Patent Grant
10289025
Field of the Invention
The present disclosure relates to image forming apparatuses using electrophotographic processing or the like.
Description of the Related Art
For electrophotographic image forming apparatuses, there is a known configuration in which toner images are sequentially transferred from image forming units of individual colors to an intermediate transfer member, and the toner images are transferred collectively from the intermediate transfer member to a transfer material.
In such image forming apparatuses, each of the image forming units of individual colors includes a drum-shaped photosensitive member serving as an image bearing member. At the time of image formation, toner images developed on the photosensitive members are primarily transferred from the photosensitive members to the intermediate transfer member in a primary transfer portion at which the photosensitive members and the intermediate transfer member are in contact with each other. The toner images of individual colors that are primarily transferred to the intermediate transfer member are secondarily transferred collectively from the intermediate transfer member to a transfer material, such as paper or an overhead projector (OHP) sheet, in a secondary transfer portion in which the intermediate transfer member and a secondary transfer member are in contact with each other and are thereafter fixed onto the transfer material by a fixing unit.
Japanese Patent Laid-Open No. 2004-117722 discloses a configuration in which the surface speed of the intermediate transfer member is set to be higher than the surface speed of the photosensitive member so as to improve the transfer performance of the primary transfer of the toner images from the photosensitive members to the intermediate transfer member. In such a configuration, the primary transfer is performed using a shearing force of shearing the toner images carried by the photosensitive member with the intermediate transfer member.
However, in a so-called cleanerless configuration in which a blade serving as a cleaning member in contact with each photosensitive member is not provided, when the surface speed of the intermediate transfer member is set higher than the surface speed of the photosensitive members, as in Japanese Patent Laid-Open No. 2004-117722, as in Japanese Patent Laid-Open No. 2004-117722, the following problem can occur. That is, in the cleanerless configuration, the load for rotationally driving the photosensitive members is small, so that the photosensitive members are taken along the surface of the intermediate transfer member, causing the positions of the toner images formed on the surface of the photosensitive member to be misaligned to generate image defect.
The present disclosure provides a configuration for an image forming apparatus in which the load for rotationally driving photosensitive members is small in which generation of image defect is prevented while a difference is provided between the surface speed of the photosensitive members and the surface speed of the intermediate transfer member.
The present disclosure provides an image forming apparatus including a photosensitive member, a developing unit configured to develop a toner image on the photosensitive member, an endless rotatable intermediate transfer member in contact with the photosensitive member, and a collecting member. The toner image carried on the photosensitive member is primarily transferred to the intermediate transfer member. Toner remaining on the photosensitive member after the toner image is primarily transferred from the photosensitive member to the intermediate transfer member can be collected by the developing unit. The collecting member can collect toner remaining on the intermediate transfer member after the toner image primarily transferred from the photosensitive member to the intermediate transfer member is secondarily transferred from the intermediate transfer member to a transfer material by pressing a fixed surface of the collecting member against the rotating intermediate transfer member. The photosensitive member rotates at a first speed, and the intermediate transfer member rotates at a second speed lower than the first speed.
Further features of the present disclosure will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Embodiments of the present disclosure will be described in detail herein below with reference to the drawings. It is to be understood that the dimensions, materials, shapes, and the relative positions of the components described in the embodiments can be changed as appropriate according to the configuration of an apparatus that incorporates the present disclosure and various conditions and that the present disclosure is not limited to the embodiments.
First Embodiment
The image forming unit 3 includes a drum-shaped electrophotographic photosensitive member 4 (hereinafter referred to as “photosensitive drum 4”), a charging roller 5, which is a charging member that is in contact with the photosensitive drum 4 to charge the photosensitive drum 4, an exposing unit 6, and a developing unit 7. The developing unit 7 is disposed so as to come into and out of contact with the photosensitive drum 4 and develops an electrostatic latent image formed on the photosensitive drum 4 with toner when a voltage is applied from a developing power source (not shown). In the present embodiment, the photosensitive drum 4 is a negatively charged organic photoconductor having a diameter of 24 mm in which at least a charge generation layer and a charge transport layer containing a polyarylate resin are disposed on an aluminum cylinder.
When a control unit (not shown), such as a controller, receives an image signal, an image forming operation is started, and the photosensitive drum 4 is rotationally driven in the direction of arrow R1. In the course of rotation, the photosensitive drum 4 is uniformly charged to a predetermined voltage (charging voltage) with a predetermined polarity (in the present embodiment, negative polarity) by the charging roller 5 and is exposed to light by the exposing unit 6 according to the image signal. In this manner, an electrostatic latent image corresponding to the color component of the target color image is formed on the photosensitive drum 4. Subsequently, the electrostatic latent image is developed at a developing position by the developing unit 7 and is visualized as a toner image on the photosensitive drum 4. The regular charge polarity of the toner contained in the developing unit 7 is negative, so that the electrostatic latent image is reversely developed with the toner charged to the same polarity as the polarity of the photosensitive drum 4 charged by the charging roller 5. However, this is given for mere illustration. The present disclosure can also be applied to an image forming apparatus that develops the electrostatic latent image with a toner charged to a polarity opposite to the charged polarity of the photosensitive drum 4.
An intermediate transfer belt 9, which is an endless rotatable belt-like intermediate transfer member, is stretched round a driving roller 23a, which is an electrically conductive rotary member, a driven roller 23b, an auxiliary roller 23c, and a facing roller 23d, which is a facing member. The driving roller 23a, the driven roller 23b, and the auxiliary roller 23c are electrically connected to the ground. The driving roller 23a rotates in the direction of arrow R2, so that the intermediate transfer belt 9 rotates at a circumferential speed of 100 mm/sec. A primary transfer roller 10, which is a contact member that is in contact with the intermediate transfer belt 9, is disposed at a position of the inner circumferential surface of the intermediate transfer belt 9 facing the photosensitive drum 4 with the intermediate transfer belt 9 therebetween.
The intermediate transfer belt 9 of the present embodiment has an outer perimeter of about 700 mm and a thickness of about 80 μm and includes an endless polyimide (PI) base layer in which carbon is added as a conductive agent and a surface layer formed on the base layer and containing an acrylic resin. A thickness t1 of the base layer is 78 μm, and a thickness t2 of the surface layer is 2 μm. The volume resistivity of the intermediate transfer belt 9 measured with Hiresta-UP (MCP-HT450) and a ring probe of type UR (MCP-HTP12) manufactured by Mitsubishi Chemical Corporation was about 5×109 Ω·cm. The volume resistivity was measured under the condition that the ring probe was brought into contact with the surface of the intermediate transfer belt 9 at an applied voltage of 100 V, and a measurement time of 10 seconds. The measurement environment was as follows: an indoor temperature of 23° C., and an indoor humidity of 50%.
When the primary transfer roller 10 presses the intermediate transfer belt 9 against the photosensitive drum 4, the intermediate transfer belt 9 abuts the photosensitive drum 4 to form a primary transfer portion 2. In the present embodiment, the distance between the primary transfer rollers 10 in the moving direction of the intermediate transfer belt 9 is about 75 mm. The primary transfer roller 10 connects to a primary transfer power source 20 (a first power source). By applying a voltage from the primary transfer power source 20 to the primary transfer roller 10, a current flows through the intermediate transfer belt 9 via the primary transfer roller 10. The toner image formed on the photosensitive drum 4 is primarily transferred from the photosensitive drum 4 to the intermediate transfer belt 9 by applying a positive voltage from the primary transfer power source 20 to the primary transfer roller 10 while passing through the primary transfer portion 2.
The image forming apparatus 1 of the present embodiment has a so-called cleanerless configuration in which toner remaining on the photosensitive drum 4 after the toner image is transferred from the photosensitive drum 4 to the intermediate transfer belt 9 is collected by the developing unit 7.
In the cleanerless configuration, a blade in contact with the photosensitive drum 4 is not provided between the primary transfer portion 2 at which the photosensitive drum 4 and the intermediate transfer belt 9 are in contact and a charging unit 8 at which the photosensitive drum 4 and the charging roller 5 are in contact in the rotating direction of the photosensitive drum 4. The blade here is a contact member disposed in contact with the photosensitive drum 4 to clean the toner remaining on the photosensitive drum 4. The toner remaining on the photosensitive drum 4 after passing through the primary transfer portion is again charged to negative polarity while passing through the charging unit 8 at which the charging roller 5 and the photosensitive drum 4 are in contact and is thereafter collected by the developing unit 7 at the position where the developing unit 7 and the photosensitive drum 4 are in contact.
In the image forming units 3 of the individual colors, toner images are primarily transferred in sequence from the photosensitive drums 4 to the intermediate transfer belt 9, so that a four-color toner image corresponding to the target color image is formed on the intermediate transfer belt 9. Then, the four-color toner image primarily transferred to the intermediate transfer belt 9 is secondarily transferred collectively to the surface of a transfer material P, such as paper or an OHP sheet, while passing through a secondary transfer portion 19 formed between a secondary transfer roller 14 and the intermediate transfer belt 9 into contact with each other. The transfer material P is supplied from a sheet feeding cassette 11 by a sheet feeding unit 12 and is conveyed to the secondary transfer portion 19.
The secondary transfer roller 14, which is a secondary transfer member in contact with the outer circumferential surface of the intermediate transfer belt 9, is driven to rotate together with the intermediate transfer belt 9. The facing roller 23d is disposed at a position facing the secondary transfer roller 14, with the intermediate transfer belt 9 therebetween. A current flows from the secondary transfer roller 14 to the facing roller 23d by applying positive voltage from a secondary transfer power source 21 to the secondary transfer roller 14, so that the four-color toner image is secondarily transferred from the intermediate transfer belt 9 to the transfer material P at the secondary transfer portion 19.
The transfer material P to which the four color toner image is transferred by a secondary transfer is heated and pressed by the fixing unit 30, so that the four color toners are fused and fixed onto the transfer material P. The transfer material P to which the four color toner image is fixed is discharged from the interior of the image forming apparatus 1 to an output tray 15 by a discharge roller pair 31.
The toner remaining on the intermediate transfer belt 9 after the secondary transfer is collected by a cleaning unit 16 opposed to the facing roller 23d, with the intermediate transfer belt 9 therebetween, downstream from the secondary transfer portion 19 in the moving direction of the intermediate transfer belt 9. The cleaning unit 16 includes a cleaning blade 16a that is in contact with the outer circumferential surface of the intermediate transfer belt 9 and a residual toner container (not shown). The cleaning blade 16a is a collecting member capable of collecting toner remaining on the intermediate transfer belt 9 into the residual toner container by pressing a fixed surface against the rotating intermediate transfer belt 9. In the present embodiment, the cleaning blade 16a is made of urethane rubber whose hardness measured by an ASKER micro-rubber hardness tester MD-1capa is 70°. The cleaning blade 16a is disposed at a pressure of 1,200 gf against the intermediate transfer belt 9.
The image forming apparatus 1 of the present embodiment forms a full-color print image by the above operation.
The image forming apparatus 1 of the present embodiment has a configuration in which a speed difference ΔV is provided between the surface speed Va (a first speed) of the photosensitive drum 4 and the surface speed Vb (a second speed) of the intermediate transfer belt 9. In the present embodiment, the surface speed of the driving roller 23a obtained from the rotational speed of the driving roller 23a that transmits driving to the intermediate transfer belt 9 and the outside diameter of the driving roller 23a is defined as the surface speed Vb of the intermediate transfer belt 9. Specifically, the surface speed Vb of the intermediate transfer belt 9 was set to 100 mm/sec, and the surface speed Va of the photosensitive drum 4 was set to 103 mm/sec. At that time, the speed difference ΔV between the photosensitive drum 4 and the intermediate transfer belt 9 was obtained using the following expression with reference to the surface speed Vb of the intermediate transfer belt 9.
In other words, in the present embodiment, the surface speed Vb of the intermediate transfer belt 9 is lower than the surface speed Va of the photosensitive drum 4, and the speed difference ΔV between the surface speed Vb of the intermediate transfer belt 9 and the surface speed Va of the photosensitive drum 4 is 3%. In the present embodiment, the driving source for the rotation of the intermediate transfer belt 9 and the photosensitive drum 4 is one motor, and the driving is branched and obtained from the common driving source. The speed difference ΔV is set by adjusting the gear speed transmission ratio of a gear train that transmits driving from the common driving source to the intermediate transfer belt 9 and the photosensitive drum 4. For the setting of the speed difference ΔV, at least one of the speed transmission ratio of a gear that transmits driving to the photosensitive drum 4 and the speed transmission ratio of a gear that transmits driving to the intermediate transfer belt 9 may be adjusted.
When the surface speed Va of the photosensitive drum 4 and the surface speed Vb of the intermediate transfer belt 9 differ, of the photosensitive drum 4 and the intermediate transfer belt 9, one with a lower surface speed is given the driving force from one with a higher surface speed. Such a driving force is likely to occur remarkably when the amount of toner at the primary transfer portion 2 is small. This is because, when the amount of toner at the primary transfer portion 2 is small, the area of contact between the surface of the photosensitive drum 4 and the surface of the intermediate transfer belt 9 is wide, so that the frictional force tends to be high. In contrast, when the amount of toner at the primary transfer portion 2 increases, the toner present between the photosensitive drum 4 and the intermediate transfer belt 9 acts as a lubricant, decreasing the frictional force generated between the photosensitive drum 4 and the intermediate transfer belt 9.
In the configuration in which the surface speed Va of the photosensitive drum 4 and the surface speed Vb of the intermediate transfer belt 9 differ, a member with a lower surface speed can be taken along a member with a higher surface speed by the driving force described above. This can cause blurring or color misalignment in an image transferred from the photosensitive drum 4 to the intermediate transfer belt 9, posing the risk of image defect. Whether the member is taken along can be determined by measuring the rotational driving loads of the members.
The operational advantages of the present embodiment will be described herein below with reference to
In the configuration of the present embodiment, the surface speed Vb of the intermediate transfer belt 9 was set lower than the surface speed Va of the photosensitive drum 4, while in the configuration of the comparative example, the surface speed Vb of the intermediate transfer belt 9 was set higher than the surface speed Va of the photosensitive drum 4. Specifically, the surface speed Vb of the intermediate transfer belt 9 was set to 100 mm/sec, while the surface speed Va of the photosensitive drum 4 was set to 97 mm/sec. At that time, the speed difference ΔV between the photosensitive drum 4 and the intermediate transfer belt 9 in the comparative example was 3%.
First, a method for measuring the respective rotational driving loads of the photosensitive drum 4 and the intermediate transfer belt 9 will be described. The rotational driving load of the photosensitive drum 4 was measured by directly connecting an external motor for measurement to the rotation shaft of the photosensitive drum 4 via a torque transducer in a state in which the photosensitive drum 4 is disposed in the image forming apparatus. The external motor for measurement was of Model No. PK566AE manufactured by Oriental Motor, and the torque transducer was of Model No. TM36-10 manufactured by SSK Co. Ltd. The rotational driving load of the intermediate transfer belt 9 was measured by directly connecting an external motor for measurement to the rotation shaft of the driving roller 23a for the intermediate transfer belt 9 via a torque transducer.
The measurement of the rotational driving loads of the photosensitive drum 4 and the intermediate transfer belt 9 was performed on two kinds of image of a solid white image (blank image) and a halftone image. The halftone image is an image in which a black color of 80 mm with a concentration of 20%, a cyan color of 80 mm with a concentration of 20%, and a magenta color of 80 mm with a concentration of 20% are formed continuously. The rotational driving loads in forming a halftone image were measured at the timing when toner images of the individual colors are present at their respective primary transfer portions 2 at the same time. The solid white image is an image obtained when no toner image is transferred to the transfer material. In forming the solid white image, no toner image is transferred from the photosensitive drum 4 to the intermediate transfer belt 9.
As illustrated in
In contrast, as illustrated in
In forming a halftone image, the value of the rotational driving load of the photosensitive drum 4 was positive, and the photosensitive drum 4 was not taken along the intermediate transfer belt 9. This is because the toner present at the primary transfer portion 2 when forming the halftone image is larger than the toner present at the primary transfer portion 2 when forming the solid white image, and the toner acts as a lubricant. Thus, in the configuration of the comparative example, the photosensitive drum 4 is taken along the intermediate transfer belt 9 according to the amount of toner of the image to be formed, so that the surface speed Va of the photosensitive drum 4 fluctuates.
In the configuration of the present embodiment, as illustrated in
Meanwhile, the intermediate transfer belt 9 whose surface speed is lower than the surface speed of the photosensitive drum 4 is subjected to a force in a direction in which it is taken along the photosensitive drum 4. However, as illustrated in
Next, whether an image defect and color misalignment have occurred was determined, and the transfer efficiency was evaluated, with the surface speed Va of the photosensitive drum 4 changed with respect to the surface speed Vb (100 mm/sec) of the intermediate transfer belt 9. Specifically, three kinds of image were formed for seven cases in which the surface speed Va of the photosensitive drum 4 is 97, 99, 100, 101, 103, 105, and 106 mm/sec, and were individually evaluated. At that time, an environment for forming the images was as follows: the temperature was 23° C., the humidity was 50%, the processing speed was 100 mm/sec (throughput: 18 per minute), and the image forming mode was a plane paper mode. The transfer material P was an A4-size Red Label Presentation having a basis weight of 80 g/m2.
The transfer efficiency was evaluated by measuring the concentration of toner remaining on the photosensitive drum 4 without being transferred to the intermediate transfer belt 9 when a black solid image was formed. The transfer residual concentration was measured using a reflectometer (type: TC-6DS/A) manufactured by Nippon Denshoku Industries.
As illustrated in
This image defect occurs because a frictional force between the photosensitive drum 4 and the intermediate transfer belt 9 decreases when the leading end of the toner image carried on the photosensitive drum 4 enters the primary transfer portion 2, and the rotational driving load of the photosensitive drum 4 abruptly changes. When the rotational driving load of the photosensitive drum 4 at a portion carrying no toner image is negative, as illustrated in
The color misalignment will be described with reference to Table 1 and
In the case where the photosensitive drum 4 is taken along the intermediate transfer belt 9 with higher surface speed, when the leading end of the toner image carried on the photosensitive drum 4 reaches the primary transfer portion 2, the toner acts as a lubricant, so that the state in which the photosensitive drum 4 is taken along the intermediate transfer belt 9 is resolved. At that time, the gears for transmitting driving to the photosensitive drum 4 come from the loose state to an engaged state, so that the photosensitive drum 4 is switched from the state of being taken along the intermediate transfer belt 9 to a rotating state by receiving the driving force from the driving source. During the switching, no rotational force is given to the photosensitive drum 4 from both of the intermediate transfer belt 9 and the driving source, so that the rotation of the photosensitive drum 4 temporarily stops. This causes misalignment of the leading ends of the toner images transferred from the photosensitive drums 4 to the intermediate transfer belt 9. In particular, the larger the force of taking the photosensitive drum 4 along the intermediate transfer belt 9, the longer the time during which the photosensitive drum 4 stops, increasing the misalignment of the leading ends of the toner images.
In forming the image as illustrated in
Therefore, as illustrated in
In contrast, in the case where the surface speed Vb (100 mm/sec) of the intermediate transfer belt 9 is lower than the surface speed Va of the photosensitive drum 4, a sufficient load is applied to the intermediate transfer belt 9 by the cleaning blade 16a, as illustrated in
In a configuration in which the surface speed Vb of the intermediate transfer belt 9 and the surface speed Va of the photosensitive drum 4 are equal, that is, the speed difference ΔV is 0%, the photosensitive drum 4 is not taken along the intermediate transfer belt 9, so that color misalignment is prevented.
For the transfer efficient, as illustrated in
If the value of the speed difference ΔV is too great, the toner image is rubbed at the primary transfer portion 2 at which the photosensitive drum 4 and the intermediate transfer belt 9 are in contact, so that an image defect can occur, that is, the toner image may lose its shape. In the present embodiment, the image defect due to the loss of the shape of the toner image occurred when the surface speed Va of the photosensitive drum 4 was set to 106 mm/sec with respect to the surface speed Vb (100 mm/sec) of the intermediate transfer belt 9. For that reason, it is more preferable to set the speed difference ΔV within 5% in the viewpoint of preventing the image defect, described above.
As described above, the configuration of the present embodiment allows the cleanerless image forming apparatus 1 including no cleaning blade, which is a cleaning member in contact with the photosensitive drum 4, to have the following advantages. By providing a speed difference ΔV between the photosensitive drum 4 and the intermediate transfer belt 9 to improve the transfer efficiency and setting the surface speed Vb of the intermediate transfer belt 9 lower than the surface speed Va of the photosensitive drum 4, an image defect caused by the photosensitive drum 4 being taken along the intermediate transfer belt 9 can be prevented.
In the present embodiment, a cleanerless configuration in which there is no toner collecting member is provided between the primary transfer portion 2 and the charging unit 8 in the rotating direction of the photosensitive drum 4 has been described for the image forming apparatus 1 in which the load of rotationally driving the photosensitive drum 4 is small. However, the present disclosure may not have this configuration. For example, a brush or another member for temporarily collecting the toner remaining on the photosensitive drum 4 may be provided in the cleanerless configuration in which the toner remaining on the photosensitive drum 4 after passing through the primary transfer portion 2 is collected by the developing unit 7. Another alternative example is a configuration including a charging roller that charges the toner remaining on the photosensitive drum 4. The configuration including a brush or a charging roller that rotates in contact with the photosensitive drum 4 has a lower load for rotationally driving the photosensitive drum 4 than that of the configuration in which the cleaning blade or another member is pressed against the photosensitive drum 4. Consequently, when the surface speed Vb of the intermediate transfer belt 9 is set higher than the surface speed Va of the photosensitive drum 4, the photosensitive drum 4 may be taken along the intermediate transfer belt 9. For that reason, using the configuration of the present embodiment prevents image defects while improving the transfer efficiency.
In the present embodiment, the speed difference ΔV is provided between the photosensitive drum 4 and the intermediate transfer belt 9 by adjusting the speed transmission ratio of the gears of the gear train using a single motor, which is a common driving source. However, this is given for illustration purposes only. The speed difference ΔV may be set not by adjusting the gear speed transmission ratio but by adjusting the diameter of the driving shaft of the photosensitive drum 4 or the diameter of the driving roller 23a for the intermediate transfer belt 9. Alternatively, the speed difference ΔV may be set by providing separate driving sources for the photosensitive drum 4 and the intermediate transfer belt 9.
Second Embodiment
In the first embodiment, the configuration of the image forming apparatus 1 including the intermediate transfer belt 209 including the endless polyimide (PI) base layer in which carbon is added as a conductive agent and the surface layer containing acrylic resin formed on the outer circumferential surface of the base layer has been described. In contrast, an image forming apparatus 200 of a second embodiment includes an intermediate transfer belt 209 including a base layer 209a, a surface layer 209b formed on the outer circumferential surface of the base layer 209a, and an inner surface layer 209c formed on the inner circumferential surface of the base layer 209a. The configuration of the image forming apparatus 200 of the present embodiment is similar to that of the first embodiment except the configuration of the intermediate transfer belt 209 and that the respective primary transfer rollers 10 of the four image forming units 3 are given a voltage from a common primary transfer power source 20. The same components as those of the first embodiment are therefore denoted by the same reference signs, and descriptions thereof will be omitted.
As illustrated in
The surface resistivity of the intermediate transfer belt 209 measured from the inner surface layer 209c side was 4.7×106Ω/□, and the surface resistivity measured from the surface layer 209b side was 2.6×1011Ω/□. The surface resistivity was measured with the same measuring instrument as that for the volume resistivity and a ring probe of type UR100 (type MCP-HTP16) under the measurement conditions of an applied voltage of 10 V and a measuring time of 10 seconds. The environment for measurement was a room temperature of 23° C. and a room humidity of 50%.
In the configuration of the present embodiment, the surface resistivity on the inner circumferential surface of the intermediate transfer belt 209 is sufficiently lower than the surface resistivity on the outer circumferential surface of the intermediate transfer belt 209 because of the presence of the inner surface layer 209c. For that reason, when a voltage is applied from the primary transfer power source 20 to the primary transfer rollers 10, a current flows via the inner surface layer 209c with lower electrical resistance, so that a uniform potential is formed across the intermediate transfer belt 209. As a result, electrical discharge (hereinafter referred to as upstream discharge) is likely to occur upstream from each primary transfer portion 2 in the moving direction of the intermediate transfer belt 209 due to the potential difference between the photosensitive drum 4 and the intermediate transfer belt 209. This upstream discharge causes a decrease in the potential of the photosensitive drum 4 at the primary transfer portion 2 at which the photosensitive drum 4 and the intermediate transfer belt 209 are in contact, decreasing the electrostatic attracting force acting between the photosensitive drum 4 and the intermediate transfer belt 209 at the primary transfer portion 2. As a result, the frictional force between the photosensitive drum 4 and the intermediate transfer belt 209 decreases.
As illustrated in
As illustrated in
As described above, the configuration of the present embodiment reduces or eliminates fluctuations in the rotational driving loads of the photosensitive drum 4 and the intermediate transfer belt 209 depending on whether toner is interposed at the primary transfer portion 2. In other words, the present embodiment reduces or eliminates fluctuations in the rotational driving loads of the photosensitive drum 4 and the intermediate transfer belt 209 when the leading end of the toner image carried on the photosensitive drum 4 enters the primary transfer portion 2.
Next, evaluation of color misalignment in the present embodiment will be described using Table 2. A method for evaluating the color misalignment is the same as the method of the first embodiment. The image illustrated in
As illustrated in Table 2, the configuration of the present embodiment allows the value of the amount of color misalignment to be lower than that of the first embodiment. This is because the presence of the inner surface layer 209c reduces or eliminates fluctuations in the rotational driving loads of the photosensitive drum 4 and the intermediate transfer belt 209 when the leading end of the toner image carried by the photosensitive drum 4 enters the primary transfer portion 2.
As described above, the configuration of the present embodiment can not only offer the same advantages as those of the first embodiment but also reduce or eliminate the color misalignment of an image formed on the transfer material P regardless of the amount of the toner of the toner image transferred to the intermediate transfer belt 209.
In the present embodiment, the presence of the inner circumferential surface 209c allows a uniform potential to be formed across the intermediate transfer belt 209. This allows a stable potential to be formed at each primary transfer portion 2 even in the configuration in which a single primary transfer power source is used in common to apply a voltage to each primary transfer roller 10, and the single primary transfer power source 20 is connected to the individual primary transfer rollers 10, as illustrated in
In the present embodiment, carbon is added as an electron conductive agent to the base layer 209a of the intermediate transfer belt 209. The conductive agent added to the base layer 209a is not limited thereto. An ion conductive agent, such as multivalent metal salt or quaternary ammonium salt, may be added. The ion conductive agent is easier to adjust the electrical resistance of the substance to which the conductive agent is added than the electron conductive agent. Therefore, adding the ion conductive agent to the base layer 209a can extend the range of adjustment of the electrical resistance of the intermediate transfer belt 209. The intermediate transfer belt 209 to which the ion conductive agent is added has the property that the electrical resistance hardly fluctuates even if the magnitude of the voltage to be applied is changed. For that reason, even when the magnitude of the voltage to be applied to the primary transfer roller 10 is changed, a desired current can be made to flow from the intermediate transfer belt 209 to the photosensitive drum 4.
Another Embodiment
In the second embodiment, the configuration in which a voltage is applied from the common primary transfer power source 20 to each primary transfer roller 10 at each image forming unit 3 for primary transfer has been described. In contrast, in the present embodiment, as illustrated in
The Zener diode 25, which is a constant voltage element, is an element that maintains a predetermined voltage (hereinafter referred to as “breakdown voltage”) by the passage of electric current, in which a breakdown voltage is generated on the cathode side when a certain amount of current flows. In the present embodiment, the cathode (one end) of the Zener diode 25 is connected to the facing roller 23d and the primary transfer rollers 10, and the anode (the other end) is electrically connected to the ground.
In the configuration of the present embodiment, when a voltage is applied from the transfer power source 321 to the secondary transfer roller 14, a current flows from the secondary transfer roller 14 to the Zener diode 25 via the conductive intermediate transfer belt 209 and the facing roller 23d. At that time, when a current of a predetermined value or more flows through the Zener diode 25, a breakdown voltage occurs at the cathode of the Zener diode 25, so that the facing roller 23d and each primary transfer roller 10 are maintained at the breakdown voltage of the Zener diode 25. This causes a primary transfer current to flow from the primary transfer roller 10 to the photosensitive drum 4, so that a toner image is primarily transferred from the photosensitive drum 4 to the intermediate transfer belt 209.
Thus, in the present embodiment, since the intermediate transfer belt 209 includes the inner surface layer 209c, a desired potential can be formed at each primary transfer portion 2 even with the configuration in which the primary transfer power source and the secondary transfer power source are commonalized, providing a stable primary transfer performance. This configuration reduces the number of primary transfer power sources, thereby simplifying and reducing the size and cost of the power supply board.
The present embodiment has a configuration in which the primary transfer roller 10 in contact with the inner surface layer 209c of the intermediate transfer belt 209 and the facing roller 23d are electrically connected so that a current flows from the primary transfer roller 10 to the photosensitive drum 4 via the intermediate transfer belt 209. This is given for illustration purpose only. Alternatively, the toner image may be transferred from the photosensitive drum 4 to the intermediate transfer belt 209, without providing the primary transfer roller 10, but by making a current flow in the circumferential direction of the intermediate transfer belt 209 from the facing roller 23d. At that time, the current flows from the facing roller 23d maintained at the breakdown voltage along the circumference of the intermediate transfer belt 209 via the inner surface layer 209c with low surface resistivity in contact with the facing roller 23d.
While the present disclosure has been described with reference to exemplary embodiments, it is to be understood that the disclosure is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2017-016205 filed Jan. 31, 2017, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2017-016205 | Jan 2017 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 8396395 | Aoyagi | Mar 2013 | B2 |
| 9141058 | Saito et al. | Sep 2015 | B2 |
| 9645529 | Onishi et al. | May 2017 | B2 |
| Number | Date | Country |
|---|---|---|
| 2001-201902 | Jul 2001 | JP |
| 2004-117722 | Apr 2004 | JP |
| 2004-233696 | Aug 2004 | JP |
| 2008-170955 | Jul 2008 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20180217522 A1 | Aug 2018 | US |
