GB2176025A

GB2176025A - Electrophotographic process

Info

Publication number: GB2176025A
Application number: GB08611132A
Authority: GB
Inventors: Tetsuro Konno; Yutaka Kanai; Tetsuya Fujita
Original assignee: Seikosha KK
Current assignee: Seikosha KK
Priority date: 1985-05-10
Filing date: 1986-05-07
Publication date: 1986-12-10
Also published as: GB8611132D0; JPS61256358A; GB2176025B; DE3615387C2; FR2581772A1; DE3615387A1; SG54589G; HK29490A

Abstract

An electrophotographic process in which use is made of a photosensitive member (1) comprising in succession a transparent support (1a), a transparent electrode (1b) and a photoconductive layer (1c), the process comprising a first step in which a charged toner (4) is applied substantially uniformly to a surface region of the photoconductive layer (1c); a second step in which a portion of said photoconductive layer (1c) at said surface region is irradiated with light (5) so as to reduce the electrical resistance of said portion, a third step in which the toner on said portion is subjected, by way of the transparent electrode (1b) and the said portion, to an electrical charge of a polarity opposite to its original charge; and a fourth step in which the toner on said portion is transferred onto a record medium (2) disposed opposite to the photoconductive layer (1c). The second, third and fourth steps may be substantially simultaneous. <IMAGE>

Description

SPECIFICATION Electrophotographic Process The present invention relates to an electrophotographic process, e.g. for use in copying machines, facsimile machines or optical printers.

Xerography is one of the most important processes used in conventional electrophotographic processes. Xerography consists of six basic steps as follows; a first step in which a-photosensitive member is charged with electricity; a second step in which the photosensitive member is exposed by irradiation with light to form an electrostatic latent image thereon; a third step in which toner particles are attached to the electrostatic latent image on the photosensitive member to develope this image; a fourth step in which the developed image is transferred to a record paper by utilizing an electric field; a fifth step in which the image transferred to the record paper is fixed; and a sixth step in which the photosensitive member is cleaned of the toner remaining thereon.In a known xerography apparatus, devices for respectively carrying out the first to fourth and sixth steps are separately disposed along a drum-or sheet-shaped photosensitive member having a relatively large diameter, and a device for carrying out the fifth step is disposed in the path for transporting the recording paper (see e.g., "Electrophotography", written by R.M. Schaffert, published by The Focal Press Limited (London and Newyork)).

There is another type of conventional xerography apparatus designed to reduce the number of steps and shorten the time required for printing, e.g. one disclosed in Japanese Laid-Open Patent Specification No. 77848/1981. This type of xerography apparatus includes a photosensitive member having a photoconductive layer formed on a transparent electrode layer, an electrode provided opposite to this photosensitive member, a power supply for applying a voltage between the said opposite electrode and the transparent electrode layer, and an exposure device which produces a light image from the side of the photosensitive member which is closer to the transparent electrode layer.A toner ribbon, which is charged in advance, and record paper are interposed between the photosensitive member and the said opposite electrode in such a manner that they are laid one upon the other and the toner ribbon is in contact with the photoconductive layer. In these circumstances, production of a light image by the exposure device is effected.

The toner which has been fused in a pattern corresponding to the light image by the irradiation is transferred to the record paper, thereby forming an image on the paper.

photoconductive layer. In these circumstances, production of a light image by the exposure device is effected. The toner which has been fused in a pattern corresponding to the light image by the irradiation is transferred to the record paper, thereby forming an image on the paper.

In the above-described known xerography processes, the primary charging step and the cleaning step are indipensable; therefore, the number of steps is relatively large. In apparatus for carrying out the above-described processes, various devices for carrying out respective steps are disposed separately from each other. For this reason, the apparatus is complicated, and the overall size thereof is relatively large; it is difficult to reduce the thickness or width of the apparatus and obtain a compact system. In addition, the developing device has a complicated mechanism and, in the developing step, the toner comes in contact with and rubs against the surface of the photosensitive member at high speed, which has an adverse effect on the lifetime of the photosensitive member.

The prior art disciosed in the above-mentioned Japanese Laid Open Patent Specification No.

77848/1981 further suffers from the following problems. Since the toner ribbon overlies the record paper so that the toner ribbon is in contact with the whole surface of the paper, when the toner is fused at a position irradiated with light and is transferred to the record paper, the toner may adhere to peripheral portions around the transferred image, thus easily causing a so-called "ghost" to occur.

It is therefore an object of the present invention to provide an electrophotographic process which enables the number of steps in the process to be reduced by a large margin.

According, therefore, to the present invention, there is provided an electrophotographic process in which use is made of photosensitive member comprising in succession a transparent support, a transparent electrode and a photoconductive layer, the process comprising a first step in which a charged toner is applied substantially uniformly to a surface region of the photoconductive layer; a second step in which a portion of said photoconductive layer at said surface region is irradiated with light so as to reduce the electrical resistance of said portion; a third step in which the toner on said portion is subjected, by way of the transparent electrode and the said portion, to an electrical charge of a polarity opposite to its original charge; and a fourth step in which the toner on said portion is transferred onto a record medium disposed opposite to the photoconductive layer.

Preferably, said second, third and fourth steps are substantially simultaneous.

In the electrophotographic process according to the present invention, at the same time as the portion of the photosensitive member is irradiated with light, the toner on the irradiated portion may be transferred directly to the record medium by means of coulomb force or by the force of the electric field. Accordingly, an electrostatic latent image forming step, a developing step and a transfer step, which have heretofore been carried out separately from each other, can be executed in one intensive step. In addition, it becomes unnecessary to carry out steps of charging and cleaning the photosensitive member, which are conventionally required.

The photosensitive member may be rigid, e.g. it may have a flat plate shape or a drum shape. Al ternatively, it may be flexible and may be constituted by an endless member.

The invention also comprises electrophotographic apparatus comprising a photosensitive member comprising in succession a transparent support, a transparent electrode and a photoconductive layer; toner supply means for charging a toner and supplying the latter substantially uniformly to a surface region of the photoconductive layer; irradiating means for irradiating a portion of said photoconductive layer at said surface region with light so as to reduce the electrical resistance of said portion, means for subjecting the toner on the said portion, by way of the transparent electrode and the said portion, to an electrical charge of a polarity opposite to its original charge; and means for supporting a record medium opposite to the photoconductive layer so that in operation the toner on the said portion is transferred onto the record medium.

The toner supply means may comprise a toner stirring member disposed in a toner reservoir, means being provided for supplying the toner stirring member with a bias voltage. Moreover, the toner supply means may comprise at iease one doctor blade for producing a toner layer of substantially uniform thickness.

Alternatively, the photosensitive member may be carried by a reciprocable member which is provided on each of the opposite sides of the photosensitive member with atoner reservoir, the reciprocable member being provided at an outlet of each toner reservoir with an electrode plate, reciprocation of the reciprocable member causing the toner in the alternate reservoirs to be forced past the respective electrode plates so as to be charged thereby and formed thereby in a layer on the photoconductive layer.

The invention is illustrated, merely by way of example, in the accompanying drawings, in which; Figure 1 shows the principle of the electrophotographic process according to the present invention; Figure 2 is a perspective view of an arrangement to which one embodiment of the electrophotographic process according to the present invention is- applied; Figure 3 is a sectional view showing another embodiment of the present invention; and Figure 4 is a sectional view showing still another embodiment of the present invention.

Terms such as "upper" and "lower" as used in the description below, are to be understood to refer to directions as seen in the accompanying drawings.

The principle of the electrophotographic process according to the present invention will first be described with reference to Figure 1. - A photosensitive member 1 consists of three successive layers, namely a transparent support 1a made of a glass or plastics material; a transparent electrode 1b formed on the upper surface of the transparent support la; and a photoconductive layer 1c formed on the upper surface of the transparent electrode 1b. A record medium 2, such as an ordinary paper, is transported past the photosensitive member 1, as indicated by arrow 6, a slight gap being provided between the opposing surfaces of the record medium 2 and the photoconductive layer 1c.A charged toner 4 (the toner 4 being charged positive, in this example) is substantially uniformly attached to virtually the whole upper surface of the photoconductive layer. A chargind device 3, such as a corona-charging device, which constitutes a toner transfer means, is disposed at the upper side of the record medium 2.

When a light beam 5, such as a laser beam, is applied to the photosensitive member 1 from -the lower side thereof, that is, from the side of transparent support la, there is decrease in the electri-cal resistance of the portion of the photoconductive layer 1c which has been irradiated by the light beam 5. If the transparent electrode 1b is reverse-biased by means of a power supply E, charges which are opposite in polarity to the charges in the toner 4 are injected into the toner 4 which covers the irradiated portion of thephotoconductive layer 1c. In consequence, those toner particles that have been subjected to charges of the said opposite polarity are transferred to the record medium 2 by means of the coulomb force acting between the toner 4 and the charging device 3 or by the force of the electric field produced by the charging device 3.In other words, the toner 4 covering the exposed portion of the photoconductive layer 1c is directly transferred to the record medium 2 without pre-charging of the photosensitive member 1.

Referring next to Figure 2, which shows one embodiment of the present invention based on the above-described principle, a photosensitive member 11 consists of three layers, that is, a transparent support, a transparent electrode and a photoconductive layer, similar to that shown in Figure 1. The transparent support has a flexible endless sheet-like configuration. The photosensitive member 11 is passed over transport rollers 16a, 16b, 16c and transported in one direction. A portion of a record medium 12 is transported parallel to and in the same direction as the photosensitive member 11, she said portion of the record medium 12 facing the upper part of the photosensitive member 11. A charging device 13, which constitutes a toner transfer means, is disposed above, i.e. to the rear of, the record medium 12. A rotary polygonal mirror 17 is disposed within the spaced surrounded by the rollers 16a, 16b and 16c and is rotatable in one direction. A light beam 15 is made incident on the polygonal mirror 17 after being reflected by a reflecting mirror 18. The light beam 15 reflected by the polygonal mirror 17 scans across the rear surface of the photosensitive member 11 below the charging device 13 in a direction perpendicular to the direction of travel of the photosensitive member 11 in response-to the rotation of the polygonal mirror 1-7. A charged toner 14 is substantially uniformly supplied to the photosensitive member 11. More specifically, a toner reservoir 19 accommodates the toner 14 which has not yet been charged and also incorpo rates a stirring member 20 to which a bias voltage is applied. The toner 14 is charged by this stirring member 20.When the toner 14 comes in contact with an insultated roller 21, charges opposite in polarity to the charges in the toner 14 are induced inside the roller 21, and coulomb force acts between the roller 21 and the charged toner 14, whereby a charged toner layer is formed on the roller 21. The toner layer on the roller 21 is controlled by a toner layer thickness adjusting member (doctor blade) 22 so that the thickness of the toner layer becomes substantially uniform. The roller 21 is disposed in close proximity to the surface of the photosensitive member 11 with a predetermined gap e.g. a gap substantially the same as the thickness of the toner layer on the roller 21.

The roller 16a is constituted by a permanent magnet, and the toner 14 on the roller 21 is attracted to and held on the photosensitive member 11 by means of the magnetic force from the transport roller 16a.

In this embodiment, the light beam 15 is reflected by the reflecting mirror 18 and further reflected by the rotary polygonal mirror 17 so as to scan across the rear surface of thephotosensitive member 11. Charges of opposite polarity are injected into the toner 14 in the manner described above, and the toner 14 which has received such a charge of opposite polarity is transferred to the record medium 12 by the action of the charging device 13.

Figure 3 shows another embodiment of the present invention.

In this embodiment, a photosensitive member 31 has a flat plate-like configuration and consists of three layers, that is, a transparent support 31a, a transparent electrode 31b and a photoconductive layer 31c arranged in a manner similar to that of Figure 1. The photosensitive member 31 is buried in the centre of the bottom portion of a support member 38 which also serves as a toner casing. A pair of electrode plates (doctor blades) 36a and 36b are provided above the photosensitive member 31 with a predetermined gap provided therebetween.

The electrode plates 36a and 36b are respectively secured at predetermined positions by electrode support members 37a and 37b and connected to a power supply E1. A toner 34 is accommodated in pair of toner reservoirs 39a and 39b defined between the support member 38 and the electrode support members 37a, 37b. The distal end of each of the electrode plates 36a and 36b is disposed so that a predetermined gap is provided between the same and the photoconductive layer 31c, thereby also carrying out a toner layer thickness adjusting function. A record medium 32 is provided so as to be transported from the left to the right (as viewed in Figure 3) while facing the photosensitive member 31. A charging device 33, which constitutes a toner transfer means, is disposed above, i.e. at the rear of, the record medium 32.A relatively high voltage is applied to the electrode plates 36a. 36b through the power supply E, for the purpose of charging the toner 34. The transparent electrode 31b is connected to a power supply E2 for the purpose of injecting charges into the toner 34 which are opposite is polarity to the charges which have already been injected therein by pre-charging.

The support member 38 is adapted to be aboe to reciprocate horizontally together with the photosensitive member 31, so that the toner 34 accommodated in the toner reservoirs 39a, 39b is supplied under the electrode plates 36a, 36b by the reciprocating motion of the support member 38.

Since a high voltage is applied to the electrode plates 36a, 36b-through the power supply E" when the toner 34 comes in contact with the electrode plates 36a, 36b, charges are injected into the toner 34. The charges in the toner 34 induces charges in the surface of the photosensitive member 31 which are opposite in polarity to the charges in the toner 34, thus attracting the toner 34. The toner 34 on the surface of the photosensitive member 31 is formed into a toner layer having a uniform thickness by the motion of the photosensitive member 31 which reciprocates horizontally below the electrode plates 36a, 36b.When a light beam 35 is applied to the rear surface of the photosensitive member 31 directly below the charging device 33 while the support member 38 is moving from the left to the right, charges of opposite polarity are injected into the toner 34 in a manner similar to that described above and, at the same time, the toner 34 in the irradiated portion is transferred to the record medium 22. Although the toner 34 on the photosensitive member 31 is partially consumed by this transfer, it is compensated for in the following manner. Namely, the toner 34 on the photosensitive member 31 passes under the electrode plate 36b on the right-hand side and enters the toner reservoir 39b and then returns or moves from the right to the left.During this backward movement, when the toner 34 on the photosensitive member 31 passes under the electrode plate 36b so as to be charged, this tomer 34 is reformed into a toner layer having a uniform thickness. In addition, since the photosensitive member 31 also reciprocates together with the support member 38, the position on the photosensitive member 31 which is irradiated with the light beam 35 changes, and this allows the photosensitive member 31 to recover from light fatigue. Accordingly, it is possible to extend the lifetime of the photosensitive member 31.

Figure 4 shows still another embodiment of the present invention. In this embodiment, a photosensitive member 41 has a drum-like configuration and is provided so as to be rotatable in one direction. The photosensitive member 41 consists of three layers, that is, a transparent support 41a made of a rigid material such as glass, a transparent electrode 41b and a photoconductive layer 41c.

A toner reservoir 49, which is similar to that shown in Figure 2, is disposed at one side of the photosensitive member 41. An insulated stirring member 40 is incorporated in the toner reservoir 49. The toner 44 is frictionally charged by the rotation of the stirring member 40. A toner layer thickness adjusting member (doctor blade) 46 is provided such as to face the photosensitive member 41 across a predetermined gap, thereby adjusting the toner 44 on the surface of the photosensitive member 41 so that the thickness of the toner 44 becomes substantially uniform. A record medium 42 is disposed so as to face the upper part of the photosensitive member 41, the record medium 42 being transported in a direction corresponding to that in which the photosensitive member 41 is rotated.A charging device 43, which constitutes a toner transfer means, is provided at the rear of the record medium 42. A rotary polygonal mirror 47 is disposed inside the photosensitive member 41, the mirror 47 being rotated in one direction. A light beam 45 is reflected by a reflecting mirror 48 before being made incident on the polygonal mirror 47. The light beam 45 is reflected by the polygonal mirror 47 so as to scan across the photosensitive member 31 from the inner side thereof and in a direction perpendicular to the direction of rotation of the photosensitive member 41, whereby the toner 44 on the surface of the photosensitive member 41 is transferred to the record medium 42 in a manner similar to that described above.

It should be noted that, although all the embodiments described above employ a corona-charging device alone as a toner transfer means, an opposing roller electrode may, if desired, be employed in place of the corona-charging device.

It is thus possible, according to the electrophotographic process of the present invention, to carry out an electrostatic latent image forming step, a developing step and a transfer step in one intensive step, whereas these steps are carried out separately in the known xerography processes.

Accordingly, the number of steps can be reduced by a large margin. In addition, it is unnecessary to effect primary charging and cleaning of the photosensitive member. Since the toner and the photosensitive member do not come in contact with each other at high speed, there is no frictional adverse effect on the photosensitive member. Further, since the toner on the photosensitive member, other than that on the irradiated portion, is subjected to the force of the repulsion which acts between the same and the record medium, the generation of a "ghost" is suppressed, so that it is possible to effect reproduction with excellent printing quality.

Claims

1. An electrophotographic process in which use is made of a photosensitive member comprising in succession a transparent support, a transparent electrode and a photoconductive layer, the process comprising a first step in which a charged toner is applied substantially uniformly to a surface region of the photoconductive layer; a second step in which a portion of said photoconductive layer at said surface region is irradiated with light so as to reduce the electrical resistance of said portion; a third step in which the toner on said portion is subjected, by way of the transparent electrode and the said portion, to an electrical charge of a polarity opposite to its original charge; and a fourth step in which the toner on said portion is transferred onto a record medium disposed opposite to the photoconductive layer.

2. An electrophotographic process according to claim 1 wherein said second, third and fourth steps - are substantially simultaneous.

3. An electrophotographic process according to claim 1 or 2 wherein said photosensitive member is rigid.

4. An electrophotographic process according to claim 3, wherein said photosensitive member has a flat plate shape.

5. An electrophotographic process according to claim 3 wherein said photosensitive member has a drum shape.

6. An electrophotographic process according to claim 1 wherein said photosensitive member is flexible.

7. An electrophotographic process according to claim 6 wherein said photosensitive member is endless.

8. An electrophotographic process substantially as hereinbefore described with reference to any of Figures 1-4 of the accompanying drawings.

9. Electrophotographic apparatus comprising a photosensitive member comprising in succession a transparent support, a transparent electrode and a -photoconductive layer; toner supply means for charging a toner and supplying the latter substantially uniformly to a surface region of the photoconductive layer; irradiating means for irradiating a portion of said photoconductive layer at said surface region with light so as to reduce the electrical resistance of said portion; means for subjecting the toner on the said portion, by way of the transparent electrode and the said portion, to an electrical charge of a polarity opposite to its original charge; and means for supporting a record me dium oposite to the photoconductive layer so that in operation the toner on the said portion is transferred onto the record medium.

10. Apparatus according to claim 9, wherein the toner supply means comprises a toner stirring member disposed in a toner reservoir, means being provided for supplying the toner stirring member with a bias voltage.

11. Apparatus according to claim 9 or 10, wherein the toner supply means comprises at least one doctor blade for producing a toner layer of substantially uniform thickness.

12. Apparatus according to claim 9 wherein the photosensitive member is carried by a reciprocable member which is provided on each of the opposite sides of the photosensitive member with a toner reservoir,the reciprocable member being provided at an outlet of each toner reservoir with an electrode plate, reciprocation of the reciprocable member causing the toner in the alternate reservoirs to be forced past the respective electrode plates so as to be charged thereby and formed thereby in a layer on the photoconductive layer.

13. Apparatus according to any of claims 9-12 in which the irradiating means comprises a rotary polygonal mirror.

14. Electrophotographic apparatus substantially as hereinbefore described with reference to and as shown in any of Figures 1-4 of the accompanying drawings.

15. Any novel integer or step, or combination of integers or steps, hereinbefore described and or shown in the accompanying drawings irrespective of whether the present claim is within the scope of, or relates to the same or a different invention from that of, the preceding claims.

16. An electrophotographic process comprising; a first step in which a toner charged in advance is uniformly attached to substantially the whole surface of a photosensitive member composed of a transparent support a transparent electrode formed on the surface of said support and a photoconductive layer formed on the surface of said electrode; a second step in which a portion of said photoconductive member is irradiated with light from the side of said transparent support, thereby lowering the electrical resistance of said photoconductive layer at the irradiated portion; a third step in which charges which are opposite in polarity to the charges in said toner are injected into said toner, through said transparent electrode and the selected photoconductive layer at said irradiated portion at which the electrical resistance has been lowered; and a fourth step in which the toner on said irradiated portion is transferred to a recording medium positioned so as to face said photoconductive layer.