JP3344792B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image in which a plurality of toner images are sequentially primary-transferred to an intermediate transfer member to form a multi-toner image, and then collectively secondary-transferred to recording paper or the like. The present invention relates to a forming apparatus.

2. Description of the Related Art In an electrophotographic full-color image forming apparatus, development is performed using a single photoconductor (image carrier) in different colors every rotation, and toner images of the respective colors are sequentially superimposed on an intermediate transfer member. And a photoconductor for each color is separately provided to transfer the toner image of each color to the intermediate transfer body at a time.

[0003] Of the two types of apparatuses, the former has a feature that it can be manufactured compactly and at low cost because it has a small number of parts, and the latter has a feature that high-speed recording is possible. The image forming apparatus of the present invention corresponds to the former of the above two types.

[0004]

2. Description of the Related Art In such an image forming apparatus, when a full-color image is formed, yellow, magenta, cyan and black toner images are transferred from a photoreceptor to an intermediate transfer member every time the intermediate transfer member makes one rotation. Are transferred sequentially (primary transfer) so that a full-color image is formed.

[0005] In such primary transfer from the photoreceptor to the intermediate transfer member, a voltage (primary transfer voltage) having a polarity opposite to the charging polarity of the toner is applied to the transfer device to apply an electrostatic Coulomb force to the toner. This is done by acting. Therefore, in order to transfer toner images of different colors onto the intermediate transfer member in a superimposed manner, the primary transfer voltage must be increased with the number of superpositions.

FIG. 5 is a model diagram showing a state in which a second color toner image 203 of a photosensitive member 202 is superimposed and transferred on a first color toner image 201 transferred to an intermediate transfer member 200. Reference numeral 204 denotes a primary transfer device.

In order to transfer the toner image 203 on the photosensitive member 202 onto the intermediate transfer member 200, the transfer gap 2
It is already known that it is necessary to set the electric field between F.05 and F.05 in the range of 23-50 MV / m.
The primary transfer voltage V _{R1 is} set so that the electric field between them becomes such a value.
Must be set.

Considering the electrical equivalent circuit of the primary transfer section from the transfer model of FIG. 5, as shown in FIG. 6, the capacitance C1 of the photosensitive layer of the photosensitive member and the static capacitance of the toner layer on the photosensitive member The capacitance C2, the capacitance C3 of the transfer gap (air layer), and the capacitance C of the toner layer already transferred on the intermediate transfer member
4, and the capacitance C5 of the intermediate transfer member can be considered as being connected substantially in series.

As described above, the primary transfer voltage V _R1 is divided by the capacity ratio of each part such as the photoconductor and the toner layer. Therefore, the primary transfer voltage must be set so that the voltage required for the electric field of the gap 205 to fall within the above range is applied to both ends of the capacitance C3 of the air layer in FIG.

Incidentally, the capacitance C4 of the toner layer already transferred on the intermediate transfer member varies depending on the number of times of superposition transfer. That is, in the primary color transfer (first superposition), C4 is zero because there is no toner layer already transferred to the intermediate transfer body, but in the secondary color (second time), the primary color toner is already Since the image is transferred to the intermediate transfer member, a capacitance C4 due to the primary color toner layer is generated.

Similarly, in the case of the tertiary color (the third time), since the primary and secondary color toners have already been transferred onto the intermediate transfer member, C4 is the static color of the toner layer in which the primary color and the secondary color toner layers are combined. It becomes electric capacity. As described above, the value of the capacitance C4 of the toner layer on the intermediate transfer member changes depending on the number of superpositions.

Therefore, in order to always perform a constant transfer irrespective of the number of superpositions, the voltage V3 applied to both ends of the air layer C3 is constant even if the capacitance C4 of the toner layer on the intermediate transfer member changes. , The primary transfer voltage V _R1 must be changed with the change of C4.

The relationship between the primary transfer voltage V _R1 and V 3 is as follows: V _R1 = ((1 / C1) + (1 / C2) + (1 / C3) + (1 / C4) + (1 / C5)) × C3x
Represented by V3. C1, C2, C3, C5, and V3 are constants, and only C4 is a variable because it changes according to the number of superpositions. V3 is a voltage for setting the electric field between the transfer gap gaps to 23 to 50 MV / m.
５０50 (MV / m) × g (m).

From the above equation, it is clear that the capacitance value of the toner layer C4 on the intermediate transfer member increases as the number of times of superposition increases, so it is necessary to increase the primary transfer voltage V _R1 with the number of times of superposition. It is.

[0015]

However, when the primary transfer is performed while being superimposed on the intermediate transfer member, the toner image already transferred on the intermediate transfer member returns to the primary transfer portion and is removed therefrom. During the passage, a reverse transfer phenomenon occurs in which the toner returns from the intermediate transfer body to the photoconductor side.

FIG. 7 shows the results of an experimental study of such a reverse transcription phenomenon. Here, the toner weight is 1.1.
A toner image of mg / cm ² was formed on the intermediate transfer member, and the toner image was passed through the primary transfer portion up to 14 times to determine a weight change of the toner image on the intermediate transfer member.

As a result, it became clear that about 10% of the toner image on the intermediate transfer member is transferred to the photosensitive member every time the toner image passes through the primary transfer portion. When the cause of the reverse transfer phenomenon was investigated, it was found that the cause was the charge injection into the toner image in the primary transfer portion.

FIG. 8 is a diagram for explaining the concept of charge injection in the primary transfer section. In order to primarily transfer the toner image 203 from the photoreceptor 202 to the intermediate transfer member 200, a voltage having a polarity opposite to the charge polarity of the toner is applied to the primary transfer device 204. Polar charges are injected into the toner. In this way, the oppositely charged toner 207 charged to the opposite polarity by the charge injection is mixed in the toner image primarily transferred to the intermediate transfer body 200.

When the toner image in which the oppositely charged toner is mixed passes through the primary transfer portion again, the oppositely charged toner 207 has the same polarity as the voltage polarity of the primary transfer device 204.
Coulomb force due to the electric field of the primary transfer device 204 does not act,
It moves to the photoconductor 202. In fact, when the charge polarity of the toner transferred to the photoconductor 202 was investigated, it was confirmed that the toner was clearly reverse-charged.

In order to suppress the charge injection into the toner during the primary transfer, the primary transfer voltage may be reduced. However, as described above, in order to perform the overlay transfer, the transfer is performed according to the overlay. Since the voltage must be increased, it is not possible to eliminate the reverse transfer by suppressing the charge injection into the toner, and the image quality has deteriorated due to the reverse transfer of the reversely charged toner.

Therefore, the present invention eliminates the reverse charging of the toner which has already been primary-transferred onto the intermediate transfer member, so that the toner passing through the primary transfer portion returns from the intermediate transfer member to the image carrier. Suppress the occurrence of photography phenomena,
It is an object to provide an image forming apparatus capable of obtaining a high-quality image.

[0022]

In order to achieve the above object, an image forming apparatus according to the present invention uses a toner formed on an image carrier 1 as shown in FIG. An image forming apparatus in which an image is sequentially superimposed on an intermediate transfer body 11 and primary-transferred, and a multi-toner image formed on the intermediate transfer body 11 is secondarily transferred collectively to recording paper 100 or the like, In the secondary transfer section 20, a secondary transfer corona discharger 21 and then a paper separation corona discharger 22 are juxtaposed in the direction of movement of the intermediate transfer body 11, and a multi-toner for the intermediate transfer body 11 is provided. Until all the primary transfer of the image is completed, static elimination is performed by the corona discharger 21 for secondary transfer, and recharge of the toner on the intermediate transfer body 11 is performed by the corona discharger 22 for paper separation. It is characterized by.

Until the primary transfer is completed, an alternating voltage is applied to the corona discharger 21 for secondary transfer, and the toner on the intermediate transfer body 11 is applied to the corona discharger 22 for paper separation. A DC voltage having the same polarity as the original charging polarity is applied, and after the completion of the primary transfer, a DC voltage having a polarity opposite to the original charging polarity of the toner on the intermediate transfer body 11 is applied to the secondary transfer corona discharger 21. An alternating voltage may be applied to the paper separating corona discharger 22 while applying a voltage, and toner images of four colors of yellow, magenta, cyan and black are superimposed on the intermediate transfer body 11. It is applied to those formed by

[0024]

Until the primary transfer from the image carrier 1 to the intermediate transfer member 11 is repeated and all the transfer is completed, the potential of the toner layer on the intermediate transfer member 11 is reduced to zero by static elimination by the corona discharger 21 for secondary transfer. Corona discharger 2 for paper separation
By the recharging by 2, the toner on the intermediate transfer body 11 is uniformly charged to the correct polarity. When the toner thus charged returns to the primary transfer section and passes there,
The phenomenon of reverse transfer to the image carrier 1 does not occur.

[0025]

An embodiment will be described with reference to the drawings. FIG.
1 shows an electrophotographic full-color printer to which the present invention is applied.

Here, first, the photosensitive drum (image carrier) 1 is uniformly charged by the charger 2. Next, the exposure unit 3
Forms an electrostatic latent image on the photosensitive drum 1 by the
Thus, toner of each color is attached to the latent image portion and developed.

The developing unit 4 includes a developing unit 4a using a yellow (Y) toner, a developing unit 4b using a magenta (M) toner, a developing unit 4c using a cyan (C) toner, and a black (B) ) Developing unit 4 using toner
and development is performed one color at a time each time the photosensitive drum 1 makes one rotation.

The developed toner image is transferred from the intermediate transfer belt 11 by the primary transfer roller 5 at a contact portion with an intermediate transfer belt (intermediate transfer member) 11 rotating at the same surface speed as the photosensitive drum 1. Primary transfer to the surface. The toner on the photosensitive drum 1 that has not been transferred is removed by the cleaning unit 6, and subsequently, an image forming process using the next color toner is performed.

As described above, when the photosensitive drum 1 makes one rotation, the intermediate transfer belt 11 also makes one rotation, so that four color toner images are sequentially superimposed on the intermediate transfer belt 11 from the photosensitive drum 1 and transferred. Is done.

When the superposition of the four color toner images on the intermediate transfer belt 11 is completed, the toner images are transferred to the second transfer unit 2.
At 0, they are collectively transferred to the recording paper 100 (secondary transfer), and are fixed to the recording paper 100 by the fixing device 8.

Thus, a full-color image is formed on the recording paper 100. After the transfer to the recording paper 100, the intermediate transfer belt 11 is cleaned of residual toner by the cleaner 9, and the operation is repeated again from the primary transfer of the first color.

The secondary transfer section 20 includes a corona discharger 21 for secondary transfer for performing secondary transfer, and the recording paper 100 in the secondary transfer section 20 by AC charge elimination.
1 and a paper separation corona discharger 22 for electrostatically separating the intermediate transfer belt 1 from the first transfer belt 11 are arranged in the rotation direction of the intermediate transfer belt 11 in that order. The configuration of both corona dischargers 21 and 22 is a corotron.

FIG. 2 shows a drive circuit for the corona discharger 21 for secondary transfer and the corona discharger 22 for paper separation. A first solid state relay is provided for the corona discharger 21 for secondary transfer. One of a high voltage power supply 33 for AC corona discharge and a DC high voltage power supply 34 for secondary transfer is connected by a first transfer relay 32 switched by the (SSR) 31.

On the other hand, for the corona discharger 22 for separating paper, a DC transfer high voltage power supply 43 for recharging and a high voltage power supply 44 for AC neutralization are provided by a second transfer relay 42 switched by a second solid state relay 41. Is connected.

The switching of each relay is controlled by a control unit (mechanical controller) 50 incorporating a microprocessor.
And the secondary transfer enable signals 1 and 2 are set to T
In the TL level “H” state, both corona dischargers 21 and
No high voltage is supplied to the corona wires No. 2 and the respective corona wires are stopped.

When the enable signal 1 is "L" and the enable signal 2 is "H", the secondary transfer corona discharger 21
The high voltage of the same polarity as the charging polarity of the toner is supplied to the corona wire of the corona discharger 22 for the paper separation, and the corona discharger 21 for the secondary transfer is supplied with the high voltage of the AC. It operates as a corona discharger, and the paper separating corona discharger 22 operates as a recharger.

Further, when both the enable signal 1 and the enable signal 2 are in the "L" state, the charge polarity of the toner necessary for performing the secondary transfer is applied to the corona wire of the corona discharger 21 for the secondary transfer. High voltage of opposite polarity is supplied,
The corona discharger 22 for paper separation is supplied with an AC high voltage required for paper separation, and operates as a secondary transfer corona discharger and a paper separation AC corona discharger, respectively. As described above, the operation of both corona dischargers 21 and 22 is switched by the combination of the two enable signals.

FIG. 3 is a time chart showing the operation control of the corona dischargers 21 and 22. The secondary transfer corona discharger 2 is provided until all of the four-fold primary transfer is completed.
1 operates as an AC corona discharger when a high alternating voltage is applied, and a high-voltage DC voltage having the same polarity as the original charging polarity of the toner on the intermediate transfer belt 11 is applied to the paper separating corona discharger 22. Thus, it acts as a recharger for the toner on the intermediate transfer belt 11.

When the primary transfer is completed for all four color toner images, the secondary transfer corona discharger 21 applies a high DC voltage having a polarity opposite to the original charge polarity of the toner on the intermediate transfer belt 11. Then, the paper separation corona discharger 22 acts as an original secondary transfer corona discharger, and the paper separation corona discharger 22 acts as an original AC corona eliminator when a high alternating voltage is applied to perform paper separation.

In this manner, until all the primary transfer is completed, the corona discharger 21 for the secondary transfer operates as an AC corona eliminator to eliminate the oppositely charged toner.
The paper separation corona discharger 22 recharges the toner layer to suppress reverse transfer.

After the completion of the primary transfer, the secondary transfer corona discharger 21 is switched to the discharge polarity for performing the secondary transfer, and at the same time, the paper separation corona discharger 2 is switched.
2 is also switched to the AC discharge polarity for separating the paper, and the secondary transfer to the recording paper 100 is performed.

Actually, the transfer toner amount was 1.1 mg / cm
^Two, The toner charge amount is -12 μc / g, and the intermediate transfer body is transported.
Speed 100 mm / s, thickness of intermediate transfer body 150 μm
m, the resistance of the intermediate transfer member is 10⁸Ωcm, Coronawa for recharging
Ear voltage -5kV, corona wire voltage for secondary transfer
+ 5kV, Corona wire voltage for AC neutralization is 10kV
_(PP)FIG. 4 shows the results of an experiment at a frequency of 500 Hz.
As shown, reverse transcription could be substantially suppressed.

[0043]

According to the present invention, it is possible to eliminate the reverse charge phenomenon of the toner generated on the intermediate transfer member by the primary transfer and to suppress the reverse transfer phenomenon at the primary transfer portion due to the reverse charge toner. As a result, a stable, high-quality image can always be formed.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of an embodiment.

FIG. 2 is a control circuit diagram of the embodiment.

FIG. 3 is a time chart illustrating the operation of the embodiment.

FIG. 4 is a diagram showing experimental results of an example.

FIG. 5 is a model diagram of primary transfer.

FIG. 6 is an equivalent circuit diagram of a primary transfer unit.

FIG. 7 is a diagram showing experimental results of a conventional example.

FIG. 8 is a conceptual diagram of charge injection into toner in a primary transfer section.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photosensitive drum (image carrier) 11 Intermediate transfer belt (intermediate transfer member) 20 Secondary transfer part 21 Corona discharger for secondary transfer 22 Corona discharger for paper separation 100 Recording paper

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-4-138483 (JP, A) JP-A-4-296774 (JP, A) JP-A-4-27987 (JP, A) JP-A-1- 273077 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G03G 15/16 G03G 15/01 114 G03G 15/14 101

Claims (3)

(57) [Claims] A first transfer unit that superimposes the toner images formed on the image carrier on the intermediate transfer body in a superimposed manner;
In the image forming apparatus in which the multiple toner images formed on the intermediate transfer body (11) are secondarily transferred collectively to a recording paper (100) or the like, the secondary transfer unit (20) performs the secondary transfer. Corona discharger (2
1) and then a paper separating corona discharger (22) are juxtaposed in the direction of movement of the intermediate transfer member (11), so that the primary transfer of the multi-toner image to the intermediate transfer member (11) is completed. Until the termination, the secondary transfer corona discharger (21) is used to remove static electricity, and the paper separation corona discharger (22) is used to recharge the toner on the intermediate transfer body (11). Characteristic image forming apparatus. 2. An alternating voltage is applied to the corona discharger for secondary transfer (21) and the intermediate transfer to the corona discharger for paper separation (22) until all of the primary transfer is completed. A DC voltage having the same polarity as the original charge polarity of the toner on the body (11) is applied, and after the completion of the primary transfer, the intermediate transfer body (1) is supplied to the secondary transfer corona discharger (21).
2. The image forming apparatus according to claim 1, wherein a DC voltage having a polarity opposite to the original charge polarity of the toner is applied and an alternating voltage is applied to the paper separating corona discharger. 3. The image forming apparatus according to claim 1, wherein toner images of four colors of yellow, magenta, cyan and black are formed on the intermediate transfer member in a superimposed manner.