latent image charge on the surface of the photosensitive drum to the sleeve 5B from the bias power supply 13, reversal development characteristics can be obtained. The developing conditions vary depending on the properties of the one-component magnetic toner 12 used. In the case of a high-resistance non-charged magnetic toner with a weight ratio of magnetic powder and resin of 45:55, the developing conditions are as follows:
The thickness of the magnetic brush is regulated so that the toner 12 lightly rubs the surface of the photosensitive drum 1, and the sleeve 5B is coated with charge remaining on the unexposed area of the photosensitive drum 1. It is preferable to apply a bias voltage approximately equal to the potential. 1-component magnetic toner 1
2, when using a high-resistance charged magnetic toner that contains a small amount of dye as a charge control agent in addition to magnetic powder and resin and is positively charged, the distance between the photosensitive drum 1 and the sleeve 5B is set to 0.2. ~0.3mm, and the thickness is regulated so that the magnetic brush formed on the sleeve surface does not come into contact with the photosensitive drum surface.
Good reversal development characteristics can be obtained by applying a bias potential of about 0.5 to 1 times the potential of the residual charges to the sleeve 5B. The surface of the photosensitive drum on which the first toner image 12A has been formed by the first developing device 5 is negatively exposed to the second light beam 6, as in the previous embodiment, and is exposed again by the second developing device 8. A second toner image 7A is formed by reversal development. Also in this case, a part of the first toner 12 gets mixed into the second developing device, but as in the above embodiment,
The first toner 12 is triboelectrically charged in a magnetic carrier used in the second developing device 8 and the second toner 7 .
Since the mixed toner 12B is selected from a material that is located in the middle of
C, which adheres to the charge remaining area on the photosensitive drum surface and is removed from the second developing device.

In this embodiment, by using a one-component magnetic toner as the first toner 12, the first developing device 5 can be made smaller and simpler, and the one-component magnetic toner has a portion of magnetic powder on its surface. is exposed and has a strong frictional charging property with the second toner 7, which has the advantage that mixed toner can be easily charged to the opposite polarity and removed.

FIG. 4 shows that the first toner 4 in the electrophotographic apparatus shown in FIGS. 1 and 2 is made into a magnetic toner containing 10 to 50% by weight of magnetic powder and mixed with a magnetic carrier. The developing device 8 of No. 2 is provided with mixed toner removing means. In FIG. 4, the first developing device 5 is omitted for simplicity. A conductive rotating electrode 8B is provided in the second developing device 8, and a voltage having the same polarity as the charge on the surface of the photosensitive drum is applied from the power source 14 to the rotating electrode 8B, and the toner adsorbed on the rotating electrode 8B is It is removed by a scraping plate 8C and falls into a collection section 8D.

In this way, the first toner 4C that has entered the first developing device 8 and has been charged with a different polarity is reattached to the surface of the photosensitive drum 1 and removed, and is also attached to the rotating electrode 8B. It is collected into the collection section 8D. In this embodiment, since the first toner 4 contains magnetic powder, it has strong frictional electrification with the second toner 7 and is easily charged to the opposite polarity.
Since the toner 4 is mixed with a carrier and charged to the same polarity as the latent image charge, a bias power source for reversal development is not required.

The present invention can also be implemented by using both the first and second toners as one-component magnetic toners.

In the present invention, the charging characteristics of the first toner must be reversed by frictional charging with the second toner to be charged to a polarity different from the latent image charge formed on the surface of the photosensitive drum. It can be freely adjusted by adjusting the type of resin used in the first and second toners, charge control agents such as pigments and dyes, and addition of magnetic powder.

As an auxiliary means for removing the first toner mixed into the second developing device, it is possible to use a difference in scattering properties and a difference in magnetism between the two toners. The first toner mixed into the second developing device has reversed charge polarity, but the amount of charge is relatively small and easily scatters, so it can also be dispersed by suction air. Since some of the mixed toners cannot be completely reversed in charge polarity, this makes it possible to remove these toners.

As described above, the present invention uses a material whose charging polarity is reversed by frictional charging with the second color toner as the first color toner, and uses a material that reverses the charging polarity of the first color toner when it is mixed into the second color developing device. By frictionally charging the toner with the second color toner, the toner is charged to a polarity different from the second latent image charge, and the toner is attached to the charge remaining area on the surface of the photosensitive drum, and the toner is transferred into the reversal developing device for the second color. In addition to preventing the first color toner from accumulating, the first and second toner images on the surface of the photosensitive drum are then electrostatically transferred to the recording paper using a bias electric field of opposite polarity to be charged to different polarities. This prevents the excess first color toner adhering to the charge remaining area on the photosensitive drum surface from being transferred to the recording paper, resulting in a stable high-quality two-color toner image on the recording paper without color mixing. It has the effect obtained by Further, the present invention can be developed as a toner image forming method of three or more colors by increasing the number of repetitions of electrostatic latent image formation and reversal development.

[Brief explanation of drawings]

Fig. 1 is an overall side view of a two-color electrophotographic apparatus used in the present invention, Fig. 2 is an enlarged view of its developing section, Fig. 3 is a side view showing another example of the developing section, and Fig. 4 is a further FIG. 7 is a side view showing another example of the developing section. DESCRIPTION OF SYMBOLS 1... Photoconductive photosensitive drum, 3... Light beam containing first image information, 4... First toner, 4A...
...First toner image, 4B... Mixed first toner, 4C... First toner charged with different polarity, 5
...First developing device, 6... Light beam containing second image information, 7... Second toner, 7A... Second toner image, 8... Second developing device, 9... Recording paper, 10... Charger for transfer.

Claims (1)

[Claims] 1 The surface of a rotating photoconductive photosensitive drum is uniformly charged, the charged photosensitive drum surface is imagewise exposed to form a first electrostatic latent image, and this first electrostatic latent image is transferred to a second electrostatic latent image. A first developing device having one toner performs reversal development to form a first toner image, and the surface of the photosensitive drum on which the first toner image is formed is exposed to light to form a first toner image.
forming a second electrostatic latent image of the same polarity as the electrostatic latent image;
This second electrostatic latent image is reversely developed by a second developing device having a second toner having a different color from the first toner to form a second toner image, which is formed on the surface of the photosensitive drum. In a method of forming a two-color toner image on recording paper by electrostatically transferring first and second toner images onto recording paper, the charging polarity of the first toner is changed by frictional charging with the second toner. A second reversal development is performed by using a reversible material and charging the first toner mixed in the second developing device to a polarity different from the second latent image charge through frictional charging with the second toner. At the same time, the second toner is attached to the area where the electric charge has disappeared on the surface of the photosensitive drum to form a second toner image, and the first toner mixed into the second developing device is applied to the area where the electric charge has disappeared on the surface of the photosensitive drum. A method for forming a two-color toner image, which comprises adhering the first and second toner images to the remaining area, and then electrostatically transferring the first and second toner images onto a recording paper using a bias electric field having a polarity different from those of the first and second toner images.