JP2000155471A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an image forming device utilizing reversal developing with good separation of transfer material and high image quality by carrying out irradiation of light at the time of separation of the transfer material. SOLUTION: In this image forming device, the surface of an electrostatic latent image carrier member 21 is uniformly electrified by corona discharge of an electrifying means 22. An electrostatic latent image 41 is formed by exposure corresponding to image information by an electrostatic latent image forming means 23. Then, a developing member 32 is stuck to the electrostatic latent image 41 by a developing means 24 and the developing member image 42 is formed. Next, the developing member image 42 is transferred to a transfer material 37 by utilizing a transferring means 25. A auxiliary separation means 50 is provided in the back of a separation means 26 and the surface of the electrostatic latent image carrier 21 is exposed at separation position C. At this time by providing a transfer material discrimination means 56 and an exposure quantity control means 57, the exposure quantity of the auxiliary separation means 50 is controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus provided in a copying machine, a facsimile, a printer, or the like, for forming an image using an electrophotographic process.

[0002]

2. Description of the Related Art An electrophotographic image forming apparatus forms an electrostatic latent image by charging and exposing a photoconductive electrostatic latent image holding member, and develops the electrostatic latent image onto the electrostatic latent image holding member. This is a device that forms a developing member image by attaching members by electrostatic force, and transfers the developing member image to a transfer material to visualize the image. 2. Description of the Related Art In recent years, the market for image forming apparatuses using electrophotography has been expanding and maturing with the amenity of offices and the spread of personal computers. In the future, high-speed and high-quality performance will be required for image forming apparatuses.

A conventional image forming apparatus using electrophotography will be described below with reference to the drawings. FIG. 10 is a sectional view showing a configuration of a main part of a conventional image forming apparatus.
FIG. 11 is an explanatory diagram showing a change in the surface potential of the electrostatic latent image holding member in the conventional image forming apparatus. FIG. 12 is an explanatory diagram showing a change in the surface potential of the electrostatic latent image holding member when the image forming apparatus shown in FIG. 10 is provided with a pre-transfer exposure unit.

As shown in FIG. 10, as a basic component of the image forming apparatus, a charging unit 22, an electrostatic latent image forming unit 23, and an electrostatic latent image holding member 21 disposed substantially at the center are provided.
A developing unit 24, a transfer unit 25, a separating unit 26, a fixing unit 27, and a cleaning unit 28 are provided.

The electrostatic latent image holding member 21 is formed by coating a photoconductive material on the surface of a rotating drum. Charging means 2
Numeral 2 is provided in a dark place and gives a uniform charge 30 to the photoconductive film of the electrostatic latent image holding member 21 by corona discharge. The electrostatic latent image forming means 23 emits a laser beam 31 whose luminance has been modulated according to image information, and scans the laser beam 31 in a direction parallel to the central axis of the electrostatic latent image holding member 21. Energy distribution 4 of laser beam 31
Corresponding to 0, the charge 30 remains or is erased, and an electrostatic latent image 41 is formed on the surface of the photoconductive film.

The developing means 24 has a cartridge for accommodating the developing member 32 and the carrier 33, and uses the sleeve 34 and the carrier 33 to transfer the developing member 32 to the electrostatic latent image holding member 2.
It is a guide to one side. Here, the developing member 32 adheres according to the potential of the electrostatic latent image 41, and a developing member image 42 is formed. The transfer material 37 is a sheet-shaped recording paper for printing a latent image by visualizing the latent image, and generally, plain paper is used. The transfer guide member 38 guides the transfer material 37 transferred from a tray (not shown) to the electrostatic latent image holding member 21 side.

The transfer means 25 transfers a developing member image 42 formed on the electrostatic latent image holding member 21 to a transfer material 37, and generates a high voltage having a polarity opposite to that of the charging means 22 by corona discharge. The separating unit 26 generates a high AC voltage by discharging to separate the transfer material 37 from the electrostatic latent image holding member 21. The developing member 3 is provided at the transfer unit 25.
2 is transferred to the transfer material 37, and the developing member image 43 (visible image)
Is formed. The fixing unit 27 includes two heating rollers, and forms the output image 44 by fusing the developing member 32 transferred to the transfer material 37 by heating and pressing.

The cleaning means 28 removes the charge from the surface of the photoconductive film and removes the remaining developing member 32 so that the electrostatic latent image holding member 21 can be reused. Image formation is continuously performed on the transfer material 37 in sheet units according to the above process procedure.

Here, the function of the transfer means 25 will be described in more detail. The transfer material 37 is guided to a transfer position B by a transfer guide member 38. In a digital copying machine, a printer, and the like, a reversal developing method is often used as a developing method. For this reason, the transfer unit 25 applies a potential having a polarity opposite to the polarity of the charge of the developing member 32 from the rear surface of the transfer material 37 to transfer the developing member image 42 formed on the electrostatic latent image holding member 21 to the transfer material 37. Transfer onto 37. At this time, the transfer material 37 is charged to a polarity opposite to that of the developing member 32 by the transfer means 25. When a white background portion of an image to be printed, that is, a portion where the developing member 32 does not adhere is referred to as a background portion, the background portion of the electrostatic latent image holding member 21 is not exposed by the electrostatic latent image forming unit 23. As shown in FIG. 11, the potential (absolute value) is high even after the development member image 42 is formed, and a large electrostatic attraction force is generated between the electrostatic latent image holding member 21 and the transfer material 37. For this reason, there is a problem that the transfer material 37 is difficult to be separated from the electrostatic latent image holding member 21.

As a conventional countermeasure against this problem, there has been proposed a method of disposing a pre-transfer exposure means 35 in front of the transfer means 25 as shown in FIG. The pre-transfer exposure unit 35 includes a light emitting element group in which a large number of LEDs are linearly arranged, or a rod-shaped lamp, and uniformly exposes the surface of the electrostatic latent image holding member 21. When the pre-transfer exposure means 35 having such a function is provided, the transfer means 2
12, the surface potential of the electrostatic latent image holding member 21 changes from the state (1) to the state (5) as shown in FIG.

[0011]

FIG. 12A shows the initial charging potential on the surface of the electrostatic latent image holding member 21 due to the discharge of the charging means 22, and the value VO is, for example, -750V. FIG. 12B shows the potential after image exposure by the electrostatic latent image forming unit 23, and the background potential VN is VO (= −7).
50 V), whereas the image portion potential VI is VL (= −
100V). Next, after the development of (3), the negatively charged developing member 32 adheres to the image area. And for example L
When light is irradiated (exposed) to the electrostatic latent image holding member 21 using the pre-transfer exposure means 35 constituted by the ED, the background portion potential (absolute value) decreases. Therefore, before the transfer in (4),
The background portion potential VN becomes VBG (= −300 V). If the forward jumping potential difference VF is defined as the difference between the background section potential VN and the image section potential VI, the forward jumping potential difference VF = VN−VL
= VS-VL = -200V. Separation-related potential V
S becomes -300 V, and its absolute value is significantly lower than the initial charging potential VO as shown before (5). Therefore, the separability of the transfer material 37 is improved.

Such a method is adopted because, after the development member image 42 is formed, the electrostatic latent image holding member 21 is uniformly exposed, the background potential (absolute value) is reduced, and the This is because the transfer material 37 is easily separated by weakening the electrostatic attraction force generated between the electrostatic latent image holding member 21 and the transfer material 37.

However, as shown in FIG. 10, the intensity of the electric field in the area A where the transfer guide member 38 is close to the electrostatic latent image holding member 21 is 40 kV / m or more, and the developing member for forming the developing member image 42 is formed. 32 is attracted to the background portion having a lower potential (absolute value) before transfer, and the developing member 3
The image quality is degraded due to the scattering of 2. Further, the developing member 32 is attracted to the transfer guide member 38, and a new problem arises in that the image quality is deteriorated due to the forward jump or the transfer material 37 is stained due to the stain on the transfer guide member 38.

The present invention has been made in view of such a conventional problem, and reduces the forward jump of the developing member and generates a gap between the electrostatic latent image holding member 21 and the transfer material 37. An object of the present invention is to provide an image forming apparatus capable of printing high-quality images and characters by facilitating separation of the transfer material 37 by weakening the electrostatic attraction force.

[0015]

According to a first aspect of the present invention, there is provided an electrostatic latent image holding member for holding an electrostatic latent image by a surface charge, and the electrostatic latent image holding member. Charging means for uniformly charging the surface of the member, and discharging a part of the surface charge by exposure according to image information with respect to the surface charge uniformly charged on the surface of the electrostatic latent image holding member An electrostatic latent image forming unit that forms an electrostatic latent image by the electrostatic latent image forming unit, the electrostatic latent image formed on the electrostatic latent image holding member by the electrostatic latent image forming unit, and has the same polarity as the surface charge. A developing unit that forms a developing member image by attaching a charged developing member to an uncharged area; and a developing unit formed by the developing unit by applying an electric field having a polarity different from the surface charge from the back surface of the transfer material. A transfer means for transferring the member to the surface of the transfer material; An image forming apparatus comprising: a transfer unit; and a separation unit that discharges an electric charge remaining on the electrostatic latent image holding member with an AC electric field, wherein the electrostatic latent image holding member is located near the separation unit. Separation assisting means for irradiating the surface with light to lower the back potential in the exposure area of the electrostatic latent image holding member is provided.

According to such a configuration, by providing the separation assisting means for forming the light irradiation area near the separation position where the transfer material is separated from the electrostatic latent image holding member, the background is provided before the transfer. The difference between the partial potential and the image potential is increased, and the absolute value of the background potential is reduced during separation. In this case, good separability is ensured, and image quality deterioration due to scattering of the developing member and forward jump can be reduced. Further, it is possible to form an image having stable quality without transfer material contamination due to transfer guide member contamination.

According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the separation assisting means is provided between a position where the transfer means is provided and a position behind the separation means. Is what you do.

According to a third aspect of the present invention, in the image forming apparatus of the second aspect, an exposure amount control unit is further provided to change an exposure amount of the separation assisting unit.

According to such a configuration, by controlling the exposure amount of the separation assisting means by the exposure amount control means, the optimum exposure condition from the back of the transfer material can be set, and an image having stable quality can be formed. .

According to a fourth aspect of the present invention, in the image forming apparatus of the third aspect, the exposure amount control means changes the exposure amount of the separation assisting means in accordance with the charge amount of the charging means. Is what you do.

According to such a configuration, since the optimal exposure amount can be set according to the surface potential of the electrostatic latent image holding member, deterioration of the electrostatic latent image holding member due to overexposure can be prevented, and image quality due to insufficient exposure can be prevented. An image having stable quality without deterioration can be formed.

According to a fifth aspect of the present invention, in the image forming apparatus of the third aspect, the exposure amount control means changes the exposure amount of the separation assisting means according to the type and thickness of the transfer material. It is a feature.

According to such a configuration, the optimum exposure amount from the back surface of the transfer material can be set according to the type and thickness of the transfer material, so that deterioration of the electrostatic latent image holding member due to overexposure can be prevented. In addition, it is possible to form an image having stable quality without image quality deterioration due to insufficient exposure.

According to a sixth aspect of the present invention, in the image forming apparatus of the third aspect, the exposure amount control means changes the exposure amount of the separation assisting means in accordance with the charge amount of the developing member. Is what you do.

According to this configuration, the optimum exposure amount can be set according to the charge amount of the developing member, and an image having stable quality can be formed.

According to a seventh aspect of the present invention, in the image forming apparatus of the third aspect, the exposure amount control means changes an exposure amount of the separation assisting means in accordance with a position of the transfer material in a moving direction. It is a feature.

According to an eighth aspect of the present invention, in the image forming apparatus of the third aspect, the exposure amount control means controls the separation assisting means so as to expose at least a leading end region of the transfer material. Things.

According to such a configuration, different exposure amounts from the back surface of the transfer material can be set according to the position of the transfer material in the moving direction. For this reason, deterioration of the electrostatic latent image holding member due to overexposure can be prevented, and an image having stable quality without image quality deterioration due to insufficient exposure can be formed.

According to a ninth aspect of the present invention, in the image forming apparatus according to any one of the fourth to sixth aspects, in order to change an exposure width of the separation assisting means, a width direction orthogonal to a moving direction of the transfer material is provided. The exposure width control means for changing the exposure amount is further provided.

According to such a configuration, the exposure amount can be changed in the width direction of the transfer material, the deterioration of the electrostatic latent image holding member due to overexposure can be prevented, and the image quality does not deteriorate due to insufficient exposure. High quality images can be formed.

According to a tenth aspect of the present invention, in the image forming apparatus of the ninth aspect, the exposure width control means controls exposure of a transfer area of the transfer material.

With this configuration, it is possible to prevent the electrostatic latent image holding member from being deteriorated due to overexposure in the external region of the transfer material, and to set an optimal exposure amount for the area of the transfer material.
Therefore, an image having stable quality can be formed.

[0033]

(Embodiment 1) An image forming apparatus according to Embodiment 1 of the present invention will be described with reference to FIGS. In the following description, it is assumed that the image forming apparatus is used in a digital copying machine of a negative charge reversal developing system. FIG. 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus according to Embodiment 1. The same parts as those in the conventional example shown in FIG. 10 are denoted by the same reference numerals, and detailed description is omitted.

In this image forming apparatus, as in the prior art, a charging unit 22, an electrostatic latent image forming unit 23, a developing unit 24, a transfer guide, and the like are provided around an electrostatic latent image holding member 21 disposed substantially at the center. A member 38, a transfer unit 25, a separation unit 26, a fixing unit 27, and a cleaning unit 28 are provided.

The electrostatic latent image holding member 21 is formed by coating a photoconductive material on the surface of a metallic rotating drum. The charging means 22 applies a uniform negative charge 30 to the photoconductive film of the electrostatic latent image holding member 21 by corona discharge. The electrostatic latent image forming means 23 emits and scans a laser beam 31 modulated in accordance with image information, and scans the charged electric charge 30 on the electrostatic latent image holding member 21 according to the intensity of the laser beam. To discharge the charge. An electrostatic latent image 41 is formed on the surface of the photoconductive film corresponding to the energy distribution 40 of the laser beam 31.

The developing means 24 holds the developing member 32 and the carrier 33, and guides the developing member 32 toward the electrostatic latent image holding member 21 using the sleeve 34 and the carrier 33 for development. The transfer material 37 is a sheet-shaped recording paper for printing an image, and generally, plain paper is used. The transfer guide member 38 guides the transfer material 37 transferred from a tray (not shown) to the electrostatic latent image holding member 21 side.

The transfer means 25 transfers the developing member image 42 adhered to the electrostatic latent image holding member 21 to the transfer material 37. The transfer means 25 generates a high voltage having a polarity opposite to that of the charging means 22 by corona discharge to generate the transfer material 37. Give to. The separating means 26 generates a high AC voltage by discharging in order to separate the electrostatic latent image holding member 21 from the transfer material 37.

Unlike the conventional example, a separation assisting means 50 is provided behind the separating means 26. The separation assisting means 50 includes a plurality of light emitting elements such as LEDs arranged in a line. The separation assisting means 50 irradiates (exposes) the electrostatic latent image holding member 21 with uniform light 51 via the transfer material 37, thereby transferring the charge remaining on the photoconductive film to the transfer material 37.
During the separation of As the separation assisting means 50, a rod-shaped incandescent lamp may be used instead of a plurality of LEDs.

The fixing means 27 is composed of two heating rollers, and fuses the developing member 32 transferred to the transfer material 37 by applying heat and pressure to form an output image 44.
The cleaning unit 28 removes the charge and the remaining developing member 32 from the surface of the photoconductive film so that the electrostatic latent image holding member 21 can be reused in the next print cycle.

The operation of the image forming apparatus thus configured will be described. The photoconductive electrostatic latent image holding member 21 rotates at a constant speed, is uniformly charged in a dark place by the charging means 22, and charges 40 are accumulated. Then, the electrostatic latent image forming unit 23 forms an electrostatic latent image 41 corresponding to the image information. Here, the portion irradiated with the laser beam has an electric charge of 40.
Is lost, and the charge 40 remains in the portion that is not irradiated by the modulation. Then, the developing member 32 charged to the same polarity as the charging unit 22 is supplied by the developing unit 24 together with the carrier 33. Then, the developing member 32 adheres according to the potential of the electrostatic latent image 41, and the developing member image 42 is formed.
Here, the developing member 32 adheres to a portion where there is no charge 40.

Next, the transfer material 37 is conveyed from a tray (not shown) and guided to the leading end of the transfer guide member 38. The transfer unit 25 generates a high voltage having a polarity opposite to that of the charging unit 22, and the developing member image 42 attached to the electrostatic latent image holding member 21.
Is transferred to the transfer material 37. At this time, the laser beam 31
Is irradiated with the high electric field of the opposite polarity, and the developing member 32 adheres to the surface of the transfer material 37 according to the density of the image area. Developing member 32 in this state
The adhesive force to the surface of the transfer material 37 is only electrostatic force.

The separating means 26 generates an AC high voltage by corona discharge and discharges the electric charges held in the transfer material 37, thereby substantially reducing the attraction between the transfer material 37 and the electrostatic latent image holding member 21. To 0. The separation assisting means 50 provided near the separation position C emits uniform light 51 and discharges the charge remaining on the electrostatic latent image holding member 21 to the drum side via the photoconductive film. For this reason, the separation-related potential VS at the time of separation decreases, and the transfer material 37 is
Easily peeled off from the surface.

The transfer material 37 is in a state where the developing member image 43 is formed, and is conveyed to the fixing means 27. Here, the developing member 32 is fixed by heating and pressing of the heating roller, and an output image 44 is formed. The cleaning unit 28 completely removes the charge and removes the remaining developing member 32 so that the electrostatic latent image holding member 21 can be reused in the next print cycle. According to the above-described procedure, image formation is continuously performed for each sheet of the transfer material 37.

For example, -4k is applied to the discharge wire of the transfer means 25.
A voltage of V is applied to perform corona discharge. The air gap length between the transfer guide member 38 and the electrostatic latent image holding member 21 is 1 mm. When the potential of the transfer guide member 38 is +500 V and the angle between the transfer guide member 38 and the electrostatic latent image holding member 21 is 30 °, the results of the numerical analysis of the electric field distribution show that the transfer guide member 38 and the electrostatic latent image A high electric field was generated in a gap between the image holding member 21 and the image holding member 21. In the present embodiment, by providing the separation assisting means 50 at the separation position C in FIG. 1, the background potential (absolute value) at the position C can be reduced instead of the position A.

FIG. 2 is an explanatory diagram showing a change in the surface potential of the electrostatic latent image holding member 21 in the image forming apparatus of the present embodiment. When the charge 30 is given to the surface of the electrostatic latent image holding member 21 by corona discharge of the charging means 22, the initial charging potential VO of the electrostatic latent image holding member 21 after the charging shown in (1).
Becomes -750V. Next, for example, LSU (Laser Scanin)
When the image exposure is performed by the electrostatic latent image forming unit 23 composed of (g Unit), the image portion potential VI becomes VL (= −100 V) as shown after the exposure in (2). Next, after the development of (3), the developing member 32 adheres to the image area. At this time, the forward jump-related potential difference VF is VN−VI = VO−VI = −
650 V, and its absolute value is larger than the involved potential difference VF shown in FIG. The electric field strength in region A is 40
Although it is kV / m or more, a part of the developing member 32 forming the developing member image 42 is difficult to be attracted to the background portion having a low potential (absolute value), and the image quality is deteriorated due to the forward jump or the transfer guide member is stained. This prevents the transfer material from being stained.

When the background portion of the electrostatic latent image holding member 21 reaches the separation position C, light 51 is irradiated by the separation assisting means 50, and the surface potential (absolute value) as shown at the time of separation in FIG. Decreases, and the separation participation potential VS becomes VBG (= −300
V). For this reason, the transfer material 37 is used as the electrostatic latent image holding member 2.
Easily separated from 1.

As described above, the separation assisting means 5 is located near the separation position where the transfer material 37 is separated from the electrostatic latent image holding member 21.
By arranging 0, a light irradiation area is formed at the separation position. By doing so, the difference between the background portion potential and the image portion potential is kept large before transfer, and the background portion potential (absolute value) can be reduced during separation. For this reason, it is possible to form a stable high-quality image without splattering of the developing member 32, deterioration in image quality due to skipping forward, and dirt on the transfer material 37 due to dirt on the transfer guide member 38, while ensuring good separation. it can.

(Embodiment 2) Next, an image forming apparatus according to Embodiment 2 of the present invention will be described with reference to FIG. FIG. 3 is a cross-sectional view illustrating a schematic configuration of the image forming apparatus according to the second embodiment. The same parts as those in the first embodiment are denoted by the same reference numerals, and the description of the configuration of the same parts and the description of their operations will be omitted. The image forming apparatus according to the present embodiment is characterized in that a separation assisting unit 52 composed of a light emitting element group is provided below the separating unit 26, and light 53 is emitted from the separation assisting unit 52.

The surface potential of the electrostatic latent image holding member 21 of the present embodiment changes in a manner similar to that shown in FIG. For this reason, while ensuring good separability, stable and high-quality image formation can be realized without scattering of the developing member 32, deterioration of image quality due to skipping forward, and contamination of the transfer material due to contamination of the transfer guide member. The position of the separation assisting means is effective at any position as long as it is between the position of the transfer means 25 and the position behind the separating means 26.

(Embodiment 3) Next, an image forming apparatus according to Embodiment 3 of the present invention will be described with reference to FIG. FIG. 4 is a sectional view showing a schematic configuration of the image forming apparatus according to the fourth embodiment. Here, the same portions as those in the first embodiment are denoted by the same reference numerals, and the description of the configuration of the same portions and the description of the operation thereof will be omitted. The image forming apparatus according to the present embodiment is characterized in that the amount of light exposure by the separation assisting unit 50 is controlled in conjunction with the amount of charge by the charging unit 22. The high voltage applied to the discharge wires of the charging means 22 is detected by a grid 54 near the discharge wires. here,
An exposure control means 55 is provided between the separation assisting means 50 and the grid 54, and the potential of the grid 54 is controlled by the exposure control means 5.
Give 5 Then, the light emission intensity (exposure amount) of the separation assisting means 50 is controlled in accordance with the grid potential.

The surface potential of the electrostatic latent image holding member 21 of this embodiment also changes in the same manner as that shown in FIG. In particular, when the charging amount of the electrostatic latent image holding member 21 by the charging unit 22 changes, the optimum exposure amount is set in conjunction with the change, and the background portion potential is controlled. In this case, while ensuring good separability, deterioration of the electrostatic latent image holding member 21 due to overexposure,
In addition, stable high-quality image formation without image quality deterioration due to insufficient exposure can be realized.

Fourth Embodiment Next, an image forming apparatus according to a fourth embodiment of the present invention will be described with reference to FIG. FIG. 5 is a sectional view showing a schematic configuration of the image forming apparatus according to the fifth embodiment. Here, the same portions as those in the first embodiment are denoted by the same reference numerals, and the description of the configuration of the same portions and the description of the operation thereof will be omitted. The image forming apparatus of the present embodiment is provided with a transfer material discriminating means 56 for discriminating the type and thickness of the transfer material 37, and controls the exposure amount of the separation assisting means 50 based on the discrimination result of the transfer material discriminating means 56. Exposure amount control means 57
Is operated.

The surface potential of the electrostatic latent image holding member 21 of the present embodiment changes in the same manner as that shown in FIG. Transfer material 3
The type and thickness of 7 are input by, for example, a setting switch provided on an operation panel of a digital copying machine. Transfer material 37
When the type and thickness change, the exposure control means 57 controls the exposure of the separation assisting means 50 in conjunction with the change. In this case, an optimal exposure amount is set regardless of the type and thickness of the transfer material 37. For this reason, while ensuring good separability, the electrostatic latent image holding member 21
, And stable high-quality image formation without image quality deterioration due to insufficient exposure can be realized.

(Embodiment 5) Next, an image forming apparatus according to Embodiment 5 of the present invention will be described with reference to FIG. FIG. 6 is a sectional view showing a schematic configuration of the image forming apparatus according to the sixth embodiment. Here, the same portions as those in the first embodiment are denoted by the same reference numerals, and the description of the configuration of the same portions and the description of the operation thereof will be omitted. The image forming apparatus according to the present embodiment is provided with a developing member charge amount detection unit 58 and an exposure amount control unit 59, and controls the exposure amount of the separation assisting unit 50 in conjunction with the charge amount of the development member 32. It is characteristic.

The developing member charge amount detecting means 58 is provided inside the developing means 24 and detects the charge amount of the developing member 32, and outputs a signal proportional to the charge amount to the exposure amount controlling means 59.
Given to. Exposure amount control means 59 controls the exposure amount of separation assisting means 50 based on a signal provided from developing member charge amount detection means 58, as in the third or fourth embodiment.

The surface potential of the electrostatic latent image holding member 21 of the present embodiment also changes in the same manner as that shown in FIG. When the charge amount of the developing member 32 changes, the exposure amount control means 59 controls the exposure amount of the separation assisting means 50 in conjunction with the change. Therefore, the background potential is controlled to be constant regardless of the charge amount of the developing member 32. As a result, while ensuring good separability, it is possible to realize stable quality image formation without deterioration of the electrostatic latent image holding member 21 due to overexposure and image quality deterioration due to insufficient exposure.

Embodiment 6 Next, an image forming apparatus according to Embodiment 6 of the present invention will be described with reference to FIGS. FIG. 7 is a sectional view showing a schematic configuration of an image forming apparatus according to the sixth embodiment. Here, the same portions as those in the first embodiment are denoted by the same reference numerals, and the description of the configuration of the same portions and the description of the operation thereof will be omitted. The image forming apparatus of the present embodiment is provided with a transfer material discriminating means 60 and an exposure width control means 61, and controls the exposure width of the light 63 of the separation assisting means 62 in conjunction with the width of the transfer material 37. It is characteristic.

The transfer material discriminating means 60 discriminates the size of the transfer material 37, and particularly discriminates the width in the transport direction. Since a plurality of transfer materials 37 are held in a cassette corresponding to the size, the transfer material 3 is determined based on the cassette type.
You can see the size of 7. The separation assisting unit 62 is, for example, a light emitting element group in which a plurality of LEDs are arranged in a line in the width direction of the transfer material 37, and is attached to the separation position C so as to be opposed. The exposure width control unit 61 controls the exposure width of the separation assisting unit 62 based on the determination result of the transfer material determination unit 60. That is, the surface of the electrostatic latent image holding member 21 is exposed only in a region corresponding to the width of the transfer material 37.

FIG. 8 is an explanatory diagram showing a change in the surface potential of the electrostatic latent image holding member 21 by the separation assisting means 62 of the present embodiment. FIG. 8A shows a state in which the transfer material 37 is in close contact with the surface of the electrostatic latent image holding member 21, and is a view as seen from the transport direction of the transfer material 37. Here, a transfer material 37 smaller than the maximum allowable width is used. FIG. 8B is an explanatory view showing a light emitting state of the separation assisting means 62, and only the LED corresponding to the width portion of the transfer material 37 emits light.

FIG. 8C is an explanatory diagram showing the surface potential of the electrostatic latent image holding member 21 immediately after passing through the separation assisting means 62. A indicates the potential distribution when the separation assisting unit uniformly exposes the electrostatic latent image holding member 21 in the width direction as in the first embodiment. In this case, the electric charge generated by the developing member 32 exists only in the lateral width portion of the transfer material 37, and therefore, the surface potential becomes lower in the portion exceeding the lateral width of the transfer material 37.
However, in the present embodiment, since only the lateral width portion of the transfer material 37 is exposed by the separation assisting unit 62, the transfer material 37 is not exposed on the electrostatic latent image holding member 21 as shown in FIG. The surface potential of the portion exceeding the lateral width of can be kept high. Therefore, it is possible to prevent the unnecessary developing member 32 from scattering when the transfer material 37 is separated.

As described above, when the size (width) of the transfer material 37 changes, the exposure amount can be changed in the width direction of the transfer material, and the electrostatic latent image holding member 21 due to overexposure can be changed.
, And stable image quality without image quality deterioration due to insufficient exposure and scattering of the developing member.

Embodiment 7 Next, an image forming apparatus according to Embodiment 7 of the present invention will be described with reference to FIG. FIG. 9 is a sectional view illustrating a schematic configuration of an image forming apparatus according to the seventh embodiment. Here, the same portions as those in the first embodiment are denoted by the same reference numerals, and the description of the configuration of the same portions and the description of the operation thereof will be omitted. The image forming apparatus of the present embodiment is provided with the transfer material position determining means 64 and the exposure control means 65, and controls the exposure of the separation assisting means 50 in conjunction with the transfer position of the transfer material 37. Is the feature.

The transfer material position determining means 64 determines the transfer position of the transfer material 37, and particularly determines the position of the transfer material 37 when viewed from the separation position C, for example, the leading end, the center, or the end. The exposure control unit 65 controls the exposure of the separation assisting unit 50 based on the determination result of the transfer material position determining unit 64.

The surface potential of the electrostatic latent image holding member 21 according to the present embodiment basically changes in the same manner as that shown in FIG. 5
By changing the exposure amount of 0, the surface potential of the electrostatic latent image holding member 21 can be controlled. Here, at the leading end of the transfer material 37, the background potential VN after the exposure is changed to the potential VBG (=
(−300 V). In other areas, the exposure amount of the separation assisting means 50 is set to 0, and the background potential VN after the exposure is controlled to be VO (= -750 V). In this way, it is possible to prevent the deterioration of the electrostatic latent image holding member 2 due to overexposure and to realize image formation with stable quality.

In the above embodiment, an example in which an LED is used as the separation assisting means has been described. However, other light sources such as a rod-shaped lamp can be used as long as linear exposure is performed.

Further, in the above embodiment, the case where the electrostatic latent image holding member is negatively charged by using the charging means has been described as an example. Can be provided.

In the above embodiment, the image forming apparatus is used for a digital copying machine. However, the present invention can be applied to an apparatus using an electrophotographic process such as a laser printer.

[0068]

As described above, according to the present invention, a large difference between the background portion potential and the image portion potential can be maintained before transfer by exposing from the back surface of the transfer material that has reached the separation position. At the time of separation, the absolute value of the background portion potential can be reduced. For this reason, while ensuring good separation of the transfer material,
It is possible to prevent the image quality from being deteriorated due to the scattering of the developer and the forward jump. Further, a stable image can be formed without contamination of the transfer material due to contamination of the transfer guide member.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a structure of an image forming apparatus according to Embodiment 1 of the present invention.

FIG. 2 is an explanatory diagram illustrating a change in a surface potential of an electrostatic latent image holding member in the image forming apparatus according to the first embodiment;

FIG. 3 is a cross-sectional view illustrating a structure of an image forming apparatus according to a second embodiment of the present invention.

FIG. 4 is a cross-sectional view illustrating a structure of an image forming apparatus according to Embodiment 3 of the present invention.

FIG. 5 is a cross-sectional view illustrating a structure of an image forming apparatus according to Embodiment 4 of the present invention.

FIG. 6 is a cross-sectional view illustrating a structure of an image forming apparatus according to Embodiment 5 of the present invention.

FIG. 7 is a cross-sectional view illustrating a structure of an image forming apparatus according to Embodiment 6 of the present invention.

FIG. 8 is a diagram illustrating a change in surface potential caused by a separation assisting unit in the image forming apparatus according to the embodiment;

FIG. 9 is a sectional view illustrating a structure of an image forming apparatus according to a seventh embodiment of the present invention.

FIG. 10 is a cross-sectional view illustrating a structural example of a conventional image forming apparatus.

FIG. 11 is an explanatory diagram showing a change in surface potential of an electrostatic latent image holding member in a case where a conventional image forming apparatus does not have a pre-transfer exposure unit.

FIG. 12 is an explanatory diagram showing a change in the surface potential of the electrostatic latent image holding member when a pre-transfer exposure unit is provided in a conventional image forming apparatus.

[Explanation of symbols]

 Reference Signs List 21 electrostatic latent image holding member 22 charging means 23 electrostatic latent image forming means 24 developing means 25 transfer means 26 separating means 27 fixing means 28 cleaning means 30 charge 31 laser beam 32 developing member 33 carrier 34 sleeve 35 pre-transfer exposure means 36 Light of pre-transfer exposure means 37 Transfer material 38 Transfer guide member 40 Light energy distribution 41 Electrostatic latent image 42, 43 Developing member image 44 Output image 50, 52, 62 Separation assisting means 51, 53, 63 Light by separation assisting means 54 Grid 55, 57, 59, 65 Exposure amount control means 56, 60 Transfer material discriminating means 58 Developing member charge amount detecting means 61 Exposure width control means 64 Transfer material position discriminating means

Claims (11)

[Claims] An electrostatic latent image holding member configured to hold an electrostatic latent image by a surface charge; a charging unit configured to uniformly charge a surface of the electrostatic latent image holding member; An electrostatic latent image forming means for forming an electrostatic latent image by discharging a part of the surface charge by exposure according to image information with respect to the surface charge uniformly charged on the surface; Developing to form a developing member image by attaching a developing member charged to the same polarity as the surface charge to an uncharged area with respect to the electrostatic latent image formed on the electrostatic latent image holding member by the image forming means. Means for transferring a developing member formed by the developing means to the surface of the transfer material by applying an electric field having a polarity different from the surface charge from the back surface of the transfer material; and The charge remaining on the image holding member is released by the AC electric field. And a separation unit for causing the electrostatic latent image holding member located near the separation unit to emit light, thereby irradiating the surface of the electrostatic latent image holding member with light. An image forming apparatus comprising a separation assisting means for lowering a potential. 2. The image forming apparatus according to claim 1, wherein the separation assisting unit is provided between a position where the transfer unit is provided and a position behind the separation unit. 3. The image forming apparatus according to claim 2, further comprising an exposure amount control unit for changing an exposure amount of said separation assisting unit. 4. The image forming apparatus according to claim 3, wherein said exposure amount control means changes an exposure amount of said separation assisting means in accordance with a charge amount of said charging means. 5. The image forming apparatus according to claim 3, wherein the exposure amount control unit changes the exposure amount of the separation assisting unit according to the type and thickness of the transfer material. 6. An image forming apparatus according to claim 3, wherein said exposure amount control means changes an exposure amount of said separation assisting means in accordance with a charge amount of said developing member. 7. The image forming apparatus according to claim 3, wherein the exposure amount control unit changes the exposure amount of the separation assisting unit according to a position of the transfer material in a moving direction. 8. An image forming apparatus according to claim 3, wherein said exposure amount control means controls said separation assisting means so as to expose at least a leading end region of said transfer material. 9. An exposure width control means for changing an exposure amount in a width direction orthogonal to a moving direction of the transfer material, in order to change an exposure width of the separation assisting means. The image forming apparatus according to any one of claims 1 to 6, wherein 10. The image forming apparatus according to claim 9, wherein the exposure width control unit controls exposure of a transfer area of the transfer material. 11. The apparatus according to claim 1, wherein the transfer means performs corona discharge.
The image forming apparatus according to any one of claims 10 to 10.