JPH0644175B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Purpose of Generation (Field of Industrial Use) The present invention relates to an image forming apparatus using an electrostatic transfer process such as an electrostatic copying machine and a printer.

(Problems to be solved with the prior art) Transferable images that become charged toner formed on the surface of the image carrier,
An image forming apparatus including a step of contacting a transfer material mainly composed of paper and transferring a toner image to the transfer material by the action of a transfer charger and then separating the transfer material from the image carrier is well known. Is.

In this main device, in order to transfer the toner image to the transfer material, a transfer charger applies a charge of the opposite polarity to the toner to electrostatically transfer the image. The material tends to be adsorbed to the image carrier, so that it is necessary to positively separate the transfer material from the image carrier at the position after the transfer.

As a separating means for this purpose, conventionally, a mechanical means such as a separating claw or a separating belt is used, an air flow is used, a transfer charger is used to neutralize the charges applied to the transfer material, Alternatively, many proposals have been made, such as a curvature separation method in which a large curvature is given to the transfer material in the vicinity of the transfer site, and then the transfer material itself is separated by utilizing its elasticity or its own weight. , It has some effect.

On the other hand, recently, small and compact image forming apparatuses of this type have been increasingly used. From this point of view, the above-mentioned curvature separating means is suitable because it does not require a special additional mechanism. However, on the other hand, in the case of a transfer material which is thin and weak against strain, this material suffered from the drawback of easily causing defective separation.

Therefore, in order to avoid such a defect, a very small separation electrode formed in the shape of a needle or a plate is arranged on the downstream side of the transfer charger as viewed in the running direction of the transfer material. It has been proposed to apply a bias voltage lower than the voltage for initiating self-discharge with polarity to remove the charge of the transfer material.

With such a configuration, it is possible to obtain a small and compact separating device without damaging the photoreceptor or disturbing the toner image as in the separating charger described above.

However, even in such a separating device, the paper most often used as a transfer material has a property which is significantly changed depending on the environment, especially the humidity, so that a preferable result is not always obtained in all cases. Absent.

That is, in a low-humidity environment, the paper has a high resistance and holds electric charges well, so that the attracting force to the image carrier after transfer is strong, and in order to separate this, the bias voltage applied to the separation electrode is increased. On the contrary, in a high humidity environment, the resistance of the transfer paper becomes low and the charge easily moves, so that the charge applied to the transfer charger leaks to the separation electrode through the transfer material and the transfer It is not possible to obtain sufficient electric field strength for
There is a risk of transfer failure such as transfer failure, and in order to prevent this, it was necessary to keep the bias voltage of the separation electrode low.

In order to avoid such an inconvenience, it is immediately conceivable that the environmental humidity and the resistance value of the transfer paper may be detected and the applied voltage for separation may be adjusted accordingly. It can be easily understood that such a method requires an additional mechanism such as a sensor and a control circuit, which leads to an increase in the size and complexity of the device and is impractical.

The present invention has been made to cope with such a situation, and it is an object of the present invention to provide an image forming apparatus capable of always obtaining a good charge removing effect of a transfer material regardless of the environment and the characteristics of the transfer material. It is intended.

(2) Configuration of the Invention (Technical Means for Solving the Problem and Its Action) In order to achieve the above object, in the present invention, a transfer charger for transferring an image formed on an image carrier to a transfer material,
In an image forming apparatus having a charge eliminating electrode provided on the downstream side of the transfer charger in the moving direction of the transfer material to eliminate the charge of the transfer material, the charge eliminating electrode is provided in the vicinity of a position facing the transfer material, and a resistance due to a moisture absorption state is generated. It has a variable resistance member that changes, and the static elimination current by the static elimination electrode changes according to the moisture absorption state of the variable resistance member, and the variable resistance member is brought into an electrically floating state.

With this configuration, discharge of the charge eliminating electrode is accelerated or suppressed in accordance with changes in environmental humidity and characteristics of the transfer material, and a stable charge eliminating action is always obtained.

(Explanation of Embodiments) (Technical Means for Solving the Problems and Their Actions) FIG. 1 shows a copying machine using a cylindrical image carrier (hereinafter referred to as a photoconductor) 1 rotating in the direction of arrow A according to the present invention. It is a side view showing a main part of the applied example, and a transfer charger 3 is arranged near the surface thereof.

The toner image formed on the surface of the photoconductor reaches the transfer site where the transfer charger 3 is present as the photoconductor rotates, and at this position, a transfer paper (not shown) conveyed in the direction of arrow B by the conveyance path 2. ) And contact with each other at the same timing, and transfer is performed by the action of the transfer charger.

A separating device 4 is disposed on the downstream side of the transfer charger 3 adjacent to the transfer charger 3 as viewed in the traveling direction of the transfer material.

This separating device includes a pair of insulating members 4a and 4b closely attached to the side wall portion of the transfer charger, and a metal plate member sandwiched between the insulating members 4a and 4b and having a sawtooth shape on the side facing the photosensitive member. It is formed by a separation electrode 5 having a structure in which needle-shaped members are arranged in a row, and is connected to a high voltage power supply 7.

Further, in the vicinity of the separation electrode 5, a moisture absorbing member 6 such as paper whose resistance value changes depending on humidity is arranged in the insulating member.

The transfer material that has completed the transfer process then reaches the position of the separating device, and the corona discharge of the opposite polarity to that applied at the time of transfer is applied by the separating electrode to eliminate the charge at the time of transfer. It shall be separated from the photoconductor and conveyed to the next step.

In this case, in a low humidity environment, since the resistance value of the moisture absorbing member 6 is high and is in an insulating state, the potential increase of the member due to electrostatic induction is slow even if a high voltage is applied to the separation electrode 5, and after the transfer is completed. Until the transfer paper passes through the separating device, the distribution of the lines of electric force by the separating electrodes is not concentrated and disturbed as shown in FIG. 2, and sufficient charge elimination is performed.
Separation action is also secured.

On the other hand, in a high-humidity environment, the hygroscopic member has a low resistance, and when a high-voltage bias is applied to the separation electrode 5 for this reason, the hygroscopic member is rapidly charged by electrostatic induction and the potential rises, which causes As shown in FIG. 3, the corona discharge between the transfer material and the separation electrode is suppressed, and the leakage of the charge of the transfer material can be prevented to prevent the transfer omission. That is, the static elimination current by the separation electrode changes according to the moisture absorption state of the moisture absorption member.

Next, an experimental example of the present invention will be described.

In the copying machine, a cylindrical photosensitive member having a diameter of 30 mm was used, and as a separating electrode, a stainless steel plate having a tooth height of 3 mm and a pitch of 1 mm formed in a sawtooth shape was used. This is placed 25 mm downstream from the shield wall of the transfer charger, and has a width of 1 mm as a moisture absorbing member.
The paper was attached and arranged at a position 1 to 2 mm from the tip of the separation electrode.

When such a separator was installed and operated at a transfer voltage of -5.3 KV, a separation electrode K bias of +3.5 KV, and a process speed of 50 mm / sec, a wide humidity range from thin paper to thick paper and O
Stable separation action was obtained without deterioration of image quality even on HP paper.

Although not shown in the drawing, as described above, the separation electrode is
A needle electrode may be used, or a thin wire may be spread.

As the moisture absorbing member, various materials such as synthetic fibers and ceramics can be used in addition to paper, and an appropriate moisture absorbing substance may be applied in the vicinity of the separation electrode.

(3) Effects of the Invention Since the present invention has the above-described configuration, it is possible to obtain a stable and stable charge removing action of the transfer material without deterioration of image quality regardless of the environment in which the image forming apparatus is used. Obtainable.

[Brief description of drawings]

FIG. 1 is a side view of the essential parts of an embodiment in which the present invention is applied to a copying machine, and FIGS. 2 and 3 are enlarged side views of the essential parts showing the operation of a separating apparatus according to the present invention. 1 ... photoreceptor, 2 ... transport path, 3 ... transfer charger, 4 ...
… Separation device, 5 …… Separation electrode, 6 …… Hygroscopic member.

Claims (1)

[Claims] 1. An image having a transfer charger for transferring an image formed on an image bearing member to a transfer material, and a neutralizing electrode provided on the downstream side of the transfer charger in the transfer material moving direction for removing the charge of the transfer material. In the forming apparatus, the static elimination electrode has a variable resistance member which is provided in the vicinity of the position facing the transfer material and whose resistance changes depending on the moisture absorption state, and the static elimination current by the static elimination electrode depends on the moisture absorption state of the variable resistance member. The image forming apparatus is characterized in that the variable resistance member is changed into an electrically floating state while changing.