Image forming apparatus in which toner is recycled between toner applying and cleaning stations

#This application is related to cofiled U.S. patent application Ser. No. 07/973,802, filed Nov. 9, 1992 of Hilbert et al, U.S. patent application Ser. No. 07/975,449, filed Nov. 12, 1992 of Weitzel et al and U.S. patent application Ser. No. 07/975,258, filed Nov. 12, 1992 of Kamp et al.

#This invention relates to image forming apparatus having separate devices for applying toner to and for cleaning toner from an image surface. Although not limited thereto, it is particularly usable in image forming apparatus in which a uniform layer of toner is applied to a surface, the toner is imagewise tacked to the surface, and untacked toner is cleaned off the surface. It can also be used in conventional electrostatic image forming apparatus.

#U.S. patent application Ser. Nos. 07/632,698, now U.S. Pat. No. 5,138,388(Kamp et al); 07/673,509 (DeBoer et al); 07/621,691, now abandoned (DeBoer et al); and PCT Application No. 91/08815, filed Nov. 26, 1991 disclose a process in which a uniform layer of toner is applied to a surface. The toner is imagewise tacked, preferably with a laser, to the surface and then the untacked toner is cleaned off the surface, leaving a toner image corresponding to the tacked toner. The tacked toner image can then be transferred to another surface, or it can be fixed to the surface to which it is tacked. This process can provide extremely high resolution and high density with fine toner particles and a precise laser. It does not require the use of light sensitive materials.

#FIG. 1 is a front schematic of an image forming apparatus.

#FIG. 2 is a side view of the apparatus shown in FIG. 1 with a portion of a cleaning station broken away and other elements eliminated for clarity of illustration.

#FIG. 3 is a front section, partially schematic illustrating toner applying and cleaning stations of the apparatus shown in FIG. 1.

#According to FIG. 1, a drum 10 is rotated by a motor 27 about an axis of rotation 9 to bring its peripheral surface 12 past a series of stations to form toner images on an image surface. The image surface can be the peripheral surface 12. However, it is preferably a surface of a receiving sheet fed from a receiving sheet supply 18 and held to drum 10 as it is rotated. According to the latter embodiment, a receiving sheet is fed out of receiving sheet supply 18 and into contact with peripheral surface 12 where it is held by gripping fingers, vacuum or electrostatics. The surface of the receiving sheet facing away from drum 10 in this embodiment is the image surface. A uniform layer or layers of toner is applied to the image surface as it phases a toner applying means or station 42 which, as explained below, can be a magnetic brush toner applying device similar to that used for developing electrostatic images. Toner can be applied to the image surface without pretreatment of the surface, by appropriate choice of bias on station 42. Alternatively, the image surface can be uniformly charged by a corona charger 2 to assist in the toner applying function.

#After a uniform layer of toner has been applied to the image surface, the toner applying station 42 is turned off, by means to be described. An imagewise tacking means, for example, a laser 5, is turned on and the toner is imagewise tacked to the image surface. Laser 5 can be a single, relatively high powered laser. Alternatively, a printhead comprised of a linear array of optical fibers powered by a series of laser diodes and constructed, as described in U.S. Pat. No. 5,164,742, can be used to tack a plurality of lines of image at a single pass.

#The toner is tacked to the image surface by sintering or softening the toner where it contacts the surface or softening the image surface itself or both. If the image surface is to be softened, it should be defined by an outer layer of a heat softenable thermoplastic. If the toner is to be sintered or softened, it must include a material that increases its tendency to adhere when heated, for example, a heat softenable thermoplastic. After the toner has been imagewise tacked to the image surface, it can be subjected to a neutralizing AC corona from a corona source 21 which makes the untacked toner easier to clean. Preferably, such an AC corona should have a small or no DC bias. The toner is then passed past a cleaning station 41 where the loose toner is cleaned from the image surface, leaving only the toner that had been tacked by laser 5. Cleaning station 41 can also be used to clean the image surface before toner is applied to it to improve the uniformity of laydown or application of the toner.