JP5163107B2 - Belt transfer device and image forming apparatus using the same - Google Patents

Description

  The present invention relates to a belt transfer device and an image forming apparatus using the same.

Among image forming apparatuses such as electrophotographic systems, the type that transports the recording material by adsorbing it to the transport belt uses a high-resistance transport belt, and the recording material is peeled off from the transport belt after transfer to the recording material. For the purpose of facilitating or preventing unnecessary charge accumulation on the conveyor belt, there is known a device provided with a charge eliminating means at a post-transfer site or a peeling site so as to attenuate the accumulated charge of the conveyor belt itself (for example, (See Patent Documents 1 and 2).
Japanese Patent Application Laid-Open No. H10-228561 discloses a method of removing electricity from one side or both sides of a conveyance belt at at least one location between adjacent photoconductors. Japanese Patent Application Laid-Open No. 2004-228561 discloses a method of performing static elimination on the downstream side of the transfer unit.

On the other hand, in an apparatus that uses an intermediate transfer belt that temporarily holds a toner image and then transfers the toner image to a recording material instead of a conveyance belt that conveys the recording material, a technique for suppressing charge attenuation on the intermediate transfer belt is disclosed. (For example, see Patent Documents 3 to 5).
Patent Document 3 discloses a technique in which a leakage prevention roller is brought into contact with the intermediate transfer belt on the back side of the intermediate transfer belt before and after the primary transfer roller, and the charge transfer of the intermediate transfer belt is suppressed by applying a bias from a power source. It is disclosed. Further, in Patent Document 4, rollers that contact the intermediate transfer belt are provided before and after the primary transfer unit, and these rollers are grounded via a resistor, so that the charge attenuation at the roller is less than that directly grounded. A technique is disclosed in which is made small. Further, Patent Document 5 provides a potential holding means for holding the charging potential of the back surface of the belt on the contact member in contact with the back surface of the intermediate transfer belt after the primary transfer, or a static elimination preventing means for preventing the charge of the belt from being removed. It is disclosed.

JP-A-9-96966 (Example, FIG. 1) JP 2001-331014 A (Embodiment of the Invention, FIG. 3) JP-A-5-341669 (Example, FIG. 1) Japanese Patent Laid-Open No. 3-192281 (Example, FIG. 1) JP 2000-298408 A (Embodiment of the Invention, FIG. 3)

  The technical problem of the present invention is that when the recording material is conveyed by the belt member, the discharge charge on the belt member after the transfer is suppressed, so that the recording material can be conveyed by the belt member without using a discharging means. The purpose is to ensure the contradictory performance of peelability.

In other words, the invention according to claim 1 is a belt that is provided facing a plurality of image holding members that hold toner images and that transfers the toner image on the image holding member onto the recording material while conveying the recording material. A surface resistivity of 10 ¹⁰ Ω / □ or more and 10 ¹⁴ Ω / □ or less, which is a transfer device, circulates by being stretched by a plurality of stretching members and electrostatically conveys a recording material at a part of the outer peripheral surface. An endless belt member, a plurality of transfer members that are provided on the inner peripheral surface side corresponding to the recording material conveyance surface of the belt member and transfer a toner image to the recording material on the recording material conveyance surface, and at least the belt member provided between the transfer member of the inner, comprising: a charge holding member for holding the charge of the recording material conveying surface of the belt member or a recording material capable of adsorption level, and the charge holding member is made of a dielectric material, From the transfer member upstream in the recording material conveyance direction It has a charge holding surface extending along the back side of the belt member toward the transfer member on the flow side, and the induced charge is electrostatically induced on the charge holding surface by the charge on the recording material conveyance surface of the belt member. In the belt transfer device, the charge holding surface is disposed so as to face the inner peripheral surface of the belt member so that a proximity distance to the belt member is 3 mm or less .

According to a second aspect of the present invention, in the belt transfer apparatus according to the first aspect, the charge holding member is provided so as to extend along the inner peripheral surface of the belt member immediately after the transfer member on the upstream side in the recording material conveyance direction. It is a transfer device.
The invention according to claim 3 is the belt transfer apparatus according to claim 1, wherein the charge holding member is provided in an electrically floating state .
According to a fourth aspect of the present invention, in the belt transfer device according to the first aspect, at least a support frame made of a synthetic resin that supports the transfer member is provided on the inner peripheral surface side of the belt member, and the charge holding member is The belt transfer device is constituted by a part of the support frame.
According to a fifth aspect of the present invention, in the belt transfer apparatus according to the first aspect, a tension is provided without arranging the charge holding member at a position adjacent to the downstream side of the transfer member located on the most downstream side in the recording material conveyance direction. A belt transfer device provided with a frame member.
According to a sixth aspect of the present invention, in the belt transfer apparatus according to the first aspect, the charge holding member is a belt transfer apparatus disposed at an upstream side portion in the recording material conveyance direction between the transfer members.

The invention according to claim 7 is the belt transfer apparatus according to claim 1, wherein the belt member is stretched by two stretch members.
The invention according to claim 8 is the belt transfer apparatus according to claim 7 , wherein at least one of the two stretching members is grounded.
According to a ninth aspect of the present invention, in the belt transfer device according to the seventh aspect , the tension member on the most downstream side in the recording material conveying direction of the two tension members is constituted by a roll-shaped member having an outer diameter of 20 mm or less. Belt transfer device.

A tenth aspect of the present invention is a belt according to any one of the first to ninth aspects, wherein a plurality of image carriers that are rotatably provided and hold toner images, and the belts that are disposed to face these image carriers. An image forming apparatus including a transfer device.
According to an eleventh aspect of the present invention, in the image forming apparatus according to the tenth aspect , the rotation speed of the plurality of image holding members is set larger than the circulation speed of the belt member.

According to the first aspect of the present invention, when the recording material is conveyed by the belt member, the discharge charge on the belt member after transfer can be suppressed, and the discharge time constant τ of the belt member can be kept large. Without using it, it is possible to secure the contradictory performances of the transportability and peelability of the recording material on the belt member. In particular, according to the present invention, the induced charge due to the charge of the belt member by the charge holding member is effectively generated, and the discharge charge at the belt member is effectively suppressed.
According to the second aspect of the present invention, the charge attenuation of the belt member after transfer can be suppressed early, as compared with the case without this configuration, the charge attenuation amount from the belt member can be kept small, The adsorption power for the recording material can be improved.
According to the third aspect of the present invention, inductive charges can be generated more stably than when the present configuration is not provided .
According to the fourth aspect of the present invention, compared to the case where the present configuration is not provided, by configuring the support frame body as a part, a separate member is not used as the charge holding member, and the device configuration is simplified. And member reduction.
According to the fifth aspect of the present invention, since the charge holding member is not provided, the charge attenuation of the belt member is made faster than in the case where the charge holding member is provided, and the adsorptivity of the recording material on the belt member is increased. As soon as it is damaged, the recording material can be easily peeled off from the belt member.
According to the invention of claim 6 , by not providing the charge holding member on the downstream side between the transfer members, the charge holding effect on the belt member can be reduced, and the transfer conditions on the transfer member can be stabilized. Will be able to.

According to the seventh aspect of the present invention, the configuration of the belt transfer apparatus itself can be reduced in size and simplified as compared with the case where the present configuration is not provided.
According to the eighth aspect of the present invention, the charge accumulation of the belt member can be stabilized and the adsorbability of the recording material by the belt member can be maintained as compared with the case where this configuration is not provided, and the recording material transportability is maintained. Can be stabilized.
According to the ninth aspect of the present invention, the recording material is peeled off from the belt member at this portion by increasing the curvature of the tension member installed on the most downstream side as compared with the case without this configuration. Will be made easier.
According to the tenth aspect of the present invention, there is provided an image forming apparatus capable of ensuring good performance with respect to transportability and releasability of a recording material when the recording material is transported by a belt member and having good color registration. Can be provided.
According to the eleventh aspect of the present invention, the recording material on the belt member can be used even in the type of the recording material and the environmental conditions in which the adsorptive power to the belt member is weak in the image forming apparatus as compared with the case without this configuration. Therefore, the color registration can be kept good.

First, an outline of an embodiment model to which the present invention is applied will be described.
Outline of Embodiment Model FIG. 1 shows an outline of a belt transfer apparatus according to an embodiment model embodying the present invention. Here, one of the typical models of the belt transfer device is, as shown in FIG. 1, provided with a plurality of image carriers 1 (1a, 1b) for forming and holding toner images and having a recording material 2 disposed thereon. A belt transfer device that transfers a toner image on the image holding member 1 onto the recording material 2 while being conveyed, and is stretched around a plurality of stretching members 4 (4a, 4b) and circulated. The endless belt member 3 having a surface resistivity of 10 ¹⁰ Ω / □ or more and 10 ¹⁴ Ω / □ or less for electrostatically adsorbing and transporting the recording material 2 at the portion, and an inner portion corresponding to the recording material transport surface of the belt member 3 A belt member provided between a plurality of transfer members 5 (5a, 5b) provided on the peripheral surface side and transferring a toner image to the recording material 2 on the recording material conveying surface and at least the transfer member 5 in the belt member 3. 3 Keep the charged charge on the recording material transport surface at or above the recording material adsorbable level. A charge holding member 6 includes a charge holding member 6 is composed of a dielectric material, along the backside of the belt member 3 toward the transfer member 5b on the downstream side from the recording material conveyance direction upstream side of the transfer member 5a The charge holding surface is opposed to the inner peripheral surface of the belt member 3 to such an extent that induced charge is electrostatically induced on the charge holding surface by the charged charge on the recording material conveying surface of the belt member 3. The belt member 3 is arranged in the proximity so that the proximity distance to the belt member 3 is 3 mm or less .

Here, the tension member 4 may be a roll-shaped member or a belt-shaped member. Further, the transfer member 5 may be a roll-shaped member or a member using corona discharge, and the number of transfer members 5 should be equal to the number of corresponding image carriers 1. That's fine.
The charge holding member 6 may be provided at least on the upstream side between the transfer members 5 (5a and 5b), and may be provided across the downstream side. Further, the charge holding member 6 may be provided on the upstream side of the transfer member 5a on the most upstream side or on the downstream side of the transfer member 5b on the most downstream side. It is preferable not to provide it on the upstream side of the transfer member 5a on the side or on the downstream side of the transfer member 5b on the most downstream side. Further, the length of the charge holding member 6 is not particularly limited, and may be any length as long as the recording material transportability of the belt member 3 can be ensured, and is usually 1/4 between the adjacent transfer members 5 (5a, 5b). It is formed with the above length.

The “proximity arrangement” in the present embodiment model is preferably arranged so that the charge holding member 6 does not come into contact with the belt member 3, but may slightly vary depending on the fluctuation of the circulating belt member 3. This means that it is arranged at a distance that includes the possibility of contact.
Thus, by providing the charge holding member 6, the discharge charge from the belt member 3 after transfer can be suppressed and the discharge time constant τ can be lengthened, and the adsorbability of the belt member 3 to the recording material 2 can be increased. It becomes possible to maintain the recording material for a long time, and it is possible to maintain good recording material transportability by the belt member 3.

Further, since the surface resistivity of the belt member 3 is set to 10 ¹⁰ Ω / □ or more and 10 ¹⁴ Ω / □ or less, both characteristics of the belt member 3 which are contradictory to the conveyance property and the releasability of the recording material 2 are obtained. It becomes possible to keep good. If the surface resistivity is smaller than this value, the charge retention in the belt member 3 is insufficient, the adsorption performance of the recording material 2 is lowered, and the transportability is impaired, while the surface resistivity is reduced. If it is larger than this value, the adsorption performance is sufficiently ensured, but the peelability is impaired.

In order to ensure the effect of the charge holding member 6 as described above, the charge holding member 6 extends along the inner peripheral surface of the belt member 3 immediately after the transfer member 5a on the upstream side in the recording material conveyance direction. It is preferable to be provided. By providing it immediately after the transfer member 5a, the charge amount of the belt member 3 charged by the transfer can be maintained at a high level, and the adsorption performance of the recording material 2 can be easily secured. Needless to say, “immediately after” is a position that does not affect the transfer area of the transfer member 5.
Furthermore, the charge holding member 6 is preferably provided in an electrically floating state. As a result, the attenuation of the charge itself induced in the charge holding member 6 can be suppressed, and the charge attenuation in the belt member 3 facing the charge holding member 6 can be further suppressed. Stable charge retention is possible. If the charge holding member 6 is grounded, the charge induced in the charge holding member 6 may be attenuated, and the charge stabilization of the belt member 3 may be impaired.

In addition, from the viewpoint of improving the charge holding effect (discharge suppressing effect) on the belt member 3 by the charge holding member 6 as described above, the charge holding member 6 needs to be arranged at 3 mm or less from the belt member 3. . If the charge holding member 6 is spaced apart from the belt member 3 so as to exceed 3 mm, the induced charge generated in the charge holding member 6 due to the charge of the belt member 3 becomes too small, and the effective charge holding effect is impaired. Become.
From the viewpoint of easily forming the charge holding member 6, a support frame made of synthetic resin that supports at least the transfer member 5 is provided on the inner peripheral surface side of the belt member 3. It is preferable that it is constituted by a part of the support frame. In this way, by integrally forming the charge holding member 6 with a synthetic resin, the charge holding member 6 can be easily manufactured using a molding technique using a mold, and it is possible to easily achieve uniform dimensions and stabilization of performance. become able to.
Further, from the viewpoint of keeping the belt potential higher, the charge holding member 6 is preferably arranged at the upstream side portion in the recording material conveyance direction between the transfer members 5 (5a, 5b). The sheet adsorbability up to 5 can be maintained, and the shift of the sheet can be suppressed.

On the other hand, from the viewpoint of facilitating the peelability of the recording material 2 from the belt member 3 in the belt transfer device, the charge holding member is located at a position adjacent to the downstream side of the transfer member 5 located on the most downstream side in the recording material conveyance direction. It is preferable to provide the tension member 4b without disposing 6.
Further, from the viewpoint of simplifying the device configuration of the belt transfer device itself, the belt member 3 is preferably stretched by the two stretch members 4a and 4b. From the viewpoint of stabilizing charge accumulation, it is preferable that at least one of the two stretching members 4a and 4b is grounded. According to this, the charge accumulated in the belt member 3 can be discharged and refreshed with respect to the circulating belt member 3, and the amount of accumulated charge in the belt member 3 after transfer can be made substantially constant. It also becomes.
Further, from the viewpoint of facilitating the peeling of the recording material 2 from the belt member 3, the stretching member 4b on the most downstream side in the moving direction of the recording material 2 is a roll having an outer diameter of 20 mm or less among the two stretching members 4a and 4b. It is preferable to be comprised with the member. Thus, by reducing the outer diameter, the curvature of the belt member 3 at the peeling site where the recording material 2 peels from the belt member 3 can be increased, and the peeling can be easily performed.

  As an image forming apparatus using the belt transfer device of the present embodiment model, a plurality of image holding bodies 1 (1a, 1b) which are rotatably provided and form and hold toner images, and these image holding bodies. Belt transfer device disposed opposite to the belt transfer device 1, and the belt transfer device described above may be used as the belt transfer device. Further, in such an image forming apparatus, when a recording material type having a weak adsorbing force is used as the recording material 2, for example, the adsorbing performance with respect to the recording material 2 with the belt member 3 under a high humidity environment condition is ensured. From the viewpoint, it is preferable that the rotational speed of the plurality of image carriers 1 is set to be larger than the circulation speed of the belt member 3. As described above, by increasing the rotational speed of the image carrier 1, a force in the direction of pressing toward the belt member 3 is applied to the recording material 2 in the direction to be peeled from the belt member 3. The adsorption force of the member 3 can be improved. The number of the image holding members 1 is not particularly limited as long as it is plural, but usually four pieces are used for forming a full-color image.

Hereinafter, the present invention will be described in more detail based on embodiments shown in the accompanying drawings.
Embodiment FIG. 2 shows an embodiment of an image forming apparatus to which the belt transfer apparatus of the present embodiment model is applied. In the figure, in the image forming apparatus according to the present embodiment, a recording material supply unit 11 for supplying a recording material is provided in a lower portion of the apparatus housing 10 so as to be able to be drawn, and above the recording material supply unit 11, Image forming engines 20 (20a to 20d) for forming toner images of four colors of yellow (Y), magenta (M), cyan (C), and black (K) on a recording material are arranged linearly in the vertical direction. Is.
A fixing device 14 for fixing the toner image formed on the recording material by the image forming engine 20 is provided above the image forming engine 20, and the recording material fixed by the fixing device 14 is further provided. Is provided on a part of the upper surface of the apparatus housing 10 with a recording material receiving receptacle 10a which is discharged from the apparatus housing 10 and stored therein.

  Further, the recording material is electrostatically adsorbed and conveyed between the recording material supply unit 11 in the apparatus housing 10 and the fixing device 14 at a position facing the four image forming engines 20a to 20d. A belt transfer device 30 configured to be peeled off at a predetermined peeling site is provided.

  In the present embodiment, the image forming engine 20 is electrostatically connected to a process cartridge 21 capable of forming each color toner image, and a photoconductor 22 provided behind the process cartridge 21 and holding the toner image in the process cartridge 21. For example, a laser exposure device 24 for forming a latent image, and a transfer roll 27 provided at a position facing the photosensitive member 22 in the process cartridge 21 in a belt transfer device 30 to be described later. Around the photosensitive member 22 in the process cartridge 21, a charging roll 23 for charging the photosensitive member 22, a developing roll 25 for visualizing the electrostatic latent image formed on the photosensitive member 22 with toner, and A toner supply roll 26 that supplies toner to the developing roll 25 is provided.

  Further, the recording material supply unit 11 in the present embodiment has a supply cassette 11a in which a recordable recording material is accommodated, and in the vicinity of the downstream end portion of the supply cassette 11a in the recording material conveyance direction, the supply cassette 11a. A separating mechanism 12 is provided for unloading and feeding recording materials one by one from 11a. In this winding mechanism 12, the recording material fed from the supply cassette 11a using the pickup roll 12a is rolled by the action of the feed roll 12b and the retard roll 12c, and only the uppermost one recording material is on the downstream side. It is to be sent out.

On the upstream side of the belt transfer device 30, there is a registration roll 13 that once regulates the positioning of the recording material to be transported and then transports the recording material whose positioning is regulated at a predetermined timing to the belt transfer device 30 side. Is provided.
On the other hand, the fixing device 14 includes, for example, a heating roll 14a and a pressure roll 14b so that the toner image is sufficiently fixed. Further, a discharge roll 15 for discharging the recording material onto the recording material accommodation receiver 10a is provided facing the opening of the apparatus housing 10 on the downstream side of the fixing device 14 in the recording material conveyance direction. The discharge roll 15 performs a reversing operation as necessary to enable reversal conveyance for image formation on both sides of the recording material.

The recording material conveyance path in the present embodiment is a normal conveyance path 41 where the recording material conveyed from the supply cassette 11a reaches the discharge roll 15 via the registration roll 13, the belt transfer device 30, and the fixing device 14. The recording material reversed by the discharge roll 15 is configured by a return conveyance path 42 from which the recording material is returned and conveyed to the registration roll 13 through a path different from the normal conveyance path 41.
Further, in the present embodiment, a part of the return conveyance path 42 is also provided inside the recording material supply unit 11. The normal conveyance path 41 and the return conveyance path 42 are appropriately provided with conveyance members (such as a conveyance roll and a conveyance guide) for ensuring the conveyance of the recording material.

Next, the belt transfer device 30 that is a characteristic point of the present embodiment will be described.
As shown in FIG. 3, the belt transfer device 30 in the present embodiment is stretched around two stretch rolls 32 and 33 having an outer diameter of 20 mm, and circulates, for example, using the upper stretch roll 33 as a drive roll. A conveying belt 31 as an endless belt member having a surface resistivity of 10 ¹⁰ Ω / □ or more and 10 ¹⁴ Ω / □ or less for electrostatically adsorbing and conveying a recording material at a part of the outer peripheral surface; A transfer roll 27 provided on the inner peripheral surface side corresponding to the recording material conveyance surface, a support frame 35 provided in the conveyance belt 31 and supporting at least the transfer roll 27, and recording on the recording material conveyance surface of the conveyance belt 31. A charging device 34 for electrostatically adsorbing the recording material on the conveying belt 31 provided at a position facing the stretching roll 32 at the upstream end in the conveying direction of the material with the conveying belt 31 in between; Not A cleaning member 36 that is provided so as to press the conveyor belt 31 toward the support frame 35 at a downstream position in the circulation direction of the conveyor belt 31 from the stretching roll 33 on the material conveying surface and that cleans the conveyor belt 31. Has been.

The support frame 35 in the present embodiment is formed of a member that is injection-molded using, for example, a polymer alloy of polycarbonate resin and ABS resin. Further, the support frame 35 has a surface projecting toward the inner peripheral surface so as to be disposed close to and opposed to the inner peripheral surface of the recording material conveyance surface of the conveyance belt 31 at a downstream portion adjacent to the transfer roll 27. On the other hand, a side protrusion surface 35 a is formed, and a back surface protrusion surface 35 b that protrudes toward the non-recording material transport surface side of the transport belt 31 is formed at a portion corresponding to the transfer roll 27 and an upstream portion adjacent to the transfer roll 27. Yes. Further, the support frame 35 is insulative and is in a so-called float state without being connected to a power source or grounded. Note that such a protruding surface is not provided on the upstream side of the most upstream transfer roll 27a or the downstream side of the most downstream transfer roll 27d.
The surface-side protruding surface 35 a of the support frame 35 is formed with a length of about 1/3 of the length between the adjacent transfer rolls 27, and the surface thereof is substantially parallel to the transport belt 31. The surface-side protruding surface 35a functions as a charge holding surface of the charge holding member.
The conveyance belt 31 has a surface resistivity so that it can be realized without providing a static eliminating member for both the opposite characteristics of the conveyance property of the recording material on the conveyance belt 31 and the releasability of the recording material from the conveyance belt 31. 10 ¹⁰ to 10 ¹⁴ Ω / □.

  Further, the charging device 34 provides a good electrostatic attracting property to the conveyor belt 31 by applying a predetermined charging bias from a bias power source (not shown) between the stretching roll 32 grounded as a backup roll. By charging with the charging device 34, the conveyed recording material is attracted onto the conveying belt 31, so that the conveying of the recording material by the conveying belt 31 can be started.

  Next, the operation on the recording material conveyed on the conveyance belt 31 when such a belt transfer device 30 is used will be described. 4A and 4B are schematic views showing the charge state of the transport belt 31 after being transferred by the transfer roll 27. FIG. 4A shows a model in the present embodiment, and FIG. 4B shows a surface side protruding surface 35a as a comparative model. The model without.

  When the toner to be used is a negatively charged toner, a transfer bias is applied between the photoconductor 22 and the transfer roll 27 in a direction in which the transfer roll 27 side is a positive polarity side. As described above, when transfer is performed at a transfer portion that is a region where the photoconductor 22 and the transfer roll 27 face each other, the transfer belt 31 is charged immediately after the transfer portion by the transfer bias at that time, for example, as shown in the figure. After that, charge is accumulated. The electric charge accumulated in the conveyance belt 31 gradually attenuates due to charge dispersion, recombination, etc. inside the conveyance belt 31, but in this embodiment, as shown in FIG. Since the surface-side protruding surface 35a of the support frame 35 serving as a charge holding member is disposed close to the transport belt 31, an induced charge is generated on the surface-side protruding surface 35a side due to the charge of the moving transport belt 31. As a result, the generated induced charges can suppress the movement of charges that attempt to disperse or recombine in the transport belt 31, for example, and as a result, the discharge charge amount ( Attenuating charge amount) is suppressed, and the discharge time constant τ of the conveyor belt 31 can be kept large. Therefore, the recording material adsorption force by the conveyance belt 31 can be kept high, and the color of the image transferred onto the recording material can be suppressed by suppressing the deviation of the recording material conveyed by the conveyance belt 31. The occurrence of image quality defects such as shifts can be suppressed.

On the other hand, when the transport belt 31 is moved as it is after the transfer as in the comparative model of FIG. 4B, the charge amount of the transport belt 31 is gradually dispersed and recombined and attenuated. The recording material adsorption force on the belt 31 is reduced. For this reason, the recording material conveyed by the conveying belt 31 is likely to be displaced, and image quality defects such as color displacement are likely to occur.
In order to maintain such a recording material adsorption force high, the high-resistance conveyance belt 31 may be used in order to increase the discharge time constant τ of the conveyance belt 31, but when a high-resistance one is used. When the recording material is peeled off from the conveyance belt 31, it becomes difficult, and installation of a charge removal member or the like is required. Such a phenomenon is particularly remarkable when thin paper is used as a recording material. In the case of thin paper, even if the recording material adsorption force is small, it is difficult to cause a shift, but peeling is more difficult. Because. Further, the high-resistance transport belt 31 may cause unnecessary charge accumulation.

  That is, in the present embodiment, as shown in FIG. 3, the recording material adsorbed on the conveying belt 31 by the charging device 34 is sequentially transferred from the transfer portion (the portion facing the photoconductor 22 and the transfer roll 27) to the surface side. By being conveyed to the portion facing the protruding surface 35a, the recording material attracting force on the conveying belt 31 is maintained high, and good recording material conveying property on the conveying belt 31 can be achieved. In addition, the front-side protruding surface 35a is not provided on the downstream side of the most downstream transfer roll 27d. However, this is because there is no new transfer portion of the toner image downstream from this transfer portion. It is better to give priority to the peeling performance because the recording material transportability is not a problem and the distance from the transfer portion to the recording material peeling point where the recording material is peeled from the conveying belt 31 is short. Is because it is better not to provide the surface side protruding surface 35a. Furthermore, in order to reduce the size, there is no space for providing the surface-side protruding surface 35a between the transfer roll 27d and the peeling point.

In this embodiment, since the downstream tension roll 33 has an outer diameter of 20 mm, the curvature at the peeling point is increased, and the recording material peelability from the transport belt 31 is further improved. By grounding the upstream tension roll 32, unnecessary charge accumulation in the conveyor belt 31 can be suppressed, and a refreshing action of the conveyor belt 31 itself can be brought about. Needless to say, the downstream tension roll 33 may be grounded.
In addition, such a charge holding action is further exhibited when the support frame 35 is in a float state. That is, the charge induced on the surface-side protruding surface 35a is discharged at a very slow speed, and the charge attenuation at the transport belt 31 is further slowed down.

  Further, the surface side protruding surface 35a in the present embodiment is provided with a length of about 1/3 between the adjacent transfer rolls 27, but this length is not particularly limited and may be longer. However, the upstream side adjacent to the downstream side transfer roll 27 is not provided with the surface side protruding surface 35a. Therefore, compared with the case where the front side protruding surface 35 a is provided across the transfer rolls 27, the transfer conditions on the downstream transfer roll 27 are stabilized by facilitating charge attenuation on the transport belt 31. ing.

Further, although the support frame 35 of the present embodiment is configured integrally, for example, a member that supports the transfer roll 27 and a member that forms the surface-side protruding surface 35a are configured separately. It does not matter even if these are combined.
Furthermore, in the present embodiment, an apparatus using four photoconductors 22 is shown, but the number of photoconductors 22 is not limited to this, and may be small or even larger.

  Further, as the front-side protruding surface 35a in the present embodiment, it is preferable that the capacitance component is large in order to maintain the charge of the transport belt 31. That is, it is preferable to use a material having a large relative dielectric constant as the surface-side protruding surface 35a, or to make the thickness thin enough not to cause dielectric breakdown. That is, in the present embodiment, since the front-side protruding surface 35a is provided as a part of the support frame 35, the ratio is from the point of being a material used as the support frame 35 and the strength of the support frame 35 itself. Although the size and thickness of the dielectric constant are restricted, it is also possible to remove the restriction by configuring the front-side protruding surface 35a as a separate member from the support frame 35. For example, a PVDF sheet may be affixed on the support frame 35, or a sheet in which ferroelectric fine particles are kneaded with a synthetic resin may be affixed.

Next, the back side protruding surface 35b of the support frame body 35 of the belt transfer device 30 in the present embodiment will be described. As the back side protruding surface 35b, there is no problem in particular if it is arranged away from the conveyor belt 31 so that it does not contact the conveyor belt 31, but it does not come into contact with the circulating conveyor belt 31. In such a case, there is a possibility that the conveyance belt 31 may be stuck to the rear-side protruding surface 35b due to frictional charging between the two and not circulated.
In this embodiment, in particular, the cleaning member 36 is pressed against the support frame 35 side, so that it is assumed that the conveyor belt 31 and the rear surface-side protruding surface 35b come into contact with each other when the circulating conveyor belt 31 flutters. Is done. For this reason, the following contrivance is made on the rear surface side protruding surface 35b so that the circulation of the conveyor belt 31 is not impaired even if such contact occurs.

  That is, a charging suppression unit is provided that suppresses the amount of frictional charge generated when the back surface-side protruding surface 35b and the transport belt 31 are in contact with a region where the back surface-side protruding surface 35b and the transport belt 31 may contact. I am doing so. FIGS. 5A to 5C show specific examples of the charge suppression unit. FIG. 5A shows a contact with the conveyor belt 31 by forming a minute uneven surface 351 by embossing on the back surface-side protruding surface 35b. The frictional charge generated by reducing the area is suppressed. In (b), for example, ribs 352 along the circulation direction of the conveyor belt 31 are formed on the rear surface-side protruding surface 35b, and the contact area with the conveyor belt 31 is reduced to reduce the frictional charge amount. It is. Furthermore, (c) is a sheet in which a sheet 353 made of a material having a small amount of triboelectric charge that is generated when it comes into contact with the conveyor belt 31 is attached to the rear surface side protruding surface 35b. As the material having a small amount of triboelectric charge, a material having a close charging series with the transport belt 31 to be used is preferable. You just have to do it.

  And as such a charge suppression part, you may make it provide over the whole surface of the back surface side protrusion surface 35b, and you may make it provide in part, Furthermore, it is orthogonal to the circulation direction of the conveyance belt 31. It may be provided over the entire region in the width direction, for example, may be provided near both ends, or may be provided near the center. That is, although both ends are more likely to come into contact with the conveyor belt 31 than the center, the sticking of the conveyor belt 31 is more likely to occur at the center.

Next, a method for replacing the process cartridge 21 and a method for supplying the recording material to the recording material supply unit 11 in such an image forming apparatus will be described.
FIG. 6A shows a state in which a main body cover 10b provided on the apparatus housing 10 side is released from the apparatus housing 10. The main body cover 10b has a part of the return conveyance path 42 and a belt transfer device. When 30 is integrally attached by a bracket or the like (not shown) and the main body cover 10b is opened, it moves accordingly. The main body cover 10b can be opened in the direction of arrow A with a pivot 50 provided below the apparatus housing 10 as a pivot. Therefore, by opening the main body cover 10b, the belt transfer device 30 is integrally opened. For example, as shown in the drawing, the process cartridge 21 (corresponding to the process cartridge of the image forming engine 20c in this example) is indicated by an arrow. It can be easily pulled out in the B direction. In this example, the transfer roll 27 also moves integrally with the belt transfer device 30, but the charging device 34 remains on the apparatus housing 10 side.

  FIG. 6B shows a state in which the recording material supply unit 11 provided at the lower part on the apparatus housing 10 side is pulled out from the apparatus housing 10 in the arrow C direction. Normally, the recording material is replenished in such a state that the recording material supply unit 11 is pulled out from the apparatus housing 10 as described above. Therefore, it is possible to realize a downsized image forming apparatus with excellent maintainability.

Comparison Mode Next, in order to clarify the operation of the surface side protruding surface (charge holding surface) 35a of the above-described embodiment, an image forming apparatus of a comparison mode will be described.
FIG. 7 shows an outline of a comparative image forming apparatus. Unlike the image forming apparatus of the present embodiment (see, for example, FIG. 2), instead of using a conveying belt that sucks and conveys a recording material, An intermediate transfer belt that primarily holds a toner image is used, and the toner image is transferred from the intermediate transfer belt onto a recording material.

In the drawing, an intermediate transfer belt 102 that is stretched and circulated by a plurality of stretching rolls 103 to 106 is disposed to face the photoreceptor 101. A primary transfer roll 107 for primary transfer of the toner image on the photosensitive member 101 to the intermediate transfer belt 102 is provided at a position facing the photosensitive member 101 with the intermediate transfer belt 102 interposed therebetween. The transfer bias is applied. Further, a secondary transfer roll 108 having the tension roll 106 as a backup roll is provided at a position facing the tension roll 106 and the intermediate transfer belt 102, and the toner on the intermediate transfer belt 102 is provided on the recording material. The images are transferred at once.
Further, in this comparative embodiment, the bias power source 110 is connected to the stretching roll 104 disposed at a position adjacent to the primary transfer roll 107 on the downstream side in the moving direction of the intermediate transfer belt.

  With this configuration, in this comparative embodiment, the bias power supply 110 is supplied so that the surface potential of the stretching roll 104 is held at a potential equal to or higher than the charging potential of the intermediate transfer belt 102 after the primary transfer. Thus, it is characterized in that the toner held on the intermediate transfer belt 102 after the primary transfer is prevented from being scattered. Further, it is possible to suppress the neutralization of the intermediate transfer belt 102 by connecting a high resistance instead of the bias power supply 110.

  However, such a tension roll 104 (contact member to the intermediate transfer belt 102) functions only when it comes into contact with the intermediate transfer belt 102, and the intermediate transfer belt 102 as in the present embodiment. It does not act in the vicinity of In addition, it does not exhibit an action assuming an induced charge. Therefore, it is understood that this comparison form and this embodiment are completely different.

Example 1
This example evaluates how the conveyance performance and suction performance of the recording material change depending on the surface resistivity of the conveyance belt in the configuration of the embodiment.
In this example, the distance between the conveying belt and the front-side protruding surface was 2 mm, and the following seven types of surface resistivity were evaluated as the conveying belt to be used with a thickness of 100 μm. Seven types of surface resistivity of 10 ⁹ , 10 ¹⁰ , 10 ¹¹ , 10 ¹² , 10 ¹³ , 10 ¹⁴ , 10 ¹⁵ Ω / □ were used, respectively.
In addition, as evaluation items, the peelability of thin paper (about 56 to 60 gsm) that is difficult to peel off from the conveyance belt and the deviation of the recording material (about 72 to 80 gsm) being conveyed are visually confirmed, and the recording material storage receptacle is used. Was visually confirmed. Note that the peelability and capacity of the thin paper were evaluated in an environment of 10 ° C. and 15% RH, and the displacement of the recording material was evaluated in an environment of 28 ° C. and 85% RH. In addition, the evaluation was made into three levels of ○, Δ, and ×, ○ is a level that is not problematic, Δ is a level that is slightly inferior but practically problematic, and × is a level that is problematic.

As shown in FIG. 8, the results show that the peelability of the thin paper is good except for the highest surface resistivity of 10 ¹⁵ Ω / □, and the deviation of the recording material has a low surface resistivity of 10 ⁹ Ω / □ gave bad results. Further, in terms of the capacity, 10 ¹⁵ Ω / □, which has the highest surface resistivity, showed a bad result, as with the peelability of thin paper. In other words, the capacity is to confirm the charge state of the recording material when it is peeled off from the conveying belt from another element. When the charge held by the recording material at the time of peeling is small, recording is performed. Although there is no problem in the storage capacity in the material storage portion, if the charge held by the recording material at the time of peeling is large, when the recording material is stored in the recording material storage portion, the charge of the previously stored recording material and the subsequent charge The mutual electric charge affects the recording material, and the recording material is accommodated in a shifted state.
From these things, the surface resistivity of the belt may not be too high or too low, and by using a surface resistivity of 10 ¹⁰ to 10 ¹⁴ Ω / □, without using a separate member such as a static elimination member, It has been found that both the transportability and the peelability of the recording material can be satisfied. In addition, this is presumed that the surface resistivity of the belt also defines a resistance component in the thickness direction of the belt, and it was understood that the characteristics of the conveying belt can be grasped by the surface resistivity.

Example 2
In this embodiment, when the height of the surface-side protruding surface (referred to as a resin surface) is changed, the change in surface potential in the recording material conveyance direction of the conveyance belt after transfer is confirmed. The surface potential was measured by inserting an electrode plate on the back surface of the transport belt after transfer and measuring the surface potential on the transport belt surface side with a probe of a surface potential meter. Note that the measurement position was set to a substantially central position in the width direction of the conveyor belt.
FIG. 9 shows the result of the attenuation curve of the belt potential when the voltage applied to the transfer roll is 3000 V under the environmental condition of 22 ° C. and 55% RH, and the conveyor belt has a surface resistivity of 10 ¹² Ω / □. is there. The distance between the transfer rolls was about 50 mm.

  From this result, the belt potential (the surface potential of the transport belt) is about 10 mm away from the transfer roll, regardless of the distance to the surface-side protruding surface (resin surface) (without the resin surface, the distance is infinite). It was found that a sharp drop occurred to the position, and then the drop was small. It has also been found that the belt potential is higher when the resin surface is closer than without the resin surface.

Here, A4 size plain paper (about 64 gsm) was used as the recording material, and it was confirmed what the adsorption force to the conveyance belt would be when the voltage applied to the transfer roll was changed. At this time, a conveyance belt having a surface resistivity of 10 ¹² Ω / □ is used, and the peeling force when the recording material after transfer is peeled off from the conveyance belt under an environmental condition of 22 ° C. and 55% RH is peeled off. The test was conducted according to the strength test. As a result, as shown in FIG. 10, it was understood that the adsorption force is increased by increasing the voltage applied to the transfer roll.

  Further, the relationship between the voltage applied to the transfer roll (transfer bias) and the potential of the conveying belt (belt potential) under an environmental condition of 22 ° C. and 55% RH was obtained. The measurement position was about 10 mm away from the transfer roll. As a result, as shown in FIG. 11, it was confirmed that when the voltage applied to the transfer roll was increased, the belt potential also increased, and at this time, a belt potential larger than the applied voltage was obtained. This is presumed that when the surface resistivity of the conveyor belt is such a value, the charge in the conveyor belt is not completely eliminated and charges are accumulated.

  Therefore, from the result of the measurement of the attractive force in FIG. 10, if the required attractive force is 2N, the applied voltage to the transfer roll in this case is about 1200 V, which is the result of the transfer bias and belt potential in FIG. Therefore, when the applied voltage to the transfer roll is 1200 V, a belt potential of about 1500 V can be obtained. Therefore, if the belt potential is maintained at 1500 V or more, it is determined that there is no particular problem with the adsorption force of the recording material. did.

Considering the belt potential attenuation curve of FIG. 8 based on the above criteria, in order to maintain the belt potential of 1500 V even when the distance from the transfer roll is increased, the resin surface should be close to 3 mm or less. It was confirmed that this should be done. Furthermore, when the surface resistivity of the conveying belt was confirmed between 10 ¹⁰ to 10 ¹⁴ Ω / □, the same result was obtained. From this, it was confirmed that the proximity distance should be 3 mm or less.

Example 3
In this example, in order to confirm the peelability of the tension roll, the outer diameter of the tension roll and the surface resistivity of the conveying belt were evaluated as factors. As in Example 1, the three levels of φ22 mm and the surface resistivity were 7 levels of 10 ⁹ , 10 ¹⁰ , 10 ¹¹ , 10 ¹² , 10 ¹³ , 10 ¹⁴ , 10 ¹⁵ Ω / □. The recording material used was thin paper as a condition that makes it difficult to peel off, and the environmental condition was set to 10 ° C. and 15% RH as a condition that makes the recording material difficult to peel. In addition, evaluation was made into three levels of (circle), (triangle | delta), and x, (circle) was a level which does not have a problem, (triangle | delta) was the level which a peeling defect generate | occur | produces rarely, and x was the level which does not peel.

As shown in FIG. 12, although the peelability is not a problem at any surface resistivity at φ18, φ20 has a surface resistivity of 10 ¹⁵ Ω / □, which is slightly inferior. Other than that, peeling was performed without any problem. Further, at φ22, the surface resistivity was 10 ¹³ Ω / □ or more, and no peeling was made.
From this, it is confirmed that if the outer diameter of the stretching roll at the recording material peeling site is φ20 mm or less, no peeling problem occurs when the surface resistivity of the belt is 10 ¹⁰ to 10 ¹⁴ Ω / □. It was.

Example 4
In this example, the color misregistration when the rotational speed of the photosensitive member and the circulation speed of the conveying belt are changed in the image forming apparatus according to the embodiment is evaluated and confirmed.
The transport belt used had a surface resistivity of 10 ¹² Ω / □, and the distance from the transport belt to the resin surface was 2 mm, using plain paper under environmental conditions of 22 ° C. and 55% RH.
FIG. 13 shows the result. The horizontal axis shows the change in speed ratio (Drum / Belt speed ratio) between the photosensitive member and the conveyor belt, centering on the constant speed, for example, −0.6. Indicates that the photoreceptor is 99.4% speed of the conveyor belt. On the other hand, the vertical axis represents the amount of color misregistration when a standard color image is formed.

  From this result, when the speed of the photosensitive member is slower than the speed of the conveying belt, the amount of deviation increases, and the amount of deviation gradually decreases as the speed of the photosensitive member increases. It turned out to be a local minimum at a rate of 99.4% of the body). This is because, with respect to the deviation of the recording material conveyed by the conveyance belt, the force in the direction of pressing the recording material against the conveyance belt can be applied by increasing the speed of the photosensitive member. It was judged that it could be kept small.

Example 5
In this example, the length of the front side protruding surface (resin surface) was evaluated. The distance between the transport belt and the resin surface was 2 mm, the resin surface was provided from a position close to the transfer roll, and the length was Evaluation was made with the lengths of 1/5, 1/4, 1/3, and 1/2 between the transfer rolls, and the surface potential of the conveyor belt at the position of 1/2 was measured.
The result is that the belt potential is smaller than the other at 1/5, and it is not possible to confirm whether the effect of the resin surface clearly appears, but the same surface potential was obtained at other lengths. As a result, it was confirmed that there is no problem if the length is 1/4 or more between the transfer rolls.

It is explanatory drawing which shows the outline | summary of the belt transfer apparatus which concerns on this Embodiment model. 1 is an explanatory diagram showing an overview of an image forming apparatus according to an embodiment. It is explanatory drawing which shows the belt transfer apparatus of embodiment. (A) is explanatory drawing explaining the state of the belt charge at the time of providing the surface side protrusion surface in embodiment, (b) demonstrates the state of the belt charge when not providing the surface side protrusion surface. It is explanatory drawing. (A)-(c) is explanatory drawing which shows the structure of the back surface side protrusion surface of embodiment. (A) shows a process cartridge replacement method of the image forming apparatus of the embodiment, and (b) is an explanatory diagram showing a paper feed method to a paper feed cassette. It is explanatory drawing which shows the image forming apparatus which concerns on the form of a comparison. 2 is a table showing the results of Example 1. 10 is a graph showing the results of Example 2. It is a graph which shows the adsorptive power measurement result used in Example 2. 6 is a graph showing a relationship between a transfer bias used in Example 2 and a belt potential. 10 is a table showing the results of Example 3. It is a graph which shows the result of Example 4.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 (1a, 1b) ... Image holding body, 2 ... Recording material, 3 ... Belt member, 4 (4a, 4b) ... Stretch member, 5 (5a, 5b) ... Transfer member, 6 ... Charge holding member

Claims (11)

A belt transfer device that is provided opposite to a plurality of image carriers that hold toner images and that transfers a toner image on the image carrier onto the recording material while conveying the recording material,
An endless belt member having a surface resistivity of 10 ¹⁰ Ω / □ or more and 10 ¹⁴ Ω / □ or less that is circulated by being stretched by a plurality of stretching members and electrostatically conveys the recording material at a part of the outer peripheral surface. When,
A plurality of transfer members provided on the inner peripheral surface side corresponding to the recording material conveyance surface of the belt member and transferring a toner image to the recording material on the recording material conveyance surface;
It provided between the transfer member of at least the belt member, comprising a charge holding member for holding the charge of the recording material conveying surface of the belt member or a recording material capable of adsorption level, and
The charge holding member is made of a dielectric, and has a charge holding surface extending along the back surface side of the belt member from the upstream transfer member in the recording material conveyance direction toward the downstream transfer member. The charge holding surface is opposed to the inner peripheral surface of the belt member so that the induced charge is electrostatically induced on the charge holding surface by the charged charge on the recording material conveying surface, and the proximity distance to the belt member is 3 mm or less. A belt transfer device characterized in that the belt transfer devices are arranged close to each other. The belt transfer device according to claim 1,
The belt transfer device, wherein the charge holding member is provided so as to extend along an inner peripheral surface of the belt member immediately after the transfer member on the upstream side in the recording material conveyance direction. The belt transfer device according to claim 1,
The belt transfer apparatus, wherein the charge holding member is provided in an electrically floating state. The belt transfer device according to claim 1,
A support frame made of synthetic resin that supports at least the transfer member is provided on the inner peripheral surface side of the belt member, and the charge holding member is constituted by a part of the support frame. Belt transfer device. The belt transfer device according to claim 1,
A belt transfer apparatus, wherein a tension member is provided at a position adjacent to a downstream side of a transfer member positioned on the most downstream side in the recording material conveyance direction without disposing the charge holding member. The belt transfer device according to claim 1,
The belt transfer device according to claim 1, wherein the charge holding member is disposed at an upstream side portion in the recording material conveyance direction between the transfer members. The belt transfer device according to claim 1,
The belt transfer device, wherein the belt member is stretched by two stretch members. The belt transfer apparatus according to claim 7 , wherein
A belt transfer apparatus, wherein at least one of the two tension members is grounded. The belt transfer apparatus according to claim 7 , wherein
2. A belt transfer apparatus according to claim 1, wherein the tension member on the most downstream side in the recording material conveyance direction of the two tension members is constituted by a roll-shaped member having an outer diameter of 20 mm or less. A plurality of image holders rotatably provided and holding toner images;
An image forming apparatus, comprising a belt transfer device according to any one of claims 1 to 9 is arranged opposite to those of the image carrier. The image forming apparatus according to claim 10 .
An image forming apparatus, wherein a rotation speed of the plurality of image holding members is set to be larger than a circulation speed of the belt member.

Images