JP5556981B2 - Developing device, process cartridge, and image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus using an electrophotographic method such as a copying machine, a printer, a facsimile machine, or a multifunction machine thereof, and a developing device and a process cartridge installed therein, and particularly uses a two-component developer. The present invention relates to a developing device, a process cartridge, and an image forming apparatus.

2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine or a printer, a developing device that stores a two-component developer (including a case where an external additive or the like is added) composed of toner and a magnetic carrier and performs a developing process. Many are used (for example, refer patent documents 1-3).
In such a two-component developing type developing apparatus, there is a problem that the developing roller (developer carrier, developing sleeve) is bent and image density unevenness occurs on the output image.

Japanese Patent Application Laid-Open No. H10-260260 discloses a technique for suppressing the bending of the developing sleeve by cutting out a part of the magnet in the developing sleeve, embedding a bending suppressing member in the portion, and bringing the bending suppressing member into contact with the developing sleeve. Has been.
Patent Document 2 and the like disclose a technique for suppressing the deflection of the developing sleeve by bringing a crown-shaped elastic roller into contact with the developing sleeve.
Patent Document 3 and the like disclose a technique for preventing the developing sleeve from being bent by increasing the rigidity of the developing sleeve.

JP 2006-251289 A JP-A-11-316496 Japanese Patent Laid-Open No. 9-54501

  The developing apparatuses described in Patent Documents 1 to 3 and the like described above are large-sized with respect to various types of developing apparatuses in which the position of the developer carrier relative to the image carrier and the position of the developer regulating member relative to the developer carrier are different. Therefore, it has been impossible to reliably solve the problem that the image density unevenness occurs on the output image without increasing the cost and cost.

  The present invention has been made to solve the above-described problems, and even when the position of the developer carrier relative to the image carrier and the position of the developer regulating member relative to the developer carrier are different, the apparatus It is an object of the present invention to provide a developing device, a process cartridge, and an image forming apparatus in which image density unevenness does not occur on an output image without increasing the size and cost.

As a result of repeated researches to solve the above problems, the present inventor has come to know the following matters.
The developer carrying member supported at both ends in the longitudinal direction receives a large force from the developer at the position of the developer regulating member, and the central portion in the longitudinal direction is bent in an arcuate shape. Therefore, depending on the position of the developer carrier relative to the image carrier and the position of the developer regulating member relative to the developer carrier, both longitudinal ends and the length of the gap (development gap) of the developer carrier relative to the image carrier The magnitude relationship with the central portion in the direction fluctuates, resulting in a difference between the developing ability at both ends in the longitudinal direction and the developing ability at the central portion in the longitudinal direction. For this reason, image density unevenness occurs in the direction orthogonal to the conveyance direction of the recording medium on the output image.
In particular, recent image forming apparatuses are highly demanded by users for higher image quality, and in order to improve dot reproducibility, the development gap is set narrow with high precision to reduce the influence of the edge effect. The problem can no longer be ignored.

The present invention is based on the matters described above, that is, the developing device according to the first aspect of the present invention is a developing device for developing a latent image formed on an image carrier, and A developer carrying body facing the image carrying body and carrying a developer composed of a carrier and toner, and an amount of the developer carrying the developer carrying body and facing the developer carrying body are regulated. A developer regulating member that is arranged such that the rotation center position of the developer carrying member is located above the rotation center position of the image carrying member, and the rotation center position is the developer regulating member. The amount of developer carried on the developer carrying member after passing through the position of the developer regulating member is higher than the opposite position with respect to the central portion in the longitudinal direction as compared with both longitudinal ends. The development to increase In which the gap of the developer regulating member against the bearing member is formed to gradually increase toward the longitudinal center from the longitudinal ends.

According to a second aspect of the present invention, there is provided the developing device according to the first aspect, wherein the toner has a volume average particle diameter of Dv (μm) and a number average particle diameter of Dn (μm). sometimes,
3 ≦ Dv ≦ 8
1.00 ≦ Dv / Dn ≦ 1.40
It is formed so that the following relationship is established.

According to a third aspect of the present invention, in the developing device according to the first or second aspect, the toner has a shape factor SF-1 in the range of 100 to 180, and the shape factor SF- 2 is formed in the range of 100 to 180.

A process cartridge according to a fourth aspect of the present invention is a process cartridge that is detachably installed on the main body of the image forming apparatus, and the developing device according to any one of the first to third aspects. And the image carrier.

An image forming apparatus according to a fifth aspect of the invention includes the developing device according to any one of the first to third aspects and the image carrier.

  In the present application, the “process cartridge” refers to a charging unit that charges the image carrier, a developing device (developing unit) that develops a latent image formed on the image carrier, and a cleaning on the image carrier. It is defined as a unit in which at least one of the cleaning units and the image carrier are integrated and configured to be detachable from the image forming apparatus main body.

  According to the present invention, depending on the position of the developer carrier relative to the image carrier and the position of the developer regulating member relative to the developer carrier, the developing ability at both ends in the longitudinal direction and the developing ability at the central part in the longitudinal direction are determined. Since the difference is provided, the development apparatus, the process cartridge, and the apparatus that does not cause uneven image density on the output image without increasing the size and cost of the apparatus with respect to various types of apparatuses, and An image forming apparatus can be provided.

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.

Embodiment 1 FIG.
A first embodiment of the present invention will be described in detail with reference to FIGS.
FIG. 1 is a configuration diagram illustrating a laser printer as an image forming apparatus. FIG. 2 is a cross-sectional view showing the vicinity of a process cartridge installed therein. FIG. 3 is a cross-sectional view of the developing device and the photosensitive drum of the process cartridge of FIG. 2 as viewed from above (longitudinal direction in FIG. 2). FIG. 4 is an enlarged view showing the periphery of the developing roller.

  As shown in FIG. 1, process cartridges 6Y, 6M, 6C, and 6K as image forming units corresponding to the respective colors (yellow, magenta, cyan, and black) are arranged so as to face the intermediate transfer belt 8 of the intermediate transfer unit 15. It is installed side by side. Since the four process cartridges 6Y, 6M, 6C, and 6K installed in the apparatus main body 100 have substantially the same structure except that the color of the toner used in the image forming process is different, the process cartridges in FIGS. The alphabets (Y, M, C, K) of the reference numerals for the cartridge 6, the photosensitive drum 1, and the primary transfer bias roller 9 are omitted.

  Referring to FIG. 2, a process cartridge 6 includes a photosensitive drum 1 as an image carrier, a charging unit 4 disposed around the photosensitive drum 1, a developing device 5 (developing unit), and a cleaning unit 2. Are integrated with each other and are detachable from the apparatus main body 100. Thus, the maintainability of the image forming unit is improved by integrating the components of the image forming unit. Then, an image forming process (charging process, exposure process, developing process, transfer process, cleaning process, charge eliminating process) is performed on the photosensitive drum 1 to form a desired toner image on the photosensitive drum 1. It will be.

  In the first embodiment, the photosensitive drum 1, the charging unit 4, the developing device 5, and the cleaning unit 2 are integrated to form the process cartridge 6. However, the apparatus main body 100 includes each component as a single unit. It can also be installed detachably. Specifically, the developing device 5 can be configured to be detachable from the apparatus main body 100 as a single unit. Further, it can be configured to be detachable from the apparatus main body 100 as a unit in which at least one of the photosensitive drum 1, the charging unit 4, and the cleaning unit 2 and the developing device 5 are integrated.

Referring to FIG. 2, the photosensitive drum 1 is rotationally driven in a clockwise direction in FIG. 2 by a drive unit (not shown). Then, the surface of the photosensitive drum 1 is uniformly charged at the position of the charging unit 4 (a charging process).
Thereafter, the surface of the photosensitive drum 1 reaches the irradiation position of the laser beam L emitted from the exposure unit 7 (see FIG. 1), and an electrostatic latent image is formed by exposure scanning at this position. (It is an exposure process.)

Thereafter, the surface of the photosensitive drum 1 reaches a position facing the developing device 5, and the electrostatic latent image is developed at this position to form a desired toner image (developing process).
Specifically, a two-component developer G composed of toner and a carrier (magnetic carrier) is accommodated in the developing device 5. The developer G in the developing device 5 is adjusted so that the toner concentration (the ratio of toner in the developer G) detected by the magnetic sensor 57 falls within a predetermined range. That is, according to the toner consumption in the developing device 5, toner is supplied from the toner transport pipe 43 (toner transport unit) into the second developer storage unit 54 through the toner supply port 44.

Referring to FIG. 1, the toner transport pipe 43 communicates with a corresponding toner bottle among the toner bottles 32 </ b> Y, 32 </ b> M, 32 </ b> C, and 32 </ b> K installed in the bottle container 31 above the apparatus main body 100. Although not shown in the figure, the toner transport unit includes a drive unit that rotationally drives the toner bottles 32Y, 32M, 32C, and 32K, a toner transport pipe 43, an air pump connected to the toner transport pipe 43, and the like. The toner transport unit configured as described above transports the respective color toners from the toner bottles 32Y, 32M, 32C, and 32K containing the respective color toners to the respective developing devices 5 through the toner transport pipe 43. .
The toner conveying unit is not limited to the above-described configuration, and various configurations can be used. For example, a configuration in which toner is supplied from the toner bottle to the developing device 5 via the relay hopper without using the toner transport pipe can be used.

  Thereafter, the toner replenished in the second developer accommodating portion 54 is mixed and stirred together with the developer G by the second conveying screw 56 and the first conveying screw 55, and is separated by the partition portion 59a. It circulates through the agent container 53 and the second developer container 54 (circulation in the direction of the broken line arrow in FIG. 3).

  Specifically, with reference to FIG. 3, the developer G in the first developer accommodating portion 53 is transported from the right side to the left side by the first transport screw 55. Thus, a first transport path for transporting the developer along the longitudinal direction of the developing roller 51 is formed. On the other hand, the developer G in the second developer accommodating portion 54 is conveyed from the left side to the right side by the second conveyance screw 56. Thus, a second transport path for transporting the developer in the direction opposite to the first transport path is formed.

  Further, the first developer accommodating portion 53 in which the first conveying path is formed and the second developer accommodating portion 54 in which the second conveying path is formed are partitions arranged in areas excluding both ends in the longitudinal direction. It is isolated by the member 59a and communicates at both longitudinal ends where no partition member 59a is interposed. That is, the developer transported by the first transport screw 55 flows to the second developer accommodating section 54 side through the communication section 63 and is then transported by the second transport screw 56. The developer transported by the second transport screw 56 flows to the first developer accommodating section 53 side through the communication section 64 and is then transported by the first transport screw 55. Thus, a developer circulation path is formed between the two developer accommodating portions 53 and 54.

Thus, the toner in the developer G circulating in the circulation path is attracted to the carrier by frictional charging with the carrier, and is carried on the developing roller 51 together with the carrier by a plurality of magnetic poles formed on the developing roller 51. The
Here, referring to FIG. 3, the developing roller 51 includes a magnet 51b that is fixed inside and forms a plurality of magnetic poles on the peripheral surface of the roller, and a sleeve 51a that rotates around the magnet 23a1. . Then, when the sleeve 51a rotates around the magnet 51b in which a plurality of magnetic poles are formed, the developer G moves on the developing roller 51 (on the sleeve 51a) with the rotation.

  The developer G carried on the developing roller 51 as the developer carrying member is conveyed along with the rotation of the developing roller 51 in the direction of the arrow, and reaches the position of the doctor blade 52 as the developer carrying member. Then, after the developer G on the developing roller 51 is regulated to an appropriate amount at this position, the developer G is conveyed to a position facing the photosensitive drum 1 (developing area). The toner is attracted to the latent image formed on the photosensitive drum 1 by the electric field (developing electric field) formed in the developing area.

More specifically, a plurality of magnetic poles formed around the developing roller 51 by the magnet 51b are formed at positions facing the magnetic drum (main magnetic pole) facing the photosensitive drum 1 and the doctor blade 52. A second magnetic pole (doctor pole magnetic pole), a third magnetic pole (pumping magnetic pole) formed at a position facing the first conveying screw 55, and a fourth magnetic pole (agent separation) formed above the first developer accommodating portion 53. Magnetic pole), a fifth magnetic pole (conveying magnetic pole) formed between the main magnetic pole and the fourth magnetic pole, and the like.
First, the third magnetic pole acts on a carrier as a magnetic body, and the developer G accommodated in the developer accommodating portion 53 is carried on the developing roller 51. Part of the developer G carried on the developing roller 51 is scraped off at the position of the doctor blade 52 and returned to the developer containing portion 53. On the other hand, the development carried on the developing roller 51 through the doctor gap M (see also FIG. 4) between the doctor blade and the developing roller 51 at the position of the doctor blade 52 where the magnetic force by the second magnetic pole acts. The agent G rises at the position of the main magnetic pole and comes into sliding contact with the photosensitive drum 1 in the development region. Thus, the toner in the developer G carried on the developing roller 51 adheres to the latent image on the photosensitive drum 1. Thereafter, the developer G that has passed the position of the main magnetic pole is transported to the position of the fourth magnetic pole by the fifth magnetic pole. Then, at the position of the fourth magnetic pole, a repelling magnetic field acts on the carrier, and the developer G after the developing process carried on the developing roller 51 is detached from the developing roller 51. The detached developer G is returned again to the developer container 53 and circulates in the developer containers 53 and 54. Such a flow of the developer G is repeated.

In the first embodiment, the outer diameter of the developing roller 51 is set to 18 mm. Further, the development gap N is set to about 0.3 mm in order to improve the dot reproducibility of the output image.
In the first embodiment, the doctor blade 52 is made of a nonmagnetic metal material having a thickness of about 1.5 to 2 mm. The straightness of the tip of the doctor blade 52 (the portion facing the developing roller 51) is set to about 0.05 mm. An auxiliary plate made of a magnetic metal material having a thickness of about 0.2 mm can be placed on the doctor blade 52 described above.

  After the development process described above, the surface of the photosensitive drum 1 reaches a position facing the intermediate transfer belt 8 and the first transfer bias roller 9, and the toner image on the photosensitive drum 1 is transferred to the intermediate transfer belt 8 at this position. Transferred upward (this is a primary transfer step). At this time, a small amount of untransferred toner remains on the photosensitive drum 1.

Thereafter, the surface of the photoreceptor 1 reaches a position facing the cleaning unit 2, and untransferred toner remaining on the photoreceptor drum 1 at this position is collected by the cleaning blade 2a (cleaning process).
Finally, the surface of the photosensitive drum 1 reaches a position facing a neutralization unit (not shown), and the residual potential on the photosensitive drum 1 is removed at this position.
Thus, a series of image forming processes performed on the photosensitive drum 1 is completed.

  The image forming process described above is performed by each of the four process cartridges 6Y, 6M, 6C, and 6K. That is, referring to FIG. 1, laser light L based on image information is directed onto the photosensitive drums of the process cartridges 6Y, 6M, 6C, and 6K from the exposure unit 7 disposed below the process cartridge. Is irradiated. Specifically, the exposure unit 7 emits laser light L from a light source, and irradiates the photosensitive drum through a plurality of optical elements while scanning the laser light L with a polygon mirror that is rotationally driven. Thereafter, the toner images of the respective colors formed on the respective photosensitive drums through the developing process are transferred onto the intermediate transfer belt 8 in an overlapping manner. In this way, a color image is formed on the intermediate transfer belt 8.

  Here, referring to FIG. 1, the intermediate transfer unit 15 includes an intermediate transfer belt 8, four primary transfer bias rollers 9Y, 9M, 9C, and 9K, a secondary transfer backup roller 12, a counter roller 13, and a tension roller 14. And the cleaning unit 10 and the like. The intermediate transfer belt 8 is stretched and supported by the three roller members 12 to 14 and is endlessly moved in the direction of the arrow in FIG.

The four primary transfer bias rollers 9Y, 9M, 9C, and 9K respectively sandwich the intermediate transfer belt 8 with the photosensitive drums 1Y, 1M, 1C, and 1K to form a primary transfer nip. A transfer bias having a polarity opposite to the polarity of the toner is applied to the primary transfer bias rollers 9Y, 9M, 9C, and 9K.
The intermediate transfer belt 8 travels in the direction of the arrow and sequentially passes through the primary transfer nips of the primary transfer bias rollers 9Y, 9M, 9C, and 9K. In this way, the toner images of the respective colors on the photosensitive drums 1Y, 1M, 1C, and 1K are primarily transferred while being superimposed on the intermediate transfer belt 8.

  Thereafter, the intermediate transfer belt 8 on which the toner images of the respective colors are transferred in a superimposed manner reaches a position facing the secondary transfer roller 19. At this position, the secondary transfer backup roller 12 sandwiches the intermediate transfer belt 8 with the secondary transfer roller 19 to form a secondary transfer nip. The color toner image formed on the intermediate transfer belt 8 is transferred onto a recording medium P such as transfer paper conveyed to the position of the secondary transfer nip. At this time, untransferred toner that has not been transferred to the recording medium P remains on the intermediate transfer belt 8.

Thereafter, the intermediate transfer belt 8 reaches the position of the cleaning unit 10 for the intermediate transfer belt 8. At this position, the untransferred toner on the intermediate transfer belt 8 is collected.
Thus, a series of transfer processes performed on the intermediate transfer belt 8 is completed.

Here, the recording medium P transported to the position of the secondary transfer nip is transported from a paper feeding unit 26 disposed below the apparatus main body 100 via a paper feeding roller 27, a registration roller pair 28, and the like. It is a thing.
Specifically, a plurality of recording media P such as transfer paper are stored in the paper supply unit 26 in a stacked manner. When the paper feed roller 27 is driven to rotate counterclockwise in FIG. 1, the uppermost recording medium P is fed toward the rollers of the registration roller pair 28.

  The recording medium P transported to the registration roller pair 28 temporarily stops at the position of the roller nip of the registration roller pair 28 whose rotation drive has been stopped. Then, the registration roller pair 28 is rotationally driven in synchronization with the color image on the intermediate transfer belt 8, and the recording medium P is conveyed toward the secondary transfer nip. In this way, a desired color image is transferred onto the recording medium P.

Thereafter, the recording medium P on which the color image is transferred at the position of the secondary transfer nip is conveyed to the position of the fixing unit 20. At this position, the color image transferred on the surface is fixed on the recording medium P by heat and pressure generated by the fixing roller and the pressure roller.
Thereafter, the recording medium P is discharged to the outside of the apparatus through the rollers of the discharge roller pair 29. The transferred P discharged from the apparatus main body 100 by the discharge roller pair 29 is sequentially stacked on the stack unit 30 as an output image.
Thus, a series of image forming processes in the image forming apparatus is completed.

Hereinafter, the configuration and operation of the developing device 5 which are characteristic in the first embodiment will be described in detail.
The developing device 5 according to the first embodiment has the developing ability at both ends in the longitudinal direction according to the positional relationship between the photosensitive drum 1 and the developing roller 51 and the positional relationship between the developing roller 51 and the doctor blade 52. There is a difference in the developing ability at the center in the longitudinal direction.
Specifically, referring to FIG. 4, in developing device 5 according to the first exemplary embodiment, the rotation center position of developing roller 51 is disposed at a distance H higher than the rotation center position of photosensitive drum 1. Yes. Further, the rotational center position of the developing roller 51 is disposed above the position facing the doctor blade 51 (the position where the doctor gap M is formed). The developing device 5 is set so that the developing ability at both ends in the longitudinal direction (the direction perpendicular to the paper surface in FIG. 4) is lower than the developing ability at the center in the longitudinal direction. Here, the “development capability” is the capability (ease of development) of developing the electrostatic latent image formed on the photosensitive drum 1 in the development region.

This is because when the positional relationship between the photosensitive drum 1 and the developing roller 51 and the positional relationship between the developing roller 51 and the doctor blade 52 are as described above, the development at both ends in the longitudinal direction is performed. This is because the developing gap N1 at the center in the longitudinal direction becomes larger than the gap N0, and the developing ability at the center in the longitudinal direction is lowered as compared with the developing ability at both ends in the longitudinal direction.
Specifically, referring to FIG. 4, the developer G carried on the developing roller 51 is blocked by the upstream side of the position where the developing roller 51 and the doctor blade 52 face each other without passing through the doctor gap M. It is in a state. The developing roller 51 (the shafts at both ends in the longitudinal direction are supported via bearings by a component force F2 acting in the vertical direction of the doctor blade 52 out of the force F1 by which the developer G that is blocked is pressed against the doctor blade 52. Is bent in a bow shape. That is, the developing roller 51 is deformed as indicated by a broken line in FIG. 5 (the maximum deformation amount is about 0.03 mm). It should be noted that the developing roller 51, not the doctor blade 52, is bent because the sleeve 51a of the developing roller 51 is a thin-walled cylinder and has low mechanical strength, or the developing roller 51 is at both ends thereof. This is because the doctor blade 52 is fixedly supported at both ends other than the both ends while being supported rotatably.

  Then, when bending occurs in the central portion in the longitudinal direction of the developing roller 51 as described above, the central portion in the longitudinal direction of the developing roller 51 is displaced as shown by a broken line in FIG. 4, and the developing gap N1 in the central portion in the longitudinal direction is displaced. Becomes larger than the developing gap N0 in the central portion in the longitudinal direction. As a result, in the developing region, the developing electric field at the longitudinal center is lower than the developing electric field at both longitudinal ends, and the developing ability at the longitudinal central part is lower than the developing ability at both longitudinal ends. .

FIG. 6 is a graph showing the relationship between the developing gap N and the toner adhesion amount in the developing device 5 (conventional device) in which the developing ability at the central portion in the longitudinal direction is equal to the developing ability at both ends in the longitudinal direction. It is.
In FIG. 6, “toner adhesion amount” on the vertical axis is the toner adhesion amount of the toner image that adheres to the photosensitive drum 1 under a predetermined condition, and is a value proportional to the above-described “development ability”. In FIG. 6, “●” indicates data at the center in the longitudinal direction, and “■” and “♦” indicate data at both ends in the longitudinal direction.
As shown in FIG. 6, in the conventional developing device, the toner adhesion amount (developing ability) at the longitudinal center is longer as the developing gap at the longitudinal center is larger than the developing gap at the longitudinal center. It can be seen that the toner adhesion amount (development capability) at both ends in the direction is about 10% lower.

FIG. 7 shows changes in the image density depending on the position on the output image in the developing device 5 (conventional device) in which the developing ability at the center in the longitudinal direction and the developing ability at both ends in the longitudinal direction are equal. It is a graph to show.
In FIG. 7, “ID measurement position” on the horizontal axis indicates the measurement position of image density (ID) in the output image (recording medium) on which the image is printed, and “left”, “middle”, and “right” are the longitudinal direction. (The direction perpendicular to the conveyance direction of the recording medium), and “upper” and “lower” are the positions in the conveyance direction of the recording medium. Also, the difference in the line type of the graph in FIG. 7 is the difference in the recording medium (one of a plurality of printed recording media) to be measured.
As shown in FIG. 7, as the toner adhesion amount at the central portion in the longitudinal direction becomes smaller than the toner adhesion amount at the central portion in the longitudinal direction, the image density at the central portion in the longitudinal direction is lower than the image density at both ends in the longitudinal direction. I understand that it becomes. That is, it can be seen that the image density unevenness occurs in the direction orthogonal to the conveyance direction of the recording medium P on the output image.

Here, in the first embodiment, the magnetic force and the longitudinal direction of the main magnetic poles at both ends in the longitudinal direction of the developing roller 51 are used as means for increasing the developing ability at the central portion in the longitudinal direction as compared with the developing ability at both ends in the longitudinal direction. There is a difference in the magnetic force of the main magnetic pole in the center. Specifically, the magnetic force of the main magnetic pole at the center in the longitudinal direction of the developing roller 51 is set to be larger than the magnetic force of the main magnetic poles at both ends in the longitudinal direction.
FIG. 8 is a graph showing the relationship between the developing gap N and the toner adhesion amount when the magnetic force of the main magnetic pole of the developing roller 51 is varied. In FIG. 8, a solid line graph is when the magnetic force of the main magnetic pole of the developing roller 51 is high, and a broken line graph is when the magnetic force of the main magnetic pole of the developing roller 51 is low. As shown in FIG. 8, when the main magnetic force of the developing roller 51 is set to be high, the amount of developer that comes into sliding contact with the photosensitive drum 1 in the developing region is also increased, so that the developing ability is increased.

  As described above, in the first embodiment, even if the development gap N1 at the center in the longitudinal direction is larger than the development gap N0 at both ends in the longitudinal direction, the developing ability at both ends in the longitudinal direction is larger. Since the developing ability at the central portion in the longitudinal direction is set high, the image density on the photosensitive drum 1 is made uniform over the entire longitudinal direction. That is, it is possible to suppress the occurrence of image density unevenness on the output image. Note that the above-described method of providing a difference in the magnetic force of the main magnetic pole in the developing roller 51 does not cause an increase in the size of the developing device and causes almost no change in cost.

The means for increasing the developing ability at the central portion in the longitudinal direction as compared with the developing ability at both ends in the longitudinal direction is not limited to the above-described means, and is carried on the developing roller 51 after passing through the position of the doctor blade 52. This can also be achieved by providing a difference between the amount of developer at both ends in the longitudinal direction (hereinafter referred to as “pumping amount” as appropriate) and the amount of developer at the center in the longitudinal direction (pumping amount).
Specifically, the magnetic force of the second magnetic pole (doctor pole magnetic pole) of the developing roller 51 formed at a position facing the doctor blade 52 is different between the longitudinal center and both longitudinal ends. Specifically, the magnetic force of the second magnetic pole (doctor pole magnetic pole) at the center in the longitudinal direction of the developing roller 51 is set to be larger than the magnetic force of the second magnetic pole (doctor pole magnetic pole) at both ends in the longitudinal direction.
FIG. 9 is a graph showing the relationship between the developer pumping amount and the image density (ID) on the recording medium when the developer toner density is varied. In FIG. 9, the solid line graph is when the toner concentration is 10% by weight, the broken line graph is when the toner concentration is 7% by weight, and the alternate long and short dash line graph is when the toner concentration is 4% by weight. It is. As shown in FIG. 9, as the developer pumping amount increases, the developing ability increases and the image density on the output image increases.
FIG. 10 is a graph showing the relationship between the magnetic force of the second magnetic pole (doctor pole magnetic pole) of the developing roller 51 and the developer pumping amount. As shown in FIG. 10, when the magnetic force of the second magnetic pole (doctor pole magnetic pole) of the developing roller 51 is increased, the developer pumping amount is proportionally increased.
Thus, even if the developing gap N1 at the longitudinal center is larger than the developing gap N0 at both longitudinal ends, the second magnetic pole at the longitudinal central portion compared to the second magnetic poles at both longitudinal ends. Is set high, the image density on the photosensitive drum 1 is made uniform over the entire longitudinal direction. The method of providing a difference in the magnetic force of the second magnetic pole in the developing roller 51 does not cause an increase in the size of the developing device, and there is almost no change in cost.

Further, the means for increasing the pumping amount in the central portion in the longitudinal direction as compared with the pumping amount at both ends in the longitudinal direction provides a difference in the doctor gap M (the gap between the developing roller 51 and the doctor blade 52). But it can be achieved.
Specifically, as shown in FIG. 11, the opposing portion of the doctor blade 52 is formed in a concave shape so that the doctor gap M1 at the center in the longitudinal direction is larger than the doctor gap M2 at both ends in the longitudinal direction. As a result, the pumping amount at the central portion in the longitudinal direction is larger than the pumping amount at both ends in the longitudinal direction, and the image density on the photosensitive drum 1 is made uniform over the entire longitudinal direction. Note that the method of forming the doctor blade 52 in a concave shape in this way does not cause an increase in the size of the developing device, and there is almost no change in cost.

Here, the toner used in the developing device 5 in Embodiment 1 has a volume average particle diameter of Dv (μm) and a number average particle diameter of Dn (μm).
3 ≦ Dv ≦ 8
1.00 ≦ Dv / Dn ≦ 1.40
It is formed so that the following relationship is established. Note that the closer the value of Dv / Dn is to 1, the sharper the particle size distribution.
In this way, by using a toner having a small particle size and a narrow particle size distribution, the toner charge amount distribution becomes uniform, minute dots of 600 dpi or more can be reproduced, background fog is small, and transfer efficiency is high. A high-quality image can be formed.
The volume average particle diameter (Dv) and number average particle diameter (Dn) of the toner are measured with a particle size measuring device “Multisizer III” (manufactured by Beckman Coulter, Inc.) at an aperture diameter of 100 μm. Beckman Coulter Multisizer 3 Version 3.51 "was analyzed.
Specifically, 0.5 ml of 10 wt% surfactant “alkylbenzene sulfonate Neogen SC-A” (Daiichi Kogyo Seiyaku Co., Ltd.) is added to a 100 ml glass beaker, and 0.5 g of each toner is added. The mixture was stirred with a micropartel, and then 80 ml of ion-exchanged water was added. The resulting dispersion was subjected to a dispersion treatment for 10 minutes with an ultrasonic disperser “W-113MK-II” (manufactured by Honda Electronics Co., Ltd.). Further, the dispersion was measured using the above-mentioned Multisizer III and “Isoton III” (manufactured by Beckman Coulter, Inc.) as the measurement solution.

The toner used in the developing device 5 according to the first embodiment is formed so that the shape factor SF-1 is in the range of 100 to 180 and the shape factor SF-2 is in the range of 100 to 180. It is.
The shape factor SF-1 indicates the ratio of the roundness of the toner shape, and the square of the maximum length MXLNG of the shape formed by projecting the toner onto a two-dimensional plane is divided by the graphic area AREA and multiplied by 100π / 4. Value. That is, it can be expressed by the following formula.
SF-1 = {(MXLNG) 2 / AREA} × (100π / 4)
When the value of SF-1 is 100, the shape of the toner is a true sphere, and becomes irregular as the value of SF-1 increases.
The shape factor SF-2 indicates the ratio of irregularities in the shape of the toner. The square of the perimeter PERI of the figure formed by projecting the toner on the two-dimensional plane is divided by the figure area AREA to obtain 100 / 4π. The value multiplied by. That is, it can be expressed by the following formula.
SF-2 = {(PERI) 2 / AREA} × (100 / 4π)
When the value of SF-2 is 100, there is no unevenness on the toner surface, and the unevenness of the toner surface becomes more prominent as the value of SF-2 increases.
By using such a substantially spherical toner, the adsorbing force between the toners is weakened to increase the fluidity of the toner, and the adsorbing force between the toner and the photosensitive drum 1 is weakened to improve the transferability.
Specifically, the shape factor was measured by taking a photograph of the toner with a scanning electron microscope “S-800” (manufactured by Hitachi, Ltd.) and introducing it into an image analyzer “LUSEX3” (manufactured by Nireco). Analyzed and calculated.

  As described above, in the first embodiment, the position of the developing roller 51 (developer carrier) relative to the photosensitive drum 1 (image carrier) and the doctor blade 52 (developer carrier) relative to the developing roller 51 (developer carrier). Depending on the position of the developer regulating member, there is a difference between the developing capability at both ends in the longitudinal direction and the developing capability at the central portion in the longitudinal direction. Therefore, it is possible to suppress the occurrence of uneven image density on the output image.

Embodiment 2. FIG.
A second embodiment of the present invention will be described in detail with reference to FIG.
FIG. 12 is an enlarged view showing a part of the developing device in the second embodiment, and corresponds to FIG. 4 in the first embodiment. In the developing device 5 of the second embodiment, the positional relationship between the developing roller 51 and the doctor blade 52 is different from that of the first embodiment.

  As shown in FIG. 12, in the developing device 5 according to the second embodiment, the rotation center position of the developing roller 51 is disposed above the rotation center position of the photosensitive drum 1 by a distance H. Further, the rotation center position of the developing roller 51 is arranged below the position facing the doctor blade 51 (the position where the doctor gap M is formed). The developing device 5 is set such that the developing ability at both ends in the longitudinal direction is higher than the developing ability at the central part in the longitudinal direction.

This is because when the positional relationship between the photosensitive drum 1 and the developing roller 51 and the positional relationship between the developing roller 51 and the doctor blade 52 are as described above, the development at both ends in the longitudinal direction is performed. This is because the developing gap N1 in the central portion in the longitudinal direction becomes smaller than the gap N0, and the developing capability in the central portion in the longitudinal direction becomes higher than the developing capability at both ends in the longitudinal direction as it is.
Specifically, the developing roller 51 is bent in an arcuate shape due to the component force F2 of the force F1 that presses the doctor blade 52 against the upstream side of the position where the developing roller 51 and the doctor blade 52 face each other. That is, the central portion in the longitudinal direction of the developing roller 51 is deformed to the position indicated by the broken line in FIG. 12 and approaches the photosensitive drum 1. The development gap N1 at the longitudinal center is smaller than the development gap N0 at both longitudinal ends. As a result, in the developing region, the developing electric field at the longitudinal center is higher than the developing electric field at both ends in the longitudinal direction, and the developing ability at the longitudinal center is higher than the developing ability at both ends in the longitudinal direction. End up.

Here, in the second embodiment, the magnetic force and the longitudinal direction of the main magnetic poles at both ends in the longitudinal direction of the developing roller 51 are used as means for lowering the developing ability at the central portion in the longitudinal direction as compared with the developing ability at both ends in the longitudinal direction. There is a difference in the magnetic force of the main magnetic pole in the center. Specifically, the magnetic force of the main magnetic pole at the center in the longitudinal direction of the developing roller 51 is set to be smaller than the magnetic force of the main magnetic poles at both ends in the longitudinal direction.
As a means for lowering the developing ability at the central portion in the longitudinal direction as compared with the developing ability at both ends in the longitudinal direction, the magnetic force of the second magnetic pole at the central portion in the longitudinal direction of the developing roller 51 is used. The opposing portion of the doctor blade 52 can be formed in a convex shape so that the doctor gap M1 at the center in the longitudinal direction is smaller than the doctor gap M2 at both ends in the longitudinal direction. .

  As described above, in the second embodiment, even if the developing gap N1 at the center in the longitudinal direction is smaller than the developing gap N0 at both ends in the longitudinal direction, the developing capability in the longitudinal direction is compared with the developing ability at both ends in the longitudinal direction. Since the developing capability of the central portion is set low, the image density on the photosensitive drum 1 is made uniform over the entire longitudinal direction.

  As described above, in the second embodiment, as in the first embodiment, the position of the developing roller 51 (developer carrier) with respect to the photosensitive drum 1 (image carrier) and the developing roller 51 (development) The developing device 5 has a difference between the developing ability at both ends in the longitudinal direction and the developing ability at the center in the longitudinal direction according to the position of the doctor blade 52 (developer regulating member) with respect to the agent carrying member). Therefore, it is possible to suppress the occurrence of uneven image density on the output image without increasing the size and cost.

Embodiment 3 FIG.
A third embodiment of the present invention will be described in detail with reference to FIG.
FIG. 13 is an enlarged view showing a part of the developing device in the third embodiment, and corresponds to FIG. 12 in the second embodiment. In the developing device 5 of the third embodiment, the positional relationship between the developing roller and the doctor blade is different from that of the second embodiment.

  As shown in FIG. 13, in the developing device 5 according to the third embodiment, the rotation center position of the developing roller 51 is disposed below the rotation center position of the photosensitive drum 1 by a distance H. Further, the rotation center position of the developing roller 51 is disposed below the position facing the doctor blade 51. The developing device 5 is set so that the developing ability at both ends in the longitudinal direction is lower than the developing ability at the center in the longitudinal direction.

  This is because when the positional relationship between the photosensitive drum 1 and the developing roller 51 and the positional relationship between the developing roller 51 and the doctor blade 52 are as described above, the longitudinal direction of the developing roller 51 By deforming the central portion to the position indicated by the broken line in FIG. 13, the developing gap N1 at the central portion in the longitudinal direction becomes larger than the developing gap N0 at both ends in the longitudinal direction. This is because the developing ability at the central portion in the longitudinal direction is lower than that in the comparative example.

  Here, in the third embodiment, the magnetic force and the longitudinal direction of the main magnetic poles at both ends in the longitudinal direction of the developing roller 51 are used as means for increasing the developing ability at the central portion in the longitudinal direction as compared with the developing ability at both ends in the longitudinal direction. There is a difference in the magnetic force of the main magnetic pole in the center. Specifically, the magnetic force of the main magnetic pole at the center in the longitudinal direction of the developing roller 51 is set to be larger than the magnetic force of the main magnetic poles at both ends in the longitudinal direction.

  As described above, in the third embodiment, even if the developing gap N1 at the center in the longitudinal direction is larger than the developing gap N0 at both ends in the longitudinal direction, the developing capability in the longitudinal direction is larger than the developing ability at both ends in the longitudinal direction. Since the developing capability at the center is set high, the image density on the photosensitive drum 1 is made uniform over the entire longitudinal direction.

  As described above, also in the third embodiment, the position of the developing roller 51 (developer carrier) relative to the photosensitive drum 1 (image carrier) and the developing roller 51 (development) are the same as in the above embodiments. The developing device 5 has a difference between the developing ability at both ends in the longitudinal direction and the developing ability at the center in the longitudinal direction according to the position of the doctor blade 52 (developer regulating member) with respect to the agent carrying member). Therefore, it is possible to suppress the occurrence of uneven image density on the output image without increasing the size and cost.

Embodiment 4 FIG.
The fourth embodiment of the present invention will be described in detail with reference to FIG.
FIG. 14 is an enlarged view showing a part of the developing device in the fourth embodiment, and corresponds to FIG. 13 in the third embodiment. In the developing device 5 of the fourth embodiment, the positional relationship between the developing roller 51 and the doctor blade 52 is different from that of the third embodiment.

  As shown in FIG. 14, in the developing device 5 in the fourth embodiment, the rotation center position of the developing roller 51 is disposed below the rotation center position of the photosensitive drum 1 by a distance H. Further, the rotation center position of the developing roller 51 is disposed above the position facing the doctor blade 51. The developing device 5 is set such that the developing ability at both ends in the longitudinal direction is higher than the developing ability at the central part in the longitudinal direction.

  This is because when the positional relationship between the photosensitive drum 1 and the developing roller 51 and the positional relationship between the developing roller 51 and the doctor blade 52 are as described above, the longitudinal direction of the developing roller 51 By deforming the central portion to the position of the broken line in FIG. 14, the developing gap N1 at the longitudinal central portion becomes smaller than the developing gap N0 at both longitudinal end portions, and as it is, the developing ability at both longitudinal end portions is improved. This is because the developing ability at the central portion in the longitudinal direction is higher than that.

  Here, in the fourth embodiment, the magnetic force and the longitudinal direction of the main magnetic poles at both ends in the longitudinal direction of the developing roller 51 are used as means for lowering the developing ability at the center in the longitudinal direction as compared with the developing ability at both ends in the longitudinal direction. There is a difference in the magnetic force of the main magnetic pole in the center. Specifically, the magnetic force of the main magnetic pole at the center in the longitudinal direction of the developing roller 51 is set to be smaller than the magnetic force of the main magnetic poles at both ends in the longitudinal direction.

  As described above, in the fourth embodiment, even if the developing gap N1 at the center in the longitudinal direction is smaller than the developing gap N0 at both ends in the longitudinal direction, the developing capability in the longitudinal direction is compared with the developing ability at both ends in the longitudinal direction. Since the developing capability of the central portion is set low, the image density on the photosensitive drum 1 is made uniform over the entire longitudinal direction.

  As described above, also in the fourth embodiment, the position of the developing roller 51 (developer carrier) with respect to the photosensitive drum 1 (image carrier) and the developing roller 51 (development) are the same as in the above embodiments. The developing device 5 has a difference between the developing ability at both ends in the longitudinal direction and the developing ability at the center in the longitudinal direction according to the position of the doctor blade 52 (developer regulating member) with respect to the agent carrying member). Therefore, it is possible to suppress the occurrence of uneven image density on the output image without increasing the size and cost.

  It should be noted that the present invention is not limited to the above-described embodiments, and within the scope of the technical idea of the present invention, the embodiments can be modified as appropriate in addition to those suggested in the above-described embodiments. it is obvious. Further, the number, position, shape, and the like of the constituent members are not limited to the above-described embodiments, and the number, position, shape, and the like that are suitable for implementing the present invention can be used.

1 is an overall configuration diagram illustrating an image forming apparatus according to Embodiment 1 of the present invention. FIG. 3 is a cross-sectional view showing the vicinity of a process cartridge in the image forming apparatus. FIG. 3 is a cross-sectional view of a part of the process cartridge of FIG. 2 as viewed from above. It is an enlarged view showing a part of the developing device. It is a figure which shows the state which the developing roller bent. 6 is a graph showing a relationship between a development gap and a toner adhesion amount. It is a graph which shows the change of the image density by the position on an output image. 6 is a graph showing the relationship between the development gap and the toner adhesion amount when the magnetic force of the main magnetic pole of the developing roller is varied. 6 is a graph showing the relationship between the developer pumping amount and the image density on a recording medium when the developer toner density is varied. It is a graph which shows the relationship between the magnetic force of the 2nd magnetic pole of a developing roller, and the pumping amount of a developing agent. It is the figure which looked at the developing roller and the doctor blade in the longitudinal direction. It is an enlarged view which shows a part of developing device in Embodiment 2 of this invention. It is an enlarged view which shows a part of developing device in Embodiment 3 of this invention. It is an enlarged view which shows a part of developing device in Embodiment 4 of this invention.

Explanation of symbols

1, 1Y, 1M, 1C, 1K photosensitive drum (image carrier),
5 Development device (development unit),
6, 6Y, 6M, 6C, 6K process cartridge (imaging part),
51 Development roller (developer carrier),
52 Doctor blade (developer regulating member),
100 Image forming apparatus body (apparatus body),
G developer,
M Doctor gap,
N, N0, N1 Development gap.

Claims (5)

A developing device for developing a latent image formed on an image carrier,
A developer carrying body facing the image carrying body and carrying a developer composed of a carrier and a toner;
A developer regulating member that faces the developer carrying member and regulates the amount of the developer carried on the developer carrying member;
With
The developer carrier has a rotational center position disposed above the rotational center position of the image carrier, and a rotational center position disposed above the position facing the developer regulating member. And
The amount of developer carried on the developer carrying member after passing through the position of the developer regulating member is larger than the both ends in the longitudinal direction so that the central portion in the longitudinal direction is larger than the both ends in the longitudinal direction. 2. A developing apparatus according to claim 1, wherein a gap of the developer regulating member is formed so as to gradually increase from both ends in the longitudinal direction to a central portion in the longitudinal direction. The toner has a volume average particle diameter of Dv (μm) and a number average particle diameter of Dn (μm).
3 ≦ Dv ≦ 8
1.00 ≦ Dv / Dn ≦ 1.40
The developing device according to claim 1, wherein the following relationship is established.   3. The toner according to claim 1, wherein the toner is formed so that a shape factor SF-1 is in a range of 100 to 180 and a shape factor SF-2 is in a range of 100 to 180. Development device. A process cartridge that is detachably installed on the main body of the image forming apparatus,
4. A process cartridge, wherein the developing device according to claim 1 and the image carrier are integrated.   An image forming apparatus comprising the developing device according to claim 1 and the image carrier.

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