JP4040964B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus such as a copying machine or a printer, and more particularly to an image forming apparatus having improved separation characteristics from an image carrier when an OHP sheet is used as a transfer sheet. In particular, the present invention relates to a color image forming apparatus that forms a color toner image by superimposing at least two monochromatic toner images on an image carrier.
[0002]
[Prior art]
In an electrostatic copying machine, a toner image formed on the surface of an image carrier such as a photoreceptor or an intermediate transfer member is transferred to a transfer sheet, and then the transfer sheet is separated from the image carrier and conveyed to a fixing device. And fixing. As the transfer sheet, plain paper is generally used. When the photosensitive member is a small-diameter drum, so-called curvature separation is possible depending on the rigidity of the paper (stiffness, strength of paper, etc.) without providing any separation means. However, in the photosensitive drum and the intermediate transfer drum that have not been reduced in diameter, the separation by the curvature separation is not complete, and winding may occur due to poor separation.
[0003]
In particular, in a full-color image forming apparatus, each color toner image formed on the surface of the photoreceptor is sequentially transferred to an intermediate transfer drum, and a toner image for one transfer sheet is carried on the outer peripheral surface of the intermediate transfer drum. However, since the diameter of the intermediate transfer drum is inevitably increased, separation due to the rigidity of the transfer material is difficult, and furthermore, the amount of toner adhering to the intermediate transfer drum is large due to color superposition. In many cases, a separating means for separating the transfer sheet from the image carrier is provided separately because it is necessary and is more difficult to separate.
[0004]
For example, in the following Patent Document 1, an AC corona separation method is used as a separation means. Since the electrostatic attraction between the transfer sheet and the image carrier is very strong for the reasons described above, if the application of the AC voltage is stopped when the front half of the paper is separated from the image carrier, the image is separated from the middle. Since a defect occurs, the AC voltage is continuously applied while the sheet is passing.
[0005]
On the other hand, an OHP sheet may be used as a transfer sheet for creating presentation materials. When an OHP sheet is used in an image forming apparatus provided with a separation unit, a transfer failure phenomenon such as transfer unevenness or image density failure occurs at the rear end portion of the OHP sheet. As a countermeasure against such a transfer failure, for example, in Patent Document 2 below, a control unit that determines whether the transfer material P is plain paper or an OHP sheet and controls the bias value of the transfer roller according to the type of the transfer material. A technique using is disclosed.
[0006]
[Patent Document 1]
JP-A-5-142955 [Patent Document 2]
JP-A-8-123221 [0007]
[Problems to be solved by the invention]
However, as disclosed in the above-mentioned Patent Document 2, even when a technique for determining the type of transfer material (transfer sheet) and controlling the bias value of the transfer roller is used, transfer in the latter half of the transfer material is performed. There is a problem in that the adhesiveness between the material and the image carrier is lowered and transferability is deteriorated. That is, when an OHP sheet is used as a transfer material, since the OHP sheet has higher rigidity than plain paper, the suction force between the OHP sheet and the image carrier tends to decrease as the rear end approaches. Regardless, since the voltage applied to the separation charger remains high, separation is performed rapidly at the rear end of the OHP sheet, resulting in insufficient adhesion to the image carrier and a deterioration in toner transferability. It is considered.
[0008]
As a result of various studies based on the above-mentioned considerations to solve the above problems, the inventor of the present application has found that the rear end of the OHP sheet reaches the separation charger, that is, the portion where the separation charger section of the OHP sheet has not passed. In order to complete the present invention, it has been found that the transferability of toner can be improved by turning off the voltage applied to the separation charger when the toner remains over a predetermined length to improve the adhesion to the OHP sheet image carrier. It has come.
[0009]
That is, an object of the present invention is to provide an image forming apparatus that does not have a separation failure and a transfer failure phenomenon in the latter half even when an OHP sheet is used. It is a second object of the present invention to provide an image forming apparatus having both separability and transferability in both cases of OHP sheets and plain paper.
[0010]
[Means for Solving the Problems]
The above object of the present invention can be achieved by the following constitution.
That is, according to the first aspect of the present invention, the toner image formed on the surface of the intermediate transfer drum carrying the toner images of a plurality of colors on the surface is obtained by sequentially transferring the toner images of the respective colors formed on the surface of the photoreceptor. A transfer means for transferring the image to the transfer sheet; and a separating means installed on the downstream side of the transfer means for separating the transfer sheet on which the toner has been transferred from the intermediate transfer drum ,
An image forming apparatus that applies a separation voltage to the separation unit while conveying the transfer sheet between the separation unit and the intermediate transfer drum ,
When the transfer sheet having a rigidity higher than that of plain paper has one separation voltage application member as the separation means and a member to which a separation voltage is applied, the axis of the intermediate transfer drum and the separation voltage application member Or a plane including the axis of the intermediate transfer drum and an intermediate position between the two separation voltage application members at least when the first predetermined length is passed. A first control mode in which the application of the voltage is turned on and the application of the separation voltage is turned off when the non-passing portion remains for a second predetermined length or more; and the application of the separation voltage while the plain paper is passing through the plane And a second control mode in which the application of the separation voltage is turned off after the non-passing portion is eliminated,
One of the first control mode and the second control mode can be selected.
[0012]
According to such a configuration, in the case of plain paper, the separation voltage is continuously applied from the leading end to the trailing end, so that separation failure can be prevented.
In the case of a transfer sheet having a higher rigidity , a separation voltage is applied at least when the front end of the transfer sheet passes through the first predetermined length separation region, so that separation failure can be prevented and the unpassed portion at the rear end is second predetermined. Since the application of the separation voltage is turned off when it remains longer than this, transfer failure due to abrupt separation at the rear end is prevented, and a good transfer image is transferred onto a rigid transfer sheet.
[0014]
According to such a configuration, since a high transfer current is passed through the transfer sheet in order to transfer a toner image having a plurality of colors overlapped, the adhesion between the transfer sheet and the intermediate transfer drum is high, and the outer diameter of the intermediate transfer drum is large. Even in a color image forming apparatus in which curvature separation is hardly expected, a transfer sheet having high rigidity is completely separated from the intermediate transfer drum, and a transfer failure phenomenon at the rear end is prevented.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be exemplarily described in detail with reference to the drawings.
As will be described later, the secondary transfer roller 24 is used as a transfer unit for transferring the toner image on the surface of the intermediate transfer drum onto the transfer sheet, and the separation charger 22 is used as a separation unit for separating the transfer sheet onto which the toner has been transferred from the intermediate transfer drum. is doing.
[0016]
FIG. 1 is a schematic cross-sectional view of an image forming apparatus showing an embodiment of the present invention. In FIG. 1, an image forming apparatus 1 includes a photosensitive member 11, an exposure unit 13 disposed around the photosensitive member 11, a charger 12, a cleaning unit 19, developing units 15 to 18, and a drum-shaped intermediate transfer member 20 (hereinafter referred to as an intermediate transfer member). A secondary transfer roller 24, a separation charger 22, a cleaning unit 23, a paper feed cassette 3, a registration roller pair 4, a transport belt 5, a vertical transport path 7, a discharge tray 8, and the like disposed around the drum). And a fixing device 6 disposed between the conveyance belt 5 and the vertical conveyance path 7 and a digel heater 30 installed below the secondary transfer roller 24 and the separation charger 22. It is arrange | positioned in the housing | casing 2 by the positional relationship of these.
[0017]
The photoconductor 11 is a drum-shaped photoconductor (hereinafter referred to as a photoconductor drum) having a photoconductor made of amorphous silicon (a-Si). A developing device 15, 16, 17, 18 having a unit 13 and developing sleeves 15a, 16a, 17a, 18a, an intermediate transfer drum 20, and a cleaning unit 19 are arranged, and the developing sleeves 15a, 16a, 17a, 18a have carriers and Development comprising a mixture of 5 parts by weight of black, yellow, magenta and cyan toners having a positive triboelectric charge polarity and a volume average particle diameter of 8 μm and 100 parts by weight of a ferrite carrier having a weight average particle diameter of 70 μm. The photosensitive drum 11 and the developing sleeves 15a, 16a, 17a, and 18a are respectively connected to the intermediate transfer drum 20. Each image is rotated in the direction of arrow A in the figure to form an image.
[0018]
The amorphous silicon (a-Si) photosensitive member of the photosensitive drum 11 is uniformly charged to about +400 [V] by the charger 12, and light 14 corresponding to the image data is irradiated by the exposure unit 13, and the photosensitive drum. An electrostatic latent image is formed on 11. At this time, the surface potential of the a-Si photosensitive member after exposure is about +10 [V]. The intermediate transfer drum 20 has a three-layer structure of an aluminum base tube as an inner layer, a conductive rubber layer as an intermediate layer, and a fluororesin layer as a surface layer, and has an outer diameter of 150 mm. The conductive rubber layer is a urethane rubber layer having a thickness of 8 mm, and the volume resistivity is adjusted to 3 × 10 7 Ω · cm by dispersing carbon. The surface fluororesin layer is PTFE having a thickness of 100 μm, and the volume resistivity is adjusted to 8 × 10 9 Ω · cm by dispersing carbon.
[0019]
An alternating electric field (Vdc = 160 [V], Vpp = 1.0 [kV], f = 3.6 [kHz]) is applied between the photosensitive drum 11 and the developing sleeve 15a to expose the photosensitive member. The toner image is developed on the portion. Next, a bias of +350 V is applied to the base tube of the photoconductive drum 11 to generate a potential difference with the intermediate transfer drum 20 grounded to the ground through the inner aluminum base tube, so that the toner image on the surface of the photoconductive drum 11 is obtained. Is transferred to the intermediate transfer drum 20. Similarly, the toner image by the developing device 16 is transferred to the intermediate transfer drum 20, and similarly transferred to the developing device 17, the developing device 18 and the intermediate transfer drum 20, and then transferred onto the paper P to be colored toner. Form an image. Each time the transfer of each color toner to the intermediate transfer drum 20 is completed, the untransferred residual toner on the surface of the photosensitive drum 11 is removed by the cleaning unit 19 and returned to a clean state.
[0020]
As described above, as the toner image is formed on the surface of the intermediate transfer drum 20 and the leading edge approaches the transfer position, the paper P stored in the paper feed cassette 3 is 134 mm / sec. The paper is fed along the path indicated by the arrow B, and the timing is adjusted by the registration roller pair 4 so as to pass through the transfer region between the secondary transfer roller 24 and the intermediate transfer drum 20. The secondary transfer roller 24 is applied with a negative transfer voltage, and is controlled by a constant current method so that a transfer current of 20 μA in the color mode and a transfer current of 15 μA in the monochrome mode flows in the sheet direction of the paper P.
[0021]
At this time, the toner image on the surface of the intermediate transfer drum 20 is transferred to the sheet P and is AC separated by the separation charger 22.
The separation charger 22 is a shield case having an opening on the side of the intermediate transfer drum 20 provided with two charger wires (separation voltage applying member) having a distance of 10 mm. A DC voltage of +400 V is applied to the charger wire. An alternating voltage with a peak-to-peak voltage of 12.5 kV is superimposed and applied.
[0022]
The separated paper P is transported on the transport belt 5 and reaches the fixing unit 6. The paper P on which the toner image has been fixed by passing through the fixing unit 6 is discharged to the paper discharge tray 8 via the vertical conveyance path 7. After the toner image is transferred to the paper P, the intermediate transfer drum 20 returns to a clean state after the untransferred toner is removed by the cleaning unit 23. The cleaning units 19 and 23 are constituted by a cleaning blade or a fur brush.
[0023]
Below the separation charger 22 and the secondary transfer roller 24, a planar digel heater 30 is attached in the axial direction of the photosensitive drum so as to be substantially the same as the length of the photosensitive drum. The digel heater 30 prevents an image flow phenomenon due to moisture adsorption on the intermediate transfer drum 20 and the photosensitive drum 11, and has a rated power of 10 W and a surface temperature of about 70 ° C.
[0024]
Next, with reference to the timing chart of FIG. 2, the energization control (first control mode) to the separation means and the transfer means of the present invention when an A4 size OHP sheet is used will be described in detail. FIG. 2 is a timing chart showing energization control of each part in the image forming apparatus according to the present invention when an OHP sheet is used. (A) is a registration clutch, (b) is a separation charger 22, and (c) is a timing chart. The secondary transfer roller 24, (d) is a diagram showing energization waveforms of the lifting clutch of the secondary transfer roller 24.
[0025]
The transfer area described below is a line portion where the plane including the central axis of the intermediate transfer drum 20 and the central axis of the secondary transfer roller and the nip between the intermediate transfer drum 20 and the secondary transfer roller intersect. The separation region is a line portion where a plane including the central axis of the image carrier and the charger line intersects with the transfer sheet. Although not shown in the present embodiment, it has two charger wires. In this case, an intermediate position between the charger lines is set as a reference charger line position that defines the separation region. In the present embodiment, the distance between the transfer region and the separation region is 25 mm.
[0026]
When a registration sensor (not shown) detects the leading edge of the A4-size OHP sheet fed from the sheet feeding cassette 3, the rotation of the registration roller pair 4 stops and the OHP sheet stops once just before the registration roller pair 4. . As the toner image on the surface of the intermediate transfer drum 20 approaches the secondary transfer roller 24, a registration clutch (not shown) is turned on, the rotation of the registration roller pair 4 is restarted, and the OHP sheet starts to be conveyed. .
[0027]
The registration roller pair 4 starts transporting the OHP sheet based on the registration clutch ON signal, and after 100 msec, the secondary transfer lifting / lowering clutch is operated to bring the secondary transfer roller 24 into contact with the intermediate transfer drum 20, and after 320 msec. Starts applying a predetermined high voltage to the separation charger 22 and the transfer roller 24. Immediately after that, 321.6 msec later, the leading edge of the OHP sheet passes through the transfer region.
[0028]
As described above, since the transfer speed of the transfer sheet is 134 mm / sec and the distance between the transfer area and the separation area is 25 mm, the time required for the leading edge of the OHP sheet to pass between them is 25 mm / 134 mm / sec × 1000. = 186 msec. Therefore, the end of the OHP sheet passes through the separation region after (321.6 + 186.6) = 508.2 msec. That is, the leading edge of the OHP sheet passes through the transfer area after 321.6 mm / sec, and passes through the separation area after 508.2 msec.
[0029]
Since the length of the A4 landscape size in the sheet passing direction (conveyance direction) is 210 mm, the time required for the trailing end to reach the leading end position is 210/134 × 1000 = based on the sheet passing speed of 134 mm / sec. 1567.2 msec. Therefore, the rear end of the OHP sheet passes through the transfer area after 1567.2 + 321.6 = 1888.8 msec, and the rear end of the OHP sheet after 1567.2 + 508.2 = 2075.4 msec, based on the ON signal of the resist clutch. Passes through the separation region.
[0030]
Since the energization time of the high voltage to the separation charger is 1415 msec, the voltage off timing of the separation charger is 1735 msec later with reference to the on signal of the registration clutch. Since the energization time of the high voltage to the secondary transfer roller is 1757 msec, the energization off timing to the secondary transfer roller based on the registration clutch on signal is after 2077 msec. Simultaneously with the energization-off control to the secondary transfer roller, the secondary transfer raising / lowering clutch operates to separate the secondary transfer roller from the intermediate transfer drum.
[0031]
According to the above first control mode, when the leading edge of the OHP sheet reaches the separation region, the energization to the separation charger is turned on, which corresponds to 2077-1735 = 342 msec, 134 mm / sec × 342 msec / 1000 msec = 45. The separation charger voltage is not applied to the rear end portion of the OHP sheet by the size of 8 mm. In other words, the separation charger is turned off when the OHP sheet is passed by a distance of 210 mm−45.8 mm = 164.2 mm from the front end of the OHP sheet. The OHP sheet is only A4 horizontal size, and the separation and secondary transfer OFF timing is also energized and controlled by a timing chart starting from the ON signal of the registration clutch.
[0032]
On the other hand, since each size of plain paper is used, the energization-off control of separation and secondary transfer is not performed by the timing chart starting from the on-signal of the registration clutch, but the passage of the rear end portion. This is done by time control after detection by the registration sensor.
[0033]
Based on the timing chart of FIG. 3, the energization control (second control mode) to the separation means and transfer means of the present invention when A4 size plain paper is used will be described in detail. FIG. 3 is a timing chart showing energization control of each part in the image forming apparatus according to the present invention when plain paper is used. (A) is a registration clutch, (b) is a separation charger 22, and (c) is a timing chart. The secondary transfer roller 24, (d) is a lifting clutch of the secondary transfer roller 24, and (e) is a diagram showing energization waveforms of the registration sensor.
[0034]
When the registration sensor (not shown) detects the leading edge of the A4 horizontal size plain paper sheet fed from the paper feed cassette 3, the rotation of the registration roller pair 4 is stopped and the plain paper sheet is immediately before the registration roller pair 4. Stop. As the toner image on the surface of the intermediate transfer drum 20 approaches the secondary transfer roller 24, a registration clutch (not shown) is turned on, the rotation of the registration roller pair 4 is resumed, and the plain paper sheet is started to be conveyed. The
[0035]
Using the registration clutch on signal as a reference, the secondary transfer elevating clutch is operated 103 msec later, and the secondary transfer roller is brought into contact with the intermediate transfer drum 20. After 320 msec, application of a predetermined high voltage to the separation charger 22 and the transfer roller 24 is started. The leading edge of the plain paper sheet passes through the transfer area after 321.6 msec. As described above, since the transfer speed of the transfer sheet is 134 mm / sec and the distance between the transfer area and the separation area is 25 mm, the time required for the plain paper sheet to pass through the transfer area is 25 mm / 134 mm / sec × 1000 = 186 msec.
[0036]
Therefore, the leading edge of the plain paper sheet passes through the separation region after (321.6 + 186.6) = 508.2 msec. That is, the leading edge of the plain paper sheet passes through the transfer area after 321.6 msec, and passes through the separation area after 508.2 msec.
[0037]
Since the length of the A4 horizontal size in the sheet passing direction is 210 mm, the time required for the trailing end to reach the leading end position is 210/134 × 1000 = 1567.2 msec based on the sheet passing speed of 134 mm / sec. . Therefore, based on the on signal of the registration clutch, the trailing edge of the OHP sheet passes through the transfer area after 1567.2 + 321.6 = 1888.8 msec, and further after the plain paper sheet after 1567.2 + 508.2 = 2075.4 msec. The end passes through the separation region.
[0038]
The registration clutch is turned off 110 msec after the registration sensor detects the passage of the trailing edge of the plain paper sheet, and the energization to the secondary transfer roller and the separation charger is turned off after 462 msec. The trailing edge of the plain paper passes through the transfer area after 273.8 msec, and the energization of the transfer roller is thereafter turned off. Further, it passes through the separation region after 460 msec, and the separation charger is turned off thereafter.
[0039]
According to the second control mode described above, when the leading edge of the plain paper reaches the separation region, the energization to the separation charger is turned on and turned off after the trailing edge of the plain paper has passed through the separation charger. . That is, in the second control mode, energization to the separation charger is continued while the entire length of the plain paper passes through the separation area.
[0040]
The first control mode and the second control mode can be switched between the case where the transfer sheet to be used is a plain paper and the case of an OHP sheet. It is also possible to configure such that the transfer material is discriminated and automatically switched and selected, or when the transfer sheet is set, it can be manually switched and selected.
[0041]
In the first control mode, if the OHP sheet, a result of various studies from dimensions of each part mechanism, and indicia pressure to the separation voltage at the time the leading end portion of the at least OHP sheet passes a 5mm isolation region, the rear end portion It is preferable that the application of the separation voltage is turned off when the non-passing portion remains for a predetermined length, for example, 35 mm or more, thereby preventing the transfer failure due to the abrupt separation at the rear end while preventing the separation failure at the front end. And a good transfer image is transferred onto the OHP sheet.
Further, according to the second control mode, the case of plain paper, since continued indicia pressurized isolation voltage from the tip to the rear end, it can be to prevent separation failure.
[0042]
【The invention's effect】
As described above in detail, according to the image forming apparatus according to the present invention, in the case of plain paper, since continued indicia pressurized isolation voltage from the tip to the rear end, thereby preventing separation failure.
Further, in the case of an OHP sheet, at least because its tip is marked pressurized isolation voltage at the time of passing through the separation region, the separation voltage upon with the separation failure can be prevented, the non-passed portion of the rear end portion remains larger than a predetermined length Therefore, transfer failure due to abrupt separation at the rear end can be prevented, and a good transfer image can be transferred onto the OHP sheet.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention.
FIG. 2 is a timing chart showing energization control of each part when an OHP sheet is used, (a) is a registration clutch, (b) is a separation charger 22, (c) is a secondary transfer roller 24, (d). FIG. 4 is a diagram illustrating energization waveforms of the lifting clutch of the secondary transfer roller 24.
FIG. 3 is a timing chart showing energization control of each part when using plain paper, (a) is a registration clutch, (b) is a separation charger 22, (c) is a secondary transfer roller 24, (d). FIG. 7 is a diagram showing energization waveforms of the elevating clutch of the secondary transfer roller 24, and FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus 2 ... Housing 3 ... Paper feed cassette 4 ... Registration roller pair 5 ... Conveying belt 6 ... Fixing part 7 ... Vertical conveying path 8 ... Discharge tray 11 ... photosensitive member 12 ... charger 13 ... exposure unit 14 ... exposure light 15, 16, 17, 18 ... developer 15a, 16a, 17a, 18a ... development Sleeve 19 ... Cleaning unit 20 ... Intermediate transfer member 22 ... Separation charger 23 ... Cleaning unit 24 ... Transfer roller 30 ... Digel heater

Claims (1)

Transfer means for transferring the toner images formed on the surface of the intermediate transfer drum carrying the toner images of the plurality of colors onto the transfer sheet by sequentially transferring the toner images of the respective colors formed on the surface of the photoreceptor, and the toner A separation means installed downstream of the transfer means for separating the transferred transfer sheet from the intermediate transfer drum ;
While it transported between the separating means and the intermediate transfer drum to the transfer sheet, a separation voltage An image forming apparatus for indicia pressure to the separating means,
When the transfer sheet having a rigidity higher than that of plain paper has one separation voltage application member as the separation means and a member to which a separation voltage is applied, the axis of the intermediate transfer drum and the separation voltage application member Or a plane including the axis of the intermediate transfer drum and an intermediate position between the two separation voltage application members at least when the first predetermined length is passed. A first control mode in which the application of the voltage is turned on and the application of the separation voltage is turned off when the non-passing portion remains for a second predetermined length or more;
A plain paper has a second control mode in which the application of the separation voltage is turned on while passing through the plane, and the application of the separation voltage is turned off after the non-passing portion disappears;
An image forming apparatus, wherein either the first control mode or the second control mode can be selected.

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