JP3165625B2 - Color image forming equipment - 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 using an electrostatic transfer process, such as an electrostatic copying machine and a printer, and more particularly to a color image forming apparatus using a color multiple transfer process.

[0002]

2. Description of the Related Art Conventionally, in a color image forming apparatus using an electrophotographic system or an electrostatic recording system, a multiplexing method for sequentially transferring a plurality of colors of a visible image to a recording material carried on a recording material carrier. The transfer method is widely used.

[0003] Among them, an example of a general image forming apparatus having many advantages, such as easy realization of high-speed recording and applicability of various kinds of recording materials by a linear conveyance path, is cited. Technology and problems will be described.

In FIG. 4, an endless belt 8 running in a direction indicated by an arrow X in FIG.
First, the recording material 6 taken out of the cassette 60 is supplied to the endless belt 8 via the registration roller 13 and further conveyed to the left in the figure. On the upper surface of the endless belt 8, four image forming units Pa, Pb, and
Pc and Pd are arranged in series.

Since all the image forming units Pa to Pd have the same configuration, only the image forming unit Pa will be briefly described. The image forming unit Pa includes a rotating cylindrical image carrier 1a, and peripherally includes image forming members such as a primary charger 2a, a developing unit 3a, and a cleaner 5a. Note that magenta toner, cyan toner, yellow toner, and black toner are stored in the developing devices 3a, 3b, 3c, and 3d disposed in the respective image forming units.

An image signal based on the magenta component color of the document is projected onto an image carrier 1a via an exposure device such as a polygon mirror (not shown) to form an electrostatic latent image, and magenta toner is supplied from a developing device 3a. Thus, the latent image becomes a magenta toner image. When this toner image arrives at the transfer site where the image carrier 1a and the endless belt 8 come into contact with each other as the image carrier 1a rotates, the recording material 6 removed from the cassette 60 reaches the transfer site by this time. Transfer means 4
The magenta toner image is transferred to the recording material 6 by the transfer bias applied by a.

Thereafter, the residual toner remaining on the image carrier 1a is removed by the cleaner 5a, and the residual charge is removed by the pre-exposure means 21a, so that the image carrier 1a is ready for the next image formation.

When the recording material 6 carrying the magenta toner image is conveyed to the image forming portion Pb by the endless belt 8,
By this time, in the image forming section Pb, the cyan toner image formed on the image carrier 1b is transferred to the recording material by the same process as described above.

Similarly, the recording material 6 is used for the image forming portions Pc, Pd
After the yellow toner image and the black toner image are superimposed and transferred on the toner images at the respective transfer portions, the recording material 6 carrying the toner images is separated from the endless belt 8 and is fixed by a fixing device (not shown). Transported to The fixing device is provided with a fixing roller and a pressure roller that is in pressure contact with the fixing roller. The recording material 6 is fed to the nip portion of these rollers and is pressed and heated to fix and fix the color image. Emitted outside the machine.

After that, the charge on the belt, the toner attached to the belt, and the like are removed by the static eliminator 12 and the cleaning roller 16 disposed at a position corresponding to the return path of the endless belt 8.

The endless belt 8 is made of a polyethylene terephthalate resin film (hereinafter abbreviated as a PET film), a polyvinylidene fluoride resin film (hereinafter abbreviated as PV).
dF), polycarbonate resin (hereinafter abbreviated as “PC”), polyurethane resin (hereinafter abbreviated as “PU”), polyimide (hereinafter abbreviated as “PI”), and many other dielectric resins and rubbers. A material using a conductive filler having electric characteristics and strength is used.

[0012] Also. Transfer charging means include a blade,
In the form of a roller or the like, the material is a contact and proximity charging means in which conductive elastomers, foams, fibers and the like are widely used. On the other hand, a typical example of the non-contact charging means is a charging method using a corotron or a scorotron. In this case, a contact auxiliary member such as a pressing member or an electric field regulating member is generally used.

However, in the case of the non-contact method, the total applied current is divided into the current in the drum direction contributing to the transfer electric field and the current in the shield direction, and the ratio varies depending on the impedance during transfer. For this reason, when the impedance changes due to the thickness or the material of the recording material, there is a defect that the transferability changes.

In addition, when applying a transfer electric field, it has been conventionally suggested that restricting the spread of the transfer electric field is more effective for transferring high-quality images, as has been proposed to regulate the electric field. Are known. For this purpose, it has been conventionally proposed to use a conductive rubber blade or a conductive fiber. Of these, when a brush using a conductive fiber is used, discharge due to hair loss, fiber breakage, and the like are caused. There were drawbacks that occurred. Therefore, in order to realize more stable and high image quality, transfer means using a conductive rubber blade has come to be widely used.

[0015]

However, in the above-mentioned prior art, the close contact between the image carrier and the recording material, and the close contact between the recording material carrier and the recording material are maintained by a conductive rubber blade as a transfer charging means or a pressing member thereof. Therefore, a contradiction arises between the stable transportability of the recording material and the transferability. This example will be described with reference to the color image forming apparatus shown in FIG.

First, when the recording material 6 is fed during image formation, the recording material 6 is conveyed onto a transfer belt 8 as a recording material carrier in accordance with the image forming timing, and the image forming unit Pa It is charged by the transfer charging means 4a and is electrostatically attracted and carried.

At this time, if the recording material 6 is distorted or wavy, electric field unevenness occurs during transfer charging, and uniform transfer is not performed. That is, if a space is formed between the image carrier 1a, the recording material 6, the recording material carrier 8, and the transfer charging means 4a, the space becomes defective in transfer, resulting in image unevenness. This image unevenness can be suppressed by increasing the pressing force of the transfer charging means 4a. On the other hand, if there is an excessive pressing force at the time of transfer, the toner is aggregated, and the mirror force of the toner and the image carrier is reduced. Increases the transfer efficiency. In particular, this is remarkable in the center of the thin line, etc.
In order to suppress this, a light pressure transfer unit has been conventionally proposed.

Further, when the pressure of the transfer charging means is high, the conductive rubber blade is scraped off, and a space is formed between the recording material and the conductive rubber blade during the transfer charging, so that discharge occurs, There is a disadvantage that the durability life is shortened due to the unsuitable electric field.

Further, there is a problem peculiar to double-sided output. That is, in a multi-color image forming apparatus, for example, a four-color full-color image forming apparatus, four different color toners are used, and these four color toner images are printed on a recording material.
Since the layers are laminated, good melting and color mixing properties when heated by a fixing device are required. If the melting and color mixing are poor, the air gap between the toner particles increases, and the scattering of light at the interface with air causes the original color tone of the toner dye to be lost. This is because the color reproducibility is reduced due to being hidden by the toner in the upper layer.

As a toner satisfying these melting properties and color mixing properties, a so-called sharp melt toner having a low softening point and a low melt viscosity is used. By using such a toner, color reproducibility can be enhanced and a color copy faithful to a document can be obtained.

However, since the sharp-melting toner has a high affinity, there is a disadvantage that the toner is easily offset to the fixing roller.

The recording material on which the toner images of four colors are stacked is subjected to pressure in addition to heating in the fixing device.
Therefore, the toner having a high affinity tends to be transferred to and adhered to the fixing roller by the heating device. When the toner is transferred to the fixing roller, the toner is transferred to the next recording material, or is solidified on the fixing roller, both of which cause image defects.

Therefore, a release agent is used to prevent such image defects. Prior to the fixing of the toner image on the recording material in the fixing device, a liquid release agent such as oil is applied onto the fixing roller. As a result, when the toner image is heated and pressed, the fixing roller comes into contact with the toner image on the recording material via the release agent without directly contacting the toner image, and the toner is transferred to the fixing roller side. Can be effectively prevented from adhering.

However, when copying is performed on both sides of the recording material, the release agent adhered from the fixing roller to the first surface (first surface) of the recording material is transferred to the next surface (second surface) of the recording material.
When an image is formed on a recording medium, the first surface of the recording material comes into contact with the surface of the endless belt, so that the recording material is transferred to the surface of the endless belt.

Thereafter, the release agent on the endless belt is transferred and adheres to the surface of the photosensitive drum, which is the image carrier, which is in contact with the endless belt. The release agent cannot be sufficiently wiped off by a photosensitive drum cleaning device which is originally intended to remove residual toner on the photosensitive drum. As a result, the release agent on the photosensitive drum causes residual toner and toner during development to adhere to portions of the photosensitive drum to which toner should not originally adhere, and these toners are transferred to the recording material thereafter. Then, a dirty image is formed.

As described above, when the pressing force of the transfer charging means is high during the formation of a double-sided image, the release agent is transferred onto the endless belt and from the endless belt to the photosensitive drum, and the amount of the release agent is promoted. There was a disadvantage that the load on the release agent removing means was increased.

Accordingly, a first object of the present invention is to provide a color image forming apparatus capable of achieving both good conveyance stability of a recording material and excellent transferability.

Further, a second object of the present invention is to improve the effect of suppressing the transfer of the release agent without imposing a load on the release agent removing means during the double-sided image formation, and to improve the recording material. An object of the present invention is to provide a color image forming apparatus capable of achieving both excellent transport stability and excellent transferability.

Further, a third object of the present invention is to provide a color image forming apparatus capable of achieving both good conveyance stability and excellent transferability for any recording material.

[0030]

The above object is achieved by a color image forming apparatus according to the present invention. In summary, the first
According to the present invention, a plurality of image carriers each carrying a plurality of color images, a recording material carrier carrying a recording material and transporting the recording material to each transfer portion, and the recording in each transfer portion A plurality of plate-shaped transfer charging means for sequentially transferring an image on each of the image carriers to a recording material carried on the recording material carrier in contact with a back surface of the material carrier. A plurality of pressing members that press the recording material carrier in the vicinity of the transfer portions and in the moving direction of the recording material carrier with respect to the transfer portions, and are pressed by the pressing members. A color image forming apparatus is provided, wherein the position of the recording material carrier is set on a side on which the image carriers are provided with respect to a tangent line of the image carrier in each transfer section. According to one embodiment of the first aspect of the present invention, each of the pressing members can be moved toward and away from the recording material carrier. According to another embodiment of the first aspect of the present invention, each of the transfer charging units is capable of coming into contact with and separating from the recording material carrier. According to another embodiment of the first aspect of the present invention, after the visible image transferred to the first surface of the recording material is fixed by a fixing unit coated with oil, the image on each of the image carriers is removed. The transfer material can be sequentially transferred to a second surface of the recording material carried on the recording material carrier opposite to the first surface by the transfer charging means. According to another embodiment of the first aspect of the present invention, the pressing operation of the transfer charging means on the recording material carrier is performed independently of the pressing operation of the pressing members on the recording material carrier. Done. According to another embodiment of the first invention, the position of the recording material carrier pressed by each of the pressing members is in contact with each of the image carriers. According to another embodiment of the first aspect of the present invention, a plurality of pressing members which press the recording material carrier near the respective transfer portions and downstream of the respective transfer portions in the moving direction of the recording material carrier. And the position of the recording material carrier pressed by each of the downstream pressing members is closer to the side on which each of the image carriers is provided than the tangent line of each of the image carriers in each of the transfer units. You.

According to the second aspect of the present invention, a plurality of image carriers each carrying an image of a plurality of colors, a recording material carrier carrying a recording material and transporting the recording material to each transfer section, A plurality of transfer charging units that contact a back surface of the recording material carrier at a transfer unit and sequentially transfer images on the image carriers to a recording material carried on the recording material carrier. The forming apparatus further includes a plurality of pressing members that press the recording material carrier in the vicinity of each of the transfer units and on the upstream side in the moving direction of the recording material carrier with respect to each of the transfer units. The position of the recording material carrier pressed by is set on the side where each image carrier is provided with respect to a tangent line of each image carrier in each transfer unit, and is in contact with each image carrier. A color image forming apparatus characterized by the following is provided. According to one embodiment of the second aspect of the present invention, each of the pressing members can be moved toward and away from the recording material carrier. According to another embodiment of the second invention,
Each of the transfer charging means can be brought into contact with and separated from the recording material carrier. According to another embodiment of the second aspect of the present invention, the pressing operation of the transfer charging means on the recording material carrier is performed independently of the pressing operation of the pressing members on the recording material carrier. Done.

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a color image forming apparatus according to the present invention will be described in more detail with reference to the drawings. In the embodiment described below, the present invention is embodied in a color image forming apparatus which is substantially the same as the color image forming apparatus described above with reference to FIG. Therefore, a detailed description of the overall configuration and functions of the color image forming apparatus will be omitted, and features of the present invention will be described.

Embodiment 1 Embodiment 1 of the transfer charging means of the color image forming apparatus according to the present invention will be described with reference to FIGS. In FIG. 1 and FIG. 2, a transfer charging unit 4 is disposed opposite to a photosensitive drum 1 as an image carrier with an endless belt 8 as a recording material carrier therebetween. The transfer charging means 4 includes a plate-shaped conductive rubber blade 401 and an electrode 402, and the end of the conductive rubber blade 401 presses the endless belt 8,
It is in close contact with the photosensitive drum 1. In addition, a high voltage application unit 415 is connected to the electrode 402.

Further, a point at which the conductive rubber blade 401 comes into contact with the endless belt 8 (hereinafter, a mechanical contact portion of the transfer means is abbreviated as a transfer nip) is referred to as an endless belt 8.
An upstream pressing member 411 is provided on the upstream side in the moving direction of the. Further, a static elimination needle 412 is arranged downstream of the transfer nip.

As shown in FIG. 1, the upstream pressing member 411 is arranged such that the dotted line m connecting the lower end contact Q of the photosensitive drum 1 is in contact with the dotted line m 'passing through the lower end contact Q and inclined from upstream to downstream. , Endless belt 8. That is, the position of the endless belt 8 pressed by the upstream pressing member 411 is located closer to the photosensitive drum 1 than the tangent (m) passing through the lower end contact point Q.

Here, in the case where the recording material 6 to be transferred is a paper that has lost its planarity as if repeated absorption and dehumidification, the upstream pressing member 411 is drawn along the endless belt 8 while squeezing the recording material 6. Can apply a transfer electric field. If there is no upstream pressing member 411, the conductive rubber blade 40
1 applies a transfer electric field at the same time as the recording material 6 is being squeezed, so that an electric field is also applied to the upstream side of the mechanical contact, so that an uneven electric field is easily applied.

Further, when the recording material 6 is used in combination with the upstream pressing member 411, the pressing force can be dispersed even with the same total pressure, compared with the case where the recording material 6 is stiffened only with the conductive rubber blade 401. Can be. In other words, toner condensation on the photosensitive drum due to local pressure concentration can be avoided. As a result, it is possible to prevent the dropout during transfer and the scraping of the conductive rubber blade as described above.

In this embodiment, the upstream pressing member 411 has 5
Using a 00 μm PET film, conductive rubber blade 4
For 01, carbon-dispersed EPDM rubber was used, and the total pressure of both was 1 kg weight. The static elimination needle 412 used was a sawtooth member made of stainless steel and grounded.

With the above configuration, the ironing force (or the pressing force of the conductive blade) of the recording material, which was conventionally applied with 1 kg weight, can be dispersed. And both good transport stability and good transferability were realized.

[0040]

Second Embodiment The pressing member in the first embodiment is always in the pressed state, but it is not always necessary to always be in the pressed state.

As described above, a release agent such as silicone oil is widely and generally used in an electrophotographic recording apparatus at the time of fixing. However, when the release agent adheres to an endless belt, the recording agent is gradually applied to a photosensitive drum. It transfers and induces toner adhesion, causing image stains.

The reason why the release agent adheres to the endless belt is that when the double-sided image is output, the release agent adhered to the first transfer image surface during the transfer of the second side or the recording material is conveyed. Transfer to the endless belt surface. For this reason, when the position of the recording material carried at the time of the transfer of the first side and the second side is different on the endless belt, and when the sheets having different paper sizes are continuously recorded, the place where the paper is carried on the endless belt is obtained. In various cases, such as when the toner is insufficient, the release agent on the endless belt may transfer onto the photosensitive drum.

Therefore, in the second embodiment, when no transfer electric field is applied, the pressing force of the pressing member is released together with the transfer charging means. Thereby, the transfer of the release agent described above can be prevented.

Third Embodiment In the second embodiment, the pressing member is released from the pressing force together with the transfer charging means. However, the pressing member is not necessarily limited to this.

In the third embodiment, as shown in FIG. 3, in addition to the above-mentioned upstream pressing member 411, the transfer charging means 4 is interposed between the downstream side in the moving direction of the endless belt 8 and the upstream side of the discharging needle 412. This is an example in which the downstream pressing member 410 is employed at the same time. A case in which this embodiment is adopted in an image forming apparatus as shown in FIG. 2 will be described. Also in this embodiment, as shown in FIG. 3, the position of the endless belt 8 pressed by the downstream pressing member 410 is located closer to the photosensitive drum 1 than a tangent (m) passing through the lower end contact point Q.

As one of the features of an image forming apparatus having an endless belt and a plurality of image carriers as in the color image forming apparatus shown in FIG. 2, a linear paper conveyance path is used. There is support for strong recording materials.

However, when the upper and lower pressing members 410 and 411 are provided in the transfer section as in the present embodiment, a temporary curvature conveyance path is particularly generated. Therefore, when a strong recording material is conveyed, if the pressing force is not sufficient, the upstream / downstream pressing members 410 and 411 or the transfer charging means 4 will be pressed down.

At this time, if any one of these members is pressurized, if one of them is pushed down, the conductive rubber blade 401 separates from the endless belt 8 at the time of transfer, and an image defect due to discharge occurs. Would.

On the other hand, if the pressing force is increased to such an extent that the paper cannot be pushed down, the above-mentioned adverse effects such as abrasion will be caused, and a shock in which the paper conveyance speed will temporarily change at the time of transfer entry and exit will occur, causing a color shift. Becomes

Therefore, the above-mentioned problem is solved by providing a structure in which at least one of the pressing member, the upstream and the downstream, and the transfer charging means 4 can be independently pressurized, and high image quality can be obtained even with various recording materials. As a result, an image forming apparatus that achieves stable transportability can be realized.

Further, the effect according to the present invention can be more suitably obtained by providing each of the upper and lower pressing members and the transfer charging means with means for independently pressing.

The means for independently pressing is a spring member. For example, the upstream pressing member 411 is made of an elastic material.
When the pressing member 411 and the conductive rubber blade 401 are simultaneously spring-pressed, when the elastic force of the pressing member 411 is lower than the pressing force of the spring member, the spring member presses independently. For example, 100 μm
When the PET film was pressed by a spring having a total pressure of 1 kgf, the amount of deformation was absorbed by the deflection of the PET film, and the above effect could be obtained.

[0054]

As is apparent from the above description, the present invention provides: (A) a plurality of image carriers each carrying an image of a plurality of colors, and a recording material carried thereon and transported to each transfer section; Recording material carrier, and a plurality of plate-shaped members that contact the back surface of the recording material carrier in each transfer section and sequentially transfer the image on each image carrier to the recording material carried on the recording material carrier. And a plurality of pressing members that press the recording material carrier in the vicinity of each transfer portion and on the upstream side in the moving direction of the recording material carrier from each transfer portion. The position of the recording material carrier pressed by each pressing member is set on the side where each image carrier is provided with respect to the tangent line of each image carrier in each transfer unit, or (B) images of a plurality of colors And a plurality of image carriers each carrying a recording material, and A recording material carrier that conveys the material, and a plurality of transfer units that contact the back surface of the recording material carrier at each transfer unit and sequentially transfer the image on each image carrier to the recording material carried on the recording material carrier. Charging means, and in a color image forming apparatus having:
It has a plurality of pressing members that press the recording material carrier on the upstream side in the moving direction of the recording material carrier from each transfer unit, and the position of the recording material carrier pressed by each pressing member is Since each image carrier is located on the side where the image carrier is provided with respect to the tangent line of the image carrier and is configured to be in contact with each image carrier, the pressing force against the recording material can be dispersed, and good conveyance stability of the recording material can be achieved. And excellent transferability.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating a transfer unit according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram illustrating a color image forming apparatus to which the present invention is applied.

FIG. 3 is a configuration diagram illustrating a transfer unit according to a third embodiment of the present invention.

FIG. 4 is a configuration diagram illustrating an example of a conventional color image forming apparatus.

[Explanation of symbols]

 Reference Signs List 1 photosensitive drum (image carrier) 4 transfer charging means 8 endless belt (recording material carrier) 410 downstream pressing member 411 upstream pressing member 412 static elimination needle

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G03G 15/16 G03G 15/01 114

Claims (11)

(57) [Claims] A plurality of image carriers each carrying an image of a plurality of colors; a recording material carrier carrying a recording material and transporting the recording material to each transfer unit; A plurality of plate-shaped transfer charging means for sequentially transferring the image on each image carrier to the recording material carried on the recording material carrier, in contact with the back surface of the body, and a color image forming apparatus comprising: In the vicinity of each of the transfer portions, a plurality of pressing members that press the recording material carrier at a position upstream of the transfer portions in the moving direction of the recording material carrier, and are pressed by the respective pressing members. The color image forming apparatus according to claim 1, wherein the position of the recording material carrier is on a side where each of the image carriers is provided with respect to a tangent line of each of the image carriers in each of the transfer units. 2. The color image forming apparatus according to claim 1, wherein each of said pressing members is capable of coming into contact with and separating from said recording material carrier. 3. The color image forming apparatus according to claim 2, wherein each of said transfer charging means is capable of coming into contact with and separating from said recording material carrier. 4. A recording material in which the images on the respective image carriers are carried on the recording material carrier after the visible image transferred to the first surface of the recording material is fixed by a fixing unit coated with oil. 4. A color image forming apparatus according to claim 3, wherein said transfer charging means is capable of sequentially transferring to a second surface opposite to said first surface. 5. The method according to claim 1, wherein the pressing operation of each of the transfer charging units on the recording material carrier is performed independently of the pressing operation of the pressing members on the recording material carrier. 5. The color image forming apparatus according to any one of Items 1-4. 6. The color image according to claim 1, wherein the position of the recording material carrier pressed by each of the pressing members comes into contact with each of the image carriers. Forming equipment. 7. A plurality of downstream pressing members for pressing the recording material carrier in the vicinity of each of the transfer units and downstream of the transfer units in the moving direction of the recording material carrier,
The position of the recording material carrier pressed by each of the downstream pressing members is on a side where the respective image carriers are provided with respect to a tangent line of the respective image carriers in each of the transfer units. A color image forming apparatus according to any one of Items 1 to 6. 8. A plurality of image carriers each carrying a plurality of color images, a recording material carrier carrying a recording material and transporting the recording material to each transfer unit, and a recording material carrier at each of the transfer units. A plurality of transfer charging means for contacting the back surface of the body and sequentially transferring the images on each of the image carriers to the recording material carried on the recording material carrier. And a plurality of pressing members for pressing the recording material carrier in the vicinity of the transfer portion and in the moving direction of the recording material carrier relative to the transfer portions, wherein the recording material pressed by the pressing members is provided. A color image forming apparatus, wherein the position of the carrier is on the side where the respective image carriers are provided with respect to a tangent line of the respective image carriers in each of the transfer units, and is in contact with the respective image carriers. apparatus. 9. The color image forming apparatus according to claim 8, wherein each of said pressing members is capable of coming into contact with and separating from said recording material carrier. 10. The color image forming apparatus according to claim 9, wherein each of said transfer charging means is capable of coming into contact with and separating from said recording material carrier. 11. The method according to claim 8, wherein the pressing operation of each transfer charging unit on the recording material carrier is performed independently of the pressing operation of the pressing members on the recording material carrier. , 9 or 10.