ELECTROPHOTOGRAPHIC PROCESS AND APPARATUS

Abstract: A recording member (10) consists, for example, of one endless film-like belt that is folded in a recessed shape. A plurality of printing portions (1-4) are disposed in such a manner as to face the outer peripheral surface of the belt. This recording member is developed simultaneously by toners having different colors. The toner image is transferred to recording paper by transfer units that are disposed in such a manner as to face the upper projecting portion of the belt while interposing therebetween the recording paper that moves linearly along the upper part of the printing portions (1-5, 2-5, 3-5, 4-5).

Description: FIELD OF THE INVENTION The invention relates to an electrophotographic printing apparatus according to the precharacterizing part of claim 1. Such an electrophotographic printing apparatus is known from WO-A-84/04604. BACKGROUND OF THE INVENTION A conventional full-color printing method is disclosed, for example, in Fig. 1 of JP-A- 134439/1979 entitled "COLOR ELECTROPHOTOGRAPHIC COPYING MACHINE" laid open to public on October 18,1979. In accordance with this prior art reference, a plurality of photoreceptor drums corresponding to three primary colors of cyanate (C), Magenta (M) and yellow (Y) or to the three primary colors of (C),(M), (Y) plus black (B) are disposed independently and after a toner image is formed simultaneously on each of these photoreceptor drums, each toner image is transferred in order to transfer paper moving linearly. In the electrophotographic copying machine of this kind, degradation of each photoreceptor member is likely to occur non-uniformly because a plurality of photoreceptor drums are disposed, and a printing position error is therefore likely to occur on the transfer paper. The above mentioned WO-A-84/04604 describes an electrophotographic apparatus which develops sequentially an electrostatic latent image using toners of different colors to obtain a multi-color image. This document shows that it is already known to use an endless belt-like recording member. This endless belt is conveyed along a non folded path. A plurality of development portions are disposed along the outer peripheral surface of the endless belt-like recording member, each for developing an electrostatic image with a different color toner. After the plurality of development portions in the moving direction of the endless belt-like recording member, there is disposed one transfer unit for sequentially transferring the resulting toner images of different color on recording paper. The known electrophotographic printing apparatus comprises one exposure unit which directs light onto an exposed part of the endless belt-like recording member. As the known electrophotographic printing apparatus comprises only one exposure unit and one transfer unit it cannot achieve multi-color printing in the same period of time as required for monochromic printing with a single photosensitive drum. Accordingly it is an object of the present invention to provide an electrophotographic printing apparatus which can achieve multi-color printing in the same period as required for monochromic printing and which achieves a compact printing apparatus. The above object is solved according to the invention by the features specified in the independent claim 1. The dependent claims 2 to 5 characterize advantageous developments thereof. In accordance with the present invention, one recording member is conveyed along a folded path so that it forms at least one recess and printing stations are alternately disposed inside and outside of the recess so that a plurality of toner images can be superposed with one another when the recording paper passes. Therefore, multi-color of full-color images can be obtained at the same printing speed as monochromic printing. Furthermore, since at least one printing station is fitted into said at least one recess of the belt-like photosensitive member, it has no dead space and the apparatus can be made compact as a whole. Furthermore, a positional error of the printing process is not likely to occur. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a side view of a full-color printing machine in one embodiment of the present invention; Fig. 2 is a side view of a two-color printing machine in another embodiment of the present invention; and Fig. 3 is a side view of still another embodiment of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Fig. 1, a recording member belt 10 made of an organic photoconductor is moved while being driven by a roller 11 for driving the belt 10. The recording member belt 10 is conveyed while being bent in a concaved form as shown in the drawings,and first, second, third and fourth printing stations 1, 2, 3 and 4 are disposed along its outer peripheral portion. The recording member belt 10 is charged uniformly by a charging device 1-1 and the rays of light emitted from an LED array light source 1-3 on the basis of printing signals are radiated to the recording member belt 10 through a rod lens array 1-2 to form an electrostatic latent image thereon. The latent image is developed by a cyanate toner of a first developing machine 1-4. The toner image thus formed is transferred to paper 12 by a transfer unit 1-5. Each of the second, third and fourth printing stations 2, 3 and 4 consists of an exposure unit consisting of a charging device 2-1, 3-1, 4-1, a rod lens array 2-2, 3-2, 4-2 and an LED array light source 2-3, 3-3, 4-3, a developing machine 2-4, 3-4, 4-4 containing the Magenta toner, the yellow toner and the black toner, a transfer unit 2-5, 3-5, 4-5, a cleaner 2-6, 3-6, 4-6 and an eraser lamp 2-7, 3-7, 4-7, 1-7 in the same way as the first printing station 1. Charging, exposure and development are carried out in the second, third and fourth printing portions 2, 3 and 4 in synchronism with the charging, exposure and developing steps in the first printing station 1. In this case, the printing process in the second, third and fourth printing stations is sequentially deviated by the image formation time so that the toner images formed after the paper 12 has passed sequentially through the transfer units 1-5, 2-5, 3-5, 4-5 overlap exactly with one another and form a full-color image. The toners remaining on the recording member belt 10 after transfer are removed by the cleaner lamps 2-6, 3-6, 4-6, 1-6 and the residual charge of the toner is then erased by the erasers 2-7, 3-7, 4-7, 1-7. By the time when the paper 12 passes through the transfer unit 1-5, the next printing process has already been started in the first printing station 1. The full-color image thus formed on the paper is fixed by heat rollers. Since full-color printing can be made while the recording paper 12 moves linearly between transfer unit 1-5, 2-5, 3-5, 4-5 and a paper conveyor roller 19, this embodiment provides the effect that multi-color printing can be made at the same printing speed as monochromic printing. Since a single recording member belt is used, there can be obtained the effect that no position error occurs when the toner images are sequentially superposed. Furthermore, the printing station of each color is disposed along the outer peripheral surface of the recording member belt which is bent in a concave form, the embodiment provides the effects that no dead space exists and the apparatus can be made more compact as a whole. When a plurality of photoreceptor drums are used, degradation of each photoreceptor drum does not occur at the same time. Fig. 2 shows a two-color printing process consisting of the first printing portion 1 and the fourth printing station 4 shown in Fig. 1. In accordance with this embodiment, two-color printing can be made at the same printing speed as the monochromic printing in various combinations of colors by changing the first developing machine 1-4 of the first printing station 1 and the fourth developing machine 4-4 of the fourth printing station 4 by developing machines having toners of other colors. In the embodiments described above, the recording member belt 10 is made of an organic photo-conductor, but organic and inorganic photo-conductors can be used without specific limitation so long as they can be shaped in the belt form. It is also possible to use an organic film having no photoconductivity for the recording member belt 10 and an ion radiation array for forming the electrostatic latent image by ion radiation in place of the exposure unit consisting of the rod lens array and the LED array. In such a case, the charging device and the eraser become unnecessary and it is advisable to use an A.C. corona charge remover in place of the eraser. Furthermore, it is possible to form a magnetic latent image in place of the electrostatic latent image and to develop it by a magnetic toner having a different color. In the first embodiment, it is further possible to use a liquid crystal shutter array in place of the LED array light source. If the charging device, the exposure unit, the developing machine, the cleaner and the eraser to be inserted into the inner peripheral surface of the recess of the recording member in such a manner as to face the recording member are assembled in the unit construction, the assembly and production of the apparatus become easier. Moreover, the first developing machine in this embodiment contains the cyanate toner but since a sufficient space can be secured with respect to the outer wall surface of the recess, a developing machine having a greater size can be disposed and a toner having the highest use frequency (such as black) is preferably used. Fig. 3 shows a third embodiment of the present invention. Though the recording member 10 is conveyed in the substantially concave form in the first and second embodiments, it is conveyed through a cylindrically folded path by a cylinder 14 and a guide 15. The recording member 10 is conveyed by driving at least one of two conveyor rollers 16. The recording member 10, the conveyor rollers 16, the cylinder 14 and the guide 15 are assembled in the cassette form so that the recording member 10 can be replaced easily. The first printing station containing the black toner that is used most frequently is disposed outside the cylinder 14 having a wide space, and exposure is made by a laser beam 18. The second printing station containing the color toner is incorporated in the cylinder 14. The two conveyor rollers constituting the transfer unit are disposed close to each other, and the black toner image and the color toner image formed on the surface of the recording member 10 are transferred simultaneously to the paper 12 by one transfer roller 17 to obtain a two-color image.

Claims: An electrophotographic printing apparatus for sequentially developing an electrostatic latent image, said apparatus comprising a recording member (10) on which surface a latent image is formed by toners of different colors and transferring sequentially the resulting toner images to recording paper in superposition to obtain a multi-color or full-color image, wherein said recording member is shaped in an endless belt-like form being conveyed in a bent path and a plurality of printing stations (1-4) are disposed along the outer peripheral surface of said belt-like recording member, characterized in that said belt-like recording member is conveyed along a folded path, each printing station (1-4) includes exposure/recording and developing means, and there are disposed transfer units (1-5, 2-5, 3-5, 4-5) respectively arranged in the moving direction of said portion belt-like recording member after every printing station (1-4) for sequentially transferring the resulting toner images to recording paper (12) moving linearly along the upper part of said path. The electrophotographic printing apparatus according to claim 1, wherein said recording member is formed in a substantially continuous recessed shape, and a first printing station (2, 3, 4) constituted in a unit structure is disposed inside said recess in such a manner as to face the inner peripheral surface of said recess of said recording member. The electrophotographic printing apparatus according to claim 1, wherein said belt-like recording member is driven by conveyor rollers (16) disposed along the outer peripheral surface of a cylinder (14) having one of its ends open and a guide (15) having a smaller diameter than said cylinder and disposed substantially concentrically with said cylinder, a first printing station (1) is disposed outside said cylinder in such a manner as to face said recording member and a second printing station (2) having a unit structure is assembled inside said guide. The electrophotographic printing apparatus according to claim 2, wherein a second printing station (1) is disposed on the outer peripheral surface of said recess of said recording member. The electrophotographic printing apparatus according to claim 3, wherein a transfer roller (17) forming part of said transfer units for transferring multiple colors to said recording paper is disposed in such a manner as to face said conveyor rollers (16).

Inventors: ANZAI, MASAYASU, HOSHI, NOBUYOSHI
Applicants: HITACHI, LTD.
Application year: 1987
Main classification: G03G15
IPC codes: G03G15