JPH039385A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain a clear image without generating the uneveness of density and fogging even when continuous image forming is performed by providing a separating device which charges an image supporting body with at least two different kinds of alternating current charges. CONSTITUTION:When an image carrier is passing through, a first alternating current voltage is impressed, and when the image carrier is not passing through, a second alternating current voltage, which is higher than the first alternating current voltage, is impressed and the separating device 24, which charges the image supporting body 10 with the alternating current charges of different quantity, is provided. Thus, even when continuous copying is performed by a photosensitive body 10 composed of a negative organic photoconductive body 12 and a part 10a of the photosensitive body 10 is positively electrostatically charged by a transfer charger 21, the part is charged with about double alternating current charges 23b at the separating time, by a separat ing charger 24. And since the positive charges on the photosensitive body 10 are all neutralized and removed by the separating charger 24, the whole photosensitive body 10 is uniformly electrostatically charged to the desired surface potential. Thus, the belt-shaped fogging and the uneveness of the density are dissolved and the excellent image is obtained for a long period.

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 an image support having a negative polarity organic photoconductor. (Prior Art) Image forming apparatuses, particularly color copying machines and laser printers, expose a negatively charged photoreceptor, which is an image support, to form an electrostatic latent image on the photoreceptor. Further, a visible image is often obtained by a so-called reversal development method in which this electrostatic latent image is developed with a toner having a charge of the same polarity as that of the photoreceptor. In such a device, during transfer, an electric charge of opposite polarity, such as the '@-electrode of the photoreceptor, is applied to the sheet paper from the back surface of the sheet paper, which is an image bearing member, in the transfer section. The visual image is transferred and an image is obtained. On the other hand, in recent years, photoreceptors suitable for such image forming apparatuses have been recognized as being non-polluting and requiring no recovery treatment, as well as being able to change the spectral sensitivity by selecting the material, thus increasing versatility. 5. Photoreceptors, which are inexpensive and have an organic photoconductor coated on a drum-shaped or belt-shaped conductive support, are increasingly being used. Compared to conventional inorganic materials such as selenium (Se), this organic photoconductor 1j has the drawbacks of low sensitivity and short lifespan due to rapid deterioration of characteristics. However, recently, efforts have been made to improve the sensitivity and life of these devices by selecting the monthly charge and improving the layer structure. However, when a photoreceptor having such an organic photoconductor is used to form an image by the above-mentioned reversal development, a negative electrode formed by sequentially laminating a charge generation layer and a charge transport layer on the conductive support 1 is produced. In the case of a photoreceptor made of an organic photoconductor, the image forming step 1. If an attempt is made to repeatedly and continuously obtain images, there is a problem in that part of one image is covered with fog K1, which becomes bulge-like in the longitudinal direction of the photoreceptor, and the image quality is significantly reduced. (Problem M to be solved by the invention) As mentioned above, conventionally, when a photoreceptor consisting of a negative polarity photoconductor is used and images are formed continuously by a reversal development method, only a portion of one image is formed. The problem is that fog occurs in band-like areas in the white background area, and image density increases in the image area, causing density unevenness, which partially contributes to the deterioration of image quality. Therefore, in order to eliminate the following drawbacks, the present invention makes it possible to obtain clear images without causing density unevenness or fogging even when images are formed continuously. The purpose is to provide an image forming device. [Structure of the Invention] (Means for Solving the Problems) In order to achieve the above-mentioned problems, the present invention provides a method in which a positive charge is particularly imparted to an image support having a negative polarity organic photoconductor by an image forming means. The transfer device and the first one when the image carrier passes through.
an AC voltage is applied thereto, and a second AC voltage greater than the first AC voltage is applied when the image carrier does not pass through, and a peeling device is provided that applies different amounts of AC charge to the image support. It is. (Function) By the above-mentioned means, the present invention prevents fogging or density unevenness from occurring in a part of the image even during continuous image formation using an image support having a negative polarity organic photoconductor. , which aims to improve image quality. (Example) First, the cause of fogging during continuous copying will be explained using a photoreceptor as an image support made of one negative polarity organic light lXff. For example, if development is performed using a reversal development method in which development is performed using a negative toner having the same polarity as the surface potential of the photoreceptor, such as during continuous copying, after the reversal development is completed, the visible When transferring a toner image from a photoreceptor to a sheet of paper that is an image carrier, a transfer device applies a positive @4 charge from the back surface of the sheet t-m, thereby electrostatically transferring the toner image to the sheet of paper. It will be adsorbed and transferred. On the other hand, when copying continuously,
Although sheets of paper are continuously fed to the transfer section according to the toner image on the photoreceptor, the preceding sheet of paper and the following sheet of paper are separated by a certain period of time, and each sheet of paper is A gap is formed in between. Moreover, during continuous copying, since the transfer device remains in continuous operation, each sheet
- The transfer device directly applies a positive charge to the gap between the paper sheets, and that area on the photoreceptor is positively charged. Although an alternating current charge is applied to the photoconductor and the positive charge is removed, the amount of charge applied is small enough to allow the sheet paper to be peeled off, so it is unlikely that the positive electrode will be directly applied to the part of the photoreceptor. In this case, all the positive charges cannot be removed and will remain. On the other hand, 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.
Among the carriers generated in the charge generation layer by light irradiation,
It has the property of allowing holes to pass through, but not electrons. From this, when a negative organic photoconductor is charged to the DE polarity, the positive charge cannot be removed by light irradiation. For this reason, the positively charged gaps between each sheet of paper on the photoreceptor are not completely neutralized and reach the next charging process with positive charges, especially for continuous copying. Sometimes, by repeating such operations, the residual seiden tsukuda in the gap area gradually increases, and gradually the keiden device =! Even with IV voltage, it is no longer possible to raise the desired surface potential, and this is the cause of fogging during the next copy. Having considered the above-mentioned causes, an embodiment of the present invention will now be described with reference to FIGS. FIG. 1 is a schematic explanatory diagram showing a part of a laser printer that is an image forming apparatus, in which 10 is a photoreceptor that is an image support, a drum-shaped conductive support 11, and this R conductive support. A negative organic photoconductor 12 in which a charge generation layer 12a and a charge transport layer 12b are sequentially laminated so as to be supported by a body 11.
have

【,ing. The electromotive force generation layer 12a is made by mixing an azo pigment represented by the formula (1st formula) and phenoxy, which is a binder resin and represented by the formula (2nd formula). 1・1・2-
1-Licro0. The conductive support 11 is immersed in a liquid dissolved in a J-tan solvent and dried to form the conductive support 11. Next, the charge transport layer 12b is formed by mixing hydrazone represented by Formula 1... (Formula 3) with phenoxy represented by Formula 2, and dissolving them in a cyclohexane solvent. The conductive support 11 having the generation layer 12a is soaked and dried for 14 hours. Further, each image forming means 13 is provided around the photoreceptor 10. This image forming means 13 includes: a charging device w14 to which a voltage of -6 [kV] is applied, a cod light device ff117 that emits image information from an original (not shown), etc., and a magnet roller 18a with a voltage of -450 [kV]. A developing device ig having negative polarity toner 18b to which a developing bias of V] is applied, is a transfer device provided in a transfer section, and is powered by +5K (V) by a first power source 20.
transfer charger 2 to which a voltage of is applied and generates a positive charge;
1. A peeling device provided in the peeling section, and a switch 22
Therefore, the first AC @g23a applies +4K[ν], which is an AC voltage of -th], and the second AC voltage, which is +6, which is 15 [times] the applied voltage of the AC power supply 23a of ]th.
It is equipped with a peeling charger 24 to which any of the second AC power supplies 2313 that apply K (V), a cleaning device [2G], and a static elimination lamp 27 are provided. Next, we will discuss the effect. When copying starts, the photoreceptor 10 is rotated in the direction of arrow X, and the photoreceptor 10 is rotated accordingly.
is uniformly charged to about -050 EV) by the charging device 14. Next, an image portion of the photoreceptor 10 is irradiated with light by an exposure device 17 to form an electrostatic latent image. Thereafter, a toner of negative polarity is applied 9#j to the image portion of the photoreceptor 10 irradiated with light by the developing device 18, and a toner image is formed by reversal development. Next, the photoreceptor IO reaches the transfer section, and in synchronization with this I-color image, sheet 1-paper (not shown), which is an image carrier, is also fed to the transfer section. 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 primary sheet (not shown) to be electrostatically attracted and transferred reaches the peeling charger 24, but at this time the switch 22 is activated as shown by the solid line in FIG. The peeling charger 24 is controlled by a control device (not shown) that controls the image forming device, such as the image forming means 13, and is connected to the first AC power source 23a. : By applying voltage through 3a, an alternating current charge is applied to the photoreceptor 10 and the sheet paper, and the sheet paper is peeled off.After this, the sheet paper is placed in a fixing bag [(not shown) After the residual toner is removed from the photoreceptor 10 by the cleaning device 26 (C), the charge is removed by the charge removal lamp 27 and the copy image is made ready for the first copy. The transfer charger 21 continues to operate even after the preceding sheet has passed, and the transfer charger 21 continues to operate until the next sheet arrives. A positive charge is applied, and a portion 10a of the photoreceptor 10 is charged with positive polarity in a band shape as shown in FIG. In the stripping charger 24, the switch 22 is connected to the second AC power source 23b by a control device (not shown) as shown by the dotted line in FIG. Approximately twice as much alternating current charge as that of peeling is applied to the positively charged portion (Oa), which neutralizes and removes the positive charge on the photoreceptor.Then, the next sheet of paper is When reaching the peeling charger 24, the switch 22 is again connected to the AC power supply 23.l side of node 1, and the sheet paper is peeled off.When copies were repeatedly made in this manner, the amount of 40K [
Even with a single sheet of paper, there was no band-like fogging or density unevenness that had conventionally occurred, and deterioration in image quality due to fogging was prevented, and both excellent images could be obtained. If the configuration described above is used, continuous copying is performed by the photoreceptor 10 made of the negative Mifl organic photoconductor 12, and a portion 10 of the photoreceptor 10 is made by the transfer charger 21.
Even if a is positively charged, the peeling charger 24 applies an alternating current charge approximately twice that of the peeling to that part, and the positive charge on the photoreceptor 10 is transferred to the peeling charger 24. Since all of the photoreceptor 10 is neutralized and removed at the next charging time, the entire surface of the photoreceptor 10 will be charged to a desired surface potential in a --like manner. Therefore, it is possible to eliminate the band-like fog and m degree unevenness that conventionally occur due to the inability to obtain a desired surface potential during charging, and it is possible to obtain good images over a long period of time. Note that the present invention is not limited to the above embodiments. Although the magnitude of the power supply applied to the transfer device or the stripping device is arbitrary, the magnitude of the second AC voltage for removing positive charges in the stripping device is at least 1. It is desirable to set it to 2 [times] or more. The power supply applied to the peeling device may be switched arbitrarily, such as in response to a signal from a switch that detects the position of the image carrier in the conveyance path, or a variable power supply may be used to change the power supply voltage &sl.
You can also use J. Furthermore, the material of the organic photoconductor is also optional. [Effects of the Invention] As detailed above, according to the present invention, even if the image forming process is performed continuously using a negative polarity organic photoconductor suitable for color copying machines, laser printers, etc. A part of the negative organic photoconductor remains positively charged 1
Since the next image forming step is not performed and all positive charges are removed before the start of the next charging step, the organic photoconductor is uniformly coated with the desired charge during the following step 11): It is possible to obtain a surface potential, eliminate band-like fog and density unevenness that conventionally occur, and obtain clear and good images.

[Brief explanation of drawings]

1 to 3 show an embodiment of the present invention. FIG. 1 is an a+qii clear view of the surroundings of the 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, I
2... Organic photoconductor, 13... Image forming means. 14... Charging device, 21... Transfer charger, 22
...Switch, 23a...first AC power supply.

Claims (1)

[Claims] An image forming apparatus comprising an image support having a negative organic photoconductor on a conductive support, and an image forming means for forming an image on the image support, the image forming means comprising:
a transfer device that faces the image support and applies a positive charge at least in the transfer section;
An alternating current voltage is applied, while a second alternating current voltage larger than the first alternating voltage is applied when the image carrier does not pass, thereby imparting at least two different types of alternating current charges to the image support. An image forming apparatus comprising: a peeling device.