JP4863719B2 - Transfer device, image forming device - Google Patents

Description

  The present invention relates to a transfer apparatus and an image forming apparatus, and in particular, a plurality of image carriers, an intermediate transfer belt stretched by a plurality of rollers, and a secondary transfer unit that transfers an image on the intermediate transfer belt to a transfer material. And an image forming apparatus.

  As a typical method for forming a color image, there is an intermediate transfer method in which toner images of different colors formed on a plurality of photosensitive members are transferred while being superimposed on an intermediate transfer member, and then transferred onto a transfer sheet in a lump. This system is called a tandem system because a plurality of photoconductors are arranged facing the transfer paper or intermediate transfer body, and each photoconductor is yellow (Y), magenta (M), cyan (C), black For each color of (K), an electrophotographic process such as formation and development of an electrostatic latent image is performed, and the image is transferred onto the running intermediate transfer member in the intermediate transfer process.

  In such a configuration, when the transfer material is inserted through the resist portion into the secondary transfer portion where transfer from the intermediate transfer body to the transfer paper is performed, the speed fluctuation of the transfer belt occurs, and the image of the primary transfer portion or 2 There is a tendency that the image at the next transfer portion becomes a horizontal streak-like abnormal image (shock jitter). In particular, when a firm transfer paper such as thick paper is passed through, the force when being conveyed from the resist portion is directly transmitted to the paper, so that the secondary transfer portion is affected and the influence becomes remarkable. On the other hand, when passing plain paper such as plain paper, the paper sag between the resist portion and the secondary transfer, so that an abnormal image of shock jitter is relatively unlikely to occur. However, as the size of the machine is reduced, it has become difficult to secure the distance of the portion that caused the slack in the paper.

  Conventionally, in such an intermediate transfer type image forming apparatus, in order to avoid the above-described problems, the distance between the registration unit and the secondary transfer roller is increased, and the paper conveyance force of the registration unit is transmitted to the secondary transfer unit. In order to reduce the influence of the resist portion on the transfer portion.

  As another measure for avoiding the above-described troubles, an adjustment process is performed to make the paper transfer speed of the secondary transfer portion and the resist portion almost constant at the time of passing the thick paper, and the influence of the resist portion is applied to the secondary transfer portion. I try not to communicate. In this method, adjustments and the like are required, which increases the cost.

  In order to solve the above-mentioned problems, the following has been proposed. In Patent Document 1, four color process cartridges are stacked in the vertical direction, and the distance from the primary transfer completion position of the toner image on the intermediate transfer belt to the secondary transfer position to the transfer material is defined as the transfer material. Is set to be longer than the length in the conveyance direction, and thereby, the intermediate transfer belt can be set to a low speed mode with a sheet of OHP without idling once.

  In Patent Document 2, contact between the photosensitive drum and the intermediate transfer belt is released before the transfer of the toner image on the intermediate transfer belt to the transfer material, whereby the toner image on the photosensitive drum is transferred to the intermediate transfer belt. Describes that the rotation of the photosensitive drum can be stopped immediately after the transfer is completed, and the life of the image forming unit including the intermediate transfer belt and the photosensitive drum can be extended.

  In Patent Document 3, the distance from the primary transfer position to the secondary transfer position having the shortest distance to the secondary transfer position along the surface movement direction of the intermediate transfer member is set to be longer than the length in the conveyance direction of the recording medium. Things are listed.

In Patent Document 4, an intermediate transfer belt having a volume resistivity of 10 ¹² Ωcm or more is used, and before transferring a visible image to the intermediate transfer belt, an output of zero V is output by a secondary transfer charger. The one which performs the charge removal of is described.
JP 2000-235289 A JP 2002-99132 A JP 2002-372899 A JP 2000-56593 A

  However, in order to reduce shock jitter at the time of paper entry, the length from the final color to the secondary transfer is set to be longer than the paper passing length so that the influence at the time of paper entry does not reach the primary transfer portion. However, there is a problem that the shock jitter after the second sheet during continuous paper feeding cannot be prevented.

  In addition, the actual situation is that no consideration is given to the slip at the secondary transfer portion which occurs when the thick paper affects the resist speed when the thick paper is passed.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a transfer device and an image forming apparatus in which abnormal images due to shock jitter do not occur on the second and subsequent sheets even when continuous paper is passed using thick paper.

The invention of claim 1
A plurality of image carriers on which toner images of respective colors are respectively formed; an intermediate transfer belt stretched by a plurality of rollers on which toner images are superimposed and primary-transferred from these image carriers;
A secondary transfer roller for transferring the superimposed image on the intermediate transfer belt to a transfer material,
The final stage image bearing member and the length of the intermediate transfer belt along the belt moving direction of the intermediate transfer belt from the point of contact to the secondary transfer portion by the secondary transfer roller of said plurality of image bearing members In the image forming apparatus, the length of the transfer material in the traveling direction is not less than the maximum sheet passing length,
It performs a transfer process to end before the start of the primary transfer for the secondary transfer by the secondary transfer roller of the transfer material adjacent at continuous printing to the front side of the transfer material following transfer material,
When transferring a superimposed image of a plurality of colors on the intermediate transfer belt to a transfer material, it is possible to switch between a thick paper mode and a plain paper mode, and the transfer process is performed in the thick paper mode.
The drive speed of the intermediate transfer belt can be switched between a first drive speed and a second drive speed lower than the first drive speed,
In the thick paper mode, control is performed to switch the drive speed of the intermediate transfer belt from the first drive speed to the second drive speed between the end of the primary transfer and the start of the secondary transfer.
The secondary transfer roller is configured to be able to select a driven rotation driving driven by an opposing member or a driving rotation driven by a driving force from a driving source. In the normal paper mode, the driven rotation driving and the thick paper mode are selected. In this case, the drive is rotated,
The drive rotation of the secondary transfer roller uses a roller disposed opposite to the secondary transfer roller via a gear as a drive source,
The plurality of image carriers are arranged above the intermediate transfer belt, and the intermediate transfer belt is stretched by two rollers, a driving roller and a driven roller, and has a roller facing the secondary transfer roller. As drive roller,
The drive roller and the secondary transfer roller are connected by the drive roller side roller and the secondary transfer roller side roller so that the secondary transfer roller can be driven to rotate together with the drive roller, and the secondary transfer roller The transfer device is characterized in that the gear on the transfer roller side can be moved in the thrust direction by a drive source such as a solenoid .

A second aspect of the invention is an image forming apparatus comprising the transfer device of the first aspect.

According to the transfer device and the image forming apparatus according to the present invention, even if continuous paper is used using thick paper, an abnormal image due to shock jitter does not occur after the second sheet , and this occurs due to the stiffness of the thick paper. possible to avoid abnormal images can be prevented slipping of the secondary transfer roller constituting the next transfer portion and that Do.
Further, the rotation of the secondary transfer roller is performed by using a roller disposed opposite to the secondary transfer roller via a gear as a drive source, and using a roller facing the secondary transfer roller as a drive roller. In addition, the configuration for driving each roller and the gear configuration for driving transmission can be accommodated in a space having a small secondary transfer portion, and the apparatus configuration can be reduced in size.
Furthermore, the drive roller and the secondary transfer roller are connected by a gear, the secondary transfer roller can be rotated together with the drive roller, and the gear on the secondary transfer roller side can be moved in the thrust direction by a drive source such as a solenoid. As a result, it is possible to select driving rotation or driven rotation with a gear with a simple configuration that only switches the presence or absence of gear connection.

  Embodiments as the best mode for carrying out the present invention will be described below with reference to the drawings.

  Embodiments of an image forming apparatus according to the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing the structure of an image forming apparatus according to an embodiment of the present invention. In this example, the image forming apparatus includes four cylindrical photosensitive members 1 and rotates the photosensitive drum 1 in the arrow direction at a peripheral speed of 150 mm / sec. A roller-shaped charger 4 serving as charging means is pressed against the surface of the photosensitive drum 1, and is driven to rotate by the rotation of the photosensitive drum 1, and AC and DC biases are applied from a high voltage power source (not shown). Thus, the surface potential is uniformly charged to -500V. The photosensitive drum 1 is exposed to image information by an exposure unit 5 which is a latent image forming unit, and an electrostatic latent image is formed. This exposure process is performed by a laser beam scanner or LED using a laser diode.

  The photoreceptor cleaning unit 3 includes a blade 2 and cleans transfer residual toner on the surface of the photoreceptor drum. The developing means in this embodiment is a one-component contact developing, and is composed of four developing units, a yellow developing unit 6, a cyan developing unit 7, a magenta developing unit 8 and a black developing unit 9, and is supplied from a high voltage power source (not shown). The electrostatic latent image on the photosensitive drum 1 is visualized as a toner image by a predetermined developing bias.

  Four photosensitive drums 1 are arranged in parallel, and when full-color images are formed, visible images are formed in the order of yellow, cyan, magenta, and black, and the visible images of each color are sequentially transferred onto the intermediate transfer belt 10. As a result, a full-color image is formed.

  The intermediate transfer belt 10 is stretched by a drive roller 20 and a driven roller 21, and primary transfer bias rollers 11, 12, 13, and 14 are disposed therein, and are driven to rotate in the direction of the arrow in the figure by a drive motor (not shown). It has come to be. In this example, the drive roller 20 is configured to also serve as a secondary transfer bias roller facing the secondary transfer roller. In this example, since the intermediate transfer belt is stretched by two rollers, a unit with a minimum space can be provided. Further, by using the secondary transfer counter roller as a driving roller, the belt and the secondary transfer counter roller can be configured not to slip with respect to belt speed fluctuations when paper enters.

  The primary transfer bias roller 14 is held by a primary transfer bias roller holding member 15 and is pressed toward the photosensitive drum 1 by a contact / separation cam 16. In the normal state, the contact / separation cam 16 presses the primary transfer bias roller 14 toward the photosensitive drum 1, and the contact / separation cam 16 rotates only when the photosensitive drum 1 or the intermediate transfer belt 10 is attached / detached. The transfer bias roller 14 is separated. In the embodiment, the drive roller 20 is made of polyurethane rubber (thickness: 0.3 to 1 mm). However, a thin layer coating (thickness 0.05 to 0.1) or the like is preferable for use as a driving roller because the change in diameter due to temperature is small.

  A belt cleaning unit 24 is disposed on the driving roller 20, and cleaning is performed by scraping off transfer residual toner on the intermediate transfer belt 10 with a built-in blade 23.

  Each roller that stretches the intermediate transfer belt 10 is supported from both sides of the intermediate transfer belt 10 by an intermediate transfer belt unit side plate (not shown). Materials used for the intermediate transfer belt 10 include PVDF (vinylidene fluoride), ETFE (ethylene-tetrafluoroethylene copolymer), PI (polyimide), PC (polycarbonate), TPE (thermoplastic elastomer), and carbon black. It is possible to use a resin film-like endless belt in which a conductive material such as the above is dispersed.

  The intermediate transfer belt 10 used in this example has a single-layer structure in which carbon black is added to PC (polycarbonate), and the thickness thereof is adjusted to 140 μm.

  The volume resistivity and the surface resistivity of the intermediate transfer belt 10 are desirably in the range of 108 to 1012 Ωcm and the surface resistivity of 109 to 1012 Ω / □.

  The resistance of the intermediate transfer belt 10 is measured by connecting a probe (inner electrode diameter 50 mm, ring electrode inner diameter 60 mm: JIS-K6911 compliant) to a digital ultrahigh resistance microammeter (manufactured by Advantest: R8340A). A voltage of 1000 V (surface resistivity is 500 V) was applied to the front and back of the substrate, measurement was performed at a discharge of 5 sec and a charge of 10 sec, and the environment during the measurement was fixed at 22 ° C. and 55% RH.

  When the volume resistivity and surface resistivity of the intermediate transfer belt 10 exceed the above-described ranges, the transfer belt is charged. Therefore, it is necessary to take a measure such as setting the set voltage value higher as it goes downstream in the image forming order. Therefore, it becomes difficult to use a single power supply for the primary transfer unit. This is because the charge generated on the surface of the intermediate transfer belt 10 becomes high due to the discharge generated in the transfer process, the transfer material peeling process, and the like, and self-discharge becomes difficult. Need arises. Also, if the volume resistivity and surface resistivity are below the above ranges, the charge potential decays faster, which is advantageous for static elimination by self-discharge, but toner scattering occurs because the current during transfer flows in the surface direction. End up. Therefore, the volume resistivity and surface resistivity of the intermediate transfer belt 10 in the present invention must be within the above ranges.

  The secondary transfer roller 22 is configured by covering a metal core such as SUS with an elastic body such as urethane adjusted to a resistance value of 106 to 1010 Ω by a conductive material. Here, if the resistance value of the secondary transfer roller 22 exceeds the above range, it becomes difficult for the current to flow. Therefore, a higher voltage must be applied in order to obtain a required transfer property, resulting in an increase in power supply cost. . In addition, since it is necessary to apply a high voltage, discharge occurs in the gaps before and after the transfer portion nip, and white spots are lost due to the discharge on the halftone image. This is remarkable in a low-temperature and low-humidity environment (for example, 10 ° C. and 15% RH). On the contrary, if the resistance value of the secondary transfer roller 22 is below the above range, the transferability between the multi-color image portion (for example, three-color superimposed image) and the single-color image portion existing on the same image cannot be achieved. This is because the resistance value of the secondary transfer roller 22 is low, so that a sufficient current flows to transfer the monochrome image portion at a relatively low voltage. However, it is optimal for the monochrome image portion to transfer the multiple color image portion. This is because a voltage value higher than the voltage is required, and setting a voltage that can transfer a plurality of color image portions causes an excessive transfer current in a single color image, resulting in a decrease in transfer efficiency.

  The resistance value of the secondary transfer roller 22 is measured by installing the secondary transfer roller 22 on a conductive metal plate and applying a load of 4.9 N on one side (total of 9.8 N on both sides) to both ends of the core metal. It was calculated from the value of the current that flows when a voltage of 1000 V was applied between the cored bar and the metal plate in the above state. The measurement of the resistance of the secondary transfer roller 22 was also performed with the environment fixed at 22 ° C. and 55% RH. In this embodiment, the resistance of the secondary transfer roller 22 was adjusted to be 7.8 LogΩ when measured by the method described above.

  In this example, the primary transfer bias rollers 11, 12, 13, and 14 have the same configuration as the above-described secondary transfer bias roller. This is because, since the intermediate transfer belt 10 is in contact with the photosensitive drum 1, the primary transfer nip cannot be secured unless the primary transfer bias roller has an appropriate elastic layer. However, the resistance range is not as severe as the secondary transfer bias roller of the intermediate transfer belt layer, but in this embodiment, the resistance of the primary transfer bias roller is 7.0 LogΩ when measured by the above-described method. It was adjusted.

  The transfer material 29 is fed by the pick-up roller 28, the paper feeding / conveying roller 27, and the registration roller 26 in accordance with the timing at which the leading edge of the toner image on the surface of the intermediate transfer belt 10 reaches the secondary transfer position. As a result, the toner image on the intermediate transfer belt 10 is transferred to the transfer material 29. The transfer material 29 is separated from the intermediate transfer belt 10 by the curvature of the secondary transfer counter roller 19 and a predetermined separation bias applied by the separation means 30, and the toner image transferred to the transfer material 29 is fixed by the fixing means 25. Then it is ejected.

  In this embodiment, a single color mode for forming an image of any one color of yellow, magenta, cyan, and black, a two-color mode for forming an image of two colors of yellow, magenta, cyan, and black, and yellow , Magenta, cyan, and black, a three-color mode that forms an image with three colors superimposed, and a full-color mode that forms a four-color superimposed image as described above. These modes can be specified on the operation unit. is there.

  Further, in this embodiment, the process speed at the time of fixing is changed depending on the type of the transfer material 29. Specifically, when using a transfer material with a continuous weight of 110 kg or more, the process speed is set to half speed, and the transfer material takes twice the normal process speed over the fixing nip formed by the fixing roller pair. The toner image can be secured.

  Hereinafter, the configuration of the transfer device according to the above-described embodiment will be described. FIG. 2 is a schematic diagram showing a transfer device of the image forming apparatus shown in FIG. In this example, the black (K) photoreceptor 1a (K), the magenta (M) photoreceptor 1b (the cyan (C) photoreceptor 1c, and the yellow (Y) photoreceptor from the upstream side of the intermediate transfer belt 10. An image forming unit having a photosensitive member 1d is disposed, and an intermediate transfer belt is stretched by a driving roller 20 and a driven roller 21. The driving roller 20 also serves as a counter roller of the secondary transfer roller. , T = 0.05 to 0.1, and in this example, a distance L1 from the most downstream photoconductor 1d to the secondary transfer roller 22 as shown in FIG. Is made longer than the length L2 of the transfer material 29. Thus, it is possible to avoid the influence of shock jitter when the first transfer material enters.

  Next, the operation of the image forming apparatus according to this embodiment will be described. The image forming apparatus according to this example is controlled as follows. First, the first one image formation will be described. FIG. 3 is a diagram illustrating an example of the transfer bias application timing of the image forming apparatus according to the embodiment. As in this example, in the case of an image forming apparatus in which the distance from the most downstream photoreceptor, that is, the photoreceptor 1d to the secondary transfer roller 22 is longer than the sheet passing length, the most downstream yellow photoreceptor 1d After the final processing of the image processing is completed, the leading edge of the transfer material enters the secondary transfer portion. By performing the bias application process at such timing, the belt speed fluctuation caused by the paper in the secondary transfer part during the transfer process in the primary transfer part does not occur.

  Next, the timing when two sheets are continuously passed will be described. 4 is a timing chart showing the operation of the image forming apparatus shown in FIG. 1 in the plain paper mode. FIG. 5 is a timing chart showing the operation of the image forming apparatus shown in FIG. 1 in the thick paper mode. In the plain paper mode to be used, the secondary transfer of the first transfer material is started during the primary transfer process of the second sheet at timing a in FIG. With plain paper, the transfer material is not stiff and the transfer belt is not affected by the speed.

  On the other hand, in the thick paper mode using thick paper with stiffness, each timing is adjusted so as not to perform the secondary transfer during the primary transfer, as shown in FIG. That is, the time between the transfer end timing c on the first most downstream photoconductor 1d and the transfer timing d on the second most upstream photoconductor 1a is lengthened, and between the timing c and the timing d. In addition, the second transfer of the first transfer material is performed. For this reason, image degradation due to belt speed fluctuations due to the influence of the transfer material does not occur during the primary transfer.

  Next, another control example of the image forming apparatus according to the embodiment will be described. FIG. 6 is a timing chart showing the operation of another embodiment of the image forming apparatus shown in FIG. In this example, by changing the input control signal to the drive roller, the drive speed of the drive roller is changed to the first speed and the second speed that is slower than the first speed. When an image is formed on the intermediate transfer belt, driving is performed at the first speed, and when the toner image is secondarily transferred onto the transfer material, driving is performed at the second speed. Thereby, since heat energy is required for fixing, it is possible to improve print productivity even when printing on thick paper or OHP where the paper conveyance speed is set to a low speed.

  In particular, when the above-described thick paper mode is executed, the print timing is delayed to take a countermeasure against shock jitter. Therefore, the print productivity is inevitably lowered, but the productivity can be improved by this implementation.

  Next, another example of the transfer device according to the embodiment will be described. FIG. 7 is a side view showing a configuration of a transfer apparatus according to another embodiment. The transfer device according to this example enables the secondary transfer roller 22 that contacts the drive roller 20 to be interlocked. In this example, the driving roller 20 and the secondary transfer roller 22 are connected by gears 31 and 32, and the secondary transfer roller can be rotated together with the driving roller 20. In this example, the gear 31 of the secondary transfer roller 22 can be moved in the thrust direction by a drive source such as a solenoid, and the secondary transfer roller 22 can be selected as gear-driven rotation or driven rotation. In this embodiment, it is preferable to use a driven rotation for plain paper and a gear drive rotation for the thick paper mode, thereby preventing slippage of the secondary transfer portion caused by thick paper. It is possible to avoid abnormal images.

1 is a cross-sectional view illustrating a structure of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a front view showing a transfer device of the image forming apparatus shown in FIG. 1. 2 is a timing chart illustrating an operation of the image forming apparatus illustrated in FIG. 1. 2 is a timing chart illustrating an operation in a plain paper mode of the image forming apparatus illustrated in FIG. 1. 3 is a timing chart illustrating an operation in a thick paper mode of the image forming apparatus illustrated in FIG. 1. 6 is a timing chart showing the operation of another embodiment of the image forming apparatus shown in FIG. It is a side view which shows the structure of the transfer apparatus which concerns on another Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Photoconductor 1a ... Photoconductor 1b ... Photoconductor 1c ... Photoconductor 1d ... Photoconductor 2 ... Blade 3 ... Photoconductor cleaning unit 4 ... Charger 5 ... Exposure means 6 ... Yellow developing unit 7 ... Cyan developing unit 8 ... Magenta developing unit 9 ... Black developing unit 10 ... Intermediate transfer belts 11, 12, 13, 14 ... Primary transfer bias roller 15 ... primary transfer bias roller holding member 16 ... contact / separation cam 19 ... secondary transfer counter roller 20 ... drive roller 21 ... driven roller 22 ... secondary transfer roller 23 ... Blade 24 ... Belt cleaning unit 25 ... Fixing means 26 ... Registration roller 27 ... Paper feed roller 28 ... Pickup roller 29 ... Transfer material 30 ... Separating means 31, 32 ... Ya

Claims (2)

A plurality of image carriers on which toner images of respective colors are respectively formed; an intermediate transfer belt stretched by a plurality of rollers on which toner images are superimposed and primary-transferred from these image carriers;
A secondary transfer roller for transferring the superimposed image on the intermediate transfer belt to a transfer material,
The final stage image bearing member and the length of the intermediate transfer belt along the belt moving direction of the intermediate transfer belt from the point of contact to the secondary transfer portion by the secondary transfer roller of said plurality of image bearing members not less than the maximum paper feed length direction of travel of the length of the transfer material in the image forming apparatus,
It performs a transfer process to end before the start of the primary transfer for the secondary transfer by the secondary transfer roller of the transfer material adjacent at continuous printing to the front side of the transfer material following transfer material,
When transferring a superimposed image of a plurality of colors on the intermediate transfer belt to a transfer material, it is possible to switch between a thick paper mode and a plain paper mode, and the transfer process is performed in the thick paper mode.
The drive speed of the intermediate transfer belt can be switched between a first drive speed and a second drive speed lower than the first drive speed,
In the thick paper mode, control is performed to switch the drive speed of the intermediate transfer belt from the first drive speed to the second drive speed between the end of the primary transfer and the start of the secondary transfer.
The secondary transfer roller is configured to be able to select a driven rotation driving driven by an opposing member or a driving rotation driven by a driving force from a driving source. In the normal paper mode, the driven rotation driving and the thick paper mode are selected. In this case, the drive is rotated,
The drive rotation of the secondary transfer roller uses a roller disposed opposite to the secondary transfer roller via a gear as a drive source,
The plurality of image carriers are arranged above the intermediate transfer belt, and the intermediate transfer belt is stretched by two rollers, a driving roller and a driven roller, and has a roller facing the secondary transfer roller. As drive roller,
The drive roller and the secondary transfer roller are connected by the drive roller side roller and the secondary transfer roller side roller so that the secondary transfer roller can be driven to rotate together with the drive roller, and the secondary transfer roller The transfer device, wherein the transfer roller side gear is movable in the thrust direction by a drive source such as a solenoid . An image forming apparatus comprising the transfer device 請 Motomeko 1.