JP4802301B2 - Developing device, process unit, and image forming apparatus - Google Patents

Description

  The present invention relates to a developing device that develops a latent image carried on a latent image carrier such as a photoconductor, and more specifically, by rotating a helical member having a helical shape around the center of the helix. In contrast, the present invention relates to an improvement in a transport body that transports the developer in the axial direction while revolving the developer.

  2. Description of the Related Art Conventionally, a developing device described in Patent Document 1 is known as a developing device that uses this type of conveyance body. This developing device has a first stirring screw and a second stirring screw which are conveying bodies in which spiral blades are projected from a peripheral surface of a rotating shaft member in a developer storage chamber for storing a developer. Yes. In addition, the developer carried on the surface is transported to a position facing the latent image carrier with its own rotation in a developing unit provided next to the developer storage chamber, and the latent image on the latent image carrier is conveyed. A developing roller as a developing member for developing the image is provided. No partition wall is provided between the developer accommodating chamber and the developing portion, and the developing roller in the developing portion and the second agitating screw in the developer accommodating chamber are mutually peripheral while maintaining a parallel relationship with each other. It arrange | positions so that a surface may be opposed. A first storage chamber and a second storage chamber partitioned by a partition wall are formed in the developer storage chamber, and a second stirring screw is disposed in the second storage chamber closer to the developing unit. A first stirring screw is disposed in the first storage chamber far from the developing unit. The developer in the first storage chamber is conveyed in the direction of the screw axis while being revolved around the screw shaft as the first stirring screw rotates. And if it conveys to the one end part of the axial direction of a 1st stirring screw, it will be delivered to a 2nd storage chamber from a 1st storage chamber through a communicating port. Next, in the process of being conveyed in the axial direction of the screw while being rotated along with the rotation of the second agitating screw in the second storage chamber, a part thereof is pumped up to the developing roller and contributes to development, or the developing roller To the second conveying screw. The developer transported to one end of the second transport screw is returned to the first storage chamber through the communication port because there is no second storage chamber.

  In such a configuration, the developer density unevenness corresponding to the undulation may be generated by the undulation of the surface of the developer conveyed by the second agitating screw. Specifically, the cross section of the second stirring screw has a shape in which a protrusion by a spiral blade protrudes from a part of the outer edge of the circular shaft member. This protrusion revolves around the shaft member as the shaft member rotates. In the process in which the protrusion moves from the position farthest away from the developing roller along with the revolution in a direction approaching the developing roller, the developer is pushed toward the developing roller by the protrusion. It gradually rises toward. Then, this rise increases the amount of developer between the second stirring screw and the developing roller, and the developing density increases. On the other hand, in the process in which the protrusion at the position closest to the developing roller moves away from the developing roller, the developer moves in the same direction following the protrusion, so that the surface of the developer gradually increases. To descend. This lowering reduces the amount of developer between the second stirring screw and the developing roller, thereby lowering the developing density. Since the protrusions formed by the spiral blades are formed in a spiral shape in the axial direction of the shaft member, such rising and lowering of the developer surface occurs with a phase shift in the axial direction. As a result, the surface of the developer undulates in the screw axis direction, and uneven development density corresponding to the undulation occurs.

  On the other hand, conventionally, a developing device using a multi-thread screw having a plurality of spiral blades having a multi-strand structure as a transport body is known. For example, Patent Documents 2 and 3 each describe a developing device using a two-thread screw having two spiral blades that form a two-strand structure (double spiral structure). The cross-section of the two-thread screw is such that the protrusion of the first spiral blade protrudes from a part of the outer edge of the circular shaft member, and the second stripe screw is symmetrical with respect to the protrusion by 180 [°]. The protrusion by the spiral blade protrudes. In the two-thread screw having such a shape, in the process in which one protrusion moves from the position farthest away from the developing roller in the direction approaching the developing roller, the other protrusion at the position closest to the developing roller is Move away from the developing roller. This offsets the rise of the developer surface due to the movement of one protrusion and the decrease in the surface of the developer due to the movement of the other protrusion, thereby suppressing uneven development density due to the undulation of the developer surface. it can.

  However, in the two-thread screw, in the transverse cross-sectional direction, the developer is caused to be inactive by revolving while being sandwiched between the protrusion by the first spiral blade and the protrusion by the second spiral blade. Become. For this reason, there is a possibility that the stirring ability of the developer is lowered as compared with the single screw, and various problems are caused. For example, when a two-component developer containing a toner and a magnetic carrier is used as the developer, toner density unevenness of the two-component developer due to insufficient stirring may appear and cause development density unevenness. In addition, when a one-component developer that does not contain a magnetic carrier is used as a developer, stirring of sufficiently charged toner and poorly charged toner becomes insufficient, and a large amount of poorly charged toner is locally added. May cause soiling due to the presence. The background stain is a phenomenon in which a poorly charged toner adheres to a non-image portion.

  The present invention has been made in view of the above background, and an object thereof is to provide the following developing device, a process unit using the same, and an image forming apparatus. That is, a developing device or the like that can suppress background unevenness due to developer agitation failure and development density unevenness while suppressing development density unevenness due to the surface of the developer conveyed by the transport body.

In order to achieve the above object, according to the first aspect of the present invention, the spiral member having a spiral shape is rotated around the center of the spiral so that the developer is revolved with respect to the axis and conveyed in the axial direction. A plurality of conveying members, and a developing member that develops the latent image on the latent image carrier by conveying the developer carried on the surface to a position facing the latent image carrier of the image forming apparatus as the surface moves. And supplying the developer to the developing member while transferring the developer between the adjacent conveying members, and among the plurality of conveying members, the conveying member is the conveying member disposed closest to the developing member. In the developing device for supplying the developer to the developing member by a body, among the plurality of transport bodies, the supply transport body is a member having a plurality of spiral members having a multi-strand structure, and For other transport bodies, the above spiral member Or used as forming the Article 1 helical structure, or a plurality of helical members forming a multi-start helical structure is characterized in that using the one having a smaller number of threads than the feed carrier.
Further, the invention of claim 2 is the developing device according to claim 1, wherein, as the supply transport body, the number of the spiral members is an even number, and the phase of each spiral member is 360 [°]. What is different from each other by the angle divided by is used.
According to a third aspect of the present invention, in the developing device of the first or second aspect, as the spiral member of the supply transport body, the cross-sectional shape in the thickness direction is asymmetric between the upstream side and the downstream side in the developer transport direction. And the thing whose thickness of the downstream is larger than the upstream is used.
According to a fourth aspect of the present invention, in the developing device according to any one of the first to third aspects, as the plurality of transport bodies, the one in which the spiral member protrudes from the peripheral surface of the rotating shaft member is used. The supply transport body is characterized in that the diameter of the shaft member is larger than the diameter of the shaft member of the other transport body and the spiral diameter of the spiral member is the same as that of the other transport body. To do.
According to a fifth aspect of the present invention, in the developing device according to any one of the first to fourth aspects, as the supply transport body, the spiral pitch in the axial direction of the multi-strand spiral structure is 0.3 to 0 of the other transport body. It is characterized by using a thing which is .7 times.
According to a sixth aspect of the present invention, in the developing device according to any one of the first to fifth aspects, the value obtained by dividing the bending elastic modulus M [MPa] by the length L [mm] in the axial direction as the supply transport body. Is characterized in that a material having a value of 25 or more is used.
According to a seventh aspect of the present invention, there is provided the developing device according to any one of the first to sixth aspects, wherein the space between the tip of the spiral member of the supply transport body and the wall for holding the developer around the supply transport body. This clearance is characterized in that it is smaller than the clearance in the other transport bodies.
In the invention of claim 8, at least a latent image carrier that carries a latent image and a developing device that develops the latent image on the latent image carrier are held as a single unit on a common holder. In the process unit that is detachable integrally with the image forming apparatus, the developing device according to any one of claims 1 to 7 is used as the developing device.
According to a ninth aspect of the present invention, there is provided an image forming apparatus having a latent image carrier that carries a latent image and a developing device that develops the latent image on the latent image carrier. 7 to 7 is used.
According to a tenth aspect of the present invention, in the image forming apparatus according to the ninth aspect, the developing device is provided with a plurality of developing devices for developing latent images in different colors.

In order to achieve the above object, the invention of claim 1 comprises a rotating shaft member and a helical member having a helical shape projecting on the peripheral surface of the shaft member, the shaft member being the center . by rotating Te, a plurality of carrier for transporting the developer in the axial direction while revolving with respect to the shaft member, the latent image bearing member of an image forming apparatus with a developer carried on the surface to surface movement and A developing member that develops the latent image on the latent image carrier and conveys the developer toward the developing member while transferring the developer between adjacent conveying members. Of the plurality of transport bodies, the supply transport body in the developing device that supplies the developer to the developing member by a supply transport body that is a transport body disposed adjacent to the developing member among the transport bodies. It is those having a plurality of the helical member having a multi-start helical structure There are and used as the diameter of the shaft member is larger than the diameter of the shaft member of another carrier, and, for the other carrier, use those forming the Article 1 helical structure by 1 above helical member Or a member having a plurality of spiral members having a multi-spiral spiral structure with a number of strips smaller than that of the supply and transport body.
Further, the invention of claim 2 is the developing device according to claim 1, wherein, as the supply transport body, the number of the spiral members is an even number, and the phase of each spiral member is 360 [°]. What is different from each other by the angle divided by is used.
Further, the invention of claim 3, in the developing apparatus according to claim 1 or 2, as a helical member of the supply conveyance member, the cross-sectional shape of the developer conveying direction is the boundary of the center line of the developer conveyance direction in the spiral outer edge be asymmetric between the upstream portion and the downstream portion, and the developer size in the conveying direction of the upper flow side portion is used as less than developer size in the conveying direction of the downstream side portion It is characterized by.
The invention of claim 4, in any of the developing apparatus of claims 1 to 3, as the upper Symbol supply conveyance member, the helical diameter of the upper Symbol helical member is used as the same as the other carrier It is characterized by.
According to a fifth aspect of the present invention, in the developing device according to any one of the first to fourth aspects, as the supply transport body, the spiral pitch in the axial direction of the multi-strand spiral structure is 0.3 to 0 of the other transport body. It is characterized by using a thing which is .7 times.
According to a sixth aspect of the present invention, in the developing device according to any one of the first to fifth aspects, the value obtained by dividing the bending elastic modulus M [MPa] by the length L [mm] in the axial direction is used as the supply transport body. What is more than 25 is used .
Also, the invention of claim 7, at least, is held and the latent image bearing member for bearing a latent image, the common holding member and a developing device as a unit for developing a latent image on the latent image bearing member Further, in the process unit that is detachably attached to the image forming apparatus, the developing device according to any one of claims 1 to 6 is used as the developing device.
According to an eighth aspect of the present invention, there is provided an image forming apparatus having a latent image carrier that carries a latent image and a developing device that develops the latent image on the latent image carrier. A developing device according to any one of 6 to 6 is used.
According to a ninth aspect of the present invention, in the image forming apparatus according to the eighth aspect of the present invention, the developing device is provided with a plurality of devices for developing latent images into different colors.

1 is a schematic configuration diagram illustrating a printer according to an embodiment. FIG. 2 is an enlarged configuration diagram illustrating a developing device of the printer. The perspective view which shows the lower case of the developing device. The perspective view which shows the upper case of the developing device. The side view which shows the 1st conveyance screw of the developing device. The longitudinal cross-sectional view which shows the 1st conveyance screw. The side view which shows the 2nd conveyance screw of the developing device. The longitudinal cross-sectional view which shows the 2nd conveyance screw. The schematic diagram which shows the said 2nd conveyance screw and the two-component developer conveyed by this. FIG. 3 is a schematic diagram showing the first conveying screw and a two-component developer conveyed thereby. The expanded longitudinal cross-sectional view which shows the 1st example of a 2nd conveyance screw. The expanded longitudinal cross-sectional view which shows the 2nd example of a 2nd conveyance screw. The graph which shows the relationship between the specification of a 2nd conveyance screw, the toner density | concentration of a two-component developer, and a development density nonuniformity rank. The graph which shows the relationship between ML ratio (M / L) of a 2nd conveyance screw, the shake amount of a 2nd conveyance screw, and a development density nonuniformity rank. The schematic block diagram which shows an example of the process unit to which this invention is applied. 6 is a graph showing the relationship between the difference in height of the two-component developer at the end of the first storage chamber and the end of the second storage chamber of the developing device and the helical pitch magnification of the supply transport body relative to another transport body. The graph which shows the relationship between the development density nonuniformity rank of a printout image, and the helical pitch magnification with respect to the other conveyance body of a supply conveyance body.

Hereinafter, an electrophotographic printer (hereinafter simply referred to as “printer”) will be described as an embodiment of an image forming apparatus to which the present invention is applied.
First, a basic configuration of the printer according to the present embodiment will be described. FIG. 1 is a schematic configuration diagram illustrating a printer according to the present embodiment. This printer includes a charging device 2, an optical writing device 3, a developing device 10, a transfer device 5, a drum cleaning device 6, and a charge eliminating device 7 around a drum-shaped photoconductor 1 as an image carrier. Further, a fixing device 8 disposed on the right side of the transfer device 5 in the drawing is also provided.

  The photosensitive member 1 that is driven to rotate clockwise in the drawing by a driving means (not shown) has a photosensitive layer formed on the surface of a raw tube made of aluminum or the like, and is positively or negatively charged by the charging device 2 as it rotates. Is uniformly charged. Then, the potential of the exposure unit is attenuated by scanning with laser light emitted from the optical writing device 3 that constructs optical scanning information based on image information sent from a personal computer (not shown) or the like. As a result, an electrostatic latent image having a lower potential than the background portion around the exposed portion is carried. This electrostatic latent image contains toner and a magnetic carrier carried on the developing sleeve 13 of the developing device 10 when passing through the developing position which is a position facing the developing device 10 as the photosensitive member 1 rotates. Is rubbed against the two-component developer. Then, for example, a negatively charged toner contained in the two-component developer is electrostatically adhered to be developed into a toner image.

  A transfer position where the photoconductor 1 and the transfer device 5 face each other is formed downstream of the developing position in the rotation direction of the photoconductor 1. When the toner image developed on the photosensitive member 1 enters this transfer position as the photosensitive member 1 rotates, the toner image is conveyed onto a sheet-like recording paper P that is conveyed in time by a sheet feeding unit (not shown). Superimposed. Then, it is electrostatically transferred onto the recording paper P under the influence of a transfer electric field formed between the photoreceptor 1 and the transfer device 5. The recording paper P electrostatically attached to the photosensitive member 1 during the transfer is separated from the photosensitive member by the action of the weight, rigidity, paper, and a member for separating and conveying the paper. The recording paper P on which the toner image is electrostatically transferred in this way is sent from the transfer position to the fixing device 8.

  The fixing device 8 forms a fixing nip by contact between a heating roller 8a having a heat source (not shown) and a pressing roller 8b pressed against the heating roller 8a. These rollers are rotationally driven so as to move the respective surfaces in the same direction at the mutual contact portions. The recording paper P sent to the fixing device 8 having such a configuration is sandwiched in the fixing nip and conveyed in the roller surface moving direction. At this time, the toner image is fixed by the influence of nip pressure and heating. After fixing, the recording paper P is discharged out of the apparatus via a paper discharge means (not shown).

  When the surface of the photoreceptor 1 that has passed through the transfer position passes through a position facing the drum cleaning device 6 as it rotates, the transfer residual toner is cleaned. Then, after the residual charge is removed by the static eliminator 7, it is uniformly charged by the charging means and returns to the initial state.

  In FIG. 1, the charging device 2 is a system in which a biasing member such as a charging roller to which a charging bias is applied is rotated while being opposed to the photoconductor 1, but a non-contact system such as a charging charger is used. May be used. Moreover, although the example which provided the optical writing device 3 which forms an electrostatic latent image by irradiation of a laser beam was shown, what performs optical writing by the LED light from an LED array may be used. Further, an electrostatic latent image may be formed by ion ejection or the like instead of optical writing. Further, as the transfer device 5, a roller contact type in which a transfer roller to which a transfer bias is applied is brought into contact with the photosensitive member 1 is shown, but a belt contact type in which a belt is brought into contact or a non-contact type such as a transfer charger. May be used. Further, the drum cleaning device 6 has a scraping method using a cleaning blade, but an electrostatic recovery method that contacts a brush or a roller to which a cleaning bias is applied may be used. Further, although an example in which the drum-shaped photoconductor 1 is provided as the latent image carrier has been described, a belt-shaped photoconductor may be used. Alternatively, the photosensitive unit 1 and an apparatus including at least the developing device installed around the photosensitive unit 1 may be a process unit that is housed in a common casing as a single unit. For example, the process unit is configured such that the photosensitive member 1, the charging device 2, the developing device 10, and the drum cleaning device 6 are detachable from the printer body as one process unit.

  FIG. 2 is an enlarged configuration diagram illustrating the developing device 10. FIG. 3 is a perspective view showing the lower case 11 of the developing device 10. FIG. 4 is a perspective view showing the upper case 12 of the developing device 10. In FIG. 2, the casing of the developing device 10 can be divided into a lower case 11 and an upper case 12. The lower case 11 forms a first storage chamber 11 a and a second storage chamber 11 b that store the two-component developer, and a developing portion 11 c that stores the developing sleeve 13. Further, the upper case 12 forms an initial agent storage chamber 12a for storing an initial agent described later above the first storage chamber 11a of the lower case 11.

  In the lower case 11, the first storage chamber 11a and the second storage chamber 11b are partitioned by a partition wall 11d. And in the 1st storage chamber 11a, the 1st stirring screw 14 which is a conveyance body is arrange | positioned rotatably. In addition, a second stirring screw 15 serving as a supply / conveyance body is rotatably disposed in the second storage chamber 11b. As shown in FIG. 3, the second storage chamber 11 b and the developing unit 11 c that stores the developing sleeve 13 that is a developing member are not partitioned by a partition wall, and the second transport screw 15 and the developing sleeve 13 are parallel to each other. Keep each other's peripheral surfaces facing each other.

  In FIG. 2, an opening is provided in the side wall of the developing portion 11c of the lower case 11, and the developing sleeve 13 in the developing portion 11c is exposed by a driving means (not shown) while exposing a part of its peripheral surface from the opening. It is driven to rotate counterclockwise in the figure.

  In the developing device 10 when shipped from the factory, the sealing film 15 is sandwiched between the initial agent storage chamber 12 a of the upper case 12 and the first storage chamber 11 a of the lower case 11. In the initial agent storage chamber 12a, an initial developer containing a toner and a magnetic carrier (not shown) having a toner concentration of about 7% by weight is stored. When the user pulls out the sealing film 15, the initial developer in the initial material storage chamber 12a falls into the first storage chamber 11a by its own weight. Then, along with the rotation of the first conveying screw 11 that is rotationally driven by a driving means (not shown), the screw axial direction is conveyed from the rear side to the front side (the direction of arrow A in FIG. 3). A communication port (not shown) is provided in the partition wall 11d that partitions the first storage chamber 11a and the second storage chamber 11b at the rear end and the front end of the developing device 10 in the drawing. The initial developer transported to the end on the near side in the figure by the first transport screw 14 is sent from the first storage chamber 11a into the second storage chamber 11b through the communication port. And this time, it is conveyed from the near side in the figure to the far side (in the direction of arrow B in FIG. 3) by the second conveying screw 15 that is rotationally driven by a driving means (not shown), and the second end is located at the end on the far side in the figure. It returns to the 1st storage chamber 11a through the communication port from the storage chamber 11b. As described above, in the developer accommodating chamber of the developing device 10, the two-component developer is circulated and conveyed between the first accommodating chamber 11a and the second accommodating chamber 11b, and the initial developer is circulated by this circulating conveyance. Spread throughout the developer chamber.

  In the cylindrical developing sleeve 13, a magnet roller 18 having a plurality of magnetic poles in the circumferential direction is fixed so as not to rotate with the developing sleeve 13. When the printing operation is started, a part of the two-component developer conveyed in the second storage chamber 11b by the second conveying screw 15 is caused by the magnetic force generated by the pumping magnetic pole (not shown) of the magnet roller 18 to Attracted to the surface. Then, the surface of the developing sleeve 13 that is driven to rotate counterclockwise in the figure is pumped up from the second storage chamber 11b by the surface movement of the developing sleeve 13, and the doctor blade 19 facing the developing sleeve 13 with a predetermined gap on the sleeve. Layer thickness is regulated. Thereafter, when the developing sleeve 13 rotates, the toner passes through the above-described developing position, contributes to the development, consumes the toner, and returns to the lower case 11. Then, due to the influence of the repulsive magnetic field formed by the two repulsive magnetic poles provided on the magnet roller 18, it is separated from the developing sleeve 13 and returned to the second storage chamber 11b.

  The two-component developer whose toner density has been reduced by development enters the first storage chamber 11a from the second storage chamber 11b and is transported by the first transport screw 14 to the bottom wall of the lower case 11. It passes directly above the provided toner density sensor 17. The toner concentration sensor 17 is a known magnetic permeability sensor, and outputs a voltage corresponding to the magnetic permeability of the two-component developer. Since there is a correlation between the magnetic permeability of the two-component developer and the toner concentration, the toner concentration sensor 17 detects the toner concentration of the two-component developer.

  In FIG. 4, a part of the upper case 12 is an upper wall of the first storage chamber 11a shown in FIG. 2, and a toner supply port 12b is provided at the upper wall. The printer includes a toner cartridge (not shown) and a toner conveying device (not shown) that conveys toner inside the toner cartridge toward the developing device 10 and replenishes the toner into the first storage chamber 11a from the toner supply port 12b. Further, a control circuit (not shown) for monitoring a decrease in the toner concentration of the two-component developer based on the output voltage value from the toner concentration sensor 17 shown in FIG. 2, and driving and controlling the toner conveying device based on the monitoring result. Also have. By the drive control of the toner conveying device by this control circuit, the toner is appropriately supplied to the first storage chamber 11a, and the toner concentration of the two-component developer in the developer storage chamber is maintained within a certain range.

  The upper case 12 is provided with an exhaust port for discharging the gas in the developing portion 11c to the outside when the pressure in the casing rises, and a filter 20 covering the exhaust port. In the developing unit 11 c, the gas around the developing sleeve 13 is exhausted to the outside through the filter 20 from the exhaust port due to the airflow generated as the developing sleeve 13 rotates. As a result, the gas existing between the developing sleeve 13 and the photosensitive member is taken into the developing unit 13c from the casing opening and discharged from the exhaust port, and the toner scattering from the developing sleeve 13 into the printer is created. Can be prevented.

Next, a characteristic configuration of the printer will be described.
FIG. 5 is a side view showing the first conveying screw 14. FIG. 6 is a longitudinal sectional view showing the first transport screw 14. In these drawings, a first transport screw 14 as a transport body includes a round bar-shaped shaft member 14a that is rotated by a driving means (not shown), and a spiral blade 14b that is a spiral member projecting spirally on the surface thereof. have. Then, by rotating the spiral blade 14b around the center of the shaft member 14a that is the center of the spiral, the two-component developer (not shown) is rotated with respect to the shaft member 14a while being in the axial direction. Transport in the direction of arrow A. When the two-component developer is transported to the vicinity of the screw end in the direction of arrow A in the drawing, it is transferred to a second transport screw (not shown). As shown in the figure, the first conveying screw 14 is a single-thread screw having a single-strand structure having only one spiral blade 14b on the circumferential surface of the shaft member 14a.

  FIG. 7 is a side view showing a second conveying screw 15 which is a supply conveying member for supplying a two-component developer to a developing sleeve (not shown). FIG. 8 is a longitudinal sectional view showing the second transport screw 15. The second conveying screw 15 has a round bar-shaped shaft member 15a that is rotated by a driving means (not shown), and two spiral blades 15b and 15c that are spiral members protruding in a spiral manner on the surface of the shaft member 15a. Yes. These spiral blades 15b and 15c have a double spiral structure (double spiral structure), and are fixed on the shaft member 15a so that the phases of the spirals are shifted by 180 [°]. Each of the two-component developers (not shown) is conveyed in the direction of the arrow B in the figure, which is the axial direction, while revolving a two-component developer (not shown) with respect to the shaft member 14a. When the two-component developer is transported to the vicinity of the screw end in the direction of arrow B in the figure, it is transferred to a first transport screw (not shown). In addition, the 2nd conveyance screw 15 is a conveyance body arrange | positioned nearest to the developing sleeve 13 which is a developing member among two conveyance screws, as shown in FIG.

  The second conveying screw 15 having a two-helix structure shown in FIG. 7 and FIG. 8 is a two-component developing centering on the shaft member 15a by two helix blades 15b and 15c whose helix phases are shifted from each other by 180 [°]. Revolve the agent. In such a revolution, the undulations in the axial direction of the surface of the two-component developer are offset from each other by the two undulations having a phase difference of 180 [°]. As shown in the figure, the amplitude becomes gentle with a small amplitude. In this way, by suppressing the undulation of the surface of the two-component developer 30, it is possible to suppress the occurrence of development density unevenness (screw pitch unevenness) due to the undulation.

  As a method of reducing the surface undulation of the two-component developer 30, there is a method of further reducing the helical pitch of the conveying screw having a single-helix structure. In this method, development in the axial direction is performed by the amount of the reduced helical pitch. The agent conveyance speed is reduced. Due to this decrease, there is a possibility that the balance of the transport amount of the two-component developer among the plurality of transport screws in the developer accommodating chamber is lost, or the toner supply amount to the developing sleeve cannot catch up with the toner consumption accompanying the development. . On the other hand, the two spiral blades 15b and 15c shown in the figure have a spiral pitch as a double spiral structure that is half the length of the first conveying screw. The same as the first conveying screw. In such a configuration, the developer conveyance speed is the same as that of the first conveyance screw, so that the occurrence of the above-described problems can be avoided.

  On the other hand, since the first conveying screw 14 shown in FIGS. 5 and 6 has a single spiral structure, the surface of the two-component developer 30 is greatly undulated as shown in FIG. The agent is not supplied to the developing sleeve. For this reason, even if the surface of the two-component developer is greatly undulated, it does not cause uneven development density. Rather, there is an advantage that the two-component developer is stirred well by the large undulation and then transferred to the second conveying screw. As described above, in this printer, the second conveying screw serving as the supply conveying member is formed in a multi-helix structure to suppress development density unevenness due to the undulation of the surface of the two-component developer, and the first conveying screw 14 serving as the other conveying member. Can be prevented from various problems due to poor stirring of the two-component developer.

  In addition, as the 1st conveyance screw 14, it is not necessary to use the thing of a 1 line | wire spiral structure, but it is necessary to use a thing with fewer stripes than a 2nd conveyance screw (15). The second conveying screw (15) does not necessarily need to have a two-strand structure, but the number of strips is an even number and the phase of each spiral blade is 360 [°]. It is desirable to use the one shifted by the divided angle. By using such a configuration, in the cross section, the protrusions by other spiral blades are always positioned at a position that is 180 [°] point-symmetric with respect to the protrusions by a certain spiral blade. This is because the undulations of the surface of the component developer can be offset each other.

Next, printers according to the respective examples in which a more characteristic configuration is added to the printer according to the embodiment will be described.
[First embodiment]
FIG. 11 is an enlarged longitudinal sectional view showing a first example of the second transport screw 15. FIG. 12 is an enlarged longitudinal sectional view showing a second example of the second transport screw 15. In these drawings, an arrow B indicates the conveyance direction of the two-component developer. As shown in the drawing, the two spiral blades 15b and 15c in the second conveying screw 15 of the first example shown in FIG. 11 have cross-sectional shapes in the thickness direction of the blades, respectively, upstream and downstream in the developer conveying direction. The line is symmetrical. Specifically, the cross-sectional shape in the thickness direction is a trapezoid as shown in the figure, and the left and right are symmetrical with respect to the dashed line in the figure drawn vertically from the midpoint of the upper base toward the shaft member 15a. It has become. On the other hand, the two spiral blades 15b and 15c in the second conveying screw 15 of the second example shown in FIG. 12 are, as shown, the cross-sectional shape in the thickness direction of the blades is upstream in the developer conveying direction. It is asymmetrical with the downstream side. Specifically, the cross-sectional shape in the thickness direction is a trapezoid as shown in the figure, and the left and right are asymmetrical with respect to the dashed line in the figure drawn perpendicularly from the midpoint of the upper base toward the shaft member 15a. It has become. The thickness on the right side in the drawing, that is, the location on the downstream side in the developer conveyance direction, is larger than the thickness on the left side in the drawing, that is, the location on the upstream side in the developer conveyance direction.

  In the second conveying screw 15 of the first example shown in FIG. 11, the surface of the two-component developer 30 slightly falls between the first spiral blade 15b and the second spiral blade 15c as shown in the figure. It is out. On the other hand, in the second conveying screw 15 of the second example shown in FIG. 12, the surface of the two-component developer 30 between the first spiral blade 15b and the second spiral blade 15c is illustrated. There is almost no decline. This is because the portion on the right side in the figure, which is thicker in the thickness direction of the spiral blades 15b and 15c, lifts the two-component developer between the spiral blades.

  Therefore, the printer according to the first embodiment uses the second transport screw 15 of the second example shown in FIG. Thereby, it is possible to further suppress the undulation of the surface of the two-component developer in the axial direction.

[Second Embodiment]
In the printer according to the second embodiment, the second transport screw 15 serving as the supply transport body has the following configuration. That is, the diameter (for example, 6 mm) of the shaft member 15 a is larger than the diameter (for example, 5 mm) of the shaft member 14 a of the first transport screw 14, and the spiral diameters of the spiral blades 15 b and 15 c are the same as those of the first transport screw 14. This is the configuration. In such a configuration, the developer holding amount of the second transport screw 15 is smaller than that of the first transport screw 14 by the amount of the diameter of the shaft member 15a. Then, the thickness of the two-component developer above the screw is larger in the second storage chamber 11b than in the first storage chamber 11a, and the surface of the two-component developer is more suppressed. Furthermore, since the rigidity of the second conveying screw 15 is increased by the amount of the shaft member 15a having a larger diameter, the bending of the second conveying screw 15 is suppressed. Accordingly, it is possible to reduce waviness of the two-component developer due to the eccentric rotation of the second conveying screw 15 by bending.

  For reference, FIG. 13 is a graph showing the relationship between the toner density of the two-component developer and the development density unevenness rank when various specifications are prepared as the second conveying screw 15 and each of them is used individually. As shown. This graph was created based on the results of an experiment in which a second transport screw 15 of each specification was actually mounted on a printer testing machine having the same configuration as the printer shown in FIG. is there. The development density unevenness rank was determined based on an evaluation by visually checking the density unevenness in the printout image. The smaller the development density unevenness value is, the larger the development density unevenness is. In the figure, a curve La connecting the rhombus plot points (♦) shows the result when a single spiral structure is used as the second conveying screw 15. The curve Lb connecting the rectangular plot points (■) shows the result when a single spiral structure is used and the cross-sectional shape in the thickness direction of the spiral blade is asymmetric as in Example 1. ing. Further, a curve Lc connecting triangular plot points (を) shows the result when a double spiral structure is used. Further, the curve Ld connecting the “x” -shaped plot points is the result when a double spiral structure and the cross-sectional shape in the thickness direction of the spiral blade is non-target as in Example 1 is used. Show. The curve Le connecting the “*”-shaped plot points has a double-helix structure, the cross-sectional shape in the thickness direction of the spiral blades is asymmetric, and the diameter of the shaft member is larger than that of the first conveying screw 14. Is shown (the diameter of the shaft member of the second conveying screw is 6 mm with respect to the diameter of the shaft member of the first conveying screw is 5 mm). In any specification, the spiral pitch per spiral blade is the same.

  As shown in the figure, regardless of the specifications of the second conveying screw 15, as the toner concentration of the two-component developer is controlled to be lower, the development density unevenness caused by the wavy surface of the two-component developer is reduced. It turns out that it becomes easy to generate | occur | produce. This is because the lower the toner concentration, the smaller the volume (volume) of the two-component developer, and the smaller the thickness of the two-component developer above the second conveying screw 15, the more the surface is wavy. This is thought to be due to the fact that it is likely to occur. From the comparison between the curve La and the curve Lc, it was confirmed that the waviness of the surface of the two-component developer can be reduced by increasing the number of spiral blades. In addition, from the comparison between the curve Lc and the curve Ld, it can be confirmed that the waviness of the surface of the two-component developer can be further reduced by making the cross-sectional shape in the thickness direction of the spiral blade asymmetric as in the first embodiment. It was. Further, from the comparison between the curve Ld and the curve Le, in addition to the condition of asymmetry, the condition that the diameter of the shaft member is made larger than that of the first conveying screw 14 is added, thereby making the surface of the two-component developer corrugated. It was confirmed that it could be further reduced.

[Third embodiment]
In the third embodiment, as the supply transport body, one having a spiral pitch in the axial direction of the multi-strand spiral structure that is 0.3 to 0.7 times that of the other transport body is used. The spiral pitch in the conveyance direction of the multiple spiral structure referred to here represents the pitch in the axial direction of the protrusion formed by each of the multiple spiral members. For example, in the case of a two-row spiral structure, the distance between the protrusions formed by the first spiral member and the protrusions formed by the second spiral member. The spiral pitch of the other transport body means the spiral pitch of the single spiral member if the other transport body is a single spiral structure. This represents the pitch in the axial direction of the protrusion formed by each of the spiral members. In the third embodiment, the two conveying screws, the first conveying screw 14 and the second conveying screw 15 serving as the supply conveying member, are used. Therefore, the spiral pitch of the two-helix structure of the second conveying screw 15 is used. Is 0.3 to 0.7 times that of the first conveying screw 15. For example, as the second transport screw 15, a multi-spiral structure having a spiral pitch of 10 mm in the axial direction is used, while as the first transport screw 14, the spiral pitch of one spiral blade 14 a is set. What is 20 [mm] is used (0.5 times).

  The reason why the helical pitch in the axial direction of the multi-helix structure of the supply conveyance body is 0.3 to 0.7 times that of the other conveyance bodies is as follows. That is, the inventors of the present invention experimentally set the developer transport speed between the supply transport body and the other transport body when the spiral pitch of the supply transport body is set to less than 0.3 times that of the other transport body. It has been found that the difference becomes excessive and the distribution of the two-component developer in the developer accommodating chamber is largely offset. FIG. 16 shows the difference in height of the two-component developer between the end of the first storage chamber 11a and the end of the second storage chamber 11b of the developing device 10, and the helical pitch magnification of the supply transport body relative to the other transport bodies. It is a graph which shows the relationship. As shown in the figure, it can be seen that when the spiral pitch of the supply conveyance body is less than 0.3 of the other conveyance bodies, the height difference between the two-component developers increases rapidly. On the other hand, when the spiral pitch of the supply conveyance body is set to be greater than 0.7 times that of the other conveyance bodies, the present inventors have adequately corrugated the surface of the two-component developer conveyed by the supply conveyance body. It has been found that it is impossible to suppress it. FIG. 17 is a graph illustrating the relationship between the development density unevenness rank of the printout image and the helical pitch magnification of the supply transport body with respect to the other transport body. A development density unevenness rank of 3.5 or more is an allowable range. As shown in the figure, it can be seen that if the spiral pitch of the supply transport body is set to be larger than 0.7 times that of the other transport bodies, development density unevenness exceeding the allowable range will appear.

[Fourth embodiment]
FIG. 14 is a graph showing the relationship between the amount of shake of the screw and the development density unevenness rank when the second transport screws 15 having different ML ratios (M / L) are used individually. The ML ratio here is a value obtained by dividing the flexural modulus M [MPa] according to JIS K7171 by the length L [mm] in the axial direction. The length L in the axial direction is the length of a region sandwiched between two bearings that receive the shaft member at both ends in the length direction of the shaft member. Further, the amount of shake of the screw is the difference between the shortest diameter locus and the longest diameter locus of the outer edge of the screw when the screw is rotated. The screw cannot be formed completely straight due to the limit of processing accuracy, and is slightly bent. When the screw is rotated due to the bending, slight vibration occurs. Moreover, when the rigidity of the screw is low, the screw is slightly bent due to the centrifugal force when it is rotated. This deflection also causes the screw to shake.

  As shown in the figure, it can be seen that the uneven development density becomes worse as the ML ratio (M / L) of the second conveying screw 15 becomes smaller, that is, as the rigidity becomes lower. This is because, as the rigidity of the second conveying screw 15 is lowered, the waviness on the surface of the two-component developer is increased due to an increase in the amount of deflection caused by bending by the centrifugal force. In the same figure, even with the same ML ratio (M / L), the amount of deflection is different because of the bending degree of the screw in a state where it is not rotated due to good or bad processing accuracy in addition to bending due to centrifugal force. Because. The figure also includes the results of experiments using the second conveying screw 15 that intentionally deteriorates the machining accuracy and increases the bending. If the processing accuracy is improved, even if the ML ratio (M / L) = 25, the shake amount can be suppressed to about 0.2 [mm] and the uneven development density can be within the allowable range (rank 3.5 or more). I understand. Therefore, in the printer according to the fourth embodiment, a second conveying screw 15 having an ML ratio of 25 or more is used.

[Fifth embodiment]
As previously shown in FIG. 2, the bottom wall of the first storage chamber 11 a that stores the first transport screw 14 has a semicircular shape that follows the curvature of the spiral blades of the first transport screw 14. . In addition, the bottom wall of the second storage chamber 11 b that stores the second transfer screw 15 has a semicircular shape along the curvature of the spiral blade of the second transfer screw 15. In the printer according to the second embodiment, the curvature radius (for example, 8 mm) of the bottom wall of the second storage chamber 11b is made smaller than the curvature radius (for example, 8.5 mm) of the bottom wall of the first storage chamber 11a. . When the curvature radius is made smaller, the clearance between the tip of the spiral blade of the second transfer screw 15 and the bottom wall in the second storage chamber 11b becomes smaller than that in the first storage chamber 11a. In the second storage chamber 11b, the thickness of the two-component developer above the screw is larger than that in the first storage chamber 11a, and the surface of the two-component developer is more suppressed from being waved.

  Up to now, an example of a printer equipped with the developing device 10 to which the present invention is applied has been described. However, the present invention can also be applied to a process unit equipped with a developing device. For example, as shown in FIG. 15, the photosensitive member 1 as a latent image carrier, the developing device 10 to which the present invention is applied, and the drum cleaning device 6 are held as a single unit on a common holding member to form an image. It is a process unit that is detachable integrally with the apparatus.

  Further, an example in which a conveying screw having a spiral blade projecting on the peripheral surface of the shaft member has been described as the conveying member. For example, in the axial direction as shown in FIG. 7 of JP-A-10-221937. You may use what a center part consists only of a spiral blade and attached the rotating shaft to the edge part of the spiral blade.

  Further, although an example of a developing device using a two-component developer has been described, the present invention can also be applied to a developing device using a one-component developer.

  Although a printer that forms a single color image using one developing device 10 has been described, the present invention is also applicable to an image forming device that forms a color image using a plurality of developing devices that develop latent images into different colors. Can be applied. As such an image forming apparatus, for example, as described in Japanese Patent Laid-Open No. 10-221937, an apparatus having a large number of developing devices around one photoconductor, as described in Japanese Patent Laid-Open No. 8-76582, One provided with a revolver developing device that revolves a plurality of developing devices at a position facing the photoconductor, or one provided with a plurality of process units having a photoconductor and a developing device as described in JP-A-2003-57929, etc. Can be illustrated.

  As described above, in the printer according to the embodiment, as the second transport screw serving as the supply transport body, the number of spiral blades (15b, 15c) serving as the spiral member is an even number, and the phase of each spiral member is 360 [°. ] Are shifted by an angle obtained by dividing the number by the number of stripes, so that the projections by other spiral blades must be in a position that is 180 [°] point-symmetric with respect to the projections by one spiral blade in the cross section. Can be positioned so that the undulations on the surface of the two-component developer caused by the respective revolutions can be offset each other.

  Further, in the printer according to the first embodiment, as the spiral member of the second transport screw 15, the cross-sectional shape in the thickness direction is asymmetric between the upstream side and the downstream side in the developer transport direction, and the downstream thickness is The spiral blades 15b and 15c are larger than the upstream side. In this configuration, as described in the first embodiment, the surface of the two-component developer conveyed by the second conveyance screw 15 can be further suppressed.

  Further, in the printer according to the second embodiment, a plurality of conveying bodies are used in which spiral blades are projected from the peripheral surfaces of the rotating shaft members. Moreover, as the 2nd conveyance screw 15 which is a supply conveyance body, the diameter of the shaft member 15a is larger than the diameter of the shaft member 14a of the 1st conveyance screw 14 which is another conveyance body, and the spiral diameter of the spiral blades 15b and 15c. Is the same as the first conveying screw 15. In this configuration, as described in the second embodiment, the thickness of the two-component developer above the screw in the second storage chamber 11b is larger than that in the first storage chamber 11a, so that the two-component developer in the second storage chamber 11b is increased. Waves on the surface of the component developer can be further suppressed. Furthermore, it is possible to suppress waviness of the two-component developer due to eccentric rotation of the second conveying screw 15 due to bending.

  In the printer according to the third embodiment, the second transport screw 15 is one having a spiral pitch in the axial direction of the double spiral structure that is 0.3 to 0.7 times that of the first transport screw 14. ing. In such a configuration, as described in the third embodiment, the surface of the two-component developer conveyed by the second conveying screw 15 is corrugated while suppressing the deviation of the distribution of the two-component developer in the developer containing chamber. It can be suppressed sufficiently.

  In the printer according to the fourth embodiment, the second conveying screw 15 is one having a value obtained by dividing the bending elastic modulus M [MPa] by the length L [mm] in the axial direction is 25 or more. For this reason, even if the waviness of the surface of the two-component developer is deteriorated due to the shake of the second conveying screw 15, the uneven development density can be kept within the allowable range.

  In the printer according to the fifth embodiment, the clearance between the tips of the spiral blades 15b and 15c of the second conveying screw 15 and the bottom wall for holding the two-component developer around the second conveying screw 15 is also provided. Is made smaller than the clearance in the first conveying screw 15. In this configuration, as described in the fifth embodiment, the thickness of the two-component developer above the screw in the second storage chamber 11b is larger than that in the first storage chamber 11a, and the surface of the two-component developer is corrugated. Can be further suppressed.

1: Photoconductor (latent image carrier)
10: Developing device 13: Developing sleeve (developing member)
14: 1st conveyance screw (other conveyance bodies)
14a: Shaft member 14b: Spiral blade (spiral member)
15: 2nd conveyance screw (supply conveyance body)
15a: shaft member 15b: spiral blade (spiral member)
15c: Spiral blade (spiral member)

JP 2003-57929 A JP-A-9-197782 Japanese Patent Laid-Open No. 11-24380

Claims (9)

Shaft member that rotates, and comprising a helical member having a projecting allowed was a spiral shape on the peripheral surface of the shaft member, by rotating around a shaft member, a developing agent to the shaft member A plurality of conveyance bodies that convey in the axial direction while revolving, and
A developer member for developing the latent image on the latent image carrier by transporting the developer carried on the surface to a position facing the latent image carrier of the image forming apparatus as the surface moves. The developer is transported toward the developing member while being transferred between adjacent transport bodies, and the developer is developed by the supply transport body, which is a transport body disposed adjacent to the developing member among the plurality of transport bodies. In the developing device that supplies the member,
Among the plurality of transport bodies, the supply transport body has a plurality of spiral members having a multi-helix structure, and the diameter of the shaft member is larger than the diameter of the shaft member of another transport body. Use a large one and use another one that has a single-helix structure with the above-mentioned one-line spiral member, or a plurality of helical members that have a multi-helix structure than the supply carrier. A developing device using a small number of strips. The developing device according to claim 1.
The supply and transport body is characterized in that the number of spiral members is an even number and the phase of each spiral member is shifted by an angle obtained by dividing 360 [°] by the number of strips. Development device. The developing device according to claim 1 or 2,
As the helical member of the supply conveyance member, the cross-sectional shape of the developer conveying direction be asymmetric between the upstream portion and a downstream portion where the boundary of the center line of the developer conveyance direction in the spiral outer edge, and the upstream side portion A developing device in which the size in the developer transport direction is smaller than the size in the developer transport direction at the downstream portion . The developing device according to any one of claims 1 to 3 ,
As above Symbol supply conveyance member, a developing device, characterized in that the helical diameter of the upper Symbol helical member is used as the same as the other carrier. In the developing device according to any one of claims 1 to 4,
A developing device using a multi-spiral structure having a helical pitch in the axial direction of 0.3 to 0.7 times that of the other conveyance bodies. The developing device according to any one of claims 1 to 5,
2. A developing apparatus according to claim 1, wherein a value obtained by dividing the bending elastic modulus M [MPa] by the length L [mm] in the axial direction is 25 or more . At least a latent image carrier that carries a latent image and a developing device that develops the latent image on the latent image carrier are held as a single unit on a common holder, and are attached to and detached from the image forming apparatus. In the enabled process unit,
As the developing device, a process unit, characterized in that it uses one of the developing apparatus of claims 1 to 6. In an image forming apparatus comprising a latent image carrier that carries a latent image and a developing device that develops the latent image on the latent image carrier.
As the developing device, an image forming apparatus characterized by using any of the developing apparatus of claims 1 to 6. The image forming apparatus according to claim 8 .
An image forming apparatus comprising a plurality of developing devices for developing latent images in different colors.

Images