JPS6180166A - Formation of color image - Google Patents

Abstract

PURPOSE:To prevent disturbance of a toner image and to obtain a good color image by providing a step for irradiating corona ions to a photosensitive body in each image forming step to remove an electrostatic charge of a latent image and a retained charge of the toner. CONSTITUTION:A reflected light 6 is passed through one of color filters 7-9 rotated in the direction of an arrow 10 and successively selected, introduced through a corona charger 3, and projected on the surface of a photosensitive body 1. The formed electrostatic latent images are developed to each color with each of color developing devices 11-13, respectively. The charge retained with these toners and those of the electrostatic latent images are both removed with corona discharge of a destaticizing charger 18. The full color toner image formed on the photosensitive body is transferred onto a paper 15 in one time with a transfer charger 14, thus permitting disturbance of the toner image to be prevented at the last destaticizing stage of each image forming step and a good color image to be formed.

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to a color image forming method used in copying machines, etc., and more specifically, the present invention relates to a color image forming method used in copying machines, etc. The present invention relates to a color image forming method in which a multicolor toner image is formed on an image carrier and the toner image is transferred onto the toner image carrier at once to obtain a color image.

[Technical background of the invention and its problems]

Although various ideas have been made for methods of forming color images on plain paper by applying indirect electrophotography techniques, only a few examples have been put into practical use at present. Among the methods that have been successfully put into practical use, all of the methods that allow full-color recording involve wrapping paper around a transfer drum and sequentially transferring toner images for each color to this, which makes it difficult for single-color electrophotographic devices. In comparison, the larger, more complex, and more expensive equipment as a whole has become an unavoidable problem. In addition, a two-color color process using a special photoreceptor with a multilayer structure (Japanese Patent Publication No. 55-7798
Although prototypes have been made of a two-color printer using a laser beam (Hoshi et al.: "Two-color printing semiconductor laser printer" 1 Proceedings of the Institute of Image Electronics Engineers 81.02, 2.1981), the former The latter has problems with manufacturing and reliability due to the complexity of the photoreceptor structure, while the latter has problems such as slow recording speed, and it is said that neither method can be easily applied to full-color recording. There are drawbacks.

On the other hand, after forming a multicolor toner image on the photosensitive drum by sequentially performing a series of image forming processes for each color, consisting of image exposure and development through a nine-color charged filter on the entire surface of the photosensitive drum, A method has been devised in which this is transferred onto plain paper at once (Japanese Patent Application Laid-Open No. 55-69167, etc.). This method eliminates the need for a transfer drum, so it is possible to solve the various problems mentioned above, and it is also easy to apply to full-color recording.

However, this method has a serious problem in that the toner image formed on the photosensitive drum is disturbed in the subsequent image forming process for another color. In fact, when the inventor experimented with this method, he found that the toner image of the color formed earlier was removed during the image exposure step in the later image forming process.

It was confirmed that the disturbance was particularly significant in the developing process and the static elimination process. Disturbances in the developing process cause a magnetic brush or the like to come into sliding contact with the photosensitive drum. This problem occurs when a so-called contact type developing method is used, and this problem can be avoided by applying a so-called non-contact type developing method described in, for example, Japanese Patent Publication No. 41-9475.

On the other hand, disturbance of the toner image during the image exposure process and the static elimination process results in phenomena such as line images, bleeding at the edges of the image area, and even phenomena such as toner scattering from the photosensitive drum surface and the image disappearing. appear. This problem is particularly noticeable in the static elimination process because strong light is irradiated. This problem in the static elimination process is: (1) The toner particles constituting the toner image are charged with an excessive charge in the subsequent charging process.

(2) In the static elimination process, toner particles absorb irradiated light and reduce the amount of light i reaching the photosensitive drum surface.

This seems to be due to two points.

This problem will be explained in more detail as follows.

In the color image forming method described in the above-mentioned JP-A-55-69167, etc., the entire surface of the photoreceptor is charged by a corona charger, and a series of image formation steps are performed, including image exposure through a one-color filter and development with color toner. A first color toner image is formed on the photoreceptor through a process, and the same image forming process is then performed for the remaining colors to form a multicolor toner image, which is then transferred onto plain paper at once. ,
Fix it and get a color image.

Here, in the image forming process for the second and subsequent colors, the toner image previously formed on the photoreceptor is uniformly charged by the corona charger and is charged with an extremely large electrostatic charge. Immediately after passing through the corona charger, the surface potential of the area to which the toner image is attached is expressed as Va + Δ■, where Vo is the surface potential of the area to which no toner image is attached. ΔV is the increase in surface potential resulting from the electrostatic charge acquired by the toner. After being charged, the photoreceptor and toner image are subjected to image exposure, and then undergo a development process and then a charge removal process.

FIG. 4 schematically shows changes in the charge distribution on the photoreceptor at the neutralization position. As shown in FIG. 4(a), the toner 42 deposited on the photoconductor 41 in the previous image forming process has a large charge during the charging process in the next image forming process (image process), and the toner 42 is charged during the charging process in the image forming process. Immediately before, the charges are distributed as shown in the figure.Although the surface charge of the photoreceptor 41 has already attenuated during the image exposure process, there is generally a residual charge equivalent to several tens of volts in surface potential.

When the static eliminating light 43 is irradiated from above in the state shown in FIG. 4(a), the surface potential of the photoreceptor 41 disappears in the area i11 where no toner 42 exists, as shown in FIG. 4(b), and on the other hand, In the area where the toner 42 is present, the surface charge of the photoreceptor 41 remains due to the light shielding effect of the toner 42, so that electric lines of force 44 are generated as shown by broken lines in the figure.

The transition from the state shown in FIG. 4(a>) to the state shown in FIG. 4(b) is carried out in an extremely short time under the neutralizing light.

Therefore, a Coulomb force of F suddenly acts on the toner 42 along with the generation of the electric force 1144, and as a result, the toner 42
is ejected from the surface of the photoreceptor 41 toward the outer space.

As described above, in the conventional method, there is a problem in that the toner image is greatly disturbed in the static elimination step, and a solution to this problem has been desired.

[Purpose of the invention]

An object of the present invention is to perform static elimination at the end of each image forming process when a multicolor toner image is formed by sequentially performing a series of image forming processes for each color, including at least an electrostatic latent image forming process and a developing process. It is an object of the present invention to provide a color image forming method that prevents toner images from being disturbed during the process and enables formation of good color images.

[Summary of the invention]

According to the present invention, the above object includes a step of forming an electrostatic latent image by charging and imagewise exposure on a latent image carrier comprising at least a photoconductor, and developing this electrostatic latent image with color toner. A multicolor toner image is formed on the latent image carrier by performing a series of image forming processes for each color, and this toner image is transferred onto the toner image carrier at once to obtain a color image. In the color image forming method, between the developing step and the electrostatic latent image forming step in the next image forming process, the latent image holding member is irradiated with corona ions to remove the latent image holding member. This is achieved by providing a step of eliminating the image charge and the charge held by the toner. Corona ions used in the static elimination process include:
Particularly suitable are corona ions generated by alternating current corona discharge.

〔Effect of the invention〕

According to the present invention, by performing the static elimination process electrically using corona ions, it is possible to eliminate not only the latent image charge but also the retained charge of the toner at the same time. Therefore, the toner image is not disturbed due to the large force acting on the toner that still retains the charge during charge removal, unlike in the case of the charge removal process using only light irradiation, and the image is free from blurring. This makes it possible to form colorful color images.

[Embodiments of the invention]

FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus to which a color image forming method according to the present invention is applied. In the figure, a photosensitive drum 1, which serves as a latent image holder and has a selenium-based photoconductor layer provided on its surface, rotates in the direction of an arrow 2. As shown in FIG.

In this embodiment, the corona charger 3 consists of a corona wire 4 and metal side plates 5 placed on both sides of the corona wire 4. At the same time as charging, reflected light 6 from a full-color original (not shown) is introduced from above to expose the image. It is made of Keizo that can be used. The reflected light 6 moves in the direction of the arrow 10 and is introduced into the corona charger 3 through one of the color filters 7.8.9 of different colors which are sequentially selected. As a result, the photoreceptor 1
Electrostatic latent images corresponding to each color are formed thereon.

In this embodiment, the metal side plate 5 in the corona charger 3
The distance between the corona wire 4 and the photosensitive drum 1 is 11 mm, the diameter of the corona wire 4 is 80 μm, the circumferential rotational speed of the photosensitive drum 1 is 1oOJIII/sec, and the corona wire 4 is charged. Because image exposure is sometimes performed at the same time, the applied voltage (usually +
A DC voltage of +8 kV, which is slightly higher than 6 kV), was applied. Note that the opening width of the corona charger 2 on the photosensitive drum 1 side is 12 scales, and the exposure width matches this opening width.

Note that the opening width and exposure width of the corona charger 3 refer to the dimensions of the opening and the exposure area in the rotation direction 2 of the photosensitive drum 1, respectively.

In the first image forming process, reflected light 6 from a full-color original is color-separated by a blue filter 7 and irradiated onto the surface of the photosensitive drum 1 via a corona charger 3 . The electrostatic latent image thus formed on the surface of the photosensitive drum 1 is developed and visualized by the first developing device 11 using yellow toner, which is a complementary color of blue. The toner of this toner image is charged, but the retained charge of this toner, together with the latent image charge on the photosensitive drum 1, is removed by irradiation with corona ions generated by AC corona discharge from the charge removal charger 18. In this way, the first image creation process is completed. In this first image forming process, the other developing bags @12 and 13 stop the developing roller, apply a voltage bias to the developing roller that makes it impossible to develop the latent image, or stop the developing device. By means such as keeping the entire photosensitive drum 1 away from the photosensitive drum 1, the photosensitive drum 1 can be substantially removed.
It is assumed that it is maintained in a non-functional state.

Hereinafter, in the second image forming process, an electrostatic latent image is formed by charging by the corona charger 3 and image exposure through the green filter 8, and then developed with magenta toner by the second developing device 12. In the third image forming process, after an electrostatic latent image is formed by charging by the corona belt N unit 3 and image exposure through the red filter 9, it is developed with cyan toner by the third developing device 13. will be carried out. Incidentally, as the developing devices 11 to 13, a one-component non-magnetic type developing device disclosed in Japanese Patent Application Laid-Open No. 59-45468 can be used.

These second. In the third image forming process as well, the charge held by the toner after development and the latent image charge on the photosensitive drum 1 are eliminated by irradiation with corona ions by alternating current corona discharge from the charge elimination charger 18.

The full-color toner image formed on the photosensitive drum 1 in this manner is transferred at once onto plain paper 15 as a toner carrier by a transfer charger 14, and is further fixed by a fixing device 16 to complete the entire image forming process. finish. Thereafter, residual toner on the photosensitive drum 1 is removed by a cleaning device 117.

In this embodiment, the corona wire 19 of the static elimination charger 18 has an effective voltage of 11116 kV and a frequency of 5.
An alternating current voltage of 0 Hz was applied via a high voltage capacitor with a capacity of 0.03 μF. Corona ions generated by alternating current corona discharge generally have an excess of negative ions, but if power is supplied via a capacitor as described above, positive and negative ions can be made almost equal in amount. Therefore, the charge on the object to be removed (toner, photosensitive drum) is substantially completely erased regardless of its polarity.

The full-color image obtained by this method was of high quality with little image bleeding, and in particular, almost no toner scattering was observed during the static elimination process. The reason why image blurring is eliminated can be explained as follows.

That is, as explained using FIG. 3, image blurring in the prior art occurs when light is irradiated to a toner image in the static elimination process, between the toner-adhered area and the non-toner-adhered area on the photoreceptor, that is, the toner The cause is that a large electric field is generated between the toner forming the image and the surface of the photoreceptor drum, causing the toner to scatter due to Coulomb force. On the other hand, when snow is removed electrically by corona ion irradiation as in the present invention, not only the charge (latent image charge) on the surface of the photoreceptor drum to which toner is not attached, but also the retained charge of toner can be effectively removed. Therefore, the Coulomb force acting on the toner during static elimination is small, and its scattering is suppressed.

The following table shows the results of measuring the surface potential of each part of the photosensitive drum after static electricity removal by light irradiation alone in the prior art and static electricity removal by corona ion irradiation in the present invention.

From this result, when static electricity is removed only by light irradiation as in the past, a potential difference of 80V occurs between the toner-attached area and the non-toner-attached area, which causes toner scattering. When static electricity is removed by corona ion irradiation according to the present invention, the electric charge not only on non-toner adhering areas but especially on toner adhering areas is removed much better than in the past, so the potential difference between the two can be suppressed to only 5V. and
It can be seen that this suppresses toner scattering.

Next, another embodiment of the present invention will be described. In the embodiment shown in FIG. 2, a static elimination lamp 20 is disposed after the static elimination charger 18, and after static elimination by corona ion irradiation, static elimination is further performed by light irradiation as in the prior art. According to this embodiment, charge removal, particularly latent image charge removal, can be performed more reliably. In this embodiment, it is particularly important in the present invention that the static elimination lamp 20 is disposed after the static elimination charger 18.

This is because if the arrangement of the two is reversed, toner scattering will occur due to static elimination by the static elimination lamp, just as in the conventional case.

In the embodiment shown in FIG. 3, an opening is provided above the defrosting charger 18, and light from the defrosting lamp 20 is irradiated onto the photosensitive drum 1 through this opening. Even if the static elimination by the method and the static elimination by light irradiation are performed simultaneously, the same static elimination effect as in the embodiment shown in FIG. 2 can be obtained.

The present invention is not limited to the above-described embodiments; for example, in the above-described embodiments, it was explained that the image is created using reflected light from the original, considering application to a color copying machine.
A so-called printer can also be configured by performing image exposure using an optical scanning system such as a laser beam. In addition, various modifications can be made to the present invention without departing from the scope thereof.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus for explaining a color image forming method according to an embodiment of the present invention, and FIGS. 2 and 3 are image forming methods according to other embodiments of the present invention. FIG. 4 (a) is a schematic configuration diagram of an image forming apparatus for explaining the
) and (b) are diagrams schematically showing changes in charge distribution on a photoreceptor for explaining problems in the static elimination step of a conventional color image forming method. DESCRIPTION OF SYMBOLS 1... Photosensitive drum (latent image holder), 3... Corona charger, 4... Corona wire, 5... Metal side plate, 6...
...Reflected light from full color original, 7.8.9.
...Filter, 11.12.13...Development device, 14
... Transfer charger, 15... Plain paper (toner image bearing member), 16... Fixing device, 17... Cleaning device, 18... Static elimination charger, 19... Corona wire, 20...・Static electricity removal lamp. Applicant's agent Patent attorney Takehiko Suzue Figure 1 Figure 2 Figure 3

Claims (3)

[Claims] (1) A series of steps including a step of forming an electrostatic latent image by charging and imagewise exposure on a latent image carrier comprising at least a photoconductor, and a step of developing this electrostatic latent image with color toner. A color image forming method in which a multicolor toner image is formed on the latent image carrier by performing an image forming process for each color, and a color image is obtained by transferring this toner image onto the toner image carrier at once, During the period from the developing step to the electrostatic latent image forming step in the next image forming process, the latent image charge and toner on the latent image holding member are retained by irradiating the latent image holding member with corona ions. A color image forming method comprising a step of removing electric charge. (2) The scope of the present invention is characterized in that the static elimination step is performed by irradiating the latent image carrier with corona ions generated by AC corona discharge to eliminate the latent image charge and the retained charge of the toner. 2. The color image forming method according to item 1. (3) In addition to the irradiation with corona ions, the charge removal step is performed by irradiating the latent image carrier with light after or simultaneously with the irradiation with corona ions, thereby removing latent image charges and toner-retained charges. 3. The color image forming method according to claim 1 or 2, wherein static electricity is removed.