JP4096145B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus such as an electrophotographic copying machine, and more particularly to an image forming apparatus of a type that transfers an image directly on a recording / conveying belt or via a recording material.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, for example, an intermediate transfer type image forming apparatus includes a photosensitive drum on which a toner image corresponding to an electrostatic latent image is formed, and an intermediate transfer belt on which the toner image on the photosensitive drum is transferred intermediately. A primary transfer device for transferring the toner image on the photosensitive drum to the intermediate transfer member, and a secondary transfer device for secondary transfer of the toner images transferred on the intermediate transfer belt to the sheet collectively. Is known.
Here, as the primary transfer device, for example, a transfer roll disposed in contact with the intermediate transfer belt is used. This transfer roll forms an electric field that moves the toner image on the photosensitive drum to the intermediate transfer belt side between the photosensitive drum and the intermediate transfer belt.
[0003]
[Problems to be solved by the invention]
In this type of image forming apparatus, the intermediate transfer belt is usually arranged in a stretched manner on a plurality of roll groups. At this time, for example, if the tension applied to the intermediate transfer belt is too large, the direction in which the tension is applied. In other words, streaky concave portions or convex portions (hereinafter referred to as tension lines) may occur in the intermediate transfer belt along the conveyance direction of the intermediate transfer belt.
[0004]
When such a tension line is generated, a gap (gap) is formed between the photosensitive drum and the intermediate transfer belt in the primary transfer portion, so that the holding force of the toner transferred to the tension line forming portion becomes weak, There was a technical problem that when the gap discharge occurred in this gap, a round-hanging image quality defect occurred.
[0005]
Japanese Patent Laid-Open No. 9-152791 describes a technique for preventing image quality defects at the primary transfer portion by defining the relative position between the photosensitive drum and the primary transfer device. Depending on the means, it is not possible to completely prevent the above-mentioned round defect-like image quality defect.
[0006]
SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of effectively preventing image quality defects caused by the generation of tension lines.
[0007]
[Means for Solving the Problems]
  That is, according to the present invention, as shown in FIG. 1, an image carrier 1 on which a toner image T corresponding to image information is formed and carried;While stretched across multiple roll groupsA transfer nip region N is formed between the recording / conveying belt 2 that is circulated and conveyed through a portion facing the image carrier 1 and the image carrier 1 via the recording / conveying belt 2. Transfer means 3 for transferring the toner image T formed on the image carrier 1 directly or via the recording material K,Along with excessive tension of the recording / conveying belt 2Along the conveying direction of the recording and conveying belt 2An elongated streak or protrusionThe judging means for judging whether or not the tension line L is formed, and the judgment result of the judging meansSaidUnder the environmental conditions in which the tension line L is formed on the recording / conveying belt 2, the holding force of the toner transferred to the region corresponding to the tension line L is larger than in the environmental condition in which the tension line L is not formed. And a holding force adjusting means 4 for adjusting the holding force of the toner.
[0008]
In such technical means, the image forming method of the image forming apparatus which is the subject of the present application may be appropriately selected such as an electrophotographic method or an electrostatic recording method, and the toner image T directly on the recording / conveying belt 2 may be used. A method for transferring the toner image, a method for transferring the toner image T onto the recording material K carried and conveyed on the recording and conveying belt 2, and the like may be appropriately selected. Further, the number of the image carrier 1 may be one or a plurality.
In FIG. 1, the toner image T formed by one image carrier 1 is transferred to the recording / conveying belt 2 (intermediate transfer belt) by the transfer means 3, and the toner image transferred onto the recording / conveying belt 2 is transferred. A mode in which T is collectively transferred onto the recording material K via the batch transfer means 5 is illustrated.
The recording / conveying belt 2 is not limited to the intermediate transfer belt shown in FIG. 1 but also includes a recording material conveying belt for carrying and conveying the recording material K.
The present application is particularly effective in the case of using the recording / conveying belt 2 in which the image quality defect is likely to occur in a round shape, specifically, the recording / conveying belt 2 having a volume resistivity of 12 logΩcm or more under normal temperature and humidity conditions. .
Further, in the present application, the tension line L is formed along the conveyance direction of the recording / conveying belt 2, which means that it includes a conveyance direction component, and accordingly, the conveying direction of the recording / conveying belt 2. Including those formed obliquely.
[0009]
In the present invention, the transfer means 3 is connected to the image carrier 1 via the recording / conveying belt 2 in addition to the normal transfer function, ie, the function of transferring the toner image T formed on the image carrier 1. It is also necessary to have a function of forming the transfer nip area N.
Here, in a mode in which, for example, a contact transfer member (for example, a transfer roll) arranged in pressure contact with the recording / conveying belt 2 is employed as the transfer unit 3, the contact transfer member also functions to form the transfer nip N. It becomes. On the other hand, in a mode in which a non-contact transfer member (for example, corotron) arranged in a non-contact manner on the recording / conveying belt 2 is employed, the recording / conveying belt 2 is used as the transfer unit 3 in addition to the non-contact transfer member. It is necessary to provide a functional member (pressing member) that presses toward the body 1 side.
[0010]
  Further, the holding force adjusting means 4 has a holding force of toner transferred to an area corresponding to the tension line L of the recording / conveying belt 2.Than the case of environmental conditions where tension line L is not formedTo be bigger,As long as the toner holding power is adjusted, it may be selected as appropriate.,An aspect in which the pressing force of the transfer means 3 is adjusted by the pressing force adjustment means (hereinafter referred to as the first aspect), and an aspect in which the bias application amount applied to the transfer means 3 is adjusted by the bias adjustment means (hereinafter referred to as the second aspect). (Referred to as aspect)Or a combination of bothIs mentioned.
[0011]
  In the first aspect described above, in the aspect in which the recording / conveying belt 2 is made of a material having a large hygroscopic expansion coefficient, the tension line L is likely to be generated in the recording / conveying belt 2 under a high temperature and high humidity environment.
  Therefore, from the viewpoint of effectively preventing the tension line L and the image quality defect associated therewith caused by such environmental fluctuations, the pressing force adjusting means is configured to press the pressing force of the transfer means 3 based on environmental information. AdjustThe method is adopted.
[0013]
  On the other hand, also in the above-described second aspect, when the recording / conveying belt 2 is made of a material having a large hygroscopic expansion coefficient, a tension line L is generated in the recording / conveying belt 2 in a high-temperature and high-humidity environment. It's easy to do.
  Therefore, from the viewpoint of effectively preventing the tension line L and the image quality defect accompanying the tension line L caused by the environmental change, the bias adjusting unit applies the bias application amount to the transfer unit 3 based on the environmental information. AdjustThe method is adopted.
[0014]
In the embodiment using a transfer roll disposed in contact with the recording / conveying belt 2 as the transfer means 3, the bias adjusting means is utilized by utilizing the fact that the system resistance of the transfer nip area N varies with the environment. However, the amount of bias applied to the transfer roll may be adjusted based on the system resistance.
[0015]
By the way, three or more image carriers 1 are arranged opposite to the recording / conveying belt 2, and toner images T of a plurality of colors (for example, yellow, magenta, cyan, or yellow, magenta, cyan, black, etc.) are superposed on one pass. In a so-called tandem type image forming apparatus that can perform this, the tension span of the recording / conveying belt 2 at a portion facing the plurality of image carriers 1 becomes long. There is a possibility that sagging occurs at the end portion on the central side in the conveyance direction, and the portion becomes a gap portion to generate a round-shaped discharge mark.
[0016]
  Therefore, the present inventionAmong these, in the embodiment having three or more image carriers 1,Regarding the pressing force with which each transfer unit 3 presses the recording and conveying belt 2, the pressing force of the transferring unit 3 disposed on the most upstream side in the conveying direction of the recording and conveying belt 2 and the maximum conveying direction of the recording and conveying belt 2. The pressing force of the transfer means 3 disposed between them is set higher than the pressing force of the transfer means 3 disposed on the downstream side.It is preferable to do.
[0017]
  In addition, the present inventionAmong these, in the embodiment having three or more image carriers 1,Regarding the bias application amount to be applied to each transfer unit 3, the bias application amount of the transfer unit 3 disposed on the most upstream side in the conveyance direction of the recording and conveying belt 2 and the most downstream side in the conveyance direction of the recording and conveying belt 2. The bias application amount of the transfer means 3 arranged between them is set larger than the bias application amount of the transfer means 3 provided.It is preferable to do.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
Embodiment 1
FIG. 2 shows Embodiment 1 of a color image forming apparatus to which the present invention is applied.
In the figure, the color image forming apparatus according to the present embodiment includes a plurality of image forming units 100 (specifically, 100Y, 100M, 100C, and 100K) on which each color component toner image is formed by, for example, electrophotography. The intermediate transfer belt 110 as a recording carrier for sequentially transferring (primary transfer) holding each color component toner image formed in each image forming unit 100, and the superimposed image transferred on the intermediate transfer belt 110 as a recording material. A batch transfer device 120 for batch transfer (secondary transfer) to the paper P and a fixing device 150 for fixing the batch transferred image on the paper P are provided.
[0019]
In the present exemplary embodiment, the image forming unit 100 for each color component includes a yellow image forming unit 100Y, a magenta image forming unit 100M, a cyan image forming unit 100C, and a black image forming unit 100K from the upstream side in the transport direction B of the intermediate transfer belt 110. Are arranged in this order.
Then, each image forming unit 100 has a uniform charger 102 on which the photosensitive drum 101 is charged around the photosensitive drum 101 serving as an image carrier that rotates in the direction of arrow A. A laser exposure device 103 in which an electrostatic latent image is written (exposure beam is indicated by a symbol Bm in the drawing), and a developing device 104 in which each color component toner is accommodated and an electrostatic latent image on the photosensitive drum 101 is visualized. An electrophotographic device such as a primary transfer roll 105 as a transfer device for transferring each color component toner image on the photosensitive drum 101 to the intermediate transfer belt 110 and a drum cleaner 106 for removing residual toner on the photosensitive drum 101. Are sequentially arranged.
[0020]
As shown in FIG. 3, each primary transfer roll 105 (specifically, 105Y, 105M, 105C, and 105K) has a direct current having a polarity (positive in this embodiment) opposite to the charged polarity of the toner. A transfer bias power source 107 (specifically 107Y, 107M, 107C, 107K) to which a bias is applied is provided. Each of these transfer bias power sources 107 can change the voltage applied to each primary transfer roll 105, and applies a constant current (30 μA in this embodiment) to each primary transfer roll 105.
[0021]
Further, as shown in FIG. 2, the intermediate transfer belt 110 is stretched around a plurality of (in this embodiment, five) support rolls 131 to 135. Here, the support roll 131 is a drive roll of the intermediate transfer belt 110, the support rolls 132 and 135 are driven rolls, the support roll 133 is a tension roll that adjusts the tension of the intermediate transfer belt 110, and the support roll 134 is batch transfer as described later. This is a backup roll of the device 120.
[0022]
The intermediate transfer belt 110 uses a resin such as polyimide or polyamide containing an appropriate amount of an antistatic agent such as carbon black, and has a volume resistivity of 10^Ten-10¹³It is formed to be Ωcm, and its thickness is set to 0.1 mm, for example.
[0023]
Further, the batch transfer device 120 is a secondary transfer roll 113 arranged in pressure contact with the toner carrying surface side of the intermediate transfer belt 110 and a counter electrode of the secondary transfer roll 113 arranged on the back side of the intermediate transfer belt 110. A backup roll 114 (also used as a support roll 134) is provided, and a bias having the same polarity as the toner charging polarity is stably applied to the backup roll 114 from a bias power source 112 as shown in FIG. A metal power supply roll 115 is disposed in contact therewith.
[0024]
In this embodiment, the secondary transfer roll 113 is made of urethane rubber tube with carbon dispersed on the surface, the inside is made of foamed urethane rubber with carbon dispersed, and further, the roll surface is coated with fluorine, and its volume resistance is 10^Three-10^TenThe roll diameter is 28 mm and the hardness is set to 30 ° (Asuka C), for example.
[0025]
The backup roll 114 is made of EPDM and NBR blend rubber tube with carbon dispersed on the surface, and the inside is made of EPDM rubber.⁷-10^TenThe roll diameter is Ω / □ and the roll diameter is 28 mm, and the hardness is set to 70 ° (Asuka C), for example.
[0026]
Note that a roll brush 161 is attached to the secondary transfer roll 113, and the dirt on the back surface of the paper P is prevented by removing the dirt attached to the secondary transfer roll 113.
Reference numeral 136 denotes a belt cleaner that cleans the surface of the intermediate transfer belt 110 after the secondary transfer, and reference numeral 137 denotes an image density sensor that detects the image density of an image formed on the intermediate transfer belt 110.
[0027]
Further, in the present embodiment, the paper transport system feeds the paper P from the paper tray 116 at a predetermined timing by the pickup roll 117 and sends it to the secondary transfer position via the transport roll 118 and the transport chute 119. Then, the sheet P after the secondary transfer is guided to the transport belt 140 and transported to the fixing device 150 by the transport belt 140.
[0028]
Next, the arrangement method of each primary transfer roll 105 according to the present embodiment will be described in detail.
In this embodiment, the primary transfer roll 105 is made of urethane foam rubber in which carbon is dispersed, has a diameter of 28 mm, and has a volume resistivity of 10⁷-10⁹The hardness is set to 35 ° (Asuka C), for example.
[0029]
In the present embodiment, as shown in FIG. 4, each primary transfer roll 105 is provided with a pressing mechanism 180 that adjusts the pressing force against the intermediate transfer belt 110 (not shown).
The pressing mechanism 180 includes an eccentric cam 181 disposed in contact with the rotation shaft 105 a of the primary transfer roll 105, and a motor 183 that transmits a driving force to the eccentric cam 181 via a gear 182. Is rotated in the forward / reverse direction to vary the pressing force of the primary transfer roll 105 against the intermediate transfer belt 110.
The pressing mechanism 180 is not limited to a type driven by a motor, but may be driven by a solenoid, for example.
[0030]
In addition, the intermediate transfer belt 110 according to the present embodiment has a high hygroscopic expansion coefficient, and a tension line is easily generated in a high temperature and high humidity environment.
Therefore, in the present embodiment, as shown in FIG. 5, a control device 200 that controls the pressing force of each primary transfer roll 105 according to the environmental conditions is provided.
[0031]
In the present embodiment, the control device 200 receives the temperature detection signal from the temperature sensor 171 and the humidity detection signal from the humidity sensor 172 into the CPU 202 via the input interface 201, and then the CPU 202 includes the ROM 203 and the RAM 204. After appropriately performing data processing between each of the press mechanisms 180 (specifically, yellow transfer rolls) that press each primary transfer roll 105 (specifically, 105Y, 105M, 105C, 105K) via the output interface 205. Drive signals are sent to the pressing mechanism 180Y, the magenta transfer roll pressing mechanism 180M, the cyan transfer roll pressing mechanism 180C, and the black transfer roll pressing mechanism 180K).
[0032]
Next, an image forming process of the color image forming apparatus according to the present embodiment will be described.
Now, when a start switch (not shown) is turned on, a predetermined image forming process is executed.
Specifically, for example, when this color image forming apparatus is configured as a digital color copying machine, a document set on a document table (not shown) is read by a color image reading device, and the read signal is image signal processing means. The digital image signal is converted into a digital image signal and temporarily stored in the memory, and toner images of each color are formed based on the stored digital image signals of four colors (Y, M, C, K). .
[0033]
That is, each image forming unit 100 (specifically, 100Y, 100M, 100C, 100K) is driven according to the digital image signal of each color input from the image signal processing means. In each image forming unit 100, an electrostatic latent image corresponding to the digital signal is written on the photosensitive drum 101 uniformly charged by the uniform charger 102 by the laser exposure unit 103.
Each electrostatic latent image is developed by a developing device 104 containing toner of each color to form the toner image of each color.
In the case where the color image forming apparatus is configured as a printer or the like, the toner image of each color may be formed based on an image signal input to the image signal processing means from the outside.
[0034]
The toner image formed on each photoconductive drum 101 is transferred from the photoconductive drum 101 to the surface of the intermediate transfer belt 110 by the primary transfer roll 105 at a primary transfer position where the photoconductive drum 101 and the intermediate transfer belt 110 are in contact with each other. Sequentially transferred. The toner remaining on the photosensitive drum 101 after the primary transfer is cleaned by the drum cleaner 106.
[0035]
The toner image primarily transferred to the intermediate transfer belt 110 in this way is superimposed on the intermediate transfer belt 110 and conveyed to the secondary transfer position as the intermediate transfer belt 110 rotates.
On the other hand, the paper P is supplied to the secondary transfer position at a predetermined timing, and the secondary transfer roll 113 nips the paper P with respect to the backup roll 114.
[0036]
Then, at the secondary transfer position, the toner image carried on the intermediate transfer belt 110 is transferred to the sheet P by the action of a transfer electric field formed between the secondary transfer roll 113 and the backup roll 114 as the batch transfer device 120. Are collectively transferred. The sheet P on which the toner image is transferred is conveyed to the fixing device 150 by the conveying belt 140 and the toner image is fixed.
Further, the toner remaining on the intermediate transfer belt 110 after the secondary transfer is cleaned by the belt cleaner 136.
[0037]
Next, the control of the pressing force on each primary transfer roll 105 by the control device 200 will be described in detail based on the flowchart shown in FIG.
In the image forming apparatus according to the present embodiment, it is known that there is a relationship shown in FIG. 7 between the environment (temperature, humidity) and the load applied to the primary transfer nip area (primary nip load). . That is, if the primary nip load is excessively large, the intermediate transfer belt 110 and the photosensitive drum 101 are damaged and image quality defects occur. On the other hand, if the primary nip load is excessively small, the retention force of the toner transferred to the tension line forming portion is reduced. It becomes weak and causes a round stamp-like image quality defect (discharge mark). And the area | region (non-occurrence | production area | region) where such a malfunction does not generate | occur | produce is a little different in low temperature low humidity environment, normal temperature normal humidity environment, and high temperature high humidity environment.
[0038]
When image formation is started, a temperature detection signal from the temperature sensor 171 and a humidity detection signal (environment information) from the humidity sensor 172 are input, and if the environment is a low temperature / low humidity environment or a normal temperature / humidity environment, intermediate transfer is performed. It is determined that no tension line is formed on the belt 110, and the primary nip load of each primary transfer roll 105 is set to 98 mN / cm (10 gf / cm). On the other hand, when the environment is a high temperature and high humidity environment, it is determined that there is a danger that a tension line is formed on the intermediate transfer belt 110, and the primary transfer nip load of each primary transfer roll 105 is doubled to 196 mN / cm. (20 gf / cm).
Then, the primary transfer from the photosensitive drum 101 to the intermediate transfer belt 110 is executed, and this process is repeated until the image formation is completed.
[0039]
In this embodiment, the primary transfer nip region is set by setting a large pressing force (primary nip load) against the primary transfer roll 105 in an environment in which a tension line is likely to be generated in the intermediate transfer belt 110, that is, in a high temperature and high humidity environment. Since the intermediate transfer belt 110 is forcibly smoothed, the holding force of the toner transferred to the area where the tension line is formed can be increased. Good transfer performance can be obtained while preventing this.
[0040]
In this embodiment, the primary transfer nip load in a low temperature and low humidity environment and a normal temperature and normal humidity environment is set to 98 mN / cm, and the primary nip load in a high temperature and high humidity environment is set to 196 mN / cm. For example, the primary nip load in the low temperature and low humidity environment and the normal temperature and normal humidity environment is in the range of 98 to 147 mN / cm (10 to 15 gf / cm), and the primary nip load in the high temperature and high humidity environment. It may be appropriately selected from the range of 196 to 294 mN / cm (20 to 30 gf / cm).
[0041]
Embodiment 2
The present embodiment is substantially the same as the first embodiment, but further, the primary transfer current is controlled according to the environmental conditions.
Of the components of the image forming apparatus according to the present embodiment, the same components as those of the image forming apparatus according to the first embodiment are denoted by the same reference numerals as those in the first embodiment, and detailed descriptions thereof are given here. Description is omitted.
[0042]
In the present embodiment, as shown by the broken line portion in FIG. 5, the control device 200 further supplies each transfer bias power source 107 (specifically, a yellow transfer bias power source 107Y, a magenta transfer bias power source) via the output interface 205. 107M, a cyan transfer bias power source 107C, and a black transfer bias power source 107K) are each sent with a bias control signal.
[0043]
Next, control of the pressing force and transfer bias for each primary transfer roll 105 by the control device 200 will be described in detail based on the flowchart shown in FIG.
In the image forming apparatus according to the present embodiment, it is known that there is a relationship shown in FIG. 9 between the environment (temperature, humidity) and the primary transfer current. That is, when the transfer current is too large, discharge due to excessive transfer current and the accompanying primary transfer retransfer occur. On the other hand, when the transfer current is too small, a round-shaped image quality defect due to insufficient transfer current occurs. And the area | region (non-occurrence | production area | region) where such a malfunction does not generate | occur | produce is a little different in low temperature low humidity environment, normal temperature normal humidity environment, and high temperature high humidity environment.
[0044]
When image formation is started, a temperature detection signal from the temperature sensor 171 and a humidity detection signal (environment information) from the humidity sensor 172 are input, and if the environment is a low temperature / low humidity environment or a normal temperature / humidity environment, intermediate transfer is performed. It is determined that no tension line is formed on the belt 110, the primary nip load of each primary transfer roll 105 is set to 98 mN / cm (10 gf / cm), and the primary transfer current to be applied to each primary transfer roll 105 is set. Set to 30 μA. On the other hand, when the environment is a high temperature and high humidity environment, it is determined that there is a danger that a tension line is formed on the intermediate transfer belt 110, and the primary transfer nip load of each primary transfer roll 105 is doubled to 196 mN / cm. (20 gf / cm) and the primary transfer current applied to each primary transfer roll 105 is set to 35 μA, which is larger than the primary transfer current in the environment.
Then, the primary transfer from the photosensitive drum 101 to the intermediate transfer belt 110 is executed, and this process is repeated until the image formation is completed.
[0045]
In this embodiment, the primary transfer nip region is set by setting a large pressing force (primary nip load) against the primary transfer roll 105 in an environment in which a tension line is likely to be generated in the intermediate transfer belt 110, that is, in a high temperature and high humidity environment. Since the intermediate transfer belt 110 is forcibly smoothed and the primary transfer current is further increased, the holding force of the toner transferred to the area where the tension line is formed can be further increased.
[0046]
Embodiment 3
The present embodiment is substantially the same as the first embodiment, but the primary transfer current is controlled in accordance with the system resistance of the primary transfer portion.
Of the components of the image forming apparatus according to the present embodiment, the same components as those of the image forming apparatus according to the first embodiment are denoted by the same reference numerals as those in the first embodiment, and detailed descriptions thereof are given here. Description is omitted.
[0047]
In the present embodiment, as shown in FIG. 10, the control device 300 receives a resistance detection signal from a resistance measurement device 173 that measures the system resistance of the primary transfer unit via the input interface 301 into the CPU 302. The CPU 302 performs appropriate data processing between the ROM 303 and the RAM 304, and then outputs each transfer bias power source 107 (specifically, a yellow transfer bias power source 107Y, a magenta transfer bias power source 107M, and a cyan transfer bias via the output interface 305). Bias control signals are sent to the power supply 107C and the black transfer bias power supply 107K, respectively.
[0048]
Next, the control of the transfer bias for each primary transfer roll 105 by the control device 300 will be described in detail based on the flowchart shown in FIG.
When the image formation is started, a resistance detection signal (resistance information) is input from the resistance measuring device 173, and when the resistance value R is equal to or higher than a predetermined resistance value Rs, it is in a low temperature / low humidity environment or a normal temperature / humidity environment. That is, it is determined that no tension line is formed on the intermediate transfer belt 110, and the primary transfer current applied to each primary transfer roll 105 is set to 30 μA. On the other hand, if the resistance value R exceeds the predetermined resistance value Rs, it is determined that there is a risk that a tension line is formed in the intermediate transfer belt 110 in a high temperature and high humidity environment, and each primary transfer roll The primary transfer current applied to 105 is set to 35 μA.
Then, the primary transfer from the photosensitive drum 101 to the intermediate transfer belt 110 is executed, and this process is repeated until the image formation is completed.
[0049]
In this embodiment, the primary transfer current applied to the primary transfer roll 105 is set to be large in an environment where the system resistance is lowered, that is, in a high temperature and high humidity environment where tension lines are likely to occur in the environmental intermediate transfer belt 110. Therefore, it is possible to increase the holding force of the toner transferred to the area where the tension line is formed in the primary transfer nip region, and it is possible to obtain a good transfer performance while preventing the occurrence of a round-hanging image quality defect. .
[0050]
Embodiment 4
  FIG. 12 shows the main part of the primary transfer part of the image forming apparatus according to the fourth embodiment.The present embodiment shows a reference form for adjusting the pressing force of the primary transfer roll 105.
  In the drawing, the rotation shaft 105a of the primary transfer roll 105 is supported by a support member 185 made of a material having high hygroscopic expansion such as cellophane.
  Therefore, the support member 185 expands in a high-temperature and high-humidity environment, and the pressing force of the primary transfer roll is increased by that amount. Therefore, even if the pressing force is not controlled, the supporting member 185 is automatically pressed according to the surrounding environment. The pressure can be adjusted.
[0051]
Embodiment 5
The present embodiment is substantially the same as the first embodiment, but in FIGS. 2 and 3, of the primary transfer rolls 105 (specifically, 105Y, 105M, 105C, and 105K), the intermediate transfer belt 110 is the same. The pressure on the magenta primary transfer roll 105M and the cyan primary transfer roll 105C disposed on the center side is set higher than the pressure on the yellow primary transfer roll 105Y and the black primary transfer roll 105K disposed on the end side in the transport direction. It is what I did.
[0052]
FIG. 13 is a top view of the primary transfer surface of the color image forming apparatus shown in FIG. Note that the description of the photosensitive drum 101 is omitted.
In the same figure, under the condition that excessive tension is applied to the intermediate transfer belt 110, in the vicinity of the driving roll 131 and the driven roll 132, the wavy (tension line L) of the intermediate transfer belt 110 in the conveying direction of the intermediate transfer belt 110 is obtained. (Shown in phantom lines in the figure) can be seen remarkably. On the other hand, although there is little generation of the tension line L at the center between the drive roll 131 and the driven roll 132, Dripping becomes noticeable.
[0053]
In such a case, the magenta primary transfer portion and cyan primary transfer portion between the yellow primary transfer portion in the vicinity of the drive roll 131 and the black primary transfer portion in the vicinity of the driven roll 132 are on both side ends 110E of the intermediate transfer belt 110. As the sag increases, the reaction force received by the primary transfer rolls 105M and 105C from the intermediate transfer belt 110 increases, and the effective value of the pressing force decreases. As a result, a gap is generated in the primary transfer nip area of magenta and cyan, and electric discharge is generated, resulting in a round-hanging image quality defect.
[0054]
Here, the inventor paid attention to the pressing force of each primary transfer roll 105, combined various combinations of the pressing forces, and conducted an experiment for confirming whether or not a discharge phenomenon occurred.
As a result, as shown in FIG. 14, the pressing force for the magenta primary transfer roll 105M and the cyan primary transfer roll 105C disposed on the center side is set higher than the pressing force for the yellow primary transfer roll 105Y and the black primary transfer roll 105K. In this case (see No. 1), it was confirmed that the discharge phenomenon in the primary transfer nip region disappeared and a good image without image quality defects was obtained.
In addition, when the pressing force for each primary transfer roll 105 is set to be substantially the same (see No. 2), it is confirmed that a slight discharge phenomenon occurs and a slight image quality defect occurs. When the pressing force for the yellow primary transfer roll 105Y and the black primary transfer roll 105K disposed on the end side is set higher than the pressing force for the magenta primary transfer roll 105M and the cyan primary transfer roll 105C (see No. 3). ), It was confirmed that a discharge phenomenon occurred and an image quality defect occurred.
[0055]
【The invention's effect】
  As explained above, according to the present invention,Due to excessive tension of the recording / conveying beltAlong the conveyance direction of the recording conveyance beltAn elongated streak or protrusionIt is determined whether or not the environment in which the tension line is formed, and the holding force adjusting means holds the toner transferred to the area corresponding to the tension line formed on the recording and conveying belt based on the determination result of the environment. Since at least one of the pressing force of the transfer unit and the amount of bias applied to the transfer unit is adjusted so that the force is larger than in the case of an environmental condition where no tension line is formed, the image quality associated with the generation of the tension line is adjusted. Defects can be effectively prevented.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing an outline of an image forming apparatus according to the present invention.
FIG. 2 is a schematic configuration diagram of Embodiment 1 of an image forming apparatus to which the present invention is applied.
3 is an enlarged view of a primary transfer device of the image forming apparatus according to Embodiment 1. FIG.
FIG. 4 is an explanatory view showing a pressing mechanism of a primary transfer roll.
FIG. 5 is a block diagram of a control device of the image forming apparatus according to the first and second embodiments.
FIG. 6 is a flowchart showing a control flow of the control device according to the first embodiment.
FIG. 7 is a graph showing the relationship between environment and primary nip load.
FIG. 8 is a flowchart showing a control flow of the control apparatus according to the second embodiment.
FIG. 9 is a graph showing the relationship between environment and primary transfer current.
FIG. 10 is a block diagram of a control device of an image forming apparatus according to a third embodiment.
FIG. 11 is a flowchart showing a control flow of the control device according to the third embodiment.
12 is an explanatory diagram illustrating a primary transfer roll support mechanism in an image forming apparatus according to Embodiment 4; FIG.
13 is a schematic diagram illustrating a tension state of an intermediate transfer belt in an image forming apparatus according to Embodiment 5. FIG.
FIG. 14 is a chart showing the relationship between the pressing force on each primary transfer roll and the occurrence of a discharge phenomenon.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Image carrier, 2 ... Recording conveyance belt, 3 ... Transfer means, 4 ... Holding force adjustment means, 5 ... Batch transfer means, K ... Recording material, L ... Tension line, T ... Toner image

Claims (7)

An image carrier on which a toner image corresponding to image information is formed and supported;
A recording and conveying belt that is stretched over a plurality of roll groups and is circulated and conveyed through a portion facing the image carrier;
Transfer means for forming a transfer nip region between the image carrier and the image carrier via the recording and conveying belt, and transferring a toner image formed on the image carrier directly or via a recording material to the recording and carrier belt When,
Judgment means for judging whether or not it is an environment in which a tension line that is a streak-like concave portion or convex portion extending along the conveyance direction of the recording and conveying belt due to excessive tension of the recording and conveying belt is formed;
Under environmental conditions in which the tension line is formed on the recording conveyor belt by the determination result of the determination means, than the holding force of the toner to be transferred in a region corresponding to the tension lines of the environmental conditions in which the tension lines are not formed An image forming apparatus comprising: a holding force adjusting unit including a pressing force adjusting unit that adjusts the pressing force of the transfer unit so as to increase. An image carrier on which a toner image corresponding to image information is formed and supported;
A recording and conveying belt that is stretched over a plurality of roll groups and is circulated and conveyed through a portion facing the image carrier;
Transfer means for forming a transfer nip region between the image carrier and the image carrier via the recording and conveying belt, and transferring a toner image formed on the image carrier directly or via a recording material to the recording and carrier belt When,
Judgment means for judging whether or not it is an environment in which a tension line that is a streak-like concave portion or convex portion extending along the conveyance direction of the recording and conveying belt due to excessive tension of the recording and conveying belt is formed;
Under environmental conditions in which the tension line is formed on the recording conveyor belt by the determination result of the determination means, than the holding force of the toner to be transferred in a region corresponding to the tension lines of the environmental conditions in which the tension lines are not formed An image forming apparatus comprising: a holding force adjusting unit including a bias adjusting unit that adjusts a bias application amount to the transfer unit so as to increase. An image carrier on which a toner image corresponding to image information is formed and supported;
A recording and conveying belt that is stretched over a plurality of roll groups and is circulated and conveyed through a portion facing the image carrier;
Transfer means for forming a transfer nip region between the image carrier and the image carrier via the recording and conveying belt, and transferring a toner image formed on the image carrier directly or via a recording material to the recording and carrier belt When,
Judgment means for judging whether or not it is an environment in which a tension line that is a streak-like concave portion or convex portion extending along the conveyance direction of the recording and conveying belt due to excessive tension of the recording and conveying belt is formed;
Under environmental conditions in which the tension line is formed on the recording conveyor belt by the determination result of the determination means, than the holding force of the toner to be transferred in a region corresponding to the tension lines of the environmental conditions in which the tension lines are not formed An image forming apparatus comprising: a pressing force adjusting unit that adjusts the pressing force of the transfer unit and a bias adjusting unit that adjusts a bias application amount to the transfer unit so as to increase. 4. The image forming apparatus according to claim 2, wherein the transfer unit includes a transfer roll disposed in contact with the recording and conveying belt.
The image forming apparatus, wherein the bias adjusting unit adjusts a bias application amount to the transfer roll based on a system resistance in the transfer nip region. The image forming apparatus according to claim 1,
An image forming apparatus, wherein the recording / conveying belt has a volume resistivity of 12 log Ωcm or more under normal temperature and humidity conditions. In the image forming apparatus according to any one of claims 1 to 3, in an aspect having three or more image carriers.
Regarding the pressing force with which each transfer unit presses the recording and conveying belt, the pressing force of the transferring unit disposed on the most upstream side in the conveyance direction of the recording and conveying belt and the most downstream side in the conveying direction of the recording and conveying belt. An image forming apparatus characterized in that the pressing force of the transfer means disposed between them is set higher than the pressing force of the transfer means. In the image forming apparatus according to any one of claims 1 to 3, in an aspect having three or more image carriers.
Regarding the bias application amount to be applied to each transfer unit, the bias application amount of the transfer unit disposed on the most upstream side in the conveyance direction of the recording and conveying belt and the transfer disposed on the most downstream side in the conveyance direction of the recording and conveying belt. An image forming apparatus characterized in that a bias application amount of a transfer unit disposed therebetween is set larger than a bias application amount of the unit.

Images