DEVELOPING APPARATUS

Abstract: This invention relates to a developing apparatus, used in an electrophotographic system or an electrographic system for converting an electrostatic image formed on a sensitive material or a dielectric material into a visible image with a one-component developing agent formed solely of a non-magnetic toner (21). The developing apparatus has a carrier roll (24) serving as a movable developing agent carrier which supplies the developing agent to an electrostatic latent image. An elastic coating member (25) presses against the surface of the carrier roll (24) and is supported at one end thereof. The elastic coating member (25) is so directed that its free end is directed opposite the direction of movement of the carrier roll (24). A developing agent container (22) is provided together with a toner stirring member (29) disposed contiguously to or in sliding contact with the carrier roll (24) such that the applied toner (21) is uniformly spread.

Description: The present Application claims priority of Japanese Patent Application Serial No.60-60928 filed on March 27th, 1985, No.60-61836 filed on March 28th, 1985 and No.60-143504 filed on June 29th, 1985. This invention relates to a developing apparatus, and more particularly relates to improvements in and concerning a developing apparatus to be used in an electrophotographic system or an electrographic system for converting an electrostatic image formed on a photosensitive material or a dielectric material into a visible image with a one component developing agent formed solely of a non-magnetic toner. In the developing apparatus of this type, technical advances are taking place in the direction from the type using a two-component developing agent composed of a toner and a carrier to the type using a one component developing agent composed solely of a magnetic toner and are destined to take their course from the type using a one component toner composed solely of a magnetic toner to the type using a one component developing agent composed solely of a non-magnetic toner. The developing apparatus of the type using a one component developing agent composed of a non-magnetic toner effects desired image development by applying the non-magnetic toner uniformly in the form of a thin layer on the surface of a rotating carrier roll and allowing the applied toner to be transferred onto an electrostatic image on a rotating sensitive drum disposed parallelly to and opposite the carrier roll across a fine gap in proportion to the charge lodged. The developing apparatus of the type using a one component developing agent composed of a non-magnetic toner, however, has one serious problem that it is difficult to form a uniform thin layer of the toner stably on the surface of the carrier roll. This problem has impeded practical adoption of the developing apparatus. In view of this true state of affairs, the inventors formerly succeeded in enabling formation of a thin layer of a non-magnetic toner by perfecting a developing apparatus illustrated in Fig. 1 (Japanese Patent Application SHO 58(1983)-182, 743). The developing apparatus of this former invention accomplishes desired development of an electrostatic image by disposing a metal plate blade 2 in such a manner as to keep the rear side of the free end thereof, namely the flat surface on the downstream side thereof relative to the flow of a developing agent, in pressed contact with the peripheral surface of a carrier roll 1 having irregularities formed on a surface serving as a flexible developing agent carrier thereby enabling a non-magnetic toner 4 supplied as from a toner container 3 to be applied in the form of a thin layer of toner on the surface of the carrier roll 1 with the aid of the aforementioned metal plate blade 2 and opposing the thin layer of toner to a photosensitive drum 5 serving as an image carrier. In this developing apparatus, when the carrier 1 having irregularities formed on the surface thereof is rotated clockwise, the non-magnetic toner 4 in the toner container 3 is transferred along the carrier roll 1 to the interface between the metal plate blade 2 possessing elasticity and the carrier roll 1. The metal plate blade 2 has a large modulus of elasticity as compared with a rubber plate and meagerly lacks uniformity of the amount of deformation due to lack of uniformity of the pressure as of a fitting jig and exhibits minimal plastic deformation. Thus, the force with which the metal plate blade 2 is pressed against the carrier roll 1 is made uniform and the thin layer of toner, therefore, is formed in a uniform thickness. Moreover, since the metal plate blade 2 possesses electroconductivity, it can prevent the rear surface charging due to the triboelectricity possibly caused when the metal plate blade 2 is placed into pressed contact with the non-magnetic toner 4. As a result, the shear strength exerted on the aggregate of toner is constant at all times and the thin layer of toner can be formed in an uniform thickness. This formation of the thin layer of toner is effected, as illustrated in Fig. 2, by the repetition of the shear strength of the toner aggregate 7 under the exertion of the inhibiting force F₁ generated by the metal plate blade 2 and the conveying force F₂ generated by the carrier roll 1. When the surface smoothness of the carrier roll 7 is high, the toner aggregate 7 stagnates between the carrier roll 1 and the metal plate blade 2 because slippage occurs between the toner aggregate 7 and the carrier roll 1. As a result, the subsequent toner cannot pass this position and the thin layer of toner is liable to sustain comby streaks thereon. This trend gains in prominence when the toner adopted has a strong self-aggregating property. As regards this problem, the slippage between the toner aggregate 7 and the carrier roll 1 can be prevented to permit formation of an uniform thin layer of toner despite the toner's self-aggregating property by imparting irregularities 6 to the surface of the carrier roll 1. As means of giving irregularities to the surface of the carrier roll 1, a method which comprises subjecting the surface to a treatment of sand blasting and/or a subsequent treatment of metal plating may be cited. For the developing apparatus of the type using a one component developing agent composed solely of a non-magnetic toner, it is extremely important that the irregularities should be formed on the surface of the carrier roll 1. The conventional method for the fabrication of the surface of the carrier roll 1 has not been sufficient for stable reproduction of images of satisfactory quality. In the developing apparatus described above, the thin layer of toner is obtained in a thickness of about 60 to 120 µm, generally above 80 µm by keeping the metal plate blade 2 pressed strongly against the carrier roll 1. The images, therefore, are reproduced in sufficient density. The application of such high pressure, however, has entailed a problem that the pressure is transmitted also to the toner to give birth to frictional force and fogging of image. When the pressure applied to the metal plate blade 2 is increased to decrease the thickness of the thin layer of toner, although the desired decrease of the layer thickness is indeed obtained, the toner is more liable to conglomeration and aggregation and the electric charge applied to the toner is apt to assume an unwanted opposite polarity. Thus, it is difficult to maintain the formation of an uniform thin layer of toner for a long period of time and to ensure stable reproduction of images of high quality. It is known from DE-A-3431967 to provide developing apparatus as defined in the pre-characterising portion of Claim 1 below; the stirring member is entirely separate from the developing roller and this apparatus would still have the disadvantages indicated immediately above. We acknowledge, for the sake of completeness, that JP-57-14858 discloses a brush roller in contact with the surface of a developing agent carrier drum in order to remove toner and allow it to be redeposited. According to the present invention there is provided a developing apparatus as defined in Claim 1 below. Embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings, in which:- Fig. 1 is a cross section schematically illustrating a conventional developing apparatus; Fig. 2 is a cross section illustrating, to an enlarged scale, the metal plate blade part of the conventional developing agent, Fig. 3 is a cross section schematically illustrating a typical developing apparatus embodying the present invention; Fig. 4 is a schematic perspective view illustrating a typical toner stirrer; and Fig. 5 is a cross section showing the shape of the toner stirrer of Fig. 4. In the embodiment illustrated in Fig. 3, as the toner stirrer an elastic roller 29 is used, the roller having a layer of polyurethane foam superposed concentrically on the peripheral surface of a shaft 27. Inside a developing agent container 22, this elastic roller 29 is revolved clockwise as kept in contact with the peripheral surface of a developing roller 24. On the peripheral surface of the polyurethane foam layer 28, helical grooves are inserted as shown in Fig. 4. In the present embodiment, the grooves have a width of 2 mm and a depth of 2 mm and a cross section of the shape shown in Fig. 5. Though these grooves may be formed as inclined in one direction, they are desired to be formed as inclined in two directions as illustrated for the purpose of producing effective stirring of the toner and preventing possible deflection of the toner distribution within the developing agent container 22. A metal plate blade 25 and a sensitive drum 23 used in the present embodiment are identical with the corresponding components used in the embodiment of Fig. 3 of co-pending application 86302265.3 (the parent application, published as EP-A-196231). In the developing apparatus constructed as described above, of the toner in the thin layer formed in consequence of the rotation of the developing roller 24, the part of the toner which has not participated in the development of an image, has passed under the pressure of the elastic sheet member 26 for toner recovery, and has been returned to the interior of the developing agent container 22 comes into contact with the rotating elastic roller 29. At this point, part of the toner on the surface of the developing roller 24 is scraped off by a porous polyurethane foam 28 inside the developing agent container 22 and then forwarded in the direction of length of the roller along the helically intersecting grooves. By the stirring effect produced as described above by the elastic roller 29, the electrostatic cohesion of toner particles is repressed and the formation of streaks in the peripheral direction of the roller is prevented. When the peripheral surface of the elastic roller 29 is wrapped with a porous material such as polyurethane foam as illustrated in the present embodiment, since the toner is retained in the grooves of irregularities on the surface, the toner is readily supplied to the roller surface and the uniform toner layer is formed at all times even when the toner is supplied smoothly to the surface of the developing roller 24 and, as a result, the toner is amply consumed in the development of images of numerous line pairs. Further when helical grooves are formed in two intersecting directions on the surface of the elastic roller as illustrated, the possibility of the toner being unevenly distributed inside the developing agent container is nil. Now, an experiment in which image duplications by the conventional method were carried out by the use of the developing apparatus of this invention will be described below. Experiment (Conditions) Developing roller : A developing roller was produced by subjecting the peripheral surface of an aluminum cylinder 24 mm in outside diameter to a polishing treatment, a sand blasting treatment to obtain surface roughness, and an electroless nickel plating treatment. To the developing roller, a DC bias voltage of +100 V was applied for the purpose of preventing the occurrence of image fogging. Elastic sheet member for foramtion of toner layer : An elastic sheet member for the formation of a toner layer was made of a phosphor bronze sheet 0.2 mm in thickness. The pressure, P, applied to the roller was 100g/cm. The pressure, P, mentioned above is the value calculated by the formula, P = Po/l where "l" stands for the length of the blade and "Po" for the total pressure applied on the roller. Non-magnetic toner : A toner consisting preponderantly of a polyester type substance and further incorporating therein a pigment such as carbon and other additives and having an averqage particle diameter of 12 µm was used. Photosensitive drum : A photosensitive drum produced by forming a layer of selenium type photoconductive material on the peripheral surface of an aluminum cylinder and having an outer diameter of 80 mm was used. The peripheral speed of this sensitive drum was equal to that of the aforementioned developing roller. This sensitive drum was rotated counterclockwise, namely, in a direction opposite the direction of the rotation of the aforementioned roller. The maximum potential of the elctrostatic image formed on the surface of the sensitive drum was +800 V. The sensitive drum was disposed so that the distance of the surface of the sensitive drum to the surface of the roller would be 0.2 mm when the two members approached most to each other. Elastic roller : An elastic roller consisted of a stainless steel shaft 8 mm in outside diameter and polyurethane foam coating 15 mm in outside diameter. The elastic roller was disposed so that a nipping width of 3 mm would occur between the elastic roller and the developing roller. The development was carried out by a method which comprised rotating the developing roller 24 at a peripheral speed of 130 mm/sec and the elastic roller at a peripheral speed of 30 mm/sec respectively both in the clockwise direction, forming a thin layer of toner about 25 µm in thickness on the surface of the developing drum 24, and allowing the toner which has been negatively charged by the frictional electrification with the elastic sheet member 25 for the formation of a toner layer to be transferred toward the sensitive drum 23 by the Coulomb force. Even after 10,000 cycles of the duplication mentioned above, the developed images showed no discernible lack of uniform density and the toner layer on the surface of the developing roller showed no sign of unevenness. The embodiment has been described as using an elastic roller as the toner stirrer. This invention does not require the toner stirrer to be limited to the elastic roller. For example, a mesh plate possessing elasticity and wrapped around a developing roll as illustrated in Fig. 4 an elastic sheet formed of an elastic flat sheet possessing minute irregularities on the surface thereof may be used instead. Attention is hereby directed to co-pending application number 86302265.3 from which the present application is a divisional application.

Claims: A developing apparatus comprising a movable developing agent carrier (24) adapted to carry and move a one-component developing agent composed of a non-magnetic toner (21) and supply said developing agent to an electrostatic latent image and a flexible coating member formed of an elastic plate (25) which is pressed on the surface of said movable developing agent carrier (24) and supported in place at one end thereof, the developing apparatus further comprising a developing agent container (22) provided therein with a toner stirring member (29), characterised in that the flexible coating member (25) is disposed so that the free end thereof will be directed opposite the direction of movement of said movable developing agent carrier, and in that the toner stirring member is disposed contiguously to or in sliding contact with said developing agent carrier (24) and adapted to make uniform the toner (21) on the surface of said developing agent carrier (24). A developing apparatus as claimed in claim 1, further characterised in that said toner stirring member (29) comprises an elastic roller adapted to be rotated while kept in contact with the surface of said developing agent carrier (24). A developing apparatus as claimed in claim 1 or 2, further characterised in that said toner stirring member (29) comprises an elastic roller made of polyurethane foam. A developing apparatus as claimed in claim 1 or 2, further characterised in that said toner stirring member (29) comprises an elastic roller made of polyurethane foam and said elastic roller is provided on the surface thereof with helical grooves.

Inventors: FUJIWARA, SHIGERU C/O PATENT DIVISION, HOSOYA, MASAHIRO C/O PATENT DIVISION, UEHARA, TSUTOMU C/O PATENT DIVISION
Applicants: KABUSHIKI KAISHA TOSHIBA
Application year: 1986
Main classification: G03G15
IPC codes: G03G15