JPH0348269A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent the offset of a photosensitive drum and irregularities in an image by providing corona electrifiers imparting charges with the same polarity as that of toner transferred onto a transfer material before a toner image of plural colors is further transferred. CONSTITUTION:The corona electrifiers 16 and 17 for imparting charges with the same polarity as that of the toner transferred onto the transfer material P before a toner image of plural colors is further transferred are provided on the moving path for the transfer material P. A voltage obtained by superimposing an AC voltage on a DC voltage with the same polarity as that of the toner on the transfer material P is applied to the outside electrifier 16, and an AC voltage is applied to the inside electrifier 17 using as the opposite pole to the outside electrifier 16. Then, charges with the same polarity as that of the toner are imparted to the toner on the transfer material P by corona discharge. Thus, toner offset from a previously transferred color tone image to an image carrier and irregularities in an image can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION In the present invention, a transfer material carried on a transfer material carrier is placed facing an image carrier, and an electric field is applied by a transfer means such as a corona charger to transfer the transfer material onto the image carrier. Regarding an image forming device or device equipped with a transfer device that transfers a formed toner image onto a transfer material, in particular, a plurality of color toner images sequentially formed on an image carrier are transferred onto a transfer material in a superimposed manner. This relates to a color image forming device equipped with a transfer device. In color image forming apparatuses, various transfer devices have been proposed that apply an electric field to transfer toner images of multiple colors onto the same transfer material in a layered manner. FIG. 4 is a schematic diagram showing an example of a conventional color image forming apparatus. The image forming apparatus basically includes a photosensitive drum 1, a mobile developing device 4, a transfer device 30, and a fixing device (not shown). In this image forming apparatus, a primary charger 2 uniformly charges a photosensitive drum l as an image carrier rotating in the direction of an arrow a, and an exposure means such as a laser beam exposure device generates an optical image according to image information. 3, an electrostatic latent image is formed on the photosensitive drum L. The mobile developing device 4 includes a magenta developing device 4M, a cyan developing device 4C, a yellow developing device 4Y, and a black developing device 4B. The electrostatic latent image on the photosensitive drum L is developed and visualized as a toner image. In this image forming apparatus, the transfer device 30 is drum-shaped, and has a transfer material carrier 32 made of a dielectric sheet on its surface. The transfer material P is supplied to the transfer material carrier 32 in synchronization with the toner image formed on the photosensitive drum 1 by the registration roller 6, and the supplied transfer material P is gripped by a gripper (not shown) or the like. The transfer material is supported on a transfer material support 32. The transferred material P is transported by the transfer material carrier 32 to a transfer area facing the photosensitive drum l, where a transfer electric field is applied by the transfer charger 15 to the back surface of the carrier 32. The toner image on the photosensitive drum 1 is transferred onto the transfer material P by applying an electric charge having a polarity opposite to that of the toner on the photosensitive drum 1. As described above, the transfer is repeated each time each of the toner images of multiple colors is formed on the photosensitive drum L, and when the transfer of the multiple color toner images superimposed onto the transfer material P is completed, the transfer is completed. The material P is peeled off from the transfer material carrier 32 by the action of the peeling charger 54 and the separating claw 4°2. After the residual toner on the surface of the photosensitive drum 1 is cleaned by the cleaning device N20, it is repeatedly subjected to the above-described image forming process, and the surface of the transfer material carrier 32 is also cleaned by the cleaning device 2l. Similarly, it is repeatedly subjected to the image formation process. By the way, in the conventional image forming apparatus described above, the transfer electric field received from the transfer charger l5 when the first color toner image is transferred by the transfer device 30 causes the transfer material carrier 32 made of a dielectric sheet and its The upper transfer material P is charged. Therefore, when transferring the second color toner image onto the transfer material P, the transfer electric field applied by the transfer charger l5 is
Affected by the electrical charge during the transfer of the color, the charge on the back surface of the transfer material carrier 32 due to the transfer electric field of the second color decreases, and the holding power of the first color toner image on the transfer material P weakens. As a result, when transferring the second color toner image, a phenomenon occurs in which toner particles are offset from the first color toner image onto the photosensitive drum L, or the toner image is disturbed on the transfer material P. Something happened. Therefore, in order to prevent this phenomenon, for example,
In No. 3-1026, a corona charger is installed close to the moving path of the transfer material, and each time a toner image of each color is transferred, a corona discharge is performed to charge the toner constituting the toner image on the transfer material. Countermeasures are being taken to deal with this by neutralizing or reducing the charge. However, in the above method, since the amount of charge held by the toner on the transfer material P is reduced, the holding power of the toner on the transfer material P is weakened, and as a result, the purpose is not achieved. (On the contrary, the amount of toner offset from the toner image on the transfer material to the photosensitive drum increased, and the toner image on the transfer material was further disturbed. Therefore, in view of the above-mentioned current situation, it is an object of the present invention to transfer each toner image of a plurality of color toner images sequentially formed on an image bearing member such as a photosensitive drum onto a transfer material in order by using a transfer device. When transferring the toner image of the color to be transferred later, such as the toner image of the second color, to the toner image of the first color,
To provide an image forming device capable of performing image formation well without causing offset of toner from a previously transferred color toner image onto a photosensitive drum or causing image disturbance of the toner image. It is. The above object is achieved by an image forming apparatus according to the present invention. To summarize, the present invention sequentially forms toner images of a plurality of colors on the same or separate image carriers by applying an electric field onto a transfer material carried on a transfer material carrier, thereby superimposing them one after another. In an image forming apparatus equipped with a transfer device for transferring, after transferring each of the toner images of the plurality of colors onto the transfer material and before transferring each toner image following the toner image of the plurality of colors, the The image forming apparatus is characterized in that a corona charger is installed on the moving path of the transfer material for imparting an electric charge of the same polarity as the toner to the toner image transferred onto the transfer surface. According to the eighteenth aspect of the present invention, the corona charger is placed on the opposite side of the corona charger across the transfer material carrier. ? An opposite pole of the corona charger is provided, which is composed of an F electric charger and another corona charger. Example 31 Below, embodiments of the present invention will be described in detail. FIG. 1 is a schematic diagram showing an embodiment of the image forming apparatus of the present invention. The image forming apparatus of the present invention basically consists of a photosensitive drum l, a mobile developing device 4, a transfer device 30, and a fixing device (not shown) as shown in FIG. l6 and medial? i'F? This image forming apparatus differs greatly from the conventional image forming apparatus shown in FIG. 4 in that it further includes a li device 17. In this image device, a primary charger 2 uniformly charges a photosensitive drum l as an image carrier rotating in the direction of an arrow a, and an exposure means such as a laser beam exposure device generates an optical image according to image information. 3 is irradiated and static electricity is generated on the photosensitive drum 1? ! An image is formed. The electrostatic latent image is a mobile image ftma! 4 and is visualized as a toner image on the photosensitive drum 1. The mobile developing device 4 includes a magenta developing device 4M, a cyan developing device 4C, a yellow developing device 4Y, and a black developing device 4B, and a guide that holds these four developing devices and moves in the horizontal direction (Fig. (not shown). The mobile developing device 4 transports a developing device of a color corresponding to the electrostatic charge am on the photosensitive drum 1 to a developing position facing the photosensitive drum 1, and there, adheres toner to the electrostatic WI image on the photosensitive drum 1. Develop. The transfer device 30 is drum-shaped and includes a transfer material carrier 32 made of a dielectric sheet on its surface. The transfer material P is supplied to the transfer material carrier 3z by the registration roller 6 in synchronization with the toner image formed on the photosensitive drum 1. In this embodiment, the supplied transfer material P is electrostatically In order to hold the image on the carrier 32, the transfer device 1i30 is equipped with an adsorption charger 5l consisting of a corona charger instead of a gripper.
and a conductive roller 52. The adsorption charger 5l is installed inside the transfer material carrier 32. The attraction charger 5l functions to attract the transfer material P to the transfer material carrier 32 and cause it to be electrostatically attracted thereto. The conductive roller 52 is installed outside the transfer material carrier 32 on the side opposite to the attraction charger 5l and is grounded. The conductive roller 52 serves as a pole opposite to the attraction charger 51, and also functions to inject charges into the transfer material P so that the transfer material P is electrostatically attracted onto the transfer material carrier 32. When the electrostatic attraction of the transfer material P to the transfer material carrier 32 is completed, the conductive roller 52 is moved away from the transfer material carrier 32 by a clutch (not shown). As described above, the transfer material P electrostatically attracted and supported on the transfer material carrier 32 is transferred to the photosensitive drum by the carrier 32.
It is transported to the transfer area facing the transfer charger l.
The toner image on the photosensitive drum 1 is transferred onto the transfer material P by applying a transfer electric field by applying a transfer electric field to the back surface of the carrier 32 with a charge having a polarity opposite to that of the toner on the photosensitive drum 1. In this way, the transfer material P on which the first color toner image, for example, the magenta color toner image has been transferred, is conveyed from the transfer material carrier 32 to the recharging area at the top thereof. According to the present invention, in this recharging area, the transfer material carrier 3
The above-mentioned outer charger l6 is installed on the outside and inside of 2, respectively.
and an inner charger l7. These outer chargers l6
and the inner charger 17 are for recharging the toner on the transfer material P so as to impart charges of the same polarity as the toner, thereby increasing the specific charge amount of the toner. A voltage obtained by superimposing an AC voltage with a DC voltage of the same polarity as the toner on the transfer material P is applied to the outer charger l6, and an AC voltage is applied to the inner charger l7, which also serves as an opposite pole of the outer charger l6. By causing corona discharge, the toner on the transfer material P is charged with the same polarity. Incidentally, in some cases, when it is possible to discharge only with the outer charger 16, the provision of the inner charger 17 can be omitted. As an example, when using negative polarity toner, the outer charger 1
Examples of the AC voltage applied to the inner charger 17, the DC voltage applied to the inner charger 17, and the AC voltage applied to the inner charger 17 are
C voltage: sine wave voltage with effective value 2.5K■, outer charger 1
6 AC voltage: effective value 4. 3KV sine wave voltage, DC voltage of outer charger l6: as shown in Table 1. Note that I in Table 1 indicates that the outer charger 1 is
The effective current value measured on the high voltage output side of the power supply No. 6 is shown. Table 2 shows the specific charge of the negative toner particles used. The transfer material P that has passed through the recharging areas shown in Table 1 and Table 2 and above is again conveyed to the transfer area, where the toner image of the second color formed on the photosensitive drum 1 is transferred. At this time, the specific charge amount of the toner on the transfer material P that has passed through the recharging area is changed by applying charges of the same polarity to the toner by recharging in the outer charger 16 and the inner charger l7. The specific charge amount is larger than the specific charge amount at the time when the transfer of the first color toner image onto the material P is completed. For this reason,
The transfer electric field applied by the transfer charger 15 when transferring the second color toner image onto the transfer material P is affected by the electric charge during the first color transfer, and the transfer due to the second color transfer electric field is affected by the electric charge during the first color transfer. Even if the charge on the back surface of the material carrier 32 decreases, the reduction in the retention force of the first color toner image on the transfer material P is small;
The first color toner image is firmly held on the transfer material P. Therefore, when transferring the second color toner image onto the transfer material P, the toner may be offset from the first color toner image on the transfer material P onto the photosensitive drum 1, or the first color toner image may be disturbed. There is nothing to do. The transfer material P, on which the transfer of the second color toner image has been completed in the same manner as the first color toner image, repeats recharging and transfer up to the fourth color in the same manner in the recharging area and the transfer area. Then, the transfer material P on which the fourth color toner image has been transferred is peeled off from the transfer material carrier 32 by the action of the separation claw 42 while being subjected to AC corona discharge by the separation charger 54 as in the conventional case. The separation claw 42 enters between the transfer material P and the surface of the transfer material carrier 32 by a width in a separation claw guide groove (not shown) provided on a part of the circumferential surface of the transfer material carrier 32. do,
Separate the transfer material P. At the time of this separation, if corona discharge is performed by the outer charger 16 and the inner charger 17 immediately before to remove unnecessary charges from the transfer material P, the toner image on the transfer material P will be disturbed due to the peeling discharge during separation. It is better to use a corona discharge during the measurement as this can prevent the occurrence of The transfer material P separated from the transfer material carrier 32 is conveyed to a fixing device (not shown), where the four-color toner images are fused and fixed onto the transfer material P. A color image is thus obtained on the transfer material P. After the residual toner on the surface of the photosensitive drum 1 is cleaned by the cleaning device R20, it is repeatedly subjected to the above-described image formation process, and the surface of the transfer material carrier 32 is also cleaned by the cleaning device 3l21, and then Similarly, it is repeatedly subjected to the image formation process. Embodiment 2 FIG. 2 is a schematic configuration diagram showing a transfer device in another embodiment of the image forming apparatus of the present invention. This image forming apparatus is
This image forming apparatus differs from the image forming apparatus shown in FIG. 1 in that a conductive roller l8 is provided in place of the inner charger in the transfer device 30, but the other configurations are basically the same. In Fig. 2, the same reference numerals as in Fig. 1 indicate the same members. The conductive roller 18 is provided on the opposite side of the transfer material support 32 from the outer charger 16, similar to the inner charger l7 in FIG. Even with such a configuration, a voltage obtained by superimposing an AC voltage with a DC voltage of the same polarity as the toner on the transfer material P is applied to the outer charger l6, and an AC voltage is applied to the conductive roller 18.
By causing corona discharge, it is possible to impart charges of the same polarity to the toner on the transfer material P, increasing the specific charge amount of the toner, and making it possible to firmly support the toner on the transfer material P. Therefore, it is possible to transfer a toner image of the next color onto the transfer material P without causing an offset of the toner from the toner image of the previously transferred color to the photosensitive drum 1 or causing disturbance of the toner image. Can be done. Also, its structure is simple. Embodiment 3 FIG. 3 is a schematic configuration diagram showing still another embodiment of the image forming apparatus of the present invention. This image forming apparatus uses four photosensitive drums as image carriers.
a. lb. lc and 1d are provided to form a magenta toner image, a cyan toner image, a yellow toner image, and a black toner image, respectively. Photosensitive drum la, lb. lc and ld are arranged in series in the direction of the tree and are primarily charged by primary chargers 2a, 2b, 2c and 2d provided around them, respectively, and the optical images 3a. 3b, 3C and 3d are irradiated to form an electrostatic latent image, which is developed by developing units 4M, 4C, 4Y and 4B,
A magenta toner image, a cyan toner image, a yellow toner image, and a black toner image are formed. The transfer device 1130 of the present image forming apparatus includes a transfer material carrier 32 provided in a horizontal endless orbit below the horizontally arranged photosensitive drums la to 1d. The transfer material P is supplied to the transfer material carrier 32 by a registration roller 6 provided upstream of the transfer material carrier 32 in synchronization with the toner image formed on the photosensitive drum la. The transfer material carrier 32 is electrostatically attracted and supported by an attraction charger 51 and a conductive roller 52 provided on the inner and outer sides thereof. The transfer material P carried on the transfer material carrier 32 is
2 to the transfer area facing the photosensitive drum 1a, where the transfer charger 1 provided inside the carrier 32 is transferred.
By applying a charge of opposite polarity to the toner on the photosensitive drum l to the back surface of the carrier 32 by the transfer electric field at 5a,
The toner image on the photosensitive drum 1 is transferred onto the transfer material P.
In this way, the transfer material P on which the first color toner image, that is, the magenta color toner image has been transferred, is transferred to the transfer material carrier 3.
The outer charger 16a and the inner charger 17 are transported to a recharging area downstream of the photosensitive drum la by 2, and are provided there.
a, the toner on the transfer material P is recharged, and the toner is given an electric charge of the same polarity. This is also A
This is performed by applying a voltage obtained by superimposing a DC voltage of the same polarity as the toner on the transfer material P on the C voltage, and applying an AC voltage to the inner charger 17 provided inside. As a result, the specific charge amount of the toner on the transfer material P increases and it is strongly held on the transfer material P, so that the toner on the next photosensitive drum t
When the second color toner image on b is transferred onto the transfer material P, the toner may be offset from the first color toner image on the transfer material P to the photosensitive drum lb, or the first color toner image may be disturbed. There is nothing to do. As in the case of the first color toner image, the transfer material P is transferred with the second color toner image on the photosensitive drum lb by applying a transfer electric field by the transfer charger 15b.
Recharging with inner chargers 16b and 17b, transfer charger 15
Transfer of the third color toner image onto the photosensitive drum lc by applying a transfer electric field at step c, then the outer and inner chargers 16c,
Recharging at 17C, transfer of the fourth color toner image onto the photosensitive drum ld by applying a transfer electric field at the transfer charger 15d,
Then, recharging is performed using the outer and inner chargers 16d and 17d. In this way, the four-color toner images are transferred onto the transfer material P, and a color image is obtained on the transfer materials P and h by fixing with a fixing device (not shown). AC applied to the outer chargers 16a-16d in this embodiment
Table 3 shows examples of voltages, DC voltages, and AC voltages applied to the inner chargers 17a to 17d. In this embodiment, not only can offset of the toner from the toner image on the transfer material P to the photosensitive drum 1b and disturbance of the image can be prevented, but also because four photosensitive drums la-1d are provided, the image forming process can be improved. This makes it possible to increase the speed. Table 3 As explained above, in the image forming device of the present invention, each toner image of a plurality of colors sequentially formed on an image bearing member such as a photosensitive drum is sequentially transferred onto a transfer material by a transfer device. After each toner image is transferred onto the transfer material and before the next toner image is transferred, the toner image transferred onto the transfer material has the same polarity as that toner. By imparting a charge of The transfer of the toner image can be performed satisfactorily without causing an offset of the toner from the toner image of the previously transferred color onto the image carrier or causing image disturbance of the toner image. Therefore, a color image of good quality can be obtained.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a schematic configuration diagram showing a portion of a transfer device in another embodiment of the image forming apparatus of the present invention. FIG. 3 is a schematic configuration diagram showing still another embodiment of the image forming apparatus of the present invention. FIG. 4 is a schematic configuration diagram showing an example of a conventional image forming apparatus. 1: Photosensitive drum l5: Transfer charger 16: Outer charger 17: Inner charger l8: Conductive roller 30: Transfer device 32: Transfer material carrier 1 Fig. 1654 tl Fig. 2 Fig. 4

Claims (1)

[Claims] 1) Toner images of a plurality of colors sequentially formed on the same or separate image carriers are sequentially superimposed by applying an electric field onto a transfer material carried on a transfer material carrier. In the image forming apparatus equipped with a transfer device that transfers the toner image using a plurality of colors, after transferring each of the toner images of the plurality of colors onto the transfer material and before transferring each of the toner images subsequent to the toner image of the plurality of colors, An image forming apparatus characterized in that a corona charger for applying an electric charge of the same polarity as the toner to the toner image transferred onto the transfer material is installed on a moving path of the transfer material. 2) The image forming apparatus according to claim 1, further comprising an opposing pole of the corona charger including the corona charger and another corona charger provided on the opposite side of the corona charger with the transfer material carrier in between.