JP2014085553A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide separability and transferability required for a sheet even when both a low-density area and a high-density area coexist in a formed image in an image forming apparatus.SOLUTION: After the input of job content to control means included in an image forming apparatus such as a computer and before the start of optical writing, the image forming apparatus acquires the size of a paper tray, the type of paper fed, environment, a printing surface, and image density information. When the image forming apparatus determines that both a low-density area and a high-density area coexist in an image to be transferred onto a sheet at a secondary transfer part, the image forming apparatus makes values of secondary transfer bias and separation bias variable in an area of the sheet to which the image is to be transferred. The operation improves separability of sheets at the secondary transfer part, and suppresses the occurrence of abnormal images such as transfer failure due to failure in secondary transfer conditions and toner disturbance due to excessive separation bias.

Description

  The present invention relates to an image forming apparatus.

  Electrophotographic image forming apparatuses have been widely used in home offices and general user areas. In order to provide a product corresponding to this area, a high paper handling capability is required in addition to a technology that realizes cost reduction, long life, and miniaturization.

  Intermediate transfer type image forming apparatuses are widely used because of the advantages of paper compatibility and layout flexibility. In order to realize further paper handling capability, it is necessary to pass thin paper that cannot be separated by curvature separation. However, since thin paper tends to be poorly separated due to charging of the paper at the secondary transfer portion, it is particularly disadvantageous for separation when the paper is made of a low-density image that is easily charged.

  As a method for separating thin paper, there are a method in which a separation claw is provided after the secondary transfer nip and a method in which a charge eliminating needle is provided. However, since the separation claw is provided on the paper printing surface so as to prevent the belt from being wound around the belt side, the toner image before fixing may be damaged. Further, in the method of applying the separation bias from the static elimination needle, if the image has a high density, the toner image may be disturbed if the separation bias is high.

  Therefore, the separation bias is increased and the secondary transfer bias is lowered when the sheet front end region is a low density image which is unfavorable for separation, and the separation bias is set lower and the secondary transfer bias is set higher when the paper front end region is a high density image. There is a method.

  For example, Patent Document 1 discloses a method of ensuring separation and transferability by setting a separation bias and a secondary transfer bias according to the density of the paper front end region. Further, when dark in the sub-scanning direction, the separation bias and the secondary transfer bias cannot be changed in the image. Therefore, if the amount of toner in the rear end region of the image is large, toner disturbance and transfer failure are likely to occur.

  Note that the direct transfer type image forming apparatus that directly transfers the toner image formed on the photosensitive drum to the paper also has the same problem as the above-described intermediate transfer type image forming apparatus.

  According to the present invention, in an image forming apparatus, even when a low density area and a high density area are mixed in a formed image, it is possible to obtain required sheet separation and transfer characteristics.

The image forming apparatus of the present invention performs image transfer on the intermediate transfer member by performing toner transfer on each of the plurality of image carriers, the intermediate transfer member, and the plurality of image carriers on the intermediate transfer member. A secondary transfer unit is disposed opposite to the intermediate transfer member at a position different from the primary transfer portion to be formed and the plurality of image carriers, and is used to collectively transfer the image on the intermediate transfer member onto a transfer material. A secondary transfer portion having a transfer member; a charge removal member for separating the transfer material at the secondary transfer portion; a secondary transfer bias applied at the secondary transfer portion; and a separation bias applied to the charge removal member. An image forming apparatus comprising: a control unit configured to identify density information of a leading end region of the image before the image reaches the secondary transfer unit; When the back end area consists of high density images The absolute value of the secondary transfer bias applied at the secondary transfer portion is low at the front end region and high at the rear end region, and the absolute value of the separation bias applied to the charge eliminating member is high at the front end region, Control to lower in the rear end area,
It is characterized by that.

  The image forming apparatus of the present invention also includes an image carrier on which an image is formed on the surface, a transfer unit having a transfer member for transferring the image on the image carrier to a transfer material, and the transfer material transferring the image. In an image forming apparatus, comprising: a charge eliminating member for separating at a transfer portion; and a control means for controlling a transfer bias applied at the transfer portion and a separation bias applied to the charge removing member. Until the image reaches the transfer portion, and the control means determines the transfer bias applied by the transfer portion when the image is composed of an image having a low density in the front end region and a high density in the rear end region. The absolute value is controlled to be low in the front end region and high in the rear end region, and the absolute value of the separation bias applied to the static elimination member is increased in the front end region and low in the rear end region. To do.

  According to the present invention, even when a low density area and a high density area are mixed in the formed image, the transfer bias and separation bias values can be varied within the paper area, so that the requirements for the paper on which the image is transferred can be obtained. Separation and transferability can be obtained.

Schematic of a tandem type image forming apparatus that is an object of the present invention Conceptual diagram for explaining the definition of dividing the paper area into a leading edge area and a trailing edge area Flow chart for controlling secondary transfer bias and separation bias The figure explaining control of a secondary transfer bias and a separation bias The figure shown about the various numerical value in the Example and comparative example of this invention

Embodiments of the present invention will be described below.
As described above, in the image forming apparatus using the intermediate transfer member, the sheet is charged by the secondary transfer bias. Therefore, the sheet having a small basis weight passes through the secondary transfer nip and then is electrostatically moved to the belt side. Winding may cause poor separation. However, when the separation bias is high, image problems such as toner disturbance occur.

  As an avoidance means, there is a method of preventing separation failure by setting a separation bias and a secondary transfer bias in accordance with the image density at the leading edge of the sheet. That is, when the leading edge region of the sheet is composed of a low density image, the sheet is easily charged and a separation failure is likely to occur. Therefore, the separation bias is set high and the secondary transfer bias is set low. When the front end area of the sheet is composed of a high density image, the separation bias is set low and the secondary transfer bias is set high because the sheet is difficult to be charged.

  However, when the image at the front end area of the paper becomes low density and dark in the sub-scanning direction, the separation bias and the secondary transfer bias cannot be changed within the area of the paper. Defects occur. Countermeasures are necessary for these points.

  Therefore, in the embodiment of the present invention, when it is determined from the control means that the image to be transferred is mixed with the low density area and the high density area, the values of the secondary transfer bias and the separation bias are transferred to the image. By varying within the area of the paper to be used, the separation property is improved, and the occurrence of abnormal images such as transfer failure due to insufficient secondary transfer and toner disturbance due to excessive separation bias is prevented.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic diagram illustrating a tandem type image forming apparatus. Around the photosensitive drum 1 which is an image carrier, a charging device 2 for charging the surface of the photosensitive drum 1 and a laser for forming a latent image on the surface of the uniformly charged photosensitive drum 1 A developing device 5 for forming a toner image by attaching charged toner to the latent image on the surface of the photosensitive drum 1 with light (exposure 3), and an intermediate toner image on the formed photosensitive drum 1 as a transfer target A transfer device 7 for transferring to the transfer belt 13 and a cleaning device 12 for removing residual toner on the photosensitive drum 1 are sequentially arranged. A toner replenishing container 4 for storing replaceable toner and connecting the developing device 5 to supply the toner into the developing device 5 is disposed above the developing device 5.

  Although the toner replenishing container 4 is shown in FIG. 1 as having a configuration in which toner is directly conveyed into the developing device 5, a toner replenishing path is provided in the main body of the image forming apparatus, and the developing device 5 is provided via this replenishing path. The toner may be replenished.

  In the tandem type electrophotographic image forming apparatus as shown in the figure, a monochromatic image such as black, magenta, cyan, and yellow is mainly formed on the surface of the photosensitive drum 1.

  In such a configuration, when image formation is performed by a negative positive method (lowering the exposure portion potential and attaching toner), the photosensitive drum 1 whose surface is uniformly negatively charged by the charging roller 2a of the charging device 2 is used. An electrostatic latent image is formed on the surface of the surface by exposure 3, and toner is attached by the developing device 5 to visualize the image. The toner image is transferred from the surface of the photosensitive drum 1 by the transfer device 7 including the intermediate transfer belt 13 and the like. Residual toner that has not been transferred from the photosensitive drum 1 to the intermediate transfer belt 13 is removed from the surface of the photosensitive drum 1 by the cleaning blade 11 of the cleaning device 12. The toner image transferred to the surface of the intermediate transfer belt 13 is transferred to a sheet P such as a recording material conveyed from the sheet feeding tray by applying a bias to the secondary transfer roller 8 constituting the secondary transfer unit. . Toner components and external additive components remaining on the surface of the intermediate transfer belt 13 after the transfer of the toner image are removed by the cleaning member 26.

  A separation bias is applied to the static elimination needle 19 so that the transferred paper can be separated without being wound around the intermediate transfer belt 13. The toner image transferred onto the paper is welded onto the paper by the fixing device 9 and is discharged from a paper discharge port (not shown). In the figure, reference numeral 15 denotes a sensor used to adjust the image density and alignment by measuring the amount of toner transferred onto the intermediate transfer belt 13 and the position of each color. For example, a sensor that combines regular reflection and diffuse reflection is used. Used. In the figure, 16 is a cleaning unit for cleaning the toner remaining on the surface of the intermediate transfer belt 13, and the cleaning blade 14 is in contact with the moving direction of the intermediate transfer belt 13 so as to be in the counter direction. Thus, a metal cleaning facing roller 17 is provided. The toner removed by the cleaning blade is conveyed by the coil 18 or the like and stored in a waste toner storage unit (not shown).

  FIG. 2 is a diagram for explaining the definition of the leading edge area and the trailing edge area of the paper P. The leading edge region P1 of the paper P is a region from the leading edge of the paper P to the boundary between the low density image and the high density image (from the leading edge of the paper P to the position indicated by symbol A in FIG. 2). However, when the area of the low density image exists more than the leading margin area of the paper P, the leading edge area P1 is defined as having a low density. The rear end region P2 is a region from the boundary (reference A) between the low density image and the high density image to the rear end of the paper P. The rear end region P2 may be formed only from a high density image as shown in FIG. 2A, or a low density image and a high density image may be mixed as shown in FIG. 2B. But you can.

If the area consisting only of the low density image does not exist on the trailing edge side beyond the leading margin area of the paper P, the leading edge area P1 of the paper P is set as a high density area, and a low separation bias and a high secondary transfer bias are applied. To do. At this time, the secondary transfer current and the separation bias are not changed in the area of the paper P. Incidentally, for example, low concentration and minimum configuration toner layer thickness of the image area deposition amount ^0g / m 2 ~6g / m ^2, the high density can be defined as more.

FIG. 3 is a flowchart of control of the secondary transfer bias and separation bias, and control of the secondary transfer bias and separation bias will be described with reference to FIG.
First, the paper tray size, paper feed type, environment, printing surface, and image density information are acquired (steps S1 and S2) after the job contents are input to the control means provided in the image forming apparatus such as a computer. What is necessary is just before the start of optical writing. Thereafter, optical writing is started (step S3), paper feeding of the paper P is started (step S4), and the registration roller (paper P is transferred so that the paper P is transferred in synchronization with the toner image on the photosensitive drum 1). A roller or a pair of rollers for controlling the conveyance timing of the paper, which is also referred to as a paper top roller (not shown), is turned on (step S5) and fed.

  From the data acquired in steps S1 and S2 (or data acquired by other detection means such as a sensor may be included), it is determined whether or not the image existing in the leading edge region P1 of the paper P is only a low density image ( In step S6), a bias value to be applied to the tip region P1 is determined according to the determination result (steps S7 and S8). That is, if the image of the tip region P1 is only low in density, the application of the high separation bias / low secondary transfer bias is performed (step S7). If the image of the tip region P1 is not only low density, the low separation bias is used. / Application of high secondary transfer bias (step S8).

  After the application of the high separation bias / low secondary transfer bias (step S7), it is determined whether or not the image density of the trailing edge area P2 is high, and the secondary transfer bias value is determined according to the information on the image density of the trailing edge area P2. Is switched (step S9). That is, when the rear end region P2 includes a high density image, the separation bias is set high and the secondary transfer bias is set low (step S10). If the rear end region P2 does not contain a high density image, the secondary transfer bias is set low and the separation bias is set high (step S8). Then, the application of the separation bias and the secondary transfer bias is finished (step S11), and the paper P is discharged out of the image forming apparatus main body (step S12).

FIG. 4 is a diagram for explaining control of the secondary transfer bias and the separation bias.
Switching between the secondary transfer bias and the separation bias is performed until the boundary between the leading edge region P1 and the trailing edge region P2 of the paper P reaches the secondary transfer nip portion. T1 and T2 in the figure represent the time until the current is stabilized at the time of switching. This value is set in advance by experiment, experience, etc. By switching the bias until the rear end region P2 including the high density image is reached, abnormal images such as blur and dust in the high density image region are prevented.

FIG. 5 is a diagram for explaining an embodiment of the present invention and a comparative example for the embodiment.
The color printer was modified so that the secondary transfer bias and the separation bias can be controlled from an external power source at a desired timing. The product name IPSiO SP C320 manufactured by Ricoh Co., Ltd. was used for the color printer. The secondary transfer bias may be used with either a constant current or a constant voltage. In the embodiment of the present invention, constant current control was used. One set of 25 sheets was passed. The volume resistance of the belt is 1.0 × 10 ¹⁰ (Ω · cm). The transfer belt is formed of two layers, a base layer and a laminated layer. The image area of the minimum configuration corresponds to 1 dot of the printer. In the example of the present invention, the evaluation is performed with an image of 600 dpi, and therefore, it is 42 μm. Then, the toner adhesion amount of 1dot has a high concentration if the ^0g / ^{m 2 ~6g} / m 2 low density, the more. A low density image was formed at a position of 10 mm from the leading edge of the paper, and the subsequent image was formed and evaluated so as to be a high density image. The room temperature and normal humidity environment represents an environment of 23 ° C. and 50%, and the low temperature and low humidity environment represents an environment of 10 ° C. and 15%. Chile and blur were evaluated as phenomena caused by the toner disturbance phenomenon.

<Evaluation (1) Image evaluation>
A case where an abnormal image such as blurry or dust occurred was judged as “X”, and a case where no abnormal image occurred was judged as “◯”.
<Evaluation (2) Separation evaluation>
When 25 sheets were passed, the case where even one sheet had a separation failure was determined as “X”, and the case where it did not occur was determined as “◯”.
<Comprehensive evaluation>
Only when the image evaluation and the separation evaluation were all “◯” as the comprehensive evaluation, the comprehensive evaluation “◯” was determined. In other cases, the overall evaluation was “x”.

<Example 1>
Evaluation was made on the surface of A4 size thin paper (basis weight 52 g / m ² ). The secondary transfer bias of the region up to the tip 10 mm (hereinafter referred to as the tip region) was 15 μA, the region after that (hereinafter referred to as the rear end region) was 25 μA, the separation bias up to the tip 10 m was −2500 V, and the subsequent bias was −500 V. . Evaluation was performed in a normal temperature and humidity environment.
<Comparative Example 1>
Compared to Example 1, the secondary transfer bias in the tip region was set to 30 μA. When the secondary transfer bias in the leading edge region was high, sheet charging occurred and separation failure occurred.
<Comparative example 2>
Compared to Example 1, the secondary transfer bias in the rear end region was 15 μA. Since the rear end region has a high density, transfer failure occurred when the secondary transfer bias was low.
<Comparative Example 3>
Compared to Example 1, the separation bias in the rear end region was set to -2500V. Since the trailing edge region has a high density, dust is generated when the separation bias is high, because the charge on the non-printing surface of the paper is excessively removed.
<Comparative Examples 4 and 5>
In contrast to Example 1, Comparative Examples 4 and 5 were evaluated in a low temperature and low humidity environment. The paper was immediately opened. In Comparative Example 4, the discharge due to discharge occurred unless the secondary transfer bias was lowered in a low temperature and low humidity environment. In addition, since the paper is easily charged, a separation failure occurred. In Comparative Example 5, the secondary transfer bias was 8 μA in the front end region and 15 μA in the rear end region, the separation bias was −3000 V in the front end region, and −500 V in the rear end region.
<Comparative Examples 6 and 7>
In contrast to Example 1, Comparative Examples 6 and 7 were evaluated using paper having a basis weight of 256 g / m ² . Since the paper having a large basis weight has high resistance, Comparative Example 6 had a discharge due to discharge unless the secondary transfer bias was lowered. Also, because of the high paper resistance, dust was generated by applying a separation bias. In Comparative Example 7, the secondary transfer bias was set to 7 μA at the front end region and 15 μA at the rear end region, and the separation bias was set to 0 V at both the front and rear ends. Since the basis weight was large, separation was possible even with a separation bias of 0V.
<Comparative Examples 8 and 9>
In contrast to Example 1, Comparative Examples 8 and 9 were set to the automatic duplex printing mode and evaluated on the back side after the front side printing. In Comparative Example 8, the paper resistance on the back surface was high, so that winding and discharging caused the discharge. In Comparative Example 9, the secondary transfer bias was 10 μA at the front end region, 18 μA at the rear end region, and the separation bias was −2700 V at the front end region.
<Comparative Examples 10 and 11>
In contrast to Example 1, in Comparative Examples 10 and 11, the paper size was A5. In Comparative Example 10, in the case of paper smaller than the width of the transfer belt, the secondary transfer bias leaks from the paper-free portion, and transfer failure occurs. Also, since the paper is easily charged, a separation failure occurred. In Comparative Example 11, the secondary transfer bias was 30 μA at the front end region, the rear end region was 60 μA, and the separation bias was −3000 V at the front end region.

That is, the toner layer thickness adhering minimum configuration image area at the tip region of the color image in the above control and ^{0g / m 2 ~6g / m 2} , the toner layer thickness deposition amount of the rear end region 6 g / m ² or more Thus, even if a high separation bias is applied to the tip region, toner disturbance does not occur. Further, when the control is finished before the secondary transfer bias is applied to the rear end area, when the front end area is a low density image and the rear end area is a high density image, toner disturbance or transfer current due to a delay in switching timing. Prevents blurring due to shortage. Furthermore, the optimum secondary transfer bias and separation bias can be set depending on the environment. Further, it is possible to set an optimal secondary transfer bias and separation bias depending on the paper type. Moreover, it can also be made to isolate | separate by a low separation bias by applying an AC bias.

The present invention is not limited to the embodiments described above, and many variations are possible by those having ordinary knowledge in the art within the technical idea of the present invention.
For example, a drum-shaped intermediate transfer drum may be used instead of the belt-shaped intermediate transfer belt. The present invention is also applicable to a so-called direct transfer type image forming apparatus that directly transfers a toner image formed on a photosensitive drum to a sheet. That is, a photosensitive drum that is an image carrier on which an image is formed on a surface, a transfer unit that includes a transfer roller that is a transfer member for transferring the image on the photosensitive drum to a sheet, and a sheet that is a transfer unit In the image forming apparatus, comprising: a charge eliminating member for separating at a transfer portion; and a control means for controlling a transfer bias applied at the transfer portion and a separation bias applied to the charge removing member. When the image reaches the transfer portion, the control means identifies the absolute value of the transfer bias applied by the transfer portion when the image is composed of an image having a low density in the front end region and a high density in the rear end region. An image forming apparatus that performs control to lower a value in the front end region, increase a value in the rear end region, and increase an absolute value of a separation bias applied in the neutralization unit in the front end region and lower in the rear end region. It is applicable.

1: Photoconductor drum 2: Charging device 2 a: Charging roller 3: Exposure 4: Toner supply container 5: Developing device 7: Transfer device 8: Secondary transfer roller 9: Fixing device 11: Cleaning blade 12: Cleaning device 13: Intermediate Transfer belt 14: Cleaning blade 17: Metal cleaning counter roller 18: Coil 19: Static elimination needle 25: Paper 26: Cleaning member P: Paper P1: Front end area P2: Rear end area

JP-A-61-138974

Claims (11)

A plurality of image carriers;
An intermediate transfer member;
A primary transfer portion that forms an image on the intermediate transfer member by performing toner transfer from each of the plurality of image carriers onto the intermediate transfer member;
A secondary transfer portion having a secondary transfer member disposed opposite to the intermediate transfer member at a position different from the plurality of image carriers and collectively transferring the image on the intermediate transfer member to a transfer material When,
A charge eliminating member for separating the transfer material at the secondary transfer portion;
Control means for controlling a secondary transfer bias applied at the secondary transfer portion and a separation bias applied to the charge removal member;
In an image forming apparatus having
Identifying the density information of the tip region of the image before the image reaches the secondary transfer portion;
When the image is composed of an image having a low density in the front end region and a high density in the rear end region, the control means lowers the absolute value of the secondary transfer bias applied in the secondary transfer unit at the front end region, and Performing control to increase the absolute value of the separation bias to be applied to the charge removal member to be high in the tip region and to be low in the rear end region,
An image forming apparatus. That the toner layer thickness adhering minimum configuration image area at the tip region of the image and ^{0g / m 2 ~6g / m 2} , and the toner layer thickness deposition amount of the rear end region 6 g / m ² or more The image forming apparatus according to claim 1, wherein:   3. The control unit according to claim 1, wherein the control unit can perform control to end switching of the secondary transfer bias and the separation bias until a secondary transfer bias is applied to the rear end region. 4. Image forming apparatus.   The image forming apparatus according to claim 1, wherein the control unit can perform control to set the secondary transfer bias and the separation bias according to an environment.   5. The image forming apparatus according to claim 1, wherein the control unit can perform control to set the secondary transfer bias and the separation bias according to a paper type.   The image forming apparatus according to claim 1, wherein the control unit can perform control to set the secondary transfer bias and the separation bias according to a sheet size.   The image forming apparatus according to claim 1, wherein the control unit can perform control to set the secondary transfer bias and the separation bias in accordance with a size of an image forming surface of the sheet.   8. The image forming apparatus according to claim 1, wherein the separation bias is an AC bias.   The intermediate transfer member is an endless belt shape, and is an intermediate transfer belt that is rotated around a driven roller that absorbs at least the expansion and contraction of the belt and a driving roller that conveys the intermediate transfer belt. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 9, wherein the secondary transfer member is disposed to face the driving roller or the driven roller. An image carrier on which an image is formed on the surface;
A transfer portion having a transfer member for transferring the image on the image carrier to a transfer material;
A static elimination member for separating the transfer material at a transfer portion;
Control means for controlling a transfer bias applied at the transfer section and a separation bias applied to the charge removal member;
In an image forming apparatus having
Identifying the density information of the tip region of the image before the image reaches the transfer section,
When the image is composed of an image having a low density at the front end area and a high density at the rear end area, the control means lowers the absolute value of the transfer bias applied at the transfer unit at the front end area and higher at the rear end area. Then, the absolute value of the separation bias applied to the static elimination member is controlled to be high in the front end region and low in the rear end region.
An image forming apparatus.