Patent Grant
8027624
The disclosure of Japanese Patent Application No. 2007-314663 filed on Dec. 5, 2007 including specification, drawings and claims is incorporated herein by reference in its entirety.
1. Technical Field
The present invention relates to a developer apparatus which comprises a toner carrier roller whose surface carries toner, and an image forming apparatus for and an image forming method of developing an electrostatic latent image with toner using this roller.
2. Related Art
In techniques for developing an electrostatic latent image carried on an image carrier with toner, an apparatus is widely used which includes a toner carrier roller which is shaped approximately like a cylinder, carries toner on a surface thereof, and is arranged opposed facing the image carrier. For the purpose of improving the characteristics of toner carried on the surface of such a toner carrier roller, the applicant of the present application has earlier disclosed a structure of a toner carrier roller having a cylindrical shape that the surface of the roller includes convex sections which are regularly arranged and a concave section which surrounds the convex sections (JP-A-2007-121949). Since the concavo-convex patterns in the surface are regulated and uniform, such a structure is advantageous in that it permits easy control of the thickness of a toner layer which is carried on the surface of the roller, the charge level and the like.
In an image forming apparatus having the structure above, for the purpose of restricting the thickness of a toner layer carried by the convex and the concave sections formed in the toner carrier roller to a predetermined thickness, a layer thickness restriction member (restriction blade) abuts on the toner layer which is on the surface of the toner carrier roller.
However, in the case where a toner carrier roller having the structure above is used, owing to the evenness of the convexoconcave, scattering of toner from the surface of the toner carrier roller, fog and the like will be a problem unless a toner layer thickness on the toner carrier roller is strictly controlled. Particularly when toner becomes compressed powder due to the pressing force from the restriction blade, the toner gathers together as large aggregations or clusters of an additive, wax and the like falling off from the toner serve as cores around which even larger toner aggregations are created. They may leak out to outside a developer and get scattered or may adhere to an image carried on the image carrier and cause fog. Further, toner aggregations thus created may fixedly adhere to the toner carrier roller, thereby resulting in filming, image defects, etc.
An advantage of some aspects of the invention is to provide technology for preventing problems such as leakage and scattering of toner and fog attributable to creation of toner aggregations in a developer apparatus, an image forming apparatus and an image forming method which use a toner carrier roller whose surface is provided with convexoconcave.
According to a first aspect of the invention, there is provided a developer apparatus, comprising: a toner carrier roller that is shaped approximately like a cylinder, rotates while carrying a toner layer of charged toner on a surface thereof, and is provided, on the surface thereof, with plural convex section rows, each of which has plural convex sections arranged in a row in a width direction parallel to a rotational axis of the toner carrier roller and which are arranged in a circumferential direction orthogonal to the width direction and parallel to a circumferential surface of the toner carrier roller, the convex sections being so constructed and arranged that top surfaces of the convex sections coincide with a part of a curved surface of a single cylinder; and a restriction member that abuts on the surface of the toner carrier roller to restrict the toner layer carried on the surface of the toner carrier roller, includes an elastic abutting member which is made of an elastic material and has an edge part which extends in the width direction, the edge part being pressed into contact with the surface of the toner carrier roller, wherein a virtual surface which is obtained by extending the top surface of each convex section in the width direction and forms a part of the curved surface of the single cylinder is defined as a convex section extending surface of each convex section, and the convex section extending surfaces overlap each other between the convex sections belonging to the same convex section row, whereas the convex section extending surfaces do not overlap each other between the convex sections belonging to mutually different convex section rows.
In the first aspect of the invention constructed as above, by bringing the edge part of the elastic abutting member into contact with the convex sections of the toner carrier roller, the toner is carried in an area (hereinafter, referred to as a “concave section”) which is located between the convex sections and at a shorter distance to the rotational axis of the toner carrier roller than the convex sections and surrounds the convex sections, whereas no toner is carried on the convex sections. Since the toner is not pressed by the restriction member on the convex sections in this way, the formation of toner aggregates resulting from the pressing of the restriction member can be suppressed.
The elastic abutting member of the restriction member is elastically deformed by being pressed into contact with the convex sections of the toner carrier roller. On the other hand, since the surface of the toner carrier roller is recessed from the convex sections between one convex section row and the convex section row adjacent thereto, a pressure exerted to the edge part of the elastic abutting member is reduced to decrease a deformation amount caused by elastic deformation. In other words, the elastic abutting member cyclically repeats elastic deformation and relaxation caused by pressure contact when the convex section rows that come into contact with the elastic abutting member are successively switched as the toner carrier roller is rotated. Thus, the edge part of the elastic abutting member comes to project toward the bottoms of the concave sections. The edge part projecting toward the bottom of the concave section in this way acts to hit the toner carried in the concave section.
Mere application of pressing force upon toner carried by the concave sections could flocculate toner or press toner against and fixedly adhere toner to the surface of the toner carrier roller. However, the edge part vibrates to alternately apply and mitigate pressing force upon the concave section according to the above structure. Hence, it is possible to crush toner aggregations which are at or around the concave section. This was confirmed through experiments as described later. According to the invention, destruction of toner aggregations at an early stage makes it possible to prevent growth of larger toner aggregations and hence associated leakage, scattering, fog, filming, etc. In addition, stimulation of toner at or near the concave section attains an effect of increasing the fluidity of the toner and improving the uniformity of a toner layer.
According to a second aspect of the invention, there is provided an image forming apparatus, comprising: an image carrier that carries an electrostatic latent image; a toner carrier roller that is shaped approximately like a cylinder, is arranged opposed to the image carrier, rotates while carrying a toner layer of charged toner on a surface thereof, and is provided, on the surface thereof, with plural convex section rows, each of which has plural convex sections arranged in a row in a width direction parallel to a rotational axis of the toner carrier roller and which are arranged in a circumferential direction orthogonal to the width direction and parallel to a circumferential surface of the toner carrier roller, the convex sections being so constructed and arranged that top surfaces of the convex sections coincide with a part of a curved surface of a single cylinder; and a restriction member that abuts on the surface of the toner carrier roller to restrict the toner layer carried on the surface of the toner carrier roller, includes an elastic abutting member which is made of an elastic material and has an edge part which extends in the width direction, the edge part being pressed into contact with the surface of the toner carrier roller, wherein a virtual surface which is obtained by extending the top surface of each convex section in the width direction and forms a part of the curved surface of the single cylinder is defined as a convex section extending surface of each convex section, and the convex section extending surfaces overlap each other between the convex sections belonging to the same convex section row, whereas the convex section extending surfaces do not overlap each other between the convex sections belonging to mutually different convex section rows.
According to a third aspect of the invention, there is provided an image forming method, comprising: preparing a toner carrier roller that is shaped approximately like a cylinder, rotates while carrying a toner layer of charged toner on a surface thereof and is provided, on the surface thereof with plural convex section rows, each of which has plural convex sections arranged in a row in a width direction parallel to a rotational axis of the toner carrier roller and which are arranged in a circumferential direction orthogonal to the width direction and parallel to a circumferential surface of the toner carrier roller, the convex sections being so constructed and arranged that top surfaces of the convex sections coincide with a part of a curved surface of a single cylinder, a virtual surface which is obtained by extending the top surface of each convex section in the width direction and forms a part of the curved surface of the single cylinder being defined as a convex section extending surface of each convex section, the convex section extending surfaces overlapping each other between the convex sections belonging to the same convex section row, whereas the convex section extending surfaces not overlapping each other between the convex sections belonging to mutually different convex section rows; preparing a restriction member that includes an elastic abutting member which is made of an elastic material and has an edge part which extends in the width direction; arranging the toner carrier roller opposed to an image carrier which carries an electrostatic latent image; and developing the electrostatic latent image carried by the image carrier with toner while restricting an amount of toner carried by the toner carrier roller by pressing the edge part into contact with the surface of the toner carrier roller.
In these aspects of the invention, similar to the above first aspect of the invention relating to the developer apparatus, the formation of toner aggregates can be suppressed and the formed toner aggregates can be crushed by vibrating the edge part of the elastic abutting member, wherefore the occurrence of problems such as leakage, scattering and fog resulting from the growth of the toner aggregates can be prevented.
The above and further objects and novel features of the invention will more fully appear from the following detailed description when the same is read in connection with the accompanying drawing. It is to be expressly understood, however, that the drawing is for purpose of illustration only and is not intended as a definition of the limits of the invention.
In the engine part EG, a photosensitive member 22 is disposed so that the photosensitive member 22 can freely rotate in an arrow direction D1 shown in
An exposure unit 6 emits a light beam L toward the outer circumferential surface of the photosensitive member 22 charged by the charger unit 23. This exposure unit 6 exposes the photosensitive member 22 by the light beam L in accordance with the image signal given from the external apparatus to form an electrostatic latent image corresponding to the image signal.
The developer unit 4 develops thus formed electrostatic latent image with toner. Specifically, the developer unit 4 includes a support frame 40 which is provided rotatable about a rotational axis orthogonal to a plane of
In the developer 4K, a feed roller 43 and a developing roller 44 are rotatably attached with a shaft to a housing 41 which houses monocomponent toner T inside. When the developer 4K is positioned at the developing position described above, the developing roller 44 is positioned at a facing position which is faced with the photosensitive member 22 over a developing gap DG, and these rollers 43 and 44 are engaged with a rotation driver (not shown) which is provided in the main body to rotate in a predetermined direction. The feed roller 43 is shaped like a cylinder and is made of an elastic material such as foamed urethane rubber and silicone rubber. The developing roller 44 is shaped like a cylinder and is made of metal or alloy such as copper, aluminum and stainless steel. The two rollers 43 and 44 rotate while staying in contact with each other, and accordingly, the toner is rubbed against the surface of the developing roller 44 and a toner layer having a predetermined thickness is formed on the surface of the developing roller 44. Although negatively-charged toner is used in this embodiment, positively-charged toner may be used instead.
The space inside the housing 41 is divided by a partition wall 41a into a first chamber 411 and a second chamber 412. The feed roller 43 and the developing roller 44 are both provided in the second chamber 412. With a rotation of these rollers, toner within the second chamber 412 flows and is fed to the surface of the developing roller 44 while getting agitated. Meanwhile toner stored inside the first chamber 411 would not be moved by the rotation since it is isolated from the feed roller 43 and the developing roller 44. This toner is mixed with toner stored in the second chamber 412 and is agitated by the rotation of the developer unit 4 while holding the developer.
As described above, in this developer, the inside of the housing is separated into the two chambers, and the side walls of the housing 41 and the partition wall 41a surround the feed roller 43 and the developing roller 44, and accordingly, the second chamber 412 of relatively small volume is provided. Therefore, even when a remaining toner amount is small, toner is supplied efficiently to near the developing roller 44. Further, supply of toner from the first chamber 411 to the second chamber 412 and agitation of the whole toner are performed by the rotation of the developer unit 4. Hence, an auger-less structure is realized that an agitator member (auger) for agitating toner is not provided inside the developer.
Further, in the developer 4K, a restriction blade 46 is disposed which restricts the thickness of the toner layer formed on the surface of the developing roller 44 into the predetermined thickness. The restriction blade 46 includes a plate-like member 461 made of elastic material such as stainless steel, phosphor bronze or the like and an elastic member 462 which is attached to a front edge of the plate-like member 461 and is made of a resin member such as silicone rubber and a urethane rubber. A rear edge of the plate-like member 461 is fixed to the housing 41. The elastic member 462 attached to the front edge of the plate-like member 461 is positioned on the upstream side to the rear edge of the plate-like member 461 in a rotation direction D4 of the developing roller 44 shown by an arrow in
The toner layers thus formed on the surface of the developing roller 44 are transported, by means of the rotation of the developing roller 44, one after another to the opposed positions against the photosensitive member 22 on the surface of which an electrostatic latent image is formed. The developing bias from a bias power source 140 controlled by the engine controller 10 is applied to the developing roller 44. As shown in
A rectangular-wave voltage having a peak-to-peak voltage of 1500V and a frequency of about 3 kHz, for example, may be used as the developing bias voltage Vb. Since an electric potential difference between the direct current component Vave of the developing bias voltage Vb and a residual potential Vr of the photosensitive member 22 constitutes a so-called development contrast which affects image density, the direct current component Vave may be set to a required value for obtaining a predetermined image density.
The housing 41 further includes a seal member 47 which is pressed against the surface of the developing roller 44 on the downstream side to the opposed position facing the photosensitive member 22 in the rotation direction of the developing roller 44. The seal member 47 is a belt-like film made of a flexible material such as polyethylene, nylon or fluororesin extending in a direction X parallel to a rotational axis of the developing roller 44. One end of the seal member 47 in a direction perpendicular to the direction X is fixed to the housing 41, and the other end of the seal member 47 abuts on the surface of the developing roller 44. The other end of the seal member 47 is allowed to abut on the developing roller 44 as directed toward the downstream side in the rotation direction D4 of the developing roller 44, or directed in a so-called trail direction. The other end of the seal member 47 guides toner which remains on the surface of the developing roller 44 after moving past the opposed position facing the photosensitive member 22 to inside the housing 41 and prevents toner inside the housing from leaking to outside.
Each one of the convex sections 441 projects forward from the plane of
Referring back to
At this time, for the purpose of correctly transferring the image on the intermediate transfer belt 71 onto the sheet S at a predetermined position, the timing of feeding the sheet S into the secondary transfer region TR2 is controlled. To be more specific, there is a gate roller 81 disposed in front of the secondary transfer region TR2 on the transportation path F. The gate roller 81 starts to rotate in accordance with the timing of rotation of the intermediate transfer belt 71, and accordingly, the sheet S is fed into the secondary transfer region TR2 at a predetermined timing.
Further, the sheet S on which the color image is thus formed is transported to a discharge tray 89 which is disposed at a top surface of the apparatus main body via a pre-discharge roller 82 and a discharge roller 83 after the toner image is fixed to the sheet S by a fixing unit 9. Meanwhile, when images are to be formed on the both surfaces of the sheet S, the discharge roller 83 starts rotating in the reverse direction upon arrival of the rear end of the sheet S, which carries the image on its one surface as described above, at a reversing position PR located behind the pre-discharge roller 82, thereby transporting the sheet S in the arrow direction D3 along a reverse transportation path FR. The sheet S is returned back to the transportation path F again before arriving at the gate roller 81. At this time, the surface of the sheet S which abuts on the intermediate transfer belt 71 in the secondary transfer region TR2 and is to receive a transferred image is opposite to the surface which already carries the image. In this fashion, it is possible to form images on the both surfaces of the sheet S.
Further, as shown in
Further, as shown in
In
Further, there is a cleaner 76 in the vicinity of the roller 75. The cleaner 76 moves nearer to and away from the roller 75 driven by an electromagnetic clutch not shown. In a condition that the cleaner 76 is moved nearer to the roller 75, a blade of the cleaner 76 abuts on the surface of the intermediate transfer belt 71 mounted on the roller 75 and scrapes off the toner remaining on and adhering to the outer circumferential surface of the intermediate transfer belt 71 after the secondary transfer.
Furthermore, a density sensor 60 is disposed in the vicinity of the roller 75. The density sensor 60 confronts a surface of the intermediate transfer belt 71 and measures, as needed, the density of the toner image formed on the outer circumferential surface of the intermediate transfer belt 71. Based on the measurement results, the apparatus adjusts the operating conditions of the individual parts thereof that affects the image quality such as a developing bias applied to each developer, the intensity of the exposure beam L, and tone-correction characteristics of the apparatus, for example.
The density sensor 60 is structured to output a signal corresponding to a contrasting density of a region of a predetermined area defined on the intermediate transfer belt 71 using a reflective optical sensor, for example. The CPU 101 is adapted to detect image densities of individual parts of the toner image on the intermediate transfer belt 71 by periodically sampling the output signals from the density sensor 60 while moving the intermediate transfer belt 71 in rotation.
Restriction of a toner layer on the developing roller 44 within the developer 4K, . . . of the image forming apparatus having the structure above will now be described in detail. In a structure as that described above in which the surface of the developing roller 44 for carrying toner has concavity and convexity, it is possible for both the convex sections 441 and the concave section 442 of the developing roller 44 to carry toner. However, in this embodiment, it is structured that the restriction blade 46 abuts on the developing roller 44 within the surface of the developing roller 44 directly to remove toner on the convex sections 441. The reason is as described below.
First, the distance between the restriction blade 46 and the convex sections 441 needs be controlled precisely in order to form a uniform toner layer on the convex sections 441. However, for carrying of toner only by the concave section 442, the restriction blade 46 may abut on the convex sections 441 and remove all toner on the convex sections 441, which can be realized relatively easily. Further, since the volume of the space defined between the restriction blade 46 and the concave section 442 determines the amount of transported toner, it is possible to stabilize a transported toner amount.
This provides another advantage with respect to superiority of a transported toner layer That is, carrying of toner by the convex sections 441 tends to degrade toner because of friction contact of the toner with the restriction blade 46. More specifically, there are problems such as reduction of the fluidity and the charging performance of toner, clumping together due to toner particles pressed to each other, and filming due to fixedly adherence of toner to the developing roller 44. In contrast, carrying of toner by the concave section 442 which is less influenced by the pressure from the restriction blade 46 is less likely to give rise to such problems. Further, the manner of friction contact on the restriction blade 46 is greatly different between toner carried by the convex sections 441 and toner carried by the concave section 442. Hence, their charge levels are predicted to largely vary from each other. However, carrying of toner by the concave section 442 alone makes it possible to suppress such variations.
The recent years in particular have seen a growing demand for size reduction of toner particles and a lower fixing temperature to enhance the resolution of an image and reduce the amount of consumed toner and electric power consumption. The structure in this embodiment meets the demand. Small-particle toner generally has a high saturation charge level but gets charged slowly at the beginning, and hence, toner carried by the convex sections 441 tends to have a significantly higher charge level (get excessively charged) than toner carried by the concave section 442. Such a charge level difference shows itself as a development history in an image. Further, with respect to toner having a low melting point, fixing of toner to each other and fixing of the toner to the developing roller 44 and the like could easily occur by the friction contact of toner with each other or with the developing roller 44. However, such a problem is less likely to occur in the structure of the embodiment in which only the concave section 442 carries toner.
As shown in
Dimensions of the respective sections are illustrated with reference to
In this embodiment, the convex sections are arranged such that the convex section extending surfaces of the convex sections belonging to different convex section rows do not overlap. In other words, the convex section extending surface S1 of the convex sections belonging to the first row and the convex section extending surface S2 of the convex sections belonging to the second row are parallel to each other while being spaced apart by a specified distance (=(L2−L1)/2) and do not overlap each other. This means the following when viewed in a cross-sectional direction of the developing roller 44.
On the other hand, in a comparative example shown in
In the rotation direction D4 of the developing roller 44, the upstream-side end of the elastic member 462 is on the downstream side to a perpendicular from the rotation center of the developing roller 44 to the top surface of the elastic member 462. Hence, the amount of deformation of the elastic member 462 due to elastic deformation near the upstream-side end is maximum at the edge part but decreases toward the downstream side. The width of the restriction nip N1 and the abutting pressure from the elastic member 462 upon the surface of the developing roller 44 can be controlled through adjustment of the position of the restriction blade 46 in an adjustment direction denoted at an arrow in
Toner carried on the surface of the developing roller 44 on the upstream side to the restriction nip N1 could contain both favorably charged toner and poorly charged toner. However, as a result of toner layer restriction by the restriction blade 46, toner having a high charge level and strongly adhering to the developing roller 44 stays within the concave section 442. Whereas, since toner having a low charge level is pushed away by the toner having the high charge level, it is unlikely to remain in the concave section 442. Therefore, toner carried by the concave section 442 on the downstream side to the restriction nip N1 is mostly favorably charged toner.
As described above, in order to cause the concave section 442 to selectively carry the satisfactorily charged toner at a side upstream of the restriction nip N1 in the rotation direction D4 of the developing roller 44, an upstream end surface 462a of the elastic member 462 is preferably perpendicular to or nearly perpendicular to the surface of the developing roller 44. In this way, the toner on the convex sections 441 can be reliably scraped off and the replacement of the toner in the concave section 442 can be promoted by letting the scraped-off toner remain near the restriction nip N1. Further, in order to ensure the fluidity of the toner near the restriction nip N1, the upstream end surface 462a of the elastic member 462 is preferably smoothly finished.
On the other hand, if the upstream end surface 462a of the elastic member 462 is inclined toward the surface of the developing roller 44, the toner remaining upstream of the restriction nip N1 is pushed toward the restriction nip N1 to be pressed or the elastic member 462 is raised by the toner present between the restriction nip N1 and the developing roller 44, wherefore proper toner restriction may not be performed. If the upstream end surface 462a of the elastic member 462 is inclined in an opposite direction, the scraped-off toner is carried from the vicinity of the restriction nip N1 to a distant position along the upstream end surface 462a of the elastic member 462, whereby the replacement of the toner is unlikely to occur.
When the developing roller 44 is rotated in this state, the edge 462e of the elastic member 462 moves to a position of the surface of the developing roller 44 facing the concave section 442 as shown in
The edge 462e of the elastic member 462 undulates in this way as the developing roller 44 is rotated, whereby an impact is given to the toner carried in and in the vicinity of the concave section 442 by the edge 462e of the vibrating elastic member 462 at an upstream end side of the restriction nip N1 in the rotation direction D4 of the developing roller 44. This impact force merely acts to fluidize the toner in the concave section 442 for the toner having small particle diameters and high fluidity. On the other hand, the impact force by the edge 462e acts to crush aggregates for toner aggregates formed by massing the toner together to have large particle diameters. In this way, the toner aggregates are crushed utilizing the vibration of the leading end of the elastic member 462 according to the rotation of the developing roller 44 to prevent problems of leakage and scattering of the toner and fogging resulting from the aggregation of the toner and external additives in this embodiment.
Here, as shown in
On the other hand, a contact state of the elastic member in the construction of the comparative example shown in
For a similar reason, a dimension (nip width) in the circumferential direction Y of the restriction nip N1 narrow and extending in the width direction X is preferably set smaller than the spacing L4 of the convex sections shown in
When the surface of the developing roller 44 moves in its rotation direction D4 (upward in
When the edge 462e further moves to a line D-D passing the second row of the convex section rows shown in
From the above, in this embodiment, as the developing roller 44 is rotated, the edge 462e of the elastic member 462 repeats cyclical vertical movements as a whole while locally makes fine undulating movements. By bringing the elastic member 462 into contact with the surface of the developing roller 44 while vibrating the edge 462e in this way, the masses of the toner that came to have large diameters by aggregation are prevented from passing the restriction nip N1. Further, by hitting the toner aggregates by the vibrating edge 462e, the aggregates can be crushed. Even for the toner that is not aggregated, the toner can be agitated to further improve the fluidity thereof by giving an impact. In this way, a sufficient amount of toner can be made jump at the position facing the photosensitive member 22 and development performance can be improved. Further, by vibrating the leading end of the elastic member 462, the adhesion of the toner to this part can be prevented.
In the example shown in
Next, it is described at which values the elevation difference G1 between the convex sections 441 and the concave section 442 of the developing roller 44 and the opening height G2 to the edge 462e of the elastic member 462 in the concave section 442 shown in
G1≧Dave (Formula 1)
In the meantime, considering variations of a toner particle diameter, the elevation difference G1 between the convex sections 441 and the concave section 442 may be equal to or larger than the diameter of the largest toner particles among toner T. The maximum particle diameter of toner can be defined as described below statistically. That is, the maximum particle diameter Dm can be defined by the following formula:
Dm=D50+3 σ (Formula 2)
where the symbol D50 denotes the 50% particle diameter at the quantity standard of toner T and the symbol σ denotes the geometrical standard deviation. In this way, the proportion of toner whose particle diameter exceeds the maximum particle diameter Dm can be extremely small. When the elevation difference G1 is small, toner having a large particle diameter could stay indefinitely within the developer without getting fed to the concave section 442 so that the particle diameter distribution of toner will gradually shift toward the large diameter side to the extent not usable for development. When the elevation difference G1 is equal to or larger than the maximum particle diameter Dm, the concave section 442 can carry almost all toner particles contained in toner T held inside the developer, which makes it possible to use all toner inside the developer to the very end. That is, it is preferable to satisfy the following formula:
G1≧Dm=D50+3 σ (Formula 3)
The opening height G2 to the edge 462e of the elastic member 462 in the concave section 442 is basically similar, but it is desirable that the edge 462e projects into the concave section 442 to a certain large extent in the short time to improve the effect of crushing the toner aggregates and the effect of agitating the toner in the concave section 442. However, if the edge 462 excessively projects to reach the bottom of the concave section 442, the toner may be raked out and the conveyance of a sufficient amount of toner cannot be ensured or the toner may be pressed in the concave section 442 to be even more aggregated. Accordingly, even if the edge 462e maximally projects, it is at least necessary to leave a certain clearance between the edge 462e and the bottom of the concave section 442. In other words, a minimum necessary condition to be satisfied is:
G2>0 (Formula 4)
In light of ensuring the sufficient toner conveyance amount, the opening height G2 is preferably large, and may satisfy the following conditions similar to the above elevation difference G1 between the convex sections 441 and the concave section 442:
G2≧Dave (Formula 5)
or
G2≧Dm (Formula 6)
However, if the opening height G2 is excessively large, it is permitted that the toner aggregates having come to have larger diameters by aggregation are carried in the concave section 442. Thus, in reality, it is desirable to suppress the opening height G2 to a value slightly larger than the toner maximum particle diameter Dm at a maximum.
As shown in
On the other hand, the edge 462e of the elastic member 462 projecting toward the concave section comes into contact with the slant 1444b of the convex section 1441b to be brought into contact next, and the leading end is elastically deformed to move onto this slant. If the inclination of the slant is moderate at this time, the leading end of the elastic member 462 is more smoothly guided to the top surface of the convex section 1441b and there is no likelihood that the edge 462e is cracked upon colliding with the slant 1444b or becomes large resistance against the rotation of the developing roller 144. In other words, by making the inclination of the front ones of the slants of the respective convex sections in the rotation direction of the developing roller moderate, the crack of the elastic member can be prevented and a load torque can be reduced when viewed from a driving mechanism (not shown) for the developing roller.
Next, an effect in the case where a line in the width direction (X-direction) formed by the edge 462e of the elastic member 462 is deviated from an ideal straight line is studied.
In light of creating a period during which the entire edge 462e is released from the pressure contact with the top surfaces of the convex sections 441 in the width direction during the rotation of the developing roller 44, it is sufficient to provide a period during which the entire edge is located between the two convex section extending surfaces S1 and S2 shown in
In practice, the effect of crushing the toner aggregates is obtained if there is any period during which the entire edge 462e is released from the pressure contact with the top surfaces of the convex sections 441 in a certain collective area in the width direction. Thus, the above relationship needs not necessarily hold true in the entire area of the edge 462e. In other words, if the above relationship holds true in an interval of a specified width (e.g. about several cm) with respect to the entire line formed by the edge 462e extending in the width direction, a sufficient effect of crushing the toner aggregates can be practically obtained.
As described above, in this embodiment, the convex sections 441 and the concave section 442 are arranged on the surface of the developing roller 44 such that the convex section extending surfaces obtained by virtually extending the top surfaces of the convex sections 441 in the width direction overlap each other between the convex sections belonging to the same convex section row in the width direction, whereas do not overlap between the convex sections belonging to the different convex section rows. The edge 462e of the elastic member 462 disposed in the restriction blade 46 is pressed to the surface of the developing roller 44. By rotating the developing roller 44 in this condition, toner is removed from the convex sections 441 so that excessive pressure is not applied upon toner, and creation of toner aggregations is suppressed. Further, the entire edge 462e is moved up and down by repeating elastic deformation and restoration, which makes it possible to prevent toner from being fixed to the elastic member 462 and to crush toner aggregations if any. It is therefore possible in this embodiment to prevent leakage or scattering of toner from the developer, fog, filming, and the like caused by creation of toner aggregations.
While the particle diameter of the toner used in the above embodiment is not particularly limited, a significant effect can be obtained particularly when a toner of a small particle diameter is used. The term “toner of a small particle diameter” as used herein means one having a volume average particle diameter of about 5 μm or less, for example. As the particle diameter of toner decreases, van der Waals' force which acts upon toner increases, and this tendency is particularly notable when the particle diameter of toner is 5 μm or less. Such toner has a very high possibility of adhering to the developing roller 44 or of clumping together of toner with each other due to the van der Waals' force. Further, in the case where a material produced by mixing different substances such as silica and titania is used as an additive which is added to core particles in order to enhance the fluidity of toner, there are some cases that aggregation of toner is caused whose core is an aggregate of the additive. In the apparatus using such toner, the above-described structure makes it possible to effectively prevent the problems such as the leakage, scattering, and image defects resulting from the toner aggregation.
It should be noted that the invention is not limited to the embodiments above, but may be modified in various manners in addition to the embodiments above, to the extent not deviating from the object of the invention. For example, although the convex sections 441 of the developing roller 44 are lozenge-shaped in the above embodiments, this is not limiting The convex sections may be shaped differently such as circles and triangles for instance.
Although the developing roller 44 is metallic cylinder in the above embodiments, the invention is also applicable to an apparatus comprising a developing roller made of other material. However, experiments performed by the inventors of the invention have identified that the effect of applying the invention was remarkable when a developing roller whose surface is made of a conductive material such as a metallic developing roller and a developing roller made of non-metal with metal-plating thereon is used. In this respect, the invention is also effective to an apparatus comprising a developing roller which is made conductive by dispersing a conductive material such as carbon black or metallic fine powder in a cylinder made of rubber, resin or the like for instance.
Further, although the restriction blade 46 is prepared by attaching the elastic member 462 made of resin to a plate-like member 461 made of metal in the embodiment above, this structure is not limiting. The restriction blade may be a metal plate coated with resin, for example. In addition, since it is not necessary that the blade is conductive, the whole of a restriction blade may be made of resin.
The image forming apparatus in the above embodiment is a color image forming apparatus in which the developers 4K, . . . are attached to the rotary developer unit 4. However, the application of the invention is not limited to this. The invention is also applicable to a so-called tandem type color image forming apparatus in which a plurality of developers are arranged along an intermediate transfer belt, and to a monochromatic image forming apparatus which includes only one developer and forms a monochromatic image for example.
As described above, in the embodiment above, the photosensitive member 22 and the developing roller 44 function as an “image carrier” and a “toner carrier roller” of the invention, respectively. Further, the restriction blade 46 functions as a “restriction member” of the invention and the elastic member 462 functions as an “elastic abutting member” of the invention.
In an embodiment according to the invention, in a state where the edge part of the elastic abutting member faces a concave section surrounding the convex sections on the toner carrier roller surface, a spacing between the edge part and the concave section is preferably larger than zero. If the edge part excessively projects into the concave section, a force for pressing the toner carried in the concave section increases to give an excessive pressure to the toner. In order to prevent this, a certain clearance is preferably defined between the edge part and the concave section even in a state where the edge part faces the concave section and projects toward the bottom of the concave section.
For example, the spacing between the edge part and the concave section can be made larger than the volume average particle diameter of the toner in a state where the edge part of the elastic abutting member faces the concave section. By doing so, at least one layer of toner not pressed by the restriction member can be carried in the concave section.
Further, the spacing between the edge part and the concave section may be larger than a maximum particle diameter of the toner. This makes it possible for the concave section to carry toner having a maximum particle diameter. This solves a problem that only toner having a large particle diameter is left unused. The maximum particle diameter of toner can be defined for instance as a value which is calculated by adding triple the geometrical standard deviation to the 50% particle diameter at the quantity standard in the particle diameter distribution of the toner. This makes it possible for the concave section to carry almost all (approximately 99.7% of) toner particles.
It is preferable that an upstream one of end surfaces of the elastic abutting member in the rotation direction of the toner carrier roller is substantially perpendicular to the surface of the toner carrier roller. By doing so, a stable amount of the toner can be carried in the concave section by preventing the toner in the concave section from being raked out more than necessary and the restriction member from being lifted up from the toner carrier roller by excessive toner.
A position difference in the circumferential direction between a foremost part and a rearmost part of the edge part of the elastic abutting member in the rotation direction of the toner carrier roller is preferably smaller than a spacing in the circumferential direction between two adjacent convex section extending surfaces.
The edge part of the elastic abutting member is ideally perfectly straight in the width direction, but it is not always like that in an actual apparatus. There is a possibility that the straight line formed by the edge part is slightly skewed from the width direction or the edge part is curved or wavy other than being straight. It is preferable to permit such a slight displacement of the edge part. However, if this displacement is excessively large, there exists no period during which the entire edge part is released from the pressure contact with the convex sections and the effect of crushing the toner aggregates is weakened. As described above, when the position difference in the circumferential direction between the foremost part of the edge part in the rotation direction of the toner carrier roller and the rearmost part thereof in the rotation direction is kept in such a range as to be smaller than the spacing between two adjacent convex section extending surfaces, the period during which the entire edge part is released from the pressure contact with the convex sections inevitably exists and the effect of crushing the toner aggregates can be effectively fulfilled.
Further, the width in the circumferential direction of a restriction nip formed by the contact of the elastic abutting member with the toner carrier roller is preferably smaller than a spacing between two convex sections belonging respectively to the convex section rows adjacent in the circumferential direction. The nip width smaller than the spacing between the convex sections means that the elastic abutting member does not simultaneously come into contact with two or more convex section rows. In such a case, a displacement amount of the edge part can be larger than in the case where the nip width is large and the elastic abutting member simultaneously comes into contact with two or more convex section rows, wherefore the effect of crushing the toner aggregates by the edge part can be improved.
The positions of the respective convex sections in the width direction may mutually differ between two convex section rows adjacent in the circumferential direction. By doing so, the contact positions of the elastic abutting member with the convex sections cyclically differ as the toner carrier roller is rotated. Thus, the edge part of the elastic abutting member undergoes a complicated deformation accompanied by undulating movements, wherefore the effect of crushing the toner aggregates can be improved and the adhesion of the toner to the elastic abutting member can be prevented.
With respect to the toner carrier roller, it is preferable that a normal line to side surface parts which connect the convex sections to the concave section contains a component which is in a direction away from the rotational axis of the toner carrier roller. In other words, it is preferable that the convex sections and the concave section are connected to each other by moderate slants. The convex sections are one after another fed to abutting zones with the elastic abutting member and are brought into friction contact with the edge part as the toner carrier roller rotates. However, since the surfaces which connect the convex sections to the concave section are moderate slants, the edge part will not get stuck at the side surfaces of the convex sections and the drive torque of the toner carrier roller will therefore be small. In addition, it is possible to prevent permanent deformation, chipping and the like of the edge part at those areas of the edge part which abut on the convex sections first.
In this instance, it is preferable that a gradient of the side surface parts is steeper on the rear side to the convex sections rather than on the front side to the convex sections in the rotation direction of the toner carrier roller. This makes the edge part abut on the moderate slants and accordingly, the edge part is elastically deformed gradually on the front-end side of the convex sections which move toward the edge part in accordance with rotation of the toner carrier roller, whereas the deformation is mitigated on rear-end side of the convex sections at once in a short period of time. Hence, the striking force upon toner increases further and the crushing effect upon toner aggregations enhances.
This invention exhibits a particularly remarkable effect in the case of application to a developer apparatus in which the volume average particle diameter of the toner is 5 μm or smaller. Since van der Waals' force acting between toner particles are strong in such toner with small particle diameters, the aggregation of the toner is likely to occur. Particularly in an apparatus employing a jumping developing method using nonmagnetic monocomponent toner, the fluidity of the toner needs to be increased so that a sufficient amount of toner jump. Specifically, the added amount of additives with small particle diameters such as silica and titania needs to be increased. Thus, free additives tend to increase, the additives are likely to be separated from toner base particles and the fluidity thereof is likely to decrease with time. Therefore, toner aggregates are easily formed. By applying the invention to an apparatus using such toner, various problems resulting from the formation of toner aggregates can be effectively solved.
Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiment, as well as other embodiments of the present invention, will become apparent to persons skilled in the art upon reference to the description of the invention. It is therefore contemplated that the appended claims will cover any such modifications or embodiments as fall within the true scope of the invention.
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