JP2011203351A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus in which the shift of each electrification component included in a developer to an image carrier and the density unevenness of a formed image are suppressed when the image carrier is stopped.SOLUTION: The image forming apparatus includes: a background potential-applying unit which applies a background potential being the background of an image to the circumferential surface of the image carrier; a latent image-forming unit which forms an electrostatic latent image by applying an image potential to the image carrier; a developing unit which forms a toner image by developing the electrostatic latent image with charged toner; a transfer unit which electrostatically transfers the toner image on the image carrier to a body to be transferred; and a power supply part which is a power supply part having the application of a voltage to the background potential-applying unit and the application of a potential to the developing unit, stops the application of the voltage to the background potential-applying unit after the formation of the electrostatic latent image by the latent image-forming unit is completed and then, the circumferential surface of the image carrier makes at least one rotation, and controls the potential of the developing unit so that the potential of the developing unit may follow the change of the potential of the circumferential surface of the image carrier caused by the action of the transfer unit, after the application of the voltage is stopped.

Description

  The present invention relates to an image forming apparatus.

  2. Description of the Related Art Conventionally, there has been known an image forming apparatus of a type that charges a surface of a photoreceptor by direct current charging and forms an electrostatic image on the surface of the photoreceptor. As this type of image forming apparatus, there is also known an apparatus for removing the charge on the surface of the photosensitive member by utilizing the potential of the transfer device when the rotation of the photosensitive member is stopped (see Patent Document 1).

JP 2001-350385 A

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus in which the transfer of each charged component contained in a developer to an image holding member and density unevenness of a formed image are suppressed when the image holding member is stopped.

An image forming apparatus according to claim 1 is provided.
An image holding body for holding the image, wherein an image is formed on the peripheral surface, at least the peripheral surface is circulated;
A background potential applying unit that applies a background potential to be a background of the image on the peripheral surface of the image holding body when a voltage is applied;
A latent image forming unit that forms an electrostatic latent image by applying an image potential different from the background potential to the peripheral surface of the image carrier;
A developing potential between the background potential and the image potential having a developer containing at least a charged toner disposed opposite to the peripheral surface of the image carrier is applied to the developer in the developer. A developing unit for developing the electrostatic latent image with charged toner to form a toner image;
The toner image on the image carrier is electrostatically transferred onto the image receiving member. The toner image on the image holding member passes between the image holding member and the peripheral surface of the image holding member. A transcription section;
A power supply unit that is responsible for applying a voltage to the background potential applying unit and applying a potential to the developing unit, and at least a peripheral surface of the image holding member after the formation of the electrostatic latent image by the latent image forming unit is completed. After one round, the voltage application to the background potential applying unit is stopped. After the voltage application is stopped, the potential of the developing unit is changed due to the potential change of the peripheral surface of the image carrier due to the action of the transfer unit. A power supply unit that controls the potential of the developing unit so as to follow,
It is provided with.

An image forming apparatus according to claim 2
The transfer portion has a peripheral surface that faces the peripheral surface of the image carrier and circulates with the circular movement of the peripheral surface,
The image carrier has a circumference that is a non-integer multiple of the circumference of the transfer portion.

An image forming apparatus according to claim 3
The background potential applying portion has a peripheral surface that faces the peripheral surface of the image carrier and circulates and moves with the circular movement of the peripheral surface,
The transfer portion is a peripheral surface that faces the peripheral surface of the image carrier and circulates as the peripheral surface circulates, and has a surface roughness that is rougher than the surface roughness of the peripheral surface of the background potential applying portion. It is characterized by having a peripheral surface.

An image forming apparatus according to claim 4
After the formation of the electrostatic latent image and before the voltage application to the background potential applying unit is stopped, the power supply unit controls the voltage applied to the background potential applying unit to control the peripheral surface of the image carrier. Is controlled to a potential between the background potential and a potential changed from the background potential by a single action of the transfer portion.

An image forming apparatus according to claim 5
An environment detection unit that detects at least one of the temperature and humidity of the environment of the image forming apparatus,
The power supply unit is further responsible for applying a potential to the transfer unit, and the potential applied to the transfer unit after the formation of the electrostatic latent image is in accordance with a detection result of the environment detection unit. It is characterized by being controlled to a potential.

An image forming apparatus according to claim 6
A counting unit that cumulatively counts the number of circulations of the peripheral surface of the image carrier,
The power supply unit is further responsible for applying a potential to the transfer unit, and after the formation of the electrostatic latent image, the potential applied to the transfer unit is a potential corresponding to the counting result of the counting unit. It is characterized by being controlled.

  According to the image forming apparatus of the first aspect, when the image carrier is stopped, it is possible to suppress the transfer of each charged component contained in the developer to the image carrier and the density unevenness of the formed image.

  According to the second and third image forming apparatuses, when the image carrier is stopped, it is possible to further suppress the transfer of each charged component contained in the developer to the image carrier and the density unevenness of the formed image. .

  According to the image forming apparatus of the fourth aspect, when the image carrier is stopped, the transfer of each charged component contained in the developer to the image carrier and the density unevenness of the formed image can be effectively suppressed.

  According to the image forming apparatus of the fifth and sixth aspects, when the image carrier is stopped, the transfer of each charging component contained in the developer to the image carrier and the density unevenness of the formed image can be stably suppressed.

1 is a schematic configuration diagram of an image forming apparatus. FIG. 6 is a graph schematically showing changes in the surface potential and developing bias of a photoreceptor roll. It is a figure which shows the table which a control part refers. It is a graph which shows the relationship between a space | gap ratio and the grade of the speckles which generate | occur | produced on the image. It is a graph which shows the change of the surface potential of a photoreceptor roll.

  Hereinafter, embodiments of the image forming apparatus of the present invention will be described.

  FIG. 1 is a schematic configuration diagram of an image forming apparatus.

  An image forming apparatus 1 shown in FIG. 1 includes a photosensitive roll 11 that rotates in the direction of an arrow A, and a charging roll that contacts the photosensitive roll 11 while rotating in the direction of an arrow B and applies a charge to the surface of the photosensitive roll 11. 12. An electrostatic latent image formed by the exposure device 17 and the exposure device 17 that irradiates exposure light for forming an electrostatic latent image as a basis of an image on the surface of the photosensitive roll 11 to which an electric charge is applied, The developing device 13 that develops with toner out of the developer containing toner and magnetic carrier, and rotates in the direction of arrow D, the toner image formed by developing the toner by the developing device 13 is transferred from the paper feeding cassette 20. A transfer roll 14 for transfer onto a recording sheet conveyed along the conveyance path R, a cleaning blade 15 for scraping off residual toner remaining on the photoreceptor roll after the toner image is transferred, a conveyance path Conveying rolls 18 to convey the recording sheet along the R and, a fixing device 16 for fixing a toner image on a recording sheet by applying heat and pressure to the recording sheet on which the toner image has been transferred. This image forming apparatus 1 is an embodiment of the image forming apparatus of the present invention.

  The transfer roll 14 is a foam roll urethane roll.

  The developing device 13 holds a developing roller 131 that rotates in the direction of arrow C inside the housing 132 and accommodates a developer containing toner and a magnetic carrier. The magnetic carrier is a charge imparting particle that frictionally charges the toner by friction with the toner, and is also a magnetic particle. In the developing device 13, the developer stored therein is stirred, and the toner and the magnetic carrier are rubbed by the stirring. By this friction, the toner is negatively charged and the magnetic carrier is positively charged. For this reason, in the developing unit 13, the toner and the magnetic carrier are electrically adsorbed to each other and are united. The developing roll 131 holds the developer on the surface and rotates opposite to the photoreceptor roll 11 to convey the developer to a region between the developing roll 131 and the photoreceptor roll 10.

  The image forming apparatus 1 shown in FIG. 1 outputs the signal according to the ambient temperature and humidity around the photosensitive roll 11 and the environment sensor 19, which will be described in detail later. And a control unit 10 that receives signals representing temperature and humidity.

  Further, the control unit 10 controls the emission of exposure light by the exposure device 17 based on an image signal received from the outside, and further applies the voltage applied to the charging roll 12 and the developing roll 131. Controls development bias.

  The control unit 10 also has a counter 101 that counts the cumulative number of rotations of the photoconductor roll 11.

  Here, the flow of the image forming operation in the image forming apparatus 1 shown in FIG. 1 will be briefly described.

  First, a background potential is applied to the photoreceptor roll 11 that rotates in the direction of arrow A by the charging roll 12 that rotates in contact with the surface of the photoreceptor roll 11. Next, when the exposure device 17 irradiates the surface of the photoreceptor roll 11 with exposure light corresponding to the formed image and the surface of the photoreceptor roll 11 is neutralized, the potential of the neutralized portion becomes the image potential with respect to the background potential. It becomes. Due to the background potential and the image potential, an electrostatic latent image is formed on the surface of the photoreceptor roll 11. The latent image is developed with toner by the developing unit 13 to form a toner image on the photoreceptor roll 11. The toner image is transferred by the transfer roll 14 onto the paper transported along the transport path R. The toner image transferred onto the paper is pressed and fixed on the paper by the fixing device 16. The above is a brief description of the flow of image formation and the operation of each unit in the image forming apparatus 1.

  Development of the electrostatic latent image with toner by the developing unit 13 is performed as follows.

  Although not shown, the developing roll 131 has a hollow cylindrical sleeve that rotates in the direction of arrow A, and a plurality of magnets fixed in the sleeve independently of the sleeve. It consists of an arrayed magnet roll. The developer accommodated in the housing 132 is adsorbed on the sleeve surface by the magnetic force from the magnet roll provided in the sleeve. Further, a developing bias is applied to the developing roll 131. The developer adsorbed on the surface of the developing roll 131 by an electric field generated by a potential difference between the developing bias of the developing roll 131 and the latent image potential of the electrostatic latent image formed on the photosensitive roll 11 is obtained. The toner is electrostatically pulled toward the electrostatic latent image side of the photoreceptor roll 11. Thereby, the electrostatic latent image is developed with toner.

  Further, the transfer of the toner image formed on the surface of the photoreceptor roll 11 onto the recording paper by the transfer roll 14 is performed by performing positive current control of the transfer roll 14 with the positive polarity. This is performed by generating an electric field from the transfer roll 14 to the photoreceptor roll 11 between the roll 11.

  The image forming apparatus 1 according to the present embodiment applies only a DC voltage to the charging roll 12 instead of a voltage in which DC and AC are superimposed in order to simplify the apparatus configuration.

  Here, in order to save power, after a series of image forming jobs are completed, a standby mode for stopping the rotation of the photosensitive roll 11 is entered, and voltage is immediately applied to the charging roll 12 with high power consumption. It is conceivable to stop.

  However, after the job is completed, there is a portion on the surface of the photoreceptor roll 11 where the background potential from the most recent image formation remains. Therefore, if the application of the developing bias to the developing roll 131 is immediately stopped in the standby mode, a large electric field is generated in the direction from the developing roll side to the photosensitive roll, and the carrier in the developer is transferred to the photosensitive roll. Will move to the side. If so, there is a risk that the resumption of image formation will be adversely affected.

  In addition to the background potential due to the most recent image formation, an image potential is also present on the surface of the photoreceptor roll 11, and toner is transferred to the photoreceptor roll side between the followed development bias and the image potential. Even if an electric field is not generated, and even if an electric field sufficient to transfer toner is not generated, static elimination is repeated with potential unevenness remaining. Therefore, density unevenness due to the potential unevenness may appear in the image immediately after resuming image formation.

  Therefore, in the image forming apparatus 1, the background potential remaining on the surface of the photoreceptor roll 11 is neutralized by using the electric field generation function of the transfer roll 14 in order to stop the rotation of the photoreceptor roll 11. On the other hand, with respect to the developing roll 131, a potential difference that is not so large as to transfer a carrier charged to a positive polarity to the surface of the photoreceptor roll 11 is compared with the surface potential of the photoreceptor roll 11 that is gradually neutralized. The potential on the earth side generated during the period is applied in a follow-up manner.

  Further, in this image forming apparatus 1, the background potential is once applied to the entire surface of the photoreceptor roll 11 before the application of the voltage to the charging roll 12 is stopped in response to an instruction from the control unit 10 in order to stop the photoreceptor roll 11. Is applied to make the surface potential of the photoconductor roll 11 uniform, and then charge removal is started. The charging roll 12 corresponds to an example of a background potential applying unit according to the present invention, and the exposure unit 17 corresponds to an example of a latent image forming unit according to the present invention. The developing device 13 corresponds to an example of a developing unit according to the present invention, and the transfer roll 14 corresponds to an example of a transfer unit according to the present invention.

  FIG. 2 is a graph schematically showing changes in the surface potential and developing bias of the photoreceptor roll.

  In FIG. 2, the change in the surface potential of the photoconductor roll 11 is indicated by a solid line, and the change in the developing bias is indicated by a dotted line, with the horizontal axis representing time and the vertical axis representing potential. Further, a period T shown in the figure indicates the rotation period of the photoconductor roll 11.

  Part (a) of FIG. 2 shows a case where the voltage application to the charging roll is stopped immediately after the end of the most recent image formation, and the charge is removed by the transfer roll 14, and part (b) of FIG. ) Shows the case where the surface potential of the photoconductor roll 11 is once set to the background potential after the end of the most recent image formation, and then the charge is removed by the transfer roll 14.

  Also, part (a) of FIG. 2 shows a state in which static elimination (about 200 V) is performed by the transfer roll 14 on both the image potential and the background potential in the most recent image formation. Although the portion that originally had the background potential is 0 V on the third turn due to the charge removal by the transfer roll 14 with respect to 11, the portion that originally had the image potential exceeds 0 V and is charged to the plus side. It shows that the potential unevenness remains.

  Further, from part (a) of FIG. 2, although the developing bias is followed by a potential difference of about 150 V with respect to the background potential on the photoreceptor roll, the image potential on the photoreceptor roll is It can be read that this developing bias has generated an electric field in the direction in which the toner is transferred to the photoreceptor roll 11.

  On the other hand, in part (b) of FIG. 2, after the image formation is completed, once the background potential (−600 V) is applied to the entire circumference of the photoconductive roll 11, the voltage application to the charging roll 12 is stopped. The case is shown. Further, it is shown that the developing bias follows with a potential difference of about 150 V with respect to the surface potential of the photoreceptor roll 11, but the toner as shown in part (a) of FIG. Generation of an electric field directed to the roll 11 is not observed. Further, the surface potential during charge removal by the transfer roll 14 does not show potential unevenness as seen in part (a) of FIG. The control unit 10 of the image forming apparatus 1 corresponds to an example of a power supply unit referred to in the present invention.

  Next, a device for stabilizing the static elimination potential (here, 200 V) in the image forming apparatus 1 will be described.

  The controller 10 also performs transfer based on both the temperature and humidity detected by the environmental sensor 19 provided in the vicinity of the photoconductor roll 11 and the cumulative number of times the photoconductor roll 11 is counted by the counter 101. The current value of the constant current control of the roll 14 is changed.

  FIG. 3 is a diagram illustrating a table referred to by the control unit.

  FIG. 3 shows three categories of temperature and humidity (A: 28 ° C./85%, B: 22 ° C./55%, C: 10 ° C./15%), and three categories of cumulative rotational speed (a: 200K rotation). Less than, b: 200K rotation or more and less than 400K rotation, c: 400K rotation or more and less than 600K rotation, d: 600K rotation or more), and a table in which the transfer current value (μA) is set.

  It can be seen from the table shown in FIG. 3 that the transfer current value is set higher as the temperature / humidity increases and as the cumulative rotational speed increases.

  The resistance value of the transfer roll 14 changes due to changes in temperature and humidity. Specifically, the resistance of the transfer roll 14 increases at low temperatures and low humidity. For this reason, in order to apply a constant voltage between the photosensitive roll 11 and the transfer roll 14 even when the temperature and humidity change, that is, to maintain a constant charge removal performance, the resistance of the transfer roll 14 becomes high. When the humidity is low, the transfer current value is decreased, and when the resistance value of the transfer roll is low, the transfer current value is increased at a high temperature and high humidity.

  Further, as the cumulative number of rotations of the photoreceptor roll 11 increases, the film thickness decreases. When the film thickness is reduced, the amount of charge on the surface increases even when the surface potential is the same as when the film thickness is thick. That is, the capacitance of the photoconductor roll 11 is increased. Therefore, in order to keep the static elimination potential constant for each rotation as the photosensitive roll 11 becomes thinner, it is necessary to increase the static charge removal amount of the surface charge. For this purpose, the transfer current value is increased. Thus, it is necessary to increase the voltage applied between the photoconductor roll 11 and the transfer roll 14. The environmental sensor 19 corresponds to an example of an environment detection unit according to the present invention, and the counter 101 corresponds to an example of a counting unit according to the present invention.

  In the image forming apparatus 1, the peripheral length 94.2 mm of the photosensitive roll 11 having a diameter of 30 mm is 1.67 times the peripheral length 56.52 mm of the transfer roll 14 having a diameter of 18 mm. For this reason, while the photoreceptor roll 11 is rotated about three times, the same place on the photoreceptor roll is not discharged at the same place on the transfer roll, and the tendency to remove electricity is prevented.

  In the image forming apparatus 1, the surface roughness of the transfer roll 14 is made larger than the surface roughness of the charging roll 12. In the following, the surface roughness is represented by the void area, and the larger the surface roughness, the larger the void area.

  FIG. 4 is a graph showing the relationship between the air gap ratio and the grade of speckles generated on the image.

  FIG. 4 is a graph showing the relationship between the gap ratio of the charging roll 12 with respect to the gap area of the transfer roll 14 as the abscissa and the generated spot grade as the ordinate.

  From FIG. 4, the spot ratio becomes an acceptable level by making the surface roughness (void area) of the transfer roll 14 larger than the surface roughness (void area) of the charging roll 12, that is, the gap ratio is larger than 1. Furthermore, it can be seen that the spot grade is most improved when the void ratio is 10. This is because, when a material having a rough surface such as a foaming sponge member is used for the transfer roll 14, the sponge is caused by minute discharge unevenness generated by a minute gap generated between the photosensitive roll 11 and the transfer roll 14. If the surface roughness of the charging roll 12 is less than the surface roughness of the transfer roll, transfer of the image is resumed when the surface potential is applied by the charging roll 12 by restarting image formation. This is because unevenness in static elimination that has occurred at the time of static elimination is smoothed by the minute gaps in the roll 14.

  It can also be seen from FIG. 4 that even if the air gap ratio is greater than 10, there is no effect. Therefore, in the image forming apparatus 1, the gap area of the transfer roll 14 is 6.05 l, the gap area of the charging roll 12 is 0.59, and the gap ratio is about 10.

  Next, a second embodiment of the image forming apparatus of the present invention will be described.

  The difference between the image forming apparatus of the second embodiment and the image forming apparatus 1 of the first embodiment is that in the image forming apparatus 1 of the first embodiment, the surface potential of the photosensitive roll 11 after the image formation is finished. In the second embodiment, the application of the voltage to the charging roll 12 is stopped after the charging roll 12 once sets the same potential as the background potential (−600 V). In the second embodiment, the photosensitive roll 11 after the image formation is completed. The surface potential of the photoreceptor roll after the surface potential is once removed by the charging roll 12 and once the background potential (−600 V) is removed by the transfer roll 14 from the background potential (−600 V) (−200 V). 400V), the charging roll 12 is stopped.

  FIG. 5 is a graph showing changes in the surface potential of the photoreceptor roll.

  Part (a) of FIG. 5 shows a case where, for comparison, the surface of the photoreceptor roll 11 after completion of image formation is charged at −300 V by the charging roll 12 and then the charging roll 12 is stopped. A change in the surface potential of the photoconductor roll 11 is shown in a graph. Part (b) of FIG. 5 shows a change in the surface potential of the photoconductor roll 11 in the image forming apparatus of the second embodiment. .

  As shown in part (a) of FIG. 5, when the surface of the photoreceptor roll 11 after completion of image formation is charged to −300 V by the charging roll 12, the potential unevenness is not eliminated. This is because if the charging potential by the charging roll 12 is a negative potential from −400 V calculated from the discharging potential 200 V by the transfer roll 14 and the back surface potential −600 V, the background potential is obtained by discharging. This is because there is no potential difference from the image potential. Therefore, in the image forming apparatus according to the second embodiment, the surface potential of the photoreceptor roll 11 after completion of image formation is temporarily set to −400 V by the charging roll 12.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Control part 101 Counter 11 Photoconductor roll 12 Charging roll 13 Developing device 131 Developing roll 14 Transfer roll 16 Fixing device 17 Exposure device 19 Environmental sensor

Claims (6)

An image holding member for holding the image, wherein at least the peripheral surface circulates and an image is formed on the peripheral surface;
A background potential applying unit that applies a background potential as a background of the image to the peripheral surface of the image holding body by applying a voltage;
A latent image forming unit that forms an electrostatic latent image on the peripheral surface of the image carrier by applying an image potential different from the background potential;
A developing potential between the background potential and the image potential is provided by having a developer containing at least a charged toner disposed opposite to the peripheral surface of the image carrier. A developing unit for developing the electrostatic latent image with a charged toner to form a toner image;
The transferred object passes between the image holding member and the peripheral surface of the image holding member, and the toner image on the image holding member is electrostatically transferred onto the transferred member. A transcription section;
A power supply unit that is responsible for applying a voltage to the background potential applying unit and applying a potential to the developing unit, and at least a peripheral surface of the image holding member after completion of the formation of the electrostatic latent image by the latent image forming unit After one round, the voltage application to the background potential applying unit is stopped. After the voltage application is stopped, the potential of the developing unit is changed by the potential change of the peripheral surface of the image holding member due to the action of the transfer unit. A power supply unit for controlling the potential of the developing unit to follow,
An image forming apparatus comprising: The transfer unit has a peripheral surface that faces the peripheral surface of the image carrier and circulates and moves with the circular movement of the peripheral surface,
The image forming apparatus according to claim 1, wherein the image carrier has a circumference that is a non-integer multiple of the circumference of the transfer portion. The background potential applying unit has a peripheral surface that faces the peripheral surface of the image carrier and circulates and moves with the circular movement of the peripheral surface,
The transfer unit is a peripheral surface that faces the peripheral surface of the image carrier and circulates as the peripheral surface circulates, and has a surface roughness that is rougher than the surface roughness of the peripheral surface of the background potential applying unit. The image forming apparatus according to claim 1, wherein the image forming apparatus has a peripheral surface.   After the formation of the electrostatic latent image, before the voltage application to the background potential applying unit is stopped, the power supply unit controls the applied voltage to the background potential applying unit to control the peripheral surface of the image carrier. 4. The electric potential of the first and second potentials is controlled to be a potential between the background potential and a potential that changes from the background potential by a single action of the transfer portion. 5. 2. An image forming apparatus according to item 1. An environment detection unit that detects at least one of temperature and humidity of the environment of the image forming apparatus;
The power supply unit is further responsible for applying a potential to the transfer unit, and the potential applied to the transfer unit after the formation of the electrostatic latent image is in accordance with a detection result by the environment detection unit. 5. The image forming apparatus according to claim 1, wherein the image forming apparatus is controlled to a potential. A counting unit that cumulatively counts the number of circulations of the peripheral surface of the image carrier,
The power supply unit is further responsible for applying a potential to the transfer unit, and after the formation of the electrostatic latent image, the potential applied to the transfer unit is a potential corresponding to a counting result by the counting unit. The image forming apparatus according to claim 1, wherein the image forming apparatus is controlled as follows.

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