JP2008216532A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small-sized, long-lifetime, and inexpensive image forming apparatus which allows a recorded image of high quality to be formed without giving an influence of a seam part of a transfer belt upon formation of a toner image on a photoreceptor. <P>SOLUTION: A means for detecting the position of the seam part existing on an intermediate transfer belt 100 is provided in a non-image area of an end part in a turning direction of the intermediate transfer belt 100, and a transfer voltage to a transfer means for transferring a toner image onto the intermediate transfer belt is switched on the basis of the detection result to prevent a potential history from occurring on a photoreceptor drum by the seam part. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or the like that employs an image forming method such as an electrophotographic method, an electrostatic recording method, an ionography method, or a magnetic recording method, and particularly forms an image on a transfer belt. The present invention relates to an image forming apparatus.

  Conventionally, as an image forming apparatus for forming an image by transferring a toner image formed on a photosensitive drum onto an endless transfer belt, one shown in FIG. 11 is known (Patent Document 1).

  FIG. 11 is a schematic diagram showing a tandem color image forming apparatus in which four photosensitive drums 50 (50Y to 50K) are arranged in series along the rotation path of the intermediate transfer belt 100. FIG. In this apparatus, toner images of yellow Y, magenta M, cyan C, and black BK are sequentially formed on the photosensitive drums 50 with a predetermined time difference, and the toner images are overlapped on the intermediate transfer belt 100 to be multiplexed. A transfer toner image is formed, and the toner images of a plurality of colors are retransferred to the recording material 60. Finally, the recording material 60 is inserted into the fixing device 70 to obtain a color image.

  The photoconductor drum 50 is formed by applying and forming a photoconductor made of an organic photoconductor (OPC) on the outer peripheral surface of an aluminum cylinder having a diameter of 24 mm, and is driven to rotate in the direction of the arrow by a driving means (not shown). The photoreceptor drum 50 may be one using a photoreceptor such as a-Si, CdS, or Se.

  The surface of the photosensitive drum 50 is uniformly charged to approximately −600 V on the photosensitive drum 50 by the charging roller 51 by applying a DC voltage of −1200 V to the charging roller 51 (51Y to 51K).

  The image forming apparatus is provided with a laser diode, an exposure device (not shown) including a polygon mirror, a lens and a folding mirror that are rotationally driven by a high-speed motor. For example, from a laser diode modulated by a signal according to yellow image information Is irradiated onto the surface of the charged photosensitive drum 50Y, the potential of the irradiated portion is attenuated to about -50V, and an electrostatic latent image corresponding to image information is formed on the surface of the photosensitive drum 50Y. The

  This electrostatic latent image moves to the developing position as the photosensitive drum 50Y rotates, and is developed by the developing roller 40Y positioned there, and visualized as a yellow toner image. The yellow toner image formed on the photoreceptor drum 50Y is transferred to the intermediate transfer belt 100 by applying a DC primary transfer voltage of +600 V to the primary transfer roller 101Y from a primary transfer power source (not shown) at a transfer portion facing the intermediate transfer belt 100. Transferred to the surface of the belt 100.

  By repeating the same process as above for three colors of magenta, cyan, and black, a color image in which toner images of four colors of yellow, magenta, cyan, and black are superimposed and transferred to the intermediate transfer belt 100 is formed. The four color toner images on the intermediate transfer belt 100 are applied with a secondary transfer voltage from a secondary transfer power source (not shown) to the secondary transfer roller 102 on the surface of the recording material 60 conveyed to the intermediate transfer belt 100. Are collectively transferred. The recording material 60 is fed from a cassette 61 or a multi-tray. In this example, the recording material 60 is plain paper, but may be an OHP sheet.

  The recording material 60 onto which the four color toner images have been transferred is conveyed to a fixing device 70 where the toner is melted and fixed by heating and pressing to complete a full color image, and then discharged to a face-down tray (not shown). .

  The photoreceptor drum 50 is cleaned and removed by the cleaning device 52 such as a blade from the primary transfer residual toner remaining on the surface. The intermediate transfer belt 100 is cleaned and removed by the cleaning device 103 such as a fur brush or a blade after the secondary transfer residual toner remaining on the surface.

  Here, the intermediate transfer belt 100 is made of a dielectric resin having a thickness of 30 to 300 μm in which resistance is adjusted by mixing carbon or the like into a resin such as polycarbonate resin, polyurethane resin, polyethylene terephthalate resin, or polyethersulfane resin. It is a film.

  The endless intermediate transfer belt 100 as described above can be manufactured seamlessly so-called seamlessly. However, in recent years, an intermediate transfer belt that has been processed into an endless shape by joining both ends of the endless belt using a technique such as ultrasonic welding in view of difficulty in molding, difficulty in packaging during transportation, cost, etc. The use is increasing.

  However, these endless intermediate transfer belts that have been joined have a seam portion that is a seam, and this seam portion is welded with the belt end overlapping, so that the thickness increases compared to other portions. ing. In addition, a phenomenon such as paper powder or toner easily entering a stepped portion generated by increasing the thickness tends to occur.

  For this reason, the resistance value of the seam portion of the intermediate transfer belt 100 is greatly different from that of other portions. When the seam portion having a greatly different resistance value comes into contact with the photosensitive drum 50, the contacted photosensitive drum 50. There has been a problem that a special potential history is formed only in the upper region.

  When the next toner image is formed on the area on the photosensitive drum 50 that is in contact with the seam portion, a toner image having a desired density cannot be obtained for the area, and the seam portion is added to the formed recorded image. This causes a problem that the horizontal horizontal stripes corresponding to the above occur.

  Up until now, horizontal streaks due to potential history on the photosensitive drum have been inconspicuous due to a lot of jitter and toner scattering due to uneven rotation of the drive, etc. With the technical progress, the image quality has been remarkably improved, and the horizontal stripes due to the potential history on the photosensitive drum 50 are beginning to be noticeable.

  In view of this, the conventional technology for solving this problem is that, with respect to the photosensitive drum after the transfer of the toner image, the electrostatic latent image history in the previous cycle is erased prior to the next toner image formation cycle. And a static eliminator such as a static elimination lamp 30 (30Y to 30K).

  Further, in order to more effectively erase the history of the electrostatic latent image, it has a detecting means for detecting the position of the seam portion existing on the intermediate transfer belt 100, and based on the detection result by the detecting means, The voltage applied to the static elimination corotron and the static elimination lamp is changed so that the seam portion corresponds to the portion in contact with the photosensitive drum, and the potential on the photosensitive drum is controlled to be uniform.

In other words, in order to erase the history of the electrostatic latent image generated on the photosensitive drum 50 by areas having different electrostatic characteristics on the intermediate transfer belt 100, potential unevenness correcting means for correcting the surface potential of the photosensitive drum is provided. ing.
Japanese Patent No. 3365154

  By the way, in the image forming apparatus configured as described above, it is necessary to dispose the potential unevenness correcting means such as the static eliminating corotron and the static eliminating lamp between the transfer position on the photosensitive drum and the cleaning device. Therefore, it is necessary to secure a space for arranging the potential unevenness means. In order to secure the space, it is necessary to increase the diameter of the photosensitive drum. As a result, there is a problem that the entire image forming apparatus is increased in size.

  In addition, in order to arrange the potential unevenness correction means such as the static elimination corotron and the static elimination lamp, not only the correction means but also a power source and a harness for applying a voltage to the correction means are required, and the entire apparatus is expensive. There is also a problem.

  Further, since the potential unevenness correcting means is disposed in the vicinity of the above-described cleaning device, the toner on the photosensitive drum scraped off by the cleaning device easily adheres to the potential unevenness correcting means, and is desired as time passes. There is also a problem that the neutralization effect cannot be obtained.

  Further, since the potential unevenness correcting means is arranged at a certain distance from the photosensitive drum, it is difficult to correct the surface potential of only the portion where the seam portion is in contact with the photosensitive drum. There are also problems such as potential unevenness remaining on the photosensitive drum, and the effect of removing static electricity acting more strongly than desired to shorten the life of the photosensitive drum. For example, when an optical static eliminator is used as the potential unevenness correcting means, there is a problem that light deterioration (exposure) is likely to occur on the photosensitive drum, and the lifetime of the photosensitive drum becomes shorter than a desired lifetime.

  The present invention has been made in view of the above points, and corrects the surface potential for erasing the history of the electrostatic latent image generated on the photosensitive drum by using regions having different electrostatic characteristics on the intermediate transfer belt. It is an object of the present invention to provide an image forming apparatus that forms an inexpensive and good image without providing potential unevenness correcting means.

In order to solve this problem, an image forming apparatus of the present invention transfers an image carrier that carries a toner image, a toner image on the image carrier, and includes at least a first transfer region and the first A transfer belt having a second transfer region having a different electrostatic property and a transfer means for transferring the toner image on the image carrier onto the transfer belt. The transfer condition when the toner on the image carrier is transferred to the second transfer area is the transfer condition when the toner on the image carrier is transferred to the first transfer area of the transfer belt. It is controlled so that it differs from conditions.
In the above feature of the present invention, the electrical resistance value in the second transfer region is higher than the electrical resistance value in the first transfer region, and the second transfer region of the transfer belt is compared with the second transfer region. The voltage applied to the transfer means when the toner on the image carrier is transferred is transferred when the toner on the image carrier is transferred to the first transfer area of the transfer belt. It is preferable that the voltage is controlled to be larger than the voltage applied to the means.
Further, in the above feature of the present invention, during the transfer operation in which the toner on the image carrier is transferred to the second transfer region of the transfer belt, the voltage value applied to the transfer unit is set at a predetermined time. It is preferable to change.
Further, in the above feature of the present invention, the transfer operation has charging means for charging the image carrier to a predetermined polarity, and the toner on the image carrier is transferred to the second transfer region of the transfer belt. It is preferable that the voltage value applied to the transfer unit is changed to the opposite polarity side to the charge charged by the charging unit.
Further, in the above-described feature of the present invention, when the toner on the image carrier is transferred to the second transfer area of the transfer belt, the pressing force by the transfer unit on the transfer belt is It is preferable that when the toner on the image carrier is transferred to the first transfer area of the belt, the pressing force applied by the transfer unit to the transfer belt is set differently.
Further, in the above feature of the present invention, during the transfer operation in which the toner on the image carrier is transferred to the second transfer region of the transfer belt, the contact pressure between the image carrier and the transfer belt is increased. It is preferable that the pressure is set to 10 k · Pa or more and less than 100 k · Pa.
Furthermore, it is preferable that the image forming apparatus further includes a detection unit that detects a predetermined portion of the transfer belt, and the position of the second transfer region of the transfer belt is determined by detecting the predetermined portion by the detection unit. It is.
Furthermore, in the above-described feature of the present invention, it is preferable that the second transfer region of the transfer belt is a seam portion of the endless transfer belt.
More specifically, the present invention has detection means for detecting a second transfer area that exists on the intermediate transfer belt and has a different electrostatic property from the first transfer area where normal transfer is performed. The transfer condition of the transfer means for transferring the toner image on the photosensitive drum onto the intermediate transfer belt is changed based on the detection result of the detection means.

  According to the present invention, the history of the electrostatic latent image generated on the photosensitive drum is erased by using the second transfer area having different electrostatic characteristics from the first transfer area on the intermediate transfer belt. Without setting potential unevenness correction means such as a static elimination corotron or a static elimination lamp for correcting the surface potential, the set value of the transfer condition of the transfer means can be set according to the transfer to the first transfer area and the transfer to the second transfer area. It is an object of the present invention to provide an image forming apparatus having a small size, long life, and low cost that does not generate an electrostatic latent image history itself on the photosensitive drum.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the component and equivalent part which have the same structure or function, and the description is not repeated.

(Embodiment 1)
An image forming apparatus according to Embodiment 1 of the present invention will be described with reference to FIGS. 1, 2, 3, 4, and 5. FIG. FIG. 1 is a schematic sectional view of an image forming apparatus according to Embodiment 1 of the present invention. The mechanical configuration of the image forming apparatus itself is basically the same as, for example, the conventional image forming apparatus shown in FIG. 11, and thus the drawing and description of the image forming apparatus are omitted.
As shown in FIG. 1, the image forming apparatus includes an intermediate transfer belt 100 that intermediately transfers a toner image formed on a photosensitive drum 100.

Here, the intermediate transfer belt 100 occupies most of the intermediate transfer belt, and has a first transfer area 100A in which normal transfer is performed and a second transfer area corresponding to the seam portion 120 of the intermediate transfer belt. is doing. In the intermediate transfer belt, the second transfer region has a configuration in which electrostatic characteristics are different from those of the first transfer region (hereinafter, for convenience of explanation, the second transfer region is described as a seam portion and described). .
In the non-image area of the intermediate transfer belt 100, a through hole 110 is formed as a recognition display indicating the position of the seam portion 120 of the intermediate transfer belt 100 as shown in FIG.
At one place of the intermediate transfer belt 100, a light-passing through-hole sensor 111 is disposed across the end of the intermediate transfer belt 100 to detect the through-hole 110. Since the length from the through hole 110 to the seam portion 120 is determined to be a predetermined length, when the position of the through hole 110 is detected, the position on the intermediate transfer belt 100 where the seam portion 120 exists is grasped. be able to.

  The through hole 110 may have a notch shape, or may be detected by a light reflection plate or a light reflection type reflected light detection sensor instead of the through hole 110 and the through hole sensor 111.

  As shown in FIG. 1 and FIG. 2, an intermediate transfer belt 100 is formed by ultrasonic welding both ends of a dielectric film having a thickness of 100 μm, and ultrasonic welding is performed at one place on the circumference thereof. There is a seam portion (joint) 120 formed by. The intermediate transfer belt 100 is wound around four rolls including a driving roller 104 and an edge guide roll 105, and is given a predetermined tension by an edge guide roll 105 biased by a spring (not shown). As a method of joining the intermediate transfer belt 100, a conductive adhesive or seal may be used instead of ultrasonic welding.

Next, a schematic enlarged view of the seam portion 120 is shown in FIG. 3, and the seam portion where the end portions of the belt are joined together using ultrasonic welding will be described. The seam portion 120 forms a heterogeneous region having different electrostatic characteristics from the first transfer region 100A of the intermediate transfer belt 100.
As shown in FIG. 3A, since the seam portion 120 of the intermediate transfer belt 100 is ultrasonically welded with the intermediate transfer belt ends overlapped, the convex portion as shown in FIG. Since it is formed, the thickness t ′ of the seam portion is thicker than the thickness t = 100 μm of other portions. Further, since the seam portion 120 has a convex shape, paper dust and toner of the recording material 60 are easily collected at a step portion between the convex portion of the seam portion 120 and another flat portion. Therefore, in the seam portion 120, the resistance value in the thickness direction of the intermediate transfer belt 100 tends to be higher than that in the first transfer region 100A.

  On the other hand, a positive charge for transferring the toner image on the photosensitive drum 50 to the intermediate transfer belt 100 exists on the back side of the intermediate transfer belt 100. When a portion other than the seam portion 120 of the intermediate transfer belt 100 passes through the transfer portion where the primary transfer roller 101 is disposed and contacts the photosensitive drum 50, the positive charge on the back surface side of the intermediate transfer belt 100 is negatively charged. Since the surface of the photosensitive drum 50 is neutralized and the surface of the photosensitive drum 50 is neutralized, as shown in FIG. 4A, the surface potential of the photosensitive drum 50 that has passed through the primary transfer position is substantially zero. A close value.

  However, when the seam portion 120 passes through the transfer portion on which the primary transfer roller 101 is disposed and comes into contact with the photosensitive drum 50, the positive charge on the back surface side of the intermediate transfer belt 100 passes through the high resistance seam portion 120. It becomes difficult to flow into the drum 50, and a positive charge is not injected into a part of the photosensitive drum 50 that is used for negative charging, and a residual negative charging region is generated. It becomes a uniform state.

  As a result, the surface potential on the photosensitive drum 50 that has passed through the primary transfer portion remains negatively charged only in the region in contact with the seam portion 120 as shown in FIG. 4B. If negative charges remain on the surface of the photosensitive drum 50 as described above, if negative charges are again applied to the photosensitive drum 50 by the charging roller 51, as shown in FIG. The negative potential is increased, and the negative charging potential is increased only in the region in contact with the seam portion 120. For this reason, even when the laser beam from the laser diode modulated by the signal according to the image information is irradiated onto the photosensitive drum 50, as shown in FIG. And the non-uniform electrostatic latent image is formed on the surface of the photosensitive drum 50. In other words, the potential after irradiation on the photosensitive drum 50 cannot be attenuated only in the portion in contact with the seam portion 120, the negative potential becomes high, and a negatively charged toner image is formed on the photosensitive drum 50 in that region. As a result, white horizontal streaks occur and the quality of the color image is significantly impaired.

  In order to solve this problem, the conventional technique shown in Japanese Patent Application Laid-Open No. H10-228561 makes the potential on the photosensitive drum 50 non-uniform after the transfer as described above uniform, as shown in FIG. The potential unevenness correcting means 30 such as the above is provided, but the cost increases due to the addition of parts, and a space for arranging the parts around the photoreceptor is required, and the diameter of the photoreceptor drum 50 must be increased. As a result, the entire image forming apparatus is increased in size.

  Further, since the potential unevenness correcting means is arranged at a certain distance from the photosensitive drum, the potential unevenness is corrected over a wide range, and the seam portion is not shown in FIG. 5A. The potential unevenness is corrected in a wider range than the contacted portion. For this reason, the potential is fluctuated up to a portion other than the seam portion, and as a result, as shown in FIG. 5B, even if a negative charge is again applied to the photosensitive drum 50 by the charging roller 51, the surface of the photosensitive drum. There is also a problem that the potential is not uniform and a non-uniform toner image is formed.

  Therefore, in this embodiment, the timing at which the seam portion 120 existing on the intermediate transfer belt comes into contact with each photosensitive drum is calculated based on the detection result of the through-hole sensor 111 that can grasp the position of the seam portion 120. The voltage value applied to the primary transfer roller 101 is changed with respect to the applied voltage value when the toner image is transferred to the first transfer area 100A at the timing when the seam portion 120 and the photosensitive drum 50 come into contact with each other. To do.

  As described above, the resistance value of the seam part and the resistance value other than the seam part are higher due to the influence of the thickness of the belt, contamination of foreign matter, etc., and the plus current is less likely to flow in the seam part. When the transfer applied voltage value at the seam portion is V and the transfer applied voltage value of the first transfer region is V ′, the relationship between V and V ′ is set so that V> V ′, and the through hole sensor By switching between V and V ′ based on the detection result, potential unevenness can be suppressed.

  Accordingly, it is possible to provide an image forming apparatus having a simple and small configuration, a long life, and a low price without adding new parts.

  Further, when the voltage applied to the primary transfer roller 101 is switched from V ′ to V, the voltage is switched from V ′ to V over a certain period of time, not instantaneously. That is, by switching the voltage with a shape similar to the shape of the seam portion (smooth parabolic shape), the occurrence of potential unevenness can be suppressed more accurately. Next, when the voltage applied to the primary transfer roller 101 is switched from V to V ′ when the seam portion 120 passes through the primary transfer roller 101, by switching in a gentle parabolic shape, as described above, A more uniform surface potential on the photosensitive drum is formed.

  In the present invention, as the means for correcting the potential unevenness on the photosensitive drum, the transfer voltage value is switched only at the seam position by the transfer means in contact with the photosensitive drum. Thus, a uniform surface potential on the photosensitive drum can be obtained.

  On the other hand, as a known technique, as a transfer means in the primary transfer portion, a method of controlling with a constant current is known. When this means is used, the seam width is larger than the nip width between the photosensitive drum and the transfer belt. When the width is narrower, a large amount of current flows into a portion other than the seam portion, and conversely, a difference in current value between the seam portion and a portion other than the seam portion increases, resulting in conspicuous potential unevenness.

  Here, the present invention has been described using a tandem type color image forming apparatus in which four photosensitive drums 50 (50Y to 50K) are arranged in series along the rotation path of the intermediate transfer belt 100. However, the present invention is a monochrome image forming apparatus using an intermediate transfer belt or a revolver type color image forming apparatus that forms a color image on the intermediate transfer belt 100 while sequentially rotating a plurality of photosensitive drums 50. However, any image forming apparatus using an intermediate transfer belt is applicable.

  As described above, in the image forming apparatus of the present example, the surface potential is corrected in order to erase the history of the electrostatic latent image generated on the photosensitive drum by the seam portion which is a different area on the intermediate transfer belt. Without providing potential unevenness correction means such as a static elimination corotron or a discharge lamp, by varying the transfer voltage applied to the transfer means, the potential unevenness correction means does not generate the electrostatic latent image history itself on the photosensitive drum. Therefore, it is possible to provide an image forming apparatus having a small size, a long life, and an inexpensive configuration that does not require the above.

(Embodiment 2)
Next, an image forming apparatus according to Embodiment 2 of the present invention will be described with reference to FIG. 6, FIG. 7, and FIG. 6, FIG. 7 and FIG. 8 are diagrams showing a schematic sectional view and a surface potential on the photosensitive drum when the seam portion according to the second embodiment of the present invention passes through the primary transfer roller portion.

  In the image forming apparatus according to the first embodiment, the shape of the seam portion 120 that is a heterogeneous region has been described as a mountain shape with a smooth surface, but the shape after welding by ultrasonic welding is less likely to be a smooth surface, As shown in FIG. 6, the surface often has an uneven shape.

  Therefore, as shown in FIG. 6, a space is formed between the seam portion 120 and the photosensitive drum 50 at the portion where the surface is recessed (B and D portions), and the photosensitive drum 50 and the intermediate transfer belt 100 are in contact with each other. Absent.

  Therefore, the positive transfer potential does not flow onto the photosensitive drum 50 in the recessed portions (B and D portions) of the seam portion 120, and the photosensitive drum 50 after passing through the primary transfer portion as shown in FIG. The upper surface potential becomes a higher value in the recessed portions (B and D portions), and an uneven and uneven potential history occurs.

  To solve this problem, as shown in FIG. 8, the spring pressure of the pressing spring 130 of the primary transfer roller 101 is increased when the seam portion 120 passes, so that the space between the photosensitive drum 50 and the seam portion 120 ( B portion and D portion) decrease or disappear, and the primary transfer voltage easily flows into the photosensitive drum 50.

  In addition, as in the first embodiment, by raising the primary transfer voltage when the seam portion 120 passes, the electrostatic latent image history itself is not generated on the photosensitive drum, and the potential unevenness correcting unit is not required. An image forming apparatus having a small size, a long life, and an inexpensive configuration can be provided.

  Specifically, as shown in FIG. 8, the seam portion 120 existing on the intermediate transfer belt comes into contact with each photosensitive drum based on the detection result of the through-hole sensor 111 that can grasp the position of the seam portion 120. Since the timing can be calculated, the primary transfer roller support plate 131 is slid laterally by a solenoid (not shown) when the seam portion 120 and the photosensitive drum 50 come into contact with each other. As a result, the primary transfer roller pressing spring support plate 132 on the primary transfer roller support plate 131 is positioned on the convex portion 131 (a) on the primary transfer roller support plate 131, and the length of the primary transfer roller pressing spring 130 is increased. As a result, the pressing force of the primary transfer roller 101 against the seam portion 120 of the intermediate transfer belt 100 increases. As a result, the space (B, D portion) existing between the photosensitive drum 50 and the seam portion 120 is reduced or eliminated, and a positive primary transfer voltage is obtained in a region where the seam portion 120 passes through the photosensitive drum 50. Uniformly flows into the photosensitive drum 50. Thereafter, when the seam portion 120 passes through the primary transfer portion, the primary transfer roller support plate 131 slides again, the primary transfer roller pressing spring support plate 132 moves to a predetermined position, and the predetermined spring pressure is applied to the primary transfer roller. It takes.

  The contact pressure between the intermediate transfer belt 100 and the photosensitive drum 50 is preferably 1 k · Pa or more and preferably 5 k · Pa or less during normal printing, and the contact pressure when the seam portion passes is 10 k · Pa or more. However, it is desirable to set it to less than 100 kPa.

  On the other hand, the pressing force to the primary transfer roller 101 is not increased only at the position of the seam portion 120, but the seam is always increased even in the first transfer region other than the seam portion 120. It is possible to obtain a uniform surface potential without generating a space between the portion 120 and the photosensitive drum 50.

  However, if the design value of the primary transfer roller 101 pressing force during normal printing is set to a high value, a force greater than the pressing force necessary to transfer the toner to the intermediate transfer belt is always applied to the intermediate transfer belt. Problems arise such that the transfer belt and the photosensitive drum are extremely worn and the life is shortened, and that a large torque is required to rotate the intermediate transfer belt 100.

  In the color machine, when toners of different colors are overlapped, if the pressing force is set higher than necessary, the toner is crushed and the predetermined toner is not transferred from the photosensitive drum to the intermediate transfer belt 100. The toner on the intermediate transfer belt adheres to the photosensitive drum side, and a defect phenomenon generally called “boring” or “worm-eaten” occurs.

  Therefore, by increasing the pressing force of the primary transfer roller 101 only when the seam portion 120 passes, it is possible to provide a small, long-life and inexpensive image forming apparatus without affecting the life. it can.

(Embodiment 3)
Next, an image forming apparatus according to Embodiment 3 of the present invention will be described with reference to FIG. 9 and FIG. 9 and 10 are schematic configuration diagrams showing detection means for detecting different regions of the intermediate transfer belt according to the third embodiment of the present invention.

  In the image forming apparatus according to Embodiments 1 and 2, the detection unit that detects the seam portion existing on the intermediate transfer belt 100 is provided in one place. Therefore, in order to recognize the different region, the intermediate transfer belt is rotated once or more. It is necessary to rotate, and then the printing operation is started.

  For this reason, it takes not only a long time to receive the print data, start the printing operation, and transfer the toner image to the recording material 60, but also increases the number of rotations of the intermediate transfer belt 100. There is a problem that the life of parts such as the belt 100 and the photosensitive drum 50 is shortened.

  Therefore, as shown in FIG. 9, a plurality of through-hole sensors 111 that detect the through-holes 110 on the intermediate transfer belt 100 are arranged on the intermediate transfer belt 100 to rotate the intermediate transfer belt 100 one or more times. The position of the seam part 120 can be calculated by detecting the through hole 110 in a short time.

  Further, as shown in FIG. 10, by providing a plurality of through holes 110a and 110b having different lengths in the traveling direction on the intermediate transfer belt 100, it is not necessary to rotate the intermediate transfer belt 100 more than once, and in a short time. The position of the seam portion 120 can be calculated by detecting the through hole 110.

  As shown in FIGS. 9 and 10, if the configuration has a plurality of through-hole sensors 111 and a plurality of through-holes 110 having different lengths at the same time, the through-hole 110 can be detected in a shorter time, and the seam portion 120 positions can be calculated.

As described above, in the image forming apparatus of this example, the position of the seam portion (second transfer region) can be calculated in a short time, and is generated on the photosensitive drum by the seam portion on the intermediate transfer belt. In order to erase the history of the electrostatic latent image, by changing the transfer voltage applied to the transfer unit, the printing operation is started in a short time without generating the history of the electrostatic latent image on the photosensitive drum. Thus, it is possible to provide an image forming apparatus having a small size, long life, and low cost that does not require potential unevenness correction means.
In the above embodiment, the seam portion is exemplified as the second transfer region. However, the second transfer region is not limited to the seam portion, and the second transfer region is the first transfer region. The present invention can be applied to any transfer belt having a structure having different electrostatic characteristics with respect to a region.
The present invention also provides an image forming apparatus including a transfer belt having a first transfer area and a second transfer area having electrostatic characteristics different from those of the first transfer area. The present invention can also be applied to an image forming apparatus including a transfer belt having a configuration having a different third transfer region. In short, a transfer belt having at least a first transfer region and a second transfer region having different electrostatic characteristics. The present invention can be applied to an image forming apparatus including

  Since the image forming apparatus according to the present invention can form a uniform toner image without disposing the potential unevenness correcting means, image forming such as electrophotographic method, electrostatic recording method, ionography, magnetic recording method, etc. It is useful as an image forming apparatus such as a black-and-white and color copier, printer, facsimile, etc. that employs this method.

1 is a schematic cross-sectional view showing the appearance of an image forming apparatus according to Embodiment 1 of the present invention. 1 is a schematic diagram showing the configuration of an intermediate transfer belt according to Embodiment 1 of the present invention. (A) Schematic diagram before ultrasonically welding the end of the intermediate transfer belt (b) Schematic diagram of the seam portion of the intermediate transfer belt subjected to ultrasonic welding (A) Photosensitive drum surface potential state before and after transfer portion insertion (b) Photosensitive drum surface potential state after contact of the intermediate transfer belt seam portion (c) Seam portion contacted with the drum FIG. 4D is a diagram showing the surface potential state of the photosensitive drum when a negative charge is applied to the exposed portion by the charging roller. (D) When the portion where the seam portion is in contact with the drum is irradiated with a laser beam to form an electrostatic latent image. Of the surface potential of the photosensitive drum (A) A diagram showing a surface potential state after the residual potential on the photosensitive drum due to the seam portion is corrected by a non-contact static elimination lamp. (B) A negative charge is given to the portion corrected by the static elimination lamp by the charging roller. Of the surface potential of the photosensitive drum when The figure which shows the state which an uneven | corrugated seam part passes a photoreceptor drum Diagram showing residual potential on photosensitive drum due to uneven seam Schematic which shows the structure of the primary transfer roller part which concerns on Embodiment 2 of this invention. Schematic which shows the structure of the intermediate transfer belt which has several through-hole sensors which concern on Embodiment 3 of this invention. Schematic showing the configuration of an intermediate transfer belt having a plurality of through holes according to Embodiment 3 of the present invention. Schematic sectional view showing the appearance of an image forming apparatus according to the prior art

Explanation of symbols

30 Static elimination lamp (potential unevenness correction means)
DESCRIPTION OF SYMBOLS 40 Developing roller 50 Photosensitive drum 51 Charging roller 52 Cleaning device 60 Recording material 61 Cassette 70 Fixing device 100 Intermediate transfer belt 100A 1st transfer area 101 Primary transfer roller 102 Secondary transfer roller 110 Through-hole 111 Through-hole sensor 120 Seam part (Second transfer area)

Claims (8)

An image carrier for carrying a toner image;
A toner image on the image carrier, and a transfer belt including at least a first transfer region and a second transfer region having electrostatic characteristics different from that of the first transfer region;
Transfer means for transferring the toner image on the image carrier onto the transfer belt,
The transfer conditions when the toner on the image carrier is transferred to the second transfer area of the transfer belt are as follows:
The first transfer area of the transfer belt is controlled to be different from the transfer conditions when the toner on the image carrier is transferred.
An image forming apparatus. The electrical resistance value in the second transfer region is higher than the electrical resistance value in the first transfer region,
The voltage value applied to the transfer means when the toner on the image carrier is transferred to the second transfer area of the transfer belt is:
The first transfer area of the transfer belt is controlled to have a value larger than the voltage value applied to the transfer means when the toner on the image carrier is transferred.
The image forming apparatus according to claim 1. During a transfer operation in which the toner on the image carrier is transferred to the second transfer region of the transfer belt, a voltage value applied to the transfer unit is changed at a predetermined time.
The image forming apparatus according to claim 2. And a charging means for charging the image carrier to a predetermined polarity,
During the transfer operation in which the toner on the image carrier is transferred to the second transfer area of the transfer belt, a voltage value to be applied to the transfer unit is set on the opposite polarity side to the charge charged by the charging unit. Change,
The image forming apparatus according to claim 2. When the toner on the image carrier is transferred to the second transfer region of the transfer belt, the pressing force by the transfer unit on the transfer belt is:
When the toner on the image carrier is transferred to the first transfer area of the transfer belt,
It is set to be different from the pressing force by the transfer means on the transfer belt,
The image forming apparatus according to claim 2. During the transfer operation in which the toner on the image carrier is transferred to the second transfer area of the transfer belt, the contact pressure between the image carrier and the transfer belt is 10 k · Pa or more and less than 100 k · Pa. The image forming apparatus according to claim 2, wherein the image forming apparatus is set as follows. Furthermore, it has a detecting means for detecting a predetermined portion of the transfer belt,
The image forming apparatus according to claim 1, wherein the position of the second transfer region of the transfer belt is determined by detecting the predetermined portion by the detection unit. The image forming apparatus according to claim 1, wherein the second transfer region of the transfer belt is a seam portion of the endless transfer belt.

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