JPH0980936A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely separate transfer paper regardless of the thickness of the transfer paper and secular or environmental condition by making a transfer current at the leading edge part of the transfer paper higher than at an image part and changing the value of the transfer current according to the moisture content of the paper. SOLUTION: A transfer charger 19 and a separation charger 20 are connected to a power source circuit 25 generating a transfer current and a separation current. A current control means 26 to which a paper kind detecting sensor 27 detecting the kind of the transfer paper and temperature sensors 28 and 29 detecting temperature near transfer and separation parts are connected controls the current supplied to the chargers 19 and 20. The control means 26 makes the transfer current at the leading edge part or the trailing edge part of the transfer paper by the charger 19 higher than at the image part, and changes the value of the transfer current at the leading edge according to the moisture content of the paper.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus, and more particularly to a transfer / separation apparatus thereof.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus such as a copying machine, when a toner image on an image carrier (photoreceptor) is transferred onto a transfer sheet, the transfer charging device acts to transfer the toner image on the transfer sheet. Charges are applied to the back surface (back surface), and charges having the opposite polarity to this charge are induced on the back surface side of the image carrier. For this reason, the transfer paper adheres to the surface of the image carrier due to the electrostatic force between the induced charges and the charges applied to the transfer paper, making it difficult to separate the transfer paper from the image carrier.

Therefore, the charge on the back side of the transfer paper is removed by corona discharge by the separating charger to reduce the charge applied to the transfer paper and weaken the electrostatic force. As a result, the weight of the transfer paper exceeds the electrostatic force, and the transfer paper is separated from the image carrier.

[0004]

However, in the above-mentioned conventional image forming apparatus, various environmental conditions, for example, transfer paper from thin paper to thick paper, soft paper to hard paper, and from the beginning of work to lapse of time, surroundings at that time. It is difficult to always perform stable separation of the transfer paper under changes in temperature and humidity, and the transfer paper may have separation claw marks for forcibly peeling the transfer paper from the image carrier. There was a problem that it was not possible to maintain a good image.

Further, recently, as the copying speed, that is, the linear velocity of the image carrier is increased, there is no room for separation of the transfer paper, and separation claw marks are likely to occur on the transfer paper. In order to allow room for the separation of the transfer paper, the corona discharge by the separation charger is strengthened to further eliminate the charge on the transfer paper, and the toner on the image carrier is retransferred to the image carrier (printing). Is likely to occur. As described above, achieving both the separation nail trace and the elimination of the print has reached the limit in the conventional technology.

In order to obtain sufficient transferability, a non-uniformly increased transfer is applied to the leading edge of the transfer paper so as to provide an electrostatic transfer electric field which is substantially increased as compared with a portion other than the leading edge of the transfer paper. A technique for applying an electric charge is introduced in JP-A-55-48771. This technique aims to secure the transfer efficiency at the leading end of the transfer paper by utilizing the overshoot of the power supply of the charge applying means to form a non-uniform electric field at the front edge of the transfer paper. In this technique, it is not preferable that the electric field be kept nonuniform at the leading edge of the transfer paper.

Since the separation of the transfer paper utilizes the rigidity of the paper due to its own weight, the separation is not improved unless the transfer charger is uniformly charged within a certain range from the leading end. Although this conventional technique aims at high transfer efficiency, it can be said that it is a technique that is disadvantageous in terms of separability, that is, charging at uneven edges of paper.

In view of the above, the present invention solves the above-mentioned problems of the prior art, and the transfer paper is always stable and reliable regardless of the thickness and hardness of the transfer paper, the type, the paper size, the passage of time, and the environmental conditions. It is an object of the present invention to provide an image forming apparatus capable of performing the above separation.

[0009]

In order to achieve the above object, the invention according to claim 1 is a transfer section having a transfer charger for transferring a toner image formed on an image carrier onto a transfer paper. And an image forming apparatus including a separation unit having a separation charging device for separating the transferred transfer paper from the image carrier, in the transfer paper leading end portion or the transfer paper rear end portion by the transfer charging device. It is characterized in that it has a current control means for making the transfer current larger than that of the image portion and changing the value of the front end transfer current depending on the moisture content of the paper.

According to a second aspect of the present invention, in the first aspect of the invention, a current control means for changing the separation current at the leading end of the transfer paper by the separation charger is provided.

According to a third aspect of the present invention, in the first and second aspects of the present invention, there is provided a paper type detecting means for detecting the type of the transfer paper, and the current depends on the paper type detected by the paper type detecting means. The control means is characterized by performing control for changing the transfer current.

The invention according to a fourth aspect is characterized in that, in the invention according to the first aspect, the current control means performs control for changing a switching timing of the transfer current.

The transfer paper left in a low humidity environment has a low water content, and as a result, the resistance value is very large. As a result, charges tend to accumulate on the transfer paper,
If the transfer current is too large, abnormal discharge tends to occur between the transfer paper and the image carrier. Therefore, in the invention according to the first aspect, the transfer current is controlled according to the water content so as to obtain a stable image without abnormal discharge.

Further, since the separability of the transfer paper also changes when the transfer current changes, the invention according to claim 2 simultaneously solves the contradictory problems of the separation claw mark and the print by changing the separation current at the same time. .

Further, the optimum transfer / separation current condition, in which the separation claw trace and the print are compatible, the moisture content and the current value condition in which abnormal discharge occurs, and the like differ depending on the paper type. Therefore, in the invention according to claim 3, by changing the transfer current depending on the paper type, it is possible to simultaneously solve the contradictory problems of the separation claw mark and the print.

Further, since the separability of the transfer paper is greatly changed by changing the switching timing of the transfer current, the invention according to claim 4 contradicts the separation claw mark and the print by appropriately switching the timing. Balance problem solving.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a block diagram showing an embodiment of an image forming unit of the image forming apparatus of the present invention. The image forming apparatus includes a photosensitive drum (image carrier) that rotates in the direction of the arrow.
11, a charging charger 12 that uniformly charges the surface of the photoconductor drum 11, an exposure unit 13 that forms an electrostatic latent image on the surface of the photoconductor drum 11, and a toner image is formed by attaching toner to the electrostatic latent image. A developing device 14 for charging, a pre-transfer charge eliminator 15 for lowering the surface potential of the photoconductor drum 11 in order to improve transfer efficiency, a pre-transfer charge erasing lamp 16, and a transfer sheet fed from a sheet feeding means (not shown). Registration roller pair 17 that is conveyed toward the photoconductor drum 11 at the timing, a guide plate 18 that guides the transfer paper that is conveyed by the registration roller pair 17, and a transfer charging that transfers the toner image on the photoconductor drum 11 to the transfer paper. And a charging device 2 for separating the transfer paper from the photoconductor drum 11 by removing charge from the transfer paper.
0, a separation claw 21 for surely separating the transfer paper from the photoconductor drum 11, a cleaner 22 for removing the residual toner on the photoconductor drum 11, and a discharge lamp 23 for erasing the residual charge on the photoconductor drum 11. , And a conveyor belt 24 for conveying the transfer paper separated by the separation charger 20.

Transfer charger 19 and separation charger 20
Is connected to a power supply circuit 25 that generates a transfer current and a separation current. The power supply circuit 25 includes a transfer charger 19,
A current control means 26 for controlling the current supplied to the separation charger 20 is connected. A paper type detection sensor 27 that detects the type of transfer paper, a humidity sensor 28 that detects the humidity and temperature near the transfer / separation unit, and a temperature sensor 29 are connected to the current control unit 26.

The paper type detection sensor 27 may be one that detects the resistance of the transfer paper. Further, a service person or a user may set the paper type by providing a paper type setting unit for setting the paper type of the transfer paper such as thin paper, thick paper, soft paper, and hard paper.

The current control means 26 uses the sensors 2
The magnitudes of the transfer current, the separation current, and the transfer current switching timing are changed according to the detection information from 7, 28, and 29. The power supply circuit 25 is of a constant current type which supplies a constant output current, which is useful for always giving a constant charge to the resistance variation due to the thickness and width of the transfer paper, the environment and the like.

Note that changing the transfer current switching timing means switching the transfer current at a distance of several mm from the front end of the transfer paper. The switching timing of 30 mm means 30 mm from the front end of the transfer paper, for example, a transfer current of 450 μA. Tell them to switch to 350 μA.

The separation claw 21 is a shaft 21a supported by the housing.
It is rotatably attached to the surface of the photosensitive drum 11 with a predetermined pressure by the elastic force of a spring (not shown).

Next, the operation based on the above configuration will be described.
The surface of the photoconductor drum 11 is uniformly charged by the charging charger 12, and the charge on the photoconductor drum 11 is erased by the intensity of the light emitted from the exposure unit 13, and the surface of the photoconductor drum 11 is electrostatically charged. A latent image is formed, and the developing device 1 is formed on the electrostatic latent image.
Toner is attached by 4 and a toner image is formed. When the developing process is completed, the potential on the surface of the photoconductor drum 11 is lowered by the pre-transfer charge eliminating charger 15 and the pre-transfer charge eliminating lamp 16 in order to improve the transfer efficiency.

Next, the toner image on the photoconductor 11 is transferred by the transfer charger 19 onto the transfer paper conveyed through the guide plate 18 by the registration rollers 17 at a predetermined timing.

The transfer paper on which the toner image has been transferred is electrostatically separated from the photosensitive drum 11 by the action of the separating charger 20 (if the separating charger 20 does not separate it, the separating claw 2).
(Separated by 1), and is conveyed by the conveyor belt 24 and sent to a fixing unit (not shown). Photoconductor drum 11 after transfer
The cleaner 22 removes the residual toner on its surface, and the static elimination lamp 23 erases the residual charge.
Return to the initial state.

2 (a), 2 (b) and 2 (c) are schematic views showing the process of transferring the toner image and separating the transfer paper P. As shown in FIG. The operation of separating the transfer paper P from the photosensitive drum 11 will be described in detail below with reference to FIG.

The photosensitive drum 11 is made of aluminum 32 and selenium 33. Before the transfer, the toner T charged with a negative polarity is attached to the surface of the selenium 33 as shown in FIG.

Next, as shown in FIG. 3B, the transfer charger 19 applies a positive polarity charge to the back surface of the transfer sheet P, and the negative polarity toner T is attracted to the transfer sheet P. While being transferred and transferred, a charge f having a polarity opposite to that of the charge is induced on the back surface side (the surface of the aluminum 32) of the photosensitive drum 11. Therefore, the electrostatic force F between the induced electric charge f and the electric charge applied to the transfer paper P makes it difficult for the transfer paper P to adhere to the surface of the photoconductor drum 11 and separate. .

Then, by the corona discharge by the separating charger 20, as shown in FIG.
The charge f induced on the back side of the sheet is neutralized, and the charge applied to the transfer paper P is reduced to weaken the electrostatic force F. As a result, the waist strength H and the own weight W of the transfer paper P overcome the electrostatic force F, and the transfer paper P is separated from the photoconductor drum 11.

As described above, in order to improve the separability of the transfer paper P, it has generally been considered preferable to weaken the output of the transfer charger 19. This is because the smaller the amount of electric charge applied to the transfer paper P, the easier it is to be separated by the separation charger 20.

However, in practice, the charge by the transfer charger 19 is applied not only to the transfer paper P but also to the toner T and the photosensitive drum 11, as shown in FIG. As shown in FIG. 7B, the electrostatic repulsive force R acts between the photoconductor drum 11 and the transfer paper P due to the electric charge, so that the output by the transfer charger 19 should be increased. The separability of the paper P is improved.

FIG. 4 is an explanatory diagram showing the level of separability of the transfer paper from the photosensitive drum 11. A is a separation level along the tangential direction of the photoconductor drum 11 in the transfer / separation portion, and has the highest separability. B indicates the separation level between the separation charger 20 and the separation claw 21. C indicates the separation level by the separation claw 21. D indicates the minimum level at which the trace of the separation nail 21 is generated on the transfer paper.

FIG. 5 is a characteristic diagram showing how nail prints and prints are generated when the transfer current and the separation current are changed. A transfer paper T6200 manufactured by Ricoh was used for the experiment. In the figure, a print was generated in the area above the chain line, and a separation nail mark was generated in the area below the solid line. As is clear from this figure, the area where separation traces and prints do not occur is very narrow, and it is difficult to always ensure stable separability with respect to changes in the environment and the type of transfer paper.

FIG. 6 is a characteristic diagram showing changes in the moisture content of the transfer paper. This figure shows the change in moisture content of the transfer paper when the T6200 and the paper source S (recycled paper for copying made by Ricoh) are left in an environment of 20 ° C. and 10%.
After being left to stand, the water content decreased sharply and became almost saturated in about 5 hours. From this, it is understood that the water content of the transfer paper changes greatly depending on the environment. Generally, the higher the temperature and the lower the humidity, the easier the transfer paper is to dry.

FIG. 7 is a characteristic diagram showing the relationship between transfer current, moisture content and abnormal discharge at T6200, and FIG. 8 is a similar diagram for the paper source S. As you can see from these figures,
At a place where the moisture content is low and the transfer current is high, abnormal discharge occurs in which a large number of granular white spots appear in the solid black portion. Further, it can be seen that the relationship between the moisture content and the abnormal discharge differs depending on the paper type (T6200 and paper source S). Therefore, the abnormal discharge can be prevented by changing the transfer current depending on the moisture content and the paper type.

FIG. 9 is a table showing the separability for each paper type and the state of a print when the timing of switching the leading end transfer current is changed. In this figure, the rank of separability is shown,
A, B, C, D indicate the levels of A, B, C, D in FIG. 4 described above. In the prints, ◎ indicates that there is no print, ○ indicates that there is some (but within 1 cm from the tip),
Δ indicates a state within 3 cm from the tip, and x indicates a state further than that. It can be seen that the print generation situation varies depending on the width of the transfer paper.

At this time, the transfer current is 200 μA at the front end of the transfer paper, 160 μA at the image portion, and the separation current is 450 μA at the front end and 350 μA at the image portion.
The separation current is switched at the same time.

As shown in this figure, it can be seen from the separability and the state of the prints that the optimum switching timing differs depending on the paper type.

When the water content of the transfer paper is very low,
It is better to control the tip transfer current to a lower value.At that time, the set value will deviate from the optimum transfer separation current condition that takes account of the scratches and prints.Therefore, either slightly increase the separation current or delay the switching timing to resolve the scratches and prints. It is advisable to set the optimum condition for the transfer separation current that satisfies both of the above.

The cause of the abnormal discharge is that the resistance rapidly increases due to the decrease in the water content, so it is considered best to measure the resistance value of the transfer paper and control the transfer current. However, this method is difficult because of the configuration of the device, the cost, and the like.

Here, it is generally considered that the user, once the transfer paper is set in the tray, is left as it is until it is used up, and it takes a considerable number of days before the transfer paper is used up. Therefore, if several hours have passed since the transfer paper was replenished, the moisture content is replaced by the humidity. Utilizing this, the humidity sensor 28 and the temperature sensor 29 detect the humidity and temperature in the vicinity of the transfer / separation portion, and the transfer current is controlled according to these changes, so that abnormal discharge can be easily prevented. can do.

[0042]

According to the first aspect of the present invention, by controlling the transfer current according to the water content, it is possible to obtain a stable image without abnormal discharge.

According to the second aspect of the present invention, by simultaneously changing the separation current, it is possible to simultaneously solve the contradictory problems of separation claw marks and prints.

According to the third aspect of the present invention, by changing the transfer current depending on the paper type, it is possible to simultaneously solve the contradictory problems of separation claw marks and prints.

According to the fourth aspect of the present invention, by appropriately switching the transfer current switching timing, it is possible to simultaneously solve the contradictory problems of the separation claw mark and the print.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of an image forming unit of an image forming apparatus of the present invention.

FIG. 2 is a schematic diagram showing a process of transferring a toner image and separating a transfer sheet.

FIG. 3 is a schematic diagram showing a process of separating transfer paper when the output of a transfer charger is increased.

FIG. 4 is an explanatory diagram showing a level of separability of a transfer sheet from a photosensitive drum.

FIG. 5 is a characteristic diagram showing how nail prints and prints are generated when the transfer current and the separation current are changed.

FIG. 6 is a characteristic diagram showing changes in moisture content of transfer paper.

FIG. 7 is a characteristic diagram showing a relationship between a transfer current, a moisture content and an abnormal discharge on a predetermined transfer paper.

FIG. 8 is a characteristic diagram showing a relationship between a transfer current, a moisture content and an abnormal discharge on a predetermined transfer paper different from FIG.

FIG. 9 is a chart showing the separability for each paper type and the state of a print when the timing of switching the selective transfer current is changed.

[Explanation of symbols]

 19 Transfer Charger 20 Separation Charger 26 Current Control Means 27 Paper Type Detection Sensor 28 Humidity Sensor 29 Temperature Sensor

Claims (4)

[Claims] 1. A transfer unit having a transfer charger for transferring a toner image formed on an image carrier to a transfer paper, and a separation charger for separating the transferred transfer paper from the image carrier. In the image forming apparatus equipped with a separation unit having a transfer unit, the transfer current at the transfer paper front end or the transfer paper rear end by the transfer charger is set to be larger than that at the image unit, and the front end transfer current is changed depending on the moisture content of the paper. An image forming apparatus comprising a current control unit that changes a value. 2. The image forming apparatus according to claim 1, wherein
An image forming apparatus comprising: a current control unit that changes a separation current of a transfer paper front end portion by a separation charger. 3. The image forming apparatus according to claim 1, further comprising a paper type detection unit for detecting the type of transfer paper, wherein the current control unit transfers the transfer based on the paper type detected by the paper type detection unit. An image forming apparatus characterized by performing control for changing an electric current. 4. The image forming apparatus according to claim 1, wherein
The image forming apparatus is characterized in that the current control means controls the switching timing of the transfer current.