Recording apparatus

Abstract

 The recording apparatus comprises an electrostatic latent image base (1), charging means (13) for equally charging the surface of the electrostatic latent image base (1), means for attenuating part of electric charges on the surface of the electrostatic latent image base charged by the charging means and for forming an electrostatic latent image, developing means (3) for adhering toner particles on the electrostatic latent image so as to form a toner image, and transferring means (5) for transferring the toner image onto an image base. The developing means (3) attracts and collects residual toner particles into the developing means and develops the electrostatic latent image at the same time. The charging means (13) has a particular charging function and a residual toner image equalizing function for disturbing a residual toner image left on the electrostatic latent image base and for equalizing the distribution of the toner particles. The charging and residual toner image equalizing means securely charges the electrostatic latent image base and equalizes the residual toner particles at the same time. The recording apparatus can be readily structured in small size and at low cost. The recording apparatus is free from contamination due to by-product in the discharging operation. Furthermore, the recording apparatus can usually output ghost-free high quality images.

Description

[0001] The present invention relates to a recording apparatus according to the electrophotographic process, in particular, relates to a cleanerless recording apparatus for recording an image without providing a cleaning device for cleaning toner particles which are left after the image is transferred.

[0002] A recording apparatus according to the electro-photographic process for developing an image and collecting toner particles which are left after the image is transferred by means of a developing device, hereinafter named cleanerless recording apparatus, has been disclosed in the publications of Japanese Patent Laid Open No. SHO 59-133573, SHO 59-157661, and so forth. In these publications, a basic engineering concept for the cleanerless recording apparatus has been disclosed. The concept can be summarized as follows. As shown by a sectional view of principal structure of FIG. 1, in an electrophotographic printer such as a laser printer, the reverse development process is widely used. In this reverse development process, toner particles 2 with the same polarity as an electrostatic latent image base (photosensitive substance). The toner particles 2 are adhered to the portion where electric charges are absent (or the amount of electric charges is small) on the surface of the electrostatic latent image base 1. The toner particles 2 are not adhered to the portion where electric charges are present. To selectively adhere the toner particles 2, it is necessary to apply a voltage between the potential V_o at the charged portion on the surface of the electrostatic latent image base 1 and the potential V₁ at the non-charged portion, namely V_b (|v₁| < |V_b| < |v₀|) so as to prevent the toner particles from being adhered to the electrostatic latent image base 1 by means of the electric field against the charged portion on the surface of the electrostatic latent image base 1. On the other hand, the toner particles 2 are adhered to the electrostatic latent image base 1 with the electric field against the non-charged portion on the surface of the electrostatic latent image base 1. The toner particles 2 adhered on the electrostatic latent image base 1 are transferred to an image base 6 by a transferring device 5. In this transfer process, all the toner particles are not transferred. On the surface of the electrostatic latent image base 1, residual transfer particles 2' are distributed in an image shape.

[0003] In the conventional electrophotographic process, by a cleaner 7 shown by the dashed line of FIG. 1, the remaining toner particles 2' are collected. Thereafter, by an discharging lamp 8, the electric charges on the electrostatic latent image base 1 are cleared. Thereafter, an electrostatic latent image forming process consisting of an equalizing and charging process by the charger 9 and an exposing process by light beam 10 takes place. On the other hand, in the cleanerless recording apparatus, since it is not provided with the cleaner 7, the residual toner particles 2' are developed. The electrostatic latent image is developed and the residual toner particles 2' are collected into the developing device 3 at the same time. Strictly speaking, the residual toner particles 2' which exist at the charged portion of the latent image formed by the exposure of the light beam 10 (namely, non-exposed portion or non-image portion) are securely charged to the same polarity as that of the latent image by the charger 9. Thus, by the electric field which disturbs the toner particles 2 from being moved from the toner carrier 4 to the electrostatic latent image base 1 (namely, the electric field by the potential between V₀ and V_b), the residual toner particles 2' are moved to the toner carrier 4. At the same time, the residual toner particles 2' which are present at the non-charged portion (namely, the exposed portion or image portion) is affected by a force which acts from the toner carrier 4 to the electrostatic latent image base 1 and thereby the residual toner particles 2' stay on the electrostatic latent image base 1. At the non-charged portion where the residual toner particles 2' stay, new toner particles 2 are moved from the toner carrier 4. Thus, the latent image is developed and the toner particles 2 are cleaned at the same time.

[0004] As was described above, in the cleanerless recording apparatus, since the cleaner 7 and a toner disposal box for collecting cleaned toner particles (namely, used toner particles) are not necessary. Thus, the apparatus becomes small in size and simple in structure. In addition, since the residual toner particles 2' are collected into the developing device 3 and reused, the disposal toner particles are not present. Thus, the apparatus can be economically operated. In addition, since the electro-static latent image base 1 is not abraded by the cleaning blade, the life of the electrostatic latent image base 1 can be prolonged.

[0005] However, in the cleanerless recording apparatus, due to the following reasons, ghost images may be present.

[0006] First, in a high humidity condition, paper as the image base 6 is moistened and thereby the resistance decreases. Thus, generally, the transfer efficiency decreases. Consequently, a large amount of toner particles tend to stay on the electrostatic latent image base 1. When the amount of residual toner particles 2' becomes excessive, they cannot be completely cleaned by the developing device (developing means) 3. Thus, at the non-image portion, the residual toner particles 2' stay and thereby a positive ghost appears on the white background of the transfer image (hereinafter named positive ghost or positive memory).

[0007] Second, when the amount of residual toner particles 2' becomes excessive, in the exposing process by the light beam 10, since the residual toner particles 2' insulate the light beam 10, the attenuation of the surface potential of the electrostatic latent image base 1 becomes insufficient. Thus, an intermediate potential V₁' between the voltage at the charged portion V₀ and the voltage at the non-charged portion V₁ takes place. In the area where the intermediate potential takes place, the development voltage becomes V_b - V₁' and thereby the development voltage at the peripheral exposed portion becomes lower than V_b - V₁. Thus, the amount of toner particles moved from the toner carrier 4 to the electrostatic latent image base 1 becomes smaller than that at the peripheral portion. Consequently, the residual toner image appears at the transferred image portion as a white image (hereinafter named, negative ghost or negative memory). This phenomenon remarkably takes place in a mesh image or a half tone image consisting of a set of line images.

[0008] On the other hand, the publication of Japanese Patent Laid-Open No. SHO 62-203183 discloses that by applying a voltage to a conductive brush 11 in the shape shown in FIG. 2 and lightly contacting it with the surface of the electrostatic latent image base 1, the ghost can be cleared. In other words, by applying a voltage with opposite polarity to the toner particles with a DC power supply 12, the residual toner particles 2' are temporarily attracted to the conductive brush 11 by the Coulomb's force. Thus, the amount of the residual toner particles 2' on the surface of the electrostatic latent image base 1 can be remarkably reduced, thereby preventing such ghosts from taking place.

[0009] However, in the above method, there are following two problems.

(1) Rather than using the cleaner, an equalizing means 11 such as the aforementioned brush is required. Thus, in considering the small type and low cost of the apparatus, it cannot be said that remarkable effects are obtained. In particular, when the apparatus is produced, the adjustment of the electric resistance of the conductive brush 11 is not easy. In addition, the fibers of the brush tends to be broken. Thus, the yield of the conductive brush 11 is low and thereby the price tends to rise. Moreover, it is necessary to prepare a new power supply for applying a voltage to the conductive brush 11.

(2) When a corona charger as shown in FIG. 1 is used as the charging means 9 for equally charging the electrostatic latent image base 1, a large amount of ozone is produced as a by-product of the corona discharging process. The large amount of ozone produced is not only harmful to the human bodies, but deteriorates the parts of the apparatus such as the electrostatic latent image base 1.

[0010] As was described above, since the conventional cleanerless recording apparatus is large in size and high in price and generates harmful by-product, it cannot be said that the cleanerless recording apparatus satisfies the practical requirements.

[0011] Therefore, an object of the present invention is to provide a recording apparatus which is small in size and low in price.

[0012] In addition, another object of the present invention is to provide a safe recording apparatus which does not generate a harmful gas as the by-product during the operation.

[0013] Moreover, another object of the present invention is to provide a recording apparatus which is free from deterioration of parts such as the electrostatic latent image base 1 and which has a high durability.

[0014] The present invention is a cleanerless recording apparatus in the aforementioned structure and with the aforementioned functions, wherein the charging means has an residual toner image equalizing function along with the conventional charging function.

[0015] The recording apparatus according to the present invention comprises an electrostatic latent image base, charging means for equally charging the surface of the electrostatic latent image base, means for attenuating part of electric charges on the surface of the electrostatic latent image base charged by the charging means and for forming an electrostatic latent image, developing means for adhering toner particles on the electrostatic latent image so as to form a toner image, and transferring means for transferring the toner image onto an image base, wherein the developing means attracts and collects residual toner particles into the developing means and develops the electrostatic latent image at the same time, and wherein the charging means has a particular charging function and a residual toner image equalizing function for disturbing a residual toner image left on the electrostatic latent image base and for equalizing the distribution of the toner particles.

[0016] Since the cleanerless recording apparatus according to the present invention has a charging means with a residual toner image equalizing function, it is necessary to provide a residual toner cleaner and a residual toner image equalizing means. Namely, the real cleanerless recording apparatus can be accomplished. In other words, by structuring the charging means with a contacter where a voltage is applied, when the electrostatic latent image base is equally charged by the charging means, the residual toner particles left on the electrostatic latent image base are slid, a particular voltage being applied. The applied voltage disturbs the distribution of the toner particles. Thus, the distribution of the toner particles is totally equalized. Consequently, the residual toner particles do not cause ghosts to appear on the subsequent image. In addition, the electrostatic latent image base is not charged by so-called corona discharging process, but known field emission process or ion conduction process. Thus, the apparatus scarcely generates a by-product in the operation thereby it does not disadvantageously affect the human bodies and the electrostatic latent image base.

FIG. 1 and FIG. 2 are sectional views showing the principal portions of conventional recording apparatuses which differ each other; and

FIG. 3, FIG. 4, and FIG. 5 are sectional views showing the principal portions of a recording apparatus according to the present invention.

[0017] Now, with reference to the accompanying drawings, embodiments of the present invention will be described.

[0018] FIG. 3 is a sectional view of the principal portions of a recording apparatus according to the present invention. A developing device 3 is provided for developing a latent image of an electrostatic latent image base (photosensitive substance) 1. The developing device 3 is provided with a toner carrier 4. The toner carrier 4 supplies toner particles 2 charged with the same polarity as the electrostatic latent image base 1 to the surface of the electrostatic latent image base 1. At the portion on the surface of the electrostatic latent image base 1 where the electric charges are absent (or where the amount of electric charges is small), the toner particles 2 are adhered. At the portion where the electric charges are present, the toner particles 2 are not adhered. Such selective toner particle adhesion is accomplished in the structure where an intermediate voltage between the potential V₀ at the charged portion on the surface of the electrostatic latent image base 1 and the potential V₁ at the non-charged portion, namely V_b (|V₁| < |V_b| < |V₀| ), is applied to the toner carrier 4 in the developing device (developing means), the electric field against the charged portion on the surface of the electrostatic latent image base 1 disturbing the toner particles from being adhered to the electrostatic latent image base 1, the electric field against the non-charged portion on the electrostatic latent image base 1 causing the toner particles 2 to be adhered to the electrostatic latent image base 1.

[0019] The apparatus is also provided with a transferring device 5, a discharging lamp 8, a conductive brush roller 13, and light beam 10 for transferring the toner particles 2 adhered on the electrostatic latent image base 1 to the image base 6. In the transfer operation, generally, all the toner particles are not transferred. After the transfer operation, on the electrostatic latent image base 1, residual toner particles 2' are left in an image shape. After the transfer operation is completed, the electric charges on the electrostatic latent image base 1 are cleared by the discharging lamp 8. Thereafter, the electrostatic latent image base 1 is equally charged by the conductive brush roller 13 and then an electrostatic latent image is formed by the exposure with the exposing means 10.

[0020] In the cleanerless recording apparatus, the residual toner particles 2' are developed. The electrostatic latent image is developed and the residual toner particles 2' are collected into the developing device 3 at the same time. Strictly speaking, the residual toner particles 2' which stay at the charged portion (namely, non-exposed portion or non-image portion) of the latent image formed by the exposure with the exposing means 10 are securely charged with the same polarity as that of the latent image by the conductive brush roller 13. By the electric field for disturbing the toner particles 2 from being moved from the toner carrier 4 to the electrostatic latent image base 1 (namely, the electric field by the potential between V₀ and V_b), the residual toner particles 2' are moved to the toner carrier 4 side. At the same time, the residual toner particles 2' stay at the non-charged portion (namely at the exposed portion or image portion) are affected by a force which acts from the toner carrier 4 to the electrostatic latent image base 1 is left on the surface of the electrostatic latent image base 1. At the non-charged portion where the residual toner particles 2' stay, new toner particles 2 are moved from the toner carrier 4. Thus, the latent image is developed and the residual toner particles 2' are cleaned at the same time.

[0021] The recording apparatus according to the present invention is basically in the same structure as that shown in FIG. 2 except that the former is not provided with the conductive brush 11 and that is provided with the conductive brush roller 13 instead of the charger 9, a voltage being applied to the conductive brush roller 13.

[0022] The conductive brush roller 13 is provided with conductive fibers (brush) 14 whose volume specific resistance is in the range from 10² to 10¹⁰ohms cm, preferably in the range from 10³ to 10⁸ ohms cm disposed on the outer periphery thereof. A roller substrate 15 on which the brush 14 is disposed is a rigid conductive substance such as a metal or a resilient conductive substance such as a conductive rubber or conductive foam. The thickness of fibers structuring the brush 14 is preferably in the range from 0.5 to 10 deniers. The fiber density is preferably in the range from 5000 pieces/cm² to 100,000 pieces/cm². The length of the fibers is preferably in the range from 0.5 mm to 5.0 mm. These values are chiefly based on the requirements of the charging function which will be described later.

[0023] An AC power supply, a DC power supply, or a power supply 17 connected to one of them is connected to the conductive substrate 15 of the conductive brush roller 13 through an ammeter 16 so that an AC voltage or a DC voltage is applied to the conductive substrate 15.

[0024] When the electrostatic latent image base 1 is equally and negatively charged, a negative voltage or an AC voltage which is negatively deflected is applied to the conductive brush roller 13. In this case, the direction of the rotation of the conductive brush roller 13 may be the same or reverse rotating direction of the electrostatic latent image base 1. However, the peripheral speed preferably differs from the surface speed of the electrostatic latent image base 1. In other words, the peripheral speed of the conductive brush roller 13 is preferably faster than or slightly slower than that of the electrostatic latent image base 1. In particular, when the surface speed of the electrostatic latent image base 1 is 1, the peripheral speed of the conductive brush roller 13 is preferably in the range from 1.2 to 5.0. In addition, the contacting width of the conductive brush roller 13 and the electrostatic latent image base 1 is preferably 0.5 mm or more.

[0025] The result of a test conducted in the following conditions will be described.

[0026] The peripheral speed of the electrostatic latent image base 1 is 40 mm/sec; the outer diameter of the conductive brush roller 13 is 25 mm; the resistance of the fibers structuring the conductive brush roller 13 is 105 ohms cm; the length of the fibers is 2.5 mm; the thickness of the fibers is 3 deniers; the fiber density is 40,000 pieces/cm²; the peripheral speed of the conductive brush roller 13 is 60 mm/sec; a DC voltage of -500 V is superimposed to an AC voltage of 800 V_p-p as a voltage to be applied; and the contacting width of the conductive brush roller 13 and the electrostatic latent image base 1 is 3 mm.

[0027] In the above conditions, the surface of the organic photosensitive substance (electrostatic latent image base) 1 was equally charged with a voltage in the range from -450 V to -500 V. The charged surface was exposed with a laser beam. Thereafter, the organic photosensitive substance was developed by the two component development method or the one component development method. Thereafter, the toner image was transferred to transfer paper 6 with a known transferring charger 5. After the toner image had been transferred, residual toner particles 2' stayed on the organic photosensitive substance (electrostatic latent image base) 1 in an image shape. The surface of the organic photosensitive substance on which the residual toner particles 2' had been adhered was discharged by the discharging lamp 8. Thereafter, the organic photosensitive substance 1 arrived at the position of the conductive brush roller 13.

[0028] Since the residual toner particles 2' are equalized by the sliding force of the conductive brush roller 13 and vibrated by the AC electric field, they are much equalized. At the same time, the conductive fibers 14 of the conductive brush roller 13 contacted with the surface of the organic phtosensitive substance 1 cause the surface of the organic photosensitive substance 1 to be negatively charged. Thus, the organic photosensitive substance 1 is equally charged.

[0029] When only a DC voltage in the range from -500 V to -800 V is applied to the conductive brush roller 13, the similar equalizing effect and charging effect can be obtained. However, by superimposing the AC voltage, the effects can be much improved. The AC voltage and the frequency are preferably in the range from 300 V_p-p to 2000 V_p-p and in the range from 200 Hz to 5 kHz, respectively. In addition, the absolute value of the DC voltage to be superimposed is preferably the potential of the electrostatic latent image base 1 or a larger value than that (particularly, a large value in the range from 200 to 500 V). Examples of the material of the fibers 14 of the conductive brush roller 13 include rayon, polyamide, acrylic resin, tetraphloro polyethylene, and so forth where conductive treatment has been applied.

[0030] In such a manner, with the conductive brush roller 13, the equalization process of the residual toner particles 2' and the charging process of the organic photosensitive substance 1 can be accomplished at the same time.

Embodiment 2

[0031] Instead of the conductive brush roller 13 in the embodiment 1, a fixed type conductive brush 13a shown in FIG. 4 may be used. The fixed type conductive brush 13a is provided with a conductive fibers 14 disposed on a concave surface of a fixed substrate piece 15a.

[0032] In this embodiment, in the same conditions as the embodiment 1, the same operation and effects as that were obtained. In this embodiment, the contacting width of the conductive brush 13a, namely a means for accomplishing both the charging function and equalizing function of the residual toner image, and the electrostatic latent image base 1 is preferably 3 mm or more.

Embodiment 3

[0033] Instead of the conductive brush roller 13 in the embodiment 1, a conductive roller 13b shown in FIG. 5 may be used. In the present embodiment, when the electrostatic latent image base 1 is composed of a rigid substance, the conductive roller 13b is preferably a resilient substance. FIG. 5 exemplifies the conductive roller 13b comprising a metal shaft 15, a conductive rubber layer 18 disposed at the outer periphery thereof, and a surface layer 18a made of a conductive resin or elastomer disposed on the surface thereof. The conductive roller 13b may be of a single layer type without the surface layer 18a.

[0034] In the structure of the aforementioned recording apparatus, experiments were conducted by using the conductive rollers 13b whose surface roughness is 0.3 µm Rz, 1.2 µm Rz, and 15 µm Rz. In all the cases, the desired charging effect and the equalizing effect were accomplished. Except for the conductive shaft 15, the material of the conductive roller 13b is preferably a conductive rubber layer 18 and a surface layer 18a whose specific resistance is in the range from 10³ to 10¹⁰ ohms cm. The electric and mechanic conditions of the present embodiment may be nearly same as those of the embodiment 1.

Embodiment 4

[0035] Instead of the conductive brush roller 13 in the embodiment 1, a magnetic brush 19 as shown in FIG. 6 may be used. The magnetic brush 19 comprises a fixed type or rotating type magnet roller 20, a fixed type or rotating type sleeve 21 disposed at the periphery thereof, and a magnetic particle layer 22 adhered at the periphery thereof. The magnetic particles may be iron powder, ferrite, or the like whose volume specific resistance is in the range from 10² to 10¹⁰ ohms cm and whose average particle diameter is in the range from 10 µm to 200 µm. In the nearly same conditions as the embodiment 1, the same operation and effects were accomplished in the present embodiment. Other electric and mechanical conditions may be the same as those of the embodiment 1.

[0036] As was described above, according to the recording apparatus of the present invention, the charging and residual toner image equalizing means securely charges the electrostatic latent image base and equalizes the residual toner particles at the same time. In addition, the recording apparatus can be readily structured in small size and at low cost. Moreover, the recording apparatus is free from contamination due to by-product in the discharging operation. Furthermore, the recording apparatus can usually output ghost-free high quality images.

Claims

1. A recording apparatus, comprising:
   an electrostatic latent image base;
   charging means for equally charging the surface of said electrostatic latent image base;
   means for attenuating part of electric charges on the surface of said electrostatic latent image base charged by said charging means and for forming an electrostatic latent image;
   developing means for adhering toner particles on said electrostatic latent image so as to form a toner image; and
   transferring means for transferring said toner image onto an image base;
   wherein said developing means attracts and collects residual toner particles into said developing means and develops said electrostatic latent image at the same time; and
   wherein said charging means has a particular charging function and a residual toner image equalizing function for disturbing a residual toner image left on said electrostatic latent image base and for equalizing the distribution of the toner particles.

2. The recording apparatus as set forth in claim 1, wherein said charging means for providing said particular charging function and said residual toner equalizing function is composed of a conductive contacter at which a voltage is applied.

3. The recording apparatus as set forth in claim 2, wherein the contacting width of said conductive contacter and said electrostatic latent image base is set to 0.5 mm or more against the rotating direction of said electrostatic latent image base.

4. The recording apparatus as set forth in claim 2, wherein a voltage applied to said conductive contacter is an AC voltage or a voltage where a DC voltage is superimposed to an AC voltage.

5. The recording apparatus as set forth in claim 2, wherein a voltage applied to said conductive contacter is a negative voltage or a voltage negatively deflected.

6. The recording apparatus as set forth in claim 2, wherein said conductive contacter is a conductive brush roller.

7. The recording apparatus as set forth in claim 6, wherein said conductive roller comprises a roller substrate and a group of conductive fibers disposed at the periphery thereof.

8. The recording apparatus as set forth in claim 7, wherein the roller substrate of said conductive brush roller is a rigid metal.

9. The recording apparatus as set forth in claim 7, wherein the roller substrate of said conductive brush roller is a resilient conductor.

10. The recording apparatus as set forth in claim 7, wherein the specific resistance of said conductive fibers disposed at the periphery of the roller substrate of said conductive brush roller is in the range from 10² to 10¹⁰ ohms cm.

11. The recording apparatus as set forth in claim 7, wherein the thickness of the conductive fibers disposed at the periphery of the roller substrate of said conductive brush roller is in the range from 0.5 to 10 deniers.

12. The recording apparatus as set forth in claim 11, wherein the fiber density of the conductive fibers disposed at the periphery of the roller substrate of said conductive brush roller is in the range from 5000 to 100,000 pieces/cm².

13. The recording apparatus as set forth in claim 6, wherein said conductive brush roller rotates at a different speed from said electrostatic latent image base.

14. The recording apparatus as set forth in claim 13, wherein the rotation speed of said conductive brush roller is set to 1.2 times to 5 times as much as that of said electrostatic latent image base.

15. The recording apparatus as set forth in claim 2, wherein said conductive contacter comprises at least a roller substrate and a conductive resilient substance layer disposed at the periphery thereof.

16. The recording apparatus as set forth in claim 15, wherein said conductive resilient substance layer has a surface protecting layer on the surface thereof.

17. The recording apparatus as set forth in claim 2, wherein said conductive contacter is a magnetic brush.

18. The recording apparatus as set forth in claim 2, wherein said conductive contacter is a conductive fixed brush.

19. The recording apparatus as set forth in claim 18, wherein said conductive fixed brush comprises a conductive substrate with a concave surface and a group of conductive fibers disposed on the concave surface thereof.

Drawing