JPH0365974A - Image forming device - Google Patents

Abstract

PURPOSE:To surely prevent electrostatic offset in a fixing part by electrically connecting an electrode plate disposed on a primary electrostatic charger with a carrier which is insulated from other member and impressing a bias voltage having an opposite polarity to toner. CONSTITUTION:The carrier 6 is insulated from other member and the electrode plate 9 disposed on the primary electrostatic charger 8 is electrically connected to the carrier 6 to provide a means 12 for impressing the bias voltage having the opposite polarity to the toner. The electrode plate 9 receives a discharging current from an electrostatic charging wire W and conducts the voltage to the carrier 6. Thus, the electrostatic offset is prevented. By setting the length of the electrode plate longer than an image area, uniform discharging is executed in the image area, so that the unevenness of electrostatic charging is not caused.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Object of the Invention (Field of Industrial Application) The present invention relates to an image forming apparatus using an electrostatic transfer process, such as an electrostatic copying machine and a printer thereof.

(American technology and problems to be solved) In the well-known image forming apparatus as described above, after a charged toner is attached to the surface of an image carrier charged to a predetermined polarity to form a toner image, a toner image is formed at a transfer site. A transfer material such as paper is brought into contact with this toner image, and a bias voltage for transfer is applied at this position, and the toner image on the image carrier side is electrostatically transferred to the transfer material by the action of the electric field formed. After that, in order to separate the transfer material that tends to be attracted to the surface of the image carrier, a bias voltage of opposite polarity to that during transfer is applied to the transfer material to neutralize the charge acquired by the transfer material during transfer. A device configured to remove and separate static electricity is widely used.

In an image forming process such as this, the electrostatic adhesion of the toner to the transfer material is inevitably weakened depending on the polarity of the bias voltage applied during separation.

This transfer material, which electrostatically carries the toner image, is then supplied to the nip portion of a pair of rollers of a fixing device, which usually includes a pair of rollers that are in pressure contact with each other, and is subjected to heat and pressure to perform fixing. However, as mentioned above, because the electrostatic adhesion of the toner image to the transfer material is weakened, some of the toner is attracted to the fixing roller, causing electrostatic offset, which causes the transfer There was a risk of contaminating the material and the fixing roller.

In order to avoid such inconveniences, the conveying device between the transfer site and the fixing site is insulated from other parts, and a transfer charger is installed on the transfer material so that the charge polarity is opposite to that of the toner image. Alternatively, a method has been proposed in which a bias voltage is applied by an electrode provided in the primary charger to strengthen the adsorption effect of the toner image onto the transfer material.

However, in general, the transfer charger is located below the image forming area including the image carrier, and is often located below the developing device, and furthermore, the electric field is formed in the direction that attracts the toner. Therefore, scattered toner within the apparatus is easily captured, and toner supplied from the developing device to the latent image on the image bearing member is also attracted, which may promote contamination within the apparatus. Naturally, this will also contaminate the electrodes in the charger, and the bias voltage may become insufficient, making it difficult to obtain the desired effect.

- By providing the above-mentioned electrodes on the charger,
Although it is conceivable that the above-mentioned drawbacks can be avoided, no specific configuration for realizing the above has been proposed so far, and the problem has remained virtually unsolved.

The present invention has been made in view of the above-mentioned current situation, and it insulates the transport system from other parts, applies a bias to the system by means of an electrode disposed in a negative charger, and By making it possible to clean the image bearing member, it is possible to reliably prevent electrostatic offset at the fixing site and to always perform stable and good fixing, and by arranging the electrode outside the image area, uneven charging of the image carrier can be prevented. It is an object of the present invention to provide an image forming apparatus that can also prevent the occurrence of.

(2) Structure of the invention (technical means for solving the problem, its effect) In order to achieve the above object, the present invention provides a method for uniformly charging the surface of an image carrier with a charger, and then charging the surface of the charged surface. In an image forming apparatus configured to form a toner image on a surface, transfer the toner image onto a transfer material, and then transport the transfer material to a fixing site via a transport device, the transport device is insulated from other members. Further, means is provided for electrically connecting the electrode plate disposed in the negative charger and the conveying device to apply a bias voltage having a polarity opposite to that of the toner forming a toner image to the device. This is a characteristic feature.

With this configuration, it is possible to strengthen the adhesion of the toner image to the transfer material, especially after the conveyance site, and prevent electrostatic offset.

(Explanation of Examples) FIG.

In the case of the illustrated device, the surface photosensitive layer of the photoreceptor 1, which has an axis perpendicular to the plane of the paper and rotates in the direction of the arrow, is negatively charged by a negative charger 8, and is provided with an image signal applying means. 10 projects an optical image to form an electrostatic latent image.

It is assumed that positively charged toner is supplied to this latent image by the developing device 2 to form a toner image, and as the photoreceptor 1 rotates, the toner image is transferred between the photoreceptor 1 and the transfer charger 4. When the transfer material (not shown) is conveyed from the conveyance path 3 to the transfer site in synchronization with the toner image, the toner and A bias voltage of opposite polarity, in this case negative polarity, is applied, and the toner image is transferred from the photoreceptor to the transfer material.

Since the transfer material tends to be attracted to the photoreceptor due to the application of the transfer bias, a separation charger 5 is provided downstream of the transfer charger 4 when viewed from the direction in which the photoreceptor travels, and thereby the transfer material is attracted to the photoreceptor. By applying a polar bias voltage, the transfer material is separated from the photoreceptor by neutralizing and eliminating the charge that the transfer material has acquired during transfer.
This transfer material is then transported to a fixing device 7 via a transport device 6.

The fixing device 7 has a heating roller 7a equipped with an appropriate heater 7b inside, and a pressure roller 7C in pressure contact with the heating roller 7a, and the toner image on the transfer material supplied to the pressure nip N is Here, it is assumed that after being heated and pressurized to be fixed and fixed on the transfer material, it is discharged from the apparatus.

Although not shown in the figure, a cleaner for removing residual toner remaining on the surface of the photoreceptor 1 without contributing to the transfer at the transfer site, and a pre-discharge means for removing residual electric charge are provided around the photoreceptor i. Of course there is.

As shown in a schematic side view in FIG. 6 and a plan view in FIG. 7, the conveying device includes a plurality of semi-conductive belts ( In the illustrated case, it consists of two belt supporting members 6a, 6a, and a belt supporting member 6b made of a conductive member.

In addition to the above-described configuration, the illustrated cylindrical device has -
An electrode plate is disposed on the shield plate of the charger 8 so as to be electrically insulated from the shield plate, and the electrode plate 9 and the conveyor belt 6a of the conveyor device, which is insulated from each part inside the image forming apparatus, are electrically connected. It is connected to.

With such a configuration, the support member 6
A voltage of opposite polarity to that of the toner is applied to b. As a result, charges of opposite polarity to the toner (in this case, negative charges) are injected onto the back side of the transfer material moving through the conveying device, and the toner enters the fixing device 7 while being strongly attracted to the transfer material, so that during fixing. The electrostatic offset of the fixing roller is reduced, and even if a simple mechanism such as a felt pad is used as a cleaner for the fixing roller, sufficient cleaning can be carried out over a long period of time.

FIG. 1 is a perspective view showing the configuration of the charger 8 described above,
A charging wire W extends inside a shield plate 8a whose both ends are supported by insulating support frames Fl and F2.

An insulating electrode holder 11 is attached to one side of the shield plate, and an electrode plate 9 is attached to this, and a conductor 12 connected to the electrode plate 9 attaches the charger 8 to a predetermined position in the image forming apparatus. At this time, the electrode plate 9 is connected to a transport device and a bias voltage is applied thereto.

As shown in the figure, when the electrode plate 9 is in the mounting position,
It is assumed that the image area is located inside both ends A and B of the electrode plate.

By arranging such a charger, the electrode plate 9 receives the discharge current from the charging wire and guides the voltage to the conveying device 6, thereby preventing electrostatic offset as described above. By setting the length of the plate as described above, -like discharge occurs within the image area, so that uneven charging does not occur.

FIG. 2 shows another embodiment of the primary charger, in which parts corresponding to those of the charger described above are designated by the same reference numerals, and a description thereof will be omitted.

In this charger, two electrode plates 9a and 9b, which are electrically connected by a conductive wire 17a, are placed on one surface of a shield plate 8a at a position outside one image area, and are connected to an insulating support member 11a.
, llb.

It is easy to understand that a device having such a configuration has the same effect as the charger described above.

FIG. 3 shows an embodiment including a member for cleaning an electrode plate that applies a bias voltage to the conveyance device, and this device also has the basic configuration as a charger as shown in FIG. 1 above. Corresponding parts are indicated by the same reference numerals.

The figure is a plan view of the charger, and it is assumed that the charger is inserted into and removed from the image forming apparatus by moving vertically in the figure. An electrode plate 9 is attached to the inside of one surface of the shield case 8a of the charger, and a terminal 12 for applying a voltage to a transport device (not shown) is provided.

A long hole 25 is formed in the bottom of the shield plate 8a in the longitudinal direction for insertion into and removal from the image forming apparatus (in the direction of movement). The front end portion is formed into a wide portion 25a via a tapered portion.

A cleaner 24 that is elastically deformed in a direction away from the electrode plate 8 under normal conditions is disposed on the front side of the image forming apparatus main body. When installed, the cleaner 24 is in the position shown by the dotted line in FIG. 3, and at this time the cleaner 24 does not come into contact with the electrode plate 9, as shown in FIG.

When the charger is displaced downward in the figure in order to be inserted into and removed from the image forming apparatus, the cleaner 24 resists its elasticity and reaches the narrow part of the elongated hole 25 through the tapered portion, and at this position, the cleaner 24 As shown in FIG. 5, the cleaner 24 is displaced in the direction of the electrode plate 9 and comes into contact with it, and as the charger moves, the cleaner 24 rubs and cleans the electrode plate 9.

In the illustrated device, a cleaner for the charging wire W is also provided, and this cleaner is formed at the bottom of the shield plate parallel to the wire W, and is fitted into an elongated hole 23 having a wide portion 23a at the end. Due to their own elasticity, they are separated from each other when they are in the wide part of the elongated hole (see Figure 4), and come into contact with each other when they are in other parts (see Figure 5). , a pair of liners 22 and 22 sandwiching the wire W therebetween.

It will be easily understood that the cleaner configured in this manner can clean the charging wire W when the charger 8 is inserted into and removed from the image forming apparatus.

Note that, as described above, the cleaner 24 is provided on the image forming apparatus side.
Even if the cleaner pair 22 and 22 are fixedly installed, for example, a through space Σ may be formed at the end of the charger shown in FIG. Therefore, there is no particular problem in inserting and removing the charger into the image forming apparatus.

(3) As described in detail of the invention, according to the present invention, the electrode plate disposed on the shield plate of the charger and the transfer material carrying the toner image are conveyed and are insulated from other members. By electrically connecting the conveyance device and applying a bias of opposite polarity to the toner carried by the transfer material during conveyance, it is possible to strengthen the adsorption effect of the toner image onto the transfer material. It is possible to obtain a high quality image by preventing the occurrence of electrostatic offset at Since the electrode plate can be cleaned by the cleaner, a predetermined bias can be constantly applied to the conveying device, so that the above-mentioned effects can be stably obtained over a long period of time.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing an embodiment of a charger according to the present invention, FIG. 2 is a perspective view of a charger showing another embodiment, FIG. 3 is a plan view showing still another embodiment, and FIG. is Fig. 3 D-D
FIG. 6 is a schematic side view of an image forming apparatus to which the present invention is applied, and FIG. 7 is a plan view of the same conveying device. l... Photoreceptor, 4... Transfer charger, 5... Separation charger, 6... Conveyance device, 7... Fixing device, 8a...
・-Charger, 8... Shield plate, 9... Electrode plate,
22.25...Cleaner. Figure 5 is a cross-sectional view taken along line E-E in Figure 3.

Claims (4)

[Claims] (1) After uniformly charging the surface of the image carrier with a primary charger, a toner image is formed on the charged surface, this toner image is transferred to a transfer material, and then the transfer material is fixed via a conveyance device. In an image forming apparatus configured to be transported to a site, the transport device is insulated from other members, and an electrode plate disposed on the primary charger and the transport device are electrically connected to the image forming device. An image forming apparatus that is provided with means for applying a bias voltage having a polarity opposite to that of toner forming a toner image. (2) The image forming apparatus according to claim 1, wherein both ends of the electrode plate disposed on the primary charger are outside the image area. (3) The image forming apparatus according to claim 1, wherein the electrode plate disposed on the primary charger is located outside the image area. (4) The image forming apparatus according to any one of claims 1 to 3, further comprising means for cleaning an electrode plate disposed on the primary charger.