JP2012063406A - Secondary transfer device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten a switching time when a first voltage whose polarity is different from the charge polarity of toner is applied to perform secondary transfer and then, an applied voltage is switched to a second voltage whose polarity is the same as the charge polarity of the toner.SOLUTION: A secondary transfer device 120 includes a drive roller 109B (first transfer means) which presses an intermediate transfer belt 107 (transfer body) against a recording paper 115 (transfer material) and to which the voltage having a negative polarity (first voltage) is applied to transfer a toner image transferred on the intermediate transfer belt 107 to the recording paper 115 and a drive roller 109B' (second transfer means) which is provided on the downstream side of the drive roller 109B in the moving direction of the recording paper 115 and presses the intermediate transfer belt 107 against a part of the toner image transferred by the drive roller 109B and to which the voltage having a positive polarity (second voltage) is applied to return a part of the toner image to the intermediate transfer belt 107.

Description

  The present invention relates to a secondary transfer device and an image forming apparatus.

  In Patent Document 1, an electrode is disposed downstream of a region where the photoconductor and the intermediate transfer belt are in contact (nip region), and a voltage having the same polarity as the charging polarity of the toner is applied to the electrode. A technique for preventing generation of transfer dust due to charge-up of a toner image is disclosed. Patent Document 2 discloses a technique in which two rollers are arranged to face each other and the intermediate transfer belt and the transfer material are brought into close contact with each other, and the toner image is secondarily transferred from the intermediate transfer belt to the transfer material. .

Japanese Patent Laying-Open No. 2005-077861 JP 2009-199054 A

  The present invention applies an applied voltage to return a control toner image for managing image quality to a transfer body after a secondary transfer of the toner image by applying a first voltage having the same polarity as the charging polarity of the toner. The purpose is to shorten the switching time when switching to the second voltage having a polarity different from the charging polarity of the toner.

  In order to solve the above problems, a secondary transfer device according to claim 1 of the present invention is formed to manage a first toner image formed on a recording material and the image quality of the first toner image. A second transfer device for transferring the second toner image from the transfer member onto which the toner image is transferred to a recording material, and is disposed at a position facing the transfer member with the recording material interposed therebetween. The belt-like member stretched by two or more rollers and the first toner image transferred to the transfer body are pressed against the recording material, and the second toner image transferred to the transfer body is pressed. The first toner image is pressed from the transfer member to the recording material by being pressed against the secondary transfer member and applying a first voltage having the same polarity as the charging polarity of the toner forming the first toner image. And transferring the second toner image to the transfer body. A first transfer means for transferring to the belt-like member; and provided downstream of the position of the first transfer means in the moving direction of the recording material. The transfer member is pressed against the transferred second toner image, and the second toner image is applied by applying a second voltage having a polarity different from the charging polarity of the toner forming the first toner image. And a second transfer means for transferring the toner from the belt-like member to the transfer body.

  The secondary transfer device according to claim 2 is the secondary transfer device according to claim 1, wherein the secondary transfer device is viewed from a position where transfer is performed by the first transfer unit and the second transfer unit. The transfer member and the belt-shaped member are in contact with each other on at least one of the upstream side and the downstream side in the moving direction of the recording material.

  The secondary transfer device according to claim 3 is applied when the first toner image is transferred by the first transfer means in the secondary transfer device according to claim 1 or 2. The magnitude of the first voltage is different from the magnitude of the first voltage applied when the second toner image is transferred by the first transfer means.

  The image forming apparatus according to claim 4 forms a first toner image formed on the recording material and a second toner image formed for managing the image quality of the first toner image. Forming means, primary transfer means for transferring the first toner image and the second toner image formed by the forming means to a transfer body, and the first transfer means transferred to the transfer body by the primary transfer means. One or more toner images transferred to a recording material, and the second toner image transferred to the transfer body by the primary transfer unit is disposed at two or more positions facing the transfer body with the recording material interposed therebetween. The secondary transfer device according to any one of claims 1 to 3, wherein the image is transferred to a belt-like member stretched by a roller, and then transferred to the transfer body, and the second image transferred by the secondary transfer device. 1 toner image on the recording material Characterized in that it comprises a fixing means for.

  According to the secondary transfer apparatus of the first aspect, compared to the case where this configuration is not adopted, after the secondary transfer is performed by applying the first voltage, the applied voltage is switched to the second voltage. Switching time can be shortened.

  According to the secondary transfer apparatus of claim 2, at least the upstream side or the downstream side in the moving direction of the recording material when viewed from the position where the transfer is performed by the first transfer unit and the second transfer unit. It is possible to suppress image disturbance due to peeling discharge at a gap generated on either side.

  According to the secondary transfer apparatus of the third aspect, the secondary transfer can be performed at a higher speed.

  According to the image forming apparatus of the fourth aspect, compared to the case where this configuration is not adopted, after the second transfer is performed by applying the first voltage, the applied voltage is switched to the second voltage. Switching time can be shortened.

1 shows an internal configuration of an image forming apparatus 100. The structure of the secondary transfer apparatus 120 is shown. 2 shows a configuration of a toner image formed on the intermediate transfer belt 107. FIG. The relationship between the voltage applied to the transfer roller and time is shown. The relationship between process speed and maximum transfer voltage is shown. Shows the relationship between process speed and switching time. The required switching time is shown for each maximum transfer voltage. The structure of the secondary transfer apparatus 120 of 2nd Embodiment is shown.

(First embodiment)
Hereinafter, preferred embodiments will be described in detail with reference to the drawings.
FIG. 1 is a schematic diagram illustrating an example (one embodiment) of a configuration of an image forming apparatus to which a transfer device according to a preferred embodiment is applied. The image forming apparatus 100 according to the present embodiment is a so-called tandem method, and charging apparatuses 102a to 102d are sequentially arranged around the four image holding bodies 101a to 101d formed of an electrophotographic photosensitive member along the rotation direction thereof. , Exposure devices 114a to 114d, developing devices 103a to 103d, primary transfer devices (primary transfer rollers) 105a to 105d, and image carrier cleaning devices 104a to 104d are arranged. It should be noted that a static eliminator may be provided in order to remove residual potential remaining on the surfaces of the image carriers 101a to 101d after transfer.

  The intermediate transfer belt 107 is stretched around tension rollers 106a to 106d, a drive roller 111, and backup rollers 108B and 108B '. By these tension rollers 106a to 106d, drive roller 111, and backup rollers 108B and 108B ′, the intermediate transfer belt 107 is in contact with the surfaces of the image carriers 101a to 101d and the primary transfer rollers. It is conveyed in the direction of arrow A between 105a-105d.

  The primary transfer rollers 105a to 105d are disposed in contact with the inner peripheral surface of the intermediate transfer belt 107 so as to sandwich the intermediate transfer belt 107 between the image carriers 101a to 101d. A site where each of the primary transfer rollers 105a to 105d and each of the image carriers 101a to 101d are in contact with each other is a primary transfer portion (primary transfer nip). A primary transfer voltage is applied to each primary transfer portion by each primary transfer roller 105 a to 105 d, whereby each toner image held on each image holding body 101 a to 101 d is transferred onto the intermediate transfer belt 107. Is done. The image forming apparatus 100 corresponds to an example of the image forming apparatus of the present invention, and the intermediate transfer belt 107 corresponds to an example of the transfer body of the present invention. Further, the image forming apparatus 100 includes a secondary transfer device 120 on the downstream side in the transport direction of the intermediate transfer belt 107 with respect to the image carrier 101d. The secondary transfer device 120 includes a drive roller 109 (109A, 109B), a backup roller 108 (108B, 108B ′), a contact roller 119A, 119A ′, an idler roller 106e, a secondary transfer belt 116, and a secondary transfer voltage application unit 119. 119 ′ and a drive unit (not shown). The secondary transfer belt 116 corresponds to an example of a belt-shaped member of the present invention, the backup roller 108B corresponds to an example of a first transfer unit, the backup roller 108B ′ corresponds to an example of a second transfer unit, and is driven. The rollers 109 (109A and 109B) correspond to an example of two or more rollers disposed at positions facing the intermediate transfer belt 107 as a transfer body.

  In the secondary transfer device 120, the backup rollers 108 </ b> B and 108 </ b> B ′ and the secondary transfer belt 116 are positioned so as to face each other via the intermediate transfer belt 107. The intermediate transfer belt 107 and the secondary transfer belt 116 rotate in opposite directions to sandwich the recording paper 115 (an example of a recording material). The recording paper 115 is conveyed in the direction of arrow B while being sandwiched between the intermediate transfer belt 107 and the secondary transfer belt 116, and then passes through the fixing device 110. Here, a portion where the driving roller 109B contacts the backup roller 108B via the intermediate transfer belt 107 and the secondary transfer belt 116 becomes a secondary transfer section (secondary transfer nip), and a voltage is applied to the contact roller 119A. Thus, a secondary transfer electric field is formed between the backup roller 108B and the drive roller 109B whose shaft shaft is grounded. Further, intermediate transfer belt cleaning devices 112 and 113 are arranged so as to come into contact with the intermediate transfer belt 107 after the secondary transfer.

  In the full-color image forming apparatus 100 having this configuration, the image carrier 101a rotates in the direction of the arrow C, and after the surface is charged by the charging device 102a, the first color static light is exposed by the exposure device 114a such as laser light. An electrostatic latent image is formed. The formed electrostatic latent image is developed (visualized) with toner by a developing device 103a containing toner corresponding to the color to form a toner image. The developing devices 103a to 103d contain toners (for example, yellow, magenta, cyan, and black) corresponding to the electrostatic latent images of the respective colors.

  The toner image formed on the image carrier 101a is electrostatically transferred (primary transfer) to the intermediate transfer belt 107 by the primary transfer roller 105a when passing through the primary transfer portion. Thereafter, the primary transfer rollers 105b to 105d perform primary transfer so that the second color, third color, and fourth color toner images are sequentially superimposed on the intermediate transfer belt 107 holding the first color toner image. Thus, a full color multiple toner image can be obtained.

  The toner image formed on the intermediate transfer belt 107 is electrostatically collectively transferred (secondary transfer) to the recording paper 115 when passing through the secondary transfer section. The recording paper 115 onto which the toner image has been transferred is conveyed to the fixing device 110, subjected to fixing processing by at least one of heating and pressing, and then discharged outside the apparatus.

  Residual toner is removed from the image carriers 101a to 101d after the primary transfer by the image carrier cleaning devices 104a to 104d. On the other hand, residual toner is removed from the intermediate transfer belt 107 after the secondary transfer by the intermediate transfer belt cleaning devices 112 and 113 to prepare for the next image forming process.

  Each configuration will be described below. In addition, below, when the structure (member) which has the same function is demonstrated, the code | symbol of said ad is abbreviate | omitted and demonstrated. For example, the image holders 101a to 101d will be described as the image holder 101 when collectively referred to.

[Image carrier]
As the image carrier 101, known electrophotographic photoreceptors are widely used. As the electrophotographic photoreceptor, an inorganic photoreceptor having a photosensitive layer made of an inorganic material, an organic photoreceptor having a photosensitive layer made of an organic material, or the like is used. In the organic photoconductor, a function-separated type organic photoconductor in which a charge generation layer that generates charges upon exposure and a charge transport layer that transports charges are stacked, and a function that generates charges and a function that transports charges are the same. A single layer type organic photoreceptor fulfilled by the layer is preferably used. In addition, as the inorganic photoconductor, a photoconductive layer composed of amorphous silicon is preferably used. The shape of the image carrier is not particularly limited, and a known shape such as a cylindrical drum shape, a sheet shape, or a plate shape is employed.

[Image carrier cleaning device]
The image carrier cleaning device 104 is for removing residual toner adhering to the surface of the image carrier 101 after the primary transfer process, and in addition to a cleaning blade, brush cleaning or roller cleaning can be used. . Examples of the material for the cleaning blade include urethane rubber, neoprene rubber, and silicone rubber.

[Charging device]
The charging device 102 is not particularly limited. For example, a contact-type charger using a conductive or semiconductive roller, brush, film, rubber blade, or the like, a scorotron charger using a corona discharge, or a corotron charger. For example, known chargers can be widely applied. Among these, a contact charger that generates less ozone and can perform efficient charging is preferable.

[Exposure equipment]
The exposure device 114 is not particularly limited. For example, a light source such as a semiconductor laser light, an LED light, or a liquid crystal shutter light, or a desired light source from these light sources via a polygon mirror is provided on the surfaces of the image carriers 101a to 101d. A known exposure apparatus such as an optical system apparatus for imagewise exposure is widely applied.

[Developer]
The developing device 103 is selected according to the purpose. For example, a known developing device that develops a one-component developer or a two-component developer in contact or non-contact with a brush, a roller, or the like can be used.

[toner]
The toner used in the image forming apparatus 100 of the present embodiment is not particularly limited, and for example, a binder resin
And a colorant. In addition, the toner may be subjected to an internal addition treatment or an external addition treatment with a known additive such as a charge control agent, a release agent, and other inorganic particles. As a toner production method, a polymerization method such as an emulsion polymerization aggregation method or a dissolution suspension method is used. In addition, a manufacturing method may be performed in which the toner obtained by these methods is used as a core, and agglomerated particles are further adhered and heated and fused to give a core-shell structure.

[Intermediate transfer belt]
The intermediate transfer belt 107 in the present embodiment has a configuration in which a plurality of layers are stacked in the thickness direction.

  In the intermediate transfer belt 107, the content of carbon black contained per unit volume in the outermost layer is smaller than the content of carbon black contained per unit volume in the innermost layer. By controlling the content of carbon black contained in the outermost layer to be less than that of the innermost layer, occurrence of image quality defects due to discharge on the output image is suppressed.

[Intermediate transfer belt cleaning device]
As the intermediate transfer belt cleaning devices 112 and 113, brush cleaning, roller cleaning, and the like can be used in addition to the cleaning blade. Examples of the material for the cleaning blade include urethane rubber, neoprene rubber, and silicone rubber.

[Primary transfer roller]
The primary transfer roller 105 may be either a single layer or a multilayer. For example, in the case of a single layer structure, it is composed of a roller in which an appropriate amount of a conductive agent such as carbon black is blended in foamed or non-foamed silicone rubber, urethane rubber, EPDM, or the like. For example, a current of 30 μA or more and 100 μA or less is applied to the primary transfer roller 105, and the toner image held on the image carrier 101 is transferred onto the intermediate belt by an electric field formed between the primary transfer roller 105 and the image carrier 101. It is transcribed.

[Fixing device]
As the fixing device 110, for example, a known fixing device such as a heat roller fixing device, a pressure roller fixing device, or a flash fixing device is widely applied.

[Secondary transfer device]
The configuration of the drive rollers 109B and 109B ′, the secondary transfer belt 116, and the backup rollers 108B and 108B ′ provided in the secondary transfer device 120 will be described.

  The drive rollers 109B and 109B ′ are configured in a cylindrical shape, and are arranged in contact with the outer peripheral surface of the intermediate transfer belt 107 via the secondary transfer belt 116 so that the axial direction coincides with the width direction of the intermediate transfer belt 107. Yes. In this embodiment, the driving rollers 109B and 109B 'are configured such that one or more conductive layers are laminated on the outer periphery of a core material that is a metal shaft. This conductive layer is made of a foamed material such as silicone rubber, urethane rubber, or EPDM in which a conductive agent such as carbon black is dispersed. The hardness of the conductive layer is preferably in the range of 15 ° to 50 ° in Asker C hardness. If the Asker C hardness is in the range of 15 ° to 50 °, the stability of the contact state with the intermediate transfer belt 107 can be obtained. The Asker C hardness is measured by pressing a measuring needle of an Asker C type hardness meter (manufactured by Kobunshi Keiki Co., Ltd.) on the surface of a 5 mm thick measurement sheet.

  The secondary transfer belt 116 is stretched by driving rollers 109B and 109B ′ and an idler roller 106e, and rotates in the opposite direction to the intermediate transfer belt 107, so that the recording paper 115 in the secondary transfer nip is placed on the intermediate transfer member. It has a function of transporting the recording paper 115 in the direction of the fixing device 110 simultaneously with the secondary transfer of the toner image. In the secondary transfer nip, rubbing between the secondary transfer belt 116 and the intermediate transfer belt 107 occurs. Therefore, when a resin such as polyimide in which a conductive agent such as carbon black is dispersed is used for the intermediate transfer belt 107, The next transfer belt 116 is preferably made of an elastic member such as silicone rubber, urethane rubber, or chloroprene rubber in which a conductive agent such as carbon black is dispersed. Conversely, a conductive agent such as carbon black is dispersed in the intermediate transfer belt 107. When an elastic member such as silicone rubber, urethane rubber, or chloroprene rubber is used, the secondary transfer belt 116 is preferably made of a resin such as polyimide in which a conductive agent such as carbon black is dispersed.

  The backup rollers 108B and 108B 'form counter electrodes of the drive rollers 109B and 109B'. In this embodiment, the backup rollers 108B and 108B ′ are formed in a columnar shape, and the inner direction of the intermediate transfer belt 107 is such that the axial direction coincides with both the width direction of the intermediate transfer belt 107 and the axial direction of the backup roller 108. It is arranged in contact with the peripheral surface. Further, the backup rollers 108B and 108B 'are disposed to face the driving rollers 109B and 109B' via the intermediate transfer belt 107. The backup rollers 108B and 108B 'may be a single layer (single layer) or multiple layers, like the conductive layers of the drive rollers 109B and 109B'. For example, when the conductive layer has a single layer structure, it is made of a material in which an appropriate amount of a conductive agent such as carbon black is blended with silicone rubber, urethane rubber, EPDM, or the like, like the conductive layers of the drive rollers 109B and 109B ′. What is necessary is just to comprise. In the case where the conductive layer 109B has a two-layer structure, the outer peripheral surface of the layer made of the rubber material may be covered with a surface layer.

  A voltage is applied to the contact rollers 119A and 119A 'so that a voltage of 0.1KV to 10KV is normally applied to the backup rollers 108B and 108B'. The core members 109A and 109A ′ of the drive rollers 109B and 109B ′ are rotatably supported by a support member (not shown), and a drive unit (not shown) that rotates the support member is a component of the image forming apparatus 100. It is connected to a control unit (not shown) for controlling the signal so as to be able to send and receive signals. Similarly, the core members 108A and 108A ′ of the backup rollers 108B and 108B ′ are also rotatably supported by a support member (not shown), and a drive unit (not shown) that rotates the support member forms an image. Signals are connected to a control unit (not shown) that controls each part of the device 100.

  Further, the driving rollers 109B and 109B ′ and the backup rollers 108B and 108B ′ are in contact with each other via the intermediate transfer belt 107 and the secondary transfer belt 116, and the amount of pressing against the intermediate transfer belt 107 at this time is the amount of biting. This amount of biting is preferably adjusted by the recording paper 115. For example, when the basis weight of the recording paper 115 is 60 to 186 g / m 2, the biting amount is preferably 0.9 mm, and when the paper is 187 g / m 2 or more, the biting amount is 0.3 mm. It is preferable that In this case, it is preferable that the wrap angle between the drive rollers 109B and 109B 'and the backup rollers 108B and 108B' is set to around 27 °. In the present embodiment, the driving rollers 109B and 109B 'move according to the type of the recording paper 115 to adjust the distance from the backup rollers 108B and 108B'.

  It is preferable that the system resistance when the resistance detection current of 60 μA flows between the driving rollers 109B and 109B ′ and the backup rollers 108B and 108B ′ satisfies 6.7 LogΩ to 8.0 LogΩ. If the system resistance is less than 6.7 LogΩ, good transferability to the recording paper 115 cannot be obtained, and if it exceeds 8.0 LogΩ, mottled density unevenness may occur.

  Here, the configuration of the toner image will be described. FIG. 2 shows a configuration of the toner image 400 formed on the intermediate transfer belt 107. In FIG. 2, the toner image 400 formed on the intermediate transfer belt 107 includes a toner image 410 to be formed on the recording paper 115 and between the toner image 410 and the toner image 410 (so-called inter image). A control toner image 420 which is a control image used for managing the image quality of the toner image 410 is included. The toner image 410 is an example of a first toner image, and the toner image 420 is an example of a second toner image. The control toner image 420 is read by an optical sensor (not shown), the density thereof is specified, and the control toner image 420 is used for image quality management based on the density.

  The intermediate transfer belt 107 moves, and the toner image 410 on the intermediate transfer belt 107 is sent to a position between the drive roller 109B and the backup roller 108B, and the recording paper 115 is transferred to the drive roller 109B and the backup roller 108B. Then, the drive roller 109B acts to press the recording paper 115 against the intermediate transfer belt 107 (the toner image 410 on the intermediate transfer belt 107). At this time, the contact roller 119A is applied to the backup roller 108B so that a negative voltage (first voltage) having the same polarity as the charging polarity (negative electrode) of the toner forming the toner image 410 is applied to the backup roller 108B. A voltage is applied. As a result, the toner image 410 is secondarily transferred from the intermediate transfer belt 107 to the recording paper 115. On the other hand, when the control toner image 420 on the intermediate transfer belt 107 is sent to a position between the drive roller 109B and the backup roller 108B (at this time, the recording paper 115 is not sent), the drive roller 109B is The secondary transfer belt 116 is pressed against the intermediate transfer belt 107 (the control toner image 420 on the intermediate transfer belt 107). At this time, the contact roller 119A is applied such that a negative voltage (first voltage) having the same polarity as the charging polarity (negative electrode) of the toner forming the control toner image 420 is applied to the backup roller 108B. A voltage is applied to. As a result, the control toner image 420 is secondarily transferred from the intermediate transfer belt 107 to the secondary transfer belt 116.

  Further, the intermediate transfer belt 107 moves, and the control toner image 420 transferred to the secondary transfer belt 116 is located between the drive roller 109B ′ and the backup roller 108B ′ on the downstream side in the moving direction of the recording paper. When fed to the position, the driving roller 109B ′ acts to press the control toner image 420 against the intermediate transfer belt 107. At this time, the contact roller 119A ′ is applied so that a positive voltage (second voltage), which is a voltage different from the charging polarity (negative electrode) of the toner forming the control toner image 420, is applied to the backup roller 108B ′. A voltage is applied to. At this time, when the toner image 410 is located between the driving roller 109B ′ and the backup roller 108B ′ so that even the toner image 410 is not transferred to the intermediate transfer belt 107, the voltage application as described above is performed. Absent. As a result, only the control toner image 420 is transferred to the intermediate transfer belt 107. That is, the control toner image 420 returns to the intermediate transfer belt 107 and is finally cleaned and removed on the intermediate transfer belt 107 side.

  FIG. 3 is a diagram showing the relationship between the voltage applied to the backup roller 108 </ b> B ′ and time, the solid line is the transition of the applied voltage in the present embodiment, and the dotted line is the transition of the conventional applied voltage. The transition of the conventional applied voltage is a transition under the configuration as shown in FIG. In addition, in order to understand the relationship between the toner image 410 and the control toner image 420 shown in FIG. 2 and the applied voltage, the timing at which the toner image 410 and the control toner image 420 pass the nip position of the backup roller 108B ′, The transition of the applied voltage (solid line) in the form is expressed in association with time series. Similarly, in the conventional configuration, the time when the toner image 410 ′ and the control toner image 420 ′ pass through the nip position of the backup roller 208 (FIG. 4) and the transition of the applied voltage (dotted line) are expressed in association with each other in time series. is doing.

  4, 208 is a backup roller, 209 is a drive roller, 207 is an intermediate transfer belt, 216 is a secondary transfer belt, and 206 is an idler roller. In the conventional configuration, when the toner image 410 ′ passes through the nip position of the backup roller 208, the toner image 410 ′ is applied to the recording paper 115 ′ by applying a voltage having the same polarity (negative polarity) as the toner to the backup roller 208. 410 ′ is secondarily transferred. On the other hand, when the control toner image 420 ′ passes through the nip position of the backup roller 108B ′, the control toner image 420 ′ is applied to the recording paper 115 ′ by applying a voltage (positive polarity) different from the toner to the backup roller 208. 'Will not be secondary transferred. Therefore, the transition of the voltage applied to the backup roller 208 is as shown by the dotted line in FIG.

  In contrast, in the present embodiment, the toner image 410 is secondarily transferred to the recording paper 115 and applied to the secondary transfer belt 116 by applying a voltage having the same polarity (negative polarity) as the toner to the backup roller 108B. The control toner image 420 is secondarily transferred. At this time, the magnitude of the voltage applied to the backup roller 108B is constant regardless of time. Thereafter, the applied voltage is varied according to time so that only the control toner image 420 is transferred to the intermediate transfer belt 107 to the backup roller 108B '. That is, when the toner image 410 passes through the nip position of the backup roller 108B ′, the toner image 410 is not transferred onto the recording paper 115 by applying a voltage having the same polarity (negative polarity) as the toner to the backup roller 108B ′. (Do not return). On the other hand, when the control toner image 420 passes through the nip position of the backup roller 108B ′, the control toner image 420 is applied to the intermediate transfer belt 107 by applying a voltage (positive polarity) different from the toner to the backup roller 108B ′. Is transferred back to the intermediate transfer belt 107.

  As can be seen from the comparison between the dotted line graph and the solid line graph in FIG. 3, the negative electrode maximum voltage V1 'in the dotted line graph is smaller than the negative electrode maximum voltage V1 in the solid line graph (the absolute value is large). In the conventional configuration, in order to secondarily transfer the toner image 410 ′ to the recording paper 115 ′, a voltage V1 ′ having a relatively large absolute value as a voltage having the same polarity as the polarity (negative electrode) of the toner is used as a backup roller. In this embodiment, the toner image 410 is not transferred to the recording paper 115 (so that it does not return), so that the same polarity as the toner is applied to the backup roller 108B ′. This is because the absolute value of the voltage V1 when the (negative electrode) voltage is applied is smaller than V1 ′.

  Then, in the conventional configuration, it is necessary to switch the voltage applied to the backup roller 208 from the negative voltage V1 ′ to the positive voltage V2 having the opposite polarity, but in the present embodiment, from the negative voltage V1. What is necessary is just to switch to the positive voltage V2 which is the reverse polarity. In this embodiment, the switching start time to the voltage V2 is advanced by Δt compared to the conventional configuration. Accordingly, the interval L between the toner image 410 and the control toner image 420 becomes smaller than the interval L ′ between the toner image 410 ′ and the control toner image 420 ′.

  Here, the principle that the secondary transfer voltage increases as the speed of the secondary transfer process increases will be described. If the secondary transfer process is simply speeded up, the transfer current per unit time in the secondary transfer nip is insufficient, resulting in insufficient effective system resistance and insufficient transfer electric field. In this case, in order to obtain an appropriate transfer electric field, it is necessary to apply a higher secondary transfer voltage. FIG. 5 shows the relationship between process speed and maximum transfer voltage. The maximum transfer voltage referred to here is a secondary transfer voltage required when thick paper (350 gsm (Gram per Square Meter)) is used as the recording paper 115 in an environment where the temperature is 10 degrees and the humidity is 15%. FIG. 5 shows that a higher maximum transfer voltage is required as the process speed is further increased. For example, if the process speed is “60 (ppm (print per minutes))”, a maximum transfer voltage of about “5 (−kv)” is required, whereas the process speed is “ If it is “80 (ppm)”, a maximum transfer voltage of about “6.5 (−kv)” is required.

  As described above, when the maximum transfer voltage is increased in order to eliminate the shortage of the transfer electric field, the switching time for switching the polarity of the secondary transfer voltage becomes long. This longer switching time leads to an increase in the time required for the secondary transfer process, and the speed of the secondary transfer process cannot be realized. FIG. 6 shows the relationship between process speed and switching time. FIG. 6 shows that the higher the process speed, the higher the required maximum transfer voltage, and the longer the switching time. For example, when the process speed is “352 (mm / s)”, the switching time is “20 (msec)”, whereas when the process speed is “616 (mm / s)”, the switching time is “ 40 (msec) ".

  FIG. 7 shows the required switching time for each maximum transfer voltage. FIG. 7 shows the switching time required when L (the distance between the control image and the image to be printed) is 5 mm. The required switching time increases as the maximum transfer voltage decreases. It is shown. For example, if the maximum transfer voltage is “12 (−kv)”, the required switching time is “10 (msec)”, whereas the maximum transfer voltage is “6.5 (−kv)”. The necessary power source switching time becomes “20 (msec)”.

  As described above, according to the secondary transfer device 120 of the first embodiment, the negative voltage is always applied to the backup roller 108B, and the positive and negative voltages are switched and applied to the backup roller 108B ′. Even when the secondary transfer voltage is increased by shortening the distance between the toner image to be originally printed and the control toner image, or by increasing the toner image conveyance speed, Compared to this, the switching time does not increase, so that the secondary transfer process can be speeded up.

(Second Embodiment)
Next, a second embodiment of the present invention will be described. FIG. 8 shows the configuration of the secondary transfer device 120 of the second embodiment. As shown in FIG. 8, in the second embodiment, a roller 110B and a roller 2110B ′ are provided between the drive roller 724 and the drive roller 726 around which the secondary transfer belt 116 is stretched. The rollers 110B and 2110B ′ play the same role as the driving rollers 109B and 109B ′ of the first embodiment except that they do not have a function of driving the secondary transfer belt 116.

  In the second embodiment, a backup roller 108B and a backup roller 108B 'are provided between a roller 704 and a roller 706, which are a pair of roller members around which the intermediate transfer belt 107 is stretched. Unlike the first embodiment, the backup roller 108 </ b> B and the backup roller 108 </ b> B ′ do not apply tension to the intermediate transfer belt 107, and do not have a function of suspending the intermediate transfer belt 107.

  In FIG. 1, there is a gap (gap) on the upstream side in the moving direction of the recording sheet as viewed from the position where the transfer is performed by the backup roller 108B. In FIG. There is no gap on both the upstream side and the downstream side in the recording sheet moving direction. A gap on the upstream side of the recording sheet moving direction is called a pre-gap. However, if this pre-gap exists, peeling discharge may occur due to a transfer electric field during transfer, and the toner image may be disturbed. In the configuration of FIG. 8, since there is no pre-gap, the toner image is prevented from being disturbed due to the peeling discharge in the pre-gap.

  Further, in FIG. 1, there is a gap on the downstream side in the moving direction of the recording paper as viewed from the position where transfer is performed by the backup roller 108B ′, but in FIG. 8, it is viewed from the position where transfer is performed by the backup roller 108B ′. Thus, there is no gap on both the upstream side and the downstream side in the moving direction of the recording paper. The gap on the downstream side of the recording paper moving direction is called a post gap. If this post gap is present, a separation discharge may occur due to a transfer electric field at the time of transfer, and the toner image may be disturbed. . In the configuration of FIG. 8, since this post gap is not present, the disturbance of the toner image due to the peeling discharge in the pre-gap is suppressed.

  In the example of FIG. 8, the roller 704 provided upstream of the secondary transfer section and the driving roller 724 are provided so as not to face each other. Further, in the example of FIG. 8, the roller 706 provided downstream of the secondary transfer section and the driving roller 726 are provided so as not to face each other. According to this configuration, the impact at the time of taking in the recording paper is suppressed rather than providing the roller 704 and the driving roller 724 to face each other. Further, the impact at the time of discharging the recording paper 115 is suppressed as compared with the roller 706 and the driving roller 726 that are opposed to each other.

(Modification)
The present invention is not limited to the embodiment described above, and may be modified as follows. Further, the following modifications may be combined.

(Modification 1)
The magnitude of the first voltage applied when the toner image 410 is transferred by the backup roller 108B is different from the magnitude of the first voltage applied when the control toner image 420 is transferred by the backup roller 108B. It may be. For example, when the process speed is 880 (mm / s), the first voltage applied when the toner image 410 is transferred is -18 (kv), and is applied when the control toner image 420 is transferred. The first voltage is -12 (kv). The control toner image 420 is transferred to the secondary transfer belt 116 by making the absolute value of the applied voltage when transferring the control toner image 420 smaller than the absolute value of the applied voltage when transferring the toner image 410. The amount of toner when transferred is reduced. This makes it easier to transfer the control toner image to the intermediate transfer belt 107 even if the second voltage applied when the control toner image 420 is transferred back to the secondary transfer belt 116 by the backup roller 108B ′ is small. The fact that the absolute value of the second voltage may be small means that it takes less time to switch from the first voltage to the second voltage having the opposite polarity.
In each embodiment, while the positive voltage is applied to the drive roller 109B ′, no voltage may be applied to the drive roller 109B, or the applied voltage may be reduced, but the voltage is not reduced. There is no problem even if is applied. Therefore, during the period in which the intermediate transfer belt 107 on which the toner image is transferred is moving, without switching the voltage application (ON / OFF switching or increase / decrease switching) to the driving roller 109B, It is preferable to always apply a voltage. As a result, the switching time of the voltage applied to the drive roller 109B is not required in the above period, so that the secondary transfer process can be performed at a higher speed.

(Modification 2)
In each embodiment, since the number of times of switching required for the secondary transfer process is one, the two transfer rollers of the drive roller 109B and the drive roller 109B ′ are arranged side by side accordingly. Depending on the number of times of switching required for the transfer process, three or more transfer rollers may be provided side by side.

(Modification 3)
In each embodiment, the control device 102 controls the application of voltage to the driving roller 109B and the driving roller 109B ′. For example, the main control device provided in the image forming apparatus 100 may have a function of the control device 102 and may be configured to control application of voltage to the driving roller 109B and the driving roller 109B ′. . In short, as long as it has a function of controlling the application of voltage to the driving roller 109B and the driving roller 109B ′, the operation subject may be any hardware or software.

(Modification 4)
In each embodiment, the charging polarity of the toner is a positive electrode, the voltage (first voltage) applied to the driving roller 109B is a negative electrode, and the voltage (second voltage) applied to the driving roller 109B ′ is a positive electrode. The reverse of these may be used. That is, the charging polarity of the toner may be a negative electrode, the voltage (first voltage) applied to the drive roller 109B may be a positive electrode, and the voltage (second voltage) applied to the drive roller 109B ′ may be a negative electrode.

(Modification 5)
In each embodiment, an intermediate transfer belt is used as an example of a transfer body. However, the transfer body is not limited to this, and may be other than the intermediate transfer belt such as an intermediate transfer roller. In each embodiment, a transfer roller is used as an example of the first transfer unit and the second transfer unit. The transfer roller is not limited to this, and may be other than the transfer roller such as a transfer belt. In each embodiment, transfer paper is used as an example of a transfer material. Not limited to these, the transfer material may be other than transfer paper.

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 10 ... Intermediate transfer belt, 18 ... Transfer paper, 100 ... Secondary transfer device, 102 ... Control device, 104 ... First transfer roller, 106 ... Second transfer roller, 108 ... Conveyor belt, 114 ... first power source 116 ... second power source 124 ... backup roller 108B '... second transfer auxiliary roller

Claims (4)

A secondary transfer device that transfers a first toner image formed on a recording material and a second toner image formed to manage the image quality of the first toner image,
A belt-like secondary transfer member stretched by two or more rollers arranged at a position facing the transfer body across the recording material;
The first toner image transferred to the transfer body is pressed against the recording material, the second toner image transferred to the transfer body is pressed to the secondary transfer member, and the first toner image is By applying a first voltage having the same polarity as the charging polarity of the toner being formed, the first toner image is transferred from the transfer body to the recording material, and the second toner image is transferred from the transfer body to the recording medium. First transfer means for transferring to a secondary transfer member;
For the second toner image provided on the downstream side in the moving direction of the recording material from the position of the first transfer means and transferred to the secondary transfer member by the first transfer means, the transfer body And the second toner image is transferred from the secondary transfer member to the transfer body by applying a second voltage having a polarity different from the charging polarity of the toner forming the first toner image. And a second transfer unit. When viewed from the position where transfer is performed by the first transfer unit and the second transfer unit, at least one of the upstream side and the downstream side in the moving direction of the recording material, The secondary transfer device according to claim 1, wherein the secondary transfer member is in contact with the secondary transfer member. The magnitude of the first voltage applied when the first toner image is transferred by the first transfer means, and when the second toner image is transferred by the first transfer means The secondary transfer apparatus according to claim 1, wherein the magnitude of the first voltage to be applied is different. Forming means for forming a first toner image formed on the recording material and a second toner image formed for managing the image quality of the first toner image;
Primary transfer means for transferring the first toner image and the second toner image formed by the forming means to a transfer body;
The first toner image transferred to the transfer body by the primary transfer unit is transferred to a recording material, and the second toner image transferred to the transfer body by the primary transfer unit is sandwiched between the recording materials. 4. The secondary transfer according to claim 1, wherein the secondary transfer member is transferred to a secondary transfer member stretched by two or more rollers disposed at a position facing the transfer body, and then transferred to the transfer body. A transfer device;
An image forming apparatus comprising: a fixing unit that fixes the first toner image transferred by the secondary transfer device to the recording material.

Images