JPH0675483A - Color image forming device - Google Patents

Abstract

PURPOSE:To always obtain an excellent transferred image regardless of the kind of a transfer material and a processing mode, etc., by controlling a transfer condition according to a detected current value and a correspondence table. CONSTITUTION:A current flowing in a charge applying means such as a brush 34 by which recording paper P is attracted to a transfer belt by giving charge to the recording paper P through the recording paper P is detected by a current detection circuit 41, and a current for a corona discharger for transfer 36 is controlled according to the detected current value and the correspondence table. Namely, the correspondence table of each processing speed, each glossy or non-glossy mode, each monocolor or multicolor mode, each transfer material and each developer or plural correspondence tables prepared for each combination of the above are provided, and the correspondence table is stored in the ROM 43 of a control part 42 so as to control the transfer current based on the detected current value. Therefore, the transfer condition of each mode of each kind, each transfer material and each developer is controlled by detecting the current, and the excellent transferred image is obtained regardless of the kind of the transfer material and the processing mode.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus such as a printer, in which a multicolor developing means is provided at the peripheral portion of an image carrier to develop a latent image on the image carrier. The present invention relates to a color image forming apparatus in which a recording belt having a toner image attached thereto is conveyed to a fixing unit and fixed after the toner image thus formed is transferred onto a recording sheet by a transfer belt device having a rotating transfer belt by a physical means.

[0002]

BACKGROUND OF THE INVENTION In an image forming apparatus such as an electrophotographic copying machine, after uniformly charging a peripheral surface of a photosensitive drum, which is an image carrier, by a charger, image exposure is performed on the peripheral surface of the photosensitive drum. To form an electrostatic latent image. This latent image is developed and visualized by developing means to become a toner image. The toner image formed on the peripheral surface of the photoconductor drum is transferred by a physical means onto a recording paper fed at a timing.
The recording paper on which the toner image has been transferred is separated from the photoconductor drum and conveyed to the fixing means. The toner image is fixed on the recording paper and then discharged to the outside of the apparatus.

As a transfer means for transferring the toner image adhering to the peripheral surface of the photoconductor drum onto the recording paper, a toner having a polarity opposite to that of the toner is charged by a transfer device which discharges from the back of the recording paper. Is transferred to the recording paper, and after transfer, a high AC voltage is applied by the separator to remove the charge.
The recording paper is designed to be separated from the photosensitive drum. However, it is difficult to reliably maintain transferability and separability, and particularly when the drum diameter of the photoconductor drum is large, it is difficult to separate, and the recording paper after the transfer of the toner image adheres to the photoconductor drum without being separated. It has the drawback that it tends to cause paper jams. A transfer belt device is used as a technique for improving this drawback.

The transfer belt device rotates a transfer belt stretched by a plurality of holding rollers at the same speed as the photosensitive drum. The transfer belt device is provided with a charge applying unit that applies an electric charge to the recording paper and causes the recording paper to be attracted to the transfer belt by an electrostatic force. And a high voltage having a polarity opposite to that of the toner charge is applied under constant current control at the transfer portion to transfer the toner image.
With such a transfer belt device, excellent transfer efficiency and separation effect can be obtained at the transfer portion.

Such a transfer belt device is used as a particularly preferable device in a color image forming device in which a toner image is superposed on a photosensitive drum and transferred onto a recording sheet at a time. In such a color image forming apparatus, since a plurality of developing devices are provided at the peripheral portion of the photoconductor drum in order to superimpose toner images on the photoconductor, the drum diameter becomes large, and sufficient separation performance cannot be obtained by the conventional electrostatic transfer separation system. Therefore, more reliable separation performance is required, and in the method of superposing toner images, the toner adhesion amount is large, so that a large transfer charge amount is required, and thus it is necessary to have a large transfer charge holding ability. This is because the transfer belt device is excellent in two respects.

[0006]

OBJECTS OF THE INVENTION Although the transfer belt device has excellent transfer performance, the transfer speed of the recording paper is greatly changed when, for example, a glossy image or a non-glossy image is to be obtained. Not all transferred images were uniformly good when transferred under transfer conditions. It was also found that the transferability of the toner attached to the photosensitive drum as a toner image is slightly different depending on its type or its attachment condition.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a color image forming apparatus having a transfer belt device which can always perform good transfer even under such different conditions.

[0008]

SUMMARY OF THE INVENTION The present invention achieves the above object. The first invention is to transfer a toner image obtained by developing a latent image on an image bearing member onto a recording paper by a transfer belt device having a rotating transfer belt. In a color image forming apparatus that transfers the recording paper to the recording paper and conveys the recording paper, a charge applying means for applying an electric charge to the recording paper to attract the recording paper to the transfer belt is provided, and a current flowing through the recording paper to the charge applying means. For each processing speed,
Gloss / non-gloss mode, mono / multi-color mode,
A plurality of correspondence tables are provided for each transfer material, each developer, or each combination thereof, and the transfer condition is controlled by the detected current value and the correspondence table. A second aspect of the present invention provides a color image forming apparatus, which forms a latent image on an image carrier using toner of a plurality of colors, and has a transfer belt that rotates the obtained toner image. When a toner image formed on the image bearing member is image-formed by toner of only one color in a color image forming apparatus that transfers the recording paper by a device and conveys the recording paper, the color of the toner depends on the toner color. The present invention provides a color image forming apparatus characterized by controlling to change a transfer output current or a transfer output voltage of the transfer belt device.

[0009]

FIG. 1 is a sectional view showing the construction of an embodiment of a color image forming apparatus of the present invention.

First, the configuration and operation will be described.

In FIG. 1, reference numeral 10 denotes a photosensitive drum which is an image bearing member, which is formed by coating an OPC photosensitive member on the drum and is grounded and driven and rotated clockwise. Reference numeral 12 is a scorotron charger, and _VH (-600 to -800) is applied to the peripheral surface of the photosensitive drum 10.
V) uniform charging is provided by corona discharge with a grid and corona discharge wire whose potential is held at V _G (-550 to 850 V). Prior to the charging by the scorotron charger 12, the peripheral surface of the photoconductor is neutralized by exposure by the PCL 11 using a light emitting diode or the like in order to eliminate the history of the photoconductor until the previous printing.

After uniformly charging the photosensitive member, the image exposing means 13 performs image exposure based on the image signal. Image exposure means
Reference numeral 13 is a reflection mirror 1 through a polygon mirror 131 that rotates using a laser diode (not shown) as a light emitting source, an fθ lens, and the like.
The optical path is bent by 32 and scanning is performed, and a latent image is formed by the rotation (sub-scanning) of the photosensitive drum 10.
In this embodiment, the character portion is exposed to form a reverse latent image in which the character portion has a lower potential V _L (-100V to 0).

Yellow (Y) on the periphery of the photosensitive drum 10,
Developers each containing a developer composed of toner such as magenta (M), cyan (C), black (K), and a carrier.
14 is provided, and first, the development of the first color is performed by the developing sleeve 141 which contains a magnet and holds the developer and rotates. The developer is a carrier in which a ferrite core is coated with an insulating resin around it, a polyester as a main material, a pigment according to the color, and a charge control agent,
It consists of toner to which silica, titanium oxide, etc. have been added.
The layer is regulated to a layer thickness (developer) of ˜600 μm and conveyed to the developing area.

The gap between the developing sleeve 141 and the photosensitive drum 10 in the developing area is 0.4 to larger than the layer thickness (developer).
As 1.0 mm, DC bias of V _AC AC Baaisu and V _DC of _{(1.5~3.0KV pp) (-500~-700V} ) is applied to overlap therebetween.

Since the charge of V _DC and V _H and the toner are all of the same polarity, the toner given the opportunity to be separated from the carrier by V _AC does not adhere to the V _H portion having a higher potential than V _DC. , visualized attached to lower V _L portion of potential than V _DC (reversal development) is carried out.

After the visualization of the first color is completed, the image forming process for the second color is started, the uniform charging is performed again by the scorotron charger 12, and a latent image by the image data of the second color is formed by the image exposing means 13. To be done. At this time, the charge elimination by the PCL 11 performed in the image forming process of the first color is not performed because the toner attached to the image portion of the first color scatters due to the rapid decrease in the potential around the image.

Once again, V is applied over the entire surface of the photosensitive drum 10.
A latent image similar to that of the first color is formed on the portion of the photoconductor having the _H potential and the image of the first color is not developed, but development is performed again on the portion having the image of the first color. In the portion to be performed, the latent image of V _M ′ is formed due to the light shielding by the toner of the first color and the electric charge of the toner itself, and V _DC
And development is performed according to the potential difference between V _M 'and V _M '. In the overlapping portion of the images of the first color and the second color, the development of the first color is V _L
Performed to create a latent image, since the balance between the first color and the second color is lost, reducing the exposure amount of the first color V _H> V _M (-
It may be an intermediate potential such that 100 to −300 V)> _VL .

An image forming process similar to that of the second color is performed for the third and fourth colors, and a visible image of four colors is formed on the peripheral surface of the photosensitive drum 10.

On the other hand, the recording paper P fed from the paper feeding cassette 21 by the paper feeding mechanism 22 is fed to the transfer area by the transfer belt device 30 in which the transfer belt 31 is stretched, and the peripheral surface of the photosensitive drum 10 is fed. The above multicolor image is collectively transferred onto the recording paper P.

The transfer belt 31 has a thickness of 0.4 having a resistance of 10 ⁶ to 10 ¹⁴ Ω · cm formed by forming an outer FLC layer of a urethane rubber base.
An endless rubber belt of ~ 1.0mm, ribs may be provided at the ends to prevent deviation during rotation.

It should be noted that a film such as PET or a high resistance belt such as a film coated with these may be provided by providing a charge removing mechanism or the like.

A holding roller 3 for stretching the transfer belt 31.
A voltage of V _PC is applied to the shaft 32a of the upstream side holding rollers 32 of Nos. 2 and 33, and at the position where the shaft 32a is installed via the transfer belt 31, as a means for imparting charge to the recording paper P. A conductive brush 34 is installed in a grounded state. The fed recording paper P enters between the brush 34 and the transfer belt 31, and the brush 34 injects an electric charge into the recording paper P, so that an attraction force is exerted between the recording paper P and the transfer belt 31. Occurs. After that, the recording paper P enters the nip portion (transfer area) 35 formed by the photoconductor drum 10 and the transfer belt 31, and the transfer electric field is generated from the back surface of the transfer belt 31 by the corona discharger 36 or the bias roller instead. A multicolor image is transferred onto the recording paper P.

The recording paper P separated from the photosensitive drum 10 is
The shaft 33a of the holding roller 33 on the downstream side which stretches the transfer belt 31.
Transfer belt 31 after receiving static electricity by AC corona discharge with the counter electrode as the counter electrode, or while receiving AC corona discharge.
Separate from. A cleaning blade 37 removes the toner attached to the rotating transfer belt 31. The transfer belt 31 of the transfer belt device 30 is separated from the photosensitive drum 10 about a shaft 33a of a holding roller 33 on the downstream side as a rotation center during the formation of a multicolor image.

The recording paper P holding the multicolor image separated from the transfer belt device 30 is conveyed to a fixing device 23 composed of two pressure bonding rollers having a heater inside at least one of the rollers, and is transferred between the pressure bonding rollers. The applied toner is melted by applying heat and pressure, fixed on the recording paper P, and then discharged to the outside of the apparatus.

After the transfer, the residual toner remaining on the peripheral surface of the photosensitive drum 10 is subjected to static elimination by a static eliminator 15 using an AC corona discharger, and then the cleaning device 16 or the rubber material contacting the photosensitive body is removed. It is scraped off into the cleaning device 16 by the cleaning blade 16a and is discharged or stored by a screw or the like. The above static eliminator 15
Depending on the arrangement of the recording sheets, it is possible to also serve as static elimination of the recording paper as shown in FIG.

The photosensitive drum 10 from which the residual toner has been removed by the cleaning device 16 is exposed by the PCL 11 and then uniformly charged by the scorotron charger 12.
Enter the next image forming cycle. The cleaning blade 16a is separated from the surface of the photoconductor during the formation of the multicolor image,
AC neutralization by 15 is kept in OFF state.

In the above-mentioned image forming apparatus shown as an embodiment of the present invention, the first invention of the present invention is a charge applying means such as a brush 34 for applying an electric charge to the recording paper P and adsorbing the recording paper P on the transfer belt 31. , The current flowing through the recording paper P is detected, and the detected current value and the correspondence table described later
The current control of the transfer corona discharger 36 is performed, and FIG. 2 shows this circuit configuration.

[0028] 38 V _PC to the axis 32a of the upstream-side holding roller 32
A power supply for applying the bias voltage of the holding roller 32
Is a roller made of a conductive metal material. The brush 34 made of a conductive fiber material is always in a grounded state, or is in a grounded state via a non-linear element such as a Zener or a resistor, and the tip of the brush 34 contacts the transfer belt 31 during transfer. The recording paper P coming in contact with and fed is the brush 34
And the transfer belt 31. Here, the recording paper P
In the present invention, electric charge is injected and uniformly charged, and is adsorbed by the transfer belt 31 and sent to the transfer area. The current flowing through the charge applying means is detected. FIG. 3 shows a specific circuit configuration of the current detection circuit 41. The current value is output to the input interface 45 at 0.18 V / μA in a voltage-converted form.

The color image forming apparatus of the present invention controls the transfer conditions by the detected electric current value flowing through the recording paper to the charge giving means and the correspondence table. Prior to the explanation of the correspondence table, The function of the color image forming apparatus according to the embodiment of the present invention described above will be additionally described.

Y, M, C, K are provided on the periphery of the photosensitive drum 10.
Each of the multi-devices 14 is provided with a developing device 14 in which a developer including a toner and a carrier is provided, and a multicolor color toner image is formed on the peripheral surface of the photoconductor drum 10 by repeating the process of charging, exposing, and developing. There is a mono color mode as well as a color mode. In the mono color mode, any one of Y, M, C, and K is selected in advance, and only the developing device containing the toner operates, and charging, exposure, and development are performed during one rotation of the photosensitive drum 10. The formed monochromatic toner image is immediately transferred onto the recording paper. When the image information formed on the photoconductor is limited to character information, the mono color mode is often set.

In the multi-color mode, Y + M, Y
There are two-color combinations such as + C, three-color combinations such as Y + M + C and M + C + K, and four-color combinations.

This color image forming apparatus has a function of selecting a gloss (G) mode or a non-gloss (N) mode. In order to set the gloss mode where the toner on the recording paper that has been fixed is half-melted and adhered to the non-gloss mode, the toner is heated and melted until it becomes a glass state and the surface has gloss. In the color image forming apparatus of the embodiment, the conveyance speed of the recording paper (processing speed including transfer) is 1
It has been reduced to about / 6.

In this color image forming apparatus, a color image can be recorded as a transfer material in addition to recording paper including thick paper and thin paper, as well as transparency for overhead projectors. A photocoupler (not shown) is provided in the transfer material conveying path, and has a function of discriminating the photocoupler from reflected light or transmitted light.
When it is determined that the transparency is set, the processing in the gloss mode is performed. Further, it has a manual feed function, and it is possible to record an image including an address and the like on an envelope in addition to the above transfer material.

As described above, this color image forming apparatus has a function of changing the processing speed, and when the processing speed in the non-gloss (N) mode is 1, the gloss (G) is set.
The processing speed in the mode is ⅙, and the processing speed is set to ½ for the envelope due to the fixing property and the glue.

In the color image forming apparatus described above, the present invention is designed so that good transfer can be achieved regardless of the type and mode of transfer material, for each processing speed, for each gloss / non-gloss mode, and for each mono / multi-color mode. , A correspondence table for each transfer material, each developer, or a plurality of correspondence tables provided for each combination thereof, and the correspondence table is stored in the ROM of the control circuit to transfer from the paper charging current. It controls the current. Note that the correspondence table for each developer is provided to obtain more stable transferability because the transferability is slightly different depending on the toner type. Especially, in the case of a monochrome image in monochrome mode, the toner type (color ) Is a correspondence table for switching the transfer current value for each.

As an example of the correspondence table, the inventor of the present invention has prepared a correspondence table in which the type of transfer material and the processing speed are combined, and good transferability is obtained by this, so this will be described.

The present inventor has studied the N speed (processing speed in the non-gloss (N) mode) and the G speed (gloss (gloss (gloss (gloss)) for recording papers other than envelopes and transparency, and for many recording papers having different thicknesses and types. G) The processing speed in the mode, 1/6 of the N speed in this embodiment, of the current value of the paper charging brush of the charge applying means of the recording paper and the appropriate transfer power supply current value applied to the corona discharger 36. The relationship was experimentally determined. FIG. 4 shows this relationship curve.

Separately from this, an envelope having a processing speed of H speed (N speed 1/2) and a processing speed of G speed have different transfer characteristics from the recording paper. Regarding the transparency, the relationship between the current value of the paper charging brush and the current value of the transfer power source was determined separately. The following correspondence table was created from the relationship curve for the recording paper of FIG. 4 and the experimental data for the envelope and transparency described above.

[0039]

[Table 1]

The above correspondence table is stored in the ROM 43 as a program necessary for the arithmetic processing of the input signal. Note that P _{0 to} P ₄ shown in the correspondence table indicate points for each mode corresponding to the detection circuit output voltage, and each point (P ₀ , P ₁ ,
...) is interpolated with a straight line.

The control circuit of the present invention has an input interface.
It has a control unit 42 for performing a predetermined calculation based on a program stored in the ROM 43 for the current signal input to the 45, and a RAM 44 for temporarily storing the calculation result, data, etc., and the copy button is pressed. First, whether it is a recording paper, envelope, or transparency is detected by a manually input or automatically detected. If it is a recording paper, is the current process in N mode? Whether or not the mode is the G mode is read as information from the main body of the apparatus, the control unit 42 performs a calculation according to the corresponding correspondence table, and outputs a signal based on the calculation result via the output interface 46.
The corona discharge voltage is varied so as to control the current value of the constant current control circuit 39 of the transfer corona discharger 36, and the intended purpose can be achieved by such a configuration.

The present invention is not limited to the above embodiment, but a correspondence table having a plurality of processes is prepared in advance and is input to the ROM 43 of the control circuit of the present invention to form an image. It is included in the present invention to select one program based on the information obtained from the main body side and control the transfer current.

In this embodiment, the brush is used as the charge applying means for the recording paper, but the same applies to the case where a conductive roller rotating on the transfer belt is used instead of the brush. Although the corona discharger provided on the back surface of the transfer belt has been described as the transfer means for the recording paper, the bias roller which is in contact with and rotates behind the transfer belt can also be applied.

The first aspect of the invention described above detects the current flowing through the recording paper in the charge applying means to detect each mode,
The transfer condition is controlled for each transfer material and each developer, but one color of Y, M, C, and K is selected,
A mono-color mode in which only the developing device containing the toner is operated and charged, exposed, and developed during one rotation of the photoconductor drum 10 to form a single-color toner image, which is immediately transferred onto the recording paper. In, it is possible to control the transfer conditions by detecting the current of the charge applying means, but since the transfer efficiency and the like differ depending on the toner color used for development, optimum transfer is performed by changing the transfer conditions depending on the toner color. It The reason for this is that the pigments and charge control agents contained in the toner differ depending on the color, and different physical properties and electrical characteristics also change the optimal transfer conditions.
When forming toner images of multiple colors on the same screen, some misalignment must be compromised, but in the mono-color mode in which the screen is formed with toner of only one color, transfer suitable for that toner is performed. By selecting the current value or the transfer current value, more efficient and uniform transfer becomes possible.

According to the second aspect of the present invention, when an image is formed with toner of only one color, the transfer output current or the transfer output voltage is controlled according to the toner color. In the forming device, the mono color mode is designated, and further, the gloss (G) mode or the non-gloss (N) mode is selected. By designating the toner color, the control unit sets an appropriate transfer output current, and image formation is performed. Done. That is, the control unit inputs, for example, the following table to the ROM, and calls the corresponding transfer current value from the ROM according to the information obtained from the main body in the image formation.
Controls the transfer current of the corona discharger.

[0046]

[Table 2]

The image forming apparatus described above has a transfer belt device provided with a corona discharger for constant current control, but the image forming apparatus provided with a corona discharger for constant voltage control is a ROM. The transfer voltage value of the corona discharger is controlled by calling the corresponding transfer voltage value from.

[0048]

According to the present invention, a correspondence table having a plurality of such programs is preliminarily entered in the ROM so that the transfer material of the transfer material can be formed by using the charge imparting means for the recording paper provided in the image forming apparatus. An image forming apparatus will be provided that can always obtain a good transferred image regardless of the type and processing mode. In the mono color mode, a transferred image with high transfer efficiency can be obtained by changing the transfer current value depending on the color. It became a thing.

[Brief description of drawings]

FIG. 1 is a configuration sectional view showing an embodiment of an image forming apparatus of the present invention.

FIG. 2 is a diagram showing a circuit configuration of a main part of the present invention.

FIG. 3 shows an example of a current detection circuit diagram.

FIG. 4 is a graph showing a relationship among a processing speed, a paper charging brush current, and an appropriate transfer power supply current.

[Explanation of symbols]

 10 Photoconductor drum 11 PCL 12 Scorotron charger 13 Image exposure means 14 Developing device 15 Static eliminator 16 Cleaning device 21 Paper feeding cassette 22 Paper feeding mechanism 23 Fixing device 30 Transfer belt device 31 Transfer belt 32, 33 Holding roller 34 Brush (charge Applying means) 35 Nip (transfer area) 36 Corona discharger (for transfer) 37 Cleaning blade (transfer belt) 38 Power supply 39 Constant current control circuit 41 Current detection circuit 42 Controller 43 ROM 44 RAM 45 Input interface 46 Output interface face

Claims (2)

[Claims] 1. A color image forming apparatus for transferring a toner image obtained by developing a latent image on an image carrier onto a recording paper by a transfer belt device having a rotating transfer belt, and carrying the recording paper. In the above, a charge applying means for applying an electric charge to the recording paper to attract the recording paper to the transfer belt is provided, and a current flowing through the recording paper is detected in the charge applying means, and the processing speed, gloss / non-gloss mode, It has a plurality of correspondence tables provided for each mono / multi-color mode, for each transfer material, for each developer, or for each combination thereof, and the transfer conditions are determined by the detected current value and the correspondence table. A color image forming apparatus characterized by controlling the. 2. A latent image on an image carrier is formed with toners of a plurality of colors, and the obtained toner images are transferred onto a recording paper by a transfer belt device having a rotating transfer belt, and the recording paper is transferred. When a toner image formed on the image carrier is image-formed by a toner of only one color in a color image forming apparatus that conveys the image, the transfer output current or the transfer output of the transfer belt device depends on the toner color. A color image forming apparatus characterized by controlling to change a voltage.