Developing apparatus and process cartridge with same

Abstract: A developing apparatus includes an elastic blade (11) contacted to a developing roller (8) to regulate a thickness of a layer of a developer to be formed on the developing roller. To the longitudinal end portions of the developing roller, seals (9) are press-contacted to prevent leakage of the developer. Each of the seals has a projection (9a) toward the longitudinally central portion of the developing roller. The projection (9a) is overlaid on the blade (11) at a position where the blade and the developing roller are contacted.

Description: FIELD OF THE INVENTION AND RELATED ART The present invention relates to a developing apparatus for developing an electrostatic latent image in an electrostatic recording apparatus such as an electrophotographic copying machine or an electrophotographic laser beam printer and to a process cartridge or unit including an image bearing member and at least the developing apparatus. In the developing apparatus, a developer carrying member usually in the form of a roller rotates to carry a developer to a developing zone where the image bearing member is disposed. In the developing zone, the developer is supplied from the developer carrying member to the image bearing member to develop the electrostatic latent image. A part of a travel of the peripheral surface of the developer carrying member is exposed and faced to a developer supply chamber, in which the developer is supplied onto the peripheral surface of the developer carrying member. The developer applied on the developer carrying member is subjected to a layer thickness regulating operation by a regulating member, and then, is carried to the developing zone. As for the regulating member, U.S. Patent No. 4,387,664, for example, proposes an elastic plate contacted to the developer carrying member, wherein the elastic member is contacted to the developer carrying member, and the developer is passed through a nip formed therebetween, by which the thickness of the layer of the developer is regulated. This method is advantageous since a uniformly thin layer of the developer can be formed and since the developer can be sufficiently triboelectrically charged. In order to prevent the developer from leaking out through longitudinal ends of the developer carrying member, U.S. Patent No. 4,387,664 proposes a sealing member mounted on a side wall of the developer supply chamber, and the sealing member is contacted to each of the ends of the developer carrying member over generally one half of the circumference of the developer carrying member. The similar method is disclosed also in U.S. Patent 4,341,179 and 4,373,468, for example. When there is a gap between the regulating member and the developer carrying member, and therefore, the regulating member may be made of rigid material, the sealing member may be abutted with strong pressure to each of the end surfaces, and therefore, no gap is required to be provided between the regulating member and the sealing member. However, where the regulating member is made of elastic material because of the contact thereof with the developer carrying member, the regulating member can be deformed elastically if the sealing member is abutted with strong force to the end surface of the regulating member. If this occurred, the thickness of the developer layer formed may be non-uniform. Even if the sealing member for the leakage prevention is abutted to each of the end surfaces of the regulating member with weak force in an attempt to solve the problem, the pressure of abutment is not uniform with the result that the leakage prevention of the developer at the longitudinal ends is not reliable. In addition, the dimensional accuracies of the parts of the developing apparatus such as the regulating member are required to be even higher, which is not desirable from the standpoint of the productivity, cost or the like. EP-A-309 586 discloses sealing members sandwiched between the developer carrying member and a regulating member. On the other hand, U.S. Patent No. 4,785,319, for example, discloses a process unit detachably mountable to an image forming apparatus and including an image bearing member and a developing device, or further a charger or a cleaning device supported by supporting means as a unit. Such a process unit is desired because a high quality image can be maintained for a long period of time by exchanging the process unit, while the necessity of the maintenance by the expert is reduced. However, since the process unit is mounted to or dismounted from the main assembly of the image forming apparatus by manual operation by an operator, it is desired that the size of the unit is small. Therefore, the developing device therein is required also to be small. Then, the size of the developer carrying member is desired to be small. In order to regulate the layer of the developer on the developer carrying member having the small size into a thin layer while maintaining the sufficient triboelectric charge of the developer, it is effective to use an elastic plate contacted to the developer carrying member as the layer thickness regulating member. However, if the developer leaks out through the end portions of the developer carrying member, the leaked developer contaminates the inside of the process unit and also the main assembly of the image forming apparatus, thus reducing the advantage of using the process unit. SUMMARY OF THE INVENTION Accordingly, it is a principal object of the present invention to provide a developing apparatus wherein the leakage of the developer at the longitudinal ends of the regulating member can be prevented by leakage preventing sealing members, and in addition, the productivity thereof is good with low cost. It is another object of the present invention to provide a process unit having an image bearing member and a developing device as a unit, the developing device including a developer regulating member contacted to the developer carrying member, wherein the leakage of the developer through the end portions of the developer carrying member is prevented to reduce the contamination of the inside of the process unit or the inside of the image forming apparatus. These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a sectional view of an image forming apparatus to which the present invention is applicable. Figure 2 is a sectional view of a developing apparatus according to an embodiment of the present invention. Figure 3 is a perspective view of a part of the developing device, partly broken away. Figure 4 is a perspective view of a sealing member. Figure 5 is a perspective view of a part of the developing apparatus illustrating the mounting between the sealing member and the blade. Figure 6 is a perspective vie of the developing apparatus without the sleeve. Figures 7, 8 and 9 are developed views of the blade and the sealing member, as seen from the side of the sleeve. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Figure 1, there is shown a laser beam printer as an exemplary image forming apparatus to which the present invention is applicable. The laser beam printer contains a process unit 20 which will be described in detail hereinafter. The process unit 20 is detachably mountable into the main assembly of the printer along a guide rail 221 provided inside the main assembly of the printer 21, by manual operation of the operator. The operator takes the unit 20 out of the printer main assembly after it reaches the service life, and mounts a fresh unit 20 to the main assembly of the printer. The unit 20 contains an electrophotographic photosensitive member 1 in the form of a drum. The photosensitive member 1 is scanned by a laser beam L, by which an electrostatic latent image is formed on the photosensitive member 1 through a known process. A semiconductor laser 22 produces a laser beam L modulated in accordance with record image signals supplied from an original reader, computer or the like. The laser beam L is scanningly deflected by scanning means such as a rotational polygonal mirror or the like. The laser beam is incident on the photosensitive member 1 through a lens 24. The electrostatic latent image formed on the photosensitive member 1 is developed by a developing device which will be described hereinafter. The visualized image provided by the development by the developing means is transferred from the photosensitive member 1 to a transfer material 26 such as paper. The transfer material 26 is conveyed from a cassette 27 by a conveying roller 28 through a guide 29 toward an image transfer roller 25. After receiving the image transferred, the transfer material 26 is conveyed to an image fixing device 31 through a guide 30. The image fixing device 31 fixes the image on the transfer material, and the transfer material is discharged outside the apparatus. A voltage source 32 is connected with the developing sleeve of the developing device when the unit 20 is mounted in the main assembly of the printer 21 to supply a vibratory bias voltage to the developing sleeve during the developing operation. Figure 2 shows a sectional view of the process unit 20. Various members in the process unit are supported as a unit by a frame 10. Through a slit-like exposure window 6 formed in a rear side of the unit 20, the laser beam L is projected into the unit 10 substantially horizontally, and it is incident through an optical path 17 on the photosensitive member (image bearing member) 1 at an image exposure position 19, the photosensitive member 1 having been charged by a charger 2. By the projection of the laser beam L, an electrostatic latent image is formed on the photosensitive member. The photosensitive member 1 is rotationally driven in the direction indicated by an arrow. After the image transfer, the residual developer remaining on the photosensitive member 1 is removed by a blade 4 (cleaning means). At a position between the blade 4 and the exposure position 19, the charger 2 is disposed which includes a contact type charging member or a friction charging roller. The charger 2 may be in the form of a corona charger. Below the optical path 17 leading the image information beam L, there is a developer container 3 for containing a one component developer T. Adjacent to the container 3, there is a developer supply chamber 7. The unit 20 includes a rotatable developing sleeve 8 in the form of a cylinder. The circumferential travel thereof is partly exposed to the inside of the developer supply chamber 7, and partly faced to the photosensitive member 1. Into the developer supply chamber 7, the developer is supplied by a developer conveying member 3c rotating in the direction indicated by an arrow through an opening 3b formed in a partition wall 3a of the container 3. The developing sleeve 8 is rotatable in the direction indicated by an arrow. In the developer supply chamber 7, there are provided a developer amount regulating member (regulating blade) 11 and a developer leakage preventing member 9. When a magnetic developer is used as the one component developer T, or a two component developer containing magnetic carrier particles and toner particles, the sleeve 8 is non-magnetic, and a magnet is disposed within the sleeve 8. When a non-magnetic developer is used as the one component developer, the magnet is not necessary, and the developer carrying member 8 may be in the form of a solid roller. The developer T in the developer supply chamber 7 is deposited on the sleeve 8 by electrostatic attraction force or magnetic attraction force or the like. The thickness of the layer of the developer applied on the sleeve 8 is regulated by a regulating blade 11 of elastic material elastically press-contacted to the sleeve 8 at a side surface thereof at the position N, into a thickness smaller than the minimum clearance between the photosensitive member 1 and the sleeve 8 in the developing zone. Thus, in this embodiment, the so-called non-contact development operation is carried out. In order to increase the development efficiency in the non-contact development, a vibratory bias voltage (a DC biased AC voltage, for example) is applied to the developing sleeve 8 conveying the developer to the developing zone D, by which a vibratory electric field having periodically alternating directions is formed in the developing zone D. A DC bias voltage may be applied on the sleeve 8. The minimum clearance between the photosensitive drum 1 and the sleeve 8 is preferably 0.05 - 0.7 mm in the developing zone D. As for the blade 11 for forming the thin layer of the developer on the sleeve is made of rubber plate (urethane rubber, silicone rubber or the like) having a thickness of 0.5 - 1.5 mm, an elastic metal plate (phosphor bronze, stainless steel or the like) having a thickness of 0.02 - 0.2 mm, or a synthetic resin plate (polyethylene terephthalate or the like) having a thickness of 0.05 - 0.5 mm, or the like. Such plates have sufficient bending elasticity. Among them, a rubber plate is preferable because it can be press-contacted to the surface of the sleeve with uniform pressure. The blade 11 is fixed on a supporting plate 11A by bonding agent or the like. As shown in Figures 3 and 6, the supporting plate 11a is fixed by screws 12 to end portions of a mounting portion 10b extending between the arcuate internal end walls 10a of the developer supply chamber 7 at its both longitudinal ends. The blade 11 is curved in the developer supply chamber 7, as shown in Figure 2, and is elastically contacted to the sleeve 8. The developer is regulated in its layer thickness during passage through the nip formed between the blade 11 and the sleeve 8, and in addition, during this, the developer is triboelectrically charged by the friction with the sleeve and with the blade to such an extent as to be sufficient to develop the latent image. In the shown example, the blade 11 is counter-directionally contacted to the sleeve 8 relative to the rotational direction of the sleeve 8. More particularly, the free end 11b of the blade 11 is upstream of the fixed end 11c at which the blade is fixed to the supporting plate 11a. With this arrangement, the thickness of the developer layer becomes small. However, the blade 11 may be contacted to the sleeve 8 codirectionally with respect to the rotational direction of the sleeve 8, that is, in the direction opposite to the shown example. In this case, the free end 11b of the blade 11 is disposed downstream of the fixed end 11c, relative to the rotational direction of the sleeve 8. In the shown example, the side of the blade 11 is contacted to the sleeve 8 at a position slightly downstream of the free end 11b of the blade 11 toward downstream with respect to the rotational direction of the sleeve. Therefore, a slight gap or slit is formed between the free end 11b of the blade 11 and the sleeve 8 surface. Since the developer is introduced into the nip formed between the blade 11 and the sleeve 8 through the gap, it is important that the gap is formed when the blade 11 is counter-directionally contacted to the sleeve in the sleeve rotation direction. When, on the other hand, the blade 11 is contacted to the sleeve codirectionally, the free end 11b may be or may not be contacted to the sleeve 8 if the side of the blade 11 is contacted to the sleeve 8. In order to prevent the leakage of the developer through the opposite longitudinal ends of the sleeve 8, developer leakage preventing seal members 9 are provided in sliding contact with the sleeve 8 adjacent its longitudinal ends and outside the opposite longitudinal ends of the blade 11. As shown in Figure 2, the sealing members 9 are press-contacted to the outer peripheral surface of the sleeve 8, as if it is wrapped therearound, in the range from an inlet where the developer on the sleeve 8 having passed through the developing zone D returns to the supply chamber 7 by the rotation of the sleeve 8 to an outlet where the developer is discharged from the supply chamber 7 toward the developing zone D. As shown in Figures 2, 3, 5 and 6, each of the sealing members 9 is bonded on and along each of an arcuate internal end walls 10a of the developer supply chamber 7, and the top end portion thereof is confined by the supporting plate 11a of the regulating blade 11 fixed to the end portions of the mounting portion 10b of the developer supply chamber 7, by which each of the sealing member is fixed on the arcuate internal wall portion 10a. Thus, the sealing member 9 is sandwiched between the side wall of the developer supply chamber 7 and the sleeve 8, so that it is elastically compressed to a certain extent. The sealing member 9 is made of felt or sheep wool, tetrafluoroethylene resin fibers or the like, or porous (foam material or continuous pore material) such as urethane foam rubber, Goatex (trade name, porous tetrafluoroethylene resin) or the like, and therefore, each of the sealing members 9 is flexible. In this embodiment, in order to assure that the sealing member 9 prevents leakage of the developer from opposite longitudinal end portions of the regulating blade 11 adjacent the opening faced to the photosensitive member 1, the sealing member 9 is provided with a projection 9a projected toward the regulating blade 11, as shown in Figure 4. The projection 9a projects toward the regulating blade 11, that is, toward the longitudinal central portion of the sleeve 8 at a position where the regulating blade 11 is contacted to the peripheral surface of the developing sleeve 8. Therefore, as shown in Figures 2, 5 and 6, when the sealing member 9 is mounted on the arcuate internal wall portion 10a of the developer supply chamber 7, the projection 9a is urged to the regulating blade 11 by the internal wall portions continuing from the arcuate internal wall portion 10a of the developer supply chamber 7 at a position where the regulating blade 11 is in contact with the outer peripheral surface of the developing sleeve 8, by which the projection 9a is elastically compressed and deformed. By this, the longitudinal end portions of the regulating blade 11 are overlaid with the projections 9a in the manner that the end portions are sandwiched between the projections 9a of the sealing member 9 and the peripheral surface of the developing sleeve 8. As shown in Figure 7, a gap S between the sealing member 9 and the regulating blade 11 is substantially sealed by the projection 9a of the sealing member 9 at the position where the longitudinal end portions of the regulating blade 11 are contacted to the developing sleeve 8 surface. This assures that the leakage of the developer through the gap S toward the outside is prevented. As shown in Figure 8, a cut or a slit 13 extending along a length of the sealing member 9 may be formed at a base portion of the projection 9a adjacent the free end of the blade 11. By doing so, the pressure to the longitudinal end portions of the regulating blade 11 resulting from the provision of the projection 9a can be reduced, so that the uniformity of the thickness of the developer layer is enhanced, and in addition, the driving torque required for driving the developing sleeve 8 can be reduced. As shown in Figure 9, a tapered surface 9b may be formed at the free end of the projection 9a, the tapered surface 9b being such that its downstream portion is closer to the longitudinally central portion of the sleeve 8 than its upstream portion with respect to the rotational direction of the sleeve 8. By doing so, the flow of the developer may be made toward the longitudinally central portion of the sleeve 8 along the tapered surface 9b, by which the leakage prevention by the sealing member 9 adjacent the opposite longitudinal ends of the developing sleeve 8, can be further assured. In Figures 7, 8 and 9, an arrow A indicates a movement direction of the developer which is the same as the rotational direction of the sleeve in this embodiment. The projection 9a of the sealing member 9 is preferably not contacted to the free end 11b of the blade 11 but is contacted to the end portions of the blade 11 slightly away from the free end 11b toward the fixed end of the blade 11, because, if the free end 11b of the blade 11b is urged by the sealing member to the sleeve 8, the amount of developer leaking under the free end 11b becomes not uniform along the length of the blade with the possible result of non-uniformity in the developer layer thickness. During the regulation of the layer thickness of the developer, a thin layer of the developer is present in the nip between the blade 11 and the sleeve 8, and therefore, the blade 11 is not contacted to the sleeve 8 in a strict sense. However, when the developer is not present between the blade 11 and the sleeve 8, the blade 11 is elastically contacted to the sleeve 8, and in addition, the blade 11 is elastically urged to be contacted to the sleeve 8, and therefore, it is said in this specification for convenience that the blade 11 is "contacted" to the sleeve 8, and that the developer is passed through the nip or "contact portion" therebetween. In the foregoing embodiment, the developing device is contained in a process unit containing a photosensitive member. However, the present invention is applicable to a developing device fixed in the main assembly of an image forming apparatus, or to a developing device which is detachably mountable to an image forming apparatus independently from the photosensitive member. As for the means for exposing the photosensitive member to image information light, an array of light emitting diodes may be used in place of the laser beam. As a further alternative, the photosensitive member may be exposed to the light reflected or passed through an original to be reproduced. The image bearing member may be a member having an insulative surface to which a flow of ions modulated in accordance with record signal is applied to form a latent image. While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the scope of the following claims.

Claims: A developing apparatus for developing an electrostatic latent image formed on an image bearing member (1), comprising: a developer supply chamber (7); a developer carrying member (8), facing said developer supply chamber at least partly, for carrying the developer supplied thereto in said developer supply chamber to a developing zone (D) where an image bearing member moves; a regulating member (11) contacted to said developer carrying member (8) to regulate the thickness of a layer of the developer to be carried to said developing zone by said developer carrying member; a sealing member (9) contacted to an end portion of said developer carrying member to prevent leakage of the developer at an end portion of said developer carrying member; characterized in that said sealing member (9) has a projection (9a) toward a central portion of said developer carrying member (8) at a position corresponding to a position where said regulating member (11) is contacted to said developer carrying member, said projection (9a) being overlaid on an end portion of said regulating member (11) to cooperate with said developer carrying member (8) to sandwich the end portion of said regulating member (11). An apparatus according to claim 1, characterized in that said regulating member (11) is an elastic plate, and said sealing member (9) is flexible. An apparatus according to claim 2, characterized in that said projection (9a) is overlaid with said plate at a position away from a free end (11b) of said plate. An apparatus according to claim 3, characterized in that a gap is provided between a free end (11b) of said plate and said developer carrying member (8). An apparatus according to claim 2, 3 or 4, characterized in that said projection has a base portion where a cut (13 in Fig. 8) is formed. An apparatus according to claim 2, 3 or 4, characterized in that the length of said projection (9a in Fig. 9) is longer at the downstream portion than at the upstream portion with respect to a movement direction of the developer. An apparatus according to claim 2, 3 or 4, characterized in that said plate (11) is made of rubber, metal leaf spring plate or synthetic resin material, and that said sealing member (9) is made of felt or porous material. An apparatus according to claim 2, 3 or 4, characterized in that said plate (11) is contacted to said developer carrying member (8) counterdirectionally with respect to a movement direction of said developerr carrying member. A process unit (20), comprising: an image bearing member (1) on which an electrostatic latent image is formed; the developing apparatus (3, 8) according to any of claims 1 to 8 for developing the electrostatic latent image formed on said image bearing member; and supporting means (10) for supporting as a unit said image bearing member and said developing apparatus. A process unit according to claim 9, characterizing by a charging member (2) supported by said supporting means (10); an opening (6) formed at a position downstream of said charging member (2) with respect to a movement direction of said image bearing member to permit passage of image information light (17) to be projected onto said image bearing member to form the electrostatic latent image; and a cleaning member (4) supported by said supporting means for removing the developer remaining on said image bearing member before the charging operation by said charging member (2).

Inventors: SHIRAI HIROYUKI, SHIRAI, HIROYUKI
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1990
Main classification: G03G15
IPC codes: G03G15