JP6103362B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, or a facsimile, and more specifically, a toner image is transferred onto a recording material at a transfer nip between an image carrier belt such as an intermediate transfer belt and a recording material transport belt. The present invention relates to an image forming apparatus.

  Patent Document 1 discloses a belt transfer type image forming apparatus in which a secondary transfer nip is formed between an intermediate transfer belt (image carrier belt) and a secondary transfer belt (recording material conveying belt). The image forming apparatus includes a secondary transfer nip between a transfer counter member (transfer counter support roller) that supports the intermediate transfer belt from the inner peripheral surface side and a transfer pad that is pressed against the inner peripheral surface of the secondary transfer belt. Is forming. As a result, the adhesion between the sheet in the secondary transfer nip and the intermediate transfer belt is secured, and stable secondary transfer can be realized.

  In a belt transfer type image forming apparatus that forms a transfer nip between the image carrier belt and the recording material conveyance belt to transfer the toner image on the image carrier belt to the recording material, ensuring the separation of the recording material. It has become an important issue. The separation property referred to here means the ability to stably separate the recording material that has passed through the transfer nip from the image carrier belt. Among conventional image forming apparatuses, there is an apparatus that obtains high separation performance by discharging the recording material that has passed through the transfer nip to reduce the electrostatic attraction between the image carrier belt and the recording material. . There is also known an image forming apparatus that mechanically separates the leading end of the recording material adsorbed on the image carrier belt after passing through the transfer nip from the image carrier belt by a separating member.

  The conventional image forming apparatus needs to be provided with a static eliminating unit or a separating member in order to obtain high separation performance, which increases the number of parts and makes the configuration complicated, resulting in an increase in manufacturing cost. There was a problem. For this reason, a configuration is desired that provides high separability without providing such a dedicated member for improving separability.

  As described above, as a method of obtaining high separation without providing a dedicated member, an image carrier is used so that the electrostatic attraction between the recording material that has passed through the transfer nip and the image carrier belt is reduced. Examples of the belt include a belt having a low electric resistance. If the electrical resistance of the image carrier belt is lowered in this way, the electric charge accumulated on the outer peripheral surface of the image carrier belt can be easily released, so that the electrostatic attraction between the recording material and the image carrier belt can be lowered. Is possible.

  However, the smaller the electric resistance of the image carrier belt, the more easily electric discharge is generated in the transfer nip, and the toner at the electric discharge portion disappears, causing spotted toner omission on the image (hereinafter referred to as “white spot”). The problem that it becomes easy to do occurs. In particular, during an image forming operation in a low-humidity environment, an image forming operation on a recording material with a high electrical resistance, an image forming operation on the back surface after an image is formed on one surface (front surface), etc. Under circumstances where electric discharge is likely to occur, for example, white spots having a diameter of about 0.3 mm to 1 mm may occur on the image at intervals of about several mm to several tens of mm.

  The present invention has been made in view of the above problems, and the object of the present invention is to provide high separability without providing a dedicated member for improving separability and suppressing deterioration in image quality of white spots. An image forming apparatus capable of obtaining the above is provided.

In order to achieve the above object, the present invention makes contact between an endless belt-shaped image carrier belt that is stretched around a plurality of support rollers and an endless belt-shaped recording material conveyance belt that is stretched around a plurality of support rollers. Forming a transfer nip, and applying the transfer bias to the transfer nip from a bias applying member that contacts the inner peripheral surface of the recording material conveyance belt when passing the recording material through the transfer nip In an image forming apparatus for transferring a toner image on a body belt to a recording material,
As the image carrier belt , one having a volume resistivity of 10 ^7.5 [ Ω · cm] or more and 1 0 ¹³ [ Ω · cm] or less is used, and the recording material conveyance belt constitutes an outer peripheral surface thereof. A multi-layer structure having a surface layer and a base layer constituting the inner peripheral surface thereof, the surface resistivity of the outer peripheral surface is higher than the surface resistivity of the inner peripheral surface, and the bias applying member is selected from 10 ⁶ [Ω The above-described resistors are arranged so as to be in contact with the inner peripheral surface of the recording material conveyance belt at the downstream side of the transfer nip in the recording material conveyance direction from the central point in the recording material conveyance direction.

In the present invention, an image carrier belt having a high resistance is used, and a recording material conveying belt having a high resistance on the surface is used to suppress the occurrence of discharge in the transfer nip and to reduce the image quality of white spots. Suppressed. The reason why image quality deterioration of white spots can be suppressed in this way is considered to be as follows.
The discharge in the transfer nip that causes white spots occurs due to the presence of a portion having a low electrical resistance value in the image carrier belt or the recording material conveyance belt. In general, when manufacturing an endless belt-like member such as an image carrier belt or a recording material conveying belt, it is difficult to achieve uniform electric resistance over the entire belt, and there are some places where the electric resistance value is relatively high. For example, there are places where the electrical resistance value is relatively low. Here, the higher the average electrical resistance value of the endless belt member, the higher the electrical resistance value at a location where the electrical resistance value is relatively low. In the present invention, the electrical resistance value is relatively low as compared with the case where an image carrier belt having a medium resistance and a high resistance is used and the recording material transport belt having a surface having a medium resistance. Since the electrical resistance value at the location is high, the occurrence of discharge can be suppressed and the image quality deterioration of white spots can be suppressed.

On the other hand, using a high-resistance image carrier belt as described above is disadvantageous in terms of separability. Therefore, in the present invention, the bias applying member is disposed so as to be in contact with the inner peripheral surface of the recording material conveyance belt at the downstream side of the transfer nip in the recording material conveyance direction from the central point in the recording material conveyance direction. As a result of the inventor's research, it has been found that such an arrangement can ensure high separability. The reason is considered as follows.
In a general image forming apparatus, the bias applying member is disposed so as to be in contact with the inner peripheral surface of the recording material conveyance belt at the central point in the recording material conveyance direction of the transfer nip. When compared to this configuration, the mechanical action acting on the recording material in the transfer nip or the transfer nip exit is changed by shifting the bias applying member downstream in the recording material conveyance direction as in the present invention, It is considered that the leading edge of the recording material that has passed through the transfer nip is easily separated from the image carrier belt. In addition, since the bias applying member is shifted downstream in the recording material conveyance direction as in the present invention, the charge is moved by the transfer bias applied from the bias applying member to the leading end of the recording material entering the transfer nip. The reason for this is also considered to be late. That is, by delaying this timing, the amount of charge accumulated at the leading end of the recording material before passing through the transfer nip is reduced, so that the charge amount at the leading end of the recording material after passing through the transfer nip can be reduced, It is considered that the electrostatic attractive force between the recording material front end and the image carrier belt can be reduced.

  Note that the high resistance for the image carrier belt and the high resistance for the surface of the recording material conveying belt do not mean the same resistance value, and the former means that the image carrier belt has high resistance. The latter means that the surface of the recording material conveying belt has high resistance.

  As described above, according to the present invention, it is possible to obtain an excellent effect that high separability can be obtained without providing a dedicated member for improving separability and suppressing deterioration in image quality of white spots. .

1 is a schematic diagram illustrating a configuration of an image forming apparatus according to an embodiment. FIG. 4 is an enlarged view around a secondary transfer nip in the embodiment. 6 is a table showing the relationship between the surface resistivity on the outer peripheral surface of the intermediate transfer belt and the occurrence of white spots. 6 is a graph showing a relationship between an applied voltage and occurrence of white spots for a single-layer intermediate transfer belt and a laminated (here, two layers) intermediate transfer belt. 6 is a graph showing the relationship between the electrical resistance value of the secondary transfer counter roller and the occurrence of white spots. (A)-(c) arranges and shows the difference in composition of a secondary transfer part in order of good separability. It is a schematic diagram which shows the modification which provided two secondary transfer rollers.

Hereinafter, an embodiment of an image forming apparatus according to the present invention will be described.
FIG. 1 is a schematic diagram illustrating the configuration of the image forming apparatus according to the present embodiment.
In FIG. 1, the image forming apparatus 1 is provided with a transfer device 10 having an intermediate transfer belt 11 as an image carrier belt and four image stations. Each image station has a photosensitive drum 20Y, 20C, 20M, 20Bk as a latent image carrier, around which are dedicated charging devices 30Y, 30C, 30M, 30Bk, and developing devices 50Y, 50C, 50M. , 50Bk, and cleaning devices 40Y, 40C, 40M, and 40Bk. Further, the toner bottle is not shown, which replenishes toner, and toner is replenished to the developing devices 50Y, 50C, 50M, and 50Bk of each color by a predetermined replenishment amount through a conveyance path (not shown).

  In the image forming apparatus 1, a recording sheet P as a recording material is fed from a sheet feeding cassette 81 by a sheet feeding roller 82. When the leading edge of the recording paper P reaches the registration roller pair 83, it is detected by a sensor (not shown). The recording paper P is conveyed by the registration roller pair 83 to the secondary transfer nip which is a contact portion between the secondary transfer belt 15 as the recording paper conveyance belt and the intermediate transfer belt 11 while taking a timing with this detection signal.

  The photosensitive drums 20Y, 20C, 20M, and 20Bk, which are uniformly charged in advance by the charging devices 30Y, 30C, 30M, and 30Bk, are exposed and scanned with laser beams 71Y, 71C, 71M, and 71Bk by an exposure device (not shown). An electrostatic latent image of each yellow (Y), cyan (C), magenta (M), and black (Bk) is formed on the photosensitive drums 20Y, 20C, 20M, and 20Bk.

  Each electrostatic latent image is developed by each color developing device 50Y, 50C, 50M, 50Bk, and yellow, cyan, magenta, and black toner images are formed on the surfaces of the photosensitive drums 20Y, 20C, 20M, 20Bk. The A voltage is applied to the primary transfer rollers 13Y, 13C, 13M, and 13Bk, and the toner on the photosensitive drums 20Y, 20C, 20M, and 20Bk is sequentially transferred onto the intermediate transfer belt 11. At this time, the image forming operation for each color is executed while shifting the timing from the upstream side toward the downstream side in the endless movement direction of the intermediate transfer belt so that the toner image is transferred to the same position on the intermediate transfer belt 11. The

  In the present embodiment, a secondary transfer power source (not shown) is connected to the secondary transfer roller 16 as a bias applying member that contacts the inner peripheral surface of the secondary transfer belt 15. As a result, a predetermined potential difference is applied between the secondary transfer counter roller 17 as the transfer counter support roller and the secondary transfer roller 16 as the bias applying member. As a result, a secondary transfer bias is applied to the secondary transfer nip where the secondary transfer belt 15 and the intermediate transfer belt 11 are in contact, and the toner image on the intermediate transfer belt 11 is recorded by the action of the secondary transfer bias. Secondary transfer is performed on the paper P.

  The recording paper P on which the toner images of the respective colors are secondarily transferred in this manner is substantially horizontally directed toward the fixing device 60 provided on the downstream side in the recording paper conveyance direction with the endless movement of the secondary transfer belt 15. Be transported. The recording paper P conveyed to the fixing device 60 has the toner image fixed by heat and pressure, and is discharged out of the apparatus by a paper discharge roller 84. Thus, one image forming job is completed.

  The residual toner on the photosensitive drums 20Y, 20C, 20M, and 20Bk is cleaned by the respective cleaning devices 40Y, 40C, 40M, and 40Bk, and then the charging devices 30Y and 30B in which the bias of the AC component is superimposed and applied to the direct current. 30C, 30M, and 30Bk are charged at the same time as static elimination to prepare for the next image forming job. Further, the residual toner on the intermediate transfer belt 11 is cleaned by the intermediate transfer belt cleaning device 14 to prepare for the next image forming job.

FIG. 2 is an enlarged view around the secondary transfer nip in the present embodiment.
As the secondary transfer belt 15, for example, a material having a multi-layer structure having a resin layer whose resistance is adjusted by carbon dispersion or ion conductive agent blending in a material such as PI (polyimide) or PAI (polyamideimide) can be used. . The thickness of the secondary transfer belt 15 is preferably in the range of 50 [μm] to 100 [μm]. The multi-layer structure of the secondary transfer belt 15 may be formed by simply stacking a plurality of similar layers, or may be formed by stacking a plurality of layers having different resistance values. For example, the former secondary transfer belt 15 is referred to as “rear surface resistivity” in order to distinguish the surface resistivity ρSA of its outer peripheral surface and the surface resistivity of its inner peripheral surface (hereinafter, the surface resistivity of the outer peripheral surface). ) The relationship of ρSA = ρSB is established with ρSB. The latter secondary transfer belt 15 is preferably configured such that a relationship of ρSA> ρSB is established between the surface resistivity ρSA and the back surface resistivity ρSB. For example, the latter secondary transfer belt 15 can be formed by forming a high resistance layer film whose resistance is adjusted with the same material as the base layer or a different material on the base layer of the secondary transfer belt 15.

  As the secondary transfer roller 16, for example, a roller provided with a coating layer formed of a medium resistance material around a core metal can be used. The material of the coating layer can be a rubber material such as urethane rubber, silicone rubber, EPDM rubber, or a solid or foamed material such as urethane resin. Those with controlled values are preferred.

  The intermediate transfer belt 11 may be a single-layer belt or a multi-layer belt. As a belt having a single layer structure, PI (polyimide), PAI (polyamideimide), PC (polycarbonate), ETFE (ethylene-tetrafluoroethylene), PVDF (polyvinylidene fluoride), PPS (polyphenylene sulfide), etc., The thing of the single layer structure which consists of high resistance resin adjusted to high resistance by carbon dispersion | distribution or an ionic conductive agent mixing | blending can be used.

  When the secondary transfer belt 15 or the intermediate transfer belt 11 made of an endless belt-like member as in the present embodiment is manufactured, it is difficult to achieve uniform electrical resistance over the entire belt, and the relative electrical resistance value is relatively small. There are high and low points. In particular, in a belt in which resistance is controlled by dispersing carbon in a resin, variation in electric resistance value is large due to variation in the carbon dispersion state. Therefore, if a secondary transfer belt 15 or an intermediate transfer belt 11 having a relatively low electrical resistance value (average electrical resistance value) is used, the electrical resistance value at a location where the electrical resistance value is relatively low is small. In this case, the transfer current flows in a concentrated manner, whereby electric discharge is generated in the secondary transfer nip, and white spots are generated in the image.

  On the other hand, in the present embodiment, the intermediate transfer belt 11 has a high resistance, and the surface layer of the secondary transfer belt 15 has a high resistance layer. With such a configuration, even if there is a variation in the electric resistance value, the electric resistance value at a portion having a relatively low electric resistance value is not so small. Therefore, as a result of the local concentration of the transfer current being reduced, the occurrence of discharge in the secondary transfer nip is suppressed, and white spots can be reduced in the image.

  For the secondary transfer belt 15, it is preferable to make the surface resistivity (ρSA) of the outer peripheral surface higher than the back surface resistivity (ρSB). By making the surface resistivity ρSA of the secondary transfer belt 15 higher than the back surface resistivity ρSB, dielectric polarization occurs in the belt, and the recording paper P is easily attracted to the outer peripheral surface of the secondary transfer belt 15. As a result, the recording paper P that has passed through the secondary transfer nip can be easily peeled off from the outer peripheral surface of the intermediate transfer belt 11 while being adsorbed to the outer peripheral surface of the secondary transfer belt 15, thereby improving the separation property. Further, the fact that the recording paper P is easily adsorbed to the outer peripheral surface of the secondary transfer belt 15 is advantageous not only in the separation property but also in the recording paper conveyance property after separation. Furthermore, increasing the surface resistivity ρSA of the secondary transfer belt 15 relative to the back surface resistivity ρSB also has an effect of suppressing discharge in the secondary transfer nip when a secondary transfer bias is applied.

FIG. 3 is a table showing the relationship between the surface resistivity ρS on the outer peripheral surface of the intermediate transfer belt 11 and the occurrence of white spots.
As shown in this table, when the surface resistivity ρS on the outer peripheral surface of the intermediate transfer belt 11 is 10 [logΩ / □], generation of white spots exceeding the allowable range was recognized on the image. When the resistivity ρS was 12 [logΩ / □], generation of white spots exceeding the allowable range was not observed on the image.

  For the intermediate transfer belt 11 as well, it is preferable that the surface resistivity (ρSA) of the outer peripheral surface is higher than the back surface resistivity (ρSB). Similar to the case of the secondary transfer belt 15, there is an effect of suppressing discharge in the secondary transfer nip when the secondary transfer bias is applied. Such an intermediate transfer belt 11 may be a single material as long as a material satisfying the relationship of ρSA> ρSB can be manufactured. For example, as in the case of the secondary transfer belt 15, a multi-layer structure is used. In addition, a high resistance layer film whose resistance is adjusted with the same material as the base layer or with another material may be formed on the base layer.

  Further, when the intermediate transfer belt 11 having an elastic layer is used, the toner transfer property to the recording paper P rich in surface irregularities is improved. More specifically, since the outer peripheral surface of the intermediate transfer belt 11 easily deforms due to the surface unevenness of the recording paper P due to the presence of the elastic layer, the toner transferability to the recesses is particularly improved, and the overall transferability is good. can get.

  Specific examples of the intermediate transfer belt 11 having such an elastic layer include PI (polyimide), PAI (polyamideimide), PC (polycarbonate), ETFE (ethylene-tetrafluoroethylene), PVDF (polyvinylidene fluoride), PPS. (Polyphenylene sulfide), etc., carbon dispersion, or on a base layer composed of a medium resistance resin whose resistance is adjusted by blending an ionic conductive agent, carbon dispersion or ions in the same manner as rubber materials such as urethane, NBR, CR, etc. An elastic layer of 300 μm to 1200 μm made of a material whose resistance is adjusted by blending a conductive agent is provided, and the surface layer is coated with a fluorine-based rubber or resin (or a hybrid material thereof) having a thickness of about 1 to 10 μm. Can be used. In this case as well, the present embodiment needs to be configured so as to have a high resistance as a whole. Further, the intermediate transfer belt 11 having an elastic layer has a rubber hardness of 35 or less in an environment measured at 23 ° C. and 50% RH measured by “Micro Rubber Hardness Meter MD-1” manufactured by Kobunshi Keiki Co., Ltd. preferable.

  Also, when cleaning the intermediate transfer belt 11 having an elastic layer, the edge tip of the cleaning blade bites into the belt surface layer, the behavior of the edge tip of the cleaning blade becomes unstable, and cleaning failure is likely to occur. In addition, since the frictional force between the intermediate transfer belt 11 and the cleaning blade increases, problems such as the cleaning blade turning over, chattering and squealing, and the occurrence of scratches on the surface of the elastic belt and toner fusion, etc. Various harmful effects are likely to occur.

  Therefore, when the intermediate transfer belt 11 having an elastic layer is used, it is preferable to employ an electrostatic cleaning method. In the electrostatic cleaning method, for example, an electrostatic cleaning member such as an electrostatic brush in which a conductive fiber is wound around a metal core is brought into contact with the intermediate transfer belt 11 in a state where a bias having a polarity opposite to that of the toner is applied. Is electrostatically attracted to the electrostatic cleaning member, and the toner is removed from the intermediate transfer belt 11. In this method, since the contact pressure with the intermediate transfer belt 11 is smaller than in the blade cleaning method using a cleaning blade, there are few problems due to the cleaning blade as described above.

As the intermediate transfer belt 11, in order to realize high resistance, a belt having a volume resistivity in the range of 10 ⁹ [Ω · cm] to 10 ¹¹ [Ω · cm] at an applied voltage of 500 V is used. . The surface resistivity is preferably in the range of 10 ¹¹ [Ω / □] to 10 ¹³ [Ω / □] when the applied voltage is 500V. Further, the Young's modulus (longitudinal elastic modulus) of the base layer is preferably 3000 [Mpa] or more, and sufficient mechanical strength is required to withstand elongation, bending, wrinkling, and undulation by driving.

FIG. 4 is a graph showing the relationship between the applied voltage and the occurrence of white spots for a single-layer intermediate transfer belt and a laminated (here, two layers) intermediate transfer belt.
The occurrence of white spots was ranked so that the number was smaller as the occurrence of white spots was more pronounced. In the single-layer belt, white spot generation deteriorates as the applied voltage increases, but in the laminated belt, white spot does not deteriorate at a high applied voltage, indicating that good transfer is performed.

  In the present embodiment, the surface resistivity value of the intermediate transfer belt 11 is preferably smaller than the surface resistivity value of the secondary transfer belt 15. Further, the volume resistance value of the intermediate transfer belt 11 is preferably smaller than the volume resistance value of the secondary transfer belt 15. In general, the recording paper P that has passed through the secondary transfer nip tends to be attracted to the high-resistance belt. This is particularly noticeable in a low-temperature and low-humidity environment where resistance increases. Therefore, separability can be improved by setting it as the above conditions.

FIG. 5 is a graph showing the relationship between the electrical resistance value of the secondary transfer counter roller 17 and the occurrence of white spots.
This graph is an evaluation of white spots when a single-layer intermediate transfer belt is used and the electrical resistance value of the secondary transfer counter roller 17 is changed. According to this, the level of white spots can be improved by using a secondary transfer counter roller of at least 10 ⁷ [Ω]. Although the detailed cause is unknown, according to the evaluation of the present inventor, a secondary transfer counter roller of 10 ⁶ [Ω] or less cannot apply a sufficient bias to the recording paper P. It is considered that a transfer failure is caused in an image on which the toner is superimposed. On the other hand, if it is higher than 10 ⁹ [Ω], the bias applied to the recording paper P becomes too high, and a leak image is generated particularly in a low temperature and low humidity environment.

FIGS. 6A to 6C show the difference in the configuration of the secondary transfer portion in order of good separability.
In general, the belt transfer method shown in FIGS. 6A and 6B is more advantageous in separation than the roller transfer method shown in FIG. 6C. This is because the belt transfer method has a higher adsorption force between the recording paper P and the secondary transfer belt side (transfer roller side in the roller transfer method) than the roller transfer method. Further, even in the same belt transfer system, as shown in FIG. 6A, the secondary transfer roller 16 has a configuration in which the secondary transfer roller 16 is opposed to the center of the secondary transfer nip as shown in FIG. 6B. The configuration in which the secondary transfer roller 16 is disposed at a position shifted to the downstream side in the recording paper conveyance direction from the center of the nip has less separation of the recording paper P around the intermediate transfer belt 11 and better separation.

  As described above, when the secondary transfer roller 16 is shifted to the downstream side, the secondary transfer roller 16 holds both the secondary transfer belt 15 and the intermediate transfer belt 11 between the secondary transfer counter roller 17 and the position. However, it may be a position where it is not pinched. The shift amount (offset amount) of the secondary transfer roller 16 may be about 1 to 3 mm.

  In particular, in this embodiment, a tension roller 18 as a pressing member that pushes the intermediate transfer belt 11 from the outer peripheral surface thereof is disposed adjacent to the downstream side of the secondary transfer nip in the endless movement direction of the intermediate transfer belt. With this arrangement, the intermediate transfer belt portion downstream of the secondary transfer nip in the endless movement direction of the intermediate transfer belt (in this embodiment, the intermediate transfer belt stretched between the tension roller 18 and the secondary transfer counter roller 17 is stretched). And the secondary transfer belt portion on the downstream side of the secondary transfer nip in the endless movement direction of the secondary transfer belt (in the present embodiment, on the downstream side of the secondary transfer belt 16 in the endless movement direction of the secondary transfer belt 16). The angle formed with the outer peripheral surface of the secondary transfer belt portion) can be widened. And by making this angle 35 degrees or more, better separability can be obtained.

  In this embodiment, only one secondary transfer roller 16 is connected to the secondary transfer power source. However, as shown in FIG. 7, two or more secondary transfer rollers 16A and 16B are provided. It may be provided. In this case, even if the secondary transfer belt 15 has a high electrical resistance, an appropriate transfer bias can be applied to the secondary transfer nip.

In the present embodiment, the measurement of the volume resistivity of the roller-like member such as the secondary transfer roller 16 or the secondary transfer counter roller 17 is a rotation measurement that is performed in a state where the roller-like member is rotationally driven, and the one-side load 5N The bias is applied to the roller shaft at 1 kV, the resistance of one rotation of the roller is measured during 1 min measurement, and the average value is taken as the volume resistivity.
In the present embodiment, the measurement of volume resistivity and surface resistivity for endless belt-like members such as the intermediate transfer belt 11 and the secondary transfer belt 15 is based on JISK6911.

What has been described above is merely an example, and the present invention has a specific effect for each of the following modes.
(Aspect A)
An image carrier belt such as an endless belt-like intermediate transfer belt 11 stretched around a plurality of support rollers such as the support rollers 12 and 17, an endless belt-like secondary transfer belt 15 stretched around a plurality of support rollers, etc. The recording material conveying belt is contacted to form a transfer nip such as a secondary transfer nip, and when the recording material such as recording paper P is passed through the transfer nip, the recording material conveying belt contacts the inner peripheral surface of the recording material conveying belt. In an image forming apparatus that transfers a toner image on the image carrier belt to a recording material by applying a transfer bias to the transfer nip from a bias application member such as a secondary transfer roller 16, the image carrier belt is a high Use a resistor having a high resistance surface as the recording material conveying belt, and set the bias applying member below the central position in the recording material conveying direction of the transfer nip in the recording material conveying direction. Characterized by being placed in contact with the inner peripheral surface of the recording material conveying belt side.
According to this, it is possible to obtain a high separability without providing a dedicated member for improving the separability and while suppressing deterioration in image quality of white spots.

(Aspect B)
The aspect A is characterized in that a tension roller 18 is provided as a pressing member that presses the image carrier belt from the outer peripheral surface thereof.
According to this, even when the circumferential length of the image carrier belt may become long, it is easy to efficiently roll the image carrier belt and keep the tension constant.

(Aspect C)
In the above aspect B, the pressing member supports the inner peripheral surface of the image carrier belt at a position facing the transfer nip among the plurality of support rollers that span the image carrier belt. It is stretched between a transfer counter support roller such as the counter roller 17 and a transfer downstream support roller 12 that supports the inner peripheral surface of the image carrier belt adjacent to the downstream side in the endless movement direction of the image carrier belt. The image bearing belt portion is disposed at a position to press the outer circumferential surface of the image bearing belt portion, the outer circumferential surface of the image bearing belt portion stretched between the pressing member and the transfer counter support roller, and the bias applying member. The angle formed with the outer peripheral surface of the recording material conveyance belt portion on the downstream side in the endless movement direction of the recording material conveyance belt is 35 degrees or more.
According to this, higher separability can be obtained.

(Aspect D)
In any one of the above aspects A to C, the recording material conveyance belt carries a recording material on the outer peripheral surface of the recording material conveyance belt portion upstream of the transfer nip in the endless movement direction of the recording material conveyance belt, The recording material is fed to the transfer nip by endless movement of the recording material conveying belt.
According to this, the recording material is attracted to the outer peripheral surface of the recording material conveyance belt before entering the transfer nip, and the recording material can be conveyed more stably.

(Aspect E)
In any one of the above aspects A to D, the recording material transport belt has a multi-layer structure having a high-resistance surface layer constituting the outer peripheral surface and a medium-resistance base layer constituting the inner peripheral surface. It is characterized by being.
According to this, dielectric polarization can be generated between the high-resistance surface layer and the medium-resistance base layer, and the recording material can be easily adsorbed to the outer peripheral surface of the recording material conveyance belt. The recording material is adsorbed on the recording material conveyance belt side, so that the recording material can be easily peeled off from the image carrier belt side, and the separation property is improved.

(Aspect F)
In any one of the above aspects A to E, a transfer voltage having a polarity opposite to the normal charging polarity of the toner is applied to the bias applying member.
According to this, since a bias having a polarity opposite to that of the toner is applied to the recording material conveyance belt side, the recording material is easily pulled away from the image carrier belt side, and the separability is improved.

(Aspect G)
In any one of the above aspects A to F, the bias applying member is composed of at least a resistor having a medium resistance or higher.
In this way, by configuring the bias applying member with a medium resistor of 10 ⁶ [Ω] or more, a sufficient bias can be applied to the recording material as compared with the case of configuring with a low resistance of less than 10 ⁶ [Ω]. Appropriate images can be obtained.

(Aspect H)
In any one of the above aspects A to G, the volume resistivity of the bias applying member is 10 ⁸ [Ω · cm] or more.
According to this, a good image with few white spots can be obtained.

(Aspect I)
In any one of the above aspects A to H, at least two or more bias applying members are provided.
According to this, even if the electrical resistance of the recording material conveyance belt is high, a transfer bias can be more appropriately applied to the secondary transfer nip.

(Aspect J)
In any one of the above aspects A to I, the bias applying member is a roller-shaped member.
By making the bias applying member into a roller shape, transfer can be easily performed. The roller shape may be a cylindrical shape or a drum shape. In particular, the drum type is effective in preventing the bias applying member from being displaced and suppressing the occurrence of surface cracks in the recording material conveying belt.

(Aspect K)
In the aspect J, the bias applying member is a driven roller that rotates along with the endless movement of the recording material conveying belt.
According to this, the speed difference between the recording material conveyance belt and the image carrier belt during transfer can be reduced, and deterioration of image quality such as color misregistration can be prevented.

(Aspect L)
In the above aspect J or K, the diameter of the roller-shaped member supports the inner peripheral surface of the image carrier belt at a position facing the transfer nip among a plurality of support rollers that span the image carrier belt. It is smaller than the diameter of the transfer opposing support roller.
According to this, when the recording material passes through the transfer nip, the recording material is easily attracted to the recording material conveyance belt side and separated from the image carrier belt side.

(Aspect M)
In any one of the above aspects A to L, the transfer facing that supports the inner peripheral surface of the image carrier belt at a position facing the transfer nip among the plurality of support rollers that span the image carrier belt. The diameter of the support roller is 20 [mm] or less.
According to this, the recording material that has passed through the transfer nip can be easily separated from the image carrier belt side by the curvature of the diameter of the transfer facing support roller, and the separability is improved.

(Aspect N)
In any one of the above aspects A to M, the recording material conveyance belt is a seamless belt.
According to this, transfer can be performed at any position on the outer peripheral surface of the recording material conveyance belt.

(Aspect O)
In any one of the above aspects A to N, the recording material conveyance belt has an elastic layer.
According to this, the transferability with respect to the recording material rich in surface irregularities can be improved.

(Aspect P)
In any one of the above embodiments A to O, the surface resistivity on the outer peripheral surface of the image carrier belt is 10 ⁹ [Ω / □] or more and 10 ¹² [Ω / □] or less.
If the electric resistance of the image carrier belt is low, a target transfer bias cannot be applied to the transfer nip, particularly in a high temperature and high humidity environment, and a target image density cannot be obtained. In addition, when the electric resistance is high, there is a high possibility that a discharge that causes white spots in the transfer nip occurs particularly in a low temperature and low humidity environment. According to this aspect, it is possible to obtain a target image density while suppressing the occurrence of white spots.

(Aspect Q)
In any one of the above aspects A to P, the volume resistivity of the image carrier belt is 10 ^7.5 [Ω · cm] or more and 10 ¹³ [Ω · cm] or less.
If the electric resistance of the image carrier belt is low, a target transfer bias cannot be applied to the transfer nip, particularly in a high temperature and high humidity environment, and a target image density cannot be obtained. In addition, when the electric resistance is high, there is a high possibility that a discharge that causes white spots in the transfer nip occurs particularly in a low temperature and low humidity environment. According to this aspect, it is possible to obtain a target image density while suppressing the occurrence of white spots.

(Aspect R)
In any one of the above aspects A to Q, the image carrier belt is a seamless belt.
According to this, the toner image can be carried at any position on the outer peripheral surface of the image carrier belt.

(Aspect S)
In any one of the above aspects A to R, the image carrier belt has a multilayer structure including an elastic layer having a thickness of 300 [μm] or more and 1000 [μm] or less, and has a micro rubber hardness. It is characterized by being 35 or less.
According to this, the transferability with respect to the recording material rich in surface irregularities can be improved.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 11 Intermediate transfer belt 13 Primary transfer roller 14 Intermediate transfer belt cleaning apparatus 15 Secondary transfer belts 16, 16A, 16B Secondary transfer roller 17 Secondary transfer counter roller 18 Tension roller 20 Photosensitive drum 30 Charging device 40 Cleaning Device 50 Developing device 60 Fixing device

JP 2007-328203 A

Claims (16)

A transfer nip is formed by bringing an endless belt-shaped image carrier belt stretched over a plurality of support rollers into contact with an endless belt-shaped recording material transport belt stretched over the plurality of support rollers. By applying a transfer bias to the transfer nip from a bias applying member that contacts the inner peripheral surface of the recording material conveying belt when passing the recording material, the toner image on the image carrier belt is transferred to the recording material. In the image forming apparatus,
As the image carrier belt, a belt having a volume resistivity of 10 ^7.5 [ Ω · cm] or more and 10 ¹³ [ Ω · cm] or less is used.
The recording material conveying belt has a multi-layer structure having a surface layer constituting the outer peripheral surface and a base layer constituting the inner peripheral surface, and the surface resistivity of the outer peripheral surface is greater than the surface resistivity of the inner peripheral surface. Higher
The bias applying member is composed of a resistor of 10 ⁶ [Ω] or more, and contacts the inner peripheral surface of the recording material conveyance belt at the downstream side of the recording nip in the recording material conveyance direction from the central point of the transfer nip in the recording material conveyance direction. An image forming apparatus having the arrangement as described above. The image forming apparatus according to claim 1.
An image forming apparatus, comprising: a pressing member that presses the image carrier belt from an outer peripheral surface thereof. The image forming apparatus according to claim 2.
The pressing member includes a transfer counter support roller that supports an inner peripheral surface of the image carrier belt at a position facing the transfer nip among a plurality of support rollers that span the image carrier belt, and an image on the transfer counter support roller. At a position to press the outer peripheral surface of the image carrier belt portion that is stretched between the downstream side support roller that supports the inner peripheral surface of the image carrier belt adjacent to the downstream side in the endless movement direction of the carrier belt. Has been placed,
The outer peripheral surface of the image carrier belt portion stretched between the pressing member and the transfer opposing support roller, and the outer periphery of the recording material conveyance belt portion downstream of the bias applying member in the endless movement direction of the recording material conveyance belt An image forming apparatus, wherein an angle formed with a surface is 35 degrees or more. The image forming apparatus according to any one of claims 1 to 3,
The recording material conveying belt carries the recording material on the outer peripheral surface of the recording material conveying belt portion upstream of the transfer nip in the recording material conveying belt endless movement direction, and the recording material is conveyed by the endless movement of the recording material conveying belt. An image forming apparatus configured to be fed into a transfer nip. The image forming apparatus according to any one of claims 1 to 4 , wherein:
An image forming apparatus, wherein a transfer voltage having a polarity opposite to a normal charging polarity of toner is applied to the bias applying member. The image forming apparatus according to any one of claims 1 to 5 ,
The image forming apparatus, wherein the bias applying member has a volume resistivity of 10 ⁸ [Ω · cm] or more. The image forming apparatus according to any one of claims 1 to 6 ,
An image forming apparatus comprising at least two bias applying members. The image forming apparatus according to any one of claims 1 to 7 ,
The image forming apparatus, wherein the bias applying member is a roller-shaped member. The image forming apparatus according to claim 8 .
The image forming apparatus according to claim 1, wherein the bias applying member is a driven roller that rotates along with the endless movement of the recording material conveying belt. The image forming apparatus according to claim 8 or 9 ,
The diameter of the roller-shaped member is the diameter of the transfer counter support roller that supports the inner peripheral surface of the image carrier belt at a position facing the transfer nip among the plurality of support rollers that span the image carrier belt. An image forming apparatus characterized by being smaller than the above. The image forming apparatus according to any one of claims 1 to 10 ,
Of the plurality of support rollers that span the image carrier belt, the diameter of the transfer counter support roller that supports the inner peripheral surface of the image carrier belt at a position facing the transfer nip is 20 [mm] or less. An image forming apparatus. The image forming apparatus according to any one of claims 1 to 11 ,
An image forming apparatus, wherein the recording material conveying belt is a seamless belt. The image forming apparatus according to any one of claims 1 to 12 ,
The image forming apparatus, wherein the recording material conveying belt has an elastic layer. The image forming apparatus according to any one of claims 1 to 13 ,
The image forming apparatus according to claim 1, wherein the surface resistivity of the outer peripheral surface of the image carrier belt is 10 ⁹ [Ω / □] or more and 10 ¹² [Ω / □] or less. The image forming apparatus according to any one of claims 1 to 14 ,
An image forming apparatus, wherein the image carrier belt is a seamless belt. The image forming apparatus according to any one of claims 1 to 15 ,
The image carrier belt has a multi-layer structure including an elastic layer having a thickness of 300 [μm] or more and 1000 [μm] or less, and has a micro rubber hardness of 35 or less. .

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