Electrophotographic image forming apparatus, photoreceptor therefor and method for manufacturing the photoreceptor Number:6,803,162 from the United States Patent and Trademark Office (PTO) owispatent An image forming apparatus including a photoreceptor, wherein the photoreceptor includes an image forming portion having two ends substantially parallel to the rotating direction and a gap forming member located outside of each of the two ends of the image forming portion; a charging roller configured to charge the photoreceptor, wherein the charging roller contacts the gap forming members of the photoreceptor to form a gap g between the surface of the image forming portion and the peripheral surface thereof; an imagewise light irradiator; an image developer; and an image transfer device, wherein the relationship t.gtoreq.2g is satisfied, where g represents the gap and t represents a distance between an inside edge of one of the gap forming members and nearer one of the two ends of the image forming portion of the photoreceptor.<H Electrophotographic, photoreceptor, Electrophotogra, 6803162.html, Patent, pto, 6803162

Title: Electrophotographic image forming apparatus, photoreceptor therefor and method for manufacturing the photoreceptor

Abstract: An image forming apparatus including a photoreceptor, wherein the photoreceptor includes an image forming portion having two ends substantially parallel to the rotating direction and a gap forming member located outside of each of the two ends of the image forming portion; a charging roller configured to charge the photoreceptor, wherein the charging roller contacts the gap forming members of the photoreceptor to form a gap g between the surface of the image forming portion and the peripheral surface thereof; an imagewise light irradiator; an image developer; and an image transfer device, wherein the relationship t.gtoreq.2g is satisfied, where g represents the gap and t represents a distance between an inside edge of one of the gap forming members and nearer one of the two ends of the image forming portion of the photoreceptor.

Patent Number: 6,803,162 Issued on 10/12/2004 to Niimi

Inventors: Niimi; Tatsuya (Numazu, JP)
Assignee: Ricoh Company, Ltd. (Tokyo, JP)

Appl. No.: 10/205,413

Filed: July 26, 2002

Foreign Application Priority Data


Jul 26, 2001 [JP]			2001-226432

Current U.S. Class: 430/56 ; 399/159; 399/174; 430/127; 430/66

Field of Search: 430/56,58.7,66,127,69,133 399/159,174

References Cited [Referenced By]

U.S. Patent Documents


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Foreign Patent Documents


02-148059	Jun., 1990	JP
04-336556	Nov., 1992	JP
04-360167	Dec., 1992	JP
05-107871	Apr., 1993	JP
05-127496	May., 1993	JP
05-273837	Oct., 1993	JP
05-307279	Nov., 1993	JP
06-308807	Nov., 1994	JP
07-121002	May., 1995	JP
07-168417	Jul., 1995	JP
08-202126	Aug., 1996	JP
09-171282	Jun., 1997	JP
10-288881	Oct., 1998	JP
11-095523	Apr., 1999	JP

Primary Examiner: Goodrow; John L
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier & Neustadt, P.C.

Claims

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. An image forming apparatus comprising: an image bearing member comprising a photoreceptor configured to bear an electrostatic latent image while rotating in a direction and comprising an electroconductive substrate and at least one layer including a photosensitive layer, the photoreceptor including an image forming portion having two ends substantially parallel to the rotating direction and a gap forming member located outside of each of the two ends of the image forming portion, said gap forming member having an inside end substantially perpendicular to an axial axis of said image bearing member substantially parallel to the rotating direction; a charging roller configured to charge the photoreceptor while rotating, the charging roller contacting the gap forming members of the photoreceptor to form a gap g between a surface of the image forming portion of the photoreceptor and a peripheral surface of the charging roller; a light irradiator configured to irradiate the photoreceptor with light to form the electrostatic latent image in the image forming portion of the photoreceptor; an image developer configured to develop the electrostatic latent image with a toner to form a toner image on the image forming portion of the photoreceptor; and an image transfer device configured to transfer the toner image onto a receiving material, wherein the following relationship is satisfied:

2. The image forming apparatus according to claim 1, wherein the gap forming member is located on each end portion of the photoreceptor, and wherein the at least one layer of the photoreceptor at the end portion is thicker than the at least one layer at the image forming portion by the gap g.

3. The image forming apparatus according to claim 1, wherein the gap forming member is located on each end portion of the photoreceptor, and wherein the electroconductive substrate of the photoreceptor at the end portion is thicker than the electroconductive substrate at the image forming portion by the gap g.

4. The image forming apparatus according to claim 1, wherein the image bearing member further comprises a flange located on each end of the photoreceptor, and wherein the flange serves as the gap forming member.

5. The image forming apparatus according to claim 1, further comprising a pressing device configured to press at least one of the charging roller and the photoreceptor to the other.

6. The image forming apparatus according to claim 5, wherein the pressing device comprises a spring.

7. The image forming apparatus according to claim 1, wherein each of the charging roller and the photoreceptor has a rotating shaft, and wherein the rotating shafts are rotatably supported by a ring member.

8. The image forming apparatus according to claim 1, wherein the charging roller and the photoreceptor each have a respective driving device configured to independently drive the charging roller and the photoreceptor.

9. The image forming apparatus according to claim 8, wherein each of the driving devices is, independently, a member selected from the group consisting of gears, couplings and belts.

10. The image forming apparatus according to claim 1, wherein the charging roller and the photoreceptor rotate at a same speed.

11. The image forming apparatus according to claim 1, wherein the image bearing member further comprises a roller and the photoreceptor is a belt-form photoreceptor, wherein the roller supports the belt-form photoreceptor and has a projected portion located outside both ends of the belt form photoreceptor, and wherein the projected portions of the roller serve as the gap forming members.

12. The image forming apparatus according to claim 11, further comprising a pressing device configured to press at least one of the charging roller and the roller to the other.

13. The image forming apparatus according to claim 12, wherein the pressing device comprises a spring.

14. The image forming apparatus according to claim 11, wherein each of the charging roller and the roller has a rotating shaft, and wherein the rotating shafts are rotatably supported by a ring member.

15. The image forming apparatus according to claim 11, wherein the charging roller and the roller each have a respective driving device configured to independently drive the charging roller and the roller.

16. The image forming apparatus according to claim 15, wherein each of the driving devices is, independently, a member selected from the group consisting of gears, couplings and belts.

17. The image forming apparatus according to claim 11, wherein the charging roller and the belt-form photoreceptor rotate at a same speed.

18. The image forming apparatus according to claim 11, wherein a surface of the roller contacting the gap forming members is electrically insulative.

19. The image forming apparatus according to claim 11, wherein the electroconductive substrate of the belt photoreceptor is a seamless belt.

20. The image forming apparatus according to claim 1, wherein the gap forming members are electrically insulative.

21. The image forming apparatus according to claim 1, wherein the gap forming members have a thickness of from 10 to 200 .mu.m.

22. The image forming apparatus according to claim 1, wherein the gap g is from 10 to 200 .mu.m.

23. The image forming apparatus according to claim 1, wherein the charging roller charges the photoreceptor by applying a DC voltage overlapped with an AC voltage.

24. The image forming apparatus according to claim 1, wherein the photosensitive layer of the photoreceptor comprises a charge generation layer and a charge transport layer.

25. The image forming apparatus according to claim 24, wherein the charge transport layer comprises a polycarbonate having a triarylamine group in at least one of a main chain or a side chain thereof.

26. The image forming apparatus according to claim 1, wherein the photoreceptor further includes a protective layer, and wherein the protective layer comprises a filler.

27. The image forming apparatus according to claim 1, wherein the photoreceptor further includes a protective layer, and wherein the protective layer comprises a charge transport material.

28. The image forming apparatus according to claim 27, wherein the charge transport material is a charge transport polymer.

29. The image forming apparatus according to claim 28, wherein the charge transport polymer comprises a polycarbonate resin having a triarylamine group in at least one of a main chain or a side chain thereof.

30. A process cartridge comprising: an image bearing member comprising a photoreceptor configured to bear an electrostatic latent image while rotating in a direction and comprising an electroconductive substrate and at least one layer including a photosensitive layer, the photoreceptor having an image forming portion having two ends substantially parallel to the rotating direction and a gap forming member located outside of each of the two ends of the image forming portion, said gap forming member having an inside end substantially perpendicular to an axial axis of said image bearing member substantially parallel to the rotating direction; and a charging roller configured to charge the photoreceptor while rotating, the charging roller contacting the gap forming members of the photoreceptor to form a gap g between a surface of the image forming portion of the photoreceptor and a peripheral surface of the charging roller, wherein the following relationship is satisfied:

31. The process cartridge according to claim 30, wherein the gap forming member is located on each end portion of the photoreceptor, and wherein the at least one layer of the photoreceptor at the end portion is thicker than the at least one layer at the image forming portion by the gap g.

32. The process cartridge according to claim 30, wherein the gap forming member is located on each end portion of the photoreceptor, and wherein the electroconductive substrate of the photoreceptor at the end portion is thicker than the electroconductive substrate at the image forming portion by the gap g.

33. The process cartridge according to claim 30, wherein the image bearing member further comprises a flange located on each end of the photoreceptor, and wherein the flange serves as the gap forming member.

34. The process cartridge according to claim 30, further comprising a pressing device configured to press at least one of the charging roller and the photoreceptor to the other.

35. The process cartridge according to claim 34, wherein the pressing device comprises a spring.

36. The process cartridge according to claim 30, wherein each of the charging roller and the photoreceptor has a rotating shaft, and wherein the rotating shafts are rotatably supported by a ring member.

37. The process cartridge according to claim 30, wherein the charging roller and the photoreceptor each have a respective driving device configured to independently drive the charging roller and the photoreceptor.

38. The process cartridge according to claim 37, wherein each of the driving devices is, independently, a member selected from the group consisting of gears, couplings and belts.

39. The process cartridge according to claim 30, wherein the charging roller and the photoreceptor rotate at a same speed.

40. The process cartridge according to claim 30, wherein the image bearing member further comprises a roller and the photoreceptor is a belt-form photoreceptor, wherein the roller supports the belt-form photoreceptor and has a projected portion located outside both ends of the belt form photoreceptor, and wherein the projected portions of the roller serve as the gap forming members.

41. The process cartridge according to claim 40, further comprising a pressing device configured to press at least one of the charging roller and the roller to the other.

42. The process cartridge according to claim 41, wherein the pressing device comprises a spring.

43. The process cartridge according to claim 40, wherein each of the charging roller and the roller has a rotating shaft, and wherein the rotating shafts are rotatably supported by a ring member.

44. The process cartridge according to claim 40, wherein the charging roller and the roller each have a respective driving device configured to independently drive the charging roller and the roller.

45. The process cartridge according to claim 44, wherein each of the driving devices is, independently, a member selected from the group consisting of gears, couplings and belts.

46. The process cartridge according to claim 40, wherein the charging roller and the belt-form photoreceptor rotate at a same speed.

47. The process cartridge according to claim 40, wherein a surface of the roller contacting the gap forming members is electrically insulative.

48. The process cartridge according to claim 40, wherein the electroconductive substrate of the belt-form photoreceptor is a seamless belt.

49. The process cartridge according to claim 30, wherein the gap forming members are electrically insulative.

50. The process cartridge according to claim 30, wherein the gap forming members have a thickness of from 10 to 200 .mu.m.

51. The process cartridge according to claim 30, wherein the gap g is from 10 to 200 .mu.m.

52. The process cartridge according to claim 30, wherein the charging roller charges the photoreceptor by applying a DC voltage overlapped with an AC voltage.

53. The process cartridge according to claim 30, wherein the photosensitive layer of the photoreceptor comprises a charge generation layer and a charge transport layer.

54. The process cartridge according to claim 53, wherein the charge transport layer comprises a polycarbonate resin having a triarylamine group in at least one of a main chain or a side chain thereof.

55. The process cartridge according to claim 30, wherein the photoreceptor further includes a protective layer, and wherein the protective layer comprises a filler.

56. The process cartridge according to claim 30, wherein the photoreceptor includes a protective layer, and wherein the protective layer comprises a charge transport material.

57. The process cartridge according to claim 56, wherein the charge transport material is a charge transport polymer.

58. The process cartridge according to claim 57, wherein the charge transport polymer comprises a polycarbonate resin having a triarylamine group in at least one of a main chain or a side chain thereof.

59. A photoreceptor comprising: an electroconductive substrate; at least one layer including a photosensitive layer located overlying the electroconductive substrate; an image forming portion having two ends; and a gap forming portion located outside of each of the two ends of the image forming portion, said gap forming portion having an inside end substantially perpendicular to an axial axis of said electroconductive substrate and being configured to form a gap g between a surface of the image forming portion and a peripheral surface of a charging roller being configured to be disposed against said gap forming portion, wherein the at least one layer at the gap forming portion has a thickness greater than a thickness of the at least one layer at the image forming portion or the electroconductive substrate at the gap forming portion has a thickness greater than a thickness of the electroconductive substrate at the image forming portion, and wherein a gap t, representing a distance between one of the ends of said image forming portion and the inside end of said gap forming portion, is greater than or equal to 2 g.

60. The photoreceptor according to claim 59, wherein the at least one layer at the gap forming portion has a thickness greater than a thickness of the at least one layer at the image forming portion by 10 to 200 .mu.m.

61. The photoreceptor according to claim 59, wherein the electroconductive substrate at the gap forming portion has a thickness greater than a thickness of the electroconductive substrate at the image forming portion by 10 to 200 .mu.m.

62. The photoreceptor according to claim 59, wherein the photosensitive layer comprises a charge generation layer and a charge transport layer.

63. The photoreceptor according to claim 62, wherein the charge transport layer comprises a polycarbonate resin having a triarylamine group in at least one of a main chain or a side chain thereof.

64. The photoreceptor according to claim 59, wherein the photoreceptor further includes a protective layer located overlying the photosensitive layer, and wherein the protective layer comprises a filler.

65. The photoreceptor according to claim 59, wherein the photoreceptor further includes a protective layer located on the photosensitive layer, and wherein the protective layer comprises a charge transport material.

66. The photoreceptor according to claim 65, wherein the charge transport material is a charge transport polymer.

67. The photoreceptor according to claim 66, wherein the charge transport polymer comprises a polycarbonate having a triarylamine group in at least one of a main chain or a side chain thereof.

68. A photoreceptor comprising: an electroconductive substrate; at least one layer including a photosensitive layer located overlying the electroconductive substrate; an image forming portion having two ends substantially parallel to the rotating direction; a non-image portion located outside of each of the two ends of the image forming portion; and a flange provided on the non-image portion such that the flange covers the non-image portion and, when said photoreceptor is positioned against a charging roller, said flange being configured to form a gap g between a surface of the image forming portion and a peripheral surface of the charging roller, wherein a gap t, representing a distance between one of the ends of said image forming portion and an inside end of said flange, is greater than or equal to 2 g.

69. The photoreceptor according to claim 68, wherein the flange has a diameter greater than a diameter of the image forming portion of the photoreceptor by 10 to 200 .mu.m.

70. The photoreceptor according to claim 68, wherein the photosensitive layer comprises a charge generation layer and a charge transport layer.

71. The photoreceptor according to claim 70, wherein the charge transport layer comprises a polycarbonate having a triarylamine group in at least one of a main chain or a side chain thereof.

72. The photoreceptor according to claim 68, wherein the photoreceptor further includes a protective layer located overlying the photosensitive layer, and wherein the protective layer comprises a filler.

73. The photoreceptor according to claim 68, wherein the photoreceptor further includes a protective layer located on the photosensitive layer, and wherein the protective layer comprises a charge transport material.

74. The photoreceptor according to claim 73, wherein the charge transport material is a charge transport polymer.

75. The photoreceptor according to claim 74, wherein the charge transport polymer comprises a polycarbonate having a triarylamine group in at least one of a main chain or a side chain thereof.

76. A method for manufacturing a photoreceptor comprising: coating a coating liquid to form a photosensitive layer overlying an electroconductive substrate having two ends; end cutting the surface of a central portion of the photoreceptor so as to form a flange at both ends of said substrate and to prepare the photoreceptor such that the photoreceptor has an image forming portion having two ends substantially parallel to the two ends of electroconductive substrate, and has a non-image portion located outside of each of the two ends of image forming portion, wherein said flange is configured to form a gap g between a surface of the image forming portion and a peripheral surface of a charging roller when said photoreceptor is positioned against the charging roller, and a gap t, representing a distance between one of the ends of said image forming portion and an inside end of said flange, is greater than or equal to 2 g.

77. The method according to claim 76, wherein the photoreceptor at the non-image forming portion has a thickness greater than a thickness thereof at the image forming portion by 10 to 200 .mu.m.

78. The method according to claim 76, wherein the coating step is performed by a spray coating method.

79. The method according to claim 76, further comprising: coating an outermost layer coating liquid overlying the photosensitive layer to form an outermost layer overlying the photosensitive layer.

80. A method for manufacturing a photoreceptor comprising: coating a coating liquid to form a photosensitive layer overlying an electroconductive substrate having two ends and a recessed portion at a central portion thereof, to prepare the photoreceptor such that the photoreceptor has an image forming portion having two ends substantially parallel to the two ends of electroconductive substrate, and has a non-image portion located outside of each of the two ends of image forming portion, wherein said recessed portion is configured to form a gap g between a surface of the image forming portion and a peripheral surface of a charging roller when said photoreceptor is positioned against the charging roller, and a gap t, representing a distance between one of the ends of said image forming portion and an inside end of said recessed portion, is greater than or equal to 2 g.

81. The method according to claim 80, wherein the photoreceptor at the non-image forming portion has a thickness greater than a thickness thereof at the image forming portion by 10 to 200 .mu.m.

82. The method according to claim 80, wherein the coating step is performed by a spray coating method.

83. The method according to claim 80, further comprising: coating an outermost layer coating liquid overlaying the photosensitive layer to for an outermost layer overlaying the photosensitive layer.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electrophotographic image forming apparatus and a process cartridge for electrophotographic image forming apparatus. In particular, the present invention relates to an electrophotographic image forming apparatus using a proximity charger, and a process cartridge therefor. In addition, the present invention also relates to a photoreceptor for use in the electrophotographic image forming apparatus, and to a method for manufacturing the photoreceptor.

2. Discussion of the Background

Recently the growth of electrophotographic information processing apparatus using a photoreceptor, such as copiers, printers and facsimiles, is remarkable. In particular, photo-printers capable of recording digital information using light have been drastically improving in recording qualities and reliability. This digital recording technique is applied to copiers as well as photo-printers. The copiers to which both the conventional analogue copying technique and this digital technique are applied have various image forming functions. Therefore it is considered that the demand for such copiers increases more and more.

In attempting to reduce the quantity of ozone and NOx generated in an electrophotographic image forming apparatus and the electric power consumption of the image forming apparatus when performing charging, charging methods using a charging roller have been proposed.

For example, Japanese Laid-Open Patent Publication No. (hereinafter referred to as JOP) 4-336556 discloses a contact charging device in which a charging roller charges a photoreceptor while contacting the photoreceptor. In this contact charging device, the surface of the charging roller is made of a dielectric material, and the rotating direction of the charging roller is the same as that of the photoreceptor used (i.e., at the contact point between the charging roller and the photoreceptor, the moving direction of the charging roller is opposite to that of the photoreceptor).

In this case, even when there is a pinhole on the surface of the photoreceptor, a problem in that a non-charged area is not formed on the area around the pin hole does not occur. This is because the surface of the charging roller is dielectric and therefore the charges of an area around the portion of the charging roller, which portion faces the pinhole of the photoreceptor, do not decay when performing charging. In addition, even when the photoreceptor and dielectric charging roller are frictionally charged due to friction between the photoreceptor and the charging roller, which rotates in a direction opposite to the rotating direction of the photoreceptor at the contact point thereof, a surface area of the photoreceptor to be charged can be contacted with a surface area of the charging roller having a relatively low charge potential (i.e., a surface area of the charging roller which is not the surface area having a high potential because of having been just rubbed with the photoreceptor). Thereby, the photoreceptor can be charged to a desired potential even when a relatively low voltage is applied thereto. Since the charging roller charges the photoreceptor while contacting the photoreceptor, the applied voltage is relatively low compared to non-contact chargers such as scorotrons, and therefore the quantity of the above-mentioned reactive gasses to be generated, such as ozone and NOx, can be reduced.

However, the contact charging devices have the following drawbacks: (1) unevenly charging a photoreceptor (i.e., traces of the charging roller used can be observed in the resultant images) due to uneven contact of the charging roller with the photoreceptor used, etc.; (2) producing large charging noise; (3) charging ability deteriorates when toner particles, etc. present on the surface of the photoreceptor adhere on the surface of the charging roller; (4) photosensitive properties of the photoreceptor change when one or more constituents of the charging roller adhere (migrate) to the photoreceptor; and (5) the charging roller deforms when the photoreceptor is stopped for a long period of time, resulting in uneven charging.

The uneven charging mentioned above in item (1) is caused by adhesion of the constituents of the charging roller on the photoreceptor when the photoreceptor is stopped because the constituents migrate from the charging roller to the photoreceptor. The large noise mentioned above in item (2) is caused by vibrational contact of the charging roller with the photoreceptor. The vibration of a charging roller is caused when an AC voltage is applied to the charging roller.

In attempting to solve these problems, proximity charging devices have been proposed. In the proximity charging devices, a photoreceptor is charged by applying a voltage to a charger, which faces the photoreceptor while a narrow gap of from 0.005 mm to 0.3 mm is formed between the charger and the photoreceptor.

The proximity charging devices do not cause the problems mentioned above in items (4) and (5) because the charger does not contact the photoreceptor. In addition, with respect to the problem mentioned above in item (3), the proximity charging devices are superior to the contact charging devices because the quantity of toner particles adhered on the charger is less than in the case of the contact charging devices.

Proximity charging has been disclosed in, for example, JOPs 2-148059, 5-127496, 5-273837, 5-307279, 6-308807, 8-202126, 9-171282 and 10-288881.

These publications relate to proximity charging methods and it is described therein that a photoreceptor is experimentally charged with a charger while a gap is formed therebetween to observe whether the photoreceptor is evenly charged. However, there is no specific description in the publications as to how the charger is set closely to the photoreceptor, namely, ideas of constitution of proximity chargers are merely described therein. Actually, it is not easy to form a uniform gap not greater than hundreds of micrometers between a charger and a photoreceptor and stably maintain the gap. Namely, the proximity charging methods have a big problem of how to stably maintain a gap not greater than hundreds of micrometers between a charger and a photoreceptor.

In contrast, specific embodiments of a charger set closely to a photoreceptor are described in JOPs 5-107871, 5-273873, 7-168417 and 11-95523.

JOPs 5-107871 and 5-273873 have proposed a method in which an insulating tape whose ends are fixed by springs or the like and which serves as a gap forming member is set between a charger and a photoreceptor, to form a gap between the charger and the photoreceptor. This method is effective in forming a gap between a photoreceptor and a charger. However, when such a gap forming member is practically set in an image forming apparatus, a tension is applied to the springs in only one direction because the photoreceptor rotates in only one direction. Therefore, the springs are easily fatigued. In addition, when such a member is set in the image forming apparatus, the configuration of the resultant image forming apparatus becomes complex although this member has a simple mechanism. Therefore the maintenance of the image forming apparatus cannot be easily performed. For example, the image forming apparatus has a drawback in that when the gap forming member is changed, the photoreceptor has to be also changed.

JOP 7-168417 discloses a method in which a gap is formed between a photoreceptor and a charging roller by setting spacers on bearings of the charging roller, wherein the spacers contact the surface of the photoreceptor. In this case, the spacers have to be a part which is different from the charging portion of the charging roller in size and material, resulting in complication of the constitution of the charging roller. In addition, in this case the charging roller is made of an insulating material, and therefore a voltage applying roller which applies a voltage to the charging roller is needed, resulting in further complication of the constitution of the charging roller and increase of manufacturing costs of the charger.

JOP 11-95523 discloses a method in which a gap is formed between a charger and a photoreceptor by setting a gap forming member on at least one of the charger and the photoreceptor. This apparatus has a simple constitution, but there is no specific description about the specific constitution of the gap forming member and how to set the gap forming member. Therefore, the gap can be stably maintained (i.e., the photoreceptor can be stably charged) when the charging device is used for a long period of time.

JOP 4-360167 discloses a proximity charging device using a charger, on both ends of which a projected portion is formed to form a gap between the charger and a photoreceptor. By charging the photoreceptor with this charger while contacting the projected portion of the charger with the photoreceptor, proximity charging can be performed. However, there is no description about how to support the gap forming member and the photoreceptor and how to arrange the gap forming member relative to the image forming portion of the photoreceptor. Therefore, it is unknown whether a gap can be stably maintained (i.e., the photoreceptor can be stably charged) when the charging device is used for a long period of time.

In addition, there is no description about the measures against uneven charging around the edge portions of the photoreceptor close to the projected portions. Further there is no description about the measures against accumulation of toner particles on the edge portions of the photoreceptor close to the projected portions when the charger is repeatedly used. Therefore, it is unknown whether this proximity charging device can be stably used for a long period of time. Namely, the reliability of this proximity charging device is unknown in particularly when the charging device is practically used repeatedly.

JOP 7-121002 discloses an image forming apparatus in which a ring-form spacer is set on both ends of a cylindrical photoreceptor to form a gap between the photoreceptor and a charger. Around the photoreceptor, other devices such as an image developer, an image transferer and a cleaner are set while contacting the photoreceptor or being close to the photoreceptor. When such a ring spacer as mentioned above is set on both ends of the photoreceptor, the devices mentioned above cannot be provided on the ring spacer. Therefore the length of the photoreceptor in the axial direction needs to be extended to secure the desired image forming portion on the photoreceptor.

In addition, in this charging method charging near the ring spacers tends to become uneven (i.e., the potential on the edge portions tends to decrease). When such a charging method is used in combination with a nega-posi developing method which is suitable for digital image writing methods because image writing time can be saved, a problem such that background development is observed in these edge portions of the photoreceptor tends to occur.

Further, the spacers themselves and/or the charger tend to be contaminated. Therefore, the edge portions of the photoreceptor near the spacers should be cleaned such that there are no residual toner particles. However, since the spacers are formed on the photoreceptor, the edge portions cannot be cleaned. Accordingly, it is considered that this charging device has poor reliability when practically used repeatedly.

Because of these reasons, a need exists for a proximity charging device which has a simple constitution and in which a uniform gap is formed between the charger and a photoreceptor even when the charging device is repeatedly used.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide an electrophotographic image forming apparatus including a simple and low-cost proximity charging device which hardly causes the above-mentioned problems of the contact charging methods and which can be practically used. Specifically, a gap can be stably maintained between a charger and a photoreceptor without forming a toner film on the surface of the charger even when the charging device is repeatedly used.

Another object of the present invention is to provide an electrophotographic image forming apparatus including a proximity charging device which does not cause uneven charging, such as a banding problem specific to proximity charging, even in long repeated use, resulting in formation of good images for a long period of time.

Yet another object of the present invention is to provide a highly durable electrophotographic image forming apparatus and process cartridge, by which images having good image qualities can be stably produced even when repeatedly used without frequently changing the photoreceptor and charger due to abrasion resistance.

A further object of the present invention is to provide a photoreceptor for use in the electrophotographic image forming apparatus and process cartridge mentioned above.

A still further object of the present invention is to provide a method of manufacturing the photoreceptor.

Briefly these objects and other objects of the present invention as hereinafter will become more readily apparent can be attained by an electrophotographic image forming apparatus including at least a photoreceptor which rotates in a direction and which includes a gap forming member on both ends, wherein the photoreceptor includes an image forming portion having two ends substantially parallel to the rotating direction; a charger which is configured to charge the photoreceptor while rotating, wherein a gap is formed between the surface of the image forming portion of the photoreceptor and the periphery surface of the charger by the gap forming member and wherein the gap forming members do not contact the image forming portion of the photoreceptor; a light irradiator configured to irradiate the photoreceptor with light to form an electrostatic latent image in the image forming portion of the photoreceptor; an image developer configured to develop the latent image with a toner to form a toner image thereon; and an image transfer device configured to transfer the toner image onto a receiving material, wherein the following relationship is satisfied:

where g represents the gap and t represents a distance between the inside edge of one of the gap forming members and one of the two ends of the image forming portion of the photoreceptor, which is closer to the inside edge of the one of the gap forming members.

The gap is preferably from 10 .mu.m to 200 .mu.m.

The gap forming members can be formed, for example, by forming a layer (projection) at the edge portions of the photoreceptor; by forming a thicker photosensitive layer at the edge portions of the photoreceptor than the photosensitive layer at the image forming portion thereof; by using a substrate for the photoreceptor, wherein the substrate has a thickness larger than that at the image forming portion thereof; or by providing a flange on the edge portions (i.e., non-image forming portions) of the photoreceptor.

The photoreceptor may be a belt-form photoreceptor which is supported and driven by at least a driving (or driven) roller. In this case, the width of the roller is longer than that of the belt photoreceptor, and the extended portions of the roller has a diameter larger than that of the central portion of the roller to form a gap.

It is preferable that at least one of the charger and the photoreceptor (or the driving or driven roller) is pressed toward the other by a spring, etc.

It is preferable that the rotating shaft of the charging roller is coupled with the rotating shaft of the photoreceptor by a ring member.

In addition, it is preferable that each of the charging roller and the photoreceptor has a respective driving device such as gears, couplings and belts so as to be independently rotated.

In another aspect of the present invention, a process cartridge is provided which includes at least the above-mentioned photoreceptor having a gap forming member on both ends; and the charging roller mentioned above, wherein a gap is formed between the image forming portion of the photoreceptor and the periphery surface of the charger, and wherein the following relationship is satisfied:

wherein g represents the gap and t represents a distance between the inside edge of one of the gap forming members and one of the two ends of the image forming portion of the photoreceptor, which is closer to the inside edge of the one of the gap forming members.

In yet another aspect of the present invention, a photoreceptor is provided which includes at least an electroconductive substrate and a coating (i.e., a layer or layer) including at least a photosensitive layer located overlying the electroconductive substrate, wherein the thickness of the coating at the edge portions (i.e., the non-image portions) of the photoreceptor is thicker than that at the image forming portion of the photoreceptor. Alternatively, the thickness of the substrate at the edge portions may be greater than that at the image forming portion of the photoreceptor.

The photoreceptor may be provided with a flange on both ends thereof such that the flange covers the non-image portions, wherein the diameter of the flange is greater than that of the photoreceptor at the image forming portion.

It is preferable that the thickness difference of the coating or the substrate or the difference in diameter between the flange and photoreceptor at the image forming portion is preferably from 10 to 200 .mu.m.

The photosensitive layer preferably includes a charge generation layer and a charge transport layer located on the charge generation layer. The charge transport layer preferably includes a polycarbonate resin having a triarylamine unit in the main chain or side chain thereof.

The coating of the photoreceptor preferably includes a protective layer located overlying the photosensitive layer. The protective layer preferably includes a filler and/or a charge transport material.

In a further aspect of the present invention, a method for preparing the photoreceptor is provided which includes the steps of forming a coating including at least a photosensitive layer on a surface of an electroconductive substrate; and cutting a central portion of the coating, to form a thickness difference between the central portion and the edge portions thereof.

Alternatively, the method may include the steps of providing an electroconductive substrate in which the thickness (or diameter) of the edge portions is larger than that at the central portion, for example, by cutting; and forming a coating including at least a photosensitive layer on the surface of the edge portions and central portion of the surface of the electroconductive substrate.

The coating is preferably formed by a spray coating method.

These and other objects, features and advantages of the present invention will become apparent upon 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

Various other objects, features and attendant advantages of the present invention will be more fully appreciated as the same becomes better understood from the detailed description when considered in connection with the accompanying drawings in which like reference characters designate like corresponding parts throughout and wherein:

FIGS. 1 to 3 are schematic views illustrating cross-sections of embodiments of the photoreceptor for use in the image forming apparatus of the present invention;

FIG. 4 is a schematic view illustrating an embodiment of the configuration of the charging roller and the photoreceptor in the image forming apparatus of the present invention;

FIG. 5 is a schematic view illustrating the positional relationship between the charging roller and the photoreceptor, which are shown in FIG. 4;

FIGS. 6 to 8 are schematic views illustrating cross-sections of other embodiments of the photoreceptor for use in the image forming apparatus of the present invention;

FIG. 9 is a schematic view illustrating another embodiment of the configuration of the charging roller and the photoreceptor in the image forming apparatus of the present invention;

FIGS. 10A and 10B are schematic views illustrating embodiments of a seam of the gap forming member formed on both ends of the photoreceptor;

FIGS. 11 and 12 are an elevational view and a side view illustrating an embodiment of the combination of the charging roller and the photoreceptor, which are connected by a ring member;

FIGS. 13 and 14 are schematic views illustrating other embodiments of the configuration of the charging roller and the photoreceptor;

FIGS. 15 and 16 are schematic views illustrating the cross-sections of embodiments of the chargers for use in the image forming apparatus of the present invention;

FIGS. 17 and 18 are schematic views illustrating embodiments of the main portion of the image forming apparatus of the present invention;

FIG. 19 is a schematic view illustrating an embodiment of the process cartridge of the present invention;

FIGS. 20 to 22 are schematic views illustrating cross-sections of other embodiments of the photoreceptor for use in the image forming apparatus of the present invention;

FIG. 23 is a schematic view illustrating another embodiment of the configuration of the charging roller and the photoreceptor in the image forming apparatus of the present invention;

FIG. 24 is a schematic view illustrating the positional relationship between the charging roller and the photoreceptor, which are shown in FIG. 23;

FIGS. 25 and 26 are an elevatoinal view and a side view illustrating another embodiment of the combination of the charging roller and the photoreceptor, which are illustrated in FIG. 23 and which are connected by a ring member;

FIGS. 27 and 28 are schematic views illustrating other embodiments of the configuration of the charging roller and the photoreceptor;

FIGS. 29 to 31 are schematic views illustrating cross-sections of other embodiments of the photoreceptor for use in the image forming apparatus of the present invention;

FIG. 32 is a schematic view illustrating another embodiment of the configuration of the charging roller and the photoreceptor in the image forming apparatus of the present invention;

FIG. 33 is a schematic view illustrating the positional relationship between the charging roller and the photoreceptor, which are shown in FIG. 32;

FIGS. 34 and 35 are an elevational view and a side view illustrating another embodiment of the combination of the charging roller and the photoreceptor, which are connected by a ring member;

FIGS. 36 and 37 are schematic views illustrating other embodiments of the configuration of the charging roller and the photoreceptor;

FIG. 38 is a schematic view illustrating the cross section of another embodiment of the photoreceptor for use in the image forming apparatus of the present invention;

FIG. 39 is a schematic view illustrating another embodiment of the configuration of the charging roller and the photoreceptor;

FIG. 40 is a schematic view illustrating the positional relationship between the charging roller and the photoreceptor, which are shown in FIG. 39;

FIGS. 41 and 42 are an elevational view and a side view illustrating another embodiment of the combination of the charging roller and the photoreceptor, which are connected by a ring member;

FIGS. 43 and 44 are schematic views illustrating other embodiments of the configuration of the charging roller and the photoreceptor;

FIGS. 45 to 50 are schematic views illustrating the cross-sections of embodiments of the photoreceptor for use in the image forming apparatus of the present invention;

FIG. 51 is a schematic view illustrating an embodiment of the configuration of the charging roller and the belt photoreceptor for use in the present invention;

FIG. 52 is a schematic view illustrating the positional relationship between the charging roller and the belt photoreceptor, which are shown in FIG. 51;

FIG. 53 is a side view of the charging roller and the belt photoreceptor as illustrated in FIG. 51;

FIGS. 54 and 55 are an elevational view and a side view illustrating an embodiment of the combination of the charging roller and the belt photoreceptor, which are connected by a ring member;

FIGS. 56 and 57 are schematic views illustrating other embodiments of the configuration of the charging roller and the belt photoreceptor;

FIGS. 58 to 61 are schematic views illustrating the cross section of other embodiments of the photoreceptor for use in the image forming apparatus of the present invention;

FIG. 62 is a schematic views illustrating another embodiment of the image forming apparatus of the present invention; and

FIG. 63 is a schematic views illustrating another embodiment of the process cartridge of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

As mentioned above, when contact charging devices are used for electrophotographic image forming apparatus, problems which occur are that a toner film is formed on the charger and a charger deforms, resulting in uneven charging or defective charging. In attempting to solve these problems, proximity charging devices have been proposed. However, there is no proximity charging device which has a low cost and a simple structure and in which a gap is stably formed between the charger and the photoreceptor used and maintained even when used for a long period of time.

As a result of the present inventors' investigation, it is discovered that by providing a gap forming member on both end portions (i.e., non-image portions) of the periphery surface of a photoreceptor and arranging the charging roller such that the charging roller and the image forming portion of the photoreceptor have a specific positional relationship, the above-mentioned problems can be solved. Thus, the present invention is made.

In the present invention, the image forming portion of the photoreceptor is defined as an area of the photoreceptor in which charging, imagewise irradiation, developing and transferring processes are performed. In addition, the ends of the image forming portion are defined as the outermost side edges of the image forming portion. If the outermost side edges are different for the image forming portions of the charging, imagewise light irradiation, developi