JPH02308283A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain a clear image without generating density nonuniformity and fogging when continuously forming the images by the use of a negative organic photoconductive body even when the image is formed on large-sized sheet paper by charging the negative organic photoconductive body with alternating current charges before reaching a destaticizing part from a transfer part. CONSTITUTION:The continuous copying is performed by the photosensitive body 10 constituted of the negative organic photoconductive body 12, and when the size of the sheet paper is small, a part of the photosensitive body 10 is directly charged with positive charges by a transfer charger 21 when transferring. However, when the continuous copying is completed, before the subsequent copying starts, the photosensitive body 10 is charged with the alternating current charges by a destaticizing charger 23 and after the positive charges are removed, the body 10 is uniformly destatidized by a destaticizing lamp 24. Therfore, for the subsequent copying, when copying on the larger-sized sheet paper, the photosensitive body 10 is uniformly electrosatically charged throughout the body, and the uniform and excellent image is obtained without permitting the image density of a part of the image to be denser and without generating the fogging as the previous cases.

Description

[Detailed description of the invention]

``Object of the Invention'' (Industrial Application Field) The present invention relates to an image forming apparatus such as an electrophotographic apparatus that forms an image using a negative polarity organic photoconductor. (Prior Art) Image formation In devices, especially color copying machines and laser printers, a uniformly charged photoreceptor is exposed to light.
A visible image is often obtained by a so-called reversal development method in which an electrostatic latent image is formed on a photoreceptor and this electrostatic latent image is developed with a toner having a charge of the same polarity as that of the photoreceptor. ing. In such a device, during transfer, a visible image is transferred onto a sheet of paper by applying a charge with a polarity opposite to that of the photoreceptor from the back side of the sheet of paper, which is an image carrier, in the transfer section. , you are getting the image. On the other hand, in recent years, as a photoreceptor suitable for such image forming devices, it is non-polluting and does not require collection processing, and the spectral sensitivity can be changed by selecting the material, expanding versatility and reducing costs. Photoreceptors in which inexpensive organic photoconductors are coated on conductive supports in the form of drums or belts are increasingly being used. Conventionally, this organic photoconductor has the drawbacks of low sensitivity and short lifespan due to rapid deterioration of properties compared to inorganic materials such as selenium [Se1]. Although it was only applied to image forming apparatuses, recently, efforts have been made to improve the sensitivity and life of these devices by selecting materials and improving the layer structure. Moreover, in an image forming apparatus using such an organic photoconductor as a photoconductor, the diameter of the photoconductor is being reduced as a result of the demand for miniaturization of the drum-shaped photoconductor. In particular, in the case of a photoconductor with a diameter of 40φ or less, the installation space for each image forming means around it is reduced, which places restrictions on the arrangement. Because the diameter of the photoreceptor is small, the sheet paper can be peeled off naturally from the photoreceptor due to its stiffness, even without the use of a peeling device such as a peeling charger.
Devices that do not use a peeling device have also been developed. However, with a device that does not use such a peeling device,
When an image is formed by the above-mentioned reversal development using a photoreceptor made of an organic photoconductor, it is particularly difficult to form a negative organic photoconductor in which a charge generation layer and a charge transport layer are successively laminated on a conductive support. For example, if you repeat the image forming process and, for example, continuously form an image on a sheet of paper of the same size, then try to form an image on a sheet of paper of a larger size, some parts of the image may be There is a problem in that the image density is high in the black background area in the middle, and if fog occurs in the white background area, a blank area is generated and the image quality is significantly reduced. (Problems to be Solved by the Invention) As mentioned above, in the past, images were formed continuously using a negative organic photoconductor by a reversal development method, and then images were formed on a large sheet of paper. When this is done, there is a problem in that some parts of the image have a high density and cause fogging, and the image quality deteriorates due to density unevenness. Therefore, in order to eliminate the above-mentioned drawbacks, the present invention aims to form images continuously on sheets of paper of any size when forming images using a negative organic photoconductor, and then to form images on sheets of paper of a larger size. An object of the present invention is to provide an image forming apparatus capable of obtaining a clear image without causing density unevenness or fogging even when the image is formed. [Structure of the Invention] (Means for Solving the Problems) In order to realize the above-mentioned aspects, the present invention provides an image forming means for forming an image on a negative-polarity organic photoconductor. An image forming apparatus is provided that includes a transfer device that applies a positive charge and a charge application device that is provided between the transfer section and the static elimination section and applies an AC charge to a negative organic photoconductor. (Function) According to the present invention, after the completion of continuous image formation on a sheet paper of any size using a negative polarity organic photoconductor,
An alternating current charge is applied to the negative organic photoconductor by the charge applying device, and unnecessary positive charges are removed. Therefore, when images are subsequently formed on larger sheets of paper, density unevenness and fogging may occur in parts of the images. This does not occur and a good image can be obtained. (Example) Here, first, using a photoconductor consisting of a negative polarity conductor,
The causes of density unevenness and fog that occur when copying is performed on a larger sheet of paper after continuous copying is performed using reversal development will be explained. In other words, when continuous copying is performed using a reversal development method in which development is performed with toner of negative polarity that is the same polarity as the surface charge of the photoreceptor, after the reversal development is completed, the toner image, which is a visible image, is When transferring the toner image to sheet I paper, a transfer device applies a positive charge from the back side of the sheet paper, so that the toner image is electrostatically attracted to the sheet paper side and transferred. If the sheet paper that is continuously supplied to the transfer unit in advance is, for example, [A4] size, the area of positive charge applied by the transfer device is wider than the width of the sheet paper. Therefore, the portion outside the width of the [A4] size on the photoreceptor is directly given a positive charge by the transfer device,
This will result in a positive charge. In addition, a negative polarity organic photoconductor has a layered structure in which a charge generation layer and a charge transport layer are sequentially laminated on a conductive support, and the charge transport layer on the surface becomes a charge generation layer when exposed to light. Among the generated carriers, it has the property of allowing holes to pass through but not electrons. And from this, the negative polarity organic photoconductor is
Once charged to a positive polarity, this positive charge cannot be removed by light irradiation. For this reason, [A
・4] The positively charged part outside the size width is
The charge will not be removed and the next copy cycle will start with a positive charge, and even if the charging device charges the sheet paper as it is, the surface will be smaller than the part inside the supplied [A/4] size width. The potential will be reduced. When continuous copying is performed while repeating this state, the portion outside the [^・4] size width of the photoconductor is given a positive charge each time it is transferred, and the surface potential due to charging is further reduced. It happens. When all preceding continuous copies are completed in this way,
The next copy will be made, but at this time, even if the area outside the [^・4] size width on the photoreceptor is charged by the charging device, it will not be transferred during the transfer of the previous continuous copy. Due to the positive charge received from the transfer device, the desired surface potential required during charging cannot be obtained, which causes density unevenness and fog to occur during the next copy. For this reason, for example, the sheet paper used for the next copy is

If the size is [Aψ3], the image density will be high in a portion wider than the [A4] size, further causing fog. Next, one embodiment of the present invention will be described with reference to FIGS. 1 to 3. FIG. 1 is a schematic explanatory diagram showing a part of a laser printer that is an image forming apparatus, and lO is a diameter of 30 mm.
A conductive support 11 made of a drum-shaped aluminum [Al1 tube] of φ, and a negative polarity organic photoconductor in which a charge generation layer 12a and a charge transport layer 12b are successively laminated so as to be supported by the conductive support 11. It is a photoreceptor consisting of 12. The charge generation layer 12a is composed of an ab pigment and a binder resin represented by the formula:
. . . (The conductive support 11 is immersed in a liquid in which phenoxy represented by II2C is mixed and dissolved in a solvent of 1,1,2-trichloroethane, and then dried to form the conductive support 11. Next, the charge transport layer 12b is formed by adding the charge generating layer 12a to a liquid in which hydrazone represented by the formula % (313) is mixed with phenoxy represented by the formula (2nd formula), and these are further dissolved in a cyclohexane solvent. The conductive support 11 having a
Each image forming means 13 is provided around the periphery. The image forming means 13 includes a charging device 14 to which a voltage of -0 [kV] is applied, an exposure device 1f that irradiates image information from a document (not shown), etc., and a magnet roller 18a with a voltage of -45 kV.
A developing bias of 0 [V] is applied and the negative polarity toner tab
a developing device 18, a transfer charger 21 which is a transfer device provided in the transfer section and to which a DC voltage is applied by a DC power supply 21a of ÷BK [V], and a cleaning device 22.
, a static elimination charger 23 which is a charge imparting device and to which an AC voltage is applied by an AC power supply 23a of ±4.5K [V].
, a static eliminating lamp 24 provided in the static eliminating section. Next, we will discuss the effect. First, when continuous copying onto [A.4] size sheet paper (not shown) is started, the photoreceptor 10 is rotated in the direction of arrow X, and the photoreceptor 10 is rotated in the direction of arrow X.
0 is uniformly charged to about -650 [V] by the charging device 14. Next, the image portion of the photoreceptor 10 is irradiated with light by the exposure device 17, and an electrostatic image of about -50 [V] is formed. Thereafter, a developing device 18 applies a negative polarity toner to the image portion of the photoreceptor 10 irradiated with light, and a toner image is formed by reversal development. Next, the photoreceptor lO having the toner image reaches the transfer section, and a sheet of paper is also fed to the transfer section in synchronization with the toner image. Then, when a positive charge is applied from the back side of the sheet paper by the transfer charger 21, the toner image on the photoreceptor 10 is transferred to the sheet paper (not shown).
The image is electrostatically attracted and transferred. However, since the charge application width of the transfer charger 21 extends over the entire width of the photoreceptor 1O, in a portion wider than the width of the sheet paper, the photoreceptor 1O is directly provided with a positive charge by the transfer charger 21, and has a positive polarity. is charged with electricity. Next, when the sheet paper (not shown) reaches its peeling position [A], since the diameter of the photoreceptor 10 is small, the paper sheet (not shown) is naturally peeled off from the photoreceptor 1O due to its stiffness. Thereafter, the sheet of paper passes through a fixing device (not shown) to complete the copy image. After residual toner is removed from the photoreceptor 10 by the cleaning device 22, the photoconductor 1O passes through the static elimination charger 23 whose operation is stopped, reaches the static elimination unit, is neutralized by the static elimination lamp 24, and is ready for the next copy. be done. However, at this time,
The positively charged portion of the photoreceptor lO outside the width of the sheet cannot be neutralized by the static elimination lamp, and since positive charge remains, the surface potential of the surface potential reaches -850rVE the next time it is charged. It is not raised and is reduced compared to the portion through which the sheet paper passes. Then, when continuous copying is repeated, the portion of the photoreceptor 10 outside the sheet paper width is given a positive charge each time it is transferred, so that its surface potential is gradually reduced each time it is charged. . After completing all the continuous copies in this way, another new copy will be started, but at this time, the first copy of the [A4] width shown in FIG. In the portion 10a, the residual charge is of negative polarity, so the residual charge is completely eliminated by the static elimination lamp 24, but in the second portion 10b outside the width [A.4], the residual charge is of negative polarity. , the positive charge remains without being removed. Therefore, before starting the next new copy, the photoreceptor 1O is rotated once in the direction of the arrow X while the image forming means 13 except the static elimination charger 23 and the static elimination lamp 24 are temporarily stopped. During this time, the photoreceptor lO is given an alternating current charge by the static elimination charger 23, and the remaining positive charge is removed. Next, the entire surface of the photoreceptor 10 is exposed to light by the charge eliminating lamp 24 to uniformly eliminate the charge. After this, the next copy starts for the first time, and the charging device 14 charges the photoreceptor 10.
The entire area is uniformly charged to -650 [V]. Therefore, even if the next copy size is [A or 3] size, the toner image obtained on the sheet paper (not shown) will be a uniform and clear image without density unevenness or fog. Note that at the start of the next copy, the operation of the static elimination charger 23 is stopped. After that, when all the repeated copies using sheet paper of size [^. Rotate lO once in the direction of arrow X. As a result, the photoreceptor 10 has its positive charge removed by the alternating current charge, and is further exposed to uniform discharge light by the discharge lamp 24 before starting the next copy. With the configuration described above, continuous copying is performed using the photoreceptor 10 made of the negative organic photoconductor 12, and depending on the size of the sheet paper, the transfer charger 21 may partially copy the photoreceptor lO during transfer. Even if a positive charge is directly applied and the photoreceptor is charged to a positive polarity, between the end of continuous copying and the next copy, the photoreceptor IO will be applied with an AC charge during the charge removal charge 23 and the positive charge will be removed. After that, the static electricity is uniformly removed by the static elimination lamp 24. Therefore, even if the next copy is to be made on a larger sheet of paper, the entire area of the photoreceptor can be charged uniformly during charging, and the image density of a part of the image will be higher than before. It is uniform and does not cause fogging or fogging.
Good images can be obtained. It should be noted that the present invention is not limited to the above-mentioned embodiments, and the diameter of the photoreceptor may be arbitrarily determined. However, in order to ensure peeling without using a peeling device and using only the stiffness of the sheet paper, 40
φ or less is preferable. Further, the installation position of the charge applying device may be set according to the space distribution around the photoreceptor as long as it is between the transfer section and the static eliminating section, and the size of the power supply applied to the charge applying device is not limited. In addition, in the embodiment, after the continuous copying is completed, a cycle is always carried out to uniformly apply an AC charge to the entire surface of the photoreceptor, but if the sheet paper size of the preceding continuous copying and the next copying is the same Or, if the next sheet size is smaller than the sheet size of the preceding continuous copy, and the uneven surface potential on the photoreceptor is in an area that does not affect image formation, In order to shorten the image forming process time, it is not necessary to perform a cycle of AC charge application by the charge application device. However, in this case, it is necessary to provide means for detecting and comparing the sheet size of the preceding continuous copy and the next sheet size. Furthermore, the charge applying device operates even during the image forming process, and removes the positive charge on the organic lead conductor at each cycle of the image forming process, and also removes the positive charge on the organic lead conductor after each cycle of the image forming process, and also when continuous copying with sheets of paper of the same size is completed. After that, the organic photoconductor may be rotated one more time and an AC charge may be applied by a charge application device to more reliably remove the positive charge, or alternatively, the AC charge may be applied only during the cycle of the image forming process. If the positive charge can be removed, the next copy may be started immediately after the completion of continuous copying without rotating the organic photoconductor once in order to apply an alternating current charge. Furthermore, when charging the next copy following the preceding continuous copy, as long as the surface potential of the photoreceptor is at least a predetermined value, fogging or an increase in image density will not occur even if there is some variation. It is also possible to just uniformly apply alternating current charges using the applying device and neutralize the positive charges on the photoreceptor.
As shown in the examples, AC type (4
After application of No. 7, the photoreceptor is irradiated with light using a static elimination lamp, so that the photoreceptor is uniformly exposed to static electricity, and when it is next charged, the surface potential is made uniform, so that image formation can be performed in a more stable state. Note that the material of the organic photoconductor is also arbitrary. [Effects of the Invention] As detailed above, according to the present invention, after performing a continuous image forming process using a negative polarity organic photoconductor suitable for color copying machines, laser printers, etc., even larger size images can be formed. Even if the next image forming process is performed using a sheet of paper, the next image forming process will start with a part of the negative organic photoconductor still positively charged as in the conventional method. It is possible to obtain at least the desired surface potential when charging in the next image forming process, eliminating the density inconsistency in the image area and fogging in the white background area that conventionally occurred, and producing a clear and good image. Obtainable.

[Brief explanation of the drawing]

1 to 3 show one embodiment of the present invention. FIG. 1 is a schematic explanatory diagram of the surroundings of a photoreceptor, FIG. 2 is a partial sectional view of the photoreceptor, and FIG. 3 is a diagram of the photoreceptor. It is a schematic perspective view. 10... Photoreceptor, 11... Conductive support,
12a...charge generation layer, 12b...charge transport layer,
12... Organic photoconductor 13... Image forming means,
14... Charging device, 21... Transfer charger, 23... Static elimination charger.

Claims (1)

[Claims] In an image forming apparatus comprising a negative organic photoconductor and an image forming means for forming an image on the negative organic photoconductor, the image forming means applies an image to the negative organic photoconductor in a transfer section. An image characterized by comprising: a transfer means that faces each other and applies a positive charge; and a charge application means that is provided between the transfer section and the static elimination section and applies an AC charge to the negative organic photoconductor. Forming device.