JPS6364784B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention develops a latent image formed on an electrostatic latent image carrier such as a photoreceptor in electrophotography or an insulator in electrostatic recording using a particulate developer (dry development). Thereafter, in a transfer type image forming apparatus that transfers the visible image to a transfer material and fixes the transferred visible image on the surface of the transfer material to obtain a copy, the electrostatic latent image is separated from the surface of the electrostatic latent image carrier after the image is transferred. The purpose of the present invention is to prevent an unfixed image on a transfer material from being disturbed by electrical influence during the conveyance process of the transferred transfer material until it reaches a fixing section, thereby obtaining a high-quality copy.

For convenience of explanation, FIG. 1 shows a very schematic structure of a drum type electrophotographic copying machine according to the Carlson process as an example of a transfer type image forming apparatus. Since the process and image forming principles of this copying machine are well known, only the reference numerals of the constituent parts will be explained here. That is, reference numeral 1 denotes a drum-shaped electrophotographic photosensitive member (hereinafter simply referred to as a drum) which is rotationally driven in the direction of arrow a about a shaft 2. 3 is a charging device that uniformly charges the drum surface positively or negatively to impart photosensitivity. Reference numeral 4 denotes an exposure section, which forms an electrostatic latent image on the drum surface by receiving a light image L (slit exposure) from a light image exposure device (not shown). 5 is a dry developing device that develops the latent image (toner development). A transfer charger 6 charges the back side of the transfer material P fed between the drum 1 and the charger 6 in synchronization with the rotation of the drum 1 from a paper feed section (not shown). As a result, the toner powder image, which is the developed image on the side of the drum 1, is transferred to the side of the transfer material P. Reference numeral 7 denotes a transfer material separation device that separates the transfer material P that has passed through the transfer section and is electrostatically adhered to the drum surface from the drum surface. The separated transfer material P is then conveyed to a fixing device (not shown), where the transferred toner powder image is fixed, and the transferred material P is discharged outside the machine as a copy. Reference numeral 8 denotes a drum surface cleaning device, which removes dirt on the drum surface such as a transfer residual image remaining on the drum surface, thereby cleaning the drum surface and allowing the drum to be used repeatedly.

By the way, in the above-mentioned transfer type image forming apparatus, the transferred toner powder image on the transfer material P separated from the drum 1 surface and reaching the fixing device is different from the transferred corona charge given to the transfer material in the transfer section 6. Since the transfer material P is simply held electrostatically attached to the surface of the transfer material P by the electrostatic attraction, it is unstable and easily disturbed.

In addition to vibration and shock, factors that cause disturbance include
Examples include electrical effects.

That is, the transfer material P receives the transfer corona for image transfer in the transfer section 6 and is electrostatically in close contact with the surface of the drum.
When the transfer material P is then separated from the surface of the drum 1 by the separation device 7, a change occurs in the electric field acting between the drum 1 and the transfer material P at the separation part, but if the change in the electric field is sudden and large, the electric field Due to this change, unfixed toner powder on the surface of the transfer material is blown away, causing disturbances in the image.
In addition, as recent image forming apparatuses have become smaller and their mechanisms have become more complex, the conveyance path of the transfer material is sometimes forced to bend, and unfixed toner powder images are held in the path with such bends. When the transferred transfer material is transported,
At the bending portion of the transfer material, the electric field due to the transfer corona charge held by the transfer material changes. If the change in the electric field at the bending portion of the transfer material is sudden and large, the toner powder will fly off, causing image disturbance, as described above.

The above electric field change when the transfer material is separated or when the transfer material is bent undergoes a sudden and large change if the charge applied to the transfer material P during transfer is maintained in a high charge state. For example, if the transfer material P is made of insulating resin such as polyester film, or even plain paper is dried in a low humidity environment and has a high resistance value of 10 ¹² Ω-cm or more, the transfer material The charged charges are retained as they are in a high charge state.

Conventionally, in order to prevent the phenomenon of disturbance of unfixed toner powder images due to the above-mentioned electrical influence,
By providing a ground electrode 9 close to or in contact with the back surface of the conveyed transfer material near the transfer material separation section or transfer material bending section, self-discharge is generated between the transfer material P and the ground electrode. That is, by reducing the charge held on the side of the transfer material P, changes in the electric field when the transfer material is separated or when the transfer material is bent are alleviated.

However, this method does not allow the transfer material to absorb moisture in a high humidity environment.
If the resistance value of is in a state of decreasing, the electric charge held on the transfer material P side leaks more than necessary, and the electrical adhesion retention force of the unfixed toner powder image to the transfer material surface is weakened. Or the holding power is lost. As a result, the toner powder image becomes extremely easily disturbed, and the phenomenon that the toner powder goes around to the back side of the transfer material occurs.
This was a major cause of stains on the back of the transfer material.

In addition, if the transfer material P originally has low resistance, it becomes a substantial conductor in a high humidity environment, so even after the tip of the transfer material P reaches the ground electrode 9, the transfer portion 6 is still connected. The transfer corona charge applied to the back surface of the transfer material part that is passing through the transfer material immediately leaks to the ground electrode 9 through the conductive transfer material, thereby impeding the transfer and causing a so-called transfer void (white void) phenomenon.

The present invention also uses the ground electrode 9 to prevent disturbance of unfixed toner powder images due to electrical influence, but the ground electrode effect is selectively activated depending on the environmental humidity to prevent the unfixed toner powder image from being disturbed in a high humidity environment. The system also allows image transfer, separation of the transfer material, and conveyance of the transfer material holding the unfixed toner powder image without the above-mentioned adverse effects, and the ground electrode 9 is electrically insulated from the ground state (electrically insulated state). It is configured so that it can be switched between two states: a floating state and a floating state.

The present invention relates to an image forming apparatus in which a latent image formed on an electrostatic latent image carrier is developed with a particulate developer, and then the developed image is transferred to a transfer material by a transfer means. It has a static eliminating member provided close to or in contact with the back surface, a detection means for detecting humidity, and a means for switching the static eliminating member to a grounded state or an electrically insulated state in response to a detection signal from the detection means. It is characterized by this.

That is, in the example in FIG. 1, 10 is a switching circuit, and when the switch 11 is switched to the ground terminal 12 side, the ground electrode 9 is grounded, and when it is switched to the float terminal 13 side, the electrode 9 is electrically insulated. Become. In this example, the switching circuit 10 and the environmental humidity sensor 14 are related, and when the environmental humidity is below 80% relative humidity, the switching circuit 10 is switched based on the sensor detection signal in that state. 11 is automatically switched and held at the ground terminal 12 side, and conversely, in a higher humidity environment, it is automatically switched and held at the float terminal 13.

In other words, when the environmental humidity is lower than a predetermined value (relative humidity 80% in this example), the transfer material is
Excess charge held on the side is appropriately leaked, and as a result, changes in the electric field when the transfer material is separated or bent are alleviated, and disturbances of the unfixed toner powder image on the transfer material due to electrical influence are prevented. .

On the other hand, in a high humidity environment exceeding the above value, by keeping the ground electrode 9 in an electrically insulated state, excessive leakage of charges held on the transfer material P side via the ground electrode 9 and transfer corona in the transfer section 6 can be prevented. Leakage of charge is prevented, and adverse effects such as the back staining phenomenon of the transfer material and the transfer omission phenomenon described above do not occur.

In other words, image transfer, separation of the transfer material, and conveyance of the transfer material holding the unfixed toner powder image can be carried out smoothly in both low-humidity and high-humidity conditions without electrically harmful effects.
The intended purpose is well achieved.

In the example shown in FIG. 2, a ground electrode 9 is provided in the transfer material separating section, and a sub-ground electrode is placed close to or in contact with the back surface of the transfer material that is in close contact with the surface of the drum 1 immediately after passing through the transfer section 6. 15, and when the humidity is low, the auxiliary ground electrode 15 is grounded together with the ground electrode 9. In this way, excess charge on the transfer material P can be removed before and after the transfer material is separated. This is done in two stages using electrodes 15 and 9, respectively, and is effective in suppressing sudden changes in the electric field when separating the transfer material. During high humidity, both electrodes 15 and 9 are kept electrically insulated.

Figure 3 shows an example of the ground electrodes 9 and 15, which are made of stainless steel plate with a thickness of about 0.1 to 0.2 mm, and are made of a stainless steel plate with a thickness of about 0.1 to 0.2 mm, and are made of a stainless steel plate with a number of electrodes arranged at approximately equal intervals along the upper longitudinal direction at a pitch P of about 2 to 15 mm. It is manufactured by punching into an elongated strip shape having chevron-shaped barbed portions 9 ₁ and 15 ₁ . The tip angle θ of the chevron-shaped barbed portions 9 ₁ and 15 ₁ is preferably 110° or less. The chevron-shaped barbed portions 9 ₁ and 15 ₁ are arranged facing the back surface of the transfer material P. Other conductive material rollers, conductive plates, rods, wires, etc. can also be used as the ground electrodes 9 and 15.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram of an example of an electrophotographic copying machine equipped with a ground electrode according to the present invention, FIG. 2 is a diagram of an example in which a sub-ground electrode is provided, and FIG. 3 is an example of a ground electrode. Front view of part of. 1 is a drum type electrophotographic photoreceptor, 6 is a transfer charger, P is a transfer material, 9 and 15 are ground electrodes, and 14 is a humidity sensor.

Claims (1)

[Scope of Claims] 1. In an image forming apparatus that develops a latent image formed on an electrostatic latent image carrier with a particulate developer, and then transfers the developed image to a transfer material by a transfer means, A static eliminating member provided in close proximity to or in contact with the rear surface of the subsequent transfer material, a detection means for detecting humidity, and a means for switching the static neutralizing member to a grounded state or an electrically insulated state in response to a detection signal from the detection means. An image forming apparatus comprising: 2. The image forming apparatus according to claim 1, wherein the charge eliminating member is a charge eliminating member that generates self-discharge between itself and the transfer material.