This invention relates to a device for cleaning toner from a moving 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 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.
In this process, tacking can be accomplished by softening a heat softenable layer on the image surface, softening a toner particle where it touches the image surface, or both. Toner can be applied by a device comparable to that conventionally used to develop electrostatic images, for example, a magnetic brush development station. However, cleaning is somewhat more difficult, since the loose toner must be cleaned off without disturbing what may be quite lightly tacked imagewise toner. A preferable approach to this cleaning problem is to use a magnetic brush cleaner employing hard magnetic carrier particles and a rotating magnetic core which provides a relatively soft cleaning brush that will clean off the loose toner while leaving the lightly tacked toner image.
U.S. Pat. No. 4,797,704, granted to Hill et al Jan. 10, 1989, shows a magnetic brush development apparatus in which a rotating magnetic core drives developer, including a hard magnetized carrier around a noncylindrical shell. The shell is shaped to control the movement of the developer through an extended development or toning zone. The developer is moved in the same direction as an electrostatic image being developed, and the development zone is extended generally upstream with respect to that movement of the position at which the magnetic core is closest to the image. The shell curves rapidly away from the electrostatic image downstream of the core so that the magnetic field from the core can prevent pickup of the magnetized carrier by the electrostatic image. This extended zone has a tendency to increase the density of the image and thoroughness of the development. Some carrier pickup is tolerated to obtain thorough developing with this apparatus.
Other references which show extended development zones with rotating core development systems include U.S. Pat. No. 5,080,038, Rubin, Jan. 4, 1992; U.S. Pat. No. 4,235,549, Eisbein et al, Nov. 25, 1980; U.S. Pat. No. 4,287,850, Yamamoto et al, Sep. 8, 1981; Japanese Utility Model No. 51-164622, Laid-Open No. 53-81040, Jul. 5, 1978; and U.S. Pat. No. 4,804,994, Sasaki et al, Feb. 14, 1989.
U.S. Pat. No. 4,638,759, granted to Ville et al shows a rotating core magnetic brush development apparatus in which a magnetic shunt is positioned around a portion of the core to interrupt the magnetic field and alter the development characteristics of a two-component magnetic developer.