JP3347254B2 - 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 forming apparatus such as a copying machine and a laser printer, and more particularly, to an image forming apparatus that conveys transfer paper by using a belt-shaped conveying means.

[0002]

2. Description of the Related Art As an image forming apparatus of this type, for example, in a color laser printer, a yellow (Y), magenta (M), cyan (C), black ( K) is configured by arranging four printing stations successively. Each printing station is provided with an electrophotographic process mechanism, and performs printing at each printing station on a sheet conveyed by a sheet conveying belt, thereby forming a color image by superimposing respective colors. .

In such a color laser printer, the recording paper is conveyed by being placed on a paper conveyance belt. Therefore, when the paper is sucked onto the paper conveyance belt, the recording paper is misaligned, and a top margin defect and paper Missing tip transfer,
Problems such as skew and pitch shift may occur. In order to solve this problem, an electrostatic attraction device for electrostatically attracting recording paper onto the paper transport belt has been provided on the paper suction side of the paper transport belt.

FIG. 4 shows a color laser printer provided with such an electrostatic attraction device. In the figure, reference numeral 101 denotes a paper transport belt, and reference numeral 102 denotes a yellow (Y) printing station. The yellow (Y) printing station includes a charger 104, an exposure device 105, a developing device 106, a drum cleaner 107, and a discharge lamp 10 around a photosensitive drum 103.
8 are arranged opposite to each other. The developing device 106 stores yellow (Y) color toner, and supplies the toner to the photosensitive drum 103 by a developing roller 106a rotatably provided below. Also, the photosensitive drum 103
A transfer roller 109 is disposed at an opposite position via a sheet conveying belt 101.

On the paper suction side of the paper transport belt 101, a transport roller 110 and a registration roller 111 for guiding recording paper onto the paper transport belt 101 are provided. Further, an electrostatic attraction device 112 is provided at the paper suction position of the paper transport belt 101.

This electrostatic attraction device 112 is provided in contact with the front side (paper transport surface) of the paper transport belt 101 and has an electrostatic attraction roller 113 for applying electrostatic attraction to recording paper. . This electrostatic attraction roller 113 is
The electrostatic attraction roller 113 is grounded via a power supply 114 that supplies an electrostatic attraction voltage. Electrostatic suction roller 113
A tension roller 115 is provided at a position opposing the sheet conveyance belt 101 via the sheet conveyance belt 101. This tension roller 115 is grounded.

In such a laser printer, when printing is performed, recording paper is picked up from a paper storage cassette (not shown) disposed below the paper transport belt 101, and is transported by a transport roller 110 and a registration roller 111. It is guided onto the conveyor belt 101. This recording paper is made up of an electrostatic attraction roller 113 and a tension roller 11.
5 is inserted.

In this case, the leading end of the recording sheet abuts on the sheet conveying belt 101. However, since the electrostatic attraction roller 113 has a roller shape, the recording sheet is pressed against the sheet conveying belt 101, and Lifting can also be prevented. Further, an electrostatic attraction charge is applied to the recording paper from the electrostatic attraction roller 113, and the recording paper is electrostatically attracted onto the paper transport belt 101. As a result, gaps between the recording sheet and the sheet conveying belt are reduced, so that the transfer efficiency is improved. Further, since the recording sheet can be prevented from being displaced, problems such as a top margin defect, transfer loss at the leading end of the sheet, skew, and a pitch shift are eliminated.

[0009]

However, since the electrostatic attraction roller 113 in such an image forming apparatus has a roller shape and thus has a small contact area with the recording paper,
The charging efficiency is not very good. In particular, when the recording medium is a recording medium having a high resistance value, a poor smoothness, or a thick recording paper having a large capacitance, the efficiency is extremely low.

In order to increase the charging efficiency, it is conceivable to increase the electrostatic attraction voltage. However, the power supply becomes large, and excessive charging is not appropriate because it causes transfer failure. It is also conceivable that the electrostatic attraction roller 113 is pressed against the recording paper to cause a nip to increase the contact area with the recording paper. However, if the electrostatic attraction roller 113 is pressed against the recording paper too much, the electrostatic attraction may be reduced. Since the recording paper is likely to be rolled up before and after the contact portion of the suction roller 113,
At the time of charging by the electrostatic attraction roller 113, a gap is generated between the sheet and the recording sheet, and the charging efficiency is rather deteriorated.

Further, since the electrostatic attraction roller 113 is grounded via the semiconductive paper transport belt 101 and the metallic tension roller 115, when the recording paper absorbs moisture at high temperature and high humidity, the electric charge in the recording paper is reduced. The resistance value becomes low, and the film becomes almost like a conductor. Therefore, no matter how much voltage is applied to the electrostatic attraction roller 113, the electrostatic attraction charge flows out to the ground via the recording paper, the paper transport belt 101, and the tension roller 115. As described above, there has been a problem that the adsorbing force of the recording paper decreases at high temperature and high humidity.

Further, when a transfer bias is supplied to the transfer roller 109, the recording paper is
9 and the electrostatic attraction roller 113, the recording paper becomes almost conductive due to moisture absorption at high temperature and high humidity, so that the transfer charge from the transfer roller 109 passes through the recording paper and further from the transfer roller 109. Also flows out to the ground through the electrostatic attraction roller 113 having a low voltage.
As a result, there has been a problem that the transfer is insufficient and the print result is blurred. In this case, the suction force of the electrostatic attraction roller 113 on the recording paper is also reduced, and the above-described problems such as the top margin defect also occur.

Therefore, the present invention can improve the charging efficiency of the recording medium by the electrostatic attraction roller, can reliably prevent the occurrence of a top margin defect, a transfer failure at the leading edge of the sheet, skew, pitch shift, and the like, and can further prevent the occurrence of high temperature. An object of the present invention is to provide an image forming apparatus capable of preventing a decrease in transfer efficiency at high humidity.

[0014]

According to the first aspect of the present invention, a surface of an electrostatic latent image holding member is charged, an electrostatic latent image is formed by exposure, and the electrostatic latent image is visualized. arranging a plurality of print stations on a media transport belt comprising an endless belt-like semi-conductive material, the toner image visualized by the printing station in a recording medium conveyed placed on a front surface of the conveyance belt, From the multiple printing stations
Having a plurality of transfer rollers for transferring to the recording medium,
At least one of the plurality of arranged printing stations
One stores black toner and in color mode
For the printing station containing the black toner
Each of the plurality of transfer rollers excluding the corresponding transfer roller
Or all of the plurality of transfer rollers,
Each of said plurality of printing stations corresponding to said media.
Abut on the conveyor belt, and in monochrome mode
The black toner among the plurality of printing stations;
Transfer roller corresponding to the printing station
A printing station containing the black toner only
In the image forming apparatus contacted via the medium transport belt, the image forming apparatus contacts the back side surface of the medium transport belt, and supplies the electrostatic adsorption charge to the recording medium via the medium transport belt when the recording medium is transported. and electrostatic attraction roller for electrostatically adsorbing the recording medium on the front side of the conveyance belt, electrostatic attraction comprising a counter roller which is disposed opposite to the electrostatic attraction roller
Device in the monochrome mode.
It works only with .

According to a second aspect of the present invention, there is provided the image forming apparatus according to the first aspect, further comprising a bias holding unit that applies a constant bias to the opposing roller and suppresses an electrostatic amount of the recording medium attracted to the medium transport belt. is there.

In the present invention having such a configuration, when the electrostatic attraction roller supplies electrostatic attraction charges from the back side surface of the medium transport belt during the transport of the recording medium, the electrostatic attraction roller supplies the electrostatic attraction charge to the back side of the recording medium via the medium transport belt. Electrostatic adsorption charge is supplied,
The recording paper is electrostatically attracted to the front surface of the medium transport belt.

Further, at high temperature and high humidity, the recording medium absorbs moisture and the electric resistance value of the recording medium is lowered to generate conductivity, so that the electrostatically attracted charge from the electrostatic attraction roller passes through the recording medium. However, since a constant bias is applied to the opposing roller, it does not flow out of the opposing roller.

[0018]

1 and 2 show a first embodiment in which the present invention is applied to a color laser printer.
This will be described with reference to FIG.

FIG. 1 is a cross-sectional view showing the configuration of a color laser printer according to the present embodiment. Reference numerals 21 to 24 are continuous with a paper transport belt 1 as an endless belt-shaped medium transport belt stretched inside the apparatus main body. Four printing stations arranged in the same manner.

Each of the printing stations 21 to 24 includes a charger 4, an exposing device 5, a developing device 6, a drum cleaner 7, and a discharging lamp 8 around a photosensitive drum 3 as an electrostatic latent image holding member.
Are arranged facing each other. The developing devices 6 of the printing stations 21 to 23 store yellow (Y), magenta (M), and cyan (C) color toners, respectively.
The developing device 6 of the printing station 24 stores black (K) toner, and the developing roller 1 rotatably provided below.
0 supplies toner to the photosensitive drum 3.

The paper transport belt 1 is made of a conductive material.
The surface is covered with an insulating layer. Then, it is stretched over a pair of guide rollers 14 and 15. The guide roller 15 on the downstream side in the belt conveyance direction is a drive roller,
It is connected to a drive device (not shown). The guide roller 14 on the upstream side in the belt transport direction is a driven roller, and is suspended by a spring (not shown) to apply tension to the paper transport belt 1. The rotation of the guide roller 15 causes the paper transport belt 1 to move in the direction of the arrow at a predetermined speed.

The shafts of the guide rollers 14 and 15 are rotatably mounted on the housing of the printer body in a state where the tangents to these shafts are separated from each other so as not to contact the photosensitive drum 3 of the printing station. The printing stations 21 to 24 are also fixed to this housing.

Further, inside the paper transport belt 1,
The transfer roller 9 is disposed so as to face each photosensitive drum 3 with the sheet conveyance belt 1 interposed therebetween, and the slack of the sheet conveyance belt 1 is reduced by the action of an urging spring (not shown) attached to the rotation shaft of the roller. A tension roller 12 for maintaining a predetermined tension is provided. The transfer roller 9 is made of a conductive material, and supplies a transfer voltage by a high-voltage power supply. Further, as described above, since the sheet transport belt 1 is also made of a conductive material, the transfer roller 9 and the transfer roller 9 as a whole constitute a transfer device.

Further, below the paper transport belt 1, a paper feeder 19, in which recording papers 18 as recording media are stacked and stored, is provided detachably, and a fixing device 20 is provided outside the guide roller 15. They are located close together. A paper feed roller 23 for picking up the recording paper 18, a conveyance roller 24 for guiding the recording paper 18 to the conveyance path 13, and an aligning for guiding the recording paper 18 from the conveyance path 13 onto the paper conveyance belt 1 above the paper feeding device 19. A roller 25 and the like are provided.

In this apparatus, for example, an image signal is supplied from a host computer (not shown), and this image signal is sent to each exposure device 5 as a signal corresponding to each color. The exposure device 5 emits a laser beam according to the image signal, and exposes the photosensitive drum 3 uniformly charged by the charging unit 4 to form an electrostatic latent image. The photosensitive drum 3 rotates in the direction of the arrow, the electrostatic latent image on the photosensitive drum 3 is developed by the developing device 6, and the image is transferred to the recording paper on the paper transport belt 1 by the transfer roller 9. .

Thereafter, the surface of the photosensitive drum 3 is cleaned by the cleaning device 6, and the residual potential on the photosensitive drum 3 is uniformly reduced by the illumination of the charge removing device 8 to prepare for the next electrophotographic process. Image formation is performed for magenta, cyan, and black in a similar process.

In the above-described image formation, while the recording sheet is conveyed by the sheet conveying belt 1, the images of the respective colors are transferred one after another, and then separated from the sheet conveying belt 1 by the curvature of the guide roller 15, and the fixing device 20. Sent to Further, the recording paper is subjected to image fixing by the fixing device 20,
The sheet is discharged to 1 or 22.

On the paper feeding side of the paper transport belt 1, that is, on the printing station 21 side, an electrostatic attraction device 31 for electrostatically attracting the recording paper 18 to the paper transport belt 1 is provided.

As shown in FIG. 2, this electrostatic attraction device 31 is provided in contact with the back side of the paper transporting surface of the paper transporting belt 1 to apply electrostatic attraction charges to recording paper. An electrostatic attraction roller 32 is provided. Further, the electrostatic attraction roller 32 is formed of a semiconductive rubber roller, and also serves as a tension roller.

The electrostatic attraction roller 32 is pressed against the paper transport belt 1 so as to have a nip. The electrostatic attraction roller 32 is grounded via a power supply 33 that supplies an electrostatic attraction voltage to the electrostatic attraction roller 32.

An opposing roller 34 is provided on the sheet conveying belt 1 so as to abut on the sheet conveying surface and oppose the electrostatic attraction roller 32. The opposing roller 34 is grounded via a zener diode (constant voltage diode) 35 having the illustrated polarity.

In this embodiment having such a configuration, when a signal for forming an image is input from a host computer or the like (not shown), the recording paper in the paper feeding device 19 is picked up by the paper feeding roller 23. Then, the sheet is conveyed onto the sheet conveying belt 1 at a timing adjusted by the conveying roller 24 and the registration roller 25, and first passes through the electrostatic attraction device 31.

At this time, the electrostatic attraction charge from the electrostatic attraction roller 32 is supplied to the lower surface of the recording paper via the paper transport belt 1. This makes it possible to prevent the recording paper from rising or rolling up, and to reliably electrostatically attract the recording paper to the paper transport surface of the paper transport belt 1.

Further, since the electrostatic attraction roller 32 is provided on the back side of the paper transport belt 1 and indirectly supplies the electrostatic attraction charge to the back side of the recording paper via the paper transport belt 1, the electrostatic attraction roller 32 is provided on the recording paper. The suction roller 32 does not directly contact,
Further, since the opposing roller 34 does not supply the electrostatically attracted electric charges, it is not necessary to press the sheet conveying belt 1 so that a nip is generated.

Further, even if the electrostatic attraction roller 32 is pressed to the paper transport belt 1 to some extent, the recording paper does not fly up. Therefore, the opposing roller 34 can be brought into contact with the paper transport belt 1 so that the recording paper does not float, and the electrostatic attraction roller 32 can be pressed to nip the paper transport belt 1. Can be increased, and as a result, the charging efficiency of the recording paper can be improved. In particular, even when the recording medium is a recording medium having a high resistance value, a poor smoothness, or a thick recording sheet having a large capacitance, the electrostatic adsorption can be efficiently performed.

In this manner, the recording sheet moves together with the sheet conveying belt 1 without causing a positional shift during conveyance, and printing is performed at each of the printing stations 21 to 24 to form an image. As a result, problems such as a top margin defect, a transfer loss at the leading end of the sheet, skew, and a pitch shift can be reliably solved.

Further, since the Zener diode 35 is connected to the opposing roller 34 provided on the paper transport belt 1 to maintain a constant voltage, the recording paper absorbs moisture at high temperature and high humidity, and the electric resistance in the recording paper is reduced. Even when the value becomes low and the electrostatic attraction charge from the electrostatic attraction roller 32 passes through the recording paper, the electrostatic attraction charge can be prevented from flowing out to the ground, and the recording can be prevented. The paper continues to be sucked. Thereby, not only a recording medium having a thin recording medium, but also a recording medium having a high resistance value as described above,
Even when the recording paper has poor smoothness and large recording paper with large capacitance, it can be efficiently electrostatically attracted.

Further, since the opposing roller 34 maintains a constant voltage, even when the recording paper is in contact with both the transfer roller 9 and the opposing roller 34 at the time of high temperature and high humidity, the transfer charge and the electrostatic attraction charge are reduced. Can also be prevented from flowing out to the ground via the interface, and as a result, problems such as insufficient transfer and poor top margin during high temperature and high humidity can be reliably solved.

Next, a second embodiment in which the present invention is applied to a color laser printer will be described with reference to FIG. In this embodiment, the same portions as those in the above embodiment are denoted by the same reference numerals, and detailed description will be omitted.

FIG. 3 is a diagram showing a configuration near the paper suction portion of the paper transport belt 1 in the color laser printer according to the present embodiment. The difference from the one shown in FIG. The point is that the opposing roller 34 is grounded via the resistance element 41 instead of grounding via the resistance element 41. The resistance element 41 preferably has a resistance value of, for example, about 10 M ohm.

In this manner, when an attraction voltage is applied to the electrostatic attraction roller 32, the electrostatic attraction device 3
1 makes it difficult for the electric charge to flow out to the opposing roller 34 when the sheet passes through the sheet. For this reason, even when the recording paper absorbs moisture at high temperature and high humidity, the electric resistance value in the recording paper decreases, and even if the electrostatic attraction charges from the electrostatic attraction roller 32 pass through the recording paper, the static electricity is maintained. It is possible to prevent the electroadhesive charges from suddenly flowing out to the ground.

In the above embodiment, the opposing roller 34 is a dielectric roller, that is, an insulator or one of the tenth roller.
It may be constituted by a roller using a material having a resistance value of about the fifth power or more. In this case, the zener diode 35 is unnecessary. Also, there is no need to ground the opposing roller 34.
By doing so, the paper transport belt 1 is made dielectric, and the recording paper is dielectrically polarized from the opposing roller 34, so that the electrostatically adsorbed charge of the recording paper absorbed at the time of high temperature and high humidity flows out. Can be prevented.

Thus, the recording paper is transported to the paper transport belt 1.
The recording paper is conveyed while being efficiently and reliably adsorbed on the recording paper, thereby preventing the occurrence of a gap between the recording paper and the paper conveyance belt 1. Therefore, transfer efficiency can be improved, image quality can be prevented from deteriorating due to the environment, and stable transfer efficiency and print quality can be provided.

The present invention may be applied to an image forming apparatus having two types, a color mode and a monochrome mode. In such an image forming apparatus, in the color mode, only the transfer rollers 91 to 93 of yellow (Y), magenta (M), and cyan (C) or all the transfer rollers 91 are used.
To 94 are in contact with the corresponding photosensitive drums 3 to perform color printing. In the monochrome mode, only the black (K) transfer roller 94 is in contact with the corresponding photosensitive drums 3 to perform monochrome printing. .

In this case, unlike the color mode in which the paper transport belt 1 is almost horizontal, in the monochrome mode, only the transfer roller 94 rises and the paper transport belt 1 skews, so that the necessity of electrostatic attraction is reduced. Especially large. Therefore, in the image forming apparatus having the monochrome mode, the electrostatic attraction may be performed only in the monochrome mode.

More specifically, in the monochrome mode, for example, the electrostatic attraction bias is turned on after a certain period of time from the ON signal of a feed sensor (not shown) for detecting the end of the recording sheet. Normally, a suction bias polarity of about -1500 V is applied in a polarity opposite to the charging polarity of the developer (toner).

[0047]

As described above in detail, according to the present invention, the electrostatic attraction roller is provided on the back side of the medium transport belt so as not to directly contact the recording medium. Since the problem of the rising of the recording medium does not occur, the electrostatic attraction roller can be pressed against the medium transport belt so as to have a nip. As a result, a sufficient electrostatic attraction charge can be supplied to the recording medium, and the charging efficiency can be improved.
It is possible to reliably prevent the occurrence of skew, pitch shift, and the like, and to prevent the image quality from being degraded.

Further, since a constant bias is applied to the opposing roller, the recording medium absorbs moisture at high temperature and high humidity, the electric resistance value of the recording medium decreases, and conductivity is generated. Even if the electrostatically attracted charges pass through the recording medium, they can be prevented from flowing out of the opposing roller. In this way, it is also possible to reliably prevent the occurrence of a top margin defect, a loss of transfer at the leading end of the sheet, a skew, a pitch shift, and the like, thereby preventing a deterioration in image quality.

Further, since a constant bias is applied to the opposing roller, when the recording medium is in contact with the transfer portion during electrostatic adsorption at high temperature and high humidity, the recording medium becomes conductive, and Even if the transfer charge from the recording medium passes through the recording medium, the transfer charge does not escape from the opposing roller. As a result, a decrease in transfer efficiency can be prevented, and a decrease in image quality can be prevented.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a configuration of a main part of a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration of a sheet conveying side of a sheet conveying belt illustrated in FIG.

FIG. 3 is a diagram illustrating a configuration according to a second embodiment of the present invention.

FIG. 4 is a diagram illustrating a configuration of a paper conveyance belt on a paper suction side in a conventional image forming apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Paper conveyance belt (medium conveyance belt) 21-24 ... Printing station 3 ... Photosensitive drum (electrostatic latent image holding body) 6 ... Developing device 9 ... Transfer roller 18 ... Recording paper (recording medium) 31 ... Electrostatic adsorption device 32: electrostatic attraction roller 34: opposing roller 35: zener diode (bias applying means) 41: resistance element

Continuation of front page (56) References JP-A-5-270686 (JP, A) JP-A-1-96669 (JP, A) JP-A-5-249797 (JP, A) (58) Fields investigated (Int) .Cl. ⁷ , DB name) G03G 15/00

Claims (2)

(57) [Claims] 1. A printing station for charging a surface of an electrostatic latent image carrier, forming an electrostatic latent image by exposure, and visualizing the electrostatic latent image, is made of an endless strip-shaped semiconductive material. The printing station is arranged on a plurality of media transport belts, and the recording station is mounted on a recording medium transported on the front side of the media transport belt.
In the printing of the toner images visualized, it is more disposed
Transfer from a station to the recording medium;
A plurality of printing stations having transfer rollers
At least one of them contains black toner,
In the color mode, printing that contains the black toner
The plurality of rollers excluding the transfer roller corresponding to the station
Each of the transfer rollers or all of the plurality of transfer rollers
Each of the plurality of printing stations and the corresponding printing stations.
Abut each other via the medium transport belt, and
In ROHM mode, the front of the plurality of printing stations
Compatible with printing stations containing black toner
Only the transferred transfer roller contains the black toner.
Abuts the printing station via the media transport belt
An image forming apparatus that abuts a back side surface of the medium transport belt, supplies an electrostatic attraction charge to the recording medium via the medium transport belt when the recording medium is transported, and transfers the recording medium to the medium transport belt. A static roller composed of an electrostatic attraction roller for electrostatic attraction on the front side of the device and an opposing roller disposed opposite to the electrostatic attraction roller.
An electroadsorption device, and the electrostatic adsorption device is connected to the monochrome
An image forming apparatus which is operated only in a system mode . 2. The image forming apparatus according to claim 1, further comprising a bias holding unit that applies a constant bias to the opposing roller and suppresses a static amount of a recording medium attracted to the medium transport belt. .