JP2668439B2 - Image forming device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to an image forming apparatus, and in particular, a toner image on an image carrier formed by an electrophotographic method or an electrostatic recording method, The present invention relates to an image forming apparatus that obtains an image by applying a transfer electric field to a transfer material carried on a transfer material carrier to transfer the material. Such image forming apparatuses include black-and-white, mono-color or full-color electrophotographic copying machines, printers, and various other recording devices.

2. Description of the Related Art Conventionally, for example, various multi-color (full-color) image forming apparatuses have been proposed, but a multi-color electrophotographic copying apparatus including a developing apparatus called a so-called rotary developing apparatus as shown in FIG. Is illustrated.

Briefly described with reference to FIG. 4, the multicolor electrophotographic copying apparatus is provided with an image carrier, that is, a photosensitive drum 1, which is rotatably supported in a rotatable manner and rotates in the direction of an arrow, and an image forming means is provided on the outer periphery thereof. Is arranged. The image forming means may be any means, but in this example, a primary charger 2 for uniformly charging the photosensitive drum 1 and a color-separated light image or a light image corresponding thereto are radiated to form Exposing means 3 for forming an electrostatic latent image on the
A rotary developing device 4 for converting an electrostatic latent image on the photosensitive drum 1 into a visible image.

The rotary developing device 4 includes four developing devices 4Y, 4M, 4C, and 4BK that respectively store four color developers of a yellow developer, a magenta developer, a cyan developer, and a black developer.
And a substantially cylindrical housing which holds these four developing units 4Y, 4M, 4C, and 4BK and is rotatably supported. The rotary developing device 4 conveys a desired developing device to a position facing the outer peripheral surface of the photosensitive drum 1 by rotating the housing, and develops an electrostatic latent image on the photosensitive drum. Is rotated once, so that the so-called full-color development for four colors is possible.

The visible image on the photosensitive drum, that is, the toner image is transferred to a transfer material P carried and transported by the transfer device 5. In this embodiment, the transfer device 5 is a rotatably supported transfer drum, and the transfer drum 5 is provided in the cylinder 5a and the cylinder 5a, as will be understood with reference to FIG. It has a charger 5b and a transfer material gripper 5c for gripping the transfer material fed from a sheet feeding device (not shown). Further, inside and outside of the transfer drum 5, an inner static eliminator 5d and an outer static eliminator 5e constituting static elimination means are arranged.
The transfer material carrier 501 is provided in the outer peripheral surface opening area of the cylinder 5a.
Is installed. The transfer material carrier 501 is usually, for example,
A film-like dielectric sheet such as polyethylene terephthalate or polyvinylidene fluoride film is used.

The process of forming a full-color image by the multicolor electrophotographic copying machine having the above-described configuration will be briefly described as follows.

First, a blue color-separated electrostatic latent image is formed on the outer peripheral surface of the photosensitive drum 1 by driving the charger 2 and the image exposure means 3, and the electrostatic latent image is stored in the developing device 4Y. It is developed with a yellow developer.

On the other hand, the transfer material fed to the transfer drum 5 is gripped by the gripper 5c and abuts on the toner image formed on the outer peripheral surface of the photosensitive drum 1 as the transfer drum 5 rotates. . The toner image is transferred onto the transfer material by the operation of the transfer charger 5b, and at the same time, the transfer material is attracted to the transfer material carrier 501.

The above image forming and transferring operations are repeated for each of the colors magenta, cyan, and black. When the superimposed transfer of the four colors of the visible image onto the transfer material P is completed, the transfer material P is neutralized by the inner charger 5d and the outer charger 5e, and then separated from the transfer drum 5, and the heat roller fixing device 6
Is discharged out of the machine via. On the other hand, the residual toner on the photosensitive drum is removed by the cleaner 7, and the photosensitive drum is subjected to the next image forming process.

Problems to be Solved by the Invention Although the multicolor electrophotographic copying apparatus having the above-described configuration operates extremely favorably, according to the experiments conducted by the inventors of the present invention, in the transfer step, particularly, the transfer material carrying of the transfer apparatus 5 is carried. Using polyvinylidene fluoride resin film etc. as the body 501,
It has been found that when a transfer paper is used as the transfer material P, a problem occurs especially when the humidity is low. This will be described below.

As can be understood with reference to FIG. 6, the neutralization means for neutralizing the transfer material P on which the toner image has been transferred includes an inner neutralization corona charger 5d, which usually comprises an AC charger to which a DC bias can be applied, As shown in FIG. 8 showing the operation sequence of the image forming apparatus, the inner charger 5d and the outer charger 5e are constituted by an outer charge removing corona charger 5e composed of an AC charger. The transfer material is separated from the transfer drum at the time of pre-rotation before the image forming process is started (the number of rotations of the photosensitive drum is 3, 4) and at the start of the operation of the image forming process of the last color separation image, and the image forming process ends. (The number of rotations of the photosensitive drum is 10, 11, 12).

The polarity of the transfer voltage supplied to the transfer charger 5b is
For example, when a latent image is formed with a negative charge and the toner of each developer is negatively charged to reversely develop the latent image, the value is set to be positive.

According to the research experiments of the present inventors, when the inner charger 5d and the outer charger 5e are operated after the transfer in a low humidity environment (in FIG. 8, the photosensitive drum rotation speed is 10 to 12), the transfer material P It was found that the toner scattered and left the transfer material and soiled the shield of the outer charger 5e. It was also found that when the amount of the scattered toner was large, the transferred image on the transfer material was disturbed and became a defective image.

The present inventors have studied such toner scattering.As a result, the transfer current was increased in a low humidity environment to transfer the toner image on the photosensitive drum, and then, during the charge removal performed prior to separating the transfer material from the transfer drum, In particular, it has been found that when the DC component superimposed on the inner charger 5d is strong, toner scattering as described above is likely to occur.

 FIG. 7 shows the principle of toner scattering, which will be described below.

The DC component superimposed on the inner charger 5d is used for continuous copying.
Prior to the next transfer, a DC voltage having a polarity opposite to that of the transfer voltage is applied to eliminate the charge of the transfer material supporting member 501.
In a low humidity environment in which transfer is performed by increasing the transfer current, it is necessary to increase the DC current applied to the charge removal. At this time,
When a charge having the same polarity as the toner is applied to the surface of the transfer material carrier 501 on the transfer charger 5d side, the toner having the same polarity receives a repulsive force due to the electric field generated by the charge and is separated from the transfer material. I understood that.

Further, in a low humidity environment, as a factor for increasing the transfer current, since the resistance of the transfer material P becomes high, the transfer material carrier 501 and the transfer material carrier 501 are particularly required when multiple transfer is required as in full-color image formation. Good transfer may be performed by compensating for the charge-up of the transfer material P.

Further, as for the toner on the photosensitive drum, the higher the charge of the toner per unit volume, the more the transfer current for drawing to the transfer material is required. This means that when the particle size of the toner used for development is reduced, the toner charge applied in the developing device increases, so that the above-described problem is likely to occur in the small particle size toner used for high image quality. .

According to the results of research conducted by the present inventors, it has been found that this tendency is increased when the average particle diameter is 10 μm or less as compared with a commonly used toner having an average particle diameter of about 12 μm.

Therefore, it is an object of the present invention to prevent toner on the transfer material from scattering and causing image deterioration even when the image forming operation is performed in a low humidity environment when the transfer material is separated from the transfer material carrier. An object of the present invention is to provide an image forming apparatus.

Another object of the present invention is to provide an image forming apparatus capable of effectively preventing toner scattering even when using a small particle size toner used for high image quality or the like and obtaining a good quality transferred image. It is to provide.

Means for Solving the Problems The above objects are achieved by an image forming apparatus according to the present invention. In summary, the present invention provides an image carrier capable of carrying a plurality of color toner images, a transfer material carrier carrying a transfer material, and the transfer material carrier carrying the plurality of color toner images on the image carrier. Transfer charging means for sequentially superimposing and transferring onto a transfer material carried on the transfer material, and after transferring the final color toner image by the transfer charging means,
Before the transfer material is separated from the transfer material carrier, an outer static eliminator provided on a side of the transfer material carrier that supports the transfer material, in order to eliminate the charge of the transfer material and the transfer material carrier at a charge removing position; A direct-current voltage having a polarity opposite to the charging polarity of the transfer charging means, the inner charge-removing means being provided on the side of the transfer material-carrying member on which the transfer material is not carried and facing the outer charge-eliminating means. An image forming apparatus for applying a voltage obtained by superimposing an AC voltage to the outer static eliminator and the inner static eliminator, wherein the DC voltage is applied to the outer static eliminator and the inner static eliminator while the entire transfer material passes the static elimination position. The image forming apparatus is characterized by being applied to the image forming apparatus.

Preferably, detecting means for detecting the temperature and humidity in the apparatus is provided, and the DC voltage applied to the outer static eliminating means is made variable according to the detection result of the detecting means.

Next, an image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

The present invention can be suitably implemented in a multicolor electrophotographic copying machine having the rotary developing device described above with reference to FIG. Therefore, in this embodiment, the image forming apparatus is embodied in the multicolor electrophotographic copying apparatus shown in FIG. 4, and the configuration and operation are as described above. In this embodiment, the diameter of the photosensitive drum 1 is, for example, 80 mm, and the diameter of the transfer device, ie, the transfer drum 5, is 160 mm (twice the diameter of the photosensitive drum).

Also, the photosensitive drum 1 is rotated in the direction of the arrow at 160 mm / sec, and the surface of the photosensitive drum 1 is −500 by the primary charger 2.
It is charged to -800V. Each developing device of the rotary developing device 4 has a toner of each color having a negative charge, and visualizes a latent image formed on the photosensitive drum 1 by reversal development.

According to the present invention, as can be understood with reference to FIG. 1, the visible image on the photosensitive drum 1, ie, the toner image, is transferred to a transfer material P carried and carried by the transfer device 5.

In this embodiment, the transfer device 5 has a structure similar to that of the transfer device shown in FIG. 5, and is a drum-shaped transfer drum that is rotatably supported. The transfer drum 5 is a transfer material carrier. Cylinder 5a on which 501 is stretched, transfer charger 5b disposed in transfer drum 5, transfer material gripper gripping transfer material P fed from a paper feeding device (not shown).
Has 5c. Further, inside and outside of the transfer drum 5, an inner static eliminator 5d and an outer static eliminator 5e constituting static elimination means are arranged.

The transfer material carrier 501 has a thickness of, for example, 100 μm to 175 μm.
Dielectric sheet such as poly (vinylidene fluoride) film having m and volume resistance of 10 ¹³ Ω · cm is used.

As can be better understood with reference to FIG. 1, the transfer charger 5b is a corona charger, for example, +6 kV to +9 kV.
Is applied, and the transfer current is set to +100 μA to +500 μA. The static eliminator for neutralizing the transfer material on which the toner image has been transferred is a DC bias (−0.7 kV to −3.7 kV,
AC charger (12kVp) capable of applying -50μA to -265μA)
p, 800 μA) and an inner corona charger 5d for static elimination, and a DC bias (−0.2 KV to −1.0 KV, −10 μA) during AC oscillation
AC charger (8kV, 600μA) which can apply ~ -50μA)
, And the AC components of the outer charger 5d and the inner charger 5e are controlled to have opposite phases.

In the above configuration, static elimination means, that is, the inner charger 5d
As shown in FIG. 2 showing the operation sequence of the image forming apparatus, the outer charger 5e is in the pre-rotation state before the image forming process of the image forming apparatus is started as in the conventional image forming apparatus. (The number of rotations of the photosensitive drum 3 and 4), and from the start of the image forming process operation of the last color separation image to the time when the transfer material is separated from the transfer drum and the image forming process ends (the number of rotations of the photosensitive drum 10 to Further, according to the present invention, during the transfer of the final color and the separation of the transfer material (photosensitive drum rotation speed 10 to 12), minus DC having the same polarity as the toner is applied to the outer charger 5e of the charge removing means. Is done.

According to the present invention, by applying a negative DC having the same polarity as the toner to the outer charger 5e, it is possible to prevent the toner from separating from the transfer material during the operation of the inner and outer chargers. FIG. 3 shows a principle diagram, which will be described in more detail.

The outer charger 5e acts in a direction to suppress the amount of negative charge applied to the transfer material carrier 501 from the inner charger 5d, which has the same polarity as the toner applied to the toner on the transfer material P, to the toner on the transfer material P. In addition, it reduces the force of the toner to separate from the transfer material. Therefore, it is necessary to apply the negative charge to the toner so as not to hinder the neutralization of the transfer material carrier 501 positively charged by the transfer charger 5b.

In the embodiment of the present invention, when the DC bias when AC is applied is −260 μA (−3.7 KV) to the inner charger 5d, the outer charger is
The optimum DC bias applied to 5e was −25 μA (−0.6 KV).

The present inventors conducted a study on the present invention having the above configuration in an actual use environment, and as a result, in a low humidity environment, the static elimination current according to the present invention is strong, and in a high humidity environment, the static elimination current according to the present invention is weak or zero. Turned out to be good. The reason for this is that the charge removal current is set to a high level because the charge charge of the toner increases at low humidity, but the transfer material carrier and the transfer material are removed when the transfer material is separated due to the high resistance of the transfer material. It can be said that this is due to the need for a strong current.

On the other hand, in a high-humidity environment, on the other hand, the above-described static elimination can be easily performed.On the other hand, when the static elimination current is strong, electric charges of the same polarity as the toner are transmitted from the outside to the transfer material to reach the transfer section, and a transfer electric field is generated. Transfer weakening may occur due to weakening.

FIG. 10 and FIG. 11 show the relationship between the humidity and the current of the internal and external chargers. That is, in FIG. 10 shows the relationship between the humidity and the temperature, in FIG. 11 during the operation of the inner and outer neutralization in each zone of h ₁ to h ₇ water approximately equal contained in the air shown in FIG. 10 Indicates the optimal DC current to be applied. In the figure, the symbol h indicates the amount of DC applied to the inside static elimination, and the symbol i indicates the DC amount applied to the outside static elimination.

Further, regarding the present invention having the above-described structure, the present inventors relate to the relationship between the toner particle size of the toner image formed on the photosensitive drum 1 and the amount of toner scattered on the transfer material and separated from the transfer material. Examined. The experimental results are shown in FIG.

In this experiment, the amount of scattering toner was measured by the weight of the toner adhering to the outer charger 5e, and the same image was used for A4 size paper passing 10
The amount after 00 sheets was compared. The images used were those having a yellow, magenta, cyan and black color area ratio of 30%.

In FIG. 9, reference numeral 1 denotes the amount of toner scattering in the conventional apparatus, and reference numeral m denotes the amount of toner scattering according to the embodiment of the present invention.
In addition, the amount of toner adhering indicated by the symbol X in FIG.
Since the shield of 5e was soiled and discharge unevenness was generated at the time of static elimination, it was found that the static elimination of the transfer material carrier during the pre-rotation (rotation of the photosensitive drums 3 and 4) was also uneven and a defective image was generated.

The reason why the toner scattering amount increases when the toner particle size is reduced is that the toner particle size reduced is smaller in the toner layer thickness, and the total charge amount is substantially the same in the toner layer thickness on the transfer material. However, it is considered that the repulsive force between them is increased because the distance is close to the charge of the same polarity as that of the toner, which is the charge removed on the back surface of the transfer material carrier.

From this point, it can be said that, in the toner having an average particle diameter of 10 μm or less, the scattering development which is likely to occur at low humidity in the toner having an average particle diameter of 10 μm or more easily occurs even in a normal environment.

As described above, in the image forming apparatus according to the present invention, the entire transfer material and the entire portion of the transfer material carrier that supports the transfer material are properly discharged, while the entire transfer material is at the charge removal position. By applying a DC voltage to the outer static eliminator while passing, it is possible to prevent the toner on the transfer material from scattering and causing image deterioration, especially after transfer of the toner of the final color in a low humidity environment. Even when a small particle size toner used for high image quality is used, it is effective not only in a low humidity environment but also effectively against toner scattering that tends to occur, and it is possible to obtain a high quality image. Have.

[Brief description of the drawings]

FIG. 1 is a partial configuration diagram of a transfer device used in an image forming apparatus according to the present invention. FIG. 2 is a diagram showing an operation sequence of the transfer and charge elimination means with respect to the number of rotations of the photosensitive drum and the transfer drum interlocked in the image forming apparatus according to the present invention. FIG. 3 is a model diagram of discharge means for explaining the effect of the present invention. FIG. 4 is a schematic diagram of one embodiment of a multicolor electrophotographic copying apparatus to which the present invention can be applied. FIG. 5 is a perspective view showing one embodiment of a transfer device used in the image forming apparatus of FIG. FIG. 6 is an apparatus configuration diagram of a conventional transfer apparatus. FIG. 7 is a model diagram of a discharging unit showing a state of toner scattering in the related art. FIG. 8 is an operation sequence diagram of the conventional image forming apparatus. FIG. 9 is a graph showing the relationship between the toner particle size and the amount of toner scattering showing the effect of the present invention. FIG. 10 is an explanatory diagram showing an equal moisture region in the air. FIG. 11 is an explanatory diagram showing the relationship between the amount of DC component applied to the static elimination current and the amount of moisture in the air. 1: Image carrier (photosensitive drum) 5: Transfer device (transfer drum) 5b: Transfer charger 5d, 5e: Charger 501: Transfer material carrier

Claims (2)

(57) [Claims] An image carrier capable of carrying a plurality of color toner images; a transfer material carrier carrying a transfer material; and the transfer material carrier carrying the plurality of color toner images on the image carrier. Transfer charging means for sequentially superimposing and transferring to the transferred transfer material, and after transferring the toner image of the final color by the transfer charging means, before separating the transfer material from the transfer material carrier, the transfer material and the transfer material carrier are An outer static eliminator provided on a side of the transfer material carrier for supporting the transfer material, and a side of the transfer material carrier which does not support the transfer material, for facing the outer static eliminator for static elimination at the static elimination position And an inner static eliminator provided as an image forming means for applying a voltage obtained by superimposing a DC voltage and an AC voltage having a polarity opposite to the charging polarity of the transfer charger to the outer static eliminator and the inner static eliminator. In the apparatus, the entire transfer material is discharged as described above. The image forming apparatus, wherein the DC voltage is applied to the outer charge eliminating means and the inner charge eliminating means while passing through the position. 2. The apparatus according to claim 1, further comprising detecting means for detecting temperature and humidity in said apparatus, wherein said DC voltage applied to said outer static eliminating means is made variable in accordance with a detection result of said detecting means. Item 1. The image forming apparatus according to Item 1.