JPH06186860A - Color image forming device - Google Patents

Abstract

PURPOSE:To improve the quality of a transferred image without making an image output time longer by giving additional rotation for separating transfer paper from a transfer drum to the transfer drum after finishing the final transfer in the case of superimposing transfer when humidity is high. CONSTITUTION:When detection by a humidity sensor 30 shows that absolute humidity is <14g/m<3>, the transfer paper 6 is destaticized by a separation destaticizer 7 and rushes in a fixing part 8 after a final color is transferred to the transfer paper 6. In the case the absolute humidity is >=14g/m<3>, the transfer drum 2 is rotated once further without separating and destaticizing the paper 6 after the final color is transferred to the paper 6. At such a time, the drum 2 is separated from a photosensitive drum 4 and does not come in contact therewith. Namely, by releasing a rotary shaft 5 by a cam member 1, the drum 2 is separated to be at a distance where the toner image on the paper 6 is not disturbed by the drum 14. When the drum 2 is rotated in such a state and the leading edge of the paper 6 comes near to the periphery of the drum 4, the separation destaticizer 7 works, and the paper 6 is separated from the drum 2 and carried to the fixing part 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multicolor image forming apparatus capable of forming a color image on a latent electrostatic image bearing member by using a developing apparatus for a plurality of colors. The present invention relates to a color image forming apparatus including a transfer drum that can be additionally rotated.

The present invention relates to a color image forming apparatus, and more specifically, it transfers an image on an image bearing member carrying a developed image onto an intermediate image bearing member, and then reprints the image on the intermediate image bearing member onto a transfer material all together. The present invention relates to a transfer color image forming apparatus.

The present invention relates to an image forming apparatus such as a color copying machine or a color printer using an electrophotographic method, and more particularly to a transfer apparatus capable of obtaining a clear image.

[0004]

[Prior art]

[First Conventional Example] In this type of color image forming apparatus, a process of transferring a recording image formed by charging, exposing, and developing on a photoconductor drum onto a transfer paper is repeated a plurality of times to form a plurality of colors on the transfer paper. There is a method of obtaining a color image by forming a superimposed image of.

In this type of image forming apparatus, the DAS 260 is used.
7727, Japanese Patent Application Laid-Open No. 50-50935 and the like have been put to practical use. FIG. 10 is a vertical cross-sectional view of the color image forming apparatus. As shown in the figure, the photosensitive drum 501, the corona charger 502, the roller charger 503 are provided in A of the entire apparatus, and a plurality of them are provided on the right side of the photosensitive drum. Developing device 5
04a, 504b, 504c, and 504d are supported by a rotatable support, and the developing opening surfaces 505a, 505b, 505c, and 505a, 505b, 505c of the developing devices 504a, 504b, 504c, and 504d are mounted on the same cylinder around the support rotation axis. 505d is set.

Further, the developing devices 504a, 504b, 50
As shown in FIG. 11, yellow toner, magenta toner, cyan toner, and black toner are contained in 4c and 504d, respectively. Further, coating rollers 506a and 506 are provided.
b, 506c, 506d, toner regulating members 507a, 5
07b, 507c, 507d, and the developing roller 508
a, 508b, 508c, and 508d are rotated, toner application rollers 506a, 506b, 506c, and 506 are rotated.
on the developing roller 508a, 508b, 508c, 50
8d is coated with toner, and the toner regulating member 507
The necessary tribo is imparted to the toner by a, 507b, 507c, and 507d.

The material of the regulating member is preferably nylon or the like when the toner has a negative polarity, and silicone rubber or the like when the toner is positively charged, and is a material which is charged opposite to the extreme positive of the toner. preferable. Further, it is preferable to select the peripheral speed in the range of 1.0 to 2.0 times the peripheral speed of the photosensitive drum 501. Further, the developing devices 504a, 504b, 504c, and 504d attached to the support rotating shaft 509 are the developing device 5
The developing opening surfaces 505a, 505b, 505c, 505d of 04a, 504b, 504c, 504d are driven so as to always face the photosensitive drum surface. One means of driving method is described in detail in JP-A-50-93437.

A transfer roller 510, which holds a transfer sheet (not shown) and has a function of transferring an image on the photosensitive drum 501 onto the transfer sheet (not shown), is arranged on the left side.
With the above configuration, the photosensitive drum 501 is driven in the direction of the arrow in the figure by a driving unit (not shown) at a peripheral speed of 100 mm / sec.

The photosensitive drum 501 is constructed by coating a photoconductor made of an organic photoconductor (OPC) on the outer peripheral surface of an aluminum cylinder having a diameter of 40 mm.
A-Si, CdS, Se or the like may be used.

Next, in the upper part of the main body of the apparatus, a laser diode 511 and a high speed motor 51 which constitute an exposure apparatus.
A polygonal mirror 513 and a lens 51 that are driven to rotate by two
4 and a folding mirror 515 are arranged, and the charging roller 503 has a DC voltage of −700V and an AC frequency of 7V.
Vpp (peak-to-peak) at 00 Hz: -1500V
The AC voltage is superimposed and uniformly charged to about -700V.

When a signal according to the yellow image pattern is input to the laser diode 511, the optical path 516 is input.
The photosensitive drum 501 is irradiated through the
In No. 1, the light-irradiated portion is about -100V. When the photosensitive drum 501 further advances in the direction of the arrow, the developing device 504
a, 504b, 504c, 504d are visualized.

More specifically, the transfer process will be described in detail. In synchronization with the image on the photosensitive drum 501, the transfer paper is fed from the transfer paper cassette 517 by the pickup roller 518 and is attracted to the transfer roller 510. 510
Is a metal cylinder 519 having a diameter of 156 mm, and an elastic layer 520 having a thickness of 2 mm is wound on the metal cylinder 519.
PVDF521 is wound around the photosensitive drum 5
For the elastic layer that rotates in the arrow direction at substantially the same speed as 01, urethane foam made by Inoac was used.

When the transfer paper is supplied to the transfer roller 510, the transfer paper (not shown) is moved by the gripper 522.
The toner image on the photosensitive drum 501 is transferred onto a transfer paper (not shown) by a voltage between the photosensitive drum 501 and the transfer roller 510 by a power source (not shown). At the same time, the charge is injected into the transfer paper (not shown) so that the transfer paper 510 is attracted to the transfer roller 510. If necessary, the suction roller 523
A voltage may be applied between them to adsorb them in advance.

By performing the above steps for magenta, cyan and black, toner images of a plurality of colors are formed on the transfer paper. The recording paper is peeled from the transfer roller 510 by the separating claw 524, and the transfer paper is melted and fixed by a conventionally known heating and pressure fixing device 525 to obtain a color image.

The transfer residual toner on the photosensitive drum 501 is cleaned by a cleaning device 526 such as a known fur brush and blade means. In addition, the transfer roller 51
It is also preferable to clean the toner on No. 0 with a transfer roller cleaning device 527 such as a fur brush or a web, if necessary. [Second Conventional Example] Conventionally, in a color image forming apparatus such as a color laser beam printer, toner images of three colors or four colors are sequentially formed on an image bearing member such as an electrophotographic photosensitive member, and the toner images are formed. Are finally transferred onto a transfer material and heat-fixed to obtain a full-color image. Various types of color image forming apparatuses have been proposed.

As one of the systems of such a color image forming apparatus, the toners of respective colors formed on an image bearing member such as a photosensitive drum are transferred onto an intermediate image bearing member such as a transfer drum so as to be superposed and transferred. There is a system in which toner images of three colors or four colors on an intermediate image carrier are collectively transferred onto a transfer material. [Third Conventional Example] A conventional apparatus for forming a high-definition image has the following two configuration examples.

An image is formed on the image bearing member by the processes of charging, exposing and developing, and the image is once transferred to an intermediate transfer member such as a medium resistance film. This process is repeated a plurality of times to form a multicolored superimposed image on the intermediate transfer member, and the images are collectively transferred to the transfer material, which is a so-called intermediate transfer system.

An image is formed in the same manner as described above, and the step of transferring the image to a transfer material that is held in close contact with an insulating film as a holding means is repeated a plurality of times to obtain a multicolor superimposed image on the transfer material. The method of forming.

In FIG. 13, reference numeral 600 denotes an image carrier,
Reference numeral 601 is a transfer belt, 602 is a transfer roller, and 603 is a power source.

[0020]

[Problems to be Solved by the Invention]

[First Conventional Example] However, in the conventional example having the above-described configuration, when the whole apparatus is to be compactly assembled, as shown in FIG.
The fixing roller 525 and the transfer roller 5 will be described below.
Since 10 approached, there were the following defects.

That is, when the length (L1) of the paper 517 is longer than the distance between the transfer unit and the fixing unit (L2) (L1 ≧ L2), after transfer, the transfer paper 517 is separated and discharged, and is separated from the transfer roller 510 by the separation claw 524. When the electric resistance value of the transfer paper 517 is low when the transfer sheet 517 enters the fixing roller 525, the transfer current flows from the photosensitive drum 501 to the fixing roller 525 side rather than from the photosensitive drum 501 to the transfer roller 510.

Therefore, the toner on the photosensitive drum 501 may not be sufficiently transferred to the transfer paper 517, and the density may be reduced or the image may be disturbed. In particular, when the humidity becomes high, this phenomenon appears, and when the absolute humidity is 14 g / m ³ or more, the electric resistance value of the transfer paper 517 decreases and the disorder of the image becomes noticeable.

In order to solve the above-mentioned drawbacks, for example, Japanese Patent Laid-Open No.
As shown in 6-92552, after the final transfer is completed, the transfer roller may be additionally rotated to separate the transfer paper from the transfer drum. However, as described above, the transfer paper length (L1) Is longer than the fixing-transfer interval (L2),
Since the transfer roller has to be always separated from the photosensitive drum and additionally rotated, there is a problem that it always takes time to output an image. [Second Conventional Example] However, the conventional color image forming apparatus according to the above method has the following problems.

When the toner images on the transfer drum are collectively transferred to the transfer material, when the bias voltage applied to the transfer drum is switched to an optimum value in order to improve the transfer efficiency (for example, the bias voltage is lower than when transferring the final color). If the transfer of the final color from the image carrier to the transfer drum is not completed, the toner image on the transfer drum is offset on the photosensitive drum, and uneven transfer is likely to occur in the image.

When a transfer roller is used in the transfer step from the transfer drum to the transfer material, when the transfer roller comes into contact with the transfer drum, the shock tends to cause uneven transfer in the image. [Third Conventional Example] However, in the above-described conventional example, the transfer operation is performed by disposing electrodes applied with a polarity opposite to that of the toner on the image carrier or corona transfer in the transfer step.
In the case of corona transfer, ozone and nitrogen oxides (NOx) from the corona discharger
Grows and pollutes the surrounding environment.

Before contact with the image carrier and the transfer paper or the intermediate transfer member, the toner on the image carrier is disturbed by the influence of the electric field, so-called pre-scattering occurs, and the transferred image is fogged.
Scattered images occur.

In order to prevent this, as shown in the figure, the corona discharger on the upstream side in the transfer paper entrance direction is covered with a Mylar film or the like as an insulator, but the corona discharger becomes large.

When the electrodes are arranged, unnecessary organisms due to corona are not generated unlike the corona discharger, but front scattering is generated as described above.

However, even if the above-mentioned electrode upstream side is covered, when an intermediate resistance film is adopted as the intermediate transfer member as in the intermediate transfer method, the intermediate transfer member transfer position has the same electric potential as the transfer electric field, and the intermediate transfer member has the same electric potential. Then, an electric field E as shown in the figure is generated between the photosensitive layers, and toner scatters before transfer. [Object of the first invention] To improve the quality of a transferred image without increasing the image output time. [Object of the Second Invention] It is an object of the present invention to provide a color image forming apparatus having high transfer efficiency and capable of obtaining a good image quality without transfer unevenness. [Object of the third invention] According to the present invention, by providing an electrode having substantially the same potential as the image carrier on the transfer paper or on the upstream side of the transfer position in the direction in which the intermediate transfer member moves, the transfer medium is moved to the upstream side of the transfer position. The toner is prevented from scattering without generating an unnecessary electric field.

[0030]

[Means for Solving the Problems]

[First Invention] In a color image forming apparatus provided with a humidity sensor and a mechanism for sequentially transferring a toner image on a photosensitive drum onto a transfer paper wound on a transfer drum, a final image in the overlapping transfer at high humidity. After the transfer is completed, the transfer drum is provided with an additional rotation for separating the transfer paper from the transfer drum.

The absolute humidity when detected and controlled by the humidity sensor is 14 g / m ³ or more. [Second invention] A first transfer step in which toner images of respective colors sequentially formed on an image carrier are sequentially superposed and transferred onto an intermediate image carrier having at least a conductive support and an elastic body coating layer, In a color image forming apparatus for forming a color image on a transfer material by a second transfer step of retransferring the image on the intermediate image carrier to a transfer material, after the first transfer step, the image carrier The second transfer step is performed after the intermediate image carrier is separated from the intermediate image carrier, and the intermediate image carrier rotates idly without being transferred to the transfer material.

In the second transfer step, a DC bias voltage lower than the transfer bias voltage of the final color in the first transfer step is applied to the intermediate image carrier, or the intermediate image carrier is grounded, or A DC bias voltage having the opposite polarity to that in the one transfer step is applied.

Further, the idle rotation peripheral speed of the intermediate image carrier after the completion of the first transfer step is made higher than that during the first transfer step.

Furthermore, when transferring to a transfer material such as OHT or thick paper, the peripheral speed of the intermediate image carrier at the time of the second transfer step is made slower than at the time of the first transfer step.

Further, a transfer roller is used during the second transfer step. [Third invention] In an image forming apparatus in which an image is formed on an image carrier and the step of transferring the image onto a sheet by a transfer electric field is performed plural times, a contact electrode is provided on the upstream side of the transfer position in the sheet advancing direction. .

The volume resistivity of the sheet is 10 ⁷ to 10
It is within the range of ¹² Ω-cm.

Further, the transfer paper is superposed and conveyed on the sheet.

[0038]

[Action]

[First Invention] According to the present invention, it is not always necessary to perform additional rotation even when L1 ≧ L2, and the toner image on the photosensitive drum is sequentially transferred onto the transfer paper wound on the transfer drum. In a color image forming apparatus provided with a mechanism and a humidity sensor, after the final transfer in the overlap transfer at high humidity is completely completed, additional rotation for that is performed so that the transfer paper is separated from the transfer drum. When the humidity sensor detects an absolute humidity of 14 g / m ³ or more, the control is performed as described above so that the image is not disturbed and the density is not lowered. You can get a nice image. That is, when the absolute humidity is less than 14 g / m ³ , the image output time can be shortened. [Second invention] In the second transfer step, since the photosensitive drum and the surface of the transfer drum are separated from each other, the bias voltage applied to the transfer drum after the end of the transfer of the final color, which is seen in the conventional apparatus, is set to the optimum value. There is no transfer unevenness due to offset to the photosensitive drum when switched to, or transfer unevenness due to shock when the transfer roller contacts the transfer drum during the second transfer process, and a good transfer image with a high transfer rate can be obtained. To be

Further, the peripheral speed in the second transfer step can be easily reduced, and low-speed fixing can be performed by the heat roller fixing device without causing transfer deviation or image rubbing. Alternatively, a good fixed image can be obtained on a transfer material such as an envelope that requires a heating amount.

Further, in the color image forming apparatus of the present invention, by using the transfer drum, the transfer roller, the charging roller and the charge eliminating roller, it is possible to eliminate the use of the corona discharger and to substantially achieve ozoneless. [Third Invention] A clear image without scattering can be formed by providing an electrode on the upstream side in the direction in which the transfer electric field having the intermediate transfer belt acts.

[0041]

【Example】

[First Invention] (Embodiment 1) FIG. 1 (A) is a drawing best showing the features of the present invention. In FIG. 1 (A), the final color is obtained when the humidity sensor 30 detects an absolute humidity of less than 14 g / m ^3. After being transferred onto the transfer paper 6, the charge is removed by the separation charge eliminator 7 and directly enters the fixing unit 8. A latent image is formed on the photosensitive drum 4 by the laser diode, and each color (yellow,
The developing process using magenta, cyan, and black) and the toner transfer process onto the transfer paper 6 on the transfer drum 2 are similar to those of the conventional example. A cam member 1 is in contact with the shaft 5 of the transfer drum 2. The rotating shaft 5 is movable in the guide 50.

That is, the final color is transferred from the photosensitive drum 4 to the transfer paper 6 on the transfer drum 2. For example, when the fourth color is black, the bias value applied to the transfer drum 4 is +4 KV.
The toner is applied, and the toner is transferred by this electric field force. When the absolute humidity is less than 14 g / m ³ , the transfer current flows in the direction of the arrow (solid line) as shown in the figure, so that the toner is smoothly transferred to the transfer paper 6. When the front end of the transfer paper 6 reaches the separation charge eliminator 7, the transfer paper 6 is discharged from the transfer drum 2, and the paper front end is caught by the separation claw 3 and conveyed to the fixing unit 8.

The bias value applied to the separation static eliminator 7 is
An AC bias of 12 KVP-P is superimposed on DC +4 to +5 KV. When the front end of the transfer paper 6 is projected into the fixing roller 8, a part of the transfer paper 6 is still sandwiched by the nip portion between the photosensitive drum 4 and the transfer drum 2. In this embodiment, the distance L2 from the nip portion between the photosensitive drum 4 and the transfer drum 2 to the fixing roller portion 8 was 246 mm, and the length L1 of the transfer paper 6 was 300 mm. (Embodiment 2) Absolute humidity 1 detected by the humidity sensor 30
In the case of 4 g / m ³ , after the final color is transferred to the transfer paper 6, the transfer drum 2 is rotated once more without being separated and discharged. At this time, the transfer drum 2 is separated from the photosensitive drum 4 and is not in contact therewith.

As shown in FIG. 1 (B), the rotating shaft 5 is released by the cam member 1 to transfer the transfer paper 6 by the photosensitive drum 4.
The upper visible image (toner image) is separated by a distance that is not disturbed by the photosensitive drum 4. In this embodiment, the distance is 3 mm to 10 mm.

In this state, the transfer drum 2 is further rotated, and when the leading edge of the transfer paper 6 approaches the periphery of the photoconductor 4 again, the transfer separation charge eliminator 7 operates to separate the transfer paper 6 from the transfer drum 2. It is caught on the separating claw 3 and is conveyed to the fixing unit 8. After the transfer paper 6 passes through the fixing unit 8 and is discharged, the transfer drum 2 is pressed against the photosensitive drum 4 again by the cam member 1 to prepare for the next image output. (Example 3) Absolute humidity 1 detected by the humidity sensor 30
In the case of 4 g / m ³ , after the final color is transferred to the transfer paper 6, the transfer drum 2 is rotated once more without being separated and discharged. At this time, the transfer drum 2 is separated from the photosensitive drum 4 and is not in contact therewith.

By releasing the rotary shaft 5 by the cam member 1 as shown in FIG. 2, the visible image (toner image) on the transfer paper is separated by the photosensitive drum 4 to a distance that is not disturbed by the photosensitive drum 4. In this embodiment, the distance is 3 mm to 10 mm.

When the transfer drum 4 is further rotated in this state, the transfer paper 6 may be peeled off from the transfer drum 2 due to the attenuation of the charge. Therefore, as shown in FIG. 2, in order to further enhance the attraction force between the paper and the transfer drum 2 after the separation claw 3 in the rotation direction of the transfer drum 2, a corona charger 9 is provided to charge and enhance the attraction force. .

In the present embodiment, in order to transfer the toner having a negative charge, +4 to +5 KV is applied to the transfer drum 2 for the fourth color (final color), and -3 to the corona charger 9. -4 KV is applied. As a result, the transfer paper 6 is further rotated without separating from the transfer drum 2, the transfer paper 6 is discharged again by the separation charge eliminator 7, peeled off by the separation claw 3, and conveyed to the fixing unit 8. In this embodiment, a bias of +4 to +5 KV is applied to the separation static eliminator.

As described above, in the present invention, the transfer drum 2 is additionally rotated only when the humidity sensor 30 detects an absolute humidity of 14 g / m ³ or more, and the transfer is performed in an office where the temperature and humidity are controlled appropriately. Regardless of the length of the paper 6, after the transfer without additional rotation, the charge can be separated and discharged, and the paper can be directly conveyed to the fixing unit 8. Therefore, it is possible to provide a compact color image forming apparatus which can shorten the image output time and save energy. [Second Invention] (Embodiment 1) An embodiment of the present invention will be described below based on the color laser beam printer shown in FIG.

First, the OPC photosensitive drum 1 having a diameter of 70 mm
A photosensitive drum (hereinafter abbreviated as a photosensitive drum) is rotatably supported by the shaft 2 and rotates in the direction of arrow 3.

The surface of the photosensitive drum is negatively charged by the roller charger 4, and then the photosensitive drum 1 is subjected to scanning exposure based on the image signal of the first color from the exposure device 5 having a laser light source. A latent image is formed.

Next, the latent image is developed by the rotary-moving type developing device 6.
Is developed (reverse development) by the developing device 61 having a negative polarity yellow toner provided in the above, and a yellow toner image is formed.

The developing device 6 includes yellow, magenta, cyan, and black developing units 61, 62, 63, which are supported by two circular side plates on the back and front sides in the vertical direction in the figure.
64, each developing device is concentrically rotated in the direction of arrow 8 while keeping each developing device horizontal with respect to the shaft 7, and the predetermined developing device faces the photosensitive drum.

Next, at the first transfer position A, the yellow toner image on the photosensitive drum 1 is an intermediate image carrier having a diameter of about 143 mm, which is rotatably supported by the shaft 9, which will be described in detail with reference to FIG. A transfer bias voltage having a polarity opposite to that of the toner, for example, +1.
0 KV is applied, and the yellow toner on the photosensitive drum is transferred onto the transfer drum 10.

The photosensitive drum 1 and the transfer drum 10 are driven by separate pulse motors, but in the first transfer step, the surfaces of the photosensitive drum and the transfer drum are kept in contact with each other and the peripheral speeds are substantially the same. (For example, 80mm / sec)
To rotate.

More specifically, the surface of the transfer drum has elasticity as described later, and the amount of penetration of the transfer drum into the photosensitive drum is set to 1 mm in order to obtain a nip at the time of contact with the photosensitive drum. The nip width is about 10 mm), and the peripheral speed of the portion where the transfer drum is in contact with the photosensitive drum is about 1% faster than the peripheral speed of the photosensitive drum. This prevents the image dropout phenomenon.

As shown in the perspective view of FIG. 2, the transfer drum 10 has a semiconductive foam having a volume resistivity of 10 ⁴ to 10 ¹² Ω · cm on an aluminum cylinder 101 having a diameter of 140 mm which is a conductive support. The body elastic layer 102 is provided to have a thickness of 3 mm, and the volume resistivity is further 100 2 μm of 10 ¹² Ω · cm or more.
A thick insulating coating layer 103 is provided in an overlapping manner.

As the foam elastic layer, carbon,
Urethane rubber whose resistance value is controlled by fine particles such as TiO ₂ and SnO ₂ , foamed materials such as EPDM rubber or low hardness urethane rubber, chloroprene rubber. Silicone rubber or the like is used.

As the insulating coating layer, polyvinylidene fluoride, polyvinylidene chloride, polycarbonate, polyethylene terephthalate, polyurethane or the like is used. This insulating coating layer is required to have a smooth surface property in consideration of transferability and cleaning property of the toner image.

Similarly to the yellow toner image, the transfer drum 1
Magenta, cyan, and black toner images on top of 0,
It is formed and sequentially aligned and transferred onto the transfer drum 10. At this time, the bias voltages applied to the transfer drum are, for example, +1.2 KV, +1.5 KV, and
Increase sequentially with + 2.0KV.

After the transfer of the toner of each color, the surface of the photosensitive drum 1 is cleaned by the cleaning device 12 composed of an elastic blade, and the process proceeds to the next developing cycle.

The transfer drum 10 once passes through the second transfer position B in a state where the front end of the transferred black toner image of the fourth color is separated from the transfer roller 16 provided so as to be able to contact and separate from the transfer drum surface. That is, that is, idle rotation is performed without transfer to the transfer material.

Immediately after the transfer of the trailing edge E of the black toner image of the fourth color is completed, the shaft 9 of the transfer drum is illustrated as shown in the explanatory view (a cross-sectional view of only the main part is shown) shown in FIG. 5A. When the eccentric cam rotates, it moves along the shaft guide that supports the shaft of the transfer drum and separates it by about 1 mm so that the surface of the photosensitive drum and the surface of the transfer drum do not come into contact with each other.

While keeping this separated state, the transfer drum 1
The peripheral speed of 0 is approximately twice the peripheral speed of the photosensitive drum 1 (160
The rotation speed of the transfer drum 10 is switched so that the speed becomes (mm / sec).

On the other hand, the transfer paper 14 in the cassette 13 is sent to the second transfer position B by the feeding roller 15.

When the leading edge T of the image (shown at T in FIG. 4) on the transfer drum 10 that has been idling once approaches the second transfer position B (shown in the sectional view of FIG. 5B). The bias voltage applied to the transfer drum is switched to +0.5 KV, and the peripheral speed of the transfer drum 10 is returned to the same value (80 mm / sec) as in the first transfer step.

At this time, as the bias voltage applied to the transfer drum, a lower voltage with the same polarity, a voltage with the opposite polarity or a ground (0V) voltage is used as compared with the applied bias voltage at the time of transferring the final color in the first transfer step. To be

The larger the difference between this bias voltage and the applied bias voltage at the time of transferring the final color, the higher the transfer efficiency in the second transfer step. However, the bias voltage having a large unnecessary difference does not affect the transferred image. Generate splatter.

Next, the transfer roller 16 having a diameter of 20 mm comes into contact with the non-image portion immediately before the image front end T on the transfer drum. This transfer roller 16 has a conductive support, and the conductive support is made of the same elastic material (volume specific resistance value of 10 ⁴ to 10 ¹² Ω · cm) used for the transfer drum 10. It is covered. An insulating coating layer for coating the elastic layer may be provided, but it is not particularly required.

A bias voltage of the opposite polarity to the toner; +2.0 KV is applied to the transfer roller 16. Transfer drum 1
When the leading edge T of the image on 0 reaches the transfer portion B, the leading edge of the transfer paper 14 and the transfer drum 10 and the transfer roller 1 almost at the same time.
It is sent to the nip with 6 (width is about 4 mm), and the four color toner images on the transfer drum are collectively retransferred onto the transfer paper 14. At this time, the peripheral speed of the transfer roller 16 is the same as that of the transfer drum 1.
Approximately 1% faster than 0 to prevent the dropout of the transferred image.

The toner remaining on the transfer drum 10 without being transferred, when the portion corresponding to the front end T of the image reaches the cleaning position, the blade of the cleaning device 17 having a blade capable of coming into contact with and separating from the surface of the transfer drum is transferred to the transfer drum. Contact the surface for cleaning.

After that, the charge eliminating roller 18 (an AC bias voltage is applied) capable of coming into contact with and separating from the surface of the transfer drum comes into contact with the surface of the transfer drum to eliminate the charge on the charged surface of the transfer drum, thereby electrostatically charging. Initialize to.

When the portion of the transfer drum 10 corresponding to the image front end T reaches the first transfer portion A, the transfer drum 10
The surface comes into contact with the surface of the photosensitive drum 1 that continues to rotate backward, and the peripheral speed of the transfer drum 10 becomes substantially the same speed as the photosensitive drum 1, and the process proceeds to the next cycle.

The transfer paper 13 is conveyed to the heat roller fixing device 20 via the conveyance guide 19, and is almost equal to the transfer speed of the transfer paper 14.
It is heated and fixed at the same speed, and then discharged to the tray 21.

In the full-color image obtained by the above steps, there was no transfer unevenness when the transfer bias was switched in the second transfer step or transfer unevenness when the transfer roller was in contact with the transfer drum. Also, high transfer efficiency (finally 80% or more for each color) was obtained.

Furthermore, during idle rotation after the transfer drum is separated,
Since the peripheral speed of the transfer drum is doubled as compared with the first transfer step, the time required for printing can be kept to a minimum delay as compared with the conventional apparatus. (Embodiment 2) In the second transfer process of Embodiment 1, after transferring the final color to the transfer drum 10, the photosensitive drum surface and the transfer drum surface are separated from each other, and then the transfer drum is set to the ground (0 V) potential. Further, +1.5 KV was applied to the transfer roller 16 in the second transfer step.

As a result, the transfer rate in the second transfer step was improved. (Embodiment 3) In Embodiment 1, in the second transfer step, the peripheral speeds of the transfer drum 10 and the transfer roller 16 are approximately 1/2 (4) of the peripheral speed of the transfer drum in the first transfer step.
It was transferred to OHT (Overhead Transparency) cardboard or envelope at a slow speed of 0 mm / sec.
For example, the front end of the OHT that has passed the second transfer position B is conveyed to the heat roller fixing device 20 where the fixing speed is substantially the same as the peripheral speed of the transfer drum and is heat-fixed, but part of the OHT is fixed by the heat roller. When it is fixed by a container, even if a part of the latter is being transferred, it is heated and fixed without causing a transfer deviation,
A full-color image excellent in transparency and color mixture after projection was obtained. In addition, a full-color image excellent in color mixture and gloss was obtained by the same process on thick paper and envelopes. [Third Invention] FIG. 6A is a laser beam color printer which is an embodiment of the image forming apparatus showing the first embodiment of the present invention. In the figure, 3 is a cylindrical image carrier, and the image carrier 3 has a photosensitive layer 2 such as an organic photoconductor (OPC), zinc oxide, selenium compound, and amorphous silicon on the upper surface of an aluminum cylinder 1 having a diameter of 80 mm. It was applied or vapor-deposited, and OPC was applied in this example.
The image carrier 3 is driven and rotated in the direction of arrow A at a peripheral speed of 63 mm / sec, and the charging device 4 uniformly charges the image carrier 3 to -600V.

Next, a signal according to the cyan image pattern is applied from the signal source 5 to the laser diode 6 to generate the image light L. The image light L is reflected by a polygon mirror 8 rotating by a high-speed motor 7, the reflected light is transmitted through a lens 9, and then reflected by a folding mirror 10 to be radiated onto an image carrier 3 to form a latent image.

Cyan toner is adhered to the latent image on the upper surface of the image carrier 3 according to an image pattern by a cyan developing device 11C (a known developing method such as magnetic brush two-component development, non-magnetic-component development and cascade development). .

At this time, the latent image is an inverted image (image carrier 3
(Toner is attached to a place where there is no electric charge exposed to light), a direct current voltage substantially equal to the charged potential on the image carrier 3 is applied to the developing device 11, and an alternating electric field is superposed if necessary. You can do it. In the present invention, the image was formed by reversal development.

In the present invention, non-magnetic component development is used.
(B) is cyan development 11C and magenta development 11 of (A)
M, yellow development 11Y, and black development 11BK will be described. The development devices 11C, 11M, 11Y, and 11BK have substantially the same configuration, and will be described below with reference to FIG.

In (B), the container 111 is filled with a toner T for the product name CLC200 from Canon Sales as a toner. The toner T is transported in the direction of arrow 11A by stirring and toner transport (hereinafter referred to as toner transport blade) 112, and the toner T is applied by the coating roller 113 to the developing roller 1.
The toner is evenly coated on the developing roller 114, and the developing roller 114 rotates in the direction of the arrow 11C, so that the toner leveling blade 115 coats the toner on the developing roller 114 in a tooth layer.

Further, by facing the image carrier 3, the toner on the developing roller 114 adheres according to the electrostatic latent image on the image carrier 3. A voltage in which a DC electric field is superimposed on an AC electric field is applied between the image carrier 3 and the developing roller 114.

Specifically, the latent image potential is -600 V in the back shadow area,
When the toner adhering portion potential is -80V, the AC electric field is Vp-p.
(Peak to peak) 1600V frequency 1.5KH
z and a DC electric field of -400V are applied. The distance between the image carrier 3 and the developing roller 114 is 300 μm.

After a cyan image is formed in the apparatus shown in FIG. 6A by the above developing apparatus, the toner on the image carrier 3 is subjected to the action of the electric field applied to the intermediate transfer roller 13 to cause the intermediate transfer belt 12 to move. Transcribed on.

The intermediate transfer belt 12 usually has a thickness of 100 μm.
In addition, a material having a volume resistivity of 10 ⁷ to 10 ⁹ Ω · cm is adopted. In this example, carbon was dispersed in polycarbonate to adjust to 10 ⁸ Ω · cm.

On the upstream side of the transfer position in the traveling direction of the intermediate transfer belt 12 (B in the figure), an electrode 14 is arranged so that the toner on the image carrier 3 does not fly before the transfer position.
The effect of the electrode 14 will be described later.

The transfer belt 12 transfers the cyan image while moving in the direction of arrow B. The residual toner on the image carrier 3 is cleaned by the cleaning device 15. Next, similar to the cyan image, primary charging 4, exposure device 5, 6, 7, 8,
An electrostatic latent image of magenta color is formed on the image bearing member 3 at 9, 10 and L, and at the same time, cyan development 1 is performed as described in detail in JP-A-50-50935, JP-A-50-93437 and the like.
1C and magenta development 11M are switched, and magenta color is developed.

This is transferred onto the cyan image on the transfer belt 12 in an overlapping manner. Similarly, a yellow image and a black image are also formed.
The images of four colors obtained on the intermediate transfer belt 12 are transferred by the transfer belt transfer roller 17 and the transfer roller 16 onto the transfer paper P which is transferred by a transfer system (not shown), and are subjected to heating, pressing, etc. (not shown). It is fixed by the fixing device.

The main points of the present invention will be described below with reference to FIG. 7A, which are the transfer positions of the image carrier 3 and the intermediate transfer belt 12. FIG. 13 shows a conventional example, which will be described below by comparing the two. In FIG. 13, the image carrier 600 and the transfer roller 6
When a transfer voltage is applied from the power source 603 during 02, the intermediate transfer belt 601 has a low resistance value as described above, and a potential substantially equal to the potential of the transfer roller 602 is formed.

For this reason, a dashed electric field is formed from the intermediate transfer belt 602 toward the image carrier 600. When this electric field E is formed, the toner T on the image carrier 600 becomes
It flies to the side of the intermediate transfer belt 12. Usually, the intermediate transfer belt 12 is made by dispersing carbon as conductive particles in polycarbonate and adjusted to have a volume resistance of 10 ⁷ to 10 ¹² Ω · cm.

The transfer voltage is from 1 KV to 4 from the power source 603.
It is applied within the range of KV. This transfer voltage is 1.5 KV for the first color and 2 KV for the second color, which is 250 for each superposition.
It is configured to gradually increase from V by 500V.
With this configuration, the tribo amount of the toner T is from 10 μc to 20 μc
In the case, the distance between the intermediate transfer belt 601 and the image carrier 600 causes the toner to fly at an applied voltage of 500 V per 100 μm.

This means that the transfer voltage is from 1 KV to 4 KV.
When applied, it flies from a distance of 200 μm to 800 μm.
This means that the toner T on the image carrier 600 flies before contact with the intermediate transfer belt 601 on the upstream side of the transfer position in the rotational direction of the image carrier 600, so that the toner T on the image carrier 600 is uniformly transferred. The transferred image at the transfer position is a disordered image, that is, a scattered image.

On the other hand, FIG. 7A shows the upstream side of the transfer position and the back side of the intermediate transfer belt 12 (transfer roller side).
Since a conductive electrode 14 is disposed on the intermediate transfer belt 13 and the current from the transfer roller 13 flows to the electrode 14 side through the intermediate transfer belt 12, the intermediate transfer between the transfer roller 13 and the electrode 14 is accompanied by the current passing through the intermediate transfer belt 12. A potential gradient is generated by the resistance of the belt 12, and no electric field pressure is generated until the toner flies as illustrated.

In this experiment, in the explanation device of FIG. 6A, 5 mm to 15 mm from the contact center of the transfer roller 13 and the image carrier 12
By arranging the tip C of the electrode 14 within the range of mm, an image without scattering can be formed.

FIG. 7B shows another embodiment. Figure (A)
The same numbers as indicate the same functions. Although the transfer roller 13 has been described, in the present embodiment, the conductive fibers 13 'of conductive carbon fibers are bundled in the conductive folder 13 ",
Similar to (A), the same effect can be obtained by applying a transfer voltage from the power supply 18 between the image carrier 3 and the conductive folder 13 ″.

When the apparatus shown in FIG. 5B was incorporated into the apparatus shown in FIG. 5 to form an image, the image on the transfer belt 12 was a good image without scattering.

FIG. 8 shows still another embodiment. The same reference numerals as those in FIG. 5 have the same functions, and the major difference from FIG. 5 is that images of each color are not output to the same image carrier 3 and each color independently forms an image.

Explained below, a yellow image is formed on the image carrier 3 of 101 as in FIG. 5, and this yellow image is transferred onto the intermediate transfer belt 12 which is moved by the driving roller 19 as in the description of FIG. .

Next, a magenta color image is formed by 102, a cyan color image is formed by 103, and a black image is formed by 104. The four color images obtained on the intermediate transfer belt 12 are as follows.
A transfer power source 2 similar to the transfer onto the intermediate transfer belt 12 described above.
From 0, a transfer electric field is applied to the conductive brush 22 and the transfer is collectively performed on the transfer paper P.

When the transfer paper P has a low resistance value, a conductive contact member may be similarly provided.

FIG. 9 shows another embodiment. In FIG. 9, the transfer paper P is directly conveyed onto the intermediate transfer belt 12 of FIG.
It was confirmed by the above method that the same effect can be obtained even with such a method even with a volume resistivity of 10 ⁷ to 10 ¹² Ω · cm or less where the resistance center of the intermediate transfer belt 12 is low.

[0103]

【The invention's effect】

[First Invention] As described above, the transfer drum is additionally rotated only when the absolute humidity is detected by the humidity sensor to be 14 g / m ³ or more, and the length of the transfer paper is appropriately adjusted in the office in which the temperature and humidity are controlled. Regardless of the type, after the transfer without additional rotation, the charge can be separated and discharged, and can be directly conveyed to the fixing unit.

Therefore, it is possible to provide a compact color image forming apparatus which can shorten the image output time and save energy. [Second invention] In the second transfer step, since the photosensitive drum and the surface of the transfer drum are separated from each other, the bias voltage applied to the transfer drum after the end of the transfer of the final color, which is seen in the conventional apparatus, is set to the optimum value. There is no transfer unevenness due to offset to the photosensitive drum when switched to, or transfer unevenness due to shock when the transfer roller contacts the transfer drum during the second transfer process, and a good transfer image with a high transfer rate can be obtained. To be

Further, the peripheral speed in the second transfer step can be easily reduced, and the heat roller fixing device can perform low-speed fixing without causing transfer deviation and image rubbing. Alternatively, a good fixed image can be obtained on a transfer material such as an envelope that requires a heating amount.

Further, in the color image forming apparatus of the present invention, by using the transfer drum, the transfer roller, the charging roller and the charge eliminating roller, it is possible to eliminate the use of the corona discharger and to substantially achieve ozoneless. [Third Invention] As described above, a clear image without scattering can be formed by providing an electrode on the upstream side in the direction in which the transfer electric field having the intermediate transfer belt acts.

[Brief description of drawings]

1A and 1B are front views showing first and second embodiments of the first invention.

FIG. 2 is a front view of a third embodiment of the first invention.

FIG. 3 is a sectional view showing the configuration of a color laser beam printer which is an embodiment according to the second invention.

FIG. 4 is a perspective view of the transfer drum shown in FIG.

5A is a cross-sectional view showing only the main configuration of the transfer drum in the embodiment of FIG. 3, and FIG. 5B is a second transfer process in the embodiment of FIG. FIG. 6 is a cross-sectional view illustrating only the main configuration for explaining the above.

FIG. 6 is a third invention, (A) is a front view of the entire configuration,
FIG. 3B is a sectional view of the developing device of FIG.

7A and 7B are third inventions, FIG. 7A is an enlarged view of the transfer position of FIG. 6, and FIG. 7B is an explanatory view of another embodiment.

FIG. 8 is an overall view of another embodiment of the third invention.

FIG. 9 is a partial view of another embodiment of the third invention.

FIG. 10 is a front cross-sectional view of the overall configuration of a first conventional example.

11 is a front sectional view of the developing device in FIG.

FIG. 12 is a front view of the vicinity of the fixing unit in FIG.

FIG. 13 is a front view of a main part of a second conventional example.

[Explanation of symbols]

 4 Photosensitive Drum 2 Transfer Drum 6 Transfer Paper 30 Humidity Sensor 1 Photosensitive Drum 6 Developing Device 10 Transfer Drum 14 Transfer Material 16 Transfer Roller 12 Intermediate Transfer Belt 14 Electrode 13 Transfer Roller

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical indication location G03G 15/01 114 A (72) Inventor Masami Takeda 3-30-2 Shimomaruko, Ota-ku, Tokyo Kyano (72) Inventor Takao Aoki 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Haruo Fujii 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (10)

[Claims] 1. A color image forming apparatus provided with a humidity sensor and a mechanism for sequentially superposing a toner image on a photoconductor drum onto a transfer paper wound on the transfer drum, and performing a superposition transfer at high humidity. A color image forming apparatus including applying additional rotation to the transfer drum so that the transfer paper is separated from the transfer drum after the final transfer in step 1 is completely completed. 2. The color image forming apparatus according to claim 1, wherein the absolute humidity when detected and controlled by the humidity sensor is 14 g / m ³ or more. 3. A first transfer step in which toner images of respective colors sequentially formed on an image bearing member are sequentially superimposed and transferred onto an intermediate image bearing member having at least a conductive support and an elastic body coating layer, In a color image forming apparatus that forms a color image on a transfer material by a second transfer step of retransferring the image on the intermediate image carrier to a transfer material, after the first transfer step, the image carrier A color image forming apparatus, characterized in that the intermediate image carrier is separated from the intermediate image carrier, and the intermediate image carrier performs idle rotation without transfer to a transfer material, and then performs the second transfer step. 4. The color image forming apparatus according to claim 3, wherein a DC bias voltage lower than the transfer bias voltage of the final color at the first transfer step is applied to the intermediate image carrier during the second transfer step. Apply or ground the intermediate image carrier,
Alternatively, the color image forming apparatus is characterized in that a DC bias voltage having a polarity opposite to that in the first transfer step is applied. 5. The color image forming apparatus according to claim 3 or 4, wherein the idle rotation peripheral speed of the intermediate image carrier after the completion of the first transfer step is faster than that during the first transfer step. A color image forming apparatus characterized by the above. 6. The color image forming apparatus according to claim 3, 4, or 5, when transferring to a transfer material such as OHT or thick paper, the intermediate image carrier during the second transfer step. A color image forming apparatus characterized in that the peripheral speed of is lower than that in the first transfer step. 7. The color image forming apparatus according to any one of claims 3 to 6, wherein a transfer roller is used during the second transfer step. 8. An image forming apparatus in which an image is formed on an image carrier and a step of transferring the image on a sheet by a transfer electric field is performed a plurality of times, and a contact electrode is provided on the upstream side of the transfer position in the sheet advancing direction. A color image forming apparatus characterized by the above. 9. The sheet has a volume resistivity of 10 ⁷ to 1 1.
9. The color image forming apparatus according to claim 8, which is within a range of 0 ¹² Ω-cm. 10. The color image forming apparatus according to claim 8, wherein the transfer paper is superposed and conveyed on the sheet.