JP3153695B2 - 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 a color copying machine, a color printer, etc., in which a plurality of developer images formed on a plurality of image carriers are transferred onto a single sheet supported and transported by a transfer belt. The present invention relates to an image forming apparatus for obtaining a color image by performing multiple transfer.

[0002]

2. Description of the Related Art Conventionally, when a full-color image is obtained by an image forming apparatus such as a copying machine or a printer, four drums of black, yellow, magenta and cyan are placed on a photosensitive drum.
Each developer image is formed with a color developer, and then a transfer belt made of a charged insulative or conductive material is electrostatically adsorbed onto the transfer belt by a transfer belt made of a charged insulating or conductive material. While the paper is conveyed so as to be in contact with the paper, a charge for transfer is applied by a corona charger or the like at a position where the paper and the respective photoconductors are in contact with each other, and each developer image is multiply transferred onto the paper from the photoconductors.

[0003]

Conventionally, when a plurality of developer images are transferred onto a sheet in a multiplex manner, the sheet is electrostatically attracted to an insulating or conductive transfer belt and transported. For this reason, in the case of an insulating transfer belt, although the sheet can be reliably electrostatically attracted and conveyed by the charging of the transfer belt, it is required when the developer image is transferred to the sheet because of the insulating property. 6k applied voltage to corona charger
V and a very high pressure, which is dangerous and causes a problem that ozone harmful to the human body is generated during corona discharge.

On the other hand, in the case of a conductive transfer belt, the voltage applied to the corona charger at the time of transfer may be about 1-2 kV, so that there is an advantage that danger is reduced and ozone is less generated. However, since the transfer belt itself has a weak charge holding force, the electrostatic attraction force of the paper is weak, and the suction position on the transfer belt is shifted while the paper is being conveyed. This has caused a serious problem that color misregistration is caused, image quality is significantly reduced or the image quality becomes unusable.

In view of the above, the present invention has been made to solve the above-mentioned problem, and uses a conductive transfer belt capable of reducing the applied voltage at the time of transfer. Provided is a high-precision image forming apparatus capable of obtaining a clear and good color image without causing a shift in a suction position on a transfer belt during conveyance, and without causing a color shift even when a developer image is transferred multiple times. The purpose is to do.

[0006]

In order to solve the above-mentioned problems, the present invention provides an image forming means for forming a developer image on each of a plurality of image carriers, and an image forming means comprising a conductive material. A transfer supporting portion for supporting an image forming portion of the image forming medium on which the developer image on the body is sequentially transferred in a multiple transfer manner, and a material having a higher electric resistance in a thickness direction per 1 cm ² than the transfer supporting portion. A conveying unit for electrostatically adsorbing a non-image area of the image forming medium, a conveying unit for sequentially conveying the image forming medium to a plurality of image carriers on which the developer images are formed, and First voltage applying means for supplying a transfer bias voltage for transferring the developer images formed on the plurality of image carriers onto the image forming medium to a conveying means;
And a second application unit for supplying a bias voltage for adsorbing the image-receiving area of the image-forming medium to the suction-conveying unit.

[0007]

According to the present invention, since the applied voltage can be reduced at the time of transfer by the above means, the safety at the time of operation can be improved, and the surrounding environment can be improved by reducing the generation of ozone. The non-image area of the paper is electrostatically attracted to the transfer belt with a high charge-retention force, which prevents the paper from shifting on the transfer belt. It is intended to prevent displacement and obtain a clear and good color image.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the embodiments shown in FIGS.

FIG. 1 is a schematic structural view showing an image forming section of a laser beam color printer which is an image forming apparatus of the present invention. Provided are drum-shaped photoconductors 10a to 10d,
Around the photoconductors 10a to 10d, first to fourth charging rollers 11a to 11d respectively convert image signals into optical signals, and first to fourth exposure positions 12a of the photoconductors 10a to 10d.
To 12d, the first to fourth exposure devices 13a to 13d for scanning and exposing with a laser beam, black, yellow,
Each of the photoconductors 10a to 10a is made of magenta and cyan developers.
First to fourth developing devices 1 for developing an electrostatic latent image on 0d
4a to 14d, a transfer belt 16 serving as a conveying unit to be described later
A first voltage for applying a voltage of 1 kV to supply a transfer bias voltage to a sheet P which is an image forming medium that is in contact with the photoconductors 10a to 10d at the first to fourth transfer positions 17a to 17d via First to fourth power supply rollers 20a to 20a-2 connected to a common bias power source 18 as an application means
0d, first to fourth blade cleaning devices 21a
To 21d, and first to fourth static elimination lamps 22a to 22d are sequentially provided.

Next, the transfer belt 16 will be described in detail. Between the first and second conductive holding rollers 23a and 23b having an interval of about 300 mm, an endless transfer having a width of 250 mm substantially equal to the width of the photoconductors 10 a to 10 d, a film thickness of 10 μm, and an annular length of 668 mm. A belt 16 is stretched. The transfer belt 16 is made of conductive carbon particles 25
It consists of 75 parts by weight of thermosetting polyimide mixed with parts by weight and has an electric resistance value of 10 ¹¹ Ω in the thickness direction per 1 cm ^2.
· Cm ² transfer support portions 16a and made of a conductive material is conductive carbon particles made of thermosetting polyimide without additives that does not enter the electric resistance in the thickness direction per 1 cm ² is 10 ¹⁴ Ω · cm ² and a suction conveyance section 16b of 10 mm in length made of an insulating material.

A black point 24 for position detection is written at the rear end of the suction conveyance section 16b, and the light reflection type detection device 26, which is a detection means provided around the transfer belt 16, performs suction conveyance. The arrival of the portion 16b is detected.

Further, provided upstream of the transfer belt 16 are a paper feed cassette device 27 for storing paper P as a transfer material and a pickup roller 28 for taking out the paper P from the paper feed cassette device 27. Pickup roller 28
A registration roller pair 30 serving as a regulating means is provided between the transfer roller 16 and the transfer belt 16 so that the non-image area at the leading end of the paper P is suction-conveyed to the suction conveyance section 16b. The paper P is transferred to the transfer belt 16 at a timing so as to coincide with the leading edge of the image area of P.
Sent to the side.

Reference numeral 31 denotes a metal roller made of SUS having a diameter of 6 mm and made of 1.5 mm by a power source 32 serving as a second application means.
kV is applied to the sheet P, and the sheet P is transferred to the transfer belt 16.
This is a suction roller for electrostatically attracting the toner. Reference numeral 33 denotes a neutralization brush that is slidably brought into contact with the transfer belt 16 after the conveyance of the paper P.

On the other hand, downstream of the transfer belt 16, a sheet P
Leveler 36, a pair of fixing rollers 37, and a sheet discharge tray 38 for separating the sheet from the transfer belt.

Next, the operation will be described. When a color image signal is sent by the start of printing, each device of the image forming unit is driven, and the image forming process is sequentially performed according to the rotation of each of the photoconductors 10a to 10d in the direction of the arrow s. That is,
Each of the photoconductors 10a to 10d first has a corresponding one of the charging rollers 11a to 11d.
11d uniformly charges to about -500V.

Next, the photoreceptors 10a to 10d are irradiated with laser beams from the exposure devices 13a to 13d at the respective exposure positions 12a to 12d to form electrostatic latent images corresponding to image signals, respectively. The development is carried out through to 14d, and a developer image of each color is formed.

Next, the operation of transferring the developer image onto the sheet P will be described with reference to the flowchart shown in FIG.

After the start of copying, while a developer image is formed on each of the photoconductors 10a to 10d, a paper transport operation is started,
In step 100, the pickup roller 28 is driven, and the sheet P is taken out of the sheet cassette 27 and sent to the registration roller pair 30. At the same time, the transfer belt 16 starts to be driven. Then step 101
Compare whether the light reflection type detection device 26 has detected the passage of the transfer belt 16 through the suction conveyance unit 16b, and if the light reflection type detection device 26 has detected the passage of the point 24, proceed to step 102. After a predetermined time has passed since the detection, the transfer belt 16 is temporarily stopped. During this predetermined time, after the light reflection type detection device 26 detects the point 24, the suction conveyance section 16b of the transfer belt 16 moves the suction roller 31 and the registration roller pair 30.
This is the time required to reach a position where the distance between the suction roller 31 and the tip of the suction conveyance unit 16b is equal.

Next, in step 103, when the control device instructs that the leading ends of the developer images formed on the photoconductors 10a to 10d have reached predetermined positions, in step 104,
At the same time as the registration roller pair 30 is driven, the transfer belt 16 is rotated again, and the sheet P is sent out at the timing when the leading edge of the developer image on the photoconductors 10a to 10d coincides with the leading edge of the image area of the sheet P. The transfer belt 16 is rotated. As a result, the non-image forming area at the leading end of the sheet P and the suction conveyance section 16b of the transfer belt 16 are also matched.

Therefore, the leading end of the non-image area of the sheet P sent from the registration roller pair 30 is aligned with the leading end of the suction conveyance section 16b of the transfer belt 16 at the position of the suction roller 31.
Further, since the electric charge is applied by the suction roller 31 together with the insulating suction conveyance section 16b, the non-image area of the sheet P is sufficiently electrostatically adsorbed to the suction conveyance section 16b, and is transferred according to the rotation of the transfer belt 16 in the direction of the arrow t. It will be conveyed in the direction of position 17a-17d. During this time, the registration roller pair 30 makes one rotation after the start of driving in step 106 to transmit the conveyance of the sheet P to the transfer belt 16 and then stops driving.

In step 107, the transfer of the developer image onto the sheet P is performed. That is, each transfer position 17a
17d, a transfer electric field is formed between the photoconductors 10a to 10d and the paper P by the bias voltage applied by the power supply rollers 20a to 20d. , A yellow developer image, a magenta developer image, and a cyan developer image.

During the transfer to the peeling leveler 36 via the transfer positions 17a to 17d, the suction and transport section 16b can hold the initial charge and reliably electrostatically suction the sheet P.

The paper P on which the developer image has been multiplex-transferred in this manner is separated from the transfer belt 16 by a separation leveler 36, conveyed to a fixing roller pair 37, and heated and fixed to the developer image. The paper is discharged to the tray 38.

On the other hand, after the sheet P is peeled off, the transfer belt 16
The charge is removed by the first holding roller 23a, and furthermore, by the sliding contact of the charge removing brush 33, the charge removal of the insulative suction conveyance section 16b is also reliably performed. Next, in step 108, after the light reflection type detection device 26 detects the suction conveyance unit 16b, it is compared whether a predetermined time has elapsed.
Proceeding to step 110, the drive of the transfer belt 16 is stopped,
All the transfer operations are completed. However, the predetermined time here is a time from when the light reflection type detection device 26 detects the suction conveyance unit 16b to when the rear end of the paper P is conveyed to the fixing roller pair 37.

Here, the evaluation of the adsorption performance (adsorption force) of the paper P by the transfer belt 16 according to the present embodiment will be described. FIG. 3 shows an attraction force measuring device 41. Using an arbitrary transfer belt [A] stretched between conductive holding rollers 42 and 43, a voltage of -1.5 kV is applied to paper P and attraction voltage by attraction roller 31. The sheet P is applied to the transfer belt [A] to convey the sheet P to the center between the holding rollers 42 and 43. In this state, the spring 46 is attached to the sheet P and pulled in the conveying direction, and the memory of the spring 46 at that time is read. , The suction force of the paper P by the transfer belt [A].

The same transfer belt [A] is used at normal temperature (21 ° C.) and normal humidity (50% RH) and at high temperature (35% RH).
° C) and high humidity (85% RH), and the experiment was performed. The results shown in [Table 1] were obtained.

[0027]

[Table 1] That is, at normal temperature and normal humidity, all of the transfer belt provided with an insulating suction conveyance unit in a part of the conductive transfer support unit and the transfer belt not provided with the insulation suction conveyance unit are all 1000 g. It was found that the paper was very strongly attracted to the transfer belt. On the other hand, at the time of high temperature and high humidity, the transfer belt 16 having the insulative suction and conveyance unit 16b described in the above-described embodiment can obtain the insulative suction and conveyance unit in comparison with the transfer force of 400 g. If it is not provided, the adsorbing power of the paper is very weak at 20 to 30 g,
The result was that the position was easily shifted on the transfer belt. This is because the transfer supporting portion 16a contains conductive carbon, and at high temperature and high humidity, the electric resistance value is reduced, the charge holding ability is lost, and the electrostatic attraction force is lost. It is thought that it is.

In the case where no insulating adsorption / transport portion is provided, the electric resistance is set to 10 ¹² Ω · cm ² and 10 ¹³ Ω · cm ² by changing the amount of conductive carbon particles added. Transfer belt, the higher the electric resistance, the higher the electrostatic attraction force, and the transfer belt having an electric resistance of 10 ¹² Ω · cm ² can obtain 100 g of an attraction force and 10 ¹³ Ω
-With a transfer belt of cm ² , a suction force of 200 g was obtained.

When color printing was performed by the image forming apparatus described in the above embodiment using each of the transfer belts actually used in the above experiment, under the normal temperature and normal humidity environment, all of the transfer belts were used. Although a clear color image without color misregistration can be obtained, in an environment of high temperature and high humidity, there is no insulating suction conveyance section and the electric resistance value is 10 ¹¹ Ω · c.
When the transfer belt of m ² was used, color shift was clearly observed.

With this configuration, the transfer support portion 16a of the transfer belt 16 that supports the image area of the paper P is made of a conductive material, and the transfer voltage can be reduced to about 1 kV. It is relatively safe even when touching one power source, does not generate ozone, and can be held well without polluting the environment to improve safety, while adsorbing to support the non-image area of the paper P. Since the transport section 16b is made of an insulating material, the non-image area of the sheet P can be reliably electrostatically attracted. Therefore, during the multiple transfer from each of the photoconductors 10a to 10d, the sheet P A clear and high-quality color image without color misregistration can be obtained without any misalignment of the adsorption position.

The present invention is not limited to the above-described embodiment, but can be modified without departing from the spirit of the present invention. For example, the material of the transfer support portion and the suction transport portion of the transport means may be arbitrary. If the electrical resistance of the transfer support portion is in the range of 10 ^{6 to} 10 ¹² Ω · cm ² so as to have conductivity, polycarbonate, polyethylene terephthalate, polytetrafluoroethylene (Teflon), polyfukkavinylidene (PVDF) Resin or synthetic various polymer alloys mixed with a predetermined weight part of conductive carbon particles may be used. The above resin or the like to which carbon is not added may be used, but it is more preferable that the electric resistance is 10 ¹² Ω · cm ² or more because of the insulating property.

Further, the number of image carriers for performing multiple transfer is arbitrary, and the means for imparting electric charge to the image carrier during transfer may be a corona charger. Also, after the transfer,
It is also optional to provide a static eliminator in order to peel the paper from the insulating suction conveyance unit.

[0033]

As described above, according to the present invention,
Compared to using a transfer belt made of an insulating material,
The transfer voltage applied to the image carrier can be significantly reduced, safety during operation can be improved, and even when a corona charger is used, the generation of ozone can be significantly reduced, and the human body can be cleaned without polluting the environment. While improving safety,
A non-image area of the paper can be reliably electrostatically adsorbed by providing a suction conveyance section with a high electric resistance value on a part of the transfer belt, so that the conveyance means can obtain sufficient paper suction power even in a high temperature and high humidity environment. As a result, there is no possibility that a positional shift occurs on the conveying means, and a clear and high-quality color image without color shift can be obtained at the time of multiple transfer, and the image quality is improved.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram illustrating an image forming unit according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a transfer belt according to one embodiment of the present invention.

FIG. 3 is a schematic configuration diagram illustrating an apparatus for measuring a sheet attraction force using various transfer belts including a transfer belt according to an embodiment of the present invention.

FIG. 4 is a flowchart illustrating a transfer operation according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Apparatus main body 10a-10d ... Photoconductor 16 ... Transfer belt 16a ... Transfer support part 16b ... Adsorption conveyance part 20a-20d ... Power supply roller

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Minoru Yoshida 70, Yanagimachi, Yuki-ku, Kawasaki-shi, Kanagawa Prefecture Inside the Yanagimachi Plant, Toshiba Corporation (56) References JP-A-6-208309 (JP, A) JP-A-4 -190274 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G03G 15/16 G03G 15/01 114

Claims (4)

(57) [Claims] An image forming means for forming a developer image on each of a plurality of image carriers, and an image to be transferred, wherein the developer images on the plurality of image carriers are sequentially multiplex-transferred. A transfer supporting portion for supporting an image forming portion of the forming medium, and an attraction for electrostatically adsorbing a non-image area of the image forming medium, the material being made of a material having a higher electric resistance in a thickness direction per 1 cm ² than the transfer supporting portion. A conveying unit that has a conveying unit and sequentially conveys the image forming medium to the plurality of image carriers on which the developer images are formed; and the conveying unit transfers the developer images formed on the plurality of image carriers. First voltage applying means for supplying a transfer bias voltage for transferring the image on the image forming medium, and supplying a bias voltage for sucking the image area of the image forming medium to the suction conveyance section. And 2 application means. Image forming apparatus. 2. An image forming means for forming a developer image using a developer of a different color on each of the first to fourth image carriers adjacent to each other, and the first to fourth image carriers comprising a conductive material. A transfer supporting portion for supporting an image forming portion of the image forming medium on which the developer images on the image carrier are sequentially transferred in a multiplex manner, and a material having a higher electric resistance in a thickness direction per 1 cm ² than the transfer supporting portion. And a suction unit for electrostatically sucking a non-image area of the image forming medium, and sequentially transferring the image forming medium to the first to fourth image carriers on which the developer images are formed. A first conveying means for supplying a transfer bias voltage for transferring the developer images formed on the first to fourth image carriers onto the image forming medium;
An image forming apparatus comprising: a voltage application unit configured to supply a bias voltage for adsorbing an image-receiving area of the image-forming medium to the suction conveyance unit; 3. An electric resistance of the transfer supporting portion is 10 ^{6 to} 10
A ^{12 Ω} · cm ^2, the image forming apparatus according to claim 1 or claim 2, wherein the electrical resistance of the suction conveyance unit is 10 ¹² Ω · cm ² or more. 4. A detecting means for detecting a suction conveyance section, and in accordance with a detection result by the detection means, a non-image area of the transfer material is suctioned by the suction conveyance section in a direction of the transfer material conveyance means. The image forming apparatus according to claim 1, further comprising a regulating unit that regulates the transfer timing of the image.