JP4245434B2 - Image forming apparatus - Google Patents

Description

The present invention includes first and second image carriers on which toner images are formed on the surface, and each toner image made of toner of the same polarity and formed on the first and second image carriers. The present invention relates to an image forming apparatus that obtains a recorded image by transferring the image to one side and the other side of a recording medium.

  An image forming apparatus of the above type configured as an electronic copying machine, a printer, a facsimile, or a complex machine of these is conventionally known (for example, see Patent Document 1). According to this type of image forming apparatus, a recorded image can be formed on both sides of the recording medium in a short time. At that time, the following configuration can be employed to transfer the toner images formed on the first and second image carriers to one surface and the other surface of the recording medium, respectively.

  First and second transfer members are provided along contact portions where the first and second image carriers are in contact with each other, and the first and second transfer members are provided with the first and second image carriers as compared with the second transfer member. Arranged upstream in the direction of body movement. Then, the recording medium is fed between the first and second image carriers that are in contact with each other, and the toner image on the first image carrier is acted upon by the action of one of the first and second transfer members. Is electrostatically transferred to one surface of the recording medium, and the toner image on the second image carrier is electrostatically transferred to the other surface of the recording medium by the action of the other transfer member.

According to the above configuration, the toner image can be transferred to each surface of the recording medium by passing the recording medium between the contact portions of the first and second image carriers. However, according to this configuration, the toner image electrostatically transferred to one or the other surface of the recording medium by the first transfer member is transferred onto the other or one surface of the recording medium by the second transfer member. When the image is transferred, it is electrostatically retransferred to the image carrier side, which may deteriorate the image quality of the recorded image formed on the recording medium.
JP-A-1-209470 (page 2-3, FIG. 1)

  The present invention has been made based on the above recognition, and an object of the present invention is to record a toner image transferred to a recording medium by the action of the first transfer member by the action of the second transfer member. An object of the present invention is to provide an image forming apparatus of the type described at the beginning, which effectively suppresses a problem that a toner image is re-transferred to an image carrier when a toner image is transferred to the image bearing member.

  In order to achieve the above object, according to the present invention, in the image forming apparatus of the type described at the beginning, the first and second transfer units arranged along the contact portion where the first and second image carriers are in contact with each other. A first transfer member positioned upstream of the second transfer member in the moving direction of the first and second image carriers, and one of the first and second transfer members. By the action of the transfer member, the toner image formed on the surface of the first image carrier is transferred to one surface of the recording medium sent between the first and second image carriers in contact with each other, A second image carrier on the other surface of the recording medium sent between the first and second image carriers in contact with each other by the action of the other of the first and second transfer members. And transferring the toner image formed on the surface of the first transfer member to the first transfer member. The transfer electric field formed by the first transfer member is defined as E (U), and the charge amount of toner per unit volume of the toner image transferred by the action of the first transfer member is defined as q1. When the transfer electric field is E (D) and the charge amount of the toner per unit volume of the toner image transferred by the action of the second transfer member is q2, F (U) = q1 × E (U) and F Transfer of the toner image so that the relationship between the absolute values of the forces to transfer the toner image represented by (D) = q2 × E (D) to the recording medium satisfies F (U) ≧ F (D). An image forming apparatus characterized in that conditions are set is proposed.

  2. The image forming apparatus according to claim 1, wherein a non-contact type transfer member that does not contact the first and second image carriers is used as the first and second transfer members, and toner image transfer is performed. It is advantageous to provide a charge-removing means for removing the residual charges of the first and second image carriers later.

  3. The image forming apparatus according to claim 1, wherein the first and second image carriers are endless belts wound around a plurality of support rollers, and each end in the width direction of the endless belt. A belt slip prevention rib that engages with each end face of the support roller is fixed to the back side of the portion, and the belt slip prevention rib is made of a material having a volume resistivity and a relative dielectric constant substantially equal to the endless belt. (Claim 3).

  The image forming apparatus according to any one of claims 1 to 3, wherein the second image carrier is formed of an endless belt wound around a plurality of support rollers, and is provided on one surface and the other surface. When the recording medium to which the toner image has been transferred is separated from the second image carrier, the second image carrier part is a separation part, and the support roller around which the separation part is wound It is advantageous if an application member to which a voltage of the same polarity is applied is provided, and an earth member for grounding the second image carrier is provided downstream of the application member in the moving direction of the second image carrier. (Claim 4).

  Furthermore, in the image forming apparatus according to any one of claims 1 to 3, the first image carrier is composed of an endless belt wound around a plurality of support rollers, and is provided on one surface and the other surface. When the recording medium to which the toner image is transferred is separated from the first image carrier, the first image carrier part is a separation part, and the support roller around which the separation part is wound is connected to the charging polarity of the recording medium. It is advantageous if an application member to which a voltage of the same polarity is applied is provided, and a grounding member for grounding the first image carrier is provided downstream of the application member in the moving direction of the first image carrier. (Claim 5).

  In the image forming apparatus according to claim 4 or 5, it is advantageous that the diameter of the support roller constituting the application member is set to 20 mm or less (claim 6).

  According to the present invention, the toner image transferred to the recording medium by the action of the first transfer member is retransferred to the image carrier when the toner image is transferred to the recording medium by the action of the second transfer member. It is possible to effectively suppress such problems and to form high quality images on both sides of the recording medium.

  FIG. 1 is a vertical sectional view showing an example of an image forming apparatus configured as a printer. The image forming apparatus shown here includes a plurality of photoconductors arranged in a main body housing 1, in the illustrated example, First to fourth four photosensitive members 2Y, 2M, 2C, and 2BK are provided. Toner images of different colors are formed on the respective photoreceptors. In the example shown in FIG. 1, a yellow toner image, a magenta toner image, and a cyan toner image are formed on these photoreceptors 2Y, 2M, 2C, and 2BK. And a black toner image are formed.

  Although each of the photoconductors 2Y, 2M, 2C, and 2BK shown in FIG. 1 is formed in a drum shape, an endless belt-like photoconductor that is wound around a plurality of rollers and driven to rotate can also be used. The drum-shaped photosensitive member can be constituted by, for example, a surface of an aluminum cylindrical substrate having a diameter of about 30 to 100 mm and an organic semiconductor layer that is a photoconductive substance. Photoconductive materials other than organic semiconductors can also be used.

  A first image carrier 3 configured as an intermediate transfer member is disposed opposite to the first to fourth photoconductors 2Y, 2M, 2C, and 2BK, and each of the photoconductors 2Y, 2M, 2C, and 2BK is the first. Is in contact with the surface of the image carrier 3. The first image carrier 3 shown here is constituted by an endless belt which is wound around support rollers 4, 5, 6 and 7 and is driven to rotate in the direction of arrow A. One of these support rollers is provided. A predetermined tension is applied to the first image carrier made of an endless belt by a roller or another roller. The first image carrier 3 is made of a heat-resistant belt having, for example, a resin film or rubber as a base. On the surface of the first image carrier 3, the toner images of the respective colors formed on the photoreceptors 2Y, 2M, 2C, 2BK are transferred in an overlapping manner.

  The configuration for forming a toner image on the first to fourth photoconductors 2Y, 2M, 2C, and 2BK and the configuration for transferring each toner image onto the first image carrier 3 are substantially the same. The only difference is the color of each toner image formed. Therefore, only the configuration and operation for forming a toner image on the first photoconductor 2Y and transferring the toner image onto the first image carrier 3 will be described.

  The photoconductor 2Y is rotationally driven in the clockwise direction in FIG. 1. At this time, the surface of the photoconductor is irradiated with light from the static eliminating device 8, and the surface potential of the photoconductor 2Y is initialized. The initialized photoreceptor surface is uniformly charged by the charging device 9 to a predetermined polarity, in this example, a negative polarity. The charged surface is irradiated with a light-modulated laser beam L emitted from the exposure apparatus 10, and an electrostatic latent image corresponding to writing information is formed on the surface of the photoreceptor 2Y. In the image forming apparatus shown in FIG. 1, an exposure apparatus 10 including a laser writing apparatus that emits a laser beam is used. However, an exposure apparatus having an LED array and an image forming unit can also be used.

  The electrostatic latent image formed on the photoreceptor 2Y is visualized as a yellow toner image when it passes through the developing device 11. The developing device 11 shown as an example has a developing roller 12 that carries and conveys dry toner, and the toner carried and carried by the developing roller 12 electrostatically forms an electrostatic latent image. Then, the latent image is visualized as a toner image. The toner is charged with either positive or negative polarity. In this example, it is assumed that the toner is negatively charged.

  On the other hand, on the inner side of the first image carrier 3 made of an endless belt, there is a transfer member 13 constituted by a transfer roller located opposite to the photoreceptor 2Y with the first image carrier 3 interposed therebetween, and a back surface. A contact roller 14 is disposed. The transfer member 13 and the backing roller 14 are in contact with the back surface of the first image carrier 3 to ensure an appropriate transfer nip between the photoreceptor 2Y and the first image carrier 3.

  The transfer member 13 is applied with a transfer voltage having a polarity opposite to the toner charging polarity of the toner image formed on the photoreceptor 2Y, in this example, a positive polarity. As a result, a transfer electric field is formed between the photoconductor 2Y and the first image carrier 3, and the toner image on the photoconductor 2Y is rotated in synchronization with the photoconductor 2Y. It is electrostatically transferred onto the body 3. The transfer residual toner adhering to the surface of the photoreceptor 2Y after the toner image is transferred to the first image carrier 3 is removed by the cleaning device 15, and the surface of the photoreceptor 2Y is cleaned.

  In exactly the same manner, a magenta toner image, a cyan toner image, and a black toner image are respectively formed on the second to fourth photoreceptors 2M, 2C, and 2BK, and the toner images of the respective colors are transferred to the yellow toner image. The first image carrier 3 is subjected to electrostatic transfer while being sequentially superimposed. The toner image thus formed on the first image carrier 3 is transferred to a second image carrier 16 which will be described below. The toner image transferred to the image carrier 16 is referred to as a first toner image as necessary.

  On the other hand, the above-described second image carrier 16 is arranged on the right side of the first image carrier 3. The second image carrier 16 is also constituted by an endless belt that is wound around support rollers 17, 18, 19, 20, and 21 and is driven to rotate in the direction of arrow B in synchronization with the first image carrier 3. ing. In this case, a predetermined tension is applied to the second image carrier 16 formed of an endless belt by one of the plurality of support rollers 17 to 21 or another roller. The second image carrier 16 is also formed of a heat resistant belt having a resin film or rubber as a base, for example.

  The first image carrier 3 and the second image carrier 16 are in contact with each other at a portion indicated by C in FIG. 1, and are formed on the surface of the first image carrier 3 as described above. The first toner image is electrostatically transferred to the surface of the second image carrier 16 in a manner described later. The transfer residual toner adhering to the surface of the first image carrier 3 after the first toner image is transferred to the second image carrier 16 is removed by the cleaning device 22 together with paper dust and the like. The surface of the image carrier 3 is cleaned.

  When the first toner image transferred to the second image carrier 16 moves to a predetermined position as the second image carrier 16 rotates, a plurality of toner images are transferred in the same manner as described above. Each color toner image starts to be sequentially formed on the photoreceptors 2Y, 2M, 2C, and 2BK, and these toner images are electrostatically transferred to the surface of the first image carrier 3. The toner image formed on the first image carrier 3 in this way is referred to as a second toner image as necessary.

  On the other hand, a recording medium feeding device 23 is provided at the lower part in the main body casing. The recording medium feeding device 23 exemplified here has two sheet feeding cassettes 24 and 24A in which recording media P made of transfer paper, resin sheets, and the like are stacked and accommodated, and sheet feeding for feeding the recording medium P from each sheet feeding cassette. The roller 25, 25A has one of its paper feed rollers in contact with the upper surface of the uppermost recording medium and rotates, so that the uppermost recording medium is fed out through the conveying path formed by the guide member. Then, it is conveyed to the registration roller pair 26.

The registration roller pair 26 transfers the second toner image on the first image carrier 3 and the first toner image on the second image carrier 16 in alignment with each surface of the recording medium P, respectively. The recording medium P is sent out at the timing. The recording medium sent out from the registration roller pair 26 in this way is sent between the first image carrier 3 and the second image carrier 16 that are in contact with each other, and passes therethrough. At this time, the second toner image on the first image carrier 3 is electrostatically transferred to one surface of the recording medium P in a manner described later, and the second toner image formed on the second image carrier 16 is also transferred. One toner image is electrostatically transferred to the other surface of the same recording medium. As described above, the image forming apparatus of the present example includes the first and second image carriers 3 and 16 on which toner images are formed, and the first and second image carriers 3 and 16 are provided on the surface. Each toner image made of toner of the same polarity and charged , that is, the second toner image and the first toner image are transferred to one side and the other side of the recording medium P to obtain a recorded image. It is configured.

  The recording medium P to which the first toner image and the second toner image have been transferred is transported further away from the contact portion C of the first and second image carriers 3 and 16 and passes through the fixing device 27. To do. At this time, the first toner image and the second toner image transferred to the recording medium P are fixed to the recording medium P at a time by the action of heat and pressure. The recording medium P that has passed through the fixing device 27 is discharged by the discharge roller pair 28 to the recording medium discharge portion 29 as indicated by an arrow D. In this way, a recording medium having a full color image formed on both sides is obtained.

  The surface of the first image carrier 3 after the second toner image is transferred to one surface of the recording medium P is cleaned by the cleaning device 22. Further, the transfer residual toner adhering to the surface of the second image carrier 16 after the first toner image is transferred is cleaned by the cleaning member 31 of the cleaning device 30 that is in pressure contact with the surface of the second image carrier 16. It is removed and its surface is cleaned. The removed toner is collected in a storage unit (not shown) by a toner transport unit (not shown). The cleaning member 31 is separated from the surface of the second image carrier 16 when the first toner image carried on the second image carrier 16 passes through the cleaning member 31, and the transfer residue adhered to the surface of the second image carrier 16 is removed. When the toner is removed, it contacts the surface.

  In order for both the second toner image transferred to one surface of the recording medium P and the first toner image transferred to the other surface to be a normal image, the first toner image When each toner image is formed on each photoconductor 2Y to 2BK, an electrostatic latent image of a reverse image is formed on each photoconductor, and each toner image for the second toner image is formed on each photoconductor 2Y to 2BK. However, the exposure switching is controlled by a writing controller (not shown).

  When the recording medium discharge unit 29 is arranged as shown in FIG. 1, the recording medium is discharged with the surface onto which the second toner image is transferred directly from the first image carrier 3 facing down. In order to align the page order of the recording media discharged to the recording medium discharging unit 29, the first toner image becomes the second page image, and the second toner image is A toner image may be formed on each photoconductor so that an image of the first page is obtained. In this way, even when a large number of recording media are ejected to the recording media ejecting section 29, all the page order can be aligned.

  Further, the image forming apparatus shown in FIG. 1 can form an image only on one side of the recording medium. In this case, the toner images of the respective colors formed on the respective photoconductors 2Y to 2BK are transferred onto the first image carrier 3 so as to contact the first image carrier 3 and the second image carrier 16. The toner image transferred onto the first image carrier 3 is transferred to one surface of the recording medium P fed to the part C. The recording medium that has exited the contact portion C of the first and second image carriers 3 and 16 again passes through the fixing device 27. At this time, the toner image on the recording medium P is fixed. It is discharged to the recording medium discharge unit 29.

  Next, a configuration for transferring the toner image formed on the image carriers 3 and 16 to the recording medium P will be described.

  First, first and second transfer members are arranged along the contact portion C of the first and second image carriers 3 and 16 shown in FIG. These transfer members can be configured in various forms. In the image forming apparatus shown in FIG. 1, a conductive support roller 4 that supports the first image carrier 3 and a second image carrier. One of the conductive support rollers 17 that support the body 16 constitutes the first transfer member, and the other constitutes the counter electrode of the first transfer member. Similarly, the second transfer member is constituted by one of the conductive support roller 5 that supports the first image carrier 3 and the conductive support roller 18 that supports the second image carrier 16. Depending on the direction, the counter electrode of the second transfer member is formed. Support rollers other than the support roller constituting the transfer member and the counter electrode are grounded.

  As an example of FIG. 2, the support roller 4 is configured as a first transfer member, the support roller 17 facing the support roller 17 is configured as a counter electrode, and the support roller 5 is configured as a second transfer member. An example is shown in which the support roller 18 facing this is configured as a counter electrode. The first transfer member made up of the support roller 4 is located upstream of the second support roller 5 made up of the support roller 5 in the movement direction of the first and second image carriers 3 and 16. In the example shown in FIG. 2, a positive transfer voltage is applied to the first transfer member made of the support roller 4, and a negative transfer voltage is applied to the second transfer member made of the support roller 5. The support roller 17 constituting the counter electrode of the first transfer member and the support roller 18 constituting the counter electrode of the second transfer member are grounded as shown in FIG. 2, or the first and second A voltage having a polarity opposite to the transfer voltage applied to the transfer member is applied.

  In FIG. 2, the toner particles T1 constituting the first toner image formed on the second image carrier 16 and the second toner image formed on the first image carrier 3 are constituted. Each of the toner particles T2 is schematically shown. These toner particles T1 and T2 are both negatively charged. Accordingly, the recording medium P fed between the first and second image carriers 3 and 16 that are in contact with each other is first subjected to the action of the first transfer member comprising the support roller 4 on the other surface P2. The first toner image on the second image carrier 16 is electrostatically transferred. Next, the second toner image on the first image carrier 3 is electrostatically transferred to one surface P1 of the recording medium P by the action of the second transfer member including the support roller 5.

  If a negative transfer voltage is applied to the support roller 4 constituting the first transfer member and a positive transfer voltage is applied to the support roller 5 constituting the second transfer member, first, the first transfer member The second toner image on the first image carrier 3 is transferred to one surface P1 of the recording medium P by the action, and then the first toner on the second image carrier 16 is acted on by the second transfer member. The toner image is transferred to the other surface P2 of the recording medium P.

  As described above, one of the support rollers 4 and 17 is the first transfer member, and one of the support rollers 5 and 18 is the second transfer member, and on the first image carrier 3. The second toner image formed on the recording medium P is electrostatically transferred to one surface P1 of the recording medium P, and the first toner image formed on the second image carrier 16 is transferred to the other surface P2 of the recording medium P. Thus, a transfer voltage having an appropriate polarity is applied to the first and second transfer members so as to be electrostatically transferred to each other.

  In the example shown in FIG. 1, the first and second transfer members are configured by the support roller for the first image carrier 3 or the support roller for the second image carrier 16. A transfer member made of, for example, a transfer charger, a brush, or a blade that discharges from the electrode can be used along the contact portion C of the second image carrier.

  As described above, the image forming apparatus includes the first and second transfer members disposed along the contact portion where the first and second image carriers are in contact, and the first transfer member is the first transfer member. The first and second transfer members are located upstream of the two transfer members in the moving direction of the first and second image carriers and are in contact with each other by the action of one of the first and second transfer members. The toner image formed on the surface of the first image carrier is transferred to one surface of the recording medium fed between the two image carriers, and the other of the first and second transfer members is transferred. By the action of the member, the toner image formed on the surface of the second image carrier is transferred to the other surface of the recording medium fed between the first and second image carriers in contact with each other. It is configured.

  When the first toner image formed on the first image carrier 3 is transferred to the second image carrier 16, the first image carrier 3 is formed on the first image carrier 3 so as to form an image only on one side of the recording medium. Even when the formed toner image is transferred only to one surface of the recording medium P, the first or second transfer member described above can be used. For example, when transferring the first toner image on the first image carrier 3 to the second image carrier 16 or transferring the toner image on the first image carrier 3 to the recording medium P, FIG. A negative transfer voltage is applied to the second transfer member comprising the support roller 5 shown in FIG. Alternatively, a negative transfer voltage is applied to the first transfer member composed of the support roller 4 to transfer the first toner image on the first image carrier 3 onto the second image carrier 16, or The toner image on one image carrier 3 is transferred to one surface of the recording medium P.

  Here, as described above, the second toner image on the first image carrier 3 is transferred to one surface of the recording medium P by the first and second transfer members, and the second image carrier is obtained. When the configuration in which the first toner image on 16 is transferred to the other surface of the recording medium P, the toner image on the image carrier is recorded by the action of the second transfer member as described above. When transferring to the medium, the toner image that has already been transferred to the recording medium by the first transfer member may be electrostatically returned to the image carrier and retransferred. For example, as shown in FIG. 2, a negative transfer voltage is applied to the second transfer member made of the support roller 5 to transfer the second toner image on the first image carrier 3 to one of the recording media P. When the image is transferred to the surface P1, the first toner image already transferred to the other surface of the recording medium P may be electrostatically retransferred to the surface of the second image carrier 16.

  Therefore, in the image forming apparatus shown in FIG. 2, the transfer electric field formed when a transfer voltage is applied to the first transfer member composed of the support roller 4 is E (U), and is transferred by the first transfer member. A transfer electric field formed when a transfer voltage is applied to the second transfer member composed of the support roller 5 where q1 is the charge amount of the toner per unit volume of the toner image on the second image carrier 16 to be applied. E (D), where the toner charge amount per unit volume of the toner image on the first image carrier 3 transferred by the action of the second transfer member is q2, each toner image is recorded on the recording medium. The force to be transferred to P is expressed by F (U) = q1 × E (U) and F (D) = q2 × E (D). At this time, the absolute value of both forces is F The transfer conditions are set so that (U) ≧ F (D). According to this configuration, the first toner image is first transferred from the second image carrier 16 to the other surface P2 of the recording medium P with a strong force by the first transfer member, and the toner image is recorded. The medium P is adhered to the medium P with a strong force, and the second toner image on the first image carrier 3 is then recorded by the second transfer member with a smaller or equivalent force than that of the first toner image. The toner image transferred to the other surface P2 of the recording medium P can be transferred to the second image carrier when the second toner image is transferred by the second transfer member. The trouble of retransferring to the body 16 side can be eliminated, or this can be effectively suppressed. Thereby, high-quality images can be formed on both sides of the recording medium P.

  The technical idea described above can also be applied when a configuration other than that shown in FIG. 2 is adopted. In short, the transfer electric field formed by the first transfer member is E (U) and is transferred by the action of the first transfer member. The toner charge amount per unit volume of the toner image to be transferred is q1, the transfer electric field formed by the second transfer member is E (D), and the unit of the toner image transferred by the action of the second transfer member When the charge amount of toner per volume is q2, an attempt is made to transfer a toner image represented by F (U) = q1 × E (U) and F (D) = q2 × E (D) to a recording medium. The toner image transfer conditions are set so that the relationship between the absolute values of the forces to be applied satisfies F (U) ≧ F (D).

  Each configuration described above can be widely applied to image forming apparatuses other than the image forming apparatuses shown in FIGS. For example, the image forming apparatus shown in FIG. 3 is constituted by a photoconductor composed of an endless belt in which both first and second image carriers 3 and 16 are wound around a plurality of support rollers. A toner image obtained by superimposing yellow, magenta, cyan, and black toner images is formed on 3 and 16, respectively. Are transferred to one surface and the other surface of the recording medium P fed to the toner image, and the transferred toner images are fixed by the fixing device 27.

  In the image forming apparatus shown in FIG. 4, a first toner image is formed by superimposing a plurality of toner images of different colors on a first image carrier 3 configured as a photoreceptor composed of an endless belt. The first toner image is transferred onto a second image carrier 16 configured as an intermediate transfer member composed of an endless belt, and again a second toner image composed of a superimposed toner image on the first image carrier 3. Are formed, and the second toner image and the first toner image on the second image carrier 16 are transferred to one surface and the other surface of the recording medium P.

  The image forming apparatus shown in FIG. 5 is configured as an intermediate transfer member in which the first and second image carriers 3 and 16 are both endless belts, and the first to second images are formed on the image carriers 3 and 16. The toner images of different colors formed on the four photoconductors 2Y to 2BK are transferred, and the respective toner images are transferred to one surface and the other surface of the recording medium P, respectively.

  In the recording medium shown in FIG. 6, the first image carrier 3 is constituted by a drum-shaped photoconductor, and a first toner image obtained by superimposing four color toner images on the first image carrier 3 is obtained. The first toner image is formed and transferred onto a second image carrier 16 formed of an intermediate transfer member of an endless belt. Next, as described above, a second toner image in which four color toner images are superimposed is formed on the first image carrier 3, and the second toner image and the second image carrier 16 are formed. The first toner image is transferred to one side and the other side of the recording medium P.

  In the image forming apparatus shown in FIG. 7, toner images of different colors are sequentially formed on one photoconductor 2, and each toner image is formed on a first image carrier 3 made of a drum-shaped intermediate transfer member. The images are sequentially transferred to form a first toner image on the first image carrier 3. This first toner image is transferred onto a second image carrier 16 made of an intermediate transfer member of an endless belt. Subsequently, toner images of different colors are sequentially transferred from the photoconductor 2 onto the first image carrier 3, and a second toner image is formed on the first image carrier 3. The second toner image and the first toner image on the second image carrier 16 are transferred to each surface of the recording medium P.

  The configuration described above can also be adopted in each of the image forming apparatuses shown in FIGS. Next, other specific examples and comparative examples will be described.

FIG. 8 shows first and second transfer chargers 33 and 34 along the contact portion C of the first and second image carriers 3 and 16 of the image forming apparatus shown in FIG. The specific example which has arrange | positioned 2 transfer members is shown. In this example, the support rollers 4, 5, 17, and 18 do not have a function as a transfer member. The first transfer charger 33 is located upstream of the second transfer charger 34 in the movement direction of the first and second image carriers 3 and 16, and both the transfer chargers 33 and 34 are the first and second transfer chargers 33 and 34. The image carriers 3 and 16 are positioned on opposite sides of each other. The first and second image carriers 3 and 16 are made of a polyimide belt having a surface resistivity of 10 ¹¹ Ω / □ and a volume resistivity of 10 ⁷ Ω · cm.

  A positive transfer voltage is applied to the first transfer charger 33 so as to obtain a transfer current of +300 μA, and a positive transfer voltage is applied to the second transfer charger 34 so as to obtain a transfer current of +150 μA. did. The recording medium P is fed between the first and second image carriers 3 and 16 that are in contact with each other, and the toner images on the first and second image carriers 3 and 16 are transferred to each surface of the recording medium P. Then, when each toner image was fixed on a recording medium by a fixing device, a high-quality image could be obtained.

  As a comparative example, when a transfer voltage is applied to each transfer charger so that a transfer current of +150 μA is obtained in the first transfer charger 33 and a transfer current of +300 μA is generated in the second transfer charger 34, recording is performed. Satisfactory transfer was possible only on one side of medium P.

In the image forming apparatus shown in FIG. 9, the first image carrier 3 is constituted by a photosensitive member made of an endless belt wound around a plurality of support rollers. That is, the first image carrier 3 is constituted by a belt photoreceptor in which an organic semiconductor layer as a photoconductive substance is provided on the surface of a heat-resistant (thermal deformation temperature 350 ° C. or higher) belt made of rubber. Yes. The second image carrier 16 is constituted by an intermediate transfer member of an endless belt made of polyimide having a surface resistivity of 10 ¹² Ω / □ and a volume resistivity of 10 ⁸ Ω · cm. The first image carrier 3 and the second image carrier 16 are driven in the directions of arrows A and B, respectively, and between the first image carrier portion between the support rollers 4 and 5 and the support rollers 17 and 18. The second image carrier portions are contact portions C in contact with each other.

  As in the case of FIG. 2, the support rollers 4 and 5 are configured as first and second transfer members, and the support rollers 17 and 18 that oppose the support rollers 4 and 5 are configured as counter electrodes. The support roller 4 is located upstream of the second support roller 5 in the moving direction of the first and second image carriers 3 and 16. These support rollers 4 and 5 are made of conductive rubber rollers, and the support rollers 4, 17 and 5 and 18 have a nip width of 2.5 mm and a transfer pressure of 22 N through the first and second image carriers 3 and 16, respectively. It is in pressure contact.

  The first toner image formed on the first image carrier 3 is transferred onto the second image carrier 16 by the second transfer member composed of the support roller 5 to which a negative transfer voltage is applied, This first toner image and the second toner image subsequently formed on the first image carrier 3 are applied to each surface of the recording medium P sent between the image carriers 3 and 16 in contact with each other. Transcribed. The charge polarity of the toner is negative. At that time, positive transfer is performed so that each transfer current of +50 μA is generated on the support roller 4 which is the first transfer member on the upstream side and −30 μA is generated on the support roller 5 which is the second transfer member on the downstream side. A voltage and a negative transfer voltage were applied, and the first and second toner images on the second and first image carriers 16 and 3 were transferred to one surface and the other surface of the recording medium P, respectively. Each toner image was transferred to each side of the recording medium by a fixing device, and high-quality recorded images were obtained on both sides of the recording medium.

  As a comparative example, a transfer voltage is applied to the upstream support roller 4 and the downstream support roller 5 shown in FIG. 9 so that a transfer current of +30 μA and −50 μA is generated. When the transfer operation was performed so that F (D) ≧ F (U), satisfactory transfer could be performed only on one side of the recording medium.

  By the way, as shown in FIG. 8, the first and second transfer members and the counter electrodes 35 and 36 are non-contact type transfer members that do not contact the first and second image carriers 3 and 16. If used, large charges remain on the first and second image carriers 3 and 16 after transfer of the toner image, which may adversely affect the image quality of the toner image to be formed next on these image carriers. is there. Therefore, in this case, it is preferable to provide a charge eliminating means for removing the residual charges on the first and second image carriers 3 and 16 after the toner image is transferred. In the example shown in FIG. 8, the residual charges are removed by grounding the first and second image carriers 3 and 16.

  Further, in the image forming apparatus shown in FIGS. 10 and 11, the first and second image carriers 3 and 16 are constituted by an intermediate transfer member made of an endless belt made of polyimide. A first transfer member made of the first transfer charger 33 is arranged on the upstream side of the contact portion C, and a second transfer member made of the transfer charger 34 is arranged on the downstream side thereof. The transfer chargers 33 and 34 are not in contact with the first and second image carriers 3 and 16. Using these transfer chargers 33 and 34, the second toner image formed on the first image carrier 3 is transferred to one of the recording media P in the same manner as described above with reference to FIG. The first toner image formed on the second image carrier 16 was transferred to the other surface of the recording medium P. At that time, in the image forming apparatus shown in FIG. 10, the first image carrier 3 is neutralized by the neutralization means comprising the corona discharger 37, and the second image carrier 16 is rendered by the neutralization means comprising the support roller 20. It is configured to remove static electricity. Further, in the image forming apparatus shown in FIG. 11, the first image carrier 3 is neutralized by the neutralizing means comprising the neutralizing brush 38, and the second image carrier 16 is neutralized by the neutralizing means comprising the neutralizing blade 41. It is configured. With this configuration, it is possible to remove the charge remaining on the first and second image carriers 3 and 16 for each transfer, and to obtain continuous and good double-sided images.

  In each of the image forming apparatuses described above, when the first and second image carriers 3 and 16 are endless belts wound around a plurality of support rollers, as shown in FIG. When the belt slip prevention rib 39 that engages with each end surface of the support roller R shown in FIG. 13 is fixed to the back side of each end portion in the width direction, the endless belt is moved in the axial direction during operation of the endless belt. We can prevent approach. At that time, it is preferable that the belt slip prevention rib 39 is made of a material having a volume resistivity and a relative dielectric constant substantially equal to those of the first or second image carrier 3 or 16 made of an endless belt. For example, the first and second image carriers 3 and 16 made of an endless belt and the belt slip prevention rib 39 fixed thereto are integrally formed of polyimide. As a result, a transfer current of the same level as that of the first and second image carriers 3 and 16 can also flow through the belt slip prevention rib 39, and the surface of the image carriers 3 and 16 corresponding to the rib 39 is applied. Also, a toner image can be formed. In the example shown in FIG. 13, a toner image can be formed over the entire width W of the first and second image carriers 3 and 16 formed of endless belts, and the image carriers can be used effectively.

  FIG. 14 is an explanatory diagram showing a part of the image forming apparatus shown in FIG. The recording medium P on which the toner image is transferred from the first and second image carriers 3 and 16 to one surface and the other surface is separated from the second image carrier 16 and is the fixing device 27 shown in FIG. At this time, the recording medium P may not be separated from the second image carrier 16 due to the electrostatic force due to the residual charge of the second image carrier 16 and the charged charge of the recording medium P. Therefore, a voltage having the same polarity as the charging polarity of the recording medium P is applied to the support roller 19 around which the recording medium P is separated from the second image carrier 16 by the power source 40, thereby recording the recording medium. It is preferable to electrostatically repel P from the second image carrier 16 to efficiently separate the recording medium P from the second image carrier 16 to prevent the recording medium from jamming. At that time, the support roller 20 on the downstream side of the support roller 19 in the moving direction of the second image carrier is grounded so that no charge remains on the second image carrier 16. As described above, in this example, the support roller 20 constitutes a grounding member that neutralizes the second image carrier 16, but another grounding member may be provided.

  As described above, the second image carrier is composed of an endless belt wound around a plurality of support rollers, and the recording medium on which the toner image is transferred to one surface and the other surface is the second image carrier. When the second image carrier part away from the separation unit is a separation unit, the support roller around which the separation unit is wound is configured as an application member to which a voltage having the same polarity as the charging polarity of the recording medium is applied. If a grounding member for grounding the second image carrier is provided downstream of the member in the moving direction of the second image carrier, the recording medium is wound around the second image carrier and causes a jam. Can be prevented.

  The configuration described above can also be applied to the first image carrier 3. That is, the first image carrier is composed of an endless belt wound around a plurality of support rollers, and the recording medium on which the toner image is transferred to one surface and the other surface is separated from the first image carrier. When the first image carrier portion is a separation portion, the support roller around which the separation portion is wound is configured as an application member to which a voltage having the same polarity as the charging polarity of the recording medium is applied. If a grounding member for grounding the first image carrier is provided on the downstream side in the moving direction of the first image carrier, it is possible to prevent the recording medium from being wound around the first image carrier and causing a jam. .

  Further, when the diameter of the support roller constituting the application member of each configuration described above is set to 20 mm or less, particularly 16 mm or less, the recording medium P is separated from the second image carrier 16 or the first image by curvature separation. Separation from the image carrier 3 can be performed more stably, and jamming of the recording medium can be more effectively prevented.

1 is a cross-sectional view illustrating an example of an image forming apparatus. FIG. 6 is an explanatory diagram showing a state in which toner images are transferred from a first image carrier and a second image carrier to a recording medium. It is the schematic which shows the other example of an image forming apparatus. It is the schematic which shows the other example of an image forming apparatus. It is the schematic which shows the other example of an image forming apparatus. It is the schematic which shows the other example of an image forming apparatus. It is the schematic which shows the other example of an image forming apparatus. It is explanatory drawing which shows the example in which the 1st and 2nd transfer member consists of transfer chargers. FIG. 3 is an explanatory diagram showing an example in which the first image carrier is made of a photoconductor. It is explanatory drawing which shows the other example of an image forming apparatus. It is the schematic which shows another example of an image forming apparatus. FIG. 3 is a perspective view showing the back side of the first and second image carriers made of an endless belt. It is a fragmentary sectional view which shows the relationship between the endless belt shown in FIG. 12, and the support roller which supports this. It is explanatory drawing which shows the example by which one support roller for 2nd image carriers was comprised as an application member.

Explanation of symbols

3 First image carrier 4, 5, 6, 7, 17, 18, 19, 20, 21 Support roller 16 Second image carrier 39 Belt misalignment prevention rib C Contact portion P Recording medium P1 One side P2 The other Side T1, T2 toner

Claims (6)

The first and second image carriers on which toner images are formed are formed on the surface, and each toner image made of toner of the same polarity formed on the first and second image carriers is recorded on the recording medium. In an image forming apparatus that obtains a recorded image by transferring to one side and the other side,
The first and second transfer members are disposed along contact portions where the first and second image carriers are in contact with each other, and the first transfer member has a first transfer member and a second transfer member that are more than the first transfer member. It is located between the first and second image carriers that are in contact with each other by the action of one of the first and second transfer members, which is located upstream in the movement direction of the second image carrier. The toner image formed on the surface of the first image carrier is transferred to one surface of the recorded recording medium, and the first and second transfer members are in contact with each other by the action of the other transfer member. The toner image formed on the surface of the second image carrier is transferred to the other surface of the recording medium fed between the first and second image carriers, and the first transfer The transfer electric field formed by the member is E (U), and is transferred by the action of the first transfer member. The charge amount of toner per unit volume of the toner image is q1, the transfer electric field formed by the second transfer member is E (D), and the unit volume of the toner image transferred by the action of the second transfer member A toner image represented by F (U) = q1 × E (U) and F (D) = q2 × E (D) is transferred to the recording medium when the charge amount of the toner per unit is q2. An image forming apparatus, wherein a toner image transfer condition is set so that a relationship between absolute values of force is F (U) ≧ F (D). As the first and second transfer members, non-contact type transfer members that do not contact the first and second image carriers are used, and the residual charges of the first and second image carriers after the transfer of the toner image are used. The image forming apparatus according to claim 1, further comprising a charge removing unit for removing the toner. The first and second image carriers are composed of endless belts wound around a plurality of support rollers, and are engaged with the end surfaces of the support rollers on the back side of each end in the width direction of the endless belt. The image forming apparatus according to claim 1, wherein a belt slip prevention rib is fixed, and the belt slip prevention rib is made of a material having a volume resistivity and a relative dielectric constant substantially equal to the endless belt. The second image carrier is composed of an endless belt wound around a plurality of support rollers, and a recording medium having a toner image transferred to one surface and the other surface is separated from the second image carrier. When the second image carrier portion is a separation portion, the support roller around which the separation portion is wound is configured as an application member to which a voltage having the same polarity as the charging polarity of the recording medium is applied. 4. The image forming apparatus according to claim 1, wherein a grounding member for grounding the second image carrier is provided on the downstream side in the moving direction of the second image carrier. The first image carrier is composed of an endless belt wound around a plurality of support rollers, and a recording medium having a toner image transferred to one surface and the other surface is separated from the first image carrier. When the first image carrier portion is a separation portion, the support roller around which the separation portion is wound is configured as an application member to which a voltage having the same polarity as the charging polarity of the recording medium is applied. 4. The image forming apparatus according to claim 1, wherein a grounding member for grounding the first image carrier is provided on the downstream side in the moving direction of the first image carrier. 5. 6. The image forming apparatus according to claim 4, wherein a diameter of a support roller constituting the application member is set to 20 mm or less.

Images