Developing apparatus

Abstract: It is an object of the present invention to provide a developing apparatus that can protect a developer holder and a layer thickness control member from damages and a developer from scattering in itself, while preventing a surplus supply of the developer to both ends on the peripheral surface of the developer holder. In a developing apparatus (DA1), at the back side of a layer thickness control member (1) is provided a back side elastic sealing member (7) coming in contact with the side edges of a both-end elastic sealing members (2) to seal the developer together with the back side elastic sealing member and the both-end elastic sealing members at both ends. The both-end elastic sealing members (2) seals the developer at both ends of a developer holder (3) thereof peripheral surface. In another developing apparatus (DA6), the width of the layer thickness control member (1) in a longitudinal direction is set wider than the width of the developer holder (3) in a longitudinal direction and both side edges (la) of the layer thickness control member (1) are positioned outside both side edges (3a) of the developer holder (3). Furthermore, the inner side edges (2a) of the sealing member (2) are positioned inside the side edges (3a) of the developer holder (3) and outside the side edges of the image area (I) of the image holder (5) or aligned to an extended lines of this side edges.

Description: 1. Field of the Invention The present invention relates to a developing apparatus for developing images held on an image holder, and is particularly applicable where the apparatus uses a single component developer, and where the image to be developed is an electrostatic latent image produced by a copying machine, a printer, etc. 2. Description of the Related Art Generally, the following method is well known for developing electrostatic latent images formed on an image holder using the developing apparatus such as in an electrophotographic copying machine that generally uses a non-magnetic or magnetic single component developer (toner). At first, a layer thickness control member contacts a rotating developer holder in a longitudinal direction in the developing apparatus, so that the developer is formed into a uniform thin film on the developer holder and charged as necessary for a developing process by frictional electrification at the same time. This thin developer layer is fed to a developing position where the image holder contacts the developer holder. As a result, the developer is supplied to the electrostatic latent image formed on the image holder, so that the latent image is developed. In this case, the developer present around both ends of the developer holder facing the non-image areas of the image holder is not consumed, and due to scattering caused by the rotation of the developer holder, the developer flies to both ends of the developer holder almost in parallel to the longitudinal direction of the developer holder. Also, it results in a surplus supply of the developer, causing the developer to scatter in the apparatus. This flight of developer then causes problems of contamination in the copying machine and unnecessary consumption of the developer. A technology for preventing such a surplus supply of development and protecting the developing apparatus from such a contamination is disclosed in the official report of Unexamined Published Japanese Patent Application No.4-62391. The developing apparatus disclosed in this document, as shown in Fig.20, is provided with an elastic plate-like layer thickness control member 101, a cylindrical developer holder 103, and elastic sealing members 102 covering both side edges 101a of the layer thickness control member 101 from the back side of the leading edge 101b. Furthermore, the elastic sealing members 102 cover portions on the face of the developer holder 103, which are close to both side edges 101a of the layer thickness control member 101. Consequently, the movement of the developer to both ends of the developer holder 103 in an axial direction parallel to a rotary shaft line of the developer holder 103 is restricted. When the elastic sealing members 102 cover both side edges 101a of the layer thickness control member 101 and the face of the developer holder 103 around those side edges 101a as described above, to restrict the movement of the developer in the axial line direction, both side edges 101a of the layer thickness control member 1 are pressed against the face of the developer holder 1 directly. If the developing apparatus is kept used in this status, a local damage occurs at a contact portion between the developer holder 103 and both side edges 101a of the layer thickness control member 101. This damage generates a gap between those items 103 and 101a, resulting in degradation of the performance of the elastic sealing members 102. Consequently, the movement of the developer to both side edges of the developer holder 103 cannot be restricted completely, causing a surplus supply and scattering of the developer to both edges 101a and resulting in problems such as contamination in the developing apparatus and unnecessary consumption of the developer. These problems are especially evident when the layer thickness control member 101 and the developer holder 103 are composed of materials, each of which has mechanical characteristics significantly different from each other, for example, when the layer thickness control member 101 is composed of a plate-like metallic material and the developer holder 103 is composed of a roller-like rubber material. As shown in Fig.21, since the edges 101c at both sides 101a of the layer thickness control member 1 in the axial line direction contact the elastic sealing members 102, a problem arises from this contact as follows; each of the elastic sealing members 102 is stepped and the developer leaks from the gap S generated from this stepped portion and flies to both ends of the developer holder 103. Japanese Unexamined Patent Publication JP-A 4-249273 (1992) discloses a technology for eliminating such a stepped portion generated by the layer thickness control member 111 by dividing each sealing member 112 into a sealing member 112a used for the developer holder 113 and a sealing member 112b used for the layer thickness control member 111 as shown in Fig. 22. Furthermore, since both side edges 101a of the layer thickness control member 101 are restricted by the elastic sealing members 102 in the developing apparatus disclosed in Japanese Unexamined Patent Publication JP-A 4-62391 (1992), the pressure applied to both side edges 101a of the layer thickness control member 101 differs from the pressure applied to other portions. Consequently, a layer of developer is not uniformly formed on the developer holder 103, so a problem that the copying machine forms images at an uneven density of developer arises. Furthermore, Japanese Unexamined Patent Publications JP-A 3-109587 (1991) and 2-287471 (1990) disclose technologies for restricting the movement of the developer in every direction other than in the expected one for feeding the developer in the developing apparatus having a configuration as described above. The developing apparatus disclosed in JP-A 3-109587 forms sealing members for restricting the movement of the developer in every direction other than in the expected one for feeding the developer using bristle set sealing members, each of which is composed of plural types of materials. The developing apparatus disclosed in JP-A 2-287471(1990) is provided with a sheet for preventing developer leakage from a developing tank, which sheet is in contact with the outer peripheral surface of the developer holder in the developing tank, and the pressure with which the sheet is in contact with the outer peripheral surface is higher at end portions of the sheet than in the center portion. Furthermore, Japanese Unexamined Patent Publication JP-A 4-115271 (1992) discloses a prior art for preventing the developer holder or the layer thickness control member from damage in the developing apparatus described above. In the case of the layer thickness control member in the developing tank provided for the image forming apparatus disclosed in this document, the width of the layer thickness control member in the direction parallel to the rotary shaft of the developer holder is wider than the width of the developer holder. However, even when any of the developing apparatuses and the developing units in the three documents described above is used, it is difficult to prevent the developer holder and the layer thickness control member from local damage and to restrict the movement of the developer in every direction other than the expected one for feeding the developer simultaneously. US 5,212,521 discloses a developing unit having a rotatable developing roller rotatably mounted on a housing frame. At each end of the roller there is a sealing assembly having a first part which seals the gap between the roller and the housing and a second part which seals the gap between a thin blade, which limits the toner layer thickness on the roller, and the housing frame. US 5,488,462 discloses a developing device in which sealing members at opposite ends of a developing roller each comprise a seal film in contact with the roller surface and a sponge sheet lining adhered to the device casing. SUMMARY OF THE INVENTION The present invention aims to provide a developing apparatus capable of forming images at a uniform developer density by forming a uniform layer of developer without damaging a developer holder and a layer thickness control member. The invention also aims to provide a developing apparatus capable of alleviating problems such as contamination by scattering of the developer in the apparatus itself and unnecessary consumption of the developer while protecting the developer holder and the layer thickness control member from damage and prevent a surplus supply of the developer to both ends of the developer holder. In a first aspect the invention provides a developing apparatus for developing images held on an image holder, comprising: developer holder for holding a developer material and for feeding the developer to a developing position at which the developer holder faces the image holder; a layer thickness control member for slidably contacting a face of the developer holder at a face portion adjacent a leading edge of said thickness control member so as to form a layer of the developer material on said face of the developer holder; and a sealing assembly including a pair of elastic sealing members arranged for slidably contacting said face of the developer holder at positions which are spaced apart in a direction transverse to the direction of movement of said face relative to the layer thickness control member for substantially sealing the developer material supplied onto said face so as to confine it to a region defined between said sealing members; wherein each of said elastic sealing members is composed of first and second sealing member portions having relatively large and relatively small elasticity, respectively, the first sealing member portions being disposed closer to said region in said transverse direction than the second sealing member portions. In a second aspect the invention provides a developing apparatus for developing images held on an image holder, comprising: a developer holder for holding a developer material and for feeding the developer to a developing position at which the developer holder faces the image holder; a layer thickness control member for slidably contacting a face of the developer holder at a face portion adjacent a loading edge of said thickness control member so as to form a layer of the developer material on said face of the developer holder; and a sealing assembly including a pair of elastic sealing members arranged for slidably contacting said face of the developer holder at positions which are spaced apart in a direction transverse to the direction of movement of said face relative to the layer thickness control member for substantially sealing the developer material supplied onto said face so as to confine it to a region defined between said sealing members; wherein each of said elastic sealing members is composed of first and second sealing member portions having relatively large and relatively small elasticity, respectively, the first sealing member portions being disposed upstream of the second sealing member portions relative to the feeding direction of the developer. According to the first and second aspects of the invention, the large elasticity first sealing member portions of the sealing members restrict the movement of the developer to both sides of the developer holder and the small elasticity second sealing member portions wipe off the developer that cannot be restricted by the other sealing member portions, so that the movement of the developer to both sides of the developer holder is restricted and it is possible to prevent problems such as contamination by scattering of the developer in the apparatus itself and unnecessary consumption of the developer, more effectively. Furthermore, the developing apparatus can restrict the movement of the developer to both ends of the developer holder even when the particles of the developer are finer so as to cope with finer image resolution of images. The small elasticity second sealing member portions may be made of a fibre material. In this case, the small elasticity fibre elastic sealing member portion wipes off the developer that cannot be restricted by the large elasticity sealing member portion, so the developer that cannot be restricted by the latter sealing member portion can be wiped off more effectively. It is thus possible to restrict the movement of the developer to both ends of the developer more effectively. The developing apparatus may further include: a back side elastic sealing member provided on the back of the layer thickness control member, the back side elastic sealing member being in contact with the inner side edges of the elastic sealing members adjacent said region, wherein the developer is sealed by the back side elastic sealing member and the elastic sealing members. With this construction, the developing apparatus can protect the developer holder and the layer thickness control member from damage. The back side elastic sealing member is preferably smaller in hardness than the elastic sealing members. In the embodiments, the elastic sealing members are arranged to contact both the layer thickness control member and the developer holder; a width of the layer thickness control member in said transverse direction is wider than a width of the developer holder in said transverse direction and the inner side edges of the sealing members adjacent said region are positioned inside side edges of the developer holder respectively. With this arrangement it is possible to prevent both side edges of the layer thickness control member from touching the face of the developer holder directly, as well as to protect the developer holder and the layer thickness control member from local damage. Accordingly, it is possible to prevent problems such as scattering of the developer caused by such a damage. The inner side edges of the sealing members may be aligned to side edges of a predetermined image area on the image holder. The elastic sealing members may be arranged to contact both the leading edge of the layer thickness control member and the developer holder; both side edges of the layer thickness control member being disposed outside the side edges of the developer holder, or at the same positions as said side edges of the developer holder, the elastic sealing members being spaced so that the distance between their inner side edges is equal to or a little wider than the width of a predetermined image area on the image holder, and said inner side edges of the sealing members being disposed inside the side edges of the developer holder respectively. In this case, since both side edges of the layer thickness control member do not contact directly with the face of the developer holder, it is also possible to protect the developer holder and the layer thickness control member from local damages to occur by a contact therebetween. Consequently, the developing apparatus can prevent both the problem caused by such local damages and the problem caused by scattering of the developer. The first sealing member portion of each of the sealing members is preferably pressed against the developer holder with a pressure which is larger than the pressure with which the second sealing member portion is pressed against the layer thickness control member. In this case, the sealing member is in contact with the developer holder with a strong pressure to suppress a surplus supply of the developer to the developer holder and disable the movement of the developer to both ends of the developer holder. On the other hand, the sealing member is in contact with the layer thickness control member with a weak pressure to prevent thereof deformation. Thus, the layer thickness control member can contact the developer holder on fixed contact conditions to stabilize the layer of the development, preventing images from being disturbed. The inner side edges of the parts of each of the sealing members in contact with the developer holder may be inclined so as to guide the developer on said developer holder inwardly toward said region. In this case, it is possible to surely restrict the movement of the developer to both ends of the developer holder. The developing apparatus may further comprise a developing tank for housing the developer material, said developing tank supporting the developer holder, the layer thickness control member, and the sealing members, and including an opening formed at a portion facing the image holder, and the sealing assembly may include a further sealing member disposed between the developer holder and a portion around the opening provided on an inner wall of the developing tank to prevent developer leaks from the developing tank. In this case, the sealing members are disposed to cover a gap between the developer holder and the developing tank and a gap between layer thickness control member and the developing tank, so that developer leakage can be prevented. Consequently, there is no need to provide special seals and accordingly, the number of members can be reduced and the assembly work can be simplified. The developing apparatus may further comprise: a developing tank for housing the developer material, said developing tank supporting the developer holder, the layer thickness control member and the sealing members, end portions of the layer thickness control member in said transverse direction being bonded at a rear side thereof to the developing tank, said rear side being opposite to the face on which the layer thickness control member contacts the developer holder. The layer thickness control member may be bonded to the developing tank using a double-sided adhesive tape. In this case, when compared with a case in which an adhesive is used to bond the layer thickness control member, the bonding step becomes easy and the bonding yield is significantly improved. In an embodiment, a hardness at both ends of the developer holder in the transverse direction may be lower than that in a center portion, the layer thickness control member being pressed against the developer holder. In another embodiment, a hardness of the developer holder is 40° or under (JIS K6301) and the layer thickness control member is pressed against the developer holder. Using such a developer holder whose hardness is lower than the specified value or whose hardness is reduced at both ends of the developer holder in the longitudinal direction relative to the hardness in the center portion, the friction between the layer thickness control member and the developer holder can be prevented from increasing. Consequently, an increase of the rotation torque caused by an increase of the friction is suppressed, so that the driving source of the developer holder is not loaded. It is thus possible to reduce the driving torque of the motor used as a driving source, reduce the torque of the whole image forming apparatus, and use a low cost motor as a driving source. In an embodiment, the layer thickness control member is arched toward the developer holder at a center portion in the transverse direction and both ends of the layer thickness control member in the transverse direction are disposed so as to be separated from the developer holder. In this case, the contact area of the layer thickness control member and the developer holder is increased, so that the layer thickness control member can be pressed against the developer holder evenly in a wide range. BRIEF DESCRIPTION OF THE DRAWINGS Other and further objects, features, and advantages of the invention will be more explicit from the following detailed description taken with reference to the drawings wherein: Fig. 1 is a schematic vertical cross sectional view of a developing apparatus DA1 in a first embodiment. Fig. 2 is a side view of the major portion of the developing apparatus DA1 in the first embodiment. Fig. 3 is a perspective view of the major portion of the developing apparatus DA1 in the first embodiment. Fig. 4 is a side view of the major portion of a developing apparatus DA2 in a second embodiment. Fig. 5 is a schematic vertical cross sectional view of a developing apparatus DA3 in a third embodiment. Fig. 6 is a schematic vertical cross sectional view of a developing apparatus DA4 in a fourth embodiment. Fig. 7 is a perspective view of the major portion of the developing apparatus DA4 in the fourth embodiment. Fig. 8 is a side view of the major portion of the developing apparatus DA4 in the fourth embodiment. Fig. 9 is a horizontal cross sectional view of the major portion of the developing apparatus DA4 in the fourth embodiment. Fig. 10 is a side view of the major portion of a developing apparatus DA5 in a fifth embodiment. Fig. 11 is a side view of the major portion of a developing apparatus DA6 in a sixth embodiment. Fig. 12 is a schematic vertical cross sectional view of a developing apparatus DA7 in a seventh embodiment. Fig. 13 is a schematic vertical cross sectional view of a developing apparatus DA8 in an eighth embodiment. Fig. 14 is a side view of the major portion of a developing apparatus DA9 in a ninth embodiment. Fig. 15 is a schematic vertical cross sectional view of a developing apparatus DA10 in a tenth embodiment. Fig. 16 is a perspective view of the major portion of the developing apparatus DA10 in the tenth embodiment. Fig. 17 is a side view of the major portion of the developing apparatus DA10 in the tenth embodiment. Fig. 18 is a top view of the major portion of a developing apparatus DA11 in an eleventh embodiment. Fig. 19A and Fig. 19B illustrate shapes of a layer thickness control member 71 before and after the developer holder 3 is provided in the developing apparatus DA11 in the eleventh embodiment. Fig. 20 is a perspective view of the major portion of a prior art developing apparatus disclosed in Japanese Unexamined Patent Publication JP-A 4-62391 (1992). Fig. 21 is a cross sectional view of a prior art developing apparatus disclosed in Japanese Unexamined Patent Publication JP-A 4-62391 (1992). Fig. 22 is a cross sectional view of the major portion of a prior art developing apparatus disclosed in Japanese Unexamined Patent Publication JP-A 4-249273 (1992). The second, third, sixth, seventh and eighth embodiments (DA2, DA3, DA6, DA7, DA8) are embodiments of the present invention. The other embodiments are presented herein as. background to aid the understanding of the aforesaid embodiments of the invention and for explaining certain features which can be applied in the embodiments of the invention. DETAILED DESCRIPTION OF THE EMBODIMENTS Now referring to the drawings, background embodiments and preferred embodiments of the invention are described below. Fig. 1 is a schematic vertical cross sectional view of a structure of a developing apparatus DA1 in a first embodiment. Figs. 2 and 3 are a side view and a perspective view of the major portion of the developing apparatus DA1. At first, a schematic configuration of the developing apparatus DA1 will be described with reference to Figs. 1 to 3. The developing apparatus DA1 is applicable for an electrophotographic laser printer, for example. The developing apparatus DA1 comprises a layer thickness control member 1; a pair of both-end elastic sealing members 2; a developer holder 3; a developer case 4; a back side elastic sealing member 7; an upper sealing member 8; and a lower sealing member 9. The developer case 4 stores a developer D. The developer case 4 has an opening 11. In Figs. 2 and 3, the developer case 4, the upper and lower sealing members 8 and 9 are omitted. The cylindrical developer holder 3 is disposed at the opening 11 of the developer case 4 so that the holder 3 supplies the developer D on its surface little by little properly. The developer holder 3 is formed with, for example, a conductive rubber material. The developer D is, for example, high resistant toner whose average particle size is about 15µm. The developer holder 3 is disposed so that its face faces the side face of the image holder 5 provided in the laser printer and part of its surface contacts or nearly contacts the image holder 5. A position where the developer holder 3 contacts or nearly contacts the image holder 5 is referred to as a developing position DP. The image holder 5 is composed of, for example, a photosensitive drum or a photosensitive belt and rotated in a direction of the arrow AR1. At a position that faces both ends of the developer holder 3 in a longitudinal direction on the peripheral surface and is in the vicinity of an opening 10 in the developer case 4 are disposed both-end elastic sealing members 2 used to prevent the developer D from a surplus supply of to both ends of the developer holder 3. The longitudinal direction is in parallel to the rotary shaft of the developer holder 3 and lies transverse to the direction in which the developer holder 3 feeds the developer D, at right angles thereto. The developer holder 3 is rotatably supported at its opposite ends via, for example, a shaft 21 and rotated at a specified speed in a direction of the arrow AR2 so as to hold the developer D supplied from the developer case 4 on its surface and feeds the developer D up to the developing position DP. Thus, an electrostatic latent image is formed on the surface of the image holder 5. The developing apparatus DA1 visualizes the electrostatic latent image using the developer D fed to the developing position DP by the developer holder 3 to form a developed image. At the downstream side of the developing position DP in the rotating direction AR2 of the developer holder 3 of the developer case 4, the layer thickness control member 1 is disposed. As shown in Figs.2 and 3, a leading edge 22 on the face of the layer thickness control member 1 or a portion around the leading edge 22 is disposed so as not to touch the both-end elastic sealing members 2 provided at both ends of the developer holder 3. At the back side of the layer thickness control member 1 is disposed a back side elastic sealing member 7 so that the side end faces of the back side sealing member 7 contact the side end faces of the both-end elastic sealing members 2 of the developer holder 3. The back side elastic sealing member 7 and the both-end elastic sealing members 2 are used together to seal the developer D. Since the elastic sealing members 2 and 7 are disposed like this, both ends 23 of the layer thickness control member 1 are not pressed directly from the back side by the both-end elastic sealing members 2 of the developer holder 3. Consequently, the developer holder 3 is protected from local damage , and accordingly, the developer is not fed excessively. As a result, the developing apparatus is prevented from contamination caused by scattering of the developer inside itself, as well as other problems such as unnecessary consumption of the developer, etc. The layer thickness control member 1 restricts the developer D supplied from the developer case 4 onto the surface of the developer holder 3 to form a thin developer layer T on the surface of the developer holder 3. The upper sealing member 8 seals between the developer case 4 and the upper portion of the layer thickness control member 1. The lower sealing member 9 seals between the developer case 4 and the lower portion of the layer thickness control member 1. In the first embodiment, the concrete configuration of the developing apparatus DA1 is as follows. The layer thickness control member 1 is composed of a stainless steel plate of 0.1mm in thickness. The layer thickness control member 1 is fixed to the developer case 4 so that the leading edge 22 or a portion around the leading edge 22 of the layer thickness control member 1 is pressed against the developer holder 3 due to its own elastic force. The distance between the portion of the layer thickness control member 1 fixed on the developer case 4 and the portion of the layer thickness control member 1 in contact with the developer holder 3 is 10mm and the deflection is 1mm. Since the layer thickness control member 1 is pressed against the developer holder 3 with such a uniform force, the thickness of the thin developer layer T and the charge of the developer can be kept stably. At both ends of the developer holder 3 are disposed a pair of both-end elastic sealing members 2 as described above to prevent a surplus supply of the developer D to both ends of the peripheral surface of the developer holder 3. Each inner side edge of the both-end elastic sealing members 2 is positioned (when viewed from one side of the developing apparatus DA1) between a side edge of the developer holder 3 and a side edge of an image area on the image holder where electrostatic latent images are formed, so that the sealing members 2 are in contact with the face of the developer holder 3 and the back of the layer thickness control member 1. Furthermore, on the back side of the layer thickness control member 1 is stuck the back side elastic sealing member 7. Both ends of the back side elastic sealing member 7 are in contact with the side ends of the both-end elastic sealing members 2 under a certain pressure. More concretely, the back side elastic sealing member 7 composed of flexible urethane sponge is stuck on the back side of the layer thickness control member 1 with a double-sided adhesive tape. On the other hand, the both-end elastic sealing members 2 are composed of moquette having a certain elastic force. The both-end elastic sealing members 2 are held at their near sides by projections 11 in the developer case 4. The thin developer layer T formed on the developer holder 3 is used for developing the electrostatic latent images on the image holder 5 after it is fed to a position or around the position where the image holder 5 contacts the developer holder 3, that is, the developing position DP. In the first embodiment, the same polarity voltage as that of the charge voltage of the thin developer layer T is applied to the developer holder 3, and a potential difference from the potential of the electrostatic latent image formed on the image holder 5 is used to develop the image. 'This completes the explanation for the concrete configuration of the developing apparatus DA1. Hereunder, the developing apparatuses DA2 and DA3 in the second and third 'embodiments will be described with reference to Figs.4 and 5. Each of the developing apparatuses DA2 and DA3 in the second and third embodiments includes parts having the same structures and the same functions as those of the developing apparatus DA1 in the first embodiment. Those parts are all positioned and disposed in the second and third embodiments just like in the first embodiment. In the following explanation, parts which are the same as those in the developing apparatus DA1 of the first embodiment. Will be denoted by the same reference numerals, and the explanation for them will be omitted, avoiding unnecessary repetition. In Fig. 4, the developer case 4 and the upper and lower sealing members 8 and 9 are omitted. The developing apparatus DA2 in the second embodiment will be described with reference to Fig. 4 (a side view). The developing apparatus DA2, when compared with the developing apparatus DA1 in the first embodiment, has a difference that a pair of both-end elastic sealing members 2 in the DA1 is replaced with a pair of both-end elastic sealing members 27, which have the following structure respectively. Other items are the same in both embodiments. Each of the pair of both-end elastic sealing members 27 is composed of two types of sealing members 27a and 27b disposed along the width direction of the developer holder 3 and given a different elasticity from the other. Although both sealing members 27a and 27b are elastic to both ends of the developer holder 3, the elasticity of the sealing member 27a is set stronger than the sealing member 27b. In the second embodiment, concretely, the inner sealing member 27a is composed of solid-like rubber of 40° in hardness and the outer sealing member 27b is composed of urethane sponge of 10° in hardness at both ends of the developer holder 3 so that a difference is generated in elasticity between the sealing members 27a and 27b. Consequently, the developer D moving toward both ends of the developer holder 3 is restricted once by the sealing member 27a having a large elasticity at first. Then, the developer D that cannot be restricted by the sealing member 27a is wiped off by the sealing member 27b having a small elasticity. As a result, the developer D is restricted so as not to be supplied excessively to both ends of the developer holder 3. Since the developing apparatus DA2 has such a configuration, the developer holder 3 is protected from an excessive supply of the developer more effectively and accordingly, the developing apparatus DA3 is prevented from contamination by scattering of the developer inside itself, and unnecessary consumption of the developer is suppressed more effectively. When the less elastic sealing member 27b is composed of a fiber sealing member, the developer can be wiped more effectively, preventing the developing apparatus from contamination by scattering of the developer inside itself and from unnecessary surplus consumption of the developer. Next, the developing apparatus DA3 in the third embodiment will be described with reference to Fig.5 (a vertical cross sectional view). The developing apparatus DA3, when compared with the developing apparatus DA1 in the first embodiment, has a difference that a pair of both-end elastic sealing members 2 in the DA1 is replaced with a pair of both-end elastic sealing members 28, which have the following structure respectively. Other items are the same in both embodiments. Each of the pair of both-end elastic sealing members 28 is composed of two types of sealing members 28a and 28b disposed along the peripheral surface of the developer holder 3 and given a different elasticity from the other. Each of the sealing members 28a and 28b is disposed so as to contact the peripheral surface of the developer holder 1. The elasticities of the sealing members 28a and 28b are set so that the elasticity of the sealing member 28a provided at the upstream side in the rotating direction of the developer holder 3 is stronger than that of the other sealing member 28b provided at the downstream side. In the third embodiment, concretely, the sealing member 28a provided at the upstream side in the rotation direction of the developer holder 3 is composed of solid-like rubber of 40° in hardness and the sealing member 28b at the downstream side is composed of urethane sponge of 10° in hardness so that a difference is generated in elasticity between the sealing members 28a and 28b. Consequently, the developer D moving toward both ends of the developer holder 3 is first restricted by the sealing member 28a having a large elasticity. Then, the developer D that cannot be restricted by the sealing member 28a is wiped off by the sealing member 28b having a small elasticity. As a result, the developer D is restricted so as not to be supplied excessively to both ends of the developer holder 3. Since the developing apparatus DA3 has such a configuration, the developer holder 3 is prevented from excessive supply of the developer more effectively and accordingly, the developing apparatus DA3 is prevented from contamination by scattering of the developer in the apparatus, and unnecessary consumption of the developer is suppressed more effectively. When the less elastic sealing member 28b is composed of a fiber sealing member, the developer can be wiped more effectively, preventing the developing apparatus from contamination by scattering of the developer in the apparatus and suppressing unnecessary consumption of the developer more effectively. Fig. 6 is a schematic vertical cross sectional view of a structure of the developing apparatus DA4 in a fourth embodiment. Figs. 7 to 9, are perspective, side, and horizontal cross sectional views of the major portion of the developing apparatus DA4. Hereunder, a schematic configuration of the developing apparatus DA4 will be described with reference to Figs. 6 to 9. The developing apparatus DA4 in the fourth embodiment includes parts having the same structures and the same functions as those of the developing apparatus DA1 in the first embodiment. Thus, the same reference numerals will be given to those parts. The developing apparatus DA4 includes a layer thickness control member 31; a pair of seals 32; a developer holder 3; a developer case 4; an upper sealing member 8; and a lower sealing member 9. The developer D is stored in the developer case 4. The developer case 4 is provided with an opening 10, as well as a stirring member, a feeding member, etc. The developing apparatus DA4 in the fourth embodiment is applicable for the electrophotographic laser printer. The cylindrical. developer holder 3 is disposed in the developer case 4 that feeds the developer D composed of a non-magnetic single component onto the surface, that is, the peripheral surface of the developer holder 3 little by little properly. The developer D is composed of, for example, a high resistant toner whose average particle size is 10µm. The developer holder 3 is composed of a conductive rubber roller and both ends of the developer holder 3 are rotatably supported at the developer case 4 via a shaft. The developer holder 3 is rotated at a specified speed. The developer holder 3 is disposed so as to contact or nearly contact the image holder 5 composed of a photosensitive drum or a photosensitive belt to be rotated and holds the developer D supplied from the developer case 4 on its surface and feeds the developer D up to a developing position DP facing the image holder 5. The developer holder 4 is provided with a layer thickness control member 31 that forms a thin layer T of the developer D on the surface of the developer holder 3 by restricting the layer thickness of the developer D fed from the developer case 4. The layer thickness control member 31 is composed of a stainless steel plate of, for example, 0.1mm in thickness. The layer thickness control member 31 is fixed to the developer case 4 at its one end at the developer case side. The layer thickness control member 31 is disposed at the downstream side of the developing position DP in the feeding direction AR2 of the developer by the developer holder 3. The leading edge portion 33 or a portion around the leading edge 33 of the layer thickness control member 31 on its surface contacts the developer holder 3 all along the longitudinal direction. The distance between the portion to contact the developer case 4 in the layer thickness control member 31 and the portion to contact the developer holder 3 is 10mm and the deflection is 1mm. The layer thickness control member 31 is pressed against the developer holder 3 due to its own elasticity. Since the layer thickness control member 31 is uniformly pressed against the developer holder 3 due to its own elasticity, the developer layer can be kept at a specified thickness T and the developer D can be charged necessarily by frictional electrification. The width O of the layer thickness control member 31 in the longitudinal direction is set wider than the width N of the developer holder 3 in the longitudinal direction (O>N) so that the layer thickness control member 31 contacts the developer holder 3 all along the longitudinal direction. Both side edges 31a of the layer thickness control member 31 are positioned outside both side edges 3a of the developer holder 3 and do not contact the surface of the developer holder 3. The width O of the layer thickness control member 31 in the longitudinal direction may be equal to the width N of the developer holder 3 in the longitudinal direction. Also, in order to prevent excessive supply of the developer D to both ends of the developer holder 3, a pair of elastic seals 32 are provided in the developer case 4. Each of the seals 32 is composed of flexible urethane sponge or an elastomer such as synthetic rubber, etc. The seals 32 are disposed around both ends of the developer holder 3. The seals 32 are held at their rear sides by projections 11 in the developer case 4 and pressed against the developer holder 3 and the layer thickness control member 31 so as to contact both the face of the developer holder 3 and a back side of the layer thickness control member 31 Since the seals 32 are elastic, they can follow up the developer holder 3 and the layer thickness control member 31 regardless of the difference in level between the layer thickness control member 31 and the developer holder 3 so that the member 32 can contact closely the holder 3 and the layer thickness control member 31. In addition, no action is restricted around the leading edge of the layer thickness control member 31. When seen from the side of the developing apparatus DA4 (reference to Fig.8), the seals 32 are separated from each other so that inner edges 32a of the seals 32 are positioned between the side edges 3a of the developer holder 3 and the extended lines of the side edges of the image area I on the image holder 5 respectively. In other words, the width M between the inner edges 32a of the seals 32 is set wider than the width L of the image area I (M>L). The upper sealing member 8 seals between the developer case 4 and the layer thickness control member 31. The lower sealing member 9 seals between the developer case 4 and the developer holder 3. Hereunder, explanation will be made for the procedure for developing an electrostatic latent image on the image holder 5 using the developing apparatus DA4 constructed as described above. The developer D is supplied from the developer case 4 little by little properly onto the surface of the developer holder 3 rotating in the direction of the arrow AR1. At this time, the developer D in the developer case 4 is moved by a stirring member, a feeding member, etc. to the developer holder 3, but the seals 32 restrict the movement of the developer D to both ends of the developer holder 3. Excessive supply of the developer D to these areas is thus prevented. The developer D fed to a portion between both seals 32 on the peripheral surface of the developer holder 3 is restricted by the layer thickness control member 31 so that the developer layer T on the developer holder 3 is kept properly thin. At this time, the developer D is charged by frictional electrification to a level of charge necessary for developing on the developer. This thin developer layer T is fed to the developing position DP where the image holder 5 is in contact or near contact with the developer holder 3 according to the rotation of the developer holder 3. The developer holder 3 receives the same polarity voltage as that of the thin the developer layer T of the developer charged by frictional electrification at this time. Thus, the developer is supplied to the electrostatic latent image on the image holder 5 by using the potential difference from that of the latent image formed on the image holder 5, so that the image is developed. Since the developer D is not fed excessively to both ends of the developer holder 3, which are non-image areas, the developer D that is not used for development does not scatter. In addition, since both side edges 31a of the layer thickness control member 31 are prevented from touching the surface of the developer holder 3 directly, no local damage is caused by the contact of the developer holder 3 with both side edges 31a of the layer thickness control member 31. Consequently, excessive supply of the development D to both ends of the developer holder 3, caused by such a local damage, is prevented and accordingly, contamination by scattering of the developer D inside the developing apparatus is also prevented. In addition, other problems such as unnecessary consumption of the developer D can be prevented. Next, the developing apparatuses DA5 to DA9 in fifth to ninth embodiments will be described with reference to Figs. 10 to 16. Each of the developing apparatuses DA5 to DA9 in the fifth to ninth embodiments include some parts having the same structures and the same functions as those of the developing apparatus DA4 in the fourth embodiment. Those parts are all positioned and disposed in the fifth to ninth embodiments just like in the fourth embodiment. Thus, the same reference numerals will be given to those parts and the explanation for them will be omitted, avoiding unnecessary repetition. In Figs. 10, 11 and 14 (side views), the developer case 4, the upper and lower sealing members 8 and 9 are omitted. Hereunder, the developing apparatus DA5 in the fifth embodiment will be described with reference to Fig. 10 (side view). The developing apparatus DA5, when compared with the developing apparatus DA4 in the fourth embodiment, has a difference that a pair of seals 32 in the DA5 apparatus is disposed differently from those in the DA6 apparatus. Other items are the same in both embodiments. In the apparatus DA5, the extended lines of the side edges of the image area I on the image holder 5 may be aligned to the inner edges 32a of the seals 32 (M=L). In other words, in the developing apparatus DA4 in the fourth embodiment, the distance between the seals 32 may be equal to the width of the image area I so that the inner edges 32a of the seals 32 are disposed on the extended lines of the side edges of the image area I. Consequently, a surplus supply of the developer D to both ends of the developer holder 3 can be suppressed more effectively, so that contamination by scattering of the developer D inside the developing apparatus, as well as other problems such as unnecessary consumption of the developer D can be minimized. Fig.11 is a side view of the major portion of a developing apparatus DA6 in the sixth embodiment. The developing apparatus DA6, when compared with the developing apparatus DA4 in the fourth embodiment, has a difference that a pair of seals 32 in apparatus DA4 is replaced with a pair of seals 35, which have the following structure respectively. Other items are the same in both embodiments. Each of the pair of seals 35 is divided into two types of sealing members 36 and 37, each of which has an elasticity different from the other in the longitudinal direction. The elasticity of each of those sealing members 36 and 37 is set as follows; the sealing member 36 positioned inside in the longitudinal direction of the developer holder 3 is stronger in elasticity than the sealing member 37 positioned outside. For example, the inner sealing member 36 is composed of solid-like rubber of 40° in hardness and the outer sealing member 37 is composed of urethane sponge of 10° in hardness, and both members 36 and 37 are bonded together or they are put in the developer case 4 so as to be in contact closely with each other. Other items such as configuration and disposition of the seals 35 are the same as those of the seals 32 in the fourth embodiment. Consequently, the developer D moving toward both ends of the developer holder 3 is first restricted by the inner sealing member 36 having a large elasticity. Then, the developer D that cannot be restricted by the inner sealing member 36 is wiped off by the outer sealing member 37 having a small elasticity. Especially, when the particles of the developer D are finer to cope with higher resolution of images, the sealing members 35 are more effective than a case where the sealing members 32 in the fourth embodiment are pressed simply against the developer holder 3. Since such seals 35 having different elasticities in the longitudinal direction of the developer holder 3 are used, one part of the seal 35 restricts the developer D with its elastic portion and the other part of the seal wipes off the developer D that cannot be restricted by the former one with its elastic portion. Thus, a surplus supply of the developer D to the developer holder 3 can be suppressed more effectively. When the less elastic outer sealing member 37 is composed of a fiber sealing member, the developer D can be wiped more effectively, preventing the developing apparatus from contamination by scattering of the developer D inside itself and suppressing unnecessary consumption of the developer D more effectively. Fig. 12 is a vertical cross sectional view of the developing apparatus DA7 in the seventh embodiment. The developing apparatus DA7, when compared with the developing apparatus DA4 in the fourth embodiment, has a difference that a pair of seals 32 is replaced with a pair of seals 38, which have the following structure respectively. Other items are the same in both embodiments. Each of the sealing members 38 is divided into two types of sealing members 39 and 40, each of which has an elasticity different from the other in the rotating direction of the developer holder 3. The elasticity of each of the sealing members 39 and 40 is set as follows; the elasticity of the upstream sealing member 39 positioned at the upstream side in the feeding direction of the developer holder 3 is set stronger than the downstream sealing member 40 positioned at the downstream side. The upstream sealing member 39 is in contact with the face of the developer holder 3 and the downstream sealing member 40 is in contact with both the face of the developer holder 3 and the back side of the layer thickness control member 31. For example, the upstream sealing member 39 is composed of solid-like rubber of 40° in hardness and the downstream sealing member 40 is composed of urethane sponge of 10° in hardness, and both members 39 and 40 are bonded together or they are put in the developer case 4 so as to be in contact closely with each other. Other items such as configuration and disposition of the sealing members 38 are the same as those of the sealing members 32 in the fourth embodiment. Consequently, the developer D moving in the longitudinal direction of the developer holder 3 due to the rotation of the developer holder 3 is first restricted by the upstream sealing member 39 with stronger elasticity. Then the developer D that cannot be restricted by the upstream sealing member 39 is wiped off by the downstream sealing member 40. Since the sealing members 38 whose elasticity is different from each other along the feeding direction of the developer holder 3 are used, one of the sealing members 38 restricts the developer D with its elastic portion and the other sealing member wipes off the developer D that cannot be restricted by the former one with its elastic portion. Thus, a surplus supply of the developer D to both ends of the developer holder 3 can be suppressed more effectively. When the less elasticity downstream sealing member 40 is composed of the fiber sealing member, the developer D can be wiped more effectively. Hereunder, the developing apparatus DA8 in the eighth embodiment will be described. In the developing apparatus DA8, the force with which the sealing members 45 are pressed against the developer holder 3 is set differently from the force with which the sealing members 45 are pressed against the layer thickness control member 31. The reason for this is as follows. The pressure with which the sealing member is pressed against the developer holder 3 should normally be set large enough to prevent the movement of the developer D to both ends of the developer holder 3 from being restricted. In this case, however, the pressure with which the sealing member is pressed against the layer thickness control member 31 is also increased, so that the layer thickness control member 31 is deformed to change the contact condition on which the layer thickness control member 31 comes in contact with the developer holder 3 at a position close to the sealing member. As a result, the thin developer layer T goes unstable in thickness to printed out disturb images and cause damage in the developer holder 3 and the layer thickness control member 31. Also, when the pressure with which the sealing member is pressed against the layer thickness control member 31 is reduced to prevent such problems of disturbed images and damage in the developer holder 3 and the layer thickness control member 31, the pressure with which the sealing member 32 is pressed against the developer holder 3 is also reduced. As a result, it comes difficult to restrict the movement of the developer D toward both ends of the developer holder 3 and accordingly, the developer D scatters around. To avoid such problems, it is proposed to change the pressure onto the sealing member 32 at plural points differently from each other therein so that the sealing member is pressed against the developer holder 3 and the layer thickness control member 31 properly. As shown in Fig. 13, the developing apparatus DA8 in the eighth embodiment, when compared with the developing apparatus DA4 in the fourth embodiment, has a difference that a pair of sealing members 32 in the DA6 is replaced with a pair of sealing members 45, which have the following structure respectively. Other items are the same in both embodiments. Each of the pair of sealing members 45 is divided into a high pressure sealing member 46 and a low pressure sealing member 47. The high pressure sealing member 46 comes in contact with the face of the developer holder 3 and the low pressure sealing member 47- comes in contact with the back of the layer thickness control member 31. The high pressure sealing member 46 is composed of solid-like rubber of 40° in hardness and the low pressure sealing member 47 is composed of urethane sponge of 10° in hardness. The pressure applied onto the high pressure sealing member 46 is set larger than that onto the low pressure sealing member 47. Consequently, the high pressure sealing member 46 is pressed against the developer holder 3 by a strong force to suppress a surplus supply of the developer D to the developer holder 3. On the other hand, the low pressure sealing member 47 is pressed against the layer thickness control member 31 by a weak force to prevent the layer thickness control member 31 from deformation, so that generation of disturbed images is suppressed, as well as the developer holder 3 and the layer thickness control member 31 are protected from damage. Fig. 14 is a side view of the major portion of a developing apparatus DA9 in the ninth embodiment. The developing apparatus DA9 in the ninth embodiment, when compared with the developing apparatus DA4 in the fourth embodiment, has a difference that a pair of sealing members 32 in the DA4 apparatus is replaced with a pair of sealing members 56, which have the following structure respectively. Other items are the same in both embodiments. Each sealing member 56 is notched at the upstream side end of the inner edge 56a to form an inclined plane 57. Consequently, the movement of the developer D fed on the developer holder 3 is restricted by the sealing members 56 in the longitudinal direction, but the developer D that cannot be restricted is guided by the inclined plane 57 of each sealing member 56 to the inner portion in the longitudinal direction of the developer holder 3. The movement of the developer D to both ends of the developer holder 3 is thus suppressed surely to prevent a surplus supply of the developer D there. It is also possible to obtain the same effect by inclining each sealing member 32 in the fourth embodiment so that the interval between the sealing members 32 is narrowed from the upstream to the downstream in the developer feeding direction. Fig. 15 is a schematic vertical cross sectional view of a structure of a developing apparatus DA10 in the tenth embodiment. Figs.16 and 17 are a perspective view and a side view of the major portion of the developing apparatus DA10. Hereunder, the schematic configuration of the developing apparatuses DA10 will be described with reference to Figs. 15 to 17. The developing apparatuses DA10 includes some parts having the same structures and the same functions as those of the developing apparatuses DA1 and DA4 in the first and fourth embodiments. Thus, the same reference numerals will be given to those parts. The developing apparatus DA10 includes a developer holder 3; a layer thickness control member 61; sealing members 62; fixing plates 63; a developer case 64; and a lower sealing member 9. The developer case 64, when compared with the developer case 4, has differences that the shapes around an opening 66 and projections 67 are different from those of the developer case 4. Other items are the same. The layer thickness control member 61 slidably contacts the face of the developer holder 3 to form a developer layer T at a specified thickness. The sealing members 62 contact the developer holder 3 to restrict the movement of the developer D on the developer holder 3 in the longitudinal direction. The layer thickness control member 61 allows its one end to be fixed to the developer case 64 via the fixing plates 63 all along the longitudinal direction of the developer holder 3. At the leading edge on the back of the layer thickness control member 61, which is not in contact with the developer holder 3, both ends of the layer thickness control member 61 in the longitudinal direction are bonded to the projections 67 in the developer case 64 using a bonding material 68. The bonding material 68 is an epoxy or acrylic resin instant adhesive. When such an adhesive is used, problems occur when in a coating work; the adhesive sticks on other portions, for example, on the developer holder 3 or the adhesive, after being coated, flows onto other portions and is cured there. To avoid such problems, an adhesive tape that has an adhesive on both sides, that is, a so-called double-sided adhesive tape should be used. Use of such a double-sided adhesive tape will also improve the workability. Thereby, there is no trouble of flowing of the adhesive. At first, the double-sided adhesive tape is stuck on the layer thickness control member 61 in advance, then the other adhesive side of the member 61 is stuck on the developer case 4. This will not only eliminate the above problems, but also improve the work yield rate more than when an adhesive is used. This layer thickness control member 61 is composed of, for example, a stainless steel plate of 0.1mm in thickness and the width of the member 61 in the longitudinal direction is set less than that of the developer holder 3. The leading edge on the face or a portion around the leading edge is in contact with the developer holder 3 all along the longitudinal direction. The distance between the portion where the layer thickness control member 61 is fixed to the developer case 64 and the portion where the member 61 is in contact with the developer holder 3 is 10mm and the deflection is 1mm. Since the layer thickness control member 61 is uniformly pressed against the developer holder 3 by its own elastic force, both the thickness and charge level of the thin developer layer T are stabilized. The layer thickness control member 61 may be equal to or greater in width than the developer holder 3. The sealing members 62 are disposed at the upstream side of the layer thickness control member 61 and around both ends of the developer holder 3 respectively so that they contact the leading edge of the layer thickness control member 61 without being overlapped thereon. Each sealing member 62 is held at its back by the projection 67 in the developer case 64. The pair of sealing members 62 are separated from each other so that the inner edge 62a of each sealing member 62 is positioned between a side edge 3a of the developer holder 3 and an extended line of a side edge of the image area I on the image holder 5. Other configuration items of the developing apparatus DA10 may be the same as those in each of the above embodiments. Furthermore, the structure of each sealing member 62 may be the same as any of those in other embodiments described above to obtain the same effect. In this embodiment, both edges 61a of the layer thickness control member 61 contact the face of the developer holder 3 directly, but they are not pressed by the sealing members 62 against the developer holder 3. Thus, local damage caused by such forced contact between the developer holder 3 and both edges 61a of the layer thickness control member 61 is prevented, so that excessive supply of the developer D to both ends of the developer holder 3 is suppressed. Hereunder, explanation will'be made for the procedure for developing an electrostatic latent image on the image holder 5 using the developing apparatus DA10. When the developer D is supplied little by little properly from the developer case 64 onto the face of the developer holder 3 rotating in the direction of the arrow AR1, the sealing members 62 restrict the movement of the developer D, so that a surplus supply of the developer D to both ends of the developer holder 3 is suppressed. The thickness of the developer D supplied to a portion between both the sealing members 62 on the peripheral surface of the developer holder 3 is restricted by the layer thickness control member 61, so that a thin developer layer T is formed on the developer holder 3. Consequently, the developer D is sufficiently charged by frictional electrification for development. This thin developer layer T is transferred according to the rotation of the developer holder 3 up to the developing position DP where the image holder 5 is in contact or almost contact with the developer holder 3 to be used for development. At this time, at the leading edge of the layer thickness control member 61, the face of the member 61 is pressed against the developer holder 3 and the back of both ends of the member 61 is in contact with the developer case 4. Thus, there is no gap generated around the leading edge of the layer thickness control member 61 and no developer D leaks there. Since an adhesive or an adhesive tape functions as a sealing member, the adhesive or adhesive tape, used together with the pair of sealing members 62,can suppress the movement of the developer D to both ends of the developer holder 3, which are non-image areas. Thus, no surplus developer D is supplied to both ends of the developer holder 3 and no problem that the developer D that is not used for development scatters arises and accordingly, the developing apparatus is protected from contamination by the scattering of the developer in the apparatus, and unnecessary consumption of the developer D is prevented. It is also possible to obtain the same sealing effect for the developer D by letting the sealing members 62 contact the layer thickness control member 61 so as to be overlapped thereon so that the back of the layer thickness control member 61 contacts with the sealing members 62 directly. Hereunder, the developing apparatus DA11 in the eleventh embodiment will be described with reference to Figs. 18, 19A, and 19B. The developing apparatus DA11 when compared with the developing apparatus DA10 in the tenth embodiment, has a difference that the layer thickness control member 61 in the DA10 apparatus is replaced with a layer thickness control member 71. Other items are the same in both embodiments. The developing apparatuses DA11 includes some parts having the same structures and the same functions as those of the developing apparatus DA10 in the tenth embodiment. Thus, the same reference numerals will be given to those parts and the explanation will be omitted, avoiding redundant explanation. The layer thickness control member 71 is arched toward the developer holder 3 in the center portion in the longitudinal direction of the developer holder 3. And, just like the layer thickness control member 61 in the tenth embodiment, one end of the member 71 is fixed to the developer case 64. Both ends of the leading edge of the member 71 are also fixedly bonded to the projections 67 in the developer case 64, but both the ends are separated from the developer holder 3 and the receiving members 64a of the developer case 64 are in contact with the face of the member 71. The receiving members 64a support the developer holder 3. In other words, when the developer holder 3 is not present, the center portion in the longitudinal direction is arched toward the outside of the developer case 64 as shown in Fig. 19A and when the developer holder 3 is present, the layer thickness control member 71 is in contact with the face of the developer holder 3 as shown in Fig. 19B. Other configuration items are the same as that the sealing member 62 in the tenth embodiment. Consequently, the contact area between the layer thickness control member 71 and the developer holder 3 is increased, so that the layer thickness control member 71 can be pressed against the developer holder 3 equally over a wide range. In this case, however, it is only necessary that the area where the layer thickness control member 71 contacts the developer holder 3 should be at least larger than the image area I of the image holder 5 and each side edge 71a should be outside the inner edge 62a of each sealing member 62. Consequently, even when the developer D whose movement is restricted by the layer thickness control member 71 moves to both ends of the developer holder 3 along the back of the layer thickness control member 71, the developer D cannot reach there, since the adhesive material 68 seals the portion between the developer holder 3 and the developer case 4. The layer thickness control member 71 having such a structure and the sealing members 62 can thus prevent a surplus supply of the developer D to both ends of the developer holder 3. The developer D that is not used for development is not scattered, protecting the developing apparatus from contamination by the scattering of the developer D and suppressing unnecessary consumption of the developer D. In the developing apparatuses DA10 and DA11 in the tenth and eleventh embodiments, both ends of the layer thickness control member 61,71 are attached to the developer case 4 and the control member 61,71, for example, is arched to be pressed against the developer holder 3. In this case, however, because of the deflection of the outer shape of the developer holder or the roughness of the adhesive face of the developer case 4, etc., as well as because of variation of the mounting accuracy, both ends of the layer thickness control member 61,71 do not contact the developer holder 3. In order to stabilize the thickness of the developer layer T, therefore, the layer thickness control member 61,71 must be pressed strongly against the developer holder 3 so as to ensure contact with the developer holder 3. When the external shape of the developer holder 3 is maximized and the adhesive surface of the layer thickness control member 61,71 is highest, the layer thickness control member 61,71 is bitten deepest into the developer holder 3 and the friction to generate between the layer thickness control member 61,71 and the developer holder 3 is increased, so that the rotation torque is increased to load the driving source of the developer holder 3, such as a motor, etc. significantly. In order to protect the developer holder 3 from such variation of mounting accuracy, therefore, the hardness of the developer holder 3 composed cf soft rubber materials such as urethane rubber or nitrile rubber (NBR) becomes a very important item. In other words, the hardness of the developer holder 3 should preferably be 65° or under when measured with an Ascar C (a rubber hardness meter of Koubunshi Keiki Co., Ltd. Conforming to Japan Rubber Association Standard SRIS 0101). This hardness is equivalent- to 40° or under in the hardness conforming to JIS K6301,and equivalent to about 26° or under in the hardness conforming to ASTM D2240. The lower limit of the hardness is not specified as long as a soft rubber material is used. Since the hardness of the developer holder 3 is set lower than the specified value such way, when the layer thickness control member 61,71 is bitten deepest into the developer holder 3, an elastic deformation is apt to occur in the layer thickness control member 61,71 on the face of the developer holder 3. Thus, the friction to generate between the layer thickness control member 61,71 and the developer holder 3 is not increased, so that the rotation torque is not increased by frictional resistance. This is why the driving source of the developer holder 3 is not loaded and the driving torque can be reduced. The torque of the whole image forming apparatus including the developing apparatus DA10, DA11 provided with the layer thickness control member 61,71 can thus be reduced, enabling a less expensive motor to be used as the driving source of the developer holder 3. To confirm the effect of the developer holder 3 concerning the hardness of the material, the rotation torque measuring test was performed using a conductive urethane rubber roller as the developer holder 3 in the developing apparatus DA6 in the sixth embodiment. In the test, the hardness of the urethane rubber was changed within 50° to 75° (Ascar C Standard). Table 1 shows the test results. The layer thickness control member 31 is composed of the stainless steel plate of 0.1mm in thickness and one end of the layer thickness control member 31 is fixed to the developer case 4. The layer thickness control member 31 is pressed against the developer holder 3 by the elastic force of the layer thickness control member 31 itself. The distance between the portion where the layer thickness control member 31 is fixed to the developer case 4 and a portion where the control member 31 is in contact with the developer holder 3 is 10mm and the deflection is 1mm. As understood from the Table 1, as the rubber hardness is increased, the rotation torque of the developer holder 3 is also increased. When the rubber hardness is 65° or over, it is found that the rotation torque is increased sharply. Even when both ends of the layer thickness control member 61, 71 are bonded to the developer case 4 as seen in the developing apparatuses DA10 and DA11 in the tenth and eleventh embodiments, the layer thickness control member 61,71 is pressed against the developer holder 3 by its own elastic force. Thus, the test results are true. From the test results shown in the Table 1, it is understood that the hardness of the developer holder 3 should be preferably 65° or under when in conforming to the Ascar C Standard. Even in the developing apparatuses DA1 to DA15 in the first to ninth embodiments, the hardness of the developer holder 3 should be preferably 65° or under when in conforming to the Ascar C Standard. Roller Rubber Hardness (Ascar C) The developer Holder Rotating Torque (kgf·cm) 50 0.15 55 0.20 60 0.24 65 0.43 70 0.65 75 0.98 Another method for avoiding scattering due to mounting accuracy, etc. described above is to reduce the hardness at both ends of the peripheral surface of the developer holder 3 in the longitudinal direction relative to the hardness in the center portion in the longitudinal direction thereof. More concretely, one type of soft rubber material is used for the developer holder 3 so that the hardness is reduced gradually from the center to the end portions (inclined characteristics). Otherwise, the developer holder 3 should be a laminated one obtained by bonding plural soft rubber materials, each of which has a hardness different from the others. In the latter case, the soft rubber materials should be bonded outside- the image area I of the image holder 5, so that even when a the developer layer T is formed on the developer holder 3, images are not affected by a scattering due to hardness and joints of those materials for the reasons described below. In other words, since both ends of the layer thickness control member 61,71 are most affected by a scatteringdue to mounting accuracy, etc., those portions of the control member 61,71 are bitten into the developer holder 3, so that the frictional resistance is increased more than in the center portion. This is why the hardness at both ends of the layer thickness control member 61,71 is made less than in the center portion. Then, the friction is reduced-even when both ends of the layer thickness control member 61,71 are bitten into the developer holder 3 to prevent the rotating- torque from increasing. Furthermore, a certain hardness exists in the center portion, so the contact state between the layer thickness control member 61,71 and the developer holder 3 can be kept properly and the control member 61,71 is pressed evenly against the developer holder 3 to stabilize the thickness of the developer layer T. The invention is not limited only to the embodiments described above. The embodiments may be modified and varied-freely, of course. For example, in the fourth to eleventh embodiments, it is only needed that the inner edge of each sealing member is positioned between the side edge of the developer holder and the side edge of the image area. The outer edge of the sealing member may also be positioned at or outside the side edge of the developer holder so that the sealing members cover both ends of the developer holder. Furthermore, one end of each sealing member is engaged with a supporting right-hand or left-hand threaded rod and the supporting rod is rotated by the motor etc., to move each sealing member in the opposite direction of the other one. Consequently, the interval of the pair of sealing members can be varied according to the width of each electrostatic latent image formed on the image holder, so that supply of surplus developer to the developer holder can be suppressed more effectively. Furthermore, the improvements described in the case of the developing apparatuses DA1 to DA11 in the first to eleventh embodiments may be combined as needed properly to apply the result to a single developing apparatus.

Claims: A developing apparatus for developing images held on an image holder (5), comprising: a developer holder (3) for holding a developer material and for feeding the developer to a developing position at which the developer holder faces the image holder; a layer thickness control member (1; 31; 61; 71) for slidably contacting a face of the developer holder at a face portion adjacent a leading edge of said thickness control member so as to form a layer of the developer material on said face of the developer holder; and a sealing assembly including a pair of elastic sealing members (27; 35) arranged for slidably contacting said face of the developer holder at positions which are spaced apart in a direction transverse to the direction of movement of said face relative to the layer thickness control member for substantially sealing the developer material supplied onto said face so as to confine it to a region defined between said sealing members; wherein each of said elastic sealing members is composed of first and second sealing member portions (27a, 27b; 36, 37) having relatively large and relatively small elasticity, respectively, the first sealing member portions (27a; 36) being disposed closer to said region in said transverse direction than the second sealing member portions (27b; 37). A developing apparatus for developing images held on an image holder (5), comprising: a developer holder (3) for holding a developer material and for feeding the developer to a developing position at which the developer holder faces the image holder; a layer thickness control member (1; 31; 61; 71) for slidably contacting a face of the developer holder at a face portion adjacent a leading edge of said thickness control member so as to form a layer of the developer material on said face of the developer holder; and a sealing assembly including a pair of elastic sealing members (28; 38; 45) arranged for slidably contacting said face of the developer holder at positions which are spaced apart in a direction transverse to the direction of movement of said face relative to the layer thickness control member for substantially sealing the developer material supplied onto said face so as to confine it to a region defined between said sealing members; wherein each of said elastic sealing members is composed of first and second sealing member portions (28a, 28b; 39, 40; 46, 47) having relatively large and relatively small elasticity, respectively, the first sealing member portions (28a; 39; 46) being disposed upstream of the second sealing member portions (28b; 40; 47) relative to the feeding direction of the developer. A developing apparatus according to claim 2 wherein the first sealing member portion (28a; 39; 46) is in contact with said face of the developer holder, and the second sealing member portion (28b; 40; 47) is in contact with a rear face of said layer thickness control member. A developing apparatus according to any of claims 1 to 3, wherein the second sealing member portions (27b; 28b; 37; 40) are made of a fibre material. A developing apparatus according to any preceding claim, further including: a back side elastic sealing member (7) provided on the back of the layer thickness control member (1), the back side elastic sealing member being in contact with the inner side edges of the elastic sealing members (27, 28) adjacent said region, wherein the developer is sealed by the back side elastic sealing member (7) and the elastic sealing members (27, 28). A developing apparatus according to claim 5, wherein the back side elastic sealing member (7) is smaller in hardness than the elastic sealing members (27, 28). A developing apparatus according to any of claims 1 to 4, wherein said elastic sealing members (35, 38, 45, 56, 59) are arranged to contact both the layer thickness control member (31) and the developer holder (3); and wherein a width (O) of the layer thickness control member (31) in said transverse direction is wider than a width (N) of the developer holder (3) in said transverse direction and the inner side edges of the sealing members (35, 38, 45, 56, 59) adjacent said region are positioned inside side edges of the developer holder (3) respectively. A developing apparatus according to claim 7, wherein said inner side edges of the sealing members are aligned to side edges of a predetermined image area (I) on the image holder (5). A developing apparatus according to any of claims 1 to 4, wherein said elastic sealing members (35, 38, 45, 56, 59) are arranged to contact both the leading edge of the layer thickness control member (31) and the developer holder (3); and wherein both side edges of the layer thickness control member (31) are disposed outside the side edges of the developer holder (3), or at the same positions as said side edges of the developer holder (3), the elastic sealing members (35, 38, 45, 56, 59) being spaced so that the distance (M) between their inner side edges is equal to or a little wider than the width of a predetermined image area (I) on the image holder (5), and said inner side edges of the sealing members (35, 38, 45, 56, 59) are disposed inside the side edges of the developer holder (3) respectively. A developing apparatus according to any of claims 7 to 9 when dependent on claim 3, wherein the first sealing member portion of each of the sealing members (45) is pressed against the developer holder (3) with a pressure which is larger than the pressure with which the second sealing member portion is pressed against the layer thickness control member (31). A developing apparatus according to any of claims 7 to 9, wherein the inner side edges of the parts of each of the sealing members (56) in contact with the developer holder are inclined so as to guide the developer on said developer holder (3) inwardly toward said region. A developing apparatus according to any preceding claim, further comprising a developing tank (4; 64) for housing the developer material, said developing tank supporting the developer holder (3), the layer thickness control member (31; 61), and the sealing members, and including an opening formed at a portion facing the image holder (5), wherein the sealing assembly includes a further sealing member (9) disposed between the developer holder (3) and a portion around the opening provided on an inner wall of the developing tank (4; 64) to prevent developer leaks from the developing tank (4; 64). A developing apparatus according to any of claims 1 to 11, further comprising: a developing tank (64) for housing the developer material (D), said developing tank supporting the developer holder (3), the layer thickness control member (61, 71) and the sealing members (62), wherein end portions of the layer thickness control member (61, 71) in said transverse direction are bonded at a rear side thereof to the developing tank (64), said rear side being opposite to the face on which the layer thickness control member (61, 71) contacts the developer holder (3). A developing apparatus according to claim 13, wherein the layer thickness control member (61, 71) is bonded to the developing tank (64) using a double-sided adhesive tape (68). A developing apparatus according to claim 13, wherein a hardness at both ends of the developer holder (3) in said transverse direction is lower than that in a center portion and the layer thickness control member (61, 71) is pressed against the developer holder (3). A developing apparatus according to claim 13, wherein a hardness of the developer holder (3) is 40° or under (JIS K6301) and the layer thickness control member (61, 71) is pressed against the developer holder (3). A developing apparatus according to claim 13, wherein the layer thickness control member (71) is arched toward the developer holder (3) at a center portion in the transverse direction and both ends of the layer thickness control member (71) in the transverse direction are disposed so as to be separated from the developer holder (3).

Inventors: ARAKI HIROSHIGE, IMAI YASUO, ISHII HIROSHI, KIDO EIICHI, OHGOSHI TOSHIHIDE, OHTSUKA YOSHINORI, WAKADA SHIGEYUKI, YUI YUHI, ARAKI, HIROSHIGE, IMAI, YASUO, ISHII, HIROSHI, KIDO, EIICHI, OHGOSHI, TOSHIHIDE, OHTSUKA, YOSHINORI, WAKADA, SHIGEYUKI, YUI, YUHI
Applicants: SHARP KK, SHARP KABUSHIKI KAISHA
Application year: 1998
Main classification: G03G15
IPC codes: G03G15