JPH0310107B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an image forming apparatus, in particular, a method of bringing a transfer material into contact with an image carrier, and irradiating the transfer material at this contact position with a corona flow by a corona discharge means, thereby transferring the transfer material from the image carrier to the transfer material. The present invention relates to an image forming apparatus equipped with a transfer device that transfers an image.

In this type of image forming apparatus, the first
As shown in Figure a, corona charges C adhere to the lower surface of the transfer material 12. After the transfer, the corona charge C in the image-transferred area Ea is neutralized with the toner charge T, as shown in FIG. remain on top. Due to the influence of this residual corona charge C', if the transfer material is bent while moving from the transfer position to the fixing position (not shown), or if the transfer material comes into contact with another member, a change in the electric field will occur, causing the transfer. A phenomenon occurred in which the image on the material was disturbed, and especially at low humidity, a polka dot pattern appeared in the image due to the above-mentioned phenomenon. .

Therefore, conventionally, after transfer, a charge eliminating needle serving as needle-shaped charge eliminating means is provided opposite to the transfer material immediately after being separated from the image carrier, and residual corona charge C' on the image carrier is eliminated through the charge eliminating needle. JP-A No. 52-125331, Utility Model Application No. 56-23955, etc.). However, due to the shape of the needle-like static eliminator, the discharge tends to become unstable.
The absolute amount of discharge due to only the needle-shaped static eliminating means is also small. Therefore, in order to perform stable discharge, it is necessary to receive some transfer corona discharge current. That is, in order to increase the static elimination efficiency and prevent image disturbance, it is necessary to provide the static elimination needle close to the transfer corona charger which is the corona discharge means.

However, when the static eliminator is installed close to the transfer corona charger, the corona flow from the transfer corona charger during transfer not only flows onto the transfer material and through it to the image carrier, but also flows to the static eliminator described above. A considerable amount flows. The corona flow flowing to the static eliminator needle varies greatly depending on, for example, environmental changes such as humidity (FIG. 2) and the height of the wire from the bottom of the charger (FIG. 3). Therefore, as is clear from the second and third figures, when a large amount of corona flow flows toward the static elimination needle, such as when the humidity is low or the wire height is high, the corona flow acting on the image carrier decreases. As a result, the transfer effect deteriorated, and there were drawbacks such as deterioration of halftones and unevenness in transferred images.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus which eliminates the above-mentioned drawbacks and can improve the efficiency of charge removal by a charge removal means and stably obtain a high-quality transferred image.

That is, the present invention provides an image forming apparatus in which an image is obtained by transferring a toner image formed on an image bearing member to a transfer material by means of a corona discharge means, in which the corona discharge means is arranged to face the transfer material after transfer. Immediately after the means, a needle-like static eliminating means having a discharge tip is provided at a position receiving the corona discharge current of the corona discharge means,
This image forming apparatus is characterized in that an alternating bias voltage is applied to the needle-like static eliminator.

The drawings will be explained below. FIG. 4 is a schematic diagram of an apparatus according to an embodiment of the present invention. This example device was first proposed by the applicant and was developed using an electrophotographic method (Japanese Patent Publication No.
23910)). 1
1 is a drum-shaped photoreceptor as an image carrier, in which a photoreceptor whose basic components are a conductive support, a photoconductive layer, and an insulating layer is formed on the drum circumferential surface;
It is rotatably supported by a machine frame (not shown) in the direction of the arrow. Around this drum-shaped photoreceptor 1, there are 1
Next charger 2, image exposure optical system 3, simultaneous exposure charger 4, full-surface exposure lamp 5, developer 6, transfer charger 7, cleaning blade 8, pre-exposure lamp 9,
Each electrophotographic process device of the static eliminator 10 is arranged. 11 is a register roller that feeds the transfer material 12 between the drum-shaped photoreceptor 1 and the transfer charger 7 via the guide plate 14, and 13 is a register roller (not shown) for fixing the transfer material 12 separated from the drum-shaped photoreceptor 1 after transfer. Conveyance roller 15 conveys to the device, transfer charger 7
This is a static eliminating needle which is a needle-like static eliminating means and has a discharging tip facing the transfer member 12 at a position immediately after the transfer. A plurality of discharging tips of the static eliminating needles are lined up in a direction perpendicular to the transfer direction of the transfer material, that is, in a direction perpendicular to the plane of the paper in FIG.

An alternating current power source 16 is connected to apply an alternating current bias, which is an alternating bias voltage, to the static eliminating needle 15. This AC bias is applied to the transfer charger 7.
In order to suppress the corona flow from the transfer charger 7, a direct current component having the same polarity as the applied voltage of the transfer charger 7 is included.

FIG. 5 shows a waveform diagram of the alternating current bias applied to the static eliminating needle 15. Between t ₀ and t ₁ , a voltage with the same polarity as the transfer corona is applied, so the corona flow from the transfer charger 7 is Almost no electricity flows into the static eliminating needle 15. Furthermore, since a voltage with a polarity opposite to that of the corona charge is applied between t ₂ and _{t 3} , the corona flow from the transfer charger 7 flows into the static elimination needle 15 , which improves the static elimination efficiency of the residual corona charge existing on the transfer material. increases. By repeating this cycle, the flow of corona from the transfer charger 7 to the static elimination needle 15 is suppressed as a whole, and a stable corona is efficiently applied to the transfer material. Static elimination needle 1
5 faces the transfer material 12 at a position immediately after transfer, so the residual corona charge on the transfer member 12
Static charge of C′ can be efficiently eliminated.

Residual corona charge on the transfer material due to the above static elimination needle 15
Static elimination of C' is a discharge phenomenon due to the concentration of a non-uniform electric field between the tip of the static eliminating needle and the residual charge. Therefore, in terms of time, static electricity is removed in a pulsed manner in a limited area of the transfer material 12, and even if static electricity is not removed between t ₀ and _{t 1} , the period between t ₀ and _{t 1} is fixed relative to the process speed. There is no problem if you keep it short enough.

Further, between t ₂ and t ₃ , the corona flow from the transfer charger 7 tends to flow into the static elimination needle 15, but the transfer area is approximately 10 mm, and furthermore, the transfer performance is less time dependent in the case of a dry type. , the effective corona flow is t ₀ ~
If it reaches the transfer material 12 during _t1 , the transfer can be completed within that time. That is, the time it takes the transfer material 12 to pass through the transfer area (for example, the transfer area is 10 mm, the process speed is 250
There is no problem as long as the period of the AC bias is sufficiently small compared to 10/250=1/25 sec (mm/sec). Therefore, it is desirable that the frequency of the AC bias be higher, and it may be set to 50 Hz or higher. Further, at this time, the peak-to-peak voltage of the AC bias is preferably set to 3 KV or more in order to improve transfer efficiency and static elimination efficiency.

FIG. 6 shows another embodiment, in which an insulator 17 is provided between the transfer charger 7 and the static elimination needle 15. In this example, from the transfer charger 7 to the static elimination needle 15
The corona flow flowing to the insulator 17 is suppressed by the above-mentioned alternating current bias application and also by the insulator 17. Therefore, the corona flow from the transfer charger 7 effectively acts on the transfer material 12, and transfer is performed efficiently.

In short, the present invention provides that the static eliminating means is disposed at a position immediately after the corona discharging means and receives the corona discharge current of the corona discharging means so as to face the transfer material after transfer; A transfer corona discharge current that flows into the static elimination means from the corona discharge means side is generated by combining the following three configuration conditions: the needle-shaped static elimination means has a needle-shaped static elimination means, and the alternating bias voltage is applied to the needle-shaped static elimination means. is controlled to prevent a decrease in transfer efficiency, and the charge held by the transfer material after passing through the transfer section is also reliably removed, thereby preventing the occurrence of toner image disturbance due to residual charge.

The acicular static eliminator 15 of the present invention requires stable discharge in order to achieve its effect, but as described above, the acicular static eliminator tends to cause unstable discharge. Therefore, in order to perform stable discharge, the acicular static eliminator must receive some amount of transfer corona discharge current, and in the present invention, the acicular static eliminator is placed immediately after the transfer corona discharge means, and By applying an alternating bias voltage to the needle-like static eliminator,
This controls the amount of corona discharge current flowing into the needle-like static eliminator. .

As described above, the present invention applies an alternating bias voltage to the static eliminating needle, which is a needle-like static eliminating means having a discharge tip, to control the flow of the corona flow from the transfer charger to the static eliminating needle. Even if the transfer charger is placed close to the transfer charger, the above-mentioned corona flow acts stably on the transfer material and the image carrier, and transfer is performed efficiently. In addition, there are effects such as the ability to efficiently eliminate residual corona charges on the transfer material using the static elimination needle.

The image carrier may be a flat photoreceptor or an endless photoreceptor in addition to the drum-shaped photoreceptor shown in the drawing.

Further, in the above embodiment, an AC bias containing a DC component is applied to the needle-like static eliminator, but the present invention is not limited to this, and it is of course possible to apply an AC bias that does not include a DC component.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the generation of residual corona charge on the bottom surface of the transfer material, Figure 2 is a characteristic diagram of humidity versus current to the static elimination needle, and Figure 3 is the current to the static elimination needle versus wire height from the bottom of the transfer charger. FIG. 4 is a schematic diagram of an image forming apparatus according to one embodiment, FIG. 5 is a waveform diagram of an AC bias applied to a static eliminating needle, and FIG. 6 is a diagram of another embodiment. C is a corona charge, C' is a residual corona charge, T is a toner charge, 1 is a drum-shaped photoreceptor, 7 is a transfer charger, 12 is a transfer material, 15 is a static elimination needle, and 16 is an AC power source.

Claims (1)

[Scope of Claims] 1. In an image forming apparatus that obtains an image by transferring a toner image formed on an image carrier to a transfer material by a corona discharge means, An image forming apparatus characterized in that a needle-like static eliminator having a discharge tip is provided at a position immediately after the corona discharge means to receive the corona discharge current of the corona discharge means, and an alternating bias voltage is applied to the needle-like static eliminator. .