JPS6275465A - Two-color image forming method - Google Patents

Abstract

PURPOSE:To form a two-color image which has no mixed colors, can be satisfactorily transferred to plain paper, is free from a decrease and uneveness of an image density and has high image quality by selectively executing the electrostatic charge in the 2nd electrostatic charge stage only in the non-image part after the 1st developing stage. CONSTITUTION:A latent image holding body is uniformly electrostatically charged to +1,000V by a corona charger impressed with a voltage of a prescribed polarity and the 1st light information is irradiated on said body to form the 1st latent image. A color toner, except black, for example, red toner dharged to a negative polarity is thereafter stuck to the dark part of the 1st latent image formed in the above- mentioned manner and the latent image is subjected to normal development. The photosensitive body is again uniformly charged and in this case only the non-image part of the 1st latent image is selectively charged. The 2nd light information is thereafter irradiated on the photosensitive body to form the 2nd latent image. The image is subjected to the normal development by the color toner, for example, black toner, charged to the negative polarity, which is the 2nd color toner. The two-color image which is free from the defective transfer, uneven transfer or mixed colors and has the high image quality is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a two-color image forming method, and in particular, a method for forming two-color toner images according to different optical information on a photoreceptor that is a latent image holding member, The present invention relates to a two-color image forming method for obtaining a two-color image by transferring the image onto recording paper such as plain paper.

[Technical Background of the Invention and Problems thereof] In recent years, with the spread of computers, facsimiles, etc., there has been a strong desire to improve the functionality of printers that output data. One of the requirements is a printer that can output documents not only in black but also in other colors, such as red, and that can change the color of characters, symbols, figures, etc. as necessary. has been done.

Conventionally, as such two-color printers, various electrophotographic methods that can print at high speed and have good image quality have been studied and many proposals have been made.

For example, after a photoreceptor, which is a latent image holder, is uniformly charged, it is exposed to an image-modulated laser beam to generate a first electrostatic charge Fl! A method (Japanese Unexamined Patent Application Publication No. 1983-1981) of forming an image Im, developing it with a first color developer, or toner, and then similarly forming a second electrostatic latent image and developing it with a second color toner.
-83069).

However, this method uses so-called reversal development, in which the toner is deposited by a developing bias on the area where the surface potential on the photoconductor is attenuated by exposure, that is, at the well of the surface potential. During development, the second color toner is developed so as to overlap the first color toner image already formed on the photoreceptor. As a result, the color of the first color image obtained on plain paper has the disadvantage that the color is a mixture of the first color toner and the second color toner.

Therefore, as a way to improve this defect, the current color of the first color □
□□ A method has been proposed (Japanese Patent Laid-Open No. 58-57139) in which the photoreceptor is subsequently recharged to fill in the surface potential wells. However, this recharging causes the first color toner image formed at the surface potential well to be extremely strongly charged, resulting in decreased transfer efficiency or uneven transfer when transferred to plain paper.

On the other hand, the charge polarity of the first color toner and the charge polarity of the second color toner are set to different polarities, positive and negative, and the first color is developed by reversal development and the second color is developed by regular development, so that the developed toners overlap, In other words, how to prevent color mixing (Unexamined Japanese Patent Publication No. 5)
7-2047).

In this method, one of the two color toner images obtained on the photoreceptor is charged with positive polarity and the other with negative polarity, so the charged polarity of the two color toner images is adjusted before transferring to plain paper. It is necessary to align them. However, in reality, it is extremely difficult to charge toner images of two colors that are charged with different polarities to the same polarity and the same amount of charge, and as a result, a reduction in transfer efficiency or a transfer error occurs as before.

As described above, the conventional two-color image forming method has a problem in that it is not possible to develop the image without mixing colors and to efficiently transfer the image onto plain paper.

[Objective of the Invention] The present invention was made in response to the above-mentioned circumstances, and it is possible to obtain a high-quality two-color image without color mixing, good transfer to plain paper, and no decrease in image density or unevenness. An object of the present invention is to provide a two-color image forming method.

[Summary of the Invention] The present invention includes a first charging step of uniformly charging a latent image carrier including at least a photoconductor to a predetermined surface potential, and a first latent image forming step of forming a first latent image. a forming step; a first copying step of developing the first latent image with a color toner other than black toner;
a second charging step of uniformly charging the latent image carrier to a predetermined surface potential having the same polarity as the charging polarity in the first charging step; a second latent image forming step of forming a second latent image; 2, which consists of a second developing step of developing the latent image with a second color toner;
In the color image forming method, the development in the first and second development steps is performed by regular development, and the charging in the second charging step is performed by selectively charging only the non-image area after the first development step. , no color mixing;
Further, the transfer to plain paper is good, and a high-quality two-color image with no decrease in image density or unevenness can be formed.

[Embodiments of the invention] Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 1 is a diagram showing changes in the surface potential of a photoreceptor in each step of an embodiment of the present invention.

In this two-color image forming method, first, in the first band 78 step, a photoreceptor as a latent 1Φ holder is uniformly charged to +i ooov by a corona charger to which a predetermined polarity voltage is applied (first band 78 step).
Figure (A)).

Next, in the first exposure step, the photoreceptor is irradiated with first optical information to form a first latent image (FIG. 1(B)).

In this case, the light irradiation intensity is set to such an intensity that the bright area potential of the photoreceptor is sufficiently lower than the dark area potential (for example, +100 V or less).

Thereafter, in the first developing step, a negatively charged color toner other than black, for example, a red toner, is attached to the dark portion of the first latent image formed in the above step, that is, the non-light irradiated portion, and regular development is performed (see Fig. 1). (C)).

Next, in the second charging step, the photoreceptor is uniformly charged again, but in this case, the non-image area (bright area) of the first latent image of light, that is, the first
Only the areas to which the colored toner is not attached are selectively charged (FIG. 1(D)).

Thereafter, in a second exposure step, the photoreceptor is irradiated with second light information to form a second latent image (Fig. 1 (E)), and in a second development step, the second latent image is irradiated with a second color toner. Perform regular development with a negatively charged color toner, such as black toner.

Note that the optical information in the first exposure and second exposure steps described above is positive optical information.

As described above, two-color toner images corresponding to different optical information are formed on the photoreceptor, and this image is transferred to a transfer material such as plain paper to complete recording.

In this embodiment, the means for performing the second charging step, that is, the means for selectively charging only the non-image area (bright area) of the first latent image, is the corona charging shown in FIGS. 2, 3, and 4. It is preferable to use a vessel.

The corona charger shown in FIG. 2 includes a corona discharge wire 2,
It is comprised of a shield electrode 3 provided surrounding it, and is placed opposite to the photoreceptor 1 comprising a conductive substrate 1a and a photoconductor layer 1b. An AC high voltage power supply 4 is connected to this corona discharge wire 2, and an AC high voltage in which a DC voltage is superimposed is applied by this AC high voltage power supply 4 and a DC power supply 5 connected in series to this, while the shield electrode 3 is grounded.

This corona charger can not only arbitrarily adjust and set the supply of positive and negative corona ions generated by AC corona discharge to the photoreceptor by changing the polarity and voltage value of the superimposed DC voltage. When the photoreceptor has a potential distribution, that is, when the first latent image is formed as in this embodiment, the image area (dark area) of this latent image contains corona and
Ions are not supplied, and corona/corona is applied only to non-image areas (bright areas).
Ions can be supplied.

For example, a photoreceptor charged with a potential of +980V in the image area of the first latent image and +90V in the non-image area is charged to +1500V.
When charged by a corona charger to which a sinusoidal AC high voltage of 50 Hz and an effective voltage of 5.6 KV on which a DC voltage of V is superimposed is applied, no change in the potential of the image area is observed, only the non-image area. is recharged to +980V, and as a result, the entire surface of the photoreceptor can be charged almost uniformly.

Further, the corona charger shown in FIG. 3 is composed of a corona discharge wire 2 and a shield electrode 3 provided surrounding the corona discharge wire 2, like the corona charger shown in FIG.
An AC high voltage is applied to the shield electrode 3 by an AC high voltage power supply 4, and a DC voltage is applied to the shield electrode 3 by a DC power supply 5.

Furthermore, the corona charger shown in FIG. 4 includes a corona discharge wire 2, a shield electrode 3 provided surrounding the corona discharge wire, and a grid electrode 7 provided close to the toner image at the opening of the shield electrode 3. , a positive or negative DC high voltage is applied to the corona discharge wire 2 by a DC high voltage power supply 6, a DC voltage is applied to the grid electrode by a DC power supply 5, and the shield electrode 3 is grounded. .

The corona chargers shown in FIGS. 3 and 4 both have
By changing the polarity and voltage value of the DC voltage applied to the shield electrode 3 and the grid electrode 7, it is possible to charge only the non-image portion of the first latent image, similar to the corona charger shown in FIG. . By the way, when forming the second latent image in this embodiment, it is necessary to bring the surface potential of the photoreceptor under the already developed first color toner image to the non-image area (bright area) potential by irradiating light. Therefore, a problem arises in which the sensitivity of the photoreceptor decreases due to toner adhesion.

That is, when a color toner other than black toner, for example, red toner, is used as the first color toner, the fifth color toner is used as the first color toner.
As shown in the figure, the sensitivity of the photoreceptor does not decrease significantly, and there is no problem in practice. On the other hand, when black toner is used, even if the light intensity is sufficiently increased, the sensitivity of the photoreceptor decreases significantly, making it impossible to form a latent image in accordance with optical information.

In this embodiment, since a color toner other than black is used as the first color toner, a decrease in the sensitivity of the photoreceptor is unlikely to occur.

Incidentally, a developing device that develops a static N latent image generally has a structure in which a developer made of toner or carrier comes into contact with a photoreceptor, but when the method of this embodiment is carried out using such a developing device, the photoreceptor is already exposed. A problem arises in that a portion of the first color toner image formed thereon is stripped off in the second development step.

Therefore, as the developing device used to carry out the two-color image forming method of this embodiment, a -component non-magnetic type non-contact developing device is most suitable.

FIG. 6 is a schematic sectional view of this developing device.

This developing device includes a toner container 12 that stores toner 11 and has an opening at the bottom, and a developing roll (toner carrying roll) 13 made of an aluminum cylinder with a diameter of 24 mm and arranged to cover this opening. , thickness 0.211
1111. An elastic sheet-like member 14 made of a phosphor bronze plate with a length of 270 mm and a width of 35 mm, which uniformly stores toner on the developing roll, a DC power supply 15 which applies a developing bias voltage of 100 μm to this developing roll, and a 75 μm thick The main part consists of a sealing member 16 for preventing toner spillage made of polyester film.

The surface of this developing roll 13 is roughened by sandblasting, and electroless nickel plating with a thickness of 10 μm is applied to the surface, and the final surface roughness is 3 μm.
It is m. Here, the surface roughness is based on the 10-point average roughness of the JIS standard (JIS B12O3).

Further, one end side of this elastic sheet-like member 14 is attached with a screw 1.
7 to the support body 18, and the other end is pressed against the developing roll 13 so that a certain area of the side surface is in contact with the surface of the developing roll 13. However, the edges, that is, the free ends, of the elastic sheet-like member 14 do not contact the surface of the developing roll 13.

In this developing device, for example, the minimum gap between the developing roll 13 and the photosensitive drum 1 is Q, 2.
mm, and an electrostatic latent image with a surface potential of 900 V is formed on the surface of the photosensitive drum 1. At this time, when the developing roll 13 and the photosensitive drum 1 are rotated, the toner 11 in the toner container 12 is transferred to the elastic sheet member 1.
4 (thickness: 40 μll1), and at the same time, a negative electrostatic charge is applied by triboelectrification. Developing roll 1
The toner approaches the electrostatic latent image on the photosensitive drum 1, flies through the gap between the developing roll 13 and the photosensitive drum 1 due to Coulomb force, and is transferred to the photosensitive drum 1. A developed toner image is formed by adhering to the surface.

This developing device has a simple configuration that allows it to be small, lightweight, and low-cost, and it is easy to maintain because it does not use a carrier. In addition, the toner is non-magnetic. It has very great advantages, such as good coloring properties and non-contact development, which does not disturb the toner image previously formed on the surface of the photoreceptor drum. FIG. 7 shows a two-color laser that implements the method of this example.
Bee 1. - It is a schematic configuration diagram of a printer.

This two-color laser beam printer consists of a photosensitive drum 1 having a selenium-based photoconductive layer provided on an aluminum substrate, a charging corona charger 22 configured as shown in FIG. 3, and a laser beam using a semiconductor laser as a light source. A first optical information irradiation light 23 modulated into positive image information, a first developing device 24 containing negatively charged red 1 hener configured as shown in FIG. 6, and a first corona charger 22. A second charging corona charger 25 having the same configuration as that of the first developing device 22 that contains a second optical information irradiation light 26 using a semiconductor laser as a light source, and a negatively charged black toner. A device 27, two transfer corona chargers that transfer the two-color toner image formed on the photoreceptor drum 1 to the normal super 28, a cleaning device 30 that removes residual toner after transfer, and a charge removal device for the photoreceptor drum 1. It is composed of a lightning removal lamp 31 that performs lightning removal, and a heat roll 32 that fixes the toner image transferred to the passing paper 28.

With a two-color laser beam printer configured in this manner, a good two-color image can be obtained by implementing the method of this embodiment.

In addition, in the two-color laser beam printer described above, a method of image-modulating and irradiating laser light was used as the optical information illumination means, but the method of this embodiment can also be applied to light-emitting elements such as LED arrays or It can also be implemented using a liquid crystal optical shutter array or the like.

Furthermore, the two-color image forming method of the present invention is capable of forming an electrostatic latent image on a dielectric drum using an electron beam or the like, in addition to the above-mentioned image forming apparatus using a photoreceptor such as a laser beam printer. It can also be applied to image forming apparatuses that develop with toner.

[Effects of the Invention] As explained above, according to the present invention, since only the non-image area of the first latent image is charged in the second charging step, the first latent image that has already been formed on the latent image carrier is charged. It is possible to prevent the colored toner image from being charged with corona, and since the development in the first and second developing steps is performed using a normal vision image, it is possible to prevent the second color toner from overlapping the first color toner image. It is possible to obtain high-quality two-color images without transfer defects, uneven transfer, or color mixture.

[Brief explanation of drawings]

FIG. 1 is a diagram showing changes in the surface potential of a photoreceptor for each step in a two-color image forming method according to an embodiment of the present invention, and FIGS. v? A schematic configuration diagram of a corona charger used in the electrostatic process, Figure 5 is a graph showing the relationship between the amount of attached color toner and the decrease in sensitivity of the photoreceptor, and Figure 6 is a diagram of the developing device used in the developing process of the same example. A schematic cross-sectional view of the apparatus, FIG.
FIG. 1 is a schematic configuration diagram of a one-beam printer. 1...... Photoreceptor drum 11...... Toner

Claims (3)

[Claims] (1) A first charging step of uniformly charging a latent image carrier including at least a photoconductor to a predetermined surface potential, a first latent image forming step of forming a first latent image, and a first latent image forming step of forming a first latent image. a first developing step in which the latent image is developed with a color toner other than black toner; and a second charging step in which the latent image holder is uniformly charged to a predetermined surface potential having the same polarity as the charging polarity in the first charging step. , a second latent image forming step of forming a second latent image; and a second latent image forming step of forming a second latent image.
In a two-color image forming method comprising a second developing step of developing with a colored toner, the development in the first and second developing steps is performed by regular development, and the second developing step is performed by regular development.
A two-color image forming method, wherein charging in the charging step selectively charges only the non-image area after the first developing step. (2) The two-color image forming method according to claim 1, wherein the second charging step is performed by corona discharge from a corona charger to which at least an AC voltage component is applied. (3) The two-color image forming method according to claim 1, wherein the second charging step is performed by corona discharge from a corona charger having a grid electrode to which a voltage is applied.