JP6098408B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image carrying rotator that carries and rotates a toner image that has been visualized by a developing device, and the toner image on the image carrying rotator is transferred to a transfer target and then remains on the image carrying rotator. The present invention relates to an image forming apparatus having a cleaning blade for removing residual toner.

  In an electrophotographic image forming apparatus such as a printer or a copying machine, an electrostatic latent image formed on the surface (image carrying surface) of a photosensitive drum that is an image carrying rotating body is visualized (developed) by a developing device. As a result, a toner image is obtained. In an image forming apparatus that forms a monochrome image, a toner image on a photosensitive drum is directly transferred and fixed onto a recording sheet such as a recording sheet or an OHP sheet.

  The surface of the photosensitive drum after the toner image is transferred is cleaned by a cleaning member. As the cleaning member, for example, a cleaning blade that is in sliding contact with the surface of the photosensitive drum is used. The cleaning blade is formed in a band plate shape, and a side edge portion (tip portion) along the longitudinal direction is pressed against the surface of the photosensitive drum. Residual toner adhering to the surface of the photosensitive drum is scraped off by the cleaning blade.

  Further, in an intermediate transfer body type image forming apparatus capable of forming a full-color image, toner images of different colors are formed on each of a plurality of photosensitive drums. The toner image on each photoconductive drum is transferred to an intermediate transfer belt (image bearing rotating body) and then transferred to a recording sheet. The surface (image carrying surface) of the intermediate transfer belt after the toner image is transferred is also cleaned by the cleaning blade.

JP 2000-131003 A

If the cleaning blade that is in sliding contact with the photosensitive drum is pressed against the surface of the photosensitive drum, and the adhesive force with the surface of the photosensitive drum is large, the cleaning blade is smoothly slid in contact with the surface of the photosensitive drum. do not do. In this case, the tip of the cleaning blade may move and bend along with the surface of the photosensitive drum.
Such deformation of the cleaning blade is usually referred to as “turning over”. When “turning” occurs in the cleaning blade, the residual toner attached to the surface of the photosensitive drum cannot be reliably removed.

Conventionally, in a new (unused) printer, when the number of printed sheets reaches about several thousand, the probability of “turning up” in the cleaning blade pressed against the photosensitive drum has increased rapidly.
The inventor of the present application investigated the cause and found the following facts.
(1) The toner particles of the developer are usually in a state where an external additive is added (externally added state) for the purpose of improving the fluidity of the toner particles. However, since the binding force of the external additive on the toner particles is not uniform, the external additive may be peeled off from the toner particles (the external additive peeled off from the toner particles is referred to as “free external additive”). To do). When such a free external additive is present in the developing device, the free external additive flies from the developing device together with the toner particles during development and adheres to the surface of the photosensitive drum. The free external additive adhering to the surface of the photosensitive drum functions as a lubricant in the portion where the cleaning blade is pressed.

(2) Since the surface of the new photoconductor drum is very smooth, the adhesion with the tip of the cleaning blade is high. In such a state, if a relatively large amount of free external additive does not adhere to the surface of the photosensitive drum, there is a high risk of “turning” on the cleaning blade.
As the number of printed sheets increases, the surface of the photoconductive drum decreases in smoothness due to friction caused by sliding contact of the cleaning blade, and the surface roughness of the photoconductive drum gradually increases. Thereby, the adhesiveness of the front-end | tip part of a cleaning blade falls gradually. For this reason, when the surface roughness of the photosensitive drum becomes a certain level, the cleaning blade does not "turn over" even if there is not much free external additive attached to the surface of the photosensitive drum. become.

  (3) The toner particles are produced by mixing and stirring a material that becomes a toner base and a material that becomes an external additive. In this case, the binding force of the external additive to the toner base is increased by stirring the material at high speed or by stirring for a long time. However, the toner particles may deteriorate due to changes in shape, charging characteristics, and the like due to high-speed stirring or long-time stirring. When deteriorated toner particles are used in the developing unit, the image quality of the toner image formed on the photosensitive drum may be deteriorated.

For this reason, the toner (initial developer) accommodated in a new developer unit is usually made up of toner particles that have been prepared so as not to deteriorate. For this reason, the initial developer includes a free external additive or an external additive having a very weak binding force only by contacting the surface of the toner particles (hereinafter referred to as “low-binding external additive”). There are relatively many.
Since the external additive has a very small mass compared to the toner particles, the free external additive and the low binding external additive in the developing device are caused by the toner particle due to the potential difference between the photosensitive drum and the developing roller during development. It flies more easily from the developing device and adheres to the photosensitive drum.

  Immediately after the start of use of a new printer, a relatively large amount of free external additives or low-binding external additives are contained in the initial developer of the developing device as described above, so that a large amount of toner is present on the photosensitive drum. Free external additives are supplied. As a result, the effect of lubrication of the cleaning blade on the surface of the photosensitive drum is enhanced, and there is no risk of “turning” on the cleaning blade even if the surface roughness of the photosensitive drum is small.

  However, when a large amount of free external additive is supplied from the developing device onto the photosensitive drum in this way, the speed of the free external additive consumed from the developing device increases, and the surface roughness of the photosensitive drum is reduced. At a stage earlier than reaching the above-described stable state, the free external additive in the developing device cannot be sufficiently supplied to the photosensitive drum. As a result, a sufficient amount of the free external additive cannot be supplied onto the photosensitive drum, and at that time, the danger rate of occurrence of “turning” in the cleaning blade increases drastically.

Although the cleaning blade for cleaning the photosensitive drum has been described above, the same applies to the case where an intermediate transfer member such as an intermediate transfer belt used in a color printer is cleaned by the cleaning blade.
That is, the surface of the new intermediate transfer belt is also very smooth, but the surface roughness increases as the number of printed sheets increases. Further, when a free external additive is supplied from the developing device to each of the plurality of photosensitive drums, the free external additive adheres from each photosensitive drum to the surface (image carrying surface) of the intermediate transfer belt. The free external additive attached to the intermediate transfer belt functions as a lubricant for the cleaning blade.

However, the amount of the free external additive of the developing device can be sufficiently supplied to the photosensitive drum at a stage earlier than the surface roughness of the intermediate transfer belt becomes a stable state where no “turning” occurs in the cleaning blade. If you can't do that, the risk of "turning over" will increase dramatically.
The present invention has been made in view of the circumstances as described above, and at the initial stage of the start of use of a new developing device and an image carrier rotator, “turning” is applied to the cleaning blade that is in sliding contact with the image carrier rotator. An object of the present invention is to provide an image forming apparatus capable of preventing the occurrence.

  In order to achieve the above object, an image forming apparatus according to the present invention includes an image carrying rotator carrying a toner image visualized by toner supplied from a developing device, and a toner image carried on the image carrying rotator. An image forming apparatus comprising: a transfer unit that transfers toner to a transfer target; and a cleaning blade that removes residual toner remaining on the image carrying surface of the image carrying rotating body after transferring the toner image. In the initial stage until the image carrying surface reaches a state where the risk of turning over in the cleaning blade is eliminated after the carrying rotating body is in a new state, image formation is performed in the first image forming mode. And a control means for executing image formation in the second image forming mode after reaching the state where the risk of occurrence of turning has been eliminated, and the image in the first image forming mode is provided. The formation condition is that the amount of the external additive supplied together with the toner from the developing device is more than the amount necessary for preventing the cleaning blade from turning over in the initial stage, and the initial stage The image forming operation is set to be less than that in the case where the image forming operation is executed under the same conditions as in the second image forming mode.

  In the image forming apparatus according to the present invention, when the image bearing rotator and the developing device are new, the state of the image bearing surface reaches the state where the risk of occurrence of turning up of the cleaning blade has been eliminated. The image formation is executed under the image forming conditions in the first image forming mode. In this case, since the speed at which the external additive is consumed in the developing device is suppressed, the image carrying surface of the image carrying rotating body is removed from inside the developing device until the risk of turning up in the cleaning blade is eliminated. There is no possibility that the external additive supplied to the image bearing rotator will be insufficient. As a result, there is no possibility that the cleaning blade will turn up until the state of the image carrying surface of the image carrying rotating body is eliminated.

  When the image carrying surface reaches a state where the risk of occurrence of turning of the cleaning blade is eliminated, the cleaning blade does not turn even if the amount of the free external additive supplied to the image carrying surface is reduced. For this reason, when reaching the state in which the risk of turning up of the cleaning blade is eliminated, the amount of the external additive supplied to the image carrying surface is larger than that in the first image forming mode. Image formation is executed under image formation conditions in the formation mode. Thus, it is possible to avoid the case where the image formation is continued in the first image forming mode and thus the density unevenness or the like occurs in the toner image and the image quality becomes unstable.

Preferably, the image carrying surface of the image carrying rotator further comprises a judging means for judging whether or not the risk of turning over the cleaning blade has been eliminated. .
Preferably, the determination means includes a surface roughness of the image bearing surface of the image bearing rotator, a driving torque when the image bearing rotator is rotated, a deformation amount of the cleaning member, and an image bearing in the unused state. An acquisition means for acquiring at least one of the information related to the cumulative number of image formations from the start of use of the rotating body and the cumulative travel distance from the start of use of the unused image-bearing rotating body is provided. Based on the information, it is determined whether or not the state of the image carrying surface of the image carrying rotating body has reached a state in which the risk of turning over the cleaning blade has been eliminated.

Preferably, the developing device includes a developer carrying rotator that carries and rotates a developer containing toner particles, and the rotation speed of the developer carrying rotator in the first image forming mode is set to be the first speed. It is characterized in that it is set lower than the rotation speed in the second image forming mode.
Preferably, the developing device includes a developer carrying rotator that carries and rotates a developer containing toner particles, and a development bias supply unit that applies a development bias voltage to the developer carrying rotator. In the first image forming mode, the developing bias supply means develops so that the amount of the external additive supplied from the developer carrying rotator during development is smaller than in the second image forming mode. A bias voltage condition is set.

Preferably, the developing bias voltage is obtained by superimposing an AC bias voltage on a DC bias voltage, and by changing the waveform of the AC bias voltage, the amount of toner particles supplied from the developer-carrying rotator during development. Is set so as to decrease in the first image forming mode than in the second image forming mode.
Preferably, the developing device includes a developer carrying rotator that carries and rotates a developer containing toner particles, and a stirring member that supplies the developer to the developer carrying body while stirring the developer. The degree of stirring of the developer by the stirring member in the first image forming mode is set to be stronger than that in the second image forming mode.

Preferably, a developer replenishing mechanism for replenishing the developer to the developer is further provided, and the unused developer is replenished from the developer replenishment mechanism with a bond strength with the toner particles of the external additive. The developer processed so as to be stronger than the replenished toner is stored in advance.
Preferably, the image forming apparatus includes an acquisition unit that acquires information indicating that both the developing unit and the image bearing rotating body have been replaced with new ones that are not used, and the control unit includes both the developing unit and the image bearing rotating unit being new. When the information indicating that the replacement has been performed is acquired, control is performed such that image formation is performed by setting the first image formation mode.

FIG. 2 is a schematic diagram for explaining a configuration of a monochrome printer that is an example of the image forming apparatus according to the first exemplary embodiment of the present invention. It is a cross-sectional schematic diagram for demonstrating the structure of the image development apparatus provided in the monochrome printer. FIG. 4 is a schematic diagram for explaining toner particles used in a developing device. (A)-(d) is a schematic diagram for demonstrating the state in which the toner which exists in a developing device respectively changes with the increase in the frequency | count of execution of developing operation. (A) And (b) is a schematic diagram for demonstrating the state of the cleaning blade which slidably contacts with a photoreceptor drum, respectively. (A) is a graph showing the relationship between the accumulated number of printed sheets and the quantitative value of the weight of the external additive flying from the developing device, and (b) is the relationship between the accumulated number of printed sheets and the surface roughness of the photosensitive drum. It is a graph to show. 6 is a table showing the relationship between the quantitative value of the weight of the external additive flying from the developing device and the surface roughness of the photosensitive drum, and the occurrence of “turning” in the cleaning blade. It is a block diagram which shows the structure of the principal part of the control system of a monochrome printer. It is a flowchart which shows the process sequence of the development control performed by a monochrome printer. 6 is a table showing development conditions in an initial mode and a normal mode of development control in Embodiment 1. (A) is a graph showing the relationship between the cumulative number of printed sheets when the development control of Embodiment 1 is executed and the quantitative value of the weight of the external additive flying from the developing device, and (b) is the cumulative print in that case. 6 is a graph showing the relationship between the number of sheets and the surface roughness of the photosensitive drum. (A) is explanatory drawing of the developing bias voltage applied to a developing roller, (b) is explanatory drawing of 1 period of the developing bias voltage. 10 is a table showing development bias conditions set in each of an initial mode and a normal mode of development control in Embodiment 2. 10 is a table showing the rotation speeds of a developing roller, a supply screw, and a stirring screw set in each of an initial mode and a normal mode of development control in Embodiment 3. FIG. 10 is a schematic diagram for explaining a configuration of a tandem type color printer that is an example of an image forming apparatus according to a fourth embodiment.

Hereinafter, embodiments of an image forming apparatus according to the present invention will be described.
[First Embodiment]
<Configuration of image forming apparatus>
FIG. 1 is a schematic diagram for explaining a configuration of a monochrome printer which is an example of an image forming apparatus according to Embodiment 1 of the present invention. This monochrome printer forms a monochrome image on a recording sheet such as a recording sheet or an OHP sheet by a known electrophotographic method based on image data input from an external terminal device or the like via a network (for example, LAN). .

  The monochrome printer shown in FIG. 1 has a photosensitive drum 11 provided on one side (a position closer to the right side from the front side to the back side) in a substantially central portion in the vertical direction. The photosensitive drum 11 is rotationally driven in the direction indicated by the arrow Z. The photosensitive drum 11 is rotated by a drum motor 43 (see FIG. 8). In the following, the right side and the left side from the front side to the back side are simply referred to as “right side” and “left side”, respectively.

A charger that uniformly charges the surface (image carrying surface) of the photosensitive drum 11 to a predetermined potential on the left side (downstream in the rotation direction of the photosensitive drum 11) with respect to the upper portion of the photosensitive drum 11. 12 is provided.
The photosensitive drum 11 charged to a predetermined potential by the charger 12 is exposed by the laser beam LB emitted from the exposure device 13 on the downstream side of the charger 12 in the rotation direction of the photosensitive drum 11. An electrostatic latent image is formed on the surface of each charged photosensitive drum 11 by irradiation with the laser beam LB from the exposure device 13.

  On the left side of the photosensitive drum 11, a developing device 14 that develops the electrostatic latent image on the photosensitive drum 11 on the downstream side in the rotation direction from the position where the surface of the photosensitive drum 11 is exposed by the laser beam LB. Is provided. The developing device 14 visualizes (develops) the electrostatic latent image formed on the surface of the photosensitive drum 11 with black toner. A specific configuration of the developing device 14 will be described later.

Above the developing unit 14, a toner replenishing mechanism 17 that supplies toner to the developing unit 14 is provided. The toner replenishment mechanism 17 stores replenishment toner in advance, and replenishes the developer 14 with toner when the amount of toner in the developer 14 drops below a predetermined value.
A transfer roller 15 is disposed opposite to the developing device 14 on the downstream side in the rotation direction of the photosensitive drum 11. The transfer roller 15 is in pressure contact with the right side portion of the photosensitive drum 11. A transfer nip Nt is formed at the pressure contact portion between the transfer roller 15 and the photosensitive drum 11. The toner image formed on the surface of the photosensitive drum 11 is conveyed to the transfer nip Nt by the rotation of the photosensitive drum 11.

A paper feed cassette 22 is provided below the developing unit 14. A recording sheet S such as a recording sheet or an OHP sheet is accommodated in the sheet feeding cassette 22. The recording sheet S accommodated in the paper feed cassette 22 is fed out to the sheet conveyance path 21 by the paper feed roller 23. The sheet conveyance path 21 extends toward the upper transfer nip Nt.
The recording sheet S fed from the sheet feeding cassette 22 to the sheet conveyance path 21 is conveyed to the transfer nip Nt. The recording sheet S is temporarily stopped on the upstream side of the transfer nip Nt in the sheet conveyance path 21 and then conveyed to the transfer nip Nt when the toner image on the photosensitive drum 11 arrives at the transfer nip Nt. .

A transfer bias voltage is applied to the transfer roller 16 at the timing when the recording sheet S passes through the transfer nip Nt. As a result, an electric field is formed between the transfer roller 16 and the photosensitive drum 11, and the toner image on the photosensitive drum 11 is transferred to the recording sheet S by the action of the electric field.
A cleaning blade 16 that is in sliding contact with the upper portion of the photosensitive drum 11 is provided on the downstream side in the rotation direction of the photosensitive drum 11 with respect to the transfer nip Nt. The cleaning blade 16 removes toner adhering to the surface of the photosensitive drum 11. The cleaning blade 16 is formed in a band plate shape by an elastic material, and the longitudinal direction is arranged along the axial direction of the photosensitive drum 11.

  The cleaning blade 16 is arranged in a state where the longitudinal direction is along the axial direction of the photosensitive drum 11, and the direction orthogonal to the longitudinal direction (width direction) is inclined with respect to the surface of the photosensitive drum 11. ing. One side edge portion (tip portion) along the longitudinal direction of the cleaning blade 16 extends from the downstream side (left side) in the rotation direction of the photosensitive drum 11 to the surface of the photosensitive drum 11 over almost the entire area in the axial direction. It is in pressure contact.

The cleaning blade 16 removes residual toner and the like adhering to the surface of the photosensitive drum 11 by the tip portion being in pressure contact with the surface of the rotating photosensitive drum 11 being in sliding contact with the surface of the photosensitive drum 11. .
The recording sheet S that has passed through the transfer nip Nt is conveyed to the fixing device 30 disposed above the transfer roller 15. The fixing device 30 includes a heating roller 31 and a pressure roller 32 that are pressed against each other, and a fixing nip Nf is formed between the heating roller 31 and the pressure roller 32 due to the pressure contact between them. ing. A heater lamp 33 is disposed at the axial center of the heating roller 31, and the heating roller 31 is heated by the heater lamp 33.

In the fixing device 30, the unfixed toner image on the recording sheet S is fixed on the recording sheet S by being heated and pressurized while passing through the fixing nip Nf. The recording sheet S on which the toner image is fixed is discharged onto a paper discharge tray 26 by a paper discharge roller 24.
Note that each of the photosensitive drum 11 and the developing device 14 in the monochrome printer can be replaced, and the attached state with respect to the monochrome printer is released by pulling them out to the front side. The monochrome printer is provided with a photosensitive drum sensor 48 and a developing device sensor 49 (both see FIG. 8) for detecting that the photosensitive drum 11 and the developing device 14 are mounted.

<Developer configuration>
Next, the configuration of the developing device 14 will be described in detail with reference to FIG.
The developing device 14 has a developing housing 14h disposed along the photosensitive drum 11, and a two-component developer containing nonmagnetic toner particles and a magnetic carrier is accommodated in the developing housing 14h. In the following, the non-magnetic toner particles are simply referred to as “toner particles”, and the magnetic carrier is simply referred to as “carrier”.

A hollow developing roller 14r is provided in the developing housing 14h so as to face the photosensitive drum 11. The developing roller 14r is disposed in parallel with the photosensitive drum 11 on the downstream side in the rotation direction with respect to the irradiation position of the laser beam LB on the photosensitive drum 11.
A cylindrical magnet body 14m is coaxially arranged inside the developing roller 14r. The magnet body 14m is fixed so as not to rotate, and magnetic poles (not shown) along the axial direction are provided over a whole area in the axial direction at a plurality of positions in the circumferential direction. The developing roller 14r is rotated around the magnet body 14m in a direction indicated by an arrow W in FIG. 2 by a developing motor 44 (see FIG. 8). A predetermined developing bias voltage is applied to the developing roller 14r by a developing bias power source 47 (see FIG. 8).

  A supply screw 14b is provided inside the developing housing 14h. The supply screw 14b is disposed close to each other in a state parallel to the developing roller 14r on the lower side of the developing roller 14r. In addition, a stirring screw 14c is provided in the developing housing 14h on the lower left side with respect to the supply screw 14b. The stirring screw 14c is arranged in parallel with the supply screw 14b.

The supply screw 14b and the stirring screw 14c are rotated in opposite directions at the same rotational speed by, for example, one screw drive motor 45 (see FIG. 8).
When the stirring screw 14c is rotated by the screw drive motor 45, a two-component developer (hereinafter simply referred to as “developer”) inside the developing housing 14h is conveyed while being stirred along the axial direction.

  When the developer conveyed by the stirring screw 14c is stirred, the toner particles contained in the developer are charged and supplied to the supply screw 14b. The supply screw 14b supplies the developer onto the circumferential surface of the rotating developing roller 14r while transporting the developer along the axial direction. Thereby, the developer is carried on the peripheral surface of the developing roller 14r. Thus, the developing roller 14r is a developer carrying rotator that carries and conveys the developer.

  The developer carried on the peripheral surface of the developing roller 14 r is conveyed to a position facing the photosensitive drum 11. An electric field is formed at a position where the developing roller 14r and the photosensitive drum 11 face each other by applying a developing bias voltage to the developing roller 14r. The toner particles contained in the developer on the developing roller 14r adhere to the electrostatic latent image on the photosensitive drum 11 by the action of this electric field. As a result, the electrostatic latent image on the photosensitive drum 11 is visualized (developed) by the toner particles, and a toner image is formed on the photosensitive drum 11.

  In the above description, the supply screw 14b and the agitation screw 14c are rotationally driven by one screw drive motor 45, but the present invention is not limited to such a configuration. Instead of such a configuration, each of the supply screw 14b and the agitation screw 14c may be driven to rotate by an individual screw drive motor. Also in this case, the developer is conveyed in opposite directions by the supply screw 14b and the stirring screw 14c.

  The developing housing 14h is provided with a toner concentration sensor 14g for detecting the toner concentration of the internal developer. The toner concentration sensor 14g is attached to the outside of the developing housing 14h below a stirring screw 14c provided in the developing housing 14h. When the toner concentration detected by the toner concentration sensor 14g falls below a predetermined value, the toner is supplied from the toner supply mechanism 17 into the developing housing 14h of the developing device 14 as described above.

<Toner particles>
Next, the toner particles housed in the developing housing 14h together with the carrier will be described. FIG. 3 is a schematic diagram for explaining toner particles.
The toner particles T are composed of a toner base Tm having a particle diameter of about 8 μm composed of a resin such as low melting point polyester and a colorant, and an external additive Tg attached (bonded) to the surface of the toner base Tm. Yes. FIG. 3 shows three particles of the external additive Tg having different binding states with respect to the toner base Tm in order to explain the binding state of the external additive Tg with the toner base Tm.

The external additive Tg has a particle size of 1/10 or less of the average particle size of the toner base Tm, and its mass is very small compared to the toner particles T. Such an external additive Tg is added (externally added) to the toner base Tm for the purpose of improving the charging property of the toner particles T, the cleaning property of the photosensitive drum 11, and the like. In the present embodiment, the external additive Tg contains silica (SiO ₂ ), titanium oxide (TiO ₂ ), zinc oxide (ZnO), and calcium carbonate (CaCO ₃ ).

The toner particles T are produced by mixing and stirring the material that becomes the toner base Tm and the material that becomes the external additive Tg using a mixing stirrer such as a mixer. The external additive Tg is bonded to the toner base Tm of the individual toner particles T by stirring at the time of manufacture.
The binding force of the external additive Tg to the toner base Tm is increased (intensified) by high-speed stirring or long-time stirring. However, since the toner particles T deteriorate due to high-speed or long-time agitation, the toner particles T are usually manufactured by adjusting the agitation speed and the agitation time so that the toner particles T do not deteriorate. In the toner particles T thus produced, the binding force of the external additive Tg to the toner base Tm is not uniform.

FIG. 3 shows a strong binding external additive Tga having a strong binding force to the toner base Tm, a low binding external additive Tgb having a lower binding strength to the toner base Tm than the strong binding external additive Tga, and a toner base Tm. 2 shows a free external additive Tgc peeled (free).
The stronger the external additive Tga is more strongly bonded to the toner base Tm as it is embedded in the surface of the toner base Tm. The low bonding external additive Tgb is in a bonded state (adhered state) such that the toner base Tm is not deformed.

  Since the strong binding external additive Tga has a strong binding force to the toner base Tm, even if an external force such as vibration, electric field, centrifugal force or the like acts on the toner particles T, there is no possibility of being released from the toner base Tm. Therefore, when developing the electrostatic latent image on the photosensitive drum 11, even if the toner particles T move from the developing housing 14h to the photosensitive drum 11, the strong external additive Tga is released from the toner base Tm. Without moving, the toner moves to the photosensitive drum 11 together with the toner base Tm. Accordingly, the amount of the strong binding external additive Tga in the developing housing 14h decreases in proportion to the decrease in the toner particles T.

On the other hand, the low binding external additive Tgb has a binding force to the toner base Tm that is not as strong as the strong binding external additive Tga, and therefore, when an external force such as vibration, electric field, centrifugal force or the like acts on the toner particles T, There is a possibility that it is released from the toner base Tm and becomes a free external additive Tgc.
As described above, the toner particles T are usually manufactured by adjusting the stirring speed or stirring time so as not to deteriorate. Therefore, a relatively large amount of free external additive Tgc is contained in the developer (initial developer) accommodated in the unused (new) developer housing 14h. Each toner particle T also contains a relatively large amount of the low binding external additive Tgb.

  The free external additive Tgc in the developing housing 14h flies from the developing housing 14h together with the toner when developing the electrostatic latent image on the photosensitive drum 11. The amount of the free external additive Tgc flying from the developing housing 14h includes the rotational speed of the developing roller 14r when supplying the toner particles T to the photosensitive drum 11, the electric field strength between the developing roller 14r and the photosensitive drum 11, and the like. It depends on. However, since the mass of the free external additive Tgc is much smaller than that of the toner particles T, the amount of the free external additive Tgc flying from the developing housing 14h cannot be controlled as accurately as the toner particles T.

FIG. 4A is a schematic diagram for explaining the amounts of the toner particles T and the external additive Tg in the developing housing 14h when the developing device 14 is unused. 4B to 4D are schematic diagrams for explaining changes in the amounts of the toner particles T and the external additive Tg in the developing housing 14h as the number of printed sheets increases.
When the developing device 14 is not used, a predetermined amount of toner particles T are previously stored in the developing housing 14h together with the carrier. In this case, as shown in FIG. 4A, a relatively large amount of free external additive Tgc is present.

  When the developing operation is started in the developing device 14 in such a state, the toner particles T in the developing housing 14 h are supplied from the developing roller 14 r to the photosensitive drum 11. Accordingly, as shown in FIG. 4B, the amount of toner particles T in the developing housing 14h is reduced. Further, since the free external additive Tgc in the developing housing 14h flies to the outside of the developing housing 14h together with the toner particles T, the amount of the free external additive Tgc existing inside the developing housing 14h is also reduced.

Most of the free external additive Tgc flying to the outside of the developing housing 14 h is considered to adhere to the photosensitive drum 11.
In this case, since the free external additive Tgc is lighter than the toner particles, the decreasing rate of the free external additive Tgc in the developing housing 14h is larger than that of the toner particles.
Thereafter, as the number of executions of the developing operation by the developing device 14 increases, as shown in FIG. 4C, the amount of toner particles T existing inside the developing housing 14h further decreases. At the same time, the amount of the free external additive Tgc in the developing housing 14h is also reduced.

Furthermore, when the number of executions of the developing operation by the developing device 14 increases, the amount of toner particles T inside the developing housing 14h decreases to a predetermined amount or less. When such a state is detected by the toner concentration sensor 14g, the toner particles T are supplied from the toner supply mechanism 17 into the developing housing 14h.
In this case, together with the toner particles T to be replenished, the free external additive Tgc is also replenished to the developing housing 14h. As shown in FIG. 4D, the amount of the free external additive Tgc in the developing housing 14h. Increases with the toner particles T. However, since the amount of the free external additive Tgc increases only in accordance with the amount of the toner particles T to be replenished, the amount of the free external additive Tgc is relatively small, and the free external additive Tgc is released in the unused development housing 14h. It does not increase to the amount of the external additive Tgc.

<Cleaning blade>
Next, the cleaning blade 16 that comes into sliding contact with the photosensitive drum 11 will be described with reference to FIGS. FIG. 5A is a schematic diagram for explaining the cleaning blade 16 in sliding contact with the photosensitive drum 11. FIG. 5A shows a state in which the cleaning blade 16 is viewed from the back side (the side opposite to the direction shown in FIG. 1). Further, the surface of the photosensitive drum 11 is shown in a flat state, and the direction indicated by the arrow Z in FIG. 5A is the rotational direction of the photosensitive drum 11.

  The cleaning blade 16 is pressed against the surface of the photosensitive drum 11 after the toner image is transferred to the recording sheet S at the transfer nip Nt. The portion of the cleaning blade 16 that is in pressure contact with the surface of the photoconductor drum 11 is opposed to the photoconductor drum 11 along the rotation direction of the photoconductor drum 11 from the side edge located upstream in the rotation direction of the photoconductor drum 11. doing. A tip portion of the cleaning blade 16 that is in pressure contact with the surface of the photosensitive drum 11 is referred to as a “cleaning portion 16a”. A pressure contact force indicated by an arrow acts on the cleaning portion 16a.

  The free external additive Tgc flying from the developing device 14 is conveyed to the transfer nip Nt (see FIG. 1) while adhering to the surface of the photosensitive drum 11. In the transfer nip Nt, when the toner image is transferred from the surface of the photosensitive drum 11 to the recording sheet S, a part of the free external additive Tgc attached to the surface of the photosensitive drum 11 adheres to the recording sheet S. The free external additive Tgc on the photosensitive drum 11 that does not adhere to the recording sheet S is conveyed to the pressure contact position of the cleaning unit 16a in the cleaning blade 16.

The free external additive Tgc is colorless or white. For this reason, even if the free external additive Tgc adheres to the recording sheet S, there is no possibility that the image quality of the toner image on the recording sheet S will deteriorate.
At the pressure contact position of the cleaning blade 16, as shown in FIG. 5A, the toner particles T remaining on the surface of the photosensitive drum 11 without being transferred to the recording sheet S are pressed against the surface of the photosensitive drum 11. It comes into contact with the tip of the cleaning blade 16. As a result, the toner particles T are blocked by the tip of the cleaning blade 16. The toner particles T blocked by the tip of the cleaning unit 16a are scraped off from the surface of the photosensitive drum 11 because the adhesion force with the photosensitive drum 11 is weakened.

The free external additive Tgc adhering to the surface of the photosensitive drum 11 is also blocked by the tip of the cleaning blade 16 together with the toner particles T. However, a part of the free external additive Tgc smaller than the toner particles T passes between the cleaning unit 16 a and the photosensitive drum 11 without being blocked by the tip of the cleaning blade 16.
The free external additive Tgc passing between the cleaning unit 16a and the photosensitive drum 11 functions as a “lubricant” that reduces friction between the two. Therefore, when the amount of the free external additive Tgc passing between the cleaning unit 16a and the photosensitive drum 11 is large, the cleaning unit 16a is in a low friction state with the surface of the rotating photosensitive drum 11. Smooth sliding contact. In such a state, there is no possibility that the tip of the cleaning blade 16 moves together with the surface of the photosensitive drum 11.

  When the amount of the free external additive Tgc passing between the cleaning unit 16a and the photosensitive drum 11 decreases, the frictional force between the cleaning unit 16a and the surface of the photosensitive drum 11 increases. When a large frictional force is applied to the cleaning unit 16a from the surface of the photosensitive drum 11, the cleaning unit 16a moves integrally with the surface of the photosensitive drum 11, and the cleaning unit 16a is moved as shown in FIG. Then, a “turn-up” that is bent downstream in the rotation direction of the photosensitive drum 11 occurs.

  When “turning” occurs in the cleaning blade 16, the pressure of the cleaning portion 16 a against the surface of the photosensitive drum 11 becomes small. In this case, the cleaning unit 16a may not be able to block the toner particles T adhering to the surface of the photoconductive drum 11 and cannot be reliably removed from the surface of the photoconductive drum 11. When the toner particles T that are not removed from the surface of the photosensitive drum 11 are transferred to the recording sheet S, the image quality of the toner image on the recording sheet S deteriorates.

  If the surface roughness of the photosensitive drum 11 is very small, the risk of such “turning” of the cleaning blade 16 increases. That is, when the surface roughness of the photosensitive drum 11 is small, the amount of unevenness on the surface of the photosensitive drum 11 is small (small), and the area where the cleaning unit 16a contacts the surface of the photosensitive drum 11 is large. For this reason, the frictional force acting between the surface of the cleaning unit 16a and the surface of the photosensitive drum 11 is increased, and the risk that the cleaning blade 16 is turned up is increased.

  However, even if the surface roughness of the photosensitive drum 11 is small, as described above, there is a risk that the cleaning blade 16 may be “turned up” due to the free external additive Tg adhering to the photosensitive drum 11. descend. Further, even if the surface roughness of the photosensitive drum 11 is small, if the free external additive Tg adhering to the photosensitive drum 11 is small, there is a high risk that the cleaning blade 16 will be “turned up”.

  The surface roughness of the photoconductive drum 11 is the smallest in the unused state (new article). However, since the cleaning portion 16a of the cleaning blade 16 is always pressed against the surface of the photosensitive drum 11, the surface of the photosensitive drum 11 is worn as the number of image formations (number of printed sheets) increases. As a result, the surface roughness of the photosensitive drum 11 also increases sequentially as the number of printed sheets increases.

  When the surface roughness of the photoconductor drum 11 is increased, the contact area between the cleaning unit 16a and the surface of the photoconductor drum 11 is reduced, and the frictional force acting between the two is smaller than when the surface roughness is small. Become. This reduces the risk of “turning” on the cleaning blade 16. Therefore, in the state where the surface roughness of the photosensitive drum 11 is increased, the risk of “turning up” on the cleaning blade 16 is eliminated even if the amount of the free external additive Tgc is decreased.

<Verification of free external additives in the developer>
Next, in the monochrome printer of this embodiment, the amount of the free external additive flying from the developing device 14 was verified when it was in a new state (both the photosensitive drum 11 and the developing device 14 were unused).
First, when the developing device 14 is unused, the weight of the external additive Tg present in the developing housing 14h of the developing device 14 was quantified.

  In this quantification process, first, the developer in the developing housing 14h was sampled and its weight (milligram) was measured. The weight of the sample in this case is referred to as “sample weight WDs”. Next, the weight of Si (silicon), Ti (titanium), Zn (zinc), and Ca (calcium) contained in the collected sample (developer) was measured using an X-ray analyzer (manufactured by Horiba, Ltd., trade name “EMAX- 7000 ").

In this case, each of Si, Ti, Zn, and Ca includes silica (SiO ₂ ), titanium oxide (TiO ₂ ), zinc oxide (ZnO), and calcium carbonate (CaCO ₃ ), which are substances constituting the external additive Tg. It is a substance contained in each. From this, it is considered that the total weight (total weight) of Si, Ti, Zn, and Ca contained in the sample corresponds to the weight of the free external additive Tcg contained in the developer in the developing housing 14h. .

The total weight of Si, Ti, Zn, and Ca was measured five times, and the average value WDa was calculated.
Further, the total weight WDt of the toner in the developing housing 14h in the unused developing device 14 was obtained based on the detection result of the toner density sensor 14g.
Thereafter, the total weight of the free external additive Tgc in the developing housing 14h is expressed by the following quantification formula (1) based on the free external additive weight average value WDa, the sample weight WDs, and the total toner weight WDt. Quantified by However, [WD] is a quantitative value of the weight of the free external additive Tgc.

[WD] = WDa × WDt / WDs (1)
The quantitative value [WD] of the weight of the free external additive Tgc obtained by the above quantification formula (1) is defined as “initial quantitative value [WDf]”.
In this way, when the initial quantitative value [WDf], which is the quantitative value of the weight of the free external additive Tgc, is obtained in the unused developing device 14, the image forming operation is executed in the monochrome printer. When the number of printed sheets reaches a predetermined number (m), the weight of the free external additive Tgc present in the developing housing 14h of the developing device 14 is quantified based on the quantification formula (1), and free The quantitative value [WD] of the external additive Tgc was determined.

In this case, the developing condition of the developing device 14 in the image forming operation is set to a preset normal mode (second image forming condition). The development conditions in this normal mode are set to the development conditions that provide the optimum toner density when a text (character) toner image that does not require gradation processing is formed on the recording sheet S, which is plain paper. Yes.
Thereafter, each time the cumulative number of printed sheets reaches m × n (where m is a preset number of printed sheets and n is the number of times the number of printed sheets has reached m (an integer greater than or equal to 1)) The quantitative value [WD] of the free external additive Tgc was determined by the chemical formula (1).

When the cumulative number of printed sheets reaches m × n, the quantitative value [WD] of the free external additive Tgc obtained by the quantification formula (1) is expressed as “cumulative quantification of the free external additive Tgc”. Value [WDn] ".
Next, when the accumulated quantitative value [WDn] of the free external additive Tgc was obtained at the time when the cumulative number of printed sheets reached m × n, the difference from the initial quantitative value [WDf] was calculated. This difference is defined as “[ΔWDn]” ([ΔWDn] = [WDf] − [WDn]). This difference [WDn] corresponds to the weight of the free external additive Tgc that has jumped to the outside from the developing housing 14h from the unused developer 14 until the cumulative number of printed sheets reaches m × n. Yes. From this, the difference [ΔWDn] between the quantitative value [WDn] obtained when the cumulative number of printed sheets reaches m × n and the initial quantitative value [WDf] is determined as the “flight quantitative value of the free external additive Tgc. "

Next, the weight of the free external additive Tgc that is attached to the surface of the photosensitive drum 11 and is dammed at the tip of the cleaning blade 16 that is in pressure contact with the photosensitive drum 11 is also quantified. Went.
For this purpose, first, when the cumulative number of printed sheets reaches m × n, all the deposits attached to the tip of the cleaning unit 16a are collected, and the total weight WEt (milligram) of the deposits is measured. did. Next, a predetermined weight WEs (milligram) was sampled from the collected deposit. The weight WEs of the collected sample is defined as “sample weight”.

Furthermore, the weight of Si, Ti, Zn, and Ca contained in the collected sample was measured by the above-described X-ray analyzer, and the total of them was calculated. In this case, the total weight of Si, Ti, Zn, and Ca is considered to correspond to the weight of the free external additive Tcg contained in the sample.
The total weight of Si, Ti, Zn, and Ca was measured five times, and the average value WEa was calculated.

Thereafter, the actual weight of the free external additive Tgc contained in the deposit is determined based on the weight average value WEa of the external additive contained in the deposit, the sample weight WEs of the deposit, and the total sample weight WEt of the deposit. Quantified by the following quantification formula (2). However, [WE] is a quantitative value of the weight of the free external additive Tgc contained in the deposit.
[WE] = WEa × WEt / WEs (2)
The quantitative value [WE] obtained by the quantification formula (2) is calculated every time the cumulative number of printed sheets reaches m × n. Therefore, the quantitative value [WE] of the free external additive Tgc obtained when the cumulative number of printed sheets reaches m × n is referred to as “conveyed quantitative value [WEn]”.

  Next, the flight quantitative value [ΔWDn] of the free external additive Tgc calculated when the cumulative number of printed sheets reached m × n was compared with the transport quantitative value [WEn]. As a result, the conveyance quantitative value [WEn] was lower than the flight quantitative value [ΔWDn]. In this case, each of the flight fixed value [ΔWDn] and the transport fixed value [WEn] decreased at the same rate even when the cumulative number of printed sheets increased.

From this, it is considered that the free external additive Tgc flying from the developing housing 14 h is transferred to the recording sheet S at a substantially constant rate and then conveyed to the pressure contact position of the cleaning blade 16.
Note that it is considered that a part of the free external additive Tgc passes between the cleaning unit 16 a and the photosensitive drum 11 at the pressure contact position of the cleaning blade 16. Further, it is considered that the free external additive Tgc adhering to the photosensitive drum 11 is scraped off from the surface of the photosensitive drum 11 while the photosensitive drum 11 is rotating.

  Thus, as the number of printed sheets increases, the amount of free external additive Tgc conveyed to the cleaning blade 16 decreases sequentially. For this reason, the amount of the free external additive Tgc that contributes to the reduction of the friction between the cleaning blade 16 and the photosensitive drum 11 also decreases as the number of printed sheets increases. In this case, the possibility of “turning” in the cleaning blade 16 increases.

FIG. 6A is a graph showing the relationship between the cumulative number of printed sheets and the flight fixed value [ΔWDn] when an image forming operation is executed by a monochrome printer. In FIG. 6A, the horizontal axis represents the cumulative number of printed sheets, and the vertical axis represents the flight fixed value [ΔWDn]. However, the intersection with the vertical axis on the horizontal axis corresponds to the cumulative number of printed sheets of m sheets (n = 1).
In the unused developer 14, the developer (initial developer) accommodated in the developing housing 14 h contains a relatively large amount of free external additive Tgc. For this reason, at the beginning of the developing operation by the developing device 14, a relatively large amount of the free external additive Tgc jumps to the outside from the developing housing 14h by one developing operation (corresponding to the number of printed sheets). Thus, a relatively large amount of the free external additive Tgc adheres to the photosensitive drum 11 and is conveyed to the cleaning unit 16a. Therefore, the amount of the free external additive Tgc passing between the photosensitive drum 11 and the cleaning unit 16a is also relatively large. As a result, even when the surface roughness of the photosensitive drum 11 is small, the friction between the photosensitive drum 11 and the cleaning unit 16a is reduced, and there is no possibility that the cleaning blade 16 will be “turned up”.

  However, at the beginning of the developing operation by the developing device 14, since many free external additives Tgc fly from the developing housing 14h for each developing operation, the increase in the number of printed sheets causes the inside of the developing housing 14h. The amount of free external additive Tgc decreases rapidly. Thereby, at the beginning of the developing operation by the unused developing device 14, the flying fixed value [ΔWDn] also rapidly decreases as the number of printed sheets increases.

Thereafter, when it is detected that the number of printed sheets has increased and the toner amount in the developing housing 14h has fallen below a predetermined value, the toner is replenished in the developing housing 14h. In this case, the free external additive Tgc is supplied together with the supplied toner, and the amount of the free external additive Tgc in the developing housing 14h increases. Accordingly, the flight fixed value [ΔWDn] also increases.
However, in this case, the amount of free external additive Tgc replenished in the developing housing 14h is relatively small. For this reason, the fixed flight value [ΔWDn] after toner replenishment is the fixed flight value [ΔWDn] (n = 1) at the time when the number of sheets printed is m (n = 1) from the start of development in the unused state. ) Will not increase.

Thereafter, the flying fixed value [ΔWDn] decreases as the number of printed sheets increases, but increases every time toner is supplied into the developing housing 14h. Therefore, the flight fixed value [ΔWDn] repeats such a decrease and increase.
The relationship between the decrease in the amount of the free external additive Tgc flying from the developing housing 14h and the occurrence of “turning” on the cleaning blade 16 as the number of printed sheets increased was examined. As a result, when the flight fixed value [ΔWDn] decreased to about 300 from the initial stage, the occurrence of “turning” was confirmed. In this case, the toner was not replenished until the flying fixed value [ΔWDn] decreased to about 300.

<Verification of surface roughness on photosensitive drum>
Next, the change in the surface roughness of the photosensitive drum 11 was verified. In this case, in the monochrome printer in which the photosensitive drum 11 is not used, the image forming operation is executed with the developing condition of the developing device 14 as the normal mode. Each time the cumulative number of printed sheets reached m × n, the photosensitive drum 11 was taken out and its surface roughness was measured. The surface roughness was measured with an optical interference type surface shape roughness meter (manufactured by Veeco, trade name “Wyko NT9000”).

  The result is shown in FIG. In FIG. 6B, the horizontal axis indicates the cumulative number of printed sheets, and the vertical axis indicates the surface roughness of the photosensitive drum 11. Note that the intersection of the horizontal axis with the vertical axis in FIG. 6B corresponds to the cumulative number of printed sheets of m (n = 1), as in FIG. 6A. As shown in FIG. 6B, the surface roughness of the photosensitive drum 11 increases almost in proportion to the increase in the number of printed sheets.

<Verification of "turn over" in cleaning blade>
Next, the relationship between the occurrence of “turning” in the cleaning blade 16, the flying fixed value [ΔWDn], and the surface roughness of the photosensitive drum 11 was verified.
In this case, as shown in FIG. 7, the number of prints corresponding to the flight fixed value [ΔWDn] corresponding to each of 800, 700, 600, 500, 400, 300, 200, and 100 is obtained and A developing device 14 was prepared in which the same number of development operations as in the above were performed. In addition, photosensitive drums 11 having surface roughness of 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 60 nm, 70 nm, and 100 nm were prepared. Then, an image forming operation was performed by a monochrome printer in which each developing device 14 and the photosensitive drum 11 were combined, and it was confirmed whether or not “turning” occurred in the cleaning blade 16. The result is shown in FIG.

As shown in FIG. 7, when the surface roughness of the photosensitive drum 11 is 40 nm or more, “turning” occurs in the cleaning blade 16 even if the flight fixed value [ΔWDn] is less than 300. I did not.
Further, even if the surface roughness of the photosensitive drum 11 was less than 40 nm, “turning” did not occur in the cleaning blade 16 if the flying fixed value [ΔWDn] was 300 or more.

However, when the surface roughness of the photoconductive drum 11 is less than 40 nm (each of 20, 25, 30, and 35 nm), the flying fixed value [ΔWDn] is less than 300 (each of 100, 200, and 250). When it was, “turning” occurred in the cleaning blade 16.
The flying fixed value [ΔWDn], which is the lower limit value at which “turning” does not occur in the cleaning blade 16, is 300 as described above, and is indicated by a dotted line in the graph of FIG. When this flight fixed value [ΔWDn] is 300, it corresponds to the cumulative number of printed sheets of about 3000 sheets.

  Further, the cumulative number of printed sheets where the surface roughness of the photosensitive drum 11 is 40 nm (indicated by a broken line in the graph of FIG. 6B) is larger than the cumulative number of printed sheets where the flying fixed value [ΔWDn] is 300. Yes. For this reason, depending on the image forming operation from when the flying fixed value [ΔWDn] reaches 300 until the surface roughness of the photosensitive drum 11 reaches 40 nm, “turning” may occur in the cleaning blade 16. There is.

  In this embodiment, in order to suppress the occurrence of such “turning” of the cleaning blade 16, when the developing operation of the unused developing device 14 is started, the developing conditions different from those in the normal mode are set. In the initial mode (first image forming mode), development control of the developing device 14 is executed. In the initial mode in this case, the developing condition is such that the amount of the free external additive Tcg flying from the developing device 14 is smaller than that in the normal mode. Such development conditions in the initial mode are continued until the surface roughness of the photosensitive drum 11 reaches a predetermined value.

<Control system configuration>
Next, the configuration of the main part of the control system of the monochrome printer will be described with reference to FIG. FIG. 8 is a block diagram showing the configuration of the main part of the control system of the monochrome printer. The monochrome printer is provided with an engine control unit 41 that controls an image forming operation.
The engine control unit 41 controls a drum motor 43 that rotates the photosensitive drum 11. The drum motor 43 is controlled by the engine control unit 41 so that the photosensitive drum 11 is rotated at a predetermined rotational speed.

The drum motor 43 is provided with a drive torque detector 46 that detects the drive torque of the photosensitive drum 11. The detection result by the drive torque detector 46 is given to the engine control unit 41.
The engine control unit 41 controls the charger 12. The charger 12 is controlled by the engine control unit 41 so that the surface of the photosensitive drum 11 has a predetermined charging potential.

Further, the engine control unit 41 controls the developing motor 44 that rotates the developing roller 14r in the developing device 14. The developing motor 44 is controlled by the engine control unit 41 so that the developing roller 14r has a predetermined rotation speed.
In addition, the engine control unit 41 controls the developing bias power supply 47. The development bias power supply 47 is a development bias supply unit that generates a development bias voltage to be applied to the development roller 14 r of the development device 14. The development bias voltage generated by the development bias power supply 47 is obtained by superimposing a DC voltage on an AC voltage. The engine control unit 41 controls the development bias power supply 47 so that a predetermined development bias voltage is generated in the development bias power supply 47.

Further, the engine control unit 41 controls a screw drive motor 45 that rotates the supply screw 14b and the stirring screw 14c of the developing device 14. The screw drive motor 45 is controlled by the engine control unit 41 so that the supply screw 14b and the stirring screw 14c are rotated at the same speed in opposite directions.
Further, the engine control unit 41 is given the output of the toner density sensor 14g provided in the developing device 14. The engine control unit 41 drives the toner supply mechanism 17 based on the output of the toner concentration sensor 14g. When the toner supply mechanism 17 is driven, toner is supplied from the toner supply mechanism 17 into the developing housing 14 h of the developing device 14.

  Further, the engine control unit 41 is also provided with the outputs of the above-described photosensitive drum sensor 48 and developing device sensor 49. The photosensitive drum sensor 48 and the developing device sensor 49 detect that the photosensitive drum 11 and the developing device 14 are not attached when the photosensitive drum 11 and the developing device 14 are replaced. Thereafter, when each of the new (unused) photosensitive drum 11 and the developing device 14 is mounted on the monochrome printer, the photosensitive drum sensor 48 and the developing device sensor 49 are respectively connected to the photosensitive drum 11 and the developing device 14. Detects that it is in the wearing state.

  The engine control unit 41 displays various information on the operation panel 42. The operation panel 42 displays that the respective replacement of the photosensitive drum 11 and the developing device 14 is necessary when the replacement is necessary. The engine control unit 41 determines whether it is necessary to replace the photosensitive drum 11 and the developing device 14 based on the cumulative number of printed sheets.

<Development control>
Next, the development control executed by the engine control unit 41 will be described based on the flowchart of FIG.
When the development control is started, the engine control unit 41 confirms whether both the developing device 14 and the photosensitive drum 11 are unused (new) (step S10 in FIG. 9). If both the developing device 14 and the photosensitive drum 11 are unused ("Yes" in step S10), the process proceeds to step S11. When the monochrome printer is new, it is preset that both the developing device 14 and the photosensitive drum 11 are unused. Accordingly, in this case, the process proceeds to step S11.

If both the developing device 14 and the photosensitive drum 11 are not unused (“No” in step S10), the process proceeds to step S15. This case will be described later.
In step S11, the developing condition for developing the electrostatic latent image on the photosensitive drum 11 is set to an initial mode (first image forming mode) different from the normal mode (second image forming mode). The development conditions in the initial mode and the normal mode in this case are shown in the table of FIG.

  In the present embodiment, in the initial mode, the peripheral speed of the developing roller 14r in the developing device 14 is set lower than that in the normal mode. Therefore, in the normal mode, the rotation speed of the photosensitive drum 11 is set to 165 mm / s, and the rotation speed of the developing roller 14r is set to 300 mm / s. In contrast, in the initial mode, the rotational speed of the photosensitive drum 11 is set to 165 mm / s as in the normal mode, but the rotational speed of the developing roller 14r is set to 80% of the normal mode, that is, 240 mm / s. Set to.

If the development conditions in the initial mode are set as described above, the apparatus is in a standby state until an instruction for an image forming operation (printing) is issued to the monochrome printer (step S12). When there is a print instruction (“Yes” in step S12), the developing device 14 performs a developing operation under the set initial mode developing conditions (step S13).
In this case, the developing conditions are the same as those in the normal mode except that the developing roller 14r is rotated at a low speed of 240 mm / s. For this reason, the centrifugal force of the developing roller 14r is lower than that in the normal mode, and the amount of the free external additive Tgc flying from the developing housing 14h by the centrifugal force of the developing roller 14r is smaller than that in the normal mode. To do.

As a result, when the image forming operation is executed under the development conditions in the initial mode, a relatively large amount of free external additive Tgc remains (exists) in the development housing 14h even if the number of printed sheets increases. . Therefore, in this case, there is no possibility that the amount of the free external additive Tgc flying from the developing housing 14h greatly decreases as the number of printed sheets increases.
The free external additive Tgc flying from the developing housing 14 h adheres to the surface of the photosensitive drum 11 and is conveyed to the cleaning unit 16 a of the cleaning blade 16. A part of the free external additive Tgc conveyed to the cleaning unit 16 a passes between the cleaning unit 16 a and the surface of the photosensitive drum 11. Thereby, both frictional forces are reduced. As a result, even if the surface roughness of the photosensitive drum 11 is small, there is no possibility of “turning” on the cleaning blade 16.

As described above, the amount of the free external additive Tgc flying from the developing housing 14h decreases, so that the cumulative number of printed sheets until the flying fixed value [ΔWDn] decreases to 300 becomes larger than that in the normal mode. As a result, when the cumulative number of printed sheets reaches 3000, the flying fixed value [ΔWDn] is not likely to decrease to 300.
In such an initial mode, the rotation of the developing roller 14r is lower than that in the normal mode. However, the rotation speed of the developing roller 14r deteriorates the image quality of the toner image formed on the photosensitive drum 11. It is set not to be. However, if the image forming operation is continued in a state where the rotation of the developing roller 14r is lowered, there is a risk that density unevenness or the like occurs in the toner image, and the image quality of the toner image may become unstable.

Thereafter, when the instructed printing is completed (step S13), it is confirmed based on the detection result of the driving torque detector 46 whether the driving torque of the photosensitive drum 11 has decreased below a threshold value (step S14).
In this case, the threshold value of the driving torque of the photosensitive drum 11 is the driving torque of the photosensitive drum 11 when the surface roughness of the photosensitive drum 11 becomes 40 nm when the developing operation is executed under the development conditions in the initial mode. It corresponds to. Such a driving torque of the photosensitive drum 11 is obtained in advance by experiments or the like.

  At the beginning of the development operation under the development conditions in the initial mode, the surface roughness of the photosensitive drum 11 is small and smaller than 40 nm. For this reason, the frictional force between the cleaning blade 16 and the photosensitive drum 11 is increased when there is no free external additive Tgc between them. However, in this case, since a relatively large amount of the free external additive Tgc is present in the developing device 14, the amount of the free external additive Tgc supplied to the photosensitive drum 11 is also relatively large. Thereby, since the frictional force between the cleaning blade 16 and the photosensitive drum 11 is reduced, the driving torque of the photosensitive drum 11 is also reduced.

Thereafter, as the number of printed sheets increases, the surface roughness of the photosensitive drum 11 increases, so even if the amount of the free external additive Tgc supplied to the photosensitive drum 11 decreases, The driving torque is further reduced from the beginning when the development operation is started under the development conditions in the initial mode.
In step S14, it is confirmed whether the driving torque of the photoconductive drum 11 has decreased below a preset threshold value. If it has not decreased below the threshold value (“No” in step S14), it is determined that the surface roughness of the photosensitive drum 11 has not reached 40 nm. In this case, the process returns to step S12, and the development operation under the development conditions in the initial mode is repeated every time printing is instructed. As a result, the “turn-up” of the cleaning blade 16 is prevented from occurring due to the free external additive Tgc flying from the developing housing 14h.

  On the other hand, when the driving torque of the photosensitive drum 11 has decreased below the threshold value in step S14 (“Yes” in step S14), it is determined that the surface roughness of the photosensitive drum 11 has reached 40 nm. Then, the process proceeds to step S15. In step S15, the development condition is changed from the initial mode to the normal mode. In this case, when the developing operation is performed, the rotation speed of the developing roller 14r is changed to 300 mm / s, which is faster than the initial mode (240 mm / s). Except for this, the development conditions are the same as in the initial mode.

After that, the printer enters a standby state until printing is instructed (step S16). When printing is instructed (“Yes” in step S16), the developing operation is executed under the set normal mode developing conditions (step S17). .
When the developing operation is performed under the normal mode developing conditions, the centrifugal force of the developing roller 14r increases as compared with the initial mode, and thus, a free external additive flying from the developing housing 14h for each developing operation. The amount of Tgc is also increased than in the initial mode. Thereby, the remaining amount of the free external additive Tgc in the developing housing 14h is rapidly reduced. When the remaining amount of the free external additive Tgc in the developing housing 14h decreases, the amount of the free external additive Tgc flying from the developing housing 14h also decreases.

  However, the surface roughness of the photosensitive drum 11 has already become larger than 40 nm at the time when execution of the developing operation under the normal mode developing conditions is started. For this reason, even if the amount of the free external additive Tgc supplied to the photosensitive drum 11 is reduced, the risk of “turning” on the cleaning blade 16 is eliminated. Therefore, even if the surface roughness of the photosensitive drum 11 further increases with an increase in the number of printed sheets thereafter, the cleaning blade 16 is given a “regardless of the amount of the free external additive Tgc flying from the developing housing 14h. There is no risk of turning over.

As described above, in the present embodiment, control is performed so that a state in which a necessary amount or more of the external additive Tgc is not supplied to the photosensitive drum 11 is continued until the end of the initial mode.
Further, when the developing operation is executed under the normal mode developing conditions, the developing roller 14r is rotated at a higher speed (original rotation speed) than in the initial mode. Therefore, thereafter, there is no possibility that density unevenness or the like occurs in the toner image formed on the photosensitive drum 11, and the image quality of the toner image is stabilized.

  When the developing operation in step S17 is completed, it is confirmed based on the accumulated number of printed sheets whether or not both the photosensitive drum 11 and the developing device 14 need to be replaced (step S18). The cumulative number of printed sheets that needs to be replaced for each of the photosensitive drum 11 and the developing device 14 is set in advance. If it is not necessary to replace both the photosensitive drum 11 and the developing device 14 (“No” in step S18), the process returns to step S15, and the processes in steps S16 to S17 are repeated. Therefore, in this case, when printing is instructed, the developing operation under the normal mode developing conditions is executed.

On the other hand, when it is necessary to replace both the photosensitive drum 11 and the developing device 14 (“Yes” in step S18), it is necessary to replace both the photosensitive drum 11 and the developing device 14. Is displayed on the operation panel 42 (step S19), and the development control is terminated.
In this case, thereafter, both the photosensitive drum 11 and the developing device 14 are replaced, and the start of the development control is instructed, whereby the development control is resumed. When the development control is resumed, in step S10, it is confirmed based on the respective outputs of the photosensitive drum sensor 48 and the developing device sensor 49 whether both the photosensitive drum 11 and the developing device 14 have been replaced.

  If both the photosensitive drum 11 and the developing device 14 are not replaced, it is determined that both are not replaced with new ones (unused state) (“No” in step S10). In this case, the process proceeds to step S15, and the development condition is set to the normal mode. That is, when only one of the photosensitive drum 11 and the developing device 14 is replaced, or when both are not replaced, the developing condition is set to the normal mode without setting the initial mode.

  When the photoconductor drum 11 is not replaced with a new one, the surface roughness of the photoconductor drum 11 is larger than that when the photoconductor drum 11 is new, and the occurrence of “turning” in the cleaning blade 16 is suppressed. It is thought that. In such a state, since it is not necessary to execute the developing operation under the initial mode developing conditions, the developing operation is executed under the normal mode developing conditions.

  Further, when the developing device 14 is not replaced with a new one, it is considered that the amount of the free external additive Tgc flying from the developing housing 14h is lower than that in the new case. If the development operation is executed under the development conditions in the initial mode in such a state, density unevenness may occur in the toner image formed on the photosensitive drum 11 as the number of developments increases. For this reason, the development operation is executed under the development condition in the normal mode without setting the development condition in the initial mode.

When both the photosensitive drum 11 and the developing device 14 are replaced, it is determined that both are replaced with a new one that is not used. In this case (“Yes” in step S11), the developing condition of the developing operation in the developing device 14 is set to the initial mode. After that, the process after step S12 is performed.
Note that if it is necessary to replace either the developing device 14 or the photosensitive drum 11 after the development condition is set to the normal mode, it is necessary to set the development condition in the initial mode as described above. Absent. Therefore, in this case, the development conditions in the normal mode are maintained, and the development operation is executed under the development conditions in the normal mode even when printing is instructed thereafter.

In the development control of the present embodiment as described above, the amount of the free external additive Tgc flying from the development housing 14h when the development operation was executed under the development conditions in the initial mode was verified.
For this verification, in a new monochrome printer, the image forming operation is executed according to the development conditions in the initial mode (the rotation speed of the development roller 14r is 240 mm / s), and the development conditions are switched from the initial mode to the normal mode. There wasn't. During the execution of such an image forming operation, every time the cumulative number of printed sheets reaches m × n, the amount of free external additive Tgc flying from the developing housing 14h in the same manner as the quantification process described above. The flight quantitative value [ΔWDn], which is the quantitative value of the above, was determined. The result is shown by a solid line in the graph of FIG. The intersection with the vertical axis on the horizontal axis of the graph of FIG. 11A corresponds to the cumulative number of printed sheets of m (n = 1), as in FIG. 6A.

  In this case, in the graph of FIG. 11A, the amount of the free external additive Tgc flying from the developing housing 14h is shown to decrease proportionally as the number of printed sheets increases. However, in actuality, when the toner concentration in the developing housing 14h decreases, toner replenishment is executed, so that the amount of the free external additive Tgc also temporarily increases. However, the increase in the amount of free external additive Tgc due to toner replenishment is slight, and overall, the decrease rate of free external additive Tgc with respect to the increase rate of the number of printed sheets is substantially constant. For this reason, in the graph of FIG. 11A, it is omitted that the amount of the free external additive Tgc once increases due to the execution of toner replenishment.

  In addition, as a comparative example, in a new monochrome printer, the image forming operation was performed in the normal mode (the rotation speed of the developing roller 14r is 300 mm / s) without setting the development conditions to the initial mode. The flight fixed value [ΔWDn] obtained in this case is shown by a two-dot chain line in FIG. The flight fixed value [ΔWDn] of this comparative example corresponds to the flight fixed value [ΔWDn] shown in the graph of FIG.

In the initial mode indicated by the solid line in the graph of FIG. 11A, the flight fixed value [ΔWDn] at the time when the cumulative number of printed sheets from the start of the developing operation reaches m (n = 1) is the comparative example. It was about 65% with respect to the flight fixed value [ΔWDn], and a decrease of about 35% was recognized.
As described above, in the initial mode, the amount of the free external additive Tgc flying from the developing housing 14h is suppressed for each number of printed sheets. Therefore, if the number of printed sheets is the same as in the comparative example, more free external additive Tgc remains in the developing housing 14h than in the comparative example. As a result, the amount of the free external additive Tgc flying from the developing housing 14h decreases more gradually than the comparative example as the number of printed sheets increases.

As a result, under the development conditions in the initial mode, the number of printed sheets reaching the flying fixed value [ΔWDn] (= 300), which may cause “turning” on the cleaning blade, is more than twice that of the comparative example (about 3000 sheets). Increased to.
Further, even after the flying fixed value [ΔWDn] reaches 300, the amount of toner in the developing housing 14h consumed for each number of printed sheets is also decreased at the same rate, and therefore, the toner is first consumed. The number of printed sheets at the timing of replenishment also increased compared to the comparative example.

  In the development control of this embodiment, when the driving torque of the photosensitive drum 11 reaches a value corresponding to the surface roughness of the photosensitive drum 11 of 40 nm, the mode is switched from the initial mode to the normal mode. In this case, as shown by a dotted line in FIG. 11A, the flying fixed value [ΔWDn] also decreased more rapidly than the case where the developing operation in the initial mode was executed as the number of printed sheets increased. As a result, as the number of printed sheets increased, the amount of free external additive Tgc flying from the developing housing 14h also decreased rapidly. However, in this case, since the surface roughness of the photosensitive drum 11 is already 40 nm or more, the risk of “turning over” in the cleaning blade 16 is eliminated. Therefore, even if the amount of the free external additive Tgc supplied to the photosensitive drum 11 is decreased, “turning” does not occur in the cleaning blade 16.

  As described above, in the present embodiment, when the photosensitive drum 11 and the developing device 14 are unused, the development condition at the beginning of the development operation is set to the initial mode. As a result, during the initial mode period, it is possible to prevent the cleaning blade 16 from being “turned up” by the free external additive Tgc flying from the developing housing 14h. Further, under the development conditions in the initial mode, the amount of the free external additive Tgc adhering to the photoconductor drum 11 is suppressed, so that the occurrence of filming in which the free external additive Tgc adheres thinly to the surface of the photoconductor drum 11 is generated. Can also be suppressed.

Thereafter, when it is determined that the surface roughness of the photosensitive drum 11 has reached the state where the risk of “turning” of the cleaning blade 16 has been eliminated, the development condition in the normal mode is set. Thereby, thereafter, even if the amount of the free external additive Tgc flying from the developing housing 14h is reduced, there is no possibility that “turning” occurs in the cleaning blade 16.
Therefore, according to the present embodiment, it is possible to prevent the cleaning blade 16 from being “turned up” from the beginning of the developing operation until the developing device 14 reaches the end of its life.

  In the above description, the rotation speed of the developing roller 14r in the initial mode is set to 80% of that in the normal mode. However, the configuration is not limited thereto. The rotation speed of the developing roller 14r in the initial mode is appropriately set based on the amount of the free external additive Tgc flying from the developing housing 14h. The rotation speed of the developing roller 14r in the initial mode is preferably about 70 to 90% of that in the normal mode.

In the initial mode, the rotational speed of the developing roller 14r is not limited to a lower speed than the normal mode, and the peripheral speed of the photosensitive drum 11 may be changed. For this reason, the peripheral speed ratio of the developing roller 14r may be the same as that in the normal mode, and the peripheral speed (rotational speed) of the photosensitive drum 11 may be set to be lower than that in the normal mode.
[Embodiment 2]
In the second embodiment, as a developing condition in the initial mode, the potential difference between the developing roller 14r and the photosensitive drum 11 is different from that in the normal mode.

  FIG. 12A is an explanatory diagram of the developing bias voltage applied to the developing roller 14r. When the developing bias voltage Vr is applied to the developing roller 14r, an electric field is formed by the potential difference with the charging potential Vc on the surface of the photosensitive drum 11. Due to the action of the electric field, the negatively charged toner particles T carried on the peripheral surface of the developing roller 14 r adhere to the electrostatic latent image formed on the surface of the photosensitive drum 11.

In the developing bias voltage Vr, an AC voltage Va having a predetermined frequency f is superimposed on a negative DC bias voltage Vd.
FIG. 12B is an explanatory diagram of one cycle of the developing bias voltage Vr. As shown in FIG. 12B, the development bias voltage is centered on a negative DC bias potential Vd, and the negative minimum potential Vmin where the absolute value is minimized and the negative maximum potential Vmax where the absolute value is maximized. The voltage changes over the range. The difference between the maximum potential Vmax and the minimum potential Vmin (corresponding to the amplitude of the AC voltage Va) is defined as “peak-to-peak potential Vpp”.

In this case, the negatively charged toner particles T are applied to the photosensitive drum 11 during a period in which the absolute value of the developing bias voltage Vr is smaller than the absolute value of the DC bias potential Vd during one cycle of the developing bias voltage Vr. Easy to be supplied. Therefore, this period is referred to as “development period Tg”.
On the other hand, during a period of the developing bias voltage Vr, during the period when the absolute value of the developing bias voltage Vr is larger than the absolute value of the DC bias potential Vd, the negatively charged toner particles T are in the photosensitive drum. 11 is hardly supplied. For this reason, this period is referred to as “collection period Tk”. The ratio between the development period Tg and the collection period Tk in one cycle of the development bias voltage Vr is generally called “duty ratio”.

The surface of the photosensitive drum 11 is set to a predetermined charging potential Vc (minus) by the charging device 12. In FIG. 12A, the surface potential of the photosensitive drum 11 is indicated by a broken line. This charging potential Vc has an absolute value greater than the negative DC bias potential Vd at the developing bias voltage Vr.
When the photosensitive drum 11 having the charged potential Vc is irradiated with the laser beam LB by the exposure device 13, the irradiated portion (hereinafter referred to as “image portion”) has a toner whose absolute value is smaller than the charged potential Vc. The adhesion potential becomes Vt (minus). The absolute value of the toner adhesion potential Vt is smaller than the minimum potential Vmin of the developing bias voltage Vr.

In this case, an electrostatic latent image is not formed on the surface of the photosensitive drum 11 where the laser beam LB is not irradiated, since the charged potential Vc is maintained. For this reason, even if the surface of the photosensitive drum 11 passes through the exposure position of the laser beam LB, the surface portion of the photosensitive drum 11 that maintains the charged potential Vc is defined as a “non-image portion”.
Within the electric field formed between the photosensitive drum 11 and the developing roller 14r, the negatively charged toner particles T on the developing roller 14r behave in accordance with the potential difference between the photosensitive drum 11 and the developing roller 14r.

  In this case, in the image portion where the surface of the photosensitive drum 11 is at the toner adhesion potential Vt, the variation in the potential difference between the toner adhesion potential Vt of the photosensitive drum 11 and the development bias voltage Vr of the developing roller 14r becomes large. In such an electric field, the negatively charged toner particles T vibrate greatly, so that they adhere to the surface of the photosensitive drum 11 and the image portion (electrostatic latent image) is developed with the toner particles T.

  On the other hand, in the non-image area where the surface of the photosensitive drum 11 is at the charging potential Vc, the variation in the potential difference between the photosensitive drum 11 and the developing bias voltage Vr applied to the developing roller 14r becomes small. In such an electric field, since the vibration of the negatively charged toner particles T is small, the negatively charged toner particles T are suppressed from adhering to the surface of the photosensitive drum 11, and the image portion (electrostatic latent image) is formed. The toner particles T are not developed.

However, when the potential difference ΔVm between the charging potential Vc of the photosensitive drum 11 and the DC bias potential Vd in the non-image portion is small, the toner particles T are likely to move from the surface of the developing roller 14r to the photosensitive drum 11. Become. For this reason, “fogging” in which the toner particles T adhere to the non-image portion of the photosensitive drum 11 is likely to occur.
In contrast, when the potential difference ΔVm between the charging potential Vc of the photosensitive drum 11 and the DC bias potential Vd in the non-image portion increases, the toner particles T can move from the surface of the developing roller 14r to the photosensitive drum 11. The sex becomes smaller. For this reason, it is possible to suppress the occurrence of “fogging” in which the toner particles T adhere to the non-image portion of the photosensitive drum 11.

Thus, the potential difference ΔVm between the charging potential Vc of the photosensitive drum 11 and the DC bias potential Vd becomes an index value for the occurrence of “fogging” in which the toner particles T adhere to the non-image portion of the photosensitive drum 11. Yes. For this reason, this potential difference ΔVm is usually called a “fogging margin”.
As described above, when the developing bias voltage Vr applied to the developing roller 14r and the charging potential Vc of the photosensitive drum 11 change, the amount of toner particles T that move from the developing roller 14r to the photosensitive drum 11 changes. To do. In this case, the amount of the free external additive Tgc carried on the developing roller 14r also changes in the same manner as the toner particles T. Accordingly, when the amount of toner particles T moving from the developing roller 14r to the photosensitive drum 11 decreases, the amount of free external additive Tgc moving from the developing roller 14r to the photosensitive drum 11 also decreases.

  From the above, in this embodiment, in the initial mode, the condition of the developing bias voltage Vr applied to the developing roller 14r or the fog margin ΔVm is set to a condition different from that in the normal mode. In this case, with respect to the developing bias voltage Vr, one or more of the conditions (hereinafter referred to as “developing bias conditions”) of the peak-to-peak voltage Vpp, the frequency f, and the duty ratio are set to conditions different from those in the normal mode. Set. The development bias condition can be changed by the engine control unit 41 controlling the development bias power supply 47.

  Further, as the initial mode, only the fog margin ΔVm may be set to a condition different from that in the normal mode. Furthermore, the fog margin ΔVm. The initial mode condition may be set together with any one or more of the development bias conditions. The fog margin ΔVm is changed by the engine control unit 41 controlling the charger 12 to change the charging potential of the photosensitive drum 11 or by changing the DC bias potential Vd applied to the developing roller 14r. can do.

  In this case, the developing bias condition and the fog margin ΔVm are set so that the amount of toner particles T moving from the developing roller 14r to the photosensitive drum 11 in the initial mode is smaller than that in the normal mode. Thereby, in the initial mode, the amount of the free external additive Tgc flying from the developing housing 14h can be reduced as compared with the normal mode.

  FIG. 13 shows an example of the developing bias condition and the fog margin ΔVm in each of the normal mode and the initial mode of the present embodiment. In the normal mode, the development bias condition and the fog margin ΔVm are set so that the toner density of the toner image formed on the photosensitive drum 11 is appropriate. For this reason, in the normal mode, the peak-to-peak voltage Vpp is 1.4 kV, the frequency f is 7 kHz, the duty ratio (the ratio (Tg / Tk) between the development period Tg and the collection period Tk) is “50% / 50%”, The fog margin ΔVm is set to 70V, respectively.

On the other hand, as an initial mode, the peak-to-peak voltage Vpp is 1.0 kV, the frequency f is 3 kHz, the duty ratio (Tg / Tk) is “30% / 70%”, and the fog margin ΔVm is 150 V in advance. It is prescribed.
As the initial mode, when the peak-to-peak voltage Vpp is changed to 1.0 kV which is smaller than 1.4 kV in the normal mode, the developing bias voltage Vr, the surface potential of the photosensitive drum 11 (toner adhesion potential Vt and charging potential Vc), and The fluctuation of the potential difference becomes smaller. This suppresses the toner particles T from adhering to the surface of the photosensitive drum 11. In this case, the amount of free external additive Tgc flying from the developing housing 14h is also suppressed.

  Further, as the initial mode, when the frequency f of the developing bias voltage Vr is set to 3 kHz, which is lower than 7 kHz in the normal mode, the number of vibrations of the toner particles T due to the electric field between the developing roller 14r and the photosensitive drum 11 is Less than. As a result, the amount of toner particles T moving from the developing roller 14r to the photosensitive drum 11 is smaller than that in the normal mode. In this case, the amount of the free external additive Tgc flying from the developing housing 14h is also smaller than that in the normal mode.

  Furthermore, as an initial mode, the ratio of the development period Tg in the duty ratio of the development bias voltage Vr is set to 30%, which is lower than 50% in the normal mode. In this case, the movement of the toner particles T from the developing roller 14r to the photosensitive drum 11 is suppressed. As a result, the amount of toner particles T moving from the developing roller 14r to the photosensitive drum 11 is reduced as compared with the normal mode. Also in this case, the amount of the free external additive Tgc flying from the developing housing 14h together with the toner particles T is reduced.

Further, as the initial mode, when the fog margin ΔVm is changed to 150 V, which is larger than 70 V in the normal mode, the toner adhesion amount in the non-image area is reduced as compared with the normal mode. Also in this case, the amount of the free external additive Tgc flying from the developing housing 14h is reduced.
As described above, when any one or more of the developing bias condition and the fog margin ΔVm are set to the initial mode, the free external additive Tgc flying from the developing housing 14h at the beginning of the developing operation by the unused developing device 14 is started. The amount of can be reduced. Thereby, the rate at which the free external additive Tgc in the developing housing 14h decreases as the number of printed sheets increases can be suppressed.

  As a result, until the surface roughness of the photoconductive drum 11 is eliminated until the risk of “turning up” in the cleaning blade 16, the occurrence of “turning up” in the cleaning blade 16 is prevented by the free external additive Tgc. be able to. Thereafter, when the surface roughness of the photosensitive drum 11 reaches a state in which the risk of “turning” in the cleaning blade 16 is eliminated, the development condition is switched from the initial mode to the normal mode.

When the development condition is switched to the normal mode, the surface roughness of the photosensitive drum 11 increases as the number of printed sheets increases, so that there is no possibility of “turning” on the cleaning blade 16.
In the normal mode, the toner image formed on the photosensitive drum 11 is stably formed without causing density unevenness or the like.

In this embodiment, when only the peak-to-peak voltage Vpp is set to 1.0 kV, which is smaller than 1.4 kV in the normal mode, as the initial mode, the amount of the free external additive Tgc flying from the developing housing 14h. It verified about.
For this verification, the image forming operation was executed under the development control shown in the flowchart of FIG. 9 described above, with only the peak-to-peak voltage Vpp being set as the initial mode different from the normal mode. Then, by the above-described quantification process, a flying quantitative value [ΔWDn], which is a quantitative value of the amount of the free external additive Tgc flying from the developing housing 14h, was obtained.

As a result, the flying fixed value [ΔWDn] (n = 1) at the time when the cumulative number of printed sheets reaches m (n = 1) is determined by performing the developing operation in the normal mode without executing the developing operation in the initial mode. It is about 70% of the case of execution, and a reduction of about 30% was recognized.
Further, when the photosensitive drum 11 has a surface roughness corresponding to 40 nm, the peak-to-peak voltage Vpp is changed to 1.4 kV in order to switch to the normal mode. At this time, the flight fixed value [ΔWDn] was 300 or more.

Furthermore, the occurrence of “turning” in the cleaning blade 16 was confirmed at the time of switching to the normal mode, but “turning” did not occur. Further, although the image quality of the toner image formed on the recording sheet S was confirmed, the image quality was satisfactory with no density unevenness or the like.
After that, even if the image forming operation is executed by the development control in the normal mode, the “turning” does not occur in the cleaning blade 16. Further, even when image formation is executed by development control in the normal mode, a toner image formed on the recording sheet S does not cause density unevenness and the like, and a stable and good-quality toner image can be obtained.

As described above, by performing development control with the setting in which only the peak-to-peak voltage Vpp is changed as the initial mode with respect to the development conditions in the normal mode, the occurrence of “turn-up” can be prevented. In addition, the image quality of the formed toner image was good.
In order to demonstrate the effect when only one of the frequency f, the duty ratio, and the fog margin ΔVm is set as the initial mode condition shown in FIG. 13 instead of the peak-to-peak voltage Vpp, The same verification as the verification of the amount of the additive Tgc was performed. In any case, the same verification results as in the above case where only the peak-to-peak voltage Vpp was set as the initial mode condition were obtained.

[Embodiment 3]
In the third embodiment, as the initial mode of the development conditions, the degree of developer stirring in the developing device 14 is set to be stronger than in the normal mode. In the developing device 14, the higher the stirring speed of the developer and the longer the stirring time, the stronger the degree of stirring of the developer. As described above, when the degree of stirring of the developer in the developing device 14 is increased, the free free external additive Tgc contained in the developer is in a low binding state with respect to the toner particles T. Is likely to become. As a result, the amount of free free external additive Tgc flying from the developing device 14 to the photosensitive drum 11 can be reduced.

For this reason, in the third embodiment, as the initial mode, the rotation speeds of the supply screw 14b and the stirring screw 14c are set to be larger than those in the normal mode.
FIG. 14 shows the rotation speeds of the developing roller 14r, the supply screw 14b, and the stirring screw 14c in each of the normal mode and the initial mode of the third embodiment. As shown in FIG. 14, in the normal mode, the rotation speed of the developing roller 14r is set to 6.0 (rps), and the rotation speeds of the supply screw 14b and the stirring screw 14c are set to 5.5 (rps), respectively.

On the other hand, in the initial mode, the rotation speed of the developing roller 14r is set to 6.0 (rps) as in the normal mode, but the rotation speeds of the supply screw 14b and the stirring screw 14c are respectively set to It is set to 6.6 (rps), which is higher than that in the normal mode.
Thus, in the initial mode, when the developing operation is executed, the supply screw 14b and the stirring screw 14c are rotated at a slightly higher speed than in the normal mode. As a result, the degree of stirring of the toner particles T in the developing housing 14h is slightly stronger than in the normal mode.

In this case, the amount of the free external additive Tgc present in the developing housing 14h becomes a low binding external additive Tgb, and the amount of the free external additive Tgc flying from the developing housing 14h decreases.
Thereby, it is possible to prevent the amount of the free external additive Tgc in the developing housing 14h from being greatly reduced as the number of printed sheets increases. As a result, until the danger of “turning” on the cleaning blade 16 is eliminated, it is possible to prevent the “turning” from occurring on the cleaning blade 16 due to the free external additive Tgc flying from the developing housing 14h. .

In this case, the low bond external additive Tgb is relatively easily separated from the toner particles T by the external force such as vibration of the developing device 14 and becomes the free external additive Tgc. As a result, the flying of the free external additive Tgc from the developing housing 14h is continued until reaching the state where the risk of “turning” of the cleaning blade 16 is eliminated.
Thereafter, when the state where the risk of “turning” of the cleaning blade 16 is eliminated, the development condition is switched from the initial mode to the normal mode. As a result, the supply screw 14b and the stirring screw 14c are rotated at a rotational speed of 5.5 (rps), which is lower than the rotational speed in the initial mode. Therefore, after that, the degree of stirring of the developer is weakened.

In this case, the toner particles T are suppressed from being deteriorated by continuing the state of strong stirring. Thereby, there is no possibility that the image quality of the toner image formed on the photosensitive drum 11 is deteriorated.
In the third embodiment, the initial mode is set to the above condition, and the development control shown in the flowchart of FIG. 9 is executed. Then, by the above-described quantification process, a flying quantitative value [ΔWDn], which is a quantitative value of the amount of the free external additive Tgc flying from the developing housing 14h, was obtained.

As a result, the flight fixed value [ΔWDn] (n = 1) when the cumulative number of printed sheets reaches m (n = 1) is obtained when the development control in the normal mode is performed without setting the initial mode. It was about 80%, and a decrease of about 20% was recognized.
When the driving torque of the photosensitive drum 11 reaches a predetermined value corresponding to the surface roughness of the photosensitive drum 11 of 40 nm, the rotation speed of the supply screw 14b and the stirring screw 14c is changed to 5.5 (rps), Switched to normal mode. At this time, the flight fixed value [ΔWDn] was 300 or more.

  Furthermore, the occurrence of “turning” of the cleaning blade 16 was also confirmed at the time of switching to the normal mode, but “turning” was not generated. At the same time, the image quality of the toner image formed on the recording sheet S was confirmed, but the image quality was good. Thereafter, “turning” did not occur in the cleaning blade 16, and the image quality of the toner image formed on the recording sheet S was good.

[Embodiment 4]
In each of the above embodiments, the configuration for preventing the occurrence of “turning” of the cleaning blade 16 that removes the residual toner on the surface of the photosensitive drum 11 in the monochrome printer has been described. However, the present invention is not limited to such a configuration, and can be applied to a color printer capable of forming a full-color image.

In the fourth embodiment, a configuration for preventing the occurrence of “turning” of a cleaning blade that removes residual toner on an image carrying surface of an intermediate transfer belt used in a color printer will be described.
FIG. 15 is a schematic diagram for explaining a configuration of a tandem type color printer (hereinafter simply referred to as “color printer”) as an example of an image forming apparatus according to the fourth embodiment. This color printer uses a known electrophotographic method based on image data input from an external terminal device or the like via a network (for example, a LAN) to record a full color image or a monochrome image on a recording sheet such as a recording sheet or an OHP sheet. To form.

The color printer includes four process units 10Y, 10M, 10C, and 10K that form toner images with toners of yellow (Y), magenta (M), cyan (C), and black (K), and above them. The intermediate transfer belt 51 is disposed.
The intermediate transfer belt 51 is wound around a pair of belt rotation rollers 52 and 53 at a substantially central portion of the color printer, and is arranged in a state along the horizontal direction. The intermediate transfer belt 51 rotates (rotates) in the direction indicated by the arrow X when one of the belt rotation rollers 52 and 53 is rotationally driven by a motor (not shown).

The process units 10Y, 10M, 10C, and 10K are arranged in that order along the traveling direction of the lower traveling portion of the intermediate transfer belt 51.
The process units 10Y, 10M, 10C, and 10K have substantially the same configuration except that only the color of the toner used is different. Therefore, in the following, the configuration of the process unit 10Y will be described, and detailed description of the other process units 10M, 10C, and 10K will be omitted. In addition, as for the components of the process unit 10Y, those having the same functions as those of the monochrome printer shown in FIG. 1 are given the same reference numerals as those of the monochrome printer shown in FIG. The configuration and the like will be briefly described.

  The process unit 10 </ b> Y includes a photosensitive drum 11 provided to face a lower traveling portion of the intermediate transfer belt 51. The photosensitive drum 11 of the process unit 10Y is rotationally driven in the direction indicated by the arrow Z. Note that the rotation direction of the photosensitive drum 11 in the process unit 10Y is opposite to that of the photosensitive drum 11 of the monochrome printer shown in FIG.

As in the monochrome printer shown in FIG. 1, the process unit 10Y forms a toner image on the surface of the photosensitive drum 11 by electrophotography while the photosensitive drum 11 is rotated. The toner image formed on the surface of the photosensitive drum 11 is transferred to the intermediate transfer belt 51 at a position facing the intermediate transfer belt 51.
A cleaning brush 18 is provided as a cleaning member for the photosensitive drum 11 on the downstream side in the rotation direction of the photosensitive drum 11 with respect to the position facing the intermediate transfer belt 51. The cleaning brush 18 is disposed along the axial direction of the photosensitive drum 11, and rotates in contact with the surface of the photosensitive drum 11 to remove residual toner on the photosensitive drum 11.

A charger 12 is provided downstream of the cleaning brush 18 in the rotation direction of the photosensitive drum 11. The charger 12 uniformly charges the surface of the photosensitive drum 11.
Under the process units 10Y, 10M, 10C, and 10K, an exposure device 55 that forms an electrostatic latent image by exposing the photosensitive drums 11 of the process units 10Y, 10M, 10C, and 10K with the laser beam LB. Is provided.

In the process unit 10Y, a developing device 14 is provided on the downstream side in the rotation direction from the exposure position of the photosensitive drum 11 by the laser beam LB. The developing device 14 has substantially the same configuration as the developing device 14 shown in FIG. 2, and includes a developing roller 14r, a supply screw 14b, and a stirring screw 14c as shown in FIG.
As described above, the photosensitive drum 11 of the process unit 10Y is rotated in the opposite direction to the photosensitive drum 11 of the monochrome printer shown in FIG. Accordingly, the rotation directions of the developing roller 14r, the supply screw 14b, and the stirring screw 14c shown in FIG. 15 are also opposite to those shown in FIG.

  Above the intermediate transfer belt 51, toner supply mechanisms 58Y, 58M, 58C, and 58K that supply Y, M, C, and K toner particles to the developing units 14 of the process units 10Y, 10M, 10C, and 10K, respectively. Is provided. Each of the toner supply mechanisms 58Y, 58M, 58C, and 58K is disposed above the process units 10Y, 10M, 10C, and 10K, respectively. Each of the toner supply mechanisms 58Y, 58M, 58C, and 58K stores toner for supplying each color of Y, M, C, and K in advance.

  Four primary transfer rollers 57 are provided above the process units 10Y, 10M, 10C, and 10K in the circumferential movement region of the intermediate transfer belt 51. Each primary transfer roller 57 is opposed to the photosensitive drum 11 of each of the process units 10Y, 10M, 10C, and 10K with the belt running portion below the intermediate transfer belt 51 interposed therebetween. The respective toner images formed on the respective photosensitive drums 11 are transferred onto the lower belt running portion (on the lower surface) of the intermediate transfer belt 51 by the opposing primary transfer roller 57.

In the case of forming a full-color image, the toner images formed on the respective photosensitive drums 11 in the process units 10Y, 10M, 10C, and 10K are multiple-transferred to the same area on the intermediate transfer belt 51.
When a monochrome image is formed, an image forming operation is performed by only one selected process unit (for example, the process unit 10K for K toner), and a toner image is formed on the photosensitive drum 11. The formed toner image is transferred onto a predetermined area on the intermediate transfer belt 51.

  In the intermediate transfer belt 51, a secondary transfer roller 56 is pressed against a portion (right side portion in FIG. 15) wound around one belt rotation roller 52. A transfer nip Nt is formed at the pressure contact portion between the secondary transfer roller 56 and the intermediate transfer belt 51. The toner image transferred to the intermediate transfer belt 51 is conveyed to the transfer nip Nt by the circumferential movement of the intermediate transfer belt 51.

The recording sheet S is conveyed to the transfer nip Nt from a paper feed cassette 22 provided below the exposure unit 55. The toner image transferred to the intermediate transfer belt 51 is secondarily transferred to the recording sheet S conveyed to the transfer nip Nt.
The recording sheet S that has passed through the transfer nip Nt is conveyed to the fixing device 30 disposed above the secondary transfer roller 56. The fixing device 30 fixes the unfixed toner image on the recording sheet S on the recording sheet S. Since the fixing device 30 has the same configuration as the fixing device 30 of the monochrome printer shown in FIG. 1, the same components as those of the fixing device 30 of FIG. Description is omitted.

The recording sheet S on which the toner image is fixed is discharged onto a paper discharge tray 26 by a paper discharge roller 24.
A belt cleaning blade 54 is in sliding contact with a portion (left side portion in FIG. 1) wound around the other belt rotating roller 53 of the intermediate transfer belt 51. The belt cleaning blade 54 removes residual toner and the like attached on the intermediate transfer belt 51 after the toner image is transferred to the recording sheet S.

  Also in such a color printer, in each of the process units 10Y, 10M, 10C, and 10K, the electrostatic latent image formed on the photosensitive drum 11 is developed by the developing device 14. In each developing device 14, as in the monochrome printer shown in FIG. 1, if the free external additive Tgc exists inside, the free external additive Tgc is developed when developing the electrostatic latent image on the photosensitive drum 11. It flies from the container 14 and adheres to the photosensitive drum 11.

  When the toner images formed on the respective photosensitive drums 11 of the process units 10Y, 10M, 10C, and 10K are transferred to the intermediate transfer belt 51, free external additives Tgc attached to the respective photosensitive drums 11 are transferred. A part of the toner image is transferred (attached) to the surface of the intermediate transfer belt 51. Accordingly, the free external additive Tgc transferred from the four photosensitive drums 11 adheres to the surface of the intermediate transfer belt 51. In this case, the free external additive Tgc transferred from the photosensitive drum 11 to the surface of the intermediate transfer belt 51 and the free external additive remaining on the photosensitive drum 11 without being transferred to the intermediate transfer belt 51. The ratio to Tgc is substantially constant even when the cumulative number of printed sheets increases.

Part of the free external additive Tgc transferred from the photosensitive drum 11 of each of the process units 10Y, 10M, 10C, and 10K to the intermediate transfer belt 51 is transferred to the toner image at the transfer nip Nt where the secondary transfer roller 56 is pressed. Is transferred to the recording sheet S when it is transferred to the recording sheet S.
Also in this case, the ratio of the free external additive Tgc transferred to the recording sheet S from the surface of the intermediate transfer belt 51 and the free external additive Tgc remaining on the intermediate transfer belt 51 without being transferred to the recording sheet S. Is almost constant even when the cumulative number of printed sheets increases.

The free external additive Tgc remaining on the intermediate transfer belt 51 without being transferred to the recording sheet S is conveyed to a position where the belt cleaning blade 54 is slidably contacted by the circumferential movement of the intermediate transfer belt 51.
The free external additive Tgc conveyed to the sliding contact position between the belt cleaning blade 54 and the intermediate transfer belt 51 functions in the same manner as the free external additive Tgc at the sliding contact position between the photosensitive drum 11 and the cleaning blade 16 described above. To do. Therefore, when the free external additive Tgc passes between the belt cleaning blade 54 and the intermediate transfer belt 51, the frictional force of both is reduced by the free external additive Tgc. As a result, the occurrence of “turn-up” in the belt cleaning blade 54 is suppressed.

Further, the surface roughness of the intermediate transfer belt 51 in a state where the belt cleaning blade 54 is in sliding contact increases as the number of printed sheets increases. Also in this case, when the surface roughness of the intermediate transfer belt 51 increases, the risk of “turning” in the belt cleaning blade 54 is eliminated.
Also in the color printer having such a configuration, the developing devices 14 in the process units 10Y, 10M, 10C, and 10K are controlled in the same manner as any one of the development controls described in the first to third embodiments. That is, when the intermediate transfer belt 51 is not used (new), and the developing devices 14 of the process units 10Y, 10M, 10C, and 10K are not used (new), the developing operation is performed under the development conditions in the initial mode. Execute.

  The development conditions in the initial mode in this case are set so that the amount of the free external additive Tgc flying from each developer 14 in each developer 14 is smaller than that in the normal mode. Accordingly, the amount of the free external additive Tgc in the developing housing from each developing device 14 is reduced from the start of the developing operation until the risk of occurrence of “turning” of the belt cleaning blade 54 is eliminated. , Can be reduced than the normal mode.

As a result, the “flip” of the belt cleaning blade 54 is generated by a part of the free external additive Tgc adhering to the intermediate transfer belt 51 after flying from each developing device 14 and adhering to the photosensitive drum 11. Can be prevented.
Thereafter, when the surface roughness of the intermediate transfer belt 51 is in a state in which the risk of occurrence of “turning” of the belt cleaning blade 54 has been eliminated, each developing device 14 performs a developing operation in the normal mode. In this case, even if the amount of the free external additive Tgc decreases thereafter, there is no possibility that “turning” occurs in the belt cleaning blade 54.

  It is determined based on the surface roughness of the intermediate transfer belt 51 that the intermediate transfer belt 51 has reached the state where the risk of occurrence of “turning” of the belt cleaning blade 54 has been eliminated. As described in the first embodiment, the surface roughness of the intermediate transfer belt 51 is the same as the method described for the determination of the surface roughness of the photosensitive drum 11, and the driving torque of the motor that moves the intermediate transfer belt 51 around. Can be determined based on

[Embodiment 5]
In the color printer according to the fourth embodiment, the photosensitive drums 11 of the process units 10Y, 10M, 10C, and 10K are cleaned by the cleaning brush 18. On the other hand, in the fifth embodiment, the respective photosensitive drums 11 are cleaned by the cleaning blade, and the “turning” is prevented from occurring in each cleaning blade. The intermediate transfer belt 51 is cleaned with a cleaning brush.

  In this case, the development control of each developing device 14 in the process units 10Y, 10M, 10C, and 10K is executed in the same manner as any one of the development controls described in the first to third embodiments. Therefore, until the surface roughness of the photoconductive drum 11 of each process unit 10Y, 10M, 10C, 10K reaches a state where the risk of occurrence of “turning” of the cleaning blade for cleaning the photoconductive drum 11 is eliminated. Controlled in initial mode. Thereafter, when the risk of “turning” of the cleaning blades of the process units 10Y, 10M, 10C, and 10K is eliminated, the developing operation in each is switched to the normal mode.

  With such a configuration, it is possible to prevent “turning” from occurring in the cleaning blade that cleans the photosensitive drums 11 of the process units 10Y, 10M, 10C, and 10K. Moreover, there is no possibility of uneven density in the toner images formed on the photosensitive drums 11 of the process units 10Y, 10M, 10C, and 10K.

[Modification]
<Modification 1>
The above-described monochrome printer is configured to determine based on the driving torque of the photosensitive drum 11 that the surface roughness of the photosensitive drum 11 has reached the state where the risk of turning over the cleaning blade has been eliminated. However, the configuration is not limited to this.

  For example, when the surface roughness of the photoconductive drum 11 is directly detected by the surface roughness detecting means and the surface roughness of the photoconductive drum 11 reaches a threshold value, there is a risk that the cleaning blade 16 will be “turned over”. It is good also as a structure which determines with being the state by which was eliminated. As the surface roughness detecting means in this case, the above-described optical interference type surface shape roughness measuring instrument (manufactured by Veeco, trade name “Wyko NT9000”) can be used. Alternatively, a measuring meter that irradiates light on the surface of the photosensitive drum 11 and detects the surface roughness based on the reflected light may be used.

Further, it is determined that the risk of “turning” on the cleaning blade 16 has been eliminated based on the cumulative number of printed sheets (cumulative image formation count) where the surface roughness of the photosensitive drum 11 is a threshold value. It is good. In this case, the cumulative number of printed sheets for which the surface roughness of the photosensitive drum 11 is a predetermined threshold value is obtained in advance by experiments.
Further, the risk of “turning over” on the cleaning blade 16 is eliminated based on the cumulative number of printed sheets corresponding to the driving torque of the photosensitive drum 11 corresponding to the threshold value (for example, 40 nm) of the surface roughness of the photosensitive drum 11. It is good also as a structure which determines with it being in the state. Also in this case, the cumulative number of printed sheets that becomes the driving torque of the photosensitive drum 11 in which the surface roughness of the photosensitive drum 11 corresponds to the threshold value is obtained in advance by experiments.

Further, the amount of displacement of the cleaning blade 16 in the cleaning unit 16a may be detected, and based on the amount of displacement, it may be determined that the risk of “turning” in the cleaning blade 16 has been eliminated. .
When the development operation is started under the development conditions in the initial mode, since the surface roughness of the photosensitive drum 11 is small, when there is no free external additive Tgc between the photosensitive drum 11 and the cleaning blade 16, The displacement amount of the cleaning blade 16 increases. However, in this case, since a relatively large amount of the free external additive Tgc is supplied to the photosensitive drum 11, the displacement amount of the cleaning blade 16 becomes lower than that in the case where the free external additive Tgc is not present. ing.

Thereafter, the surface roughness of the photosensitive drum 11 increases as the number of printed sheets increases, so that the displacement of the cleaning blade 16 is reduced even when the amount of the free external additive Tgc supplied to the photosensitive drum 11 decreases. The amount becomes smaller than that at the beginning of the development operation under the development conditions in the initial mode.
Accordingly, for example, an imaging unit that monitors the cleaning unit 16a is provided, and the amount of displacement of the cleaning unit 16a with respect to the surface of the photosensitive drum 11 is detected by the imaging unit. When it is detected that the displacement amount of the cleaning unit 16a is smaller than a predetermined value, it is determined that the risk of “turning” in the cleaning blade 16 is eliminated. In this case, the predetermined value of the displacement amount in the cleaning unit 16a (the surface roughness of the photosensitive drum 11 corresponds to 40 nm) is obtained in advance by an experiment or the like.

  Further, instead of the configuration in which the displacement amount in the cleaning unit 16a is directly monitored, the risk of occurrence of “turning up” in the cleaning blade 16 is eliminated based on the cumulative number of printed sheets corresponding to the displacement amount. It is good also as a structure to determine. The cumulative number of printed sheets that eliminates the risk of occurrence of “turning” in the cleaning blade 16 is obtained in advance by experiments or the like.

Further, instead of the respective cumulative number of printed sheets described above, there is a risk of occurrence of “turning” of the cleaning blade 16 based on the cumulative travel distance (cumulative rotational distance) of the photosensitive drum 11 corresponding to the respective cumulative number of printed sheets. It is good also as a structure which performs the determination of the state by which the was canceled. Each cumulative travel distance is also obtained in advance by experiments or the like.
Further, a state in which the risk of occurrence of “turning” of the cleaning blade 16 is eliminated may be determined using the above-described plurality of configurations. In this case, when the state in which the risk of “turning” of the cleaning blade 16 is eliminated by any one configuration is detected, the risk of “turning” of the cleaning blade 16 is eliminated. It is determined that it is in a state.

Note that the surface roughness of the photosensitive drums 11 of the process units 10Y, 10M, 10C, and 10K in the case of the color printer of Embodiment 5 may be determined in the same manner as in the first modification.
Further, in the case of the color printer of the fourth embodiment, the determination that the risk of occurrence of “turning” of the belt cleaning blade 54 has been eliminated in the intermediate transfer belt 51 is also the same as that of the first modification. A similar configuration may be used. In this case, the risk of occurrence of “turning” of the belt cleaning blade 54 is eliminated based on the surface roughness of the intermediate transfer belt 51, not the surface roughness of the photosensitive drum 11. Determined.

<Modification 2>
In each of the first and second embodiments, the toner particles T accommodated in the developing housing 14h in the unused developing device 14 and the toner particles T accommodated in the toner replenishing mechanism 17 are manufactured under the same manufacturing conditions. Has been. Therefore, each toner particle T has substantially the same physical properties. However, instead of such a configuration, the physical properties of the toner particles T accommodated in the developing housing 14h and the toner particles T accommodated in the toner replenishing mechanism 17 are made different so that the free external additive Tgc in the initial mode. It is good also as a structure which suppresses generation | occurrence | production of this more reliably.

  For this reason, in this modification, the toner replenishing mechanism 17 stores toner particles T having the same physical properties as the toner particles T used in the above embodiments. Hereinafter, the toner particles T having such physical properties are referred to as “standard toner particles TS”. On the other hand, the toner particles T in which the binding force of the external additive Tg is stronger than the standard toner particles TS are accommodated in the unused (new) development housing 14h. Hereinafter, the toner particles T in which the binding force of the external additive Tg is stronger than that of the standard toner particles TS are referred to as “initial toner particles TF”.

Such initial toner particles TF are manufactured by making the stirring intensity at the time of manufacturing stronger than the standard toner particles TS.
As described above, the toner particles T are manufactured by mixing and stirring the material to be the toner base Tm and the material to be the external additive Tg using a mixing stirrer such as a mixer. In this case, if the stirring time of the material is increased, the binding force between the toner base Tm and the external additive Tg is increased.

  From this, the initial toner particles TF are manufactured by making the material stirring time at the time of manufacturing longer than that of the standard toner particles TS compared to the standard toner particles TS manufactured by stirring the material with the standard stirring time. Has been. The standard agitation time is an agitation time at which there is no possibility of deterioration of characteristics such as shape and charging in the toner particles. For example, the stirring time of the material at the time of manufacturing the standard toner particles TS is set to 300 seconds. In this case, the stirring time of the material at the time of manufacturing the initial toner particles TF is 1.2 times (360 seconds) that of the standard toner particles TS.

  If the initial toner particles TF have a longer stirring time than that of the standard toner particles TS, the initial toner particles TF may contain deteriorated toner whose characteristics such as shape and charge have changed. is there. However, if the stirring time during the production of the initial toner particles TF is about 1.2 times that of the standard toner particles TS, the initial toner particles TF are unlikely to contain deteriorated toner, and deteriorated toner is not included. Even so, the content of deteriorated toner is relatively low.

  When the initial toner particles TF are manufactured in this way, the amount of the free external additive Tgc generated at the time of manufacture is smaller than that at the time of manufacturing the standard toner particles TS. Further, the produced initial toner particles TF contain the low-binding external additive Tgb in a relatively large proportion. For this reason, in the developing operation in the initial mode, the amount of the free external additive Tgc flying from the developing device 14 can be suppressed.

In this case, since there is a low possibility that the initial toner particles TF contain the deteriorated toner, there is no possibility that the image quality of the toner image formed by the initial toner particles TF is deteriorated.
Thereafter, when the toner amount in the developing housing 14 h is reduced to a predetermined amount or less, the standard toner particles TS are supplied from the toner supply mechanism 17. Therefore, thereafter, as the number of printed sheets increases, the toner particles T used for developing the electrostatic latent image on the photosensitive drum 11 sequentially shift from the initial toner particles TF to the standard toner particles TS. Thereby, a toner image of appropriate quality can be formed by the standard toner particles TS.

This modification can also be applied to the color printers of the fourth and fifth embodiments. In this case, the initial toner particles TF are respectively stored in the new developing devices 14 of the process units 10Y, 10M, 10C, and 10K, and the standard toner particles TS are stored in the toner supply mechanisms 58Y, 58M, 58C, and 58K, respectively. It is set as the structure which accommodated.
In addition, the monochrome printer of this modification may be configured not to execute the development control described in the first and second embodiments. In this case, the developing device 14 is not controlled under the development conditions in the initial mode, but is controlled under the development conditions in the normal mode.

  In such a configuration, the amount of the initial toner particles TF and the free external additive Tgc contained in the unused developing device 14 is small. For this reason, until the surface of the new photosensitive drum 11 reaches a state where the risk of occurrence of “turning” of the cleaning blade 16 is eliminated, the “turning” is performed by the free external additive Tgc flying from the developing device 14. "Can be prevented.

In the case of such a configuration, the flying quantitative value [ΔWDn], which is a quantitative value of the amount of the free external additive Tgc flying from the developing housing 14h, was obtained by the quantification process described above. The initial toner particles T have a stirring time during production of 1.2 times (360 seconds) that of the standard toner particles T (300 seconds).
In this case, the flying fixed value [ΔWDn] (n = 1) in the cumulative number of printed sheets of m sheets (n = 1) is about 90% when the standard toner particles T are accommodated in the developing housing 14h. A decrease of about 10% was observed. Thereafter, as the number of printed sheets increased, the flying fixed value [ΔWDn] decreased. In this case, the rate of decrease in the flying fixed value is relatively gradual, and the cumulative number of prints until the flying fixed value [ΔWDn] is lower than 300 is twice or more than when the standard toner particles T are used. Increased to. Further, the occurrence of “turning” in the cleaning blade 16 was also confirmed, but “turning” was not generated.

  The same configuration may be applied to the color printers of the fourth and fifth embodiments. That is, the configuration is such that the initial toner particles TF are respectively stored in the new developing devices 14 of the process units 10Y, 10M, 10C, and 10K, and the development control is not executed in the process units 10Y, 10M, 10C, and 10K. Also good. In any case, until the surface of the new intermediate transfer belt 51 or the photosensitive drum 51 reaches a state in which the risk of “turning” of the cleaning blade is eliminated, the free external additive flying from the developing device. Owing to Tgc, the occurrence of “turning over” can be prevented.

<Other variations>
The present invention can be applied not only to a printer but also to a copying machine, an MFP (Multiple Function Peripheral), a FAX, and the like.

  The present invention prevents the occurrence of “turn-up” in the cleaning blade in an image forming apparatus that cleans the image carrying surface of an image carrying rotating body carrying a toner image with a cleaning blade after the toner image is transferred to a transfer target. It is useful as a technology to do.

DESCRIPTION OF SYMBOLS 11 Photosensitive drum 12 Charger 14 Developing device 14b Supply screw 14c Stirring screw 14g Toner concentration sensor 14h Developing housing 14r Developing roller 16 Cleaning blade 16a Cleaning unit 41 Engine control unit 47 Developing bias power supply 51 Intermediate transfer belt 54 Belt cleaning blade

Claims (9)

An image carrying rotator carrying a toner image visualized by toner supplied from a developing device, a transfer means for transferring the toner image carried on the image carrying rotator to a transfer target, and after the toner image is transferred An image forming apparatus having a cleaning blade for removing residual toner remaining on the image bearing surface of the image bearing rotor,
After the developing device and the image bearing rotating body are in a new state, the first image is in an initial stage until the image bearing surface reaches a state where the risk of turning over in the cleaning blade is eliminated. Control means for executing image formation in the second image forming mode after executing image formation in the formation mode and reaching a state in which the risk of the occurrence of turning has been eliminated;
The image forming conditions in the first image forming mode are such that, in the initial stage, the amount of the external additive supplied together with the toner from the developing unit is more than the amount necessary for preventing the cleaning blade from turning up. In addition, the image forming apparatus is set to be smaller than that in the case where the image forming operation is executed in the initial stage under the same condition as in the second image forming mode.   2. The image forming apparatus according to claim 1, further comprising determination means for determining whether or not the state of the image carrying surface of the image carrying rotating body has reached a state in which the risk of turning over the cleaning blade has been eliminated. The image forming apparatus described in 1. The determination means includes
Surface roughness of the image bearing surface of the image bearing rotator, driving torque when rotating the image bearing rotator, deformation amount of the cleaning member, accumulation from start of use of the unused image bearing rotator An acquisition means for acquiring at least one piece of information about the number of times of image formation and information relating to the cumulative travel distance from the start of use of the unused image bearing rotator;
The determination as to whether or not the state of the image carrying surface of the image carrying rotating body has reached a state in which the risk of turning over the cleaning blade has been eliminated based on the acquired information. Item 3. The image forming apparatus according to Item 2. The developer has a developer carrying rotating body that carries and rotates a developer containing toner particles,
The rotation speed of the developer carrying rotator in the first image forming mode is set lower than the rotation speed in the second image forming mode. The image forming apparatus described in the item. The developer includes a developer carrying rotating body that carries and rotates a developer containing toner particles;
Development bias supply means for applying a development bias voltage to the developer carrying rotor,
In the first image forming mode, the developing bias supply means develops so that the amount of the external additive supplied from the developer carrying rotator during development is smaller than in the second image forming mode. The image forming apparatus according to claim 1, wherein a bias voltage condition is set. The developing bias voltage is formed by superimposing an AC bias voltage on a DC bias voltage, and by changing the waveform of the AC bias voltage, the amount of toner particles supplied from the developer-carrying rotator at the time of development is increased. The image forming apparatus according to claim 5, wherein the image forming apparatus is set to decrease in the first image forming mode than in the second image forming mode. The developer includes a developer carrying rotating body that carries and rotates a developer containing toner particles, and a stirring member that supplies the developer carrying body while stirring the developer,
The degree of stirring of the developer by the stirring member in the first image forming mode is set to be stronger than that in the second image forming mode. The image forming apparatus according to claim 1. A developer replenishing mechanism for replenishing the developer to the developer;
In the unused developer, a developer that has been processed in such a manner that the binding strength of the external additive to the toner particles is stronger than the replenishment toner replenished from the developer replenishment mechanism is stored in advance. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus. An acquisition means for acquiring information indicating that both the developing device and the image bearing rotating body have been replaced with new ones that are not used;
When the control unit acquires information indicating that both the developing device and the image bearing rotator have been replaced with new ones, the control unit sets the first image forming mode and performs control to execute image formation. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

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